Method of manufacturing a wind turbine blade

Abstract

In a first aspect of the application, there is provided a method of manufacturing a wind turbine blade. The method comprises providing a blade shell mould, providing a plurality of substantially planar strips of reinforcing material, and arranging the plurality of strips in a first stack in the mould to form at least part of a first spar cap. The method further comprises providing a retaining clip having a substantially planar body and an upper flange and a lower flange projecting transversely to the planar body, wherein the flanges and the body together define a first receiving area at a first side of the retaining clip, and the method further comprises arranging the retaining clip at a side of the first stack such that the strips in the first stack are received in the first receiving area.

Description

TECHNICAL FIELD

[0001] The present application relates generally to wind turbine blades, and more specifically to an improved method for manufacturing a wind turbine blade. BACKGROUND

[0002] Modern wind turbine blades typically comprise a shell defining the aerodynamic profile of the blade and one or more longitudinally extending spars serving as the main load carrying structure of the blade. The spars typically comprise shear webs connected between opposing spar caps provided on the windward and leeward sides of the blade, respectively. The spar caps are configured to absorb the bending loads experienced by the blade in use, and thus typically comprise a material with high tensile strength, such as carbon fibre reinforced plastic (CFRP).

[0003] In some wind turbine blades, the spar cap comprises a plurality of strips of reinforcing material in a stacked arrangement. However, when arranged on an inclined mould surface during manufacture of the blade, the strips tend to move relative to each other due to the influence of gravity. The mould surface can be particularly steep near the root end of the mould, and correct alignment of the reinforcing strips in this region is particularly challenging. The spar cap can alternatively be formed from two or more adjacent stacks of strips to allow the spar cap to conform to the chordal curvature of the blade. This introduces further challenges during manufacture of the blade, as the strips can butt up against or overlap adjacent strips or stacks.

[0004] Misaligned reinforcing strips can be detrimental to the load carrying capacity of the wind turbine blade, and can also cause other blade components arranged adjacent to the spar cap to be incorrectly positioned. The stacks of reinforcing strips can be very heavy, and in some examples can extend over 70m in length, making them difficult to handle and reposition once misaligned. Furthermore, due to the tensile nature of the reinforcing material, the strips typically comprise an inherent elastic restoring force. When the strips are arranged in a mould having complex curved geometry to form a blade shell having an aerodynamic profile, the elasticity in the strips can cause them to spring apart from each other and in some cases overlap with strips of adjacent stacks.

[0005] It is against this background that the present application has been developed. SUMMARY

[0006] In a first aspect of the application, there is provided a method of manufacturing a wind turbine blade. The method comprises providing a blade shell mould, providing a plurality of substantially planar strips of reinforcing material, and arranging the plurality of strips in a first stack in the mould to form at least part of a first spar cap. The method further comprises providing a holding fixture having a substantially planar body and an upper flange and a lower flange projecting transversely to the planar body, wherein the flanges and the body together define a first receiving area at a first side of the holding fixture, and the method further comprises arranging the holding fixture at one side of the first stack such that the strips in the first stack are received in the first receiving area.

[0007] The upper flange of the holding fixture preferably engages an upper surface of the first stack. The lower flange of the holding fixture preferably engages a lower surface of the first stack. The first stack preferably abuts the first side of the fixture body.

[0008] Preferably, the holding fixture is designed to clamp the first stack of strips between the upper flange and the lower flange. Thus, the first flange and the second flange are preferably spaced apart at the first side of the fixture body by a distance substantially corresponding to the height of the first stack. Preferably, the holding fixture fixes the strips in the stack relative to each other by means of a tight interference fit between the fixture and the stack.

[0009] With the strips of the first stack located in the first receiving area, the body of the fixture can be substantially perpendicular to the plane of the strips and can restrict movement of the strips within the plane. The flanges of the fixture can respectively overlap the upper strips and the lower strips in the first stack to restrict out of plane movement of the strips.

[0010] The step of arranging the plurality of strips in the mould can comprise arranging the strips in a first stack and a second stack side by side to form at least part of the first spar cap. The holding fixture can be arranged such that its planar body is located between the first stack and the second stack and maintains a predetermined spacing between the stacks.

[0011] The stack of strips can comprise two or more strips of reinforcing material stacked on top of each other.

[0012] The flanges and the body of the holding fixture can together define a second receiving area at a second side of the holding fixture. The method can further comprise arranging the holding fixture at one side of a second stack such that the strips of the second stack are received in the second receiving area.

[0013] The upper flange of the holding fixture preferably engages an upper surface of the second stack. The lower flange of the holding fixture preferably engages a lower surface of the second stack. The second stack preferably abuts the second side of the fixture body.

[0014] Preferably, the retaining clamp is designed to clamp the second stack of strips between the upper flange and the lower flange. Preferably, the first flange and the second flange are spaced apart on the second side of the clamp body by a distance substantially corresponding to the height of the second stack.

[0015] With the second stack of strips located in the second receiving area, the body of the clamp can restrict in-plane movement of the strips in both stacks. The flanges of the clamp can overlap and prevent out-of-plane movement of the upper and lower strips in each stack, respectively. Thus, the retaining clamp can hold the strips in their respective stacks and can prevent the strips of one stack from moving or sliding into overlap with an adjacent stack. The body of the clamp can maintain the necessary spacing between the stacks.

