Balancing is the process of reducing the unbalanced force (mass) by removal or addition of weight to a rotating component (Brake Rotor see Fig. 1) so that this effective mass center line approaches the true axis.
Cause of Imbalance:
The imbalance is caused by an effective displacement of the mass center line from the true axis. This can result from a mass eccentricity in the unit, such as sand core shifting during the casting process or nonuniform shrinkage of the rotor casting.
Effect of Imbalance:
Vibration, noise, and pedal pulsation will occur, which can result in excessive wear and damage to wheel bearing. This can cause premature failure of the rotor hub assembly. The higher the speed (RPM), the more severe the imbalance effect.
Method of Imbalance Correction:
A balancing machine can detect the area of imbalance. Shaving off excess weight from a location (see Fig. 2) or adding weight (weight wing like lead in the wheel rim) to the opposite side will achieve the same result of balancing the rotating unit.
Specification of Balancing:
The best one can do is reduce this imbalance to a level that will not adversely effect the operation of the vehicle, and will reduce noise and vibration levels to an acceptable level. Unfortunately, in practice or reality, the ideal or perfect balance cannot be achieved and some inherent cause of vibration, or imbalance, will remain.
Dynamic Balancing is a process where the rotors are mounted onto a purpose built "Balancing Machine" which has its bearings connected to displacement or acceleration sensors which detect the "heavy" point in relation to a datum on the unit, as it is being rotated. This increases the sensitivity and the accuracy of the balance.