The gravity process begins by preheating the mould to 150-200 °C (300-400 °F) to ease the flow and reduce thermal damage to the casting. The mould cavity is then coated with a refractory material or a mould wash, which prevents the casting from sticking to the mould and prolongs the mould life. Any sand or metal cores are then installed, and the mould is clamped shut. Molten metal is then poured into the mould. Soon after solidification the mould is opened and the casting removed to reduce chances of hot tears. The process is then started all over again, but preheating is not required because the heat from the previous casting is adequate and the refractory coating should last several castings. Because this process is usually carried out on large production run work-pieces automated equipment is used to coat the mould, pour the metal, and remove the casting.