Polymer bearings can be found in almost any industry and environment, and this includes the clean rooms of electronics to the harsh conditions of the oil and gas industry. And this is no surprise considering the host of benefits that polymer bearings provide, including their resistance to corrosive chemicals, low maintenance, lightweight, and low friction.
So, what exactly are the top five materials used in polymer bearings? The top five polymer bearing materials include Torlon PAI, Bearing Grade PEEK, Bearing Grade PPS, Lubricated PET, and Lubricated Nylon.
1. Torlon PAI
PAI stands for Polyamide-imide and it is the highest performing polymer that is melt-processable. It offers excellent wear resistance, has an extremely low coefficient of friction, and can handle operating temperatures up to 500°F. The primary drawback of Torlon PAI lies in its relatively high level of moisture absorption. On the other hand, it has a low coefficient of thermal expansion and a high level of creep resistance, both of which are key characteristics for an effective bearing. Torlon PAI is often used in bushings, bearings, and wear rings.
2. Bearing Grade PEEK
Bearing grade PEEK is known for its excellent wear characteristics, good abrasion resistance, extremely low coefficient of friction, and outstanding chemical resistance. It can handle environmental operating temperatures up to 500°F and performs well even when continuously exposed to hot water and steam. Bearing grade PEEK is also easy to machine, has low moisture absorption, and possesses a high PV rating.
3. Bearing Grade PPS
PPS (polyphenylene sulfide), like the other bearing grade polymers discussed so far, has excellent wear resistance and a low coefficient of friction. However, it also offers very good wear resistance and dimensional stability even at elevated temperatures. Bearing grade PPS has a rated operating temperature of 425°F and offers outstanding chemical resistance. In addition, bearings can be made to extremely high tolerances when PPS is used.
4. Lubricated PET
Lubricated PET combines the stiffness, wear resistance, and dimensional stability of PET with the low friction demands of bearing applications. It offers extremely low water absorption, good abrasion resistance, and can be machined to very tight tolerances. It is internally lubricated using a dispersed solid and is dry running (needing no additional lubrication). The internal lubrication is released during operation, further reducing the naturally low coefficient of friction that PET possesses.
The primary drawback of PET lies in its limitations with regard to temperature: its continuous service temperature is 210°F, which makes it unsuitable for extreme temperature service conditions.
5. Lubricated Nylon
Nylon does an excellent job of balancing toughness and strength while combining good abrasion resistance with the ability to be extruded, cast, or machined. Lubricated Nylon, much like lubricated PET, includes a solid dispersal of lubricants that greatly reduces the standard coefficient of friction of virgin Nylon and allows it to be used in dry running applications. One of the more common lubricants used is MDS or Molybdenum Disulfide.
The primary issue with Nylon is its ability to absorb up to 7% of its weight water, which can affect its dimensions. However, it does have an extremely high limiting PV rating and excellent wear characteristics.
The top five polymer bearing materials–Torlon PAI, bearing grade PEEK, bearing grade PPS, lubricated PET, and lubricated Nylon–are commonly used to replace metal bearings in a variety of applications. They offer the wear resistance, high PV ratings, low friction, and chemical resistance that are required. If you are in the market for new or replacement bearings, be sure to consider polymer bearings and bushings, also.