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Cavities filled efficiently and cost-effectively

Bayer MaterialScience AG : 15 October, 2004  (Company News)
Engine performance is by no means the only factor that distinguishes a good car. Safety and comfort are equally important selling points, possibly more so.
Both these factors can be boosted through the use of polyurethane supplied as a raw material by Bayer MaterialScience AG and used by automotive industry suppliers to produce materials developed specifically for cavity filling. The new Bayfill® ST system enhances the stiffness of load-bearing bodywork parts. Another polyurethane foam, Bayfill® NV, reliably stops noise emissions being relayed through cavities. Both systems are simple and cost-effective to process.

“After test driving high-quality automobiles, drivers are often left with the impression of a distinctive sound usually produced in particular sound spaces,” says Klaus W. Huland, polyurethane expert at Bayer MaterialScience. Sounds produced by the air column resonating in bodywork cavities coupled with noise propagation through various “sound channels” can provide an unwanted counterpoint to the satisfying drone of a powerful engine.

“However, this problem can easily be rectified by filling these cavities with foam,” he says. “Ideally, the foam should be light and provide a seamless filling for the sections and cavities without excessive additional outlay on production.” The solution offered by Bayer MaterialScience does just that. The cavity is simply filled with the Bayfill® NV polyurethane system – “NV” stands for “Noise and Vibration” – via a suitable opening. Here, the material expands of its own accord, filling the resonance space to the required extent and specifically molding itself to each structure. “Our polyurethane system has considerable advantages over competitors’ soundproofing materials,” observes Klaus Huland. “Because polyurethanes are liquid in their raw state, they can reach even remote parts of the cavity quickly and effectively. This eliminates the need for complex manufacturing of pre-formed inserts in high-outlay molds.” The cost-effective polyurethane solution from Bayer MaterialScience is also low-density in its expanded state, which keeps the vehicle as lightweight as possible.

Bayfill® ST (ST stands for “Structural”) is also ideal for high-efficiency filling of cavities with foam. “Bayfill® ST helps increase the stiffness and flexural strength of load-bearing bodywork parts such as A, B and C columns, cross-members, side members and sills,” says Klaus Huland. To do this, the steel sections are also filled with a polyurethane rigid foam, though for this application the foam has been specially developed for optimum rigidity. When applied, the foam, whose density can be adjusted to between 200 and 600 kg/m3, forms a strong, lasting bond with the metal surface. This bond provides additional resistance to external forces. It increases the stability of the member in the same way as some plants increase the stability of their stems by means of lightweight but effective “filling”. “This system can be used in automotive engineering to reduce the weight of the member – or to significantly increase the structural stability and safety of the vehicle while maintaining the same weight,” says Klaus Huland.

In addition to its stabilizing qualities, Bayfill® ST rigid foams also have a very high energy-absorption capacity, as Klaus Huland and his colleagues proved in initial simulations and crash tests, working with specialist testing institutes. Bayer MaterialScience sees its role not only as a supplier of raw materials, but also as a research group with the extensive experience and know-how needed to help its partners in the industry secure and maintain competitive advantages.

“It’s important for us to develop polyurethane systems jointly with users. For instance, we help users ensure Bayfill® NV cures in a precise amount of time, to the second, or adapt Bayfill® ST exactly to a required application. Every customer has their own philosophy, and we take this into account in our efficient, customized development solutions. There are doubtless other applications for our foams that we haven’t even thought of yet, and we’re looking forward to these new challenges,” says Klaus Huland.
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