US2625719A

US2625719A - Vacuum casting apparatus

Info

Publication number: US2625719A
Application number: US187016A
Authority: US
Inventors: James H Moore
Original assignee: Nat Res Corp
Current assignee: National Research Corp
Priority date: 1950-09-27
Filing date: 1950-09-27
Publication date: 1953-01-20
Anticipated expiration: 1970-01-20
Also published as: FR1068069A

Description

Jan. 20, 1953 J. H, MOQRE 2,625,719

VACUUM CASTING APPARATUS Filed Sept. 27, 1950 5 Sheets-Sheet 1 baaaw 22 9 to:- E0..

2 v: QN D1 OK E0+m m OER-cam Easuu o INVEN TOR.

James H Moore BY GAL- w. Ne

ATTORNEY 5 Sheets-Sheet 3 INVENTOR.

James H Mao/e ATTORNEY Ezmxm mcifiam Gin-00 OF .1 H MOORE VACUUM CASTING APPARATUS Jan. 20, 1953 Filed Sept. 27, 1950 Jan. 20, 19 53 1 MOORE 2,625,719

VACUUM CASTING APPARATUS Filed Sept. 27, 1950 5 Sheets-Sheet 4 AfTORNEY Jan. 20, 1953 J. H. MOORE 2,

VACUUM CASTING APPARATUS Filed Sept. 27, 1950 5 Sheets-Sheet 5 lnaam 530m IN VEN TOR.

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p 933 vczoou 9r!IIIIIIIIIIII/dllfllfflllrllldlilI!!! I James H Moore BY (74% fi/e ATTORNEY Patented Jan. 20, 1953 UNITED STATES PATENT OFFICE VACUUM CASTING APPARATUS James H. Moore, Swampscott, Mass., assignor to National Research Corporation,

Middlesex 4 Claims.

This invention relates to the production of metals and more particularly to the melting and casting of metals in a vacuum. One of the basic problems in vacuum melting and casting is the long time requirement imposed on batch operation and the consequent effect on production cost. In particular, when one metal or alloy is being melted or cast in quantity, it is desired that a maximum number of melts be obtained from one crucible. To achieve this purpose there are several important features of the operation to be considered. The first of these is the minimizing of oxidized residue created between runs when a hot crucible containing some residual metal is exposed to air. The second consideration is the avoidance of thermal stresses in the crucible so as to prevent cracks which greatly shorten the crucible life. Both of these difficulties can be avoided by keeping the melting chamber continuously at a low atmospheric pressure to avoid oxidation of the crucible or its contents, and by making melts in rapid succession so as to avoid undue cooling of the crucible between melts.

Accordingly, it is a principal object of the present invention to provide a vacuum melting and casting furnace which can be operated in a semicontinuous manner so as to avoid oxidation of the crucible or its contents, and which can be so handled that cooling of the crucible between melts is substantially avoided.

Still another object of the invention is to provide such a melting and casting furnace which may be charged with rondelles, flake, lump, shot, powder, pig, or various types of scrap, and from which ingots or castings may be discharged without necessitating venting to atmosphere of the crucible portion of the furnace.

Still another objects of the invention is to provide a furnace having a high production rate for a given crucible capacity and power input.

Still another object of the invention is to provide such a melting and casting furnace which is equally adapted for making cast shapes or for the production of ingots.

Still another object of the invention is to provide a melting and casting furnace capable of producing high purity metals at low cost.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

The invention accordingly comprises the apparatus possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings wherein:

Fig. 1 is a diagrammatic, schematic, elevation view of one preferred form of the invention;

Fig. 2 is a plan view of the furnace of Fig. l with parts thereof broken away for better illustration of the interior of the furnace;

Fig. 3 is a sectional view along the line 33 of Fig. 1;

Fig. 4 is an enlarged, fragmentary, sectional view along the line 44 of Fig. 2;

Fig. 5 is a fragmentary, sectional view along the line 5-5 of Fig. 4; and

Fig, 6 is an enlarged, fragmentary, sectional view along the line 6-6 of Fig. 3.

