Method and apparatus for removing foil or tape from inner surface of mold

Abstract

A method of removing a foil (17) or strip (46) from an inner surface (14) of a mould (7) for casting a wind turbine blade (3) or a part thereof, the foil (17) or strip (46) comprising a non-stick material (18) on the inner side configured to not react with resin during casting (S1, S2, S3) and an adhesive material (19) on the outer side, the adhesive material (19) being adhered to the inner surface (14) of the mould (7), the non-stick material (18) being configured to react with resin during casting (S1, S2, S3). The method comprises: a) locally heating (S5) the foil (17) or strip (46) in order to soften the adhesive material (19); and b) applying (S6) a pulling force on the foil (17) or strip (46) to remove the foil (17) or strip (46) from the inner surface (14) of the mold (7). By means of local heating of the foil or strip, it is no longer necessary to rely on the waste heat of the mold after the removal of the cast wind turbine blade This has ergonomic advantages and makes the process more flexible.

Description

Technical Field

[0001] The present invention relates to a method and apparatus for removing foil or strip from the inner surface of a mold. Background Technology

[0002] One way to generate more electricity from wind turbines under given wind conditions is to increase the size of the blades. However, manufacturing wind turbine blades is becoming increasingly difficult in order to increase their size.

[0003] Currently, many wind turbine blades are manufactured by prefabricating blade components, such as pressure-side and suction-side housings, separately and then gluing these components together. For example, these components are prefabricated in a mold by infusing fiber layups with resin and curing the resin.

[0004] In another method disclosed in EP 1 310 351 A1, the blade is manufactured by encapsulating a fiber layup on a mandrel (mold core) for the entire blade or for a longitudinal blade segment, and by vacuum-assisted instillation of resin and curing the resin in a mold.

[0005] Therefore, large molds are required when producing large composite structures such as blades or their components. These molds are typically made of fiber composite materials. This is because it provides a great deal of freedom in the shape of the mold surface. Furthermore, these molds are lightweight.

[0006] However, the mold surface must be protected to ensure that the molded part, also made of fiber composite material, can be demolded from the mold. For this purpose, according to a method known in the art, the mold surface is covered with a self-adhesive PTFE (polytetrafluoroethylene) foil. The adhesive used in such foil is typically silicone-based to withstand the high temperatures during the curing stage.

[0007] The foil needs to be replaced if it is worn or otherwise damaged. It is known to pull or tear worn foil from the mold surface. If this pulling or tearing is not done at elevated temperatures, the pull force will be high if the silicone-based adhesive is attached to the mold surface. In particular, this can cause damage to the mold surface if filler, coating, or even fibers are torn off along with the foil.

[0008] Therefore, it is common practice to remove the worn foil while the mold is still hot after the part has been demolded. In particular, if the resin used in molding the part has a polymer matrix with exothermic crosslinking, it can still benefit from the heat generated therefrom. This heat keeps the adhesive of the foil soft, so the foil can be removed more easily.

[0009] However, working inside a hot mold housing presents a very challenging working environment for human operators. Depending on the size of the blades, the operator may be able to stand entirely inside the mold housing. The mold housing, immediately after demolding, typically has a temperature between 60 and 80 degrees Celsius. This places a significant thermal load on the human operator, especially when considerable force is required to pull the foil off the mold surface.

[0010] Furthermore, the residual heat in the mold may not always be sufficient, so the worn foil needs to be cut into narrow strips to allow it to be pulled down or torn off, as the pulling force could otherwise become too high for a human operator. Additionally, if the adhesive has cooled too much, a scraper may be needed to remove any remaining adhesive adhering to the mold surface where the foil has been removed. This scraping can leave scratches and marks on delicate mold surfaces. Summary of the Invention

[0011] Therefore, one object of the present invention is to provide an improved method for removing foil or strip from the inner surface of a mold.