[0016] In a second aspect of the application, there is provided a wind turbine blade comprising a spar cap comprising a plurality of substantially planar strips of reinforcing material arranged in at least a first stack. The wind turbine blade further comprises a retaining clamp having a substantially planar body and an upper flange and a lower flange protruding transversely to the planar body. Together, the flanges and the body define a first receiving area on a first side of the retaining clamp. The retaining clamp is arranged on one side of the first stack such that the strips in the first stack are received in the first receiving area.

[0017] The spar cap can comprise a first stack and a second stack side-by-side. The planar body of the retaining clamp can be arranged between the first stack and the second stack and can set a predetermined spacing between the stacks.

[0018] Preferably, the planar body has a thickness corresponding to the predetermined spacing between the stacks. Preferably, the thickness of the body is between 0.5 mm and 10 mm, preferably between 0.5 mm and 5 mm, and most preferably between 0.5 mm and 2.5 mm. Thus, the spacing defined between adjacent stacks of strips can have a width of between 0.5 mm and 10 mm, preferably between 0.5 mm and 5 mm, and most preferably between 0.5 mm and 2.5 mm.

[0019] The flanges and the body of the retaining clamp can together define a second receiving area on a second side of the retaining clamp. The retaining clamp can be arranged on one side of the second stack such that the strips of the second stack are received in the second receiving area.

[0020] The cross-section of the retaining clamp can be substantially H-shaped. The H-shaped cross-sectional shape of the clamp can define the first receiving area and the second receiving area on opposite sides of the planar body, respectively. Alternatively, the retaining clamp can have any other suitable shape. For example, the cross-section of the retaining clamp can be substantially C-shaped. In this case, the retaining clamp can define only a single receiving area on one side of the body.

[0021] The first and / or second receiving regions can be open structures. That is, the receiving regions are bounded on three sides by the planar body and the upper and lower flanges. Preferably, the retention clips consist of the planar body and the upper and lower flanges.

[0022] The retention clips can have a substantially constant cross-sectional profile along their length. The retention clips can have a length of between 20mm and 50mm.

[0023] A plurality of retention clips can be arranged at a spaced apart pitch between the first and second stacks along the length of the stack. The planar bodies of the retention clips can each have substantially the same thickness such that a substantially constant pitch is maintained between the first and second stacks along their entire length.

[0024] Preferably, the retention clips are arranged at a span of between 1.5m and 4m, and more preferably between 2m and 3m, along each stack.

[0025] The height of the first and second stacks can vary moving from the root end towards the tip end. The distance between the upper and lower flanges of each retention clip can substantially correspond to the height of the stack at the location of the respective clip. Thus, the height of the retention clips can vary along the length of the spar cap whilst having bodies of equal thickness to one another.

[0026] The thickness of the upper and / or lower flanges can taper towards their edges. The tapered thickness can minimise the step height at the edges of the flanges to avoid wrinkles and stress concentrations in the laminate.

[0027] The upper and / or lower flanges can have a cross-sectional profile that is substantially triangular or shaped as a segment of a circle. Preferably, the upper and / or lower flanges are substantially shaped as an isosceles triangle having an apex angle aligned with the clip body. The apex angle is preferably greater than 90 degrees and the base angle is preferably less than 45 degrees. Thus, the triangular flanges can define an outer surface having a relatively shallow gradient.

[0028] The retention clips can be formed from a polymeric material. For example, the retention clips can be formed from a polymer such as nylon. The retention clips can be injection moulded parts. Alternatively, the retention clips can include reinforcing fibres, for example glass fibres. The retention clips can be formed in a pultrusion process.

[0029] The spar cap can be formed from any number of side-by-side stacks. The retention clips can be arranged between adjacent stacks to maintain a predetermined pitch between the stacks. The retention clips also limit the relative movement of the strips, thereby preventing the strips from sliding relative to one another.

[0030] The strips of reinforcing material can comprise reinforcing fibres, such as glass fibres or carbon fibres. Such reinforcing fibres can be unidirectional fibres. Preferably, the strips of reinforcing material comprise reinforcing fibres in a cured resin matrix. Most preferably, the strips are pultrusions comprising unidirectional carbon fibres fixed in a cured polymer resin. BRIEF DESCRIPTION OF DRAWINGS

[0031] Embodiments of the application will now be described, by way of non-limiting example only, with reference to the accompanying drawings in which:

[0032] Figure 1 is a schematic exploded view of a wind turbine blade comprising a spar cap formed from a plurality of stacks of strips of reinforcing material arranged side by side;

[0033] Figure 2 is a schematic perspective view of a blade shell mould during a layup process in the manufacture of a blade;

[0034] Figure 3 is a cross-sectional view of the mould after the layup process;

[0035] Figure 4 is a schematic perspective view of a retaining clamp for retaining strips of reinforcing material in position relative to one another in a stack;

[0036] Figure 5 is a schematic perspective view of a plurality of retaining clamps arranged with a first stack of strips;

[0037] Figure 6 is a schematic perspective view of a plurality of adjacent stacks of strips and a plurality of retaining clamps arranged between the adjacent stacks;

[0038] Figure 7 is a schematic perspective view of a retaining clamp having a substantially C-shaped cross-section;

[0039] Figure 8a is a schematic cross-sectional view of a stack of strips comprising C-shaped retaining clamps arranged on each side of the stack; and

[0040] Figure 8b is a schematic perspective view of two adjacent stacks of reinforcing strips, wherein the strips of each stack are held in position by a plurality of C-shaped retaining clamps. DETAILED DESCRIPTION

[0041] Figure 1A schematic exploded view of a wind turbine blade 10 is shown. The blade 10 comprises a first half shell 12a and a second half shell 12b, both extending along a spanwise direction (S) from a root end 14 to a tip end 16 of the blade 10 and along a chordwise direction (C) between a trailing edge 18 and a leading edge 20. The first and second half shells 12a, 12b are joined together to form a blade shell 22. The blade shell 22 defines an aerodynamic profile and is configured to capture energy from wind incident on the blade 10.

