Shear web for a wind turbine blade

Abstract

The method of manufacturing a shear web comprises: providing a shear web mould (50) shaped to form the web panel and the web foot; arranging a plurality of layers of fibrous reinforcing material (62, 64, 70) on the mould to form a layup (52) of the web panel and the web foot; arranging a radius filler (36) in the radius region of the web foot layup, the radius filler comprising reinforcing fibres held together in a predefined cross-sectional shape by a binder; supplying infusion resin to the layup in a resin infusion process such that the resin infuses the layers of fibrous reinforcing material and such that the resin also infuses the reinforcing fibres of the radius filler; and curing the resin to form a homogenous matrix encapsulating the fibrous reinforcing material of the web panel, web foot and individual fibres of the radius filler.

Description

[0001] Shear web for a wind turbine blade

[0002] Technical field

[0003] The present invention relates generally to wind turbine blades and more specifically to a shear web and a method of manufacturing a shear web for a wind turbine blade.

[0004] Background

[0005] Modern wind turbine blades typically comprise a shell defining the aerodynamic contour of the blade and one or more longitudinally-extending spars which act as the main loadbearing structures of the blade. A spar typically comprises a pair of mutually opposed spar caps, which are longitudinal reinforcing structures configured to take up the bending loads experienced by the blade in use. One or more shear webs are attached between the spar caps. The shear webs are configured to take up the shear loads experienced by the wind turbine blade in use.

[0006] A shear web typically comprises a web panel arranged between first and second web feet. The web feet define mounting flanges for attaching the shear web to the spar caps. The shear web may be generally l-shaped or C-shaped in transverse cross-section, with the mounting flanges being arranged transversely to the web panel. The web feet include curved sidewalls that provide a smooth transition between the panel and the transverse mounting flanges.

[0007] The geometry of the shear web, including the angle of the mounting flanges relative to the web panel, typically varies along the length of the shear web to accommodate changes in blade geometry along the length of the blade, such as blade twist. Accordingly, a shear web may have a relatively complicated geometry, and this presents manufacturing challenges.

[0008] Shear webs are typically moulded composite structures formed by arranging layers (plies) of fibrous material in a web mould to form a layup having the general shape of the shear web. The layup may then be infused with liquid resin, for example in a process such as vacuum-assisted resin transfer moulding (VARTM).

[0009] When forming the layup, a hollow space, referred to herein as a ‘radius region’ is inevitably created inside the web feet in the region of the curved sidewalls in view of the shear web geometry. A ‘radius filler’, also sometimes referred to as a ‘gusset filler’ or ‘noodle’ is typically provided in the radius region. Known radius fillers may comprise core material, such as foam or balsa wood, or pre-cured composite materials such as glass or carbon fibres in a cured resin matrix. The radius filler substantially fills the radius region and slows the passage of resin during the infusion process to avoid resin racing uncontrollably through the radius region without respecting the resin flow front. The radius filler may also perform a structural role providing additional reinforcement in the radius region of the web foot.

[0010] A radius filler used in existing wind turbine shear webs comprises a length of braided rope of generally circular cross section, which is formed of blown unidirectional glass fibres. Such ropes are similar to those used as heat-resistant seals in the doors of wood burning stoves. The blown glass fibre is very soft, having a consistency similar to cotton wool, which makes the rope highly compressible. This allows the radius filler to conform and take up most of the space within the radius region, despite the shape of the radius region varying along the length of the web due to the changing web geometry.

[0011] However, blown glass rope radius fillers present some disadvantages. Most notably, these radius fillers do not provide much support for the plies forming the shear web and tend to compress too much or compress uncontrollably due to their softness during the vacuum infusion process. This can make it difficult to control the geometry of the web foot, for example it is difficult to control the radius of curvature of the sidewalls. Uncontrolled compression of the radius fillers may also cause wrinkles to develop in the plies forming the web feet and lead to other surface deformations in the web feet where the plies are not sufficiently supported in their intended positions. When the plies become wrinkled or deformed, a resin rich pocket is formed in the web foot adjacent the wrinkle. Wrinkles and resin rich pockets introduce structural weaknesses in the web foot and are therefore undesirable.

[0012] In general it is difficult to achieve consistent results using existing radius fillers such as the blown glass rope discussed above. Accordingly, there is a need for an improved radius filler that avoids the problems described above and which enables more consistent results to be achieved. Summary of the invention

[0013] According to a first aspect of the present invention there is provided a method of making a shear web for a wind turbine blade. The shear web comprises a web panel and a web foot. The web foot comprises a mounting flange arranged transversely to the panel, first and second opposed sidewalls extending between the mounting flange and the panel, and a radius region defined inside the web foot between the mounting flange and the first and second sidewalls. The method comprises: providing a shear web mould shaped to form the web panel and the web foot; arranging a plurality of layers of fibrous reinforcing material on the mould to form a layup of the web panel and the web foot; arranging a radius filler in the radius region of the web foot layup, the radius filler comprising reinforcing fibres held together in a predefined cross-sectional shape by a binder; supplying infusion resin to the layup in a resin infusion process such that the resin infuses the layers of fibrous reinforcing material forming the web panel and the web foot and such that the resin also infuses the reinforcing fibres of the radius filler; and curing the resin to form a homogenous matrix encapsulating the fibrous reinforcing material of the web panel, web foot and individual fibres of the radius filler.

