CF cloth fraying

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#1

I started laying up some carbon fiber by hand on some structural parts. This is a prototype, so I’m using a 1/4" wood core. As a test, I bonded two layers of my CF cloth to a piece of 1/2" foam that is 4" X 12". I then put my full body weight on it to see if it was strong enough. It was, of course. Didn’t even flex.

So anyway, I keep running into fraying problems at the edges. I place the cloth on the part and start brushing in the resin, but the edges fray badly. It doesn’t affect strength, but it looks horrible. How do I keep it from happening?

I’m using 5.7OZ X 50" 4HS 3k 1ST GRADE “CUSTOM” Carbon cloth. Thanks!

#2

Here’s a photo of what I’m talking about. This is a cured part. This is after I cut off the edges overhanging the part (I had at least an inch of overhang on all sides) and sanded it with a belt sander to the proper profile. The surface is flat as a board- which makes the whole issue look like an optical illusion to the naked eye. When I put the cloth on the piece it was perfect, but as I worked in the resin, well, you see what happened. I didn’t even notice it until this morning…

My worry is that I have to now run a ribbon of reinforcement around the parameter of the part to cover the end (and hide the core). The strip will be about an inch wide, and I know it will fly apart once I cut it.

#3

are you bagging the part afterwards? little trick i found works nice with bagging is to over saturate the bottom layer and go much lighter on the top layers, allowing the resin to flow up from the bottom into the top layers. Lets you be much more gentle with the top layers. This only works if your core isn’t going to absorb too much of the resin because it could always just wick into the core leaving your outside layers without enough resin. also if the stack is too thick or you have things like uni in there it can trap the resin in the bottom.

also don’t brush, stab/poke/push the resin into the fabric with your brush. helps get it into the weave and will make less of a mess of the fabric than brushing it on as you are getting.

also taping the edges of the carbon, with masking tape or what ever you have lying around when you cut it will help stop the ends from fraying. So tape your cut lines, cut through the middle of the tape, then lay up leaving the tape in place. Sand/cut off the excess afterwards. Make sense?

Every situation is different, a little experimenting goes a long way but for the most sense just use a little thinking and don’t be intimidated by the fact that it’s carbon. Just cloth and a liquid (glue), it’ll do exactly what you expect it to, no real magic.

#4

Try using a roller as this will cause less disturbance at the edge of the fabric.
Regards Chris
www.carbonfibreworks.co.uk

#5

Spray glue the carbon to glass fabric. (dry)

Finish the edges with a braid rather than cut woven.

#6

You can impregnate cloth between a layer of waxed paper or release film and bagging material for a clean no frayed edge. But you would probably need to make some templates. If you are still working on an airfoil I would keenly suggest this as you can peel back the release once you’ve laid your ply. If it doesn’t want to stay down go over with a heat gun and the release film wil separate very easily as will waxed paper… But if you get the wax paper hot it will leave behind stuff you don’t want behind.

I use Cadillac brand films for exactly this purpose.

Inside female molds its much easier to spray tack and trim dry fabric. Make molds I prefer preinpregnating generally speaking.

#7

Some people like to also use blue masking tape as once resin hits it it loses its grip… generally. You can trim a straight line and then wet it out. And peel it back. This is 50/50 tho

#8

Thanks for all the ideas! I really appreciate it. Great ideas.

#9

3m masking film is an ideal product to sandwich carbon between when wetting out
it is VERY cheap a 4 ft wide by 180 ft long roll is less than $20

#10

Spray glue some fiberglass veil to the CF; it holds the ends in place when laying up dry, and adds little weight to the fabric. Other than doing this, I agree with pre-impregnating the cloth prior to layup.