GB2360483A

GB2360483A - Improvements in the manufacture of resin-impregnated components

Info

Publication number: GB2360483A
Application number: GB0005106A
Authority: GB
Inventors: James Anthony Keld
Original assignee: SLINGSBY AVIAT Ltd
Current assignee: SLINGSBY AVIAT Ltd
Priority date: 2000-03-02
Filing date: 2000-03-02
Publication date: 2001-09-26
Also published as: GB0005106D0

Abstract

A vacuum-assisted resin infusion method of manufacturing a component in or on a mould 1, wherein a resin distribution medium 5a, 5b, 5c, 5d is provided as part of a lay-up which is to provide the eventual component, with there being no such resin distribution medium 5a, 5b, 5c, 5d laid between the or at least one surface of the mould 1 and an adjacent surface of the lay-up. The lay-up may comprise a substantially central layer of rigid foam plastic 3, with reinforcing fibre layers 4a, 4b being laid at the two opposite sides of the substantially central layer of rigid foam plastic 3. The resin distribution medium 5a, 5b, 5c, 5d may comprise a 100% polyethylene monofilament. Also claimed is a component manufactured by the above method.

Description

2360483 IMPROVEMENTS IN THE MANUFACTURE OF RESIN-IMPREGNATED COMPONENTS

This invention relates to improvements in the manufacture of resin-impregnated components using the vacuum-assisted resin infusion method, and to the components themselves.

Traditionally,'such components for marine and general use were made using the well-known "hand lay-up process". This involved laying layers of glass fibre cloth or glass fibre mat onto a male or female mould member to provide a lay-up, and working liquid polyester resin into the layers of glass fibre as the layers of the lay-up were built up. After a period of is time the resin would start to solidify, and the component would eventually cure into a strong hard laminate. There are several draw-backs to this process, among them being:

The process is slow. Because the resin exotherms as it cures, a layer only a few millimetres thick can be built up before work has to stop,to allow the layer to cure- If too thick a layer is laid, temperature will build up to a level which damages the laminate and can even cause combustion. Practically, this means that only perhaps Smm can be laid per day; The process is poorly controlled. The quality of the laminate, and the ratio of resin to glass, relies on the skill of the operator; Styrene vapour is given off by the resin as it cures. The styrene vapour is harmful to health, and Health & Safety regulations specify the maximum possible concentrations. Thus it is necessary to continuously monitor the styrene vapour concentration and to use vapour extraction equipment to keep it to acceptable levels.

To overcome these drawbacks, various resin infusion systems have been developed, such as the vacuum-assisted method of resin infusion.

one version of this technique is described in GB A-2257938. Briefly, although full details of the technique can be obtained from that document, the layers of dry fibre reinforcement material of the component are all initially laid up one on top of another on the surface of a mould. The layers are fibre layers, e.g. glass fibre.

A flexible cover sheet which is impervious to air and which has one or more air-exhaustion ports is placed over the lay-up of solid layers, and is sealed to the mould in an airtight manner along its entire peripheral edge.

is A vacuum is applied to the ports to exhaust air from the lay-up beneath the flexible cover sheet, and liquid resin is drawn into the lay-up via one or more resin inlets in the mould. Between the bottom surface of the component lay-up and the mould surface is provided a layer of resin distribution medium, and a further layer of resin distribution medium is provided between the top surface of the component lay-up and the flexible cover sheet. These layers of resin distribution medium promote the free flow of the resin within the lay-up, to enable the resin to saturate fully and uniformly the glass fibre layers making up the lay-up.

When the whole of the lay-up between the mould and the flexible cover sheet is saturated with resin, the resin supply is halted, and the resin impregnated lay up is cured. No styrene vapour can escape to the atmosphere through the flexible cover sheet.

After the resin has cured, the vacuum applied to the air exhaustion ports of the flexible cover sheet is withdrawn, and the flexible cover sheet and the upper and lower layers of resin distribution medium are peeled from the completed fibre-reinforced plastic structure, which is usually in the form of a plate or shell depending upon the application.

The removal of the two surface layers of resin distribution medium from the cured component results in a rough surface on each corresponding face of the component.

on most resin-impregnated components, one face of the component is visible when the component is in use, and this surface is normally the smooth surface which was against the mould face during manufacture. In the vacuum-assisted resin infusion technique as just described however, the lower resin distribution medium was against the mould surface, and is removed leaving a is rough lower surface of the component which requires substantial work (rubbing down with abrasive paper and filling) to bring it back to a smooth paintable surface which will be visually acceptable when the component is in use It is an object of the present invention to improve the quality of that surface of the component, thereby to reduce or remove the necessity for work to be carried out on the surface.

