Contact element with integrated heating cable

Abstract

A contact element (2) made from a resilient material is disclosed. The contact element (2) comprises an integrated heating cable (4), wherein the contact element (2). The heating cable (4) comprises a reinforcement (28) arranged to protect the heating cable (4) against stretching.

Description

[0001] Contact Element with Integrated Heating Cable

[0002] Field of invention

[0003] The present invention relates to a contact element made from a resilient material, wherein the contact element comprises an integrated heating cable. The present invention also relates to a method for manufacturing a contact element that comprises an integrated heating cable.

[0004] Prior art

[0005] It is known to integrate heating elements in pads and hereby provide heating pads for handling objects such as wind turbine blades during transport and storage. The prior art heating pads, however, comprise cables that cannot withstand the force of compression and expansion, when molded into a rubber mass. The heating wire / heating cable will break, leaving the heating pad without any heating capacity.

[0006] WO2023131383A1 discloses a module for supporting a blade for a wind turbine as well as a method for using such a module during handling and transport of a wind turbine blade. The module comprises a main body made from a resilient material integral with a base plate. The module can be equipped with an electrical heating element formed as a thread. The prior art heating pads, however, comprise cables that cannot withstand the force of compression and expansion, when molded into a rubber mass.

[0007] Thus, there is a need for a solution that reduces or even eliminates the above mentioned disadvantages of the prior art.

[0008] Summary of the invention

[0009] The object of the present invention can be achieved by a contact element as defined in claim 1 and by a method as defined in claim 20. Preferred embodiments are defined in the dependent subclaims, explained in the following description and illustrated in the accompanying drawings.

[0010] The contact element according to the invention is a contact element made from a resilient material, wherein the contact element comprises an integrated heating cable, wherein the heating cable comprises a core member and a heating element that is wound around the core member, wherein the core member is made of an electrically non-conductive material, wherein the core member and the heating element is enclosed by a jacket, wherein the heating cable comprises a reinforcement arranged to protect the heating cable against stretching.

[0011] The reinforcement protects the heating cable against tensile or compressive pull forces when the contact element is deformed (compressed, expanded or bent) e.g. during handling of object. The weight of an object (e.g. wind turbine blade) can exert a large forces to contact elements supporting the blade during storage and transportation. Since the reinforcement is configured to protect the heating cable against tensile or compressive pull forces when being deformed, the heating cable can generate sufficient heat to maintain a sufficiently large coefficient of friction between the contact element and the object (e.g. a wind turbine blade) during use under cold conditions.

[0012] Moreover, the reinforcement protects the heating cable and its insulating jacket from being damaged due to high temperatures and compression during the molding process.

[0013] In an embodiment, the heating cable is a multi-conductor cable.

[0014] In an embodiment, the heating cable is a single conductor cable

[0015] In an embodiment, the reinforcement surrounds at least a part of the heating cable.

[0016] In an embodiment, the reinforcement completely surrounds the heating cable along the length of the heating cable that the reinforcement extends.

[0017] In an embodiment, the reinforcement completely surrounds the heating cable along the entire length of the heating cable.

[0018] In an embodiment, the heating element is formed as a wire. In an embodiment, the heating element is formed as a wire having a circular cross-section.

[0019] In an embodiment, the heating element is formed as a band.

[0020] In an embodiment, the reinforcement is formed as a braiding.

[0021] In an embodiment, the reinforcement is formed as a braiding surrounding the jacket.

[0022] It may be advantageous to apply a braiding because it protects the heating cable against tensile or compressive pull forces when the contact element is deformed (compressed, expanded or bent).

[0023] In an embodiment, the reinforcement is cylindrical.

[0024] Hereby, the reinforcement ensures that the heating wire and the jacket are not damaged under high temperature and compression during the molding process (when the heating cable is integrated in the resilient material).

[0025] In an embodiment, the contact element designed to be heated to a temperature in the range 50-150°C inside the contact element. This can be achieved by carefully selecting the materials and the configuration of the elements of the contact element.

[0026] In an embodiment, the core member is made of glass fibre.

[0027] In an embodiment, the core member is made of para-aramid (Kevlar).

[0028] In an embodiment, the core member is made of a material having substantially the same tensile strength as the heating element.

[0029] In an embodiment, the resilient material is an elastic polymer material that can stretch and return to its original shape.

