ISO 19499:2007

INTERNATIONAL ISO
STANDARD 19499
First edition
2007-07-15
Mechanical vibration — Balancing —
Guidance on the use and application of
balancing standards
Vibrations mécaniques — Équilibrage — Lignes directrices pour
l'utilisation et l'application de normes d'équilibrage

Reference number
©
ISO 2007
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ii © ISO 2007 – All rights reserved

Contents Page
Foreword. iv
Introduction . v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions. 1
4 Fundamentals of balancing . 1
4.1 General. 1
4.2 Unbalance distribution. 2
4.3 Unbalance representation. 2
5 Balancing considerations . 3
5.1 General. 3
5.2 Rotors with rigid behaviour . 3
5.3 Rotors with flexible behaviour . 4
5.4 Rotors with special behaviour. 5
5.5 Examples of rotor behaviours . 5
5.6 Influencing factors. 6
6 Balance tolerances . 7
6.1 General. 7
6.2 Permissible residual unbalances. 7
6.3 Vibration limits . 7
7 Selection of a balancing procedure. 7
7.1 General. 7
7.2 Selection of a balancing procedure when none is specified . 8
8 International Standards on balancing . 13
8.1 General. 13
8.2 Vocabulary. 13
8.3 Balancing procedures and tolerances. 14
8.4 Balancing machines . 15
8.5 Machine design for balancing . 15
8.6 Machine vibration . 16
Annex A (informative) Mathematical and graphical representation of unbalance . 17
Annex B (informative) Examples of different rotor behaviours. 27
Annex C (informative) How to determine rotor flexibility based on an estimation from its
geometric design . 32
Bibliography . 35

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.
International Standards are drafted in accordance with the rules given in the ISO/IEC Directives, Part 2.
The main task of technical committees is to prepare International Standards. Draft International Standards
adopted by the technical committees are circulated to the member bodies for voting. Publication as an
International Standard requires approval by at least 75 % of the member bodies casting a vote.
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.
ISO 19499 was prepared by Technical Committee ISO/TC 108, Mechanical vibration, shock and condition
monitoring.
iv © ISO 2007 – All rights reserved

Introduction
Vibration caused by rotor unbalance is one of the most critical issues in the design and maintenance of
machines. It gives rise to dynamic forces which adversely impact both machine and human health and well-
being. The purpose of this International Standard is to provide a common framework for balancing rotors so
that appropriate methods will be used. This standard serves essentially as guidance on the usage of other
International Standards on balancing in that it categorizes types of machine unbalance. As such, it can be
viewed as an introductory standard to the series of International Standards on balancing developed by
ISO/TC 108.
Balancing is explained in a general manner, as well as the unbalance of a rotor. A certain representation of
the unbalance is recommended for an easier understanding of the necessary unbalance corrections.

INTERNATIONAL STANDARD ISO 19499:2007(E)

Mechanical vibration — Balancing — Guidance on the use and
application of balancing standards
1 Scope
This International Standard provides an introduction to balancing and directs the user through the available
International Standards associated with rotor balancing. It gives guidance on which of these standards should
be used. Individual procedures are not included here as these will be found in the appropriate International
Standards.
2 Normative references
The following referenced documents are indispensable for the application 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 1925:2001, Mechanical vibration — Balancing — Vocabulary
ISO 2041, Vibration and shock — Vocabulary
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 1925 and ISO 2041 apply.
4 Fundamentals of balancing
4.1 General
Balancing is a procedure by which the mass distribution of a rotor (or part or module) is checked and, if
necessary, adjusted to ensure that balance tolerances are met.
Rotor unbalance may be caused by many factors, including material, manufacture and assembly, wear during
operation, debris or an operational event. It is important to understand that every rotor, even in series
production, has an individual unbalance distribution.
New rotors are commonly balanced by the manufacturer in specially designed balancing machines before
installation into their operational environment. Following rework or repair, rotors may be rebalanced in a
balancing machine or, if appropriate facilities are not available, the rotor may be balanced in situ (see
ISO 20806 for details). In the latter case, the rotor is held in its normal service bearings and support structure
and installed within its operational drive train.
The unbalance on the rotor generates centrifugal forces when it is rotated in a balancing machine or in situ.
These forces may be directly measured by force gauges mounted on the structures supporting the bearings or
indirectly by measuring either the motion of the pedestal or the shaft. From these measurements, the
unbalance can be calculated and balancing achieved by adding, removing or shifting of correction masses on
the rotor. Depending on the particular balancing task, the corrections are performed in one, two or more
correction planes.
4.2 Unbalance distribution
In reality, unbalance is made up of an infinite number of unbalance vectors, distributed along the shaft axis of
the rotor. If a lumped-mass model is used to represent the rotor, unbalance may be represented by a finite
number of unbalance vectors of different magnitude and angular direction as illustrated in Figure 1.

