Advantages of Plastic Gear
Plastic gear is a highly flexible, lightweight and durable industrial component that transmits power. Its flexibility reduces vibration and noise, while allowing it to operate in wet environments. There are many different blends of unique plastic polymers that can be used to make gears, each offering a specialized property characteristic. Some, such as the Delrins (acetals), are self-lubricating. Others, like nylon and phenolics, are fortified with solid-state lubricants such as molybdenum disulfide to reduce friction. Some, such as linear polyphenylene sulfide, are even more durable and offer greater heat and chemical resistance than nylon and acetals.
The ability to flex allows plastic gears to absorb shock and vibration, which helps them perform at higher levels of accuracy than their metal counterparts. This feature also helps to limit the number of sudden failures caused by stress concentration in a narrow area. Unlike metal, plastic gears are also able to resist corrosion, which makes them well suited for use in marine applications or other wet environments.
Another significant advantage of plastic gear is that it can often be meshed with a metal mate without the need for a lubricant. However, this is not always the case, and good design practice requires allowance to be made for a larger backlash than would be necessary with metal gears.
The tolerances required to produce plastic gears are significantly higher than those of metal gears, but this gap is closing as material technology advances. Closer tolerances are now achievable using many plastic polymers that were previously not considered to be suitable for gearing.
One of the most important factors to consider when designing a plastic gear is the contact stresses that are placed on the tooth surfaces while they are meshed. This stress can bend or shear the teeth, resulting in failure by teeth breakage. This type of failure is referred to as static fatigue. The best way to avoid this problem is by providing a wide, smooth contact surface and limiting the amount of mesh pressure that can be exerted.
In addition to the bending stresses that occur, plastic gears must also be designed to handle compressive loads. This is generally not a problem for unlubricated gears, but lubricated gears must be careful to provide a smooth interface with the mate in order to minimize the risk of oil leakage.
Plastic gears can be molded to such high levels of precision that they can have a similar load carrying capacity as metal gears in the same size. However, they are unable to withstand the same level of temperature and humidity fluctuation that metals can, which limits their operating life.
To maximize the life of a plastic gear, its root fillet radius should be large enough to support conjugate gear action, and sharp corners should be avoided. In addition, the gear should be annealed after molding to relieve any residual stresses that may have developed during the molding process. If the application requires high-temperature operation or close tolerances, a thermoset can be used to increase the toughness of the gear.plastic gear