METALLURGY A CONDENSED TREATISE FOR THE USE OF College Students and Any Desiring a General Knowledge of the Subject BY HENRY WYSOR, B.S. t ASSISTANT PROFESSOR OF ANALYTICAL CHEMISTRY AND METALLURGY IN LAFAYETTE COLLEGE EASTON, PA.: THE CHEMICAL PUBLISHING CO. ^ THE TY J LONDON, ENGLAND : ^X WILLIAMS & NORGATE 14 HENRIETTA STREET, COVENT GARDEN, W. C. COPYRIGHT, 1908, BY EDWARD HART. PREFACE I offer this book as a guide to the science of Metallurgy. The general scheme is the setting forth of the principles in- volved in the subject; the description of processes or groups of processes, and such reasoning as is calculated to show the applications of natural law in the operations considered. The ideal is the embodiment of the history, practice and philosophy of metallurgy in a single volume, admitting only such matter as is essential to the student. So composite a subject as metallurgy is not easily presented in a short course of lectures, nor can it be elaborated in a treatise of this size. Exhaustive literature, however, is not lacking. From the classic works of Percy to the standard texts and journals of the present time, and with the numerous transla- tions, there is ample reference literature in the English language. I have felt from my own experience, and from the opinions of others engaged in teaching and in practical work, that a condensed manual is needed in the colleges of this country. It is therefore expected that this book will be of assistance to stu- dents, teachers and others who need some general information in different branches of metallurgy. I take pleasure in acknowledging my indebtedness to co- operators. Among these are the several manufacturers of metallurgical appliances, who have furnished the excellent plates and drawings to which their names are appended. I extend my hearty thanks to personal friends for their as- sistance, and especially to my teacher, Prof. R. C. Price, whose suggestions were invaluable and whose interest is highly ap- preciated. H. W. Easton, Pa., May, 1908. 177755 INTRODUCTION The science of Metallurgy treats of the properties of the metals and of the processes by which they are prepared from their ores. The science embraces a study of the ores, fuels and all the mate- rials used in metallurgical industries, together with the structures and machinery employed. Metallurgical processes are essentially chemical. The metals generally occur in such stable combinations as to require reacting substances and often the powerful agency of heat to bring about their separation and purification. As viewed in this light, metal- lurgy might be classed as a branch of industrial chemistry. The industry has, however, grown to such enormous proportions, and is so closely linked with other branches of engineering, as to war- rant its being studied as a separate branch. An understanding of the physical and chemical properties of the metals, fuels and refractory materials is essential to the metal- lurgist, and he must also familiarize himself with machinery, which has come to play so important a part in modern practice. With these facts in view, the principles upon which metallurgical opera- tions in general are conducted, are laid down in the opening chapters of this treatise, and a special study is made of the fuels and refractory earths, the construction of furnaces and combus- tion. It is the aim throughout this book to show the application of scientific principles in winning the useful metals, and while much of the matter is necessarily descriptive, it is to the end stated that the student's attention is especially called. CONTENTS INTRODUCTION CHAPTER I Physical Properties of the Metals Fracture i Tenacity 2 Elasticity 2 Testing machines 3 Toughness 5 Malleability 5 Ductility 5 Wire drawing 5 Flow 6 Brittleness 6 Drop testing 6 Hardness 6 Fusibility and volatility 6 Diffusion 7 Welding 7 Occlusion '. 7 Conductivity 8 Magnetism 8 Density 8 Tables of Tenacity, Malleability and Ductility 8 Table of Physical Constants 9 CHAPTER II Refractory Materials and Fluxes Classification 10 Acid Materials Silica 10 Sand II Silica brick n Clay , ii Testing fire-clay 12 Canister 13 VI CONTENTS Basic Materials Magnesia ! 3 Lime T 3 Dolomite H Bauxite 1 4 Neutral Materials Graphite 14 Chromite J 4 The Fluxes CHAPTER III Theory of Combustion and Thermal Measurements Offices of fuels 16 Calorific power by experiment 17 Calorific power by calculation 19 Calorific intensity 19 Pyrometry 19 Fusion point pyrometer 20 Metal expansion pyrometer 20 Specific heat pyrometer 20 Heat conduction pyrometer 20 Air pyrometer 20 Optical pyrometer 21 Electric resistance pyrometer 21 Thermo-electric pyrometer 21 Bristol pyrometer 21 Table of calorific values 23 CHAPTER IV Classification and Description of the Fuels The Natural Fuels Wood 24 Peat 24 Lignite 25 Coal 26 Coals classified - 27 Bituminous coal 27 Class i. Cannel coals 27 Class 2. Long flame caking coals 27 Class 3. Short flame coking coals 28 Anthracite 28 Natural gas 28 CONTENTS Vll CHAPTER V The Prepared Fuels Charcoal ^i Coke 32 The beehive oven 33 Ovens excluding air and burning the by-products 35 Ovens excluding air and recovering the by-products 35 Otto-Hoffman oven 36 Coke quenching machines 38 Desulphurization of coke 38 Theoretical considerations status of coke manufacture 38 Producer gas 40 Water gas 44 Typical analyses of fuels 45 CHAPTER VI Ore Dressing Ores 46 Ore deposits 46 1. Ore dressing 47 2. Extraction of the metal 47 3. Refining 47 4. Mechanical treatment 48 Weathering 48 Hand picking 48 Breaking 49 Pulverizing 51 Stamp mill 51 Chilian mill 53 Huntington mill 53 Screening 53 Washing 54 J'g 54 Frue vanner 55 Magnetic separating 56 Wetherill separator 57 Calcining and roasting 57 Mixing ores 57 CHAPTER VII Furnaces 1. Furnaces in which the fuel and substance treated are in contact .... 60 2. Furnaces in which the substance treated is in contact with the flame and products of combustion, but not in contact with the fuel 62 Vlll CONTENTS 3. Furnaces in which the substance treated is not in contact with either the fuel or the products of combustion 62 4. Electric furnaces 63 Regenerative firing 63 Retrospective 63 CHAPTER VIII Iron Ores and Properties History 65 Ores Oxides '. . . 65 Hematite 65 Magnetite 66 Carbonates 66 Sulphides 67 Some impurities in iron ores . 67 Dressing iron ores 68 Properties Pure iron 68 Effects of other elements on iron 69 Chemical properties 76 CHAPTER IX Iron Smelting Chemistry of the Blast Furnace Process Pig iron 77 Preliminary description of the blast furnace process 77 Chemical changes in the blast furnace 79 Blast furnace slag 83 Wall accretions 84 Blast furnace gas 85 CHAPTER X Iron Smelting The Blast Furnace Plant and Process Description of the plant 86 The stack 87 Tuyeres 89 Charging apparatus 90 Dust catchers 9I Stoves 93 Blowing engines 95 Blowing in 97 Burdening 9 g Fuels and fluxes Ioo Management of the blast IOI CONTENTS ix Dry blast apparatus IO 5 Casting IO5 Disposal of slag 107 Disposal of flue dust roy Thermal requirements and economy of fuel 108 CHAPTER XI Cast Iron Properties and uses no Grading m Iron Founding Melting 1 13 Mixing II5 Casting TI 6 Malleable castings j jg Testing cast iron ! I9 CHAPTER XII Wrought Iron Historical 121 Properties 1 23 Manufacture of Wrought Iron The puddling process 124 Dry puddling 125 Pig boiling process 126 Modifications of the puddling process 1 29 Mechanical puddling 130 CHAPTER XIII Steel The Cementation and Crucible Processes Definition 131 The Cementation Process The furnace 131 The process 132 The Crucible Process Crucibles 134 The melting furnace 135 The process 135 CHAPTER XIV Steel The Bessemer Process Acid History 137 The iron mixer 138 X CONTENTS The converter 138 The process 141 Theory of the process 143 Basic The process 144 CHAPTER XV Steel The Open Hearth Process History 145 Acid The process 147 Basic Details 150 Chemistry of the Open Hearth Process Silicon 152 Carbon : 152 Phosphorus 153 Manganese 153 Sulphur 153 Acid and Basic processes compared 154 Recent Advances in Open Hearth Practice Tilting furnaces 155 The Talbot process 156 The Bertrand-Thiel process 157 CHAPTER XVI Further Treatment of Iron and Steel Casting the ingots 158 Stripping the ingots 159 The soaking pits 160 Forging 161 The Blooming or slabbing mill 161 The three-high mill 163 The continuous mill 164 Hammer forging 164 Press forging ^4 Reheating 165 Tempering !66 Development of surface hardness case hardening 1 68 Specifications 168 CHAPTER XVII Copper, Ores, Properties, Etc. Historical 170 CONTENTS xi Ores Native copper ! 70 Chalcopyrite ! 70 Chalcocite jyo Tetrahedrite 171 Malachite jy r Cuprite and melaconite 17! Properties Pure copper jyj Effect of impurities ij 2 Chemical properties 173 Preliminary Treatment Heap roasting !74 Stall roasting x^tj Furnace roasting 176 Hand reverberatory furnaces 176 Mechanical furnaces 1 78 Shaft furnaces xgo Chemistry of roasting 182 CHAPTER XVIII Copper Smelting Reverberatory Smelting Fusion for matte 184 Fusion for blue or white metal 187 Fusion for blister copper 187 Chemistry of reverberatory smelting 188 Blast Furnace Smelting Forehearths 192 The process 192 Treatment of matte in Bessemer converters 193 The process 195 Pyritic Smelting Elimination of impurities during smelting 197 Extraction of Copper in the Wet Way The sulphate process 199 The chloride process 200 CHAPTER XIX Copper Refining The Furnace Process Elimination of impurities 202 Xll CONTENTS Electrolytic Process General principles of electrolysis 203 Refining plant and process 205 Purification of the electrolyte - 207 Treatment of the anode mud 208 CHAPTER XX Lead, Ores, Properties, Etc. History 209 Ores Galena 209 Cerusite 209 Pyromorphite 209 Properties Effect of impurities 210 Chemical properties 211 Preparation of Lead Ores for Smelting Roasting 212 The process 212 CHAPTER XXI Lead Smelting Reverberatory Smelting The process 215 Hearth Smelting The process 216 Blast Furnace Smelting Chemistry of lead smelting 220 Lead fume 222 CHAPTER XXII Lead Refining Softening Desilverizing 1. By the Pattinson process 225 2. By the Parkes process 227 Desilverization ... 2 27 Distillation 228 Electrolytic Refining CHAPTER XXIII Zinc History 23I CONTENTS Xlll Ores Sphalerite 231 Smithsonite 231 Willemite 231 Calamine 231 Franklinite 231 Properties Chemical 232 Impurities in zinc 232 Preparation of Zinc Ores for Smelting Mechanical concentration 233 Zinc Smelting Manufacture of retorts and condensers 234 Form and size of retorts 235 Drying and annealing retorts 236 The distillation furnace 236 The distillation process 237 Refining Spelter 239 CHAPTER XXIV Tin and Mercury Tin Cassiterite 240 Properties " 240 Smelting 241 Refining 241 Uses 242 Mercury Properties 242 Smelting 243 Uses 244 CHAPTER XXV Silver Ores Native 245 Argentite 245 Horn silver 245 Tetrahedrite 245 Properties Chemical properties . . . 245 XIV CONTENTS Extraction of Silver 1. Smelting 246 2. Amalgamating 246 Crushing 247 Chloridizing in the dry way '. 247 Chloridizing in the wet way 247 The patio process 248 The Washoe process 249 Barrel amalgamation 253 Chemistry of Chloridizing and amalgamating 254 3. Leaching 255 Ziervogel process 255 Augustin process 255 Patera process 255 Russell process 256 Cyanide process 257 Silver Refining CHAPTER XXVI Gold Ores 258 Properties 258 Chemical properties 259 Extraction of Gold 1 . Washing 259 2. Smelting 260 3. Amalgamating 260 Hydraulicing 260 Dredging 261 Milling 263 4. Leaching 264 Plattner process 264 Cyanide process 264 Electro-cyanide processes 268 Refining Gold By chlorine 270 By sulphuric acid 270 By aqua regia 270 By electrolysis 271 CHAPTER XXVII Nickel, Aluminum, Manganese and Rarer Metals Nickel Ores 272 CONTENTS XV Properties 272 Extraction of nickel 273 Cobalt 275 Aluminum History 275 Ores 276 Properties - 276 Aluminum smelting 276 Manganese Ores 278 Properties 278 Smelting 278 Rarer Metals Chromium 279 Tungsten 279 Molybdenum * .... 280 Vanadium 280 Platinum . 280 CHAPTER XXVIII Alloys Properties 282 Constitution 283 Cooling curves 284 Conditions necessary for alloying 285 The Preparation of Alloys on the Industrial Scale Tables showing composition 287 Notes on the Manufacture of Alloys Alloy steels 288 Brass 289 Other alloys 289 Welding Electric welding 290 Thermit welding 290 Plating Tin plating 291 Zinc plating 292 The dipping process 293 The electrolytic process 293 Plating with other metals 294 ILLUSTRATIONS Figure Page 1 Pulling test 3 2 Riehle testing machine opposite 4 3 Tests of fire-clay 13 4-5 Parr calorimeter 17-18 6 Principle of Bristol pyrometer 22 7 Bristol indicating and recording unit opposite 22 8 Charcoal mound 31 9-10 Beehive coke oven 33~34 1 1 Otto-Hoffman coke oven 36 12 Diagram of coking process 39 13 Siemen's gas producer 40 14 Morgan gas producer opposite 4 1 15 Blake ore crusher 49 16 Gates ore crusher opposite 50 17 Stamp battery opposite 51 18 Stamp mill mortar 52 19 Chilian mill opposite 53 20 Huntington mill opposite 52 21 Jig 54 22 Frue vanner opposite 55 23 Principle of Wetherill separator opposite 57 24 Wetherill separator opposite 58 25 Cleveland kiln 61 26 Iron blast furnace 78 27 Iron blast furnace plant 86 28 Bosh construction 88 29 Gayley plate 89 30 Cooler and tuyere 90 31 Brown distributor opposite 91 32 Dust catcher 92 33 Hot blast stove 94 34 Blowing engine opposite 96 35-3 6 -37 Pyrometer records 102 38 Arrangement for skimming iron 106 39 Pig bed 107 40 Showing manner of cooling in casting in 41 Whiting cupola and details 114 42 Casting roll in chill 117 43 Showing effect of chill 117 44 Catalan forge 122 45 American bloomary 123 ILLUSTRATIONS XV11 46 Muffles for experimental furnace 125 47 Reverberatory furnace 127 48 Principle of rotary squeezer 129 49 Cementation furnace 132 50 Bessemer steel converter 139 5 1 Showing method of rotating converter 140 52 Steel-pouring ladle 142 53-54 Open hearth furnace 146 55 Diagram of open hearth heat 155 56 Campbell furnace 156 57 Ingot molds and bogie 159 58 Universal slabbing mill opposite 162 59 Wobbler and coupling box for rolls 162 60 Three-high mill 163 6 1 Steam hammer opposite 164 62 Hand reverberatory furnace 177 63 Brown roaster 179 64-65 Herreshoff furnace 180-181 66-67 Copper matting furnace 185-186 68 Round, copper blast furnace 190 69 Rectangular copper blast furnace opposite 191 70 Bisbee converter opposite 193 7 1 Principle of electrolysis 204 72-73 Arrangement of electrodes in copper refinery 206 74 English, lead reverberatory furnace 215 75 Lead blast furnace 218 76-77 Parkes desilverizing plant 227 78 Cupellation furnace 229 79 Zinc distillation furnace 237 80 Mercury furnace 244 81 Amalgamating pan 251 82 Silver concentrating and amalgamating plant. -opposite 254 83 Gold dredge 262 84 Gold precipitating boxes 267 85 Aluminum reduction furnace 277 86 Tin cooling curve 285 87 Tin-copper alloy cooling curve 286 88 Tinning pot 292 THE UNIVERSITY OF CHAPTER I THE PHYSICAL PROPERTIES OF THE METALS The value of metals depends almost entirely upon their phys- ical properties. Their great strength and rigidity, together with their pleasing appearance, have commended them for economic and ornamental uses from the earliest times. To the manufacturers of to-day, who supply the markets with the useful metals, a knowledge of these properties, and of the ways in which they may be devel- oped and improved, is indispensable. Some of these are well known as characteristics of all the common metals, while others are observed only when the metal is subjected to peculiar condi- tions. The subject is taken up here in a general way, and the properties are carefully defined without reference to any specific metal. As the individual metals are studied, reference will be made to their characteristics and acquired properties. Fracture. The fracture, or appearance of the freshly broken surface of a metal is to some extent an index to its other proper- ties. Each metal has its characteristic fracture, and the same metal under varying conditions of purity and mechanical treat- ment presents fractures differing accordingly. In some instances the quality of a metal may be inferred, and an approximate esti- mate made of the amount of impurities it contains, by simply ex- amining its fracture. When metals cool from a state of fusion, like most other solidi- fying substances, they tend to form crystals. But the conditions attending the cooling of metals do not, as a rule, permit of any high degree of crystallization. As seen by the naked eye, the structure appears granular in most instances, but upon polishing and carefully etching a surface, the crystalline structure may be seen with the aid of a microscope. The structure of metals, as shown by their fracture, is affected by any impurities present, by heat treatment and by such mechanical treatment as hammering or rolling. 2 METALLURGY Tenacity. By tenacity is meant the property of resisting a ten- sile or stretching force. The extent to which a metal will resist being pulled apart is termed its tensile strength. The tenacity of metals varies with the composition, temperature and treatment, it being improved in most metals by the addition of certain other elements in the proper proportions. Most of the metal that comes on the market is bought under certain specifications relative to its physical properties. These properties are largely interpreted from chemical analysis, but in many instances mechanical testing is required. By this means the effort is made to expose a piece of the metal, representing the whole, to strains similar to those encountered in actual service, the force applied being measured, and its effect upon the test- piece noted. The test-piece is broken if it is desirable to know the ultimate strength. The tenacity is of greatest importance in many instances, and it is determined directly by breaking a bar of the metal in a machine which indicates the force used. Elasticity. Any substance which is capable of returning to its original form and size after being distorted is said to be elastic. A substance that is perfectly elastic will retain this property after being distorted an infinite number of times. Liquids and gases are perfectly elastic, but solids are only approximately so. It is a well known fact that metal springs, after long usage become "set," their original shape being permanently altered. Glass is shown to be elastic by bending a straight rod, which will remain straight afterward. If, however, the rod is supported at the ends in a horizontal position, with a weight attached at the middle, and allowed to remain for a few weeks, it will be permanently bent. When the elasticity of a metal has been destroyed to such an extent that it shows little or no tendency to return to its original form it is said to be plastic. Some metals, such as lead and gold, are naturally plastic. These are less of the nature of true solids. The extent to which a metal can be stretched or compressed without rupture is termed its elastic limit. This value may be measured and expressed numerically as the units of force neces- sary to rupture a bar, the area of whose cross-section is given. If PHYSICAL PROPERTIES OF METALS 3 the composition of the bar is homogeneous, and it is of uniform thickness between the points at which the force is applied, equal additions of force will produce equal elongations or depressions,, until the elastic limit is reached. The spring balance serves to illustrate the above statement. The pointer, moving over a scale or dial is attached to, or operated by the loose end of a spring. The other end of the spring being" fastened, it is compressed or stretched when weights are placed on the pan. The pointer is seen to move equal distances for equal ad- ditional weights. From what has been said it is clear that the amount of force required to produce any elongation, within the elastic limit, can be estimated, provided it is known how much is required to produce a given elongation. If the elasticity remained perfect, Fig. i. the force necessary to double the length of a bar is termed its modulus of elasticity. Suppose, for example, that a bar of steel is stretched from eight inches to 8.03 inches by a force of 126,000 pounds. The modulus of elasticity would be 0.03 :8 :: 126,000 :x, or 33,600,000 pounds. This value is, of course, purely theoretical, as no metal has so high a limit of elasticity. Testing Machines. Machines are now regularly used for break- ing bars by direct pull, the stress used being measured and re- corded. Fig. i represents a "pulling test" before and after it is broken. The size and shape of these test-bars is not fixed, but the one described is the best form for general purposes. It is turned down on a lathe to a uniform diameter, which is ac- curately measured with a micrometer. Punch marks are made 4 METALLURGY at the points A A, which are usually eight inches apart. The bar is grasped by the machine at the points B B. After the bar has been broken, measurements are again taken of the length and the diameter at the point of fracture, to ascertain the elongation and contraction. The primary object in making the pulling test is to determine elasticity and tensile strength, but other valuable information is gained, as shown below. The construction of a testing machine is shown in Fig. 2. The base of the machine consists of a substantial, cast iron box, M, enclosing the driving mechanism. The power is transmitted by gearing to the two large screws, one of which is visible, R. By turning these screws the pulling head is moved. The top and pull- ing heads, I I, are fitted with hardened steel wedges for gripping the specimens. The top head is supported on two cast iron columns which are bolted to the weighing table, T. The table rests upon the two main levers of the weighing mechanism. One of the levers is enclosed within the other, A, and each lever branches into a Y to give a broad support for the table. The friction at the points of support is minimized throughout the weighing apparatus by the use of steel knife edges resting on steel plates. The intermediate lever, B, and its connection with the main lever and the beam, C, are clearly shown in the cut. With this system of levers the strain exerted upon the specimen may be counterbalanced by moving the weight, W, along the beam. The stress is measured in pounds or kilograms which are marked on the beam. Transverse tests may be made by aid of the V-shaped tools, one of which is shown attached to the under side of the pulling head and the other two set up on the weighing table. The tools upon the table are set at equal distances from the middle, and the specimen is supported on these in the horizontal position. The pulling head is lowered upon the specimen until it is sufficiently bent or broken. Crushing tests are made by placing the specimen between two dies, one of which rests upon the center of the table and the other is attached to the pulling head. Fig. 2 Riehle, Standard Testing Machine. PHYSICAL PROPERTIES OF METALS 5 Toughness. The resistance which a metal offers to being pulled apart after its elastic limit has been reached is due to tough- ness. The tough metals are scarcely elastic if either one of these properties is developed in a metal, it is usually done at the ex- pense of the other. As a rule, metals are toughest when in the pure state. An expression for toughness in a metal is gained from the mechanical test described above. It is observed that the toughest bars give the greatest percentage of elongation and contraction. The figures for these values are an expression for the toughness of the metal tested. Toughness is further tested by what is known as the "cold bending test." The test-bar is bent, without heating, at a sharp angle until the ends meet, or overlap. If there is not considerable toughness the bar will either break or rupture on the outer surface where the greatest strain is imposed. Although no numerical expression is obtained, this test is invaluable to metal workers and engineers as a guide to the purity and quality of some grades of iron. Toughness is greatly influenced by heat. Malleability. Metals which can be permanently extended with- out fracture are termed malleable. Degree of malleability is shown by the thinness of the rheet into which the metal can be hammered. As a rule, this property is most perfect in a metal when it is pure, and it is generally increased with temperature. If hardness or elasticity is developed in a metal, its malleability is diminished. It is chiefly upon this property that the processes of rolling and hammering depend. Ductility. The ductile metals are those which are capable of being drawn into wire. The property of ductility depends mostly upon tenacity, malleability and toughness. It will be seen by referring to the table (p. 8) that the malleable metals are the most ductile. Most metals show great changes in their ductility with changes in temperature. The property is improved by annealing. Wire Drazi'ing. Wire is made by drawing a bar of metal, some- what larger in diameter than the resulting wire, through funnel- shaped holes in dies of hard steel. A number of dies may be employed, depending upon the size to which the wire must be re- 6 METALLURGY duced. The end of the bar is first sharpened until it will pass through the openings, and is gripped by the forceps of the machine. The pressure that is brought to bear by the funnel- shaped holes is about the same in effect as that of rolling, while the stretching force compels extension in the one direction. The tenacity of the finished wire is tried, since it sustains the entire drawing force. Flow. The term flow relates to the molecular movements of metals in the solid state. With the exception of mercury, none of the metals flow in the usual sense of the term, but all of them become mobile under sufficient pressure, i. e., they flow as viscid liquids do. This property is associated with that of malleability. It is made use of in various manufactures, examples of which are the manufacture of lead pipe and coin striking. Brittleness. The brittle metals are those which, relatively speaking, are neither malleable nor ductile. Such metals are usually hard, but can be easily broken, and in some cases powdered under a hammer. Brittleness is opposed to toughness, and is rarely desired in any metal. It is influenced chiefly by foreign elements, but it frequently develops where strains are applied in different directions, or in metal that is subjected to violent shocks. 1 Changes in temperature have a marked effect upon the brittleness of metals. The best way to remove brittle- ness is by annealing. Drop Testing. Metals are examined for brittleness by means of the "drop test." The test-piece is subjected to blows from a hammer of a certain weight dropped from a stated height. Hardness. In determining the hardness of metals the dia- mond is taken as 10, the other substances being referred to that. Hardness is opposed to flow, and is especially required in tools and the wearing parts of machinery. It is not a common prop- erty of pure metals, but in most instances requires to be developed. Fusibility and Volatility. All the metals are fusible and all 1 Car axles may break after long service, the fracture showing a crys- talline structure which the metal did not have when the axle was made. The pistons of large steam hammers sometimes break after being used but a short time. PHYSICAL PROPERTIES OF METALS 7 are volatile. Some are infusible, and but few are volatile at ordinary furnace temperatures. The metals of commerce may have much lower melting points, as a result of impurities. In all processes for extracting metals by smelting, advantage is taken of their fusibility. It is of importance to know the melt- ing points of metals, and as well their behavior in the liquid state, in connection with the foundry industries. Diffusion. Most metals have the property of forming homo- geneous mixtures with other metals. This is known as the alloy- ing property or the property of diffusion, and the mixtures are called alloys. Some metals alloy with great readiness and in all proportions, while with others it is very difficult to bring about any union at all. It has been found possible to develop properties in alloys to a degree which has never been attained with any single metal. As might be supposed, some of the prop- erties of alloys are intermediate between those of the constituent metals, but this is not true of all. It is generally understood that metals diffuse only when one or both are in the liquid state, but it is possible with moderate pressure to make plastic metals diffuse slightly, and under enor- mous pressure the more brittle metals may unite. This obviously makes use of the flowing property. The subject of alloys is more fully discussed in Chapter XXVIII. Welding. This is the property of uniting without fusion. The requirements for welding are that the pieces to be united shall be in a plastic condition, fairly pure, and the faces to come in contact clean. Enough pressure must be applied to bring the molecules into intimate contact. A hard metal may be welded by heating it until it becomes plastic. If a coating of oxide forms, it must be removed. As a rule, the pieces to be welded must be of the same kind of metal. Exceptions are found with iron and platinum, lead and tin and some others, Occlusion. By this term is meant the absorption and retention of gas. The property varies greatly with the metals, and the same metal absorbs different quantities of the different gases. As a rule, gases are dissolved most freely when the metal is pure and in the molten state. On cooling most of the gas is dis- 8 METALLURGY charged, often producing the effect of boiling, while some is re- tained as accumulated bubbles ("blow-holes") under the harden- ing surface, or held by the metal in "solid solution." The phys- ical properties in general are known to be effected in metals by occlusion. Conductivity. The metals are the best conductors of heat and electricity. The extended use of the electric current has led to the improvement of the conductivity of the metals used in the transfer of power. The property is much altered by the pres- ence of impurities, only a trace in some instances affecting it. Conductivity varies inversely with the temperature of the metal. Magnetism. The magnetic property of iron has long been known and studied. It has been discovered in some other metals and alloys, but it is much weaker in these and is not of practical value. It is affected by impurities and temperature. Magnetism in iron will be dealt with under the study of that metal. Density. One of the distinguishing features of metallic sub- stances is their superior density, or specific gravity. While it is true that metals, taken as a class, are heavier than othen sub- stances, there are exceptions, and there is no relationship between the density and the other properties of metals. This property is made use of in practically all processes of metal extraction. The following groups show the orders of tenacity, malleability and ductility : TENACITY. 1 Steel 4 Copper 7 Zinc 2 Nickel 5 Aluminum 8 Tin 3 Iron 6 Gold 9 Lead 1 Gold 5 Tin 8 Zinc 2 Silver 6 Platinum 9 Iron 3 Copper 7 Lead 10 Nickel 4 Aluminum DUCTILITY. 1 Gold 5 Iron 8 Zinc 2 Silver 6 Nickel 9 Tin 3 Platinum 7 Copper 10 Lead 4 Aluminum PHYSICAL PROPERTIES OF METALS w* W rt >> His CO Tf M ON vO 10 O co M r^ vo . 10 10 O iO CO W O - 8 111 2 o 3 : , vo VQ cs O> lO . co . rt O 10 CM M Eg 3 II . o . ! co co 1-1 od ; H( I CO 8 vo ^ 5 : * g .1 i- IO iO vO co O iO O CN M Q CO t-^ Tt >-l W vO rf CM ON OOOO OOOOO d d 6 o o d c/3 .So .5 .gO O > WtoO l OOrOfOO^O^Oto i -'iOCM 00 k "^ V- ^j ^f co CO CN *^ O CO vO O ^ O *^O O t^ *O O^ *O * *^ rt ^ 55 VO VO ^^ tO *-O iO O O VO *O O^ I * VO t^ 1 ^ O^' CS * ^^ Q s s CN O O O d d d d fMQ M OW p< OcOVOQVOCOrt 'Oi-iO^OOt-ioOfOOo d d d d d d d d d d d d d o A< 10 i^ vo vq GO 10 co M' vo' io co' vo' co co MCOCOOOOOMOO M >), pyrrhotite (Fe~S 8 ) and the magnetic sulphides. The sulphide ores are not as yet sources of iron, though large quantities are now being roasted for the recovery of sulphur. If the sulphur can be suf- ficiently removed from the residues of the roasters, they will be utilized in this way, and this seems possible. Some Impurities in Iron Ores. Iron ore gangue is generally acid in character, the bases alumina, lime, magnesia, etc., being insufficient to neutralize the silica. Sulphur and phosphorus are deleterious elements often encountered, and in rare cases arsenic is present. Manganese is contained in almost all iron ores, its presence being rather desirable. Titanium, chromium and zinc are not uncommon impurities. In some instances these metals have so far replaced the iron as to justify a special name for the ore. The mineral ilmenite, for example, contains a mixture of ferric and ferrous oxides with the dioxide of titanium. The best known American deposits of high titanic iron are in New York. Chromite, the sesquioxide of chromium mixed with fer- rous and ferric oxides, is another well known and very valuable compound ore. Chrome-iron ore occurs at various points in the 68 METALLURGY United States in small quantities, but this country's supply is drawn chiefly from abroad. A more remarkable mixed ore oc- curs in New Jersey, known as Franklinite. It contains three metals, iron, manganese and zinc in workable quantities. Dressing. The larger part of iron ores smelted in the United States are exceptionally pure, and require no preliminary treat- ment. In foreign countries a much larger percentage of the ores requires some kind of treatment, and there are few ores that could not be improved for the smelter by a concentrating process. Car- bonate ores, and those containing a high percentage of moisture may be profitably calcined ; those containing sulphur, roasted ; coarse ores containing much gangue, washed ; and fine ores, con- centrated with magnetic machines. Many of the ores of the Eastern and Southern states are concentrated by the latter meth- ods, roasting being occasionally resorted to. PROPERTIES Pure Iron. Iron is grayish white in color and highly lustrous. The specific gravity is 7.8 and the fusion point is about i,6ooC. It is remarkably tough, malleable and ductile, and its tensile strength is about 30,000 pounds per square inch. 1 Iron possesses the property of magnetism to a higher degree than any other metal. Iron welds readily, can be welded to a few other metals, and will form alloys with most all metals. While in the molten state iron occludes oxygen, nitrogen and other gases which may be in contact with it. Pure iron is a very uncommon article of commerce, though there are some grades which contain so little foreign matter as to possess properties approximately the same as those above noted. Since the properties of a metal are governed by its composition and by heat and mechanical treatment, the possibility of develop- ing or improving these properties is readily seen. In no metal has this been realized to so great an extent as in iron. Within certain limits, by alloying or combining other elements with iron in varying proportions, a metal of any desired property may be produced. Hence has arisen the great variety of commercial irons, each designed for specific purposes. A knowledge of 1 Roberts- Austen's Metallurgy. IRON ORES AND PROPERTIES 69 the effect of impurities is indispensable to iron manufacturers. Effects of Other Elements on the Properties of Iron. It is im- possible to state accurately and completely the effect of the var- ious elements found in iron a full and systematic research has never been made. The only way to gain full information on this subject would be to add the elements to iron separately and in varying proportions, and then to test each product. This would be an exceedingly laborious task, which the end would not justify. Since the effect of any ingredient is influenced more or less by the presence of others, and since commercial iron usually contains a number of foreign elements, the information is for the most part, drawn from tests made on the several grades as manufactured. The principal non-metallic elements combined in iron are car- bon, silicon, sulphur, phosphorus and oxygen. Carbon. When practically free from other elements molten iron may be made to dissolve as much as 4.63 per cent, of its own weight of carbon. 1 On cooling some of this carbon is retained in combination with the iron, while the rest separates in scale- like crystals of free, graphitic carbon. Some of this graphitic carbon escapes during the cooling, but the larger part of it is in- corporated in the mass of solidifying metal. Graphite obtained from pig iron is called "kish." That in the iron may easily be detected with the eye on a fractured surface. If the molten iron be cooled slowly the greater part of the carbon will separate in this way, while in rapid cooling the crystals do not have time to grow, and most of the carbon is retained in the combined form. Although the saturation point for total carbon in iron, as deter- mined by experiment, is 4.63 per cent., it is rare that iron is made to contain more than 3.50 per cent., unless some other substance is present, which raises the saturation point. The saturation point may be either raised or lowered by the presence of other elements. Graphitic carbon imparts to iron a dark-gray color, furnishing a most ready means of detection. It renders the fracture coarse and rough, presenting the faces of graphitic scales, often one- fourth inch across. These destroy, to a large extent, the con- tinuity of the metal, impairing its strength. The tenacity, elastic- 1 See Howe's Metallurgy of Steel, p .5. 7O METALLURGY ity, toughness, malleability and ductility are checked or suppressed. The hardness is not much altered; the fusion point is lowered, and welding is made difficult or impossible. The presence of graphitic carbon in iron prevents to a large extent the occlusion of gases, and is often desirable. It is rarely found in any other than cast iron. Those containing a high percentage of graphitic carbon are known in commerce as "gray irons." Combined carbon exerts a more profound influence upon the properties of iron than that of any other element. The relation of carbon to iron has been studied exhaustively from both the scientific and practical points of view. The fracture of carbon iron varies from fibrous or hackley (the fracture of pure iron) to fine granular (the fracture of high carbon steel). So marked is this effect in iron which does not contain interfering elements, that an experienced observer can estimate the carbon to within a few hundredths per cent., from the appearance of the fracture. The effect of combined carbon, in general, is to increase ten- acity, elasticity, and hardness. The maximum tensile strength, and the highest limit of elasticity are gained with about one per cent, of carbon. The hardness is increased by adding carbon until the saturation point is reached. At this point iron is so brittle that it can be powdered. Carbon lowers the fusion point, and inter- feres with welding. Iron containing a high percentage of car- bon can not be welded. High carbon iron is employed for mak- ing "permanent magnets", since on being magnetized, it retains the property indefinitely. 1 Besides being influenced by the pres- ence of other elements, the effect of carbon is governed by heat treatment. It is believed that carbon forms a number of definite compounds with the iron in which it has been dissolved, the com- position of these varying with the amount of carbon present, the heat conditions, etc., and that these carbides determine the pro- perties of the iron. The probable number of carbides and their formulas are unsettled questions, but there is sufficient evidence of their existence. The carbide, Fe 3 C, has been isolated, and an- other, having approximately the formula, Fe 2 C, is supposed to 1 The permanency and efficiency of steel magnets is increased by add- ing carbon up to 0.85^ (Metcalf). IRON ORES AND PROPERTIES 7! exist. Two forms of carbon are generally recognized by the pro- perties which they impart to iron. Cement carbon takes its name from the fact that it enters and migrates through unfused iron by a process known as cementation. The "cement bars/' made by this process, furnish the best example of the existence of this carbide. It is the same that was first isolated by Abel and assigned the formula Fe 3 C, and is the principal carbide in annealed steels. The effect of cement carbon is to increase the tensile strength of iron. Another form known as hardening carbon, the composition of which is undetermined, is found in high carbon irons, especially those which have been cooled suddenly. If iron containing cement carbon is heated to redness and quenched, that carbide is de- composed into one containing more carbon, and iron is liberated. The physical effect is that the iron is hardened. Ledebur states that hardening carbon is formed when iron is quenched from a temperature of 200 C. In addition to this, its most marked effect, hardening carbon promotes tenacity and elasticity in iron and lengthens the duration of magnetism. For a further study of the relation of carbon to iron see p. 165. Silicon. Like carbon, silicon may exist in iron in both the free and the combined state. Free silicon, however, separates only under peculiar conditions, and is rarely met with. It combines with iron, probably in several proportions, and the silicon-iron compounds are readily absorbed in molten iron. Rich alloys or mixtures containing from 5 to 15 per cent, of silicon are manu- factured under the name of ferro-silicon. The silicon-iron com- pounds are readily absorbed in 'molten iron. Iron is rarely made to carry more than four per cent, of silicon. The fracture of silicon irons is bright and crystalline, becoming coarser as the silicon is increased. In the purer forms of iron silicon is an ob- jectionable element, its tendency being always toward weakening the metal and rendering it hard, brittle and unworkable. It lowers the fusion point and checks occlusion. It is sometimes added to iron when it is cast to increase soundness (see p. 158). An in- crease of silicon in cast iron is attended with a greater separa- tion of graphite. Sulphur. This element is found in all grades of iron except 72 METALLURGY that made from very pure ore, and smelted with charcoal. It ex- ists as FeS, which is readily dissolved in molten iron. Sulphur is a most objectionable element in the purer irons. A few hun- dredths of a per cent, may cause iron to crack while it is being- forged at red heat. This failing is termed "red shortness." The effect of sulphur is less marked in iron containing a high per- centage of manganese. The effect on finished iron is not consid- ered serious if not over 0.06 per cent, is present. Phosphorus. The phosphide of iron, like the sulphide, is read- ily diffused in the metal. There are probably several phosphides of iron, though their composition has not been determined. Fer- ro-phosphorus, containing as much as 25 per cent, of phosphorus is now manufactured. In the purer irons phosphorus is a dan- gerous ingredient. The metal containing it may be quite easily forged, showing no sign of weakness while hot, but when cold the toughness, malleability and ductility are impaired. As much as half a per cent, would render iron very brittle when cold, though it shows no signs of failure while hot. Phosphorus is practically eliminated from some grades of iron. The highest grades of steel made for structural purposes carry from o.oio to 0.035 P er cent., and a great many carry from 0.035 to o.io per cent. The effect of phosphorus is but slight under 0.06 per cent. Cast iron carries from 0.5 to 1.5 per cent., some phosphorus being desirable. Oxygen. The scale of oxide that forms when iron is burnt is not dissolved or diffused in the molten metal. A chemical analy- sis, however, will generally show in iron treated by any refining process, a small quantity of oxide. These mechanically incor- porated particles weaken the metal in proportion to their number and size. If scale is left on surfaces to be welded, it will uther prevent the pieces from uniting altogether, or make the point of union weak. The principal metallic elements alloyed with iron are manganese nickel, chromium, tungsten, molybdenum, vanadium and alumi- num. Manganese. After carbon, manganese is the most important element that is added to iron. It is manufactured for this pur- pose and marketed under the names spiegel-eisen and ferro-man- IRON ORES AND PROPERTIES 73 ganese. These are rich alloys with iron, the former containing about 25 and the latter about 80 per cent, of manganese. The low carbon or soft steels are made to contain from 0.30 to 0.50 per cent, of manganese, and the high carbon steels from 0.60 to 1.25 per cent. Manganese hardens iron, but not in the way that carbon does. It does not develop elasticity and tenacity. As much as two or three per cent, produces extreme brittleness. When carbon and other elements are present, the effect of man- ganese is largely counteracted, and its presence is highly bene- ficial. Thus, in cast iron it is said to act as a softener 1 and in the carbon irons or steels it may be said to intensify the effect of car- bon. The chief value of manganese lies in its indirect influence upon the properties of iron. On account of the readiness with which it diffuses with iron, and its stronger affinity for oxygen and sulphur, it has proved an excellent agent for the removal of these impurities from iron, insuring at once soundness and free- dom from red-shortness. If more than seven per cent, of manganese is added to iron, remarkable toughness and hardness are developed. The famous Hadfield steels contain about 13 per cent, of manganese, and are at once so tough and so hard that they can not be machined. Nickel. The extreme toughness of nickel, its melting point, and its resistance to oxidizing agents would seem to recommend it as an ingredient in iron. Nickel increases tenacity and elasticity in iron, and to some extent hardness. Welding is made more diffi- cult and conductivity is diminished. When the nickel is increased beyond 20 per cent, the properties become impaired. The well- known nickel steels contain about three per cent, of nickel. Larg- er quantities are sometimes added to iron to render it non- corrodible. Chromium. This metal is manufactured chiefly from chrome- iron ore which yields an alloy (ferro-chromium) containing up- wards of 65 per cent, of chromium. In this form it is added to steel to improve its wearing and cutting power. The tensile strength and elastic limit are raised in iron by the presence of chro- mium. In pure iron the hardness is not much affected, but high 1 Turner's Metallurgy of Iron, p. 205. 