TURBINE BLADE, METHOD FOR PRODUCING SAME AND METHOD FOR DETERMINING THE POSITION OF A CASTING CORE USED WHEN CASTING A TURBINE BLADE

Abstract

A turbine blade has a blade geometry defined in a coordinate system and at least one cavity which is open to the outside and which has a blade internal surface. At least one planar detection surface, which is accessible for the measuring head of a coordinate measuring device, is formed in the blade internal surface, wherein the at least one planar detection surface is assigned a defined design position and/or a defined design orientation with respect to the coordinate system in which the blade geometry is defined.

Claims

1. A method for producing turbine blades with a blade geometry that is defined in a coordinate system and with at least one outwardly open cavity having a blade inner surface, in which the turbine blades are cast, the method compromising: forming the at least one outwardly open cavity by means of at least one casting core which has a casting core outer surface that forms the blade inner surface and which is removed from the cavity after a casting process, wherein the casting core outer surface has at least one planar reference surface with a defined setpoint position and/or a defined setpoint orientation in relation to the coordinate system in which the blade geometry is defined, and arranging the planar reference surface in the casting core surface such that it forms, in the blade inner surface, at least one planar scanning surface that is accessible for a measuring head of a coordinate measuring device.

2. The method as claimed in claim 1, wherein the outwardly open cavity has at least one opening in an outer surface of the turbine blade, the at least one casting core has a casting core section that forms the at least one opening, and the at least one planar reference surface is formed in or close to the casting core section forming the opening such that the at least one planar scanning surface, formed in the blade inner surface by the at least one planar reference surface, is easily accessible, from outside the turbine blade, for the measuring head of the coordinate measuring device.

3. The method as claimed in claim 2, wherein a planar reference surface is formed in at least one casting core section forming an opening such that there is formed, as the scanning surface, a shoulder which surrounds the corresponding opening in the outer surface of the turbine blade and is recessed with respect to the outer surface of the turbine blade.

4. The method as claimed in claim 1, wherein the at least one casting core has a planar reference surface with a surface normal running in the radial direction of the turbine blade that is to be produced or counter to the radial direction of the turbine blade that is to be produced, and/or the at least one casting core has a planar reference surface with a surface normal running in the axial direction of the turbine blade that is to be produced or counter to the axial direction of the turbine blade that is to be produced, and/or the at least one casting core has a planar reference surface with a surface normal running in the circumferential direction of the turbine blade that is to be produced or counter to the circumferential direction of the turbine blade that is to be produced.

5. The method as claimed in claim 4, wherein the at least one casting core serves for forming a cavity that is open counter to the radial direction of the turbine blade that is to be produced, and the at least one casting core has a planar reference surface with a surface normal running in the radial direction of the turbine blade that is to be produced.

6. The method as claimed in claim 4, wherein the at least one casting core serves for forming a cavity that is open in the radial direction of the turbine blade that is to be produced, and the at least one casting core has a planar reference surface with a surface normal running counter to the radial direction of the turbine blade that is to be produced.

7. A method for determining the position of a casting core used when casting a turbine blade, after completion of the turbine blade in the context of a refurbishment process after operation of the turbine blade, the method comprising: using a turbine blade produced according to the method as claimed in claim 1, and scanning the at least one planar scanning surface in the blade inner surface with the measuring head of a coordinate measuring system in order to determine the position and/or orientation of the at least one planar scanning surface in relation to the blade geometry, and using the determined position and/or orientation of the at least one planar scanning surface to determine the position and/or orientation of the casting core used when casting the turbine blade.

8. A turbine blade comprising: a blade geometry that is defined in a coordinate system and with at least one outwardly open cavity having a blade inner surface, wherein there is formed, in the blade inner surface, at least one planar scanning surface that is accessible for a measuring head of a coordinate measuring device, wherein the at least one planar scanning surface is assigned a defined setpoint position and/or a defined setpoint orientation in relation to the coordinate system in which the blade geometry is defined.

