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Lost-wax casting – also called investment casting, precision casting, or cire perdue (French: [siʁ pɛʁdy]; borrowed from French) [1] – is the process by which a duplicate sculpture (often a metal, such as silver, gold, brass, or bronze) is cast from an original sculpture. Intricate works can be achieved by this method.
The fragile wax patterns must withstand forces encountered during the mould making. Much of the wax used in investment casting can be reclaimed and reused. [2] Lost-foam casting is a modern form of investment casting that eliminates certain steps in the process.
One key in casting metal cores is to make sure they do not contain any porosity as it will induce flaws into the molded part. In order to minimize porosity the metal may be gravity cast or the molding cavity may be pressurized. Another system slowly rocks the casting dies as the molding cavity fills to "shake" the air bubbles out. [9]
The lost wax process originated in ancient Mesopotamia. The earliest known record of lost-wax casting is a clay tablet written in cuneiform in the ancient city of Sparta, Babylon, which specifically records how much wax is needed to cast a key. [6] The earliest-known castings in the global archaeological record were made in open stone molds. [7]
Wax patterns are used in an alternative casting process called investment casting. A combination of paraffin wax, bees wax and carnauba wax is used for this purpose. In this case the wax "pattern" is melted out from the mould cavity which is normally a rigid plaster like material rather than sand, so the wax "pattern" can only be used once. [5]
The lost-wax casting technique Robinson developed is a modified version of the bronze casting technique. It involves creating a plaster mould which is filled with molten wax. The mould is then removed (and can be reused) and the wax is encased in a heat-resistant covering and placed in the kiln.
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Bronze poured from a crucible into a mold, using the lost-wax casting process. In a foundry, molten metal is poured into molds. Pouring can be accomplished with gravity, or it may be assisted with a vacuum or pressurized gas. Many modern foundries use robots or automatic pouring machines to pour molten metal.