GB2481046A

GB2481046A - Method for producing a wind turbine component using a water-based coating compound

Info

Publication number: GB2481046A
Application number: GB1009678.2A
Authority: GB
Inventors: Jed Prouty Richter
Original assignee: Vestas Wind Systems AS
Current assignee: Vestas Wind Systems AS
Priority date: 2010-06-09
Filing date: 2010-06-09
Publication date: 2011-12-14
Anticipated expiration: 2030-06-09
Also published as: GB201009678D0; GB2481046B

Abstract

Method for producing a wind turbine component using a water-based coating compound A process for producing a wind turbine blade component comprises: applying a water-based coating compound (e.g. water soluble acrylate) onto the inner surfaces of a mould 12, 18 and drying the coating compound to provide a continuous coating layer 14; applying one or more layers of an uncured composite material directly onto the coating layer in the mould; curing the composite material to form a moulded blade component; releasing the cured, moulded component with the coating layer on the surface thereof from the mould; removing the coating layer with water to expose an outer surface of the composite material forming the blade component; and applying a layer of paint directly onto the exposed outer surface of the component. The coating may be applied by spraying or rolling.

Description

METHOD FOR PRODUCING A WIND TURBINE COMPONENT USING A

WATER-BASED COATING COMPOUND

The present invention relates to a method for the production of a wind turbine component such as a wind turbine blade and to the wind turbine component produced by such a method.

Composite materials comprising reinforcement fibres within a resin matrix are widely used in the manufacture of modern wind turbines and in particular, in the production of wind turbine blades. During the production process of a wind turbine blade component, io fibrous reinforcement material and resin are introduced into a shaped mould cavity and the resin is cured in order to harden the material and form the shaped component.

I Wind turbine blades formed of composite material typically require an outer surface coating in order to achieve an acceptable surface finish which optimises the aerodynamic properties of the blades and forms a protective barrier layer on the outside of the blade.

is The surface coating may be applied onto the component after moulding, or may be applied as an in-mould coating. This is commonly provided in the form of a gel coat layer.

Typically, a further paint layer will be applied to the gel coat layer to provide the outer surface of the blade.

Use of a gel coat layer yields a painting surface on the outside of the blade component with very few voids or pinholes. Without this layer, large areas of the component are likely to be covered with such voids. As a result, the blade needs extensive repair and the lifetime of the paint layer is likely to be limited. When the gel coat is provided as an in-mould coating, the gel coat has the additional function of protecting the mould surface from attack by the epoxy resin materials in the composite materials forming the blade during curing at high temperatures. In some cases, the gel coat may also seal any vacuum leaks on the mould surface, thereby improving the laminate quality that can be achieved.

In conventional moulding methods for forming a wind turbine blade, a release agent is applied to the surface of the mould in order to prevent the component sticking to the mould. A layer of gel coat is then applied to the mould surface and allowed to cure or harden. Layers of fibrous reinforcement material are placed on top of the gel coat in the mould and the fibrous material is infused with resin. After curing of the resin, the component is released from the mould and the gel coat forms an outer surface layer on the component. Typically, in order to provide a surface that is suitable for painting, the gel coat will be abraded using a grinding process to remove an upper portion of the gel coat.

Finally, paint will be applied to the abraded surface to provide a smooth, aesthetic finish to the blade.

The use of a gel coat in the manufacture of wind turbine blades has many advantages, as set out above. However, the handling of gel coats during the manufacture of wind turbine blades can be difficult and the effective application of the gel coat to the mould surface requires specialised equipment and skilled personnel. The gel coat is typically formed of two or more resin components, which must be combined prior to the moulding process. The resultant gel is applied directly onto the mould surface and allowed to dry, or gel within the mould to achieve cross-linking and hardening.

The application of a uniform layer of gel is often difficult, in particular due to the viscous nature of the gel and the complex shape of the mould. Furthermore, any variations io in humidity, temperature or other operating conditions may adversely affect the quality of the surface finish provided by the gel coat. Due to the nature of the materials used to form * the gel coats, it is usually preferable to use a rolling technique to apply the layer of gel coat to the mould surface, so that the generation of fumes can be minimised. However, such techniques are typically carried out manually and can be time consuming. The time required for the gel coat to gel or harden also increases the overall manufacture time for the blade.

The surface of the gel coat is typically relatively smooth and glossy, and therefore not ideal for receiving a further coating of paint. Residual amounts of the release agent on the blade surface may also prevent the adhesion of the paint layer to the surface. Once the blade has been formed and demoulded, the surface of the gel coat must therefore be abraded so that a roughened surface is provided for painting.

