Abstract:
A method of making a wind turbine blade having at least one pultruded strip of fibrous reinforcing material integrated with a shell of the blade is described. The method comprises the steps of: providing at a first location a feed apparatus for dispensing a pultruded strip of fibrous reinforcing material; supporting a coiled pultruded strip of fibrous reinforcing material for rotation in the feed apparatus; causing the coiled strip to rotate in the feed apparatus at the first location; and feeding a free end of the strip from the feed apparatus in a feed direction towards a second location remote from the first location. An associated feed apparatus for use in the method is also described.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to wind turbine blades and to methods of manufacturing wind turbine blades. More specifically, the present invention relates to wind turbine blades that include a stack of load-bearing reinforcing strips integrated within the structure of the shell. 
       BACKGROUND 
       [0002]      FIG. 1   a  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 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 foam (e.g. polyurethane), which is sandwiched between inner  13  and outer  14  GRP layers or ‘skins’. 
         [0003]    The blade  10  comprises a first pair of spar caps  15   a  and  15   b  and a second pair 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 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 the 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. 1   b  and  1   c . Referring to  FIG. 1   b , 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   a , are stacked in the respective channels  26 . Three strips  18  are shown in each stack in this example, but in reality there may be any number of strips  18  in a stack. 
         [0007]    Referring to  FIG. 1   c , 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 No. 1121649.6. 
         [0009]    The CFRP pultruded strips  18  extend along the majority of the length of the wind turbine blade  10 . Modern wind turbine blades may be in excess of eighty metres long, and so it will be appreciated that these strips are very long and heavy. The length and weight of the strips presents challenges relating to the manufacture of the blades, and relating to the handling and transportation of the strips. The present invention aims to address these challenges by providing a convenient method of manufacturing this type of wind turbine blade, and by providing apparatus for use in the method. 
       SUMMARY OF THE INVENTION 
       [0010]    According to the present invention, there is provided a method of making a wind turbine blade having at least one pultruded strip of fibrous reinforcing material integrated with a shell of the blade, the method comprising the steps of:
       a. providing at a first location a feed apparatus for dispensing a pultruded strip of fibrous reinforcing material;   b. supporting a coiled pultruded strip of fibrous reinforcing material for rotation in the feed apparatus;   c. causing the coiled strip to rotate in the feed apparatus at the first location; and   d. feeding a free end of the strip from the feed apparatus in a feed direction towards a second location remote from the first location.       
 
         [0015]    The invention also provides a feed apparatus for feeding pultruded strips of fibrous reinforcing material in a feed direction, the apparatus comprising: an enclosure for housing a coiled pultruded strip of fibrous reinforcing material and retaining the strip in a coiled formation as the coil rotates within the enclosure, wherein the enclosure has an outlet through which a free end of the strip exits the enclosure as the coil turns within the enclosure. 
         [0016]    The method may involve feeding the strips to a blade part manufacturing tool. The feed apparatus may be placed at one end of the blade part manufacturing tool, and the strips may be fed into or onto the tool. In preferred embodiments of the invention, the blade part manufacturing tool is a wind turbine blade mould. Hence, the method may involve feeding the strips directly into the wind turbine blade mould. 
         [0017]    Alternatively, the blade part manufacturing tool may be an assembly jig or other such tool, and the method may involve feeding the strips to the tool and then transferring the strips from the tool into a wind turbine blade mould. In other embodiments, the method may involve feeding the strips onto another suitable surface, such as the factory floor, before transferring the strips to the wind turbine blade mould. 
         [0018]    Preferably the method involves stacking the strips one on top of the other to form a stack of strips. The strips may be fed into the blade mould and stacked inside the blade mould, or alternatively the strips may be stacked outside the blade mould, for example on the blade part manufacturing tool or on the factory floor, and then the stack may be transferred into the blade mould. To facilitate transferring the stack to the mould, the blade part manufacturing tool may be substantially the same height as the wind turbine blade mould. The method preferably involves integrating the stacked strips together to form a stiff spar cap unit. The integration process may take place inside the blade mould, or alternatively the strips may be integrated before being transferred to the mould. 
