PARIS – Little by little, volcanic rocks are working their way into the automotive industry. Basalt fibers, extruded from molten basalt rocks at high temperatures, are beginning to compete with less-expensive glass fibers in making composite components.
To make the tiny threads, just 9 microns in diameter, basalt is melted at 4,352° F (2,400° C) and spun into a monofilament that has 40% more tensile strength than glass fibers, is 60% more resistant to shocks and resistant to heat up to 1,292° F (700° C).
Azdel Inc., a Virginia subsidiary of Korean supplier Hanwha Living & Creative Corp., uses basalt fibers in a version of its SuperLite composite sandwich product.
Azdel began life as a 50-50 joint venture between PPG Industries Inc. and GE Plastics (now SABIC Innovative Plastics Holding BV). The company developed a process for making a long-fiber thermoplastic sheet used in door panels, headliners, sunshades and load floors. The sheet, 0.08-0.16 ins. (2-4 mm) thick, rises like bread dough when heated to 0.16-0.24 ins. (4-6 mm) thick, leaving a porous interior that absorbs sound and adds no weight between two thermoplastic skins.
A second-generation sheet under development will loft to 0.31-0.47 ins. (8-12 mm) for even better sound absorption, Azdel says.
At a presentation during the recent JEC Composites show here, Azdel Technical Director Thomas Ebeling says some customers have been asking for a substitute for glass fibers. Even though they are cheaper than basalt, glass fibers cost more at the end of a vehicle’s life.
“Glass adds cost to the incineration process, because the glass coats the inside of the furnace and must be cleaned off,” Ebeling says. “We were asked if we could replace the glass filler.”
Azdel has experimented with carbon fiber, polymer fibers and natural fibers, “but we chose basalt because it drops to the bottom of the incinerator,” when composite panels are burned, he says.
Azdel’s Volcalite product, made with basalt, was used in the headliner of the ’07 Acura MDX cross/utility vehicle and is “on vehicles today,” Ebeling says, while declining to provide details.
“Scoping studies showed basalt to have the greatest chance of acceptance and strongest customer pull,” he says. “It has reduced end-of-life cost penalties due to its glass-free status and has incremental improvement in mechanical properties.”
Cost is a disadvantage of carbon and polymer fibers, while natural fibers have problems with mechanical properties and water absorption. Basalt has properties similar to glass, including high strength and stiffness, plus an intermediate cost well below carbon.
Its disadvantage, Ebeling says, is a lack of suppliers. Most basalt fibers come from Russia, Ukraine and China, partly because the process was developed for the Russian military and aerospace programs after World War II.
Textiles woven from basalt threads have found a use at the high end of the automotive market as a partner for carbon fiber. The instrument panel in the $250,000 Alfa Romeo 8C Competizione coupe has a visible carbon-fiber surface, but underneath is a layer of basalt fabric and aramid fibers, a class of heat-resistant and strong synthetic fibers, at stress points.
Additional layers of carbon fiber in the IP would make it too stiff for safety purposes, says
Paolo Nieri, administrator at Delta-Tech S.r.l., which makes the part for Alfa Romeo.
“The laminate must yield on impact,” he says, and basalt is more flexible than carbon fiber, so the dashboard will absorb some energy if an occupant comes in contact with it in an accident.
Basalt fibers, which are golden or olive in color when dry, turn black when combined with thermoplastic resins, while a glass textile might show tiny specs of white through the weave of the carbon fiber.
Additionally, basalt costs about a third as much as carbon fiber, according to Corbin Cunningham, president of the Dutch company Fibers Unlimited. Basalt is being developed in America for bullet-proof panels on vehicles, he says, and his company is marketing a fabric woven from both carbon and basalt threads.
Flocart Textile Design NV, another supplier of basalt fabric, says it has been approached by several auto makers about the material, including Audi AG. Meanwhile, Flocart Business Development Engineer Pauline Koslowski says Belgian exhaust supplier Bosal Group is studying basalt for sound and heat insulation on exhaust systems.