[0014] The resin infusion process is preferably a vacuum-assisted resin infusion process, for example vacuum-assisted resin transfer moulding (VARTM).

[0015] The pre-shaped radius filler supports the fibrous reinforcing material of the web foot during the infusion process and allows the geometry of the web foot to be controlled. As the fibrous reinforcing material is supported by the radius filler on both sides of the shear web, wrinkles are prevented from developing in the side walls of the web foot. The radius filler may also support the fibrous reinforcing material forming the mounting flange and prevents wrinkles from developing in the mounting flange without requiring additional pre-cured layers to be included in the layup of the mounting flange.

[0016] The shear web may be substantially l-shaped or substantially C-shaped in transverse cross-section. The angle of the mounting flange relative to the panel may vary in different longitudinal sections of the web in order to accommodate blade twist. The sidewalls of the web foot are preferably curved between the mounting flange and the web panel. The curvature of the sidewalls is preferably concave when seen from outside the shear web. In other words, the curvature is concave along an external surface of the shear web. The sidewalls preferably have an outer radius of curvature. The outer radius of curvature preferably varies in different spanwise sections of the shear web.

[0017] The first and second opposed sidewalls of the web foot may both form outer walls of the web foot. In other words, the first and second opposed sidewalls do not form an interior wall of the web foot.

[0018] The step of arranging a plurality of layers of fibrous reinforcing material on the mould to form a layup of the web panel and the web foot may comprise the steps of: arranging a first plurality of layers of fibrous reinforcing material (e.g. first plies) on the mould; optionally arranging a core material on the first plurality of layers; arranging a second plurality of layers of fibrous reinforcing material (e.g. second plies) above the first plurality of layers of fibrous reinforcing material such that the optional core material is sandwiched between the first plurality of layers and the second plurality of layers.

[0019] The first plurality of layers of fibrous reinforcing material may form part of the web panel and the first opposed sidewall of the web foot. The second plurality of layers of fibrous reinforcing material may form part of the web panel and the second opposed sidewall of the web foot.

[0020] The mould may provide a predefined radius of curvature to the first plurality of layers of fibrous reinforcing material. The first opposed sidewall may thus have a predefined radius of curvature.

[0021] The radius filler may be arranged on the first plurality of layers of fibrous reinforcing material. The second plurality of layers of fibrous reinforcing material may then be arranged on the radius filler. In other words, the radius filler is sandwiched between the first plurality of layers of fibrous reinforcing material and the second plurality of layers of fibrous reinforcing material.

[0022] The radius filler may have a base with first and second sides that extend from opposite sides of the base. The first and second sides of the radius filler may converge at an apex.

[0023] The predefined cross-sectional shape of the radius filler may comprise sides having a predefined radius of curvature, i.e. the first and second sides of the radius filler may have a predefined radius of curvature. The first and second sides of the radius filler may be concave.

[0024] The first side of the radius filler may have a first radius of curvature, and the second side of the radius filler may have a second radius of curvature. The first radius of curvature may be different to the second radius of curvature. This allows the web panel to be inclined at desired angle relative to the web foot.

[0025] The radius filler may provide a predefined radius of curvature to the first plurality of layers of fibrous reinforcing material. In other words, the predefined radius of curvature of the first side of the radius filler provides a predefined radius of curvature to the first plurality of layers of fibrous reinforcing material. The first plurality of layers of fibrous reinforcing material is sandwiched between the mould and the radius filler (in particular, the first side of the radius filler) and so both the mould and the radius filler may provide the predefined radius of curvature to the first plurality of layers of fibrous reinforcing material. The first opposed sidewall may thus have a predefined radius of curvature.

[0026] The radius filler may provide a predefined radius of curvature to the second plurality of layers of fibrous reinforcing material. In other words, the predefined radius of curvature of the second side of the radius filler provides a predefined radius of curvature to the second plurality of layers of fibrous reinforcing material. The second opposed sidewall may thus have a predefined radius of curvature.

[0027] The method may further comprise covering the layup with a vacuum bag. The vacuum bag may be sealed to create a sealed region encapsulating the layup. Air may be evacuated from the sealed region which causes the vacuum bag to contract around the layup and to consolidate the layup.

