Aprs 4§ 
 
 MDDC - 1126 
 (LADC - 279) 
 
 UNITED STATES ATOMIC ENERGY COMMISSION 
 
 THE DESIGN AND SOME CONSTRUCTION DETAILS OF TWO 
 LABORATORY VACUUM FURNACES FOR CASTING METALS 
 
 by 
 
 Eugene D. Selmanoff 
 
 Los Alamos Scientific Laboratory 
 
 Date of Manuscript: June 29, 1946 
 
 Date Declassified: February 20, 1947 
 
 Issuance of this document does not constitute 
 authority for declassification of classified 
 copies of the same or similar content and title 
 and by the same author. 
 
 Technical Information Branch, Oak Ridge, Tennessee 
 AEC, Oak Ridge, Tenn., 4-20-49--850-A1320 
 
 Printed in U.S.A. 
 PRICE 10 CENTS 
 
THE DESIGN AND SOME CONSTRUCTION DETAILS OF TWO 
 LABORATORY VACUUM FURNACES FOR CASTING METALS 
 
 By Eugene D. Selmanoff 
 
 ABSTRACT 
 
 The designs of two laboratory furnaces for vacuum casting metals are described in detail. The 
 first furnace employs a tungsten or molybdenum resistance winding. The furnace is constructed in two 
 parts, an upper brass cylindrical "can" containing the heating coil, resting on a similar lower can in 
 which the mold is placed. Bottom pouring technique is employed in both furnaces. The second furnace 
 uses high frequency induction heating, but may be adapted for resistance heating. It consists of an 
 open-end silica tube resting on a brass cylindrical can. The induction coil fits around the silica tube 
 and the crucible stands inside the tube. The mold is accommodated by the brass can. In both furnaces 
 temperatures in the neighborhood of 1500 degrees C at pressures of 10~3 t 10 _ 5 mm jjg have been 
 obtained. The design of a vacuum gate valve, compression gland are also given. 
 
 Techniques for vacuum casting metals, both in the laboratory and in industry, have been greatly 
 improved and developed during the war period. New furnace designs and methods of construction 
 should be of considerable interest to the metallurgist and others concerned with the problem of casting 
 metals in vacuum. This is especially true in view of the scarcity of metallurgical or other scientific 
 literature in this field. 
 
 Furnaces for melting or casting metals may be divided into two groups, (1) glass systems, and 
 (2) metal systems. The former similar in construction to the glass systems commonly used in 
 chemical and physical laboratories for carrying out reactions or experiments in vacuum. The ma- 
 jority of the parts and connections are usually made by the fusion of the glass or by the use of ground 
 glass joints of one type or another. Such a system, as far as melting of metals is concerned, is 
 usually limited to small melts, from less than 1 g to several hundred grams. A strict upper limit 
 cannot be set. For melts of greater size and especially where casting is required it is desirable to 
 go to metal systems primarily because of their greater mechanical strength and ease of construction 
 when dealing with large parts. In these systems the majority of the parts are metal, usually brass, 
 copper or steel, and the various components of the system are connected by soft or hard- soldering, 
 welding, or bolting. The furnaces discussed in this paper are parts of metal systems. 
 
 LITERATURE ON VACUUM CASTING 
 
 The writer could find no literature on furnaces designed for vacuum casting. However some litera- 
 ture is available on the design of vacuum melting furnaces. The Arsem 7 vacuum furnace is probably 
 the most widely known of this type. It employs a helical graphite coil as an electrical resistance unit 
 and the vacuum is produced within a cylindrical gun-metal casting. Temperatures of 3100 degrees C 
 were obtained in the original furnaces constructed by Arsem. 
 
 MDDC - 1126 [ 1 
 
2 ] 
 
 MDDC - 1126 
 
 List of Parts for Figure 1. 
 
