What is the Permanent Mold?
Here, the two halves of the mold are made of metal, usually cast iron, steel, or refractory alloys. The cavity, including
the runners and gating system are machined into the mold halves. For hollow parts, either permanent cores
(made of metal) or sandbonded ones may be used, depending on whether the core can be extracted from the part
without damage after casting. The surface of the mold is coated with clay or other hard refractory material – this
improves the life of the mold.
Before molding, the surface is covered with a spray of graphite or silica, which acts as a lubricant. This has two
purposes– it improves the flow of the liquid metal, and it allows the cast part to be withdrawn from the mold
more easily. The process can be automated, and therefore yields high throughput rates. Also, it produces very
good tolerance and surface finish. It is commonly used for producing pistons used in car engines, gear blanks,
cylinder heads, and other parts made of low melting point metals, e.g. copper, bronze, aluminum, magnesium, etc.