Wind turbine blades

Abstract

A pultrusion process for making a strip for an elongate reinforcing structure of a wind turbine blade, the process comprising drawing fibres (42) and resin through a pultrusion die (40) in a process direction to form a strip (102); and applying an infusion-promoting layer (110) to a surface of the strip down-stream from the die in the process direction. A pultrusion apparatus is also disclosed.

Claims

1. A method of making a wind turbine blade, the method comprising: providing a plurality of strips, each strip made by a pultrusion process comprising: drawing fibres and resin through a pultrusion die in a process direction to form a pultruded strip; and applying a resin-free, infusion-promoting layer to a surface of the pultruded strip down-stream from the die in the process direction, placing the plurality of strips in a wind turbine blade mould tool to form a stack having at least one infusion-promoting layer between two pultruded strips, wherein each infusion-promoting layer remains substantially resin-free when the plurality of strips is placed in the wind turbine blade mould tool; infusing resin into the wind turbine blade mould tool such that the resin infiltrates around the stack and between the pultruded strips via each infusion-promoting layer; and curing the resin to form the wind turbine blade.

2. The method of claim 1, comprising bonding the infusion-promoting layer to the surface of the pultruded strip.

3. The method of claim 2, comprising applying the infusion-promoting layer to the surface of the pultruded strip when the pultruded strip is in an uncured or semi-cured state, and curing the pultruded strip to bond the infusion-promoting layer to the surface of the pultruded strip.

4. The method of claim 1, comprising curing the pultruded strip before applying the infusion-promoting layer to the surface of the pultruded strip.

5. The method of claim 4, comprising applying an adhesive layer to the surface of the pultruded strip after curing the pultruded strip and before applying the infusion-promoting layer.

6. The method of claim 5, comprising spraying the adhesive layer onto the surface of the pultruded strip.

7. The method of claim 1, wherein the infusion-promoting layer is a fibrous layer.

8. The method of claim 7, wherein the infusion-promoting layer is a glass fabric layer.

9. The method of claim 7, wherein the infusion-promoting layer has a fibre density of between approximately 100 grams per square metre and 300 grams per square metre.

10. The method of claim 1, comprising applying the infusion-promoting layer to an upper surface or a lower surface of the pultruded strip.

11. The method of claim 1, wherein the applying a resin-free, infusion-promoting layer to a surface of the pultruded strip includes applying a first, resin-free, infusion-promoting layer to an upper surface of the pultruded strip down-stream from the die in the process direction, and applying a second, resin-free, infusion-promoting layer to a lower surface of the pultruded strip down-stream from the die in the process direction.

12. The method of claim 1, wherein the pultruded strip has a length of between approximately 2 metres and approximately 1000 metres.

13. The method of claim 12, wherein the pultruded strip has a length of between approximately 10 metres and approximately 150 metres.

14. The method of claim 13, wherein the pultruded strip has a length of between approximately 10 metres and approximately 80 metres.

15. The method of claim 1, wherein the pultruded strip is substantially flat and has a substantially rectangular cross-section.

16. A method of making a wind turbine blade, the method comprising: providing a plurality of strips, each strip made by a process comprising: drawing fibres and resin through a pultrusion die in a process direction to form a pultruded strip; and applying a resin-free, infusion-promoting layer to a surface of the pultruded strip down-stream from the die in the process direction, placing the plurality of strips in a mould tool to form a stack having at least one infusion-promoting layer between two pultruded strips, wherein each infusion-promoting layer remains substantially resin-free when the plurality of strips is placed in the mould tool; infusing resin into the mould tool such that resin infiltrates between the pultruded strips via each infusion-promoting layer; curing the resin in the stack of the plurality of strips; placing the cured stack in a wind turbine blade mould tool; infusing resin into the wind turbine blade mould tool such that the resin infiltrates around the stack; and curing the resin to form the wind turbine blade.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Reference has already been made to FIGS. 1 to 3 of the drawings. In order that the invention might be more readily understood, reference will now be made, by way of example only, to the remainder of the drawings, in which:

(2) FIGS. 4a and 4b are perspective and front views respectively of a strip according to an embodiment of the invention for an elongate reinforcing structure of a wind turbine blade according to an aspect of the invention;

(3) FIG. 5 is a front view of the strip of FIG. 4 arranged in a stack with a plurality of similar strips;

