Had my first experience with runaway exotherm

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#1

Was trying to degas epoxy so I placed it in a microwave to heat it up, degassed it and the whole bit but when I started infusing I was holding the tube and noticed it was getting pretty hot, but then it just kept getting hotter and hotter and before I knew it the cup was smoking. Quickly threw it in my pressure pot and put away.

Long story short the infusion was ruined and I learned not to microwave epoxy directly the hard way! Cool experience though seeing resin that usually cures in two days cure in less than 10 minutes.

#2

+1 moron… :slight_smile:

Do you have a vacuum pump that draws a deep vacuum? If so, toss the mixed epoxy in your pressure pot, and pull a vacuum. This will degass the resin. You can add a scotchbrite in the mixed epoxy (just a cutoff piece) to aid in degassing. No heat, no smoke.

#3

Is it really working this trick with scotchbrite? I have never tested it.Does it need to sink in the bottom?

#4

The vacuum pump available doesn’t draw that deep of a vacuum, maybe 26 in Hg. Next time I’ll bring a container and warm water up instead of epoxy directly

#5

When I see people degassing they say they let it sit for 1/2hr. Doesn’t this cramp the working time of an already “rushed” process or are the people degassing using a really slow hardener? The epoxy I was looking at using only has a 25min pot life at 80F to start with. :confused2:

I thought ~30 inHg was the max you could ever pull. 26 seems like allot. Did I miss something?

#6

When I’m degassing epoxy I find you only need 5 to 7 minutes at 29 to 30 in Hg. At 26 in Hg no bubbling at all occurs.

#7

We haven’t experienced problems with microwaving epoxy in general, but like any process, it needs to be debugged a bit, and it doesn’t take much time to make it run away. We have used it for non-structural small infusions or occassionally for a quick hand layup.

#8

26 isn’t much at all compared to what people here regularly pull. 30 is the max so I’m 4 inches of hg off the vacuum possible and I’m near sea level too. Barely any bubbling occurs for me which is why I hoped heating it up would help and it did except I heated it too much!

#9

You will need to go as low as 98% or preferably better vacuum for a decent degas. A scotchbrite definately helps It provides a surfoace on which gas can form. One other thing that helps is running air through the mixture. A local university once ran some experiments. (unfortunately the text is in Dutch)

#10

You mean the sparging method ;)? I’ve read about it, it seems cool! Never tried it though…

#11

that’s kinda funny. sorry you lost your infusion lay up though.

remember not to store or heat epoxy or lay ups in ovens you plan to cook food in or store food in a refrigerator you store resin or chemicals inside of.

on a different note: I am learning to try and keep your epoxy stored at room temp ( 70f to 78f) and mix it at that temperature also, or the mfg’s recomended temp. It has been kinda cold here at our shop and epoxy gets very viscous and traps air much more easily.

For epoxy: if you heat the resin ( part A) before mixing in the hardener the resin will flow more easily and trap less air. Experiment and see what works best. Keep in mind even heating the resin will shorten pot life. I was using a heated bowl of water to set the resin cup into… but my concern now is moisture and void content in the laminate, by using water to heat with. I am considering using a heat lamp on low setting to preheat the resin side.

Will degassing in a vacuum chamber raise the temperature of the epoxy any?

#12

A hair dryer on low setting (like you use for warming pre-preg in a lay up is sufficient at warming resin to release bubbles I have found. Quick, not messy and little risk of exotherm occuring unless you are using a fast hardener.

#13

No worries, in retrospect it was pretty cool to see a really thin liquid heat up and suddenly solidify. Didn’t care much for the fumes though. And I only lost half my infusion to boot, since I was infusing panels I cut the dry side off and was left with a good panel!

#14

Epoxy does not heat up much when degassing using vacuum. But keep in mind that vacuum is the best insulator, so you ARE placing a reacting liquid (epoxy + hardener) in a very well isolated environment.

Most resins I use are in the range of 3-10 hours cure time, so no worries about that.

#15

Just to throw it out there I don’t know what the pros use to heat their resin. I was watching “How it’s Made” on Discovery awhile ago, just don’t remember what they were making. :o But I do remember they had about a gallon or 2 of resin they needed to keep hot, and to keep it hot it looked like they used a deep fryer. I have this Presto model http://www.sears.com/shc/s/p_10153_12605_SPM681250501P?sid=IDx20101019x00001a&ci_src=14110944&ci_sku=SPM588975801 and it looks similar to the one they used. This fryer seems like it would be real easy to thread a fitting/nipple onto the bottom of the fryer to make dispensing a breeze. The bottom is just a stamped piece of steel with no insulation. I’m just not sure how dangerous this would be? What do the pros use?

#16

You can always make a pot/small oven with heating elements and a controller. Even if you need to heat the resin as you infuse it you can install heaters ON the infusion tube. ALWAYS follow manufactures recommendations. I had one resin that was molasses at RT, and had to heat it to 140f just to infuse. Was NOT fun. But I would heat it, mix it, heat it again at 120f, degass, heat again and infuse with the resin and part in the oven. But even at 140f, the gel time they said was I think 6 hours!!! Hope I don’t have to use that stuff again.

#17

This might be a stupid question. :o But how do you infuse in the oven? You don’t stand in there at 120 F do you? :nuts: hot hot hot!
Or does the resin intake tube just run outside of the oven?

Also how do you install heaters on the tube? Would this work? http://www.mcmaster.com/#heat-tape/=b8vqwt

#18

You can use inline heaters, ITW Binks has nice ones.