The gears used in mechanical power transmission systems are often made from metals but more and more manufacturers are choosing plastic as a cost-effective alternative. Plastic gear run lubrication free, are lightweight, chemical resistant, and able to withstand high levels of vibration and shock. But their ability to do this is significantly impacted by four often overlooked variables.
The type of polymer used for the gear, how it is manufactured (machined or molded), and ambient environmental conditions will all affect the performance of the plastic gear. The gear’s temperature, lubrication level and duty cycle will also impact the strength of the material and its creep characteristics. A wide range of engineering plastics are available for gearing, including acetal resins such as Delrin and Duracon; nylon resins such as ZYTEL, NYLATRON, and MC901; and polyphenylene sulfide (PPS)/polyacetal copolymers such as Celcon. Many of these materials can be augmented with fillers and additives to modify the material’s physical and chemical properties.
A major drawback of molded gears is their sensitivity to dimensional stability (creep). Plastic gears must be designed so that they are not loaded statically. Otherwise the teeth will deflect from their normal position and the molded gear may not perform as intended. Creep is accelerated with higher temperature, which in turn reduces the material’s modulus and strength.
Another consideration is that plastic gears are usually made by injection molding, which can take weeks to months for a new mold to be made and the parts to be produced. The best plastic gear manufacturing method for smaller quantities is CNC machining.
Plastics have an advantage over metal gears in that they are quieter and less prone to heat buildup. They also do not resonate as loudly, making them an ideal choice for equipment that requires a clean, quiet, and safe working environment such as medical devices, office equipment and electrical motor-driven applications.
The low density of plastics allows them to absorb vibration and shock, which is especially important in high-speed applications. This helps to protect the components and prevent premature failures. In addition, plastic gears typically do not require lubrication and are very easy to clean.
Another advantage is that the plastics used for gears come from petroleum as a byproduct of oil production and are therefore highly recycled. This helps to reduce the amount of waste that ends up in landfills.