Improvements relating to the manufacture of wind turbine blades

Abstract

Improvements relating to the manufacture of wind turbine blades A method of making a wind turbine blade component is described. The method comprises: providing a rigid mould (20) shaped to form the wind turbine blade component; arranging fibrous reinforcing material (36) in the mould; covering the fibrous reinforcing material with a vacuum bag (14); sealing the vacuum bag against a surface (12) of the mould or against another surface to create a closed space (18) between the mould and the vacuum bag in which the fibrous reinforcing material is encapsulated; removing air from the closed space to create a negative pressure within the closed space; supplying resin to the fibrous reinforcing material; and curing the resin. The method further comprises providing a sealed bag (10) in the closed space. The sealed bag is at least partially filled with a gas. The pressure inside the sealed bag is greater than the pressure within the closed space outside the sealed bag. The sealed bag shapes and / or supports a portion of the fibrous reinforcing material during the moulding process.

Description

[0001] Improvements relating to the manufacture of wind turbine blades

[0002] Technical field

[0003] The present invention relates generally to wind turbine blades, and more specifically to improved methods of manufacturing wind turbine blades and component parts of wind turbine blades.

[0004] Background

[0005] Modern utility-scale wind turbine blades are large structures comprising an aerodynamic shell supported by a spar structure.

[0006] The shell is typically formed from composite materials such as fibre reinforced plastic (FRP). Parts of the shell may have a sandwich structure consisting of a lightweight core material such as foam or balsa sandwiched between inner and outer composite skins. The shell may be formed from two half shells, a windward shell and a leeward shell, each moulded from composite materials in a respective mould. The half shells may be bonded together with adhesive provided between flanges extending along leading and trailing edges of the half shells.

[0007] The spar may comprise a box-spar structure, which is bonded inside the blade shell between the windward and leeward halves. Alternatively, the spar may comprise spar caps in each half shell, which are joined by shear webs. The spar caps are often integrated in the shell structure or bonded separately to the inner surfaces of the shell. The shear webs are bonded between opposed pairs of spar caps.

[0008] The blade shells are typically formed using a vacuum-assisted resin infusion process, which is commonly referred to in the art as vacuum-assisted resin transfer moulding (VARTM). The process involves arranging blade material such as fibrous reinforcing material and lightweight core material in a mould. The blade material is then covered with a vacuum bag, which is sealed against a surface of the mould to create a closed space in which the blade material is encapsulated. A vacuum pump is used to remove air from the closed space to create a negative pressure under the vacuum bag. Resin is then supplied to the evacuated closed space. The resin infuses throughout the blade material and is then cured. After curing the resin, the vacuum bag is removed. The present invention provides a new technique that can be used during a moulding process to improve the manufacture of wind turbine blades or component parts of the blades.

[0009] Summary of the invention

[0010] The present invention provides a method of making a wind turbine blade component.

[0011] The method comprises: providing a rigid mould shaped to form the wind turbine blade component; arranging fibrous reinforcing material in the mould; covering the fibrous reinforcing material with a vacuum bag; sealing the vacuum bag against a surface of the mould or against another surface to create a closed space between the mould and the vacuum bag in which the fibrous reinforcing material is encapsulated; removing air from the closed space to create a negative pressure within the closed space; supplying resin to the fibrous reinforcing material; and curing the resin.

[0012] The method further comprises providing a sealed bag in the closed space. The sealed bag is at least partially filled with a gas. In some embodiments the sealed bag may be fully filled with gas. A pressure inside the sealed bag is greater than the pressure within the closed space outside the sealed bag. Accordingly, the sealed bag provides a region of increased pressure within the closed space. The sealed bag shapes and / or supports a portion of the fibrous reinforcing material during the moulding process, for example during a vacuum-assisted resin infusion and curing process.

[0013] The curing of the resin takes place after the step of providing the sealed bag in the closed space.

