WO2012136222A1

WO2012136222A1 - Method and apparatus for preparing a fibre reinforced composite component

Info

Publication number: WO2012136222A1
Application number: PCT/DK2012/050110
Authority: WO
Inventors: Giancarlo GIROLOMINI
Original assignee: Vestas Wind Systems A/S
Priority date: 2011-04-06
Filing date: 2012-04-04
Publication date: 2012-10-11

Abstract

A method of preparing a fibre reinforced composite component where fibrous material is provided on a carrier (300) and enclosed by an elastic membrane (203) forming a first vacuum chamber (201). A second vacuum chamber (202) is established enclosing the first vacuum chamber, and the pressure in the vacuum chambers is decreased to extract air from the composite material. Subsequently, the composite material is compacted by increasing the pressure in the second vacuum chamber, which is then opened while said first vacuum chamber remains depressurized. The carrier (300) with the compacted material is then transported to a heating station to initiate curing of the resin. The invention further relates to an apparatus for preparing a fibre reinforced composite, comprising a vacuum and a heating station, and a first vacuum chamber transportable between the different stations. The vacuum station comprises a second vacuum chamber adapted to enclose the first vacuum chamber.

Description

METHOD AND APPARATUS FOR PREPARING A FIBRE REINFORCED

COMPOSITE COMPONENT

Field of the invention

The present invention relates to a method of preparing a fibre reinforced composite component and to an apparatus for preparing a composite component including the stages of pressure and heat treatment.

Background

In the manufacturing of composites, layers of reinforcing material and resin, pre-impregnated layers, dry fibres, or combinations hereof are first laid or stacked in a mould or on a supporting surface according to the material properties and shape desired of the finished component. The impregnation of the reinforcing material by resin may be performed by resin infusion or injection, or in case of pre-impregnated materials by the application of heat and pressure to make the resin flow and impregnate the reinforcing material. The curing of the composite may be performed in one or in several stages depending on the resin material. A component may thus be pre-consolidated by heating to a certain temperature and for a certain time effectuating only part of the resin to cure, whereby the component can be stored, handled, moved around, and deformed to some extend without curing fully. The final fully cured component may then be obtained after a further heating step to a higher temperature or for a longer time.

In order to fully impregnate the material and to obtain the desired fiber to resin ratio, the composite material is depressurized prior to any resin transfer or to the heating. By a conventional vacuum bagging process, the composite material is covered by a release film and a vacuum bag which is then sealed along all edges to the mould. The vacuum bagging however may be a rather time consuming and manually intensive process which is difficult to combine with an automated manufacturing process. Further, a complete air and gas extraction is difficult if not impossibly in part by the gasses getting trapped inside the composite material or in wrinkles and folds of the vacuum bag as the composite material is compacted by the vacuum bag thereby closing off bleed paths for air to escape.

To ensure paths for the air to escape during the application of vacuum, a breather film is often placed between the composite material and the vacuum bag to. The release film then needs to be perforated for the air to pass up into the breather film. However, a breather film may still not ensure a complete air extraction from the material and further leads to a considerable material waste as the breather gets filled with resin material during the process and cannot be reused. Description of the invention

It is therefore an object of embodiments of the present invention to overcome or at least reduce some or all of the above described disadvantages of the known vacuum bagging of composite components by providing a method for the preparation of composites with improved compaction and consolidation cycles allowing for high production rate and automated handling.

It is a further object of embodiments of the invention to provide at least partly cured composites with reduced void content and increased material quality.

It is a further object of embodiments of the invention to provide a method of preparation of composites allowing for use of reusable vacuum membranes and reduced waste.

It is a further object of embodiments of the invention to provide an apparatus for a composite compaction and at least partly consolidation process of a reduced tact time and of reduced down-time in case of repair or maintenance. It is a yet further object of embodiments of the invention to provide an apparatus suitable for the preparation of composites where the material is not restricted to lay-up of prepregs, but may be provided by different means such as e.g. by robot.

