Journal bearing problem

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
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

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