It is also an object of the present invention to increase the thickness of a structure which can be satisfactorily manufactured using the vacuum-assisted resin infusion method.

According to one aspect of the present invention there is provided a vacuum-assisted resin infusion method of manufacturing a component in or on a mould, wherein resin distribution medium is provided as part of a lay-up which is to provide the eventual component, with there being no such resin distribution medium lying between the or at least one surface of the mould and an adjacent surface of the lay-up.

According to a second aspect of the present invention, there is provided a cured component which has been manufactured using the method of the first aspect of the invention so that the component comprises within it material which was employed as resin distribution medium in the manufacture of the component.

Having resin distribution medium within the component can increase the thickness of a component which can be successfully impregnated with resin, and thus the thickness of a structure which can be satisfactorily manufactured using the vacuum-assisted resin infusion method.

In a preferred method and/or component of the present invention, one or more resin distribution medium layers are laid between fibre layers providing at least part of the component. The or each resin distribution medium layer then becomes incorporated into the cured laminate, and the component can come away from the mould with a smooth "as moulded" surface which needs little or no work done on it before painting.

Mechanical tests on a laminate manufactured according to the present invention show little degradation of mechanical properties compared to a laminate which, after manufacture, does not contain resin distribution medium.

The invention can be applied equally to the manufacture of a component comprising layers of a single material, such as glass fibre, as to a component comprising layers of different materials. A component of the latter type could comprise, for example, a central layer of rigid foam plastic, with reinforcing layers of glass fibre at the two opposite sides of the rigid foam core.

Each type of component can be manufactured according to the present invention with a resin distribution medium layer buried within it at any appropriate position depending on the design of the actual laminate, having regard to its composition, thickness etc-, and also to the physical size of the component being produced.

By way of example, in each type of component one or more layers of resin distribution medium can be located between layers of fibre cloth, whilst in the second type of component one or more layers of resin distribution medium may be sandwiched alternatively or in addition between the rigid foam core and one or both of the adjacent glass fibre layers.

Preferably the invention is employed in a method wherein an airtight flexible cover sheet is applied to a lay-up constructed on a mould surface, with the region under the sheet being evacuated of air to draw resin into the lay-up.

Alternatively, the sheet could be replaced by a second mould facing the first-mentioned mould.

In a preferred method, resin distribution medium can additionally be applied to the side faces or edges of the lay-up to promote resin flow further. This additional resin distribution medium can be left on, or peeled-away from, the finished component as required.

A preferred material to be used as resin distribution material is a 100% polyethylene monofilament style N1014 suppled by Newbury Engineered Textiles Limited. It is nevertheless to be appreciated that the present invention is not restricted to this preferred material, and there are several other different types of material on the market, any one of which might be the best for a particular application.

Developments of the invention may employ particular examples of the various materials as are described hereinafter with reference to the drawings and/or in Examples 1 and 2.

For a better understanding of the invention and to show how the same may be put into effect reference will now be made, by way of example, to the accompanying drawings in which:

Figure 1 shows diagrammatically a laminate being manufactured on a mould conventionally; Figure 2 shows the laminate of Figure 1 when removed from the mould; Figure 3 shows diagrammatically a laminate being manufactured on a mould in accordance with an example of the present invention; Figure 4 shows the laminate of Figure 3 when removed from the mould; and Figure 5 shows a laminate being manufactured on a is mould by a method according to a first detailed example of the present invention.

In Figure 1 a plate-like mould 1 is shown, with which cooperates an airtight flexible cover sheet 2 in the form of a vacuum bag, to provide a vacuum-assisted resin infusion method of manufacturing a composite laminated component which is shown between the mould 1 and the flexible cover sheet 2.

only a relatively small lateral extent of the plate-like component is shown, in section, it being a laminate which is a composite of a rigid plastic foam core 3 which is approximately 5Omm thick, sandwiched between two cushions 4 of glass fibre cloth, each cushion 4 comprising a plurality of layers of glass fibre cloth and being approximately 1Omm thick. When impregnated with resin and then cured, the cushions 4 will provide reinforcement for the plastic foam core 3 of the finished component.

