Liquid jet removal of plasma sprayed and sintered coatings

Abstract

Gas turbine engine coatings must often be removed during engine maintenance and repair. The techniques utilized to accomplish this task, machining, chemical stripping, machining followed by chemical stripping, or grit blasting, frequently result in component damage or destruction. Liquid jet erosion can be utilized to remove seals, coatings, or portions thereof without damaging the engine hardware.

We claim: 
     
       1. A method for removing a top coat from a bond . .coating.!. .Iadd.coat .Iaddend.adhered to a substrate, utilizing a liquid jet, said liquid jet having means for directing the liquid jet, means for creating sufficient pressure to remove the . .coating.!. .Iadd.top coat.Iaddend., means to provide the relative motion between the . .coating.!. .Iadd.top coat .Iaddend.and the liquid jet, and means for supplying the liquid, which comprises: a. creating sufficient pressure to remove the . .coating.!. .Iadd.top coat.Iaddend.;   b. providing relative motion between the . .coating.!. .Iadd.top coat .Iaddend.and the liquid jet;   c. supplying the liquid;   d. causing the liquid to strike the top coat, wherein the liquid striking the top coat causes top coat erosion until the bond coat is exposed; whereby the bond coat and the substrate suffer essentially no damage and can be reused.     
     
     
       2. A method as in claim 1 wherein the top coat is selected from the group of plasma sprayed, flame sprayed, and sintered coatings. 
     
     
       3. A method as in claim 1 wherein the top coat is an abradable .Iadd.coating.Iaddend.. 
     
     
       4. A method as in claim 1 wherein the top coat is a thermal barrier .Iadd.coating.Iaddend.. 
     
     
       5. A method as in claim 1 wherein the top coat is an abrasive .Iadd.coating.Iaddend.. 
     
     
       6. A method as in claim 1 wherein the . .coating.!. .Iadd.top coat .Iaddend.is a hard facing .Iadd.coating.Iaddend.. 
     
     
       7. A method as in claim 1 wherein the liquid pressure is from about 20,000 psi to about 60,000 psi. 
     
     
       8. A method as in claim 1 using a nozzle as the means for directing the liquid flow. 
     
     
       9. A method as in claim 1 wherein the liquid is selected from the group of liquids consisting of all liquid which does not degrade the bond coat, and has a viscosity between about 0.25 centipoise and about 5.00 centipoise at 25° C. and 1 atm. 
     
     
       10. A method as in claim 1 wherein the liquid is selected from the group consisting of water based liquids. 
     
     
       11. A method as in claim 1 wherein the liquid is essentially water. 
     
     
       12. A method as in claim 1 wherein the angle between the liquid stream and the top coat is between 20° and 70°; whereby the angle causes the liquid stream to clean away the . .coating.!. .Iadd.top coat .Iaddend.fragments. 
     
     
       13. A method . .as in claim 1 further comprising the step of removing the bond coating, wherein.!. .Iadd.for removing a coating, said coating comprised of at least a top coat and a bond coat adhered to a substrate, which comprises: directing a pressurized liquid jet at a pressure above about 20,000 psi at the coating such that said liquid jet strikes said coating, thereby removing said coating from the substrate, whereby .Iaddend.the substrate . .material suffers essentially no damage.!. .Iadd.may be reused.Iaddend.. .Iadd. 
     
     
       14.  A method as in claim 13, wherein said top coat and said bond coat are removed simultaneously..Iaddend..Iadd.15. A method as in claim 13, wherein said liquid jet pressure is between about 20,000 psi and about 60,000 psi..Iaddend..Iadd.16. A method for removing a protective coating applied to a substrate which comprises: directing a liquid jet at a pressure above approximately 20,000 psi at the protective coating such that the liquid jet strikes the protective coating thereby removing the protective coating from the substrate whereby the substrate may be reused..Iaddend..Iadd.17. A method as in claim 16, wherein the protective coating is a thermal barrier coating..Iaddend..Iadd.18. A method as in claim 16, wherein the protective coating is an abrasive coating..Iaddend..Iadd.19. A method as in claim 16, wherein the protective coating is an abradable seal..Iaddend..Iadd.20. A method as in claim 16, wherein the protective coating is a hard facing..Iaddend..Iadd.21. A method as in claim 16, wherein the liquid jet pressure is between about 20,000 psi and about 60,000 psi..Iaddend..Iadd.22. A method as in claim 16, wherein the protective coating was applied by a pre-sintering and brazing or a partial 
     
     
        sintering and brazing process..Iaddend..Iadd.23.  A method as in claim 16, wherein the protective coating was applied by a partial sintering and brazing process..Iaddend.