A Practical Guide To In-Place Balancing

PaperPg. 113-129.Rotor unbalance remains one of the leading causes of deterioration and vibration of rotating machinery; but, if physical weight corrections can be made, many machines can be successfully balanced in-place with considerable savings in downtime and labor costs. In-place balancing can, however, pose some unique problems, and a prime concern is the time, expense, and wear and tear to simply start and stop the machine for trial data. Therefore, this paper is presented to provide guidelines for recognizing and overcoming some of the more common in-place balancing problems so that the number of balance runs can be kept to a minimum. Vibration analysis techniques are presented as the first step to verify that the problem is truly unbalance and not looseness, weakness, distortion, resonance, misalignment, eccentricity, or other problems which could be mistaken for unbalance. Problems such as repeatability, rotor sag, stratification, thermal distortion, load effects, rotor speed and other variables which can influence rotor balance are discussed. Measurement techniques and common sources of measurement error are also presented. The importance of identifying the type of rotor unbalance (static, couple, quasi-static, or dynamic) is presented along with a review of common single- and two-plane balancing procedures with emphasis on their suitability for in-place balancing. Methods are presented for determining suitable trial weights - both amount and position - to achieve the desired results. Finally, guidelines are presented for establishing realistic balance and vibration tolerances for rotors balanced in-place