Abstract:
A method for manufacturing a wind turbine rotor blade having a trailing edge by Vacuum Assisted Resin Transfer Molding is described. A number of layers having fiber material are laid up onto the inner surface of a first mold part. A plurality of fiber rovings is laid up onto the number of layers at a position which forms the trailing edge of the blade. The blade is cast using Vacuum Assisted Resin Transfer Molding.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority of European Patent Office application No. 12151903.7 EP filed Jan. 20, 2012, which is incorporated by reference herein in its entirety. 
     FIELD OF INVENTION 
     The present application relates to a method for manufacturing a wind turbine rotor blade comprising a trailing edge by Vacuum Assisted Resin Transfer Moulding (VARTM). It further relates to a wind turbine rotor blade and to a wind turbine. 
     BACKGROUND OF INVENTION 
     From the document EP 1 310 351 B1 it is known to cast an integrated wind turbine rotor blade in one moulding process using for example a VARTM process. It is furthermore known to add core material such as balsawood or PVC foam in the blade, such as at the trailing edge of the blade, to increase the stability and stiffness of the blade. The purpose of putting core material in the trailing edge of the blade is to build stiffness to this part of the rotor blade. 
     To integrate for example triangular shaped trailing edge core material it is necessary to establish extra layers of reinforced material around the triangular shaped trailing edge core material and it all is established in between the outer shell layers of the blade composite structure. Hereby a trailing edge “web” is created which helps in transferring forces and creates stiffness between the upper and lower parts of the blade construction. However, one difficulty with this solution is that it is relatively time consuming to lay up the reinforced fibre material around the core material in a proper manner so that the desired construction and properties are achieved. 
     SUMMARY OF INVENTION 
     A first objective of the present application is to provide an improved method for manufacturing a wind turbine rotor blade which is less time consuming and saves costs. It is a second objective of the present application to provide a wind turbine rotor blade. A third objective is to provide a wind turbine. 
     The disclosed method for manufacturing a wind turbine rotor blade comprising a trailing edge is performed by Vacuum Assisted Resin Transfer Moulding (VARTM). The disclosed method comprises the steps of laying up a number of layers comprising fibre material onto the inner surface of a first mould part, laying up a plurality of fibre rovings onto the number of layers at a position which forms the trailing edge of the blade, and casting the blade using Vacuum Assisted Resin Transfer Moulding. The plurality of fibre rovings can be laid up onto the innermost or inner or uppermost layer of the previously laid up number of fibre layers. 
     The application is in that the construction uses lesser and cheaper material and thus is lighter than the construction of prior art though still providing the transfer of forces between upper and lower part of the blade. Moreover, reinforcement of the trailing edge is achieved, in combination with shear force transfer between the two blade sides. 
     The application is further in that the construction is relatively simple to build up during the manufacturing of the blade i.e. during lay-up of fibre material. The effect of this is that it is cost effective as less man-hour is spent. 
     The application is even further in that bundles of rovings are very flexible and will absorb process tolerances between the blade sides at the trailing edge and consequently adapt its form to the cavity which the mould form creates. 
     The used rovings may have a longitudinal direction. The rovings can be laid up with the longitudinal direction running parallel to the trailing edge or parallel to the blade longitudinal direction or span direction. 
     Bundles of roving can be used in order to be able to control the lay-up of the fibre rovings in the mould before casting and for holding the fibre rovings. A number of rovings may be bundled or joined or connected or combined to a bundle before laying up the number of rovings onto the number of layers. 
     For example, a wrapping or wrapping coating or sock or a similar means with a similar function can be used to form the bundle of rovings. The wrapping or wrapping coating or sock or the similar means can comprise fibre material, for example glass fibre material or carbon fibre material, and/or paper and/or plastics and/or a polymer. Moreover, the wrapping or wrapping coating or sock or similar means can at least partly dissolve during the casting process. This has the feature that the rovings can perfectly adapt to the shape given by the mould parts during the casting process. 
     The plurality of rovings can be established in parallel inside the said wrapping or wrapping coating or sock or similar means. 
