30 November 2022

Different types of Bearings -Friction -Stiffness -Speed -Life

 

Bearing compare with different friction, stiffness, speed, life and application at a glance…

 

Type Description Friction Stiffness† Speed Life Notes
Plain bearing Rubbing surfaces, usually with lubricant; some bearings use pumped lubrication and behave similarly to fluid bearings. Depends on materials and construction, PTFE has coefficient of friction ~0.05-0.35, depending upon fillers added Good, provided wear is low, but some slack is normally present Low to very high Low to very high – depends upon application and lubrication Widely used, relatively high friction, suffers from stiction in some applications. Depending upon the application, lifetime can be higher or lower than rolling element bearings.
Rolling element bearing Ball or rollers are used to prevent or minimise rubbing Rolling coefficient of friction with steel can be ~0.005 (adding resistance due to seals, packed grease, preload and misalignment can increase friction to as much as 0.125) Good, but some slack is usually present Moderate to high (often requires cooling) Moderate to high (depends on lubrication, often requires maintenance) Used for higher moment loads than plain bearings with lower friction
Jewel bearing Off-center bearing rolls in seating Low Low due to flexing Low Adequate (requires maintenance) Mainly used in low-load, high precision work such as clocks. Jewel bearings may be very small.
Fluid bearing Fluid is forced between two faces and held in by edge seal Zero friction at zero speed, low Very high Very high (usually limited to a few hundred feet per second at/by seal) Virtually infinite in some applications, may wear at startup/shutdown in some cases. Often negligible maintenance. Can fail quickly due to grit or dust or other contaminants. Maintenance free in continuous use. Can handle very large loads with low friction.
Magnetic bearings Faces of bearing are kept separate by magnets (electromagnets or eddy currents) Zero friction at zero speed, but constant power for levitation, eddy currents are often induced when movement occurs, but may be negligible if magnetic field is quasi-static Low No practical limit Indefinite. Maintenance free. (with electromagnets) Active magnetic bearings (AMB) need considerable power. Electrodynamic bearings (EDB) do not require external power.
Flexure bearing Material flexes to give and constrain movement Very low Low Very high. Very high or low depending on materials and strain in application. Usually maintenance free. Limited range of movement, no backlash, extremely smooth motion

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