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Old Dec 07, 2014, 01:46 PM
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Canada
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Questions about Liquid sheeting/styrospray

I have to make mutiparts so I'm thinking about building a plug out of blue styrofoam
then coating it with many coats of Liquid Sheeting / styrospray. My question is this going to be strong enuf for vacum forming. Or is the heat going to go through the sheeting and melt the foam?
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Old Dec 07, 2014, 02:37 PM
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Jim.Thompson's Avatar
Australia, NSW, Bellingen
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I would not use foam of any description if I was making a plug for vacuum forming of (presumably), styrene or similar plastic sheet.
My first choice would be some laminated MDF sheet. Or even a well seasoned lump of timber that has good carving properties.
Much depends upon the shape you have in mind. One of the above will be preferred over the other for certain shapes and vice versa.
If it is a simple symmetrical shape, the laminated MDF has certain advantages; the joins make for a good guide for symmetry. The MDF can be sealed and stabilised by applying 3 coats of epoxy resin; the first coat thinned a bit with alcohol. Sanding in between.
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Old Dec 07, 2014, 03:42 PM
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Can I ask why not? It's just easy to carve the blue styroform
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Old Dec 07, 2014, 03:46 PM
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I don't think it would be rigid enough. Also, I have doubts about the heat problem you mention.
Give it a go if you think it would work though. A small sample plug could be shaped quickly as a test piece.
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Old Dec 07, 2014, 06:18 PM
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You are vacu-forming plastic sheet over this plug? The question then is what is the vacu-forming temperature going to be? As I recall, the melt point of EPS (blue foam) is somewhere in the mid 200s*F range (googling will find the exact number), so if your working temp is below that you should be fine. I don't know what liquid sheeting/styrospray is, but you'd want to check the melting point of that too. As Jim said, easy enough to cob up a test piece and see what happens. It is possible that styrofoam and styrene sheet have very close melting points? I haven't done any vacu-forming, but I doubt the vacuum used is strong enough to crush blue foam.

Then again, if you're pulling a lot of parts off this plug, foam might not be the best choice....very easy to accidentally scratch or dent it. I have enough trouble keeping a a foam wing core pristine before I can get it into the vac. bag.

- Jim
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Last edited by JimZinVT; Dec 07, 2014 at 06:41 PM. Reason: terrible spelling!
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