[0042] The blade 10 further comprises longitudinally extending spar caps 24 to absorb bending loads experienced by the blade 10 in use. In this example, each half shell 12 comprises two spar caps 24 embedded in the laminate layers of the half shell 12, forming a so-called structural shell. The spar caps 24 comprise a stack 26 of strips 28 of reinforcing material arranged side-by-side and extending longitudinally in the blade 10. The blade 10 further comprises shear webs 30 incorporated between mutually opposing spar caps 24 of the first and second half shells 12a, 12b to form a spar structure that provides structural support to the blade 10 in use.

[0043] Figure 2 A stage in the process of forming a half shell 12 during manufacture of a wind turbine blade 10 is shown. It will be appreciated that the method of manufacturing the first half shell 12a is substantially the same as the method of manufacturing the second half shell 12b.

[0044] In this example, each half shell 12a, 12b is formed in a separate blade shell mould 32 before the half shells 12a, 12b are joined together with adhesive to form the blade shell 22. The mould 32 comprises a mould surface 34 that is concavely curved in cross-section and is configured to form a half shell 12 having a curved aerodynamic profile. The mould 32 extends longitudinally from a root end 36 to a tip end 38 and laterally between a first longitudinal edge 40 and a second longitudinal edge 42. Figure 2 The mould 32 shown in the example is configured to form a leeward side half shell 12a, and the first longitudinal edge 40 thus forms the trailing edge 18 of the half shell 12a and the second longitudinal edge 42 forms the leading edge 20 of the half shell 12a.

[0045] Shell material is arranged on the mould surface 34 during a lay-up process to form the half shell 12. In this example, the half shell 12 has a laminate structure and comprises a plurality of layers as most clearly shown in Figure 3a and Figure 3b Figure 3a is a cross-sectional view of the mould 32 after the lay-up process has been completed, and Figure 3b is Figure 3a is a detailed view of part A of the cross-sectional view of Figure 2 ​、 Figure 3a and Figure 3b The lay-up process is briefly described.

[0046] Reinforcing fibre material 44 is arranged on the mould surface 34 to form an outer layer of press skin 46 of the half-shell 12. In this example, the fibre material 44 comprises a layer of glass fibre fabric, such as a chopped strand mat (shown most clearly in Figure 3b ). The spar cap 24 is then arranged or assembled in the mould 32 on top of the outer skin layer 44. In this example, each spar cap 24 comprises a plurality of longitudinally extending strips 28 of reinforcing material arranged in three side-by-side stacks 26. As described later with reference to Figure 5 and Figure 6 , in this example, each spar cap 24 is assembled as a sub-assembly off-line and arranged in the mould 32 to reduce the complexity and time involved in arranging the shell material in the mould 32.

[0047] Core material 48 can also be arranged in the mould 32 adjacent to and between the spar caps 24 to increase the structural rigidity of the half-shell 12. In this example, the core material 48 comprises a structural foam, such as a closed cell polyvinyl chloride (PVC) foam. The core material 48 is butted against the spar caps 24 to position the core material 48 in the mould 32.

[0048] Further reinforcing fibre material 50 is arranged in the mould 32 to form an inner layer of press skin 52 of the half-shell 12. In this example, the inner skin 52 similarly comprises a layer of glass fibre fabric. The inner skin 52 extends over the other shell material arranged in the mould 32. In this example, a vacuum film 54 is arranged over the inner skin 52 and a vacuum assisted resin transfer moulding (VARTM) process is carried out. The shell material is thereby infused with resin which cures to integrate the shell material together. The shell 12 has a sandwich construction with the core material 48 and spar caps 24 sandwiched between the inner skin 52 and the outer skin 46. The spar caps 24 are thus embedded in the shell structure to form a so-called structural shell.

[0049] As shown most clearly in Figure 3a and Figure 3b , the stacks 26 of strips 28 are held together during manufacture of the half-shell 12 by a plurality of holding clamps 56. The clamps 56 ensure that the strips 28 in each stack 26 are held in place relative to each other during manufacture of the shell 12. In this example, the clamps 56 also serve to ensure that adjacent stacks 26 are held in place relative to each other during manufacture of the shell 12. The holding clamps 56 and spar caps 24 in this example will now be described in more detail. Figure 3a to Figure 6

[0050] The holding clamps 56 each comprise a substantially planar body 58 and an upper flange 60a and a lower flange 60b projecting transversely to the clamp body 58 (see​Figure 4 In this example, the upper and lower flanges 60a, 60b extend from the clamp body 58 at both the first and second sides 62, 64 of the retention clamp 56. As such, the flanges 60a, 60b and the clamp body 58 define a first receiving area 66a at the first side 62 of the retention clamp 56 and a second receiving area 66b at the second side 64 of the retention clamp 56. The first stack 26a of strips 28 is received in the first receiving area 66a. In this example, an adjacent second stack 26b of strips 28 is received in the second receiving area 66b.

