Full-mold casting is an

evaporative-pattern casting Evaporative-pattern casting is a type of casting process that uses a pattern made from a material that will evaporate when the molten metal is poured into the molding cavity. The most common evaporative-pattern material used is polystyrene foam.. ...

process which is a combination of sand casting and lost-foam casting. It uses an

expanded polystyrene Polystyrene (PS) is a synthetic polymer made from monomers of the aromatic hydrocarbon styrene. Polystyrene can be solid or foamed. General-purpose polystyrene is clear, hard, and brittle. It is an inexpensive resin per unit weight. It is a ...

foam pattern which is then surrounded by sand, much like sand casting. The metal is then poured directly into the mold, which vaporizes the foam upon contact. Vollformgiessenschema

Process

First, a pattern is usually made from

polystyrene foam Polystyrene (PS) is a synthetic polymer made from monomers of the aromatic hydrocarbon styrene. Polystyrene can be solid or foamed. General-purpose polystyrene is clear, hard, and brittle. It is an inexpensive resin per unit weight. It is a ...

, which can be done many different ways. For small volume runs the pattern can be hand cut or machined from a solid block of foam; if the geometry is simple enough it can even be cut using a hot-wire foam cutter. If the volume is large, then the pattern can be mass-produced by a process similar to

injection molding Injection moulding (U.S. spelling: injection molding) is a manufacturing process for producing parts by injecting molten material into a mould, or mold. Injection moulding can be performed with a host of materials mainly including metals (for ...

. Pre-expanded beads of polystyrene are injected into a preheated aluminum mold at low pressure.

Steam Steam is a substance containing water in the gas phase, and sometimes also an aerosol of liquid water droplets, or air. This may occur due to evaporation or due to boiling, where heat is applied until water reaches the enthalpy of vaporization ...

is then applied to the polystyrene which causes it to expand more to fill the die. The final pattern is approximately 97.5% air and 2.5% polystyrene. The finished patterns can be

hot glue Hot-melt adhesive (HMA), also known as hot glue, is a form of thermoplastic adhesive that is commonly sold as solid cylindrical sticks of various diameters designed to be applied using a hot glue gun. The gun uses a continuous-duty heating eleme ...

d to pre-made pouring basins, runners, and risers to form the final pattern.. The pattern is then coated with a refractory material. The coated pattern (2) is placed in a flask and packed carefully with green sand (4) or a chemically bonded sand. Finally, the molten metal (1) is poured into the mold, which vaporizes the foam (3) allowing the metal to fill the entire mold. The vapor is simultaneously extracted from the flask through the sand. The casting is allowed to cool and then dumped out of the flask (5) ready to use. The sand does not need to be reprocessed so it can be directly reused..

Details

The minimum wall thickness for a full-mold casting is . Typical dimensional tolerances are 0.3% and typical surface finishes are from 2.5 to 25 µm (100 to 1000 µin) RMS. The size range is from to several tonnes (tons).. Full-mold casting is often used to produce cylinder heads, engine blocks,

pump A pump is a device that moves fluids (liquids or gases), or sometimes slurries, by mechanical action, typically converted from electrical energy into hydraulic energy. Pumps can be classified into three major groups according to the method they u ...

housings, automotive

brake A brake is a mechanical device that inhibits motion by absorbing energy from a moving system. It is used for slowing or stopping a moving vehicle, wheel, axle, or to prevent its motion, most often accomplished by means of friction. Background ...

components, and

manifold In mathematics, a manifold is a topological space that locally resembles Euclidean space near each point. More precisely, an n-dimensional manifold, or ''n-manifold'' for short, is a topological space with the property that each point has a n ...

s. Commonly employed materials include aluminium, iron,

steel Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistant ty ...

, nickel alloys, and copper alloys.

Advantages and disadvantages

This casting process is advantageous for very complex castings, that would regularly require cores. It is also dimensionally accurate, requires no draft, and has no parting lines so no flash is formed. As compared to investment casting, it is cheaper because it is a simpler process and the foam is cheaper than the wax. Risers are not usually required due to the nature of the process; because the molten metal vaporizes the foam the first metal into the mold cools more quickly than the rest, which results in natural directional solidification. The two main disadvantages are that pattern costs can be high for low volume applications and the patterns are easily damaged or distorted due to their low strength. If a die is used to create the patterns there is a large initial cost.

History

The first patent for an evaporative-pattern casting process was filed in April 1956, by H.F. Shroyer. He patented the use of foam patterns embedded in traditional green sand for metal casting.

References

Notes

Bibliography

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