[0028] The vacuum bag may be arranged against the second plurality of layers of fibrous reinforcing material which forms part of the web panel and the second opposed sidewall of the web foot. The expression “arranged against” does not necessarily mean that the vacuum bag is in direct contact with the second plurality of layers of fibrous reinforcing material, as process aids such as peel ply and breather fabric may be arranged between the vacuum bag and the second plurality of layers of fibrous reinforcing material. However, the vacuum bag is arranged against the second plurality of layers of fibrous reinforcing material such that the vacuum bag adopts the predefined radius of curvature provided by the radius filler, e.g. the predefined radius of curvature of the second side of the radius filler. In other words, when the vacuum bag contracts around the layup, the vacuum bag adopts the predefined radius of curvature provided by the radius filler to the second plurality of layers of fibrous reinforcing material.

[0029] The mould side of the layup, that is where the first plurality of layers of fibrous reinforcing material is arranged may be referred to as an A-side. The vacuum bag side of the layup may be referred to as a B-side.

[0030] On the A-side of the layup, i.e. the mould side, the first side of the radius filler provides a firm support above the first plurality of layers of fibrous reinforcing material. The first plurality of layers of fibrous reinforcing material are therefore prevented from developing wrinkles. On the B-side of the layup, the second side of the radius filler supports the second plurality of layers of fibrous reinforcing material forming the second opposed sidewall so that these second plurality of layers can be laid up against a firm support with a predefined shape and predefined radius of curvature. This advantageously allows the shape and radius of curvature on the B-side of the web foot to be controlled easily and prevents wrinkles developing in the second plurality of layers of fibrous reinforcing material when the vacuum bag is contracted against the B-side of the layup.

[0031] The radius filler is an elongate component and extends longitudinally along the length of the shear web. The cross-sectional shape of the radius filler may be different in different longitudinal sections of the radius filler. The radius filler may be continuous along the length of the shear web. Alternatively the radius filler may comprise a plurality of separate sections arranged or joined end-to-end along the length of the shear web. Each section of the radius filler may have a constant cross-sectional shape along its length. Two or more sections may have different predefined cross-sectional shapes.

[0032] The predefined cross-sectional shape of the radius filler is preferably substantially triangular. The radius filler may have a substantially flat base. The radius filler may have curved sides. The radius filler may be pre-shaped such that the curved sides of the radius filler have a predefined radius of curvature. The radius of curvature of the sidewalls is selected according to the required local geometry of the shear web in the position where the radius filler is incorporated. The radius filler supports the fibrous reinforcing material forming the web foot during the resin infusion process. The radius filler does not compress uncontrollably during the infusion process, and therefore enables the shape of the web foot to be controlled and avoids the formation of wrinkles in the web foot.

[0033] The curved sides of the radius filler support the fibrous reinforcing material (e.g. plies) forming the first and second opposed sidewalls of the web foot during the infusion process. This allows the sidewalls to be formed with a predefined radius of curvature and prevents wrinkles from developing in the plies forming the sidewalls. The sides of the radius filler preferably have a different radius of curvature in different spanwise sections of the shear web. The radius filler can thereby accommodate varying mounting flange angles along the length of the web.

[0034] The flat base of the radius filler supports the fibrous reinforcing material (e.g. base plies) forming the mounting flange and prevents wrinkles developing in the base plies. This advantageously avoids the need for additional pre-cured layers in the mounting flange, for example it avoids the need for a pre-cured mesh, which is necessary for preventing wrinkles when using a radius filler made from blown glass rope.

[0035] The binder of the radius filler advantageously holds the fibres of the radius filler together in the predetermined shape. The binder is a chemical binder such as a resin or adhesive binder. Preferably the binder is in the form of a solid powder. Preferably the binder is an epoxy powder. Preferably the infusion resin is also an epoxy resin. Accordingly, the radius filler is preferably formed from a so-called ‘powder bound’ material. The binder may be applied to the fibres of the radius filler as a coating, or it may be integrated with the fibres when the fibres are made.

[0036] The radius filler is a pre-shaped component. The radius filler may be formed by compressing powder bound fibrous material into an elongate component with a predefined cross-sectional shape. The binder holds the fibres together in the compressed state to maintain the predefined cross-sectional shape of the radius filler. However, unlike precured radius fillers, the radius filler is an infusible component. Accordingly, the infusion resin can infiltrate between the individual fibres of the radius filler during the infusion process. The infusion resin may dissolve, mix with or displace the binder during the resin infusion process. In the finished shear web, the individual fibres of the radius filler are advantageously encapsulated in a homogenous matrix together with the fibrous reinforcing material of the web panel. The shear web therefore has an advantageously homogeneous structure in which all the reinforcement fibres are encompassed within the same matrix. This is in contrast to shear webs incorporating radius fillers made from pre-cured composite material, in which the fibres of the radius filler are incorporated in a different matrix to the matrix formed by the infusion resin. When such pre-cured radius fillers are used, cracks or delamination may occur at the interfaces between the radius filler and the sidewalls or mounting flange of the shear web. These problems are eliminated with the present invention.

