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Old Jun 18, 2014, 02:15 AM
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FlyRob's Avatar
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How are large Carbon Tubes made ?

Hi, I was wondering what process professionals in composites use to make large diameter carbon/composite tubes, like the ones used for the fuselage of some RC gliders or for windsurf mast ?
Do they use a mold, do they use prepreg, do they use the same method than for the small carbon tubes made for stunt kites (Skyshark) ?
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Old Jun 18, 2014, 06:00 AM
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Filament winding, pultrusion and roll wrapping are the main processes to manufacture tubes. There are other ways but if you're buying something commercially those are the main 3

The carbon rods you'd by at the hobby store are Pultruded. These are the rods with all the fibers running in a single direction along their length.You would find these in stunt kites.

The carbon tubes that have a weave pattern are usually roll wrapped from prepreg carbon. Some rc glider booms are roll wrapped.

Filament wound tubes are rarely seen in this hobby. Windsurf masts I believe are sometimes made from filament wound tubes. Common applications for filament winding are usually pressure vessels and large diameter piping.
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Old Jun 18, 2014, 01:35 PM
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Hi, Thanks a lot for the answer. I checked a few videos and documents from the processes you mention the pultrusion seems like a technique used by big industries, not small composite artisan right ?

Also for the roll wrapping, do they use a kind of mold ?
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Old Jun 18, 2014, 05:35 PM
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Quote:
Originally Posted by FlyRob View Post
Also for the roll wrapping, do they use a kind of mold ?

Hey FlyRob,
Search Carbon Tail Boom and you find lot's of great info here. (I am thinking of a few posts by Roydor, DrFragnasty, and perhaps Tom Siler's threads, others too for sure). Here's how I do it for tail booms (similar to others you'll find for low volume production). I use a typical pool cue for a mandrel to roll the cloth over. Here are some pics to illustrate the process. 1 large layer of 0.75 oz cloth first, then 3 layers of carbon that are ~3/8" larger than the cue circumference and staggered by 1/3 circumference to even the overlap when rolled. The layers are laid outside to inside on the 0.75 oz cloth with the cloth extending about a circumference on either side. The cloth here is as follows: outside is Spread tow (on bias), middle is Uni, and inside is PW or Twill (0-90). Remember you will roll the cloth on from the inside to the outside.
I cover the cue with release film that can slip on and off the cue (i.e. tape it to itself like a sleeve to fit over the cue). Start rolling the 0.75 cloth around the cue and the carbon will follow nicely with out distorting (the 0.75 cloth is active as a carrier/binder). Roll on a flat surface and use care to make sure that it stays TIGHT against the cue. Keep rolling until you finish wrapping all the 0.75oz around. After this I roll peel ply around, and finish off with perforated release film and paper towels. then wrap the whole thing with plastic (stretchy) packaging tape. If you don' t get the cloth around the cue absolutely tight then the when you stretch the packaging tape around the it will put creases in the carbon....not good!
When cured, unwrap everything (note here: before I wrap the peel ply I put an edge of Kapton tape to give me an unbounded edge to pull the peel ply off). The surface will be "peel ply texture" that will require some careful sanding and then a light coat of Clear Coat acrylic urethane and you're done. The booms I show here are from heavier carbon (5 oz. ST, 2.4 oz. UD, and 5.7 oz twill)...way overkill!, but not too bad on weight: 75 gr for a 32mm x 750mm x 20mm boom...certainly okay with me for a 4m F3J. Others use lighter carbon and come in closer to 45 gr. These guys have real talent
I've tried using a final mylar to achieve a smooth outer surface but it is very difficult to get the alignment right and achieve a uniformly smooth surface without "waviness"...perhaps others have had success here and are willing to share
Hope that helps
-Erik
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Old Jun 18, 2014, 05:51 PM
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FlyRob,
I think SlowBarless has answered your question well. However, were you leading up to asking how to make carbon tubes yourself? Or was it just an academic question?
If you do want to know, as well as the method described above, I have a favourite method too. I can post details here if you want.
I made a tube just yesterday and took a short video. I have not had a look yet to see if it came out or not yet though!
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Old Jun 18, 2014, 06:41 PM
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SlowBarless's Avatar
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Quote:
Originally Posted by FlyRob View Post
Hi, Thanks a lot for the answer. I checked a few videos and documents from the processes you mention the pultrusion seems like a technique used by big industries, not small composite artisan right ?

Also for the roll wrapping, do they use a kind of mold ?
Pultrusion is large scale manufacturing of composites. Not something I'd recommend trying at home . Pultrusion is good if you need to make thousands of meters of product.

Roll wrapping uses a mold, in this case called a mandrel.
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Old Jun 18, 2014, 07:14 PM
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Quote:
Originally Posted by Jim.Thompson View Post
If you do want to know, as well as the method described above, I have a favourite method too. I can post details here if you want.
I made a tube just yesterday and took a short video. I have not had a look yet to see if it came out or not yet though!
Jim, I don't mean to hijack FlyRobs thread, but I'd love to see your progress/methods...perhaps you could post on your Wompoo build thread (fantastic stuff! ).
FlyBoy, Jim brings up a key point, if your question was purely "academic" and more related to large mass production of carbon tubes in general, then you may have to broaden your search....if you do want to fabricate your own (which I assumed initially, hence my detailed post) then I think you will get lot's of great knowledge/experience here, lot's to share...and Jim will post his video

-Erik
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Old Jun 19, 2014, 02:47 PM
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Thanks a lot for all those very interesting information, you guys are great.

