The elements necessary for the production of sound castings are considered throughout this chapter. These include molding materials, molding equipment, tools, patterns, and melting equipment. These basic ingredients must be combined in an orderly sequence to produce a sound casting. Castings have specific important engineering properties; these may be metallurgical, physical, or economic. Thus sand castings may be made in: (1) green sand molds, (2) dry sand molds, (3) core sand molds, (4) loam molds, (5) shell molds, and (6) cement-bonded molds. The major methods of making these molds are called: (1) bench molding, (2) machine molding, (3) floor molding, and (4) pit molding. Molding machines serve in two general capacities: (1) to pack sand firmly and uniformly into the mold, and (2) to manipulate the flasks, mold, and pattern. A core is a body of material, usually sand, used to produce a cavity in or on a casting. A pattern is a form used to prepare and produce a mold cavity. It has been said that a poor casting may be produced from a good pattern, but a good casting will not be made from a poor pattern. Common practice for pouring is to run the molten metal from the cupola or furnace into a large receiving ladle. A wide variation in the properties of castings is obtainable from the selection of materials put into the melt, control of the rate of cooling, and subsequent heat treatment. An engineer must learn how to design castings that do their jobs adequately and can be made economically.
Product ID: BK00PUB8_E_CH-8