By John Hovell - 4/18/2021 6:44:28 PM
Help please. I make model glider wings by vag bagging carbon onto foam cores. Whilst in general I am very pleased with the result I find that handling the wings leaves finger prints on the surface, even a week after making it. I use the EL2 laminating resin wing the slow hardener. The model is vac overnight at an elevated temp (Electric blanket). It is then stored at room temp. Can you advise how to avoid this please?
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By John Hovell - 4/29/2021 8:21:36 AM
+xThe slow resin takes a minimum of 30 hours at 20C to cure so you may just need more time if the temperature drops off. If the resin constantly stays with a bit of a tack/soft nature to it then I would look closely at your mixing and measuring as the El2 cures with a hard finish in normal use. You need to ideally be as accurate as you can with the mixing ratio and also you may need a reasonable batch size. Generally 1-2% accuracy is fine and a batch 50g or bigger should eliminate "small batch size" issues.
I warm the resin and hardener to mix but, as my workshop is probably at a max of 15°C at this time of the year, everything else will be cold. This includes the tools and materials. Hence the layup will be done with cold resin.
I bag wings at 800mPa. The bag is enclosed in the foam blanks and the whole stack weighted down with a board and piles of magazines. This is all wrapped in an old electric blanket and insulated with old sleeping bags. So, the resin is cold when I put it in the vac bag and will take quite a time to warm up, when it does, I guess it will exceed the 20°C you recommend.
My final issue is that I tend to leave it over night which is short of your 30hr.
Will you please comment on possible problems with my process and recommend improvements? Also do you have any technical data on the performance of the EL2 resin relating to temp and does holding it under a vac impact the curing time?
Thanks
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