In accordance with the invention this is obtained by a method of preparing a fibre reinforced composite component comprising fibrous material and resin material, the method comprising providing the fibrous material on a carrier; - sealingly connecting an elastic membrane to said carrier to thereby form a first vacuum chamber enclosing said composite material;

- establishing a second vacuum chamber enclosing said first vacuum chamber;

- decreasing the pressure in said first and second vacuum chamber to extract air and gasses from the composite material ;

- subsequently increasing the pressure in the second vacuum chamber to compact the composite material by the pressure exerted by the membrane on the composite material; - opening said second vacuum chamber while said first vacuum chamber remains depressurized, and transferring the carrier with the compacted composite material to a heating station, and

- subsequently heating the composite material at the heating station to initiate curing of the resin.

Hereby may be obtained a method of preparing a composite member where the composite material may be prepared and treated at different stations without affecting the quality of the composite. Rather, the quality of the finished composite component may be improved by the use of the two separate vacuum chambers which together with the use of the elastic membrane facilitates a high compaction, an increased air and gas extraction, and a reduced void content in the consolidated composite.

The possibility to prepare and treat the composite component at different stations, such as at a lay-up station where the composite material is placed on the carrier, a vacuum station, a heating, optionally a cooling station, and a station for extraction of the component makes it possible for multiple composite components on different carriers to be treated on the same time. Hereby the tact time of the component may be decreased considerably and the production rate increased correspondingly compared to a process where the material lay-up, the vacuum, heating, and cooling treatments are all performed in the same apparatus sequentially. This separation of the different stages is facilitated by the composite material being provided on a carrier and by the use of the framed vacuum membrane enclosing the material on the carrier, which enables a vacuum to be established and upheld on the material independently of the pressure in the second surrounding vacuum chamber, thereby making it possible to transport the carrier with the composite material remaining depressurized under the vacuum membrane. A further advantage with the proposed method is that as the pressure is decreased and the vacuum is applied within both the first and the second vacuum chambers, the elastic membrane is not at this stage pressing on the material, the material is loose thereby allowing air and gasses to escape quickly. As the pressure is then increased in the second vacuum chamber, the air and gasses have already been removed from the material, resulting in a much reduced void content. Further, the vacuum sequence according to the above makes the use of a breather film or filter under the vacuum membrane superfluous thereby resulting in shorter time needed for preparing the composite material, and in material savings both in relation to the breather film and to the resin which would otherwise flow into the breather layer. The proposed method may further be advantageous by the use of an elastic membrane in the establishment of the first vacuum chamber. Hereby may be obtained that the membrane may be reused which is not the case with the vacuum films used in conventional vacuum bagging processes. Further, in case a release film is applied in between the composite material and the elastic membrane to ensure safe and easy removal of the membrane, the release film need not be semi-permeable or perforated, which otherwise is needed for the release films applied in conventional vacuum bagging where the air needs to be evacuated through a breather cloth placed below the vacuum foil.

The elastic membrane may be of any material with a sufficient elasticity to deform onto and thereby essentially follow the shape of the composite material during vacuum extraction such that essentially no air pockets around the composite material will sustain during vacuum extraction. The elastic membrane may be of e.g. a rubber material, a latex rubber or a silicone rubber. The elastic membrane may have a thickness in the range of 0.5-5.0 mm such as e.g. 1-2 mm like for example 1.5 mm. An elastic membrane may furthermore be advantageous compared to the vacuum foils used in conventional vacuum bagging in that the otherwise unavoidable wrinkles and folds on the surface and air pockets trapped therein can be avoided. Hereby may be obtained a more smooth and even composite surface essentially without any marks from the vacuum membrane.

As the composite material is provided on a carrier, the preparation of the composite component is not bound to be performed inside the vacuum chamber but may according to embodiments of the proposed method be performed outside the vacuum chamber at another location. In this way the proposed method does not impose any limitations to how or where the composite material is prepared in terms of e.g. the required working space, accessibility during lay-up, special equipment for providing the composite materials, specific working conditions (e.g. temperature, humidity), or the like.