74 METALLURGY carbon iron with two per cent, of chromium is harder than any carbon iron. It is believed that the extreme hardness of chrome steels is due to the fact that chromium raises the saturation point of iron for carbon, the alloy holding more carbon in the harden- ing form than it is possible for iron alone to hold. Chrome steel is readily forged though difficult to weld. Chrome-nickel steel is manufactured, combining the properties of chromium and nickel steels. Tungsten. The use of this metal is more limited, it being much rarer than either of the last two. Ferro-tungsten is prepared from wolframite, and contains a high percentage of tungsten (about 75 per cent.). The metal is usually added to iron in this form. Like chromium, tungsten exerts no remarkable influence upon the properties of iron except in the presence of carbon. When alloyed with high carbon iron, hardness is developed, which may exceed even that of chrome-steel. Tungsten steels are known as "self- hardening," because they do not require tempering. Tungsten steels are difficult to forge and can not be worked at all when cold. A small percentage of tungsten is said to improve mag- netism in steel. The famous Mushet steel contains about two per cent, of carbon and about eight per cent, of tungsten. Other steels are made richer in tungsten, and are consequently harder and more brittle. The temper of steel that is hardened with tungsten is not im- paired like that of ordinary carbon steel by heating. It appears that the carbon is the real hardening element and that the action on the tungsten is to hold the carbon in solution. Some evidence of that is found in the following experiment which was first ob- served by Langley. If a piece of carbon steel be held against a revolving emery wheel a shower of tiny stars of great brilliancy is produced, due to the explosive combustion of the particles of carbon, if, however, the steel contains three per cent, of tungsten the sparks emitted are mostly of a dull-red color, and a red band is seen to cling to the periphery of the wheel. Molybdenum is similar to tungsten in its relation to iron. About half as much molybdenum as tungsten, however, is re- quired to produce the same result. In other words, approximate- IRON ORES AND PROPERTIES 75 ly the same result may be obtained by adding tungsten or molyb- denum to iron in the ratio of their atomic weights, the atomic weight of tungsten being 184 and that of molybdenum being 96. These metals are also added together and with chromium in iron. Vanadium. The high price of this metal has, until recently, precluded any extended use of it in making alloys even for ex- perimental purposes. Experiments so far indicate that vanadium strengthens and hardens iron in somewhat the same way that car- bon does when but a few tenths of a per cent, are present. Aluminum. It has not yet been proved that aluminum, by its direct action, develops any useful properties in iron. Its princi- pal use is for removing oxygen from iron and for quieting "wild heats" of steel while casting. This, as will be explained later, is due to the power of aluminum to prevent occlusion. Other Metals. Titanium, copper, tin and arsenic may occur as impurities in iron. If present at all, they usually amount to but traces, and their effect is not noticeable. In rare cases, however, large quantities of iron have been ruined by these impurities, and materials containing them in any considerable quantity are not suitable for making the ordinary grades of iron. Gases. The property of occlusion, or the solution of gases is important in the metallurgy of iron. In all processes wherein iron is melted, the air or other gases which come in contact with it will be absorbed to a certain extent. The larger part of this gas is expelled during cooling. Some separates in globules ("blow-holes") while the metal is in the semi-solid con- dition, and that which remains is held in the metal as a solid solution, i. e. } forming no visible cavities, but diffusing or alloying with the metal. As a rule, the purer iron is, the less will be its solvent power for gases. Aside from the weakening effect of blow-holes, it is impossible to state fully and accurately the ef- fect of dissolved gases on iron. But it is recognized in the re- fining of iron that, other things being equal, the best results are gained under those conditions which permit the least amount of occlusion. It is possible that many cases of red-shortness and failures of various kinds in both hot and cold iron are due to oc- cluded gases. Oxygen, nitrogen and hydrogen gases are dis- 76 METALLURGY solved by iron, and carbon monoxide and carbon dioxide are said to be dissolved under certain conditions. 1 According to Percy, nitrogen imparts to iron hardness and brittleness, also a brassy luster. Chemical Properties of Iron. Iron combines with all the non- metallic elements, generally forming two or more distinct com- pounds with each. It is dissolved by all the mineral acids with which it forms well known salts. In dry air, at ordinary tempera- tures, iron undergoes no change, but when moisture and carbon dioxide are present it rusts, i. e., it is slowly converted into a hy- drated oxide, approximately the same in composition as some hematites. When heated in the air iron is converted into the magnetic oxide. In metallurgy this is known as ''scale." Ferric oxide is partially reduced to the magnetic oxide by heat, and at a temperature far below its melting point iron is reduced from its oxides by carbon, hydrogen, and some metals to the metallic state. Ferrous oxide is basic in character and forms readily fusi- ble compounds with silica. It may also be made to combine with phosphoric acid and other acid substances at high temperatures. The oxides of iron are highly refractory. At a red heat iron de- composes water into its elements, and finely divided iron burns readily in the air. 1 Harbord and Hall's Metallurgy of Steel, pp. 612-614. CHAPTER IX IRON SMELTING- CHEMISTRY OF THE BLAST FURNACE PROCESS Pig Iron. Primitive methods for smelting iron employed tem- peratures much below its melting point and wood or charcoal be- ing the fuel used, a soft and almost pure iron was reduced directly from the ore. The direct production of pure iron is dealt with elsewhere, it being no longer practiced on the large scale. In all civilized countries iron is first prepared in the impure form known as pig iron, the purer forms being prepared from this by separate, refining processes. Preliminary Description of the Blast Furnace Process. The drawing (Fig. 26) represents in section a blast furance, without the accessory apparatus. The foundation is laid in concrete and masonry, and upon this a circle of cast iron columns is placed to support the superstructure. The walls of the furnace above the region of the bosh are encased in boiler plates riveted together, and the bosh walls are reenforced by heavy iron bands. The walls and hearth of the furnace are thickly lined with fire-brick, and in the region of the bosh and hearth the walls are water-cooled. The blast is introduced into the furnace through a number of openings near the bottom, one of which is shown in the drawing. The bustle-pipe, which branches from the blast main, surrounds the furnace, and to this the pipes delivering the air into the furnace (blow-pipes) are connected by means of goose-necks. The gases are taken from the furnace through one or more openings at the top. The furnace has two hoppers, the bottoms of which are closed by means of conical castings known as bells. The bells are hung on counterpoised beams and are lowered when the hop- pers are to be emptied. All the older furnaces have but a single bell and hopper. For further descriptions see Chapter X. The components of the blast furnace burden are the ore, flux and fuel, and the air supply is known as the blast or the wind. METALLURGY Fig. 26. IRON SMELTING 79 The gangues of iron ores in this country are generally siliceous, and are fluxed with alumina, lime and magnesia. Lime is gen- erally added as limestone, the other bases being supplied by the ore itself and by the stone and fuel. The common fuel is coke, though charcoal and anthracite are used in some localities. The blast is heated in regenerative chambers called stoves before it is delivered into the furnace, the combustible gas taken from the top of the furnace being utilized for this purpose. Under normal working conditions the furnace is kept almost full, and the blast is maintained at as near a uniform temperature and pressure as possible. The blast, at the moment it enters the furnace, reacts with the fuel and is largely converted into a reducing gas, which in passing upward through the mass of ore, reacts with it and sets the metal free. The first reaction of the blast with the fuel together with the initial heat carried in by the former, creates a very high temperature in the bosh of the furnace. This facilitates the final reductions, the formation of slag and the fusion of the iron. The metal and slag, being completely liquidized, run down into the crucible of the furnace, the slag floating on the metal as oil floats on water. These are tapped out when they have been accumulated in sufficient quantity. Since the ascending current of gases is in contact with coke all the way to the top, the gases taken from the furnace are largely combustible. They are util- ized for heating the blast, generating steam, and for other pur- poses. Fine particles of ore, coke, etc., are carried over with the gases. This is known as blast furnace, downcomer, or flue dust. Chemical Changes in the Blast Furnace. The reactions oc- curring in a blast furnace are exceedingly intricate, and beyond the reach of a thorough investigation. The more important reactions may be known, and the ultimate changes can be as- certained with exactness by an examination of all the raw ma- terials and the products, but the transitionary changes can not be observed. Furthermore the conditions existing in a blast furnace can not be reproduced on the experimental scale, these being dependent in a measure upon the large quantities of substances treated. The blast introduces the elements, oxygen, nitrogen and hydrogen into the furnace, the hydrogen being in a form 8O METALLURGY of water vapor, which is always present in the air. The action of the principal elements of the blast and burden may be out- lined as follows : Oxygen. The oxygen of the blast, being already at a high tem- perature, and cpming in contact with a large excess of glowing coke, becomes saturated almost instantly with carbon C -f O 2 = CO 2 C + CO 2 = 2CO. Nitrogen. The nitrogen of the blast is for the most part inert and may be said to play no economic part in the process. It is an interesting fact, however, that the conditions necessary for the formation of cyanide exist in the blast furnace. The alkali which is derived from the ash of the coke, is reduced by carbon, and nitrogen is added K 2 C0 3 +C 4 +N 2 =2KCN+ 3 CO. It has been suggested that this reaction is responsible for the re- duction of a large portion of iron, but this would seem hardly possible from the small amount of cyanide that is known to be formed. 'Hydrogen is formed by the decomposition of water vapor as in the gas producer. It would seem to play some part in the re- duction of iron oxide, thus H 6 +FeA,=Fe 2 + 3 H 2 0. But the water formed would again be decomposed into steam, and though this would restore the hydrogen for further action, the net result would be a loss of heat, as explained on p. 42. The principal solid substances in the burden which enter into the chemistry of the process are carbon, iron, manganese, phos- phorus, sulphur, silicon, lime, alumina and magnesia. Carbon. In addition to the reactions with oxygen, as given above, carbon reacts directly with the oxides of iron, manganese, silicon and phosphorus, reducing them completely Fe, 2 3 +C 3 =Fe 2 + 3 CO SiO 2 +Co=Si+2CO P 2 5 +C 5 =P 2 + 5 CO. IRON SMELTING 8l Some of the carbon enters into combination with the iron, as shown below, and a smaller portion is cemented into the lining of the furnace, as will be explained later. Iron. The iron is almost completely reduced by the action of carbon and carbon monoxide. Where rich ores are smelted, not more than o.oi per cent, of the total iron in the charge should escape reduction. The reduction begins with the descent of the ore and is finished above the region of the bosh. Upon reaching the bosh the iron is in the form of a spongy mass or a black powder. It now takes up carbon, fuses and trickles down into the hearth of the furnace. It is at this time that phosphorus and silicon combine w r ith the iron, and manganese is alloyed with it. The small amount of ferrous oxide that is not reduced is com- bined with silica in the slag. Fe 2 0,+3CO=Fe 2 +3C0 2 Fe 2 O 3 +CO=:2FeO+CO 2 2FeO+Si0 2 =2FeO.Si0 2 Fe + C, + Si. + P. -f Mn, = Pig iron. Manganese, which occurs in iron ores chiefly as the sesqui- oxide and the dioxide, requires a higher temperature than iron does for its reduction. Generally, about half that is in the ore is reduced, the rest acting as a basic flux. Manganese is desira- ble in the blast furnace for its desulphurizing effect on the iron. The reduction of manganese is analogous to the reduction of iron. Phosphorus is completely reduced by carbon, and passes im- mediately into the iron. Only traces of phosphorus are to be found in the slag. The reduction seems to take place only in the hottest part of the furnace and in the presence of a large amount of silica. Phosphorus is present in the raw materials chiefly as phosphates of iron and calcium. Sulphur is always present in coke and not infrequently in iron ores as pyrite. A part of this is absorbed by the iron as the monosulphide. The larger part is taken into the slag as calcium sulphide FeS+CaO=FeO+CaS. The conditions favoring the absorption of sulphur by the slag are a high temperature of working and a high percentage of 82 METALLURGY bases in the charge. A very liquid slag in large bulk naturally promotes the removal of sulphur from the iron. Silicon is reduced only in the hottest part of the furnace, and by solid carbon. The larger part of the silica in the charge re- acts witli lime and other basic oxides to form the slag. The silica, always retaining its two atoms of oxygen, combines in different proportions with the bases, which are either in the pro- toxide or the sesquioxide state. These proportions are expressed by the ratio of the oxygen in combination with the base to that in combination with the silica. The ratio in blast furnace slags is generally i to I, or, representing the metal by M, the general formula for the slag would be ( 2 MO.Si0 2 ), (2M 2 3 -3Si0 2 L. Lime and Magnesia. These substances act similarly in the blast furnace, the one replacing the other in the charge. They are formed by the calcination of the raw stone, which is usually brought about 'nside the furnace CaOO 8 +MgCO 8 =CaO+MgO+2CO 2 . A note on the use of previously burnt lime as a flux will be found on p. 101. Lime is the chief basic flux in the blast furnace, uniting with the silica of the charge as monosilicate. If this ratio is changed the slag becomes less fusible, absorbs more heat, and the temperature of the furnace is raised. The silicate of lime alone is difficultly fusible and would not be fluid at the tempera- ture of the furnace hearth, but the fusion point is lowered by the presence of other bases, and especially by alumina. Aluminum is in no wise reduced, but it enters into combina- tion with silica as the sesquioxide (alumina), forming the mono- silicate. Gredt has found that a mixture of alumina, lime and silica is most fusible when the proportion is 1.07 parts A1 2 O 3 , 1.75 parts CaO, and 1.87 parts SiCV Other Metals. The metals titanium, zinc, copper, arsenic and chromium are sometimes present in blast furnace charges in sufficient quantity to affect the working of the furnace or the quality of the iron produced. Titanium is scarcely, if at all, reduced, unless present in con- 1 Stahl und Eisen, 9, 756. IRON SMELTING 83 siderable quantity. Being a highly refractory substance, titanic oxide may render the slag difficult to fuse, unless the proper mixtures are used in the charge to flux it. High titanic ores have been smelted successfully in blast furnaces by allowing the titanic oxide to replace silica in the slag. 1 An interesting com- pound of titanium with carbon and nitrogen, known as cyano- nitride of titanium, is often found in the hearth and wall accre- tions of blast furnaces. It is in the form of small cubes, which are very hard and look strikingly like copper. 2 Zinc, if reduced, does not reach the hearth of the furnace, owing to its volatility. Any zinc vapor becomes oxidized in the cooler part of the furnace, probably by the action of carbon dioxide. The oxide is deposited on the upper walls of the furnace and in the stoves and flues. Some enters the slag, rendering it less fusible. Arsenic is almost totally reduced, entering the iron as arsenide or arsenate. Copper is reduced and alloyed with the iron.- Chromium is more difficult to reduce than iron, but it may be reduced in considerable quantity if a high temperature is em- ployed. Owing to the refractory nature of chromium oxide, special fluxes are required for smelting chrome-iron ores in blast furnaces. Blast Furnace Slag. It is seen from the foregoing that blast furnace slag is a mixture of the silicates of alumina, lime and magnesia, the silicates of iron, manganese and other bases being present in smaller quantities, or as impurities. Sulphur is pres- ent, chiefly as sulphide of calcium. It has also been shown that the composition of slags varies with that of the raw materials and with the temperature at which they are formed. Otherwise expressed, the slag is an indicator of the condition of the fur- nace. Some idea of the composition of a slag may be gained from its viscosity while fused and from its appearance after cooling. For example, a slag of the proper composition will flow neither too sluggishly nor too readily, but in a manner well 1 Paper on the smelting of titaniferous ores by A. J. Rossi. Trans. Amer. Inst. Min. Eng., 21, 832. 2 Percy, " Iron and Steel," pp. 163, 510. 84 METALLURGY known to the trained observer. Too much silica in the slag will be indicated by free flowing, and too much lime by the reverse. The fracture of a high silica slag is glassy, while a limey slag presents a granular fracture with a dull-gray color. Siliceous or "lean" slags are apt to contain a good deal of iron, which may render them dark-brown in color, or even black. If much manganese is present the color will be green. A siliceous slag indicates that the furnace is working at a low temperature, and the iron is likely to be high in combined carbon and high in sul- phur. No fixed rule can be laid down for these indications, since the condition of the furnace is subject to irregularities, the effect of which on the product is indeterminable. TYPICAL BLAST FURNACE SLAG. SiO 2 A1 2 O 3 MnO FeO CaO MgO CaS P 2 O 5 K 2 O, TiO 2 , etc. 43 14-50 i 0.25 34 3.50 2 0.05 2.70 Wall Accretions. Particles of coke, lime, ferrous oxide and other refractory substances are agglomerated and cemented to the walls of the furnace by a slag. The deposited material increases to some thickness and forms a protective coating over the lining. It extends all the way from the upper limit of fusion in the fur- nace to the crucible, its composition varying with the conditions at different heights. Aside from the beneficial result of wall accretions, there is danger of an irregular growth on the walls of blast furnaces. The accretion may extend inward for a con- siderable distance around the furnace and form a "scaffold." With this as a starting point the stock may arch above the melt- ing zone and hang for some time. This is followed by a "slip," which is the falling and settling of the burden. This upsetting of the furnace burden is a most undesirable occurrence, being specially disastrous to the working of tall furnaces. Hanging and slipping are not, however, always to be attributed to wall accretions. Abnormal accretions or scaffolds are less likely to form in furnaces that are charged and blown with regularity and in which regularity of working is aided by an even distribu- tion of the stock. Accretions may be removed by increasing the temperature at that point. This may be done by introducing a special tuyere or injecting oil in the region of the obstruction. IRON SMELTING 85 Blast Furnace Gas. The composition of blast furnace gas is about the same as unenriched producer gas, the conditions under which it is formed being similar. The analysis here given may be taken as typical for gas from a coke-burning furnace. Nitrogen Carbon dioxide Carbon monoxide Carburets Hydrogen 60 14 24 II The gas also contains small amounts of sulphur compounds, water vapor and fine particles of solid matter. CHAPTER X IRON SMELTING THE BLAST FURNACE PLANT AND PROCESS Description of the Plant. The principal parts of a blast fur- nace plant are outlined in the elevation (Fig. 27). Referring to the numbers, I is the furnace and 2 the regenerative stoves for Fig. 27. heating the blast. The down-take, 3, conducts the gas from the furnace to the dust catcher, 5. The small, vertical pipes, 4, are called "bleeders." They are fitted with relief doors at the top to allow gas to escape when the pressure exceeds a certain limit. IRON SMELTING / From the dust catcher the gas is conducted to the stoves through the main, 6. A part of the gas is burned in the stoves and the remainder is burned under boilers. The cold blast is brought from the blowing house in the main, 7. The blast is let into the stoves in turn by means of control valves. After passing through one of the stoves the air is conducted to the furnace in the hot blast main, 8. The products of combustion from the stoves enter the tunnel,. 9, which leads to the tall chimney, 10. The gate valves controlling the entrances to the tunnel are outlined in the drawing. The hot blast and gas valves are on the other side of the stoves, n shows the outline of the casting shed, and 12 the skip car for hoisting the material. The Furnace Stack. The drawing on p. 78 shows the lines of a typical American furnace. The quality of the ore and fuel and the output are governing points in the construction of blast furnaces. A furnace that is rather low (not over 75 feet) and wide at the bosh seems to be most suitable for smelting lean ores, since it affords a high temperature and a large melting area in that region. Tall stacks (such as the drawing represents) are suitable for rich ores and are necessary to the greatest yields of iron. As large producers of iron, they require a firm coke, to withstand the weight of the burden and a high pressure of blast. The well or crucible of a furnace with a high stack is made larger in proportion, and the bosh walls are made steeper, for the reduction and fusion zones are higher than in low stacks, and the burden is thus made to descend more rapidly. While building a furnace some special precautions are taken in constructing the bosh walls. These are subjected to greater wear from the stock than the upper walls, since their slope is out- wards, and with the higher temperature and scouring slag they are more rapidly fluxed away. The life of the bosh walls is greatly lengthened by water cooling. This is accomplished by introducing hollow blocks of cast iron or bronze into the walls, in the manner shown in Fig. 28, and causing water to circulate through these. The hearth of the furnace is cooled by allowing the water which is discharged from the coolers to circulate in a trench, which, surrounds the furnace at the base. Gayley's bosh- 88 METALLURGY SCOTT'S PATENT BOSH PLATE. Fig. 28 Showing Arrangement of Cooling Plates and Tuyeres. (Best Manufacturing Co.) IRON SMELTING 8 9 cooling, bronze plate is represented by Fig. 29. The water is admitted through one of the openings and discharged through the other, having but the one course. The webs inside the plate permit of its being made light without danger of crushing in the furnace wall. The plate is cast smooth on the top and bottom and is wedge-shaped, so that it can easily be inserted in the fur- nace wall or removed when renewal is necessary. The tuyeres, or openings through which the blast enters, are also water-cooled. The general arrangement is shown in Fig. 30. The tuyere, into which the blast pipe is fitted, projects through Fig. 29 Gayley Plate. (Best Manufacturing Co.) the wall of the furnace to the interior, as shown in Figs. 26 and 28. The tuyere, in turn, fits into the larger cooler in the manner shown. The large cooler is a protection to the brick work, since it does not have to be renewed often, and in drawing and insert- ing tuyeres the bricks are not disturbed. Water is circulated through the tuyere and cooler by means of separate supply and waste pipes. The number and size of the tuyeres is largely a matter of judgment. Within certain limits, the fewer the number of tuy- eres and the larger their diameter, the greater will be the pene- trating power of the blast, while with a larger number of tuyeres, the blast is more evenly distributed. The number of tuyeres at different furnaces varies from 8 to 16, 12 being common. METALLURGY Charging Apparatus. At the older plants the stock is raised to the level of the furnace top by means of elevators or platform hoists, the materials having been loaded into barrows and weighed, and from these it is wheeled by laborers and dumped into the furnace hopper. The modern blast furnace charging apparatus consists of the bell and hopper (Fig. 26), and often a special device for dis- tributing the materials in the hopper. The materials are hoisted by means of a skip car or bucket traveling over an inclined track from the stock bins to the furnace top. From the drum BOSH FITTING. STYLE E, WITH UNIVERSAL UNION ON SUPPLY. N?l WITH THREE WAY TUYERE COCK AT C. N?2 WITH Two WAY COCK AT C. Fig. 30. of the hoisting engine on the ground level a wire rope is passed over a sheave on the top of the furnace, and fastened to the car. At some plants a double skipway with two cars is employed, the loaded car being hoisted while the empty is returning. Among the first successfully operated, mechanical hoists are those of the Carnegie Steel Company's furnaces at Duquesne, Pa. This hoist consists of a bucket suspended from a truck which traverses the track. The bucket is filled by running in the materials from opposite bins, thus effecting a good mixing. The bottom of the bucket is closed by a cone or bell, which can be lowered to empty it. The material is therefore not dumped 3 1 Brown Hoist and Distributor. (Brown Hoisting Machinery Co.) IRON SMELTING 9 1 but discharged around the bell after the bucket has been hoisted and placed in position over the furnace hopper. With the usual style of hoist the material is dumped from one side into the hopper, and though it be made to pass over two bells, there may be an uneven distribution leading to irregularities in the working of the furnace. Stock distributors have been in- troduced to offset this defect. The photographic view (Fig. 31) shows a style of hoist and distributor invented by Alex. E. Brown of Cleveland. It consists of a conical hood or gas seal placed over the furnace hopper and supporting the distributing hopper into which the materials are dumped by the skip car. The car is shown in the position for dumping, which is done automatical- ly. The rope wheel shown at the top is geared to the hopper, which it revolves through a definite angle with each return of the car to the bins. A ratchet arrangement prevents the dis- tributor from turning in the opposite direction while the car is ascending. The distributor is a hopper or chute, terminating within the hood, and provided with a hinged door at the bottom. By an arrangement of levers the door is closed when the bell is lowered to empty the main hopper. It remains open while the bell is in the normal position. By thus changing the position of the chute each car load of material is thrown to a different place in the main hopper and piling to one side is prevented. 1 The charging bells are hung on counterweighted beams, and are operated by means of steam cylinders on the ground level. The size of the lower bell is important in effecting the proper distribution of the stock. If it is too large in diameter the ma- terial is thrown to the sides a*d the lumps roll back to the cen- ter ; if the diameter is too small the material forms a circular pile away from the walls, causing the lumps to roll both to the cen- ter and to the walls. 2 In either case the tendency is toward an unequal distribution of the ascending current of gases, since channels are at once formed by the large lumps. Such condi- tions lead to irregular reduction and fusion. Dust Catchers. A large part of the dust that is carried over 1 Trans. Amer. Inst. Min. Eng., 16, 194. 2 Ibid., 35, pp. 224 and 553. METALLURGY with the gases from the top of the furnace is detained by check- ing the velocity of the current and leading it abruptly in a dif- ferent direction. A form of dust catcher is shown in Fig. 32. It Fig- 32. is a cylindrical vessel with a hopper bottom, and provided with an opening in the bottom for letting out the accumulated dust. The opening is closed by means of a counterweighted cone. The vessel is constructed of boiler plates and lined with fire-brick, and is supported on cast iron columns. As indicated by the ar- rows the gas enters the side of the vessel and is withdrawn at IRON SMELTING 93 the top, the head of the outlet pipe being situated below the center of the chamber. The gas enters the chamber at a tangent, swirls around, and the dust loses momentum by friction against the walls. Moreover, the current loses head by reason of the enlargement of the conduit. The dust settles in the hopper, from which it is removed periodically. Other types of dust catchers take the gas in at the top and deliver it at the side, but the above type has been found to be more efficient, especially for fine dust. If a more thorough cleaning is required the gas is sprayed or led through scrubbers. Stoves. The introduction of the hot blast by Neilson in 1828 marked a new era in blast furnace construction and practice. While the inventor realized that by heating the air beforehand he could intensify the heat of combustion, his methods were crude and wasteful, employing solid fuel and in no way utilizing the waste gases from the furnace. Neilson's invention led to the construction of many forms of appliance for heating the blast, and finally to the utilization of the gases, which had be- fore been allowed to burn at the top of the furnace. 1 Of the earlier forms of blast heaters or stoves, there is but one sur- vivor in this country. It consists of a rectangular, brick cham- ber through which the blast is conducted in numerous cast iron tubes. The gas is burned in the chamber and heat is trans- mitted to the blast through the walls of the tubes. The very high temperatures now carried in the blast were never possible with the old style of heater, but were attained after the regen- erative system of firing was applied. The first regenerative stove put into successful operation was built by Cowper in 1860. A stove of the Cowper type is shown in section in Fig. 33. It is essentially a fire-brick chamber, cylindrical in shape, and en- cased in iron plates. The combustion chamber, C, is located at the side or center and the rest of the space is filled with the division walls and vertical flues, F. The flues are open at both ends and communicate with the combustion chamber at the top. The space underneath the flues and the combustion chamber 1 Aubertot is said to have been the first to utilize blast furnace gas, employing it for roasting ore in 1814. 94 IRON SMELTING 95 communicates with conduits leading from the stove at the base, as shown. The gas enters the stove through the pipe, G, air being ad- mitted for its combustion. The flame and products of combustion pass upward through C and downward through the flues, F, and heat is absorbed by the large mass of brick work. The valve, Vj, being open, the products of combustion pass into the tunnel or flue by which they are conducted to the chimney. When the .stove has been heated the gas is shut off, and air is admitted from the cold blast main through the valve, V 2 , the chimney valve be- ing now closed. The air takes the opposite direction of the gas through the stove and becomes heated by contact with the hot bricks. It passes into the hot blast main through the valve, V 3 . For the management of Cowper stoves the following rules are given i 1 "To change from gas to blast close the chimney valve; note if hot air comes out of the air valve. If so, close the air valve, and if not, see that the chimney valve is fully closed; then close the air valve; open the cold blast valve slowly; open the hot blast valve quickly." "To change from blast to gas close the hot blast valve; close the cold blast valve within bale until the pressure is nearly gone ; then throw it wide open ; open the chimney valve fully, and then open the gas valve." Blowing Engines The steam engine was employed for blow- ing iron furnaces soon after its invention. The blowing engine was substituted for the water blowers of medieval days, which had replaced the ancient hand bellows. The increase in the size and output of blast furnaces has been dependent directly upon the volume of air with which they are blown. Since blast fur- nace possesses are generally the most rapid and economical in smelting, the progress of metallurgical industries in general is due in no small measure to the development of blast apparatus. In operations requiring blast under but a few ounces pressure the ordinary fan blower is used. For higher pressure a positive blower is required, i. e., one which compresses the air until the 1 Iron Age, 47, i77- 96 METALLURGY resistance offered to its passage is overcome. Rotary blowers are commonly used for small blast furnaces, and for large ones reciprocating blast engines are used. Engines which deliver the air under a pressure of more than 30 pounds per square inch are commonly called air compressors. The engine shown in Fig. 34 is designed for blowing iron furnaces, Bessemer converters, etc., and has a capacity of 30,000 cubic feet of air per minute, against a pressure of 30 pounds per square inch. It is of the horizontal, cross-compound type. The steam and air cylinders are placed tandem, the piston heads being carried practically on a continuous rod. The engine is given steadiness of motion by aid of a large fly-wheel. The air cylinders are shown in the foreground. Air passages are provided in the cylinder castings, leading from the middles to the heads. The air is admitted and discharged under the con- trol of mechanically operated valves on the heads of the cylin- ders. The outside mechanism of the air valve gear is shown on the cylinder to the right in the illustration. The valves are operated in time with the piston by means of a wrist plate, which has a bearing on the side of the cylinder. The wrist plate is given a slight, rotary motion in opposite directions alternately, by an eccentric attached to the main shaft of the engine. The motion is communicated to the valves by shafts on the ends of the cylinder to which the arms of the wrist plate are attached. The discharge valves are closed by plungers at the moment the piston, in approaching them, reaches the end of the stroke. The plun- gers recede after seating the valves, leaving them to be opened automatically by the pressure of the air in the cylinder. The in- take valves are operated entirely by the mechanism, their open- ing and closing being timed with the stroke of the piston. With each stroke of the piston the cylinder is filled with air from one end and emptied from the opposite end. Uneven wear on the piston heads and cylinders is prevented by extending the piston rods through the ends of the cylinders and supporting the weight of the pistons on slides. The vertical type of blowing engine is in very general use. It has the advantage over the horizontal type in taking up less floor IRON SMELTING 97 space. The horizontal engine, however, has the advantage of being more easily accessible, and is less liable to vibrations. The gas engine, which has recently been developed for indus- trial uses, is replacing the steam engine to a considerable extent for blowing purposes. A number of large gas engines have been built by European manufacturers, and extensive preparations are being made in this country for their installation. It has been de- monstrated that blast furnace gas can be used successfully for running gas engines. The cleaning of the gas has offered one of the chief difficulties in using it, since it is essential that all dust and grit be removed from the gas before it is introduced into the cylinders of the engine. The cleaning apparatus now in use is efficient though expensive. The main economy gained in the conversion o-f the gas directly into mechanical power is in the elimination of the boiler plant. Blowing In. The starting of the blast furnace process is known as "blowing in" the furnace. With a new furnace the lining must be thoroughly dried and heated up gradually before the regular, charging is begun. James Gayley has described a; method of blowing in furnaces as used at the Edgar Thomson Works. "In placing the wood in the furnace the practice is to support on posts a platform about two feet above the tuyere arch, and under the bottom of each post to place a piece of fire-brick on which is a sheet of thick asbestos. The wood is put on in the morning, the firing being stopped the evening before, so that the brick work will be partially cooled. After the skeleton parts of the scaffold are in, a charge of coke is made, sufficient to fill the hearth up to the bottom of the cinder-notch opening. On the platform planks are placed sufficiently close to prevent the cord wood from falling through. Above the platform three lengths of cord wood (hard wood is preferred) are placed on end, with a cribbing in the center to allow space for the work- men to pass up the wood. On top of the wood a blank charge of 250 barrows of coke is put in. With this coke there is charged 98 METALLURGY sufficient limestone to flux the ash, and in addition a few bar- rows of spiegel-eisen or ferro-manganese slag. The regular charges consist of 12 barrows of coke, 12 barrows of ore and 6 barrows of limestone. The weight of a barrow of coke is 830 pounds. To the first few charges an extra barrow of slag is often added. The space between the scaffold above and the bed of coke beneath is then filled with kindling wood, and the fur- nace is ready for lighting. In addition to lighting the wood at the cinder-notch, red-hot bars are thrust in at each tuyere to start the combustion uniformly. When the scaffold has burned away, allowing the stock to settle gently, and bringing hot coke or charcoal in front of all the tuyeres, the blast is put on. The time from lighting to turning on the blast varies from six to ten hours. The blast is put on slowly at first, and increased hourly until the volume of air is one-half the normal quantity, at which point it is held until the first cast of iron is made. In order to avoid explosions, which frequently happen at the start, the valves in the boiler and stove gas mains are closed, and all the gas is allowed to escape until after the first cast is made." Burdening the Furnace. The furnace burden consists of a number of charges, each charge in turn consisting of weighed amounts of fuel, ore and flux. The charging is practically con- tinuous, except in case of accident or other interruption, until tfie furnace is "blown out." The term "damping down" means the shutting off of the air from the furnace and filling it with coke, a scheme that is resorted to when the process has to be sus- pended for a few days. The furnace fire may be held for a con- siderable length of time in this way. The mixtures for blast furnace charges can easily be calcu- lated from the compositions of the materials to be used. Sup- pose, for example, that a furnace is to be burdened for the re- duction of 1,000,000 pounds of iron in a day of 24 hours, and that the daily burden is to consist of 100 charges. Each charge must then contain 10,000 pounds of iron. Further, suppose that the conditions require a pound of coke for each pound of iron reduced, and that the analyses of the coke, ore and stone are as follows : IRON SMELTING Mnjt SiO 2 # A1 2 O 3 + CaO* MgO* 0.00 4.00 2.00 O.OO O.OO I.OO 18.00 2.00 0.50 0.50 0.70 8.00 3-00 I.OO 0.50 0.40 3.00 I.OO 0.00 0.00 0.70 9.00 2.40 0.70 0.40 0.00 5.00 0.50 50.00 I.OO Fe Ibs. IOO Mn Ibs. Si0 2 Ibs. 4OO.OO A1 2 3 Ibs. 2OO.OO CaO Ibs. MgO Ibs. 9,900 129.29 1,662.30 443.28 129.29 73-88 30 298.15 29.82 2,981.50 59.63 10,030 129.29 2,360.45 673.10 3,110.79 I33-5I Coke i.oo Ore No. i 45.00 " " 2 55.00 " " 3 58.00 " (Average) 1 .... 53.60 Stone 0.50 The burden sheet should contain, in addition to the analyses of the materials and the number of charges, the actual weights of silica and bases in tabular form. The calculations are given below. Stock Ibs. Coke 10,000 Ore Mixture 18,470 Stone 5,963 Totals 34,438 The 10,000 pounds of coke in the charge yields 100 pounds of iron, leaving 9,900 pounds to be supplied by the ore. Since the mixture of ores yields 0.536 pound of iron for each pound of ore, the amount of the mixture required is 9,900-^0.536=18,470 pounds. The weights of silica and bases in the coke and ore are now computed and the deduction made for self-flux. Using the ratios given on page 82, the weight of silica which i pound each of the bases will flux is found by the following proportions : 2A1 2 O 3 : 3SiO 2 : : i : x = 0.8823 pound SiO 2 2CaO : SiO 2 : : i :x = 0.5357 " " 2MgO : SiO 2 : : i : x = 0.7500 " Multiplying the weights of the bases by these factors the totaJ silica is found to be By A1 2 O S , 643.28 X 0.8823 = 567.57 pounds SiO 2 " CaO, 129.29 X 0.5357 = 69.26 " " " MgO, 73-88 X 0.75 = 55-41 " Total == 692.24 " The weight of silica that remains to be fluxed by the stone is 2,062.30 692.24=1,370.06 pounds. The fluxing power of the stone is found by subtracting the 1 NOTE: The ores are to be mixed in the proportions of one part of No. i, three parts of No. 2 and one part of No. 3. The average composition is therefore computed on this mixture. IOO METALLURGY silica in I pound from the total amount of silica that would be satisfied by the bases in i pound of the stone By A1 2 O 3 , 0.005 X 0.8823 = 0.00441 pound Sio 2 " CaO, 0.50 X Q-5357 = 0.26785 " " MgO, o.oi X 0.75 = 0.00750 " " 0.27976 SiO 2 present 0.05000 " " Fluxing power = 0.22976 " " The amount of stone needed is found by dividing this factor into the weight of silica to be fluxed 1,370.06 -i- 0.22976 == 5,963 These calculations are simplified by using the slide-rule, pro- posed by Jenkins. 1 As in most other metallurgical processes, more has been learned about burdening blast furnaces from prac- tice than from theoretical reasoning. There are times when the furnace becomes irregular in its working, and the burden must be changed to suit the conditions. At such critical times the remedies lie entirely with the judgment of the manager. The Fuels and Fluxes of the Blast Furnace Process. The quan- tity of fuel used in the blast furnace is generally referred to the quantity of iron produced. For coke furnaces the consumption varies from 1,600 to 3,000 pounds per ton of iron, depending upon the purity of the raw materials, the humidity of the blast and the general efficiency of the plant. It is desirable to carry as little coke as possible in the burden, not only for economic rea- sons, but also for the sake of introducing the least amount of im- purities into the iron. Coke is generally superior to most other fuels, though the sulphur and phosphorus it contains are often serious defects. The firm, hard varieties of coke are always pre- ferred, since they sustain the weight of the burden and keep passages open for the circulation of gases. The coke and iron industries are indispensable to each other and are often con- trolled by the same interests. The remoteness of some of the great ore deposits in the United States from the supply of coke has been a hindrance to the growth of the iron industry, though 1 Jour. Iron and Steel Inst., 1891, 1, 151. IRON SMELTING IOI it is largely responsible for the wonderful transportation facili- ties which now exist. Charcoal is still used in some heavily wooded localities where coal does not abound, as in the Lake Superior district. The fuel consumption is lower in charcoal than in coke furnaces. A record given by J. C. Ford of a furnace in Michigan shows an average consumption of about 1,630 pounds to a ton of iron made. 1 Charcoal iron is prized for its purity, though it is not made to compete with ordinary pig. The use of coal also continues. There are a number of an- tracite furnaces in Eastern Pennsylvania still in blast, though many that were first blown in with anthracite have since been changed to coke. Anthracite is inferior to coke on account of its dense structure and its tendency to split and crumble in the furnace. The attempt has been made to substitute gas for solid fuel in the blast furnace, but without success. Raw limestone, in conjunction with alumina, has been found to be the most satisfactory flux in the blast furnace. The fuel consumption may be lessened by using caustic lime or burnt lime- stone, but when the fuel used in burning the limestone and the extra labor are taken into account, there is very little if any economy. In the low English furnaces, smelting poor ores, there seems to be some advantages gained in the use of lime. 2 Magnesian limestone and dolomite are not uncommonly used. The prevalence of this character of stone in the Lehigh Valley accounts for its usage in that section. F. Firmstone has shown some results of his experience with magnesian stone. He iavors its use, if the alumina is kept low (below 10 per cent.), having found that the slag is more fluid and that less sulphur passes into the iron. 3 Management of tile Blast. The working of a blast furnace depends no more upon the manner in which it is burdened than it does upon the management of the blast. The efficiency of the accessory apparatus is proved by the condition of the blast in 1 Jour. U. S. Assoc. of Charcoal Iron Workers, 8, 272, 274. 2 Jour. Iron and Steel Inst., 1894, 2, 38-57, and 1898, 1, 69-88. 3 Trans. Amer. Inst. of Min. Eng., 24, 498. 102 METALLURGY its four phases temperature, pressure, volume and humidity. Temperature. The construction and management of the stove are explained on pp. 93-95. Four stoves are generally built with one furnace, the use of this number allowing three hours for heating the brick work, if the blast is kept on each for one t 2 3 , Time. 5 // ^c i ufS 7 ^ y /o /.too /.aoo /oae 100 V f X' f\ r\ r\ ^ _r . r x r\ D s r LOO ^>J 7 ' ^J ^^ -J x - xj ^j Sao Fig. 3;, Fig. 36. Fig. 37- hour. Some blowers prefer to use two stoves at once for heat- ing the blast, one having been put on half an hour before the other. This of course involves the changing of stoves every half hour, since the blast is to be kept on no stove longer than an hour, but a more uniform temperature may be maintained by this method of heating. It is the aim not only to return all the IRON SMELTING IO3 heat possible to the furnace, but also to keep the temperature of the blast as nearly uniform as possible. By equalizing the temperature of the blast there will be less irregularity in the working of the furnace. Equalization may be accomplished by carefully admitting air from the .cold blast to the hot blast main just at the time the stoves are changed, and gradually shutting off this air as the stove cools down. Another advantage may be gained by this practice from the fact that there is aways a re- serve of heat in the stoves which can be drawn upon in case of an emergency by shutting off the cold air entirely. The temperature of the blast is generally taken just before it enters the bustle-pipe. The continuous recording pyrometer has largely displaced the older forms, from which only periodic readings can be obtained. The average temperature carried in the blast does not much exceed 750 C at any furnace. 1 The pyrometer records here shown (Figs. 35, 36, and 37) are from actual practice. The first one shows regular heating of the stoves, the temperature being taken from the hot blast main. The sudden rise and regular fall of the recording pen shows that the stoves were changed at the end of every hour, but that no at- tempt was made to equalize the temperature. At the time of the second record, however, the temperature was leveled in the way above described. The third record shows irregular heating, due to the condition of the gas. The above method of leveling the blast temperature requires considerable skill and vigilance on the part of the blower, and it has not proved entirely satisfactory. Several forms of regen- erative apparatus known as "equalizers" have been proposed, but their adoption does not as yet seem probable. If adopted the equalizer will probably be constructed on the principle suggested by L. F. Gjers and J. H. Harrison. 