[0037] The reinforcing fibres of the radius filler preferably comprise multidirectional fibres. The radius filler is preferably made exclusively or predominantly from multidirectional fibres. The multidirectional fibres may be biaxial fibres or randomly orientated fibres. Preferably the fibres are short fibres. Preferably the fibres are chopped fibres. Preferably the fibres are dry fibres. Preferably the fibres are glass, carbon or aramid fibres. Most preferably the fibres are randomly oriented dry chopped glass fibres. Such fibres are advantageously inexpensive whilst having suitable mechanical properties.

[0038] Preferably the radius filler does not include unidirectional fibres extending in the spanwise direction of the blade. However, if unidirectional fibres are used they are preferably minimised. Forming the radius fillers from multidirectional fibres, and avoiding or minimising unidirectional fibres, avoids the radius fillers carrying appreciable bending loads, and ensures that these loads are carried by the spar caps. This also allows the radius fillers to be formed in multiple end-to-end sections with joints in between sections without any significant load drop offs occurring at these joints.

[0039] The method may comprise forming the radius filler in a continuous process involving feeding a length of reinforcing fibres including the binder through a heated die configured to compact the fibres into the predefined cross-sectional shape. The reinforcing fibres may be supplied to the heated die in the form of uncompressed bound fibres (e.g. powder bound fibres). The uncompressed bound fibres may be provided in the form of a rope, bundle, tow etc. The method may further comprise adjusting the heated die to vary the predefined cross-sectional shape imparted to the radius filler. The method may comprise cooling the radius filler downstream from the heated die, preferably by feeding the radius filler through a cooling die. Alternatively, the radius filler may be cooled by other means, for example by blowing cool air over it. The radius filler may be produced in the same factory as the web, e.g. using equipment provided alongside or nearby the shear web mould.

[0040] According to a second aspect of the present invention there is provided a shear web for a wind turbine blade. The shear web comprises a web panel and a web foot comprising fibrous reinforcing material. The web foot has a mounting flange arranged transversely to the panel, first and second opposed sidewalls extending between the mounting flange and the panel, and a radius region defined inside the web foot between the mounting flange and the first and second sidewalls. A pre-shaped radius filler having a pre-defined cross- sectional shape is located in the radius region. The radius filler comprises reinforcing fibres. Individual fibres of the radius filler are encapsulated in a homogenous resin matrix together with the fibrous reinforcing material of the web panel and the web foot.

[0041] Optional features described above in relation to the first aspect of the invention are equally applicable to the second aspect of the invention. Repetition of these optional features is avoided purely for reasons of conciseness.

[0042] Brief description of the drawings

[0043] Embodiments of the invention will now be described, by way of non-limiting example only, with reference to the accompanying schematic figures, in which:

[0044] Figure 1 is an exploded perspective view of a wind turbine blade comprising a shear web;

[0045] Figure 2 is a transverse cross-section of a shear web;

[0046] Figure 3 shows a shear web layup on a shear web mould; and

[0047] Figure 4 shows a process for manufacturing radius fillers for a shear web.

[0048] Detailed description

[0049] Figure 1 is a schematic exploded view of a wind turbine blade 10. The blade 10 extends longitudinally in a spanwise direction (S) between a root end 12 and a tip end 14, and in a chordwise direction (C) between a leading edge 16 and a trailing edge 18. The blade 10 comprises an outer shell 20 which may be formed of a first (e.g. windward) half shell 20a and a second (e.g. leeward) half shell 20b. When the half shells 20a, 20b are connected together, the outer shell 20 defines a substantially hollow interior.

[0050] The blade 10 further comprises a shear web 22 that extends longitudinally in the spanwise direction (S) inside the outer shell 20, i.e. inside the hollow interior of the blade 10. The shear web 22 forms part of a spar structure which is configured to absorb bending and torsional loads experienced by the blade 10 in use. The shear web 22 is connected between a pair of spar caps (not shown), which are embedded respectively in the first and second half shells 20a, 20b.

[0051] It will be appreciated that Figure 1 is a simplified diagram for ease of illustration and does not show the twist in the wind turbine blade 10, which is present along the length of the wind turbine blade 10.

[0052] Referring to the transverse cross-sectional view of Figure 2, the shear web 22 comprises a longitudinally-extending web panel 26 extending between upper and lower web feet 28. Each web foot 28 comprises a mounting flange 30 arranged transversely to the panel 26. In this example, the mounting flanges 30 are angled obliquely to the web panel 26.

[0053] In the web section illustrated in Figure 2, the angle a between the web panel 26 and the lower mounting flange 30 on an A-side of the panel 26 is greater than ninety degrees, whilst the angle between the web panel 26 and the lower mounting flange 30 on a 13- side of the web panel 26 is less than ninety degrees. Conversely, the angle between the web panel 26 and the upper mounting flange 30 on the A-side of the web panel 26 is less than ninety degrees, whilst the angle between the web panel 26 and the upper mounting flange 30 on the B-side of the web panel 26 is more than ninety degrees.