Further, the provision of the composite on the carrier is advantageous in making it possible to work with composite material in between the steps of vacuum treatment, heating and cooling. For instance the composite material may be shaped e.g. by bending or otherwise deforming, or the composite may be subjected to inspection. The composite material may be provided on the carrier by different methods such as e.g. by lay-up of layers of pre-pregs or semi-pregs, fiber layers of any type (e.g. fabrics, woven, non-woven, felts etc) and resin, by laying of fiber tows, by fiber bundles of fibre material and resin, by spraying or painting of resin in strips or other patterns, by extrusion or pulltrusion, or combinations hereof. According to an embodiment of the invention, the composite material is provided by fiber tows layed out by a robot and held in position by strips of resin material and optionally adhesive sprayed onto the fiber tows. The fiber tows may be placed as multiple unidirectional layers. The fibrous material may comprise fiber material of e.g. Carbon, glass, Kevlar, or wood and may be applied as continuous or discontinuous fibers. The composite material may likewise comprise non-fibrous reinforcing materials such as foams like PVC foam or PET foam.

The resin may comprise e.g. epoxy, Vinylester, or polyester, and may comprise different hardeners curing at different temperatures allowing for the resin to cure partially or intermediately (B-stage resin type).

During the heating the resin may be fully cured or partially cured by raising the temperature to a level where only a part of the resin initiates curing or where the curing of the resin is only initiated in certain parts or regions.

The establishing of the second vacuum chamber may be realized e.g. by placing the carrier with the membrane covered material in a vacuum chamber or by otherwise enclosing the carrier such as in a vacuum bag or by the closing of a lid onto the carrier or onto a surface supporting the carrier. The second vacuum chamber hence comprise a rigid enclosure or a deformable enclosure or combinations of both.

The pressure in the first and second vacuum chamber may be decreased such as to establish vacuum. By vacuum is here and throughout the description to be understood a much reduced pressure compared to the atmospheric pressure such as a reduced pressure of e.g. 0,05-1% of atmospheric pressure, 0, 1-10 mbar absolute or in the range of 0, 5- 2 mbar absolute. The pressure reduction and control may be achieved by means of one or more vacuum pumps connected to the vacuum chambers through different openings or valves in e.g. the carrier, the supporting surface in the second vacuum chamber, in the elastic membrane or in its connection to the carrier, in the lid to the second vacuum chamber or in combinations hereof. The vacuum may be held for a period of time of e.g. 0-8 minutes such as e.g. 2-6 min.

When the pressure is again increased in the second vacuum chamber, the pressure may be increased to atmospheric pressure thereby depressurizing the second vacuum chamber. The decreasing of the pressure may be obtained by simply opening the second vacuum chamber. Alternatively or additionally, the pressure in the second vacuum chamber may be increased above atmospheric pressure to thereby obtain an increased compaction of the composite material.

The first vacuum chamber may remain depressurized at the same or essentially the same pressure by continuously extracting air from the enclosure or by holding the vacuum by closing off the chamber e.g. by means of valves.

The heating station may comprise an oven or any other heating means. The composite may be heated such as to decrease the viscosity of the resin material to impregnate the fibrous material. Further, the composite may be heated to a temperature where the curing process of some or all of the resin begins or where the B-stage curing is activated for some or all of the resin. In embodiments of the invention the composite may be heated to temperatures between 50-90 °C, such as in a range between 60-80°C, such as between 65-72°C. The optimal heating temperature depends on the material properties of the resin material. The heating may advantageously be held until a homogeneous temperature is achieved for the entire component and until a desired percentage of resin cure is obtained within the component.

The carrier onto which the composite material is provided may be flat, convex, or concave or combinations hereof, and may in general be shaped according the desired shape of the finished composite component. The function of the carrier is primarily to support the composite material during its manufacture, to provide a sufficient support for the elastic membrane to thereby form the first vacuum chamber, and to provide a simple means to transport and move the composite material during the manufacture.

The method may further comprise releasing the pressure in the first vacuum chamber, removing the membrane from the carrier, and extracting the at least partly cured composite component from the carrier. In an embodiment of the invention at least a part of the resin of the composite material is provided on the carrier together with said fibrous material. Hereby is obtained a simple yet effective method where the heat and pressure enables an effective compaction and full resin impregnation of the reinforcing materials with reduced risk of void contents.

