EP3990203B1 - Arrangement for low-pressure casting of high melting point metals - Google Patents

Description

Technical field of application

The present invention relates to an arrangement for the low-pressure casting of refractory metals, which has a furnace chamber with one or more gas supply and gas outlet openings and a riser pipe through a cover of the furnace chamber, a melting container for the refractory metals arranged in the furnace chamber, and a heating device for heating the refractory metals Has metals in the melting container.

In the low-pressure casting process, a melting container containing the material to be cast is placed in a pressure-tight furnace chamber which is closed off by a lid. A riser tube runs through the lid between the melting container and the exterior space, onto which a mold is placed. Depending on the casting material and application, permanent metallic molds (moulds), sand casting molds or investment casting molds are used as casting molds. In the case of metallic casting material, the material is usually heated up via an inductive heating device which is arranged in the furnace chamber. To cast the component, a gas such as nitrogen or argon is introduced into the furnace chamber, which exerts pressure on the melt pool in the melting container. This pressurization causes the melt to rise slowly through the riser pipe to the mold above. The pressurization is maintained until the entire component has solidified. After the gas pressure has been released, the remaining melt can flow out of the riser pipe back into the melting container. The component is then removed from the mold. The basic advantage of a low-pressure casting process compared to a classic casting process is, on the one hand, the easily controllable, slow mold filling, which leads to high component quality, and, on the other hand, the reduction in the proportion of circulation due to the backflow of the melt in the riser pipe.

In the low-pressure permanent mold casting process, non-ferrous metals such as aluminum and copper alloys are mainly processed. For this purpose, standardized crucibles made of aluminum oxide or silicon carbide are usually used as melting containers, which are placed free-standing in the furnace chamber of the low-pressure casting arrangement. This has the advantage that if the alloy is changed, the crucible can be exchanged very easily via the open lid.

However, such an arrangement cannot be used for the low-pressure casting of high-melting metals such as steel. A ceramic crucible would not withstand the high mechanical and thermal loads in this case without additional support. However, a support with a steel structure is not possible, as this would also be heated by the inductive heating of the molten metal and would lose its mechanical stability. Furthermore, due to the high temperature differences between the inside of the Crucible, which is in the range of the melting or casting temperature, usually > 1600°C for steel, and the significantly lower temperatures on the outside, high mechanical stresses occur that can lead to cracks in the crucible.

State of the art

For the low-pressure casting of higher-melting materials, such as steel, the known casting arrangements therefore have a significantly different structure. The casting system usually consists of a steel hollow body, which has a solid furnace lining (lining) to form a crucible. The furnace has various openings that are used for charging, melt treatment or sampling. The casting moulds, in particular sand moulds, are positioned on a funnel-shaped upper furnace opening, the casting nozzle. The melt is inductively heated or kept warm. A distinction is made here between crucible and channel furnaces or inductors. After applying increased gas pressure to the melt surface, the mold is slowly filled with molten metal via the casting nozzle. Here, too, the casting pressure is maintained until the component has solidified. The gas pressure is then released again and the remaining melt runs back into the crucible. Here, too, the advantages of the process lie in the slow and easily controllable mold filling and the reduction in the proportion of circulation (smaller gating system, no feeder).

For example, an arrangement for vertical low-pressure casting that has such a structure is described at https://www.ottojunker.com/de/produkte-technologies/anlagen-fuergusseisen-stahl/giessofen-fuer-niederdruckguss/ . With this arrangement, the heating can take place via trough or crucible inductors. The entire oven is supported by a substructure.

The well-known low-pressure casting furnaces for steel have a solid furnace lining that is tailored to the material to be processed. As a result, a quick change of the casting material is not possible. To change the material, the entire furnace lining would have to be removed and relined.

From the company Griffin Wheel Division a technique for the production of railway wheels in steel low-pressure casting is known, which enables a quick exchange of the melting vessel. Here, a casting ladle filled with the already molten steel is placed in an airtight housing and closed with a lid. A casting ladle basically consists of a steel container lined with a ceramic lining. Just as with the other low-pressure casting systems, a casting mold located above the ladle is filled with increased gas pressure via a riser pipe. The disadvantage of this system, however, is the ongoing cooling of the melt in the ladle, so that the pouring time is correspondingly limited. Especially in the production of thin-walled cast structures limitations due to the flowability decreasing with the melting temperature.

The object of the present invention is to specify an arrangement for the low-pressure casting of high-melting metals that enables the metals or metal alloys to be changed quickly and is also suitable for the production of thin-walled cast structures.

Both documents U.S. 6,684,934 B1 and U.S. 4,726,414A disclose exemplary arrangements for the low-pressure casting of refractory metals, which have melting receptacles as exchangeable inserts.

