Abstract:
A method of making a wind turbine blade, and the turbine blade resulting form the process, is described in which correct alignment of the shear webs ( 42   a   , 42   b ) upon mould ( 30 ) closing is ensured. The method involves providing a first half shell ( 32   a ) and a second half shell ( 32   b ) to be joined together to form the wind turbine blade. A first edge ( 46 ) of a shear web ( 42 ) is attached to an inner surface ( 36   a ) of the first half shell ( 32   a ). A shear web mounting region is defined on an inner surface ( 36   b ) of the second half shell ( 32   b ). At least one guide block ( 60   a   , 60   b ) is attached to the inner surface ( 36   b ) of the second half shell ( 32   b ) adjacent to the shear web ( 42 ) mounting region. The guide block ( 60   a   , 60   b ) has a guide surface ( 70 ) oriented transversely to the inner surface of the second half shell ( 36   b ). Upon mould ( 30 ) closing, the first and second half shells ( 32   a   , 32   b ) are brought together whilst a second edge ( 52 ) of the shear web ( 42 ) is guided over the guide surface ( 70 ) of the mounting block ( 60   a   , 60   b ) towards the shear web mounting region defined on the inner surface ( 36   b ) of the second half shell ( 32   b ).

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates generally to the manufacture of wind turbine blades, and more specifically to a method and apparatus for ensuring the correct position of shear webs during blade manufacture. 
       BACKGROUND 
       [0002]    Wind turbine blades, such as the long blades employed on modern utility-scale wind turbines, generally comprise a hollow blade shell made primarily of composite materials, such as glass-fibre reinforced plastic. The blade shell is typically made up of two half shells, a windward shell and a leeward shell, which are moulded separately in respective female half moulds, before being bonded together along flanges at the leading and trailing edges of the blade. This method of manufacturing a blade is illustrated schematically in  FIG. 1   a.    
         [0003]    Referring to  FIG. 1 a   , this shows a mould  10  for a wind turbine blade divided into two half moulds, a windward mould  10   a  and a leeward mould  10   b , which are arranged side by side in an open configuration of the mould. A windward blade shell  12   a  is supported on a mould surface  14   a  of the windward mould  10   a  and a leeward blade shell  12   b  is supported on a mould surface  14   b  of the leeward mould  10   b . The shells  12   a ,  12   b  are each made up of a plurality of glass-fibre fabric layers, which are bonded together by cured resin. 
         [0004]    After forming the shells  12   a ,  12   b  in the respective mould halves  10   a ,  10   b , shear webs  16  are bonded to an inner surface  17  of the windward blade shell  12   a . The shear webs  16  are longitudinally-extending structures that bridge the two half shells  12   a ,  12   b  of the blade and serve to transfer shear loads from the blade to the wind turbine hub in use. In cross-section, as shown in  FIG. 1 a   , the shear webs  16  each comprise a web  18  having a lower edge  19  comprising a first longitudinally-extending mounting flange  20  and an upper edge  21  comprising a second longitudinally-extending mounting flange  22 . Adhesive such as epoxy is applied along these mounting flanges  22  in order to bond the shear webs  16  to the respective half shells  12   a ,  12   b.    
         [0005]    The relative terms ‘upper’ and ‘lower’ are used herein for convenience and refer to the orientation of the blade as shown in the figures. These terms are not intended to limit the scope of the invention. 
         [0006]    Referring now to  FIG. 1 b   , once the shear webs  16  have been bonded to the windward blade shell  12   a , adhesive is applied along the second (upper) mounting flanges  22  of the shear webs  16 , and along the leading edge  24  and trailing edge  26  of the blade shells  12   a ,  12   b . The leeward mould  10   b , including the leeward blade shell  12   b , is then lifted, turned and placed on top of the windward blade mould  10   a  in order to bond the two blade half shells  12   a ,  12   b  together along the leading and trailing edges  24 ,  26  and to bond the shear webs  16  to an inner surface  28  of the leeward blade shell  12   b . The step of placing one mould half on top of the other is referred to as closing the mould. 