In a further embodiment of the invention the method according further comprises infusing or injection at least a part of the fibrous material with resin after increasing the pressure in the second vacuum chamber. Hereby composite components comprising dry fibres to be impregnated by resin transfer and optionally pre-impregnated materials may effectively be prepared, in that the use of the two vacuum chambers act to ensure an optimal extraction of gasses and air from the reinforcing material prior to the resin transfer.

According to one embodiment of the invention, the pressure exerted by the membrane on the composite material during the gas extraction is reduced by decreasing the pressure in the second vacuum chamber prior to decreasing the pressure in said first vacuum chamber.

Hereby is obtained that the elastic membrane is lifted slightly off the composite material due to the initially lower pressure in the second vacuum chamber whereby more passages for the air and gasses to escape are kept open during the application of vacuum to the first vacuum chamber. In an embodiment of the invention the composite material is provided in an exchangeable mould part on the carrier. Hereby the same carrier may be used for the lay-up of composites of different shapes simply by the use of ne or more suitable mould parts. Further, multiple composite components may be prepared on the same time on the same carrier thereby increasing the manufacturing capacity. According to a further embodiment of the invention, the method comprises cooling the composite material to at least partly discontinue the curing of the resin. Hereby the curing process of the resin material is at least partly stopped providing a pre-consolidated composite component, which allows for the handling or storing of the component for some time before the composite cures completely. In this way the component may e.g. be adjusted or adapted size- or shape-vise, such as being bent or cut into a desired shape, or optionally incorporated in a larger component before a final cure of the composite. In an embodiment the composite may be cooled to e.g. 15- 40°C, such as in a range between 20-30°C, such as between 22- 28°C. The heat distribution is advantageously applied homogeneously to the entire composite component to obtain homogenous or at least comparable material properties of all parts of the component. The cooling may be performed in a separate cooling station or cooling chamber or may additionally or alternatively be performed by a temperature change at the heating station.

In yet a further embodiment of the invention according to the above, the first vacuum chamber remains depressurized during the cooling, whereby an increased compaction and a reduced void content of the composite component may be obtained.

According to a further embodiment of the invention, the method comprises deforming the compacted composite material prior to the step of heating. Hereby the deformability of the compacted material is exploited so that more specific shapes of the finished composite components may be obtained. In this way a 3-dimensionally shaped composite component may be obtained even for the cases where the composite material is initially provided on a flat carrier or support.

According to a further embodiment of the invention, the composite material is provided on a carrier surface of a material with a thermal expansion coefficient corresponding to the thermal expansion coefficient of at least part of the fibrous material. Hereby may be obtained that the carrier surface deforms to the same extent as the fibrous material during the processing. In this way the carrier or mould surface does not prevent or counteract any fiber movements during the vacuum, heating, or cooling steps, which may result in a higher quality of the finished composite component.

According to yet a further embodiment of the invention the elastic membrane is sealingly connected to a frame member along its edges. Hereby is obtained that the elastic membrane may be handled in a simple yet effective way in that it may simply be lifted on and off the carrier e.g. by a crane. This enables this part of the manufacturing method to be automated even for large composite components. Further, the process time may be reduced considerably by use of such framed membrane. A further advantage of the frame member is the possibility to make air extraction openings to the first vacuum chamber in the frame member.

In yet a further embodiment of the invention according to the above, the frame member comprises a deformable sealing member arranged to fit the carrier in order to seal the first vacuum chamber formed by the carrier and the elastic membrane. Hereby the establishment of the first vacuum chamber may be achieved without the need for sealant tape and any manual sealing, thereby both reducing the production time, and deriving savings in both man hours and material costs. In yet a further embodiment of the invention, the frame member according to the above comprises a further deformable sealing member placed at a distance to the first sealing member, and the method comprises sucking the elastic membrane onto the carrier by decreasing the pressure in the space in between said sealing members and the carrier. Hereby is obtained an effective, yet simple and low cost sealing of the first vacuum chamber without the need for special sealing parts on the carrier or in the second vacuum chamber.

An embodiment of the invention further comprises providing a release film on the carrier before the fibrous material is placed on the carrier and/or placing a release foil between the fibrous material and the membrane. Hereby is obtained that the composite component may readily be removed from the carrier at any time and that the membrane may likewise be readily removed from the composite material. Further, the use of a release paper facilitates a fast an immediate reuse of the membrane and the membrane without any time consuming cleaning or preparation needed. Further, the invention relates to a part of a wind turbine blade comprising a fibre reinforced composite component prepared by a method according to any of the above. The advantages hereof are as explained in relation to the previously described manufacturing method.

