A METHOD OF MANUFACTURING A WIND TURBINE BLADE

Abstract

The present invention relates to a method of manufacturing a wind turbine blade, comprising arranging one or more layers of fibre material and a preform in a mould (66), injecting the one or more layers of fibre material and the preform (76) with a curable resin, and curing the resin. The preform (76) is impregnated with a curing promoter such that the concentration of curing promoter varies spatially within the preform.

Claims

1. A method of manufacturing a wind turbine blade, the blade having a profiled contour including a pressure side and a suction side, and a leading edge and a trailing edge with a chord having a chord length extending therebetween, the wind turbine blade extending in a spanwise direction between a root end and a tip end, said method comprising: providing a mould (66), arranging one or more layers of fibre material in the mould for providing a skin element (70), arranging a preform (76) on at least part of the one or more layers of fibre material for providing a reinforcing element, injecting the one or more layers of fibre material and the preform (76) with a curable resin, and curing the resin, wherein the preform (76) is impregnated with a curing promoter such that the concentration of curing promoter varies spatially within the preform (76).

2. A method according to claim 1, wherein the preform (76) has a cross section with a central portion (78) and two opposing outer edges (80, 82), wherein the thickness of the preform (76) decreases from the central portion (78) towards each of the two outer edges (80, 82), and wherein the preform (76) is impregnated with the curing promoter such that the concentration of curing promoter decreases from one or both outer edges (80, 82) towards the central portion (78) of the preform (76).

3. A method according to claim 1, wherein the preform (76) has two edge regions (81, 83), each edge region extending laterally within a distance of 100 mm or less from the respective outer edge (80, 82) towards the central portion (78) of the preform (76), wherein the preform (76) is impregnated with the curing promoter within one or both edge regions (81, 83), e.g. wherein the preform (76) is not impregnated with the curing promoter outside of said edge regions (81, 83).

4. A method according to claim 1, wherein the preform (76) is impregnated with the curing promoter prior to the step of arranging the preform (76) on at least part of the one or more layers of fibre material.

5. A method according to claim 1, wherein the preform (76) comprises at least one fibre layer or fibre fabric.

6. A method according to claim 1, wherein the curing promoter is a curing accelerator comprising a transition metal such as cobalt, manganese, iron or copper.

7. A method according to claim 1, wherein the curing promoter is a curing initiator such as a peroxide, preferably an organic peroxide.

8. A method according to claim 1, wherein the resin comprises a polyester, such as an unsaturated polyester.

9. A method according to claim 1, wherein the curing of the resin is performed without external heating.

10. A method according to claim 1, wherein the reinforcing element is a load-carrying main laminate or spar cap of the wind turbine blade for supporting one or more shear webs.

11. A preform (76) of an elongate reinforcing element for a wind turbine blade, the preform (76) comprising a fibre material, wherein the preform (76) is impregnated with a curing promoter such that the concentration of curing promoter varies spatially within the preform (76).

12. A preform (76) according to claim 11, wherein the preform (76) has a cross section with a central portion (78) and two opposing outer edges (80, 82), wherein the thickness of the preform (76) decreases from the central portion (78) towards each of the two outer edges (80, 82), and wherein the preform (76) is impregnated with the curing promoter such that the concentration of curing promoter decreases from one or both outer edges (80, 82) towards the central portion (78) of the preform (76).

13. A preform (76) according to claim 11, wherein the preform (76) has two edge regions (81, 83), each edge region extending laterally within a distance of 100 mm or less from the respective outer edge (80, 82) towards the central portion (78) of the preform (76), wherein the preform (76) is impregnated with the curing promoter within one or both edge regions (81, 83).

14. A preform (76) according to claim 11, wherein the curing promoter is present in the edge region in a concentration of 0.01 to 10 parts by weight of curing promoter relative to the weight of the fibre material.

15. A wind turbine blade obtainable by the method of claim 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0052] The invention is explained in detail below with reference to embodiments shown in the drawings, in which

[0053] FIG. 1 shows a wind turbine,

[0054] FIG. 2 shows a schematic view of a wind turbine blade,

[0055] FIG. 3 shows a schematic view of an airfoil profile through section I-I of FIG. 4,

[0056] FIG. 4 shows a schematic view of the wind turbine blade, seen from above and from the side,

[0057] FIG. 5 is a schematic cross-sectional view of a mould for moulding a blade part according to the present invention,

[0058] FIG. 6 is a perspective view of a preform according to the present invention,

[0059] and FIG. 7 shows a cross sectional view of the preform taken along the line A-A′ in FIG. 6.

