Abstract
A method for manufacturing a composite structure (24), such as an epoxy composite structure, is disclosed Layers of fibre mats (13) are arranged in a mould (18), the fibre mats (13) comprising oriented fibres. A resin is infused in the layers of fibre mats (13), and the resin is cured to form the composite structure (24). The fibre mats (13) are recycled fibre mats (13), e.g. retrieved from an original composite structure, such as a wind turbine blade (6).
Claims
1. A method for manufacturing a composite structure, the method comprising: arranging layers of fibre mats in a mould, the fibre mats comprising oriented fibres, infusing a resin in the layers of fibre mats, and curing the resin to form the composite structure, wherein the fibre mats are recycled fibre mats.
2. The method according to claim 1, further comprising selecting the recycled fibre mats from a pool of recycled fibre mats.
3. The method according to claim 2, further comprising categorising the recycled fibre mats of the pool of recycled fibre mats based on quality of the recycled fibre mats, and wherein the step of selecting the recycled fibre mats includes taking the categorisation of the fibre mats into account.
4. The method according to claim 2, further comprising categorising the recycled fibre mats of the pool of recycled fibre mats based on fibre orientation and/or dimensions/shape of the recycled fibre mats, and wherein the step of arranging layers of fibre mats in a mould includes optimizing orientation of fibre mats so as to provide anisotropic properties of the composite structure.
5. The method according to claim 3, wherein categorising the recycled fibre mats is performed at least partly by means of automated visual inspection.
6. The method according to claim 1, wherein arranging layers of fibre mats in a mould comprises arranging at least some of the recycled fibre mats of a given layer side by side with overlapping edge sections, preferably a width of the overlapping edge sections is above a first threshold value, such as at least 1 cm and/or the width of the overlapping edge sections is below a second threshold value, such a below 20% of a width the recycled fibre mats arranged side by side with overlapping edge sections.
7. The method according to claim 1, wherein the recycled fibre mats comprise oriented glass fibres and/or oriented carbon fibres.
8. The method according to claim 1, further comprising arranging at least one layer of core material along with the layers of fibre mats in the mould, prior to the step of infusing a resin in the layers of fibre mats.
9. The method according to claim 1, further comprising the step of adjusting a shape and/or a size of at least one of the recycled fibre mats prior to or after arranging the at least one of the recycled fibre mats in the mould.
10. The method according to claim 1, further comprising chemically and/or mechanically cleaning at least one of the recycled fibre mats prior to arranging the recycled fibre mats in the mould.
11. The method according to claim 1, further comprising the step of providing a sizing and/or a primer to at least one of the recycled fibre mats prior to or after arranging the at least one of the fibre mats in the mould.
12. The method according to claim 1, wherein the mould is generally flat.
13. The method according to claim 1, wherein the fibre mats are of standardized size and/or shape having dimensions of less than 25 cmless than 25 cm and the layer of fibre mats are formed by randomly arranging a plurality of the fibre mats.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0044] The invention will now be described in further detail with reference to the accompanying drawings in which
[0045] FIG. 1 is a perspective view of a wind turbine,
[0046] FIGS. 2 and 3 illustrate a wind turbine blade to be processed for recycling,
[0047] FIGS. 4-7 illustrate steps of a method for retrieving a recycled fibre mat from a composite structure,
[0048] FIG. 8 illustrates steps of an alternative method for retrieving a recycled fibre mat from a composite structure,
[0049] FIGS. 9-15 illustrate method steps of a method for manufacturing a composite structure according to an embodiment of the invention, and
[0050] FIG. 16 shows a composite structure having been manufactured in accordance with a method according to an embodiment of the invention.
[0051] FIG. 17 shows another composite structure having been manufactured in accordance with a method according to an embodiment of the invention.
DETAILED DESCRIPTION OF THE DRAWINGS
[0052] FIG. 1 is a perspective view of a wind turbine 1 comprising a tower 2 and a nacelle 3 mounted on top of the tower 2. A rotor 4 with a hub 5 carrying three wind turbine blades 6 is mounted rotatably on the nacelle 3. Accordingly, wind acting on the wind turbine blades 6 causes the rotor 4 to rotate, and the mechanical energy is transformed into electrical energy by means of a generator (not shown), in a manner which is known per se.
[0053] When the wind turbine 1, or one or more components of the wind turbine 1, has reached its end of life, it will be decommissioned. To this end, it is desirable to recycle the material of the various components to the greatest possible extent. In particular, the material of the wind turbine blades 6, which is often a composite material, may advantageously be fully or partly recycled, e.g. by applying a method according to an embodiment of the invention.
