US2983973A

US2983973A - Methods and apparatus for melting and casting metals in a vacuum

Info

Publication number: US2983973A
Application number: US629557A
Authority: US
Inventors: Conrad A Parlanti
Original assignee: Individual
Current assignee: Individual
Priority date: 1956-12-20
Filing date: 1956-12-20
Publication date: 1961-05-16
Anticipated expiration: 1978-05-16
Also published as: BE603658A

Description

y 6, 1961 c. A. PARLANTI 2,983,973

METHODS AND APPARATUS F OR MELTING AND CASTING METALS IN A VACUUM Filed Dec. 20, 1956 3 Sheets-Sheet 1 IN VEN TOR. CON RAD A. PARLANTI A TTORNEYS.

May 16, 1961 c. A. PARLANTI 2,983,973

- METHODS AND APPARATUS FOR MELTING AND CASTING METALS IN A VACUUM Filed Dec. 20. 1956 3 Sheets-Sheet 2 5 FIG. 2.

JNVENTOR. FIG,3 CONRAD A. PARLANTI ATTORNEYS.

May 16, 1961 c. A. PARLANTI 2,933,973

METHODS AND APPARATUS FOR MELTING AND CASTING METALS IN A VACUUM Filed Dec. 20, 1956 3 Sheets-Sheet 3 x FIG. 4.

' Ill INVENTOR. CON RAD A. PARLANTI ATTORNEYS.

United States Patent METHODS AND APPARATUS FOR MELTING CASTING METALS IN A VACUUM Conrad A. Parlanti, 11 Bradford Road, Natick, Mass.

Filed Dec; 20, 1956, Ser. No. 629,557 6 Claims. c1. zzj-ziz 'Ihis inventionrelates to the casting of metals, and pertains more particularly to methodsand apparatus for melting and casting metals in a vacuum.

It has long been an accepted fact that for certain purposes the melting and casting of metals in a vacuum has many advantages over melting and casting at atmospheric pressure. However, the methods, machines and apparatus presently available for this purpose are expensive to build and are difiicult and costly to operate.

It is an object of the present invention to provide methods and apparatus which are simpler and less costly than those hitherto available;

Other objects and advantages of the invention will appear hereinafter. A

A preferred embodiment of the" invention selected for. purposes of illustration isshown in the accompanying drawings, in which,' f' j Figure 1 is aplan'view.

Figure 2 is a front elevation. J h r Figure3 is a side elevation. t

Figure 4 is a section onfthe line 4--4 of Figure 1.

Figure 5 is a section through a mold shroud.

Vacuum casting apparatuses now known and used in the melting. and casting of metals is of two general types. In both types, the apparatus comprises a sealed melting or furnace chamber containing a crucible equipped with. suitable means for melting metal therein, usually by electrical induction. The chamber 'is connected to a suitable vacuum pump adapted to create and maintain the desired degree of vacuum within the chamber The ehamberis .also provided with suitable means v .In one type-of apparatus, the mold or molds are placed within the furnace chamber. But since the vacuum which is maintained within the chamber retards the transfer of heatto the walls of the chamber through which the heat must pass for dissipation, the rate of cooling is slow. In order to obtain maximum advantage from vacuum casting, the vacuum should be maintained at least until the cast metal isisolidified, andconsiderable time must be permitted to elapse before the vacuumcan be released and the chamber opened for the removal of theca'stings.

:In theother type of apparatus, the mold is mounted exteriorly of the ,furnaceor melting chamber with its interior cavity communicated with the furnace chamber. By the provision of suitablevalvesjand connections the interior of thermold may. be opened to "the furnace cham= berttopermit pouring of molten metal into the mold and may then be sealed off fromthefurnace chamber to permit removal of the mold without breaking the vacuum in the chamber. Means are. usually .provided for water cooling the mold, so that themold' may be removed fairly promptly. y n this type, also, means a'refrequently provided by harged without breaking 2,983,973 Patented May 16, 1961 the vacuum in the furnace chamber. Such means usually comprise an auxiliary, charging chamber provided with suitable valves and connections to permit the auxiliary chamber to be opened to the furnace to permit recharging, and to be sealed ofit while receiving an additional charge. In cases where recharging is possible, the apparatus may be kept in continuous operation for long periods of time.

