Method for the production of a casting mold

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority of the European application No. 04030823 EP filed Dec. 27, 2004, which is incorporated by reference herein in its entirety.

FIELD OF THE INVENTION

The invention relates to a method for the production of a casting mold as claimed in the claims.

BACKGROUND OF THE INVENTION

Components designed as hollow bodies and having complexly shaped geometries and complex passage holes in the region of an outer wall of the component can be produced in various ways.

Many components, in particular metallic components consisting of alloys, are produced by means of casting methods, for example by means of the lost-wax casting method.

In this case, in a first step, a casting mold, which at least partially constitutes the negative of the component to be produced, is produced from a wax model of the component by the wax model being encased with ceramic or a sand mold.

Passage holes in the walls of hollow components, such as, for example, film-cooling holes of turbine components, are always introduced subsequently by means of a laser and its laser beams, as shown in U.S. Pat. No. 6,329,015 B1. The guidance of the laser beam is in this case highly complicated.

Methods for the production of a casting having subsequently introduced holes, in particular passage holes, are therefore time-consuming.

SUMMARY OF THE INVENTION

The object of the invention is, therefore, to indicate a method for the production of a casting mold, by means of which the production of a component with holes, in particular with passage holes, can be carried out more simply and more quickly. The object is achieved by means of a method for the production of a casting mold as claimed in the claims.

In this case, a casting mold is produced which has corresponding projections which at least partially constitute the negative of a hole.

Further advantageous measures are listed in the subclaims.

The measures listed in the subclaims may advantageously be combined with one another in any desired way.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 shows a component with a passage hole,

FIGS. 2, 3, 4 and 5 show casting molds with various projections for forming a passage hole,

FIG. 6 shows a top view of an inner surface of a casting mold,

FIGS. 7-15 show part steps of the method,

FIG. 16 shows a gas turbine,

FIG. 17 shows a combustion chamber, and

FIG. 18 shows a turbine blade.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1 shows a component 1 which has, for example, at least in part of its volume, a cavity 31 and which can be produced by means of the casting mold 16 (FIGS. 2, 3, 4 and 5). In this case, the component 1 has at least one component wall 4, 4′, in particular outer component walls 4, 4′.

For example, at least one hole 13, here a passage hole 13, is formed in the wall 4. The hole 13 may also be a blind hole.

The component 1 may be, for example, metallic or ceramic. For example, it is a turbine component 1 of a gas turbine 100 (FIG. 15) or steam turbine and, for example, is a turbine blade 120, 130 (FIGS. 15, 17) or a heat shield element 155 (FIG. 16) which consists, for example, of an iron-based, nickel-based or cobalt-based superalloy.

Where such components 1 are concerned, passage holes 13 are provided, for example, as cooling-air holes 13, in order to cool the component 1 by film cooling.

The passage hole 13 in this case has, for example, a hole part 7 of round or oval form which widens from the cavity 31 toward the outer surface 11 of the wall 4 into a diffuser 10, so that the hole 13 deviates there from the shape of the hole part 7.

The casting mold 16 for such components 1 having complex shapes of a passage hole 13, 7+10, can be produced more simply and more quickly by means of the method according to the invention.

The wall of the component 1 in this case has, for example, a thickness of 2 to 6 mm, in particular of 3 to 4 mm.

The hole part 7 has a diameter of 0.3 to 1.2 mm, in particular of 0.6 to 0.8 mm.

The diffuser 10 has, for example, a trapezoidal design on the outer surface 11, has dimensions of 1.5 to 5 mm×1.5 to 5 mm and merges into the component wall 4, 4′ to a depth of 1 to 1.5 mm.

FIG. 2 shows diagrammatically part of the casting mold 16 which consists of an inner wall 25, in particular of a core 25, and of an outer wall 28.

Material 22, for example metal melt, is poured into the interspace 26 (cavity of the casting mold 16) between the inner wall 25 and the outer wall 28 and, after cooling, forms, for example, the wall 4 of the component 1.

The core 25 forms, for example, part of the cavity 31 of the component 1.

At least one projection 19, 34, 37 consisting of molding material is formed in this interspace 26.

