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Working with Kevlar?

Posted by SeanP 
SeanP
Sean Lane
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Working with Kevlar?
June 09, 2013 10:55PM
My car has a kevlar skid on the gas tank. There are a couple of areas that have gotten worn thin and I would like to undertake a repair/patch.

Does anybody have a link to working with Kevlar? Is it fundamentally the same as working with Fiberglass?

Sean
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Re: Working with Kevlar?
June 09, 2013 10:59PM
Robert might know (rallymech) I know he just made a Kevlar skid plate for a tank.
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Re: Working with Kevlar?
June 10, 2013 12:36AM
Working with kevlar is very similar to fiberglass. You have to use epoxy instead of polyester resin. The Kevlar is a pain in the ass to cut because it is so slipery. The guys at the store showed me how to put a strip of masking tape on the cloth and cut through it.

I just covered a fuel tank. Two layers on the bottom and three on the leading edge. It feels strong and didn't add mutch weight. I would have preferred to use an aluminum skid plate but there was no good way to mount it.



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Robert Culbertson
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Re: Working with Kevlar?
June 10, 2013 12:56AM
Works just like fiberglass, and as Robert said "use epoxy instead of polyester resin." I also really like the tape trick, I'll have to try that on an upcoming project.
If you are new to fiberglass/composites, look at some boat repair how-to's on the interlinks. They should have some tricks that could be helpful.
How big are the holes/patches? How thick is the skidplate in those areas?
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SeanP
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Re: Working with Kevlar?
June 10, 2013 01:26AM
The skid is about 3/16s to 1/4" thick by my estimation. The tears aren't all the way through, but up to 1.5-2" long and .5" wide. My plan would be to lay some Kevlar on the inside of the skid in the areas that are getting worn. I would assume it's as easy as cleaning the existing kevlar, brushing the epoxy resin on the area, lay in the kevlar and brush my epoxy over the top and let dry. Wash, rinse, repeat.

Thanks for the help!
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Re: Working with Kevlar?
June 10, 2013 10:43AM
Quote
SeanP
The skid is about 3/16s to 1/4" thick by my estimation. The tears aren't all the way through, but up to 1.5-2" long and .5" wide. My plan would be to lay some Kevlar on the inside of the skid in the areas that are getting worn. I would assume it's as easy as cleaning the existing kevlar, brushing the epoxy resin on the area, lay in the kevlar and brush my epoxy over the top and let dry. Wash, rinse, repeat.
Thanks for the help!
I've done some working with composites in a completely different application. So, fwiw...

Clean the area first and make sure it is completely dry
Scuff up the area to be repaired and clean off any 'dust'
Probably best to clean with something that will cut any oils or grease and let dry.
lay in epoxy
lay down 1 ply of kevlar
lay in epoxy
lay down another ply of kevlar at 45deg offset to the first (you probably want the outside most layer to be at 45 deg to the direction of travel)
Do all of this in one 'lay-up' NOT in repeated set-up, cure, set-up again steps.
Use quality resin
if possible, cure in a vacuum bag for best results.* (under vacuum, of course)
Make sure your kevlar is completely sealed. It will soak-up water/humidity that will lead to delamination fairly quickly (moreso with freeze/thaw cycles, but not good nonetheless)

*Under vacuum you can use a very small amount of resin and still have some squeased out of the actual area being laminated. More resin is not the same as more strength.



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SeanP
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Re: Working with Kevlar?
June 10, 2013 11:31AM
Thanks, Morrison.
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Re: Working with Kevlar?
June 10, 2013 11:41AM
Ask Dave Kern. He spends more time doing that than anything else on his race cars. smiling smiley



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Re: Working with Kevlar?
June 10, 2013 12:11PM
Quote
SeanP
Thanks, Morrison.
No problem.
Caveat: That's all been from my experience, by all means weigh other thought opinions as well. My application was in R/C Gliders at a reasonably high level of spec. Strength and light weight were priorities.



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Edited 1 time(s). Last edit at 06/10/2013 12:11PM by Morison.
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Re: Working with Kevlar?
June 10, 2013 01:26PM
One thing I've always wondered, how well do people think Kevlar works for fuel tank protection? Does it disperse load or just prevent impacts? Thinking mostly about the BMW plastic fuel tanks and if Kevlar (or aluminum for that matter) will really prevent them from still breaking.



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SeanP
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Re: Working with Kevlar?
June 10, 2013 01:49PM
I am more concerned with puncture than big impacts.
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Re: Working with Kevlar?
June 10, 2013 02:38PM
Quote
SeanP
I am more concerned with puncture than big impacts.

I'm more concerned with blowing up or burning to death.



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Re: Working with Kevlar?
June 10, 2013 03:34PM
The one thing to be mindful of with the 'tape trick' is that the tape will never come off. If you have the luxury of making the piece oversized and trim it down later, its not much of a problem. But if you're the kind of person who sees blue painters tape laminated into the tank...just take the time to cut it as-is.