2 They propose to build an additional stove, or a double regenerative chamber, and to lead the hot blast in through the checker-work of one-half the cham- ber and out through the other half. The idea is that the bricks will absorb heat when the blast is above the average temperature and give it back to the blast when it is cooler than the average. 1 Turner's Metallurgy of Iron, pp. 112-114. 2 Jour. Iron and Steel Inst., 1900, 1, 154-162. 104 METALLURGY Pressure. Increased pressure gives the blast greater pene- trating power, facilitating more rapid combustion and conse- quently more rapid reduction and fusion. There are serious diffi- culties in the way of increasing the blast pressure beyond a cer- tain limit, since it would cause more dust to be carried over with the gases, and would require additional blowing power and better construction throughout the entire system in which the pressure is to be withstood. The pressure at different furnaces varies from 8 to 15 pounds. Furnaces in the Pittsburg district not uncommonly carry 15 pounds, and some have been made to carry 20 pounds and more. Volume. The rate at which the furnace works is largely de- termined by the volume of the blast. This in turn is determined by the rate at which the blowing engines are driven and the capacity of the air cylinders. In practice the rate at which the engines are driven, i. e. } the number of revolutions the fly-wheel makes per minute, is recorded as expressing the volume of the blast at atmospheric pressure.' This does not take into account any loss sustained through the working of the intake valves and leaking of the fittings. At the large works, engines are em- ployed which can deliver as much as 25,000 cubic feet of air per minute. Two engines are generally used for one furnace. Humidity. The effect of moisture in the blast upon the work- ing of a furnace has long been a subject of discussion among metallurgists. Attention was called to the subject at a meeting of British iron masters by Joseph Dawson in 1800. * It has been observed that furnaces work better in dry than in wet weather and that their condition is apt to be better in the winter months, when the humidity of the atmosphere is relatively low, than at other seasons. Taking the average amount of moisture in the air as 3 grains, it is seen that in a furnace taking 2,400,000 cubic feet of air per hour, in the same time 123 gallons of water must be decomposed. The effect of this would perhaps not be notice- able if it were not for the fact that the decomposition must take place in the bosh or melting zone of the furnace, any cooling of which has the most marked effect upon the working of the fur- 1 Reprint of Dawson 's paper in Jour. Iron and Steel Inst., 1907, 2, 221. IRON SMELTING IO5 nace. The irregularities caused by changes in the moisture in the air are well known to all furnace managers. Some appliance for drying the air before it is used in the fur- nace has been advocated from time to time, but only recently the problem seems to have been successfully solved. A process look- ing to the partial or ultimate desiccation of air on the large scale has been worked out under the directions of James Gayley. 1 Mr. Gayley's first experiments along this line were conducted at the Lucy furnace, in Pittsburg, and the first complete air drying apparatus is now in operation in connection with one of the fur- naces at Etna, near Pittsburg. The method, as so far used, con- sists in freezing the moisture. Before it enters the cylinders of the blowing engine the air is led through a huge refrigerator a large chamber almost filled with the cooling pipes. These pipes are cooled by means of ammonia and they expose a large surface area to the air. The moisture is deposited upon these as frost, which is removed after it has accumulated sufficiently by letting steam into the pipes. The results gained after using the dried blast in the above furnace from August 25th to September 9th were made public in October of 1904. These show an increase of 25 per cent, in the output after the application of the dry blast, with 20 per cent, decrease in the consumption of coke. These figures were a great surprise to metallurgists both in this country and abroad. Later records, covering longer periods of time and including the winter months, show gains of from 10 to 20 per cent, in the product and an economy of 10 to 20 per cent, in the consumption of coke by the use of the dry blast. The Gayley process is to be used at several of the large plants in this coun- try and in England. Casting. From the position of the tap-hole (Fig. 26) it is seen that all the iron is never tapped from the furnace, a residue being left for the protection of the hearth and to prevent chilling. It is customary to tap the iron six times per day of 24 hours. The tap-hole is kept closed with clay or a mixture of clay and coke, which has been rammed in tightly to prevent the iron from break- 1 For description and illustration Mr. Gayley's invention, see Trans. Amer. Inst. Min. Eng., 35, 746. Supplementary Paper, Ibid., 36, 315. io6 METALLURGY ing out. The clay bakes into a hard mass, which has to be drilled through when the furnace is to be tapped. After the drill has reached the softer interior a bar is driven through and the iron flows out when this is withdrawn. The iron is received first in a trough (Fig. 38) about 18 feet long, 22 inches wide at the top and 15 inches deep, and sloping slightly from the furnace. For a distance of about 12 feet from the furnace the trough is permanent, consisting of heavy castings, protected with sand. At the lower end of the trough is a dam, D, and the skimmer, S, is placed a few inches above this as shown. The iron, which is at first free from slag, flows from the dam, and soon rises to the level of the skimmer. Since the slag floats on the surface of the iron it is prevented by the skimmer from passing on with the iron. Moreover, sand is thrown above the skimmer, and pressed down, and the skimmer itself is lowered as the level of the iron falls. The slag overflows into the trough, C. Fig. 38. If immediate use is to be made of the iron it is run into brick- lined ladles, 1 otherwise it is cast into "pigs." As a rule, the pigs are molded in sand, the molds being prepared for each cast with the aid of wooden models. The arrangement of the casting bed is shown in Fig. 39. The main channel through which the iron is led traverses the middle of the bed, and tributary channels lead the iron to the pig molds on either side. The lowest set of molds having been filled, the iron is turned into the other sets successive- ly by placing dams at the points 2, 3, 4, etc., and cutting out the side of the main channel. After cooling the pigs with water they are broken from the "sows" by means of sledge hammers and taken out. The sows also are broken into lengths which can be handled. Pig machines are used at many of the large plants, thus dis- . 138. IRON SMELTING I0 7 pcnsing with laborers in the casting shed. In the type of machine now in general use the molds are of steel, and are carried on an endless belt which is slowly revolved over sprockets as the iron is poured in from a ladle. The iron is cooled by water, and is solid by the time it passes over the sprocket from which it falls to the ground or into railway cars. Disposal and Use of the Slag. The cinder-notch, or tap-hole for the slag is situated some distance around the furnace from and about 4 feet higher than the iron-notch. The opening is through Hlllllllllllllllllllll 39- a water-cooled, bronze plate, and it is closed by means of an iron plug. The slag is tapped as often as is necessary to keep it well below the tuyere line. It is run into iron ladles, which are mounted on standard-gage trucks, and are provided with the necessary mechanism for tilting them down on side when the slag is to be dumped. Of the enormous quantity of blast furnace slag now produced yearly, the larger part goes to waste. It is being used, however, for road beds, and several railway companies have adopted it as IO8 METALLURGY a standard ballast. A very good quality of cement is now manu- factured from slag, after extracting the sulphur and adding lime. Mineral wool is prepared by blowing a jet of steam through molten slag. As the steam escapes it carries out globules of slag to which ar-e attached thin fibers or filaments. The material is drawn by suction through an iron pipe which is bent twice at right angles and exhausts into a large wire gauze enclosure. The turns in the pipe 'serve to break off the heads from the filaments, the former passing through the rneshes of the gauze and the latter be- ing detained. Mineral w 7 ool is used as an insulating, non-inflamma- ble packing. The slag is granulated for various purposes by allowing it to fall into water. Disposal of Flue Dust. This is a difficult problem, which has not yet been satisfactorily solved. Consisting chiefly of iron oxide and' coke dust, it is a good material chemically to charge again into the furnace. But it is difficult to deal with on account of its being so finely divided. It has been briquetted and used as ore, but so far the processes for this treatment are too expensive. Now that softer ores are smelted the amount of dust produced is much greater. Thermal Requirements and Economy of Fuel in the Blast Fur- nace Process. The chief improvements in blast furnace practice have been in the way of increasing the output and lessening the fuel consumption. Until the year 1880 no furnace had been built to make more than 100 tons of iron in a day, even with the rich- est ores, and an average of about 3,000 pounds of coke per ton of iron was considered good practice. The output has now been increased in many plants to 600 tons per day, and a number of furnaces have made runs of more than 800 tons of iron in a day, with the ratio of 1,900 pounds of coke to the ton of iron pro- duced. These economies have been attained by better manage- ment of the hot blast with the use of improved heating appar- atus; rapid driving, which has been made possible by altering the shape of the furnace and increasing the pressure and volume of the blast, and finally by drying the blast, the effect of which has been so lately demonstrated at Pittsburg. IRON SMKLTING IOO, In connection with the disbursement of heat in the blast furnace it may be interesting to note the requirements from a purely theo- retical standpoint. Of the total amount of heat evolved by the combustion of the fuel, one portion is absorbed in bringing about the reduction and the fusion of the metal and slag ; a second por- tion is lost to the process, being represented by the -gas that is burned outside of the stoves, and a third portion is lost altogether through radiation and leakage. The amount of heat represented in the first portion may be calculated from the composition of the charge, and that in the second portion may be calculated from the composition and volume of the gas. The amount of heat wasted can not be calculated at all with any degree of accuracy. The calculations of Lothian Bell for the amount of heat required for smelting iron in the Cleveland district, England, may be stud- ied with profit. 1 The example below is given to show how the heat units usefully applied may be calculated. The assumed con- ditions are that the iron is reduced from dry, hematite ore ; that the ratio of iron to slag is 2 to 1.3, and that the iron has the com- position : Iron Manganese Silicon Phosphorus Carbon 93 2 1-5 O- 1 34 The heat units absorbed in smelting a ton of the iron are found as follows : Weight of materials Calories required Calories and changes wrought per unit weight total Iron reduced 1,860 1,780 3,310,800 Manganese reduced 40 2,290 9 1, Goo- Silicon reduced '.... 30 6,414 192,420 Phosphorus reduced 2 5,747 u494 Carbon absorbed... 68 8,080 549, 440 Metal fused 2,000 28s 2 57o,ooo Slag fused 1,300 5 2 650,000 5,375,754 Taking the average consumption of carbon as 1,750 pounds per ton of iron smelted, the heat units found in the above calculation represent 38 per cent, of the total heat derivable from the fuel. 1 " Principles of the Manufacture of Iron and Steel," p. 95. 1 Gredt's estimate. CHAPTER XI CAST IRON Cast iron is, generally speaking, iron saturated with carbon, and containing other impurities in varying percentages according to the conditions of manufacture. Practically, it represents all the iron made in blast furnaces, which has not been submitted to a refining process. Properties and Uses. The main properties to which cast iron owes its wide applications are its low fusibility, and the ease with which it can be molded into the shapes desired. In most other properties it is inferior to the other forms of iron, the tenacity, elasticity and malleability being very low, and it can not be forged or welded. The crushing strength is, however, greatest of all ordinary forms of metal. The cooling of fluid cast iron is at- tended, first by a slight expansion, but following this there is a contraction bringing the metal into smaller space that was orig- inally occupied. In making a casting a mold is first prepared, the interior of which bears the shape of the casting. The molten iron is poured in, and on expanding it is forced into every part of the space and reproduces the shape. The contraction or shrinkage follows, mak- ing the casting smaller than the pattern. Cavities are often form- ed in castings, and are known as "pipp" or "blow-holes," accord- ing to their origin. Piping in castings is due to shrinkage. The metal coming in contact with the sides of the mold, forms a solid shell, while the interior of the mass is still liquid. Solidification now proceeds in lines perpendicular to the planes of the surfaces, as shown in Fig. 40. The outside being rigid, any contraction that takes place will result in the softer iron of the interior being drawn toward the outside, leaving a cavity near the middle. The middle and upper portion of the casting is the last to solidify, and there may be enough fluid metal above to fill the cavity, produc- ing a depression in the top of the castings, blow-holes are caused CAST IRON III by dissolved gases. The greater portion of these gases passes out of solution during the cooling. This accumulates in small bubbles, which gather into larger ones as they pass upward through the molten metal. While the metal is liquid they escape, but when the crust forms the bubbles are arrested, and they now accumulate and form cavities in the softest portions of the viscid mass. The prevention of these defects in castings will be studied in connection with steel casting. Fig. 40. Grading. Like all other forms of iron the properties of cast iron depend principally upon its composition. It generally con- tains the elements, carbon,, silicon, sulphur, phosphorus and man- ganese, which in their varying proportions to the iron, and to each other, afford the possibility of numerous varieties or grades, differing in properties.. In the manufacture of castings for var- ious purposes these different grades of iron are used. A great many manufacturers base their selection of pig iron for castings largely upon the appearance of the fracture, which is to a certain extent, an index to the composition and properties. This relates specially to carbon and silicon. The analyses and properties of several commercial grades of pig iron have been given by J. M. Hartman, 1 as follows : 1 Jour. Frank. lust., 134, 132-144. 112 METALLURGY Grade 12345 6 Iron 92.37 92.31 94.66 94.48 94-oS 94.68 Graphitic Carbon 3.52 2.99 2.50 2.02 2.02 Combined " 0.13 0.37 1.52 1.98 1.43 2.83 Silicon 2.44 2.52 0.72 0.56 0.92 0.41 Phosphorus 1.25 1.08 0.26 0.19 0.04 0.02 Sulphur 0.02 0.02 ... 0.08 0.04 0.02 Manganese 0.28 0.72 0.34 0.67 . 2.02 0.98 No. I. Gray, with a large, dark, open-grain fracture; softest of all the numbers, and used exclusively in the foundry. Tensile strength and elastic limit very low. No. 2. Gray, with a mixed large and dark grain; tensile strength, elastic limit and hardness greater than No. i, and the fracture smoother. Used exclusively in the foundry. No. j. Gray, with a small close grain ; tenacity, elasticity and hardness superior to No. 2, though more brittle. Used either in the rolling mill or the foundry. No. 4. White background, dotted closely with small spots of graphite (mottled iron), and little or no grain to the fracture. Tenacity and elasticity lower than No. 3, but hardness and brit- tleness increased. Used exclusively in the rolling mill. No. 5. White, with smooth grainless fracture; tenacity and elasticity much lower than No. 4, and still harder and more brit- tle. Used exclusively in the rolling mill. The general effects of the common elements in cast iron may be summed up as follows: Carbon, in the combined form, im- parts strength and hardness, excessive amounts causing brittle- ness. It lowers the melting point and produces a light, granular fracture. Silicon lowers the melting point and renders molten cast iron more fluid. It acts as a "softener" in white cast iron, in which it causes the precipitation of graphite. High percent- ages of silicon cause brittleness and weakness. Silicon con- duces soundness and to a large extent prevents the formation of blow-holes in castings. Silicon irons have^characteristic, crystal- line fractures. Sulphur is generally very objectionable in cast iron, since it causes brittleness and general weakness. As much as 0.25 per cent, is usually allowable. Phosphorus in large pro- portions develops extreme brittleness and weakness. The shrink- CAST IRON 113 age of cast iron during cooling is considerably lessened, and it remains fluid longer if much phosphorus is present. Greater smoothness may be brought about on the surface of castings by the use of phosphorus. The range of phosphorus in ordinary cast iron is from 0.5 to 1.5 per cent. Manganese, in the normal proportions of 0.2 to I per cent., is beneficial in cast iron, in- creasing its hardness and density and suppressing the formation of blow-holes. Excessive amounts of manganese develop brittle- ness. It should be borne in mind that none of the properties of cast iron are affected entirely by a single element. They may be influenced by the like or counter effects of two or more elements. IRON FOUNDING No elaborate equipment is necessary to the manufacture of iron castings. A melting furnace and molds are needed, and these under shelter, with plenty of room for carrying on the work. A foundry plant, however, may include pattern-making and machine shops and other equipment. A brief description of the methods of melting and casting in general use is here given. Melting. Iron for castings is most commonly melted in a cupola. This is a small, cylindrical blast furnace, built of steel plates and lined with fire-brick. Fig. 41 represents a style of cupola in general use. It is provided with two working doors, tap-holes for the iron and slag and a double row of tuyeres, to which the air is supplied by way of an annular blast box. The walls are contracted at the top, the shaft terminating in a stack. Sufficient explanation of the details are given in the figure. The cupola charge is made up of alternate layers of iron and fuel (generally coke), with enough limestone added to flux the ash. The blast is cold and at a pressure of but a few ounces. It is generally supplied by a fan or a blower of the Root type. A little more than 100 pounds of coke are required to melt a ton of iron. It is desirable to keep the fuel consumption as low as possible, for the sake of economy and to prevent, as far as possible, the further addition of impurities to the iron. The rate of melting depends upon the size of the cupola, the blast pressure and the composition of the iron. METALLURGY Tfepnkoltod Swinpij DtmfK wiik PW, fcta. DunpwRod. Mica PNP lob ia ItemonMe PltH. blidt Shtll. Section on Upper Tiiyere STANDARD WHITING CUPOU Fig. 41. CAST IRON H5 The iron tapped from the cupola will not be the same in com- position as the charge of pig iron. A part of the iron is oxidized (burnt) before fusion takes place, and this takes some of the silicon with it into the slag. There is also a loss of manganese by oxidation, and the carbon may be largely changed from the graphitic to the combined form. Sulphur and phosphorus may be partially removed, or more absorbed from the fuel, depending upon the conditions. Reverberatory furnaces are used instead of cupolas in some foundries. Contamination from the fuel is thus avoided, and the entire charges being put in and tapped alternately, the iron can be mixed as desired and the composition controlled. The atmosphere of the furnace is made reducing by regulating the supply of air and directing the flame downward on the metal. The fuel may be either soft coal or gas. This way of melting iron is slow and expensive, the fuel consumption being very high. Mixing Iron in the Foundry. While it is true that the composi- tion of iron may vary considerably without apparent loss of strength, the best castings are made from iron that is mixed to a definite composition, as the tests go to prove. Foundrymen are now conducting an industry on a scientific basis, which for many years had recognized no need for scientific aid. The heavy strains to which castings are now often subjected calls for the best that can be made and these to be the best must ha ve the proper composition, as well as the proper shapes and thicknesses. It is not possible always to draw the supply of iron of the composition desired from a single source. Most foundrymen keep several brands in stock from which to make their mixtures. Some require the analysis with all the iron they buy. With the analyses furnished, the mix- tures of the composition desired may be calculated, due allowance being made for the losses during fusion. It not infrequently happens that the required amounts of sili- con and manganese can not be maintained in the charge, owing to the loss of these elements in the cupola. The deficiency may be restored by adding these substances in the form of rich alloys after the iron has been tapped (p. 149). As is well known, the very ingredients which give desirable properties to a metal are 1 1 6 METALLURGY most injurious when present in excessive amounts. If in making a mixture of pig iron, it is found that there is too much impurity, this may be corrected by melting relatively pure iron with it. Old material such as rails, boilers and machinery are cut in pieces that can be handled and sold as "scrap." A quantity of such mate- rial may be judiciously used for the above purpose. The use of scrap is specially to be recommended with iron high in silicon. Casting. Iron is most commonly molded in sand or clay. Chills are molds made of cast iron, and are used to develop sur- face hardness. Sand. The sand used in a foundry is known as "green" or "dry." By the former term it is meant that the Sand is moist enough to cohere under slight pressure. In making a green sand mold a pattern in wood is prepared corresponding to the shape of the casting. The pattern is made larger than the casting on account of the shrinking of the iron. 1 The pattern is placed in the proper position and sand is carefully packed around it. Except in case the casting is to be a very large one, the sand is held in a portable frame or box, made of iron or wood and in sections which can be removed to take out the casting. Air vents are necessary in such parts of the mold as would be blocked from communication with the mouth by the inflowing metal ; otherwise the expansive force of the air would destroy the mold. For hollow castings a "core" is needed. This is made of sand and it is supported by small wires in the proper position to form the interior of the casting. When a great many castings are to be made from the same pat- tern, machines are used for making the molds. Dry sand molds are made with sand containing enough clay to make it coherent when baked. The mold is shaped roughly in the moist sand, and it is finished with a tool after baking. No pat- tern is needed in making dry sand molds, and they are cheaper than wet sand if but a single casting is to be made. They also have the advantage of making a smoother casting, since water vapor and other gases are not evolved when the hot iron comes in contact with the sides. 1 The pattern maker uses a " shrink rule," which is ^ inch longer than the ordinary foot rule. CAST IRON 117 Loam. This is a clayey mixture to which carbon is often added. It cements much better than sand does when baked, and it is used in molds whose walls must be firm and not be eroded by the run- ning metal. It is especially adaptable to the molding of large, hoi- Fig. 42. low castings, when the metal has to travel some distance before reaching every part of the mold. They are used exclusively in the Fig. 43- manufacture of sewer pipes. The molds are made by hand with the aid of some machinery, and are usually faced with a carbon- aceous material. Since loam molds can be used but once, loam castings are more expensive to manufacture than sand castings. Chills. The conditions under which gray iron is changed to white iron are recognized in the manufacture of chilled castings. A chilled casting is made from gray iron, but the outer portion, Il8 METALLURGY or a part of it, is rapidly cooled to a certain depth, producing white iron in that portion. This is accomplished by using molds made of cast iron, which cools the surface by reason of its high conducting power. The section (Fig. 42) shows the method of casting a roll from the bottom, using chill plates for the body of the roll and sand for the ends. The effect of the chill is shown by the sketch (Fig. 43) in which the graphite is represented by the pen dashes. The depth of the chill is determined somewhat by the composition of the iron. A deep chill is secured by using a mold with very thick walls. The uneven cooling of a roll sometimes causes internal stress sufficient to crack it. Malleable Castings. By a special process of annealing, tough- ness and malleability may be developed to a remarkable degree in white cast iron. In this way castings are made to answer for lorgings in many cases, the casting being cheaper to make. The castings must, in the first place, be of the proper grade of iron. The carbon must be almost or entirely in the combined form, and it should not fall below 1.50 per cent. The silicon should be below one per cent., the sulphur not over 0.025, and the phos- phorus under 0.25 per cent. The castings to be annealed are first cleaned of any adhering sand, and then carefully packed in iron boxes with hematite, iron scale or a slag rich in oxide of iron. The material should be fine but not powdered. The boxes are made with removable bot- toms. The tops are covered with an iron lid or luted with mud. When packed the boxes are placed in the annealing oven, which is heated by a direct flame. The temperature of the oven is main- tained at about 700 C. for three days, or longer, depending upon the size of the castings. Another day is required for cooling the oven, it being essential that the cooling proceed slowly. The principal change that takes place in the annealing process is the conversion of combined carbon into graphite. The graphite is not, however, of the form observed in gray cast iron, the flakes being very small and evenly distributed. About 20 per cent, of the carbon is burnt out during the annealing, and some sulphur CAST IRON 119 is eliminated. The iron oxide used in the annealing box is par- tially reduced, some being entirely spent in each operation. The wasting away of the box furnishes good packing material, which is utilized. Testing Cast Iron. With the increased knowledge of the pro- perties of cast iron and the relation of these properties to its composition, and with the higher duty that is required of cast iron in the progress of manufactures, naturally the methods of testing it have been improved. It is recognized and understood that the properties of cast iron are directly dependent upon its composition. Practically all the pig iron, that is made for foundry purposes, is graded by the smelter according to analysis, for he expects to sell his product in this way. But the analysis does not reveal all. In many instances more practical knowledge of the quality of iron is gained from the me- chanical test than could be interpreted from its composition. These tests are made, as far as possible, to imitate the stresses that will be put upon the iron in actual service. The strains that are ex- erted during the testing are measured and recorded. They are usually increased until the test-piece is broken, showing the ulti- mate resistance. The test is either made upon a finished casting, which represents a number of other similar ones, or upon a spec- ially prepared piece of convenient form. In either case the test- piece is taken from the same lot of iron as the castings which it represents. Testing by the first method gives a direct value, while the latter method gives only the relative value. The tests most commonly applied to cast iron are two trans- verse and impact. Transverse Testing. This shows the resistance of the metal to cross breaking. It represents a condition that is most common in actual service. It is applied by supporting the test-bar at both ends, and applying weights in the middle until it is broken. Impact Testing. This shows the resistance offered to shocks or blows. It is applied both directly and indirectly. When the material in question is in the shape of castings from the same pat- tern, and such that can be submitted to the test, it is usually made directly. Otherwise a test-piece of convenient size and shape is I2O METALLURGY used. The test is applied by allowing a hammer of definite weight to fall from a certain height, or if supported like a pendulum, to swing through a certain distance, and strike the iron. The dis- tance of the fall is increased until rupture occurs. Note. The Pennsylvania Railroad requires the following test for car wheels : From each lot of 50 wheels one is selected for the test. It is placed flange downward on an anvil block weighing 1,700 pounds. The block is set on rubble masonry two feet deep. It has three supports, not more than five inches wide, for the wheel to rest upon. The wheel is struck centrally, on the hub by a weight of 140 pounds, falling from a height of 12 feet. If the wheel breaks in two or more pieces, after eight blows or less, the fifty wheels represented by it are rejected. If the wheel stands eight blows without breaking, the fifty are accepted. The test- wheel is furnished by the manufacturers with each fifty ordered. 1 In addition to the above tests for cast iron, tests of tension and compression are sometimes made. The tension test is chiefly used for iron made into steam or air cylinders. Compression tests are rarely needed, since cast iron is not often weak in this respect. The hardness is sometimes tested in iron that is to be machined. Turner's method of making this test is to determine the weight that must be brought to bear upon a standard diamond point to make it scratch upon the polished surface of the iron. 1 Iron Age, 48, 292. CHAPTER XII WROUGHT IRON Historical. The origin of wrought iron is not known. It is probably the form in which the metal was first prepared, though the practice of hardening iron with carbon is also of unknown origin. So far as there is any evidence, the primitive method for making wrought iron was to reduce it with wood direct from the ore in small, rude furnaces. The air supply was furnished by natural draft, or by means of rawhide bellows operated by hand a process still used in Africa and India by the savage tribes. Throughout civilized Europe, where the iron industry was really developed, various forms of forges were instituted, their product being malleable iron. Most notable among these was the Catalan forge, which the illustration represents (Fig. 44). The term hearth is also used to designate this type of furnace. The furnace was built of brick in the form of a shallow hearth with no stack. A blast of air was supplied through a single tuyere, by means of a water blower known as the trompe. The water was allowed to fall from a reservoir, through a tall pipe, into a blast box, as shown in the drawing. Small openings were made in the pipe near the top for the admission of air. The air was drawn in through these openings by the suction, and passing with the water into the box it was there slightly compressed. The air for the blast was drawn from the top of the box, and the water was allowed to flow through an opening at the bottom. The trompe was built almost entirely of wood. The ore mixed with burning charcoal was re- duced to spongy iron. The American bloomary is a more highly developed type of forge. Fig. 45 shows a bloomary half in section and half in ele- vation. The chief differences between this and the older forges are in the tall stack above the hearth and the arrangement for heating the blast. The hearth is enclosed partly by brick work and partly by water-cooled, iron blocks. The stack is built of brick and reenforced with iron. The blast is led through pipes 122 METALLURGY (commonly three), which are bent to fit in the stack as shown. The blast may acquire a temperature of 400 C. or more. The blast is delivered to the hearth by a single tuyere. The iron ore is reduced in contact with burning charcoal, the iron being removed Fig. 44- from the hearth in the form of a spongy mass or bloom. It is possible, however, by increasing the temperature to make cast iron in the bloomary. 1 Furnaces of the above type have also been used in Germany and other parts of Europe. They mark the transition between the forge and the modern blast furnace. About the year 1784, Henry Cort invented the indirect or pud- dling process for making wrought iron from pig iron. 1 The American bloomary is illustrated, and the process fully described by T. Egleston in Trans. Atner. Inst. Min. Eng., 8, 515 WROUGHT IRON 123 Properties. The better grades of wrought iron represent the purest form of commercial iron. The properties, therefore, most dearly approach those of pure iron. It is recognized by its tough- Fig. 45- ness, combined with softness, and especially by its fibrous fracture. The filaceous structure is developed during the forging of the iron by reason of intermingled slag. Wrought iron is the smith's favorite, it being the easiest to forge and weld. It is well adapted to the manufacture of thin 124 METALLURGY sheets, owing to its malleability. It is said that wrought iron wil! riot stand vibrations so well as iron containing carbon. 1 MANUFACTURE OF WROUGHT IRON As was pointed out in the historical sketch, wrought iron may be prepared from the ore by a single operation, or from pig iron by a refining process. These are known as the direct and the in- direct processes. The latter process is more commonly termed puddling. Direct processes have been practically abandoned, and no further space will be given to their description. It is worthy of mention in this connection, however, that pure iron and steel have been made directly from the ore in electric furnaces. Whether or not these experiments have any commercial value remains to be proved. The Puddling Process. A great deal of importance is attached to the process about to be described, not so much for its direct bearing on the metallurgy of iron, but because the principles in- volved are essentially those underlying all iron refining processes. A study of the simple experiment, as outlined below, will give the student the keynote to the theory of puddling. The sections A and B (Fig. 46) represent the muffles of a small, gas-fired furnace. The atmosphere in these muffles is oxi- dizing, and the temperature can be raised above the melting point of pig iron. In muffle A, is placed a brick, and upon this is placed a piece of pig iron. In B another piece of pig iron is placed upon the bottom of the muffle, clay or sand being packed around the piece to form a basin as shown. The temperature of the muffles is now raised and kept just below the melting point of the iron. The surface of the pigs soon becomes coated with oxide of iron. The silicon is also oxidized, and combines with the ferrous oxide forming a fusible slag (ferrous silicate). This runs away leav- ing the surface of the metal exposed to further action. The carbon in the iron is converted into carbon monoxide, and then into car- bon dioxide which escapes. The manganese is oxidized like tht iron and passes into the slag. Now it is seen that if there is enough silicon in the pig to combine with all the iron and form a fusible slag that will be the ultimate result of the experiment in 1 Trans. Amer. Inst. Min. Eng., 26, 1026. WROUGHT IRON 125 muffle A. The result in muffle B will be different, since the slag covers the iron and protects it from further oxidation. If when -enough slag has formed, the temperature is raised to melt the iron, the impurities will be removed by the oxidizing power of the slag. The slag is mingled with the metal so as to bring the impurities into contact with it. It must obviously become richer in silica and poorer in ferrous oxide than the slag in A. The carbon in the iron has a reducing action with the ferrous oxide in the slag. By virtue of this, the carbon is removed and the metallic content of the charge is increased. Since purification raises the melting point of iron the metal in B is left in a plastic state. Fig. 46. The essential difference between the above experiment and the puddling process, is that in puddling most of the oxide is sup- plied from another source and not derived from the iron. Dry Puddling. This name has been given to Cort's original process, because no slag forming substance was added with the metal charge. His furnace was a small reverberatory having a sand or silicious bottom. As would be expected, the hearth was badly fluxed with each heat. It was considered necessary that the iron be low in silicon. Such iron does not become so fluid in the puddling furnace, and much less slag is formed. Gray iron, liigh in silicon, was therefore subjected to a partial refining before puddling. The description given below of the refining process or "Running Out Fire," is taken from Percy's Metallurgy. "The refinery consists essentially of a rectangular hearth, with three water tuyeres on each side inclining downwards. The sides and back are formed of hollow iron-castings, called 'water-blocks,' through which water is kept flowing, the front of a solid cast iron plate containing a tap-hole, and the bottom of sand resting on a solid platform of brick work. Coke is the fu,el used with cold blast blast at a pressure of three pounds per square inch." "The refinery being in operation, the folding doors at the back 126 METALLURGY are opened and coke is thrown in, the charge of about one ton 01 one ton, two cwts. of pig iron is placed upon it and heaped over with coke, after which the blast is let on. The operation is facilitat- ed by the addition of 30 pounds of hammer-slag or scale. The metal, which melts in about one and one-half hours, is then ex- posed to the action of the blast, which is strongly oxidizing, not- withstanding the superincumbent layer of incandescent coke. A considerable quantity of cinder is formed, consisting for the most part of tribasic silicate of protoxide of iron. In about two hours after charging, tapping occurs, the blowing usually lasting about one-half hour. The consumption of coke is about four cwts. Cinder and the molten metal flow out together along the run- ning-out-bed in front, the cinder, of course, forming the upper- most stratum. This bed being refrigerated, as previously stated, the metal is speedily consolidated. Water is copiously thrown over the whole, while the accompanying cinder is still liquid, when the latter puffs up into beautiful little volcano-like craters : and it is curious to watch the molten cinder and water dancing r as it were, together ...... The water, which may be conven- iently applied in a strong, jet, promotes the separation of the cinder from the metal. The cinder is thrown aside to be either smelted or used for certain other purposes ; and the metal, usual- ly about three inches in thickness, is removed and broken up in pieces of the proper size for puddling. The metal is white cast iron." Pig Boiling Process. This is the modern puddling process. It takes its name from the fact that the bath of metal and slag arer very liquid at a certain stage, and the escape of gases gives the boiling effect. The chief difference between modern puddling and the older methods is in the use of a fettling of iron oxide on the furnace hearth, from which oxide is supplied to the slag in- stead of its being supplied entirely by the oxidation of the metal. Credit for this invention is given to Joseph Hall, who is said to- be the first to use the fettling (1830). The sectional elevation of a common type of puddling furnace is shown in Fig. 47. This is a small, direct-fired reverberatory furnace. The grate, G, is rather large in proportion to the size WROUGHT IRON 127 of the hearth, H. The flame from the fuel bed passes over the fire-bridge, A, and is deflected upon the hearth by the low roof. The products of combustion pass into the tall chimney, C, by which a strong draft is maintained. The furnace is provided with a single working door at the side, which serves both for introduc- ing and withdrawing the charge. Puddling furnaces are some- times fired with gas and oil, though the coal-fired type is the most common. The hearth of the furnace is thickly lined with iron ore, roll scale or rich, ferruginous slag. The fettling, as it is called, ex- Fig. 47- tends up the sides from the hearth, so that it will be well above the surface of the bath when a charge has been melted. Before charging, the melter examines the hearth of his furnace and makes the necessary repairs to the fettling. This must of necessity be renewed often since it not only acts as lining, but is also the flux. The furnace being ready some slag from a previous operation is first charged. The charge of pig iron usually weighs about four and one-half tons and is charged cold. The process is de- scribed as progressing in four stages ; viz., the melting down, the quiet fusion, the boiling and the balling up. 128 METALLURGY 1. The Melting Down. This begins soon after the iron has been charged, the temperature of the furnace being raised as rap- idly as possible. Fusion is further hastened by turning the pigs over and stirring them in the slag that forms. 2. Quiet Fusion. When fusion is complete the bath is thor- oughly rabbled, bringing the metal into more intimate contact with the fettling. It is during this stage that the silicon is almost completely removed. No little skill is needed, on the part of the melter in determining when the silicon has been completely trans- ferred from the metal to the slag. He learns to judge this from the appearance of the bath. The manganese is also largely re- moved during this stage. 3. The Boil. So far, most of the carbon has remained in the iron. Its removal is hastened by first cooling the furnace until the slag becomes more viscous and will not separate so quickly from the metal, and_then by stirring the bath thoroughly to mix the slag with the metal. Since the slag is now rich in iron oxide, this reacts rapidly with the carbon, as is evident from the evolution of gases from the surface of the bath. The carbon monoxide that is formed takes fire with its characteristic pale-blue flame the in- stant it bursts from the surface of the slag. The reactions cause a rise in temperature and the slag becomes more liquid. The large amount of gas escaping during the removal of carbon gives rise to the boiling effect. There is also a swelling of the charge, the slag rising several inches up the sides of the furnace, and often flowing out the door. A quantity of slag may be drawn off at this time, and the difficulty in handling the metal at the end of the operation will be lessened if the bulk of slag is reduced to the- least that is necessary. The boiling diminishes with the removal of the carbon, and when the bath becomes quiet the operation is finished. 