Abstract:
A method of manufacturing a wind turbine rotor blade includes, in one embodiment, the steps of providing a core, and applying at least one reinforcing skin to the core to form a blade subassembly. Each reinforcing skin is formed from a mat of reinforcing fibers. The method also includes applying a micro-porous membrane over the at least one reinforcing skin, applying a vacuum film over the micro-porous membrane, introducing a polymeric resin to the core, infusing the resin through the core and through the at least one reinforcing skin by applying a vacuum to the blade assembly, and curing the resin to form the rotor blade.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates generally to wind turbines, and more particularly to methods of fabricating wind turbine rotor blades utilizing a micro-porous membrane. 
     Recently, wind turbines have received increased attention as an environmentally safe and relatively inexpensive alternative energy source. With this growing interest, considerable efforts have been made to develop wind turbines that are reliable and efficient. 
     Generally, a wind turbine includes a rotor having multiple blades. The rotor is mounted on a housing or nacelle, which is positioned on top of a truss or tubular tower. Utility grade wind turbines (i.e., wind turbines designed to provide electrical power to a utility grid) can have large rotors (e.g., 30 or more meters in diameter). Blades on these rotors transform wind energy into a rotational torque or force that drives one or more generators, rotationally coupled to the rotor through a gearbox or directly coupled to the rotor. The gearbox, when present, steps up the inherently low rotational speed of the turbine rotor for the generator to efficiently convert mechanical energy to electrical energy, which is fed into a utility grid. 
     Known wind turbine blades are fabricated by infusing a resin into a fiber wrapped core. A layer of distribution mesh is used to feed resin into the core material. The infusion flow front is controlled by breaks in the distribution mesh which require exact positioning for the desired results. Also, the distribution mesh is discarded along with the resin that is retained in the mesh, about 650 grams per square meter. 
     BRIEF DESCRIPTION OF THE INVENTION 
     In one aspect, a method of manufacturing a wind turbine rotor blade is provided. The method includes the steps of providing a core and applying at least one reinforcing skin to the core to form a blade subassembly. Each reinforcing skin is formed from a mat of reinforcing fibers. The method also includes applying a micro-porous membrane over the at least one reinforcing skin, applying a vacuum film over the micro-porous membrane, introducing a polymeric resin to the core, infusing the resin through the core and through the at least one reinforcing skin by applying a vacuum to the blade assembly, and curing the resin to form the rotor blade. 
     In another aspect, a method of manufacturing a wind turbine rotor blade is provided. The method includes the steps of providing a core, applying at least one reinforcing skin to the core to form a blade subassembly, and positioning the blade subassembly in a mold. Each reinforcing skin is formed from a mat of reinforcing fibers. The method also includes applying a micro-porous membrane over the at least one reinforcing skin, applying a vacuum film over the micro-porous membrane, introducing a polymeric resin to the core, infusing the resin through the core and through the at least one reinforcing skin by applying a vacuum to the blade assembly, and curing the resin to form the rotor blade. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side elevation schematic illustration of an exemplary configuration of a wind turbine. 
         FIG. 2  is a side schematic illustration of the wind turbine rotor blade shown in  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A method of fabricating a wind turbine rotor blade utilizing a micro-porous membrane is described below in detail. The micro-porous membrane prohibits the passage of resins while permitting gas to pass through. This permits a vacuum to be applied to the entire rotor blade rather than peripherally as in known processes. The micro-porous membrane also facilitates a controlled flow front and eliminates any race-tracking of the resin flow. Cycle time along with labor time is reduced along with a reduction in the cost of process consumable materials. The use of the micro-porous membrane provides improved blade quality, for example, lower void content and optimized reinforcing fiber to resin ratios. 
     Referring to the drawings,  FIG. 1  is a side elevation schematic illustration of a wind turbine  100 , such as, for example, a horizontal axis wind turbine. Wind turbine  100  includes a tower  102  extending from a supporting surface  104 , a nacelle  106  mounted on a bedframe  108  of tower  102 , and a rotor  110  coupled to nacelle  106 . Rotor  110  includes a hub  112  and a plurality of rotor blades  114  coupled to hub  112 . In the exemplary embodiment, rotor  110  includes three rotor blades  114 . In an alternative embodiment, rotor  110  includes more or less than three rotor blades  114 . In the exemplary embodiment, tower  102  is fabricated from tubular steel and includes a cavity  120  extending between supporting surface  104  and nacelle  106 . In an alternate embodiment, tower  102  is a lattice tower. 
