On carbon and carbon fibre

Sunday, 13 March 2011

carbon structure
Carbon is everywhere. Can you name another atom that has so many branches of science, knowledge and uses, from carbon chemistry to carbon trading, carbon dating to carbon copies? This atom of six neutrons, six protons and six electrons can be found in the air, in the ground, in the seas and in your body. As well as your bike.

Brief history
Carbon was created by the fusion of helium atoms inside stars. It’s the fourth most abundant element in the universe (after hydrogen, helium and oxygen) and your body is about 20% carbon. It has the highest melting point of all elements. It comes in three main forms: diamonds, graphite and amorphous carbon (like coal), as well as a fourth, fullerine that was discovered in the 1980s. In diamonds it forms the hardest naturally occurring substance, in graphite it is one of the softest.

Carbon fibre
Carbon fibre uses carbon but this is just one ingredient, it requires epoxy resin. Indeed the carbon fibre is just the reinforcing element, the same way steel is used to reinforce concrete. Here’s how it’s done. Apologies if you’re a chemist but I’ve summarised for the sake of brevity.

The carbon bit
The original ingredients are propylene, ammonia and oxygen which are burned with the presence of catalysts to produce acrylonitrile. A pungent liquid substance and dangerous too, being highly flammable and carcinogenic. Acrylonitrile is polymerised – ie the molecules are combined into longer chains – into polyacrylonitrile, more commonly known as PAN. Polyacrylonitrile is more stable, a rubbery and resinous vinyl polymer.

PAN

In go the polyacrylonitrile (PAN) fibres...

The PAN is then pyrolised, a fancy word for baked. It’s done without oxygen or flame, meaning the PAN fibres undergo a controlled decomposition in the heat, giving up non-carbon elements. The fibres come out black and richer in carbon. In addition the carbon crystallises, forming stronger bonds at the molecular level.

Carbon fibre spool

...out comes the carbon fibre filament

Typically the carbon fibres are thinner than a human hair. These fine filaments are then woven into yarn, just like tiny fibres of wool are made into a yarn of wool. The yarn in turn often used to create the weave-patterns you often see on many bike parts.

Weave

The fibres are woven like cloth

Sometimes the weave matters, sometimes it does not. Like a fine suit, the language of tailoring becomes apparent with talk of threads, twill and weave for carbon. Indeed a good quality weave ensures air isn’t trapped and the alignment can matter too. But there’s still a long way to go once the weave is ready.

Epoxy
Epoxy is a substance made from two chemicals. They harden when mixed together. Indeed this setting process is often crucial to the quality of the composite material and is done in very controlled conditions, for example the temperature has to be right. It is the epoxy added to the carbon fibres that creates the real composite material and the strength. A sheet of woven carbon fibres resembles woven cotton, it is lose and soft. The curing with epoxy turns this “cloth” into material than can rival steel.

Plastic frame?
Just as a steel-reinforced concrete building is a concrete building, perhaps a “carbon” frame should really be called an epoxy frame or even a plastic frame? Maybe composite is better term? Note the full term is carbon fibre-reinforced polymer or carbon fibre-reinforced plastic.

I’m not looking to rewrite the language, no it’s just that when you look at the materials involved, remember carbon is only one ingredient amongst many others. Obviously the typical bike part or frame is very far removed from a lump of coal. Indeed it requires a significant investment in chemistry, materials science and engineering.

The future
The discovery of fullerene is leading the way to carbon nanotechnology. Some companies, for example Easton, claim to exploit this in their composite tubing for BMC and their other bike parts but this is only the beginning. Genuine exploitation of nanotechnology here could reduce the weight of carbon composite frames by substantial amounts, there is talk of increasing the strength to weight ratio by 60 times.

In recent times the cutting edge of “carbon” frame tech has gone from 1000g to about 650-700g of with Cervélo’s R5ca, the Guru Photon and the Storck Fascenario 0.6 as good examples. Each year we see a few grams saved as manufacturers find stronger fibres and master the lay-up, design, epoxies and more. But with nano technology there’s a chance we get a leap in frame performance one day.

frank March 13, 2011 at 7:10 pm

bmc for example has big problems with their impec manufacturing. the machine is simply not working as intended.

