FLOUR MILLING FLOUR MILLING A THEORETICAL AND PRACTICAL HANDBOOK OF FLOUR MANUFACTURE FOR MILLERS, MILLWRIGHTS, FLOUR-MILLING ENGINEERS, AND OTHERS ENGAGED IN THE FLOUR-MILLING INDUSTRY BY PETER A. KOZMIN OF THE POLYTECHNIC INSTITUTE, PETROGRAD EDITOR OF THE RUSSIAN MILLER TRANSLATED FROM THE RUSSIAN M. FALKNER and THEODOR FJELSTRUP NEW YORK D. VAN NOSTRAND COMPANY 25 PARK PLAGE 1917 PREFACE IT is a singular fact that there is no serious modern work on flour milling in English. This fact was recently stated by Mr. Arthur E. Hawker, secretary of the National Association of British and Irish Millers, in a letter to the Editor of Milling. Even the rich American technical literature has no modern works of this kind, and the Americans were compelled four or five years ago to translate the old book of Professor Fr. Kick, the last edition of which was published over twenty years ago (1 894) . The want of serious scientific literature on flour milling is noticeable even in the German language, in which dialect during all the time which has elapsed since the appearance of Professor Kick's book not one objective scientific work has been published. As a characteristic feature of the German literature of the last few years (Baumgartner 1902, Baum- gartner and Graf 190 4, Baumgartner 1907, Pappenheim 1903,Ketten- bach 1907), one may point out the absence of descriptions of English and American machinery. I refrain from judging whether this is a result of the Germans not being acquainted with the machinery of English and American manufacture, or whether it is to be ascribed to the peculiar German patriotism in science. Be this as it may, the German authors do not give a broad scientific technical statement to their readers when they omit to mention English and American machinery. Having been for twenty years engaged in this industry as a theoretical and practical worker, and having studied the technology of milling in Russia, Germany, Austria, Hungary, France, Belgium, England, and the United States, I made up my mind to write a book on this subject, keeping to the most scientific basis. The object I had in view was to produce a practical and theoretical text-book for operative millers and for milling engineers, who have to construct flour mills and to design flour milling machinery. I thought it necessary to begin my book with an historical outline of the manufacture of flour. I drew up this outline on the basis of the materials which I found in the richest library of the world, that of the British Museum, as well as in the Congressional Library of the United 382938 vi PREFACE States, in which I worked on the occasion of my visits to these two countries. I have given an outline of the most important development the milling industry has undergone from the ancient period of the civilised nations of Asia Minor and Egypt till the period when practice determined the correct way of improving the technology of flour milling. The historical outline is important in that it presents the general development of the craft to the mind of the student and forces him to think more logically. After having spoken of the product which is to be treated, I pass to the study of the construction of the cleaning and grinding machines. The designs of the machines performing a very particular operation in the cleaning and grinding processes are almost infinitely variable. In order to train the student promptly and logically to analyse and estimate the numerous machines, I have classified them according to the principles of their action, having pointed out the most economical principles of operation. Then I have illustrated the fundamental principles from the most characteristic and most popular European and American machines. To explain my idea, I will take for instance the study of the roller mill. I consider this machine from the point of view of feeding the rolls (German, English, and American systems of feeding), disposition of the rolls (hori- zontal, vertical, or diagonal), driving of the rolls (gear drive in the European makes, belt drive in America), methods of ventilation, etc. Describing the principles of the action and design of certain machines, I make also a critical estimate of them, basing my contentions on practical and scientific considerations. Such is my method of describing machines, the idea always being to give the student a conception of the most important designs and to force him to think critically. In the chapter on milling diagrams I give typical diagrams of systems at work in European and American countries, in order that the student may compare all the different schemes of grinding. In each chapter I give the practically established capacities of the machines and a basis for the calculation of the necessary number and dimensions of them corresponding to a given capacity of a Russian, German, English, or American mill. No author has as yet paid attention to the problem of the motion of the plansifter and of the movement of the product in the purifier. I thought it therefore necessary to solve this problem, and this makes it possible scientifically to estimate the advantages and disadvantages of the different types of these machines. PREFACE vii In writing my book I have attempted to instruct and prepare the way for learned and scientifically thinking specialists. It is for others to judge as to whether I have succeeded in my achievement. In writing this book I have largely availed myself of the materials and advice of my professional colleagues working theoretically and practically in England and America for the benefit of the Milling Industry. I consider it therefore my duty most earnestly to thank Mr. W. Jago, the author of the excellent work on The Technology of Bread Making, for his kind permission to reproduce some of its tables and photographs of the wheat grain. Further, to Mr. R. A. Sidley, editor of The Miller ; to Mr. Geo. J. S. Broomhall, editor of Milling ; Mr. A. R. Tattersall, Mr. Chas. E. Oliver of the Dixie Miller, and many others who have rendered me their kind assistance. In addition, many English and American firms have supplied me with detailed drawings of their machines, which I have reproduced in my book. I am therefore most grateful to Messrs. Thos. Robinson & Son, Rochdale, England ; Messrs. E. R. & F. Turner, Ipswich, England ; Messrs. Nordyke & Marmon Co., Indianapolis, Ind., U.S.A. ; Messrs. The S. Howes Co., Silver Creek, N.Y. ; Allis-Chalmers Co., Milwaukee, Wis. ; and many others. Finally, I desire to express my heartiest thanks to Messrs. Geo. Routledge & Sons Ltd., for their kind consent to publish my book in English, and thus to give me a chance to offer it to the judgment of the specialists of England and America, to whom I shall be most obliged for their impartial criticism. P. KOZMIN. PUBLISHERS' NOTE The Publishers desire to add their thanks to Mr. Edward Bradfield, Associate and Technical Editor of Milling, for his assistance in revising the proof sheets of this book. CONTENTS PAGE PREFACE . . . . ... . v CHAPTER I HISTORICAL OUTLINE OF FLOUR MILLING I. FLOUR MILLING ACCORDING TO RELIGIOUS LEGENDS AND CLASSICAL LITERA- TURE. MODERN RELICS OF ANCIENT FORMS OF MILLING . . .1 II. TYPES OF MILLS DRIVEN BY ANIMAL POWER . . . .11 III. THE UTILISATION OF WATER POWER FOR MILLS . . . .16 IV. THE AMERICAN AUTOMATIC MILL . . . . . . .23 V. THE INFLUENCE OF AMERICAN TECHNICS IN EUROPE . . .26 VI. MILLS IN FRANCE ........ 27 VII. PROGRESS OF TECHNICS IN GERMANY . . . . . .29 VIII. FURTHER DEVELOPMENT OF MILL BUILDING IN EUROPE . . .34 IX. THE STRUGGLE BETWEEN THE ROLLER AND STONE-MILLS . . .37 CHAPTER II GENERAL IDEAS OF THE RAW MATERIALS FOR FLOUR PRODUCTION I. THE BERRIES OF THE CEREALS . . . . . . .39 II. PHYSICAL STRUCTURE OF THE WHEAT GRAIN . . . .41 III. CHEMICAL COMPOSITION OF WHEAT . . . . . .47 CHAPTER III PREPARATION OF GRAIN FOR GRINDING I. IMPURITIES AND THE PRINCIPLES OF CLEANING . . . .58 II. EXTRACTION OF PIECES OF METAL FROM THE STOCK . . . .59 III. SEPARATION OF LARGE AND SMALL IMPURITIES .. ..- . .61 1. Separation according to Size . . . . . .61 2. Separation according to Shape . . . . .82 IV. MACHINES FOR SEPARATING STONES . . . . . .92 b ix CONTENTS PAGE V. SCOURING AND POLISHING THE GRAIN . . . . .93 1. Principles of the Processes and the Character of the Working Parts . 93 2. Construction of Scouring Machines . . . . .100 3. Special Machinery . . . . . . .118 4. The Wet Scouring and Washing Process .... 120 VI. DAMPING THE GRAIN . . . . . . . . 143 VII. GRAIN- CLEANING DIAGRAMS 147 CHAPTER IV GRINDING THE GRAIN I. THE FUNDAMENTAL PRINCIPLES OF MILLING . . . . .153 II. THE CONSTRUCTION OF THE GRINDING MACHINES . . . .155 III. MACHINES OF REITERATED ACTION OF THE WORKING SURFACES . .156 1. Stone Mills Horizontal (Vertical Axis of Rotation) . . . 157 2. Composition and Design of Millstones . . . . .160 3. Under-Runner Millstones . . . . . .180 4. Stone Mills Vertical (Horizontal Axis of Rotation) . . . 187 5. The Capacity and Calculation of Stone Mills . . . .191 6. Mills with Metal Grinders . . . .. - . .195 IV. MACHINES ACTING BY IMPACT . . . . . . . 198 V. MILLING MACHINES HAVING THE Axis OF ROTATION OF THE WORKING ORGANS IN DIFFERENT PLANES . . . . . . 204 VI. ROLLER MILLS . t . . , . . , . 209 1. Conditions of Reduction of the Product . '. . . .209 2. Corrugating the Rolls . .- . . . . . . 218 3. Adjustment of the Distance between the Working Surfaces . . 233 4. A General Survey of the Roller Mill . . . . .236 5. The Feeding of the Rolls . . . . . .243 6. Types of Roller Mills 258 7. Transmission of Motion to the Rolls ..... 296 8. Capacity of Roller Mills . . . . - . . .299 9. Brush Machines . . . . . ' .312 10. Detachers ........ 313 CHAPTER V GRADING THE PRODUCT ACCORDING TO SIZE I. SIFTING THE PRODUCT . . . . . . . .316 II. RELATIVE POSITION OF THE SIEVES . . . . . . 326 III. THE SIFTING PROCESS . . . .331 CONTENTS xi PAGE IV. CONSTRUCTION or SIFTING MACHINES . . . f t 335 1. Reels and Centrifugals . . . 335 2. Plans if ters *>AA * Orrrr 3. Dynamics of Plansifters . . ' , " . 3^5 4. American Sifters .' . . . 374 5. Free Swinging Plansifters . . . . 382 6. Capacity of Plansifters .... 386 CHAPTEE VI GRADING THE PRODUCT ACCORDING TO SPECIFIC GRAVITY I. GRADING MIDDLINGS AND DUNST ACCORDING TO SPECIFIC GRAVITY. . 392 II. MIDDLINGS- AND DUNST-GRADING MACHINES OF TO-DAY . . . 406 III. CAPACITY OF PURIFIERS . . . . . . 420 CHAPTER, VII ACCESSORY APPLIANCES AND MECHANISMS I. PURIFICATION OF THE INTERMEDIATE PRODUCTS . . . . 423 II. DUST -COLLECTORS ........ 426 III. EXHAUST SYSTEMS ........ 434 1. Group Exhaust Systems . ...... 434 2. General Exhaust Systems ...... 438 3. Calculation for an Exhaust Plant ..... 442 IV. TRANSPORTATION OF STOCK . . . . . . 445 1. Spouts and Elevators ....... 445 2. Horizontal Transport ....... 458 V. APPARATUS FOR MIXING AND PACKING FLOUR .... 469 VI. APPARATUS FOR RECKONING AND REGULATING THE QUANTITY OF PRODUCT 476 VII. FLOUR BLEACHING . . . . . . . . 480 CHAPTER VIII MILLING DIAGRAMS I. CLASSIFICATION OF MILLING SYSTEMS . . . . . . 489 II. PLAIN GRINDING . . .. ... .491 III. DIAGRAMS OF IMPROVED PLAIN MILLING SYSTEMS . . 494 IV. HIGH GRINDING . . '. ... . . 500 V. SHORTER GRADUAL REDUCTION SYSTEMS ,. . . 511 VI. RYE GRINDING . , . . .527 xii CONTENTS PAGE VII. MAIZE GRINDING . . . . . ^ . . .536 VIII. SCHEME OF OATMEAL GRINDING . . . . . v . 538 IX. QUANTITY OF INTERMEDIATE PRODUCTS AND THE CALCULATION OF CORRE- SPONDING MACHINES . . . . . . ." . 541 X. RUSSIAN GRINDING . . . . . . " . . 547 CHAPTER IX CONSTRUCTION OF MILL BUILDINGS I. CONDITIONS DETERMINING THE CHARACTER OF BUILDINGS . . . 554 II. CONSTRUCTION OF MILL BUILDINGS . . . , . 559 III. BUILDINGS OF COMPLICATED GRINDING MILLS . . . . 561 IV. CONSTRUCTION OF AMERICAN MILLS . . . . . 565 V. PLANS OF MILLS . . . . . . . 570 CHAPTER X THE COST OF ERECTING AND OF WORKING MILLS I. THE MILL BUILDING AND EQUIPMENT . . . . . 575 II. CALCULATION OF WORKING EXPENSES . . . . . . 577 III. SELECTION OF A PRIME MOTOR . . . . . . 579 INDEX . 583 FLOUR MILLING CHAPTER I HISTORICAL OUTLINE OF FLOUR MILLING FLOUR MILLING ACCORDING TO RELIGIOUS LEGENDS AND CLASSICAL LITERATURE. MODERN RELICS OF ANCIENT FORMS OF MILLING MODERN culture of mankind, indissolubly connected with the technics of production, is the last link of a long chain of human endeavour stretch- ing away into the dark space of past millenniums. The culture of mankind has not developed spasmodically ; although history relates of whole peoples vanishing and their culture with them, this is but a seeming disappearance of culture. It is an undoubted fact with us, that a more perfect technical knowledge corresponds with a more perfect culture. Culture never vanished, it simply underwent an evolution. Its old forms were gradually modified and perfected. When studying the history of the technics of any particular kind of production, we come to the conclusion that the perfecting of the process of production was never brought about by leaps and bounds. On the contrary, it has been a slow process of gradually collecting grains of human knowledge. Out of an inexhaustible source of knowledge, the gains of culture, i.e. the weapons of the victorious battle of man for existence and happiness, passed from one people to another ; neither racial, social, nor national and territorial partitions of humanity could bar their passage. An empire might vanish, even a people, but the weapons of the struggle for life in the first place, the implements of production remained in the hands of others, and the culture did not disappear. The law of evolution of the technics of production is a curve having no solution of continuity. The study of the development of a produc- tion gives us the law of inflection 'in that curve. Parallel to this curve, i.e. in accordance with that law, runs uninterruptedly the line 2 :^f>UR MILLING [CHAP, i of human culture. That is the reason why historical catastrophes of human culture are impossible, however powerful the wave of barbarians on the cultured people may be. An intimate acquaintance with technical history is indispensable to every engineer, because history gives us the law of evolution of the implements and processes of production. Only by carefully studying the historical development of the technics of production does the creative power of an engineer receive its true education and evade retrogression. The most brilliant example of culture and its evolution to date is the technics of procuring and preparing the nutritive substances for food. Since man left the cave epoch behind him, vegetable food has constituted undoubtedly the most substantial part of his nourishment. Even the biblical legend of paradise tells us that man lived on the abundance of the fruits of the earth, and was allowed to use them for food. Traditions about a human paradise on earth reached even the time of Ovid, who depicts the life of primeval man as the golden epoch, when men were content with the food the earth yielded them without constraint. But people multiplied, formed numerous groups, the abundance of the fruits of the earth did not suffice, and the curse of pro- curing food by the sweat of man's brow began to gain ground. The struggle against that curse is the history of human culture, the history of the technics of production. In the end, a perfect technical knowledge will, of necessity, liberate mankind from this curse. Since time immemorial, bread has been the most essential element of man's vegetable food. How it happened that man stumbled upon the cereals, why he began to cultivate this unsightly plant, we know not, but. in selecting the cereal plant out of the mass of other fruit, man made no blunder, for the grain of corn contains more nutritive substance than any other fruit ; but out of the gloom of ages, traditions slightly varying in import have reached us. Moses says that Cain tilled the soil, that Noah, after the flood, likewise began to cultivate land. Pliny speaks of a tradition which ascribes the origin of agriculture to a deity. 1 Tradition tells us men were taught to cultivate corn by the goddess of agriculture, Ceres (by Demeter, sister of Zeus, according to the Greeks). " Before this, people fed on acorns." Pliny adds that men learned the grinding of corn to flour also from Ceres. From this myth we understand that the art of grain grinding, a contemporary of agriculture and proceeding from one and the same deity, has its origin in the same depth of ages as the cultivation of corn. 1 Pliny the Elder (A.D. 23-79), Historic, Naturalis. CHAP, i] FLOUR MILLING A Spartan tradition ascribes the art of making flour to Miles, and says that the chief milling town in Greece of that epoch was Alesia. According to Hommel, 1 Asia is the native country of the cultivated cereals. He maintains that the Sumerians coming to Egypt from Mesopotamia, eight thousand years ago, had a great influence on the culture of Egypt, having taught the aborigines to procure and work metals and cultivate corn. About the grinding instruments of the pre-mythological ages the traditions give us no information, but relics of the classical and the Egyptian culture exist, which can give -us an idea what the antique Egyptian machine was like. Excavations and the hieroglyphics of the ancient Egyptians indicate that the primitive milling implements were first wooden, then stone, FIG. 1. Grinding in Ancient Egypt. and later on metal mortars, in which the grain was crushed by blows from pestles. Fig. 1 shows the whole process of flour-making by the Egyptians. This drawing is a reproduction from one of the pictures that decorated the house walls in the town of Thebes, according to Wilkinson's Account of the Ancient Egyptians. The mortars here are marked a, the pestles with two working ends b, the basket of grain or semi-product d, the basket of ready flour c. The loading (/) is done by a man, who pours the grain out of the vessel g into the mortar. Two men (//) are grinding ; one (///) is emptying the crushed grain out of the mortar into a sieve ; the last man (IV) is sifting. The sifting of crudely-crushed grain was known apparently even in these very remote times. The sieve e, a kind of rudely-shaped plate, was prob- ably made of papyrus. On either side of the bas-relief at the top are hieroglyphic inscriptions h and /, explaining the meaning of the picture. It is supposed that the 1 Fr. Hommel, Prehistorische Indo-Europeer. 4 FLOUR MILLING [CHAP, i ancient Egyptians roasted or heated the grain until dry, previous to grinding it. That is very possible, as the dryer the grain is, the more easily it is broken by blows from the pestle. The same type of the primitive mill existed in ancient Greece, and some of the excavated vases bear the drawing of a similar mortar and pestle. Besides that, Pliny gives us a de- scription of apparently similar mills in Greece, saying that " in Etruria, the ears of corn are roasted, and then crushed by means of pestles with sharp saw- like edges below and a cogged wheel in the middle." And yet the primitive milling in Etruria required tech- nical knowledge, for Pliny says (ibid.) if the work was done care- lessly, the grain was crushed more finely than was necessary and the iron parts of the pestle were soon worn out or broken. But what strikes us most is the fact that after thousands of years living relics of antique Egyptian technics are found. Some of the negro tribes in the valley of the Nile use the mortar and pestle for grain grinding at the present day. The photograph (Fig. 2) shows a striking likeness between the milling of a negro tribe near Khartum l and that of ancient Egypt. Here are the same two baskets one with grain, the other for flour a stone mortar, and 1 Elis6e Reclus, L'Homme et la Terre, vol. ii. FIG. 2. Negro Milling at the Present Time in Africa. CHAP. I] FLOUR MILLING wooden pounder. There is but a sieve wanting to make the picture identical. In China, where traditions of great antiquity, concerning gramen, the gift of gods, also exist, wheat was cultivated 2700 years B.C. and the ancient Egyptian type of grinding machine was in use. Until recently, in many parts of China the mortar and pestle were used for clipping and polishing rice, i.e. freeing it of the coatings. In several out-of-the-way places in that country, wheat is still crushed to a coarse flour in that mortar. Fig. 3 represents such a mill supplied with a foot drive. 1 FIG. 3. A Chinese Mill of the most Ancient Type. An interesting mill of a similar type, but driven by water, is described by Bridd 2 in the American Miller. This mill (Fig. 4) is used by the Indians, who settled in the state of Kentucky, for maize-grinding. The mortar is hollowed out in a tree stump. A lever, with a stone pestle attached to one end, and a box to the other, is placed on a fork. A jet of water from a stream is con- ducted along a groove into the box. When the box is filled with water, outweighing the stone, it drops to the lower position, the water runs out 1 Staunton, British Ambassador in China. His Report to the Embassy 1797, 2 American Miller, 1907. FLOUR MILLING [CHAP, i FIG. 4. Indian Water-mill in Kentucky, of the box, and the pestle falls quickly into the mortar, crushing the grain. The capacity of the mortar is about 28 Ibs. of grain; that quantity is ground in eight to ten hours. The mill, consisting of a mortar and pestle, belongs to the first period of prehistoric technics. The next stage of its develop- ment is a transitory type from the mortar and pestle to two mill- stones, between which the grain is ground. The primitive type of such a mill 1 was produced apparently also in Egypt (Fig. 5). The grain was ground on the larger stone by means of the small one. We find this mill nowadays in the hands of the natives of Africa in the Nile Valley. Fig. 6 represents a negress preparing flour in the same manner Egyptians did some 4000 years ago. Fig. 7 shows the up-to-date milling of the Nu- bians. The work is performed by children here. It is curious to note that the same principle^ of milling has been retained, up to this day, by the Mexican Indians, who are considered to be the descendants of the Aztecs. Fig. 8 reproduces that " mill " used by Mexican Indians of to- day ; they grind their corn on it. These illustrations of primi- tive grain- crushing show us how slowly ancient man ac- quired the principles of a more economical system. The mill of the first type is very simple it is based on the impact principle. The primeval man had no difficulty in coming upon this principle, knowing, as he did, the destructive power of a blow and the 1 Photo of a stone implement found at the excavations in Upper Egypt, FIG. 5. Ancient Egyptian Milling. CHAP. I] FLOUR MILLING solidity of stone, for he fashioned his axes and arrowheads from that material. But gradually the human mind became conscious that such work is not efficient. It is evident, besides, that the blows of the pestle, by degrees, wear out the mortar and the pestle itself. Thus the question of the greatest efficiency of work and of a better constructed machine arises. The impact principle is rejected, and that of grinding is adopted. That principle was ad- hered to in the mills of the improved type, that might be called " grinding mills," for thousands of years. When the mills consisting of two grindstones appeared is not known. At any rate, it may be supposed that they made their appearance in Egypt, and 3500 years be- fore our time at the very latest. The Jews, leaving Egypt, doubtless brought much technical knowledge of various productions out with them. FIG. 6. Negro Milling to-day in the Nile Valley. FIG. 7. Modern Milling : Natives of Nubia. It was from the Egyptians that they learned to grind their grain to flour on millstones. We find traces of that fact in the fifth book of Moses (xxiv. 6), where it is written, " No man shall take the 8 FLOUR MILLING [CHAP, i nether or the upper millstone to pledge." Evidently the grindstone mill was an indispensable utensil of a Hebrew household during their searches for the blessed land, since Moses forbade by law loans on the pledge of a millstone. In the fourth book of Moses (xi. 8) the heavenly manna is spoken of in the following terms ; " And the people went about and gathered it in mills, or beat it in a mortar." The contemporary use of the mortar and grinding mill points to the period of the migration of the Jews, as the beginning of the use of grinding mills, which at the time had not yet succeeded in supplanting the pestle and mortar. Grinding mills are spoken of more definitely (about 1000 years B.C.) in Homer's Odyssey (song 7, vv. 103, 104), where domestic life at the court of King Alcinous is described : l " Full fifty handmaids form the household train ; Some turn the mill, or sift the golden grain." and then canto 20, vv. 105-111 : 2 " Beneath a pile that close the dome adjoin'd, Twelve female slaves the gift of Ceres grind ; Task'd for the royal board to bolt the bran From the pure flour (the growth and strength of man). Discharging to the day the labour due, Now early to repose the rest withdrew ; One maid, unequal to the task assign'd, Still turned the toilsome mill with anxious mind." The grindstones of those mills were very small, a proof of which is to be found in the fact of ancient heroes using them as missiles for throwing at their enemies during battle. A stone of this description weighs some 45 Ibs., and does not exceed 1 foot in diameter. The upper stone, slightly conical, is 4J inches thick. The nether one is flat and 2 \ inches thick. Such stones are disinterred in Abbeville (Picardy). Fig. 9 shows grindstones belonging to an age not 1 Pope's translation, p. 12, Odyssey, Book VII, 11. 132, 133. 2 Ibid., Book XX, 11. 132-139, CHAP. l] FLOUR MILLING 9 distant from that of Homer (found in Syria). The working surfaces of the upper and nether stones are of conic shape. Later on, we shall FIG. 9. Millstones of the Age of Homer. find proof that this mill was the predecessor of that of the Romans. We ventured the opinion that the double stone mill was invented in FIG. 10. Milling by the Natives of Morocco. ancient Egypt, and then brought into Greece. Indeed, the kind of mill described by Homer is still used in Morocco. These mills are also in use in the Orient and in China. A celebrated 10 FLOUR MILLING [CHAP, i traveller and explorer of the Orient, Journefause, says he saw a similar mill on the isle of Nicaria. Giving a description of it, he tells us that the grain was poured into an aperture in the upper stone and fell in be- tween the two stones. The upper stone (2 feet in diameter) was made to rotate by means of a stick fixed into its edge. Similar millstones are mentioned by Clark, who saw them in Nazareth ; they were worked by two women. One of them was turn- ing the upper stone, taking the handle with her right hand half way round, and passing the handle to the second woman, who after performing the same mo- tion, returned it to the first from the other side, &c. With their left hands they poured the grain into the hole in the upper stone. The Chinese rice-mills are of the same con- struction according to Staunton, though de- signed not for the grinding of grain, but for freeing it of its outer cover. He describes it in the follow- ing manner : " The rice is placed in between two flat cylindric stones, which are so far apart that with the rotation of the upper stone the grain is but freed of its covering, and not ground." The type of hand-mill alluded to by Moses and Homer is still preserved among the natives of Morocco. Fig. 10 is a photograph of such a mill, made in 1908. But not only the semi-savage aborigines of Africa use these mills ; Fig. 1 1 shows us an almost identical hand-mill, with a few improvements, that the " Dukhobors " from the Caucasus used, before migrating to America. The improvements in this mill, when compared to the Morocco one, consist in the fixing of the stones to a block hollowed out in the shape of FIG. 11. A Hand-Millstone Set of the Caucasian " Dukhobors." CHAP, i] FLOUR MILLING 11 a trough. The hole a, bored in the side of the trough, serves for discharg- ing the flour. This type of hand-mill brings us to the end of the first period of milling technics of the antique, mainly slave-owning culture. The consumption of bread not being high, there was no need for large production of it, and therefore the milling was successfully performed by slaves and women. The work being very difficult, criminals were condemned to do it for punishment. As to the woman, it was one of the items of her ordinary household work. 1 To this day, in Mecca, a place is shown where Fatima, daughter of Mohammed, worked a hand-mill. II TYPES or MILLS DRIVEN BY ANIMAL POWER The new mill, where mainly animal power and only partly human power is utilised, appears with the passing of flour milling from the family, which only satisfied its private needs, into the hands of the pro- ducer, working for the market. The principle of grinding the grain between two millstones remains in the new mill, but it is larger, and has undergone some modification in its construction tending to reduce the expenditure of power. This mill was invented at a later period, yet we find no traces of it among the relics of antique Egyptian, Roman, and Greek cultures. Only the latest J FIG. 12. Mill of the Period of the Kings excavations of Pompeii have given of Rome, us pictures of the improved mill of the time of Roman dominion, as well as nearly perfectly preserved mill- stones. In all probability this type of mill was invented by the Romans at least 150 to 200 years B.C. Fig. 12 represents the outer view of the mill in question, and the same in section. 1 It is a curious fact that in Little Russia, millet is still ground with a " makogon " in a "makitra" (pestle and mortar) to flour, for preparing "borshch" (a kind of soup), because millet meal is not produced on our mills, 12 FLOUR MILLING [CHAP, i The foundation of the Roman mill consists of a cylindrical pillow of stone. A is about 5 feet in diameter and 1 foot thick. To this founda- tion is rigidly fixed a conic stone (the nether stone'' meta " ) with the top truncated about 2 feet in height. The cone is provided with an iron journal at the top. The revolving upper stone ("catillus") B has two bell-shaped hollows, thus resembling a sand-glass. In the place where the tops of the bells are joined an iron cross beam is fixed, like a dove-tail in shape at the ends. In the middle of this beam is a round hole, into which the journal is inserted, so that in between the inner sides of the lower bell and the outer surface of the cone there is FIG. 13. Roman Mill turned by a Horse. just the space needed for grinding the grain which is put there. The grain is poured into the hollow C of the upper bell B, acting the part of hopper, from whence it falls into the space FIG. 14. Roman Mill driven by Slaves and Asses. between the grinding surfaces. The upper stone is revolved by means of levers D, which are inserted into the two or four rectangular cavities made in it. CHAP. I FLOUR MILLING The product is discharged into the ring-shaped groove below, made on the surface of the foundation. We have detailed information concerning the nature of stones used FIG. 15. Pompeian Mills. in milling from Pliny. Judging by his descriptions, it was known that not every stone can be used for milling purposes. The grindstones of FIG. 16. A Chinese Mill. the Pompeian mills were shaped of lava from Vesuvius. Coarse and fine sieves, made of horse-hair and linen, were used for separating the flour from the bran and whole grains that passed unground. There were usually 14 FLOUR MILLING [CHAP, i several kinds of flour known on the market. He mentions even the number of flour grades and refuse obtained from one medimnum holding 108 laurels, viz. : Flour of finest quality (pollen) . . . . 17 laurels. Flour of medium quality (similago) . . . v 50 ,, Flour of semolina, 1st quality (farini tritici) . . 30 J ,, Flour of semolina, 2nd quality (secundarii panis) . 2| ,, Flour of semolina, 3rd quality (cibarii panis) . 2J ,, Bran (furfur) 3 Various refuse . . . . ..'.- 2J ,, Total. . . , . ;.. . 108 laurels. It was mentioned above that working the mill was the occupation of women, chiefly female slaves. Men were employed in that work later serfs and criminals, sometimes forced to wear wooden discs round their necks, to prevent any possibility of reach- ing their mouth with the hand and eating the flour. After it was dis- covered that larger and heavier stones work with greater efficiency, animal power was put to use, especially that of horses and asses. For that purpose a fencing of beams with shafts for the harnes- sing of horses was ar- ranged round the runner, as shown in Fig. 13, which represents part of a bas-relief in the Vatican. Blinkers were placed on the eyes of the animals, probably to prevent giddiness. The mill driven by an ass is reproduced in a book on Herculaneum and Pompeii, by Rou-Barre (vol. 2, tab. 83). This drawing was made FIG. 17. A Hindoo Mill. CHAP. I FLOUR MILLING 15 from a picture at the entrance to the Pompeian Pantheon. Besides the mill there are the mill-demons shown in the picture. 1 The mill is in the middle of the picture, and seven spirits are seen round about it, some working, others resting from their work over a glass of wine. One of the spirits is about to harness an ass and to start his work. Fig. 14 shows a similar mill at work. Fig. 15 is a photograph of four such mills after their disinterment, in perspective. Those mills were found close to a bakery, and probably formed a complete bread factory. Mills with a lever-drive evidently kept their place a long time in ^H^^^l FIG. 18. A Chinese Mill worked by Buffaloes. milling. They are to be met with in the classic world as well as in the far Orient. A Chinese mill, worked with the aid of a horizontal lever by a man, is represented in Fig. 16. Fig. 17 is a picture of a Hindoo mill driven by oxen. Though it is furnished with a lever-drive, the primitive mortar and pestle system has been retained here. The crushing of grain, however, is based on the principle of grinding. This mill was described by the traveller Sonerat in his book, Reise nach Ostindien und China. Animal power is still used in modern China for driving mills. Fig. 18 shows a mill driven by buffaloes. Yet we must note that modern Chinese mills, where buffaloes are employed as motive power, have received considerable improvements, in comparison with those of the Romans. 1 A belief that an unholy power lives in the mill exists also among the Slavs. FLOUR MILLING [CHAP. 1 III THE UTILISATION OF WATER POWER FOR MILLS As the construction of a mill grew heavier, in response to the need of greater output, men were forced to apply a greater driving power, which should be more efficacious than the muscles of a slave, woman, or FIG. 19. A Water-mill as described by Vitruvius. animal. Naturally, they turned to water and air first of all, and utilised the power of these moving elements. The first veracious information concerning mills driven by means of under-shot water-wheels, and a minute explanation of their construction, we find in Vitruvius. 1 It is to be regretted that Vitruvius in his immense work about the art of building did not furnish it with drawings ; all illustrations given in some of the later editions of his work, are only attempts to depict what he described. 1 Vitruvius, a Roman architect, wrote De Architectures about 16-13 years B.C. CHAP. l] FLOUR MILLING 17 Such is the drawing in Fig. 19, taken from an edition of Vitruvius' work, published in 1521 in Camo, in Old Italian. Here A represents a wooden water-wheel. On its rim are radially- fixed paddles B, receiving the pressure of moving water, and boxes or ladles C, which serve to bring up the water used for special purposes. 1 The shaft of the water-wheel is turned with the long end inwards. On the square part of the shaft D is fixed a comb-wheel E engaged with a mangle gear. The cogs of the collar comb-wheel enter into the mangle wheel F, set on G, the spindle of the millstone, which rests with its lower end on a beam L, the upper end passing through a fixed (not shown in the drawing) lower grindstone, and is hermetically fastened to the runner H, into the opening of which the product to be ground is poured. The latter is fed from a pyramidal hopper K, where the grain is kept. The lower opening of the hopper is furnished with an ad- justable vibrating shoe. The water lifted by the wheel A pours out of the boxes G into a tank R, whence through an Opening X it passes FIG. 20. Arabian Water-mill. into the spout 7, and may be used for irrigation. Possibly a fullery was attached to the mill, which may explain the presence of a hammer in the drawing, though it may have been used for hammering a stopper into the outlet X. We may suppose the use of horizontal water-wheels or turbines on mills to be nearly as old as the use of vertical water-wheels. Simple turbines are found in mountainous regions in almost all lands where the population is slightly touched by civilisation, however low their mechanics may stand. Fig. 20 proves this surmise to be correct. It is a drawing of an Arabian water-mill, made at Rollet's by a captain of the French artillery soon after the taking of Constantinople by the French. A denotes the wall of the mill-building, B the hopper for pouring the grain in, C a cross bar communicating a vibratory motion to the hopper, D a revolving grindstone (making 112 revolutions in the present case), E the spindle of the grindstone, F masonry serving as nether stone at the same time, i Probably for irrigation. 18 FLOUR MILLING [CHAP, i G a cavity, where the ground product (flour semolina) is collected, H a shaft on which a turbine I is mounted, K a ladder, L a lever for the runner D, M a gate in front of the spout N. It is also mentioned that the turbine is 1'6 metres in diameter, and is furnished with thirty paddles. With the aid of a spout, through a small opening in the dam, the water is directed on to one half of that wheel, so that it falls into the concave side of the paddles bringing the wheel, the shaft H, and grinder D into motion. As to horizontal water-wheels in the mills, M. Riihlmann quotes an extract from the French encyclopaedia. In the 14th vol. of the Dictionnaire Technologique, p. 207, it is stated that horizontal water-wheels in the so-called bazacle mills in Tumra were built in the twelfth century (1190). Then, in the issue of Neues Hannoversches Magasin on Oc- tober 4, 1802, p. 1277, is the following description of a Bashkir mill that was evidently a contemporary of the vessel mills of Belisarius : " The Bashkirs have mills of a peculiar construction, apparently an invention of the people. With the view of economising labour, they choose the smallest rivulets for their mills, make a hedge of twigs which is filled with earth, and dam the stream with it (or an ordinary dyke of brushwood). On the dyke is built a hut on piles. In that hut grindstones are placed on a scaffolding standing in the middle with railings running round its edge. The grinders are not of stone, but of a hard tree stump or block of wood ; and are shaped in the form of plates, studded in an orderless way with flat iron nails, so laid that their prominent parts run lengthways from the centre to the periphery. The nether wooden grinder is rigidly attached to the scaffolding, while the 'upper one may be raised and revolves conjointly with the vertical shaft that runs through the opening in the nether grinder and rests with the point of an iron crutch in a cavity made in the centre of the upper grinder. The vertical shaft is usually made of one block of wood, so that its lower part ends in a round thick knob, into which a good number of flat wings or paddles, slightly concave on one side, may be hammered in a manner resembling the spokes in a wheel, and forming the water-wheel proper. A bolt is hammered into the thick end of the shaft below, by means of which the vertical shaft rests in the rivulet on a beam and revolves in it, as in a bearing. " The grain to be ground into semolina or coarse flo,ur is ppure$ CHAP. I] FLOUR MILLING 19 into a hopper built of planks. Under the opening of that hopper, a short horizontal spout is placed, leading to the opening in the middle of the upper grinding disk. The corn-bin with grain is hung to the cross-beam of the mill, free to be shifted. A handle, tied % to the corn-bin, which touches the upper grinder with one end, imparts a vibrating motion to it." We presume, however, that the author errs in ascribing the inven- FIG. 21. tion of this mill, with a horizontal water-wheel, to the Bashkirs. From the oldest times and up to this day, such a mill is a common object in the Caucasus. Possibly the author has mistaken the natives of Caucasus for Bashkirs. The mountaineers, and even the people of the plains of the northern Caucasus, chiefly use maize flour, of which an unleavened bread is pre- pared, "Chureck." Wheat is also ground, but is used only with an 20 FLOUR MILLING [CHAP, i admixture of maize flour, as the use of pure wheat flour is a luxury among the natives. The whole amount of maize and wheat is ground for local FIG. 22. A Caucasian Mill with one Set of Grinders. consumption in the water-mills depicted in 1802 by the Neues Hanno- ver sches Magasin. Pig. 21 is a sketch of this mill. The shaft of a horizontal water- wheel rests with one end e on a step-bearing in the shaft d, which may rise CHAP. I FLOUR MILLING 21 and fall with the aid of a stem / and a wedge in its upper end. To the upper end of the shaft is fixed a runner by means of a driving iron a. On the lower end of the shaft is set a wooden hub furnished with ten to twelve paddles. The number of revolutions of the water-wheel is from forty to eighty per minute, the fall of the water being 3J to 7 feet. The diameter of the grinders is Ij to 3| feet, the thickness 3j to 7 inches. FIG. 23. A Caucasian Mill with three Sets of Grinders. These mills are usually furnished with one burr, and are built on mountain brooks. Their capacity varies from 1 to 8 or 10 poods l per day. Fig. 22 is a photograph of such a mill, with a single set of grinders. It is of brushwood wicker-work, with a thatched roof. Fig. 23 shows a mill with three sets of grinders, and lastly, Fig. 24 gives us a view of nine such mills, situated along a mountain torrent, clinging to the mountain side like swallow nests. i lpood = 361bs. 22 FLOUR MILLING [CHAP. I In these mills the work is usually performed by women. This type of water-wheel became known in France and Germany only in the FIG. 24. A Row of Mills along a Mountain River. fifteenth century. Therefore, the supposition that these mills were brought to Europe by the crusaders at the end of the thirteenth century is quite just. CHAP, i] FLOUR MILLING 23 IV THE AMERICAN AUTOMATIC MILL A strong impetus was given to the development of milling technics in Europe by the Americans. The idea of an automatic mill, as of many other improvements in machines connected with the principle of auto- matism, belongs to them. It is astonishing, but a fact nevertheless, that the discovery of the French quarry " La Ferte-sous-Jouarre," producing the famous French stones, was made by the Americans. That stone was used in America for making grinders a long time before it became known to the French millers. The Americans threw away the sifting bag of the old European mill, and substituted for it cylindrical and polygonal reel-separators, which are also American inventions. For the transportation of the product the Americans adapted elevators and conveyors. For the cooling of flour special apparatus called hopperboys were planned. The flaxen tissue in sifting bags was supplanted first by wool, then by wire, and lastly by silken tissue. Thus everything tending to progress in the technics of the furnishing of mills in the end of the eighteenth and first quarter of the nineteenth centuries belongs to the initiative of the Americans. For nearly forty years, up to the thirties of last century, the teacher of the Europeans was the celebrated American engineer, Oliver Evans, whose book has passed into thirteen editions, 1 and was translated into French and German. In the review of European mill building the great influence of America on Europe in that respect will be pointed out. At present, we shall give a description of a typical American automatic mill, the design of which was completed by Evans as early as 1783. Fig. 25 illustrates the whole process of milling in a longitudinal section of Evans' mill (Evans' automatic mill). The mill is situated on a river. The reception of the grain is effected either by means of an elevator from a vessel, or from carts brought up to the mill. We shall first examine the reception from carts. The grain is poured out of sacks down spout 1 on to a scale 2. After being weighed it is let down into the grain bin 3 (black pit), and thence through spout t conducted to the elevator 4-5, which supplies the large bin 6. Part of the floor below 6 is also occupied by bins, ending in a 1 Oliver Evans, The Young Millwright and Miller's Guide, the thirteenth and last edition published in Philadelphia, 1850. 24 FLOUR MILLING [CHAP. 1 pyramidal bin 7, on the next floor but one below. Out of bin 7 the grain passes through the hopper 8 into the burr, the purpose of which is to rub off the outer husk, remove the germ and dirt. Consequently this grinder is the same as the German Spitzgang. The grain, comparatively cleaned of husk, germ, and dirt, is aspirated in passing out of the grinder, the clean grain falling again into bin 3 (no dirty grain is mixed with it, as it- was all passed into bin 6), the heavy refuse into bin 9 lying below, while FIG. 25. the air and light refuse are blown out through an opening in the bin 9a. In proportion to the freeing of the grain of its husk, it is taken by the same elevator 4-5, this time into bins 10 and 11. From these bins it is conveyed into the reel- separator 12, where the small grain and chaff are sifted away. The throughs of that separator are fanned, therefore the good grain falls into bin 14, the light kernels and chaff are blown by the ventilator into bin 32, and still lighter refuse into bin 33. Out of bin 14 the cleaned grain passes into conveyor 15-16 with paddles right and left, which discharges the grain into conveyor boxes 17, 7, 18, which feed the grinders 8, 19, 20. CHAP, i] FLOUR MILLING 25 After the grinding the product is conducted into the common con- veyor 21-22 and then into elevator 23-24, which passes it into the hopper- boy 25, a kind of flour mixer designed by the Americans for the purpose of cooling the product. On leaving the hopperboy, the flour flows first on to two cylindrical reel-separators 26, where the throughs are conveyed into bins 28 and 29 with a chamber for flour, and the refuse left on them is once more sifted on the controlling separator 27. The refuse from separator 27 is taken by conveyor 31 either to bin 32 to the light kernels and chaff, and then reground on grinder 8, or ground apart. Thus we have a complete automaton, with grain-cleaning and repeated grinding of the product, if needed. The principle of sorting the product according to quality was known to Americans long before the Europeans learned of it, and effected with much greater success. It is ne- cessary to describe the sorting cylinder 12, where the coarse im- purities as well as chaff or small grains are sorted away (Fig. 26). This cylindrical reel-separator is an invention of Evans (called " Rolling Screen and Fan "), and works in the following manner : F IG 2 6. out of the conveyor box r the grain flows into the inner cylinder b concentric to cy Under a. The meshes in the cloth of cylinder a are smaller than the grain, those of cylinder b larger. The two sieves are joined to each other. The refuse of sieve 6, large admixtures, passes into box e, the throughs into sieve a. The refuse of sieve a, the good grain, flows into bin k, and the throughs, fine dust, &c. . fall through a crevice in the air-pipe. The grain and throughs are subjected to the effect of a current of air blown by fan g along /. The dust is carried out and the heavy refuse falls into bins i and h. The diameters of these cylinders are 2, 5, and 3 feet ; the number of revolutions 15 to 18 per minute. When the mill is supplied with grain from a barge or vessel, the re- ception is accomplished by an elevator, 39, which ascends and descends with the aid of chain sheaves 42-43. The elevator pours the grain into the conveyor 45, which carries it into bins 10 and 11, the conveyor being exhausted the while. The dusty air is discharged out of the conveyor 45 on its left side, and out of the grain-cleaning chamber of the mill through the outlet Q. 26 FLOUR MILLING [CHAP. 1 V THE INFLUENCE OF AMERICAN TECHNICS IN EUROPE In the civilised countries of Western Europe for many centuries the system of a single milling passage reigned, and is still adhered to, in peasant windmills. In those mills both grain and husks were ground in millstones, and the flour was sifted through hand-sieves of horsehair preparatory to baking. Some 250 years ago the sifting bag was adapted to the mill and performed the work of a sifting apparatus. Over 150 years have elapsed since the French technics introduced a new style of milling the repeating type (mouture economique), which is beginning slowly to spread in Europe. Up to the end of the eighteenth century the milling technics of Europe remained the same with scarcely any alterations, there being no motive cause for progress, either in social organisation or in the trade- corpora- tion industry. Flour mills were working almost exclusively to supply local needs, and seldom for neighbouring districts. The last quarter of the eighteenth century witnessed the beginning of the gigantic breaking up of the economic structure of feudal Europe, caused by three powerful historical factors, which brought about a new era of progress. Those factors were : the perfecting of Watt's steam- engine, the struggle for liberty in America, and the French Revolution. Technical progress and the victory of the middle-class over the feudal system in Europe rendered possible the organisation of industry on new principles of production, those of capital. The first country benefited by the principle of capitalism in the flour- milling sphere was America, as the production of flour in the United States required a great number of mills. The want of hands and the high wages forced the Americans to have recourse to a rational technical organisation of production. To that end, in the beginning of the nineteenth century hundreds of automatic mills, similar to the one described, were built in America, chiefly in the state of Pennsylvania and along the river Mississippi. The influence of American milling technics became noticeable first in the English milling industry, partly by reason of their economic relations, which were closer between these two countries than between the others, partly owing to their common tongue. Yet that influence commenced only after 1781, as is proved by the fact that the most reliable English CHAP, i] FLOUR MILLING 27 work of the time (Bees' Cyclopcedia) in its chapter on flour milling * gives a detailed description of English mills, in which no mill of American type is mentioned. It also speaks of a celebrated English engineer, Smitton, who built in 1781, in Deptford, a mill for the needs of the fleet, called by him " The Steam Mill," according to his own system that he had worked out as early as 1754. The motor adapted by Smitton was Newcomen's steam pump, which pumped water into tanks, placed at a sufficient height. The water, flowing from these tanks on to the water-wheels, worked the mill. At the end of 1782, Watt had so far perfected his steam-engine, that it was possible to adapt it for immediate use in working a factory. In 1785 was built the first steam-mill in London close to Blackfriars' Bridge, which was called Albion Mills. It was built and arranged by the engineer John Rennie, and the Watt's steam-engine was purveyed by the works of Boulton & Watt, in Soho. The mill only began operating in 1786, having ten millstones for wheat grinding. The capacity of the steam-engine was 50 h.p., 1 h.p. grinding 63 Ibs. of wheat per hour, and burning about 3| cwt. of coal per hour ! But even that great expenditure of fuel was considered to be very profitable, and, judging by the results of milling, Rennie's mill was recognised to be exemplary. During the end of the eighteenth century, mill-building in England made rapid progress. Besides the brothers Rennie (George and John), in that department, the names of Modsley, Etken, and Steel in London, Fenton, Murrey, and Woods in Leeds, and Fairbairn and Lille in Man- chester are renowned. George and John Rennie built a mill, the largest in the world 2 at the time, in Plymouth, for the victualling of the fleet, containing twenty- four millstone sets. This was probably the first fireproof mill, as the building was constructed of iron and stone. The millstone sets were divided into four groups, each group of six being driven by one large cogged wheel. VI MILLS IN FRANCE Flour milling in France of the eighteenth century was far superior that in other European countries. In a book by Malouins, published in 1767, we find the description of a mill where the product was twice 1 Rees' Cyclopcsdia, vol. xxiii., 1781. 2 Ibid. 28 FLOUR MILLING [CHAP. I sifted by means of reel- separators. Fig. 27 is a rather primitive, but sufficiently characteristic drawing of the inner arrangement of the mill. The millstone set GK rests on a timber bursting M. The feed- hopper B is filled with grain by a workman. The float D in the feed is a sufficiently heavy plank attached by a string C to the bell E. When the grain is spent and the hopper is empty, the falling plank D pulls the string, and rings the bell as a signal. A large wooden box L and two separators K-K are placed under the FIG. 27. bursting. The ground product flows into the upper separator or dresser. The refuse from that separator passes on into the lower one. The throughs of the separators yielded flour which was collected in the box L. To prevent the flour from escaping into the building, the box and separators were hooded with a curtain which formed a kind of dust chamber. The tissue* in the separators was woollen. In proportion to the flour collected in the box the curtain was lifted and the flour removed with shovels. CHAP, i] FLOUR MILLING 29 The influence of American milling technics began to penetrate into France much later than into England. In the celebrated Methodical Encyclopedia of Diderot and D'Alambert (1788), a mill of the end of the eighteenth century is described greatly resembling the type of mills constructed in the beginning of that century, depicted by Belidor in a work called Architecture Hydrolique, as early as 1737. Such stagnancy in milling technics and industrial life generally has its explanation in the stormy period of the French Revolution and in the wars of the succeeding Empire. Only after the continental wars had ended did the industry of France revive, and flour milling adopt the Anglo-American type of mills. These new types of mills in France were built by English fmns. In 1818 the English engineer, Modesley, was building a mill of four millstone sets in St. Quentin. In 1825 Atkins and Steel built a mill in St. Denis, near Paris, for Bensit, who acquired a name in the French milling literature later. But the vivacious and creative mind of the French was not satisfied in the further development of mill-building with imitating the English and Americans. French engineers have introduced many original inven- tions, chiefly in the sphere of transportation, cleaning of grain/and dress- ing the product. The building of their mills excelled in beauty of archi- tecture, and the departments in proportionality of sizes. One of the greatest inventions of the French of that time is the cleaner and separator, the most indispensable machine of the grain-cleaning de- partment. Doubtless the development of milling technics pushed the question of perfecting the water-wheel, adapted then almost exclusively in mills, to the front, and it was Fourneyrond who produced the first turbine. This was of no less importance to the development of milling in France than was Watt's steam-engine in England. VII PROGRESS OF TECHNICS IN GERMANY The old German mill which was in use up to the fifties of the nine- teenth century l is illustrated in Fig. 28. Such mills (section in Fig. 28 A) were driven by a water-wheel with the aid of a mangle gearing m-l. The mangle gear I is set on a spindle resting on the step-bearing K dng on a beam p which may be raised and lowered, regulating the Listance between the grinding surfaces. The adjustable grinder B is con- lected with the spindle by a driving iron i. Fig. 28 B gives the side view, 1 Prechtl, Technologische Encyclopadie, vol. x. Stutthard, 1840, 30 FLOUR MILLING [CHAP, i From the millstone the flour flows into a woollen sifting bag K, to which a vibratory motion is communicated by a fork v, performing returning oscillations from shaft v r The fine flour, sifted through the bag K, passes into the box L. The bran, semolina, and coarse meal (overtails) fall on sieve M, where the bolting is repeated. In this manner, two kinds of flour were obtainable, and semolina, which was then reground. Sometimes the sifting bag was replaced by sieves of different density, to obtain a greater number of kinds of flour. C is a solid driving iron. D a ratchet wheel for the vibratory motion of the shoe set into the opening of the runner (see A) ; Fig. E, a mechanism communicating the vibratory motion to the fork v which shakes the sifting bag. The mechanism shown in Fig. F, and the working of which is obvious, was frequently adapted for the same purpose. In the first and second case the revolving cross-head w acting upon a wooden spring v 2 effects a vibration of the rollers on which the spring is set. Fig. G is a sieve M for sifting the overtails from the sifting bag ; Fig. H is a wooden spring counterbalancing the vibrations of the sieve M . The tightening of the spring is regulated either by transposing the taper-pin i, or tightening the string s. On Figs. K and N we find the shaft and screw apparatus for raising the vertical journal p when the distance between the grinding surfaces is to be regulated. The new mill made its appearance in Germany later than in England and France. The feudal system, the corporate organisation of the trades, and the conservatism in technics maintained by them were the chief causes of this tardiness. The feudal law had created the so-called " compulsory grinding " in the mills belonging to the landowner, thus putting the monopoly of production into the hands of the lord of the manor, and precluding any possible competition. Yet the necessity of competing in the market and fighting against the imported French and English flour forced the Germans to adopt the American type of mill, as more efficient and pro- ducing better flour. Having grasped the advantages of the American mill, the German engineers and industrial promoters commenced studying that type with the carefulness and minuteness characteristic of the nation. The first German flour mills of the Anglo-American type were built and began operating in Prussia. As early as in 1825, such a mill was arranged in Magdeburg by F. Murrey of Leeds; in Guben, under the supervision of an enterprising leaseholder, Korti. Jn Berlin there sprang into existence a steam-mill of Schuhmann CHAP. l] FLOUR MILLING 31 FIG. 29. 32 FLOUR MILLING [CHAP, i and Kratzeke arranged by an engine-builder Freund after the fashion of English mills ; and on the upper Oder a steam-mill of the American type, similar to that in Guben, was working. The Prussian trade committee furthered these beginnings in every way, by publishing, for instance, in 1825 detailed drawings and descrip- tions of the best English and American mills, and sending in 1827 two pupils of the Imperial Trade Institute (Hantzel and Wulf), who were studying mill building, to America and England, to acquire practical knowledge in everything pertaining to the question. Hantzel and Wulf's report was published by order of the Prussian Government of 1832, and these two builders erected with great success several large mills and very skilfully performed the milling operations. In the western provinces of Prussia the Ober-President von Winke became renowned, having built about 1830 the first standard mill of the American type on the river Leine. In the south of Germany the first to introduce mills of American con- struction was the Royal Government of Wurtemberg. The first mill of that type was erected on the site of an old mill belonging to the treasury in Berg, by Stutthart. The building of that mill was begun in the summer 1830, and ended in 1831. It commenced operating on the 1st September 1831. Here three water-wheels set into motion ten millstones, three aspirators and three separators with silk cloth, one sieve, two product elevators, one sorting dresser, and several sifting machines. In a short time the flour from this mill commanded so extensive a market that by 1832 an en- largement of the mill was thought of. But the greatest good the mill wrought, was the example it set, for soon in different parts of the kingdom mills of the Berg type sprang up. Such mills were erected in Althausen, Zeflingen, 'Urach, Reutlingen, Tubingen, Esslingen, and Heilbronn. Some time before the mill in Berg was built, the attention of the Royal Government of Bavaria was attracted to the question, and it published on 27th February 1828 the following announcement : " A remuneration of 3000 guldens will be allotted to the man, who in two years' time shall have built and commenced working a flour-grinding mill of at least three stones, constructed after the manner of those suc- cessfully operating for several years, in England and North America." The sole claimant of that prize,a mechanic, Spat of Nurnberg,announced in 1831 that a mill of the type mentioned, containing four millstones and driven by an overshot water-wheel, had been erected by him, and was CHAP, i] FLOUR MILLING 33 working. Spat was awarded the prize in 1832, notice being taken of the fact that " the mill is indeed of the Anglo-American type, but somewhat modified." This improved mill of Spat's enjoyed no great success as an example to be imitated, and in 1837 a miller, Bachmann, was sent by royal order for the Bavarian Millers' Union to Wiirtemberg to study the American mills of that country. A far larger field was gained by the Anglo-American mills in the following years (1833-35) in Prussia, where the Royal Sea Trading Society took a prominent part in their diffusion. From 1822 that Society, acting on behalf of the merchants of Dantzig, distributed the grain purchased by it among the local mills and sent the fine flour partly to England, partly to Transatlantic ports. Thereby the traders soon arrived at the conclusion that German flour milling was too far behind that of foreign countries, particularly of North America, to enable them to compete successfully on the outland markets. In consequence, the Society purchased a milling plant situated on the Oder in Tiergarten, in the neighbourhood of Ohlan (in Silesia), and entrusted its reconstruction in the American fashion to an experienced technical miller named Hantzel. In 1834 eight stones of the rebuilt mill were installed and started, two more flaking mills being added to the number later on. This mill was the standard for mills built in after years, and produced flour of a higher quality for home use, as well as for export. At the same time private industry did not remain inactive. Par- ticular attention must be called to the effort of a merchant, Witt by name, who greatly assisted the development of the flour-milling industry in Dantzig. In a mill with twenty pairs of stones, rented by him in Dantzig, he had twelve reconstructed, on the American system, and added new ones to them, so that in a short time he had no less than thirty-one millstone sets of perfected construction in operation. The second of the above-mentioned engineers who had been sent to America, Wulf, had an open field here for developing his activity on a large scale in the capacity of director of the technical side of the business. Biischer of Neustadt-Eberswalde next deserves mention. He was a government engineer, and with his five-stones mills of the American type strove to enable the owners of small mills, without any marked alterations to the plants, to produce flour which only slightly differed in quality from the product of the most perfect mills of the day. In 1835, Kriickmann, the owner of a mill in Berlin, adapted his 34 FLOUR MILLING [CHAP, i three-stones mill for hard grain, and shortly afterwards a councillor of commerce, Grunau in Elbing, reconstructed his mill in the improved style. Before that, on the Rhine, opposite to the town Neuwied, on an estate, "' Zur Nette," belonging to Karl Winz, a mill on the American system was erected and worked. This mill contained four sets of stones driven by two water-wheels. VIII FURTHER DEVELOPMENT OF MILL-BUILDING IN EUROPE In 1823, after unsuccessful attempts by Helfenberg in Rohrschach (Switzerland, cant. St. Gallen), Ballinger in Vienna, and von Kollio in Paris, a certain von Miiller of Lucerne began building, first in Warsaw, then in Triest, and lastly in Frauenfeldt in Switzerland, mills which operated by means of iron rolls instead of millstones. These rolls did not fulfil the hopes placed in them, and it was only in 1834 that a Zurich engineer, Sulzberger, eliminated the defects of the roller mill and attained real success. The joint stock company established by Miiller in Frauen- feldt began to build roller mills with an unusual energy, and not only successfully erected Muller's mill in Warsaw, Triest, and Frauenfeldt, but took pains to build such mills in other localities too. These mills were driven by steam-engines. With a steam-engine and a sufficient quantity of fuel and water for feeding the boilers, it was possible to set up a reliable motor anywhere. In 1836 there were several steam-mills in Prussia ; Berlin alone was in possession of three of the number. In Austria-Hungary the first steam-mill began working on the 26th September 1836 in Odenburg (in Hungary in the neighbourhood of the lake Neusiedler). About that time a similar mill came into existence in the Grand Duchy of Baden in Mann- heim ; a little later, in the Grand Duchy of Hessen, two large steam-mills began operating, one owned by Schneider & Co. in Oppenheim, close to the banks of the Rhine, the second in the vicinity of Weissenau by Mainz. In Hanover a leaseholder, Fiedler, had mill-plants of the American type in Klickmuhle (capital of Hanover) in 1832, and the first steam-mill in Rehden was started by Hartmann in 1836. All these enterprises enjoyed great success, as, thanks to them, wheat gained near markets, and local consumers received flour of a higher CHAP. l] FLOUR MILLING 35 FIG. 29. 36 FLOUR MILLING [CHAP, i quality. The Hanover steam-mill in Rehden, which ran some two years only, proved to be the sole exception. The main causes of its failure were the restrictions it was placed under by the restrictive and archaic regulations imposed by the trade corporation ; besides which its being situated among large water-mills, and the excessive consumption of coal by the boilers, were factors which influenced its fate. The first wind-propelled mill of the American type in Germany is the mill by Breslau, constructed by Hofmann, a then well-known factory warrant officer, about 1836. Fig. 29 shows a vertical section of the mill with its full equipment. On the top floor, under the roof, is a hollow main shaft of cast iron cc, with spider a and wings &, which may be brought into any position (to assume a working taper of the surface of the wings) by the aid of straight and angle shafts, moved by shaft d and rope e with a shaft k and counterbalance m. The motion of the wind propeller is transmitted by means of cogged wheels e and / to the vertical main shaft A of the whole plant. The seventh floor (some 20 ft. in diameter) contains supply bins KK for grain and an appliance for elevating it. The sixth floor is designed for grain- cleaning apparatus, of which only the so-called smutters (machines for freeing the grain of its husk) GG, driven by gears H and J, are shown here. From this floor the grain passes into bins EE on the fifth floor. In all probability, other cleaning machines were stationed on the third floor, as the smutters would not be sufficient for that purpose. On the fourth floor we find the stones DD, set symmetrically in a circle, the radius of which is self-defined, owing to a large cogged wheel B, which couples with the gears of the spindles of all four millstones. On the third floor are stationed the cogged wheels driving the mill- stones and gears, and two mill-drives MM for collecting the grain and cooling the product. We may add that of the four pairs of millstones (5 ft. in diameter), two pairs were from a French factory (La Ferte), the other two being from the Rhine (of volcanic basalt in the environs of Andernach). These stones made from 100 to 110 revolutions per minute, the wind pro- peller making 10 to 12 in the meantime. On the second floor are the sifting bolters NN. The middle part of that section, supported by strong wooden pillars, serves for storage. In the ground floor is the hand-press QR for packing the flour pur- posed for export into barrels S. CHAP, i] FLOUR MILLING 37 IX THE STRUGGLE BETWEEN THE ROLLER AND STONE MILLS The first steam roller mill of the Sulzberger (Frauenfeldt) type appeared at the end of 1837 in Mainz ; it was followed by similar mills in Stettin, Munich, and, at the end of 1837, in Leipzig. Steam roller mills made their appearance in Austrian dominions, Buda-Pest, and Milan, probably at the same time. The costs of arranging such a mill, with a capacity up to 300 centners l of wheat per day, amounted to 156,500 guldens, with a floating capital of 93,500 gulds. These Sulzberger roller mills were adapted solely for factory pro- duction of flour, suitable chiefly for export, as the product did not become heated in grinding, while it was possible to grind only perfectly dry grain. The roller-ground flour first gained great popularity from its good outward appearance and high quality. It was even maintained that this flour contained more nutritive matter than flour ground on stones. In Prechtl's Technological Encyclopedia were given the results of the analysis of flour from a Milan flour mill made by a professor of chemistry, Ottavio Ferrario. Roller-ground flour Stone-ground flour Gluten . . / . . 0-152 0'131 Starch ... . . 0'706 0'680 Sugar . \. . . . . 0-052 0'048 Gum .-.. . . . 0-031 0-027 Water . . . . . 0-054 0'095 Silicic acid ..... 0*005 0*015 Alum . . 0-003 Lime . 0-001 1-000 I'OOO , But gradually the opinion as regards roller mills began to change, to which assistance was lent by the circumstance of a quick discovery that on the roller mills of the day a perfectly pure product was not to be obtained, and special stone sets had to be built for that purpose. The owners of roller mills soon began to complain of heavy expenses incurred by the repair and oiling of the rollers, and particularly of the 1 Centner = hundredweight. 38 FLOUR MILLING [CHAP, i excessive expenditure of power and the necessity of employing many hands. Thus, for instance, the Ludwig mill in Munich produced 13,000 Bavarian bushels of flour per year on thirty-six roller mills, whereas the thirteen stones that were substituted in their place later, gave 26,000 bushels of flour, while the number of hands was reduced from twenty-eight to nine. In Saxony the mills of the Anglo-American type were first adopted at the end of 1838 in two localities : in Neumiihle by Dresden, and in Kloster-Miihle in Chemnitz. Both these mills were worked by water- wheels driving millstone sets. In the following year (1839), in Austria, a splendid mill was started in the town of Fiume (Croatia). This mill was situated within a half- hour's journey from the sea. It contained eighteen sets of French stones, 4J to 5 J ft. in diameter, driven by three overshot water-wheels with a total capacity of 95 h.p. Its capacity was to be 198,000 centners of flour from the best kinds of wheat Banatka, Russian, and Rumanian. In 1840 the plan of construction of a steam-driven mill, previously rejected, was worked out anew, and after a short time one of the best Austrian mills, the licensed steam mill in Vienna, was erected. The renowned firm of Coquerille, in Seraing, near Liege, supplied the mill with machinery, arranged it, supervised the erection of it, and took the whole responsibility upon itself. In 1842, when the mill began working, it was equipped with sixteen sets for wheat grinding, and two for that of corn. In course of time, it was enlarged to twenty-two sets driven by three Wolf's steam-engines, of the joint capacity of 200 h.p. When arranging the mill, it was designed merely for the Anglo-American low grinding which was not adapted for producing the so-called " Imperial Flour " (Kaiser mehl), which goes to the baking of rolls, very popular in Vienna. Therefore it soon had to be reconstructed for semolina grinding, on the French system or " Mouture economique," to be discussed later in the section treating of grists. In this manner the stone mill won the battle almost everywhere. Between the forties and to the sixties, the roller mill struggled in vain against the millstone set, improved by a system of exhausts and dust collection. However, at the end of the sixties, the factories of Escher, Wyss & Co.. near Vienna, and F. Wegmann in Zurich, brought out the perfected roller mills, which began successfully to supplant the stone set in the indus- trial flour mills. CHAPTER II GENERAL IDEAS OF THE RAW MATERIALS FOR FLOUR PRODUCTION THE BERRIES OF THE CEREALS THE berries of the cereals are the pre-eminent raw materials of the milling industry. In order to understand the working of the various grain-clean- ing and grain-grinding machines and to study the nutritive qualities of the products of the grain, it is necessary to be acquainted with the structure and the chemical composition of the berries of the different cereals. On first examination we see that the berry of the cereals has an oval form. If viewed through a magnifying glass some hairs, either forming a sort of beard (wheat, rye) or covering the whole body of the grain (oats), are perceived at one end of it, and the germ or the embryo at the other. On examining a slightly magnified section through the berry we can see that it consists of a starchy nucleus, surrounded by several coats or skins ; if we magnify the section 150 times we can discern six such coats which may be detached more or less easily from the berry. Flour or groats are made of the nucleus, and the skins yield bran, a by- product of flour manufacture. Each of the skins consists of several separate layers that cannot be easily detached one from another. We shall investigate them more closely when examining the wheat berry, and will now proceed to consider them briefly. The first three skins of the cereal berry (see Fig. 30) are called outer envelopes or envelopes of the fruit, the two second are the envelopes of the seed proper, the last one is (inaccurately) called the gluten envelope. The first envelope A (Epidermis, Epicarpium) consists of thick-walled cells filled with air, and disposed along the longitudinal axis of the berry. Its outer surface is either smooth or shrivelled, its colour varies according to the species of the cereal. It is often pierced through by hairs, acting as air-conducting channels while the grain is ripening. The second envelope B (Mesocarpium, Sarocarpium) consists of 39 40 FLOUR MILLING [CHAP, it colourless, or sometimes yellowish, loosely built cells. It is very thin and possesses no well-outlined characteristics. The third envelope C (Endocarpium) is composed of cells disposed at right angles to the axis of the berry. While this latter is still unripe the envelope is of a greenish colour, when quite ripe it becomes colourless. These three envelopes may be comparatively easily taken off the seed. The fourth envelope D (Testa Episperm) has oblong cells, much smaller in size than those of the outer envelopes. The fourth envelope D and the fifth E (Embryonic membrane) are called envelopes of the berry proper. They are both very thin, adjoin closely to each other, and it is most difficult to detach them one from another. The sixth envelope F (Perisperm) is a layer of aleurone, and is also called the gluten envelope. Its volume constitutes one third of the total volume of all the envelopes. Its cells have very stout walls ; they are very hygroscopic, and being put in water soon become swollen. It was formerly supposed that they con- tained gluten (anendosperm-nitrogen^ ous substance), and the envelope was therefore called the gluten envelope. And though the careful analyses made by Shenk and Brucke have shown that these cells do not contain any gluten at all, the term is still in use. The gluten envelope comes into a close touch with the endosperm and the envelopes of the seed proper. It is therefore possible to take off the three inner envelopes of the berry without breaking this latter. The nucleus G (Endosperm) that yields flour when broken, consists of comparatively small cells with thin, colourless walls. The cells of the endosperm are filled with granules of starch and very small granules of gluten (cleber). The nearer to the centre of nucleus the smaller is the proportion of gluten in the cells. The largest quantity of it is contained by the cells that adjoin the sixth envelope of the berry. A section through the nucleus is either flour- white, or has the appear- FIG. 30. CHAP, n] FLOUH MILLING 41 ance of a glassy, somewhat yellowish substance. The colour of the nucleus darkens gradually from the centre towards the outer cells. The germ H of the berry is firmly attached to the nucleus. Its cells are tiny and very compact, and contain much nitrogen, mineral salts, and fats. While the plant is developing the germ is fed on the starch and the cleber of the nucleus. This accounts for the so-called germina- tion of the raw grain kept in a warm place. The envelopes are not, as we are going to see, of a nutritive nature, and must therefore be removed before the endosperm is finally reduced to flour. Their total weight constitutes from 17*6 per cent, to 30 per cent, of the weight of the berry. Let us now examine in detail the wheat berry. II PHYSICAL STRUCTURE OF THE WHEAT GRAIN The functions of the grain are those of reproduction, hence its struc- ture. The grain consists of three distinct parts : the germ, the endosperm, and the bran. The germ is the seed properly speaking, for it develops ultimately into the plant. The endosperm consists of a starchy sub- stance ; it constitutes the main body of the grain, and is destined to supply food to the germ in the early period of its growth. The bran consists of several separate coverings, which enclose both germ and endosperm, and are destined to protect the grain. The study of the physical structure of the grain requires the use of the microscope. Fig. 31 represents a section through the crease of the grain, shown in elevation by shading on the left-hand side of the sketch. The figure has been obtained by tracing from typical slides, and reproduces fairly well the relative dimensions of the germ and the endosperm. The bran is seen to enclose both. With the aid of a microscope one can see the so-called aleurone cells or the square cells of the bran lining the interior. The name "gluten" cells, though commonly used, is not accurate, for these cells contain no gluten. Fig. 32 shows a cross section through the germ of a Kubanka wheat grain. Here we see the pigment-containing cells going all round the grain and forming in the crease a thick spot of colour. The aleurone cells of the bran do not continue round the germ. The next figure (33) represents the same section, but examined with a higher power objective. 42 FLOUR MILLING [CHAP, it Hairs of Heard. Cuticle. Epicarp. Endocarp. Episperm. Aleut-one Cells. -BRAN. It shows more clearly the outer skins of the bran and allows us to see quite distinctly the square aleurone or cerealin cells. At the bottom of the crease they become more numerous and form a double line. The bifurcation of the crease is perfectly distinct. The rather large dark yellow spot of pigment cells is plainly seen in the middle of the fork. The starch granules are also seen. In order to examine the bran and the endosperm we must select a very thin section. The bran consists of the outer envelopes of the grain and those of the seed proper. Fig. 34 shows them all on a longitudinal section. a is the outer " epidermis " or cuticle. It constitutes, ac- cording to Mege Mouries, 0'5 per cent, by weight of the whole grain, and consists of thick- walled, longitudinally disposed cells. It is often pierced through by hairs acting as air-conduct- ing channels while the grain is ripening. 6 is the "epicarp." This amounts to about 1 per cent, of the grain ; it is very thin and possesses no well-defined characteristics. c is the " endocarp " and the last of the outer series of the grain envelopes. Its cells t Starch eett fitted (with granules, f Parenchymatous I cellulose dividing \ endosperm into \8tarch cells. (Compressed empty \cellsofeiidosperm. ( Termination of \ aleurone cells at *- commencement of Germ. ) Absorptive & secre- \tive epithelium. Plumula sheath. Scutellum. f Elongated cells of .. I scutellum. I Rudimentary leaves ) of Plumula. f Testa or continuous J envelope enclosing | both Endosperm \and Germ. Radicle. Root Sheath. Radicle Cap. E. Endosperm. G. Germ. FIG. 31. Longitudinal Section through a Grain of Wheat, magnified about 10 Diameters. are disposed at right angles to the axis of the grain, and appear to be almost round on the longitudinal section. Its weight constitutes 1*5 per cent, of that of the grain. d is the " testa," the first of the two envelopes of the seed proper. It is also called "episperm." It consists of oblong cells much smaller in size than those of the outer envelopes and contains most of the colouring matter of the grain. e is the " embryonic membrane " and the second envelope of the seed proper. It is very thin and closely adjoins the testa. Together they constitute 2 per cent, of the grain. CHAP. II] FLOUR MILLING / is the layer of " aleurone " cells. These cells appear to be almost square in outline and have very stout walls. They absorb moisture easily, and being put in water, soon become swollen. As already men- tioned, they only enclose the endosperm and do not envelop the germ. FIG. 32. Transverse Section of Grain of Wheat, magnified 13 Diameters. FIG. 33. View of Crease in Grain of Wheat, as shown in a Transverse Section. g is the layer of parenchymatous cellulose, which divides the endo- sperm into comparatively large cells. These latter are filled with granules of starch and very small granules of gluten. Towards the centre of the endosperm the proportion of gluten becomes smaller. FIG. 34. Longitudinal Section through Bran and Portion of Endosperm of Grain of Wheat, magnified 440 Diameters. FIG. 35. Outer Layer of the Bran of Wheat, magnified 250 Diameters. h is the " hilum " of an individual starch granule. The envelopes must be also examined on the flat. They can be detached easily enough off the body of the grain in three layers, (1) epi- 44 FLOUR MILLING [CHAP, it dermis and epicarp, (2) endocarp and episperm, and (3) the inner skin which contains the cerealin cells. Fig. 35 shows the structure of the outer layer. Its cells are arranged longitudinally in the direction of the grain and are four to six times larger in length than in breadth. Fig. 36 represents the hairs of the beard at the end of the grain. We can see on the section itself how they are attached to the skin ; the mount also shows canals ex- tending about half the length of the hair. Fig. 37 shows the structure of the second layer. We see that it consists of two layers, one over the other, which FIG. 36. Beard of Grain of Wheat. . J . ,. are not both in focus at the same time. The upper layer consists of a series of long cells often termed " girdle " cells, and arranged transversely to the longitudinal section of the grain, as shown on Fig. 34 (marked c). On this they seem to be almost round. Underneath the girdle cells are the pigment- containing cells. Fig. 38 shows the aleurone or cerealin cells of the bran to be of an FIG. 37. Middle Layer of the Bran of Wheat, magnified 250 Diameters. FIG. 38. Inner or Aleurone Layer of the Bran of Wheat, magnified 440 Diameters. irregular outline, though when viewed on section, either longitudinal or transverse, they appear to be square or rectangular, and are therefore often termed cubical. Let us now compare the longitudinal section through the bran of wheat, as shown on Fig. 34, with its transversal section shown on Fig. 39. CHAP. II] FLOUR MILLING 45 Though the latter section was not so good as the longitudinal, the drawing shows clearly enough the general structure of the bran. The cells of the middle skin appear to be of considerable length when we see them on the flat. When we look on them lengthwise, we must, of course, notice the ends of the cells of the outer skin. The aleurone cells appear more irregular in outline on the transversal section than on the longitudinal. The study of these drawings must, of course, be followed by an examination of the actual slides under the microscope. The bran of the wheat berry is chiefly composed of cellulose FIG. 39. Transverse Section through Bran of Wheat, magnified 250 Diameters. or woody fibre and of solu- ble albuminous matter. When treated with hot dilute solutions of acid and alkali it yields cellulose in a fairly pure state. The following is the way to obtain cellulose for the purpose of microscopic study : pieces of the different layers of bran are put in separate test-tubes and subjected for an hour to the action of dilute FIG. 40. Cellulose of Outer Skin of Bran, magnified 250 Diameters. FIG. 41. Cellulose of Middle Skin of Bran, magnified 250 Diameters. sulphuric acid. Then this latter is poured off and substituted by caustic soda solution, in which the pieces of bran are digested for another hour. Then solutions of 1 part respectively of acid and alkali and 20 parts of water are used, and the resulting cellulose can be mounted on glass glides, 46 FLOUR MILLING [CHAP, ii Figs. 40, 41, 42, and 43 show respectively the cellulose of the outer, middle, and aleurone layers of bran as viewed under the microscope. The structure of the first and second pieces of cellulose does not differ much from the structure of the original layer of skin. The first appears to be almost transparent, and in the second the underlying pigment cells are partly stripped off. The aleurone layer changes considerably in appearance, when treated with alkali, for it contains a large quantity of protein matter. Fig. 42 shows a piece of this layer, in which the greatest part of protein has been removed by the action of the caustic soda. Fig. 43 shows another specimen, in which there remains almost no protein at all. The outer layer of wheat bran is thus largely composed of cellulose, FIG. 42. Cellulose of Aleurone Layer of Bran, with Portion of Protein re- maining, magnified 440 Diameters. FIG. 43. Cellulose of Aleurone Layer of Bran, with only the slightest Trace of Protein still remaining in some of the Cells, magnified 440 Diameters. and cannot, therefore, be used for human food. The middle layer contains less cellulose, but a larger quantity of colouring matter. The inner contains but a very small proportion of cellulose and large quantities of protein. This latter is injurious to the flour, for it exerts a strong action on broken starch granules. None of the three must be therefore admitted as a part component of the flour. If separated from the bran and subjected to acid and alkali treat- ment, the endosperm yields traces of cellulose. It is most instructive to subject to the same treatment several different varieties of flour. CHAP. II] FLOUR MILLING 47 This will allow the student to examine (1) whether the flour contains a large proportion of particles of bran, and (2) whether the latter remains intact, or portions of it have been detached from one of the surfaces and ground into flour. III CHEMICAL COMPOSITION OF WHEAT The grains of the cereals consist, as shown by analysis, chiefly of the following substances : fat, starch, cellulose, dextrin, sucrose, probably also other kinds of sugar ; soluble protein bodies ; albumin, globulin, and proteose ; insoluble protein bodies ; glutenin and gliadin, which together constitute gluten ; mineral matters, principally potassium phosphate, and finally water. Bell has tabulated as follows the average composition of the different cereals : TABLE I Wheat. Carolina CONSTITUENTS. Long- eared English Oats. Maize. Rye. Rice without Winter. Spring. Barley. Husk. Fat 148 1-56 1-03 5-14 3-58 1-43 0-19 Starch . . 63-71 65-86 63-51 49-78 64-66 61-87 77-66 Cellulose 3-03 2-93 7-28 15-53 1-86 3-23 Traces. Sugar (as cane) 2-57 . 2-24 1-34 2-36 1-94 4-30 0-38 Albumin, &c., insol-| uble in alcohol . / 10-70 7-19 8-18 10-62 9-67 9-78 7-94 Other nitrogenousl matter soluble in I 4-83 4-40 3-28 4-05 4-60 5-09 1-40 alcohol . . J Mineral matter 1-60 1-74 2-32 2-66 1-35 1-85 0-28 Moisture 12-08 14-08 13-06 11-86 12-34 12-45 12-15 Total 100-00 100-00 100-00 100-00 100-00 100-00 100-00 Another comparative table of the composition of cereals was drawn ip later by Clifford Richardson. In this the moisture figures are con- siderably lower than in Bell's analyses, a fact that is due probably the greater dryness of the American climate. 48 FLOUR MILLING [CHAP, ij TABLE II AVERAGES or DETAILED ANALYSES OF CEREALS NUMBER OP ANALYSES. Wheat 27 Barley 14 Oats 18 . Maize 21 Rye 17 Fat 2-30 2-67 7-87 5-54 1-83 Starch . 67-88 62-09 56-91 66-91 61-87 Cellulose 1-90 3-81 1-29 1-41 1-47 Sugar, &c. ..... 3-50 7-02 6-07 2-18 7-57 Dextrin and soluble starch 2-30 3-55 3-47 2-18 4-75 Proteins insolublein 80 per cent. alcohol 7-45 7-86 13-43 4-96 9-07 Proteins soluble in 80 per cent, alcohol 3-58 3-66 1-82 5-84 2-53 Mineral matter .... 1-84 2-87 2-22 1-54 2-06 Moisture 9-25 6-47 6-92 9-34 8-85 Total 100-00 100-00 100-00 100-00 100-00 Ratio of proteins to carbohydrates . 6-9 6-5 4-8 7-6 6-5 Still later Hutchinson represented the general composition of the cereals in the following table : TABLE III CONSTITUENTS. Wheat. Barley. Oats, Rolled. Maize. Rye. Rice, no Husk. Millet. Buck- wheat. Fat . 1-7 1-9 8-1 5-4 2-3 2-0 3-9 2-2 Carbohydrates . 71-2 69-5 68-6 68-9 72-3 76-8 68-3 61-3 Cellulose . 2-2 3-8 1-3 2-0 2-1 1-0 2-9 11-1 Proteins . 11-0 10-1 13-0 9-7 10-2 7-2 10-4 10-2 Mineral matter 1-9 24 2-1 1-5 2-1 1-0 2-2 2-2 Water . 12-0 12-3 6-9 12-5 11-0 12-0 12-3 13-0 Analyses of Wheats from Different Countries. The tables on pp. 50-54 are the results of a series of analyses made by W. Jago. The first eighteen were made in 1884 on specimens of English wheat of the 1883 and 1884 harvests, and still represent fairly well the general composition and character of English wheats. Nos. 1-18 are samples of 1883 wheats, except where otherwise men- tioned. The figures of moisture, of soluble extracts and proteins are rather high, while those of gluten are lower than in foreign wheats. The Revitts yielded exceedingly small traces of gluten, so small that it was practically impossible to recover them from the bran, CHAP, n] FLOUR MILLING 40 Nos. 19-27 are all 1883 samples of wheats used by the millers of the south of England. Nos. 19 and 20 are samples of the same variety, but grown in different localities. No. 21 is a sample damaged during growth. Nos. 28-38 are fine quality samples of the south and western counties, all of the harvest of 1884. If compared to those of 1883 the figures of moisture, soluble extract, and soluble proteins are rather low. The average of the glutens is also lower. In the 1883 series No. 18, a Scotch west-country specimen, yielded the lowest percentage of gluten, 5*00, and the highest of moisture, 16- 18. Similarly, No. 38 of the 1884 series, grown in a damp climate, South Devon, yields 5'00 per cent, of gluten and 16*20 per cent, of moisture. Since 1884 several new varieties of wheat have been introduced in England. Among these, two varieties, " Tiverson's " and " Webb's Stand-up," are largely cultivated now. French wheats and the Hard Fife are also grown to some extent. The foreign wheats present, of course, a greater number of varieties than the English. A comparison between the moistures and the glutens of wheats and the flours produced from them is most instructive. Russian wheats yield generally a higher percentage of gluten than the American. The Indian are, as a rule, rather poor, both in gluten and in moisture. They appear to be almost sandy. When worked up with water, and only after long " conditioning," they acquire the charac- teristic ductility of wheaten flours. The Persian wheats contain more gluten than the Indian, especially the clean Persian, No. 68. No. 78 comes from Winona, U.S.A., and serves to make flours Nos. 8 and 9. The upper set of gluten estimations was obtained after the dough had stood for two hours. The wheat itself and the flours pro- duced from it absorb water extremely slowly. No. 80 comes from Manitoba. The comparatively high percentage of moisture, soluble extract, and proteins are characteristic of the cold climate. The sources of British supply have greatly changed since the time when these analyses were made. London gets now almost none of the United States spring wheats. The Duluth wheats have been largely substituted by the Manitoba. Durum wheat is imported from the United States in considerable quantities. * The winter Americans are known as Red Winter and Hard Winter. 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Il] FLOUR MILLING 55 Composition and Weight of Wheats according to Professor Fleurent.- Professor Fleurent has analysed certain hard wheats, Russian, Algerian, and Canadian (the last contained 25 to 30 per cent, of soft wheat), and tabulated the results as follows : TABLE VII Russian Wheat. Algerian Wheat. Canadian (loose Wheat. Average weight of grain in grams . 0-030 0-048 0-037 Constitution, per cent. : Endosperm . . 84-95 84-99 84-94 Embryo . . . . 2-00 1-50 2-05 Husk , : .;. . . 13-05 13-51 13-01 Composition of the Entire Wheat. Water . -. .'^ |> . 1142 11-34 11-36 Nitrogenous matter : Gluten ... . ..." 14-76 11-00 10-88 Soluble (diastases, &c.) . ".. 2-25 1-82 1-67 Ligneous, of husk 1-82 1-90 1-91 Starch . . 50-15 55-05 54-55 Fatty matters . . . . 1-18 1-93 2-70 Soluble carbohydrates : Sugars . . ; . 2-17 2-68 2-18 Galastose 0-65 0-46 0-75 Of husk . . . . 1-76 2-19 1-90 Cellulose " . , v 9-73 9-40 -21 Mineral matters . . . .'- 1-56 1-42 1-35 Undetermined and loss . 2-48 0-81 1-54 Total . . 100-00 100-00 100-00 The gluten contained by the Russian wheat consisted of gliadin, 46' 45 per cent., glutenin 37 '89 per cent., and congluten 15-66 per cent. Fleurent considers the congluten to be the cause of the want of elasticity of the flour obtained from hard wheats. Composition and Properties of Durum Wheat and Flour. Durum wheat, Tricitum durum, is cultivated in considerable quantities near the Mediterranean and in Southern Russia, and is chiefly grown for the manu- facture of macaroni. It has been also introduced recently in America, where bread flours are manufactured from it. Its grains are hard, am- bertiated, and almost twice as large as those of ordinary Russian wheats Norton, of the South Dakota Agricultural Experiment Station, has 56 FLOUR MILLING [CHAP, ii analysed durum wheat and investigated its properties. Also comparative analyses of Kubanka, one of the best Russian durum wheats, and Min- nesota, one of the best American bread wheats, have been carried out and tabulated together with the mean of American wheats (by the Bureau of Chemistry of the Department of Agriculture, U.S.A.). TABLE VIII CONSTITUENTS. Kubanka Durum Wheat. Minnesota Bread Wheat. Mean of American Wheat. Water r . '. . . $i 3-32 6-00 10-62 Mineral matter . 1-71 2-46 1-82 Fat . .'-,- . ' ' ,:-. , 2-34 2-49 1-77 Crude fibre . . . 2-52 3-35 2-36 Crude protein N x 5-7 -...' 14-46 13-21 12-23 Carbohydrates other than crude fibre 69-65 72-49 71-18 Sugar V . .. v- 3-26 1-42 . . Dextrin . . . 1-25 . . Invert sugar, soluble starch Nil Nil The percentage of sugar and of dextrin is remarkably high. Accord- ing to Stone, ordinary wheats contain 0'27 to 0*41 per cent, of dextrin. The flour obtained from durum wheat is estimated to contain 1 to 2 per cent, of sucrose, while the ordinary samples analysed by Stone only gave 0'18 to 0-20 per cent. The American durum wheat contains more protein than that origin- ally imported. Calculations on a water-free basis have given the following results : TABLE IX Number of Analyses. Protein NX 57. Imported seed .. . '' 7 15-73 per cent. Crop of 1901 . . 31 18-13 1902 . 32 14-57 1903 . , :.: . 45 17-34 The harvest of 1902 was rather bad. The durum flour has a deep yellow tint, that shows 0*25 yellow -f 0*17 orange on the Lovibond tintometer scale. The colouring substance is insoluble in distilled water, but can be dissolved in ether, alcohol, and CHAP, ii] FLOUR MILLING 57 dilute alkalies. From the later solutions it may be discharged by acids. This accounts probably for the fact that flour is stained yellow by the addition of sodium carbonate. A series of determinations made on durum flours gave the following figures (the gliadins were calculated on a water-free basis) : Crude protein . . , :' ' . W 15-00 per cent. Wet gluten . . . ' . .. -; 53-77 Dry gluten * ~ ' . . . . 17-68 Gliadin . . . . . . : '-. 7-87 Gliadin of total protein . . . . 