DK201570491A1 - Improvements relating to wind turbine blades - Google Patents

Abstract

A shear web for a wind turbine blade is described. The shear web comprises a web head defining a slot and a panel having a longitudinal edge region received in the slot. One or more spacing features protrude beyond first and second sides of the longitudinal edge region of the panel. The spacing features are arranged to abut first and second sidewalls of the slot to align the panel in the slot and to ensure space for adhesive is provided on both sides of the panel in the slot. The spacing features are preferably arranged to centre the panel in the slot. In a preferred embodiment, the spacing features are discrete elements arranged at intervals along the longitudinal edge of the panel.

Description

Improvements relating to wind turbine blades

Technical field

The present invention relates generally to wind turbine blades and their manufacture, and more specifically to an improved shear web for a wind turbine blade and a method of manufacturing a wind turbine blade comprising the improved shear web.

Background

Modern wind turbine blades are typically constructed from two half shells: a windward shell and a leeward shell. The half shells are formed in separate mould halves of a mould assembly. After forming the half shells in their respective mould halves, adhesive is applied along leading and trailing edges of one or both half shells. One mould half is then lifted, turned and positioned on top of the other mould half. This is known as closing the mould, and results in the two half shells being positioned in contact along their respective leading and trailing edges. The adhesive between the two half shells is then cured, which results in the half shells being firmly bonded together to form the complete blade.

The wind turbine blade typically includes one or more shear webs located inside the blade and bonded between inner surfaces of the windward and leeward half shells. The shear webs are longitudinal structures, which when viewed in cross-section are substantially l-shaped or C-shaped and comprise a web having first and second flanges at its respective ends. The flanges are bonded respectively to the inner surfaces of the respective half shells and the web thereby forms a bridge between the half shells.

Prior to closing the mould to bond the half shells together, a longitudinal strip of adhesive is applied to the inner surface of one of the half shells and the shear web is positioned on top of the adhesive. The shear web is typically arranged vertically such that a lowermost flange of the shear web sits on top of the adhesive. A further strip of adhesive is applied along the uppermost flange of the shear web. If the blade has multiple shear webs then this process is repeated for each shear web. The mould is then closed. The adhesive between the flanges of the shear web(s) and the respective inner surfaces of the blade shells is compressed when the mould is closed and cures at the same time as the adhesive between the half shells.

It is important to ensure sufficient squeezing of adhesive between the shear webs and the respective half shells during mould closure in order to form consistent bond lines between the flanges of the shear webs and the inner surfaces of the respective half shells. One way of achieving this is described in the applicant’s prior PCT application W02008/104174, whereby the shear web incorporates a resilient member arranged to compress during mould closure and subsequently expand during curing of the adhesive. This results in the flanges of the shear web being forced towards the respective inner surfaces of the half shells such that they exert a compressive force on the adhesive during curing.

The shear web described in W02008/104174 is illustrated in Figure 1. Referring to Figure 1, the shear web 10 is formed in multiple parts and comprises a web panel 12 and a web head 14 fitted over an upper edge 16 of the panel. The web panel 12 is substantially L-shaped and defines a lower flange 18 of the shear web 10 for bonding to an inner surface of a first half shell of the blade. The web head 14 is substantially T-shaped in cross-section and defines an upper flange 20 for bonding to an inner surface of the second half shell of the blade.

The T-shaped web head 14 includes a longitudinal slot 22. A strip of foam 24 is provided at the base of the slot 22, and the slot 22 is filled with adhesive. The upper edge 16 of the panel 12 is then inserted into the slot 22 such that the strip of foam 24 is located between the upper edge 16 of the panel 12 and the base of the slot 22. When the mould is closed to bond the shell halves together, the strip of foam 24 is compressed initially and then subsequently expands slightly to force the web head 14 towards the inner surface of the half shell. Accordingly the foam 24 functions as a spring.

One problem identified with the above solution in practice is that it can be difficult to ensure that the web panel 12 is inserted centrally into the slot 22 in the web head 14. Once the mould is closed, it is then not possible to inspect the position of the panel 12 inside the web head 14. If the web panel 12 is not inserted centrally in the slot 22, then it may wipe away adhesive from one side of the slot 22 during insertion. This can result in a sub-optimal bond forming between the web panel 12 and the web head 14 because the panel 12 may only then be bonded on one side of the slot 22.