[0012] According to a first aspect, a method is provided for removing a foil or strip from the inner surface of a mold for casting wind turbine blades or parts thereof, the foil or strip comprising a non-adhesive material on an inner side and an adhesive material on an outer side, the non-adhesive material being configured not to react with resin during casting, and the adhesive material being adhered to the inner surface of the mold, the method comprising: a) Locally heat the foil or strip to soften the adhesive material; and b) Apply tension to the foil or strip to remove the foil or strip from the inner surface of the mold.

[0013] Using this method, the adhesive material can be locally heated to remove the foil or strip. Therefore, it is not necessary to rely on residual heat after casting wind turbine blades or their components to ensure the adhesive material is sufficiently flexible. Thus, the foil or strip can be removed after the mold has sufficiently cooled, allowing for an ergonomic working environment. Another advantage of this method is the greater flexibility it offers in terms of the processes surrounding the mold. Therefore, the removal of the foil or strip can be delayed until a point in time that allows for more efficient use of the mold.

[0014] For example, the non-stick material can be PTFE. The non-stick material can be integrated with a fiber mesh (e.g., a fiberglass mesh). This makes the foil or tape more robust. For example, the adhesive material can include or be composed of silicone.

[0015] For example, when the foil or strip is brought to the production site, the adhesive material may be covered with a backing layer, such as paper. The backing layer is removed, and the foil or strip is adhered to the surface of the inner mold by means of the adhesive material.

[0016] The non-stick material faces the interior of the mold. For example, fiber layups comprising glass fiber, carbon fiber, and / or aramid fiber and / or resin (especially epoxy resin) do not adhere to the non-stick material. This is true even when heat and pressure are applied to the fiber material and / or resin. The resin may be an exothermic crosslinking type resin.

[0017] Unless otherwise indicated, “inner” and “outer” currently refer to the center of the mold, where “outer” means the direction away from the center of the mold and “inner” means the direction facing the center of the mold.

[0018] As used herein, “foil” refers to a thin layer of material used to cover most of the mold surface. The thickness of the foil may be less than 2 mm, preferably less than 1 mm, and most preferably about 0.8 mm.

[0019] As used herein, a "ribbon" is typically used to repair a portion of foil that has already been placed previously. Another use of the ribbon is to cover the mold surface in areas of mold flanges. The ribbon is also used to cover butt joints between different layers of foil. The ribbon typically has a much smaller width than its length. In some embodiments, the ribbon may be constructed without embedded fiber webs and thus consists only of non-adhesive and adhesive materials.

[0020] The foil and strip can be supplied in rolls at the production site. The foil or strip is then cut from these rolls to provide the desired length of material.

[0021] In this context, "casting" refers to the process of infusing a fiber layup with resin in a mold and curing the resin to form a wind turbine blade or a component thereof. Infusion can be performed using a vacuum (particularly a vacuum pump). Curing can be accomplished by applying pressure and / or heat. This heat can be supplied by a heating system positioned on the outer surface of the mold.

[0022] When the word "mold" is used, it can refer to a complete (closed) mold or an open mold, especially the mold shell.

[0023] According to one embodiment, during step a), the temperature of the foil or strip is controlled to exceed 60 degrees Celsius.

[0024] Preferably, the temperature is controlled within a range of 65-120±5 degrees Celsius. This control can be open-loop or closed-loop. In this way, it is ensured that the adhesive material is always soft enough to apply tension to remove the foil or strip in step b).

[0025] According to another embodiment, the temperature is controlled using a temperature sensor that senses the temperature of the foil or strip.

[0026] This allows for closed-loop control of the temperature of the foil or heat in the localized heating area, so as to provide a sufficiently soft adhesive material for removing the foil or strip. The temperature sensor can be an infrared sensor.

[0027] According to another embodiment, in step a), a heat source arranged on the inside of the mold is used to supply heat.

[0028] Therefore, the heat source can be easily arranged and adjusted by the operator inside the mold.

[0029] According to another embodiment, the heat source moves inside the mold during, before, and / or after step a).

[0030] For example, the heat source can be moved within the mold by means of wheels. In one embodiment, the heat source is attached to a robot manipulator that moves the heat source along the inside of the mold. With a movable heat source, heat can be easily applied locally to the desired area.

