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NATIONAL BUREAU OF STANDARDS -1963
MICROCOPY RESOLUTION TEST CHART
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ORAL-P-1946
Conf.660305-10 MASTERS
HOT PRESSES FOR GLOVE BOX AND MANIPULATOR CELI*
OUTC- OFFICIAL
FEB 23 15
T. C. Quinby, E. E. Pierce, and R. E. Mallannya
RELEAST FOR ANNCUNCEMENT
Isotopes Development Center
Oak Ridge National Laboratory
IN NUCLEAR SCIENCE ABSTRACTS
· Oak Ridge, Tennessee

I
OFFICIAL
STA!.
In most applications of large quantities of radioisotopes as either radiation or
heat sources, it is desired that the source material be fabricated as a dimen-
sionally accurate compact which exhibits to a high degree the desired physical
properties. The desired properties include high density, high melting point,
high thermal stability, high thermal conductivity, and good mechanical propert
These properties greatly affect the efficiency of the source design, especially
the shield weight and heat transfer characteristics. This paper describes two
hot presses - & research press and a production scale press - which have been used
to fabricate a wide variety of source compounds to near theoretical density:
:
.
1
:
. The several forming methods applicable to radioisotope sources can be divided
into three groups: (1) cold forming, (2) hot forming, and (3) melt forming...
The hot forming method has two distinct advantages over the other two methods...
These advantages are the dimensional accuracy of the compact and the small amount
of experimental effort required to adapt the method to the forming of a wide :
variety of materials. Cold forming methods are sensitive to a number of process
variables which are not amenable to precise control with radioactive materials.
Particle size, for example, is impossible to control if self-heating of a powder
temperature above that required for sintering. The hot forming
. . method also has the advantage that two materials may be reacted to give the
re quired compound and formed simultaneously (reactive hot pressing).
In the hot forming method, which consists essentially of the simultaneous appli-
cation of heat and pressure, the pressure may be applied uniaxially (hot press-
ing and hot swaging) or multiaxially (isostatic pressing). Hot pressing was
chosen for the present work because of its simplicity and safety.
A hot pressing operation consists of applying pressure to a sample in a heated
die. Several hot presses have been described in the literature. 1-3 McClelland
and Smith* describe a hot press which they designed for versatility as a research
tool.
The two hot presses described in this paper were designed to serve two different
functions. The miniature. press was intended for research and development and for
glove-box operation (and with minor modifications, for use in a manipulator cell).
The larger press was designed primarily for production applications in a manipu-
lator cell. In the miniature press, emphasis was placed on compactness and i
simplicity by incorporating self-alignment in the pressing column and eliminating
.. : packed insulation in the furnace. The design of this hot press allows for very
rapid heating and cooling cycles as well as for rapid pumpdown or purging and it
can be readily disassembled and reassembled in a glove box through the access
ports.
ORNI MAEC - OFFICIAL
*
*Research sponsored by the U. S. Atomic Energy Commission under contract:
with the Union Carbide Corporation.
ORNL - AEC - OFFICIAL
.
.
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Although the miniature press was designed primarily for radioactive materials, it is
is also useful for general development work where easy operation, small sample
size, and rapid heating-cooling cycles are desired.
The production hot press was designed for fabrication of sources up to 3-in. ir
diameter. Design emphasis was placed on ease of operation in a manipulator cell...
The production press has a self-aligning pressing column with an induction ::
heated furnace. .
APPARATUS
The two presses are described separately.
Miniature Hot Press
The miniature hot press (Figs. I and 2) consists of three components: (1) the
heater, which includes a carbon resistance element and variable-voltage, high-
amperage power supply; (2) the die column, which includes the die assembly and
the hydraulic cylinder for applying pressure to the die plunger; and (3) the
containment shell, which confines the heated zone and contains the vacuum
other atmosphere).
lor.
Containment Shell
The containment shell assembly has three main parts: the base plate, the cover
vessel, and a multilayer heat shield. The molybdenum heat reflectors are the
only insulation. Since the greatest heat loss occurs through the die columri,
packed-type insulation would only increase the size of the press without signi-
ficantly reducing heat loss. The entire containment shell is provided with
water cooling. The power requirement (3300 watts at 1500PC) is not considered
excessive for a furnace of this size.
