Arrangement for low-pressure casting of refractory metals

Abstract

The present invention relates to an arrangement for low-pressure casting of refractory metals, with a furnace chamber with one or a plurality of gas supply openings (6) and gas outlet openings (7), and a riser pipe (8) through a cover (5) of the furnace chamber, a melting container (3, 12) for the refractory metals arranged in the furnace chamber, and a heating device for heating the refractory metals in the melting container (3, 12). In the proposed arrangement, the melting container (3, 12) is formed as an exchangeable insert for a receiving mould (2) supporting the melting container (3, 12), which is arranged in the furnace chamber, wherein a thermally insulating layer (4, 17) is formed between the receiving mould (2) and the melting container (3, 12), or is integrated into the melting container (3, 12). With the proposed arrangement, a quick and easy exchange of the melting container for different alloys can also be carried out in the low-pressure casting of refractory metals.

Claims

1. Arrangement for a low-pressure casting of refractory metals, which has a furnace chamber with one or a plurality of gas supply (6) and gas outlet (7) openings, and a riser pipe (8) through a cover (5) of the furnace chamber, onto which a casting mould (9) can be positioned, a melting container (3, 12) for the refractory metals, arranged in the furnace chamber, and a heating device for heating the refractory metals in the melting container (3, 12), wherein the melting container (3, 12) is designed as an exchangeable insert for a receiving mould (2), which supports the melting container (3, 12) and is arranged in the furnace chamber, and a thermally insulating layer (4, 17) is formed between the receiving mould (2) and the melting container (3, 12), or is integrated into the melting container (3, 12); wherein the melting container (3, 12) is formed from an inner casing (3) of a ceramic or another heat-resistant material, an outer casing (12) of a ceramic or another heat-resistant material, and an intermediate fill (4) of a heat-resistant material as said thermally insulating layer (4, 17) wherein a receiving opening of the receiving mould (2), and the melting container (3, 12), have a conical shape; and wherein the outer casing (12) is formed by a plurality of conical rings (15) on a base plate (16).

2. Arrangement according to claim 1, characterised in that, the receiving mould (2) is supported by a steel structure (1).

3. Arrangement according to claim 1, characterised in that, the furnace chamber is formed by a steel structure (1), and the receiving mould (2) is designed as cladding of the furnace chamber.

4. Arrangement according to claim 1, characterised in that, the receiving mould (2) is formed from a ceramic or another heat-resistant material, in which one or a plurality of induction coils (11) of the heating device are embedded.

5. Arrangement according to claim 1, characterised in that, the melting container (3, 12) and the receiving mould (2) are formed such that the melting container (3. 12) is removable downwards from the receiving mould (2), and a mechanism (14) is arranged on a base plate (13) of the furnace chamber, said mechanism can press the melting container (3, 12) into the receiving mould (2) from below.

6. Arrangement according to claim 5, characterised in that, the base plate (13) of the furnace chamber is designed to be removable or detachable.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The proposed arrangement is again explained in more detail below with reference to examples of embodiment in conjunction with the drawings. Here:

(2) FIG. 1 shows in cross-section a first example of an arrangement according to the present invention;

(3) FIG. 2 shows in cross-section a second example of an arrangement according to the present invention;

(4) FIG. 3 shows in cross-section a third example of an arrangement according to the present invention;

(5) FIG. 4 shows in cross-section a fourth example of an arrangement of the present invention;

(6) FIG. 5 shows in cross-section a fifth example of an arrangement according to the present invention;

(7) FIG. 6 shows in cross-section a sixth example of an arrangement according to the present invention; and

(8) FIG. 7 shows in cross-section a seventh example of an arrangement according to the present invention.

PATHS TO THE EMBODIMENT OF THE INVENTION

(9) In the proposed arrangement, the melting container is designed as an exchangeable insert of a receiving mould, which is arranged in the furnace chamber, or forms a cladding of the furnace chamber.

(10) To this end, FIG. 1 shows a first example of the proposed arrangement in a cross-sectional view. The furnace chamber is here formed by a steel frame 1, which is closed off by a removable cover 5. In this example, a gas supply 6 and a gas outlet 7 for increasing or decreasing the pressure in the furnace are located in the cover. Furthermore, a riser tube 8 extends through the cover, onto which tube a casting mould 9 is positioned. By increasing the gas pressure in the furnace chamber, the melt 10 in the melting container rises via the riser pipe 8 into the casting mould 9, so as to solidify there into the component to be cast.

(11) In this arrangement, the melting container is formed by an inner crucible 3, which is inserted into a thick-walled outer crucible 2 as a receiving mould, and can also be later removed from the latter. Windings of the induction coil(s) 11 of the heating device are integrated into the outer crucible 2, which is formed from a heat-resistant material. In the present example, this outer crucible 2 forms a cladding of the steel frame 1, and is connected to supply lines for the induction coil(s) 11. The inner crucible 3 for receiving the molten metal is inserted into the outer crucible 2 as a receiving mould, wherein the cavity between the two crucibles is filled with a heat-resistant fill 4, for example of high alumina. The mechanical load during casting of refractory metals, for example steel, is absorbed by the outer steel frame 1. There is no need to worry about inductive coupling into this steel structure, since the induction coils 11 are located inside the outer crucible 2, and the steel frame 1 lies outside the magnetic field of the coils. Furthermore, the thermally insulating effect of the fill 4 results in a more uniform heating of the inner crucible 3 over the wall thickness, and thus lower thermally-induced mechanical stresses.

