METHOD OF MOLDING A SHELL PART OF A WIND TURBINE BLADE

Abstract

The present invention relates to a method of molding a shell part of a wind turbine blade comprising the steps of providing a mold (64) comprising a mold cavity (66) with a root end (68) and an opposing tip end (70), arranging one or more preformed sheets (72a, 72b, 72c) in the mold cavity (66), wherein each preformed sheet comprises a mixture of fibre rovings (82) and a binding agent, wherein the fibre rovings are at least partially joined together by means of the binding agent, and injecting the one or more preformed sheets (72a, 72b, 72c) with a resin to mold the shell part. The present invention also relates to a shell part of a wind turbine blade obtainable by said method, to a preformed sheet for use in said method and to a method of manufacturing said preformed sheet.

Claims

1. A method of molding a shell part of a wind turbine blade, the blade (10) having a profiled contour including a pressure side and a suction side, and a leading edge (18) and a trailing edge (20) with a chord having a chord length extending therebetween, the wind turbine blade (10) extending in a spanwise direction between a root end (16) and a tip end (14), said method comprising: providing a mold (64) comprising a mold cavity (66) with a root end (68) and an opposing tip end (70), arranging one or more preformed sheets (72a, 72b, 72c) in the mold cavity (66), wherein each preformed sheet comprises a mixture of fibre rovings (82) and a binding agent, wherein the fibre rovings are at least partially joined together by means of the binding agent, and injecting the one or more preformed sheets (72a, 72b, 72c) with a resin to mold the shell part.

2. A method according to claim 1, wherein at least two or more preformed sheets (72a, 72b, 72c) are arranged in the mold cavity (66).

3. A method according to claim 1, wherein each preformed sheet further comprises at least one fabric.

4. A method according to claim 1, wherein the binding agent is present in an amount of 0.1-15 wt %, preferably 0.5-5 wt %, relative to the weight of the fibre rovings.

5. A method according to claim 1, wherein the melting point of the binding agent is between 40 and 220 C., preferably between 40 and 160 C.

6. A method according to claim 1, wherein the preformed sheets have an elastic modulus (Young's modulus) of between 0.01 and 100 GPa, preferably between 0.01 and 45 GPa.

7. A method according to, wherein the binding agent comprises a polyester, preferably a bisphenolic polyester.

8. A method according to claim 1, wherein the preformed sheets (72a, 72b, 72c) are arranged in the mold cavity (66) such that a longitudinally extending lateral edge (76a) of at least one preformed sheet abuts a longitudinally extending lateral edge of an adjacent preformed sheet (76b).

9. A method according to claim 1, wherein the preformed sheets are arranged in the mold cavity (66) such that a longitudinally extending lateral edge (76a) of at least one preformed sheet (72a) overlaps with an adjacent preformed sheet (72b).

10. A method according to claim 1, wherein each preformed sheet has a length (Ls), width (Ws) and thickness (Ts), wherein its length-width ratio is at least 5:1.

11. A method according to claim 1, wherein each of the preformed sheets further comprises a top fibre mat (86) and a bottom fibre mat (84) in between which the fibre rovings are arranged.

12. A method according to claim 1, wherein the length (Ls) of each preformed sheet is at least 15 m, preferably at least 20 m.

13. A method according to claim 1, wherein the thickness (Ts) of at least one preformed sheet (72) decreases from its front edge (88) to its back edge (90) of said sheet as seen in its longitudinal direction (74a).

14. A method according to claim 1, wherein the preformed sheets (72a, 72b, 72c) are arranged in the mold cavity such that the angle () between the horizontal plane and a line that is tangential to the vertex of a curved bottom surface (73) of a preformed sheet (72) is different for each preformed sheet.

15. A method according to claim 1, wherein at least one preformed sheet (72) is arranged in the mold cavity such that the angle () between the horizontal plane and a line (79) that is tangential to the vertex of a curved bottom surface (73) of said preformed sheet (72) is more than 45, preferably more than 60.