[0014] The term ‘negative pressure’ used herein is intended to mean a pressure lower than atmospheric pressure. Preferably the pressure is approximately zero atm. The pressure inside the sealed bag is therefore preferably greater than zero atm, and is more preferably approximately one atmosphere. The pressure inside the sealed bag is referred to herein as a ‘positive pressure’, which is intended to mean a pressure that it is higher than the ‘negative pressure’ within the closed space, outside of the sealed bag. The term ‘positive pressure’ therefore includes pressures that may be lower than atmospheric pressure. Accordingly, the sealed bag provides a region of positive pressure inside the closed space. The method preferably comprises supplying resin to the closed space such that the resin infuses the fibrous reinforcing material. The fibrous material may be dry fibrous material. The resin is preferably supplied as liquid resin. Alternatively, the resin may be sprayed onto the fibrous reinforcing material. The step of supplying resin to the fibrous material may also comprise providing fibrous reinforcing material that is pre-impregnated with resin, i.e. so-called prepreg.

[0015] The wind turbine blade component may be a shell of a wind turbine blade or a part of a shell, for example a half shell or a part of a half shell. The wind turbine blade component may alternatively be another moulded component of a wind turbine blade, for example a shear web.

[0016] The vacuum bag is a flexible membrane or film, typically made from plastic, which is impermeable to air. The sealed bag may be at least partially filled with any suitable gas. Preferably the gas is air. Air is advantageous because it is readily available at no cost.

[0017] The steps of the method may be performed in any suitable order. For example, the sealed bag may be arranged in the mould before or after the fibrous reinforcing material is arranged in the mould. The sealed bag may be at least partially filled with gas before it is arranged in the mould or after it is arranged in the mould. The sealed bag may be at least partially filled with gas before or after the vacuum bag is arranged in place.

[0018] The resin may be supplied to the fibrous reinforcing material before or after air is removed from the closed space. In the case of resin infusion, the resin is preferably supplied to the fibrous reinforcing material after removing air from the closed space. However, if prepreg is used, the resin is already supplied to the fibrous reinforcing material before the fibrous reinforcing material is arranged in the mould. If resin is sprayed onto the fibrous reinforcing material, this may be done before or after arranging the fibrous reinforcing material in the mould.

[0019] The sealed bag may expand in volume when air is removed from the closed space. The sealed bag may deform or otherwise change shape to adapt to the space between the vacuum bag and the mould. The sealed bag is sealed to prevent gas from escaping from the bag and to prevent resin from entering inside the bag.

[0020] The sealed bag may be made from an elastic or other stretchable material. This advantageously enables the sealed bag to adapt in shape to conform to a shape of the mould during evacuation of the closed space. Alternatively, the sealed bag may be made from an inelastic material. This may be advantageous in that the sealed bag may adopt a predictable size and shape when the closed space is evacuated.

[0021] The sealed bag may be a balloon, for example a latex balloon or a balloon formed from another elastic material. Alternatively, the sealed bag may be any other type of bag capable of retaining a gas inside when sealed. In certain embodiments, the sealed bag may be formed from a length of plastic layflat tubing that is sealed at both ends. Alternatively, the sealed bag may comprise an impermeable film sealed against a surface of the mould or sealed against a surface of another component inside the closed space. The impermeable film may be a second vacuum bag.

[0022] The sealed bag may advantageously be made from a thermoplastic material. This enables the bag to be conveniently heat sealed.

[0023] The method may comprise arranging the sealed bag between a first layer and a second layer of fibrous reinforcing material such that the sealed bag forms a cavity between the first and second layers. In a particular example, the cavity is a ballast chamber. Accordingly, the method can advantageously be used to form a ballast chamber integrally with the blade shell.

[0024] In other examples, the portion of the fibrous reinforcing material supported by the sealed bag may form a stiffening element such as a corrugation or stringer. For example, the method may be used to form stringers integrally with the blade shell during manufacture of the shell.

[0025] The method may comprise arranging one or more outer layers of fibrous reinforcing material in the mould to form an outer skin of the component. The sealed bag or a plurality of sealed bags at least partially filled with a gas may be arranged on the outer layers. One or more intermediate layers of fibrous reinforcing material may be draped over the or each sealed bag. The method may further comprise arranging one or more inner layers of fibrous reinforcing material over the intermediate layers to form an inner skin of the component.