47-17 The percentage of gluten runs very high, as well as that of sugar. And yet the flour possesses but little elasticity and very poor adhesive qualities, properties that are usually ascribed to lack of gliadin. Bread made with the poorer durum flours rises neither during the fermentation, nor in the oven. The baker's sponging test shows that good durum flours have as high a volume as the bread wheat flours. But durum flour becomes more sticky than these latter ; when the doughs are somewhat stiff they do not rise properly, and the bread obtained is heavy and poor of texture. Yet, when water is used in sufficient quantity, the volume, weight, and texture of durum breads are not below those prepared with ordinary wheat flours. CHAPTER III PREPARATION OF GRAIN FOR GRINDING I IMPURITIES AND THE PRINCIPLES OF CLEANING As we have already seen in the general review of the grain, the impurity of the stock is due to the character of the production. An admixture of seed of other plants is unavoidable even when the culture of the cereals is most careful. The separation of the seeds of foreign plants from the grain, although performed on the larger farms, is not satisfactory, the grain being usually prepared for sowing and not for sale. The grain of the large rationally worked farms is comparatively clean ; that of the Russian peasantry and small farms, on the other hand, some- times contains up to 6 per cent, of impurities. In addition to the seeds of foreign plants, the grains of bad quality of the corn itself belong to the impurities. Those are mainly the so-called " shrivelled " kernels, unripe at the time of harvesting and dried to light meagre grains, or those appertaining to harvests caught by drought and admixed to the normal grain. Kernels of corn stricken by some disease, e.g. smut, are also of this group. Assuming the corn to be ground at the mill is wheat, the kernels of other cereals, such as rye, barley, oats, &c., are to be added to the number of foreign matters. Besides being impure through admixtures of vegetable origin, the grain acquires impurities of organic and mineral substances, and particles of metals. The method of production, storage, and transportation of corn make the admixture of particles of straw, empty cobs, stones, dust and dirt that cover the grains, small stones, and lumps of earth inevitable. And then during the threshing and cleaning of grain on the farm more or less often nails, woodscrews, nuts, and other metal parts of machinery fall into it. All impurities may be classified in three groups : (1) Poisonous admixtures that may bring about an empoisonment, CHAP, in] FLOUR MILLING 59 not to mention the deterioration of the qualities of flour (its colour and baking qualities) : ergot, cockle, smut, &c., pertain to this class. (2) Impurities reducing the quality of flour. Here we find the seeds of non-poisonous plants, dust, and dirt. (3) Impurities that may do some damage to the machinery, e.g. rapid wearing out of sieves, breakage of parts of the machinery, &c. Stones and pieces of metal form this group. Now, if the mill is to yield a wholesome product of good quality, and the milling machinery is to be set in normal working condition, the grain should be freed of all this foreign matter. The impurities we have been examining usually differ from the sound product by one, or several tokens conjointly, of the following categories : (1) size, (2) specific gravity, (-3) shape, (4) natural peculiarity of the ad- mixture. The machine, designed for the extraction of foreign bodies out of the grain, is constructed in accordance with the particular manner in which the impurities differ from the main product. Thus four types of machinery, each taking advantage of the peculiar differences of the admixtures, have been evolved. But often the separation of the grain, and the extraneous bodies differing from it in size and specific gravity, is combined in one machine. II EXTRACTION OF PIECES or METAL FROM THE STOCK Magnetic Separators. Before feeding the grain into a machine all pieces of metal, that might damage the working parts of the machine, must be extracted. These pieces being exclusively of iron or steel, their extraction is based on the property of the magnet to attract and detain both metals. A magnetic apparatus adapted for that purpose is shown in its simplest form in Fig. 44. It consists of two cast-iron frames C, between which a cast-iron box D is placed. The frames and the box are bolted together. In the box is set a row of magnets, their poles a and 6 coming out on the surface, of the cast-iron or timber tapering plank E. The poles a and b are disconnected by an insolated interlayer. On the plank E is placed a cast-iron or timber feed-hopper A with a gate B, by the lifting and dropping of which the flow of grain may be regulated. The grain is poured in as shown by the arrow S and, falling through the lower crevice between the gate B and the magnet table E (arrow S), 60 FLOUR MILLING [CHAP, in From time to time leaves the iron and steel pieces on the magnet line, these admixtures are removed by hand. This is the most simple apparatus, though sometimes a still plainer appliance is used. Horseshoe magnets of the common kind are in- serted into corresponding spouts down which the grain passes. Usually FIG. 44. FIG. 45. a wooden stopper, with three to four magnets set into it, is fitted into a hole in the spout (Fig. 45). At intervals the stopper is taken out, and the metal particles attracted by the magnets removed. The removal of the particles detained by the magnet offers some inconvenience, demanding constant attention from a workman occupied on other machines. There- fore another type of mag- netic apparatus, removing the iron particles automatically, is in use. Such an apparatus, from Howes' factory in America, is represented in Fig. 46. The whole apparatus is of timber. The arrangement of the magnet is the same as in the simple apparatus. But here cast-iron scrapers r set on an endless belt (other factories make a chain-gearing) pass over the magnet surface. These scrapers catch up the iron particles stuck to the magnets and throw them into the bucket E. The belt is driven by a pulley t, the axle of which, passing through the feed-hopper, communicates the rotation to the belt pulley n with the aid of a bevel gearing k. By means of gears 8-8, on the left-hand side of the apparatus, a feed roll in the hopper is brought into play. The taper of the hopper gate is regulated by screw nuts b-b, thus altering the FIG. 46. CHAP. Ill FLOUR MILLING 61 feed opening between the roll and the gate. The belt R is tightened and loosened by screw-nuts g-g. The number of revolutions the belt of such an apparatus performs per minute is between 15 and 25, its capacity 9 to 16'5 tons per hour, accord- ing to the size of the apparatus. One of the defects of this apparatus is that the scrapers carry some grain away and interrupt its even flow. Besides the magnetic apparatus just examined, there are other apparatus with a revolving working magnet, and with an electro magnet, but those of the latter kind are rather complicated in construc- tion, and are seldom used in mills, since the simple apparatus works satisfactorily. The capacity of the simple magnet apparatus varies between 3'5 cwt. and 4'5 tons, depending on its size. A magnetic separator with revolv- ing magnets is shown in Fig. 47. The magnets are enclosed in the cylinder A with a worm-wheel E which couples with the worm D fixed on the axle of the belt-pulleys (loose and fast) T. The flat sur- face of the cylinder containing the magnet B coincides with the surface of the spout, where a hole corre- sponding in size with the area of the working surface of the magnet is cut. The product flowing along the spout, the iron particles stick to the magnets, which are then scraped off with bar F and fall out through the channel a. A link mechanism C serves for setting the magnet. FIG. 47. Ill SEPARATION OF LARGE AND SMALL IMPURITIES 1. Separation according to Size Sifting. Previously to the further cleaning of grain, a product has to be obtained of an approximately equal size, i.e. a product of which all the measurements would be correspondingly equal. The working surfaces serving to that purpose are the sieves. As shown in Fig. 48, there are sieves either of woven iron, steel, copper or bronze wire, or of a perforated sheet of metal. When a mass of corn passes over such a sifting surface, the separate grains will fall through the s^eve when the meshes are slightly larger than 62 FLOUR MILLING [CHAP.* m the grains. The larger matter rolls off the sieve. In this manner the throughs supply the grain, while the overtails consist of the larger impurities. The removal of the smaller impurities is attained by rocking the grain on a sieve of which the meshes are smaller than the smallest grains. In this case the grain tails over, and the small matter dresses through. Before passing on to the construction of the machines separating the impure matter from the grain by sifting, the sizes of the meshes and the numeration of cloths have to be explained. The sizes of the square meshes in wire sieves are defined by the number of cloth which, in its turn, is defined according to the number of wire threads to the linear inch. If the number of the sieve is 6, the number FIG. 48. of threads is 6, forming 36 meshes to a square inch. No. 40 corresponds to 40 threads and 1600 meshes, &c. It is to be noted, however, that the reckoning is made in English inches, 25 mm. (in England and in America), Viennese inches, 26 mm. (in Austria, Hungary, and Germany), and French inches, 27 mm. (in France). This must be kept in view, when selecting fine sieves, No. 42 and upwards, from various factories. Besides that, the thickness of wire plays a prominent part in the definition of the size of the cloth-meshes. Generally speaking, the diameter of the wire varies between 2J and 0*1 mm. Within the bounds of Nos. 1 and 8 the diameter of the wire does not vary (in No. 8 it is 0*5 to 0'65 mm.) ; outside of that limit it may differ. For this reason the density of the cloth is greater or smaller, which is reflected in the number of the cloth, though the meshes be of the same size. For instance, No. 16, a cloth of greater density, corresponds to the finer No. 20, the meshes of the two cloths being equal, but those of No. 20 CHAP, in] FLOUR MILLING 63 exceeding No. 16 in their number. The density of the cloth is usually defined by the weight of a square yard or metre. Nos. 1 to 8 are applied for sorting away the matter larger than the grain, of which Nos. 1,2, and 3 are used in front of the primary storage bins, which receive the grain to be fed into the mill. These sieves detain large stones, chips of wood, strings, &c. on their surface. Nos. 4 to 8 are set in sifting machines where the sieves separate the smaller matter as screenings, the grain falling through. The rest of the numbers of wire cloths above 8 keep tail over the grain, and let the fine impurities through. . As to the quantity of numbers of cloths for cleaning the grain, in Germany and Austria-Hungary forty are in use, beginning with the 4th, and ending with the 75th. These numbers are arranged in the following way : from 4th to 26th a successive increase by one number ; 28th to 46th, by two ; 50th to 70th, by four ; and the last is No. 75. The Russian factories produce generally with the difference of one the Nos. 1 to 8, of two Nos. 10 to 28, and of four Nos. 32 to 60. In Russia, besides the numeration to the inch, there exists a numera- tion to the vershok, and according to the number of threads. It is adopted here and there on the Volga and in the central region. It is advisable, however, to keep to the inch numeration, more especially as the vershok numeration is quoted only by the peasant hand workers in the government of Nijni-Novgorod. Speaking of perforated sheet-iron sieves, the fact is to be pointed out that their numeration is exactly the reverse of that adopted in woven- wire clothing. No. 1 is the sieve with the finest meshes, | mm. in diameter, and No. 24 has the largest, 25 mm. in diameter. There are twenty-four numbers, No. 1 containing the greatest quantity of meshes, 1600 to 2025 to a square inch. The shape of the meshes is mostly round, though rectangular ones are also made. (i.) The Construction of Sifting Machines During the sifting process the product must be made to travel over the bolting surface. This is done by means of moving sieves, which compel the grain to travel in the direction defined by the kind of motion peculiar to the sifting surface. On examining the various constructions of the machines, we may divide them into two groups in respect of the kind of motion of the sieves: (1) machines with vibratory motion, and (2) with rotary motion. 64 FLOUR MILLING [CHAP, in FIG. 49. The sieve in the old German mill (Fig. 28, G] may be regarded as the most primitively constructed machine of the first type that can be used for grain cleaning. Sieves of that kind are set at a slight angle to the horizontal plane. When the sieve frame moves in a longitudinal-reci- procal direction, the grain is displaced by force of inertia, the movement of the sieve being straight, parallel to the axis of oscillation. When the sieve moves cross ways, the grain travels in a zigzag line. A comparison of the two methods of moving the pro- duct over the sieve persuades us that the second is prefer- able, as travelling in a zigzag way the stock remains on the working surface a longer while, and the separation is more perfect. "Eclipse " Bolter of Nordyke & Harmon Co. The "Eclipse " bolter of the American factory of Nordyke & Marmon Co. (Fig. 49) presents a simple and original construction of a sieve with longitudinal oscillations. A wooden box D has at its upper end a receiving hopper A. Two sieve trays B are fixed in the box. The frame is set on four U-shaped springs a and is oscillated by a connecting rod b, communicating with the crank rod of the driving shaft. C are the spouts delivering the product and small impurities. The overtails of the upper sieve is the large refuse. The number of revolutions is 450 per minute, the capacity of the machine 6 to 18 cwt. per hour. Reel-separators. Machines extracting foreign matter by bolting, but with their working surfaces revolving, are called reel-separators. It has already been mentioned that they are an American invention, and the simplest form of that machine was examined on p. 25, Fig. 26. The fundamental principle of its construction is the same to-day. Besides the use of the round reel-separator, practical flour milling has introduced hexagonal reels into the industry, by reason of their simple construc- tion and cheapness. A reel-separator of the most simple kind (Fig. 50) is generally a timber FIG. 50. CHAP, in] FLOUR MILLING 65 hexagon shell A, 1250 to 3500 mm. long, its diagonal measurements 350 to 1000 mm., covered with bolting cloth and placed in a timber chamber B, its axis inclined at an angle of O'OS to O'l to the horizon. The reel-shaft is mounted on bearings p, outside the chamber. The grain flows to the reel-separators through a spout N, and on this side the separa- tor is sheltered by a lid H revolving with the reel-separators conjointly. A round cover 0, with an aperture F, for the passage of grain, is fixed to the interior wall of the chamber and is stationary. Between H and G there is a small clearance, besides an opening with a clearance in G for the reel shaft. The right end of the reel-separators remains open. In the sides of the chamber there are apertures for inspection, closed with solid timber gates or frames clothed with linen. The reel-separator is operated by a bevel gearing C, and the worm conveyor S by a belt (sometimes geared) drive on belt-pulleys D D v The head of the reel-separator (the inlet of the product) is generally clothed with one. two, or three num- bers for sifting the small matter, the tail part (outlet of the product) with cloths with larger meshes for the discharge of the grain. The work is performed in the following manner : the grain is fed through N into the rotating reel-separator, which being inclined, it travels in a zigzag line towards t. The small impurities, passing to the lower part of chamber B, are discharged by the worm S through the opening a. The grain flows into the conveyor box E, and runs out into 6, while the large impurities fall out as refuse through the opening c. A plainer reel has no conveyor, and the lower part of the chamber is divided into hoppers (outlined in dots) delivering the small impurities through openings a and a 2 . Figs. 51 (longitudinal section) and 52 (cross section) represent a reel-separator constructed of metal (cast-iron frame and iron hoppers) by Thomas Robinson & Son, Rochdale, England. No conveyor is adopted here ; the dust, sand, &c., small impurities falling automatically out of the first conical hopper, the grain out of the second, while the large refuse passes out the same way as in the preceding reel- separator. The simplest kind of a round reel-separator with a timber frame and boxes is shown in Fig. 53. The reel is clothed with three cloths of various numbers. Two sections, A-A, for small refuse, sand and dust, are clothed with No. 14 ; two other sections, B-B, for larger matter and very small grain, have Nos. 10 to 12 ; the last two sections, C-C, for the passage of grain, Nos. 5 to 6. The large impurities tail over. The product moves in the direction indicated by the arrow. The hopper D receives the small impurities, E the medium, and F the pure grain. The 66 FLOUR MILLING [CHAP, m doors are removable from the side walls of the reel-chamber ; one of them, 6r, is shown in the drawing. The cylindrical reel-separator generally con- sists of two semi-cylinders, so as to afford the possibility of their clothing. Sometimes the clothing used for reel-separators is of perforated sheet- iron with round or rectangular holes. The reel-separator in Fig. 54 is furnished with three sieves, of which A has rectangular and round holes, B only round, and C only rectangular. The product is fed as indicated by arrow S. In section A the throughs are small impurities, and long but thin seeds (of oats, rye, shrivelled grains in wheat cleaning) ; section B CHAP, m] FLOUR MILLING 67 gives only the small refuse as throughs, and the clean grain is sifted through in section C. The larger refuse constitutes the overtails. In this way, m the first part of this reel-separator, impurities differing in size as well as in shape (oats, wild oats, rye) are separated away. Another type of machine, however, for sorting the grain according to shape remains to be noted. Therefore the use of reel-separators supplied with these covers is expedient only where a simplification of the grain-cleaning pro- cess is unavoidable from considerations of economy, and the grain- cleaning department is deprived of machinery sorting the grain according to shape. However, an outline may be given of the modern type of reel-separa- tors, which are mainly used on mills for separating the large and small grain, though also capable of sorting the seeds of other plants away from the chief bulk of product to be milled. Fig. 55 represents a cylindrical grader reel from the factory formerly known as " Bros. Seek," in Dresden. The product is fed into the receiving spout, and falls into the reel, covered with a bolting cLoth with rectangular meshes. (The sieve next to cloth A is removed.) The meshes of the sieve A may be the same throughout the whole length of the reel. In that case the throughs will be the small grain and the large grain will remain as overtails. If half of the reel- separator is clothed with meshes for rye and oats (when wheat is treated), the second half must carry meshes for small wheat. Then tho box containing the conveyor C will have two discharge spouts, Z l and Z 2 . 68 FLOUR MILLING [CHAP in The peculiarity of this reel-separator consists in its being furnished with brushes B of iron wire. These brushes revolve and, being pressed against the cover of the reel, clear the meshes of the grains stuck in them. The reel- chamber is of timber, and its parts of metal. T are timber doors (one is off), K and K l are lids for the inspection of the worm. The reel-separator is driven by a bevel gearing, .and the worm by means of a belt-drive on pulleys b and a. Vibro-motor Plansifters. - The small capacity of the reel, and the "detrimental effect FIG. 55. " f ^ ne inertia of the mass of machinery with flat bolting trays reciprocating, compelled builders to design a type of machine supplied with flat sieves. The first machine of that style was dis- played at the Universal Exhibition in Vienna, 1873, by a miller from Pfalz, Johann Pfoltz. 1 The principle of operation in this machine, which afforded K. Haggenmacher later a basis for the flat-bolter, in- vented by him in 1888, is the following : a flat sieve s (Fig. 56) is suspended from the ceiling by means of four rods, a, b, c, and d, and is connected with a rotating crank shaft A. The product falling on the tray is bolted, while travelling in a gyratory line. A progressive displacing of the product is attained by an in- clination of the tray, which is the method adopted by the firm of G. Luther in their aspirators of latest type, or by means of guiding scrapers as suggested by Haggenmacher in his flat bolter. If a horizontal flat-bolting frame is divided by cross partitions 1,2, 3, . . . as shown in Fig. 57, the product will travel pro- gressively as indicated by the arrow r, the partitions stopping it half-way and propelling it to run another circle. Were the frame not furnished with FlG - 1 In 1878 another inventor, Pieter van Gelder, patented a flat bolter in England, based on the same principle. CHAP. Ill] FLOUR MILLING 69 partitions, the product would describe full circles, as shown in 0, remaining always on one and the same spot. Flat grain-bolters of the Haggenmacher type are built at the English works of Thos. Robinson (Rochdale). The construction of machinery with flat sieves will be examined later. The construction of the machinery we have become acquainted with enables us to extract the large and small impurities and sort the grain in respect to its size, which is of great importance to the further cleaning processes, to be considered later. Therefore it follows out of the very idea of cleaning, that the positions and numbers of sieves must be as shown below (English notation). FIG. 57. Grain No. 14 No. 12 Nos. 8-10 Nos. 5-6 Throughs | Throughs | Throughs Small Medium Small Normal impurities, impurities. grain. grain. Tailing over of large impurities. In this way, first of all on covers Nos. 14 and 12, small impurities, sand and dust, are sifted through ; on cover No. 8 or 10, small grain ; on cloth No. 5 or 6, the normal grain, the large impurities being tailed over. If the grain contains a large amount of impurities (stones particu- larly), to save the covers Nos. 14, 12 and 8, 10 from the wear and tear, a separate reel-separator may be fitted up for separating the large refuse, and another for cleaning the grain of small impurities and sorting it. Then the scheme of cleaning is : No. 5 No. 1 Throughs 1 Grain L No. 14 No. 12 Nos. 8-10 Discharge of normal grain. Small Medium Small impurities, impurities. grain. 70 FLOUR MILLING [CHAP, in Both the schemes refer to grain cleaning on reel- separators. The system of cleaning on sieve-separators, and the order of the numbers, will be examined later. (ii.) The Quality and the Quantity of the Work of Sieve-Bolters Let us now compare the quality and quantity of work of flat sieves and two types of reel-separators. The working quality is defined by the uniformity of the effect resulting from the operations of any particular working organ the bolting surface, in this case. Figs. 58, 59, and 60 represent a cross section of reel-separators FIG. 58. FIG. 59. and part of a hexagon reel-separator. We see in Figs. 59 and 60 that the full working surface of the reel-separators is not utilised in the operations, and Fig. 59 illustrates the fact that not all the sieve actually bolting is capable of doing equal work. Fig. 59 exhibits the small grain 6 and impurities a that are to pass through, on the lower part of the hexagon reel or flat sieve, and on the side wall of the reel. In the first position, a and b will easily pass through the meshes of the sieve, if fitting them ; in the second position, they cannot fall through, being wedged in between the facets of the mesh, as the area of the passage here, projected on the horizontal plane, is diminished in proportion to the angle of inclination of the reel. Those impurities must be again thrown on the horizontal plane of the bolter, to attain the position favourable to sifting. It is clear, consequently, that not every part of the working surface produces the same effect, and thus the capacity of the machine is diminished. If we CHAP. Ill] FLOUR MILLING 71 have a flat sieve with a fixed incline, the impurities passing through the layer of grain to the meshes will necessarily pass through them. An examination of the distribution and motion of the product in reels shows firstly that only to J of the sifting surface is in actually sifting; 1 secondly, the bulk of product Q (hexagon reel), thrown off the side- walls, when the reel is in rotation, hits the lower wall, and wears it out more rapidly, though effecting a more energetic sifting. If, on the other hand, the bolting is performed on a flat sieve, firstly the whole surface is utilised, and secondly, all the parts of the working surface are subject to the same wear and tear, as the grain travels in a compact mass over the whole sieve. These are the reasons why, in regard to their operating qualities, capacity, and wear, flat sieves are to be preferred to other bolt- ers. Besides these advan- tages, flat sifters are much more compact, and economy of space plays a great part in the choice of machin- ery. The only advantage of reel-separators is their comparative cheapness and simplicity of construction. No clearly definite capacity of flat sieves and reel-separators per unit of surface may be spoken of, as flour milling technics have as yet no records of accurate tests. That is the cause of contradictions in the data of German authors (Kick, Wiebe, Pappenheim, Ketten- bach, &c.), and we shall not quote them. It is to be kept in mind that the capacity of the bolters depends on the amount of impurities mixed with the product, a fact never alluded to by the above-mentioned authors. Practical experience has shown that the capacity of flat sieves is two to four times as great as that of reel-separators. As to the cylindrical reels their sifting capacity for various sizes is defined by the following 1 Some authors accept only | of the surface in the hexagon bolter (one facet). However, we cannot agree with that, for bolting is effected by the lower side too in consequence of the impetus acquired by the stock Q when thrown about. FIG. 60. 72 FLOUR MILLING [CHAP, in table, giving the average of data from European and American works verified in practice. The incline of the reel is 80 mm. to 1000 of length. TABLE X Dimensions of Cylinder. Number of Capacity per Nos. Revolutions per Minute. Hour in Kilogrammes. Diameter. Length. 1 350 1250 34 250 2 400 1500 31 450 3 450 1750 28 625 4 500 2000 26 825 5 500 2250 24 1000 6 600 2500 22 1250 7 700 2750 20 1850 8 800 3000 18 2500 9 900 3250 16 3100 10 1000 3500 15 3500 The first three numbers of reels have but three numbers of cloths each. By means of the first sheet, the reels separate the dust, sand, &c. (sieve No. 14). The second bolts the small refuse (No. 12) ; in the third (Nos. 5 and 6) the grain passes through, the large impurities tailing over. The rest of the numbers of reels, i.e. those beginning with 2000 mm. length of cylinder upwards, successfully work with four sheets of cloth. Here the throughs consist of small refuse (Nos. 14 to 12), small grain (Nos. 10 to 8), and normal grain (Nos. 6 and 5), while the large refuse tails over. (iii.) Cleaning according to Specific Gravity and Size After the impurities have been separated away by bolting, the mass of product, though uniform in size, still often contains foreign matter in the shape of light grains, shells, &c., which have to be extracted. That is done by winnowing the grain. The primitive method of winnowing is the utilisation of the natural power of wind on peasant farms, where the grain is thrown up with shovels, and the wind carries the light matter away. If machinery is used for that purpose an air-current is artificially induced by fans. The simplest form of machine, called an aspirator, is shown in Fig. 61. The simple separator consists of a chamber A with a fan v. The lower part of the chamber ends in a hopper closed by a balanced valve d. The lid of the chamber carries a valve e opening inwards, also counter- CHAP - ni] FLOUR MILLING 73 balanced. The grain passing down the spout a encounters on its way in 6 a current of air aspirated by a fan, which removes the light impurities. The light impurities are carried to the chamber A, where those lightest are ejected by the fan, the less light particles falling into the hopper. When a large quantity of refuse has collected in the hopper, the valve d is pushed open by its weight, and after discharging it, closes again. The valve e automatically admits air into the rarefied space in the chamber. If the fan works too power- FlG - 61< fully, then the current of air takes the normal . grains away with it. With a view to a more effective cleaning A. Fisher suggested the construction of an aspirator with a triple aspiration. Through the feed tube a (Fig. 62), in the direction of the arrow S, the grain flows on to a spout furnished with three partitions, the height of which may be regulated by the screw d. The air-current, passing up (arrows r), encounters the stock thrice, and removes the light matter, which is carried through c to a chamber similar to the one just described. The heavier ex- traneous matter falls into the spout d by the way of s lt s 2 , and s& and is discharged into a sack. The defect of Fisher's aspirator lies in the fact that a mass intermixed to a greater extent with light impurities meets a current of air weakened and dirtied by its preceding work. The manifold exhaust, based on the principle of Fig. 63, is much more effective. In that machine, the grain discharged into the feeder A (arrow S) undergoes a quad- ruple aspiration, with pure air each time. FlG 62 The construction of this machine is very simple. A timber chamber B, containing a fan F, is baffled by inclined partitions, which form a spout for the grain 'delivered through M after the aspiration. The upper wall of the chamber carries an automatic valve k, regulating the rarefication of the air in B. The hopper D receiving the heavy screenings ends in valves a-b, which, opening under the pressure of the mass of impurities. 74 FLOUR MILLING [CHAP, in discharge them. The lighter refuse falls into box D t and is conveyed out by c and d, while the lightest matter is ejected with the air current by the fan. Robinson's Aspirator. For the removal of light extraneous matter, there exists machinery constructed on the principle of utilising centrifugal power. Of the novel types of such machinery Robinson's aspirator must be described (Fig. 64). The grain falls through the feeder and down a spout, run- ning vertically through the exhaust chamber, on to a revol- ving cast-iron disc. From the disc, it is distributed fan-wise, and then encounters a current of aspirated air, which carries the light matter away, and then conveys it down a spout to its exit. The heavier refuse, encountering a deflecting partition on its way, falls into the box, while the lighter matter passes through the fan either to the dust collector or out of the mill. In this aspirator the feed spout may be raised and dropped by means of a lever-gear and screw for regulating the flow (cross section between the disc and the spout). The disc runs at 190 revolutions per minute. An inspection- glass is fitted in the top of the screenings channel. The capacity of this aspirator, according to the data of the factory, is from 250 to 83 bushels per hour, corresponding to the size of the machine (Nos. 1, 2, and 3). Robinson's Cyclo-pneumatic Separator. Another machine of Robin- son's, constructed on the same principle and connected with a cyclone for VALVC 4 QUADRAN7 \ HAHDLt rOK TUJVS7IH6 LfHfTH \aFFCED3POUT.} FlG CHAP. Ill] FLOUR MILLING 75 collecting light impurities, is the cyclo-pneumatic separator. 1 Here (Fig. 65) the disc receiving the grain is esnclosed in the cyclone C, and the fan is above the cyclone. The fan draws the air out of the cyclone through a passage in the axis, and impels it into the space B, by which it is conducted through a side aperture into the cyclone. In this way, the work is performed by the same volume of air which undergoes purification in space B. Part of the lighter refuse settles on the sides of the cyclone, owing to centrifugal force, and sliding down the incline, on reaching the worm-conveyor, is taken to the discharge spout. The heavier screenings are delivered to the worm- conveyor out of the chamber B. The light and heavy impurities are discharged into one spout in the present case, but a separate passage for either can be afforded by placing another spout along the route of the worm-con- veyor before the outlet for the light impurities in the cyclone. The cyclo-pneumatic separ- ator's capacity is 100 to 335 bushels per hour. Horde's .Combined Ma- chine. For the simultaneous extraction of foreign bodies differing in size and specific gravity, machines operating by sieves and aspiration are constructed. Horde's separator (Fig. 66) belongs 1 A machine of a similar type, Holt's separator, was offered some twenty years ago, but owing to the defects in its construction it did not succeed, FiG. 65. 76 FLOUR MILLING [CHAP, in to the simplest class of combined machine. It is a common separator, on the top of which a frame 8 with two bolts is set on four flexible timber stands t. The frame is reciprocated by means of two rods r, connected with a crank-axle u, carrying weights rotating on it, the object of which is to counterbalance vibration of the bolting frame. The grain is fed on to the first sieve, No. 6, which retains the large impurities and delivers them through the side- spouts a-a. On sieve No. 9 the grain is separated from the small matter and flows down the spout b to the expansion chamber A, where it undergoes a triple aspiration i, i lt and * 2 , making its exit, cleaned, through c. The throughs from No. 9 pass down sheet-iron J IG. DO. bottoms p-p to the side-spout 0. Driven by a stream of air the heavier screenings fall into the hopper d, and thence to the expansion chamber B, where they are fanned once more in i s before leaving the machine through e. The lightest impurities are drawn in by the fan along the air- trunk /, and ejected with the air, while the medium refuse travels out of the machine down the inclined planes /. The defect of this ma- chine is identical with that of Fisher's separator, i.e. the first aspiration i is performed with impure air. For this reason the bolting separator of Fig. 67, with a five-fold aspiration, each time with a fresh volume of air s, is preferable. The grain is delivered through the spout c, the heavy refuse falls into conveyor box a, mediums into 6, and the light matter passes out with the air. In modern machines of this type the fan generally runs at 500 to 600 revolutions per minute, the crank axle at 250 to 300, their capacity being 40 to 165 bushels, varying with the size of^the machine, FIG. 67. . Ill] FLOUR MILLING T. Robinson's Separator. In mills of great capacity and in ware- houses, where a large quantity of grain has to be cleaned, Robinson's type of machinery is found. 1 The grain flows into the feeder (Fig. 68), and presses open with its weight the valve, which is counterbalanced by weights on shafts. It passes on to the first sieve of perforated steel, No. 20 (meshes 10 mm. in dia- meter), and in falling on the sieve is subjected to the effect of a strong cur- rent of air, which carries away all light extraneous matter. The tails of the first sieve are large im- purities, while the grain and the remaining im- purities pass to the second bolting tray with two numbers of clothing, 14 and 1 3 . Here the medium impurities are separated away, while the grain falling through is bolted on the third sieve, No. 3, with meshes of f mm. On the third sieve the grain is sifted off, and is then exhausted with fresh air in the discharge spout ; the throughs here consist of fine impurities. The three trays are enclosed in one common box which is suspended from the frame of the machine on four flat steel rods, and is reciprocated in the same way as the trays of an ordinary separator. The air-draught is induced by two fans running at about 600 revolutions per minute. Light impurities 1 This type has been appropriated from its American constructors, and is being built, with unimportant variations, by all large European works Seek, Daverio, Luther, Amme Giesecke and Konegen, &c. FIG. 68. 78 ^ FLOUR MILLING [CHAP, in are blown through the fan to the dust collector, while the heavy refuse falls into hoppers and slides out down inclined spouts. The main shaft, which imparts a rocking motion to the sieve, makes about 550 r.p.m. The capacity of such machines varies between 216 and 2400 cwt. per hour. Aspirator of form. Seek Bros. This aspirator is generally used for cleaning the grain to be kept in warehouses, and in mills of a large capacity. Through the feeder a (Fig. 69), the grain is delivered on to the first sieve with large meshes, which tails over the coarse, extrane- ous matter, while the grain falls on the sieve c with finer meshes, which remove the smaller impurities, such as corn-cobs, straws, stones, &c., which pass out through a side-spout d. The sifted product is then bolted on sieve e, which separates the still smaller impurities and flows in a thin, even stream through the discharge spout /, where it is exhausted by a current of air, and freed from the dust, chaff, &c. When entering in the machine, the feed is subjected to the action of exhausts gg, which suck out the loose dust, before it is passed to the sieves. Owing to this, the machine, when in operation, produces no dust. The cleanness of the reverse side of the sieves is maintained by automatic brushes hh or india-rubber balls which are distributed over the clothing, and the trays moving from side to side, hit the perforated sheets, thus freeing them of dust. The feed may be regulated, and is performed automatically, viz. the force of the stream varies in accordance with the quantity of the stock fed, in this manner preventing any stoppage, and continuously keeping a certain amount of grain in the hopper. This arrange- ment lacking, the bolting surface would not be supplied with the stock evenly over its full breadth, thus the aspiration would be inefficient. The heavy particles of dust lifted by the stream of air collect in two chambers ii, whence they are discharged through rocking channels kk, arranged on the sieve. The fine dust, at the same time, is driven by the fan to the dust collector. When mounted, the machine has to be carefully adjusted by means of a spirit-level. By means of weights L, adjustable by screws placed at the mouth of the feeder, the force of the stream of stock must be regulated, so as to keep the hopper continually filled to three-fourths of its capacity. The same is to be said of the regulation of the product in I, when, on leaving the trays, it flows into the suction drum at the FLOUR MILLING 79 CHAP. Ill] exit. At the feeding and the discharge apertures the air-draught is con- trolled by means of valves mm, arranged in the expansion chamber, which are worked from the outside by levers. The levers are adjusted in their places by means of screws. In addition, a more satisfactory control may be attained by means of two timber distributing slide- 80 FLOUR MILLING [CHAP, ill valves rtri, set in the partitions between the refuse collecting chambers and the common expansion chamber of both the exhausts. These slide-valves may be reached through a sheltered aperture in the middle of the upper plank of the aspirator. The slide-valves must never be quite closed. The aspirator can only be adjusted accurately after a trial operation. The removal of all light impurities from the stock by the air-current is to be aimed at ; the good particles of stock, however, should not be carried to the refuse chamber. The aspirator legs are connected by a spout, which further is connected with the common air-trunk. The trunk opens into the dust chamber, or communicates with some dust-collector. The new bore of the air- trunk may not be smaller than the sum of the bores of both the aspirator legs. Any slight curves of the air-trunk must be made with as large a radius as possible. The machine is worked from the shaft of the fan making 570 revolutions per minute ; by means of belts the motion is transmitted to a crank-shaft which rocks the sieves, and runs at 650 revolutions. The capacity of such machines varies between 60 and 2000 bushels for warehouses, and 20 to 620 bushels per hour for mills, according to the size of the machine. The Zigzag Separator. In 'this machine (Fig. 70), which does the same work as the preceding one, the trays are arranged in a zigzag line. All five sieves are enclosed in a common box, but its reciprocative motion runs athwart the direction the stock travels. We shall first follow the travel of the stock, and then compare this construction with that of the preceding machine. From the feed-hopper, having opened the counterbalanced slide, and exhausted by an air current, the grain falls on the first sieve (longitudinal section) with round holes (diameter 12 mm.), which shakes the large impurities off and sifts the grain and other matters through. This tray is rocked longitudinally, its axis being perpendicular to the axes of sieves 2, 3, and 4. The throughs of the first sieve falling on the second with meshes d = 5 mm. leave the large impurities of the second order on its surface, the grain and smaller screenings passing through to a plate, lying parallel to the sieve, and are conveyed to the head of the third tray. The third sieve, having meshes d=4:% mm., retains ex- traneous matters of the third order in size, giving as throughs the rest of the stock, which collects on a similar plate under the sieve, which in a like manner conducts the product to the head of the fourth sieve, meshes d=4 mm. CHAP, m] FLOUR MILLING 81 Large impurities of the last size are sifted off on the fourth sieve, and the throughs reach the fifth sieve, the axis of which is set perpen- dicularly to those of the preceding sieves. The meshes of the fifth sieve are d=2 mm. It tails the grain over and bolts small refuse, dust, and sand. The grain from the last sieve passes through the exhaust leg to the fan and is freed of the remaining impurities and dust (cross section). In comparing this machine to the one preceding we notice that the zigzag arrangement of sieves makes it less compact. But its enlarge- ment goes to the account of its height, and has no influence on the area Air Currents FlG. 70. occupied by it. The advantages afforded in return by the zigzag appear in the quality of the bolting, as the distance the grain travels is longer, besides which the product is sifted from the head of the sieve, whereas in the first machine the passing stock falls on different parts of the next sieve, and does not travel the whole length of it. The fan of this zigzag of Robinson's makes 600 revolutions, the sieves 520 vibrations per minute, the capacity being 60 to 260 bushels per hour. Machines with an Inclined Rotating Sieve. With the view of obvia- ting vibration generated by the reciprocating motion of the working parts, which has a bad effect upon the machine and the building, engineers suggested separators with flat inclined sieves gyrating 82 FLOUR MILLING [CHAP. HI on the principle already explained. The box C (Fig. 71) contains four sieves, 1, 2, 3, and 4. This box is suspended from the frame on four reed-springs c and connected in with the driving-pin of the fly wheel Q by counterweights. The fly-wheel is set on a shaft rotated by a belt drive. The stock is delivered into the feed hopper A, its flow being controlled by a gate balanced either by a spring, as shown in the drawing, or by a weight. The roll B feeds evenly the sieve 1, an air-current s removing at the same time the light im- purities. Sieve 1, inclined to the left, sifts off the large refuse d, dropping the throughs on to sieve 2, which gives the medium im- purities r as refuse, and sifts the grain through to sieve 3. The tails of the third sieve are the large grain o, and the throughs are thrown on sieve 4, where the small grain o is retained, and the sand, dust, and other fine particles m pass through. The grain o and o 1 passes down the air- tube v, and once more undergoes the process of separation from the light im- FIG. 71. purities. The heavier particles of dirt a settle in boxes t, and are taken out through inclined spouts fixed to the bolting box. The number of revolutions of the box is 250, and the capacity is 160 bushels per hour. Machines of the kind described are built by the firms of G. Luther (aspirator " Triumph ") and others. 2. Separation according to Shape In the process of cleansing of the grain of foreign matters by sifting, we have seen that their removal is possible when they greatly differ from the kernels in size. But the sieves will not remove impurities of another shape, yet of a size that agrees with the small dimension of the stock cleaned. To those foreign bodies pertain mostly spherical grains, or particles of grain (broken grain) of the product treated. For instance, the seeds of cockle, or sweet -pea, their diameter CHAP, m] FLOUR MILLING 83 coinciding in size with the thickness of a grain of wheat, cannot be separated from it. They cannot, too, be removed when the stock is sorted according to specific gravity, only the light impurities being extracted here. If oats are mixed with wheat, their cross-sections coinciding, they cannot be separated by sifting. All machinery by means of which impurities, differing from the main stock in shape, are removed, is constructed on principles based on the following properties of these extraneous matters : (1) Spherical grains roll down an inclined plane or curving surface with a greater speed, and thus developing a greater kinetic energy, leap over obstacles which detain the oblong grains. (2) Spherical grains roll off a slightly inclined plane, overcoming the friction of rolling, while the oblong grains remain immovable on. the surface. (3) If we have a curved surface or inclined plane with semi-spherical sockets, and stock moving over it, the spherical and broken seeds, will fall into the sockets, and the main stock will roll off. (i.) Machines of the First Principle The Conic Apparatus. The apparatus based on the first principle is exceedingly simple (Fig. 72). There are two conic surfaces K and K 2 . The diameter of the base of the lower reversed end K 2 is greater than the diameter of the base of cone K lm The plane of the base of the bottom cone is set higher than the plane of the base of the upper one. The grain flows out of the spout a on to the surface of cone K. The round grains of cockle, pea, &c., developing a greater rolling velocity, have a larger kinetic energy. Hitting the prominent circular surface cc 1 of the cone K z these grains leap over the , , FIG. 72. ring cc 1 , while the grains of wheat or rye, in their descent, move slowly, and pass into the cone K 2 and tube b. The angle of the cones is 35, the diameters of their bases about three metres. The cones are of polished timber. Though this appliance is bulky, its capacity is great. Open cones would raise dust, therefore they may be encased, which allows the feed to be exhausted. The Worm Trieur. The construction of the worm trieur depends on the same principle (Fig. 73). This apparatus consists of helicoidal conic 84 FLOUR MILLING [CHAP, ni surfaces, of which one, two, or three, 6, of a smaller diameter, are inscribed in respect of the surface of the large diameter a. These surfaces are encased in a box K. This trieur operates in the following manner : the stock, generally cockle, broken grain, vetch, and undersized grain, passes through the feeder s to 6, a worm of smaller diameter running close to the axle, to which the helicoidal surfaces are fixed. By reason of the action of gravity, the product descends with an according velocity. The round grains (cockle, &c.) develop a greater speed, and roll over the rim b into the larger worm, as shown by arrows. At the base there are exits for the sorted product, c for non-round grain, and d for the round. The machine is often built with- out a case, but it is better encased, as this appliance affords the possi- bility of aspirating the machine by means of an exhaust tube fixed as shown by the arrow e. For in- specting purposes the machine may be furnished with closely fitting doors. This machine operates very effi- ciently ; the thread of the worm and the angle of the cone being carefully calculated, it requires no motive power, and it is of an exceedingly simple construction. The flights of the worm are made of iron plate. The case is also of iron. The capacity of a machine with a worm 2000 mm. in height, the larger worm a being 500 mm. in diameter, is from 25 to 40 bushels per hour. FIG. 73. (ii.) Machines of the Second Principle Two types of construction belong to machines operating by a moving inclined plane : the first kind moves parallel to the direction of the rolling grains, the second at right angles. Fig. 74 exhibits a double machine of the first type manufactured by CHAP. Ill] FLOUR MILLING 85 Rober. On a timber stand are placed a feed box A for the stock, and a frame B with working surfaces Z), which are endless leather cloths rotating in the direction pointed by arrows 6% by means of a belt-pulley C and guides r enclosed in the cloths. Through the feed box J, the stock is fed on to D by the feed rolls a. The round grains roll down (arrow n), the grains of wheat, rye, &c., are lifted up on D and thrown off into a box F below. The flow is regulated by a gate b. The incline of the working surface ^t>' r t* ~^ ar is adjusted with the aid of a ^^frf^ toothed gearing E and bolts v, FIG ?4 which are screwed into nuts u, and support the lower parts of the frame. The lower guides f or D are mounted on adjustable bearings, which makes it possible to adjust the tension of the cloths. The capacity of such a machine attains 12 bushels per hour, the breadth of the cloths being 250 mm., their length 2500 mm., and the speed is 80 revolutions per minute. Another type of machine in which the cloth travels in a direc- tion at right angles to the fall of grain is shown in Fig. 75. It is likewise a machine of double action. Receiving the grain from the I feed hopper the feeding rolls strew the stock on the cloths. The round grains roll off (arrow s), and the rest, remaining on the cloths, are carried (arrow n) to the receiving box. As in the preceding machine, the adjustment of the incline and tension of the cloths is provided for. The utmost capacity of this machine is 20 bushels per hour, having cloths 300 mm. broad and 2200 mm. long running at the rate of 50 revolutions per minute. FIG. 75. 86 FLOUR MILLING [CHAP, in FIG. 76. (iii.) Machines of the Third Principle The Normal Trieur Type. In 1845 two Frenchmen, Vachon (father and son), in Lyons, invented a machine which they named a "trieur." The machine was a sheet-iron cylinder bossed on the interior surface with cylindrical sockets. Inside the cylinder, set at an incline, was enclosed a conveyor box, almost throughout its full length, at the same angle of inclination. Into the raised end of the cylinder the grain was poured, and when rotating the round grains of foreign plants, fall- ing into the sockets, were lifted to a sufficient height and then dropped into the stationary conveyor box. The grain travelled down the cylinder by gravity, shaken also by the longitudinal rocking of the cylinder, while the round particles of impurities rolled down the inclined plane of the conveyor box. Both grain and impurities fell into conveyor boxes placed under the lower end of the cylinder. During the seventy years' existence of Vachon's cleaner and separator its working principle has not undergone any modification. The modern sorting cylinder has but received modifications of construction, and Fig. 76 gives us its present plan. A cylinder G turns on a stationary shaft v in the direction of the arrow s. The mass of stock Q rolls along the cut surface of the cylin- der ; the round kernels of the admixture, and the broken grain of the stock to be cleaned, fall into the sockets, and are lifted up and dropped into a stationary conveyor box D, rolling down its sloping surface b. The impurities are pushed along the conveyor box by a worm T revolving in the opposite direction. A full drawing of this machine is to be found in Fig. 77. The shaft of the cylinder is placed on props t-t. When the set screws of the props are loosened the shaft may be turned. On the revolving hub of the cylinder is set a gear z coupling with the gear z 1 of the worm conveyor T FIG. 77. CHAP, in] FLOUR MILLING 87 of the box which is fixed to the shaft. The refuse is delivered by means of the worm down 6. The taper imparted to the cylinder is usually 0*08 to 0*1, i.e. 8-10 mm. to 100 mm. of its length. The capacity of the trieurs depends on the circumferential velocity of the cylinder. It is obvious that their capacity increases with the velocity. Nevertheless that velocity must have a highest limit of signi- fication, otherwise the centrifugal force of the grains will press them to the surface of the cylinder, and they will not fall into the conveyor box. Let us examine the conditions which allow of the most profitable work. Fig. 78 shows us various positions of a socket with a grain. If the re- volving velocity of the cylinder is v, the grain develops a centrifugal force ^ , r being the radius of the cylinder. Besides that the grain is under the influence of its proper weight p=mg. When the grain is in a diametrical plane, position /, it is evident that it will not fall out of its socket, whatever the rotatory velocity may be, as the resultant Z= Vc 2J rp 2 will press it into the socket. When in position //, the grain being raised to an angle a, the resultant is (in the triangle ! v -K-T-^-'V Sin a FIG. 78. Thus, Z differentiates in accordance with the angle not only in size but also in direction, which is of great importance to us. The angle X, defining the direction of Z, is gradually widened to 180 for the third position of the grain, when a = 90. Let us see when the grain will begin to drop out of the socket. If op, we have seen that the grain remains in the socket. When c=p, position III proves that the grain is balanced, seeing that Z=0(sina = l, Z=V2c 2 -2c 2 = 0). Therefore the dropping of the grain is possible only when cf ( cos a +mg sin a or wiv* r /mv i mgcos a- -- sin a >f( cos a-j-ragr sin a), and we define the significance of v supplanting f=tg

- 3 W JNj _ If the Water from the feed piphxj. n E :nd floor. To canalisation. To canalisation. FIG. 108. the guiding paddles in turbines. The grain falls out of the spout M on the cone, while the water flows out of tank No. 4 down the tube E under CHAP, in] FLOUR MILLING 123 a pressure of up to 0'35 atm. Impelled in this manner, the water, in passing between the guiding paddles and gyrating as in a vortex, encoun- ters the grain which rolls down the slopes of the cone. Tank No. 2 is also named the stoning tank, for the stones, overcoming the pressure of water, fall to the bottom, while the grain is washed over the rim of the cylinder on to the lid K, and thence through the spout L to the conveyor B. The lower end of the tank which may deli ver the stones through the cock without interrupting the work of the conveyor, rests in the tank No. 1. The water level in No. 1 depends on the degree of humidity of the grain, and is maintained by the tube W, which receives the exhaust water through the holes in the projecting end and transmits it to tank No. 3. If the water exceeds its level limit, it will drain away, not through the small holes in the sides of the tube, but through the open upper end. The level of water in No. 1 determines the period to be spent by the grain in the worm. The worm B resting in a copper spout with holes through which the grain cannot drop, conveys it to the vertical whizzer. During its upward journey, the grain is in- cessantly washed by streams of fresh water out of the cocks in the pipe A, communicating with the water-piping or with a reserve tank. Here only is the removal of a certain amount of soaked dirt possible. The water circulates in the following way. The exhaust water from No. 1 is conveyed to tank No. 3, and then taken by a centrifugal pump G to tank No. 4, out of which tank No. 2 receives its supply. The fresh water is conducted from the water-piping to tank No. 4 through the tube R. If the outflow of water during the washing operation exceeds the inflow of fresh water from the tube A, the deficient quantity is sup- plied through the tube R to tank No. 4 ; the superfluous water, on the other hand, is let out of tank No. 4 into the canal or sewer through a pipe with an open funnel. The water-level in tank No. 4, controlled by the height of the outflow-funnel, determines the steady pressure in tank No. 2. The tank No. 3 and the pump G may be discarded, if the water in the mill is so cheap as to allow of its being thrown away out of tank No. 1, when dirty. In the conic bottom of tank No. 4 there is a refuse tube for the discharge of the mud that settles there. For the damping of grain of harder kinds Robinson has the appara- tus shown on Fig. 109, with two worms. The end of worm No. 1 is immersed in the water of the tank B. At the lower end of the worm casing is a box in which the stones collect. Worm No. 1 carries the grain to the stone separator C, described above, from whence it passes to worm No f 2 (the angles of the conveyor worms are 70), 124 FLOUR MILLING [CHAP, in and is then delivered to the vertical whizzer. Out of the general tank the water is supplied by a centrifugal pump A . Both worms are played on with fresh water from a series of cocks. The tanks F and B are isolated and have different water levels. The drives of the conveyors and pumps are clearly marked out. Fig. 110 represents the general view. (2) Mechanical Removal of Water from the Grain. After being well dampened the grain falls through spout P (Fig. 108) to the vertical whizzer to remove the water. This operation must be performed very rapidly, otherwise the water will penetrate the starchy part of the grain, and its moisture content will exceed the normal limit. Robinson's centrifugal or vertical whizzer (Fig. Ill) consists of a vertical rotating drum containing beaters arranged spirally. The grain is fed in at the base of the drum by an inclined spout from the worm through the inlet, and is met by the beaters revolving at the rate of 70 feet per second (the drum makes 360 to 600 revolutions per minute). The beaters fling the grain against a steel casing, perforated to let the water and abraded bran escape. The grain impelled by the beaters hits the casing, and by the blow, owing to the decrease of the great velocity of motion of the grain, the coating of water is thrown off by centri- fugal force and expelled through the holes of the casing. This is the action named whizzing. The casing consists of separate sections, eight or more in number (general view). For the retention of the splashing water, the perforated casing is enclosed in another casing of solid iron. The CHAP. Ill FLOUR MILLING 125 spiral lif ters rapidly raise the grain to the top and deliver it through an out- let spout. Besides the removal of water, part of the beeswing, bran, and beards is separated on the way up. Consequently, by a second operation the grain is simply scoured, when thrown by the lifters against the casing. (3) The Drying of Grain. The most important stage of the wet scouring process is the drying of the grain. It is dangerous to leave the grain with a moisture above the normal, for that would lead to unfavour- able consequences in the treatment to follow. Overdrying is likewise to 126 FLOUR MILLING [CHAP, in be avoided, as the grain then becomes brittle, and gives a large percentage of broken kernels when subjected to dry scouring. In addition, the bran of the over-dry grain will be ground to bran powder during the milling process, from which it is impossible to extract the flour. It is only by careful experimental treatment of the grain in drying and cooling machines, coupled with observations on the moisture of the grain to be dampened, that the temperature and the volume of the drying air and the quantity of grain to be dried may be defined. For this reason, a rationally constructed drying and cooling apparatus must be adjustable in respect to the temperature and volume of the air in use, and the quantity of grain to be treated at a time. Robinson's dryer (Fig. 112), like machines of other design, is of a rectangular section (Fig. 96). Two sides of the column are solid, while the other two consist of two parallel perforated walls. The grain fed in through hoppers A and B flows between those walls, and is sub- jected to the action of a draught from the chamber 0, which penetrates through the holes in the walls. The warm air is aspirated from the steam chamber through the aperture Z by a fan, and, after passing through the stock, is exhausted through trunk J '. For about one-third of its way the grain is exhausted with cold air (temperature of the mill apartments) aspirated by another fan and ejected through the trunk D. At the warm air inlet Z, the column is divided by a solid bottom which prevents the cold air from penetrating into the chamber G. Before proceeding to further descriptions of the construction, the signi- ficance of cooling the stock must be explained. The temperature of the drying air, depending on the dampness of the grain, varies between 25 and 60 C. Sometimes, when the stock is very dry, the column is filled with air of the outside temperature un warmed. In that case the functions of both the upper and the lower division of the column are identical. But when the temperature of the air has to be raised to 30-60 C, a cooling of the grain is necessary for the following reasons. The dried and warm grain is deposited in bins to be tempered for the space of eight to twelve hours, to allow the moisture collected in the bran to spread evenly in the endosperm as well, to facilitate the treatment of the stock in dry scouring and milling. The grain deposited in bins without having been cooled previously, retains its high temperature, which acts detrimentally upon it, because, if tempered for a long time, it may first germinate, and secondly the starch may become soaked to a paste. Moreover, during the conditioning the bran becomes cooled first, thus accelerating the process of evaporation CHAP, in] FLOUR MILLING 121 128 FLOUR MILLING [CHAP, itt in the 'outer covers, and the tempering period in consequence is shortened. For regulating the feeding of the column there are valve flaps K in FIG. 112. B K W the hoppers A and B, which may be opened wider or less by means of a crank mechanism M . That mechanism controls at the same time the FLOUR MILLING 129 CHAP. Ill] grain delivery by a valve flap L worked by a gear wheel and rack on the flap. The opposite end of the crank mechanism carries a weight FIG. 113. to counterbalance the load of grain on the flaps K. Another dryer and conditioner built by Robinson's works (Mallin- son's patent), of a more complicated construction, is shown in Fig. 113, 130 FLOUR MILLING [CHAP, in A more equable drying of grain is realised by means of the following appliances. In the working space in the right-hand side of the column, there are vertical spouts fed with steam from the heating chamber E. At the top, in the hopper A, these spouts are connected by a common horizontal trunk. Within the working space, the grain travels in a zigzag line, owing to the inclined partitions, thus assisting the stirring of the grain. Through openings in the partitions, the warm air exhausted through the spout G by a fan penetrates into the stock from the chamber H. The vertical steam pipes are designed to maintain an even temperature in the working space, for in the column of CHAP. Ill] FLOUR MILLING 131 the first type, the grain descending close to the outer wall of the working space is treated with air of a lower temperature, and is consequently less dried than the grain travelling close to the inner wall. On leaving the right-hand side division of the column the grain flows through the feeder B into the left division which is not heated by steam pipes. This part of the column in its upper range operates with air from the general chamber E,but in its lower part the grain is cooled from the trunk N. The dryers and coolers of various constructions will be compared later. Washers by Turner, H. Simon, Briddon and Fowler, &c. The Damping of Grain. A damping machine of another type (Fig. 114) 132 FLOUR MILLING [CHAP, in is the English machine for washing coke, slightly modified. The machine consists of a tank divided into six sections, in which the water circulates in the following manner. The fresh water playing the grain is delivered through holes in the piping, and collecting in No. 1 (Fig. 115) is pumped along the tube d to the chamber F by a centrifugal pump C ; from F it flows over into No. 5 and No. 6, two vessels communicating with each other (Fig. 116) ; out of Nos. 5 and 6 the water fills No. 4, which likewise has Section through EF. FIG. 116. a connecting channel. In this manner, divisions Nos. 1 and 2 separated from Nos. 3, 4, 5 and 6 have a communicatory opening b, while the dirty water flows out of No. 2 through the pipe g. The divisions Nos. 5 and 2 (Fig. 117) are covered on different heights with perforated screens ; Nos. 6 and 4 encase wooden pistons ra and / driven by an eccentric. During the operation of the machine these pistons agitate the surface of the water over the perforated lid, giving from 180 to 200 vibrations per minute. The work is performed as follows : the grain is fed into worm C in the stream of water. Then it is carried by the worm to the hopper, whence the feed roller r passes it on to the surface of the screen of division CHAP. Ill] FLOUR MILLING 133 PLAN OF H. SIMON'S WASHING MACHINE. Section through AH SECTION THROUGH A B. FlG. 117. 134 FLOUR MILLING [CHAP. Hi No. 5, where the vibrating stream washes it away to the overflow p, and further to the lower end of conveyor B. In travelling to the overflow p the grain passes over division No. 3 with a lowered screen and leaves the heavy extraneous matter (stones, &c.) on it, so that No. 3 serves as a stoner. To prevent a heavy overflow of water being pumped from the chamber F into division No. 5, there is a funnel-shaped opening in F over the water inlet, which is the end of the tube supplying No. 4 with water. Owing to this tube the water level in Nos. 5 and 6 is kept at about the same height. The washing-machine just examined (H. Simon's) has two worms, though it may be provided with but one, B (Turner's machine). In the latter case the grain is fed straight into the hopper, and thence to division No. 5. We must point out some defects of this machine before proceeding to describe whizzing and drying machinery of other makes. The mistake the makers of these machines make, lies in their supposing the washing of grain to be the chief function of the machine. That is why its construction is complicated by the divisions Nos. 5 and 3 in the tank with vibrating surfaces. This principle is adaptable in the case of coke, a porous substance, which is indeed washed by the water impelled into the pores by strokes. As to the grain, all it needs is to be well damp. The grain must not be immersed for longer than thirty to forty seconds, which is not a long enough period for the dirt firmly sticking either to the surface of the grain, or in its crease, to be washed off. A vibratory mechanism is therefore not required. If, on the other hand, the agitation of the water surface is to be abolished, it is evident that Robinson's type of washing-machine, or one akin to it, must be adopted. Besides this essential defect, resulting from a misunderstanding of the principle of the machine, faults in construction must be mentioned. A wish to make the machine solid induced the engineers to utilise the pressure of the pump in driving the grain to the overflow. This results in a fluctuation of the water levels, in spite of the tube e devised for the compensation of the strokes. The opening in the partition between No. 1 and No. 2 regulates the water level of No. 1, but violates the principle of counter current (dirty water washing dirty grain), for there is a possibility of the dirty water being exhausted through the opening out of the divi- sion No. 2. The Removal of Water from the Grain. As regards the separation of CHAP, in] FLOUR MILLING 135 water, H. Simon's centrifugal whizzer (Fig. 117) in its constructive basis differs in no respect from that of Th. Robinson's. A few general remarks have to be made concerning the whizzing process. There exist two types of whizzing or centrifugal machines having more or less important differences in the construction of their lifters. The first is Robinson's type, where separate paddles disposed in a spiral line play the part of lifters, or that of Seek (Fig. 118), which has lifters FIG. 118. FIG. 119. arranged on a generating line, and of a saw-like shape, with teeth bent to one side, also in a spiral line. The lifters in the second type of machinery (Fig. 119) are set at an angle to the generating line of the cylinder, as in scouring machines. In this case not only the wide flanged blades, but the whole lifter is employed in elevating the grain (the construction belongs to the Italian works of S. A. Meccanica Lombarda). Of a much greater significance is the position of the rotatory axis of the lifter drum, which is either horizontal or vertical. In the former case, the whizzer is placed so as to receive the grain together with the water out of the stone- separating and the washing apparatus. There- fore, the lifters in taking the grain scoop up the water at the same time. 136 FLOUR MILLING [CHAP, itt Under such circumstances the grain is certainly well rinsed, but this process is somewhat dangerous, because the grain may remain in the water for too long a time, so that the starchy part may absorb too much moisture. For this reason horizontal whizzers are gradually dropping out of use. The grain is generally fed into the whizzer after the water has been FIG. 120. drained off. Some engineers wish not only thoroughly to soak the grain, but actually to wash it. In this respect the washing pro- cess of the firm of " Seek Bros." (Fig. 120) deserves attention. Here we have the full process. From the stoner A the grain and water flow into the first whizzer B. At the bottom of the apparatus the grain is well rinsed in the second apparatus C. If the time is accu- rately calculated, this process _ may bring good results. Yet the CHAP. Ill] J^LOUR MILLING 137 engineers ought not to concentrate their whole attention on the washing of the grain, but should remember that we have here an example of the process of scouring by washing. Fig. 121 represents the washing plant from the works of Luther. Here 1 is a bin, 2 a stone separator, 3 a rinsing appliance, 4 a centrifugal pump, 5 a vertical whizzer, 6 a dryer, 7 a collecting funnel, 8 a hot air exhaust, 9 a cold air exhaust, 10 the heating chamber, 11 a dirt collector, 12 a dryer, 13 a delivery pump, 14 a water cistern, and 15 a dust collector. The Drying of the Grain. In drying grain, that most important stage in the wet scouring process, the selection of the type of drying apparatus is a very serious ques- tion. In the first place, we must acknowledge that the most active agent in the drying process is the air. This absorbs the greater a- mount of water- vapour, the higher is its temperature, and the smaller the pressure. The absolute quan- tity of the vapour absorbed by the air is proportionate to its volume. It follows, therefore, that an effi- cient, i.e. rapid, drying demands : (1) The highest temperature. (2) A pressure below that of the atmosphere. (3) The greatest possible quan- tity of working air. These three conditions are defined by the duration of the drying process. The faster the drying is to be performed, the higher must be the temperature, the more rarefied the air, and the larger the quantity of it used. On the other hand, given the limit of significance of the temperature and pressure, and the air consumption, we are enabled to define the length of the drying procedure and the amount of grain, according to .its primary and final moisture. An experimental drying of moist grain has shown that the highest limit of temperature is 60 C. If that limit is exceeded, the bran as FIG. 121. 138 FLOUR MILLING [CHAP, in well as the kernels burst. However, as far as possible high tempera- tures ought to be avoided, because firstly, when heated to 60 C. the starch may turn to paste, 1 and secondly, a lower drying temperature requires less fuel. These two circumstances suggest the necessity of using rarefied air. And the best result is actually obtained by drying the stock in rarefied air, 2 as is done in large granaries. However, such enormous structures as a vacuum drying apparatus of E. Passburg's are im- possible in mills, because we have a washing plant which must be included in the cycle of machinery belonging to the grain - clean- ing department, and space is limited. We have two types of dryers for drying the grain in the wet scouring process : (1) operating by forced air, and (2) by aspirated, i.e. rarefied air. The Robinson dryer we have examined operates by rarefied air. " V scraper Fig. 122 shows o> type of dryer (Turner's works in Ipswich) working with forced air. Nearly all European and American milling engineers favour the second type of dryers. On Fig. 123 we have a drying arrangement of Simon's (known under the name of " Biihler Bros." in Russia). Here A is the air- heating chamber, T 1 a fan im- pelling the warm air into the trunks B-B, and T another fan filling the trunks with cold air. Engineers, however, should avoid build- ing dryers which work by forced air, i.e. with increased pressure. Besides considerations respecting greater security and economy in drying, there are considerations in regard to their construction. Inner & outer cylinde perforated metal Delivery spout 1 Profs. Kick and Zworykin set the limit at 60, F. Baumgartner at 55. 2 Vacuum drying apparatus of E. Passburg's system, Russian Miller, 1909, No. 10. CHAP. Ill] FLOUR MILLING 139 Though the apparatus may be fitted up perfectly, there is always a possibility of the dust penetrating into the crevices if the dryer operates by forced air. Its inspection is very much hindered by the fact of the dust blowing into the apparatus through the window when it is opened. Now, if the machine works with aspirated air, these defects cannot obtain in the process. In the second type of dryer from the works of Robinson (Fig. 113) we see that its right-hand working part is heated by steam-pipes which are adapted for the purpose of completely removing the mois- ture with the aid of a higher temperature. It must be kept in mind, however, that in employing such a construction we run the risk of choking the grain which moves in the neighbourhood of the tubes. Besides, the air pipe which supplies the left part of the column with cold air is warmed by the hot air, an undesirable effect. In this column the adaptation of a step par- tition, owing to which the stock travels in zigzag line and becomes mixed, must be acknowledged to be useful; it also promotes a more equable drying of the grain. Touching modern grain-drying, Pro- fessor Zworykin suggests a few very interesting consi- derations as to the principle and the construction. He finds the following defects in the dryers just spoken of : (1) The stock which travels along the vertical canal on the side of the drying air inlet is dried more thoroughly than the stock moving on the opposite side of the canal. (2) The grain flowing down the central part of the drying canal FIG. 123. 140 FLOUR MILLING [CHAP, m Wet grain moves faster than the grain on either side of it, and is consequently dried to a different degree. (3) The air, during the drying process, in passing through a thin layer of grain equal to the breadth of the drying canal is not saturated enough with moisture, and is therefore insufficiently utilised. As concerns the two first defects, they are effectually done away with in Mallinson's dryer with step-canals. This is confirmed in the types of machinery suggested by Professor Zworykin. The third defect is to be overcome by the principle of counter-currents adapted by Pro- fessor Zworykin in the following two sketches of drying columns. Fig. 124 represents a hollow column AB of a square or rectangular section provided with a series of jutties of a triangular section in- side (1, 2, 3, 4, 5, 6, 7, 8, 9, 10) and a hopper D at the top, which contains a feed roll C and an arrangement for regulating the feeding. The moist grain passes through the hopper and the feeding apparatus into the column, rolls down the jutties (1, 2, 3, 4, . . . 10), as pointed by whole arrows, and is discharged through the valve K below. In the direction opposite to its course a current of air is driven through the inlet E : it ventilates the grain several times at the moment it falls from the even on to the odd jutty or vice versa, and then humid with the moisture drawn off the grain, it passes to the fan through the outlet Z. Naturally the grain must flow in a thin layer and must not block up the space. For the action to be regular, Professor Zworykin recommends heat- ing all the jutties or only one side of them with steam or water, while the period spent by the grain in the apparatus may be regulated by making at least one range of boxes (for instance, the even numbers) adjustable so as to alter the angle of inclination of the surfaces down which the grain rolls from 45 to 70. In Professor Zwory kin's opinion, there is no especial need artificially to cool the dried grain, if after drying it is not to be tempered in bins, but, continually passes from machine to machine, and undergoes a gradual treatment. The second variation of that design is a round cylindrical column with conic (Fig. 125) surfaces B. The central part A of the apparatus Dry ffrai FIG. 124. 1 41 Grain inlet CHAP, m] FLOUR MILLING is heated. The grain flowing through the hopper travels over the conic surface of the heated central part A, and aspirated on its way, falls on the conic surface B. Then it rolls off B on to the second cone A and is again fanned, &c., till it reaches the outlet. Calculations in Reference to Dryers. An approximate computation of the quantity of air and heat required for drying purposes may be based on the following considerations : x If the capacity of the dryer is stated to be P kilogramme of grain per hour, the quantity of water to be extracted from the grain in one hour will be defined in ^~ffo) 100 kilogramme, where p signifies the per- centage of moisture in the damp grain, and Po in the dried grain. Each cubic metre of air extracts y kilogramme of moisture, consequently the drying of the stated quantity of grain requires ^ " of air. The quantity of water-vapour which a cubic metre of air may hold, when fully saturated, depends on the temperature, and is given in kilogramme weight in the following table : TABLE XV cubic metres Degrees C. Weight of Vapour, Kilogramme. Degrees C. Weight of Vapour, Kilogramme. Degrees Weight of Vapour, Kilogramme. -30 0-00074 -5 0-00368 20 0-0171 -25 0-00095 0-00497 25 0-0281 -20 0-00129 5 0-00676 30 0-0301 -15 0-00189 10 0-00935 40 0-0509 -10 0-00268 15 0-01275 50 0-0830 60 0-1306 If the air entering the dryer contains k per cent, of moisture and its temperature is T, on leaving the apparatus it is not perfectly saturated, having k per cent, of humidity and t temperature. Then the total quantity of moisture y absorbed by 1 cubic metre of air in relation to the temperature of air after usage, t, is formulated thus : kl -* v r 'The Grain Dryer," by Prof. K. Zworykin, Russian Miller, 1910, No. 11. 142 FLOUR MILLING [CHAP, m where I and 1 signify the quantity of steam in kilogrammes saturating 1 cubic metre of air having a temperature of T and t respectively, while a is the coefficient of expansion of the air, equal to 0*003665. Hence the formula defining the volume of air required for drying, in cubic metres at a temperature t : kl The term . ^- is insignificant if cold air is employed, and in a L -\-a(t Q J. ) rough calculation may be left out ; and the quantity K does not exceed 0*7, for the dampness of the air discharged is assuredly not to be increased beyond 70 per cent, of the absolute dampness. Assuming the temperature of the medium supplying the air to be 10 C., the temperature of heating and at the discharge of the air 60 C., the per- centage of moisture in the air in both cases is 70 per cent., the primary dampness of the grain 30 per cent., and 10 per cent, when dry, after due substitution, the formula of V will be presented as follows : _ 30-10 _ _,_ 1 , 1 v/n-7 n.iqofi 0-7.0-00935 d"5 . 0-7 . 0-1305-I-0-045 "1+0-003665(60-10)) -|-2| cubic metres at 60 C. of temperature. To define the quantity of warmth required in the drying process, it must be known how much warmth is needed for the moisture to evaporate from the grain, and for the heating of the grain and the air supplied out of medium, to the temperature it has when leaving the dryer. That quantity, Q , is defined as : + V d c (t -T). Here c x is the specific heat of the grain amounting to about 0'6 ; c that of the air under steady pressure, equal to 0'237 ; and d the weight of 1 cubic metre of air heated to 60 C., equal to 1*06 kilogrammes. Substituting these significations in Q, we have : # =i(606-5+0-305 . 60-10)+t(60-10)c 1 +2'25 . 50 . T06 . 0'237. o o . T06 So, under the conditions alluded to, 1 kilogramme of dried grain demands the expenditure of about 175 units of heat. Once the heat CHAP, m] FLOUR MILLING 143 expenditure is known, it is easy to calculate the quantity of fuel consumed by the heating source of any one particular machine. Professor Zworykin attaches much importance to the principle of counter- currents, wishing to utilise the absorbing capacity of the air to its utmost within the bounds of possibility. The adaptation of this principle to grain drying in the wet scouring process is not defensible, because the coefficient of the best results in drying, in the pre- sent case, is defined not by the greatest saturation of the air, but by a more rapid drying of the bran. If we accept the principle of counter- currents as basis for grain drying in the wet scouring process, the gradually drying grain will not shell in the column apparatus, a fact mentioned at the commencement of our explanation of the wet scouring process. Before ending the discussion of grain scouring by washing, mention must be made of the fact that by far the greater number of European works favour the Robinson type of washing, or rather stone-separating machine. Vertical whizzers, further, very often receive the grain together with the dirty water (the works of Kapler, Daverio, Seek, and several others). Lastly, the dryers of all the works, except that of Robinson, operate with forced air. As regards the consumption of energy, fuel, and water in the wet scouring process, it is to be noted that the plants of the Robinson, Luther, and similar types, are in all respects more economic than the Simon or Turner type. The first cost and working expenses of the wet scouring process are considerably greater than in the usual dry grain cleaning, but the improvement of the medium and the lower grades of flour covers the expenses over and over again. The expenditure of water in the wet scouring process amounts to from 4'0 to 4' 9 gallons for 1 bushel of grain in plants where the dirty water is returned to repeat its work (to the pressure tank by the principle of counter-currents), and 12 gallons for 1 bushel when working constantly with fresh water. VI DAMPING THE GRAIN When the grain reaches the milling department it is important that the offal particles should not be reduced to a fine dust together with the stock. It is impossible to extract finely ground offals from flour. But 144 FLOUR MILLING [CHAP, in if the bran coat is broken up into particles larger than the flour, they may be removed by bolting. It is of great consequence, therefore, that the process of milling should be performed so as to leave the bran coats whole. If we have dry grain during the milling process, the dried bran is very easily ground to dust which mixes with the flour. If, on the other hand, we dampen the bran, it becomes more elastic and offers greater resistance to pulverisation than the starchy mass of the grain. In that case the force sufficient to break the kernel will leave the bran coats intact. If an elasticity is to be imparted to the bran, it is necessary to temper it. Naturally, a damping is needed only when the grain is dry, and in its process of cleaning has not been scoured by washing. The damping of the bran of the dry grain in the dry process of cleaning is performed (if ~ the grain is very dry) either previous to the second scouring, or be- fore it is fed into the first break roll. In the first case, the bran en- velops the grain so closely that, without breaking it up, it cannot be re- moved ; when softened by water, it is separated with greater ease. In the second case, the elasticity of the dampened bran resists the triturating effect of the grinding. There are two types of apparatus for conditioning the bran : (1) the wetting apparatus, and (2) the apparatus for steaming the grain. Damping. The grain is wetted with the aid of an apparatus (Fig. 126) which consists of a paddle-wheel resembling the overshot water-wheel, set in an iron casing A. The grain fed through a spout hopper a, as marked by arrow s, falls on the paddles and brings the wheel into rotation. The motion is communicated through gear wheels b-c to the wheel D which carries a series of cups d drawing up water out of the cistern B. On reaching a certain height the water pours out of the cups into a long inclined trough E, down which it runs and is spouted through tube e (arrow s 2 ) on to the grain, which on leaving the paddle- wheel has passed through the conveyor and is now flowing (arrow s-^) to the bin. The tank B is filled from the water-piping along s. 3 . If the FIG. 126. CHAP. Ill] FLOUR MILLING 145 FIG. 127. consumption of water is low, its overflow runs out of B down tube / set on a certain level. The inflow of water is regulated automatically : when the flow of grain diminishes, the revolving velocity of the paddle- wheel diminishes also, and consequently that of wheel D, thus reducing the water supply to B. With the stoppage of the feeding of grain, the work of the wetting apparatus is discontinued. The water flowing to B flows out at /, which gives the sign to those attending the grain- cleaning division. Another less cumbrous apparatus is shown in Fig. 127. Here the conic cups a are screwed on to tubes r/i. The water scooped up by these boxes is conveyed by pipes d 1 to 6, whence it pours into the box c : from e the water flows to the box d and then along the pipe s x falls on the grain in the worm conveyor A, which is carrying it by the way of 0. There being no movement of the product in the direction perpen- CHAP, iv] FLOUR MILLING 167 dicular to t, the total of the projections of all forces acting in this direction must be equal to zero : ppi cos afpi sin a=0. By placing the signification of P=PI cos a+fp 1 sin a in the preceding inequality and performing the corresponding alterations, we obtain : Sin a (1 / 2 )> 2/cos a, or tg a> 2f _ J or a> because f=tg f dressing. The idea of such grinders deserves careful atten- tion. Too small a number of experiments, how- ever, has been performed, to allow us sufficient grounds completely to reject the old construction of millstones. The Erection of Millstones. A correct fitting up of the millstones and the balancing of their motion is of great importance. The fixing up and balancing of the stationary stone is very easy. Only a spirit-level is required here for establishing the working surf ace in a hori- zontal plane and a plumb-bob for centring it. The setting of the rotating stone is much more difficult. If we set the lower working surface of the runner in a horizontal plane while at rest, this surface may assume a slanting position when rotating, should the structure of the stone not be uniform, as frequently happens. This phenomenon is easily explained. Supposing we have (Fig. 149) a wire cylinder k k 1 Tc 2 k s set on a spindle A with the aid of a movable connection c. At points k k 2 there are equal weights attached FIG. 148. A FIG. 149. In a state of repose the cylinder will be balanced, i.e. its axis will coincide with the axis of the spindle. But as soon as we commence revolving it, the cylinder will slant (Fig. 150), because the centrifugal forces T at points &! and & 3 form a couple of forces the shoulder of which is equal in size to k k z . The axis of rotation of the couple T k l k 2 will be in the fulcrum point FLOUR MILLING [CHAP, iv of support c of the spindle. To obviate slanting similar weight must be attached at the points k and k 2 . It is necessary to find a general solution of the problem, which would show how the supplementary weights are to be disposed in the grinder, so as to attain an equiponderate motion. Let us suppose we have an immobile axis 00 x (Fig. 151), and a stone A of irregular shape rotating on it. The centrifugal power developed exercises a pressure upon the axis. If we mark the reaction of the axis by forces P 1 and P 2 , applied in the fulcrum of the axis and 15 then, including those forces in the number of active forces, we may regard the whole system as free, and apply to it D'Alambert's principle. The motion of the stone being a steady rotation, l the sum total of projections and the sum total of moments in respect to the three reciprocally perpendicular axes OZ, OX, Y must be equal to zero. By denoting the angular velocity of rotation through co, through m the mass of any particular part of the stone, x, y, z its co-ordinates in respect to the corresponding axes, P the weight of the whole stone, a and b the distance of the centre of gravity of the stone from the planes yoz and xoz, M its mass, and h the quality 00 lt we obtain the following equations : The sum total of projections : ...... (1) O . . . . . . (2) P-Z=0 ..... . . . (3) The sum total of moments : ..... (4) ..... (5) The moments of each acting force in respect to the axis OZ are equal to zero, for the direction of those forces intersects the axis OZ. If the axis of rotation passes through the centre of gravity, a and b are equal to zero ; the forces X 19 X 2 , Y 1 and Y 2 then are equal to zero. If, at the same time, OZ is the main axis of inertia, then 2myz= and Zmxz = Q. Under such conditions the axis of rotation of the stone will be exposed to no side pressures, i.e. we obtain a free axis. CHAP. IV] FLOUR MILLING 173 As regards the millstone the first condition is fulfilled when the axis of the spindle coincides with the axis of the stone, i.e. passes through its centre of gravity. Should the grinder, however, be of different density Smyz and Zmxz will differ from zero. The millstone will then slant like the wire cylinder. In that case supplementary weights must be added. If a and b are equal to zero, we shall obtain from equations (1) and (2) : X 1 = X 2 , and YI = Y 2 . The resultants of X 1 and Y lt X 2 and 7 2 will be P x and P 2 . A couple of forces are thus obtained, which tend to overthrow the axis of the stone. For counteracting this couple of forces (Fig. 151) there might be applied weights M l and M 2 of a size which would produce centrifugal forces oPM-iT, equal to P x and P 2 . In general practice the supplementary weights are applied by means of a special adjustment in the revolving grinder. Three or four cavities are made in the stone, in which cast-iron boxes FIG. 152. FIG. 153. (Fig. 152) A covered with a lid B are deposited. In such a box there is a cast-iron weight p, which is adjustable along the rod a to the right or left and up or down with the aid of screws b and nuts c. By moving the weight p to the periphery of the millstone we augment its centrifugal force, while by moving one weight up, and the other, on the opposite side of the stone, down, we lengthen the shoulder of the counterbalancing couple. Another appliance is shown in Fig. 153. The weight H here slides along the rod F with a collar t, which rests on a spring E and is fixed to the rod by a bolt. The rod passes through a cast-iron ball which is held by a bearing D. In the opposite side of the box there are openings J. By placing the end of the rod in different sockets, the height of the weight may be altered. Simpler appliances consist of boxes with lead in them, the quantity of which may be either increased or diminished. Sometimes there simply are cavities made in the stone and filled with melted lead. If too 174 FLOUR MILLING [CHAP, iv much lead is poured in, part of it is cut but; if too little, more is added. On Fig. 154, showing the building of a millstone of pieces of French stone, we see the cast-iron boxes E for lead, which are hermetically set in when the top part of the stone is covered with concrete. When the stone (runner) is ready, it is balanced in the following way (Fig. 155). An apparatus consisting of three plates ef, cd } and ab, and two bolts, g and h, is set in the eye of the stone. The plate cd slides freely on the bolts and is kept back by nuts k. By the upper nuts, the appar- atus is screwed up in the eye. Then the stone is placed on a bursting, in which an iron rod m is set upright, tapering to its point n. The rod passes through the opening in the plate ab and rests with its point n in the small cavity made with a centre-mark in the plate cd. This plate must be set so that its centre (the cavity for n) would correspond to the fulcrum of the driving iron. The rod mn rests with its lower end on a lever which lifts it together with the stone. The stone raised by FIG. 154. llr FIG. 155. the rod is carefully revolved and watched, to see if it slants. In case of a slant, the position of the apparatus is altered in the direction required and the weights in the boxes are transposed, the stone having been previously lowered on to the bursting, and the upper screws loosened. These manipulations are repeated until the stone rotates without a CHAP. IV] FLOUR MILLING 175 slant. Once the right centre of the driving iron is found, the stone is lifted oft the rod mn, placed on its side, and a circle is drawn with a pair of compasses from the centre n of the plate cd on the grinding surface of the stone. On this circle in two or three places holes are drilled, 3 to 4 mm. in diameter and 7 to 8 mm. deep, filled with melted lead, which is smoothed to the face of the stone and then the circle on them is redrawn. These lead dots serve for proving the centre of the cross-head in marking the spot for it. Fixing the bed -stone. In fixing up a stone mill either on the floor of the mill or on a hursting pre- pared for it, a circular hole is made in the boards d (Fig. 156), and a cast-iron ring c is placed in it with a flange in which holes r are drilled for the bolts, by means of which the circle is fixed to the hursting. Besides FlG< 156< those small holes there are three larger ones for bolts e, which support the cast-iron frame /with ribs g on its lugs t. By tightening the bolts e the working surface of the stone may be brought to a horizontal position. For adjusting the axis of the stone, there are wedges i (six in number) placed in between the grinder and the ring c. If the stone is to be moved to the left, for instance, the two wedges FIG, 157. on the left side are loosened, while the other four are driven in deeper with lead hammers. A better frame is shown in Fig. 157. It is a cast-iron cylinder with a perforation in the bottom for the spindle. The frame is fixed to the floor with bolts, which are screwed into the lugs c. At three points of the bottom there are ribs a with holes for the bolts, by means of which 176 FLOUR MILLING [CHAP, iv the working surface of the stone is set in a horizontal plane. In the sides of the cylinder are three holes for bolts, which help to centre the stone. To make the construction lighter, the solid bottom of the cylinder may be substituted by three lugs. A still lighter design is represented on Fig. 156. There are simply three castings A made with regulating bolts. These lugs are set independently on the floor in a circle at an angle of 180. For the plainest kinds of machinery in peasant mills, a simple planting on beams may be recommended. The ad- justing borts may be let through the beams into which threaded nuts are set. The dimensions in all the figures are given in mm. The spindle supporting the runner is an iron or steel shaft A (Fig. 158) with a vertical journal a set in its base. The top part of the shaft B is turned to a cone or planed smooth to a truncated pyramid. In the first case it is coupled with the cross-head of the driving iron by means either of a wedge or a key. The mill-bush (Figs. 159 and 160), stationed in the eye of FIG. 158. fa e bed-stone, and arresting the side-movement of the shaft, has timber (oaken, beech-tree, or pock-wood) or bronze wedge-shaped FIG. 159. FIG. 160. bushes a. In it the centring of the shaft is done with the aid of bolts and nuts 6. This mill-bush is attached to the stone by means of lugs d, CHAP. IV] FLOUR MILLING 177 which are covered with a cementing composition in their respective seats in the stone. The lubricant is poured into the cup e. There are mill-bushes of various design but always with bushes. Sometimes those mill-bushes are set on the frame. A step-bearing of the ordinary kind is shown in Fig. 161. A is the lower end of the shaft, into which is set a journal B, resting on a steel bush c. The side-bush d is of bronze. The oil is poured into s, and after passing through the bearing is drained through drilled canals /. The hole g in the end of the shaft is to afford access to the journal B, which is knocked out with a wedge-shaped plug in case a breaking off must be made. The liner E of the step- bearing, cylindric in shape, is generally of cast iron. The frame of the step-bearing is shown in Fig. 