GB2535697A

GB2535697A - Improvements relating to wind turbine blade manufacture

Info

Publication number: GB2535697A
Application number: GB1502598.4A
Authority: GB
Inventors: Smith Jonathan
Original assignee: Vestas Wind Systems AS
Current assignee: Vestas Wind Systems AS
Priority date: 2015-02-17
Filing date: 2015-02-17
Publication date: 2016-08-31
Also published as: GB201502598D0

Abstract

A method of making a wind turbine blade 10 using a two-stage join up process is described. The blade includes a longitudinal reinforcing structure 34, such as a spar structure or shear web, connected between first and second blade shells 22, 24. During the first stage of the join-up, the reinforcing structure is bonded to an inner surface of the first shell by means of adhesive 60 provided between the reinforcing structure and the first shell. The second shell is positioned on top of the first shell during the first stage in order to exert a compressive load on the reinforcing structure and squeeze the adhesive between the reinforcing structure and the first shell. According to the invention, a shim 70 made from compressible material is positioned between the reinforcing structure and the second shell during the first stage of the join-up. The shim compresses together with the adhesive. Subsequent gradual expansion of the shim results in a gradual further compression of the adhesive between the reinforcing structure and the first shell. Preferably, the shim has a compressive modulus substantially matched to that of the uncured adhesive; the shim may be made from foam, particularly neoprene, or rubber material. During the second stage of the join-up; preferably, the shim is removed and the reinforcing structure is bonded to an inner surface of the second shell and the first and second shells are joined together.

Description

IMPROVEMENTS RELATING TO WIND TURBINE BLADE MANUFACTURE

Technical Field

The present invention relates generally to the manufacture of wind turbine blades, and more specifically to an improved method of bonding a reinforcing structure between first and second blade shells.

Background

Figure 1 shows a typical wind turbine blade 10 for a utility-scale wind turbine. The blade 10 extends longitudinally from a root end 12 to a tip end 14 in a so-called Espanwise' direction S, and transversely between a leading edge 16 and a trailing edge 18 in a so-called 'widthwise' or ichordwise' direction C. Referring to Figure 2, this shows a cross-sectional view of the wind turbine blade 10. The blade 10 comprises an outer shell 20, which is made up of two half shells: a windward shell 22 and a leeward shell 24, which are bonded together along a leading edge 26 and a trailing edge 28 of the respective shells 22, 24. Each half shell 22, 24 is made up of a plurality of glass-fibre fabric layers and other structural components such as foam core material 30 and carbon fibre reinforcements 32, which are bonded together by cured resin.

A pair of shear webs 34 are bonded between the respective shells 22, 24. The shear webs 34 are longitudinally-extending structures that bridge the half shells 22, 24 of the blade 10 and serve to transfer shear loads from the blade 10 to a wind turbine hub in use. The shear webs 34 are I-beams, i.e. each shear web 34 is substantially I-shaped in cross section, and comprises a generally vertical web 36 disposed between leeward and windward mounting flanges 38, 40. The leeward and windward mounting flanges 38, 40 are arranged transversely to the web 36 and define substantially flat surfaces 38a, 40a for mounting the shear webs 34 to the leeward and windward blade shells 24, 22 respectively.

More specifically, the windward mounting flange 40 of each shear web 34 is bonded to a respective windward web mounting region 42 defined on an inner surface 44 of the windward shell 22, whilst the leeward mounting flange 38 of each shear web 34 is bonded to a respective leeward web mounting region 46 defined on an inner surface 48 of the leeward shell 24. The flanges 38, 40 of the shear web 34 are bonded to the respective shells 24, 22 using a polymeric adhesive, typically epoxy.

The polymeric adhesives used to join the shear web 34 to the blade shells 22, 24 are so-called 'non-Newtonian' fluids, which have a viscosity that is dependent upon the shear rate of the adhesive. As the polymeric adhesive is compressed in a vertical direction it squeezes outwards in a horizontal direction leading to shear stress in the adhesive. In this case, the viscosity of the adhesive tends to increase under compression and hence the adhesive has a tendency to resist compression to an extent during the bonding process. This can lead to inadequate compression of the adhesive and result in suboptimal bond lines between the shear web 34 and the blade shells 22, 24.

