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A Brief Guide to Selecting Polymer Gears Over Metal Gears

August 24, 2022

One option you may not think of when selecting a gearbox for your application? The material of the gears! Gear material can be classified into two types: metal and non-metallic (such as polymer/plastic). Metal gears have several advantages over plastic gears, including higher strength, improved accuracy grades, a greater degree of reliability, and the ability to sustain higher temperatures. However, they come with some limitations, including higher noise and vibration, higher weight, and an increased cost. These limitations play important role in selecting polymer gears over metal gears for specific applications. Let’s cover a few of the key benefits and selection criteria for polymer gears, as well as Portescap’s capabilities with this gearing material.

3-stage planetary gearbox with polymer planet gears

Figure 1: Typical 3-staged planetary gearbox with polymer planet gears

Benefits of Selecting Polymer Gears

The specific gear material is selected by focusing on specific application requirements and critical design features, including gearing strength, required lifespan, working temperature, and cost. As mentioned above, polymer gears are characterized by a few traits that make them ideal for a wide range of applications. These traits include:

  • Lower Noise and Vibration. Polymer gears are quieter and feature less vibration than metal gears due to their excellent noise and vibration dampening properties. This makes them an ideal choice for medical device applications such dental tools, cataract surgery tools and tattoo machines that demand lower noise due to sensitive working environments.
  • Lightweight. As you might can guess, polymer gears aren’t as heavy as metal gears! In fact, polymer gears have a lower density than metal gears and are, on average, four times lighter than their metal counterparts. Their lower weight and moderate strength gearing mean that they are well-suited for applications prioritizing these qualities, including robotics, prosthetics, exoskeletons, and electrical bicycles.
  • Lower Cost. Because polymer gears at higher volumes are a lower cost option than metal gears, they’re typically a more economical solution for applications that require higher motor volumes, like fork finger actuation, conveyors, and general-purpose robots. Since most polymer gears are made through molding, they are much economical than metal gears which must be made through machining.
  • Optimum Torque Carrying Capacity at Moderate Speed. While a tradeoff does exist in terms of accuracy and life for polymer gears vs. metal gears, the strength and dampening properties of polymer gears are nevertheless balanced by their reinforcement by adding various fillers. These fillers, which can include glass fiber, carbon fibers, aramide fibers, and mineral fibers, among others, are added to the base polymer material and improve the strength of the gear, as the load is carried by these high density, high strength fillers.

Portescap’s Capabilities with Polymer Gears

Portescap’s polymer gears selection is ideal for markets where factors like low noise, lighter weight, and lower cost dominate over characteristics such as strength, accuracy, higher life, and high-temperature sustainability; medical infusion systems, robotics, dental and surgical tools, tattoo machines, and automotive are only a few of these. We’re not only able to provide polymer gearing solutions for specific requirements in gearboxes of varying sizes, including 10mm, 16mm, 22mm, and 27mm, but we also offer various polymer materials for gears like POM, PEEK, Ryton, Nylon, as well as different grades of these materials. In addition, we have molding capabilities for different modules and sizes of gears, where the quality grade maintained in the molded gears is up to DIN 8. Another key capability is our testing and simulation process - all Portescap gears are carefully designed and simulated using sophisticated gearing simulation software at given load conditions for specific application requirements.

Application in Focus: Testing of Polymer Gears for a Low-Noise Dental Tool

Portescap was approached by a dental tool manufacturer to engineer a 16mm planetary gearbox to be used in a low torque, low-speed dental tool application; the manufacturer requested a gearbox with lower noise than their existing solution comprised of metal planet gears. During the testing (Figure 2), polymer planet gears were used instead of metal gears, and the noise of the two gearboxes was compared. As you can see in Figure 3, a significant improvement of 10% to 15% lower noise and lower vibration is achieved using polymer planet gears instead of metallic planet gears.

test set-up for noise and vibration measurement for polymer gears

Figure 2: Test set up for noise and vibration measurement

typical NVH measurement with planetary gearbox

Figure 3: Typical NVH measurement conducted on a planetary gearbox with metallic and polymer planet gears

Note - Since plastic has a non-linear behavior towards load vs. life, it becomes difficult to closely estimate the life of polymer gears with simulations and calculations. Thus, in addition to simulation, robust life testing of the gearbox with polymer gears is carried out using the test set up in the reliability lab with the load parameters as per customer requirements.

Think polymer gearing might be the best option for your application? Reach out and touch base with our engineers – they’re ready to partner with you and develop the ideal gearbox solution!