National foreword

This British Standard is the UK implementation of ISO 21940‑11:2016/Amd.1:2022. It replaces BS ISO 21940‑11:2016, which is withdrawn.

The start and finish of text introduced or altered by amendment is indicated in the text by tags. Tags indicating changes to ISO text carry the number of the ISO amendment. For example, text altered by ISO amendment 1 is indicated by .

The UK participation in its preparation was entrusted to Technical Committee GME/21/5, Vibration of machines, vehicles and structures.

A list of organizations represented on this committee can be obtained on request to its committee manager.

Contractual and legal considerations

This publication has been prepared in good faith, however no representation, warranty, assurance or undertaking (express or implied) is or will be made, and no responsibility or liability is or will be accepted by BSI in relation to the adequacy, accuracy, completeness or reasonableness of this publication. All and any such responsibility and liability is expressly disclaimed to the full extent permitted by the law.

This publication is provided as is, and is to be used at the recipient’s own risk.

The recipient is advised to consider seeking professional guidance with respect to its use of this publication.

This publication is not intended to constitute a contract. Users are responsible for its correct application.

Compliance with a British Standard cannot confer immunity from legal obligations.

This British Standard was published under the authority of the Standards Policy and Strategy Committee on 30 November 2016.

Foreword

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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.

A list of all parts in the ISO 21940 series can be found on the ISO website.

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Introduction

Rotor balancing is a procedure by which the mass distribution of a rotor (or part or module) is checked and, if necessary, adjusted to ensure the unbalance tolerance is met. This document covers the balancing of rotors with rigid behaviour. A rotor is said to be rigid when the flexure of the rotor caused by its unbalance distribution can be neglected with respect to the agreed unbalance tolerance at any speed up to the maximum service speed. For these rotors, the resultant unbalance, and often moment unbalance, are of interest, which when combined are expressed as a dynamic unbalance of the rotor.

The balancing machines available today enable residual unbalances to be reduced to very low limits. Therefore, it is necessary to specify an unbalance quality requirement for a balancing task, as in most cases it would not be cost-effective to reduce the unbalance to the limits of the balancing machine.

In addition to specifying an unbalance tolerance, it is necessary to consider the errors introduced by the balancing process. This document takes into account the influence of these errors to distinguish clearly between the specified permissible residual unbalance and the reduced residual unbalance values to be achieved during the balancing process.

1 Scope

This document establishes procedures and unbalance tolerances for balancing rotors with rigid behaviour. It specifies

the magnitude of the permissible residual unbalance,
the necessary number of correction planes,
the allocation of the permissible residual unbalance to the tolerance planes, and
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 21940‑1, which introduces balancing.

This document does not cover the balancing of rotors with flexible behaviour. Procedures and tolerances for rotors with flexible behaviour are dealt with in ISO 21940‑12.

2 Normative references

3 Terms and definitions

4 Pertinent aspects of balancing

4.1 General

4.2 Representation of the unbalance

4.3 Unbalance effects

4.4 Reference planes for unbalance tolerances

4.5 Correction planes

4.6 Permissible residual unbalance

5 Similarity considerations

5.1 General

5.2 Permissible residual unbalance and rotor mass

5.3 Permissible residual specific unbalance and service speed

6 Specification of unbalance tolerances

6.1 General

6.2 Derivation of the unbalance tolerances

6.3 Balance quality grade G

6.4 Experimental evaluation

6.5 Unbalance tolerances based on bearing forces or vibrations

6.6 Methods based on established experience

7 Allocation of permissible residual unbalance to tolerance planes

7.1 Single plane

7.2 Two planes

8 Allocation of unbalance tolerances to correction planes

8.1 General

8.2 Single plane

8.3 Two planes

9 Assembled rotors

9.1 General

9.2 Balanced as a unit

9.3 Balanced on component level

10 Accounting for errors in the verification of permissible residual unbalances

10.1 General

10.2 Unbalance tolerance

10.3 Combined error of unbalance measurements

10.4 Verification of the permissible residual unbalance

11 Notification of necessary balancing information at the design stage

Bibliography

BS ISO 21940-11:2016+A1:2022

Mechanical vibration. Rotor balancing - Procedures and tolerances for rotors with rigid behaviour

Current

Published:

30 Jun 2022