The present invention aims to overcome this problem.

Summary of the invention

According to the present invention there is provided a shear web for a wind turbine blade, the shear web comprising: a longitudinally-extending web head comprising first and second longitudinally-extending sidewalls being mutually spaced apart to define a longitudinally-extending slot therebetween, the slot having a width defined by the distance between the first and second sidewalls; a longitudinally-extending panel having a longitudinal edge region defining a longitudinal edge of the panel, the longitudinal edge region being located within the slot, the longitudinal edge region having a thickness less than the width of the slot; and one or more spacing features protruding beyond first and second sides of the longitudinal edge region of the panel, the one or more spacing features being arranged to abut the first and second sidewalls of the slot such that the first and second sides of the longitudinal edge region of the panel are thereby respectively spaced apart from the first and second sidewalls of the slot.

The shear web of the present invention is preferably assembled by inserting the longitudinal edge region of the panel into the slot in the web head. Adhesive is preferably provided in the slot prior to insertion of the shear web, although the adhesive could be supplied to the slot after insertion of the shear web.

Upon insertion of the panel into the slot in the web head, the spacing features ensure that the panel is spaced apart from both of the respective sidewalls of the slot. This prevents adhesive from being scraped from one side of the slot. It also ensures that suitable spaces are formed on both sides of the panel between the panel and the respective sidewalls of the slot for adhesive to accumulate in. In the case that adhesive is already provided in the slot prior to insertion of the shear web, the adhesive redistributes to fill the spaces on both sides of the panel. The spacing features therefore ensure that the first and second sides of the longitudinal edge region of the panel are bonded respectively to the first and second sidewalls of the slot. A double lap joint is therefore formed between the panel and the web head.

In preferred embodiments the one or more spacing features protrude by substantially equal amounts beyond the first and second sides of the longitudinal edge region of the panel. This results in the panel being located substantially centrally within the slot. This is advantageous because it results in substantially equal quantities of adhesive accumulating on both sides of the panel within the slot, and thus results in similar bonds on both sides of the panel.

The one or more spacing features are preferably provided on the longitudinal edge of the panel. As the longitudinal edge of the panel is inserted first into the slot, this arrangement ensures that the edge region of the panel is centered, or at least suitably aligned in the slot immediately upon insertion of the panel into the slot. It therefore substantially avoids any significant scraping of adhesive during insertion of the panel in the slot. As will be appreciated from the detailed examples provided later, providing the spacing features on the longitudinal edge of the panel also allows for convenient attachment of the spacing features to the panel.

In other examples, the spacing features could be provided elsewhere on the longitudinal edge region of the panel. For example the spacing features may protrude from the first and second sides of the longitudinal edge region of the panel. The spacing features on one side of the panel may be aligned or staggered with respect to the spacing features on the other side of the panel, or there may be no correlation between the spacing features on one side of the panel and spacing features on the other side.

The one or more spacing features preferably comprise a plurality of discrete spacing features arranged at intervals along the length of the longitudinal edge of the panel. In a preferred embodiment the spacing features are arranged at one-metre intervals along the length of the panel, however any suitable intervals may be used. Providing discrete spacing features at intervals along the panel is advantageous because it results in regions between the spacing features where spacing features are absent. In these regions the panel is still centred or at least suitably aligned in the slot but the bonds between the panel and the slot are not affected by spacing features. The spacing features can therefore be arranged to occupy a relatively small area of the overall bond area between the panel and the web head and hence the spacing features have a minimal impact on integrity of the bond.

In a preferred embodiment, the one or more spacing features are substantially cylindrical. Preferably, the one or more spacing features are substantially circular in cross-section. The circular cross-section facilitates the travel of the spacing features in the slot since adhesive can flow easily around the spacing features and the circular cross-section minimises the contact area between the spacing features and sidewalls of the slots. The spacing features may of course have any other suitable cross-sectional shapes.

The one or more spacing features preferably each comprise a longitudinal slit in which the longitudinal edge of the panel is received. The one or more spacing features may conveniently form a ‘push fit’ with the longitudinal edge of the panel. This allows the spacing features to be connected to the panel simply by locating the edge of the panel in the slit and pushing the spacing feature onto the panel. This method of coupling the spacing features and the panel does not require adhesive or other retaining means and can be formed quickly and easily. Depending upon the relative dimensions of the slit and the longitudinal edge of the panel, the spacing features may form an interference fit, a close fit or a loose fit with the panel.

