ISO 21940-1:2019

INTERNATIONAL ISO
STANDARD 21940-1
First edition
2019-02
Mechanical vibration — Rotor
balancing —
Part 1:
Introduction
Vibrations mécaniques — Équilibrage des rotors —
Partie 1: Introduction
Reference number
©
ISO 2019
© ISO 2019
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ii © ISO 2019 – All rights reserved

Contents Page
Foreword .v
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Fundamentals of balancing . 1
4.1 General . 1
4.2 Unbalance of a single disc . 2
4.3 Unbalance distribution . 4
4.4 Unbalance representation . 4
5 Factors to consider when balancing . 5
5.1 General . 5
5.2 Rotors with rigid behaviour . 5
5.3 Rotors with flexible behaviour . 6
5.3.1 General. 6
5.3.2 Shaft-elastic behaviour . 6
5.3.3 Component-elastic behaviour . 7
5.3.4 Settling behaviour . 7
5.4 Examples of rotor behaviours . 7
6 Selection of a balancing procedure . 8
7 Unbalance tolerances . 9
7.1 General . 9
7.2 Permissible residual unbalance . 9
7.2.1 General. 9
7.2.2 Permissible residual unbalance for rotors with rigid behaviour . 9
7.2.3 Permissible residual unbalance for rotors with flexible behaviour . 9
7.3 Vibration limits .10
7.4 Influence of modes above service speed .10
7.5 Factors influencing balancing procedures .11
7.5.1 General.11
7.5.2 Tolerances .11
7.5.3 Speed and support conditions .12
7.5.4 Initial unbalance . .12
8 Selection of a balancing machine .12
8.1 General .12
8.2 Special requirements .13
9 International Standards on balancing .13
9.1 General .13
9.2 Vocabulary .14
9.2.1 ISO 21940-2 — Balancing vocabulary .14
9.2.2 ISO 2041 — Vibration and shock vocabulary .14
9.3 Balancing procedures and tolerances .14
9.3.1 General.14
9.3.2 ISO 21940-11 — Procedures and tolerances for rotors with rigid behaviour .14
9.3.3 ISO 21940-12 — Procedures and tolerances for rotors with flexible behaviour .14
9.3.4 ISO 21940-13 — Criteria and safeguards for the in-situ balancing of
medium and large rotors .14
9.3.5 ISO 21940-14 — Procedures for addressing balancing errors.15
9.4 Balancing machines .15
9.4.1 ISO 21940-21 — Description and evaluation of balancing machines .15
9.4.2 ISO 21940-23 — Enclosures and other protective measures for the
measuring station of balancing machines .15
9.5 Machine design for balancing.16
9.5.1 ISO 21940-31 — Susceptibility and sensitivity of machines to unbalance .16
9.5.2 ISO 21940-32 — Shaft and fitment key convention .16
Annex A (informative) Mathematical and graphical representation of unbalance .17
Annex B (informative) Examples of different rotor behaviours as indicated on a typical
hard-bearing balancing machine .24
Bibliography .30
iv © ISO 2019 – All rights reserved

Foreword
ISO (the International Organization for Standardization) is a worldwide federation of national standards
bodies (ISO member bodies). The work of preparing International Standards is normally carried out
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ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of
electrotechnical standardization.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www .iso .org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www .iso .org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
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World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT) see the following
URL: www .iso .org/iso/foreword .html.
This document was prepared by Technical Committee ISO/TC 108, Mechanical vibration, shock and
condition monitoring, Subcommittee SC 2, Measurement and evaluation of mechanical vibration and shock
as applied to machines, vehicles and structures.
This first edition of ISO 21940-1 cancels and replaces ISO 19499:2007, which has been technically
revised. The main changes are as follows:
— reference made to all International Standards in the ISO 21940 series;
— deletion of former Table 2 "Guidelines for balancing procedures";
— deletion of former Annex C "How to determine rotor flexibility based on an estimation from its
geometric design".
A list of all parts in the ISO 21940 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body.
A complete listing of these bodies can be found at www .iso .org/members .html.
Introduction
Vibration caused by rotor unbalance is one of the most critical issues in the design and maintenance
of rotating machines. It gives rise to dynamic forces which adversely affect both machine and human
health and well-being. The purpose of this document is to give guidance on the usage of the other parts
of the ISO 21940 series.
Balancing is explained in a general manner, using the specific terms and definitions, to help readers to
select the appropriate balancing approach for their application.
vi © ISO 201
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