[0054] In order to accommodate blade twist, the angles of the mounting flanges 30 with respect to the panel 26 vary along the length of the shear web 22. In some sections of the web 22, such as near the blade root 12, the or each mounting flange 30 may be substantially perpendicular to the web panel 26.

[0055] The web feet 28 further comprises first and second opposed sidewalls 32 extending between the mounting flange 30 and the panel 26. The sidewalls 32 are curved and provide a smooth transition between the mounting flange 30 and the web panel 26. The curvature of the sidewalls 32 is concave when seen from outside the shear web 22. In other words, the curvature is concave along an external surface of the shear web 22.

[0056] The sidewalls 32 have an outer radius of curvature r0, which is indicated in Figure 2 by way of example for the lower web foot 28. In the web section illustrated in Figure 2, the outer radius of curvature of the sidewall 32 between the panel 26 and the lower mounting flange 30 on the A-side of the panel 26 is greater than the outer radius of curvature of the sidewall 32 between the panel 26 and the lower mounting flange 30 on the B-side of the panel 26. Conversely, the outer radius of curvature of the sidewall 32 between the panel 26 and the upper mounting flange 30 on the A-side of the panel 26 is less than the outer radius of curvature of the sidewall 32 between the panel 26 and the upper mounting flange 30 on the B-side of the panel 26.

[0057] The outer radii of curvature of the sidewalls 32 is different to those shown in Figure 2 in other longitudinal sections of the shear web 22 because the inclination of the mounting flanges 30 varies along the length of the shear web 22 to accommodate blade twist.

[0058] A radius region 34 is defined inside each web foot 28 between the mounting flange 30 and the first and second sidewalls 32. The radius region 34 is a space inside the web foot 28 that inevitably arises from the curved transition between the web-panel 26 and the transverse mounting flanges 30. In this example the radius region 34 is generally triangular in cross section and extends longitudinally along the length of the shear web 22. The shape of the radius region 34 varies along the length of the shear web 22 in dependence upon the angle of the mounting flanges 30 relative to the web panel 26 and the outer radii of curvature of the sidewalls 32.

[0059] A radius filler 36 is provided in the radius region 34. The radius filler 36 is a pre-shaped elongate component having a geometry corresponding substantially to the geometry of the radius region 34. Accordingly, the radius filler 36 substantially fills the radius region 34 along the length of the shear web 22. The radius filler 36 has a predefined cross-sectional shape, which in this example is generally triangular. The radius filler 36 has a base 38 with first and second sides 40, 42 that extend from opposite sides of the base 38 and converge at an apex 44. The base 38 of the radius filler 36 is substantially flat. The first and second sides 40, 42 curve inwardly, i.e. they are concave. As illustrated in Figure 2 for the upper web foot 28, the first side 40 has a first radius of curvature H, and the second side 42 has a second radius of curvature r2. The geometry of the radius filler 36, and in particular the first and second radii of curvature n, r2, varies along the length of the radius filler 36 to accommodate the varying inclination of the mounting flanges 30 along the length of the shear web. The radii of curvature n, r2of the sides 40, 42 are predefined during the manufacture of the radius filler 36 and are designed to support the plies forming the sidewalls 32 of the web feet 28 during a vacuum infusion process in order to control the geometry of the shear web 22.

[0060] The radius filler 36 is formed from fibres, preferably glass fibres, held together in the predefined cross-sectional shape by a binder. In this example, the radius filler 36 is formed from randomly orientated chopped dry glass fibres held together with a powder-based epoxy binder. The binder holds the fibres together and maintains the generally triangular cross-sectional shape of the radius filler 36 with sides 40, 42 having predefined radii of curvature n , r2.

[0061] A method of making a shear web 22 incorporating the radius filler 36 will now be described with reference to Figure 3.

[0062] Figure 3 shows a shear web mould 50 supporting a shear web layup 52. The shear web mould 50, which is shown in cross-section, extends longitudinally perpendicular to the plane of Figure 3. The mould 50 comprises a main mould surface 54, which may be substantially horizontal, and first and second side surfaces 56, which extend generally downwardly from the main mould surface 54. The mould 50 has curved shoulder portions 58 between the main mould surface 54 and the side surfaces 56.

[0063] The side surfaces 56 are inclined at an angle to the main mould surface 54, and this angle may vary along the length of the mould 50. The shoulder portions 58 have an inner radius of curvature rsindicated in Figure 3. The inner radii of curvature rsof the shoulder portions 58 corresponds to the outer radius of curvature r0of the sidewalls 32 of the web feet 28 on the A-side of the shear web 22 (indicated in Figure 2). This inner radius of curvature rsvaries along the length of the mould 50 in order to produce a shear web 22 adapted to accommodate blade twist. The mould 50 may further comprise removable upstands 60 positioned opposite the side surfaces 56. To make the shear web 22, a plurality of first plies 62 are stacked on the main mould surface 54. The plies 62 are layers of fibrous reinforcing fabric, for example glass fibre fabric. The first plies 62 are also draped over the shoulders 58 and side surfaces 56 of the mould 50. The first plies 62 will form part of the web panel 26 and web feet 28 on the A- side of the shear web 22.