16. A shell part of a wind turbine blade obtainable by the method of claim 1.

17. A preformed sheet (72) for use in a method according to claim 1, the preformed sheet comprising fibre rovings (82) and a binding agent, wherein the fibre rovings (82) are at least partially joined together by means of the binding agent, and wherein the binding agent is present in an amount of 0.1-15 wt % relative to the weight of the fibre rovings.

18. A method of manufacturing a preformed sheet (72) according to claim 17 comprising the steps of contacting fibre rovings with a binding agent, and subsequently heating the fibre rovings and the binding agent for forming the preformed sheet.

19. A method according to claim 18, wherein the mixture of the fibre rovings and the binding agent is laid in preform mold (80), followed by heating the laid up fibre rovings (82) and binding agent for forming the preformed sheet (72).

20. A method according to claim 18, wherein the preform mold (80) has a curved mold cavity (81), wherein the ratio of the width (Wm) and the maximum height (H) of the curved mold cavity is 10:1 or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0059] The invention is explained in detail below with reference to embodiments shown in the drawings, in which

[0060] FIG. 1 shows a wind turbine,

[0061] FIG. 2 shows a schematic view of a wind turbine blade,

[0062] FIG. 3 shows a schematic view of an airfoil profile through section I-I of FIG. 4,

[0063] FIG. 4 shows a schematic view of the wind turbine blade, seen from above and from the side,

[0064] FIG. 5 is a perspective drawing of a mold for manufacturing a shell part of a wind turbine blade using the method of the present invention,

[0065] FIG. 6 is a front view of a mold for manufacturing a shell part of a wind turbine blade using one embodiment of the present invention,

[0066] FIG. 7 is a front view of a mold for manufacturing a shell part of a wind turbine blade using another embodiment of the present invention,

[0067] FIG. 8 is a perspective drawing of a mold for manufacturing a shell part of a wind turbine blade using another embodiment of the method of the present invention,

[0068] FIG. 9 is a schematic drawing of a method for manufacturing the preformed sheet of the present invention,

[0069] FIG. 10 is a perspective drawing of a mold for manufacturing the preformed sheet of the present invention,

[0070] FIG. 11 is a cross-sectional view of the mold of FIG. 8, and

[0071] FIG. 12 is a perspective view of one embodiment of a preformed sheet according to the present invention.

DETAILED DESCRIPTION

[0072] 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. The rotor has a radius denoted R.

[0073] 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.

[0074] 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.

[0075] 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.

[0076] 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.

[0077] FIGS. 3 and 4 depict parameters which are used to explain the geometry of the wind turbine blade according to the invention.

[0078] 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 usei.e. during rotation of the rotornormally 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.

[0079] 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.

[0080] 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.

[0081] 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 y, which corresponds to the out of plane deflection from a pitch axis 22 of the blade.

[0082] FIG. 5 illustrates a mold 64 comprising a mold cavity 66 for molding a shell part of a wind turbine blade. The mold cavity has a root end 68 and an opposing tip end 70 corresponding to the respective root and tip ends of the blade to be manufactured. In the embodiment shown in FIG. 5, three preformed sheets 72a, 72b, 72c are arranged in the mold cavity 66 for subsequent infusion with a resin to mold the shell part, e.g. by Vacuum Assisted Resin Transfer Molding. The respective longitudinal axes 74a, 74b, 74c of the preformed sheets 72a, 72b, 72c are arranged such that they are aligned substantially parallel to each other. A different embodiment of the method is illustrated in FIG. 8. Here, only one preformed sheet 72 is arranged in the mold cavity 66, acting as a main laminate extending along substantially the entire blade length.

[0083] As best seen in the root end front view of FIG. 6, the preformed sheets 72a, 72b, 72c are arranged such that a longitudinally extending lateral edge 76a of each preformed sheet abuts a longitudinally extending lateral edge 76b of an adjacent preformed sheet (as exemplified for sheets 72a and 72b). The sheets 72a, 72b, 72c are then joined together in the subsequent resin infusion step, optionally after laying a vacuum foil 78 as the topmost layer.

