Journal bearing problem often generates vibration peaks at frequencies lower than 1xRPM. These peaks are called sub synchronous peaks. Sometimes even harmonics to these peaks exist, which indicates a much worn bearing. One type of journal bearing problem is oil whirl.
Oil whirl is an oil film that excites vibrations between 0.38xRPM and 0.48xRPM. The vibrations are caused by an unusual large margin and minor radial load, which puts a press on the oil film and forces the axle to move around in the bearing. Oil whirl can result in the oil not greasing the axle. Changes in the viscocity and pressure of the oil and related loads can affect oil whirl.
|Source of vibration||Exciting frequency||Dominating direction||Amplitude||Spectral characteristic||Comments|
|Oil Whirl||0,38 X till 0,48X||radial||Sharp peak|
|Oil Whip||0,38X till 0,48X||radial||Sharp peak|
|Severe large clearance||1X multiples||radial||Hump of 1X multiples||4X to 8X and/or 7X to 15X|
|Looseness or loose bearings||0,5X, 1X||radial||0,5X multiples|
|Axial bearing Kingsbury||1X; number of Kingsbury element||axial||1X multiples multiples on element pass frequency for Kingsbury||Normally 6 elements|