CN1318160C - Method for producing hollow casting with internal coating and turbine component - Google Patents

Abstract

The invention discloses a method for producing a hollow cast component (1) with an inner coating (14, 16, 18, 20), wherein the component (1) is cast from a matrix material using a casting core ( 22), according to the method of the invention, the coating material for the inner coating (14, 16, 18, 20) of the component (1) is applied in at least one casting mold before casting the component (1). on the casting core (22), and the casting core (22) is removed from the cavity (3, 5, 7, 9) after casting is completed.

Description

Method for producing hollow casting with internal coating and turbine component

technical field

The invention relates to a method for producing a hollow cast component, in particular a hollow cast turbine component, the inner wall of at least one cavity of which is provided with an inner coating.

Background technique

Components exposed to high thermal loads can have a coating on their outer sides in order to protect them from corrosion and/or oxidation in thermally loaded areas. MCrAlY coatings are particularly suitable for this purpose. A MCrAlY coating can be understood within the scope of this specification as a metal alloy coating comprising chromium (Cr) and aluminum (Al), where Y represents yttrium or a rare earth element, M represents iron (Fe ), cobalt (Co) or nickel (Ni).

However, under certain working conditions, the inner wall of the hollow casting working in the high thermal load area will also bear high temperature, so it is also necessary to prevent the inner wall from being corroded and/or oxidized, so that the component can really achieve the intended use life.

An example of such a hollow cast component subjected to high thermal loads is a turbine component, in particular a turbine blade. Turbine blades are exposed to high temperatures during operation and usually have cavities through which cooling fluid is guided. Under certain operating conditions, the temperatures in these cavities lead to the need to protect the inner walls from oxidation and/or corrosion.

Hitherto, the inner walls of hollow castings have been more or less protected by diffusion aluminizing. However, as the temperature increases, this aluminized layer reaches its limit and is therefore practically no longer effective against corrosion.

It is almost impossible to apply a particularly effective MCrAlY coating in parts of relatively complex cavities or interior cavities of hollow castings, such as cavities of turbine blades, using conventional methods. The spraying process cannot be satisfactorily applied to spray coating the inner walls of hollow castings.

Contents of the invention

Therefore, the technical problem to be solved by the present invention is to provide a method with which, in particular, complex interior spaces of hollow castings can be coated with an inner coating, in particular an MCrAlY inner coating.

A further problem underlying the invention is to provide an improved hollow cast turbine component.

The above-mentioned first technical problem is solved by a method for producing a hollow cast component, in particular a hollow cast turbine component, the hollow cast component having an inner coating in at least one cavity, wherein The component is cast from a matrix material using a casting mold comprising at least one casting core for defining said at least one cavity, according to the method of the present invention, to be used for the inner coating of the component coating material is applied to at least one casting core prior to casting the component, the component is then cast using a mold comprising such a casting core and allowed to solidify and harden, after which the casting core is removed from the cavity is removed in such a way that the coating material is not removed together, so that a hollow casting with an inner coating is obtained.

The above-mentioned second technical problem is solved by a hollow cast turbine component which, according to the invention, has at least one closed cavity and an MCrAlY inner coating in the closed cavity.

According to the invention, therefore, the inner coating is first produced and the component is then cast around this inner coating. According to this method, particularly complex cavities or interior spaces of components such as hollow cast gas turbine blades can also be coated with an inner coating, in particular an MCrAlY inner coating. Here, the material used for the casting core can be selected in such a way that it can be removed from the cavity of the cast component without at the same time causing the coating material to be removed as well.

The material for the casting core is particularly suitable to be a material that can be removed from the cavity by chemical means that do not attack the coating material and matrix material of the component. For example, casting cores of ceramic material can be produced. Such a ceramic insert can be removed from the cavity of the turbomachine component by means of a suitable caustic which does not attack the MCrAlY inner coating and matrix material of the turbomachine component. Ceramic materials are therefore particularly suitable as materials for casting cores for casting turbine components, such as turbine blades.

In the production method according to the invention, in particular the casting temperature when casting the component can be selected below the melting temperature of the coating material. This prevents the coating material from melting during the casting process and thus mixing with the matrix material of the component.

The coating material can be applied to the casting core, for example, by means of a high-energy spraying method, such as High Velocity Oxygen Fuel Spraying (abbreviated HVOF) or plasma spraying (abbreviated APS).

A hollow cast turbine blade according to the invention has at least one cavity and an inner coating, in particular an MCrAlY inner coating, in the cavity.

As a result of the inner coating, the hollow cast turbine component according to the invention has better oxidation and corrosion resistance than prior art turbine components and can therefore withstand higher temperatures.

Description of drawings

Further advantages and details of the invention will be explained in detail below with reference to the embodiments shown in the drawings.

Figure 1 is a schematic view of a hollow cast turbine component;

FIGS. 2 to 7 are each a highly simplified schematic illustration of various stages in the manufacture of the hollow cast turbine component shown in FIG. 1 .