The invention furthermore relates to an apparatus for use in the preparation of a fibre reinforced composite component according to any of the above, where the apparatus comprises a vacuum station, a heating station, and a first vacuum chamber to be transported between said stations, the first vacuum chamber comprising a carrier and an elastic membrane arranged on the carrier such as to enclose a composite material of said fibre reinforced composite component placed on said carrier, the vacuum station comprising a second vacuum chamber for enclosing said first vacuum chamber; the apparatus further comprising means for individually controlling the pressure in each of said first and second vacuum chambers thereby controlling the pressure exerted by the elastic membrane on the composite material in the first vacuum chamber, and the apparatus further comprising means for establishing said first vacuum chamber independently of said second vacuum chamber such that said first vacuum chamber may be maintained depressurized while being transported from said vacuum station to said heating station.

Hereby is obtained an apparatus allowing for the preparation of composite components at separate stations of secondary vacuum and heating whereby multiple composite components on different carriers may be treated on the same time thereby decreasing the tact time considerably. Further, by the use of two vacuum chambers which may be individually controlled enables a high compaction of the composite material, an increased air and gas extraction, and a reduced void content in the consolidated composite. Further advantages are as explained in relation to the previously described manufacturing method.

Brief description of the drawings

In the following different embodiments of the invention will be described with reference to the drawings, wherein :

Fig. 1 shows a sketch of the gas evacuation of a composite during vacuum bagging according to prior art, Figs. 2A and 2B are sketches of the gas evacuation according to an embodiment of the invention,

Figs. 3A-E and 4A-E are sketches of the different steps in the preparation of composite members according to an embodiment of the invention, Figs. 5A and 5B illustrate an apparatus for the making of a composite member according to an embodiment of the invention as seen in an end view and in a perspective view, respectively,

Fig. 6 is a sketch of two slabs of composite material in the vacuum chambers according to an embodiment of the invention and in a cross sectional view, Fig. 7 is a cross sectional view of a frame member to which the vacuum membrane is attached according to an embodiment of the invention,

Fig. 8 shows an embodiment of the framing of the vacuum membrane in a perspective view,

Figs. 9A-C shows sketches of different embodiments of sealing the elastic membrane to the carrier, and Fig. 10 illustrates a wind turbine blade comprising a composite slab prepared according to the invention.

Detailed description of the drawings

Figure 1 illustrates a composite 100 during air and gas extraction according to a conventional vacuum bagging process. The fibrous material and the resin material 101 is applied to a mould 102 and covered with a vacuum foil 103 sealed along its surfaces to the mould. As vacuum is applied by air extraction from inside the vacuum foil, while atmospheric pressure 104 acts on the exterior, the material is compacted thereby, however, at least to some extent closing off bleed paths for the air to escape. This therefore results in some air being trapped within the composite 100. Figure 2 illustrates the principle of vacuum extraction according to an embodiment of the invention, where two vacuum chambers are formed; a first chamber 201 inside or beneath an elastic vacuum membrane 203, and a second or outer vacuum chamber 202 above the vacuum membrane. In a first step, figure 2A, the vacuum is applied to both chambers 201, 202 both below and above the vacuum membrane. Hereby, the composite material 101 is loose while the pressure is decreased allowing air to escape quickly. Next, figure 2B, the pressure is increased in the second vacuum chamber 202, as illustrated by the arrows 104 whereby the material 101 is compacted by the pressure exerted by the vacuum membrane 203 on the composite material. As the air and gasses has already been removed from the material at this step, a much reduced void content and a higher compaction may be obtained when compared to the conventional vacuum bagging process as illustrated in the previous figure 1.

Figure 3 illustrates the different stages and stations in the preparation of a composite. First, A, the material of the composite is provided in a mould or directly on a carrier 300. The material may as an example be composed by the stacking of layers of fibers and resin, by the stacking or otherwise placing of pre-pregs or semi-pregs, by the placing of fibrous material and resinous material or combinations hereof. As an example, the composite may be built up by the placing of individual fiber tows and resin placed in between e.g. as discontinuous layers or strips to some extent holding the fiber tows in place.

