Abstract:
A method of making an elongate wind turbine blade is described. The wind turbine blade extends longitudinally between a root end and a tip end in a spanwise direction, and the method comprises: (a) providing an elongate mould tool ( 20 ) extending longitudinally in a spanwise direction; (b) arranging an elongate spar structure ( 40 ) in the mould tool, the spar structure ( 40 ) N extending longitudinally in the spanwise direction; (c) arranging core material ( 24 ) adjacent to the spar structure ( 40 ); (d) providing resin-permeable material ( 114 ) between the spar structure ( 40 ) and the core material ( 24 ); and (e) administering resin into the mould during a resin infusion process. The resin-permeable material ( 114 ) restricts the flow of resin between the spar structure ( 40 ) and the core material ( 24 ) in the spanwise direction and thereby substantially prevents lock-offs from forming during the infusion process.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an improved method of making a wind turbine blade and to a wind turbine blade made according to the method. 
       BACKGROUND TO THE INVENTION 
       [0002]      FIG. 1  is a cross-sectional view of a wind turbine rotor blade  10 . The blade has an outer shell, which is fabricated from two half shells: a windward shell  11  a and a leeward shell  11   b.  The shells  11   a  and  11   b  are typically moulded from glass-fibre reinforced plastic (GRP). Parts of the outer shell  11  are of sandwich panel construction and comprise a core  12  of lightweight material such as foam (e.g. polyurethane) or balsa, which is sandwiched between inner  13  and outer  14  GRP layers or ‘skins’. Other core materials will be apparent to persons skilled in the art. 
         [0003]    The blade  10  comprises a first pair of load-bearing structures in the form of spar caps  15   a  and  15   b  and a second pair of load-bearing structures in the form of spar caps  16   a,    16   b.  The respective pairs of spar caps  15   a  and  15   b,    16   a  and  16   b  are arranged between sandwich panel regions of the shells  11   a  and  11   b.  One spar cap  15   a,    16   a  of each pair is integrated with the windward shell  11   a  and the other spar cap  15   b,    16   b  of each pair is integrated with the leeward shell  11   b.  The spar caps of the respective pairs are mutually opposed and extend longitudinally along the length of the blade  10 . 
         [0004]    A first longitudinally-extending shear web  17   a  bridges the first pair of spar caps  15   a  and  15   b  and a second longitudinally-extending shear web  17   b  bridges the second pair of spar caps  16   a  and  16   b.  The shear webs  17   a  and  17   b  in combination with the spar caps  15   a  and  15   b  and  16   a  and  16   b  form a pair of I-beam structures, which transfer loads effectively from the rotating blade  10  to the hub of the wind turbine. The spar caps  15   a  and  15   b  and  16   a  and  16   b  in particular transfer tensile and compressive bending loads, whilst the shear webs  17   a  and  17   b  transfer shear stresses in the blade  10 . 
         [0005]    Each spar cap  15   a  and  15   b  and  16   a  and  16   b  has a substantially rectangular cross section and is made up of a stack of pre-fabricated reinforcing strips  18 . The strips  18  are pre-cured pultruded strips of carbon-fibre reinforced plastic (CFRP), and are substantially flat and of rectangular cross section. The number of strips  18  in the stack depends upon the thickness of the strips  18  and the required thickness of the shells  11   a  and  11   b,  but typically the strips  18  each have a thickness of a few millimetres and there may be between three and twelve strips in a stack. The strips  18  have a high tensile strength, and hence have a high load bearing capacity. 
         [0006]    The blade  10  is made using a resin-infusion process as will now be described by way of example with reference to  FIGS. 2 and 3 . Referring to  FIG. 2 , this shows a mould  20  for a half shell of a wind turbine blade in cross-section. A glass-fibre layer  22  is arranged in the mould  20  to form the outer skin  14  of the blade  10 . Three elongate panels  24  of polyurethane foam are arranged on top of the glass-fibre layer  22  to form the sandwich panel cores  12  referred to above. The foam panels  24  are spaced apart relative to one another to define a pair of channels  26  in between. A plurality of pultruded strips  18  of CFRP, as described above with reference to  FIG. 1 , are stacked in the respective channels  26 . Three strips  18  are shown in each stack in this example, but there may be any number of strips  18  in a stack. 
