About Ball Bearings, All Types

Ballbearingsare used to provide smooth, low friction motion in rotary applications. Ballbearingstypes include Radial BallBearings(Deep Groove and Angular Contact) and Thrust Ball Bearings. Radial ballbearingsare designed to carry both radial and axial (thrust) loads, while thrust ballbearingsare designed for pure thrust loads only.  Radial, or deep groovebearings, can take radial and axial loads to varying degrees but are used when the primary load is in the radial direction.  They consist of an inner ring, an outer ring, balls and sometimes a cage to contain and separate the balls.  Angular contact ballbearingsare designed such that a contact angle between the races and the balls is formed when thebearingis in use.  The major design characteristic of this type of ballbearingis that one or both or the ring races have one shoulder higher than the other.  In order for thesebearingsto function properly, they must be assembled with a thrust load.  This loading (or preload) creates a line of contact (or contact angle) between the inner race, the ball and the outer race. The preload can be built in to thebearingor created when thebearingis inserted into an assembly.  The contact angle varies from 15° to 40° and is measured relative to a line running perpendicular to thebearingaxis.  Angular contactbearingsare one-directional thrustbearingsthat can withstand heavy thrust loads and moderate radial loads.  Thrust ballbearingsare designed for pure thrust loads.  Thesebearingscan handle little or no radial loads.  The rolling element can be a ball, needle, or roller.  Slewing ring or turntablebearingscan accommodate axial, radial and moment loads.  They are not mounted in a housing or on a shaft, but instead are mounted directly to a seating surface.  The inner and outer rings are supplied with mounting holes.  The inner ring, outer ring, or both may have integral gears.  Thesebearingsare referred to as tabletopbearings, turntablebearings, and slewing rings.

Important dimensions to consider when specifyingbearingsinclude bore, outside diameter, and overall width.  Thebearingindustry uses a standard number system for bearingswith metric diameter bores.  For bore sizes 04 and up multiply by 5 to obtain the bore in millimeters.  If the bore is a hex this refers to the dimension across the flats.  If the bore is tapered this refers to the smaller diameter.  The outside diameter of thebearingincludes the housing if a housed unit, but excludes the flange if a flangedbearing.  The outer ring width is the overall width of the outside of thebearing.  The overall width of thebearingorbearingassembly includes the locking collar, if present.  Important operating specifications to consider when searching forbearingsinclude rated speed, dynamic axial or thrust load, and dynamic radial load.  The rated speed for a bearing running with grease lubrication is lower than abearingwith oil lubrication.  The dynamic axial or thrust load is the calculated constant axial load, which a group of identicalbearingswith stationary outer rings can theoretically endure for a rating life of 1 million revolutions of the inner ring.  The dynamic radial load is the calculated constant radial load, which a group of identicalbearingswith stationary outer rings can theoretically endure for a rating life of 1 million revolutions of the inner ring.

Bearingquality is rated by ABEC (AnnularBearingEngineers' Committee).  These ratings classify different accuracy and tolerance ranges for ballbearings. The higher the ABEC number the tighter thebearingtolerances.  ANSI -American National Standards Institute and AFBMA - Anti-frictionBearingManufacturers Association specifies other standards.  Special materials and plating options to consider for ballbearingsinclude stainless steel, plastic, ceramic hybrid, ceramic races, and platings.  Special applications forbearingsinclude airframe or aircraft control, aerospace, agriculture, automotive, ball screw support, instrument or miniature, medical or dental, military, pump, spindle or super precision, and sporting and consumer goods.