EP2460604A1

EP2460604A1 - Method and apparatus for casting a hollow component of a turbomachine

Info

Publication number: EP2460604A1
Application number: EP10193284A
Authority: EP
Inventors: Fathi Ahmad; Oliver Lüsebrink; Thomas Malow; Uwe Paul
Original assignee: Siemens AG
Current assignee: Siemens AG
Priority date: 2010-12-01
Filing date: 2010-12-01
Publication date: 2012-06-06

Abstract

An apparatus (1) for casting a hollow component of a turbomachine from a melted material is provided. The apparatus includes a core (2), a shell (3) surrounding the core (2) forming a cavity (6) therebetween for receiving the melted material, wherein a boundary (7) of the cavity (6) is defined by the core (2) and the shell (3), a plurality of separator elements (4, 10, 15, 18) for separating the core (2) and the shell (3) having a spherical portion (12, 16, 17, 19), wherein the boundary (7) includes indentations (5) to receive the spherical portion (12, 16, 17, 19) of the separator elements(4, 10, 15, 18).

Description

The present invention relates to a method and an apparatus for casting a hollow component of a turbomachine.
Casting process such as investment casting process, or lost wax process is used to produce hollow components, such as a blade or a vane of a turbomachine. During the casting process for a hollow component, it is important that a core, which is used to cast hollow components, does not shift within a shell surrounding the core, to prevent the component with wall that is too thick or too thin for later application. Such components are of critical importance in aerospace and power generation industries, which require high quality parts which meet close tolerances to provide peak performance and prevent catastrophic failure in an aircraft or power generator.
Currently, investment casting pins made of a meltable material such as Platinum (Pt), Nickel (Ni), Molybdenum (Mo) or their alloys are employed to maintain the core at fixed position during casting and are sometimes coated with oxidation resistant material to prevent oxidation during high temperatures. Such types of casting pins are known from US patent number 7036556 . However, casting pins produce high stress on the core and the shell during core production or casting process, which may sometimes result in core or shell damage or even breakage. Furthermore, the casting pins have to be embedded in the core which may also result in core breakage. In addition, such pins can be a reason for metallurgical defects in the microstructure of the cast component. Furthermore, the pins may also break during model and shell production as well as during the casting process. It is therefore an object of the present invention to reduce stress in the core and the shell due to casting pins during the core production or casting process.
The object is achieved by providing an apparatus for casting a hollow component of a turbomachine according to claim 1 and a method for casting the hollow component of the turbomachine according to claim 14.
By having a spherical portion in plurality of separator elements, such that the spherical portion is receivable at indentations in boundary of a cavity formed between the core and the shell, the spherical portion of the separator element reduces stress on the core and the shell since the spherical portion exerts least stress at the boundary of the cavity. In addition, spherical portion provides stability to the separator elements by preventing them to leave the indentations during casting process and are more durable as compared to casting pins.
In one embodiment, the hollow component is a blade or a vane of a turbomachine.
In one embodiment, the separator element has two spherical portions receivable at the core and the shell respectively. Stress is reduced at the core and the shell due to the spherical portions.
The separator elements extend from the core to the shell. Extent of separator elements determines the width of the cavity formed between the core and the shell.
In one embodiment, the separator element is spherical in shape which reduces stress on the core and the shell during casting process.
In another embodiment, the separator element is a hemispherical shell, which prevents damage or even breakage of the core and the shell due to thermal expansion during casting process. Furthermore, a thin wall component is created using the hemispherical shell shaped separator elements.
The hemispherical shell shaped separator element includes a brim which defines a thickness of the wall of the hollow component.
In another embodiment, the separator element is a cylinder with spherical ends on at least one side receivable at the indentations on the boundary of the cavity. Spherical portions reduce stress at the core and the shell.
In one embodiment, the indentation is present in the core to securely place the separator element and have a smooth outer surface of the hollow component.
In another embodiment, the indentation is present in the shell to enable a smooth inner surface of the hollow component without the need of further processing.
The depth of indentation is less than half the width of the cavity to enable a wall formation of the hollow component.
The separator element is formed from a second material which is meltable by contact with the melted material. This enables the wall of the hollow component to be formed from the second material and the melted material.
A pressure difference is created at the inside of the indentation by an opening. The pressure difference helps in holding the spherical portion of the separator element inside the indentation thereby providing a stable arrangement.
The above-mentioned and other features of the invention will now be addressed with reference to the accompanying drawings of the present invention. The illustrated embodiments are intended to illustrate, but not limit the invention. The drawings contain the following figures, in which like numbers refer to like parts, throughout the description and drawings.

