What is Balance?

Balancing operation is an operation applied on the rotating bearings of a body, which has the purpose of improving the mass balance distribution so as not to affect the centrifugal forces. It is a fact that the operation shall give results only up to a certain point and there will be an unbalance in the rotating members also after the balancing operation. This Standard relates to the amount of the permitted permanent unbalance

It is possible to decrease unbalance to very low limits using the measurement instruments today. However, it may not be economical to excessively decrease the limits. The degree down to which unbalance will be decreased may be determined through technical and economical comparison and the optimum value can be determined using wide measurement technique, laboratory and in situ use accuracy.

Since usually there is no noticable relation between the rotor unbalance and the vibrations under the operational conditions of the machines, it is impossible to derive a result relating to the permissible permanent unbalance from the available standards relating to the vibration conditions of the machines. The amplitude of vibration is affected by many factors such as the masses of the vibrating machine body and base, frequency of the bearing and the base, operational speeds converging to various resonance frequencies, etc. Furthermore, the effects of unbalance vary in accordance with the mutual angular positions. As a result, the vibrations of the machine are caused by some of the rotor unbalance. .

These proposals have the target of preventing the excessive or inaccessible conditions and rough defects rahther than determining the acceptable characteristics for any rotating member group. On the other hand, these also serve as detailed studies (For example, it gives the exact determination of the time required for special conditions for the requested balance quality.) When the recommended limits are paid attention, it should be expected to obtain succesful operational conditions with a great probability. However, in some compulsory cases, it may be necessary do deviate from such recommendations.

Unbalance effects
An unbalanced rotating member does not only apply a force on the bearings and base, but also causes the machine to vibrate. Both effects depend on the geometrical ratios and mass distribution of the rotating member and the machine as well as bearing and base frequency.

In many cases, when static unbalance is compared with force pair unbalance, it is found to be more important, because it causes much bigger problems in comparison with two unbalances with the same direction on different planes.

Similarly, there are cases where force pair unbalance especially causes problems. For example, a rotating member, whose distance between the bearings is bigger than the distance between two correction planes is as disk suspended on both sides. In case the total of the opposite unbalances on the correction plane showing force pair unbalance exceeds a definite fraction of the static unbalance, which is accepted to be placed in the middle between the beds, the bearing load caused by the force pair unbalance is bigger than the load caused by static unbalance. If the distance between the bearings is 1, the permitted permanent unbalance between the correction planes is U, than the the permitted permitted permanent unbalance decreases and creates the force pair unbalance having a value U = U L/2 a.

We can understand whether the work part will be balanced on a single plane or two planes by using the following table as a guide. .

Rotors with one correction plane
For the rotating members having a disk shape having a sufficient distance between the bearings and rotating with a sufficiently low axial deviation, it may be sufficient to use one correction plane. In both cases, these created conditions have to be separately examined for both cases. After applying single plane balancing operation to a special type rotating member, the biggest permanent unbalance moment is determined and it is divided into the distance between the bearings. If the unbalances found in this way are at an acceptable level even in the worst case condition, that is, if these unbalances are smaller than half of the multiplication of the rotor mass with the recommended values, the balancing operation can be accepted to be sufficient.

Rotors with two planes

In case the rigid rotor does not comply with the conditions of rotating member in disk shape, two correction planes are necessary. In opposite to the single plane (static) balancing operation, this type of balancing operation is called two – plane (dynamic) balancing operation. In single plane balancing operation, the member is requested to comply with only the static balance condition at any angular position. In two – plane balancing operation, rotation of rotor is requested, otherwise the unbalance of the permanent force pair unbalance can not be noticed.
In each of the two correction planes, the permitted permanent unbalance depends on the position of the bearings and the correction axises and at the same time on the relative phase angle between two permanent unbalances.