COLD SPRAY METHOD OF APPLYING ALUMINUM SEAL STRIPS

Abstract

A method for applying a seal strip to a surface of a turbine component by accelerating solid particles to a velocity sufficient to cause the solid particles to plastically deform and bond to the surface and each other when impacted on the surface, and impacting the solid particles on the surface so as to cause the solid particles to deform and bond to the surface and each other to form the seal strip on the surface.

Description

CROSS REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND OF THE INVENTION

This invention is generally in the field of gas turbine power generation systems. More particularly, the present invention is directed to a method of efficiently producing high quality seal strips on turbine components, such as on bucket dovetails.

Aluminum seal strips are commonly applied to turbine components, such as bucket dovetails, to prevent fluids from passing between joined components. FIG. 1 illustrates a typical application of the aluminum seal strips 14 to a dovetail 12 of a turbine bucket 10. The aluminum seal strips 14 generally prevent cooling air from leaking past the dovetail 12 when the turbine bucket 10 is attached to the turbine wheel. It should be noted that the precise configurations and locations where the aluminum seal strips 14 are applied to a component may vary from one component to another. For example, turbine buckets attached to a turbine wheel close to the combustors will typically have different geometries than turbine buckets attached to the turbine wheel further downstream from the combustors.

Aluminum seal strips 14 are typically applied to turbine components by an arc-wire spray coating process. When performing an arc-wire spray coating process, a pair of electrically conductive wires are melted by an electric current in or adjacent to a spray nozzle. Air is simultaneously fed through the spray nozzle to atomize the molten material and deposit the material on a substrate surface. The molten particles rapidly solidify to form a coating when the particles strike the substrate surface.

Before the aluminum seal strips 14 are applied to the surfaces of dovetail 12 by an arc-wire spray coating processes, the turbine bucket 10 must first be prepared to receive the spray coating. The preparation of the surface is typically a multi-step process involving (1) a cleaning step, (2) a taping or “masking” step, and (3) a grit blasting step. During the taping step, all surfaces which are not to be coated by aluminum must be covered with masking. Because turbine buckets often have a complex geometry which varies from one bucket to another depending upon where along the turbine wheel the bucket is designed to attach, masking must often be customized for each bucket and applied carefully by hand. After the surface is prepared, the coating is sprayed onto the substrate surface and the masking is removed.

Such a seal strip application process often requires a significant amount of man hours and cost to the turbine manufacturer. Furthermore, the spray-coated seal strips are often applied in a non-uniform manner due to the imprecise spray pattern produced by the arc-wire spray nozzle. As such, it would be desirable to provide a more time and cost efficient method of applying high-quality aluminum seal strips to turbine components.

BRIEF SUMMARY OF THE INVENTION

In one aspect, the present invention comprises a method for applying a seal strip to a surface of a component by accelerating solid particles to a velocity sufficient to cause the solid particles to plastically deform and bond to the surface and each other when impacted on the surface, and impacting the solid particles on the surface so as to cause the solid particles to deform and bond to the surface and each other to form the seal strip on the surface.

In another aspect, the present invention comprises a method for applying a seal strip to a surface of a component utilizing a spray coating apparatus having a deposition nozzle, a powder fluidizing unit, and a pressurized gas source. The powder fluidizing unit is configured to disperse solid particles into a carrier gas and the pressurized gas source provides sufficient pressure to accelerate the solid particles dispersed in the carrier gas through the deposition nozzle at a velocity sufficient to cause the solid particles to plastically deform and bond to the surface and each other when impacted on the surface. The method further comprises accelerating the solid particles through the deposition nozzle, and impacting the solid particles on the surface so as to cause the solid particles to deform and bond to the surface and each other to form the seal strip on the surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view, illustrating a turbine component with aluminum seal strips.

FIG. 2A is a section view, illustrating a seal strip produced by an arc-wire spray coating process.

FIG. 2B is a section view, illustrating a seal strip produced by kinetic metallization.