Presentation of the invention

The object is achieved with the arrangement according to claim 1. Advantageous configurations of the arrangement are the subject matter of the dependent patent claims or can be found in the following description and the exemplary embodiments.

The proposed arrangement has a furnace chamber with one or more gas supply and gas outlet openings and a riser pipe through a cover of the furnace chamber, onto which a mold can be placed, a melting container for the high-melting metals or metal alloys arranged in the furnace chamber and a preferably inductive heating device the refractory metals in the melting container can be heated. The arrangement is characterized in that the melting container is designed as a removable insert for the melting container in particular laterally supporting receiving form in the furnace chamber and that a thermally insulating layer between receiving form and Melting container is designed or integrated in the melting container.

The furnace chamber can be closed off gas-tightly from the outside in a known manner in order to press a melt present in the melting container via the riser pipe into a mold placed on the riser pipe by increasing the gas pressure in the furnace chamber. Due to the design of the melting container as a removable and thus exchangeable insert, it can be exchanged quickly and easily in order to change the alloy. The design as an insert in a receiving mold that preferably supports the entire circumference of the melting container, ie the bottom surface and side surface(s), enables the necessary mechanical support when processing metals with high density, such as steel. The thermally insulating layer significantly reduces temperature differences between the inside and outside of the melting container or the receiving mold, so that thermally induced mechanical stresses that can lead to the melting container breaking are prevented or at least significantly reduced. The receiving opening of the receiving form is geometrically adapted as far as possible to the outer shape of the melting container in order to be able to support it over as large an area as possible. The one or more induction coils of the heating device can be integrated into the receiving form.

In an advantageous embodiment, the recording form has an inner formwork of a preferably ceramic material, in which one or more induction coils of the heating device for heating the metal casting material are embedded. The inner formwork is supported by an outer support structure, preferably of steel. The outer walls of the furnace chamber preferably represent this supporting structure, so that the inner formwork forms a lining of the furnace chamber. In principle, however, there is also the possibility of placing the receiving mold as a separate component in a furnace space.

The meltable container can be designed as an insert that can be removed upwards in a receiving form that correspondingly has the receiving opening facing upwards. In this case, a bed of a high-temperature-resistant material, for example high-alumina, is preferably introduced between the walls of the receiving opening and the melting container, which forms the thermally insulating layer. For this purpose, the receiving opening and the external dimensions of the melting container are matched to one another in order to form a sufficiently large gap for the bed.

The receiving opening has a conical shape, which preferably narrows towards the top. In this embodiment, the meltable container is realized with a correspondingly complementary conical shape, so that the outside of the meltable container is in full contact with the inside of the receiving opening after it has been inserted into the receiving opening. The melting container is here from below in the introduced below open receiving opening and pressed by a suitable mechanism in this opening and held there. This mechanism can be designed in different ways and can work, for example, by means of compression springs or else by a motor or hydraulic drive. For this purpose, the furnace chamber has a detachable base plate, which makes it easy to change the melting container. In one possible configuration, the thermally insulating layer forms the outside of the melting container and is applied to an internal circuit, which is preferably formed from a ceramic material. For this purpose, the thermally insulating layer can be formed, for example, by a fleece that is resistant to high temperatures. In another embodiment, the melting container has an inner formwork, preferably made of a ceramic material, an intermediate bed made of a high-temperature-resistant material, for example high alumina, and an outer formwork, preferably also made of a ceramic material. This outer formwork can also be formed by several rings lying loosely one on top of the other and a base plate. In the aforementioned configurations, the melting container can be very easily removed from the receiving mold and changed by simply loosening or removing the base plate of the furnace chamber.

The proposed arrangement is particularly suitable for low-pressure casting of high-melting metals, in which the metals should be changed easily and quickly.

Brief description of the drawings

Fig. 1

ein erstes Beispiel für eine Anordnung außerhalb des Umfangs der Ansprüche im Querschnitt;

Fig. 2

ein zweites Beispiel für eine Anordnung gemäß der vorliegenden Erfindung im Querschnitt;

Fig. 3

ein drittes Beispiel für eine Anordnung gemäß der vorliegenden Erfindung im Querschnitt;

Fig. 4

ein viertes Beispiel für eine Anordnung der vorliegenden Erfindung im Querschnitt;

Fig. 5

ein fünftes Beispiel für eine Anordnung gemäß der vorliegenden Erfindung im Querschnitt;

Fig. 6

ein sechstes Beispiel für eine Anordnung gemäß der vorliegenden Erfindung im Querschnitt; und

Fig. 7

ein siebtes Beispiel für eine Anordnung außerhalb des Umfangs der Ansprüche im Querschnitt.