[0064] Subsequently, the pre-shaped radius fillers 36 are arranged in position. The first curved side 40 of each radius filler 36 is arranged opposite a respective curved shoulder 58 of the mould 50 with the first plies 62 extending in-between. The first curved sides 40 of the radius fillers 36 have a radius of curvature (n - indicated in Figure 2) similar to the outer radius of curvature rsof the corresponding curved shoulder 58 of the mould 50.

[0065] Base plies 64 (e.g. glass fibre plies) may be stacked on the upstands 60, which may then moved into position opposite the sidewalls 32 and secured in place. The base plies 64 may at least partially form the mounting flanges 30 of the shear web 22. A central portion of the base plies 64 may be positioned against the flat base 38 of the radius filler 36. The edges of the base plies 64 may overlap the edges of the first plies 62 to form a stack of parallel plies defining first edges 66 of the mounting flanges 30 on the A-side of the shear web 22.

[0066] Core material 68 (e.g. structural foam) is positioned on top of the portions of the first plies 62 that are supported by the main mould surface 54. A plurality of second plies 70 (e.g. glass fibre plies) are stacked on top of the core material 68 on the main mould surface 54. The second plies 70 will form part of the web panel 26 and web feet 28 on the B-side of the shear web 22. The core material may be positioned on the first plies before or after the pre-shaped radius fillers 36 are arranged in position. Core material 68 may be omitted in other embodiments and the second plies 70 may instead be stacked directly on top of the first plies 62 on the main mould surface 54.

[0067] The second plies 70 extend over the second curved sides 42 of the radius fillers 36. The pre-shaped radius fillers 36 support the second plies 70 when they are laid up in the mould 50 so that the second plies 70 are supported along a predefined curved path between the panel 26 and the mounting flange 30. The second curved sides 42 of the radius fillers 36 have a radius of curvature r2 (indicated in Figure 2) which is designed to form the sidewalls 32 on the B-side of the shear web with a desired outer radius of curvature r0(indicated in Figure 2). Edges of the second plies 70 may overlap edges of the base plies 64 to form stacks of parallel plies defining second edges 72 of the mounting flanges 30 on the B-side of the shear web 22.

[0068] The web layup 52 is then covered with a vacuum bag 74, which is sealed, such as against a surface 76 to create a sealed region encapsulating the web layup 52. Air is evacuated from the sealed region, which causes the vacuum bag 74 to contract around the layup 52 and to consolidate the layup. Liquid resin (not shown) is then supplied to the layup 52 inside the vacuum bag 74. The liquid resin may be an epoxy resin or other resin suitable for resin infusion processes.

[0069] The liquid resin infuses throughout the layup 52. In particular, the resin infuses throughout the fibrous plies forming the panel 26 and the web feet 28. The resin also infuses through the radius fillers 36 in the web feet 28, i.e. it infiltrates between the individual fibres of the radius fillers 36.

[0070] The liquid resin used in the infusion process dissolves or otherwise displaces the powderbased binder of the radius fillers 36 during the infusion process. The liquid resin is then cured, for example by heating, which causes the resin to harden and form a homogeneous matrix encapsulating the fibrous plies 62, 64, 70 of the web panel 26, web feet 28 and the individual fibres of the radius fillers 36.

[0071] As the radius fillers 36 comprise fibres held together with a binder, as opposed to being pre-cured components, the radius fillers 36 are infusible components. The radius fillers 36 can still deform and compress slightly during the vacuum infusion process to adapt to changes in web geometry along the length of the web. However, the radius fillers 36 are not as soft as the blown glass rope radius fillers of the prior art, and therefore do not compress too much or compress uncontrollably during the vacuum infusion process. Consequently, the radius fillers 36 of the present invention support the plies 62, 64, 70 of the web feet 28 during the vacuum infusion process and prevent wrinkles developing in these plies.

[0072] On the A-side of the layup 52, i.e. the mould side, the first curved sides 40 of the radius fillers 36 provide a firm curved support behind the first plies 62. The first plies 62 are therefore prevented from developing wrinkles. On the B-side of the layup 52, i.e. the bag side, the second curved sides 42 of the radius fillers 36 support the second plies 70 forming the sidewalls 32 of the web feet 28 so that these plies 70 can be laid up against a firm support with a predefined shape and predefined radius of curvature. This advantageously allows the shape and radius of curvature on the B-side of the web feet 28 to be controlled easily and prevents wrinkles developing in the second plies 70. In comparison, the blown glass rope radius fillers of the prior art do not present a concave surface on the B-side of the mould 50 for supporting the second plies 70 and have a tendency to over compress under the vacuum pressure resulting in the second plies 70 in the web feet sidewalls 32 being unsupported and developing wrinkles and surface deformations. The flat base 38 of the radius fillers 36 supports the base plies 64 of the web feet 28 and prevents these plies from developing wrinkles. This avoids the need to use a pre-cured structure such as a precured mesh in the mounting flange 30, which is necessary when using radius fillers made from blown glass rope.