[0030] In an embodiment, the resilient material is rubber.

[0031] In an embodiment, the resilient material is natural rubber.

[0032] In an embodiment, the resilient material is synthetic rubber.

[0033] In an embodiment, the heating element is wound around the core member with 48 - 1000 turns per meter.

[0034] In an embodiment, the heating element is wound around the core member with 100 - 800 turns per meter.

[0035] In an embodiment, the heating element is wound around the core member with 120 - 600 turns per meter.

[0036] In an embodiment, the jacket is made of polytetrafluoroethylene.

[0037] Polytetrafluoroethylene has an extremely low friction - in fact one of the lowest known coefficients of friction of any solid material. It has high chemical resistance and is inert to most chemicals, acids, and solvents. It can withstand temperatures from -200°C to 260°C. It is electrically non-conductive.

[0038] In an embodiment, the jacket is made of fluorinated ethylene propylene.

[0039] Fluorinated ethylene propylene has high chemical resistance and is inert to most acids, bases, and solvents. It has a low coefficient of friction similar to polytetrafluoroethylene.

[0040] In an embodiment, the jacket is made of tetrafluoroethylene.

[0041] Ethylene tetrafluoroethylene has high chemical resistance and is resistant to acids, solvents, and bases. It has excellent thermal stability and can withstand temperatures up to 150°C. It is electrically non- conductive. It has a low coefficient of friction similar to polytetrafluoroethylene but has a higher mechanical strength.

[0042] In an embodiment, the reinforcement is made of metal, Kevlar or glass fibre.

[0043] In an embodiment, the reinforcement is made of Kevlar.

[0044] In an embodiment, the reinforcement is made of glass fibre.

[0045] In an embodiment, the reinforcement is made of a combination of metal, Kevlar or glass fibre.

[0046] In an embodiment, the reinforcement is formed as a concentric conducting shield made as a braiding (like often used in a coaxial cable)

[0047] The contact element is configured to generate heat (delivered by the heating cable) even when the contact element is deformed under use. Accordingly, the friction between the contact element and the object handled by the contact element can maintained so high that the contact element can provide and maintain a grip even at low ambient temperatures.

[0048] The contact element is configured to prevent overheating and to generate sufficient heat to keep the resilient material soft, flexible and have high friction at low ambient temperatures.

[0049] In an embodiment, the thickness of the contact element is in the range 2-10 mm.

[0050] In an embodiment, the thickness of the contact element is in the range 2-8 mm.

[0051] In an embodiment, the thickness of the contact element is in the range 2-6 mm.

[0052] In an embodiment, the thickness of the contact element is in the range 2-4 mm.

[0053] In an embodiment, the thickness of the contact element is in the range 2-3 mm.

[0054] In an embodiment, the thickness of the contact element 2.4 mm.

[0055] In an embodiment, the heating cable comprises a core member and a heating element that is wound around the core member. In an embodiment, a jacket encloses the core member and the heating element.

[0056] In an embodiment, the core member is cylindrical and comprises a circular cross-section.

[0057] In an embodiment, the core member comprises at least one types of heat-resistant synthetic fibre. In an embodiment, the core member is made of at least one types of heat-resistant synthetic fibre.

[0058] In an embodiment, the core member comprises Kevlar (para-aramid).

[0059] In an embodiment, the core member is made of Kevlar (para-aramid).

[0060] In an embodiment, the core member comprises glass fibre.

[0061] In an embodiment, the core member is made of glass fibre.

[0062] In an embodiment, the jacket 22 is an insulator. In an embodiment, the jacket is made of fluorine resin. In an embodiment, the jacket is made of a high temperature insulator.

[0063] In an embodiment, the jacket is made of fluorinated ethylene propylene (FEP). In an embodiment, the jacket is made of polytetrafluoroethylene (PTFE).

[0064] In an embodiment, the braiding is made of steel wires. In an embodiment, the braiding is made of 3 x 15 0 0.10 mm steel wires.

[0065] In an embodiment, the braiding is made of Kevlar wires. In an embodiment, the braiding is made of 3 x 15 0 0.10 mm Kevlar wires.

[0066] In an embodiment, the braiding is made of glass fibre wires. In an embodiment, the braiding is made of 3 x 15 0 0.10 mm glass fibre wires. In an embodiment, the reinforcement is made of a steel wire braiding.