 Number 
 
 1 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 
 10 
 11 
 12 
 13 
 14 
 15 
 16 
 17 
 18 
 19 
 20 
 21 
 22 
 23 
 24 
 25 
 26 
 27 
 28 
 29 
 30 
 31 
 32 
 33 
 34 
 
 35 
 36 
 37 
 38 
 39 
 
 Material 
 
 Brass or steel 
 
 Rubber 
 
 Brass 
 
 Brass 
 
 Brass 
 
 Glass 
 
 Rubber 
 
 Brass 
 
 Brass 
 
 Copper 
 
 Steel 
 
 Brass 
 
 Brass 
 
 Stainless steel 
 
 Stainless steel 
 
 Brass or copper 
 
 Copper 
 
 Suitable refactory 
 
 Steel 
 
 Brass 
 
 Rubber 
 
 Brass 
 
 Brass 
 
 Brass or copper 
 
 Brass 
 
 Brass 
 
 Copper 
 
 Suitable refractory 
 
 Suitable refractory 
 
 Steel 
 
 Alundum 
 
 Alundum-60 mesh 
 
 Alundum 
 
 Tungsten or 
 
 molybdenum 
 Suitable refractory 
 Sil-o-Cell 
 Suitable material 
 Steel 
 Copper 
 
 Part (nonimal dimensions in inches) 
 
 3/8-16 x 1-1/4 Hex head screw 
 
 1/8 x 1/8 Gasket 
 
 8 Diam x 1/2 Top plate 
 
 8-32 x 1/2 Filister head screw 
 
 Window cover plate 
 
 1 Diam x 1/8 Pyrex window 
 
 1/8 x 1/8 Gasket 
 
 1/4 Diam Pouring rod extension 
 
 1/4 Wilson seal 
 
 1/4 OD Cooling water coil 
 
 6-13/16 OD x 6-11/16 ID x 1/4 Split ring 
 
 8 OD x 6-3/4 ID x 1/2 Ring 
 
 3/8 x 3/8 x 1-3/4 Bar 
 
 Pouring rod extension, 1/4 Diam 
 
 Pouring rod coupling 
 
 6-3/4 OD x 6-1/2 ID x 10 Furnace can 
 
 1/4 OD Cooling water coil 
 
 3/8 Diam Pouring rod 
 
 6-1/2 OD Furnace support 
 
 8 OD x 6-3/4 ID x 1/2 Ring 
 
 1/4 x 1/4 Gasket 
 
 8 OD x 6-3/4 ID x 1/2 Ring 
 
 1/4 Compression gland 
 
 6-3/4 x 6-1/2 x 6 Mold can 
 
 8 Diam x 1/2 Bottom plate 
 
 Flange, See Figure 2-11 
 
 Water-cooled lead 
 
 1/4 Coverplate 
 
 1/4 Crucible cover 
 
 5 OD x 4-15/16 ID x 5-1/4 Coil can 
 
 Insulating tube 
 
 Insulation 
 
 3-3/4 OD x 3-1/4 ID x 4-1/4 Coil tube 
 
 30 mil wire 
 
 Crucible 
 
 Insulation 
 
 Mold 
 
 5 Diam x 1-1/4 Mold stool 
 
 1/4 OD Cooling water coil 
 
MDDC - 1126 
 
 [3 
 
 CROSS- SECTION THROUGH CENTER 
 
 Figure 1. Resistance heated vacuum casting furnace. 
 
MDDC - 1126 
 
 W. F. Ehret and David Gurinsky 8 have described a carbon tube resistance furnace which they 
 claim has the advantages of low cost, compactness, and rapid heating. The metal vacuum can is 
 roughly 7 inches in diameter by 7 inches in height and operates in the pressure range 10-3 to 10 _ 5 
 mm Hg or with a special atmosphere. Twenty- five g melts have been made at 1550 degrees C in 6 
 minutes, and charges up to 100 g can be used. 
 
 Two vacuum distillation furnaces which are suitable for melting and employing high-frequency 
 induction heating have been described by J. B. Friauf. 9 In these furnaces, the vacuum is produced 
 within a fused quartz tube aroind which the induction coil fits. In one furnace, the silica tube is 4 
 inches inside diameter and 2 feet long; and in the other, it is 6 inches inside diameter and 30 inches 
 long. The furnaces differ principally only in size. The upper end of the silica tube is sealed to a 
 brass ring which has a side tube leading to the vacuum pumps. The vacuum connection at the top of 
 the quartz tube has some advantage over one at the bottom of the furnace, because it allows the entire 
 furnace to be placed at a lower, more convenient location. 
 
 F. M. Walters 12 has described a high-frequency induction furnace used for melting under a con- 
 trolled atmosphere (argon). It consists of a fused quartz tube 10 inches in diameter and 24 inches 
 long, closed at the bottom by a water cooled brass casting, and at the top by a brass ring and water 
 cooled cover. The high-frequency coil is placed inside the quartz tube, three leads passing through 
 one inch holes drilled in the quartz tube. Melts of 2-5 lbs. were made in this furnace. 
 