[0026] The intermediate layers form stiffening webs or corrugations in the composite structure that maintain a predetermined spacing between the inner and outer skins and avoid the need for core material between the skins. The intermediate layers of fibrous reinforcing material may be draped over the or each sealed bag such that they develop a substantially S-shaped or top-hat-shaped cross-sectional profile.

[0027] The sealed bag may be used as a supplementary mould tool inside the vacuum bag. For example, the sealed bag can be used in highly concave portions of a mould to press the fibrous material against the concave mould surface. This method can be used to achieve a high-quality laminate without resin-rich areas.

[0028] In a particular embodiment the mould may be shaped to form a shell of a wind turbine blade having a flatback trailing edge. The sealed bag may be arranged in a trailing edge region of the mould. The trailing edge region may have a concave or U-shaped profile. The sealed bag may press the reinforcing material against the mould surface in the trailing edge region of the mould.

[0029] After the gas has been removed from the closed space, the vacuum bag contracts against the sealed bag. As the gas inside the sealed bag has a positive pressure an equilibrium state between the vacuum bag and the sealed bag may be reached.

[0030] The step of removing air from the closed space to create a negative pressure within the closed space applies a primary force to the sealed bag. The method may further comprise applying a secondary force to the sealed bag from outside the closed space to change the shape of the sealed bag before the step of curing the resin.

[0031] The secondary force is not a vacuum force. The secondary force may comprise applying tooling pressure to the sealed bag from outside of the closed space, such as for example with a pressure plate. This has the result of disturbing the equilibrium state so that the sealed bag will adopt a different shape. This is beneficial in that the shape and / or the position of the B-surface of the fibrous reinforcing material, i.e. the surface facing the vacuum bag can be tightly controlled. For example, the surface above the sealed bag may be subsequently used in a bonding process, and applying the secondary force can accurately shape the fibrous reinforcing material to provide a bonding surface with the desired geometry. Because the secondary force is applied from outside the closed space, the tooling that provides the force is not in contact with any resin and thus can be used again in subsequent processes without needing to be cleaned.

[0032] The invention also provides a wind turbine blade comprising a shell of composite construction formed according to the method described above. The wind turbine blade may include a ballast chamber formed integrally with the shell. The shell may comprise an inner skin, an outer skin and one or more stiffening webs or corrugations between the inner and outer skins. The stiffening webs may be substantially S-shaped or top-hat-shaped in cross section. The wind turbine blade may further comprise one or more stiffening structures such as ribs or stringers integrally formed with an internal surface of the shell.

[0033] Brief description of the drawings

[0034] Embodiments of the invention will now be described, by way of non-limiting example, with reference to the following figures, in which:

[0035] Figure 1a shows an air-filled sealed bag encapsulated within a closed space defined between a mould surface and a vacuum bag;

[0036] Figure 1b shows the sealed bag after air has been evacuated from the closed space;

[0037] Figures 2a and 2b show a wind turbine blade shell layup in a mould in which a sealed bag is used to form a ballast chamber integrally with the blade shell;

[0038] Figure 3a shows a mould arrangement for making a half shell of a flat back wind turbine blade;

[0039] Figure 3b shows a problem in the flat back mould arrangement of Figure 3a caused by bridging of the vacuum bag in a trailing edge region of the mould;

[0040] Figure 3c shows a sealed bag arranged in the trailing edge region of the flat back mould before air is evacuated from the mould; Figure 3d shows the mould arrangement of Figure 3c after air has been evacuated and the sealed bag deforms to fill the trailing edge region of the mould;

[0041] Figure 4 shows a wind turbine blade shell layup in a mould in which sealed bags are used to form stiffening webs between inner and outer skins of the blade shell; and

[0042] Figure 5 shows a wind turbine blade shell layup in a mould in which sealed bags are used to form stringers integrally with the blade shell.