4. The Balling Up. The iron is now in the form of a por- ous, unfused mass, in which a quantity of slag is still incorporated.. The melter breaks up the cake of metal with a bar, and then manipulates the pieces on the hearth of the furnace until they be- come somewhat rounded or roughfy shaped into balls. This is done for convenience in handling, the balls weighing about 75 pounds- WROUGHT IRON 129- each. These balls of wrought iron, being now at the temperature for welding, are taken from the furnace, grasped with tongs sus- pended from an overhead carrier, and placed under the hammer or in the squeezer for removing the slag. The principal of the rotary squeezer for wrought iron blooms is shown in Fig. 48. A heavy cast iron cylinder revolving with- in an eccentric shield in the direction indicated by the arrow car- ries a ball around, revolving it in the opposite direction. The cor- rugated surfaces of the cylinder arid shield prevent the ball from slipping while it is forced into the diminishing space. The rolling of the bloom is conducted in a manner similar to the rolling of steel ingots (chapter XVI). Fig. 48. Modifications of the Puddling Process. Although permitting of many alterations, the practice of iron puddling, with the excep- tion of one important advancement, has continued essentially the same since its inception. The more common practice, jiist des- cribed, looks mainly to the removal of carbon, silicon, manganese and some phosphorus. In some special high grades of iron it is required that the phosphorus be practically eliminated. This is ac- complished by the use of a basic slag. The slag may be rendered basic by increasing the percentage of ferrous oxide, or by adding lime. Soda ash (impure carbonate of sodium) has been employed with small quantities of iron for the removal of phosphorus and sul- 5 130 METALLURGY phur. While iron may be desulphurized with mixtures contain- ing soda ash, this material is far too expensive to use on the large scale. A mixture of manganese dioxide and salt is sometimes added to the charge at the beginning of the heat. This renders the slag more liquid and more strongly oxidizing, favoring the removal of phosphorus and sulphur. Mechanical Puddling. Many attempts have been made to con- struct a puddling furnace which can be rocked, tilted or revolved by machinery, thus bringing about the disturbance of the bath in- stead of stirring it by hand. Such a furnace would be desirable from more than one point of view. The labor of a puddler is exceedingly severe and might well be dispensed with ; the process might be cheapened by doing away with such expensive labor, and the output would be increased, assuming that more material could be treated at the same time. The mechanical furnace has not, however, proved entirely satisfactory, and most of the wrought iron is still made by the brawn and skill of the puddler. A me- chanical furnace has been designed and used for some time by J. P. Roe, of Pottstown, Pa. 1 1 Trans. Atner. Inst. Min. Eng., 33, 551, also Iron and Steel Inst. Jour., 1906, 3, 264. CHAPTER XIII STEEL THE CEMENTATION AND CRUCIBLE PROCESSES Definition. When steel was manufactured solely by the cemen- tation and crucible processes, it was understood as refined iron to which a definite amount of carbon had been added. If it contained less than 0.5 per cent, of carbon it was known as "mild steel," while the hardest steel contained 1.50 per cent, of carbon. Since the introduction of the Bessemer and open hearth processes for making steel, the term has had a wider meaning. By these pro- cesses iron practically saturated with carbon, and iron that is al- most free from carbon may be prepared, but the product is always designated as steel. Furthermore, there are now on the market a number of alloys of iron with other metals, all of which are known as steel, so that the term as now used does not signify any special composition. Since there are now among civilized nations four distinct processes in use for its production, steel may be de- fined as iron that has been refined by one of these processes ce- mentation, crucible, Bessemer and open hearth. THE CEMENTATION PROCESS When iron and carbon are placed in contact and heated to about 600 C., they combine slowly, the carbon penetrating the iron to a greater depth as the heating is prolonged. This phe- nomenon is known as cementation. The process of cementation is one in which the commercially pure iron is heated without fusion in a suitably constructed furnace, and in contact with solid car- bon, until the required amount of carbon has been absorbed. The Furnace. Fig. 49 shows the cementation furnace in sec- tion. The rectangular converting pots or boxes, in, which the! iron is carburized, are built of fire-brick or stone. They are heat- ed by means of flues, F, leading from the fire-place, G, under- neath the boxes and up their sides. The flues terminate in the short chimneys, C. Air is excluded from the boxes by the arched roof of fire-brick, and the entire furnace is enclosed in a conical -- ^^* v^ OF T Ht ^X ; ! V i? D O i T- vr a 132 METALLURGY stack. The manhole and the charging holes, H, are bricked up during the operation. The test bars are drawn from the boxes through the small ports, T. Fig. 49. The Process. The steel is made from selected bars of the pur- est commercial iron. Wrought iron is preferred, though Bes- semer and open hearth steel are sometimes employed. The bars are placed in layers in the fire-brick boxes or pots, and between the layers charcoal free from dust is packed. Each set o-f bars is placed at right angles to those in the layer below, and a covering of charcoal is put over the last layer when the box is full. The boxes are made to hold from 10 to 15 tons of bars. The boxes having been filled and air excluded from the charge, the fire is lighted and the temperature of the furnace is slowly raised until the maximum is reached. This requires about 48 hours. The heating is continued for from 4 to 10 days, depend- ing upon the amount of carbon wanted in the steel. The degree 133 of carburization is ascertained from time to time by taking out a bar through the port provided and examining its fracture. When the process has proceeded as far as desired, the fire is drawn, or allowed to die out, and the furnace cools slowly. Within five days the furnace may be entered and the bars, which are now carbon steel, are removed. The carbon, however, has not been uniformly distributed throughout the bars. The outer portion may be saturated, while the center is almost free from carbon. It now remains to convert these bars into steel of uniform com- position. They are cut into convenient lengths, and these are bundled, heated to the welding temperature and forged into a single piece. The metal is first coated with a wash of clay and borax, which checks oxidation and serves as a flux, giving a clean surface for welding. Having been cut and welded once, the steel is known as "single shear." A higher grade of steel is made by cutting up the bar and welding as before, this being termed "double shear" steel. As some carbon is burnt out during the re- heating, the bars to be sheared are selected which contain more carbon than is required in the finished product. It is possible to combine a little over two per cent, of carbon with iron by cementation. A further addition would require a higher temperature, which would result in the fusion of the steel. It is not known whether the carbon diffuses through the iron as carbon, or as a carbide of iron. It is probably similar to the mi- gration of carbon in other instances, but wherein the conditions are different, as in chilled and malleable castings. If the steel has been converted from wrought iron the surfaces of the bars, as they are drawn from the furnace, are covered with blisters. This has given rise to the term "blister steel." The cause of the blisters has been satisfactorily explained by Percy. The ferrous oxide, which is always present in wrought iron, is reduced by the carbon with the formation of carbon monoxide, and the gas, seeking its escape, distorts the plastic metal. Cement steel that is made from iron containing no oxide or slag is not blistered. The output of cement steel is relatively very small. It still holds its own in the manufacture of some tools and machinery 134 METALLURGY pieces, but the cheaper processes have obliterated any future for it. The most famous works are at Sheffield, England. THE CRUCIBLE PROCESS Modern steel manufacture may be said to have begun with the crucible process. Although steel had been converted in a molten condition before this time, it had never been cast as is done in the crucible process, and other important details were lacking. The term "cast steel" was significant at the time that steel was made either in the cementation furnace or in the crucible. The crucible process is the invention of Benjamin Huntsman, an English manu- facturer. His first plant was erected at Sheffield and put into operation about I74O 1 The process was in every essential the same as it is to-day. Crucibles. Steel melting crucibles are generally manufactured from a mixture of clay and graphite. Graphite alone is not cohesive enough to make x a strong crucible and is expensive, while clay crucibles have too great a tendency to shrink and crack when in use. Clay crucibles are preferable for soft steel since their walls do not give up carbon to the charge. As a rule, they do not last for more than one melting. The graphite crucibles are much more durable. A good crucible of American make con- tains about 50 per cent, graphite, 40 per cent, clay and 10 per cent. sand. Ceylon graphite is considered the best for crucibles. Other materials have been substituted for natural graphite. Kish and coke dust are used, and old crucibles are regularly ground and mixed with the new material. The clay and the graphite for the crucibles are ground and then mixed. After making the clay into a thin paste with water the graphite and sand are sifted in. The thickened mass is then mixed in a pug mill and allowed to stand for a few days. By allowing it to' stand, or tempering as it is called, the clay loses some water and incorporated gases and becomes stiffen It is now ready to be turned into crucibles. A lump of the clay is kneaded and thrown into a plaster of Paris mold, corresponding in shape to the outside of a crucible. The mold is centered on a potter's wheel, and as it revolves a 1 Jour. Iron and Steel Inst, 1894, 2, 224. STEEL 135 knife blade is lowered into the clay to form the interior of the crucible. The knife is set at the proper angle to force the clay upward and against the walls of the mold. The top of the crucible is trimmed, and it is allowed to remain in the mold for about three hours. During this time the porous plaster absorbs so much water from the clay that it is left rigid enough to stand up. The crucible is dried for a week, and is then ready for firing. It is enclosed in a shell of two clay seggars and placed with other crucibles in a potter's kiln. Both the rise and fall of temperature during the firing are carefully controlled, as sudden changes would weaken or fracture the crucibles. The temperature of the kiln should be at least as high as that of the furnace in which the crucibles are to be used. The Melting Furnace. The furnaces used for melting steel in crucibles are often of very simple construction, consisting es- sentially of a melting hole in which the crucibles are placed, and in which coke is burned, and a tall chimney for creating a draft. The melting hole is covered with a fire-clay lid during the opera- tion. Gas-fired furnaces, employing regenerators are also in use. The Process. Each crucible receives a charge of from 60 to 90 pounds of metal. The materials converted are wrought iron or steel made by one of the cheaper processes and pig iron. The pig iron serves as the carburizer, or charcoal or anthracite may be used instead. A little oxide of manganese is usually added, and sometimes a "physic" such as salt, potassium cyanide, etc., is used. The crucible is covered and placed in the melting hole of the furnace. Some time after the charge has fused the melter takes off the crucible lid and examines the contents with the aid of a rod. From the appearance of the slag and certain other indications he determines when the crucible should be with- drawn from the furnace. The crucible is lifted out by means of tongs, which are made to encircle it a few inches below its largest diameter, giving support to its sides. The steel is usually allowed to stand for a few minutes before pouring. This is termed "killing," as it serves to quiet 136 METALLURGY the metal. 1 The steel is then slowly poured into the ingot molds, and the crucible is thrown aside for inspection. A crucible lasts for from four to six heats. The molds, just referred to, are com- monly about 30 inches long and three inches square inside. They are made in two pieces, the joint running lengthwise, and held together with rings and keys. This mechanism facilitates the removal of the ingot after it has cooled. The large molds are of one piece. In case the contents of one crucible is not enough to fill a mold, two or more heats are poured at the same time. The ingots are reheated to the forging temperature and rolled or hammered into the shapes desired. About 10 per cent, of the steel is rejected in the mill on account of piping in the in- gots. It is not possible in the crucible process to determine the amount of carbon that should be added to a charge to produce the grade of steel desired, since the losses are not constant. It is therefore necessary to estimate the carbon in the steel after it is made and to grade it accordingly. The fracture test is here made use of to great advantage. The tops of the ingots are broken off and the fractures examined by a skilled inspector. The superior quality of crucible steel is due to the selection of high grade materials to begin with as well as to the process itself. With so small an amount of metal, and that in a closed vessel, the composition of the charge and the temperature of working can be almost completely controlled. The occlusion of gases is largely prevented by these conditions and by the manner of pouring, which is to allow the metal to run in a very small stream. 1 The same result is arrived at by adding silicon or aluminum to the charge and pouring immediately. CHAPTER XIV STEEL THE BESSEMER PROCESS ACID History. The Bessemer process fittingly bears the name of the illustrious inventor, Henry Bessemer. The process is not, however, the invention of a single man, but of a number whose names should be as closely linked with it as that of Bessemer. The original idea was not to make steel directly by this process, but to make wrought iron, from which steel was to be converted. Wm. Kelly was the first to show that pig iron could be purified by blowing air through it while in a molten state. Kelly's in- vention was what he termed a "Pneumatic Process" for making 1 malleable iron. He first carried out his idea at Eddyville, Ky., in 1847. About ten years later he built a tilting converter for the Cambria Steel Works, at J6hnstown, Pa., where it has been preserved. His lack of financial backing prevented Kelly from making a commercial success of the process he had originated. However much may have been suggested to Bessemer, no one can doubt that the unique construction of plant and the details of the process were his own achievement. The result of Besse- tner's experiments were first made public in a paper before the British Association, in 1856. He termed his invention "The Manufacture of Malleable Iron and Steel Without Fuel." The success of the process was no less a surprise to the inventor than it was to other metallurgists, though it had failed as yet to con- vert iron into steel. The product was simply iron from which the impurities, except sulphur and phosphorus, had been remov- ed, and this was often red-short and difficult to work. After some unsuccessful efforts to remove phosphorus Bessemer abandoned the idea, since he was able to buy Swedish pig iron which was practically free from phosphorus. The other diffi- culties were overcome by adding spiegel-eisen to the iron after it had been blown, the manganese correcting the red-shortness 138 METALLURGY and" the carbon producing the necessary hardness and tenacity in the steel. This very essential improvement was suggested by Mushet. The improvements in the building of Bessemer plants, and the development of the process are attributed largely to Alexander Holley, a famous, American engineer. The Iron Mixer. At the large iron and steel plants the iron is delivered to the steel works in the molten condition. It is run directly from the blast furnace into brick-lined ladles, which are mounted on railway trucks, and conveyed immediately to the Bessemer or open hearth shop. 1 It is obvious that a great sav- ing must be realized by converting the iron without further hand- ling or allowing it to cool. The ideal practice would be to pour all the iron directly from these ladles into the converters, and this would be done if the iron were always of the proper com- position, but this is not the case. The silicon, in particular, is too high in some casts and too low in others, making it neces- sary to mix the different grades of iron to obtain one of the proper composition for blowing. Remelting cupolas are gen- erally used in converting mills for the sake of having a reserve of hot metal. By skillful management it is possible to convert a good deal of iron "direct," the iron from the cupolas being mixed in the converters with the iron from the furnace. The difficulty is most completely solved, however, by the use of the hot metal mixer, an invention of W. R. Jones, of Braddock, Pa. The mixer is a large vessel, built of steel plates and lined with fire-brick. It has a circular bottom, and is mounted on rollers so that it can be revolved to pour out the contents. The iron is run in from a ladle through an opening near the top of the mixer, and is poured out from an opening on the opposite side. The capacity of the mixer is usually about 300 tons, which is the equivalent of three or four casts from a large blast furnace. The Converter. The section of a modern converter is shown in Fig. 50. The converter consists of an outer shell of heavy, 1 Hot metal roads have been built by the Carnegie Steel Co. from their blast furnaces at Braddock across the Monongahela River to their steel plants at Homestead and Duquesne. The molten iron is supplied to the Bessemer and open hearth plants at a distance of two miles from the blast furnaces. STEEL 139 cast steel plates and a thick lining of ganister or other acid re- fractory material. It is mounted on hollow trunnions, through one of which connection is made for the passage of the blast. The converter is made in three sections, any one of which may be repaired independently. The top section is held to the middle section or body of the vessel by means of bolts, and the bot- tom section is attached with hangers secured by keys, an ar- Fig. 50. rangement which permits of the bottom being renewed in a very short time. The converter is lined with ganister, mica-schist or other silicious material. The stone is ground and mixed with water for use as a mortar. The lining is made by setting the cut stone in the mortar, or by using the mortar exclusively. When the latter method is adopted the mortar is rammed in place after placing a wooden core to form the interior of the vessel. The lining is dried by a fire before the vessel is put into use. 140 METALLURGY The bottom is the weakest part of a converter. The lining in the upper and middle sections may need but slight repair dur- ing a year of constant running ; while the bottom lasts but for a few heats, usually 15 to 20. A number of bottoms prepared for immediate use are therefore kept on hand in converting mills. The construction of the converter bottom warrants special notice. As shown in the cut the blast is received in a cast iron box through a gooseneck, which is connected with the trunnion. The blast is let into the charge through a number of fire-brick tuyeres, which are set in openings in the metal top of the blast box and surrounded by the lining material. The tuyeres are perforated by numerous holes, about half an inch in diameter, through which the blast is delivered. In this way the blast is distributed through the charge at the moment it enters. De- fective tuyeres are plugged by turning the vessel down, remov- ing the blast box lid and tamping in clay from the bottom. Fig. 51 shows the method of rotating a converter, the dot- ted outline indicating the position for charging. A sliding rack, driven by a double-acting, hydraulic ram, meshes with a pinion keyed to one of the trunnions on which the converter rotates.. STEEI* 141 \\"ith this device the converter may be turned through an angle of 180 or more. A casting of iron prevents injury to the mechanism from slag ejected during the blow. The Process. The vessel is turned down to the horizontal position and a charge of 8 to 15 tons of molten pig iron is run in. The blast is turned on as the vessel is raised to the vertical position. A cloud of dense, brown fume is evolved, followed by a shower of sparks. A voluminous flame also ap- pears and vanishes with the cloud. This is followed by a shower of sparks, and then a short and not very luminous flame appears. As the temperature increases the flame grows in length and luminosity until at the end of about eight minutes it reaches the maximum of twenty feet or more, and is of dazzling white- ness. If the blow is continued the flame soon declines rapidly until it disappears. At the moment the flame drops, or before that time, the vessel is turned down and the blast is shut off. The ladle being in place, the mouth of the vessel is brought down until all the metal and most of the slag run out, and when the ladle is swung around the vessel is completely inverted to empty it of the remaining slag. The blower is guided by the appearance of the flame in deter- mining the time at which the blow should be ended. He w r atches it through stained glasses, and with remarkable precision he can tell when the carbon has been eliminated to the necessary degree. The usual practice is to stop the blow when the carbon has been diminished to 0.08 per cent., and if necessary, to carburize the steel after it has been poured into the ladle. The duration of a blow is from 7 to 14 minutes. The purer the iron and the higher the pressure of the blast the shorter will be the duration. The manganese is added to the steel as it runs into the ladle, or if much is required, it is added during the blow from an over- head chute. In ordinary soft steel (0.07 to 0.09 carbon) about 0.4 per cent, of manganese is generally added, which is suffi- cient to prevent red-shortness. If higher carbon steel is wanted the carbon may be added to the ladle in the form of anthracite coal, or more commonly, the steel is carburized with pig iron, if spiegel-eisen is used carbon is introduced with it, since it 142 METALLURGY carries about 4.00 per cent, of carbon. The ladle is hoisted by the crane and brought directly over the ingot molds into which the steel is poured. Fig. 52 represents a steel-pouring ladle with a part of the wall cut away to show the interior. The ladle is built of heavy, steel plates, rivetted together, and lined with two courses of fire-brick. It is supported on trunnions projected from the sides slightly above the center of gravity. The hole through which the steel is poured is situated in the bottom and near the side. The flow of steel is controlled by means of a stopper which is carried on a sliding device attached to the outer wall of the ladle. The stopper is raised and lowered by aid of a hand lever. The rod which is suspended inside the ladle to carry the stopper is protected from the molten steel by a fire-clay sleeve which is made in sections. The sections fit one into the other, and the joints are sealed with clay. Fig. 52. The slag from the acid converter consists chiefly of the sili- cates of iron and manganese, silica being far in excess. The con- verter lining is gradually fluxed away, adding silica and alumina to the slag. Any titanium present is oxidized and absorbed by the slag. Converter slag is often employed as a silicious flux in the blast furnace. It is difficultly fusible, being viscid at the temperature in the converter. Converter dust is a mixture of slag and metallic oxide which 143 is ejected during the blow. It also contains particles of iron. About 1.25 per cent, of the weight of a charge is thrown out with each blow. SiO 2 FeO MnO A1 2 O 3 P.O 5 Fe (Metallic) Converter Slag 64.0 15.0 12.0 1.5 0.007 7.00 " Dust 23.0 60.0 4.0 0.5 0.045 11-5 Theory of the Process. The chemical changes that occur in the Bessemer converter, though proceeding much more rapidly, are probably almost identical with those of the puddling process. The air entering through the multiple tuyere openings- is at once distributed throughout the charge, accounting for the rapidity with which the metalloids are removed. Carbon, silicon and manganese are almost completely removed, phosphorus and sul- phur remaining with the iron. If the blow is continued until the flame drops only about 0.03 per cent, of carbon will be left. The heat generated by the oxidation of the metalloids is more than sufficient to keep the steel in a molten condition. Most of the heat is derived from the oxidation of the silicon on -account of its high calorific power, and consequently, high silicon irons cause an overheating of the charge, leading to "wild heats." This may be prevented by lowering the pressure of the blast or by diluting the charge with cold steel scrap. Steam is often introduced into the blast for the same purpose. BASIC Some of the foremost metallurgists were early led to attempt the dephosphorization of iron in the converter. Bessemer him- self worked toward this end, though without success. The basic process, by which phosphorus may be practically eliminated, was finally worked out by Sidney Thomas with the assistance of Gilchrist, Martin, Stead and others. The essential feature of all basic processes for refining iron is in the use of a basic slag ? the lining of the furnace being necessarily of basic material. The basic converting plant is, in general construction and appointment, similar to the acid plant. The converter is of the same form, but is lined with dolomite in- stead of a siliceous material. The dolomite is first thoroughly calcined, then crushed and mixed with hot tar. The mixture 144 METALLURGY is either rammed into place, a core being used for shaping the interior, or it is pressed into bricks which are burnt at a low temperature and carefully set. The Process. The vessel is heated either from a previous charge, or if new, by means of a coke fire. Lime, equal in weight to about 15 per cent, of the weight of the charge, is first thrown in, then the metal is added and the blow follows. To all appear- ances the first part of the blow is in no way different from the *same period in the acid process. It is seen, however, that there is -more "boiling" and frothing of the charge from the amount of slag ejected. The blow is continued a few minutes after the flame drops, the oxidation of the phosphorus requiring a longer time than that of the silicon and carbon. The excess of lime absorbs the phosphorus rapidly, the phosphorus reactions being the main source of heat after the silicon is gone. With high silicon irons it is necessary to add more lime during the "after blow" to keep the slag sufficiently basic. High silicon iron is obviously not wanted for basic converters. As with the acid ; process the mixer is almost indispensable for keeping the iron of uniform composition. The iron should contain not less than 2 per cent, of phosphorus. But few basic Bessemer plants have been built in America. Most American irons are comparatively low in phosphorus, and most of the high phosphorus iron is used in the foundry. Plants have been erected at Troy, N. Y., and at Pottstown, Pa. Neither >f these are now in operation. CHAPTER XV STEEL THE OPEN HEARTH PROCESS This is the latest process that has been introduced for manu- iacturing steel. The work of William Siemens in England and of E. P. Martin in France was the foundation upon which open hearth practice has been built. Siemens was the first to em- ploy a reverberatbry furnace for melting and converting steel, the high temperature necessary being easily attained after he had developed the regenerative system of firing with gas. The principal feature in his process was the oxidation of the im- purifies in pig iron with iron ore, while that of Martin's method was in the use of soft iron or "scrap" with the charge of pig iron, and in making the necessary additions of carbon and man- ganese at the end of the operation. The work of these men was contemporary, having been begun in the early sixties, and the process which they put on so successful a basis is rightly called the Siemens-Martin process. The rapid growth of this method of steel making is due to the fact that high grade steel can be made from all grades of iron, and that the composition of the product is easily controlled. The open hearth process is divided, according to the practice, into the Acid and the Basic processes. ACID All open hearth furnaces are of the Siemens type. The sec- tional drawings (Figs. 53 and 54) show the principal parts of an ordinary open hearth furnace. The hearth is supported on I-beams resting on girders, which in turn, are supported on the masonry below. The regenerators, shown in Fig. 53, are for heating the air and gas before they enter the combustion cham- ber of the furnace. They are admitted into the regenerators on one side while the products of combustion are heating those on the opposite side. The products of combustion are led first into dust chambers (not shown in the drawings), which prevent the 146 METALLURGY larger portion of the dust and slag, carried over by the draft, from clogging the checker-work. The products of combustion Fig. 53- are led from the regenerators through horizontal flues to tall chimneys. The heat on the furnace hearth is intensified by the arched roof which acts as a reflector. Fig. 54- Open hearth furnaces are commonly built of silica brick set without mortar, the brick work being held together by means of T-rails, I-beams and tie-rods. Some of the older furnaces STEEL J 47 are almost entirely enclosed in plates of iron rivetted together. The roof of the furnace is the weakest part, lasting on an average for about 275 heats. The hearth of the acid furnace is thickly lined with sand. Three doors are provided for introducing the charge. The doors are hollow, iron castings, water cooled and lined with fire-brick. They are raised by hydraulic power. The furnaces are charged by means of electric machines, which operate on the floor in front of the furnaces. A number of furnaces are com- monly built in line and worked together. The materials to be charged are loaded in iron boxes mounted on bogies. The bogies are drawn on a track in front of the furnaces so that the boxes can be handled by the charging machine. The tap-hole is at the back of the furnace. From this the steel is conveyed to the ladle in a detachable, clay-lined spout (Fig. 54). The slag that overflows is received in the pit underneath the ladle. The Process. In early practice the amount of metal refined in the open hearth did not exceed 15 tons. From 30 to 60 tons are now treated in each operation. The charge may consist en- tirely of pig iron, or it may be made up largely of iron and steel "scrap." * The pig iron is charged either hot or cold. At some plants it is brought directly from the blast furnace. The use of the mixer is now becoming common in open hearth practice, the advantages of which have already been explained. If the furnace is new the gas is kept on it for twenty- four hours before charging, so that the hearth and chambers will be thoroughly heated. The furnace is then given a light charge of finishing slag from a previous heat, and this is melted and swashed over the hearth, and then tapped. The grains of sand are now cemented together and a hard crust formed on the hearth which will the better withstand mechanical abrasion from the stock. The materials are loaded on the charging bogies and 1 The development of the open hearth process has furnished a ready market for the waste product of billet and finishing mills, and for old material of all kinds. There is, in fact, a steady demand for such material, and steel makers often stock quantities of scrap to draw upon in times of scarcity. A great deal of condemned steel is also worked up in the open hearth. 148 METALLURGY weighed, and charged in the following order: light scrap (tin plate, etc.), then the heavy scrap, and lastly the pig iron. The following example may be taken to represent a charge for an acid furnace: phosphorus pig (Hot) 31,000 Ibs. " " cast iron scrap (Cold) 7,400 " Steel scrap 93,900 " The time required for charging with the improved machines is about 30-45 minutes. As an average, about 30 minutes are re- quired for preparing the furnace bottom for another heat. The time required for melting down the charge is of course considerably shortened if the pig iron is charged hot. Ordinarily about six hours would be required for the complete fusion of such a charge as the above. Until this stage is reached but little attention is needed on the part of the melter, except to re- reverse the gas and air valves at regular intervals. A thin slag forms at the beginning, and its volume increases rapidly in proportion to that of the metal during the progress of the heat. This slag consists of ferrous silicate and the silicates of any other basic oxides present. The silicon, manganese and some iron are thus transferred during the melting down stage, and the slag resulting soon forms a protecting layer which pre- vents further oxidation of the iron. As soon as the bath is in a liquid condition the melter throws in lumps of hematite ore to hasten the decarburization. The ore is added at intervals, between which tests are taken and their fracture examined, until the carbon is as low as desired. The bath "boils" soon after the first addition of ore on account of the quantity of carbon dioxide evolved. The frothing and swelling may cause an overflow of slag through the working doors. It is during this stage that the greatest skill is needed on the part of the melter. He should have the bath in proper condition for tapping as soon as the impurities are eliminated. By this is meant that the slag should be very liquid, so that it will separate well from the metal, and as nearly neutral as possible at the time of tapping. The tem- perature should not be higher than is necessary to prevent vis- cosity in pouring. In case the slag has been made strongly oxidizing and the carbon has been "worked down" below the required limit (the heat not being in condition for tapping) the carbon may be restored by adding pig iron. Tests are taken with which to ascertain the composition of the steel. When a test is to be taken the bath is first stirred to establish uniformity. A long-handled, soft iron spoon is then thrust, first into the slag, and then into the metal. The coating of slag that chills on the spoon prevents the metal from sticking. The spoon, holding about two pounds of metal, is withdrawn quickly and the contents poured into a rectangular, cast iron mold. As soon as it is solid the test is knocked out, quenched under water and broken. From the appearance of the fracture the melters learn to estimate the carbon with remarkable accuracy when it is as low as 0.50 per cent. When the heat is ready to tap, the ladle is placed in the posi- tion shown in Fig. 54, the spout being placed so as to throw the stream of metal a little to one side of the center of the ladle. This gives a whirling motion to the steel, and facilitates a thorough and uniform distribution of the substances added. The tap-hole is opened by two men working from the outside with a hand drill. A signal is given when a small stream of metal ap- pears, and a heavy bar is thrust through from the inside of the furnace. This together with the rush of the metal so enlarges the opening that the furnace is emptied within a few minutes. The substances to be added are thrown in with the steel as it runs into the ladle. Manganese is always added, since this ele- ment is wanted in the steel, the initial manganese having been transferred to the slag. Ferro-silicon and aluminum are also used to deoxidize and to "quiet'' open hearth heats. "Wild heats," or those which are highly charged with occluded gases, occur in the open hearth as well as in the converter. They are said to have been held in the furnace too long and at too high a tem- perature. The milder steels are always more active while pour- ing. The common method of adding carbon is to throw crush- ed anthracite into the ladle. About 50 per cent, of the weight of coal added is lost. Some specifications call for an increase over the initial phosphorus and sulphur. The former is added" 150 METALLURGY in the form of a rich iron phosphide (ferro-phosphorus), manu- factured from apatite, and the latter in the form of stick sulphur or iron pyrites. All substances are added, so far as possible, before the slag comes, and they are generally in the form of small lumps. If a large quantity of manganese is to be added it is previously heated to insure complete absorption. As soon as the furnace is empty the gas is shut off, and the hearth is prepared for the next heat. The tap-hole is closed by placing a rabble over the mouth and ramming in sand mixed with a little clay from the outside. A layer of sand is spread over the hearth and places that have been worn or fluxed out are patched with chrome ore. The further treatment of the steel is the same as that of Bessemer steel and is described in Chapter XVI. For chemistry of the process see next page. BASIC The acid and basic open hearth processes bear the same relation to each other as do the acid and basic Bessemer processes. The general construction of the basic furnace is identical with that of the acid, and the same materials are put into the walls, roof and flues. The hearth is lined with calcined dolomite which has been crushed on a disc with 34-inch circular holes. Magnesite is also used in the same way. Carbon or chrome bricks are used at the juncture between the basic bottom and the silica brick walls to prevent the two substances from fluxing. Details. The following represents the charge for a 5O-ton furnace : High phosphorus pig iron (Hot) 77,700 pounds " " (Cold) 8,000 " Heavy steel scrap 41,900 " Light " " " 200 " Limestone 9,000 Hematite 12,600 " The limestone and ore are charged first so that the hearth will be protected from the acid slag which forms at the beginning, and so that their chemical action will begin as soon as the metal fuses and trickles down. The limestone is generally charged STEEL IS 1 raw, the idea being that the carbon dioxide evolved from its decomposition assists chemical action by agitating the bath. The action of the lime is not pronounced during the first part of the melting down stage, but as the slag increases in volume and the temperature rises the lime reactions become more ap- parent. After the metal charge has melted the melters say that the lime "comes up/' and this naturally does occur, for the limestone is the lightest substance in the furnace. There is much frothing of the bath at this stage, due to the decomposi- tion of the stone and to the oxidation of carbon. The steel would be completely decarburized if left alone, but time is saved as in the acid process by adding lumps of ore. The tests are taken and examined as before described. If the steel is to contain more than 0.50 per cent, of carbon the Eggertz test is generally used. In some instances chemical tests are made for phosphorus and other ingredients, to determine the progress of the heat. The fact that phosphorus as well as carbon is to be worked down generally means that the basic process requires more care and watching than the acid process. It is essential to the com- plete elimination of phosphorus that the slag be basic and at the same time liquid, and since a liquid slag will not stay mixed with the heavier metal, frequent stirring is required. Fluor- spar is added if the slag becomes too thick from excess of lime. The melters gain some idea of the condition of the bath from the appearance of the slag. The bubbles of gas that escape dur- ing the period in which the limestone is decomposing are small and there is much frothing. Later on the bubbles become larger, and while the carbon is reacting with the ore there is likely to be violent boiling. The bath becomes tranquil at the time of tap- ping. The basic heat is tapped in the same way as the acid, the tap- hole being made up and the hearth renewed with dolomite or magnesite. CHEMISTRY OF THE OPEN HEARTH PROCESS As has been said before the main difference between acid and basic processes, so far as the result is concerned, is that phos- phorus is removed by the basic treatment. The reactions by 152 METALLURGY which carbon, manganese and silicon are removed are alike in both processes, and are identical with those of the puddling pro- cess, except for the differences that are brought about by greater mass and higher temperature. It is to be borne in mind that a much larger quantity of metal is treated in the open hearth than in the puddling furnace, and that the temperature is so high that the metal is kept in a liquid state even after the impurities have been removed. Silicon. This element appears to be the most readily oxidized of all the impurities. In all refining processes it is commonly said that "the silicon goes first." The presence of basic ferrous oxide accounts for the removal of silicon during the beginning or melting down stage of the process. The ferrous oxide is formed in two ways by the oxidizing flame sweeping over the exposed metal, and by the partial reduction of the ore Fe + O 3 + Si = FeO.SiO,. Fe 2 O s + Si0 2 + C 2 = Fe -f FeO.SiO, + 2CO. By the second reaction it is seen that so long as carbon is present there is a gain of metallic iron to the charge. Other bases such as lime and magnesia would effect the transfer of silicon to the slag, but their action is shown not to be considerable, from the fact that most of the silicon is in the slag before the lime reac- tions come into prominence. If the iron contains much manganese this element removes the silicon rapidly, since its oxides are strongly basic and readily formed. It is obvious that the more silicon that is present in the charge, whether combined with the metal or in the ore and flux, the greater will be the volume of slag, if a certain degree of basicity is to be attained. The per- centage of silicon in the metal charge should not exceed 0.75 per cent. Of course pig iron much richer in silicon may be used if the heat be made up largely of steel scrap. Only very low silica ore and limestone are permissible. Carbon. The removal of carbon is effected chiefly by the ox- ides of iron. It is possible that the carbon dioxide from the limestone plays some part, that gas being reduced by carbon. The ore that is added should be in the form of large lumps, since fine stuff would float and be absorbed by the slag. STEEI, 153 Phosphorus. This element, like silicon, is acid forming and has strong affinity for basic o>xides. These are neutralized by silica in the acid process, and therefore, phosphorus is not re- moved. Phosphorus is more easily reduced than silicon and it is not so readily, eliminated from iron that is rich in carbon. The addition of carbonaceous material to the bath in a basic furnace will cause the reduction of phosphorus, and consequently an in- crease of the element in the metal. Phosphorus may be almost completely removed in the basic furnace if the bath is agitated, and fluor-spar is added. Manganese. In the acid furnace the manganese is practically eliminated, while under a basic slag a considerable portion may be retained in the iron. In the basic process the behavior of manganese appears somewhat erratic. The separation from the iron is confined, for the most part, to the melting down period. Later tests not infrequently show an increase of metallic man- ganese in the bath. It is probably reduced by carbon under the influence of a limey slag. Sulphur. This element may well be termed the greatest enemy to the steel maker. There is no reasonably cheap method by which it can be eliminated to any great extent. Manganese has been shown to be the best desulphurizer in the open hearth. High manganese irons always yield a product that is proportion- ately low in sulphur. It is probable that in an alloy of iron and manganese the sulphur combines with the latter rather than with the former, and that the sulphur is oxidized simultaneously with the manganese as it passes into the slag. Some of the sul- phur is undoubtedly volatilized, since an analysis of the slag does not account for all that has been eliminated. A considerable amount of sulphur may be removed by continued stirring in the basic process, but even under the conditions that seem to be most favorable the results are uncertain. The figures below, taken from actual practice, show the his- tory of an acid and a basic heat. The composition of the charges before fusion is estimated, the other figures representing chemical analyses. 