I was reading a website where a guy was using a sand casting technique to make Al. parts. He would create the part in Styrofoam and then coat it with some drywall compound slurry, then buried it in sand within a larger box. From the pictures it looks like the molten Al. would replace the foam, I assume via burning it up, and the part was made.
What is this process called? Thanks
"Lost Foam Casting", I believe.
Be careful what you use for the slurry -- some things (like Plaster Of Paris) have too much water, and decompose at the aluminum temperatures, releasing steam, and perhaps generating dangerous geysers of molten metal.
Find the *right* materials to use, for safety, if no other reason.
Enjoy, DoN.
The lost foam casting is a version of the lost wax method which has another variation in lost plastic casting. One of the attempts with lost foam is the reduction of the amount of plastic that gets burned out of the mold. Wax and plastic need to be removed by heating before the metal is poured into the mold and the foam just reduces the amount of plastic that is used.
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Also, the foam doesn't have to be coated before casting. You can take the foam pattern (with a sprue), cover it with loose, dry sand, and pour. The molten aluminum pretty much "instantly" replaces the foam so that the sand never has a chance to collapse.
With lost wax, the wax pattern is used to make a mold by coating it with a shell and then melting out the wax, leaving the mold.
Yet another difference is that with lost wax, there can be a master mold which the wax pattern is cast from, allowing many, many copies. This can be done with foam, but not by the ordinary hobbiest. Commonly, lost-foam is one-shot - if it doesn't pour right the first time, you make a another pattern. Repeat as necessary.
Bob
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