Wednesday, April 24th, 2013

More Plastics Technology to Improve Auto Fuel Economy

The resurgence of the automotive market may seem to have stoked the fires of innovation in the plastics sector, but the reality is that automotive plastics innovation has been bubbling along during the recent slowdown, and the results are just now appearing. For example one recently announced development has great potential for helping boost fuel economy and reducing emissions.

The polyurethane (PUR) supplier Henkel (Düsseldorf, Germany) and the composite component maker Benteler-SGL (Ried im Innkreis, Austria) jointly have developed a process they say will allow automakers to switch from the heavy steel leaf springs used in auto suspensions to composite leaf springs that can be up to 65% lighter.

This composite leaf spring of PUR resin weighs up to 65% less than metal leaf springs.

This composite leaf spring of PUR resin weighs up to 65% less than metal leaf springs.

That’s a big savings. Auto designers who replace metal parts with plastics alternatives that save 10%, even 5%, are happy. Saving weight means better fuel economy, which translates into reduced emissions, two important goals in the transportation sector. A 65% weight reduction in a heavy steel part should get a party started.

It’s not that composite leaf springs are something new. They have been designed into a number of GM cars, the Corvette probably being the best known, as well a few Volvos, a Mercedes van, and the Smart ForTwo, to name a few. However, getting the production volume needed for mass-market cars remained a stumbling block. Cycle times were too long, so Henkel and Benteler-SGL developed a solution.

Henkel’s Loctite MAX 2 provides a polyurethane-based matrix resin that Henkel says cures significantly faster than the epoxy products usually used. In addition, the PUR’s low viscosity lets it penetrate the fiber material more easily and thoroughly, resulting in short injection times. Without releasing specifics, the  companies say  cycle time with this process will allow sufficiently high volume production.

A resin transfer molding press at Benteler-SGL.

A resin transfer molding press at Benteler-SGL.

Benteler-SGL is an established producer of carbon- and glass-fiber composite auto components such as side panels and doors, and uses the resin transfer molding (RTM) process to reach the output needed for mass-market autos. The RTM process enables control of the curing reaction by adjusting the temperature or by adding an accelerator.

Using Henkel’s PUR resin in Benteler-SGL’s RTM process reduces the risk of local overheating that can cause part shrinkage. The PUR generates less heat during curing than do the generally used epoxies. Even thick parts with many fiber layers cure quickly.

Henkel says it and Benteler-SGL  have developed a process that will make composite leaf springs on cycles short enough for high volume production, and the parts have an attractive properties profile. Add that to that 65% weight reduction from steel leaf springs and this definitely has possibilities.

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