Long-fiber SRIM technology has yet to make as many inroads in North America as in Europe. But this highly automated process for producing structural polyurethane composites may soon become more familiar here thanks to a new applications-development facility launched last month by Bayer Corp.
Long fiber processing replaces traditional two-step SRIM, or "structural reaction injection molding," in which preforms or glass mats are placed in the tool prior to the introduction of a poured polyurethane resin. With long fiber technology, a robotic mix head injects the glass fibers and resin into an open mold at the same time. Only then does the mold close to form the finished part at pressures of roughly 150 psi—somewhat higher than standard RIM. The length and loading of the glass fibers can vary, depending on application and mechanical property requirements. A typical level would be 30% of 1-inch fibers, reports Technician Specialist Jim Kotar.
Equipment-wise, Bayer's lab features a 150-ton press whose 4×6 ft platens can handle production-sized molds. The lab has a few twists that set it apart: Its custom-built robot—a Class I, DIV2, six-axis model from Fanuc—has been designed to work not just in a clean-room environment but also in close proximity to combustible materials. The line can also use a variety of in-mold coatings and decorations. These include two-component polyurethane paints, elastomer coatings, and in-mold decorations that use films, fabric, or vinyl skins. "These decorating techniques allow production of high-quality decorated parts out of the mold and often offer significant cost savings compared to secondary painting operations," says Snyder. Finally, the line can produce not just solid urethane parts but also foamed components.
Compared to the traditional two-step RIM method, which has far lower capital equipment costs, long fiber will gain ground in applications that see a cost reduction from the elimination of process steps. "Automation is the key," says Bayer technical specialist Craig Snyder.
In fact, he predicts that automation will help make the process competitive with SMC composites—especially in the case of foamed urethane composites. Snyder concedes that foamed urethanes don't match SMC when it comes to a flex modulus. "But some SMC applications don't need all the material's modulus," he says. In these applications, the case for foamed urethane comes down to a strength-to-weight ratio. Snyder points out that the foamed urethane offers specific gravities as low as 1.0 and flex moduli of up to 500,000 psi. "There are a lot of opportunities for weight reduction," he says.
With its potential for cost and weight reduction, long fiber technology seems unlikely to stay a European process for long. Until recently, all ten of the production lines built by Krauss Maffei, the inventor and primary supplier of long fiber equipment, have remained outside of North America, according to company vice president John Mead. Last fall, however, saw the launch of the first North American production (see sidebar). And Mead predicts that more local production lines will soon follow. "We're starting to see some serious interest from the automotive suppliers," he says.
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