In all forms of such vacuum melting and casting ap-' paratus of which I am aware, the walls of the furnace chamber are fabricated of steel and provision is made for water cooling the walls. A common form of construction is a double wall with provision forcirculating cooling water between the walls.

According to the present invention I provide a furnace chamber, the walls of which, instead of being water cooled, are constructed of aluminum or aluminum alloy, with both the inside and outside surfaces of said walls anodized to provide a thin skin of aluminum oxide thereon. The anodizing of such surfaces greatly increases the reflectivity of the surfaces and affects very substan- Thus;

tially their ability to absorb and dissipate heat. I have found that by anodizing the interior surfaces of the walls of the furnace chamber, the rate of absorption of heat emanating from the crucible and its heating unit is retarded and an increased amount of heat is reflected back toward the source On the other hand, by anodizing the exterior surfaces of the walls, of the furnace chamber} the rate of dissipation of heat by radiation from the ex-f terior surfaces is increased. As a result, despite the high water cooling is required.

Also, according to the present invention, I provide a mold shroud to receive and hold the casting mold while the molten metal-is being poured and coo-led. Such mold shroud comprises a container having an interior space of a size to receive the mold, which said containerv is also formed of aluminum or aluminum alloy having walls which'are anodized on both their interior and exterior surfaces. Again, as in the case of the walls of the furnace chamber, the anodized surfaces retard the ab-j sorption of heat from the mold and casting into the shroud and increase the rate of dissipation of heat from the exterior surfaces of the shroud. As a result the tern-. perature of the walls of the shroud remains within toler-I able limits even when relatively high melting point metals such as titanium or steel are being cast.

Each mold shroud is provided with a valve closure which may be opened to permit molten metal to be poured into the mold, and which may be closed to seal the shroud and the enclosed mold. Each shroud is also provided with valves and connections through which the sealed shroud may be evacuated to create and maintain a vacuum therein, and through which non-oxidizing and preferably inert gas may be introduced, if desired, all as hereinafter explained.

The shroud and furnace chamber are provided with vacuum tight connections by means of which the shroud; may be connected to the furnace chamber while metal is being poured into the mold. The furnace chamber. connection is provided with a valve for sealing the chain ber whenever the shroud is removed. i

Thus, referring to the drawings, the apparatus com-' prises a furnace chamber 1, preferably cylindical in shape, and having a removable cover 2 at one end. The interior of the chamber is connected by a conduit 3 to a vacuum pump 4 of sufiicient capacity to maintain a relativelyhigh vacuum within the chamber during the,

Such constructions are expensive to build and costly to maintain and operate."

melting and casting operation. In vacuum casting operations, it is common practice to maintain pressures of the order of 1 to 5 microns Hg absolute, and such pressures are contemplated in the use of the present apparatus, although higher pressures are permissible in some cases. A suitable valve 5 may be mounted in the conduit 3 to seal off the chamber from the vacuum pump when desired.

Mounted within the chamber 1 is a crucible 6 which is preferably surrounded by an induction coil 7 for heating and melting metal which is charged into the crucible. Suitable connections for the supply of electric current and for cooling the induction coil are supplied as known in the art, and are not shown in detail herein. The crucible may be supported within the chamber in any suitable manner, but means are preferably provided by which the crucible may be manipulated from the exterior of the chamber so that it may be tilted to pour molten metal into a launder or trough 8 through which it is conducted to the casting molds as hereinafter described. Means are also preferably provided for exterior manipulation of the crucible cover Q, and of the stirring rod 10, but all such means are well known in the art, as exemplified by the disclosure of US. Patent No. 2,625,719, and are not shown in detail herein, since they form no part of the present invention.

Means are also provided for charging the crucible 6 comprising a conduit 11 terminating in a chute 12 which passes through the chamber wall in position to discharge material into the crucible. The conduit 11 is provided with a vacuum tight valve 13 and, if desired, means (not shown) may be provided for recharging the crucible without breaking the vacuum in the furnace chamber.