[0067] In an embodiment, the heating cable is attached to a base member by using an attachment member shaped as a wire (e.g. of metal) or a thread or twine.

[0068] In an embodiment, the base member is shaped as a mesh comprising a plurality of mesh openings each configured to receive the attachment member.

[0069] In an embodiment, the reinforcement is a braiding made of wires, wherein the braiding so tight that the heating cable can be stretched less than 5% when loaded with a pressure of up to 600 kPa (600,000 Pa).

[0070] In an embodiment, the reinforcement is a braiding made of wires, wherein the braiding so tight that the heating cable can be stretched less than 3% when loaded with a pressure of up to 600 kPa.

[0071] In an embodiment, the reinforcement is a braiding made of wires, wherein the braiding so tight that the heating cable can be stretched less than 1% when loaded with a pressure of up to 600 kPa.

[0072] In an embodiment, the contact element comprises one or more electrical connections accessible from an outside of the contact element, wherein the one or more electrical connections are electrically connected to the heating cable.

[0073] Hereby, it is possible to electrically connect an external power source to the contact element by using the one or more electrical connections. This may be done by using power cables that are electrically connected to a battery, a generator or the mains. In an embodiment, the one or more electrical connections protrude from the outside of the contact element. Hereby, access to the electrical connection may be eased.

[0074] In an embodiment, the one or more electrical connections are shaped as an indentation protrude provide in the outside of the contact element.

[0075] In an embodiment, the contact element comprises a cast-in heating cable.

[0076] In an embodiment, the contact element comprises:

[0077] - a first electrical connection and

[0078] - a second electrical connection, wherein the first electrical connection is shaped to engage with the second electrical connection.

[0079] In an embodiment, the first electrical connection is shaped as a male structure, wherein the second electrical connection is shaped as a female structure.

[0080] In an embodiment, the contact element comprises an integrated plate. The plate may prevent undesired bending of the contact element and hereby reduce the stress force exerted to the heating cable.

[0081] The plate may be arranged and configured to distribute heat from the heating cable towards the outer surface of the contact element. Hereby, heat can be conducted from the heating cable in a faster manner then if the contact element did not comprise a plate.

[0082] In an embodiment, the contact element comprises several integrated plates arranged and configured to distribute heat from the heating cable towards the outer surface of the contact element.

[0083] In an embodiment, the integrated heating cable is mechanically attached to the plate.

[0084] In an embodiment, the plate is made of metal.

[0085] In an embodiment, the plate is made of aluminium.

[0086] In an embodiment, the plate is made of steel.

[0087] In an embodiment, the integrated plate is provided with one or more holes.

[0088] In an embodiment, the integrated plate is provided with plurality of holes.

[0089] In an embodiment, the integrated plate is arranged on an outer surface of the contact element.

[0090] In an embodiment, the heating cable is arranged in a layer positioned in a non-zero distance from the outer surface of the contact element.

[0091] Contact element assembly according to the invention is a contact element assembly comprising a plurality of contact elements according to one of the preceding claims, wherein the contact elements are electronically connected to each other.

[0092] The gripping tool according to the invention is a gripping tool for handling a wind turbine blade, wherein the gripping tool comprises at least one contact element according to the invention. In an embodiment, the gripping tool comprises a contact element assembly according to the invention.

[0093] The method according to the invention is a method for manufacturing a contact element according to the invention, said method comprising:

[0094] - inserting a heating cable into a mold;

[0095] - adding a resilient component into the mold while maintaining the inserting a heating in a predefined position of the mold;

[0096] - curing the resilient component and hereby integrating the heating cable in the contact element;

[0097] - removing the resilient component from the mold.

[0098] In an embodiment, the method comprises a step in which the heating cable is attached to a base member that maintains the position of the heating cable during the molding process.

[0099] In an embodiment, the contact element comprises a reinforcement that is formed as a braiding surrounding the jacket, wherein the resilient component is a liquid rubber material having a viscosity low enough to ensure that air being present between the heating element and the reinforcement is displaced.

[0100] Hereby, it is possible to provide an improved contact element.

[0101] The gripping tool according to the invention is suitable for handing wind turbine blades.

[0102] The function of the braiding is to protect the heating cable against stretching.

[0103] The function of the braiding is to increase the resistance against pull forces of the heating cable, so the heating cable can withstand expansion of the resilient material (e.g. rubber), when the contact element is compressed during use.

