Colorless precursor fibers come from a joint venture with Mitsubishi Rayon in Japan. In a 200 meter-long plant in Moses Lake, Washington state, the fibers are pulled over hundreds of reels and baked at temperatures as high as 1,400 Celsius (2,550 Fahrenheit).
This evaporates all the elements they contain except carbon atoms, which remain neatly arranged to give the fibers both their black color and unique strength.
What's left over are filaments one-tenth the width of a human hair. When about 50,000 of them are bundled into a thin thread for further processing, they can lift almost a tonne in weight.
The threads are shipped to Wackersdorf in southern Germany where they are woven into mats in a plant twice the size of an American football field.
At another site about 70 miles south in the town of Landshut, the mats are cut and layered into moulds, put under a vacuum and immersed in a resin. Cured at about 100 degrees Celsius (212 degrees Fahrenheit), this hardens within minutes to create three-dimensional car body parts that are harder and more rigid than steel, for half the weight.
From here they travel to BMW's Leipzig plant to be assembled.
For SGL, carbon fibers are a diversification from its main business of producing graphite electrodes, parts built into steel companies' furnaces to help turn iron and scrap metal into steel. Carbon fibers for the automotive sector account for less than 3 percent of group sales.
(Reporting by Ludwig Burger, additional reporting by Frank Siebelt; Editing by Sara Ledwith)
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