 Methods and applications of melting and evaporating metals in vacuum have been discussed by 
 Kroll. 10 The paper mentions several more unusual methods of vacuum melting, such as an arc furnace, 
 and the Hultgren 10 electron-bombardment furnace. 
 
 This article will describe the design and some details of construction of two laboratory furnaces 
 designed for vacuum casting, one employing resistance heating and the other employing induction or 
 resistance heating. The reader desiring merely a melting furnace can easily simplify the designs 
 given to meet this single function. In addition some accessory metal vacuum system equipment will 
 be described. 
 
 A RESISTANCE -HEATED FURNACE 
 
 A furnace designed for resistance heating is shown in Figure 1. The furnace is composed of two 
 parts, the upper "can"* (16) which contains the heating coil, and the lower can '(24) which contains the 
 mold. The advantage of this type of construction is that the heating coil, which tends to become quite 
 fragile with use, is not disturbed (as would probably be the case if the entire furnace were in one part) 
 when the mold is placed in, or removed from the furnace. 
 
 The design and method of construction can be seen by an examination of Figure 1 and Figure 1- 
 List of Parts. In the List of Parts, some of the dimensions are given only nominally, and some were 
 omitted if they were of little importance. 
 
 Upper Can 
 
 The upper furnace can, which may be made of either brass or copper, is 6 3/4 inches in diameter 
 and 10 inches high. It is cooled by water flowing through several turns of 1/4 inch diameter copper 
 refrigerator tubing (17). The turns are spaced 1 inch or slightly more apart and are soft-soldered to 
 the can. The can is closed at its upper end by a brass plate (3) bolted to the can by six machine 
 screws (1) and a ring arrangement (11, 12). 
 
 * The figures in parentheses in this section refer to parts shown in Figure 1, unless otherwise 
 indicated. 
 
MDDC - 1126 [5 
 
 The plate has a Pyrex window (6), a sliding (or Wilson) seal (9) for introduction of translatory 
 motion into the vacuum, ana is water cooled (10). The window shown is 1 inch in diameter, but in 
 general a larger window facilitates visual and pyrometric observations of the melts. Suitable Pyrex 
 windows of various dimensions may be obtained from the Corning Glass Works. A window shutter 
 (not shown) has been found effective in preventing or decreasing fogging of the window due to con- 
 densation of volatile constituents from the melts. Such a shutter may be fashioned from a 20 gauge 
 piece of sheet steel, roughly teardrop in shape and pivoted at the narrow end by a screw threaded to 
 the underside of the top plate. The shutter can be opened and closed by sliding an Alnico magnet in 
 the desired direction along the topside of the plate. The construction and dimension of the Wilson 
 seal have been thoroughly described by Wilson. 17 It is probably desirable, where possible, to inter- 
 change the position of the Wilson seal and the window as shown in Figure 1, because an off-center 
 window usually provides a better view of the melt. 
 
 It is necessary to have some play in the pouring rod connections to compensate for the small 
 misalignments of the crucible or the whole heating coil assembly that usually occur. A sloppy fit 
 where extension (14) is threaded into coupling (15) has usually been sufficient. The pouring rod (18) 
 fits into a hole in the coupling and is secured by an Allen head screw. When the crucible is loaded 
 the pouring rod together with the coupling (15) and extension (14) is placed in position. After the 
 crucible is lowered into the furnace, extension (14) fits into a hole in arm (13) and is fastened with 
 a thumbscrew. This operation is performed as the top plate is held in a horizontal position several 
 inches above the can. 
 
 The rubber gaskets (2, 7, 21) can be obtained, in various cross sections, by the foot. Circular 
 cross section gaskets can also be used. 
 
 The heating coil consists of 30 mil tungsten or molybdenum wire inside wound on a 3 1/4 inch 
 inside diameter alundum tube. It was not possible to purchase inside-threaded tubes so the threads 
 were ground by an abrasive wheel; six threads per inch, approximately 1/3 inch deep. Tungsten wire 
 is easier to wind than molybdenum, due to the greater stiffness of the tungsten. The two ends of the 
 coil winding are fastened to 50-60 mil molybdenum wire which is run to the water-cooled leads (27). 
 Several methods of fastening two pieces of resistance wire together have been used successfully. The 
 two pieces may be placed alongside and running parallel to each other and be tied together with 1-2 mil 
 molybdenum wire. Another method is to run a single loop of 20-30 mil molybdenum wire around the 
 two pieces, placed in any position, and tightening the loop by twisting its ends together. The heating 
 coil unit rests on a steel ring (19) which in turn rests on three pins (not shown) fastened to the wall of 
 the can. Heat loss by radiation may be reduced by introducing one or more metal shields between the 
 heating coil assembly and the can. 
 
