HOW IT’S MADE
What is it?
Carbon-fibre is produced in sheets woven from strands of fibre, using polymers such as polyacrylonite and rayon, but can also include other materials such as Kevlar, or Diolem, for extra strength. As it is, the sheets are flexible and weak. So they are then mixed with epoxy resin that, once hard, gives the shape its strength.
How’s it made?
All methods start with a mould of the part needed, which is polished to within an inch of its life to help the finished part come out once it’s set. Some parts, like mudguards or covers, seem much cheaper than other parts made from carbonfibre. This is because they often use a layer of carbon sheet as the surface you see, while underneath will be fibreglass sheet. They are laid into the mould, with cheaper polyester resin painted on to help it cure. The part will look great, but have no benefits of carbon. Better parts will be made with just carbon and use epoxy resin. Multiple layers are used with thought going into which direction the weave is pointing, so that you can build up the strength where you need it. It’s then placed in a vacuum bag which is attached to a pump that sucks and squeezes as much of the air out as possible, which in turn squeezes much of the resin out of the part. This helps it to be a lighter and stronger part, as the resin cures the carbon, but too much of it introduces weaknesses. The best parts are made with carbon sheet that has been impregnated with resin already, called pre-preg carbon. This has to be kept in the freezer before use so as not to cure. Its benefits are that the resin is spread evenly throughout the sheet, giving more uniform strength and it also has less resin in it, making the part lighter and stronger. It is then placed in the vacuum bag and put in an oven and heated, or an autoclave – basically an enormous oven that you can suck all the pressure out of. Temperatures will be between 120-250°c and pressure will be 100lb/in2. This is how the strongest, lightest parts will be made, like wheels and frames.
Make your own!
You can have a go at making your own parts, like covers. Make a mould from an original part, polish it up, apply a gel coat for a nice glossy finish, then lay your carbon fibre sheet in, painting epoxy resin on sparingly as you lay it down. Apply several layers, and leave to cure. Be prepared for the first few to be a little rough! Try www. easycomposites.co.uk for more information and advice.