- In general, the present invention relates to a vacuum furnace for melting and casting metal under a vacuum for the purposes of making highpurity ingots, castings, or alloys from initially high-purity metals, or for purifying metals as a result of melting thereof under vacuum and subsequently forming castings or ingots of the purilied melts. The vacuum furnace of the present invention comprises a vacuum-tight furnace chamber having a metal-melting crucible therein, this portion of the furnace being provided with ameans for evacuating this furnace chamber to a low pressure on the order of l-5 microns Hg abs. or less. The furnace also includes a second vacuum chamber, a means for evacuating this second vacuum chamber, and a means for introducing metal to be melted into the second vacuum chamber, this last-named means including a vacuum-tight closure. Between these two chambers there is provided a means, including a second vacuum-tight closure, for transferring metal to be melted from the second vacuum chamber into the crucible positioned in the furnace chamber. The furnace chamber includes electrical means for heating the metal in the crucible to a ternperature above its melting point, and a means for discharging the molten metal from the crucible into a mold therefor. The furnace is also pro vided with a means constituting a vacuum-tight closure for isolating the mold from the furnace chamber after the molten metal has been poured into the mold, and means including another vacuum-tight closure for removal of the isolated mold from the furnace.

In a preferred form of the invention illustrated in the accompanying drawings, the mold is positioned in, or forms a part of, a third vacuumtight chamber which can be isolated from the furnace chamber to permit removal and replacement of the mold.

Referring now more particularly to Figs. 1, 2 and 3, wherein like numbers refer to like elements of these and the other figures, there is shown one preferred form of the invention wherein there is provided a vacuum-tight furnace chamber 10 arranged to be evacuated through a pipe ll (Fig. 2) which is connected to a suitable vacuum pumping system not shown. For feeding metal to be melted there is included a second vacuum-tight chamber i2 which can be evacuated through a pipe l3 which is also connected to a suitable vacuum pumping system. For casting an ingot there is provided a third vacuumtight chamber M, a portion of which is formed.

by the ingot mold itself, this vacuum-tight chamber l4 being arranged to be evacuated through a third pipe 45 connected to a suitable vacuum pumping system. Positioned within the furnace chamber is a crucible, generally indicated at l6, which is arranged to be heated by an electrical heating means, such as an induction coil 1 8.

For transferring metal to be melted from the feeding chamber l2 to the furnace chamber [0 there is provided a transfer means which includes a bucket 20. A trough 22 is positioned so as-to transfer molten metal from the crucible l6 to'the casting chamber M. A plurality of vacuum-tight closures or valves are provided in connection with the above furnace, there being a firstsuch vacuum-tight closure 24 associated with the feeding chambe l2 through which metal may be introduced into this feeding chamber [2. Between the feeding chamber I2 and the furnace chamber I0 is a second vacuum-tight closure 26, while between the furnace chamber Ill and the casting chamber M is a third vacuum-tight closure 28. A fourth vacuum-tight closure 30 permits removal of the ingot from the casting chamber l4.

Melting section Referring now more specifically to the details of the elements outlined briefly above, the furnace chamber Ill, as shown best in Fig. 3, comprises a removable cover 32 through which access to the interior parts may be had for repair or rep-lacement. A sight glass 34 is preferably provided in the cover 32 so that the melting operation may be observed. A water-cooled stirring rod 36 is also preferably provided for agitating the melt or breaking down any bridges which may form at the top of the melt. The furnace chamber Ill includes a double wall 37 which is arranged to be cooled by circulating water therethrough from suitable connections not shown. The crucible assembly, generally indicated at l6, comprises, a refractory pct 38 supported by a carriage 40, this carriage 40 being pivotally mounted on bearings 42 supported by a bracket 44 attached to the wall 31 of the furnace chamber Ill. The heating means [8 comprises aplurality of turns of copper tubing 46, each turn being surrounded by insulating material such as a composite lamina.-

tion of phenolic resin and glass tape. The two ends of the copper tubing 46 extend through an insulating block 48 associated with the crucible carriage 40. These two ends of the tubing 46 are connected to insulated flexible water-cooling lines (not shown). The electrical connection to the portions of the tubing 46, which pass through the insulating block 48, are shown in more detail inFig. 6.

As can be seen in this Fig. 6 these terminal portions of the tubing 36 are adapted to be energized from a coaxial element 56 having a pair of electrical contacts 52 thereon. Each contact 52 makes an electrical connection with a con ductor element 54 which is, in turn, in electrical connection with one end of the tubing 46. For shielding the connection between the

elements

52 and 54 there is provided a compressible gasket 56 around each contact 52. This arrangement has been found to be particularly suitable for preventing any ionizin discharge at very low free air pressures in the system andat voltages in excess of 200 volts. The coaxial element 50 is preferably rigid and comprises an insulating block 58 separating the two contacts 52 and also supporting the outer ends of two coaxial tubes 60 and 62, these two tubes cc and 62 serving as the two current leads. The outer tube "62 is preferably grounded as indicated at 53, to prevent ionization discharge between the outer tube 62 and the furnace walls 3? o the crucible support 40. This rigid assembly is supported by a flange 63 which is clamped, by means of the arrangement generally indicated at $5, in vacuum-tight relationship to a flange 55 supported on the wall 31 of the furnace chamber. Suitable current supply and cooling water connections are rovided for the rigid coaxial element 50.

