EP4719735A1

EP4719735A1 - Reuse of pultrusion elements

Info

Publication number: EP4719735A1
Application number: EP24726290.0A
Authority: EP
Inventors: Lars Nielsen; Klavs Jespersen
Original assignee: LM Wind Power AS
Current assignee: LM Wind Power AS
Priority date: 2023-05-25
Filing date: 2024-05-22
Publication date: 2026-04-08
Also published as: WO2024240793A1; CN121548490A

Abstract

A method of separating a pultrusion element from a wind turbine blade part. The method comprises providing a wind turbine blade part comprising a plurality of embedded pultrusion elements arranged in a stack. The plurality of pultrusion elements includes a first pultrusion element and a second pultrusion element, wherein each pultrusion element comprises a first side and an opposite second side. The wind turbine blade part comprises an interlayer between the first side of the first pultrusion element and the second side of the second pultrusion element. A peel strength between the interlayer and the first and/or second pultrusion element is weaker than a peel strength within the first and/or second pultrusion element. The method comprises separating the first pultrusion element from the second pultrusion element at a separation line extending in the interlayer arranged between the first and second pultrusion elements.

Description

REUSE OF PULTRUSION ELEMENTS

TECHNICAL FIELD

The present disclosure relates to a wind turbine blade, in particular pultrusion elements, such as spar caps of wind turbine blade parts. The present disclosure relates to the reuse by separating pultrusion elements from a wind turbine blade part. The present disclosure also relates to manufacturing a composite part using such pultrusion elements.

BACKGROUND

With an increasing demand to implement a green transition for companies, more resources are delegated to recycling and reuse of components. For example, thermoset materials are exchanged for the reusable thermoplastic materials and readily extractable and intact components from a retired wind turbine may be given new life in a new wind turbine. Furthermore, there is a desire to reduce the costs related to decommissioning of retired wind turbines and wind turbine blades.

A wind turbine blade, such as a wind turbine blade shell part, is typically built up from layers of different materials that are infused with resin and cured. Thus, different layers are bonded to each other and reuse of the layers and how to reuse them is not straightforward. A simple and fast methods for separating the layers without causing damage is needed on order to provide a cost benefit of reuse of the layers. Furthermore, there is also a consideration related to which layers to extract and where to reuse them.

Lastly, there is a desire for methods supporting reuse and recycling of components for a wind turbine blade, which require minimal or no space, as the manufacturing of new wind turbines already require large spaces.

SUMMARY

On this background, it may be seen as an object of the present disclosure to provide a method of separating a pultrusion element from a wind turbine blade part.

Another object of the present disclosure is to provide a method of manufacturing a composite part, preferably a wind turbine blade part, from a plurality of pultrusion elements.

One or more of these objects may be met by aspects of the present disclosure as described in the following.

A first aspect of this disclosure relates to a method of separating a pultrusion element from a wind turbine blade part. The method comprises providing a wind turbine blade part comprising a reinforcing structure. The reinforcing structure comprises a plurality of embedded pultrusion elements arranged in a stack. The plurality of pultrusion elements includes a first pultrusion element and a second pultrusion element. Each pultrusion element comprises a first side and an opposite second side. The wind turbine blade part comprises an interlayer between the first side of the first pultrusion element and the second side of the second pultrusion element. A peel strength between the interlayer and the first and/or second pultrusion element is weaker than a peel strength within the first and/or second pultrusion element.

The method further comprising separating the first pultrusion element from the second pultrusion element at a separation line extending in the interlayer arranged between the first and second pultrusion elements. Separating the first pultrusion element from the second pultrusion element may comprise peeling the first pultrusion element from the second pultrusion element, e.g., at a separation line extending in the interlayer arranged between the first and second pultrusion elements.

The separation or peeling of the first pultrusion element from the second pultrusion element at the separation line extending in the interlayer arranged between the first and second pultrusion elements is due to the weaker peel strength between the interlayer and the first and/or second pultrusion element than a peel strength within the first and/or second pultrusion element. In other words, a separation will occur at the interlayer because the peel strength holding the material together is weaker in the interlayer compared with the peel strength holding the material together in the first and/or second pultrusion element. As such, the separation does not occur in the first and/or second pultrusion element before a separation in the interlayer due to the stronger peel strength in the first and/or second pultrusion element.

A second aspect of this disclosure relates to a method of manufacturing a composite part, preferably a wind turbine blade part, from a plurality of pultrusion elements. The method comprises performing a method according to the first aspect of this disclosure to obtain a plurality of separate pultrusion elements. The method further comprises arranging the plurality of separate pultrusion elements in a mould with an interlayer arranged between adjacent pultrusion elements. The plurality of separate pultrusion elements may be joined in the lengthwise direction. The method further comprises infusing the plurality of separate pultrusion elements with a resin. The method further comprises causing or letting the resin cure so as to form the composite part.

By providing a method for separating a pultrusion element from a wind turbine blade part and a method for manufacturing a composite part, pultrusion elements may be reused, which provides a sustainable chain of life for wind turbine blades. Each pultrusion element may be a carbon fibre reinforced pultrusion element. The carbon fibre reinforced pultrusion element preferably consists of carbon fibres embedded in a cured first resin. The cured first resin is preferably made of epoxy. The pultrusion element preferably comprises a plurality of tows or rovings of carbon fibre material. Each pultrusion element may comprise 20-200 tows of carbon fibre material in total. The tows will usually extend in the length direction of the pultrusion element, i.e., substantially parallel to its longitudinal axis, or parallel to the spanwise direction when arranged in the blade shell. Carbon fibres are an expensive material, and the material in a wind turbine may comprise around 40% or even more carbon fibres. Thus, reuse of carbon fibre reinforced pultrusion elements could reduce the cost of manufacturing a wind turbine blade significantly. Carbon fibre reinforced pultrusion elements embedded in epoxy provide the necessary tensile strength and endurance to vibrational loads to act as a reinforcing structure. Furthermore, it has been surprisingly found that most failures of carbon fibre pultrusion elements occur before or during initial operation. Furthermore, it was found that the fatigue life of carbon fibre pultrusion elements is much longer than other parts of the wind turbine blade part. Therefore, carbon fibre pultrusion elements separated after decommissioning of the wind turbine blade part, e.g., after 20 years of running on site, can be expected to have at least as low a failure rate or even lower compared to new carbon fibre pultrusion elements.

