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 wind turbine 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), wherein the shell part comprises a shell half, said method comprising: providing a mold (64) comprising a mold cavity (66) with a root end (68) and an opposing tip end (70), said mold cavity (66) having a semicircular cross-section at the root end (68); arranging a plurality of preformed sheets (72a, 72b, 72c) in the mold cavity (66), the plurality of preformed sheets (72a, 72b, 72c) each extending in the mold cavity (66) from the root end (68) towards the opposing tip end (70), wherein each of the preformed sheets comprises a mixture of fibre rovings (82) and a binding agent, wherein the fibre rovings are at least partially joined together by the binding agent, wherein the plurality of preformed sheets (72a, 72b, 72c) are arranged in the mold cavity (66) such that a longitudinally extending lateral edge (76a) of each of the preformed sheets (72a) abuts a longitudinally extending lateral edge (76b) of an adjacent one of the preformed sheets, or such that the longitudinally extending lateral edge (76a) of each of the preformed sheets overlaps an adjacent one of the preformed sheets (72b), each of the preformed sheets having a length (Ls) of at least 15 m, wherein the plurality of preformed sheets comprises at least three of the preformed sheets, and wherein each of the preformed sheets is positioned circumferentially adjacent and contiguous with respect to the adjacent ones of the plurality of preformed sheets; and injecting the plurality of preformed sheets (72a, 72b, 72c) with a resin to mold the shell part of the wind turbine blade.

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

3. The method according to claim 1, wherein each of the preformed sheets further comprises at least one fabric.

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

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

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

7. The method according to claim 1, wherein the binding agent comprises a polyester.

8. The method according to claim 1, wherein each of the preformed sheets has a width (Ws) and thickness (Ts), wherein a length-width ratio of each of the preformed sheets is at least 5:1.

9. The 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 roving s are arranged.

10. The method according to claim 1, wherein the length (Ls) of each of the preformed sheets is at least 20 m.

11. The method according to claim 1, wherein a thickness (Ts) of at least one of the preformed sheets (72) decreases from a front edge (88) thereof to a back edge (90) thereof along a longitudinal direction (74a).

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

13. The method according to claim 4, wherein the binding agent is present in an amount of 0.5-5 wt % relative to the weight of the fibre rovings.

14. The method according to claim 5, wherein the melting point of the binding agent is between between 40° C. and 160° C.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The invention is explained in detail below with reference to embodiments shown in the drawings, in which

(2) FIG. 1 shows a wind turbine,

(3) FIG. 2 shows a schematic view of a wind turbine blade,

(4) FIG. 3 shows a schematic view of an airfoil profile through section I-I of FIG. 4,

(5) FIG. 4 shows a schematic view of the wind turbine blade, seen from above and from the side,

(6) 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,

(7) 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,

(8) 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,

(9) 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,

(10) FIG. 9 is a schematic drawing of a method for manufacturing the preformed sheet of the present invention,

(11) FIG. 10 is a perspective drawing of a mold for manufacturing the preformed sheet of the present invention,

(12) FIG. 11 is a cross-sectional view of the mold of FIG. 8, and

(13) FIG. 12 is a perspective view of one embodiment of a preformed sheet according to the present invention.

DETAILED DESCRIPTION

(14) 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.

(15) 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.

(16) 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.

(17) 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.

(18) 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.

(19) FIGS. 3 and 4 depict parameters which are used to explain the geometry of the wind turbine blade according to the invention.

(20) 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.

(21) 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.

(22) 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.

(23) 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.

(24) 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.

(25) 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.

(26) 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 α between the horizontal plane 83 and a line 79 that is tangential to the vertex of a curved surface of the sheet exceeds 45°.

(27) 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.

(28) 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.

(29) 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.

(30) 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.

(31) 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

(32) 2 wind turbine 4 tower 6 nacelle 8 hub 10 blade 14 blade tip 16 blade root 18 leading edge 20 trailing edge 22 pitch axis 30 root region 32 transition region 34 airfoil region 40 shoulder/position of maximum chord 50 airfoil profile 52 pressure side 54 suction side 56 leading edge 58 trailing edge 60 chord 62 camber line/median line 64 mold 66 mold cavity 68 root end of mold cavity 70 tip end of mold cavity 71 top surface of preformed sheet 72 preformed sheet 73 bottom surface of preformed sheet 74 longitudinal axis of sheet 76 lateral edge of sheet 78 vacuum foil 79 tangent to vertex 80 preform mold 81 mold cavity of preform mold 82 fibre rovings 83 horizontal plane 84 bottom fibre mat 86 top fibre mat 88 front edge of sheet 90 back edge of sheet 92 heating station 94 lamination station c chord length d.sub.t position of maximum thickness d.sub.f position of maximum camber d.sub.p position of maximum pressure side camber f camber L blade length r local radius, radial distance from blade root t thickness Δy prebend Ls length of sheet Ws width of sheet Ts thickness of sheet H height of preform mold cavity

(33) Wm width of preform mold cavity