Casting is the production of objects of desired form by pressing the raw material (e.g., alloys, fiberglass, plastics, steel) in liquid form into a suitably shaped mold. Both the mold and the pattern from which it is made may be either permanent or expendable.
Permanent-mold techniques include die casting, where the molten material is forced under pressure into a die; centrifugal casting, used primarily for pipes, the molten material being poured into a rapidly rotating mold (see centrifuge); and continuous casting, for bars and slabs, where the material is poured into water-cooled, open-ended molds. Most important of the expendable-mold processes is sand casting (founding): here fine sand is packed tightly around each half of a permanent pattern, which is removed and the two halves of the mold placed together. The material is poured in through a channel (sprue); after setting, the sand is dispersed. In some processes, the mold is baked before use to remove excess water. See also cast iron.
Cire perdue(French for "lost wax") A method of casting metal objects (usually bronzes) used since classical antiquity. First, the object is molded in clay or plaster in roughly the desired shape but slightly smaller. This core is covered in wax, not more than 1.5cm (0.5in) thick, and further modeling is undertaken. Straws of wax pipes are fitted to admit the molten metal and release hot gases. The whole is then covered in a heat-proof mold, the wax melted away and the metal poured into the space it occupied.
Related category• INDUSTRIAL CHEMISTRY
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