154 METALLURGY ACID HEAT. METAI, SI.AG C Mn S P 0.80 i. oo 0.030 0.065 0.75 0.003 0.026 0.064 0.76 0.003 0.023 0.074 0.59 0.003 0.033 0.068 0.58 0.003 0.027 0.070 C 1.50 Metal Mn S SiO 2 (FeOAl 2 3 ) MnO CaO MgO Time 3:35 45.ii 38.98 15 15 0.6o O.IO 10:30 48.25 34.70 16 4i 0.48 0.09 11:00 11:15 51.20 32.64 3 65 0.41 0.09 11:30 BASIC HEAT. Slae SiO, FeO A1 2 3 MnO CaO MgO Time 5:00 24.65 9.00 9- 70 7 53 35-45 11.70 12:00 23-33 10.40 9 86 8 .42 37.13 10.78 1:10 ao.Si II. 80 10 07 5 75 39-38 11.91 2:00 22.38 11.83 9- 95 7 58 39.38 8.44 3^5 i. oo 0.030 0.075 1.05 0.21 0.028 0.058 0.78 0.15 0.028 0.034 0.48 O.I4 O.O25 O.OI4 o.io 0.14 0.026 0.013 The diagram (Fig. 55) shows graphically the rate at which the impurities are eliminated in the basic process. Relative Merits of Acid and Basic Processes. The quality and supply of iron will determine the method adopted for converting j it into steel. It costs more to convert steel in the basic furnace, I basic refractories being more expensive. The acid process can be more easily controlled, and there is more certainty as to the composition of the steel. The acid furnaces would undoubtedly predominate if the larger part of the iron supply was low in phosphorus. But such is not the condition in the United States. Most of the low phosphorus iron is treated in Bessemer con- verters, and the supply of Bessemer ores is rapidly being ex- hausted, unless new important discoveries are to be made. High phosphorus iron is cheaper and more abundant, and there is an ever increasing supply of scrap which is unsuitable for the acid treatment. Thus the higher cost of the basic process is offset. As to the quality of the steel it may be said that while the stock is superior to begin with and the product more even in the acid process, just as good, and even better steel may be made by the basic process. The danger of overheating while the heat is prolonged for the removal of phosphorus may be guarded against by proper management. The basic furnaces now greatly outnumber the acid. Judging from its phenomenal growth and STEEL 155 present conditions, the basic open hearth process seems destined to take first rank in the output of steel in America. RECENT ADVANCES IN OPEN HEARTH PRACTICE Tilting Furnaces. The improvements in the open hearth pro- cess have been chiefly mechanical. The exceedingly laborious 156 METALLURGY -and expensive method of charging- by hand has been superseded by machine charging, and the electric crane has been instituted for hoisting and moving materials about the plant. With the 75-ton ladle crane, the heat of steel is poured and removed from the shop within 15 minutes from the time of tapping. One of the most important inventions is the tilting furnace, which has paved the way to some remarkable improvements in recent prac- tice. The Campbell furnace is mounted on rollers as shown in Fig. 56. The furnace is tilted for charging and pouring by Fig. 56. means of a hydraulic ram. Aside from the mechanical feature the furnace is similar in construction to the stationary hearth. The Wellman furnace is constructed and operated in somewhat the same manner as the Campbell furnace, except that it is mounted on rockers instead of rollers, and when tilted the whole furnace moves forward, instead of rotating about its own axis. The Talbot Process. This process, the invention of Benjamin Talbot, has been in successful operation for several years. It is otherwise known as the "Continuous" process. A tilting furnace of the Campbell or Wellman type is employed and the process STEEL : 57 is conducted as follows : The charge consists entirely of molten pig iron and limestone, and the heat is worked down in the usual way with the necessary additions of ore and stone. When iinished the bulk of the slag is poured off and a part of the metal is taken. The larger portion of the metal is left in the furnace to which pig iron is immediately added until the weight of the metallic charge is restored. A new slag is formed with the further addition of limestone and iron oxide, and the purifica- tion of the bath is continued as before. The large amount of refined iron that is left in the furnace after each pouring takes the place of the steel scrap used in ordinary practice, while it protects the furnace hearth from the corrosive action of slags. The time required for tapping is saved, and there is a further gain of time in the charging and from the fact that no cold metal is used. Talbot furnaces have been installed at the Jones & Laughlin Works, Pittsburg, with satisfactory results. The capacity of one of these furnaces is 200 tons per day, or nearly double that of the stationary furnace. The Bertrand-Thiel Process. This process as applied to the basic treatment employs two furnaces, the iron being charged into one furnace and transferred to the other after partial con- version. The primary furnace, or the one receiving the charge, is generally built on a higher level than the secondary furnace, so that the metal can be transferred by gravity. The molten pig iron, limestone and ore are charged into the primary furnace, and treated in the usual way until the silicon and phosphorus are removed. The charge is then tapped into the secondary furnace, and the decarburization is finished under a new slag. The slag of the first operation is separated from the metal as far as possible before it is transferred. The de- carbonization is completed in a much shorter time with the foul slag thus disposed of, and further purification as regards other elements is more easily accomplished. CHAPTER XVI FURTHER TREATMENT OF IRON AND STEEL The mechanical and heat treatment of steel are the subjects dealt with in this chapter. In this connection special reference is made to Bessemer and open hearth steel, since these represent so large a proportion of the total steel produced. The history of the steel is given, as it passes through the several mills which prepare it for the market. Casting the Ingots. The quality of steel depends very largely upon the conditions under which it is cast. The so called "wild heats" are those which have been held in the furnace too long and poured at too high a temperature. A large quantity of gas is absorbed by the overheated steel, causing the motion in the ladle and molds, and resulting in red-shortness, blowholes and general unsoundness. Very pure steel is specially liable to in- jury under such conditions. These defects may be largely dimin- ished by pouring at the lowest temperature possible, and allowing the metal to run in a very small stream. It is not practicable, however, to resort to such measures with the quantities of steel to be handled from converters and open hearth furnaces, and special methods for treating ingot metal have been resorted to. The use of manganese, silicon and aluminum as deoxidizers has already been mentioned. Blowholes and red-shortness may be almost completely eliminated by adding one of these substances : while the steel is being poured. The closing of cavities in steel ingots by compression has been practiced for some time, though the cost of installing and operat- ing compression machinery precludes its general use. The pres- sure is applied while the ingot is cooling from the liquid state, and is exerted upon the ends or the sides. Lateral pressure would appear to be preferable for closing pipes and preserving the structure of ingots. The value of liquid compression has not been fully demonstrated. Cavities are closed and the steel is made more compact, but weakness may remain from failure of FURTHER TREATMENT OF IRON AND STEEL, 159 the cavity walls to unite, as for example, if the surfaces are coated with oxide. Instead of casting from the top, as is usually done, sounder ingots may be made by casting from the bottom, the tops of the molds being closed. This method of casting has only been used for small ingots, except in rare instances. Mention is also made of the method of preventing piping by keeping the upper part of the ingot hot during the cooling of the mam portion, so that the pipe will be filled with molten metal. Stripping the Ingots. The train of bogies, each bearing, two ingots in their molds is brought from the Bessemer or open Front Elevation of mold Fig. 57- hearth shop directly to the stripper. Fig. 57 represents a bogie with the ingots in position as they were cast. The bogie has a fiat top and upon this rests the stool, or receptacle for the mold. One of the molds with the stool and ingot is shown in section. The stools are heavy slabs of cast iron with guards at the corners to hold the molds in position. The molds are also of cast iron, and are made in different sizes to hold from 2 to 4 tons and more of steel. They are tapered slightly toward the top and open at both ends, the bottom being closed when the mold is placed upright on the stool. Lugs are cast at the top of the mold for use in lifting it. 160 METALLURGY The usual style of stripper is an overhead crane, spanning two tracks, and provided with a travelling hoist. From the hoist are suspended two pairs of loops properly spaced for engaging the lugs of both molds as they stand on the bogie. The hoist is also provided with two rams, operated by water, and capable of striking heavy blows upon the heads of the ingots while they are suspended a short distance above the bogie. The crane and hoist are propelled by means of motors so that the stripping can be carried on with great rapidity. The loaded bogies are brought in on the one track, and the molds are lifted until they are clear of the tops of the ingots, and then placed on empty bogies on the other track. Any ingots that stick may be knocked out by means of the rams. The Soaking Pits. If the ingots were allowed to stand in the air they would at no time during the cooling be in the proper condition for forging. When the interior has become solid the outer portion will have become too cold. If the initial heat were evenly distributed the ingot could be forged without applying any external heat. It was in recognition of this fact that the first "soaking pits" were designed. They were simply brick-lined cells, built underground and adjacent, each cell or pit being large enough to hold one ingot. The cover for the pits, also lined with fire-brick, was mounted on wheels to facilitate open- ing and closing. On being placed in the pits, immediately after stripping, the rapid cooling of the ingot was arrested, heat being reflected upon its surface from the walls of the pit, and the heat trom the interior was given time to soak out. This kind of pit has gone out of general use, since it was found difficult to have the ingots in the proper condition at the time they were needed in the mill, and of course it was impossible to heat cold ingots to the rolling temperature. The soaking pits as now used are arranged to be heated in- dependently with coal or gas. Cold ingots may therefore be charged and brought to the rolling temperature and those direct- ly from the stripper are quickly tempered. The pits are usually large enough to hold four ingots. The train of ingots is brought in from the stripper, and the ingots are placed in the pits by an FURTHER TREATMENT OF IRON AND STEEL 161 overhead, travelling crane. The ingot is seized near the top by tongs which are suspended from the hoist. The same crane is used for drawing the ingots from the pits when they are to be rolled. . Forging. Steel is forged by rolling, hammering and pressing. The rolling process is the most used, being most economical and rapid. The other processes serve special purposes and will be described later. The ingot is rolled down to different sizes and shapes, depending upon the requirements of the finishing mills. If it is reduced to sizes less than 6 inches square and sheared, the pieces are called billets; if larger than that the pieces are blooms, and if rolled flat they are slabs. There are a number of types of rolling mills, each type being designed for special work. Mills take their names from their general construction, size of the rolls, manner of working and nature of the product. Brief descriptions of a few important types of mills are given below. The Blooming or Slabbing Mill. This mill is designed for re- ducing ingots to blooms o,r slabs. It may also be run as a billet mill. It commonly consists of two large rolls, driven by a re- versing engine, and a series of "live rollers" for moving the steel. The succession of rollers extends from both sides of the mill rolls in a horizontal plane. The rollers are revolved col- lectively, to move the steel in either direction, by means of a small, reversing engine. The mill rolls are of cast steel, which is superior in strength to chilled, cast iron, of which most rolls are made. The bearings or chocks for the rolls are supported in heavy, cast iron housings. The upper roll, with its chocks, is adjustable to the thickness of the piece of steel. In reducing the size of the piece the pressure must be applied in two directions, so that the thickness both ways will be as de- sired, and the sides true. This is accomplished by turning the piece over between passes, or by employing, in addition to the usual, horizontal rolls, a pair of vertical rolls to act upon the piece at the same time. In the former type of mill, mechanically operated tilters are employed for turning the work over. The latter type, employing two sets of rolls, is known as the universal mill 6 102 METALLURGY The phoi >graphic view of a universal, slabbing mill is shown in Fig. 58. The power for this mill is furnished by separate, reversing engines, the horizontal rolls being driven by the larger engine, the base of which is on the floor level. The vertical rolls, which are driven from the top by the smaller engine, are not visible in the cut. The live rollers, together with the small engine and gear for driving them, are shown. By a closer examination of the cut the connection between the engine and the horizontal rolls may be traced. The driving shaft of the engine carries a pinion which meshes into the pinion of a short, horizontal shaft in line with the lower roll. The pinions are split, and the two parts set so that the teeth are staggered. This gives; a steadier motion to the gearing and diminishes shock to the teeth. The shaft, above mentioned, is coupled with the lower of two pinions, which are enclosed in the Section through Wobbler Section through Coupling 59- housings shown between the engine and the roll housings. The pinions are coupled with the rolls by spindles with wobblers at both ends. The mechanism of these couplings will be under- stood from the cross-sections shown in Fig. 59. The ends of the spindles and of the roll necks are cast in the form shown in the section to the left. Three-lobed wobblers are also in use, but this is the most common form. The coupling box, shown also in cross-section, is a heavy, steel casting which fits loosely over the wobblers of the two members in line. In the union Fig. 58 -Slabbing Mill at Bethlehem Steel Works. (Mesta Machine Co.) FURTHER TREATMENT OF IRON AND STEEL 163. thus made there is considerable play when the mill is reversed.. The ends of the spindle wihich drives the upper roll are tapered so that they can work freely in the coupling boxes when the roll is raised or lowered. The bearing for this spindle is sup- ported on beams which are hung from the pinion housing and the chock of the upper roll, so that it follows the spindle to any angle. The upper roll is raised and lowered by means of two large screws driven by a motor, and a similar mechanism is employed for adjusting one of the vertical rolls. Indicators are provided for showing the distance between the rolls. The Three-High Mill. This mill employs three horizontal rolls Fig. 60. in vertical line as shown in Fig. 60, which represents the ar- rangement of rolls in a rail mill. The end elevation to the right shows the directions in which the rolls turn. The mill is not reversed, but the piece, after passing between the middle and bottom rolls, is passed in the opposite direction between the middle and top rolls. The rolls are so cut as to give the pro- per openings for diminishing the cross-section and imparting the proper shape to the piece. This obviates the necessity of adjusting the rolls after each pass. Different sets of rolls are substituted for shapes that can not be rolled by the set in the stand. The three-high mill was invented by John Fritz, and first operated in 1857, at the Cambria Steel Works, Johnstown. It was offered as an improvement over the aid-fashioned "pull- 164 METALLURGY over" mill, which had two rolls, and not being reversible, neces- sitated the return of the metal idle after each pass. The Continuous Mill. A very large percentage of the costs to manufacturers arises from the handling of material. The numerous shapes now in demand require as many different kinds of rolls, and in most instances the metal must be carried from the bloom- ing or billet mill to the finishing mills. Here the piece must be reheated to the rolling temperature, adding another serious ex- pense. The ideal in rolling mill practice is continuous rolling under the initial heat, not allowing the metal to stop in its course until finished. Continuous mills are now in use for manu- facturing billets, rods, rails, angle-bar^ and other standard shapes. They consist of a series of rolls, working in pairs, and all driven by a single engine. Since the metal must travel faster in front of each pair of rolls, on account of the reduction in size, each pair of rolls must turn faster than the preceding pair to prevent the piece from buckling. "Flying shears," an ingenious device for cutting the metal while in motion, in pieces of any length, may be used if sawing can be dispensed with. Aside from the savings above noted, and a saving in labor, the "crop ends" are less when continuous rolling is practised. The con- tinuous mill can be made to pay only when there is a steady de-' mand for the shapes which it is possible for it to make. The cost of installation is high, though the output is correspondingly high. Hammer Forging. The steam hammer has supplanted the older forms. As seen from the illustration (Fig. 61) it consists of a steam . cylinder mounted upon massive columns, the piston rod carrying the hammer, and the anvil in position to receive the impact. The structure is seated upon a rubble and concrete, foundation. The hammerman, in operating the steam valve, has such complete control of the machine that he can cause the ham- mer to exert a pressure of a few pounds upon the work or to strike a blow of many tons. The rapidity of the blows can also be regulated as desired. Press Forging. The forging of metal by continuous pressure differs from rolling in that the pressure is exerted on the entire Fig. 61 Double-stand, Steam Hammer. (Alliance Machine Co.) FURTHER TREATMENT OF IRON AND STEEL 165 piece at once. It differs from hammering in the same respect and in that there is no sudden impact. The press is now used for heavy forging, especially in the manufacture of armor plates. Hydraulic presses are the most satisfactory, the pressure cylin- ders being made from solid steel castings. A pressure of several tons per square inch is exerted. Of the three methods of forging iron and steel, rolling is by far the cheapest and most rapid. Hammered forgings are superior to rolled, being more compact and less liable to crys- talline structure. There are many shapes which can not be formed between rolls, and for forgings of irregular shapes the hammer is indispensable. Still more compactness and uniformity of structure is gained in press forging. The large, unwieldy pieces are more easily handled in the press, since the position of the piece does not have to be changed as with the hammer. In all forging operations the force of the pressure or impact should be sufficient to take affect with the particles of the in- terior of the piece as well as those of the exterior. If insuffi- cient force is used, as by employing too light a hammer, the ef- fect will be shown at the edge of the piece. This will appear concave, indicating that the interior of the piece has not been extended as much as the exterior. The failure of forgings has often been ascribed to this unequal working of the metal. Reheating. Iron or steel to be forged should be carefully heated, and shielded as far as possible from the air. At the high temperature to which it must be heated, the metal itself becomes "burnt" and red-short by exposure to air, and in the case of steel, some carbon is lost by oxidation. To avoid burning the furnace is heated with a reducing flame. The proper temperature for forging has not been determined with exactness. It varies with different grades of steel, being lower for the high carbon steels. The application of pyrometry to the heat treatment of steel will doubtless aid metal workers in securing and controlling the proper temperatures in the heating furnaces. The modern reheating furnace is fired with gas, and is of the reverberatory type. Billets are heated in a long, narrow chamber through which the flame passes. They are introduced at the 1 66 METALLURGY flue end and advanced in succession toward the fire end from which they are discharged, the operation being continuous. By this method of heating the billets are raised gradually to the forging temperature, and all are exposed to the same conditions. Tempering. The word temper as applied to steel denotes de- gree of hardness. It is unfortunately used in two senses. With the steel maker it often refers to different steels containing vary- ing amounts of carbon, the hardening element, while the steel worker uses the same term in referring to the hardness of the same steel under different treatment, affecting the hardness. Car- bon has the property, more than any other element, of imparting different degrees of hardness, tenacity, etc., under different con- ditions of heat treatment. Tempering, as here dealt with, re- fers to the heat treatment of carbon iron. It is a subject that has directed the attention of men from very remote times, and it is still an important one for experiment and research. The hardness of steel containing less than 0.25 per cent, of carbon is not greatly altered under different conditions of cool- ing. The effect of heat treatment is most marked in steels con- taining from 0.80 to 1.25 per cent, of carbon. Such steels, though relatively very hard, still retain some toughness and malleability, when cooled from a bright, cherry-red heat. If cooled sudden- ly they become exceedingly hard and brittle, the hardest steels often cracking from internal stresses. The properties of steel are therefore affected by {he rate of cooling. A slow cooling or toughening process is known as annealing, and a rapid cooling or hardening process is quenching. Steel to be annealed may be kept in the furnace in which it was heated, the temperature being slowly diminished, cooled in the air, or surrounded and cooled in lime, charcoal or other material of low heat conduc- tivity. In quenching the heated steel is commonly placed un- der water or oil. When a piece of steel is heated it begins to redden at about 400 C. As the temperature is raised, bright redness develops, a further rise giving a dark-yellow. Higher temperatures develop a bright-yellow, approaching whiteness. At some point, varying under different conditions, the temperature of the steel sudden- FURTHER TREATMENT OF IRON AND STEEL 167 ly rises, as is indicated by a brightening of the color. The same phenomenon occurs during the cooling from higher tempera- tures, though not at the same temperature. It is due to some change which the carbon and iron undergo, not fully under- stood, and is termed recalescence. When heated to the recales- cence point the metal is in the plastic state, and at the best tem- perature for forging, annealing and quenching. At a tem- perature above the heat of recalescence the steel loses plasticity and passes into the granular state, malleability being much impaired, and lastly it melts. The heat of recalescence, or the best temperature for annealing, etc., is about 665 C. This varies slightly with steels containing different percentages of carbon. One other point is to be considered in adjusting the temper of steel. Due regard has not only to be paid to the amount of carbon in the steel and to the rate of cooling, but also to the temperature at which the piece is cooled. The range of tem- peratures from which steel is quenched for the hardness desired is between 220 and 320 C, the lowest temperature yielding the hardest steel. The common practice is to heat the hardened steel somewhat above the maximum temperature and to quench at the proper stage of cooling. If the surface of the piece be brightened the changes of temperature will be indicated by the changes of color due to films of oxide. Though not always so convenient, better results may be obtained by raising the steel to the proper temperature instead of to a higher temperature and cooling down. In careful work the pieces to be tempered are heated in a bath of oil or lead, the temperature of which is regulated by aid of a thermometer. In the table below are given the approximate temperatures and their characteristic colors, above mentioned. c 221 232 243 254 265 277 288 293 316 F 430 45 470 49 5 10 530 550 560 600 Color Very pale yellow Pale Straw Full yellow Brown Brown, dappled with purple spots Purple Bright blue Full blue Dark blue Articles Lancets Surgical razors Common razors, pen-knives Small scissors, cold chisels,hoes Axes, planes, pocket knives Table knives, large shears Swords, watch springs Fine saws, augers Hand and pit saws Percy- 1 68 METALLURGY The Development of Surface Hardness Case Hardening. By the process known as case hardening the surface only of a piece of iron is hardened with carbon while the interior is soft and tough. The piece is finished in soft steel, which is then packed with nitrogenous, organic material in an iron box and heated for some time at redness. The materials commonly used are clippings of hoof, leather, bone and other animal matter. On heating, a destructive distillation takes place, and the carbon enters the iron by cementation. As the workman removes the piece from the box he drops it immediately into a quenching liquid, being careful to shield it from the air to prevent oxida- tion. By skillful manipulation, however, a beautiful mottled appearance may be secured from short, unequal exposure. Some parts of light machinery, and of firearms, which should be tough, and at the same time hard on the surface, are case hard- ened. A process, similar to case hardening in principle, is in use on the large scale for improving armor plates. In this country it is known from the name of its inventor as the Harvey pro- cess, or as "Harveyizing." Two plates are placed one upon the other in a reheating furnace, a layer of charcoal being packed between so that it comes in contact with the surfaces to be hardened. These surfaces are quenched with water after the plates have been taken from the furnace. Krupp's method is .similar to this, except that hydrocarbon gases are led between the plates, the gases depositing carbon at the temperature re- quired for cementation. Specifications. The "International Association for Testing Materials" has for its aim the perfection of methods for testing steel and the determination of the requirements that should be made of the different grades of steel for all important work. The American and foreign specifications differ somewhat, though the effort is being made to have standards adopted which will be accepted in all countries. Specifications are in- tended to cover the modes of manufacture, physical properties, composition, finishing, testing, branding and inspecting the steel. The requirements of course differ with steel intended for FURTHER TREATMENT OF IRON AND STEEL 169 different purposes. The American standard specifications for steel rails are here given. 1 CHEMICAL COMPOSITION. Weights per yard Carbon # Manganese # Silicon % Phosphorus % 50-59 Ibs 0-35-0.45 0.70-1.00 O.2O O.IO 60-69 " 0.38-0.48 0.70-1.00 O.2O O. 10 70-79 " 0.45-0.55 0.75-1.05 O.2O O. 10 80-89 " 0.48-0.58 0.8o-l.IO O.2O O. IO 9O-IOO " 0.50-0.60 0.8o-I.IO O.2O O. 10 DROP TEST. Weights per yard Height of Drop Foot-pounds 45-55 Ibs 14 feet 28,000 55-65 < < 15 " 30,000 65-75 16 " 32,000 75-85 < < 17 " 34,000 85-100 " 18 " 36,000 The steel for rails may be either Bessemer or open hearth. If it is Bessemer steel a test-piece is taken from every fifth heat. The test-piece is four to six feet long, and it is cut from the rail while hot. The piece is supported at the ends with the head upwards while the drop test is being applied. 1 A. L. Colby's paper "Comparison of American and Foreign Rail Specifications." Jour. Iron and Steel Inst., 1906, 3, 189. CHAPTER XVII COPPER ORES, PROPERTIES, ETC. Historical. Copper was the best known and the most abun- dant of the metals before the age of iron. Records show that it was manufactured and used in the remotest times. Numer- ous specimens of copper utensils and ornaments have been pre- served, many of which are known to be thousands of years old. Ancient tools were made of copper, it being hardened by the presence of some impurity, probably oxygen. It was also employ- ed by the ancients in alloys of brass and bronze. Perhaps the chief use of copper was in this capacity until electricity became known. ORES Native Copper occurs in many localities in small quantities,, usually associated with other copper ores. The famous Lake Superior deposit, which is worked chiefly in Michigan, is the only one of metallurgical significance. It was the chief source of copper in this country until the Western mines became so productive. The Lake ore is disseminated through silicious rock from which it is separated by stamping. Often large masses of tough metal are encountered, making the mining difficult. Chalcopyrite (Cu^S, Fe,S 3 ) is a widely distributed and very important ore of copper. It commonly occurs in silicious and other crystalline rocks, and is rarely ever pure. The ratio of the iron to the copper is quite variable. Lead, zinc, nickel and the precious metals are sometimes associated with chalcopyrite. The copper deposits of the New England and Middle Atlantic states consists largely of chalcopyrite as do those of the Rocky and Sierra Nevada Mountains. Chalcocite (Cu 2 S) otherwise known as copper glance is an ex- ceedingly rich ore when pure, though it is usually mixed with other sulphides. It is commonly met with in the Montana mines, and it is now regarded as the most abundant ore of cop- COPPER 171 per. Chalcocite is the original ore from which the others are derived. Tetrahedrite, (Cu 2 S, FeS, ZnS, AgS, PbS) 4 (Sb 2 S 3 , As 2 S 3 ) is rarely ever a valuable ore of copper, though it often contains enough silver to pay for its treatment. It is sometimes an ob- jectionable ingredient of other ores on account of the arsenic, antimony, etc. it contains. The more valuable occurrences of this ore are in Colorado. Malachite, (CuCO 3 , CuOH 2 ) is relatively an unimportant ore, though a very valuable one when sufficiently pure. It is com- mon in Arizona and New Mexico. Cuprite and Melaconite, the oxides of copper occur as pro- ducts of the natural decomposition of sulphide ores, though in but small quantities. The most remarkable occurrences are in Virginia, North Carolina and Tennessee. The leading copper- producing states are Montana, Arizona, Michigan and Utah. It is mined in almost every state of the West, and in many of the Eastern and Southern states, notably, Tennessee and Vir- ginia. PROPERTIES Pure Copper. With but one exception, copper is the only metal with a distinct color. The fractured surface is pinkish- red, and a somewhat lighter color is developed when the sur- face is polished. The specific gravity is 8.945, according to Hampe. Owing to the porosity of commercial copper the specific gravity varies from 8.2 to 8.5. Copper ranks among the softer metals; it is exceedingly tough and tenacious, highly malleable and ductile. These properties may be illustrated in this way a vessel of the shape desired and with very thin walls may be hammered from a solid block of the cold metal a bar of iron plated with copper and drawn into a fine wire, is still coated with the red metal. The melting point of copper is given by Violle as about 1,054 C. When molten it appears a sea-green, mobile liquid. Just before reaching the fusion point copper is so brittle that it may be powdered. While in the liquid state it will absorb most gases except carbon dioxide. 1 1 Hampe states that with hydrocarbon gases only the hydrogen is absorbed, the carbon being liberated. 172 METALLURGY Upon solidification the gases are released. For this reason sound copper castings can not be made unless the operation be carried on in an atmosphere of carbon dioxide, or unless some substance is added to hold the gas in solution. One of the most useful properties of copper is its electric con- ductivity, which is excelled only by that of silver. Copper dif- fuses readily with most of the common metals. Its alloys are numerous and widely used. Effect of Impurities. The properties of copper are greatly altered by the presence of foreign elements, some rendering it quite unfit for certain purposes even when present in minute quantities. Of the more important impurities that have to be dealt with are bismuth, arsenic, antimony, silicon, sulphur, phos- phorus and oxygen. Bismuth has been termed the copper maker's worst enemy, on account of its deleterious effects and the difficulty of eliminat- ing it. The presence of but 0.05 per cent, of this element ren- ders the metal both red-short and cold-short. Extreme brittle- ness is developed in copper containing more than o.io per cent. of bismuth. Arsenic is the most objectionable impurity in conductivity copper. This property is greatly diminished if but a few hundredths of a per cent, of arsenic be present. The metal may be readily worked, however, if as much as 0.50 per cent, be pres- ent. A small amount of arsenic is said to increase the tensile strength of copper. Antimony has a similar effect to that of arsenic. Its effect seems to be less pronounced with very small proportions, while with quantities exceeding 0.50 per cent, the effect is more marked than that of an equal amount of arsenic. Silicon lowers the conductivity of copper when as much as 0.50 per cent, is present. Three per cent, does not seriously impair the toughness and malleability. Larger proportions pro- duce brittleness. Silicon is always to be found in unrefined copper. Sulphur is usually present in unrefined copper. It lowers COPPER 173 the malleability, as much as 0.50 per cent., causing cold-short- ness. Phosphorus is not often present in sufficient quantity to in- jure the properties of copper. Red-shortness develops with as much as 0.50 per cent, of phosphorus. Oxygen is always present. In small quantities it may be dis- regarded entirely. With increasing amounts above one per cent, the copper becomes harder and finally unworkable. Compounds and Reactions Especially Useful in the Study of the Metallurgy of Copper. Oxides. Two oxides of copper are known cuprous oxide (Cu.,0) and cupric oxide (CuO). Both of these compounds are formed when copper is heated in oxygen, the latter being the ultimate product of oxidation. The higher oxide is reduced to the lower when heated with metallic copper. Cuprous oxide is readily dissolved in all proportions by molten copper. Both oxides are reducible by carbon and both are solu- ble in mineral acids. Sulphides. There are two sulphides of copper, analogous to the oxides. Cupric sulphide (CuS) is the form in which the metal is generally combined in its ores. One-half of this sul- phur is evolved at a moderately high temperature, so that roasted ere contains cuprous sulphide (Cu 2 S). Upon further heating in an oxidizing atmosphere cuprous sulphide is partially converted into the oxides, which in turn react with the sulphide, liberating copper and sulphur dioxide. Under certain conditions cuprous sulphide is changed by roasting to the sulphate ("sulphate roast- ing"). When roasted with salt cuprous and cupric chlorides are formed ("chloridizing roasting"). Silica reacts readily with cuprous oxide at furnace tempera- tures, forming a liquid slag. From cuprous silicate copper may be reduced by carbon, and cuprous oxide may be set free by the substitution of a stronger base such as ferrous oxide or lime. Copper is precipitated from aqueous solutions of its salts by iron, aluminum and zinc, and by the electric current. PRELIMINARY TREATMENT The processes for smelting copper differ considerably on ac- count of the character of the ores and other conditions in dif- 174 METALLURGY ferent localities. But practically all processes are similar in theory, being universally applied to sulphide ores. It is not practicable to separate copper from the ore by a single opera- tion. There is usually a large amount of sulphur to be eliminat- ed, and the large excess of mineral matter present would yield an overwhelming quantity of slag to entangle the metal. The practice is to first roast the ore, thereby getting rid of a large part of the sulphur and other volatile matter, and then to fuse the ore under proper conditions, when the heavier, metal-bearing portion separates from the barren gangue by liquation. This concentrated material is a mixture of copper and iron sulphides and is known as matte or regulus. A concentrate in which the sulphur is replaced by arsenic is called a speiss. Matte is further treated by fusion in an oxidizing atmosphere, the iron being oxidized first and fluxed out by means of silica, leaving the en- riched sulphide of copper. This is known as blue metal if it still contains a considerable amount of iron and about 65 per cent, of copper. White metal is almost pure cuprous sulphide, and contains 75 per cent., or more, of copper. Upon further fusion in an oxidizing atmosphere metallic copper is obtained. It will be seen that the processes now to be studied are based upon two facts; ist, that copper has a stronger affinity for sul- phur than the other metals associated with it have; 2nd, that copper being oxidized reacts on its own sulphide with the libera- tion of metallic copper. The preliminary treatment of the ore con- sists principally in roasting. This is done in several ways and will be described at length. Heap Roasting. This is the cheapest way in which ores are roasted. It requires the least amount of fuel and the minimum expenditure of labor, but it is not adaptable to all ores and is open to several objections. The ore must be for the most part in lump form, and should contain at least 15 per cent, of sul- phur. With ores lower in sulphur it is necessary to mix fuel through the heap to produce the necessary amount of heat. While heap roasting may be very efficient, it requires great care both in the building and firing of a heap to turn out a product that is up to present day requirements. The consequences COPPER 175 of setting free so much sulphurous acid are to be considered. In many places the practice is prohibited by law. The site for the operation should be sheltered from the winds, which would cause uneven burning. A spot is generally chosen which is large enough to accommodate a number of heaps. The heap is built upon a foundation of rock or slag. The dimensions of a heap are determined largely by the character of the ore. According to Peters a heap 24 by 40 feet at the base and 6 feet high contains about 240 tons of ordinary ore. In building a heap a layer of wood is first placed for kindling the ore. Sev- eral chimneys are set up along the middle line of the foundation, and canals are left in the layer of wood leading from the chimneys to the outside. This is done to facilitate the combustion of the ore by creating a draft and drawing air into the heap. The large lumps of ore are placed upon the wood, and the heap is finished with smaller lumps and covered with fine ore. A portion of the top and a space around the bottom are left uncovered so that the heap will be open enough for the circulation of air. The heap may be fired at the outer openings of the canals, or in the chimneys. The aim is to effect a uniform kindling of the entire heap. During the first twenty-four hours of the burn- ing the products of distillation from the wood are driven off with some sulphur, producing exceedingly foul odors. After the wood has been consumed the sulphur becomes the fuel and the combustion continues. The surface of the heap is examined at intervals for indications of local overheating. This is shown by the fumes, which issue from every opening, becoming thin- ner and rising more rapidly. The combustion is checked in such cases by throwing on some fine ore. In case the combustion is too much retarded at any point vents are made in the covering to admit air. The time required for roasting a heap of the above dimensions is about 70 days, depending upon the com- position of the ore and the weather. For the recovery of cop- per sulphate from heap roasting see p. 200. Stall Roasting. Stalls are partial enclosures in which the ore is protected from the wind while burning. The common form is rectangular, three of the sides being permanent masonry.- 176 METALLURGY The floor is paved and the top is left open. A number of stalls are built adjacent, with the openings on the same side, an ar- rangement which facilitates the handling of the ore. For the building material either brick or stone is used. Stall roasting may be considered a step toward furnace roasting, though no more advantage can be claimed for the practice than that of roasting in heaps so far as the quality of the product is concern- ed. Stalls have not been favored in this country. Furnace Roasting. The largest proportion of ore by far is now roasted in furnaces. All classes of ores may be roasted more completely and in the manner desired in furnaces. Many styles of furnaces are in use, each kind being chosen for the particular grade or quality of ore to be treated. The ore must in all cases be in the pulverulent form. Rock breakers are used for crushing the large lumps and the finer crushing is done in stamp and roller mills. A description of crushing machinery is given in Chapter VI. The furnaces in use for roasting ores may be classed as hand reverberatory, mechanical reverbera- tory and shaft furnaces. Hand Reverberatory Furnaces. This style of furnace is alter- ed to suit different grades of ore. The essential parts are the flat hearth for receiving the charge; the grate, which is separat- ed from the hearth by a bridge wall; the side working doors, giving ready access to the hearth; the low, arched roof, con- structed so as to reflect heat upon the hearth, and the tall flue. The furnace is commonly constructed with two or more hearths at different levels, the ore being raked from one down upon the other, or the hearth is elongated on the same level for several times its width as shown in Fig. 62. In the operation of this furnace the ore is charged on the upper hearth, or at the end farthest from the grate, and is raked successively to the hearths or portions of the hearth nearer the grate. The temperature of the roasting is therefore gradually raised, since the portion of the hearth nearest the grate is the hottest. The ore is left on the last hearth until it is roasted "dead," and then drawn. A furnace with two or three hearths is preferred for ores containing more than 10 per cent, of sul- COPPER m m phur, and if the sulphur content exceeds 20 per cent, the four hearth furnace is found most satisfactory. The advantage of the long hearth lies both in economy and effectiveness of roast- 178 METALLURGY ing, as may be understood from what has been said about roast- ing. If ore rich in sulphur is charged upon a hearth that is hot enough to kindle it, the ore roasts of itself, and the necessary heat is generated by the burning sulphur. Mechanical Furnaces. The cost of operating the hand re- verberatory furnace is rather high on account of the labor re- quired. The labor of moving the ore on the hearth and of dis- charging it from the furnace is dispensed with by the use of power-driven stirrers or furnaces which are rotated mechanical- ly. The Brown roaster represents the type of furnace in which the ore is stirred mechanically on a stationary hearth. Fig. 63 shows the plan and section of the "Horseshoe" form of Brown roaster. The circular hearth is heated by three fire-places, one of which is shown in the illustration as an enlarged section. As shown in the sectional view, A-B, spaces are partitioned on both sides of the hearth. The partition walls are projected from the roof and floor of the furnace, and a horizontal slot, extending the entire length of the hearth, is left between the parts projected. In these spaces or conduits, exterior to the hearth, rails are laid, and upon these two or more carriages are driven by means of a wire rope. The carriages support the arms of the stirrers which pass through the slotted walls. The stirrers are armed with shoes which plow through the thin layer of ore on the hearth and move it toward the fire-boxes. The path of the stirref carriages is a complete circle, the space between the flue and the first fire-box being uncovered. This space in the outer air serves to cool the carriages. The ore is fed into the furnace by an automatic device, outlined in the drawing. The smoke is led into a tall chimney, the location of which is also shown. The Bruckner and the White-Howell furnaces are common representatives of the -rotating type. They consist of brick-lined cylinders, mounted upon friction rollers between a fire-place and flue. The cylinders are slowly revolved while an oxidizing Hame passes into them, coming into intimate contact with the constantly moving ore. The Bruckner furnace is charged from COPPER 179 hoppers supported directly over the cylinder, the ore being charged and removed intermittently through manholes in the side of the cylinder. At seme plants a number of furnaces are operated in i8o METALLURGY line, and the fire-box is carried on a truck which runs on a track at right angles to the axes of the cylinders. After ignit- ing the ore in one cylinder the fire-box is moved to another, leaving a free access of air to continue the roasting of the ignited ore. In the White-Howell type of roaster the cylinder is slightly inclined toward the fire-box. The ore is fed in automatically at the flue end, and advanced toward the fire-box by the motion of Fig. 64 Herreshoff Furnace. (Nichols Copper Co.) the cylinder. The roasted ore drops between the end of the cylinder and the fire-box into a vault. Shaft Furnaces are used when the sulphur from the ore is to be recovered for the manufacture of sulphuric acid. These vary much in style and are adaptable only to ores rich in sul- phur. All of the improved furnaces have mechanically operated parts. The Herreshoff furnace is of recent develop- ment though it has found considerable application for the treat- COPPER 181 ment of copper and iron sulphide ores, especially in connection with the manufacture of sulphuric acid. As shown in the sec- tion and elevation, (Figs. 64 and 65) the furnace is cylindrical in form. It is lined throughout with fire-brick. Inside the furnace are five circular shelves, built of fire-brick and slightly arched toward the center. The ore is fed into the furnace auto- matically from a hopper at the top. Beginning with the upper- most there are alternately peripheral and central openings Fig. 65 Herreshoff Furnace. (Nichols Copper Co.) through the shelves which permit the ore to pass downward and the gases to pass upward. A large, vertical shaft revolves in the center of the furnace and carries two arms over each shelf. Teeth are attached to the arms for stirring and advancing the ore. The teeth are set at such angles that they move the ore on each shelf toward the openings. After passing from shelf to shelf the ore is discharged from the bottom shelf through two openings at its circumference. The shaft carrying the stirrers 1 82 METALLURGY is hollow, and it is cooled by a draft of air. The doors on the side of the furnace (Fig. 65) give access to the shelves and stir- rers. The latter are replaced with new ones when disabled by the heat and acid gases. After once igniting it the ore is roasted without fuel, and the process is continuous. Chemistry of Roasting. The principal reactions which take place when copper ores are roasted may be represented thus : FeS 2 + 2 = FeS + SO, 2 CuS -f O, = Cu 2 S -f SO, FeS -f O 3 = FeO -f SO 2 S0 2 -f- O = S0 3 FeO + S0 3 = FeSO, Cu 2 S + O 3 == Cu 2 O -f SO 2 Cu 2 O + FeS = Cu 2 S + FeO Cu 2 O -f- 2FeSO 4 + 2 = 2CuS0 4 f Fe 2 O 3 3 FeO -f O = = Fe 3 4 . No elaborate or exact information has been gathered covering the many changes which take place from the time the ore is charged until it is withdrawn from the furnace, though some very valuable data has been obtained from the analysis of the ore at different stages of the operation. Iron pyrites is the first compound to give off sulphur. Cupric sulphide also decomposes at a comparatively low temperature, giving up one atom of its sulphur and yielding cuprous sulphide. With an increase in temperature the monosulphide of iron is converted into the protoxide. This is either oxidized immediately to the higher form or combined with any acid present. The formation of sul- phuric anhydride is believed to be due to the catalytic action of silica or other inert material in the ore with sulphur dioxide and oxygen. The sulphate of iron is formed in considerable quan- tity if the temperature is not too high. This is largely decom- posed by cuprous oxide, copper sulphate resulting. It will be seen that the roasting and each succeeding operation in the smelting process depend largely upon the basic properties of copper. Having superior affinity for sulphur it remains in combination with this element as the iron is being oxidized, and being fusible in this form, it is readily separated from the gangue or slag by liquation during the smelting process. COPPER The burning of the sulphur gives rise to enough heat, in most cases, to complete the roasting without the addition of extrane- ous heat. As a rule, however, in practice most of this heat goes to waste. In the heaps the roasting is generally finished without the use of other than kindling fuel, and in all furnaces a saving of fuel is appreciated from the fact that the ore burns and thus- raises the temperature of the furnace. This subject is further studied in the next chapter. CHAPTER XVIII COPPER SMELTING Copper smelting comprises two or more distinct operations. It begins with the fusion of the oxidized ore, the product of the first operation being a matte, and ends with the oxidizing fusion of the matte, the product of the last operation being unrefined copper. The entire process of copper smelting was formerly conducted in reverberatory furnaces, a practice which is still adhered to in many places, but the blast furnace has new largely replaced the reverberatory. Smelting may be classed accord- ing to the practice as reverberatory, blast furnace and pyritic smelting. REVERBERATORY SMELTING This process was developed in England and Wales, and has undergone but few important changes. It is still the most used process in Europe, and is more adaptable to some grades of ore than any other. Reverberatory smelting consists of a series of fusions and roastings, each roasting eliminating sulphur and each fusion separating matte in a more concentrated form. Fusion for Matte. For this operation a large reverberatory furnace is used. A recently built furnace for matting copper ores is shown in plan and elevation in Figs. 66 and 67. The walls of the lurnace are of red brick and the lining is of fire- brick. The brick work is held together by steel rails and tie- rods. The hearth and lower walls of the furnace are protected by a lining or fettling of sand. The pear-shaped hearth is com- mon to copper smelting furnaces. Since a high temperature is required in this furnace the fire-box is large in proportion to the hearth area. 1 The furnace is provided with skimming doors on both sides for removing tne slag, and a tap-hole for drawing off the matte. The ore is charged through circular openings in 1 Some furnaces are equipped with air heating apparatus which facili- tates the maintaining of the temperature desired. COPPER SMELTING 18=; COPPKR SMELTING 187 the roof of the furnace from three double hoppers. The coal is likewise let into the fire-box through the funnels of one double hopper. A tall chimney carries away the sulphurous smoke and maintains a steady draft. The charge is made up of roasted and raw ore, slag from re- fining furnaces, etc., mixed to produce the matte and slag of thp proper compositions. After leveling down the charge the tem- perature of the furnace is raised rapidly. Within a few hours time the ore is completely fused. A quantity of slag is formed and a portion of the sulphur is evolved. The bath is well rab- bled, and after it becomes tranquil it is left undisturbed for half an hour to allow the matte to settle. The slag is then skimmed off through the working doors, and the matte is tapped. Enough matte is left in the furnace to protect the hearth from sudden cooling and from the corrosive action of fresh ore. The fer- rous oxide and other bases exert a constant scorification of the hearth lining or fettling, and this must be frequently renewed. Fusion for Blue or White Metal. If the matte from the above operation is a rich one it may be converted by a single fusion in- to white metal, otherwise it yields the intermediate product, blue metal. If very poor the matte is roasted before fusion. It is first granulated by running it into water directly from the furnace, or by grinding it in a mill, so that the roasting will be more ef- fective. During the fusion the iron is fluxed out by adding some silicious slag from a previous operation, or by means of raw ore or other material. The furnace used for the fusion of mattes is similar in construction to the one above described. It is gen- erally smaller and the fire-place is larger in proportion to the hearth. A higher temperature is employed than is needed in the fusion for matte, but the operation is very similar. At the end of the operation the enriched copper sulphide forms the lower layer in the bath, and the oxidized slag floats on top. After skimming the slag the product is tapped and run into molds. Fusion for Blister Copper. This operation is conducted in a furnace of somewhat the same construction as the matte furnace, except for the increased grate capacity. The hearth is well soaked before use with high grade matte, and upon this a layer of copper is melted. This protects the hearth from the corro- 1 88 METALLURGY sive action of the charge. The white metal is charged in the form of pigs, and the temperature is raised slowly, air being freely admitted. The oxidation proceeds rapidly, and the es- cape of sulphur dioxide causes "boiling" after the bath has be- come liquid. A much smaller amount of slag is formed than in the preceding operation, and the slag is much richer in copper. This is skimmed from time to time. When tests show the proper degree of purity the copper is tapped and run into molds, or transferred at once to the refining furnace. Metal that is al- lowed to cool becomes covered with blisters from the escaping sulphur dioxide hence the term "blister copper." There is one per cent, or more of impurity in reverberatory smelted copper. Chemistry of Reverberatory Smelting. The separation of the matte from the ore gangue is largely mechanical. The most important reactions are in the fluxing of the iron oxide by silica FeO 4- SiO 2 = FeO.SiO 2 . Of course the same reactions that occur during the roasting are largely repeated here. The final reactions by which copper is liberated may be expressed thus Cu 2 S + 3 == Cu 2 + S0 2 Cu 2 S + 2Cu 2 == 6Cu + S0 2 . The following table, prepared by E. D. Peters, Jr., from his own experiments, shows the rate of matte oxidation in rever- beratory furnaces. Table of Matte Concentration by Oxidation Fusion Percentages of Copper in Fractions Omitted. Char- ged. Mel- ted. No. of Hours in Furnace. O 5 6 7 8 10 12 14 16 18 20 22 24 26 28 3 3 2 34 36 48 16 16 17 16 19 20 20 21 22 21 23 23 25 29 21 23 22 25 27 27 33 37- i; 4i 39 41 41 44 49 45' 47 53 54 58 50 55 57 59 61 61 64 58 62 62 62 61 61 62 65 65 67 68 63 67 70 72 75 78 84 69 73 73 74 74 77 78 77 82 85 89 94 98 74 82 84 88 94 99 80 86 89 93 98 86 94 99 92 96 96 98 99 99 96 98 99 COPPER SMELTING 189 Composition of Copper and Slag in Roasting-Smelting for Blister Copper. Welsh "Roaster" Slag. Kaafiord. Silica 47.5 36.0 Protoxide of Iron 28.0 7.0 Alumina 3.0 6.0 Cuprous Oxide 16.9 43.2 L/ime 2.7 Magnesia 0.8 Nickel and Cobalt Oxides 0.9 4.9 Oxide of Tin 0.3 0.6 Oxide of Zinc 2.0 3. 