     A second mould part comprising an inner surface, onto which a number of layers comprising fibre material is laid up, can be placed onto the first mould part creating a closed mould cavity. Moreover, an airtight membrane can be placed onto the fibre rovings and the number of layers, such as the innermost fibre layer, for creating vacuum in the space between the membrane and the inner surface of the first mould part and/or the inner surface of the second mould part. Creating vacuum is necessary for performing the VARTM process. 
     Furthermore, the fibre rovings can be compressed and/or adapted to a shape defined by the first mould part and/or second mould part and/or the airtight membrane, for example by applying vacuum. 
     The disclosed wind turbine rotor blade comprises a trailing edge and an inner surface. The inner surface of the blade at the trailing edge comprised a plurality of fibre rovings. The disclosed wind turbine rotor blade can be manufactured by the previously described method. 
     The disclosed wind turbine comprises a wind turbine rotor blade as previously described. 
     The present application has the feature, that lesser and cheaper material can be used compared with the state of the art and thus a lighter construction is obtained. Furthermore, an improved transfer of forces between upper and lower part of the blade, i.e. between pressure side and suction side, and also an additional reinforcement of the trailing edge are provided. Furthermore, the construction is relatively simple and cost effective as less man-hour is spent. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features of the present application will become clear from the following description of an embodiment in conjunction with the accompanying drawings. The embodiment does not limit the scope of the present application which is determined by the appended claims. All described features are as separate features or in any combination with each other. 
         FIG. 1  schematically shows a wind turbine. 
         FIG. 2  schematically shows a rotor blade in a plan view on the plane defined by the blade&#39;s span and the blade&#39;s chord. 
         FIG. 3  schematically shows a chord wise section through the airfoil portion of the blade shown in  FIG. 2 . 
         FIG. 4  schematically shows the process of putting core material in the trailing edge of the blade. 
         FIG. 5  schematically shows a bundle rovings in a perspective view. 
         FIG. 6  schematically shows a first mould part in a sectional view. 
         FIG. 7  schematically shows the first mould part and a second mould part forming a closed mould cavity in a sectional view. 
         FIG. 8  schematically shows part of the manufactured wind turbine blade in a sectional view. 
     
    
    
     DETAILED DESCRIPTION OF INVENTION 
       FIG. 1  schematically shows a wind turbine  1 . The wind turbine  1  comprises a tower  2 , a nacelle  3  and a hub  4 . The nacelle  3  is located on top of the tower  2 . The hub  4  comprises a number of wind turbine blades  35 . The hub  4  is mounted to the nacelle  3 . Moreover, the hub  4  is pivot-mounted such that it is able to rotate about a rotation axis  9 . A generator  6  is located inside the nacelle  3 . The wind turbine  1  is a direct drive wind turbine. 
       FIG. 2  shows a rotor blade in a plan view on the plane defined by the blade&#39;s span  10  and the blade&#39;s chord  8 .  FIG. 2  shows a wind turbine blade  35  as it is usually used in a three-blade rotor. However, the present application shall not be limited to blades for three-blade rotors. In fact, it may as well be implemented in other rotors, e.g. one-blade rotors or two-blade rotors. 
     The rotor blade  35  shown in  FIG. 1  comprises a root portion  23  with a cylindrical profile and a tip  22 . The tip  22  forms the outermost part of the blade  35 . The cylindrical profile of the root portion  23  serves to fix the blade  35  to a bearing of a rotor hub  4 . The rotor blade  35  further comprises a so-called shoulder  24  which is defined as the location of its maximum profile depth, i.e. the maximum chord length of the blade. Between the shoulder  24  and the tip  22  an airfoil portion  25  extends which has an aerodynamically shaped profile. Between the shoulder  24  and the cylindrical root portion  23 , a transition portion  27  extends in which a transition takes place from the aerodynamic profile of the airfoil portion  25  to the cylindrical profile of the root portion  23 . 
     A chord-wise cross section through the rotor blade&#39;s airfoil section  25  is shown in  FIG. 2 . Their aerodynamic profile shown in  FIG. 2  comprises a convex suction side  13  and a less convex pressure side  15 . The dash-dotted line extending from the blade&#39;s leading edge  29  to its trailing edge  11  shows the chord of the profile. Although the pressure side  15  comprises a convex section  17  and a concave section  19  in  FIG. 2 , it may also be implemented without a concave section at all as long as the suction side  13  is more convex than the pressure side  15 . 