In addition to maintaining containment, the base plate of the shell serves as
a base' for assembly and alignment, and provides connection for vacuum or purge.
The heating element, die assembly, and cover vessel are attached directly to:
the base plate. The bellows seal, which transmits pressure to the containment
shell, is fixed to the top of the cover vessel.
The cover vessel is constructed of stainless steel and is water cooled by an:
external copper coil which is attached by brazing. The bottom of the cover -
vessel is sealed on the base plate with a neoprene rubber channel gasket and is
aligned by two interior pins that mate with two blind holes in the base plate.
A sealed quartz window on the front of the cover vessel provides visibility for
temperature measurement by optical pyrometry. The top of the cover vessel has
a flange for the attachment of a sealed push rod to transmit force to the die
plunger. A vacuum seal is attained around the push rod by two concentric bel-
lows that are sealed by solder. Water is passed between the two bellows to
provide cooling.
LEGAL NOTICE
This report was prepared as an account of Government soumored worth, Malther the United
mate, mor the Commission, nor su partem noting on behalf of the Commissions
:: A, Makou may warranty or representation, expressed or implied, wo wpret to the root-
racy, completeasul, or ustalon d the taformation contatod a do report, or that the
o of any information, appuratus, method, or procou dinoland to the report may not
t
.. . privately owned rectes or
B. Aamun any liabiliday with topoet to the tool, or for dengue moltes from the
un of any information, appunto, method, or focus dirolowed in the report ;** .. .
• As wond in the above, "person soting on behalf of the counteddon" moting -
ployee or contractor of the Commission, or wmploys of mail contornotor, to the two that
enol employw or contractor of the Comunicator, of omployee of me contractor prepares, i
denominaton, or providos acomo to, any hudormation puremat to Wo employment of contract
. .. with the Commission, or hin employment was made contrmotor.
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The molybdenum heat reflector consists of five concentric sheet-metal cylinders
assembled with molybdenum wire. Viewing ports in each cylinder, in line with
the quartz window of the cover vessel, permit observation. During operation,
the reflector assembly is placed around the graphite heating element and is sup-
ted by the annular projections at the bottom of the heating element. Thorium
oxide discs are placed between the reflector assembly, and the graphite projections
to provide electrical insulation..
Heater
.
The die assembly is heated by a graphite resistance element fabricated from bar-
stock ATJ graphite and consisting of a cylinder milled to produce two parallel
spiraled conductors with crigins and terminations spaced radially at 180°. Two
.: annular projections at the bottom of the heating element fit into clamps on two
water-cooled, threaded current posts for electrical contact. Tapered sections
of the posts are fitted with tapered Teflon sleeves to furnish electrical insu-
. : lation as well as a vacuum seal where the posts pass through the base plate."
Below the base plate, the posts provide water and electrical connections.
.
.
.. Power for the heating element is obtained from a 600-amp transformer and
rectifier provided with a 400-volt variable input to the primary.
.
:::
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Die Column
.
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T'he die column consists of the base plate, die support, die body with bottom die
plunger, top die plunger, graphite push rod, and brass push rod. The die column
components are self-aligning, with the aid of centering projections and mating
indentations. The brass push rod does not certer but is free to position itself
to eliminate misalignment. The mechanism to provide hydraulic force to the
bellows-sealed push rod consists of a Blackhawk Model R-618 hydraulic cylinder
mounted on a reinforced circular plate. The flange that contains the hydraulis.
· cylinder is secured to the base plate by four adjustable threaded rods.
Production Hot Press
::::
::.
The production hot press (Figs. 3, 4, and 5) consists of three components: :
the frame assembly, which allows the furnace to be tilted for loading and
contains the hydraulic ram; (2) the. furnace, which includes the radio-frequency
work coil, the graphite susceptor, and the furnace insulation and shell; and
(3) the die column including the die assembly, plungers, and push rods. ..
'
.
Frame Assembly
.
.::::....
The frame assembly is designed so the furance (and die assembly) can be tilted
to à horizontal position for loading and unloading the press. This arrangement
also reduces the vertical reach required of the manipulators during operation :
of the press. Views of the furnace in the horizontal and vertical positions,
(pressing operations are carried out in the vertical position) are shown in':
Figs. 3 and 4, respectively. The pressing force to the die assembly is supplied
: by a 10-ton hydraulic ran at the top of the frame. The ram has a 6-in, travel
and spring return...