162. The spindle is lifted by a lever D. The bearing F supports the shaft of the toothed gearing to the spindle. The design of the step-bearings varies very much, but the ball collar thrust-bearings are to be preferred most. The driving iron. By means of the driving iron the spindle is connected with the rotating stone. The plainest style of a driving iron (Fig. 163) is an iron cross-head which is hermeti- cally set in the grinder, or a tripod driving iron (Fig. 164), also tightly fitted in the stone. But these designs should be avoided, for the proper balancing of a fast coupled runner in m.otion is '[an FIG. 161. - FIG. 162. impossibility. A type of driving iron in vogue is shown in Figs. 165 and 166. In the stone there are set two cast-iron cups N, on which the journals e of the cross-head b rest. This cross-head likewise has sockets for journals e of a second cross-head c. The spindle is set with its conic end in the cross-head c, and fastened to it M 178 FLOUR MILLING [CHAP, iv This forms a flexible fastening on the principle with one or two keys, of Hooke's joint. Instead of cups a it is better to set (Fig. 167) a cylindric cast-iron ring B with ribs P for the journals of the cross-head. In that case the load chipping the stone is distributed over a larger area. The second FIG. 163. FIG. 164. FIG. 165. cross-head D here, is coupled to the spindle by wedges i, though keys t may also be employed. To prevent any curling up of the ring, it is provided with protruding ribs which are sunk into sockets hollowed out in the stone for that purpose, and fixed there with cement when the ring is laid on. In the upper cross-head of the driving iron there is usually made a FIG. 166. FIG. 167. hole K for setting the plate e (Fig. 167) which receives and flings the grain by centrifugal force into the eye of the millstone. Sometimes a cup (Fig. 168) is set in the place of a flat plate. The advantages sup- posed to be afforded by this cup are that the heavy extraneous matter (stones, small pieces of iron, &c.) drop to its bottom and do not reach the milling area. This is, however, an unnecessary complication of the design, because previous to being milled, the grain has to be freed of all impurities. And if unclean grain is milled (as in primitive CHAP. IV] FLOUR MILLING 179 peasant mills), this cup is too small to serve as a heavy impurities collector. The feeding of the millstones is done through feeding tubes or other more complicated mechanisms. Fig. 169 represents an iron feeding tube B with a hopper B . With a view to regulating the feed, the FIG. 168. FIG. 169. distance between the end of the tube and the plate is measured by means of a cast-iron sleeve b having a square thread, firmly joined to the tube, and a hand-wheel T, with an inversely threaded hub, which is held by the collars of the cast-iron cross-head M . By rotating the hand-wheel, the tube may be raised or lowered, thus regulating the diameter of the stream of product between the tube and the plate. ^W^VtU *2 3 FIG. 170. The ordinary feeding device employing a rocking shoe is shown in Fig. 170. The hopper A is set on a small timber frame which stands on the cover of the casting. Under the hopper, on three or four rods (bolts i and two rods k) the shoe B is suspended aslant. To the pro- truding plank of the shoe g is attached a square block d, which receives the blows from a cross-head set on an axle, which in its turn is set in a plate. In the cross bar of the frame, h serves as an upper bearing to the 180' FLOUR MILLING [CHAP, iv axle. A slide a, lowered or lifted with the aid of a hand- wheel b, regulates the flow of product. The inclination of the shoe is adjustable by means of belts /, which may be wound on and off the axle c by turning it with the hand- wheel e and keying on with wedges I. Another feeding appliance we see in Fig. 171. Here we have a cast- iron trunk A mounted on the cover of the casing by its wall-brackets. The spout T is cast jointly with the trunk. Through the bottom of the trunk is let an axle v connected by sleeve m with an axle v^ running from the driving iron. The sprocket b feeding the grain into the spout T, FIG. 171. and the cross-head a which loosens the grain fed into the trunk, are both set on the axle v. By raising and lowering axle v with lever d, attached with its fork to the spout, the flow of product is regulated. The gate valve e held by a screw n regulates the delivery of the grain into the spout ; the lid g is an inspecting door, r the lubricator oiling the axle v. 3. Under-Runner Millstones In studying designs of stone mills we saw that the product treated travels to the outlet from the working space under the action of the force of friction, if large enough and subjected to pressure between the stones, or travels down the furrow r s of the stone and the working surface of the bed-stone, driven by an air-current if it is so finely broken that the top runner cannot act upon it. In the stone mills with an under runner, the delivery of the milled product takes place under much more favourable conditions, since its particles acquire a centrifugal force. As to the large stock to be milled, . iv] FLOUR MILLING 181 its treatment also obtains under better conditions, for, owing to the centrifugal force, the pressure being equal to that of the upper- runner mills, it is treated more vigorously, and the actual grinding takes less time. In respect of under runners, the important question as to the outline of the furrows, and even their indispensability, arises. If in a mill with a fixed bed-stone the ventilating air carries the fine ground product out, in the case of a rotating under stone the unground particles of grain will be ejected by centrifugal force if the line of the furrows coincides with the direction of the product which is propelled by centri- fugal force, and by the pressure of air. Owing to this, if the line of the furrow is badly chosen, the finished product will be unsatisfactory, i.e. it will be intermixed with unground particles of grain. To solve the question of the pattern of the furrows we must know the direction in which the product travels, and then a design of furrows can be selected which will result in the crossing between the route of the grain and the direc- tion of these furrows. Only in this way will the unground product be ejected from the furrows to be re- duced to flour in the grinding area. Professor Kick gives the following solution of the problem concern- ing the route of the stock. o Let us suppose that the under stone rotates with an angular velocity. If a particle of product at a distance r from the axis of rotation acquires a centrifugal force ma) 2 r, equal to the- friction force fmg, it is bound to slip off the stone at that moment, and move uniformly, i.e. as a free body, with a speed ro>, so that its motion will be directed at a tangent to the circumference of the radius r. The denotations employed here are : m, the mass of particles ; g, the acceleration of gravity ; and /, the coefficient of friction between the product and the stone. The free motion of the particle in respect to the uniformly rotating stone is an involute of circle, a fact easily grasped (Fig. 172). The stone revolves as pointed by arrow 8. The particle m having slipped off at point a 1} at a distance r from the axis of rotation, flies at a tangent a 3 in the direction the stone moves, with the speed rco. The motion of a 3 is absolute. To find the trajectory of motion in respect to the rotating runner, let us suppose that in a unit of time the FlG 172> 182 FLOUR MILLING [CHAP, iv runner has turned at an angle a, and the particle m has travelled the distance a lf Then the resulting position m x of the particle will be at the intersecting point of the circle described with radius o l and the circle drawn from centre b of the radius of the straightened arc 6a 1? corresponding to the angle a. A series of points a l9 a 2 , 3 , &c. obtained in this manner, forms an involution of circle. This opinion of Professor Kick's cannot be agreed with, for he has not taken into consideration the power of wind which will impart a uniformly accelerated motion to the particle m. Besides that, taking for granted that the particle will slip off the surface of the stone (which is impossible, the gravity playing a part here), it will move in a parabola under the effect of the power of gravity and of wind and will certainly fall upon the stone. Consequently we see that the trajectory of motion of the particle, influenced by its gravity, centrifugal force, and the power of wind, pre- sents a .very complicated curve, and in no case an involute of circle, as Professor Kick supposes. It is possible to construct this curve in theory for one particle. But if we consider that in the working area of the stones there is a large quantity of product undergoing friction in its mass, and that the rough surface of the millstone excludes the very idea of friction in the fine particles, for the cutting crystals of the stone impede the motion of the reduced particles, and, consequently, exclude the possibility of friction in the sliding motion over the surface of the stone (the motion must be performed in a zigzag line between the crystals), these circumstances make the problem insoluble. As to general practice, it would have been possible to answer the question respecting the most advantageous tracing of furrows, had strictly scientific experiments been performed to that end. However, in our opinion, the furrows ought to be completely discarded on the lower runner, and retained only on the upper fixed stone for ventilating the working area : the shape of the furrows in the fixed upper stone, at the same time, being of no great importance, they may therefore be of the simplest kind, i.e. rectilinear. Before proceeding to describe the designs of under-runner mills, we must mention the experiments performed by Buisson in connection with his observations concerning the influence of exhausting mill- stones. All the three types of stone mills were driven by 6 h.p. each. The experiments were made on wheat grinding, and the stones employed were French, of equal diameter, and with similar furrows. CHAP, iv] FLOUR MILLING The results of an hour's grinding were as follows : (1) An upper-runner mill without exhaust yielded 182 Ib. (2) An upper-runner mill with exhaust yielded 279 Ib. (3) An under-runner exhausted mill yielded 373 Ib. (4) The last mill, with both the upper and lower stones revolving in opposite directions, with ventilation, yielded 468 Ib. per hour. As regards the fourth case, the flour produced was of a worse quality than in the first three cases. These experiments prove that stone mills with revolving upper and lower grinders ought not to be employed, because of the low quality of the grist. Besides, these mills are so complicated in design that in this respect, likewise, they may be regarded as unsatisfactory. At any rate they were rejected long since in general practice, and we shall pass them by. In comparing the capacity of upper-runner and under-runner mills, we notice that the capacity of the latter exceeds the former by 33*5 per cent. Buisson's experiments are naturally insufficiently exact, for he used stones with uniform furrows, but undoubtedly under-runner mills grooved in the most advantageous manner would yield a larger quantity of product of a higher quality. But the comparatively great pressure of the spindle upon the vertical journal is a defect in the design of under- runner mills. Indeed, if to a unit of working surface, the pressure of the upper runner necessary for grinding the product is p and the weight of the stone to the same surface P, then the pressure of the spindle upon the vertical journal, the common working area being w, will be (P-p)w, because p is the reaction of crushing of the bed-stone. If, on the other hand, we have an under runner, then the pressure upon the vertical journal may be expressed, employing the same denominations, by the formula (P+p)w, for the weight of the stone and the reaction of its pressure upon the grain both act in the same direction. Owing to this, the vertical journal becomes worn much faster in under-runner mills than in those with upper runners. However, this defect is reparable, as will be seen in the constructive description of stone mills. An ordinary type of an under-runner mill is shown in Fig. 173. The stationary top stone B is encircled with an iron ring a (set on the stone hot) with three clutches q. The cast-iron casing c serves as frame to the upper stone ; the stone rests on the casing on bolts b, by means of which the working surface of the stone may be set horizontally. The chamber of the casing is closed by a timber ring d. The runner C is supported on 184 FLOUR MILLING [CHAP, iv an ordinary balancing driving iron e, the first cross-head of which rests on a disc i, furnished with a lid which serves at the same time as a plate supplying the grinding area. In its bottom surface the runner has boxes with weights for counterbalancing it. In the sides of the stones there are iron sockets n for lifting it. Every stone ought to be provided with such sockets, because in mounting or dismantling of the mills the stones must necessarily be lifted. The feeding is performed by the tube A described earlier (Fig. 169). The side -travellings of the spindle D are arrested by an ordinary vertical bearing k. On the spindle is set a washer I, its turned down ends entering the ring reservoir m, which is filled with water (or empty) to prevent the meal -dust from penetrating into the bearing. As to the remaining details, the shafting of the rotation of the spindle, the step-bearing and the tram pot not given in the drawing, they are similar to those of the above examined upper- runner mills. The constructive advantages of under-runner mills are the following : (1) Simplicity of the bearing substituting the complicated mill- bush here, and its accessibility for inspection and lubrication. (2) The driving iron does not impede the free passage of the product through the eye, and consequently the grinding surfaces are more evenly supplied with grain. The heavy loading of the step-bearing is, as we have seen, an important defect more or less successfully combated almost exclusively by Russian engineers. To counteract the rapid wearing of the vertical journal and the step-bearing resulting from the heavy load, they replaced the sliding friction by a rolling friction, employing ball collar thrust-bearings of a corresponding design. Fig. 174 represents an under-runner mill designed by Mr. Panshin. The revolving under stone A is fixed on a cast-iron frame B forming one block with the pulley D, which is set into motion from a belt drive. The whole system is mounted on a cast-iron frame E bolted to the foundation. The frame supporting the runner A rests on two ball collar thrust-bearings, the first one, /, being set below on the main frame, the second, 77, on the FLOUR MILLING 185 CHAP. IV] vertical stationary cylindric steel column with a collar. The hardened steel balls receiving the pressure of the under runner, roll between the steel rings, likewise hardened. In this wise the pressure of the under runner is supported by two horizontal planes, which reduces the wear of the steel balls and rings. The third, upper, row of balls ///, also rolling in steel washers, does duty for the mill-bush. The distance be- tween the grinding surfaces is adjusted with the aid of a cogged hand- wheel 0, having a long square-threaded hub. The hand-wheel is turned FIG. 174 by a lever H. The lifting is done as follows : the tripod drop-hanger frame K supporting the fixed upper stone is screwed with its hub on the hub of the hand- wheel and lifts the stone ; with the retrograde motion of the hand-wheel, the drop-hanger frame is screwed off and the upper stone is lowered. The regulation of the flow of grain is performed by lowering or raising the feed-tube L with a hopper, which is done with a hand- wheel having a screw thread on the inside of its hub. The lubrication of the mill-bush and step-bearings is sufficiently clearly depicted in the drawing. To the bottom of the frame on which the runner is mounted are riveted iron scrapers M, which convey the flour to the discharge spout T. 186 FLOUR MILLING [CHAP. iV W. Joukovsky's stone mill (engineer Fuhrman's patent) has a fixed frame T carrying (Fig. 175) a step-bearing R with three rows of balls. The frame P is cast in a single block with the pulley 8 of pig iron ; the cylindric rib U of the frame constitutes the mill-bush K. The steel shaft V, connected with the frame T by means of keys, is stationary, and has an axle V 1 inside, which, with the aid of a ratchet wheel gearing a and lever h, may rise and fall by being screwed into the screw hub b of the shaft V. The shaft V t supports the fixed upper stone on a tripod drop-hanger frame, and thus affords the possibility of adjusting the distance between the grinding surfaces. The product is supplied by the hopper Q, and a tube r which may be raised and lowered by a crank mechanism po driven by a hand- wheel n. The oil is supplied from lubricator-box m through a copper pipe t, directed to the mill-bush. From the mill- bush it is conveyed to the step- bearing by a canal i. The step-bearing and the mill-bush are completely isolated from dust. The product is shovelled from the bottom of the casing into the spout Z by means of scrapers s. In comparing the two designs of stone mills and attaching supreme importance to ball bear- ings, we are inclined to favour engineer Fuhrman's design, for the assembling of a ball step-bearing in one plane presents no difficulties. In Mr. Panshin's design, the fitting up has to be done in two planes, and a slight inaccuracy in this case compels one to work but in one plane. At first sight the three rows of balls in Fuhrman's step- bearing also present inconveniences, namely, all the three rings of balls are evenly loaded, and therefore the balls of the outer ring, having a longer course to run, ought to wear out more rapidly. It has to be taken into consideration, however, that the number of balls in that ring is greater, and consequently the load per ball is less. Thus a judicious choice of diameters in the rings of the three rows of balls will equalise the wear of the balls. The under-runner stone mills with ball-bearings have undoubtedly a FIG. 175. CHA?. IV] FLOUR MILLING 187 good future, and will certainly supplant the mills of the ordinary style with an upper runner, as they require a smaller consumption of power, and have an equal capacity, and are more compact than the common mills. The problem of the rapid wearing of balls has now been completely solved, for the development of motor car production has furnished us with ball-bearings more durable than slide-bearings. 4. Stone Mills Vertical (Horizontal Axis of Rotation) While studying the question of setting the working surfaces (p. 99, Fig. 90), we pointed out some defects of the vertically set surfaces, and FIG. 176. will therefore not discuss them now. In spite of those defects, the mills with vertically mounted stones, rationally designed, owing to the con- venience and easiness in taking them to pieces, simplicity of attendance, and their compactness, fulfil their purpose successfully. " Selecta " of the Works of form. Seek Bros." Selecta " built by the Dresden works of Seek Bros., is a characteristic construction of stone mills having a horizontal axis of rotation, and is used for a single grinding, as well as for reducing the integuments (Fig. 176). 18B FLOUR MILLING [CHAP, iv In a cast-iron casting a, easily removed, there is fixed the immov- able grinding stone b. The runner b 1 is set in the left section a l of the casing. The shaft h with the runner set on it by means of a cone and nut, rotates in three bearings with ring lubrications, two of which are attached to the parts a and a of the box. The third bearing is set on a bracket. The casing a~a 1 and the bracket are established on a cast-iron founda- tion-frame, and riveted to it by bolts. If the frame is correctly placed on the foundation or on the floor, the correctness of the position of the millstone is perfectly guaranteed, for the setting of the bracket and the casing aa : is done accurately at the works. The throwing of the stones apart and together is performed by means of a lever \ connected by an eccentric with a screw ending in a hand- wheel /. This hand- wheel serves for a more accurate adjustment of the distance between the fixed stone b and the runner fej. This is done in the following manner : the shaft h carrying the runner 6 X rests on a horizontal pivot- journal z, which is connected with the box p. Into this box enters a screw connected with a box g v which rests with its collars F 177 on a spring set in between the hub of the box and the casing of the bracket. The spring will resist a certain normal pressure. By turning the hand- wheel / to the right or to the left, one may accurately regulate the distance between the grinding surfaces. But when a big, hard object (nail, nut, &c.) is caught in between them, the runner presses hard upon the shaft h, which transmits the pressure to the box g r Then the spring contracts and the object leaves the working space having caused no breakage, while the runner acted upon by the spring returns to its former position. The slight displacements of the bed-stone while being mounted are likewise provided for. This is done in the following way : in the right- hand bottom of the casing a containing the bed-stone, there are set four adjusting screws (only one is visible in the drawing, they are seen more clearly in the general view, Fig. 177). Through the bodies of the screws there pass bolts by means of which the casing of the bed -stone can be tightly pressed to the ends of the adjusting screws. At the beginning CHAP, iv] FLOUR MILLING 189 the grinders are adjusted in proportion to their wear, with the aid of the hand-wheel /. But once the wear of the working surface has reached the stage when the turning of the hand-wheel becomes purpose- less, then, having freed the bolts and screws of their nuts, the fixed stone is pushed together with its casing in the direction of the runner, the hand- wheel / having previously been brought to its former position. The fur- ther adjustment is performed as far as circumstances permit, again by the hand- wheel, until the displacing of the adjusting screws has to be renewed. This manipulation is repeated so long as the length of the adjusting screws permits, i.e. until these screws completely sink into the hollow of the casing a. When the fixed stone, in consequence of wear, has attained the last- mentioned position, the runner can be further transposed. To this end (Fig. 178), the adjusting screws I are screwed out of the casing and the runner, keyed on to the shaft, is pushed with the aid of a cone-shaped entasis i to the right towards the fixed stone. To assist in transposing the runner, a box o is set on the shaft and the runner with its casing is shifted more to the right. During the operation following the stones are adjusted in the manner explained above, until they are totally worn. In dismounting the mill, special hoops are screwed on to the frame, and after the bolts coupling both halves a t and a have been loosened, with due precautions the frame is shifted with the aid of rollers over the hoops to the right. This mill may be furnished with stones of various types. For the purposes of aspiration the machine is either included in the general aspira- tion, if there is a centrifugal appliance, or provided with a special dust- collector. During the ventilation the opening in the left-hand side section of the casing a^ usually covered with wire cloth, is hermetically stopped up. The feeding appliance consists of a hopper with an adjustable bottom, similar to the rocking shoe in the hopper of an ordinary stone mill. The hopper is driven by a pulley t which can be shifted along the shaft h. For regulating the feed there is a distributing slide valve by means of which the outlet in the adjustable bottom may be enlarged or made smaller. The product fed into the millstone slides over a magnet which extracts all pieces of iron, and is then conveyed by the worm n to the working space of the grinders. When the mill is in operation and filled with product the lever h l set 190 FLOUR MILLING [CHAP, iv on the box gr/is brought into a position denned by the pawl of the ratchet wheel, i.e. it is turned to an angle of 90 in respect to its former position. Then by means of the hand- wheel /, the runner is brought by the screw so close to the fixed stone as to produce a grist of the desirable fineness. If the process has to be quickly stopped, it is sufficient to turn the lever on box g l back the 90 and the stones acted upon by the spring will move apart. At the same time the movement of the rocking shoe must be stopped with the aid of a disengaging gear. If any hard foreign object is fed into the mill together with the grain, the runner may be thrown out of action by pressing the spring, which forces back the box g 1 and the adjusting mechanism. This set may be furnished with quartzose stones, but the artificial emery stones are preferable, as they require redressing much more rarely. There is no need to make slanting furrows here, it is sufficient to deepen the ventilatory furrows from time to time and smooth the spout for the ready product. Of stone mills of this type Thos. Robinson's " Dreadnought," the " Monarch " of Dobrovy and Nabholtz, have a name, as have the mills of a similar type from many American works, whence the European engineers have borrowed the design. Below are given the data of the capacities of all three types of stone mills obtained in general practice. In the second table, D denominates the diameters of the stones in quarters, 1 n the number of revolutions, P capacity per hour, N the number of effective horse-powers, and Q the weight of the mill without the stones. TABLE XVII THE CAPACITY OF STONE MILLS (1) Upper-Runner Mitts Diameter of Stones, in Quarters. 1 Number of Revolutions per Minute. Number of H.P. required. Capacity per Hour, in Bushels. Weight of Mill without Stone, in Lbs. f (35 in.) 160-170 4-5 6-8 4140-4320 f (42 in.) 145-155 5-6 8-10 4500-4680 I (49 in.) 135-145 6-7 10-14 4860-5040 f (56 in.) 120-130 7-8 14-16 5120-5300 Quarter =7 in. " Quarter "Js aTRussian measure used in measuring millstones. CHAP. IV] FLOUR MILLING 191 (2) Under-Ruuner Mills on Balls D. n. P. N. Q. 4 quarters 180-200 6-10 3-5 900-1080 5 170-180 10-16 5-10 1260-1440 r> 145-150 23-26 10-15 1730-1800 7 135-140 30-35 15-20 2050-2780 8 120-125 40-48 20-25 2780-2960 (3) Stone Mills of the, " Selecta " Type Diameter of Stones Number of Capacity per Hour, in Bushels. Number I Full Weight in Millimetres Revolutions of of Mill, and Verschokes. per Minute. H.P. in Lbs. Coarse Flour. Soft Flour. 256 mm. = 5-Jv. 1000-1200 6-10 2-6 2-4 396-432 400 = 9 v. 900-1000 16-24 8-14 6-10 828-900 600 =13iv. 750-800 45-60 20-25 15-20 1908-1980 711 =16 v. 700-750 60-75 25-32 20-25 2720-2512 The considerable difference in the weight of machinery given in this table should be taken notice of. The light weight of the under-runner mills on balls and sets of the " Selecta " type in comparison to the upper- runner mills does not speak in favour of mills of the old type, which are, in fact, losing ground to the new type of machinery, owing to their cheapness and satisfactory operation. 5. The Capacity and Calculation of Stone Mills On examining the practical data of the capacity of stone mills with grinders of natural and artificial stone, we see that it does not exceed 1 to 2 bushels to an effective horse-power. The data of capacity given here pertain to the single grinding, and have been obtained from the materials of large works, which give us no reason to doubt their veracity. Those data are confirmed, with insignificant reductions, by our immediate observations. The reduced capacity, however, results from the millstones being badly attended to by inex- perienced millers rather than from any inaccuracy in the data given by 192 FLOUR MILLING [CHAP, iv the factories. For this reason, in calculating the capacity of stone mills it ought to be set at 5 to 10 per cent, lower than as per catalogues of large firms ; it is still better to employ an experienced miller able to handle the machinery well. Detailed investigations of the capacity per horse-power per hour are published by Wiebe, 1 and are based upon his experiments on mills in Budapest (Pester Miihlen). These researches, in spite of their dating from so early a period, have not lost their value in a comparative sense, owing to the fact that the standard of millstone grinding was very high at the time mentioned. The stones, the capacity of which was investigated, were 5 feet in diameter, and ran at the rate of 120 r.p.m. Those data relate to the plain and high grinding on stones. The first figures (belonging to plain grinding) approach our modern data. If they are rectified in proportion to the increased number of revolutions of the millstones and an improved ventilation, 108 Ibs. per horse-power- hour will be a perfectly normal capacity for modern millstone sets. TABLE XVIII CAPACITY PER HORSE-POWER (STEAM) PER HOUR ACCORDING TO WIEBE. WHEAT. Without Ventilation, Ibs. With Ventilation. Ibs. (1) Single grinding with a regrind- ing of the rest (2) Grinding in two passages . (3) Grinding in three passages 59-4 50-4 45-0 58-3 34-9 28-4 79-6 67-3 59-4 78-8 47*2 37-1 RYE. (1) Grinding in a single passage (2) Grinding in two passages . (3) Grinding in three passages In passing to the question of the design of stone mills, it must be pointed out that the calculation of exact details of this machinery de- pends on the weight of the stones, which, in its turn, is determined by the force necessary to crush the grain. The natural stone, being diverse ajid variable in its structure, does not allow of the evolution of any 1 Wiebe, Die Mahlmiihlen. CHAP, iv] FLOUR MILLING 193 analytical formula as regards the normal dimensions or for the velocity of rotation of the stones. Owing to this fact we must have recourse to the empiric data evolved by factories and mills in their long years of practical experience, according to which to one square metre of the working surface 700-1000 kilogrammes' weight of the runner is accepted. Availing himself of those data, Navier suggests the fol- lowing formula for the weight P of the runner : P=668D 2 kilogrammes, D being the diameter of the stone in metres. If the height h of the stone is to be determined, then, denominating the density of the stone as 6, the diameter of the stone D, the diameter of the eye d, we obtain the pressure to one square metre of the working surface : for the weight of the millstone P=~ - (the volume of thecylindric ring multiplied by the specific gravity of the stone), while ^ ' is the area of the base of this ring. Seeing that the density 8 of the natural stone is equal to 2000, and taking the average of p as 850 kilo- grammes, we obtain ^=0*425 metres, which closely approaches the dimensions of the stones made by French manufacturers. Results of a greater accuracy may be obtained for artificial stones, as the uniformity in their structure enables us to find more accurate limits of weight. As regards the circumferential velocity of the millstones, Wiebe proposes 9*42 metres per second for the utmost limits, Fairbairn 10 metres per second, and modern constructors place the highest limit at 16 metres per second for good French stones. No scientific experimental operations with the view to calculating the power consumed in the working and the empty run of the stones have been made as yet, while the imperfect observations give the following general rule : it is considered that to move a grinding stone a force equal to -^ to -^ of the weight of the stone is required, applicable at the distance of f from the axis of rotation. Then the work T per second will be expressed by the formula : __P_ % nDn _ P.nDn ~~ 20-22 ' 3 60 1800-1980 where D is the diameter of the stone, n the number of revolutions per minute. General practice in Russia has established a still more simple N 194 FLOUR MILLING [CHAP, iv rule, according to which one H.P. is reckoned to each quarter, i.e. 28 inches require four H.P., 35 inches five H.P., 42 inches six, &c. In calculating the consumption of power of the stone mills, it must be kept in mind that the power consumption depends on how the grinding is done. The numbers of horse-power given above are to be regarded as an average. A stone mill running empty consumes 20 to 25 per cent, of power. Wiebe offers the following inference for the definition of the relation between the velocity of rotation of the stone and the consumption of power : Let us suppose that h is the distance between the working surfaces at the inflow of the product, u the speed at which the product is dis- charged in a radial direction. The volume of product V delivered per second will be equal to nDhu, D being the diameter of the stones. If we grant, with a great approximation, that the volume of the reduced product is proportionate to the volume Q flowing into the mill, then V=aQ, where a is the coefficient of proportionality. Reckoning that the speed of the product delivered is proportionate to the circum- ferential velocity of the grinder, we obtain u=f$v, where v is the velocity of the stone, and /? the coefficient of proportionality. Substituting those significations in the formula for V, we shall obtain for the bulk discharged per second : T7 ^ nDnnDKh , V=aQ= - r , whence Q ~ = ~7?7i 60a By substituting the mean values of n and Q in this formula, we shall define this constant quantity. The following problem may be solved as an example. Granted D=l'5 metres. The number of revolutions n = 120, 48 litres of wheat per one horse-power have been fed in per hour. Then per minute Q=0'S N, N denominating the number of horse-power, Hence (reckoning Q per hour to be equal to 275 litres) : Consequently, N=D*n . 0-019. The constant - may be regarded JLJ Tl as equal to 0*02, then the formula defining the number of powers will be N=D 2 n . 0-02. But seeing that the capacity of the stone mills in modern technics has risen, the coefficient 0'02 should be slightly increased, CHAP. IV] FLOUR MILLING 195 6. Mills with Metal Grinders Repeated attempts have been made in Europe to supplant the stone grinders by metal ones cast iron or steel but no" satisfactory results have been obtained. In Europe, chiefly in Germany, up to this day such mills are made only for laboratory purposes. The American technical science, however, has evolved a series of splendid designs of mills with steel grinders for industrial purposes, mainly for grinding forage products maize, barley, oats, cotton seeds, &c. The Americans build mills of this style with a horizontal axis of rotation, and mostly with twin rotating grinders. Figs. 179 and 180 represent a universal attrition mill " Scientific " FIG, 179. built by " The Food Manufacturing Co.," Springfield, Ohio. The product is fed into hopper A with a feeding and crushing roller 4 with pulley 44 driven from a special shafting. The regulation of the feed is per- formed by a cast-iron valve 38 by means of a screw 39, which are set apart on B. If whole ears of maize are to be ground, a narrow passage is left open between the valve and the side of the hopper : should the product fed in be the grain of barley, oats, &c., the valve is kept almost quite open. From the hopper the product streams (arrows s) into the working space through the eye of the left-hand stone. The grinders are cast-iron discs 28 and 33 with cover plates 32 of hard tempered steel with cutting edges (Fig. 180), The reduced product is 196 FLOUR MILLING [CHAP, iv discharged as pointed by arrows s lt The grinders are enclosed in a cast- iron built-up casing 27. The shafts of the grinders are set each on two bearings with bronze bushes and ring lubrication and have ball step- bearings 9. The right-hand grinder has a tension adjustment drawn in FIG. 180. detail on C, which is arranged as follows : the pivot journal of the shaft transmits the pressure to the bolt 2, which in its turn presses upon the cross-head 3 resting with its ends on springs 48 ; the spring and the ends of the cross-head are set on guides 49 fixed to the frame of the bearing. The bolts 2 and 47 of the end bearings also serve for the fitting up. For lifting and inspecting the grind- ing surfaces there is a rack and pinion 52 operated by a ratchet wheel with the aid of a lever 56. One end 54 of this rack is connected by a joint to the base plate on which the bearings are set. The bearings and the casing are set on the foundation frame. The accuracy in the setting of the shafts of the grinders is guaranteed by the con- struction of the bearings, which may be raised or lowered by bolts a, and pushed backwards or forwards by bolts D (see general view). For the inspection and cleaning of the grinders the casing is broken off, the belt removed, and the whole side with the tension adjustment is lifted with the rack and pinion. The plate 20 of this side is placed on FIG. 181. CHAP, iv ] FLOUR MILLING 197 the base plate free and is not bolted to it ; while the plate of the other side is cast in one block with the base plate. By the first bearing on the left (section) a collar 63 is set, and the bush of the pulley 22 serves as guard for the shaft of right-hand grinder. The holes E-E in the frame are made for the belts to pass through. This machine has been rationally designed, and its sole defect is the absence of ventilation, which is particularly important for cooling, when hard mineral substances are ground. The worn grinding steel discs (Fig. 181) are easily replaced by new ones. The capacity of the machines of this type and the power consumption are given in the following table : TABLE XIX CAPACITY or MILLS WITH METAL GRINDING Discs Diameter of Grinding Discs. Number of Revolutions. Capacity per Hour, in Bushels. Number of H.P. General Weight, in Lbs. 16 inch. 2000 14-18 10-12 1800 19 1900 25-45 15-18 1800 22 1800 35-50 20-25 2100 24 1700 70-110 25-30 2100 26 1450 90-125 25-35 3950 30 1350 125-165 35-45 4740 36 1200 145-185 45-60 5950 This table gives us the produce of feed, this type of mills not being employed for milling flour for human consumption, because the energetic activity of the cutting discs reduces to powder the bran too, which cannot be extracted from the meal. Lately in the West European countries the use of mills with steel grinding plates also for other kinds of grinding has begun rapidly to spread. These machines have also appeared in Russia. The absence of any definite data in general practice, however, allows us to utter no positive opinion concerning them. As to the firms selling them, they give but advertisements. At any rate, owing to the cheapness of these mills and the simplicity in attending to them, they may play a considerable role in supplanting the heavy machinery on the peasantry market. The grinding discs constitute an essential detail of this machinery. Fig. 182 represents two kinds of those discs. One has the cutting facets arranged after the type of the circular furrows, the other is with figure 198 FLOUR MILLING [CHAP, iv rim collars A and radial edges B at the outlet of the product. Undoubt- edly the first design of the facets is more rational than the second. In FIG. 182. the discs, the heads of the bolts riveting them to the millstones rest in square sockets D of a sufficient depth for the heads to be sunk to a level with the working surface of the disc. IV MACHINES ACTING BY IMPACT The machines acting by impact are constructed on the principle of transforming the kinetic energy into a crushing action, which is the result of pressing a body beyond the elastic limits. Supposing we have a body weighing P kilogrammes for the crushing of which work equal to E kilogram meters is required. Then, reckoning the initial velocity of motion of the body to be equal to zero, we obtain the following formula for the destructive work : p As =m, herefrom is defined the velocity v of motion of the striking element or the velocity of the body, with which it must hit against an immobile object, to be destroyed : J2E v=\j 7 ra It the hitting element and the body to be broken are moving towards each other and the velocities corresponding to their motions are F x and F 2 the resulting velocity will be F x + F 2 . Disintegrators. One of the first machines of this type (Fig. 183) was suggested by Carr. The working organs in this machine are iron discs A and J5, with steel taper-pins a and 6 set in concentric circles. Both the discs are brought into rotatory motion in opposite directions by means of CHAP. IV] FLOUR MILLING 199 belt pulleys E and E^ The disc A on the left-hand side is attached to the bush A! with taper-pins e. The cast-iron casting H encloses both discs. The tube G which conveys the grain to the working space on receiving it from the tank F and hopper JV, likewise passes through that casing. Speaking generally, the design of this machine greatly reminds one of the American grinding machines of the " Scientific " type, differing from them in the character of action performed by the working surfaces. The grain falling on the moving taper-pins receives an impact, is rejected, and meets the next pin, which again strikes it. In this manner the product travels in a zigzag line to the outlet, being gradually reduced. Though the disintegrators are mentioned in catalogues of some fac- FIG. 183. tories, they cannot be recommended for milling, for they do not work economically, and require a great quantity of power. For instance, the disintegrator that worked at the exhibition in Paris (1878) expended some 30 horse-power yielding about 1800 Ib. per hour, i.e. 60 Ib. per hour power. This was on the average 15 to 20 per cent, below the capacity of the stone mills of the time. The dimensions of the working parts of those machines were generally the following : the diameters of the discs were 350 to 1800 mm., the diameters of the taper-pins 10 mm., their length and the distance between the discs almost the same, 230 to 280 mm., the number of revolutions 1200 to 400. The Nagel and Kamp's disintegrator (Fig. 184) differs from the one preceding, one of its discs A being stationary. This machine serves for the further reduction of the product obtained after passing the grain 200 FLOUR MILLING [CHAP, iv once or twice through the roller mills. On leaving the roller mill the semolina passes into the hopper 1, whence by a feeding roller H it is delivered into the working space. In this machine the constructor tried FIG. 184. to obviate the ventilating effect of the disintegrator, ' which results in pulverisation of the meal ; this explains the presence of the stuffing boxes 2 and 3. The disproportionately large cisterns D and D t serve to collect the exhaust oil and drain it through cocks i. T is the driven belt-pulley, while the loose belt- pulley J is the tightener. To get a clear idea of the process of movement of the product over the working area in a machine of the first type, let us suppose we have it (Fig. 185) in section over the taper - pins parallel to the discs. The pins P 15 P 3 , and and the direction of the pins The angular velocity of rotation P 5 are moving in the direction 8, P 2 and P 4 is pointed by the arrow S t . of the two discs is co, then the velocity of the pins is rjw, r 2 w, &c. The berry A falling through the eye of the disc encounters the pin P 15 which throws it with an impact at tangent a t with the speed r^o. On its way CHAP, iv] FLOUH MILLING 201 the berry meets the pin P 2 of the second disc and is rejected at a tangent line a 2 to the pin P 3 moving in a contrary direction, with the velocity r 2 a). At the moment the grain and the pin P 2 meet, the velocity of the impact is equal to r^-^r^a} cos a 15 for the velocity of the pin P 2 is pro- jected upon the direction of the motion a l5 by the quantity r 2 w cos a r With a slight inaccuracy, however, we may mark r l =r 2 cos c^. Sub- stituting the r 2 of this equation into the formula of the velocity of the impact, we obtain : F 1 =2r 1 co. By reasoning in the same manner with regard to the percussion of the grain or its particle by the taper-pins P 3 , P 4 , P 5 . . ., we shall accordingly obtain the velocities : F 2 =2r 2 co F 3 =2r 3 o> F 4 =2r 4 a>, &c. If we mark the distance in a radial line between the pins P l3 P 2 , P 3 , &c., through n, the result will be : F 1 =2r 1 co ,, &c., which means that the velocities of the impact accelerate in proportion to the product's approach to the outlet in arithmetic progression, the denominator of which is 2nw. In accordance with it increases the force of the impact. This conclusion is arrived at on the supposition that in every element of the route n to the outlet, the product encounters taper- pins of the forward and backward motion of the discs. Other, often occurring cases, when the product encounters the pins of the retrograde motion only on its 2n way, are also possible. Then the law of acceleration of the velocities in arithmetic progression is infringed. If the law we deduced respecting velocities were not infringed through the blow r s of some of the pins being missed, then, the calculation of the number of revolutions of the discs being correct, and the distance n definite, the grain would gradually be reduced and leave the working space in the shape of a product uniform in size. In reality, however, those omissions do occur, and Wyngaert's experi- 202 FLOUR MILLING [CHAP, iv ments have shown the following results of grinding on a disintegrator of Carr's type : Flour 33 per cent. Fine middlings . . . . . . 20 Semolina . . . . . .. 14 Coarse middlings . . . . . 31 Offal. 2 Total FIG. 186. . 100 per cent. Thus, after a passage through the disintegrator, 66 per cent, of the product needs further treatment. Before giving a definite estimation of this machine we shall examine the action of the Nagel and Kamp's type of disintegrator, i.e. with one rotating disc. The disc with taper-pins T lt T 2) T 3 . . . rotates as indicated by arrow 8. The grain, struck by the pin T l (Fig. 186), moves in the direction a t . On encountering on its way the fixed pin T 2 , the grain is crushed and loses its velocity r^. If the grain does not break, still, owing to its insignificant elasticity when compared to the steel pin, it loses its velocity. We suppose in the first, as well as in the second, case that it will not rebound from the fixed pin, having lost its velocity, and will drop in the direction a 2 influenced by its gravity. Therefore, the pin T 3 will give it the direction a B . In this wise the way of the product will he a 1? a 2 , a 3 , a 4 , a 5 , . . . Seeing that the speed of the free drop is quite insignificant in comparison to the velocity of the pins, we may ignore the item of the speed down a 2 to a s . Consequently, the velocities of the impact T lt T 2 , &c., will accordingly be : Y l =r 1 co, V 3 =r 3 co, F 5 =r 5 o>, &c. Let us compare these velocities with those of the first case : F a =2(r i: f 2 Thence it is clear that the homonymous impacts in the first case have doubled the velocity of those of the second. This means that to attain CHAP, iv] FLOUR MILLING 203 the crushing effect it is necessary to double the speed of rotation of the discs in the disintegrators of the second type. In drawing this inference, we rested upon the supposition that the grain or a particle of it loses its speed in striking the fixed taper-pins* thus simplifying the problem considerably. But it may be maintained that the product possesses a certain elasticity, and on striking the pin T 2 will rebound in compliance with the law of percussion of elastic bodies, the mass of one of which (the pin) is infinitely great. Then the resultant velocity of the impact of the pin T% and of the grain will be greater than in our preceding inference. The process, probably, is performed in this manner, because for crushing the product a velocity less than the double velocity required in the first case suffices, as we see in general practice and in the factory data. At any rate, the resultant velocity of the blow, conditionally denominated here as the total sum of velocities in the direction the grain is travelling, needed for breaking the grain, attains 150 metres per second. Similarly to the first case, we have been examining the disintegrator of the second type operating in ideal conditions, supposing that the pro- duct is subjected to impacts from pins of each row. This is close to the fact ; however, gaps in the series of blows are possible. Altogether the phenomenon of the impacts here is extremely complicated, and the char- acter of the process may be judged of only by the final product, as it is an absolute impossibility to observe its movements in the working space. The grist from the disintegrator of the second type is likewise not uniform, and requires further treatment. We shall now proceed to estimate these machines. First of all, the grist yielded not being uniform, these machines cannot be used inde- pendently, but only in a cycle of other grinding machinery. For a primary breaking of the grain also they cannot be employed, because the meal is rendered impure by an admixture of bran. It was attempted, therefore, to employ them for grinding the grain bruised along the crease and for semolina. But even here there is no reason to use them, for they are exceedingly uneconomical. Experiments have proved that the energy expended in an empty run amounts to 44 per cent, of the total power, whereas the millstones require a maximum of 25 per cent. Attempts have been made lately to use the disintegrator for separat- ing the particles of endosperm from the offal, after the third or fourth passage. However, these attempts we also consider to be useless, for the machine will grind the good semolina and admix bran to the meal ob- tained. These attempts have been made in high rye milling. 204 FLOUR MILLING [CHAP, iv Lastly, if the disintegrators were to produce results of as high a quality as those obtained from other milling machines, even in that case they would not be worth employing, for the capacity of a disintegrator per horse-power per hour is considerably below that of other machines. Gener- ally speaking, the machines acting on the principle of a blow consume a great quantity of kinetic energy unproductively, and if there is any possibility of replacing them by others, the use of them should be avoided. This question of disintegrators has been raised in our manual only with a view to making an end of them once and for ever, and to warn the engineers against losing time in perfecting the designs of machines of the impact type. ** MILLING MACHINES HAVING THE Axis OF ROTATION OF THE WORKING ORGANS IN DIFFERENT PLANES Our examination of the machines of repeated action has shown that these machines have a common axis of rotation, if both the surfaces have a gyratory motion ; if, on the other hand, one of them is fixed, its axis of symmetry coincides with the axis of rotation of the other. Passing now to machines in which the stock is treated by the work- ing organs but once, it must be noted in the first place that their axes of rotation lie in different planes. Speaking, next, of the form of the working surfaces, we can accept only planes and cylinders, because other rotatory bodies (cone, hyperboloid, &c.) cannot produce equal circular velocities of rotation along the line of the treatment of the pro- duct ; under such conditions of work, therefore, the product ground will not be uniform and the wear of the working surfaces will be unequal. Taking these circumstances into consideration, general practice and theory have produced three combinations of working surfaces (Fig. 187). The first of them (/) is a cylinder A and plane B. In practice we know but one type of machinery of the / combination, the runner (Fig. 188) employed in oil-manufacturing. The second combination (//) is two cylindric surfaces with an inner contact, and lastly, the third (///), two cylindric surfaces with an outer contact. In all those combinations the working surface is theoretically defined as a straight line, and therefore the product is considered to be treated only once by the working surfaces. The machines of the runner type differ from the single action machines, for the rotating surface B carries CHAP. IV] FLOUR MILLING 205 the product under treatment several times to A. We shall not occupy our attention with machines of that type, as they are in no way connected with flour milling. The machines of the second type are used for grind- ing hard substances, for instance, gravel for artificial millstones. For this reason we shall later on give a description of a typical machine of that kind. The third combination (///), two cylindric surfaces with an outer contact, revolving with different velocities, is the basis of construction of the roller mill, the most widely used grinding machine. In studying the designs of machines subjecting the product to a simple treatment, we notice that their working organs, very rarely, have equal velocities (runner), or the speed of one of the surfaces equals zero (//). Usually, however, the velocities of rotation are different, as shown in combination ///. In that case the surface B 2 brings the product up to the surface A 2 , which performs the cutting or chipping FIG. 187. FIG. 188. action. Of the degrees of velocities we shall speak below, and point out now that, owing to their variety, the product undergoes several cutting or chipping operations before being discharged from the working space. We shall now proceed to give a description of the designs of these machines, and commence with a type of the second (//) combination. The Mill " Griffin." The single roUer miU "Griffin" (Bradley Pulveriser Co.) shown on Figs. 189 and 190 is an original type of a grinding apparatus for hard materials such as cement clinker, Thomas' scoria, superphosphates, &c. Its principle of operation consists in crushing and grinding the material by a roller, which runs over the casing and thus acquires a centrifugal power. This is attained by means of the following construction : On a cast-iron base plate 24, in shoes 66, which rests on rubber buffers, there are set timber stands 23, supporting a belt-pulley frame 4. This frame is of cast iron, and consists of two box-shaped parts riveted 206 FLOUR MILLING [CHAP, iv together by two bolts 63 below and joined by a cross-piece 22 at the top. By means of four iron rods 5 it is supported in a correct position in respect to the foundation. With their upper ends those rods are screwed into the frame 4, while the lower ends run through bolt-holes in the corners of the foundation and are screwed up by nuts, under which are laid two rubber buffers 64 apiece, separated by an iron lining. The first machines of this type, however, were furnished with cast- 23 iron stands, but the vibration of the casing during the grinding process was communicated, it appears, by the rigid stand to the frame, and had a detrimental effect upon the bearings. The necessity of obviating this vibration has led to the above-mentioned construction of an elastic junction between the frame and the foundation. In the frame 4 there are set a fast belt-pulley 17 and an auxiliary one 14. The latter, by means of the belt-pulley 40 set on the axle 41 and carrying the gear 60, turns the worm 49 of the feeding apparatus CHAP. IV] FLOUR MILLING 207 with the aid of the worm wheel 61. The fast belt-pulley 17 rotates in the step-bearing 20 which is adjusted by means of bolts 37. On the inside of the fast belt-pulley the shaft of the roller 1 is suspended on a universal joint 9. The joint consists of a ball 9 provided with journals : the latter operate in bearings which slide in suitable slots of the belt- pulley coupling. On the lower end of the shaft 1 is set the roller 2 FIG. 190. furnished with a change ring 31. Owing to a drop-hanger frame inside it, the joint can swing in the cup 24 in all directions. The cup or base 24 carries a casting 70 on which the roller runs ; the grinding is thus performed between them. Owing to the difference in the diameter at the top and at the bottom of the ring, its velocities in relation to the casing in the generating circle are unequal, which causes the reduction of the product under treatment. Round the casing outside there are several slightly oblong apertures, 208 FLOUR MILLING [CHAP, iv through which the product falls into a funnel-shaped chamber under the cup, whence it is removed by a transporting appliance (a worm, in Fig. 190). On the foundation is fixed a sieve 38, a cylindric cone 45 surrounds it covered with a lid 44 carrying a cone-shaped casing 25, through which the shaft 1 passes. In Fig. 190, above the roller are seen the wings of the fan 6, which are designed to propel the triturated product through the sieve 38. Under the roller, and attached to it by nuts, there are the wings 8 for stirring the product. There are no moving parts in the dusty atmosphere of the cup. The joint in the belt-pulley is hermetically covered with a lid 13. The lubrication of all moving parts is done through the hole 12 drilled in the spindle fixed in the cross-piece 22. The spindle centres the lid aided by cannon steel bush 27. The dimensions of the machines are the following : Height above the foundation .... 2600 mm. Size of the base plate 2100 X 1600 mm. Height of the middle of the belt-pulley above the foundation ...... 2045 mm. Diameter of the belt-pulley V . . . 760mm. Number of revolutions per minute . . . 200 mm. Consumption of work . . between 15 and 25 powers Weight of the whole mill 10800 Ib. Diameter of the roller ..... 460-470 mm. Diameter of the casing ..... 760 mm. Length of the generating circle . . . .150 mm. Weight of the casing , 285 Ib. Weight of the change ring of the roller . . * 145 Ib. According to the data of the factory, the mill reduces to fine meal from 264 to 6400 cells to a square centimetre of the sieve between 1*5 and 2 tons per hour of hard, up to 3.5 of soft phosphate, and from 1*5 to 2*5 tons of Portland cement, quartz, or ore, depending on the hard- ness and the largeness desired of the product. The machine operates in the following manner : when brought into motion, the roller rotates in the same direction with the belt-pulley, and on reaching its normal number of revolutions is jerked out of its central position by hand. The centrifugal force, which attains 3000 kilogrammes when at full speed, presses the roller to the casting. CHAP, iv] FLOUR MILLING 209 Now the roller commences to revolve around the casing, moving in the direction opposite to the one it started with. The product is poured into the hopper 50. As soon as there has collected enough material in the cup to be scooped up by the wings 8, it is flung by them on the casing and the milling commences. While in full operation the contents of the cup are stirred by the roller, and when reduced are bolted through the sieve by the paddles 6 which do the duty of a fan at the same time. The pieces remaining unsifted fall back under the roller. The paddles on the axis of the roller in revolving draw the air in through the conic casing and impel it through the sieve, so that the dust does not escape outside. The sieve chosen is slightly larger than the final product, to avoid choking up. In spite of the ingenuity of the design described, its considerable complexity must be pointed out, as well as the circumstance that a large part of the work in grinding goes to overcome the resistance offered to the motion by the wings 8 and the continuous stirring of the heavy product. The application of rubber buffers also cannot be regarded as a happy thought, for india-rubber exposed to the open air rapidly loses its elasticity and will do so the quicker because of the vibration. Steel plate springs would serve that purpose with success. Then, if the action of the fan be regular, the dust may fly out of the hopper 50 if there is no product in it, and therefore a lid to the hopper would be an acceptable device. Lastly, our attention is drawn to the unsheltered position of the feed- worm 49 set on the free end of the shaft, if anything large were to fall into it. This defect could likewise be obviated by carrying the bearing 53 over to the left, behind the hoppers. VI ROLLER MILLS 1. Conditions of Reduction of the Product Before we direct our attention to the construction of roller mills, it is necessary to become acquainted with the character of action of the working surfaces and the conditions under which the reduction of the stock is possible, 210 FLOUR MILLING [CHAP, iv We have (Fig. 191) two cylindric surfaces and O l rotating at differ- ent velocities in the directions 8 and S t . At a certain moment there is a berry (or a particle of one) A in between them, which is to pass through the working space. The surfaces of the cylinders may be either smooth or consist of a series of chisels spoken of on p. 153, Fig. 135. In that case the rolls are said to be corrugated or grooved, and the product may be impelled into the working space by their corrugations in any combination of velocities and diameters of rollers. As to the operation of smooth rolls, the conditions of work- ing will be deduced from the following considerations : First, the working surfaces and the product under treatment must have a certain coefficient of friction /. If the material of the rolls gives a very small coefficient, the grain A will not be drawn into the work- ing space, but will remain sliding above it. But, as the working surfaces are prepared of a definite kind of material (cast iron and porcelain), / is likewise a definite quantity. Therefore the definite / has to be combined with other elements characterising the working surfaces. For the coefficients of friction / and the angle of friction y Kick gives the following quantities : TABLE XX FIG. 191. Material of Rollers. For Fine Middlings. For Semolina. * / f. /. Cast iron smooth, polished Dead cast iron Cast iron used . ;.' Porcelain '"'. -.. . . 12 16 18 22 0-213 0-287 0-325 0-404 11 15 17 20 0-194 0-268 0-300 0-364 Let us examine now the conditions needed for the product to be drawn into the working space with the quantities

2p sin a, or f>tga, tg(p>tga, i.e. a. Hence the condition allowing the product to be drawn into the working space may be formulated thus : It is requisite that the angle of grasping a should be less than the angle of friction of tJie product and the working surface. Considering that, given one and the same size of product, the angle a depends on the radius of the rollers, by modifying this radius we are always able to select a < (p. The dependence of the length of the radius on the size of the product may be deduced from the following considerations. Let us imagine we have two rolls of a radius r, the distance between them is i? (Fig. 191), the size of the product fed in r\. After the product has passed between the rolls it is reduced to the size j? . It is clear that O l =2r cos a-{-??=2r-f-*7 ; by deducing herefrom the r, we obtain : Consequently, knowing the primary and the final size of the product, we can define the radius of the rolls, for a is known to us it must in its limit be equal to 9?. Generally speaking the angle a is comparatively small, and therefore with a more or less admissible approximation, may accept sin ~=~. Then L L Hence it follows, that the greater the angle of friction the less is the radius of the rolls for grasping the product of a given size. This means that the diameter of the porcelain rolls ought to be less than the diameter of the cast iron ones, for the coefficient of friction of porcelain and the product is greater than that of cast iron and the same product. Such material as porcelain, however, cannot always be successfully employed for making rolls, as the very great stresses set up in the process of reduction, which in such cases can have a detrimental effect upon the porcelain, must be taken into consideration, 212 FLOUR MILLING [CHAP, iv The Materials and Design of Rolls. The materials of which rolls are prepared must be hard and wear-resistant. If the product is to be reduced by cutting, it is necessary that the coefficient of friction should be the least possible, as the force of friction is obnoxious here. But if the rolls operate on the principle of trituration (Fig. 136, p. 154), then the force of friction renders useful service ; a high coefficient of friction, therefore, is desirable in that case. The choice of material, however, is determined by its durability, wear-resistancy, and mouldability. General practice has shown that cast iron, steel, and porcelain answer those requirements. The iron rolls are cast so that their surface is hardened 5 to 10 mm. deep from the surface. The hardening of the surface of the rolls is brought about by casting them in metal fining-pots or by other means, which are the secrets of the factories. The attempt to use steel was unsuccessful ; it must be admitted, though, that this question has been but little treated by engineers. It is probable, however, that rolls of ingot iron with a cemented (hardened) surface would give better results than cast iron, and the engineering firms ought to work in that direction. Porcelain rolls were first introduced by Wegmann's factory. The durability of porcelain rolls is not as great as that of cast iron, but for semolina-grinding they are indispensable. At first, some twenty years ago, the porcelain rolls were not quite satisfactory, often bursting on becoming heated, and they became rapidly and irregularly worn. Nowa- days, however, the exhausting of roller mills having been improved and durable porcelain being available, they compete with cast-iron rolls quite successfully. The composition of the roll-porcelain is approximately : Pure china clay ..... 61-62 per cent. Fine quartz 16-17 Feldspar 16-17 Chalk 4 As regards the designs of rolls, those of cast iron are generally hollow cylinders A (Figs. 192 and 193) which are set on the shaft B hot, and are seldom keyed on. This construction (Fig. 193) is more convenient if cast ; when at work the roll warms more evenly, and therefore its expan- sion evenly modifies tke dimensions, leaving the cylindric shape unaltered. The porcelain rolls (Fig. 194) consist of a full cylinder A, caught be- tween cast-iron washers C by means of coupling bolts d. In the washers CHAP. IV] FLOUR MILLING 213 there are holes for the shaft B. A general view of a grooved roll is given in Fig. 195. Position of the Rolls. The position of the rolls in the frame materially in- fluences the design of other parts of the machine, the degree of wear of the rolls themselves, and the compactness of the whole machine. In choosing a position for the rolls the constructor must be guided in the first place by considerations of a convenient supply of the product to the milling surfaces, \Wmm^^M ^ 6OQ. FIG. 192. FIG. 193. and easy access for inspecting the operation. Modern practice allows eight different combinations of the rolls, which we shall examine now (Fig. 196). The first three combinations 1, 2, and 3 relate to double roller mills. Combination 1 with the axes lying in a horizontal plane, in re- spect to the supply of the product and inspection of the work offers an undoubted advantage over the second, which was suggested with a view to reducing the breadth of the machine, which is important for mill-buildings deficient in space. But a material defect of the vertical position of the rolls is the more complicated feeding of them, i.e. the supply- FIG. 194. FIG. 195. ing of the product to the working surfaces. Combination 3 gives a diagonal disposition of the rolls, owing to which the complex construction of the feeding device is discarded, and at the same time the machine gains in compactness in comparison to combination 1. Combinations 4 and 5 are designed to afford the product two passages between three rollerk These combinations, however, should be most decidedly rejected, as the middle rolls are placed in working conditions different from those on either side. In doing double work, they wear out considerably faster than the outer rolls, owing to which the operation of the mill becomes irregular and inferior in quality. In addition, the feeding of the rolls requires 214 FLOUR MILLING [CHAP, iv a complicated apparatus and the inspection of the work is difficult. Combination 8 offers a double passage of the product. The designs of machines of that combination, purporting to give two passages, one succeeding the other, are senseless, if only from the fact that they infringe the principle of a single treatment of the product. Machines of this type are offered for use in plain farm milling, which is quite successfully performed by stone mills. The machines where the product after the first passage is delivered to be bolted, and the large product sifted off is then fed to the lower pair FIG. 196. of rolls for further treatment, are complicated in construction and are now almost entirely discarded. There remain but two combinations 6 and 7. The fact is that the four-roller machines are the usual modern type of the roller mill. Not only in industrial mills, but in small country mills also, two-roller mills are a rarity. This is easily understood since one four-roller mill is considerably cheaper than two mills with two rolls each. Combination 6 is accepted by all American factories, and but at one, Hantz in Austria-Hungary, in Europe. Combination 7, with a diagonal disposition of the rolls, has been accepted by all European makers. When studying the designs of mills with a horizontal and diagonal CHAP, iv] FLOUR MILLING 216 disposition of the rolls, we shall estimate the merits and point out the defects of those combinations. The Character of the Surface and the Motion of the Rolls. The process of reducing grain to flour in the form it exists in modern flour milling technics is divided into two parts. At first the grain is crushed into small particles (middlings and dunsts very fine middlings), and then after the middlings and dunsts have been graded according to size (sifted) and quality, they are reduced to flour. The first operation is named breaking and the second is the reduction proper. At a compara- tively recent date, there has been introduced into Russian milling plants another operation or second breaking of the cleaned middlings (called " Auflosung " in Germany) or the polishing of middlings, as we name it. The aim of breaking is, by only slightly crushing the integument, and obtaining as little flour as possible, to reduce the grain to middlings coarse and fine, from which it is easy to extract the particles containing bran and imparting a dark colouring to the flour. These two fundamental operations determine the character of the working surfaces of the rolls. For breaking the rolls are covered with grooves, having an effect similar to the chipping (p. 154, Fig. 135) or cutting. The chisels on the surface of the roll are named l corrugations or grooves, and the rolls are said to be corrugated. In accordance with the size of the product, which is broken up into smaller particles by the corrugations, the size of the grooves, fluting or corrugations varies. The shape, size, and dispositions of the corrugations will be spoken of in a special chapter ; at present the fact must be mentioned that the stock is passed through the corrugated rolls from two to nine times, depending on the kind of milling. Consequently the size of the corrugations as well as other elements, which define them, likewise are varied. But the general character of the break rolls remains the same, i.e. the surface is covered with grooves of a greater or smaller size. As there are coarse middlings yielded during the process of breaking, the treatment of which cannot be performed on break rolls, they are separated and conveyed to special machines, also with corrugated rolls, for further reduction. Such rolls are called rebreaks in Russia and are used almost exclusively in Russian mills (the Germans call them " Koppenstiihle "). Thus both first and second break rolls have a corrugated surface. For the reduction of cleaned coarse and fine middlings the surface of the rolls is smooth. Here the reduction is performed on the 1 Corrugations, grooves, flutes are all quite synonymous terms. " Grooves " are perhaps more commonly spoken of in England than either of the other terms. 216 FLOUR MILLING [CHAP. IV principle of trituration (p. 154, Fig. 136). When studying the principles of reduction, we saw that the work of trituration is performed by the force of friction Nf, where N is the pressure of the working organ upon the product, and / the coefficient of friction of the product against the working surface. The greater / is, the less is the pressure of the rolls upon the stock, and the less will the wear of the working surface and of other parts of the machine be. Besides that, if the pressure of the rolls upon the product be heavy, the quality of the flour deteriorates ; the flour is " dead," i.e. has a low baking quality, as proved by experiments. Great pressure produces bad results in the milling of flour of high quality, while the lower kinds are less influenced by it. For this reason the surface of the grinding rolls should have the largest possible coefficient of friction /. In this respect porcelain rolls or the dull surface of cast-iron rolls produce satisfactory results, though the dull surface of the cast iron becomes polished rapidly and requires frequent renovation. To procure flour out of the branny particles (dark middlings), a heavy pressure has to be applied, which the porcelain cannot support. The dull surface of the cast-iron rolls is so rapidly worn, that there is no sense in using it. Therefore a polished cast-iron surface has to be used and a strong pressure given to the rolls, so as to obtain a sufficiently great force of friction Nf. Thus we have three kinds of roller-surfaces : (1) corrugated for breaking, (2) rough surfaces with a large coefficient of friction (porcelain, dull cast iron) for reducing the middlings, and (3) the smooth-polished cast-iron surface for milling the lower kinds of flour. Let us now turn to the character of motion of the rolls. When studying the movement of the product in the working space of the rolls, we noticed that the rolls rotate in opposite directions, pushing the grain, or particles of it, in the direction of the line of grinding. The greater the revolving speeds of the rolls, the higher is their capacity. But this velocity has a limiting signification, which is determined by the degree of heating of the product, which must not exceed 30 to 40, otherwise the flour may likewise become deadened. The limiting significa- tion of the circumferential velocities of the rolls will be given later, while it must be pointed out now that their magnitudes are different for each roll. This is indispensable to obtain a cutting effect on the corrugated rolls and trituration on smooth rolls. If the velocities of both the rolls were equal, the stock would be chipped radially on the corrugated rolls, and would blind the space between the corrugations by a radial pressure. CHAP, iv] FLOUR MILLING 217 A continued operation of the rolls would lead to a crushing of the product to cake, if the grain were sufficiently soft, or to flour, if it were very hard. Consequently, there could be no idea of breaking in the sense we under- stand it. The same kind of crushing the product to cakes would take place on the smooth rolls too. Our aim, however, in the breaking process is to obtain a uniform product approximately corresponding to half the size of the least distance between the working surfaces. For this reason different velo- cities are imparted to the rolls. 1 Then the slowly rotating roll carries the product to the one revolving rapidly, which cuts off part of the product with the chisel of the corrugation in the breaking process and chips it off by the force of friction in grinding. 'Only under such conditions does the direction of the active force coincide with the route of the product, and part of it, the size of which is determined by the distance between the working surfaces, is separated off. It is important to note that even if it were possible to avoid crushing the product to cakes by rolls rotating with equal velocities, the pressing forces, acting perpendicularly to the direction in which the product travels, would crush it to particles of various sizes, depending but little on the least distance between the working surfaces. The circumferential velocity of the rolls is determined according to their diameter and number of revolutions, the relation of velocity of the slowly and the rapidly revolving rolls varying between 1-1:1 and 5:1. The following table gives a clear idea of the limits of the sizes of the diameters, number of revolutions, and velocities of the rolls. In this table D denotes the greatest and the least diameters of the rolls, N the number of revolu- tions of the fast roll, V their circumferential velocities in metres per second, V : F! the differential velocities of the fast and slow rolls. TABLE XXI Rolls. D mm. N, Fmt. per sec. V:V 1 6-9 breaks 150-350 225-480 3-0-4-7 2-5 : 1-5 : 1 2-5 breaks 220-380 250-600 3-0-6-0 2 : 1-3 ."1 1-3 rebreaks . '.' 220-350 250-400 2-5-3-5 1-2 1-1-6:1 Grinding cast iron . . 150-400 180-380 3-0-3-6 1-1 1-1-3:1 Grinding porcelain . 220-350 150-180 2-0-2-75 1-1 1-1-5:1 The factories in Europe, England excepted, generally give the averages of those quantities, namely, D of the corrugated rolls 220-300 mm., 1 This is known as the " Differential." FLOUR MILLING [CHAP, iv smooth 250-350 mm., ^=200-320. Some of the English factories (Thos. Robinson) give D = 150-400 mm., and N up to 480. So great a diameter as 400 mm. is used, but in one make of Robinson's mills the different velocities of a pair of rolls are obtained through their different diameters. This construction is described below. The American factories (Allis-Chalmers Co.) usually give D= 175-250 mm., but with a much higher number of revolutions, up to 600 for the rapidly rotating rolls with a diameter of 175 mm., which corresponds to the circumferential velocity of 5*35 metres per second. The mills of Nordyke & Marmon Co., designed for the preparation of various cereal flakes of barley, oats, maize, &c. (the celebrated American " Hercules " oat flakes, known in Russia but in the form of unsuccessful adulterations), have rolls up to 460 mm. in diameter, and the greatest number of revolu- tions of the fast roll is 120, which corresponds to a circumferential velocity of 2*9 metres per second. Having become acquainted with the general character of the working organs of roller mills we shall proceed to study in detail the corrugating of break and scratch rolls. 2. Corrugating the Rolls General State of the Question. The question concerning the most advantageous operation of the breaking mills may not be regarded as solved until the question touching the correct corrugating of rolls is settled. Until now, the specialist, when a problem of corrugating the rolls of break mills was set before him, solved it by simply pointing out the number of corrugations, and never touched the other essential sides of corrugating. It is not surprising, therefore, that not only flour-millers, but by far the greater number of specialists too, would express astonishment if ques- tioned as to the incline of the corrugations. It is a totally unknown fact to them that the incline of the corrugations in respect to the generating circle of the rolls varies from the first to the last break, and that the degree of perfection of the break process depends on it. How is the cutting of rolls done in mills provided with corrugating machines, or at factories undertaking such work ? Almost always with the same inclination of the corrugations. And yet this is a grave error. But besides the inclination of the corrugations, there is another side to the cutting, to which no serious attention has been paid by the Euro- pean, not to mention the Russian, experts. It is the disposition of the angles of the corrugations, of their cutting edges in respect to the product CHAP, iv] FLOUR MILLING 219 treated at the different moments of breaking. Almost at all the mills in Russia without exception the corrugations on the breaking rolls are set so that the product is subject to the effect of the sharp cutting angles of the corrugations. This is looked upon in a totally different light by the Americans, who, beginning with the fifth break in high milling, discon- tinue the carrying of the product by the sharp angles of the corrugations on the slow roll to the likewise sharp cutting angles of the fast roll. Besides the number of corrugations, their inclination, and the position of the cutting angles in respect to the product under treatment, the shape of the corrugation is likewise an important item. Thus, before giving an exhaustive answer to 'the question, how the corrugations of the rolls should be cut, this question has to be decided. In investigating the question concerning the corrugating of the rolls, the following items must be settled upon : (1) Shape of the corrugations. (2) Their incline. (3) Disposition of the cutting angles of the corrugations in respect to the product. (4) Number of corrugations. It were an error to think that any of these four demands are of a greater or less importance. The number of corrugations, their position, incline, and form are all equally important in the breaking process. Even if our mills are able to supply us with a satisfactory kind of flour, while giving attention but to the number and shape of the corrugations (the latter is not always the case), there is yet no doubt the milling would rise in quality, if a correct inclination and positioning of the cutting angles were imparted to the corrugations. Shape of the Corrugations. When examining the question of the shape of the corrugations it must be noted that the theory and practice existing afford too little material. In such important works as the books of Professor K. A. Zworykin and Professor F. Kick, we find but the most general remarks. In the more recent works of Baumgartner and Ketten- bach there are more data touching that question. But both of these German authors do not look deeply enough into it, alluding only to the results obtained in factory practice, and giving no time to a necessary critical estimation of the corrugating of rolls in vogue. The milling engineers, regarding the breaking process as a cutting of grain or particles of it, produce corrugations of one shape mostly, with FLOUR MILLING [CHAP, iv sharp angles, characterising it only by the size of the angle of the corruga- tion itself. Fig. 197 shows us the angle of 50, established by practice for corrugations in high milling of wheat, and Fig. 198 reproduces the shape of the corrugation with an angle of 75 employed in the simplified wheat and high rye milling. The drawings of Figs. 197 and 198 prove that those angles of corruga. tions are easily obtained. The front facet of the corrugation (Fig. 197) forms a diametrical plane of the rolls for an angle of 50, and a segmental plane (Fig. 198) for an angle of 70-75, the r in the second case being equal to f- ^ E. It is not difficult to show (Fig. 197) that given such angles and a \ \ \ \ FIG. 197. certain number of corrugations, their height is a quite definite quantity. Indeed, if we denote through n the number of corrugations to a centi- metre of circumference of the roll, t their height, and h = - ' the circular pitch of the corrugations, 1 then from the triangle ABC we shall obtain for t in millimetres : p) ....... . (1), supposing, with a slight error, that the tangent passing through the point A of the corrugation passes at the same time through its point B. Hence it is clear that with an increased number of corrugations to a centimetre their t decreases. If we take the number of corrugations n 1 The circular pitch of the corrugations is the part of the area between two points of the corrugations, but for the simplicity of the inference h may denote a chord of this arc or a tangent, as the mistake occurring from this inference is insignificant. CHAP, iv] FLOUR MILLING 221 equal to 5 and 10, and /?=50, then, according to formula (1) we obtain corresponding t's in millimetres : *==i^gr40 = l-68 mm ., and J=~ty40 =0'84 mm. o 1U The shape of the corrugations, having an angle of 50, defined by the construction derived from Fig. 197, is generally used in high grinding. For the medium, low, and rye grinding general practice has established the shape of corrugations given in the design on Fig. 198, the radius r accepted for the medium grinding being less than the one used in low and rye grinding. Let us see how the height of the corrugation will be defined in this case, the number of corrugations to a centimetre being given. Having denoted the angle of the corrugation ft, the angle formed by FIG. 198. the radius R passing through the point of the corrugation and its lower facet 7, the circular pitch of the corrugation h, and its height through t, we can define the height t of the corrugation. The angle y, usually equal to 75, and the radius of the roll R and r being given, previously to defining t the angle y and the circular pitch of the corrugation h have to be defined in accordance with the quantities given. The angle y is deduced from AAOC by sin y, r=R sin y, hence sin y =-5. K The circular pitch of the corrugation h may be easily defined, with a slight error, either as an arc AB, taken as a straight line, or as its chord. In the latter case the circular pitch h is defined as the side of an oblique- angled triangle ABD. We shall take the second case, it being more simple and giving an 222 FLOUR MILLING [CHAP, iv insignificant error. Granted that the tangent AS passes through the top of the second corrugation B, i.e. coincides with the chord, and forms like- wise with the radius OB a right angle. Then we obtain L BAD = 90 a, LABD = 90 - y, and, consequently, L ABD = 180 -(90 - a) -(90 - y) The triangle ABD gives : AB BD . sin (180-0) sin (90 -a)' If t is the height of the triangle ABD dropped on to AB, i.e. the height sought for of the corrugation, we obtain t=BD sin (90 y). Hence, by substituting the signification in the place of BD and per- forming the simplifications (a=0 y), we obtain the t sought for : cosj^-vjw sin p In this formula all the quantities are known, for h is defined in accord- ance with the number of corrugations per centimetre, the angle /? is given, and the angle y is defined, as explained above. If we take the diameter of the roll to be 250 mm., i.e. .8 = 125 mm., r=40 mm., 0=75, and, having defined y out of the formula sin y=-^= (y = 1840 / ), substitute them into the formula (2) then, the number of corrugations being 5 and 10 to 1 centimetre, we obtain after a calculation : Having reckoned out and compared the signification t of the corruga- tions for high milling, with the same number of them 10 per 1 cm., and an angle of 75, we obtain Z=0'76 mm. This shows that the height of the corrugations in the second case is considerably less 0'54 mm., i.e. by 0*22 mm. Besides the corrugations of a triangular shape just examined, the use of corrugations with rounded cutting edges has been suggested. But this form is justified neither by theory nor by practice, whence the theoretical premises are deduced. The third shape of corrugations, trapezoidal in section, as shown on Figs. 199 and 200, is still recommended by some factories and specialists, 1 who maintain that the cutting of the grain, or * FT. Kettei*bach, Der Muller und Muhlenbauer, 1907 ? CHAP. IV] FLOUR MILLING 223 particles of it, is more perfect in that case, for the integument of the grain remains whole. There is no logical justification for this, however, for in the breaking process the cutting up of the bran is unavoidable. Further, the cutting of such corrugations is undoubtedly in worse con- dition even by the type itself of the cutting operation, not to mention the fact that the friction of the flat part of the corrugations against the product generates superfluous work. The French factory, Teisset, Chapron & Brault Fr., very seriously recommends corrugations, shown on Fig. 201 with a large circular pitch for the main corrugation, and small intermediate corrugations, main- Ist break FIG. 199. 4th break FIG. 201. FIG. 200. taining that such an arrangement increases the yield of semolina, and consequently the number of breaks may be reduced. The utility of this arrangement, however, is doubtful, for the inner corrugations will not work. In addition, the corrugating of the rolls has to be performed either with a forming tool or in two turns, which presents great difficulties. For feed milling, G. Barat (France) has lately suggested the use of pyramidal corrugations obtained by cross-corrugating at a right (Fig. 202) and a sharp (Fig. 203) angle, but up to the present corrugations of this shape have been used in America only for stone-crushing and compressing refuse in the production of oil from cotton seeds. This is all that has been evolved by practice and theory regarding the shape of corrugations. 224 FLOUR MILLING [CHAP, iv Let us see now what requirements the shape of corrugations should answer, from the point of view of the least expenditure of energy in the breaking process. The aim of the breaks is to obtain as many middlings as possible with the least possible breaking of the bran coverings. The ideal position of the grain in first break rolls is shown in Fig. 204. In this FIG. 202. FIG. 203. case the grain would be broken through its crease. The transversal position given on Fig. 205 is less favourable for the first breaking. From the point of view of the theory of cutting, the shapes of corru- gations examined exclude all possibility of cutting. Indeed, the shape of corrugations, defined by Fig. 197, gives a cutting angle of 90, for this angle is defined by the front edge of the chisel (Fig. 204) and the direction of its motion, which may, with an insignificant error, be re- FIG. 204. FIG. 205. FIG. 206. garded as straight. The cutting force l P=P 2 tga, for P 2 , the force of pressure, is perpendicular to the front edge of the chisel A ; P 3 , the chipping force, is perpendicular to the direction in which the chisel moves, and a is the cutting angle. If a = 90, then P= oo. That is to say, the grain is not cut, but broken. Should the shape of the corruga- tion be as defined by Fig. 198, a>90. Then P is a negative quantity, which means that the breaking of grain is performed under worse con- ditions than in the first case (Fig. 206). In the so-called " Hochschrot," 1 >ee Prof, I. Time's theory of cutting. FLOUR MILLING 225 CHAP. IV] when the slowly-rotating roll is smooth (Fig. 207) or has fine corrugations (Fig. 208), it is quite plain that the grain is broken and that part of the bran, coming in contact with the smooth or finely-cut surface of the slowly revolving roll, is ground. That is the reason why " Hoch- schrot " produces the so-called " blue flour," which is generally extracted on the brush machine. Now, if we set before ourselves the problem of obtaining a perfect cutting of grain or particles of it in the breaking process and leaving the integu- ment whole, with the view of obtaining a greater amount of broad bran, then the fast roll has to be supplied with corrugations having cutting angles of 45, as shown on Fig. 209, which proves that the feeding roll may have ordinary corrugations. The cutting of corrugations of that shape on cast iron, however, would present some difficulty by reason of its brittleness. Therefore, taking into consideration the incline of the FIG. 207. FIG. 208. corrugation in regard to the generating circle of the roll, this angle may be accepted as exceeding 45, namely 60-65, which has a small cutting effect. A solution of this question is likewise possible if the rolls are made of ingot iron, and not of cast iron with a hardened surface. It is quite possible to use ingot iron (open-hearth steel). The rolls may be consider- ably lighter, and a cementation of the corrugations which would guarantee their wear to be less than that of the corrugations on cast-iron rolls is attainable, as proved by Professor Zworykin's experiments. 1 The question of the preparation of rolls of ingot steel is very important. Serious attention ought to be paid to it by engineers, because a satis- factory solution of that question would cause a revolution in respect to the shape of the corrugations, resulting in a more perfect breaking pro- cess, owing to the sharper angle of the corrugations. Incline of the Corrugations. Two directions for the cutting edges of the corrugations were suggested at the beginning of the development of 1 See "Cementation of Iron by Gas," by Prof. Zworykin, Russian Miller, 1911, No. 2. 226 FLOUR MILLING [CHAP, iv roller-milling ; down the circumference of the roll and along its generat- ing circle. But this produced unsatisfactory results. For this reason general practice in the end adopted the direction of the corrugations at an angle to the generating circle of the roll. In their attempt to give a theoretical explanation of the results ob- tained in practice, some of the German authors (Fr. Kettenbach and F. Baumgartner) regard the breaking down of grain or particles of it as a process of shearing. Fig. 210 represents the edges of two corrugations : N of a slowly rotating roll and N of a rapidly revolving one. The cutting of the grain takes place when the corrugations cross at the point 0. For the sake of clearness we shall carry this point out to O x . When the edge of the corrugation JV^ presses upon the berry, the direction of the cutting ZSn*. force P is perpendicular to the direction of the corrugation. If the inclinations a (the angle a in respect to the generating circle) of the corru- gations of both rolls are equal in size, but opposite in their directions, the angle between them is 2 a. Let us divide the active power P according to the law of parallelograms into Z horizontal and 8 vertical. The cutting forces will be S 8. The force Z tends to push the product in a horizontal direction, and if this force exceeds the force of friction of the product against the surface of the corrugation, it will drive the product to the end of the rolls, having annulled the cutting force 8. The forces P and Z depending on L a will be formulated thus : 8P cos a ; Z=P sin a. It is evident that the power Z must not exceed Pf, i.e. the force of friction of the product on the cast iron, where P is the normal pressure and / the coefficient of this friction. The highest and the limit significa- CHAP, iv] FLOUR MILLING 227 tion of Z is when it equals Pf. Hence it is clear that L a depends on /, which may be defined by experiment. 1 The coefficient of friction f=tgq>, q> being = 16-1 8 for cast iron, and up to 22 for porcelain. But if Z=PfP sin a, the result is : Sin a=f=tg (for the limit of signification Z=Pf), because the L y modifies within the limits of 12 and 25 maximum. The inclination of the corrugations, therefore, has to be accepted at 10 to 16 per cent., i.e. -at 10 mm. to 16 mm. to 100 mm. of length of the roll. Position of the Cutting Edges of the Corrugations. The position of the cutting angles of the corrugations in respect to the product treated plays no small part in the process of breaking the berry. The practice of this process in Russia generally recognises but one position of corrugations, viz. the product is fed in by the sharp edges of the slowly revolving roll and is subjected to the cutting effect of the likewise sharp edge of the fast roll. The general practice partly of the West and chiefly of America, has evolved four types of position for corrugations. Those types are to be seen on Fig. 211. Here a shows a sharp edge opposite to a sharp one, b sharp to dull, c dull to sharp, and lastly, d dull to dull. The Germans recognise only three types of position of the corruga- tions, namely, a, b, and d, while in America also the type c is used. In F. Baumgartner's opinion the type a is to be employed for breaking, CHAP, iv] FLOUR MILLING 229 type b for loosening the bran, and type d for rebreaking of pure middlings (" Auflosing " named " Polishing " in Russian milling). The well-known German factory form. Seek Bros, and the Austrian firm of Selmar Hecht (Vienna), apply the one type a for the whole break- ing process. Let us examine every one of those types apart. Undoubtedly in high milling the type a should be used only while the break semolina is sufficiently large and sharp. But beginning with the fifth break, it ought to be replaced by the type 6, because only in that case can a large quantity of broad bran be obtained and the coarse meal and middlings be less dirtied by the small particles of reduced bran. It is evident that if the product is fed in by the dull edges, the sharp edges of the fast roll will scrape out the middlings without breaking up the covers, which offer greater resistance to the cutting force. When we turn to the last break, the purpose of which is to clean the bran and separate from it the mealy particles of endosperm lying Fia. 211. immediately beneath the integument, then, to avoid the reduction of bran, it is reasonable to use the type d. The opinion expressed by Baumgartner, who recommends the type b for the loosening process, is to be regarded as erroneous, for the cutting of the bran is inevitable in that case. The type d must be employed for polishing the middlings (Aunosung), i.e. the scratch rolls, and for the passages following after the first one in rye milling. As to the type c, it is used only in America partly in the rye, partly in maize milling, mostly for the first passage. In several American mills, however, wejiad the occasion to see the type c applied to the grinding of very hard wheats. One of the oldest American firms, Nordyke & Marmon Co., in Indianapolis, also mentions the use of type c for very hard wheats, commencing with the third break, though it gives no definite considerations in favour of that type. The Number of Corrugations. The number of corrugations in the breaking passages depends on the degree of perfection of the milling. In high, protracted milling the number of corrugations increases more slowly than in the semi-high. In the cases where one is obliged to use 230 FLOUR MILLING [CHAP, iv the same pair of rolls for two passages (as in the sack milling or in the semi-automaton), an intermediate number of corrugations is taken. The number of corrugations is generally denned to a centimetre of the circumference of the roll ; in Russia, however, the number of corru- gations is generally given per inch. The table adduced below gives a general view of the number of corrugations for breaking and cleaning of the bran (the last passage) in different kinds of milling. There the average numbers, evolved by practice, are given. In the same table will be pointed out the desk-able inclination of the corrugations and the position of their cutting edges according to the above-mentioned types. This table must be regarded as giving the normal quantity of corru- gations to a given number of breaks. As the number of breaking passages fluctuates, according to the type of the grinding or the hard- ness of the wheat, the number of corrugations on the intermediate breaks may vary. The first and the last breaks, however, have to retain the mentioned numbers of corrugations, if it is desirable to obtain broad bran. For the first break (if there is no " Hochschrot," i.e. break- ing of grain along the crease) there remain three to four corrugations to a centimetre, and for the last twelve corrugations. It must be noted that we considered the number of corrugations in connection with the generally accepted differential velocity of rolls, and with the normal number of revolutions for the fast roll, established by German and English factories and based on the normal productivity of the breaking process. For this reason we give tables of different types of grinding here, which also characterise the definite productivity of the breaking process in connection with the accepted corrugating. From this table we learn that for high grinding (eight breaks without " Hochschrot ") with a normal number of corruga- tions and spiral, the joint working length of the break rolls to one sack of grist per day is defined to be 21-24-7 mm. To obtain the length of the first break rolls for a mill of, for instance, 300 sacks capacity of high grinding per twenty-four hours, we must evidently multiply 2-7-3 mm. by 300. That will give us the length of the rolls for the first break, which will be 810 to 900 mm. in eight breaking passages. This being the length, the general incline of the corrugations is 120 mm. For medium grinding, with a normal number of corrugations and their incline, the joint working length of the break rolls to one sack of grist per day is 19" 8-22 -3 mm., for low grinding 17*9-20 mm., and lastly 23*3-24-5 mm. for English grinding. CHAP. IV] FLOUR MILLING 231 till !! S'c ;ee^^^e^ |tp 3^5 y d 11=1 II s ! M O C i fl si 8 U-- to a 5 2*3 s-s XOOIOIO II AH C Rg-Sj': :..::;:.:: Si W 'S g . CO L^* Oi i i I . . . . I I . 