 Water-Cooled Leads 
 
 The construction of the water cooled leads is shown in Figure 2. The brass flange* (11) is soft- 
 soldered to the back of the upper can (Figure 1-26). An insulating plate (7) is screwed to the flange and 
 the two leads protrude through and are secured to this plate. The drawing does not show the small hole 
 through the extreme right end of (8) through which the furnace lead passes and is held by an Allen 
 head screw. An electrical input wire is fastened to a hose clamp which is clamped on the excess 
 threaded portion of (8) next to nut (4). The water inlet and outlet (I, 2) are soft- soldered to disc (3) 
 which is soft-soldered to (8). Two or three 3 inch diameter sheet metal radiation shields are placed 
 in front of the insulating plate to protect it from direct radiation. Pyrex tubes are slipped over the ends 
 of the leads to prevent contact and subsequent electrical shorting by the shields. 
 
 * The figures in parentheses in this section refer to parts shown in Figure 2, unless otherwise 
 indicated. 
 
6] 
 
 MDDC - 1126 
 
 CROSS-SECTION THROUGH CENTER 
 
 Number 
 
 Material 
 
 1 
 2 
 3 
 4 
 
 Copper tubing 
 Copper tubing 
 Copper 
 Brass 
 
 5 
 
 Brass 
 
 6 
 
 Rubber 
 
 7 
 
 Micarta 
 
 8 
 9 
 
 Copper 
 Brass 
 
 10 
 
 Rubber 
 
 11 
 
 Brass 
 
 12 
 
 Brass or Copper 
 
 Figure 2. Construction of water-cooled leads. 
 Figure 2 - List of Parts 
 
 Part (nominal dimensions in inches) 
 
 1/8 OD hard drawn, Water inlet 
 
 1/8 OD hard drawn, Water outlet 
 
 1/2 Diam x 3/16 End piece 
 
 3/4 - 16 Hex head nut 
 
 1 OD x 3/4 ID x 1/4 Washer 
 
 1 OD x 3/4 ID x 1/4 Gasket 
 
 4-3/4 Diam x 1/2 Insulating Plate 
 
 Lead Body 
 
 Filister head screw 
 
 1/8 x 1/8 Gasket 
 
 4-3/4 OD x 3 ID x 1/8 Wall x 3-1/4 Flange 
 
 Furnace can wall 
 
 ^^^ 
 
 CROSS SECTION THROUGH CENTER 
 
 Number 
 
 1 
 2 
 3 
 4 
 
 Figure 3. 1/4 inch compression gland. 
 Figure 3- List of Parts 
 Material Part (nominal dimensions in inches) 
 
 Brass 
 Brass 
 Brass 
 Rubber 
 
 Hex head screw 
 Body 
 Washer 
 Gasket 
 
MDDC - 1126 [7 
 
 Lower Can 
 
 The upper can rests on the lower (mold) can. A vacuum tight seal is provided by the gasket (21). 
 It should be noted that this gasket is protected from direct radiation of heat by a slight projection of 
 the upper can (B). It is important that no rubber gaskets in the system be subjected to direct radia- 
 tion. The rings (20, 22) are hard-soldered to their respective cans (A). 
 
 Four 1/4 inch compression glands (23 and Figure 3) are soft-soldered roughly 45 degrees apart 
 around the back side of the can. They are used for the introduction of vacuum gages, thermocouple 
 wires, electrical connections to a mold heating coil, etc., into the system. A convenient method of 
 interchanging vacuum gage tubes in the system is to fuse the female part of a semiball joint to each 
 tube. By means of an L-shaped glass tubing having a stopcock, the male part of a semiball joint on 
 one end, and the other end in the compression gland, tubes may be changed during a run without 
 breaking the vacuum. 
 
 The bottom plate is secured to the lower can in the same way that the top plate is secured to the 
 upper can. The bottom plate has a 4 inch diameter vacuum outlet and a 1/2 inch diameter hole for 
 connection to a roughing system. It is also water cooled (39). The mold (37) which rests on a short 
 metal stool (38) can be raised if it is desired to shorten the distance through which the metal drops 
 from crucible to mold. 
 