[0104] In an embodiment, the braiding has a non-fiber mesh function as a media to keep the lay-out of the heating cable along the sewing thread.

[0105] In an embodiment, the heating cable has a diameter in the range 1-4 mm.

[0106] In an embodiment, the heating cable has a diameter in the range 1.5-

[0107] 3.5 mm.

[0108] In an embodiment, the heating cable has a diameter in the range 2.0-

[0109] 2.5 mm.

[0110] In an embodiment, the heating cable diameter is 2.2 mm.

[0111] In an embodiment, the heating cable is configured to generate a heat output of 20 - 200 Watt / meter cable.

[0112] In an embodiment, the heating cable is configured to generate a heat output of 40 - 120 Watt I meter cable.

[0113] In an embodiment, the heating cable is configured to generate a heat output of 60 - 80 Watt / meter cable.

[0114] Description of the Drawings

[0115] The invention will become more fully understood from the detailed description given herein below. The accompanying drawings are given by way of illustration only, and thus, they are not limitative of the present invention. In the accompanying drawings:

[0116] Fig. 1A shows a top view of a contact element according to the invention;

[0117] Fig. IB shows a heating cable and a base member of a contact element according to the invention;

[0118] Fig. 2A shows elements of a heating cable of a contact element according to the invention;

[0119] Fig. 2B shows the heating cable shown in Fig. 2A comprising a reinforcement arranged to protect the heating cable against stretching;

[0120] Fig. 2C shows a close-up view of an embodiment of reinforcement suitable for protecting a heating cable against stretching;

[0121] Fig. 3A shows a perspective top view of a contact element according to the invention;

[0122] Fig. 3B shows a perspective top view of another contact element according to the invention;

[0123] Fig. 4A shows a contact element assembly according to the invention comprising two contact elements that are configured to be detachable attached to each other;

[0124] Fig. 4B shows a contact element assembly according to the invention comprising three contact element that are configured to be detachable attached to each other;

[0125] Fig. 4C shows a contact element assembly according to the invention comprising nine contact element that are configured to be detachable attached to each other;

[0126] Fig. 4D shows the contact element assembly shown in Fig. 4C in an assembled configuration;

[0127] Fig. 5A shows a schematic cross-sectional view of a contact element according to the invention and

[0128] Fig. 5B shows a graph illustrating a surface temperature of a contact element according to the invention as function of time;

[0129] Fig. 6A shows a cross-sectional view of a contact element according to the invention; Fig. 6B shows a cross-sectional view of a contact element according to the invention;

[0130] Fig. 7 shows a gripping tool for handling a wind turbine blade;

[0131] Fig. 8A illustrates a mold used to carry out a step of a method according to the invention;

[0132] Fig. 8B shows another step of the method according to the invention;

[0133] Fig. 8C shows another step of the method according to the invention and

[0134] Fig. 8D shows the last step of the method according to the invention, in which the contact element has been removed from the mold.

[0135] Detailed description of the invention

[0136] Referring now in detail to the drawings for the purpose of illustrating preferred embodiments of the present invention, a contact element 2 of the present invention is illustrated in Fig. 1A.

[0137] Fig. 1A illustrates a top view of a contact element 2 according to the invention. The contact element 2 comprises a body portion 10 made of a resilient material. In an embodiment, the body portion 10 is made of rubber. In an embodiment, the body portion 10 is made of polyurethane rubber.

[0138] The contact element 2 is provided with several holes 8. It may be an advantage that the holes are evenly distributed along a central axis of the body portion 10. In an embodiment the holes 8 comprises a cylindrical portion. In an embodiment the holes 8 comprises a conical portion.

[0139] The contact element 2 is provided with several grooves 6. In an embodiment, grooves 6 extend along a central axis of the body portion 10. In an embodiment, grooves 6 extend perpendicular to along the central axis of the body portion 10.

[0140] In an embodiment, the contact element 2 comprises no holes 8.

[0141] Fig. IB illustrates a heating cable 4 and a base member 12 of a contact element according to the invention. The heating cable 4 is attached to the base member 12 by using an attachment member 14 shaped as a wire (e.g. of metal) or a thread or twine. The base member 12 may be shaped as a mesh comprising a plurality of mesh openings each configured to receive the attachment member 14.