1 t^ 00 i 1 -* i 1 i 1 r-H i-H r 1 (N C<1 lo n IB 10 S 10 U? M xj ococoi-i-ooo la e J) 53 -g . O E f 3 o OC [> I-H HH > bo JIOBg J8d tutu ui snou jo qcjSuai CO 1 I CO 1 CO t^ CO CO tO CO O CO CO CO cb cb co GO co xo co to to i> XO CO GO CO 00 C^l CO CO CO I-H 1 ^U80 J8d UI O i-H r 1 CO CO CO Th to jo ompui S 5 tuo to; suoi^BSnjjoQ jo aaquin^ I CO to CO !> 00 Oi O GO M. HH HH HH HH HH HH t> ^> 1 i HH 1 1 HH t> ^ |Z| 5 CHAP, iv] FLOUR MILLING 233 Consequently, with a normal number of inclined corrugations, the following capacity is denned for four kinds of grist (in Ibs.) to a centimetre or an inch of the working length of all the breaking passages per twenty- four hours : TABLE XXIV CAPACITY OF THE ROLLS PER TWENTY-FOUR HOURS TO 1 CM. OR 1 INCH IN LBS. Kind of Grinding. Per 1 cm. of Length of the Roll. Per 1 inch of Length of the Roll. High grinding Medium Low ... English ... Ibs. 107-125 122-135 134-153 97-117 Ibs. 268-313 302-336 333-382 243-302 But as the capacity of the breaking process is defined by the absolute and differential velocity of the rolls, the number of corrugations and the other elements characterising the corrugating (their inclination and position) were dealt with in connection with the generally accepted velocities of the rolls : the absolute velocity of rotation of the rolls is 3* 5-4 '5 metres per second, and the ratio of velocity of the slow and fast rolls is 1 : 2'5-l : 3. Here we may close our investigation of the question concerning the corrugating of rolls. All that has been said proves that this question, which opens out a new line of thought, as, for instance, of the shape of the grooves in connection with the investigation of the process of break- ing, demands serious experimental treatment. Since the time of Professor F. Kick and K. A. Zworykin in the course of almost twenty years this question has not stirred from its place, whereas in other regions of mechanical technology we witness gigantic progress. 3. Adjustment of the Distance between the Working Surfaces The degree of reduction of the product depends not only on the form (corrugated or smooth) but also on the distance between the working surfaces. In accordance with the size and the hardness of the product, it is neces- sary to alter the distance between the break rolls with the view of obtain- ing the quantity of coarse and fine middlings given in the plan, as the machines, which divide the product according to its quality (purifiers), are calculated for a certain quantity and size of this product. For this reason every roller-mill must be furnished with a mechanism which will afford the possibility of adjusting the distance between the rolls 234 FLOTJK MILLING [CHAP, iv at any moment. The necessity of adjusting the distance is likewise evident in the case of smooth rolls, on which coarse and fine middlings of various sizes have to be reduced, and meal of different fineness obtained. The possibility of adjusting the distance between the rolls can be attained by making only one of them adjustable, so as not to complicate the construction of the machine. The adjusting mechanisms are named "brakes." x As it is impossible to reckon upon an ideal freeing of the grain of metal admixtures before milling, and there is also the possibility of their dropping in out of the machinery during grinding, the construction of the brake must be such, that in case of a nail or any other metal object falling in, the surface of the rolls shall not become spoilt, or the driving organs of the machine FIG. 212. break. The brakes satisfying those requirements are called tension brakes. We shall explain the idea of the tension brake on schematic con- structions. On Fig. 212 we have four sketches of tension brakes. Sketch 1 exhibits the form of the simplest brake. The roll B is set in stationary bearings D fixed in the frame C of the mill. The roll A lies in bearings E, which may be displaced to the right and to the left within the slippers P-P* of the frame. If the rolls are to be set at a certain distance, the bolts I, screwed into the frame with their threaded part and their conic heads resting against the adjustable bearing E, are turned. With the aid of these bolts also the evenness of the axes of the rolls may be adjusted. From the opposite side, the bearings are pressed by the springs k, resting 1 This term is used throughout the work to denote what is now generally termed hi England "adjustment mechanism" or "adjustments." It is short, and correctly expresses what otherwise entails needless circumlocution. CHAf. iv] FLOUR MILLING 235 on the collars of the bolt a screwed into the hub b with a corresponding thread. In this manner we have obtained the desired distance between the rolls and a definite grade of pressure upon it by the spring k. If a piece of iron that the rolls cannot break down passes in between them, the pressure is communicated to the journals of the rolls. Now, as the spring is calculated to withstand a certain utmost strain for the reduc- tion of the product, whereas the pressure of the metal particle exceeds it, the springs acted upon by this pressure will contract and the bearings E move to the left. The widened space between the rolls allows the metal particle to pass through without damaging the machine, after which the spring pushes the bearings back into their former position. To adjust the tension of the springs the bolts a are screwed in or out by means of a hand-wheel M . To prevent the screwing out of the bolts a, there are nuts with wings M j on the outside, serving as lock-nuts. The type of brake just examined has the defect, that it requires a complicated mechanism for the throwing out of the rolls, as the adjustable bearings move rectilinearly. Therefore the brakes shown on sketches //, ///, and IV are more rational types of construction. The right-hand roll of all those constructions is adjustable. Its adjustable bearing A is set in a movable arm B, which has a stationary axis of rotation 0. The other end of the arm rests on the spring (7, which may be adjusted as in the first case. On the side opposite to the spring there is set a lever D with an eccentric on a stationary axis . The springs in the // and /// plans are compressed by the end of the arms B, and stretched in the /Fth. Plan // represents a lever of the first order, and the plans /// and IV levers of the second order. The advantage of these three designs lies in the fact that owing to the pressure being transmitted through levers, there is no need of a spring so strong as in plan /. To throw out the rolls it is sufficient to turn the lever D as pointed by the arrow S. During the run of the rolls "in gear" the lever D is fastened by various means, to be examined later. The construction of the brakes on these plans may be infinitely varied according to the type of mills. Besides the spring brakes there have been suggested constructions where the spring is replaced by a weight. The plan of one of such brakes, corresponding to the second spring plan, is shown in Fig. 213. The spring is replaced here by a crank mechanism with a weight G, rotating on a rigid axle d 2 . The setting of the rolls at the distance required, and the dressing of the parallelity of their axes, is done by means of the bolts s and Sj. When the pressure upon the adjustable roll b exceeds the 236 FLOUR MILLING [CHAP, iv normal, the deflecting tail n of the lever transmits the pressure to the crank mechanism through the bolt s l3 and after the hard particle has passed between the rolls the weight G brings the roll to its established position. From time to time the inventors patent such weight brakes. But we must say that this bulky appliance offers no advantages in compari- son to the spring brake and at the same time complicates the construction of the roller mill ; for this reason such makes ought to be rejected. As regards the first design, it is to be met with in the simplest American mills for crushing hard materials (quartz, &c.). Of the roll sets for mills there is known only one American construction of Noye's FIG. 213. FIG. 214. in Buffalo, who very unsuccessfully adapted the principle of direct action of the pressure of the spring (Fig. 214). The resistance of the spring here is placed below the axes, therefore the pressing force P gives a vertical component Fj and a couple Th, which causes friction of the bearings in the guide parallels. It is only the component F, directed to the left, that transmits the pressure to the spring. For this reason the mechanism must be less sensitive. 4. A General Survey of the Roller Mill To understand the meaning and importance of the details of the roller mill one ought previously to become acquainted with the general character of its construction, where those details may be seen and their purpose understood. For this purpose we shall inspect the construction of the four-roller mills, for those mills represent double two-roller mills and constructionally in no way differ from the twin rollers set in separate frames. CHAP. IV] FLOUR MILLING 237 Roller Mill of Ganz & Co. in Budapest. Fig. 215 illustrates Ganz's roller mill in section. Let us examine the right-hand half of this mill. The product flows into the hopper b of the mill, with its weight presses open the gate w, and falls upon the feeding rolls which are rotating in the direction of the clock hand. With the view of letting through these rolls a stream of product of the desired thickness there is a gate down the whole length of the hopper, which may be opened more or less by means of a FIG. 215. hand- wheel h. From the feeding rolls the stock runs to the reduction rolls, and on passing between them falls through the hopper a into the spout. During the milling of a moist product there is the possibility of its sticking to the surface and blinding the corrugations, and therefore, under the rolls down their full length there are scrapers set (knives for the smooth, brushes for the corrugated rolls) to free them of the adhering particles. For the inspection of the feed there is a gate opposite to the feed rolls, and another one, for inspecting the operation of the rolls, is set in 238 FLOUR MILLING [CHAP, iv the frame below the rolls. Through both of them at any moment the stock may be seen and reached with the hand on opening the gate. Let us see now how the problem of adjusting the distance between the working surfaces is solved here. In modern mills the regulation of the working distance and the mechanism for throwing the rolls out of gear are joined in one common construction. When the mill is in working order the gate w is either in a vertical position or inclined to a certain degree, which depends on the quantity of the product fed. The gate w rotates on an axis, which has a lever on the outside (Fig. 217) with a weight z counterbalancing the FIG. 216. pressure of the grain upon the gate w. This lever is joined by means of a finger with another lever y with the axis of rotation at the side of the feed-hopper. On the right-hand side of the lever y there is a cavity for the finger of the handle of the lever x (Fig. 218) leading to the rod r of the brake M (Fig. 217). The lever x is set on the roll u which runs through the whole length of the mill. The end of the lever x is connected by a rod r with the brake or adjustment mechanism proper, the joint being of the ball and socket kind. The brake corresponds to our fourth plan. Its construction is as follows. In the levers M which have their axis of rotation in N, there are held by means of screws g the bearings of the slowly revolving side rolls d and d v These same bolts afford the possibility of setting the axes CHAP. IV] FLOUR MILLING 239 I! 240 FLOUR MILLING [CHAP, iv of the rolls horizontally. The top end of the lever M (Fig. 219) is a ten- sion brake of the following construction. The hub of the lever contains a spring c, resting on the right-hand side against the washer m which is screwed to the hub, and on the left against the ring n. Through the hub there freely runs the bolt o joined with the rod r. If a hard object is caught in between the rolls and the pressure exceeds the normal, the hub of the lever transmits the pressure through the washer m to the spring c, and, compressing the spring, moves to the left, and when the hard object has passed the working area of the rolls, the spring compels the lever to return to its former position. The tension of the spring is increased by turning the hand-wheel h, the square pin j having been previously pressed in and stopped by screw k. We shall now examine the operation of the whole mechanism. To FIG. 219. bring the rolls into working position, we must lift the lever x, which with its pin raises the lever y and the lever with a weight z (Figs. 217 and 218). Then the gate w drops and the product flows to the feed rolls. With its weight the product keeps back the gate and prevents the weight z from disjoining the levers x and y. As soon as the flow of the product into the hopper is stopped, the pressure upon the gate w is removed, and the weight z will drop down, lift the lever y, and disengage it with x. Then, acted upon by the springs of the brake, the levers M will force the bearings apart. But as there is the possibility of the grain recommencing to flow from the hopper, there must be arranged an adjustment to retain it there. For this purpose each mill is supplied with a mechanism stop- ping the action of the feed rolls, which in Ganz's mill is effected in the following manner. The axle u, connecting the brakes of the roll, carries pn a key a hub with the lever A (Fig. 219) which is connected by means of CHAP. IV] FLOUR MILLING 241 levers B and C with the hub c, freely running on a key of the axle F of the bottom feed roll. The left-hand part of the coupling is furnished with cross-heads. On the end of that same roll there is a freely rotating belt-pulley with a jutting out pin and a hub which also ends in cross- heads corresponding to those of the hub c. A bell is attached to the end of the roll F. When the machine is set operating the axle u turns so that the levers A, B and C push the hub c to the left and bring it with its cross-head end into connection with the hub of the belt-pulley. Then the feed-roll also commences rotating. As soon as the mill runs empty, the hub c becomes disengaged with the hub of the belt-pulley, which from this moment freely rotates on the now stationary roll F. The pin of the belt-pulley hits the spring with the small hammer, which having got loose at a certain part of the turn, hits the bell. This serves FIG. 220. as a signal that there is no stock in the machine. The spring is attached on the hub, which is pressed to the shoulder on the end of the axle. A detail of the adjustable bearing is illustrated on Fig. 220. Here the box a of the bearing has a cavity for the stopping and adjusting bolts , owing to which the flow of grain increases or decreases. In the lever G there is a cross-head and guide which changes the posi- tion of the gate A within the space marked K and Q, when the spring L is pressed by the nut J. The first feed roll N up to 100 mm. in diameter runs at about fourteen revolutions per minute ; it is provided with longitudinal corrugations 1 English patent, Nos. 6501 and 11,992. CHAP, ivj FLOUR MILLING 249 of different sizes, to answer the definite purpose of the roller mill for breaking, the grinding of middlings, or cleaning the bran. The duty of the second feeding roll, making 150 revolutions per minute, is to supply the stock to the grinding rolls, which is done by means of a plate between the roll and the bottom slowly rotating roll. The second feeding roll is brought into motion from a belt-pulley on FIG. 230. the axis of the bottom roll, by transmitting the motion to the roll N through toothed wheels. Both the rolls are of the same diameter. G. Luther's factory in Brunswick gives a construction of the feeding device (Fig. 230) totally different from the ordinary type, in that the supplying and the feeding rolls are removed from each other by a consider- able distance. The feed is thrown out of the hopper by the roll C on to the plate /, which together with the vertical partition forms a kind of second hopper. From this second hopper the roll d carries the stock to the slowly rotating bottom roll a. Thus the characteristic peculiarity 250 FLOUR MILLING [CHAP, iv of this construction is the division of one hopper into two parts and the absence of the supplying plate between the feeding roll d and the reduc- tion rolls. The adjustment of the feeding by means of the gate e is a very common combined construction of the feeding mechanisms already examined. The European constructors have lately begun to attach great im- portance to improvements in the regulation of the flow of the stock by means of a gate in the hopper, and have a tendency to discard the supplying plates. This is of great consequence, and we shall speak of it when giving an estimate of the various types of feeding. On Fig. 231 we have H. Bruner's feeding construction without a supplying plate, which operates as follows. 1 The feed rolls 2-2 have the same diameter, 90 to 100 mm. The top roll rotates with the speed of 40-50 revolutions per minute, and the one at the bottom 90-150, which depends on the product (grain, semolina, middlings, or bran) for which the mill has been fitted. Under the rolls there is a trough for collecting the heavy and hard extraneous matter. The gate 3 is adjusted with the aid of crank mechanisms and a spring 10. The axis of rotation of the gate is marked 24. The crank lever 7 revolving round its axis, when drawn off by the spring 10 presses the gate with its screw 8, which rests upon the support 9 screwed on. When the stock flows into the hopper and presses the gate 3, the pressure is communicated to the upper part of the crank lever 7, which stretching the spring inclines to the left. With the view to give the greatest declination desired to the gate there is set a screw 20, with the aid of which the limit declinations may be adjusted. The connecting rod 6 in its lower end has an oblong hole for the pin of the lever 7. The length of this connecting rod 6 may be adjusted by means of a nut connected with the joint part of the connecting rod and set on the screw part of the coupling rod. The pressure of the levers 7 upon the gate is adjusted by tightening the spring with the screw to which it is joined. To open the gate the axis 4 is turned with a handle on the outside (not shown in the drawing) in the direction opposite to that of 1 French patent, No. 429,736, of 1911. FIG. 231. CHAP, iv] FLOUR MILLING 261 the clock hand. The finger 22 lifts the axis 24, together with the gate connected with this axis, by a wall bracket 17. When the axis 4 is turned back, the gate 3 drops under the influence of its proper weight and is pressed to by the screw 8, as the connecting rod 6 turns the crank lever 7 round its axis in the direction of the clock hands. Simultaneously with the closing of the gate 3 the feeding rolls come to a standstill, which is effected with the aid of an ordinary appliance of cross-head couplings set in the same manner as in Ganz's mill. Single-roll Feeding. The single-roll feeding of the factory of Thos. Robinson in Rochdale is shown in Fig. 232. The stock flows into the hopper A and presses with its weight upon the gate 23 connected by a joint 24 with the fixed wall 7 of the hopper. The pressure is transmitted through a joint-stop 26 to the crank lever 20 set fast on the axis 13. M FIG. 232. On the same axis there are set, also fast, the levers 12 with bearings 11 for the roll 3 (Fig. 232, //I). When the lever moves to the right and turns the axis 13 the roll 3 likewise moves to the right (arrows) and opens the passage for the product between itself and the feeding roll 2. Though the roll 3 also rotates, the feeding is performed by the roll 2, while the first one only closes the passage of the product conveyed to the rolls 28 down the plate a. The pressure upon the gate 23 is adjusted by the spring 21 by means of the screw 22, and the widest opening is set by the spring 27. The feed-rolls are brought into motion in the following manner (Fig. 232, // and ///) ; the roll 2 is revolved by a flexible gearing from a pulley set on the axis of the grinding roll and a belt-pulley on the axis 8 of the feed-roll 2. On the left-hand side (// and ///) of the axis 13 there is shown a chain gear to the loose-toothed wheel 18 on the axis 13. The chain wheel 16 is made in one piece with 18. From 16 the rotation is transmitted to the roll 3 by a chain wheel 15. When the axis 13 is turned by a handle or by the pressure of the product upon FLOUR MILLING [CHAP. iV the lever 20 through the gate 23, the chain wheel 15 rolls over the chain wheel 16 but is not disengaged from it. To prevent the dirt in the product from penetrating into the joints 24 and those of the stop 26, the ends of the gate 23 are covered over with a leather lining 25. The roll 2 is 90 mm. in diameter and runs at fifty re- volutions per minute, while the diameter of the roll 3 is 25 mm. and its velocity eight to ten revolutions. A more simple single-roll feeding mechanism, evolved also by Thos. Robinson, is shown on Fig. 233. From the hopper A the stock flows on to the roll d and is thrown upon the supplying plate c by pressing off the gate B rotating on the axis o. The pressure of the gate is adjusted by a spring E which transmits the pressure by levers (7, while the tension of the spring is varied by a nut a running on the screw b. The left-hand end of the screw is joined by the fork G screwed into an arm on the frame F. The de- tails are given in the drawings / and //. The diameter of the roll is 100 mm. and its speed reaches up to forty revolutions. In this mill the different velocities of the rolls performing an equal number of revolutions is obtained owing to their diameters being different. The channel Z serves for ventilating the mill. On Fig. 234 the single-roll feeding of the mill from G. Wegmann's factory is shown. The left half of the mill is for breaking, the other one with porcelain rolls for the reduction of middlings. Let us examine the feeding process in the former section of the mill. The stock flows FIG. 234. CHAP. IV] FLOUR MILLING 253 into the hopper A, presses open with its weight the gate d, and is stirred loose if it is in lumps (this happens when the grain is moist) by a paddle roll ]_. By turning the gate g, as indicated by the arrow, the passage is opened to the feed roll a from which the product runs to the grinding rolls. The plate / isolates the product from the space between the partitions of the mill and of the bottom roll, where it might fall in acci- dentally. The number of revolutions of the feeding roll is about sixty, and the diameter is 40 to 50 mm. The feeding of the porcelain rolls is similar to the system of Thomas Robinson's examined above. Both the halves of the mill are ventilated on the principle of counter currents through the channel B. American Feeding Mechanisms. Just as complicated as are the feeding FIG. 235. mechanisms of the European constructors, so simple are those of the Americans. Very many American factories prefer a type of feeding de- vice analogous to the intermittently shaken shoe for feeding millstones or a single-roll system, but in none of the American constructions do we find a two-roll feed. Further, in the American feeding mechan- isms, the plates supplying the stock to the grinding rolls are totally absent. On Fig. 235 may be seen both the types of American feeding mechanisms, from the factory of Nordyke & Marmon Co. On the right- hand side of the mill we have two gates N and M which form the hopper. Influenced by the weight of the product the gate M turns round the axis of the fastening and the stock falls on the gate N, which is kept vibrating by cross-heads k. The cross-heads run at the rate of up to 250 revolutions per minute. Fig. 236 shows a section in perspective of this feeding mechanism. Both the receiving and the feeding gates are 254 FLOUK MILLING [CHAP, iv furnished with taper pins set in chess-board order, the purpose of which is to break up any lumps in the product. Receiving a large number of oscillations, the gate B loosens the product well and feeds it in an even sheet to the grinding rolls. On Fig. 237 is shown a perspective section of the roller-feed. The FIG. 236. gate B is suspended on an axis to the ends of which on the outside the counterweights C are fixed for regulating automatically the passage of the stock between B and the feeding roll. Fig. 238 represents the feeding device of the factory of AUis-Chalmers FIG. 237. Co. in Milwaukee. The stock runs into the distributing box A divided by an adjustable partition B, with the aid of which the quantity of product flowing into the right- and the left-hand section of the mill may be regulated. The feeder C is formed of a fixed plank h and a gate a suspended on CHAP. IV] FLOUR MILLING 255 two bolts * passing through holes in the lid of the feeder. The clear- ances in the lid and the ball-washer e allow the gate a to swing to the left under the pressure of the product. The gate a may be drawn up with the aid of the nuts g. The automatic adjustment of the flow is performed by means of fingers c and counterweights d. The largest desired opening is set by the stopbolts k. For ventilating both the pairs of rolls there is a channel D wherefrom the air is exhausted through the side holes E. The channel down the full length of the box A is covered over by an iron lid F. Besides vibrations by cross-heads some factories make connecting- rod gears. Fig. 239 illustrates such a feeding mechanism from the factory of Noye Manufacturing Co. From the hopper A the product falls into the shoe B suspended on springs a by an eccentric connecting- rod C. The flow is regulated by the gate b with counterweights c. FIG. 238. FIG. 239. From the shoe B the product passes directly to the slowly rotating roll. The number of vibrations of the shoe reaches up to 200 per minute. The results of feeding with an American mechanism, as was said above, are quite satisfactory. Still the reciprocating motions of the working organs ought to be avoided, even though the inertia of the masses, as it is in the present case, be insignificant. Estimation of the Feeding Mechanisms. The types of feeding mechan- isms examined may be divided into two principal groups : those where, after the feed rolls, the stock is passed to the grinding rolls down a plate, we shall name mechanisms with compulsory feeding ; while those in which the stock falls free upon the working surfaces of the rolls will be called mechanisms with free feeding. In the beginning of the preceding chapter, the requirements which the feeding mechanism should satisfy were mentioned. Basing our estimate of the mechanisms with compulsory and free feeding upon the third and fourth requirements, i.e. the shortest route from the feeding 256 FLOUR MILLING [CHAP, iv mechanism to the rolls and absence of injurious resistances on the way of the stock, we must give preference to the mechanisms with free feeding. If we turn to the constructions of compulsory feeding we shall see that in the most favourable case the supplying plates offer an inclined plane, and often a rather long way over a curved surface. In the first and in the second case, this way is longer than the falling of the product from the feed roll straight upon the rolls (the line of fall will lie in a parabola, for the stock is under the influence of its weight, and is flung off the roll with the initial velocity at an angle to the vertical). Spending more time on its way the product becomes heated to a greater extent before reaching the rolls. But if the ventilation is good, this circumstance is of little consequence. The chief point is that in travelling over the plate, the product has to overcome the power of friction, owing to which its velocity, and consequently the capacity of the mill, diminishes. Another very injurious circumstance lies in the fact that on the plates, especially when a moist product is being reduced, knots are formed which break up the solid sheet of stock into separate streams. This disorder in feeding is particularly noticeable if semolina and middlings are the products treated. The formation of the streams, or the so-called paths, is brought about in the following manner. When different kinds of product, besides the grain, run down the plate, the soft, mealy, glutinous particles stick to its surface. Around them fresh particles collect and stick to them, thus forming a knot, and the path is ready. The stock running in is turned aside by those bunches, and the sheet of product consists of separate thick streams. The feeding is uneven ; one part of the work- ing length of the rolls remains unused, while the other is overloaded and crushes the stock to flakes. The capacity of the mill decreases. The supporters of compulsory feeding adduce in its defence the consideration that, if the process of reduction on rolls is correctly per- formed, the necessary movement and a rationally arranged ventilation will prevent the mealy, glutinous particles, which cause the formation of the paths, from falling upon the feed rolls. However, these arguments are feeble. It should be noted that there is no idea of supplying the grinding rolls with a product totally free of moist, glutinous particles, however perfectly the movement might be arranged. When the middlings are ground those particles are nearly always present. The miller attending the operation can easily obtain proofs of it. A constant flaking of the meal, and an excessive heating of CHAP, iv] FLOUR MILLING 257 the product discharged, very often points to an unevenness in the feeding, caused by the paths formed on the plate. An inspection of the feeding appliance, and putting the plate in order, is of great assistance in the process. This inspection should be performed every four to six hours. In the breaking process the paths are found more seldom ; the rough break stock cuts the knots off as soon as they appear. The danger of the mealy particles sticking to the plate and gathering into knots is considerably alleviated if a perfectly dry stock is fed in. This is attained by the arrangement of ventilation, the main purpose of which in a roller mill is to exhaust the warm, moist air. The fact must be kept in mind, however, that a perfect ventilation in this respect appears only as a palliative, which impedes but does not obviate the formation of knots on the surface of the plate. We must also not forget that so fine and tender a product as the fine middlings are to be dealt with. The very least obstacle is sufficient to build a path. The slightest traces of moisture would suffice for the exceedingly small hygroscopic particles of meal to form a knot. But moisture is always present even with the best of ventilation. The following proves this statement to be true. With a rational ventilation the particles of meal reach the feed rolls in a state of normal moisture, but on their way from the feed to the grinding rolls they may undergo a change in that respect. In fact, with the passage of the product, both the product itself and the working rolls become heated. Owing to this, a part of the moisture contained in the product passes into air, which will be slightly warmer than the product. This air enriched with moisture, in spite of a perfect ventilation, will have time to return this moisture to a cooler hygroscopic product the gluten ; the moisture will precipitate upon the product. It will be absorbed by the finest hygroscopic particles of the meal, rich in gluten, which will settle in the lower end of the plate. To this we must add that the air impregnated with moisture settles immediately on the cold plate, which facilitates the formation of paths. This latter remark, however, is applicable only to the beginning of the operation, for the plate also becomes heated soon. It goes without saying that we have in view formations of dew (both on the product and on the plate) imper- ceptible to the eye and the hand, and such formations are possible even if the mill is ventilated, which is proved by experiment, for the plates of the ventilated mills have to be cleaned just as those of the non- ventilated mills, though more rarely. The harmfulness of the use of plates, even if used with the best modern ventilation, is perceptible. 258 FLOUR MILLING [CHAP, iv In appraising the feeding mechanisms, the accessibility of their parts and operation for inspecting purposes must be considered. In this respect the compulsory feeding almost in all makes is placed in an unfavourable light. This defect in feeding is particularly notice- able on Fig. 223, p. 245. Here the product may be seen through the inspection window B only at the moment it leaves the feeding-roll 5 and partly when on the plate r. The plate r itself is quite inaccessible to inspection, and so far removed from B that its extraction with the view to freeing it of the knots is extremely difficult. The constructors upholding the compulsory feeding ought to accept it as a rule, that the supplying plates should be easy of access and loosely suspended, as this will facilitate the removal of the adhering product from them. Whatever be the kind of feeding, forced or free, the stock must be delivered to the slow roll ; it is required by the very idea of the process of reduction, that the slowly rotating roll should hold back the pro- duct. If the stock falls on the fast roll, it will be thrown against the slow one, rebound from it again, and hinder the other particles from reaching the grinding surfaces, thus lowering the quality of the work. 6. Types of Roller Mills (i.) Two-roller Mills Having become acquainted with the principal details of roller mills, we can formulate the requirements which must be satisfied by a ration- ally constructed machine. Those requirements are as follows : (1) An even feeding of the grinding surfaces, automatic adjustment and stoppage of the feeding mechanism. (2) A tension brake for the adjustable roll. (3) The tramming of the parallelity of the rolls. (4) The ventilation of the working chamber of the mill, for cooling the product and the working parts, and for removing the meal-dust. (5) The work of the mill easy of inspection ; ease in the observation of the feeding process and in taking samples of the grist while the mill is in operation without any danger of mutilation. (6) Removal of the adhering product from the working surfaces. (7) Simple dismantling of the frame for removing the rolls. (8) Economical transmission of power to the working organs. Let us now examine the European and American types of mills, and see how far they satisfy the above requirements. CHAP. IV] FLOUR MILLING 259 Mills of Amme, Giesecke, and Konegen. Fig. 240 represents a two- roller mill with the lever for the brake, to which we shall return later, taken off. To understand its construction better, let us watch the dismantling and fitting up of this mill. The frames of the bottom adjustable bearings b are supported by timber blocks to shield them from the blow of the axles when lowered against the frame of the roll. Next with the aid of ratchet-braces d the lifting lever c connected with FIG. 240. FIG. 241. the bushes of those ratchet-braces by a screw (Fig. 243) is lowered. This is accomplished by turning the ratchet-braces d in the direction opposite to the movement of the clock hand. Further, the nuts and lock-nuts e are screwed off up to the plugs /. Then the whole system on which the adjustable bearings are suspended becomes free, and is easily deflected by the rotation round the axis of its eccentric fastening, as the fork-shaped tail of the bearing frame (Fig. 244) rests free on the cup of the brake. The lever c assumes the position shown on Fig. 241, after which the upper part of the frame is removed. On taking away 260 FLOUR MILLING [CHAP, iv the timber blocks the adjustable bearings are carefully lowered, until the axles of the rolls are lying in the cavity in the casing of the frame. The lids e of the stationary bearing and i of the adjustable bearing are removed ; it is then easy to take out first the upper then the bottom roll. The construction of the ball-bearings will be examined below, while for the present we shall occupy our attention with a four-roller mill l) FIG. 242. (Fig. 242), where the feeding mechanism and the brake may be inspected. The feeding is performed in the following manner : a loosely sus- pended gate w has an adjusting valve g, which may be lowered and raised by means of screws k, increasing and reducing the passage of stock. By the pressure of the product the gate declines to the right and is retained in the position of the largest desired opening by a stop -screw e, with the aid of which the width of that opening may be altered. On the outside, the gate w has a counterweight running along the lever e, or, in other CHAP. IV] FLOUR MILLING 261 makes of the same factory, pushed by a spring, as in G. Luther's mill already examined. From the fast feeding roll the stock flows down the plate n to the fast grinding roll, which passes it to the plate o ; the plate o directs the stock to the slowly revolving bottom roll. Both the plates are suspended, and may easily be removed through the doors in the hopper of the mills. The adjusting mechanism has the following arrangement : the frame of the adjustable bearing has two arms (Fig. 243), of which the right-hand one with a fork-shaped tail rests on the cup d with a spring, while the left-hand one is set on an axis of rotation fixed in the frame of the mill. The finger set in the hub p of the frame has an end F of a hexahedral section (Fig. 244). On F there is set an eccentric ball hub q fastened to the collar of the finger by a bolt 5, the nut of which is covered by the washer t, held by a- nut u. Between the hubs p and q there is a washer v. Turning the nut s, after having previously removed the nut u and the washer t, we turn the hub q together with the finger F, thus setting the axis of the adjustable bearing in a position parallel to the axis of the fixed bearing. This fitting up is generally performed accurately in the factory. A more simple truing up is performed with the aid of a spring brake already examined. In Fig. 243 is shown this brake for porcelain rolls. The same fork-shaped tail rests upon the cup d, in which there is a spring resting with its lower end upon a nut m, its tail entering into the aperture of the cup. The top end of the brake rod is set on a finger eccentrically positioned in respect to the axis of rotation of the lever A (Fig. 242). The raising or lowering of the bearing 771 FIG. 243. IS FIG. 244. performed roughly by turning the nut m, and more accurately by a ratchet- wheel nut connecting the top and the bottom part of the rod. Over the roundly ground fork of the lever there is set a washer with a ball-shaped cavity, held by a nut r and a lock-nut s. When the pressure upon the rolls exceeds the set limit, the fork of the tail presses upon the cup and, compressing the spring, drops down. If the bearing is to be lowered and the rolls put out of gear, the lever d is 262 FLOUR MILLING [CHAP, iv disengaged from the lever /, and then the fork, pressed by the weight of the roll, lowers the whole rod. A more accurate adjustment of the dis- tance is attained with the aid of a hand- wheel E which, when turned, pushes forward the lever A and lifts the front and the back rods t, since the roll with eccentric fingers is let through the box of the frame. The motion is communicated to the feed rolls from the fast grind- ing roll by belting to the larger and by a gear drive from the larger to the smaller roll. The feeding rolls rotate with the ordinary velocities. The throwing off and in of the feed rolls is performed by a cross-head coupling on the axis of the large roll, as in Ganz's mill. The rotation is transmitted from the fast to the slow grinding roll also by means of a gear drive. The mills in question have ordinary ring lubricating- or ball-bearings. The fitting of the gear-wheels, belt-pulleys and ball-bearings on -.- FIG. 245. FIG. 246. FIG. 247. these mills is of some interest, and we shall therefore direct our attention to those details. Figs. 245 and 246 illustrate the keying on of the gear-wheels or belt- pulleys by means of two wedge-shaped keys b and c. The chain-wheel is set on the shaft so as to allow easy access to the screw-threaded holes a, made for taking the chain-wheels off. Then the key b is set in first, the key c laid on it, and both are hammered in with the calculation that the end of the key c should protrude not more than 7 to 8 mm. outside the hub of the gear-wheel. When the pulley is to be taken off the key b is knocked aside a little to the left, which causes the key c to become loosened and easy to extract. The gear-wheel is taken off with the aid of a cross-head (Fig. 247) with bolts running freely through it and screwed into the holes a. The middle bolt, entering into the thread of the cross- head, rests against the centre of the shaft. In screwing the middle bolt into the cross-head, we obtain a tension in the side bolts, which evenly, without any crookedness, draw off the chain-wheel or the belt-pulley. The essential part of the ball-bearing is the steel rings with balls between them, of which one is set fast on the journal of the shaft, while the other one is held in the frame of the bearing. The rings with balls CHAP. IV] FLOUR MILLING 263 fitted in beforehand are warmed during a period of about half an hour in machine oil of 40 C. and set on the journal (Fig. 248). To bring them up to the collar of the journal a free cast-iron hub / is set on the journal, and a piece of wood having been placed under the right-hand end, it is knocked with a lead hammer until the hub pushes the rings to the collar. For taking the bearings off there is also a cross-head (Figs. 249 and 250) with bolts d and a flange b. On the journal between the bottom ring of the bearing and the flange a built-up bush a is placed so that its section lies on a plane with the axes of the bolts d. Then the bolt e resting against the centre of the journal is screwed into the cross-heads, and in this manner tightens the rings with the balls without damaging the journal. The feeding mechanism of the Amme, Gieseke, and Konegen's mill'we have examined has the defects common to all inaccessible feed plates. In attempting to avoid these defects the factory has evolved a new design TT FIG. 248. Fia. 249. FIG. 250. for setting the plates, the aim of which is to curtail the route of supply and make the removal of the knots from off the feed plate more easy. This construction was patented only in the end of 1911, and has not made its appearance on the market yet. Here (Fig. 251) we have already only one supplying plate a connected by a joint rod b with the controlling door c. ' The axis of rotation of the plate below is a. Another plate is set to prevent the product from accidentally slipping through on to the bottom roll. This position of the plate a allows any knots to be removed without taking it out. The " Diagonal " from the works of Dobrovy and Nabholtz.As in the case of the preceding mill too, both the halves of the Dobrovy and Nabholtz mill operate quite independently of each other, having only a common ventilation chamber (Fig. 252). From the hopper A the product runs to the two feeding rolls aa : the slowly rotating top roll passes the stock to the fast bottom one, which in its turn throws it upon the nickel-plated feed plate b. This 264 FLOUR MILLING [CHAP, iv plate delivers the product to the grinding rolls in a tangential direction. The distance between the feed-hopper and the grinding surface of the rolls has been reduced to a minimum, in comparison to the preceding mill. The rolls are put in gear by means of a rod c with a handle d, which when pressed is caught by the lever e. At the same time a system of levers / and g turns the axis o, which with the aid of the lever h eccen- trically set on it, raises the bottom grinding roll. The feeding device is thrown in by a lever c with an inclined segment k acting upon the fork- shaped rod i. The parallelism of the grinding rolls is set by means of hand- wheels m. By turning the levers q with the screws r, the gate t may be set in any position, in which it will be retained by the springs s. The automatic throwing out of the rolls and the stoppage of the feed are effected by the action of the weight g upon the levers c and p in a manner already known. The grinding rolls are aspirated in the direction indicated by the arrows 1, 3, and 4 in the drawing, and the air on entering the chamber of the mill through the fissures under the lid exhausts the grinding rolls from below and then passes up. The bearings of the rolls are made of phosphor-bronze and furnished with ring lubrication. The gear-wheels for transmitting the motion to the rolls with double helical- like teeth are set in special cases serving them as oil boxes. The slow feed roll is turned by a belt-drive from the belt-pulley on the axis of the fast grinding roll, and from the slow feeding r6ll to the fast by toothed gearing. The built cross-head coupling is set on the axis of the slow feeding roll. French Roller Mill. On Fig. 253 may be seen the mill of one of the largest French milling machinery works, Teisset, Chapron & Brault Freres, in Paris and Chartres. The section illustrates the position of the feeding mechanism and grinding rolls, showing the fast grinding roll with fixed bearings to be at the top, and the slow roll with the brake below. The incline of the plane of the axes forms an angle of 50 with the horizontal plane. The feeding is performed by two rolls a and b with corresponding FIG. 251. CHAP, iv] FLOUR MILLING 265 differential velocities and an adjustable gate c discharged by means of a spring set on the outside of the mill. The stream of product observed through the glass door d in the upper part of the frame glides down two inclined plates. From those plates the stock falls upon the slow grinding roll A, which carries it to the fast roll B. FIG. 252. On opening the door D in the mill, the delivery of the milled product may be watched and samples obtained without any difficulty. From the feeding rolls and on leaving the grinding roite the product may be taken by hand without fear of any danger. The exhaust air enters through the top part of the hopper, follows 266 FLOUR MILLING [CHAP. IV the stock all along its route, and is exhausted by the aspirator after the stock passes through the grinding rolls. The cast-iron frame, judging by the outward appearance of its con- struction, is rigid, and vibration apparently obviated. The frame is lined with timber on the inside to prevent the walls from becoming cooled, in which case the moisture is deposited and settles on them and the meal turns to a paste. The adjustment of the grinding rolls here, as in other types of mills too, consists of two separate processes : (1) tramming the adjustable FIG. 253. roll in respect to the fixed one, and (2) setting the adjustable roll nearer to or farther from the fixed. The tramming in respect to the fixed roll in every bearing is performed by means of a hand-wheel G resting upon a spring encased in a box H . The brake-mechanism, as well as the automatic stoppage of the feed, in construction is similar to those of Seek, with the sole difference that the brake is fitted to the bottom roll, while in Seck's mill it is applied to the top roll. G. Daverio's Mill. The Swiss works of G. Daverio (Zurich) was the first to adapt the vertical position of rolls and very soon began to set them diagonally, convinced by experience of the inconvenience of the plates supplying the stock to rolls so positioned. Simultaneously with CHAP, iv] FLOUR MILLING 267 the English works of Turner, Daverio patented mills with a diagonal disposition of rolls, in which the operation of the feed plates is placed in more favourable circumstances. At last, for the first time in Europe, the Daverio works launched on the market in 1908 a model of a mill without any feed plates, and this was soon imitated by other works. Fig. 254 shows a Daverio mill of the latest model. The grain runs into the hopper and with its weight presses open the feed gate adjusted by a counterweight b. The utmost opening of the feed gate is set by FIG. 254. means of a screw c. The adjustment of the feed gate by hand is per- formed with the lever d set on the axis r of the flap. The slowly rotating top feed roll carries the stock to the fast roll, which throws it directly on the slow grinding roll. Under the frames there is placed a plate, the duty of which is to collect the heavy extraneous matter. The tension brake in general is the same as in other mills, with this difference only, that the cup with the spring forms one single piece with the tail I of the adjustable bearing. With the aid of the lever a, connected by an ordinary distance eccentric with the tail I of the adjustable bearing, the grinding rolls may be either thrown out of gear or thrown in for ordinary work. In throwing out the bottom roll the lever a 268 FLOUR MILLING [CHAP, iv at the same time turns a horizontal crooked lever round its axis, which by means of a cross-head coupling throws the rapidly rotating bottom feeding roll out of motion. The spring of the brake is adjusted by means of nuts hf-li. An accurate tramming of the axes of the grinding rolls is performed with a hand-wheel g. The dismantling of the frame and ex- traction of the grinding rolls is performed in the following manner. The removable parts o on either side, of the frame are taken off. Then the cotters i are taken out and the nut k loosened, which allows the cup m to be lifted off, when the lids of the bearings are removed and the grind- ing rolls may be lifted out. The ventilating air enters through the holes in the lid of the hopper covered over with a dense sieve, exhausts the rolls from below, and escapes through the side openings. The transmission of motion from the fast top roll to the bottom one is done by means of toothed wheels enclosed in cast-iron casings filled with oil through the inlet q up to the level p. (ii.) American Roller Mills Not only in Russian literature but in Western Europe as well a total absence of descriptions of American milling machinery in general, re- specting roller mills, is observable. Even so eminent an author as Pro- fessor Kick speaks only of Howes' scouring machine. This circumstance is all the more striking, since the first teachers of the European automatic milling engineers were Americans. One could learn a good deal from them even now. However, not only in monographs and lectures, but even in the periodical literature of Europe, we find no material dealing with the American construction of milling machinery. Is this the usual conser- vatism of Europe, or the patriotism of the Old World ? We cannot under- take to judge, but the fact is, that the European constructors have been deprived of rich material in the possession of their transatlantic colleagues. The American roller mills are so different and original in their con- structive ideas, and besides that so little known to us, that we have deemed it expedient to dedicate a whole chapter to their description. We are already acquainted with the feeding devices of the American mills, and shall now examine the brakes and the mill in their full outfit. Fig. 255 represents J. Stevens' two-roller mill with a brake of direct action. The bearings a are fixed, the adjustable ones a run in the parallel guides of the frame. The brake has the following arrangement. The screw F freely passes through the screw 1-2, entering the box of the CHAP. IV] FLOUR MILLING 269 bearing and its end protruding out of it. The screw 1-2 is screwed into the arm G of the frame. On this screw a spring is set which presses upon the bearing. The grinding rolls are thrown apart by pressing the lever D down with the handle d, when the cross-heads C (on Fig. 1, with another curve of the lever D, it is more clearly seen) press upon the protruding parts of the screw F and draw the bearings and the grinding roll with them, to the left. When the lever is turned back, the spring brings the bearings to their former position. The distance of the working surfaces is defined by the size of the protruding ends of the screws F. The parallelity of the axes of the rolls in a horizontal plane is set by those same screws being deeper or less screwed into the frame of the bearing. FIG. 255. The head 3 of the screw 1-2 serves for screwing it into the arm of the frame, and thus adjusting the distance to which the bearings are removed ; the nut 4 regulates the tension of the spring. The motion is transmitted to the roll by belt-gearing, and the receiving belt-pulley is on the journal H of the fast grinding roll, which transmits the motion to the slow roll by means of jockey -pulleys 1^-1 and II~II l ; from the shaft of the slow roll a cross drive Ill-Ill \ runs to the feeding roll. The tension of the belts is adjusted by a screw B with a spring to mitigate the shocks. This spring presses upon the adjustable bearing of the jockey-pulley /-//, while the degree of its pressure is regulated by a nut and a lock-nut L The defects of the brake of direct action were noted when examin- ing Noye's brake. But those mills do good service in the rough fodder- grinding of maize, barley, oats, &c. Among the reparable defects of 270 FLOUR MILLING [CHAP, iv this mill we may place the transmission of motion to the feeding roll from the adjustable grinding roll, for when the grinding rolls are being drawn apart the belt becomes stretched and then begins to work badly. It is to be remarked here that the belting transmission of motion to the grinding rolls is a peculiarity characteristic of American roller mills. Only in mills doing rough, coarse work do the Americans employ toothed gearing. T. W. Graham's original brake is shown on Fig. 256. The adjustable grinding roll E is set in a bearing F, one tail of which is connected with the rod D, while the other, G, with its point H turned to a globe, enters into a cylindrical socket in the frame of the fixed bearing A, which forms a part of the roller frame. Through the arm K of the lower tail there passes a rod L to the spring M . The rod P eccentrically set with its clip X on the finger n, the screw D, and the spring hold the bearings in a settled position. By turning the handle N down and pushing the rod P likewise down, the bearing F is made to revolve round the horizontal axis of the apple Q. To allow a free lowering of the left end of the spring rod Z there is a clearance I in the FIG. 256. frame. A rough tramming of the roll-axes is done by means of nuts o and o lt a more accurate setting by the screw D which also regulates the working distance. The pressure of the spring is adjusted by a nut 1 2 . The brake of J. Dawson's four-roller mill is given in Fig. 257. The lower tails D of the adjustable bearings E are freely set on the hubs G with levers K. These hubs are eccentrically fitted on the journals of the shaft H, the rotatory motion of which is stopped by bolts L. The top tails of the bearings rest on the spring V. The screw rods N are fitted with their slips on the fingers of the discs R, one of which has a handle X with a lock 7. The discs are fixed on the journals E l of the shaft E 1 with keys. By turning the handle X to the right or left one can bring the grinding rolls to a fast or a loose run. The tension of the spring is ad- justed by a nut W (having a washer on the rod with a clearance behind CHAP. IV] FLOUR MILLING 271 it). Seeing that the hub G is an eccentric, by turning the levers K, having previously loosened the bolts L, one may set the axis of the roll in a hori- zontal plane ; the parallelity of the axes of the grinding rolls is established by turning the hand- wheels U to the right or to the left, depending on the direction in which the axis slants. Special attention is due to the idea of adjusting the axis of the grind- ing roller in two planes vertical (by means of an eccentric hub G) and horizontal, so simply brought into execution. We must remark that all European factories do not give consideration to this question. Fig. 258 shows us the brake of a two-roller mill, constructed by W. D. Gray, an eminent American engineer (Allis-Chalmers Co. works). Here both the bearings D and D 1 are adjustable ; their axes of rotation are , FIG. 257. o and o v The section of the brake is illustrated on Fig. 260, which shows the rod E to be an eccentric coupling with the axis b Q of the lever H . The second end of the rod passes through the cup d with a spring d of the tail of the bearing D resting against the screw d 3 with a hand-wheel. On the same axis 6 6 there is eccentrically set the tail of the bearing D lf The grinding rolls are thrown apart by pulling the rod / to the right. The friction drive to the feeding roll is arranged as follows : on the rod E there is a coupling Q with an offshoot q to which the loose belt-pulley M is screwed by the bracket of its hub. The coupling Q may be moved up and down the rod and fastened with a bolt a. When the rolls are set for a working run, the belt-pulley M comes into contact with the belt-pulley N on the journal of the right- hand roll, and the belt-pulley L on the journal of the feeding roll. Fig. 259 illustrates the brake of a four-roller mill. The bearings of 272 FLOUR MILLING [CHAP, iv The details need no explanation, being a the middle rolls here are fixed, repetition of those preceding. A more simple friction drive to the feeding rolls is to be seen on Pig. 261. Here only one friction roll E is loose ; to the second feeding roll the motion is transmitted by a crossed belt. The defects of the friction drive, in the first case (Figs. 258 and 259) lying in the fact that FIG. 258. FIG. 259. with the change in the working distance of the grinding rolls the position of the friction roll has likewise to be altered, are removed here since the position of the friction drive is independent of the position of the brake rod. In Fig. 262 we see a very ingenious device for stopping the operation of the feed rolls by means of an ordinary cross-head coupling and a loose belt-pulley on the axis of the feeding roll. On the left-hand end FIG. 261. (top left-hand drawing) of the roll communicating the motion to the rods E of the brakes, there is set fast a hub p with a screw arm P (Figs. 3 and 4) which catches the flange a of the hub of the belt-pulley L, on the axis of the feeding roll J. This hub on its left-hand side is a cross-head coupling cogging in with the hub of the loose belt-pulley N. When the rolls are in a working position the roll G is turned so that the screw flange of the hub p points downwards and the spring / pushes the belt-pulley L for- ward till it couples with the belt-pulley N. When the grinding rolls are CHAP. IV] FLOUR MILLING 273 running empty the flange P disengages the belt-pulleys L and N, and the operation of the feed rolls is discontinued. A similar device for a loose and fast run of the feed rolls with toothed couplings and friction 2 is illustrated in Fig. 263, with this FIG. 262. difference only, the disengaging mechanism of the grinding roll connected to brake hand- wheel, and the connecting of the couplings or of -the friction, is performed not by a spring but by a crank Lever R (with or without a fork at the end). On the rod H, which brings the FIG. 263. adjustments into action, there are two slides made to fit the free end of the crank lever R. When the rolls are in gear, and the rod H is pushed to the right, the end of the lever R falls into the slide a and keeps the coupling Q engaged with the hub of the belt-pulley N ; when the run is loose, it is held by the slide a, 274 FLOUR MILLING [CHAP, iv The latest model of W. D. Gray's roller mill is represented in Figs. 264, 265, and 266. A characteristic peculiarity of the American roller mills is, as has already been mentioned, the total absence of toothed gearings. Let us note first how the motion is communicated to the rolls. From the pulley of the transmission shaft, the belt runs first (Fig. 264) over the belt-pulley A of the outermost fast grinding roll and then over the jockey-pulley C to B, the belt-pulley of the third on the left-hand side FIG. 264. fast grinding roll. In this manner, the fast rolls of the American roller mills are disposed asymmetrically the inevitable result of transmission by belting. This arrangement cannot be avoided if the machine is to be compact. The slow grinding rolls with belt-pulleys D and E, the second and the fourth, receive their motion (Fig. 265) from the belt-pulleys F and G placed on the same shaft as the belt-pulley C. The belt-pulley C has a double function : firstly, it affords the possi- bility of enlarging the gripping angle of the belt-gearing of the pulleys A and B, secondly, by rising or falling it adjusts the tension of the belt, CHAP. IV FLOUR MILLING 275 An adjustment of this kind of the tension of belts is a feature of the construction of roller mills of all American works, and is of very great importance. First of all, the tension of the belts being regulated in the manner described above, there is no need to take up the stretched belt ; but the main point is that by increasing the tension, we can within a limit of 10 to 20 per cent, increase the capacity of the mill, which has often to be done when the mills are overloaded. The raising and the lowering of the jockey pulleys (7, F and G is performed by means FIG. 265. of hand- wheels j and screw rods connected by joints with the tails of the bearings L, which turn round the axis 0. The screw rods pass through a consolidated bracket Q with a screw thread. Before proceed- ing any further, we must point out a material defect in Gray's adjustment of tension. The planting of independent adjustable bearings for the belt-pulleys C and F-G does not exclude the possibility of the shaft getting out of line, since its horizontality cannot be trued up on the belt- pulleys F and G ; this tends to make the bearing L work hot and wear irregularly. Proceeding now to describe the mill, we must point out that the 276 FLOUR MILLING [CHAP, iv mechanism adjusting the distance here is improved in so far that the eccentric rods E of the brake have one common axis S, which simplifies the construction. On the same axis is set the tail of the hub of the loose belt-pulley, over which there runs a belt transmitting the motion from the slow roll to the feeding rolls. In throwing apart the outer grinding rolls by turning the lever P to the left this loose belt-pulley is dropped down, the belt slackens, and the feeding rolls stop operating. This belt- FIG. 266. pulley, similarly to the guide belt-pulleys and the belt-pulleys on the axes of the feed rolls, has collars (Fig. 266) which prevent the belt from running off. When the tension of the belt to the pulleys of the feed rolls is to be increased the bolt holding the hub of the tail of the loose belt-pulley is dropped, the tail turned to the right, and the bolt is again fastened. Nordyke & Mormon Co.'s Mill. On Figs. 267, 268, and 269 we see the construction of a roller mill of one of the largest American works that , iv] FLOUR MILLING 277 of Nordyke & Marmon Co. at Indianapolis. Fig. 267 illustrates the FIG. 267. general view of the mill (1), and the plan (2) with the hopper off, Fig. 268 two sections, longitudinal (3), and along the brake mechanism (4), Fig. 269 FLOUR MILLING [CHAP. iV details of the drive to the brake mechanism and to the feeding apparatus (5, 6, 7, 8, 9, 10, 11). The mill is driven by the belt-pulleys 1, 2, 3, 4 1 and 3 by means of the belt 12 running from the belt-pulleys on the shafting, 2 and 4 by means of separate belts 13 and 14 on the belt- pulleys 6 and 7. The jockey-pulleys 5, 6 and 7 run through the frame of the mill. The adjustable bearings are built in the following manner : the two- tailed boxes D for the bearings E below (Fig. 268, 4) have an axis of rota- tion d (a bolt screwed into the frame) on which they are set with their eccentric d t . This eccentric determines the distance to which the adjust- FIG. 268. able grinding roll springs open in case a nail or any other piece of metal falls in between the rolls. The bearings E have surfaces e and e z turned in to the corresponding surfaces of the boxes D, to which the frame of the bearings is attached by bolts e v If the axes of the rolls require adjusting vertically, the bolts e are loosened and the wedges e 3 tightened. When the regulation is ended, the bolts e l are readjusted. The rods F of the brake pass through the lower ends of the shoulders D, under their joints, having the spring F l on one side, and the regulat- ing brake of the spring hand- wheel F* on the other. These hand- wheels are screwed up till the shoulders have a tension sufficient to com- CHAP. IV] FLOUR MILLING 279 municate a pressure of the desired force to the rolls. When a hard body falls in between the rolls and presses them apart, the springs contract, FIG. 269. for .the shoulders, owing to the eccentric couplings on the bolts, may travel along the axis d. The rods G serve to move the upper ends of the shoulders D to the right and to the left, owing to which the grinding rolls approach or 2SO FLOUR MILLING [CHAP, iv separate, i.e. the throwing in or apart takes place. At its inner end every one of those rods is connected by a joint g with a lever H, which draws the shank with it when moving. The levers H have in the frame A 1 axes of rotation d by turning the cross-heads j the throwing in and out of the rolls is performed. The handles J 1 are set on the journals of the cross-heads J. Those handles have segments of toothed wheels J 2 at their lower ends. One of the toothed segments may be thrown off and act independently of its lever, if it be desired that only one side of the mill should be at work. This is effected by making the toothed wheel and the lever in two parts, as shown in Fig. 269 (6 and 11), with a slot for the bolt i 1 . When it is desired to fasten both parts together, the bolt i l is brought down, as shown, to the lower part of the slot and fastened there, so that the levers and the segments form one whole body and operate together. If it is in- tended that only one half of the machine should work, the bolt i l is pushed up to the top part of the slot, and then the handle and the segment are independent of each other. As this segment does not sit firmly on the shaft, the opposite lever may be displaced without touching the shaft it is set on. With the aid of the above described adjustment both pairs of rolls, or either pair singly, can be thrown apart and then again brought together to exactly the same distance. The lower ends of levers j 1 are provided with pins i 2 , which, during the motion of the levers backwards and forwards, catch the claws 11 of the rods L (Fig. 269, 7), which are consequently brought into motion and draw the shoulders K l and the shafts K of the regulating gate by means of levers K l and pins Z x with them. It is quite clear that when the levers j are disconnected and are working independently of each other, they bring into action each one of the rods independently. The feed plates J are of thin metal and run along the feeding rolls J 1 with claws j and j 1 at the top. One of these claws j on each one of the plates couples with claw k of the corresponding axle K (see Figs. 8 and 9), and in this way the gate rises and falls with the revolution of the axle. Other claws, j 1 , are fitted, so as to be able to catch the stop screws j 2 , and consequently the gate is allowed to rise only to a certain height. It is best for the regulating screws to do the service of stop claws (see the fig.) ; in that case the rise and fall of the feed gate is under control. The feeding rolls J 1 are brought into motion in the direc- tion pointed by the arrow by means of belts, the distribution of which in the machine is marked in dotted lines on the right-hand side of the plan of the roller mill (Fig. 267). . iv] FLOUR MILLING 281 The shaft M through a connecting gearing of the pulleys 5, 6, and 7 is set on bearings N. With the rising and falling of that shaft the driving belts 12, 13 and 14 are tightened and loosened. The bearings N are set on hatchet stakes n fixed in the arms of the bearings and pass through guides a 3 and a 4 of frame A. The stems are connected by joints with the upper parts of the frame n, ending in toothed racks at the top. The toothed wheels P are set on axles P 1 and engaged with the toothed racks of the stems 0, which are thus enabled to rise and fall, dragging the shaft M and the belt-pulleys with them. The motion is transmitted in the following manner : the main belt 12 drives the pulleys 1, 3 and 5, turning the grinding rolls C l and <7 3 in one direction and the shaft M in another. With the aid of belt-pulleys 6 and 7, and belts 13 and 14 running to the belt-pulleys 2 and 4, the shaft M turns the grinding rolls C 2 and <7 4 in the direction opposite to that of the rolls C l and O 3 . There is a small pulley 8 on the shaft of the roll C 2 , which drives the pulley 9 by means of a belt, one of the feed rolls J 1 , and pulley 10 set on the same shaft. The pulleys 10 and 11 are connected by a belt which drives the other feed roll. The belts connecting the pulleys 8 and 9, 10 and 11 are not shown in the drawing, but their arrange- ment is marked by dotted lines on (2) Fig. 267. On the axles K, the closer to the centre the better, there are claws KI (6) coupling with the claws j on the brushes and thus capable of raising and lowering the gates, according to the direction in which the rolls are turning. On these rolls (5) there are levers K 1 which with their weight turn the shafts in one direction ; in the other direction they are turned by means of claws I 1 1 1 on blocks L, which in moving lift the shoulders K 1 when they come in contact with those claws. By means of the rods L the rolls K turn in one direction, covering the plates. When it is desired to shut the feed gates (or plates), the blocks L are moved in such a manner that the claws Z 1 touch the shoulders K 1 , which are lifted and turn the rolls K, thus causing the plates to drop, as is shown on (5) and (6) Fig. 269. When the gates are to be opened, the rods L are moved in the opposite direction, and the shoulders K 1 with their weight turn the rolls K back, thus opening the gate. As has been mentioned above, the levers J 1 have fingers i* which enter into the claws II on the blocks L, thus lifting and lowering the gates with the same, motion that brings the rolls together and apart. To keep this action of the apparatus effective in the operation of each block separately, the fingers i 2 are so arranged in respect to the claws / that they couple only 282 FLOUR MILLING [CHAP, iv if displaced from one position to another. The rods L are so placed that their ends are slightly raised, and when during the movement of the rod from one side to the other the finger i 2 touches the claw /, the rod rises and the finger i 2 passes under the claw I and stops between that claw and the one following ; if the rod continues moving, the finger i 2 comes into contact with tne next claw I, and brings the rod to a normal position when it is stopped. When the levers J 1 are turned to one or the other side to the extreme point (Fig. 269) 5 and 7, the fingers i 2 do not touch A B FIG. 270. the claw I at all, and the rods L may be moved backwards and forwards quite independently of them. The latest model examined of the Nordyke & Marmon Co. mill is shown on Fig. 270. Here the adjustable bearings H are placed in the middle and the fixed ones are in the neighbourhood of the outer walls, and the bearings 8 of the outer rolls are so set as to allow of regulating them, and this is performed as follows : the bearings 8 have two tail- shaped arms a and 6, one of which, a, rests freely on the bolt K screwed into the arm L of the frame ; the arm b is fastened to the frame by a bolt j screwed into it. The planes of contact O of the bearing and the frame are planed to each other and determine the direction of motion of the bearing. If the bearing S is to be lifted or lowered, we loosen the FLOUR MILLING 283 CHAP. IV] bolt j and turn the bolt K to the right or to the left. When the axis of the grinding roll is set in a horizontal position, the bolt j is again tightened. The adjustable bearings H with brake are, generally speaking, constructed similarly to those of the preceding model. The levers E for throwing in are eccentrically set on the hubs of the handles A with toothed sectors, and their rolls are thrown together in the required position. The axle d runs through the hopper and is supported by bearings in brackets 3 bolted to the arms of guards of the fixed bearings for the axles of the 284 FLOUR MILLING [CHAP. IV feeding rolls. By means of a screw with a hand-wheel C, and the hand- wheel D doing service as a lock-nut, the working distance between the grinding rolls is adjusted, and the parallelity of their axes set. The bearings of the jockey shaft are lifted by a rod T which has a square thread and is brought into motion by conic gears B. The cap of the bearings of the jockey shaft is kept on by the bolts 1 and 2. The tension of the spring is regulated by the screws P. Figs. 271 and 272 illustrate the front and the back view of the mill. Fig. 272 clearly shows how the feeding rolls are driven by belt gearing. The" belt-pulleys 1 and 2 are set FIG. 273. on the axes of the feeding rolls ; on the hub of the bearing of the belt- pulley 1 is set a bracket 4 for the belt-pulley 3 : this bracket is joined with a crank mechanism 5, its crank set fast on the axle d (see Fig. 270), owing to which at the moment of throwing the rolls apart the belt-pulley 3 is drawn to the left, the belt is loosened, and the feeding discontinued. A more simplified construction of simultaneous lifting or lowering of the jockey shaft belonging to the same works is shown on Fig. 273, where the general hoop A carrying the bearings of the driving belt-pulleys is seen. The ends of the hoop rotate on journals fixed on the sides of the frame, while the middle has a ratchet stop. A Feed-Crushing Roller Mill. The feed-crushing roller mill shown in CHAP. IV] FLOUR MILLING 285 Figs. 274 and 275 is used by the Americans to reduce the cakes obtained as a by-product in oil-pressing. The rolls of such mills with pyramidal corrugations are cast in open-hearth steel and their surfaces hardened. The arrangement of this mill is very simple. The roll 1 is set in fixed bearings, the other roll, 2, is placed in adjustable bearings A, furnished with a brake of direct action. The bearings A have cylindrical arms with which they are set into the slippers B lying in parallel guides D. The cups C holding the springs are attached to the frame by bolts. The ten- FIG. 274. FIG. 275. sion of the spring is adjusted by bolts. On the reverse side of the bearings there are bolts by means of which the distance between the rolls is regu- lated. The diameters of the rolls of such mills are 300 to 350 mm., their length 600 to 800 mm., the number of revolutions of the fast roll 650, that of the slow 325, the number of powers required 15 to 25. (iii.) Roller Mills of the Fourth and Fifth Schemes. Three-High Mills. C. Kapler's mill (Fig. 276) has three grinding rolls w v w 2 and w s , placed diagonally one over the other. The hopper is divided by a partition O 2 into two chambers. In the lower part of those chambers are disposed the feeding rolls a l -a 2 , to which the gates m approach, sliding on the outside surfaces of the inclined walls of the feeder. In each gate m there is a toothed rack m 1 , coupling with the toothed wheel l on the axis I, passing through the feeder. On the end of each axis I a worm wheel n is freely set with slots q, through which the screws of the stationary stems p at the end of the axes I can pass ; with these screws the wheels n may be fixed to the stems p. The worm wheels n are coupled up with the screws o l on the transversal axis o at one enc) 286 FLOUR MILLING [CHAP, iv of the feeder ; on the ends of this axis there are hand- wheels. When both worm wheels n are fixed on the axes I and the axis o turns, both the gates m accordingly draw away from the feed rolls a l -a z and the feed- ing in this manner is regulated equally on both rolls. If it is wished to bring only one gate into operation, the worm wheel n of the other gate is disconnected with the stem p or with the axis I. On the ends of the axes of the feeding rolls a l -a 2 there are set the belt-pulleys R, through which the driving belt (see dotted lines in Fig. 3) runs. FIG. 276. On the opposite end of one of the feeding roll axes there is freely set the belt-pulley S l , which may be connected with the axis of the feed rolls by means of a toothed coupling G. The driving belt marked by a dotted line on Fig. 4 passes over the belt-pulleys S l and S 2 on the axis of the top roll W . Under the feeder two inclined plates 7 X and Y 2 are arranged. The first supplying plate is placed over the top roller W j. and from the lower edge of the plate Y 2 parallel to one side of the chamber M there runs a vertical partition e. An endless belt T 1 runs over the feeding rolls n* 1 , which have a groove-like hollow on their circumference, so that the middle part of the belt lies lower than the rims ; this belt runs parallel CHAP, iv] FLOUR MILLING 287 to the middle grinding roll W 2 beside it. The feeding rolls lie inside the pockets c 1 and c 2 , which protrude at the ends of the chamber, as shown on Fig. 4. The lower part of the pocket c 2 has an incline and forms a hopper c through which the product can flow out into the delivery hopper d 2 . The axis of the feed-roll r 1 has a conic toothed wheel g 1 engaging the conic toothed wheel g on the same axis with the belt- pulley B 1 over which runs the belt which passes likewise over the belt- pulley B on the axis of the middle grinding roll W z . The journal of the belt-pulley r 2 is joined with a screw i with the aid of which the tension of the belt T 1 may be regulated. On the outer surface of the roll W^ there rests a scraper 6 1 , on the upper part of the roller W 2 the scraper 6 2 , on the lower part another scraper & 3 , and lastly close to the side of the roll W 3 the scraper 6 4 . All those scrapers remove the product adhering to the rolls. The partition c has windows h 3 closed by doors h opening to the out- side, and fixed on joints to the upper part of the windows. On the inside these doors have V-shaped projections h 1 . When the door is opened to a position shown on Fig. 2, allowing of the insertion of one's hand through the window h 3 to get a sample of the product reduced between the upper and the middle rolls W x and TF 2 , the product falling on the plate 7 2 opens the gate h and flows down the supplying plate / to the nip of the rolls W 2 and W 3 . A door h 2 in the' wall of the box affords an access to the windows h*. The shaft of the middle roll W 2 is set in the fixed bearings of the boxes, and the shafts of the top and the bottom rolls W t and W 3 in adjustable bearings supported by levers 1 1 fixed at the points t 1 t l at the ends of the box. The rods v 2 form eccentric joints with the axle v ; the other ends of those rods rest on springs encased in the cups of the levers of the bearings t. The axle v may be turned by means of the lever w moving on the curved guide w 1 to which it may be attached by -a suitable screw. By turning the shaft v one can approach the bearings of the rolls W^ and W 3 to the middle roll W 2 or remove them from it, thus regulating the degree of fineness of the grist. G. Daverio's Three-High Mill. On Fig. 277 is given the more simple construction of G. Daverio's three-high mill. The feed B is divided into two parts, every one of which has a separate feeding mechanism. For lifting and lowering the gate JT there is the lever P, and a stop-screw with a hand- wheel C, for the more accurate feeding of the product. The feed roll of the right-hand side section supplies the stock to the working space between the upper and the middle roll, the roll on the left serves the 288 FLOUR MILLING [CHAP, iv middle- and the lower grinding rolls. The rotation is communicated to the feed-rolls by a direct and cross-belt drive from the axis of the top grinding roll to the belt -pulleys M , which may be thrown off and in by hand with a cross-head coupling H with the aid of the lever 0. The adjustable bearing for the lower grinding roll has a tail D, with a cup for the spring K. The lower roll is thrown in and out by the top lever A, with the aid of which this roll may be placed at any working distance. A more accurate setting is performed by means of a hand-wheel E. The tension of the spring is ad- ^? justed by nuts on the right- hand side of the brake rod. The top roll is thrown in and out by the lower lever A . The brake of this roll is arranged similarly to the one at the top. When this mill works in divisions the supplying plates are generally arranged as shown on Fig. 278, i.e. the product from the upper and the middle rolls passes through the isolated open- ings in the plate which directs the stock to the middle and the lower roll. Wittford's Three - High Mill The defects of the three-high mills with rolls of equal diameter lies in the fact that the middle roll, in doing double work, becomes worn more rapidly and requires a more frequent renewal of the corruga- tions. This causes a quick decrease in its diameter, an, and two adjustable rolls, D' '. Inside the frame, parallel to the rolls, there are placed three feed plates, N, N', and N". The top shelf N directs the grain flowing from the feeder into the space between the fixed top roll D and its adjustable neighbour D'. Having passed to the opposite surfaces of those rolls, the reduced grain is conducted by the plate N f to the working space between the upper adjustable roll .D' and the second fixed roll D. After this passage its flow is deflected by the plate N" to the space between the fixed bottom roll D' and then pours down as shown by arrows. The top shelf N is stationary, the other two, JV' and N", have joints below, shown in n, and* their upper edges are joined by a slewing head P with a fixed rack 0, so that when it is necessary to examine the pro- duct, the plates N' or N" may be lowered after loosening the slewing head, and the product then passes through corresponding doors into the frame, sliding down the inclined plate. 294 FLOUR MILLING [CHAP, iv (iv.) Roller Mills of the, Eighth Scheme W. Gray and R. Birkholtz's Four-Roller Mill. The roller mills of European constructions for successive passages of the eighth scheme (p. 214) represent the ordinary types of two-roller mill with the shafts of the corresponding pairs of rolls lying in a vertical plane. The number of passages is from two to four, and this process is performed in plain milling or the milling of feed stuffs. Of those mills we shall examine the American construction of W. Gray and Birkholtz, as the most original. FIG. 281. This mill is shown in Fig. 281. The rolls EG of each pair are set in fixed bearings, the other two rolls DD' in adjustable bearings with tail frames and brakes already familiar to us. The bearings have ball-arms (Sellers' type) for self-adjustment, and on the lower side they have longi- tudinal arms e 2 with which they drop into the slides D and prevent the bearings from rolling out of their seats. The bearings are held in their set positions by screws e 3 screwed into the arms e 4 which hang over the bearings. The position of e 4 is such as to allow of removing the bearing from its place, once the screw has been loosened. For this purpose the hollow is left open on one side, and its shape is such that whilst the box or the bearing CHAP. IV] FLOUR MILLING 295 has a solid stay on the lower and the outer sides, which carry the pressure of the journals, the box may be easily removed by lifting it up and out. This means of supporting the bearings has proved in general practice to be very convenient, as it affords the possibility of removing any one of the adjustable rolls, together with its bearings, at a moment's notice, without touching anything in the mill. The rolls are brought into operation by means of belts and belt-pulleys in the following manner. The jockey shaft passes through the lower part of the mill from one wall to the other, resting in bearings fixed in the frame J. One end of the shaft carries a belt-pulley i, the other end two belt- pulleys i l and i 2 . The fixed rolls B and G have belt-pulleys b and c on the same side as the belt -pulleys i l and i 2 are placed. The adjustable rolls B' and C' have belt-pulleys b' and c'. The driving belt T runs through the belt-pulley c' under the belt- pulley i of the jack-shaft and above the belt- pulley b', bringing directly into action both the adjustable rolls and the jack-shaft. From the belt-pulley i l of the jack-shaft the belt b 2 passes to the belt-pulley c and rotates the fixed bottom roll, while another belt c 2 runs to the belt- pulleys i z and b rotating the fixed top roll. For such an arrangement of the belts and belt- pulleys, it is necessary that the lower rolls should be moved aside, owing to which the belts and belt-pulleys may operate freely, occupying at the same time little space. For an accurate adjustment of the rolls, and the possibility of quickly throwing them apart and together, W. Gray's construction, already examined, has been adapted. The upper and the lower rolls are simultaneously thrown apart and together by means of a handle K fixed to the lower roll c 6 with an eccentric and connected through a stem k with the crank k l on the top roll 6 6 . For regulating the feeding of the mill, in the hopper L there is (Fig. 282) on one side a movable gate I which may be moved in a vertical direction. The bottom in the hopper is a shaking inclined toothed plate m placed above the top roll and attached to the top part of the shaking shoe M , to which, under the bottom rolls, is fixed another inclined plate m' of greater breadth. The shoe consists of two iron sideplates m 3 fixed to the edges of the feeding plates and strengthened by suitable cross pieces. FIG. 282. 296 FLOUR MILLING [CHAP, iv On the one side the shoe is supported by one or several belts m 4 attached by their upper ends to the frame ; at the front edge it is supported by one or several belts or wires m 5 also attached to the frame ; the shoe can move in a direction perpendicular to the shafts of the rolls. This motion is communicated to it by means of two eccentric drives m 6 -m 7 from the general axle, receiving the motion with the aid of a belt-pulley set on it, and connected by a belt m 8 with the pulley on the axle of the roll C' . The feeding top shoe passes under the flap valve of the hopper and con- veys the stock from the bottom part of the hopper to the fixed supplying plate n, which directs it to the working space of the rolls. Having passed through the top rolls the stock falls on the lower feeding plate w' which directs its course to the second pair of rolls. To prevent the product from falling in behind the shoe, a piece of lining I" is attached to the back wall. 7. Transmission of Motion to the Rolls Toothed Gearing. We have already examined the details of the roller mills having a special function the feeding and the adjustment mechan- isms, for instance. Now we must note the details of a general character, which are of no less importance than the feeding and the brake devices. Of the details of a general character, the parts of machinery trans- mitting the motion are the most important. In our general review of roller mills we have noted that there are two types of gearing : the toothed gearing adopted by the European engineers and partly in American mills for rough grinding (the reduction of forage products), and the belt- gearing employed by the Americans only. Here we are speaking of transmitting the motion from roll to roll. To communicate motion to the feeding rolls, the European engineers generally use combined gearing, the flexible and the toothed, while the Americans employ only the former in their mills of the latest type. Consider the toothed gearing given in Fig. 283 (1, 2 and 3). The first one, the simplest, is used for mills of small capacity, and in cases where the degree of evenness plays no great part. The second type of toothed gearing represents doubled chain wheels with a chess-board-like disposition of the teeth to lessen vibration in working. It has been adopted by some of the American works. The ordinary toothed gearing with a helical-like disposition of the teeth, shown on 3, has been adopted by almost all works. In this last gearing the wheels are provided with CHAP, iv] FLOUR MILLING 297 ring lubrication, used by Seck's works and by the American works of Wolf (both patents were claimed simultaneously). In speaking of the merits of toothed gearing the accuracy it attains in the ratio of gearing must be pointed out. But the grave defect of the toothed gearings in the roller mills, where the distance between the FIG. 283. shafts has to be altered, is the decreased efficiency when in operation and the shafts have to be brought nearer to each other in proportion to the wear of the rolls. The necessity of altering the distance between the axles of the gears demands an outline of the teeth according with the involute of the circle. Under our conditions, however, the axes of the wheels, in the most favourable circumstances, may only be brought 10 mm. nearer than the normal. Consequently the wear 298 FLOUR MILLING [CHAP, iv and renewal of the working surfaces may go only 5 mm. deep for each roll, otherwise the toothed gearing will be operating at a great disadvan- tage. Thus, if each of the rolls has worn 5 mm., new gear wheels with smaller diameters have to be installed, otherwise the gear will cause a great waste of power. In Russian mills this is generally not taken into con- sideration, and economising in new pinions the work is performed till the teeth break, regardless of the fact that more is lost in the expenditure of energy, and the fact that the motor has to be overloaded without increasing the capacity of the mills is regarded with surprise. Thus the expediency of the toothed gearing may be acknowledged, but, when the rolls are in working position, the axes of the pinions can only at most be brought nearer together by about 10 mm. If the distance between them is to be still further decreased, the pinions must be changed. Belt-gearing. Several of the belt-gearing con- structions were dealt with when describing the makes of American mills. The shafts of the driving belt-pulleys are usually attached to the frame. But often, to simplify the construction of the mill, they are stationed outside and apart, as shown in Fig. 284. Here B is the axle of the shafting, C the jockey- shaft, 1 the driving belt to the fast rolls, and 2 to the slow. The tension of the belt is adjusted by toothed gears A, and the supplementary regula- tion of tension of the belts to the slow rolls is brought about by lowering or raising the bearing by screws 3. Some twenty years ago, when the European engineers attempted to introduce belt-gearing, the principal argument against it was the impossi- bility of maintaining an accurate number of revolutions of the rolls, owing to the belt slipping. The work of the American mills of the contemporary makes, however, proved that this argument had no solid ground under it. The. slipping of the belt within such limits, as to affect the accuracy of the transmitted number of revolutions of the FIG. 284. CHAP. IV] FLOUR MILLING 299 rolls, is possible when the belt has stretched and its tension consequently has slackened. But the American construction of belt-drives obviates this defect by regulating the tension. The presence of an insignificant slipping motion cannot be denied, but, as we have seen, the ratio of velocities of the fast and the slow rolls for every break and reduction passage is within certain limits ; while the influence of the slipping is so in- significant, as shown by practice in America, that these limits are never exceeded. The advantages the American belt-driving has as against toothed gearing are very material, viz. : (1) Noiseless and easy run of the mill. (2) No relacing of the belt in case it becomes extended is required, the tension being regulated by a jockey-pulley. (3) The reserve strength of the belt being sufficiently great, the capacity of each mill separately may be increased by 10 to 20 per cent, by a corresponding increase in the tension of the belt. The latter is very important, as it permits overloading the mill FlGt 2 85. without any injurious effect to the quality of the work, which cannot be attained on European roller mills, as the tension of the gear-belt from the shafting axle to the mill cannot be altered without relacing the belt. In some mills with belt-gearing each roll has a separate belt-pulley, as shown in Fig. 285. The necessity of compactly disposing the belt-gearing leads to setting the fast rolls asymmetrically. 8. Capacity of Roller Mills Useful Work of Roller Mills. In examining the action of the work- ing organs in the roller mills, we saw that a rather complicated process of cutting the grain on break rolls or chipping by friction of the particles on reduction rolls is performed. Therefore the useful work of the roller mill may be defined only by experiment. However, the attempts to evolve theoretic formulae of useful work which partly explain the pro- cess of milling, and partly may have a practical effect through the intro- duction of practical coefficients into them, should receive due attention. 300 FLOUH MILLING [CHAI*. IV The first and sole attempt to give theoretic formulae of the useful work of the roller mills was made by Professor Afanasyeff , l and was based on his experiments on the resistance of the grain to pressure, performed at the mechanical laboratory of the Technological Institute, St. Peters- burg. Repeated experiments with the resistance to pressure of grains (200 grains or more each time) of a normal moisture content and of approxi- mately equal size, placed in between steel plates under a press, produced the following results : TABLE XXV Pressure in Klgs. 1000 2000 3000 4000 5000 Distance between the plates | (thickness of the grain) in ! 2-723 2-395 2-068 1-753 1-542 1-391 mm. J Compression in successive) loadings / ... 0-328 0-327 0-315 0-211 0-151 This table shows that the absolute quantity of elastic pressure is equal to one-third of the size of the gram. The full loading up to the limits of elasticity of the grain fluctuated between 10 and 20 klg. to each grain in proportion to its moisture content, the less limit referring to the grain with more moisture. This corresponds to the loading of 50 to 100 klg. to 1 square cm. In defining the law of changing the pressure of the rolls on the grain or particles of it, Professor Afanasyeff reasoned in the following manner : supposing we have two rolls of equal radii r (Fig. 286) with the distance between the working surfaces and the size of the stock to be treated . Suppose that the pressure of the rolls upon the stock on the route it travels from n to n l is proportionate to its compression. If we mark the quantity of the pressing forces along the centre line P, and Q is some intermediate position of the stock u-u, then Q is defined from the proportion : Q:P=su:qn 1 (l), FIG. 286. 