Patent Application
20100260932
Not applicable.
Not applicable.
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.
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.
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.
The present invention comprises methods of efficiently producing high-quality seal strips on turbine components. In some embodiments, as illustrated in
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.
As illustrated in
In another aspect, as illustrated in
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
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.
