METHOD OF MANUFACTURING A SPAR CAP

Abstract

Provided is a method of manufacturing a wind turbine rotor blade spar cap, which method includes providing a plurality of carbon profile elements; providing a number of adhesive film layers; preparing a spar cap assembly by arranging the carbon profile elements in a stack and arranging an adhesive film layer between adjacent carbon profile elements of the stack; and curing the spar cap assembly. The embodiments further describe a wind turbine rotor blade spar cap, and a wind turbine rotor blade including such a spar cap.

Claims

1. A method of manufacturing a wind turbine rotor blade spar cap, which method comprises providing a plurality of carbon profile elements; providing a number of adhesive film layers; preparing a spar cap assembly by arranging the carbon profile elements in a stack and arranging an adhesive film layer between adjacent carbon profile elements of the stack; and curing the spar cap assembly.

2. The method according to claim 1, wherein the spar cap assembly is cured under the application of pressure and/or heat.

3. The method according to claim 1, comprising a step of arranging a first stack adjacent to a second stack, and joining the opposing longitudinal side faces by a vertical adhesive film layer.

4. The method according to claim 1, comprising a step of arranging an outer layer on an outer face of the spar cap assembly.

5. The method according to claim 1, comprising a step of connecting a number of electrical terminals to the spar cap assembly.

6. The method according to claim 5, wherein the curing step is performed by applying a voltage across two electrical terminals of the spar cap assembly.

7. A wind turbine rotor blade spar cap comprising a plurality of carbon profile elements and a number of adhesive film layers, arranged in a stack and cured using the method according to claim 1.

8. A spar cap according to claim 7, wherein a carbon profile element comprises a preformed carbon element.

9. The spar cap according to claim 7, wherein the carbon profile elements are shaped to give a stack with slanted longitudinal side faces.

10. The spar cap according to claim 7, wherein an adhesive film layer in its uncured state comprises an adhesive in solid sheet form.

11. The spar cap according to claim 7, wherein an adhesive film layer comprises a conductive adhesive material.

12. The spar cap according to claim 7, comprising at least one conductive mat arranged to electrically connect an electrical terminal to the spar cap assembly.

13. The spar cap according to claim 7, constructed to extend from a blade root end towards a blade tip end, and wherein the spar cap comprises a greater number of carbon profile elements at the root end and a smaller number of carbon profile elements at the tip end.

14. The spar cap according to claim 7, constructed to extend from a blade root end towards a blade tip end, and wherein the thickness of the carbon profile elements at the root end exceeds the thickness of the carbon profile elements at the tip end.

15. A wind turbine rotor blade comprising a spar cap according to claim 7.

Description

BRIEF DESCRIPTION

[0023] Some of the embodiments will be described in detail, with references to the following Figures, wherein like designations denote like members, wherein:

[0024] FIG. 1 indicates the locations of spar caps inside a wind turbine rotor blade;

[0025] FIG. 2 illustrates the assembly of a stack of CFRP profiles and adhesive film sheets;

[0026] FIG. 3 shows a cross-section through a first possible spar cap assembly for the inventive spar cap;

[0027] FIG. 4 shows a cross-section through a second possible spar cap assembly for the inventive spar cap;

[0028] FIG. 5 shows a cross-section through a third possible spar cap assembly for the inventive spar cap;

[0029] FIG. 6 shows a perspective view of a cross-section though an embodiment of the inventive spar cap; and

[0030] FIG. 7 shows an embodiment of the prior art spar cap assembly.

[0031] In the diagrams, like numbers refer to like objects throughout. Objects in the diagrams are not necessarily drawn to scale.

DETAILED DESCRIPTION

[0032] FIG. 1 shows a wind turbine rotor blade 2 and indicates the position of a spar cap 1, 7 on both sides of an airfoil portion of the blade 2. The rotor blade 2 can be very long, for example a rotor blade of a multi-megawatt wind turbine can easily have a length L in the region of 50 m or more, so that the materials used for the blade 2 should be as light as possible while also contributing to the structural strength of the rotor blade 2.

[0033] The spar caps 1, 7 with length Ls are effectively embedded in the composite layers of the rotor blade body, and a shear web 23 extends between the spar caps 1, 7. A down conductor 24 of a rotor blade LPS can be arranged along the shear web 23 as shown here.

[0034] The diagram shows a single spar cap 1, 7 on either side of the web 23, but it will be understood that a rotor blade may be constructed to incorporate more than two spar caps, and may for example be constructed using four spar caps and two webs.

[0035] The spar cap 1, 7 usually starts at a distance of up to 4 m from the blade root 20, and extends to within 0.5-2 m from the blade tip 21. Generally, any CFRP elements of the spar cap are not used at the outer end of the spar cap (close to the blade tip 21) in order to reduce the risk of a direct lightning strike. Instead, the CFRP portion of the spar cap transitions to GFRP used to construct the thin outer section of the spar cap.