         [0007]    Referring to  FIG. 3 , once the strips  18  have been stacked, a second glass-fibre layer  28  is arranged on top of the foam panels  24  and the stacks of pultruded strips  18 . The second glass-fibre layer  28  forms the inner skin  13  of the blade  10 . Next, vacuum bagging film  30  is placed over the mould  20  to cover the layup. Sealing tape  32  is used to seal the vacuum bagging film  30  to a flange  34  of the mould  20 . A vacuum pump  36  is used to withdraw air from the sealed region between the mould  20  and the vacuum bagging film  30 , and resin  38  is supplied to the sealed region. The resin  38  infuses between the various laminate layers and fills any gaps in the laminate layup. Once sufficient resin  38  has been supplied to the mould  20 , the mould  20  is heated whilst the vacuum is maintained to cure the resin  38  and bond the various layers together to form the half shell of the blade. The other half shell is made according to an identical process. Adhesive is then applied along the leading and trailing edges of the shells and the shells are bonded together to form the complete blade. 
         [0008]    The integration of the spar caps  15   a  and  15   b  and  16   a  and  16   b  within the structure of the outer shells  11   a  and  11   b  avoids the need for a separate spar cap such as a reinforcing beam, which is typically bonded to an inner surface of the shell in many conventional wind turbine blades. Other examples of rotor blades having spar caps integral with the shell are described in EP 1 520 983, WO 2006/082479 and UK Patent Application GB 2497578. 
         [0009]    When manufacturing wind turbine blades using a resin infusion process, it is important to control the resin flow front during the infusion process to ensure that the resin infuses evenly and completely throughout the laminate layup and between all of the shell components. If the flow front is not carefully controlled, then air pockets (also referred to as ‘lock offs’ or voids) may develop in the blade structure. Air pockets are caused by the incomplete infusion of resin in certain regions of the blade, and can result in localised weaknesses in the blade structure. 
         [0010]    The present invention has been developed against this background, and provides an improved method of manufacturing a wind turbine blade. In particular, the invention provides increased control over the resin flow front during resin infusion and eliminates or at least significantly reduces the possibility of air pockets forming. The present invention resides both in the identification of the problem, and in the solution to the problem. 
         [0011]    The particular problem identified by the inventors will now be described in detail with reference to  FIGS. 4 to 8 . 
         [0012]      FIG. 4  is a schematic representation of a spar structure  40  for a wind turbine blade arranged between first and second foam panels  42   a  and  42   b.  Referring to  FIG. 4 , the spar structure  40  in this example is a spar cap and comprises a plurality of CFRP pultrusions  44  arranged one on top of another to form a stack. The foam panels  42   a  and  42   b  are made from polyurethane foam. The spar cap  40  and foam panels  42   a  and  42   b  are arranged side by side in a suitable mould, for example a wind turbine blade shell mould (not shown), as described previously by way of introduction with reference to  FIG. 2 . Both the spar structure  40  and the foam panels  42   a  and  42   b  extend longitudinally in the mould, in a generally spanwise direction. A resin inlet channel  46  is also shown in  FIG. 4 , and will be described in further detail later with reference to  FIG. 7 . 
         [0013]    As shown in  FIG. 4 , a small gap  48  is present on each side of the spar cap  40 , between the spar cap  40  and the adjacent foam panel  42   a  or  42   b.  Whilst the spar caps  40  and foam panels  42   a  and  42   b  are arranged in the mould in close abutment, a small gap  48  is inevitable for reasons as will now be explained with reference to  FIGS. 5 and 6 . 
         [0014]      FIG. 5  is a schematic representation of a transverse cross section taken through a wind turbine blade shell mould  50 . A spar cap  40  and adjacent foam panel  42  are also shown schematically inside the mould  50 . The blade shell mould  50  has a concave curvature generally in the chordwise direction C, corresponding to part of the airfoil profile of the blade to be produced. The curvature of the mould  50  prevents the spar cap  40  and foam panel  42  from abutting closely across the entire interface  52  between the two components  40  and  42 , and results in a longitudinally-extending gap  48  at the interface  52 . 
         [0015]    Referring now also to  FIG. 6 , this is a schematic representation of part of the spar cap  40 . Here it can be seen that there may be a slight misalignment between the stacked pultrusions  44  comprising the spar cap  40 . The misalignments are exaggerated for clarity in  FIG. 6 , and in practice any misalignment may only be a fraction of a millimetre. In any event, misalignment between the stacked pultrusions  44  results in the longitudinal sides of the spar cap  40  not being perfectly flat, and this also contributes to the longitudinally-extending gaps  48  between the spar cap  40  and the adjacent foam panel  42  at the interface  52  between the abutting components  40  and  42 . 