[0051] The upper and lower flanges 60a, 60b of each side of the retention clamp 56 engage the respective upper and lower surfaces 68a, 68b of the first and second stacks 26a, 26b of strips 28. The flanges 60 are configured such that the clamp 56 clamps the stacks 26 of strips 28 between the opposing flanges 60a, 60b in each receiving area 66a, 66b. Thus, at the first side 62 of the retention clamp 56, the upper and lower flanges 60a, 60b are spaced apart by a distance Di that substantially corresponds to the height h of the first stack 26a at the location of the clamp 56. Similarly, in this example, the upper and lower flanges 60a, 60b are spaced apart by a distance D2 at the second side 64 of the clamp 56 that substantially corresponds to the height h of the second stack 26b of strips 28 at the location of the clamp 56.

[0052] The retention clamp 56 is configured such that the upper and lower flanges 60a, 60b are substantially parallel to the respective upper and lower surfaces 68a, 68b of each of the first and second stacks 26a, 26b. For example, Figure 4 The retention clamp 56 in the example of FIG. 6 is configured for placement in a spanwise position in which the upper and lower surfaces 68a, 68b of each of the first and second stacks 26a, 26b are substantially parallel. As such, the distances Di and D2 between the upper and lower flanges 60a, 60b are substantially constant from the first end of the clamp 70 to the second end of the clamp 72. Thus, in this example, the cross-section of the retention clamp 56 is substantially uniform from the first end 70 to the second end 72 of the clamp 56.

[0053] The close interference fit between the retaining clips 56 and the given stacks 26 fixes the bars 28 in the stacks 26 relative to each other. In particular, the flanges 60a, 60b serve to limit movement of each bar 28 in the out-of-plane direction Z of each bar 28. In this way, the retaining clips 56 ensure that the bars 28 in the stacks 26 cannot pop out in the direction Z when arranged in the mould 32. In this example, each clip 56 retains the bars 28 in both the adjacent first and second stacks 26a, 26b, thereby also ensuring that the stacks as a whole do not move relative to each other in the out-of-plane direction Z. The retaining clips 56 ensure that the upper and lower surfaces 68a, 68b of the adjacent stacks are flush, i.e. substantially coplanar, such that there is substantially no step in the out-of-plane direction Z between the adjacent stacks 26.

[0054] In this example, the first and second stacks 26a, 26b of bars 28 are arranged side-by-side, and the body 58 of each retaining clip 56 is arranged between the adjacent stacks 26. The planar body 58 of each clip 56 has a thickness T defined between a first side 74a and a second side 74b of the body 58 (shown in Figure 4 The first stack 26a abuts the first side 74a of the clip body 58, and the second stack 26b abuts the second side 74b of the clip body 58. In this way, the thickness T of the clip body 58 is configured to maintain a predetermined spacing of the width w between the adjacent stacks 26 that is substantially the same as the thickness T of the clip body 58.

[0055] For optimal structural performance, the spacing between the adjacent stacks 26a, 26b should be small, without allowing the stacks 26 and / or bars 28 to collide or overlap. It is additionally important to ensure that the adjacent stacks 26 are spaced apart in order to facilitate thorough resin infusion throughout the layup. In this example, the thickness T of the clip body 58, and hence the width w of the spacing between the adjacent stacks 26, is 1 mm.

[0056] The longitudinally extending reinforcing material bars 28 are substantially planar, i.e. flat elongate members. When the bars are arranged in the first and second stacks 26a, 26b in the first and second receiving regions 66a, 66b of the retaining clips 56, the planar body 58 of the retaining clips 56 is substantially perpendicular to the plane of the bars 28. With the stacks 26 abutting the planar body 58 of the retaining clips 56, the retaining clips 56 serve to limit movement of the bars 28 in their plane in the general chordwise direction (C) such that the stacks 26 and / or the bars 28 of each stack 26 do not abut each other, and a predetermined minimum spacing is maintained between the stacks 26.

[0057] The upper and lower flanges 60a, 60b comprise inner surfaces 76a, 76b (see Figure 4The inner surfaces 76a, 76b of the upper flange 60a and the lower flange 60b engage the upper surface 68a and the lower surface 68b of each of the adjacent stacks 26a, 26b. Each flange 60 has a thickness t defined between the inner surface 76 and the outer surface 78 of the flange 60. f Thus, the outer surface 78 of the flange 60 is the surface of the given flange 60 opposite to the corresponding inner surface 76. The flange 60 also includes a longitudinal edge 80 that extends in a direction substantially parallel to the longitudinal direction Y of the stack 26 when the stack 26 is received in the receiving area 66 of the holding clamp 56.

[0058] In this example, the thickness t of flange 60 f They taper towards their longitudinal edges at 80 degrees. Therefore, the thickness t of each flange 60 is... f The distance from the fixture body 58 decreases. In this example, the inner surface 76 of the flange 60 is substantially perpendicular to the fixture body 58, and the outer surface 78 of the flange 60 is a basically flat surface inclined relative to their respective inner surfaces 76. Therefore, in this example, the cross-sections of the upper flange 60a and the lower flange 60b are basically triangular.