         [0019]    Due to the length of the pultruded strips, it is convenient to store and transport the strips in the form of a coil or roll. Restraining straps may be used to retain the strip in a coiled formation. The straps must be cut in order to uncoil the strip. However, it will be appreciated that a significant amount of potential energy is stored in a pultruded strip of CFRP when coiled. The stored potential energy results from the long unidirectional fibres in the strip seeking to straighten when the restraining straps are cut. Hence, when the straps are cut, the strip will attempt to uncoil rapidly and potentially uncontrollably. 
         [0020]    The feed apparatus of the present invention serves to contain the strip when the straps are cut so that the strip does not uncoil in an uncontrolled and potentially dangerous manner. The enclosure of the feed apparatus may partially or fully encapsulate the coil. Further the feed apparatus is configured to feed the strip from the roll to the tool in a steady and controlled manner. 
         [0021]    Whilst other materials used in blade manufacturing are commonly supplied as a roll, for example rolls of glass-fibre fabric, these materials generally do not have significant amounts of stored potential energy and so can be unrolled in the mould in a conventional manner. The conventional way of unrolling such materials is to position the free end of the material at a desired location and then to unroll the coiled part of the material manually along the mould. 
         [0022]    The stored potential energy in a coiled pultruded strip makes it impossible to unroll the strip in the conventional manner. It will be appreciated that a significant difference between the present invention and the conventional unrolling technique described above is that in the present invention the coiled part of the strip remains at a fixed location, e.g. at the root of the blade mould, and the free end of the strip is fed in the feed direction, whilst in the conventional method the coiled part of the material is moved whilst the free end remains in a fixed position. 
         [0023]    Factory floor space is saved by virtue of the apparatus and method of the present invention because the strip remains coiled until it is fed to the tool. The feed apparatus and method of the present invention significantly facilitates the handling of the strips during the manufacturing process and allows the placement of the strips on the tool to be overseen by a single operator as relatively little (if any) manual handling of the strips is required. 
         [0024]    Various other optional features of the invention are set out in the appended sub-claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0025]      FIGS. 1   a ,  1   b  and  1   c  have already been described above by way of background to the present invention. 
           [0026]    In order that the present invention may be more readily understood, embodiments of the invention will now be described, by way of example only, with reference to  FIGS. 2 to 20  of the accompanying drawings, in which: 
           [0027]      FIG. 2  shows a feed apparatus according to the present invention arranged at a root end of a wind turbine blade mould, and a placement system arranged in the mould; 
           [0028]      FIG. 3   a  shows the feed apparatus of  FIG. 2  in more detail; 
           [0029]      FIG. 3   b  is a close-up view of part of  FIG. 3   a;    
           [0030]      FIG. 4  is a perspective view of the wind turbine blade mould of  FIG. 2  as viewed from the root end, and showing the placement system of  FIG. 2  extending longitudinally in the mould; 
           [0031]      FIG. 5  is a further perspective view of the wind turbine blade mould of  FIG. 2  showing the placement system being lifted into the mould; 
           [0032]      FIG. 6  is a side view of part of the placement system; 
           [0033]      FIG. 7   a  is a transverse cross-sectional view of the placement system, in which a pair of runners is arranged in a closed position; 
           [0034]      FIG. 7   b  shows the runners of  FIG. 7   a  arranged in an open position; 
           [0035]      FIG. 8   a  is a partial longitudinal cross-sectional view of part of the placement system showing a power drive unit; 
           [0036]      FIG. 8   b  is a transverse cross-sectional view through part of the power drive unit of  FIG. 8   a;    
           [0037]      FIG. 9   a  is a transverse cross-sectional view of the placement system showing a carbon fibre composite strip supported on the runners with the runners in the closed position; 
