No more "girlie man" gears

Advanced polymers let designers replace metals in large, complex gear sets that can carry heavy loads and survive harsh environments. A washing-machine-transmission gear set features a housing and two gears with spindles that extend through the case made from long-glass-fiber-reinforced Celstran polypropylene. Polypropylene was used because it withstands hot, soapy, chlorinated water. The long-fiber reinforcement creates an exceptionally stiff and dimensionally stable housing. The other gears shown are made of Celcon acetal copolymer. Close-up of a Celcon GC25A acetal-copolymer gear used in the washingmachine transmission has cored teeth. Coring was used to make wall thickness more uniform and to gain accuracy and better control of tooth dimensions. The P-Gear test unit evaluates potential gear resins for wear, fatigue, noise, and other properties in simulated working environments. Fatigue strength curves generated by the P-Gear unit are measured on standard 2-in. test gears. The data shown was taken using gears made from Celcon M15HP acetal copolymer, a high-performance gear material. Plastic gears have had a successful run in automobiles, appliances, office equipment, and power tools. Polymer performance and processing techniques have advanced to a point where plastic gears will handle higher-torque applications, previously the domain of their metal counterparts. Plastic gears can be good load carriers. They resist chemicals and heat, don't wear much, and keep noise to a minimum. In automotive electrical systems, they replace hydraulic and cable assemblies in interior and exterior mechanisms. These systems rely on plastic gears to quiet and smooth lift-gate operation and give stealthy movements to tracking headlights, windows, and underhood throttle body controls. have all spec'd plastic over metal in recent electronic-parkingbrake gears. The brakes employ 1.2-in. (30-mm) spur gears made from Fortron linear polyphenylene sulfide (PPS). A motor-drive belt powers the gear that drives a transmission for actuating the rear brakes. Designers chose Fortron PPS for its dimensional stability over a broad temperature range, as well as its good chemical resistance and ease of processing. But cost alone is often a stronger motivator for designers to investigate plastic gear materials. Plastics frequently get chosen over metal because of multiple cost-cutting benefits. They provide greater design freedom, letting designers build gears too difficult or expensive if made from metal. They can consolidate parts in existing metal drives to cut fabrication and assembly costs. This includes cluster gears where advanced processing techniques let multiple gears mold as a single part. Molded gears can take on complex shapes for split-path planetary drives and modern, high-efficiency worm and