Plastics have come a long way since they were invented over a century ago. But that does not mean they should be used in every application.
Here are a few pros and cons of plastic bearings to help guide engineers in when to specify them.
Plastic bearings are the better option:
To handle edge loads. Plastics are more flexible than metal, so plastic bearings handle edge loads well. Metal bearings might shatter on an edge load that plastic bearings would withstand. This same flexibility, however, can be a weakness if precision is required. Metal bearings can manage a level of precision that plastics cannot.
For self-lubricating, maintenance-free operation. Plastic bearings can be made with solid lubricants embedded in them. For these bearings, no additional greasing is needed, which decreases maintenance and costs over time. They also do away with dripping grease, which is a safety hazard in food-handling applications and can lead to slips and falls by factory personnel. And plastic bearings do not corrode.
To reduce weight. Plastics bearings are lighter than their metal counterparts. This can be advantageous for cars, trucks, aircraft and other applications where differences in weight of even a gram can matter.
Plastic bearings should not be used when there are:
Extreme loads. It should not surprise anyone that plastics top out at a lower point in terms of load capacity compared to metals. Where that line is drawn though, may surprise you. Some plastic bearings can handle loads of up to 2,600 lb—the weight of a small car. As loads become more extreme, however, metal bearings become a more appropriate choice. Metal bearings can handle pressure velocity values (psi x fpm) of up to 3,000,000.
Consistently extreme temperatures. Although plastic bearings can function well at nearly 500°F for short periods of time, they cannot handle extreme temperatures for long-term operations. Metals, on the other hand, can handle thousands of degrees Fahrenheit above zero as well as many hundreds of degrees below zero.
High rpms. Plastic bearings can withstand low speeds, high loads and high speeds, or low loads. Unfortunately, at about 500 rpm, plastic bearings can no longer hold their shape. Metals fare much better at these high speeds.
Shizu Yamaguchi is a digital marketer at igus.