         [0016]    The gaps  48  described above may cause undesirable resin flow during the infusion process as will now be described with reference to  FIGS. 7 and 8 . 
         [0017]    Referring to  FIG. 7 , during the resin infusion process, resin is admitted into the mould via the resin inlet channel  46 . The resin inlet channel  46  has a generally omega-shaped cross section, and extends longitudinally and substantially centrally in the mould. Resin is admitted into one end of the channel  46 , for example the end  54  shown in cross-section in  FIG. 7 , and the resin flows along the channel  46  in a generally spanwise direction S. Resin also flows out of the channel  46  in a generally chordwise direction C across the foam panel  42  and spar cap  40  in the mould as represented by the arrows  56  in  FIG. 7 . The aim of this arrangement is to achieve an angled flow front of the resin across and along the components  40 ,  42  as represented schematically by the shaded region  58  in  FIG. 7 . 
         [0018]    However, and referring now to  FIG. 8 , when the resin reaches the longitudinally-extending gaps  48  between the spar cap  40  and the foam panels  42 , the gaps  48  act as ‘race tracks’ for the resin, and the resin flows quickly along the gaps  48  in the spanwise direction S. The fast and uncontrolled resin flow along the gaps  48  can result in resin lock offs  60  forming, as shown in  FIG. 8 . The air contained in the lock off  60  cannot escape and so this region will not be infused. This lock off  60  may be present between individual pultrusions  44  of the spar cap  40 . 
         [0019]    The present invention provides a solution to this problem in the form of a method of making an elongate wind turbine blade extending longitudinally between a root end and a tip end in a spanwise direction, the method comprising:
       a. providing an elongate mould tool extending longitudinally in a spanwise direction;   b. arranging an elongate spar structure in the mould tool, the spar structure extending longitudinally in the spanwise direction;   c. arranging core material adjacent to the spar structure;   d. providing resin-permeable material between the spar structure and the core material; and   e. administering resin into the mould during a resin infusion process,
 
wherein the resin-permeable material restricts the flow of resin between the spar structure and the core material in the spanwise direction.
       
 
         [0025]    Steps b, c and d of the method may be performed in any order. 
         [0026]    According to the present invention, resin-permeable material is provided between the spar structure and the core material. The resin-permeable material restricts the flow of resin in the spanwise direction at the interface between the spar structure and the core material as compared to the situation where resin-permeable material is not provided at these interfaces. Thus, the race track effect described above, and the associated resin lock offs, are effectively prevented, and a more controlled resin flow front is achieved in the chordwise direction. 
         [0027]    The spar structure referred to above is a load-bearing structure and in preferred embodiments of the invention it is a spar cap comprising a stack of pultruded strips of reinforcing material as described previously. However, it should be appreciated that the invention is not limited in this respect and the spar structure may be another suitable load-bearing structure. The spar structure may be made of pre-cured material. For example the spar structure may be made of carbon-fibre reinforced plastic (CFRP). 
         [0028]    The core material may be any suitable core material, for example of the type typically used as the core of sandwich panels. Preferably the core material is foam, for example polyurethane foam, but it may instead be balsa or another suitably-lightweight material. In preferred examples of the invention, the core material is in the form of panels that are arranged in abutment with the spar structure, as described earlier. 
         [0029]    The resin-permeable material may be any compliant material that is capable of reducing the flow rate of resin at the interface between the spar structure and the core material. In preferred embodiments of the invention, the material is breather fabric, for example breather fabric made from polyester, nylon or blended fibreglass. Suitable breather fabrics include those produced by Tygavac Advanced Materials Ltd., such as the ‘Econoweave’, ‘Airweave’ and ‘Ultraweave’ series of fabrics. The breather fabric typically has a weight in the range of approximately 100-700 g/m 2 , although other weights may be suitable. As an alternative to breather fabric, the resin-permeable material may include polystyrene beads, spun polyester, or sponge material. The material will typically undergo some compression during the moulding process, and suitable materials are those that still allow resin to flow (albeit at a reduced flow rate) at the interface between the spar structure and the core material when the resin-permeable material is compressed to such an extent. 
         [0030]    The method may involve securing the resin-permeable material to the core material and/or to the spar structure. This has the advantageous effect of maintaining the breather fabric in the desired position during the layup process and during the subsequent infusion process. The resin-permeable material may be secured to the spar structure and/or to the core material when the associated component is arranged in the mould. For example the method may involve arranging the core material in the mould and subsequently attaching the resin-permeable to the core material, for example before the spar structures are arranged in the mould. 