FIG. 3 is a schematic, illustrating an apparatus for performing methods of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention comprises methods of efficiently producing high-quality seal strips on turbine components. In some embodiments, as illustrated in FIG. 1, the seal strips 14 comprise aluminum and are applied to surfaces of the dovetail 12 of a turbine bucket 10. The precise location and configuration of the seal strips 14 may vary from one bucket to another, depending upon where on the turbine wheel the bucket is to be installed.

In one aspect, the present invention comprises a method for applying the seal strip 14 to the surface by accelerating solid particles to a velocity sufficient to cause the solid particles to plastically deform and bond to the surface and each other when impacted on the surface, and impacting the solid particles on the surface so as to cause the solid particles to deform and bond to the surface and each other to form the seal strip 14 on the surface. This deformation and bonding process, which is an entirely solid-state process, may be referred to as “kinetic metallization”. When undergoing kinetic metallization, the solid particles experience a very large strain upon collision with the surface which causes the particles to flatten, increasing each particle's surface area. Other particles collide and flatten against the previously flattened and deposited particles and metallurgical bonds are formed between the particles and the surface.

In some embodiments, the solid particles comprise a metal powder, such as powdered aluminum. The particles may be accelerated to speeds greater than about 350 m/sec and impacted upon the surface to deposit the aluminum as a strip on the surface. The solid particles may be accelerated using a high-pressure gas, such as pressurized helium or air.

It has been discovered that seal strips produced by kinetic metallization have superior properties to seal strips produced by arc-wire spray processes. It has further been discovered that kinetically-metallized seal strips may be applied more efficiently and without surface preparation steps typically required for applying seal strips by arc-wire spray processes.

FIGS. 2A and 2B are illustrative of seal strips produced by an arc-wire coating process and a kinetic metallization process, respectively. As illustrated in FIG. 2A, an arc-wire coated strip 18 possesses a non-uniform and irregular coating pattern. The depth of the coating, measured from the exterior surface of the coating to the surface of the substrate 16, varies unpredictably across the width of the strip 18. Also, pockets of entrained air are prolific throughout the coating. These qualities result from air being mixed with the molten material while the material solidifies.

As illustrated in FIG. 2B, the kinetically-metallized strip 20 possesses a more uniform and regular coating pattern compared to the arc-wire coated strip 18 of FIG. 2A. The coating depth is predictable across the width of the strip 18. Also, pockets of entrained air are only sparsely present throughout the coating. It has been discovered that such a coating pattern produced a superior seal between turbine components.

In another aspect, as illustrated in FIG. 3, the present invention comprises a method for applying a seal strip utilizing a spray coating apparatus 34 having a deposition nozzle 30, a powder fluidizing unit 26, and a pressurized gas source 22. The powder fluidizing unit 26 is configured to disperse solid particles into a carrier gas 32. The pressurized gas source 22 provides sufficient pressure to accelerate the solid particles dispersed in the carrier gas 32 through the deposition nozzle 30 at a velocity sufficient to cause the solid particles to plastically deform and bond to the surface and each other when impacted on the surface. The solid particles may be fed to the powder fluidizing unit 26 from a hopper 24. The carrier gas 32 may be supplied from the pressurized gas source 22 or a different source. The apparatus 34 may further include a thermal conditioning unit 28 the gas to the desired operating temperature.

The method further comprises accelerating the solid particles through the deposition nozzle 30, and impacting the solid particles on the surface so as to cause the solid particles to deform and bond to the surface and each other to form the seal strip on the surface.

The apparatus 34 is capable of depositing solid particles on a turbine component surface to form a coating substantially as illustrated in FIG. 2B. Further, the deposition nozzle 30 may be configured to deposit a coating of a predefined width with excellent edge control (i.e., the coating produced using the deposition nozzle 30 may have a well-defined edge). Such a feature allows apparatus 34 to be used to apply a kinetically-metallized seal strip 14 to a turbine component without requiring additional preparation steps, including taping the turbine component with protective masking. Further, the steps of surface cleaning and grit blasting the surface of the turbine component may be omitted since the solid particles may be bonded to an unprepped surface by kinetic metallization.