In the case that the spacing features have a circular cross-section, the slit may advantageously be radially arranged. This results in the spacing feature protruding to equal extents beyond the first and second sides of the panel and hence results in the panel being substantially centred in the slot.

The slot preferably tapers in width moving from a mouth of the slot towards a base of the slot. The tapered slot advantageously guides the spacing feature towards the base of the slot when the edge of the panel is inserted into the slot. The one or more spacing features may have a width corresponding substantially to the width of the slot near the base of the slot. The mouth of the slot may be wider than the spacing features to allow the spacing features to be inserted into the slot.

The web head preferably comprises a longitudinally-extending flange for bonding to an inner surface of the wind turbine blade. The sidewalls of the web head are preferably arranged transversely to the flange. In certain embodiments, the web heads may be integrated with the blade shells such that the sidewalls of the web head project from the inner surface of the shell.

The first and second sidewalls are preferably defined by first and second legs of the web head. Each leg extends from a proximal end to a distal end. The proximal ends of the legs are preferably located near the inner surface of the blade shell, and the distal ends are preferably spaced further from the inner surface of the blade shell. The mouth of the slot may be defined between the distal ends of the legs and the base of the slot may be defined between the proximal ends of the legs.

In embodiments in which the web head comprises a flange, the proximal ends of the legs may be located at the flange, whilst the distal ends may be spaced from the flange. The legs are preferably arranged transversely to the flange, and preferably splay outwards from the flange to define the tapered slot therebetween.

The shear web may include a spring located within the slot. The spring may be provided in the form of a strip of foam or other biasing means. The spring may be compressed when the panel is inserted into the slot. The compressed spring expands slightly during curing of the adhesive and exerts a force on the longitudinal edge of the panel. This causes a slight extension in the height of the shear web and ensures compression of adhesive between the flange of the web head and the blade shell in cases where the shear web is bonded between opposed inner surfaces of the blade shells.

The present invention also provides a wind turbine blade comprising a shear web as described above.

According to a second aspect of the present invention, there is provided a method of making at least part of a wind turbine blade, the method comprising the following steps in any suitable order: - providing a first half shell of the blade; - providing a shear web comprising: a longitudinally-extending web head having a flange and first and second sidewalls arranged transversely to the flange, the sidewalls being mutually spaced apart to define a longitudinally-extending slot therebetween, the slot having a width defined by the distance between the first and second sidewalls; and a longitudinally-extending panel having a longitudinal edge region defining a longitudinal edge of the panel, the longitudinal edge region having a thickness less than the width of the slot; - providing one or more spacing features on the longitudinal edge region of the panel, the spacing features protruding beyond first and second sides of the longitudinal edge region; - providing adhesive in the slot of the web head; - inserting the longitudinal edge region of the panel into the slot of the web head; - arranging the web head against an inner surface of the first half shell; - forcing the panel towards the web head such that the longitudinal edge region of the panel is inserted further into the slot, wherein the one or more spacing features abut the first and second sidewalls of the slot in the web head when the panel is inserted into the slot such that the first and second sides of the longitudinal edge region of the panel are spaced apart from the first and second sidewalls of the slot respectively to define spaces between the panel and the first and second sidewalls of the slot for the adhesive in the slot to accumulate.

The method preferably involves providing a second half shell on top of the first half shell. The second half shell exerts a force on the panel and forces the panel towards the web head such that the longitudinal edge region of the panel is inserted further into the slot.

Optional features described in relation to the invention when expressed in terms of an apparatus apply equally to the present invention when expressed in terms of a method.

Brief description of the drawings

Figure 1 has already been described above by way of background and shows a prior art shear web as described in in W02008/104174.

Embodiments of the present invention will now be described with reference to the remaining figures, in which:

Figure 2 is a plan view of a wind turbine blade according to the present invention;

Figure 3a is a cross-section through the wind turbine blade taken along the line 3-3 in Figure 2, and shows a pair of shear webs according to the present invention located inside the blade;

Figure 3b is an enlarged view of part of Figure 3a showing a spar cap embedded in the shell of the wind turbine blade;

Figure 4 is an exploded perspective view of a panel and a web head of one of the shear webs of Figure 3a, and shows a plurality of centring features for centring the web panel in the web head; and

Figures 5a-5c show a series of stages involved in bonding the web panel and the web head together.

