It is a question that is still widely debated ― how do plastic and metal bearing compare? In some industries, plastic is regarded as a premium bearing material, while in others there is a prevailing misconception that plastic is inferior to metal. We decided to compare the two by looking at a few of the key factors that determine bearing performance ― namely maintenance, durability and service life. Here’s what we discovered:
Bearing lubrication is extremely important to overall performance, particularly at initial equipment start-up when machines are starting “dry.” Without the right level of lubrication, aging and wear rates are accelerated.
Plastic bearings have the maintenance advantage. They have built-in lubrication properties so components are continuously greased from initial start-up. Plastics resist the force of stick/slip to deliver longer wear without ever needing additional maintenance.
Conversely, metal bearings require regular manual greasing to reach the proper level of lubrication. These greasing schedules are a burden to equipment maintenance crews, and contribute to a lower productivity as the manufacturing lines are halted for greasing.
Another common misconception in bearing design is that thin-walled plastic bearings do not last as long as their thick-walled metal counterparts. Nothing could be further from the truth. Thin-walled bearings are able to dissipate heat, which extends their durability. A thinner wall design also contributes to better clearance between shaft and bearing for lower friction levels.
Metal bearings are designed thickly to compensate for wear, but even with the extra material, the metal surface can fail. Ultimately, bearing materials should be chosen based on their predicted wear, not on the thickness of the part.
Generally speaking, plastic bearings routinely deliver longer service than oil-impregnated bronze bearings. In fact, service life can be predicted through tribology testing, which measures friction and other properties of plastic materials in simulated industrial applications. Tribology can also protect the end user of the material by ensuring that the components meet all applicable industry standards. Metal bearings are not regularly tested for service life.