         [0007]    It is important that the shear webs  16  are bonded in the correct position to both the windward and leeward blade shells  12   a ,  12   b . Ensuring the correct position of the shear webs  16  on the windward blade shell  12   a  is relatively straightforward because the blade mould  10  is in an open configuration when the shear webs  16  are bonded to the windward shell  12   a  and hence the inner surface  17  of the windward shell  12   a  is readily accessible. It is more difficult to ensure the correct position of the shear webs  16  in relation to the leeward shell  12   b  as the mould  10  is in a closed configuration when the shear webs  16  are bonded to the leeward shell  12   b  and hence the inner surface  28  of the leeward shell  12   b  is not accessible during the bonding process. Presently, therefore, the position of the shear webs  16  relative to the leeward shell  12   b  is measured with the mould  10  open and one must rely on the shear webs  16  staying in position on their own during mould closure and squeezing of the adhesive. 
         [0008]    Referring now to  FIG. 1 c   , a problem can arise when the mould  10  is closed whereby the shear webs  16  may move slightly relative to the leeward shell  12   b . For example, the shear webs  16  may move slightly under their own weight during mould closing or they may be dislodged by contact with the leeward shell  12   b . The concave curvature of the leeward shell  12   b also has a tendency to force the shear webs  16  together slightly, as shown in  FIG. 1 c   . The extent to which the shear webs  16  may move has been exaggerated in  FIG. 1 c    for illustrative purposes, whereas in practice the extent of movement may be as little as a few degrees or just a few millimeters. Still, small levels of movement of the shear webs  16  during mould closing may result in the shear webs  16  being bonded to the leeward shell  12   b  at a sub-optimal position. 
         [0009]    The present invention addresses this problem. 
       SUMMARY OF THE INVENTION 
       [0010]    According to the present invention there is provided a method of making a wind turbine blade, the method comprising:
       a. providing a first half shell and a second half shell to be joined together to form the wind turbine blade, the half shells each extending in a longitudinal direction;   b. attaching a first edge of a shear web to an inner surface of the first half shell;   c. defining a shear web mounting region on an inner surface of the second half shell;   d. attaching at least one guide block to the inner surface of the second half shell adjacent to the shear web mounting region, the guide block having a guide surface oriented transversely to the inner surface of the second half shell;   e. bringing the first and second half shells together whilst guiding a second edge of the shear web over the guide surface of the mounting block towards the shear web mounting region defined on the inner surface of the second half shell; and   f. attaching the second edge of the shear web to the shear web mounting region of the second half shell.       
 
         [0017]    The or each guide block advantageously serves to guide and direct the shear webs into the correct position on the second half shell as the shells are brought together. 
         [0018]    The guide surface of each guide block is oriented transversely to the local inner surface of the second half shell, where the guide block is located. 
         [0019]    Preferably a plurality of guide blocks is attached to the inner surface of the second half shell adjacent to the shear web mounting region. The guide blocks are spaced at intervals in the longitudinal direction. 
         [0020]    The or each guide block is preferably made from lightweight material such as foam, polystyrene or balsa wood. In a preferred embodiment of the present invention, the guide blocks are made from polyurethane foam. 
         [0021]    The guide block(s) are preferably bonded to the inner surface of the second half shell by means of adhesive. 
         [0022]    The second edge of the shear web is preferably bonded to the shear web mounting region of the second half shell. Accordingly, the method preferably involves applying adhesive to the second edge of the shear web and/or to the shear web mounting region defined on the inner surface of the second half shell. 
         [0023]    A shear web mounting region may be defined on the inner surface of the first half shell. The first edge of the shear web may be attached to the first shear web mounting region, for example it may be bonded in place using adhesive. 
         [0024]    The method may involve projecting a pre-determined pattern onto the inner surface of the second half shell, and/or onto the inner surface of the first half shell using laser projection or other projection technique. The pattern may indicate the position of the shear web mounting region(s) and/or predetermined mounting location(s) for the or each guide block. 
         [0025]    In a preferred embodiment of the present invention, the or each guide block is substantially wedge shaped. The or each guide block may taper in thickness from a thick end towards a thin end. The thick end of the guide block defines a mounting surface, which is attached to the inner surface of the second half shell. In use, when the blade shells are brought together, the shear web is guided over the guide surface in a direction from the thin end of the guide block towards the thick end. 