Figure 1 — Unbalance distribution in a rotor modelled as 10 elements perpendicular to the z-axis

If all unbalance vectors were corrected in their respective planes, then the rotor would be perfectly balanced.
In practice, it is not possible to measure these individual unbalances and it is not necessary. A more
condensed description is needed, leading to practical balancing procedures.
4.3 Unbalance representation
Rotor unbalance can be expressed by a combination of the following three kinds of unbalance
representations:
G
a) resultant unbalance, U , the vector sum of all unbalance vectors distributed along the rotor;
r
G
b) resultant moment unbalance, P , the vector sum of the moments of all the unbalance vectors distributed
r
along the rotor about the arbitrarily selected plane of the resultant unbalance;
G
c) modal unbalance, U , that unbalance distribution which affects only the nth natural mode of a
n
rotor/bearing system.
Mathematical and graphical representations of unbalances are shown in Annex A.
NOTE Resultant unbalance [see 4.3 a)] and resultant moment unbalance [see 4.3 b)] can be combined. The
combination is called “dynamic unbalance” and is represented by two unbalances in two arbitrarily chosen planes
perpendicular to the shaft axis.
2 © ISO 2007 – All rights reserved

5 Balancing considerations
5.1 General
In the past, International Standards classified all rotors to be either rigid or flexible, and balancing procedures
for these two main classes of rotors are given in ISO 1940-1 and ISO 11342, respectively (see Table 1).
However, the simple rigid/flexible classification is a gross simplification, which can lead to a misinterpretation
and suggests that the balance classification of the rotor is only dependent on its physical construction.
Unbalance is an intrinsic property of the rotor, but the behaviour of the rotor and its response to unbalance in
its normal operating environment are affected by the dynamics of the bearings and support structure, and by
its operating speed. Furthermore, the balance quality to which the rotor is expected to run and the magnitude
and distribution of the initial unbalance along the rotor will dictate which balancing procedure is necessary;
see Table 1.
Table 1 — Overview of rotor behaviour, related International Standards and balancing procedures
Rotor behaviour Example Related Balancing task or procedure
International
(Numbers refer to (Letters as used in ISO 11342:1998)
Standard
subclauses in this
International Standard)
a
Rigid behaviour (5.2) Figure 4 a) ISO 1940-1
One- and two-plane balancing
Six low-speed balancing procedures (A to F)
Balancing procedure at multiple speeds (G)
Flexible behaviour (5.3) Figure 4 b)
Balancing procedure for one speed only (usually
service speed) (H)
b
ISO 11342
Component elastic
Figure 4 c) Fixed-speed balancing procedure (I)
behaviour (5.4.2)
Component seating
c
Figure 4 d)
Settling of components at high speed
behaviour (5.4.3)
a
One- and two-plane balancing includes balancing the resultant unbalance and the resultant moment unbalance.
b
ISO 11342:1998 uses “flexible” as a generic term that includes flexible, component elastic and component seating behaviours.
c
This procedure is mentioned in Clause 7 of ISO 11342:1998, but no designated letter is given.

