Vertically parted molding machines, normally used for high-produc- tion runs, are automated and compact molding sand by squeezing.
in a one-piece flask, which is then placed onto a compaction or vibrating table. As the dry, unbonded sand is poured into the flask and pattern, the compaction and vibratory forces cause the sand to flow and densify. The sand flows around the pattern and into the internal passageways of the pattern. As the molten metal is poured into the mold, it replaces the
EPS pattern, which vaporizes. After the casting solidifies, the un- bonded sand is dumped out of the flask, leaving the casting with an attached gating system. With larger castings, the coated pattern is covered with a facing
of chemically bonded sand. The facing sand is then backed up with more chemically bonded sand. The lost foam process offers the following advantages:
• no casting size limitations; • improved casting surface finish due to the pattern’s refractory coating;
• no fins around coreprints or parting lines; • in most cases, no separate cores are needed; • excellent dimensional tolerances. V-Process—In the V-Process, the cope and drag halves of the
mold are formed separately by heating a thin plastic film to its deformation point. The mold is then vacuum-formed over a pat- tern on a hollow carrier plate. The process uses dry, free-flowing, unbonded sand to fill the
special flask set over the film-coated pattern. Slight vibration com- pacts the fine grain sand to its maximum bulk density. The flask is then covered with a second plastic sheet. The vacuum is drawn on the flask, and the sand between the two sheets becomes rigid. The cope and drag then are assembled to form a plastic-lined
mold cavity. Sand hardness is maintained by holding the vacuum within the mold halves at 300-600 mm/Hg. As molten metal is poured into the mold, the plastic film melts and is replaced im- mediately by the metal. After the metal solidifies and cools, the vacuum is released and the sand falls away.
2010 Casting sourCe DireCtory Metal Casting Design & PurChasing 9
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