Overview

Rotor balancing is a highly specialized technology, which has been dealt with in several books and handbooks, sometimes published by firms that build balancing machines [77, 78]. This appendix will only summarize some of the basic concepts, without any attempt in dealing with this subject in any depth. The interested reader can find all of the required details in specialized texts, in particular, those mentioned above.

All rotors, particularly those intended to operate at high rotational speed, must be balanced before they start their service life. Sometimes balancing procedures must be repeated during the life of a machine. The designer must then take into account this requirement to provide the possibility of removing or adding masses in proper locations from the early design stages. Balancing must be regarded as one of the construction stages, to be performed after assembling the whole rotor or before, on its component, if they must be balanced separately (which usually does not avoid a further balancing process on the assembly), and balancing tolerances must be stated in a way that is not conceptually different from what is done for other types of tolerances, dimensional or geometrical. The balance conditions of a rotor can change in time, and periodic rebalancing may be needed. In some cases, this phenomenon can be severe and is usually referred to as wandering unbalance. It can be caused by thermal deformations of the rotor, material inhomogeneity, cracks, loose tolerances in built-up rotors, and the like. Some rotors must be...