The abrading or grinding step increases the time and cost of the manufacturing process and apparatus and is generally undesirable due to the high levels of dust that are generated. Furthermore, not all of the gel coat will be removed during the grinding step and the remaining gel coat increases the overall weight of the blade, which may have a negative impact on the efficiency of the wind turbine. A further potential problem is that the abrading step does not completely remove the residual release agent from the blade surface and so even after abrading the surface, the adhesion of the paint to the surface may be adversely affected.

In view of the negative aspects associated with the use of a gel coat, it would be desirable to provide an alternative method for manufacturing wind turbine blade components, which achieves a suitable surface finish whilst avoiding the use of the gel coat layer. It would also be desirable to provide a more efficient and cost effective method for producing wind turbine blade components.

According to the present invention there is provided a method for producing a wind turbine blade component comprising the steps of: a) applying a water-based coating compound onto the inner surfaces of a mould and drying the coating compound to provide a continuous coating layer; b) applying one or more layers of an uncured composite material directly onto the coating layer in the mould; C) curing the composite material to form a moulded blade component; d) releasing the cured, moulded blade component with the coating layer on the surface thereof from the mould; e) removing the coating layer with water to expose an outer surface of the composite material forming the blade component; and f) applying a layer of paint directly onto the exposed outer surface of the blade component.

In the method of the present invention, the conventional step of applying a gel coat to the mould surface prior to placement of the fibrous reinforcement material in the mould is replaced with step (a), in which a water-based coating compound is used to form a coating layer. The coating layer is subsequently removed from the component to leave behind a surface which is suitable for the direct application of a paint coat. Advantageously, the use of the coating layer to provide a suitable surface finish therefore avoids the need for a gel coat layer.

As well as providing a suitable surface to the blade component, the coating layer acts as a protective layer between the mould surface and the resin materials of the composite material, which protects the mould surface, as described above in relation to the gel coat. As with the gel coat layer, the coating layer substantially prevents the formation of voids or pinholes on the blade component surface and seals vacuum leaks in the mould surface in order to provide an optimal surface to the blade component. As such, the coating layer used in the method of the present invention provides many of the advantages of the gel coat layer during manufacture of the blade component, whilst avoiding the disadvantages and any adverse effects on the final blade component.

A major advantage of the invention is that the method does not require any further processing of the surface between removal of the coating layer and application of a paint coat. The abrading and grinding steps that are required in conventional manufacturing techniques to ensure that the blade surface is suitable for painting are therefore eliminated.

This not only reduces the time required to manufacture each blade, but also reduces the cost of the apparatus and reduces the health and safety risks associated with the manufacturing method.

In step (a) of the moulding method according to the invention a continuous coating layer is formed on the mould surface, which will form an outer coating layer on the moulded blade component once the component is removed from the mould. It is essential for the later steps of the method that the coating layer is formed of a water-based coating compound, that is, a coating compound that uses water as carrier for suspended or dissolved coating solids. This enables the resultant, water-based and water soluble coating layer to be readily removed by washing the component with water in step (e).

The coating layer is formed by applying an even layer of the fluid coating compound to the mould surface and then drying the coating compound by allowing the water to flash off' or evaporate, leaving behind a layer of the dry solids from the coating compound. The water may be allowed to evaporate at room temperature or can be more quickly removed S from the coating layer through the application of heat to the mould surfaces. If desired, one or more additional coating layers may be applied after drying of the initial layer, depending on the desired thickness of the layer.

The coating layer may be applied directly onto the mould surface. Preferably, a water-based release agent may first be applied to the mould surface, prior to the application of the coating compound.

The water-based coating compound may be applied in any suitable way, for example, by rolling it onto the mould surface, or by spraying. Suitable techniques are commonly used in the production of wind turbine components. Since the coating compounds are safe, water-based compounds, these processes can be manually carried out using a variety of application techniques, with greater control over the potential risks to the personnel. Alternatively, it may be preferred to apply the compound using automatic procedures.

The coating compound will typically be formed of a single component, so unlike with the formation of complex gel coats, no prior mixing or processing of components will be required. Advantageously, the application and drying of the coating compound can also be carried out more quickly and simply than the application of a gel coat to the mould surface.

The overall production time is thereby significantly reduced compared to the conventional method where a gel coat is applied. Furthermore, the water-based coating compounds will typically be significantly lower cost than the compounds used to form gel coats and the use of lower cost equipment is possible.

Preferably, the water-based coating compound is an acrylate compound. Suitable acrylate coating compounds, such as those used in matt and textured paints would be well known to the skilled person.

Preferably, the thickness of the coating layer is at least 0.1 mm and preferably between 0.1 mm and 1.0 mm, more preferably between 0.2 mm and 0.6 mm and most preferably between 0.3 mm and 0.6 mm. Depending on the desired thickness of the coating layer, the layer may be applied in a single step, or may be built up in a number of successive application steps.

Step (b) of the moulding method according to the invention involves the placement or lay-up' of fibrous reinforcement material in the mould, typically on the mould surface.

