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The lightweight that's tough to the core

Bayer MaterialScience AG : 24 March, 2005  (Company News)
Extremely strong composite sandwich elements, manufactured using the sprayable Baypreg
Impressive features of the sandwich components are their low weight, high impact strength and stiffness, and high-quality surface. One of the many applications are steps for various motor homes and caravans from renowned manufacturers in this sector. The steps are produced by Formtec PUR Verarbeitungs GmbH of Dornstetten, Germany.

“The sandwich composite is comprised of an expanded polystyrene core and two natural fiber outer layers that reliably absorb all tensional forces,” says Dr. Marc Schütze, a polyurethane expert at Bayer MaterialScience. “To produce this composite, natural fiber mats are impregnated with the liquid, black-pigmented Baypreg® polyurethane system and then placed in an open mold. This is followed by the core layer and an additional layer of impregnated fibers. Upon closing the mold, the components are automatically pressed into the desired shape. The finished part is then demolded about six to eight minutes later.”

A major advantage of this production method is the gentler processing temperature of 65 °C, as the polystyrene core is only resistant up to about 68 °C. It also guarantees high levels of design freedom and optimum shaping. More important however are the light weight and outstanding mechanical properties of the composite element. Measuring 30 x 60 x 30 cm, the steps weigh just 2.6 kg and can withstand compressive stress of up to 400 kg at the front and loads of over 500 kg at the rear.

The production process is extremely cost-effective thanks to the short cycle time and low processing temperature. It also offers manufacturers of the composite sandwich elements a great deal of flexibility as the natural fiber mats can still be processed between 30 and 45 minutes after impregnation with the Baypreg® system – a relatively long time for polyurethane.

“The polyurethane system is therefore very well suited to manufacturing large components, e.g. for vehicles produced in small series,” says Dr. Schütze. “The flexibility of the process is also evident in the wide range of materials available for the core. In addition to expanded polystyrene, paper or thermoplastic honeycombs and rigid foams may also be used depending on the requirements profile. These core materials even allow manufacturers to opt for a higher processing temperature and thereby reduce the cycle time even further.” Given all this potential, the development of polyurethane composite elements for further fields of application is really just a question of time.
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