ISO 11342 pdf download.Mechanical vibration — Methods and criteria for the mechanical balancing of flexible rotors
1 Scope
This International Standard presents typical flexible rotor configurations in accordance with their characteristics and balancing requirements, describes balancing procedures, specifies methods of assessment of the final state of unbalance, and gives guidance on balance quality criteria. This International Standard may also be applicable to serve as a basis for more involved investigations, for example when a more exact determination of the required balance quality is necessary. If due regard is paid to the specified methods of manufacture and limits of unbalance, satisfactory running conditions can be expected. This International Standard is not intended to serve as an acceptance specification for any rotor, but rather to give indications of how to avoid gross deficiencies and/or unnecessarily restrictive requirements. The subject of structural resonances and modifications thereof is outside the scope of this International Standard. The methods and criteria given are the result of experience with general industrial machinery. They may not be directly applicable to specialized equipment or to special circumstances. Therefore, there may be cases where deviations from this International Standard may be necessary 1) .
2 Normative references
The following standards contain provisions, which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged to investigate the possibility of applying the most recent editions of the standards listed below. Members of IEC and ISO maintain registers of currently valid International Standards. ISO 1925:1990, Mechanical vibration — Balancing — Vocabulary ISO 1940-1:1986, Mechanical vibration — Balance quality requirements of rigid rotors — Part 1: Determination of permissible residual unbalance
3 Definitions
For the purposes of this International Standard, the definitions relating to mechanical balancing given in ISO 1925 and the definitions relating to vibration given in ISO 2041 apply. NOTE — Definitions from ISO 1925 relating to flexible rotors are given for information in annex H.
4 Fundamentals of flexible rotor dynamics and balancing
4.1 General Flexible rotors normally require multiplane blancing at high speed. Nevertheless, under certain conditions a flexible rotor can also be balanced at low speed. For high-speed balancing two different methods have been formulated for achieving a satisfactory state of balance, namely modal balancing and the influence coefficient approach. The basic theory behind both of these methods and their relative merits are described widely in the literature and therefore no further detailed description will be given here. In most practical balancing applications, the method adopted will normally be a combination of both approaches, often incorporated into a computer package. 4.2 Unbalance distribution The rotor design and method of construction can significantly influence the magnitude and distribution of unbalance along the rotor axis. Rotors may be machined from a single forging or they may be constructed by fitting several components together. For example, jet engine rotors are constructed by joining many shell, disc and blade components. Generator rotors, however, are usually manufactured from a single forging, but will have additional components fitted. The distribution of unbalance may also be significantly influenced by the presence of large unbalances arising from shrink-fitted discs, couplings, etc.Since the unbalance distribution along a rotor axis is likely to be random, the distribution along two rotors of identical design will be different. The distribution of unbalance is of greater significance in a flexible rotor than in a rigid rotor because it determines the degree to which any flexural mode is excited. The effect of unbalance at any point along a rotor depends on the mode shapes of the rotor. The correction of unbalance in transverse planes along a rotor other than those in which the unbalance occurs may induce vibrations at speeds other than that at which the rotor was originally corrected. These vibrations may exceed specified tolerances, particularly at, or near, the flexural critical speeds. Even at the same speed such correction can induce vibrations if the flexural mode shapes on site differ from those dominating during the balancing process.