FIG. 1 is a sectional view of an exemplary apparatus for casting a hollow component;
FIG. 2 is a diagrammatical illustration of an embodiment of a separator element;
FIG. 3 is a diagrammatical illustration of another embodiment of the separator element;
FIG. 4 is a diagrammatical illustration of another embodiment of the separator element; and
FIG. 5 is a partial view of the core with an opening.

FIG. 1 is a sectional view of an exemplary apparatus 1 for casting a hollow component of a turbomachine, such as a gas turbine. It may be noted that the apparatus may also be used for casting components of a turbofan and the like. The exemplary apparatus and the method of casting the hollow component as described in the present application can be applied to any device or article which is a hollow component.
A core 2 is surrounded by a shell 3 in a manner such that a cavity 6 is formed between the core 2 and the shell 3. During the casting process the cavity 6 receives a melted material which on solidification forms a hollow component. A boundary 7 of the cavity 6 includes one or more indentations 5. It may be noted that the boundary 7 is defined by the cavity 6 between the core 2 and the shell 3. The indentations 5 are present in the core 2, the shell 3 or both the core 2 and the shell 3. A plurality of separator elements 4 for separating the core 2 and the shell 3 are depicted. The separator element 4 is receivable at the indentations 5 along the boundary 7 of the cavity 6. The separator element 4 includes a spherical portion which is receivable at the indentation 5. The separator element 4 defines the width of the cavity 6.
In accordance with aspects of the present technique, the core 2 is in the shape of a hollow area of an airfoil. The core 2 may be formed from a ceramic material. As previously noted, the shell 3 surrounds the core 2 to form a cavity 6 on which the melted material which is at a high temperatures from about 1300 degrees Centigrade to about 1850 degrees Centigrade is poured and therefore the shell 3 is also formed from a material such as ceramic or other material capable of withstanding such high temperatures.
The separator elements 4 are used to support the core 2 and the shell 3 and also maintain the core 2 and the shell 3 accurately at a fixed position during the casting process. In one embodiment, the separator element 4 is a sphere (see FIG. 1) formed from a metal or metal alloy. The separator element 4 extends from the core 2 to the shell 3. More particularly, the separator element 4 is receivable at the indentation 5 in the core 2 and the shell 3. The indentation 5 in the core 2 and the shell 3 maintain the separator element 4 at the fixed position which is achieved due to spherical shape receivable at the indentation 5.
It may be noted that the depth of the indentation 5 is less than half the width of the cavity 6 formed between the core 2 and the shell 3 which ensures the existence of a wall for the hollow component.
In one embodiment, the separator element 4 is formed from a material which is same as the melted material for casting the hollow component. Alternatively, the separator element 4 is formed from a second material which is meltable when coming in contact with the melted material used for casting. More particularly, the melting point of the second material is less than or equal to the melting point of the melted material which ensures that the second material is melted and also forms the wall of the hollow component on solidification.
Additionally, the separator element 4 is coated with a corrosion resistant material which may include a non-oxidizing metal or a metal which resists oxidation at high temperatures, such as, but not limited to platinum. Corrosion resistant material prevents formation of oxidation layers during mold firing and subsequent casting process. Coating on the separator element 4 may be applied using methods such as, but not limited to, electroplating, vacuum metalizing, vapor deposition and slurry deposition.
In accordance with aspects of the present technique, the thickness of the wall of the hollow component may be modified by altering the dimensions of the separator element 4. As an example, if the wall of the hollow component is thicker than required, the dimensions of the separator element 4, such as the diameter, are increased to make the wall thinner. Alternatively, if the thickness of the wall of the hollow component is greater than the required thickness, the dimensions of the separator element 4 are decreased to increase the thickness of the wall of the hollow component.
FIG. 2 is a diagrammatical illustration of an embodiment of the separator element 4 of FIG. 1. As depicted, the separator element 10 is in the form of a hemispherical shell. The hemispherical shell has a spherical portion 12, which is receivable at the indentation 5 in the core or the shell.
In addition, the separator element 10 includes a brim 11 having a thickness forming a base of the separator element 10. The brim 11 is positioned parallel to the cavity formed between the core and the shell. The brim 11 defines the thickness of the cavity between the core and the shell. The exemplary separator element 10 may be used for casting of hollow component with a thin wall. However, it may be noted that the width of the brim 11 ensures the thickness of the wall of the hollow component since the brim 11 defines the width of the cavity, that is, the distance between the core and the shell.
FIG. 3 illustrates another embodiment of the separator element. As depicted, the separator element 15 is cylindrical in shape with spherical ends. The separator element 15 has a first spherical portion 16 and a second spherical portion 17 receivable at the indentations 5 in the core and the shell respectively. The spherical portions 16, 17 of the separator element 15 reduce stress on the shell and the core during the shell firing and subsequent casting process.
FIG. 4 illustrates another embodiment of the separator element 4 of FIG. 1, in accordance with aspects of the present technique. As depicted, the separator element 18 is a cylinder and includes a single spherical portion 19 and a flat portion 20. The spherical portion 19 is receivable at the indentation 5 (see FIG. 1) in the core or the shell. The spherical portion 19 maintains the separator element 18 at the fixed position. The flat portion 20 provides a smooth surface on a wall of the hollow component without the need of further processing. More particularly, if the spherical portion 19 is secured in the indentation on the core, the out surface of the hollow component would be a smooth surface. Alternatively, if the spherical portion 19 is secured in the indentation on the shell, the inner surface of the hollow component would be a smooth surface.
FIG. 5 illustrates a partial view of the core 2 with an opening 21 in accordance with aspects of the present technique. The core 2 includes an indentation on which the separator element 4 is receivable. To maintain the separator element 4 at the indentation 5, the core 2 is provided with the opening 21 to create a pressure difference between the inside of the indentation and the outside of the core 2. The pressure difference may be created by creating a vacuum inside the indentation 5 which maintains the separator element 4 inside the indentation 5. It may be noted that a pump may be used to create a low pressure inside the indentation 5, for example.
In accordance with aspects of the present technique, a method for casting a hollow component of a turbomachine is also provided. The method includes surrounding a core 2 with a shell 3 such that a cavity 6 is formed between the core 2 and the shell 3, separating the core 2 and the shell 3 through a plurality of separator elements 4 by positioning the separator elements 4 in indentations 5 on a boundary 7 of the cavity 6, the separator elements 4 are extended from the core 2 to the shell 3. Thereafter, a melted material is introduced or poured into the cavity 6. The melted material dissolves the separator elements 4 and forms the hollow component on solidification.