Detailed Description

Figure 2 shows a wind turbine blade 30 according to the present invention. The wind turbine blade 30 extends in a longitudinal/spanwise direction L between a root end 32 and a tip end 34, and extends in a widthwise/chordwise direction W between a leading edge 36 and a trailing edge 38.

Referring now to Figure 3a, which is a transverse cross-section through the blade 30 taken along the line 3-3 in Figure 2, the wind turbine blade 30 comprises a windward half shell 40 and a leeward half shell 42, which are bonded together along the leading and trailing edges 36, 38 of the blade 30. As described by way of introduction, each half shell 40, 42 is formed in a respective mould half of a mould assembly prior to the half shells being bonded together to form the complete blade 30. The shells 40, 42 are formed primarily from GRP, but may include other structural materials in regions of the shells 40, 42, for example core materials such as foam panels.

Referring to the enlarged view of Figure 3b, spar caps 44 are integrated within the shells 40, 42. The spar caps 44 are formed from stacks of pultruded strips 45 of carbon-fibre reinforced plastic (CFRP). The spar caps 44 extend along the majority of the blade 30, from the root 32 to near the tip 34.

Referring again to Figure 3a, shear webs 46 are provided inside the blade 30, and are bonded by means of adhesive to inner surfaces 48 of the windward and leeward half shells 40, 42 between opposed spar caps 44. The shear webs 46 therefore bridge the opposed spar caps 44 of the windward and leeward shells 40, 42. In this example, the blade 30 includes first and second shear webs 46. The shear webs 46 extend longitudinally in the spanwise direction of the blade 30, and run along the majority of the length of the blade 30 from the root 32 of the blade 30 to near the tip 34 of the blade 30.

The shear webs 46 are substantially I-shaped in cross-section, and each shear web 46 comprises a longitudinally-extending web panel 50 and first and second longitudinally-extending web heads 52a, 52b. The first and second web heads 52a, 52b are bonded respectively to first and second longitudinal edges 54a, 54b of the web panel 50. In the orientation of the blade shown in Figure 3a, the shear webs 46 are substantially vertical and accordingly for ease of understanding the first and second longitudinal edges 54a, 54b are hereafter referred to as ‘upper’ and ‘lower’ longitudinal edges, and the first and second web heads 52a, 52b are hereafter referred to as ‘upper’ and ‘lower’ web heads.

The web panel 50 has a sandwich construction and comprises a foam core disposed between first and second GRP skins. To accommodate the curvature of the inner surfaces 48 of the blade 30, the web panel 50 in this example includes kinks 55.

The web-heads 52a, 52b are pultruded parts formed from GRP and are generally T-shaped in cross-section. As shown best in Figure 3b, each web head 52a, 52b comprises a flange 56 for bonding to the inner surface 48 of the blade shell 40, 42, and a pair of legs 58 that extend transversely from the flange 56. Each leg 58 extends from a proximal end 60 integrated with the flange to a distal end 62 spaced apart from the flange 56. The legs 58 splay outwards from the flange 56 to form a longitudinal slot 64 in between for receiving a longitudinal edge 54a, 54b of the web panel 50.

The slot 64 comprises first and second opposed sidewalls 65 defined respectively by the first and second legs 58. The slot 64 further comprises a mouth 68 defined between the respective distal ends 62 of the legs 58 and a base 70 defined between the respective proximal ends 60 of the legs 58. The distance between the legs 58 defines a width of the slot 64. Due to the splayed legs 58, the slot 64 tapers in width moving from the mouth 68 to the base 70. Expressed in other terms, the slot 64 becomes narrower with increasing depth.

As will be explained in further detail later with reference to Figures 5a-5c, the upper and lower longitudinal edges 54a, 54b of the web panel 50 are bonded inside the respective slots 64 of the upper and lower web heads 52a, 52b. It should be noted that the web panel 50 has been omitted from Figure 3b for ease of illustration.

Figure 4 shows a perspective view of a lower part of a web panel 50 and a lower web head 52b of one of the shear webs 46 of Figure 3a. Figure 4 only shows a relatively small longitudinal section of the shear web 46 (approximately 1 metre), whereas in practice the shear web 46 may have a length in excess of 80 metres when incorporated in the blades of current large utility-scale wind turbines.

