Method and coating for protecting and repairing an airfoil surface using molded boots, sheet or tape

Abstract

Disclosed is a field repairable airfoil structure such as a wing or a rotor blade and a method for repair and removal of erosion or impact damage to elastomeric coatings on surfaces such as the leading edge of the airfoil using special hand sandable coatings and preformed molded boots, preformed sheets or tapes with an optional topcoat applied thereto having higher sand erosion resistance.

1 . A method for protecting an airfoil leading edge surface from sand and water erosion comprising the steps of:
 a) applying to said leading edge surface a preformed molded covering having a complementary shape to said leading edge surface;   b) bonding said preformed molded covering to said leading edge surface; and   c) applying a sand erosion resistant topcoat   
     
     
         2 . The method according to  claim 1  wherein said applying a sand erosion resistant topcoat step comprises brushing or spraying a plurality of layers to form said topcoat. 
     
     
         3 . The method according to  claim 1  wherein said preformed molded covering is a molded boot having an interior surface complementary in three dimensional shape to the outer surface of said airfoil leading edge surface. 
     
     
         4 . The method according to  claim 1  wherein said preformed molded covering is a molded sheet conformable to said airfoil leading edge surface and said basecoat being configured to have a sand erosion rate expressed, as mass weight loss, of greater than 0.024 grams, and said topcoat being configured to have a sand erosion rate of less than 0.020 grams. 
     
     
         5 . The method according to  claim 1  wherein said preformed molded covering is a preformed tape conformable to said airfoil leading edge surface. 
     
     
         6 . An elastomeric erosion protection composite for airfoil leading edge surfaces comprising: a basecoat selected from the group consisting of a hand sandable preformed molded elastomeric boot and a preformed elastomeric sheet, said basecoat being bonded to said airfoil leading edge surface and a layer of sand erosion resistant topcoat disposed on top of said preformed molded boot or preformed elastomeric sheet. 
     
     
         7 . The elastomeric erosion protection composite according to  claim 6  wherein said basecoat is configured to have a sand erosion rate, expressed as mass weight loss, of greater than 0.024 grams and said topcoat is configured to have a sand erosion rate of less than 0.020 grams. 
     
     
         8 . The elastomeric erosion protection composite according to  claim 6  wherein said basecoat has a sand erosion rate, expressed as mass weight loss, of greater than 0.040 grams and said topcoat has a sand erosion rate of less than 0.01 grams. 
     
     
         9 . The elastomeric erosion protection composite according to  claim 6  wherein said basecoat has a sand erosion rate of greater than 0.050 grams. 
     
     
         10 . The elastomeric erosion protection composite according to  claim 6  wherein said basecoat is configured to have a sand erosion rate expressed as mass weight loss of greater than 0.040 grams and said topcoat is configured to have a sand erosion rate of less than 0.040 grams. 
     
     
         11 . A single layer erosion resistant elastomeric coating for protecting airfoil leading edge surfaces from erosion comprising a single layer of an elastomeric, hand sandable basecoat adhered on said leading edge of said airfoil having a sand erosion rate above 0.020 grams/cm 2  and a water erosion rate of greater than 100 minutes wherein said water erosion rate is performed with water droplet size of 1.8-2.0 mm, 90 degree impact angle and rainfall rate of one inch per hour. 
     
     
         12 . The single layer erosion resistant elastomeric coating according to  claim 11  wherein said elastomeric hand sandable basecoat composition is selected from the group consisting of a liquid resin, a brushable coating, a sprayable coating, a preformed solid sheet, a molded boot and a preformed tape. 
     
     
         13 . The single layer erosion resistant elastomeric coating according to  claim 11  wherein said elastomeric hand sandable basecoat composition is disposed on top of a primer selected from the group consisting of a liquid brush applied coating, a liquid spray applied coating, a liquid adhesive, and a solid adhesive. 
     
     
         14 . The single layer erosion resistant elastomeric coating according to  claim 13  wherein said primer layer includes a gap spacer comprising a material having interstices capable of holding said primer. 
     
     
         15 . The single layer erosion resistant elastomeric coating according to  claim 14  wherein said gap spacer is selected from the group consisting of a fabric and an open mesh. 
     
