The vibration caused by bent shaft looks like the vibrations caused by misalignment. An axle can be bent due to, for example uneven heat distribution in the rotor caused by a defect rotor bar. If the bending is situated at the centre of the axle the dominating vibration frequency is 1 x RPM. If the bending is situated near a coupling the dominating vibration frequency is 2 x RPM.
|Source of vibration||Exciting frequency||Dominating direction||Amplitude||Spectral characteristic||Comments|
|Minor bent shaft||1X, 2X||axial, radial, tangential||constant||narrow band||Out of true in rotor shows as an unbalance.|
|Bent shaft at coupling||1X, 2X||axial, radial, tangential||constant||narrow band, possibly with 2X, 3X multiples||Out of true in a coupling shows as a misalignment|