[0084] In an alternative embodiment shown in the root end front view of FIG. 7, the preformed sheets 72a, 72b, 72c are arranged such in the mold 64 that a longitudinally extending lateral edge 76a, 76b of each preformed sheet 72a, 72b, 72c overlaps with an adjacent preformed sheet. Again, the sheets 72a, 72b, 72c are subsequently joined together in by resin infusion and curing (vacuum foil not shown). FIG. 7 also shows that at least the preformed sheet 74c is arranged in the mold cavity such that the angle a between the horizontal plane 83 and a line 79 that is tangential to the vertex of a curved surface of the sheet exceeds 45.

[0085] FIG. 9 illustrates a possible manufacturing method for a preformed sheet 72 of the present invention, in particular one that can be used as main laminate. Herein, the fibre rovings 82 and binding agent are sandwiched between a number of fabrics, or top and bottom mats 84, 86, heated in a heating station 92, and subsequently laminated in a lamination station 94 to produce the preformed sheet 72.

[0086] FIG. 10 shows a schematic drawing of another embodiment of a preformed sheet 72 as molded in a substantially horizontally oriented preform mold 80. The sheet 72 has a length Ls, a thickness Ts, and a width Ws. It is formed by sandwiching a plurality of fibre rovings 82 in between a bottom fibre mat 84 and a top fibre mat 86. This could be done by laying a mixture of fibre rovings 82 and a thermoplastic binding agent on top of the bottom fibre mat 84, covering the rovings 82 with the top fibre mat 86, followed by heating to form the preformed sheet. As best seen in FIGS. 8 and 10, the preformed sheet 72 has a longitudinally extending lateral edge 76 extending in between a top surface 71 and a bottom surface 73 of the sheet 72.

[0087] The cross-sectional view of FIG. 11 shows some dimensions of the preform mold 80. It has a curved mold cavity 80 with a width Wm and a maximum height H, wherein the width Wm and maximum height H have a ratio of 10:1 or more.

[0088] FIG. 12 shows another embodiment of a preformed sheet 72 according to the present invention. Here, the thickness of the preformed sheet 72 decreases from its front edge 88 to its back edge 90 as seen in its longitudinal direction. Typically, the front edge 88 with the higher thickness will be located at the root end of the blade mold cavity when laying the preformed sheets, while the back edge 90 with the lower thickness will be closer to the tip end of the mold cavity.

[0089] The invention is not limited to the embodiments described herein, and may be modified or adapted without departing from the scope of the present invention.

LIST OF REFERENCE NUMERALS

[0090] 2 wind turbine [0091] 4 tower [0092] 6 nacelle [0093] 8 hub [0094] 10 blade [0095] 14 blade tip [0096] 16 blade root [0097] 18 leading edge [0098] 20 trailing edge [0099] 22 pitch axis [0100] 30 root region [0101] 32 transition region [0102] 34 airfoil region [0103] 40 shoulder/position of maximum chord [0104] 50 airfoil profile [0105] 52 pressure side [0106] 54 suction side [0107] 56 leading edge [0108] 58 trailing edge [0109] 60 chord [0110] 62 camber line/median line [0111] 64 mold [0112] 66 mold cavity [0113] 68 root end of mold cavity [0114] 70 tip end of mold cavity [0115] 71 top surface of preformed sheet [0116] 72 preformed sheet [0117] 73 bottom surface of preformed sheet [0118] 74 longitudinal axis of sheet [0119] 76 lateral edge of sheet [0120] 78 vacuum foil [0121] 79 tangent to vertex [0122] 80 preform mold [0123] 81 mold cavity of preform mold [0124] 82 fibre rovings [0125] 83 horizontal plane [0126] 84 bottom fibre mat [0127] 86 top fibre mat [0128] 88 front edge of sheet [0129] 90 back edge of sheet [0130] 92 heating station [0131] 94 lamination station [0132] c chord length [0133] d.sub.t position of maximum thickness [0134] d.sub.f position of maximum camber [0135] d.sub.p position of maximum pressure side camber [0136] f camber [0137] L blade length [0138] r local radius, radial distance from blade root [0139] t thickness [0140] y prebend [0141] Ls length of sheet [0142] Ws width of sheet [0143] Ts thickness of sheet [0144] H height of preform mold cavity

[0145] Wm width of preform mold cavity