sticks from tow

I tried a few not so successful methods of making a tube from carbon tow and one that seems to work ok.
I have some bought carbon pipes that I wanted to be stronger. Not made successful release from a mandrel yet.
I have a tow that will spread about an inch without very big gaps. I made one with two helixes each way (16mm stick), layed dry, secured at each end with thin tow whipping. Massaged some 285/285 mgs epoxy into it, wrapped it with strips of uhmwpe fabric, then a strong, transparent, fiber-less 2 inch "building tape". It's a bit like heavy drop cloth with pressure sensitive adhesive. When I carved it up at the end I was not convinced that the ep had soaked totally everywhere. No way to know how the carbon distribution ended up either because of the white uhmwpe.

So the next one I layed on a wet stick, and wetted as I wrapped. This was a messy and heroic task. Much more difficult to spread the tow.
Same tape. The tow wasn't strung enough and moved while wrapping the tape. Lots of filing due to the large bumps made by the tape - hence some local repair needed afterwards.

So then I wrapped one dry with the four helixes - tight - and securing at the ends with thin tow whipping and scotchweld 90 - fast, bubbling pu(?) glue on spraycan - cool stuff.
Made a bag and tried to infuse. Far too high viscosity, wouldn't go an inch up the stick even.
I had anticipated that, and made a hot water bath for the epoxy to lower the viscosity. Really clever. There was probably over 200C in the ep to melt the 1time coffee mug I was mixing in, and the PET soda bottle with the water.
Rescued the stick and massaged new ooze WELL in - quite possible with a tight carbon wrap.
Then, electrician tape, approx half inch wide. Started with wrapping it around a piece of towel at the end of the stick to get a better grip while wrapping the tape. I don't think I will carve it up, but I have a good feeling about it. Looks good. Very small grooves from the tape.

The UHMWPE / dyneema / spectra fabric feels like a layer of "smearable" plastic - dull sounding. I feel that the ding-ability of the sticks, by rock etc, is going to be a fair bit improved by it.

The first stick was made with 1:3.2 instead of proper 1:2 hardener/base by volume, and it still cooked off similar and feels the same as the others. Very forgiving. Seems like I have forever geltime and hard after an hour+ in the oven.

So that was my contribution to twig technology, for now.

So long,
Pango.

 

Update. I was very surprised to be able to pull off two layers of dyneema fabric and a hoop wrap of carbon tow from a 16mm aluminium mandrel after treating it with r-g.de primiming wax and pva - no intermediate layer of tape, taper or anything. A few soft whacks on the mandrel and off it went. Perfect!

 

Pango,

Do you have any pictures?

I have no idea what you're talking about...

-Tom

 

No pictures, but if you are looking for some way to make carbon tubes from tow, maybe just ask a few questions. Only reason I put up the description was that it took me a few tries to get it sort of right. It's probably just lazy and superfluous writing that makes it unreadable.

In short: TIGHT wrappings of dry tow, two layers probably ok, a whipping plus 3M 90 glue to secure the ends of the wrappings, massage the epoxy WELL into it, wrap tightly with narrow-ish electrician tape (assuming that is an international term for the same thing), bake in oven.
The products at www.r-g.de called priming wax and PVA release agent were adequate to pull it off an aluminium mandrel, which surprised me, given what I had read before. Maybe just lucky.

 

With the alimunum mandrel and the oven bake, thermal expansion during cure helped you with separation later at room temp.

For your build, how long and what diameter?

 

Ah, I did not think about that. Mandrel is 16mm OD 14mm ID, 50cm long sticks.

 

For us mentally challenged non-metric types, the caclulator says 0.63" diameter x 19.7" long.

 

Tow is carbon fiber ribbon. Some use it to wrap damaged parts, like a bike frame. Tow can be bought in unidirectional scrimmed banding, where it can even be used like here:http://www.fortecstabilization.com/casestudies.php?casestudy=ParkGarage
The beauty of the stuff in tow form it's cheap--and awkward to work with. One carbon tow supplier (ebay) in London points out that an autoclave can readily be created by sliding a softplastic sleeve over the epoxied work, then inserting the work into an plastic or aluminum pipe, sealing the sleeve at either end of the capped pipe so it's vented to the atmosphere. Pump compressed air into the capped pipe via a third hole in an end cap, and you should be able to get a reduced ratio of epoxy to your work piece. Excess epoxy should ooze out either end. Nope, I haven't tried it. Nicely done, Sigurd

 

P Flados said it: an aluminum mandrel subjected to heat will expand in diameter and tension the tow fibers, creating a denser tube. Once cured and the temp brought down, parting should be easy.
http://www.hallspars.com/hall_method.php
The Hall folks describe doing this on a large scale.
Designing and working with carbon will continue to provide big rewards. When you conceive of the masses of wood or aluminum or stainless gyrating high in the sky above your sailing vessel, and then exchange those masses for lightweight carbon, the structural requirements become dramatically less, the boat and sails become far less affected by moment inertias, and sailing makes giant advances. Nothing new here--except the availability of tow and experimenters like Sigurd are bringing new levels of sophistication into diy boatbuilding.