         [0031]    A particularly advantageous effect may be realised by pre-attaching the resin-permeable material to the spar structure or to the core material before arranging the blade components in the mould. For example in a particular example of the invention, the resin-permeable material is pre-applied to the core material before the core material is arranged in the mould. This operation can be performed offline and hence reduces the blade production time in the mould. The resin-permeable material may be secured to the core material and/or to the spar structure by any suitable means, for example it may be bonded by a suitable adhesive or secured using scrim tape. 
         [0032]    During the resin-infusion process, the method may comprise administering resin into the mould in a direction transverse to the spanwise direction. Preferably the method comprises administering resin into the mould substantially in a chordwise direction, i.e. across the width of the mould. 
         [0033]    The method may further comprise providing a resin inlet channel extending longitudinally in the spanwise direction through which the resin is administered into the mould during the resin infusion process, and preferably the elongate spar structure is positioned between the resin-permeable material and the resin inlet channel. This prevents resin lock offs between the spar structure and the core material. 
         [0034]    The mould is preferably a blade shell mould. The mould may be a mould for making a half shell of a wind turbine blade. Alternatively the mould may be configured to make an entire wind turbine blade. As a further alternative, the mould may be for making a section of a wind turbine blade, for example in the case of a modular blade. Hence, the method may involve making only part of a wind turbine blade according to the present invention. For example, a mid-section of a blade may be made according to the above method, and the mid-section may subsequently be joined to a root and/or tip portion of the blade, or to another longitudinal section of the blade. 
         [0035]    Accordingly, the present invention provides a wind turbine blade made in accordance with the above method, and a wind turbine comprising the wind turbine blade. 
         [0036]    The invention therefore provides a wind turbine blade extending longitudinally between a root end and a tip end in a spanwise direction, the wind turbine blade having a blade shell made of fibre-reinforced plastic, and at least part of the blade shell comprising: an integral elongate spar structure extending longitudinally in the spanwise direction; core material arranged adjacent to the spar structure; and resin-permeable material provided between the spar structure and the core material. 
         [0037]    The wind turbine blade is formed by resin infusion according to the method described above. During the resin-infusion process, the resin-permeable material serves to restrict the rate of flow of resin between the spar structure and the core material in the spanwise direction. The resin-permeable material substantially fills any gaps at the interfaces between the spar structure and the core material and eliminates the race-track effect at such interfaces. 
         [0038]    Optional features described above in relation to the method are equally applicable to the invention when expressed in terms of a wind turbine blade, but these features will not be repeated herein for reasons of conciseness. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0039]    The background to the present invention has already been described above with reference to  FIGS. 1 to 3  in which: 
           [0040]      FIG. 1  is a schematic transverse cross-sectional view through a wind turbine blade having a fibre-reinforced shell of sandwich panel construction and having spar structures integrated with the shell and located between regions of core material; 
           [0041]      FIG. 2  is a schematic transverse cross-section through a wind turbine blade shell mould for making the blade shown in  FIG. 1 , and illustrating the core material and spar structure being arranged in the mould; and 
           [0042]      FIG. 3  illustrates a resin-infusion process for making the wind turbine blade of  FIG. 1 . 
           [0043]    A particular problem addressed by the method of the present invention has also been described above with reference to  FIGS. 4 to 8 , in which: 
           [0044]      FIG. 4  schematically illustrates longitudinal gaps at the interfaces between a spar structure and panels of core material when these components are arranged in a wind turbine blade mould; 
           [0045]      FIG. 5  schematically illustrates how the curvature of a wind turbine blade mould causes a gap between abutting spar structures and core panels; 
           [0046]      FIG. 6  is a schematic illustration of part of a spar structure comprising a stack of pultrusions and showing slight misalignments between the pultrusions; 
           [0047]      FIG. 7  illustrates resin flow during a resin-infusion process, in which resin flows in a chordwise direction across the core panel and spar structure; and 
           [0048]      FIG. 8  illustrates a lock off created by uncontrolled resin flow in a spanwise direction at the interface between the core panel and the spar structure. 
