Metals for investment casting

Any metal capable of being cast can be cast by these methods, although advantage is most readily gained when using those difficult to work by other methods. Metals for investment casting are the subject of British Standard BS 3146. 

Investment Casting. A process for the casting of small metal components to a close tolerance. In the usual process a wax replica of the part to be cast is coated ( invested ) with refractory powder, suitably bonded, and the whole is then warmed (150°C) to melt out the wax - hence the alternative name Lost-wax Process the refractory mould is then bred at 1000-1100 C. The refractory used may be powdered sillimanite or alumina, or specially prepared cristobalite the latter is particularly used in the application of the process in dentistry. B.S 1902 Pt 10 specibes methods for the determination of resistance to deformation at elevated temperatures permeability and standard air bow capacity at elevated temperatures thermal proble determination, for refractories for investment casting shell mould systems prefabricated brickwork, in which reinforcement is provided by steel rods running horizontally across perforations in the blocks. 

Components made from plastic, metal, and ceramics can be manufactured with 3D printing processes. The standards are gypsum-ceramic and starch powders for illustrative models and lost molds for investment casting. 

Casting Investments. Casting investments are used to form molds into which molten metal may be cast. The cavity for receiving the metal is formed by the lost wax process. The composition of investments used for alloys cast from low (<1100° C) temperatures are different from those used for alloys cast from higher (>1300° C) temperatures. 

With an economizer, the feed water temperature entering is of dominant importance for investment efficiency. This temperature should be high enough to avoid corrosion, especially when high-sulfur fuels are fired. A feed water temperature of about 280° F or higher can be safely handled with high-sulfur fuels. Part of the economizer can be made of cast iron, depending on the metal skin temperature and dew point. 

Chem. Descrip. Carnauba wax CAS 8015-86-9 EINECS/ELINCS 232-399-4 Uses Wax for cosmetics, pharmaceuticals, ointments, tablet coatings, candles, confections, investment casting, auto/floor/shoe polishes, carbon paper, inks, paper coatings, fruit coatings Regulatory FDA21CFR 184.1978 CTFA listed Properties Yel. flakes, lumps, or powd. m.p. 80-86 C min. acid no. 2-7 sapon. no. 78-95 0.004% max. heavy metals Toxicology TSCA listed... 

After compaction, molten metal is poured into the mould causing the foam to burn up and vaporise as the molten metal replaces the foam pattern, exactly duplicating all the features of the original pattern. Like other investment casting methods, for each new casting produced, a new pattern must be made hence the name lost foam casting. 

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