METHOD FOR CASTING A TURBINE BLADE

Abstract

Provided is a method for casting a turbine blade including a blade root, a blade extending in the radial direction from the blade root, and a hollow chamber that passes through the turbine blade in the radial direction from the blade root up to the free end of the blade, wherein the method is carried out using a casting molding defining an outer surface of the turbine blade and using a core accommodated in the casting mold and aligned with positioning means, wherein at least one second core is accommodated in the molding part and aligned with positioning means, wherein the first core and the second core are spaced at a distance from one another and behind one another in the radial direction in the casting mold in such a way that a gap is formed between said cores.

Claims

1. A method for casting a turbine blade having a blade root, a blade airfoil extending in a radial direction from the blade root, and a cavity which passes through the turbine blade in the radial direction from the blade root to a free end of the blade airfoil, the method comprising: utilizing a casting mold defining an outer surface of the turbine blade and a first core that is received in the casting mold and is oriented with a positioning means; wherein at least one second core is received in the casting mold and is oriented with the positioning means, wherein the first core and the second core are arranged one behind the other in the radial direction and are spaced apart from one another in the casting mold such that a gap is formed between the first core and the second core.

2. The method as claimed in claim 1, wherein the first core and the second core each comprise multiple core sections that extend in the radial direction and are arranged next to and spaced apart from one another, the multiple core sections being connected to one another by means of connecting pins.

3. The method as claimed in claim 1, wherein the gap extends essentially transversely to the radial direction.

4. The method as claimed in claim 3, wherein a size of the gap decreases evenly inward from the casting mold.

5. The method as claimed in claim 1, wherein guide pins extend between the first core and the second core, the guide pins being received in corresponding bores of the first core and of the second core so as to be displaceable in their longitudinal direction, further wherein the guide pins extend parallel to one another and/or in the radial direction.

6. The method as claimed in claim 1, wherein spacer pins, which extend between the first core and the casting mold and/or between the second core and the casting mold), are used as the positioning means, further wherein at least some of the spacer pins are arranged adjacent to the gap.

7. The method as claimed in claim 1, wherein as positioning means, use is made of at least one tongue which is designed in one piece with the first core or the second core and projects outward therefrom in a direction of the casting mold, is arranged in a region of the free end of the blade airfoil or in a region of the blade root and extends in the radial direction.

8. The method as claimed in claim 7, wherein the at least one tongue is received in the casting mold and is in engagement therewith.

9. The method as claimed in either of claim 7, wherein the at least one tongue has a recess extending transversely to the radial direction and/or a projection extending transversely to the radial direction.

10. The method as claimed in claim 1, wherein after casting, connecting openings between a cavity created by the first core and a cavity created by the second core are bored in a rib created by the gap.

11. A turbine blade having a blade root, a blade airfoil extending in a radial direction from the blade root and a cavity which passes through the turbine blade in the radial direction from the blade root to a free end of the blade airfoil, wherein the cavity is divided by at least one rib which extends transversely to the radial direction and is provided with connecting openings, wherein the rib is arranged in a central region of the turbine blade, with regard to the radial direction.

12. The turbine blade as claimed in claim 11, wherein the turbine blade has a length of at least one of: at least 70 cm, at least 80 cm, and at least 100 cm.

Description

BRIEF DESCRIPTION

[0022] Some of the embodiments will be described in detail, with references to the following figures, wherein like designations denote like members, wherein:

[0023] FIG. 1 is a side cross-sectional view of a turbine blade according to one embodiment of the present invention, which has been produced using a method according to one embodiment of the present invention;

[0024] FIG. 2 is a side cross-sectional view of two cores arranged in a casting mold for the purpose of producing the turbine blade shown in FIG. 1; and

[0025] FIG. 3 is a radial cross-sectional view of the first core which is shown in FIG. 2 and is arranged in a casting mold, along the line III-III.

DETAILED DESCRIPTION

[0026] FIG. 1 shows a turbine blade 1 for a gas turbine, which has been produced using a method according to embodiments of the present invention. The turbine blade 1 comprises a blade root 2 and a blade airfoil 3 that extends in the radial direction R from the blade root 2. The turbine blade 1 has an overall length in the radial direction of at least 70 cm, but can advantageously be at least 80 cm and preferably at least 100 cm long. In the present case, four cavities 4, which each pass through the turbine blade 1 in the radial direction from the blade root 2 to a free end 5 of the blade airfoil 3, extend through the turbine blade 1, where the number of cavities 4 can vary. The cavities 4 are divided by a rib 6 which extends transversely to the radial direction R and is arranged in a central region of the turbine blade 1, with regard to the radial direction. Accordingly, four connecting openings 7 are provided in the rib 6 and connect mutually aligned cavities 4 on either side of the rib 6. Four inlet openings 8 are formed at the blade root 2, and four outlet openings 9 are provided at the free end 5 of the blade airfoil 3.

[0027] During operation of the gas turbine, a cooling fluid flows radially outward through the inlet openings 8 in to the turbine blade 1 and through the cavities 4 created by the first core 12, the connecting openings 7 and the cavities created by the second core 13 to the free end 5 of the blade airfoil 3. The cooling fluid then leaves the turbine blade 1 through the outlet openings 9, and thus the heat absorbed by the cooling fluid is removed from the turbine blade 1.