9. The turbine blade as claimed in claim 8, wherein the outwardly open cavity has at least one opening in an outer surface of the turbine blade, and the planar scanning surface is located in or close to the opening such that it is easily accessible, from outside the turbine blade, for a measuring head of a coordinate measuring device.

10. The turbine blade as claimed in claim 9, wherein in the case of at least one opening, the scanning surface is a shoulder which surrounds the corresponding opening in the outer surface of the turbine blade and is recessed with respect to the outer surface of the turbine blade.

11. The turbine blade as claimed in claim 9, wherein the opening is provided with a plate that rests at least partially on the scanning surface.

12. The turbine blade as claimed in claim 8, wherein the blade inner surface has at least one planar scanning surface whose surface normal runs in the radial direction of the turbine blade or counter to the radial direction of the turbine blade, and/or the blade inner surface has at least one planar scanning surface whose surface normal runs in the axial direction of the turbine blade or counter to the axial direction of the turbine blade, and/or the blade inner surface has at least one planar scanning surface whose surface normal runs in the circumferential direction of the turbine blade or counter to the circumferential direction of the turbine blade.

13. The turbine blade as claimed in claim 12, wherein the outwardly open cavity is open counter to the radial direction of the turbine blade, and the at least one planar scanning surface has a surface normal running counter to the radial direction of the turbine blade.

14. The turbine blade as claimed in claim 11, wherein the outwardly open cavity is open in the radial direction of the turbine blade, and the at least one planar scanning surface has a surface normal running in the radial direction of the turbine blade.

15. A gas turbine having a turbine blade as claimed in claim 8.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] FIG. 1 shows an exemplary embodiment for a turbine blade according to the invention, which represents a rotor blade, designed according to the invention, of a gas turbine.

[0026] FIG. 2 shows, schematically, a first casting core for producing the turbine blade shown in FIG. 1.

[0027] FIG. 3 shows, schematically, a detail of a second casting core for producing the turbine blade shown in FIG. 1.

[0028] FIG. 4 shows a second exemplary embodiment for a turbine blade according to the invention, which represents a rotor blade, designed according to the invention, of a gas turbine.

[0029] FIG. 5 shows, schematically, a casting core for producing the turbine blade shown in FIG. 4.

[0030] FIG. 6 shows an opening in the blade root of a turbine blade.

[0031] FIG. 7 shows a plate to be inserted into the opening shown in FIG. 6.

DETAILED DESCRIPTION OF INVENTION

[0032] There follows a description of an exemplary embodiment of the invention, with reference to FIG. 1. The figure shows a turbine blade 1 designed according to the invention, which in the present exemplary embodiment is designed as a rotor blade of a gas turbine. The turbine blade 1 shown comprises a blade root 3, a blade platform 5 and a blade airfoil 7, wherein the blade root 3 and the blade airfoil 7 extend in essentially opposite directions from opposite sides of the blade platform. The turbine blade 1 has a radial direction R which corresponds to the radial direction of the turbine when the turbine blade 1 is installed in a turbine. The turbine blade 1 also has an axial direction A which corresponds to the axial direction of the turbine when the turbine blade 1 is installed in a turbine, and a circumferential direction which runs perpendicular to the radial direction R and perpendicular to the axial direction A and corresponds to a tangent of the circumferential direction at the location of the turbine blade when the turbine blade is installed in a turbine.

[0033] In the present exemplary embodiment, the turbine blade 1 comprises two cavities which are outwardly open, that is to say that they are accessible via openings 11, 12 in the outer surface of the turbine blade 1. The first of these cavities is the cavity 9 which is shown in part by dashed lines in the region of the blade root 3 and which extends through the blade root 3, the blade platform 5 and the blade airfoil 7, and which channels cooling air for cooling the turbine blade 1 during operation of the turbine in which the turbine blade 1 is installed. The cooling air cools the blade and can for example leave the turbine blade 1 via cooling air openings, primarily in the region of the blade airfoil 7 (not shown), for example in order to form a cooling air film over surface regions of the turbine blade.

