Lost-wax casting

Lost-wax casting (also called "investment casting", "precision casting", or cire perdue in French) is the process by which a duplicate metal sculpture (often silver, gold, brass or bronze) is cast from an original sculpture. Intricate works can be achieved by this method.

The oldest known examples of this technique are the objects discovered in the Cave of the Treasure (Nahal Mishmar) hoard in southern Israel, and which belong to the Chalcolithic period (4500–3500 BC). Conservative estimates of age from carbon-14 dating date the items to c. 3700 BC, making them more than 5,700 years old.[contradictory][1][2]. Another example from a similar period is found in a 6,000-year old amulet from Pakistan.[3] Lost-wax casting was widespread in Europe until the 18th century, when a piece-moulding process came to predominate.

The steps used in casting small bronze sculptures are fairly standardized, though the process today varies from foundry to foundry. (In modern industrial use, the process is called investment casting.) Variations of the process include: "lost mould", which recognizes that materials other than wax can be used (such as: tallow, resin, tar, and textile);[4] and "waste wax process" (or "waste mould casting"), because the mould is destroyed to remove the cast item.[5][6]

Casts can be made of the wax model itself, the direct method, or of a wax copy of a model that need not be of wax, the indirect method. These are the steps for the indirect process:

Prior to silica-based casting moulds, these moulds were made of a variety of other fire-proof materials, the most common being plaster based, with added grout, and clay based. Prior to rubber moulds gelatine was used.

The methods used for small parts and jewellery vary somewhat from those used for sculpture. A wax model is obtained either from injection into a rubber mould or by being custom-made by carving. The wax or waxes are sprued and fused onto a rubber base, called a "sprue base". Then a metal flask, which resembles a short length of steel pipe that ranges roughly from 1.5 to six inches tall and wide, is put over the sprue base and the waxes. Most sprue bases have a circular rim which grips the standard-sized flask, holding it in place. Investment (refractory plaster) is mixed and poured into the flask, filling it. It hardens, then is burned out as outlined above. Casting is usually done straight from the kiln either by centrifugal casting or vacuum casting.

The lost-wax process can be used with any material that can burn, melt, or evaporate to leave a mould cavity. Some automobile manufacturers use a lost-foam technique to make engine blocks. The model is made of polystyrene foam, which is placed into a casting flask, consisting of a cope and drag, which is then filled with casting sand. The foam supports the sand, allowing shapes that would be impossible if the process had to rely on the sand alone. The metal is poured in, vaporizing the foam with its heat.

In dentistry, gold crowns, inlays and onlays are made by the lost-wax technique.Application of Lost Wax technique for the fabrication of cast inlay was first reported by Taggart. A typical gold alloy is about 60% gold and 28% silver with copper and other metals making up the rest. Careful attention to tooth preparation, impression taking and laboratory technique are required to make this type of restoration a success. Dental laboratories make other items this way as well.

This page was last edited on 11 July 2018, at 17:41 (UTC).
Reference: https://en.wikipedia.org/wiki/Lost-wax_casting under CC BY-SA license.

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