WO2013049966A1 - Manufacturing moulded articles of fibre-reinforced resin composite material - Google Patents

Abstract

A method for manufacturing a moulded article of fibre-reinforced resin composite material comprises the steps of: a. disposing a body comprising fibrous reinforcement and resin into a mould cavity portion of a first mould part (84); b. locating a second mould part (86) relative to the first mould part (84) to form a mutually spaced configuration and to enclose the body within an intermediate mould cavity (100) defined between the spaced first and second mould parts; c. providing a peripheral hermetic seal between the first and second mould parts; d. applying a source of vacuum to the intermediate mould cavity (100) through at least one conduit (92) extending into the intermediate mould cavity (100), the vacuum extracting air from the intermediate mould cavity (100); e. moving at least one of first and second mould parts so as relatively to move the first and second mould parts together to define a final mould cavity; and f. heating the body to form the moulded article within the final mould cavity. An apparatus for manufacturing a moulded article of fibre-reinforced resin composite material is also disclosed. This manufacturing process has a low cost and a high quality product.

Description

Manufacturing Moulded Articles of Fibre-reinforced Resin Composite Material

The present invention relates to a method of, and apparatus for, manufacturing a moulded article of fibre-reinforced resin composite material. The present invention also relates to a unidirectional fibre-reinforced resin composite material for the manufacture of elongate structural elements, such as spar caps for wind or tidal turbine blades, bridge spars, and to a spar or a spar cap of such a wind or tidal turbine blade.

For many wind or tidal turbine blades (WTB), the structural element or spar extending along the blade length is composed of a spar cap which is manufactured either as integral part of a shell infusion or, more commonly, as a premade component. The most common processing route for spar cap components is by vacuum assisted resin infusion of glass fibre fabric. The fabric consists of predominantly unidirectional (UD) fibres, aligned in the length of the spar. Typical fabric consists of 95% longitudinal fibres supported by a much smaller amount of lateral fibres. The lateral fibres are usually interwoven or stitched to the longitudinal fibres. Such stitching or weft weave causes crimping and non-collimation of the load bearing UD fibres. This can decrease compression strength properties, particularly in carbon fibre composites.

Typical resin systems for the spar cap are amine curing epoxy infusion resins, formulated specifically to have low viscosity during the manufacturing process in the ambient environment, and ambient temperature curing conditions. Sometimes the cure is accelerated by increasing the temperature, but typically to only 60°C or thereabouts in order to avoid excessive exotherm temperature rises since spar cap thicknesses can reach 60 to 100 mm in parts of the spar cap. Often an elevated temperature postcure is used to develop full material properties, but usually the post cure is carried out at a temperature of less than 70-80°C due to constraints of tooling materials. This higher temperature post cure is often needed to ensure full cure of the thinner parts of the spar cap which do not receive significant exotherm heat and so do not heat up to as high temperatures in the initial cure as do the thicker parts of the spar cap. Consolidation of fabric prior to infusion is usually achieved by vacuum bagging of dry laminated materials. The same vacuum being utilised during the infusion process to pull, or transfer, resin from the feed pots through the laminate stack to ensure complete impregnation of the reinforcing material. This transfer of resin gives rise to the name vacuum assisted resin transfer moulding (VARTM) for this type of manufacturing process. By its nature the vacuum has a practical limit of 0 mbar absolute, or 1 atmosphere of pressure differential between the material inside the vacuum bag and the outside environment. The pressure is applied via an airtight membrane (vacuum bag). This practical limit on consolidation pressure, coupled with the physical properties of the typical resin systems (viscosity, typically from 200 to 350 centipoise, more typically from 225 to 295 centipoise, both measured at a temperature of 25°C) means a practical upper limit of fibre volume fraction (FVF) in the region of 55% is typical.

Increasing the FVF would be desirable as this allows improved specific properties, along with reduction in resin usage during processing i.e. cost reduction.

A materials and processing combination which allows the use of pure unidirectional fibre rovings, coupled with lower cost resin system, and utilising a closed mould system which can apply considerably higher consolidation pressure would be desirable to produce lower cost, higher quality, higher performance spar components.

The present invention aims at least partially to overcome these problems in the prior art with respect to known moulding processes and in particular aims to provide a process and associated apparatus which allow the production of low cost, high quality spar cap components.

The present invention accordingly provides a method of manufacturing a moulded article of fibre-reinforced resin composite material, the method comprising the steps of:

a. disposing a body comprising fibrous reinforcement and resin into a mould cavity portion of a first mould part;

b. locating a second mould part relative to the first mould part to form a mutually spaced configuration and to enclose the body within an intermediate mould cavity defined between the spaced first and second mould parts, c. providing a peripheral hermetic seal between the first and second mould parts; d. applying a source of vacuum to the intermediate mould cavity through at least one conduit extending into the intermediate mould cavity, the vacuum extracting air from the intermediate mould cavity;

e. moving at least one of first and second mould parts so as relatively to move the first and second mould parts together to define a final mould cavity; and f. heating the body to form the moulded article within the final mould cavity.

The present invention also provides an apparatus for manufacturing a moulded article of fibre-reinforced resin composite material, the apparatus comprising a first mould part defining a mould cavity portion for receiving a body comprising fibrous reinforcement and resin, a second mould part located adjacent to the first mould part, a movement mechanism adapted relatively to move the first and second mould parts between a first mutually spaced configuration defining an intermediate mould cavity therebetween and a second clamped configuration defining a final mould cavity therebetween, a peripheral seal device located to form a hermetic seal between the first and second mould parts in the first mutually spaced configuration, at least one conduit adapted to communicate the intermediate mould cavity with a source of vacuum for extracting air from the intermediate mould cavity, and a heating mechanism for heating the body to form the moulded article within the final mould cavity

The present invention further provides an elongate structural element composed of a fibre-reinforced resin composite material, the composite material comprising unidirectional fibres in a matrix of thermosetting resin system, the unidirectional fibres extending along a longitudinal direction of the element, the element having a length of at least 10 metres and at least some of the unidirectional fibres extending along the entire length of the element, the composite material having a fibre volume fraction of from 57 to 70% and a void content of less than 0.5% by volume based on the volume of the fibre- reinforced resin composite material.