5.2 Rotors with rigid behaviour
An ideal rotor when rotating, with rigid behaviour on elastic supports, will undergo displacements that are
combinations of the two dynamic rigid-body modes, as seen in Figure 2 for a simple symmetric rotor with
unbalance. There is no flexure of the rotor and all displacements of the rotor arise from movements of the
bearings and their support structure.

Figure 2 — Rigid-body modes of a symmetric rotor on a symmetric elastic support structure

In reality, no rotor will be totally rigid and will have small flexural deflections in relation to the gross rigid-body
motion of the rotor. However, the rotor may be regarded as rigid provided these deflections caused by a given
unbalance distribution are below the required tolerances at any speed up to the maximum service speed. The
majority of such rotors, and indeed many manufactured rotors, can be balanced as rigid rotors, in accordance
with the requirements of ISO 1940-1. This aims at balancing the resultant unbalance with at least a single-
plane balance correction, or the dynamic unbalance with a two-plane balance correction.
NOTE Rotors designated to have rigid behaviour in the operating environment can be balanced at any speed on the
balancing machine provided the speed is sufficiently low to ensure the rotor still operates with a rigid behaviour.
5.3 Rotors with flexible behaviour
5.3.1 General
If the speed is increased or the tolerance reduced for the same rotor described in 5.2, it may become
necessary to take flexible behaviour into account. Here the deflection of the rotor is significant, and rigid-body
balancing procedures are not sufficient to achieve a desired balance condition. Figure 3 shows typical flexural
mode shapes for a symmetric rotor. For these rotors that exhibit flexural behaviour, the balancing procedures
in ISO 11342 should be adopted.
5.3.2 Low-speed balancing
In special circumstances, even rotors with flexible behaviour may be balanced satisfactorily at low speed.
ISO 11342:1998 describes procedures A to F, which, as far as possible, all aim to correct the unbalance in
their planes of origin.
5.3.3 Multiple-speed balancing
This procedure should be used to balance the resultant unbalance, the resultant moment unbalance and the
relevant modal unbalances, according to ISO 11342:1998, procedure G.

a)  First mode
b)  Second mode
c)  Third mode
Figure 3 — Schematic representation of the first three flexural modes of a rotor with flexible behaviour
on an elastic support structure
4 © ISO 2007 – All rights reserved

5.3.4 Service speed balancing
These rotors are flexible and pass through one or more critical speeds on their way up to service speed.
However, due to operating conditions or machine construction, high levels of vibration can be tolerated at the
critical speeds and the rotor is only balanced at the service speed according to ISO 11342:1998, procedure H.
5.4 Rotors with special behaviour
5.4.1 General
The majority of rotors will exhibit either rigid or flexible behaviours, but the following special behaviours can
exist and must be considered to achieve a successful balancing of the rotor.
5.4.2 Elastic behaviour of components
These rotors can have a shaft and body construction that either requires low-speed or high-speed balancing
procedures. However, in addition, they have one or more components that themselves are either flexible or
are flexibly mounted so that the unbalance of the whole system might consistently change with speed.
Examples of such rotors are a rotor with tie bars that deflect at high speed, rubber-bladed fans and single-
phase induction motors with a centrifugal switch. These should be balanced in accordance with
ISO 11342:1998, procedure I.
5.4.3 Seating behaviour of components
These rotors can have a construction where components settle after reaching a certain speed or other
condition. This movement will then become stable after one or just a few events. The components will reach a
final position and become re-seated, after which the rotor may require further balancing. Examples are
shrunk-on turbine discs, built-up rotors, copper winding in generators and generator retaining rings.
Subsequent behaviour of the rotor will then dictate the balancing procedure required. This rotor behaviour is
mentioned in Clause 7 of ISO 11342:1998, but no procedure is specified.
5.5 Examples of rotor behaviours
The different behaviours may be represented by the following rotors (see Figure 4):

