Bearing

An angular measurement of the direction of an object from a reference direction, such as true north.

Primarily two types, rolling element and sleeve or plain bearing. Rolling element bearings consist of four parts: an inner race, an outer race, balls or rollers, and a cage to maintain the proper separarion of the rolling elements. A sleeve bearing is a cylinder of alloy metal surrounding the rotating shaft. Contact between the shaft and sleeve is prevented by a lubrication film.

Bearing Frequencies

Faults in any of the four bearing components will generate specific frequencies dependent upon the bearing geometry and rotating speed.

BPFO - Ball Pass Frequency, Outer Race

BPFI - Ball Pass Frequency, Inner Race

BSF - Ball Spin Frequency

FTF - Fundamental Train Frequency

Bearing Misalignment

A misalignment that results when the bearings supporting a shaft are not aligned with each other. The bearings may not be mounted in parallel planes, cocked relative to the shaft, or distorted due to foundation settling or thermal growth.

Bearing Nomenclature

Each bearing manufacturer has specific codes applied as prefixes and suffixes to their bearings. These codes inform the user of the construction, materials, clearances, and other factors used in the construction of the bearing. Consult the individual manufacturer's handbook for specific code meaning.

Cage

The bearing cage is a device used to seperate the rolling elements of a bearing.

Cage pocket

A section of a bearing cage that retains the ball.

Double row bearing

A bearing having two rows of rolling elements. Normally used where radial loads are high and a compact bearing solution is required.