It is an object of the present invention to provide a method of making a wind turbine that overcomes the problem of inadequate compression of adhesive and results in improved bond lines between the shear webs and blade shells.

Summary of the Invention

The present invention provides a method of making a wind turbine blade having first and second blade shells and at least one longitudinally-extending reinforcing structure located inside the blade and bonded between the first and second blade shells, the method comprising the following steps in any suitable order: providing first and second blade shells to be joined together, each shell extending longitudinally and having an inner surface that defines an interior surface of the blade when the shells are joined together; providing a longitudinally-extending reinforcing structure having a first surface for attaching to the inner surface of the first shell and a second surface for attaching to the inner surface of the second shell; applying adhesive to a longitudinally-extending first mounting region defined on the inner surface of the first shell and/or to the first surface of the reinforcing structure; positioning the reinforcing structure relative to the first shell such that the first surface of the reinforcing structure is in opposed relation with the first mounting region and the adhesive is located between said first surface and said first mounting region; arranging the first and second blade shells so that the second surface of the reinforcing structure is in opposed relation with a longitudinally-extending second mounting region defined on the inner surface of the second shell; positioning a shim comprising compressible material between the second surface of the reinforcing structure and the second mounting region; moving the first and second blade shells together such that the shim is compressed between the second surface of the reinforcing structure and the second mounting region and a compressive load is transmitted via the reinforcing structure to the adhesive causing the adhesive to compress between the first surface of the reinforcing structure and the first mounting region; and curing the adhesive.

As discussed in more detail below, the method according to the present invention results in more consistent squeezing of adhesive and hence improved bonding between the reinforcing structure and the blade shells.

The reinforcing structure is preferably a spar structure for example a beam, a box spar, a shear web or other similar structure to be connected between the blade shells. In preferred embodiments the reinforcing structure is a shear web and the first and second surfaces are defined by respective first and second mounting flanges of the shear web.

The compressible shims advantageously absorb some compressive load during mould closure. This advantageously reduces the risk of damage to the reinforcing structure, e.g. the shear webs upon mould closure because the shim is able to absorb some of the compressive load that may be resisted by the non-Newtonian nature of the adhesive, which resists compression as described by way of background. As a consequence, flexing of the reinforcing structure during the blade join-up process is prevented and the associated risk of damage is avoided.

Preferably the shim is resiliently deformable. For example, the shim may be configured to expand following compression such that expansion of the shim exerts a compressive load on the adhesive via the reinforcing structure. This is particularly advantageous because the subsequent expansion of the shim when the blade shells are together forces the reinforcing structure gradually further towards the first shell. A gradual compressive force is therefore exerted on the adhesive which the adhesive resists less than a more rapid compressive force. Consequently, the adhesive is able to be compressed further resulting in improved squeezing of adhesive along the bond line, and hence an improved bond.

In a particularly advantageous embodiment, the shim has a compressive modulus that is substantially matched to the compressive modulus of the uncured adhesive. The compressive modulus of a material is the ratio of the compressive stress applied to the material compared to the resulting compression; essentially it is a measure of how easy it is to compress the material. Matching the compressive moduli of the shim and adhesive ensures that both the shim and the adhesive are compressed to similar extents when the blade shells are brought together. If the compressive modulus of the shim is significantly greater than that of the adhesive, then the shim may not compress appreciably, whilst if the compressive module of the shim is significantly lower than that of the adhesive then the shim may compress in preference to the adhesive. It is therefore advantageous to select the materials for the adhesive and the shim such that similar levels of compression occur in each when the blade shells are brought together, and references herein to matching the modulus of the shim and adhesive should be interpreted accordingly.

The shim may comprise any suitable material or have any suitable structure. For example the shim may be formed of rubber or foam or may comprise bias means such as springs. In preferred examples the shim is made from foam, and preferably neoprene foam. Neoprene foam is particularly suitable when the adhesive is epoxy as neoprene foam has a compressive modulus similar to uncured epoxy.

