DEVICE FOR HVOF SPRAYING PROCESS HAVING A HOT GAS SECTION INSERT

Abstract

The invention relates to a device for High Velocity Oxygen Fuel thermal spraying process for coating a component, especially a gas turbine component. The device includes a liquid fuel fired combustion chamber, a de-Laval section, a powder injector block with powder injectors and a barrel all arranged around and along an axis. The powder injector block includes at least four powder injectors arranged in an equal circumferential distance around the axis and an exchangeable hot gas section insert inside the powder injector block designed as a cylindrical bush with at least four openings, the openings being arranged in an equal circumferential distance around the axis in the cylinder, wherein the bush is fixed by the at least four powder injectors extending through said openings.

Claims

1. Device for High Velocity Oxygen Fuel thermal spraying process for coating a component, comprising: a liquid fuel fired combustion chamber, a de-Laval section, a powder injector block with powder injectors and a barrel all arranged around and along an axis (A), wherein the powder injector block having at least four powder injectors arranged in an equal circumferential distance around the axis (A) and an exchangeable hot gas section insert inside the powder injector block configured as a cylindrical bush with at least four openings, said openings being arranged in an equal circumferential distance around the axis (A) in the cylinder, wherein the bush is fixed by the at least four powder injectors extending through said openings.

2. Device according to claim 1, wherein the cylindrical bush comprises: a guiding groove for a definite orientation of said bush around the axis (A) and that-the bush is inserted from the outside of the powder injector block.

3. Device according to claim 1, wherein the de-Laval section has a bell-shaped configuration.

4. Device according to claim 3, wherein the bell-shaped de-Laval section is combined with a cylindrical barrel.

5. Device according to claim 3, wherein the bell-shaped de-Laval section is combined with a conical barrel.

6. Device according to claim 5, wherein the bell-shaped de-Laval section is combined with a full conical configuration of the powder injector block.

7. Device according to claim 1, in combination with a gas turbine component, the device being arranged for coating the gas turbine component.

8. Device according to claim 1, in combination with metallic protective coatings of the MCrAlY type for performance of a spraying process.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The present invention is now to be explained more closely by means of different embodiments and with reference to the attached drawings.

[0026] FIG. 1 shows in a simplified drawing a configuration for a HVOF thermal spraying device according to the prior art;

[0027] FIG. 2 shows a photo of the powder injector block according to the prior art with two powder injectors;

[0028] FIG. 3 shows a photo of the powder injector block according to the invention with four powder injectors;

[0029] FIG. 4 shows a schematic cut through the injector block according to a first embodiment of the invention;

[0030] FIG. 5 shows a photo of the exchangeable hot gas section device (cylindrical bush) according to an embodiment of the invention and

[0031] FIG. 6, 7, 8 show in simplified drawings three embodiments of the de-Laval section and the barrel of the device.

DETAILED DESCRIPTION OF DIFFERENT EMBODIMENTS OF THE INVENTION

[0032] The invention uses state of the art and commercially available liquid fuel fired HVOF equipment as basis and implements several improvements regarding process stability/capabilities/maintainability. At the same time, compatibility to the existing spraying equipment is preserved.

[0033] A first feature is the application of additional powder injectors to the injector block that enables the reliable processing of higher powder feed rates, which leads to time reduction, stabilizes the spray spot geometry due to a symmetry increase and enables the simultaneous processing of different powder types with or without time consuming retooling.

[0034] This feature is shown in FIG. 3 compared to FIG. 2. FIG. 2 is a photo of the standard powder injector block 9 according to the prior art. The two powder injectors 8 are clearly visible. FIG. 3 is a photo of the powder injector block 9 according to the invention with four powder injectors 8. The powder injectors 8 are symmetrically arranged in circumferential direction that means in an equal circumferential distance around the axis A (A is not shown in FIG. 3).

[0035] A second feature of the device according to the present invention is the arrangement of an exchangeable insert 10 into the flow section of the injector block 9 in order to reduce maintenance costs and to improve the maintainability of the HVOF burner's injector block 9. FIG. 5 shows a photo of that insert in form of a cylindrical bush 10 with openings 11 and a guiding groove 12, while FIG. 4 shows a schematic cut through the injector block 9. The openings 11 (here four) are arranged in an equal circumferential distance around the axis A (see FIG. 4) in the cylinder. The four powder injectors 8 extend through the openings 11 and fix the bush 10 in the powder injector block 9. The guiding groove 12 is the warrantor for a definite orientation of said bush 10 around the axis A. The bush 10 is inserted from the outside of the powder injector block 9 and can be exchanged in an easy way when it is necessary because of wear.

[0036] Such a prototype of a modified HVOF injector block 9 having four powder injectors 8 and an exchangeable hot gas section insert 10 was tested at an existing spraying booth of the applicant. For coating a gas turbine blade for a GT of the applicant, the deposition rate could be doubled at remaining coating quality (bonding, coating thickness distribution, porosity) resulting in about 40% lead time reduction with respect to coating the blade with a commercially available HVOF injector block. The spray spot of the modified HVOF device was found to be highly symmetric (round) even without special adjustment of carrier gas flows as usually needed for the standard setup.

[0037] The following advantages could be reached:

[0038] The modified injector block was implemented into the existing equipment within few minutes, uses the standard parameter set as well as the standard robot program (solely the amount of repetitions has needed adjustment) and obtains the same deposition efficiency when compared to the standard setup. The flame (i.e. amount/distance of diamond shocks) was found to be the same for standard as well as modified injector block.

[0039] There is only a low risk for residual stresses caused crack formation in the coating at critical locations of the components due to the increases deposition rate. The implementation is not complicated. Besides possible additional powder feeders, the presented hardware modifications do not require adaption of existing spraying equipment/setup, i.e. use of the same controller/robot program/fuel/gas etc.

[0040] Of course the invention is not limited to the described embodiment, for example more than four powder injectors could be used.

[0041] In addition, CFD investigations have demonstrated the potential for design improvement of the commercial available baseline equipment with respect to losses by thermodynamic shocks. The de Laval section 4 of the device 1 can be improved by several options, which are described as the following embodiments:

[0042] 1. Removal of steps and phases in current baseline design by rounding out of edges. This option does not need time consuming CFD investigations and attenuates the thermodynamic losses by shocks resulting in slightly increased particle velocities and lower coating porosity, respectively (see FIG. 6).

[0043] 2. Bell-shaped design of the de Laval section 4 in combination with a cylindrical barrel 7. In this option, the gas reaches already the final velocity before entering the powder injector block 9. No further expansion is needed and the powder injection 8/barrel section 7 is designed cylindrically without edges and phases. The improved layout removes also the significant overexpansion at barrel 7 exit of the baseline. Less shocks and thermodynamic losses result in higher particle velocity and lower coating porosity, respectively (see FIG. 7).

[0044] 3. Bell-shaped design of the de-Laval section 4 in combination with a full conical design of the powder injector block 9/barrel section 7. The improved layout removes also the significant overexpansion at barrel 7 exit of the baseline.

[0045] The device according to the invention is preferably used for coating gas turbine components with metallic protective coatings of the MCrAlY type.

LIST OF REFERENCE NUMERALS

[0046] 1 HVOF device

[0047] 2 combustion chamber

[0048] 3 fuel

[0049] 4 oxygen

[0050] 5 gaseous mixture, combustion gas

[0051] 6 nozzle, de Laval section

[0052] 7 barrel

[0053] 8 powder injector

[0054] 9 powder injector block

[0055] 10 hot gas section insert, cylindrical bush

[0056] 11 opening

[0057] 12 guiding groove