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All Forums >> RC Airplanes >> Composites Fabrication And Repair >> Working with carbon tissue
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Working with carbon tissue - 1/10/2005 4:15 PM   
saramos



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From: Northridge, CA, USA
Status: offline 		I went to the AMA convention over the weekend and picked up some carbon tissue from CST. I've been thinking of using it for glassing a sheeted wing.
I picked up some .2 oz and .5 oz tissue. The guy at the booth warned that the .5 tissue soaks up a fair amount of resin and could add excess weight. I had recently read an article where a builder was using brushing lacquer and .5 oz fiber. He said his results were a hard light finish. With this in mind, I decided to do a couple of test samples with the .5 tissue.
I decided to do one sample with epoxy, and the other with lacquer. On the epoxy sample, I used thinned 30 minute epoxy. Just like the guy said, it really soaked up the resin. After it cured, I added a second coat. To my surprise, the tissue still soaked up the resin. On the second sample, I used Depp brushing lacquer. After applying 3 coats, the results were not looking too good. The weave ( or I should say voids as the tissue is random oriented strands) had not filled, and when the sample was flexed, the tissue would wrinkle. I decided to try some microballoons mixed in with the lacquer on the fourth coat. This time, the weave filled in, but the tissue still wrinkled a little when flexed. It looked like the test was a failure. Just before heading off to bed, i decided to try one more coat of lacquer (without microballoons). This time, the lacquer didn't just soak in to the tissue, but stayed on the surface. This morning, when I looked at the results, things looked a lot better. The sample was almost as hard as the epoxy and the sample no longer wrinkles when flexed. I don't have a balance that is capable of measuring the added weight, but just holding the samples, it seems like the lacquer sample is lighter than the epoxy sample. I'll have to find a way of weighing the samples.

Has anyone else tried using carbon tissue and/or brushing lacquer? If so, what were your results?

Any comments would be greatly appreciated
Scott

< Message edited by saramos -- 1/11/2005 2:47 PM >

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RE: Working with carbon tissue - 1/22/2005 2:59 PM   
Downtrodden


 

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Status: offline 		I'd suggest you try damping the tissue with lacquer thinner first, before you apply the brushing lacquer. The lacquer thinner will saturate the tissue and thin the lacquer enough to flow into the voids. Remember that the lacquer thinner should not be allowed to evaporate entirely, but just enough to thin the lacquer without destroying the lacquer matrix. (It would take a 50/50 mix of lacquer and thinner to accomplish that) I haven't the experience in modeling to make the above statement definitively, only years of experience in custom furniture, which I feel applies in your case. I think you're on the right track.

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RE: Working with carbon tissue - 1/26/2005 4:08 PM   
DH71TIGER


 

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Status: offline 		Saramos Hi,

I have never used carbon tissue but have beeen giving some thought to trying it, so realy interested in your experiments. I have used ordinary tissue with Ronseal floor Varnish also used on this side of the pond is a product called Poly C, again a polyurethane based material. I had good results with the finish but the system lacks a little strength, hence the interest in carbon tissue. A definite reduction in weight over glasscloth and epoxy though. Did you seal the wood before applying the tissue? I would just use regular cellulose sanding sealer. Usually two coats sanding between coats and at the end, so you start off with a smooth hard surface. then commence laying the tissue. I look foward to reading the results of your next experiments!!!!

Cheers for now

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RE: Working with carbon tissue - 1/26/2005 9:11 PM   
saramos



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Status: offline 		I did another test. This time with three test segments of a wing. Each test was on two bays (4" wide) of a wing section with an 8 1/2" cord. I used a single coat of a lacquer based sanding sealer before applying the test cloth. One I used .6 oz fiberglass with epoxy. The second was with the .5 oz carbon tissue with epoxy, and the third was with .5 oz carbon tissue with Deft brushing lacquer. I then used a sandable paint primer on each wing section. I have not yet applied enough primer to fill the weave on any of the samples, but the weave on the fiberglass sample is almost filled. The samples with the carbon really soak up the primer. After several coats of the primer, the surface is still showing the black from the carbon fibers and was still soaking up primer on the last coat I sprayed.
Each sample wing section started out at 16 grams after the sanding sealer had been applied.
So far, the fiberglass sample is the lightest, Weighing 20 grams, followed by the carbon tissue with epoxy at 22 grams, and the carbon tissue with brushing lacquer comes in the heaviest at 24 grams. Thats double the weight gain of the fiberglass sample. I have not tried applying pressure to the point a failure but all the samples produced similar hardness.

So far, I am disappointed by the results. If I can find a way of filling the weave of the tissue, there may still be some potential. Perhaps using microballoons in the resin or lacquer before using the primer. I'll have to explore this further. For now, I'll use .6 glass and West Systems epoxy for my current project.
I've only built balsa structure wings, but I suspect construction using vaccume bagging may yeald better results.

Scott

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RE: Working with carbon tissue - 2/27/2005 12:33 PM   
Jetman007


 

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Status: offline 		We don't recommend using tissue as your finish layer for exactly the reasons you cite. Once you put teh tissue on, we receommend it is covered with one layer of 3/4 ounce fiberglass cloth to serve as the final surface. Apply both fabrics in one session.



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RE: Working with carbon tissue - 2/27/2005 5:34 PM   
saramos



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From: Northridge, CA, USA
Status: offline 		Thanks, I had not considered a glass coat on top. This still appears to be a much heavier finish than a traditional glass finish.
Scott


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