CASTING CORE

Abstract

A casting core includes a main portion made of molybdenum or a molybdenum alloy, and, at the surface of the main portion, at least two protuberances made of a refractory material, the whole of the main portion and the protuberances being covered with an anti-oxidation coating.

Claims

1. A casting core comprising a main portion made of molybdenum or a molybdenum alloy, and, at a surface of the main portion, at least two protuberances made of a refractory material, the whole of the main portion and the at least two protuberances being covered with an anti-oxidation coating, the refractory material of the at least two protuberances being a ceramic.

2. The casting core according to claim 1, wherein the anti-oxidation coating comprises, from the core outwards, at least on adhesion layer and one protective layer, the adhesion layer being selected from a layer of titanium carbonitride TiCN, titanium carbide TiC, titanium nitride TiN, silicon carbide SiC, hafnium carbide HfC, or aluminium nitride AlN and the protective layer being a layer of alumina Al.sub.2O.sub.3.

3. The casting core according to claim 1, wherein the at least two protuberances are formed by a single refractory material rod passing through the main portion of the core from one side to the other.

4. The casting core according to claim 3, wherein the refractory material of the refractory material rod is selected from alumina or zirconia.

5. The casting core according to claim 1, wherein of the main portion of the core has the shape of the cooling circuits of a turbomachine blade.

6. A process for manufacturing a casting core comprising: forming a main portion of the core made of molybdenum or molybdenum alloy in the desired shape; disposing at least two protuberances made of refractory material at the surface of the main portion, the refractory material of the protuberances being a ceramic; coating the main portion and the protuberances with an anti-oxidation coating.

7. The manufacturing process according to claim 6, wherein the disposing of the at least two protuberances is achieved by shrinking a refractory material rod in a through-opening of the main portion.

8. The manufacturing process according to claim 6, wherein the core is coated by a chemical vapour deposition or physical vapour deposition process.

9. The manufacturing process according to claim 6, wherein the main portion is formed by additive manufacturing or by injection moulding of metal.

10. A process for manufacturing a hollow part made of metal material by casting, comprising: disposing a casting core according to claim 1 in a casting mould, the casting core being disposed in the mould such that the protuberances are in contact with the mould; pouring a molten metal material into the moulding cavity of the mould comprising the core; and shakeout of the mould and removal of the core.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0070] FIG. 1 shows a schematic representation of a casting core in a first embodiment.

[0071] FIG. 2 shows a schematic representation of a casting core in another embodiment.

[0072] FIG. 3 shows a schematic representation of a casting core according to an embodiment of the invention disposed in a lost-wax casting mould.

[0073] FIG. 4 shows a flow chart illustrating a process for preparing a casting core in an embodiment.

[0074] FIG. 5 shows a flow chart illustrating a process for manufacturing a hollow part from a metal material in an embodiment.

DESCRIPTION OF THE EMBODIMENTS

[0075] The invention is now described by means of figures, having the descriptive aim of illustrating certain embodiments of the invention and which must not be interpreted as limiting the latter.

[0076] FIG. 1 shows a schematic representation of a casting core 101 in an embodiment.

[0077] The casting core comprises a main portion 11, two protuberances 12 at the surface of the main portion 11, the whole being coated with an anti-oxidation coating 13.

[0078] The protuberances 12 can be fixed by embedding, bonding or any other method for ensuring the fixing of the core in the mould, it being understood that this fixing must withstand the molten metal pouring step.

[0079] In the embodiment shown in FIG. 1, the two protuberances 12 are distinct from each other, in that they are formed separately.

[0080] FIG. 2 shows an alternative embodiment which differs from FIG. 1 in that the two protuberances are formed by a single rod of refractory material 15.

[0081] This embodiment makes it possible to obtain two protuberances 12 in a simplified manner. In addition, since this requires a through-opening to be made in the main portion 11 of the core 102, this embodiment ensures precise and simplified positioning of the protuberances 12 on the main portion 11, and therefore better reproducibility.

