Aerodynamic article with protective coating and method of bonding metal to polyurethane
To protect an article with an aerodynamic surface, such as an aeroplane propeller or helicopter rotor, from erosive damage caused by flying particulate matter, a thin elastomeric protective covering is provided. This layer covers approximately 15% of a forward face ( 15 ) a leading edge ( 12 ), and approximately 90% of the rear face ( 13 ) of the article. Typically, it is made of polyurethane with hardness between 85 Shore A and 80 Shore D. It is applied by centrifugal casting using a silane log gammaglycidoxporpyl-tri-methoxysilane as a coupling agent when bonding to a metal surface such as aluminum.
1. An article having an aerodynamic surface with a portion having a protective covering thereon which is adapted to provide resistance to wear, the portion including an end edge of the article, a minor forward face, and a major rearward face portion, wherein said end edge is prone to erosion from particulate matter when in use and wherein the protective covering comprises an elastomer substance which is bonded to the portion.
2. The article as claimed in claim 1 wherein the protective covering has a hardness between 85 Shore A and 80 Shore D.
3. The article as claimed in claim 2 wherein the portion comprises a minor forward face portion, an end edge portion and a major rearward face portion of the article.
4. The article as claimed in claim 3 wherein the minor forward face portion extends from the outermost 15% of the length of the forward face edge of the blade to the outermost edge of the blade.
5. The article as claimed in claim 1 wherein the minor forward face portion extends from the outermost 15% of the length of the forward face edge of the article to the outermost edge of the article.
6. The article as claimed in claim 5 wherein the edge portion extends from the forward face to the rearward face portion.
7. The article as claimed in claim 6 wherein the major rearward face portion extends along the length of a rearward edge of the article from the trailing edge to the leading edge portion.
8. The article as claimed in claim 7 wherein the end edge portion comprises approximately 6% of the major length of the article as measured from the end edge inwardly.
9. The article as claimed in claim 8 wherein the end edge portion comprises a leading edge and has a convex arcuate shape.
10. The article as claimed in claim 9 wherein the end edge portion tapers toward the front and rearward face portions.
11. The article as claimed in claim 10 wherein the elastomer substance comprises polyurethane bonded with a silane coupling agent to an aluminum surface of the article.
12. The article as claimed in claim 11 wherein the end edge portion has a radial width of 1 to 6 mm.
13. The article as claimed in claim 12 wherein the portion is part of a propeller.
14. The article as claimed in claim 13 wherein the portion excludes a major part of a top surface of the article.
15. A method of covering a portion of a metal surface comprising the steps of treating the surface of a portion with a silane coupling agent to allow bonding of a polyurethane substrate thereto, applying a polyurethane prepolymer to the treated surface of the portion and polymerising the prepolymer, whereby the polyurethane substrate is bonded to the surface of the portion.
16. The method as claimed in claim 15 where the metal surface comprises an aerodynamic surface.
17. The method as claimed in claim 16 wherein the metal surface is aluminum.
18. The method as claimed in claim 17 wherein the metal surface is the surface of a blade of one of a propeller, rotor, or impeller.
19. The method as claimed in claim 15 further including the step of placing an article having the portion in a mould, placing the mould in a centrifuge and operating the centrifuge to set the polymeric substance in the mould.
20. The method as claimed in claim 19 wherein the silane coupling agent is gammaglycidoxypropyltrimethoxysilane.
21. The method as claimed in claim 20 wherein the silane is applied as a 2% aqueous solution.
22. The method as claimed in claim 21 wherein the polyurethane substance which is bonded to the surface of the potion has a Shore hardness of between 85 Shore A and 80 Shore D.
23. The method claimed in claim 19 wherein the portion includes from 1 to 6 mm of the leading edge of the article.
24. The method as claimed in claim 23 wherein the portion includes between 0 and 0.5 mm at the trailing edge of the blade and 1 and 2 mm at the leading edge of the blade, along the rear face of the blade.
25. The method as claimed in claim 24 wherein the portion includes a section of the forward face of the blade extending inwardly from the leading edge approximately 15% of the length of the blade.