[0028] FIGS. 2 and 3 show a casting mold 10 which is used for the production of the turbine blade 1 and which defines an outer surface 11 of the turbine blade 1. The casting mold 10 receives a first core 12 and a second core 13 that are arranged one behind the other in the radial direction and are spaced apart from one another in the casting mold 10. Each core comprises multiple core sections 14 that extend in the radial direction R and are arranged next to and spaced apart from one another transversely to the radial direction R. The core sections 14 of a core 12, 13 are respectively connected to one another by means of connecting pins 15. A gap 16 extending essentially transversely to the radial direction is formed between the first core 12 and the second core 13. The size of the gap 16 decreases evenly inward from the casting mold 10, such that in a side cross-sectional view the gap is essentially in the shape of two wedges pointing toward one another. The shape of the gap 16 depends on the shape of the turbine blade and expected deformations and/or displacements of the cores 12, 13, and can vary. Guide pins 17 extend between the first core 12 and the second core 13, which pins are received in corresponding bores 18 of the first core 12 and of the second core 13 so as to be displaceable in their longitudinal direction, wherein the guide pins 17 extend parallel to one another in the radial direction R.

[0029] The first core 12 and the second core 13 are oriented in the casting mold 10 with positioning means 19, 20, 21. Spacer pins 19, which extend between the first core 12 and the casting mold 10 and/or between the second core 13 and the casting mold 10, are used as positioning means. In that context, some of the spacer pins 19 are arranged adjacent to the gap 16. As further positioning means, a tongue 20 is designed in one piece with the first core 12 in the region of the blade root 2 and extends in the radial direction. As further positioning means, two tongues 21 that are integral with the second core 13 project outward therefrom in the direction of the casting mold 10 from the free end 5 of the blade airfoil 3, and extend in the radial direction. The tongues 20, 21 are received in the casting mold 10 and are in engagement therewith. The tongue 20 has two recesses 22 that extend transversely to the radial direction R and are arranged on opposite sides of the tongue 20. The two tongues 21 each have a projection 23 extending transversely to the radial direction. In order to fix the two cores 12, 13 in the radial direction, the tongues 20, 21 can also have undercuts in addition to recesses 22 or projections 23. Optionally, further outlet openings can be provided by casting on the trailing edge side of the turbine blade 1, using appropriately positioned opening pins 24 that extend between the cores 12, 13 and the casting mold 10. Alternatively, such outlet openings can also be formed afterwards by mechanical machining such as drilling.

[0030] During casting, the interspaces formed between the cores 12, 13 and the casting mold 10, or between the respective core sections 14, are filled with a heated, liquid casting material. In the process, the core sections 14 of the first core 12 and of the second core 13 are heated by the casting material and expand also in the radial direction. The longitudinal expansion of the first core 12 or of the second core 13 causes a constriction of the gap 16 since the core sections 14 of the first core 12 are held radially securely in the casting mold 10 in the region of the blade root 2 and the tongues 21 of the second core 13 are held radially securely in the region of the free end 5 of the blade airfoil 3. In the case of a twisted turbine blade 1, the different longitudinal expansion (owing to the different longitudinal extent) of the cores 12, 13 means that the gap 16 narrows more in the lateral edge regions of the turbine blade 1 than in the middle. As a result, this leads to a flattening of the wedge shape of the gap 16 and thus of the rib 6 of the turbine blade 1, which is evident when comparing FIGS. 1 and 2. The change in the size of the gap 16 during casting depends on the shape of the turbine blade 1 and of the cores 12, 13, and can vary.

[0031] The guide pins 17 create connecting openings 7 which connect mutually aligned cavities 4 on either side of the rib 6 formed by the casting material that has solidified in the gap 16, and through which the cooling fluid can flow from the cavities created by the first core 12 into the cavities created by the second core 13. If, by contrast, no guide pins 17 are used, the rib 6 separates the cavities 4 created by the first core 12 and by the second core 13 in the manner of a partition, so that a cooling fluid would not be able to flow through the turbine blade 1. In this variant, connecting openings 7 are therefore introduced subsequently into the rib 6 by drilling, in order to interconnect mutually aligned cavities 4 created by the first core 12 and by the second core 13.

[0032] One advantage of the method according to embodiments of the invention is that, when using two cores 12, 13, each core 12, 13 is shorter, which on one hand facilitates production and handling of the core and on the other hand reduces its longitudinal expansion. This makes it possible to reliably cast longer turbine blades 1 through which pass cavities 4 that extend from the blade root 2 to the free end 5 of the blade airfoil 3. Thus, the method according to embodiments of the invention makes it possible to produce long turbine blades 1 that can be cooled effectively. This permits a high temperature of the hot gas, which is associated with high efficiency of the gas turbine. In addition, the rib 6 that is formed in the gap 16 in the method according to embodiments of the invention can substantially damp the natural vibration of the turbine blade 1, and avoid a fault in the gas turbine.

[0033] Although the invention has been illustrated and described in greater detail with reference to the preferred exemplary embodiment, the invention is not limited to the examples disclosed, and further variations can be inferred by a person skilled in the art, without departing from the scope of protection of the invention.

[0034] For the sake of clarity, it is to be understood that the use of a or an throughout this application does not exclude a plurality, and comprising does not exclude other steps or elements.