Laminate pre-form for a wind turbine blade

Abstract

A laminate preform is disclosed, having a top side and a back side extending between respective edge portions, the laminate preform comprising a plurality of layers of fiber tows extending in a length direction of the laminate pre-form, the fiber tows being at least partly fixed by resin. The laminate pre-form is in between a first and a second prepreg or semi-preg layer including fibers extending in an oblique direction with respect to the length direction, and at least one distribution channel is provided at the back side extending in the length direction. Also disclosed is a method for manufacturing such a laminate pre-form.

Claims

1. A pre-consolidated laminate pre-form for a wind turbine blade having a top side and a back side extending between respective edge portions, the laminate pre-form comprising: a plurality of layers of continuous fibre tows extending in a length direction of the laminate pre-form, the fibre tows being at least partly fixed by at least one non-continuous layer of resin, wherein the plurality of layers of continuous fibre tows are positioned in between a first and a second prepreg or semi-preg layer, the first and second prepreg or semi-preg layers including fibres extending in an oblique direction with respect to the length direction, and wherein at least one distribution channel is provided at the back side of the laminate pre-form extending in the length direction.

2. The laminate pre-form according to claim 1, wherein the at least one distribution channel is arranged to redistribute evacuation flow from a first area of the laminate pre-form having lower air permeability to a second area having higher air permeability.

3. The laminate pre-form according to claim 1, wherein the first and the second prepreg or semi-preg layers form an envelope that is a biaxial prepreg.

4. The laminate pre-form according to claim 1, wherein the pre-form is arranged in a mold, where the back side of the pre-form faces the mold.

5. A wind turbine blade comprising a laminate pre-form according to claim 1.

6. A method for preparing a laminate pre-form having a top side and a back side extending between respective edge portions, the pre-form comprising a plurality of layers of fibre tows being at least partly fixed by a resin, the method comprising: distributing a first fibre layer of fibre tows, the fibre tows extending in a length direction of the laminate pre-form; providing at least one non-continuous layer of resin material; locating the first fibre layer of fibre tows in between a first and a second prepreg or semi-preg layer, the first and second prepreg or semi-preg layers including fibres extending in an oblique direction with respect to the length direction of the laminate pre-form; and providing at least one distribution channel at the back side of the laminate pre-form, the distribution channel extending in the length direction.

7. The method according to claim 6, further comprising: removing air from the laminate pre-form.

8. The method according to claim 6, further comprising: providing a mold on which the pre-form is prepared.

9. The method according to claim 6, further comprising: redistributing air via the at least one distribution channel provided at from a first area of the laminate pre-form having lower air permeability to a second area having higher air permeability.

10. The method according to claim 6, further comprising: distributing a further fibre layer of fibre tows onto a second layer of resin, the fibre tows extending in a length direction of the laminate pre-form.

11. The method according to claim 6, wherein the first and the second prepreg or semi-preg layers form an envelope that is a biaxial prepreg.

12. The method according to claim 6, further comprising: curing the pre-form.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows a schematic view of a pre-form according to the present invention.

(2) FIG. 2 shows examples of geometries of the distribution channels included in the pre-form according to the present invention.

(3) FIG. 3 shows a schematic cross sectional view of a pre-form.

DETAILED DESCRIPTION OF THE INVENTION

(4) With reference to FIG. 1, the present invention relates to a pre-consolidated laminate pre-form 1 having a top side 2 and a back side 3 extending between respective edge portions 4.

(5) The laminate pre-form 1 comprises a plurality of layers of fibre tows 5 extending in a length direction of said laminate pre-form 1.

(6) Different types of fibres, such as glass fibres, carbon fibres, synthetic fibres, bio fibres, mineral fibres, and metal fibres can be used depending on the final use of the pre-form. For reinforcing a large composite structure, which is subject to significant stress, such as a wind turbine blade spar, carbon fibres are preferred, since they are much stronger than e.g. glass fibres. The pre-form comprises fibres in fibre tows which are bundles of a large number of individual fibres, i.e. bundles of unidirectional fibres.