           [0038]      FIG. 9   b  shows the runners moved to the open position causing the strip to drop into the mould; 
           [0039]      FIG. 9   c  shows a stack of carbon fibre composite strips which have been arranged in the mould successively using the placement system; 
           [0040]      FIG. 10   a  is a side view of part of the placement system showing a stack of strips arranged in the mould and a further strip supported on the runners to be added to the stack; 
           [0041]      FIG. 10   b  is a close-up view of part of  FIG. 10   a  showing a protective sleeve provided on a tapered end of the strip; 
           [0042]      FIG. 11   a  shows an optional carrier plate of the feed apparatus; 
           [0043]      FIG. 11   b  shows a coiled carbon fibre composite strip supported on the carrier plate; 
           [0044]      FIG. 12  is a transverse cross-sectional view of the feed apparatus; 
           [0045]      FIG. 13  is a side view of part of the feed apparatus showing the carrier plate mounted inside an enclosure of the feed apparatus; 
           [0046]      FIG. 14  is a transverse cross-sectional view through the centre of the carrier plate of  FIG. 11   a;    
           [0047]      FIGS. 15   a  and  15   b  illustrate how the carrier plate is reversibly mountable inside the enclosure of the feed apparatus to enable strips of different widths to be accommodated within the enclosure; 
           [0048]      FIG. 16  illustrates an alternative method in the manufacture of a wind turbine blade in accordance with an embodiment of the present invention; 
           [0049]      FIG. 17  shows an assembly jig on which a plurality of strips may be stacked in in accordance with a further embodiment of the present invention; 
           [0050]      FIG. 18   a  shows a roll comprising a plurality of pultruded strips coiled sequentially and having their respective ends connected together in series; 
           [0051]      FIG. 18   b  is a close-up view of a connector for connecting the ends of adjacent strips in the roll shown in  FIG. 18   a;    
           [0052]      FIG. 19  illustrates a further embodiment of the present invention in which the roll comprises a single strip which is cut to form a plurality of strips during the feed process by a cutting tool arranged in line with the feed apparatus; and 
           [0053]      FIG. 20  illustrates a further embodiment of the present invention in which a motorised pulley is located adjacent the tip end of the mould and arranged to pull the strip from the feed device across the mould. 
       
    
    
     DETAILED DESCRIPTION 
       [0054]      FIG. 2  shows a longitudinal cross-section of part of a mould  40  for a wind turbine blade. The mould  40  extends longitudinally from a root end  42  to a tip end  44 . Only the root end  42  of the mould  40  is shown in  FIG. 2 , but the entire mould  40  including the tip end  44  is shown in  FIG. 5 . The mould  40  is for a half shell of the blade, such as the windward shell or the leeward shell. The mould  40  has an inner surface  46 , which is generally concave-curved in a chordwise (i.e. widthwise) direction, and which undulates in a spanwise (i.e. lengthwise) direction. The mould  40  is supported on a frame  48  having a truss structure. 
         [0055]    A feed apparatus  50  is located adjacent the root end  42  of the mould  40 . The feed apparatus  50 , which is shown in further detail in  FIG. 3   a , comprises a circular enclosure  52  and an exit ramp  54 , which are supported on a frame  56 . The exit ramp  54  extends outwardly from the circumference of the enclosure  52  towards the mould  40 , and a support plate  57  is arranged between the enclosure  52  and the exit ramp  54 . The feed apparatus  50  further includes a door  58  for accessing the enclosure  52 . The door  58  includes a plurality of apertures  59 , which provide a means of access to the enclosure  52  when the door  58  is closed. Alternatively or additionally, the apertures may be provided on the opposite side of the enclosure  52 . 
         [0056]    A series of mutually spaced rollers  60  are circumferentially arranged inside the enclosure  52 . The rollers  60  have their axes of rotation substantially perpendicular to the circular plane of the enclosure  52 . A plurality of guide plates  62  are arranged respectively in the spaces between adjacent rollers  60 . The guide plates  62  have a coating  64  of polytetrafluoroethylene (PTFE) on an inner side, as shown in the close-up view of  FIG. 3   b.    