That's too much... March 13, 2011 at 7:47 pm

“Each year we see a few grams saved as manufacturers find stronger fibres and master the lay-up, design, epoxies and more.”

I’m sorry, but that’s pure and utter crap!!

The Inner Ring March 13, 2011 at 8:16 pm

frank: care to explain more?

That’s too much… : the same, can you explain more? Frames to get lighter as the quality of fibres improves, as does their use and the engineering behind the frame. Early carbon frames used polyurethane epoxies, that’s normally no longer the case etc.

12 speed March 13, 2011 at 10:28 pm

I still think there is some way to go in improvement, for example you say there are frames at 700 grams but a pair of cranks weighs the same, true also for some aerobars. I wonder if more design could go into these parts to make them better, perhaps a whole review of the bike to stop it being an assembly of so many parts and bolts.

Tom March 13, 2011 at 11:50 pm

12speed, your point o how many parts make a bike is interesting. But I don’t think that will change in the near future. Most cyclists love their bike and love tuning it as well. There is a big market for manufacturers who offer cyclingparts. Making the bike simpler would make that market smaller It would also make for a big rise in the running-cost of a bike since more comprehensive parts would have to be replaced, let alone tuned.

Gillis March 14, 2011 at 3:00 am

To my best recollection, this is your first tech related post. The last time I checked I didn’t read Leonard Zinn’s name anywhere here. And I’m going to assume that your readership is on the up and up about this kind of stuff. So it makes me curious about the reasoning behind your post. Also because nothing new is offered up either.
There’s no mention of pre-preg carbon fiber which is standard these days. Much of the technology these days is going into the molding techniques and layup design(mentioned). Nanotube tech used by the likes of Easton and BMC is old news. Graphene is the next likely candidate to take us further in weight and strength (although that’s probably 5-10 years away).
All in all it’s largely a hand done process that will never see a trickle down effect and remain at the highend of the spectrum. I’ll also add that its a highly wasteful and toxic process with the end product having a short life ending in a landfill.

dbaas March 14, 2011 at 6:18 am

12 speed – That’s already happening. If you look at the design of the latest TT bikes the front end is fast becoming a integrated unit. Whilst this is being driven by aerodynamics, I’d guess there were some weight savings involved as well. I would be very surprised if this didn’t trickle through to the conventional road bike eventually (UCI rules permitting).

Gillis March 14, 2011 at 6:27 am

I realized I may have come off sounding a little brash. Not my intent.

The Inner Ring March 14, 2011 at 8:20 am

12 speed / tom / dbaas: see the integrated seatpost as one attempt to remove parts and bolts, I think this is an idea to stop the use of the seat post and the seat collar etc. Plus we’ve seen integrated bars and stems. Both are not without their disadvantages though.

Gillis: no, I’ve looked at some things before like spokes, the possibility of a SRAM electric groupset, what frames/groupsets are being used by each team and more. Here I wanted to look at the ingredients of a carbon frame starting from the basic elements. And it’s a mere blog here, if readers are interested, great but I just wanted to take a look at things!

Vicky March 14, 2011 at 1:31 pm

I had not thought of the ‘raw materials’ before. Are they hard to find and expensive?

Oliver March 14, 2011 at 1:55 pm

I enjoyed the post, found it informative since I know little about carbon frames. I will stick with my aluminium frame though, as I’ve heard carbon frames offer litttle or no visual indication of damage possibly leading to “surprise” failure down the road…

The Inner Ring March 14, 2011 at 4:33 pm

Vicky: the raw chemicals are cheap, the fibres are more expensive but the real cost of a frame are the manufacturing, the design and the other costs like marketing etc.

Oliver: yes, people say that but there’s nothing ever that catastrophic. Often you can see the damage, like a crack or maybe some white dust from the damaged epoxy.

Matt March 15, 2011 at 5:01 pm

I’d say what I’ve said to lots of people looking to buy a bike. “Are you going to weigh it or ride it?”. Of course, for the top pros with no body fat, losing weight can only be done from the components. Also, one can use the F1 analogy for trickle down technology being a great thing and it’s good that the top manufacturers are pushing the envelope. However, people seem to focus more and more on the weight of their bike rather than whether or not it rides well or if they can get some enjoyment out of it. We are only talking a matter of grams. Go to the loo before you go for a ride and you’ll reduce the overall weight of the combo!

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