Rolling Element Bearings

Rolling Element Bearings
(4 Failure Phases)

Stages of Progressive Deterioration
Stage 1	Stage 1 : Earliest indications of bearing problems appear in ultrasonic frequencies ranging from approximately 20,000 - 60,000 Hz (1,200,000 - 3,600,000 CPM). These are frequencies evaluated by spike energy (gSE), HFD(g) and shock pulse (dB). Foe example, spike energy may first appear at about .25 gSE in stage 1 (actual value depending on measurement location and machine speed.


Stage 2	Stage 2 : Slight bearing defects begin to "ring" bearing component natural frequencies (fn) which predominantly occur in the 30K - 120K CPM range. Sideband frequencies appear above and below natural frequency peak at end of stage 2. Spike energy grows (for example .25 to .50 gSE).

Stage 3	Stage 3 : Bearing defect frequencies and harmonics appear when wear progresses. More defect frequency harmonics appear and a number of sidebands grow, both around these and around bearing natural frequencies (see Vibration Case History Number 3 for actual example). Spike energy continues to increase (for example, from .5 to over 1 gSE). Wear is now usually visible and may extend throughout periphery of bearing, particularly when well formed sidebands accompany any bearing defect frequency harmonics. replace the bearings now.

Stage 4

Stage 4 :Towards the end, the amplitude of the 1x RPM is even effected. It grows, and normally causes growth of many running speed harmonics. Discrete bearing defect and component natural frequencies actually begin to "disappear" and are replaced by random, broadband high frequency "noise floor". In addition, amplitudes of both high frequency noise floor and spike energy may in fact decrease, but just prior to failure, spike energy will usually grow to excessive amplitudes.

Formulae to Calculate Specific Bearing defect Types.

-::- This site is designed and authored by David Stevens IEng MIET FIDiagE MICML -::-