The projection 19, 34, 37 extends at least over part of the interspace between an inner surface 20 of the inner wall 25 and an inner surface 21 of the outer wall 28.

Here, the continuous projection 19 extends continuously from the inner surface 20 of the inner wall to the inner surface 21 of the outer wall.

The continuous projection 19 has been formed by filling a passage hole 13 with ceramic in a wax model 43 (FIG. 7) of the component 1 (FIG. 9-15).

The continuous projection 19 in the interspace 26 prevents a filling-up with material 22 during casting, so that, after the removal of the casting mold 16 together with its inner wall 25 and its outer wall 28 and together with the continuous projection 19, a passage hole 13 is obtained.

The continuous projection 19 is built up, for example, as follows:

an inner projection 34 constitutes the round or oval (FIG. 6) hole part 7 of the passage hole 13.

An outer projection 37 constitutes the diffuser 10.

The continuous projection 19 may, however, be of round or oval design even over its entire cross section and, for example, even have a constant cross-sectional surface.

If appropriate, after the casting of the component 1, a minimal remachining of the passage orifice 13, albeit markedly reduced in comparison with previous methods, may also be carried out.

FIG. 3 shows a further exemplary embodiment of a casting mold 16 which is produced by means of the method according to the invention. In contrast to the casting mold 16 according to FIG. 2, the inner projection 34, 37′ does not extend continuously from an inner surface 20 of the inner wall 25 to an inner surface 21 of the outer wall 28.

The inner projection 34 is formed only on the inner surface 20 of the inner wall 25 and extends as far as a certain distance d from the inner surface 21 of the outer wall 28.

During casting, that is to say when the cavity 26 is being filled up with material 22, the passage orifice 13 is thus not formed completely. After the casting of the component 1, material 22 is present in the region between the inner projection 34 and the inner surface 21 of the outer wall 28. However, the region is correspondingly thin, in particular membrane-like, so that it can be removed simply in a very short time. It may also be said that, at the end of the casting process, the passage orifice 13 of the component 1 to be produced is still closed somewhat.

This is expedient, for example, when at least one coating is also applied subsequently to the outer surface 11 of the component 1. Since the passage orifice 13 is still closed, the passage orifice 13 is also not contaminated or narrowed by material of the coating.

Only as a result of a last machining step are the material of the coating, which is thin in comparison with the thickness of the wall 4, and the little material 22 which still closes the passage orifice 13 removed quickly and simply.

The coating is, for example, an MCrAlX alloy (M=Fe, Co, Ni and X=Y and/or a rare earth element) and, if appropriate, a ceramic coating as a heat insulating layer (for example Y₂O₃—ZrO₂) on it.

The inner projection 34 may also may also have a supporting connection 40 (indicated by dashes), so that the inner projection 34 projecting freely into the interspace 26 is supported on the outer wall 28.

The supporting connection 40 is designed in cross section to be smaller than the cross section of the inner projection 34, 37′ which lies opposite the outer wall 28. The supporting connection 40 therefore constitutes only part of the passage hole 13 to be produced.

The inner projection 34 may have at the end an advantageous region 37′ which corresponds partially to the outer projection 37 (FIG. 4) and which does not touch the wall 21, but, if appropriate, has the supporting connection 40.

In particular, the complex shape of the diffuser 10 has hitherto had to be worked in to the cast component in a complicated way. This is for the most part dispensed with here, since only a relatively small upper region of the diffuser 10 has to be reworked by the removal of material.

Since, in particular, the production of the regions lying at a greater depth in the wall 4 entails a considerable outlay, for example in terms of laser guidance, this casting mold 16 has considerable advantages.

FIG. 4 shows a further exemplary embodiment of a formed casting mold 16 which has been produced by means of the method according to the invention.

Here, the outer projection 37 is formed only on the inner surface 21 of the outer wall 28. The outer projection 37 constitutes the negative 37 of the diffuser 10, to be produced, of the passage orifice 13. In particular, the diffuser 10 has a more complex geometry than a simple symmetrical hole and would therefore have to be produced in only a highly complicated way if it were worked in subsequently. However, if the diffuser region 10 is already integrally formed in the surface of the component 1 to be produced, it no longer has to be worked in subsequently. It is necessary merely to work in at comparatively low outlay a simply designed hole part 7 (FIG. 1) in the wall 4 of the component 1 from the diffuser region 10. This may take place by laser machining or spark erosion and also by means of other methods.

