Injection-molded thermoplastic engine cowls for Mercury Marine, Fond du Lac, Wis. (www.mercurymarine.com), Verado outboard engines weigh about 70% of equivalent thermoset SMC (sheet-molding-compound) parts and cost 46% less to make.
The cowl parts of Zytel and Minlon nylon resins from DuPont Engineering Polymers, Wilmington, Del. (www.dupont.com), are finished in a threecoat system that gives first-pass acceptance yields of 95% or better at each stage, according to Mercury Marine. In contrast, SMC cowling parts used in the company's other marine engines need filler, primer, and two finish coats. Painting yields are low using this approach because each coat requires multiple passes to fix defects caused by porosity and solvent popping.
The scoop-shaped top cowl of 33% glassreinforced Zytel nylon is said to be the largest component ever injection molded from the material. The rear cowl is also molded from Zytel and the front of DuPont Minlon mineral/glass-reinforced nylon for added flatness. The lower cowling consists of two parts molded from DuPont Surlyn Reflection Series supergloss alloy and needs no paint. Bemis Manufacturing Co., Sheboygan Falls, Wis. (www.bemismfg.com), molds the six parts.
At the annual Product Design Competition sponsored by the Society of the Plastics Industry's Structural Plastics Div., the engine cowl won the Conference Award, the People's Choice Award, the IDSA/Plastics News Design Award, and was also recognized as the most innovative entry in the competition's Recreation and Leisure category.
— Lawrence Kren