DETAILED DESCRIPTION

[0060] FIG. 1 illustrates a conventional modern upwind wind turbine according to the so-called “Danish concept” with a tower 4, a nacelle 6 and a rotor with a substantially horizontal rotor shaft. The rotor includes a hub 8 and three blades 10 extending radially from the hub 8, each having a blade root 16 nearest the hub and a blade tip 14 furthest from the hub 8.

[0061] FIG. 2 shows a schematic view of a first embodiment of a wind turbine blade 10 according to the invention. The wind turbine blade 10 has the shape of a conventional wind turbine blade and comprises a root region 30 closest to the hub, a profiled or an airfoil region 34 furthest away from the hub and a transition region 32 between the root region 30 and the airfoil region 34. The blade 10 comprises a leading edge 18 facing the direction of rotation of the blade 10, when the blade is mounted on the hub, and a trailing edge 20 facing the opposite direction of the leading edge 18.

[0062] The airfoil region 34 (also called the profiled region) has an ideal or almost ideal blade shape with respect to generating lift, whereas the root region 30 due to structural considerations has a substantially circular or elliptical cross-section, which for instance makes it easier and safer to mount the blade 10 to the hub. The diameter (or the chord) of the root region 30 may be constant along the entire root area 30. The transition region 32 has a transitional profile gradually changing from the circular or elliptical shape of the root region 30 to the airfoil profile of the airfoil region 34. The chord length of the transition region 32 typically increases with increasing distance r from the hub. The airfoil region 34 has an airfoil profile with a chord extending between the leading edge 18 and the trailing edge 20 of the blade 10. The width of the chord decreases with increasing distance r from the hub.

[0063] A shoulder 40 of the blade 10 is defined as the position, where the blade 10 has its largest chord length. The shoulder 40 is typically provided at the boundary between the transition region 32 and the airfoil region 34.

[0064] It should be noted that the chords of different sections of the blade normally do not lie in a common plane, since the blade may be twisted and/or curved (i.e. pre-bent), thus providing the chord plane with a correspondingly twisted and/or curved course, this being most often the case in order to compensate for the local velocity of the blade being dependent on the radius from the hub.

[0065] FIGS. 3 and 4 depict parameters which are used to explain the geometry of the wind turbine blade according to the invention. FIG. 3 shows a schematic view of an airfoil profile 50 of a typical blade of a wind turbine depicted with the various parameters, which are typically used to define the geometrical shape of an airfoil. The airfoil profile 50 has a pressure side 52 and a suction side 54, which during use—i.e. during rotation of the rotor—normally face towards the windward (or upwind) side and the leeward (or downwind) side, respectively. The airfoil 50 has a chord 60 with a chord length c extending between a leading edge 56 and a trailing edge 58 of the blade. The airfoil 50 has a thickness t, which is defined as the distance between the pressure side 52 and the suction side 54. The thickness t of the airfoil varies along the chord 60. The deviation from a symmetrical profile is given by a camber line 62, which is a median line through the airfoil profile 50. The median line can be found by drawing inscribed circles from the leading edge 56 to the trailing edge 58. The median line follows the centres of these inscribed circles and the deviation or distance from the chord 60 is called the camber f. The asymmetry can also be defined by use of parameters called the upper camber (or suction side camber) and lower camber (or pressure side camber), which are defined as the distances from the chord 60 and the suction side 54 and pressure side 52, respectively.

[0066] Airfoil profiles are often characterised by the following parameters: the chord length c, the maximum camber f, the position d.sub.f of the maximum camber f, the maximum airfoil thickness t, which is the largest diameter of the inscribed circles along the median camber line 62, the position d.sub.r of the maximum thickness t, and a nose radius (not shown). These parameters are typically defined as ratios to the chord length c. Thus, a local relative blade thickness t/c is given as the ratio between the local maximum thickness t and the local chord length c. Further, the position d.sub.p of the maximum pressure side camber may be used as a design parameter, and of course also the position of the maximum suction side camber.

[0067] FIG. 4 shows other geometric parameters of the blade. The blade has a total blade length L. As shown in FIG. 3, the root end is located at position r=0, and the tip end located at r=L. The shoulder 40 of the blade is located at a position r=L, and has a shoulder width W, which equals the chord length at the shoulder 40. The diameter of the root is defined as D. The curvature of the trailing edge of the blade in the transition region may be defined by two parameters, viz. a minimum outer curvature radius r.sub.o and a minimum inner curvature radius r.sub.i, which are defined as the minimum curvature radius of the trailing edge, seen from the outside (or behind the trailing edge), and the minimum curvature radius, seen from the inside (or in front of the trailing edge), respectively. Further, the blade is provided with a prebend, which is defined as Ay, which corresponds to the out of plane deflection from a pitch axis 22 of the blade.