Here, too, a corresponding supporting connection 40 may likewise be present (indicated by dashes) between the projection 37 and the inner wall 25.

FIG. 5 shows a further exemplary embodiment of a formed casting mold 16 which has been produced by means of a method according to the invention.

Starting from FIG. 4, an inner projection 34 is also formed on the inner surface 20 of the inner wall 25. The inner projection 34 forms a further part of this passage orifice 13, to be precise the region of the hole part 7. The outer projection 37 constitutes the region of the diffuser 10 of the component 1 to be produced.

By virtue of the outer projection 37 and of the inner projection 34, the machining time for producing the hole 13 in the component 1 to be produced is shortened, as compared with a component 1 which has been produced by means of a casting mold according to FIG. 4.

In particular, those casting molds 16 in which there is no continuous connection between the inner wall 25 and the outer wall 28 are simple to produce, since the core 25 can be produced separately from the wall 28 and, for casting, is introduced into the casting mold 16.

The projections 34, 37 may bear directly one against the other or have a defined distance between them.

FIG. 6 shows a top view of an outer wall 28 of a formed casting mold 16 which has been produced by means of the method according to the invention.

A plurality of projections 19 are formed on the inner surface 21 of the outer wall 28. Reference symbol 34 designates the region starting from which the hole part 7 will be formed.

Reference symbol 37 designates that region of the projection 19 which constitutes the diffuser region 10 of the passage hole 13 to be produced.

FIGS. 7 to 14 show how a casting mold 16 according to FIGS. 2 to 6 is to be produced according to the invention.

FIG. 7 shows the inner wall 25 or the core 25 of the casting mold 16, on which there is a model 43, in particular consisting of wax, which corresponds in its geometry and thickness to the component 1 to be produced. The inner wall 25 in this case constitutes, for example, the core 25. The model 43 is therefore a hollow component, for example like the component 1 to be produced by means of the casting mold 16.

According to the prior art, the wax model 43 on the inside is filled with a ceramic 25 (FIG. 7) and on the outside is encased in an outer wall 28 (FIG. 8), the model, in particular a wax model 43, then being removed (for example, by being melted out), so that a casting mold 16 (FIGS. 2, 3 and 4) is formed.

When material, for example liquid material, is introduced into the casting mold 16, the component 1 is obtained.

According to the invention, at least one depression 46 according to FIGS. 9 to 12 is introduced into this model 43.

This depression 46 is not the cavity of the model 43, but emanates, for example, from the surface 58 of the model 43.

The depression 46 extends, for example, entirely through the model 43, that is to say as far as the inner wall 25 (FIG. 9), or is designed as a blind hole (FIG. 10) which does not extend as far as the inner wall 25, that is to say extends only over part of the wall thickness of the model 43.

The depression 46 may be introduced into the model 43 when the inner wall 25 or the core 25 is already combined with the model 43 (FIG. 9) or before this takes place (FIG. 12).

The depression 46 may be produced in various ways, for example by drilling, milling or laser machining.

In particular, this depression 46 may have an oblique hole or oblique “bore” 49, such as is illustrated in FIGS. 11 and 12.

To be precise, an inner wall 25 or outer wall 28 which has an oblique projection cannot be produced by pouring a ceramic into a corresponding mold and by releasing the mold by pulling it off or loosening it.

In a further step, the continuous depression 46 (FIGS. 9 and 12) is filled up completely with a material 52 which corresponds, for example, to the ceramic of the inner wall 25 or of the outer wall 28 (FIG. 13). This may take place together with the introduction or application of the material for the core 25 or for the outer wall 28.

For the outer wall 28, a sand mold is often used, which is applied to the surface 58 of the model 43 and at the same time fills the depressions 46 in the desired way.

The depression 46 may likewise be filled up with material 52 separately before the application of the outer wall 28. The material 52 is introduced, for example, in the form of a slip and, for example, is cured when the outer wall 28 lies in place, so the material 52 is connected to the inner wall 25 or the outer wall 28.