The element may optionally contain further fibres which are inclined to the longitudinal direction of the element, for example in the form of a biaxial or triaxial fabric laminated together with the unidirectional fibres. The present invention yet further provides a spar cap of a wind turbine blade composed of the composite material of the present invention.

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: -

Figure 1 is a schematic side view of an apparatus for producing a spar cap composed of a fibre reinforced resin composite material in accordance with an embodiment of the present invention;

Figure 2 is a schematic front view of a fibre condenser board in the apparatus of Figure 1;

Figure 3 is a schematic section on line C-C through a mould for a spar cap in the apparatus of Figure 1, the mould being in a closed moulding configuration;

Figure 4 is a perspective view of a cutter, when in an open configuration, the cutter being incorporated in the apparatus of Figure 1;

Figure 5 is a perspective view of the cutter of Figure 4 when in a closed configuration;

Figures 6a to 6e are schematic sections on line C-C and illustrate successive steps in the moulding process for manufacturing a spar cap of fibre reinforced resin composite material in accordance with an embodiment of the present invention;

Figure 7 is a perspective view of an edge of the mould of Figure 1; and

Figures 8a to 8c are schematic sections on line C-C of part of the mould and illustrate successive steps in the moulding process.

Referring to Figures 1 to 8, there is shown an embodiment of an apparatus for producing a fibre reinforced resin composite material, in particular a spar cap, in accordance with an embodiment of the present invention. The apparatus, designated generally as 2, includes a fibre rack 4 on which are disposed a plurality of wound spools 6 of wound fibre 8. The spools 6 are arranged in a plurality of stacked layers and one end face 10 of the fibre rack 4 includes fibre feed-out mechanisms 12, for example fixed spreader bars 12. The spools 6 are arranged in the rack 4 with longitudinally adjacent spools 6, arranged in the direction of fibre feed-out from the rack 4, being spliced together by a fibre splice 14. Such slicing together of plural spools 6 provides substantially continuous fibre length feed-out from the fibre rack 4. In turn, as described hereinafter, the fibres are formed into a continuous web of substantially indeterminate length.

The fibres typically comprise carbon fibres, but may alternatively provide glass fibres. The fibres each comprise a fibre roving, comprising a plurality of individual fibres bundled or wound together. For example, the fibres may comprise 2400 to 4800 tex glass fibres or 12000 to 50000 filaments per tow carbon fibres.

The plurality of fibres 8 are fed out in a downstream direction from the rack 4 to a condenser plate 16. The condenser plate 16 is shown in greater detail in Figure 2. The condenser plate 16 is a rigid plate, typically composed of metal, which has a plurality of holes 18 extending therethrough, the holes 18 forming a patterned array. Typically, ceramic inserts may be fitted into each hole 18 to guide but not damage the fibre and avoid excessive wear to the guide insert and metal plate 16. The condenser plate 16 converges together the plurality of fibres 8 fed out from the fibre rack 4 in order to form a desired multiple-fibre configuration.

The condenser plate 16 is used to guide the fibre tows at the correct spacing and to control the areal weight of the impregnated web. The arrangement and spacing of holes in the condenser board depends upon the selected fibre tex, and the desired areal weight of the resultant web. This constitutes a first upstream fibre control mechanism.

The condensed fibres 20 are then fed to a web forming apparatus 22, typically comprising a pair of opposed non-rotating nip bars 24. The bars 24 do not rotate to avoid inadvertent wrapping of fibre which would tend to occur around a rotating roller. The nip bars 24 urge the condensed fibres 20 into a substantially planar elongate web 26 of indeterminate length. This constitutes a second downstream fibre control mechanism. The bars 24 are fixed in position and may be parallel, or alternatively concave or convex along their length to control the web width. A concave configuration can condense the web width whereas a convex configuration can spread the web width. The web 26 so formed is then fed through a liquid dip impregnation bath 28 which comprises a bath body 30 containing a reservoir of liquid resin 32. The liquid resin typically comprises a thermosetting resin, such as an epoxy resin.

A web conveying system 34 is located in the bath 28 and comprises a succession of pairs of opposed fixed non-rotating nip bars 36 which are located at the bottom of the interior of the tank body 30. The bath 28 is sufficiently filled with the liquid resin 32 so that the web 26 conveyed through the succession of nip bars 36 is fully submerged within the liquid resin 32. The bath 28 is also provided with guide members 38 which are located at least at one position within the bath so as to control the width of the web 26 thereby to be no greater than a predetermined maximum dimension. The guides 38 also keep the opposite longitudinal edges of the web 26 from contacting the longitudinal sides of the bath body 36 which would otherwise inadvertently cause snagging of the web 36 on the bath body 30.

Each of the pairs of nip bars 36 is set to provide a desired nip pressure on the web 26 as the web 26 travels through the liquid resin 32 in the bath 28. In a preferred embodiment, the nip pressure increases from the first upstream-most pair of nip bars 36 to the last downstream-most pair of nip bars 36. The increase in nip pressure may be progressive or continuous or stepped. Such an increase in nip pressure sequentially in a downstream direction assists achievement of maximum wet-out of the fibrous web 26 by the liquid resin 32 during impregnation.

The web 26 may be pulled through the bath 28 manually but preferably a drive mechanism, indicating generally at 40, may be provided which clamps on the web 26 and pulls the web 26 by an indexed translational motion in a forward longitudinal direction, as shown by arrow A, through the bath 28, the indexed length being predetermined and optionally selectively variable. The bath 28 may be provided with a heater mechanism illustrated schematically at 45, to heat the liquid resin 32 within the bath 28 in order to lower the viscosity of the resin to enhance wetting out of the fibres by the resin. In an embodiment, the bath 28 is provided with an ultrasonic agitator, illustrated schematically at 44, which causes ultrasonic agitation of the liquid resin 32 in the bath 28 to enhance wetting out of the fibres by the liquid resin.