[0068] FIG. 5 is a schematic cross-sectional view through a mould 66 for use in a method of manufacturing a wind turbine blade. The mould comprises a moulding surface 68, which defines an outer surface of the finished wind turbine blade, here shown as the pressure side of the blade.

[0069] A number of fibre layers, core parts and reinforcement sections are arranged on the moulding surface 68, these parts forming a skin element 70 of the aerodynamic shell part or pressure side shell part 72 of the wind turbine blade (details not shown). The aerodynamic shell part 72 may for instance be manufactured by first applying a waxy substance to the moulding surface in order to be able to remove the shell part after moulding. Also, a gelcoat may be applied to the moulding surface. The skin element may comprise a recess 74 for receiving a preform of a reinforcing element 76, such as a spar cap or main laminate. The preform of the reinforcing element 76 extends in a longitudinal direction of the blade and forms a load carrying structure of the finished blade after resin infusion and curing.

[0070] The preform 76 has a cross section with a central portion 78 and two opposing outer edges 80, 82. The thickness of the preform 76 decreases from the central portion 78 towards each of the two outer edges 80, 82. Preferably prior to arranging the preform 76 in the mould, it is impregnated with a curing promoter such that the concentration of curing promoter decreases from one or both outer edges 80, 82 towards the central portion 78 of the preform. The skin element 70 and the preform 76 are injected with a curable resin which is then cured to form the wind turbine blade part 72.

[0071] FIG. 6 is a perspective view of a preform 76 of the present invention, wherein FIG. 7 shows a cross-sectional view of the preform 76 taken along the line A-A′ in FIG. 6, substantially perpendicular to the longitudinal direction LO indicated in FIG. 6. As indicated by the shaded areas in FIG. 6, the preform 76 is impregnated with the curing promoter along both its lateral edges 80, 82 within longitudinally extending strips or edge regions 81, 83 adjacent to the lateral edges 80, 82. Preferably, the remainder of the preform 76 is not impregnated with the curing promoter.

[0072] As best seen in FIG. 7, the preform 76 has a thicker central portion 78 and two edge regions 81, 83, each edge region extending laterally within a distance E1, E2 of, for example, 100 mm or less from the respective outer edge 80, 82 towards the central portion 78 of the preform 76. The lower part of FIG. 7 illustrates a concentration profile 84 across the preform 76 extending between both outer edges 80, 82, wherein the concentration c.sub.p of the curing promoter is plotted versus the horizontal distance d from outer edge 80. The vertical and horizontal dimensions V, H are also indicated in FIG. 7. As seen in the graph of FIG. 7, the preform 76 is impregnated with curing promoter within the edge regions 81, 83, while the preform 76 is not impregnated with the curing promoter outside of said edge regions 81, 83. While a concentration profile 84 is illustrated in FIG. 7, a smoother or more transient concentrations profile is also possible according to the present invention.

LIST OF REFERENCE NUMERALS

[0073] 2 wind turbine [0074] 4 tower [0075] 6 nacelle [0076] 8 hub [0077] 10 blade [0078] 14 blade tip [0079] 16 blade root [0080] 18 leading edge [0081] 20 trailing edge [0082] 22 pitch axis [0083] 30 root region [0084] 32 transition region [0085] 34 airfoil region [0086] 40 shoulder/position of maximum chord [0087] 50 airfoil profile [0088] 52 pressure side [0089] 54 suction side [0090] 56 leading edge [0091] 58 trailing edge [0092] 60 chord [0093] 62 camber line/median line [0094] 66 mould [0095] 68 moulding surface [0096] 70 skin element [0097] 72 shell part [0098] 74 recess [0099] 76 preform of reinforcing element [0100] 78 central portion of preform [0101] 80 first outer edge [0102] 81 first edge region [0103] 82 second outer edge [0104] 83 second edge region [0105] 84 concentration profile [0106] c chord length [0107] c.sub.p concentration of curing promoter [0108] d distance [0109] d.sub.t position of maximum thickness [0110] d.sub.f position of maximum camber [0111] d.sub.p position of maximum pressure side camber [0112] E1, E2 distances from outer edge [0113] f camber [0114] H horizontal direction [0115] L blade length [0116] LO longitudinal direction [0117] r local radius, radial distance from blade root [0118] t thickness [0119] V vertical direction [0120] Δy prebend