[0059] exist Figure 3b The thickness t of the tapered flange can be seen most clearly in the detailed cross-sectional view. f The benefits of tapered flange 60 include minimizing the height of step 82 between the upper surface 68a or lower surface 68b of stack 26 and the corresponding upper flange 60a or lower flange 60b of retaining clamp 56. Tapered flange 60 allows the fiber materials 44, 50 (i.e., the outer skin 46 and inner skin 52 of half-shell 12) to conform smoothly around spar cap 24 and retaining clamp 56. This avoids kinking or wrinkling of the fiber materials 44, 50 in the laminate at the transition of the stack 26 of cover strip 28 to the cover retaining clamp 56. Therefore, tapered flange 60 minimizes stress concentration in the inner skin 52 and outer skin 46 of half-shell 12 and minimizes the occurrence of resin-rich areas without fiber reinforcement.

[0060] Even after the blade 10 is manufactured, the retaining clamp 56 remains embedded in the spar cap 24. In this example, the retaining clamp 56 has a length L of 25 mm. C And therefore very small relative to the size of the wind turbine blade 10 and / or the length of the spar cap 24. The clamp 56 is kept separate from the stack 26 and does not interfere in any way with the reinforcing strip 28. Therefore, including the clamp 56 in the laminated structure of each half-shell 12 has no adverse effect on the load-bearing capacity of the spar cap 24.

[0061] The stacking of strip 28 and 26 typically has the maximum height h in the wingspan region. maxIn this wingspan region, the blade 10 requires the greatest structural support. In this example, the stack 26 has the maximum height h in the central portion 84 of the spar cap 24 between the root end 86 and the end end 88. max (like Figure 6 (As shown in the diagram). Thus, in this example, the stack 26 includes a greater number of strips 28 stacked one on top of the other in the central portion 84 than near the root end 86 or the end 88.

[0062] When the spar caps 24 are arranged in the mold 32, the increased stacking height h and / or the increased number of strips 28 can make the stack 26 unstable. The stack 26 may be particularly unstable in steep areas of the mold 32, such as the central portion 90 of the mold 32. Figure 2 (As shown in the image) Between the root end 36 and the mold surface 34, the cross-section of the mold surface 34 is approximately a semi-circular profile. (As shown in the image) Figure 3a and Figure 3b As shown, the use of clamps 56 is therefore particularly beneficial in the steep areas of the mold 32 to maintain the necessary spacing between the stacks 26 and to hold the strips 28 in their respective stacks 26.

[0063] Referring to the spar cap 24a closer to the rear edge 18 of the half-shell 12, a retaining clamp 56 is arranged between adjacent stacks 26 to prevent the strips 28 of the first stack 26a from sliding in the chord direction (C) within the mold 32 and colliding with or overlapping the strips 28 of the second stack 26b. Similarly, a retaining clamp 56 arranged between the second stack 26b and a third stack 26c of strips 28 prevents the second stack 26b from sliding into the third stack 26c in the chord direction. Therefore, the retaining clamp 56 facilitates accurate alignment of the reinforcing material strips 28 and maintains a predetermined spacing between adjacent stacks 26. Precise alignment of the stacks 26 to form the spar cap 24 further results in the precise positioning of the core material 48, which abuts the spar cap 24 in the mold 32.

[0064] Now, we mainly refer to the appendix. Figure 5 and Figure 6 In this example, assembling the spar cap 24 includes arranging multiple reinforcing material strips 28 into a first stack 26a. In this example, the spar cap 24 consists of multiple strips L of different lengths. Strip Strip 28 is formed. Strip 28 is arranged such that the height h of the stack 26 is from the minimum height h near the end 88 of the spar cap 24. min The maximum height h is reached in the central portion 84 between the end 88 and the root 86 of the wing cap 24. max In this example, the longest strip 28i is positioned at the bottom of the stack 26 and defines the lower surface 68b of the stack 26. Subsequent reinforcing strips 28 reduce the length L. StripThe arrangement progresses to the shortest strip 28ii, which is positioned at the top of the stack 26 in the central portion 84, where the wing cap 24 has the maximum height h. max .

[0065] Then, retaining clamps 56 are positioned on one side 92 of the first stack 26a, such that the first stack 26a is received in the first receiving region 66a. The upper flange 60a and lower flange 60b of the first side 62 of each clamp 56 engage the upper surface 68a and lower surface 68b of the first stack 26a. One side 92 of the first stack 26a abuts the first side 74a of the body 58 of each retaining clamp 56. In this example, the retaining clamps 56 extend along the length L of the stack 26. Stack They are spaced apart at intervals of 2m and 3m.

[0066] In this example, multiple reinforcing material strips 28 are arranged to form a second stack 26b. The second stack 26b is then arranged adjacent to the first stack 26a such that the second stack 26b is received in the second receiving area 66b of each clamp 56. The upper flange 60a and lower flange 60b of the clamp 56 engage the corresponding upper surface 68a and lower surface 68b of the second stack 26b, and the second stack 26b is adjacent to the second side 74b of the clamp body 58.

[0067] Therefore, the second stack 26b is arranged side-by-side with the first stack 26a, wherein the clamp body 58 of each retaining clamp 56 is arranged between adjacent stacks 26. In this example, each retaining clamp 56 includes a clamp body 58 having the same thickness T. Thus, the arrangement of the retaining clamps 56 between adjacent stacks 26 of the strip 28 is used to maintain a spacing of width w between adjacent stacks 26, which extends along the entire length L of the stack 26. Stack It is basically constant.