(4) FIG. 6 is an enlarged front view of an infusion region between two strips in the stack of FIG. 5;

(5) FIG. 7 is a schematic of a method of making the strip of FIGS. 4a and 4b according to another embodiment of the invention;

(6) FIG. 8 is a schematic of another method of making the strip of FIGS. 4a and 4b;

(7) FIG. 9 is a front view of a strip according to another embodiment of the invention for an elongate reinforcing structure of a wind turbine blade;

(8) FIG. 10 is an enlarged front view of an infusion region formed between the strip of FIG. 9 and another strip, when the strips are arranged in a stack;

(9) FIG. 11 is a schematic of a method of making the strip of FIG. 9 according to another embodiment of the invention; and

(10) FIG. 12 is a schematic of another method of making the strip of FIG. 9.

DETAILED DESCRIPTION OF EMBODIMENT OF THE INVENTION

(11) FIGS. 4a and 4b show a strip 100 for an elongate reinforcing structure for a wind turbine blade. In the embodiment described, the elongate reinforcing structure is a spar cap, similar to that described above in relation to FIG. 1.

(12) The strip 100 is a pultruded strip of fibre-reinforced polymeric material 102 that extends longitudinally between opposed ends 104. The pultruded strip 102 comprises sides 103, and upper and lower surfaces 106, 108. Each of the upper and lower surfaces 106, 108 is provided with an infusion-promoting layer 110 that is bonded to the respective upper or lower surface 106, 108.

(13) The infusion-promoting layers 110 cover the entirety of the upper and lower surfaces 106, 108 of the pultruded strip 102. In particular, the infusion-promoting layers 108 extend continuously between the ends 104 of the strip 102 in a longitudinal direction, and continuously between the sides 103 of the strip 110 in a transverse direction.

(14) To integrate the strip 100 into a spar cap, as shown in FIG. 5, a plurality of strips 100 are stacked one-on-top-of-another to form a stack 112 in a mould (not shown). The strips 100 are stacked with the upper surface 106 of one strip 100 facing the lower surface 108 of a neighbouring strip 100 in the stack 112. In this way, the outer surfaces 113 of the infusion-promoting layers 110 of neighbouring strips 100 are in contact with one another. Together, the adjacent infusion-promoting layers 110 form an infusion region 114 between each pair of neighbouring strips 100.

(15) Once the strips 100 have been arranged in the stack 112, resin is introduced to the stack 112. The resin infiltrates around the stack 112 and also between the strips 110 in the stack 112 via the infusion regions 114 between the strips 100.

(16) FIG. 6 shows the infusion-promoting layer 110 and the infusion region 114 in greater detail, and reveals that the infusion-promoting layer is a fibrous layer having a relatively loose weave.

(17) In the embodiment shown, the infusion-promoting layer 110 is a layer of glass fibre material, and specifically is a layer of Hexcel weave glass fibre fabric having a density of 200 grams per square metre (gsm).

(18) The fibre density of the glass fibre material is relatively low; for example between approximately 100 and approximately 300 gsm. In particular, the fibre density of the glass fibre material is sufficiently low that resin is able to infuse relatively easily among the glass fibres, so that the layer of glass fibre material enhances resin flow. The fibre density is also sufficiently low to allow the glass fibre material to bond to the surface 106, 108 of the pultruded strip 102.

(19) The infusion-promoting layer 110 presents an inner surface 111 and an outer surface 113. The inner surface 111 is bonded to the upper or lower surface 106, 108 of the pultruded strip 102, for example by means of an adhesive layer 116. The outer surface 113 forms the external surface of the strip 100. The outer surface 113 is textured due to the fibrous nature of the infusion-promoting layer 110. When strips 100 are placed one on top of another, this textured surface serves to space the strips 100 apart, increasing the size of the interstitial space between the strips 100 and further facilitating resin flow between the strips 100.

(20) The adhesive layer 116 does not penetrate all the way into the infusion-promoting layer 110, but remains only in a region of the infusion-promoting layer 110 that is nearest the pultruded strip 102. In this way, the spaces between the fibres of the infusion-promoting layer 110 are not blocked by the adhesive, and are instead open to receive infusing resin. In other words, and in contrast to a peel ply layer, the infusion-promoting layer is a dry fabric and is not infused with resin.