a)  Rigid behaviour (a solid gear wheel) b)  Flexible behaviour (a disc on an elastic shaft,
for example a Laval rotor)
c)  Component elastic behaviour (a drum with tie bars, d)  Seating behaviour (a generator rotor with windings,
elastically deflecting under the centrifugal load) once for all seating under a certain centrifugal load)
Figure 4 — Examples of rotor types that demonstrate particular rotor behaviours
Such illustrations are not sufficient for a full description: obviously, rotors such as those shown in Figures 4 c)
and 4 d) may also show flexible behaviour; on the contrary, a rotor such as Figure 4 b) could be a low-speed
fan without considerable flexible behaviour, i.e. a rotor with a rigid behaviour. Details of these types of
behaviour are further explained in Annex B.
5.6 Influencing factors
5.6.1 General
A rotor’s response characteristic is defined by its physical properties and those of its supporting structure. The
vibration response measured at the supporting structure or on the rotor will depend on these physical
properties plus the magnitude of unbalance and its distribution along the rotor, as well as the speed of rotation.
Balancing to a required tolerance will therefore depend on all these parameters, and changing these or the
tolerance specified may change the procedure needed to meet that tolerance.
5.6.2 Tolerances
By simply reducing the balance tolerance, it may be necessary to reconsider the behaviour of the rotor and
adopt a different procedure to bring the rotor within tolerance, as given in the following examples.
a) A rotor with rigid behaviour, balanced using a single-plane procedure to reduce resultant unbalance, may
simply require additional more accurate single-plane balancing.
b) A rotor with rigid behaviour, balanced using a single-plane procedure to reduce resultant unbalance, may
also require a two-plane procedure to take into account the moment unbalance (or both resultant and
moment unbalance together as a dynamic unbalance).
c) A rotor with rigid behaviour, balanced in two planes to reduce both resultant and moment unbalance (or
both resultant and moment unbalance together as a dynamic unbalance), may additionally require flexible
behaviour procedures to reduce contributions from the modal unbalances, even though the rotor is
running below its first flexural critical speed.
d) A rotor with flexible behaviour, for which a flexible rotor behaviour procedure has been carried out to
reduce the dynamic unbalance and a number of modal unbalances, may require additional flexible rotor
behaviour procedures to reduce modal unbalances of even more (higher) flexural modes of the rotor,
even though the rotor is running below the flexural critical speeds of the higher modes.
e) A rotor with either rigid or flexible behaviour, successfully balanced using the appropriate procedure, may
need to consider special procedures to take into account component elastic or component seating
behaviours.
f) Where a tighter tolerance can only be achieved at a single speed, the service speed balancing procedure
may need to be considered.
5.6.3 Speed and support conditions
Other changes of rotor behaviour may occur if operational conditions are changed (e.g. by changing speed or
support conditions).
5.6.4 Initial unbalance
The initial unbalance distribution has an influence on the response of the rotor system. It determines which
unbalance (see Clause 4) is out of tolerance and therefore needs treatment. Different manufacturing and
assembling procedures can lead to different levels of initial unbalance.
6 © ISO 2007 – All rights reserved