The interlayer may comprise a flow medium material embedded in a cured second resin. The interlayer may comprise fibres. The flow medium material of the interlayer may comprise fibres. The fibres are preferably a mixture of carbon fibres and glass fibres. The interlayer, e.g., the flow medium material of the interlayer, may be electrically conductive so as to electrically connect the first pultrusion element and the second pultrusion element. The flow medium material may provide a space for the resin to flow and/or fill during infusion of the wind turbine blade part. The interlayer may bind adjacent pultrusion elements together in a reinforcing structure.

The cured second resin of the interlayer may be a thermoset resin. Preferably the thermoset resin of the interlayer is made of vinyl ester. A thermoset resin may be cheaper, more robust and provide a stronger bonding of the pultrusion elements than a thermoplastic resin.

Alternatively, the cured second resin of the interlayer may be a thermoplastic resin. By providing a thermoplastic resin the resin may be re-mouldable and recycled. Separating the first pultrusion element from the second pultrusion element at the interlayer may comprise heating at least the first pultrusion element, the second pultrusion element and the interlayer to a melting point of the thermoplastic resin of the interlayer. The melting point may be the temperature where the thermoplastic resin transforms from a solid to a non-solid phase, such as a soft, formable state. The melting point may be dependent on the type of thermoplastic resin provided. The first pultrusion element, the second pultrusion element and the interlayer may be heated to a temperature between 100-300 °C, such as between 105-150 °C.

The interlayer may have a thickness between 0.05-1.5 mm, such as between 0.2-0. mm, such as 0.3 mm. The interlayer may have a width between 200-700 mm, such as between 300-600 mm and/or a length between 30-120 m, such as between 50-100 m.

The peel strength is used to measure the bond strength of a material. Peel strength is the average load per unit width of bond line required to separate bonded materials where the angle of separation is 180 degrees. The higher the peel strength the tighter the bond and more force is needed to separate the bonded materials. The weaker peel strength between the interlayer and the first and/or second pultrusion element than the peel strength within the first and/or second pultrusion element, can be achieved by the first resin of the first and/or second pultrusion element being different than the second resin of the interlayer. For example, the first resin of the pultrusion elements may consist essentially of a different material than the second resin of the interlayer, e.g. the first resin of the pultrusion elements may comprise epoxy while the second resin of the interlayer may comprise vinyl ester. Alternatively, the composition of the first resin of the pultrusion elements may be different than the composition of the second resin of the interlayer. For example, the first resin of the pultrusion elements may comprise different additives than the second resin of the interlayer. Additionally, or alternatively, the first resin of the pultrusion elements may be thermoset while the second resin of the interlayer may be thermoplastic.

Separating the first pultrusion element from the second pultrusion element at the interlayer may comprise applying a peeling force between the first pultrusion element and the second pultrusion element. For example, the peeling force may be applied at the interlayer, e.g., at the separation line. The peeling force may be applied by a wedge element introduced between the first pultrusion element and the second pultrusion element. For example, the wedge may be introduced at the interlayer, e.g., at the separation line. The peeling force may be applied to the wedge element. The peeling force may be applied in a direction substantially parallel to the lengthwise direction of the first and/or second pultrusion element. Alternatively, the peeling force may be applied in a direction substantially parallel to the width wise direction of the first and/or second pultrusion element. The method of applying a peeling force is simple and may be performed outside of manufacturing sites.

The wind turbine blade part may be a shell part for a wind turbine blade, a spar cap for a wind turbine blade, blade segment for a wind turbine blade, a spar box for a wind turbine blade, or a spar beam for a wind turbine blade. The wind turbine blade part may comprise carbon fibres. The method is versatile and part of a wind turbine blade comprising a pultruded element may be subject to the method. Providing the wind turbine part may comprise a step of providing a wind turbine blade comprising the wind turbine blade part, preferably a spar cap, and separating the wind turbine blade part from the wind turbine blade. The wind turbine blade part may be cut out from the wind turbine blade. The wind turbine blade part may be separated from the wind turbine blade, such that the other parts which are not subject to the method can be left at the dismantling site of the wind turbine blade.

Each pultrusion element may be a pultrusion plank or pultrusion plate. The first pultrusion element may comprise a first thickness extending between the first side and the second side of the first pultrusion element. The first side may be a top side of the pultrusion element, which may be adapted to face the interior of the wind turbine blade part. The second side may be a bottom side of the pultrusion element, which may be adapted to face the exterior of the wind turbine blade part. The first thickness of the first pultrusion element may be between 3-10 mm, such as between 4-7 mm. The first pultrusion element may comprise a width extending between a first lateral side and an opposite second lateral side of the first pultrusion element. The width of the first pultrusion element may be between 20-300 mm, such as between 80-150 mm. The first pultrusion element may comprise a length extending between a first end and an opposite second end of the first pultrusion element. The length of the first pultrusion element may be between 30-150 m, such as between 50- 100 m, such as 70-100 m. The first pultrusion element may have a pre-treatment thickness, pretreatment length, and pre-treatment width. The pre-treatment thickness, pre-treatment length and pre-treatment width may correspond to the length of the first pultrusion element before removal of the one or more interlayers and/or one or more cover layers and/or one or more transition layers.

