ISO 21940-21:2022

INTERNATIONAL ISO
STANDARD 21940-21
Second edition
2022-11
Mechanical vibration — Rotor
balancing —
Part 21:
Description and evaluation of
balancing machines
Vibrations mécaniques — Équilibrage des rotors —
Partie 21: Description et évaluation des machines à équilibrer
Reference number
ISO 21940-21:2022(E)
© ISO 2022

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ISO 21940-21:2022(E)
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© ISO 2022
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Published in Switzerland
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ISO 21940-21:2022(E)
Contents Page
Foreword . vi
Introduction .vii
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Capacity and performance data of the balancing machine . 1
4.1 General . 1
4.2 Data for horizontal balancing machines . 1
4.2.1 Rotor mass and unbalance limitations . 1
4.2.2 Production efficiency . 2
4.2.3 Rotor dimensions . 3
4.2.4 Balancing machine drive data . 4
4.2.5 Torque . 4
4.2.6 Type of rotor drive . 5
4.2.7 Brake . 5
4.2.8 Motor and controls . 5
4.2.9 Speed regulation . . 5
4.2.10 Couple moment interference ratio, I . 5
sc
4.2.11 Air pressure requirements . 5
4.3 Data for vertical balancing machines . 5
4.3.1 Rotor mass and unbalance limitations . 5
4.3.2 Production efficiency . 6
4.3.3 Rotor dimensions . 6
4.3.4 Balancing machine drive data . 8
4.3.5 Torque . 8
4.3.6 Type of drive to rotor . 8
4.3.7 Brake . 8
4.3.8 Motor and controls . 8
4.3.9 Speed regulation . 8
4.3.10 Couple moment interference ratio . 8
4.3.11 Air pressure requirements . 8
5 Machine features . 8
5.1 Principle of operation . 8
5.2 Machine arrangement . 8
5.3 Measuring system . 9
5.3.1 General . 9
5.3.2 Unbalance indicators . 9
5.3.3 Additional features . 9
5.3.4 Operation of the indicating system . . 10
5.4 Plane separation system . 10
5.4.1 Multi-plane balancing machines. 10
5.4.2 Single-plane horizontal or vertical balancing machines . 10
5.5 Setting and calibration of the measuring system . 10
5.5.1 General . 10
5.5.2 Soft-bearing machines . 11
5.5.3 Hard-bearing machines . 11
6 Production efficiency .11
6.1 General . 11
6.2 Time per balance cycle .12
6.3 Unbalance reduction ratio, R . 13
UR
7 Performance qualifying factors . .14
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ISO 21940-21:2022(E)
8 Installation requirements .14
8.1 General . 14
8.2 Supply requirements . 14
8.3 Foundation . 15
9 Proving rotors and test masses . .15
9.1 General . 15
9.2 Standardized proving rotors . 15
9.3 User defined proving rotors . 17
9.4 Test masses . 17
9.4.1 General . 17
9.4.2 U test masses . 24
mar
9.4.3 R test masses . 25
UR
9.4.4 Permissible test mass errors . 26
9.4.5 Material. 27
10 Balance machine verification tests .27
10.1 General . 27
10.2 Requirements for evaluating balance machine performance .28
10.3 Test speed .29
10.4 Test for establishing the minimum achievable residual unbalance, U .29
mar
10.4.1 General .29
10.4.2 Initial balancing machine setting .29
10.4.3 Unbalance added . 31
10.4.4 Readings . . 32
10.4.5 Correction . 32
10.4.6 Reference change . 32
10.4.7 Plane setting for U test . 32
mar
10.4.8 Test runs . 32
10.4.9 U evaluation . 32
mar
10.5 Test for unbalance reduction ratio, R . 33
UR
10.5.1 R tests on single-plane balancing machines . 33
UR
10.5.2 R tests on two-plane balancing machines . 33
UR
10.5.3 General . 33
10.5.4 Test data sheet completion . 36
10.5.5 Plane setting .36
10.5.6 R test runs . 36
UR
10.5.7 Plotting R test data . 37
UR
10.5.8 Evaluation . 41
10.6 Test for couple moment interference on single-plane machines . 42
10.6.1 Starting point . 42
10.6.2 Procedure . 42
10.6.3 Evaluation . 42
10.7 Compensator test . 42
10.7.1 Initial point . 42
10.7.2 Procedure . 42
10.7.3 Evaluation . 43
10.8 Simplified tests . 43
10.8.1 General . 43
10.8.2 Simplified U test . 43
mar
10.8.3 Simplified R test .44
UR
Annex A (informative) Information provided by the user to the balancing machine
manufacturer .45
Annex B (informative) R limit diagrams .51
UR
Annex C (informative) Shafts of outboard Type C proving rotors .54
Annex D (informative) User defined proving rotors for special cases including using a user
production part .56
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ISO 21940-21:2022(E)
Annex E (informative) Modifications to proving rotors prepared in accordance with
ISO 2953 to this document .57
Annex F (informative) Optional repeatability test .59
Annex G (informative) Optional speed range test .61
Bibliography .62
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ISO 21940-21:2022(E)
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
through ISO technical committees. Each member body interested in a subject for which a technical
committee has been established has the right to be represented on that committee. International
organizations, governmental and non-governmental, in liaison with ISO, also take part in the work.