(7) Each fibre tow may comprise fibres which are twisted in a manner known, e.g. from rope making etc., or may comprise fibres arranged side by side in a straight non-twisted fashion. The fibre tows may contain only fibres, or it may contain fibres and a binder for binding the fibres. The binder may comprise resin, e.g. similar to that resin fixing the fibre tows.

(8) The pre-form may include identical types of fibre tows. Alternatively, different layers of fibre tows may contain different types of fibre tows, e.g. one layer of fibre tows may be made of carbon fibre tows, whereas another layer of fibre tows may be made of glass fibre tows.

(9) The fibre tows are arranged substantially parallel to each other and are at least partly fixed to each other by a resin.

(10) The resin may be an organic polymeric liquid resin which, when converted into its final state for use, consolidates and becomes solid. As an example, the resin may be an epoxy-based resin or a polyester-based resin, though other resin types may also be applied. Furthermore, one or more different resin types may be applied. If using different types of resin, it may however be an advantage to use resins of one family to ensure compatibility between them. The resin may be provided by impregnating or by providing a separate layer of resin adhering to one or mare layers of fibre tows.

(11) The process of pre-consolidated pre-form may involve a limited curing. Alternatively the pre-consolidation process will not involve any significant effects of curing. The limited curing may involve a release of up to 50% or the energy that will be released by a complete curing of the resin. However, it is preferred that the extent of curing is limited to an extent that will allow the pre-form to be deformed plastically. The degree of curing that will allow for plastically deformation of a pre-consolidated pre-form depends amongst others on the exact resin as well as on the fibre type and fibre content. Generally, it is preferred that the limited curing involves less than about 20% of the energy that will be released by a complete curing of the resin and more preferably that the limited curing involves between 3 to 15% of the energy that will be released by a complete curing.

(12) Generally speaking, the pre-consolidation process should reduce the porosity of a pre-form, however, it is preferred that the resulting porosity of the pre-consolidated pre-form is less than 5% by volume, preferably less than 2% by volume and more preferably less than 1% by volume. In some cases, a porosity of even 1% may reduce the properties of a composite considerably. In these cases, it will be appreciated that the method and the pre-consolidated pre-forms may be produced with porosities well below 1%. For example, a reproduced porosity of about 0.2% by volume was realised for a composite with 60% carbon fibres in epoxy. The reduction of the porosity may for example be a result of exposing the pre-form to a pressure and/or a vacuum in relation to the pre-consolidation process.

(13) The porosity of the pre-consolidated pre-form can not be established directly, as a density is not known and may vary throughout the material. Hence, the porosity should be established by optical method on a materialographic sample. Preparation of materialographic samples from an uncured pre-consolidated pre-form is very demanding, since the material comprises both a very soft element (i.e. a resin) and a very hard element (i.e. the fibre). To establish a reproducible result, it is hence necessary to cure the pre-form prior to materialographic preparation. This curing should be pressureless to ensure that the porosity is unaffected by the process.

(14) The pre-form may comprise an arbitrary number of layers of fibre tows and resin depending on the use of the pre-form. A fibre tow contains a high number of parallel individual fibres, typically ranging from a couple of hundred fibres to several thousand fibres.

(15) The pre-form will have varying properties along the length extension due to variations in permeability of the resin layers.

(16) The fibre tow layers are positioned between a first and a second prepreg or semi-preg layer 6a, 6b which includes fibres extending in an oblique direction with respect to the length direction along which the fibre tows extend. In the embodiment shown, the first and second layers 6a, 6b are parts of an envelope 6 enclosing the laminate pre-form. The envelope 6 is preferably a biax prepreg orsemipreg having an extension at typically +45 degrees with respect to the length direction. Other inclinations at +30 degrees or orthogonally to the length direction are also possible.

