A specialised part of the manufacturing/engineering world is casting or foundry work as it is properly called. In schools and colleges this usually involves casting molten aluminium. Before any casting can take place a wooden pattern is made precisely. This is called pattern making and in industry this is a very skilful job. Any inaccuracy at this stage will result in the final cast being wrong or even failing. In schools the pattern is usually made from a softwood and its sides are given a draft (an angle) so that it can be removed from the sand easily.

The diagrams to the left shows the pattern on a flat board and a casting box called a ‘drag’ being placed over it.

Special casting sand will soon be packed around the pattern but to ensure to can be removed easily from the sand, parting powder is sprinkled over and around it. (parting powder is similar to talcum powder). It stops the casting sand sticking to the pattern and pulling away with it when the pattern is finally removed from the sand.

Casting sand is then shaken through a sieve (called riddled sand) so that only fine particles fall around the pattern. This is called facing sand and it must be fine so that detail on the pattern shows up on the final casting.
Different types of sand are available. The safest is called petro-bond. This is a mixture of quality sand and oil. The cheapest is called green sand and this is mixed with water. Green sand must be mixed carefully as if too much water is added - when molten aluminium is poured into the mould an explosion can result.

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