At the outer surfaces of the two glass fibre cushions 4, there are laid respective layers of resin infusion or distribution medium 5 which is designed to promote the flow of resin into the glass fibre cushions 4 when a vacuum is applied between the mould 1 and the flexible cover sheet 2. The layers of resin distribution medium 5 have a rough surface texture, indicated by them being shown in Figure 1 by wavy lines.

Figure 2 shows the composite laminate of Figure 1 after the flexible cover sheet 1 has been removed from the cured lay-up, after the composite laminate has then been removed from the mould 1, and after the two outer layers of resin distribution medium 5 have been peeled from the opposite surfaces of the composite laminate.

As is shown in Figure 2, the two opposite surfaces of the laminate are extremely rough once the corresponding roughly-textured resin distribution medium layers 5 have been removed from the component.

Any one or both of those surfaces which in the finished component will be visible, requires substantial work (such as rubbing down with abrasive paper and filling) on it in order to render the surface smooth and paintable.

Figure 3 shows the same view as Figure 1 of a composite laminated component on a mould 1, but the method being modified in accordance with the present invention. In Figure 3 therefore, the resin distribution medium layers 5 are not placed on the opposed outer surfaces of the laminate, but each is sandwiched between adjacent glass fibre cloth layers of the associated cushion 4 of glass fibre cloth.

In this way the upper surface of the laminate lies adjacent the flexible cover sheet 2, whilst the lower surface of the laminate lies adjacent the mould 1.

Figure 4 shows the composite laminate of Figure 3 when removed from the mould 1, and in the same condition as the composite laminate of Figure 2. In the case of Figure 4 however, unlike the case of Figure 2. both the upper and lower surfaces of the laminate are smooth. Usually however it is the surface of the laminate which has been adjacent the mould 1 which has the better finish, and which will therefore be the visible surface in the finished component.

Thus, since there has been no resin distribution medium layer 5 between the mould 1 and the bottom surface of the lower cushion 4 of glass-fibre material, the lower surface of the lower cushion 4 is smooth and requires less or even no work done on it in order to render it smooth and pleasing in appearance, and paintable.

Since moreover the layers of resin distribution medium 5 remain buried within the finished component, is the time-consuming step of peeling these layers away from the laminate after it is removed from the mould 1, can be dispensed-with. Each cushion 4 will be extremely rigid and will substantially retain its reinforcing properties, since like Figure 2 it will be resin-infused throughout, including the resin infusion medium 5.

Although Figures 1 to 4 show a composite laminate component wherein a rigid foam core 3 is sandwiched between two cushions 4 of glass fibre cloth, it is to be appreciated that the laminate could be made entirely of layers of glass fibre cloth or similar material.

Here again, according to the invention one or more layers of resin distribution medium could be sandwiched between layers of the glass fibre cloth.

Figure 5 shows diagrammatically in more detail how a laminate could be manufactured according to the present invention.

Firstly, on the upper smooth surface of the mould 1 is laid a layer of resin permeable peel-off plies 6, which is a layer of fabric woven from fibres such as polyester to which the resin will not adhere, so -9 enabling the peel-off plies to be readily removed from the lower surface of the laminate after curing.

The layer of peel-off plies 6 facilitates removal of the cured laminate from the upper smooth surface of the mould 1, leaving the lower face of the laminate in a smooth condition ready for painting if required.

It is to be understood that the material of the peel-off plies 6 provides a pervious membrane, perforated film or the like which is not in any sense a resin distribution medium assisting the resin to flow within the laminate.

On top of the layer 6 are laid a plurality of layers of fibre reinforcement. Although glass fibre has been mentioned specifically hereinbefore, the is fibres can be of glass, carbon (graphite) or kevlar or a combination of these. Each layer can be either a woven cloth, a mat constructed from randomly oriented fibres, or bundles of straight (in-plane) fibres stitched together. The layers of fibre reinforcement make up a lower reinforcement cushion 4a. If the mould 1 has vertical or overhanging surfaces, the glass fibre can be lightly attached using a spray adhesive which is subsequently dissolved by the resin during the impregnation stage.

On top of this lower reinforcement cushion 4a is then laid a first layer Sa of resin distribution medium, which is a knitted or woven fabric made from organic or other fibres and constructed in such a way as to leave a passage for air or resin through the layer even when subjected to compression due to a vacuum.