         [0026]    Preferably the guide surface is oriented so as to guide the shear web in a direction outwards from a central longitudinal axis of the blade towards a leading or trailing edge of the blade as the first and second half shells are brought together to form the blade. 
         [0027]    Preferably a first portion of the guide surface is located adjacent to the shear web mounting region and oriented substantially perpendicular to the inner surface of the second half shell. The first portion of the guide surface is orientated substantially perpendicular to the local surface of the second half shell. A second portion of the guide surface is preferably inclined relative to the first portion. As the shells are brought together, the shear web is preferably guided firstly over the second portion of the guide surface and subsequently over the first portion of the guide surface onto the inner surface of the second half shell. 
         [0028]    The perpendicular first portion of the guide surface adjacent to the mounting region serves to guide the shear web in a direction substantially perpendicular to the inner local surface of the second half shell, directly onto the mounting region, at the point of mould closure. This advantageously prevents shear forces being applied to the guide blocks and on the adhesive between the shear web and the second shell at mould closure. A strong bond between the shear webs and the second half shell is thereby ensured and the guide blocks are prevented from being dislodged by shear forces. 
         [0029]    The method preferably comprises applying adhesive to leading and trailing edge flanges of one or both of the first and second half shells. The adhesive serves to bond the shells together. The method preferably involves moving the second half shell relative to the first half shell in order to bring the shells together. However, in other examples the first half shell could be moved relative to the second half shell or both shells could be moved. Preferably the second half shell is placed on top of the first half shell. 
         [0030]    The shells are preferably each formed in a respective half mould of a wind turbine blade mould, and the method preferably involves bringing the half moulds together to join the first and second shells. The mould preferably has an open configuration and a closed configuration. In the open configuration, the half moulds are preferably arranged side by side, whilst in the closed configuration the half moulds are brought together, with one half mould typically being placed on top of the other. Preferably steps (c) and (d) of the method are performed with the mould open. Step (e) preferably involves closing the mould. For example, step (e) may comprise lifting and turning the second mould half and lowering the second mould half onto the first mould half. At the point of mould closure, the shear web is preferably guided in a substantially vertical direction into engagement with the second half shell, for example via the first portion of the guide surface as described above. 
         [0031]    The invention comprises a wind turbine blade made according to the above method, and a wind turbine comprising such a wind turbine blade. 
         [0032]    The invention also provides a wind turbine blade comprising: a blade shell formed from first and second half shells joined together and extending in a longitudinal direction; an interior region defined between opposed inner surfaces of the first and second half shells; at least one shear web located in the interior region of the blade, the shear web having a first edge attached to the inner surface of the first half shell and a second edge attached to the inner surface of the second half shell; and at least one guide block attached to the inner surface of the second half shell adjacent to the second edge of the shear web, the guide block having a guide surface oriented transversely to the inner surface of the second half shell. 
         [0033]    Preferably a plurality of guide blocks are spaced at intervals in the longitudinal direction adjacent to the second edge of the shear web. The or each guide block may be located on an inner side of the shear web with respect to a central longitudinal axis of the blade. The or each guide block is preferably made from lightweight material such as foam, polystyrene or balsa wood. In a preferred embodiment, the guide blocks are made from polyurethane foam. The or each guide block may be bonded to the second half shell by means of adhesive. 
         [0034]    In a preferred embodiment, the or each guide block is substantially wedge-shaped. Specially, the or each guide block tapers in thickness from a thick end towards a thin end. The thick end of the guide block is attached to the inner surface of the second half shell and the thin end of the guide block faces the first half shell. 
         [0035]    The guide surface of the or each guide block may comprise a first portion arranged adjacent to the second edge of the shear web and substantially perpendicular to the inner surface of the second half shell. The guide surface of the or each guide block may comprise a second portion inclined relative to the first portion. 
         [0036]    The first edge and/or the second edge of the shear web is preferably bonded to the respective half shell by means of adhesive. 
         [0037]    Optional features of the invention described in relation to the method apply equally to the invention when expressed in terms of an apparatus and vice versa. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0038]      FIGS. 1 a -1 c    illustrate a prior art method of making a wind turbine blade and have been described above by way of background to the present invention. 
