A highly successful metal replacement application is a new supercharger outlet elbow/duct made of DuPont™ Zytel® HTN PPA from DuPont Performance Polymers. The intermediary duct for the outboard engine captures all the value of engineering polymers – parts consolidation, high-temperature resistance, lower weight and reduced cost – with no performance tradeoffs. The high-performance duct is the first use of a thermoplastic in a pressure-charged air handling duct for outboard engines. The thermoplastic duct, which delivers charged air from the supercharger to the charged air cooler, operates in an extremely hot environment (up to 175°C). Zytel® HTN51-series resin, a high-temperature resistant PPA, meets the stringent thermal requirements, replacing thin-gauge 1018 formed steel which also required a heat sleeve for added thermal protection. The 7-in-long, 2.4-in dia. thermoplastic duct doesn’t require a heat shield and provides a cooler touch. The conversion from metal to Zytel® HTN PPA reduces the number of parts (six to five) and lowers associated part costs. The plastic design eliminates the corrosion layer and a related painting step which was required on the steel version and also offers more pleasing aesthetics (better surface appearance). Also eliminated was a failure of the metal to repeatedly cut the rubber cuffs at the end of the duct. Known for its exceptional temperature and load resistance, Zytel® HTN resin also provides 15% faster cycles than competitive PPA materials. The material’s high-glass transition temperature of 145°C facilitates better flow and faster part ejection. The supercharger elbow duct was manufactured by using a rotating core to produce a gentle, curved design which helped minimize pressure drops. The injection molding process also produced parts with greater dimensional stability than those made of formed steel.
The plastic supercharger outlet duct is used on all four- and six-cylinder models of Mercury Marine’s flagship Verado supercharged outboard engine. Mercury was an early adopter of engineering thermoplastics in outboard engine components and has increasingly used DuPont materials for their unique benefits over traditional materials like metal.