6 Balance tolerances
6.1 General
The balancing equipment and techniques available enable unbalances to be reduced to low limits. However, it
would be uneconomic to over-specify the quality requirements. It is therefore necessary to define the optimum
balance quality for the rotor to operate with acceptable vibration and dynamic forces in its normal service
environment.
6.2 Permissible residual unbalances
There is a direct relation between rotor unbalance and the once-per-revolution vibration under service
conditions. The relationship depends on the machine’s dynamic characteristics (i.e. rotor, structure and
bearing dynamic properties). However, the overall machine vibration may be due only in part to the presence
of rotor unbalance. Other sources of vibration could be magnetic or fluid forces.
Guidance on the derivation of permissible residual unbalance tolerances is given in
⎯ ISO 1940-1 for a rigid rotor behaviour, and
⎯ ISO 11342, using tolerance data from ISO 1940-1, for other rotor behaviours.
6.3 Vibration limits
There is no easily recognizable relationship between the machine vibration under service conditions and
vibration in the balancing machine. The relation depends on the differences between the bearings and the
support structure used in the balancing machine and installed condition. Further, the rotor in the balancing
machine is tested in isolation and does not include effects from other rotors in the shaft line, as experienced
when installed in its operational environment. It should be noted that different balancing machines may have
different pedestal stiffness and therefore vibration limits have to be set individually for each balancing machine.
Where detailed information is available concerning these parameters, a method to estimate these limits is
presented in ISO 11342. In-situ vibration limits are presented in the appropriate parts of ISO 7919 for rotating
shafts and ISO 10816 for non-rotating parts.
Where insufficient detail is available to obtain these parameters, guidance should be taken from the balancing
machine facility from which rotors have operated satisfactorily in situ.
7 Selection of a balancing procedure
7.1 General
Since different balancing procedures require different types of balancing machines and resource input, it is
important to select an appropriate procedure (see Table 1) to optimize the balancing process to meet the
required balance tolerances.
Rotors with a rigid behaviour (see 5.2) can be balanced using the single- and two-plane balancing guidelines
provided in ISO 1940-1.
In general, rotors with a flexible behaviour (see 5.3) should be dealt with in accordance with the guidelines
given in ISO 11342, where a number of procedures are defined for different rotor configurations:
⎯ the general procedure is that for multiple-speed balancing, see 5.3.3 (procedure G of ISO 11342:1998);
⎯ rotors that spend most of their time at a single speed can use service speed balancing (see 5.3.4;
(procedure H of ISO 11342:1998);
⎯ rotors that have flexible behaviour that can be adequately balanced at low speed (see 5.3.2; procedures
A to F of ISO 11342:1998).
The procedure for rotors with component elastic behaviour, see 5.4.2, is given in ISO 11342:1998
(procedure I).
For rotors with component seating behaviour (see 5.4.3), it is first necessary for the rotor to be taken to the
speed (or condition) at which the unbalance is stabilized and then balanced using the appropriate procedure
for the rigid rotor behaviour (see ISO 1940-1) or flexible rotor behaviour (see ISO 11342).
Where possible, consult the rotor manufacturer or the user for a recommended balancing procedure. In the
case of the rotor with flexible behaviour, a definition of the rotor configuration, as defined by ISO 11342, would
suffice.
7.2 Selection of a balancing procedure when none is specified
7.2.1 Identify the rotor behaviour
Clause 5 introduces the major types of rotor behaviour and Table 2 gives guidance on selection of the
balancing procedure together with the expected balancing machine to be used. A consideration of the balance
tolerances must be taken into account when identifying the rotor behaviour, as discussed in 7.2.2.
WARNING — Guidance given in Table 2 should be used with care as the ratio of rotor speed to first
flexural resonance in situ is only a typical value. This will be highly dependent on the dynamic
characteristics of the bearings and their supports, initial unbalance, the balance quality required, and
the detailed design of the rotor.
Although the behaviour of many rotors can be easily identified from the simple guidance given in both
Clause 5 and Table 2, others will require a full analysis, particularly when making the distinction between rigid
and flexible behaviours. Table 2 requires knowledge of the critical speeds, which are often unknown. Annex C
presents an analytical method to obtain estimates of rotor flexibility in the operating environment.