The resin-impregnated web 50 exiting from the bath 28 is then conveyed in the direction A out of the bath 28 towards a cutter mechanism 46. The cutter mechanism 46 includes a blade 48 which intermittently cuts the web 50 transversely across its width to form individual lengths 52 of the impregnated web 50, each length 52 being of a predetermined longitudinal dimension. A typical length for manufacturing a spar is at least 4 metres and the spar may have a length of more than 50 metres. The cut lengths 52 of impregnated web are laid up in a mould 56 as a stack of web layers 54. The mould 56 may be downstream of the cutter mechanism 46 in an in-line configuration as shown in Figure 1, or may be off-line. However, in-line configuration has the advantage of minimising manual handling of the resin-impregnated web 50, which may damage the web, in particular be reducing the uniformity of the orientation of the longitudinally oriented fibre tows within the web 50.

The cutting mechanism 46 is illustrated in greater detail in Figures 4 and 5. Figure 4 illustrates the cutting mechanism 46 in an open configuration. The cutting mechanism includes a lower transverse part 62 which is elongate and, in the apparatus of Figure 1, extends below and across the entire width of the impregnated web 50. The lower transverse first part 62 includes a central slot 64. A complementary elongate upper transverse part 66 is hingedly mounted at one end 68 thereof to the lower transverse part 62. The upper transverse part 66 carries a translationally slidable blade assembly 70, which can slide along the upper transverse part 66. The blade assembly 70 carries the blade 48, the cutting edge of which is downwardly and forwardly oriented.

When the web 50 is conveyed in the direction A shown in both Figures 1 and 4 through the cutter mechanism 46, the upper transverse part 66 carrying the blade 48 is in the open raised configuration to permit unhindered motion of the web 50. When it is desired to cut the impregnated web 50 to form the desired length 52, the upper transverse part 66 is rotated downwardly about the hinged connection so as to be disposed in the closed lowered configuration illustrated in Figure 5. The lower and upper transverse parts 62, 66 are mutually engaged. The free end 58 of the upper transverse part 66 is clamped to the lower transverse part 62 by a clamping mechanism 60. This action clamps the web 50 securely between the lower and upper transverse parts 62, 66. The blade 48 is received in the slot 64. A handle 74 of a blade carrier 76 of the blade assembly 70 is manually pulled so as to traverse the blade 48 along the slot 46 and across the entire width of the web 50 in the direction of arrow D, thereby cutting the cut length 52 of the web 50 away from the remainder of the web 50 exiting the impregnation bath 28. After the cutting operation, the upper transverse part 62 is undamped and returned to its raised open configuration. This permits the web 50 to be pulled out of the bath 28, and a subsequent length 52 to be cut.

In an alternatively embodiment, an automatic transverse drive mechanism for the blade carrier 76 is provided.

As described above, the mould 56 comprises a two-part, closed mould which has integral heating and pressure application. The mould 56 is used to both apply consolidation pressure and heat for curing the resin. Alternatively, the mould can be placed in a press for application of a high curing pressure. The mould 56 is also designed to allow application of vacuum before complete closing of the mould 56. Alternatively, the mould can be placed in a vacuum chamber for application of a vacuum in a de-gassing operation prior to curing of the resin at elevated temperature and pressure. This "degassing" stage ensures that any trapped air between the plies of consolidated material is substantially completely removed. The low viscosity of the resin system, in combination with the low reactivity at ambient temperature, means that the degas process can be implemented for as long as is necessary to ensure the highest quality fibre reinforced resin composite material. Unlike the known VARTM method discussed above, this mould allows "holding off of the upper mould during closing, before clamping pressure is applied to the laminate. This creates a low pressure cavity above the liquid resin. As the resin is not pressurised, any air dissolved in the resin or trapped between the plies comes out of solution and rises to the surface where it is then removed by the vacuum system. This degas cycle is highly effective at removal of air from within the laminate of resin impregnated fibres laid up in the mould.

In Figure 1 the mould 56 is shown schematically in an open configuration to enable the cut lengths 52 to be laid up within the mould 56 to form the stack 54, with an upper mould part 84 raised relative to, and separated from, a lower mould part 86 by using a plurality of hold-off devices 88 and clamping devices 87 spaced along the length of the mould 56 on both longitudinal sides thereof. The hold-off devices 88 constitute a spacer mechanism selectively, when actuated, to maintain the upper and lower mould parts 84, 86 in a mutually spaced configuration and the hold-off devices 88 can be disabled to permit relative movement together of the upper and lower mould parts 84, 86 under a clamp pressure applied, for example, by the clamping devices 87.

In this embodiment the mould 56 is elongate and is adapted to mould an elongate spar cap, which may be many metres in length, for example at least 10 metres or even more than 40 metres in length. However, the mould may alternatively be shaped and dimensioned to manufacture a mould part of any other shape or dimensions, with appropriately shaped and dimensioned cut lengths being laid up within the mould 56. In further alternative embodiments, additional material can be laid up within the mould 56 in addition to the cut lengths 52, for example fibrous layers of different material and/or orientation.

The successive cut lengths can be selectively varied in length. This enables a spar cap to be formed which has a varying thickness along its length, which is achieved by cutting different lengths of impregnated lengths and then laying them up in the mould to provide thicker regions with a greater local number of stacked lengths than in thinner regions. The mould is correspondingly shaped to provide a mould cavity of varying height along its length. In contrast, a conventional pultrusion to form an elongate spar tends to have a constant thickness. The element may optionally contain further fibres which are inclined to the longitudinal direction of the element, for example in the form of a biaxial or triaxial fabric laminated together with the unidirectional fibres.

Referring to Figure 3, which is a section on line C-C, the mould 56 is shown in its closed moulding configuration.