     The suction side  13  and the pressure side  15  in the airfoil portion  25  will also be referred to as the suction side and the pressure side of the rotor blade  35 , respectively, although, strictly spoken, the cylindrical portion  23  of the blade  35  does not show a pressure or a suction side. 
       FIG. 4  schematically shows the process of putting core material in the trailing edge of the blade to build stiffness to this part of the rotor blade as it is known from for example EP 1 310 351 B 1. Extra layers of reinforced material  42  and  42   a  are established around a triangular shaped trailing edge core material  43  and it all is established in between outer shell layers  41  of the blade composite structure. Hereby, a trailing edge web  42   a  is created which helps in transferring forces and creates stiffness between the upper and lower parts of the blade construction. 
     An embodiment of the present application will now be described with reference to  FIGS. 5 to 8  in conjunction with  FIGS. 1 to 3 . In the context of the present application the trailing edge core material  43  as well as the said extra mats or layers of reinforced material  42 ,  42   a  in the trailing edge  11  are replaced with a plurality of composite fibre rovings extending along the trailing edge  11 . 
     In order to be able to control the lay-up of the fibre rovings  44  in the mould before casting, it may be necessary to hold the fibre rovings  44 , for example in a glass or carbon fibre sock or wrapping coating  45 . This is schematically illustrated in  FIG. 5 .  FIG. 5  schematically shows a bundle rovings  40  in a perspective view. A number of rovings  44  are combined to a bundle by a sock or wrapping coating  45 . The rovings  44  comprise a longitudinal direction  48  and are arranged parallel to each other and parallel to the longitudinal direction  48 . The wrapping coating  45  comprises reinforcement material, for example glass fibre or carbon fibre material, and/or paper and/or plastics and/or a polymer. The sock or wrapping coating  45  at least partly dissolves during the casting process. 
       FIG. 6  schematically shows a first mould part  46   a  in a sectional view showing a position which forms the trailing edge  11  of the blade  35 . The first mould part  46   a  comprises an inner surface  49   a . A number of layers  41  comprising fibre material are laid up onto the inner surface  49   a  of the first mould part  46   a.    
     The bundle of rovings  40  is laid up onto the number of layers  41 , more precisely onto the innermost or uppermost layer of the number of layers, at a position which forms the trailing edge  11  of the blade  45 . 
       FIG. 7  schematically shows the first mould part  46   a  and a second mould part  46   b  forming a closed mould cavity in a sectional view. The second mould part  46   b  also comprises an inner surface  49   b  onto which a number of layers comprising fibre material  41  are laid up as previously described in conjunction with  FIG. 6  and the first mould part  46   a . The second mould part  46   b  is placed onto the first mould part  46   a  forming a closed mould cavity. An airtight membrane  47  is placed onto the inner side of the construction, which means onto the number of layers  41  and onto the bundle of rovings  40 , so that it is possible to create a vacuum in the space between the membrane  47  and the inner surfaces  49   a  and  49   b  of the mould parts  46   a  and  46   b  as required for the VARTM process. In other words, the bundle of rovings  40  or sock  45  comprising the plurality of fibre rovings  44  is laid up and also placed in the “vacuum space”. 
     When applying vacuum the sock or wrapping coating  45  and the rovings  44  will be compressed and adapted to the shape defined by the mould forms  46   a  and  46   b  and the vacuum bag  47 . Then the blade is casted using VARTM. During this process resin is injected into the space between the inner surfaces  49   a  and  49   b  of the mould parts  46   a  and  46   b  and the airtight membrane  47 . In a variant of the application, the wrapping coating or sock  45  enclosing the said rovings  44  dissolves during the casting process. 
     Then the resin is set. Consequently, after ending the moulding process and after removing the airtight membrane  47  the casted blade trailing edge  11  schematically looks like illustrated in  FIG. 8 .  FIG. 8  schematically shows part of the manufactured wind turbine blade, more precisely part of the wind turbine rotor blade close to the trailing edge  11 , in a sectional view. The manufactured wind turbine rotor blade  35  comprises an inner surface  39 . The inner surface  39  close to the trailing edge  11  comprises a plurality of fibre rovings  44 .