2 Welsh Blister Copper. Kaafiord. Copper 99.2-99.4 Iron 0.7-0.8 0.1-0.2 Nickel and Cobalt... 0.3-0.9 0.2- 0.3 Zinc 0.0-0.2 Tin 0.0-0.7 Arsenic 0.4-1.8 Sulphur 0.1-6.9 o.i- o.i 2 BLAST FURNACE SMELTING^ Blast furnaces for smelting copper ores were first used in Germany. They have been successfully introduced in all im- portant copper producing countries, and have been specially favored in the United States. The evolution of the copper furnace has been quite as remarkable as that of the iron furnace, though no doubt a great deal has been borrowed from the iron smelter. There are a number of styles of furnaces in use for the treatment of copper ores, the differences being brought about by the varying character of the ores, fuel and other local condi- tions. Fig. 68 represents the round style of furnace commonly used in the West. It is built of steel plates, rivetted together, and is supported on four cast iron columns. The annular base plate is also of cast iron. In the center of this is a larj e, circular opening which is closed by two drop doors. The crucible is lined with fire-brick, and the bottom is tamped with clay. The walls above the crucible are water-jacketed almost t. the charg- ing door. These jackets consist of outer and inner walls of steel plates rivettecl or welded together to form a shell through which the water is circulated. The inner wall of the jacket is often Fig. 68 Round Type of Blast Furnace. (Allis-Chalmers Co.)' Fig. 69 Rectangular Type of Blast Furnace. (Allis-Chalmers Co.) COPI'ER SMELTING 19 r made of copper, since copper is not so readily corroded by the charge as steel is. At the top the furnace walls are contracted to form a hood, which terminates in the stack. The out- line in the region of the hood shows the location of the charg- ing door. The blast is furnished by means of a positive blower of the rotary type. It is received in a box surrounding the furnace, and is delivered to the charge through tuyeres which pierce the water-jacket. Access to the tuyeres is gained from the outside through small openings in the blast box. The openings are closed with sliding doors. The location of the slag spout is shown in section, and the matte spout is shown in outline. These furnaces are used both with and without the forehearth. In order to increase the capacity of the copper cupola the cru- cible is widened. Since it is necessary that the blast penetrate the charge fully, the limit to which the crucible may be widened is soon reached. It may, however, be extended in one direction, leaving the opposite tuyeres the same distance apart. This has been done in the development of the elliptic and rectangular styles of furnace. The photographic view (Fig. 69) shows the rectangular style of furnace. This furnace is water-jacketed in double tiers, the upper jackets extending below the tuyere line. .Both the upper and lower jackets are supported from a mantle frame of heavy beams and channels carried on four cast iron columns. The tap-holes and spouts are shown at the front side and end of the furnace. The slag spout is of bronze and water- jacketed. The bottom plate is supported on jack-screws which are carried on a truck. This arrangement facilitates the re- moval of the bottom when it becomes necessary. In the older -furnaces the base plate is supported on short columns. The furnace walls above the water-jackets are of brick, reenforced as shown. 1 The hood is made of cast iron or steel, and is pro- vided with two openings for charging. The hood carries the stack and downtake pipes, which are of steel. The blast pipes and water connections are easily traceable in the illustration. 1 Brick walls are less destructible than metal in this part of the furnace, since the metal is corroded by sulphates in the ore. 192 METALLURGY Forehearths. Copper blast furnaces are commonly equipped with forehearths, the duty of which is to take the slag and matte from the furnace as fast as it accumulates. In other words, the forehearth is an outside crucible which relieves the inner crucible or furnace hearth of the scorifying melt. The forehearth is lined with fire-brick or water-jacketed, and is provided with a spout at the top for the overflow of slag and a tap-hole for drawing off the matte. It is usually kept covered to prevent the rapid cool- ing and crusting of the contents. The forehearth is mounted on wheels so that it can quickly be replaced by a new one when disabled. The Process. When a furnace is to be blown in it is never begun with the regular charges. The first charges contain a rather large proportion of coke, and the rest is principally slag from previous running. When the temperature is high enough ore is introduced, and is increased with each charge until the regular burden is reached. The furnace is charged continuously as in iron smelting, and the blast pressure is regulated to suit the con- ditions of working. Limestone is added as a flux. Much skill is required in maintaining the proper mixture of ore and flux, so that the slag will contain a minimum amount of copper. The fuel is gaged to supply sufficient heat and to permit of some oxidation. The matte and slag run out of the furnace as fast as they are melted and collect in the forehearth, where they separate by gravity in layers. The slag runs away through the spout pro- vided, and is usually rejected. The matte is tapped at inter- vals into ladles and taken away for further treatment. The principles of blast furnace and reverberatory smelting do not differ materially. In blast furnace practice the charges are calculated more closely, so that the mixture will throw down the proper grade of matte. Blast furnace slags generally contain less copper, and the tenor of copper in the mattes is lower. A great deal of importance is attached to the selection of ore for the charges. If there is a large quantity of fully oxidized ore in stock, raw sulphide is mixed with it, lest copper be fully reduced and carried into the slag. On the other hand, care is taken not OF THE [UNIVERSITY Fig. 70 Bisbee Converter. (Allis-Chalmers Co.) COPPER SMELTING 195 to allow too much sulphur in the charge, since that would carry down more iron into the matte, rendering it too low in copper. It is the aim to make as uniform a grade of matte as possible, and the furnaces are usually pushed to their full capacity. Up to a certain limit, the greater the blast pressure, the more rapid will be the melting, and the lower will be the consumption of fuel per ton of matte. The disposal of the matte as fast as it is melted greatly length- ens the life of the furnace hearth. It has been found best in most American works to aim at a matte containing 45 to 55 per cent, of copper. The effort is made to concentrate any gold and silver into the matte so that they will be recovered with the copper, and to discard as much of the slag as possible. This may be done if so little copper passes into the slag that it is worthless. The example given on next page may be taken as representa- tive of modern blast furnace practice. 1 Treatment of Matte in Bessemer Converters. This process was invented in 1880 by John Hollway, of England, and was intro- duced into the United States shortly afterwards. The idea was borrowed from Bessemer's patent, the general form of the con- verter and the handling of it being similar. The Bisbee converter, representing an improved style, is shown in Fig. 70. This is built in the form of a short cylinder, the cuter shell of which is of steel plates and the lining of crushed quartz or silica in other form. The cylinder is mounted hori- zontally on four friction rollers, and is rotated by means of a vertical rack and hydraulic power. The rack is held against a spur gear on the head of the vessel. The blast conduit, attached to the converter shell, is shown in the illustration. This is con- nected with the blast pipe from the blowing engines in line with the axis of the converter, so that it does not interfere with the rotation of the latter. Since the level of the tuyere openings 1 Peters-" Copper Smelting," p. 367. 7 194 METALLURGY 'S $ CO % S 8 CO vo ? 3- 2 IO O^ M CO VO O^ O^ cO 00 tO 3 *> co cs M CO s a*; r cen rO ~ q o TJ. ON o> oo -" O co CO o o cr* J (i 5 (N rO 9 c? 5 ^ S P 00 CO CO CO C< CO 9 R $ 3* S q M CS _1 q |4 u 10 *^ VO 10 w 00 CO co 5 Q\ CS IO ^ 00 ^ O vo o X co' 4 VO co Tj- VO w CO ^O ^ CS M CS t^ tO 2 fi.j vo CO ON fO ON Tj- rO VO OO vo cs' 1 "* co Tf CS s IO ;? ft 8> 8O cO *O t^ VO vo vo co ^ I s * cs' CO JO cs cs vo f^ 1 Cs ON ^- cs CM co - vo \,O "5 ^'"3 f^ 10 q q ? oo o o r *' C !, \yj h4 ^" vo o CS VO M Ov M M CS co rr cs s CO Tj- s 5 i? S 1 O n co Tt O t^ M g 2^ 2 55* cs" M r? cs : ' : : : I 1 ffi 03 3 : <5 * % V ' % : Calcines . S g s 5 S S g 5. CJ - P > G J^ fl o -~ 3 o U M U 8 : 2 : o -3 ; y o rt fl _M ?5 'S b* S S .2 -o o 2 2 CO n4 O H pu, t/3 S T. Q COPPKR SMELTING 195 is above the bottom of the converter, the metal that settles to the bottom during a blow is not disturbed by the blast. 3 The Process. Before charging the first time the converter is heated by means of a coke fire. It is turned down to the hori- zontal position and the molten matte is run in. At the same time a light blast is turned on, and this is increased to the full pres- sure as the converter is raised to the upright position. Desul- phurization begins at once and proceeds rapidly as shown by the rise of a bluish-white flame from the mouth of the converter. The blow is continued until all the iron is oxidized and fluxed, a point which can only be ascertained from experience. The blower is guided by the appearance of the flame, the border of which is greenish while the iron is being oxidized. The appearance of the flame is altered by such volatile impurities as lead, zinc and arsenic. If much slag forms it is poured off before the blow is finished. Being so much lighter than the copper sulphide the slag separates in a distinct layer, and it is poured off by tilting the vessel. The slag generally retains too much copper to be discarded, and it is returned to the matte smelter. The residue in the converter is almost pure cuprous sulphide. The blowing is continued until the sulphur is practically removed, leaving 1 the copper from 97 to 99 per cent. pure. The copper is cast into pigs or into anode plates, according to the way in which it is to be refined. In theory the Bessemer process is similar to the other pro- cesses by which blister copper is made. The reactions of course take place much more rapidly in the converter, since by blowing air through the molten matte the entire charge is acted on at once. Instead of silicious ore as is added in the reverberatory process, the supply of silica is drawn from the converter lining. If the charge of matte is low in copper the slag will of course be great in bulk. It is high in silica and very liquid. A rich matte yields a small quantity of thin slag, rich in iron. A quan- 1 Copper converters are universally side-blown, since bottom blowing would oxidize the metallic copper before the oxidation of the matte was complete. METALLURGY (I) l) 21 6 (2) c o O' u jo 4 57-9 7.8 tity of dnst passes out of the mouth of the converter with the flame. This contains the oxides of such volatile impurities as lead, zinc, arsenic, etc., some copper and not infrequently gold and silver. The higher the percentage of volatile matter the greater will be the loss of precious metals. Peters gives the following analyses of flue dust from two different works : Silver (oz. per ton) Copper (per cent. Lead Zinc " The time required for converting a 55 per cent, matte is about one hour. The following analyses, given by W. R. Vanliew, show the rate of oxidation in a Bessemer charge. 1 Time Copper per cent. Iron Sulphur per cent. Zinc Arsenic ' ' Antimony " Silver ounce Gold The Bessemer process is now firmly established, though it is likely still to undergo some important changes. The practice has grown considerably within recent years in spite of serious difficulties in the way of improvements. One of the most seri- ous objections to it lies in the cost of repairs. The attempt has been made to substitute a more durable material for the lining, thus doing away with the expensive practice of renewing the lining of crushed quartz. Basic linings have been tried, the necessary silica being added to the charge, but so far no practical results have been gained from these experiments. 1 Trans. Amer. Inst. Min. Eng., 34, 418. ; Cupola Tap 10 Min. 20 Min. 30 Min. 40 Min. 70 Min. Blister Copper nt. 49.72 50.20 56.88 64.60 76.37 99.120 ' 23.31 23-I5 17.85 10.50 2.40 0.038 cent... 21.28 20.95 19-74 18.83 16.30 0-159 " .. 1.19 1. 2O 0.84 0.70 0-45 0.090 " -. o.n 0.09 0.08 0.08 0.08 0.0012 " . 0.14 A A OCi 0.12 42 QO 0.10 C T AQ 0.13 rr O 0.13 *7O OO O.OO6 r\f\ $\C\C\ Tfi q.z.yu O- T/i 1 .^.V O.2O GO' 00 O 2/1 O.72 yLJ.OvJU n 7^0 COPPER SMELTING IQ7 PYRITIC SMELTING The term pyritic smelting refers to those methods of smelting ores in which no fuel is used save the sulphur which the ore con- tains. As has been stated, all processes, to a certain extent, utilize the heat from the oxidation of the sulphur in the ore or rnatte, but additional heat has been supplied from extraneous sources in all processes heretofore studied. Theoretically, it is possible to smelt some ores to the production of blister copper without extra fuel, and in practice this has been accomplished to the extent of reducing the fuel cost to insignificance. Copper metallurgists have devoted a great deal of attention and energy of late years toward the perfection of such a process, and much has been gained as the result of experimental practice. A blast furnace is employed in pyritic smelting, and as a rule, the blast is preheated. A small amount of coke is added to the charge, as occasion requires, and the process is conducted sim- ilarly to ordinary blast furnace smelting, for the production of matte. The matte is treated by the Bessemer process, which is in itself "pyritic smelting." Pyritic smelting has been found especially adaptable to rich sulphide ores bearing gold and silver. The Elimination of Impurities from Copper Ores During Smelting. A complete study of the metallurgy of copper would involve not only the processes by which copper itself is extracted, but also those by which various other metals, associated with copper ores, are recovered. For example, some ores carry nickel as well as copper in workable quantity, and it is not infrequent that gold and silver are present in sufficient amounts to justify more expensive methods of treating the ores in order to recover them. Furthermore, there are often objectionable impurities in copper ores which require special care for their removal. The most important of the foreign elements met with, and their be- havior during the smelting are summarized below. Silicon. This element occurs as silica and silicates in the ore. It is fluxed (as silica) by any basic, metallic oxides present, lime IQ8 METALLURGY * being added as a special flux to prevent its combination with cuprous oxide. In the blast furnace some silicon is reduced and this may escape oxidation and be found in the blister copper. Sulphur, owing to its affinity for copper, is not eliminated until the concentrated cuprous sulphide is obtained. It is finally separated by oxygen at the high temperature of the converter or the reverberatory furnace. Iron exists chiefly as a sulphide in the ore. It mixes as such with cuprous sulphide in the matte smeltery. In an oxidizing atmosphere iron parts with its sulphur at a comparatively low furnace temperature, and it is readily fluxed and separated from cuprous sulphide by means of silica. A small amount of iron is reduced, and alloyed with the copper. Arsenic should be, for the most part, removed from the ore (luring the roasting, being volatile. Most of the arsenic that is left in the ore is retained by the copper, either as arsenide or arsenate. Antimony is similar in its behavior to arsenic. It is concen- trated like arsenic in the matte or speiss. Antimony is less volatile than arsenic, and is more difficult to remove from the ore by heating. Nickel behaves much like copper during the roasting and fusion. But nickel matte is heavier than copper matte, and when a sufficient amount is present it may be separated by liqua- tion. See nickel smelting, p. 273. Zinc is oxidized during the roasting, and in the fusion a large portion passes into the slag as silicate, often causing annoyance to the smelter on account of its infusibility. In a reducing atmosphere some of the zinc is reduced and volatilized. It is again oxidized upon reaching the upper part of the furnace and the flues, where it is deposited. Lead, if present in any considerable quantity in the ore, will COPPER SMELTING 199 be found in every product of the smeltery. A large part of it is reduced in the matte, and most of this is subsequently volatiliz- ed during the fusion for blister copper. A smaller portion re- mains alloyed with the copper. It should be understood that lead is not volatilized like zinc, as a metal, but in the form of oxide and sulphide. Silver and Gold are almost entirely retained in the matte if it is made under a very liquid slag. During the conversion of the cop- per some of the precious metals escape with the slag, and in the dust of the converter, but the larger portion remains alloyed with the copper. EXTRACTION OF COPPER IN THE WET WAY The so-called wet processes look to the conversion of the cop- per in the ore into a soluble form. It is subsequently extracted with water and precipitated with iron or by means of the elec- tric current. The fact that a large amount of copper-bearing material can be treated in this way at a comparatively low cost makes the wet methods adaptable to low grade ores and products carrying a small amount of copper. The Sulphate Process. This consists in converting copper sulphide into sulphate by oxidation. If the material is very poor in copper, and fuel is dear, the oxidation may be brought about In a slow way by the atmosphere. The ore is exposed to the weather in heaps which are arranged over a floor of clay or some material that will not soak up water. Ditches are led from the piles to a pond in which the drainage is collected. As the oxida- tion proceeds by natural processes, the rains leach out the ferric and cupric sulphates, and this solution is caught and poured over the piles repeatedly. Finally the ore is leached with clear water, and the combined solution is evaporated and the copper is precipitated. This crude method is not of importance in this country. The more usual method of oxidizing ores is by roasting them at a low temperature. With proper care almost the entire con- tent of copper in the ore may be converted into sulphate by roasting. The roasted ore, being in the form of fines, is extract- ed in suitable tanks or vats. 2OO METALLURGY A considerable saving may result from the recovery of drain- age water from ore heaps during the roasting. If the heaps are exposed to the rains, no small portion of the sulphate formed will be leached out. Waste slags from smelteries often contain a sufficient amount of soluble copper to pay for its extraction. The Chloride Process. The copper is converted into the chlo- ride by treating the ore with a solution of ferric chloride 3 CuS + 2Fe 2 Cl 6 = 2 Fe 2 Cl 4 + Cu 2 Cl 2 + CuCl 2 + 3 S. Or, more commonly, the ore is first roasted to drive off the ex- cessive sulphur, and then roasted with salt CuS0 4 + 2NaCl = CuCl 2 + Na 2 SO 4 Cu 2 -f 4 NaCl = 2CuCl 2 -f 2 Na 2 O. The copper is precipitated from the solution of the chloride as from the sulphate solution. CHAPTER XIX COPPER REFINING As has been already stated, the properties of copper are in- iluenced by the presence of very small amounts of impurities. The purification of copper for the market must therefore be most thorough. It is said that in this country a rather high ideal exists on account of the remarkable quality of Lake Superior copper. No doubt the phenomenal growth of the refinery has been largely due to the competition between the copper producers of this and other localities. Two distinct processes are in use for the purification of blister copper the furnace and the elec- trolytic processes. THE FURNACE PROCESS The furnace used for the melting and refining of native and blister copper is a large reverberatory. It is provided with doors for charging and tapping, and a large grate for main- taining a high temperature. Gas furnaces are also in use. The hearth is well soaked with copper by melting down successively small charges which have been spread over the surface. Pure metal should be used for this purpose, since it stands the wear better, and besides, impure metal would be the means of con- taminating many charges after they had been refined. The furnace, having been made ready, is charged with blister copper. The doors are closed and the charge is melted down under a reducing flame. The thin slag which forms is skimmed off, and the furnace doors are opened to expose the surface of the metal to the air. A coating of cuprous oxide is iormed at once, and this gives rise to more slag by its fluxing action on the impurities. Such action is hastened by skimming off the slag at intervals of an hour. The escape of sulphur dioxide has the beneficial effect of agitating the bath, thus bring- ing the oxidizing medium into more intimate contact with the impurities. After the bath becomes more quiet and the slag is 202 METALLURGY rich in cuprous oxide it is rabbled continuously for a period of about two hours. The copper now becomes "dry" from the absorption of cuprous oxide, and a test shows the characteristic brick-red color. The foreign matter has been removed, and it now remains only to reduce this oxide. This is accomplished by the method known as "polling." A long pole of green timber, as large as can be managed, is thrust into the bath. The hy- drocarbon gases and other agents reduce the copper, the sur- face of the bath being covered with fine charcoal to prevent further oxidation. Tests are taken and submitted to mechanical treatment, and when these show the properties of pure copper the metal is tapped and cast into pig molds for the market. The slag is returned to the smelter. Elimination of Impurities. Metals of low melting point may be separated from copper by heating the alloy to a temperature insufficient to fuse the copper but considerably above the fusion point of the other metal. 1 The older process for separating gold and silver was to melt the copper with lead, the bulk of the lead separating from the copper by liquation and carrying with it the heavy metals. The recovery of the precious metals from the lead is explained under the metallurgy of lead. The ele- ments which are most completely removed in the refinery are sulphur, iron, silicon, arsenic, antimony, bismuth and oxygen ; also lead and zinc, when present in small quantity. Copper of less than 96 per cent, purity is treated in a separate furnace. Sometimes a small quantity of white metal is added at the be- ginning of the operation to aid in the elimination of arsenic and antimony. The impurities are oxidized in the refinery, and are either transferred to the slag or volatilized. The copper itself acts as a carrier of the oxygen. This is shown by the fact that a much more rapid elimination of the impurities results from mixing cuprous oxide with the metal. The oxygen is not completely removed from the bath by polling. According to Egleston it can not be reduced to o.i per 1 See p. 224. COPPKR REFINING 203 cent. About 4 to 6 per cent, of the total charge of copper is removed in the slag of the refinery. A tilting furnace, operated like the tilting furnaces of the steel maker, has been recently introduced for melting copper and matters. With such a furnace there is a great saving of labor, since both the slag and the metal are discharged mechanically. THE ELECTROLYTIC PROCESS The fact that copper can be precipitated from aqueous solu- tions by means of an electric current has been known for more than a hundred years, though it had but few practical applica- tions until after Faraday's discoveries (1833). Following these were the inventions of electrotyping and electroplating. The refining of copper by solution and precipitation is suggested from the fact that practically pure copper may be precipitated from solutions containing other metals. The art was introduced by Elkington, and his first commercial refinery was built at Pem- bry, Wales in 1869. It is interesting to compare this date with that of the advent of the dynamo (1867). So great an under- taking as electric refining on a large scale could never have been continued had not the dynamo been invented and the cost of the electric current greatly lessened. The demand for highly purified copper and the price it commands have more than justi- fied the cost of refining it by electrolysis. Electrolytic refining is now practiced in all copper producing countries, being most adaptable to copper containing arsenic, antimony, bismuth and the precious metals. In the United States more than 80 per cent, of the entire output is refined in this way, the cost having "been reduced to four or five dollars a ton. 1 General Principles of Electrolysis. In the drawing (Fig 71) are represented two copper plates, A and C, immersed in a dilute solution of sulphuric acid. To the heavy plate, A, is attached a wire, which is connected with the positive terminal of a direct current generator, the wire from C is connected with the nega- tive terminal. If no current connection were made the copper of both plates would be slowly dissolved, the acid being decom- posed 1 Ulke, "Modern Electrolytic Copper Refining." 2O4 METALLURGY Cu + H 2 S0 4 = CuS0 4 + H,. But copper sulphate, according to the theory of Arrhenius, is dissociated in an aqueous solution into copper and SO 4 ions, and the current in passing through the solution gives direction to these ions, causing copper to form at the negative and SO 4 at the positive plate * CuS0 4 = = Cu + S0 4 . The positive plate is thus exposed to the action of the acid radi- cal as long as the process of electrolysis is continued. If the SO 4 is not immediately combined it breaks up into sulphur trioxide and oxygen. Both of these products may be detected at the positive plate. The chemical action, resulting from the Fig. 71. solution of the copper in the positive plate, largely neutralizes the back pressure that is set up as the current passes through the solution. For this reason a lower pressure is needed to drive the current through the solution than would be required if the plate were insoluble in the acid. The proportion of acid in the solution gradually diminishes, while the copper sulphate increases. In the application of the principle of electrolysis on the large scale the impure copper is the positive plate, and the pure cop- per is deposited on the negative plate. The positive plate is call- ed the anode, and the negative plate is the cathode. Collectively they are spoken of as electrodes, and the solution is the elec- trolyte. The amount of current that passes through the elec- trolyte is measured in units called amperes. One ampere is the 1 Z. phys. Ch., 1887, 1, 631. COPPER REFINING 2O5 amount of current that will precipitate 1.18656 grams of copper in an hour. The electromotive force, or pressure under which the current is used is measured in volts, and the unit of resist- ance that is offered to the passage of the current is the ohm. in conducting the process of electrolysis on the commercial scale a number of electrodes are placed in each vessel holding the solution, and they are arranged close together to minimize the resistance. Since the amount of copper deposited is directly pro- portional to the current density or amperage, as much current as is practicable is employed. This is limited by the increase in the cost, of generating the current and by the condition of the electrolyte. Other metals in solution with the copper may like- wise be deposited on the cathode, depending upon the current strength and the condition of the electrolyte. Practically, about one dunce of copper is deposited in 24 hours for each ampere of current. The Refining Plant and Process. The refinery consists essen- tially of the power house; the tank house, containing the tanks for supporting the electrodes in the solution, also the appliances for regenerating the electrolyte; remelting furnaces, and other equipment for working up the products. The tanks for holding the electrolytes are constructed of wood, and lined with lead or other acid-proof material. The larger tanks measure 10 feet in length, 3 feet in width and 4^/2 feet in depth. Double tanks are commonly used, the two being sep- arated by a longitudinal wall. The anodes are of cast copper from the smeltery. They are of the shape shown in Fig. 72. The rectangular dimensions are about 30 inches x 24 inches and the thickness i l A inches. The arms at" the top support the anode in the tank. The cathodes are of electrolytic copper, rolled down to 7/32 inch thickness and cut in the same rectangular dimensions as the anodes. The cathodes are supported from copper rods passing through loops, which are rivetted on in the manner shown. The drawing is a section through a double tank in which copper is refined. The plan of a double tank with the current connections is shown in Fig. 73. The heavy lines represent the anodes and the 2O6 METALLURGY narrow lines the cathodes. The direction of the current is in- dicated by the arrows. The strength of current employed in American refineries is 12 to 15 amperes per square foot of cathode surface. The voltage is increased with the number of tanks in series. As there is /? NODE CATHODE Fig. 72. clanger of loss from leakage under high voltage it is not safe to supply "a large number of tanks from a single feed wire. The theoretical pressure of 1.16 volts required to precipitate copper from the sulphate solution is reduced in practice to 1/6-1/3 volt, by virtue of the soluble anode. The electrodes may be- Fig. 73- come short circuited in one of two ways. The growth of cop- per on the cathode may be irregular, accretions of crystals ex- tending to the anode, or, the deposit of "anode mud" on the bot- .tom of . the tank may accumulate more rapidly than was ex- COPPER REFINING 207 pccted, and touch both electrodes. Frequent inspection is needed to remove these obstructions, since electrolytic action ceases as soon as a short circuit is established. Under normal conditions the electrolyte contains about 19 per cent, of copper sulphate, 6 per cent, of sulphuric acid and 75 per cent, of water. The solution is frequently tested for free acid and the necessary amount is restored. The circula- tion of the solution keeps its composition uniform, but the im- purities and the excessive amount of copper sulphate must be removed from time to time. Purification of the Electrolyte. The components of the anode are transferred to the cathode; dissolved and precipitated as chemical compounds; dissolved and kept in solution, or left undissolved altogether. The heavy, undissolved matter falls to the bottom of the tank, forming what is termed anode mud or slime. It is the aim to keep the composition of the solution and the strength of the current such that only the copper will be electrolyzed. In this brief outline of the methods of treat- ing the electrolyte, the history of the several impurities of the anode may be followed. A part of the electrolyte is drawn off for treatment. The copper sulphate, which is all the time increasing in the solution is removed by crystallization, special tanks being provided for this purpose. Cuprous oxide and cuprous sulphide go into the slime, but they are to a certain extent decomposed and added to the solution. Gold and Silver fall down with the anode mud. Iron, Zinc, Nickel and Cobalt dissolve and remain in ttye solution. Bismuth is dissolved and partly precipitated as the sulphate. Arsenic dissolves and precipitates as an arsenite as the solu- tion becomes more saturated. If the bath is deficient in acid or copper, arsenic will be added to the cathode. Antimony is dissolved and partly precipitated as a basic sul- phate. Like arsenic it follows the copper if the electrolyte becomes neutral or low in copper. 2O8 METALLURGY Lead is precipitated as the sulphate, most of which settles with the slime. The soluble impurities must be removed, as noted above, since pure copper can not be precipitated from a solution which is heavily charged with other metals. A portion of the solu- tion is therefore under treatment all the time, and after purifica- tion it is returned to the circulation. The purification of the solution is quite an intricate process in itself, some of the methods of treatment being kept secret. The iron, nickel and cobalt may be removed by crystallization. Arsenic, antimony and bismuth are precipitated by oxidizing the hot solution by means of fine streams of air, and by neutralizing the acid with scrap copper. These operations are carried on in lead-lined vats or tanks. Treatment of the Anode Mud. This is removed from the tanks once a month, or as often as necessary, and treated for the recovery of silver and gold. It is first boiled with sulphuric acid to dissolve most of the base metals, and after decanting off the acid the residue is washed with water. The residue is dried and smelted in a small furnace with soda-ash and sand. The silver obtained carries both copper and gold, and is separated by acid parting or by electrolysis. (See p. 270). CHAPTER XX LEAD ORES, PROPERTIES, ETC. History. The date of the discovery of lead is not known. It was employed by the Egyptians, Greeks and Romans long be- fore the Christian Era. The Romans opened mines in Britain, {Saxony and Spain, some of which are still operated. Lead was one of the first metals mined in this country, though it is probable that in the treatment of lead ores by early American prospectors silver was the metal sought. Mines were operated before the Revolution in the states of New York, Virginia and North Carolina, and in the Mississippi Valley. The Rocky Mountain deposits came into prominence in 1867, and the lead industry has grown rapidly in the West since that time. The West now leads in the production of lead. ORES Galena (PbS). This is by far the most important ore of lead. It occurs both crystalline and massive, associated with dolomite, limestone and silicious rocks. Galena is not in- frequently associated with pyrites and ores of zinc and silver. It may also contain arsenic, antimony and other impurities in smaller quantities. Cerusite (PbCO 3 ) is an important ore in the West, occurring but sparingly elsewhere. It is usually impure, and carries other oxidized forms of ore, such as the sulphate and oxide. Pyromorphite (PbCl 2 +3Pb 3 P 2 O 8 ) is met with, but it is not an important ore. Lead ores occur but sparingly in the Eastern states, though some of the mines in the Appalachian region are still productive. Next to those of the Rocky Mountains the Mississippi Valley deposits are the most important. Idaho, Colorado, Utah, Mis- souri and Kansas are the leading lead-producing states. PROPERTIES Pure lead is of a bluish-gray color and highly lustrous. It J 21 METALLURGY does not ordinarily present a crystalline structure to the naked ey~, but under proper conditions of cooling from the molten state it solidifies in octahedrons. The principal properties to which lead owes its usefulness, are its malleability, flow and density. Lead melts at 327 C., and boils at about 1,500. It alloys readily with arsenic, antimony and tin, less readily with copper, gold and silver, and with zinc it is said to form no true alloy. Effect of Impurities. The impurities more commonly met with in commercial lead are antimony, arsenic, bismuth, copper, iron, zinc and silver. Antimony. This metal is frequently associated with lead ores. If a large proportion is present the ore yields an alloy of the two metals. This is known as "hard lead." Besides hard- , eninj lead and destroying its malleability, antimony has the peculiar property of causing the alloy to expand when cooled from the molten state. Arsenic is also frequently associated with lead ores and its effect upon the properties of lead is similar to that of antimony, rendering it hard and brittle. Bismuth is much less frequently met with and is not often present in sufficient quantity to injure lead. It lowers the melting point, and renders the lead hard and crystalline. Copper is a very common impurity in unrefined lead, and is often added in the manufacture of certain alloys. The small amount that is left in refined lead is not sufficient to interfere with its working properties. Silver in small quantities is a very common ingredient of lead ores, and is therefore to be expected in the lead as it comes from the smelter. Silver-lead alloys that are purposely made in the extraction of silver are known as "work lead." Small percentages of silver lower the melting point of lead, and large quantities harden it and raise the melting point. Iron alloys with lead only under special conditions, and is never an interfering element. Commercial lead contains but a few hundredths of a per cent, of iron. LEAD 211 Zinc is not a common impurity in lead. It imparts a lighter color and renders lead hard and brittle. Chemical Properties. The chemical properties of special in- terest in the metallurgy of lead are its action toward oxygen and sulphur, its basic character, and the ease with which it is reduced from all its compounds. When exposed to moist air, or when heated in air just above the fusion point lead becomes coated with a dull-gray film of suboxide (Pb 2 O). At a higher temperature litharge (PbO) is formed, and at a still higher temperature litharge is further oxidized to red lead (Pb 3 OJ. The most important of these oxides in metallurgy is litharge. This melts at a red heat and is very volatile at higher tempera- tures. It is strongly basic, forming an easily fusible slag with silica. The oxides of lead are reducible with carbon. Lead combines with sulphur at a moderately high tempera- ture, forming a lustrous, brittle, gray mass (PbS). Tjhis is also volatile at furnace temperatures, and is less fusible than lead. Heated in the air lead sulphide is converted into the oxide and sulphate. If either the sulphide or the sulphate is fused with the oxide, decomposition of both compounds takes place with the liberation of sulphur dioxide and lead. Roasted galena contains all three of these compounds. The sulphide of lead is also decomposed when heated with some metals, notably iron, and with strong basic oxides such as lime. Lead com- pounds in general are decomposed by fusion with strong bases. The sulphate is soluble in alkaline acetate solutions, and from these lead may be precipitated by electrolysis. Lead is not readily acted on by either sulphuric or hydro- chloric acid, but it is freely dissolved by nitric acid. PREPARATION OF LEAD ORES FOR SMELTING The oxidized ores are easily reduced with carbonaceous fuel and require no special treatment beforehand, other than some separation from the gangue. Galena, to which attention is here directed, may be further concentrated with great advantage by roasting. The ores of lead are extremely variable in composi- tion, and their treatment for the recovery of lead and other metals presents one of the most complicated propositions in 212 METALLURGY metallurgy. The first operation is to separate, as far as pos- sible, the lead-bearing mineral from the vein stuff or from other associated ores. Copper and iron pyrites and zinc blende are often present. A good deal of concentrating may be done at the mine by hand picking. Further concentration is af- fected by washing, the jig being specially adaptable to washing lead ores. A process employing magnetic machines for concen- trating pyritous ores of zinc and lead is outlined on p. 233. Roasting. There are but few instances in which lead ores are not roasted before smelting. The roasting process is, how- ever, often inseparable from that of smelting, both being per- formed in the same furnace. If the ore is rich in sulphur and in lump form it may be roasted in heaps or stalls, but open air roasting is rarely, if ever, resorted to in this country. The ore is usually fine, crushed if necessary, and is roasted in some form of reverberatory furnace. The hand reverberatory, described on p. 176, is the most common. Mechanical roasters, and in a few instances, shaft furnaces are employed. The roaster is often heated by means of waste heat from the smelting furnace, the two furnaces being under the same roof, and the hearth of the smelting furnace being situated on a lower level than, and close to that of the roaster. With such an ar- rangement there is a considerable saving in the handling of the ore. In connection with the roaster,, chambers or flues are built for settling the fume. The subject of lead fume will be dealt with in the next chapter. The Process. The ore is. charged through a hopper in the roof of the furnace and leveled down over the hearth. It is charged at the cooler end of the hearth and during the roasting it is turned and moved toward the fire-bridge. The furnace temperature is regulated and the ore is frequently stirred to prevent fusion. It is readily seen how fusion or caking would check oxidation. The temperature employed and the extent of the roasting depend upon the nature of the ore and the way in which it is to be smelted. As a rule, the ore is allowed to sinter but slightly on the finishing hearth. As it is withdrawn LEAD 21$ the roasted ore contains lead sulphate, oxide and unaltered sul- phide, with possibly some metallic lead. The analyses below show the composition of an ore before and after roasting. 1 Pb Fe Zn SiO 2 S SO 3 O Raw Ore 47.29 20.36 0.67 0.49 29.86 ... Sintered Ore 54.27 24.06 0.87 0.80 2.72 2.25 13.41: Hofman's "Metallurgy of Lead," p. 167. CHAPTER XXI LEAD SMELTING Lead is at once a very easy metal to reduce from its ores and one of the most difficult to recover completely. Unless properly guarded against, serious losses will result from vola- tilization and the tendency of lead compounds to enter the slags. The subject being a very complex one, only typical processes will be described in this text. The subject will be studied un- der three heads, according to the types of furnaces employed. REVERBERATORY SMELTING Though not so much used in America, reverberatory furnaces are favored among foreign smelters. They belong to older prac- tice, but in many cases they are undoubtedly more adaptable to the localities in which they are used than any other furnace. They are cheaper to construct and make purer lead than is made in blast furnaces, but their output is smaller and they are not so well suited for ores of low or irregular grades. As a representative of this style the English reverberatory may be taken. The main differences in the construction of this and other reverberatory furnaces, designed for smelting pur- poses, may be understood from the hearth plan (Fig. 74). The fire-box is shown at the right of the drawing and the flue entrances to the stack at the left. Thei furnace has three working doors on both sides and a charging hole in the roof. It is built of common brick and lined throughout with fire- brick. The walls are held together with buckstaves and tie- rods. The bottom is built up with fire-brick, giving the proper slope from both ends and the back toward the front of the fur- nace. Upon the brick work is laid a deep lining of sand and slag from previous operations. The hearth slopes toward the middle door on the front side of the furnace, and in the low- est part there is a sump or well in which the lead accumulates. A tap-hole is provided for drawing off the lead from the well, and an iron pot is placed outside to receive it. LEAD SMELTING 215 The Process. About one ton of fine ore is charged and spread over the hearth. The ore begins to decrepitate at once since the furnace is preheated. The temperature of the furnace is kept low at first and the atmosphere strongly oxidizing. Should any ore begin to fuse it is raked away to a cooler part of the hearth. The ore is turned and stirred on the hearth to facilitate even and complete roasting. The roast- ing requires about two hours, at the end of which time the doors are closed and the fire is urged, to bring on the melting stage. A quantity of lead now runs from the ore and collects in the well from which it is tapped into the pot outside. Some undecomposed galena also melts and forms a layer on top of the lead. This is "set up" by mixing it with lime, and the now stiffened mass is raked back on the upper part of the hearth Fig. 74- with the ore. This is followed by another roasting and fusing, which results in the liberation of most of the remaining lead. If a large amount of galena still remains more lime is added, and the roasting and fusing are repeated. The lead is pro- tected by a covering of slack while in the well. After tap- ping into the pot it is ladled and cast into molds. The slag contains too much lead to be rejected, and is smelted in a separate furnace. This process is only suitable for smelting rich sulphides. It belongs to those known as the "air reduc- 2l6 METALLURGY tion" or "reaction" processes, in which no reducing agent is added, the lead being liberated by the double decomposition of its own compounds. With silicious ores the treatment is different. Formerly the roasted ore was fused with scrap iron in a reverberatory fur- nace (Cornish process). The ore is first roasted somewhat as above described, until the residue yields no more lead. The residue is then mixed with coal, spread over the furnace hearth and the iron is added. The temperature is then raised very high, the air being excluded. The lead and a small amount of unaltered sulphide run out, leaving a slag which is almost free from lead. This process has been practically abandoned in favor of hearths and blast furnaces. HEARTH SMELTING The ore hearth in lead smelting may be considered as inter- mediate between the reverberatory and the blast* furnace. The style of hearth used in England, better known as the Scotch hearth, is described by Percy. 