The proposed arrangement is explained in more detail below using exemplary embodiments in conjunction with the drawings. Here show:

1

a first example of an arrangement outside the scope of the claims in cross-section;

2

a second example of an arrangement according to the present invention in cross section;

3

a third example of an arrangement according to the present invention in cross section;

4

a fourth example of an arrangement of the present invention in cross section;

figure 5

a fifth example of an arrangement according to the present invention in cross section;

6

a sixth example of an arrangement according to the present invention in cross section; and

7

a seventh example of an arrangement outside the scope of the claims in cross section.

Ways to carry out the invention

In the proposed arrangement, the melting container is designed as an exchangeable insert of a receiving form which is arranged in the furnace space or forms a lining of the furnace space.

1 shows a first exemplary embodiment of the proposed arrangement in a cross-sectional representation outside the scope of the claims.

In this case, the furnace chamber is formed by a steel frame 1 which is closed by a removable cover 5 . In this example, the cover contains a gas inlet 6 and a gas outlet 7 for increasing or reducing the pressure in the furnace. Furthermore, a riser pipe 8 runs through the cover, onto which a mold 9 is placed. By increasing the gas pressure in the furnace chamber, the melt 10 in the melting container rises via the riser pipe 8 into the mold 9 in order to solidify there into the component to be cast.

In this arrangement, the melting container is formed from an inner crucible 3, which is inserted into a thick-walled outer crucible 2 as a receiving mold and can also be removed from this again. Windings of the induction coil(s) 11 of the heating device are integrated into the outer crucible 2, which is formed from a refractory material. In the present example, this outer crucible 2 forms a lining 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 in the outer crucible 2 as Recording form used, the cavity between the two crucibles with a refractory bed 4, such as high alumina, is filled. The mechanical stress when casting high-melting metals, such as steel, is absorbed by the outer steel frame 1. There is no need to fear inductive coupling into this steel construction, since the induction coils 11 are located inside the outer crucible 2 and the steel frame 1 is outside the magnetic field of the coils. Furthermore, the thermally insulating effect of the bed 4 results in a more uniform heating of the inner crucible 3 over the wall thickness and thus lower thermally induced mechanical stresses.

The furnace chamber is closed with the pressure-tight cover 5, which has a central opening for the riser pipe 8. Due to the compact structure of this arrangement for low-pressure casting, a small gas volume is required for applying the pressurization, whereby costs (less gas consumption) and the time for applying the gas pressure can be reduced. The interchangeable inner crucible 3 enables the alloys to be changed more quickly and easily. To prevent contact between the induction coil(s) 11 and the melt 10 if the inner crucible 3 breaks, a melt detection system 18 can be placed between the outer crucible 3 and the bed 4, for example a wire mesh connected to a measuring device. Upon contact with the molten metal, the heating device would then switched off automatically. Such a melt detection system 18 can also be used in the further configurations described below.

2 shows a further exemplary embodiment of the proposed arrangement, which enables the melting container to be changed quickly. In this case, the melting container is designed in a conical shape and is inserted into a receiving mold 2 with a conical receiving opening. The furnace chamber is in turn formed by a steel frame, not shown in this figure and the following figures, by which the receiving mold 2 is supported. The receiving form 2 here has a continuous receiving opening with a conical shape. The induction coils 11 are again integrated in the recording form 2, as is shown in FIG 2 is indicated. In the same way as with 1 the furnace chamber is closed off by a cover 5 with a gas inlet 6, gas outlet 7 and a continuous riser pipe 8. The casting mold 9 is in turn placed on the riser pipe 8 or the cover 5 .

In the present example, the melting container is formed from a double-walled construction with an inner crucible 3 and a conical insert 12, between which there is a loose bed 4 of a refractory 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 or the receiving mold 2 and leads to a desired thermal insulation effect. On the other hand, the bulk material 4 can also absorb melt in the event of a crack in the crucible, the melt then solidifying within the fine passages of the bed 4 and further outflow of the melt is prevented.

The melting container is taken out of the receiving mold 2 downwards in this example. For this purpose, a removable base plate 13 is provided, on which a spring system 14 is arranged in the present example, which presses the melting container into the conical receiving opening 2 . As a result, the melting container is fully supported by the receiving mold 2 . The furnace body is lifted off the base plate 13 in order to fill the melting container with liquid melt. The bottom plate 13 is then pulled out from under the furnace body and is free to fill the melting container with the melt. The base plate 13 with the melting container is then placed again under the furnace body and the latter is lowered onto the base plate. The conical insert 12 of the melting container ensures good centering and the spring system 14 can ensure that the conical insert 12 of the melting container rests against the inner walls of the receiving mold 2 over the entire surface. The execution by means of a spring system 14 is only one design variant. Other options for adjusting the height of the melting container are mechanisms that work using hydraulics, pneumatics or screw jacks. With this configuration of the arrangement, the melting container or just the inner crucible 3 of the melting container can be very easily and quickly exchanged to carry out an alloy change.