[0031] According to another embodiment, the distance between the heat source and the foil or strip is constant during step a).

[0032] This ensures a constant heat distribution along the mold. Furthermore, it avoids errors such as applying excessive heat locally due to placing the heat source too close to the foil or strip. For example, this (constant) distance can be between 1 cm and 1 m, preferably between 10 cm and 30 cm. Specifically, this distance remains constant as the heat source moves within the mold. In another embodiment, this distance can be adjusted (via a corresponding device) or can be adjusted to a desired value between, during, or after step a).

[0033] According to one embodiment, the heat source is an irradiation source, particularly an infrared light source.

[0034] An irradiation source is particularly useful when attempting to heat a layer (currently the adhesive material) that is not directly on the surface of the foil but on the back of the non-stick material, as is currently the case. Radiation easily penetrates the non-stick material to heat the adhesive material.

[0035] According to another source, the heat source is part of a handheld and / or hand-operated tool.

[0036] "Handed" refers to a tool that is entirely supported by the operator's hand, except for possible power supply cables. "Hand-operated" in this context refers to a tool that is partially held, supported, or manipulated by a human operator.

[0037] According to another embodiment, when the position of the heat source is constant, the surface area of ​​the foil or strip heated in step a) is less than 1 m. 2 .

[0038] In this way, another human operator (e.g., the person performing step b) can stand close to the operator performing localized heating according to step a). The heated area can also be less than 1 m. 2 For example, less than 0.5 m 2 Or especially in the case of handheld tools, less than 0.1 m 2 .

[0039] According to a second aspect, there is provided an apparatus for removing a foil or strip from the inner surface of a mold for casting wind turbine blades or parts thereof, the foil or strip comprising a non-stick material on an inner side and an adhesive material on an outer side, the non-stick material being configured not to react with resin during casting, the adhesive material being adhered to the inner surface of the mold, the apparatus being configured to locally heat the foil or strip to soften the adhesive material.

[0040] According to one embodiment, the device includes control circuitry to control the temperature of the foil or strip to exceed 60 degrees Celsius.

[0041] The control circuit can have an open-loop or closed-loop control design.

[0042] According to another embodiment, the device includes a heat source that can move within the mold.

[0043] According to another embodiment, the device includes a frame for maintaining a constant distance between the heat source and the foil or strip.

[0044] According to another embodiment, the device includes a reflector for reflecting heat onto the foil or strip.

[0045] For example, the reflector is made of thin-walled metal, particularly stainless steel or aluminum (especially polished aluminum). The reflector may have a concave, curved shape relative to the mold surface. The reflector may also include insulating material. Specifically, this insulating material prevents temperature loss caused by the reflector and / or the heated area. As a result, the operator handling the heat source also experiences less heat. The insulating material may be configured to protect the operator, a second operator, or bystanders from the risk of burns.

[0046] According to another embodiment, the irradiation source is configured as a heat source and is mounted in front of the reflector so as to face the foil or strip.

[0047] For example, the irradiation source can be attached to a reflector, particularly to its concave side.

[0048] According to another embodiment, the device includes at least two wheels that support the frame.

[0049] In one example, even one wheel may suffice. In other examples, three or four wheels may be preferred. In particular, two wheels may be arranged as a pair. These wheels may also be arranged as two sets (pairs). For example, the wheels and / or frame may be arranged such that, as the wheels move along a curved surface, the heat source and / or reflector pivots about an axis parallel to the axis of rotation of the one or more wheels. The one or more wheels may be made of a soft rubber material. This ensures that the mold surface and / or foil or strip are not scratched or damaged by the wheels.

[0050] According to another embodiment, a rod is mounted to the frame or reflector for manipulation by the operator along the inside of the mold.

[0051] The rod may be adjustable in length. It can be pivotally connected to the frame or reflector to allow relative rotation on the curved surface of the mold. This makes it easier for the operator to manipulate the device. The pivoting motion can be about a first and / or a second axis. The first axis can be arranged parallel to the axis of rotation of the one or more wheels. The second axis can be arranged perpendicular to the first axis and perpendicular to the longitudinal axis of the rod.