(17) By a prepreg is meant pre-impregnated fibres containing fully wet-out fibres/filamentswhereas semi-preg is partially-impregnated materialsusually the fibre bundles are not impregnated. The degree of wet-out can vary from almost zero (the fibres sit-on top of a dry resin film) through to materials where the resin has flowed around the fibres to present a wet surface on both sidesbut the fibre bundles (yarns, tows, etc.) are not wet-out themselves. The latter is more typical of the materials used in wind-energy currently.

(18) A release film 9 may be applied on the top side 2 of the pre-form (1). The release film provides a barrier between the structual prepregs and the vacuum-consumables used for evacuating air and consolidating the materials. The release film preferably provides a clean rough surface to the laminate. The release film is easily separated from the laminate.

(19) The laminate pre-form encapsulated in the prepreg envelope is generally positioned inside a mold 8, where the back side 3 of the pre-form 1 faces the mold 8.

(20) At least one distribution channel 7 extending in the length direction of the laminate pre-form is provided at the back side 3 of the pre-form 1. Thus, the distribution channel 7 is located at the side of the pre-form facing the mold 5. In the following, where distribution channel is mentioned in singular, it is to be understood to include also the case when two or more distribution channels are used.

(21) This longitudinally extending distribution channel 7 serves to redistribute air along the length extension of the pre-form 1. In particular, the distribution channel 7 is arranged to redistribute an evacuation flow from an area of the laminate pre-form having lower air permeability to an area of the laminate pre-form having higher air permeability.

(22) It is possible to include one or more distribution channels in the pre-form depending on the use of the pre-form. If one single distribution channel is included, it may take the form of a hemispherical channel with a diameter of e.g. 1-15 mm. Other geometries such as top hat section, square, rectangular, triangular or omega shape may also be contemplated.

(23) Alternatively, if several distribution channels are included, they make take the form of hemispherical channels with a diameter of 3-10 mm, preferably 3-6 mm. The distribution channel(s) is/are generally distributed along the entire length of the pre-form. The use of longitudinal distribution channel(s), i.e. channels arranged in the same direction as the fibres, is advantageous as compared with distribution channels arranged vertically to the fibres. The reason is that the fibres may be damaged if they would have to be shaped into the same geometry as the distribution channel(s).

(24) With reference to FIG. 2, examples of possible channel geometries are shown. Geometry A shows an example of several distribution channels, while geometry B shows an example of one single distribution channel.

(25) The fibres of the prepreg or semi-preg envelope provide evacuation channels directed toward the edge portions 4 of the laminate pre-form, and also toward the distribution channel 7. Thereby, trapped air is conveniently removed from the pre-form.

(26) The pre-form generally has a thickness of 6-25 mm, preferably 6-20 mm. A plurality of pre-forms may be used with intermediate layers, e.g. of biaxial fabric or carbon tissue/veil. In either case, a prepreg or semi-preg envelope encapsulates the laminate pre-form.

(27) The inventive pre-form may be uncured or only partly cured. This allows the pre-form to be bent and formed to fit in a composite structure which it should reinforce. The fixing resin could be chosen such that it has a viscosity, under the relevant storage conditions, high enough to maintain the integrity of the pre-form even in an uncured state.

(28) Preferably, the laminate pre-form is semi-rigid at room temperature, such that the channel geometry is maintained. In this embodiment, the distribution channel has the ability to collapse and disappear into the laminate, e.g. when the pre-forms are sucked together by the applied vacuum, and/or when heated during the cure of the pre-form. By collapsing the distribution channel, a better and stronger connection between the pre-forms is obtained, thereby improving the strength of the structure.

(29) In the inventive method for preparing a laminate pre-form 1, a mold 8 is usually provided as a work surface on which the pre-form is prepared. Then, an arbitrary number or layers of fibre tows and resin are provided until the number of layers makes the pre-form suitable for a specific purpose.