The reinforcing structure may comprise a length extending between a first end and an opposite second end of the reinforcing structure. The length of the reinforcing structure may be between 30- 120 m, such as between 50-100 m. The reinforcing structure may comprise a thickness extending between the first side and the second side of the reinforcing structure. The thickness of the reinforcing structure may be between 1-70 mm, such as between 5-60 mm. The reinforcing structure may comprise a width extending between a first lateral side and an opposite second lateral side of the reinforcing structure. The width of the reinforcing structure may be between 200-700 mm, such as between 300-600 mm.

In a preferred embodiment, the reinforcing structure, such as the spar cap, comprises between 1- 15 stacks of pultrusion elements arranged next to each other, preferably in the width wise direction, more preferably between 3-9 stacks. Each stack may comprise up to 20 pultrusion elements arranged on top of each other, such as 2-20 pultrusion elements or 2-10 pultrusion plates. Thus, each reinforcing structure, such as each spar cap, may comprise 10-200 pultrusion elements.

The wind turbine blade part may comprise one or more cover layers covering the plurality of embedded pultrusion elements. The method may comprise removing, preferably by machining, the one or more cover layers to expose the first pultrusion element of the plurality of embedded pultrusion elements. Removing the one or more cover layers may comprise grinding and/or milling the one or more cover layers. The one or more cover layers may be removed, e.g., grinded and/or milled, to expose the second side of the first pultrusion element. The one or more cover layers may be removed, e.g., grinded and/or milled, to expose the first side of the second pultrusion element.

The wind turbine blade part may comprise one or more transition layers arranged between the reinforcing structure and one or more core elements of the wind turbine blade shell part. A transition layer may be arranged between each of the stacks of the reinforcing structure. The transition layer comprises a resin and provides a bond between the reinforcing structure and the core elements of the wind turbine blade shell part together. The transition layer may provide a bond between adjacent stacks of the reinforcing structure. The one or more cover layers may be removed, e.g., grinded and/or milled, to expose the first lateral side and/or the second lateral side of the first pultrusion element and/or the first lateral side and/or the second lateral side of the second pultrusion element.

The method may comprise a step of removing the interlayer or residue of the interlayer from the first and/or second side of the first pultrusion element. Removing the interlayer or residue of the interlayer from the first and/or second side of the first pultrusion element may comprise machining. Machining the interlayer or the residue of the interlayer may comprise griding and/or milling the interlayer or residue of the interlayer. The interlayer or the residue of the interlayer may be removed, e.g., grinded and/or milled, to expose the first side of the first pultrusion element. The interlayer or the residue of the interlayer may be removed, e.g., grinded and/or milled, to expose the first side of the second pultrusion element.

Removing the interlayer or residue of the interlayer from the first side of the first pultrusion element may comprise machining the first pultrusion element to a thickness which is 100%, 99%, 95% or 90% of the first thickness, e.g. the pre-treatment thickness. Removing the cover layer or residue of the cover layer from the second side of the first pultrusion element may comprise machining the first pultrusion element to a thickness which is 100%, 99%, 95% or 90% of the first thickness, e.g. the pre-treatment thickness.

Removing the transition layer or residue of the transition layer from the first and/or second lateral side of the first pultrusion element may comprise machining the first pultrusion element to a width which is 100%, 99%, 95% or 90% of the pre-treatment width. Removing the transition layer or residue of the transition layer from the first and/or second end of the first pultrusion element may comprise machining the first pultrusion element to a length which is 100%, 99%, 95% or 90% of the pre-treatment length. The first pultrusion element may have a pre-treatment size. The pre-treatment size may correspond to the size of the first pultrusion element has when it was first time first arranged in a mould. The pre-treatment size may correspond to the size of the first pultrusion element before machining. The first pultrusion element may be machined to an undersize, i.e., a size smaller than the pre-treatment size, e.g., a length, width and thickness smaller than the pre-treatment length, width and thickness. The undersize may be a first undersize, a second undersize and/or a third undersize corresponding to 99%, 95% or 90% of the pre-treatment size, respectively. By machining the first pultrusion element to an undersize, a pultrusion element with a higher ratio of carbon may be provided. By removing the one or more cover layers and/or the interlayer or residue of the interlayer and/or one or more transition layers, a pultrusion element with a higher ratio of carbon may be provided. By machining the first pultrusion element to an undersize the probability that all of the layers are removed is higher.

The method may comprise a step of coiling up the first pultrusion element. The first pultrusion element may be cut before coiling up the first pultrusion element. The first pultrusion element may be cut before arranging the first pultrusion element in the mould.

A third aspect of this disclosure relates to a pultrusion element obtained by the method of the first aspect.

A fourth aspect of this disclosure relates to the use of a pultrusion element of the third aspect of this disclosure for a method of the second aspect of this disclosure. The pultrusion element may alternatively be used for a method of manufacturing construction parts, e.g., construction parts in buildings where reinforcing structures are needed.

A fifth aspect of this disclosure relates to a separation station for use in a method for separating a pultrusion element from a wind turbine blade part. The separation station comprises a work surface configured for receiving a wind turbine blade part comprising a reinforcing structure. The reinforcing structure comprises a plurality of embedded pultrusion elements arranged in a stack. The plurality of pultrusion elements includes a first pultrusion element and a second pultrusion element. Each pultrusion element comprises a first side and an opposite second side. The wind turbine blade part comprises an interlayer between the first side of the first pultrusion element and the second side of the second pultrusion element. A peel strength between the interlayer and the first and/or second pultrusion element is weaker than a peel strength within the first and/or second pultrusion element.