[0043] Detailed description

[0044] Figures 1a and 1b illustrate the principle underlying the present invention. Figure 1a shows a sealed bag 10, in this case a balloon, arranged on a mould surface 12 and covered by a vacuum bag 14. The vacuum bag 14 is sealed against the mould surface 12 using sealing tape 16 to define a closed space 18 between the vacuum bag 14 and the mould surface 12. The balloon 10 is located within the closed space 18. The balloon 10 is at least partially filled with air in Figure 1a. The closed space 18 also contains air at atmospheric pressure in Figure 1a and the vacuum bag 14 loosely covers the balloon 10.

[0045] Figure 1b shows the balloon 10 after air has been evacuated from the closed space 18. As air is removed from the closed space 18, e.g. using a vacuum pump (not shown), the vacuum bag 14 contracts against the surface of the balloon 10. At the same time, the reduction of pressure in the closed space 18 causes the balloon 10 to expand slightly. The net result of the vacuum bag 14 pulling towards the balloon 10 and the balloon 10 pushing against the vacuum bag 14 results in an equilibrium being reached, whereby the balloon 10 deforms in shape and fills the space between the vacuum bag 14 and the mould surface 12.

[0046] In the equilibrium state shown in Figure 1 b, the balloon 10 provides a very stable and durable structure inside the closed space 18 and does not burst even if placed under considerable external force. The behaviour of the balloon 10 under the vacuum bag 14 when air is evacuated from the closed space 18, as shown in Figure 1 b, was surprising. It had been assumed that the balloon 10 may expand and eventually burst when air was evacuated from the closed space 18. It had not been expected that the vacuum bag 14 and the balloon 10 would work in concert to find a natural equilibrium in which the balloon 10 provided such a stable and durable structure inside the vacuum bag 14. The principle described above with reference to Figures 1a and 1b has several advantageous applications in the manufacture of wind turbine blades and component parts of wind turbine blades, as will now be described with reference to the remaining figures.

[0047] Figures 2a and 2b show an example where a sealed bag 10 under a vacuum bag 14 is used to form a ballast chamber integrally with the shell of a wind turbine blade.

[0048] Referring to Figure 2a, a female mould 20 is shaped to form one half of a wind turbine blade shell, for example a windward shell or a leeward shell, or a section thereof. A similar mould (not shown) is used to form the other half shell. A shell layup 22 is formed on a surface 12 of the mould 20.

[0049] To form the shell layup 22, a first layer 24 of fibrous reinforcing material is initially arranged on the surface 12 of the mould 20. A sealed bag 10 is then arranged on top of the first layer 24. A second layer 26 of fibrous reinforcing material is arranged on top of the first layer 24 and such that it covers the sealed bag 10. Accordingly, the sealed bag 10 is arranged between the first and second layers 24, 26. A vacuum bag 14 covers the layup 22 and is sealed against flanges of the mould 20 using sealing tape 16. Accordingly, a closed space 18 is formed between the vacuum bag 14 and the mould 20 in which the layup 22 is encapsulated.

[0050] The first and / or second layers 24, 26 of fibrous reinforcing material may comprise a single layer or a plurality of layers of fibrous reinforcing material, for example glass-fibre fabric or ‘plies’. A single layer of 1000 gsm biax glass fabric has been found to be sufficient for the second layer 26. Alternatively, multiple layers of a reduced density fabric may be used for the second layer 26, for example two layers of 600 gsm biax glass fabric.

[0051] In this example, the sealed bag 10 comprises a section of polyethylene layflat tubing. Layflat tubing is readily available and is typically supplied on a roll. It is commonly used as a packaging material for carpets. The tubing can be cut to any desired length and sealed at both ends using tape or heat sealed to form a bag. In this example, a 5-metre length of tubing is cut from a roll. A first end of the tubing is heat sealed to form the tubing into a bag 10. The second end is then heat sealed except a small hole is left, which allows a tube to be inserted into the bag 10. Air is blown or pumped into the bag 10 until the bag 10 is approximately 60-70% filled with air. The small hole is then heat sealed closed so that the air cannot escape from the bag 10.