[0142] The base member 12 is provided with apertures 16. In an embodiment, the apertures 16 are evenly distributed and extend along a central axis of the base member 12. In another embodiment, the base member 12 is not provided with any apertures.

[0143] It can be seen that the heating cable 4 is arranged in wound configuration to increase the length of the heating cable 4 being attached to the base member 12. The heating cable 4 comprises a first distal end 18 and a s second distal end 20.

[0144] The first distal end 18 and the second distal end 20 are configured to be electrically connected to a power supply in order to heat the heating cable 4.

[0145] The heating cable 4 may be made of a nickel-chromium alloy. Nickelchromium alloys are widely used materials for heating elements due to their ductility, high resistivity, and oxidation resistance at high temperatures. In an embodiment, the heating cable 4 comprises a composition of 60-90% nickel and 10-40 % chromium. In an embodiment, the heating cable 4 comprises a composition of 80% nickel 20% chromium. Fig. 2A illustrates elements of a heating cable 4 of a contact element according to the invention. The heating cable 4 comprises a core member 26 and a heating element 24 that is wound around the core member 26. A jacket 22 encloses the core member 26 and the heating element 24.

[0146] In an embodiment, the core member 26 is cylindrical and comprises a circular cross-section.

[0147] In an embodiment, the core member 26 comprises at least one types of heat-resistant synthetic fibre. In an embodiment, the core member 26 is made of at least one types of heat-resistant synthetic fibre.

[0148] In an embodiment, the core member 26 comprises Kevlar (paraaramid). In an embodiment, the core member 26 is made of Kevlar (para-aramid).

[0149] In an embodiment, the core member 26 comprises glass fibre. In an embodiment, the core member 26 is made of glass fibre.

[0150] The jacket 22 is typically an insulator. In an embodiment, the jacket 22 is made of fluorine resin. In an embodiment, the jacket 22 is made of a high temperature insulator.

[0151] In an embodiment, the jacket 22 is made of fluorinated ethylene propylene (FEP). In an embodiment, the jacket 22 is made of polytetrafluoroethylene (PTFE).

[0152] Fig. 2B illustrates the heating cable 4 shown in Fig. 2A comprising a reinforcement 28 arranged to protect the heating cable 4 against stretching. The reinforcement 28 is formed as a braiding. In an embodiment, the reinforcement 28 is cylindrical. In an embodiment, the reinforcement 28 is made of metal. In an embodiment, the reinforcement 28 is made of steel. In an embodiment, the reinforcement 28 is made of Kevlar metal. In an embodiment, the reinforcement 28 is made of glass fibre.

[0153] In an embodiment, the reinforcement 28 is a braiding made of wires. In an embodiment, the braiding is 3x15 0 0.10mm wires.

[0154] In an embodiment, the reinforcement 28 is a braiding made of wires, wherein the braiding so tight that the heating cable 4 can be stretched less than 5%.

[0155] In an embodiment, the reinforcement 28 is a braiding made of wires, wherein the braiding so tight that the heating cable 4 can be stretched less than 3%.

[0156] In an embodiment, the reinforcement 28 is a braiding made of wires, wherein the braiding so tight that the heating cable 4 can be stretched less than 1%.

[0157] Fig. 2C illustrates close-up view of an embodiment of a reinforcement 28 (made as a braiding) suitable for protecting a heating cable against stretching.

[0158] The reinforcement 28 is formed as a braiding made of metal wires.

[0159] Fig. 3A illustrates a perspective top view of a contact element 2 according to the invention. The contact element 2 comprises a plurality of sections separated by grooves 6.

[0160] The contact element 2 is made from a resilient material. In an embodiment, the contact element 2 is designed to bear against a blade (not shown) of a wind turbine object during a handling (e.g. storage or transport) of the blade. The contact element 2 may be placed in a handling tool such as blade lifting yoke or a blade gripper.

[0161] Fig. 3B illustrates a perspective top view of another contact element 2 according to the invention. The contact element 2 is box-shaped.

[0162] The contact element 2 in Fig. 3A or Fig. 3B comprises an integrated heating cable that comprises a reinforcement element that surrounds at least a part of the heating cable. In an embodiment, the reinforcement is configured to ensure that heating cable 4 can be stretched less than 3%. In an embodiment, the reinforcement is configured to ensure that heating cable 4 can be stretched less than 1%.