Referring to Figure 4, the web panel 50 has first and second opposed major surfaces 72a, 72b defined by the first and second skins of the web panel 50. Only the first major surface 72a is visible in the perspective view of Figure 4. The distance between the first and second major surfaces 72a, 72b defines the thickness of the panel 50. It can be seen from Figure 4 that the thickness of the panel 50 decreases moving from the lower kink towards the lower longitudinal edge 54b of the panel 50. In other words, the panel 50 tapers in thickness towards the lower longitudinal edge 54b.

The panel 50 therefore has a tapered lower longitudinal edge region 74, which defines the lower longitudinal edge 54b of the panel. As will be described later with reference to Figures 5a-5c, the tapered lower longitudinal edge region 74 of the panel 50 is received within the slot 64 in the lower web head 52b. The thickness of the lower longitudinal edge region 74 of the panel is less than the width of the slot 64 in the web head 52b to allow space for adhesive between the sides 72a, 72b of the panel 50 and the legs 58 of the web head 52b. Whilst not shown in Figure 4, the panel 50 has a similarly tapered upper longitudinal edge region which is received within the slot 64 of the corresponding upper web head 52a.

Referring still to Figure 4, a plurality of spacing features 76 are provided on the lower longitudinal edge 54b of the web panel 50. The spacing features 76 are mutually-spaced at regular intervals along the length of the longitudinal edge 54b. In this example, the spacing features 76 are spaced at intervals of approximately one-metre. Whilst not shown in Figure 4, a plurality of spacing features are also provided on the upper longitudinal edge 54b of the web panel 50.

As will be discussed later with reference to Figures 5a-5c, the spacing features 76 are arranged to space the longitudinal edge region 74 of the web panel 50 apart from both the first and second sidewalls 55 of the slot 64 in the web head 52b when the edge region 74 of the panel 50 is inserted into the slot 64. In this embodiment, the spacing features 76 are arranged to centre the web panel 50 in the slot 64 with respect to the sidewalls 66, and hence the spacing features 76 will hereafter be referred to as ‘centring features’.

The centring features 76 are substantially cylindrical injection-moulded parts of circular cross-section. Each centring feature 76 has a length of approximately five centimetres (cm) in the longitudinal direction L, parallel to the longitudinal edges 54a, 54b of the web panel, and a width of approximately 1.5 cm perpendicular to its length. As the centring features 76 in this example are of circular cross-section, they have a cross-sectional diameter of approximately 2.5 cm.

Each centring feature 76 comprises a longitudinal slit 78 running parallel to the length of the centring feature 76. The slit 78 extends radially with respect to the circular cross-section of the centring feature 76. The slit 78 extends approximately half way through the depth of the centring feature 76 and accordingly the slit 78 has a depth of approximately 0.75 cm. The slit 78 accommodates the longitudinal edge 54b of the web panel 50. In this example the slit 78 is sized to allow the centring feature 76 to be conveniently pushed onto the longitudinal edge 54b of the panel 50, and retained on the longitudinal edge 54b without requiring adhesive or other retaining means. This is referred to herein as a ‘push fit’.

In order for the centring feature 76 to form a push fit with the longitudinal edge 54b of the panel 50, the slit 78 may have a width that is slightly less than the width of the panel 50, in which case the centring feature 76 forms an interference fit or friction fit with the panel. Alternatively, the slit 78 may have a width that is substantially the same as or slightly greater than the thickness of the longitudinal edge 54b of the panel. In such cases, the centring feature 76 forms a close fit or loose fit with the longitudinal edge 54b of the panel 50. Both cases are examples of ‘push fits’ within the present definition of this term.

The function of the centring features 76 will now be explained with reference to Figures 5a-5c, which show a series of steps involved in bonding the web panel 50 to a lower web head 52b.

Referring to Figure 5a, this shows a centring feature 76 fitted to the lower longitudinal edge 54b of the panel. As the slit 78 is arranged substantially radially with respect to the circular cross-section of the centring feature 76, the centring feature 76 protrudes beyond the first and second sides 72a, 72b of the panel 50 by substantially equal amounts.

A strip of foam 80 is optionally provided at the base 70 of the slot 64 in the web head 52b. The foam 80 extends substantially along the entire length of the slot 64. The foam strip 80 functions as a spring, as described by way of background with reference to Figure 1.

After insertion of the foam strip 80 in the slot, the slot is then partially filled with adhesive 82, such as an epoxy adhesive.