1 In this the or is roasted and fused simultaneously, but the furnace can not be operated con- tinuously on account of overheating. The hearths used in this country work on the same principle except that the process is not interrupted, the hotter portions of the furnace being water- cooled. The hearth consists essentially of a rectangular, cast iron box. set in masonry, and above this a rectangular enclosure formed by water-cooled blocks of cast iron, with one of the longer sides left open. This is the front side of the hearth from which the lead flows over an inclined plate when the box or well is full. The blast is supplied from three tuyeres pass- ing through the back wall. A hood communicating with a stack is placed directly over the hearth for carrying away the fumes. The Process. A new hearth is heated for some time with a good fire before any ore is charged. The first charges are light and consist largely of silicious slag. The ore, mixed with lime, is increased to the normal charge and is covered with a layer of fuel. The blast in playing upon the burning fuel brings the 1 Metallurgy of Lead, pp. 278-289. LEAD SMELTING entire mass to a glowing heat. The lead is rapidly reduced and trickles down into the basin and overflows through the spout. The slag accumulates on the ash bed until it is tapped. The hearth is well suited for smelting coarsely crushed ores. The lead made by this process may be of a high degree of purity, but the slags are not clean. They are usually smelted in a specially constructed blast furnace. BLAST FURNACE SMELTING Blast furnaces have practically superseded all others in this country for smelting lead ores. They have been found to be the most suitable, largely on account of the non-uniformity of the ores that have to be treated at the same smeltery. The blast furnace is of German origin, though it has undergone many changes since it was introduced into this country. Fig. 75 represents a modern, American furnace for smelting lead ores. This furnace is rectangular in cross-section, and in some respects it resembles the rectangular copper cupola. The bosh walls are water-jacketed, and the upper walls are built of common brick with a lining of fire-brick. These walls are very thick especially toward the base, and are supported on cast iron columns. In this style of furnace the shaft terminates at the level of the charging floor, the top being covered with cast iron or steel plates. The fumes and products of combustion are led downward through a steel pipe to dust chambers. The en- trance to the downtake is below the level of the charging floor as shown by the circular outline. The crucible .of the furnace is lined with fire-brick. Since these are penetrable by molten lead, a bottom plate is placed directly under the hearth to prevent wasting of the lead. The lead runs from the furnace automatically through a siphon tap from which it flows into an outside retainer. Above the level of the lead in the furnace there is a tap-hole for the slag. The Process. The furnace is carefully heated with a wood lire followed by coke and light charges of slag. The blast is turned on and increased as required. Ore is introduced and the amount is gradually increased to the normal charges. The slag- is carefully watched, this being the best indicator of the con- dition of the furnace. 218 METALLURGY The furnace having been started, the regular charging is con- tinued. The materials are loaded in barrows, weighed and charged by hand. Materials classed as ores consist of raw and roasted ores and slags. The fuel is generally coke, though charcoal and wood are used in some places. Iron and iron oxide are added as reducing and fluxing agents. Lime is add- ed as a flux and a desulphurizer. In regular working the Level of Charging Floor 75- analysis of the materials is made the basis for calculating the charges. The condition of the slag is the constant means of knowing how the furnace is working. The smelter is warned by its appearance, as it runs from the furnace and cools, of trouble which he may avert by altering the blast or the burden. Experience has taught him to estimate roughly the composition of a slag and to ascertain the presence of abnormal ingredients in it, from the physical state. The example below is of a typical blast furnace charge. 1 1 Hofman's "Metallurgy of Lead," p. 215. LEAD SMELTING 219 4 1 cs* cs *! CO 00 4 3" 2" o3 a s cs* 5 c4 10 M* "= o 10 10 ? s )-> C t/5 00 00 N cs" cs* o . UJ j o o es U-M" PH *{ O W 2 fe j fiS 8M CO q M q -j cr\ SO cO *^ *^ M IO 8 5- T^ O^ 3 8 q vq rO ro s : o" "3- i C/3 * 2 AgCl -f Cu 2 S 2 AgCl + Hg 2 == Hg 2 Cl 2 + Ag 2 4 AgCl + Fe 2 + Hg, = = Fe 2 Cl, -f Ag 4 Hg A .. With the exception of the last, these reactions are common to SILVER 255 all amalgamating processes. By the last reaction it is seen that there is a saving of mercury in the use of iron. Iron is pur- posely added in the barrel process, and in the pan process it is derived from the mortars, pans, etc. Egleston has estimated that for a ton of ore crushed 3*4 to 6^2 pounds of iron are worn from the battery and from 7^ to n pounds from the pan. 3. Leaching The leaching or so called wet methods depend upon the conversion of the silver, if necessary, into soluble form, leach- ing it from the ore, and subsequently precipitating it from the aqueous solution. They are used chiefly for ores containing large quantities of foreign sulphide. The processes are com- monly named after their inventors or improvers. Ziervogel Process. The ore is carefully roasted, beginning with a low temperature, to convert the silver into sulphate. The roasted ore is lixiviated with water to dissolve the sulphate, and the silver is precipitated with copper, the copper being re- covered by precipitation with scrap iron. This process is adapt- able only to ores containing iron, copper or lead, since the sulphate of silver can not be readily formed directly by roast- ing. Augustin Process. The ore is roasted and chloridized with salt. It is then lixiviated with a saturated solution of salt which slowly dissolves the silver chloride. The silver is sub- sequently precipitated from the solution with copper. The pro- cess is seldom used. Patera Process. In this process the silver is chloridized by roasting with salt, the chloride is dissolved in a solution of sodium or calcium thiosulphate and silver sulphide is pre- cipitated from this solution by adding sodium or calcium sul- phide. The ore is lixiviated in large wooden vats provided with false bottoms, over which filtering cloth is spread. The solu- tion is conducted from the bottom of the vat into the precipitat- ing tank by means of pipes. If the ore contains a large amount of foreign matter which is soluble in water it is first leached in 256 METALLURGY the vat with cold water. The thiosulphate solution is run on the top and allowed to percolate through the mass of ore until the silver has been dissolved out as far as is practicable. The precipitation of the silver sulphide is hastened by agitat- ing the solution with wooden stirrers or by means of compress- ed air. The following equations show the principal chemical changes in the solution and in the precipitation. 2 AgCl + Na 2 S 2 3 = Ag 2 S 2 3 -f 2NaCl 2AgCl + 2Na 2 S 2 O 3 = Ag 2 S 2 O 3 .Na 2 S 2 O 3 -f 2 NaCl Ag 2 SA + Na 2 S == Ag 2 S + Na 2 S 2 O 3 Ag 2 S 2 3 .2Na 2 S 2 3 -f Na 2 S - Ag 2 S -f 3Na 2 S 2 O ;r The strength of the thiosulphate varies from X to T /^ P er cent, of the salt, depending upon the richness of the ore. Strong solutions are objectionable since they dissolve more of the base, metallic compounds in the ore. The precipitate is separated by filtration, and is either dried and smefted, or dissolved in hot, concentrated sulphuric acid, from which solution the silver is precipitated with copper, (Dewey- Walter Process.) The Russell Process is a modification of the Patera process. It is used in connection with the latter for recovering silver from incompletely roasted ores and for treating ores contain- ing galena and blende. The ore is chloridized and leached as in the Patera process. Without removing the ore from the vat it is further leached with a solution of copper-sodium thiosulphate which dissolves the undecomposed silver sulphide 3 Ag 2 S -f 2 Na 2 S 2 3 .3Cu 2 S 2 3 = 3 Ag 2 S 2 O 3 .2N aj2 S 2 O 3 + 3Cu 2 S. The solution of the double salt requires to be circulated through the ore for a long time as its action is very slow. With ores containing galena the lead is dissolved by the thio- sulphate solution and appears with the silver in the precipitate, and subsequently in the bullion. Russell's method for getting rid of the lead is to add sodium carbonate to the thiosulphate solution and to filter off the precipitated lead carbonate. This necessitates the use of the sodium salt in the solution of the ore, since calcium would be precipitated by sodium carbonate. SILVER 257 Zinc is dissolved in the preliminary, hot water leaching, being- converted into sulphate by the roasting. The Cyanide Process. The use of cyanides in the extraction of silver is a recent practice, and one that has not, as yet, gained much headway. Cyanide of sodium or potassium may be used to dissolve either metallic silver or the chloride. A double cyanide of silver and the alkali metal, soluble in water, is formed, and from the solution the silver may be precipitated with hydrochloric acid or with zinc and other metals. The cyanide process has so far been used chiefly for native silver ores, carrying gold. SILVER REFINING The silver which has been obtained by the distillation of amalgam or by . the cupellation of the lead alloy is further purified by remelting with the proper fluxes for removing the base metals. The silver is melted in graphite crucibles, the crucible being heated in a muffle furnace. If base metals are present niter is added to oxidize them and the oxides are dis- solved by adding borax. If lead is present it is removed by throwing some bone ash over the surface of the molten silver, the lead oxide that forms being absorbed. The bone ash with any dross is easily skimmed off without loss of silver by first flux- ing it with borax. The silver is not kept in the furnace any longer than is needed as there would be loss from volatilization. It is cast into molds and kept covered with charcoal while cool- ing to prevent the absorption of oxygen. For the parting of silver and gold see p. 270. CHAPTER XXVI GOLD Ores. Gold is only known to occur native and in combina- tion with tellurium. Telluride ores have been met with in various localities, but they are rarely of importance. Native gold is generally alloyed with silver and often occurs with pyrites, galena and other sulphides. It also occurs in oxidized ores, is often in quartz and in other rocks. Gold ores are either found in rock mass (reef gold) or beds of earth and gravel (alluvial gold). Alluvial deposits are commonly called placers. They have been carried down by water after the disintegration of gold-bearing veins. The gold is generally found in the form of small grains or scales, disseminated through the rock mass or mingled with the sands. The larger pieces sometimes found are called nuggets. Gold has been mined in almost every country. The richest deposits so far known are those of Australia, South Africa and North America. Most of the gold in the Western Hemi- sphere has been found along the Pacific slope. It occurs all the way from Alaska to Chili, the richest deposits being in Alaska and California. Properties. Gold is easily recognized by its distinct yellow color, malleability and insolubility in acids. While of a yellow or in mass, finely divided gold or gold leaf shows colors in nation from green to blue and red by transmitted light. The tenacity of gold is about the same as that of silver, and in mal- leability and ductility it exceeds all other metals. A film of gold has been reduced to 1/870,000,000 inch in thickness. The melting point, as determined by different experimenters, varies somewhat, the average falling a little below i,iooC. At high temperatures it is perceptibly volatile, the volatility being in- creased by the presence of other metals. Gold alloys with the common metals and is readily amalgamated. It absorbs various gases, even in the solid state, when heated to redness. It is GOLD 259 a good conductor of heat and electricity. The specific gravity * 19-3- The presence of but minute quantities of most metals renders gold brittle. The metals which have the most marked effect upon the properties of gold are lead, bismuth, arsenic, antimony and tin. Silver and copper and the metals of the platinum group harden gold but do not seriously affect its malleability when al- loyed in small proportions. Copper is commonly alloyed to prevent the rapid wear of gold in jewelry, coins, etc. Chemical Properties. Two oxides of gold are known, but neither can be prepared directly from the metal and oxygen. Gold is not dissolved by any single acid, but it is dissolved in the presence of chlorine, bromine, thiosulphates and cyanides. Dry chlorine does not attack gold unless it be in the form of leaf or powder. Gold is readily precipitated from its solutions, and all its compounds are decomposed by heating in the air. THE EXTRACTION OF GOLD The metallurgy of gold is closely allied to that of silver. The methods for its extraction might well be classed in a similar way, an exception being allowed for the recovery of gold by simple washing. i. Washing These refer to the recovery of gold from alluvium by settling the gold from a suspension of the material in water. Such methods are not of much significance, though they are widely used by unp regressive people, and serve to some extent the purposes of prospectors. Mention only is made of the washing in pans and by means of the cradle and the torn. The pan is usually a shallow, sheet iron vessel with a depression in the bottom for retaining the gold. The pan with the earth is held under running water and given a rotary motion. The gold settles and the lighter material is carried away with the stream. The cradle is a trough-like box, mounted on rockers and in- clined slightly. On the bottom of the box are riffles and above the bottom is a sieve. As the ore is thrown on the sieve with water the fine material is washed through and flows down the inclined bottom. The earthy matter is carried over the riffles 2(50 METALLURGY and the heavier gold particles are caught. The settling of the gold is aided by rocking the device. The torn works somewhat on the same principle, though it is of different construction. It consists of two stationary, in- clined troughs so placed that the one delivers the stream into the other. The upper trough, which receives the ore, is pro- vided with a sieve at the lower end to prevent gravel from pass- ing out. Sufficient water is run into the upper trough to sluice out the ore. The stream passes over riffles in the lower trough and deposits a part of the gold. The length of the torn varies, being upwards of 30 feet. All purely washing methods are wasteful, often recovering only half of the gold. They are used by Chinese for working the tailings of some larger operations in California. 2. Smelting Gold that is associated with the base metals, copper and lead, is recovered as a by-product when the ores of these metals are smelted. In some instances, gold ores are treated by mixing them with rich lead ore and smelting for work lead. PROCESSES 3. Amalgamating The treatment of ores bearing precious metals varies greatly, owing to their variation in value and in physical condition. Gold and silver amalgamation processes are in many cases identical, but the amalgamation of gold strictly is usually a less difficult problem, and may be accomplished by simpler means. Gold ores are classed as "free milling" and "refractory," the former being such as may be amalgamated without preliminary treat- ment other than crushing. Of the gold amalgamation processes the most important are those of Hydraulicing, Dredging and Milling. Hydraulicing. This process comprises both the mining of the ore and the extraction of the gold. It consists in wearing down the bank of ore by means of a spray of water under power- ful pressure, and conducting the stream through sluices to de- posit the gold. Mercury is placed in the bottom of the sluices to collect the gold. The water for hydraulic mining is brought from upper coun- GOLD 26l try, often many miles distant, in conduits or flumes, and is de- livered at the work in an iron pipe about 30 inches in diameter. The water is led to the proper position in smaller pipes which are provided with movable nozzles called "monitors" or "giants." The direction of the stream is determined by an attendant. Sluices vary much in length. The average is about 1,200 yards, though some are several miles in length. The width is 3 to 6 feet and the depth about 2^ feet. The sluice is built of plank and given an incline of about 6 inches for each 32 feet, or more for sluggish material. The bottom is paved with wooden blocks, or more commonly, with stone. The spaces between the stones are partly filled with fine gravel and upon this the mercury is poured. The stream runs through a grizzly to separate boulders which should not be carried into the sluice. The greater part of the gold is retained in the first hundred feet of the sluice. At intervals the mercury is removed, and at long intervals the entire pavement is taken out and the mercury recovered. The amalgam is washed and the gold is separated by one of the usual methods. Hydraulic mining has been stopped by law in many localities on account of the injury to agricultural interests. The chief damage has been due to the filling of river channels with the enormous quantity of tailings from the sluices, resulting in a submerging of the low lands. The practice has been followed chiefly in California. Dredging. This process, like hydraulicing, is more of a mining than a metallurgical proposition. It has been substituted tor hydraulicing in some localities, being of more* recent de- velopment, and is now managed so as not .to seriously injure agricultural lands. The dredge is a huge machine for raising, concentrating and amalgamating soft ores. The ore is raised by bucket belts, dip- pers or other means, and is delivered to the concentrating and amalgamating apparatus. The entire machinery is floated on a scow, so that it is easily moved. The dredge can only be used on river bottoms or inland so far as it can dig its way and 262 METALLURGY Gold Dredge. (New York Engineering Co.) GOLD 263 be followed by the water. 1 It is useless if many boulders are encountered. Milling:. This has reference to those processes in which the ore is crushed before amalgamating. Of the different mills employed for crushing gold ores but two need be mentioned here the stamp and the Huntington mills. Stamp mills, designed specially for crushing gold ores, dif- fer in but few details from those used for silver ores. With free milling ores amalgamated copper plates are fastened length- wise and inside of the mortar, and the stream of pulp is led from the mortar over additional plate surface, and finally through sluices or concentrators. A small amount of mercury is usual- ly fed into the mortar. The plates are prepared by rubbing mercury over the clean surface to form an amalgam. A better amalgamating surface is made by first plating the copper with silver. The plates are more effective after some gold amalgam has been formed. Brass plates, containing 60 per cent, of cop- per and 40 per cent, of zinc (Muntz metal), have been used lately with good results. The first plate, which is necessarily the width of the battery, is called the ' "apron." It is contracted in width toward the lower end which is about 15 inches wide. The number of plates employed depends upon the capacity of the mill and the rich- ness of the ore. The pulp passes from the plates into a sluice lined with amalgamated plates, and thence over riffles in which mercury is placed. The plates near the stamps are scraped at least once a day, and those farther down at longer intervals to remove the amalgam. They are cleaned afterwards with cyanide of potassium and rubbed with mercury. The tailings from the sluices may be concentrated with frue vanners and amalgamated in pans or by means of other amalgam- ating machinery. Frue vanners are also used for concentrat- ing ores containing sulphides. Concentrates which can not be leadily or profitably amalgamated may be treated by one of the leaching processes. The gold amalgam, as obtained above, is first washed with 1 There are instances in which water is pumped to higher levels to float dredges. 264 METALLURGY mercury, and then, after squeezing out the excess of mercury, it is retorted. The methods used are the same as those for treating silver amalgam. The stamping of free milling ores is open to objections. The mineral matter is ground into the particles of gold, rendering them less readily absorbed by the mercury. This also causes a larger portion of the gold to float instead of coming in con- tact with the copper plates. Furthermore the loss of mercury is high, due to "flouring" and "sickening." By the former term is meant the loss of minute globules formed mechanically, and the latter term has reference to the darkening of the mercury due to a coating of mineral matter. These difficulties are overcome in a measure by crushing in roller mills. The Huntington mill has given satisfactory results, especially for the softer ores. For the illustration and description of this mill see p. 53. 4. Leaching Plattner Process. The gold is converted into a soluble chloride by the action of chlorine in the presence of moisture. This is leached from the ore with water, and the gold is precipitated with ferrous sulphate, charcoal, hydrogen sulphide or other agents. The process is adaptable to many ores and concentrates which can not be treated by an amalgamating process on account of the impurities they contain. The ore is commonly calcined or roasted to render it more porous, or to oxidize sulphides, arsenides, etc., which cause a high consumption of chlorine by their reaction with it. Cintering of the ore is avoided as par- ticles of gold would be enveloped in the inert mineral matter. Also, ores containing much silver are more difficult to treat, owing to the protective coating of silver chloride upon the gold. The chlorine is either prepared in a generator from manganese dioxide, sodium chloride and sulphuric acid, or in the same vessel with the ore from chloride of lime and sulphuric acid. The former method is more common. The chloridizing vat is gen- erally made of wood with a protective coating of tar. The vats hold from two to five tons of ore. Some are arranged for agitating the ore and for maintaining it under pressure during GOLD 265 the chloridizing. The action of the chlorine is thereby made more rapid and more complete. The moist ore is subjected to the action of chlorine for about two days, or less time if the ore is agitated. The vat is then uncovered, and after blowing out the excess of chlorine, the ore is leached with water which dis- solves the chloride of gold. Any mineral matter which is car- ried through is removed by settling or by filtration, and the solution is run into the precipitating tank. The precipitating agents which have so far been used successfully are ferrous sul- phate, hydrogen sulphide and charcoal. 2 AuCl 3 -|- 6FeS0 4 == Au 2 -f Fe 2 Cl 6 -f- 2Fe 2 (SO 4 ) 3 2 AuCl 3 + 3H 2 S == Au 2 S 3 + 6HC1. The reaction with charcoal is not understood, though it is supposed to be due to the reducing gases it contains. It is slower in its action than the other reagents and does not pre- cipitate the gold at all in the presence of free chlorine. The solution is filtered through charcoal powder until the gold is exhausted. The charcoal is afterwards burnt, and the gold is recovered from the ashes. Ferrous sulphate is added to the tank and thoroughly agitated with the solution. After standing, the supernatant liquid is decanted off and the gold residue is collected, washed and refined in crucibles. The liquid which is drawn off is al- lowed to stand for some time in a settling tank, since it will throw down more gold. It is finally filtered through sawdust or sand from which the gold is recovered. The precipitation with hydrogen sulphide is a more recent practice, and is more rapid than the other methods. Free chlorine is first removed from the solution in the tank by pass- ing through it a stream of sulphur dioxide, and this is followed by the hydrogen sulphide. Both reagents are generated at the plant and used in the form of gas. After settling, the bulk of the solution is decanted off, and the precipitate is recovered by filtration. The residue is dried and smelted. McArthur-Forrest or Cyanide Process. This is the most important of the leaching processes as applied to gold ores. By the use of potassium cyanide gold may be extracted with profit 266 METALLURGY from ores which are too poor for treatment by other methods. The process was patented in 1890 by Me Arthur and Forrest, who introduced it into all the leading gold producing countries. It is most adaptable to low grade, free milling ores. Ores in which the gold is in the form of coarse grains are not suitable for cyanide leaching, since the gold is not completely dissolved. The ore must be in a finely divided state or in such a porous state as will permit of ready absorption of the solution. Calcin- ing is sometimes resorted to, as it leaves the ore more open. If the ore is roasted it should be completely oxidized, so as not to leave acid salts which would react with the cyanide. Since the solution of gold in potassium cyanide is not rapid, the ore is kept in contact with the solution for a considerable length of time. The reaction is hastened by introducing air with the cyanide. Oxygen is essential, as has been demon- strated. When the supply of oxygen has been exhausted solu- tion of the gold ceases. According to Eisner the essentials of the reaction are as follows: 4 Au + 8KCN + 2H 2 + 20 == 4 KAu(CN) 2 + 4 KOH. Chemical oxidizing agents such as the chlorates, peroxides and the halogens may be used with good effect. The ore is usually leached in a large, shallow vat 1 of wood or metal properly protected with paint. The ore is supported on a false bottom, and the solution is drawn from the bottom of the vat through an iron pipe. If the ore contains sulphates or other salts which would react with the cyanide it is washed with water, and any remaining acid may be neutralized with an alkali. The cyanide solution is let in from the bottom, as in working upward there is less tendency toward the formation of channels in the mass. After standing for some time at several inches above the surface of the ore, the solution is partially drawn off and more is run on. This is done to in- troduce air into the stock. After the preliminary washing, the ore is commonly leached, first with a strong solution (0.3 to 0.6 per cent.), and after drawing this off, with a weak solu- tion (o.i to 0.3 per cent). The ore is finally washed with 1 Ores can not be leached so successfully in deep vessels. GOU3 267 water, and the washings are generally used for the preliminary leaching or washing of a fresh charge. The time required and the strength of 'the solution varies much with different ores. Naturally, the solution proceeds more slowly with weak than with strong solutions, but there is a tendency towards weakening the solvent on the part of operators, because less mineral matter is dissolved and the cyanide is economized. Sand is sometimes mixed with very fine ore to hasten the percolation. Precipitation of the Gold. This part of the cyanide process has received most attention, as it has offered the most dif- ficulties. Many of the methods offered are all right in theory, but in practice have proved too expensive or have failed to completely precipitate the gold from the solutions. The most common method of precipitating gold is with zinc in the form of thin shavings. The shavings are cut on a lathe Fig. 84. from the edges of plates of zinc, which are held together while being turned. The shavings are supported on wire screens in compartment boxes as shown in Fig. 84. The boxes are made of wood and painted on the inside with paraffine. The solu- tion is supplied through the pipe shown at the left. It passes under the first partition and overflows the next, and so on, rising through each compartment in which the shavings are contained. The spent solution is carried away through the overflow pipe shown at the right. For drawing off the pre- cipitate and cleaning up, each compartment is provided with a drain pipe in the bottom. The gold is precipitated in the form of a black powder adherent to the zinc. This falls down to the bottom of the boxes with particles of zinc as slime. There is some doubt as to the changes involved in the pre- 268 METALLURGY cipitation of gold, though it is supposed to be electrolytic. That it is not simply a substitution of zinc for gold is shown by the fact that the weight of zinc dissolved is not a chemical equivalent of the gold precipitated. The substitution would be as follows : 2 AuK(CN) 2 + Zn == K 2 Zn(CN) 4 + 2Au. In practice about 12 ounces of zinc are required for I ounce of gold deposited. The gold is never recovered completely though as little as four per cent, has been left in the solution. Impurities affect the precipitation, and when the solutions be- come heavily charged they are purified or rejected. Copper in the solution is deposited upon the zinc, retarding the deposi- tion of gold. Since strong solutions react with the zinc more rapidly than weak ones do, cyanide is sometimes added to the solution as it comes from the leaching vat. It is essential that the zinc be in finely divided form, hence the use of thin shav- ings. Furthermore, the action is not rapid until the surface of the zinc has become etched by the solution. As a substitute for shavings, zinc dust (the by-product of zinc distillation) is used at some plants. The zinc dust is stir- red into the solution, and the gold precipitate is collected by filtration. Precipitation by this method is very rapid. Another substitute for zinc shavings is the zinc-lead couple, prepared by immersing the shavings in a dilute solution of lead, acetate. The lead-coated shavings are transferred immediately after preparation to the gold solution. This method has th-^ advantage of being very rapid and of not precipitating copper. The gold residue contains a large amount of lead, which is objectionable. Electricity in the Cyanide Process. Electrolytic methods are of later origin, but they are being used quite successfully. Two processes will be noted. The Siemens-Halske process, which has been used chiefly in South Africa is applied solely to the treatment of the gold solution. The ore is leached as in the ordinary cyanide pro- cess, and the solution is electrolyzed in wooden boxes 18 feet long, 7 feet wide and 3 feet deep. In these are sus- GOLD 269 pended 89 sheet iron anodes and 88 cathodes of sheet lead. As the solution is circulated through the boxes it is subjected to the action of the current, and the gold is deposited upon the lead. The anodes are enclosed in canvas to hold the compounds that are formed by the action of the cyanide on the iron. In the Felatan-Clerici process, developed in this country, the solution is electrolyzed while it is in contact with the ore. The process is therefore a single operation. The ore is mixed in the vat with enough water to make it quite liquid, and it is stirred while solution and precipitation are in progress. A rotating agitator is employed, to the arms of which the iron anode plates are attached. The cathode is a circular plate of copper, covered with mercury, and it is supported horizontally a few inches below the anode. Besides the cyanide certain chemicals are. added to aid in the solution. About three tons of ore are treated at once, and the precipitation proceeds very rapidly. The gold and silver are deposited as amalgams. The exhausted material is drawn from the bottom of the vat and run into a settler from which the solution is recovered. Explanations of the electrochemical changes of the cyanide process are largely conjectural. Potassium cyanide in solution i.< decomposed into cyanogen and potassium, and water into hydrogen and oxygen. Potassium and water combine to form caustic potash, with the liberation of hydrogen, while hydrogen and cyanogen from hydrocyanic acid. The double cyanide of gold and potassium is split up into cyanide of gold and potas- sium hydroxide, and gold is precipitated, probably by the action of hydrogen 2 Au(CN) 2 + 4 H == 2Au + 4 HCN. Potassium cyanide may be regenerated by the reaction of hy- drocyanic acid and potassium hydroxide. According to the theory of electrolysis the gold is dissolved only at the anode, though solution may take place away from the anode by inde- pendent chemical action. The fact that oxygen is liberated at the anode gives ground for the view that chemical action is assisted by the current, thus: 4 KCN + 2Au + O -f H 2 == 2 AuK(CN) 2 + 2KOH. 270 METALLURGY The solution of the gold is much more rapid in the electro- cyanide process than by the action of cyanide alone. The chief advantages of the electrolytic methods are that time and labor are saved, the cyanide is economized and zinc is dispensed with entirely. The gold residue is much cleaner than that obtained by zinc. Among the various other substances that have been used to precipitate gold from cyanide solutions are zinc amalgam, .aluminum, charcoal and cuprous salts. Treatment of the Auriferous Residues. Gold that is de- posited upon zinc is removed, as far as possible, by shaking the .shavings in water and sifting. The residue is dried and smelted, or first treated with dilute sulphuric acid to dissolve the zinc and other impurities. It is then washed with hot water, and after decanting the washings, the remaining liquid is separated by filtration, and the residue is melted for bullion. THE REFINING OF GOLD The purification of gold involves the separation of base im- purities, and desilverization. The latter process is called part- ing. In rarer instances the metals of the platinum group are to be separated. The base metals are usually almost completely removed before parting. This is done by fusing the gold in crucibles with borax, niter, sulphur, or whatever chemical sub- stance is needed to combine with and flux the metals present. Alloys rich in copper are fused with sulphur, whereby the cop- per is separated as cuprous sulphide (Roessler's method). The parting of gold and silver may be effected in many ways. The more important only need be noted here. By Chlorine. The alloy is melted in a clay crucible with a small quantity of borax. Dry chlorine gas is passed through the charge by means of a clay pipe until the silver and any base metals are converted into chlorides. Gold may be rendered almost absolutely pure in this way, but the method is expensive. By Sulphuric Acid. This is one of the cheapest and most common methods of parting. Gold-silver alloys are either mixed or more silver is added to an alloy until the mixture has .the proper proportion of the two metals for the action of the GOLD 271 acid. Adding the silver is termed inquartation. The alloy is then converted into a thin slab or granulated by pouring it from the crucible into cold water. This is done to bring a large surface area in contact with the acid. The silver is dissolved by digesting the granules in an iron pot with hot sulphuric acid. The solution is drawn off and the gold is treated repeatedly with hot, concentrated sulphuric acid. Further purification may be effected by fusing potassium bisulphate with the gold and leaching out the silver sulphate with water. The parting may also be done with nitric acid^ but this is not much used now. "? ? ? ? ? I &Jk >*^ /tcJUt^er-/ By Aqua Regia. The highest degree t>f purity is obtained by Roessler's method^ which consists in dissolving the otherwise partially purified gold with aqua regia. The silver is converted into insoluble chloride, and the gold is precipitated from the solution with ferrous sulphate. The gold may be 999 9/1000 pure, By Electrolysis. This method is of comparatively recent origin, and is quite extensively used by refiners. The electrolyte is a dilute, acidified solution of silver nitrate. The anodes are cast from the alloy to be refined and the cathodes are of rolled silver. A dense current is employed, which precipitates the silver free from gold, while the gold slimes contain but very little silver. Ihe anodes are enclosed in cloth bags which re- tain the gold. Automatic scrapers are employed to prevent the growth of silver crystals from causing short circuits. The sil- ver is sufficiently pure for the market, and the gold is purified to 999/IOOO by boiling with acids. CHAPTER XXVII NICKEL, ALUMINUM, MANGANESE AND RARER METALS NICKEL Ores. 'Nickel occurs chiefly as silicate, sulphide, and arsenide. The principal ores are Garnierite, occurring in silici- ous rocks, and magnetic pyrites. The ore usually contains more iron or copper than nickel, but the nickel represents the main value in most cases. Arsenic is also frequently found Tnth nickel and also small quantities of antimony and chromium. The amount of nickel in different ores is exceedingly variable, ranging from less than I to more than 50 per cent. The largest known deposits are in New Caledonia and Sudbury, Canada. The metal nickel was first recognized by Cronstedt, ,about 1751 (Hadfield). Properties. Nickel is of a slight grayish-white color and highly lustrous. It is exceedingly tenacious and tough, and is both malleable and ductile. It is harder than iron or copper and in malleability it is inferior to these metals. The melting point is i, 600 C. Nickel alloys readily with most metals and it- may be welded to itself and to iron. When in the molten con- dition nickel occludes carbon monoxide and other gases. In conductivity it ranks next to zinc. It is slightly magnetic. In both its physical and chemical properties nickel appears to be intermediate between iron and copper. It is unchanged in either dry or moist air at ordinary temperatures. It is readily dissolved by nitric and slowly by hydrochloric and sul- phuric acids. There are two oxides of nickel of which the monoxide (NiO) is the more important. This may be formed directly by heating metallic nickel, or by heating either the sulphide or the arsenide in an oxidizing atmosphere. Both the oxides are reducible by carbon at a temperature below the melt- ing point of nickel. With silica nickelous oxide forms a fusible silicate. Nickel sulphide occurs naturally and it may NICKEX, ALUMINUM, MANGANESE, ETC. 273 be prepared by heating nickel with sulphur or certain other sulphides, and by reducing the sulphate with carbon. It may be decomposed by heating with it metallic copper, the products being nickel and cuprous sulphides. By melting together the sulphides of nickel, copper and iron with sodium sulphate or sulphide, the copper and iron sulphides form a readily fusible mixture with the alkaline salt, while the nickel sulphide is fused with more difficulty. In consequence of this the copper matte separates more or less completely from the heavier nickel matte. By roasting these sulphides with salt the copper may- be chloridized and the nickel with the iron converted into oxide. Nickel combines readily with arsenic. The artificially concen- trated arsenide is known as nickel speiss. Extraction of Nickel. A number of methods have been pro- posed for the recovery of nickel from its ores and furnace products. These fall under the general heads of smelting, wet and electrolytic methods. The general run of nickel ores yield most readily to smelting, though the other methods have been practiced quite successfully. The usual smelting process con- sists in concentrating the nickel into a matte or a speiss by roasting and fusing, then roasting the concentrate to free it from sulphur or arsenic, and finally reducing the nickel with carbon. The character of the ore of course largely determines the method of treatment. In most ores the content of nickel is very small, often below five per cent. Iron and usually cop- per are present in sulphide ores, and in silicious ores an over- whelming mass of silica must be dealt with. The metallurgy of nickel is often associated with that of other metals, and the operations pending its final isolation may be long and tedious. The ore is roasted in a reverberatory furnace to expel the excess of sulphur, leaving enough to form the matte. If cop- per is not present the iron is fluxed with silica and the nickel matte separates. The smelting of the matte may be conducted in a reverberatory furnace, hearth or Bessemer converter, the sil- ica being supplied from the ore itself or from the lining of the furnace. If copper is present the treatment thus far is similar. But the matte contains, beside the nickel, most of the copper and 274 METALLURGY some iron. The bulk of the iron is separated by an oxidizing fusion with a*silicious flux. The residue is then fused with an alkaline salt such as soda ash or salt cake, which serves to dis- solve or absorb the sulphides of copper and iron. The nickel sulphide, being heavier, settles to a lower level, and the two masses may be separately tapped. The concentrated nickel matte is roasted in a reverberatory furnace. The product is nickel oxide, since the oxide and sulphide of nickel do not react to liberate the metal as the corresponding compounds of copper do. The oxide is charged into crucibles or muffles with carbon and smelted for nickel. Oxidized or silicious ores are sometimes smelted directly in blast furnaces with coke to produce an alloy of nickel and iron. A process has also been in use for making nickel steel, in which the nickel ore is charged with the iron into an open hearth fur- nace. Wet and electrolytic processes are also in use for the extrac- tion of nickel. These, though rarely ever adaptable to raw ores, on account of the impurities and the low content of nickel, have had considerable application in working up nickel-bear- ing products. Wet methods usually look to the solution of the nickel in hydrochloric or sulphuric acid, its subsequent precipitation and final smelting. Having obtained the solution, the metals of the copper group may be separated by means of hydrogen sulphide. Iron may then be separated by oxidizing the solution and adding calcium carbonate. This also throws down any arsenic. The nickel is recovered from the solution by crystallizing it as the sulphate, or by precipitation with cal- cium hydroxide or soda. Electrolytic methods have been successfully used for ex- tracting nickel, especially from alloys or mattes containing 1 cop- per. Ulke has described a process for treating a matte con- taining about 40 per cent, each of nickel and copper. The matte is cast directly into anodes, and the electrolyte is an acid solution of nickel sulphate. The cathodes are of sheet copper. Upon these the copper is deposited from the solution as the anodes are dissolved. The nickel su!phate is recovered NICKEL, ALUMINUM, MANGANESE, ETC. 2/5 from the solution by crystallization when it has accumulated in sufficient quantity; or instead, it may be precipitated as above or by electrolysis. If electrolysis is adopted the solution is rendered slightly ammoniacal, and anodes of carbon or lead are introduced. The nickel is deposited upon cathodes of sheet nickel. Nickel, as it comes from the smelter is never pure. One of the more usual methods of refining consists in fusing it in crucibles and adding magnesium. This reduces any oxides present, the magnesium burning away or entering a slag. Manganese is employed to remove sulphur from nickel. Cobalt is often associated with nickel, and it is recovered by similar methods. It somewhat resembles nickel in its properties, and though comparatively rare its use is becoming extended. ALUMINUM History. The existence of aluminum was suspected some time before it was actually discovered. Davy, in 1807, pre- pared aluminum chloride, and then attempted to isolate the metal, with the aid of electricity, having already succeeded in separating the alkali metals in this way. Though this experi- ment was not successful, it is an interesting fact that electrical methods are now used exclusively in the manufacture of aluminum for the market, yet in the meantime it was manu- factured by purely chemical processes. It is believed that Oersted succeeded in preparing aluminum amalgam, in 1824. His experiment consisted in heating aluminum chloride with potassium amalgam. This lead to Wohler's experiment (1827) in which he decomposed anhydrous aluminum chloride with potassium and obtained small globules of aluminum. The same principle was made use of by Deville, Percy and others who developed processes for manufacturing aluminum. The fluoride of aluminum was substituted for the chloride and sodium was used instead of potassium, as it was cheaper. The manufactur- ing cost was greatly lessened by Castner, who cheapened and improved the processes for making aluminum chloride and sodium. The isolation of aluminum by electrolysis was ac- 276 METALLURGY complished in 1854 by Bunsen and Deville, who worked in- dependently of each other. They used the double chloride : aluminum and sodium, which they electrolyzed while in a fiu:~ ! condition. Ores. Though the most abundant metal in nature, the materials from which aluminum can be economically prepared are at present limited. The only ores of importance are Bauxite and Cryolite. The former is a mixture of the hydrated oxides of iron and aluminum and the latter is the double fluoride of sodium and aluminum. Properties. Aluminum has almost the whiteness of silver, though a slight tinge of blue is generally present, due to im- purity or to forging. The tensile strength of cast aluminum is 17,042 pounds per square inch, elongation three per cent. The tenacity is improved by working. The pulling strength of a wire which was warmed was 35,500 pounds (Schnabel). Alumi- num can be worked cold, its best forging temperature being about 200 C. It becomes brittle at higher temperatures and melts at 625C. (Le Chatelier). It is volatile at still higher temperatures. Aluminum alloys with most metals. The specific gravity is 2.58. Aluminum is not oxidized in either dry or moist air at ordinary temperatures. At high temperatures it becomes coated with oxide, and if the finely divided metal is kindled it burns with great brilliancy. Under such conditions if it be in con- tact with certain metallic oxides such as those of iron, manganese, copper, lead and chromium, the aluminum is converted into alumina and the other metal is reduced. The, oxide of alumi- num is not reduced by carbon except in the electric furnace. Aluminum is not precipitated from any aqueous solution by any metal or by the electric current. Aluminum Smelting. Since the development of electric processes the reduction of aluminum by sodium has been abandoned. Two processes have been used in this country for the production of aluminum on the large scale The Cowles- Brothers' process and the Hall process. The Cowles Brothers' process was patented in 1885, and their first plant was put into- NICKEL, ALUMINUM, MANGANESE, ETC. 277 operation in Cleveland, Ohio. The process consists in reducing aluminum from the oxide in the presence of another metal, which metal absorbs the aluminum at the moment of its libera- tion. The product is therefore an alloy. The original furnace is a rectangular box lined with fire-clay, through the opposite sides of which the current is conducted. Into this a mixture of alumina and charcoal with the alloying metal is charged. The conductors for the current terminate in bundles of carbon sticks, which are placed near each other and imbedded in the charge. A powerful current being turned on, the carbons first become heated and then heat is generated in the mixture, due to the resistance. Reduction and fusion follow, carbon monoxide being liberated. The alloy is tapped from the fur- nace, and more aluminum or more of the other metal is added to bring it to the composition desired. The extent to which electrolysis takes place in this process is not known, but the reduction is supposed to be almost entirely chemical. Fig. 85. In the Hall process aluminum is reduced from alumina in a molten bath of cryolite, and deposited by electrolysis. The alumina is dissolved in the cryolite, salts of the alkalies being added to make the bath more liquid. The furnace used is of the crucible form, and the heat is generated by the electric resistance in the bath. The anodes, which dip into the bath from above, are of specially prepared carbon, and the crucible itself is the cathode. The carbon from the anodes combines with the oxygen from the alumina, the weight of carbon consumed being about equal to the weight of aluminum deposited. The Hall process is used by the Aluminum Com- pany of America, 1 and it has been introduced into Europe. 