The mould 56 includes the upper mould part 84 which is a male moulding element and the lower mould part 86 which is a complementary female moulding element. The upper mould part 84 has a central moulding face 89 facing a corresponding central moulding face 90 of the lower mould part 86. The moulding faces 89, 90 define a central moulding cavity 100 therebetween. In the illustrated embodiment the moulding faces 89, 90 may be curved, the face 89 being convex and the faced 90 being correspondingly concave, but alternatively they may be planar or have any other surface shape or configuration.

The central moulding face 89 of upper mould part 84 has upwardly inclined opposite longitudinal walls 106, 108 extending along its length. The walls 106, 108 terminate at their upper end at a top wall 118, 120 which is recessed relative to a mould line 102 mating the upper mould part 84 and lower mould part 86 in the closed moulding configuration. The central moulding face 90 of lower mould part 86 has upwardly inclined opposite longitudinal walls 110, 112 extending along its length. The longitudinal walls 106, 108 are respectively spaced from the longitudinal walls 110, 112 to provide a respective longitudinally extending inclined gap 1 14, 116 therebetween. The walls 110, 112 terminate at their upper end at a top wall 122, 124. Each top wall 122, 124 faces and is spaced from the respective top wall 118, 120 to provide a respective longitudinally extending upper gap 126, 128.

A longitudinally extending channel 104, 105 is cut in the upper surface of the lower mould part 86 on a longitudinal side of the respective gap 126, 128. Accordingly, when the mould 56 is fully closed, each longitudinal edge of the cavity 100 communicates with the respective channel 104, 105 by a respective inclined gap 114, 116 and a respective upper gap 126, 128. In the Figure, the dimensions of the gaps and channels are exaggerated for clarity of illustration. Vacuum conduits 92 are also provided, illustrated schematically, to connect the cavity 100, and in particular the channels 104, 105 connected thereto by the gaps 114, 116, 126, 128, to a source of vacuum as indicated by the arrows V. The conduits 92 connect with the lower surface of the channels 104, 105 so that any liquid resin entering the channels 104, 105 is sucked away by the vacuum.

The upper mould part 84 is carried on an upper support member 80 and the lower mould part 86 is carried on a lower support member 82. The hold-off devices 88 and clamping devices 87 are fitted between the upper and lower support members 80, 82. As shown in greater detail in Figure 7, the hold-off devices 88 typically comprise extendable and retractable piston/cylinder devices, typically hydraulically operated but any other raising/lowering devices may be used. In the open configuration, the hold-off devices 88 support the upper mould part 84 above the lower mould part 86 in a mutually spaced configuration to enable the lengths 52 to be laid up onto the central moulding face 90 of lower mould part 86. The hold-off devices 88 can be adjusted to lower the upper mould part 84 onto the lower mould part 86 in the closed moulding configuration.

The clamping devices 87 comprise a hook 77 carried on the lower support member 82 and a rod 79 carried on the upper support member 80. In the clamping position as shown in Figure 7, the hook 77 is hooked over the rod 79. A hydraulic actuator 81 pulls the hook 77 downwardly to pull the upper mould part 84 downwardly onto the lower mould part 86 and therefore apply an elevated moulding pressure within the cavity 100 during the resin curing cycle. The hook 77 includes pins 83 which slide within slots 85 in a carrier 91 for the hook 77. The slots 85 are shaped and dimensioned, including both vertical portions and inclined portions, to permit vertical and rotational movement of the hook 77 to allow the hook 77 to be hooked onto and unhooked from the rod 79.

The upper support member 80 and the lower support member 82 are each provided with a plurality of heating conduits 96 through which a heating medium, such as water and/or polyethylene glycol, is passed during a resin curing phase. The heating medium is supplied by pipes 94, illustrated schematically and as indicated by the arrows H. Alternative heating mechanisms may be employed, for example air heating, electrical heating or induction heating.

A peripheral vacuum seal member 93 at least partly surrounds the mould 56 and is mounted to an edge of the upper mould part 84. The seal member 93 is composed of a sheet of flexible material such as a rubber. When the mould 56 is at least partly closed, an inside surface 95 of the seal member 93 bears against an outer surface 97 of the lower mould part 86 to form a hermetic seal. This provides that a vacuum can be maintained within the cavity 100 during the moulding process when the vacuum is applied to the conduits 92 when the mould 56 is in the partly or fully closed position.

The moulding operation will now be described, additionally with reference to Figures 6 and 8.

With regard to the materials employed to manufacture the fibre reinforced resin composite material, the resin is typically a thermosetting resin, for example an epoxy resin, which can produce a resin matrix in a resultant composite material having high mechanical properties. In addition, the resin has properties which render it particularly suitable to the processing conditions of the present invention. For example, the resin system has very low reactivity at ambient conditions, low viscosity, low cost, and suitable reactivity to cure in short time at a temperature of from 90 to 120°C.

A preferred resin material comprises a mixture of liquid epoxy resin (LER), and liquid anhydride, such as a hydrophthalic anhydride (TIP A). A typical resin material comprises approximately 1 : 1 weight ratio of liquid epoxy resin (LER), and liquid methyl tetrahydrophthalic anhydride (MeTFIPA), with a small constituent of one or more epoxy diluents, tertiary amine catalyst and wetting agent. A variety of other hydrophthalic anhydrides are also suitable. Typically, the liquid anhydrides MeTFIPA, methyl hexahydrophthalic anhydride (MeHUPA), and hexahydrophthalic anhydride (HUPA) are preferred for reduced cost and low viscosity. Blends of liquid anhydrides and eutectic mixtures of liquid and solid anhydrides may also be used. The liquid anhydride is less sensitive to mix ratio than an epoxy amine system, allowing good mechanical properties when mixed at ratios of from 1 epoxy equivalent weight to 0.7 anhydride equivalent weight up to 1 epoxy equivalent weight to 1.0 anhydride equivalent weight, with a preferred ratio being 1 epoxy equivalent weight to 0.9 anhydride equivalent weight. The reduced cost of the liquid anhydride, coupled with a high mix ratio, ensures a lower resin cost than for typical amine cured infusion resins currently in commercial use.