For pouring the'melt from the crucible there is provided a lip 55 (Fig. 3) associated with the crucible pct 38 and a tilting mechanism, including a pair of chains 68 engaging a pair of sprockets 10. These sprockets F8 are mounted on a shaft 12 which passe through a vacuum-tight seal M (Fig. 2) to the exterior of the furnace chamber II). On the outer end of the shaft 12 there is provided a suitable mechanical system, such as a handle '56 for turning the shaft. A pai of weights 7% (Fig. 3) attached to the ends of chains 88 assist in counterbalancing the weight of the loaded crucible. In a preferred form of the invention the lip 66 associated with the crucible pct 38 is positioned so that it is about on the axis of bearings 32. By means of this arrangement the lip remains essentially stationary during the tilting of the crucible and thus remains over the upper end of the trough 22.

The crucible 38 is also preferably provided with a cover as for preventing spattering of materials from the crucible during the melting, and also for preventing undue radiation heat loss from the melt. This cover 36 is carried by fingers 82 supported on a rod 8 3 (Fig. 2). Rod 84 preferably includes an electrical insulation section so that the cover 8i! is insulated from the remainder of the apparatus. Rod St is arranged to be swung around a pivot 86 and also to be rotated around its own axis. The pivoting movement of the rod 84 is accomplished by means of an operating connection 88 associated with an operating means such as handle 90 extending to the exterior of the furnace. During movement of the crucible cover 8i! it is first rotated about the axis of pivot 86 by operating the handle 536. As the crucible cover 89 approaches the dotted line position of Fig. 2 a detent 35 carried by the arm Bi engages another detent 8? to cause the arm 8% to rotate around its axis, thus moving the cruciblev cover into the position shown in dotted lines in Fig. 2 to prevent radiant heating of the crucible assembly by the hot cover. The cover 8!) is shown in this removed position in Fig. 3.

Metal feeding section The mechanism for feeding the metal to be melted is shown in the greatest detail in Figs. 4 and 5 wherein the metal-transferring bucket 26 is shown as being supported by a rod Hi6 which is pivotally carried by a pair of brackets l 02 connected together by clamp see (Fig. 5). Brackets H32 have rollers Hi l at their upper end, these rollers HM being supported by track IE6 which, except for short gaps under valve 25 and within the vacuum-tight valve 26, extends to the interior of the furnace chamber Ill. The left-hand side of the supporting rod I is provided with a detent I08 adapted to be engaged by another detent I09 (see Fig. 2) associated with a turning mechanism IIO positioned on the far side of the furnace chamber I0. On the right-hand side of the bucket 20 (Fig. 4) there is provided a rack H2 connected to one of the brackets I02, this rack II2 being positioned so as to be engaged by a pinion I I4. Pinion I I4 is rotated by a suitable operating means, such as a handle II5 (see Fig. 2), positioned exteriorly of the feeding chamber I2. Rack I I2 is held in engagement with the pinion II4 by means such as a roller II6. For providing space for movement of the rack II2 there is included an extension I I8 for the chamber I2, this extension being shown in the form of a long tube closed at its outer end.

The vacuum-tight valve 24 through which the loading of the bucket 20 is achieved comprises an opening I28 in feeding chamber I2, this opening being normally closed by a gasketed cover I22. Cover I22 is preferably supported by a yoke I24, this yoke carrying an operating handle I26 and being pivotally mounted at I28 to permit swinging of the cover I22 clear of the opening I20. For steadying the bucket 20, during passage of roller I04 across the gap in track I06 under valve 24, a pair of guide rods I36 are secured to the inside of chamber I2. Valve 26 is not shown in detail but may be essentially similar to the valve 28 shown in more detail in Fig. 3 and discussed hereinafter.