           [0039]    In order that the present invention may be more readily understood, non-limiting examples of the invention will now be described in more detail with reference to the following figures, in which: 
           [0040]      FIG. 2 a    shows a wind turbine blade mould comprising a windward mould half and a leeward mould half in an open configuration and with a pair of shear webs bonded to a windward half shell supported in the windward mould half and guide blocks bonded to a leeward half shell supported in the leeward mould half; 
           [0041]      FIG. 2 b    shows a wind turbine blade mould during closing with the leeward mould half upturned and supported above the windward mould half; 
           [0042]      FIG. 2 c    shows the wind turbine blade mould in a closed configuration with the first and second half shells bonded together to form a completed wind turbine blade; 
           [0043]      FIG. 3  shows the completed wind turbine blade as viewed from the root end and along a central longitudinal axis of the blade; and 
           [0044]      FIG. 4  shows a guide block in isolation. 
       
    
    
     DETAILED DESCRIPTION 
       [0045]    Referring to  FIG. 2 a   , this shows a wind turbine blade mould  30  comprising a windward mould half  30   a  and a leeward mould half  30   b  in an open configuration. A cured windward half shell  32   a  is supported on a surface  34   a  of the windward mould half  30   a  and a cured leeward half shell  32   b  is supported on a surface  34   b  of the leeward mould half  30   b . The half shells  32   a ,  32   b  each have a concave inner surface  36   a ,  36   b  extending between a leading edge  38  and a trailing edge  40  of the shell  32   a ,  32   b.    
         [0046]    First and second shear webs  42   a ,  42   b  are bonded to the inner surface  36   a  of the windward half shell  32   a . The shear webs  42   a ,  42   b  extend longitudinally along the windward shell  32   a . Each shear web  42   a ,  42   b  comprises a web  44  having a lower edge  46  comprising a first longitudinally-extending mounting flange  48  and an upper edge  50  comprising a second longitudinally-extending mounting flange  52 . The first mounting flange  48  of each shear web  42   a ,  42   b  is bonded to a shear web mounting region  54  defined on the inner surface  36   a  of the windward half shell  32   a.    
         [0047]    In accordance with the invention, a plurality of polyurethane guide blocks  60   a ,  60   b  are bonded to the inner surface  36   b  of the leeward half shell  32   b  by means of adhesive. The guide blocks  60   a ,  60   b  are substantially wedge-shaped and will be described in further detail with reference to  FIG. 4 . First and second guide blocks  60   a ,  60   b  are visible in the schematic cross-sectional view of  FIG. 2 a   . Referring to the enlarged portion of  FIG. 2 a   , the first guide block  60   a  is mounted adjacent to a first, longitudinally-extending, shear web mounting region  62   a  (illustrated by the dotted region  62   a ) defined on the inner surface  36   b  of the leeward half shell  32   b . The second guide block  60   b  is mounted adjacent to a second, longitudinally-extending, shear web mounting region  62   b  defined on the inner surface  36   b  of the leeward half shell  32   b.    
         [0048]    In practice, and as shown more clearly in the perspective view of  FIG. 3 , a plurality of first guide blocks  60   a  are spaced at longitudinal intervals adjacent to the first shear web mounting region  62   a , and a plurality of second guide blocks  60   b  are spaced at longitudinal intervals adjacent to the second shear web mounting region  62   b . The shear web mounting regions  62   a ,  62   b  each have an inner edge  64  and an outer edge  66  (also shown in the enlarged portion of  FIG. 2 a   ). The first and second guide blocks  60   a ,  60   b  are each mounted along the inner edge  64  of the respective shear web mounting region  62   a ,  62   b.    
         [0049]    The relative terms ‘inner’ and ‘outer’ are defined with respect to a central longitudinal axis C of the blade, which is indicated schematically in  FIG. 2 c    and extends substantially perpendicular to the plane of the page. 
         [0050]    Laser projection is used to determine the correct position for the shear webs  42   a ,  42   b  and the guide blocks  60   a ,  60   b  on the inner surface  36   b  of the leeward shell  32   b . Specifically, a laser-projected pattern is superimposed over the inner surface  36   b  of the leeward half shell  32   b  to indicate the correct position for locating the shear webs  42   a ,  42   b  and the guide blocks  60   a ,  60   b . A pen or other marking device is then used to mark on the inner surface  36   b  of the leeward shell  32   b  the shear web mounting regions  62   a ,  62   b  and the positions for mounting the guide blocks  60   a ,  60   b  adjacent to these regions. The blocks  60   a ,  60   b  are then mounted in these positions by means of adhesive. 
