Mass Imbalance
A condition that exists in a rotor when the mass center axis is different than its running center axis. An unbalanced rotor, when rotating, wants to revolve around its mass center axis. Because the bearings restrict this movement, the centrifugal force, due to the unbalance, causes the rotor to vibrate. This vibration causes wear to the bearings, creates unnecessary noise, and, in extreme cases, disintegration of the rotor itself. It is necessary to reduce the unbalance to an acceptable limit.