METHOD FOR IMPROVING THE EROSION RESISTANCE OF ENGINE COMPONENTS

Abstract: The present invention relates to a coating system for engine components which exhibits improved erosion resistance and a method for forming the coating system on the engine components. The coating system is formed by a fluororelastomeric material which is co-cured or bonded with the organic matrix material forming the engine component. The coating system is applied to the engine component by overlaying a thin sheet of the fluoroelastomeric material in a cured or uncured state over a preform of the engine component, placing the preform and the fluoroelastomeric material in a molding device, and heating the engine component preform and the fluoroelastomeric material to a temperature at or above about 340 DEG F to effect co-curing and/or bonding.

Description: METHOD FOR IMPROVING THE EROSION RESISTANCE OF ENGINE COMPONENTS Background Art The present invention relates to structures having improved resistance to erosion from particulate matter and a method for forming such structures. The present invention has particular utility in the manufacture of structures to be incorporated into jet engines, industrial turbines and the like. Jet engines are expected to operate under a wide variety of environmental conditions. Often, the components of the jet engines are exposed to particulate matter which impinge upon the components and cause them to deteriorate. For example, sand, debris and other particulate matter are ingested by jet engines as planes travel along taxiways and runways. Still further, jet engines encounter airborne sand, rain and particulate matter such as volcanic ash during the normal course of their airborne operations. Since the sand and other particulate matter are impinging against components of the jet engine while traveling at relatively high speeds, they often cause a great deal of erosion damage over time. Thus, efforts have been made to improve the erosion resistance of engine components. One such effort has involved the application of polyurethane and polyurethane-based coatings to engine components such as spinner caps. Typically, these coatings will last for as little as 300 hours, after which they display peeling and erosion initiation. This is far less than the 10,000 hours of operation that is desired by engine operators. Numerous field repairs become necessary to address the erosion problem. These too frequent repairs are tedious and expensive. Additionally, the use of polyurethane coating materials can be environmentally unfriendly. Thus, it is highly desirable to have a coating for jet engine components which greatly improves the erosion resistance of those surfaces of the components routinely impacted by sand, debris, and other particulate matter. Disclosure of Invention Accordingly, it is an object of the present invention to provide an improved coating for engine components encountering particulate matter for which the coating improves the erosion resistance of those components. It is a further object of the present invention to provide an improved coating as above which is environmentally friendly and economically beneficial. It is yet a further object of the present invention to provide an improved method for applying such a coating to engine components. Still other objects and advantages of the present invention will become more apparent from the following description and drawings. The foregoing objects are attained by the coating system of the present invention which comprises a highly durable fluoroelastomeric material coating applied to surfaces of engine components to be protected. Engine components to which the coating system of the present invention may be applied include spinner caps, strut covers, engine fairings and airfoils. Typically, these engine components are formed from an organic matrix material which is fiber reinforced such as an aramid, fiberglass or carbon fiber reinforced epoxy or bismaleimide (BMI) matrix material. The fluoroelastomeric material coating is applied as an overlay with the fluoroelastomeric material being in a cured or uncured state. The component, which is preferably in an uncured state, and the coating are then co-cured or bonded in a suitable molding device to form an engine component having a relatively high erosion durability. In accordance with the present invention, engine components or structures are produced by: providing a component formed from an organic matrix material in an uncured state; applying a fluoroelastomeric material in a cured or uncured state to said component; and co-curing the component and said fluoroelastomeric material, preferably in a molding device and at a temperature at or above about 340°F. It has been discovered that by co-curing the component and the fluoroelastomeric material a very strong bond forms between the organic matrix material and the fluoroelastomeric material. It also has been found that improved erosion durability is provided to the component. Still further, it has been found that the method of the present invention provides a substantial cost savings since the erosion protection system is simultaneously incorporated into the component during molding, thus eliminating such post-molding steps as surface cleaning, preparation, and spray coating. Other details and features of the coating system and method of the present invention are set out in the following description and drawings wherein like reference numerals depict like elements. Brief Description of the Drawing Figure 1 is a side view of an engine component provided with the coating system of the present invention; Figure 2 is a sectional view of the engine component of Figure 1 showing the manner in which the coating system of the present invention is applied to the engine component; Figure 3 illustrates a sectional view of another engine component to which the coating system of the present invention may be applied; Figure 4 is an exploded view of a portion of the engine component of Figure 3; and Figure 5 is a graph illustrating the weight loss of various coating systems during an abrasion test. Best Mode for Carrying Out the Invention Referring now to the drawings, Figure 1 illustrates an engine component 10 such as an airfoil to which the coating system of the present invention can be applied. The engine component to be protected may be made from any suitable organic matrix material known in the art. If desired, the matrix material may be fiber reinforced. For example, the material forming the component 10 can be an aramid, fiberglass or carbon fiber reinforced matrix material. Suitable matrix materials include epoxy and bismaleimide matrix materials. It is preferred however that the material forming the component 10 be in an uncured state. As shown in Figure 2, the component 10 has a leading edge 12 and upper and lower surfaces 14 and 16 which typically are impacted by particulate matter such as sand, debris, and ash during engine operation. Thus, it becomes highly desirable to impart erosion resistance to these portions of the component. To this end, a layer 18 of fluoroelastomeric material is laid over or wrapped around a preform of the component 10. The layer 18 covers those portions of the surfaces 14 and 16 and the leading edge 12 which typically encounter impingement