[0052] Referring now to Figure 2b, air is removed from the closed space 18 using a vacuum pump (not shown). This process creates a negative pressure within the closed space 18, i.e. a pressure lower than atmospheric pressure, preferably substantially zero atm. The vacuum bag 14 therefore contracts around the layup 22 and pushes on the layup 22 and on the sealed bag 10. The sealed bag 10 changes shape to fill a space between the first and second layers 24, 26 inside the vacuum bag 14 until an equilibrium is reached between the sealed bag 10 and the vacuum bag 14, as shown in Figure 2b.

[0053] Once the closed space 18 has been evacuated, resin is supplied to the closed space 18 using infusion apparatus as will be familiar to the skilled person. The resin infiltrates throughout the layup 22 including in the region surrounding the sealed bag 10. The resin is then cured such that it hardens. Once cured, the vacuum bag 14 is removed. The moulded half shell can then be bonded with the other moulded half shell (not shown) to form the complete blade as will be familiar to the skilled person.

[0054] During the moulding process, e.g. during resin infusion and curing, the sealed bag 10 provides a region of ‘positive pressure’ inside the closed space 18. The term ‘positive pressure’ means a pressure greater than the negative pressure inside the closed space 18. In this example, the pressure inside the sealed bag is approximately one atmosphere.

[0055] The sealed bag 10 supports a portion of the second layer 26 and forms a space between the first and second layers 24, 26. As this space is filled by the sealed bag 10, resin cannot enter this space during the infusion process. The result is that the sealed bag 10 creates a cavity 28 between the first and second layers 24, 26. The cavity 28 is formed within the laminate structure of the blade shell and is formed integrally with the shell.

[0056] The cavity 28 in this example is used as a ballast chamber in the final wind turbine blade. For this purpose, one or more holes may be drilled through an external surface of the blade into the ballast chamber 28. The sealed bag 10 inside the ballast chamber 28 may be removed through the hole(s) or it may remain in place. The ballast chamber 28 may then be filled with ballast, for example adhesive or resin, in a suitable quantity to balance the weight of the blade with the other blades of the rotor. In the prior art, a ballast chamber is typically provided by bonding additional parts inside the blade after the shell has been manufactured. For example, a separate ballast tank may be bonded inside the blade or bulkheads may be bonded within the blade to form an enclosed space that can be filled with ballast. These additional bonding processes introduce cost and complexity to the blade manufacturing process. In comparison, the present invention provides a relatively simple and inexpensive way of providing a wind turbine blade with a ballast chamber. As the ballast chamber 28 is integrally formed with the shell during the shell moulding process, no additional steps are required after the moulding process. Accordingly, the time and cost involved in making a blade is considerably reduced. The integrally formed ballast chamber 28 does not involve any bonded joints and therefore provides a more reliable and robust structure inside the blade. Furthermore, the ballast chamber 28 is well sealed because it is formed integrally, and therefore the risk of ballast escaping is considerably reduced in comparison to prior art solutions.

[0057] Experiments have shown that the layflat tubing used to form the sealed bag 10 results in an advantageously smooth transition around the base of the cavity 28, i.e. where the second layer 26 meets the first layer 24. This transition is represented by the angle (alpha) in Figure 2b, which is greater than 90 degrees. Accordingly, stress concentrations are avoided around the base of the chamber 28.

[0058] Multiple ballast chambers may be provided along the length of the blade and / or within one or both half shells using the above-described process. Whilst the sealed bag 10 in the above example is made using layflat tubing, it will be appreciated that any other suitable sealed bag 10 could be provided, for example using a balloon, multiple balloons or multiple bags, other types of sealed tubes etc.

[0059] The sealed bags 10 may advantageously be used in highly concave portions of a mould 20, as will now be discussed with reference to Figures 3a-3d. Figures 3a and 3b illustrate the problem of vacuum bag bridging, which can occur in highly concave portions of a mould, and Figures 3c and 3d show how this problem can be avoided by the present invention.

[0060] Referring to Figure 3a, this shows a female mould 20 shaped to form one half of a wind turbine blade shell having a flatback trailing edge, for example a windward shell or a leeward shell, or a section thereof. A similar mould (not shown) is used to form the other half shell.

