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. Studs, nuts, bushings, pipes and tubing maybe cast as integral parts
of the casting and can be made of aluminum, bronze, brass, iron, steel and
stainless steel. PROCESS 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. 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.
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