Abstract
Several methods attempting rotor balancing without trial runs have been published in the past. There are, however, no reports of systematic application of these procedures to field balancing of large rotating machinery. This suggests that some practical difficulties have still to be solved. An analysis on such difficulties shows that balancing a rotor without trial runs is not possible if the mode shapes are not known. Trial runs are also necessary when the residual vibration at normal operating speed, produced by the influence of higher unbalanced modes, is too high to allow continuous operation of the machine. There are, also, additional difficulties related with the angular position of the vibration transducers, which allow the determination of the magnitude and phase of the correction masses only if their position coincide with the direction of the system principal axes of stiffness. This paper describes a balancing procedure incorporating all these elements and its application to the balancing of an experimental rotor rig.
Highlights
Balancing a rotor consists in the compensation of an eccentric mass distribution that generates large centrifugal forces and high levels of vibration
In this case the calculation of the correction masses requires the previous determination of the following parameters: (a) the modal vibration vectors for each resonance, (b) the modal damping ratios, (c) the mode shapes and (d) the equivalent mass of the rotor for each mode
Modal theory indicates the possibility of identifying the unbalance components from the rotor response eliminating the necessity of trial runs
Summary
Balancing a rotor consists in the compensation of an eccentric mass distribution that generates large centrifugal forces and high levels of vibration. Other procedures used to eliminate the trial runs are closer to the modal method In this case the calculation of the correction masses requires the previous determination of the following parameters: (a) the modal vibration vectors for each resonance, (b) the modal damping ratios, (c) the mode shapes and (d) the equivalent mass of the rotor for each mode. Dierent authors have proposed speci®c procedures for the determination of these parameters, but there are no published reports describing the practical application of such procedures to the balancing of large rotating machines in the ®eld using no trial runs. This suggests that some of the practical diculties still need to be overcome, which keeps the door open for further research on this area. The following sections describe a balancing procedure incorporating all these elements together with its application to the balancing of an experimental rotor
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