If the outer wall 28 is then added, in turn, to the arrangement according to FIG. 13 and the model 43 is removed, a casting mold 16 according to FIG. 2 is formed.

The continuous depression 46, which extends as far as the inner wall 25 (FIGS. 9 and 12), may likewise be filled only partially with the ceramic 52, an empty space 55 remaining within the depression 46 (FIG. 14). In this case, for example, the core 25 is already present in the model 43.

When the outer wall 28 is added, in turn, the empty space 55 remains, and, when the model 43 is removed, a casting mold according to FIG. 3 is formed.

The material 52 which has filled the depression 46 is now an integral constituent of the casting mold 16 and consists, in particular, of the same material which is used for the casting mold 16 and which does not constitute a structural element.

If appropriate, the empty space 55 is filled with a wax which can be removed together with the model 43.

The depression 46 may likewise extend only partially in the model 43 (FIGS. 10 and 11) and, for example, is filled up completely with a ceramic material 52 (FIG. 15) before the outer wall 28 is applied to the model 43 or together with the application of the outer wall 28, so that the casting mold 16 according to FIG. 4 is formed after the removal of the model 43.

FIG. 16 shows an example of a gas turbine 100 in a longitudinal part section.

The gas turbine 100 has inside it a rotor 103 which is mounted rotationally about an axis of rotation 102 and which is also designated as a turbine rotor. Following one another along the rotor 103 are an intake casing 104, a compressor 105, a, for example, toroidal combustion chamber 110, in particular annular combustion chamber 106, with a plurality of coaxially arranged burners 107, a turbine 108 and the exhaust gas casing 109. The annular combustion chamber 106 communicates with a, for example, annular hot-gas duct 111. There, for example, four turbine stages 112 connected in series form the turbine 108. Each turbine stage 112 is formed from two blade rings. As seen in the flow direction of a working medium 113, a guide blade row 115 is followed in the hot-gas duct 111 by a row 125 formed from moving blades 120.

The guide blades 130 are in this case fastened to the stator 143, whereas the moving blades 120 of a row 125 are attached to the rotor 103 by means of a turbine disk 133. A generator or a working machine (not illustrated) is coupled to the rotor 103.

When the gas turbine 100 is in operation, air 135 is sucked in through the suction-intake housing 104 by the compressor 105 and is compressed. The compressed air provided at the turbine-side end of the compressor 105 is conducted to the burners 107 and is mixed there with a fuel. The mixture is then burnt in the combustion chamber 110 so as to form the working medium 113. The working medium 113 flows from there along the hot-gas duct 111 past the guide blades 130 and moving blades 120. At the moving blades 120, the working medium 113 expands in a pulse-transmitting manner, so that the moving blades 120 drive the rotor 103 and the latter drives the working machine coupled to it.

The components exposed to the hot working medium 113 are subjected to thermal loads while the gas turbine 100 is in operation. The guide blades 130 and moving blades 120 of the first turbine stage 112, as seen in the flow direction of the working medium 113, are subjected, in addition to the heat shield bricks lining the annular combustion chamber 106, to the most thermal load. In order to withstand the temperatures prevailing there, these are cooled by means of a coolant. The blades, 120, 130 may likewise have coatings against corrosion (MCrAlX; M=Fe, Co, Ni, X=Y, rare earths) and against heat (heat insulating layer, for example ZrO₂, Y₂O₄—ZrO₂). The turbine blade 120, 130 is often also air-cooled and has film-cooling holes 13 which are generated in the cast and/or directionally solidified turbine blade 120, 130 by means of the casting mold 16 according to the invention (FIG. 2-6).

The guide blade 130 has a guide blade root (not illustrated here) facing the inner casing 138 of the turbine 108 and a guide blade head lying opposite the guide blade root. The guide blade head faces the rotor 103 and is secured to a fastening ring 140 of the stator 143.

FIG. 17 shows an example of a combustion chamber 110 of a gas turbine 100.

The combustion chamber 110 is designed, for example, as what is known as an annular combustion chamber, in which a multiplicity of burners 102 arranged around the turbine shaft 103 in the circumferential direction issue into a common combustion chamber space. For this purpose, the combustion chamber 110 is designed in its entirety as an annular structure which is positioned around the turbine shaft 103.