The separation station further comprises a separation element configured for separating the first pultrusion element from the second pultrusion element at a separation line extending in the interlayer arranged between the first and second pultrusion elements. The separation element may be configured for applying a peeling force between the first pultrusion element and the second pultrusion element. The separation element may be a wedge element. The separation station may further comprise a first actuator configured for urging the separation element between the first pultrusion element and the second pultrusion element.

The separation station may further comprise a clamping arrangement configured for clamping the wind turbine blade part to the work surface.

The separation element may comprise a first part configured for attaching to a first longitudinal side of the wind turbine blade part extending in the lengthwise direction. The separation element may comprise a second part configured for attaching to a second longitudinal side of the wind turbine blade part extending in the lengthwise direction. The separation station may comprise a second actuator configured for urging the first and second parts of the separation element apart from each other in the thickness direction to apply the peeling force between the first pultrusion element and the second pultrusion element.

The separation station may further comprise a machining device, such as a grinding device or milling device, and a third actuator. The third actuator may be configured for moving the machining device along one or more degrees of freedom to arrange the machining device in proximity to the interlayer or residue of the interlayer on a separated first pultrusion element. The machining device may be configured to remove the interlayer or residue of the interlayer from the separated first pultrusion element.

As used herein, the term "separating" refers to an action of separating the first pultrusion element and the second pultrusion element such that the first pultrusion part can be moved independently and/or are distinct from each other. The term "separating" may also refer to the action of fully separating the first pultrusion element and the second pultrusion element such that they are disconnected, disjoined, unliked, or parted.

A person skilled in the art will appreciate that any one or more of the above aspects of this disclosure and embodiments thereof may be combined with any one or more of the other aspects of this disclosure and embodiments thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of this disclosure will be described in more detail in the following with regard to the accompanying figures. The figures show one way of implementing the present invention and are not to be construed as being limiting to other possible embodiments falling within the scope of the attached claim set. Fig. 1 is a schematic perspective view of a wind turbine,

Fig. 2 is a schematic perspective view of a wind turbine blade for a wind turbine as shown in Fig. 1,

Fig. 3 is a schematic perspective view of a wind turbine blade part,

Figs. 4a-4b are a schematic cross-sectional view of an exemplary wind turbine blade part,

Figs. 5a-5b are a schematic cross-sectional view of an exemplary wind turbine blade part, and

Fig. 6 is a diagram of an exemplary method for separating a pultrusion element from a wind turbine part and an exemplary method for manufacturing a composite part.

DETAILED DESCRIPTION

In the following figure description, the same reference numbers refer to the same elements and may thus not be described in relation to all figures.

Fig. 1 illustrates a conventional modern upwind wind turbine 2 according to the so-called "Danish concept" with a tower 4, a nacelle 6 and a rotor with a substantially horizontal rotor shaft which may include a tilt angle of a few degrees. 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.

Fig. 2 shows a schematic view of an exemplary wind turbine blade 10. The wind turbine blade 10 has the shape of a conventional wind turbine blade with a root end 17 and a tip end 15 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 8, and a trailing edge 20 facing the opposite direction of the leading edge 18.

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 region 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 from the hub. A shoulder 38 of the blade 10 is defined as the position, where the blade 10 has its largest chord length. The shoulder 38 is typically provided at the boundary between the transition region 32 and the airfoil region 34.

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.

The wind turbine blade 10 comprises a blade shell comprising two blade shell parts or half shells, a first blade shell part 24 and a second blade shell part 26, typically made of fibre-reinforced polymer. The wind turbine blade 10 may comprise additional shell parts, such as a third shell part and/or a fourth shell part. The first blade shell part 24 is typically a pressure side or upwind blade shell part. The second blade shell part 26 is typically a suction side or downwind blade shell part. The first blade shell part 24 and the second blade shell part 26 are fastened together with adhesive, such as glue, along bond lines or glue joints 28 extending along the trailing edge 20 and the leading edge 18 of the blade 10. Typically, the root ends of the blade shell parts 24, 26 have a semi-circular or semi-oval outer cross-sectional shape.

Fig. 3. shows a schematic perspective view of a blade shell part, such as a first blade shell part 24 or a second blade shell part 26 of a wind turbine as shown in Fig. 1. The blade shell part 24, 26 comprises a wind turbine blade part 42. In a preferred embodiment, the wind turbine blade part 42 comprises a reinforcing structure 50, such as a spar cap, formed by a plurality of pultrusion elements 60 arranged in at least one a stack 44 (see Fig. 4). The plurality of pultrusion elements 60 comprises carbon fibres, which is an expensive material, and therefore a method of separating the plurality of pultrusion elements 60 from a wind turbine blade part 42 for reuse is desirable. An overview of the method 200 of separating the plurality of pultrusion elements from a wind turbine blade part is also shown in Fig. 6.

The wind turbine blade part of the present invention may alternatively be a shell part for a wind turbine blade, blade segment for a wind turbine blade, a spar box for a wind turbine blade, or a spar beam for a wind turbine blade. The reinforcing structure 50 extends in the longitudinal direction L of the blade and has a length Ls between a first end 56 and a second end 58 of the reinforcing structure. The plurality of pultrusion elements 60 comprises a plurality of pultruded carbon fibres, preferably carbon fibre tows, extending in the longitudinal direction L of the blade. The wind turbine blade part 42 may be separated from the wind turbine blade 10 or the wind turbine blade shell part 24, 26, e.g., by cutting out the wind turbine blade part 42, before separating the pultrusion elements 60 from the wind turbine blade part 42. Fig. 4a and 4b show a cross-sectional view of the wind turbine blade part 42, such as the wind turbine blade part of Fig. 3 as seen from the line A-A. Fig. 4b is an expanded view of the reinforcing structure 50 of Fig. 4a. The wind turbine blade part 42 may be a shell part for a wind turbine blade, a spar cap for a wind turbine blade, blade segment for a wind turbine blade, a spar box for a wind turbine blade, or a spar beam for a wind turbine blade. The wind turbine blade part 42 comprises a reinforcing structure 50. The reinforcing structure 50 is formed by a plurality of embedded pultrusion elements 60 arranged in one or more stacks 44. The pultrusion elements 60 may be embedded in a cured first resin of epoxy.