           [0049]    In order that the present invention may be more readily understood, a method of making a wind turbine blade in accordance with particular embodiments of the present invention will now be described in further detail with reference to the following figures, in which: 
           [0050]      FIG. 9  is a schematic transverse cross-section through a wind turbine blade shell mould, and shows resin-permeable material being arranged in the mould between spar structures and panels of core material; 
           [0051]      FIG. 10  is a schematic representation of a pair of spar structures arranged between panels of core material with resin-permeable material provided at the interfaces between the core panels and spar structures; 
           [0052]      FIG. 11  illustrates a resin-infusion process for making a wind turbine blade according to the present invention; and 
           [0053]      FIG. 12  illustrates a further embodiment of the present invention in which resin-permeable material is pre-applied to core panels before the core panels are placed in the mould. 
       
    
    
     DETAILED DESCRIPTION 
       [0054]    Referring now to  FIG. 9 , this is a cross section through a wind turbine blade shell mould  100 . The mould  100  extends longitudinally in a spanwise direction perpendicular to the plane of the page. A surface  102  of the mould  100  exhibits a concave curvature in a chordwise direction C, corresponding to the curvature of the aerodynamic profile of the blade to be formed in the mould  100 . The mould  100  is suitably-shaped for moulding a half shell of a wind turbine blade. In practice, two half shells may be moulded typically in separate moulds and the completed half shells are subsequently bonded together to form a complete blade, as will be readily apparent to persons skilled in the art. However, it should be appreciated that the present invention is not limited in this respect, and may instead be employed in other such moulding operations for example in which a complete blade is moulded in a single mould, or in which only a section of the blade is formed in the mould, such as in the case of a modular blade. 
         [0055]    In order to form the blade half shell in the mould  100 , one or more glass-fibre fabric layers  104  are arranged on the mould surface  102  to form the outer skin of the blade. A plurality of polyurethane foam panels  106   a - c  are then arranged on top of the glass-fibre layer(s). Three panels  106   a - c  are shown in the cross-sectional view of  FIG. 9 , although the number of panels may vary in other examples and/or at different spanwise locations in the mould  100 , depending upon the structural requirements of the blade in such regions. The panels  106   a - c  are spaced apart from one another in the chordwise direction C such that a first spar region  108   a  is defined between a central panel  106   b  and a leading edge panel  106   a  and a second spar region  108   b  is defined between the central panel  106   b  and a trailing edge panel  106   c.  The spar regions  108   a  and  108   b  extend longitudinally in the spanwise direction of the mould  100 . 
         [0056]    A plurality of pultruded strips  110  are stacked one on top of another in the first spar region  108   a  to form a first spar cap  112   a.  The pultrusions  110  are pre-cured strips of carbon-fibre reinforced plastic (CFRP). A second spar cap  112   b  is formed by stacking a further plurality of pre-cured CFRP pultrusions  110  in the second spar cap region  108   b.    
         [0057]    In accordance with the present invention, breather fabric  114   a - d  is provided between the spar caps  112   a  and  112   b  and the foam panels  106   a,    106   b  and  106   c.  The breather fabric  114  is in the form of longitudinal strips, which extend in the spanwise direction of the mould  100 . In this example four strips of breather fabric  114   a - d  are arranged between the spar caps  112   a  and  112   b  and the adjacent foam panels  106   a - c.  Specifically, a first strip  114   a  of breather fabric is provided between the first spar cap  112   a  and the leading edge panel  106   a;  a second strip  114   b  of breather fabric is provided between the first spar cap  112   a  and the central panel  106   b;  a third strip  114   c  of breather fabric is provided between the second spar cap  112   b  and the central panel  106   b;  and a fourth strip  114   d  of breather fabric is provided between the second spar cap  112   b  and the trailing edge panel  106   c.  The strips  114   a - d  of breather fabric are not necessarily a continuous length and may comprise a plurality of individual lengths of breather fabric arranged generally end to end in the spanwise direction, and/or overlapping to an extent. 
         [0058]    Referring now to  FIG. 10 , this is a schematic cross-sectional representation of the components once assembled in the mould. Here it can be seen that the foam panels  106   a - c  and spar caps  112   a  and  112   b  are arranged side by side and the breather fabric  114   a - d  is located between the foam panels  106   a - c  and the stacks of pultrusions  110  comprising the spar caps  112   a  and  112   b.  A resin inlet channel  116  is also shown in  FIG. 10 . The resin inlet channel  116  is identical to the resin-inlet channel  46  described above by way of background with reference to  FIG. 7 , and extends longitudinally and substantially centrally in the mould  100 . For ease of illustration, the mould  100  and other blade components have been excluded from  FIG. 10 , and the foam panels  106   a - c  and spar caps  112   a  and  112   b  are shown in a flat formation whereas in reality the components would typically be arranged on the curved surface  102  of the mould  100 , as shown in  FIG. 9 . 
