Patent ID: 6883580

Claim:
A method of lost foam casting comprising the steps of positioning a polymeric foam pattern corresponding in configuration to an article to be cast in a vessel, connecting a polymeric foam gating system to the pattern in the vessel, introducing a finely divided inert material into the vessel to surround the pattern and the gating system and to fill internal cavities in the pattern, positioning a pouring cup in the vessel, connecting said pouring cup with said gating system, pouring a molten metal into the pouring cup, the molten metal providing a molten metal front to decompose the gating system and pattern with the molten metal filling the void created by decomposition of the polymeric foam material and the products of decomposition passing into the interstices of the finely divided material, sealing the pressure vessel with the pouring cup retained within said vessel, wherein a pressure equalization member is positioned over the pouring cup and in contact with the inert material, applying an external super atmospheric pressure to the inert material in the vessel and to the molten metal in the pouring cup, equalizing the pressure gradient at the molten metal front, by forcing the applied pressure to travel through said inert material and said pressure equalization member before application to the molten metal, and maintaining said pressure on said inert material and said molten metal until the molten metal solidifies to produce a cast article corresponding in configuration to the pattern.