         [0057]    A further series of mutually spaced rollers  68  are arranged along the exit ramp  54 . These rollers  68  also have their axes of rotation substantially perpendicular to the circular plane of the enclosure  52 . The feed apparatus  50  further comprises a power feed unit  70  comprising a motor  72  and a drive belt  74  (see  FIG. 2 ). The drive belt  74  is looped around a plurality  76  of adjacent rollers  60  inside the enclosure  52  and around an axle  78  of the motor  72 . As shown in  FIG. 3   a , the plurality  76  of adjacent rollers  60  are each provided with a rubber sleeve  80  to increase the friction between the drive belt  74  and the rollers  60 . A brake  82  comprising a pinch roller  84  arranged opposite a rubber brake pad  86  is provided on the exit ramp  54 . 
         [0058]    Referring again to  FIG. 2 , a pultruded strip  88  of carbon-fibre reinforced plastics material (CFRP) is formed into a roll  90  and housed inside the enclosure  52  of the feed apparatus  50 . The roll  90  is surrounded by the circumferentially arranged rollers  60  inside the enclosure  52 . The rollers  60  enclose and retain the roll  90 . Referring also to  FIG. 18   a , the roll  90  comprises a plurality of strips  88   a ,  88   b ,  88   c , which are coiled sequentially, end-to-end, to form a single coil. The adjacent ends of successive strips in the roll  90  are connected together by connectors  92 . As shown in the close-up view of  FIG. 18   b , the connectors  92  each have male and female mating parts  92   a ,  92   b . The male part  92   a  is fitted to an end of one of the strips  88   a  in the roll  90  and the female part  92   b  is fitted to the adjacent end of the next strip  88   b  in the roll  90 . The male and female parts  92   a ,  92   b  comprise mating formations that engage to connect the strips together. 
         [0059]    The strips  88  are pre-formed in a pultrusion process in which carbon fibres are pulled through molten resin and subsequently through a pultrusion die to form strips of constant cross-section. The strips  88  are substantially rectangular in cross section, and have a width of approximately 150 mm and a thickness of approximately four millimetres. The strips  88  extend along the majority of the length of the blade, which is approximately eighty metres long, and hence each strip is close to eighty metres long. 
         [0060]    A conveyance tray  94  is located in the mould  40  at the root end  42 . The conveyance tray  94  is shown more clearly in the perspective view of  FIG. 4 . Referring to  FIG. 4 , the conveyance tray  94  is elongate and of lightweight construction and features a conveyance surface  96  between a pair of sidewalls  98 . The conveyance surface  96  has a similar width to the width of the carbon-fibre strips, and has a low-friction coating of PTFE. The conveyance tray  94  extends from the root end  42  of the mould  40  up to a placement system  100 , which will now be described. 
         [0061]    The placement system  100  is located in the mould  40  and is supported by a plurality of arms  102 . The arms  102  extend inwardly from a longitudinal flange  104  at an upper edge of the mould  40 , and are regularly spaced along the length of the flange  104 . Referring to  FIG. 5 , the placement system  100  is lifted into the mould  40  by a crane and is suspended from the arms  102 . As well as supporting the placement system  100 , the arms  102  also serve to position the placement system  100  correctly in the mould  40 . 
         [0062]    The placement system  100  is substantially elongate and comprises a conveyor  106 , which is spaced above the surface  46  of the mould  40  by a pair of mutually opposed longitudinal guide walls  108  that depend downwardly from the conveyor  106 . Referring to  FIG. 7   a , in cross-section, the shape of the placement system  100  resembles an upturned U. The guide walls  108  serve to define an elongate placement region  110  of rectangular cross section between the mould surface  46  (see  FIG. 6 ) and the conveyor  106 . Mutually opposed guide blocks  112  having a tapered upper end  114  are provided on an inner surface  116  of the guide walls  108 . 
         [0063]    As shown best in the partial longitudinal side view of  FIG. 6 , the placement system  100  is of modular construction and comprises a plurality of similar modules  118  which are fitted together end-to-end. The modules  118  are fixed together by a locking device in the form of a hook  120  on one of the modules  118  which is received in a corresponding eyelet  122  on an adjacent module  118 . The modular system facilitates handling and construction of the placement system  100  and allows the placement system  100  to be adapted easily to the length of the mould  40 . The guide walls  108  of the modules  118  comprise a plurality of apertures  124  which are spaced apart between vertical support members  126 . 
