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Old Oct 29, 2007, 08:56 PM
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Ed Waldrep's Avatar
Las Vegas, NV
Joined Dec 1996
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Vacuum forming over high density urethane foam-safe or toxic gas release?

I was given a chunk of high density urethane foam, greenish grey in color, really dense, by a guy with a cnc machine. He said he used to vacuum form parts over it and that it didn't deform from the high temperatures. I've read various times over the years that you can't hot wire this stuff because it releases toxic gases (cyanide?) when heated or burned. I'm wondering if this stuff will release harmfull gases at vacuum forming temperatures (I assume no higher than say 400 degrees).

Anyone?

Wanting to vacuum form a canopy for my scratchbuilt F/A-22 over in the edf forum and don't have time to carve a plug out of balsa or jellutong.
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Old Nov 07, 2007, 04:29 PM
DLD
David Layne
Tracy, Ca
Joined Jun 2004
665 Posts
With most foam, some sort of toxic gas is released when it is heated to melting temperatures. If kept below melting, the problem should minimized. I can't say that I have specific experience with vacuum forming over urethane foam, but if you do the job in a well ventilated area, it shouldn't be a problem. The worst thing that could happen would be your plug melting, and you'd have to re-carve it.

You might try something a friend of mine used to do. He carved a canopy plug undersize from foam. then he would apply plaster of paris to it, shape it, apply epoxy to the surface, let it saok in, then wipe off the excess. He would apply epoxy this way several times, and it would develop a very smooth finish. Vacuum forming could be done right over it. It worked well, and the plaster of paris is easy to work. Just a suggestion.

DLD
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Old Nov 07, 2007, 09:50 PM
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Troy's Avatar
United States, CA, Lake Forest
Joined Feb 1999
6,004 Posts
There aren't too many Poly-U foams that can do over 300F but since it is seeing only a flash of heat rather than a soak in heat it may survive just long enough. If he says it worked for him without deformation than maybe it is good enough. If you were going to do many parts I'd say don't do it because the heat would build as more parts were made from it. If it works and the master suvives, you could make a casting out of one of the lexan parts and go from there.
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