[0082] In the application, the refractory material protuberances 12 are made of a material that is chemically inert to the molten metal and resistant to the temperatures involved in the pouring of the liquid metal.

[0083] For example, the refractory material may be a ceramic material, such as zirconia or alumina.

[0084] In the embodiment shown in FIGS. 1 and 2, the anti-oxidation coating 13 is continuous, i.e. the entire external surface of the main portion 11 and the protuberances 12 is covered.

[0085] This embodiment ensures excellent resistance to oxidation of the main portion 11, particularly close to the protuberances 12.

[0086] Indeed, it is to the inventors' credit that they have thus solved two problems presented by the cores of the prior art which do not comprise protuberances made of a refractory material.

[0087] On the one hand, the fixing of the protuberances, necessary for the correct positioning of the core 101, 102 in the mould, risks damaging the coating of the main portion 11 in the area close to the protuberances 12.

[0088] On the other hand, placing the core 101, 102 in the mould may cause localised destruction of the protective coating 13 present on the protuberances 12. This may be caused by handling tools, for example, or by contact with the mould.

[0089] A core 101, 102 according to the invention does not suffer from either of these two problems, nor does it require other methods for positioning the core 101, 102 in the mould.

[0090] The coating 13 covers both the main portion 11 and the protuberances 12. Fixing the protuberances cannot therefore damage the coating 13, which is deposited afterwards.

[0091] In addition, when the core 101, 102 is fitted, it is the protuberances 12 that come into contact with the mould. Since these are made of a refractory material, even if the coating 13 were damaged at the protuberances 12, this would have no effect on the good resistance to oxidation of the main portion 11 of the core 101, 102.

[0092] FIG. 3 schematically shows a core 102 disposed in a mould 16 for the preparation of a hollow metal part.

[0093] The mould 16 is obtained in a known manner, using a lost-wax moulding process, so that the mould cavity 20 of the mould, defined by its internal surface S.sub.int, has the shape of the desired part.

[0094] The core 102 can be positioned, for example, by disposing the protuberances 12 in portions of the mould provided for this purpose, in this case the recesses 22.

[0095] In an embodiment, the moulding cavity 20 may comprise a useful portion 18 and a non-useful portion 24, the desired part being obtained in the useful portion 18.

[0096] For example, the protuberances 12 and the recesses 22 are located in the non-useful portion 24. The presence of a non-useful area 24 makes it easier to demould and/or carry out checks.

[0097] In this way, the final geometry of the useful portion 18 of the moulding cavity 20 of the mould 16 is not constrained in any way by the presence of the core protuberances 12, and a hollow part made of metal material with the desired dimensions and shapes can be obtained.

[0098] FIG. 4 is a very schematic representation of a process for manufacturing a casting core 101, 102 as described above.

[0099] In a first step S11, the main portion 11 of the core 101, 102 is formed in the desired shape.

[0100] Any method can be used for this step, in particular additive manufacturing or metal injection moulding.

[0101] These two methods produce a main section with a perfectly defined geometry.

[0102] The specific processes for implementing these methods are well known, and will not be described here.

[0103] In some embodiments, step S11 may also comprise a specific step of creating a through-opening in the main portion 11, intended to receive the refractory material rod 15.

[0104] In a second step S12, at least two protuberances 12 are disposed at the surface of the main portion 11.

[0105] It is understood that, even when the protuberances 12 are created via the insertion of a refractory material rod 15 passing through the main portion 11, the protuberances 12 are to be understood as the portions of the refractory material rod 15 which protrude from the main portion 11, and they are therefore located at the surface of the main portion 11.

[0106] For example, the second step S12 can be carried out by bonding or embedding protuberances 12 at the surface of the previously-created main portion 11.

