Thrust Bearings

Thrust bearings are designed for pure thrust loads, and can handle little or no radial load. The rolling element in a thrust bearing can be a ball, needle or roller.  Design units can be specified in English units of inches, metric units or both.  Important dimensions to consider when searching for thrust bearings include the bore, the outside diameter and the overall width.  The bearing industry uses a standard number system for bearings with 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 the bearing includes the housing if it is a housed unit, but exclude the flange if a flanged bearing.

Important operating specifications to consider when searching for thrust bearings include rated speed, static axial or thrust load, and dynamic axial or thrust load.  The rated speed for a bearing running with grease lubrication is lower than a bearing with oil lubrication.  The static axial or thrust load is the maximum axial load bearing can endure without excessive permanent deformation.  The dynamic axial or thrust load is the calculated constant axial load, which a group of identical bearings with stationary outer rings can theoretically endure for a rating life of 1 million revolutions of the inner ring.

Bearing quality is rated by ABEC (Annular Bearing Engineers' Committee).  These ratings classify different accuracy and tolerance ranges for bearings. The higher the ABEC number the tighter the bearing tolerances.  ANSI -American National Standards Institute and AFBMA - Anti-friction Bearing Manufacturers Association specifies other standards.

Bearing design choices for thrust bearings include flat race thrust ball, grooved race thrust ball, two directional grooved thrust, needle roller thrust, cylindrical roller thrust, spherical roller thrust, and slewing ring or turntable bearing.  Flat-race thrust bearings consist of a ball retainer held between two flat washers.  Grooved race thrust bearings consist of a ball retainer held between two grooved washers.   Two directional grooved thrust bearings are 'back-to-back' grooved race thrust bearings.   Needle roller thrust bearings consist of a needle roller and cage assembly.  Cylindrical roller thrust bearings consist of a roller and cage assembly.  Spherical roller thrust bearings have a spherical raceway in the outer ring.  Slewing ring or turntable bearings can accommodate axial, radial and moment loads.

Special material considerations that are available for thrust bearings include stainless steel, plastic, ceramic, and plated.  Stainless steel is chemical and corrosion resistant and can have relatively high-pressure ratings.  Plastics include any of numerous organic, synthetic, or processed materials that are mostly thermoplastic or thermosetting polymers of high molecular weight.  A ceramic hybrid bearing is constructed of steel inner and outer rings with ceramic (typically Si₃N₄⁾ balls in place of steel.  These bearings have several advantages over all steel bearings, such as higher speed and acceleration capability, increased stiffness, higher accuracy, lower friction and heat generation, reduced lubrication requirements, low thermal expansion, extended operating life.  Bearings containing all ceramic balls are also nonconductive and are commonly used in electric motor applications.  Common plating materials are cadmium and chrome.

• Keeping Thrust Bearings Cool
  Cool ideas for thrust bearings  Keeping thrust bearings cool is a matter of design with a different cooling strategy for each type of thrust bearing. Professor, Dept. of Mechanical Engineering...
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• Know your thrust bearings
  Operating conditions and design constraints dictate which type makes sense. Thrust bearings support axial loads on rotating shafts. Designs range from simple, coin-sized flat washers in household...
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• Angular Contact Ball Bearings
  Angular contact bearings are designed such that a contact angle between the races and the balls is formed when the bearing is in use. The major design characteristic of this type of bearing is that...
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Part Numbers for Thrust Bearings