 Furnace Support 
 
 A method of supporting the entire furnace has not been shown. Four 3/8 inch diameter steel rods 
 are threaded into the bottom of a steel ring similar in cross section to (19). The rods are then bolted to 
 a table top and the furnace is placed on the ring. Sufficient distance is allowed between the ring and the 
 table top for insertion of a gate valve (Figure 5) which is bolted on to the bottom plate (25). 
 
 AN INDUCTION OR RESISTANCE -HEATED FURNACE 
 
 A furnace that was originally designed for induction heating, but which may easily be adapted for 
 resistance heating, is shown in Figure 4. The lower can is very similar in design to the lower can 
 shown in Figure 2. The crucible is placed within a fused quartz tube* (13) which rests on the top plate 
 (17) and around which the induction coil (not shown) fits. The tube shown is 3 1/2 inches in outside di- 
 ameter by 3 inches in inside diameter by 15 inches in height. A tube of this length allows one to place 
 both the crucible and mold within the quartz tube, provided the diameter of the mold is small enough 
 to fit. The crucible may then rest directly on the mold, if desired, thereby eliminating the long metal 
 drop which is unavoidable when the crucible and mold are in the positions shown in Figure 4. It is 
 always desirable to have the outside diameter of the tubes as small as possible because increasingly 
 greater magnetic coupling as obtained as the diameter of the induction coil approaches the diameter of 
 the crucible. On the other hand, the tube should be large enough to permit the use of radiation shields, 
 and to allow free passageway for gases past the crucible to the vacuum outlet. The design shown in 
 Figure 4 is useful because it permits the use of a mold which has too large a diameter to fit inside of the 
 quartz tube. 
 
 Fused quartz tubes having either a sand cast surface or a mold surface (both have been used satis- 
 factorily) may be obtained from Thermal Syndicate Ltd., New York, or Amersil Co., Inc., Hillside, New 
 Jersey. Tubes supplied by the former have had less variation in the dimensions of the inner and outer 
 diameter. Vycor (Corning Glass Works) and Pyrex tubes have also been used satisfactorily, although 
 they have thinner walls and are more easily damaged by mechanical shock. It is desirable to have a 
 radiation shield (24, 26) around the crucible (27). Refractory or metal shields may be used. Metal shields 
 must be slotted to prevent heating by induction. 
 
 * The figures in parentheses in this section refer to parts shown in Figure 4, unless otherwise 
 indicated. 
 
8] 
 
 MDDC - 1126 
 
 List of Parts for Figure 4 
 
 Number 
 
 1 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 
 10 
 11 
 12 
 13 
 14 
 15 
 16 
 17 
 18 
 19 
 20 
 21 
 22 
 23 
 24 
 25 
 26 
 27 
 28 
 29 
 30 
 31 
 32 
 33 
 34 
 35 
 
 Material 
 
 Brass 
 
 Brass 
 
 Brass 
 
 Glass 
 
 Rubber 
 
 Brass 
 
 Brass 
 
 Copper 
 
 Brass 
 
 Stainless Steel 
 
 Stainless Steel 
 
 Suitable refractory 
 
 Fused quartz 
 
 Suitable refractory 
 
 Rubber 
 
 Copper 
 
 Brass 
 
 Steel 
 
 Brass 
 
 Copper 
 
 Brass or Copper 
 
 Brass 
 
 Rubber 
 
 Suitable refractory 
 
 Suitable refractory 
 
 Suitable refractory 
 
 Suitable refractory 
 
 Suitable refractory 
 
 Suitable refractory 
 
 Brass 
 
 Rubber 
 
 Brass 
 
 Suitable material 
 
 Steel 
 
 Copper 
 
 Part (nominal dimensions in inches) 
 