The shim preferably extends longitudinally along substantially the entire length of the reinforcing structure or at least along a majority of the length of the reinforcing structure. This ensures that the load is transferred uniformly and consistently to the adhesive along the length of the reinforcing structure. The shim may comprise a plurality of sections or it may be a continuous length of material. If the shim comprises a plurality of sections then these may abut one another or spaces may be provided between adjacent sections. The sections may be the same size or different sizes.

The shim is preferably attached to the second surface of the reinforcing structure. Alternatively or additionally the shim could be attached to the inner surface of the second shell. The shim is preferably releasably attached to the second surface of the reinforcing structure, for example using a suitable adhesive such as double-sided tape. Alternative means of attachment could be used, for example clamps or other mechanical fastening means.

The shim is preferably sized to set a bond gap size between the second surface of the reinforcing structure and the inner surface of the second shell following removal of the shim. In preferred embodiments the shim is sized to set a bond gap size that is substantially uniform along substantially the entire length of the reinforcing structure or at least along a majority of the length of the reinforcing structure. To this end the height of the shim may vary along the length of the shim. The local height of the shim is preferably selected in accordance with a gap size between the second surface of the shim and the inner surface of the second shell. As discussed by way of background, the size of the gap may vary along the length of the shear web depending upon the local topography of the inner surfaces of the respective blade shells. The gap size is preferably measured during a dry fit, in which the reinforcing structure is positioned between the first and second blade shells prior to the application of adhesive.

The adhesive is preferably applied to the first mounting region of the first shell.

Alternatively or additionally, the adhesive may be applied to the first surface of the reinforcing structure.

The process described above relates to the first stage of a two-stage join-up. The method preferably also comprises the second stage of the join-up, which may involve the following further steps: moving the first and second shells apart; removing the shim; applying further adhesive to the second surface of the reinforcing structure and/or to the second mounting region; and moving the first and second blade shells back together such that the further adhesive is compressed between the second surface of the reinforcing structure and the second mounting region.

In the above method, the step of moving the first and second blade shells together preferably comprises placing the second shell on top of the first shell. The first and second shells are preferably supported in respective first and second moulds. The first and second moulds may be arranged side by side and the step of moving the first and second blade shells together may comprise arranging the second mould on top of the first mould.

Brief Description of the Drawings

In order that the present invention may be more readily understood, embodiments of the invention will now be described, by way of non-limiting example only, with reference to the accompanying drawings, in which: Figure 1 is a plan view of a wind turbine blade; Figure 2 is a schematic cross-sectional view of the wind turbine blade of Figure 1; Figures 3a-3g show various steps in a two-stage join-up process for making a wind turbine blade; Figure 4 is an exploded perspective view of a root end of a wind turbine blade during a first stage of a two-stage join up according to the present invention, in which the wind turbine blade comprises shear webs provided with compressible shims; Figures 5a-5c are side views of a shear web provided with a compressible shim in varying configurations; and Figures 6a-6e are schematic cross-sectional views illustrating various steps in a two-stage join-up process according to the present invention.

Detailed Description

A method of making the wind turbine blade 10 of Figures 1 and 2 using a two-stage join up procedure will now be described briefly with reference to Figures 3a-3g. The method involves the use of rigid plastic shims between the shear webs and blade shells, and is described to illustrate particular problems that are overcome by the use of compressible shims in accordance with the present invention.

The first stage of the join up involves bonding the shear webs 34 to the windward shell 22 (as shown in Figures 3a-3d), whilst the second stage involves bonding the shear webs 34 to the leeward shell 24 and simultaneously bonding the windward and leeward shells 22, 24 together (as shown in Figures 3e-3g).

Referring initially to Figure 3a, this shows a mould 50 for the wind turbine blade 10 divided into two female half moulds: a windward mould 52 and a leeward mould 54, which are arranged side by side in an open configuration of the mould 50. The windward shell 22 and the leeward shell 24 are moulded separately in their respective mould halves 52, 54. As shown in Figure 3a, the windward shell 22 is supported on a mould surface 56 of the windward mould 52 and the leeward shell 24 is supported on a mould surface 58 of the leeward mould 54.

