Plastic gears run lubrication free, are durable and lightweight, and offer excellent wear resistance, quiet operation, and shock absorption. But, like metal gears, they have limits on load, speed, and temperature.
These limits are often influenced by the tooth geometry, accuracy, and manufacturing constraints of the molded gears. To avoid these pitfalls, designers should understand four critical factors of plastic gear design: load capacity, tooth geometry, material, and temperature.
Plastic gears are becoming increasingly used in a wide range of applications. They are quiet in operation, have good wear resistance and can be made inexpensively by injection molding. They can also be mated with metal gears without the need for lubrication. However, they do not have the same load capacity as metal gears.
For this reason, it is important to take into account the effect of temperature on the strength of plastic gears. This is difficult to do because there are no international strength rating standards for plastic gears. Instead, engineers must rely on domestic or in-house guidelines.
The main types of plastic gears are POM (polyacetal copolymer, Duracon) and MC nylon (6-carbon polyamide). Both have excellent mechanical properties, but POM has the advantage of being injection molded. It is also dimensionally stable and resists moisture absorption. It is suitable for precision gears. However, it needs continuous lubrication under heavy loads. In contrast, MC nylon is an elastomer that can absorb shocks and vibrations.
The plastic materials that are used for gears tend to have less load carrying capacity than metal gears. They also are not as dimensionally stable and are not as resistant to temperature or humidity. However, these weaknesses are being reduced by advances in the science of plastics and injection molding.
Typically, plastic gears are made of engineering plastics such as polyacetal (POM), known as DELRIN and Duracon; and MC nylon which is a type of polyamid resin. They can be made to withstand harsh operating conditions such as high temperatures and pressures, and they do not require the use of oil to lubricate them.
The performance of plastic gears depends upon the design of the mold, the material, and the environment. It is important to understand these factors in order to arrive at a functional design for the gears. For example, the tooth strength and load capacity can be calculated using a specific formula. Likewise, the temperature rise that occurs when the gears mesh can be combatted with the addition of heat sinks or the use of internal lubrication.
Plastic gears are used in many applications, from office automation equipment to electric goods and toys. They are lightweight, quiet and non-rusting. They can also be injection molded, making them cheap and easy to produce in large quantities. These benefits make them a popular alternative to metal gears.
However, they can still suffer from dimensional change under load and have a lower strength than metal gears. They also can absorb moisture and chemicals, which affect their strength and stiffness. Therefore, they must be designed carefully to meet the required application specifications.
When designing a plastic gear, it is important to choose a polymer that can handle the expected loads. You can do this by comparing the tensile and bending strengths of different materials. For example, MC nylon is a good choice for gears that must withstand a large amount of force. It has a higher tensile strength and bending strength than POM. It also has the added benefit of being less expensive than POM.
Plastic gears are starting to replace metal gears in a growing number of applications. They can run lubrication free, are lightweight and chemically resistant. These specialized components are now used in everything from automotive windshield wiper motors to industrial equipment and medical devices.
These gears are manufactured from petroleum byproducts that would otherwise be discarded as waste. They also use less energy to manufacture than metal gears, and they produce fewer greenhouse gases during manufacturing and operation. They are also more sustainable because they do not contain any bisphenol A (BPA) or other harmful chemicals that can disrupt hormones in humans and animals.
However, it is important to note that plastic gears are different than metal gears and require special consideration when designing. They have larger coefficients of thermal expansion and can absorb moisture. They can also experience a higher degree of backlash due to the greater dimensional instability. In addition, they are subject to hysteresis heat buildup that can lead to excessive noise and vibration.