[0052] According to another embodiment, the device is configured as a handheld and / or hand-operated tool.

[0053] The embodiments and features described in the first aspect are applied to the second aspect with necessary modifications in detail, and vice versa.

[0054] Other possible embodiments or alternatives to the invention also encompass combinations of features not explicitly mentioned herein, as described above or below with reference to embodiments. Those skilled in the art can also add individual or isolated aspects and features to the most basic form of the invention. Attached Figure Description

[0055] Other embodiments, features, and advantages of the invention will become apparent from the following description and dependent claims, taken in conjunction with the accompanying drawings, in which: Figure 1 A perspective view shows a wind turbine according to an embodiment; Figure 2 The lower mold housing is shown in cross-section, to which the foil is applied by two operators; Figure 3 This illustrates the process when the foil has been placed on the mold surface and the fiber layup to form the part to be manufactured has been arranged inside the mold. Figure 2 Section III-III; Figure 4 A standing position according to an embodiment is shown. Figure 2 The mold housing and the operator operating the equipment; Figure 5 It shows Figure 4 A corresponding enlarged view of the device shown; Figure 6 Showing from Figure 5 Section VI-VI; and Figure 7 A flowchart of a method according to an embodiment is shown.

[0056] In the accompanying drawings, unless otherwise indicated, the same reference numerals denote the same or functionally equivalent elements. Detailed Implementation

[0057] Figure 1 A wind turbine 1 according to an embodiment is shown. The wind turbine 1 includes a rotor 2 having two or more blades 3 connected to a hub 4. The hub 4 is connected to a generator (not shown) arranged within a nacelle 5. During operation of the wind turbine 1, the blades 3 are driven to rotate by the wind, and the kinetic energy of the wind is converted into electrical energy by the generator in the nacelle 5. The nacelle 5 is arranged at the upper end of a tower 6 of the wind turbine 1. The tower may be connected to a monopile or concrete foundation in the ground or seabed.

[0058] Figure 2 A portion of the lower mold 7 used in the manufacture of the blade 3 or its components is shown in cross-section. In particular, it is the lower blade housing (not shown) manufactured using the mold 7.

[0059] Figure 2 Only some relevant parts of the lower mold 7 are shown, while other parts such as the support structure are not shown. The lower mold includes a mold housing 8 made of, for example, a fiber composite material. For example, the fiber composite material may include glass fibers, carbon fibers, and / or aramid fibers in a cured resin matrix. The resin may include epoxy resin or other polymers. The lower mold housing 8 has a curved (e.g., approximately semi-circular) shape with a horizontally extending flange 9.

[0060] Heating system 10 ( Figure 2 (Only a portion of it is shown in the image) is arranged on the outer side of the mold housing 8. Unless otherwise indicated, "outer" and "inner" currently refer to the mold center 11. The heating system 10 is configured to initiate the curing process of the blade 3 or its components manufactured in the mold, as explained in more detail later. The heating system 10 may include, for example, heating tubes 12 extending parallel to the mold 7. For example, the heating tubes 10 are embedded in an insulating material (such as polyurethane foam), and heat transfer to the mold housing 8 is achieved through a heat transfer layer 13. The heat transfer layer 13 may include metal particles embedded in a resin matrix.

[0061] The inner surface 14 of the mold housing 8 defines the shape of the blade 3 or its components. It is a fine surface that must not be scratched or otherwise damaged.

[0062] Figure 2 An operator 15 is also shown standing inside the mold housing 8. Another operator 16 stands adjacent to one of the two flanges 9 at the top of the lower mold 7. Operators 15 and 16 work together to process foil 17, also referred to as PTFE foil. They place foil 17 on top of the inner surface 14.

[0063] like Figure 3 As shown in cross-section, foil 17 may be composed of a non-adhesive material 18 forming a first layer of foil 17 and an adhesive material 19 forming a second layer of foil 17. Layers 18 and 19 are disposed on top of each other. For example, the non-adhesive material 18 is a PTEF layer, which may be reinforced with a glass fiber material (not shown). The adhesive layer may include silicone. For example, the thickness t of foil 17 may be less than 1 mm.

