Fault diagnosis in rotating machinery

A tutorial discussion is given of some of the main faults which may be detected and diagnosed using observed vibrational data of a rotating machine. The paper is written with large turbo-machinery in view but many of the results discussed have relevance to other types of machine. The examination begins with the simplest, yet perhaps the most important, fault namely mass unbalance. The elementary procedure for locating the source of unbalance will be reviewed and procedures for balancing will be briefly summarised. The distinction between unbalance and a shaft bend will be discussed and the consequences of permanent and temporary bends will be examined. A fault which is sometimes connected with rotor bends is rubbing and the characteristics of this phenomena will be outlined including some recent developments in the theory and the classification of the different categories of rub which can occur in practice. An overview will be given of the characteristics of a cracked rotor and examples of cracks which have been detected using vibration measurements will be described. No discussion of the dynamics of large machines would be complete without a description of the effects of misalignment. Both static and dynamic types are discussed together with their consequences.