Casting section The casting section of the furnace is shown best in Fig. 3 wherein there is preferably provided an extension I40 for the furnace chamber III. This extension I40 has an opening I42 at the bottom thereof above which is located a hole MI in the lower end of the trough 22. Opening I42 is normally closed by the vacuum-tight valve 28, this valve 28 preferably comprising a closure plate I44 which is carried by a rod I46. Rod I46 is preferably connected to the closure plate I44 by means of cam sections I48, which permit tight closure of the valve upon rotation of the rod I46 by means of handle I41. Rod I46 is thus able to move the closure plate I44 both translationally across the opening I42 and also towards the opening I42. The valve 28 also preferably includes a water-cooled radiation shield I50 mounted on a shaft I52, the purpose of the radiation shield I50 being to prevent radiation of heat from the cast metal in the mold I4, thereby preventing warping and seizing of the closure plate I44 and deterioration of sealing gaskets due to overheating thereof. The trough 22 is preferably heated to a suitably high temperature by a radiant heater I5I so that the molten metal will not be chilled to its solidification point during flow down the trough 22.

The casting chamber I4 is shown in one preferred form as comprising a double-wall ingot mold I54 having water inlet and outlet connections I56. The ingot mold is preferably provided with a flange I58 at its upper end, this flange forming the vacuum-tight closure 30 with a matching flange I59 carried by the valve 28. A sight glass IE6 is preferably located at the top of extension I40 to permit viewing of the mold during the casting of the melt therein. A sight glass cleaner is schematically indicated at I62, this cleaner being arranged to scrape condensed metal vapors from the under surface of the sight glass I60. A similar cleaner can be provided for the sight glass 34 if desired.

Vacuum system The vacuum system comprises a number of separate vacuum pumping lines which lead from the various portions of the apparatus to suitable vacuum pumps not shown. As best seen in Fig. 1 feeding chamber I2 is provided with a vacuum pumping line I3 and a vacuum cutoff valve I10 for closingthis line I3 when the vacuum-tight closure 24 is to be opened. For releasing the vacuum in the chamber I2, to permit opening of the closure 24, there is provided a vent valve I12 which, when opened, permits atmospheric pressure to enter chamber I2. A similar arrangement is provided for the casting chamber I4 wherein the vacuum pumping line I5 is provided with a vacuum cutoff valve I14 and an atmospheric vent valve I16. The pipe I5 also includes a third valve I18 which controls the flow of gas from a pipe I leading to a supply of inert gas such as argon and the like. This inert gas can be at any desired pressure such as 15 lbs. per square inch abs.

Operation of the furnace cover 32 is placed on the furnace chamber I0 and initial pumpdown of the furnace is accomplished. For this initial pumpdown the atmospheric vent valves I12 and I16 are closed. The vacuum valves I10 and I14, inert-gas valve I18, and closure 24 may be closed, in which case the whole system may be pumped down through the pipe II associated with the main furnace chamber I8, the

valves

26 and 28 being left open to permit pumpdown of all three of the vacuum chambers. During this pumpdown it is sometimes desirable to energize the induction heating means so as to assist in the outgassing of the crucible pct 38. When the furnace interior has been pumped down to a low pressure, on the order of .001 mm. Hg abs, heating of the metal in the crucible pct 38 may be continued until it is thoroughly melted, and the degassing and any necessary metallurgical reactions have been carried out. Valve 28 is then opened if it is not already open, and coolin water is passed between the double walls of the mold I54. Crucible cover 80 is then rotated from the position shown in full lines in Fig. 2 to the position shown in full lines in Fig. 3. After cutting off electrical power to the coil I 8, the crucible pct 38 is tilted around the axis of the bearings 42 by rotating the operating handle 16 (Fig. 2) so as to rotate sprockets 10, thus moving the chain 68 connected to the crucible support 40. The melt in the pct 38 flows over the lip 66 as the crucible tilts. This melt falls into the upper end of the trough 22, travels down the heated trough and out through the hole I4I at the bottom end thereof. From hole I4I, the melt falls into the watercooled mold I54, this mold being cooled, as mentioned previously, so that the hot metal does not burn through the walls of the mold or bond to the walls thereof. When the crucible has been emptied it is returned to the vertical position shown in Fig. 3, and the

valves

28 and 26 may then be closed to isolate the three main chambers. In some cases it is desirable to maintain the valve 28 open so that gases liberated during the solidification of the cast melt can be removed by the vacuum pump associated with pipe I I leading to the furnace chamber. This is particularly desirable when the vacuum pump connected to pipe H has a large capacity as compared to the Vacuum pump connected to the pipe IS.