[0061] The mould 20 has a highly concave portion 30 at the trailing edge 32, which is approximately U-shaped in this example. One side of this trailing edge portion 30 is formed by a separate mould portion 34, which is removable to facilitate de-moulding of the shell once formed.

[0062] Fibrous reinforcing material 36 is arranged in the mould 20. The fibrous reinforcing material 36 may comprise one or more layers of fibrous fabric, for example glass-fibre plies. The fibrous material 36 is pushed against the U-shaped surface 38 of the mould 20 in the concave trailing edge region 30. A spray adhesive or clamps may be used to secure the fibrous material 36 in position. The layup 22 is then covered with a vacuum bag 14, which is sealed against flanges of the mould 20 to form a closed space 18 encapsulating the layup 22. Air is then evacuated from the closed space 18 and resin is admitted to infuse the layup 22.

[0063] Figure 3b shows a problem that may occur during the infusion process. It can be seen that the vacuum bag 14 is not closely following the U-shaped profile of the mould 20 in the trailing edge portion 30. Instead the vacuum bag 14 has formed a bridge 40 across the walls of the U-shaped portion 30. This bridging of the vacuum bag 14 means that the vacuum bag 14 is not pressing against the fibrous material 36 within the U-shaped trailing edge portion 30. Instead a cavity 42 is created between the vacuum bag 14 and the fibrous material 36, which becomes filled with resin during the infusion process, thus reducing the quality of the blade shell. As the vacuum bag 14 is not pressing against the fibrous material 36, the fibrous material itself may also form a bridge across the walls of the U-shaped portion 30 in some cases, which would result in the final part not having the required shape.

[0064] This problem can be avoided by manual intervention during the moulding process, for example an operator may use their hands to push the vacuum bag 14 into the correct position. However, this requires close monitoring and is labour intensive. This problem can alternatively be avoided using a sealed bag 10 in accordance with the present invention as will now be described with reference to Figures 3c and 3d.

[0065] Figure 3c shows a sealed bag 10 positioned between the vacuum bag 14 and the fibrous reinforcing material 36 in the U-shaped trailing edge portion 30 of the mould 20. The bag 10 may be a balloon, for example a latex balloon or another suitable sealed bag 10. The sealed bag 10 is elongate and extends longitudinally perpendicular to the plane of Figure 3c. The sealed bag 10 is at least partially inflated with air, as shown in Figure 3c.

[0066] Figure 3d shows the situation after air has been evacuated from the closed space 18. As shown, the sealed bag 10 fills the U-shaped trailing-edge portion 30 of the mould 20. The sealed bag 10 pushes the fibrous reinforcing material 36 into the required position against the sides of the U-shaped trailing edge portion 30. Liquid resin is then supplied to the evacuated closed space 18. The resin infuses throughout the layup 22 and the sealed bag 10 supports and maintains the fibrous reinforcing material 36 in the correct position throughout the infusion and subsequent curing processes.

[0067] The sealed bag 10 ensures that the fibrous material 36 remains firmly pressed against the surfaces of the mould 20 within the concave trailing edge region 30. The sealed bag 10 acts as a supplementary mould tool inside the vacuum bag 14. As the sealed bag 10 fills the concave trailing edge region 30, the vacuum bag 14 is not required to enter this region and the problem of vacuum bag 14 bridging shown in Figure 3b is avoided. A high-quality laminate is produced without resin-rich regions at the trailing edge. Use of the sealed bag 10 to support the fibrous material 36 may also avoid the need to use spray adhesives or clamps to retain the fibrous material in position on the concave mould surface.

[0068] After the resin has cured, the vacuum bag 14, the sealed bag 10 and the separate mould portion 34 are removed. The half shell can then be bonded with a corresponding half shell formed in the same way using adhesive applied between the leading edges and the trailing edge flanges of the respective half shells.