1 Flour Mills, St. Petersburg, 1883. CHAP, iv] FLOUR MILLING 301 for the pressures, when the compression is elastic, are proportional to the quantities of compression (2 su and 2qn 1 ) being pressed from two sides. But since while in the drawing =2r-|-$ 2r cos a =2r(l cos a), having performed the reductions and the substitution 1 cos a =2 sin 2 ^, we obtain : qn 1 =2r sin 2 ~. A From the same drawing we obtain the signification of su for the inter- mediate position of the stock : su = 2r sin 2 ^ 2r sin 2 ^. By substituting these senses into the formula (1) we obtain : sin 2 - sin 2 - The angles a and 6 being very small, with a slight inaccuracy we may regard the sines as equal to the circular measure of these angles. Then we have : -* That is the pressure of a unit of area of the roll, whereas we are to find the pressure from n to % so as to know the full work of the pressure. If the element uu of the surface of the roll corresponds to the angle do, and the dimensions uu l on the generating circle of the cylinder is I, the elementary pressure will be : ^de . ; . (2). The full pressure R is obtained when we take the integral of this term from a to o. The point of application of this resultant pressure is obtained on our defining the moment of action of this force. The moment of action dQ is : 302 FLOUR MILLING [CHAP, iv for up=r sin 6 = rO, the 6 being small. By integrating this term, we arrive at the moment of the compressing force R in respect to the axis of the roll : On dividing (4) by (3) we obtain the shoulder of the resultant of the pressures, by which we shall define the point of application of force R. This shoulder 77 will be : rj=\ra. If we distribute these R directed parallel to the plane of the axes, over the tangent and the radius (Fig. 287), we shall obtain : 3 _3, ? p p 3 3~ 8 a- 8 ^a; X 2 - >Sga- g ^, ^ because the angles a being small, we may accept o o O sin-a=-aand cos 5 a=l. 1 o O o Then the motive power of each roll, imparting velocity to the product during the period from the null sense to the greatest v, equal to the rotating velocity of the rolls, will be But this moment is so insignificant that we may ignore it and con- sider the velocity of motion of the product between the rolls' from the beginning of its ingress to its exit to be even and equal to the rotary velocity of the rolls. These considerations prevent our accepting as correct Professor AfanasyefTs inference, who regards S=fR 2 Ri as the motive power and further defines the work of the roller mills as the work of this force 8. The work of the forces fR 2 must be defined by taking their projection upon the direction of the motion of the product, i.e. upon the vertical plane. Then the sense of the motive power will be : Professor Afanasy eft's experiments have shown that P=4*5^, where d means the thickness of a grain of wheat, and p the relative CHAP, iv] FLOUR MILLING 303 compression equal to ^2. Availing himself of Professor AfanasyefFs experimental data (P=k5- the average for dry grain) and introducing a correction with regard to the incomplete utilisation of the working surface of the rolls, Professor Zworykin suggests the following term for the efficiency of the rolls : Plra Plra*v where r denotes a k-ih part of the rolls loaded with product on the arch K nn-i, and 7~the A-j-th part of rolls over their length. #1 We must acknowledge this correction to be just, as the working part of the rolls is not fully occupied with product. Then, knowing that we introduce those terms into T. Thus we obtain : ' 0-25 to In this formula T is expressed in klgr.-mtrs., I in mm., and v in metres per second. This formula leads Professor Zworykin to the conclusion that the consumption of useful work for crushing the product fed in at a certain flow does not depend on the diameter of the rolls, but solely on its circumferential velocity and length. According to Professor Kick's experiments, who was testing soft wheat the grains of which were 6 to 7 mm. long and 3*5 mm. thick, the force crushing the grain while it is moving over 1 mm. of ground is 10 klg. Consequently, the work of crushing the grain ought to be 0*005 klg.- mtr. per second. To define the consumption of useful work according to the* data of Professor Kick, we must know the number of grains crushed per second and multiply it by 0*005. If the working surface of the roll running by per second should be given in square mm., it is equal to 1000 Iv, The 304 FLOUR MILLING [CHAP, iv area of the grain is 6' 5x3* 5 mm. Then, with Professor Zworykin's correction, we obtain : 0-005. 1000 lv_ 0'22 Iv ~~6-5x3'5fc. ki~~ kk 1 ' which closely resembles the results produced by Professor Afanasyeff's investigations. Consumption of Useful Work in Grinding. The considerations of Professors Afanasyeff and Zworykin we have adduced have a purely theoretical value. Those formulae elucidate the general character of the phenomenon but cannot be adapted to define the useful work of the roller mills, being deduced on the supposition that the rolls have equal velocities, which never happens in reality. The equal velocities of the rolls result in the crushing of the stock, whereas a cutting or chipping of the grain or particles of it is observed when the velocities are different. Thus, to define the useful work in reducing it is necessary to know the resistance to cutting, which requires an immediate experimenting on the cutting of grain. By this reason, having no other data, Professor Zworykin suggests making use of Professor Kick's experiments and evolves a series of formulae defining the useful work. According to Professor Kick's researches the resistance to the cutting of the grain increases from to 9 klg. on the stretch of 0'5 mm. ; there- fore the cutting work for one grain is equal to 0*00225 klg.-mtr. Ac- cepting for the break rolls the circular pitch of the corrugation to be t, the velocity of the fast roll v, and its length I, we obtain that the number of grains passing between the rolls per second is 1000 Iv As the circular pitch of the corrugation t must correspond to the dimensions of the stock cut, t = k l d = k 1 3'5, consequently the useful work T for corrugated rolls will be expressed thus : For smooth roller mills the useful work will be expressed by the formula : "' These formulae may become very valuable, if through the immediate definitions of the useful work of the roller mills with different I, v, and t CHAP, iv] KLOUR MILLING 305 (t is needed for corrugated rolls) we find by experiment the coefficient 1 fCiC i Theoretical Capacity of Roller Mitts. Proceeding from the foregoing inferences, we may mention several considerations regarding the theo- retical capacity of roller mills. If the thickness of the sheet of product flowing into the nip of the rolls be mark d, then its volume passing in between the working surfaces is (with the same denominations of I, v, k, and k as before) : 1000 I . v . d V = kk 1 Accepting the specific gravity of the stock to be 0*0000006 klg., we obtain the weight Q: . 0-0000006=-^^ (8). Thus we see that the capacity of a roller mill is a rather complicated function of five variables. Given the length of the rolls and the circum- ferential velocity of the fast roll, we may accept Iv for this mill as a con- stant quantity. Then the problem of defining the capacity is simplified, for the capacity will depend on 6, k and k v These variables depend on the kind of milling, which determines what their respective values are to be. But it is impossible to give any limiting values for TT-, because the milling diagrams are very variously arranged. Since we have no serious experimental data for jj- as yet, we are compelled to make use of the A/n/i data of capacities of roller mills as given by the works, with corrections founded on general observations of the capacity of these machines at modern mills. Practical Data of the Capacity of Roller Mills. The capacities of break and reduction roller mills given below were taken from the data of European works tested on the plants in Russian mills, on milling systems, which are duly mentioned in the table. Naturally the factory data fairly accurately coincided with the capacities observed at the mills, for the builders of these mills more or less strictly adhered to their data. Very often, however, the capacity of one or another mill exceeded the guarantees of reliable works ; this is always the result of overloading the machines at the expense of the quality of the work, IT 306 FLOUR MILLING [CHAP, iv X PQ ^O O ^^ 8^^ O O O 1 o o ^^ *o ^ o co t- i>- I Hill III 8 O O O O O O O O O O 8888 88|| l> O5 (M i-i rH c?q O O 1 O ^D O 1 J>* 00 O5 G 1 ^ G*l FLOUR MILLING 307 CHAP. IV] In the Table XXVI given opposite the average capacity and power- consumption are taken from the factory data. The data of that table, regarding the breaking process (corrugated rolls), refers to the first passage or break. The capacity of the smooth rolls refers to the reduction of coarse and fine middlings, and is to be taken at 10 to 15 per cent, less when the product treated is low grade middlings (reduction of the offals). We must say that the works state the capacity of their roller mills with great discretion, allowing a reserve of 20 to 25 per cent, sometimes, in comparison to the capacity attainable in practice. But we repeat, it must be borne in mind, that a capacity forced above the normal (some- times reaching 35 per cent.) is only injurious to the work. Many cases are known in which the mills compelled the steam engine to work with an overload of almost 50 per cent, without any allowance for the steam capacity of the boilers. Those mills ground 30 to 35 per cent, over the quantity of grain they were calculated to reduce, and the millers considered themselves to be the gainers. In their ignorance, however, they did not understand that by working with damp steam they almost doubled the expenses of pro- duction, not to mention the fact that the flour grew worse, which they, of course, would never admit. The above table affording us no possibility of reckoning out the capacity of the roller mills for the various breaks, we must consult the following table, in which the working length of the rolls for different grinding systems and successive breaks are given : TABLE XXVII LENGTH OF ROLLS FOB ONE SACK OF STOCK REDUCED PER TWENTY-FOUR HOURS BREAK. I. II. III. IV. V. VI. VII. VIII. High grinding . a s a J3 2-62-3-00 3-75-4-12 3-75-4-12 2-62-3-37 2-62-3-00 2-25-2-62 2-25-2-62 1-88-2-25 Medium (semi-j cj* high) grinding/ '' ^ 3-00-3-15 4-50-4-62 4-50-4-62 3 -00-3 -75^2 -62-3 -00 2-25-2-62 Low grinding High rye grind- ) ing . . . f Ilebreakor scratch Si 6-00-7-50 4-12-5-37 3-75-412 4-62-5-25 4-50-4-62 337-3-75 3-37-3-75 3-12-3-75 3-00-3-37 3-37-3-75 3-00-3-12 2-40-2-62 2-62-3-00 2-47-2-62 i (Smoot rolls 1-87 per sack i crushing -2-25fmi. The data of this table are average quantities for Russian mills working on hard and soft wheats. The smaller figures refer to the hard grain, the greater to the soft. 308 FLOUR MILLING [CHAP, iv Baumgartner offers the following capacity for break and various roller mills, which is considerably below the data of the works : TABLE XXVIII CAPACITY OF ROLLER MILLS ACCORDING TO BAUMGARTNER 1. Crushing Mills (Quetschstiihle) Diameter of rolls in mm. Capacity for 100 mm. of | length in klg. . . ( D mm. Q klg. t 250 200 300 250 350 310 400 360 450 400 500 450 2. Rolls for High Break, Hochschrot (Brechstuhle) Z> = 220 mm., Q = 250 klg. (one pair of rolls). D = 250 mm., Q = 250 klg. (three-roller mill). 3. Break Rolls (Schrotstiihle) Diameter of Rolls D mm. 220 250 300 350 400 450 Qklg. Wheat plain grinding 80 100 120 140 150 for semi-high grinding 90 110 130 150 100 mm. ,, high grinding ... 125 140 165 of length. Rye plain grinding .... ... 70 ..85 95 105 4. Porcelain Rolls (Porzellansttihle) Diameter of Rolls D mm. 220 300 350 Q klg. for j Reduction of Coarse Middlings . 25 45 65 100 mm. of length. J Fine ->, 18 30 45 5. Smooth Cast-iron Rolls (Hartguss-Glattstiihle) l_ Diameter of Rolls D mm. 220 250 300 350 1 400 1 Q klg. for } Reduction of Coarse Middlings ; I 100 mm. 45 55 70 85 100 -' of length. J Fine 30 40 50 60 70 FLOUR MILLING 309 CHAP. IV] It is to be regretted that Baumgartner does not mention the origin of these tables, which raise some doubts in our minds. We must re- mark, by the way, that in modern practice rolls of such diameters as 450 to 500 mm. are not known. By putting our data in the form of capacities to 1 cm. or 1 inch for the whole break process, we obtain the following table : TABLE XXIX CAPACITY TO 1 CM. OR 1 INCH PER TWENTY-FOUR HOURS FOR THE WHOLE BREAK PROCESS IN LBS. Kind of Grinding. To 1 cm. of Length of the Rolls. To 1 inch of Length of the Rolls. High wheat grinding .... 111-55-128-79 278-87-321-98 Medium 5J JJ .... 128-62-140-92 321-62-352-30 Low 5) .... 138-27-161-28 345-63-403-20 Rebreak or scratch rolls . Depends on the number of rebreaks High rye grinding .... 120-11-141-12 300-28-352-80 If we compare the capacities reckoned out for the first break with the factory data, we find that our table shows 15 to 17 per cent, more than is given by the works. In calculating the dimensions of the rolls it is better to follow this table, as its data define a perfectly normal capacity of the rolls, without any superfluous reserve and without injurious overloading of the machine. In computing the capacities of rolls for high rye milling we have kept in mind the fact that in the first break the grain treated has been previously split down its crease, in passing through smooth crushing rolls the capacity of which, as shown in the table, is defined at 1*87 to 2*25 mm. to one sack of rye per twenty-four hours. When calculating the sizes of corrugated rolls, we must bear it in mind that their capacity for one and the same passage increases with the diameter, remembering at the same time that a greater amount of power is consumed. In selecting corrugated rolls for high and medium grind- ing, the diameter of 220 mm. may be decided upon if their length does not 310 FLOUR MILLING [CHAP, iv exceed 1000 mm. Should the capacity of the mill, however, require rolls longer than 1000 mm., then the diameter employed ought to be 250 mm. For low grinding rolls 250 to 300 mm. in diameter should be used, and 300 to 350 mm. for single and high rye grinding. Example of Calculation. To illustrate clearly the use of the table for calculating the dimensions of the rolls, according to the capacity given of the mill, we shall take one example. We are required to calculate the dimensions of the break rolls for a wheat mill on a high grinding system yielding 400 sacks per day. Sup- posing the wheat = 450 to 700 mm., and L 1000 to 2500 mm. 10. Detachers In grinding the fine and coarse middlings, when it is necessary to impart strong pressure to the smooth rolls, the crushing of a certain per- centage of stock to flakes is inevitable the meal flakes particularly often, when the rolls are badly fed and do not receive an even sheet of product, but narrow streams, owing to the damp product sticking to the feed plates and forming knots. The meal flakes thus formed and compressed fast may pass to the sieve in that shape and be removed as overtails, if no steps are taken towards loosening them. Such flakes are loosened in detachers, which receive the product on its leaving the rolls and break the flakes down to meal. There are three types of detachers brush, pin, and screw detachers. Brush-detacher. The ordinary construction of the brush-detacher is shown in Fig. 289. The cast-iron chamber A has a timber or iron cover B with an opening D for the passage of the product down arrow 8. Inside the chamber, down its whole length, there is a fibre brush C running at 350 to 1200 revolutions. The stock passes in between the brush and the wire sieve E, where the meal flakes are reduced to flour. Part of the flour 314 FLOUR MILLING [CHAP, iv passes through the sieve and part is flung by the brush over the sieve as indicated by arrows S^ The distance between the brush and the sieve is regulated with nuts F by means of a simple link mechanism. The ends G of the screws, passing through openings in the frame, serve as guides. FIG. 289. La/oris Pin-detacher. Fig. 290 represents a double pin-detacher from the French works of F. Lafon (Tours). The product moves as shown by arrows 8 and falls into conic sieve chambers A. Here it is caught up by the pins which break down the flakes. The pins are fixed on the hub (7, which is attached to the axle B with bolts a. The covers D are cast in one block with the bearings for the journals of the axle. FIG, 290, The loosened product flows partly through the sieve and partly through the outlet down arrow 8^ The number of revolutions of the pin drum is 1100 to 1750 per minute. The bearings are ring-lubricated. SecVs Worm-detacher. Both the brush and the pin-detachers answer their purpose that of breaking down the flakes. But both again have CHAP. IV] FLOUR MILLING 315 Inlet the defect that they reduce the branny particles, owing to which the offal cannot be separated off on the dresser and give a darker colouring to the meal. Besides that, Lafon's detacher, operating by impact, has all the defects of the disintegrator already discussed. These inconveniences are done away with in the new type of a detacher, shown on Fig. 291. Its main part is a short worm, rotating with the velo- city of 250 revolutions per minute in a cylindric casing with a small dead space. This worm conveys the stock to the outlet of the machine, and the stock passes between the valve d and the roll b, which are brought into motion by the belt-pulley a with the aid of a worm gear, not shown in the draw- ing. The force of pressure of the valve upon the passage of the stock is adjusted by means of a spiral spring e and a screw g. For cleaning the roll there is a scraper /. In a detacher arranged in this manner the stock is well stirred and its particles are rigorously rubbed against each other in the space between the casing outlet, the valve, and the roll. The flakes are very thoroughly broken down, while the mealy particles are but slightly reduced during the operation. In this way all the flakes are triturated, and the particles of flour, bran, and germ separated from the middlings, after which the stock is easily and very satisfactorily dressed. Its compactness is another good quality of this machine for reducing flakes of meal. This detacher may be placed between the roller mill and the elevator, or between the elevator and the bolting machine. Outlet FIG. 291. CHAPTER V GRADING THE PRODUCT ACCORDING TO SIZE I SIFTING THE PRODUCT Purpose of Sifting. The character of the process of grain-reduction and its nature inevitably result in a product of various shapes and sizes. The break process gives us particles of flour as well as a series of middlings of various sizes. But this product can only undergo a further / and final treatment after it has been graded according to size. In fact the distance between the working surfaces of the reduction machines, millstones, or roller mills at any one period of the operation is quite definite, and calculated to yield a product of a certain size. Con- sequently, if 'the product is of various sizes, a part of it, being smaller in size than the distance between the working surfaces, will pass between them untouched. If, however, we set the working surfaces at a distance smaller than the least-sized particles, the large grains will be too violently broken down, reduced to flour, and will form flakes. Now, this is injurious to the quality of the flour, to say nothing of the unproductive consumption of power incurred by the strong pressure of the working surfaces. Hence it is clear that if the work of the reducing machines is to be satisfactory, after every passage through the breaks or reduc- tions it is necessary for the particles of the product to be graded according to size. In recommending a series of successive reduction machines, we had the complex grinding systems in view, in which the necessity of sifting is clearly demonstrable. But it is likewise evident that sifting is just as indispensable in plain milling, in spite of the grain being reduced to meal in one passage through the grinding machine. The fact is, that however great be the pressure of the working surfaces upon the grain, the offals, being more elastic than the kernel, offer greater resistance to breakage, and part of them remains in the shape of bran. Sifting is also i /necessary for extracting the bran from the mass of meal 316 CHAP, vj FLOUR MILLING 317 Thus, sifting is necessary (1) in the complex milling process, to pre- pare the intermediate products for further treatment, by grading them according to size ; (2) in plain (single) milling, to separate the branny particles from the flour. The bran must be likewise sifted off from the flour in the final stages of milling ; in the break process at the last break and rebreak, and in the reduction process at the final reduction of the dark branny particles of grain. Working Surfaces. For grading the intermediate products of milling and for separating the bran from the flour, bolting surfaces are used. We are already acquainted with the principle of action of, these surfaces, having met it in the process of separating the large and small impurities from the grain, where we saw that all the sieves tail over the large particles as refuse, while the small particles are bolted through the sifting meshes. From the same grain cleaning department we know the shapes of the sifting working surfaces and the character of their motion. For grading the reduced particles of grain we have prismatic, cylindric, and flat sieves, similar to those employed in machines for grain cleaning. But while the working surfaces in the bolting machines for grain consist of sieves of solid sheet-iron plates or of metal cloths, owing to the greater resistance these materials offer to wear, in grading the products of milling metal cloths are used only for the coarser particles. The rest of the product in the meantime is bolted on silk sieves, though many attempts are being made at present to substitute metal cloth for silk. If we take home manufacture into consideration, then the hair-cloth (mostly horse-hair) used for sieves for home sifting should be mentioned. We may say that the hair-cloth, used from the remotest time for sifting, is better than silk or wire, as it is hydroscopic and consequently never swells or grows rusty. Further, it is sufficiently strong to stand a long period of work. But the uneven size of the hairs, their unequal diameter and length, does not allow this material to be used for factory- made sieves. It was comparatively but a short time ago that woollen cloth of comb- yarn was largely used on plain short system mills owing to its cheapness. But the nappiness of the woollen threads rendered the sifting imperfect, reducing the quality and the quantity of the work. Metal Cloths. As regards solidity and durability, metal sieves are the best. But their essential defect is the liability to rust, which very rapidly destroys the sieves working in unfavourable, that is damp, conditions. 318 FLOUR MILLING [CHAP, v We must admit, however, that this defect only refers to iron sieves. Steel is more rust-resistant, while phosphor-bronze cloths excel even steel in that respect. Besides iron, steel, and bronze, the wire of the bolting surface is also made of pure copper. But copper sieves cannot be recommended, because that metal gives a poisonous oxide when the sieve works in damp air. Though metal sieves for bolting fine middlings and meal have already made their appearance on the market, they have not found their way into the ranks of the machines generally used in mills, being very expensive. When it is desired to employ metal sieves for bolting fine middlings and flour, phosphor-bronze cloths or of other rust -resistant copper com- binations should be taken. In using metal sieves we must remember that, owing to the high heat -conductivity, the moisture from the raw product precipitates upon the metal sieve (the dew phenomenon), which is dangerous, for the reason that the moistened parts of the sieve im- mediately become blinded with starchy paste and the sifting will stop. For this reason bolting machines with metal sieves should be subjected to an energetic exhaust. Silk Sieves. A tissue of white or yellow raw silk, comparatively cheap, durable, and scarcely at all hygroscopic, is very successfully adopted, where metal sieves cannot be employed. Good silk cloths, prepared of pure silk threads, are designated by the kind of their interlacing and also, like those of metal, by numbers, for products of different sizes. In making the choice of the cloth particular attention should be paid to the purity of the silk. Being an expensive material, it is often adulterated. Owing to finishing, silk of low quality often becomes firm, smooth, and glossy, i.e. possesses in its outward appearance all the good qualities of sterling cloth. In such a case even an experienced eye will not be able to distinguish it from good stuff. Finished silk, however, is very hygroscopic, and swells after absorbing a small quantity of moisture on being held a short time between slightly dampened fingers. This silk absorbs the moisture of the evaporating product, swells, and causes the meshes of the tissue to contract. The flour, turning to paste on the damp sieve, blinds it in the end and it stops working. The finishing of bad silk, 1 i.e. imparting to its threads the firmness and glossiness of good material, is done chiefly by means of starch (coarse adulteration) and by means of Arabian resin (a finer adulteration). The 1 Pr, P. Hermann, Colaric Textile Chemical Analysis, FLOUR MILLING 319 CHAP, v] adulteration of the silk may be detected by immersing the sample to be tested into pure or an 80 per cent, solution of alcohol, shaking it two or three minutes (half a glass of alcohol solution and a sample of one- sixteenth of a foolscap may be taken), and then letting the solution settle for a half to three-quarters of an hour. If the silk is finished with starch, then a white, loose sediment will remain in the glass ; if resin has been used for finishing we obtain a white turbidness, white flakes, or a white gelatinous sediment, according to the quantity of finishing stuff. * The silk sieves have two kinds of texture of their threads, linen and gauze texture. The linen texture shown on Fig. 292 is an ordinary cloth with the threads of the warp a and the woof b lying crosswise. The gauze texture (Fig. 293) differs from the linen in that its warp consists of two threads, a and 6, one of them passing under the woof c, the other over it. In between the warps those threads cross each other. The gauze bolting cloth is stronger and more durable as regards the even size of the sieve meshes (during cleaning, or in mounting). But the me.shes of the gauze tissues are less regular than in the cloth of the linen texture. To make the shape of the meshes in the linen texture cloths more stable, threads of greater thickness used to be woven into the tissue 1J to 2 cm. distant from each other, to impart more firmness to the cloth. But this was of little use, as at the same time it reduced the useful working area of the cloth, and made the cloth more expensive. These attempts were dis- continued some twenty years ago, but now they seem already to be forgotten, and such cloths have again appeared on the market. 1 Modern technics of cloth manufacture produce a quite satisfactory silk tissue of linen texture, which very firmly resists displacement of the meshes, even when cleaned with a brush. It is only necessary to use the material of good factories, and beware of adulterated silk. A good silk cloth serves for three (on coarse and sharp stock) to six years (on fine and soft stock). In choosing the cloth metal or silk one should see that the threads 1 The " Carre " cloths. The wear-resistancy depends not on the increase in weight or the solidity of the sieve caused by the thick threads, but on the standard quality of all the threads, FIG. 292. FIG. 293. 320 FLOUR MILLING [CHAP, v are of equal thickness and the meshes of equal dimensions. Only such a sieve gives throughs or overtails equal in size. Any rough unevenness of the threads and an irregular yarn strike one on the most superficial examination of the cloth. But a somewhat inferior tissue may be told from good stuff only with the assistance of a particular kind of lense shown on Fig. 294. This lense consists of two metal plates A and B folding up on a third plate, the stand C. The plate A has a square hole in it of J to 1 inch, in the plate B the lens L is set. Before inspecting the cloth it is laid on smooth black or dark paper, and then the lense is placed as shown in the drawing. In examining through the lense the square piece of the cloth framed in the square hole through the plate A , it is easy to notice the regu- larity or irregularity of the threads and the meshes, and to count them to test the number of the cloth. To examine the silk more accurately it must be inspected through the lens in several places. Numeration of the Cloths. With the numeration of the metal sieves we become ac- quainted in the part treating FJQ. 294. f grain-cleaning. As regards the numeration of silk cloths, here we also have no definite fixed international standard. Silk being used for sifting flour and grading the coarse and fine middlings according to size, numeration has been correspondingly established for the flour and the middlings cloths separately. In addi- tion there is the Swiss and the French numeration of the cloths of both kinds. Further, the numeration of the flour-cloths differs from that of the middlings cloths. Almost all European works (except the French) have accepted the Zurich numeration of flour silks, and the Swiss for middlings ; the same numeration is accepted in America, where the American Bolting Cloth Co. in St. Louis is considered to be the best factory. The quality of the silks considerably influences their numeration, which explains why a different numeration has been adopted for middlings, a coarser product requiring a stronger tissue. In respect to their strength the cloths are divided into five kinds ; CHAP. V] FLOUR MILLING 321 for reels. and centrif ls< (1) Plain cloths (Prima) (2) Heavy cloths (Extra) . . f (3) Double heavy (Double Extra). ) * (4) Treble heavy (Triple Extra) . J (5) Middlings cloths (Gazes a Gruaux). Of these five kinds of cloths those for middlings are the most dense (thicker threads). The plain cloths (Prima) have the numbers : 0000, 000, 00, 0, 1, 2, 3 up to 20, and at the American factories up to No. 25. In most cases, however, cloths over No. 17 are not manufactured. Before passing on to the further characteristics and comparison of silks, we give the numeration, number of threads, the number and size of the meshes in the Prima sieves (Swiss silks). TABLE XXX Silk No. Number of Threads to 1 cm. Number of Meshes to 1 square cm. Dimensions in mm. of each side of the Meshes. Silk No. Number of Threads to 1 cm. Number of Meshes to 1 square cm. Dimensions in mm. of each side of the Meshes. 0000 7 49 1-43 9 38J 1470 0-26 000 9 81 l;li 10 43 1844 0-23 00 Hi 133 0-87 11 46 2079 0-22 15 222 0-67 12 49J 2436 0-20 1 19 369 0-53 13 51 2591 0-19 2 21| 460 0-46 14 55 2996 0-18 3 23 529 0-43 15 59 3481 0-17 4 24i 602 0-41 16 62 3844 0-16 5 26 680 0-38 17 64 4096 0-153 6 29. 848 0-35 18 66 4290 0-151 7 32 1037 0-31 19 67 4422 0-149 8 34 1136 0-29 20 68 4624 0-145 Of these cloths Nos. 0000 to 4 give large and small middlings as throughs, Nos. 5 to 7 dunst or coarse flour, while Nos. 8 to 20 give finished flour. In practice, however, the number of silk numbers is considerably limited, as we shall see when studying the diagrams of mills. The heavy cloths (Extra) are manufactured for fine middlings and flour, and have twelve numbers from 6 to 17 inclusively. The cloths of double density (Double Extra) have three numbers less than the Prima, from No. 0000 to No. 17. x 322 FLOUR MILLING [CHAP, v The triple heavy silks (Triple Extra) like those of the double, are used only for fine middlings and flour, from No. 7 to No. 15. When denoting these four types of cloth, they are marked in the following manner (we take the flour silk No. 12 for example) : Prima 12. Extra 12 X. Double Extra 12 XX. Triple Extra 12 XXX. With these crosses the corresponding silks should be marked in draw- ing the milling diagrams. . < The middlings sieves, applied in purifiers, in the Swiss numeration are characterised in the following table ; TABLE XXXI Number Number of Dimensions in Number Number of Dimensions in Cloth No. of Threads Meshes to mm. of each side Cloth No. of Threads Meshes to mm. of each side to 1 cm. 1 square cm. of the Meshes. to 1 cm. 1 square cm. of the Meshes. 14 51 28 82 44 17 285 0-59 16 6 37 66 46 174 308 0-67 18 7 48 43 48 18J 339 0-55 20 74 58 33 50 19 369 0-52 22 84 71 18 52 20 398 0-50 24 9 82 Ml 54 21 429 0-48 26 10 99 1-00 56 214 460 0-46 28 11 116 0-90 58 221 498 0-44 30 Hi 132 0-87 60 23 529 0-43 32 12 150 0-83 62 24 565 0-42 34 13 171 0-77 64 24J 602 0-41 36 14 190 0-71 66 25J 640 0-39 38 144 213 0-61 68 26 680 0-38 40 154 239 0-64 70 27 720 0-37 42 16 258 0-61 72 28 804 0-36 In their density the middlings sieves correspond to the Triple Extra. For grading the middlings cloths from Table XXXI should be em- ployed, because the sharp product wears out the lighter cloths more rapidly. But sometimes the use of the Prima cloths (Table XXX) is preferable; because they are cheaper. For this reason we give the table of parallel numbers of the Prima and the middlings cloths (Table XXXII). CHAP. V] FLOUR MILLING TABLE XXXII 323 Prinia Middlings Nos. Nos. Prima Nos. Middlings Nos. Prima Nos. Middlings Nos. Prima Nos. Middlings Nos. 14 16 30 1 42 44 3 56 58 0000 18 32 46 4 60 20 34 48 62 22 36 2 50 5 64 00 24 38 52 66 26 40 54 7 68 The French sieves are mostly prepared of linen texture, and their numeration is totally different to the generally accepted Swiss numeration. The next table gives an approximate comparison of these two numera- tions (Table XXXIII) with the Prima cloths. TABLE XXXIII Prima Nos. French Nos. Prima Nos. French Nos. 0000 20 7 95 000 15 8 100 00 30 9 110 40 10 120 1 50 11 130 2 60 12 140 3 65 13 150 4 70 14 170 5 80 15 180 6 90 16 200 324 FLOUR MILLING [CHAP, v Characteristics of the Intermediate Products and Flour. Before con- sidering flowsheets for the grading and flour dressing, it is necessary to settle the question of the terms applied to the intermediate products in connection with the above numeration of sieves. The largest break product is obtained from the preliminary break (Hochschrot), when the grain is broken in two down the crease. If the broken grain is to tail over the scalper, sieves from No. 8 to No. 24, according to the size of the grain, must be employed. Then come the ordinary breaks from 6 to 9 in number. For high break as well as for the successive break passages we use wire sieves with meshes numbered per inch, which were spoken of on p. 322. The largest product in the break process is called semolina, and since this semolina is sharp and rough, it is necessary to use wire sieves, which are more durable. After each successive passage of the break stock through the grinding rolls, its size diminishes, and reckoning the numeration of the wire sieves to an inch, sieves with Nos. from 14 to 40 should be used for the last break. The dimensions of the break semolina may be reckoned at 1'4 mm. to 0'7 mm. and less. Further, we have the rebreak semolina, for sizing which wire sieves are also required, Nos. 20 to 40. The dimensions of the rebreak semolina are defined at 1'35 mm. and less. The product following in size is the middlings of various dimensions. Generally up to six numbers of middlings are distinguished. To obtain these middlings as overtails, silk cloths are used of the following numbers, according to the middlings numeration in Table XXXI. TABLE XXXIV NUMBERS OF MIDDLINGS AND THEIR CORRESPONDING SIEVES Middlings *, Middlings Cloth Nos. Prima Silk Dimensions of Nos. Middlings in mm. I 20-24 0000-00 1-33-1 -11 2 24-32 00-0 1-11-0-83 3 32-40 0-1 0-83-0-64 4 40-48 1-2 0-64-0-54 5 48-56 2-3 0-54-0-46 6 56-60 34 0-46-0-37 CHAP, v] FLOUR MILLING 325 In giving the dimensions of the middlings in mm., we understand this to be their largest measurement or diameter, supposing them to be of a spherical shape. After the middlings the product next in size is named "dunst." This product, dressing through grit gauze Nos. 60 to 68, is tailed over on Nos. 5 to 7 (Prima numbers). Lastly, the granular flour is obtained as throughs from sieves Nos. 5 to 7 and the finished flour from Nos. 8 to 13. 1 Diagrams of Bolting. We are already acquainted with the general outline of the operation of the graders ; we have now to study it more in detail. In examining the process of sifting and grading the break stock, we notice three methods of sifting : (1) The overtails are of uniform size, while the throughs are of various sizes. (2) The throughs are uniform in size, the overtails different. (3) The overtails and the throughs are both of various sizes. Dunst No. 2. No. 3. No. 4. No. 5. No. 6. FIG. 295. For grading by the first method, a sieve is chosen with meshes of a size which allows only the largest product to be tailed over. In the second, the dimensions of the meshes allow only the smallest product to dress through the sieve. For the third method, meshes suiting the medium of the intermediate products are selected. The application of the third method is expedient when it is desired to divide the work of one sieve among several. In most cases the second and third methods of sifting are adopted. Supposing we are required to grade middlings into sizes from Nos. 2 to 6 according to Table XXXIV. Then we must use sieves from Nos. 28 to 60. The first system (Fig. 295) overtails the middlings, the second (Fig. 296) dresses them through. The first system yields the largest middlings No. 2 as overtails, and the rest as throughs. To separate the middlings No. 3, next in size, a finer sieve has to be used No. 34, &c. In this way the numbers of the sieves decrease until we obtain as overtails 1 In modern English mills the lowest flour silk number is usually No. 9, while in large modern mills throughs of Nos. 9 and 10 and even 11 are sometimes treated as dunst and further purified and reduced on the smooth rolls. 326 FLOUR MILLING [CHAP, v the finest middlings, No. 6, and dunst, as throughs. To perform the work in accordance with this diagram, the sieves have to be disposed one below the other. We have already met with such a construction of sieves, when studying the construction of grain -cleaning machines. If employing the throughs system, we dispose the sieves in an order starting with the finer and ending with the coarser. The first product yielded as throughs by No. 56 corresponds to the finest middlings, the second larger ones, &c. In the second diagram the sieves are placed in one plane or some other form of surface. This type of machine we also met in the grain -cleaning section ; namely, the reel-separator. A comparison of these two diagrams leads us to prefer the first, in which there is little product tailed over in comparison with the general mass, and consequently each sieve will be but slightly worn. In the Break middlings Y Y Y^ YV T Y Y V No. 6. No. 5. No. 4. No. 3. No. 2. No. 1. FIG. 296. second diagram, in which the quantity of the throughs is small, the whole mass of product travels over the sieve, therefore the force of friction is much greater than in the first case, and the cloth wears more rapidly. It is best to combine both these diagrams so as to separate the coarser product by the overtails system, and grade the finer product by the throughs system. II RELATIVE POSITION or THE SIEVES Having become acquainted with the grading diagrams, we shall now proceed to work out the relative position of the sieves. We have the following diagrams of the disposition of sieves according to the system of grinding : (1) A diagram of the disposition of sieves for sifting the product of plain (single) grinding. (2) Diagrams for high grinding. (3) Diagrams for rebreak. (4) Diagrams for semi-high grinding. (5) Diagrams for sifting the products of reduction of middlings and dunst. The second and the third diagrams for sifting the products of high CHAP, v] FLOUR MILLING 327 grinding consist of diagrams for the break and rebreak products, the re- duction of middlings, and grinding of the low grade stock. In addition the diagrams of sifting for the high and the semi-high rye grinding likewise belong to this category. (1) Diagram of Sieves for Plain Grinding. The plain or single grind- ing completely reduces the grain to flour at one passage, excepting an insignificant quantity of offals, which, owing to their elasticity, remain in the shape of fine soft bran. The product obtained is soft, and there- fore the sifting may be performed by the second system, i.e. by throughs, without danger of the sieves wearing. Fig. 297 represents an arrange- ment of covers for plain grinding. Experience has shown that the more product there is on the sieve, the coarser should the sieve be to yield as throughs a product equal in size to the throughs obtained when the sieve is less loaded. Therefore the first sieve we use is No. 10 or No. 11, while the second and third is one number higher, so that the flour from the first, second, and third sieves should be of an equal size. In this way the Nos. 10-11 Nos. 11-12 Nos. 11-12 Nos. 5-6 Nos. 0-1 ^ 1 ^ Throughs Flour. Dunst. Middlings. FIG. 297. first three sieves give flour as throughs ; the fourth, dunst ; the fifth, middlings ; and the bran is tailed over as refuse. (2) Diagram of Sieves for the Long System Break Process. The break process is performed, as we already know, in such a manner as to obtain as much middlings and as little break flour as possible. But some break flour is inevitable, and therefore the sifting diagram contains sieves for middlings of different numbers and flour sieves. On Fig. 298 may be seen the diagram 2 for the first break. This diagram is a combination of the first and the second systems of sifting, i.e. the work is done by overtailing and by bolting. The product, first break, passes along the arrow A to the wire sieve No. 18 or No. 20 (we give the numbers of the wire sieves everywhere to an inch). From the over- tails we obtain the first break semolina, while the throughs, the remaining product, run to the second wire sieve, Nos. 20 to 22. This sieve supple- ments the work of the primary grader, as this could not have taken out the whole of the break semolina. Therefore this sieve likewise overtails break semolina. The next is a silk middlings sieve, Nos. 34 to 33. The overtails of this sieve are the mixed middlings, Nos. 1 to 3, and the throughs 328 FLOUR MILLING [CHAP, v likewise consist of a mixed product fine middlings, dunst, and flour. The duty of this sieve, which gives no uniform product, neither as overtails nor as throughs, is to facilitate the work of the more tender flour silks, the fourth and the fifth, by 'separating the coarse product (middlings Nos. 1 to 3). The mixed middlings overtailed on the third sieve may be subjected to a further grading if necessary ; the throughs from it, in the meantime, pass to the fourth _ A sieve, which bolts the flour. Theover- 1 tails of the fourth sieve go to the fifth, and the throughs are again flour, which mixes with the flour from the fourth sieve. Lastly, the sixth sieve gives fine middlings Nos. 4 to 6 as overtails, and the dunsts as throughs. 3 Thus, the sieves 1 and 2 give overtails, sieve 3 separates the pro- duct for further grading, sieves 4 and 5 give throughs, and the last, the sixth sieve, yields the graded product as tails and as throughs. The sixth sieve could be, and sometimes is, placed after the third. 5 Then the first four sieves would be operating on the "overtail system," and the last two giving throughs, the last sieve yielding dunst as tails, g But the first plan of disposition is preferable, for the flour on the Dunst. fourth and fifth sieves will be sifted FIG. 298. better if they are more heavily loaded with product. For a shorter break system, for instance, with six breaks, this dia- gram may be altered so that by placing instead of the second wire sieve the middlings sieve No. 24, we obtain middlings No. 1. Then the third sieve will yield middlings Nos. 2 to 3, which may remain unseparated. The other sieves can be left in their places. In the diagram reviewed there is no sieve which would yield rebreak semolina. To obtain it, the second sieve, Nos. 20 to 22, may be sub- stituted by a wire sieve, Nos. 24 to 26, which gives the rebreak The greatest quantity of middlings (amounting to 60 per cent of the v- *z- 5- Nos. 18-20 <- I - Nos. 20-22 1 <- Nos. 34-36 I - Nos. 11-12 1 i <- - Nos. 12-13 <- <- Nos. 58-60 CHAP. V] FLOUR MILLING 329 bulk of grist) in an eightfold break is obtained at the second, third, and fourth breaks, which induces us to examine the diagram of position of the sieves of, for example, the third break, the most characteristic one, as it yields up to 24 per cent, of middlings. This diagram is shown on Fig. 299. The first wire sieve overtails break semolina ; the second and third, silk cloths, yield coarse and medium middlings, Nos. 1 to 4. The fourth Break Semolina < ^~~ Nos. 25-24 < B 1 Semolina Nos. 1-2 ' Semolina . Nos. 3-4 Nos. 24-32 Coarse . Bran. Dark Middlings <- Nos. 4-5. Nos. 36-40 Nos. 40-56 Nos. 34-40 Nos. 11-12 Flour 4 Semolina Nos. 5-6 <- - Nos. 11-12 1 - <- Nos. 12-23 | * 1 - <- Nos. 58-60 Dunst. Dark Flour/ Nos. 12-13 Nos. 12-13 Dark Middlings ^_ No. 6. Nos. 60-63 FIG. 299. I Dark Dunst. FIG. 300. and fifth sieves yield flour, while the sixth sieve bolts the dunst and tails over the fine middlings, Nos. 5 to 6. Commencing with the fifth break the size of the middlings diminishes, and at the fifth break there is scarcely any middlings Nos. 1 to 2. For this reason the numbers of the middlings sieves increase, and some of these sieves may be discarded and flour or dunst numbers set in their places. The last break, which yields bran, dark middlings, dunst, and flour, is also characteristic. For the eighth break the diagram of sieves shown on Fig. 300 should be adopted. 330 FLOUR MILLING [CHAP. V According to this diagram the sieves 1 and 2 yield overtails, the sieves 3, 4, and 5 throughs, and sieve 6 both overtails and throughs. The tails from the first wire sieve, the bran, are conveyed to the brush machine to remove the mealy particles remaining on them. The tails from the second silk sieve, the soft dark middlings, are sent for reduction. The throughs from the third, fourth and fifth sieves, lowest grade of flour, and, lastly, the throughs and the tails from the sixth sieve, dark dunst and small dark middlings, are likewise conveyed for reduction and reduced to low-grade flour. (3) Diagrams of Sieves for Rebreak. The number of rebreaks em- ployed in the Russian mills varies between 1 and 5. In the last case the rebreak may be regarded as a parallel break, and the diagram of disposition of the sieves here scarcely differs from the diagrams for the shorter (semi-high) break process. But generally 1 to 3 rebreak or scratch rolls are used. For the rebreaks the diagrams of the sieves, in their general outline, are the same as those for breaking, with the sole difference that the numbers of the wire and the middlings sieves are higher, the product being finer. (4) Diagram of Sieves for Medium Break Systems . There is no essential difference in the diagrams of disposition of the sieves in the long and the medium systems ; they differ only in the numbers of their sieves and their more rapid increase at the end of the break process for break semo- lina and middlings. (5) Diagrams of Sieves for Reduction. As in the preceding cases the diagrams of disposition of the sieves for gifting the milled product present a combination of throughs and overtails differing only in the numbers of their sieves and the number of "throughs systems." This diagram of sieves should be employed (a) for the reduction of middlings, (6) for the reduction of dunst and cleaning the offals, (c) for supplementary machines. In all three cases the chief aim of the reduction is to obtain flour. Therefore, the greater number of sieves in this diagram should be set for flour, so as to separate the large product more accurately during the sifting process. (a) The diagram illustrated by Fig. 301 shows the position of the sieves for sifting the product produced by the reduction of middlings. The highest grades of flour obtained from Russian grinding being generally granular (2 and 3 grades), and not differing in size from middlings No. 6 and dunst, this diagram presents two varieties of sieves : the first flour numbers yield coarse (granular) flour, the second soft or fine. The Middlings Nos. 5-6. D CHAP, v] FLOUR MILLING first sieve tails over the required product, and yields semolina Nos. 5 and 6 ; the next two sieves give as throughs a final product in the shape of coarse or fine flour, as required. The fourth sieve separates semolina No. 6 from the dunst. We must note the fact that the numbers of sieves in all the diagrams we are examining depends on the construction of the sifting machine ; it fluctuates between 4 and 12. If the number of sieves is higher, more break, middlings, and flour sys- tems are employed, leaving one dunst sieve. This is more minutely described in the milling diagrams. (b) The diagram of sieves for reduced dunst and bran differs from the preceding in that the last sieve is missing and the numbers of the flour sieves are higher than usual (from Nos. 12 to 15), for the reduction product, if the pressure of the rolls is great, gives a fine flour. In this way one or two sieves yield overtails, separating the dunst, while three or four give flour as throughs, the last one at the same time tailing over the finer dunst. (c) In long system mills the flour obtained is often subjected to control, i.e. the middlings (in granular grades) or dunst (in fine flour) are separated away. Then the diagram resembling the one on Fig. 301, but without the last sieve, with. a less number of sieves (never exceeding three) must be used. The throughs of the flour sieves give the final product, while the tails (middlings or dunst) from the first and the last sieves are returned for further reduction. Middlings No. 6 6 we find : m r This correlation shows that with any inclination of the beaters the direction of the resultant R (Fig. 307) may be made normal to the surface of the cylinder, if suitable numbers of revolutions and radii of the reel and beaters be chosen. In inferring this correlativity of the number of revolutions and the radii the gravity of the product was not taken into consideration, and the velocity of the particle was supposed to be constant. Practical experience corrects this formula by altering the degree of ratio of the radii from 2 to 3. Finally, therefore, we obtain : m_ / r\2J 3. "VBy The theoretical considerations of Professor Zworykin given here find a brilliant corroboration in the actual construction of centrifugals, the number of revolutions and the diameters of which we proved accord- ing to his formula, having obtained a great accuracy of correlativity inferred. In this way, that which is clear from simple theoretic infer- ences, practice has been seeking many years, until it reached the correct solution of the question after groping in the dark, having passed a lengthy number of rejected unsuccessful constructions and expended much money in that way, (3HAP. V] FLOUR- MILLING 341 Construction of Centrifugals. Before deciding upon the modern type of a reel, the works offered many fairly different constructions of these machines. We shall not enumerate these types, but one of them, a reel from the works of Dost in Vienna, which at a certain period was very popular, demands our attention. Fig. 308 illustrates a cross section of the separator, and shows its reel to be of a star section. On being fed into the reel the product is lifted on the platforms 6, drops from a certain height, and is caught up by the beaters c, fixed at an angle to the generating circle with two or three (according to the length of the reel) sprockets A. The incline of the bolting side a is so chosen as to have the product rejected by a blow from the paddles fall on a at a right angle. The sifted product is conveyed by a worm B to the outside. We have already seen that the product can fall at right angles on the sieves in- dependently of their form. If this sepa- rator did work satisfactorily, evidently it was only owing to the happy choice of the velocities of rotation of the sieve and the beaters. But, speaking generally, this construction is less successful than that of the ordinary round reels. In the first place, the platforms b leave totally unsifted the product thrown by the beaters, since their motion is parallel to the planes of these platforms lying at a right angle to a. Further, the construction of the reel is rather complex, which makes clothing it with a sieve a difficult task. Lastly, the wear of the working surface was observed to be uneven, because a accepted almost the whole of the work, while b played the part of boxes supplying the paddles with product. Fig. 309 represents the modern normal type of a centrifugal dressing- machine (Thos. Robinson). The product flows to the feeder A and is conveyed by the worm to the chamber B of the centrifugal. The drum C containing beaters is rotated from the belt-pulley 1. On the shaft of this drum, at the opposite end, there is set the belt-pulley 2 from which the worm D is brought into operation. On the shaft of the worm there are two belt-pulleys, 4 and 6 ; by means of the pulleys 4 and 5 the reel is rotated, and the spiral brush E for cleaning the cloth is driven by FIG. 308. 342 FLOUR MILLING [CHAP, v the pulleys 6 and 7. With the assistance of the ribs F which constitute the frame of the reel the product is lifted to a certain height, and then dropped upon the beaters. The beaters are disposed in the generating circle, but their propellers are bent to a helical line, as shown in Fig. 310. FIG. 309. The bearings of the brushes may be transposed, so that the brush is approached to or removed from the sieve according to its wear or the necessity of a more rigorous cleaning of the bolting cloth. Centrifugals of this type are built by almost all European works. 10-tf FIG. 310. Very rarely the beaters bent to a helical line are discarded and solid beaters arranged at an angle to the generating circle of the cylinder. Fig. 311 illustrates a perspective view of Thos. Robinson's reel-separator furnished with such beaters. Capacity of Centrifugals. Since almost the whole of the working FLOUR MILLING 343 CHAP. Y] surface in the centrifugals is utilised, their capacity is far greater (nearly fivefold) than that of the ordinary reels, owing to which they are as yet not everywhere supplanted by plansifters in the merchant mills. They are generally employed for sifting the products of the final reduction, i.e. to receive them from the smooth rolls, which reduce the middlings and dunst, though formerly they used to be installed beginning with the fourth break. Table XXXVI gives us the capacity of centrifugals in accordance with their dimensions, the number 344 FLOUR MILLING [CHAP, v of revolutions of the cylinder, and of the drum containing the beaters. TABLE XXXVI CAPACITY OF CENTRIFUGALS Dimensions of Cen- trifugal in mm. Number of Revolu- tions per Minute. Capacity in Ibs. per Hour. Horse- power Required. Diameter. Length. Cylinder. Beater Drum. Break. Rebreak. Middlings. Flour. 610 650 700 800 900 1000 1500 2000 2500 3000 3500 4000 30 30 28 26 22 20 250 250 230 200 190 180 900-1080 1260-1440 1620-1800 1980-2340 2520-3060 3240-3600 828-900 1152-1368 1440-1620 1800-1980 2160-2520 2880-3240 540-720 792-900 972-1080 1260-1440 1620-1800 1980-2160 360-432 540-612 720-828 900-1008 1080-1260 1332-1512 1-0-0-4 1-5-0-6 1-8-0-8 2-2-1-0 2-8-1-2 3-6-1-6 As concerns the power consumption, the quantity the centrifugal separators absorb running empty amounts to 80 per cent., consequently their useful work is very insignificant. This circumstance is the cause of their losing ground to more economical machines, which will now occupy our attention. 2. Plansifters When studying the reel-separators, we saw that this type of sifting machine does not allow the use of the whole working surface of the sieves (plain reel-separators) or places in equal conditions of work (centrifugals). In addition, the plain as well as the centrifugal separators consume a large quantity of power. These defects induced the engineers to seek a more perfect type of machine, which was then offered by the Americans, together with the idea of an automatic mill. Modem technics possess two types of plansifters, differing in the character of motion of their working surfaces : (1) Machines with rectilinear reciprocating motion of the working organs. (2) Machines with gyrating progressive motion of the sieves. (i.) Machines with Reciprocating Motion The simplest kind of such a machine is given on p. 31, Fig. 28, G. The different machines of the " Eclipse " (p. 64) or the zigzag separators are more perfect types of it And, lastly, Soder's plansifters may CHAP. V] FLOUR MILLING 345 be pointed out as one of the best modern reciprocating bolting machines for reduction stock. This sifter is a an oblong timber box (Fig. 312) supported on steel spring stands. The box is brought into motion by an eccentric drive with a counterweight for balancing the inertia of the mass. Inside the box (Fig. 313) there are set five bolting frames. This machine can very successfully do the work of a reel in the small farm mills, in case economy of space is a great consideration. Proceeding now to give an estimate of the reciprocating machines, we must note that their advantages in comparison to the reel-separators consist only in their compactness. On the other hand, they have material Ui 1.. fc. -*(.*. FIG. 313. FIG. 312. Copper cloth, No. 26. Silk gauze, Nos. 5 & 7. X = Inlet of stock. defects, the cause of which lies chiefly in the character of motion of the machine. These defects are as follows : (1) Necessity of considering the inertia of the mass of the machine. (2) Variable velocities of motion, causing an unevenness in the bolting of the product. Owing to these defects, the application of reciprocating machines is very limited. It is only their comparative cheapness and compactness which makes their use in small short system mills possible. (ii.) Machines with Gyratory Progressive Motion The idea of the constructive principle of machines of that type is explained to us by G. Luther's grain-cleaning machine "Triumph," described on pp. 81, 82. The main parts with a gyratory progressive motion are the box, where the bolting frames are arranged, or a box built of frames joined to each other and covered with bolting cloth ; then drop -hanger frames or stands, on which the box is established, and a shaft with an eccentrically set driving finger. The diagram of that sifter is given on p. 68, Fig. 56. 346 FLOUR MILLING [CHAP, v When the shaft A is in rotation, each point of the box s performs a gyra- tory progressive motion. Before passing on to the constructive descriptions of machines of that kind, we must decide upon the fundamental requirements which should JTIF 3 R FIG. 314. FIG. 315. be answered by all machines of the type in hand, and prove this or that construction rational. These requirements are : (1) Counterbalancing the centrifugal force ot the gyratory motion of the working organ, the details of the transmission of motion being of the least possible size. (2) Utilisation of the largest area of the bolting surface. (3) Simplicity of shape and setting of the bolting trays. (4) Constant cleaning of the working surfaces to avoid blinding. To be able to make our estimate of the sifters from the point of view of the above requirements, it is necessary to become acquainted with the main types of construction. K. Haggenmacher's Sifter. The plansifter which brought about a re- volution in bolting methods was invented by a citizen of Switzerland, FIG. 316. K. Haggenmacher, at the end of the eighties of the last century. The original construction of this sifter is shown in Fig. 314. The box R, containing the bolting trays, is suspended on four rods g, and is brought into motion from the driving pulley d by a quarter-twist belt drive to the receiving pulley d. This pulley and the fly-wheel L, with a counterweight at K, have a common shaft, furnished with a collar a, with which it rests on the bearing in the cross-head T. The hub of the fly-wheel CHAP. V FLOUR MILLING 347 FIG. 317. t) L has an eccentrically set journal, cast in one piece with the hub ; this journal enters into the bearing of the cross-head S, coupled with the frame N, on which the box R with the sieves is set. The rods g are set (Fig. 315) in ball-bearings n. The product flows in down the spout E through a linen sleeve G l and is delivered after the sifting through similar sleeves G 2 . whence it is directed for further treatment, or into bins, if it is flour. For setting the sifting box in a horizontal position, the rods g, consisting of two pieces, have nuts t, by means of which the lower piece of the rod may be screwed into the hub r, provided with a screw thread, thus making the rods shorter or longer. A longitudinal section of a box with five trays is shown on Fig. 316, their fixing on Fig, 317. * The sieves of that sifter lying in a horizontal plane, the product travels with the aid of slats, which operate in the manner described on p. 69, Fig. 57. This diagram shows us that the direction of the progressive motion of the pro- duct coincides with that part of its gyrating motion which is in opposition with the arrow of the setting of the slats. The different shapes of the slats (of zinc sheet iron) sug- gested by Haggenmacher are given on Fig. 318, but the straight slats set at right angles to the direction of the motion (part y) proved to be the most practical. If the slats are arranged as shown on Fig. 318, then the product fed in through A at the top will move along the arrows s. The frame here is divided by a partition, and its right and left part work independently, directing the overtails to the outlet B. To get a clear notion of the sifting operation, we shall review W^M^ f* k _.._.* * > ,1. s ,1 ^ lit* I::J IliJ FIG. 318. 348 FLOUR MILLING [CHAP. V the diagrams of the disposition of trays for break and reduction stocks. The break product runs to the first and to the second sieves (Figs. 319 and 320) simultaneously and travels to the right, giving break semolina as overtails, and the remaining product as throughs. The product of re- breaks may be directed to the second sieve, if it is calculated for rebreak semolina. If the break product go only to the first frame, it will tail over the break semolina of the next order discharged through 6, and bolt the rebreak semolina and the rest of the products. On the second sieve the products travel in the same direction, and therefore yield rebreak semo- lina as tails delivered out of the sifter through c, while the remaining middlings and flcur pass through. The next sieve, No. 3, is designed to overtail the coarse middlings, beginning with No. 1, the throughs at the same time passing to the fourth linen (or sheet-iron) tray, where the slats are so disposed as to propel the product in the opposite direction. On reaching the openings e the pro- duct falls from the sheet -iron tray on to the fifth sieve, which FIG. 3l9.-Diagram of Longitudinal Section through the openings e, gives the of Sieves. fine middlings and dunst as tails to the seventh sieve, and throws the flour upon the cloth of the sixth tray as throughs, which is delivered through /. The bolting tray 7 is divided into three sections with different cloths, which yield dunst and fine middlings as throughs, and tail over fine middlings which are larger than those of the throughs. In this way the three first sieves operate by the " overtails system " and the two last ones by the " system of throughs." The throughs from the bolting frame 7 fall on the bottom 8 in which there are holes h, h l and h 2 for letting the dunst and the fine middlings out. The frames 1, 2, 3, 5, and 7 are called the working trays, while those of linen or sheet iron, 4, 6 and 8 are called collecting trays. This diagram contains only one flour tray, 5, but to have the flour more accurately sifted there are two or even three flour trays set in case a large quantity of break flour is yielded. The blinding of the sieves 3, 5 and 7 is overcome with the aid of shakers, which will be spoken of later. The diagram of the trays for the stock reduced on smooth rolls is shown on Figs. 321 and 322. Since those products present a mixture of fine middlings and dunst with a considerably preponderating quantity of CHAP. Vj FLOUR MILLING 349 flour, the sifting away of the latter offers greater difficulties than in the first case. For this reason each working tray is succeeded by a collecting one, and the process of sifting is done on the following lines. The bolting working frame 1 with cloth No. 60 xx receives the reduced f I 1 ~ ,,rTS t - 5 . " ?> *7 4 ' f ^ " t " '.'.' ' 'J> *r , ^ i i - 77 - __ ^ ( ^ . (1ir Sieve with shaker ^ n iT7T ^ MV.T-TT, , , , < ^ ^/2* , S t , . <-_^< ^ / 4 S * * M f* , rrr; , ( , ,7-7, 2J er ^ - - i i^-TT' , c i bS^ M. b ^^ .T>, ^ , 6 ^~ & c ! * V Si* < * *-> ' '^-^' " ' ~H i c . ^ . M ^ *>*> L'.nen or sheet iron * j c \ I I^MJJ ,,,,!! , I I I I i . , ^ >f c J * " * * "-^ "i^* ' ' '" ' " " LLi 5 c ' ' """"i^- ? eye with shakers lit* 5;el-e wi > ^' " '' -^ e -^ <_ - \ ' 5 v * ' 2J { * * Linen or sheet iron * f P - ^~ V^l | |\ B attorn /^ u 1 ' *ili' ' ' ' ' ' ' ' ' ' ' ' ' ' ' J 4 XT ' / > ^ ^ - \ t I J-IV ' ' ' " ' ' ' " ' ' ' ' ' L_L - - ^N /s 'i r' x *'x P -N O 1 >* 4! -^. - ^^ * VJ ' ' '/^V s FIG. 320. Plans of Sieves and Linen Frames stock and yields fine middlings as tails, which is ejected from the sifter at c through all the trays. The dunst and flour go to the cloth of the collect- ing tray 2, down which they travel in the opposite direction and are passed to the working tray 3 with a dunst sieve No. 5 xx, tailing over the 350 FLOUR MILLING [CHAP, v coarser dunst, which is directed to its exit through d. The throughs from the third tray travel over the fourth cloth through the openings dt to the working tray 5 clothed with sieve No. 12, which yields finished c-Sieve n Linen d Bottom p Grate e Sheet Iron FIG. 321. Diagram of Longitudinal Section of Sieves. flour as throughs, to be delivered through the outlet e. The tails from the fifth tray go to the last working surface 7, furnished with flour sieves of different numbers (Nos. 12 and 13), which sift flour through on to the collecting bottom, and tail over the finest dunst. Consequently, , -73 Uf <%* H- o r ^ O '^ 5-Shakers. D Bottom. FIG. 322. i, 3, 5, & 7 are sieves. 2, 4 & 6 are cloths. the first two sieves here, 1 and 3, are operating on the ''overtails system," separating away the fine middlings and dunst or dunst only (this depends on what the product ground on the smooth rolls is, whether it CHAP, v] FLOUR MILLING 351 is coarse or fine middlings), and the sieves 5 and 7 on the ' throughs system," yielding ready stock. In the first diagram there are marked three sifting trays with shakers, in the second four. It has already been mentioned that the shaking of the sieves is necessary to clean the meshes blinded with product. The trays 1 and 2 of the first diagram need no shaking, the sieves being fairly open (Nos. 20 and 28, wire), besides which the product is sufficiently coarse to clear the meshes by the pressure of its mass. For the silk sieves, particularly those for dunst and for flour, which dress through, a tapping action to keep them clean is indispensable, and is performed generally by means of large wheat grain, gutta-percha balls, or the grains of leguminous plants. Let us watch the travel of the tapping grains in the second diagram. Down the same spout with the product, or along a separate one, the grains Section throuyh A B. Section through C D. A-\ FIG. 323. FIG. 324. FIG. 325. of wheat or pease are conveyed to the first tray and run over the sieve, shaking it, being bodies of greater weight. On reaching the slat PQ, and falling upon an open wire cloth, the product passes through it, while the tappers travel over it and turn in the direction indicated by the arrow to the openings 6, through which they pass on to the cloth of tray 2 and proceed, together with the product, to the left. Once arrived at the opening c l the product and tappers pass on to the sieve 3, and again in the same manner go to the cloth 4. Then through openings d and d 2 they fall successively upon the sieves 5 and 7. From the tray 7, passing the open wire cloth by, the tappers fall out at the outlet b l to the ele- vating mechanism, which carries them again to frame 1. The elevating mechanism is a vertical worm with a small thread, stationed on the outside or inside the section. Figs. 323, 324 and 325 show the elevation of the tappers disposed inside the box. Here inclined planes are used in the place of a worm. From 352 FLOUR MILLING [CHAP, v the last sieve (Fig. 323), having run over the open wire cloth, through which the product passes to the outlet spout, the tappers reach the first inclined plane, along which they ascend to the first horizontal plane, in- fluenced by shocks, effected by the rotation of the sieve. From the first landing they ascend to the second over an inclined plane having a retro- grade motion, then to the third, and so on to the first bolting tray. During all the time of the work each sifting tray should be covered with tappers which form an uninterrupted chain covering the sieves and stretching through the elevator. Generally the tappers from the last sieve are carried to the first. But sometimes in the vertical canal there are made FIG. 326. openings E to the nearest trays, owing to which part of the tappers fall on the trays with the openings E, and part ascend to the first tray. Fig. 324 illustrates the plan, and Fig. 325, a section through CD, which make the construction clear. On Fig. 326 may be seen the general disposition of such a cleaning device. The defects of cleaning the sieves by means of tappers consist in the fact that the sieves have to be overloaded with superfluous weight, which are a cause of their rapid wear. The other shakers, such as spiral springs, chains, &c., have the same defects. To obviate these defects the shakers are sometimes displaced by brush cleaners, which are diagrammatically shown on the same Fig. 326 (cleaning of the second sieve). The wooden rod A has soft hair brushes CHAP. V] FLOUR MILLING 353 at the top and the bottom, and the working upper part of the brush touches the lower surface of the sieve, while the other end rests on a sheet-iron tray. At the end of the rod, free of the brushes, there is a timber finger a, which enters into the guiding canal BC and prevents it from moving to the right or to the left. When the sieve is in motion the brush travels along one side of the channels, turns back on reaching their corners, and runs along the other side. The brushes clean the sieves better, if the hair is sufficiently soft, influence their wear very little, and therefore brush cleaning has been adopted by almost all makers. This cleaning, however, has its own, though insignificant, defects. In the first place, the guiding channel annuls a certain part of the working surface of the sieve, and secondly the corners of the bolting trays remain untouched by the brush and are consequently not cleaned. The product travels in the channels of the trays of the sifters with the aid of slats, as we have seen ; the speed of motion depends on the number of revolutions and the degree of eccen- tricity defining the radius of rota- tion of each point in the sifter. The degree of eccentricity defines the width of the main channels on the trays. For an explanation of this pheno- menon we shall turn to Fig. 327. The radius of rotation of each particle of product on the sieve is equal to the degree of eccentricity. The larger this radius, the greater is the wave of the curve AB, of the resultant motion of the product under the influence of centrifugal force, of the impact from the slat, and of gravity. If the channel taken is too broad, we shall have immobile dead masses Q. To move these masses also, the slats could be made longer ; but then we should obtain dead masses Qi between the slats. The question concerning the normal width of the channels and the length of the slats is solved by general practice, since it cannot be solved theoretically, the quantity of the force of friction being indefinite. General practice gives, for instance, the following correlation of the number of revolutions, z FIG. 327. 354 FLOUR MILLING [CHAP, v the width of the channel, and the radius of rotation (Table XXXVII, European works) : TABLE XXXVII Number of Revolu- tions per Minute. Radius of Rotation in mm. Width of Channel in mm. 190 90 220 200 85 170-200 210 80 170 220 220 75 70 160 140 240 65 140 We must say, however, that these average values of the elements of the sifter and its motion do not give uniform work as regards quantity as well as quality for each bolting tray. Since each tray operates with products of various sizes, the coefficients of friction of the product against the sieve for each tray are likewise different. In practice the values given in the table are generally decided upon in accordance with results of the work of the dunst and the flour sieves, where a small number of revolutions causes a choking up of the sifter, i.e. the channels become blocked with product, which does not move forward and so chokes the machine. A high speed is also injurious to the work, because the overtails will contain a large amount of floury particles if the product travels rapidly. However, a normal speed of motion of the fine and mealy product corresponds to too great a velocity for the mixture of coarse (break, rebreak, middlings Nos. 1 to 3), and fine products previous to their separation, owing to which the overtails will consist of fine middlings, dunst, and flour. That being the case, Professor Zworykin very justly considers that the sieves grading fine middlings, dunst, and flour should be inclined upwards in the direction this product travels, to reduce the velocity of its motion. Then it would be possible to choose a number of revolutions for the sifter favourable to an efficient sifting both for coarse and fine products. It is to be regretted that this simple idea has not been utilised by any of the works, although its realisation would have imported practically no constructive complications into the sifter. Bunge's Round Bolter. Haggenmacher's sifter was succeeded by a CHAP. V] FLOUR MILLING 355 round bolter designed by Bunge ; the scheme of its construction is as follows (Fig. 328) : A cylindrical box consists of separate rings b coupled together by bolts c symmetrically at four points and suspended on three or four reed or steel rods I 1 . The box is brought into a gyratory pro- gressive motion by means of a finger i set eccentrically to the shaft h lt In the box there are fixed round bolting trays a and trays 3 with conic discs e, having the same function as the cloth in Haggenmacher's sifter. The product flows down the spout d along the axis of the sifter and falls upon the sheet-iron cone D, whence it evenly descends to the sheet-iron cone e 5 with a slighter incline. Over the cone e 5 the product runs to the ring &, where it falls on an open sieve A, which yields the large FIG. 328. product as tails and the rest as throughs. The tails, having passed down the axis spout /, drop on the conic bottom (7, and is directed to the out- let spout /j. The throughs pass to the sheet-iron cone e and fall on the sieve B. The further motion of the product is clearly seen in the drawing. The sieves B and C give flour as throughs, which is discharged through spout e 2 , and tail over middlings delivered by the spout / 2 . Under the sieves there are arranged the brushes K L fixed to angle-iron rings k, which are freely set on timber rings 3 , and rest on flat rings o. The brushes are brought into rotary movement by the motion of the sifter, and remove any stock blocking up the meshes of the sieves. An end elevation of Bunge 's bolter is given in Fig. 329. Instead of the conic sheet-iron discs, in the models of a later date horizontal flat discs were recommended, with slats on the outer and 356 FLOUR MILLING [CHAP, v inner rings, while American engineers offered spirally disposed combs, as shown in Fig. 330. Here we have a working tray over which the pro- duct travels from the axis to the periphery by a spiral route. Before proceeding to give a comparative estimate of the merits and demerits of the square and round bolters, we must become acquainted with yet another type of sifters. Konegen's Sifter. The two-box sifter, built by the Amme-Giesecke and Konegen works, is a modified construction of the two-box sifter first invente^ by Engineer Konegen, who set himself the problem of giving FIG. 329. FIG. 330. a balanced motion to the machine. The circumstances favourable in dynamical respect to the work of two-box sifters will be examined below ; at the present moment we shall turn to the modern construction of Konegen's sifters. According to the way in which the boxes or blocks of the sifters are erected, two types are distinguished : one suspended by means of four cane rods (Fig. 331), and one in which the boxes are supported on four stands (Fig. 332). The manner in which the boxes are hung is their sole difference. The sifter boxes are built of separate trays. The bottom or collecting tray of the first sifter is screwed on to two rods fixed to the main frame and the other trays, numbered in corresponding order, are laid upon it' FLOUR MILLING 357 CHAP. V] When the trays of each box are fitted up, they are coupled together by four bolts fixed on joints to brackets bolted to the main frame, which FIG. 331. consists of two parallel H-iron beams /, joined by a third cross-beam, The suspended types have riveting sets for cane rods on their longi- v L FIG. 333. tudinal beams, while those supported have brackets fixed for the stands. The stands have the following arrangement (Fig. 333) : The foundation is a cast-iron box containing a plate of the same metal with a leather 358 FLOUR MILLING (CHAP. V lining soaked in oil. A cast-iron shoe for the steel stand is set in the plate. The shoe and the plate are covered with a casing. Into the stand there is screwed a bearing i for the ball vertical journal Z, which is screwed into the bracket b, attached to the longitudinal H-iron beam. A lubricator K is screwed on the bearing i, and a cap M on the vertical journal Z to give the stand a more elegant appearance. The footstep S for the shaft transmitting the motion is set in a drop- hanger frame, and its bearing in the frame a lf The shaft W is joined to the fly-wheel, which has a counterbalance, by means of the hub h of the fly-wheel, screwed on the threaded part of the shaft. For lubrication there is the cup o, out of which the oil runs into the bearing (Fig. 334). The cup o is supplied with oil from the outside. On Fig. 335 is shown the balance-wheel from the top. Between the FIG. 334. FIG. 335. adjustable weights w, serving for additional regulation, there is a box filled with lead. The finger k of the balance-wheel enters into the adjustable bearing enclosed in the cast-iron frame, which is fixed between longitudinal H-iron beams. With the aid of bolts b the hub of the bearing may be adjusted to set it correctly when erecting to alter the degree of eccentricity. A perspective view of the Konegen sifter is shown in Fig. 336. A Two-box Sifter by " Seek Bros." Works. The plansifter shown in Figs. 337 and 338 is a model of a two-box balanced sifter of the newest type. The left- and right-hand side boxes are joined by a timber frame of joists in a square section. The frame coupled together between the boxes by two-angle channel irons forms the base of the sifter. On the one side of this frame on the stands e and supports, rest both the boxes of the sifter, which are a series of sieve trays arranged in stories, and coupled together by rods h, fastened with one end to the FLOUR MILLING 359 CHAP. V] frame ; on the other side the frame couples in with the fly-wheel e and the shaft 6, which impart a gyratory motion to the sifter. We shall first direct our attention to the dismantling of the boxes and the erection of the sifter. The rods h are fastened by joints to the frame. The top ends of the rods entering into the slots of the cast-iron FIG. 336. cross-bars over the boxes have a screw thread, and with the aid of nuts allow the frame of the sifter to be tightened. When the sifter is to be taken apart the nuts are loosened, the rods turned down, and the cross- bars removed, then the bolting trays are taken off one after the other. The bolting trays from the lower part of the box are removed downwards after the rods have been loosened. 360 FLOUR MILLING [CHAP, v As mentioned above, the whole mass of 'the sifter is supported on four stands. The stand is an iron rod e (Fig. 338), which carries a ball bearing at its upper end, and a buffer vertical journal g resting on a flat bearing g l at the other end. Between the buffer and the bearing a FLOUR MILLING 361 CHAP, v] piece of leather is placed to lessen shock. The ball vertical journals fixed to the frame of the sifter rest on the footsteps /, and in this manner the sifter is supported on rods e. The rods e being always set aslant in respect to the vertical axis of the sifter, it is evident that the horizontal component of the weight of the sifter is communicated by pressure on the shaft b. . Since the rods constitute one of the most essential details of a'sifter, Fia. 339. FIG. 340. two other types of rods evolved by Seek should be described, and more minutely. Fig. 339 illustrates a rod built of two parts connected by a two- twist nut which affords the possibility of adjusting the length of the rod. The stem a is connected by joints "6 and b l with boxes c and c 1 , which roll over the bearing surfaces d and d 1 . One of the surfaces (the top one) is fixed to the frame of the bolting machine, the other lies on the ground. In the drawing we may see that the journals of the joints are turned at an angle of 90 in respect to each other. 362 FLOUR MILLING [CHAt>. V Each one of the boxes on the side next to the support is cylindrical in shape, and the axis coincides, or nearly coincides, with the axis of the journal of the joint lying opposite. The box freely swings to either side as far as is necessary for the circular motion of the sieve. To prevent the sieve when operating from running out of the limits of FIG. 341. the motion required, the bearing surfaces of the boxes towards their rims are bound by planes tangent to the cylindric surfaces of the boxes. Fig. 340 illustrates the second type of support, Here, different from the preceding case, the boxes with the mutually perpendicular planes of swinging are transferred to one end of the prop in such a way that the top one swings over the back of the one below. Thus, both the boxes CHAP. V] FLOUR MILLING 363 form the bottom joint, which at the same time keeps the swinging rod from turning over. The top end of the rod is connected with the box of the bolting machine by means of an or- dinary universal (Hooke's) joint. The upper box c rests on the flat back of the box c 1 , which has its plane of swinging turned at an angle of 90. The lower box lies loose in the box d, and on its back has flanges c 2 , serving to direct FlG 342 the box c. The sifter is brought into motion in the following manner : the shaft b with a driving pulley, set in a bearing, is brought into rotary motion. The upper' end of the shaft b being coupled by a pin with the ; FIG. 343. hub of the balance-wheel c, the latter is likewise set rotating. This fly-wheel has a ball bearing with an adjusting device, disposed eccentri- cally to the axis of the fly-wheel. In the fly-wheel there is a counter- weight, d which may be transposed by means of a screw. The hub of the fly-wheel, serving as journal during the rotation of the fly-wheel at the same time, is set in the bearing of the frame a, which is also coupled 364 FLOUR MILLING [CHAP, v The sifter with a cross-head carrying the footstep bearing of the shaft b. runs at the rate of 190 to 200 revolutions per minute. The number of sieves is twelve ; the travel of the product is shown clearly enough. The cleaning of the sieves is performed by means of brushes, which act in the manner described on p. 352, Fig. 326. A perspective view of the Seek Bros. sifteris shown on Fig. 341. FIG. 344. After Konegen's sifters were put on the market, two-box sifters were also constructed by other makers. The mounting of two-box sifters is the same at almost all European works. The mounting by G. Daverio's works differs to a more or less extent, the perimeter of the supports of their rods lying between the boxes. A perspective view of G. Daverio's sifter is given in Fig. 342. Fig. 343 represents Dobrovy and Nabholtz's one-box sifter with a friction drive and four exterior conveyers for the shakers Fig 344 represents G. Luther's two-box sifter on cane supports CHAP, v] FLOUR MILLING 365 3. Dynamics of Plansifters Before passing to a further description of the construction of sifters, it is necessary to mention several considerations concerning favourable conditions of motion for sifters of different types. We are given a single-box sifter (Fig. 345), the motion of which generates a centrifugal force of every point of it round its axis of rotation. The centrifugal forces of each point of the sifter being parallel at any particular moment of the motion, they may be summed up after the law of parallel forces, and give us the resultant F applied in the centre of gravity of the sifter. The force F gives the moment Fa in respect to the plane, which is perpendicular to the axis of the bearing c 2 . To pre- vent any fracture of the shaft in the bearing c 2 or excessive thickening of it, it is necessary to set a counterweight on the shaft, which would give an equal and directly opposite moment in respect to the same plane of the bearing c 2 . The counter- weight is generally made in the shape of a balance- wheel with stationary and adjustable weights, as we have seen in the construction of Konegen's sifter or , Q , FIG. 345. that ot beck. Thus, if the weight in the balance-wheel gives a centrifugal force N, when rotating, then the condition from which this force is defined will be : Fa=Nb, whence we define N=F T . o But since a > b, the centrifugal force N of the balance-wheel must be greater than the centrifugal force F of the sifter. Having fitted the counterweight, we obtain two forces, F and N 9 which have a tendency to turn the axis of rotation cc 2 about the hori- zontal axis. From turning to the right, the position of the forces being as given, the axis of rotation is kept by the reaction X of the bearing. The value of X will be defined, if we take the moments of all the active forces in respect to the point c ; Xa=N(a-b). Having N=F^ and on defining X from the preceding equation through F, we obtain : . .. . The force X, with such a construction of counterbalancing the centri- 366 FLOUR MILLING [CHAP, v fugal force of the sifter, will always be present. Its direction alters with the motion of the sifter for each position, which imparts great vibration to the building. Besides that, sifters of this type, producing a very considerable moment of force F of the point c 1? require a driving journal of large size, which owing to the great pressure of the journal upon the bearing e leads to a rapid wear of its bush. Taking all that into consideration, it became necessary to invent a method of balancing the centrifugal forces of the sifter, where X would be equal to nought. Since X will be equal to nought if a=b, Engineer Konegen, taking these considerations as basis, offered the construction of a two-box sifter, shown diagrammatically in Fig. 346. In this draw- ing we see that a =b when the centre of gravity of the sifter boxes and the counterweight of the balance-wheel lie in one horizontal plane. Machines made in accordance with Konegen's diagram give a perfectly FIG. 346. FIG. 347. well-balanced run and do not require a journal of so great a size as the one employed in Haggenmacher's arrangement. An unsound idea for a two -box sifter is suggested by Biihler's works in Uzwil, which places the fly-wheel with a counterweight lower than the boxes (Fig. 347). But by setting a second fly-wheel with an inverse counterweight at c 2 , it attains the annulment of the injurious force X. For defining the centrifugal forces R and T of these two fly- wheels, the a and b given, i.e. with position of the fly-wheels to be found, we have : R = 2F + T . . ... (2). And taking the moments 2F and T in respect to the point c l5 we obtain : Tb . . . ';:.- ,J- . (3). Out of (3) we define T=~, and out of (2) we obtain jg= The same plan for cancelling the force X might be adapted to the single-box sifter, and it has been done by American engineers before CHAP. V] FLOUR MILLING 367 Biihler, as we shall see below. The necessity of making the journal excessively large, owing to the heavy pressure on it (the moment 2Fa is very great), does not allow Biihler's works to construct sifters with a large number of trays, as in sifters of Konegen's type. Therefore the largest number of trays in these sifters does not exceed seven. As it was mentioned just now, the idea of balancing the Biihler sifter has been borrowed from the Americans, but it turned out just as badly as the borrowing of the idea of the two-box sifter from Konegen. The American engineers place the second fly-wheel (Fig. 347) higher than the box of the sifter, and balance the pressure caused by the centrifugal force 2F on two fingers e. Such an arrangement of the balance-wheels gives their centrifugal forces K >1 =F and 2F in the total, whereas in Biihler's 5 * * r~ - T 7 : I e i- k,.J D...J -, * v A FIG. 348. diagram R is always larger than 2F, and is equal to 2F only when b is infinitely large, which is, of course, impossible. In drawing an inference from the above considerations, we must agree that the best, perfectly balanced makes of sifters are shown in the two-box diagram of the type illustrated in Fig. 346, after which comes the American diagram in Fig. 347, which allows the spaces A to be utilised, wasted by Biihler, owing to the idea of Konegen's two-box sifter being misunderstood. The use of the single-box sifters (Fig. 345) can be justified only by their extreme cheapness, because these sifters shake the mill buildings greatly, when disposed in the manner accepted by our builders. These machines being still erected in mills, it is necessary to point out the best way of erecting them in the buildings. The sifters are generally arranged lengthways by the plan of the floor which is necessitated by the longitudinal disposition of the roller mills (Fig. 348). To reduce the vibration of the mill by the forces X, there 368 FLOUR MILLING [CHAP, v must be an even number of sifters. In our diagram there are four, and they run in pairs to the right and to the left. But this to a certain extent involves a longitudinal vibration of the mill, since the forces X longitudinally disposed in opposite directions at the moment of the greatest longitudinal declination of the sifters cause the contraction or extension of the floor, the resistancy of which is sufficiently great. At the moment of the greatest transversal deflection of the sifters the forces X act in one direction and tend to upset the building. If the run of the sifters is so set that the sifters 1 and 2 give the greatest declen- sion to the wall CD, and the sifters 3 and 4 to the wall AB, a moment of forces 2X, twisting the building, is obtained. It is possible to plant four sifters so that the forces X of the transversal direction would also give alternately a contraction and an extension of the floor. That would be possible with a great number of sifters. However, even if this were suc- cessfully done, once started, the sifters would soon be thrown off their run, for the unequal slipping of the belts on all the sifters alters the number of revolutions. Hence the shocks imparted to the building are unequal in force, and attain the widest limits after unequal periods of time. The only means of combating the vibration of the mill building, which leads to frequent repairs, and even to its ruin, is to throw out the single-box non-balanced sifters and replace them by two-box ones. Another phenomenon when the run of the sifter loses its evenness, is called " wandering." The wandering generally takes place at the starting of the sifter, and when it has once begun it may gain in power until the stands or the drop-hanger frames of the sifter break. This phenomenon has its origin in the fact that the sifter being started, the force of friction of the pin in the bearing tends to turn the box round the axis of the pin in the direction opposite to the rotation of the finger. To make that clear (Fig. 349), we shall take the points where the supports or the suspension rods are fixed, 1 (left-hand side) and 2 (right- hand side). With the normal motion of the sifter the point 1 or 2 must travel in the circle K. But if the sifter has a tendency to turn round the axis of the finger in a circle M , the point passes into position I 1 , so that its trajectory of motion acquires an elliptic form L. At the same time the point 2 moves to point 2 1 and gives a trajectory L 1 a compressed circle. The nearer to the axis of the finger, the less is the deflection from the circular motion, and the point 3, being in contact with the finger, has no deflection from the normal circular motion K. Hence it is clear that in the stands or drop-hangers 1-1 the wandering causes an extending CHAP. V] FLOUR MILLING 369 deformation and a contracting deformation in the stands 2-2. And if the forces causing the tensions are sufficiently great they may lead to breakage. To avoid this constructive defect some of the works suggest various means of communicating a rigidness to the system joining the supports and the boxes of the sifters. Since it is necessary that the supports should be parallel during the operation of the sifters, attempts are made to hold them in that position by supplementary kinematic junctions. One such device is shown on Fig. 350. The two-box sifter illus- trated is set on four supports a of an ordinary construction. On the foundation frame v there is set a shaft b which can rotate in bearings r. At the ends of the shaft are set rods c 1 and c 2 , the ends of K K I 1 V ?' K r \ ^ FIG. 349. FIG. 350. which, 3 and 4, are connected by Hooke's joints or a spherical journal with rods d l d? attached likewise with joints to the frame of the sifter at the points 1 and 2. It is quite evident that the supplementary stands make the frame more rigid, and form no obstacle to the gyratory pro- gressive motion of the sifter. In this system the shaf tb could have been placed on the lower part of the box, and then the kinematic junction b-c-d would be reversed in respect to the plan given. These supple- mentary junctions may be also fixed to suspended sifters. Another construction of the junctions is illustrated in Fig. 351. The top ends of the system c l -b-c z here have circular discs / l -,/ 2 , which glide between two guide-plates g^-g* attached to the boxes of the sifter. The system cMj-c 2 being perfectly rigid, the centre line of the discs is always parallel to the shaft b. When the sifter is in rotation the discs will be running up and down, to the right and to the left (components of motion). therefore wandering is here impossible. 2A 370 FLOUR MILLING [CHAP, v A third method (Fig. 352) gives the system n^-b-n 1 , the ends of the levers h 1 and n 2 being joined fast to the foundation supports a 1 and a 2 . A detail of these junctions is to be seen in Fig. 353. A variation of the third method, where the diagonally set stands are joined and not the side ones, is shown on Fig. 354. Of all the systems examined, only the second prevents wandering FIG. 351. c*' FIG. 352. (Fig. 351). The two other systems do not give absolute regularity, and they therefore should be displaced in the models offered by some of the European works, which are mostly variations of the second method (Biihler Bros, and Kapler). The problem of preventing the tendency to wander has been perfectly, correctly, and expediently, from the constructive point of view, solved by the American works and by Thos. Robinson's works in England. FIG. 353. FIG 354. We shall first examine the American method. Fig. 355 illustrates the transmission of motion to the box of the sifter evolved by the I. Schultz O'Neile Co. of Minneapolis. The toothed gearing to the shaft 4 is set in the main frame, to which a cross-head 7 is bolted. On the cross-head there are set adjustable bearings, a detail of which is shown on C, for two rods 14 with rolls 15 freely set on them. These rolls enter into the guiding cross-head and slippers 17 bolted to CHAP. V] FLOUR MILLING 371 the frame. The shaft 4 is joined fast to the cross -head 24, into which the driving pin set in the lower part of the sifter box enters. To the same cross-head, with bolts having a spring thrust, is attached a counter- weight 25, which may be brought closer or farther with the aid of nuts a. When the sifter is set in motion, its box performs a gyratory progressive motion, which is composed of the motion of the rolls to the right and to the left, and of that of the guiding slippers 17 backwards and forwards. Fig. D shows the construc- tion for large sifters. In this wise, here we find adapted the principle examined in Fig. 351. It is difficult to judge of the rigidity of this machine or of its efficiency, since the sifters have made their appear- ance on the market but lately. The problem of obviating any wandering was solved in the most expedient manner by the American engineers, who first suggested adapting two driving pins. Figs. 356 and 357 illustrate the method of transmitting the motion to A. Wolf's sifter, eliminating all possibility of wandering. The box of the sifter is supported on four stands B. The driving pins / of the fly-wheels freely enter into the hubs d, which are adjusted by means of bolts d 1 . The balance-wheels F with the counterweights are brought into rotation from the belt-pulley S with the aid of toothed gears h-h l . To impart a greater smoothness to the run a belt g is set on the fly-wheels F. In this construction the turning of the sifter round its axis, i,e. the wandering motion, is impossible. Of the European works, that of Thos. Robinson in England constructs FIG. 355. 