ABSTRACT
Unbalance Unbalanced noise always occurs at the rotational frequency of the machine (Nr /60) Hz, where Nr is the speed of rotation in rpm. Unbalance can arise in two ways, in the first case, the centre of gravity of the rotating mass is off centre from the axis of rotation. This leads to static unbalance which in extreme cases can be seen to exist if the rotor always stops in the same rotational position, i.e. with the heavy side at the bottom. Even if the centre of gravity is on the centre of rotation, dynamic rotation can occur if the axis of symmetry is not parallel with the axis of rotation. This unbalance only shows when the machine is run. Both forms of unbalance can be cured by correct mass balance of the motor.