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Hot Press for Remate Operation
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Furnace
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- OFFICIAL
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Electric power is supplied to the furnace by a 20-kw, high-frequency (10,000
cycle) motor generator unit. The radio-frequency conductor is a dual spiral
coil of 3/8-in.-dia copper tubing which is 9-1/2-in. i.d. by 10-5/8-in. high.
A graphite susceptor 6-7/8-in. 0.d. (6-1/8-in. i.d.) by 12-in. high is used
to convert the high-frequency, electrical energy to heat. Heavy-duty flexible
leads permit the unit to be moved from a vertical position to a horizontal :
position without disconnecting the electrical leads.
.. Temperature measurements are accomplished by means of a Pt-10% Rh thermocouple
inserted from the top of the unit into the high temperature zone.
.
..
The jacket of the furnace is fabricated of a nonconductor to prevent coupling
to the work coil and also confines the carbon insulating material. The furnace
assembly is equipped for purging the heated zone with inert gas.
... .
.
Die Assembly
A typical compacting die consists of a high-density graphite body and two
graphite body is 6 in. in diameter by 8-1/2 in. high
and is equipped with a flange on the top to permit convenient removal from ;
the hot press furnace. The punches are right cylinders. The length of the
... long punch is 4 in. and the short punch is 2-7/8 in. The total force required
to produce the compact establishes the maximum inside diameter of the die body.
With a 2-1/4-in. i.d., compacting pressures of up to 4000 psi are employed.
::The maximum inside diameter that has been used is 3 in.
: ......
.
:..
..
::::::...
OPERATION
.
.
..
.
.
.
.
..
.
. Both the miniature hot press and the production press have been used to compact
a variety of materials. Graphite dies or lined graphite dies have been used in
all applications tested. Liners which have been used are the refractory metals
(W, Mo, and Pt) and alumina. A typical alumina-lined die assembly for the pro-
duction press is shown in Fig. 6. Sufficient clearance at room temperature must
be allowed between the alumina liner and the graphite di,e body to allow a l-mil
interference fit of the liner at operating temperature. Similar alumina-lined
the miniature press. Sample sizes on the miniature press are
1/4 to 1/2 ini dia and on the production press 3/4 to 3 in. dia.
.
. .
.
. .
.
The highest temperature at which the presses have been operated is 1800°C. The
limit on the maximum temperature in the miniature press is determined by the
effectiveness of the heat shielding and water cooling. The heat shielding for
this apparatus was designed to operate at 2000°C or below in order to permit.
relative ease of assembly and disassembly. Similar carbon resistance furnaces
with more elaborate heat shields have been operated up to 2700°C. The tempera-
ture limit in the production press: is fixed by the 20-kw power supply.
.
The power required to attain a given operating temperature in the miniature,
press is shown in Fig. 7. The heating cycle requires 26 min, while it takes
13 min for the press to cool. A hot-pressing cycle with the production press
*requires no hr. . .
.::.
.
ORNI - AEC - OFFICIAL :
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11
Power Curve for Hot Press Heating Element..
POWER (kW).
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ORNL-DWG 65-13261
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.
ORNI - ALC - OFFICIAL
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.
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.
.
ORNIAC - OFFICIAL
The miniature press operates either in an inert atmosphere' or in a vacuum. A small
mechanical pump will maintain an internal pressure in the press of a few torr.
The production press operates at atmospheric pressure with an argon purge.
REFERENCES
'
.
-
..
::
1.: I. E. Campbell, High Temperature Technology, John Wiley and Sons, Inc.,
New York, 1956, pp. 271-7.
2. A. U. Seybolt and J. E. Burke, Procedures in Experimental Metallurgy
John Wiley and Sons, Inc., New York, 1953, pp. 271-5.
3. P. Murray, É. P.: Rogers, and A. E. Williams, Practical and theoretical
aspects of the hot pressing of refractory oxides, British Report AERE
M/R 973, Atomic Energy Research Establishment (1952). . i
:.
....
.....
*
4. 'J. D. McClelland and W. M. Smith, Research hot pressing, ISAEC Rpt. :
..' NAA-SR-6441; Atomics International (October 1961), ...
•*.
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.
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OFFICIAL
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MIN
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END
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3/ 25 /66
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