(21) Furthermore, the relatively loose weave of the infusion-promoting layer 110 provides relatively large spaces between the fibres of the weave, so that resin can infuse easily within the infusion-promoting layers 110, and hence can infuse easily through the infusion region 114 between neighbouring strips 100.

(22) FIG. 6 also reveals that between the adjacent infusion-promoting layers 110 is an interstitial space 118. The interstitial space 118 is relatively large, which allows relatively fast flow of resin between the strips 100.

(23) The weave of the fibres in the infusion-promoting layers 110 is uniform across the entirety of the infusion-promoting layers 110, meaning that the resin flow rate is correspondingly uniform. The uniform weave also means that the peaks and troughs provided by the weave are regularly arranged, such that the interstitial space 118 is substantially uniform across the entire strip 100. This further helps to ensure a uniform resin flow rate. Thus, the resin flow rate is uniform across the entire infusion region 114, such that when resin is introduced between the strips 100, the resin can more easily penetrate the entirety of the infusion region 114, reducing the chances of air pockets forming between the strips 100.

(24) After the resin has been infused between and around the strips 100 in the stack 112, the resin is cured by heating the mould, and the spar cap is fully formed. The infusion-promoting layers 110 are therefore integrated into the finished spar cap as structural elements that lie between each pair of neighbouring pultruded strips 102 in the stack 112. This is in contrast to peel ply, which is removed from the surface of a strip before the strip is stacked.

(25) Referring now to FIG. 7, the strip 100 described above is made by a pultrusion process using a pultrusion apparatus 300. Resin-soaked fibres 42 are drawn through a standard pultrusion die 40 in a process direction P to form the pultruded strip 102. The pultruded strip 102 then enters a curing oven 44, where the pultruded strip 102 is heated to cure the resin.

(26) Downstream of the curing oven 44 is an adhesive application station 160. The adhesive application station 160 comprises two adhesive sprayers 162, one arranged above the pultruded strip 102 and one arranged below the pultruded strip 102. The adhesive sprayers 162 spray an adhesive layer 116 (see FIG. 6), such as a layer of epoxy resin, onto the upper and lower surfaces 106, 108 of the pultruded strip 102.

(27) Downstream of the adhesive application station 160 is an application station 150 that applies the infusion-promoting layers 110 to the upper and lower surfaces 106, 108 of the strip 102.

(28) The application station 150 comprises two roller systems 152, one arranged above the pultruded strip 102 and one arranged below the pultruded strip 102. The roller systems 152 store the infusion-promoting layers 110, and apply the layers 110 to the upper and lower surfaces 106, 108 of the pultruded strip 102 respectively. The infusion-promoting layers 110 adhere to the upper and lower surfaces 106, 108 of the pultruded strip 102 by means of the adhesive layer 116.

(29) Once the infusion-promoting layers 110 have been applied, the final strip 100 is ready for use in making a spar cap, or for transportation to a manufacturing or storage facility.

(30) An alternative method of making the strip 100, using an alternative pultrusion apparatus 400 is illustrated in FIG. 8. In this method, resin-soaked fibres 42 are pultruded through the pultrusion die 40 in the same way, but the pultruded strip 100 is then moved directly to the application station 150, which is substantially identical to the layer application station 150 already described.

(31) Because the pultruded strip 102 has not yet been cured when the infusion-promoting layers 110 are applied, the upper and lower surfaces 106, 108 of the pultruded strip 102 are tacky. This allows the infusion-promoting layers 110 to adhere to the upper and lower surfaces 106, 108 without the need for an additional adhesive.

(32) The resin in the pultruded strip 102 only infiltrates into the infusion-promoting layers 110 by a short distance, and hence only infiltrates into a small region of the infusion-promoting layer 110 that is near the pultruded strip 102. This is because in the absence of a vacuum there is relatively little driving force for resin infusion. Thus the fibres of the infusion-promoting layers 110 do not become saturated with resin, and the spaces between the fibres remain open to receive resin during a later resin infusion process.

(33) The pultruded strip 102, with the infusion-promoting layers 110 applied to its upper and lower surfaces 106, 108, is moved to a curing oven 44, where the pultruded strip 102 is heated to cure the resin. As the resin is cured, the infusion-promoting layers 110 are bonded to the pultruded strip 102. Once cured, the strip 100 is then ready for use in a spar cap.

(34) In alternative versions of the method, the strip may be semi-cured before the infusion-promoting layers 110 are applied, so as to ensure that the upper and lower surface 106, 108 have a suitable level of tackiness for adhesion.

