The pattern is made from molded polystyrene foam. The final foam pattern is approximately 97.5% air and 2.5% polystyrene.
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The foam is coated with ceramic refractory by dipping, brushing, spraying, or flow coating. The coating process creates a barrier between the smooth foam surface and the coarse sand surface, which also controls permeability and allows the gas created by the vaporized foam pattern to escape through the coating into the sand. The coating forms a shell so that the molten metal does not penetrate and avoid sand erosion during pouring.
After the ceramic coating dries, the cluster is placed into a flask and baked up with un-bonded green sand. The green sand is then compacted by using a vibration table until it is ready to be poured.
After the sand mould compacted, molten metal is poured into the gating system, in which foam pattern vaporizes and is replaced by metal. Air vents in the side of the flask allow vapor to immediately escape. Pouring will continue until the mold is filled and extreme care is taken to ensure that the correct amount of molten material is poured.
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Once the mold has been filled, it is left in sandpit, waiting for the molten material to solidify. Once solidification has taken place, the sand and shell mold are shaken off, and gating system is removed, leaving behind the final lost foam casting parts or products. A cutting process is necessary to separate the castings.
The final lost foam casting parts can then also be heat treated or undergo other finishing operations, which includes cutting away the gates, risers, and runners, sand-blasting or grinding the metal to the required degree of smoothness, and other necessary machining processes.
I would if I believed there was a small chance it would work. But to me, it won't, for all the reasons we already cited, including bad sand low compaction, and now with wallboard compound, exceeding refractory melt temp. Plus this one: when molten aluminum hits foam at what, 1500F? the reaction is fast. Raise that a thousand degrees, and it's explosive. I think the beaded foam and Satanite of the sprue blew up internally, and they were only 3-1/2" sub-surface because the cup was 4" deep. Even with good compaction I think the pressure pulse in that area yields an expanding ball of sand, metal, refractory and gas. I don't think shallow compaction can hold it. Maybe if the pouring cup was 10" long before the metal hit foam, compaction would hold.
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