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Lost Foam,refractory coating,etc.
Posted by Xandor on October 12, 1999 at 19:57:49:
The smaller pieces have been quite simple to set up, without any gating to speak of: just the pouring cup sitting atop a foam runner. Although I thought it was weird the first time I did this and it worked, I have subsequently theorized that:
1. The foam nearly instantaneously evaporates, nearly amounting to the equivalent of a void.
I'm not certain what caused the kind of "scarring" I saw on my larger piece (a two-foot high torso), but I know I was pushing my luck. At this point I think I will try some sprues so that the metal enters the foam at a few places, and I would also like to use some kind of "permeable refractory shell" that I have seen references to. The latter seems to be a difficult puppy to locate, but I'm wondering if anyone has actually tried the alcohol/graphite mixture referred to in this forum. Also, am I mistaken about the gas escaping from the sand and should I actually be using vents? Some people here (San Diego State) think I should be using bonded sand (for safety?), but I think that would increase the venting difficulties. Also, might it be better to create a sprue so that the metal pours from BELOW the foam rather than pouring in from above?
Very interested in anyone's comments!