Referring to Figure 3b, after forming the blade shells 22, 24 in the respective mould halves 52, 54, adhesive 60 is applied along the windward web mounting regions 42 defined on the inner surface 44 of the windward shell 22.

Referring to Figure 3c, the shear webs 34 are then lifted into the windward half mould 52 and the windward mounting flanges 40 of the shear webs 34 are positioned on top of the adhesive 60 in the windward web mounting regions 42. It can be seen in Figure 3c that shims 62 are positioned on top of the leeward mounting flanges 38 of the shear webs 34.

The shims 62 are formed from rigid plastic and are positioned at regular intervals of approximately 500 mm along the length of the shear webs 34. The shims 62 vary in height along the lengths of the shear webs 34, and as will be discussed in further detail below, the shims 62 serve to set a substantially uniform bond gap between the leeward mounting flanges 38 of the shear webs 34 and the inner surface 48 of the leeward shell 24 during the second stage of the join up.

Referring to Figure 3d, the mould 50 is then closed by lifting and turning the leeward mould half 54 and positioning it on top of the windward mould half 52. In this position, the weight of the leeward mould half 54 and the leeward shell 24 bear down on the shear webs 34 (via the shims 62), which causes the adhesive 60 between the shear webs 34 and the windward shell 22 to compress and squeeze out slightly between the windward web mounting flanges 40 and the inner surface 44 of the windward shell 22. The adhesive 60 is then left to cure, i.e. harden so that a strong bond is formed between the shear webs 34 and the windward shell 22.

Referring to Figure 3e, once the shear webs 34 have been bonded to the windward shell 22, the mould 50 is opened again and the shims 62 (see Figure 3d) are removed from the leeward mounting flanges 38 of the shear webs 34. A bead of adhesive 64 is then applied along the leeward mounting flanges 38 and further adhesive 66 is applied along the leading and trailing edges 26, 28 of the windward shell 22.

Referring to Figure 3f, the mould 50 is then closed again and the adhesive 64 applied to the leeward mounting flanges 38 and the adhesive 66 applied to the leading and trailing edges 26, 28 of the windward shell 22 is squeezed under the weight of the leeward mould 54 and the leeward shell 24. This adhesive 64, 66 is then allowed to cure with the mould 50 remaining closed.

Referring to Figure 3g, once the adhesive 64, 66 has cured, the leeward shell 24 is released from the leeward mould 54 and the mould 50 is then re-opened. The completed blade 10 may now be lifted from the windward mould 52 and subjected to finishing processes, such as sanding and painting.

In the blade manufacturing process described above it is important to ensure that the shear webs 34 are firmly and uniformly bonded to the windward and leeward shells 22, 24 along the entire lengths of the shear webs 34. To achieve this, it is important that the compressive load transferred via the shear webs 34 to the adhesive 60 (during mould closure in the first stage of the join up process (see Figure 3d)) is distributed substantially uniformly along the lengths of the shear webs 34. If the load is not transmitted uniformly, then the adhesive 60 in some regions will be squeezed too much, whilst the adhesive 60 in other regions will not be squeezed enough. Either way, a sub-optimal bond may result.

As described by way of introduction, the polymeric adhesives 60, 64, 66 used in the join-up process (typically epoxy) are so-called 'non-Newtonian' fluids, which have a viscosity that is dependent upon shear rate of the adhesive 60, 64, 66. As the polymeric adhesive is compressed in a vertical direction it squeezes outwards in a horizontal direction leading to shear stress in the adhesive. In this case, the viscosity of the adhesive 60, 64, 66 tends to increase under compression and hence the adhesive 60, 64, 66 has a tendency to resist compression to an extent when the mould 50 is closed. This can lead to inadequate compression of the adhesive 60, 64, 66 and result in sub-optimal bond lines.