Referring to Figure 5b, the lower longitudinal edge 54b of the web panel 50, which includes the centring features 76, is inserted through the mouth 68 of the slot 64. The mouth 68 of the slot 64 in this example is slightly wider than the diameter of the centring feature 76 to accommodate the centring feature 76. In other embodiments the mouth 68 could be the same width or narrower than the centring feature 76 if the legs 58 are sufficiently flexible that they can be deflected by the centring feature 76.

Referring to Figure 5c, the web panel 50 is pushed downwards such that the lower longitudinal edge 54b of the panel 50 and the attached centring features 76 are forced deeper into the slot 64 in the web head 52b, towards the base 70 of the slot 64. As the slot 64 narrows with increasing depth, the centring feature 76 makes simultaneous contact with both of the opposed sidewalls 55 of the slot 64 as the web panel 50 is forced deeper into the slot 64. The tapering slot 64 advantageously guides the web panel 50 towards the base 70 of the slot 64 during insertion. The width of the slot 64 near the base 70 is comparable with the diameter of the centring feature 76 and thus the centring feature 76 is constrained by the slot 64 as the panel 50 is inserted into the slot 64.

It is clear from Figure 5c that the lower longitudinal edge region 74 of the panel 50, which is received in the slot 64, has a thickness significantly less than the width of the slot 64. The centring features 76 are wider than the longitudinal edge region 74 of the panel 50 and thus protrude beyond the first and second sides 72a, 72b of the panel 50. As the centring features 76 abut the first and second sidewalls 55 of the slot 64, the centring features 76 thereby ensure that the panel 50 is spaced apart from both the first and second sidewalls 55 of the slot 64. This ensures that gaps are defined between the panel 50 and both of the sidewalls 55 of the slot 64 for adhesive 82 to redistribute into when the panel 50 is inserted into the slot 64.

As the centring feature 76 protrudes by equal amounts beyond both sides 72a, 72b of the panel 50, the centring feature 76 ensures that the lower longitudinal edge region 74 of the panel 50 is disposed substantially centrally inside the slot 64. With the panel 50 central inside the slot 64, spaces of equal size are defined between the panel 50 and the respective sidewalls 55 of the slot 64 in the web head 52b. The adhesive 82 in the slots 64 redistributes to fill these spaces when the panel 50 is inserted into the slot 64. The centring features 76 therefore ensure that the adhesive 82 is distributed evenly on both sides of the panel 50 in the slot 64 and thus ensures that the panel 50 is bonded on both sides 72a, 72b to the respective sidewalls 55 of the slot 64 to form a double lap joint with the web head 52b.

For ease of illustration, Figures 5a-5c only show the lower part of the shear web 46. However, it will be appreciated that a corresponding web head 52a is also fitted at the upper longitudinal edge 54a of the panel 50 and the plurality of centring features 76 on the upper longitudinal edge 54a ensure that the panel 50 is centrally located inside the slot 64 of the upper web head 52a so that a double lap joint is formed with the upper web head 52a in the same way.

Also, for ease of illustration, the blade shells 40, 42 are not shown in Figures 5a-5c. However, it will be appreciated that the method of bonding the shear web 46 inside the blade shells 40, 42 corresponds generally with the method described by way of background. In particular, the flange 56 of the lower web head 52b is arranged on top of a strip of adhesive applied to an inner surface 48 of one of the blade shells 40, 42. The web panel 50 is then inserted partially into the slot 64 of the lower web head 52b as shown in Figure 5b. The upper web head 52a, including a foam strip 80 and adhesive 82 in its slot 64, is then fitted over the upper longitudinal edge 54a of the panel 50. Adhesive is then applied to the flange 56 of the upper web head 52a. The blade shells 40, 42 are then brought together, e.g. by closing the blade mould assembly as discussed by way of background. This causes compression of the adhesive in the bond lines between the web heads 52a, 52b and the respective blade shells 40, 42, and forces the web panel 50 deeper inside the slots 64 of the respective web heads 52a, 52b, as shown in Figure 5c. During this mould closing and bonding process, the centring features 76 on the web panels 50 ensure that the web panel 50 is central in the slots 64, as discussed above, and thus ensure that the panel 50 is bonded on both sides 72a, 72b to the web heads 52a, 52b.

