Why Plastic In Gears?
While metal gears handle loads better than comparably sized plastic gears and have better dimensional properties as temperature and humidity changes, plastic offers many cost, design, processing, and performance advantages over metal.
molding plastic gear material
The design freedom inherent in molding plastic allows more efficient gear geometries than are possible with metal. Molding can create shapes that are hard to form at a reasonable price in metal, such as internal gears, cluster gears, and worm gears. Plastic gears can be wider than metal gears, so they enable greater load-bearing capacity and more power transfer in a single stage. Plastics have also become essential in the ongoing quest for quieter drives, which call for high precision, novel tooth shapes, and lubricious or flexible materials.
Much of the reason for the growth of plastic gears rests on advances in molding and materials that allow for larger, more precise, and more powerful gears. Early plastic gears tended to be spur gears, typically less than 1 in. across, that delivered no more than 0.25 hp. Now gears are made in many configurations and commonly operate at 2 hp in diameters of 4 to 6 in. Gears are molded with diameters as large as 18 in. By 2010, power levels should rise to 10 hp or more.
Processors face many challenges in creating gear geometries that maximize power while minimizing transmission error and noise. Such gears call for great precision in molding concentricity, tooth geometry, and other properties. Some gears, like helical types, can involve complex mold movements to release the finished product, while others need cored teeth in thicker sections to control shrinkage. Although the latest polymers, equipment, and tooling put the next generation of plastic gears within reach of most molders, the true challenge any processor faces is in adapting its entire operation for such high-precision work.