A method of manufacturing a wind turbine blade with fewer manufacturing defects

Abstract

The present invention relates to a method of manufacturing a wind turbine blade using a two-step curing process, wherein the second curing is performed in the presence of a resin flow medium (76) comprising a curing inhibitor.

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 an outer shell part (70), injecting the one or more layers of fibre material with a curable resin, and curing the resin to obtain an outer shell part (70), arranging a resin flow medium (76) on top of at least part of the outer shell part (70) followed by one or more layers of fibre material for forming a load-carrying structure (74), injecting the resin flow medium (76) and the one or more layers of fibre material for forming a load-carrying structure with a curable resin, and curing the resin to adhere the outer shell part (70) to the load-carrying structure (74) to obtain a shell half of a wind turbine blade wherein the resin flow medium (76) comprises a curing inhibitor.

2. A method according to claim 1, wherein the curing inhibitor covers at least a first part of the outer surface of the resin flow medium.

3. A method according to claim 1, wherein the resin flow medium further comprises a curing promoter and wherein the curing promoter covers at least a second part of the outer surface of the resin flow medium, which is different from the first part.

4. A method according to claim 1, wherein the curing inhibitor is uniformly coated on the surface of the resin flow medium.

5. A method according to claim 1, wherein the thickness of the resin flow medium varies spatially across the resin flow medium.

6. A method according to claim 1, wherein the curing inhibitor concentration varies spatially across the resin flow medium.

7. A method according to claim 1, wherein the curing inhibitor concentration varies within one or more layers of the resin flow medium.

8. A method according to claim 1, wherein the curing promoter comprise a transition metal such as cobalt, manganese, iron or copper or mixtures thereof.

9. A method according to claim 1, wherein the curing inhibitor is a primary antioxidant (radical scavenger).

10. A method according to claim 1, wherein the resin is a styrene based resin or polyester based resin comprising styrene, such as an unsaturated polyester.

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

12. A resin flow medium (76) for use in a method according to claim 1, wherein the resin flow medium comprises a curing inhibitor.

13. A resin flow medium according to claim 12, wherein the resin flow medium further comprises a curing promoter.

14. Use of a resin flow medium according to claim 11, for minimizing or eliminating manufacturing defects during resin curing in the manufacturing of a wind turbine blade part.

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

Description

DETAILED DESCRIPTION OF THE INVENTION

[0044] The invention is explained in detail below with reference to embodiments shown in the drawings, in which

[0045] FIG. 1 shows a wind turbine,

[0046] FIG. 2 shows a schematic view of a wind turbine blade,

[0047] FIG. 3 shows a schematic view of an airfoil profile through section I-I of FIG. 4,

[0048] FIG. 4 shows a schematic view of the wind turbine blade, seen from above and from the side,

[0049] FIG. 5 is a schematic cross-sectional view of a mould for moulding a blade part according to the present invention,

[0050] and FIG. 6A-E shows a cross sectional view of the resin flow medium taken along the line A-A′ in FIG. 7 coated with different concentration profiles of curing inhibitor and optionally promoter,

[0051] FIG. 7 is a perspective view of a resin flow medium according to the present invention, and

[0052] FIG. 8 illustrates another concentration profile across the resin flow medium.

DETAILED DESCRIPTION

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.t 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.

[0060] 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.sub.w, 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 Δy, which corresponds to the out of plane deflection from a pitch axis 22 of the blade.

[0061] FIG. 5 is a schematic cross-sectional view through a mould 66 for use in a method of manufacturing a wind turbine blade part, such as a blade half. The mould comprises a moulding surface 68, which defines an outer surface of the finished wind turbine blade, here shown as the suction side of the blade. In the first step of the two-step curing process a number of fibre layers typically together with additional material, such as sandwich material and/or balsa wood, are arranged on the moulding surface 68, followed by resin infusion and curing. These parts constitute the outer shell 70 (i.e. aerodynamic shell part) of the wind turbine blade (details not shown). The aerodynamic outer shell part 70 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. In the second step a resin flow medium 76 is arranged on at least a part of the outer shell with one or more fibre layers on top followed by resin infusion and curing. These parts constitute the load-carrying structure 74, such as a main laminate, that extends in a longitudinal direction of the blade.

