Composites combining the inertness of carbon and the strength of carbon fiber are eating into the market share of steel and metal linings as the friction braking material for large commercial aircraft. Airline operators select composites for their wide-bodies be-cause the brakes weigh 40-50 percent less, remain in service longer and can handle rejected takeoffs better. Typically, airlines replace steel brakes after 500-1,500 landings and carbon-carbon brakes after as many as 3,000 landings. Carbon-carbon brakes, however, can cost two to three times as much as comparably sized steel brakes.
The military used carbon-carbon brakes first in 1971, and now has an extensive inventory. Commercial aviation began adopting the technology about 1980. Now, carbon-carbon has about 25 percent of the commercial market and could double that amount to match metal by the year 2000.
Myriad technologies exist, but basically, carbon vapor deposition or pyrolysis of pitch or phenolic resins produces a carbon matrix reinforced by a woven fabric or mat of carbon fiber.
The technology is going toward less-costly preforms, based on fibers and the CVD process, according to John Beard, business unit manager of Fiberite Inc. in Winona, Minn.
``It's the same or better performance, but [there are] fewer steps in the process. They can get a more predictable performance because the fiber orientation gives better thermal management.''
Amoco Performance Products in Alpharetta, Ga., makes both pitch-based and polyacrylonitrile-based fibers for conversion into carbon-carbon composites.
``Pitch and PAN are very different in structure, properties and carbon yields,'' said Chris Levan, manager of technical services, and there are ``a lot of advan-tages of pitch-based products from the technical side, most especially in brakes.''
Zoltek Cos. Inc. of St. Louis and RK International Ltd. of Muir of Ord, Scotland, supply oxidized PAN fiber, a thermoset nonfusible textile product that must be carbonized to create carbon fiber. Zoltek and RK use a low-cost precursor from Courtaulds plc in Coventry, England.
Aircraft brake producers are evaluating prototypes of Textron Inc.'s carbon-carbon Rapid Densification technology.
``We deposit all the necessary carbon in a matter of hours using a hydrocarbon liquid precursor,'' said William Foulds, director of automotive and friction products for Textron's Specialty Materials division in Lowell, Mass.
Textron has demonstrated the single-cycle RD process and scaled up capacity to make full-size disks that may offer a production alternative to conventional chemical-vapor-infiltration processing, which can take several months. The Advanced Research Projects Agency, and the U.S. Air Force and Navy have funded RD development programs. Foulds said the RD process could be applied to brakes on high-speed trains and high-performance cars and also on transmission components.
On current production of large planes, Airbus Industrie uses carbon-carbon brakes, as does Boeing Co. on the 747-400, 767-300 and 777, and McDonnell Douglas Corp. on the MD-11 and MD-90. Typically, a friction material remains specified for the life of the plane and manufacturing program, which can be 40 years.
Metal gets orders for short-haul aircraft. Boeing specified steel brakes for the next-generation 737, in part because of cost and wheel-well space limitations, and McDonnell Douglas will use steel for its MD-95. Customerscan choose carbon or steel in ordering a Boeing 757 or an Airbus 319 or 320.
BFGoodrich Co. operates a Pueblo, Colo., carbon product facility and assembles carbon-carbon brakes in Troy, Ohio. Its 1994 wheel, brake and landing gear sales were $304.5 million, or 13.8 percent of total sales of $2.2 billion.
Messier-Bugatti/SEP/Carbone, which produces brakes in Paris, reported 1994 wheel and brake sales of about $100 million.
At Aircraft Braking Systems Corp., ``We consume about 200,000 pounds of carbon a year for finished composites for replacement and original equipment,'' said Frank Crampton, vice president of marketing.
ABSC produces carbon discs in Akron, Ohio, and buys similar discs from Hitco Technologies Inc. in Gardena, Calif., and Aero-lor in Paris. For the fiscal year ended March 31, that ABSC unit reported wheel, brake and brake-control-system sales of $208 million.
AlliedSignal Inc.'s Aircraft Landing Systems unit processes its carbon discs - more than 60,000 a year - at a South Bend, Ind., facility, according to Joseph Ruppe, manager of strategic planning. AlliedSignal does not disclose segment sales.
Industrywide, commercial aircraft brakes absorb about $200 million per year of carbon composite materials in finished products, and demand for carbon brake materials is growing about 12 percent per year, Ruppe said.
Growth will depend on how fast airlines buy aircraft and cycle out older planes. Ruppe said the commercial jet transport segment, the primary growth driver, tripled its use of carbon brakes between 1990 and 1995.