It should be appreciated that the deposition nozzle 30 may be integrated to a robotic arm to allow a fully-automatic coating process to be performed. The robotic arm may be controlled by a programmable controller which controls actuators or servomechanisms on the robotic arm to direct specific coating configurations at defined locations on the surface of the turbine component. For example, the robotic arm may be controlled by any controller adapted for use with CNC machining. It should be appreciated that coating depth, width, and length may be controlled by actuation of the robotic arm. For example, the robotic arm may articulate slowly to deposit a thick coating or quickly to deposit a thin coating. Also, the deposition nozzle 30 may be placed in close proximity to the surface of the turbine component to deposit a strip having a narrow width or may be placed at a greater distance from the surface to deposit a strip having a wide width. Furthermore, different control sequences may be used for each turbine component to allow unique seal strip configurations to be applied to various components. For example, different control sequences may be used for each turbine bucket to deposit the seal strip in the preferred locations with the preferred configuration.

The foregoing robotic system may be designed to operate with commercially available cold-spray devices. For example, a cold-spray device from Supersonic Spray Technologies, a division of CenterLine Ltd. (Detroit, Mich.) may be integrated with a CNC controlled robotic arm and equipped with an appropriate deposition nozzle 30 to carry out the foregoing method. The preferred design of the deposition nozzle 30 is a function of the operating pressure of the cold-spray device as well as the desired spray pattern.

The invention is not limited to the specific embodiments disclosed above. Modifications and variations of the methods and devices described herein will be obvious to those skilled in the art from the foregoing detailed description. Such modifications and variations are intended to come within the scope of the appended claims.

Claims

1. A method for applying a seal strip to a component comprising:

providing the component having a surface;

accelerating solid particles to a velocity sufficient to cause the solid particles to plastically deform and bond to the surface and each other when impacted on the surface; and

impacting the solid particles on the surface so as to cause the solid particles to deform and bond to the surface and each other to form the seal strip on the surface.

2. The method of claim 1, wherein the solid particles comprise aluminum.

3. The method of claim 1, wherein the solid particles comprise a powdered metal.

4. The method of claim 1, wherein the component comprises a turbine bucket having a dovetail, and the surface is located on the dovetail.

5. The method of claim 1, wherein accelerating the solid particles uses a high-pressure gas.

6. The method of claim 5, wherein the high-pressure gas comprises helium.

7. The method of claim 5, wherein the high-pressure gas comprises air.

8. The method of claim 1, wherein the velocity is greater than about 350 m/sec.

9. The method of claim 1, further comprising dispersing the solid particles in a carrier gas before accelerating the solid particles.

10. A method for applying a seal strip to a component comprising:

providing the component having a surface;

providing a spray coating apparatus comprising a deposition nozzle; a powder fluidizing unit; and a pressurized gas source; wherein the powder fluidizing unit is configured to disperse solid particles into a carrier gas and the pressurized gas source provides sufficient pressure to accelerate the solid particles dispersed in the carrier gas through the deposition nozzle at a velocity sufficient to cause the solid particles to plastically deform and bond to the surface and each other when impacted on the surface;

accelerating the solid particles through the deposition nozzle; and

impacting the solid particles on the surface so as to cause the solid particles to deform and bond to the surface and each other to form the seal strip on the surface.

11. The method of claim 10, wherein the solid particles comprise aluminum.

12. The method of claim 10, wherein the solid particles comprise a powdered metal.

13. The method of claim 10, wherein the component comprises a turbine bucket having a dovetail, and the surface is located on the dovetail.

14. The method of claim 10, wherein the solid particles are accelerated using a high-pressure gas.

15. The method of claim 14, wherein the high-pressure gas comprises helium.

16. The method of claim 14, wherein the high-pressure gas comprises air.

17. The method of claim 10, wherein the velocity is greater than about 350 m/sec.

18. The method of claim 10, wherein the deposition nozzle is attached to a robotic arm.

19. The method of claim 10, wherein the surface of the component is unmasked.

20. The method of claim 18, wherein the robotic arm is automatically controlled to deposit the seal strip on the surface of the component.