LIMP, ELONGATE ELEMENT WITH GLASS STAPLE FIBRES

Abstract

A rope for reinforcing joints in fibre-reinforced composite structures is described. The rope comprises chopped reinforcement fibres and retaining means for retaining the chopped fibres in a rope-shape. Further, composite structures utilising such ropes as filler elements are described as well as an apparatus for manufacturing such ropes.

Claims

1-15. (canceled)

16. A wind turbine blade comprising a composite structure made of a fibre-reinforcement material embedded in a polymer matrix and comprising a rope being embedded in the polymer matrix, wherein the rope comprises: chopped reinforcement fibres comprising glass fibres, which predominantly have a random orientation, and which have an average length between 0.5 cm and 5 cm.

17. The wind turbine blade according to claim 16, wherein ones of the chopped reinforcement fibres having the random orientation are entangled.

18. The wind turbine blade according to claim 16, further comprising retaining means for retaining the chopped reinforcement fibres in a rope shape, wherein the retaining means is an open-structured tube, and wherein the chopped fibres are retained in the open-structured tube.

19. The wind turbine blade according to claim 18, wherein the retaining means is a mesh tube.

20. The wind turbine blade according to claim 16, further comprising retaining means for retaining the chopped reinforcement fibres in a rope shape, wherein the retaining means comprises a tackifier.

21. The wind turbine blade according to claim 16, wherein the average length of the chopped reinforcement fibres is between 1 cm and 4 cm.

22. The wind turbine blade according to claim 21, wherein the average length of the chopped reinforcement fibres is about 2.5 cm.

23. The wind turbine blade according to claim 16, wherein the rope has a diameter of at least 5 mm.

24. The wind turbine blade according to claim 16, wherein the rope further comprises retaining means for retaining the chopped fibres in a rope shape.

25. The wind turbine blade according to claim 16, wherein the rope is arranged at or in a joint of the composite structure.

26. A composite structure made of a fibre-reinforcement material embedded in a polymer matrix and comprising a rope embedded in the polymer matrix, wherein the rope comprises: chopped reinforcement fibres comprising glass fibres, which predominantly have a random orientation, and which have an average length between 0.5 cm and 5 cm.

27. The composite structure according to claim 26, wherein the rope is arranged at or in a joint of the composite structure.

28. The composite structure according to claim 26, wherein ones of the chopped reinforcement fibres having the random orientation are entangled.

29. The composite structure according to claim 26, further comprising retaining means for retaining the chopped reinforcement fibres in a rope shape, wherein the retaining means is an open-structured tube, and wherein the chopped fibres are retained in the open-structured tube.

30. The composite structure according to claim 29, wherein the retaining means is a mesh tube.

31. The composite structure according to claim 26, further comprising retaining means for retaining the chopped reinforcement fibres in a rope shape, wherein the retaining means comprises a tackifier.

32. The composite structure according to claim 26, wherein the average length of the chopped reinforcement fibres is between 1 cm and 4 cm.

33. The composite structure according to claim 32, wherein the average length of the chopped reinforcement fibres is about 2.5 cm.

34. The composite structure according to claim 26, wherein the rope has a diameter of at least 5 mm.

35. The composite structure according to claim 26, wherein the rope further comprises retaining means for retaining the chopped fibres in a rope shape.

36. A method of manufacturing a composite structure of a wind turbine blade, wherein the composite structure is made of a fibre-reinforcement material embedded in a polymer matrix, the method comprising the steps of: arranging fiber-reinforcement material in a mold; arranging a rope in a joint of the composite structure, the rope comprising chopped reinforcement fibres comprising glass fibres, which predominantly have a random orientation, and which have an average length between 0.5 cm and 5 cm; infusing a liquid polymer matrix into the fiber-reinforcement material and the rope using a resin transfer molding process; and curing the liquid polymer matrix to form the composite structure of the wind turbine blade.

