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Bayer Corporation Paper Describes Evolution of High-Density Structural RIM Materials and Technology

Bayer MaterialScience AG : 01 October, 2001  (Company News)
From its initial use in making small parts with relatively simple designs to today's large parts that meet automotive OEM requirements in mass production, polyurethane high-density structural reaction injection molding (HDSRIM) technology has come a long way in a short time.
In their paper, 'High Performance Structural RIM for Large Composites: Beams, Boxes, and Beyond,' Gene Symosko, Launch Team Coordinator for Bayer Corporation's Polyurethanes Division, and his co-authors describe the evolution of HDSRIM from initial uses in bumper beam supports to its current use in manufacturing tailgates and truck boxes for the GMT800 truck box program. The paper was presented at the Alliance for the Polyurethanes Industry's Polyurethanes Conference 2001 here.

Co-authors of the paper are Ron Cageao, Ph.D., Development Scientist, Dave D'Errico, Technical Service Specialist, and Bin Lee, Ph.D., Principal Scientist, all of Bayer Corporation's Polyurethanes Division; Walter Guarnieri, Ph.D., Team Leader of the Baydur/Baypreg Marketing and Development group for Bayer AG; and Pat DePalma, who is responsible for manufacturing and engineering operations for the GM Composite Box program at Meridian Automotive Systems.

'What we learned from the truck box program will help us expand the use of high-density structural RIM across many different markets,' said Symosko. 'This polyurethane technology provides alternatives for structural components in the recreational, agricultural and industrial sectors, not just automotive. The technology offers parts with higher strength and durability yet with less weight than steel or other composites.'

When the idea surfaced of using HDSRIM to produce a large part that would need to be highly durable while maintaining a good appearance, GM turned to companies like Bayer Corporation and Meridian Automotive Systems to help turn the idea into reality.

Developments in polyurethane chemistry, such as the Baydur« 425 IMR high performance polyurethane SRIM system, which allows longer shot times and improves initial wet-out of the glass preform, combined with robot-controlled preform handling, made possible the manufacture of large complex parts with consistent glass loading. Using a 'squeeze-pour' molding technique is also important. The mold is slightly open when the polyurethane is dispensed so when the mold is closed, the polyurethane is forced through the glass fibers using the clamp tonnage of the press. The result is more even distribution of materials in the mold and less movement of the glass fibers.

In his paper, Symosko explains that the glass fiber preform plays a very important role in determining the ultimate physical properties and the heat performance of the SRIM composite. Factors that can affect the performance of the preform include glass type, binder type and glass distribution. In turn, these factors can also affect the ability of the urethane to fully wet-out the surface of the glass fibers.

'Among the key lessons we learned in the development of the truck box was the importance of the interaction between the polyurethane and the glass fiber reinforcement,' Symosko said.

While Bayer seeks to develop improved polyurethanematerials, it also looks for better processing technology. One area of promise reported in the paper is chopped fiber injection (CFI). CFI provides a way to add glass fiber to the mix as the polyurethane is injected in the mold. The CFI process reduces the need to handle glass mats and preforms and may offer significant cost advantages. There are limitations to using CFI, such as parts with steep sidewalls or deep draw sections or that are so large the polyurethane starts to gel. However, Bayer is developing a polyurethane HDSRIM system with an even more extended gel time. This system is currently being tested, the paper reports.

'We gained a lot of important information from our experience with the GMT800 box program,' Symosko said. 'Incorporating HDSRIM technology into making large complex parts is a reality.'
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