21.120.40 - Balancing and balancing machines

This document provides a general background to balancing technology, as used in the ISO 21940 series, and directs the reader to the appropriate parts of the series that include vocabulary, balancing procedures and tolerances, balancing machines and machine design for balancing. Individual procedures are not included here as these can be found in the appropriate parts of ISO 21940.

ISO 16084:2017 specifies requirements and provides calculations for the permissible static and dynamic residual unbalances of rotating single tools and tool systems. It is based on the guideline that unbalance related centrifugal forces induced by the rotational speed do not harm the spindle bearings, as well as prevent unbalance related impairments of machining processes, tool life and work piece quality. NOTE 1 Tools and tool systems covered by ISO 16084:2017 are, for example, those with hollo...view more

ISO 21940-2:2017 defines terms on balancing. It complements ISO 2041, which is a general vocabulary on mechanical vibration and shock.

ISO 21940-11:2016 establishes procedures and unbalance tolerances for balancing rotors with rigid behaviour. It specifies a) the magnitude of the permissible residual unbalance, b) the necessary number of correction planes, c) the allocation of the permissible residual unbalance to the tolerance planes, and d) how to account for errors in the balancing process. NOTE In ISO 21940‑14, the assessment of balancing errors is considered in detail. Fundamentals of rotor balancing are contained in ISO 1...view more

ISO 21940-12:2016 presents typical configurations of rotors with flexible behaviour in accordance with their characteristics and balancing requirements, describes balancing procedures, specifies methods of assessment of the final state of balance, and establishes guidelines for balance quality criteria. ISO 21940-12:2016 can also serve as a basis for more involved investigations, e.g. when a more exact determination of the required balance quality is necessary. If due regard is paid to the speci...view more

ISO 21940-31:2013 specifies methods for determining machine vibration sensitivity to unbalance and provides evaluation guidelines as a function of the proximity of relevant resonance rotational speeds to the operating speed. ISO 21940-31:2013 is only concerned with once-per-revolution vibration caused by unbalance. It also makes recommendations on how to apply the numerical sensitivity values in some particular cases. It includes a classification system that can be applied to machines which is r...view more

ISO 21940-21:2012 specifies requirements for evaluating the performance of machines for balancing rotating components by the following tests: a) test for minimum achievable residual unbalance, Umar test; b) test for unbalance reduction ratio, URR test; c) test for couple unbalance interference on single-plane machines; d) compensator test. These tests are performed during acceptance of a balancing machine and also later on a periodic basis to ensure that the balancing machine is capable of handl...view more

This part of ISO 21940 specifies the requirements for the following: a) identifying errors in the unbalance measuring process of a rotor; b) assessing the identified errors; c) taking the errors into account. This part of ISO 21940 specifies balance acceptance criteria, in terms of residual unbalance, for both directly after balancing and for a subsequent check of the balance quality by the user. For the main typical errors, this part of ISO 21940 lists methods for their reduction in an informat...view more

This part of ISO 21940 specifies requirements for enclosures and other protective measures used to minimize mechanical hazards produced by the rotor in the unbalance measuring station of centrifugal (rotational) balancing machines. The hazards are associated with the operation of balancing machines under a variety of rotor and balancing conditions. This part of ISO 21940 defines different classes of protection that enclosures and other protective measures provide and describes the limits of appl...view more

ISO 21940-13:2012 specifies procedures to be adopted when balancing medium and large rotors installed in their own bearings on site. It addresses the conditions under which it is appropriate to undertake in-situ balancing, the instrumentation required, the safety implications and the requirements for reporting and maintaining records. ISO 21940-13:2012 can be used as a basis for a contract to undertake in-situ balancing. It does not provide guidance on the methods used to calculate the correctio...view more

ISO 21940-32:2012 specifies one convention for balancing the individual components (shaft and fitments) of a keyed rotor assembly. This provides compatibility of all balanced components so that when they have been assembled the overall balance tolerance and/or vibration limit for the rotor assembly is met. ISO 21940-32:2012 specifies that half-keys be used when balancing the individual components of a keyed rotor assembly. It also specifies a marking of the components balanced in accordance with...view more

ISO 14694:2003 gives specifications for vibration and balance limits of fans for all applications except those designed solely for air circulation, for example, ceiling fans and table fans. However, it is limited to fans of all types installed with a power of less than 300 kW or to commercially available standard electric motor with a maximum power of 355 kW (following an R20 series). For fans of greater power than this, the applicable limits are those given in ISO 10816 - 3. Where the fans in a...view more