Referring still to Figure 5c, insertion of the panel 50 inside the slot 64 of the web head 52b compresses the foam strip 80 in the base 70 of the slot 64. The foam strip 80 subsequently expands slightly during curing of the adhesive, which results in the shear web 46 extending slightly in the vertical direction and ensuring sufficient compression of adhesive between the web heads 52a, 52b and the blade shells 40, 42 during the curing process.

As discussed briefly below, many modifications may be made to the above examples without departing from the scope of the present invention as defined in the accompanying claims.

Whilst the spacing features 76 in the above embodiment are arranged to centre the web panel 50 in the slot 64 of the web head 52a, 52b, it should be appreciated that it is not essential for the panel 50 to be central in the slot 64. In other embodiments the spacing features may be arranged to space the panel 50 further from one sidewall 55 of the slot than from the other sidewall 55. In such cases, the spacing features may protrude by different amounts beyond the first and second sides 72a, 72b of the panel. This could be achieved, for example, by providing non-radial slits in the spacing features 76 described above. It is however preferable for the panel 50 to be disposed centrally inside the slot 64 as this ensures the adhesive 82 is distributed evenly on both sides of the panel 50.

Whilst the spacing/centring features 76 form a press fit in the above examples, in other embodiments the spacing features may be attached to the web panel 50 by other means. For example the spacing features may be bonded or attached by mechanical fasteners such as rivets. A press fit is however preferable as it reduces the number of steps involved in the process and is thus cheaper and most efficient.

The present invention is not limited to the particular sizes and shapes of the spacing/centring features described in relation to the above examples, and any suitable features that serve to space the web panel 50 from both sidewalls 55 of the slot 64 could be used within the scope of the present invention. For example, whilst the spacing features 76 in the above embodiments have a circular cross-section, in other embodiments the spacing features may have non-circular cross-sections.

Whilst the spacing/centring features 76 in the above embodiment are arranged at one-metre intervals along the longitudinal edges 54a, 54b of the web panel 50, other suitable spacings could be employed. For example, the centring features 76 could be arranged at larger intervals, which would advantageously reduce the number of centring features 76 required.

Whilst a plurality of discrete centring features 76 are described in the above examples, other embodiments are envisaged in which a single continuous centring feature is provided on the longitudinal edge 54b of the web panel 50. However, discrete centring features 76 spaced at intervals along the longitudinal edge 54b are preferred because this arrangement advantageously allows more space for adhesive 82 in the slot 64 between the centring features 76.

Whilst the spacing features 76 are provided on the longitudinal edge 54b of the panel 50 in the above embodiment, in other embodiments spacing features could be provided elsewhere on the portion of the edge region 74 of the panel 50 that is received in the slot 64 of the web head 52b. Accordingly, embodiments are also envisaged in which the spacing features each protrude from only one side of the panel 50. In such embodiments, the longitudinal edge region 74 of the panel 50 would include one or more spacing features protruding from the first side 72a of the panel 50 and one or more spacing features protruding from the second side 72b of the panel 50. The spacing features on one side of the panel 50 need not be aligned with the spacing features on the other side of the panel 50, and embodiments are envisaged in which the spacing features on one side of the panel 50 are staggered in relation to the spacing features on the other side of the panel 50.

Whilst the above examples employ a spring in the form of a strip of foam 80 inside the slot 64, the presence of foam or other biasing means inside the slot 64 is not essential to the present invention. The panel 50 and web head 52a, 52b arrangement is itself a useful arrangement for shear webs 46 with or without biasing means because it facilitates the manufacture of the shear web 46. Embodiments are envisaged in which no biasing means are provided in the slot. In such cases the spacing/centring features 76 still function to ensure that the web panel 50 is spaced apart from or centred between the respective sidewalls 55 of the slot 64 and thus ensure that the panel 50 is bonded on both sides to the web head 52b.

Whilst in the above embodiment the shear web 46 comprises web heads 52a, 52b on both the upper and lower longitudinal edges 54a, 54b of the web panel 50, in other embodiments the shear web 46 may only comprise a web head on one of the upper or lower longitudinal edges. The other edge may comprise an integral flange, similar to the shear web shown in Figure 1, for example.

