Method of repairing an airfoil surface

• US 8,091,227 B2
• Filed: 12/14/2006
• Issued: 01/10/2012
• Est. Priority Date: 12/14/2005
• Status: Active Grant

• Current Assignee: Hontek Corporation
• Original Assignee: Hontek Corporation
• Inventors: Hong, Shek C.
• Primary Examiner(s): Omgba, Essama
• Assistant Examiner(s): Afzali, Sarang
• Application Number:
  US11/640,050
• Publication Number:
  US 20070231156A1
• Time in Patent Office: 1,853 Days
• Field of Search: 294/021.8, 294/58, 294/59, 294/60, 298/891, 427/140, 427/142, 427/290, 427/292, 427/407.1, 427/409, 427/355, 427/356, 427/368, 427/429
• US Class Current: 29/889.1
• CPC Class Codes: B05D 1/42 by non-rotary members
• CPC Class Codes: B05D 5/005 Repairing damaged coatings
• CPC Class Codes: B05D 5/06 to obtain multicolour or other optical effects B05D5/02 takes precedence
• CPC Class Codes: B05D 7/56 Three layers or more
• CPC Class Codes: B05D 7/58 No clear coat specified
• CPC Class Codes: B23P 6/007 using only additive methods, e.g. build-up welding
• CPC Class Codes: B64F 5/40 Maintaining or repairing aircraft
• CPC Class Codes: F01D 5/005 Repairing methods or devices
• CPC Class Codes: F05D 2230/10 by removing material
• CPC Class Codes: F05D 2230/30 with deposition of material
• CPC Class Codes: F05D 2230/90 Coating; Surface treatment
• CPC Class Codes: F05D 2300/43 Synthetic polymers, e.g. plastics; Rubber
• CPC Class Codes: F05D 2300/611 Coating
• CPC Class Codes: Y02T 50/60 Efficient propulsion technologies, e.g. for aircraft
• CPC Class Codes: Y10T 29/49318 Repairing or disassembling
• CPC Class Codes: Y10T 29/49746 by applying fluent material, e.g., coating, casting
• CPC Class Codes: Y10T 428/24942 including components having same physical characteristic in differing degree
• CPC Class Codes: Y10T 428/2495 Thickness [relative or absolute]

Abstract

This invention relates to the repair and removal of erosion or impact damage using hand sandable elastomeric coatings on a curved substrate, particularly such surfaces as the leading edge of the airfoil. Specialized applicators and methods of use are also disclosed.

Claims

1. A method of repairing an airfoil surface having an elastomeric protective coating adhered to a portion of said airfoil surface having a plurality of damage cavities caused by sand and water erosion or impact damage comprising:

filling said plurality of damage cavities in said elastomeric protective coating with a repair material of a hand sandable basecoat to fill said plurality of damage cavities to form filled cavities using a flexible planar applicator capable of conforming to the surface of said airfoil surface while being drawn lengthwise along the airfoil surface; and

applying a topcoat layer over the filled cavities, wherein the hand sandable basecoat has lower sand erosion resistance than the topcoat layer.

2. The method of claim 1 wherein the contact between the airfoil surface and said flexible planar applicator is a curvilinear line of contact which changes as the flexible planar applicator is drawn lengthwise along the airfoil surface.

3. The method of claim 1 wherein the portion of the airfoil surface containing the plurality of cavities is a surface surrounding the leading edge of said airfoil.

4. The method of claim 1 wherein said hand sandable basecoat constitutes at least 50% of the total thickness of topcoat layer and hand sandable basecoat.

5. The method of claim 1 further comprising a preliminary step of:

sanding the portion of said airfoil surface containing said plurality of damage cavities with abrasive material.

6. The method of claim 1 further comprising applying a primer coat in damage cavities.

7. The method of claim 1 wherein said hand sandable basecoat has an elastomeric base composition having a minimum tensile strength of 1000 psi, an elongation at break of at least 100%, and a Shore A hardness of less than 95 A as tested before incorporating additional fillers added in sufficient amount to render the elastomeric base composition sandable.

8. The method of claim 1 wherein the hand sandable basecoat disposed surrounding said leading edge surface has a sand erosion rate above 0.020 grams/cm²;

and the topcoat layer disposed on top of said hand sandable basecoat has a sand erosion rate below 0.020 grams/cm².

9. The method according to claim 1 wherein the hand sandable basecoat disposed surrounding said leading edge surface has a sand erosion rate above 0.040 grams/cm²;

and the topcoat layer disposed on top of said hand sandable basecoat has a sand erosion rate below 0.015 grams/cm².

10. The method of claim 1 wherein said flexible planar applicator is a flat sheet of elastomeric or thermoplastic material of selected thickness to allow it to be deformable around an arcuate surface and stiff enough to spread viscous material smoothly ahead of it when drawn through the viscous material.

11. The method of claim 1 wherein said hand sandable basecoat comprises an elastomeric base composition having incorporated therein at least 20 percent by weight of a filler.

12. The method of claim 1 wherein said hand sandable basecoat comprises an elastomeric base composition having incorporated therein less than 90 percent by weight of a filler.

13. The method of claim 1 wherein said hand sandable basecoat comprises an elastomeric base composition having incorporated therein between 20 percent to 80 percent by weight of a filler.

14. The method of claim 1 wherein said hand sandable basecoat comprises an elastomeric base composition having incorporated therein between 30 percent to 70 percent by weight of a filler.

