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Old Jan 09, 2013, 07:27 PM
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how to spread a carbon fiber tow into a carbon fiber band

how to spread a carbon fiber tow into a carbon fiber band? I have now 12 K carbon fiber tow. And I want to use it as the spar for my DLG wing, it seems that it's difficult to spreading a carbon fiber tow into a carbon fiber band, is there some tool or skill for that ?
Thanks in advance.
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Old Jan 09, 2013, 07:43 PM
Pilot Mike
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United States, NM, Moriarty
Joined Oct 2009
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I'm not sure what you mean entirely because all 12K carbon I've seen is relatively wide and band shaped. If its bunching up to become more cylindrical and narrow try pressing it with a hard roller (rolling pin maybe?). I've gotten 3K carbon to become pretty wide by rolling it out but that was while I was wetting it out. I would think rolling would have the same effect when dry.

If the tow is already between .5 -1 inches wide then you're in good shape and I would use it as is. Another material to consider using as a spar would be carbon tube. It is whats done on the Neo DLG which can be seen in this thread http://www.rcgroups.com/forums/showthread.php?t=1607384
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Old Jan 09, 2013, 09:39 PM
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HI Oracle
Thanks for the tips.
Here is my 12k carbon tow

And the other pics show what I want....
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Old Jan 09, 2013, 09:58 PM
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Mark Drela used alcohol, with the fibres between two layers of mylar, and a hard roller to spread the tows in cloth out to close the weave. Once the spread is achieved, you can separate the mylars and let the alcohol evaporate. Something like that might work for spreading the tow.

You can spread them out with a hard roller when you wet them with epoxy during the lay-up, but that of course cuts into your working time.

This all assumes your tows aren't twisted, in which case it is hard to do get them to spread very uniformly.

Kevin
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Old Jan 10, 2013, 06:51 AM
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You could try passing the tow(must be flat,no twists) over a roller that has shallow opposing spirals cut into it.I have no idea if it will work with carbon tow,but this kind of thing is used in textiles.Scutching roller is the name.The idea is that the tow is fed through the centre where the spirals meet,as the grooves are moving away from each other they will spreads the fibres apart.Might be worth an experiment with a 2" or so piece of plastic pipe?
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Old Jan 10, 2013, 07:39 AM
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Have you considered buying some spread tow fabric and pulling the rovings from that? Would probably be easier and quicker.
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Old Jan 10, 2013, 10:42 AM
Aurora Builder
United States, MD, Lusby
Joined Nov 2003
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12K tow isn't really ideal for a wing spar. The tow's shown in the pictures above were sliced from wide rolls of 3.7-4.1oz uni-directional carbon or similar. These you can order from 2" wide on up and are very easy to handle. This is what is typically used for spars, or high modulus carbon in the same weight range, or solid carbon rods ~0.060" diameter.

I'm using 12K tow as a leading edge reinforcement. Its tough to get it to spread flat even when wet as it tends to have twists in it. I might give Drela's tip a try, otherwise I'm switching to Textreme tows which are spread flat for you (at a substantial cost vs. standard 12K).
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Old Jan 10, 2013, 11:48 AM
A witty saying proves nothing.
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Dr. Drela's post on spreading 12k tow:

http://www.rcgroups.com/forums/showp...2&postcount=34

I found Mark's thread on spreading out Kevlar cloth fibres:

http://www.rcgroups.com/forums/showthread.php?t=742234

Kevin
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Old Jan 10, 2013, 01:35 PM
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Combat Models used 12k tow as a spar or strap across there wings. It is some nice stuff it is webbed so it stays where you put it. They used about 5 straps 1/4 inch wide on top and bottom. It looks about 3 inches wide in the pack but is precut so you just pull off a strip and cut to length and wet it out and place it. I guess you could call it being used as a spar. There is just the foam core attached to the foam fuse with the carbon tow and then glassed over with 3/4oz glass. Here is a pic of it,
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Old Jan 10, 2013, 01:59 PM
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Milwaukee G Mitchell, Wisconsin, United States
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I've got some of the same type of stuff. I flattened out a bunch to make spar caps for a DS plane I built.

You'll want to cut it into whatever lengths you need cause it will be easier to flatten shorter lengths.

I did it dry, holding two 1/4" drill bit ends I passed the tow over and under the bits and held them tightly while pulling it through.
I found that my stuff had twists in it every so often. And not the entire 12k width twisted either. Sometimes it was a third of the bundle or a half. That made it almost impossible to get the entire ribbon flat (not a big deal for what I was doing but could be a cosmetic issue). Then I'd just pass it through my fingers to do the final flattening.

If there was a part that was twisted I'd separate that part of the bundle and try to untwist it. Then just run the whole thing through your fingers to put the bundle back together.

Just pressing it with a hard roller won't remove twists in the bundle. If all the fibers are parallel it might but not if any of it is twisted.

You might be able to get some decent looking pieces but I doubt every piece will turn out. Structurally it will be all good but aesthetically there may be some flaws.

good luck,
davidk
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Old Jan 10, 2013, 03:18 PM
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The stuff Im talking about is flat no twists no mess each 1/4 inch strip has 12000 fibers.
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Old Jan 10, 2013, 05:28 PM
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USA, OH, Worthington
Joined May 2002
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Have a read here:

http://www.rcgroups.com/forums/showt...ade+spread+tow

I've made up a jig that gives me decent results as long as the tow isn't twisted significantly when it's rolled.
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