[0034] The second cavity is formed in the blade tip and consists of a depression 15 which is bounded by a wall 17 projecting beyond the bottom of the depression 15. The depression 15, together with the wall 17, forms what is referred to as a crown of the turbine blade 1 and has an opening 12 in the radial direction R of the turbine blade 1.

[0035] The turbine blade 1 is produced by a casting method which uses a casting mold with two casting cores. In that context, the casting cores each have a casting core outer surface whose shape matches the inner surface of the cavity that is to be formed. During the casting process, the casting cores are placed in the molds for the blade outer surface and form the mold for the blade inner surfaces, that is to say the inner surfaces of the cavity 9, the bottom surface 19 and the inner surfaces of the crown walls 17. The casting cores 21 and 23 are shown schematically in FIGS. 2 and 3, with FIG. 2 showing the casting core 21 for the depression 15 and FIG. 3 showing a detail of the casting core 23 for the cooling air duct 9. The casting core outer surfaces 25, 27 form, when casting the turbine blade 1, the bottom surface 18 of the depression of the crown walls 17, or the inner surface 10 of the cooling air duct 9.

[0036] The casting cores 21, 23 shown in FIG. 2 and FIG. 3 each have a planar reference surface 29, 31, wherein in the present exemplary embodiment the planar reference surface 29 of the casting core 21 for the depression 15 has a surface normal which is oriented counter to the radial direction R of the turbine blade 1 when the casting core is inserted into the mold for the turbine blade 1. The casting core 23 for the cooling air duct 9 also has a planar reference surface 31. In contrast to the planar reference surface 29 of the casting core 21, however, the planar reference surface 31 of the casting core 33 is oriented such that its surface normal points in the radial direction R of the turbine blade 1 when the casting core is inserted into the mold for the turbine blade 1.

[0037] For casting the turbine blade 1, the casting cores 21, 23 are integrated into the mold for the turbine blade 1, and then the mold is filled with a liquid superalloy, typically a nickel-based, cobalt-based or iron-based superalloy. Once the superalloy has solidified, the mold is removed from the turbine blade and then the casting cores 21, 23 are thermally or chemically removed from the depression 15 and, respectively, from the cooling air duct 9, such that the inner surfaces of the cavities 9, 15, that is to say the inner surface 10 of the cooling air duct 9 and the bottom surface 19 and the inner wall surfaces 16 of the crown walls 17, are exposed.

[0038] As already mentioned, the casting cores 21, 23 have planar reference surfaces 29, 31 whose surface normals have a defined orientation in relation to the coordinate system in which the blade geometry is defined, when the casting cores 21, 23 are in the cavities of the turbine blades 1. Since the casting core outer surfaces 25, 27 match the blade inner surfaces, the blade inner surfaces formed with the casting cores 21, 23 also have planar surfaces with defined orientation of the surface normals. In the case of the casting core 21 for the depression 15 in the blade tip, the reference surface 29 forms a planar surface 33 whose surface normal is oriented parallel to the radial direction R of the turbine blade. The planar reference surface 31 of the casting core 23 forms, in the vicinity of the opening 11 in the underside 13 of the blade root 3, a planar surface 35 whose surface normal is oriented antiparallel to the radial direction R of the turbine blade. These two planar surfaces, that is to say the planar surface 33 in the depression 15 and the planar surface 35 in the region of the opening 11 in the underside 13 of the blade root 3, represent easily accessible planar scanning surfaces for scanning with the measuring head 37 of a coordinate measuring device.

