I cut a piece of Expanded Polystyrene off a larger piece that came with my new 8 inch bench grinder. I thought I'd just give it a go as a "lost" pattern.
With the cope and drag together I rammed a 3/4" layer of moulding sand in the bottom and smoothed it off reasonably flat by tapping down on it with a flat block of wood. I then placed the EPS piece on the hard sand. I then held my sprue former stick on the EPS.
Here I have finished ramming (not too hard).
Sprue former removed, you can see the pattern at the bottom of the sprue hole.
Then I remembered, "sheesh that pattern had a hollow in the bottom", so I tipped the lot over and poked the sand in and proceeded to ram the sand in then levelled it off. Remember this was just a quick test of the procedure (sort of) of lost foam type casting.
Ok, here it is poured, everything still hot, very hot. You can see that my Experimental A furnace is still going strong, this was the 12 th melt in this furnace. When I poured I thought there would be clouds of black smoke or similar from the burning of the foam, but no there wasn't any thing much at all come out when I poured the molten metal in.
Here's the casting. That bad bit on the right hand edge near the front was where I knocked a bit of the EPS off when I was ramming the mould. The as cast surface was a bit rougher than my sand usually gives so I suspect from the sort of bubbly look of the finish that the boiling or burning away of the EPS was to blame. Maybe I should have had a decent sized outlet hole in the mould for the gases to escape more easily. At least now the lost foam type of casting procedure has lost a little of it's mystery to me.
The hollow underneath.
Here's the casting after about 15 minutes at the belt sander. It's come up quite reasonable, NOW what can I use it for, hummm.
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