JPH0586312B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method and apparatus for the gravity-defying casting of metals, and in particular to a method and apparatus for casting metals against gravity, and in particular to reacting with air at the casting temperature to form a cast product. The present invention relates to a method and apparatus for casting reactive metals, such as alloys, containing elements that form oxides and/or nitrides that are harmful to the environment.

[Conventional technology]

In order to cast such reactive metals to good quality, all casting operations are carried out under air exclusion conditions, either by vacuum treatment or by inert gas displacement of the air, during the period when the metal is at air activation temperature. Should. Methods and apparatus commonly used for such air exclusion castings against gravity are disclosed in US Pat. Nos. 3,863,706 and 3,900,064. According to these patents, a sealed exhaust compartment is provided above the sealed storage container of the metal melting crucible;
This compartment is accessible to the crucible via a sealed conduit extending from the compartment through the top of the crucible storage container, said conduit being provided with a slide valve for closing the middle. . A longitudinally divided chamber is housed within the compartment, and the lower end of a mold filling pipe protruding from the bottom of the chamber and the periphery of the vented mold are sealed.

In using the devices disclosed in these patents,
Providing molten metal for casting has been accomplished by melting a steel ingot in a crucible in a crucible container evacuated to a high vacuum. When casting, the mold is placed in a mold chamber within a compartment, both the chamber and compartment are evacuated and sealed, and they and the crucible container are filled with an inert gas such as argon at the same low vacuum. . The conduit valve is opened and the chamber is lowered through the conduit until the protruding end of the mold fill pipe is below the surface of the molten metal in the crucible. The chamber is then evacuated to a high enough vacuum to force molten metal to flow through the fill passageway to fill the mold gap. After the metal within the mold cavity has sufficiently hardened, pressure is increased within the chamber and the compartment, and the chamber is withdrawn from the crucible storage vessel;
Placed within the compartment to remove the mold from the chamber and compartment.

Although these patented methods and apparatus have been very successful in producing high-quality castings of air-reactive metals, the valved conduits connecting the outer compartment around the mold chamber and the crucible storage vessel are complex to operate. This is an expensive device and imposes certain undesirable restrictions on its use. For example, the outer compartment requires a sealable door to enter and exit the chamber in order to insert or move the mold into the chamber, which prevents these operations. The compartment is heated by conduction of heat from the crucible container through the connected conduit, and when the valve is opened, it is exposed to the heat within the valve, making it difficult to cool the compartment sufficiently. Mechanisms for lowering or raising chambers that are part of the compartment are prevented from coming into contact with the mold while the compartment is sealed, as well as by a barrier around the movable part extending into the compartment. Requires a complex mechanism to seal the chamber.

Other prior art techniques have not been successful in effectively providing an inert gas atmosphere within a crucible containing molten metal, even though they may have avoided complex equipment such as those described above.

[Problem to be solved by the invention]

The present invention allows for the elimination of a compartment for the mold chamber and effectively maintains an inert gas at the surface of the molten metal while retaining the crucible housing of the apparatus as disclosed in the aforementioned patents. A connected sealed conduit can be omitted.

[Means to solve the problem]

The important improvements described above were made possible by the invention of a new device as follows. That is, the above device cleans the surface of the molten metal in order to prevent circulating air flow (referred to as Brillion zones) where air is sucked down the metal through the opening of the crucible container. The metal surface is configured to extend beyond the opening at a sufficient distance from the source of ambient air, and the metal surface is maintained in this position except during mold filling.

In a preferred arrangement, the distance between the metal surface and the surrounding atmosphere is at least 8 inches;
More preferably, it is at least 18 inches. One example of a suitable isolation means comprises a flexible, reversibly compressible sealing member disposed between the opening of the crucible container and the exhaust chamber from which the open end of the fill pipe projects. The filling pipe is inserted below the surface of the molten metal within the crucible housing, thereby compressing the sealing member. During the insertion process, the chamber is evacuated to bring the pressure inside the mold below the pressure of the inert gas in the crucible housing. This draws inert gas and molten metal from the crucible housing into the mold. Once the mold cavity is filled, the filling pipe is pulled up through the opening of the crucible container and the sealing member returns to its original shape.

Another preferred isolation means is a movable member forming part of the crucible housing, which movable member also comprises:
When the open end of the fill pipe is projected into the crucible storage container, it is compressed. Preferably, compression occurs when the ceiling wall of the crucible container and the bottom wall of the evacuation chamber containing the mold join. Once the casting is finished and the filling pipe is pulled up, this member returns to its original position.