[0054] FIG. 2 is a perspective view of a composite structure in the form of a wind turbine blade 6. The wind turbine blade 6 extends in a longitudinal direction between a root end 7 and a tip end 8. A web 19 extends along the longitudinal direction inside the wind turbine blade 6 between a pressure side and a suction side.
[0055] The wind turbine blade 6 of FIG. 2 has been demounted from a wind turbine, and the composite material of the wind turbine blade 6 is about to be at least partly recycled by means of a method according to an embodiment of the invention. This will be described in further detail below.
[0056] FIG. 3 illustrates the wind turbine blade 6 of FIG. 2 in the process of being cut into smaller parts 6a, the cutting step being illustrated by saw blades 10. The smaller parts 6a are easier to manage than the entire wind turbine blade 6, and each of the smaller parts 6a constitutes a composite structure. It should, however, be mentioned that the cutting step illustrated in FIG. 3 is optional, and that the method steps described below could, alternatively, be performed on the intact wind turbine blade 6, as it is illustrated in FIG. 2.
[0057] FIGS. 4-7 illustrate method steps for retrieving a recycled fibre mat from a composite structure. In FIG. 4, an epoxy composite structure, in the form of a wind turbine blade 6 or a part 6a of a wind turbine blade, has been submerged in a release agent 11 accommodated in a vessel 12. The epoxy composite structure 6, 6a comprises a plurality of fibre mats 13, five of which are shown, embedded in a matrix of cured epoxy resin 14. The fibre mats 13 may comprise oriented or random fibres, e.g. glass fibres. Furthermore, the epoxy composite structure 6, 6a comprises two core members 15 and a spar cap 9.
[0058] The release agent 11 may comprise acid, such as formic acid, and it acts on the epoxy composite structure 6, 6a in such a manner that the epoxy composite structure 6, 6a disintegrates. More particularly, the release agent 11 causes swelling of epoxy polymers of the epoxy resin 14, and this causes the cured epoxy resin 14 to disintegrate into swelled epoxy particles. This, in turn, releases the fibre mats 13, as well as the core members 15 and the spar cap 9, from the matrix of epoxy resin 14.
[0059] In FIG. 5, the release agent 11 has acted on the composite structure 6, 6a for sufficiently long to have caused the disintegration of the composite structure 6, 6a described above with reference to FIG. 4. In particular, it can be seen that the fibre mats 13 are now floating freely in a mix 16 of release agent and disintegrated epoxy resin. Accordingly, the fibre mats 13 can be retrieved in one piece, and with their original fibre orientation, from the mix 16 of release agent and disintegrated epoxy resin.
[0060] In FIG. 6, the spar cap has been retrieved from the vessel accommodating the release agent 11. The core members 15 have moved upwards towards the surface of the release agent 11 and the top of the vessel 12, while the mix 16 of release agent and disintegrated epoxy resin has moved downwards towards the bottom of the vessel 12, along with the released fibre mats 13.
[0061] In FIG. 7, the core members 15 as well as the fibre mats 13 have been retrieved from the vessel 12 accommodating the release agent 11, and each of these components 13, 15 are now ready for recycling. This could, e.g., include reusing the fibre mats 13 or the core members 15 in their retrieved form, e.g. as components of a new composite structure. As an alternative, the material of the fibre mats 13 or the core members 15 may simply be recycled. This may, e.g., include remelting the fibres of the fibre mats 13.
[0062] FIG. 8 illustrates method steps of an alternative method for retrieving a recycled fibre mat from a composite structure. A wind turbine blade 6 is initially cut into smaller parts 6a, e.g. in the manner illustrated in FIG. 3. The smaller parts 6a are submerged in a release agent 11 accommodated in a vessel 12. This causes the composite structures, in the form of the smaller parts 6a, to disintegrate, e.g. in the manner described above with reference to FIGS. 4-7. Accordingly, at least one fibre mat 13 is retrieved in one piece, and with its original fibre orientation. This allows the fibre mat 13 to be reused directly, in its retrieved form. In the fibre mat 13 illustrated in FIG. 8, the fibres have a bidirectional orientation.
[0063] Furthermore, a mix 16 of release agent and epoxy resin is retrieved from the vessel 12. The mix 16 is subsequently separated into release agent 11 and epoxy resin 17. This allows for recycling of the release agent 11 as well as of the epoxy resin17.
[0064] FIGS. 9-15 illustrate method steps of a method for manufacturing a composite structure according to an embodiment of the invention. FIG. 9 shows a mould 18 and two recycled fibre mats 13a, 13b. The fibre mats 13a, 13b may, e.g., have been retrieved from one or two original composite structures, e.g. in the manner described above with reference to FIGS. 4-8.