To answer Jim.Thompson, it was both a question to satisfy my curiosity, I was wondering how the large carbon tubes you find in Hang gliders (www.compositecreations.com) were made and if they were made like the small kite tubes like that:

https://goodwinds.com/carbon.html

...but I was also asking because I'd like to make a Carbon axle for a Kite Buggy, like that:
www.carbonbuggy.com
http://www.xxtreme.nl/xxproducts/car...rbon-bacl-axle

and I was wondering if it was even possible for an amateur.
F3A-Hole described a technique I could use but it seems delicate for a large tube not to create creases in the carbon when wrapping the tape around. Maybe somebody has a method to use vacuum or even prepreg but then it start to be out of touch for an amateur.
I also learn that the nice finish comes after sanding and a clear coat :-) The result is beautiful.

I was also wondering if carbon "socks or sleeves" were used instead of wrapping a carbon around, I know it's used to make small tubes for wing junctions but for large tubes...
Also, I need to think about the advantages to wrapp unidirectional carbon fiber instead of fabric.

Jim.Thompson, don't hesitate to post your method if you can !
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Old Jun 19, 2014, 03:36 PM
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Ok FlyRob.
My favourite method is a variation on that described on the SollerComposites website. They have all the materials for sale to suit this very simple and what I think is the best method I've seen. It provides excellent finish not requiring any later sanding/ clear coating etc. due to the use of specially treated heat shrink, which they supply.
It uses biaxial woven sleaving which is designed for the purpose.
The only slight variation I use on there method is the application of the release film.
I use the thinnest available drop sheet plastic (around .001inch) and first cut it in strips around 25/30 mm wide using a long straight edge and a sharp knife.
Choose a rod for your mandrel, it must be clean and free of damage or glue residue. Wax it well and lightly polish off, allow to sit for at least 20 mins or so for the remaining solvent to flash off in the usual way.
Then I put the mandrel in a cordless drill on the bench. Tape one end of the plastic strip with a small piece of tape. Start the drill slowly and spiral wrap the mandrel with the plastic. Tension is important; not too tight or too loose, some experience and judgement required here.
Then using another small piece of tape at the end, fix the plastic to the mandrel again.
Your glass (or carbon) biaxial sleeving is then slid over the plastic covered waxed mandrel, cut to length and stretched out. It's then wet out and de-bulked using paper towels.
Allow to "green off" for a few hours (3 - 4 depending on the resin used). Then I clamp the mandrel in the vice between two pieces of wood that have a round groove routed in them to protect the mandrel (if it is carbon rod). With a pair of good gloves on, I "break" the slight bond that has (usually) established between the plastic and the mandrel by twisting back and forward, progressively along the length of the tube. When I'm satisfied it is completely free, I leave it in the sun to cure. Remove the tube with the plastic inside from the mandrel the next day.
The plastic will come out neathly if the starting end is pulled using a pair of long nosed pliers and twisting while doing so.
With some experience, the tightness of fit can be adjusted while the epoxy is still green. It can be stretched to tighten, or compressed to make it loose, even after the plastic release film is removed.
I made short video which is uploading as I write. I'll post it later, it did not come out very well as I was in shot much of the time, but it still shows the essential method.
For tubes that require a good finish like a tail boom, I use the specially treated heat shrink, also from Soller. After the wet out, slide the heat shrink on and cut to length. Then slowly heat from the centre outwards. This exudes excess resin and gives a professional finish.
Jim.

Oh, and one last suggestion. Use glass first until some experience is gained! Always a good idea.
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Old Jun 19, 2014, 04:41 PM
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Great stuff Jim! Looking forward to seeing your video... always enjoy learning and trying new techniques!
The hardest part with the peel-ply, sanding, and clear coat method is indeed the sanding, if the carbon is not tight (and has high and low spots) then you risk sanding into the outer carbon layer at the high spots. The 3/4 oz glass is a nice gauge/buffer to avoid this (thanks Roydor!)

FlyRob....when it comes to working with composites (at the hobby level), I am always reminded of a quote from Winston Churchill:

-"Success is the ability to go from one failure to another with no loss of enthusiasm"
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Old Jun 19, 2014, 05:01 PM
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I love the Winston Churchill quote! I will remember that one for sure.

See report #22 for video links.
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Old Jun 19, 2014, 05:21 PM
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While we are discussing tube making, I'll mention another variation on the above method(s).
For construction tubes, such as wing joiner and incidence pin receiver tubes which don't require a good cosmetic finish, strips of scrap glass or carbon cloth can be used instead of the sleeving. It is spiral wound on top of the release film similar to the way it is wound on first. A second layer (preferred for obvious reasons), can be wound in the opposite direction.
I make my drag spars and control surface leading edge spars this way too. Sometimes, wound on a drinking straw which is left in place.
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Old Jun 19, 2014, 06:44 PM
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Hey Jim,
Your vimeo links don't seem to work...no direct link. ??
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Old Jun 19, 2014, 09:18 PM
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I just checked again and they are working on my connection.
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Old Jun 19, 2014, 10:10 PM
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Wazmo's Avatar
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Quote:
Originally Posted by Jim.Thompson View Post
I just checked again and they are working on my connection.
That's because the link is to the videos belonging to whoever is logged in. It's only your videos when you're logged in to Vimeo. What's your user name, or the video ID number?
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