37. The method according to claim 36, wherein the resin transfer molding process is a vacuum assisted resin transfer molding process.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0046] The invention is explained in detail below with reference to an embodiment shown in the drawings, in which

[0047] FIG. 1 shows a wind turbine,

[0048] FIG. 2 shows a schematic view of a wind turbine blade,

[0049] FIG. 3 shows a schematic view of a cross-section of a wind turbine blade,

[0050] FIG. 4 shows a first embodiment of a filler rope according to the invention,

[0051] FIG. 5 shows a second embodiment of a filler rope according to the invention,

[0052] FIG. 6 shows a general layout of an apparatus for making filler ropes according to the invention,

[0053] FIG. 7 shows a schematic view of a first embodiment of an apparatus for making filler ropes according to the invention,

[0054] FIG. 8 shows a schematic view of a second embodiment of an apparatus for making filler ropes according to the invention,

[0055] FIG. 9 shows a cross-section of a variation of the second embodiment of the filler rope, and

[0056] FIG. 10 shows a cross-section of a third embodiment of the filler rope according to the invention.

[0057] 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 farthest from the hub 8. The rotor has a radius denoted R.

[0058] FIG. 2 shows a schematic view of a wind turbine blade 10. 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 farthest 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] The blade is typically made from a pressure side shell part 36 and a suction side shell part 38 that are glued to each other along bond lines at the leading edge 18 and the trailing edge of the blade 20.

[0063] FIG. 3 shows a schematic view of a cross section of the blade along the line I-I shown in FIG. 2. As previously mentioned, the blade 10 comprises a pressure side shell part 36 and a suction side shell part 38. The pressure side shell part 36 comprises a spar cap 41, also called a main laminate, which constitutes a load bearing part of the pressure side shell part 36. The spar cap 41 comprises a plurality of fibre layers 42 mainly comprising unidirectional fibres aligned along the longitudinal direction of the blade in order to provide stiffness to the blade. The suction side shell part 38 also comprises a spar cap 45 comprising a plurality of fibre layers 46. The pressure side shell part 38 may also comprise a sandwich core material 43 typically made of balsawood or foamed polymer and sandwiched between a number of fibre-reinforced skin layers. The sandwich core material 43 is used to provide stiffness to the shell in order to ensure that the shell substantially maintains its aerodynamic profile during rotation of the blade. Similarly, the suction side shell part 38 may also comprise a sandwich core material 47.

[0064] The spar cap 41 of the pressure side shell part 36 and the spar cap 45 of the suction side shell part 38 are connected via a first shear web 50 and a second shear web 55. The shear webs 50, 55 are in the shown embodiment shaped as I-shaped webs. However, other configurations, such as C-shaped webs may also be utilised. The first shear web 50 comprises a leg and two feet or flanges. The leg comprises a sandwich core material 51, such as balsawood or foamed polymer, covered by a number of skin layers 52. The second shear web 55 has a similar design with a leg and two flanges, the leg comprising a sandwich core material 56 covered by a number of skin layers 57. The sandwich core material 51, 56 of the two shear webs 50, 55 are chamfered near the flanges in order to transfer loads from the webs 50, 55 to the main laminates 41, 45 without the risk of failure and fractures in the joints between the leg and the feet. However, such a design will normally lead to resin rich areas in the joint areas between the legs and the flanges. Further, such resin rich area may comprise burned resin due to high exothermic peeks during the curing process of the resin, which in turn may lead to mechanical week points. Therefore, a number of filler ropes 60 comprising glass fibres are arranged at these joint areas. Further, such ropes 60 will also facilitate transferring loads from the skin layers of the leg to the flanges.

[0065] In an alternative embodiment, the ropes 60 are formed by injecting dry or tacky chopped fibres into voids at the joint during manufacture of the webs. This is particular suitable if the flanges are pre-manufactured. In such a case, dry chopped fibres may be injected in between the glass skins, after which resin is injected and filling the void and chopped fibres.

[0066] The blade shells 36, 38 may comprise further fibre-reinforcement at the leading edge and the trailing edge. Typically, the shell parts 36, 38 are bonded to each other via glue flanges in which additional filler ropes may be used (not shown). Additionally, very long blades may comprise sectional parts with additional spar caps, which are connected via one or more additional shear webs, which may necessitate even more use of filler ropes. Further, the filler ropes may also be used in add-ons or retrofitted parts on the blades, such as surface mounted spoilers, e.g. T- or L-shaped, flaps or the like.