372 FLOUR MILLING [CHAP, v the transmission of motion on the same principle, i.e. with the aid of two cranks. On Fig. 358 we have a diagrammatic illustration of the IT ITU FIG. 356. FIG. 357. transmission in Th. Robinson's two-box sifter of the latest type. The boxes A are joined together by H -irons 1. The cranks 4 are fixed FIG. 358. in plates 5 joined to the H -irons and cross-bars 6. The balance-wheels 2 with counterweights are brought into motion by one common belt 3, running over the driving pulley 8 and the jockeys 7-7 1 . The jockey 7 CHAP, v] FLOUR MILLING 373 at the same time serves as a belt tightener. The frame of the bearing holding this jockey is set in the guiding cross-head and slippers and joined by lever -joints 1 1-12-1 lj, the last of which has an adjust- able weight Q. By moving it to the right or to the left, we may slacken or tighten the belt. A perspective view of the sifter is shown in Fig. 359. The drive evolved by Thos. Robinson is decidedly superior to that of A. Wolf, as it discards the rigid and uneconomical tooth gearing. But Wolf's drive is better in so far that each balance-wheel has an independent 374 FLOUR MILLING [CHAP, v gearing. However, both the drives should be absolutely accurate. In Th. Robinson's drive there must be a great accuracy in the equality of diameters of the fly-wheels, otherwise, even with the difference of 1 mm. in the diameters, the belt will acquire a strong slipping motion on the smaller pulley, which will cause a rapid wear of the belt. In our opinion Robinson's construction might be improved by throw- ing the belt off one of the pulleys and connecting the driving cranks by a coupling rod. In this way even a considerable difference in diameters of the fly-wheels would be of no consequence. Thus, making an estimate of the types of sifters from the point of view of dynamics, we must give preference to two -box sifters, to such types besides, which have the balance-wheel with the counterweight set between the boxes, and the distance between the horizontal planes of the centre of gravity of the sifter and of the balance-wheel equal to nought or very small. In selecting sifters with mechanisms preventing wandering, those should be chosen where this is effected by means of two driving cranks which absolutely prevents running off. 4. American Sifters In the development of sifter construction, just as in the building of roller mills, the Americans chose a route totally different to that of the Europeans. A characteristic peculiarity of their sifters is the inclined, zigzag-shaped arrangement of the sieves. Having observed the inequi- librium of motion in the single-box sifters with one counterweight, the American engineers were the first to solve the problem of equilibrium. The first (A. Wolf's) type, designed to obviate the running off of the sifter during operation, also belongs to the Americans. These considerations, as well as the ignorance not only of the Russian but of the European technicians too, of the constructions of American sifters, 1 induced us to devote a separate chapter to them. Noye's Zigzag Sifter. Figs. 360 and 361 show us the longitudinal section and the perspective view of Noye's sifter. The box of the sifter consists of two divisions for sieves, between which there passes the driving crank-shaft v carrying two hand-wheels with counterweights q. These counterweights may be moved closer to or further from the axis of rotation by means of a screw r. The lower hand-wheel is cast in one 1 Only in Pappenheim's work is there a general description of the sifter built by the works of Nordyke & Marmon Co. CHAP. V] FLOtm MILLING 375 piece with the driving belt-pulley s. The shaft rests on the step-bearing t and is held in a vertical position by two bearings o set in the cross-bars of the frame A. The bearing p driven by a crank shaft is fixed in the bottom of the sifter box, which is suspended on four rods a with ball bearings. The product is fed in through S and falls on the sieve 1, which delivers its overtails (break semolina, middlings, or bran) through the spout s 1? while the throughs drop on to the cloth 1 1? which passes it to the sieve 2. The sieve 2 has the large tailings discharged from the sifter and passes the throughs to the sieve 3, which, together with the tails of the sieve 4, carries the product to the last sieve 5. The throughs from the sieve 4 are sent out of the sifter by the cloth 4 X together with the throughs of the sieve 5 by means of the cloths 5 t . Thus the sieves 3, 4, and 5 yield flour as FIG. 360. FIG. 361. throughs into the spout /, the sieve 5 in its lower part gives dunst as throughs to the spout //, the sieve 1 large tailings into spout ///, and the sieves 2, 5, and the cloth 6j tailings of mixed middlings into the spout IV. The cleaning of the sieves is performed by brushes brought into operation by a rather complicated device. On the wires c thrown across the guides b, there are fixed the brushes /, which run under the sieve for- wards and backwards. The wire tracking c after the guides b, doubling over the idlers d, all join together at c with the chain of the gearing, which is brought into operation from the shaft v by the pulleys 7-8 and by the conic toothed gear n. To prevent the flour from escaping, the openings in the box for wire tracking are covered with casings B. For guiding the driving belt there are the loose pulleys D. Nordyke & Harmon Co.'s Sifters. The balanced two-box sifter from the Nordyke & Marmon Co. works, with a zigzag arrangement of 376 FLOUR MILLING the sieves, is shown in Figs. 362 and 363. The boxes A are joined to their foundation frames by cast-iron parallel guides / and cross-heads T, in which the bearings of the driving shaft V are fixed. The boxes are suspended on four cane rods E : Mis the driving belt pulley, the guid- ing loose belt-pulleys, which are fixed on brackets Q adjusted by means FIG. 363. of screws G. Above and below the boxes there are counterweights 8 set on the shaft V: H and E are the oil boxes feeding the top and the bottom belt-pulleys. The rods are fixed to the thick ceiling board J, set across the ceiling beams K. A longitudinal section of the sifter box is given in Fig. 364. The bolting trays 1, 2, 3, 4, and 5 are arranged in zigzag manner with different inclines according to the size of the product, the greater incline corre- n: FIG. 364. FIG. 365. spending to the first sieve, which bolts the coarser product. Owing to the different inclination of the sieves, we obtain correspondingly different velocities of motion of the product treated. This very important con- dition of an even sifting of the coarse and fine product is not taken into consideration by European engineers. For feeding the throughs to the following sieves there are the inclined timber plates 1 1? 2 X ,3,, 4j and 5j. The sieves are cleaned by means of brushes a. CHAP, v] FLOUR MILLING 377 Into the box of the sifter, through the side, are inserted the bolting trays, the perspective view of which is illustrated in Fig. 365, and in section in Fig. 366, where it may be seen that each tray is clothed with a working sieve on the upper side, and an open wire tissue for the brushes from below. The tray is divided by transversal timber cross-pieces a to limit the area of operation of the brushes and to prevent their meeting. An ordinary arrangement of counterweights is shown in Fig. 367 (the -bottom counterweight), which likewise gives an idea of the trans- mission of motion to the boxes. The cast-iron belt-pulley has a large hub B in which there is an adjustable bearing A for the shaft. This bearing is adjusted by means of a set screw on one side and a tension spring D. The counterweight E can be moved in the guiding parallels by FIG. 366. FIG. 367. turning the set screw F. In the counterweight there are cylindric holes, in which in case of need the supplementary weights G are put, and fixed from below by bolts passing through holes in them. Sifters made at Wolfs Works. We have already partly become ac- quainted with one of the makes of Wolf's sifters. Figs. 368 and 369 represent a longitudinal and a cross-section of one half of the sifter, operating for two products. In this sifter, as almost in all American types, the sieves are set in a zigzag line. The sieves are placed into the box from the side, and held by means of cast-iron planks a fastened by thumb-screws b. The motion is communicated to the sifter, as we have seen earlier (p. 372, Fig. 358), by means of two driving cranks and balance- wheels with counterweights brought into rotation by conic toothed gears. The number of bolting trays, five, is the same as in the preceding construc- tion, with a similar flow of the product. This sifter does not wander, but its run is not balanced, therefore 378 FLOUR MILLING [CHAP, v the vibration (force X, p. 366, Fig. 347) of the shafts v, communicated to the floor through the bearings d, tends to shake the mill. A section of Wolfs balanced sifter is shown in Fig. 370, and its dif- FIG. 368. FIG. 369. ferent parts and disposition of sieves are shown in Figs. 371, 372, and 373. The drawing of Fig. 370 shows us that the counterweight Q is set inside the box A, so that its centre of gravity lies in the plane of the centre of gravity of the box. The crank-shaft is not made in one whole piece, but con- sists of two parts, v and v lt con- nected by joints at o. The top part of the shaft rotates in ball and socket bearings of the cross- heads b connected with the box of the sifter as shown in Fig. 372. Owing to a special construction of the junction at o, the sifter can fluctuate in the inclined plane, passing from position 1-1 to 2-2. Let us examine more minutely the driving mechanism shown in Fig. 371. The lower part of the shaft v is set on a ball collar thrust bear- ing a and held in a vertical position by two ball bearings c. On the top part of the shaft v there is set a split belt-pulley S on the hub P of the cup T. The upper crank part of the shaft v 1 has at its lower end a cavity for the FIG. 370. FLOUR MILLING 379 CHAP. V] finger of the ball bearing o, which enters into the steel shoe of the top end of the shaft v. The inner arms of the cup T and the cross-head ra fixed to the end of the shaft v l form a cross -head coupling of the shafts v and v lt resembling the junction of driving irons in stone mills, owing to which the rotation of v is communicated to v 1? and consequently to the sifter. The FIG. 371. shaft v is also held in two ball and socket bearings. The counterweight Q is bolted to the shaft by bolts n : such fixing of the counterweight allows of easily raising or dropping it when necessary. By means of cross-heads b and set squares d the whole system is coupled with the box of the sifter. This balancing arrangement totally obviates the possibility of vibration, since the centrifugal forces of the sifter box and the counterweight run in one plane. 3SO FLOUR MILLING In Fig. 372 is shown a horizontal section of the sifter box above the counterweight. The sifter can bolt four or eight distinct products ; in the latter case the sifter is divided into two floors. The box is suspended on brackets k for the cane rods. The wire sieves are cleaned by means of heavy tappers t, and the silk ones FIG. 372. by thin steel chains p attached with their ends to the frame of the sieve. A longitudinal section of the sifter is shown in Fig. 373. Here one part of the sieves is given in longitudinal section, and one in cross-section. The sifter we are examining is built for eight products, i.e. each section operates independently for two products. For each product there are six bolting trays, every one of which has its own cloth. The tray 1 gives CHAP. V] FLOUR MILLING 381 break I as tails, the tray 2 middlings //, trays 3, 4, and 5 yield flour as throughs, and the sixth tails over fine middlings and gives dunst as FIG. 373 throughs. The- lower floor of the first section differs in that the second semolina tray is substituted by one for flour. This sifter serves for a mill having four breaks and four reduc- tions. 382 FLOUR MILLING [CHAP, v 5. Free Swinging Plansifters As we have seen already, both the single and the double box sifters have one sole defect from the point of view of their dynamics. They both wander, i.e. tend to revolve round the axis of the crank, particularly so at the start. However, this fault- has been also obviated by the con- structors at Robinson's in England, and Wolf's in America, with the aid of two driving cranks. Thus, from the standpoint of dynamics, the sifter is a quite perfect machine at the present moment. But now a new problem has presented x FIG. 374. FIG. 375. itself to the engineers to simplify the relatively complex and heavy details, of which the crank driving the sifter-boxes and the balance- wheel with the counterweight are considered to be the parts most open to criticism. This question was worked at by American and European constructors, and finally, at the end of 1911, there appeared several patents, first in America and then in Europe, for so-called " self-balancing " sifters. Before giving an estimate of these sifters from the point of view of dynamics and of other circumstances characterising the merits and defects of the new machines, we ought to make the student acquainted with their construction. The classification of the new machines must be based on the character of the driving mechanism. In this respect there are known two kinds CHAP. V] FLOUR MILLING 383 of drives, rigid ' and flexible. Both types of construction totally obviate the crank method of obtaining the gyrating rotary motion. Fig. 374 illustrates a perspective view of the sifter from " The American Machinery Co." works, which brought out this new type of machine as early as November 1911. The new construction is a two-box sifter suspended on four sets of canes A . It is brought into rotary motion by the shaft B, which is coupled to the sifter and the driving belt-pulley as shown on Fig. 375. The steel cross-head G, ending in a hollow finger D, couples the sifter boxes. On the finger there is loosely fitted the bush E, to the base of which the shaft B is joined, by means of a screwed-on nut a covered by a box washer 6. This bush carries a weight F, which rotates freely on a joint. The top end of the shaft is supported by a ball bearing entering into the filbore of the drop -hanger frame K. The belt-pulley H is set on the shaft B so that its centre line lies on a plane with the centre of rotation of the ball bearing. When starting the sifter . the belt-pulley H receives its motion from the driving-belt and brings the shaft B into rotation. The ball bearing G glides in the filbore of the drop -hanger frame. At first the bush E glides over the finger D without bringing the sifter into operation. But in proportion as the mtmber of revolutions increases, the weight F develops a centrifugal force ; it rises and carries the finger D aside with it. In this manner the gyrating rotary motion of the sifter is obtained owing to the centrifugal force of the weight F. This system of driving the sifter we call " rigid," to distinguish it from another construction which will be examined later. After the type of the American sifter, also with a rigid drive, a new construction (Fig. 376) has recently .been evolved by the works of Am me, Giesecke, and Konegen in Brunswick. 1 So we shall conventionally name the drive from a rotating shaft- FIG. 376. 384 FLOUR MILLING [CHAP, v The idea of a free swinging sifter attracted the constructors so much that almost all more or less large European works, one after the other, began supplying the market with machines of that type. One may say that the works were seized by an epidemic of constructing sifters to work on the principle of utilisation of the centrifugal force. The works " Erste Landwirtschaftliche Maschinenfabrik," in Buda- pest, and those of J. Prokop in Pardubitz, Austria, almost simul- taneously put on the market free swinging sifters with flexible drives. Besides that several patents more were claimed for similar sifters, of which the most typical in its idea is Karl Gillesheimer's construction, shown in Fig. 377. The essence of the con- struction of Gillesheimer's sifter consists in the following. The sifter box is suspended on four rods /. The fast pulley d is made to rotate from the shaft b by means of the belt-drive a guided by two jockeys c, fixed on the box of the sifter. The belt-pulley d is set on the shaft g to which the weight n is fastened. The shaft g rotates in bearings h and i coupled to the frame e. An important part of the mechanism is the friction coupling. The top part k of the friction clutch is keyed on the shaft, and the bottom part is formed by the belt-pulley d freely rotating on the shaft g. On the upper end of this shaft is fitted a spring I, the tension of which is adjusted by a nut ra. By altering the tension of the spring, the pressure of the friction disc 1c can be altered, owing to which the force of friction of the clutch alters, and a modifica- tion in the magnitude of the moment rotating the box is thus attained. When started, the belt-pulley d at first glides over the friction disc Ic, and then gradually the force of friction forms a moment of sufficient magnitude, which brings the sifter into a gyrating rotary motion, and when the number of revolutions reaches the normal the gliding motion ceases. According to the inventor's idea the friction gear must at the same time be the regulator of the number of revolutions, since, in FIG. 377. CHAP. V] FLOUR MILLING 385 case of increase or decrease of the number of revolutions of the belt- pulley d, and consequently of the counterweight n as well, there springs up a force of friction between the disc and the belt-pulley, which either acts as a brake (if the number of revolutions increases), or drives the pulley d along with it. The Voll and Mertz free swinging sifter with a flexible drive is given on Fig. 378. The gyratory rotating motion of Voll and Mertz's sifter is based on the principle we have already examined. The weight g is set in the fly- Longitudinal section of the Sifter through AB. Cross section of the Sifter through CD. Plan of the Sifter without Sifting Trays. FIG. 378. wheel a in the same manner as the counterweight is set in the crank sifters. This fly-wheel is fastened on the shaft, which is supported by a ball-collar thrust-bearing c and a ball-bearing d, fixed to the cross-bar p of the frame coupling the sifter boxes. On the same shaft as the fly-wheel there is set the receiving belt -pulley b driven by means of a belt, which is carried to this pulley by means of jockeys / stationed on the sifter boxes. All the constructions examined show that the gyrating rotary motion of the sifters is attained owing to the action of the centrifugal force, first of the weight, and next of the sifter itself. Passing by a more minute estimate of the constructive details of free swaging sifters, which, doubtlessly, will be still more perfected, we shall 386 FLOUR MILLING [CHAP, v direct our attention to the fundamental merits of the new machines, which are ascribed to them by their inventors. 1. A free swinging sifter requires no bulky setting of the crank shaft, which makes the machine, as well as its erection, heavier, more expensive and complex. 2. From the dynamic standpoint the free swinging sifter is an ideal machine, giving no shocks to the mill building. As concerns the first point, i.e. the simplification and reduction of weight of the construction, this may be acknowledged as true, but only to a certain degree. The bulky mounting of the crank shaft is indeed discarded, but the rigid as well as the flexible drives have several defects. Firstly, the American rigid drive has a complex ball drop-hanger frame, which will hold the oil badly. Also its belt-pulley performs, besides the ordinary rotatory, a conic motion, which causes unequal tension of the edges of the belt. Secondly, the flexible drive is far from perfection, because the guide pulleys have a gyratory motion, owing to which their middle plane falls out of its normal position, and causes the belt to be drawn off the pulley and the angle of contact to alter. These circumstances must lead to an irregularity in the work of the belt-drive. However, the defects pointed out are not very considerable and may easily be avoided. For our own part, we would advise the constructors to pay serious attention to the electromotive transmission of motion to the sifters, retaining the principle of utilising the centrifugal force. If a friction clutch or a chain wheel were to be set on the shaft carrying the weight, as in the case of the American sifter, or on the fly-wheel with the weight, as Voll and Hertz's sifter has it, and bring it into rotation from the electromotor, 1 then the complex ball drop-hanger frame, driving belt-pulley, guide-pulleys, &c., become quite superfluous. To the motor of the sifter there will be only wires running from the ceiling, which will totally obviate the inconveniences of belt-drive, which work here under unfavourable conditions. 6. Capacity of Plansifters The capacity of sifters, like that of other bolting machines, is charac- terised not only by the quantity of product sifted through a unit of bolt- ing surface, but also by the quality of that work, i.e. the accuracy in separating the product according to size. If the overtails contain particles pf product, which, judging by their size, should have passed through the i The great number of revolutions of the motor prevents a direct transmission from it to the ny- wheel. CHAP, v] FLOUR MILLING 387 meshes of the sieve, the work of the bolting machine is unsatisfactory, the machine is overloaded. When testing the capacity of bolting machines we suppose the quality of the work to be defined with an accuracy of up to 5 per cent., i.e. the tails contain not more than 5 per cent, of the product which should have passed through the sieves. The, capacity of plansifters, as also of reels and centrifugals, is best determined by experiment, but a theoretical elucidation of that question, in the shape given to it by Professor Zworykin, deserves attention. First of all it is interesting to define the general bolting area for a given bulk of product, regarding the latter as the capacity of the mill in question. We have seen that the capacity of roller mills is expressed in kilo- grams thus : Q = elvd ... (1). where I is the length of the rolls, v the velocity of passage of the product through the rolls, <5 the distance between the rolls (average size of the product) or the thickness of the sheet of product, and e is the practical alterable coefficient. Professor Zworykin takes the bolting capacity proportionate to the area of the sieve and approximately proportionate to the square of the size of the product. By this reason Q obtained from the rolls and to be bolted now, is expressed by the formula : Q-e^AP .. . . . . . ... (2), where A is the bolting area, 6 largest size of the product, and e x practical alterable coefficient. From (1) and (2) we obtain : and hence the A sought for : "-,;.;." ' ' A ^J < 3 >- In this formula 77 = . The capacity Q of stone mills is formulated thus : where v is the radial velocity of the product discharged, d the average dimensions of the product. On the other hand Consequently, A-, .... . , . /:. (5). 388 FLOUR MILLING [CHAP, v If for rolls, both grooved and smooth, we accept the velocities v to be constant, as V Q for millstones, the magnitude of the areas of sieves will be : A -- d for roller mills, for millstones. These formulae are useful only if we have succceeded in deducing a series of values for tj and r)\ from practice, which requires serious experimental work on a large scale. At the present moment we are obliged to make use only of the data concerning the capacity of plan- sifters given by the works, correcting them after the results of practice. Comparing the capacity of different bolting machines, Professor Zworykin gives the following table (Table XXXVIII) : TABLE XXXVIII SYSTEM. Capacity of 1 square metre bolting surface per 1 hour. Polygonal reel Centrifugal .... Haggenmacher's sifter . up to 15 klg. of flour 70 100 In other terms, centrifugals have a capacity 4-5 times greater than reels, and the plansifters 6*5 times. According to F. Kick's researches, 1 square metre of working surface in Haggenmacher's sifter has a capacity only four times as great as that of the reel. Below we give a table (XXXIX) of the more up-to-date results as regards the capacity of reels, centrifugals and sifters according to Baum- gartner and Notovitch. TABLE XXXIX Product to be Sifted. Area of Sieves in Square Metres for Boiling 36 Ib. of Product per 1 Hour. Polygonal Reels. Round Reels. Centrifugals. Plansifter. 1 . Break Chop . 2. Fine Chop (midds etc.) 3. Reduction 50-60 per'l cent, of flour and 50-40 1 per cent, of dunst . . J 0'123sq.m. 0-350 0-50 0-110 sq.m. 0-140 0-160 0-025sq.m. 0-070 0-100 0-230 sq.m. 0-330 ' CHAP. V] FLOUR MILLING 389 When calculating the number of sifters required for the given capacity of the mill, Table XL may be used, where the capacity of two-box sifters with two, three and four sections having different numbers of bolting trays is given. TABLE XL 1 Number of Dimensions of Capacity of the Sifter Bolting Trays. in Cwts. per 1 Hour. 1 .5 *> Wheat. Rye. What Part of the e a g 8 Sifter. & "2 j . 1 S3 JS | 6 Si8 |1L| sH 1 2 c8 a n 88 eq o 8 2 53-0 27-3 33-6 Whole sifter 3 10 ! 1400 865 26-2 13-6 16-8 \ of sifter 4 ... ... 13-0 6-5 7-8 4 55 2 63-5 31-2 40-0 \ of sifter 3 12 1400 865 31-0 15-6 20-0 43 SJ 55 4 14-7 7-2 9-5 1 i cS $ 2 ... ... ... 50-0 22-0 27-3 N ^ of sifter 3 6 1600 925 25-0 11-0 13-6 \ 4 ... ... ... 12-0 4-8 6-1 O ft i 2 55-8 27-3 33-6 O IQ ^ of sifter 3 8 1600 925 27-9 13-6 16-8 O i 4 13-4 6-1 7-8 5 i ! CO ' 2 . . . ... 67-4 33-6 41-5 a ^ of sifter 3 10 1600 925 33-7 16-8 20-8 s t 4 16-3 7-8 9-8 4 55 2 79-0 40-0 49-2 i of sifter 3 12 1600 925 39-5 20-0 24-6 2" ? j 4 ... ... ... 19-0 9-5 11-9 1 The capacity of round sifters of the Bunge type is given in Table XLI. 390 FLOUR MILLING TABLE XLI [CHAP, v i (Capacity of Sifter in rp Bolting Trftys in mm. Working Surface in Mt.2 Number of Revolutions per Minute. Cwts. per Hour. Power Consumption, H.P. Break Chop. Reduction Stock. 11000 3-1 ( 12-2 7-4 0-12 1300 5-2 \ H0 J 21-0 12-2 0-15 1500 7-0 I 1 28-5 16-2 0-20 1700 9-0 J ' 36-5 20-3 0-25 ( 1000 5 1300 4-0 6-6 ( 14-8 24-3 9-0 14-8 0-15 0-20 trays 1 1500 8-8 - 150 \ 32-4 18-7 0-25 1700 11-3 40-5 1 24-3 0-30 In spite of this table showing the capacity of round sifters to be almost the same as that of rectangular ones, in reality it should be re- garded as much smaller (up to 25 per cent.), taking into consideration the quality of work, which is incomparably lower than the work of rectangular sifters, where it is performed on six trays at least. In comparing the quantity of work done by plaiisifters and the other bolting machines, we see that the sifter stands considerably higher as regards capacity. But the quality of work of the sifter is also higher than that of polygonal and round reels. Experiments prove that at the bolting of the products (reduction of middlings) some 50 per cent, of flour is tailed over, together with fine middlings and dunst, which makes a complementary bolting indispensable, in its turn requiring a considerable increase of the working surface of the sieves. Since there are no investigations of the quality of work performed by sifters and reels of a later date, we shall give the results of experiments made by I. Wingert, the president of the German Millers' Society, who tested Haggenmacher's sifter and the reel, and published the results of his investigations in Die Muhle, 1889, No. 6. The experi- ments were performed on the bolting of the product of middlings reduced on French stones. The results were as follows : Flour . Middlings Offal Sifter. Reel. 74-52 per cent. 43-83 per cent 25-36 54-46 0-12 1-71 100 per cent. 100 per cent. CHAP, v] FLOUR MILLING Thus, more than a half of the flour and dunst, which could have been discharged with the flour, were separated as middlings on the reel (54-46 per cent.), whereas the sifter yielded 25-36 per cent, of pure middlings unmixed with flour. The advantage of plansifters in comparison to other types of bolting machines needs no proofs now. And if the reels are not generally supplanted as yet, they are retained only in primitive mills, where the quality of the flour is of no importance, or this flour has to compete with flour of unsifted grinding, as in peasant windmills, or water-mills of the Caucasian type. CHAPTER VI GRADING THE PRODUCT ACCORDING TO SPECIFIC GRAVITY GRADING MIDDLINGS AND DUNST ACCORDING TO SPECIFIC GRAVITY SINCE the flour -milling technics evolved the system of high grinding, the sorting of the intermediate product according to its specific gravity has been undoubtedly one of the most important stages in the milling process. Indeed, from the moment he has separated the middlings and the dunst according to the quality, the miller proceeds to define the grades of flour. The removal of the branny and colouring particles of grain from the valuable starchy middlings, which give high grades of flour, is no easy task. A solution of this problem was being sought by flour-milling engineers for a whole century, and only now is it solved almost to perfection. Although the repeated milling (mouture bconomique) is an invention of the French, who practised it 150 years ago, the character of the wheat soft, with comparatively moist integument never suggested to the French flour-millers the idea of grading the middlings according to quality. In the old French process of repeated milling 1 the elastic coverings of the soft wheat very successfully resisted reduction when passed through grinding machines, and gave a comparatively insigni- ficant percentage of bran reduced to flour. A considerable part of the integument therefore was easily removed with the aid of bolting apparatus. The result of a repeated milling of hard wheats is totally different. The dry shells are reduced to fine bran, which it is impossible to separate from the meal by bolting machines. The fine bran imparts a darker colouring to the flour and lowers its quality and market value. The French repeated milling, widely spread in Europe, with the aid of which an excellent flour according to the standard of the time was obtained, proved to be unsuited for hard Hungarian wheats. With a view to attaining the same results in milling as with the soft wheats 1 As a type of such milling, the rye milling of to-day may be taken, with the sole difference that roller mills are substituted in the place of grindstones. CHAP, vi] FLOUR MILLING 393 the Hungarian flour-millers thought of damping the wheat, so as to moisten the bran, and in this manner make it more elastic. The imperfect damping processes, however, offered great inconveniences, in so far that the wheat was moistened too copiously, the moisture penetrated into the kernel of the wheat, the flour obtained was " damp," and could not stand long storage or export. Thus the first impetus was given to the Hungarian millers to direct their inventive faculty towards other ways of freeing the flour of branny admixtures. In the first place, Ignatz Paur, a flour miller, introduced a slight improvement into the French repeated milling, by greatly altering the distances between the working surfaces of the grinding stones, and thus making the first steps towards modern high-milling (Hochmiihlerei is derived from Hochmiihle, showing that the runner stands high over the bed-stone in the first passage), and then, winnowing the blue flour away from the heavy semolina by means of hand bellows, the primitive shape of a special type of purifiers, which, however, took no root in practice. Owing to this improvement Austria-Hungary first sent to the market a granular flour for bread of the highest grade and semolina for immediate use. That semolina, very much resembling our " manna," was called Wiener Gries, i.e. Viennese semolina. Thus, the hand bellows gave Ignatz Paur the idea of sorting the pro- duct according to quality, i.e. specific gravity. In 1810 he invented the first purifier which is known in the history of the development of flour milling under the name of " The Viennese purifier." From that date the milling process is richer by a very important stage grading of middlings according to the quality. For the period of a century flour milling has seen hundreds of con- structions of purifiers, but the fundamental principle of their action has remained the same. For this reason, before proceeding to review the purifiers in their historic succession, beginning with Ignatz Paur's, it is necessary to dwell on the theoretic foundation of the chief principle of action of every purifier. If we compare the weights of equal bulks of cleaned and uncleaned middlings, both kinds being of equal size, we shall see that the impure middlings are less in weight. This weight is lost at the expense of the grains of middlings, which have one of their facets covered with the integument of the kernel, because the bran in specific gravity is much lighter than the inner starchy parts of the wheat or rye. Further, the weight of uncleaned middlings is less owing to the splinter-like 304 FLOUR MILLING [CHAP, vi particles of the bran, which pass as throughs or overtails from one and the same sieve together with the good middlings. In this manner after sifting we have a mixture of particles equal in size but unequal in weight. It was that difference in the weight of separate particles that the constructors availed themselves of, to separate the light particles, i.e. bran and middlings with integumental elements, from the heavy or, in other terms, rich product. It is evident that if two falling grains of product, equal in size but different in weight, should be subjected to the action of an air-current, the lighter particle of grain will be carried further than the heavier one. But for the constructor of a machine sorting the middlings according \ V \ FIG. 379. //Direction of the wind. to quality, it is important to know not only this obvious fact, but also the law of motion of the particles influenced by their gravity and the constant force of wind fanning the product to be graded. And only when that law of motion has been defined, is the constructor enabled to start working out a rational type of machine confidently, and without groping about for a rational type of machine. Thus, we are to solve the following problem : to define the law of motion of a particle subjected to the action of two constant forces. We shall first examine a general case, when the particle faUs into the sphere of action of the draught with a certain initial velocity v . For simplicity's sake let us imagine (Fig. 379) we have an inclined spout T, down which the product flows into the chamber Q with that same initial velocity v . On leaving the spout the particles of middlings undergo fanning by a horizontal air-current. CHAP, vi] FLOUR MILLING 395 We suppose 0, where a particle of the stock m is on passing from the spout in Q, to be the beginning of rectangular co-ordinates, of which OX coincides with the direction of the draught, and Y with the vertical, i.e. with the direction of action of the gravity. The velocities a and 6 are components of the initial velocity v . On marking the force of the draught mw, where w is the acceleration of motion along OX, we obtain the following equations of motion for the particle of stock m : m w= mw dt* or w^ & To define the laws of motion along OX and OY, we must evidently egrat' obtain : dx integrate these equations. Then, bearing in mind that -r-=V x , we |3F To define the constant C we suppose t=o, i.e. we define V x at the initial moment of motion. Then, naturally Ca from V x -\-C=O. Consequently, the law of velocity is : , , . . . . . . (3). By integrating a second time, we obtain : \dx = \adt+ \wtdi or But since t=o, we have x=o, consequently 0-^=0. Thus the law of motion along OX is : . . ...... (I). Having done the same with the differential equation of motion (2) along the axis OF we obtain : . '. . .'. . . (II). Now, to define the trajectory of motion of the particles, we must exclude t out of (I) and (II). By reducing these equations to the same 396 FLOUR MILLING [CHAP, vi denominator, multiplying I by g, II by w, and subtracting the second from the first, we obtain : 2x=2at+wt 2 I g 2y=2bt+gt 2 \ w 2(gxwy)=2(agbw)t Hence we define t=^ X ~^ and substitute it into the second equation. ag bw Then we "have : 2 After reducing x and y to the same denominator and arranging them according to degrees, we obtain the equation of the curve : g s x 2g 2 wxy -\-gw z y 2 +2bg(ag bw)x 2ag(ag bw)y =0. Consequently, we obtain a curve of the second order of the follow- ing shape : Ax z +Bxy+Cy*+Dx+Ey=Q. The absence of the constant term F shows that the curve passes through the beginning of the co-ordinates, as it should. The term B 2 4AC, after the substitution of corresponding coefficients (A=g*, B=2gw 2 , and C=gw 2 ), is equal to 0. Hence it follows that our curve is a parabola, one branch of which passes through the point 0. Now the position of the axis of the parabola remains to be defined. For the equation of the axis of the parabola in general outlines we have the following formula : l Having substituted the corresponding coefficients A, B, C, D, and E we obtain the following equation of the axis : -g(w 2 +g 2 )x+w(w 2 +g*)y-(ag-bw)(bg+aw)=0, or l ' ' ' ^ '' In this way the axis of the parabola lies crossing the axis 7 below the point and the axis X to the left from the beginning of the co-ordinates, because we see from the equation of the parabola axis that the segment it strikes off the axis X has a negative magnitude. The direction of the parabola axis will be defined in accordance with the angular coefficient, 1 Analytical Geometry, Briot and Bonquet, p. 148. CHAP, vi] FLOUR MILLING 397 which will give us a very simple formula for the equation of the axis we have obtained : If we define now the direction of the resultant of two component forces mw and mg we obtain from the triangle OES : mgmwtgy, whence tg &i> while the offal is carried away through the tube r to the dust- chamber. The number of middlings grades here is three, and the number of fannings two, though four to six floors of k could be made, and then four to six aspirations would be obtained. The theoretic problem of motion of the particles for this type of FIG. 388. Fio. 389. purifier is most simple, but the introduction into the machine of a con- structive device in the shape of gyrating discs rendered it considerably more complicated ; that type of purifier is therefore quite extinct now. With this the history of the first period of development of purifier may be concluded. Beginning with the eighties of the last century, the machines for grading the stock according to quality begin to develop into another type. II MIDDLINGS- AND DUNST-GRADING MACHINES OF TO-DAY After the series of modifications in the constructions of machines for grading the middlings and dunst according to quality recorded above, modern technics fixed upon two types of machines. One of these types retained the principles of Haggenmacher's first purifier, which in Pro- CHAP. Vl] FLOUR MILLING 407 fessor Zworykin's terminology was called " self purifier " ; 1 the other is a machine, in which the product moves over the sieve. The air passes through the sieve and lifts the light particles of stock. This type of machines Professor Zworykin names the " sieve purifier." Haggenmacher and VolVs Gravity Purifier. The latest construction of Haggenmacher's gravity purifier, patented jointly with Voll in 1907, is designed mainly for large and partly for medium middlings. This gravity puri- fier is always set to work in conjunction with the middlings grading sifter, and is, therefore, also named " the group." The middlings, graded according to size by the sifter into from eight to six- teen grades (Figs. 390 and 391, eight grades of middlings in all), pass into the hoppers A, the outer wall m of which is a self-adjusting gate with a weight g. The feed roll a feeds the stock in an even stream to the spreader board b, in sliding over FIG. 390. _:z. FIG. 391. which the particles of middlings, equal in size but unequal in weight, 1 In England this machine is known as the " gravity purifier," in contradistinction to the *' sieve purifier." This term will therefore be employed in the text. 408 FLOUR MILLING [CHAP, vi acquire different velocities of motion. Running off the spreader board, these particles have various speeds, and therefore, when meeting a current of air, give different deflections from their initial direction. Falling in accordance with their quality into the bottomless feeding boxes c, the middlings pass through them into the chamber space, where they undergo a second fanning, after which the cleaned product drops into hoppers d, divided according to quality. Over these hoppers adjustable valves are placed, and may be moved to the right or to the left, according to the force of the draught from the fan and the size of the stock graded. From the hopper d the graded product runs to the worms and is discharged by them from the machine. The Double Gravity Purifier. In Figs. 392 and 393 is shown a double gravity purifier, also built by Haggenmacher and Voll. The stock falls first upon the top sieve S feeding the throughs to the second sieve and the tails for discharge. The second sieve S' passes the smaller throughs from the right-hand side half to the corresponding part of the purifier. The bolted product runs into the hoppers A, whence it is delivered by feed rolls a to the spreader boards b. On the way from the spreader boards b the stock is aspirated, and drops to the bottomless boxes c, from which it is directed into boxes d in streams separated according to quality and size, and undergoes fanning once more on its route. The boxes d have adjustable valves e, which are regulated in accordance with the size of the stock to be graded. From the boxes d the graded product flows to the discharge spouts / for further treatment. Between the divisions of the purifier there is the fan chamber in which the suction fan h is set. The Haggenmacher and Voll's machines we have examined are de- scribed according to specimens built by the works of Dobrovyand Nabholtz, but the same type of machines of similar principle are made by other works also, such as Daverio, Luther, Amme, Giesecke and Konegen, &c. Smith's Sieve Purifier. Smith's sieve purifier was originally invented in America, and under the name of " Reform " was evolved by the works of Seek Bros. It is constructed on a different principle of action to that of Haggenmacher 's gravity purifier, which originates in Ignatz Paur's first sieve purifier. The principle of action of that sieve purifier is as follows (Fig. 394) : If we compel the stock to travel over the sieve a-a in the direction pointed by arrows b, and at the same time impel a current of air of a sufficient force under the sieve, the state of the flowing product will be similar to that of boiling. Its light particles will be lifted over the sieve and carried CHAP. Vl] FLOUR MILLING 409 410 FLOUK MILLING [CHAP. Vi by the draught upwards. Part of that light refuse will be sucked out towards the fan, the rest, consisting of heavier offal, will collect in boxes over the sieve, into which it will drop owing to the abatement in the velocity of the air, which expands on leaving the canals between the boxes. In this way, the air- current here lies at an angle of 180 to the direction of bolting, and at an angle of 90 to the direction of motion. The light particles are lifted off the sieve and separated as light or heavy offal. The heavy product passes through the sieve, and the tails consist of the large, generally less heavy product, because the largest-sized middlings, the con- ditions of reduction of the kernels being equal, always consist of the integumental particles of grain. 1 The principle of this machine has remained unchanged up to the present day, and on this principle the machines are designed in Europe FIG. 394. as well as in America. In some constructive minutiae the works of Seek Bros, have altered their " Reform " purifier from their first model, and in its present shape it is given on Figs. 395 and 396. The stock to be treated flows into the hopper a, and is then fed in an even stream by the feed roll 6 to the surface of the sieve c, performing a reciprocating motion. Above the sieve, at no great height, are set similarly to fire- grates sheet-iron channels d, with their ends inclined to the longitudinal channels/. The sieve being placed in a closely shut up chamber, the whole of the air sucked in by the fan e must pass through the bolting cloth. The light refuse is carried away by the fan to the dust collector, the heaviest falls into the sheet-iron channels d and the side worm (Abstoss der Aspiration), and the medium refuse upon the inclined planes lying over the channels d. The refuse collecting inside the chamber generally 1 In one and the same break or rebreak passage the coloured middlings, i.e. the particles covered with bran, are always larger than the pure ones. This is due to the fact that the middlings with offal are more elastic, and, consequently, offer greater resistance to reduc- tion than middlings out of the pure endosperm. CHAP. Vl] MILLING 411 mixes together, whereas the offal settling in the worm separates, being the heaviest obtained in fanning the refuse off the sieve c. The cleaning of the sieve c is performed by means of brushes ' Inlet. A Refuse from ventilation. FlG. 396. L Inlet of air. S_Overtails of sieve. u Outlet of middlings. fastened to endless chains. The transmission of motion is sufficiently clearly illustrated by the drawing. This type of machine operates well in cleaning different sized middlings, also coarse and fine dunst. A perspective view of the machine is shown on Fig. 397. Robinson's Sieve Purifier. - - The English sieve purifier constructed by Robinson (Fig. 398) is also a modifica- tion of Smith's purifier, but in its prin- ciple of action it remains unchanged, as do also the sieve purifiers of other works. / illustrates the longitudinal section of this purifier, // a cross-section, and /// and IV are the plans. Figure 1 indicates the frame of the oscillat- ing sieve, 2 its bolting surface, 3 the deflecting boards V-shaped at their base. The air, directed upwards and aspirated by an ordinary fan 6, lifts out of the stock on the sieve 2 the light particles in such a way, that they fall upon the deflecting boards and are rejected to the sides of the FIG. 397. 412 FLOUK MILLING [CHAP, vi bolting tray, where the greater part of them land on the deposit plat- forms 7. When several trays 3 are used with spaces in between them, the air-current passing through the sieve 2 is equal in force in all parts of such a sieve. The trays are made with gravels 8 for the sake of greater lightness, and, owing to their channelled shape, serve for collecting the heavy refuse, which has a tendency to falling back on to the sieve. It is best to fix the trays 3 with their ends to the frame of FIG. 398. the sieve 1, so that, when swinging, the dust in the grooves 8 and on the side channels 7 would travel to the lower edge and fall into the dust- collecting box 9. Figure 10 indicates the spout conveying the stock into the working space, 11 the spout for overtails, 12 a hopper for the throughs, 13 the frame of the machine. If the air-current, on passing by the de- flecting trays 3, were to run directly to the fan 6, part of the offals would not settle on the side channels 7, but would be carried to the fan. To avoid this, the direction of the draught blowing by the trays 3 CHAP. VlJ FLOUR MILLING 413 is sharply altered by means of the baffle plate 14 attached to the frame 13. In the centre of the baffle plate 14 there is made a long and narrow hole 15, parallel to the spaces between the deflecting trays 3. Thus, all the air passing between the trays is deflected to the opening 15, and the greater part of the offals settle on the side channels 7. With joints FIG. 399. Cross Section of Sieve and Channel Cowl. 17 under the hole 15 there a-re attached adjustable gates 16, the free edges of which may be brought closer to or further from each other by means of rods 1 8 or some other contrivance for regulating the width of the open- ing. With figure 19 is indicated the deflecting cap over the opening 15, which compels the remaining particles of dust, owing to the centrifugal force they develop, to settle on the top side of the baffle plate 14, whence FIG. 400. Perspective View of Channel Cowl in Working Position. FIG. 401. Channel Cowl of Sieve. they may be removed by a running brush or in some other way. Having passed the baffle plate 14, the exhausted air goes through the passage 20 to the fan 6. This fan impels the air along the passage 21 to the ex- pansion chamber separator 22, which is of the centrifugal type. In the expansion chamber the air circulates spirally and makes its exit through the outlet 23. The rest of the dust deposited by centrifugal force on the casing collect in the dustbox 24, whence by means of the worm 25 jt is 414 FLOUR MILLING fCHAP. VI taken out of the machine or conveyed to one of the side channels 7. Several fans and separators may be employed. Fig. IV illustrates on a reduced scale the plan of a machine, similar to the one examined, but with two fans 6 and two dust collectors 22. For convenience sake when using the sieve purifier for coarse pro- duct or for' two kinds of stock with a stronger current of air, the sieve is divided in two parts, and the stream of product is guided separately to each half. Both the air-currents are directed into the centrifugal separa- FIG. 402. tor and the fan, as in the former case. In Fig. 402 is given the longitudinal section of such a sieve purifier. The parts corresponding to parts /, //, and /// are marked with the same figures. The sieves 2 face each other at an incline. For each of the sieves there is a separate feeding spout 10. Number 11 indicates the deposit platforms for refuse, and 9 an ordinary worm for refuse rejected by deflecting trays and the side deposit platforms of both the sieves. The dust collector 22 is furnished with two inlets adjusted by the valves 26, so that through both the sieves there should pass air-currents of equal force. In this case the air is not impelled through the collector, but drawn through it by the fan 6 sta- tioned by the outlet 23. The offal from the box 24 goes to the worm 25 ? CHAP. Vl] FLOUR MILLING 415 416 FLOUR MILLING [CHAP, vi which conveys it out of the machine. Over the divisions of the sieve there may be set boards 27 to reduce in case of need the air-current which passes through the sieve at this point, where the strength of the draught is the greatest. A perspective view of the sieve purifier is given on Fig. 403. Schneider, Jacquet cfc Co.'s Sieve Purifier. A characteristic pecu- liarity of the Schneider, Jacquet & Co. sieve purifier is that, firstly, it requires no dust- collect or for the fan offals, and secondly, it operates with one and the same volume of air, which moves in the machine in a locked current. On Figs. 404 and 405 may be seen the longitudinal (the middle part FIG. 404. of the machine is cut out) and transversal sections. The action of the machine is as follows. The air in the chamber of the machine is brought into motion by the fan a with an outside driving belt-pulley b. From the fan the current of air passes down a vertical spout to a horizontal channel c (Fig. 405). Then it travels as indicated by the arrow through the longitudinal bottom opening d of this channel to the working chambers under the sieves and returns to the fan. On its way the air passes through vibrating sieves e, on which the stock to be purified lies. The lighter particles are carried off the sieve by the air-current, to pass through the chambers / and openings g into the separating space h. In travelling from the sieves e down the chambers /, the current, owing to their de- creasing transversal section, becomes narrower. The velocity of the draught here must therefore increase ; it attains its largest magnitude when the current passes through the openings g, and then it all at once CHAP, vi] FLOUR MILLING 417 drops to its minimum, so that the light particles carried away, losing their kinetic energy, drop into the chamber of the worm i. The increase in the velocity of the air-current when passing through the chambers / is an advantage, in so far that the light particles separated from the stock on sieves e cannot fall back. Owing to the expansion of air in the collecting space, the light particles settle down, and are thence carried away by means of the worm conveyor i. The air chambers / are so arranged, that the openings g can be adjusted by the valves k. Each machine has several chambers / arranged in rows. For the stock under treatment to be evenly cleaned, it is indispensable that the air should pass through all the chambers at an equal pressure. The pressure of the current leaving the fan and running into the channel c decreases when passing down this channel. Because of this difference in pressure, the outlet d running below along the channel c is made wider behind (from the fan) than in front, and has, in this manner, the shape of a trapezium. Expelled through this opening in the channel, the air flows out with an even pressure at every point of the passage, and, owing to the backward increasing width of the openings in the sieves e, blows through the working chambers with different force. This will be clearly explained by the following. By passing through the outlet in, the channel c, the air acts upon the reverse surface of all the sieves e with equal pressure. Since the stock to be purified lies in a large mass on the first sieve, which is finely meshed, the purifying draught of air cannot pass through this layer of product as easily as through the more open back sieves where the layer of product has already been partly bolted, and is consequently not so thick. The quantity of air passing through the front sieve is therefore the least, and in proportion as we approach the last sieves it increases, since the re- sistance to be overcome by the air-current in passing through a suc- cessive row of sieves with decreasing numbers gradually diminishes. Thus the grading air-current penetrates all parts of the machine with equal pressure, but through the working chambers /, owing to the dimin- ishing resistance, the air passes in different quantities. Owing to this, the process of purification is performed evenly in all the air chambers, because the draught penetrates into them with equal pressure. Down the inlet boss I (Fig. 404) the stock to be graded runs in a manner required to the vibrating sieves e in the machine, over which it travels in a longitudinal direction. At the boss ra the coarser parts which have not passed through the sieve meshes are tailed over. The middlings which passed through the meshes into the box n are carried 2D 418 FLOUR MILLING [CHAP, vi away by worm conveyors. To allow of the frequent inspection of the purification during operation, in the chambers / there are windows o adapted especially for that purpose. The even distribution of the air- current in the whole machine down the channels c and h has this advantage, that the fine light particles are not carried by the draught to the chambers, but settle in a special compartment. The chief chamber for the precipita- tion of the light particles h, which also runs down the length of the l FIG. 406. machine, is to this end divided by suitably adapted partitions p into a certain number of sections, so that each two opposite inlets of the cham- bers g open into one such section. The partitions do not cut off the chamber h in its full height, so that the light particles of product settling in all the sections may be discharged by means of a common worm conveyor i. The surfaces on which the particles separated from the stock preci- pitated are so arranged that these particles cannot remain settled any- where, and are constantly delivered by the machine as heavy offal. CHAP. FLOUR MILLING 419 Thus the peculiarities of this middlings and dunst purifying machine consist in that under the chamber h for collecting the light particles of product passing down the full length of the machine there is arranged a channel c, for the passage of air, which also runs through the length of the machine. The longitudinal bottom opening d of this channel is arranged to correspond to the decrease in pressure in such a manner that the air- current passing out of it enters all the working chambers at an equal pressure. The chamber h for the light particles is divided by partitions into several sections, the number of which corresponds to the number of double chambers /. This is done to prevent the formation of strong air- currents in the narrow part of the chamber h about the inlets g. Fig. 406 illustrates the perspective view of the sieve purifier. H. Brunner's Purifier. In his recently patented machine Brunner aims at a simplification in the construction of the types we have ex- amined, attempting to dis- i j 6 card the collecting plates ' p'-rfekT..., ,-j^ ^"^4^1^ ^^ and worms from the purifier. His point of departure was the principle that with the decrease in the cross section of the passage of air over the sieve, the velocity of motion of the offal increases and their falling back on the sieve is an impossibility. In all the constructions illustrated in Figs. 407-410 the air from the chamber a occupying the full length of the sieve is drawn out by a suction fan. Through the open- ings adjusted by gates b the air passes out of the chamber c, which is divided into several parts. The space c containing the rarefied air contracts after this, beginning immediately from the sieve d, owing to which the air-current is evenly distributed over the full breadth of the sieve. In Figs. 408 and 409 the contraction of the space c is attained by having the walls e and / raised in the shape of a cone upwards from the sieve. In Fig. 410 are illustrated the intermediate partitions g built into c, which also assist in making that space rapidly narrower, so that directly it leaves the sieve the air -current acquires a greater speed and the light particles lifted are carried away to the outjets b and through their openings pass into the chamber a. The bottom FIG. 407. FIG. 408. FIG. 409. FIG. 410. 420 FLOUR MILLING [CHAP, vi of the chamber a may be slanting, and then the heavy refuse will run out of itself ; or the draught may also be left there of such force that it would be able to carry these particles out of the chamber with it. In the second case the heavy refuse can be collected by the dust- collect or or in some other way. Ill CAPACITY OF PURIFIERS In his book Professor Zworykin gives the capacity of the purifiers in accordance with the length of the working air fissure. Let us name the capacity of the machine Q, the length of the fissure b, the velocity of motion of the product v, and the width of the fissure (the thickness of the stream of product) e. Then we obtain : Q = abev, where a is the coefficient of proportionality. If we name the finished stock $ , it may be expressed through Q by in- troducing the coefficient of proportionality k, which is the number of pas- sages required for cleaning the product : =k = - ; . - But k, the number of passages, is proportionate to the thickness of the sheet of product fed in and inversely proportionate to its average dimensions. Therefore where ft is the coefficient of proportionality. But k, the number of pas- sages, will diminish with the increase of the number of fannings n. Therefore : By substituting k from (2) into (1), we obtain : Since practice shows that almost in all constructions of purifiers the velocity of the feed is a constant quantity, we finally obtain : Qo=Abdn (3), i.e. t^e capacity of the purifier is directly dependent on the length of the fissure, the size of the stock treated, and the number of fannings. CHAP. Vl] FLOUR MILLING 421 Experiments show that 1 cm. of total length of the draught fissures produces from 1 to | klg. per hour or 54 to 27 Ib. per day (24 hours) of pure semolina, depending on the size of the product. These data refer to Haggenmacher's type of purifier. As to the purifier of Seck's type ("Reform") this calculation is useless, for the air-current operates through the sieve. For the sieve purifiers it would be necessary to reckon the cross section of the "bolting cloth, lowering it by a certain coefficient, because the stock passing through the sieve blinds the meshes of the cloth for the moment. In calculating the number of purifiers one may use the data of the works, which deserve full confidence. The compound Table XLII of the capacities of the " Reform" type sieve purifiers, from practice, gives results almost similar to the data of the catalogues of the German works. TABLE XLII CAPACITY OF SIEVE PURIFIERS Dimensions of Machine Nos. Working Surface of the Sieve on an Average (for Different Works) in Square Metres. Capacity per Hour in Cwts. Number of Vibra- tions (Double) of the Sieve per Minute. Middlings. Dunst. 1 1-200-1-400 11-8-16-0 7-8-9-6 500 2 1-000-1-200 10-0-13-2 5-9-8-2 500 3 0-800-1-000 8-1-11-0 4-8-6-0 500 4 0-500-0-640 5-9-7-8 3-2-4-5 500 5 0-350-0-400 3-6-5-1 2-1-3-0 500 On an average it may be reckoned that 1 square metre of the sieve purifier cleans 10 cwt. of middlings and 6 cwt. of dunst per hour. In closing the section on grading the product according to the quality, we must point out that a gravity purifier of Haggenmacher's type may be employed for semolina, and sieve purifiers of the " Reform " type are preferable for cleaning fine middlings and dunst, these machines being of a more delicate structure. CHAPTER VII ACCESSORY APPLIANCES AND MECHANISMS COMPARATIVELY recently, to the fundamental mill machinery there have been added a series of appliances and mechanisms of an accessory char- acter, without the assistance of which the milling process would be impeded or would produce unfavourable results in respect to the quality of the product as well as the health of the staff operating the mill. The development of automatic grinding required an improvement in the transportation service at the mill, and the necessity for keeping a certain standard of flour on the market compelled millers to employ machines and apparatus with the aid of which the influence of the in- constancy in the quality of wheat upon the outward appearance of the flour might be neutralised to a certain degree. The most essential necessity for a mill is the ventilation of the machines. By means of exhausting the grain-cleaning machines, as we saw when studying their construction, the removal of dust and screenings is attained, which is indispensable not only for the machines, but for the mill building as well, since the penetration of dust into the parts in con- tact with the machine is injurious to them, not to speak of the danger of explosions, fires, and injury to health. In the mill proper the ventilation of machinery is of still greater importance, because not only dust but evaporation occurs here. In fact, owing to the heat generated by grinding, the water contained in the grain turns partly to steam, especially in the milling of soft kinds of rye and wheat. The heated air, saturated with steam, comes in contact with the cold walls of the machines and bedews them. This phenomenon is identical to the sweating of cold window panes when they are breathed upon. In the winter, the formation of dew in the machinery of the mills with badly arranged ventilation is so great that the water pours down the inner walls of the roller mills in thin streams. Besides the machines, the spouts, elevators, worm conveyors, and bins suffer from the warm, damp air. The timber parts rot, and the iron rusts. The flour turns to paste, clots of dough block the spouts, find their 422 CHAP, viz] FLOUR MILLING 423 way into the elevators, and thence into the bolting machines, the sieves of which become blinded by the paste, and the capacity of the mill often drops 50 per cent., and sometimes the spouts and the elevators are so badly choked that it is necessary to stop the mill and give the machines, spouts, and elevators a general cleaning. The damp air, however; has a detrimental effect not only upon the machines, but upon the meal too. The moisture contained by the flour imparts a dark colouring to it. If the flour contains a great quantity of moisture, a spirituous fermentation often sets in, and reduces its rising and baking qualities. Thus, the aim of ventilation is to remove the dust and the warm, damp air from the machines. In classifying the accessory appliances and mechanisms in the mill we may divide them into two groups : I. Ventilation of the machinery and the mill. II. Transportation, blending, and improvement of the product. The first group gives the following two sub -divisions : - 1. Mechanisms and apparatus for improving the intermediate products. 2. Dust-collectors. The second group has four sub -divisions : 3. Transportation of the stock. 4. Apparatus for blending the flour and packing. 5. Apparatus for calculating the quantity of stock. 6. Apparatus for bleaching the flour. In this order we shall now proceed to examine the construction of the accessory mechanisms and apparatus. I PURIFICATION or THE INTERMEDIATE PRODUCTS Robinson's Cyclo-pneumatic Separator. This separator is placed after the break rolls for the first four or five breaks. We know that a certain small percentage of bran is reduced to meal dust and stripped off the berry in the shape of small beeswing on the grain being passed through break rolls. In addition, part of the remaining beard is torn off, and broken up. The integumental dust darkens the break flour, the offal mixes with the middlings, and the hairs of the beard blind the meshes of the meal sieves and make sifting difficult. To separate the bran powder, offal, and beard, it is well to employ apparatus through which the break product can be passed and subjected to cleaning. Robinson's separator 424 FLOUR MILLING [CHAP, vii (Fig. 411) is such an apparatus. It is a cyclone and an aspirator com- bined. The break product runs from the rolls into the feed tube D and through it on to the rotating disc A, which flings the product up fanwise. On its route from the space E to the hopper F, the product is subjected to the action of an air-current which carries away the dust, offal, and bees- wing. Out of the hopper F the cleaned break chop flows down the spout G into the sifter for further grading. The aspiration is effected in the following manner. The fan W sucks the air out of the cyclone into the space E and drives it down arrows S into the chamber B. When the air is passing out of the right-hand side part of the chamber into the left under the dividing partition L, the heavier particles of integument develop a cen- trifugal force and fall into the worm P, and the air with the lighter dust particles flows into the cyclone. The centrifugal force presses these light particles of dust against the walls of the cyclone, and they roll down arrows S into the worm, while the pure air is again drawn up to the space E. In this way the work is performed by a con- stant quantity of air. The offal from the chamber B and the cyclone collects generally in a common worm, and is discharged as indicated by arrow I. The dust offal contains also a part of break flour, which is then separated away on a sifter. To prevent any circulation of air, there are leather partitions set in the worm. The Schneider, Jacquet & Co. Apparatus. A more simple apparatus for cleaning the break stock is the chamber illustrated on Figs. 412, 413, and 414. This apparatus is stationed before the break rolls, and separates the offal from the break semolina. If the break process has high breaking and eight breaks, it is well to set the apparatus for the semolina from the first (after the high breaking) six breaks and for the rebreaks (for the first two of the three). Fig. 412 gives the longitudinal and half of the transversal section of this apparatus, which consists of a rectangular timber cupboard, through which there pass the worms a and a for the removal of the more or less heavy offal. The break semolina flows down the spout A on to the in- clined plate B. On this plate there are set the distributors b, which break FIG. 411. CHAP. VIl] FLOUR MILLING 425 up the narrow stream of product into a broad sheet, which descends as shown by the arrow c to the outlet into the box D over the roller mill. On its route of descent the product is subjected to the action of an air- FIG. 412. current x streaming in through the crevice between the adjustable gates d and d^. Besides the regulation of the width of the crevice between the gates d and d l9 the force of the draught may be altered by the gate 0. The air is aspirated by a fan through the spout E. The longitudinal and the side view of the installation of eight machines FIG. 413. FIG. 414. is shown on Figs. 413 and 414, where it is seen that the offal passes into the aspirated worm A, whence it is conveyed tq the sack or to the bolt- ing machines. The Briddon & Fowler Pneumatic Scalper. Attempts have often been made to arrange the cleaning of the break chop in the roller mill 426 FLOUR MILLING [CHAP. Vit itself, but with no good result. Of the latest attempts, a construc- tion of the Briddon & Fowler works in Manchester (Fig. 415) deserves attention. This has been made the foundation of a system (patented) of milling. It is the outcome of experiments made by Fowler in a Yorkshire mill. He found that a pronounced natural separation takes place in break stock coming from the nip of diagonal rolls. The heavier stock, i.e. FIG. 415. partly broken wheat, semolina and heavy middlings, are thrown farthest from the roll, while the break flour, finest middlings and dunst are thrown down on the inside. An adjustable division board, under the nip of the rolls, effects, without any mechanical agency, an immediate separation of the heavy and the branny particles from the floury stock and fine dunst. Thus contamination of the break flour or the production of inferior attri- tion flour is obviated, and the colour and granularity of the break flour are improved. Currents of air working as in a gravity purifier assist the separations. The system is working most successfully in many of the largest British mills, and is regarded as one of the most successful innovations of recent years. II DUST-COLLECTORS Dust-chamber. The simplest kinds of dust-collectors are dust-cham- bers or dust-bins. Their arrangement is very simple. A free corner of CHAP, vn] FLOUR MILLING 427 the mill is partitioned off by a timber frame clothed with canvas (a simplified chamber is clothed with old flour sacks), thus forming a dust- bin. The dusty air is driven out of the machines by fans into this cham- ber, and oozes through the canvas walls of the bin, leaving the dust on them. In proportion as the dust collects on it, the canvas is shaken, the dust falls on the ground, and is removed when the fan stops working. Sometimes the dust-bin is made with an inclined bottom and discharge spout with a sack fitted to it to receive the dust. This simplest kind of dust-collector is arranged in small mills with FIG. 416. FIG. 417. the means about them. The dust-chamber occupies much room, but its filtering area is insignificant. Cyclones. The cyclone apparatus invented by the Americans is a more perfect dust-collector. On Fig. 416 is shown an ordinary kind of a cyclone, its partial section and the view from the top. The dusty air flows into the feeding tube A, passing into the ring space between the cylindric part E of the cyclone and the outlet tube C. This ring space is covered over with a lid, in consequence of which a rotary motion is im- parted to the air in the ring closed on the top, and it travels in a helical FLOUR MILLING [CHAP, vn direction downwards along the arrow 8. With the increase of resistance to motion the air-current in the narrowest part of the cone is impelled in the direction of least resistance, i.e. upwards, and passes out through the tube C. Owing to the spiral motion of the air the particles of dust de- velop a centrifugal force and press against the walls of the cyclone, down which they slide to the exit B influenced by their gravity. Thus, the air emitted through C is perfectly pure and free of dust. Such is the action of all cyclones. This apparatus is very simple, its action is satisfactory, but it is comparatively bulky. Wishing to improve the action of the cyclone, Howes' works in America suggested a more complex construction of an apparatus with a com- pulsory spiral motion of the air and dust in the chamber (Fig. 417) by furnishing it with helical arms. This complication in the construction, FIG. 418, FIG. 419. FIG. 420. however, does not improve the action of the cyclone, but the contrary, for the arms have very little influence on the direction in which the air travels, and at the same time retard the delivery of the dust. The Knickerbocker Co. Cyclone. The cyclones we examined have the defect that quite a considerable part of the pressure is lost because of meeting at a fairly large angle, as we see in Fig. 418, the air flowing into the cyclone and gyrating there. To avoid any intersection of the air- currents, the celebrated American cyclone works, the Knickerbocker Co. (Jackson, Michigan), which invented the first cyclone, suggested in 1905 a new principle for a cyclone, in which a spiral motion is immediately com- municated to the inflowing air, as it is shown in Fig. 419. Here the axis of the efflux of the air does not coincide with the axis of the cyclone. The meeting of the air-currents is obviated in the cyclone of such a con- struction. On Fig. 420 may be seen the cylindric part of such a cyclone. The CHAP. VII] FLOUR MILLING 429 air runs into the receiver A and along the arrow L passes spirally to the partitioned-off section of the chamber J. The spiral direction is com* municated to the current by the walls E and F. The first wall is closely fitted to the wall M of the cylinder, while between it and the wall F there is a clearance H through which the superfluous amount of air can pass out along the arrow L lf The current of air L acts partly as in the de- flector in respect to the chamber J, consequently the streams L and L l do not cross each other, but coincide. And if the air travelling under the walls of the chamber J has not separated away the whole of its dust and offal, then, in passing again into the fresh supply chamber, it can be totally freed of admixtures. The exhaust air passes out through the opening D, eccentrically made in the lid of the cyclone. The position of the opening D may be namr^ altered, since the ring K is eccentrically set in the lid. This is of consequence for a correct setting of the air out- let. The cyclone construc- tion we have just examined is the best of all existing types of these dust-collectors. Filters. The most gener- ally used dust-collector is the tube filter, which has almost totally driven out the cyclone in European mills. The tube filter is convenient in this respect, that occupying little space it gives a large working surface. On Fig. 421 we have a pressure tube filter. It consists of two, generally timber, boxes, A and B, the chambers of which communicate with each other by linen tubes. The dusty air carried by the fan C out of the ventilated chambers passes into the top chamber A, whence it is distributed to the tubes and filters through the cloth, leaving the dust on its inner surface. From off the tubes the dust is shaken by means of a frame D, which has a wire running from one side to the opposite on every one or two rows of tubes. The distance between the wires being less than the dia- meter of the tubes, the latter are compressed. The frame D runs up FIG. 421. 430 FLOUR MILLING [CHAP, vn and down uninterruptedly, and in this manner shakes off the dust, which falls into the bottom box B. The frame D rises and falls by means of four chain drives, it being suspended on the chains a by means of straps b. The dust fallen to the bottom of the box c is scooped away by scrapers d which run down the full length of the box and are brought into action by a chain drive g inside it, and is thrown into the worm e, whence it is delivered through the outlet spout as indicated by the arrow s. Fig. 422 illustrates the suction filter, which differs from the preced- ing in that it is enclosed in a common box. In the first case the fan should be placed between the aspirated machine and the filter, in the second after the filter. In this manner the fan sucks the air out of the box A. The dusty air which is conveyed into the top box by the air pipe from the machines precipitates into the tubes and filters through their cloth, owing to the air in the box A being rarefied. Consequently, through the fan there passes pure air. In comparing these two types of filters, we must speak in favour of the first one for cheap plants, seeing that firstly its construction is more simple, secondly it requires 15 to 20 per cent, less power, there being no such resistance to the outflow of the exhaust air as we see in the suction filter ; thirdly and lastly, its opera- tion is easily supervised, whereas in the suction filter the shaking frame is hidden in the hermetically closed box A. The latter circumstance could be obviated in the suction filters, if a glass inspection window were to be made in A ; but for some reason or other none of the works do it, though this would be very useful. Among the defects of the pressure filter we may count the fact that the exhaust air, not always free of dust, passes directly into the mill, whereas in the suction filter it is discharged by the fan into the open, and the mill does not remain free of dust if the filter works unsatisfactorily. On Figs. 423 and 424 may be seen the American tubular filters made by S. Howes' works. The first one is a type similar to the European construction, differing from it only in the greater ease it affords for inspec- FIG. 422. CHAP, vn] FLOUR MILLING 431 tion of the lower working box, the lid of which may be lifted. The second filter, likewise sectional, is more simplified, the scrapers here being discarded and a bin with a worm below placed, into which the shaken-off dust falls out of the outermost tubes down the inclined walls of the bin. The star-shaped forcing filters are much more popular in America. Fig. 425 shows such a filter, made in Europe by Luther's works. The filter consists of a stationary cylindric casing with longitudinal or round holes. Over this casing is fitted another similar one, but rotating with the aid of a ratchet wheel gear. On the rotating casing there is set a series of tubes stretched by springs on either end of the plank, which is also connected with each tube. The driving belt-pulley is the large one FIG. 423. FIG. 424. on the left ; it operates the whole mechanism, in which the lever pawl turns the filter one or two cogs, while the hammers on the axle hit the tubes approaching them from the top. Since the stationary cylinder is divided into two parts, of which the lower one receiving the dusty air communicates through the holes with the tubes, and the top one containing the worm is isolated from dusty air, the dust which remains after the air has passed through the cloth of the lower tubes falls out of the top ones, when they are hit with the hammers, to the lower part of the casing, and is dis- charged by the worm. In spite of the comparative complexity of the mechanism these filters are very widely used, owing to their being more compact than the European tubular filters. They have made their appearance in Europe, too, of late. We shall end the chapter treating of filters with a description of 432 FLOUR MILLING [CHAP, vn one of the latest types of Seck's suction tubular niters. Fig. 426 illustrates the longitudinal and the cross section, and Fig. 427 a perspective view of this filter. It consists of an iron cylindric chamber b containing the filtering tubes c closed at the top, and attached by their edges to the bottom of the chamber and open for the discharge of dust. With the aid of an aspirating air pipe k the chamber b communicates with the 6. LUTHER A.-6. BRAUNSCHWEIG FIG. 425. fan. The dusty air from the exhausted machines passes through the air pipe i, whence it runs into the tubes e and filters out, free of dust, into the chamber b owing to the rarefaction of space between the tubes and the casing of the chamber. The tubes are suspended to the lever d, which rises and falls owing to the operation of the ratchet wheel e on the shaft /. Simultaneously with the dropping of the lever d, during which the tubes receive a shake, the valve / also CHAP. VII] FLOUR MILLING 433 closes automatically, so that the suction of the air out of the filter is dis- continued for the moment of the shake. The dust descends to the box g, whence it passes into the worm. The heavy offal drops into the worm when the air flows into g, because owing to the sharp curve the current performs the offal develops a great centrifugal force and is flung down. FIG. 426. . n Recurrent of air. S Dust-laden air. J FIG. 427. Generally the suction filter plants have two chambers at the very least, as in Fig. 427. But more often three or four chambers are joined together. This guarantees continuous work of the filter also, because when one of the filters is being cleaned, i.e. the suction tube k is closed with the valve I, the others at the same time are open, the ratchets e being brought into action by turns. 434 FLOUR MILLING [CHAP, vn III EXHAUST SYSTEMS 1. Group Exhaust Systems Ventilation of Roller Mills. The removal of the bran powder and flour dust, as well as the cooling of the rolls and of the heated product, is the aim of ventilation for roller mills. There are two ways of exhausting the rolls. The first is based on the principle of counter-currents, when the draught is directed opposite to the motion of the product ; the second, when the direction of the air and the stock coincide. In most cases the first method is accepted by the works, by reason of the dust being easily separated from a thin sheet of product with an air-current. But the condensation of steam in the cooler top part of the mill chamber and the formation of paste on the walls of the frame are to be reckoned among the defects of this method. The absence of condensation owing to the constant temperature in all the parts of the chamber speaks in favour of the second method ; to its defects may be referred the smaller capacity of the air-current to remove the particles of dust and shells from the compact mass of stock travelling down the spout or the worm. How- ever, the defects of both the first and the second methods are avoidable. If the mills are not overloaded and the product is not heated much, the difference in the temperatures will be insignificant and there will be no condensation. In the second case, when the air-current crosses the sheet of product, the particles of dust are extracted out of it and do not mix in the spouts with the rest of the stock. Fig. 428 represents an American ventilating plant on the principle of counter-currents. The product is fed in at S. The air flows into the chamber of the mill through the windows A, which are covered with cloth or a metal screen, traverses the sheet of product flowing out at right angles, and passes out as indicated by the arrow S into the common trunk B, carrying the dust with it. The fan C, in sucking the air out of B, forces it into the star filter. On Figs. 429 and 430 we see Seck's system of exhausts, in which the direction in which the product travels coincides with the route of the air. In the case when the incline of the spout A is sufficient for the product to run down of itself, the plant in Fig. 429 may be used. The product leaving the mill flows down the spout A to the elevator. The air is aspi- rated through the trunk B, which directs it to the worm C, doing service for several rolls, and whence the fan sucks the air through the trunk D, In the spout A there is a freely suspended valve a, which does CHAP. VII] FLOUR MILLING 435 not allow the air to pass into the ventilated worm out of the elevator ; in the bend of the trunk B there is a valve or a gate b, with the aid of which the intensity of the exhaust in any particular mill may be regulated by opening it wider or less. The heavy offals carried away by the air-current FIG. 428. out of the stock drop into the worm and are conveyed by it into the open, while the light dust runs down the trunk D to the filter, where it collects. In case the elevators have to be stationed far from the roller mills, and the stock cannot flow to them of itself, the exhaust arrangement shown 436 FLOUR MILLING [CHAP, vn in Fig. 430 is employed. Here is set the worm E, out of which the air is aspirated by a similar trunk B. In the remaining part of the plant there is no difference. We have been examining here the exhaust systems of the most important machines, the roller mills. Before proceeding to a description of general systems of exhaust we must set several general rules for a rational construction of the plants. How important a correct calculation and construction of exhaust is we may judge by the example of a German mill, which being driven by a 260 H.P. steam engine consumed 110 H.P. for ventilation, i.e. 43 per cent, of the power used by all the milling machines. Such enormous FIG. 429. FIG. 430. consumption of power for the exhausts was caused solely by bad con- struction and incorrect calculations. One of the main details of an exhaust plant is the air trunk, down which the dusty air is driven out of the machine to the dust-collector by means of a fan in the machine itself or a fan outside it. The separate air trunks communicate with the main trunk, on which generally the main fan is set. In constructing and reckoning out the ventilation, the following general rules should be borne in mind : 1. A correct computation of the general quantity of air required for the plant given, i.e. the selection of suitable fans. 2. The sections of the air trunks should be so calculated as to have an equal quantity of air passing in their different sections, where the velo- cities may be different. 3. The coupling of the air trunks should be such as to involve no loss of air pressure. CHAP, vii] FLOUR MILLING 437 4. The dimensions of the chambers, cyclones, and filtering surfaces ought not to cause any superfluous pressure, which requires a greater consumption of power. Rules 2, 3, and 4 give the ground on which a correct choice of the fan can be made, and we shall therefore speak of them more in detail. If we have two equal machines placed at unequal distances from the fan, we cannot use air trunks of equal sections. Obviously the air trunk of the further machine will offer greater resistance to the motion of air, being the longer of the two. To have both the machines placed in equal conditions of ventilation, it is necessary to make the trunk of the further machine larger in section, taking its dimensions in accordance with the length, which defines the loss in pressure. In no case may trunks of an equal section be used for equal machines, when this section is calculated from the air consumption and the pressure of the machine farthest removed. In that case the machines lying nearer to the fan will be subjected to a more energetic exhaust than is needed, and the regulation of the air trunks by means of valves or gates will incur an extra consumption of power. The absence of sharp bends in the FIG. 431. trunks and their joints is of great import- ance. The greater the number of bends, especially at right angles, the greater is the loss in pressure of the exhaust plant. The coupling of air trunks must in no case be at right angles, as we have it on the American plant, which serves as an example of the worst kind of coupling for air trunks. If we have a coupling of two air trunks at a certain considerable angle, about 45 (Fig. 431), for instance, then the air-currents b entering into the main air channel intersect with the cur- rents a and thus hinder each other, mutually reducing the general pressure. It is necessary to have these streams almost coincide in their direction of motion. The practice of to-day has fixed the largest angle formed by the axes of the coupled air pipes at 5. As to the size of dust-collectors (chambers, cyclones, and filters), in selecting them such dimensions should be taken as will not cause any loss of the necessary pressure before the fan, owing to stoppage of the exhaust air passing out. Beyond these limits the dimensions of dust-collectors may be increased without harm to the plant if the space and the means allow it. Dust-collectors of super-normal size facilitate the work of the whole plant. 438 FLOUK MILLING [CHAP, vii 2. General Exhaust Systems Ventilation of the Grain-cleaning Department. Knowing the funda- mental requirements of a rational ventilation of machinery, we can give FIG. 432. a general type, as a more complex one, of an exhaust plant for the grain-cleaning department of automatic mills, from which it is an easy passage to simple plants. On Fig. 432 we have a cross section of the grain-cleaning department containing all types of machines. The ventilation is performed by means of CHAP. VII] FLOUR MILLING 439 FIG. 433 and FIG. 434. 440 FLOUR MILLING [CHAP, vii the fan A and the suction filter B of the Seek type we have ex- amined. The main air channel C is disposed vertically, and tributary to it are the conveying air trunks from the dusting reel separator 1, separator 2, trieurs 3. scourers 4, brush machines 5, scouring mill- stones 6. clean reel separators 7, and lastly, from the automatic elevators 8 at two points. In this plant we see that the junction of the conveying trunks with the main channel lies at the least possible angle of their axes. The vertical position of the main channel is to diminish the quantity of harmful resistance, and the fan is set on the top floor, which allows of utilis- ing the natural pressure of air in respect to the machines standing below. Ventilation of the Milling Department. In Figs. 433 and 434 we have a diagram of the exhaust system for the milling department of a rye mill of 100 sacks per day (24 hours) capacity. A fan A and a suction filter C operate for this plant. Speaking generally, the air trunks from the b machine should be set at an incline allowing the heavy particles settling in them to run down of themselves. For the heavy offals to run down in this manner it is sufficient to have the spout inclined at an angle of 60. In the plant given and those similar to it, however, the common FIG. 435. channel for the roller mills had to be made hori- zontal, and therefore it contains a worm D for the discharge of heavy refuse. The necessity of grouping the sifters for general ventilation in a similar manner required a worm E. The ventila- tion worms differ from the ordinary ones in that their chamber is made considerably higher (the area of the cross section is lJ-2 times as large), to allow the air free passage. In this plant we see that the air trunks N from the stone mills run directly to the fan, passing the filter by, as the millstones have their filters in the chamber of the casing. The heavy offals and flour collected by the worms descend along the spouts F (from the worm of the sifters) and G (from the worm for the rolls) to the nearest elevators corresponding to. the quality of offals, re- turning in this wise to the stock ; the light dust and offals, on the other hand, pass to the filter, where they collect in the worm for discharge. In the plant we are examining there are shown two variations of exhaust for rolls : one variation, with a bottom worm with ventilation of the spouts H, connected with the ventilated worm D by the air trunk /, CJHAP. VIlJ FLOUR MILLING 441 is the type accepted by Seek ; the other the one most generally used, with a top collecting worm D. outlined in dots under the ceiling (Fig. 434). FIG. 436. The comparative merits and defects of these two variations have already been spoken of. 442 FLOUR MILLING [CHAP, vn Two common air trunks, L from the worm of the rolls and M from the worm belonging to the sifters, convey the dusty air to the filter, where it deposits the dust and is discharged by the fan through the trunk B leading outside the building. The meal dust and light refuse discharged by the filters descend into the bin Q and a worm carries them out to the spout R, where they are admixed to the product going to the fifth break. The spout R can also deliver the filtered product to the centrifugal or directly into the sack. In any case this spout must have valves p-p (Fig. 435), which are opened by the pressure of the dust discharged and prevent the back draught of air into the niters, otherwise the action of the filters would be weakened. Fig. 436 illustrates the exhaust plant of a wheat mill. In com- parison with the preceding one there is an extra set of purifiers here, for which a pressure filter is installed. From the purifiers the dusty air is driven by their fans to the collecting worm, whence it passes to the filter. The sifters and roller mills are exhausted by the fan operating for the suction filter. 3. Calculation for an Exhaust Plant To calculate the correct size of an exhaust plant it is necessary to know : (1) the quantity of air required to remove the dust and warm air from each machine ; (2) the area of the filtering cloth. The Area of the Filtering Cloth. It is more convenient to begin by determining the necessary area of filtering cloth, from which we shall pass to the calculation of the volume of air required for the given working effect. Area of Filtering Surface for Machines of the Grain-cleaning Depart- ment. TABLE XLIII CAPACITY 125 SACKS PER DAY (24 HOURS) NAME OP MACHINE. Area of Filtering Cloth in Square Metres. Scales ........ Separator with one sieve ..... Separator of the zigzag type Trieurs (cylinders) . . . . . Horizontal emery scourer. .... Vertical emery (plate) scourer . . . . Brush machine, horizontal . . _^ -- .. ,, ,, vertical . . _.:., -~ ,, compound vertical * . . . Combined scouring machine of the Zolotukhin type 20-25 25-30 30-35 12-15 30-35 30-35 20-25 20-25 20-25 40-45 1 See Fig. 95, p. 103. CHAP, vii] FLOUR MILLING 443 As regards the definition of the area of the filtering cloth, there is no possibility of any theoretical reckoning. One is obliged to make use of the practical data of the best foreign and Russian plants of to-day, which we shall append. These data refer to the filtering woollen tissue " mal- ton " (German cloth) or to a Russian cloth of corresponding density. The less limits of areas refer to the drier, and the larger limits to the damper grain. Practice has proved that with the increase of capacity of the machine, the filtering area increases in proportion, but later diminishes by 10 to 15 per cent. For instance, if the capacity of a zigzag separator is 375 sacks, the filtering area for it will be : 3(3-0-3-5) -10-3 (3 1 ^ >5) =2-7(3'0-3-5), i.e. not 90-105 square metres, but 10 per cent. less. The Area of Filtering Surface for Machines of the Milling Department. The area of filtering surface for machines of the milling department is likewise defined from experimental data, which are expressed in the fol- lowing figures : To 1 metre of length of a pair of rolls for wheat . . . . . 1-25-1-75 sq. mts. To 1 metre of length of a pair of rolls for rye 2-5-3-0 ,, For a stone mill with stones 1 metre in diam. (wheat grinding) . -. ." . . 1-35-2-0 ., ,, For a stone mill with stones 1 metre in diam. (rye grinding) . . . . . 3-0-3-5 ,, ,, For sifting machines 50 per cent, of the filtering area necessary for all reduction machines is required. For purifying machines 125 sacks per day : (a) Gravity purifier " Groupe " . . . 10-15 sq. mts. (6) " Double Pur. " of Haggenmacher and Voll 25-30 (c) " Salgir " of Dobrovy and Nabholtz . 35-40 ,, (d) Sieve purifier of the " Reform " type . 35-40 ,, The quantity of air is more conveniently defined to 1 square metre of filtering area. Here practice has also established definite data. 7-8 cubic metres of air are required for 1 square metre of filtering surface. To obtain a draught of exhaust air there are set, as we have seen, fans or separate fans for machines having no fans of their own. The pressures of the fans within the machines (scouring machines, separa- tors, purifiers, &c.), or without, are generally not great, namely, from 40 to 120 mm. of the water column. 444 FLOUR MILLING [CHAP, vn We must regard the capacity of fans given in Table XLIV as the normal, which should serve as a proving capacity for the catalogue data of different firms. TABLE XLIV CAPACITY or FANS Diameter of Wings, mm. Diameter of the suction holes, mm. Number of Revolutions per 1 Minute. Volume of Air Delivered per 1 Minute in Cubic Metres. Number of Horse - Tower Required. 