permanent mold[′pər·mə·nənt ′mōld]
a metal mold for producing castings, primarily from nonferrous alloys but also from iron and steel when specific technical requirements exist. They are made from iron and steel, and sometimes from other alloys, and are capable of withstanding 100 to 10,000 pourings, depending on the weight and properties of the alloy. The use of permanent molds in series and mass production is economically advantageous.
Permanent molds may be jointless or have one or more joints in the horizontal and vertical planes or a composite parting line, depending on the configuration of the casting. The exterior of the casting is formed by the mold recesses, and the interior by sand and metal casting cores. There are gating system channels in the parting line or sand core for filling the mold with melt. The parts of the mold are usually opened and closed mechanically on special chill casting machines. Special coatings and paints are applied to the surface of the mold’s working parts to increase its durability and reduce the rate of cooling of the castings. Permanent molds coated with a thin layer (up to 0.5 mm) of fine facing sand, binding materials, and water, are used to produce castings of simple configuration, high surface density, and good hermetic qualities. Refractory-lined permanent molds, in which only specially prepared hollows are coated with molding mixture, are used for making large iron and steel castings weighing several tons.
N. P. DUBININ