Also, pulling one thread like you do for carbon to help you cut a nice straight line will make cutting kevlar even harder as the threads will have an easier time running away from the cutting action of the scissors.

Dave
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Re: Working with Kevlar?
June 10, 2013 04:10PM
Another note, most of the epoxies for composites are measured by WEIGHT not volume.



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Re: Working with Kevlar?
June 10, 2013 04:16PM
Quote
Dazed_Driver
Another note, most of the epoxies for composites are measured by WEIGHT not volume.

Maybe the industrial stuff is different, but most are metered by using different amount of pumps. System Three is 2:1 and the stuff I got from USComposites in medium cure is 3:1. Both of those have you use the same volume pump in the resin and hardener bottles. West System comes with their own pumps and I think you always use a 1:1 ratio and the volume of the pumps is where the difference is made up.

Dave
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SeanP
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Re: Working with Kevlar?
June 10, 2013 04:24PM
Is the epoxy something to try to source locally or should I find an online/ebay vendor for it? Same for Kevlar. It looks like sheets of kevlar are on ebay.
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Re: Working with Kevlar?
June 10, 2013 04:34PM
Quote
SeanP
Is the epoxy something to try to source locally or should I find an online/ebay vendor for it? Same for Kevlar. It looks like sheets of kevlar are on ebay.

I've gotten stuff both locally and shipped. I think epoxy resin is ok to ship, but polyester resin isn't. I've used poly for building molds because its way cheaper, but for the actual parts, use epoxy.

Dave
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SeanP
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Re: Working with Kevlar?
June 10, 2013 04:46PM
If I wanted to make a mold of my existing tank skid to make a whole other skid, what should I use as a release layer? Basically coat/sheet the inside and then build up my layers of fabric.
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Re: Working with Kevlar?
June 10, 2013 04:51PM
Quote
SeanP
If I wanted to make a mold of my existing tank skid to make a whole other skid, what should I use as a release layer? Basically coat/sheet the inside and then build up my layers of fabric.

I wouldn't bother. Take a couple strips of material and run them up over the top of the tank and you'll ensure there's no way the existing one could ever come off.

When I converted the Evo over to a mostly tarmac car I wanted to remove the weight of the kevlar panels. I had to use a 3' long pry bar and hang off the bottom of the car to get it to separate...it was a bitch.

But, to answer your question about building a mold, you'd use wax, more wax, even more wax, and finally some PVA release agent. Then when the mold cures, you start prying up the corners and flood it with water. Then curse, bitch, stab fingers, scrape arms, etc to get the part off.

Dave
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SeanP
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Re: Working with Kevlar?
June 10, 2013 05:27PM
LOL. Thanks for the help, Dave. I am going to build a second Neon for the inevitability of the event that wreck this one (again). Would like to have another skid ready to go built from the existing.
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Re: Working with Kevlar?
June 10, 2013 05:31PM
Quote
SeanP
LOL. Thanks for the help, Dave. I am going to build a second Neon for the inevitability of the event that wreck this one (again). Would like to have another skid ready to go built from the existing.

From my experience with molds, I don't see it being worth the time or hassle. Since all you've got to do is cut up a few strips and lay them on the tank, it won't take much time to do a 2nd or 3rd.

Keep in mind too that the mold can't have any parts that would keep you from being able to remove the part from the mold (sorta hard to explain, but think of the compound curves) and your molded part will likely end up offering less coverage than doing it on the tank.

Dave
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Re: Working with Kevlar?
June 10, 2013 06:18PM
Best price on Kevlar and epoxy I got from Aircraft Spruce shipped.



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Re: Working with Kevlar?
June 10, 2013 06:30PM
I just placed an order from USComposites.com. Showed up in good condition and was pretty quick. I have ordered some stuff from Aircraft Spruce, but I think unless they're running a special, there are cheaper places out there.

I opted for the 38" wide kevlar because with the 50" there's extra cutting you always have to do...did I mention cutting kevlar sucks balls? Also, with kevlar you don't want the standard weave pattern as it doesn't drape all that well. I use a 5.0 oz cloth with a slightly different weave pattern.

http://www.plasticareinc.com/Merchant2/merchant.mvc?Screen=PROD&Store_Code=P&Product_Code=I5720&Category_Code=Specialty_Materials

Not sure how good/bad the epoxy will be from uscomposites, but I will probably get to work with it in the next week or so. It was ~$125 for a 2.5 gallon kit and I'd paid $180 for a 1.5 gallon System Three Silvertip kit last summer. Silvertip was recommended to me as great to work with...but its damn pricey. My next project doesn't need to look good at all (air tunnels for rear radiator), so figured I'd try out some cheaper stuff.

Dave
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Re: Working with Kevlar?
June 11, 2013 02:52PM
I got the blue tape to pull off just fine after the resin had tacked up a bit.



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