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Old Feb 23, 2013, 03:08 PM
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Knoll53's Avatar
United States, CA, Marina
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Hot Epoxy

It's a good thing....Right !

Warm epoxy will flow nicely where cold epoxy is just too sticky and thick to fully wet out the glass. Even more useful when using a device like a tow wetter. But warm does not mean hot.

This morning I was trying out a new tow wetter and recognized that things would be easier if the cold epoxy was a little thinner. Sooooooo, I mixed up a cup of epoxy and put the heat gun to it and stirred until it was runny like maple syrup. Only took a minute on the low setting. Certainly not hot enough to melt or even deform the plastic cup. About 1/2" of epoxy in the bottom of the cup.

Then I got to drawing out the wetted CF tow and draping it on the model. Maybe 5 minutes later the epoxy started foaming and hissing and went off like volcano. It was "insta-cure" epoxy. This is what you don't want. Sound familiar?

2nd batch was with cold epoxy and the wetter worked just as well.

Tow Wetter 2 (0 min 0 sec)



Kent
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Last edited by Knoll53; Feb 23, 2013 at 03:24 PM.
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Old Feb 23, 2013, 04:31 PM
Deniable plausibility
Shedofdread's Avatar
Derbyshire, UK
Joined Aug 2008
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Kent,

I think at one time or another, we've all been introduced to Mr X. O'Therm.... Most annoying when he comes to visit, eh?

Hope you're well and regards from snowy Derbyshire
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Old Feb 23, 2013, 05:00 PM
Live and let Fly !
Lawrence B's Avatar
Mill Hill - London
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A long time ago, making boat hulls with polyestor resin i managed to have a small bucket of the stuff smoking thru excess exotherm ... without any external heat !!

LB
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Old Feb 23, 2013, 10:13 PM
I am actually really slow
SlowBarless's Avatar
Brisbane
Joined Jun 2008
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Heat gun is to hot, a hot box at 40deg works wonders. I know a guy that used to put resin in the microwave for a couple seconds just to 'kick it off a bit'

Till this day, I am yet to try it. I think its something you do after a couple of beers
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Old Feb 24, 2013, 06:48 AM
chetosmachine's Avatar
Madrid, Spain
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Use slower hardener and you can heat the epoxy.
You can also heat only the resin, not the mix. This prevents a bit the exothermic, but it's not magic, it will increase temperature and exo will happen.
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Old Feb 24, 2013, 09:04 AM
Registered User
Cleveland Cuyahoga, Ohio, United States
Joined Dec 2000
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Heat the resin and hardner bottles in a bucket with hot water from the tap.
15 mins from 55 F get to 80-85 degrees, then mix.
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Old Feb 24, 2013, 03:39 PM
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Vancouver, Canada
Joined Jan 2008
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Yeah, use hot tap water.

Be very careful with a heat gun and epoxy, inhaling the vapour produced can have serious health effects.


T.D.
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Old Mar 04, 2013, 06:34 PM
Composites guy
North OC, Ca.
Joined Jun 2005
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Also, heat the tow.
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Old Mar 04, 2013, 07:08 PM
Entropy is happening!
Jim.Thompson's Avatar
Bellingen NSW Australia
Joined Aug 2008
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Different resins behave differently to each other as well. Some of the better quality low viscosity resins don't need heating to start with, and when/if they are heated, don't exotherm as much and as readily as the cheaper inferior products.
Bit of a catch 22 actually!
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Old Mar 05, 2013, 11:40 AM
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Mixing epoxy in larger batches confines the heat energy from the exotherm and amplifies things. Spreading it thinner or using larger, shallower containers helps slow it down if that's your goal.

I had a quart of West Systems heat up and solidify so fast one time that I dropped the container while I was still mixing it! Most of us have had a bad day due to "premature" exotherm.

Be careful warming stuff to make it flow more easily though. Obviously you shorten the cure time but you could also significantly reduce the physical properties of the finished product when you accelerate the initial cure with heat.

I like to heat up a scrap piece of marble countertop by running it under hot water while I'm mixing the epoxy. When the epoxy is mixed, I pour some of it on the marble and it gets more flowable but still has a large enough surface area to avoid the "flash" cure. The marble is a nice place to pick up epoxy for the roller as well.
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Old Mar 05, 2013, 11:53 AM
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Knoll53's Avatar
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Quote:
Originally Posted by tom43004 View Post
Obviously you shorten the cure time but you could also significantly reduce the physical properties of the finished product when you accelerate the initial cure with heat.
I did not know this. Curing concrete has similar problems when it is allowed to dry out too quickly especially right after initial set.

I'm thinking of warming the resin to 80F as a matter of standard practice. Do you have any data showing strength vs initial heating?

Thanks,
Kent
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Old Mar 05, 2013, 12:02 PM
Father of Fr3aK, DLG Pilot
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It varies by epoxy Kent. Most of the manufacturers will post a datasheet online.

Here's an interesting full scale link:

http://www.cozybuilders.org/Oshkosh_...oxyDoDonts.pdf

and a datasheet on one particular brand:

http://www.mgs-online.com/en/techinfo/pdf/01mgs037.pdf
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Old Mar 05, 2013, 12:27 PM
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Knoll53's Avatar
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Thanks Tom. Just the tip of the iceberg for info. on epoxy, I'm sure.

Attached is possibly an easier to download version of the Do and Don'ts Tom just posted.
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Old Mar 13, 2013, 12:53 AM
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New Zealand
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+1 on the warm water bath - keeps the epoxy warm, but stops it overheating too.
standard practice in the boatbuilding industry.
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