Lost Foam Casting

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  • Topic: Casting, Lost-foam casting, Polystyrene
  • Pages : 16 (4748 words )
  • Download(s) : 34
  • Published : December 14, 2011
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LOST FOAM CASTING

--------------------------------------------------------------------------------------------------------------------- ABSTRACT:
The Report presents some theoretical and practical aspects regarding the casting of alloys in lost foam moulds. The stages of the procedure, the economic benefits and several ecological aspects are synthetically presented.

KEY WORDS:
casting, alloys, lost foam process, Expanded polystyrene
--------------------------------------------------------------------------------------------------------------------- Introduction
The lost foam casting process offers several advantages over conventional sand casting processes, such as simplified production techniques and reduced environmental waste due to binder system emissions and sand disposal. The process is well-suited for castings with complex geometries, tight tolerances, and smooth as-cast surface finish requirements. When the castings are designed to fully exploit these advantages, cleaning and machining times are dramatically reduced if not completely eliminated. Therefore, the lost foam casting process is viewed as a value-added process rather than a substitute for sand casting. Lost foam castings are produced by pouring molten metal into a foam pattern contained in a flask filled with loose sand that is compacted through vibration. Generally speaking, a foam pattern is coated with a refractory slurry and dried before being placed in the flask and surrounded by large grain fineness sand. The foam pattern degrades immediately after molten metal is introduced, leaving a casting that duplicates all features of the foam pattern. The degradation products are vented into the loose sand. In lost foam casting process, mold filling, thermal transport, and solidification are strongly influenced by the foam pattern degradation. There are three phenomena which are inherent in lost foam casting process: slow molten metal flow, reducing atmosphere, and degradation products. The first and second phenomena help reduce oxides or slag defects. The last one, however, may become casting defects if they remain in the cast parts. To improve lost foam casting design, it is essential to understand the interactions between the foam pattern and molten metal as well as the displacement of degradation products.

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. 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.

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 4.3L, V-6 diesel cylinder head, which were made in 1981 at Massena, New York.

A study found in 1997 that evaporative-pattern casting processes accounted for approximately 140,000 tons of aluminum casting in the United States. The same survey forecast that evaporative-pattern casting processes would account for 29% of the aluminum, and 14% of the ferrous casting markets in the near future.

Definition
Definition|
A casting process whereby the pettern is made of polystyrene foam and is vaporized when the mold is fill with molten metal| Lost form consist of first making a foam pattern having the geometry of the desire finish metal| Expanded polystyrene casting use a mold or sand park around a polystyrene pattern that vapourizes when the molten metal is poured into the mold| Evaporating pattern casting (lost foam) : this process is also know as lost pattern casting under a trade name “full mold process”, it use a polystyrene pattern which evaporate upon contact with molten metal to form a cavity for the...
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