It is also important to ensure that a uniform bond gap is created along the lengths of the shear webs 34 between the leeward mounting flanges 38 of the shear webs 34 and the inner surface 48 of the leeward shell 24 once the adhesive 60 used in the first stage of the join up has cured. This is so that the adhesive 64 (Figure 3e) applied to the leeward mounting flanges 38 is compressed evenly along the lengths of the shear webs 34 during the second stage of the join up.

Ensuring uniform compression of adhesive and a uniform bond gap is challenging because whilst the mounting flanges 38, 40 of the shear webs 34 are generally flat and well defined, it will be appreciated that the inner surfaces 44, 48 of the blade shells 22, 24 are not precisely defined. The blade shells 22, 24 are typically made using hand layup processes, and the inner surfaces 44, 48 will inevitably have some undulations, bumps and ridges which will vary in size, shape and position from one shell to the next. The varying geometry of the inner surfaces 44, 48 of the shells 22, 24 can result in uneven contact being made with the shear webs 34 when the mould 50 is closed. This in turn can result in the compressive load exerted on the shear webs 34 being distributed unevenly along the lengths of the shear webs 34 and hence resulting in uneven compression of the adhesive 60.

As mentioned above in relation to Figure 3c, rigid plastic shims 62 may be positioned on top of the leeward mounting flanges 38 at spaced apart intervals. The shims 62 are of varying sizes and each shim 62 is sized according to the local geometry of the blade shells 22, 24 where the shim 62 is positioned. In order to determine the appropriate sizes of the shims 62, a so-called 'dry fit' is performed prior to the first stage of the join up. This involves closing the mould 50 with the shear webs 34 in position prior to the application of any adhesive. The gap between the shear webs 34 and the inner surface 48 of the leeward shell 24 is then measured at regular intervals (e.g. every 500 mm) along the length of the shear webs 34 and the shims 62 are sized accordingly to set the required bond gap, with relatively small shims 62 being employed where the gap is small and relatively large shims 62 being used where the bond gap is large.

With the shims 62 in position, when the mould 50 is closed the leeward shell 24 will make contact with each shim 62 substantially simultaneously resulting in a more even transfer of load to the adhesive 60 between the shear webs 34 and the windward shell 22. The custom-sized shims 62 also ensure that the bond gap between the shear webs 34 and the leeward shell 24 is substantially uniform along the lengths of the shear webs 34.

A problem identified with the above method is that the shear webs may bend or flex somewhat when the mould is closed. This is caused by the non-Newtonian nature of the adhesive 60, which tends to resist compression when load is applied rapidly, which results in the shear webs 34 having to absorb some of the compressive force during mould closure. The use of rigid local shims 62 means that the compressive load is concentrated in the regions of the shear webs 34 where the shims 62 are positioned, and this causes localised flexing of the shear webs 34, which carries a risk of damaging the shear webs 34 and/or the blade shells 22, 24.

The use of compressible shims to overcome the aforesaid problems, in accordance with the present invention, will now be described with reference to the remaining figures.

Referring to Figure 4, this is an exploded perspective view of a root end 12 of a wind turbine blade 10 being manufactured according to the method of the present invention. The wind turbine blade 10 is similar to the blade described above with reference to Figures 1-3, and the same reference numerals are therefore used in the following

description to denote equivalent features.

The wind turbine blade 10 comprises a windward shell 22 and a leeward shell 24. A pair of shear webs 34 are positioned inside the blade 10. The shear webs 34 extend longitudinally, in a spanwise direction S of the blade 10, from the root end 12 of the blade 10 towards a tip end (not shown) of the blade 10. Each shear web 34 has a web portion 36 disposed between windward and leeward mounting flanges 40, 38. The web portions 36 are substantially vertical in the orientation of the shear webs 34 shown in Figure 4. As discussed in further detail below, a longitudinally extending shim 70 made from neoprene foam is provided on top of each of the leeward mounting flanges 38 of the shear webs 34.