The launder 8 extends laterally into a cylindrical launder chamber 14 which is in open communication with the furnace chamber, and terminates in a spout 18 located immediately above a vertical passage 15 which extends downwardly from the launder chamber for connection to the mold shrouds as hereinafter described. A vacuum tight valve 16 is mounted in the passage 15 so that the passage may be sealed except when the valve is opened to permit molten metal to be poured into the casting molds as hereinafter described. Said valve is provided with a flange 17 for purposes hereinafter described.

The mold shrouds 21 may be of any convenient size and shape to hold a casting mold 22, and in the embodiment illustrated comprise a container having a lid 23 on which the mold is carried by means of an adjustable platform 24 supported on the lid by rods 25. The lid 23 is held in sealed engagement with the flange 26 by clamps 27. A vacuum tight valve 28 is mounted on the lid 23, said valve having a flange 29, adapted to seat against the flange 17 when it is desired to pour molten metal as hereinafter described.

The mold shrouds are also provided with means by which the interior of the shroud may be connected to a vacuum pump, or alternatively to a supply of inert or other gas. In the embodiment illustrated two

separate conduits

30 and 31 controlled by

valves

32 and 33, respectively, one of which may be connected to a vacuum pump and the other to a supply of gas.

A series of mold shrouds are provided for economical operation of the apparatus, and each of the mold shrouds is preferably encircled by a band 34 which engages and supports the mold shroud on a carriage 35. Each of the carriages 35 is provided with rollers 36 which ride on the rails 37 of track 38. The mold shrouds may be. moved along the rails 37 to a position directly below the passage 15. At this position, the mold shroud is in position to be engaged by the movable platform 41 of the hydraulic jack 42, the operation of which is controlled by an operator through a valve 43 controlled by a pedal 44. When the valve is operated to move the jack plat form upwardly, the mold shroud is lifted from the carriage 35'to bring the flange'29'ofthe mold'shroudinto' sealing engagement with the flange 17 of valve 16 and to hold it in this position while metal is being poured.

In the operation of the apparatus, the crucible 6 is first charged with the metal to be cast, and

valves

13 and 16 are closed tightly. Valve 5 remains open and the vacuum pump 4 is operated to create and maintain the desired degree of vacuum in the furnace chamber. At the same time, the induction heating coil 7 is energized to heat and melt the metal in the crucible.

While the metal is being melted, the required number of casting molds and mold shrouds are prepared and mounted on the carriages 35. The valve 28 of each mold shroud is closed tightly. One of the

valves

32, 33 is also closed tightly While the conduit containing the other valve is connected to a vacuum pump to evacuate the interior of the mold shroud. When a suflicient degree of vacuum has been created, preferably approximating the degree of vacuum maintained in the furnace chamber, the

other valve

32, 33 is closed, and the mold shroud is ready for use.

When the metal in the crucible has been melted, the first of the evacuated mold shrouds is moved into position beneath the passage 15. The hydraulic jack 42 is then operated to raise the mold shroud to bring the flange 29 into sealing engagement with the flange 17. While held in this position,

valves

16 and 28 are opened to bring the interior of the mold shroud into open communication with the interior of the furnace chamber. The crucible is now tilted to pour metal into the launder 8 from which it flows through the spout 18 into the mold 22. As soon as the mold has been filled,

valves

16 and 28 are closed, the jack 42 and the supported mold shroud are lowered to replace the mold shroud on a carriage 35 on which it may then be moved away. Another evacuated mold shroud may then be moved immediately into casting position. Thus, it will be noted that the mold shroud may be moved as soon as metal has been poured, without waiting for even partial solidification of the casting, thus substantially increasing the possible rate of casting.

Meanwhile, the filled mold and its mold shroud are moved to another position where the conditions within the mold shroud may be controlled as desired while the casting is solidifying and cooling. Thus, if it is desired to continue to maintain a vacuum within the mold shroud, the shroud may be connected to a vacuum pump with which a vacuum may be maintained for as long a period as desired. On the other hand, the cooling of the metal may be hastened if the shroud is filled with a gaseous atmosphere which may assist in transferring heat, and the mold shroud may be connected to a suitable supply of the desired gas. Non-oxidizing gases such as hydrogen, nitrogen, helium, argon and the like may be introduced, depending on the condition desired.

