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Old Jun 24, 2012, 06:14 AM
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geoffers0_0's Avatar
Bristol, UK
Joined Jun 2008
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Vac Bagging - how long to keep pressure on?

Hi

Noob- Just venturing into vac-bagging, and I have a simple question: How long is it neccessary to keep the pressure on when vacuum bagging fibreglass onto pre-shaped foam wing cores?

I appreciate that when making (for instance) skateboard decks from layers of rigid flat laminate, where you're bending it into a moulded shape it would be neccessary to keep the pressure on until the glues are fully cured to hold the laminate in the new shape.

However is this neccessary when pressing flexible glass to the shape of the wing? Presumably the vac-bagging here is more to squeeze excess resin out of the laminate and produce a uniform smooth surface.

Is it critical to keep the vacuum applied right through the final cure?

Thanks, G
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Old Jun 24, 2012, 06:44 AM
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United States, MD, Lutherville-Timonium
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Yes
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Old Jun 24, 2012, 11:00 AM
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Cody, WY
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The "final cure" can take up to 30 days (unless you use heat). Typically, it's only necessary to apply vacuum until the resin has set. The composite laminate at this point will take on a memory. The resin set point varies from resin to resin and is also dependent upon the temperature. Most resins will set within 12 hours. Some slow hardener combinations can take over 30 hours to set at 72*F. If you remove the Mylars at this set point the fabric pattern will print through to the part surface. You don't want to remove the Mylars until the resin has progressed much further in the cure (4 days at room temp - or use heat).
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Old Jun 26, 2012, 01:42 AM
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Melbourne, Australia
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Quote:
Originally Posted by wyowindworks View Post
... If you remove the Mylars at this set point the fabric pattern will print through to the part surface. You don't want to remove the Mylars until the resin has progressed much further in the cure (4 days at room temp - or use heat).
Do I understand this correctly, if we remove the mylar before about 4 days at room temp, the fg cloth pattern will print through to the surface? So we need to keep it under vacuum with the mylars on for at least 4 days (at room temp)?

I thought that once the resin had set ~24hrs then that was it and the mylars could come off and nothing would change except for the final 10% or so of hardening which could take days-weeks.
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Old Jun 26, 2012, 08:48 AM
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Cody, WY
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You only need to keep the vacuum on until the resin has set (12-30 hours). If you want the best surface finish you shouldn't take the Mylars off for several more days. Do a test. Peel half the mylar off after set and then peel the rest after 4 days. The surface finish difference will be quite obvious.
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Old Jul 12, 2012, 08:44 AM
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Australia
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Hmm... Thanks for that, I have always keen to get the mylars off after about 24 hours and was never 100% happy with end product. Will give it try.

Cheers,
.adrian
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