One advantage of the apparatus and process described above is that casting is performed without the need for the complex sealing structures of the prior art. For this purpose, the filling pipe has a gas-impermeable surface and the pressure of the inert gas prevents air from entering or exiting the crucible storage container through the opening from an air source in the vicinity of the opening. Sufficient pressure is maintained within the container to Preferably, the inert gas pressure is slightly above atmospheric pressure.
As a result, the amount of inert gas lost to the atmosphere through the opening will be reduced if the inert gas is argon (which has a higher density than air) or nitrogen (which has a slightly lower density than air) or under the same conditions. In the case of other gases whose density is at least approximately the same as that of nitrogen, it becomes extremely small.

The above measures not only eliminate the complexity of prior art devices, but also allow the mold chamber to be separated from the crucible storage vessel by means of a filling pipe of suitable length and separated from said vessel by atmospheric air or inert gas. Thermal isolation makes it possible to cool the room more effectively and more economically.
Additionally, this operation may be facilitated if the filling pipe is closed at its end during the casting operation, for example as shown in US Pat. No. 4,589,966.

Another benefit for large cast parts is that the time to pump the system to vacuum and fill it with inert gas is reduced.

In a preferred method and apparatus, a movable cover is provided over the opening of the crucible storage container;
To enable a storage container near an opening to be sealed. The cover, which is moved before the casting operation and replaced afterward, seals the opening and does not have to withstand evacuation of the storage container, so it is relatively light and easy to handle by hand. Another large, heavy, impermeable cover is provided to seal the storage container in the vicinity of the opening in order to melt the newly supplied metal ingot under high vacuum. The cover is operated with a mechanical hoist. After the metal is melted under vacuum, the storage container is filled again with inert gas and the large cover is replaced by a small one.

In the method and apparatus described above, supplemental inert gas from the crucible storage vessel is supplied to the mold chamber to help reduce run time and/or to increase subsequent chamber pressure. The benefits of mold-related evacuation described in the aforementioned patent applications are also utilized in the present invention.

The description will be given below based on the drawings.

Referring to FIG. 1, a molten casting metal crucible 62 having a surface 64 is contained within a box-shaped container, generally indicated at 60. The storage container 60 may be placed on the floor, and its ceiling wall 6
6 may be movably provided by an O-ring seal 68 on the end of the side wall to form a passageway to the interior. The interior of the wall of the storage container 60 may include one or more coils (not shown) for circulating a cooling fluid, such as water, and have gaps therebetween for circulating a refrigerant. A double wall may also be provided. Crucible 62 is embedded within a refractory, electrically insulating block 70. The block 70 includes an induction heating coil 72 surrounding the crucible.

An opening 74 is provided in the ceiling wall 66 of the storage vessel 60 and in a central portion of the molten metal surface 64 of the crucible 62. The opening is dimensioned to allow free passage of the lower end 44 of the filling pipe 40 of the suction casting apparatus 10. A similar opening 76 is provided in a conventional heat shield 78 of insulating material, which is located above the crucible on the upper end of block 70. A movable cover 80 for the opening 74 is attached to the opening 74 by an O-ring seal 82.
The ceiling wall 66 of the nearby storage container is closed. A small opening 84 may be provided in the central portion of the cover 80 through which a thermocouple is inserted into the melt to measure the temperature of the melt. The containment vessel 60 includes a connection tube 86 to a differential pressure device (not shown) capable of drawing the crucible of the containment vessel 60 to a high vacuum when the containment vessel 60 is sealed. Connecting pipe 88 is also connected to an inert gas source (not shown).

An advantage of the apparatus described above is that it is convenient for performing airless casting in conjunction with the simplified casting apparatus of US Pat. No. 4,589,466. however,
Preferably, the very improvements shown in the attached drawings are used.

The casting apparatus 10 comprises a separable and sealable filling chamber 12 mounted on a longitudinally movable support 14 . The chamber 12 consists of two parts that are sealed together when closed by an O-ring (not shown) and opened and closed longitudinally by a suitable device (not shown). Closed. room 12
has a central opening 18 in its bottom mold support wall for supporting a vented mold, generally designated 20 and designated as a shell type mold. The mold includes a longitudinal filling passage 22 having a lower end 24 for introducing molten metal into the mold cavity 26. The chamber 20 has in its ceiling wall a connecting pipe 16 to a differential pressure device (not shown).