[0163] Fig. 4A illustrates a contact element assembly according to the invention comprising two contact elements 2, 2' that are configured to be detachable attached to each other. The first contact element 2 comprises a first electrical connection 30 and a second electrical connection 32. Likewise, the second contact element 2' comprises a second electrical connection 30 and a second electrical connection 32. Corresponding electrical connections of adjacent contact elements 2, 2' are arranged and configured to be electrically connected to each other.

[0164] The first electrical connection 30 of the second contact element 2' is arranged and configured to be electrically and mechanically connected to the of the second electrical connection 32 of the first contact element 2.

[0165] In an embodiment, the first electrical connection 30 of the second contact element 2' is a female electrical connection arranged and configured to be electrically and mechanically connected to the of the second electrical connection 32 of the first contact element 2, wherein the second electrical connection 32 of the first contact element 2 is a male electrical connection comprising one or more protruding parts, wherein the first electrical connection 30 of the second contact element 2' is a female electrical connection comprising one or more receiving structures configured to receive the one or more corresponding protruding parts of the male electrical connection 32.

[0166] Fig. 4B illustrates a contact element assembly according to the invention comprising three contact element 2, 2', 2" that are configured to be detachable attached to each other. The contact element 2, 2', 2" may correspond to the ones shown and explained with reference t Fig. 4A.

[0167] Fig. 4C illustrates a contact element assembly according to the invention comprising nine contact element 2, 2', 2", 2"', 2"", 2""' that are configured to be detachable attached to each other. The contact element 2, 2', 2", 2"', 2"", 2""' comprise electrical connections that are arranged and configured to allow adjacent contact elements 2, 2', 2", 2"', 2"", 2""' to be electrically connected to each other. The electrical connections may be formed as male and female electrical connections shown in and explained with reference to Fig. 4A.

[0168] Fig. 4D illustrates the contact element assembly shown in Fig. 4C in an assembled configuration, in which adjacent contact element 2, 2', 2" are electrically connected to each other.

[0169] By applying a contact element assembly that comprises several contact elements 2, 2', 2" that are configured to be detachable attached to each other, it is possible to build the contact element assembly in a preferred manner depending on contact surface size requirements.

[0170] Since each contact elements 2, 2', 2" comprises an iintegrated heating cable arranged and configured to heat up the contact elements 2, 2', 2", each contact element 2, 2', 2" can be heated by connecting electrical power to the contact element assembly. Accordingly, it is possible to prevent the surface of the contact element assembly to freeze even if the ambient temperature is below 0°C.

[0171] Accordingly, a contact element 2, 2', 2" according to the invention or a contact element assembly according to the invention can be used in application, in which a high friction (between the one or more contact elements 2, 2', 2" an object being handled by using the one or more contact elements 2, 2', 2") is required even at low temperatures (e.g. down to -20 °C). One field of application may be rubber items that are required to be heated to keep them soft / flexible during low ambient temperatures.

[0172] A contact element 2, 2', 2" according to the invention or a contact element assembly according to the invention can be used for rubber pads for lifting equipment of wings for wind turbines.

[0173] Fig. 5A illustrates a schematic cross-sectional view of a contact element 2 according to the invention. The contact element 2 comprises a body portion 10. The body portion 10 an integrated heating cable 4.

[0174] The contact element 2 comprises several temperature sensors 34, 34'. The temperature sensors 34, 34' are arranged close to the contact surface (the upper surface as shown in Fig. 5A). Accordingly, the temperature sensors 34, 34' are arranged and configured to detect a temperature of the contact surface of the body portion 10.

[0175] In an embodiment, however, the contact element 2 comprises a single temperature sensor only.

[0176] It can be seen that the integrated heating cable 4 generates heat 36 (indicated with arrows). The temperature sensors 34, 34' are arranged to detect the temperature of the contact surface of the body portion 10 when the integrated heating cable 4 heats the contact element 2.

[0177] The contact element 2 comprises one or more electrical connections (not shown) that are accessible from an outside of the contact element 2. The one or more electrical connections (not shown) are electrically connected to the heating cable 4.