[0064] The foil 17 is placed on top of the inner surface 14 of the mold housing 8 by operators 15 and 16, such that the adhesive layer 19 contacts and bonds with the surface 14. A tool (not shown) can be applied to the non-adhesive layer 18 after placing the foil 17 to remove any air bubbles. Thus, the foil 17 provides a smooth inner surface 20. The step of placing the foil 17 corresponds to... Figure 7 In the method step S1, the Figure 7 A flowchart illustrates a method according to an embodiment.

[0065] In step S2, the fiber layup 21 is arranged on top of the surface 20 formed by the foil 17.

[0066] The fiber layup 21 is covered with a vacuum foil (not shown), and a vacuum is applied. This causes the fiber layer to be infused with resin (e.g., epoxy resin). The mold can then be closed using an upper mold housing (not shown) having abutment... Figure 2 The flange 9 shown seals the corresponding flange. In another step, hot water is passed through pipe 12 to apply heat to mold 7, thereby curing the resin-infused fiber layup 21, see [link to relevant documentation]. Figure 7 Step S3 in the process.

[0067] During the curing of the resin in the fiber layup, even if the resin comes into contact with the non-stick material 18, the non-stick material 18 will not chemically react with the resin or with the fibers in the fiber layup 21. In fact, no bond is formed. Therefore, in step S4, the so-called green blade 3 or its parts are removed from the mold 7 (also known as "demolding") without any part of the blade 3 or its parts adhering to the foil 17.

[0068] After demolding, inspect foil 17 for any signs of wear. If significant wear is determined, foil 17 needs to be replaced. This may involve only one foil, multiple foils, or all foils in mold 7.

[0069] Next, wait until mold 7 has cooled sufficiently. Specifically, wait until the surface temperature of foil 17 is below 60 degrees Celsius, preferably below 30 degrees Celsius. At this temperature, the adhesive material 19 is hard and it is practically impossible or very difficult to remove foil 17 by human force (i.e., by pulling one end of foil 17). However, even if sufficient force can be applied, there is a high risk that the adhesive material 19 being peeled off from the inner surface 14 will tear the filler material, coating, or even fibers from said surface 14.

[0070] Therefore, as shown in step S5 and the cross-section of mold 7. Figure 4 As shown, operator 22 uses device 23 to locally heat foil 17 from the inside. Figure 5 The device 23 is shown in more detail in the perspective view. The device 23 is configured to locally maintain the temperature of the foil 17 within a range between 65° and 120° ± 5°, as will be explained in further detail. For example, the area where the device 23 is configured to raise the temperature of the foil 17 and maintain it above 65° ± 5° (or any other value in the range mentioned above) can be limited to 1 m. 2 Or smaller. The area is in Figure 5 The reference numeral 24 indicates the device 23. The device 23 can use open-loop or closed-loop control to maintain the temperature at a desired level. Closed-loop control is preferred, and therefore the device 23 may include a temperature sensor 25, such as an infrared sensor, configured to sense the temperature of the foil 17 in the sensing area 24.

[0071] Device 23 also includes Figure 6 The heat source 26 shown in the figure, Figure 6 The diagram shows... Figure 5 Section VI-VI. Heat source 26 can be configured as an infrared light source irradiating foil 17. Corresponding radiation 27 (heat) passes through non-stick material 18 and specifically heats adhesive material 19 (see section VI). Figure 3 ).

[0072] To ensure that the heat is applied only locally and that the operator 22 is exposed to as little heat as possible, a metal reflector 28 is provided. The metal reflector 28 may be made of a polished aluminum plate material formed in a concave shape relative to the mold housing 8, such as... Figure 6As seen in the image. The heat source 26 is mounted on the inner side of the reflector 28. Here, "inner side" refers to the side facing the mold housing 8 when the device 23 is used to heat the foil 17. On the outer surface, i.e., away from the mold housing 8, the reflector 28 may be provided with an insulator 29. The insulator 29 also functions to prevent heat transfer to the operator 22 and to prevent burns to other operators or bystanders. In particular, the insulator 29 allows another operator (not shown) to stand very close and to apply tension to the foil 17 in the area where the adhesive material 19 has been softened by the heat applied by the device 23.

