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A MOLD QUESTION

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Old 11-08-2004, 10:43 AM
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TOMMYSTA
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Default A MOLD QUESTION

Hi guys
After creating a mold from a plug how long should I let the mold sit before I
attempt to pull parts from?
Thanks
Tom
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Old 11-08-2004, 01:00 PM
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buttuh
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Default RE: A MOLD QUESTION

The longer the better. I normally wait a couple of days depending on the weather. You should refer to your resin spec sheet and see what the full cure time is. Generally you don't want to pop the mold out before it's fully cured.
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Old 11-15-2004, 09:02 AM
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J roc
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Default RE: A MOLD QUESTION

You want the part to be as stiff as possible, If you try to separate when not 100% cured you might end up with a big mess on your hands. Also, parts are harder to separate from mold when not cured.
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Old 11-16-2004, 12:06 AM
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Default RE: A MOLD QUESTION

Just to add another opinion...

Mine is the same as above. Longer is better. It's tempting to believe what's on the epoxy label, and try and pull the part after one day, but if you can contain your excitement, it's better to wait at least a couple of days, to be sure the epoxy is hard. No harm will come from letting it sit even longer.

And...
The same goes for all parts you make in the mold.
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Old 11-16-2004, 09:30 AM
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Default RE: A MOLD QUESTION

Any epoxy manufacturer worth their salt will tell you that room temp epoxies take approximately a week to fully cure at 77F ( 25C ).

Full cure can be reached sooner using an appropriate post-cure. See the epoxy manufacturer for details.

So, yes, the longer you leave the plug (or part) in the mold, the better.

good luck,
-David
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Old 11-18-2004, 11:00 PM
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Default RE: A MOLD QUESTION

Well, I use all polyesters. Polyester gel coat and general purpose polyester resin just likey they use in the boating industry. I think the long term exposure hazards are lower and I want to be in this a long time, so exposure is a big deal to me. Anyway. I pop the molds the next day and if I mixed my curative right I can mold a part on that mold the very next day as well. You have to be careful not to under or over catalyze. I've also seen them do it in the boating industry the same way many times.

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Old 11-18-2004, 11:46 PM
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Mike James
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Default RE: A MOLD QUESTION

Those of us who have done this a lot know that both polyesters and epoxies continue to cure (and shrink) for a while. (certainly longer than the"rated" cure times for most products, and in some cases, for years. I know this from a (bad) personal experience with ployester over epoxy, a few years ago. The polyester did eventually cure... two years later. (Luckily, I kept the plug)

This might not be obvious to a new moldmaker, though. With most systems used in our hobby, you could probably pull most parts from molds "the next day". If you were new to this, you might think they're "done". But leave something like a fiberglass fuselage hanging around the shop for a few weeks, and note how much firmer it becomes. The same goes for pulling a plug from a mold. You might be able to pull the plug "the next day", but if you can contain yourself, that's why it's safer and smarter to wait.
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Old 11-19-2004, 10:45 AM
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Default RE: A MOLD QUESTION

I have found that sometimes the flexibility of a very green part helps protect it when pulling it out of the mold. I frequently "pop" the mold hours after lay-up, but then let it sit loose in the mold while it fully hardens. In fact, some very intricate parts have never popped without damage if I let them completely harden. Am I doing something wrong?

Also, has anyone tried drilling holes in large molds and popping with compressed air? I know the big boat builders are doing this............

CJ
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Old 11-19-2004, 11:13 AM
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Default RE: A MOLD QUESTION

CJ,

what type of damages are you referring to? I for one would rather fix minor damages then pull the mold off to soon. Nicks and scratches I can fix, warp and shrinkage I cannot. I have not used polyester based resin for a while and I'd rather go broke buying epoxy before I go back. Polyester just shrinks way too much, even the ISO tooling grade polyester. And the smell... ugh.
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Old 11-19-2004, 04:17 PM
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Default RE: A MOLD QUESTION

Are you using wet layup or prepreg? I make aircraft interior parts from fiberglass and carbon fiber and we run tools up to 3 times a day. If you are oven curing you can pull the parts as soon as they cool. When we make tooling we wet layup the tool and we will postcure the tool for about 3 hours stepping the temp up every 45 minutes. As soon as the tool cools we prep it for part production.
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