The valve 26 is then opened, after venting the feeding chamber 42 by means of the vent valve H2. A fresh supply of metal to be melted is inserted in the bucket 28, the valve 2% is closed, the vent valve H2 is closed, and the vacuum valve 179 is opened to permit pumping down the feeding chamber !2 to a pressure on the order of 50 microns or less. The valve 23 is then opened, thus permitting equalization of the pressure between the feeding chamber 92 and the furnace chamber 96. lhe slight difference in the pressure between the interiors of the chambers i2 and H3 is not sufficient to cause any great increase of the pressure in furnace chamber to due to the much greater volume of the latter, this pressure increase being on the order of a very few microns. If desired, an addition to the pumping system of the feeding chamber i2 can completely eliminate even this small effect.

The operating handle H5, associated with the pinion i it, is then rotated, thus advancing the rack H2, and the bucket it connected thereto, from the chamber 52 into the chamber l8. Ehis movement is continued until the bucket 20 is over the crucible pct 38, and the detent 668 on the outer end of the rod its is in engagement with 'the corresponding detent l 89 associated with the turning mechanism 556 (Fig. 2). The turning mechanism lid is then rotated to cause a tilting of the bucket 28 so that its contents are dumped into crucible pct 38. The bucket 2a) is then righted and returned to the chamber l2. If the load of metal in the bucket 28 is not sumcient to fill the crucible pct Ed, the valve 25 is immediately closed. The vent valve H2 is opened, as is the closure lid, and the bucket 23 is refilled. Closure 2a is then replaced, vent valve H2 is closed, and the vacuum pumping valve iii} is opened. When feeding chamber i2 has again been evacuated the loading operation is repeated by again opening the valve 26 and advancing the bucket to a position over the crucible pot Such a cycle consumes on the order of 35 minutes, withoutinterruption of the melting operation, which can be carried out simultaneously.

After the ingot cast in the mold M. has been cooled sufficiently, the vacuum valve 28 is closed and vent valve H6 is opened. The vacuum-tight connection 38 between the two flanges i158 and 159 is then broken and mold 554; is removed. The cast ingot can then be removed from the mold 55 3 or a new mold can be positioned in place of the old mold. When the new mold, or emptied mold, has been secured in position, the vent valve 278 is closed and vacuum valve ii l is opened, thus allowing the vacuum casting chamber i i to be evacuated to a suitable low pressure. At the desired time before the next melt is to be cast, valve 28 is opened and the casting operation is repeated.

In many cases it is desired to solidify the ingot or casting under inert gas pressure. When this is to be achieved the valve 23 is closed immediately after casting of the melt, the vacuum pumping valve lid is closed, and the valve '58 leading to the inert gas sup-ply is opened thus allowing any desired pressure of inert gas to be created above the surface or" the solidifying casting. When a complex alloy is being cast, for instance, it has been found that an atmospheric pressure of argon gives considerably improved ingots, by reason of better filling. of interdendritic shrinkage cavities by molten metal under the increased hydrostatic pressure.

In many cases it is desirable to employ a furnace of the type described above for making precision castings. Certain such castings are particularly desirable when made under vacuum conditions since they are free of voids, are very dense, and have superior mechanical and electrical properties. In order to achieve such precision casting the vacuum casting chamber. [4 is modified to hold a precision casting mold, the mold being positioned so that it can be filled by metal pouring through hole MI in the trough 22. In other respects the arrangement of elements and the operation ofv the device may be identical to that previously discussed.

In the preferred. type of furnace illustrated in the drawings the various structural portions thereof are made of austenitic stainless steel or other nonmagnetic steel, while the crucible. 38 is made of a high-purity refractory such as magnesia or graphite, as required by the material to be melted. The trough 22 is preferably formed of magnesia or alumina. The crucible is preferably packed into the copper coil it by means of a magnesia ramming mix. The various insulating blocks such as 8 and 58, and the insulation (not shown in the arm as may comprise synthane. As mentioned previously the coil 46 is preferably wrapped with glass tape over a phenolic resin to give an arc-free coil assembly which can be operated at 3000 cycles per second and with 40c volts and'up to kilowatts power input.

Since certain changes may be made in the above apparatus without departing from the scope of the invention herein involved, it is intended that all matter contained in the above discription, or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. A semi-continuous furnace for melting and casting a metal, alloy or the like under a vacuum, said furnace comprising a vacuum-tight furnace chamber, a metal-melting crucible in said furnace chamber, means for evacuating said. furnace chamber, means forming a second vacuum-tight chamber communicating with said furnace chamber and laterally displaced from said crucible, means for evacuating said second vacuum-tight chamber, means for introducing a solid metal to be melted into said second vacuum-tight chamber, said introducing means including a vacuumtight closure, a second vacuum-tight closure positioned between said furnace chamber and said second vacuum-tight chamber for isolating said two vacuum-tight chambers, a movable bucket for transferring said metal from said second vacuum-tight chamber to said furnace chamber, means for positioning said bucket so that the contents thereof can be poured into said crucible, electrical means for heating said metal in said crucible to atemperature above its melting point, means for discharging molten metal from said cruci is into a mold therefor, means constituting a vacuum-tight closure for isolating said mold from said furnace chamber after pouring said molten metal into said mold, and means including a vacuum-tight closure for removal of said isolated mold from said furnace.

