Alnicos are precipitation-hardened alloys requiring special heat treatment techniques. The raw materials are cobalt, nickel, copper, aluminum and iron. Titanium, silicon, etc. are added in certain proportions. The raw materials in their purest form are melted in medium frequency induction furnaces and castings are made using conventional sand or shell moulds. The heat treatment consists of heating the alloy in furnace to well above its curie point, and holding it at that temperature for some time. This is followed by controlled cooling after which the castings are reheated and held for a long period at a temperature of about 6000C. This ageing process increases the coercive force and the energy product. Finally, the castings are ground to obtain close dimensional tolerances whenever necessary and inspected for physical and magnetic accuracy.