Permanent Mold Casting
Gravity pouring of molten metal into metal mold produces permanent mold castings. The molds are made from steel or iron and have a casting production life of 10,000 – 120,000 molds depending on the part. When cores are required expendable chemically bonded sand cores are used. This is called semi-permanent mold casting. The size of permanent mold castings can range from 1 oz. to 25 lbs. Parts such as studs, nuts, and bushings can be incorporated as composite integral parts of the permanent mold casting. These inserts can be made from aluminum, brass, steel, stainless steel, bronze and iron, and other materials.
A mold coating is sprayed onto the surface of the preheated steel or iron mold. If a core is used then it is inserted into the mold and the two halves are closed together. Molten metal is then poured through an opening called a sprue. The metal solidifies, the mold is opened and the casting is removed.
The permanent mold process offers the following advantages:
Permanent mold castings have a finer grain structure and increased strength properties over other processes.
Part designs can include thinner walls, lower weights and closer dimensional tolerances.
Permanent molds do not contain the products of combustion found in sand molds. Therefore, a permanent mold casting can be held to higher standards with regard to density and pressure tightness.