[0067] Prior art wind turbine blades utilise filler ropes comprising unidirectional glass fibres or twisted glass fibres. However, the glass fibres are densely packed in such ropes, and investigations have revealed that the use of the ropes may lead to dry reinforcement fibres in the centre of the rope. This in turn may also lead to mechanical weak points. The investigation has shown that the dry areas may occur even for relatively small diameter ropes, such as ropes having a diameter of approximately 6 mm. Additionally, such ropes only provide stiffness in the longitudinal direction of the blade, whereas it is the transverse strength that is of importance in order to increase the capacity of the joint. With the prior art ropes the transverse strength of the infused rope is given only by the strength of the resin used.

[0068] The present invention overcomes these problems by providing a rope comprising chopped reinforcement fibres. A first embodiment of a rope 160 according to the invention is depicted in FIG. 4. The filler rope 60 comprises chopped reinforcement fibres 162 contained in retaining means in form of a mesh tube 164. The chopped reinforcement fibres 162 have a random orientation, whereby the fibres are not as densely packed. Therefore, the ropes 162 with chopped fibres facilitate openings from the circumference of the rope to the core of the rope and ensure proper wetting through the entire rope, when used in an infusion process for manufacturing the wind turbine blade 10 or another composite structure. Further, the randomly oriented chopped fibres 162 will ensure that at least a number of the fibres 162 are oriented with a component in the transverse direction. Accordingly, the chopped fibres 162 contribute to the transverse strength and increase the capacity of the joint in which the filler rope 160 is used as filler material.

[0069] The chopped reinforcement fibres 162 are advantageously made of the glass fibres or the same type of reinforcement fibres that the rest of the composite structure is made of. The chopped reinforcement fibres advantageously have an average length of 25 mm, which has proven to provide a sufficient random orientation of the chopped reinforcement fibres 162 to ensure proper wetting and providing transverse strength to a joint in which the rope 160 is used as filler material.

[0070] The mesh tube 164 surrounding the chopped fibres 162 is advantageously made of a polymer material. The polymer material may be dissolvable in resin to that the mesh in the infusion process dissolves and becomes part of the matrix material of the final composite structure. The mask size of the mesh tube 164 may be of any desired size, but should in general be large enough for resin to penetrate and for the chopped fibres to protrude through, and small enough to ensure that the chopped fibres 162 are retained within the mesh tube 164.

[0071] FIG. 5 shows a second embodiment of a filler rope 260 according to the invention. In this embodiment chopped reinforcement fibres 262 are attached to or wrapped around a retaining means in form of a core fibre or filament 264. In addition, a tackifying material may be applied to the chopped reinforcement fibres 262 to ensure that they are retained on the core filament 264. The filler rope may also comprise further flexible core elements as shown in FIG. 9. The core filaments may be stitched, twisted or woven so that the resin is able to enter the core for a full wet out during infusion. The chopped reinforcement fibres may be stitched, wrapped or woven together with the core filaments, so as to provide a “fluffy” rope as shown in FIG. 9.

[0072] In yet another embodiment, not shown in the figures, the filler rope comprises a retaining means in form of a tackifier only. The tackifier ensures that the chopped fibres are retained in the desired rope shape. It is also possible to use a combination of a tackifier and a mesh tube as retaining means.

[0073] There are various ways to manufacture a filler rope according to the invention. An apparatus 70 for manufacturing such a filler rope generally comprises a chopping device 75, a filling device 80, and a rope shaping device 90 as shown very schematically in FIG. 6. The chopping device 75 (or chopper) cuts or chops reinforcement fibres into chopped reinforcement fibres of a predetermined length or length interval. The filling device 80 is adapted to receive the chopped fibres from the chopper 75 and feeding the chopped fibres to the rope forming device 90. The rope forming device 90 shapes the rope and provides retaining means to the chopped fibres so as to ensure that the chopped fibres stay in the desired rope shape. In principle, the chopping device may be omitted from the apparatus, if chopped fibres can be purchased or otherwise produced separately. In this case, the chopped fibres are simply fed to the filling device.