         [0064]    Referring still to  FIG. 6 , the conveyor  106  of the placement system  100  comprises a plurality of plates or ‘runners’  128 . The runners  128  are elongate steel plates  130  having a PTFE coating  132 , and are arranged sequentially along the length of the placement system  100  to form a conveyor surface. The conveyor surface is discontinuous and is interrupted by gaps  134  between adjacent runners  128  at the positions of the vertical support members  126 . 
         [0065]    Referring to the transverse cross-sectional views of  FIGS. 7   a  and  7   b , the runners  128  are arranged in the form of two side-by-side and parallel tracks, which are supported respectively on a pair of brackets  136 . A longitudinal space  138  is defined between the side-by-side runners  128 . The respective brackets  136  are arranged in telescopic relation and are moveable relative to one another in a direction perpendicular to the direction of extension of the conveyor  106  to vary the separation between the side-by-side runners  128 . Specifically,  FIG. 7   a  shows the runners  128  in a closed position, in which the side-by-side runners  128  are located relatively close together and within the placement region  110 ; and  FIG. 7   b  shows the runners  128  in an open position, in which the brackets  136  are extended relative to one another causing the runners  128  to withdraw from the placement region  110  through the apertures  124  defined in the guide walls  108 . The runners  128  are opened and closed using a hydraulic ram  140  as shown in  FIG. 6 . 
         [0066]    Referring now to  FIGS. 8   a  and  8   b , the placement system  100  includes a power drive unit  142 , which comprises a motor  144  configured to turn a pair of drive wheels  146  via a drive belt  148 . The drive wheels  146  are located at either end of an axle  150 , and the drive belt  148  is looped around the axle  150  between the drive wheels  146  and around a parallel axle  152  of the motor  144 . The drive wheels  146  are relatively large and are arranged generally above the runners  128 . Two pairs of rollers  154  are arranged directly below the respective drive wheels  146 . The rollers  154  are arranged substantially in the same plane as the runners  128 . As shown in  FIGS. 2 and 4 , the power drive unit  142  is located close to a root end  156  of the placement system  100 , close to the conveyance tray  94 . 
         [0067]    A method of making a wind turbine blade having a stack of pultruded CFRP strips integrated within the shell structure has been described above by way of background with reference to  FIGS. 1   b  and  1   c . According to the present invention, the feed apparatus  50  and placement system  100  described above may be used to facilitate the manufacturing process by feeding the pultruded strips  88  to the mould  40  and stacking the strips  88  in the mould  40 , as will now be described in further detail with reference to  FIGS. 2 to 10  of the drawings. 
         [0068]    Referring again to  FIG. 2 , the CFRP roll  90  is initially loaded into the enclosure  52  of the feed apparatus  50 . The roll  90  is held together by restraining straps (not shown) which prevent the strips  88  in the roll  90  from uncoiling during transportation. Once the roll  90  is loaded into the enclosure  52 , the enclosure door  58  is closed to retain the roll  90  and the restraining straps are cut via the apertures  59  in the enclosure door  58  using suitable shears. 
         [0069]    The roll  90  is surrounded and supported by the circumferentially arranged rollers  60  inside the enclosure  52  of the feed apparatus  50 . The power drive unit  70  is activated to drive the plurality  76  of adjacent rollers  60  inside the enclosure  52  via the drive belt  74 . This causes the roll  90  to rotate slowly inside the enclosure  52 . As the roll  90  rotates, a free end  158  ( FIG. 2 ) of an outermost strip  88  in the roll  90  exits the enclosure  52  through an outlet  160  ( FIG. 3   a ) at the interface between the enclosure  52  and the exit ramp  54 . 
