Tube with a curve. Possible?

Hi all. Next in my long line of questions is this:

I have an idea for a part that would be made out of 3/4" ID CF tubing. Would it be possible to make a tube with a bend in it like the picture below?

If so, how? What would you use as a plug to form the shape and how would you remove it once the part had cured?

Reda this thread http://www.compositescentral.net/showthread.php?t=4390&highlight=tube

Think you could do it the same way but with a different shaped tool with a bend!:slight_smile: Or if you dont want to spend much make the tool yourself out of fibreglass! Hope this helps

If you already have a part you are copying I have a VERY easy solution :wink:

  1. Make a plywood box that the whole tube will fit in.

  2. Seal ends of tube, fill box with silicon, submerge tube.

  3. After the silicon is dried, cut along the length of one side, and remove part. This will give you a kind of “C” shaped cross section.

  4. Take fiber sleeve and put over a long party balloon (or condom :eek:). Put the “bladder” into the void in the silicon, and inflate.

  5. Voila- you have made a hollow pipe with a bent axis!

Keep in mind, you will need to make the necessary adjustments to the construction to fill the bladder up!

ive made plenty of tubes using a few different methods…

1st described above is bladder… pain in the arse but when you manage to get it right works great.

2nd is creative. two halves and 2 moulds, parts joined at centerline. for centerline joint i typically use 1/8 or 1/16 sheet wax and create a small 1/4 lip along one of the halfs eop line. this makes flush out side surface but has a small overlap on the inside surface. the lip joint can be #40 drilled and bonding can be done easily with use of draw clecos. #40 holes can be filled with black resin.

3rd method was a botched sucess. it required fabrication of the tube and then carbon fiber tape wrapped around the fabricated tube. shrink tape was applied over the tape and it was bagged and placed in the autoclave… bag popped and the tape left a terrible imprint in the carbon. the part turned out some what ruined at the ends where gas burned the exposed graphite… but… in the center the shrink tape protected most of the pipe. this was a experiment per se but most times tubes are fabricated in halves…

I have a few customers making bent tubes, using the bladder method. Although the principle is simple, there are quite some tricks needed to get things right. Some of the problems you might encounter:

-moulds. Your mould split should be exactly halfway the pipe, or it will be stuck in the mould.
Moulds can be made with fiberglass or carbon. The same material as the part is preferred. Make sure there is plenty of lock between the 2 halves, using domes or dowels. Make the mould strong enough to resist some force.

-fiber placement. This is a nasty one. depending on size of the tube you can use a carbon sock, or wovens and UD, placed strategically. Either 2 seperate halves with overlap, or 1 slab of carbon, wrapped around the bladder, forced in place by the bladder.

-bladder end. One end can be a simple knot. The other end should have a connector that connects the bladder with as little leaks as possible. My customers make them theirselves on a lathe.

-epoxy laminating. As such that you will end up with a pinhole free tube, but also without excess resin. I have seen people use drain systems in the mould to get rid of the excess resin.

Airtech has gusseted tube, which can be an advantage.

Hello Herman. Could you help me little with my production of bent carbon shaft. I have 2 half composite mould and I use straight silicon tube with cabon kevlar sleeve. i have problém that when I close the mould with silicon tube and put air inside. The silicon tube tend to go straight and press in curve of mould. When the shaft is dried up I can see still the kevlar carbon sleeve at the joint especially in curve.

Herman isn’t very active anymore in composites, but I’ll guess he well be around every now and then. anyway, do you overlap the first layer?

I use like First layer carbon plain 200g/m second layer UD 300 than to conect two half of mould i use carbon kevlar braid sleeve with silicon tube. I think it’s good method. It’s works well in production of MTB handle bar and other products which has no so sharp curve like my bent shaft. I don’t know If I need customized silicon or latex blader because I sometime I have problem to put silicon tube with braid sleeve to the mould, it¨s still tend to go straight and sometime the sleeve close one.

Really? Thats a pity!

If you use an overlap(like suggested in the other topic) you at least won’t see the braid anymore. if your mould is stiff enough I wouldn’t worry about the bladder pulling straight, it will conform to mould shape anyways.

Yeah, hojo. Herman doesn’t work in composites anymore. quite a loss if you ask me. Learned a lot from him.

I still don’t know how to overlap the first layer.
The first layr is carbon 200 plain a I always let it cure lit a bit to avoid bubles than I put UD 300g/m2 and than carbon braid and in midle extra kevlar carbon braid as reinforcment , close the mould and fill the hose by air.
Tody I will try again and i will try to overlap the kevlar carbon braid with extra layer of carbon. I think the best way would be to do it in one step just wrap all material at hose and put it in mould.

Please see my post re: Curved Tube and Foil Sections as below

32mm OD Curved and Straight with a 90 deg. Bend.

POST: http://compositescentral.net/showthread.php?t=5872

Hope this helps, PM me for more info if required?.

John Hayes
www.bladerunneroutriggers.com

Hello, Thank you for your useful info, i have been trought of you post. Unfortunately I use composite mould so far not like you aluminium. I dont use prepreg but wet hand lay up technique. I think that my mould wouldn’t take such hight temperature which is nesessary for epoxy foam to expand. But is definately very interesting and I can see that you have perfect product comming out of your moulds and you have not braid squeeze on like on my bent shaft. Yestrday I produce another bent shaft with differnt material so I am curious about result.