[0107] In a particular embodiment, step S12 corresponds to the insertion of a refractory material rod 15 into a cylindrical opening provided for this purpose in the main portion 11 of the core 102. The refractory material 15 may be a refractory oxide or a refractory ceramic.

[0108] It is preferred that the refractory material rod 15 is shrunk into the cylindrical opening of the main portion 11.

[0109] Shrinking is used here in its usual definition in the mechanics of materials, and consists of the assembly of two parts by means of a press fit.

[0110] In fact, when it is fixed by shrinking, the refractory material rod 15 exhibits no play with respect to the main portion 11 of the core. The inventors have found that it is preferable for the refractory material rod 15 to have no play with respect to the main portion 11 of the core 102, as this avoids relative movement of the refractory material rod 15 with respect to the main portion 11 of the core. Such movement could cause the refractory material rod 15 to rub against the coating 13 of the main portion 11 near the protuberances 12 and damage its integrity. The core 102 is also positioned more accurately in the mould 16.

[0111] The process of preparing the casting core 102 also includes a step S13 of coating the core 102, formed by the main portion 11 and the protuberances 12, with an anti-oxidation coating 13.

[0112] For example, this step can be achieved by a chemical vapour deposition (CVD) process, a physical vapour deposition (PVD) process or even a liquid process such as electrodeposition, for example.

[0113] In an embodiment, the coating may comprise a layer of alumina Al.sub.2O.sub.3 and a layer of titanium carbonitride TiCN, both deposited by a chemical vapour deposition process.

[0114] Chemical vapour deposition ensures that the coating 13 covers the entire core 102, whatever its geometry.

[0115] In an embodiment where the refractory material rod 15 is hollow, step S13 can be carried out by hanging the core 102 in a chemical vapour deposition furnace by means of a thread passing through the refractory material rod 15.

[0116] The specific parameters of a chemical or physical vapour deposition process for depositing a protective coating 13 are known to a person skilled in the art. The same applies to an electrodeposition process.

[0117] FIG. 5 describes a process for manufacturing a hollow part from a metal material by a lost-wax casting process using a casting core as described above.

[0118] Such a process comprises a step S21 of placing a casting core 101, 102 in a casting mould 16, so that the protuberances 12 of the core are in contact with the mould 16.

[0119] Preferably, and as is frequently done in conventional lost-wax casting processes, the casting mould 16 can be obtained via a ceramic shell formed around a wax model of the part, for example by dipping the wax model in a slip followed by heat treatment.

[0120] In an embodiment, the core protuberances are disposed in recesses 22 of the mould 16.

[0121] The process comprises a step S22 of pouring a molten metal material into the mould comprising the core 101, 102.

[0122] During this stage, the molten metal fills the moulding cavity 20 of the mould 16, or at least its useful portion 18.

[0123] The moulding cavity 20 has the shape of the part to be obtained, so the molten metal takes on the desired shape of the part.

[0124] The presence of the casting core 101, 102 in the mould cavity 20 prevents the molten metal from gaining access to the space it occupies and the metal part is thus formed around the core.

[0125] In a subsequent step S23, the mould is shaken out and the core removed, using methods known per se to enable a hollow metal part to be ultimately obtained.

[0126] In an embodiment, once the monocrystalline alloy has been cast and cooled, some of the non-useful areas are cut away, exposing the core.

[0127] The latter is then exposed to one or more chemical baths and/or one or more heat treatments in order to eliminate the core and the protuberances made of refractory material.

[0128] For example, the mould can be destroyed mechanically.

[0129] For example, the casting core can be dissolved using an acidic or basic chemical solution. Alternatively or additionally, the casting core can be dissolved by an oxidation treatment, possibly carried out at temperature.

[0130] In an embodiment, the process for manufacturing a hollow part from a metal material may include, after step S23, a machining step, for example to remove some of the metal that has flowed into the non-useful area 24 of the mould 16, and to retain only the part with the desired dimensions.