(12) The furnace chamber is closed with the pressure-tight cover 5, which has a central opening for the riser tube 8. By virtue of the compact design of this arrangement for low-pressure casting, a small volume of gas is required to apply the pressurisation, whereby costs (less gas consumption) and the time required to apply the gas pressure, can be reduced. The exchangeable inner crucible 3 enables a quick and easy exchange between alloys. To prevent contact between the induction coil or coils 11 and the molten metal 10 in the event of a fracture of the inner crucible 3, a melt detection system 18 can be positioned between outer crucible 3 and the fill 4, for example a wire mesh connected to a measuring device. In the event of contact with the molten metal, the heating device would then be automatically switched off. Such a melt detection system 18 can also be used in the further designs described below.

(13) FIG. 2 shows a further exemplary design of the proposed arrangement, which enables the melting container to be exchanged quickly. Here, the melting container is designed in a conical shape, and is inserted into a receiving mould 2 with a conical receiving opening. The furnace chamber is in turn formed by a steel frame (not shown in this and the following figures), by means of which the receiving mould 2 is supported. Here the receiving mould 2 has a continuous receiving opening with a conical shape. The induction coils 11 are again integrated into the receiving mould 2, as indicated in FIG. 2. In the same manner as in FIG. 1, the furnace chamber is closed off by a cover 5 with a gas supply 6, a gas outlet 7, and a continuous riser tube 8. The casting mould 9 is again positioned on the riser tube 8, that is to say, on the cover 5.

(14) In the present example, the melting container is formed as a double-walled structure with an inner crucible 3 and a conical insert 12, between which there is a loose fill 4 of a heat-resistant material, for example high alumina. On the one hand, this porous bulk material causes the inner crucible 3 to be supported against the conical insert 12, that is to say, the receiving mould 2, and leads to a desired thermal insulating effect. On the other hand, the bulk material 4 can also absorb melt in the event of a crack in the crucible, wherein the melt then solidifies within the fine passages of the fill 4, and any further outflow of the melt is prevented.

(15) In this example, the melting container is removed downwards from the receiving mould 2. For this purpose, a removable base plate 13 is provided, on which a spring system 14 is arranged in the present example, which spring system presses the melting container into the conical receiving opening 2. By this means, the melting container is fully supported around its periphery by the receiving mould 2. To fill the melting container with liquid melt, the furnace body is lifted off the base plate 13. The base plate 13 is then pulled out from under the furnace body and stands free so as to allow the melting container to be filled with the melt. The base plate 13 with the melting container is then positioned back under the furnace body, and the furnace body is lowered onto the base plate. The conical insert 12 of the melting container ensures a good centring, and, by means of the spring system 14, a full-surface contact of the conical insert 12 of the melting container with the inner walls of the receiving mould 2 can be ensured. Here the embodiment in terms of a spring system 14 is only one design variant. Other possibilities for adjusting the height of the melting container include mechanical solutions that operate by means of hydraulics, pneumatics or a threaded advance. With this design of the arrangement, the melting container, or just the inner crucible 3 of the melting container, can be replaced very easily and quickly in order to carry out a changeover of alloy.

(16) In a further advantageous design, the conical insert 12 of the design of FIG. 2 can also consist of a conical tube or individual conical rings 15 and an associated base plate 16, as is exemplified in FIG. 3. The other components of this exemplary arrangement correspond to those of FIG. 2. For easier positioning, the conical rings 15 can also be assembled together by means of a tongue-and-groove system. The advantage of this design over the design of FIG. 2 lies in the greater flexibility of the melting container with respect to thermal expansion.

(17) FIGS. 4 and 5 show another possible exemplary design of the proposed arrangement, which is similar to that of FIG. 2. In these examples, in contrast to the design of FIG. 2, the melting container is formed from just an inner crucible of conical shape, with a high-temperature non-woven material 17 applied thereto; the latter can, for example, be applied to the preferably ceramic inner crucible 3 by means of a ceramic adhesive. Here the non-woven material 17 ensures insulation of the inner crucible 3 with the consequence of a better temperature homogeneity over the crucible wall. Furthermore, the non-woven material 17 provides support for the crucible 3 against the receiving mould 2, and provides compensation for simultaneous thermal expansions. The designs of FIGS. 4 and 5 differ only in that, in the design of FIG. 5, the interior of the inner crucible 3 has an undercut. This has the advantage that the distance to the lower windings of the induction coil(s) 11 can be reduced, and thus a better coupling of the electrical energy into the melt 10 can be achieved.

(18) FIG. 6 shows another advantageous form of embodiment of the design of FIG. 2. In contrast to the design of FIG. 2, this form of embodiment has a uniformly vertical arrangement of the induction coil(s) 11. By means of this vertical arrangement, a more uniform heating of the melt is achieved overall, by virtue of the now uniform distance from the melt 10.

(19) FIG. 7 shows another advantageous form of embodiment of the design of FIG. 1. In this form of embodiment, the low-pressure casting furnace has a separate base frame 19 with resistance heating, below the steel frame 1, which permits additional preheating of the whole crucible region, usually made of ceramic. By means of this preheating, any stress cracks in the ceramic crucible caused by heating can be reduced. Alternatively, the additional resistance heater(s) can be arranged laterally, or laterally and in the base frame.

LIST OF REFERENCE SYMBOLS

(20) 1 Steel frame 2 Outer crucible/receiving mould 3 Inner crucible 4 Loose fill 5 Cover 6 Gas supply 7 Gas outlet 8 Riser pipe 9 Casting mould 10 Melt 11 Induction coil(s) 12 Conical insert 13 Base plate 14 Spring system 15 Conical rings 16 Base plate 17 High-temperature non-woven material 18 Melt detection system 19 Base frame with resistance heating