A plastic gear is a mechanical part that converts rotational motion to linear motion. The main benefit of this type of gear is that it is much quieter than metal gears, which makes it a desirable choice for applications that require an environment with low noise. They also offer greater resilience and a higher tolerance level than their metal counterparts. These characteristics make them ideal for industrial gears such as the drive system of office automation equipment or the loader of electric goods.
The main plastics that are used to manufacture gears are polyacetal, which is often called POM, and polyphenylene sulfide, which is known as PPS. These are usually combined with other additives and fillers to improve their performance, particularly their strength, fatigue resistance and dimensional stability. They are also water-resistant, which is important for gears that work in marine environments or on machinery that can come into contact with water and other chemicals.
Plastics are generally less dense than metals, which means they are lighter in weight and have lower inertia. As such, they can typically be operated at faster rotational speeds than their metal counterparts. They are also capable of absorbing vibrations, which can be a major problem in many applications. This allows them to perform reliably under high loads, without causing shocks or sudden failures.
These characteristics make plastic gears a perfect alternative to metallic gears. However, there are some design factors that must be taken into account when using them for specific applications. These include the fact that plastics have different coefficients of thermal expansion, density and modulus of elasticity than other materials. This means that they must be properly matched with other components, including metal gears and inserts. In addition, it is necessary to consider that if the nominal wall thickness of a plastic gear changes significantly from one area to another, it can result in the formation of out-of-tolerance parts.
There are a number of ways that plastic gears can be made. They can be machined or molded, with the latter being the preferred method. Injection molding can produce plastic gears with a high accuracy, as long as the appropriate material is selected. For example, unfilled nylon or acetal can be molded to meet the needs of most gear applications.
It is important to note that the tolerances for molded plastic gears are not as tight as those of machined gears. This is because the process of molding involves heating the plastic to a certain temperature, which will cause it to shrink in different areas. This can lead to problems, such as the gears being out of alignment or the teeth slipping. However, it is possible to get a better fit by using the right plastic materials and ensuring proper mold design and quality control.
In general, the most common types of plastic gears are bevel and cross-axis helical. These are good choices for plastics because they have a point-contact geometry when new and a line contact as they wear, making them relatively forgiving of alignment and manufacturing errors. Plastic gears can also be produced in a range of capacities, from very small to very large.