[0069] This technique is not limited to use at the trailing edge of a mould 20 for a flatback blade. It will be appreciated that a sealed bag 10 could be used in a similar way inside any concave portion of a mould 20 to avoid the problems of vacuum bag 14 bridging and to ensure that the fibrous material 36 is pressed firmly against the mould surfaces and supported in this position during infusion and curing.

[0070] Sealed bags 10 can also be used during blade manufacturing to form integral stiffening elements in the blade shell, as will now be described with reference to Figures 4 and 5. Referring to Figure 4, this shows a female mould 20 shaped to form one half of a wind turbine blade shell, for example a windward shell or a leeward shell, or a section thereof. A similar mould (not shown) is used to form the other half shell.

[0071] A shell layup 22 is built up on the mould surface 12. Initially one or more outer layers 24 of fibrous reinforcing material are arranged in the mould 20 to form an outer skin of the half shell. A spar cap 44 is optionally then arranged on the outer skin layer, for example the spar cap 44 may comprise a stack of pultruded strips 46 of carbon fibre reinforcing material.

[0072] A plurality of sealed bags 10 is then arranged on the outer skin layer 24. The sealed bags 10 are at least partially filled with air. The sealed bags 10 are preferably elongate and extend in the spanwise direction of the mould 20, i.e. perpendicular to the plane of Figure 4. The sealed bags 10 are preferably long balloons, but could be any other suitable sealed bag 10.

[0073] A plurality of intermediate layers 25 of fibrous reinforcing material are then draped over each sealed bag 10. The intermediate layers 25 may be draped over a sealed bag 10 such that they develop a substantially S-shaped profile, as seen on the right-side of the spar cap 44 in Figure 4, or a top-hat-shaped cross-sectional profile, as seen on the left-side of the spar cap 44 in Figure 4. These shapes and positions are shown purely for illustrative purposes to exemplify various possibilities in a single figure. They are not intended to limit the scope of the invention.

[0074] One or more inner layers 26 of fibrous reinforcing material are arranged over the optional spar cap 44 and over the intermediate layers 25 to form an inner skin of the component. The shell layup 22 is then covered by a vacuum bag 14, which is sealed against flanges of the mould 20 to create a closed space 18 encapsulating the shell layup 22. The closed space 18 is then evacuated, which causes the vacuum bag 14 to push down against the intermediate layers 25.

[0075] The sealed bags 10, which are also encapsulated inside the closed space 18, will change shape when the closed space 18 is evacuated. The sealed bags 10 are regions of positive pressure inside the vacuum bag 14 and serve to support the intermediate layers 25 during the subsequent infusion and curing processes. Accordingly, the intermediate layers 25 maintain their draped profiles, e.g. S-shaped or top-hat-shaped, in the cured laminate. The sealed bags 10 do not add much mass to the laminate and so can remain in the laminate between the inner and outer skins.

[0076] The intermediate layers 25 form stiffening webs between the inner and outer skin layers of the shell laminate. These stiffening webs 25, which can also be described as corrugations, serve to maintain a predetermined spacing between the inner and outer skins and therefore avoid the need for core materials such as foam or balsa between the skins, which is traditionally used. The elimination of traditional core material results in a cheaper and even more lightweight structure.

[0077] Figure 5 shows a further example where sealed bags 10 at least partially filled with air can be used to form stringers 25 integrally with the blade shell. In this example, fibrous reinforcing material 36 is arranged in the mould 20. Sealed bags 10 at least partially filled with air, for example long balloons, are arranged on top of the fibrous reinforcing material 36. Additional fibrous reinforcing material 25 is then draped over the sealed bags 10. The additional fibrous reinforcing material 25 may adopt an S-shaped profile or a top-hat- shaped profile, for example. The layup 22 is covered by a vacuum bag 14 and undergoes an infusion and curing process in the same way as the previous examples. The sealed bags 10 support the additional fibrous material 25 during the infusion and curing process. The additional fibrous material 25 forms stringers on an internal surface of the blade, which are integrally formed with the blade shell.

[0078] The above examples described a number of ways in which gas filled sealed bags 10 inside a vacuum bag 14 can be used to improve the production of wind turbine blade shells. The bags 10 could be used in a similar way to make other component parts of a wind turbine blade, for example a shear web, which is another composite component formed in a mould 20.