Fig. 4a further illustrates that the reinforcing structure 50 has a width Ws extending between the first lateral side 58 and the second lateral side 59 of the reinforcing structure 50. The width Ws extends in a direction substantially parallel to the chordwise direction of the wind turbine blade and/or wind turbine blade part. The reinforcing structure 50 has a thickness Ts extending between a first side 52 and a second side 54 of the reinforcing structure 50.

The reinforcing structure 50 is arranged between cover layers 90, such as blade shell materials, and core elements 92. The core element 92 may be a core of a sandwich structure and made of suitable core materials. The cover layers 90 may be reinforced cover plies and made of fibre reinforced materials, such as glass fibres, embedded in a resin. The cover layers 90 may be removed, e.g. by machining, to expose the plurality of embedded pultrusion elements 60, e.g. the second side 64' of the first pultrusion element 60' (see Fig. 4b).

A transition layer 84 is arranged between the reinforcing structure 50 and the core elements 92. A transition layer 84 is also arranged between each of the stacks 44 of the reinforcing structure 50, such as between the first pultrusion element 60' and the third pultrusion element 60'". The transition layer 84 may be a resin and have the purpose of binding the reinforcing structure 50 and the core elements 92 together or binding adjacent stacks 44 of the reinforcing structure together. The transition layers 84 may be removed to expose the plurality of embedded pultrusion elements 60, e.g., the first lateral side 64' of the first pultrusion element 60'.

An interlayer 80 is arranged between adjacent pultrusion elements 60. Fig 4b illustrates that the interlayer 80 is arranged between the first pultrusion element 60' and the second pultrusion element 60", more specifically between the first side 62' of the first pultrusion element 60' and the second side 64" of the second pultrusion element 60". The purpose of the interlayer 80 is to hold and/or distribute a second resin and/or to electrically connect adjacent pultrusion elements 60. The interlayer 80 is a made of a flow medium material, such as a hybrid of glass and carbon fibres. The second resin in the interlayer 80 may be a thermoset or a thermoplastic resin. The interlayer has a thickness Ti. Fig. 4b further illustrates a separation line L in the interlayer 80. The separation line L may be located anywhere in the interlayer 80 and represents the location of the split of the first pultrusion element 60' and the second pultrusion element 60" when they are separated (see Fig. 5a). For example, a wedge element 86 may be introduced at the separation line L.

Fig. 5a shows a separation station 100 for separating a pultrusion element from a wind turbine part. The separation station 100 comprises a work surface 102 configured for receiving a wind turbine blade part 42 and a separation element 104 configured for separating the first pultrusion element from the second pultrusion element. The separation station 100 may comprise a clamping arrangement configured for clamping the wind turbine blade part 42 to the work surface (not illustrated). For illustrative purposes the wind turbine blade part 42 is illustrated as a first pultrusion element 60' and a second pultrusion element 60".

The separation element 104 may be a wedge element 86. The station may comprise a first actuator 106' configured for urging the separation element between the first pultrusion element 60' and the second pultrusion element 60".

The separation element 104 may comprise a first part 104' configured for attaching to a first longitudinal side of the wind turbine blade part 42 extending in the lengthwise direction and a second part 104" configured for attaching to a second longitudinal side of the wind turbine blade part 42 extending in the lengthwise direction. A second actuator 106" is configured for urging the first and second parts 104', 104" of the separation element 104 apart from each other in the thickness direction to apply the peeling force between the first pultrusion element 60' and the second pultrusion element 60".

The separation station 100 may further comprise a machining device 108, such as a grinding device or milling device, and a third actuator 106'". The third actuator 106'" is configured for moving the machining device 108 along one or more degrees of freedom to arrange the machining device 108 in proximity to the interlayer 80 or residue of the interlayer on a separated first pultrusion element 60'. The machining device 108 is configured to remove the interlayer 80 or residue of the interlayer from the separated first pultrusion element 60'.

The figure illustrates the first pultrusion element 60' separated from the second pultrusion element 60". The first pultrusion element 60' and the second pultrusion element 60" have been separated at the interlayer 80, preferably at a separation line in the interlayer (see Fig. 4b).

In the case where the second resin in the interlayer 80 is a thermoplastic resin, the first pultrusion element 60' and the second pultrusion element 60" may be separated at the interlayer 80 by heating at least the first pultrusion element, the second pultrusion element and the interlayer to a melting point of the thermoplastic resin of the interlayer. The melting point may be the temperature where the thermoplastic resin transforms from a solid to a non-solid phase, such as a soft, formable state.

In the case where the second resin in the interlayer 80 is a thermoset resin, such as vinyl ester, the first pultrusion element 60' and the second pultrusion element 60" may be separated by applying a peel force between the first pultrusion element 60' and the second pultrusion element 60", e.g., at the interlayer 80. The peel force may be applied by a wedge element 86 introduced first pultrusion element 60' and the second pultrusion element 60".