[0178] In an embodiment, the contact element 2 comprises a thermal switch arranged and configured to switch off electric power to the heating cable 4 when the detected temperature exceeds a predefined temperature limit (set point). In an embodiment, the contact element 2 comprises a thermostat (thermal switch) 54 arranged and configured to switch off electric power to the heating cable 4 when the detected temperature exceeds 70°C. The thermostat (thermal switch) 54 can be arranged near an outer surface of the body portion 10 of the contact element 2. In an embodiment, the thermostat (thermal switch) 54 is integrated in a temperature sensor 34'. In an embodiment, the thermostat (thermal switch) 54 is a separate component that is electrically connected to an electrical connect ion of the contact element 2. In an embodiment, the thermostat (thermal switch) 54 is programmable or controllable by using an extern control device (e.g. a remote controle). Hereby, it is possible to change the setpoint of the thermostat (thermal switch) 54.

[0179] Fig. 5B illustrates a graph illustrating a surface temperature of a contact element according to the invention as function of time.

[0180] During the time period At the heating cable 4 heats up the surface of the contact element from an initial temperature To to a higher temperature Ti. The temperature is detected by one or more temperature sensors. The one or more temperature sensors may correspond to the ones shown in and explained with reference to Fig. 5A.

[0181] Fig. 6A illustrates a cross-sectional view of a contact element 2 according to the invention. The contact element 2 basically corresponds to the one shown in Fig. 5A. The contact element 2, however, has no thermostat (thermal switch) but comprises an integrated plate 38, a first electrical connection 30 and a second electrical connection 32.

[0182] The integrated plate 38 is provided with holes 40. The first electrical connection 30 and the second electrical connection 32 are electrically connected to the heating cable 4. The first electrical connection 30 is a male type electrical connection while the second electrical connection 32 is a female type electrical connection configured to engagingly receive an electrical connection corresponding to the first electrical connection 30.

[0183] The integrated plate 38 is arranged in a layer arranged in a non-zero distance from a surface of the body member 10 of the contact element 2. The heating cable 4 is arranged in a layer arranged in a non-zero distance from a surface of the body member 10 of the contact element 2.

[0184] Fig. 6B illustrates a cross-sectional view of a contact element 2 according to the invention. The contact element 2 basically corresponds to the one shown in Fig. 6A. The integrated plate 38 is, however, arranged on an outer surface of the contact element 2.

[0185] Fig. 7 illustrates a gripping tool 42 for handling a wind turbine blade 44. The gripping tool 42 comprises a plurality a plurality of contact elements 2, 2', 2", 2"' according to the invention.

[0186] The contact elements 2, 2', 2", 2"' are brought into contact with and supports the wind turbine blade 44. The gripping tool 42 comprising a first support structure and a second support structure supporting the wind turbine blade 44. Each support structure comprises a contact element assembly comprising a plurality of contact elements 2, , 2", 2"' that are electronically connected to each other.

[0187] Fig. 8A illustrates a mold 46 used to carry out a step of a method according to the invention. The mold 46 comprises an inner space 52.

[0188] Fig. 8B illustrates another step of the method according to the invention. In this step, a heating cable 4 and temperature sensors 34, 34' have been put into the inner space 52 of the mold. A resilient component 48 has been filled into the inner space 52 of the mold. The resilient component 48 may be injected into the inner space 52 of the mold when the mold is closed by a lid 50 as shown in Fig. 8C.

[0189] Fig. 8C illustrates another step of the method according to the invention. In this step, a lid 50 has been attached to the mold 46. The resilient component 48 may be injected into the inner space 52 of the mold in this step. By applying a sufficiently large pressure, the resilient component 48 will displace the air from the inner space of the mold 46. Accordingly, it is possible provide a contact element 2 with very few air bubbles or even without any air bubbles.

[0190] Fig. 8D illustrates the last step of the method according to the invention. In this step, the contact element 2 has been removed from the mold.

[0191] Even though it is not shown, the contact element 2 may comprise a first electrical connection and a second electrical connection like shown in and explained with reference to Fig. 6A or Fig. 6B. List of reference numerals

[0192] 2, 2', 2" Contact element

[0193] 2"', 2"" Contact element

[0194] 4 Heating cable

[0195] 6 Groove

[0196] 8 Hole

[0197] 10 Body portion

[0198] 12 Base member

[0199] 14 Attachment member

[0200] 16 Aperture

[0201] 18 First distal end

[0202] 20 Second distal end

[0203] 22 Jacket

[0204] 24 Heating element

[0205] 26 Core member

[0206] 28 Reinforcement (e.g. braiding)