In a further advantageous embodiment, the conical insert 12 of the configuration 2 also consist of a conical tube or individual conical rings 15 and an associated base plate 16, as in 3 is shown as an example. The other components of this exemplary arrangement correspond to those of 2 . For easier positioning, the conical rings 15 can also be assembled with one another using a tongue and groove system. The advantage of this design over the design of 2 lies in the greater flexibility of the melting container with regard to thermal expansion.

The figures 4 and 5 show another exemplary embodiment of the proposed arrangement, which is the 2 resembles. In these examples, in contrast to the design of the 2 the melting container consists only of an inner crucible 3 in a conical shape with a high-temperature fleece 17 attached thereto, which can be applied to the preferably ceramic inner crucible 3, for example with a ceramic adhesive. The fleece 17 ensures the insulation of the inner crucible 3, resulting in better temperature homogeneity over the crucible wall. Furthermore, the fleece 17 supports the crucible 3 against the receiving mold 2 and compensates for simultaneous thermal expansions. The configurations of figures 4 and 5 differ only in that in the design of the figure 5 the crucible 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 is reduced and thus better coupling of the electrical energy into the melt 10 can be achieved.

In 6 is another advantageous embodiment of the design of 2 shown. In contrast to the design of 2 this embodiment has a uniformly vertical arrangement of the induction coil(s) 11 . Due to this vertical arrangement, due to the now uniform distance from the melt 10, an overall more uniform heating of the melt is achieved.

7 shows a further advantageous embodiment of the design of figure 1 outside the scope of the claims. In this embodiment, the low-pressure casting furnace has a separate base frame 19 with resistance heating below the steel frame 1, which allows additional preheating of the entire crucible area, which is usually ceramic. This preheating can reduce heat-related stress cracks in the ceramic crucible. Alternatively, the additional resistance heating(s) can also be arranged on the side or on the side and in the base frame.

Reference List

1

steel frame

2

outer crucible/mold

3

inner crucible

4

loose bulk

5

Lid

6

gas supply

7

gas evacuation

8th

riser

9

mold

10

melt

11

induction coil(s)

12

conical insert

13

bottom plate

14

spring system

15

conical rings

16

base plate

17

high temperature fleece

18

melt detection system

19

Base frame with resistance heating

Claims (6)

1. Arrangement for low-pressure casting of high melting point metals, which has

   - a furnace chamber with one or more gas inlet (6) and gas outlet (7) openings and a riser pipe (8) through a cover (5) of the furnace chamber, on which a casting mould (9) can be placed,

   - a molten metal container (3, 12) arranged in the furnace chamber for the high melting point metals, and

   - a heating device for heating the high melting point metals in the molten metal container (3, 12),

   wherein the molten metal container (3, 12) is designed as a replaceable insert for a receiving mould (2) that supports the molten metal container (3, 12), which is arranged inside the furnace chamber, and a thermally insulating layer (4, 17) is formed between receiving mould (2) and molten metal container (3, 12) or integrated in the molten metal container (3, 12), wherein the molten metal container (3, 12) either has an inner formwork (3) made from a ceramic or other refractory material on which a thermally insulating layer (4, 17) is formed from a refractory nonwoven (17), or is formed from an inner formwork (3) made from a ceramic or other refractory material, an outer formwork (12) made from a ceramic or other refractory material, and a filling (4) made from a refractory material positioned therebetween as a thermally insulating layer (4, 17),

   and wherein a receiving opening of the receiving mould (2) and the molten metal container (3, 12) have a conical shape, and the molten metal container (3, 12) and the receiving mould (2) are designed in such manner that the molten metal container (3, 12) can be removed downwards out of the receiving mould (2), and a mechanism (14) is arranged on a baseplate (13) of the furnace chamber, which mechanism is able to press the molten metal container (3, 12) into the receiving mould (2) from below.
2. Arrangement according to Claim 1,
   characterized in that
   the receiving mould (2) is supported by a steel construction (1).
3. Arrangement according to Claim 1,
   characterized in that
   the furnace chamber is formed by a steel construction (1), and the receiving mould (2) is designed as lining of the furnace chamber.
4. Arrangement according to any one of Claims 1 to 3,
   characterized in that
   the receiving mould (2) is formed from a ceramic or other refractory material, in which one or more induction coils (11) of the heating device are embedded.
5. Arrangement according to any one of Claims 1 to 4,
   characterized in that
   the outer formwork (12) is made up of a plurality of conical rings (15) on a base plate (16).
6. Arrangement according to any one of Claims 1 to 5,
   characterized in that
   the base plate (13) of the furnace chamber is constructed so as to be removable or detachable.

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