         [0059]    Referring now to  FIG. 11 , once the components have been arranged in the mould  100 , one or more further layers of glass-fibre fabric  118  are arranged on top of the components to form the inner skin of the blade. The assembly is then covered with vacuum-bagging film  120 , which is sealed against the mould flange  122  using sealing tape  124 . A vacuum is created in the sealed region defined between the vacuum-bagging film  120  and the mould surface  102  and resin  126  is admitted into the sealed region via the resin inlet channel  116  shown in  FIG. 10 . 
         [0060]    As described by way of background with reference to  FIG. 7 , the resin  126  flows out of the resin inlet channel  116  in a chordwise direction C through the mould  100 , as represented by the arrows  56  in  FIG. 7 . Corresponding arrows  128  are shown in  FIG. 10  to indicate the direction of resin flow in the chordwise direction C in the present invention. Referring again to  FIG. 10 , the resin inlet channel  116  is arranged adjacent the central foam panel  106   b,  hence the resin initially flows across the central foam panel  106   b.  When the resin reaches the respective interfaces  130   b  and  130   c  between the central panel  106   b  and the first and second spar caps  112   a  and  112   b,  the resin infuses into the breather fabric  114   b  and  114   c  at these locations. The resin then continues to flow in a chordwise direction C across the spar caps  112   a  and  112   b  until it reaches the respective interfaces  130   a  and  130   d  between the spar caps  112   a  and  112   b  and the respective leading edge and trailing edge panels  106   a  and  106   c.  The resin then infuses into the breather fabric  114   a  and  114   d  at these interfaces  130   a  and  130   d  before continuing to flow in a chordwise direction C across the respective leading and trailing edge panels  106   a  and  106   c.    
         [0061]    The breather fabric  114   a - d  at the respective interfaces  130   a - d  between the spar caps  112   a  and  112   b  and the foam panels  106   a - c  occupies the gaps  48  that were described above by way of background to the present invention with reference to  FIGS. 4 to 6 . The presence of the breather fabric  114   a - d  prevents the resin from racing in a spanwise direction at these interfaces  130   a - d.  Accordingly, the resin flows in a steady and controlled manner in the chordwise direction C across the foam panels  106   a - c  and the abutting spar caps  112   a  and  112   b,  such that lock-offs are substantially prevented. 
         [0062]    In order to maintain the breather fabric  114   a - d  in position during the layup process and during the moulding process, the breather fabric  114   a - d  may be secured to the foam panels  106   a - c  using glue, scrim tape or other suitable means. The above method may therefore involve arranging the foam panels  106   a - c  in the mould  100  and thereafter securing the breather fabric  114   a - d  to the foam panels  106   a - c  before stacking the pultrusions  110  in the spar regions  108   a  and  108   b  between the panels  106   a - c.    
         [0063]    Referring now to  FIG. 12 , this shows an alternative example of the invention in which the breather fabric  114   a - d  is pre-applied to the sides of the foam panels  106   a - c  using scrim tape before the panels  106   a - c  are arranged in the mould  100 . Pre-applying the breather fabric  114   a - d  to the foam panels  106   a - c  is particularly advantageous because this can be done offline, which can significantly reduce the time required to assemble the various components in the mould  100 , and thereby reducing the blade production time. 
         [0064]    In  FIGS. 9 to 12 , fours strips of breather fabric  114   a - d  have been provided at the interface between the foam panels and the spar caps. However, in an example, only strips  114   a  and  114   d  may be provided. The spar caps  112   a  and  112   b  are located between the two strips  114   a,    114   d  and the resin inlet channel  116 . By providing the strips of breather fabric in these locations eliminates the race track effect at the respective interfaces between the foam panels  106   a,    106   c  and the spar caps  112   a,    112   b  such that lock-offs are substantially prevented. 
         [0065]    For the avoidance of doubt, the terms ‘spanwise’ and ‘chordwise’ are used herein for convenience and should not be interpreted in such a way as to unduly limit the scope of the present invention. ‘Spanwise’ is intended to mean a longitudinal direction, generally between the root and tip of a wind turbine blade or blade mould, and is not necessarily intended to mean directions parallel to the blade axis. ‘Chordwise’ is intended to mean a widthwise direction across the blade or mould, and is not necessarily intended to mean parallel to the blade chord. 
         [0066]    Many modifications may be made to the above examples without departing from the scope of the present invention as defined in the accompanying claims.