Typically, the resin material has a viscosity at the impregnation temperature, which is typically 30°C of from 160-180 centipoise. This is lower than the corresponding viscosity, measured at ambient conditions typically used for the resin infusion step, for typical infusion resin systems, which is 200-300 centipoise. In this specification the resin viscosity is measured using a Brookfield RVT115 viscometer with a SC4-27 spindle at a speed of 100 rpm.

The low impregnation viscosity range for the resin enhances the wetting of the fibres during impregnation, in particular when the fibres are immersed within the reservoir of resin in the bath. The achievement of high wetting of the fibres during impregnation is aided by the relatively low reactivity of the system at a temperature below 80°C and the impregnation is carried out below this temperature value. Such low reactivity ensures that the impregnation and the in-mould degassing can be carried out over an extended period if necessary to enhance the wetting out and to reduce the void content in the ultimate product. When the temperature is increased to a value above 80°C, the viscosity progressively falls to a value of below about 50 centipoise, before any significant curing reaction causes the viscosity to increase.

The preferred embodiments of the invention utilise direct fibre rovings, for example of glass or carbon fibre. The fibres are unwound from spools, immediately impregnated by resin immersion, then immediately laid up into the mould. There is no intermediate processing. The use of direct rovings avoids the cost of conversion associated with typical supported unidirectional fabrics, which have additional non- structural fibres (in the weft or warp direction) to support the structural unidirectional fibres, or other woven or stitched fabrics. Careful handling of the impregnated fibres after impregnation in the bath also ensures better fibre alignment and collimation as compared to conventional stitched or woven materials. The higher degree of fibre alignment in the longitudinal direction of the spar cap results in higher mechanical properties, especially in compression loading and in fatigue.

The use of direct fibre rovings also ensures that 100% of the fibre content of the spar cap is aligned in the principal longitudinal load direction. For a simple beam, such as a wind turbine blade (WTB) spar cap, this is beneficial because in conventional spar caps conventional unidirectional (UD) fabrics are employed which contain up to 5% of lateral fibres. These lateral fibres in typical supported UD fabrics do not contribute to the load bearing capability and are, therefore, redundant material, adding to both the weight and cost of the final structural product composed of the fibre reinforced resin composite material. Such UD fabrics having lateral fibres can introduce fibre waviness into the prepreg, which in turn can reduce the compressive strength of the final spar. The achievement of high compressive strength is a key design driver for spars, particularly for use in wind or tidal turbine blades.

In the fibre impregnation process, the fibres are pulled through the liquid resin while immersed in the resin. The level of impregnation is determined by the speed of fibre movement and the pressures applied by the nip bars located serially along the length of the fibre web path inside the bath. The nip bars have been found to be particularly preferable because they can controllably apply the required tension without inadvertent tow breakage. As a contrast, rollers or bars in an S-wrap configuration were found to cause tow breakage as a result of multiplicative tensions being applied to the fibre tows.

It has been found that dip impregnation of fibres into a low viscosity liquid system results in improved wetting as compared with the use of high viscosity hot melt systems typically associated with the manufacture of prepregs. The use of nip bars beneath the surface of a bath containing the low viscosity resin can enhance wet out and result in substantially 100% resin impregnation into the fibres. The achievement of such enhanced impregnation has the benefit of ensuring good load transfer between the fibres and the resin matrix, and reduced laminate defects, in the cured fibre reinforced resin composite material. Such higher impregnation quality also contributes to high interlaminar shear and fracture toughness values of the cured fibre reinforced resin composite material.

As shown in Figure 6a, the resin-impregnated fibre web lengths 52 can be laid up in the lower mould part 86 of the mould 56 to form a stack 54 with a desired number of layers or plies. The resin-impregnated fibre web can be directly placed in the mould 56 immediately after resin impregnation. This avoids the need for any consumable materials associated with protecting the material during transport, packing, storage or transport prior to use in the moulding operation.

Typically, the stack 54 has a height which is less than half of the depth of the recess in the lower mould part 86 which partially forms the cavity 100. The additional height of the recess accommodates additional loft being introduced into the stack 54 when the stack 54 expands under the application of a reduced pressure under vacuum within the cavity 100 during a degassing step.

As shown in Figure 6b, after the required stack 54 has been formed, the upper mould part 84 is then located in position above the lower mould part 86 and lowered downwardly thereonto.

As shown in Figure 6c and Figure 8a, the hold-off devices 88 are then operated to lower (indicated by arrows L) the upper mould part 84 onto the lower mould part 86 into the partly-closed degassing configuration. This provides an intermediate mould cavity with the upper mould part 84 and the lower mould part 86 being mutually spaced. Typically, in the partly-closed degassing configuration, the upper mould part 84 is spaced a distance of at least 5mm from the lower mould part 86. The seal member 93 mounted on the upper mould part 84 comprises a downwardly depending skirt portion which slidingly engages an outer face of the lower mould part 86 as the upper mould part 84 is lowered. The seal member 93 provides a peripheral hermetic seal for the cavity 100. A reduced pressure or vacuum (indicated by arrows V) is applied from the vacuum conduits 92 in the partly-closed degassing configuration to achieve degassing from the cavity 100 of any trapped air between or in the layers or plies of resin-impregnated fibrous material before, during and after consolidation of the plies together. Alternatively, the mould can be placed in a vacuum chamber for application of a vacuum in a de-gassing operation prior to curing of the resin at elevated temperature.