To achieve a comparatively high efficiency, the combustion chamber 110 is designed for a comparatively high temperature of the working medium M of about 1000° C. to 1600° C. In order to allow a comparatively long operating time even in the case of these operating parameters which are unfavorable for the materials, the combustion chamber wall 153 is provided on its side facing the working medium M with an inner lining formed from heat shield elements 155. Each heat shield element 155 is equipped on the working-medium side with a particularly heat-resistant protective layer or is manufactured from material resistant to high temperature. On account of the high temperatures inside the combustion chamber 110, moreover, a cooling system is provided for the heat shield elements 155 or for their holding elements.

The heat shield elements 155 often have film-cooling holes 13 or passages for fuel into the combustion chamber 110, these being generated in the heat shield element 155 by means of the casting mold 16.

FIG. 18 shows a perspective view of a moving blade 120 or guide blade 130 of a turbomachine, said blade extending along a longitudinal axis 121.

The turbomachine may be a gas turbine of an aircraft or of a power station for electricity generation, a steam turbine or a compressor.

The blade 120, 130 has successively along the longitudinal axis 121 a fastening region 400, a blade platform 403 contiguous to the latter and a blade leaf 406.

As a guide blade 130, the blade 130 may have a further platform (not illustrated) at its blade tip 415.

In the fastening region 400, a blade root 183 is formed, which serves for fastening the moving blades 120, 130 to a shaft or a disk (not illustrated).

The blade root 183 is designed, for example, as a hammerhead. Other designs as a pine tree or dovetail root are possible.

The blade 120, 130 has a leading edge 409 and a trailing edge 412 for a medium which flows past the blade leaf 406.

In conventional blades 120, 130, for example, solid metallic materials are used in all the regions 400, 403, 406 of the blade 120, 130.

The blade 120, 130 may in this case be manufactured by a casting method by means of the casting mold 16 and also by means of directional solidification, by a forging method, by a milling method or by combinations of these.

Workpieces with a monocrystalline structure or structures are used as components for machines which are exposed during operation to high mechanical, thermal and/or chemical loads.

The manufacture of monocrystalline workpieces of this type takes place, for example, by directional solidification from the melt. Casting methods are involved here in which the liquid metallic alloy solidifies to form the monocrystalline structure, that is to say to form the monocrystalline workpiece, or directionally. In this case, dendritic crystals are oriented along the heat flow and form either a columnar-crystalline grain structure (columnar, that is to say grains which run over the entire length of the workpiece and here, according to general linguistic practice, are designated as directionally solidified) or a monocrystalline structure, that is to say the entire workpiece consists of a single crystal. In these methods, the transition to globulitic (polycrystalline) solidification must be avoided, since undirected growth necessarily causes the formation of transverse and longitudinal grain boundaries which nullify the good properties of the directionally solidified or monocrystalline component.

If it is generally a question of directionally solidified structures, these mean both monocrystals which have no grain boundaries or at most low-angle grain boundaries and columnar crystal structures which admittedly have grain boundaries running in the longitudinal direction, but no transverse grain boundaries. These second-mentioned crystalline structures are also referred to as directionally solidified structures.

Such methods are known from U.S. Pat. No. 6,024,792 and from EP 0 892 090 A1.

Refurbishment means that components 120, 130, after being used, must, where appropriate, be freed of protective layers (for example, by sand blasting). A removal of the corrosion and/or oxidation layers or products takes place thereafter. If appropriate, cracks in the component 120, 130 are also repaired. A recoating of the component 120, 130 and a renewed use of the component 120, 130 subsequently take place.

The blade 120, 130 may be of hollow or solid design.

If the blade 120, 130 is to be cooled, it is hollow and, if appropriate, also has film-cooling holes 418 (indicated by dashes).

As protection against corrosion, the blade 120, 130 has, for example, corresponding mostly metallic coatings (MCrAlX) and, as protection against heat, mostly also a ceramic coating.

Method for the production of a casting mold

Information

Publication Number

Date Filed

Date Published

Inventors

CPC

US Classifications

International Classifications

Abstract

Description

Claims

Priority Claims (1)