1 Formerly the Pittsburg Reduction Company. 278 METALLURGY Fig. 85 shows the arrangement of an aluminum reduction furnace. It consists of an iron box lined with graphite, form- ing the cathode, and graphite anodes supported on a metal conductor as shown. The wires, marked + an d show the connections for the current. The cryolite is melted in the crucible and the alumina is added as the bath becomes impoverished. The aluminum is deposited on the bottom of the crucible. MANGANESE Manganese was discovered in 1774 by Scheele, a Swedish chemist. It was not, however, until the early part of last century that much attention was called to manganese. Heath appears to have first manufactured manganese for the purpose of alloying it with iron, and to appreciate in a scientific way its value in steel making. It was not, however, until after the in- troduction of the Bessemer process for making steel that the manufacture of manganese on the large scale was begun. Ores. The only ores of manganese of importance are the oxides. These are known as Pyrolusite (MnO 2 ), which is also called black oxide of manganese, and Hausmanite (2MnO-|- MnO 2 ). Manganese ores are widely distributed though not abundant. They are mined in the Eastern states and in Canada. The main supply to this country comes from Brazil and Cuba. Properties. Manganese has a light-gray color, and the fracture shows a fine granular structure. It is hard and brittle and can not be forged. It fuses at about 1,90x3 C. and alloys readily with most metals. Manganese has strong affinity for oxygen and sulphur, with which elements it combines in different proportions. Manganous oxide forms silicates analogous to the silicates of iron. The oxides of manganese are reduced by carbon at high tempera- tures. Smelting. Since the ores of manganese always carry iron and the separation of the two oxides is not practicable, both metals are reduced during the smelting and the product is a ferro-alloy. That which is manufactured to contain up to 30 per cent, of manganese is known commercially as spiegel-eisen, NICKEL, ALUMINUM, MANGANESE, ETC. 279 and the higher grades are ferro-manganese. The latter may run as high as 87 per cent, or even higher in manganese. In addition to the iron, manganese alloys carry carbon, silicon and ether impurities absorbed during the smelting. Manganese ore is now regularly smelted in coke blast fur- naces, and these are operated essentially in the same way as in iron smelting. A higher temperature is required for the re- duction of manganese, and a much larger percentage of coke is used in the burden. The slag is more basic. Ferro-manganese is now manufactured in the Pittsburg District and in most every large steel center. At Bethlehem and Palmerton the New Jersey Zinc Company operate blast furnaces producing Spiegel. The residues obtained after smelt- ing Franklinite ore for zinc are smelted for the iron and man- ganese they contain. RARER METALS The metals noted below are not in all instances rare as to their occurrence, but their present applications are so limited as to warrant but little space in this treatise. Chromium. This metal occurs as the oxide (Chromite), mention of which is made under the head of Refractory Ma- terials. It is met with in the Eastern states and California. The most important deposits are in Asia Minor, Greece, Silesia and New Caledonia. Chromium was discovered by Vauquelin, of France, in 1797. Chromium may be prepared by electrolysis of the chloride in aqueous solution, by reduction in a crucible with aluminum or carbon and in other ways. I.t is usually manufactured for the market as ferro-chrome by smelting the iron-bearing ores in electric furnaces. Alloys containing upwards of 40 per cent, of chromium may be made in a blast furnace. The richer alloys may be prepared in crucibles, by reduction with carbon or aluminum. Tungsten. This metal occurs as the oxide in the mineral Wolframite, being associated with other metals (CaWO 4 , FeWO 4 and MnWO 4 ). It is also found in tin ores. Tungsten 28O METALLURGY has been found in most all of the Western states, and it has been imported from South America and the East. The properties of tungsten do not permit of any economic use of the metal except in alloys. It has a bright-gray color and high luster, and is hard and brittle. It is unaltered in the air, except at high temperatures, when it is converted into the trioxide. The melting point of tungsten is about 1,700 C. Tungsten, finding its chief application in the manufacture of tool steel, is generally prepared as an alloy with iron. The ore is mixed with carbon and smelted in an electric furnace. Molybdenum occurs chiefly as the sulphide in the mineral Molybdenite (MoS 2 ). It is also found as the oxide in smaller quantities. Molybdenum ores are found in Arizona, California, and other Western states. The ore is also imported. In its properties molybdenum resembles tungsten, being of a light-gray color, hard and brittle. The melting point which is very high, has not been accurately determined. Molybdenum is used like tungsten, in the manufacture of special steels. It is prepared by similar methods. Vanadium occurs as the oxide, associated with iron, lead, zinc, copper and other metals. Deposits of vanadium have been found in Arizona, Mexico, Argentine Republic and elsewhere. The color of vanadium is light-gray, and it is slightly crys- talline. It is hard and unworkable, and melts at about 1,700 C. It oxidizes spontaneously in the air and rapidly at high tempera- tures. At a red heat it combines with nitrogen. Vanadium is usually prepared as an alloy with iron. This is done by reducing the oxide in an electric furnace with car- bon. Molten iron is added to prevent oxidation of the vanadium. It may also be reduced in a crucible with aluminum, the principle being the same as that used in Goldschmidt's experiment. (See p. 290). Platinum. The only ore of platinum is native. It is usually alloyed with the other metals of the platinum group. Among these the best known are iridium, rhodium, palladium and osmium. Platinum is usually recovered from alluvium, ir? which a natural concentration has taken place. It has been NICKEL, ALUMINUM, MANGANESE, ETC. 28 1 found in the gold-bearing sands of California, Canada, Mexico and elsewhere. By far the most important deposits of platinum yet discovered are in the Ural Mountains. The chief properties to which platinum owes its applications are its high fusion point, malleability and its inertness toward chemical agents in general. It has about the hardness of cop- per and can be worked cold. The melting point is about I '775 C. Platinum is not oxidized at any temperature nor is it acted on by any single acid. It is attacked and dissolved by aqueous solutions containing chlorine. In the extraction of platinum the ores are concentrated by washing, and then smelted or treated by a leaching process. If the former method is used the ore is smelted in crucibles with lead or lead-bearing material, and the work-lead obtained is cupelled. With sufficiently high temperatures, as are attainable in electric furnaces and with the oxy-hydrogen flame, platinum may be removed from the ore gangue by simple fusion. The usual method for extracting it is to treat the ore with aqua legia, which converts the metal into a soluble chloride. After prolonged digestion the liquid is separated from the gangue and ammonium-platinic chloride is precipitated by adding ammonium chloride. The precipitate is dried and the platinum is recovered from it in an electric or oxy-hydrogen furnace. CHAPTER XXVIII ALLOYS The manufacture of alloys is a very ancient art and one which has been known even to savage people. No doubt many of the ancient alloys, of which preserved specimens bear record, 'were supposed to contain but one metal, or else no method was known by which the components could be separated. The ex- istence of some alloys might be accounted for by the smelting of mixed ores or ores containing more than one metal. Brass was made long before zinc was recognized as a separate metal. The bronzes and alloys of the 1 precious metals are well known examples of early manufacture. While the manufacture of alloys for ornamental purposes was borrowed from the ancients, the development of the more useful properties in metals by al- loying is peculiarly a modern practice. Properties. The great alterations in the properties of metals when alloyed has been previously shown. It has also been shown that many of the most useful properties may be devel- oped in this way. Some idea of the possibilities along this line may be formed by considering the great number of mixtures of the common metals that are possible if the ratios be varied. The properties of an alloy can not be anticipated from a con- sideration of the properties of its constituents. In binary al- loys some of the properties may be intermediate between those of the two metals, while the other properties differ entirely from those of either. The color is in some instances what would be expected from the colors of the separate metals, but there are numerous instances in which the color bears no re- lation at all to that of either constituent. The tenacity, elastic- ity, ductility and hardness may fall between or be either greater or less than those properties in the single metals. The fusion point is usually lower than the mean of the two and often be- low 'that of the more fusible metal. Electric conductivity is generally diminished by alloying, sometimes to a remarkable ALLOYS 283 degree. The specific gravity of an alloy is usually lower than the mean of its constituents. Some metals are rendered more active toward chemical agents by alloying. On the other hand, it is possible in many cases to protect metals against chemical action by alloying them with metals which resist corrosion. Constitution of Alloys. It has been shown that some metals unite with greater energy than others do, resembling chemical affinity, and that some do not appear to alloy with each other at all. Further, it has been shown that, although molten metals may be mixed in all proportions, it does not follow that the mixture will remain homogeneous. The well known processes of liqua- tion depend upon the fact that the liquid metals, from lack of affinity for each other, separate by gravity in rather distinct layers. Upon solidifying a still further separation may take place, just as chemical salts of different melting points or solubilities may be separated, by crystallization. In aqueous solutions the medium from which any substance is crystallized is called the mother liquor. Metals when fused together partial- ly or entirely dissolve each other, and the medium from which metals crystallize is called the mother metal. The greater the difference between the melting points of the metal which separates and the mother metal the more complete will the sepa- ration be. Alloys are regarded by some authorities as being analogous to aqueous solutions of salts, and to strengthen this theory at- tempts have been made to decompose molten alloys by electrol- ysis, but so far without success. 1 Matthiessen's view, which is generally accepted, is that metals pass into an allotropic form when they alloy. Evidence of this is furnished by experi- ments in which certain metals are released from alloys or amalgams by means which could not in themselves alter the metals, and they are found to have assumed an allotropic form. There are but few instances in which metals form true com- pounds with each other. They do, however, alloy in definite proportions, the alloys possessing definite properties. A jnix- 1 See Roberts- Austen's Metallurgy, p. 104. 284 METALLURGY ture of two metals in definite ratio and melting at a constant temperature is termed an eutectic alloy. The eutectic may be either a conglomerate of the metals or a solid solution. In the former the distinct metals may be seen with the aid of a micro- scope, but this is not possible in the latter. Solid solutions are not necessarily utectiferous, but they may contain metals in varying ratios, depending upon solubilities. If crystallization of a solid solution takes place the form will approach that of the metal which predominates. While it is true that metals often unite in definite ratios, these bear no relation to the atomic weights, and there is no convincing evidence of chemical action. Cooling Curves. A great deal has been learned about metals and their alloys by noting their behavior while cooling, especial- ly in the rate of cooling. The rate of cooling, as determined in any experiment, is conveniently plotted on cross-ruled paper by using the vertical distances to denote measurements of temperature and the horizontal distances to denote measure- ments of time. The temperature of the cooling mass is read from a pyrometer at certain intervals and marked at the proper points on the paper. At the end of the experiment the points are connected by a line whose direction shows graphically the changes of temperature in the given time. When a substance which does not undergo physical or chemical change is cooled from a state of fusion to the freezing point, the line of cooling is plotted as a continuous curve. Thus, in cooling molten tin from a temperature of 264 to 224, the line AB is described (Fig. 86). The point B is below the tempera- ture at which tin freezes, which is 231. When freezing com- mences it proceeds rapidly, and the heat evolved raises the temperature of th,e metal to the freezing point. 1 The phenom- enon of a liquid cooling below its normal freezing point and remaining liquid is known as sur fusion. After surfusion the freezing may be started by adding some of the substance in the 1 It should be understood that freezing is a change by which heat is evolved. ATXOYS solid form or by agitation. 1 The line CD marks the freezing of the tin. The line shows but slight fall in temperature, since the cooling is arrested by the heat evolved in the change from liquid to solid. The greater the mass of the liquid the longer will this line be. The cooling of the solid tin is represented by the regular curve DE. Fig. 87 represents the cooling of an alloy of tin and copper. Here the line AB, instead of being a continuous curve, is re- c 270 A 250 240 230 220 210 200 190 \ \ \ \ / 2 3 Min ute S Fig. 86. Tin Cooling Curve. (Alloys Research Committee). versed at B. This change is accounted for in the freezing out of pure tin. The phenomenon of surfusion occurs as before, and this is followed by the freezing of the tin-copper alloy. Conditions under which Metals Unite to Form Alloys. i. Metals may be made to unite when one or both are in the molten state. The method of making alloys by fusion is most familiar. 1 Glacial acetic acid freezes at 17. It may, however, be cooled consid- erably below that temperature without solidification. If under these con- ditions a frozen crystal is introduced or the liquid is agitated, the whole freezes almost instantaneously. 286 METALLURGY Union takes place when both or all constituents are in the liquid state, or when one is liquid and the others solid as in the formation of amalgams or any alloys at a temperature below the melting point of one of the metals. 2. The union of metals may be brought about at ordinary temperatures by compression. This appears to be due directly to the property of flow in metals. Lead and tin sheets may be united under comparatively slight pressure, while such brittle metals as antimony and bismuth may be alloyed by subjecting Fig. 87. Tin-Copper Alloy Cooling Curve. (Alloys Research Committee). .them to powerful pressure. A solid block of bismuth has been obtained under a pressure pf 6,000 atmospheres from the crys- talline powder. 3. Alloys may be made electrochemically by the simultaneous deposition of the metals from the solutions of their salts. Al- loys made in this way appear not to differ from those of the same composition prepared by fusion. THE PREPARATION OF ALLOYS ON THE INDUSTRIAL SCALE In the classified list, given below, will be found the analyses of some of the more important alloys. The composition of ALLOYS 287 Chromium 3.00 Chromium 1. 00 (Nickel 2.00) Chromium 3-70 (Tungsten 10.80) Chromium 3.00 (Molybdenum 4.25) Manganese 12.00 Nickel 3-50 Vanadium 1. 00 Copper Zinc Tin yo.O 30.0 65.0 35-0 91.0 9.0 J6S 23-5 82.0 2.O 16.0 77.0 8.0 50.0 31-9 3- 1 50.0 25.0 75-o 95-o 2-5 2-5 79-7 10.0 90.0 88.0 IO.O Lead many of the alloys of the same name is quite variable, this being especially true of the bearing metals. The analyses given are. but typical in some instances. New alloys are being in- troduced every year, and it would be impracticable here to list all that are now in use. IRON SERIES. (SPECIAL STEELS). Alloying Metal. Per Cent. Remarks. Aluminum 0.15 See Jour. Iron and Steel Inst., 1890, 2, 161. Copper 4.00 Jour. Iron and Steel Inst., 1907, 2, i. Tool steel. Armor plate and projectile. Tool steel. (Hadfield). Ordnance, nickel steel. Jour. Iron and Steel Inst., 1905, 2, 118. COPPER SERIES. Nickel Remarks Typical brass Mosaic gold. Gun metal (Bronze) Bell Bearing metal for heavy bearings 15-0 " " (P. R. R. "B") 14.8 German silver 25.0 Bearing metal 25.0 U. S. coin 9.5 (Phosphorus 0.8) Phosphor-bronze (Aluminum 10.0) Aluminum bronze (Manganese 2.0) Manganese " TIN-LEAD SERIES. Remarks Soft Solder Babbitt Metal, 1 for bearings Britannia Metal, for bearings White Antifriction " " " Magnolia " " " Type Pewter Shot 1 The original composition of this alloy is not known. Ledebur gives- Zinc, 69.0; Tin, 19.0; Copper, 4.0; Antimony, 3.0. Tin Lead Antimony 50.0 50.0 45-5 40.0 13.0 (Copper 1-5 ) 90.0 IO.O 82.0 12. (Copper 6.0 ) 40.0 55-o 5-o 4-75 80.0 15-0 (Bismuth 0.25) 3-o 82.0 15-0 80.0 20. o 99-7 (Arsenic 0-3 ) 288 BISMUTH SERIES. Bismuth Lead Tin Cadmium Remarks 50.0 31.25 18.75 Melts at 95 C (Newton) 50.0 28.10 24.64 " " 100 (Rose) 50.0 25.0 25.0 " " 93 (Darcet) 50.0 27.0 13.0 10.0 " " 60 (Lipowitz) PRECIOUS METALS. Gold Silver Copper Remarks 90.0 10.0 U. S. coin 90.0 10.0 " " 50.0 50.0 i2-carat 66.7 33.3 i6-carat 75.0 25.0 i8-carat NOTES ON THE MANUFACTURE OF ALLOYS Alloys are prepared commercially by the fusion method, which is simplest and most effective. The two or more metals may be melted together or melted separately and then mixed. A flux or covering is used with oxidizable metals, and in some instances measures must be taken to prevent volatilization and the absorption of gases. Processes in which one or more of the metals are smelted and simultaneously alloyed are common. On account of the difficulty with which some metals are made to unite and the tendency toward segregation, it is impossible to make some alloys homogeneous throughout. The rapid growth of manufactures and the high duty now required of metals are directly responsible for the large number of alloys which the market affords, as well as for their quality. Alloy Steels. These are generally prepared by adding the alloying metal to the charge of steel in the open hearth furnace, converter or crucible. With so large a quantity of steel as is treated in the open hearth or converter, the metal may be thrown into the ladle as the steel is tapped. This method has the advantage that less of the alloying metal is oxidized, though il may be necessary, for the sake of producing a uniform alloy, to mix the metals in the furnace. Another method of making alloy steel is to reduce the alloy- ing metal from its ore in contact with the steel. One of the processes for making nickel steel is to charge nickel ore into AIXOYS 289 the open hearth, the nickel toeing reduced by the carbon present at the beginning of the heat. Brass. In the melting and casting of brass the appliances used are similar to those used in iron founding, except that in brass founding the appliances are generally smaller and less ela- borate. Brass is melted in crucibles, cupolas and other styles of furnaces, crucibles being the most common. The copper is first melted or heated to near the melting point, and then the zinc is added. If the brass is to contain a large excess of copper the zinc may be added cold, otherwise it should be fused before the mixing. On account of its volatility a larger amount of zinc is charged than is required in the brass. Oxidation of the metals in brass founding is largely prevented by the use of fluxes such as glass, chloride of ammonia and fluorspar. The oxides may be removed from the fused alloy by adding a small amount of aluminum or magnesium. Other Alloys. In making bronze the tin is melted in a separate vessel and added to the molten copper. The mixture must be well stirred to make it homogeneous. Somewhat the same procedure is followed in alloying copper and lead. Bab- bitt metal, containing copper, antimony and tin, is prepared by adding the antimony to the copper, which is already fused, and then adding the tin in two portions. After the first portion is added the mixture is stirred for some time while the tempera- ture is maintained at dull-redness. The addition of the second portion is also followed by stirring to prevent the metals from separating. Phosphorus is usually introduced into alloys in the form of a phosphide. Phosphides, such as phosphor-copper and phos- phor-tin are prepared by adding stick phosphorus to the metal. The metal being fused in a crucible, the phosphorus is im- mersed in the bath by means of an inverted iron cup, and held there until it is absorbed. WELDING The weldable metals are those which can be brought into molecular union under pressure. For practical purposes it is necessary, in most instances, to heat the pieces to be welded to 10 290 METALLURGY the forging temperature, when they will unite under slight pressure. In ordinary welding operations the pieces to be united are heated in a furnace to the proper temperature, and forced together between rolls or by hammering. It is neces- sary that the surfaces at the point of contact be free from scale or other solid matter. Sometimes fluxes, such as borax and ammonium chloride are used to dissolve the metallic oxide, and the slag that forms is squeezed out in the operation of welding. The surfaces are prepared beforehand so that they will fit together, both being forged flat or into corresponding shapes. The pieces are either lapped or united at the ends, giving rise to the terms "lap" and u butt" welding. Electric Welding. This method of welding makes use of the heat from an electric arc. The pieces to be joined are gripped by bronze clamps, which are connected with the terminals of a dynamo. One of the clamps is arranged to move with the piece, so that any space needed can be opened between the sur- faces to be joined, or the pieces brought together under power- ful pressure. The surfaces having been properly prepared, are held in contact, and the current is turned on. The movable piece is then drawn back to form the arc. The heat developed soon brings the surfaces to the required temperature, when they are pressed together to make the weld. Thermit Welding. This process is the invention of Gold- schmidt. It employs a mixture of iron oxide with pulverized aluminum, to which the inventor gave the name "Thermit." In the welding operation the thermit is supported above the work in a funnel-shaped crucible, and a sand mold is fitted about the pieces to be joined so that the liquid iron which fills it will come in contact with enough area of both pieces to make a strong union. The thermit is kindled with a mixture of aluminum-barium peroxide and the aluminum continues to burn with great inten- sity to aJlumina, and reduces the iron. A small amount of metal- lic iron is sometimes added to the thermit to prevent the tem- perature from running too high. The iron is tapped into the mold, and coheres to the pieces which themselves become soft- ened on the surface by the heat. The thermit process is used ALLOYS 291 for welding rails and large forgings and castings that have been fractured. The latter application is especially useful in cases where other methods of welding would require the dismantling of cumbersome machinery. PLATING Base metals and those which are corrodible are covered with a more expensive metal for the purpose of ornament or for protection against rust. The thin sheet of metal does not adhere to the other metal as paints do, but it forms a surface alloy or molecular union, which cements the two metals to- gether. Such plating will not scale off. The metals copper, nickel, silver and gold are chiefly employed for ornamental work, and for protection against rust, zinc and tin are most cr.mmonly used. Lead, copper and nickel are also used for piotective plating. The necessaiy conditions in any plating process are that the surface of the metal to be plated be clean, and that the metal to be deposited be pure and in the proper physical condition for forming an alloy with the other metal. These conditions are brought about in two ways on the industrial scale. THie metal to be plated is either dipped in a molten bath of the other metal or placed as a cathode in a solution, from which the other metal is deposited by the aid of an electric current. These are known as dipping and electrolytic processes. Tin Plating. The most important industry of this class is the plating of sheet iron for the manufacture of roofing and tin ware. Th,e sheet iron or steel, having been rendered hard by cold rolling, is toughened by annealing. The annealing is done in a closed chamber to check oxidation. The sheets are then immersed in dilute sulphuric or hydrochloric acid to re- move the scale. This is termed "pickling." The last trace of acid is washed from the sheets after immersing them in lime water and rinsing, and they are now ready for plating. The tin is melted in a deep pot, a section of which is shown in Fig. 88. In the opening by which the sheet is introduced the tin is covered with a flux of zinc chloride and a small amount of ammonium chloride. The direction which the sheet 292 METALLURGY takes is indicated by the lines with the arrow heads. The sheet is turned and lifted by aid of the tool until it is gripped by the first pair of rolls. Four pairs of rolls are arranged as shown in the upper part of the pot. These rolls revolving 1 in the directions indicated, carry the sheet out of the bath, and give an even coat of tin. The rolls are surrounded by molten grease. Fig. 88 Tinning Pot. (Harbord and Hall). The flux of zinc and ammonium chlorides, through which the sheet passes as it is introduced into the tinning pot, serves to cleanse the surface of the iron and to remove oxides from the bath. The grease, through which the sheet passes as it leaves the bath, does not mix with the tin, but prevents exposure while the excess of tin is being removed by the rolls. The sheets are cleaned by passing them through wheat bran and then brush- ing. This is done entirely by machinery in modern plants. Zinc Plating. Though of comparatively recent origin, zinc ALLOYS 293 plate has now the most extensive usage. This is due to the rel- atively low cost of zinc and to the economy in the manufacture of zinc plate. The process of plating with zinc is commonly called "galvanizing/ 7 from the fact that iron and zinc together form a galvanic couple. Zinc is the opposite of tin in its being electropositive to iron. For this reason it is attacked first when the two metals are exposed to corrosive agents, and the iron is preserved. Zinc plate has now largely superceded tin plate for outside work, but it can not be used for cans in which food is stored, since meat and vegetable acids attack zinc and the salts formed are poisonous. Zinc plaice is manufactured both by the dipping and the electrolytic processes. The Dipping Process. The iron or steel sheets are prepared as for tin plating. The zinc is melted in a vessel constructed of soft iron plates. It is covered with a flux of ammonium chloride, which serves as a protective coating and to dissolve oxides. The sheets are introduced into the bath and carried through by means of guide rolls, the speed of which determines the length of time that the iron is kept in contact with the zinc. The thicker the sheets the longer time will be required, since it is necessary for the iron to attain the temperature of the zinc before the latter will adhere perfectly. The Electrolytic Process. This process, which is otherwise known as "cold galvanizing," is now carried on so successfully as to compete with the dipping process. Points in favor of cold galvanizing are that the toughness of the iron is not im- paired as is done by dipping it in the hot zinc, and that the plate generally adheres better. The electrolytic process is, however, slower and more costly than dipping, and it is not so suitable for plating articles of irregular shapes, since as cathodes they cause unequal resistance of the current in the electrolyte and consequently an uneven deposition of the zinc. The electrolyte used in galvanizing is a solution of zinc sul- phate or chloride containing an excess of the acid. The anodes are cast from spelter. In early practice much difficulty was met with in obtaining an even and adherent coating on account of the electrolyte becoming impoverished in zinc. A uniform 294 METALLURGY composition with the required amount of zinc could not be maintained by any arrangement of the anodes. The difficulty was overcome by Cowper Coles, whose process consists in pumping the electrolyte through tanks containing zinc dust. A large amount of zinc is thus added to the solution and its composition is kept uniform by the circulation. Plating with Other Metals. In plating with nickel, copper, silv ( er and, gold, electrolytic methods are now more commonly used than those of dipping. Nickel is used chiefly for plating iron, copper and brass. It is deposited from an ammoniacal solution of the sulphate. A better plate of nickel on iron is obtained by first plating the iron with copper and then plating with the nickel. Copper is deposited from an acid solution of the sulphate. Silver and gold are commonly deposited from cyanide solutions. Brass, german silver and some other alloys may be deposited electrochemically if it is desirable to use them for plating. INDEX A ACID, Bessemer process 137-143 open hearth process 145-150 refractory materials 10-13 Air pyrometer 20 " reduction process 215 Alloying property of metals 7 Alloys 282-294 " constitution of 283 " preparation of 286 properties of 282 steel 287, 288 " tables showing composition 287-288 Alumina as a refractory material 12, 14 " in iron blast furnace process 82 Aluminum, effect on iron 75 extraction of 276-278 history of 275 " ores 276 properties of 276 steel - 287 use in casting steel 149 Amalgamating barrel 253 pan 250 Amalgamation 47 of gold ores 260-264 of silver ores 246-255 American bloomary 121 " hearth 216 " rail specifications 169 Ampere 204 Annealing clay retorts 236 " iron castings 118 steel 166 Anode 204 " mud 207, 208 Anthracite 28 Antimony, effect on copper 172 " effect on lead 210 " in copper smelting process 198 " in copper refining procesg 207 " in lead smelting 221 " removal from lead 224 Appolt coke oven , 35 Argentite 245 Arrastra 248 Arsenic, effect on copper 172 " effect on lead 210 " in copper smelting process 198 " in copper refining process 207 296 INDEX Arsenic, in iron blast furnace process " in lead smelting 22r Atwater, on by-product coke 39 Augustin process O BAG filters for lead fume Barrel amalgamation Bar screens Basic Bessemer process " open hearth process 150-154 " refractory materials I 3~ I 4 Bauxite H, 276 Beehive coke oven Belgian process .... _ Bell charging apparatus for iron blast furnaces 77* 9 1 Bell, Sir I,., fuel calculations 109 Bertrand-Thiel process *57 Bessemer converters .... 138, 193 " process, copper !93 process, steel i37~M4 " Sir H., process for making steel 13? Billets i fil Bisbee converter 193 Bismuth, effect on copper 172 " effect on lead 210 " in copper refining process 207 Bituminous coal 2 7 Black tin 241 Blake ore crusher 5 " W. P., method of concentrating sulfides 333 Blastfurnaces (See copper, iron and lead) 61,77, 8 7. II 3, 1$%, 189, 191, 193. 217 " management of in iron smelting 101 " temperature records of 102 Blende 231 Blister copper 188 " steel i33 Blooms !6i Blooming mill 161 Blowholes 75i IIQ , Z 5 8 Blowing engines 95-97 " in iron blast furnaces 97 Blue metal 174 " powder : 238 Bogie for steel ingots 159 Bosh construction in iron blast furnaces 87 " plates 88-89 Boss process . 253 Brass 288, 289 Breaking ores 50 Briquettes, peat 25 flue dust 108 Bristol pyrometer 21 Brittleness in metals 6 Brown hoist and distributor 91 " ore roaster 178 Bruckner ore roaster 178 INDEX 297 Burdening iron blast furnaces * ... 98-100 By-product coke ovens 35-40 C CAKING coal '. 28 Calamine 231 Calcination 57 Calcining zinc ores 233 Calculation, efficiency of gas producers 42-44 for iron blast furnace charge 98-100 thermal requirement in iron blast furnace process 108-109 Calorie 17 Calorific intensity 19 Calorimetry 17-19 Campbell furnace 156 Cannelcoal 27 Carbon, effect on iron 69-7*1 112, 166 " in iron blast furnace process 80 " in open hearth process 152 Carbon in steel 166 Cast iron , 110-120 Catalan forge 121 Cathode 204 Cementation process 131-134 Cement carbon 71 " steel 133 Cerusite *. 209 Chalcocite 170 Chalcopyrite '. 170 Chamott 234 Charcoal in iron blast furnace process 101 manufacture of 25, 30-32 Chemistry of Bessemer steel process 143,144 " of copper ore roasting 182 " of copper smelting 188, 196 " of iron blast furnace process 79 " of lead smelting 188, 197-199 " of open hearth process 151-154 " of puddling process 124 " of silver amalgamating processes 254 " of zinc smelting 238 -Chilian mill 53 Chills 117 Chloridizing copper ores 200 gold ores 264 silver ores 247 " roasting 57. 200, 247 Chrome brick 15 Chrome-iron ore 14 Chrome steel 73-287 Chromite 14, 67 Chromium, effect on iron 73 in iron blast furnace process 83 metallurgy of 279 Cinder 15 Cinnabar 242 Clay 11-13, 234 298 INDEX Clay iron stone 67 Coal 26-29 " in iron blast furnace process 101 Coke in iron blast furnace process 100 " manufacture of 32-40 " quenching machines 38 Coking coal . 28 Cobalt 275 " removal from copper 207 Cold bending test 5 " galvanizing 293 Coles, C., galvanizing process 294 Combined carbon in iron 70 Combustion and thermal measurements 16-23. Compensator for Bristol pyrometer 22 Compression of liquid steel 158 tests 4 Concentration of ores (See ore dressing). Condenser manufacture (zinc) 235 Conductivity in metals 8 Converters (Bessemer) 138-193 Converter dust 143 slag 143 Continuous gas producer 41 " heating furnace 165 " open heasth process 165 " rolling mill 164 Cooling curves 284 Copee coke oven 35 Copper blast furnaces 189-191 " extraction of 184-200 " history of ....' 170 " in iron blast furnace process 83 ores 170 " properties of 171-173 " refining of 201-208 " removal from lead 224 Cornish process 216 Cort's puddling process 122,125 Cowles Bros.' process for smelting aluminum 277 Cowper stove 93 Cradle for washing gold ore 259 Crucible furnaces ^ 62, 135, 277 " process " ...... 134-136 steel '. . i 34 Crucibles, manufacture of 134 Cryolite 276 Crystallization of metals i Cupellation 229 Cupola, copper 189 iron II3 Cuprite I7 i Cyanide process for treating gold ores 265-270 process for treating silver ores 257 ID DAM used in casting pig iron io6> INDEX 299 Damping down iron blast furnaces 98 Density in metals Desilverizing lead 225-230 Destructive distillation 3 Diagram, showing history of by-product coke oven process 39 " history of open hearth heat 155 Dipping process for zinc plating 293 Direct pouring of iron in Bessemer process I3 8 " process for wrought iron and steel 121, 124 Distillation furnaces 62, 228, 236, 243, 252 Distribution of stock in iron blast furnaces 91 Dolomite 14 " in iron blast furnace process 101 Downcomer dust 79> IQ 8 Dredging 261 Drop testing 6, 120 Dry blast apparatus 105 " puddling 125 " sand molds "6 Ductility in metals 5 Duquesne blast furnace hoist 9 Dust catchers 9 1 E ELASTICITY in metals 2 Elastic limit 2 Electric furnaces 63, 277 " resistance pyrometer 21 welding 290 Electro-cyanide processes 268-270 Electrodes 204 Electrolyte 204 Electrolytic preparation of alloys 286 " process for extracting aluminum 276-278 " process for extracting nickel 274 process for plating with zinc 293 " refining of copper 203-208 refining of gold and silver 271 44 refining of lead 230 Endothermic reactions 16 English lead-smelting furnace 214 Equalizing temperature of blast 103 Eutectic alloys 284 Evaporative power 19 Exothermic reactions 16 FERRO-CHROME 73 " manganese . 7 2 > 2/9 " phosphorus 7 2 " silicon TI tungsten 74 Fettling for puddling furnace 127 Fire-clay n Flouring of mercury 264 Flow in metals 6 Flue dust . 79. 108 3OO INDEX Fluorspar ..................................... 15, 151, 222 Fluxes ........................................ *5 Flying shears .................................... 164 Forehearths ..................................... 192 Forges ........................................ 61, 121 Forging iron and steel ................................ 161-165 Foundry practice .................................. 113-120 Fracture of metals .................................. i " tests for steel .............................. 136-149 Franklinite .............................. ., ...... 68, 231 Free-milling gold ores ................ ............. . . 260 Frue vanner .............. ....................... 55 Fuels ........................................ 16, 24-45 " used in iron blast furnace process ...................... 100 Furnaces ....................................... 59-63 Fusibility of metals ................................. 6 Fusion point pyrometer ............................... 20 G GALENA ...................................... 209 Galvanizing ..................................... 293 Canister ....................................... 13, 139 Garnierite ........................ .............. 272 Gas as a fuel ..................................... 24 " producers ................................. 41, 45 Gates ore crusher ................................. 50 Gay ley bosh plate .................................. 89 " dry blast apparatus ............................. 105 " J., on blowing in iron blast furnaces .................... 97 Gjers kiln .............................. ........ 60 Goethite ....................................... 66 Gold dredge ..................................... 258 extraction of .................................. 259-270 " in copper smelting .............................. 199 " in copper refining process ........................... 202, 207 " ores ...................................... 258 " properties of ........................ ^ ......... 258 " refining of ................................... 270 Goldschmidt process ................................. 290 Grading pig iron ................................... in Graphitic carbon, effect on iron ........................... 69 Graphite ....................................... 14 " crucibles .................................. 134 Gray iron ................................ " ...... 70, 112 Grizzly ........................................ 53 Gyratory crusher .................................. 50 ff 73 Hall process for smelting aluminum ........................ 277 Hammer forging .............................. ..... 164 Hand picking ores .................................. 48 reverberatory furnace . , ........................... 176 Hardening carbon in iron .............................. 71 Hardness in metals ................................. 6 Hartman, J. M., grading iron ............................ in Harreyizing armor plates .................. 168 INDEX 3OI Hausmanite 278 Heap, charcoal 31 " roasting 174 Hearths 61 lead 216 Heat conduction p}'rometer 20 " regenerators 37, 63, 93-95, 145 '' treatment of steel 165-168 ' unit 17 Hematite 65 Herreshoff furnace 180 History, Aluminum 275 " Bessemer process ... 137 " copper 170,203 " iron 65, 121-122 " lead 209 " open hearth process 145 " zinc 231 Hofmau, H. O., composition of lead slags 222 " H. O., roasted lead ore 213 " H. O., lead blast furnace charge . . 219 Hoists for iron blast furnaces 90-91 Horn silver 245 Horseshoe roaster *..... 178 Hot blast, management of 95, 101 " blast stoves 93 Humidity of hot blast and effect of 104 Huntington mill 53, 264 Hydraulicing 260 Hydrogen, effect on iron 75 in iron blast furnace process 80 I ILMENITE 67 Impact testing 119 Ingalls, W. R., composition of clays 234 Ingots 136, 159 Inquartation . . . 271 Iron blast furnace 77, 87 " blast furnace dust 79, 108 " blast furnace gas 85 " blast furnace plant 86 " blast furnace process 77-109 " blast furnace slag 83, 107 " extraction of 77-109 " founding 113-120 " history of 65, 121 " in copper refining process 207 " mixer 138 " ores 65-68 " refining of 124-169 " use of in smelting lead 221 JAW crusher 50 Jig 54 Jones mixer 138 3O2 INDEX KELLY, Wm., process for refining iron 137 Kidney ore 66 Killing steel in crucible process 136 Kilns 60 Kish 69 Krupp's process for treating armor plates 168 L LADLE for lead matte 220 " for pouring steel 142 Langley's experiment with tungsten steel 74 Leaching processes ^ " processes for extracting copper 199 " processes for extracting gold 264-270 " processes for extracting nickel 274 " processes for extracting silver 255-257 Lead blast furnace 217 " extraction of 214-223 " fume 222 " history of . . 209 " in copper smelting process 198 " in copper refining process 208 " ores . . . j> 209 " properties of 209-211 , " refining of 224-230 " softening 224 LeChatelier pyrometer 21 Lewis and Bartlett process 222 Lignite 25 Lime as a refractory material 13 " in iron blast furnace process 82, 101 " in lead blast furnace process 221 lyimonite 66 Loam molds 117 Lodes 47 Luce and Rozan process 226 yvi MAGNESIA as a refractory material 13 in iron blast furnace process 82, 101 " in lead blast furnace process 221 Magnetic separation of ores 56 Magnetism in metals 8 Magnetite 66 Malachite 171 Malleability in metals 5 Malleable castings 118 Manganese, addition to steel 141 effect on iron 72, 112, 149 in iron blast furnace process 81 in open hearth process 153 metallurgy of 278 steel 73,287 Matte, copper 174 " lead 220 Matting furnace 184 INDEX 303 McArthur-Forrest process 265 Mechanical drawers for beehive coke ovens 35 " furnaces 62, 130, 138, 178, 180, 193 puddling 130 treatment of iron and steel 158-165 treatment of metals 48 Melaconite 171 Mercury, extraction of 243-244 " recovery from amalgams 252 " refining 244 Metal expansion pyrometer 20 Micaceous ore 66 Mica schist 13 Mild steel 131 Milling gold ores 263 Mineral wool 108 Mixer for pig iron 138 Mixing iron 115-138 Mixing ores 57 Modulus of elasticity 3 Moisture in iron blast furnace 104 Molds, ingot 136-159 " used in iron founding 116-118 Molybdenum, effect on iron 74 " metallurgyof 280 steel 74 Morgan gas producer 41 Mortar, stamp mill 52 Mottled iron 112 Muffle furnaces 62, 125 Muntz metal 263 Mushet steel . . 74 N NATIVE copper 170 " gold 258 " iron 65 " mercury 242 " silver 245 Natural gas 28 Neutral refractory materials 14 Nickel, effect on iron 73 extraction 273-275 " in copper smelting process 198 " in copper refining process 207 " ores 272 steel 73, 287 Nitrogen, effect on iron 75 " in iron blast furnace process 80 Nuggets 258 O OCCIyUSION in metals 8, 75 Optical pyrometer 21 Ore dressing 46-58 " dressing, copper ores 173-183 " dressing, gold ores 259-261 304 INDEX Ore dressing, iron ores 68 " dressing, lead ores 211-213 " dressing, silver ores 247 " dressing, zinc ores . 233 Ores 46 Otto-Hoffman coke oven 36 Oxidizing roasting 57 Oxygen, effect on copper 173 " effect on iron 72 " in iron blast furnace process 80 F PAN process for washing gold 259 Parkes process 227 Parr calorimeter 17 Parting gold and silver 270 Patera process 255 Patio process 248 Pattinson process 225 Peat 24 Pelatan-Clerici process 269 Penna. R. R., test for car wheels 120 Percy, Jno., on blister steel 133 " on running out fire 125 " " on tempers of steel 167 Peters, K. D., charge for copper blast furnace 194 " " on concentration of matte 188-189 Phosphorus, effect on copper 173 effect on iron 72, 112 in alloys 289 " in iron blast furnace process 81 in open hearth process 153 Physical properties of the metals 1-9 Pig bed 107 " boiling process 126-130 " iron, manufacture of 77-108 " machine 107 Piping in castings no, 158 Placers 258 Plasticity in metals 2, 167 Plating processes 291-294 Platinum, metallurgy of 280 Plattner process 264 Pneumatic process for refining iron "? 137 Pocket ores 47 Polling copper 202 " tin 242 Pot steel (See Crucible steel) Precipitation boxes for gold 267 Press forging 164 Producer gas 40-45 Puddling furnace 126 process 124-130 Pulling test 3 Pull-over mill 16^ Pulverizing ores 51 Pyrites 67 INDEX 305 Pyritic smelting 197 Pyrolusite 278 Pyrometer records of hot blast 102 Pyrometry 19-22 Pyromorphite 209 Pyrrhotite 67