The impermeable fill pipe 40 consists of an upper funnel-shaped section with a radially outwardly extending upper flange 42 and a lower funnel section 44 extending longitudinally downwardly therefrom. Upper flange 42 is sealingly sandwiched between the lower mold support wall of chamber 12 and the lower end of mold 20 around opening 24 . The lower part 44 is chamber 1
It extends vertically downward from there through the central opening 18 of No. 2. A hydraulic cylinder 34 connected to the movable support 14 selectively raises or lowers the chamber 12 containing the mold 20, thereby bringing the crucible 62 and the chamber 12 containing the mold 20 relatively closer together. and move away. Although not shown in the drawings, each of the two halves of the mold chamber 12 may be provided with internal cooling means, such as a surrounding coil connected to a source of coolant, such as water, or a circulation gap between the double walls. can have

The differential pressure device is selectively operated to provide a pressure within the mold 20 through the manifold 16a to the differential pressure device (not shown) that is less than the pressure simultaneously provided to the chamber 12 through the manifold 16. It can be done. Preferably, a perforated plug 47 with high air permeability but impermeable to metals fills the filling passage 22.
The opening at the upper end of the mold 20 is covered, and the opening of the connecting pipe 16a is sealed with a plug 47 by a sealing means 46.
The mold is then sealed against the upper end of the mold. As a result, the porous plug 47 and the inside of the mold immediately below it are selectively exposed to a pressure lower than the pressure inside the chamber 12 through the connecting pipe 16a. Sealing means 48 prevent leakage between duct 45 and chamber 12. Connecting pipes 16 and 16a
are connected to various vacuum pumping systems or a single system with appropriate control valves to provide a differential pressure in the two connecting pipes.

A flexible, reversibly compressible conical sealing member 89 is disposed between the ceiling wall 66 and the casting apparatus 10 .

The seal is woven with fibers of refractory material to maintain heat resistance. A preferred material for sealing member 89 includes refractory glass fiber sold under the trademark Refresil. This fiber can be purchased from Niantic Rubber Co., Cranston, Rhode Island, USA.

Molten metal surface 64 and central opening 1 of casting apparatus 10
The distance from the distal end of the sealing member 89 located at 8 is at least about 45.7 cm (18 inches). In this apparatus, the closest source of air that would contaminate the molten metal when the cover 80 is moved is the opening 18, which is relatively remote from the melt. Thus, cover 80 is moved using a wire or rod (not shown) while storage container 60 is purged with argon. The argon purge is performed at a pressure higher than ambient pressure. This allows argon to fill the sealing member 89 and pass through its pores, forcing air out of the seal. Therefore, the distance from the only potential source of air 18 to the melt surface prevents circulating flow (Brillion zones) from drawing air into the melt.

In casting according to the method and apparatus of the present invention, molten metal is fed to crucible 62 under a substantially air-free inert gas atmosphere, as described below. The chamber 12 is located on the crucible as shown in FIG. 1 by the fill pipe end 44 centered in the container opening 74, and the cover 80 is moved before starting the casting operation. By sealing between the lower wall of the chamber 12 and the lower end of the mold around the opening 24 with the upper flange 42 of the filling pipe 40, and while maintaining the inert gas pressure in the storage container 60 in the above atmosphere, the airtight seal is achieved. The use of member 89 prevents air from entering the crucible of the storage container through opening 74. Argon, which has a concentration two to three times that of air, or nitrogen, which has a slightly lower density than air, can easily eliminate the air that enters the storage container 60 through the opening 74.

During casting, the chamber 12 is moved by operation of the hydraulic cylinder 34 and the fill pipe 40 is moved to move the fill pipe through the opening 74 and into the storage container.
Relative movement of the crucible storage container 60 is provided.
Referring to FIG. 2, fill pipe end 44 is inserted through opening 74 and projected below the surface of the molten metal. The relative movement of fill pipe end 44 and crucible housing 60 compresses seal 89 into a small, relatively flat shape. According to the method of the related US patent application mentioned above, the filling pipe end 4
4 and the crucible storage container 60 are moved towards each other, a reduced pressure differential is brought into the interior of the mold 20 through the vertical passage 22 by operation of the connecting pipe 16a to suck argon, and The molten metal then rises up the fill pipe to fill the vertical passage 22 and the leading edge of the metal in the vertical passage 22 flows laterally into the mold cavity 20. A second pressure equal to or higher than the pressure provided through the manifold 16 a but lower than the pressure on the molten metal in the crucible 62 is simultaneously brought into the chamber 12 through the manifold 16 and thus also to the outside of the mold 20 . molten metal to fill the mold cavity 26 with molten metal. The magnitude of this second pressure is exactly the mold cavity 2.
It is appropriate to satisfy 6. Once filling is complete, the pressure around the mold 20 is increased while maintaining a low pressure within the mold to improve component quality and reduce tensile stresses within the mold. This pressure is maintained while the cast metal reaches the reaction temperature.
It will be raised within the chamber 12 by an inert gas which is enclosed through the manifold 50.