         [0070]    The power feed unit  70  continues to turn the roll  90 , and the strip  88  advances in a feed direction  162 , as indicated by the horizontal arrow in  FIG. 2 , over the series of rollers  68  that are spaced along the exit ramp  54 . The strip  88  is guided onto the conveyor tray  94  in the mould  40 , and as the roll  90  continues to turn within the enclosure  52 , the strip  88  uncoils further and the free end  158  of the strip  88  advances along the low-friction conveyor surface  96  ( FIG. 4 ) towards the placement system  100 . The conveyor tray  94  guides the strip  88  onto the runners  128  of the conveyor  106  of the placement system  100 . At this stage, the runners  128  are in a closed position, as shown in the cross-sectional view of  FIG. 9   a , which shows the strip  88  supported on the runners  128 . The pinch roller brake  82  ( FIG. 3   a ) of the feed apparatus  50  may be applied at any time to restrain the strip  88  and halt the feed process if required. 
         [0071]    The power feed unit  70  of the feed apparatus  50  continues to turn the roll  90  until the free end  158  of the strip  88  reaches the power drive unit  142  of the placement apparatus  100 . At this point, and as shown in  FIG. 8   b , the strip  88  is positioned between the drive wheels  146  and the opposed rollers  154  of the power drive unit  142 . Referring also to  FIG. 8   a , the motor  144  of the power drive unit  142  is then activated causing the drive belt  148  to turn the drive wheels  146 . The drive wheels  146  bear against the strip  88  and press the strip  88  against the opposed rollers  154 . The frictional force between the drive wheels  146  and the strip  88  serves to advance the strip  88  along the conveyor  106  in the feed direction  162  towards the tip end  44  of the mould  40 . 
         [0072]    The strips  88  are pre-formed to the correct length, and the power drive unit  142  operates to propel the strip  88  along the conveyor until the free end  158  of the strip  88  approaches the end of the conveyor  106  near the tip end  44  of the mould  40 , at which point the power drive unit  142  is de-activated. 
         [0073]    Referring to  FIG. 9   b , once the full length of the strip  88  is supported on the runners  128 , the hydraulic ram  140  ( FIG. 6 ) is activated to open the runners  128 , causing the strip  88  to drop onto the mould surface. The guide blocks  112  on the inner surface  116  of the guide walls  108  ensure that the strip  88  is centred in the placement region  110 . Once the strip  88  has been placed in the mould  40 , the runners  128  are re-closed and the above process is repeated to stack the subsequent strips in the roll  90  on top of one another in the placement region  110  as shown in  FIG. 9   c.    
         [0074]    In order to reduce stress concentrations in the blade, successive strips  88  in the roll  90  are each slightly shorter than the previous strip and the strips  88  are stacked such that the respective ends of the strips form a step-wise arrangement (as shown in  FIG. 16  for example). As shown in  FIG. 10   a , the ends  164  of the strips  88  are also tapered to further reduce stress concentrations in the stack. This arrangement is described in UK Patent Application No. 1121649.6. The length of the taper is typically around 450 millimetres, and so it will be appreciated that the extreme ends  164  of the strip  88  are very thin and flexible. In order to protect the tapered end  164  of the strip  88   a  relatively rigid sleeve  166  is provided over the end  164 . In this example, the sleeve  166  is made from nylon, but it will of course be appreciated that other suitable materials may be used. Referring to the enlarged view of  FIG. 10   b , the nylon sleeve  166  is suitably longer than the gaps  164  between adjacent runners  128  and thereby prevents the end  164  of the strip  88  drooping into the gaps  164  which may otherwise damage the end  164  of the strip  88  or at least may disrupt the smooth passage of the strip  88  along the conveyor  106 . 
         [0075]    Further optional constructional details of the feed apparatus  50  will now be described with reference to  FIGS. 11 to 15 . 
