Manufacturing of Carbon Fibre Shafts 1

[izax1]

I wonder if anyone can give some clue about manufacturing methods of highly loaded carbon fibre shafts other than winding. I have heard about "rolling" in the manufacturing of skiing poles. Why is not that used in manufacturing of shafts. It is incredibly much cheaper than filamnet winding.

Thanks for any clues.

 

[MikeHalloran]

Have you ever cut a piece of copper tubing with a tubing cutter? Notice that before the cutting wheel breaks through the wall of the tubing, the tubing diameter in the vicinity of the wheel is reduced, and the overall length of the tube increases.

If you do the same thing with a particularly dull wheel, you can swage the tube down by a few mm with ease. You can then displace the wheel axially by a few mm and repeat the process, and end up with a tube that's longer than the one you started with, smaller in outside diameter, less thick, and because of work hardening, stronger.

Several variations of such roller swaging or rotary swaging also work on steel tube and on aluminum tube, because of their ductility.

Carbon fibre is brittle, not ductile, so the swaging process is unlikely to produce satisfactory results on it. Carbon fibre, actually fibre reinforced polymer, is so brittle that it can be formed only in a-stage (wet) or b-stage (sticky), i.e. before the polymer has cross- linked fully.

Don't give up. If you _do_ find a fast fabrication method for frp, you'll be able to retire very young and very wealthy.





Mike Halloran
Pembroke Pines, FL, USA

 

[Pud]

Mike,

I think the op is referring to the technique of rolling pre-preg CF (or whatever) around a mandrel, taping it up with release tape and curing it, then removing the steel mandrel. Used for low volume composite tubing (e.g. Hardy's fly fishing rods, Alnwick, England - take a mortgage out!)

Whereas filament winding is used for high volume stuff (e.g. Golf club shafts) or when maximum performance is required due to the lower resin/filament ratio possible.

Cheers


Harry

 

[MikeHalloran]

Oops, my bad.



Mike Halloran
Pembroke Pines, FL, USA

 

[izax1]

Yes, Harry, you are right. If fishing rods and skiing poles are low volume, then the application I am involved in is definitely low volume.

My question is: Are there any hidden pitfalls by using the rolling method for structuraly loaded shafts. This is a drive shaft, and so we need shear strength from torque input and bending stiffness to prevent vibration.

Thanks

 

[Demon3]

Get your knitting needles out and make one of these...

http://delta7sports.com/product.html

There is not any memory with less satisfaction than the memory of some temptation we resisted.
- James Branch Cabell

 

[btrueblood]

The pitfall with a rolled piece of fabric is that you will have a discontinuity (seam) along the length of the tube, that does not occur for a continuous-wound tube. For a power tranmission shaft, the principal torsion stresses in the tube lie along a 45-degree spiral; thus torque-transmitting tubes are typically wound with a high fraction of +/-45 degree spiral fibers. For a rolled-cloth tube, you could orient the seam along a spiral (like the paper core of a roll of paper towels or toilet paper), but that works to transmit torque well (not great, just well) in one direction only: reverse the sign of the applied torque, and the tube fails quickly along one of the seams. You can correct the flaw somewhat by applying overlapping tapes/strips of cloth, but generally the tube wall will be thicker, more costly in terms of material, than a filament-wound version.

 

[izax1]

Thanks btrueblood

Yes, I am aware of the discontinuity either along the length or at 45 degr. But you would normally roll several layers of prepreg mats and thus place the seam at different circumferential angles. This will, of course, require some control of your process, but still. I am not convinced. Do we have anyone out there who can report severe problems with highly loaded rolled shafts?

Investing in a filament wound machine is extremely expensive and for low volume production I am looking for better utilisation of my cash.

 

[btrueblood]

K2 makes a line of "rolled" ski poles, an aluminum tube over-wrapped with graphite tape. Very nice, very expensive ski poles. They, however, do not ever see a torsional load, just bending loads.

Izax, I never said it couldn't be done, just that the tube wall will need to be thicker (several layers of cloth or tape pre-preg, as you noted). FWIW, I have seen torque tubes made with only two passes of very closely spaced filaments (at +45 and -45), laid down as tapes but in a continuous wind. That's awfully thin, but they work, and carry a lot of torque for the weight.