|Apr 24, 2013, 01:13 PM|
North OC, Ca.
Joined Jun 2005
just an fyi-
water boils at room temp with enough vacuum.
The partial pressure of the water vapor within the lay-up can lead to bubbles in the right circumstance.
High performance resins typically absorb up to 4% moisture in the cured composite.
In a high humidity environment, if I had a concern, I would degass the base resin before and after adding the curing agent. Dry the fabric as well if concerned.
Another problem is that moisture can inhibit a cure or act as a plasticizer- both bad.
|Apr 26, 2013, 02:45 PM|
I have found the source of my skin adhesion problem and it had nothing to do with humidity.
I cut all my cores with a hot wire CNC machine. This is non contact cutting and the hot wire leaves a thin skin on the surface of the foam. The cores are coming out so good now that I have to do very little sanding of the surface before bagging. The minor skin adhesion problems started recently and I realised that it may have something to do with the way that I am preparing the cores.
We recently had a period of fairly high humidity and I fully sanded some cores and bagged them with a very dry layup. The skin adhesion was excellent and all subsequent efforts have produced good results.
So I think that puts that issue to bed. Thanks for the input from the guys working in really humid climates. It had me questioning whether I was on the right track and it turns out that I was wrong.
|Apr 26, 2013, 09:59 PM|
That's a good outcome Graham.
What do you mean by "non contact cutting"?
Did you post cure at all?
|Apr 27, 2013, 08:05 AM|
Don't heat cloth
Has was is call sizing
It is only good for about 1 year at best.
With out sizing you can not wet out the fibers. There is nothing you can do to fix this.
Delamination is the result.
You have to get a 10x and look at the type of delam.
If the epoxies cracks at the fiber it is wetting (sizing) fault.
If the epoxies cracks at the cloth to cloth interface it is a processing problem.
Humidity has no or little effect on composite processing
Effect layup of prepregs (cloth with epoxies frozen) only by handling or stick of the prepreg but age of prepreg is more important..
Curing of epoxies is a condensation reaction
The harding (cure) of the epoxies is buy chemical linking of short polymers into longer polymers.
This chemical linking releases water (condensation reaction).
Water must be removed that is why you use breathers and a vaccum to remove the condensation water as the epoxied cures.
|Apr 27, 2013, 08:34 AM|
Thanks M3 interesting read.
Epoxy releases water ??? When curing ??
So on a 50 foot resin infused boat...once infusion Is stopped where does the water go as it cures.
|May 01, 2013, 03:37 PM|
I dont post cure but I cure all my parts at about 45 Deg C for 8 to 10 hours.
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