Attributes of Permanent Mold Casting

Permanent mold casting aluminum is similar to the process of sand casting and in this method to the pouring of molten metal is done in a metallic mold without external pressure. Molds are prepared from cast iron or steel which after every casting are not destroyed or rebuilt. The process is called Permanent mold casting as these molds last for long periods.

Usually, they are made of non-ferrous alloys, grey cast iron (having high resistance to thermal shocks), or alloy steels (for very high temperatures and withstanding surface erosion. With a refractory, the inner surfaces of the mold are coated first and then with lamp black or core oil. This is performed to reduce the chilling effect on the cast metal and to facilitate the removal of casting, and prevent the adherence of the molten metal to the mold.

In this permanent mold aluminum casting process, there is no application of external pressure but for the casting of metal in the mold hydrostatic pressure created by the risers is mainly responsible. This process is sometimes called gravity die casting as no external pressure is applied.

For hollow castings, the molds provide facilities for setting cores and ejector pins for ejecting out casting from the mold. In two halves the molds are generally made which are then hinged at one end and the other end has provision for clamping.

Because of fast conduction through the metallic mold, the heat of the molten metal is removed very rapidly. The metal shrinks very fast and then leaves an air space between the mold surface and casting.

On a sliding carriage, the two halves of the mold may be mounted where on one side one half is fixed and the other half is movable along a horizontal bed.

For hollow casting and depending upon the shape of the hollow portion required either metal cores or dry sand cores can be used. The dry sand core is used for complicated shapes having varying diameters by the permanent mold casting aluminum manufacturer. If the metallic cores are used, before the metal starts solidifying, they have to be withdrawn.