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Metal casting: appropriate technology in the small foundry by Steve Hurst

By Steve Hurst

An creation to small-scale non-ferrous casting. contains step by step directions on how you can make apparatus utilizing neighborhood fabrics; and offers details on moulding ideas, trend making, middle making, using wax and steel instruction.

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Taper or draught allowance The important surface is the sand; that is what forms the metal. The pattern is only a tool to this end. To give an example, a cylinder pattern is easy: you make the split line along the axis. You must, however, be sure to incline the ends; they too must taper. A sausage shape, or cylinder with hemispherical (evenly rounded) ends, is easier still. A cube is not difficult; you split the mould on the diagonal. But once again, you must incline the two ends. If, for some reason, you have to cast the cube square on, you must incline the sides.

Then backing sand is rammed in place as described above. 3 The mould is parted (cope lifted off the drag) and the pattern removed. The gate or sprue system, which conducts the molten metal from the runner tube into the mould cavity, is cut in the sand. Both sides of the mould are vented with wire venting rods, the edges of the mould are made good, any fallen sand removed, and the mould put together. Finally the cope is weighted, or clamped to the drag, and the mould is filled with molten metal.

Plaster moulds are an excellent substitute though, obviously enough, they do not last and you have to renew them. In both Nepal and Peru we used moulds made of ordinary builders' plaster. 2. Flexible moulds (i) Gelatine. An economical and versatile material. Problems with storage make this more suitable for a foundry with a large volume of production and a larger labour force. Gelatine is especially appropriate in a country where RTV rubbers are expensive or hard to obtain, and where labour is plentiful.

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