carbon fiber
Carbon fiber is a strong, light and very expensive material. Generally the term "carbon fiber" is used to refer to
carbon filament thread, woven carbon thread cloth. The fiber-epoxy composite made with woven carbon cloth is more properly termed
carbon fiber reinforced plastic (
CFRP or
CRP). It has many applications in
aerospace and
automotive fields, and notably in modern
bicycles, where these qualities are of importance. It is becoming increasingly common in small consumer goods as well, such as
laptops,
tripods, and
fishing rods.
Each
carbon filament is made out of long, thin sheets of carbon similar to
graphite. A common method of making carbon filaments is the oxidation and thermal
pyrolysis of
polyacrylonitrile (PAN), a
polymer used in the creation of many synthetic materials. When heated in the correct fashion, polyacrylonitrile molecules will form into chains, which eventually join to form long carbon filaments. The result is usually 93-95% carbon. Another fiber creation process uses
pitch instead of the PAN process.
These filaments are stranded into a thread. Carbon fiber thread is rated by the number of filaments per thread, in thousands. 3K (3,000 filament) carbon fiber is 3 times as strong as 1K carbon fiber, but is also 3 times as heavy. This thread can then be used to
weave a carbon fiber
cloth. The appearance of this cloth generally depends on the size of thread and the weave chosen. Carbon fiber is naturally a glossy black, but recently colored carbon fiber has become available.
The resulting cloth is usually made into carbon fiber reinforced plastic. This plastic is commonly referred to as
graphite epoxy, and materials produced with this methodology are generically referred to as
composites. The material is produced by layering sheets of carbon fiber cloth into a
mold in the shape of the final product. The alignment and weave of the cloth fibers is important for the strength of the resulting material. In professional applications all air is evacuated from the mold, however in applications where cost is more important than structural rigidity, this step is skipped. The mold is then filled with
epoxy and is heated or air cured. The resulting stiff panel will not corrode in water and is very strong, especially for its weight. If the mold contains air, small air bubbles will be present in the material, reducing strength. For hobby or custom applications the cloth can instead be draped over a mold, and the epoxy is "painted" over it, however because of the resulting lack of strength, this is usually only used for cosmetic details.
BMW has begun studying and creating methods of producing carbon fiber reinforced plastics in its
Landshut plant. To make the roof of the
BMW M3 CSL, 5 layers of carbon fiber cloth are placed in an 1,800 ton press, where epoxy is resin transfer molded and heat-cured in a
robot-automated process. The resulting roof is half the weight of the equivalent
steel roof.
The high amount of (often manual) work required to manufacture composites has hitherto limited their use in applications where a high number of complicated parts is required.
Carbon fiber cloth can also be used in air
filtration.
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