BS ISO 21940-14:2012 pdf download – Mechanical vibration — Rotor balancing Part 1 4: Procedures for assessing balance errors Formula (2) is valid only if the component is symmetric about its rotational axis and is therefore particularly applicable to the balancing of disks on arbors. The effects of radial runout and axial runout of a component mounted on the rotor can be calculated separately. For rotors with rigid behaviour, the separate unbalance components can be allocated to the bearing or correction planes and then combined vectorially. For rotors with fexible behaviour, a rigid balance quality might be maintained, but accumulated axial disk runout errors (often described as skew) can lead to signifcant vibration due to the moment unbalance generated by the skewed disk(s). 5.4 Assessment of balancing operation errors The purpose of balancing is to produce rotors that are within specifed limits of residual unbalance or vibration.To ensure that the set limits have been met, errors need to be controlled and taken into account. When a balancing machine is used, various error sources exist, for example: a) the type of rotor to be balanced; b) the tooling used to support or drive the rotor; c) the balancing machine support structure (e.g. machine bearings and cradles); d) the balancing machine sensing system; e) the electronic and read-out system. However, it is important that in those cases where the error is taken into account by calculation, both themeasured unbalance before correction and the corrected value are reported. The balancing machine used should be such that all its systematic errors are eliminated or corrected. Whenbalancing rotors that have a rigid behaviour at their balancing speed, the requirements of IS0 21940-21 apply. 5.5 Experimental assessment of randomly variable errors 5.5.1General lf significant randomly variable errors are suspected to exist it is necessary,where practical, to carry outseveral measuring runs to assess their magnitude. When carrying out measuring runs, it is important to ensure that the random errors are themselves producedrandomly in each run (e.g. by ensuring that the angular position of the rotor is different at the start of each run).The random error magnitude can be evaluated by applying standard statistical techniques to the measurementresults obtained.However, in most cases, carrying out the procedure described in 5.5.2 is adequate. 5.5.2 Procedure Plot the measured vectors of residual unbalance or vibration and find the mean vector OA from all the runs(see Figure 2). Draw the smallest circle...
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