[0062] FIG. 6A-E shows a cross-sectional view of the resin flow medium according to the invention coated with different concentration profiles of curing inhibitor and optionally curing promoter. FIG. 6A shows a resin flow medium, wherein the concentration of curing inhibitor increases gradually from both lateral edges towards the central portion of the resin flow medium. FIG. 6B shows a resin flow medium, wherein the concentration of curing inhibitor is constant across the resin flow medium over the distance d. FIG. 6C shows a resin flow medium, wherein the concentration of curing inhibitor is constant across the resin flow medium over the distance d.sub.3. FIG. 6D shows a resin flow medium, wherein the concentration of curing promoter decreases gradually to zero from both lateral edges towards the central portion over a distance (d.sub.1) and the curing inhibitor gradually increases from distance (d.sub.1) towards the central portion over a distance (d.sub.2). FIG. 6E shows a resin flow medium, wherein the concentration of curing promoter decreases abrupt from a given concentration to zero from both lateral edges towards the central portion after a distance (d.sub.i) and the curing inhibitor gradually increases from distance (d.sub.1) towards the central portion over a distance (d.sub.2).

[0063] FIG. 7 shows a resin flow medium 76 which comprise a top surface 79 and bottom surface 81 with a cross section consisting of a central portion 78 and two opposing outer edges 80, 82. The top surface 79 is usually the surface that faces the resin flow medium 76, whereas the bottom surface 81 is usually the surface that faces the outer shell part during normal use. The resin flow medium 76 further comprise two opposing edge regions E1 and E2 given by the distance d.sub.1. The resin flow medium may be impregnated with a curing promoter at one or both outer edge regions E1/E2 of FIG. 7 and a curing inhibitor around the central portion, such that the concentration of curing promoter gradually decreases to zero from one or both outer edges towards the central portion over the distance d.sub.1 of the resin flow medium and the curing inhibitor gradually increases from distance d.sub.1 towards the central portion over the distance d.sub.2. The decrease in concentration of curing promoter from one or both outer edges towards the central portion of the resin flow medium may also be an abrupt decrease from a given concentration to zero. The distance d.sub.1 may be the same for both edge regions E1, E2 or different, preferably the same.

[0064] FIG. 8 shows a resin flow medium, wherein the concentration of curing inhibitor and/or promoter gradually decreases over the length L.sub.1 of the resin flow medium such that the concentration is highest at the root end and lowest at the tip end of the load-carrying structure. Such a concentration profile may be combined with any of concentration profiles according to FIG. 6A-E.

[0065] The thickness (h) of the resin flow medium may be uniform or vary spatially within the resin flow medium such that it decreases from the central portion 78 towards each of the two outer edges 80, 82. Preferably prior to arranging the resin flow medium 76 in the mould, it is coated with a curing inhibitor according to one of the different embodiments described above.

LIST OF REFERENCE NUMERALS

[0066] 2 wind turbine [0067] 4 tower [0068] 6 nacelle [0069] 8 hub [0070] 10 blade [0071] 14 blade tip [0072] 16 blade root [0073] 18 leading edge [0074] 20 trailing edge [0075] 22 pitch axis [0076] 30 root region [0077] 32 transition region [0078] 34 airfoil region [0079] 40 shoulder/position of maximum chord [0080] 50 airfoil profile [0081] 52 pressure side [0082] 54 suction side [0083] 56 leading edge [0084] 58 trailing edge [0085] 60 chord [0086] 62 camber line/median line [0087] 66 mould [0088] 68 moulding surface [0089] 70 outer shell part [0090] 72 shell halve of a wind turbine blade [0091] 74 load-carrying structure [0092] 76 resin flow medium [0093] 78 central portion of resin flow medium [0094] 79 top surface [0095] 80 first outer edge [0096] 81 bottom surface [0097] 82 second outer edge [0098] 84 concentration profile [0099] c chord length [0100] c.sub.i concentration of curing inhibitor [0101] c.sub.p concentration of curing promoter [0102] d distance [0103] d.sub.t position of maximum thickness [0104] d.sub.f position of maximum camber [0105] d.sub.p position of maximum pressure side camber [0106] E1, E2 outer edge regions [0107] f camber [0108] H horizontal direction [0109] L blade length [0110] L.sub.1 resin flow medium length [0111] LO longitudinal direction [0112] r local radius, radial distance from blade root [0113] t thickness [0114] V vertical direction [0115] Δy prebend