As previously explained, the walls of the furnace cham ber 1 are constructed of aluminum or aluminum alloy, and both the inside and outside surfaces of the walls are anodized to provide a thin skin or layer of aluminum oxide thereon. By the provision of such anodized surfaces with the resulting increase in reflectivity of the surfaces, the absorption of heat by the interior surfaces of the walls is retarded while the dissipation of heat by the exterior surfaces of the walls is increased, with the result that the walls remain at tolerable temperatures without resort to water cooling.

Likewise, both the inside and outside surfaces of the Walls of the mold shrouds are anodized with results similar to those previously described.

It will be understood that the invention may be variously modified and embodied within the scope of the subjoined claims.

I claim as my invention:

1. The method of melting and casting high melting point metals such as titanium and steel in vacuum which comprises placing the metal in a sealed chamber the walls of which are formed of a metal selected from the group consisting of aluminum and aluminum alloys, the interior and exterior surfaces of the walls of said chamber having been anodized to increase the reflectivity of both surfaces thereof, the anodized exterior surface of said chamber being the sole means of dissipating heat from said chamber, creating a vacuum in said chamber, and melting said metal in said chamber while maintaining a vacuum therein.

2. The method claimed in claim 1 which includes placing a mold in a sealed shroud which is separated from said chamber and movable with respect thereto, creating a vacuum in said shroud, moving said shroud into sealed contact with said chamber, establishing open communication between the interior of said chamber and the interior of said shroud while maintaining a vacuum in both, pouring molten metal from said chamber into said mold, breaking communication between the interior of said chamber and the interior of said shroud while continuing to maintain a vacuum in both, removing said shroud from contact with said chamber, and cooling the molten metal in said mold before removing the mold from the shroud.

3. The method claimed in claim 1 which includes placing a mold in a sealed shroud formed of a metal selected from the group consisting of aluminum and aluminum alloys, the interior surfaces of the walls of said shroud having been anodized to increase the reflectivity of both surfaces thereof, said shroud being separated from said chamber and movable with respect thereto, creating a vacuum within said shroud, moving said shroud into sealed contact with said chamber, establishing open communication between the interior of said chamber and the interior of said shroud while maintaining a vacuum in both, forming molten metal from said chamber into said mold, breaking communication between the interior of said chamber and the interior of said shroud while continuing to maintain a vacuum in both, removing said shroud from contact with said chamber, and cooling the molten metal in said mold before removing the mold from the shroud.

4. The method claimed in claim 2 in which, after communication between the interior of said chamber and the interior of said shroud has been broken, inert gas is introduced into the interior of the shroud, and molten metal is cooled while surrounded by said inert gas.

5. The method of melting and casting metal in vacuum which comprises placing metal in a sealed chamber, creating a vacuum in said chamber, melting said metal in said chamber while maintaining a vacuum therein, placing a mold in a sealed shroud which is separated from said chamber and movable with respect thereto, creating a vacuum in said shroud, moving said shroud into sealed contact with said chamber and establishing open communication between the interior of said chamber and the interior of said shroud While maintaining a vacuum in both, pouring molten metal from said chamber into said mold, breaking communication between the interior of said chamber and the interior of said shroud while continuing to maintain a vacuum in both, removing said shroud from contact with said chamber, and cooling the molten metal in said mold before removing the mold from the shroud.

6. The method claimed in claim 5 in which, after communication between the interior of said chamber and the interior of said shroud has been broken, inert gas is introduced into the interior of the shroud, and the molten metal is cooled while surrounded by said inert gas.

References Cited in the file of this patent UNITED STATES PATENTS 1,319,500 Whalen Oct. 21, 1919 2,085,450 Rohn June 29, 1937 2,133,634 Rohn Oct. 18, 1938 2,392,267 Salkover Jan. 1, 1946 2,625,719 Moore Jan. 20, 1953 2,627,014 Kolb Jan. 27, 1953 2,825,945 Ulrech Mar. 11, 1958 FOREIGN PATENTS 481,181 Canada Feb. 19, 1952 543,577 Great Britain Mar. 4, 1942 723,699 Great Britain Feb. 9, 1955 732,298 Great Britain June 22, 1955