Plain or rolling element bearings? What's the correct choice?

SKF
Tags: bearings, maintenance and reliability

Plain bearings are available for an extremely wide variety of applications. Most are used in sliding or oscillating roles: door hinges, ball joints on cars, the fifth wheel on a tractor trailer. But when full rotation is required, plain bearings change shape to a "sleeve" that fits around the shaft. In addition to being called sleeve bearings, other names include plane, journal or babbitt bearings.

Rolling vs plain

  • The high startup torque requirement usually means plain bearings aren't suitable for machines that start and stop frequently.
  • The full fluid film in plain bearings requires up to 3x more energy to operate, even if startup losses are excluded.
  • Some journal bearings have difficulty with grease lubrication - they need a constantly replenished thick oil film.
  • Using plain bearings in vertical or thrust loaded applications requires special Kingsbury or Mitchell designs, which can add to cost. Since most rolling element bearings are available in standard sizes, changing the type of bearing in an application may be all that's needed to accommodate thrust.
  • Plain bearings are generally optimized for a single speed, while rolling bearings can tolerate a wider speed range, more suitable for variable speed drives.

When power density is extremely high, as in power generation, heavy loads might result in permanent, plastic raceway deformation in a rolling element bearing - plain bearings may be a better choice. The API 610 Standard has guidance for the recommended use of plain bearings vs. rolling element bearings in industrial machines.