15. The method of claim 1 wherein said filler is selected from a group consisting of silicates, metal sulfates, gypsum, aluminum trihydrate, graphite, metal oxides, metal sulfites, metal powders, metal flakes, milled metal fibers, metal nitrides, graphite, carbon nanotubes, milled carbon fibers, silicas, metal-coated glass spheres, metal-coated hollow spheres, buckyballs, electroactive polymers, antimony-doped tin oxide, carbon blacks, coke, micro-balloons, and the oxides, borides, carbides, nitrides and silicates of the group of compounds containing boron, aluminum, silicon, titanium, tungsten, and zirconium compounds.

16. The method of claim 1 wherein said filler is selected from a group consisting of talc, clays, montmorillonite, feldspar, mica, calcium silicate, calcium metasilicate, sodium aluminosilicate, sodium silicate, calcium sulfate, barium sulfate, sodium sulfate, aluminum sodium sulfate, aluminum sulfate, gypsum, aluminum trihydrate, graphite, calcium oxide, aluminum oxide, titanium dioxide, iron oxide, tin oxide, quartz, glass beads and glass bubbles.

17. The method of claim 1 wherein said filler is an organic based filler selected from group consisting of polycarbonate, polyetherimide, polyester, polyethylene, polysulfone, polystyrene, acrylonitrile-butadiene-styrene block copolymer, Teflon, fluoropolymers, polypropylene, acetal polymers, polyvinyl chloride, polyurethanes, nylon and combinations thereof, wherein the particle size of the fillers are nano-sized to 200 microns.

18. The method of claim 1 further comprising a preliminary step of applying a plurality of primer coats over any airfoil surface exposed within said damage cavities using a fine brush capable of controlling the primer coat deposition to about 1.0 mm, 2.00 mm and 3.00 mm in diameter.

19. The method of claim 1 further comprising a preliminary step of applying a plurality of coats of said hand sandable basecoat to damage cavities using a fine brush capable of controlling the hand sandable basecoat deposition within a range of about 1.0 mm, 2.00 mm and 3.00 mm in diameter prior to said filling step.

20. The method of claim 1 wherein said topcoat layer is from about 0.002 to 0.003 inch thick.

21. The method of claim 1 wherein said topcoat layer is at least 0.0005 inch thick.

22. The method of claim 1 wherein said topcoat layer less than 0.004 inch thick.

23. A method of repairing an airfoil surface having an elastomeric protective coating adhered to a portion of said airfoil surface having a plurality of damage cavities caused by sand and water erosion or impact damage comprising:

filling said plurality of damage cavities in said elastomeric protective coating with a repair material using a flexible planar applicator capable of conforming to the surface of said airfoil surface while being drawn lengthwise along the airfoil surface, wherein said filling step comprises applying a hand sandable basecoat to fill said plurality of damage cavities to form filled cavities; and

applying a topcoat layer over the filled cavities;

wherein the hand sandable basecoat has lower sand erosion resistance than the topcoat layer and said hand sandable basecoat constitutes at least 50% of the total thickness of topcoat layer and hand sandable basecoat and said hand sandable basecoat is a polyurethane or polyurea coating composition having incorporated therein at least one filler added at a concentration greater than 20 percent by weight.

24. The method of claim 23 said topcoat layer is a polyurethane or polyurea topcoat layer over the hand sandable basecoat.

25. The method of claim 23 further comprising applying a plurality of primer coats over any airfoil surface exposed within said damage cavities before filling said damage cavities with said hand sandable basecoat.

26. The method of claim 23 wherein said hand sandable basecoat when tested without said filler has a minimum tensile strength of 1000 psi, an elongation at break higher than 100% and a Shore A hardness of less than 95 A as measured at 68°

F.

27. The method of claim 23 wherein said filler is an organic based filler selected from group consisting of polycarbonate, polyetherimide, polyester, polyethylene, polysulfone, polystyrene, acrylonitrile-butadiene-styrene block copolymer, Teflon, fluoropolymers, polypropylene, acetal polymers, polyvinyl chloride, polyurethanes, nylon and combinations thereof, wherein the particle size of the fillers are nano-sized to 200 microns.

28. The method of claim 23 wherein the filler is selected from a group consisting of talc, clays, montmorillonite, feldspar, mica, calcium silicate, calcium metasilicate, sodium aluminosilicate, sodium silicate, calcium sulfate, barium sulfate, sodium sulfate, aluminum sodium sulfate, aluminum sulfate, gypsum, aluminum trihydrate, graphite, calcium oxide, aluminum oxide, titanium dioxide, iron oxide, tin oxide, quartz, glass beads and glass bubbles.

29. The method of claim 23 wherein the filler is selected from a group consisting of silicates, metal sulfates, gypsum, aluminum trihydrate, graphite, metal oxides, metal sulfites, metal powders, metal flakes, milled metal fibers, metal nitrides, graphite, carbon nanotubes, milled carbon fibers, silicas, metal-coated glass spheres, metal-coated hollow spheres, buckyballs, electroactive polymers, antimony-doped tin oxide, carbon blacks, coke, micro-balloons, and the oxides, borides, carbides, nitrides and silicates of the group of compounds containing boron, aluminum, silicon, titanium, tungsten, and zirconium compounds.

30. The method of claim 23 wherein the airfoil surface is a part of windmill blades, turbine blades, runner blades, fan blades, compressor blades, propeller blades, vanes, stay vanes, hydroelectric turbines, marine propellers, hydro turbines, gas turbines, tide mills, windmills, compressors, pumps, blower, impellers, propellers, and fans.

31. The method of claim 23 wherein the airfoil surface is a helicopter rotor blade.

32. The method of claim 23 wherein said polyurethane or polyurea coating composition comprises an aqueous polyurethane dispersion with or without curing agents.