Glassfibre reinforcement

Molten glass can be drawn out into a filament of glass fibre, and in this form has an ultimate tensile strength per area 10 times that of steel.The existence of the material has been known since the Egyptian XVIIIth

Dynasty, about 1500 BC (Fibreglass Ltd, 1977a). However; glass fibres of sufficient fineness and consistency for reinforced plastics were not commercially available until the 1930s.

Although several types of glass can be drawn into fibres, the standard fibre used for all resin systems is E glass, which is a high-quality electrical-grade glass fibre. This is bundled together to form strands, which in turn can be processed into various products.

Chopped strand mat

This is the most common form of general-purpose reinforcement, which is used mainly for the hand-laminating process.

Continuous strand mat

In continuous strand mat the strands are not chopped, but just allowed to swirl randomly. The product is used for press moulding and resin injection moulding.

Continuous rovings

These consist of long bundles of fibres, which are fed into a machine that chops and sprays them onto the moulding in conjunction with the resin.This spray-up technique is used very widely to reduce the labour content of normal hand lay-up moulding.

A continuous thread of glass

This can be wound round the component being impregnated with the resin as it proceeds. This filament winding process produces high-performance components such as pressure piping, but is limited in form, and is expensive to set up.

Other reinforcement materials have been developed that give improved properties, albeit at increased cost. These are carbon fibre, a crystalline fibre developed by the Royal Aircraft Establishment in I 963, with a strength and modulus superior to that of

3.1 Faults: (a) crazing of GRP surface; (b) internal dry patch.

glass fibre, and aramid fibre, a lightweight, low-modulus fibre developed by Du Pont Industrial Fibres, under the trademark of Kevlar

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