 4-1/2 Diam x 1/2 Top plate 
 8-32 x 1/2 Filister head screw 
 Window cover plate 
 
 1 Diam x 1/8 Pyrex window 
 1/8 x 1/8 Gasket 
 
 1/4 Diam Pouring rod extension 
 
 1/4 Wilson seal 
 
 1/4 Diam Cooling water coil 
 
 3/8 x 3/8 x 1 Bar 
 
 Pouring rod extension, 1/4 Diam 
 
 Pouring rod coupling 
 
 5/16 Diam Pouring rod 
 
 3-1/2 ODx 3 IDx 15 Tube 
 
 Crucible support 
 
 3-1/2 OD x 3 ID x 1/8 Gasket 
 
 1/4 Diam Cooling water coil 
 
 8 OD x 2-1/2 ID x 1/2 Top plate 
 
 6-13/16 OD x 6-11/16 ID x 1/4 Split ring 
 
 8 OD x 6-3/4 ID x 1/2 Ring 
 
 1/4 OD Cooling water coil 
 
 6-3/4 OD x 6-1/2 ID x 6 Mold can 
 
 8 OD x 4 ID x 1/2 Bottom plate 
 
 3-1/2 OD x 3 ID x 1/8 Gasket 
 
 2-3/4 Diam x 3/16 Radiation shield 
 
 2 Diam x 3/16 Crucible cover 
 2-3/4 OD Radiation shield 
 
 2 OD Crucible 
 
 2-3/4 Diam Insulating plate 
 
 2-3/4 Diam Insulating plate 
 
 3/8-16 x 1-1/4 Hex head screw 
 
 1/8 x 1/8 Gasket 
 
 1/4 Compression gland 
 
 Mold 
 
 5 Diam Mold stool 
 
 1/4 Cooling water coil 
 
MDDC - 1126 
 
 [9 
 
 
 CROSS-SECTION THROUGH CENTER 
 
 Figure 4. Induction or resistance heated vacuum casting furnace. 
 
10] MDDC - 1126 
 
 It will be noted that the quartz tube is not fastened to the plates at either end. Vacuum tight 
 seals are obtained by the use of atmospheric pressure. Top and bottom plates may be secured to the 
 quartz tube by means of a ring arrangement similar to that used on the brass lower can,* but this 
 arrangement has been found to be unnecessary. 
 
 The cooling coil (16) may be eliminated by turning a groove in plate (17) and soft soldering an 
 annular copper ring on top of the groove. This change will permit the induction coil to be lowered 
 slightly without arcing the top plate. Other design features of the lower can may be obtained from 
 the description of Figure 1. The entire furnace is supported in the same way as the resistance- 
 heated furnace. 
 
 Adaption for Resistance Heating. 
 
 The lower mold can in Figure 4 may be used "as is" to support an upper can containing a re- 
 sistance heating coil. The upper can is identical in design to that shown in Figure 1 with the excep- 
 tion of the bottom ring (Figure 1-20) which is modified to fit on to the top plate (Figure 4-17). 
 
 A VACUUM GATE VALVE 
 
 A relatively simple design of a vacuum gate valve is shown in Figure 5. The principal feature 
 of this design is that it allows an unobstructed and unrestricted flow of gas from furnace to pumps 
 when the valve is in the open position. The valve is shown in the closed position. 
 
 The principal parts of the. valve are a guide plate ' (10) which slides in a horizontal direction in 
 the valve housing (3, 8, 9), the upper and lower gates (12), and a cam (11) actuated by the rod (4). 
 
 The guide plate slides in 1/8 inch deep grooves cut in the two side walls (not shown) of the 
 housing. When in the closed position, the guide plate is at the extreme right hand end of the housing. 
 Four guide pins (15) are fastened (force fit) in the guide plate to direct the vertical motion of the 
 upper and lower gates. The pressure exerted by the cam on the gates (the position shown in Figure 5) 
 is released when the handle (14) is turned 90 degrees. Both gates are then pulled toward the guide 
 plate by the action of coil springs (16) which fit over the guide pins and are fastened to the gates 
 and to the guide plate (the upper gate is assisted by the force of gravity). The handle is then pulled 
 to the right and the entire internal assembly is removed from the position shown leaving a straight 
 unobstructed passageway for the gas molecules. 
 
 The upper flange (1) is bolted to the furnace bottom plate and the lower flange is bolted to the 
 desired part of the vacuum system. 
 
 The parts of the valve housing are screwed together (using flat head screws) and all seams and 
 screw holes are soft soldered. It is usually advisable to paint over the soldered seams with colorless 
 Glyptal (General Electric Co.). 
 
 If the valve is in the closed position for several hours, say 8 to 10, and the system above or 
 below is evacuated, some difficulty may be experienced in opening the valve. This difficulty is due to 
 leakage of air into the valve housing. The air has sufficient pressure to prevent the gate from un- 
 seating when the cam pressure is released. A roughing pump connection to the valve housing makes 
 it possible to evacuate that volume and overcome this difficulty. 
 
 ♦The ring (18) can be cemented to the quartz tube with Saureisen or Insalute cement (Central 
 Scientific Co.) 
 
 t The figures in parentheses in this section refer to parts shown in Figure 5, unless otherwise 
 indicated. 
 