Then the central rigid foam core 3 is laid down, which can be a layer of closed cell rigid foam plastic made from a material such as polyurethane or polyvinyl chloride.

On top of the rigid foam core 3 is laid a second resin distribution layer 5b, followed by another cushion 4b of layers of glass fibre cloth for example.

The lay-up of the composite laminate is finished off with an upper layer of resin permeable peeloff plies 7 similar to plies 6, on top of which plies 7 is provided a third layer of resin distribution medium Sc.

In order to improve the resin infusion or distribution properties of the lay-up, resin distribution medium is also applied around the sides of the lay-up as indicated by the side layers of resin distribution medium 5d.

When the construction of the lay-up is complete, the non-porous flexible cover sheet 2, made of plastic or rubber, is applied over the lay-up and is sealed along its entire peripheral edge to the upper surface of the mould 1, by sealant tape 8 which is a mastic material, sticky on both sides. In this way the region containing the laminate lay-up and defined between the flexible cover sheet 2 and the upper surface of the mould 1 is rendered airtight so that it can be evacuated efficiently.

For this purpose the flexible cover sheet 2 is provided with a vacuum line 9 via which the region between the mould 1 and the flexible cover sheet 2 can be evacuated of air. Also provided is a resin supply line 10 through which resin can be drawn into the evacuated region to flow throughout the layers of glass fibre or other cloth providing the cushions 4a and 4b.

This resin flow is assisted and promoted by the resin distribution medium 5a, 5b, 5c, 5d, thereby to impregnate thoroughly the glass fibre or other cloth, and the resin distribution medium itself.

After the thoroughly impregnated lay-up is cured, the flexible cover sheet 2 is removed and discarded, together with the vacuum line 9 and the resin supply line 10.

Also then removed is the upper layer of resin distribution medium 5c, together with the upper layer of resin permeable peel-off plies 7 and the resin distribution medium 5d applied to the sides of the laminate lay-up.

The laminate lay-up is then removed from the upper surface of the mould 1, assisted by the presence of the lower layer of resin permeable peel-off plies 6 which is then removed also.

The final component is the same as shown in Figure 4, except that the component produced as shown in Figure 5 has a thinner central core 3.

It is to be understood that the resin distribution medium Sa and 5b of Figure 5 could alternatively be sandwiched between individual layers making up each of the two cushions 4a and 4b of glass fibre cloth, instead of being sandwiched between the rigid foam core 3 and the two cushions 4a and 4b of glass fibre cloth layers.

In the method of Figure 5 the resin used is a liquid resin which is for example polyester, epoxide or phenolic which, when mixed with a hardener, will become hard after a period of time.

In an alternative method and component, the rigid foam core 3 of Figure 5 could be replaced by a central third cushion of layers of fibre reinforcement. The finished component would then comprise resin impregnated fibre and resin distribution medium throughout (see following Example 2).

It is to be noted that the laminated component produced according to Figure 5 will have just one surface, i.e. its bottom surface, which will be smooth and suitable for painting with little or no work having to be done on it. This is the surface which lay adjacent to the upper surface of the mould 1 except for the nonroughening intervention of the lower layer of resin permeable peel-off plies 6. The upper surface of the laminated component will, however, have the disadvantage of a surface of the laminated component made according to the prior art of Figures 1 and 2, owing to the presence of the upper layer of resin distribution medium Sc during the process as shown and described with respect to Figure 5.

In alternative methods and embodiments however, the flexible cover sheet 2 could be replaced by a second mould and the upper layer of resin distribution medium Sc omitted, so that both major faces of the laminate will be smooth.

Mechanical tests on a laminate made in accordance with the present invention, and containing one or more is layers of resin distribution medium in the finished product, show little degradation of mechanical properties compared to a laminate which does not contain layers of resin distribution medium.

Examiple 1 Flexural and Interlaminar Shear test specimens were cut from two experimental composite laminate panels which were impregnated by the resin infusion system.

Both laminate panels were constructed in basically the same way, creating a sandwich structure with five layers of E-glass quadriaxial fabric E-QX2336 style 3156 (7mm thickness), each side of a 5Omm C/70-55 Airex foam core. The E-glass (density 2336 g/m 2 per layer) was supplied by Brunswick Technologies, Europe (formerly Tech Textiles).