In common with the manufacturing process described above with reference to Figures 3a-3g, the blade 10 is made using a two-stage join-up. Figure 4 shows the first stage of the join-up (equivalent to Figures 3b-3d), whereby adhesive 60 is applied along shear web mounting regions 42 defined on an inner surface 44 of the windward shell 22 and the shear webs 34 are positioned on top of this adhesive 60. The leeward shell 24 is then lifted and positioned above the windward shell 22, before being lowered on top of the windward shell 22, as represented by the arrows 72 in Figure 4.

When the leeward shell 24 is lowered on to the windward shell 22, the weight of the leeward shell 24 bears down on the shear webs 34 causing the adhesive 60 to squeeze between the windward mounting flanges 40 of the shear webs 34 and the windward shell 22 to create windward web bond lines between the shear webs 34 and the windward shell 22. The shims 70 applied to the leeward mounting flanges 38 of the shear webs 34 are also compressed under the weight of the leeward shell 24, as will be described in further detail later with reference to Figure 6.

Aside from the use of compressible shims 70, the blade manufacturing method is broadly equivalent to the manufacturing method described above with reference to Figures 3a-3g. In order to avoid repetition, reference is made to the preceding description relating to Figures 3a-3g for further details of the blade manufacturing method such as the second stage of the join up.

Referring now to Figure 5a, this is a schematic side view (not to scale) of one of the shear webs 34 shown in Figure 4. The shear web 34 tapers in height along its length in accordance with the tapering thickness of the wind turbine blade 10 moving from root to tip. The compressible shim 70 described above in relation to Figure 4 can be seen located on top of the leeward mounting flange 38 of the shear web 34. In Figure 4a, the shim 70 is a continuous length of neoprene foam, which extends along the entire length of the shear web 34 and substantially covers the leeward mounting flange 38.

Referring to Figure 5b, this shows an alternative example of the shim 70. In this case, the shim 70 is formed from a plurality of longitudinally-extending sections 74 of neoprene foam. The sections 74 are provided end-to-end along the leeward mounting flange 38 of the shear web 34, such that they substantially cover the leeward mounting flange 38.

Each section 74 of the shim 70 abuts a neighbouring section 74 in this example. In alterative configurations, spaces may be provided between adjacent sections 74. In this example, the sections 74 are of different lengths, but in other examples the sections 74 may be the same length. Using multiple sections 74 of material to form the shim 70 facilitates handling and reduces cost in comparison with a continuous length.

Referring to Figure 5c, this shows a further example in which the sections 74 of neoprene foam are of different heights. The heights of the various sections 74 are selected according to a local gap height between the shear web 34 and the leeward shell 24, which may be measured during a dry fit as described by way of background.

Alternatively, the shim 70 may comprise a continuous section of material that varies in height along its length.

The various examples of shim configurations shown in Figures 5a-5c are not exhaustive, and other configurations of the shim 70 within the scope of the invention will be readily apparent to the skilled person. In each case, the shim 70 is temporality attached to the leeward mounting flange 38 of the shear web 34 using double-sided adhesive tape.

The function of the compressible shims 70 during the first stage of the join up will now be described in more detail with reference to Figures 6a-6e, which show a series of schematic cross-sectional views of the shear web 34 and leeward and windward blade shells 24, 22 during the first stage of the join-up.

Referring initially to Figure 6a, this shows a shear web 34 located between the windward shell 22 and the leeward shell 24 of the blade. The shear web 34 is provided with a compressible shim 70 on its leeward mounting flange 38. A bead of adhesive 60 is applied along the shear web mounting region 42 defined on the inner surface 44 of the windward shell 22. The shear web 34 is firstly lowered on to the bead of adhesive 60 in the direction of the arrow 74, and then the leeward shell 24 is lowered towards the windward shell in the direction of arrow 76.

Referring to Figure 6b, as the leeward shell 24 is lowered towards the windward shell 22, the inner surface 48 of the leeward shell 24 makes contact with the shim 70. The leeward shell 24 is then lowered further towards the windward shell 22 until the leading and trailing edges (not shown) of the respective shells 22, 24 are in contact. As the leeward shell 24 is moved towards the windward shell 22, it exerts a downward force on the shear web 34. This results in the adhesive 60 being compressed between the windward mounting flange 40 of the shear web 34 and the windward shell 22, and the shim 70 being compressed between the leeward mounting flange 38 of the shear web 34 and the leeward shell 24.