The first pultrusion element 60' and the second pultrusion element 60" may be separated at the interlayer 80 due to a weaker peel strength between the interlayer 80 and the first and/or the second pultrusion element 60', 60", than the peel strength within the first and/or second pultrusion element 60', 60". The peel strength may be weaker between the interlayer 80 and the pultrusion elements 60 in the case where the pultrusion elements 60 are embedded in epoxy resin and the interlayer 80 is embedded in vinyl ester resin. Thus, the difference in peel strength is due to the difference in bonding properties of the different first and second resins in a cured state. In the case where the second resin in the interlayer 80 is thermoplastic, the difference in peel strength is due to difference in bonding properties in an uncured, heated state. The first side 62' of the first pultrusion element 60' and/or the second side 64" of the second pultrusion element 60" may be milled or grinded to remove the interlayer 80 and/or residue of the interlayer 80.

Fig. 5b shows a pultrusion element after separation. To remove the interlayer 80 and/or residue of the interlayer 80, the pultrusion element 60 is machined. For example, the first side 62 and/or the second side 64 of the pultrusion element 60 may be milled or grinded to remove the interlayer 80 and/or residue of the interlayer 80 and/or the cover layer 90 or residue of the cover layer. The first and/or second end of the pultrusion element may be milled or grinded to remove the transition layer 84 or residue of the transition layer. The pultrusion element 60 may be machined to an undersize SI, S2, S3 which corresponds to a size smaller than the pre-treatment size S of the pultrusion element. The first undersize SI, the second undersize S2 and the third undersize S3 correspond to 99%, 95% and 90% of the pre-treatment size S of the pultrusion element, respectively.

After the interlayer 80 has been removed from the pultrusion elements 60, the pultrusion elements 60 may be coiled up to be transported and reused, e.g., in manufacturing of a wind turbine blade.

Fig. 6 shows a method 200 for separating a pultrusion element from a wind turbine blade part and a method 1200 for manufacturing a composite part.

The method 200 for separating a pultrusion element from a wind turbine blade part comprises a step of providing a wind turbine blade part 202. The wind turbine blade part may be separated from a wind turbine blade, e.g., by cutting out the wind turbine blade part. The wind turbine blade part comprises a reinforcing structure. The reinforcing structure comprises a plurality of embedded pultrusion elements arranged in a stack, including a first pultrusion element and a second pultrusion element. Each pultrusion element comprises a first side and an opposite second side. The wind turbine blade part comprises an interlayer between the first side of the first pultrusion element and the second side of the second pultrusion element.

The method 200 may comprise removing 204 the cover layer to expose the first pultrusion element, e.g., the first side of the first pultrusion element, of the plurality of embedded pultrusion elements. Removing 204 the cover layer may comprise machining 204a, e.g., milling or grinding the cover layer.

A peel strength between the interlayer and the first and/or second pultrusion element is weaker than a peel strength within the first and/or second pultrusion element. Thus, the method 200 comprises separating 206 the first pultrusion element from the second pultrusion element at a separation line extending in the interlayer arranged between the first and second pultrusion elements.

Separating 206 the first pultrusion element from the second pultrusion element may comprise applying peeling force 206a between the first pultrusion element and the second pultrusion element or alternatively, heating 206b at least the first pultrusion element, the second pultrusion element and the interlayer to a melting point of the thermoplastic resin of the interlayer.

The peeling force may be applied by a wedge element introduced between the first pultrusion element and the second pultrusion element.

The method 200 may comprise removing 208 the interlayer or residue of the interlayer from the first side of the first pultrusion element. The interlayer or residue of the interlayer may be removed 208 by machining 208a. The interlayer or residue of the interlayer may be removed from first side of the first pultrusion element by machining the first pultrusion element so as to obtain a first pultrusion element having a thickness corresponding to 100%, 99%, 95% or 90% thickness before the step of machining.

The method 200 may comprise coiling 210 the first pultrusion element in a coil, e.g., to prepare the pultrusion element(s) for transportation to a manufacturing facility.

The method 200 may be repeated to separate another pultrusion element, such as the second pultrusion element from the wind turbine blade part. The method 200 may be repeated until each of the plurality of pultrusion elements are separated from the wind turbine blade part. Fig. 6 further shows a method 1200 of manufacturing a composite part, preferably a wind turbine blade part, from a plurality of pultrusion elements. The method 1200 comprises performing 1202 the method 200 to obtain plurality of pultrusion elements, such as a first pultrusion element and a second pultrusion element.

The method 1200 comprises arranging 1204 the plurality of separate pultrusion elements in a mould with an interlayer arranged between adjacent pultrusion elements.

The method 1200 comprises infusing 1206 plurality of separate pultrusion elements with a resin, e.g., using vacuum assisted resin transfer moulding.

The method 1200 comprises causing 1208 or letting the resin cure so as to form the composite part.

ITEMS

1. A method of separating a pultrusion element from a wind turbine blade part, comprising: providing a wind turbine blade part comprising a reinforcing structure, the reinforcing structure comprising a plurality of embedded pultrusion elements arranged in a stack, the plurality of pultrusion elements includes a first pultrusion element and a second pultrusion element, wherein each pultrusion element comprises a first side and an opposite second side, wherein the wind turbine blade part comprises an interlayer between the first side of the first pultrusion element and the second side of the second pultrusion element, wherein a peel strength between the interlayer and the first and/or second pultrusion element is weaker than a peel strength within the first and/or second pultrusion element, and separating the first pultrusion element from the second pultrusion element at a separation line extending in the interlayer arranged between the first and second pultrusion elements.

2. A method according to item 1, wherein each pultrusion element is a carbon fibre reinforced pultrusion element, preferably consisting of carbon fibres embedded in a cured first resin, preferably made of epoxy.

3. A method according to any of the preceding items, wherein the interlayer comprises a flow medium material embedded in a cured second resin. 4. A method according to item 3, wherein the second resin of the interlayer is a thermoset resin, preferably made of vinyl ester.