The resin is selected to have a low viscosity to enable the trapped air to be able to migrate through the stack of resin-impregnated fibres. The resin is also selected to have a low reactivity at ambient temperature, which is the temperature of lay-up and degassing, to enable the degassing to be carried out for an extended period of time, as long as deemed necessary to achieve a desired maximum void content in the ultimate fibre reinforced resin composite material product. The vacuum pressure and air flow rate out through the vacuum, or through any part of the vacuum system, can optionally be monitored to control the process during production of the moulded part. Accordingly, any trapped air can be substantially completely removed from the moulding cavity 100.

After the degassing operation, as shown in Figure 8b the hook 77 is moved from an inoperative position shown in phantom to an operative position in which the hook 77 is hooked over the rod 79. The hold-off devices 88 are released and the clamping actuators 81 are operated to pull the hooks 77 downwardly to apply a clamping pressure (indicated by arrows C).

As shown in Figure 6d and Figure 8c, the mould 56 is then fully closed with the clamping devices 87 applying a clamped moulding pressure (indicated by arrows C) to the stack of resin-impregnated material 98 within the final mould cavity 100. The cavity 100 is still hermetically sealed by the seal members 93, which may be compressed vertically as shown in Figure 8c. If desired, the mould 56 may alternatively or additionally be incorporated into a press for applying pressure to the resin-impregnated material 98 within the cavity 100.

As the resin-impregnated material 98 is compressed, when the mould 56 is fully closed, any excess resin material, or residual air, is urged upwardly into the inclined gaps 114, 116, and then into the upper gaps 126, 128 and into the channels 104, 105, and is then sucked out of the channels 104, 105 at the periphery of the cavity 100 by the vacuum through the conduits 92 (indicated by arrows R). This ensures a highly repeatable process for the fibre reinforced resin composite material, with minimum void content, and a maximum fibre volume fraction (FVF) to reduce the amount of resin required to make a spar. A further advantage is that a higher stiffness and strength may be achieved for a spar, allowing a more aerodynamic blade profile.

Then the resin is cured. As shown in Figure 6e, the heated medium (indicated by the letters H) is flowed through the conduits 96 and raises the temperature of the resin above its curing temperature. The resin viscosity reduces at elevated temperature in the mould and this phenomenon combined with the mould pressure can complete any final impregnation and ensure good interlaminar adhesion. The result is a homogeneous wet- out of the fibres, and after resin curing the fibre reinforced laminate has low void content and high fibre volume fraction.

After a complete curing cycle, the mould 56 is opened and the moulded part 99, such as a spar cap, of fibre reinforced resin composite material is removed from the mould 56.

As an alternative to the use of conduits and a heating medium, the entire mould may be placed in a heated oven or autoclave. However, when the heating conduits are used the mould may have large dimensions, typically with a length of many meters which are not constrained by the dimensions of any oven or autoclave. As mentioned above, air, electric or induction heating may alternatively be used.

The present invention has particular application in the manufacture of low cost, high quality structural components, in particular elongate structural elements, such as spar caps for wind or tidal turbine blades, or bridge spars. The present invention employs a fibre impregnation bath, which can ensure a high degree of fibre wetting, and avoid tow breakage by using non-rotating nip bars, typically progressively increasing in pressure, to impregnate the resin into the fibres without inadvertent tow breakage. At least some of the unidirectional fibres extend along the entire length of the resultant structural component, which may have a length of at least 10 metres, optionally greater than 40 metres. The present invention also enables the handling of impregnated fibre webs directly from the impregnation process and into the moulding process. The moulding process of the present invention can be controlled to achieve in-situ degassing of impregnated fibres prior to application of external pressure during the cure cycle.

The present invention in particular relates to the production of low cost, high quality glass (or carbon) spar caps for incorporation into wind or tidal turbine blades, or other elongate structural elements.

This mixed resin provides the advantage that it has a cost which is approximately 58% of the cost of currently commercially available infusion resins. Furthermore, the direct roving has a cost which is approximately 49% of the cost of currently commercially available stitched, or supported, non-crimped unidirectional (UD) fabrics used for the manufacture of fibre reinforced resin composite materials. Yet further, as compared to a typical unidirectional (UD) fabric, a cost saving results from avoiding the need for approximately 5% of unnecessary weft fibre.

The impregnated fibre is laid up directly in the mould, leading to a further cost saving since consumables, for example vacuum bag, infusion flow mesh, resin manifolds, resin feed pipes, resin spreading conduits, omega tubes, etc., are completely eliminated as compared to typical infusion processing. For the manufacturing process, the direct laying up of cut resin-impregnated lengths in the mould requires fewer personnel as compared to the hand lamination of dry fabric as used in typical infusion processing.

During infusion processing, there is wasted resin, for example inside the infusion pipes and in the mesh, which typically amounts to about 5% of the total resin used, and such wastage can be eliminated using the direct impregnation of the invention. The excess resin squeezed out into the channels during closure of the mould can be collected and reused, since its reactivity at ambient temperature is low. Since the mould is compressed during moulding and excess resin is squeezed out of the moulding cavity, a higher fibre volume fraction (FVF) reduces the resin consumption in the fibre reinforced resin composite material component. Furthermore, by direct resin impregnation and layup, the spar cap manufacturing process has a typical cycle time of 10-12 hours; this may be compared to a 18-24 hour cycle time for typical infusion processing in spar cap manufacture. In addition, since consumables are avoided, no time is required for removal of consumables, which can reduce the cycle time. Finally, there are no infusion defects requiring rework and repair, and generally fewer defects are formed, and so this also reduces the cycle time.

The present invention is further illustrated by the following Examples.

Examples 1 and 2

An epoxy resin composition was provided which included a 1 : 1 weight ratio of two resin components A and B. Component A comprised 90 wt% of a Bisphenol-A epoxy resin and 10 wt% of a reactive diluent comprising butane diol diglycidyl ether. Component B comprised 97 wt% of MeTFIPA, 2 wt% of N,N dimethylbenzylamine catalyst and 1 wt% of a wetting agent. The neat resin, after curing at a temperature of 120°C, using a ramp up rate of 1°C per minute and a curing time of at least 30 minutes at the curing temperature of 120°C had the following mechanical properties: Tensile strength 12 IMP a, Tensile modulus 3 GPa, Tensile strain to break 6.4%.