[0036] During blade manufacture, the pre-casted CFRP spar cap assembly is incorporated in the GFRP layup using moulding techniques that will be known to the skilled person.

[0037] FIG. 2 indicates the assembly of a stack S of pultruded CFRP profiles 10 and adhesive film sheets 11 (upper left of the diagram). The resulting spar cap assembly 1A is indicated on the lower right of the diagram. The spar cap assembly 1A will be cured to result in the inventive spar cap. A carbon profile 10 can have an overall rectangular shape as well as an essentially rectangular cross-section as shown here. The adhesive film sheets 11 arranged between the profiles 10 can be any suitable kind of adhesive film that can be cut to size. The entire assembly 1A can be placed in a vacuum bag as will be known to the skilled person, so that that it can be cured by the application of pressure and/or heat. During the curing step, the adhesive softens and bonds to the faces of the carbon profile elements 10. The uniform thickness of the adhesive sheets 11 and the fact that each sheet 11 completely fills the space between adjacent carbon elements 10 ensures that defects such as kissing bonds can be greatly reduced. In this way, it is possible to manufacture a structurally reliable precast carbon spar cap in an economical manner.

[0038] FIG. 3 shows a cross-section through an embodiment of the inventive spar cap assembly 1A manufactured as explained in FIG. 2 above. Here, additional prepreg CFRP or glass fibre reinforced layers 13 are arranged on the bottom surface 1A_bottom and top surface 1A_top of the stack S, i.e. underneath and on top of the stack S before curing, in order to give transverse strength during handling of the spar cap 1 and during the lifetime of the blade. During the curing step, the resin already present in the prepreg layers softens and bonds to the outer faces 1A_top, 1A_bottom of the spar cap assembly 1A.

[0039] FIG. 4 shows a cross-section through a spar cap assembly 1A for a further embodiment of the inventive spar cap manufactured as explained in FIG. 2 above. Here, two stacks S are placed side by side and a vertical sheet 11V or block 11V of adhesive is arranged between the opposing vertical side faces of the stacks S.

[0040] FIG. 5 shows a cross-section through a spar cap assembly 1A for a further embodiment of the inventive spar cap, based on the embodiment of FIG. 4 above. Here, the outer side face 1A_side of each stack S is inclined or slanted. This is achieved by selecting carbon elements 10 that each has an appropriate width and one appropriately slanted longitudinal edge. The advantage of this design is that it provides a substitute for the balsa wedges that are usually incorporated in a prior art spar cap manufactured using VARTM.

[0041] FIG. 6 shows a perspective view of a narrow slice through a spar cap 1 manufactured as explained in FIG. 5 above. The spar cap 1 may be assumed to extend in a direction from blade root towards the blade tip as indicated by the arrows. The diagram shows how electric terminals 14 may be connected by means of conductive mats 15 to the inclined side faces 1A_side of the spar cap assembly 1A. In this exemplary embodiment, a conductive mat 15 is bonded to a side face 1A_side of the spar cap assembly 1A using a sheet 150 of conductive adhesive. These can be connected later to the down conductor of the rotor blade LPS. However, they may also be used in the curing step. By connecting a voltage between the pair of terminals 14, a current will flow through the carbon profiles 10, thereby raising the temperature of the assembly 1A and softening the adhesive sheets 11 so that all parts of the assembly are thoroughly wet by the adhesive, which hardens upon cooling to give a structurally robust spar cap. The diagram also indicates cover layers 13 that are used to wrap or enclose the spar cap assembly 1A.

[0042] FIG. 7 shows a prior art spar cap 7. Here, pultruded CFRP profiles 70 are stacked on top and beside each other. Fibre layers 71 comprising glass fibre, aramid etc., are arranged between the profiles 70. Balsa wedges 72 are arranged along the outer sides of the stack. Covering layers 73 of a glass fibre reinforced polymer are used to wrap the assembly, which is then placed in a vacuum bag for a VARTM procedure (with which the skilled person will be familiar) in which resin in liquid state is injected into the stack and drawn through the various layers by vacuum action. When resin completely permeates the assembly, heat is used to cure the assembly. As mentioned in the introduction, the VARTM process is associated with various drawbacks such as the relatively high likelihood of kissing bonds between the layers of the finished spar cap 7, and the risk of other defects such as air entrapment, voids, poor impregnation, etc. In addition, there are problems associated with handling liquid resin, costs arising from compliance with health and safety requirements, and costs arising from the generally time-consuming curing process that requires significant amounts of energy and capital expenditure.

[0043] Although embodiments of the present invention have been disclosed in the form of preferred embodiments and variations thereon, it will be understood that numerous additional modifications and variations could be made thereto without departing from the scope of embodiments of the invention. For example, although the carbon profile elements were described above as essentially straight elements, they might have any suitable shape, for example curved and/or corrugated shapes.

[0044] For the sake of clarity, it is to be understood that the use of a or an throughout this application does not exclude a plurality, and comprising does not exclude other steps or elements.