5. A method according to item 3, wherein the second resin of the interlayer is a thermoplastic resin.

6. A method according to item 5, wherein the step of separating the first pultrusion element from the second pultrusion element at the interlayer comprises heating at least the first pultrusion element, the second pultrusion element and the interlayer to a melting point of the thermoplastic resin of the interlayer.

7. A method according to any of items 3-6, wherein the flow medium material of the interlayer comprises fibres, preferably a mixture of carbon fibres and glass fibres.

8. A method according to any of items 3-7, wherein the flow medium material of the interlayer is electrically conductive so as to electrically connect the first pultrusion element and the second pultrusion element.

9. A method according to any of the preceding items, wherein the interlayer has a thickness between 0.05-1.5 mm, such as between 0.2-0.4 mm, such as 0.3 mm.

10. A method according to any of the preceding items, wherein the weaker peel strength between the interlayer and the first and/or second pultrusion element than the peel strength within the first and/or second pultrusion element can be achieved by the first resin of the first and/or second pultrusion element being different than the second resin of the interlayer.

11. A method according to any of the preceding items, wherein the step of separating the first pultrusion element from the second pultrusion element at the interlayer comprises applying a peeling force between the first pultrusion element and the second pultrusion element.

12. A method according to any of the preceding items, wherein the step of separating the first pultrusion element from the second pultrusion element comprises peeling the first pultrusion element from the second pultrusion element, e.g., at the interlayer arranged between the first pultrusion element and the second pultrusion element.

13. A method according to item 12, wherein the peeling force is applied by a wedge element introduced between the first pultrusion element and the second pultrusion element.

14. A method according to any of the preceding items, wherein the wind turbine blade part is a shell part for a wind turbine blade, a spar cap for a wind turbine blade, blade segment for a wind turbine blade, a spar box for a wind turbine blade, or a spar beam for a wind turbine blade.

15. A method according to any of the preceding items, wherein the step of providing the wind turbine part comprises a step of providing a wind turbine blade comprising the wind turbine blade part, preferably a spar cap, and separating the wind turbine blade part from the wind turbine blade.

16. A method according to any of the preceding items, wherein the wind turbine blade part comprises one or more cover layers covering the plurality of embedded pultrusion elements, and wherein the method comprises removing, preferably by machining, the one or more cover layers to expose the first pultrusion element of the plurality of embedded pultrusion elements.

17. A method according to any of the preceding items, wherein the first pultrusion element comprises a first thickness extending between the first side and the second side of the first pultrusion element, and wherein the first thickness is between 3-10 mm, such as between 4-7 mm.

18. A method according to any of the preceding items, wherein the first pultrusion element comprises a width extending between a first lateral side and an opposite second lateral side of the first pultrusion element, and wherein the width is between 20-300 mm, such as between 80-150 mm.

19. A method according to any of the preceding items, wherein the first pultrusion element comprises a length extending between a first end and an opposite second end of the first pultrusion element, wherein the length is between 30-150 m, such as between 50-100 m, such as between 70-100 m.

20. A method according to any of the preceding items, wherein the reinforcing structure comprises a length extending between a first end and an opposite second end of the reinforcing structure, wherein the length is between 30-120 m, such as between 50-100 m.

21. A method according to any of the preceding items, wherein the reinforcing structure comprises a thickness extending between the first side and the second side of the reinforcing structure, and wherein the thickness is between 1-70 mm, such as between 5-60 mm.

22. A method according to any of the preceding items, wherein the reinforcing structure comprises a width extending between a first lateral side and an opposite second lateral side of the reinforcing structure, and wherein the width is between 200-700 mm, such as between 300-600 mm. A method according to any of the preceding items, wherein the method comprises a step of removing the interlayer or residue of the interlayer from the first and/or second side of the first pultrusion element. A method according to item 23, wherein the step of removing the interlayer or residue of the interlayer from the first and/or second side of the first pultrusion element comprises machining. A method according to item 23, wherein the step of removing the interlayer or residue of the interlayer from the first side of the first pultrusion element comprises machining the first pultrusion element to a thickness which is 100%, 99%, 95% or 90% of the first thickness. A method according to any of the preceding items comprising a step of coiling up the first pultrusion element. A method of manufacturing a composite part, preferably a wind turbine blade part, from a plurality of pultrusion elements, comprising: performing a method according to any one of the previous items to obtain a plurality of separate pultrusion elements, arranging the plurality of separate pultrusion elements in a mould with an interlayer arranged between adjacent pultrusion elements, infusing the plurality of separate pultrusion elements with a resin, and

- causing or letting the resin cure so as to form the composite part. A pultrusion element obtainable by a method according to any one of items 1-26. Use of a pultrusion element according to item 28 for a method according to item 27. A separation station for use in a method according to any one of items 1-26, comprising: a work surface configured for receiving a wind turbine blade part comprising a reinforcing structure, the reinforcing structure comprising a plurality of embedded pultrusion elements arranged in a stack, the plurality of pultrusion elements includes a first pultrusion element and a second pultrusion element, wherein each pultrusion element comprises a first side and an opposite second side, wherein the wind turbine blade part comprises an interlayer between the first side of the first pultrusion element and the second side of the second pultrusion element, wherein a peel strength between the interlayer and the first and/or second pultrusion element is weaker than a peel strength within the first and/or second pultrusion element, a separation element configured for separating the first pultrusion element from the second pultrusion element at a separation line extending in the interlayer arranged between the first and second pultrusion elements. A separation station according to item 30, wherein the separation element is configured for applying a peeling force between the first pultrusion element and the second pultrusion element. A separation station according to any one of items 30-31, wherein the separation element is a wedge element. A separation station according to any one of items 30-32, further comprising a first actuator configured for urging the separation element between the first pultrusion element and the second pultrusion element. A separation station according to any one of items 30-33, further comprising a clamping arrangement configured for clamping the wind turbine blade part to the work surface. A separation station according to any one of items 30-34, wherein the separation element comprises:

A first part configured for attaching to a first longitudinal side of the wind turbine blade part extending in the lengthwise direction,

A second part configured for attaching to a second longitudinal side of the wind turbine blade part extending in the lengthwise direction, and wherein the separation station comprises a second actuator configured for urging the first and second parts of the separation element apart from each other in the thickness direction to apply the peeling force between the first pultrusion element and the second pultrusion element. A separation station according to any one of items 30-35, further comprising a machining device, such as a grinding device or milling device, and a third actuator, wherein the third actuator is configured for moving the machining device along one or more degrees of freedom to arrange the machining device in proximity to the interlayer or residue of the interlayer on a separated first pultrusion element, wherein the machining device is configured to remove the interlayer or residue of the interlayer from the separated first pultrusion element. LIST OF REFERENCES

2 wind turbine

4 tower

6 nacelle

8 hub

10 blade

13 shell

14 blade tip

15 tip end

16 blade root

17 root end

18 leading edge

20 trailing edge

24 first blade shell part (pressure side)

26 second blade shell part (suction side)

30 root region

32 transition region

34 airfoil region

36 tip region

38 shoulder

42 wind turbine blade part

44 stack

50 reinforcing structure

52 first side of reinforcing structure

54 second side of reinforcing structure

56 first end of reinforcing structure

57 second end of reinforcing structure

58 first lateral side of reinforcing structure

59 second lateral side of reinforcing structure

60 pultrusion element(s)

60' first pultrusion element

60" second pultrusion element

60"' third pultrusion element

62 first side of pultrusion element 62' first side of first pultrusion element 62" first side of second pultrusion element 64 second side of pultrusion element 64' second side of first pultrusion element 64" second side of second pultrusion element 66 first lateral side of pultrusion element 66' first lateral side of first pultrusion element 66'" first lateral side of third pultrusion element 68 second lateral side of pultrusion element 68' second lateral side of first pultrusion element 68'" second lateral side of third pultrusion element 70 first end of pultrusion element

70' first end of first pultrusion element

72 second end of pultrusion element

72' second end of first pultrusion element

80 interlayer or residue of interlayer

82 separation line

84 transition layer

86 wedge element

90 cover layer

92 core element

100 separation station

102 work surface

104 separation element

104' first part of separation element

104" second part of separation element 106 actuator

106' first actuator

106" second actuator

106'" third actuator

108 machining device

200 method of separating

202 providing a wind turbine blade part

204 removing cover layer 204a machining 206 separating 206a applying peeling force 206b heating 208 removing interlayer or residue 208a machining 210 coiling

1200 method of manufacturing

1202 performing method to obtain plurality of pultrusion elements 1204 arranging plurality of pultrusion elements

1206 infusing plurality of pultrusion elements 1208 causing or letting the resin cure

Te thickness of pultrusion element

Le length of pultrusion element

We width of pultrusion element

Ts thickness of reinforcing structure

Ts length of reinforcing structure

Ws width of reinforcing structure

Ti thickness of interlayer

L separation line

S pre-treatment size of pultrusion element

51 first undersize

52 second undersize

53 third undersize

Claims

2. A method according to claim 1, wherein each pultrusion element is a carbon fibre reinforced pultrusion element, preferably consisting of carbon fibres embedded in a cured first resin, preferably made of epoxy.

3. A method according to any of the preceding claims, wherein the interlayer comprises a flow medium material embedded in a cured second resin.

4. A method according to claim 3, wherein the second resin of the interlayer is a thermoset resin, preferably made of vinyl ester.

5. A method according to claim 3, wherein the second resin of the interlayer is a thermoplastic resin.

6. A method according to claim 5, wherein the step of separating the first pultrusion element from the second pultrusion element at the interlayer comprises heating at least the first pultrusion element, the second pultrusion element and the interlayer to a melting point of the thermoplastic resin of the interlayer.

7. A method according to any of claims 3-6, wherein the flow medium material of the interlayer comprises fibres, preferably a mixture of carbon fibres and glass fibres.

8. A method according to any of the preceding claims, wherein the step of separating the first pultrusion element from the second pultrusion element at the interlayer comprises applying a peeling force between the first pultrusion element and the second pultrusion element.

9. A method according to claim 8, wherein the peeling force is applied by a wedge element introduced between the first pultrusion element and the second pultrusion element.

10. A method according to any of the preceding claims, wherein the wind turbine blade part comprises one or more cover layers covering the plurality of embedded pultrusion elements, and wherein the method comprises removing, preferably by machining, the one or more cover layers to expose the first pultrusion element of the plurality of embedded pultrusion elements.

11. A method according to any of the preceding items, wherein the weaker peel strength between the interlayer and the first and/or second pultrusion element than the peel strength within the first and/or second pultrusion element can be achieved by the first resin of the first and/or second pultrusion element being different than the second resin of the interlayer.

12. A method according to any of the preceding claims, wherein the method comprises a step of removing the interlayer or residue of the interlayer from the first and/or second side of the first pultrusion element.

13. A method of manufacturing a composite part, preferably a wind turbine blade part, from a plurality of pultrusion elements, comprising: performing a method according to any one of the previous claims to obtain a plurality of separate pultrusion elements, arranging the plurality of separate pultrusion elements in a mould with an interlayer arranged between adjacent pultrusion elements, infusing the plurality of separate pultrusion elements with a resin, and

- causing or letting the resin cure so as to form the composite part.

14. A pultrusion element obtainable by a method according to any one of claims 1-12.

15. Use of a pultrusion element according to claim 14 in a method according to claim 13.