8 © ISO 2007 – All rights reserved

Table 2 — Guidelines for balancing procedures
Guidance given in this table should be used with care as the ratio of rotor speed to first flexural critical speed in situ is only a typical value. This will be highly dependent on
the dynamic characteristics of the bearings and their supports, initial unbalance, the balance quality required and the detailed design of the rotor.
Schematic rotor Rotor speed/first flexural Balancing process and
Rotor description
representation critical speed in situ International Standard
Single- or two-plane balancing
Any rotor configuration
< 0,30
ISO 1940-1
Single-plane balancing
Disc perpendicular to shaft axis All values
Single rigid disc installed on an
ISO 1940-1
elastic shaft whose unbalance is
Two-plane balancing
negligible
Disc with axial runout All values
ISO 1940-1
Two-plane balancing
Both discs perpendicular to
All values
shaft axis
ISO 1940-1
Two rigid discs installed on an
Two-plane balancing
elastic shaft whose unbalance is
< 0,7
ISO 1940-1
negligible
One or both disc(s) with axial
runout
Multiple-speed balancing
W 0,7
ISO 11342:1998, procedure G
Two-plane balancing
< 0,7
More than two rigid discs
ISO 1940-1
installed on an elastic shaft
Multiple-speed balancing
whose unbalance is negligible
W 0,7
ISO 11342:1998, procedure G
Single rigid section installed on
Two-plane balancing
an elastic shaft whose unbalance All values
ISO 1940-1
is negligible
10 © ISO 2007 – All rights reserved
Table 2 (continued)
Guidance given in this table should be used with care as the ratio of rotor speed to first flexural critical speed in situ is only a typical value. This will be highly dependent on
the dynamic characteristics of the bearings and their supports, the initial unbalance, the balance quality and the detailed design of the rotor.
Schematic rotor Rotor speed/first flexural Balancing process and
Rotor description
representation critical speed in situ International Standard
Two-plane balancing
< 0,7
Two or more rigid sections
ISO 1940-1
installed on an elastic shaft
Multiple-speed balancing
whose unbalance is negligible
W 0,7
ISO 11342:1998, procedure G
Two-plane balancing
< 0,6
Assumed unbalance distribution
ISO 1940-1
according to machining
Two-plane balancing in two
tolerances (generally uniform
optimum correction planes
unbalance distribution)
W 0,6
ISO 11342:1998, procedure F
Cylindrical roll
Two-plane balancing
< 0,6
ISO 1940-1
No known unbalance
distribution
Multiple-speed balancing
W 0,6
ISO 11342:1998, procedure G
Two-plane balancing
< 0,6
Rotor including roll(s) and rigid
ISO 1940-1
sections and/or discs
Multiple-speed balancing
Integral rotors
W 0,6
ISO 11342:1998, procedure G
Any other configuration No factor available ISO 11342
NOTE 1 Factors stated are based on typical balance tolerances with limited initial unbalance.
NOTE 2 These guidelines apply to assembled rotors where the individual components have not been balanced prior to assembly.
NOTE 3 In the fourth column of the table, it is the first flexural critical speed of the rotor that is considered, not the rigid-body critical speeds.
NOTE 4 There are examples where the first critical speed observed is associated with rigid-body modes of the rotor. This should not be confused with the first flexural.

7.2.2 Select the required balance tolerances for the rotor
Select the balance tolerance as recommended in Clause 6.
When low balancing tolerances or response levels are required, it may be necessary to consider shaft flexural
modes that occur at frequencies above the operating speed range of the rotor. For example, the rotor
response shown in Figure 5 is significantly affected at the service speed (50 Hz) by the higher first flexural
mode, even though the first two (rigid-body) modes have been balanced and are at a much lower level. Here a
machine would fail a balance tolerance based on r.m.s. vibration of 5 mm/s at a normal service speed of
50 Hz due to the higher mode, even though the lower modes would be acceptable. The level of excitation of
this higher mode and the balance tolerance required will determine the rotor behaviour and balancing
procedure adopted. In this case, the influence of the higher mode will require a flexible rotor-balancing
procedure to be used to achieve the required balancing tolerance at the operational speed.