Detailed ways

FIG. 1 is a schematic sectional view of a hollow cast turbine blade 1 . The turbine blade 1 includes a blade body 2 . In the exemplary embodiment shown, four cavities 3 , 5 , 7 , 9 are formed in the blade body 2 . These cavities are used, for example, for cooling air to flow through. The blade body 2 has an outer surface 12 . The outer surface is protected against oxidation and/or corrosion with a MCrAlY coating. In addition, the blade body 2 also has inner surfaces 4 , 6 , 8 , 10 . These inner surfaces define cavities 3, 5, 7, 9 and form the inner walls of these cavities. These inner surfaces 4, 6, 8, 10 are likewise provided with an MCrAlY coating 14, 16, 18, 20 to protect against corrosion and/or oxidation.

The method for producing the turbine blade 1 shown in FIG. 1 is described below with reference to FIGS. 2 to 7 . However, the method can also be used for internal coating of other hollow cast components.

As a first step, a ceramic casting core 22 is formed and sintered for the casting mold for casting the turbine blade (see FIG. 2 ). The next step (see FIG. 3 ) is to apply a MCrAlY coating 14 on the ceramic casting core 22 . For this purpose, for example, a high-energy spraying method, such as high-velocity oxyfuel spraying (HVOF) or plasma spraying (APS), can be used. The application thickness of the MCrAlY coating 14 on the casting core depends here on the desired inner coating thickness on the inner wall of the turbine blade.

After the casting core has been coated, a wax model 24 of the turbine blade is injection molded onto the casting core 22 (see FIG. 4 ). The outer casting shell 26 of the casting mold is then mounted on this wax pattern 24 . The wax is then burned out and the casting shell 26 is sintered in order to complete the manufacture of the casting mold 28 (see FIG. 5 ).

After the production of the casting mold 28 has been completed, the turbine blade 1 is cast in a vacuum. The casting of the turbine blade 1 typically takes place at a temperature below 1500°C. The melting point of the MCrAlY coating 14 is typically higher than 1600°C. Consequently, no melting of the coating 14 and thus no mixing of the coating material with the matrix material of the turbine blade 1 takes place during the casting process. Even when other coatings than MCrAlY coatings are used, the casting temperature must be lower than the melting temperature of the coating material as long as melting of the coating and mixing of the coating material with the matrix material is to be avoided.

After casting is complete, the casting shell 26 is removed and the blade 1 is cleaned (see FIG. 6 ). Finally, the casting core 22 is dipped in lye, ie the ceramic casting core 22 is removed from the cured turbine blade 1 by means of a lye. Since the MCrAlY coating 14 is as resistant to alkali as the blade material, the MCrAlY coating 14 remains on the inner side of the turbine blade 1 after the ceramic casting core 22 has been washed with alkali (see FIG. 7 ). The cast turbine blade can then be machined and coated on the outside in the usual manner.

The method described above is not only suitable for the inner coating of turbine blades, but is also suitable in principle for the inner coating of other hollow cast components. It is also possible to use this method to coat other coatings other than MCrAlY coatings. Casting cores do not necessarily have to be made of a ceramic material either. Just make sure that the casting core can be removed without removing the coating on the inside of the workpiece with it.

With regard to tools for producing casting cores or wax patterns, it should be noted that such tools must be corrected by a protective coating thickness in order to ensure a specific wall thickness of the hollow cast component.

Claims (7)

1. A method for producing a hollow cast component (1) having an inner coating (14, 16, 18, 20) in at least one cavity (3, 5, 7, 9) of the hollow cast , wherein the component (1) is cast from a matrix material using a casting core (22) comprising at least one casting core (22) for defining said at least one cavity (3, 5, 7, 9) casting mold, characterized in that the coating material for the inner coating (14, 16, 18, 20) of the component (1) is applied to said at least one casting core (22) before casting, The component (1) is then cast and allowed to solidify using a mold comprising such a casting core (22), after which the casting core (22) is removed from the cavity (3, 5, 7, 9) This is removed in such a way that the coating material is not also removed, so that a hollow casting with an inner coating is obtained. 2. The method according to claim 1, characterized in that as material for the casting core (22) a material is used which is The coating material and matrix material can be chemically removed from the cavities (3, 5, 7, 9). 3. The method as claimed in claim 1 or 2, characterized in that a ceramic material is used as material for the casting core (22). 4. A method as claimed in claim 1 or 2, characterized in that the casting temperature is below the melting temperature of the coating material. 5. The method according to claim 1 or 2, characterized in that the inner coating (14, 16, 18, 20) is a coating of MCrAlY material. 6. The method according to claim 5, characterized in that a high-energy spraying method is used to apply the coating material to the casting core (22). 7. A hollow cast turbine component having at least one closed cavity (3, 5, 7) and a MCrAlY inner coating (14, 16) in the closed cavity (3, 5, 7) , 18).

Images