(30) In order to ensure that the fibre tows remain in the length direction of the laminate pre-form, the layers of resin are distributed before distributing a layer of fibre tows, as the resin fixes the fibre tows and prevent movement of each fibre tow relative to the other fibre tows.

(31) The steps of distributing the resin may advantageously be automatically or partly automatically be carried out by the use of a nozzle device, since the resin may contain components which may irritate or may be harmful when in contact with the skin of a person distributing the resin.

(32) In the next step, all the layers are encapsulated in an enclosure comprising a prepreg or semi-preg material including fibres extending in an oblique direction with respect to the length direction of the laminate pre-form 1.

(33) The layers may e.g. be encapsulated by covering the work surface with a cover so that at least a part of the work surface forms part of the enclosure for the layers.

(34) The distribution channel 7 may e.g. be prepared by post-formation on the pre-form, by imprinting or by preparing the pre-form on a suitably shaped substrate. It is furthermore possible that the distribution channel may be provided by distributing the fibre tows in a way such that a lateral distance is present between two laterally neighbouring fibre tows at certain distances, where the gap so provided will form a distribution channel. In order to avoid that fibre tows position on top of the gap will not fall in and fill the gap, suitably a non-continuous layer of resin may act as barrier preventing an immediate collapse of the distribution channel. Finally the distribution channels may be formed in the resin as longitudinal passages present in the resin material.

(35) Trapped air may be removed from the enclosure e.g. by applying a vacuum using an external vacuum channel 10.

(36) Subsequently to removal of air, the pre-form may be heated to at least partly cure the resin. When heating the layers, the work surface may be moved to a heater so that the layers are heated while they are still arranged on the work surface. Alternatively, the pre-form may be moved to another surface on which the pre-form may be heated.

(37) During this heating step, the distribution channel may collapse and disappear into the laminate, depending on the rigidity of the laminate pre-form.

(38) In FIG. 3 an example of a schematic sectional view of a pre-form is shown indicating an example of the order of the components. In a real pre-form, the distance between the layers would be much smaller and the resin and adhesive would usually be partially absorbed into the layers of fibres. Layers of oriented fibres arranged in fiber tows 5 are provided with an adhesive 12 between them. The adhesive may be replaced with additional layers of resin. Two layers of resin 11 are also shown. The resin 11 is here distributed as a number of lines at an angle-here about orthogonal-to the fibre tows 5. The resin hence is distributed in a non-continuous layer to allow for gas to escape from the pre-form orthogonal to the direction of the fibre tows. With a non continuous layer of resin is intended a layer of resin that allows gas to escape in a vertical direction through the laminate, that is in the thickness direction of the laminate. The resin may be provided as a separate sheet which is perforated or by application of resin in a pattern, for instance as strings extending in an oblique or transversal direction with respect to the length direction of the laminate. The strings may be arranged in a biaxial fashion. The pre-form to be pre-consolidated is having at least one non-continuous layer of resin, through which gas may be removed during the pre-consolidation process. Hence, the gas need not be removed from the pre-form in a plane of a layer of resin or in a plane of a layer of fibres. The transportation distance and risk of having trapped gas inside the pre-consolidated pre-form is greatly reduced.

(39) An example of a method for securing that gas may continuously be removed from the pre-form during pre-consolidation involves a gradual activation of the pre-consolidation process starting either from the centre of the pre-form and moving towards the surfaces or from a side or edge and moving through the pre-form. For example this may be realised by heating from the reaction surface only, hence activating gradually from the side of the pre-form in contact with the reaction surface or by controlled microwave heating, hence activating gradually from the inside of the pre-form and moving towards the surfaces.

(40) The resin may be applied as a pattern of strips or as a pattern of dots or otherwise shaped elements that ensures that the resin layer form a non-continuous open surface. In FIG. 3 the resin is provided between two layers of fibre tows. This is the preferred positioning of resin and when this positioning is used. However, the resin may also be provided in contact with only one layer of fibre tows, i.e. in the top or at the bottom of the pre-form.