Key
X frequency, Hz
Y r.m.s. vibration level, mm/s
a
Operating speed of 50 Hz.
Figure 5 — Influence of rotor modes above service speed

7.2.3 Select the appropriate balancing procedure
An introduction to the available balancing procedures is presented in Table 2. For details, see the appropriate
International Standards.
7.2.4 Choose the appropriate balancing machine
Rotor behaviour, together with the chosen balancing procedure, will dictate whether a low- or high-speed
balancing machine is required. Examples of balancing machine requirements are provided in Table 3 and
these are covered in more detail in ISO 2953.
The different types of unbalance call for different types of balancing machines, as follows:
a) resultant unbalance:
a single-plane balancing machine (low-speed) is sufficient;
b) resultant moment unbalance:
a two-plane balancing machine (low-speed) is needed;
c) modal unbalances:
a high-speed balancing machine will generally be needed.
NOTE 1 Single-plane balancing can also be performed on a two-plane balancing machine.
NOTE 2 A high-speed balancing machine can usually handle both single-plane and two-plane balancing.
NOTE 3 Flexible rotors classified by procedures A to F of ISO 11342:1998 can be adequately balanced at low speed.
Table 3 — Examples of balancing machine requirements
1 Rotor mass
2 Bearing types, size and centre distance
3 Rotor length
4 Rotor diameter
5 Minimum achievable residual unbalance
6 Unbalance reduction ratio
7 Bearing support stiffness to match the installed environment
8 Vacuum facilities for high-speed bladed rotors
9 Allowable maximum speed for bladed rotors on low-speed machines
10 Induced electrical current for high-speed electrical rotors
11 Influence of rotor overhangs in the balancing test facility
NOTE This list is not exhaustive and other requirements could be appropriate for special machines.

7.2.5 Selecting specialized rotor requirements
While the rotor is in the balancing machine, additional tests may be undertaken to ensure the rotor is fit for
purpose. Table 4 gives examples of additional tests that could be performed on a large electrical generator
rotor while in the balancing machine. Similarly, the need for additional tests should be considered for other
specialized rotors whilst in the balancing machine.
Table 4 — Example of tests that may be undertaken in the balancing machine
for an electrical generator rotor
1 Over speed the rotor to settle the end rings
2 Balance the rotor while passing through the shaft critical speeds, service speed and
during over speed
3 Undertake thermal stability checks
4 Perform electrical tests to check the integrity of the windings
NOTE These tests should only be carried out provided the appropriate facilities are available and
safety requirements are satisfied.
12 © ISO 2007 – All rights reserved

8 International Standards on balancing
8.1 General
A suite of International Standards is available to aid the user in the field of balancing; see Table 5. These fall
into six main areas: introduction (this International Standard), vocabulary, balancing procedures and
tolerances, balancing machines, machine design for balancing, and machine vibration.
Table 5 — The suite of International Standards on balancing
Topic International Standard
Introduction Introduction
ISO 19499
Vocabulary Balancing vocabulary Vibration and shock
ISO 1925 vocabulary
ISO 2041
Balancing procedures Rigid behaviour Flexible behaviour In-situ balancing
and tolerances ISO 1940-1 ISO 11342 ISO 20806
Balance tolerances and
balance errors
ISO 1940-2
Balancing machines Description and Symbols and Enclosures and
evaluation instrumentation protective measures
ISO 2953 ISO 3719 ISO 7475
Machine design for balancing Susceptibility and Shaft and fitment key
sensitivity of machines convention
to unbalance ISO 8821
ISO 10814
Machine vibration Evaluation of machine Evaluation of machine
vibration by measurements vibration by measurements
on non-rotating parts on rotating shafts
ISO 10816 (all parts) ISO 7919 (all parts)