300 160 2100-2500 25-30 0-3-0-5 375 200 1650-2000 38-45 0-5-0-75 450 250 1400-1650 50-60 0-75-1-10 600 330 1050-1250 100-125 1-5-2-0 800 440 800-950 220-250 3-5-4-0 1000 550 650-750 350-400 5-0-6-0 1200 660 500-600 500-600 7-5-9-0 Once we have the above-mentioned data, the calculation of the details for any exhaust system may be undertaken. For example, we shall reckon out the plant of the rye mill (Figs. 433 and 434) with high grinding we have examined, which has three double roller mills with rolls 800, 700, and 600 mm. long, two stone mills with stones 1300 mm. in diameter, two sifters, and one reel separator. Suppose we are grinding rather damp rye. Then a larger filtering surface according to our data has to be employed. Three mills require : 3 sq. mts. x 4 -2 = 12 -6 sq. mts. of filters. Two stone mills : 3x2-6 = 7-8 sq. mts. Consequently, the reduction machines must have 20-4 sq. mts. The bolting machines, 50 per cent, of 20-4 sq. mts. = 10-2 sq. mts. The total is 30-6 sq. mts. The quantity of air necessary for venti- lation is : 30-6x8=244-8 cubic metres, which will need a fan with wings 800 mm. in diameter running at the rate of 960 revolutions per minute. If we decide upon a common pressure tubular filter for all machines, millstones included, then the diameter of the tubes being 90 mm. (3j inches), a filter with 56 or 60 tubes 2 metres long will be required. The section of the air trunks may be calculated according to the con- sumption of air. CHAP, vii] FLOUR MILLING 445 The general air trunk L for the roller mills must give passage to 12-6 x 8 = 100-8 cubic metres of air per minute, and cubic metres per second. Accepting the velocity of passage of the air from the ven- tilated machines down the air trunks (Figs. 433 and 434) /, K, and N on the average to be 1-5 metres per second and 15-25 metres per second down the collecting spouts L, M, and b, it is easy to calculate the dimen- sions of the transverse section of the air-conducting trunks. As regards the shape of section of the trunks, round is best, as it offers less resistance to the motion of air. But trunks of rectangular section being more easily made, these may be used for a short travel. IV TRANSPORTATION OF STOCK 1. Spouts and Elevators Modern industrial mills are almost exclusively automatic ; the whole travel of the stock, beginning with transportation of the stock to the storing bin and ending with the delivery of flour, takes place without any expenditure of manual work. Therefore the arrangement and a* correct calculation of dimensions of the transportation devices is of vital import- ance. The transportation devices must be so constructed as to answer the given capacity (without any reserve for the enlargement of the mill) and consume the least amount of power. That will be the basis of our estimation of the transport constructions, which we are about to examine in this part. All the modes of transportation may be divided into two groups : 1. Transposition of the stock* from one height to another down from the top or the reverse. 2. Transposition of the stock within the bounds of one horizontal plane. Delivery of the Stock Downwards : Spouts. For the transmission of the product in a downward direction there are drain pipes, automatic dis- chargers, or, as they are more often called, spouts. The spouts generally carry the stock from the machine to the elevator or the reverse, from machine to machine, and, lastly, from the binjbo the sacks for packing the finished product the flour. In the first two cases the spouts have always to be set aslant, and in the third possibility and convenience allow the position of the spouts to be vertical, because -the greater the speed of the flour flowing out of the bin, the faster and more compact will be the packing. 446 FLOUR MILLING [CHA. vii It is easy to deduce the condition under which the motion of the stock over an inclined plane is possible. If we have a spout (Fig. 437) inclined to the horizon at an angle a, and suppose the weight Q on a unit of area of the spout to be equal to 6r, and the coefficient of friction of the stock upon the surface of the spout /, the motion of the product is possible under the condition that : T-Nf>6 (1). And since T G sin a and N=G cos a, by substituting the values T and N into (1), we obtain : f^ I 00 4 : -l 1 6 |^ T-4 d * oi o" & B . . . . 90 100 110 120 130 140 150 160 170 180 190 200 A ,'...* J.y/v -. ".. ; 80 95 100 110 115 115 115 j 115 ; 115 115 120 120 H V : * . 90 95 95 110 115 115 115 130 ^ 130 130 135 140 V 0-72 0-95 1-10 1-20 1-50 1-61 1-72 1-84 -T95 ''' \' ; 2-00 2-28 2-40 The filling V of cups of the mentioned constructions must not exceed f of their capacity, otherwise, as has been proved by experience, the whole of the product will not be thrown out into the discharge spout. The diameters of the belt-pulleys, the number of cups to one metre of length, and the capacity per hour in litres, are shown in the appended table. TABLE XLVII Nos. of Cups. No. 1. Nos. 2-3. Nofc. 4-6. Nos. 7-8. Nos. 9-10. Nos. 11-12. Diameter of belt pulleys Number of cups to 1 ) metre . . f Capacity per hour in ) litres . . . f 400-500 12 12,500 500-600 12-10 15,000-10,000 500-600 600-700 10-8 8-6 20,000-25,000^30,000-40,000 700 6-5 45,000-50,000 700-800 5-4 55,000-60,000 452 FLOUR MILLING [CHAP, vn To bring the constructive description of elevators to a close we -must give an idea as to the arrangement of cups, cleaning of elevator legs, and the constructions of the boots and heads of the elevators. The preceding table shows us that the cups are generally set on the belt in such a manner as to leave a space of 10-65 mm. between them. But of late they are aiming at a total abolition of the distance between the cups, as is shown on Fig. 448, in order to increase the capacity of elevators without increasing the dimensions of the cups. In such cases the top part a of the M s^^s cups is made so much wider that the bottom of the cup above may enter into the cup below, in which sometimes a notch of the top line a is made. The construction of compact arrangement of cups just examined imparts greater rigidity to the belt, which demands a larger consumption of power to overcome the injurious resistances ; but in its final result the useful work of such an elevator is greater than with the cups set apart. For freeing the elevator legs of dust there are brushes b, which touching the walls of the spout with their edges sweep the dust off. a FIG. 448. FIG. 449. FIG. 450. The essential parts of an elevator are its boot and head, in which the belt-pulleys are set. The simplest kind of a wooden boot and head is given in Figs. 449 and 450. The boot is a plain wood box with a feed CHAP, vn] FLOUR MILLING 453 spout B. The bearings for one, or if the elevator is double, for two pulleys, are set on cross bars, fastened to the box with bolts. For inspec- tion of the chamber in the boot in case of a choke there is a door A. The head is also a box with a discharge tube S lt a door for inspection of FIG. 451. FIG. 452. FIG. 453. the belt-pulley, and a hatch C for controlling the discharge of the product by the cups. Among the defects of this construction must be mentioned the im- possibility of regulating the tension of the belt without lacing it over. In Figs. 451 and 452 may be seen the simplest construction of an FIG. 454. FIG. 455. American wooden head and boot without the possibility of adjusting the tension of the belt, and in Fig. 453 we have a wooden boot with adjustable bearings which may be lowered with the aid of screws a with hand-wheels. The metal constructions of boots of the American type are shown in Figs. 454 and 455. The first is iron and riveted, the second has a 454 FLOUR MILLING [CHAP, vn cast-iron or ingot steel frame. The bearings here are adjustable, and the regulation of tension of the belt is easy. In Figs. 456 and 457 we have the perspective view of a wood and an iron elevator of the Amme, Giesecke and Konegen system very ration- ally constructed. The bearings of the boots are adjustable, the door A allows of inspecting the lower belt-pulley, and the hatch B is made for cleaning the boot in case it is blocked up with product. The lower part C of the left-hand side leg in the iron elevator is built up and has a door for inspection. The heads of the wood and the iron ele- vator can be easily taken off and dismantled. Useful Work of the El- evators. The efficiency of an elevator depends on the following circumstances : 1. Shape of the cup, which determines its cap- acity. 2. Capability of the cup of retaining the pro- duct on the way from charging to emptying. 3. Capability of the cup of emptying at the spot given. The shapes of cups we examined de- FIG. 456. FIG. 457. termine their capacity. For the definition of the ability to retain the stock during the travel and to empty the cups the following line of reasoning is suggested. Supposing on the belt-pulley S (Fig. 458) of the elevator boot we have a cup U fastened to the belt E running upwards. The middle of the projection of the cup K lies at a distance r from the axis. of the belt-pulley, OK forming an angle with the vertical ; the angular velocity of rotation of the box is , the weight of the particle of product at K mg, and the centrifugal force of rotation of this particle CHAP. VII] FLOUR MILLING 455 Then the resultant T of the forces mg and mr w 2 will be expressed by the diagonal of the parallelogram, and its direction will be determined by the angle a : BD AB+AD Tga= DK~ DK But since we obtain : cos rt 2 sin Further, we shall define the point L intersection of the direction of the resultant and the vertical axis of the elevator : h =LF -OF =r sin Tga -r cos < = 9+ rco * s ^ _ r cog whence we obtain : Ti = ^ i.e. h is a constant quantity. In other terms, the position of the intersection point of the resultant T with the vertical M Fio. 458. axis of the elevator depends only on the angular velocity of rotation of the belt-pulley. The quantity h may be defined in accordance with the number of revolutions n, by substituting w~ -TTT, and after some altera- tion we obtain : J. 894 ' 56 /0\ h = r 2 .' v \*>' If the cup A (Fig. 459) were to contain a fluid, when in motion the level of this fluid would be defined by a cylindric surface ba, where the 456 tfLOUR MILLING [CHAP, vil point b is the highest position of the route over the circumference of the cup. But for dry substances the surface ba changes to ba 1 so that its angle of oscillation ft (the angle of the tangents at b) forms approxi- mately the angle of natural deflec- tion of the product. The data defining the favourable conditions of delivery of the stock, we can deduce starting with the supposition that the trajectory of motion of the product must be LS and not LS 1 for the product to drop into the outlet spout A, and not into the leg B of the elevator (Fig. 460). At the moment of ejection from the cup the product has the velocity of motion of the belt v. Its horizontal resultant is FIG. 460. " 1 f =V COS a (3), and the motive force in the vertical direction (gravity) mg=m ^-, whence (4). Having integrated these equations and excluded t from them, we obtain an equation of the curve, denning the law of motion of the product. For the calculation of elevator capacities Professor Fischer gives the following empiric formulae. Supposing we have : D diameter of the belt pulley. n number of revolutions per minute. A projection of the cup. B breadth of the cup. F distance of the summit of the rib / to the horizontal plane OJI. iv distance between the walls of the casing. L capacity of the elevator in kilogrammetre-seconds. M capacity per second in litres. CHAP, vn] FLOUR MILLING 457 All the lineal quantities here, D, A, J3, F, andw are given in metres. For the quantities mentioned, supposing the highest limit for r==h (Fig. 458), we have : 36-8 *-'- jp A^fl-llD, For the definition of the number N of horse-power required by the elevator, F. Baumgartner offers the following formula : l where L is the capacity of the elevator per hour in hectolitres, H the height of elevation in metres, and y the coefficient equal : for grain to 0*75, for break chop 0-5, for bran 0-35, and for middlings 0-30. If we accept the denominations V for the bulk of product lifted in litres, ri for its specific gravity, and H for the height of elevation, then the number N of horse-power for an elevator according to the data of the Nagel and Kamp works (Hamburg) will be : N = (l-33-2)VrjH. Luther's works (Brunswick) give : #=--1-66 VfjH. And, finally, Professor Fischer, taking for granted that the elevator is carefully looked after, suggests : For the definition of the working (f full) capacity / of the cup in litres Baumgartner suggests the following formula : T=- Q 3600 yt*' Where p is the same coefficient, v the velocity of motion of the belt per second in metres, z the number of cups to 1 metre of the belt. 1 F. Baumgartner does not mention the origin of his formulae. 458 FLOUR MILLING [CHAP, vtt The velocities of motion of the cups for different products are different. Velocity for grain .... 2-3 mts. per second. Velocity for middlings . . . 1-5-2-0 mts. per second. Velocity for flour .... 1-25-1-5 mts. per second. The diameters of the belt-pulleys for elevators are 300-700 mm. The number of revolutions of the belt -pulleys fluctuates between 40 and 90, depending on their diameters and the given velocity of the belt. Before closing the part treating of elevator transport we must give the bulk weights of grain and the intermediate products. Below is given a table of weights in kilograms. WEIGHT OF 1 LITRE IN KILOGRAMS Wheat .... 0-7-0-86 Wheat middlings 0-55-0-65 Rye 0-6-0-8 Large wheat bran 0-29-0-35 Barley . . . .0-6-0-78 Fine wheat bran . 0-32-0-60 Oats 0-43-0-54 Large rye bran . 0-37-0-44 Wheat semolina . . 0-35-0-43 Wheat flour . . 0-41-0-80 Rye semolina . . 0-50-0-55 Rye flour . . . 0-57-0-60 2. Horizontal Transport Archimedean Screw. The Archimedean screw, worm, or conveyor is one of the oldest mechanisms of automatic transportation. This mechanism is a rotating helical surface, encased in a box, which is the route of transport. The transporting action of the screw is based on the fact that dry substances travel down the length of the box or the axis when the angle of the helical surface is less than the angle 90 , where is the angle of friction of the product against the surface of the screw. One turn of the screw brings the product forward (theoretically) by the size of the thread, which is expressed by the formula nDtga, where D is the diameter of the screw, and a its angle. The working organ, as we have said, is the helical surface, a perspec- tive view of which is shown on Fig. 461, No. 1. This surface consists of the separate sections of "feathers" given below in A. The diameter is defined and these sections formed in the following manner. Supposing, according to our calculation, we need a worm with a dia- meter D and a thread h. We have to define d the diameter of the opening of the feather. The length of circumference of the d sought for is a helical line with a pitch h. The angle of the screw is a ; consequently, hndtga, whence we define d= . n . tga CHAP. VIl] FLOUR MILLING 450 Having defined the d, iron plate or zinc tin is taken of which the sec- tions of the worm are prepared, and several rounds cut out with the diameter D-^-dd^ where d is the diameter of the shaft, with concentric openings, d in diameter. Then they are cut and in the ends b there are holes perforated for rivet joints. The sections distributed along the screw are joined with rivets. Besides the ordinary worm No. 1 (S right-hand thread, and S left- hand) of the same sections, the paddle worm No. 2 is made by cutting FIG. 461. the feather down its radius and the concentric circle in four or five places, and the parts k are bent at an angle to the axis of the worm. In this manner an enlargement of the screw thread is attained and a more ener- getic stirring of the product. These worms are mostly used in America. The worms Nos. 3 and 4 have separate, not joined to each other, sections t. These sections are cast of malleable cast iron and screwed to the shaft of the worm, which is an ordinary gas-pipe. The worm No. 5 is called the band worm. Its arrangement is clear from the drawing without any description. It is used for the transporta- tion of light product in purifiers, &c. 460 FLOUR MILLING [CHAP, vii The worms Nos. 3 and 4 have this advantage over Nos. 1, 2, and 5, that the direction of motion of the product may be altered by turning the paddles t round their axis by 90. Besides that, by turning t round their axes to a larger or smaller angle, the pitch of FIG. 462. the worm, and consequently the velocity of motion of the product, can be altered. On B and C are illustrated the boxes or tubes of the worms generally met with in practice. Both the boxes are of timber, and the first has a timber bottom lined with tin r, to reduce friction of the product. The bottom of the working space in the second worm is of iron. The constructions of the bearings are sufficiently clear and need no description. A whole iron box of a worm is shown on Fig. 462. The most charac- FIG. 463. FIG. 464. teristic combination of transport by worms is the transmission of product at right angles, shown on Figs. 463 and 464. In the first case it is done by an ordinary bevel gear system, and in the second we have a chain gear. Turning now to the question concerning the calculation of the helical transportation, we must say that its theory is too weak and confines CHAP, vn] FLOUR MILLING 461 itself only to the above considerations respecting the angle of the worm surface. All the data of calculation are worked out by practice and grouped into empiric formulae by Professor Fischer. The diameter D of the worm accepted in European practice is 100- 500 mm., while in America it is 100 to 400-450 mm. The thread h of the worm in accordance with D : The number of revolutions n per minute : 45 n= The capacity L per second in litres is : D being taken in metres. If the capacity L is sought for, the diameter of the worm D may be defined from the preceding formula : The distance a between the bearings supporting the shaft of the worm is defined according to the formula : The consumption of work in horse-power is : where I is the length of the worm in metres, L the capacity in litres, y the weight of a litre in kilograms, and / the practical coefficient, which has a numerical value of from 1'35 to 1-8. F. Baumgartner gives another formula of capacity per hour in kilo- grams, namely : where D is the diameter of the worm in decimetres, n the number of revolutions per minute, and h the thread of. the worm in deci- metres. As in most cases, Baumgartner does not explain the origin of his formulae. Fischer's formulae are based on the experimental data of the works of Luther and of Nagel and Kamp, which date to 1890, and are consequently obsolete for modern types of constructions. Baumgartner 's formulae, on the other hand, in no respect correspond to the practical data and cannot therefore be used. 462 FLOUR MILLING [CHAP, vn The following considerations must serve as the correct basis on which the capacity of the worm is calculated. We must take the area of cross section of the product rilling the box of the worm, and the velocity of motion of the product, which depends on the thread of the worm and on the coefficient of friction of the product against the worm. This velocity may be defined only practically. By introducing a practical correcting coefficient into the formula of the quantity of product running in a unit of time through the given cross section, we obtain the capacity of the worm Q : Our researches have proved that D and v given in metres n is expressed by a numerical quantity 450. In this manner for Q we have : Experimental investigations show that v is expressed in accordance with the thread h of the worm and its number of revolutions per minute, thus : ..... for flour. v 2 = (0-40-0-43)/m . . . . ,, dunst. t; 8 = (0-50-0-54)&fl- . . . . middlings. v 4 =(0-56-0-60)&w- . . . . . break. v 5 = (0-62-0-72)/m ...... grain. For the existing factory dimensions of worms with their h = 250 mm. these velocities per minute will be expressed in round numbers : t>i=4, v. 2 =5, v 3 = 6, v 4 = 7, and v 5 S. Consequently, the capacity Q in its final shape per hour will be formulated thus : Q per hour- (84200 -168400)Z> 2 . Here D is in metres. The coefficient 84200 corresponds to the capacity for flour, and 168400 for grain. For the other products Q. may be obtained by substituting the corresponding velocities in the general formula. The formula we are suggesting fairly accurately corresponds to the factory data of capacity, which differ from our calculations by 1 to 3 per cent. Opposite is given the table of dimensions and capacity of the worms from Schmidt's works in Wiirzen, which may be acknowledged as normal. CHAP. VII] FLOUR MILLING 463 TABLE XLVIII DIMENSIONS AND CAPACITY OF WORMS d. Diameter in mm. h. Pitch in mm. n. Number of Revolutions per Minute. Q. Capacity in Hectolitres per 1 Hour of Grain. Qi. Capacity in Kilograms per 1 Hour of Flour. 105 110 100 23 950 115 110 100 28 1150 130 110 100 36 1500 140 115 100 42 1830 150 125 80 50 2800 170 125 80 64 3000 190 140 80 88 4000 210 160 70 100 4500 250 180 70 150 6000 270 200 70 180 7500 300 200 60 220 9000 330 250 60 280 11,000 . 350 250 60 310 12,000 400 250 50 350 14,000 TABLE XLIX DIMENSIONS OF AMERICAN WORMS Diameter of the Worm in Inches. Diameter of the Shaft in Inches. Diameter of the Worm in Inches. Diameter of the Shaft in Inches. 4 1-0 10 2 6 1-5 12 2 8 1-5 14 2 9 1-5 16 2 9 2-0 16 3 10 1-5 18 3 The diameter of the foundation of the box is made slightly larger than the diameter of the worm by 2-5 mm. (for flour and grain). The clearance between the worm and the box must be a little larger than the largest particle of the transported product, otherwise the worm would triturate these particles, and with a larger clearance the dead space would increase. ' Horizontal Automatic Conveyors. The ordinary type of a horizontal automatic conveyor is shown on Fig. 465. The product runs to the platform P (as, for instance, in filters), over which there pass scrapers t attached to two endless phains g. 464 FLOUR MILLING [CHAP, vii Another construction of the same principle is given on Fig. 466. Here the product flows into tube-shaped boxes with round scrapers passing through them. In the present case the transmission of the pro- duct is effected in directions lying at right angles. The transmitting action is easily understood from the drawing. At the other ends of the boxes there are two belt- pulleys like B. If the conditions of space require it another con- veying belt -pulley is set. The rope used for the traction is of wire. We must remark, however, that such transport is used by the Americans for small coal and seldom for grain. On Fig. 467 we see a band conveyor for sacks forming an endless cloth of separate timber planks attached to two endless parallel chains FIG. 465. FIG. 466. which run on four pinions. The tension is adjusted by transposing the bearing of the pinions lying on the left, which is done by turning the hand-wheels ra. This cloth is brought into play from the belt-pulley E, which carries a second pair of pinions n on its shaft. To reduce friction, every other plank there is an idler set which runs in guiding rails. CHAP. VII] FLOUR MILLING 465 Band Conveyor. The preceding construction of an endless cloth serves as an intermediate step to the band conveyor, which has become of late an indispensable appurtenance of grain elevators and large mills. The general idea of the band conveyor is shown in Fig. 468. The endless band R runs over two belt-pulleys D and D l5 the first of which is FIG. 467. brought into action by the driving belt -pulley N ; the other belt -pulley N 1 is loose. The band is supported by adjustable idlers from above and from below. The grain flows down S through the hopper A and is carried by the band to the " throw-off carriage " T, on which there are two guides, 1 and 2, with the band running over them. At the bend of the band over the pulley 1 to the 2nd the grain, which has acquired a force of inertia, is thrown off into the box B, whence it pours down the spout S lf To tighten the band, a weight G with a pulley 3 is suspended to it. The method of throwing the stock into the box B is given in Fig. 469. FIG. 468. The position of the carriage T depends on the place where the product is to be emptied. By means of brake devices it is fixed to the spot. Different construction of " live " guide-pulleys are illustrated on Figs. 470 and 471. On Fig. 470 we have a set of top and bottom pulleys supporting the band R ; the axes of the top idlers are inclined. Guide- pulleys with inclined axes should be avoided, as the bearings do not retain the oil well. 2G 466 FLOUR MILLING [CHAP, vn On the upper drawing on Fig. 471 we see the top wooden guide with a conic turning out. The incline of the axes of the pulleys or the conic turning out or, as we have it in the bottom drawing, the globular rims, are needed to impart a trough-like shape to the band, which prevents the stock from falling off the band on its travel. The arrangement of the top and the bottom guides (front and side view) is shown in Figs. 472 and 473. Here, instead of the globular guides bending the belt, we have a more simple construction conic guide-pulleys. The top part of the band A feeding in the stock is bent by these belt -pulleys to a trough. Proceeding now to consider the operation of the band conveyors, we must point out the relation existing between the velocities of motion of the product and the diameter of the guide-pulleys 1 and 2 (Fig. 469). If v is the velocity of motion of the band (the same being the cir- FIG. 469. FIG. 470. FIG. 471. cumferential velocity of the pulley 1) and r the radius of the pulley, the value of v is defined according to the condition : mv where is the centrifugal force of the product at the turning-point of the belt to the pulley, and mg the gravity of the stock. To prevent the CHAP. VII] FLOUR MILLING 467 stock from running off the band before it reaches the top point A of the pulley 1, we must accept =mg. Then v will be defined thus : v= \/rg. The maximum value of v will be defined out of the inequality v > \lrcf, the limit for v being the condition that the product should not be flung outside the bounds of the box, as indicated by the arrow 8. But this condition is indefinite, therefore it is better to accept v *frg. Given the velocity, the r of the guide-pulley may be defined. Gener- ally one takes a radius not exceeding the values 0-40-0-64 of a metre. The limit largest values of velocity are pointed out by Professor Fischer FIG. 472. FIG. 473. from the experimental data of the works to be 2-2-5 metres per second. The diameter of the idlers 1-2 is the thickness of the band taken 25 to 30-fold. In empiric formulae of calculation of band conveyors, the breadth of the band, which we shall name B, is taken as modulus. Mark- ing the thickness of the band e, we deduce the following value for it from experimental data : The breadth B of the band varies between 300 and 1000 mm. In defining the capacity of band conveyors Professor Fischer accepts a thickness of the layer of grain in the middle of the band not exceeding ^ of the breadth of the band. As a matter of consequence the area of section of the layer of product is defined for a flat band as the area of a triangle with its angles at the base equal to the natural angles of the de- flection of the stock. For bands of a trough-like shape of section (Fig. 472) that area is expressed by the area of a trapeze abed, 468 FLOUR MILLING [CHAP, vii Professor Zworykin suggests the following areas of section of a layer of grain : For a flat band . /2 =0 -07 2 . For a through-like band . . . n,=Q-lB 2 . Once the area of section of a layer of stock on the band and its velocity of motion are known, it is easy to define the capacity Q of the band conveyor, which will be expressed thus : Q=O>v, CHAt>. vn] tfLOUR MILLING 460 The consumption of power must be defined in dependence on the tension E of the band, which is taken to be equal to 1000.fi 2 klgs. The number N of horse-power for a band conveyor should be defined in accordance with the data evolved by Professor Petrov, who shows in his calculation that one horse-power carries 500 tons a distance of 1000 ft. We may consider that one horse-power transfers 400-420 klgs. per second. Consequently, N will be formulated thus : N- 400-420 ' Q being the capacity of the conveyor per second. APPARATUS FOR MIXING AND PACKING FLOUR Flour-mixers. Before sending the flour to the market, it is necessary to obtain a product of the accepted standard as regards the baking quali- ties as well as in its outward appearance. The quality of the grain depending on the conditions of the soil and the climate, the manner of treatment, &c., is very inconstant, and this naturally affects the standard of the product. Often during a day's run of a mill one does not succeed in obtaining flour of a certain kind uniform in quality. That being the case, one is obliged to blend the intermediate grades in corresponding proportion, to obtain the kind required. If the mill works for eight grades, it yields from twelve to fourteen in its grist. These grades, except the first two or three, are mostly medium, and because of their insignificant difference in quality are blended and give the finished product. Sometimes flour of better grade is admixed to the inferior ones to improve their quality, if they are below the normal. That is. the reason of the constant fluctuation in the percentages of yields o flour, especially of the medium grades. The apparatus used for mixing the flour are called flour -blenders. The flour -blenders for mixing flour are divided into two groups. Blenders without circulation belong to one of them, those with circula- tion belong to the other. The first blenders are used in cases where the intermediate grades of flour obtained at different times of the day's production are collected in bins or sacks according to uniformity, and are taken from there to be fed to the blender in a certain quantity decided upon by the miller, to obtain directly the grade required. 470 FLOUR MILLING [CHAP, vn The second type of blenders has such a construction as allows of blending without interruption the flour obtained earlier and later, owing to their circulatory arrangement. Fig. 475 shows a simple flour-blender without circulation. An essential part of this flour-blender is the disc A with pins, rotating to- gether with the shaft B from the driving belt-pulley C. Over the disc A there is another stationary disc D likewise furnished with pins. These discs, as well as the cross bar for the bearing of the shaft, are set in a large chamber where the blended flour collects. Into the hopper E simultaneously different grades of flour are poured in a proportion to give the grade required. That flour passes to the rotating disc A, and is stirred between the pins. The disc A runs at 160 revolutions per minute. The defects of this flour- blender lie in the fact that its disc acts as a suction fan, owing to which the pressure in the chamber rises and the flour escapes through the chinks of the chamber. Circulatory Flour - blenders. On Figs. 476 and 477 is illustrated the ordinary type of a circulatory blender employed nowadays. The flour flows into the hopper A down s, whence it passes to the worm P, From this worm it goes to the elevator R, which carries it to the top part of the blender on the worm N 9 which conveys it then to the chamber on to the agitators T. From the agitators the flour again passes to the worm P, the elevator, and the worm N, this circulation being performed until a finished uniform product is obtained. Then the spout of the elevator to the worm N is covered over, and the flour directed down the spout S to the packer G. The construction of this flour-blender, which is a modification of the FIG, 475. CHAP. VIl] FLOUE MILLING 471 old Weber Zeidler blender, belongs to the works of Amme, Giesecke and Konegen, but, with insignificant variations, is also built by other works. On Fig. 478 is illustrated one of the latest types of the circulatory flour -blender, the construction of which is as follows : The flour runs down the spout a and falls on the winged stirrer b, which has one common shaft with the worm c. In proportion as the flour collects at the bottom of the chamber, the worm enclosed in the pipe d lifts it up, and it again passes to the stirrer 6. When the flour is sufficiently mixed, the valve e is opened and discharges the product. FIG. 476. FIG. 477. The defects of this blender (the forcing of air into the chamber by the winged fan) are the same as in the simple disc blender without circulation. Quite recently there appeared on the market the flour-blenders of the Gebr. Meinecke Works in Germany. On Fig. 479 may be seen the more simple construction, the substance of which is almost the same as of the blender on Fig. 478. The difference is that in the hopper A there is a brush apparatus E which reduces the cakes and clots of flour before it passes into the chamber B. The worm, which is driven from a gear drive with the aid of a driving belt-puUey D, has two different diameters. At the lower pipe of the worm is suspended a conic shaker F. At the top, 472 FLOUR MILLING [CHAP, vii on the shaft of the worm, there is fitted a brush stirrer G which reduces the flour and throws it off the flange of the pipe of the top part of the worm. When the flour is sufficiently blended, it is de- livered through the boss C by opening the valve. On Fig. 480 may be seen a blender with a more complete circulation. The flour is de- livered into the hopper A, where there is a brush apparatus and a worm, as we shall see further on ; from the hopper it flows into the elevator B which carries it to the chamber of the blender, where it can circulate just as in the blender (Fig. 479) or be conveyed by the worm D again to the elevator B, if, by means of the rod E, the gate valve of the boss of the outlet in the chamber is opened. When the flour is sufficiently blended, the spout is covered over by the valve F out of the elevator into the blender, and the product directed into the spout G for packing. Figs. 481 and 482 illustrate a flour-blender from the same works with a vertical worm instead of an elevator. Fig. 482 exhibits the hopper FIG. 478. FIG. 480. A in section, showing that it contains a brush apparatus B and a hori- zontal worm C, which conveys the stock to the vertical worm D. FLOUR MILLING 473 CHAP, vn] Packing the Flour. -For flour which has to stand a lengthy trans- portation or lie a long time in warehouses, packing is of the greatest importance. In America flour is packed almost exclusively in barrels, and only small quantities from 30 to 60 Ib. are packed in sacks of cotton. Although barrel packing, where the flour is first put in a sack and then with the sack into the barrel, is considerably more expensive, its ad- vantages are very great. The caking of flour packed in barrels is totally FIG. 481. FIG. 482. obviated, since, when stored in large masses, the pressure falls upon the barrels and does not affect the flour. In Western Europe and Russia flour is packed exclusively in sacks, and consequently the heaping of sacks in large stacks is very dangerous, especially for a slightly damp flour, which cakes up and becomes heated. The ordinary simple way of sacking the flour is performed by hand through the delivery spout. This method is satisfactory when the capacity is small, but cannot be adopted in large mills in which special flour packers are used. 474 FLOUR MILLING [CHAP, vn In Fig. 483 is shown the Amme, Giesecke and Konegen packer, which differs but slightly from similar apparatus of other firms . Its nature is as follows : . The flour passes down the spout S to the auger A, in which there is a worm with a downward run of the flour. The worm is brought into action by a bevel gear system from the belt-pulley B, which is thrown in by the friction clutch C. On the auger A there runs freely the boss D, to which a sack is attached by means of a strap with a French clasp. The boss D is suspended on straps E (or on chains), which are wound on L H FIG. 483. FIG. 484. drums F. The boss is balanced by a weight H, because F and G are coupled by a rope or belt gear. The sack is lifted at first, enveloping the auger A, and then, in propor- tion as it is packed, it drops down. During operation the worm dis- charges the product out of the auger into the sack, and when the sack is full, the same worm adds more flour and presses it down with its weight to the required compactness. The rod L runs to the brake which regulates the lowering of the sack in other terms, the degree of compactness of the packing. In Fig. 484 we have Baverio's packer of a similar type, with an adjustable platform A for supporting the sacks. The lifting and lowering of the platform is done by means of chains (there are two chains for the sake of equability) winding on or off drums. The weight of the platform FLOUR MILLING 475 CHAf. VIl] is counterbalanced by the weight Q. For skidding a band brake B is provided. The motion of the worm is received by the bevel gear from the driving pulley C which is rotated from the counter shaft with a loose belt -pulley. American Packers. Fig. 485 shows the Nordyke & Marmon Co. flour packer. The discharge worm is brought into action from a bevel gear, which may be thrown on and off by means of the friction clutch a. For packing sacks of various sizes there are augers of different diameters FIG. 485. FIG. 486. with conic, funnel-shaped ends, by which they are fixed to the discharge tube of the apparatus. At the end of the discharge worm is attached a ramming worm with one pitch. The diameter of this worm is altered in accordance with the size of the sack. The sack lift is suspended on chains, which are wound on and off a drum with a brake pulley. The number of revolutions of the worm per minute is 200. The weight of the sacks packed may be from 20 to 200 lb., the number of sacks from 70 to 100 per hour. On Fig. 486 we see a packer for bran with the auger set the funnel- shaped end downwards. Since it is necessary to ram the bran down hard 476 FLOUR MILLING [CHAP, vii the sack is placed in an iron casing A, otherwise it might burst. After the packing operation is over the casing is opened and the sack removed from the lift. The number of revolutions of the discharge worm is 200 per minute, the capacity 50 to 60 100-lb., or 35 to 40 200-lb. sacks per hour. VI APPARATUS FOR RECKONING AND REGULATING THE QUANTITY OF PRODUCT Automatic Scales. The apparatus which serve for reckoning the quantity of grain stock are constructed for dry substances generally, FIG. 487. FIG. 488. FIG. 489. and their purpose is automatically to weigh the product flowing in with- out interruption to be treated or packed. The most typical representatives of this kind of apparatus are the scales " Chronos,' " Libra," &c. Figs. 487, 488, and 489 illustrate the plan of the "Chronos" scales, and the essence of their construction consists in the following. There is a cast-iron frame A L on which the hopper D for the product is set. This hopper is divided by the partition a 2 with a slot, in which there runs the valve gate d l connected by a system of levers with the balance levers. On the right-hand side of the balance levers or scale beam A and / is set a scale C for weights, on the left on rods b is suspended the scale B, which rests with steel prisms d, set into the jour- nals of the scale. The beams A and / rest with their steel prisms on steel linings in the brackets of the frame. To the beam A is attached an arm Z which indicates the correct setting of the scales when in vertical position. CHAP. VII FLOUR MILLING 477 FIG. 490. Through the left-hand side part a L of the hopper D, the grain runs into the scale B, then the right-hand side a is covered with the gate d^ When the scale is sufficiently filled with grain, it drops down and upsets, assuming the position B lt and the grain quickly pours out. At the same time the lever #, connected with the scale (see perspective view) and with the meter x, drops down and turns one division of the pinion of the counting mechanism. Simul- taneously with the dropping of the scale the valve F closes the outlet of the hopper. When the grain has run out, the weights return the scale to its former position, to take the next load of grain, c. In the perspective view (Fig. 488) is shown the lever with the adjust- able weight for accurately mounting the scales. In Fig. 489 we see the scale " Libra," which differs from the " Chro- nos " in small details. When mounting the scale it is enclosed in an iron case, which is locked or sealed, to prevent the workmen from altering the number indicated for the purpose of cheat- ing. The chamber in which the scale is en- closed must always be exhausted, otherwise the delicate cranks of the scale beams and sys- tems of levers, having become dusty, cease FIG. 491. working accurately and the balance begins to show incorrect weights. Fig. 490 illustrates a perspective view of the " Chronos " scale, and Fig. 491 a perspective view of the " Libra " scale, which is slightly 478 FLOUR MILLING [CHAP, vn different from the " Chronos " in its construction, but gives just as accurate a weighing. Columbian Feed Governor. for regulating the quantity of product fed to the roller mills, the American apparatus " Columbia " is employed. It consists of a box A (Fig. 492), through the inclined wall of which there is made an opening E. In the opening E, attached to the lever F, there is a slide valve G, by raising or lowering which the quantity of grain passing through this opening is increased or reduced. When dropped to the bottom, the slide valve G closes the opening E, but only so far as to allow passage to the least flow of the apparatus of any given size. The automatism of action and adjustability of this ap- paratus consist in the following. The lever F in its axis of rotation is fixed by hook-like rings MM, and by means of a solid rod is coupled with the lever C. On one side of the lever C there are two counterweights, the larger of which is sta- tionary, while the smaller one T freely travels over the rack part of C. By setting this adjustable counterweight T on a corresponding grade marked on the scale of the lever C. the quantity of product running per minute through the opening E is determined. The lever C, on the side opposite to the counterweights, has two handles 88, to the ends of which on wire rods a frame B with inclined planes K is suspended. The grains falling on the inclined planes K produce a pressure which imparts motion to the lever C and through it effects a corresponding alteration on the position of the slide valve G fixed to the lever F. To attain a quiet, even action of the slide valve G there is a piston J running in a cylinder / with glycerine and connected with one of the handles S of the lever C. . If the apparatus is designed to do service for a double roller mill, i.e. a roller mill with two pairs of rolls, it has to be stationed in the middle of the roller mill hopper, so that the frame B should be placed down the length of the rolls. But if the grain runs only to one pair of rolls, the apparatus is set over the hopper, FIG. 492. CHAP. VII] FLOUR MILLING 479 so that the counterweights are opposite to the feeding spout of the mill. In mounting the apparatus particular attention should be paid, that it is fixed on the hopper of the roller mill perfectly accurately in vertical and horizontal position, otherwise it will either operate badly or leave off working altogether. The inlet aperture in the hopper of the roller mill is made 5 mm. larger in length and width than the outlet of the apparatus. The spout conveying the stock has to be set if possible not vertically but aslant. If the position of the spout is vertical several plates lying across each other should be set in it and receive the blows from the grain passing through. It is still better in such a case to fit directly under the apparatus in the outlet spout a slide valve, by means of which the inflow of grain may be stopped, if there is anything to be put into order, or a part of the mill has to be inspected. On Fig. 493 is given a perspective view of this ap- paratus. Before starting the ap- paratus all movable parts must be examined to be sure that they work freely. The cylinder / must be filled with glycerine to a level 5 mm. from the top lid ; generally the glycerine is never added afterwards. Before letting the grain into the apparatus, the adjustable counter- weight T is set on the division of the lever C corresponding to the passage of the required quantity of stock. When the apparatus is in operation, the feeding rolls and the feeding slide valve have to be so far open that the grain may pass through un- hindered, and not collect under the frame B, otherwise the action of the apparatus will be incorrect. If the handles SS of the lever G fall on the block A when the least quantity is being treated, then, to make the operation of the apparatus correct, the rod is slightly shortened by bending. When cleaning the slide valve G or the passages between the inclined FIG. 493. 480 FLOUR MILLING [OHAJ>. vn plates K (in the frame B) only wooden tools should be used, and in no case sharp metal ones. The pear-shaped weight V, given in addition to each apparatus, is set on one of the handles S of the lever C when it is necessary to close the opening E completely. VII FLOUR BLEACHING Owing to the great development of milling technics during the last ten years, it has been shown that it is possible to obtain products of a perfection not conceived previously. The attempts to improve the outward qualities of flour referred to its colour as well. We must acknowledge that the consumer very soon became used to the grades of flour, which are of a better colour, for instance, and is extremely parti- cular about it. The desire of the mills to comply with these demands forced them to have recourse to a chemical action upon the flour with the view to improving its^ white colour ; the other grounds adduced in explanation of this manipulation, such as enhancing the baking qualities of the flour, &c., being only of secondary importance. The improvement in the white colour of the flour may be attained by treating it with bleaching substances. It is evident that a series of bleaching materials has to be excluded as injurious in this operation, and only those may be applied which are volatile and may be extracted after they have had their effect on the flour. Such, for instance, are all gases which have a bleaching effect on the organic substance : chlorine, sulphureous gas, ozone, oxides of nitrogen. On the ground of previous experience as to the effect of these sub- stances upon flour the following is known : though chlorine and sul- phureous gas do bleach the flour they lower its quality so much as to make them commercially impossible. Ozone likewise bleaches the flour but imparts an unpleasant odour to it. Thus, the sole adaptable bleaching substances remaining are the nitrogen peroxides. The Alsop Bleaching Process. In 1903 Alsop patented his process of flour bleaching by means of electrified air in apparatus especially invented for the purpose. Alsop's apparatus (Fig. 494) consists of four parts : a dynamo, an induction coil, an air pump for electrification, and a switchboard. The electrifying pump is the most important part of the whole system ; in it the bleaching gases are produced. Between two couples of electrodes CHAP. VII] FLOUR MILLING 481 there is a constantly interrupted contact, owing to which electric sparks 7 to 15 cm. long are caused. Under the effect of these sparks chemical re-actions take place between the nitrogen and the oxygen of the air, which give NO 2 , nitrogen dioxide. The electrode couples are placed in tubes A A, one of the electrodes in each being set fast on the bottom of the tubes, while the others move in the tubes with the aid of - 11/7 slide rods EE. The slide rods are connected with each other in such a way that they alternately ap- proach the upper elec- trodes to the bottom ones and remove them, owing to which electric sparks are formed between the electrodes. The apparatus operates in the following manner : with the aid of the double action pump B a current of pure air is by turns aspirated through the inlets HH. In the tubes A A the air is subjected to the action of the electric sparks. The aspiration of air takes place simul- taneously with the pro- duction of a spark. The electrified air is conveyed through the tubes CC away, and flows through valves into the chamber B, whence through the connecting pipes and valves, set in the back wall of the chamber (not seen in Fig. 494), it passes into the pipe which conducts to the apparatus in which the flour is agitated. Further, the marks on the figure denote : DD wires for the current, the sliding rod of the pump piston, and F the shaft on which a pulley of any particular diameter for driving the apparatus may be set. The agitating apparatus has the shape of an oblong drum in which the 2H FIG. 494. 482 FLOUK MILLING [CHAP, vn flour is kept in constant motion by a system of beaters ; owing to this the particles of flour come well in contact with the electrified air. The effect of the gases becomes manifest after about a minute's stirring of the flour. The operation of the apparatus may be regulated. First of all, the quantity of air introduced may be altered through a special globe valve ; the tension of the current and its quantity can likewise be altered. Experiments of bleaching after Alsop's method were performed with a strength of current of 5, 6, 7, 8, and 9 amperes. The stirring apparatus treated 36 to 40 sacks per hour ; the flour passed through the drum in the space of 1 J minutes and was consequently under the effect of these gases only during that time. Neither in the drum nor on leaving it did the flour smell of the gases. Three kinds of flour were tested. They were all obtained from Argentina wheat, which was just then being treated at the mill. The following were the grades : Patent wheat flour . . . . to 30 per cent. Bakers' , .... 30 to 64-5 Low grade ,, ,, . .... 64-5 to 73 The experiments were commenced with a current 5 amperes strong. It appeared that with such a strength of current it was impossible to notice any visible change in the flour definable by pekarisation. Only beginning with 6 amperes did the effect of the gases upon the patent and bakers' flour become manifest, and then grew more intense with the increasing strength of the current. Before it was bleached the flour had that peculiar colour which is demanded in Germany in good wheat flour, or, at least, is very much appreciated. That colour remained after bleaching with 5 amperes unchanged ; with 6 amperes it was per- ceptible, but seemed already to be a little lighter ; with 7 amperes it was scarcely noticeable ; on the contrary, the flour began to assume a kind of dead grey colour, which with the further increase in the strength of the current grew more intense. The effect of the gases appears to have been greater on patent flour than on bakers'. The patent flour when more strongly bleached assumes a colour reminding one of the colour of chalk, whereas the bakers' flour assumes a dead greyish-white colour. This difference is particularly visible by " Pekar's " test. As to the low grades flour, the nitrogen peroxide seems to have no effect upon it. Even after a strong bleaching with a current 8 amperes strong one could not discover by dry test any alteration, while the wet test showed a slight difference in colouring. The low grade flour is practically unbleachable. CHAP. VII] FLOUR MILLING 483 Other Bleaching Processes. Besides Alsop's process there are other methods of flour bleaching. In all cases the bleaching agent is nitrogen dioxide (NO 2 ). The various processes of bleaching differ from each other only in the manner in which the bleaching gas is obtained. This is done in different manners by electrifying the air, or as in one of the processes, chemically. Two other processes belong one to the Ozonised Oxygen Co., Ltd., and the other to the Flour Oxidising Co., Ltd. Both the companies put the building of the apparatus into the hands of Henry Simon in Manchester. In the description of the Ozonised Oxygen Co. ozone is erroneously considered to be the bleaching gas ; this idea found its way into the name of the company. In reality the bleaching gas here is also the nitrogen dioxide obtained through the discharge of a high tension current. As we see in Fig. 495, in the top part of the iron cupboard, where the whole system is placed, there is a glass tube A with six electrode couples, between which the electric dis- charges take place. Into this tube by means of a fan is drawn the fresh air, which is then forced into the air tank, whence it is directed to the drums M, where the feeding in and the stirring of the flour undergoing the bleaching process is performed. The experiments were made in London at one of the mills, where the system described operates with a steady strength of current of 15 to 17 amperes. The flour is bleached in six parallel drums, and remains under the influence of the N0 2 for only about one minute. The bleached product the investigators treated was a flour from the following mixture : eight parts of Russian wheat, three parts of Australian, four of North Manitoba, four of La Plata, and eight parts of hard winter wheat (North America). The flour was of the first grades to the amount of 35 per cent, A similar unbleached flour served for comparison, FIG. 495. 484 FLOUR MILLING [CHAP, vn The experiments performed with these products gave no signs of the properties and the baking qualities of the bleached flour being modified. Contrary to former observations, however, it was established that not only the bleached flour, but the crumb of the bread made of it as well, appeared to be whiter. Nevertheless, the differences were insignificant, and could be noticed only when directly compared. In the plant of the Flour Oxidising Co.'s bleaching apparatus the bleaching gas is procured chemically. Small quantities of ammonia gas are conveyed through a red-hot platinum tube, and thus the nitrogen dioxide obtained. As is shown on Fig. 496, a large quantity of air is forced with the aid of an air pump and reservoir into the tube generating FIG. 490. Bleaching Apparatus of the Flour Oxidising Co., Ltd. A air pump ; B reservoir for air ; C cylinder for ammonia ; D nitrogen dioxide (N0 2 ) generator; ^-reservoir for NO.,; M -drum for flour; F flour feed; G bleached flour delivery. the nitrogen dioxide, where those two gases blend and are directed to the bleaching drums. The gases forming in the electric arc lamp can also serve for flour bleaching. Besides the various oxygen combinations of carbon (CO and CO 2 ) in the voltaic arc there are also formed oxides of nitrogen, and among them the nitrogen dioxide (NO 2 ) possessing bleaching properties. Owing to the high temperature of the voltaic arc, the gases appearing are immediately destroyed ; but if the air out of the arc lamp is being steadily sucked away, a mixture is obtained consisting chiefly of air, though the above.-name v d gases are present in sufficient quantity to have a bleaching effect. Especially convenient for that purpose are the arc lamps where the carbons are set not opposite to each other but form a sharp angle, as is the case^ for instance, in the arc lamps for continuous CHAP, vn] FLOUR MILLING 485 current manufactured by the Arc Lamp Works, Ltd., in Nurnberg. Such lamp are easily joined into one system by means of a reservoir. If the electrified air were to be drawn out of this reservoir, it could be directed after cooling in the air tank to the bleaching drums. General Results of Investigation. The results of Buchwald and Neu- mann's experiments lead to the conclusion that the normal bleaching does not cause any great change of a chemical character. Attention must be especially drawn to the fact that even after a lapse of several months a test of the flour gave the same results ; consequently, the bleached flour, even in the course of time, shows no tendency to modifica- tion. At the same time it was established that the bleaching effect of the nitrogen dioxide is based on the modification of the fat in the wheat flour. Fleurent considers that the nitrogen oxide precipitates directly on the fat, since it disappears. According to Avary and to Alway and Pinkney the oxides of nitro- gen decolorise, in the same way as sunlight, the colouring substance dissolved in the fat of the wheat. The fat obtained by Buchwald and Neumann out of bleached flour, the raw fat of ether extraction, displayed no changes in colouring. The benzol extract proved to be lighter only in a strongly (9 amperes) bleached flour. In optical respect the fats showed no deflections. The quanti- tative differences in the contents of fat are caused by bleaching appar- ently only in the patent flour, the quantity of flour soluble in ether at the same time increasing, but also here the differences are insignificant. In the bakers' grades, where, owing to the larger percentage of fat, greater modifications would be expected, there were likewise no differences noticed. In its fresh condition and after it had been lying the flour contained the same amount of water. Neither was there any difference notice- able in the quantity of acid. The diastatic power of flour, manifest in its property of converting to sugar, apparently increases in case of a weak, i.e. normal bleaching, and drops when that process is exaggerated. An important point in the inventor's methods is the assertion that the quantity of protein in the flour increases owing to his method of bleaching, while the amount of carbo-hydrates diminishes. The truth of such an assertion seems incredible, but it is interesting to watch the effect the bleaching gases have on the amount of nitrogen and gluten in the flour. From the results of Buchwald and Neumann's experiments the following may be inferred : the quantity of nitrogen remains the same 436 FLOUR MILLING [CHAP. Vli if the bleaching is weak, but it diminishes, especially in the bakers' grades, if the bleaching is strong. An analogous phenomenon was observed in the gluten. The differences in the amount of gluten proved to be in- significant owing to the inaccuracy of the method of investigation, but must be regarded as correct, since the numbers obtained in the manifold repetitions of the investigation were the same. Out of these experiments the following numbers were obtained : TABLE L 1 i Patent. Bakers' Grades. i Unbleached. Bleached. . Unbleached Bleached. 6 Amp. 9 Amp. 6 Amp. 9 Amp. Water . . . . . . 10 59 10-30 10-28 10-57 10-38 10-4 Fat .... . . . 89 1-25 1-12 1-29 1-30 1.16 Total quantity of Proteins dissolved proteins ! 1 1 in water 2 50 35 11-80 1-80 11-42 2-75 12-18 1-89 12-18 1-81 11-18 2-55 Gluten . . . . . . . 10 60 11-00 10-20 12-00 12-00 10-80 Sugar (maltose) . . . 97 0-71 0-81 0-74 0-75 1-01 Diastatic power . . . 19 2 23-8 18-2 21-7 29-0 19-6 The results obtained from experiments in baking have the most weight for practice. The flour the investigators had at their disposal was tested in accurate laboratory experiments as well as practically in baking establishments ; both the results coincide well. There were no advantages or defects discovered in the bleached flour. In no case was the bleached flour found to be worse as regards the baking qualities. The experiments were so arranged as to have the process of fermenta- tion, on the one hand, take place in particularly favourable circumstances in the laboratory experiment and on the other hand, in the conditions obtaining in practice. It appeared that the water-absorbing capacity of bleached flour is slightly smaller ; the quantity of water being the same, a larger amount of flour was necessary to prepare the same dough. 'nbleached. Bleached. 6 amp. 9 amp. 1-460 1-440 1-726 1-692 Quantity of water required by patent flour . 1-380 bakers' grades . 1-640 In other words, bleached flour absorbs less water, viz. : Patents V , \ . by 4-0 per cent, to 3-1 per cent Bakers' . . . , 4-6 3-2 CHAP, vn] FLOUR MILLING 487 The fermentation took place in all kinds of flour equally and normally. The baked products were of an equal structure. The brownish colouring of the crust was a little deeper for the bleached flour. The bulks of the loaves were in all cases good, the differences fluctuating within the limits of inaccuracy in the experiment. On the average, out of ten experiments, there was obtained to 100 gr. of flour a loaf in cubic centi- metres : Unbleached. Bleached. 6 amp. 9 amp. Patent flour . . . . . ,458 453 456 Bakers' flour . . . . . 449 450 458 The numbers received in practical experiments do not materially differ from them, viz. : Patent flour . > . . . 451 450 435 Bakers' flour . ." < . . 439 469 462 Thus it appears that the bleaching of flour has no substantial influence on the baking process. The quantity of bread obtained proved to be a little less for bleached flour as regards weight, there being no difference in its bulk. It is remarkable that the bread crumb was no lighter in colour for bleached flour than for unbleached. In respect to bread baking the advantages of bleaching were, consequently, an illusion. In reviewing the results of all the experiments, the investigators arrived at the conclusion that flour bleaching is of no consequence on principle. With regard to baking, the bleaching after Alsop's, Simon's methods, and others similar to them deserve no attention. This general inference may be made seeing that the flour used for the experiments was of ex- treme types. The flour undergoes no modification, neither in its consis- tency nor in its baking qualities. Therefore the improvement in the quality of the flour which was observed (or, at least was asserted to have been observed) by the inventors of the apparatus must be denied. How- ever, the investigators point out that they never once observed any deterioration in the flour as a nutritive substance. At the second International Pure Food Congress, which took place in Paris in October 18-24, 1909, .as regards the bleaching of flour and middlings, by the majority of votes it was decided to allow the bleach- ing of flour by means of nitrogen oxides on condition that the sacks are stamped with a special mark. No injurious consequences to the health from such bleaching were discovered by the Paris Congress. The bleaching of semolina, on the contrary, was acknowledged to be 4SS M/)ttR MILLING [CHAP, vn inadmissible, since it would allow the adulteration of hard wheat mid- dlings bleached by nature itself with the aid of white rice middlings. That Congress gave utterance to what the investigators were already demanding in the interests of custom taxation, namely the establishing of standards of bleached flour. But on the other hand, in the United States, where the chemists, E. F. Ladd and K. E. Stallings (North Dakota), are stubborn antagonists of bleaching, in several of the States bleaching is considered to be an adulteration of flour injurious to health, and is forbidden by law. CHAPTER VIII MILLING DIAGRAMS I CLASSIFICATION OF MILLING SYSTEMS IN the preceding chapters, where we had to speak of the reduction of grain in connection with the character of operation of the machines, we mentioned in brief outlines the different milling systems. Now we have to give a definite and accurate classification of the various milling systems met with in practice, otherwise it will be difficult to make out the innu- merable varieties of milling schemes proceeding from the quality of grain, local conditions of production, and the demands made by the local, district, and world markets. From the remotest time up to the end of the sixteenth century the technics of flour milling knew only one method of reducing the grain, the essence of which consisted in that the grain was passed but once through the milling machine and was reduced together with the integu- ments. In the end of the sixteeenth century there was invented in France another method of milling, ascribed to the miller Pigeaud. That method was kept in secret by the French a long time, until in 1760 Bouquet, a well-known miller in Lyons, published it under the name of "Mouture a la lyonnaise," having perfected the old French method of milling of the end of the sixteenth century. In the more recent French literature that milling system is called " Mouture economique." The essence of that system lay in the fact that the grain was reduced not by one passage but by several. When letting the stock pass three or four times in be- tween the millstones, the upper stone, the runner, was set high over the lower one, and gradually the distance between them was reduced to the normal necessary for fine grinding. The product obtained after a passage through the first millstone with the runner set high was bolted on a reel- separator and gave flour as throughs, while the overtails containing the large particles of grain was fed to the second stone, the grinding and the bolting being repeated until the tails from the last reel-separator consisted 489 490 FLOUR MILLING [CHAP, viu of bran. Owing to such a method of milling, a considerable part of the bran was not admixed to the flour, and the flour obtained was whiter. That method of milling began to spread rapidly in Europe and America under the name of repeated, high or reduction system. But in Austria-Hungary, where the dry and hard wheat has brittle coverings, that method gave no good results, as the integuments were reduced together with the starchy part of the grain, and imparted a darker colour- ing to the flour. With the invention of the purifier by the Hungarian Paur the repeated milling was enriched by one very important stage in the milling process the freeing of middlings of the offals, which brought a new improving alteration into the milling process. Thus the historical course of development of grain milling and its present state defines two methods of grinding : 1. Plain grinding. 2. Repeated grinding. The substance of these methods is perfectly clear from the preceding. But milling practice demands a complication of the plain milling towards the repeated milling, not realising, however, fully the principle of modern high milling on the one hand, and on the other, often simplifies the high milling, without bringing it up to the complicated system. German flour milling technics have established three types of milling : I. Flachmiihlerei low or plain grinding. II. Halbhochmiihlerei semi-high grinding. III. Hochmiihlerei high grinding. It must be remarked, however, that the most learned Austrian scientist, Professor Kick, foUows the first classification, i.e. he divides the milling in two groups, plain and high, regarding the semi-high milling as high with a reduced number of breaks. In our further studies of milling we shall keep to the classification established by practice and defined by the substance of the process itself. For this reason we offer the following two types of milling systems : 1. Plain (low) grinding. II. High grinding. The essence of the plain milling system for wheat is defined not by the number of passages of the product through the grinding machines, bat by the purpose of these passages. The object of each passage through the grinding machine in plain milling, is to obtain flour immediately as the chief product. The total number of passages may fluctuate between one and five. The absence of purifiers must be regarded as a characteristic CHAP, vm.] FLOUR MILLING 491 feature of plain wheat grinding, for the middlings and dunst obtained are not graded according to quality, but subjected to a further immediate reduction to obtain a greater or smaller amount of flour. High grinding gives us three separate stages in the process of reduc- tion. The problem of the first stage is to obtain semolina, middlings, and dunst with the least possible quantity of flour, which is undesirable here, because it becomes dirtied with triturated bran. That part of the process is called, as we already know, break (rebreak must also be included in it). In the second stage the cleaned semolina undergoes further re- duction, which may be named rebreak (in Russia that process is called the polishing of middlings). The object of this part of high grinding is not so much the production of flour as the reduction of semolina to middlings for further grading according to quality. Finally, the third stage of high grinding is the reduction of middlings and dunst and the cleaning up of the offals. We must regard as a characteristic peculiarity of high grinding the grading of middlings and dunst according to quality, and consequently the cycle of machinery must necessarily include a purifier. The characteristic of high grinding we have just given was evolved by Hungarian flour millers, who have mostly to do with hard wheats. That system has been accepted partly in Germany and Russia. In France, England, and America the Hungarian system is simplified in so far that the number of breaks in it is seldom more than five, the rebreak of middlings is absent, but the purifiers are always included. The simpli- fied Hungarian high system is called by the Germans semi-high (Halb- hochmuhlerei). High rye milling differs according to the universally accepted plans from wheat milling, in that the grading of middlings according to quality is always absent, i.e. the cycle of machinery contains no purifiers. We shall become acquainted with this system of milling more in detail below, and turn now to the milling diagrams. II PLAIN GRINDING Single Passage Milling. This system is known under the appellation of peasant grinding in Russia, and the French have a characteristic name for it : mouture pour le pauvre (milling for the poor). The grain is passed through the stone of the roller mill once and is ground to flour together with the offals. In this manner, the system yields 100 per cent, of 492 FLOUR MILLING [CHAP, viri flour. The bolting away of the unreduced offals is done by hand sieves before baking if the bran is too large, which happens when the grain is not perfectly dry, The Single Passage Sifted Milling differs from the preceding in that the bran is sifted away in the mill by means of a reel or sifter. In the latter case the mill is generally constructed for improved plain milling, which can yield two or three kinds of flour, but in dependence on the demand for the peasant -sifted flour can produce this flour after one single passage. The single passage bolted milling yields 85 to 95 per cent, of flour. Single Passage Intense Milling. The aim of this system is the reduction to flour not only of the grain kernel, but of its integuments too. After reduction the product runs to the bolting machine, which yields flour as throughs and tails over bran. The bran goes to the same sole milling machine which receives the grain. Thus we have a locked cycle for the flow of the bran, which results in the bran being reduced to particles of flour, and the whole 100 per cent, of flour is obtained from the grain. Improved Plain Milling. The purpose of this system is to extract all the flour particles as far as possible from the grain, and to separate away the offals containing no flour. The number of reductions in this system is from two to five, the product after each reduction machine passing to the bolter. The general diagram of the improved plain milling system is this : First Reduction. ^ ^ Flour No. 1. Dunst. Middlings. Hulls. Reduction of Middlings. Flour Nos. 2 & \ Dunst. 3. 1 Cleaning up. deduction i of Dunst. I 1 Dark Flour. Coarse and Medium Bran. 1 Flour Nos. 1 & 2. Dark Dunst. I Reduction of Dunst. * I Dark Flour. Fine Offals (blue product). We can see in this plan that each reduction system yields a gradually deteriorating flour, dunst, middlings and offals. The flour deteriorates the more quickly, the less the number is of reduction systems. CHAP. VIII] FLOUR MILLING 493 It has already been mentioned that an improved plain system con- sists of two to five and seldom six reductions. With two reductions, generally up to 70 per cent, of flour is obtained from the first, and up to 15 per cent, from the second. 85 per cent, should be regarded as the limit of flour yield for the improved plain system ; a certain percentage of yields for each reduction may be at the same time taken, to calculate the milling machines. In the case given, with two reductions, the first one yields 70 per cent, of flour directly. The second reduction system 30 receives the remnant of the product, i.e. ----. If we take 50 per cent, of 100 flour from it, we obtain =15 per cent. Thus 15 per cent, will be 100 discharged as bran. 20 per cent, of flour might be taken from the second reduction, but then the flour would be too dark. As to the quantity of intermediate products on the improved plain system with three or more reductions, modern practice offers little definite material. In that case much depends on the way the miller performs the reduction. Still we must append the data of a German specialist, Wingert, for three and six reduction systems (Tables LI and LII). TABLE LI Reactions. Product Reduced. Fed in 100 Per Cent Yielded in 100 Per Cent. Flour. Middlings and Dunst. Bran. Blue Flour. 1 Cleaned grain 2 Middlings and dunst 3 Middlings and dunst 100 30 10 50 20 10-7 30 10 12 6 Total quantity in 100 per cent. 140 77-80 40 12 6 TABLE LII 1 Cleaned grain . ; 100 35 50 15 .. 2 Middlings and dunst 50 25 25 . . 3 and 4 Dunst .... 25 10 15 . . 5 Dunst . ...- . . 6 Bran . . . . : 15 15 r V- 24 Total quantity in 100 per cent. 205 76 90 15 24 494 FLOUR MILLING [CHAP, vin Let us now proceed to examine several typical diagrams of the im- proved plain milling system. Ill DIAGRAMS OF IMPROVED PLAIN MILLING SYSTEMS The improved plain milling system has lately begun to gain a wide local market. That system showed particularly rapid development after the roller mills were adopted. The number of flour grades obtained with this system is generally from one to three, and sometimes up to five. Let us examine several typical diagrams of the plain roller milling system. Fig. 497 gives a diagram of the plant for a mill of 100 to 130 sacks capacity per 24 hours. The grain is deposited in the storing bin, whence the elevator carries it to the magnet, which detains the iron extraneous matter. From the magnet apparatus, the grain flows in a broad sheet to the aspirator (separator) with a sieve and manifold fanning. On the sieve the grain is freed of the large impurities : straw, barley, wild oats, maize, &c. On the separator likewise are partly sorted away the small impurities : cockle, small and broken grain, and the dirt adhering to the stock. The diameter of the meshes on the aspirator sieves is 4 to 5| mm. the large, and 2 mm. the small. After the aspirator the grain goes to the cockle cylinder (trieur), where the grain is freed of cockle, pease, broken and small grains, and other analogous impurities. From the cockle cylinder the grain is directed to the horizontal emery scourer with triple aspiration, where the germ, beard, part of the bran coatings, and dust lying in the crease are removed, FIG. 497. 2c Flour, 2nd grade. M Flour dust. Ic Flour, 1st grade. p Corrugations. A'-Cockle. Kp Bran. TT Dust. Me Sharps. c Offals. CHAP, vm] FLOUR MILLING 496 From the emery machine the grain is carried by the elevator to be dampened, and then to the bin to be tempered for about one to four hours according to the dampness of ^ the grain. Sometimes dry grain (without any dampening) goes directly to be milled. The dust from the grain-cleaning machines passes to the dust chamber and thence into sacks. The reduction is performed by two pairs of rolls. But since it is diffi- cult to reduce the grain in two passages (much power is uselessly spent ; a whiter and a finer flour cannot be obtained, the bran discharged is very rich), an accessory breaking down passage is introduced into the scheme. The length of the break rolls is taken approximately one-third less than the reduction rolls. Length of the break rolls is . . . . 500 mm. Diameter v . t . . . . 250 mm. Number of corrugations to an inch . , 16 Differential velocity of the rolls . . . 1 : 1 or 1 : 3. If the differential velocity of the break rolls is 1 : 1, the grain will be broken in halves ; the differential velocity being 1:3, the grain is divided into several parts. From the break mill the grain passes directly to -the first reduction pair. Length of rolls in the first reduction mill . . 800 mm. Diameter . . . . . ." . 300 mm. Number of corrugations to an inch . .. '. 24 Differential velocity of rolls . ..-.. . . 1:3. From the first reduction mill the whole of the mixed product is carried by an automatic elevator to the reel-separator, which is clothed with silks Nos. VII, VIII, IX, and X. The tails of the reel-separator goes to the second reduction mill, and the throughs yield high grade flour. Number of revolutions of the reel . / .25 Diameter of the reel-cylinder . . . 900 mm. Bolting cloths .... .3 Breadth of cloths ... . 33 -25 inches. From the second reduction mill the whole mixture passes to the 4-cloth reel-separator, which is clothed in metal sieves and has the follow- ing numbers : 46, 44, 42, and 40. The tails from this reel-separator is large bran, while the throughs go to the next reel-separator with five cloths, and the numbers of silk are VII, VIII, IX, X, and III, 496 FLOUR MILLING [CHAP, vni The tails of that reel-separator are fine bran, and the throughs yield flour of the second grade and dunst, which goes to the mill. If it is desired to give a better finish to the goods of the second grade the dunst is sacked off. Length of rolls of the second reduction mill Diameter Differential velocity of the rolls Number of corrugations to an inch . Number of revolutions of the 4- and 5-cloth reel- separators Diameter of the reel-cylinder . Both the reduction and the break mill are exhausted. 800 mm. 300 mm. 1 :3 28 28 900 mm. FIG. 498. The ordinary type of the popular improved plain milling system, especially in the south of Russia, has the following form : Grain Cleaning. An aspirator or separator with a sieve, a trieur (cylinder), and a horizontal scourer. Grain Reduction. Two passages through corrugated rolls and one passage through a millstone. After the roller passages the product is bolted on sifters or on reels. After the stone, which cleans out the bran, the bolting yields flour of the last grade and the refuse gives bran. If two grades of flour are prepared, the product is yielded as follows : first grade 45 per cent., second grade 36-25 per cent., bran 17-5 per cent., different losses 1-25 per cent. If desired the first and second grades may be mixed to one straight grade. Fig. 498 illustrates a milling diagram with four passages. The grain- cleaning department of such a mill consists of the following machines : the grain goes first to the dust reel-separator, where it is freed of heavy dust and small extraneous matter. The wire cloth used for small impuri- ties and dust is No. 16, to separate the large impurities from the grain No. 5 FLOUR MILLING 407 CHAP. Vlll] (to an inch). From the reel-separator the grain goes to the trieur, whence it passes to the magnet apparatus. From the magnet apparatus it goes to the horizontal emery scourer. From the scourer into two bins, where the grain is tempered for five or six hours. Then it goes to the reduction machines. Grain Reduction. The reduction is performed in two four-roller mills. The first one is 450x200 mm. in size, the second 700x300 mm. The whole reduction process is ended in four passages. The first break gives dark flour (blue flour) and coarse middlings, which are bolted on a 3-metre reel-separator. The refuse goes to the second break, which is bolted on a 4-metre reel-separator. The flour obtained is fairly white, and the middlings are medium sized and mix with the middlings from the first break, and together with them run to the smooth rolls, where both FIG. 499. are reduced, and give white flour first grade, and overtails, the so-called flat product, which mixes with the tails from the second break and goes to the fourth passage. Here the flat product and the tails from the second passage undergo a final reduction, and are then bolted on a 4-metre reel- separator, where the flour obtained is better than the one from the first passage and darker than that from the second. Since the flour goes to a common conveyor, the grades may be combined at pleasure ; the first may be obtained separately, I, II, III, and IV, &c. Naturally, instead of reel-separators sifters may be employed. That mill can grind up to 500 bushels of wheat per day (24 hours) on this plan. Fig. 499 shows a diagram of cleaning and reduction with five reduction passages. Grain Cleaning. The inexpensive cleaning department of the mill consists of an aspirator, a trieur, a Seek scouring machine with a scouring sieve, Luther's emery scourer, a brush machine, and a clean 2i 498 FLOUR MILLING [CHAP, vm reel-separator. From the storing bin the grain is fed to the aspirator with one or two sieves, where it is freed of large and fine impurities, such as straws, cobs, clods of dirt, &c. The fan in the meanwhile carries away the dust, which is of very little value, to the cyclone or the filters. After that the grain passes to the trieur, where the cockle, pease, &c., are separated away. In this manner the grain, freed of all foreign matter, undergoes further treatment. The beard and the germ coats are broken off, the grain is polished, and then passes to the reel-separator ; from the reel-separator to the brush, where the grain is subjected to a final polishing, and at the same time the dust brushed out of the creases. The pure grain is damped and then, by means of the conveyor, more or less satisfactorily stirred and carried into bins for tempering. The grain thus prepared is then milled. The Milling Department (Fig. 499) consists of three four-roller mills, a two-box sifter with four divisions, and a reel-separator. The first mill is 32 x 12 in., the second 32 x 14 in., the third 20 x 10 in. The second mill has one pair of smooth rolls which reduce fine middlings. The bolting machines may also be set in the following order : one sifter for three products and the second sifter for two products. The number of grooves on the first pair of rolls in the first mill is 16 to an inch, on the second pair of the first mill 18. on the fourth pair of the second mill 22, and in the third mill both pairs of rolls have 26 grooves. The order of milling is the following. Before the first passage the grain runs over the magnet apparatus. In the first passage the grain is broken down, and the product of grinding goes to the first division of the sifter. The larger break chop and large semolina, and the tails of the bottom tray undergo a second passage. The product obtained passes to the second division of the sifter. The throughs from the bottom trays of the first two systems, fine semolina, are fed to the smooth rolls ///. The product ground is bolted in the third division of the sifter. The larger chop and rebreak, and the bottom tails of the second divi- sion, the tails of the top sieves, and the bottom tails of the third division, go to the fourth pair of corrugated rolls. The product received from the fourth pair runs to the fourth division of the sifter, where from the first two trays cleaned large bran is obtained. The product of the next two trays and the bottom tails, dark dunst, pass to the fifth pair of rolls. The product from the fifth rolls is fed to the reel-separator, whence fine bran and dark dunst are discharged as tails. If desired the dark dunst can be delivered separately. Then the last cloth in the reel-separator CHAP, vm] FLOUR MILLING 499 should be for dunst, i.e. No. 5. Both the order of milling, as well as the products obtained, are clearly seen in the diagram. The whole of the flour is received by the conveyor, where it blends into one grade named sifted flour. In case of need it may be separated into grades. It is evi- dent that the flour from the smooth rolls of the third system is the best. The next in quality is the flour from the second system. The darker grades are obtained from the first, fourth, and fifth systems. When milling soft kinds of wheat in the place of Nos. 48 in the first and second divisions of the sifter, Nos. 42 should be set, keeping the grinding in the first and second systems as high as possible. Then in all the divisions of the sifter flour silks coarser by one number must be placed. This milling system is in vogue in the region of the Northern Caucasus, and mills of that type work for peasants, who bring the grain from quite remote parts. Owing to the latter circumstance, the possi- bility of correctly tempering the grain is not everywhere possible. This is explained by the fact that in some places the peasants, on bringing the grain, pour it into the pit for immediate milling. Under such conditions the dampening of the grain is greatly hindered. To avoid undesirable consequences in that respect, there have to be arranged five or six bins of 25 to 35 bushels capacity each, and the milling operation performed in such a manner, that when one bin is emptied, the grist should be directed from the next one, and the empty bin filled with the grain cleaned in the scourer. Then, while the grist is flowing out of the first bin, the grain in the fifth or sixth bin, i.e. belonging to the cus- tomer standing in the fifth or sixth place, has a certain possibility of being tempered. In other parts, where the peasantry leave the grain and come to fetch the flour in two or three days' time, it is quite possible to temper the grain correctly. Still better is this operation arranged in localities where the peasants get the quantity of flour according to the weight of their grain. Now, the question arises, How are the interests of the mill customers who have grain of different qualities, in respect to its impurity as well as specific weight, to be reconciled ? To answer this case practice has evolved the following rules. For grain containing a fairly large amount of impurities the loss in the product escaped with the air and in grain cleaning allowed is from 3 to 5 Ib. per 36 lb., and not over 1 to 1J Ib. for grain of higher purity. The regulation concerning flour is similar to it. Owing to such regulations it is possible to mill the grain of different customers together. Of course, a lot ought not to have such wheat admixed to it 500 FLOUR MILLING [CHAP, vm containing any proportion of rye, even if the quantity of admixture should be small, because the flour assumes a darker colouring in conse- quence. Under such circumstances it is possible to treat all the grain together and temper it some ten or twelve hours if it is of a hard kind, and four or five if softer. It is very 'desirable that the grain cleaning should be performed in two scouring passages, it being necessary to dampen the grain before it goes to the second scouring passage. In such a grain-cleaning process the first scouring passage frees the grain of the dust and dirt. After damp- ing the grain is tempered, and then undergoes the second scouring passage. But since grain cleaning of that kind at the farm mills is compara- tively expensive, it is difficult to expect it to spread, though we must remark that good flour repays the extra expenses. The mills described grind Kubanka with a 10 or 20 per cent, admixture of winter wheat. In ending the review of the improved plain milling system, the fact should be noted that with this system it is not difficult to obtain good flour from soft wheat covered with elastic bran coats, which do not break up so much, and leave the flour undirtied. The best grades of flour prepared from hard wheats, on the other hand, become dirty owing to the offal being ground. For this reason the milling has to be performed cautiously, the dry grain being damped and the number of passages increased. IV HIGH GRINDING The high, repeated, or gradual reduction process has already been characterised in brief outline. We shall now study it more minutely. To extract the whole of the mealy part out of the grain and separate away the integuments, having removed as far as possible all mealy parts, is the purpose of high grinding. This is attained in a certain degree by the break and rebreak process, the aim of which is to break the grain down to middlings and dunst, to separate from them the particles con- taining no offals, and lastly, extract out of the particles of integument the remaining particles of meal. As regards the character of reduction, high grinding may be divided into four separate categories. In the first must be placed the breaking of the berry down the crease, which allows of the removal of dust CHAP, vin] FLOUR MILLING 501 settled in the crease from the halves, and otherwise inextractable in the cleaning process. The French call this passage " preliminary break " (lavant broyage), the Germans Hochschrot. In the second category are a series of passages in which the halves of grain are consecutively ground to middlings and dunst (" break propar." broyage proprement dit) of a better quality. In the passages of the third category, which should be named the " completion of break " (complement de broyage), middlings and dunst of a lower quality (soft) are produced. Finally, the passages of the fourth category are designed to clean off the mealy particles from the bran (curage des sons). A developed rebreaking process in which there are at least three pas- sages represents the three last categories of the breaking process, or with one or two the reduction of the rebreak middlings. The breaking and rebreaking process has to be so performed as to produce as little flour as possible, because it cannot be freed from the mealy particles of integument, and can be sent only to the worst grades. The number of breaks varies between five and ten, the breaking of the grain down the crease included ; the number of rebreaks, between one and five. The harder the wheat is and the more middlings and less break flour is it desirable to obtain, the greater is the number of passages used. The product obtained from each separate passage is sorted on bolting machines, and gives a series of middlings and dunst of various size and quality. Then they are blended according to size and quality (sharp or hard and soft), and subjected to grading according to their quality on purifiers. When the middlings and dunst are freed of bran and graded according to size and quality, the process of reduction commences. That process is divided into two parts. First the middlings are broken down finer. That part of reduction is analogous to the rebreaking process, and ought to ba named the rebreak of middlings (polishing of semolina). The sense of that part of the process has to b? explained. However well the purifier may work, we shall always have a certain percentage of middlings covered with offals. It is impossible to extract these grains of middlings, but by breaking them down on porcelain or smooth rolls, we obtain particles of these middlings covered with bran coats of a larger size than those of pure starch. Owing to that we have the possibility of separating the branny middlings on bolting machines in a second grading according to quality. 502 FLOUK MILLING [CHAP, vni Consequently, in developed high grinding, when rebreaking the middlings, the production of a large quantity of flour should likewise be avoided. Finally, when the middlings and dunst are completely graded, they are reduced to flour on smooth rolls. With the details of high grinding we shall become acquainted through the various milling diagrams ; at present we give a general plan of high grinding. 1. The Break Process (5 to 10 passages). I T Flour. Dunst. Middlings. Rebreak Semolina. Large Bran. 2. Rebreak Process (1 to 5 passages). Flour. Dunst. Middlings. < ^Medium Bran. 3. Grading according to Size. ! I Flour. <- 4. Grading according to Quality. 1 -v -- ' Offals. Dunst. Middlings. CLEANING THE OFFALS.< * 1 J>. Rebreak of Middlings (2 to 5 passages ) ; Fine Offal. Dark Flour. 6. Reduction of Dunst. *- Flour Fine Offal. Flour, including highest grades, &c. We shall now proceed to acquaint ourselves with the milling diagrams designed for this system. Hungarian High Grinding. On Fig. 500 we see the diagram of Hun- garian high grinding for a mill with a capacity of 5000 bushels of wheat per 24 hours. The grain-cleaning diagram includes the diagram of silo cleaning with a passage of the grain through a zigzag separator and its distri- bution in the fourteen silos of the elevator. From the silo the grain goes through the grain-blending apparatus to the zigzag separator of the grain-cleaning department, then through the magnet apparatus and a two-box sifter with metal sieves, which grades the grain according to size. The grain graded according to size passes to two groups of trieurs, con- sisting of cockle cylinders, barley cylinders, and re-cylinders. The product received from the trieurs may further be subjected to double CHAP. Vlll] FLOUR MILLING 503 Fio. 500. SLOtJR MILLING (CHAP, viii cleaning : dry and wet. In cases when the grain is not too dry the washing plant is missed. The grain passes consecutively two emery horizontal scourers, then it goes to the floor brush machine and through the scale into the bins for further treatment in roller mills. The small and large grain undergoes scouring on parallel separate scourers and brushes. If the wheat is very dry and hard it is subjected to wet scour- ing. Then from the trieurs the grain goes directly to the washing machine, whence, after drying and tempering in bins, it is taken to be scoured. The cleaning scheme examined here is far from perfect, since the sifting away of heavy offals between the first and the second scouring passage has not been provided for, and a magnet and a dampening apparatus after the brush machine are absent. The milling process forms three groups of roller passages, and the rebreak (polishing) of middlings and reduction of middlings and dunst are ended by the millstones for scraping out blue flour. The first break system consists of seven breaking passages and two rebreaking passages. We must note that the Hochschrot is absent here, and the whole breaking process is not developed to its utmost limit. The rebreak (scratch) rolls treat the middlings which are tailed over by the purifier. The reduced product is subjected to a preliminary grading on the first group of sifters, on which the break flour is separated and the pre- liminary grading of middlings and dunst according to size is performed. The last breaking passage cleans the bran and heavy offals of the puri- fiers which sort the large and medium semolina. The product from this passage goes first to the reel-separator which gives bran as tails, while the throughs pass to the sifter, which gives dark flour, blue flours of medium size, and dark dunst of two kinds. The blue flours go to be reduced on the stones, for middlings rebreak, and the second grade of dunst to the seventh reduction. After the preliminary grading the middlings and dunst pass to the sifters, which sort them into three to eight grades according to size. Here the breaking and rebreaking processes end. The product, graded accord- ing to size, runs next to the first group of purifiers, which sort it according to quality. After that operation the product, grouped according to size, undergoes a process we name middlings rebreak. The middlings rebreak performed on smooth rolls is in fact a process analogous to the break process. For this reason for the larger middlings we have here a system of sifters and purifiers. That process is, of course, much shorter than the breaking process. The sifters of this system supply us with flour, dunst, I trsd Erd tsd 506 FLOUR MILLING [CHAP, vm and middlings, which are subjected to a final reduction on the third reduction system of smooth rolls. The number of reduction passages is nine, the stone for cleaning up the dark dunst included. German High Grinding To illustrate a typical German high grind- ing system at the Dresden Exhibition in 1911, the firm of Seek Bros, exhibited the milling diagram shown in Fig. 501. The mill grinds about 6000 bushels of wheat per day (24 hours). We shall pass by the diagram of the silo and the wheat-cleaning system, and only point out that grain cleaning in the mill is developed considerably better than in the preceding plan. Here the wet scouring of grain with a dryer and without it is provided for. The mill proper is arranged after the same scheme that is used in the Hungarian mill, with the sole difference that the number of breaks in this case is limited to six, the number of rebreaking passages for middlings is reduced, but the number of reductions is increased. The bolting machines for semolina rebreak are centrifugals and sifters in conjunction. Besides that, to obtain the final product, flour, there are centrifugal redressers. The two diagrams of high grinding systems examined give a sufficient idea of the standard separate stages of the milling process. Since we are acquainted with a general outline of the grading of the product of the breaks, a more detailed plan of that grading should be given. Let us take, for example, the third break (Fig. 502), as character- istic of break stock, and examine the process of grading the product obtained. The product of the third break passes on to the sifter No. 1, the upper sieve of which is covered with a metal cloth No. 18. The overtails are break stock for the fourth break. The next sieve is likewise covered with a metal cloth No. 22, and yields the rebreak semolina. Then follow two silk flour sieves Nos. 10 and 11 ; next one silk sieve No. 3, for separating middlings from the dunst ; and finally, one silk sieve No. 9, for separating dunst as throughs and fine middlings as tails. Before the flour sieve very often is set a sieve for separating the large semolina (Nos. 32-38). The mixed middlings of the tails of No. 3 go to the sifter No. 2, which grades them into eight different sizes, and hence each of the eight grades passes to the purifier A for treating the semolina. All the first runs of purified stock are generally mixed together, but each size may be collected into sacks or spouts (if automatic) separately, if desired. The same may be said of the second runs. CHAP, vm] FLOUR MILLING 507 The third sizes of middlings are mixed together, &c. The offals of all the eight sections of the purifier are likewise run together. The throughs of the last sieve (No. 52) consist of dunst, which is directed to the sitter No. 3 for dunst. The dunst from the break sifter (No. 1) goes to the dunst sifter No. 3 ... --- .1 _^____ '-; ; ! _.!*_ -* 1 ' 1 1 , ' 1 <<0 II 1 5oa gro Centrifuge metallique Centrifugal with metal Refus Tails or to offals. cloth. Sasseur Purifier. Bluterie ronde de surete Round redresser. Bluterie ronde divisenr Grading reel. Detacheur Detacher. Bascule automatique Automatic scale. Ble propre Pure grain. Appareil magnetique Magnetic apparatus. Extracteuse ronde Round reel. Centrifuge Centrifugal . FIG. 507. G. Tails from, the fourth reduction mill (after the centrifugal) and the product No. 40 from the fifth go to the sixth. H. Tails from the third and sixth reduction mills and the product- No. 28 from the fifth, go for final treatment to the seventh reduction mill. CHAP, vm] tfLOUR MILLING Hj. Tails from the fourth purifier go to the seventh reduction mill or the offal sorter, depending on the quality of the product. I. Fine sharps (thirds, etc.). J. Coarse sharps (Pollard, etc.). K. Coarse Pollard. Kj. Fine bran. L. Tails from the first and third purifiers go to the sixth break mill. Lj. Liftings from the first, second, and third purifiers go to the centri- fugal with wire cover for the extraction of flour out of them. M. Dark flour. M x . Dunst from the first break mill. If the products seem to be good they may be reduced on the sixth break mill. N. Flour from the second, third, fourth, and fifth break mills. Nj. Flour from the first, second, third, fourth, fifth, and sixth reduc- tion mills. 