Once casting is complete, the aforementioned pressure is returned to ambient pressure. The chamber 12 is then opened and the filled mold 20 and fill pipe 40 are moved in preparation for another casting cycle. Since the sealing member 89 is reversibly compressible, it returns to its original shape. cover 80
may be placed back in the container 60 over the opening 74 unless another mold is prepared for casting.

The use of manifold 16a and the method of its operation described above is advantageous but not essential. If the manifold 16a is omitted, the method described above is simply modified so that the low pressure that causes the mold cavity to fill is brought through the manifold 16 to the entire chamber 12, and the low external pressure on the mold is is brought into the interior through the porous body. This result is usually not as satisfactory as when the two exhaust manifolds are operated separately. Impurities do not virtually migrate out of the casting system while filling the mold cavity. The external pressure on the mold then needs to be lower to obtain a satisfactory filling, which results in a higher metal weight load on the mold. However, the method and apparatus without the connecting tube 16a have significant advantages compared to the prior art.

Referring to FIG. 3, another means of protecting molten metal from air contamination is shown. The crucible container 60 includes a movable part 67 supported by a hydraulic cylinder (not shown) that isolates the metal surface 64 from the opening 74 (closest to the air source). , and about
A distance of at least 45.72 cm (18 inches) is maintained. This distance prevents contamination caused by air flow when moving the cover 80 under an argon jet. As shown in Figure 4, during casting,
The bottom of the device 10 from which the filling pipe 40 protrudes is connected to the ceiling wall 66 of the crucible storage container 60 and the filling pipe 4
0 and when the crucible containers 60 are moved relative to each other, the movable parts 67 are engaged in the movement and are compressed. Once casting is complete and filler pipe 40 is removed, movable part 67 is returned to its original location. The bottom of the device 10 and the wall 66 are joined by the movable part 6
7 is compressed, thus sealing the opening 74 and preventing any air from entering. Then, after the mold filling is completed, it is returned to its original position.

Referring to FIG. 5, during the initial feeding of metal into a crucible under an atmosphere of inert gas without air, which is very occasionally necessary, a displacement cover 90 is provided which covers the 80 and is stronger, and has the property of being able to withstand evacuation of the crucible storage container 60 to a high vacuum. The cover 80 is moved and the mold chamber 12 and its filling pipe 40 of FIG. 1 (not shown) are removed.
The metal ingot is moved out of the way and placed into the crucible through openings 74 and 76 to be melted, and displacement cover 90 is removed.
is movably sealed to the ceiling wall of the storage container by an O-ring 94, and covers the opening 74. The storage container is discharged almost air-free through the connecting pipe 86. The induction coil 72 is then operated to melt the ingot. When the melt reaches the desired temperature, inert gas is introduced into the storage vessel through manifold 88 to the desired pressure, cover 80 is reapplied using a handling rod (not shown), and displacement is performed. Cover 90 is moved. The cover 90 is placed on the outer periphery of the movable ceiling wall 66 of the storage container 60, so that the wall 66 is not exposed to the different pressures of atmospheric air on one side and high vacuum on the other side. Also, like the cover 80, it is easier and easier to operate than the cover 90.

The molds selected in the drawings to illustrate the invention are of the high temperature bonded ceramic type for many of the parts. However, it will be appreciated that this is only one example and that other types of molds may be used. That is, when low temperature bonded sand molds are used for single or multiple parts and for various sizes and shapes, and a low pressure connecting pipe 16a is provided and used as described above. , the selection of templates increases.