     
         16 . An article of manufacture subjected to high speed impingement of sand and debris entrained in a fluid comprising a leading edge surface which encounters said sand and debris having adhered thereto an erosion resistant elastomeric coating of an elastomeric, hand sandable basecoat adhered on said leading edge surface of said airfoil having a sand erosion rate above 0.020 grams/cm 2  and a water erosion rate of greater than 100 minutes wherein said water erosion rate is performed with water droplet size of 1.8-2.0 mm, 90 degree impact angle and rainfall rate of one inch per hour. 
     
     
         17 . An article of manufacture according to  claim 16  selected from the group consisting 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. 
     
     
         18 . An article of manufacture according to  claim 16  wherein said erosion resistant elastomeric coating is applied by spraying a plurality of layers of said coating onto said leading edge surface. 
     
     
         19 . An article of manufacture according to  claim 16  wherein said erosion resistant elastomeric coating is applied by adhering to said leading edge surface a prefabricated elastomeric coating structure selected from the group consisting of preformed molded boots, preformed elastomeric sheets and preformed elastomeric tape. 
     
     
         20 . An article of manufacture according to  claim 16  wherein said erosion resistant elastomeric coating is adhered to the leading edge surface with a binding layer selected from the group consisting of a primer and an adhesive. 
     
     
         21 . An elastomeric airfoil erosion protection coating for visual detection of water and sand erosion damage comprising:
 a) an adhesive layer of a first color applied directly on a structural substrate of said airfoil surrounding a leading edge of said airfoil;   b) a basecoat of a second color selected from the group consisting of a preformed molded boot having a shape complementary to said leading edge of said airfoil, a preformed elastomeric sheet and a preformed elastomeric tape applied over said adhesive layer; and   c) a topcoat of a third color on top of said basecoat, wherein said first color, second color and third color are contrasting colors allowing visual detection of damage to said protection coating by visual inspection to detect the appearance of the second color of said basecoat or first color of said adhesive layer indicating damage in the area.   
     
     
         22 . A method of detecting damage to an airfoil erosion protection coating having an adhesive layer of a first color, a basecoat of a second color, said basecoat selected from the group consisting of a preformed molded boot, a preformed elastomeric sheet and a preformed elastomeric tape and a top coat of a third color comprising:
 detecting erosion damage by visually inspecting the erosion protection coating to detect the appearance of the second color of the basecoat or the first color of the primer which indicates that there is erosion damage in the area of the airfoil protection coating where the first color or second color appear.   
     
     
         23 . A method of detecting and repairing damage to an airfoil erosion protection coating having an adhesive layer of a first color, a basecoat of a second color, said basecoat selected from the group consisting of a preformed molded boot, a preformed elastomeric sheet and a preformed elastomeric tape and a top coat of a third color comprising:
 a) detecting erosion damage by visually inspecting the erosion protection coating to detect the appearance of the second color of the basecoat or the first color of the adhesive layer which indicates that there is erosion damage in the area of the airfoil protection coating where the first color or second color appear; and   b) reapplying a plurality of layers of said topcoat to the areas showing said first color or said second color.   
     
     
         24 . A method of making an airfoil leading edge erosion protection coating capable of being field repairable by hand sanding, comprising:
 a) applying to an airfoil substrate a composite system comprising a hand sandable basecoat selected from the group consisting of a preformed molded boot, a preformed elastomeric sheet and a preformed elastomeric tape and a topcoat, said handsandable basecoat being of lower sand erosion resistance than the topcoat and said basecoat constituting at least 50% of the total coating thickness;   b) subjecting said erosion protection coating to service which erodes portions of the topcoat away leaving a plurality of cavities in said basecoat having irregular edges;   c) repairing said erosion protection coating by sanding said plurality of cavities   d) applying a repair basecoat to fill said plurality of cavities to form filled cavities; and   e) applying a repair topcoat layer over the filled cavities.   
     