0. Dark flour from the sixth break mill. Oj. Dark flour from the seventh reduction mill. P. Fine bran from the wire-covered centrifugal. Q. Broad bran. The flour from the fifth break mill and sixth reduction mill is sent further in the manner answering the wish to obtain a greater or smaller quantity of flour of the highest grade. If the tails of the fourth purifier is not of much value for baking, it may be directed to the seventh reduction mill with a centrifugal, having previously subjected it to strong aspiration. Very Short Milling Systems. The desire to make the equipment of a mill cheaper, and at the same time to obtain as good a flour as pos- sible, compels one to have recourse to the extremely abridged milling process, an example of which may be taken in the form of a diagram of an American process for mills of from 100 to 200 sacks capacity. According to the diagram (Fig. 508) we have but four break systems with corresponding differentials : for the first system 2:1, second 2:1, third 2J : 1, and for the fourth 3:1. The number of corrugations for the first system is 12 to 1 in., for the second 16, for the third 20, and for the fourth 24. It must be noted at the same time that often these limits are changed from 18 (instead of 12) to 28 (instead of 24) corruga- tions to an inch. The length of rolls is 30 in. and their diameter 9 in. The whole process of milling takes course as follows : from the first break system the product runs to the sifter on to the distributor (or, what 22 MILLING [CHAP, vm the Germans call Sammelboden), whence it passes to the wire sieve No. 18 (18-w). The tails of the scalping sieve No. 18 go to the second break, the middlings from No. 44 to the purifier K x . It is supposed that all the large middlings are separated away, and from the Nos. 10, 11 and 12' of flour sieves the throughs yield flour, which goes to the second grade (bakers'), while the refuse off No. 12 passes to the purifier K 2 for medium middlings. Further, if we watch the second, third and fourth breaks, we shall see that the preceding process of grading the middlings and flour is per- fectly and accurately repeated : all the tails off the middlings sieves go to the purifier K l3 the throughs from the flour sieves to the second FIG. 508. grade of flour, and the tails of the last sieves (llxx, llxx, and 12xx) to the purifier K 2 . As to the tails from the scalping sieve No. 34 of the last break sifter, it runs to the bran duster ED. Laying aside for the present the possible variations which are shown in the diagram, let us direct our attention to the work of the reduction rolls. Roll 5 (9 in. x24 in.) receives the throughs (pure middlings) of the purifier K{, rolls 6-7 (9 in. x24 in.) the cut-off and tails from the purifiers K l and K 2 , rolls 8-9 (9 in. x 18 in.) the throughs from K 2 , roll No. 10 (9 in. x24 in.) the throughs from the purifier K s , and, finally, roll 12 (9 in. x25 in.) receives the cut-off and tails from the purifier K s . First of aU, we must note that the flour from all the sifters corre- sponding to the six reductions goes to one first grade, generally named Patent. The tails from the sifters E and G (first and third) go to the purifier K 9 , CHAP, vmj FLOUR MILLING the tails of sifter F to the purifier K 2) while the tails of the sifters / and H pass to the eleventh (9 in. X24 in.) finishing roll, after which the throughs of the centrifugal (No. 14xx) go to the second grade, and the tails go to the second centrifugal, which gives the last worst grade (low grade) as throughs, sending the tails to the brush duster SD. From the machine last mentioned fine bran is obtained as tails, and the throughs are deflected to the second centrifugal. In the diagram Q denotes the fan, and P the dust-collectors, which despatch the products also to the second centrifugal. In this manner we have followed the main details of the preparation of flour of the first, second, and third grade. It must be pointed out that the tails No. 44 of the sifter F likewise goes to the bran duster BD, which tails over large bran. In recapitulating the general run of the diagram we may say that the first grade (Patent) is obtained by the Americans by reducing the purified middlings, i.e. from all the reduction systems in the throughs of the flour sieves of the sifter ; the second grade (Bakers') from the flour sieves of the break systems, the third grade (low grade) from the cleaning up rolls. The first variation V \ affords the possibility of sending the throughs of the last break sifter D (sieve 12) to the last reduction sifter H, to be controlled as it were ; by the variation F 2 the middlings from the last break sifter D are directed to the purifier K 2 or K 3 , which is more reason- able than to KI which purifies the heavy and large middlings. By the variation F 3 the throughs of the bran duster are directed to be redressed in the sifter H ; by the variation F 4 the large and the fine bran SS may be mixed ; by variation F 5 the first grade is improved by excluding the flour from the fourth and fifth reductions ; finally, in variation F 6 the first and second grades are blended together and produce the medium sort (Straight), in other terms, the whole grist is divided into two grades of flour (straight and low grade). In Fig. 509 we have a diagram of an extremely short system suggested by Baumgartner. The grain runs to the Hochschrot with one corrugated and one smooth roll. After it has been broken down the crease here the grain passes to the brush scalper, which yields as throughs blue flour or offals, which depends on how drastically and rigor- ously the grain is treated on the Hochschrot. Further, the product is subjected to a triple break, and is cleaned up on the fifth corrugated passage, which produces branny flour e, feed /, and large bran g. After the first break mill the product is bolted on a plansifter. The flour is then sacked off as second grade. 524 FLOUR MILLING . VITl The tails go to the second break. The semolina passes into a purifier with an inside sieve of four sections, the fine middlings to a purifier for dunsts of a similar construction. From the second break there is obtained bolted flour of the second grade, coarse and fine middlings, which go to the corresponding purifiers. The tails run to the third break mill. The flour produced here is turned to the third grade, a small quantity of middlings and dunst are directed to the purifier, the integuments and coarse tailings go to the last break mill. The reduction stock from this roll is graded on a hexagon reel, and yields the products e, /, and g spoken of above. ^ \ \ ^ -^ ^_^ i j 1 _-.:--. 1 r- ^7 1 r j 1 f- J r ~ I', -- h j.^ 4 4 [_ ' I -t- -!- -J .^ I FIG. 509. The liftings of the purifier are sacked off, as ready product-bran. The tails from the middlings sieves are directed to the second break, the tails of the fine stock go with the middlings from the purifier. The pure middlings pass to the first smooth rolls, thence to the detacher and plansifter. Here second grade flour i is obtained. The coarse stock is turned to the third smooth roll, while the fine middlings go to the second. The latter, after it has been ground and loosened, is bolted on a plansifter, and produces flour of the first grade k. Only the less coarse parts pass to the third smooth mill, to which likewise the worst middlings from the purifier are turned. After reduction and sifting a flour of the second grade I is produced here. The larger tails go to the second dunst millstone, the finer parts go to be recleaned in the middlings purifier. Now they are made equivalent CHAP. VIII] FLOUR MILLING 525 I *g*-4~ 526 FLOUR MILLING [CHAP, vm to the break middlings. The purified break midds pass to the first midds millstone and yield after bolting flour of the second grade m. The tails go to the second millstone, and after reduction to the centrifugal, which yields flour of the third grade n, and fine bran as overtails. The corrugated rolls should be 300 mm. in diameter and have 1 : 2J differential, the smooth rolls 350 mm. in diameter and the 2 : 3 differ- ential. We must add that this abridged diagram cannot produce the fine grades of flour obtainable in high and semi -high grinding. Still the grades of flour received are pure and fetch fair prices ; at the same time it must be borne in mind that to obtain them less machinery is needed, and therefore the expenditure of original capital is less. Semi-automatic Grinding. Up to the present we have been examin- ing plans of automatic mills, in which from the feeding in of the grain to the delivery of the flour the whole process is performed without the assistance of mill hands. Since semi-automatic mills are still used in Russia we append the general type of a scheme (Fig. 510) of such a mill, which is characterised by the limited number of reduction machines. The wheat is poured into the hopper and carried by the elevator to the automatic scale a, and thence to the separator &, which is furnished with a large meshed sieve. That sieve removes the larger impurities- stones, wood, &c. The sand and dust are separated away with the aid of a second sieve and travel to the outlet. The cleaned grain passes through the sieve to the dust cleaner or separator, whence the lighter particles are driven by the fan into the dust -collecting tubular pressure filter. The wheat cleaned in this manner passes to two cockle cylinders c. The re-cockls cylinder c x separates the half grains from the cockle. Through the magnet apparatus the product runs to the elevator, which lifts it to the horizontal scourer. In that machine iron beaters throw the grain against a sieve of steel wire, to separ- ate away the yet remaining dust and beard. The separate particles are carried to the pressure tubular filter d by a strong air current. The filter is divided, and one part serves for the separator, the other for the scourer. The total number of tubes of the filter is 2 x 60 = 120. After the ver- tical scourer the wheat flows into a horizontal emery one, on which the grain coverings are partly torn off. The light particles separated away are blown into the first half of the pressure tubular filter d, and the grain by means of the elevator passes into the vertical brush machine CHAP, vm] FLOUR MILLING 527 h, where it is freed of the dust lying in the crease of the grain and falling in during the cleaning. The separate particles go to the second half of the pressure tubular filter d, likewise with 120 tubes. The perfectly cleaned wheat flows now into the bin, and thence to three pairs of corrugated rolls (650x220, i, i v I), on which it is subjected to break six times. The cleaned wheat runs from the bin mentioned to the first half of the roller mill i. The first break chop by means of the elevator is lifted to the first quarter of the sifter k. The tails, separated on sieve No. 20, goes to the second half of the hopper ; the sieve No. 36 separates coarse semolina, sieve No. 15 first grade of flour, the tails of No. 12 yields midds to be purified, sieve No. 8 dunst to be reduced. In this manner the further breaking is performed, and the wheat is subjected to break six times. The mill ^ serves for reducing the coarse semolina and midds, and has two pairs of smooth rolls, 650 x 220 in size. The semolina and middlings are subjected to cleaning on purifier o. That machine is connected with one pressure tubular filter d> 2 , with 120 tubes. The purified middlings go to the second pair of rolls m and to the second quarter of the sifter 6 lt Since the middlings in passing through the rolls are crushed into thin flour flakes, before the sifter there are placed detachers pp l} which loosen these flakes and thus quicken the grading. The purified midds go to the first pair of rolls m and to the "first quarter of the sifter o. For re- ducing the low grade stock and bran there is a French stone mill q of 42 in. The reduction stock passes into the second half of the sifter o 2 . The duties of the trays sifter o, o 1? and o 2 are appointed as follows : sieve No. 54 separates the tailings, sieve No. 15 and No. 16 first flour, sieve No. 12 second flour, sieve No. 10 third flour, sieve No. 8 dunst. VI RYE GRINDING As in wheat grinding, rye grinding may be divided into plain and high systems. Plain Rye Grinding is characterised by the number of passages, which varies between one and four. If the milling is performed on rolls, they are all corrugated, while for a more rigorous clean up of the bran there is placed a stone mill for the last passage. The schemes for plain wheat grinding examined may be adapted for rye grinding as well, with the sole difference that for rye grinding there have to be used rolls 300 to 350 mm. in diameter, as owing to a stronger pressure the corrugations wear more rapidly and require more frequent renewal, 528 FLOUR MILLING [CHAP, vin In Russia the plain rye grinding is characterised, in addition, by the total quantity of flour obtained. In the market the plain ground flour is known under the name of " scoured " and " break " flour. The " scoured " flour is obtained to the amount of 95 per cent, of the quantity of grain fed into the mill. In other words the grain is ground to flour together with the bran, and 5 per cent, goes to the offals in clean- ing. Two or three passages suffice for complete reduction. In com- puting the length of rolls one should take the starting-point of its capacity as 130 to 145 Ib. to 1 cm. per day (24 hours). The " break " flour when ground in three to four passages, the large bran being sifted away, is obtained in the quantity of 80 to 85 per cent. One ought to reckon 115 to 130 Ib. per day to 1 cm. of rolls. The high rye grinding can be characterised by a more accurate bolting of the flour, and the number of passages from five to ten ; the crushing passage, in which the grain is broken down the crease, included. The high rye grinding is designed to produce several (two to four) grades of flour, or one higher than the scoured and break grades of flour. On the Russian market rye flour from high grinding is known under the appellation of dressed, sifted, and bolted flour. Dressed flour is obtained to the amount of 70 to 72 per cent., only one grade : sifted and bolted flour (two to four grades) yields up to 70 per cent. Bolted flour of the best grades does not exceed 20 to 30 per cent. In very rare cases in Russia purifiers for grading the middlings ac- cording to quality are adopted in bolted rye grinding. In other countries the use of purifiers in high rye grinding is not to be met with. Let us examine some of the characteristic schemes of high rye grinding. High Rye Grinding. The common plan of high rye grinding prac- tised in Russia is illustrated in Fig. 511. The mill of 400 sacks capacity per day operates in the 'south -western region, producing the best flour. The rye brought in sacks is poured out in front of the silo granary, whence it passes through the elevator to the automatic scale, hence to the preliminary cleaning apparatus, and then through the elevator and distributing worm into the bins. The zigzag separator for preliminary cleaning easily cleans the rye, separating away mainly the coarse impurities, so as to prevent these admixtures from passing together with the rye into the silo and stopping it up. The dust and light particles of impurities sucked in by the fan in the cleaning apparatus go to the pressure filter, and are thence automatically sacked off. From the silo the rye passes into the collecting worm, is blended CHAI>. VIII] FLOUR MILLING 529 in the proportion desired, and, mixed in this manner, goes to be cleaned. Then it runs through the automatic scale, aspirator, magnet apparatus, and three cockle cylinders connected with a re -cockle cylinder. Further, it passes through the first scouring machine, dust reel-separa- tor, second scourer, brush machine and apparatus and worms for FIG. 511. damping, hence it goes to the drying chamber, where it remains several hours to allow the moisture to spread well in the bran. The damping apparatus may also be passed over or not, according to the quality of the rye. All the machinery, beginning with the automatic scale, aspirator, and cockle cylinders, &c., is freed of dust by aspiration; in a like manner the heavy dust is separated from the light. 2 i . 530 FLOUR MILLING [CHAP, vm The clean rye in the drying chamber passes through the magnetic apparatus, the crushing roll 800 x 350, with smooth rolls without fluting, and is then bolted through one-third of the sifter. The broken-down rye passes through an apparatus with a filter for cleaning the break chop for the first break. The break is repeated six times. The dimensions of the mills and sifters are as follows : For the 1st break . 2 pair of rolls 1000 x 350 mm. and 1 sifter with 5 sieves. 2nd , .2 800 x 350 I 5 , 3rd , . 1 1000x350 \ 5 4th , . 1 1000x350 \ 5 ,, 5th , . 1 1000x350. \ 5 .1 6th , . 1 1000x350 \ 5 For reduction of semol. 1 800 x 350 I 5 The middlings from the first, second, and third breaks go each separ- ately to a pair of rolls with fine corrugations ; from the fourth break onwards they are all ground together. The flour mixes together with the aid of collecting worms suspended under the sifter, and all the grades can be prepared for sale. The yield of flour, depending on the quality of the rye, is 68 to 72 per cent. The roller mills, as well as the elevators, are ventilated by a powerful fan communicating with a suction filter, owing to which the heating of the running parts of the mills or the sweating of the machinery in general becomes impossible. The scheme examined is defective in so far that it contains no grading of middlings according to quality, which is a characteristic peculiar to high wheat grinding. To obtain a good white rye meal it is certainly necessary to introduce purifiers. In Fig. 512 we have a diagram including a purifier for cleaning coarse midds from the first, second, and third breaks. The mill, of 400 sacks capacity per day, operates in the government of Ekaterinoslav. The coarse midds obtained are cleaned on the purifier and subjected to rebreak on passage I with smooth rolls, the corresponding sifter yielding the dunst, which is then reduced on rolls II. The flour obtained from this dunst to the quantity of 6 to 8 per cent, is the best, and is never mixed with the best kinds of break flour. The flour from the other smooth rolls is blended with the unif orm-quality flour from the corrugated rolls, and the whole is divided into four grades. Flour No. from the smooth rolls between 6 and 8 per cent. ; No. 1 smooth rolls together with break flour, from 23 to 25 per cent. ; No. 2, from 22 to 24 per cent. ; mill- stone flour together with the last break, from 10 to 12 per cent. The CHAP. VIII] FLOUK MILLING 531 total amount obtainable with an accurate scraping is between 65 and 69 per cent. The employment of centrifugals for the fifth and sixth breaks FIG. 512. appears to be useful, as the rigorous threshing of the product to be sifted allows of a better separation of the flour from the offal. The defect of this scheme lies in the absence of Hochschrot, which is very necessary for rye, as it is generally very dirty owing to^the dust lying in the crease. 532 FLOUR MILLING [CHAP, vin On the other hand, it must be acknowledged that the adaptation of a millstone for cleaning up is very useful, because the cleaning up of the offals is performed much more successfully on stones than on corrugated rolls, as the corrugations become rapidly blunted owing to strong pressure. German Eye Grinding .The rye-grinding schemes here appended are widely practised in the Chemnitz district. Let us successively examine each diagram. In the first diagram there are three breaking passages through corru- gated rolls, the first pair of rolls (800 mm. X 300 mm.) having 15 cor- rugations to 1 in., and the two other pairs 18 corrugations to 1 in. The differentials of the corrugated pairs is 1:3. Further, there are two pas- sages through porcelain rolls, 600 mm. X 350 mm. in size, and, finally, two stone mills 1200 mm. and 100 mm. in diameter (Fig. 513). The whole grading process is performed on hexagon reels. The FIG. 513. wire sieves of the first reels begin with No. 28 and end (cleaning up of integuments) with No. 36, while the numbers of flour sieves of the flour- dressing reels have as their utmost limit fourteen (cleaning up the offals and third break). The dimensions of the reels are given in millimetres in the diagram (length and diameter), therefore we shall not repeat them here. Let us watch the milling process. After cleaning, the grain in the present case goes to the first break, though often enough the Germans employ in the first passage a pair of crushing rolls, the purpose of which is to divide the grain down the crease. Up to the third break the tails from the wire and flour sieves run succes- sively to the second and third break, while the throughs from the flour sieves yield the final product, flour, which may be directed to flour- blenders. But the tails of the wire sieve in the reel scalping the third break go to be finished on the first stone, and the tails of the flour reel (silks Nos. 13 and 14), which is a more or less pure dunst and fine middlings, pass to porcelain rolls. The tails of the wire sieves in the CHAP, vmj FLOUR MILLING 533 reels after both roller mills with porcelain rolls, and from the flour sieve of the second passage through porcelain rolls, go to the first stone. And, lastly, we have two passages on millstones, the aim of which is to give a final clean up of the offal. The capacity of such a mill varies between 120 and 160 sacks with a motor of 60 H.P., the grain cleaning included. As to the grades of flour, 9000 To the flour blender. FlG. 514. they may be combined according to the quality to three or four brands. In the region where this combined grinding on corrugated and porcelain rolls is practised, there is generally obtained 45 to 50 per cent, of the so- called " white " flour, No. 0. The second diagram (Fig. 514) differs from the first only in that it has an extra pair of porcelain rolls. Therefore, owing to the more accurate reduction of dunst and middlings, there is obtained up to 62 per cent, of flour No. and No. 1, which is also classified as white flour. There is a mill in Chemnitz on the same plan, which having the same To the flour blender. FIG. 515. capacity, requires 63 H.P. for the milling department only, i.e. not reckoning the cleaning of grain. Such great consumption of power can be explained solely by the considerable demand made by its shafting, which could have been designed more accurately. Finally, in Fig. 515 we have a third milling diagram for the same capacity per day. A mill with grain cleaning needs 60 H.P. This type of diagrams approaches the old French milling systems, in which two- thirds of the whole process in high grinding was performed on stone mills. 534 FLOUR MILLING [cHAt>. vnt Improved Scheme of German Eye Grinding. In the newest German rye grinding mills the hexagon reels are totally discarded, and the cleaning up of the offals is done not on stones but on rolls. In Fig. 516 we have the outline of an inexpensive semi-automatic mill, which shows that the grain goes first to the crushing mill with smooth cast-iron rolls, where it is broken down the crease. On the first half of the small sifter A the blue flour is pressed through No. X and sacked off, while the tails pass to the first break to rolls 2. The product of the first break runs to the first quarter of the sifter B, whence the flour goes to the second half of the sifter A, which does controlling duty in that part. The tails of the first quarter of the sifter B the break stock, middlings, and dunst runs into the bin // and awaits its turn to pass through the rolls 2. After the second passage through the rolls 2, the product is bolted on the same first quarter of the sifter, the tails going into bin /// for a third passage through rolls 3. The sifting of the third passage is performed on the second quarter of the sifter, dropping the tails into the bin IV, whence the product goes to the same rolls 3 after the passage of the third break. The rolls 4 serve also for two passages, the product of which is bolted on the third and fourth quarters of the sifter B. All 'the flour out of sifter B is directed to the controlling half of the sifter A. In this way one may obtain several grades of flour by distributing them among the bins, or, if they are run together in the blender, one grade. The rolls 5 serve for cleaning up the bran. On these rolls large as well as fine bran may be obtained, for which purpose there are three bins, VII, VIII, and IX, over them. From the controlling sifter the dunst is sent to the first quarter of the sifter B, where the flour fallen into the tails is separated from it, after which, together with the dunst and middlings, from the first break it goes to the second break. With the same machinery milling can be practised according to a more abridged scheme with four passages after the crushing mill. Then there are three breaking passages and a fourth for cleaning up the bran. All the roller mills, except the Hochschrot, are ventilated by means of fan C and a suction filter D. Thus, the whole milling plant consists of a crushing mill, two four- roller mills with corrugated rolls, two sifters for two and four sections, a filter, and a fan. A flour-blender, not given in the diagram, is likewise indispensable. CHAP. VIII ] FLOUR MILLING 535 Bran. FIG 516. 536 FLOUR MILLING [CHAP, vin VII MAIZE GRINDING In Russia there is only known a primitive system of maize grinding with a single passage through a millstone set without sifting away the offals. In the south of Russia, however, especially in Bessa- rabia, the question of rational grinding is awaiting a solution. For this reason we append a diagram of maize grinding, accepted in America and partly in Hungary. The maize (Fig. 517) is poured into the storing bin a, whence the FIG. 517. elevator carries it to the separator b with a sieve. The sieve separates the large impurities, such as stones, clods of earth, &c. By aspiration in the separator the maize is freed of straw, dust, &c., and this light refuse collects in the dust chamber. The cleaned maize is conveyed by the elevator to the bin c over the roller mill. The first break is done on one pair of rolls, and the product is crushed, and then goes to be graded in the first section of the sifter /. From the sifter the break middlings are sent to the bin e to be passed through the second pair of rolls, where the break is kept very low. After these rolls the product is graded in the second section of the sifter. The flow of the break middlings is altered in a closed chamber so as to pass through the first break rolls. CHAP. Vlll] FLOUR MILLING 537 53$ FLOUR MILLING [CHAP, vnl Thus, the product obtained here is sacked off, which allows of making four breaking passages. In the breaking process most attention is paid to the production of semolina with the least produce of break flour, i.e. as high a grinding as possible is practised. The flour from the sifters is sacked off, while the middlings, the fine as well as the large, go to a new purifier with six divisions, where the product is graded according to quality. The pure middlings are packed, and the offals are sent to the millstone, where they are reduced, and then go to be graded in the third section of the sifter. The purifier fan drives the extracted bran down a spout into the dust collector h, whence it goes to the sack. The middlings are used for baking bread, the remaining products, such as flour and other offals, serve as feed for cattle. The arrangement of the machines is such that by increasing their number the milling process can be made quite automatic, which affords economy in working power. Figs. 518 and 519 illustrate a cross and a longitudinal section of a mill for reducing 40 sacks of maize per day. This mill is operated by means of a 20 H. P. benzine motor with a belt drive to the main shafting. On the first floor of the mill are stationed: storing bin (a, 04), elevator bottoms, the main shafting, a four-roller mill 220x475 mm., and a 36-in. stone mill. In the garret apartment there are set : a separator 6, a middlings grading plansifter /, a group purifier d with six sections, a fan g, a filter dust -collector h, the elevator heads, and a shaft receiving its motion from the main shafting and transmitting it to all machines on that floor. VIII SCHEME or OATMEAL GRINDING Oatmeal manufacture is one of the branches of a widely developed industry the preparation of cereal foods. The corn, cereal, or break- fast foods are prepared of the grain of maize, oats, wheat, sometimes barley freed of the skin, crushed to a thin loaf, roasted or dried. They are used in almost every family for breakfast with sugar and milk the maize and wheat dry, and the oats boiled. In Russia oatmeal is known under the name of American flakes (" Her- cules "), which have nothing in common with American " Quaker Oats " neither in quality nor in outward appearance. FLOUR MILLING 530 CHAP. VIII] Since crushed oats are sold by American manufacturers wholesale in boxes at 5d. to Id. per lb., in barrels at 3d. to 4d., and all the offals are sold as cattle feed, no less than 1 to 1, 4s. is obtained per 1 cwt. of oats after the product is ready. That proves that the manufacture is profitable, and one ought to be- come acquainted with it. In Fig. 520 is shown the outline of a mill designed for a capacity of 20 sacks per day. 540 FLOUR MILLING [CHAP, vm First of all, the grain goes to the separator No. 1 with two sieves. The first sieve bolts the oats separating large impurities, on the second fine impurities and dust are removed. The fan carries away the light dirt and poor grains. From here the stock goes to the grading separator No. 2, which separates away the small oats useless for production. On some of the mills the cleaning is performed with the aid of flat sieves with oblong perforations and an automatic brush for cleaning, or by means of a grading reel-separator No. 3. These machines extract all fine impurities and sort away the large, heavy oats. After a careful cleaning and sorting away of the heavy grain equal in size, it is dried in the dryer No. 4 if very damp to facilitate the hulling, and at the same time slightly roasted to give it a flavour. The dryer generally employed is a metal pan for treating twenty barrels per day. The pan is 10 1 ft. in diameter and up to 9 in. deep. It is cemented into the stove which is arranged under it. To prevent the grain from getting burned, it is stirred the whole time. One load of oats of some 8 cwt. is dried in three hours. The stove is built of brick ; the pan is set on it with the aid of flanges in such wise that its bottom and sides are subjected to the effect of the hot air. Well dried and roasted oats are very brittle and friable. They pass in succession through scouring grinders of artificial stone. After each millstone passage (Nos. 5, 6 and 7) the grain goes to the separator with a sieve (No. 8, shell remover), the tails of which are guided to the stones, and the last one of them polishes the grain. After the stone No. 7 the grain goes to be finally freed of the integumental dust and the partly cut hulls, which is performed on the separator No. 9. Now the grain is ready to be steamed and crushed. The steaming machine here is similar to the one used for feed. It works unintermit- tently. In America copper steaming cylinders of continuous action are employed. The flow of grain into the hopper at the top is regulated, because with a change in the height of the column of grain the steam introduced from below into the steam pipe will burst through the grain and steam it insufficiently. The grain in the steaming machine is con- tinually stirred with a stirrer. The steamed grain passes to the rolls. The steaming machine, the rolls, and the dryer are combined into one machine, No. 10, which economises space. The process of crushing heats the product, and on leaving the rolls it is spread out in a thin layer in the cooler. This cooling dries it sufficiently for immediate packing in boxes or barrels. CHAP, vin] FLOUR MILLING 541 In case the cooling alone appears to be insufficient to dry the oat- meal the steam is let into the pipes of the refrigerator and thus a final drying is attained. IX QUANTITY or INTERMEDIATE PRODUCTS AND THE CALCULATION OF CORRESPONDING MACHINES In computing the number of corrugations and the capacity of the break and rebreak mills we availed ourselves of the practical data, taking the average quantities of break and rebreak middlings. Now after we have sufficiently become acquainted with the general scheme of milling, we may define the dimensions of the roller mills for rebreaking the semolina, for the reduction of middlings, and the cleaning up of the offals in accordance with the quantity of the intermediate products. In the plans examined we did not occupy ourselves with the estima- tion of the dimensions of the machines, acquainting ourselves only with the existing types of milling processes. Therefore we must now, at once, point out that the dimensions of the machines given in the appended milling diagrams are far from the correct calculation, especially as regards the dimensions of the roller mills. It must be noted that for break as well as for reduction roller mills, practice often establishes one and the same size of rolls, having in view only the convenience of erection and economic considerations. These considerations, however, are incorrect and injurious to the business. In fact, if at a mill with a certain capacity one were to take rolls of a size normal for the third break, and for all other passages establish the same size, then, owing to the absence of proportion of the capacity of the mills with different passages, these mills will be either overloaded or under- loaded. This is observed in fact in the mills of Russia and abroad, their builders not having proceeded on the basis of a correct calculation of the machinery. Quantity of Intermediate Products. We shall start with the more complex milling process the high grinding. In F. Baumgartner and L. Graf's book there are given tables of the quantity of intermediate products, determined, according to the authors' words, from the results of detailed investigations of the milling processes in different years. The wheat, which was treated at the mills subjected to investigation, was the ordinary market grade. * Pp. 229-233 and 305-312, 542 FLOUR MILLING [CHAP, vni Thus, the tables by Baumgartner and Graf hereto appended give us the average quantities of the intermediate products for high wheat grind- ing, the relation of the soft and the hard wheat having been 1:2. Approximately the reverse relation on the average is observed in Russia, where 60 to 70 per cent, of soft and 40 to 30 per cent, of hard wheat is generally ground. In this way, with two-thirds of hard wheat and one-third of soft after cleaning there was obtained 96 per cent, of grain ready for milling, so that the average losses in cleaning were 4 per cent. After eight breaking passages and one rebreak the results of Table LIII were obtained. TABLE LIII BREAKING PROCESS BREAK. Fed in 100 per Cent. Br Gr k ad F e OUr ! Dun.t Grade. Middlings Grade. Rebreak Middlings. Bran. Loss. 1. 2. i 3. I 1. 2. 3. 1. 2. 3. 1st break 2nd 3rd 4th 5th 6th 7th 8th 96-0 94-75 87-0 57-0 29-0 17-0 13-0 9-5 2-0 2'5 2-0 . O25 ... 025 (< i'-b ;;; ... | 1-6 ... : i-o i 2 V 2-5 2-0 ... io-25 0-5 ... i'-b '.'.I ... 2-0 ... 2-0 !.'.' 6-b 24-0 i ... 21-0 1 ... ... 7'0 0'25 2-0 0-5 1-0 2-0 2-0 1-0 ... 7-25 Rebreak 6-5 O-7fS 0-25 1 i i Total . 409-75 10-5 per cent. 13 per cent. 60-25 per cent. 6'5 % 7-25% 0-25 Thus, there were obtained 10 '5 per cent, of break flour, 13 per cent, of dunst, 60-25 per cent, of middlings, 7-25 per cent, of large bran, and 0-25 per cent. loss. One must bear in mind, however, that the grades (1,2, and 3) of break flour do not correspond in quality to the same grades of middlings and dunst. By denoting the break stock by the three grades, it is meant that each group of product is divided into three cate- gories, according to quality, which is different in the flour, the dunst, and the middlings. The process of grading the middlings and dunst according to quality, as we know already, is of very great importance, since from the moment the middlings are graded the grades and the quality of flour are computed, CHAP. VIII] FLOUR MILLING 543 w h ^ o H 5 8801 e Q 8 Us i] |r if! ill ill ill ;l s, Hoo H< H< H -Hhi H*i HOO ^i^ ^HI Hffi H* Hoc HOO iC O (M >0 O I^ O QD TH CD 07 ^ U.2 l2gJ !^S ^ J i 544 FLOUR MILLING [CHAP, vin Each break gives us a certain quantity of product, approximately uniform in quality. The products of the second, third and fourth breaks are the most closely related in quality. In Table LIV we have the results of grading the middlings and dunst according to quality. From the table it may be seen that the total quantity of purified middlings and dunst obtained was about 75 per cent., 2J per cent, being reckoned to the losses in dunst and offals. The further process, rebreak of middlings and large dunst (in Russia this dunst Pohlgries corresponds to middlings of the utmost fineness) is clear by Table LV. TABLE LV REBREAK OF MIDDLINGS (AUFLOSUNG) Rebreak of Middlings (polishing) 100 PerCent. Flour per Grade. Dunst per Grade. 1 PQ 1. 2. 3. 00. 0. ! 1. 2. 3. 1st rebreak (best mid- ) dlings Auszugsgries) } 25 1 ... 10 13 ... ... 1 ... 2nd rebreak (2nd grade > Mundgries) . . . ) 21 + 1 1 ... ... ... 10 9 ... H ... 3rd rebreak (Semmel- > gries) . . . . .) Hf + H 1 10 ... ... at ... 4th rebreak (Pohlgries) . 6| + 2| ... 1 ... ... ... 5 2| ... 5th rebreak if ... ... t ... t ... ! ... 6th cleaning up the bran 1 ... ... * ... ... J ... I Total .... ... 3 1 t 10 23 25| t In this way, as we see, three grades of flour and three grades of dunst have been obtained. In the Russian granular grinding the 00, 0, and 1 grades of dunst could be regarded as a ready product granular flour. But the Germans produce almost exclusively fine flour, 1 and therefore dunst 00, 0, and 1 is subjected to further reduction. Table LVI gives us a table of dunst reduction and the extraction of blue flour. Table LVI shows the final result of milling. There are obtained 1 Only quite recently the preparation of granular flour has begun here and there in Germany. CHAP. VIIl] FLOUR MILLING 545 s 5 59 I! J i 5 I - i '"' 43 r :::::: '** H4< 8 i i- l> ti ^ R ^ p5 & pj : co CO CO I- i i in : :::,:: . . . 1 <* i I.::':* . . A J5 *"o 1 CO : : : : H i> c 1 0) CN ! i 2 o ; il e fe d g ^3 49 .5 - # ff i ; ; II b m a j C 1 2 III ^ *o :::::: O o a5 O g ^ : o o o : : : ; . r t i i i i C^ CO CO CO b ic ;:::: iQ . o ""* o ''':::: lO 1 -HJC-) WhJI -,|y CC (M i- Hoo 25 10 I-H 1-1 -- 1 OJ Hoc , i-i + + + + + 0^ + cc -IM -IHH -th* eo ^o (M OJ 10 i-i ^ I-H OQ ( 1 r^ I-H ,0 02 II H I M O OO'~ H '~ lp ~ lG "' cy ' T * < ~t' ^0 ^^ O) C3 > *o V -g ^ O ai O '- Reductions and Scrapi I ^ a 3 . . "., . . ' . "" . ' . "': ' . "3 rC . f . . . 1 .' . 1 g 5 * 1 S s * V* -- r . .-*-'' : ' :s - T:-.S ^ s 1 *c .._, O t-t a .^3* 115 |g C^ lJ ^.TJTJ c8 G C ||.S 1 'o 4^ 3 1 546 FLOUR MILLING [CHAP, vm eight grades of flour, beginning with No. 00 and ending with No. 6, the sum total being 78 per cent. ; there is 16 J per cent, of bran of all kinds, and the losses amount to 1| per cent. In this manner the whole process of high German grinding requires no less than twenty-three passages. If the Hochschrot and yet another rebreaking passage are to be set in addition, which is very useful, the total number of passages will be twenty-five. Dimensions of the Machines. As regards the number and dimensions of the bolting machines and purifiers, they may be easily selected in accordance with the quantity of intermediate products according to the tables of capacity we gave on pp. 388-390 and 421. For the rebreak (sizing) of middlings, reduction of dunst, and finishing of offals we offer the following Table LVII. TABLE LVII REBREAK OF MIDDLINGS, REDUCTION OF DUNST, AND CLEANING UP OFFALS Passages in Order of Sequence. Length of Eolls in mm. to One Sack per Twenty-Four Hours. Porcelain Rolls. Cast-iron Rolls. Reduction of Dunst Cast-iron Rolls. Scraping of Hulls Cast-iron Rolls. 1st rebreak . 2nd 3rd 4th 5th 1-30-1-50 2-25-2-65 2-25-2-65 1-30-1-50 1-10-1-35 1-40-1-65 2-50-2-85 2-50-2-85 1-40-1-65 1-30-1-50 1-90-2-10 1-30-1-90 The differential of the rolls for rebreak of middlings should be taken as 4 : 5 with the number of revolutions for the fast roll 200 to 210 ; for reduction rolls, the fast roll running at 230 to 235 re- volutions, the differential is 5:6; and for rolls cleaning up the offals, the fast roll making 250 revolutions, the differential to be taken is 4 : 5. Kettenbach gives the following table of dimensions of rolls for break, rebreak of middlings (Auflosung), and the reduction of dunst in different grinding systems for a 50,000 klg. capacity (Table LVIII). CHAP. VIII] FLOUR MILLING TABLE LVIII 547 System of Grinding. Break. Rebreak of Middlings. Reduction of Dunst. Number of Passages. Length of Rolls. Number of Passages. Length of Rolls. Number of Passages. Length of Rolls. High ... . . 6 mm. 9000 5 mm. 5000 8 mm. 7750 Semi-high . 4 7500 4 4500 6 6000 English .... 4 1000 4 6500 8 7500 The ordinary high German grinding, i.e. with six breaking passages, is given out here. It must be noted that Kettenbach gives a capacity considerably below the established norm. According to our observations, for high grinding the following general working length of rolls may be given (Table LIX). TABLE LIX Process. Number of Passages. Length of Rolls in mm. Break .... . . 8 8600 Rebreak of middlings . ... > 5 4500 Reduction of middlings and dunst . 9 6750 RUSSIAN GRINDING As was mentioned before. Russian systems have been to a large extent borrowed from the Hungarians and Germans. The material difference between Russian high grinding and the Austro-German consists in the fact that the dunst Nos. 00, 0, and 1 corresponds approximately to the Russian coarse flour (granular), and is taken as a finished product. The Russian system not yet being stereotyped, the percentage of yields will also vary. The Siberian system is also very characteristic, the peculiarity of which consists in that there are only four, seldom five, grades of flour made. 548 FLOUR MILLING [CHAP, vin To illustrate the Russian system we shall give the percentages of the yield of flour in different parts of the country. Great inconvenience is offered to the comparison of the qualities of the grades of flour by the absence of uniformity in the brands. For this reason, when studying these tables one must compare not the brands or Nos., but the percentage of flour in connection with the general table. VOLGA REGION Hard and soft wheats were milled. The data refer to 1910 and 1911. Mixture Hard Wheat, 40 per cent. Soft Wheat, 60 per cent. Grade. Yield in 100 per Cent. blue . . . . ; . 11-00 1st blue . / V . ^ : . 7-00 2nd . ... . ; . 14-00 2nd red .- , . . -'.', . 4-75 1st black . . . ;.' . 14-00 2nd black . ^.-; . . 6-00 3rd grade . . . . . 12-00 4th .' . . . . 8-00 5th 2-5 Mixture Hard Wheat 58 per cent. Soft Wheat 42 per cent. ( Russian). Grade. Yield in 100 per Cent. 1st blue . 23-00 1st red . . 4-00 2nd blue .... . 18-75 2nd red . 8-00 1st black .... . 10-00 2nd black . 3-00 3rd grade .... . 5-75 4th .... . 6-75 5th . 3-00 Total amount of flour . 82-25 Offal .... . 16-75 Losses .... . 1-00 Total . . . 100-00 Total amount of flour Offal . . . Losses . Total 80-25 18-60 1-15 lOO'OO SOUTHERN REGION The southern region offers a great variety of grades and yields of flour, prepared mostly from local wheat. The data given below were obtained at the Ekaterinoslav District Farm and Industrial Exhibition, 1910, WHEAT MILL, EKATERINOSLAV 1909 Granular flour No. 00 (including semolina, granular flour No. 0000 and No. 000) . . , 22 per Soft flour No. 8 No. 1 . . . . . .11 NO- 2 . . ' -;'. . . . 10 No. II . ... v . . . . 8 ' No. 3 ; "... ';,/_ .:--: ... 8 No. Ill . -~; . . . , 6 No. IV felf; ' .: ';,-- i Total amount of flour r . . ,74 per cent. cent, CHAP, viii] FLOUR MILLING 549 WHEAT MILL, EKATERINOSLAV continued 1909 Fine offal . . .... . 2 per cent. Coarse sharps and small bran . . .14 Broad bran 4 Total amount of offal . . . 20 per cent. Screenings from the grain-cleaning department (wild oats, barley, cockle, and scouring dust) . 6 ,, Thus the mill yields 74 per cent, of flour, 20 per cent, of offal, and 6 per cent, of losses in the grain-cleaning department. 1910 Granular flour No. 00 (including semolina, No. 0000 and No. 000) . . . . . .20 per cent Soft flour No. 8 No. 1 . . . . . . 11 No. 2 9 No. II . ... . . . . 8 No. 3 . . . . . . 8 No. Ill ... . . .7 No. IV 1 Total amount of flour . . , . .72 per cent. Fine offal 2 Sharps and small bran . . . .17 Broad bran 3 Total amount of bran . . 22 per cent. Loss in the grain-cleaning department . . 6 ,, The milling process of 1910 is the same as that of 1909 ; the wheat is dryer, and therefore the quality of the flour is better, but the yield of the first grade and several other grades is less. The total percentage of yields is smaller, but there is more fine bran and less large bran, as may be seen in the table. This is explained by easy abrasion of the bran coats on dry wheat. Therefore it would be useful to give a stronger dampening. The wheat is very dirty, therefore the losses of the grain-cleaning department come up to 6 per cent. 550 FLOUR MILLING [CHAP. VIII WHEAT MILL, ALEXANDROVSK I. High Wheat Grinding Granular flour No. 0000 . . 0'54 per cent. No. 000 . , 3-39 Black . No. 00 . . 13-91 Red . , No. 00 . . 8-39 . Y No. . . 8-02 ; . No. 1 . . 11-55 ' - . :; No. 2 . . 9-67 . . No. 3 . . 7-18 V ; No. 4 . 5-62 Y . No. 5 . . 4-04 Large bran .... 2-15 ,, Fine . . . . 20-47 Broken grain arid small wheat . 2-11 ,, Wild oats and barley . .1-00 ,, Scouring dust . . ..1-9.6 ,, 72-31 per cent, of flour. / h22-62 percent, of bran >5'07 per cent, of offal. Flour . No. 0000 No. 000 " Hercules " No. No. 4 No. 5 Large bran Jine . . Dunst . _. . Scouring dust Broken grain . Small wheat . Weeds II. Soft Wheat Grinding (Export flour) 6-6 per cent. 9 ' 4 ll " . 48-5)| 4-8^ I ' -*- * 5 ? . 2-6 . 17-5 . 4-8 . 1-4 . 0-8 1-4 0-8 70-7 per cent of flour. 24-9 per cent, of bran. 4-4 per cent, of offals. Total 100 per cent. Flour No. 00 . No. . No. 3 . No. 4 . No. 5 . III. Soft Grinding (Without export flour) . 53-88 per cent." . ' . 1-90 .- . 5-80 . . 4-80 3-70 70-08 per cent, of flour. 4-80 per cent, of offals. CHAP, vm] FLOUR MILLING 551 III. Soft Grinding continued Large bran . . . .. 2-72 per cent. ) Fine , . . . 17-60 [25-12 per cent, of bran, Dunst . . . . . 4*80 ,, Weeds . . "."" . . 0-90 Small wheat . . . . 1-50 Scouring dust . : > . 1-40 ,, Broken grain . . . . 1-00 , , The above data from Niebuhr's mill are the average yields for the space of ten years (from 1900 to 1910). The yields in the Table II are obtained from mills adapted almost exclusively for export into ports on the Black and Mediterranean Seas. WHEAT MILL, EKATEEINOSLAV The mill yields nine grades of flour, manufacturing brands which go to the London market. The average yields per grade are represented according to the data of 1909. Percentage of Yield. Granular flour No. 000 . . . . . 4-37 per cent. Soft flour No. 00 }forexport . . . .20,9 ;; No. 1 . . . . . - 9-54 No. 2 . : . ' . . . 9-68 No. 3 . . . . . - 9-47 No. 4 . . . . . . 6-61 No. 5 ...... 5-76 No. 6 . 0-92 Total amount of flour . . 76-51 per cent. Fine offal. . ..... . 9-29 Large bran ... 11*24 ,, Total amount of produce . . . 97-04 per cent. Screenings loss . . 2-96 ,, Total . . . | . .. 100-00 per cent. WHEAT MILL, EKATERINOSLAV Before packing the flour is graded, and to flour No. 1 is added the flour from the third break, to flour No. 2 that of the fourth break, to No. 3 of the second break, to No. 4 of the second and sixth breaks, and to No. H4 the flour from the first, sixth, and seventh breaks. 652 FLOUR MILLING [CHAP, vni The yields of flour in percentages are given in the following table : . . . . .6 per cent. Flour, brand 000 00 1 2 3 4 H4 Finest offals Large bran Fine bran Wild oats Weeds . White dust Dark dust Total amount of flour Total amount of offal Hi 12 10J 7 76~ 3J 2f 11* 17 II Total amount of screenings Total 2f 7| 100J per cent. Instead of the ordinary result of exactly 100 per cent, here we have 100-5 per cent. This means that the total weight in a correct calculation increases on account of the dampening of the wheat, which absorbs the moisture. TABLE LX WHEAT MILL, MAKIOOPOL Flour Grades Belotoorka. 50 per cent. Belotoorka and 50 per cent. Banatka. 1st grade 6-50 per cent. 15-00 per cent. 2nd 6-50 10-00 3rd : . . .' 6-50 12-50 4th . , , 28-00 11-25 5th . , , 11-25 11-25 6th . 10-50 '10-00 7th 6-50 6-50 Total 75 7 5 per cent. 76 -60 per cent. Sharps 5-50 per cent. 5-50 per cent. Fine bran . , 7-75 7-00 Large bran . ,;-. 5-50 4-75 Offal in the scouring de- 1 partment . . j 7-00 7-00 Dust and dirt in them . 4-50 4-50 CHAP, viii] tfLOUR MILLING 563 WHEAT MILL, VILLAGE ALEXANDROVKA, GOVERNMENT OF EKATERINOSLAV The samples of milling are of the 1909 crop. The mill treats 90 per cent, of Ulka and 10 per cent, of Garnovka. Semolina ... . . . . . 2 -5 per cent. Flour, brand No. 000 . . . 2-5 No. 00 15-0 No. . ... 10-0 No. 1 10-0 No. 2 .... 10-0 No. 3 10-0 No. 4 7-5 No. 5 . . 6-25 Total amount of flour . . . 73 -75 per cent. Fine sharps . N . . . . 1-25 Fine bran . . . . 11-25 Large bran .... 7-50 The above tables of yields and flour brands through their variety and inconstancy greatly impede the progress of the Russian exporters on the foreign markets. For this reason, we ought most decidedly to adopt uniform brands. There is no doubt that a reduced number of grades and the definiteness of the brand will simplify the milling process, make it cheaper, and facilitate the competition of Russian mills on foreign markets. CHAPTER IX CONSTRUCTION OF MILL BUILDINGS I CONDITIONS DETERMINING THE CHARACTER OF BUILDINGS IN milling practice there are two processes which determine the character of the buildings and the arrangement of the machines : the automatic and the intermittent. For this reason, before proceeding to describe the construc- tions of mill buildings, one should compare these two methods of milling. In automatic milling, as the name itself proves, the complex milling process is performed without the assistance of human hands. In the sack mill all the intermediate products, beginning with break and middlings and ending with dunst and flour, are sacked, sorted, and fed by hand into corresponding machines, where they are subjected to further treatment. Thus, the manual operation of a workman forms the con- necting link in the independent work of the separate machines. " Sack mills " are now comparatively seldom met with, and at a well- furnished sack mill one may see special devices generally in the shape of bins with so-called caps for the automatic performance of the different parts of the milling process, such as the breaking process, middlings grading, or reduction. If, on the other hand, the arrangement of the mill is automatic, the whole process, starting at the moment the dirty grain goes into the storing bin and ending with the packing of flour per grade, is performed without the assistance of working hands. The separate products by means of various transporting devices, in the shape of bands, elevators, worms and spouts pass through all the stages of treatment, i.e. the whole operation is performed quite automatically. In this manner, the continuity of the milling process is left intact. If a certain scheme of milling is accurately followed, both the auto- matic and the sack mill, provided they are furnished with a sufficient number of machines, are 'able to give equal results as regards the quality of the milled products. But here arises the question, Which way is the best to obtain these results ? which one of them is the most expedient, technically speaking, and more economical as regards the milling costs ? Among the mass of millers, not only in Russia but also abroad, there 554 CHAP, ix] FLOUR MILLING 555 are many partisans of the full sacking or semi-automatic mill. Therefore it is necessary minutely to consider the question, What mill should one build a sacking or an automatic one ? First of all, it is an undoubted fact that every machine answers its purpose only when its work is perfectly definite both in quantity and in quality. A change in the quality of the material treated, overloading, and frequent half empty work- ing, while the material is being changed, all this has a detrimental influence on the results of the work and on the wear of the machine. All this is observed in the work of the sacking mill, in which, generally, there is no sufficient number of machines and apparatus and the process is not strictly established. In the sacking mill one and the same machine often serves for different purposes. In the medium sacking mill, for instance, there are often adopted the so-called " turn," with the aid of which one and the same roller mill and the bolting machine coupled to it treat pro- ducts different in size and quality. Under such conditions neither the number of corrugations on the rolls nor the number of the sieves in the bolting machine can be common for different products, and therefore the quality of the work is not high. The automatic mill operates according to a perfectly definite scheme of milling. A sufficient number of machines, every one of which performs a certain work, affords the possibility of establishing a definite set of dimensions for the machines, in accordance with a previously evolved and thought-out milling scheme. The whole work is performed evenly, and the corresponding products, mechanically blending, are automatically sent forward for further treatment. In an automatic mil^ having a definite milling scheme, the miller is always able to watch the general run of the process, to control at any given moment the expedience of the combinations provided for by the scheme. On the other hand, there is always provision made for the construction of alternative runs, owing to which the scheme becomes flexible, and this allows the varying demands of the market to be met, since it is possible to alter within certain limits the percentage of yields of the different grades of flour. The sacks with the intermediate products, occupying all the open spaces in the sacking mill, and the shooting of these products by hand into the bins, result in the mill apartments being constantly filled with dust. Even with the most careful attendance it is impossible to avoid the escape of flour, which lowers the total percentage of the yield. That loss may be obviated only in an automatic mill, where the products travel through closed spouts, which, coupled with a suitable system tfLOUR MILLING [CHAP. IX of exhaust, make dustless operation possible not only in the clean half of the mill the milling department but also in the grain-cleaning division. By adopting filters one can make all the apartments of an automatic mill dustless, for, not only machines furnished with fans may be included in the general exhaust system, but such machines and apparatus as the trieurs, automatic scales, and elevators as well. When selecting the type of mill, a circumstance of no less importance than the technical outfit is the economic side of the question, which touches the millers' most tender point the cost of working the milling. The most material element in the milling expenses is the cost of mill hands. If a large mill is taken, a parallel comparison of an automatic and a sacking mill shows a sharp difference. For instance, in a mill of the sacking type, with a 12,000 bushels of wheat capacity per day, the expenses in workmen during one shift amount to the round figure of seventy hands, while in an automatic mill of the same capacity the number of workmen is reduced almost fourfold down to eighteen men. That relation drops also with the lowering capacity, and, for instance, for a medium mill of 1750 bushels automatic in arrangement the number of hands does not exceed five or six. against the ten or twelve of the sack- ing system. The numbers of hands given include only the persons taking part in the process of production, for instance, roller men, purifier men, &c., whereas the workmen occupied in supplying, loading of the wheat, the packing of the flour are not reckoned, as their number depends on local conditions the situation of the mill, the mode of transport, &c. The following table gives parallel data pertaining to the number of hands employed during one shift at a sacking and an automatic mill. TABLE LXI Number of Hands. Capacity of Mill per Day in Bushels. Sacking Mill. Automatic Mill. Milling Dept. Cleaning Dept. Total. Milling Dept. j Cleaning Dept. Total. 12,000 ,. . , 66 4 70 14 4 18 8000 . . . ; ; 36 3 39 9 3 12 5500 to 6000 . 24 3 27 7 3 10 4000 .... 20 2 22 5 2 7 2700 to 3300 . 16 2 18 5 2 7 1700 to 2000 . 10 2 12 4 2 6 1000 ... .. 6 1 7 3 1 4 CHAP, ix] FLOUR MILLING 557 As may be seen in the table, in the grain- cleaning department of the automatic mills there is employed the same number of hands as in the sacking mills, because the cleaning of grain at a sacking mill is gene- rally performed automaticaUy. But in the grinding department of the mill, the number of hands in changing from the sacking to the automatic mill makes a sharp bound, as we see in Fig. 521, which presents more strikingly the data of the appended table. This diagram clearly shows that with the diminution of the capacity the difference drops, and attains an insignificant quantity in small mills. To the milling expenses, which are absent in the automatic arrange- Number of hands in the grain- cleaning department. I Number of hands in an automatic mill. s v w~m arm ^ mber f ***** sacking mill. FIG. 521. ment, must be added also the outlay in sacks for the intermediate products. Besides the cost of working, one should reckon the cost of equipping the mill, which determines the capital charges. The automatic mill requires a greater number of machines, the presence of which would exclude the necessity of a " return " to the machines which have already fulfilled one purpose. Consequently, the automatic mill requires far more machinery in the grinding section than the sacking one. For example, we shall take a mill with 650 bushels of wheat capacity per day. In mills fitted out for sacking, very frequently owing to the use of " returns " the number of roller mills is limited to four, whereas an automatic mill of the same capacity to work regularly needs seven or eight roller mills. Parallel to the number of those mills the number of bolting machines and transport devices augments, which increases the posts of the pla^nt. As the capacity increases, however, these ex* 558 FLOUR MILLING [CHAP, ix penses decrease. For a mill with 2000 bushels of wheat capacity per day, of the sacking type, eight is a sufficient number of roller mills, whereas an automatic mill needs but eleven mills. In spite of the comparatively great difference in cost of fitting out an automatic and a sacking mill at the present moment, the erection of an automatic mill may be regarded as profitable as soon as its capacity amounts to 1000 or 1300 bushels. Those against the automatic mill maintain, though without any founda- tion, that the flour produced by an automatic mill does not possess uniform qualities. Under the influence of that false opinion there sprang into existence a type of mills which find their place on the line between the automatic and the sacking mills. The peculiarity of these so-called semi-automatic mills consists in the fact that the whole process is per- formed automatically, but the flour is collected in sacks at the point of discharge out of separate bolting machines and then graded by hand and mixed in the blender to obtain the brands established on the market. But this is a palliative, which does not abolish the causes of non-uni- formity of the flour. In the meantime, not noticing it themselves, these opponents of the automatic system turn the above-mentioned argument, which has some real meaning in it, against themselves: namely, the sacking mill does not guarantee the uniformity of the consistence of flour, the whole control being based on the superficial visual sensations. But at the time of the night shift that becomes almost impossible even to an experi- enced miller. To solve the question of the homogeneity of flour in the automatic mill, one must pay due attention to the methods of blending the grain, a no less important question than the cleaning of it. For the regularity and consistency of the final results, the uniformity of the intermediate products, middlings and dunst, is equally necessary. The ideal solution of the question is to erect elevators by the mills in which the grain is stored in silos, sorted, and the mill supplied with a mixture according to a certain recipe. Then the intermediate products too, being the result of a definite milling scheme, will be homogeneous. Thus, for a mill of even a medium capacity the automatic type, unrestricted as regards the number and size of machines, is undoubtedly the most rational type, both economically and theo- retically. CHAP, ix] FLOUR MILLING 559 II CONSTRUCTION OF MILL BUILDINGS With the introduction of the automatic process in flour mills, material alterations in the construction of the mill buildings became necessary. Up to that time low mill buildings answered their purpose perfectly. At the old (village) mills of plain grinding with water-wheels the plant consisted mainly of one stone mill and one bolting reel per wheel. For small country mills an insignificant building area by the water for the machinery was sufficient, while the remaining part of the building was free for other purposes and served as lodging to the miller. The idyllic situation of the mill by the water, the rumbling torrent, and the roar of the mill, all wakened the creative powers in the poets, who sang praises to the outward picture of manual industry. With the invention of the turbine at the large sources of water energy, plants consisting of several separate wheels were substituted by the turbine, owing to which the inner arrangement became more independent of the outer. When steam power commenced its victorious march from England over all the civilised countries, and effected in all branches of industry the well-known great changes, flour milling could not remain behind in the general progressive motion. The invention of the roller mill, and the adoption of steam-engines and other heat motors together with it, imparted a totally different aspect to the milling industry. The construction of mills, which up to that time was mostly in the hands of artisans, developed into a large industry, and by the efforts of mill-building firms, during the course of the last forty years there was evolved a certain form of arrangement of the mill apartments, which may be regarded as fairly standardized. A Simple Mitt Building. Let us first examine the type of building of a simple mill for the peasant single grinding. Fig. 522 illustrates in a longitudinal section and plan a mill with one stone mill (on ball bearings), a combined grain-cleaning machine, a cyclone for dust collecting, and Soder's sifter. The single floor building has a hursting on which the sifter is set. The stone mill is planted on a foundation on a level with the hursting. On the overhead flooring, to which there runs a ladder, a cyclone and a grain-cleaning machine are stationed : under the flooring the main 560 FLOUR MILLING [CHAP, ix drive is placed, from which the motion is communicated to the elevator, the grain-cleaning machine, and the sifter. For the motor (in our case a a Grain bin. fc Grain elevator. c Scourer. d Ball mill. e Flour elevator. k Plansifter. I Hoisting device. t Dust collector. FIG. 522. naphtha-engine, but it may be a steam-engine or a turbine) a special apartment, separated from the mill by a wall, is arranged. The building may be of stone, which is better as regards security against fire. CHAP. IX J FLOUR MILLING 561 III BUILDINGS or COMPLICATED GRINDING MILLS In modern wheat or rye mills with automatic handling of the prQ- ducts we generally find four or five floors. The first (basement) floor is left for the main shafts, the second for the roller mills, the third is necessary for the purpose of communicating a sufficient incline to the spouts, the fourth for purifiers, and finally, the fifth for bolting machines. In rye mills there is no floor for purifiers. The roller mills and stone mills, as well as the purifiers and bolting FIG. 523. FIG. 524. machines, are placed in straight rows along the building. For each roller passage there is a separate elevator, which runs through all the floors ; besides that elevators are needed for other machines from which the product cannot be allowed to flow of its own accord. It is these transport devices which have a very considerable influence on the arrangement of the mill building and especially on the shape of its roofing. Let us now inspect the most typical mill buildings. In Fig. 523 may be seen the transverse section of a mill with two rows of roller mills and two rows of plansifters. The elevators are set 562 FLOUR MILLING [CHAP, ix in the middle. Such an arrangement may be particularly recommended for rye mills, by reason of its cheapness, because from both the rows of mills the product by its weight, without the aid of worms, runs to the elevators as well as into the bolting machines. The roof of such a building should have a high ridge, so as not to increase the height of the floor holding the sifters for the sake of the elevators. The sole defect of such an arrange- ment of the outfit is that the elevators block up so much space in the centre of the mill building. The free passage between the machines and the inspection of their operation are impeded. For this reason, though such an arrangement is sometimes practised in wheat mills, it cannot be recommended, as the number of elevators here is still greater. Figs. 525 and 526 show us the cross sections on which out of the above considera- tions the elevators are arranged, not in the middle, but by the wall. With such an arrangement all the sections remain free in the middle and easily accessible to inspection. The elevators are set along the wall so as not to stand opposite to the windows. The walls of the top floor have to be sufficiently high for the elevators (here they are 5 metres high, while in the first case the height is only 2 metres), so that the roof is flat in shape. Such an arrangement of the building in practice appears to be the most efficient' both for large and for small mills, and is therefore the one most frequently adopted. On Fig. 524 the mill building is divided by a longitudinal stone wall into two parts, of which one serves as the mill proper, and the other as a warehouse furnished with flour-blenders. If the mill has to be enlarged the warehouse may be used for setting the machinery in. There is no floor to allow of inclining the spouts ; instead of the spouts there are worms set over the mills. The double slope roof leaves sufficient space for the high elevators and detachers, which are situated over the sifters of the reduction rolls. With such a construction of the building one has to make much use of the worms, but by disposing the machines rationally along the building their number may be considerably reduced. Fig. 527 presents a cross section of a large modern mill. The height of the building here is quite considerable. The ground floor is so high that the product of itself runs to the elevators from both rows of mills. CHAP. IX] FLOUR MILLING 563 The floors for the spouts and the cleaning department are also sufficiently high, so as to have the product travel automatically if possible everywhere, requiring the least quantity of power for transport. The ceilings of the building are of a peculiar construction (A, Fig. 529 this construc- FIG. 526. FIG. 527. tion comes from England). Here steel joists are laid across the building at about 2J metres distance from each other. On these joists there lie narrow beams, and the whole is covered with a solid layer of square beams some 10 cm. thick, on which there is another layer 2J cm. thick. Such ceilings are comparatively expensive, but their advantage lies in the fact that the ceiling beams are nowhere in the way. The 564 FLOUR MILLING [CHAP, ix suspended bearings of the main shafts are attached directly to the iron joists. Altogether the construction of the ceilings in mill buildings has assumed a very peculiar shape, which depends on the disposition of the machines, and the practical utilisation of space in the mills. On Figs. 525 and 528 (transverse and longitudinal sections) we see a framing of joists often used in other buildings too. The cross pieces a ^,re timber beams with supports b at the fulcrums of the columns ; these supports are designed to shorten the length of the unsupported part c, in consequence of which the beam has a more rigid span. The supports b are strengthened with rafter beams d or attached to the beam a by means of bolts e, which produces the same result and is often considered to be more convenient. The joists / are disposed at a distance of 0-8 or 1 metre from each other. Care should be taken that these joists are set exactly vertically over each other in all the floors. The columns supporting the ceilings are either single like g, or double like h (Fig. 525). When using timber joists and cross pieces the distance between the supporting columns should not be over 4 or 4J metres in longitudinal and in trans- versal direction. The breadth of the build - * ing being 8 or 12 metres, there are con- FIG. 528. sequently two or three rows of columns. For mills with a capacity of 240 sacks per da^ such an arrangement is advantageous, as its erection costs comparatively little. But for mills of larger dimensions this arrangement is disadvantageous as regards the most economic use of the area of the buildings. As we see in Fig. 525, the rows of columns allow of freely setting in the 4-15 metre spans only three rows of mills and sifters, whereas with the Fig. 526 construction of ceiling there is space for four such rows. In Fig. 526 there is a row of columns only in the middle, the distance between the columns and the walls being 6J metres. For such a span the timber cross beams of the limit size would be too weak, and therefore the cross pieces here are I-beams, while the timber ceiling joists run down the length of the build- ing with a distance of 4 metres between the fulcrums. The roller mills and sifters of the second row are connected with eLvators by means of transverse worms. The advantage of the sifters over reels and centri- fugals as regards economy of the area occupied is clearly seen here, for, with centrifugals, jt is quite impossible to instal in the same space a A ix] FLOtJR MILLING 565 machine doing the same work or to keep at the same time the dressing surface as accessible to inspection as when furnished with sifters. The danger of fire that threatens the mill, led to the necessity for con- structing fireproof buildings. The machines and apparatus as well as the transport devices of the fireproof mills have no wood parts whatever. Not only the walls, ceilings, and coverings of the building have to be of fireproof materials, but A lilTL. l^ZJC! the doors and windows as well. "TT~ The buildings of a fire-resisting mill, i.e. pro- perly speaking the walls, are erected of ordinary brick. Only comparatively recently in America at- tempts at complete ferro-concrete buildings or steel constructions with a brick shell have been made . As regards ceilings, there are two types : solid ferro- concrete (B, Fig. 529) and with concrete arches (C, Fig. 529) between the longitudinal iron beams. * The last construction is the heavier of the two, and is therefore inferior to the first. Such in a general outline are the constructions of mill buildings answering the requirements of modern technics. IV CONSTRUCTION OF AMERICAN MILLS The originality of American technics shows itself also in the construc- tion of mill buildings. A more or less normal type of an American mill building, approaching the European construction, is given in Figs. 530 and 531, which illus- trate the cross section of the grain-cleaning department and a longitudinal section through the grain-cleaning and milling departments. The principal difference from the European constructions of buildings lies in the fact that the ground floor is considerably higher. That is necessi- tated by the type of roller mills used, which need overhead shafting hung from the ceiling and special tension pulleys for the flexible gearing. On the ground floor the flour is packed, on the first the roller mills are disposed, on the second the suspended filters, on the third the purifiers, on the fourth the centrifugals and vertical scouring bran dusters for freeing the bran of the flour remaining in it, on the fifth sifters. The grain-cleaning department is supplied with hard and soft wheat by the band conveyors SBC and HBC. That wheat is hauled up by the elevator and of itself flows into the worm C 10. This worm distributes . ix] FLOUR MILLING 507 the grain to the bins MR. In proportion as it is needed, it is let out of the bins into the worm C 1 and passes to the automatic scale AS, whence it pours into the elevator 7, and is then carried up to be cleaned. FIG. 532. In cases where the scale of output goes far beyond the limits of the ordinary dimensions, the American mill buildings are amazing in their size and originality. Figs. 532, 533. and 534 show us the 56S FLOUR MILLING [CHAP. sections of an American mill belonging to Hecker Jones Jewell in New York, started in 1908, and working mostly for export. The capacity of the mill is 8000 sacks of wheat grist per day. To FIG. 533. give an idea how big that mill is, it is sufficient to say that there are 115 four-roller mills 250x900 mm. in size in it, and it is brought into operation by two compound steam-engines of 1800 and 1000 indi- cated horse-power. CHAP. IX FLOUR MILLING 569 The concrete foundation of the mill is laid on concrete piles. The underground floor serves for the boots of the elevators. The first, second, and third floors do duty as temporary stores for barrels of flour, the third and partly the fourth floors being for packing. The transportation of FIG. 534. sacks and barrels to the second and first floors is performed by conveyors. The fourth floor contains the driving machinery, the fifth is for roller mills., the sixth for the transmission drive and for the corresponding deflection of the spouts, the seventh and eighth for purifiers and centrifugals, the ninth for sifters, and the tenth is the garret for star filters. The milling department (Fig. 533) 570 FLOUR MILLING [CHAP, ix is divided by a party-wall into two separate mills (4800 and 3200 sacks). The grain-cleaning department (Fig. 532) has a washing plant and roller mills on the tenth floor for the reduction of the broken grain and screenings to feed. On the fifth floor there are set the feed and part of the bran packers for the stock which is transmitted from the milling department. The longitudinal section of the mill is shown on Fig. 534. The mill is built according to the fireproof type. Worthy of notice is the truly American rapidity with which that mill was erected. The construction of the mill building, the elevator to it (for 500,000 bushels of grain), and the full equipment were ended in eight months. The building was started on the 1st of May, 1907, and on 2nd January, 1908, the milling operation was in full swing. V PLANS or MILLS The longitudinal and transversal sections of the mills we have examined illustrate to a certain extent their general plan. But it is necessary to give a general outline of the distribution of machinery and also of the position of the prime motor. In Fig. 535 may be seen the plan of the ground floor, where A is the grain-cleaning department, B the milling department, C the engine room, and D the boiler plant. This plan shows that the necessity of securing the % mill against fire compels the constructors to isolate the engine room from the mill proper. The position of the engine room pointed out is convenient in so far that it occupies a small area together with the mill building. But its inconvenience lies in the fact that a series of roller mills by the windows looking on to the wall of the boiler room D, is in the dark. It is better to arrange the boiler room down the longitudinal axis of the engine room, if space permits. Further, it is necessary to isolate by a staircase the grain-cleaning department from the milling, to prevent fires, which generally break out in the former, from penetrating into the latter. In this plan, as well as in others, we see that from the landings of the staircase the doors open into the milling and grain-cleaning departments. That is the ordinary planning in Russia and in Western Europe. It is inexpedient, however, in case of fire, because the flames can easily leap from door to door CHAP, ix ] FLOUR MILLING 571 across the landing on the staircase. It is better to have balconies made opposite to the landings, which afford communication between the grain- cleaning department and these landings, and to have the wall of that de- partment quite blind, leaving one door from the landing to the balcony and one into the milling department. To return to the engine-house, it should be noted that the area it occupies is considerably reduced when an internal combustion engine is employed, and there is np need for space for the boilers. IfHMMHSG^^ Co flu* it iHO^HMHtfHHI^iMf V IHHi<^^!^ ' i | l ,J I I 1 ..LL.- J=r FIG. 535. Fig. 536 illustrates the plan of the first and second floors in a wheat and a rye mill with a silo : A is the milling department of the wheat mill, B the stairway, C the common wheat and rye grain-cleaning department, D the milling department of the rye mill, and E an elevator with rectangular silos. The plan of the second and the following floors shows that part of the stairway is occupied by bins for tempering the grain. The flour bins are marked a. In the same plan of the second floor there are shown two types of disposition of the roller mills, in a chess-board order and along the general transversal line. In the arrangement of the roller mills, as well as of other machinery, 572 FLOUR MILLING CHAP. IX FIG. 536. CHAP. IX | FLOUR MILLING 573 -4-f- -- 537. 574 FLOUR MILLING [CHAP, ix one should be guided by their accessibility from all sides, which guaran- tees a free inspection and allows repairs to be done in situ. With the third and fourth floors (Fig. 537) the rye mill and the grain Sixth Floor. FIG. 538. elevator end. On the fourth floor of a wheat mill are set the purifiers, and on the same of a rye mill the sifters ; the fifth and sixth garret - floors of a wheat mill contain sifters (Fig. 538). The above plans represent the scheme for an 800 sacks per day mill, drawn up by the firm of Dobrovy & Nabholtz for a South Russian mill. CHAPTER X THE COST. OF ERECTING AND OF WORKING MILLS THE MILL BUILDING AND EQUIPMENT RUSSIAN general practice, and consequently literature also, give no materials whatever from which the average data concerning the area required for a mill may be deduced, not to mention its costs per certain capacity. This is explained by the fact that Russian milling conditions as a whole are so different, that the building firms very often ignore the types of mills and milling standards established in Western Europe. It is equally impossible to give the average costs of a mill equipment according to its capacity, as the prices of the machinery and of erection also fluctuate within wide limits. In Germany, where, as we have seen, a definite type of mill has been evolved, and the prices for machinery and labour are almost without variation, the average costs are deducible. We append here Kettenbach's table, which gives us the capacity per day, the total area of a wheat and a rye mill, including the mill building, and the full cost of the building machinery and equipment in German marks. TABLE LXII Total Area of the Cost of Erection in Marks. Capacity per 24 hours in Kilograms. Mill in Square Metres. Wheat Mill. Rye Mill. 20,000 700 200,000 150,000 30,000 900 300,000 240,000 40,000 1250 400,000 300,000 50,000 1500 500,000 380,000 60,000 1800 600,000 450,000 80,000 2100 800,000 600,000 100,000 2500 1,000,000 750,000 120,000 3000 1,200,000 850,000 150,000 3500 1,500,000 1,000,000 200,000 4000 2,000,000 1,500,000 575 576 FLOUR MILLING [CHAP, x The data of that table are taken from practice, but we 'presume that the quantities here are rounded off with great approximation, since according to the table the costs of one klg. of capacity for small as well as for large wheat mills is one and the same, 10 marks, whereas that cost ought to drop with an increase in the capacity of the mill. The truth of this statement may be proved by Kettenbach's other tables, where the costs of a full equipment of an automatic mill yield- ing one sack per 24 hours are given. TABLE LXIII COST OF EQUIPPING A WHEAT MILL Capacity per Day (24 Hours). Cost per 1 Sack per Day. 200 400 800 1,200 to 400 sacks = 20,000 to 40,000 klg. 800 = 40,000 80,000 1,200 == 80,000 120,000 2,000 = 120,000 200,000 350 marks 320 300 ,. 280 ,. TABLE LXIV COST OF EQUIPPING A RYE MILL Capacity per Day (24 Hours). Cost per 1 Sack per Day. to 100 sacks = to 10,000 klg. 450 marks 200 400 = 20,000 40,000 33 260 j, 400 800 33 40,000 80,000 33 240 3 3 1,000 2,000 3> 100,000 200,000 33 220 3 3 This is more clearly shown in the diagram, Fig. 539. On the horizontal line the capacity of the mill per day (from 10,000 to 200,000 klg.) is marked, on the left-hand side vertical (ordinate) the total cost of equip- ment in 1000 marks, on the right-hand vertical the cost per one sack per twenty-four hours in marks. The uninterrupted line ( ) running upwards denotes the diagram of cost of equipping a wheat mill ; the semi-dotted line ( . - - , - - , ) the cost of equipping a rye mill. CHAP. X] FLOUR MILLING 577 The diagram drawn in the broken line ( ) gives the cost of equip- ment per sack per 24 hours for a wheat mill, and the dotted line ( ) #00 sooo J2 1 ** fll 1 f oo I * o 500 1 loo JOO poo foo 4-00 300 2,00 SOO ^ ^ x ^ Xl ? ,> ^ - - , - - , - . ^r x- ^ ^' . -^ - .__ ^ - . *< - ^ ^ ^^ ^-- g 1 ^ <* > "-" K -H -- x ^.x *" ^ ^" X ^ SOOOO SOOOO SOOOOO SS0 O00 lOOOOO^fn FIG. 539. Capacity per 24 hours. for a rye mill. It is clearly seen here that with the rise in the capacity of the mill the cost of equipment per unit of capacity drops. II CALCULATION OF WORKING EXPENSES Motive Power. Before defining the cost of the motive power which constitutes the main expenditure in working the mill, the data of the sso 500 $00 ZOO M 8 II a W I* FIG. 540. Capacity of MiD. power consumption in accordance with the mill capacity should be noted briefly. In Fig. 540 we have a diagram of power consumption in effective horse-power for automatic wheat mills of from 10,000 to 200,000 2 o 578 FLOUR MILLING klg. capacity. The uninterrupted line ( [CHAP, x ) represents the out- put of the motor, the horse-power of which is shown on the left- hand side ordinate up to 550 H.P. ; the semi-dotted line indicates the power consumption for 100 klg. per day. The last diagram shows that with the increase in the capacity of the mill the power consumption to a 5 Output of the Motor for the whole Mill. V N 9* t ^ o\ * * 1 * f -1 & 2 ^ I/ ^ v ^ ^ x /- / - / ^ .. -.- / /* ^^ / / / X / ^X JOOOO SOOOO SOOOOO SSCOOO ZOO 000 1 FIG. 541. Capacity of MiU. unit of capacity drops from 0*35 H.P. for a 10,000 klg. per day mill almost to 0-25 H.P. for a mill with 200,000 klg. capacity. The diagram, Fig. 541, gives the power consumption of an automatic rye mill. The diagrams examined represent the power consumption in automatic high grinding mills according to German data. In Russia the motive power, depending on the character of the grind- ing, is expressed in the following table : TABLE LXV Number of H.P. per 1000 Poods in 24 Hours. Kind of Grinding. 23 H.P. Single grinding 27 , Scoured 30 , Break 35 , Bolted 40 . Sifted 50 , Dressed 55 , High wheat , It should be noted here that the power consumption for high grinding includes also the consumption for electric lighting. HAP. X] FLOUR MILLING 579 Number of Hands. A less substantial part of the working expenses constitutes the payment of the workmen. In an automatic mill that expenditure forms a very small part of the sum total of working costs. ^ Sacking Mill. 36 I ISOCO SOO&O JOOOOO FIG. 542. Capacity of Mill. iooooo *j The diagrams given here represent the average of hands in the German mills. Fig. 542 gives a diagram of the number of hands in the day shift for the sacking and the automatic mills, and Fig. 543 the number of hands in the night shift. Sacking Mill. """" taoooo n . FIG. 543. Capacity of Mill. As we see from the diagrams, the night shift demands a less number of hands. That is explained by the fact that in the night time the work of unloading the sacks out of the mill, and often of packing of the flour, is discontinued. Ill SELECTION OF A PRIME MOTOR One of the most important questions in making out a project for a mill is the question of selecting a prime motor, since a large part of the working expenses of the mill is taken up, as we remarked above, by the production of motive power. 580 FLOUR MILLING [CHAP, x When choosing a motor for the engine plant one has previously to solve the question concerning its power, which is found by summing up the total power required by all the mills and machines of the given plant. In some cases, when an enlargement of the output is expected, to the initial power a reserve is added, which discounts the presupposed enlargement. The desirability, and in some plants the necessity, of a reserve motor is also taken into consideration. All the difficulty, however, of selecting a motor lies not in the question of the power hi connection with the reserve motor or the presupposed development of the produce, but in the selection of the type of motor. The variety of motors offered by modern technics makes the choice of a type of motor sometimes a rather difficult problem. Besides the questions of a special character, connected with local conditions and peculiarities of the given plant, there comes up the question of a correct economic calculation of the working expenses. In technical literature one is often warned against drawing up general formulae and recipes, according to which, in a most simple manner, the suitability of this or that motor engine can be found. Nevertheless the attempt to generalise the data, which to a certain degree elucidate the above-mentioned questions, cannot be regarded as inexpedient. At such factories as some of the chemical fabrics, breweries, and saw- mills, where besides the motive power the engine-house has also to supply the caloric energy for the heating sources which serve for drying and other purposes the question concerning the selection of a motor engine is solved simply in favour of the steam plant, and in these cases the problem of the economic calculation is considerably simplified. In such cases where the power plant has to supply only the motive power, the circumstances resulting from local conditions and the char- acter of production are most essential. The reliability and simplicity of the work must be considered, the quantity of space occupied by the engine, the possibility of enlarging the output, rapid starting, the possibility of overloading and of the best adjustability, as well as the danger involved in different respects by the operation. It is evident that the coexistence of all these conditions or even only of several in one motor is impossible, and the solution has always the character of a compromise, it being necessary at the same time to reckon with the working expenses of some one or other kind of plant. When estimating the working expenses, there comes into relief the question of the uninterrupted or intermittent work of the motor, which CHAP, x] FLOUR MILLING 581 greatly influences the correlation of the direct and indirect expenses in operation. Turning now to the question of summing up the working expenses, we must note that the indirect expenses, which consist of the expenses in respect of depreciation of the plant and of the interest for the deduction of the capital expended on the plant. These are reckoned out in each separate case in accordance with the engine supplier's conditions of credit. When choosing a motor it has to be decided first how many days in the year the mill will be working, whether it will run continuously day and night during the week, with a halt on Sunday, or work days only. To define the efficiency of any particular motor one must reckon out : (1) the first cost, aftd (2) the working expenses. In calculating the first cost one has to find out : 1. The price of ground occupied by the power plant. 2. The costs of the power plant and its outfit. 3. The costs of the motor and its setting, including the costs of the foundation, erection, and the trial starting. The working expenses should be divided into two groups : A. Indirect Expenses, consisting of the following classes : 1. Interest for the price of the site occupied by the power plant (4 1 to 5 per cent.). 2. Interest on the capital spent on the building and full plant (4| to 6 per cent.). 3. Depreciation of the building (2J to 3 per cent.). 4. Depreciation of the plant (8 to 10 per cent.). 5. Insurance premium (2 to 2| per cent.). 6. Repairs of the building (J to f per cent.). 7. Repairs and upkeep of the plant (1J to 2 per cent.). B. Direct Expenses 1. Cost of fuel. 2. Engineer and the rest of the staff attending the plant. 3. Expenses in lubrication and cleaning of the plant. In this way knowing the costs of the plant and the working expenses,, the efficiency of this or that motor may be defined. The main expenditure for an engine plant is the cost of fuel. There- fore to decide upon the kind of motor for the projected mill, one must 582 FLOUR MILLING [CHAP, x know the prices of different fuels. Further, one should inquire of the firms the price of motors and boilers suitable to the given locality ; if a steam plant is in view, the price of foundation for a normal ground and outfit as well as the guaranteed expenses per hour-power. Having all these data in hand, it is easy to define what motor will be most advantageous, taking into consideration all direct and indirect expenses. When testing the motor strictest attention should be paid that the guaranteed consumption of fuel is correct. For that purpose it is best to call in a disinterested expert, who will subject the motor to a trial and test its power and consumption of fuel per horse-power per hour. INDEX Accessory appliances used in mills, 422. Alsop bleaching process, 480. America, mill used by Indians in Ken- tucky, 5 ; automatic mill first used in, 23 ; influence of American methods in Europe, 26 ; modern American roller mills, 268 ; construction of, 565. Arabia, a water-mill described, 17. Archimedean screw, the, described, 458. Bashkirs, a water-mill used by the, 18. Bleaching (flour), 480. Building, mill, builders of the eighteenth century, 27 ; present-day construction, 554 ; cost of building and equipping modern mill, 575. Caucasus, milling methods of the natives, 19. Cereals, chemical composition of, 48. China, ancient mills and methods of milling, 5, 15 ; rice mills, 10 ; modern methods, IS- Cleansing (grain), 58 ; machines described, 83 ; scouring and polishing machines, 93- Cyclones, 427. Detachers, 313. Drying (grain) machinery, 125. Dukhobors, mill used by the, 10. Dust-collectors, 426. Egypt, ancient, milling apparatus and methods, 3, 6. Elevators, 448. Equipment of mills, cost of, 575. Exhaust systems, 434. Feed governor, described, 478. Filters, 429. Flour, mixing, 469 ; packing, 473 ; bleach- ing, 480. France, modern mills and methods in, 27. Germany, development of milling in, 29. Grain, chemical composition of, 47 ; separa- tion of foreign matter from, 58 ; scouring and polishing, 93 ; drying, 125. Greece, ancient, milling apparatus and methods, 4. Grinding, machinery, 153. Grinding principle, antiquity of the, 7 ; development of, 1 1 . Grindstones, first appearance of, 7 ; early forms, 8 ; composition and design of modern stones, 160 ; erection of, 171. Hignett's stone separator, 92. Hindoos, type of mill used by the, 15. Homer, milling references, 8. Horde's separator, 75. Horizontal conveyors, 458. India, type of mill used by Hindoos, 15. Jews, milling methods in Biblical days, 7. London, first steam mill in, 27. Luther's stone separator, 92. Magnetic separators, 59. Maize, grinding systems, 536 Mexico, milling methods of native Indians, 6. Middlings- and Dunst-grading -machines, 406. Mills, mill builders of the eighteenth century, 27; present-day construction, 554; cost of erection, equipment and working of modern mill, 575. Millstones : see GRINDSTONES. Morocco, ancient Egyptian methods in, 9. Negroes, present-day milling methods of the Nile tribes, 4. Oatmeal, grinding systems, 538. Plansifters, 68, 344 ; capacity of, 386. Pompeii, type of mill used in, 13. 584 INDEX Porcelain rolls, 212. Purifying machines, 420. 392 ; capacity of, Reel-separators, 64, 336 Robinson's cyclo-pneumatic separator, 74, 423 Roller mills, 37, 209 ; types of, 258 ; capacity of, 299 ; ventilation of, 434. Rolls, used in roller mills, described, 210. Rome, ancient, milling apparatus and methods in, 12. Rye, grinding systems, 527. Scales, 476. Scouring machines, 100. Seek Bros.' aspirator, 78. Sieve-bolters, 70. Sifting, described, 61 ; construction of sifting machines, 63, 335 ; sifting after grinding, 316. Spouts, described, 445. Steam-mills, introduction and development of, 27. Stone mills, capacity of, 190. Stones : see GRINDSTONES. Systems of milling, 489. Transportation of stock, 445. Trieurs, 83. Under-runner mills, 183. Upper-runner mills, 190. Ventilation of mills, 434. Vertical mills, 187. Vibro-motor plansifters, 68. Water-mills, type of mill described by Vitruvius, 16 ; an Arabian mill, 17 ; a Bashkir mill, 18. Wheat, the grain described, 41 ; chemical composition of, 47 ; varieties] of, 48 ; composition of English and m Scotch varieties, 50 ; of foreign varieties, 52 ; of American varieties, 54. Winnowing, described ; winnowing ma- chines, 72. Zigzag separator, 80. Printed by MORRISON & GIBB LIMITED, Edinburgh D, VAN NOSTRAND COMPANY 25 PARK PLACE NEW YORK SHORT-TITLE CATALOG OF J)ttblicatton0 and Jmpovtation0 OF SCIENTIFIC AND ENGINEERING BOOKS This list includes the technical publications of the following English publishers : SCOTT, GREENWOOD & CO. JAMES MUNRO & CO., Ltd. CONSTABLE&COMPANY,Ltd. TECHNICAL PUBLISHING CO ELECTRICIAN PRINTING & PUBLISHING CO. for whom D. Van Nostrand Company are American agents. DECEMBER,. 1917 SHORT=TITLE CATALOG OF THB Publications and Importations OF D. VAN NOSTRAND COMPANY 25 PARK PLACE, N. Y. Trices marked With an asterisk (*) are JVE,T. All bindings are in cloth unless otherwise noted. Abbott, A, V, The Electrical Transmission of Energy 8vo, *$5 oo A Treatise on Fuel. (Science Series No. 9.) i6mo, o 50 Testing Machines. (Science Series No. 74.) i6mo, o 50 Adam, P. Practical Bookbinding. Trans, by T. E. Maw i2mo, *2 50 Adams, H. Theory and Practice in Designing 8vo, *2 50 Adams, H. C. Sewage of Sea Coast Towns 8vo *2 oo Adams, J. W. Sewers and Drains for Populous Districts 8vo, 2 50 Adler, A. A. Theory of Engineering Drawing 8vo, *2 oo Principles of Parallel Projecting-line Drawing 8vo, *i oo Aikman, C. M. Manures and the Principles of Manuring 8vo, 2 50 Aitken, W. Manual of the Telephone -8vo, *8 oo d'Albe, E. E. F., Contemporary Chemistry I2mo, *i 25 Alexander, J. H. Elemerltary Electrical Engineering i2mo, 2 oo Allan, W. Strength of Beams Under Transverse Loads. (Science Series No. 19.) .... . i6mo, o 50 Theory of Arches. (Science Series No. 1 1.) i6mo, Allen, H. Modern Power Gas Producer Practice and Applications. -i2mo, *2 50 Anderson, J. W. Prospector's Handbook i2mo, i 50 Andes, L. Vegetable Fats and Oils 8vo, *5 oo Animal Fats and Oils. Trans, by C. Salter 8vo, *4 oo Drying Oils, Boiled Oil, and Solid and Liquid Driers 8vo, *5 oo Iron Corrosion, Anti-fouling and Anti-corrosive Paints. Trans, by C. Salter 8vo, *4 oo Oil Colors, and Printers' Ink. Trans, by A. Morris and H. Robson 8vo. *2 50 Treatment of Paper for Special Purposes. Trans, by C. Salter. i2mo, *2 50 Andrews, E. S. Reinforced Concrete Construction i2mo, *i 50 Theory and Design of Structures .8vo, *s 50 Further Problems in the Theory and Design of Structures. .. .8vo, *2 50 The Strength of Materials 8vo, *4 oo Andrews, E. S., and Heywood, H. B. The Calculus for Engineers. i2mo, *i 50 Annual Reports on the Progress of Chemistry. Twelve Volumes now ready. Vol. I., 1904, Vol. XII., 1914 8vo, each, *a oo D. VAN NOSTRAND CO.'S SHORT TITLE CATALOG 3 Argand, M. Imaginary Quantities. Translated from the French by A. S. Hardy. (Science Series No. 52.) i6mo, o 50 Armstrong, R., and Idell, F. E. Chimneys for Furnaces and Steam Boilers. (Science Series No. i.) i6mo, o 50 Arnold, E. Armature Windings of Direct-Current Dynamos. Trans, by F. B. DeGress 8vo, *2 oo Asch, W., and Asch, D. The Silicates in Chemistry and Commerce . 8vo, *6 oo Ashe, S. W., and Keiley, J. D. Electric Railways. Theoretically and Practically Treated. Vol. I. Rolling Stock i2mo, *2 50 Ashe, S. W. Electric Railways. Vol. II. Engineering Preliminaries and Direct Current Sub-Stations i2mo, *2 50 Electricity: Experimentally and Practically Applied i2mo, *2 oo Ashley, R. H. Chemical Calculations i2mo, *2 oo Atkins, W. 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