layup too cold, then too hot, ideal temp?

[rtbrowntrout]

Hi,

I've been pulling my hair out the last couple weeks. I live in NE Wisconsin and do my wing bagging in my basement, and this winter has been very cold. My basement is cold enough that I have to wear sweatpants to work down there. I'm having trouble with controlling temperature while wetting out the layup.

One wing half I didn't use any heater during layup, so the epoxy was pretty thick. As a consequence, the carbon/kevlar/glass didn't wet out well, and I used too much epoxy, so it came out heavy.

For the other wing half I got the bright idea of buying some overhead radiant heaters mounted above the bench. I started wetting out the layup and everything was going great. The epoxy was nice and thin and really penetrated well. Unfortunately, after about 20-30 minutes everything started to cure. It is safe to say the heaters were too close to the bench. I mixed up some additional epoxy to finish the layup and it is in the vacuum bag right now, but I'd be shocked if the wing half isn't a total loss.

I use the US Composites epoxy with the medium hardener. It says on the website that the pot life times are based on 80F. Does anyone recommend an ideal temperature range for wetting out the layup?

Thanks.

Ryan

[ozmo01]

I would put a thermometer on the bench and adjust your lamp height. I think above seventy but consistent or steady should work ok. Do you use TP to blot the excess epoxy?
( I can't believe I just asked a grown man if he uses TP :eek: )

[Batmanwpg]

Did you empty the mixed epoxy out onto a foam plate? If left in the mixing container (i.e. cup) it will exotherm (set-up quicker). Spread it out on a foam plate it stays a cooler and allows more working time. What did you use to spread the epoxy? Large areas should be done with a disposable foam roller to spread it quickly.

[David Forbes]

You really need a slower set epoxy for wing layup. Try their slow hardener next time. You're going to cure it in a hot box anyway, right? so you might as well have the extra time so you don't have to rush. Batmanwpg's suggestion of the foam plate is essential if you want the full working time. Localized heaters like you are using will keep the epoxy thin, 70 to 75 on the work surface should be good. I notice my cold weather wings are always a few grams heavier than hot weather ones.
Dave

[target]

I agree with David.
You want slow hardener for a longer layup like a wing.
You'll likely have to use a hot box or an electric blanket to cure it for a couple days in the vacuum bag to make sure it's done completely, but that should work better for you.
Even in California, the temp makes a difference, and you are usually better off with more working time in a warmer environment for a good result.

Target

[lincoln]

Radiant heat is probably not good because it causes hot spots. I think it's nice, as other people have mentioned, to use slow epoxy and temps 70 to 80. But be careful of the high end of that range because some epoxies will go off pretty fast. Don't mix too much at once either. 6 oz in a cup can turn into a smoking, stinking mess. (this was for a boat)

Some epoxies are thin enough to work with when pretty cold, and sometimes have some fast hardener that keeps up. I've used epoxy that would set in temperatures in the 40's, and you could apply it at those temps too, although it was a lot less fun that way. (This was Raka epoxy)

[rtbrowntrout]

Thank you for all all the responses.

ozmo01: Yeah, a thermometer on the bench is a good idea. I left this layup a little on the wet side since I wanted to err on the side of good bonding since I'm making a 'winchable' 2m wing (no TP).

Batmanwpg: Good point about the mixing cup. Yes, I poured the epoxy out on a paper plate. I think I cooked the stuff on the plate right along with the layup since they both got nice and stiff at the same time.

David Forbes/target: I'll get some of the slower curing hardener next time. I must not have a very 'hot' hot box, since even with the medium hardener I need the better part of a day to get a cure good enough to get the mylars off and no delaminations.

lincoln: I agree with you that I might be getting some hot spots. I was reluctant to use forced air heating for fear of controlling my fabrics before the epoxy is applied.

Since my first post I re-mounted the heaters much further away (near the basement ceiling). I'm also going to go buy a thermometer and run some experiments. I'll see if I can hit the 70 to 75F range on the bench surface.

I have also taken the wing out of the bag, and it actually looks a lot better than I expected. The biggest issue is that I don't have a good bond to the foam in certain areas (no big suprise). I'll either repair it or chalk it up as a learning experience.

Thanks again for the help.

Ryan

[target]

Hi, Ryan-

I usually leave my stuff in a vacuum bag and curing overnight at least, and usually over 24hrs for sure.
I think that you'll get better results curing-wise, if you take your time a bit more with slower hardener, for more working time, and the consequentially longer curing time.
Make certain that the cores are dust free! That help ensure a good bond.

Best of Luck!

Target

[szastoupil]

Dear Mr. Trout,

You should scrap those wings and build a new set for your favorite flying buddy.

Best Regards,
Scott

P.S. See you at work tomorrow.

[rtbrowntrout]

Hi Again,

I just ran a little experiment with some cheapo thermometers on the bench and my radiant heaters running. It is safe to say I had the bench WAY too hot (>100F). I'm feeling a little dumb at this point, but at least I have a handle on things now with all the advice.

SZastoupil,

I'll give the first set to you, so your cats can use them as scratching posts. :D

Thanks,

Ryan

[target]

I would shoot for @ 80-85*F; I think that with the slow hardener will be very workable for you.

Good luck!

Post a pic of the wing??

Target