This process is well known to the skilled person. In the method of the present invention, the layers of fibrous reinforcement material are placed directly onto the dried coating layer on the mould surface, with no intervening layers.

The fibrous reinforcement material may be at least partially preformed to the desired io shape of the component, if desired. The reinforcing fibres may be provided in any suitable form including but not limited to: prepregs, semi-pregs, woven or non-woven fabrics, mats, pre-forms, individual or groups of fibres, tows and tow-pregs.

The term "prepreg" refers to a substantially or fully impregnated collection of fibres, fibre tows, woven or non-woven fabric. Woven and non-woven fabrics are collections of individual fibres or fibre tows that are substantially dry, that is, not impregnated by a resin.

Fibre tows are bundles of large numbers of individual fibres.

The term "semi-preg" refers to a partially impregnated collection of fibres or fibre tows. The partial impregnation provides for enhanced removal of gas through or along the dry fibres during consolidation and/or curing.

The term "tow-preg" refers to an at least partially impregnated fibre tow.

The term "pre-form" refers to a composite material comprising fibres and cured or uncured resin. The fibres are preferably provided in layers of oriented fibres. Examples of pre-forms and methods of preparing pre-forms are described in WO-A-20041078442. In order to reduce waste, the pre-forms may be provided as a pre-formed slab, which has been produced with the desired shape and size so that it can be incorporated directly into the mould.

The fibrous reinforcement material preferably comprises one or more types of fibres selected from: carbon fibres, glass fibres, aramid fibres, synthetic fibres, bio fibres, mineral fibres, metal fibres or boron fibres.

The resin may be a thermoplastic or thermosetting resin and may be based on, for example, unsaturated polymer, polyurethane, polyvinyl ester, epoxy or combinations thereof. Most preferably, the resin is an epoxy resin. Resin formations for use in a resin infusion method, such as resin transfer moulding, are well known in the art.

The resin may be provided as liquid, semisolid or solid resin. It may comprise two or more resin systems which may or may not be based on the same type of resin, such as two or more epoxy-based systems. Through the use of two or more resin systems, it may be possible to optiniise the properties of the resin for the subsequent steps of processing, for example with respect to viscosity and timing/controlling of the curing process.

Where the fibrous reinforcement material is dry, i.e. substantially free of resin and moisture, or only partially impregnated with resin, additional resin may be introduced into the fibrous reinforcement material in the mould using a resin infusion process, such as a resin transfer moulding (RTM) method. In processes of this type, the fibrous reinforcement material is first put in place on a first part of the mould surface, above the coating layer. A second mould part may be clamped over the first part to define a cavity containing the fibrous reinforcement material. Alternatively, a cavity may be produced through the use of a vacuum bag rather than a mould part, but in this case only one side of the component will have a moulded surface.

The resin is then drawn through the cavity so that it infuses into the fibrous reinforcement material. The resin will typically be introduced into the mould cavity under pressure and optionally, the flow of resin through the cavity may be assisted by the is application of vacuum. Once the required amount of resin has been introduced into the mould and the fibrous reinforcement material is sufficiently wet', the resin ports will be closed so that the mould cavity is sealed prior to the curing step. The infusion of the resin may take place at ambient temperature, or at an elevated temperature.

The components formed from the fibrous composite material may be unconsolidated or at least partially consolidated. The term "consolidated" means that most, if not all of the gas has been removed from the composite material, giving a lower porosity.

Pre-consolidated pre-forms are particularly suitable for use in wind turbine blade components, since they provide good reproducibility, high strength and high homogeneity, and can be connected to other pre-forms or structures.

In step (c) of the method according to the invention, the resin is cured in order to achieve cross-linking and hardening. The cure conditions will depend upon the resin system used and will typically require the application of heat over a specific period of time, although some resins may be cured at ambient temperature. Where heat is required in the curing process, the mould will typically incorporate heaters in order to heat the inner mould surfaces. In some cases, curing may be initiated or accelerated by the incorporation of curing agents into the resin, or by the application of UV light.

During the curing process, the resin comes into contact with the coating layer and upon hardening, the coating layer will become adhered or attached to the composite material forming the component. This means that when the component is released from the mould in step (d), the coating layer will remain on the outside of the component, rather than remaining on the mould surface.

After curing of the resin, the component is released from the mould, or demoulded, in the conventional manner.

In step (e) of the method according to the invention, the coating layer is removed from the blade component by washing the component surface with water. The washing step may be carried out using any suitable technique, such as spraying, and may be carried out manually, or automatically. Since the coating compound is water soluble, the application of water to the coating layer on the surface layer of the component should readily remove the layer to expose the underlying surface of the composite material.

Advantageously, step (e) also achieves the removal of any residual release agent io on the surface of the component, which could otherwise affect the adhesion of the paint to the blade component surface, as described above.