MDDC - 1126 [11 
 
 SOME ACCESSORY EQUIPMENT 
 
 The adaptation of standard plumbing valves for vacuum systems has been described by DuMond 13 
 and Rose. 16 Both methods employ a sylphon bellows to prevent leakage along the valve stem. A 
 simpler method which the writer has found to be satisfactory is substitution of a Wilson seal for the 
 valve stem packing. The Kerotest valve commonly used in refrigeration installations and the Hoke 
 valve are needle-type valves which are suitable "as is" for use in vacuum systems. 
 
 In the same articles mentioned above, DuMond has described a flexible, noncollapsible sylphon 
 coupling and Rose has described a method of bolting together metal tubing. Garner 14 has also de- 
 scribed other methods of performing this operation. 
 
 OPERATION 
 
 The furnaces described in this report were connected to identical pumping systems. The systems 
 consisted of the following parts, connected in the order given: a metal baffle, a metal diffusion pump, 
 MC-275,* a metal booster pump, MB-15,t and a Megovac forepump running at double the normal 
 speed. 
 
 About 1/2 hour before making a run, the pumping system is started, with the gate valve closed. 
 After loading and closing the furnace it is "roughed out" to about 200 microns by a Megovac roughing 
 pump. The gate valve is then opened and the furnace pumped out to the desired pressure before be- 
 ginning the melt. Pressures of 10~3 to 10~4 mm Hg have been obtained with about 1/2 hours of pump- 
 ing depending on the amount, nature, and condition of the materials in the furnace. When the systems 
 were first constructed and before any melts were made, pressures of between 10~5 and 10"" mm Hg 
 were obtained. If it is desired to run the pumping system continuously, or when no operator is in 
 attendance, it is advisable to install a safety device that will cut off the heaters in the oil pumps in 
 case of cooling water failure. Detroit pressure switches are used for this purpose. 
 
 The power input for the resistance furnace is controlled by a 28 amp Variac which is connected 
 to a 110 volt line. A maximum power input of only 2 kw, was sufficient to reach temperatures of 1400- 
 1500 degrees C. The maximum temperature of operation would probably be determined by the initia- 
 tion of a reaction between the tungsten or molybdenum winding and the alundum core (Figure 1-33). 
 Although no determination was ever made of the maximum rate of heating, charges of 500 to 1000 g were 
 heated to around 1400 degrees C in less than 30 minutes. Due to the fact that both tungsten and molyb- 
 denum wire are easily oxidized at elevated temperatures the furnace must be cooled to about 200 de- 
 grees C before opening to the atmosphere. The cooling period is greatly shortened by admitting an 
 inert gas into the system. 
 
 The crucible shown in Figure 1 has a volume of about 275 cc. Although this volume will hold about 
 2400 g of molten copper, for example, the capacity of the crucible is determined by the amount of metal 
 that can be initially charged into the crucible. 
 
 The power supply for the induction furnace was provided by a 10 kw. Thermonic high-frequency 
 converter. Very rapid heating is possible with this unit. Melts of 200-400 g can be heated to 1400-1500 
 degrees C in less than 10 minutes. The refractory properties of the crucible would determine the 
 maximum temperature of operation rather than any feature of the furnace design. 
 
 
 ♦Distillation Products Industries, Rochester, N. Y. 
 t Central Scientific Co. 
 
12] 
 ACKNOWLEDGMENT 
 
 MDDC - 1126 
 
 The designs and methods of construction which have been presented in this report were origi- 
 nated or developed by members of an entire group, of which the writer was a part, engaged in vacuum 
 melting and casting. It would be difficult if not impossible to trace each idea back to its originator, 
 but the following list includes those who made the most significant contributions in this work: G. L. 
 Butler, Noble Hamilton, Leonard Levinson, Shadburn Marshall, J. G. McChesney, A. U. Seybolt, Leston 
 Stark, and J. H. Wernick. 
 