by particulate matter. The layer 18 comprises a thin sheet of fluoroelastomeric material which has been cut and trimmed to fit the component being protected. Typically, the layer 18 will have a thickness of from about 0.005" to about 0.010"; however, this thickness may vary depending upon the expected erosion rate of the component. For components which are subjected to a relatively high angle of attack or high degree of sand, debris, rain, ash and other particulate matter impingement, the thickness of the layer 18 may be as high as 0.050". The material forming the layer 18 is in a cured or uncured state. A particularly suitable material which may be used for the layer 18 is a fluoroelastomeric material sold under the trademark EE 4515 by Eagle Elastomers. Another material which may be used is VITON fluoroelastomeric material sold by duPont. If desired, a compatible adhesive may be placed between the fluoroelastomeric material layer 18 and the portions of the component 10 being protected. However, for most applications, an intermediate adhesive layer is not necessary. After the layer 18 has been laid over or wrapped around the component preform, the preform with the layer 18 is placed in a suitable molding device (not shown) such as an autoclave molding device, a compression molding device, a resin transfer molding device, and the like. The particular molding device which is used depends upon the component being processed and the material forming that component. Within the molding device, heat, with or without pressure, is applied to the component 10 and the surrounding fluoroelastomeric material for a time sufficient to effect co-curing or bonding of the two. It has been found that at temperatures at or above about 340°F, a strong bond will develop between the fluoroelastomeric material and the material forming the component 10. The bond is so strong that the fluoroelastomeric material can not be manually peeled from the surfaces of the component 10. As can be seen from the foregoing description, the manner in which the coating system of the present invention is applied to the engine component is advantageous from a number of standpoints. First, it allows cost savings to be effected since the erosion protection system is simultaneously incorporated into the component during molding. It is also beneficial in that post molding steps such as composite surface cleaning/preparation and spraying of a protective coating can be omitted. This eliminates a substantial amount of waste. The coating system of the present invention is further advantageous in that it is environmentally friendly. That is, it does not include any spraying operation which involves the release of hazardous volatile material during application. Figure 3 illustrates yet another application for the coating system of the present invention. Figure 3 illustrates a spinner cap 20 for a jet engine. During operation, the exterior surfaces of the spinner cap come into contact with particulate matter such as sand, debris, and ash and are therefore subject to a great deal of erosion. To impart improved erosion resistance to the spinner cap, a layer 18 of fluoroelastomeric material is applied to portions of the exterior surface of the spinner cap which encounter the most particulate matter. Typically, the spinner cap 20 is formed from an epoxy resin material 19 having layers 22 and 24 of fiberglass and aramid or carbon reinforcement fibers. As before, a sheet of fluoroelastomeric material in a cured or uncured state is cut, cleaned, trimmed and placed over the preform for the spinner cap while the matrix resin material is in an uncured state. Thereafter, the spinner cap preform with the fluoroelastomeric layer material is placed within a mold and heated to a temperature at or above about 340°F for a time sufficient to effect co- curing or bonding of the matrix resin material forming the spinning cap preform and the fluoroelastomeric material. It has been found that spinner caps with the coating system of the present invention exhibit superior erosion protection as compared with spinner caps having painted polyurethane erosion coatings. To illustrate the advantages attendant to the coating system of the present invention, the following example was performed. Example I An abrasion test was performed on a number of nose caps formed from different materials and provided with a coating system. The nose cap constructions that were tested included: (1) an aluminum nose cap with a painted polyurethane coating; (2) a Fiberglass/Kevlar epoxy laminate nose cap with a painted polyurethane coating; (3) a Fiberglass/Kevlar epoxy laminate nose cap with a co-cured, 0.020" thick Viton (fluoroelastomeric material) coating; (4) a Fiberglass/Kevlar epoxy laminate nose cap with a hard epoxy coating (a mineral filled epoxy coating); and (5) a Fiberglass/Kevlar epoxy laminate nose cap with a toughened epoxy material coating. Each of the nose caps was mounted to a motor which was rotated at 1745 RPM. During the first minute of the test, a nozzle was set at a distance of 42 inches from the nose cap leading edge. Thereafter, the nozzle was moved to a distance of 84 inches. The nozzle generated a spray pattern which matched the diameter of the cap. Washed beach sand was sprayed through the nozzle at a constant pressure of 50 psi and a temperature of 70°F. The impingement angle of the sand on the nose cap was 90°. The test measurement intervals were thirty seconds, three minutes, 6 minutes and 12 minutes. The weight loss in grams of the coating was measured at each interval. Figure 5 illustrates the weight loss vs. blasting time for each coating system. As can be seen from this figure, the VITON coating performance was far superior to the performance of the other coating systems. While the present invention has been described in the context of airfoils and spinner caps, it should be recognized that the coating system of the present invention can be used on other engine components. For example, it could be used on fan exit strut covers, bifurcation doors and covers, liners, blades and vanes. It should also be recognized that the coating system of the present invention could also be used in other environments. For example, it can be used to protect components used in industrial turbines and the like. While the coating system of the present invention has been discussed in the context of engine components, it should be recognized that it has applicability on other aircraft components and other vehicle components which are formed from an organic matrix material and which are subject to erosion as a result of the impingement of sand, debris, ash, and other particulate matter. It is apparent that there has been provided in accordance with this invention a coating system for engine components having improved erosion resistance which fully satisfies the objects, means, and advantages set forth hereinbefore. While the invention has been described in combination with specific embodiments thereof, it is evident that many alternatives, modifications, and variations will be apparent to those skilled in the art in light of the foregoing description. Accordingly, it is intended to embrace all such alternatives, modifications and variations as fall within the spirit and broad scope of the appended claims.

