ROTOR BLADE ELEMENT WITH ANTI-ICING SURFACE FOR WIND TURBINE ROTOR BLADES

Abstract

A rotor blade element with a heatable foil (2, 3, 6) comprising a thermoplastic elastomer (TPE) and electric conductive elements (4), a wind power plant comprising this rotor blade element and a process for producing the rotor blade element comprising the steps: I) introducing a heatable foil (2, 3, 6), comprising a thermoplastic elastomer (TPE) and electric conductive elements (4) onto a mold; II) introducing a reinforcing material and prefabricated elements and/or additional parts onto the mold; III) vacuum-bagging of the complete setup IV) infusing curable resin; and V) curing the resin.

Claims

1.-12. (canceled)

13. A rotor blade element with a heatable foil (2, 3, 6) comprising a thermoplastic elastomer (TPE) and electric conductive elements (4), wherein the heatable foil is a multilayer foil comprising at least two layers, a top layer (3) made of a thermoplastic elastomer and an electrically heatable bottom layer (2), comprising (a) electric conductive elements (4) selected from carbon mesh, conductive sheet or tape, metal mesh or imprinted pattern of electrically conductive ink or (b) is made of thermoplastic polyurethane (TPU) comprising graphite, metal particles, graphene, carbon nanotubes, carbon black or mixtures thereof.

14. A rotor blade element according to claim 13, wherein thermoplastic polyurethane (TPU) is used as thermoplastic elastomer.

15. The rotor blade element according to claim 13, wherein the heatable foil is a multilayer foil made by co-extrusion of the top layer together with the bottom layer.

16. The rotor blade element according to claim 13, wherein the electrically heatable bottom layer (2) is made from thermoplastic polyurethane comprising aromatic organic diisocyanate and polyetherpolyols.

17. The rotor blade element according to claim 14, wherein the top layer (3) consists of aliphatic thermoplastic polyurethane.

18. The rotor blade element according to claim 13, wherein the top layer (3) consists of aliphatic thermoplastic polyurethane comprising an aliphatic organic diisocyanate and a polyether polyol.

19. The rotor blade element according to claim 13, wherein the heatable foil (2, 3, 6) has a thickness in the range from 10 to 2000 m.

20. The rotor blade element according to claim 13, wherein the heatable foil (2, 3, 6) is directly fixed onto the shell (1) of the rotor blade element structure.

21. A wind power plant comprising rotor blade elements according to claim 13.

22. A process for producing a rotor blade element according to claim 13 comprising the steps: I) introducing a heatable foil (2, 3, 6), which is a multilayer foil comprising a protective layer made of thermoplastic polyurethane produced using aliphatic diisocyanate and a bottom layer comprising heatable electric conductive elements (4) onto a mold; II) introducing a reinforcing material and prefabricated elements and/or additional parts onto the mold; III) III) vacuum-bagging of the complete setup IV) infusing curable resin; and V) curing the resin.

23. The process according to claim 22, wherein fibers are used as reinforcing material.

24. The process according to claim 22, wherein an epoxy resin system is used as curable resin.

Description

First Embodiment

Generation of an Anti/De-Icing Surface

[0126] An active anti or de-icing system is achieved by producing a blade containing a heatable top surface, which is able to melt or avoid ice formation or accretion on the surface.

[0127] A foil is produced by extruding TPU containing electrically conductive additives. The rotor blade element may be produced as described in WO 2010/121927 A2 using the heatable foil according to the invention as integrated foil. The main functionalities of such a foil are its anti or de-icing abilities, originated from its heating function, but also due to its hydrophobicity, which decreases considerably the binding energy of ice to the surface and therefore leads to an easier ice removal. The foil is not transparent due to the addition of conductive additives, which in general are of black color.

Second Embodiment

Generation of a Semi-Transparent Anti/De-Icing Surface

[0128] During the manufacturing of blades by infusion process, it is highly wished that the infused parts are well wetted by the resin, which can be epoxy, polyester, polyurethane, polyamide, etc. The quality proof is currently often visually, which turns impossible once the surface of the blade is coated with a non-transparent foil as described above. In order to solve that problem, on top of a transparent foil (i.e. made of TPU), an electrically conductive mesh is printed, maintaining the transparency of the foil. This printing process of an electrically conductive paint is done by silk-screen like printing using a template or by actually printing it by means of a printer machine. Alternatively, other printing techniques may be used As an alternative process to printing, electrically conductive elements are integrated by attaching metal wires, tapes or any electrical conductive elements to the foils. Finally, after the removal of the blade from the form and mounting the blade parts altogether, a top coating is preferably applied to this surface.

Third Embodiment

Generation of an in Mould Top Coat having Anti/De-Icing Properties

[0129] As in embodiment 2, where an electrically conductive mesh grid, able to heat the surface is printed, a foil having the needed top coat properties (e.g. anti-erosion, UV resistance, color standard) is equipped with the aforementioned conductive mesh. This conductive mesh is preferably between the composite and the foil. After demolding the blade, a coated surface with anti or de-icing properties is directly obtained, which saves surface treatment time & costs. In this example, transparency is not achieved, therefore this approach is particularly interesting for the pre-preg process (no need of infusion, the fibers are already wetted by a resin), or for processes employing quality control techniques beyond visual inspection. Examples of such analysis would be computer tomography, x-rays, RF waves, Echo techniques, any type of sound waves, surface waves (as Lamb waves), Rayleigh waves or any wave that interact with the dry regions, having wavelength in the range from 0.1 nm up to meters, or any optical test that could help to identify dry parts.

