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Raijin
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Let me just start by saying that I'm new here and the only experience with composites I've had is some simple fiberglass lay up by hand. I want to make a rectangular carbon fiber tube. I've done some preliminary research here but failed to find a thread about this specific type of project. I was, however, able to determine that I probably want to use the vacuum-bagging method. Here's a random photo I found on Google of the shape I'm going for:  I'm guessing the easiest way to do this would be to saw off a length of gutter (or something similar in shape) and try to vacuum bag the CF around it using an actual bag (as opposed to the usual method of taping a 'bag' sheet over the piece). A few questions: - How could I get a seamless piece like in the photo above? If I use carbon fiber sheets, there's bound to be a seam line running along the piece somewhere?
- Would you guys recommend using the carbon fiber that comes in tubular sleeves?
- How would you pros go about making something like this?
Thanks!
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Dravis
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I very much doubt that the tube in the picture is "seamless" -- You can not weave "Twill" in a continous "tube" ---
If you want a cosmetic outside part like the one in the picture, AND you want 2-2 Twill, then you will have a seam ..
If you use braided tube, you will have the braided finish, that looks like plain-weave - only without 90- degree angle to the weave .. it will usually be a steeper angle.
Also Braided hose CF is quite "open" in the weave, so the lower layers need to be a black material. (Not Glass-fibre)
I would make a split mould, and vac-bag with a pressurized rubber tube through the inside, to get a good cosmetic surface.. I.e. make a "plug", then make a mould from that.
Another option is to vac bag on a mandrel (slightly tapered) and use very carefully applied Peel-ply on the outside.. It can then be clear coated to give a good cosmetic finish.
"Sapere Aude"... Dare to KNOW!
The written word is the only truly efficient vehicle for transmitting a complex concept from mind to mind...
103% of all people do not understand statistics...
Do not adjust our mind, theres a fault in reality :-)
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Hanaldo
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Internal pressure mould would be my approach. Personally I'd do it with pre-preg and a silicone intensifer inside, but one could also do it with wet-lay. As Dravis said, it won't be seamless. But if you hide the seams on the radius and clear coat the final part, then it will be virtually invisible.
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Warren (Staff)
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Both silicone intensifier and bladder techniques are probably the only realistic methods for home/DIY once piece production. Mandrels for most professionally produced tubes usually need hydraulic pullers/presses and/or compressed air to remove the mandrel. If you've ever seen an unfinished roll wrapped tube, the "thrust" end of the tube that butts upto the hydraulic machine is usually made much thicker to spread the load as the mandrel is pulled out the tube.
Warren Penalver
Easy Composites / Carbon Mods - Technical Support Assistant
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Chris Scott
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I just make my own mandrel by simply polishing a metal tube. Then I wet layup and vacuum bag over the tube, I remove the tube easily with compressed air. I've successfully manufactured up to 36" without ever losing the mandrel, so I'm sure I could go up to 48-60" without problem. Depending on what I use for for bagging materials, I'll get different surface finishes on the O.D. I usually lay two initial layers at once then remove it from the mandrel and continue my layup schedule. So I use peelply until I get to the final step where I will use a release film. The I.D. is maintained perfectly with a polished finish. If I needed to maintain a certain O.D. then I would make a split mold or just compensate by the layup thickness on a smaller tube. Also worth mentioning I tried doing a wet layup on a 1" square tube with normal weave carbon fiber, while it does work... a lot of extra care and time is put into it to make sure the fabric isn't distorting. Using a woven sleeve I've saved myself a LOT of time and effort and it looks flawless.
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taikuri
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Chris Scott (25/09/2015)
I just make my own mandrel by simply polishing a metal tube. Then I wet layup and vacuum bag over the tube, I remove the tube easily with compressed air.I've successfully manufactured up to 36" without ever losing the mandrel, so I'm sure I could go up to 48-60" without problem. Sorry for hijacking topic for a one question, if you dont mind, please explain how do you use compressed air to remove laminated carbon tube from metal mandrel ? Im having hard time removing my tubes...
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Dravis
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When laying up on the metal tube Mandrel (I use Stainless steel or hard Aluminium) close off one end of the CF tube with a strong "End wrap over" The mandrel is plugged with a plug as well at that end, but with one or more small holes to let the air get from the inside of the mandrel tube to the outside, between the Mandrel and CF tube. (I put a small piece of release tape over the holes to avoid sucking resin inside the mandrel tube while vacuum is on.) At the other end of the Mandrel I put a plug with a short piece of tubing that fits my compressed air "handle" for inflating tyres.. that way the amount of pressure can be controlled better, so you do not blow apart the CF tube by adding 8 bar of pressure in one "rush" ---  I use that system to release parts from other types of moulds too ..
"Sapere Aude"... Dare to KNOW! The written word is the only truly efficient vehicle for transmitting a complex concept from mind to mind... 103% of all people do not understand statistics... Do not adjust our mind, theres a fault in reality :-)
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Chris Scott
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^ That method is seems a bit more sophisticated than mine, I'll look into that. When I layup, I make the bottom layer extend past the others, this makes it flexible. I use a nozzle at the very edge of this and the CF tube will flex away from the tube. I do this for each side, you can visually see the CF pop away from the mandrel, after that I can separate it by hand. I use aluminum mandrels, mainly because originally I was concerned with losing my mandrel. So if I ever run into any difficulties, I can toss some dry ice over the tube to shrink the aluminum to assist with removal. Thankfully I haven't needed to do that yet.
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Dravis
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I have sometimes filled the aluminium tube/mandrel with hot water for speeding up the cure of the CF .. Then used very cold water to shrink the mandrel just prior to using compressed air..
When using thick walled Aluminium tubing the heat expansion is quite strong, with stainless steel there is very little expansion or contraction by cooling.
"Sapere Aude"... Dare to KNOW!
The written word is the only truly efficient vehicle for transmitting a complex concept from mind to mind...
103% of all people do not understand statistics...
Do not adjust our mind, theres a fault in reality :-)
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