[0039] When the casting cores 21, 23 are correctly inserted into the casting mold for casting the turbine blade 1, the surface normal 33 is therefore oriented parallel to the radial direction and the surface normal of the planar scanning surface 35 is oriented counter to the radial direction. Furthermore, both scanning surfaces have a defined radial position. If, by contrast, the casting cores 21, 23 deviate in position and/or orientation from their setpoint position and/or the setpoint orientation in the casting mold for casting the turbine blade 1, this is reflected in the radial position and/or the orientation of the planar scanning surfaces 33, 35 in the depression 15 or in the cooling air duct 9, in relation to the blade geometry. The coordinate measuring device serves to determine the position and/or orientation of the respective planar scanning surfaces in relation to the blade geometry. Since the planar scanning surfaces 33, 35 represent surfaces that match the planar reference surfaces 29, 31 of the casting cores 21, 23, the position and orientation of the planar scanning surfaces 33, 35 scanned with the measuring head 37 can be used to determine the position and orientation of the casting cores 21, 23 during the casting process.

[0040] If, during the casting process, the casting cores 21, 23 have deviated in position and/or orientation from their setpoint position or setpoint orientation, this can be observed in the finished turbine blade. Since the position and/or orientation of the casting cores during casting of the turbine blade 1 can be determined non-destructively from the finished turbine blade 1, it is possible to examine a large number of turbine blades during mass production in the manner of spot checks, such that turbine blades can be checked at short intervals. It is thus possible for changes in the position and/or orientation of the casting cores 21, 23, arising during mass production, to be identified early, which permits prompt correction of the position and/or orientation of the casting cores for the subsequent casting processes of the mass production. Any deviations in the position and/or orientation of the casting cores 21, 23 can thus be corrected before they exceed a predefined degree, which makes it possible to improve the quality of the mass-produced turbine blades, in particular with regard to their wall dimensions and with regard to their thermodynamic transition zones. In that context, particularly critical wall dimensions are the wall thicknesses in the region of the blade airfoil and/or the wall thickness in the region of the bottom surface 19 of the depression 15, which is also referred to as the crown bottom height.

[0041] Although in the present exemplary embodiment the reference surfaces of the casting cores 21, 23 have surface normals with an orientation that runs parallel or antiparallel to the radial direction, the casting cores 21, 23 can additionally or alternatively also have reference surfaces whose surface normals run parallel or antiparallel to the axial direction A of the turbine blade 1. The planar scanning surfaces formed with planar reference surfaces of this type then have surface normals which, in the case of correct position and orientation of the casting cores 21, 23, run antiparallel or parallel to the axial direction. There is equally the possibility, additionally or alternatively, to provide in the casting cores 21, 23 planar reference surfaces whose surface normals run parallel or antiparallel to the circumferential direction of the turbine blade 1. The planar scanning surfaces thus formed in the inner surfaces of the turbine blade then have surface normals which run antiparallel or parallel to the circumferential direction of the turbine blade 1.

[0042] There follows a description of a second exemplary embodiment of the invention, with reference to FIG. 4. The figure shows a turbine blade 100 designed according to the invention, which as in the first exemplary embodiment is designed as a rotor blade of a gas turbine. Elements of the turbine blade of FIG. 4 which correspond to elements of the turbine blade of FIG. 1 are provided with the same reference numerals as in FIG. 1 and will not be explained anew, in order to avoid repetitions. The description of the second exemplary embodiment is therefore limited to the differences with respect to the first exemplary embodiment.

[0043] The turbine blade of the second exemplary embodiment differs from that of the first exemplary embodiment essentially in that, in addition to at least one opening 111 of the cooling air duct 109 which serves to supply cooling air into the cooling air duct 109, there is also at least one opening 112 in the blade root 3, which does not serve to supply cooling air into the cooling air duct 109, but merely represents an auxiliary opening which serves to secure the casting core 123 during the production process for the turbine blade 1. This auxiliary opening 112 has a scanning surface 135 which, in the present exemplary embodiment, is designed as a planar recess 135 surrounding the auxiliary opening 112. Thus, the auxiliary opening 112 is surrounded by a depression into which a sealing plate 137 can be sunk after completion of the turbine blade 101 and after scanning of the scanning surface to determine the core position. The sealing plate 137 can then be secured to the scanning surface 135, for example by spot soldering or spot welding. The position of the sealing plate 137 in the depression means that it does not stand proud of the underside 13 of the blade root, so that the sealing plate 137 does not impair the cooling air flow duct formed between the underside 13 of the blade root and the bottom of the slot of a rotor disk slot (not shown) into which the turbine blade 1 is inserted. Otherwise, the turbine blade 101 of the second exemplary embodiment does not differ from the turbine blade 1 of the first exemplary embodiment.