[0079] The above examples have been described with respect to a vacuum infusion process. However, the above examples are also applicable to a pre-preg process or a sprayed resin process for example.

[0080] The invention offers a cheap and flexible mouldless way to change the B-surface of composite parts, i.e. the surface facing the vacuum bag 14. As discussed above, the sealed bags 10 can be used to create air pockets in the composite for use as ballast tanks 28 or for other applications. The sealed bags 10 can also be used to support further reinforcing layers to form integral stiffening elements or to eliminate the need for core material in sandwich shells. Furthermore, the sealed bags 10 can be used in corners or other concave portions of a mould 20 to prevent bridging of vacuum bags and to improve the quality of the laminate produced. Any of the above examples, or parts of the above examples, can be used either alone or in combination in a wind turbine blade or component part thereof.

Claims

Claims1. A method of making a wind turbine blade component, the method comprising: providing a rigid mould (20) shaped to form the wind turbine blade component; arranging fibrous reinforcing material (36) in the mould; covering the fibrous reinforcing material with a vacuum bag (14); sealing the vacuum bag against a surface (12) of the mould or against another surface to create a closed space (18) between the mould and the vacuum bag in which the fibrous reinforcing material is encapsulated; removing air from the closed space to create a negative pressure within the closed space; supplying resin to the fibrous reinforcing material; and curing the resin, wherein the method further comprises providing a sealed bag (10) in the closed space, the sealed bag being at least partially filled with a gas such that the pressure inside the sealed bag is greater than the pressure within the closed space outside the sealed bag, and arranging the sealed bag to shape and / or support a portion of the fibrous reinforcing material during the moulding process.

2. The method of Claim 1 , wherein the sealed bag (10) is a balloon.

3. The method of Claim 1 , wherein the sealed bag (10) is a sealed length of plastic layflat tubing.

4. The method of any preceding claim, further comprising arranging the sealed bag (10) between a first layer (24) and a second layer (26) of fibrous reinforcing material (36) such that the sealed bag forms a cavity (28) between the first and second layers.

5. The method of Claim 4, wherein the cavity (28) is a ballast chamber.

6. The method of any preceding claim, wherein the portion of the fibrous reinforcing material (36) supported by the sealed bag (10) forms a stiffening element (25) such as a corrugation or stringer.

7. The method of any preceding claim, comprising arranging one or more outer layers (24) of fibrous reinforcing material in the mould (20) to form an outer skin of the component;arranging the sealed bag (10) or a plurality of sealed bags (10) at least partially filled with a gas on the outer layers; and draping one or more intermediate layers (25) of fibrous reinforcing material over the or each sealed bag (10).

8. The method of Claim 7, further comprising arranging one or more inner layers (26) of fibrous reinforcing material over the intermediate layers (25) to form an inner skin of the component.

9. The method of Claim 7 or Claim 8, wherein the intermediate layers (25) of fibrous reinforcing material (36) are draped over the or each sealed bag (10) such that they develop a substantially S-shaped or top-hat-shaped cross-sectional profile.

10. The method of any preceding claim, wherein the mould (20) is shaped to form a shell of a wind turbine blade having a flatback trailing edge, and wherein the sealed bag (10) is arranged in a trailing edge region (30) of the mould.

11. The method of any preceding claim, wherein the wind turbine blade component is a shell of a wind turbine blade, or a part of a shell, or a half shell or a part of a half shell, or a shear web.

12. A wind turbine blade comprising a shell of composite construction formed according to the method of any preceding claim.

13. The wind turbine blade of Claim 12 wherein a ballast chamber (28) is formed integrally with the shell.

14. The wind turbine blade of Claim 12 or Claim 13, wherein the shell comprises an inner skin, an outer skin and one or more stiffening webs or corrugations (25) between the inner and outer skins.

15. The wind turbine blade of any of Claims 12 to 14 further comprising one or more stiffening structures (25) such as ribs or stringers integrally formed with an internal surface of the shell.

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