Materials Update 19878

High-temp resins boost turbo performance

By: Michelle Maniscalco

Underhood automotive applications flourished when the first high-temperature nylons were introduced decades ago. Air intake manifolds and engine covers seemed to transform overnight from cast aluminum to injection molded plastic. In bringing these products to the auto market, designers and resin suppliers made huge technological leaps to meet performance, cost, and weight goals.

Today's automotive designers are reaping the benefits of this intensive development, and many examples can be found in the 2001 winners of SPE's Automotive Div.'s Innovation Awards. One such winning application, charge-air-cooler (CAC) end tanks for Ford F-250 through F-550 diesel pickup trucks, showcases the flexibility and performance options now available with high-temperature polyamide resins.

Let's first start with some background: A charge air cooler is also known as an intercooler. It is an air-to-air heat exchanger that cools hot, compressed air coming from a turbocharger's compressor. Before the air gets to the intake manifold, the CAC cools it to increase density.

Interestingly, the CAC end tanks were cospecified (by molder Carlisle Engineering Products and its customer Valeo Engine Cooling) in three high-temperature and dimensionally stable polyamides: DuPont Zytel HTN, Solvay Amodel, and Ems-Chemie Grivory. Each resin is a 45 percent glass-filled grade that is injection moldable in water-cooled molds. According to Larry Butterfield, vp of advanced engineering for Carlisle, each of the three resins was chosen for its ability to withstand temperature spike requirements of more than 400F and pressures of up to 40 psi. "These parts withstand repeated high pressure-temperature cycles without fatigue failure at lower cost and weight than aluminum," he says.

The CAC end tanks replaced cast aluminum versions for a weight savings of 40 percent (4 lb) per vehicle. As the first application of its kind to switch to plastics, however, the tanks received rigorous endurance testing to ensure they would perform as well or better than aluminum.

Perhaps the most dramatic change in switching to plastic tanks was found in the assembly phase. The new tanks eliminated a significant step: welding the aluminum end tanks to the CAC cooling core. At volumes of 300,000 sets per year, eliminating this step offered substantial cost savings.

To mold these highly filled resins, Carlisle built tools with multiple wear resistance coatings and custom designed sprue bushings. A specialized ejection system allows for fully robotic molding.

One of the biggest challenges in this winning application involved meeting Ford Motor's requirements in a short time frame. In fact, the project moved from concept to production in less than 12 months. To speed up the process, Carlisle used its rapid prototyping and finite-element analysis resources. "We were able to innovate without sacrificing quality or end-use performance," Butterfield says.