         [0051]    Referring now to  FIG. 2 b   , in order to join the windward and leeward half shells  32   a ,  32   b  together, adhesive is applied along the leading and trailing edges  38 ,  40  of the respective half shells  32   a ,  32   b  and along the second (upper) longitudinally-extending flanges  52  of the shear webs  42   a ,  42   b . The leeward half mould  30   b  is then lifted, turned 180 degrees and placed on top of the windward half shell  30   a.    
         [0052]    As described by way of background, and as shown in  FIG. 2 b   , the shear webs  42   a ,  42   b  may move slightly during the mould closing process. In accordance with the present invention, as the mould  30  is closed, the second (upper) edges  50  of the shear webs  42   a ,  42   b  come into contact with the guide blocks  60   a ,  60   b , and are guided by the guide blocks  60   a ,  60   b  into the correct positions defined on the inner surface  36   b  of the leeward half shell  32   b , i.e. onto the predefined shear web mounting regions  62   a ,  62   b.    
         [0053]    More specifically, and referring now to the enlarged portion of  FIG. 2 b   , each guide block  60   a ,  60   b  includes a guide surface  70  which is angled towards the appropriate shear web mounting region  62   a ,  62   b  defined on the inner surface  36   b  of the leeward shell  32   b . In this example, the first guide blocks  60   a  are mounted to the leeward half shell  32   b  such that their respective guide surfaces  70  guide the first shear web  42   a  towards the first shear web mounting region  62   a , and the second guide blocks  60   b  are mounted to the leeward half shell  32   b  such that their respective guide surfaces  70  guide the second shear web  42   b  towards the second shear web mounting region  62   b.    
         [0054]    Referring also to  FIG. 2 c   , the net effect of the guide blocks  60   a ,  60   b  is that during mould closure, the first and second shear webs  42   a ,  42   b  are moved outwards with respect to the central longitudinal axis C of the blade and towards one of the leading or trailing edges  38 ,  40  of the blade. In this example, the first shear web  42   a  is moved outwards slightly towards the trailing edge  40  and the second shear web  42   b  is moved outwards slightly towards the leading edge  38 . Hence, the shear webs  42   a ,  42   b  are moved outwards with respect to one another. As a result, and as shown in  FIG. 2 c   , when the mould  30  is completely closed the shear webs  42   a ,  42   b  are both substantially vertical and correctly positioned against the leeward half shell  32   b.    
         [0055]    Referring now to  FIG. 4 , this shows one of the guide blocks  60  in more detail. The guide block  60  is substantially wedge-shaped and has a thick end  76  and a thin end  78 . The thick end  76  of the guide block  60  comprises a mounting surface  80 , which is substantially rectangular in this example. The guide block  60  further includes a guide surface  70 , as mentioned previously, which extends between the thick end  76  and the thin end  78  of the block  60 , on one side of the block  60 . The guide surface  70  comprises a major guide surface  82  and a minor guide surface  84 . The major guide surface  82  is substantially rectangular and extends from the thin end  78  of the block  60  to an edge  86  of the block  60  spaced slightly apart from the mounting surface  80  of the block  60 . The minor guide surface  84  is substantially rectangular and is located between the major guide surface  82  and the mounting surface  80  of the block  60 . The minor guide surface  84  is orientated substantially perpendicular to the mounting surface  80  of the block  60 . The major guide surface  82  is inclined relative to the minor guide surface  84  and is inclined relative to the mounting surface  80  of the block  60 . 
         [0056]    In this example, the thickness t 1  of the block  60  at the thick end  76  is approximately 6 cm, and thickness t 2  of the block  60  at the thin end  78  is approximately 1 cm. The height (h) of the guide block  60  (i.e. the distance between the thick end  76  and the thin end  78 ) is approximately 10 cm. The major guide surface  82  of the block  60  has a length L 1  of approximately 15 cm, and the minor guide surface  84  has a length L 2  of approximately 2 cm. The major guide surface  82 , the minor guide surface  84 , and the mounting surface  80  of the guide block  60  each have a width W of approximately 5 cm. 