[0044] A casting core 123 as can be used to produce the turbine blade shown in FIG. 4, is shown in FIG. 5. This comprises a first core projection 124 for producing the opening 111 and a second core projection 125 for producing the opening 112. In the event that more than two openings are to be formed, the core 123 has a corresponding number of core projections. In the present exemplary embodiment, the second core projection 125 has, at its outer end, a broadened portion 130 which is equipped with a surrounding planar surface 131 that serves to form the surrounding scanning surface 135. Since, in the present exemplary embodiment, the auxiliary opening 112 is open radially inward, the surface normal of this surrounding planar surface 131 points radially outward. Otherwise, the casting core 123 of the second exemplary embodiment does not differ from the casting core 23 of the first exemplary embodiment.

[0045] In the present exemplary embodiment, the auxiliary opening can also be a cooling air inlet opening into the internal cooling air duct 109 of the turbine blade 101. In this case, the depression formed around the cooling air inlet opening can accommodate, instead of a sealing plate, a plate which serves to define a certain flow cross section for the flow through the opening into the internal cooling air duct. In the present exemplary embodiment, it is then possible to use a sealing plate or a plate 139 defining a certain flow cross section even if the scanning surface is a surface 135A, 135B, 135C which, although recessed with respect to the outer surface of the blade root 3, is not continuous around the opening 143 (see FIG. 6). This makes it possible, with a certain positioning of the scanning surfaces 135A, 135B, 135C at the rim of the opening 143, to predefine a certain orientation of a plate 139 when inserting the plate, for example in order to fix the orientation of a flow cross section 141. When the scanning surface also serves for securing the plate, it is advantageous if there are at least two scanning surfaces around part of the opening. These can advantageously be opposite one another. In the case of a circular opening, it is then possible for, for example, three scanning surfaces 135A, 135B, 135C to be present, which each surround the opening over a certain angle and are distributed evenly or unevenly around the opening (see FIG. 7). In particular, the number and/or size of such scanning surfaces 135A, 135B, 135C arranged around an opening can vary between different batches of turbine blades or between different openings in a turbine blade. It is thus possible for the rim of the opening to serve as a type of lock into which only certain plates can be inserted, in the manner of a key.

[0046] The present invention has been extensively described on the basis of exemplary embodiments for explanatory purposes. However, a person skilled in the art will recognize that deviations from the described embodiments are possible. It is thus possible for the surface normal of a reference surface of a casting core to have a different orientation than the orientations specified in the context of the exemplary embodiment. However, the stated orientations are advantageous with regard to the coordinate system in which the blade geometry of the turbine blade 1 is defined. Equally, the invention can also be used in the context of turbine blades other than the illustrated rotor blade of a gas turbine. For example, guide vanes of gas turbines typically have at least one cavity with two openings located at opposite radial ends of the guide vane, in the region of the head airfoils of the guide vanes. These openings generally serve as inlet and outlet openings for cooling air for cooling the guide vanes. In the region of the inlet opening and/or in the region of the outlet opening, it is possible by means of one or more planar reference surfaces to form planar scanning surfaces for determining the position and orientation of the casting core, or of the casting cores when using multiple casting cores. Also, the scanning surface described in relation to the second exemplary embodiment and forming a depression can also be present if, in the blade root, there is only a single cooling air inlet opening into the cooling air duct. Also, it is not absolutely necessary to insert a plate into the depression formed by the scanning surface. Furthermore, it is in principle possible, in the case of turbine blades with an undercut trailing edge, to configure the casting cores used to form the undercut such that planar scanning surfaces are formed in the region of the undercut. The present invention is therefore not intended to be limited to specific feature combinations of the exemplary embodiment, but solely by the appended claims.