     Various components of wind turbine  100 , in the exemplary embodiment, are housed in nacelle  106  atop tower  102  of wind turbine  100 . The height of tower  102  is selected based upon factors and conditions known in the art. In some configurations, one or more microcontrollers in a control system are used for overall system monitoring and control including pitch and speed regulation, high-speed shaft and yaw brake application, yaw and pump motor application and fault monitoring. Alternative distributed or centralized control architectures are used in alternate embodiments of wind turbine  100 . In the exemplary embodiment, the pitches of blades  114  are controlled individually. Hub  112  and blades  114  together dorm wind turbine rotor  110 . Rotation of rotor  110  causes a generator (not shown in the figures) to produce electrical power. 
     In use, blades  114  are positioned about rotor hub  112  to facilitate rotating rotor  110  to transfer kinetic energy from the wind into usable mechanical energy. As the wind strikes blades  114 , and as blades  114  are rotated and subjected to centrifugal forces, blades  114  are subjected to various bending moments. As such, blades  114  deflect and/or rotate from a neutral, or non-deflected, position to a deflected position. Moreover, a pitch angle of blades  114  can be changed by a pitching mechanism (not shown) to facilitate increasing or decreasing blade  114  speed, and to facilitate reducing tower  102  strike. 
     Referring also to  FIG. 2 , blade  114  includes a core  120  that is formed from a polymeric foam, wood, and/or a metal honeycomb. A main spar  122  and an end spar  124  are embedded in core  120 . Examples of suitable polymeric foams include, but are not limited to, PVC foams, polyolefin foams, epoxy foams, polyurethane foams, polyisocyanurate foams, and mixtures thereof. Core  120  is wrapped with at least one reinforcing skin  126 . Each reinforcing skin  126  is formed from a mat of reinforcing fibers. Particularly, the mat is woven mat of reinforcing fibers or a non-woven mat of reinforcing fibers. Examples of suitable reinforcing fibers include, but are not limited to, glass fibers, graphite fibers, carbon fibers, polymeric fibers, ceramic fibers, aramid fibers, kenaf fibers, jute fibers, flax fibers, hemp fibers, cellulosic fibers, sisal fibers, coir fibers and mixtures thereof. 
     A resin is infused into core  120  and reinforcing skins  126  to provide integrity and strength to blade  114 . Examples of suitable resins include, but are not limited to, vinyl ester resins, epoxy resins, polyester resins, and mixtures thereof. A micro-porous membrane  128  is applied to the outer surface of blade  114  to facilitate the resin infusion process. The resin is introduced into core  120  under a vacuum. The vacuum causes the resin to flow through core  120  and reinforcing skins  126 . Micro-porous membrane  128  permits air that is displaced by the resin to escape from core  120  and reinforcing skins  126 . However, micro-porous membrane  128  does not permit the resin to pass through membrane  128 . Micro-porous membrane  128 , in one exemplary embodiment, has an average pore size of about 0.01 micrometer (μm) to about 10 μm, and in another embodiment, from about 0.1 μm to about 5 μm. Micro-porous membrane  128  is formed from, for example, polytetrafluoroethylene, polyolefin, polyamide, polyester, polysulfone, polyether, acrylic and methacrylic polymers, polystyrene, polyurethane, polypropylene, polyethylene, polyphenelene sulfone, and mixtures thereof. In one embodiment, micro-porous membrane  128  also includes a backing material laminated to one surface. The backing material is formed from polymeric fibers, for example, polyester fibers, nylon fibers, polyethylene fibers and mixtures thereof. An air transporter material  129  is positioned over micro-porous membrane  128  to assist in degassing core by permitting air displaced by the infused resin to escape to the atmosphere. Air transporter material  129  can be formed from any suitable mesh material, for example, a polyethylene mesh. 
     In the exemplary embodiment, core  120  includes a plurality of grooves  130  to facilitate the flow of resin through core  120 . In alternate embodiments, core  120  does not include grooves  130 . 
     To form rotor blade  114 , reinforcing skins  126  are wrapped around core  120  to form a blade subassembly  131  that is then positioned in a mold  132 . In alternate embodiments mold  132  is not used. A resin infusion input connection  134  is positioned adjacent the outer reinforcing skin  126 . Micro-porous membrane  128  is then positioned over the outer reinforcing skin  126  and resin infusion input connection. Air transporter material  129  is then positioned over micro-porous membrane  128 , and a vacuum connection  136  is positioned adjacent air transporter material  129 . A vacuum film  138  formed from a suitable material, for example, a polyamid, is positioned over air transporter material  129  with vacuum connection extending through vacuum film  138 . The resin is introduced into core  120  and reinforcing skins  126  through input connection  134  while a vacuum is established through vacuum connection  136 . The vacuum facilitates resin flow and infuses the resin into core  120  and reinforcing skins  126 . Micro porous membrane  128  prevents the resin from flowing away from core  120  and reinforcing skins  126  while permitting air displaced by the infused resin to escape to the atmosphere. The resin is then cured and resin input connection  134 , vacuum connection  136 , air transporter material  129 , and vacuum film  138  are removed from blade  114 . 
     While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.