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The Secret World of Resins & Molds
GeneralFailure
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European Union
Joined: February 15, 2002
KitMaker: 2,289 posts
P47 Heaven: 0 posts
Posted: Sunday, February 17, 2002 - 04:03 AM UTC

Most of us have experimented with resins and molds. We know about the techniques. But some of the best kept secrets remain unexplored. It may be useful for all to share our own experiences.

I don't think there's a point in discussing the brands, since most are only available in specific markets. Other brands are "bottled" by small local chemist retailers under another brand name.

But the techniques may be interesting
1) How do you avoid bubbles?
2) Are there any shortcuts ? Easier products ?
3) What would be your special advise to newbies ?

I'll kick off with the first item.

1) bubbles.
VACUUM : A friend of mine created his own vacuum machine. He has a heavy-duty compressor hooked up to a steel box that was specially welded for this purpose. The top opens like a lid, hinging on one side. There's a rubber avoiding air getting in. A pressure meter controls the (lack of) air pressure inside.
I can only say one thing : it's wonderful. The vacuum sucks all air bubbles straigt out of the silicone / resin before it starts to cure. The result is NO bubbles. Casting results are flawless. There's a few drawbacks though: a serious vacuum-compressor costs a fortune. It takes a good plumber's instinct to hook it all up and fooling with vacuum is never without dangers.

OVERPRESSURE : A local chemist retailer explained to me that making molds and casts is also possible in a pressure cooker. the idea would be that pressure makes the bubbles so small that you won't find them in the end result. Has anyone tried this ???

ROOM PRESSURE : When I make molds and casts at home, I trie to do it under normal room conditions. Most bubbles can be avoided by vibrating the mold, or tapping on it to make air bubbles surface. Gently squeezing the mold while "fishing" for air bubble with a piece of stretched sprue also helps to avoid bubbles.
Only parts that are heavily under-cut or very thin/fine parts generally don't work that well.
Does anyone have other hints / clues ?

Thanks,

Jan
GunTruck
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California, United States
Joined: December 01, 2001
KitMaker: 5,885 posts
P47 Heaven: 0 posts
Posted: Monday, February 18, 2002 - 10:44 PM UTC
Jan - Great Post! Hopefully some really good ideas will come out along these lines...

I'm a Room Pressure kinda caster - only because I'm not as sophisticated as some others around here who do fantastic work. I haven't encountered a problem with bubbles, because I do spend some time tapping the container to force them out. I'd like to "graduate one day to a more advanced method...

Gunnie