In brief
A ball bearing is a rolling bearing in which balls roll between the inner and outer rings, supporting shafts so that they can rotate with low friction.
Contents
What is Ball bearing?
Ball bearings belong to the rolling bearing family. Unlike in a plain bearing, the surfaces do not slide on one another; instead, balls roll in raceways between the inner and outer rings. A cage keeps the balls spaced apart. Because balls transmit the load only at points, ball bearings are suited above all to moderate loads and high speeds, whereas roller bearings carry higher loads.
Important types are deep groove ball bearings, angular contact ball bearings, four-point contact bearings, self-aligning ball bearings and thrust ball bearings. They differ in whether they carry radial, axial or combined loads and whether they compensate for misalignment. Key parameters are bore and outside diameter, width, dynamic and static load rating, limiting speed, internal clearance, sealing and tolerance class. The boundary dimensions are internationally standardised, so bearings with the same designation from different manufacturers are generally dimensionally interchangeable.
Ball bearings are found in electric motors, pumps, fans, gearboxes and conveyor systems and are among the most common spare parts in maintenance. Typical causes of failure are inadequate lubrication, contamination, overload, installation errors and current passage in inverter-fed motors.
In practice: maintenance and procurement
For a spare parts enquiry, the complete bearing designation including all suffixes, for example for sealing, internal clearance and cage, is usually sufficient. If it is missing, bore, outside diameter and width as well as details of speed, temperature and installation location will help.
Synonyms and abbreviations: ball bearing · radial ball bearing · ball race (colloquial) · anti-friction bearing
Frequently asked questions
What is the difference between a ball bearing and a roller bearing?
In a ball bearing, balls transmit the load via very small contact areas; in a roller bearing, cylindrical, tapered or spherical rollers do so along a line. Ball bearings therefore run with less friction and reach higher speeds. For the same size, roller bearings carry considerably higher loads and are therefore common in heavy machinery, rolls and large gearboxes.
How do you read a ball bearing designation?
The basic designation states the bearing type, dimension series and bore code. From code 04 upwards, the code multiplied by five gives the bore diameter in millimetres; a bearing with code 05 therefore has a 25 mm bore. Suffixes describe seals or shields, internal clearance, cage material and special versions. These suffixes are coded differently by each manufacturer and should never be omitted when ordering.
Why do ball bearings fail prematurely?
The most common causes are unsuitable or missing lubrication, ingress of dirt or moisture, installation with blows on the wrong ring, excessively tight fits and overload. In motors on a frequency inverter, current passage can also cause fluting in the raceways. A damage analysis of the removed bearing usually shows which cause was involved.
Are ball bearings from different manufacturers interchangeable?
The boundary dimensions are standardised to ISO, so bearings with the same basic designation generally match dimensionally. Differences exist in suffixes, type of seal, grease fill, internal clearance and running accuracy. For critical applications, it should be checked whether all characteristics of the original are met before an equivalent bearing is used.