How Plastic Gears Are Made
A plastic gear is a mechanical component that uses a toothed profile to transmit power and motion from one end of the gear to the other. They can replace metal gears in many applications and have several advantages over their metal counterparts.
Plastic gears do not rust and can be made to operate in many different environments that would destroy or corrode gears made from metal. This means that the gears are durable, reducing maintenance and downtime needs. Also, plastic gears are generally less expensive than their metal counterparts.
The most common methods of producing plastic gears are injection molding and CNC machining. Both can be used for small batches or larger production runs. The decision of which method to use is dependent on the production volume, cost of the equipment and material savings. Injection molding tends to be cheaper for large production runs. It is also faster than machining because of the shorter lead times.
Depending on the type of plastic being used for the gear, different additives and fillers can be added to the base polymer to improve the strength, durability and performance. This can result in better load capacities, torque and life expectancy. These additives are typically in the form of lubricants that can be mixed into the base polymer to eliminate the need for external lubrication. Common lubricants include molybdenum disulfide, Delrin (acetal), graphite and colloidal silicon.
When designing plastic gears, it is important to start with a detailed application specification. This will allow for the most accurate analysis of the gear and ensure that the final product meets expectations. It is also a good idea to choose the correct polymer for the job. Choosing the wrong resin can lead to inaccurate results such as dimensional changes and out of tolerance parts. In addition, the temperature and humidity of the environment can affect gear operation, so the plastic housing should be selected to accommodate thermal and moisture expansion.
Plastic gears can be made to very high accuracy. For example, a typical injection molded plastic gear can have a total composite error between teeth of about 0.075 – 0.125 mm with a corresponding Tooth-to-Tooth Composite Error of around 0.025 – 0.050 mm. This level of accuracy can be achieved by careful mold design, tooling and quality control.
It is essential to understand that the properties of plastic gears are affected by environmental conditions such as ambient temperature, lubrication and duty cycle. This will influence the torque, noise vibration and heat generated by the gear. To minimize these effects, a gear can be annealed after molding to relieve residual stresses. This can be especially useful if maximum dimensional stability is required or if close tolerances are desired. Annealing can also add a thin layer of lubricant to the surface of the gear to help reduce wear and corrosion. The choice of a suitable lubricant is critical since it should be compatible with the plastic being used. This will prevent the lubricant from attacking the gear or causing excessive friction.plastic gear