     
         25 . A method of detecting damage to a composite protective layer adhered to a leading edge surface of an airfoil structure comprising:
 a) applying an adhesive layer of a first color to the surface surrounding the leading edge of an airfoil structure;   b) overlaying a basecoat of a second color different from the first color on top of said adhesive layer, said basecoat being selected from the group consisting of a preformed molded boot, a preformed elastomeric sheet and a preformed elastomeric tape;   c) applying over said basecoat a topcoat of a third color different from the first color and the second color; and   d) detecting damage to said airfoil structure from water and sand erosion by visually inspecting the leading edge of the airfoil to detect the appearance of the second color of the basecoat or the first color of the adhesive layer in areas where erosion damage has occurred.   
     
     
         26 . An erosion protection coating for substrates adapted to be repairable by hand sanding comprising a topcoat and a sandable basecoat selected from the group consisting of a preformed molded boot, a preformed elastomeric sheet and a preformed elastomeric tape, wherein the basecoat has lower sand erosion resistance than the topcoat and said basecoat constitutes at least 50% of the total coating thickness. 
     
     
         27 . A field repairable polymeric erosion protection composition positioned on and adhered to a leading edge surface of an airfoil comprising an elastomeric base composition loaded with fillers sufficient to render the polymeric erosion protection composition hand sandable, said base elastomeric base composition tested in accordance with ASTM D412-92 prior to incorporation of said fillers having a minimum tensile strength of 1000 psi, an elongation at break of at least 200%, and a Shore A hardness of less than 95A and said elastomeric base composition being selected from the group consisting of a preformed molded boot having a shape complementary to said leading edge of said airfoil, a preformed elastomeric sheet and a preformed elastomeric tape. 
     
     
         28 . A repairable elastomeric coating for a leading edge surface of an airfoil comprising:
 a) an elastomeric, hand sandable basecoat selected from the group consisting of a preformed molded boot, a preformed elastomeric sheet and a preformed elastomeric tape disposed surrounding said leading edge surface having a sand erosion rate above 0.020 grams/cm 2 ; and   b) an elastomeric topcoat disposed on top of said elastomeric basecoat having a sand erosion rate below 0.020 grams/cm 2 .   
     
     
         29 . The repairable elastomeric coating according to  claim 28  wherein the basecoat has lower sand erosion resistance than the topcoat and said basecoat constitutes at least 50% of the total coating thickness. 
     
     
         30 . A repairable elastomeric coating for a leading edge surface of an airfoil comprising:
 a) an elastomeric, hand sandable basecoat selected from the group consisting of a preformed molded boot, a preformed elastomeric sheet and a preformed elastomeric tape disposed surrounding said leading edge surface having an elastomeric base material having a minimum tensile strength of 1000 psi, an elongation at break of at least 200%, and a Shore A hardness of less than 95A with additional fillers added in sufficient amount to render the elastomeric base material sandable.   
     
     
         31 . An airfoil repair kit comprising:
 a) an adhesive bonding material; and   b) an elastomeric, hand sandable, basecoat selected from the group consisting of a preformed molded boot, a preformed elastomeric sheet and a preformed elastomeric tape repair material and an optional sand erosion resistant repair topcoat.   
     
     
         32 . The airfoil repair kit according to  claim 31  further comprising one or more components selected from the group consisting of a flexible applicator capable of conforming to a leading edge surface of an airfoil, a sanding disc, a primer, an elastomeric topcoat, a brush, and a disposable sprayer. 
     
     
         33 . A method for making an erosion resistant preformed elastomeric leading edge coating comprising:
 a) spraying a plurality of layers of a hand sandable elastomeric composition onto a mold surface of predetermined shape;   b) solidifying said hand sandable elastomeric composition;   c) repeating steps (a) and (b) to form a dry coating of the desired thickness;   d) removing said dry coating from said mold surface as said preformed elastomeric leading edge coating.   
     
     
         34 . The method of  claim 33 , further comprising the steps of: (e) placing said preformed elastomeric leading edge coating on an airfoil leading edge surface of complementary shape;
 and (f) adhering said elastomeric leading edge coating onto said airfoil leading edge surface of said airfoil.   
     
     
         35 . The method of  claim 34 , further comprising the steps of: (g) applying a topcoat over said elastomeric leading edge coating. 
     
     
         36 . The method of  claim 35 , wherein said topcoat has a greater sand erosion resistance than said elastomeric leading edge coating.