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How to keep larger amounts of mixed epoxy from heating up?

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How to keep larger amounts of mixed epoxy from heating up?

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Old 05-09-2004, 06:52 PM
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Rudeboy
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Default How to keep larger amounts of mixed epoxy from heating up?

When you start glassing or sheeting a wing or something, how do you prevent your epoxy from heating up when it's still in the mixing tub?

I could use very slow curing epoxy of course, but I like the speed of 30 minute epoxy... except for the fact that it starts heating up after about 15 minutes, and turns into a brick pretty fast...
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Old 05-09-2004, 07:13 PM
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Chris Moon
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Default RE: How to keep larger amounts of mixed epoxy from heating up?

You need to separate the batch of epoxy into several cups. The larger the mass of epoxy, the faster it will cure. Remember that epoxy is exothermic (gives off heat) and that heat is a catalyst that speeds up curing. When I used to lay up fuselages, I would try to mix the smallest amount possible - or separate the epoxy into 2 cups to prevent it from "kicking" too quickly.
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Old 05-09-2004, 08:14 PM
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Default RE: How to keep larger amounts of mixed epoxy from heating up?

I keep epoxy in a small office refrigerator. It slows it down somewhat, but by the time you get it layed up and bagged, (or whatever you do with it) it will have warmed up enough to cure normally.
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Old 05-09-2004, 08:27 PM
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ooooo
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Default RE: How to keep larger amounts of mixed epoxy from heating up?

Put your mixed exopy container on a tray of ice....or crush ice into a bowl and place your epoxy container on top. This slows down the hardening time. Works like a charm everytime.
If you are doing fiberglassing...mix some Isoprophyl Alcohol with the epoxy which thins it out, then use a telephone card or an old credit card to spread the epoxy. Use your heat gun to liquify the epoxy and spread it out thinner and smoother. The epoxy starts to harden in a few minutes because of the heat gun. Again....this works like a charm everytime..

I have a question for you........Isn't the building season over as yet? Hmmmmm[8D][8D]

Cheers.
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Old 05-09-2004, 08:57 PM
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Default RE: How to keep larger amounts of mixed epoxy from heating up?

I actually though about putting it on iced water... but I haven't tried it yet, as I thought it would get too thick to handle properly then... But I suppose if you start spreading it, it gets back to room temp pretty quick again... I may give that a go next time...

The epoxy I use is very watery as it comes... no need to thin it... work like charm for hinges and stuff... it seeps right into the hinge slots... so it's pretty thin...
For sheeting and glassing I use a foam paint roll, followed by a balsa "squeegee" (or whatever you call it)

Building season is NEVER over...
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Old 05-09-2004, 10:38 PM
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Default RE: How to keep larger amounts of mixed epoxy from heating up?

Yeah, chilling it does make it thicker. I use this technque mostly for sheeting foam cores, and I prefer it a little thicker. Thicker resin doesn't soak into the wood as fast. I used to thin with alcohol, but gave it up. It's not really necissary, and it weakens the epoxy.
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Old 05-10-2004, 06:34 AM
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Default RE: How to keep larger amounts of mixed epoxy from heating up?

Either mix it up on or pour it on a Styrofoam plate after mixing. it will not heat up as fast when it is in a thin layer.

Bill


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Old 05-10-2004, 07:39 AM
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Ben Diss
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Default RE: How to keep larger amounts of mixed epoxy from heating up?

Bill's got it right. Epoxy is exothermic. As it cures it makes heat. Heat makes it cure faster. Put the epoxy mix in a narrow cup and the heat stays in the mix causing a faster "kick". The fix is to stir it well then get it flat. A styrofoam plate works well. I use disposable paint trays from Home Depot.

-Ben
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Old 05-10-2004, 02:01 PM
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Default RE: How to keep larger amounts of mixed epoxy from heating up?

I use a roller for spreading the epoxy around on my layups, so I dump the epoxy in a roller tray after mixing in a cup. Keeping the epoxy spread out keeps it cooler.
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Old 05-14-2004, 09:29 AM
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Default RE: How to keep larger amounts of mixed epoxy from heating up?

dcairns,
Do you reuse your roller and tray's or do you through them out after every layup????
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Old 05-14-2004, 01:32 PM
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Default RE: How to keep larger amounts of mixed epoxy from heating up?

The tray can be reused, but the roller is a goner...
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Old 05-16-2004, 07:50 AM
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Default RE: How to keep larger amounts of mixed epoxy from heating up?

Whats the rush? Consider using aircraft grade West Systems epoxy. After you have the layup done, put it somewhere warm and it will cure pretty quick. Is the 30 min stuff even made as a finish resin? Also, strength is effected by cure time. Generaly speaking, the longer the cure, the stronger the matrix.
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Old 05-31-2004, 06:59 PM
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Default RE: How to keep larger amounts of mixed epoxy from heating up?

Not only is West superior strenghtwise, its also easier to work with. A slower epoxy has a lower viscosity. This allows for a neater layup, with less extra epoxy that just adds weight. It also soaks into the cloth easier. Also, use a filler such as milled fiberglass to thicken the epoxy. It can triple the strength. However, it will aslo speed up the cure.

William
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