The composite material is then in step B covered by a vacuum membrane 203 thereby establishing a first vacuum chamber 201, and placed in a second vacuum chamber 202 where the gas and air is extracted and the material compacted according to process described above in relation to figures 2A and 2B. When the composite material has dwelled in vacuum for a period of time, the arrangement of the vacuum membrane independent of the establishment of the outer second vacuum chamber allows for the outer second vacuum chamber 202 to be opened, and for the carrier 300 with the composite material to be moved along while maintaining the vacuum on the material. Hereby the following heating of the material, step C, may be performed at a heating station 303 separate from the vacuum station 302 with the composite material still under to be vacuum. The heating decreases the viscosity of the resin material to fully impregnate the fibrous material. Further, the composite material may be heated to a temperature initiating a curing of at least some of the resin. After the heating, the composite material while still under vacuum is cooled, step D, optionally at a cooling station 304 separate from the heating station 303. Hereafter the vacuum may be released, the vacuum membrane removed, and the composite extracted or unloaded from the carrier, step E, 305.

The process steps at the vacuum, heating, and cooling stations are described in further detail in figure 4. As a first step, Figure 4 A, the carrier 300 with the product 101 arrives from the lay-up station and is positioned at the vacuum station 302. A release film is placed on top of the product and the vacuum membrane 203 is placed on top of the product, as illustrated in figure 4B. Rather than a vacuum film or foil used in the conventional manual vacuum bagging, an elastic membrane 203 of e.g. a rubber material may be used. The elastic vacuum membrane may according to an embodiment of the invention be framed by a frame member 401 as shown in more details in figures 6-9. Hereby, the establishing of the first vacuum chamber 201 of enclosing the composite material 101 by the elastic membrane may be fully automated and achieved by placing the framed vacuum membrane over the composite material as illustrated in figure 4B. In step 4C, the second outer vacuum chamber 202 is established in this case by closing the lid 402, and vacuum is applied on both sides of the vacuum membrane, 201, 202.

In one embodiment the pressure is decreased first in the second vacuum chamber 202 thereby lifting the vacuum membrane 203 from the composite material 101 prior to decreasing the pressure in the first vacuum chamber 201 on the product side. In the step of figure 4D, the pressure is released in the second outer chamber 202, and the vacuum chamber is opened. Hereafter (figure 4E), the carrier 300 with the framed vacuum membrane and the material still depressurized is transported to the heating unit where the product is heated and further to the cooling unit for cooling the product. Hereby, multiple carriers with composites may be processed at the different stations or units at the same time, and the overall process time and tact-time may be reduced significantly.

The different stations of an apparatus for manufacturing composite members according to the process steps as described above are illustrated in figure 5. Figures 5A and 5B illustrate an apparatus 500 for the manufacture of a composite member according to an embodiment of the invention. The apparatus is seen in an end view in figure 5A and in a perspective view in figure 5B, respectively. At a first station 501 a carrier is prepared for the lay-up of the composite material. The carrier surface may be covered by a release film or paper. The carrier may optionally comprise a mould where the composite material is placed in, or the material may be layed on the flat carrier surface, which is done at the following station 502. The material may in an embodiment be layed by means of a robot 510 laying the individual fiber tows and strips or layers of resin in predefined patterns. The carrier 300 comprising the composite material is then moved to the vacuum station 302, covered first by a release film and then by the framed elastic vacuum membrane 203 which here is illustrated as being lowered onto the carrier by a crane 511 thereby establishing the first vacuum chamber enclosing the material. Next, the second vacuum chamber 202 is closed and the air and gas is extracted first from both the first 201 and second vacuum chambers 202 and thereafter released in the second chamber to compact the material. The carrier with the material depressurized underneath the framed vacuum membrane is then transported to the heating station 303 for heating and subsequently to the cooling station 304 for cooling. After the cooling sequence, the carrier may be transported to a station 507 where the framed vacuum membrane is removed and the material extracted e.g. for storing or use and final curing. The cycle of the framed vacuum membrane is illustrated by the arrows 508 indicating how the frame may be lifted off the carrier and the preconsolidated and compacted composite material, and transported back to be re-applied on another carrier just prior to or at the vacuum station 302. The same crane 511 used for the lifting and transporting of the vacuum membrane may be applied to lift the carrier 300 back to the beginning of the process line to be prepared for the manufacture of a new composite. The carrier cycle is indicated by the arrows 509.