[0207] 30 First electrical connection

[0208] 32 Second electrical connection

[0209] 34, 34' Temperature sensor

[0210] 36 Heat

[0211] 38 Plate

[0212] 40 Hole

[0213] 42 Gripping tool

[0214] 44 Wind turbine blade

[0215] 46 Mold

[0216] 48 Resilient component

[0217] 50 Lid

[0218] 52 Inner space

[0219] 54 Thermostat (thermal switch)

[0220] To, Ti Temperature

[0221] At Time period

Claims

Claims1. Contact element (2) made from a resilient material, wherein the contact element (2) comprises an integrated heating cable (4), wherein the contact element (2), wherein the heating cable (4) comprises a core member (26) and a heating element (24) that is wound around the core member (26), wherein the core member (26) is made of an electrically non-conductive material, wherein the core member (26) and the heating element (24) is enclosed by a jacket (22), characterised in that the heating cable (4) comprises a reinforcement (28) arranged to protect the heating cable (4) against stretching.

2. Contact element (2) according to claim 1, wherein the reinforcement (28) is formed as a braiding surrounding the jacket (22).

3. Contact element (2) according to claim 1 or 2, wherein the reinforcement (28) is cylindrical.

4. Contact element (2) according to one of the preceding claims, wherein the core member (26) is made of glass fibre or para-aramid.

5. Contact element (2) according to one of the preceding claims, wherein the core member (26) is made of a material having substantially the same tensile strength as the heating element (24).

6. Contact element (2) according to one of the preceding claims, wherein the resilient material is rubber.

7. Contact element (2) according to one of the preceding claims, wherein the heating element (24) is wound around the core member (26) with 48 - 1000 turns per meter.

8. Contact element (2) according to one of the preceding claims,wherein the jacket (22) is made of polytetrafluoroethylene, fluorinated ethylene propylene or ethylene tetrafluoroethylene.

9. Contact element (2) according to one of the preceding claims, wherein the reinforcement (28) is made of metal, para-aramid (Kevlar) or glass fibre.

10. Contact element (2) according to one of the preceding claims, wherein the contact element (2) comprises one or more electrical connections (6, 8) accessible from an outside of the contact element (2), wherein the one or more electrical connections (6, 8) are electrically connected to the heating cable (4).

11. Contact element (2) according to claim 10, wherein the one or more electrical connections (6, 8) protrude from the outside of the contact element (2).

12. Contact element (2) according to claim 10 or 11, wherein the contact element (2) comprises a first electrical connection (30) and a second electrical connection (32), wherein the first electrical connection (30) is shaped to engage with the second electrical connection (32).

13. Contact element (2) according to claim 10 or 11, wherein the contact element (2) comprises an integrated plate (38).

14. Contact element (2) according to claim 13, wherein one or more holes (40) are the integrated plate (38).

15. Contact element (2) according to claim 13 or 14, wherein the integrated plate (38) is arranged on an outer surface of the contact element (2).

16. Contact element (2) according to claim 15, wherein the heating cable (4) is arranged in a layer (42) positioned in a non-zero distance from the outer surface of the contact element (2).

17. Contact element assembly comprising a plurality of contact elements (2, 2') according to one of the preceding claims, wherein the contact elements (2, 2') are electronically connected to each other.

18. Gripping tool (42) for handling a wind turbine blade (44), wherein the gripping tool (42) comprises at least one contact element (2, 2') according to one of the claims 1-16.

19. Gripping tool (42) according to claim 18, wherein the gripping tool (42) comprises a contact element assembly according to claim 17.

20. Method for manufacturing a contact element (2, 2') according to one of the claims 1-16, said method comprising:- inserting a heating cable (4) into a mold (46);- adding a resilient component into the mold (46) while maintaining the inserting a heating in a predefined position of the mold (46);- curing the resilient component (48) and hereby integrating the heating cable (4) in the contact element (2, 2');- removing the resilient component from the mold.

21. Method according to claim 20, wherein the heating cable (4) is attached to a base member (12) that maintains the position of the heating cable (4) during the molding process.

22. Method according to claim 20, wherein the contact element (2) comprises a reinforcement (28) that is formed as a braiding surrounding the jacket (22), wherein the resilient component is a liquid rubber material having a viscosity low enough to ensure that air beingpresent between the heating element (24) and the reinforcement (28) is displaced.

23. Use of a gripping tool (42) according to claim 18 or 19 for handing wind turbine blades (44).

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