[0073] Figure 5 The image also shows the semi-cylindrical shape of the reflector 28, including the insulator 29. Furthermore, Figure 5 The diagram also illustrates a frame having a pair of double-arm structures 30, 31 fixedly connected to the reflector 28 on opposite sides. Each of the double-arm structures 30, 31 connects a set of two wheels 32 to the reflector 28. The wheels 32 may be made of soft rubber. When operated by the operator 22, the device 23 moves over the foil 17 as needed by means of the wheels 32 to sufficiently soften the adhesive material 19.

[0074] The distance d between the heat source 26 and the inner surface 20 of the foil 17 ( Figure 6 The reflector 28 is kept constant by means of the double-arm structures 30, 31 and the wheel 32 that support the reflector 28 and are fixedly connected to it. For example, d has a value from 1 cm to 20 cm.

[0075] To improve operability, device 23 may also include a lever 33, which is adjustable in the longitudinal direction, such as... Figure 5 As shown by the double arrows. For example, rod 33 can be made telescopic. Figure 4 As shown, lever 33 is held by operator 22 to manipulate device 23 across foil 17.

[0076] Rod 33 can be pivotally connected to reflector 28. For example, two pivot axes A and B are defined. Pivot axis A is oriented parallel to axis C, about which at least one of the wheels 32 rotates. When rod 33 pivots relative to reflector 28 about axis A, this makes it easier for operator 22 to move device 23 up or down along the curved surface of mold housing 8, such as... Figure 4 and Figure 5 As shown in the diagram. Furthermore, the pivoting movement of the reflector 28 about the axis B of the rod 33 allows the operator 22 to stand more laterally relative to the reflector 28, while still allowing it to move in the crosswise direction of the mold housing 8. This crosswise direction... Figure 4 and Figure 5 The reference numeral R is used to indicate the direction. The lateral direction R is perpendicular to the longitudinal direction L of the mold 7.

[0077] Device 23 may include an on / off switch 34 to activate or deactivate heat source 26, enabling it to provide heat or stopping it from providing heat. Additionally, device 23 may include a user interface 35, which... Figure 5 The upper right corner is shown in an enlarged view. Interface 35 includes a dial 36 (temperature selector) for setting the temperature of foil 17 in area 24.

[0078] For example, device 23 includes a closed-loop control circuit 37 ( Figure 4 Circuit 37 receives the temperature value measured by temperature sensor 25 as feedback and controls heat source 26 according to the temperature set by temperature dial 36. Circuit 37 and / or transformer 38, which converts the current used by heat source 26, may be arranged in cabinet 39, which is located on platform 40 adjacent to mold 7. Transformer 38 and / or circuit 37 may be connected to heat source 26 and / or temperature sensor 25 via (flexible) cable 41. Cable 41 extends from cabinet 39 on platform 40 to the distal end 42 of pole 33, where it is attached and from there connected to heat source 26 and / or temperature sensor 25. On / off switch 34 and interface 35 may be connected therebetween.

[0079] Returning to interface 35, interface 35 preferably includes, in addition to temperature dial 36, a display 43 that shows the current temperature of foil 17 as measured by temperature sensor 25. Furthermore, interface 35 may also include two lamps 44, 45 that emit red or green light depending on whether heat source 26 is activated.

[0080] For example, the width W of a single foil 16 can be between 0.5 m and 1.5 m, for example, 1 m. Therefore, for example, the width WR of the reflector 28 can also be between 0.3 m and 1.2 m. In particular, the width WR is smaller than the width W of the foil 17.

[0081] As in Figure 4 As can be seen, lever 33 is held by the hands of operator 22. Device 23 is also supported by wheels 32. Therefore, device 23 is referred to as a hand-operated tool.