[Brief explanation of the drawing]

1 and 2 are schematic cross-sectional side views of an example of a preferred apparatus of the present invention, showing a series of steps in the operation of the method of the present invention, and FIGS. 3 and 4 are diagrams showing a series of steps in the operation of the method of the present invention 5 is a schematic cross-sectional side view of another example of the preferred apparatus for illustrating a series of operating steps, and FIG. 5 is a similar view of the apparatus for adding metal to a crucible. 10...Casting device, 12...Filling chamber, 14...
Support body, 16... Connecting pipe, 20... Mold, 22...
... Filling passage, 26 ... Mold cavity, 34 ... Hydraulic cylinder, 40 ... Filling pipe, 47 ... Porous stopper, 60 ... Crucible storage container, 62 ... Crucible,
64... Molten metal surface, 70... Block, 80
. . . Cover, 86 . . . Connecting pipe, 89 . . . Sealing member.

Claims (1)

[Scope of Claims] 1. A method for casting molten metal against gravity by expelling air in a breathable mold sealed within an exhaust chamber, wherein the exhaust chamber has an open end projecting downward from the chamber. a filling pipe for said mold cavity having a filler pipe comprising: providing molten metal for casting into a crucible within a storage vessel under a substantially air-free inert gas atmosphere; a storage container has an opening for receiving an open end of the filling pipe, and the storage container is exposed to a source of ambient air between the opening and the chamber; the filling pipe and the crucible storage container; protrude the open end of the filling pipe into the crucible housing to a position below the surface of the molten metal in the crucible, and in the mold, the inert pipe of the crucible housing evacuating the chamber to provide a pressure sufficiently lower than that of the gas atmosphere, allowing molten metal to rise through the filling pipe and filling the void in the mold; furthermore, a split exhaust manifold; is provided above the chamber and the filling passage of the mold, so that a pressure lower than the pressure in the chamber outside the mold is maintained at the upper part of the mold passage so that the filling pipe is placed below the surface of the molten metal in the crucible. being held for at least some of the time; and thereafter moving the mold filling pipe and the crucible container in relative opposite directions to pull the filling pipe through the opening; the metal surface is located a distance of at least 8 inches from an ambient atmospheric source sufficient to prevent a return air flow that draws air through the opening into the metal; and the surface is connected to the fill pipe. A method for metal casting against gravity by air exclusion, characterized in that the distance is maintained at the above distance except when the crucible storage container moves relative to each other and during the filling period of the mold. 2. The chamber is evacuated while the filling pipe and the crucible storage container are moving relative to each other in order to draw inert gas from the storage container into the mold. The method described in 1. 3. Method according to claim 1 or 2, characterized in that the upper end of the filling pipe is sealed between the chamber and the mold. 4. A method according to claim 1, 2 or 3, characterized in that gaseous fluid is supplied from outside the mold into the chamber while the open end of the fill pipe is below the surface of the molten metal in the crucible. . 5. The method of claim 1, 2, 3 or 4, wherein the distance maintained between the metal surface and the ambient atmospheric source is at least about 18 inches. 6. The distance between the metal surface and the source of ambient air is maintained by providing a flexible, reversibly compressible sealing member between the opening of the crucible container and the opening of the exhaust chamber, and Claim characterized in that during said relative movement step, said filling pipe protrudes, compresses a sealing member and seals said chamber, restoring to its original shape according to the next relative movement step. The method according to item 1, 2, 3, 4 or 5. 7. The spacing between the metal surface and the ambient air source compresses and seals the chamber when the movable parts, i.e. the crucible storage container and the filling pipe, move relative to each other, and Claims 1, 2, and 3, characterized in that the crucible storage container is maintained by being arranged, and has a movable member that returns to its original position when the container and the filling pipe move away from each other. 4. The method described in 5. 8. A method according to claim 7, characterized in that the movable member is compressed when the top wall of the crucible container joins the bottom wall of the evacuation chamber and the filling pipe projects through the chamber. 9 said filling pipe is impervious and maintains an inert gas pressure within said crucible storage container sufficient to prevent the ingress of atmospheric air into the interior of said storage container through said opening; A method according to claim 1, 2, 3, 4, 5, 6, 7 or 8, characterized in that: 10. The method of claim 9, wherein the pressure of the inert gas maintained within the crucible container is the atmospheric pressure. 11. The method of claim 10, wherein the inert gas has at least about the same concentration as nitrogen. 12. The method of claim 11, further comprising thermally isolating the chamber from the crucible container by atmospheric air or an inert gas which removes heat transferred via the filling pipe. 13. providing a first movable cover for the opening in the crucible storage container, moving the first cover from the opening before protruding the lower end of the fill pipe through the opening; 13. A method according to claim 9, 10, 11 or 12, characterized in that said first cover is then replaced over said opening after said filling pipe is withdrawn from said opening. 14. moving the first cover from the opening; inserting the metal ingot into the crucible container through the opening in the crucible container; a larger, non-porous movable second cover; the cover has a pressure sufficient to seal the crucible storage container near the opening;