The laminates were infused using an epoxy based vinyl ester resin. The vinyl ester used was Derakane 510-A with a 6 hour gel time, supplied by K and K Polymerics.

The difference between the sample laminates was in the position of the resin distribution medium. The resin distribution medium was a 1000-t polyethylene monofilament style N1014 supplied by Newbury Engineered Textiles Limited.

In panel number 1, the N1014 resin distribution medium was positioned on both major outside surfaces of the laminate. After infusion and curing the resin distribution medium was removed leaving non-moulded surfaces which were not ideal for painting, corresponding to Figures 1 and 2 as described hereinbefore.

In panel number 2 the N1014 resin distribution medium was positioned as two layers between the two E glass cushions and the Airex foam core, corresponding is to Figure 5 as described hereinbefore. The resin distribution medium could not be removed after infusion and curing. However, a desirable panel outer surface (which had faced the mould) for painting was the result.

The Flexural and Interlaminar Shear tests on the panel numbers 1 and 2 showed little degradation of mechanical properties of the second sample as compared with the first sample.

Examiple 2 Flexural and Interlaminar Shear test specimens were cut from two experimental laminate panels which were impregnated by the resin infusion system.

Plain specimen type A consisted of five layers of E-glass quadriaxial fabric E-QX2336 style glasscloth infused with Derakane 510-A vinyl ester resin with no resin distribution medium present in the finished sample.

Test specimen sandwich type B consisted of five layers of E-glass quadriaxial fabric E-QX2336 style glasscloth infused with Derakane 510-A vinyl ester resin but this time with the resin distribution medium incorporated in the laminate, between the third and fourth layers of glasscloth.

Neither test specimen type A or B comprised a rigid foam core.

Again the mechanical tests on the sandwich type B laminate show little degradation of mechanical properties compared to the plain type A laminate which does not contain resin distribution medium.

Claims

1_ A vacuum-assisted resin infusion method of manufacturing a component in or on a mould, wherein resin distribution medium is provided as part of a lay up which is to provide the eventual component, with there being no such resin distribution medium laid between the or at least one surface of the mould and an adjacent surface of the lay-up.

2. A vacuum-assisted resin infusion manufacturing method according to claim 1, wherein one or more layers of said resin distribution medium is or are laid between fibre layers providing at least part is of the lay-up.

3. A vacuum-assisted resin infusion manufacturing method according to claim 1 or 2, wherein the lay-up comprises a substantially central layer of rigid foam plastic, with reinforcing fibre layers being laid at the two opposite sides of the substantially central layer of rigid foam plastic.

4. A vacuum-assisted resin infusion manufacturing method according to claim 3, wherein a plurality of reinforcing fibre layers is laid at each side of the substantially central layer of rigid foam plastic.

5. A vacuum-assisted resin infusion manufacturing method according to claim 3 or 4, wherein one or more layers of said resin distribution medium is or are laid between the rigid foam plastic central layer, and one or both of the adjacent reinforcing fibre layers.

6. A vacuum-assisted resin infusion manufacturing method according to any one of the preceding claims, wherein the resin distribution medium comprises a 10M6 polyethylene monofilament.

7. A cured component which has been manufactured by a vacuumassisted resin infusion moulding method, and wherein the component comprises within it material which was employed as resin distribution medium in the manufacture of the component.

8. A component according to claim 7, wherein one or more layers of said resin distribution medium is or are present between fibre layers providing at least is part of the component.

9. A component according to claim 7 or 8, which comprises a substantially central layer of rigid foam plastic, with reinforcing fibre layers at the two opposite sides of the substantially central layer of rigid foam plastic.

10. A component according to claim 9, wherein a plurality of reinforcing fibre layers is present at each side of the substantially central layer of rigid foam plastic.

11. A component according to claim 9 or 10, wherein one or more layers of said resin distribution medium is or are provided between the rigid foam plastic substantially central layer, and one or both of the adjacent reinforcing fibre layers.

12. A component according to any one of claims 7 to 11, wherein the resin distribution medium comprises a 100% polyethylene monofilament.

13. A vacuum-assisted resin infusion manufacturing method substantially as hereinbefore described with reference to Figure 3 or 5 of the accompanying drawings. 5

14. A component which has been manufactured by a vacuum-assisted resin infusion moulding method, and which is substantially as hereinbefore described with reference to Figure 4 of the accompanying drawings.