[0082] However, for other applications, especially those requiring heating... Figure 4 and Figure 5 In the case of belt 46 shown, a handheld device can be used, which is therefore supported only by the operator 22, i.e., without wheels, etc. Such a device can have a much smaller width WR, for example, between 5 cm and 15 cm.

[0083] Once the adhesive material 19 has been properly heated to, for example, 80 degrees Celsius, another operator (not shown) pulls down the foil 17 in region 24 and continues to pull down the entire foil 17 (corresponding to...). Figure 7 Step S6).

[0084] Although the invention has been described with reference to preferred embodiments, it will be apparent to those skilled in the art that modifications are possible in all embodiments.

Claims

1. A method of removing a foil (17) or tape (46) from an inner surface (14) of a mold (7) for casting a wind turbine blade (3) or a part thereof, the foil (17) or tape (46) comprising a non-stick material (18) on an inner side configured not to react with resin during casting (S1, S2, S3) and a sticking material (19) on an outer side sticking to the inner surface (14) of the mold (7), the method comprising: a) locally heating (S5) the foil (17) or tape (46) to soften the sticking material (19); and b) applying (S6) a pulling force on the foil (17) or tape (46) to remove the foil (17) or tape (46) from the inner surface (14) of the mold (7). The temperature of the foil (17) or tape (46) during step a) is controlled to be more than 60 degrees Celsius.

2. The method of claim 1, wherein, The temperature is controlled using a temperature sensor (25) sensing the temperature of the foil (17) or tape (46).

3. The method of claim 2, wherein, The heat (27) is applied in step a) using a heat source (26) arranged on the inner side of the mold (7).

4. The method of any one of claims 1-3, wherein, The heat source (26) is moved inside the mold (7) during, before and / or after step a).

5. The method of claim 4, wherein, The distance (d) between the heat source (26) and the foil (17) or tape (46) is constant during step a).

6. The method of claim 4 or 5, wherein, The heat source (26) is an illumination source, in particular an infrared light source.

7. The method of any one of claims 4-6, wherein, The heat source (26) is part of a handheld and / or hand operated tool.

8. The method of any one of claims 4-7, wherein, 10. An apparatus (23) for use when removing a foil (17) or tape (46) from an inner surface (14) of a mold (7) for casting a wind turbine blade (3) or a part thereof, the foil (17) or tape (46) comprising a non-stick material (18) on an inner side configured not to react with resin during casting (S1, S2, S3) and a sticking material (19) on an outer side sticking to the inner surface (14) of the mold (7), the apparatus (23) being configured to locally heat the foil (17) or tape (46) to soften the sticking material (19).

9. The method of any one of claims 4-8, wherein, The surface area (24) of the foil (17) or tape (46) heated in step a) is less than 1 m2when the position of the heat source (26) is constant 2 .

11. The apparatus according to claim 10, comprising a control circuit (37) to control the temperature of the foil (17) or tape (46) to be more than 60 degrees Celsius.

12. The apparatus according to claim 10 or 11, comprising a heat source (26) movable inside the mold (7).

13. The apparatus according to claim 12, comprising a frame (30, 31) to keep the distance (d) between the heat source (26) and the foil (17) or tape (46) constant.

14. The apparatus according to claim 12 or 13, comprising: a reflector (28) for reflecting heat (27) onto the foil (17) or tape (46), the reflector (28) being mounted on the frame (30, 31), 15. The apparatus according to claim 14, comprising a heat source (26) movable inside the mold (7) and a frame (30, 31) to keep the distance (d) between the heat source (26) and the foil (17) or tape (46) constant. - an irradiation source (26) as heat source, which is mounted in front of the reflector (28) so as to face the foil (17) or strip (46), - at least two wheels (32), which carry the frame (30, 31), and / or - a bar (33), which is mounted to the frame (30, 31) or to the reflector (28) for maneuvering the device (23) along the inside of the mold (7).

15. The device according to any one of claims 10 to 14, which is configured as a hand-held and / or hand-operated tool.

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