Method of manufacturing at least two preforms for moulding a wind turbine blade

Abstract

The present invention relates to a method and a mould system (66) for manufacturing at least two preforms for moulding a wind turbine blade. The preforms include at least one preform of a first shape and at least one preform of a second shape. The preform mould structure (68) has a moulding surface (70) of variable shape such that the shape of the moulding surface (70) can be varied at least between a first and a second configuration by using actuators.

Claims

1. A method of manufacturing at least two preforms for moulding a wind turbine blade, the at least two preforms including at least one preform having a first shape and at least one preform having a second shape, the second shape being different from the first shape, the method comprising the steps of: providing a preform mould structure (68) having a moulding surface (70) of variable shape such that the shape of the moulding surface (70) can be varied at least between a first and a second configuration, wherein the first configuration and the second configuration have different curvatures of the moulding surface (70) in a longitudinal direction of the moulding surface (70); providing at least one actuator (72) for changing the shape of the moulding surface (70) between the first and the second configuration; moulding at least one preform for an upwind blade half having the first shape on the moulding surface (70) having the first configuration; and moulding at least one preform for a downwind blade half having the second shape on the moulding surface (70) having the second configuration, wherein the upwind blade half and the downwind blade half correspond to the same wind turbine blade, and wherein the step of moulding the at least one preform for the upwind blade half and the step of moulding the at least one preform for the downwind blade half are both performed using preform mould structure (68).

2. The method according to claim 1, wherein the shape of the moulding surface can be varied across the entire moulding surface.

3. The method according to claim 1, wherein the first and the second configuration differ in terms of the curvature of the moulding surface (70).

4. The method according to claim 1, wherein the first and the second configuration do not differ in terms of the curvature of the moulding surface (70) in the transverse direction of the moulding surface (70).

5. The method according to claim 1, wherein the preform is for use in a main laminate portion of the wind turbine blade.

6. The method according to claim 1, wherein the moulding surface (70) can be varied between a concave shape and a convex shape.

7. The method according to claim 1, wherein the moulding steps comprises laying a fibre material and a binding agent onto the moulding surface (70).

8. The method according to claim 1, wherein the moulding surface (70) is provided on one or more bendable sheets (68).

9. The method according to claim 8, wherein the one or more bendable sheets (68) comprise one or more bendable steel sheets.

10. The method according to claim 1, wherein the moulding surface (70) is provided on a single bendable sheet, and wherein one actuator is provided at a front end of the sheet and one actuator is provided at a rear end of the sheet.

11. The method according to claim 1, wherein the moulding surface (70) is provided on two or more bendable sheets (68a, 68b, 68c), wherein adjacent sheets are hingedly interconnected along their longitudinal edges (84), and wherein one actuator (72) is provided at a front end of each sheet and one actuator (72) is provided at a rear end of each sheet.

12. The method according to claim 11, wherein the sheets are hingedly interconnected by one or more elastic strips provided in between adjacent sheets.

13. The method according to claim 1, the method comprises providing at least three actuators (72) for changing the shape of the moulding surface between the first and the second configuration.

14. A method of manufacturing a wind turbine blade, the method comprising the steps of: manufacturing respective preforms for moulding an upwind blade half and a downwind blade half according to the method of claim 1, wherein the same preform mould is used for at least one preform for the upwind blade half and for the downwind blade half, respectively; arranging the preforms in respective upwind blade moulds and downwind blade moulds, optionally together with additional material; infusing resin into the respective upwind blade moulds and downwind blade moulds containing the preforms; curing or hardening the resin in order to form an upwind blade half and downwind blade half; and joining the upwind blade half and the downwind blade half to form a wind turbine blade.

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 schematic side view of a preform mould structure of the present invention having a moulding surface in first configuration,

(7) FIG. 6 is a schematic side view of a preform mould structure of the present invention having a moulding surface in second configuration,

(8) FIG. 7 is a perspective view of one embodiment of a preform mould structure according to the present invention,

(9) FIG. 8 is a perspective view of another embodiment of a preform mould structure according to the present invention,

(10) FIG. 9 is a perspective view of a moulding system for manufacturing a preform according to the present invention,

(11) FIG. 10 is a perspective view of a moulding system according to another embodiment of the present invention,

(12) FIG. 11 is a side view of a moulding system for manufacturing a preform according to the present invention, and

(13) FIG. 12 is a perspective view showing a mould for moulding an upwind blade half and a mould for moulding a downwind blade half 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.

(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. 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.

(20) 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.

(21) 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.

