How is Carbon Fiber Made?
Carbon fiber is considered to be the dream material of every engineer as it is lightweight and, at the same time, incredibly durable. It consists of thousands of parallel strings. These strings can be twisted or woven together into carbon fiber composites. Carbon fiber is such a valuable material because it is five times stronger than steel.
To make carbon fiber, a plastic PAN fiber is used. It is composed of thousands of filaments that are thinner than a human hair. They alter it chemically to form a chain of carbon atoms which in turn are utilized for the final product. There are special machines in which they line up thousands of these fibers. After the machine, the fibers travel through an oxidation oven for several minutes.
The temperature in the oven is around 480 degrees F. Because of this temperature, the fibers pick up oxygen molecules from the air. This process rearranges the atomic structure of the fibers and makes them resistant to heat. As the fibers oxidize, they change color and turn black. After being oxidized, they are ready for the next process, which is carbonization.
The fibers are heated in an oxygen-free gas mixture. Thanks to this process, the non-carbon atoms are expelled. The remaining carbon atoms are transformed into tightly bonding crystals, running parallel to the length of the fiber. This is where the material gets its strength. The fibers then travel through a bath of electrically charged water that edges the fibers’ surface so they will better absorb resin.
Next, a light preliminary coat of resin is applied, which bolsters the fibers’ chemical bond to the molding resin. After this process, the fibers are either woven into a carbon fiber fabric or mixed with resin to mold the product. It can be a roll of continuous fiber thread, woven fabric of mesh type threads, and a prepreg product, semi-finished for use. The use of prepreg is widespread worldwide.
The resin is a formula of epoxy coupled with powdered hardeners and accelerators. Workers pour the resin into a filming machine, which prints the resin into a thin wet layer onto paper. Another machine meanwhile organizes 200 to 300 carbon fibers into a carbon fiber web. The thickness of the web determines the thickness of the prepreg sheet.
Typically, two rolls of resin-coated paper are mounted onto the resin impregnation machine. A heating element warms up the web as it enters to facilitate the absorption of the resin. Then, the heated carbon fiber web is sandwiched between two sheets of resin-coated paper. Thanks to the high-pressure heated rollers, the resin penetrates the millions of carbon fiber filaments.
In a cooling place, the liquid resin turns into a gel so that at the next station, the paper can be removed. In the next station, the top of the prepreg sheet is covered with a polyester film. After that, the sheet is wound into a roll. In the factory’s lab, technicians run quality control tests on prepreg samples. Such testing ensures that carbon fiber delivers optimum strength, durability, and heat resistance.
Needless to say, manufacturers across the world employ various techniques which are company secrets, but in the broad sense, the above-mentioned process of carbon fiber creation is the one that everyone follows.
Some of the biggest manufacturers are Hexcel, Mitsubishi Rayon Co. Ltd, Umatex, Zoltek, Toray, Toho Tenax, Nippon Graphite Fiber Corp, Solvay etc.