Bent shaft

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

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