[0068] In this example, the height h of each stack 26 is along its length L Stack Variation. As previously described, the distance D between the upper flange 60a and the lower flange 60b of a given retaining clamp 56 is configured to substantially correspond to the height h of the stack 26 held at a given wingspan position by the flanges 60a and 60b. Thus, the plurality of retaining clamps 56 extend along the length L of the stack 26. Stack The retaining clamps 56 are arranged such that the distance D between their respective upper flanges 60a and lower flanges 60b varies depending on the span position of the retaining clamps 56. For example, a retaining clamp 56 configured to be arranged near the end 88 of the spar cap 24 has a smaller distance D between the upper flanges 60a and lower flanges 60b than a retaining clamp 56 configured to be arranged in the central portion 84 of the spar cap 24 (where the spar cap 24 has a greater height h).

[0069] In this example, assembling the spar cap 24 also includes arranging a second set of retaining clips 56 with a second stack 26b of reinforcing material strips 28 in the same manner as previously described with reference to the arrangement of the clips 56 with the first stack 26a of strips. A plurality of reinforcing material strips 28 are arranged to form a third stack 26c of strips 28 and then arranged adjacent to the second stack 26b in the same manner as previously described with reference to the first stack 26a and the second stack 26b. The clip bodies 58 of the second set of retaining clips 56 protrude laterally along their length L Stack The spacing between the second stack 26b and the third stack 26c of substantially constant width w is again maintained. The retaining clips 56 also ensure that the upper and lower surfaces 68a, 68b of the adjacent second and third stacks 26b, 26c are flush, i.e. substantially coplanar.

[0070] The retaining clips 56 arranged between the stacks 26 of reinforcing material strips 28 serve to maintain the position of the stacks 26 relative to each other during assembly of the half shell 12. The retaining clips 56 remain arranged with the stacks 26 of strips 28 during infusion and curing of the resin to form the half shell 12. The clips 56 therefore also ensure that the strips 28 forming the spar cap 24 remain aligned with each other throughout the manufacturing process until the cured resin matrix permanently fixes the strips 28 in place as part of the structural shell 22 of the wind turbine blade 10.

[0071] In the example where the spar cap 24 is assembled offline, the retaining clips 56 also serve to maintain the position of the stacks 26 relative to each other during transportation of the spar cap 24 and arrangement of the spar cap 24 in the mould 32. The use of retaining clips 56 as described herein therefore facilitates a simplified process for manufacturing the half shell 12 of the wind turbine blade 10. Furthermore, the precise alignment of the stacks 26 and reinforcing strips 28 results in a spar cap 24 that provides optimal structural support to the wind turbine blade 10 and minimises the risk of stress concentration in the blade shell 22.

[0072] The lateral cross-section of the retaining clips 56 described with reference to the preceding figures is substantially H-shaped, i.e. the retaining clips 56 include an upper flange 60a and a lower flange 60b extending from the first side 62 and the second side 64 of the clip 56. However, in other examples, the retaining clips 56 can include an upper flange 60a and a lower flange 60b that protrude laterally in only one of the first side 62 or the second side 64 of the clip 56, as shown in the example of Figure 7 The lateral cross-section of such retaining clips 56 can be substantially C-shaped.

[0073] Figure 7The upper flange 60a and lower flange 60b of the retaining clamp 56 and the clamp body 58 define a first receiving area 66 on a first side 62 of the clamp 56, in which a first stack 26 of strips 28 can be received. The C-shaped retaining clamp 56 is constructed in substantially the same manner as the previously described H-shaped clamp 56, except that the flange 60 extends only on one side of the clamp 56.

[0074] A retaining clamp 56, including a flange 60 on only one side, can be arranged with a side 94 of the stack 26 that is not adjacent to another stack 26 of strip 28. In the above example, such as Figure 7 The clamp 56 shown can be arranged along one side 94 of the outer stack 26 (such as along one side 94 of the first stack 26a and / or the third stack 26c). In other examples, the H-shaped retaining clamp 56 (such as reference) Figure 4 The described ones can be arranged along the side 94 of stack 26 that is not adjacent to another stack 26 of strip 28. Arranging H-shaped or C-shaped retaining clamps 56 along the side 94 of stack 26 that is adjacent to core material 48 in the layup helps to minimize the occurrence of any steps in the Z-direction between stack 26 and core material 48, so that inner skin 52 and outer skin 46 are smooth and wrinkle-free.

[0075] In other examples, the spar cap 24 can be formed from a single stack 26 of reinforcing material strips 28. In such examples, such as Figure 7 The C-shaped retaining clamp 56 shown can be arranged along the first side 92 and the second side 94 of the stack 26 of strips 28, as... Figure 8a As shown. Figure 8a The stack 26 shown can alternatively be the first stack 26a of a plurality of side-by-side stacks 26 forming the spar cap 24. In such an example, the strips 28 in each stack 26 are held in place relative to each other, but the stacks 26 are not constrained relative to each other by the clamps 56 in the out-of-plane direction Z.

