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MOTORING: Ins and outs of aluminium 

BY ANDREW ENGLISH

ALUMINIUM is the world's third most common element but it never appears on its own. The only practical source is bauxite, a yellow ore that, after a complicated process of extraction, yields 45-60 per cent aluminium.

The metal is easily worked and, when designed well, aluminium structures can absorb as much energy as a steel structure. Drawbacks include a tendency to corrode, especially in the presence of iron or steel, electricity or salt.

Most road-car bodies are built of 16-gauge (1.625mm-thick) sheets of almost pure aluminium - as opposed to the lower aluminium -content alloys used in engine blocks, say - although some racing cars use 18-gauge (1.219mm thick). As aluminium sheets are rolled out, the grains in the metal tend to face one direction. This means it will tear accurately in one direction but not the other.

Panel-beating is a process of shrinking and stretching the metal. Tools include mallets and hammers with rubber, wood, nylon and steel faces. Flippers are flapped at the metal to stretch it and dollies and chasers are used on the underside to give the material a shape to adopt.

In addition, a good panel shop will have electric cutters, mechanical benders and a wheeling machine. A.E.