[0074] FIG. 7 shows an embodiment of an apparatus 170 according to the invention for manufacturing filler ropes 160 according to the first embodiment shown in FIG. 4. The apparatus 170 comprises a chopping device, which comprises an inlet in form of a funnel 176 in which blades, knifes, a grinder or the like (not shown) are arranged. Long reinforcement fibres 177, e.g. from fibre mats or unidirectional fibre ropes, are fed into the funnel 176, and the long fibres 177 are chopped into fibres of a predetermined length interval, e.g. around 25 mm. It is also possible to use excess glass from the layup procedure for manufacturing the wind turbine blade. It is also possible to use scrapped glass from an erroneous manufacture of a composite structure, in particular if the cured resin can be removed from the scrapped glass.

[0075] The chopped fibres are fed into a filling device 180. The filling device 180 may for instance comprise a compactor device 181, e.g. in form of a screw compactor. The chopped fibres are pushed forward in a tubular structure by the screw compactor 181. The tubular structure may comprise a tapered part 182 to further compact the chopped fibres and compress the chopped fibres to the desired rope diameter. In general, the chopped fibres have a random orientation from the chopping and compression of the chopped fibres. However, the filling device 180 may additionally comprise a mouthpiece or a nozzle 183 for facilitating further randomness to the orientation of the chopped fibres. The mouthpiece 183 may for instance be rotating in order to ensure that the chopped fibres obtain different orientations.

[0076] The rope shaping device comprises a braiding machine 191 that braids polymer fibres or threads into a mesh tube surrounding the chopped fibres, thus forming the filler rope 160. The apparatus may further comprise a pulling device to continuously pull the rope, and may additionally comprise a winding machine for winding the rope onto a roll.

[0077] FIG. 8 shows a second embodiment of an apparatus 270 for manufacturing a filler rope according to the present invention, wherein like reference numerals refer to like parts of the embodiment shown in FIG. 7. Therefore, only the differences between the two embodiments will be described. In this embodiment, the rope shaping device of the apparatus 270 comprises a tackifier bath or resin bath. The chopped fibres are pushed through the bath, e.g. in an open structured tube. The tackifier ensures that the chopped fibres are retained in the rope shape 360.

[0078] However, a filler rope utilising a tackifier as retaining means may also be manufactured in a much simpler way. The tackifier may simply be applied to the chopped fibres before they are compacted into the rope shape. The tackifier will make the chopped fibres adhere to each other and still be able to flex and compact in order to form the rope with randomly oriented chopped fibres. The tackifier may for instance be a thermoplastic resin. It is sufficient to provide 1% by volume of the finished rope so that the tackifier is dispersed through the rope as shown in FIG. 10 with white dots. According to an advantageous embodiment, the tackifier may fill 0.5-10% or 0.5-5% by volume of the finished rope. According to another embodiment, not shown, the randomly oriented chopped reinforcement fibres are entangled or entwined so that they maintain the rope shape. This entanglement is obtained through the randomly oriented chopped fibres and not through twisting or the like.

[0079] The invention has been described with reference to advantageous embodiments. However, the scope of the invention is not limited to the described embodiment and alterations and modifications may be carried out without deviating from the scope of the invention. The invention has for instance been described in relation to a wind turbine blade comprising a load carrying structure integrated in the blade shell. However, the filler ropes according to the invention may also be applied to wind turbine blades comprising a central beam or spar as the load carrying structure with an aerodynamic shell bonded to the beam. The filled ropes may also be applied in other composite structures, where filler ropes are relevant.

TABLE-US-00001 List of reference numerals 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 36 pressure side shell 38 suction side shell 40 shoulder 41 main laminate / spar cap of pressure side 42 fibre layers 43 sandwich core material 45 main laminate / spar cap of suction side 46 fibre layers 47 sandwich core material 50 first shear web 51 sandwich core material of first shear web 52 skin layer(s) 55 second shear web 56 sandwich core material of second shear web 57 skin layer(s) 60, 160, 260, 360 filler rope(s) 162, 262 chopped reinforcement fibres 164, 264 retaining means 70 apparatus for manufacturing ropes 75 chopping device 80, 180, 280 filling device 90 rope forming device 176, 276 feeding chute 177, 277 long fibres 181, 281 compactor device / screw compactor 182, 282 tapered part 183,283 mouthpiece / nozzle 191 braiding machine 291 tackifier bath