[0076] Figure 8b Another example is shown, in which each stack 26 of strips 28 is held by a plurality of C-shaped retaining clamps 56. Figure 8b In the example, the spar cap 24 includes retaining clamps 56 arranged along adjacent sides 92a, 92b of the first stack 26a and the second stack 26b, such that the body 58 of each clamp 56 is arranged between adjacent stacks 26. The retaining clamps 56 arranged with the first stack 26a and the retaining clamps 56 arranged with the second stack 26b can be offset in the spanwise direction (S), such that the orientation of the clamps 56 alternates from one clamp to the next, running from the root end 86 to the end end 88 of the spar cap 24. Figure 8bAs shown, first clamp 56a can hold first stack 26a, second clamp 56b can hold second stack 26b, third clamp 56c can hold first stack 26a, and fourth clamp 56d can hold second stack 26b, etc. In such examples, clamp body 58 serves to maintain a predetermined spacing between adjacent stacks 26, while flanges 60a, 60b of clamps 56 secure the bars 28 in each stack 26 in place relative to one another.

[0077] In yet further examples, retaining clamps 56 having flanges 60 on only one side of clamps 56 can additionally or alternatively be arranged with the root end surfaces and / or tip end surfaces of stacks 26 of bars 28 so as to limit movement of bars 28 in stacks 26 relative to one another in the spanwise direction (S).

[0078] Retaining clamps 56 in the above-described examples are formed of a polymeric material. For example, clamps 56 can be formed of a material such as acrylonitrile butadiene styrene (ABS), nylon. Forming retaining clamps 56 of a polymeric material facilitates cost- effective manufacturing of clamps 56 using processes such as injection molding or extrusion. Alternatively, retaining clamps 56 can be formed of any other suitable material. For example, retaining clamps 56 can be formed of a composite material including reinforcing fibers in a polymeric resin. In such examples, retaining clamps 56 can be formed by pultrusion or lamination.

[0079] Reinforcing material bars 28 in the examples described herein include reinforcing fibers in a cured resin matrix. Preferably, a high percentage of fibers in each bar 28 extend longitudinally, i.e. in the spanwise direction (S), to absorb bending loads experienced by a blade 10 in use. Bars 28 in the above-described examples include unidirectional carbon fibers. Bars 28 can be formed in a pultrusion process in which reinforcing fibers are coated in resin and pulled through a mold as the resin cures. Reinforcing material bars 28 in the examples described herein are therefore carbon fiber reinforced plastic (CFRP) pultrusions.

[0080] Many modifications can be made to the above-described examples without departing from the scope of the application as defined in the appended claims.

[0081] In the above-described examples, each individual reinforcing material bar 28 extends along its length L Strip has a substantially constant thickness t Strip and the height h of the stack 26 varies in a stepped manner (see, for example, Figure 5). In this way, the upper and lower surfaces 68a, 68b of the stacks 26 are generally parallel along the spar cap 24 at each spanwise location, and each retaining clamp 56 has a substantially constant distance D between its respective upper and lower flanges 60a, 60b from the first end 70 to the second end 72 of the clamp 56. However, in some examples, the height h of one or more of the stacks 26 of strips 28 forming the spar cap 24 can taper smoothly (i.e. not in a stepped manner).

[0082] The end portions of the strips 28 can be chamfered so that the upper surface 68a of the stacks 26 tapers smoothly, i.e. the individual strips 28 can comprise a tapered thickness t Strip Accordingly, in some examples, retaining clamps 56 configured for arrangement in a tapered region of the spar cap 24 can comprise diverging upper and lower flanges 60a, 60b. In such examples, the change in distance D between the flanges 60 from the first end 70 to the second end 72 of the clamp 56 preferably corresponds to the tapered height h of the respective stack 26 in the location of the clamp 56.

[0083] In some examples, the distance D1 between the upper and lower flanges 60a, 60b on the first side 62 of the clamp 56 can be different to the distance D2 between the flanges 60a, 60b on the second side 64 of the retaining clamp 56. Such retaining clamps 56 can for example be arranged at spanwise locations where the first stack 26a of strips 28 has a greater height h than the second stack 26b.

[0084] In some examples where the thickness t f of the flanges 60 decreases linearly with distance from the clamp body 58, the flange thickness t f may not decrease linearly with distance from the clamp body 58. Accordingly, the outer surface 78 of the flanges 60 can not be a substantially planar inclined surface, but can be a curved surface. In such examples, the upper and / or lower flanges 60a, 60b can have a cross-sectional profile shaped as a segment of a circle.

[0085] In some examples, the spar cap 24 can comprise one or more layers of fibre material or flow enhancement medium between the stacked strips 28. Particularly in examples where the strips 28 are cured components (e.g. CFRP pultrusions), arranging such layers between the strips 28 in a given stack 26 can help to ensure thorough infusion of resin throughout the shell material in the mould 32, so as to fully integrated layup.

[0086] In some examples, the strips of reinforcement material 28 can be arranged with the retaining clip 56 individually, i.e. the stack 26 of strips 28 is formed simultaneously with the arrangement of the stack 26 and retaining clip 56. In such examples, the bottom strip 28i of the stack 26 of strips 28 is preferably first arranged with the retaining clip 56 so that the lower flange 60b engages the bottom surface of the strip 28i. The remaining strips 28 can then be arranged with the clip 56 on top of the bottom strip 28 to form the stack 26. Due to the close interference fit between the retaining clip 56 and the stack 26, in some examples, arranging one or more strips 28 with the retaining clip 56 separately can facilitate a simpler assembly process.

[0087] In some other examples, the spar cap 24 can not be assembled off-line as a sub-assembly, but can instead be assembled in the mould 32 during the lay-up process. Whether the spar cap 24 is assembled in the mould 32 or off-line, the process for assembling the spar cap 24 is substantially the same, and the description provided above in relation to the assembly of the spar cap 24 off-line is equally applicable to the assembly of the spar cap 24 in the mould 32. Figure 5 and Figure 6 The description provided above in relation to the assembly of the spar cap 24 off-line is therefore equally applicable to the assembly of the spar cap 24 in the mould 32.