Figure 6 illustrate an embodiment of a vacuum station 302 as seen when a carrier 300 with a pressurized composite is placed within the vacuum chamber. In this example two composite members 100 are layed up on the same carrier 300. The first or lower vacuum chamber 201 is formed by the carrier 300 and the framed elastic vacuum membrane 203. An embodiment of the frame member 401 framing the membrane may be seen in larger details in the following figure 7. The second vacuum chamber 202 is established by the lid sealingly closing onto the carrier 300 or onto the chamber surface 601 on which the carrier 300 is placed. As illustrated in the figure, the lid 402 may be arranged to press down 602 on the frame member 401 thereby aiding in the sealing of the first vacuum chamber 201 of the frame onto the carrier surface. The pressure may be decreased on both or each chamber 201, 202 individually by means of one or more vacuum pumps 603. The first vacuum chamber 201 may be depressurized through evacuation openings in the frame, or through evacuation openings arranged in the carrier or carrier supporting surface, or through combinations of both as long as the vacuum in the first vacuum chamber may be established and held independently of the pressure in the second outer vacuum chamber, so that the carrier with the frame may be moved with the material still under vacuum and depressurized. Figure 7 illustrates a detail of an embodiment of a vacuum membrane 203 framed by a frame member 401 and as placed on a carrier 300 as seen in cross sectional view. The elastic vacuum membrane 203 is fixed or clamped 701 along its edges to a frame member 401 comprising a hollow profile 702 for yielding a sufficient stiffness at a reduced weight. The frame member in this embodiment comprises a set of sealing members 702 arranged to provide a vacuum cavity seal (VCS seal) to the carrier onto which the frame rests. In this embodiment, the air evacuation from the first vacuum chamber 201 underneath the vacuum membrane is established (as illustrated by arrows 703) by air extraction through openings 704 in the frame member connected to a vacuum pump. Air may also be extracted 705 from in between the sealing members 702 thereby attaching the frame to the carrier. In order to position the framed vacuum member properly on the carrier and over the composite members (not shown), elevations 706 may be placed on the carrier or on the supporting surface in the vacuum chamber 202 to guide the frame into position. In figure 8 is shown an embodiment of the framing of the elastic vacuum membrane 203 in a perspective view. Here, the membrane 203 is attached to the lower part of the frame member 401 by means of a flange 801 connected to the frame. The plate 802 may serve as a base for one or more spring loads mounted in the chamber lid ensuring the frame to be kept in position and pressed against the carrier when establishing vacuum in the outer vacuum chamber surrounding the vacuum membrane. Like in the previous embodiment of figure 7, the frame is designed as a hollow frame 702. Vacuum may be connected e.g. on top of the frame or on one or more of its outer sides. Vacuum from the interior of the first vacuum chamber may be extracted through openings (of which one may be seen 704) in the flange 801 making channels into the hollow frame. Vacuum cavity seal (VCS-seal) 702 attaches the frame to the carrier. The frame 401 and the clamping flange 801 may both be manufactured in steel. The surface of the frame may be treated with a primer to thereby attach the sealing members with adhesive.

Other embodiments of the sealing of a framed vacuum membrane 203 are sketched in figures 9A-C. Figure 9A illustrate an embodiment applying vacuum seals 901 placed in the carrier 300 onto which the frame member 401 rests. Hereby, no seals need to be fitted to the membrane or the frame member. Figure 9B illustrates the use of a so-called E-seal 902 attached in part to both the framed vacuum membrane 203 and the carrier 300. In figure 9C is shown an embodiment applying a so-called tri-seal where the membrane closes onto an elevation 903 in the carrier 300. By this configuration of the sealing may be obtained that the framed vacuum membrane 203 is not so sensitive to an accurate placement on the carrier 300.

