Until recently, the performance of polymer plain bearings has been contingent upon shaft material. Specifically, smoother shafts produced longer bearing lives. However, the polymer-encased-polymer bearing or PEP works well in rotary functions with any type of shaft material. The inner sleeve of the bearing acts as the mating surface, which allows predetermining the coefficient of friction and specific wear behavior. The design combines advantages of plain, self-lubricating bearings with the reliability of a closed ball-bearing design.
The coefficient of friction of the new bearing with 725-lb loads is 0.12 to 0.2, compared to a coefficient of friction of 0.08 to 0.3 for steel and polymer. Polymer bearings are press-fit into place with a recommended ISO tolerance of H7. The bearings are said to be easy to retrofit and maintenance-free. PEP bearings are currently available from stock for shaft diameters ranging from 6 to 20-mm ID.
This information supplied by igus inc., East Providence, R.I.