To produce cavities inside a metal casting ; as required for liquid cooling in engine blocks and cylinder heads. Special negative forms ( core boxes ) are used to produce sand cores. Cores can be made up from oil bonded sand, frequently a basic oil like linseed oil can be employed to make effective sand cores. Once made in the negative shaped core box the sand core is baked in an oven until it is cured.
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Cores are inserted into the mould box after removal of the pattern from the sand.
With a completed sand mould at the suitable moisture content, the box containing the sand mould is then positioned ready to fill with molten metal ; i.e. Ferrous iron ( cast iron ) steel, or none ferrous bronze, brass, or aluminium alloy.
After filling with molten metal the box is set aside until the metal is sufficiently cool to enable the removal of the hot casting from the sand mould. A rough casting is produced that, in the case of iron or steel, may still be glowing red.
When casting with metals like cast-iron or lead, which are noticeably heavier than the moulding sand, the flasks, called the cope & drag is covered with a heavy plate to stop a problem known as mould floatation. Floating the mould occurs when the pressure of the metal pushes the sand above the mould hole unfit, causing the casting to fail.
After casting, the inner cores are broken up by rods or shot and removed from the casting. The metal from the sprue and risers is removed from the coarse casting.Various heat treatments might be applied to relieve tensions from the initial cooling and to add hardness ; in the case of steel or solid iron, by slaking in water or oil.
The casting may be further strengthened by surface compression treatment like shot peening, which adds resistance to tensile cracking and smoothes the rough surface, solid iron engine conrods are treated in this manner.
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