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General control line discussion => Open Forum => Topic started by: Gary Dowler on August 29, 2019, 12:38:41 AM
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Ok, got an email from a fellow modeler today. He commented on an interesting occurance. I don't have anything more than the contents of the email, but it's an interesting chemical imcompatibility regarding things most of us have on the bench right now.
I would be curious to hear if anyone has encountered this before. Email contents below
"An odd thing happened today while working on my -84. I had mixed up a little 5-minute epoxy for something, and I had wiped a tiny bit of parts A & B from the tips of those bottles before putting the caps back on them. This was on the same piece of tissue.
Later, I used a tiny jeweler's screwdriver to dab thin CA glue on some loose details which might have vibrated off. I picked up the same wadded tissue to wipe the residual CA glue off the screwdriver. When the glue touched one of the epoxy spots, it went instantly to around 200°F. I yelped and tossed everything! So, can we all agree this was exothermic, then?😉 Ya never know!"
Gary
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Epoxies are exothermic. In small batches, the heat generated dissipates such that little heat is retained. Large batches seem to retain the heat generated, which causes an even faster reaction. Large batches "kick-off" suddenly, with attending rise in temp.
Never heard of any small batches actually hot enough to burn!
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more likely the CA reaction with tissue - nothing to do with the epoxy.
even on balsa you can get smoke with CA as it kicks off.
want to see how hot CA gets - put some on your finger - then spray kicker on it....its get HOT and FAST....ask me how I know n~
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Remember when first come out? It wasn't called "Hot Stuff" for nothing! I stil have a logo in my shop that says, "Control Line flying is HOT STUFF"!
Joe
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I'd say that Wynn is right. Not much fun, but right.
I once worked with a young guy that had previously worked for Livingston Boat Mfg. in Auburn. Seems they had a 55 gallon drum of polyester resin that was expired, and his boss told him to get rid of it. He popped the lid off and stirred in a pint or so of MEK Peroxide, aka the hardener. It caught on fire and things went downhill from there. y1 Steve
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Conducted my own little experiment today
While I am at a loss to understand what happened in this case, it did prompt me to conduct a quick experiment.
Using a piece of scrap ply and my infrared thermometer , I noted the following.
All starting temps were ambient temp of 70.0 deg
With thick CA, roughly 1/4" dia puddle, I applied accelerator. Heat increased to 97.5 deg F in 15 sec.
With thin CA, roughly same 1/4" spot, when accelerator was applied, temp shot to 125 deg F in 5 sec, but rose no higher.
Much greater and more rapid increase.
With thin CA dropped into a small puddle of hardener from 5 min epoxy, temp only rose to 71 deg in 15 sec.
Exothermic reaction with accelerator was much more pronounced with thin CA than with thick but in this case the heat generation was sudden, but not excessive. Essentially no heat generated by contact with hardener from 5 min epoxy.
No test done without accelerator.
Gary
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The kicker is sometimes a sort of 'liquid aromatic Freon" that I remember reading on the label once. Would have to check again. It may have a cooling affect. I think it would get totter by whicking along the fibers of the tissue, not much material like the plywood to absorb the heat. His finger got the full brunt of it. Run your IR test again with two pieces of tissue layered together but not touching anything and see what you get.
Type at you later,
Dan McEntee
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Have you ever gotten a drop on CA on your pants? I have and it got so hot I thought is going to raise a blister on my leg.
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Have you ever gotten a drop on CA on your pants? I have and it got so hot I thought is going to raise a blister on my leg.
Take a cotton ball, and drop a big dollop of thin CA on it. Do it on a non-flammable and disposable surface.
Brett