Lost foam process

The lost foam process uses a polystyrene foam having the same shape as

that of the object to be cast. In normal sand casting, molten aluminum is

poured into a cavity formed with bonded sand. In the lost foam process, the

foam pattern made of polystyrene is embedded into unbonded sand. During

pouring, the polystyrene foam pattern left in the sand is decomposed by

molten metal. The casting traces the polystyrene shape.

The foam pattern must be produced for every casting made. This process

starts with the pre-expansion of polystyrene beads, which contain pentane as a blowing agent. The pre-expanded beads are blown into a mold to form pattern sections. A steam cycle causes the beads to fully expand and fuse together in the mold. After cooling, the molded foam sections are assembled with glue, forming a cluster. The gating system (the passage liquid metal flows through) is also attached in a similar manner. Next the foam cluster is covered with a ceramic coating. The coating forms a barrier so that the molten metal does not penetrate or cause sand erosion during pouring. The coating also helps protect the structural integrity of the casting. After the coating dries, the cluster is placed into a flask and backed up with sand. Mold compaction is then achieved by using a vibration table to ensure uniform and proper compaction. Once this procedure is complete, the cluster is packed in the flask and the mold is ready to be poured. The molten metal replaces the foam, precisely duplicating all of the features of the pattern.

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