having sufficient strength to withstand evacuation of the crucible storage container to a high vacuum; applying the second cover, evacuating the crucible storage container to a low pressure substantially free of air, and applying the second cover to the crucible storage container; heating the steel ingot in the crucible to bring it into a molten state suitable for casting; supplying the inert gas flow to the crucible housing to create the inert gas atmosphere within the crucible; 14. The method of claim 13, further comprising: moving the second cover and replacing it with the first cover. 15 Apparatus for casting molten metal by excluding air in a vented mold sealed in an exhaust chamber, said chamber having an open end projecting downwardly from said chamber for forming a mold cavity. an enclosed crucible means for supplying molten cast metal within the crucible under a substantially air-free inert gas atmosphere; an opening for receiving an open end of the fill pipe therethrough; and the crucible housing is exposed to a source of ambient air between the opening and the chamber; means for relatively moving said filling pipe and said crucible means for projecting into said crucible storage vessel through and withdrawing it from said vessel; means for evacuating said chamber to lower the temperature and thereby causing molten metal to rise through said filling pipe and filling the interstitial space of said mold; in such means, a position between said filling pipe and crucible means; and the most extreme position of the surface of the metal of the crucible means is at a distance sufficient to prevent a circulating air flow drawing air through the aperture to the most extreme position of the metal, i.e. between the ambient atmospheric source and the above. A metal casting device that defies gravity by eliminating air, characterized in that the distance between the opening and the opening is 20.32 cm or more. 16. Apparatus according to claim 15, characterized in that the upper end portion of the filling pipe is sealed between the chamber and the mold. 17. Apparatus according to claim 15 or 16, characterized in that means are provided for supplying an inert gas to the chamber from outside the mold. 18. said means for evacuating said chamber comprises an exhaust manifold above the filling passage in the mold itself;
18. The apparatus according to claim 15, 16 or 17, further comprising means for lowering the pressure in the connecting pipe than in the chamber outside the mold. 19. The apparatus of claim 15, 16, 17 or 18, wherein the distance between the metal surface and a source of ambient air is at least about 18 inches. 20 A flexible, reversibly compressible sealing member, wherein said spacing means is positioned between an opening in said crucible storage container and an opening in said exhaust chamber through which said filling pipe opening end projects. , compressing and sealing the sealing member into the chamber when the opening end of the filling pipe is projected into the crucible storage container, and the opening end of the filling pipe is pulled out from the crucible storage container. Claim 15, 1, characterized in that it later recovers to its original shape.
6, 17, 18 or 19. 21 The spacing means compresses and seals the chamber when the open end of the filling pipe is projected into the crucible storage container, and the opening end of the filling pipe is extended into the crucible storage container. Claims 15, 16, 17, characterized in that it comprises a movable member forming part of the crucible storage container and returning to its original position after being pulled out of the crucible container.
20. The device according to 18 or 19. 22. Apparatus according to claim 21, characterized in that the top wall of the crucible storage vessel joins the bottom wall of the evacuation chamber to compress the movable member when the filling pipe projects therethrough. 23. The filling pipe is impermeable and passes into the crucible storage container or into the crucible storage container through the opening at a rate that maintains the gas pressure in the storage container at a pressure sufficient to prevent the ingress of atmospheric air. Claims 15, 16, 17, 1, characterized in that means are provided for supplying an inert gas.
8, 19, 20, 21 or 22. 24. The chamber is located at a sufficient distance from the crucible housing so that it is thermally isolated by atmospheric air or an inert gas apart from the heat transferred via the filling pipe. Claims 15, 16, 17, 18, 19, 2 characterized in that
0, 21, 22 or 23. 25. The apparatus includes a first movable cover for the opening of the crucible and a second movable cover for replacing the first cover, the second cover being impermeable; Claims 15, 16, 17, characterized in that the cover is larger and heavier than the first cover, is capable of sealing the vicinity of the opening of the crucible storage container, and is capable of withstanding evacuation of the storage container to a high vacuum. 18,
19, 20, 21, 22, 23 or 24.