Permanent mold casting

Permanent mold (gravity die) casting, like die casting, is suited to high-volume production. Permanent mold castings typically are larger than die castings. Maximum weight of permanent mold castings usually is about 10 kg, but much larger castings sometimes are made when costs of tooling and casting equipment are justified by the quality required for the casting.

Permanent mold castings are gravity-fed and pouring rate is relatively low, but the metal mold produces rapid solidification. Permanent mold castings exhibit excellent mechanical properties. Castings are generally sound, provided that the alloys used exhibit good fluidity and resistance to hot tearing.

Mechanical properties of permanent mold castings can be further improved by heat treatment. If maximum properties are required, the heat treatment consists of a solution treatment at high temperature followed by a quench and then natural or artificial aging. For small castings in which the cooling rate in the mold is very rapid or for less critical parts, the solution treatment and quench may be eliminated and the fast cooling in the mold relied on to retain in solution the compounds that will produce age hardening.

Some common aluminum permanent mold casting alloys, and typical products cast from them, are presented below.

    * Alloy 366.0 - Automotive pistons
    * Alloys 355.0, C355.0, A357.0 - Timing gears, impellers, compressors, and aircraft and missile components requiring high strength
    * Alloys 356.0, A356.0 - Machine tool parts, aircraft wheels, pump parts, marine hardware, valve bodies
    * Other aluminum alloys commonly used for permanent mold castings include 296.0, 319.0, and 333.0.