         [0057]    The mounting surface  80  of the guide block  60  is bonded to the leeward shell  32   b  such that the thin end  78  of the guide block  60  faces the windward half shell  32   a  when the mould  30  is closed. The guide surface  70  is oriented transversely to the inner surface  36   b  of the leeward half shell  32   b  when the block  60  is mounted to the leeward half shell  32   b . Specifically, the minor guide surface  84  is oriented approximately perpendicular to the curved inner surface  36   b  of the leeward half shell  32   b  at the location of the guide block  60 . The major guide surface  82  is inclined at an angle of approximately 135 degrees (in this example) relative to the local surface of the leeward half shell  32   b.    
         [0058]    In use, during closing of the mould  30 , the shear webs  42   a ,  42   b  are initially guided over the major guide surfaces  82  of the blocks  60  towards the respective mounting regions  62   a ,  62   b  defined on the leeward shell  32   b . The shear webs  42   a ,  42   b  initially make contact with the blocks  60  near the thin ends  78  of the blocks  60  and as the mould  30  closes, the shear webs  42   a ,  42   b  are guided along the major guide surfaces  82  in a direction towards the thick ends  76  of the blocks  60 . 
         [0059]    Immediately prior to the mould  30  closing (i.e. just prior to the point when the leeward shell and the windward shell join), the upper mounting flanges  22  of the shear webs  42   a ,  42   b  are guided by the minor guide surfaces  84  of the respective guide blocks  60  in a direction substantially perpendicular to the local surface  36   b  of the leeward shell  32   b , i.e. the shear webs  42   a ,  42   b  are guided directly onto the shear web mounting regions  62   a ,  62   b . Consequently, the final motion of the shear webs  42   a ,  42   b  as the mould  30  closes is in a vertical sense, and hence substantially no shear forces is applied to the shear webs  42   a ,  42   b  and the adhesive between the upper mounting flanges  22  of the shear webs  42   a ,  42   b  and the leeward shell  32   b  at the point of mould closure and squeezing of the adhesive. The absence of shear forces being applied upon squeezing of the adhesive ensures that a strong bond is created between the shear webs  42   a ,  42   b  and the leeward shell  32   b . The vertical motion of the shear webs  42   a ,  42   b  upon mould closure also substantially prevents the shear webs  42   a ,  42   b  from exerting shear forces on the guide blocks  60 , which advantageously prevents the guide blocks  60  from being dislodged upon mould closure. When in position in the mounting regions  62   a ,  62   b , the shear webs  42   a ,  42   b  abut the minor guide surfaces  84  of the blocks  60 , which conveniently serve to maintain the shear webs  42   a ,  42   b  in the correct positions during the bonding process. 
         [0060]    In this example, the guide blocks  60  are not removed after the blade shells  32   a ,  32   b  are bonded together, and hence remain bonded to the leeward shell  32   b  in the completed blade. The guide blocks  60  are relatively small in comparison to the overall size of the blade and are advantageously made from lightweight material (in this case PU foam) and hence do not appreciably add to the weight of the blade. Leaving the guide blocks  60  in place is advantageous because it avoids the need to remove the blocks  60  after manufacturing the blade which may be time consuming and difficult when working within the confined space inside the blade. 
         [0061]    Many modifications may be made to the specific examples described above without departing from the scope of the present invention. For example, whilst the guide blocks in the above examples are substantially wedge-shaped, the guide blocks in other embodiments may have a different shape. In particular, guide blocks having a curved major guide surface are envisaged within the scope of the present invention. 
         [0062]    Whilst in the examples above the shear webs are bonded to the windward shell with the blade mould open, i.e. the adhesive between the shear webs and the windward shell is cured prior to closing the mould, in other examples the shear webs may be bonded simultaneously to both the windward shell and the leeward shell when the mould is closed. For example, the shear webs may initially be attached to the windward shell and shortly after this the mould may be closed such that the adhesive between the shear webs and the windward shell cures at the same time as the adhesive between the shear webs and the leeward shell, thereby advantageously reducing the production time for the blade.