Method and device for repairing a damaged blade tip of a turbine blade which is armor-plated and provided with a blade coating

Abstract

The invention relates to a method for repairing a damaged blade tip of a turbine blade which is armor-plated and provided with a blade coating, of a thermal gas turbine. The method according to the invention comprises the steps of removing a blade tip armor plating of the turbine blade at least in the region of the damaged blade tip and producing a repair surface (12), removing only a part of the blade coating of the turbine blade in the region of the repair surface while preserving a part of the blade coating separated from the repair surface (14), restoring the blade tip reinforcement (20), and restoring the blade coating in the region of the repaired blade tip (22). The invention furthermore relates to a device for carrying out such a method.

Claims

1. A method for repairing a damaged blade tip of a turbine blade of a thermal gas turbine, which blade is provided with an airfoil coating and with a blade tip armor plating, wherein the method comprises: removing the blade tip armor plating of the turbine blade at least in a region of the damaged blade tip and producing a repair surface; removing only a part of the airfoil coating of the turbine blade in a region of the repair surface while preserving a part of the airfoil coating separated from the repair surface; repairing the damaged blade tip; restoring the blade tip armor plating; and restoring the airfoil coating in the region of the repair surface.

2. The method of claim 1, wherein before restoration of the blade tip armor plating repair material is applied onto the repair surface and a target contour of the blade tip is restored.

3. The method of claim 2, wherein the target contour of the blade tip is restored by a separating method after application of the repair material.

4. The method of claim 1, wherein a repair material is applied onto the repair surface by a welding method.

5. The method of claim 4, wherein the welding method comprises deposit welding.

6. The method of claim 1, wherein the blade tip armor plating is restored by a joining method.

7. The method of claim 6, wherein the joining method comprises soldering.

8. The method of claim 1, wherein the blade tip armor plating is restored by producing and/or applying a particle composite material having embedded hard material particles onto the blade tip.

9. The method of claim 8, wherein the hard material particles comprise cubic boron nitride (CBN).

10. The method of claim 1, wherein the airfoil coating is restored by a coating method.

11. The method of claim 10, wherein the coating method comprises diffusion coating.

12. The method of claim 1, wherein the blade tip armor plating and/or the airfoil coating is at least partially removed by a separating method.

13. The method of claim 1, wherein a repair material is applied onto the repair surface by an additive manufacturing method.

14. The method of claim 1, wherein a distance between the preserved part of the airfoil coating and the repair surface is not greater than 15% of a height of the blade body.

15. The method of claim 1, wherein a distance between the preserved part of the airfoil coating and the repair surface is not greater than 12% of a height of the blade body.

16. The method of claim 1, wherein a distance between the preserved part of the airfoil coating and the repair surface is not greater than 10% of a height of the blade body.

17. The method of claim 1, wherein a distance between the preserved part of the airfoil coating and the repair surface is not greater than 7% of a height of the blade body.

18. The method of claim 1, wherein a distance between the preserved part of the airfoil coating and the repair surface is not greater than 5% of a height of the blade body.

19. The method of claim 1, wherein a distance between the preserved part of the airfoil coating and the repair surface is not greater than 4% of a height of the blade body.

20. The method of claim 1, wherein a distance between the preserved part of the airfoil coating and the repair surface is not greater than 3% of a height of the blade body.

Description

BRIEF DESCRIPTION OF THE DRAWING

(1) The single FIGURE shows a flow chart of a method according to the invention for repairing a damaged blade tip of an armor-plated turbine blade provided with a blade coating.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

(2) The single FIGURE shows a flow chart of a method according to the invention for repairing a damaged blade tip of an armor-plated turbine blade provided with a blade coating, for example of a high-pressure turbine blade (HPT blade). In a first step 10, the damaged turbine blade is provided and prepared for the repair. To this end, in step 12 the blade tip armor plating of the turbine blade is removed at least in the region of the damaged blade tip, and a repair surface is produced. This may for example be done by a machining operation, for instance grinding. In step 14, the blade coating (airfoil coating) of the turbine blade is removed only in the region of the repair surface while preserving a part of the blade coating separated from the repair surface, in order to prepare the turbine blade for subsequent welding (step 16). This step may also, for example, be carried out by a machining operation. The repair method therefore obviates full decocting of the turbine blade, and therefore does not lead to a loss of wall thickness and strength, particularly of the blade body which is heavily loaded during operation. The repair is therefore substantially less aggressive for the component and can readily be carried out several times on the same turbine blade without problems.

(3) In the following step 16, repair material is applied onto the repair surface by deposit welding, and in an in principle optional step 18, is recontoured by machining (for example by grinding) in order to restore an original or target contour of the blade tip. If the desired contour of the blade tip has already been produced in step 16, step 18 is not necessary. If the pattern of damage in a specific case does not require reconstruction with repair material, step 16 may also in general be omitted.

(4) In step 20, the blade tip armor plating is then restored by a step preferably likewise acting only locally on the turbine blade, for example by local soldering. The blade tip armor plating may, for example, be produced from cubic boron nitrite (CBN) which is embedded in a matrix.

(5) In order to conclude the repair, in step 22, by locally limited touch-up diffusion coating, the blade coating, and therefore the protection of the turbine blade against thermal and chemical influences, is restored in the region of the repaired blade tip.

(6) With the procedure proposed, several steps may be obviated, in particular full decoating and subsequent recoating of the blade body, so that time and costs can be saved to a significant extent. Besides reducing the scrappage rate of reinforced turbine blades, in particular HPT blades, and the very high cost savings associated with this, an improved running time behavior of the only locally repaired turbine blade is also achieved because of a repair carried out relatively nonaggressively, in combination with relatively low repair costs.

(7) The parameter values indicated in the documents in order to define process conditions and measurement conditions for the characterization of specific properties of the subject matter of the invention are also intended to be regarded as included by the scope of the invention even in the context of deviations—for example due to measurement errors, system errors, weigh-in errors, DIN tolerances and the like.

LIST OF REFERENCE NUMERALS

(8) 10 provision of a damaged turbine blade 12 removal of a blade tip armor plating of the turbine blade and production of a repair surface 14 removal of a blade coating of the turbine blade only in the region of the repair surface while preserving a part of the blade coating separated from the repair surface 16 application of repair material onto the repair surface 18 recontouring of the repair material 20 restoration of the blade tip reinforcement 22 restoration of the blade coating