In the method of the present invention, the coating layer is used only to impart a desirable texture or surface finish to the surface of the composite material and not to provide a surface finish itself, or to provide useful properties to the component. The nature of the coating compound is preferably such that when the coating layer is removed, the underlying surface of the composite material is matt and/or textured. The textured or roughened surface of the composite material aids the long-term adhesion of the paint thereby increasing the lifetime of the paint layer and reducing the amount of repair work required.

The coating layer will otherwise have a negligible effect on the final wind turbine blade component and advantageously will not affect the weight or aerodynamic properties of a wind turbine blade produced using the method according to the invention.

In step (0 a layer of paint is applied to the exposed surface of the blade component in the conventional manner, for example, by spraying or rolling.

The surface of the component should preferably be completely dry before the paint layer is applied in step (f). If necessary, the surface of the blade component may be dried between steps (e) and (f), for example, through the exposure of the blade surface to a stream of hot air. This additional step may be preferred, for example, if it is desired to paint the surface of the component immediately after removal of the coating layer. The inclusion of a drying step may also further reduce the overall production time of the component.

The method according to the invention is suitable for the production of many different types of composite wind turbine components, but finds particular application in the production of components for wind turbine blades.

The present invention also provides a component produced by the method according to the invention set out above and in particular, a wind turbine blade component.

The invention will now be further described, by way of example only, and with reference to the accompanying Figure 1.

Figure 1 shows a schematic diagram of the moulding apparatus used to carry out a method according to an embodiment of the invention for producing a wind turbine blade component In the first step of the method, a water-based, acrylate coating compound is sprayed onto the inner surface of a first, lower mould part 12 to form a continuous, uniform layer of the coating compound. The lower mould part 12 is heated in order to flash off or evaporate the water solvent from the coating compound whereby a solid, coating layer 14 is formed on the mould surface.

In the next step of the method, once the coating layer is dry, a plurality of fibrous tows 16 are laid on the surface of the first, lower mould part 12, directly on top of the coating later 14. A second, upper mould part 18 is clamped in place over the first mould part 12 and the fibrous tows 16 to create a mould cavity 20. A source of resin 22 and a source of hardener 24 are provided and each source is connected to a pre-mixing chamber 26 in which the resin 22 and hardener 24 are combined, prior to being introduced into the mould cavity 20. The mixture of resin 20 and hardener 22 from the pre-mixing chamber 26 is introduced into the mould cavity 20 by means of a resin conduit 28 and a resin inlet port provided in the upper mould part 18.

Once the second mould part 18 has been fixed in place using clamping means 32, the flow of resin 22 and hardener 24 is started and the mixture of resin and hardener is injected into the mould cavity 20 from the pre-mixing chamber 26 using pumping means (not shown). Vacuum is applied to the mould cavity 20 to assist the infusion of the resin 22 through the fibrous tows 16.

Once the required amount of resin 22 has been pumped into the mould cavity 20, * the resin flow is stopped and the resin inlet port 26 is closed, together with any other inlet or outlet ports in the mould. The resin 22 is then cured by the application of heat to the first 12 and second 18 mould parts, in a defined heating cycle.

When the curing process is completed, the moulded component is released from the mould with the coating layer 14 forming the outer surface of the component.

The coating layer 14 is removed or washed off, by spraying the surface of the component with water and the blade component is then dried. A layer of paint is applied directly to the surface of the blade component that has been exposed through the removal of the coating layer, using a conventional spraying technique.

Claims

CLAIMS1. A process for producing a wind turbine blade component comprising: a) applying a water-based coating compound onto the inner surfaces of a mould and drying the coating compound to provide a continuous coating layer; b) applying one or more layers of an uncured composite material directly onto the coating layer in the mould; C) curing the composite material to form a moulded blade component; d) releasing the cured, moulded component with the coating layer on the surface thereof from the mould; e) removing the coating layer with water to expose an outer surface of the composite material forming the blade component; and f) applying a layer of paint directly onto the exposed outer surface of the component.
2. A process according to claim I wherein the water-based coating compound is a water soluble acrylate coating compound.
3. A process according to claim I or 2 wherein heat is applied to the mould to dry the coating compound in step (a).
4. A process according to any preceding claim wherein the coating compound is applied to the surface of the mould by spraying or rolling.
5. A process according to any preceding claim wherein the coating layer has a thickness of between 0.2 mm and 0.6 mm, preferably between 0.3 mm and 0.6 mm.
6. A process according to any preceding claim further comprising the step of drying the outer surface of the composite material between steps (e) and (1).
7. A process according to any preceding claim wherein the coating compound is selected such that the outer surface of the composite material exposed after removal of the coating layer in step (e) is matt and/or textured.
8. A wind turbine blade component produced by the process of any preceding claim.