Sunday, February 21, 2010

Lost Foam Casting 2

This is actual number three or so, so the little block is already scarred by heat from a previous pour. I forgot to take a shot of it in virgin condition. The sand is quite fine and just damp enough to hold its shape when gripped while not adhering to the skin when released from the grip. The foam is buried in the sand in some fairly heat resistant container. A flower pot here. A good polystyrene adhesive is advisable, but tape will work, just make sure that all the bits of your foam original stay up together. The sand has to be compressed tightly, first by pinching and pressing it with the fingers and then tamping down with some hard object like the handle of a hammer. Leave the top of the polystyrene L and if you can, make a little hole in the sand down to the high spot on the foam shape to let the gas escape more easily. It is easy enough to hold a stick or something in place for the last bit of sand placement and then tamp round it and pull it out at the end. Try to make a little divot in the sand around the top of the L to make it easier to hit with the stream of molten copper. Don't leave stray lumps of sand about, they will be dragged in with the molten metal and make the casting even worse.