         [0076]    Referring to  FIG. 11   a , the feed apparatus  50  optionally comprises a carrier plate  170  on which the CFRP roll is supported. The carrier plate  170  in this example is round and shaped like a wheel. The plate  170  has a central aperture  172  serving as a mounting point, and a plurality of spokes  174  which extend radially from the central aperture  172  to a circumferential rim  176 . This wheel-like construction is advantageously lightweight yet rigid. A series of radially-spaced holes  178  is provided in each spoke  174 . The holes  178  serve as mounting points for a plurality of guide blocks  180 , which are respectively fastened to the plurality of spokes  174 . The guide blocks  180  are circularly arranged and the radial position of the guide blocks  180  is selected according to the length of the strip(s)  88 , i.e. according to the annular thickness of the roll  90 . A clamping block  182  is provided opposite one of the guide blocks  180  for gripping an innermost end  184  of the strip  88 . 
         [0077]    Referring to  FIG. 11   b , this shows schematically the coiled strip  88  mounted on the carrier  170 . The innermost end  184  of the strip is gripped between the clamping block  182  and one of the guide blocks  180 . This prevents the innermost end  182  of the strip  88  from bending once the strip  88  is largely uncoiled. The strip  88  is coiled around the outside of the guide blocks  180 . The guide blocks  180  confine the strip  88  to a circumferential region  186  of the carrier  170  and prevent the strip  88  from uncoiling substantially within the enclosure  52  of the feed apparatus  50 . It will be appreciated that a significant amount of potential energy is stored within a coiled CFRP pultruded strip, and if the strip  88  is not confined it will uncoil like a spring to fill the enclosure  52 . Uncoiling in this way is dangerous and may damage the strip  88 . Feeding a loosely coiled strip is also more difficult. 
         [0078]    Referring now to  FIG. 12 , this is a transverse cross-sectional view of the feed apparatus  50 . The feed apparatus  50  includes a carrier support  188  having a horizontal axle  190  on which the carrier plate  170  is mounted in use. A free end  192  of the axle  190  is supported in a U-shaped mount  194  provided on an inner side  196  of the enclosure door  58  when the enclosure door  58  is closed. The carrier  170  can be seen mounted inside the enclosure  52  in  FIG. 13 , although no strip is shown mounted on the carrier  170  in this view. 
         [0079]    The feed apparatus  50  may be configured to feed strips  88  of different widths. Typically the strips  88  have a width of either 200 mm or 100 mm and the feed apparatus  50  is reconfigurable to accommodate either width as will now be explained with reference to  FIGS. 14 and 15 . 
         [0080]    Referring to  FIG. 14 , the carrier  170  comprises a first tubular bushing  198  centrally mounted to a first side  200  of the carrier  170  and a second tubular bushing  202  centrally mounted to a second side  204  of the carrier  170 . The bushings  198 ,  202  are coaxial and extend perpendicular to the plane of the plate  170 . The first bushing  198  has a length of 160 mm and the second bushing  202  has a length of 60 mm. As shown in  FIGS. 15   a  and  15   b , the carrier  170  is reversibly mountable in the enclosure  52  and the plate  170  serves as a spacer plate to delimit the available space inside the enclosure  52  for housing the roll  90 . 
         [0081]    Referring specifically to  FIG. 15   a , the enclosure  52  has an internal width of approximately 280 mm as indicated by the double-headed arrow  206 . The spacer plate  170  is mounted on the axle  190  with the first side  200  of the plate  170  facing the enclosure door  58  and the second side  204  of the plate  170  facing the carrier support  188 . In this orientation, the second bushing  202  spaces the plate relative to the carrier support by 60 mm, as indicated by the arrows  206 . Consequently, an available space having a width of 220 mm is defined between the plate  170  and the enclosure door  58  as indicated by the double-headed arrow  208 . This space is suitable for strips  88  having a width of 200 mm and ensures that the strips  88  are sufficiently retained inside the enclosure  52 . 
         [0082]    Referring specifically to  FIG. 15   b , here the carrier  170  is reversed such that the second side  204  of the plate  170  faces the enclosure door  58  and the first side  200  of the plate  170  faces the carrier support  188 . In this orientation, the first bushing  198  spaces the plate  170  relative to the carrier support  188  by 160 mm such that an available space having a width of 120 mm is defined between the plate  170  and the enclosure door  58 . This space is suitable for strips  88  having a width of 100 mm and ensures that the strips  88  are sufficiently retained inside the enclosure  52 . 