Common to the described sealing methods is that a robust and reliable sealing may be achieved of the frame of the vacuum membrane to the carrier without the use of sealing tape and thereby enabling a fully automated placing and arranging of the vacuum membrane.

Fig. 10 shows a sketch of a wind turbine blade 1001 comprising a spar 1003 as indicated in the airfoil section 1002 (in dark grey lines). The spar extends in the longitudinal direction of the blade. Parts of the wind turbine blade 1001 such as e.g. the blade shells or the spar 1003 may comprise composite members prepared according to embodiments of the disclosed invention.

While preferred embodiments of the invention have been described, it should be understood that the invention is not so limited and modifications may be made without departing from the invention. The scope of the invention is defined by the appended claims, and all devices that come within the meaning of the claims, either literally or by equivalence, are intended to be embraced therein.

Claims

1. A method of preparing a fibre reinforced composite component comprising fibrous material and resin material, the method comprising providing the fibrous material on a carrier; - sealingly connecting an elastic membrane to said carrier to thereby form a first

vacuum chamber enclosing said composite material;

- establishing a second vacuum chamber enclosing said first vacuum chamber;

- decreasing the pressure in said first and second vacuum chamber to extract air and gasses from the composite material ; - subsequently increasing the pressure in the second vacuum chamber to compact the composite material by the pressure exerted by the membrane on the composite material;

- opening said second vacuum chamber while said first vacuum chamber remains

depressurized, and transferring the carrier with the compacted composite material to a heating station, and

2. A method according to claim 1, wherein at least a part of the resin of the composite material is provided on the carrier together with said fibrous material.

3. A method according to claim 1 or 2 further comprising infusing or injection at least a part of the fibrous material with resin after increasing the pressure in the second vacuum chamber.

4. A method according to any of the preceding claims, wherein the pressure exerted by the membrane on the composite material during said gas extraction is reduced by decreasing the pressure in said second vacuum chamber prior to decreasing the pressure in said first vacuum chamber.

5. A method according to any of the preceding claims, wherein said composite material is provided in an exchangeable mould part on said carrier.

6. A method according to any of the preceding claims further comprising cooling the composite material to at least partly discontinue said curing of the resin.

7. A method according to claim 6, wherein said first vacuum chamber remains depressurized during said cooling.

8. A method according to any of the preceding claims further comprising deforming the compacted composite material prior to said step of heating.

9. A method according to any of the preceding claims, wherein the composite material is provided on a carrier surface being of a material with a thermal expansion coefficient corresponding to the thermal expansion coefficient of at least part of the fibrous material.

10. A method according to any of the preceding claims, wherein the elastic membrane is sealingly connected to a frame member along its edges.

11. A method according to claim 10, wherein the frame member comprises a deformable sealing member arranged to fit the carrier in order to seal the first vacuum chamber formed by the carrier and the elastic membrane.

12. A method according to claim 11, wherein the frame member comprises a further deformable sealing member placed at a distance to the first sealing member, and wherein the elastic membrane is sucked onto the carrier by decreasing the pressure in the space in between said sealing members and the carrier.

13. A method according to any of the preceding claims, wherein a release foil is provided on the carrier before the fibrous material is placed on the carrier and/or where a release foil is placed between the fibrous material and the membrane.

14. A part of a wind turbine blade comprising a fibre reinforced composite component prepared by a method according to any of the claims 1-13.

15. An apparatus for use in the preparation of a fibre reinforced composite component according to any of the claims 1-13, the apparatus comprising a vacuum station, a heating station, and a first vacuum chamber to be transported between said stations, the first vacuum chamber comprising a carrier and an elastic membrane arranged on said carrier such as to enclose a composite material of said fibre reinforced composite component placed on said carrier, the vacuum station comprising a second vacuum chamber for enclosing said first vacuum chamber; the apparatus further comprising means for individually controlling the pressure in each of said first and second vacuum chambers thereby controlling the pressure exerted by the elastic membrane on the composite material in the first vacuum chamber, and the apparatus further comprising means for establishing said first vacuum chamber independently of said second vacuum chamber such that said first vacuum chamber may be maintained depressurized while being transported from said vacuum station to said heating station.