(22) FIG. 5 illustrates a side view of a mould system 66 according to the present invention for manufacturing a preform for moulding a wind turbine blade. The system 66 comprises a preform mould structure 68, comprising a bendable sheet, having a curved moulding surface 70 of a substantially convex shape corresponding to a first configuration of the moulding surface 70. The moulding surface 70 can be provided as part of a bendable sheet, such as a bendable steel sheet, or it could be fixed to the same. The preform mould structure 68 also has an opposing bottom surface 71. In the embodiment shown in FIG. 5 the mould structure is supported by several actuators 72a-f. Each actuator comprises a fixed hollow cylinder 74 and a movable rod 76, which is movable with respect to the fixed part 74, connecting to the mould structure 68. The actuators may be supported directly on a ground surface 78 or via a suitable floor plate.

(23) As shown in FIG. 6, the moulding surface 70 can be changed to a substantially concave shape corresponding to a second configuration of the moulding surface 70. This is achieved by way of the actuators 72a-f which can change the shape of the mould structure 68 via their respective movable rods 76, which can be extended or retracted as needed. The first and the second configuration differ in terms of the curvature of the moulding surface 70 in the longitudinal direction L of the moulding surface 70, as indicated by the dashed line in FIG. 7. Thus, the preforms manufactured using the mould system of the present invention can be used both for an upwind blade half and for a downwind blade half, using the same preform mould. FIG. 12 shows a mould 224 for moulding an upwind blade half and a mould 226 for moulding a downwind blade half. The preforms may be arranged in the moulds 224, 226, optionally together with additional material.

(24) FIG. 7 is a perspective drawing of a mould system 66 according to the present invention. The system has a mould structure 68 having a moulding surface 70, which is shown in a substantially plane configuration. The mould structure 68 which here takes the form of a bendable sheet 68 is supported by a number of actuators 72a-d. Each actuator comprises a fixed hollow cylinder 74 and a movable rod 76, which is movable with respect to the fixed part 74, connecting to the mould structure 68, preferably through a connecting element 80, which is wedge-shaped in the illustrated embodiment. FIG. 7 also shows the longitudinal direction L and the transverse direction T of the moulding surface 70, and a longitudinal edge 84 of the sheet 68.

(25) FIG. 8 shows a perspective view of another embodiment of the mould system 66 of the present invention. Here, the moulding surface 70a-c is provided on three bendable sheets 68a-c, wherein adjacent sheets are hingedly interconnected along their longitudinal edges by respective elastic strips 82a, 82b. One actuator 72a, 72a′, 72 a″ is provided at a front end 86 of each sheet and one actuator 72g is provided at a rear end 88 of each sheet (only shown for sheet 68 c), with multiple actuators 72b-f installed in between. Thus, the curvature of the moulding surface can be varied both in the longitudinal direction L and in the transverse direction T of the moulding surface.

(26) FIG. 9 is an exploded perspective view illustrating one embodiment of a moulding system 100 for manufacturing a preform for a wind turbine blade according to another aspect of the present invention. The moulding system 100 comprises a mould structure 102 having the form of a frame or cassette, comprising an at least partly perforated sheet 104, the sheet comprising a moulding surface 106 for moulding a preform. In the illustrated embodiment, the perforations or holes are shown as substantially circular. The mould structure 102 is received in a table 110 for receiving and fixing the mould structure. The table comprises an air inlet 112.

(27) In the embodiment shown in FIG. 9, the sheet is only partially perforated, i.e. in a centre section 105. By contrast, the sheet 104 and moulding surface 106 of the embodiment shown in FIG. 10 (assembled view) are completely perforated. In the embodiment shown in FIG. 9, the moulding surface 106 is a convex surface. By contrast, in the embodiment shown in FIG. 10, the moulding surface 106 is a concave surface.

(28) As seen in the side view of FIG. 11, the moulding system 100 of FIGS. 9-11 also comprises airflow generation means 108, which may take the form of a fan or air pump, for inducing airflow to pass through the perforated sheet 104 towards the moulding surface 106. The air, preferably hot air, can be transported to the moulding surface 106 through a conduit 114 and through the air inlet 112 of the table 110. When manufacturing preforms, a fibre material and a binding agent are arranged on the moulding surface 106. Subsequently, an airflow having a temperature of between 40 and 200° C. is passed through the perforated sheet 104 towards the moulding surface 106 containing the fibre material and the binding agent.

(29) 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

(30) 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 66 mould system 68 preform mould structure 70 moulding surface 71 bottom surface of sheet 72 actuator 74 hollow cylinder 76 movable rod 78 ground surface 80 connection element 82 elastic strip 84 longitudinal edge of sheet 86 front end ofsheet 88 rearend ofsheet 100 moulding system 102 mould structure 104 (partly) perforated sheet 105 perforated center section 106 moulding surface 108 airflow generation means 110 table 112 air inlet 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