The main reasons for rotor mass imbalance are as follows:

Impeller wear (mainly blade) is not uniform or corrosion;

Uneven ash accumulation or attachment (e.g. rust) on blade surface;

Wing hollow blade or other parts of the cavity adhesive ash;

Local high temperature makes the shaft bend;

Impeller is not balanced after maintenance;

Impeller strength is insufficient to cause impeller cracking or local deformation;

Parts on the impeller are loose or connectors are not fastened.

Characteristics of vibration caused by rotor imbalance:

The vibration value is in the horizontal direction. Large, but the axial is small, and the bearing seat bearing vibration is greater than the thrust bearing;

Amplitude increases with revolution.

Vibration frequency is equal to speed frequency;

Vibration stability is good, not sensitive to load changes;

The measured phase Angle is unstable and the vibration frequency is 30% ~ 50% working speed when the hollow blade is displaced due to the gray inside or some parts are not welded firmly.