[0065] Fibre mat 13a has a trapezial shape, and it comprises oriented fibres arranged in a bidirectional pattern. Fibre mat 13b has a rectangular shape, and it comprises oriented fibres arranged in a unidirectional pattern. Accordingly, the shape as well as the fibre orientation of fibre mat 13a differs from the respective shape and fibre orientation of fibre mat 13b.
[0066] The fibre mats 13a, 13b have shapes and sizes which do not readily fit in the mould 18. Accordingly, as illustrated in FIG. 10A, the fibre mats 13a, 13b are cut along line 19, in order to enable the thus adapted fibre mats 13a, 13b to fit into the mould. In FIG. 10B, the mould 18 is seen from above.
[0067] As an alternative to cutting the fibre mats 13a, 13b, the fibre mats 13a, 13b may be folded along line 19, as illustrated in FIG. 10C. In this case the excess material of the fibre mats 13a is not removed, and this material will therefore form part of the resulting composite structure. However, the fibre mat 13a is still able to fit into the mould 18.
[0068] In FIG. 11 fibre mat 13a has been arranged in the mould 18, and in FIG. 12 fibre mat 13b has additionally been arranged in the mould 18. The fibre mats 13a, 13b are positioned in the mould 18 in such a manner that edge sections of the fibre mats 13a, 13b overlap in an overlapping region 20. Accordingly, the fibre mats 13a, 13b form part of a layer of fibre mats 13a, 13b, where the overlapping region 20 ensures that a weakness is not introduced in the layer of fibre mats 13a, 13b due to the fibre mats 13a and 13b being joined. Accordingly, the overlapping region 20 may compensate for the fact that the layer is constructed from multiple recycled fibre mats 13a, 13b instead of a single perfect-fit virgin fibre mat forming a sheet.
[0069] Furthermore, the fibre orientation varies across the layer of fibre mats 13a, 13b, due to the different fibre orientation of fibre mat 13a and fibre mat 13b, respectively. Thus, the fibre mats 13a, 13b may be selected and positioned in the mould 18 in such a manner that the fibre orientation of the resulting layer of fibre mats 13a, 13b matches requirements of the resulting composite structure, e.g. with respect to desired anisotropic properties of the resulting composite structure. Alternatively, multiple layers with random or preselected fibre orientation may yield a composite structure with substantially isotropic properties in the plane of the mould.
[0070] In FIG. 13, a third fibre mat 13c has additionally been positioned in the mould 18. The third fibre mat 13c comprises oriented fibres arranged in a unidirectional pattern, and it is arranged in such a manner that an overlapping region 20 is defined with fibre mat 13a. Thus, the fibre mats 13a, 13b, 13c in combination cover the entire mould 18 and form a complete layer of fibre mats 13a, 13b, 13c.
[0071] In FIG. 14, several layers of fibre mats (not shown) have been arranged in the mould 18, in the manner described above with reference to FIGS. 9-13. Furthermore, a vacuum bag 21 has been arranged on top of the layers of fibre mats to form a closure of the mould 18. A vacuum is created via vacuum tube 23 and resin is infused in the layers of fibre mats via resin tube 22. Other methods of providing the resin into the layers of fibre mats are known to the skilled person and vacuum assisted resin infusion is only one example. However, vacuum assisted resin infusion is the preferred method due to the versatility, speed and maturity of the process. The resin is allowed to cure, thereby forming a composite structure comprising the fibre mats embedded in a matrix of cured resin. FIG. 15 shows the resulting composite structure 24 released from the mould.
[0072] FIG. 16 shows a composite structure 24, which has been manufactured in accordance with a method according to an embodiment of the invention. The composite structure 24 comprises multiple alternating layers of recycled fibre mats 13 and wood 25. Applying layers of core material 25, such as wood in the composite structure 24, in addition to layers of recycled fibre mats 13, provides a composite structure 24 with a combination of relatively high stiffness and low weight.
[0073] FIG. 17 shows another composite structure 24, which has been manufactured in accordance with a method according to an embodiment of the invention. Here, the composite structure 24 is a sandwich structure with two outer layers each comprising one or more layers or recycled fibre mats 13, and a foam core material 25 arranged therebetween. The foam core material may for example be virgin core, a core prepared by remelted thermoplastic recycled core material 15 (see FIG. 7) or core material recovered from a recycling process as described in relation to FIG. 7 reused directly in the retrieved form. After infusion and curing, this allows for a composite structure 24 having high stiffness and low weight.