Various unidirectional fibres were fully wetted by the resin then laid up into a mould to form a UD body of fibrous material impregnated with the resin. The mould was partly closed to enclose the body within an intermediate mould cavity defined between the spaced upper and lower mould parts. The cavity was hermetically sealed, and then subjected to degassing under vacuum. Thereafter, the mould was fully closed under a clamp pressure and the resin was heated to the curing temperature of 120°C and fully cured for a period of 4 hours. The clamp pressure expressed excess resin from the mould cavity which was extracted by the vacuum.

The resultant unidirectional fibre-reinforced resin composite materials were then tested to determine their mechanical properties. For Example 1, the fibres comprised glass fibres sold by CPIC under the trade name ER468 having a tensile modulus of 76 GPa. The fibre volume fraction was 60.3% and the tensile strength was 1 147.7 MPa.

For Example 2, the fibres comprised glass fibres sold by CPIC under the trade name TM468G having a tensile modulus of 85 GPa. The fibre volume fraction was 64.3% and the tensile strength was 1503.0 MPa.

For each Example, the void content, optically measured, was less than 0.5% by volume based on the volume of the resultant fibre-reinforced resin composite material.

For each Example, the tensile strength was very high as a result of the achievement of a very high fibre volume fraction in the unidirectional fibre-reinforced resin composite material.

The fibre volume fraction may be varied by varying the mould cavity volume for a given amount of fibres laid up in the mould or by varying the amount of fibres laid up in the mould for a given mould cavity volume. By changing these variables, other samples using the resin and fibres of Example 1 provided a fibre volume fraction of 57.1%>, 57.5%), 64.2%) or 56.5% using a curing temperature of 80°C and a curing time of a period of 16 hours and 67.5% or 57.2% using a curing temperature of 120°C and a curing time of a period of 4 hours.

Other samples using the resin and fibres of Example 2 provided a fibre volume fraction of 66.1%), 64.0 % and 66.7% using a curing temperature of 120°C and a curing time of a period of 4 hours.

The present invention can therefore produce unidirectional fibre-reinforced resin composite material for the manufacture of spar caps having a fibre volume fraction of from 57 to 70%, typically from 60 to 67%. As a comparison, typical comparative glass fibre known spar caps made using infusion resin systems have a fibre volume fraction of only about 53% and have a tensile strength of only about 750MPa.

These Examples therefore show that the present invention can manufacture unidirectional fibre-reinforced resin composite material for the manufacture of spar caps having higher fibre volume fraction and higher tensile strength than comparative known spar caps.

Claims

Claims

1. A method of manufacturing a moulded article of fibre-reinforced resin composite material, the method comprising the steps of:

a. disposing a body comprising fibrous reinforcement and resin into a mould cavity portion of a first mould part;

b. locating a second mould part relative to the first mould part to form a mutually spaced configuration and to enclose the body within an intermediate mould cavity defined between the spaced first and second mould parts,

c. providing a peripheral hermetic seal between the first and second mould parts; d. applying a source of vacuum to the intermediate mould cavity through at least one conduit extending into the intermediate mould cavity, the vacuum extracting air from the intermediate mould cavity;

e. moving at least one of first and second mould parts so as relatively to move the first and second mould parts together to define a final mould cavity; and f. heating the body to form the moulded article within the final mould cavity.

2. A method according to claim 1, wherein in step e excess resin is extracted from the final mould cavity through the at least one conduit under vacuum.

3. A method according to claim 1 or claim 2, wherein the at least one conduit is located at a periphery of the final mould cavity.

4. A method according to any one of claims 1 to 3, wherein in step b the first and second mould parts are maintained in the mutually spaced configuration by at least one spacer mechanism, and the spacer mechanism is disabled in step e to permit relative movement together of the first and second mould parts under a clamp pressure.

5. A method according to any foregoing claim, wherein the peripheral seal is mounted around the second mould part which is disposed above the first mould part, and engages the periphery of the first mould part in step d.

6. A method according to any foregoing claim, wherein the first mould part defines a female mould cavity portion and the second mould part includes a male portion adapted to fit within the female mould cavity portion.

7. A method according to any foregoing claim, wherein the final mould cavity is elongate and the body is elongate and comprises unidirectional fibrous reinforcement and a thermosetting resin.

8. A method according to claim 7, wherein the moulded article is an elongate spar for a wind turbine blade.

9. A method according to any foregoing claim, wherein the body is comprised of plural layers of fibrous reinforcement impregnated with resin.

10. A method according to claim 9, wherein the layers of fibrous reinforcement impregnated with resin are successively laid up within the mould cavity portion.

11. A method according to claim 9 or claim 10, wherein the fibrous reinforcement impregnated with resin is of indeterminate length when laid up within the mould cavity portion and the fibrous reinforcement is cut to the length of the mould cavity portion after being laid up within the mould cavity portion.

12. A method according to any one of claims 9 to 11, wherein the fibrous reinforcement impregnated with resin is fed into the mould cavity portion directly from a fibre impregnation bath in which fibrous reinforcement of indeterminate length is conveyed longitudinally through the bath and submerged in liquid resin.

13. A method according to claim 12, wherein the fibre impregnation bath is elongate and includes a plurality of pairs of nip bars located therealong in a mutually spaced configuration, the fibrous reinforcement being fed through the pairs of nip bars when submerged in the liquid resin.

14. A method according to claim 13, wherein the plurality of pairs of nip bars apply progressively increasing nip pressure to the fibrous reinforcement being fed through the fibre impregnation bath.

15. A method according to claim 13 or claim 14, wherein the fibrous reinforcement is fed through the pairs of nip bars as a layer of controlled width.

16. A method according to any one of claims 12 to 15, wherein the fibrous reinforcement is fed into the fibre impregnation bath as a plurality of spaced fibre tows.