Whilst the web heads 52a, 52b are bonded to the inner surfaces 48 of the respective windward and leeward half shells 40, 42 in the above embodiment, in other examples one or both web heads 52a, 52b may be integrated with the respective half shells 40, 42 during the manufacture of the half shell 40, 42. For example, the web head 52a, 52b may be laid up in the blade mould together with the other structural components of the blade shells 40, 42 and integrated with those other components by means of resin infusion or equivalent process.

Whilst the web heads 52a, 52b in the above example comprise a pair of legs 58 defining the sidewalls 55 of the slot 64, in other embodiments the web heads 52a, 52b may not include legs. For example, the slot 64 may be formed by a groove in an otherwise solid web head.

Whilst the blade 30 in the above examples includes two shear webs 46, in other examples the blade 30 may include any number of shear webs 46. For example, a third shear web may be included near the trailing edge 38 of the blade 30 in some cases.

Claims (15)

1. A shear web for a wind turbine blade, the shear web comprising: a longitudinally-extending web head comprising first and second longitudinally-extending sidewalls being mutually spaced apart to define a longitudinally-extending slot therebetween, the slot having a width defined by the distance between the first and second sidewalls; a longitudinally-extending panel having a longitudinal edge region defining a longitudinal edge of the panel, the longitudinal edge region being located within the slot, the longitudinal edge region having a thickness less than the width of the slot; and one or more spacing features protruding beyond first and second sides of the longitudinal edge region of the panel, the one or more spacing features being arranged to abut the first and second sidewalls of the slot such that the first and second sides of the longitudinal edge region of the panel are thereby respectively spaced apart from the first and second sidewalls of the slot.

2. The shear web of Claim 1, wherein the one or more spacing features protrude by substantially equal amounts beyond the first and second sides of the longitudinal edge region of the panel thereby locating the panel substantially centrally within the slot.

3. The shear web of Claim 1 or Claim 2, wherein the first and second sides of the longitudinal edge region of the panel are bonded respectively to the first and second sidewalls of the slot.

4. The shear web of any preceding claim, wherein the one or more spacing features are provided on the longitudinal edge of the panel.

5. The shear web of any preceding claim, wherein the one or more spacing features comprise a plurality of discrete spacing features arranged at intervals along the length of the longitudinal edge of the panel.

6. The shear web of any preceding claim, wherein the one or more spacing features are substantially cylindrical.

7. The shear web of any preceding claim, wherein the one or more spacing features are substantially circular in cross-section

8. The shear web of any preceding claim, wherein the one or more spacing features each comprise a longitudinal slit and the longitudinal edge of the panel is received in the slit.

9. The shear web of Claim 8 when dependent on Claim 7, wherein the slit is radially arranged with respect to the circular cross-section of the spacing feature.

10. The shear web of Claim 8 or Claim 9, wherein the one or more spacing features forms a push fit with the longitudinal edge of the panel.

11. The shear web of any preceding claim, wherein the slot comprises a mouth and a base and the slot tapers in width moving from the mouth towards the base.

12. The shear web of Claim 11, wherein the one or more spacing features have a width corresponding substantially to the width of the slot near the base of the slot.

13. The shear web of any preceding claim, wherein the shear web further comprises a spring located within the slot.

14. A wind turbine blade comprising a shear web as claimed in any preceding claim.

15. A method of making at least part of a wind turbine blade, the method comprising the following steps in any suitable order: - providing a first half shell of the blade; - providing a shear web comprising: a longitudinally-extending web head having a flange and first and second sidewalls arranged transversely to the flange, the sidewalls being mutually spaced apart to define a longitudinally-extending slot therebetween, the slot having a width defined by the distance between the first and second sidewalls; and a longitudinally-extending panel having a longitudinal edge region defining a longitudinal edge of the panel, the longitudinal edge region having a thickness less than the width of the slot; - providing one or more spacing features on the longitudinal edge region of the panel, the spacing features protruding beyond first and second sides of the longitudinal edge region; - providing adhesive in the slot of the web head; - inserting the longitudinal edge region of the panel into the slot of the web head; - arranging the web head against an inner surface of the first half shell; - forcing the panel towards the web head such that the longitudinal edge region of the panel is inserted further into the slot, wherein the one or more spacing features abut the first and second sidewalls of the slot in the web head when the panel is inserted into the slot such that the first and second sides of the longitudinal edge region of the panel are spaced apart from the first and second sidewalls of the slot respectively to define spaces between the panel and the first and second sidewalls of the slot for the adhesive in the slot to accumulate.