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.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
ISO 21940-21 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 second edition cancels and replaces the first edition (ISO 21940-21:2012), which has been
technically revised.
The main changes are as follows:
— the introduction of new computer based technology into balance machine indication systems;
— the introduction of additional tests for repeatability and speed range (see Annex F and Annex G);
— the introduction of greater clarification for use with automated and special purpose machines.
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.
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ISO 21940-21:2022(E)
Introduction
The purpose of this document is to provide a common framework for the specification, comparison and
evaluation of balancing machines.
It describes a proforma on which the baseline balancing machine characteristics can be presented by
the manufacturer enabling users to compare products from different manufacturers. Additionally,
guidelines are given on the information by which users provide their data and requirements to a
balancing machine manufacturer.
This document describes the tests to be performed during the acceptance testing of a balancing
machine and later, on a periodic basis, to ensure that the balancing machine is capable of handling the
actual balancing tasks. For periodic tests, simplified procedures are specified.
Methods and requirements for preparing proving rotors (which can be of Type A, Type B or Type C, or
a user defined proving rotor e.g. based on a user supplied part) are specified, allowing a wide range of
applications to be covered.
The accuracy of all balance machines is inherently non-linear over their mass and speed range.
In normal practice, a hard bearing balance machine is calibrated over a particular part of its speed
and mass range, but outside that its accuracy cannot be assumed. As a consequence, a rotor specific
calibration should be performed to establish the machine accuracy at a specific speed and for a rotor of
a particular mass. This is normal practice for soft bearing machines or where the manufacturer states
that rotor specific calibration should be carried out.
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INTERNATIONAL STANDARD ISO 21940-21:2022(E)
Mechanical vibration — Rotor balancing —
Part 21:
Description and evaluation of balancing machines
1 Scope
This document sets out the requirements for evaluating hard and soft bearing balancing machines that
support and rotate:
a) rotors with rigid behaviour at balancing speed (as described in ISO 21940-11);
b) rotors with shaft elastic behaviour and balanced in accordance with low speed balancing
procedures (as described in ISO 21940-12).
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
ISO 21940-2, Mechanical vibration — Rotor balancing — Part 2: Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 21940-2 apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
4 Capacity and performance data of the balancing machine
4.1 General
The manufacturer shall specify the data listed in 4.2 for horizontal or 4.3 for vertical balancing
machines. Information to be provided by the user to the balancing machine manufacturer is summarized
in Annex A.
4.2 Data for horizontal balancing machines
4.2.1 Rotor mass and unbalance limitations
The maximum rotor mass, m, which can be balanced, shall be stated over the range of balancing speeds
(n , n , .).
1 2
2
The maximum moment of inertia of a rotor (given by, m r where m is the rotor mass and r the radius of
gyration) with respect to the shaft axis, which the machine can accelerate in a stated acceleration time,
shall be given for the range of balancing speeds (n , n , .) together with the corresponding cycle rate
1 2
(see Table 1, Note 2).
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ISO 21940-21:2022(E)
4.2.2 Production efficiency
The production efficiency (further requirements are described in Clause 7) is the total time taken to
carry out the individual steps necessary to perform a balance measuring run.
The individual steps to be measured are:
a) time for mechanical adjustment (s);
b) time for setting indicating system (s);
c) time for preparation of rotor (s);
d) acceleration time for a stated rotor (s);
e) time taken for the balance reading to stabilize and for it to be recorded (s);
f) deceleration time for a stated rotor (s);
g) identifying unbalance readings taken (s);
h) any other times to be taken into account for operations to be carried out but not included in 4.2.2 a)
to 4.2.2 g) (s).
Total time per measuring run is given by adding the individual times measured in steps 4.2.2 a) to
4.2.2 h) (s).
Table 1 — Horizontal balancing machine data
Manufacturer: Model:
Balancing speeds or speed ranges n n n n …
1 2 3 4
maximum, m
max
Rotor mass (kg) (see Note 1)
minimum
Occasional overload force per support (N) (see Note 1)
Maximum negative force per support (N) (see Note 1)
2
Maximum rotor moment of inertia with respect to the shaft axis (kg m )
Cycle rate per hour (see Note 2)
measurable
Maximu
...