In this example, the adhesive 60 is epoxy and the shim 70 is made from neoprene foam, which has a compressive modulus that is substantially matched with the compressive modulus of the uncured adhesive 60. Accordingly, both the adhesive 60 and the shim 70 compress at similar rates when the leeward shell 24 is lowered onto the windward shell 22. As discussed by way of background, the epoxy adhesive 60 is a non-Newtonian fluid that has a viscosity that increases according to the rate at which the compressive load is applied. Accordingly, the epoxy 60 tends to resist compression when load is applied relatively rapidly, which is the case when the leeward shell 24 is lowered onto the windward shell 22.

Referring now to Figure 6c, the compressible shim 70 has elastic properties and is resiliently deformable. Accordingly, following compression it tends to expand back to its original shape. Therefore, after the leeward and windward shells 24, 22 have been brought together, the foam shim 70 gradually expands back towards its original shape.

The gradual expansion of the shim 70 over time forces the shear web 34 downwards further towards the windward shell 22 resulting in a compressive load being exerted gradually on the adhesive 60. Due to the non-Newtonian properties of the adhesive 60, this gradual exertion of compressive force caused by the relatively slow expansion of the shim 70 means that the shear rate of the adhesive 60 and hence the viscosity of the adhesive 60 is kept relatively low and this allows the adhesive 60 to compress further resulting in very effective squeezing of adhesive 60 along the bond line. With the leeward shell 24 in place, the adhesive 60 is allowed to cure, i.e. harden, to form a strong and uniform bond between the shear web 34 and the windward shell 22 along the entire length of the shear web 34.

Referring now to Figure 6d, once the adhesive 60 has cured, the leeward shell 24 is lifted off the windward shell 22 and the shim 70 (see Figure 6c) is removed from the leeward mounting flange 38 of the shear web 34. A bead of adhesive 64 is then applied along the leeward mounting flange 38. Further adhesive (not shown) is also applied along the leading and trailing edges of the shells 22, 24 as discussed previously with reference to Figure 3e. The leeward shell 24 is then lowered again in the direction of the arrow 78 onto the windward shell 22 for the second stage of the join-up.

Referring to Figure 6e, with the leeward shell 24 lowered onto the windward shell 22, the adhesive 64 applied to the leeward mounting flange 38 of the shear web 34 is squeezed between the inner surface 48 of the leeward shell 24 and the leeward mounting flange 38. The adhesive 64 is then allowed to cure, and the blade is subject to finishing processes such as sanding and painting.

The use of a compressible shim 70, in contrast to the rigid local shims 62 (see Figure 3c) described by way of background, reduces the risk of damage to the shear webs 34 upon mould closure because the shim 70 is able to absorb some of the compressive load that may be resisted by the non-Newtonian adhesive 60. As a consequence, flexing of the shear web 34 during the first stage of the join-up is prevented and the associated risk of damage is avoided.

Providing the shim 70 over substantially the entire length of the shear web 34 is advantageous because it ensures that the load is transferred uniformly and consistently to the adhesive 60.

In the above process, the height of the shim 70 preferably varies along the length of the shim 70 (for example as shown in Figure 5c) in accordance with the local geometry of the inner surfaces 44, 48 of the respective blade shells 22, 24. The local height of the shim 70 is suitably selected to set a uniform gap height between the leeward mounting flange 38 and the inner surface 48 of the leeward shell 24 during the second stage of the join-up.

Whilst moulds are not shown in Figures 4-6, it will be appreciated that the windward and leeward shells 22, 24 may be retained in their respective moulds during the join-up in the same way as described by way of background with reference to Figure 3, and in which case the weight of the leeward mould may also act on the shear webs 34 to compress the adhesive 60.