[0130] In a preferred version, the heatable surface is used for quality inspection. After heating up the surface after demolding, defects and non-impregnated areas can be detected by distinct temperature generation This solution can also be used to support other quality control techniques.

Fourth Embodiment

Generation of an in Mould Top Coat having Anti/De-Icing Properties (Bi-Layer)

[0131] Similar to the third embodiment, top coat foils and heating functions are combined by two distinct foils. The multilayer foil contains minimum two-layers, the top coat foil attached to an electrically heatable foil. The adhesion between both foils is preferably promoted by, e.g. thermally welding both foils to each other (with the help of pressure or without it). In this case, the top coat is placed towards the mould, whereas the heatable part is attached to the resin, both chemically and physically.

Fifth Embodiment

Generation of an in Mould Top Coat

[0132] Similar to the fourth embodiment, an in mould top coat without active heating for anti or deicing properties could be produced. For that, the steps regarding the production of the electrically conductive parts should be skipped. For the case of TPU foils, extremely high anti-erosion properties can be achieved. Preferably, multi-layer foils comprising at least two layers are used, which allows to match the different requirements of the top layer and the bottom layer.

Sixth Embodiment

Repairing of an in Mould Top Coat

[0133] Repairing of the blade surfaces previously to top coating has been one of the core activities for generating a good quality blade surface on top of which a top coat is applied. This ensures the life time of the coating and therefore, of the blade as a whole. Using thermoplastic or partially cross-linked thermoplastic foils, such as TPU foils, allows for a thermal surface-repairing, i.e. the flow ability of such materials in the presence of heat, substitutes the need of sandpapering the surface since defects can be corrected by inducing material to flow from one region to another by applying heat combined with pressure. This procedure is called here ironing. The tool for such an ironing procedure is similar in function to common home iron used for ironing clothes. In order to remove excess material, a sort of cutting blade, similar to that of a shaving razor is applied (or even a wood shaver, or carrot peeler). Therrno-mechanical cutting can also be used. These procedures are applicable for the surface repairing but also during binding the shell parts together. The finishing of the adhesive lines for instance, is achieved by thermally welding the excess foils from 2 different parts to each other (let on purpose in excess). If required, a TPU or thermoplastic liquid coating is added to the surface for further repairing (again by ironing or thermo-welding).

Seventh Embodiment

Resin Curing by Using the Homogeneous Surface Heating Produced by Heatable Foils (or Surfaces)

[0134] Currently, blades are generally produced on composite moulds or forms having its own heating fields, which can be promoted by carbon fibers, metal wires or even hot water passing through integrated pipes. The heatable foil allows direct partial or complete curing of the resin (infused or pre-preg) by heating via the foil Homogeneity is significantly enhanced, the energy consumption is decreased considerably, since the heating foil is directly transferring its heat to the resin without the need of heating the entire body of the mould (which also has strong insulation properties due to the tooling epoxy resin combined with glass fibers). Apart from that, the mould costs are tremendously reduced, since no heating elements toned to be integrated to the mould. The thermal fatigue of the composite mould is also considerably decreased, because heating metal wires-resin interfaces are no longer existent.

Eights Embodiment

Generation of an in Mould Top Coat Enabled to Detect Icing Events

[0135] On the external part of the top coat foils, electrical wires are placed or even printed following the examples previously mentioned. Such wires are placed close to each other forming a sort of electrodes of a capacitor. The dielectric medium of such a capacitor can be air, water, ice, or a mixture of ice, water and dust. In any case, the presence of ice can clearly identified from the dielectric response, which in turn is completely different from that of water or air. Combined with existing anemometric detectors, it can precisely identify the presence of ice on different spot of the surface. This ability of icing detection could support the selective heating of iced regions on the blade surface, in case the heatable coating is able to show different heating fields throughout the blade surface.

[0136] Heatable thermoplastic polyurethane foils are thermoformable and show excellent adhesion to epoxy resin systems. Bubbles or pinhole formation during application is strongly reduced. They function as well as active and passive systems for preventing and reducing icing on rotor blades. Thermoplastic polyurethane (TPU) foils do not stick to the mold. Normally the manufacture of blades can be made by infusion process without the need of a separate release foil. The rotor blade according to the invention is erosion resistant and has good aerodynamic characteristics due to their high surface quality. Consequently a significant improvement in blade lifetime is achieved

[0137] The process for producing the rotor blade element according to the invention has several advantages. Tooling costs are decreased since no mixers for mixing two-component coating systems are needed. Since the top layer of the heatable thermoplastic polyurethane foil functions also as release foil, no release agents have to be applied onto the mold and to be removed after deforming the blade. This decreases production time, costs and possible adhesion faults of the top coating. No sandpapering is required and the blade surface is easy to repair.