The air-intake manifold on a high-end European car may be one sign of a renaissance for phenolics.

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Phenolic won over PPS and high-temperature nylon for this BMW air-intake manifold. (Magnesium shell is cut away to reveal phenolic housing.)

The air-intake manifold on a high-end European car may be one sign of a renaissance for phenolics. This “old-style” thermoset has been losing ground for decades to engineering thermoplastics.

Although glass-reinforced nylons dominate injection molded automotive intake manifolds, a new manifold for the eight-cylinder BMW 7 series (735i and 745i) is made of phenolic. Development of this application was a joint effort of BMW Group in Germany, system supplier Pierburg AG, injection molder Baumgarten GmbH, and materials supplier Vyncolit N.V. of Belgium.

The intake manifold was initially prototyped in glass-reinforced PPS and PPA (a high-temperature aromatic nylon). Ultimately, the housing was molded in Vyncolit X7250 phenolic filled with glass fibers and beads. One reason is that it retains high stiffness at 140 C (284 F) despite an average wall thickness of only 2.5 mm. Room-temperature flex modulus is 120,000 Mpa (1.74 million psi). Maximum temperature exposure of the housing is 338 F.

The phenolic housing is injection molded in nine pieces, which are bolted together. Eight single-piece rotors are mounted inside the phenolic housing. They are injection molded of Vyncolit X6952 phenolic with 55% glass fiber, which has even higher stiffness than the housing material. They withstand heat exposure up to 356 F. The complete unit weighs 11.88 lb, including metal inserts. The whole assembly fits inside a magnesium outer shell.

 

Phenolic renaissance

Vyncolit sources see the BMW manifold as one example of a revitalizing of phenolic applications under the hood. This market is growing 15%/yr in Europe, says Henny van Dijk, president of Vyncolit North America. After its recent acquisition of Rogers Corp.’s Moldable Composites Div., Vyncolit NA opened a Technical Market Development Center near Detroit.

Vyncolit specializes in high-end glass-filled phenolics for metal replacement. Van Dijk cites growing applications in automotive water pumps, temperature-regulator modules, fuel pumps, transmission reactor/stators, and commutators. Promising applications in development include air-conditioner compressors and throttle bodies.