Patent Application
20060073348
The present invention relates generally to wear coatings on gas turbine engine components. More particularly, this invention is directed to the application of wear coatings to selected portions of fuel nozzles and swirlers.
A gas turbine engine includes a compressor that provides pressurized air to a combustor wherein the air is mixed with fuel and burned for generating hot combustion gasses. These gasses flow downstream to one or more turbines that extract energy therefrom to power the compressor and provide useful work such as powering an aircraft in flight. In combustors used in aircraft engines, the fuel is typically supplied to the combustor through fuel nozzles positioned at one end of the combustion zone. A fuel nozzle is typically located within a surrounding assembly, known as a swirler. The fuel nozzles are bolted to the combustor case which does not see the hot combustion gasses. The swirler is configured to float radially in the combustor while being restrained in the axial direction. During engine transients, there are thermal gradients which result in axial and radial movement between the fuel nozzle tip and the swirler. It is generally desired that the fuel nozzle tip outer surface and the swirler inner bore have a 0.002 inch nominal gap, although surface contact is experienced.
Typically, a wear coating is adhered to these contacting surfaces to increase the usable life of the nozzles and swirlers. In the absence of a wear coating on these surfaces, the superalloy materials would wear and require a more frequent engine maintenance regimen. A primary concern when applying a wear coating to nozzle tips and swirlers is control of the surface portion where the wear coat is applied. Wear coat applied to an undesired surface portion of a nozzle or swirler could adversely affect the fuel or air flow within the combustor region.
These wear coatings are conventionally applied with a thermal spray technique to control the surface portion that the wear coating is applied thereon. While a thermal spray technique may be successful for a particular application, it requires that the components are wear coated individually. An adequate thermal spray process deposits about 0.0005 to 0.001 inches per pass of the thermal spray gun. To achieve a thickness of, for example, 0.003 inches, the thermal spray wear coat is typically applied in several passes. After application of several passes, the resulting thickness of a thermal spray wear coat may exceed the desired thickness and a additional machining operation may be required to remove some thermal spray wear coat.
A wear coat may also be applied with an electroplating process. To electroplate a wear coat on a selected surface portion of a component, the surface portion that is desired to remain free of wear coat must be masked. A mechanical masking means, such as covering a portion of the component with a nonconductive rubber mask, may be used where the rubber mask can be effectively used to partially cover the component. The geometry of some components, such as the swirler, does not allow the effective use of mechanical masking techniques. For these applications, the wear coat is typically not applied by electroplating.
Accordingly, there is a need for a method of wear coating gas turbine engine components that provides a predictable thickness of wear coat. A desirable method would allow for the simultaneous application of a wear coating on multiple components.
The present invention is directed to applying a wear coating to a fuel nozzle of a gas turbine engine by electro-deposition. The electroplating process adheres a predictable coating thickness accumulation during a measured amount of time. One of the benefits of this process is the repeatability of the coating thickness for the amount of time the parts are in the bath. Because the parts are totally immersed in the electroplate bath, a uniform, repeatable thickness can be achieved, such that it is not necessary to measure the coating thickness of each part. A sampling plan can be used whereby one part per coating run can be measured with a micrometer and the other parts will generally vary no more than 0.0005 to 0.001 inches in thickness when compared to the part that is measured. Therefore, post coating processing time is reduced since it is not necessary to measure the coating thickness of each part.
In one embodiment, the present invention provides a method of wear coating a portion of a fuel assembly by masking the component in wax, and demasking a portion of the wax with a fluid. In another embodiment, the present invention provides a method of partially masking a component with wax, wherein the component is immersed, at least partially, in melted wax, and at least a portion of the wax coating is removed with a fluid from a portion of the component to provide an exposed surface of the component.
In yet another embodiment, the present invention provides a interim assembly for a gas turbine engine which includes a fuel assembly manufactured of a superalloy, having a first surface and a second surface with a temporary coating adhered to at least a portion of the first surface, and where the second surface has been stripped of any temporary coating with a fluid. In a further embodiment, the present invention provides an apparatus for electroplating at least a portion of a gas turbine engine component which includes a fixture to hold the component, a supply of a liquid phase material, and a fluid sprayer.
Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.
With reference to
During manufacture, a component such as swirler 18′ is coated in mask 64. Preferably, swirler 18′ is dipped in a melted wax (not shown) and at least partially coated. It would be appreciated that the mask 64 may be applied to swirler 18′ by means other than dipping, such as spraying or pouring wax 48 onto swirler 18′, or by any other equivalent means. As used in this application, wax 48 refers preferably to plater's wax, but can also be any suitable material that can be adhered to the surface of a metal part and prevent the accumulation of an electrodeposited coat thereon.
Preferably, the swirlers 18′ are completely immersed in liquid-phase wax 48 to ensure that the entire surface portions 60, 62 are in contact with wax 48. Also preferably, wax 48 is maintained at a temperature above the melting point of wax 48 which is higher than ambient and swirlers 18′ and nozzles 16′ are initially at a general ambient temperature of a range of about 50° F. to 90° F. As is known, the wax 48 will begin to solidify onto surface portions 60, 62, of swirlers 18′, for example, due to the temperature of surfaces 60, 62 being below the melting point of the wax 48. As the swirlers 18′ are removed from the wax 48, a liquid/solid film of wax 48 adheres to surface portions 60, 62. This film of wax 48 may completely solidify to form a mask 64 when exposed to an ambient temperature below the melting point of wax 48. Further exposure to ambient temperature may allow the mask 64 to cool to a temperature below the softening point. While this process is described as a single dip in wax 48, it would be appreciated that multiple or partial dips in wax 48 may form a suitable mask. After a suitable mask 64 is formed on swirler 18′, the wax 48 contacting second surface portion 62 is removed with a fluid, as discussed below.
As best seen in
With reference to
As depicted in this embodiment, second surface portion 62′ of swirler 18′ is an inner cylindrical bore. It would be appreciated that the removal of wax 64 from second surface 62′ may be facilitated when demasking surfaces with confined geometries by a hydraulic process, such as fluid 70 spray, rather than a mechanical process, such as a blade. Furthermore, it would be appreciated that the use of a hydraulic process would provide a process which could be readily automated as the variation of parameters such as, for example, fluid temperature, fluid pressure, and fluid composition allow for optimization of the demasking.
In operation, after wax removal from second surface portions 42′, 62′ as set forth above, fuel nozzles 16 and/or swirlers 18 are stacked within the sets of support prongs with washers placed between each individual fuel nozzle 16 or swirler 18 within a stack of components. After fuel nozzles 16 and/or swirlers 18 are placed into the carousel 80, the carousel 80 is positioned above the electroplate bath and dipped thereinto. Thus provided, carousel 80 can be used for electrodeposition.
In this manner, multiple components may electroplated while attached to a common carousel 80. The carousel 80 may be constructed of material such as plastic or rubber.
Preferably, the electroplated coating 46, 66 is formed with an electro-deposition process using a chromium carbide electroplate solution. The electroplated coating 46, 66 is an entrapment coating where chromium carbide particle are entrapped in a chromium coating. Electroplated coating 46, 66 is bonded, or adhered, to second surface portion 42, 62 to provide an abrasion resistant wear coat. Thus provided, the contacting surfaces of nozzle 16 and swirler 18 are protected from undesirable wear during engine operation.
While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.