Claims: In the Claims: 1. A method for improving the erosion resistance of a desired component, said method comprising the steps of: providing a component formed from an organic matrix material in an uncured state; applying a fluoroelastomeric material to said component; and co-curing said component and said fluoroelastomeric material so as to form a high durability coating system over desired portions of said component. 2. The method of claim 1 wherein said applying step comprises applying said fluoroelastomeric material in an uncured state to said component. 3. The method of claim 1 wherein said applying step comprises applying said fluoroelastomeric material in a cured state to said component. 4. The method of claim 1 wherein said component providing step comprises providing a fiber reinforced organic matrix material. 5. The method of claim 1 wherein said fluoroelastomeric material applying step comprises providing said fluoroelastomeric material in sheet form, cutting said sheet to a desired configuration, and overlaying at least a portion of a surface of said component with said cut sheet of fluoroelastomeric material. 6. The method of claim 5 further comprising applying an adhesive material between said surface of said component and said cut sheet. 7. The method of claim 1 wherein said co-curing step comprises placing said component and said fluoroelastomeric material applied thereto into a molding device and applying at least one of heat and pressure to said component and said fluoroelastomeric material in said molding device to effect bonding between said component and said fluoroelastomeric material. 8. The method of claim 7 further comprising: heating said component and said fluoroelastomeric material in said molding device to a temperature equal to or greater than about 340°F. 9. A structure having improved resistance to erosion by particulate material, said structure comprising: a first component formed from organic matrix material; and a protective layer of fluoroelastomeric material applied to portions of said first component to increase the resistance of said component to erosion by particulate matter. 10. The structure of claim 9 further comprising: said organic matrix material and said fluoroelastomeric material being co-cured so that a bond forms between said organic matrix material and said fluoroelastomeric material. 11. The structure of claim 9 further comprising said organic matrix material and said fluoroelastomeric material being bonded to each other. 12. The structure of claim 9 wherein said organic matrix material comprises at least one of a fiber reinforced epoxy material and a fiber reinforced bismaleimide material. 13. The structure of claim 9 wherein said protective layer comprises a sheet of fluoroelastomeric material laid over said portions of said component. 14. The structure of claim 9 wherein said component comprises a spinner cap for a jet engine. 15. The structure of claim 9 wherein said component comprises a strut cover. 16. The structure of claim 9 wherein said component comprises an airfoil. 17. The structure of claim 9 wherein said component comprises a blade for a jet engine. 18. The structure of claim 9 wherein said component comprises a vane for a jet engine. 19. A method for improving the erosion resistance of a desired component, said method comprising the steps of: providing a component formed from an organic matrix material in an uncured state; applying a fluoroelastomeric material to said component; and bonding said component to said fluoroelastomeric material so as to form a high durability coating system over desired portions of said component. 20. An improved spinner cap for a jet engine comprising: a first component formed from a fiber reinforced organic matrix material; an overlay of fluoroelastomeric material applied to portions of said first component to impart erosion resistance to said portions; and said fluoroelastomeric material being at least one of co-cured with and bonded to said organic matrix material so that a bond forms between said fluoroelastomeric material and said organic matrix material.

Inventors: LESHANE JEFFREY S, MEIER SUSAN M, WALLA LISA A, LESHANE, JEFFREY, S., MEIER, SUSAN, M., WALLA, LISA, A.
Applicants: UNITED TECHNOLOGIES CORP, UNITED TECHNOLOGIES CORPORATION
Application year: 1995
Main classification: C08J7
IPC codes: B29C63, B29C70, B32B25, C08J7, F01D5