What is in this article?:
- Carbon Fiber Production Simple But Complex
- Winding Process Secret Ingredient
The physical footprint of manufacturing lines is small. However, the carbon-fiber precursor material is delicate and must be handled with care and precision.
A creel unwinds ribbons of PAN at BMW-SGL JV plant in Moses Lake, WA.
MOSES LAKE, WA – There are many steps needed for’s i electrified vehicles to come to life, but perhaps the most critical, and talked-about one, happens here.
In this small town along the Columbia River three hours east of Seattle,joint-venture partner SGL turns a stringy white plastic ribbon made of polyacrylonitrile, or PAN for short, into carbon fiber.
While it once was used only in race cars and ultra-expensive performance cars as a structural material, BMW is using rigid, but lightweight carbon fiber for major structural parts in its new family of electrified cars.
The i3 electric hatchback and i8 plug-in-hybrid sports car have passenger cabins, or lifecells in BMW-speak, made of carbon-fiber-reinforced plastics, which help offset the weight of the cars’ lithium-ion batteries.
The process BMW and SGL have created to make carbon fiber out of PAN is by turns simple and complex. The physical footprint of lines No.1 and No.2 at Moses Lake is small, with relatively few machines compared with other auto-parts manufacturing facilities. However, the material is delicate and must be handled with care and precision.
Paul Bolden, head of production at SGL Automotive Carbon Fiber in Moses Lake, recently gave media a guided tour of the facility, already undergoing an expansion.
In the first section of building No.1, ribbons of PAN, made at an SGL JV withRayon in Otake, Japan, are drawn up out of cardboard boxes onto creels and separated into fine strands in a humidity-controlled environment.
After separation, the PAN, chemically C3H3N, enters the second portion of the plant, where oxidation ovens live.
“There are four ovens per line,” Bolden says. “What’s happening in the oxidization (process) is stabilizing the material (for carbonization).”
Stabilization occurs by adding oxygen to the PAN, a 90-minute process performed at temperatures between 392° F and 500° F (200° C and 260° C). Once oxidized, the material cannot melt and is nonflammable. During oxidation the PAN changes color from white to shades of gold, then finally to black.
“We have a very defined process recipe, with time, temperature and speed that produces a very high-quality carbon fiber,” Steve Swanson, SGL plant manager, says in a production-process video.
After the PAN exits the fourth oven it is oxidized and stabilized, Bolden says. The material then makes a quick trip through low-temperature and high-temperature furnaces for the carbonization process.
Bolden says carbonization aligns the filaments with tension and heat, with furnace temperatures ranging from 392° F to 2,552° F (1,400° C).
After the material exits the high-temperature furnace it is 95% carbon and “we can refer to it as carbon fiber,” Bolden says.
A chemical then etches the outer surface of the carbon fiber so it can bond with resin, which is applied after in a later fabric-making process at SGL’s sister plant in Wackersdorf, Germany.