         [0083]    The strip(s)  88  are transported on the carrier  170  to the wind turbine blade manufacturing facility. The assembly of the strip  88  and carrier  170  is referred to herein as a cartridge. Restraining straps are used to prevent the strip  88  from uncoiling during transportation. At the wind turbine manufacturing facility, the cartridge is loaded into the enclosure  52 , the enclosure door  58  is closed, and the restraining straps are cut through the apertures  59  in the enclosure door  58 . The strip  88  is confined inside the enclosure  52  by the spacer plate  170  and the circularly arranged guide blocks  180  such that when the straps are cut, the strip  88  remains relatively tightly coiled within the enclosure  52  and does not uncoil substantially. 
         [0084]      FIG. 16  illustrates an alternative manufacturing method in accordance with the present invention, in which the pultruded strips  88  are stacked in a separate mould, provided as a U-shaped channel  210 , outside of the main wind turbine blade mould  40 , together with a matrix (resin or adhesive) which is pre-cured so that the stack is formed in the separate mould  210 . The pre-cured stack  212  is then placed in the main wind turbine blade mould  40  for a resin infusion process together with the other structural elements. The feed apparatus  50  described above is used to feed the strips  88   a ,  88   b ,  88   c  directly into the U-shaped channel  210 , or to a placement system  100  as described above and arranged to stack the strips in the U-shaped channel  210 . 
         [0085]      FIG. 17  illustrates a further alternative manufacturing method in which the strips  88  are stacked on an assembly jig  214  outside the mould  40 . The assembly jig  214  comprises a series of supports  216 , each having a rectangular cut-out  218  at an upper end  220  for retaining the strips  88 . The supports  216  are of varying heights to correspond with the undulating surface of the wind turbine blade mould  40 . Once the stack has been assembled on the jig  214 , the stack is lifted into the wind turbine blade mould  40 . The feed apparatus  50  described above is used to feed the strips directly onto the assembly jig  214 , or to a placement system  100  as described above and arranged to stack the strips on the jig  214 . The jig  214  may be substituted for a suitable process table or equivalent supporting structure. 
         [0086]      FIG. 19  illustrates a further alternative manufacturing method. In this method, rather than the roll  90  comprising a plurality of successively coiled pultruded strips  88 , the roll  90  comprises a single longer pultruded strip  222 . The method involves feeding the strip  222  from the feed apparatus  50  and cutting the strip  222  as it is fed to form a plurality of individual strips to be stacked. The apparatus comprises a cutting tool  224  arranged in line with the feed apparatus  50 . The apparatus further comprises a chamfering tool  226  also arranged in line with the feed apparatus  50  which is configured to form the tapered ends  164  of the strips as described above with reference to  FIG. 10   b.    
         [0087]      FIG. 20  illustrates a further alternative manufacturing method in which the placement system  100  described above is omitted. Here, the feed apparatus  50  comprises a motorised pulley  228  arranged adjacent the tip end  44  of the wind turbine blade mould  40  and connected to the free end  158  of the pultruded strip  88  via a cable  230 . The pulley  228  is configured to pull the strip  88  in the feed direction  162  so as to uncoil the strip  88  in the feed apparatus  50 . Whilst now shown, a further alternative embodiment is envisaged in which the placement system  100  and the pulley  228  are omitted and the power feed unit  70  of the feed apparatus  50  is used to drive the strip  88  further in the feed direction  162 , for example along substantially the entire length of the mould  40 . The feed apparatus  50  could otherwise be fitted with a handle and optionally a suitable gear system to allow the roll  90  to be turned manually to feed the strip  88 . 
         [0088]    It will be appreciated that many other modifications may be made to the examples described above without departing from the scope of the present invention as defined in the accompanying claims. For example, rather than being fed into the blade mould or onto a blade manufacturing tool, the strips may simply be fed onto the factory floor before being transferred into the mould. For example, the strips may be stacked on the factory floor adjacent the mould and then the stack may be transferred into the mould.