8.2 Vocabulary
8.2.1 ISO 1925, Mechanical vibration — Balancing — Vocabulary
This International Standard establishes a vocabulary on balancing in English and French. An alphabetical
index is provided for each of the two languages.
Annex A of ISO 1925:2001 gives an illustrated guide to balancing machines terminology and includes
equivalent terms in English, French and German.
8.2.2 ISO 2041, Vibration and shock — Vocabulary
A general vocabulary on vibration and shock, in English and French, is given in ISO 2041. An alphabetical
index is provided for each of the two languages.
8.3 Balancing procedures and tolerances
8.3.1 General
These International Standards are not intended to serve as an acceptance specification for any rotor, but
rather to give indications of how to avoid gross deficiencies and/or unnecessarily restrictive requirements.
8.3.2 ISO 1940-1, Mechanical vibration — Balance quality requirements of rigid rotors in a constant
(rigid) state — Part 1: Specification and verification of balance tolerances
ISO 1940-1 gives recommendations for determining unbalance and for specifying related quality requirements
of rigid rotors. It specifies
a) a representation of unbalance in one and two planes,
b) methods for determining permissible residual unbalance,
c) methods for allocating permissible residual unbalance to correction planes,
d) methods for identifying the residual unbalance state of a rotor by measurement, and
e) a summary of errors associated with the residual unbalance identification.
8.3.3 ISO 1940-2, Mechanical vibration — Balance quality requirements of rigid rotors — Part 2:
Balance errors
ISO 1940-2 covers
a) identification of errors in the balancing process of rigid rotors,
b) the assessment of errors,
c) guidelines for taking errors into account, and
d) the evaluation of residual unbalance in any two correction planes.
Many of the errors associated with balancing of rotors with a rigid behaviour, as outlined in ISO 1940-2, apply
equally to balancing of rotors that have a flexible behaviour.
8.3.4 ISO 11342, Mechanical vibration — Methods and criteria for the mechanical balancing of
flexible rotors
ISO 11342 presents typical flexible rotor configurations according to their characteristics and balancing
requirements, describes balancing procedures, specifies methods of assessment of the final state of
unbalance, and gives guidance on balance quality criteria in terms of both vibration and residual unbalance. It
includes low-speed balancing procedures which can be applied successfully for some rotors with a flexible
behaviour.
ISO 11342 may also be applicable to serve as a basis for more involved investigations, for example when a
more exact determination of the required balance quality is necessary. If due regard is paid to the specified
method of manufacture and limits of unbalance, satisfactory running conditions can probably be expected.
The influence of structural resonances is outside the scope of ISO 11342 but is covered by ISO 10814 (see
8.5.2).
14 © ISO 2007 – All rights reserved

8.3.5 ISO 20806, Mechanical vibration — Criteria and safeguards for the in-situ balancing of medium
and large rotors
ISO 20806 specifies procedures be adopted when balancing 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. The standard
may be used as a basis for a contract to undertake in-situ balancing.
ISO 20806 does not provide guidance on the methods used to calculate the correction masses from
measured vibration data.
8.4 Balancing machines
8.4.1 ISO 2953, Mechanical vibration — Balancing machines — Description and evaluation
ISO 2953 gives requirements for the evaluation of performance and characteristics of machines for balancing
rotating components where correction is required in one or more planes. It stresses the importance attached
to the form in which the balancing machine characteristics should be specified by the manufacturer, and also
outlines methods of evaluating balancing machines.
8.4.2 ISO 3719, Mechanical vibration — Symbols for balancing machines and associated
instrumentation
ISO 3719 establishes symbols for use on balancing machines, including instrumentation. They are intended to
complement (but not replace) those already standardized in documents such as ISO 7000. The primary
purpose of symbols in ISO 3719 is to explain the functions and uses of the indicators and controls, etc. which
are an integral part of a balancing machine.
8.4.3 ISO 7475, Mechanical vibration — Balancing machines — Enclosures and other protective
measures for the measuring station
This International Standard specifies requirements for enclosures and other safety measures used to minimize
hazards associated with the operation of balancing machines. It defines different classes of protection that
enclosures and other protective features have to provide, and describes the limits of applicability for each
class of protection.
Special enclosure features, such as noise reduction, windage reduction or vacuum (which is required to spin
some rotors at balancing speed), are not covered by ISO 7475.
8.5 Machine design for balancing
8.5.1 ISO 8821, Mechanical vibration — Balancing — Shaft and fitment key convention
ISO 8821 defines the convention for balancing the individual components of a keyed assembly. It is intended
to provide compatibility of all balanced components, so that when they are assembled they will meet the
overall balance or vibration tolerance levels for the assembled rotor.
8.5.2 ISO 10814, Mechanical vibration — Suscept
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