2. A semi-continuous furnace for melting and casting'a metal, alloy or the like under a vacuum, said furnace. comprising a vacuum-tight furnace chamber, a metal-melting :crucible in said furnace chamber, means for evacuating said furnace chamber, means forming a second vacuum-tight chamber communicating with said furnace chamber, means for evacuating said second vacuumtight chamber, means for introducing a solid metal to be melted into said second vacuum-tight chamber, said introducing means including a vacuum-tight closure, a second vacuum-tight closure positioned between said furnace chamber and said second vacuum-tight chamber for isolating said two vacuum-tight chambers, means for transferring said solid metal from said second vacuumtight chamber to said crucible, electrical means for heating said metal in said crucible to a temperature above its melting point, said crucible including a pouring lip and means for tilting said crucible around a horizontal axis which substantially coincides with said pouring lip, a trough for transferring molten metal from said crucible to a mold, one end of said trough being positioned under said pouring lip and the other end of said trough being over said mold, a vacuum-tight valve between said mold and the end of said trough for isolating said mold from said furnace chamber, and a radiation shield positionable between said mold and said last-named vacuum-tight valve.

3. A semi-continuous furnace for melting and casting a metal, alloy or the like under a vacuum, said furnace comprising a, vacuum-tight furnace chamber, a metal-melting crucible in said furnace chamber, means for evacuating said furnace chamber, means forming a second vacuum-tight chamber communicating with said furnace chamber, means for evacuating said second vacuumtight chamber, means for introducing a solid metal to be melted into said vacuum-tight chamber, said introducing means including a vacuumtight closure, a second vacuum-tight closure positioned between said furnace chamber and said second vacuum-tight chamber for isolating said two vacuum-tight chambers, means positionable in both of said vacuum-tight chambers for transferring said solid metal from said second vacuumtight chamber to said crucible, electrical means for heating said metal in said crucible to a temperature above its melting point, means for discharging molten metal in said crucible into a mold therefor, means constituting a vacuum-tight closure for isolating said mold from said furnace chamber after pouring said molten metal into said mold, and means including a vacuum-tight closure for removal of said isolated mold from said furnace.

4. A semi-continuous furnace for melting and casting a metal, alloy or the like under a vacuum, said furnace comprising a vacuum-tight furnace chamber, a metal-melting crucible in said furnace chamber, means for evacuating said furnace chamber, means forming a second vacuum-tight chamber communicating with said furnace chamber, means for evacuating said second vacuumtight chamber, means for introducing a solid metal to be melted into said second vacuum-tight chamber, said introducing means including a vacuum-tight closure, a second vacuum-tight closure positioned between said furnace chamber and said second vacuum-tight chamber for isolating said two vacuum-tight chambers, means for transferring said solid metal from said second vacuum-tight chamber to said crucible, electrical means for heating said metal in said crucible to a temperature above its melting point, means for tilting said crucible around a horizontal axis to pour a melt from said crucible to a mold, said electrical means including a first electrical contact means fixed with respect to said crucible and a second electrical contact means fixed with respect to said furnace, said two electrical contact means being in engagement when said crucible is in melting position and being out of engagement when said crucible is in pouring position, means constituting a vacuum-tight closure for isolating said mold from said furnace chamber after pouring said molten metal into said mold, and means including a vacuum-tight closure for removal of said isolated mold from said furnace.

JAMES H. MOORE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 262,625 Small Aug. 15, 1882 1,022,910 Whitney Apr. 9, 1912 1,354,286 De Bats Sept. 28, 1920 1,897,589 Reeve Feb. 14, 1933 2,133,634 Rohn Oct. 18, 1938 2,140,607 Thompson Dec. 20, 1938 2,289,484 Coley July 14, 1942 2,371,604 Brennan Mar. 20, 1945 FOREIGN PATENTS Number Country Date 367,246 Great Britain Feb. 18, 1932 439,472 Great Britain Dec. 6, 1935