 TOP VIEW 
 
 @ CROSS-SECTION THROUGH CENTER 
 
 Figure 5. Vacuum gate valve. 
 List of Parts for Figure 5 
 
 Number 
 
 1 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 
 
 10 
 11 
 12 
 13 
 14 
 15 
 16 
 
 Material 
 
 Brass 
 
 Rubber 
 
 Brass 
 
 Brass 
 
 Brass 
 
 Brass 
 
 Rubber 
 
 Brass 
 
 Brass 
 
 Brass 
 
 Brass 
 
 Brass 
 
 Brass 
 
 Brass 
 
 Steel 
 
 Steel 
 
 Part (nominal dimensions in inches) 
 
 5- 3/4 OD x 4 ID Upper flange 
 
 1/8 x 1/8 Gasket 
 
 1/4 x 5-1/2 x 12-1/2 Upper plate of housing 
 
 3/8 Diam x 11 Rod 
 
 Collar 
 
 10-32 x 5/8 Filister head screw 
 
 1/8 x 1/8 Gasket 
 
 1/4 x 3-3/8 x 6-3/8 End plate of housing 
 
 1/4 x 2-1/2 x 5-1/2 End plate of housing 
 
 3/8 x 5-1/4 x 7 Guide plate 
 
 3/8 Cam 
 
 1/4 x 5 x 6 Lower gate. 
 
 3/8 Wilson seal 
 
 1/4 x 1/2 x 3 Handle 
 
 1/4 Diam x 1-7/8 Guide pin 
 
 Spring 
 
MDDC - 1126 [13 
 
 BIBLIOGRAPHY 
 
 General 
 
 1. Diergarten, Hans, Vacuum melting on a large scale, Metal Progress (1934). 
 
 2. Dushman, Saul, Recent advances in the production and measurement of high vacua, J. Frank Inst. 
 
 211:6:689 (1931). 
 
 3. Kroll, W. J., Melting and evaporating metals in vacuum, Trans. Electrochem. Soc. Printed also in 
 
 Canadian Metals and Metallurgical Industries 8:26-30 (1945). 
 
 4. Morse, R. S., Modern vacuum practice in electronics, electronics 12:11:33-6 (1939). 
 
 5. Strong, John, et al. Procedures in experimental physics, Prentice-Hall, Inc. New York Chap. HI. 
 
 1938. 
 
 6. Vick, F. A., Vacuum practice, Science Progress 33:83-7 (1938). 
 
 Vacuum Furnace Design 
 
 7. Arsem, W. C, The electric vacuum furnace, Trans. Electrochem Soc. 9:153 (1906). 
 
 8. Ehret, W. F., and David Gurinsky, A laboratory high vacuum furnace, R. Sci. Inst. 12:151-3 (1941). 
 
 9. Friauf, J. B., The purification of manganese by distillation, Trans. ASM 18:213 (1930). 
 
 10. Hultgren, Ralph and M. H. Pakkala, Preparation of high melting alloys with aid of electron bom- 
 
 bardment, J. App. Phy. 11:643-46 (1940). 
 
 11. Lowry, E. F., A vacuum annealing furnace of novel design, R. Sci Instr. 4:606-9 (1933). 
 
 12. Walters, F. M., Jr. Alloys of iron, manganese, and carbon-part I. Trans. ASM. 19:577(1932). 
 
 Accessory Equipment 
 
 13. Du Mond, Jesse, Two applications of the sylphon bellows in high vacuum plumbing, R. Sci. Instr. 
 
 6:285-6 (1935). 
 
 14. Garner, L., Machined metal stuffing box seals adapted to high vacuum technique, R. Sci. Instr. 
 
 8:329-32 (1937). 
 
 15. Henderson, M. C, A simple protective device for vacuum systems, R. Sci. Instr. 10-43 (1939). 
 
 16. Rose, J. E., Two aids in high vacuum technique, (1) Leak Proof Valve. (2) Leak Proof Joint, 
 
 R. Sci. Instr. 8:130 (1937). 
 
 17. Wilson, R. S.,A vacuum tight sliding seal, R. Sci. Instr. 12:91-3 (1941). 
 
 18. Youtz, J. P., A device to protect large vacuum systems from accidental interruptions of mechanical 
 
 pump, R. Sci. Instr. 9:420-21 (1938). 
 
 Leak-Hunting 
 
 19. Kuper, J. B. H., A vacuum gauge for leak hunting, R. Sci. 8:131-2 (1937). 
 
 20. Manley, J. H., L. J. Haworth, E. A. Luebke, Vacuum leak testing, R. Sci. Instr. 10-389;340 (1939). 
 
 21. Webster, D. L., Vacuum leak hunting with C0 2 , R. Sci. Instr. 5:42-3 (1934). 
 
 END OF DOCUMENT 
 
UNIVERSITY OF FLORIDA 
 
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