17. A method according to claim 16, wherein the plurality of spaced fibre tows is fed from a fibre condenser board comprising a plurality of mutually spaced holes extending therethrough, each fibre tow being fed through a respective hole.

18. A method according to claim 16 or claim 17, wherein the fibrous reinforcement in the moulded article consists of the fibre tows.

19. A method according to any one of claims 12 to 18, wherein the liquid resin in the bath during impregnation has a viscosity of less than 200 centipoise, optionally from 160 to 180 centipoise.

20. A method according to any foregoing claim, wherein the fibrous reinforcement comprises carbon fibres having a fibre diameter of from 5 to 15 microns.

21. An apparatus for manufacturing a moulded article of fibre-reinforced resin composite material, the apparatus comprising a first mould part defining a mould cavity portion for receiving a body comprising fibrous reinforcement and resin, a second mould part located adjacent to the first mould part, a movement mechanism adapted relatively to move the first and second mould parts between a first mutually spaced configuration defining an intermediate mould cavity therebetween and a second clamped configuration defining a final mould cavity therebetween, a peripheral seal device located to form a hermetic seal between the first and second mould parts in the first mutually spaced configuration, at least one conduit adapted to communicate the intermediate mould cavity with a source of vacuum for extracting air from the intermediate mould cavity, and a heating mechanism for heating the body to form the moulded article within the final mould cavity.

22. An apparatus according to claim 21 comprising a spacer mechanism adapted to maintain the first and second mould parts in the mutually spaced configuration.

23. An apparatus according to claim 22, wherein the spacer mechanism comprises part of the movement mechanism, the spacer mechanism defining an intermediate stop position of the movement mechanism.

24. An apparatus according to any one of claims 21 to 23 wherein the peripheral seal is mounted around the second mould part which is disposed above the first mould part, and engages a periphery of the first mould part.

25. An apparatus according to claim 24 wherein the peripheral seal comprises a downwardly depending skirt portion which slidingly engages an outer face of the first mould part.

26. An apparatus according to any one of claims 21 to 25, wherein the at least one conduit is located at a periphery of the mould cavity.

27. An apparatus according to claim 26, wherein a plurality of conduits are located around the final mould cavity.

28. An apparatus according to claim 26 or claim 27, wherein the at least one conduit communicates with at least one channel provided in a face of the first mould part which engages a face of the second mould part in the clamped configuration.

29. An apparatus according to claim 28, wherein in the clamped configuration the channel communicates with the final mould cavity by at least one gap located between the engaging faces of the first and second mould parts.

30. An apparatus according to claim 29, wherein the at least one conduit, the at least one channel and the at least one gap are adapted to extract excess resin therethrough from the final mould cavity when the source of vacuum is applied to the at least one conduit.

31. An apparatus according to any one of claims 21 to 30, wherein the first mould part defines a female mould cavity portion and the second mould part includes a male mould cavity portion adapted to fit within the female mould cavity portion.

32. An apparatus according to any one of claims 21 to 31, further comprising a lay- up mechanism for successively laying up within the mould cavity portion layers of fibrous reinforcement impregnated with resin.

33. An apparatus according to claim 31 or claim 32, further comprising a cutting mechanism for cutting the fibrous reinforcement to a desired length when laid up within the mould cavity portion.

34. An apparatus according to any one of claims 21 to 33, further comprising a fibre impregnation bath adapted for submerging fibrous reinforcement in liquid resin and a fibre feeding mechanism for feeding fibrous reinforcement impregnated with resin from the fibre impregnation bath into the mould cavity portion.

35. An apparatus according to claim 34, further comprising conveying mechanism within the fibre impregnation bath for conveying fibrous reinforcement longitudinally through the bath when submerged in liquid resin.

36. An apparatus according to claim 35, wherein the fibre impregnation bath is elongate and the conveying mechanism comprises a plurality of pairs of nip bars located therealong in a mutually spaced configuration, in use the fibrous reinforcement being fed through the pairs of nip bars when submerged in the liquid resin.

37. An apparatus according to claim 36, wherein the plurality of pairs of nip bars are adapted to apply progressively increasing nip pressure to the fibrous reinforcement being fed through the fibre impregnation bath.

38. An apparatus according to claim 36 or claim 37, further comprising a width control mechanism for controlling a width of a layer of the fibrous reinforcement when fed through the pairs of nip bars.

39. An apparatus according to any one of claims 21 to 38, further comprising a fibre condenser board located at a fibre input end of the fibre impregnation bath, the fibre condenser board comprising a plurality of mutually spaced holes extending therethrough.

40. An apparatus according to any one of claims 21 to 39 wherein the final mould cavity is elongate.

41. An apparatus according to any one of claims 21 to 40, which is adapted to form an elongate spar for a wind turbine blade from a body which comprises unidirectional fibrous reinforcement and a thermosetting resin.

42. An elongate structural element composed of a fibre-reinforced resin composite material, the composite material comprising unidirectional fibres in a matrix of thermosetting resin system, the unidirectional fibres extending along a longitudinal direction of the element, the element having a length of at least 10 metres and at least some of the unidirectional fibres extending along the entire length of the element, the composite material having a fibre volume fraction of from 57 to 70% and a void content of was less than 0.5% by volume based on the volume of the fibre-reinforced resin composite material.

43. An element according to claim 42 wherein the unidirectional fibres glass fibres or carbon fibres.

44. An element according to claim 42 or claim 43 wherein the thermosetting resin comprises an epoxy resin.

45. An element according to any one of claims 42 to 44 having a tensile strength of at least 1500MPa.

46. An element according to any one of claims 42 to 45 having a fibre volume fraction of from 60 to 67%.

47. A spar cap of a wind turbine blade comprised of the element of any one of claims 42 to 46.

48. A spar cap of a tidal turbine blade comprised of the element of any one of claims 42 to 46.

49. A structural spar comprised of the element of any one of claims 42 to 46.