[0088] It will be appreciated that features described in relation to each of the above examples can readily be combined with features described in relation to the other examples, without departing from the scope of the application as defined by the appended claims.

Claims

1. A method of manufacturing a wind turbine blade (10), the method comprising: providing a blade shell mould (32); providing a plurality of planar strips of reinforcing material (28); arranging the plurality of planar strips of reinforcing material (28) in the mould in a first stack (26a) to form at least part of a first spar cap (24); providing a retaining clip (56) having a planar body (58) and an upper flange (60a) and a lower flange (60b) projecting transversely to the planar body, the upper flange (60a), the lower flange (60b) and the planar body (58) together defining a first receiving area (66a) at a first side (62) of the retaining clip, and the first receiving area (66a) being an open structure bounded on three sides by the planar body (58), the upper flange (60a) and the lower flange (60b); and arranging the retaining clip (56) at one side of the first stack (26a) such that the planar strips of reinforcing material (28) in the first stack are received in the first receiving area (66a).

2. The method of claim 1, wherein, The step of arranging the plurality of planar strips of reinforcing material (28) in the mould (32) comprises arranging the planar strips of reinforcing material (28) in a first stack (26a) and a second stack (26b) side-by-side to form at least part of the first spar cap (24), and wherein the retaining clip (56) is arranged such that the planar body (58) of the retaining clip is located between the first stack and the second stack and maintains a predetermined spacing between the stacks.

3. The method of claim 2, wherein, The upper flange (60a), the lower flange (60b) and the body (58) of the retaining clip (56) together define a second receiving area (66b) at a second side (64) of the retaining clip, and the method further comprises arranging the retaining clip at one side of the second stack (26b) such that the planar strips of reinforcing material (28) of the second stack are received in the second receiving area.

4. The method of any one of claims 1 to 3, wherein, The retaining clip (56) has an H-shaped cross-section.

5. The method of any one of claims 1 to 3, wherein, The retaining clip (56) has a length of between 20mm and 50mm.

6. The method of any one of claims 1 to 3, wherein, The upper flange (60a) and / or the lower flange (60b) tapers in thickness towards its edges.

7. The method of any one of claims 1 to 3, wherein, The upper flange (60a) and / or the lower flange (60b) has a cross-sectional profile that is triangular or shaped as a segment of a circle.

8. The method of any one of claims 1 to 3, wherein, The retaining clip (56) is formed from a polymeric material.

9. The method of any one of claims 1 to 3, wherein, The retaining clip (56) is an injection moulded part.

10. A wind turbine blade (10), the wind turbine blade (10) comprising: a spar cap (24) comprising a plurality of planar strips of reinforcing material (28) arranged in at least a first stack (26a); and a holding clip (56) having a planar body (58) and an upper flange (60a) and a lower flange (60b) projecting transversely to the planar body, the upper flange (60a), lower flange (60b) and the planar body (58) together defining a first receiving area (66a) at a first side (62) of the holding clip, and the first receiving area (66a) being an open structure bounded on three sides by the planar body (58), the upper flange (60a) and the lower flange (60b); wherein the holding clip is arranged at one side of the first stack such that the planar strips of reinforcing material (28) in the first stack are received in the first receiving area.

11. A wind turbine blade according to claim 10, wherein, The spar cap (24) comprises a first stack (26a) and a second stack (26b) side by side, and wherein the planar body (58) of the holding clip (56) is arranged between the first stack and the second stack and sets a predetermined spacing between the stacks.

12. A wind turbine blade according to claim 11, wherein, The upper flange (60a), lower flange (60b) and the body (58) of the holding clip together define a second receiving area (66b) at a second side (64) of the holding clip, and the holding clip is arranged at one side of the second stack (26b) such that the planar strips of reinforcing material (28) of the second stack are received in the second receiving area.

13. A wind turbine blade according to claim 10, wherein, The holding clip (56) has an H-shaped cross-section.

14. A wind turbine blade according to claim 10, wherein, The holding clip (56) has a length of between 20 mm and 50 mm.

15. A wind turbine blade according to any of claims 11 to 14, wherein, A plurality of holding clips (56) are arranged between the first stack (26a) and the second stack (26b) at a spaced apart pitch along the length of the stacks, and wherein the planar bodies of the holding clips each have the same thickness such that a constant spacing is maintained between the first stack and the second stack along their entire length.

16. A wind turbine blade according to claim 15, wherein, The height of the first stack (26a) and the second stack (26b) varies as moving from the root end (14) towards the tip end (16), and wherein the distance between the upper flange and the lower flange of each holding clip corresponds to the height of the stack at the location of the respective clip.

17. A wind turbine blade according to any of claims 10 to 14, wherein, The thickness of the upper flange (60a) and / or the lower flange (60b) tapers towards its edges.

18. A wind turbine blade according to any of claims 10 to 14, wherein, The upper flange (60a) and / or the lower flange (60b) has a triangular or a circular segment shaped cross-sectional profile.

19. A wind turbine blade according to any of claims 10 to 14, wherein, The holding clip (56) is formed from a polymeric material.

20. A wind turbine blade according to any of claims 10 to 14, wherein, The holding clip (56) is an injection moulded part.

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