Permanent mold castings

Permanent mold casting is "a metal shaping process in which molten metal is introduced into a permanent (reusable) mold, under gravity or low pressure, and held until solidification occurs. The molds are usually coated with a refractory wash and lampblack, which reduces the chilling effect on the metal and [enables] removal of the casting.

In permanent mold casting, metal is used as the mold material instead of sand. Typically cast iron, steel, bronze, graphite, or other metal alloys are treated and formed into two halves of the mold.

Some of the products made using permanent mold casting process are housings, junction boxes, impellers, valve bodies, flanges, manifolds, actuator bodies, compressor parts, electrical fittings parts, and covers.

Process Characteristics

-Molten metal is introduced into the mold using gravity or slight pressure.

-Molds are often made of cast iron.

-Molds produce both sufficient accuracy in dimensions and smooth surfaces.

-Produced castings are strong and have low porosity.

-Some complex shapes may be possible but difficult to produce.

 Casting process

The two halves of the molds are usually clamped tightly together then pre-heated to 150-200 °C (300-400 °F) to ease the flow and reduce thermal damage to the casting. Molten metal is then poured into the mold through a gating system, which decreases the chance of impurities in the metal. Molten metal should be poured at the lowest practical temperature in order to minimize the possibility of cracks and porosity.2 Once the metal has solidified the molds are opened and the casting is removed. The mold is then either cooled, or heated for another casting.

Permanent mold casting is a precision technique produced by pouring molten metal into CNC machined steel molds under gravity, centrifugal force, or low pressure. Due to the rapid heat transfer from the molten metal to the mold itself, the castings have finer grain structures and better strength properties than casts made by sand casting method. Permanent mold casting permits designs with thinner walls and less wight. Permanent mold castings are less subject to shrinkage and effects from gas such as bubbles in the casting than sand castings and do not contain the entrapped gas often found in die castings.

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