Many industrial settings use plastic gear to transmit torque and rotational motions. The flexibility of plastic gear allows it to absorb shock and vibration, reduce noise, provide a lower coefficient of friction, and be more durable than metal alloys. The most popular types of plastic gears are gear racks and bevel gears. These gears are paired with a matched metal pinion that fits into the gap between the plastic gear teeth. When the matched metal pinion is meshed with the plastic gear, they facilitate torque transmission and rotations by transferring motion between two intersecting axles.
The common types of engineering plastics used to produce plastic gear are Polyamide (Nylon) for machined gears and Acetal for molded gears. These plastics are fortified with additives and fillers that give the gear a higher level of performance and durability. Plastics fortified with molybdenum disulfide, for instance, offer good resistance to abrasion and impact. Other plastics that may be suited for gear production are phenolics, polyethylene and polypropylene.
Plastic gears are typically made of a more dense material than their metal counterparts, but they also have the benefit of being lighter. In some cases, plastic gears can be half as heavy as their metal counterparts and have the same strength. This can make the gears easier to handle and allow them to fit into a smaller space. This is important in mechanical power transmission because it reduces the size of the overall system and increases efficiency, especially when operating at high loads.
Another advantage of plastic gears is that they usually require less lubrication than metal gears. Many plastics have inherent lubricity that is sufficient to reduce gear wear under normal operation. When this lubrication is insufficient, a plastic gear can be fortified with a solid state lubricant to increase its effectiveness. Some lubricants that are appropriate for plastic gears include greases, oils and PTFE. Oils and lubricants must be compatible with the particular plastic resin being used in order to avoid a degradation of the polymer and to maintain an adequate level of lubrication.
Another way that plastic gears can improve their lubrication is through annealing. This process helps to relieve residual stresses that develop during the molding and cooling operations. The annealing process also adds a small amount of lubrication to the gear. In addition, plastic gears can be assembled using a variety of fastening methods. These can include splines, keys and integral shafts as well as plain and knurled press fits. The best method to use depends on the type of plastic and the method of assembly. The splines and keys should be designed to match the plastic gear’s coefficient of thermal expansion to prevent stress from accumulating in the gear. Other fastening methods such as set screws and plain or knurled press fits should be avoided because they can cause damage to the gear.