Many modifications may be made to the examples above without departing from the scope of the present invention as defined in the following claims.

Claims

Claims 1. A method of making a wind turbine blade having first and second blade shells and at least one longitudinally-extending reinforcing structure located inside the blade and bonded between the first and second blade shells, the method comprising the following steps in any suitable order: providing first and second blade shells to be joined together, each shell extending longitudinally and having an inner surface that defines an interior surface of the blade when the shells are joined together; providing a longitudinally-extending reinforcing structure having a first surface for attaching to the inner surface of the first shell and a second surface for attaching to the inner surface of the second shell; applying adhesive to a longitudinally-extending first mounting region defined on the inner surface of the first shell and/or to the first surface of the reinforcing structure; positioning the reinforcing structure relative to the first shell such that the first surface of the reinforcing structure is in opposed relation with the first mounting region and the adhesive is located between said first surface and said first mounting region; arranging the first and second blade shells so that the second surface of the reinforcing structure is in opposed relation with a longitudinally-extending second mounting region defined on the inner surface of the second shell; positioning a shim comprising compressible material between the second surface of the reinforcing structure and the second mounting region; moving the first and second blade shells together such that the shim is compressed between the second surface of the reinforcing structure and the second mounting region and a compressive load is transmitted via the reinforcing structure to the adhesive causing the adhesive to compress between the first surface of the reinforcing structure and the first mounting region; and curing the adhesive.
2. The method of Claim 1, wherein the shim is resiliently deformable.
3. The method of Claim 1 or Claim 2, wherein the shim is configured to expand following compression such that expansion of the shim exerts a compressive load on the adhesive via the reinforcing structure.
4. The method of any preceding claim, wherein the shim has a compressive modulus that is substantially matched to the compressive modulus of the uncured adhesive.
5. The method of any preceding claim, wherein the shim is made from foam and/or rubber material.
6. The method of any preceding claim, wherein the shim is formed primarily from neoprene foam.
7. The method of any preceding claim, wherein the adhesive comprises epoxy.
8. The method of any preceding claim, wherein the shim extends longitudinally along substantially the entire length of the reinforcing structure or along a majority of the length of the reinforcing structure.
9. The method of any preceding claim, wherein the shim comprises a plurality of sections or is a single piece.
10. The method of any preceding claim, wherein the shim is attached to the second surface of the reinforcing structure.
11. The method of any preceding claim, wherein the shim is releasably attached to the second surface of the reinforcing structure.
12. The method of any preceding claim, wherein the shim is sized to set a bond gap size between the second surface of the reinforcing structure and the inner surface of the second shell.
13. The method of Claim 12, wherein the shim is sized to set a bond gap size that is substantially uniform along substantially the entire length of the reinforcing structure or at least along a majority of the length of the reinforcing structure.
14. The method of any preceding claim, wherein the shim extends longitudinally and the height of the shim varies along its length.
15. The method of any preceding claim, wherein the method further comprises selecting a local height of the shim in accordance with a gap size between the second surface of the shim and the inner surface of the second shell.
16. The method of any preceding claim, wherein the adhesive is applied to the first mounting region of the first shell.
17. The method of any preceding claim, wherein the method further comprises: moving the first and second shells apart; removing the shim; applying further adhesive to the second surface of the reinforcing structure and/or to the second mounting region; and moving the first and second blade shells back together such that the further adhesive is compressed between the second surface of the reinforcing structure and the second mounting region.
18. The method of any preceding claim, wherein the reinforcing structure is a spar structure or part of a spar structure.
19. The method of any preceding claim, wherein the reinforcing structure is a shear web.
20. The method of Claim 19, wherein the first and second surfaces are defined by respective first and second mounting flanges of the shear web.
21. The method of any preceding claim, wherein the step of moving the first and second blade shells together comprises placing the second shell on top of the first shell.
22. The method of any preceding claim, wherein the first and second shells are supported in respective first and second moulds.
23. The method of Claim 22, wherein the first and second moulds are arranged side by side and the step of moving the first and second blade shells together comprises arranging the second mould on top of the first mould.