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.^[1]

The two major evaporative-pattern casting processes are:^[1]

• Lost-foam casting
• Full-mold casting

The main difference is that lost-foam casting uses an unbonded sand and full-mold casting uses a bonded sand (or green sand). Because this difference is quite small there is much overlap in the terminology. Non-proprietary terms that have been used to describe these processes include: cavityless casting,^[2] evaporative foam casting, foam vaporization casting, lost pattern casting, the castral process, and expanded polystyrene molding.^[3][4] Proprietary terms included Styro-cast,^[5] Foam Cast,^[6] Replicast,^[7] and Policast.^[4]

History

The first patent for an evaporative-pattern casting process was filed in April 1956, by Harold F. Shroyer. He patented the use of foam patterns embedded in traditional green sand for metal casting. In his patent, a pattern was machined from a block of expanded polystyrene (EPS), and supported by bonded sand during pouring. This process is now known as the full mold process.^[8][9]

In 1964, M.C. Flemmings used unbonded sand for the process. The first North American foundry to use evaporative-pattern casting was the Robinson Foundry at Alexander City, Alabama. General Motors' first product using these processes was the 4.3 L, V-6 diesel cylinder head, which were made in 1981 at Massena, New York.^[10]

A study found in 1997 that evaporative-pattern casting processes accounted for approximately 140,000 tons of aluminium casting in the United States. The same survey forecast that evaporative-pattern casting processes would account for 29% of the aluminium, and 14% of the ferrous casting markets by 2010.^[11][12]

References

1. Degarmo, Black & Kohser 2003, p. 321.
2. U.S. Patent 4,068,704.
3. American Society for Metals et al. 1991, p. 229.
4. Totten, Funatani & Xie 2004, p. 357.
5. Styro-cast, retrieved 2009-03-29.
6. American Foam Cast, retrieved 2009-03-29.
7. Replicast Process (CS), retrieved 2009-03-29.
8. Donahue, Raymond; Anderson, Kevin, Lost Foam Casting, ASM International, retrieved 2010-04-06.
9. U.S. Patent 2,830,343
10. Biswanath, Mondal (2004), Proceedings of the National Conference on Investment Casting: NCIC 2003, Allied Publishers, ISBN 978-81-7764-659-7
11. Bodine, Jack R. (1999-05-01), "From a monument to the Vega: the journey of the aluminum casting industry", Modern Casting: 13.
12. Success through partnership: lost foam (PDF), September 1998, retrieved 2009-03-30.

Bibliography

• American Society for Metals; Stefanescu, D M; ASM International Handbook Committee; ASM International Alloy Phase Diagram Committee (1991), ASM Handbook, 15 (10th ed.), ASM International, ISBN 978-0-87170-021-6.
• Degarmo, E. Paul; Black, J T.; Kohser, Ronald A. (2003), Materials and Processes in Manufacturing (9th ed.), Wiley, ISBN 0-471-65653-4.
• Totten, George E.; Funatani, Kiyoshi; Xie, Lin (2004), Handbook of metallurgical process design (illustrated ed.), CRC Press, ISBN 978-0-8247-4106-8.