Claims

An apparatus (1) for casting a hollow component of a turbomachine from a melted material, comprising:
- a core (2),

- a shell (3) surrounding the core (2) forming a cavity (6) therebetween for receiving the melted material, wherein a boundary (7) of the cavity (6) is defined by the core (2) and the shell (3),

- a plurality of separator elements (4, 10, 15, 18) for separating the core (2) and the shell (3) having a spherical portion (12, 16, 17, 19),
wherein the boundary (7) comprises indentations (5) to receive the spherical portion (12, 16, 17, 19) of the separator elements(4, 10, 15, 18).
The apparatus according to claim 1, wherein the hollow component is a blade or vane.
The apparatus according to claims 1 and 2, wherein the separator element (15) has two spherical portions (16, 17) receivable at the core (2) and the shell (3) respectively.
The apparatus according to any of the claims 1 to 3, wherein the separator element (4, 10, 15, 18) extends from the core (2) to the shell (3).
The apparatus according to any of the claims 1 to 4, wherein the separator element (4) is spherical in shape.
The apparatus according to any of the claims 1 to 4, wherein the separator element (10) is a hemispherical shell.
The apparatus according to claim 6, wherein the hemispherical shell comprises a brim (11) positioned in a direction parallel to the boundary (7) of the cavity (6).
The apparatus according to any of the claims 1 to 4, wherein the separator element (15, 18) is a cylinder with spherical ends (16, 17, 19) on at least one side.
The apparatus according to any of the claims 1 to 7, wherein the indentation (5) is present in the core (2).
The apparatus according to any of the claims 1 to 9, wherein the indentation (5) is present in the shell (3).
The apparatus according to any of the claims 1 to 10, wherein a depth of the indentation (5) is less than half the width of the cavity (6).
The apparatus according to any of the claims 1 to 11, wherein the separator element (4, 10, 15, 18) is formed from a second material which is meltable by contact with the melted material.
The apparatus according to any of the claims 1 to 12, wherein the indentation (5) comprises an opening for creating a pressure difference to hold the spherical portion of the separator element (4, 10, 15, 18) inside the indentation.
A method for casting a hollow component of a turbomachine comprising:
- surrounding a core (2) with a shell (3) forming a cavity (6) therebetween,

- separating the core (2) and the shell (3) through a plurality of separator elements (4, 10, 15, 18) by positioning the separator elements (4, 10, 15, 18) in indentations (5) on a boundary (7) of the cavity (6), and

- introducing a melted material in the cavity (6) to form the hollow component.
The method according to claim 14 further comprising extending the separator elements (4, 10, 15, 18) from the core (2) to the shell (3).