Permanent mold casting
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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.
Picture of the Process: [1]
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[edit] Casting process
The two halves of the molds are usually clamped together then pre-heated to 150-200 ºC (300-400 ºF) to ease the flow and reduce thermal damage to the casting. Molten metal is them poured into the mold through a gating system, which decreases the chance of impurities in the metal. 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.
[edit] Molds
Molds for the casting process consist of two halves. Casting molds are usually formed from cast iron, steel, bronze, graphite, or metal alloys. These metals are chosen because of their resistance to erosion and thermal fatigue 1.
Cores or inserts can be placed into the molds to produce inner cavities in the casting. Cores are usually made from oil-bonded or resin-bonded sand, plaster, graphite, gray iron, or low carbon steel. Cores are usually consumed in the casting process.
Coating is applied to the molds every few casts to increase the life of the mold, serve as a parting agent, and to act as a thermal barrier for the mold. When molds are worn they are either refinished or replaced.
Mechanical ejectors in the form of pins are used when coatings are not enough to remove casts from the molds. These pins are placed throughout the mold and usually leave small round impressions on the casting.
[edit] Advantages and Disadvantages
Permanent mold casting produces a good surface finish, close dimensional tolerances, and uniform mechanical properties. Equipment costs can be high, but can be compensated for by automating your casting process. This process has many advantages, but may not be economical for small production runs, or for designs with intricate designs.
[edit] See also
[edit] References
[1] "Manufacturing Engineering and Technology, Fifth Edition." Kalpakjian, Serope and Steven R Schmid. Copyright 2006 by Pearson Education, Inc. Pages 303-304.
