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Glass-fiber Reinforced Plastic (GRP)

Let's begin with the expression 'to laminate', whereby here, we don't mean the coating of (paper) documents with plastic foil. In this case, to laminate means the building up of layers. Try to imagine, e.g., the negative form of a boat with a very fine surface. First, a layer of dyed epoxide- or polyester resin is applied, then a sheet of fibre-glass matting, onto which a layer of untinted resin is again applied. This process can be repeated as often as you wish, depending on the desired stability.

Of course, the thicker it gets, the more it weighs, indeed, compared with, e.g., metallic materials, GRP (Glass Reinforced Plastic) is extremely lightweight. I remember seeing an assistant lift the complete (short) rear-end of a Porsche-917, using only one hand. Of course, the component was also deep-painted, which doesn't mean that a normal spray-job is not possible. It should however, not be allowed to dry too quickly because the possible emission of gases can ruin the job.

One further advantage is the insulation effect, whereby, GRP is very popular among the manufacturers of PCB's (Printed Circuit Boards). In the field of motor vehicles an important aspect is of course, the material's high corrosion resistance. Indeed, it is never used exclusively for the building of, e.g., car bodies, a certain amount of sheet-metal which provides a certain type of stability, is always included, unfortunately this also cancels out the advantage of corrosion resistance.

In this case, we're talking about a duroplastic (thermosetting plastic). The name is derived from the Latin word 'durus' which means 'hard'. In modern technical terminology, one speaks of an 'elasticity module'. This means, that such a material can hardly meet the stability requirements, e.g., of a strong impact. It can stand up to smaller impacts but will break off much earlier than a tough metal would. This results in a catastrophic crash behaviour, which is why, only in much earlier cars, the complete passenger compartment, including the flooring plate, was made from GRP.

It remains nonetheless, for almost any other applications, a fascinating material. In addition, it is also quite reasonably priced, if one is not buying explicitly for the motor industry. Should a particularly smooth surface not be necessary, one can produce the mold itself from cheap material, eg., gypsum (plaster of Paris). One could even smoothen the surface by sanding it down. Which again, brings us back to laminating.

In the meantime, GRP has built up a long tradition in the motor vehicle field. Colin Chapman, the boss at Lotus, can justly be considered to be the pioneer in this field. In 1957, the Lotus-Elite with it's GRP-monocoque appeared. Lotus is a small company and cannot afford to buy the expensive sheet-metal presses. Apart from this factor, for taxation reasons, some of their cars are sold in kit-form, more or less as a do-it-yourself sports car. 03/12