Effective rotor balancing in the movable conditions is not an easy task. Its successful accomplishment depends on numerous reasons. Some of them are described below. Here they are :
- interfering external impacts in the form of supports and bearings kinematic input,
- relative variability (unrepeatability of fluctuation) of rotational speed,
- randomness of unbalance,
- limited availability of correction planes,
- technical difficulties in case of precise determination of phase position in the correction planes of trial and corrective masses,
- technical difficulties related to mounting of mentioned masses or in case of removal method with their subtraction (removal),
Mandatory condition of successful balancing is a properly conducted measurement and analysis of vibrations. In order to achieve that you need precise measuring instruments, command of the machine operation, and install sensors properly. Theoretically, it seems to be obvious, however, it may not be like that in practice. It is important to remember about the essential difference between rotor balancing in movable conditions in its own bearings and balancing in substitute bearings or on piles and rolls. In the second case there are no external impacts, understood as all kinds of interferences. In the movable conditions it is more complicated. First of all, the effects of unknown unbalance should be compensated, moreover, the effects of all impacts having influence on the basic harmony of analysed vibrations should be compensated.
It is important to remember that the vibrations of the machines operating nearby may be a reason preventing rotor from being balanced. Especially machines of the same type, and therefore it is advisable to disable them temporarily or permanently.
Limited availability and access to the correction planes, the possibility of mass mounting, their finite sizes, the need of their distribution caused by considerable loads (stresses), as well as difficulties with a precise phase angle measuring at correction planes lead to the fact that the measurements should not be that precise not to prolong the time and increase costs. The experience shows that measurements of phase angle are precise enough with an accuracy 3-5⁰, amplitudes and masses with 5% relative precision.
It is also important that the change of rotational speed in movable conditions is frequently impossible, and the there may occur circumstances dictating an initial balancing of rotor due to excessive high vibrations. In such a situation, friction in bearings obstructs the use of gravitational force which is used to determine the phase position of “the heaviest” place on the rotor’s circuit. In the movable conditions it advisable to declutch the machine or engine which is being balanced.