(35) FIG. 9 illustrates an alternative strip 200 for use in an elongate reinforcing structure of a wind turbine blade. The strip 200 is similar to the strip 100 described above, but in this case an infusion-promoting layer 110 is bonded only to the upper surface 106 of the pultruded strip 102, while the lower surface 108 is exposed to the surroundings.

(36) As illustrated in FIG. 10, when the strip 200 is stacked with other similar strips 200, the infusion-promoting layer 110 lies against the lower surface 108 of a neighbouring strip 200 in the stack. In this way, an infusion region 214 is created between the strips 200 in the stack, in a manner similar to that already described.

(37) FIG. 10 shows the infusion region 214 in greater detail. In this case, the infusion region 214 comprises a single infusion-promoting layer 110. An interstitial space 218 is created between the infusion-promoting layer 110 and the lower surface 108 of the neighbouring strip 200 in the stack. The infusion region 214 enhances the infusion of resin between the strips 200, and does so substantially uniformly, as has already been described above.

(38) FIG. 11 shows apparatus 500 for making a strip 200 having a single infusion-promoting layer 110. The apparatus 500 is similar to that already described above, but is configured to bond the infusion-promoting layer 110 only to the upper surface 106 of the pultruded strip 102.

(39) Resin-soaked fibres 42 are pulled through the pultrusion die 40 to form the pultruded strip 102 in the manner already described. The pultruded strip 102 is then fed to the curing oven 44 for curing.

(40) Next, the pultruded strip 102 is fed to the adhesive application station 260. The adhesive application station 260 comprises an adhesive sprayer 162 arranged above the pultruded strip 102. The adhesive sprayer 162 sprays an adhesive layer 116 (see FIG. 6), such as a layer of epoxy resin, onto the upper surface 106 of the pultruded strip 102.

(41) The strip 102 is then fed to an application station 250. The application station 250 comprises a roller system 152 arranged above the pultruded strip 102. The roller system 152 carries the infusion-promoting layer 110, and applies the layer 110 to the upper surface 106 of the pultruded strip 102. The infusion-promoting layer 110 adheres to the upper surface 106 of the pultruded strip 102 by means of the adhesive layer 116, as has been described.

(42) FIG. 12 illustrates an alternative apparatus 600 for making a strip 200 having a single infusion-promoting layer 110. In this apparatus 600, resin-soaked fibres 42 are pultruded through the pultrusion die 40 to form the pultruded strip 102.

(43) The strip 102 is then fed to a layer application station 250. The application station 250 comprises a roller system 152 arranged above the pultruded strip 102. The roller system 152 carries the infusion-promoting layer 110, and applies the layer 110 to the upper surface 106 of the pultruded strip 102. As has been described above, the upper surface 106 of the pultruded strip 102 is tacky, so that the infusion-promoting layer 110 adheres to the upper surface 106. This method therefore avoids the need for a specific adhesive application stage.

(44) The pultruded strip 102, with the infusion-promoting layer 110 applied to its upper surface 106, is moved to a curing oven 44, where the pultruded strip 102 is heated to cure the resin, thereby bonding the infusion-promoting layer 110 to the upper surface 106 of the pultruded strip 102.

(45) Although in the embodiments described the infusion-promoting layer is a layer of glass fibre material, it will be appreciated that this need not be the case. The infusion-promoting layer may be a fibrous layer that is made of a different material, such as carbon, glass, aramid, polyester, nylon. The fibrous layers may be woven, uni-axial, multi-axial, fleece, or they may be continuous filament. Alternatively, the infusion-promoting layer may be a perforated or porous layer.

(46) In embodiments where an adhesive layer is used, the adhesive layer need not be an epoxy layer, but may be any suitable adhesive.

(47) The spar cap or other elongate reinforcing structure may be made by stacking the strips and carrying out a resin infusion process in a mould tooling, and the resulting spar cap or other elongate reinforcing structure may then be integrated into the blade. In other embodiments, the strips may be stacked directly in a mould for a blade half with other structural components of the blade, and the resin infusion process may be applied to the entire blade half, such that the spar cap is both formed and integrated into the blade half simultaneously.

(48) The present invention is therefore not limited to the exemplary embodiments described above and many other variations or modifications will be apparent to the skilled person without departing from the scope of the present invention as defined by the following claims.