Knitting a Little Magic: How Carbon Fiber Is Finally Getting Cheaper
11-13-12, 04:27 PM
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Knitting a Little Magic: How Carbon Fiber Is Finally Getting Cheaper
Knitting a Little Magic: How Carbon Fiber Is Finally Getting Cheaper
Carbon fiber (CF) has become vital to modern life. Boeing’s 787 Dreamliner contains 35 tons of the stuff, and it’s a core ingredient in our running shoes, bike frames, tennis rackets, golf clubs, and fishing poles. Spendthrift fans of the black *composite furnish their bathrooms with CF toilet seats ($300) and bathtubs ($72,000).
In the automotive world, the trickledown from motorsports—where CF composites arrived 40 years ago—to McLarens, Corvettes, Vipers, and affordable cars has been agonizingly slow. Even though this light material’s strength and stiffness *virtues are well-known [see diagram], at more than $10 per pound (when combined with epoxy resin), it’s still too expensive for mass-produced cars.
To lower that hurdle, carmakers are teaming with composite experts in a game of musical alliances: Audi and Voith, Daimler and Toray Industries, Ford and Dow Chemical, and GM and Teijin. There’s also a three-way deal between Lamborghini, Callaway Golf, and Quantum Composites. But the most interesting tie-up is between BMW, Toyota, Volkswagen, and Germany-based SGL Group. Two years ago, BMW and SGL built a $100 million facility in Moses Lake, Washington, to manufacture CF at lower cost. VW elbowed in last year by purchasing an 8-percent stake in SGL. Then a few months ago, Toyota—a loom maker since 1926*—and BMW linked up to share ultralight body technology.
The Moses Lake strategy is vertical integration, the plan Andrew Carnegie used to make cheap steel and Henry Ford employed to build affordable Model A’s at a profit. Ford’s Michigan Rouge plant assembled cars from iron, steel, glass, tires, and plastic all made on the premises.
Eliminating the middlemen and controlling the processes is key here, too, as process is a huge part of the fiber’s cost: Its $30-a-pound price is due to the electric power required to turn strands of polyacrylonitrile (C3H3N; PAN) precursor into strings of carbon atoms bonded in a crystal structure.
Wind turbines and solar arrays are fashionably green sources of electricity, but too weather-susceptible to sustain a manufacturing plant. In contrast, hydropower is green, dependable, and affordable, three reasons why BMW and SGL built their CF factory in Washington. The Wanapum Dam hydroelectric plant, located on the Columbia River 40 miles from Moses Lake, feeds the BMW-SGL facility with electricity costing 2.8 cents per kwH, 60 percent less than the national average for industrial electricity.
Another joint venture—one between SGL and the Mitsubishi Rayon Company—produces the pure-white PAN material in Otake, Japan. After shipment to Moses Lake, PAN is successively heated at temperatures ranging between 400 and 550 degrees Fahrenheit, during which the color gradually changes from white to yellow, gold, copper, and brown as hydrogen and nitrogen atoms are expelled. Then the fibers are drawn through a 1500–3100-degree carbonizing furnace devoid of oxygen. Here, the color changes to pure black and neatly aligned carbon crystals form.
A subsequent oxidation process etches the fibers’ surface to improve the bond between the CF and the resin materials that will hold the woven fibers in place in a roof panel or body structure. The final sizing step coats the CF with a protective layer of epoxy. Fifty-thousand fibers are then wound together to create a yarn called “tow,” which is placed onto bobbins for shipment to Germany. There, BMW’s Wackersdorf factory stitches the tow from Moses Lake into CF cloth that’s shipped to Landshut where individual panels for the i3 and i8 electric cars are molded. Body framing and assembly of BMW’s CF-intensive cars takes place in Leipzig, Germany.
The CF produced by BMW and SGL is one-third the cost of material purchased from competing suppliers. Other makers have made encouraging strides in composite molding processes, too. Lamborghini and McLaren now use resin-transfer molding (RTM)—instead of the time- and labor-intensive hand-layup and autoclave-curing procedures of the past—to make monocoques. Preformed CF cloth, epoxy foam, and aluminum inserts are loaded into an open, multipiece mold. The mold is closed, a precise quantity of epoxy resin is injected, and a part is cured in a few minutes. The Lamborghini Aventador’s roof is adhesively bonded to its tub, yielding a stiff, 325-pound composite body with molded-in chassis and powertrain attachment points.
In collaboration with Callaway Golf, Lamborghini developed another alternative to autoclave molding called forged composites. Here, randomly oriented CF and epoxy resin are squeezed and cured inside metal dies resulting in light, low-porosity parts.
Corvette and Viper CF manufacturer, Plasan Carbon Composites, took on the ambitious task of streamlining autoclave methods. A reusable silicone canopy replaces consumable plastic-sheet bladders. Nickel-lined dies are quickly heated and cooled with circulating oil to cut total cycle time to only 17 minutes per part. Plasan’s new facility in Walker, Michigan, can produce CF components as large as 7 feet by 7 feet for up to 40,000 cars per year. That’s enough to support a CF-intensive Corvette or, possibly, the next-generation Chevy Volt.
The Oak Ridge National Laboratory has determined that trimming a car’s weight by 10 percent improves mileage by 7 percent. That means when CF composites become affordable, their use will spread through three diverse auto categories—sports cars perpetually hungry for weight savings, hybrids and EVs burdened with heavy batteries, and mass-produced models that will need this technology to meet the 54.5-mpg CAFE standard for 2025
http://www.caranddriver.com/features...aper-tech-dept
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