[0073] An exemplary manufacturing process for making a radius filler 36 is shown in Figure 4.

[0074] Referring to Figure 4, this shows a continuous length of rope of uncompressed fibres 80, which is stored on a spool 82. The uncompressed fibres 80 in this example are chopped dry glass fibres, which are randomly orientated. A powder-based chemical binder has been applied to the fibres, which binds the fibres together in a rope form. In this example the binder is a dry epoxy powder. In view of the powder-based binder, the uncompressed fibres 80 are known as ‘powder bound’ fibres. The length of uncompressed fibres 80 has a generally circular or oval shape, and the binder holds the fibres together in this shape.

[0075] The uncompressed fibres 80 are rapidly pulled through a heated die 84 by steel pulling casters 86 (shown schematically in cross-section in the insert of Figure 4A). The heated die 84 in this example comprises a pair of rollers 88 (shown schematically in cross-section in the insert of Figure 4B). The rollers 88 define an aperture 90 between the two rollers and a fixed side 92 of the die 84. The aperture 92 of the heated die 84 has a cross-sectional shape corresponding to the predefined cross-sectional shape of the radius filler 36 described above. In this example, the die 84 is double-ended such that a second aperture 96 having the same shape as the first aperture 90 is defined at a second end of the rollers 88. The two apertures 90, 96 allow two lengths of uncompressed fibres to be processed simultaneously thereby doubling the throughput of the apparatus.

[0076] As the fibres 80 are pulled through the aperture(s) 90, 96 of the heated die 84, the die compresses and shapes the fibres to impart the predefined cross-sectional shape to the length of fibres 80. The heat of the die (100 degrees Celsius in this example) melts or otherwise softens the binder and effectively softens the length of fibres, making it easier to compress and form into the desired shape.

[0077] The compressed fibres may be cooled downstream of the heated die 84, for example by pulling the fibres through an optional cooler die 100. This serves to solidify or harden the binder ensuring that the compressed fibres remain held together in the predefined cross- sectional shape imparted by the heated die 84.

[0078] The shape of the radius filler 36 can be adjusted by skewing the rollers 88 of the heated die 84. Figure 4B shows the rollers 88 in a horizontal position, whilst Figure 4C shows the rollers 88 in a skewed position. When the rollers 88 are horizontal, the produced radius filler 36 is symmetrical in cross section and both sides 40, 42 have the same radius of curvature. When the rollers 88 are skewed, the produced radius filler 36 will be asymmetrical in cross section, and the first side 40 will have a different radius of curvature to the second side 42. The rollers may be skewed at any angle, which allows a range of different cross-sectional profiles to be achieved.

[0079] The radius filler 36 may be formed as a single piece that may extend continuously along the entire length of the shear web 22, or at least along a majority of the length of the shear web 22. The radius filler 36 may be produced by dynamically adjusting the skew angle of the rollers 88 as the fibres 80 are pulled through the heated die 84 in order to provide a continuous variation in the cross-sectional shape of the radius filler 36 along its length.

[0080] Alternatively, the radius filler 36 may be formed in a plurality of shorter sections (for example two-metre long sections) that may then be arranged end to end along the length of the shear web 22. To this end, the apparatus includes a cutting tool 98 for cutting the radius filler 36 into sections. Sections having different cross-sectional shapes may be made by changing the skew angle of the rollers 88.

[0081] Many modifications may be made to the examples described above within the scope of the present invention as defined in the accompanying claims. For example, the web could have a C-shaped cross section instead of an l-shaped cross section. The web may only have the described web foot on one side, and the manufacturing process described with respect to Figure 3 is only performed on one side of the web. The radius filler may have a different shape, for example it may be curved on one side only. The radius filler could be formed from different types of fibres. The fibres could be biaxial fibres or other multidirectional fibres. A different type of binder may be used to bind the fibres together. The wind turbine blade does not need to be twisted, and the shear web flange angles may be the same along the length of the shear web. The shear web layup could be formed in any suitable order, for example the base plies could be laid up after the second plies. The radius fillers may be arranged in the mould before or after arranging any of the plies in the mould. The first and second plies do not need to extend continuously over the web panel and the web feet, and different plies may be used to form the web feet and the web panel.

Claims

Claims1. A method of making a shear web (22) for a wind turbine blade (10), the shear web comprising a web panel (26) and a web foot (28), the web foot comprising a mounting flange (30) arranged transversely to the panel, first and second opposed sidewalls (32) extending between the mounting flange and the panel, and a radius region (34) defined inside the web foot between the mounting flange and the first and second sidewalls, wherein the method comprises: providing a shear web mould (50) shaped to form the web panel and the web foot; arranging a plurality of layers of fibrous reinforcing material (62, 70) on the mould to form a layup (52) of the web panel and the web foot; arranging a radius filler (36) in the radius region of the web foot layup, the radius filler comprising reinforcing fibres held together in a predefined cross-sectional shape by a binder; supplying infusion resin to the layup in a resin infusion process such that the resin infuses the layers of fibrous reinforcing material forming the web panel and the web foot and such that the resin also infuses the reinforcing fibres of the radius filler; and curing the resin to form a homogenous matrix encapsulating the fibrous reinforcing material of the web panel, web foot and individual fibres of the radius filler.

2. The method of Claim 1 wherein the infusion resin dissolves, mixes with or displaces the binder of the radius filler (36) during the resin infusion process.

3. The method of Claim 1 or Claim 2, wherein the method further comprises forming the radius filler (36) in a continuous process involving feeding a length of reinforcing fibres (80) including the binder through a heated die (84) configured to compact the fibres into the predefined cross-sectional shape.

4. The method of Claim 3, wherein the method further comprises adjusting the heated die (84) to vary the predefined cross-sectional shape imparted to the radius filler (36).

5. The method of Claim 3 or Claim 4, further comprising cooling the radius filler (36) downstream from the heated die (84), preferably by feeding the radius filler through a cooling die (100).

6. The method of any preceding claim, wherein the radius filler (36) is formed from a powder bound material.

7. The method of any preceding claim, wherein the reinforcing fibres of the radius filler (36) comprise multidirectional fibres.

8. The method of any preceding claim, wherein the reinforcing fibres of the radius filler (36) comprise short fibres, e.g. chopped fibres.

9. The method of any preceding claim, wherein the predefined cross-sectional shape of the radius filler (36) is substantially triangular with curved sides (40, 42) having a predefined radius of curvature (n, r2).

10. The method of Claim 9, wherein the curved sides (40, 42) of the radius filler (36) support the fibrous reinforcing material (62, 70) forming the first and second opposed sidewalls (32) of the web foot (28) during the infusion process.11 . The method of Claim 9 or Claim 10, wherein the sides (40, 42) of the radius filler (36) have a different radius of curvature (n, r2) at different spanwise positions along the length of the shear web (22).

12. The method of any preceding claim, wherein the radius filler (36) comprises a plurality of sections arranged end to end along the length of the shear web (22).

13. The method of Claim 12, wherein each section of the radius filler (36) has a constant cross-sectional shape along its length, and wherein two or more sections have different predefined cross-sectional shapes.

14. The method of any preceding claim, wherein the step of arranging the plurality of layers of fibrous reinforcing material on the mould (50) to form the layup (52) of the web panel and the web foot comprises the steps of: arranging a first plurality of layers (62) of fibrous reinforcing material on the mould; optionally arranging a core material (68) on the first plurality of layers; arranging a second plurality of layers (70) of fibrous reinforcing material above the first plurality of layers of fibrous reinforcing material such that the optional core material is sandwiched between the first plurality of layers and the second plurality of layers.

15. The method of Claim 14, wherein the radius filler (36) is sandwiched between the first plurality of layers (62) of fibrous reinforcing material and the second plurality (70) of layers of fibrous reinforcing material.

16. The method of Claim 14 or Claim 15, wherein the radius filler (36) provides a predefined radius of curvature to the second plurality of layers (70) of fibrous reinforcing material.

17. The method of any of Claims 14 to 16, wherein the method further comprises the steps of: covering the layup (52) with a vacuum bag (74); sealing the vacuum bag to create a sealed region encapsulating the layup; evacuating air from the sealed region such that the vacuum bag contracts against the layup and to consolidate the layup.

18. The method of Claim 16 and Claim 17, wherein the vacuum bag (52) is arranged against the second plurality of layers (70) of fibrous reinforcing material such that the vacuum bag adopts the predefined radius of curvature provided by the radius filler (36).

19. A shear web (22) for a wind turbine blade (10), the shear web comprising a web panel (26) and a web foot (28) comprising fibrous reinforcing material (62, 70), the web foot having a mounting flange (30) arranged transversely to the panel, first and second opposed sidewalls (32) extending between the mounting flange and the panel, and a radius region (34) defined inside the web foot between the mounting flange and the first and second sidewalls, wherein a pre-shaped radius filler (36) having a pre-defined cross- sectional shape is located in the radius region, the radius filler comprising reinforcing fibres, and wherein individual fibres of the radius filler are encapsulated in a homogenous resin matrix together with the fibrous reinforcing material of the web panel and the web foot.

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