ISO 21940-23:2012
(Main)Mechanical vibration — Rotor balancing — Part 23: Enclosures and other protective measures for the measuring station of balancing machines
Mechanical vibration — Rotor balancing — Part 23: Enclosures and other protective measures for the measuring station of balancing machines
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 applicability for each class of protection. Devices for adjusting the mass distribution of a rotor and devices to transfer the rotor are not covered by this part of ISO 21940, even if they are combined with the measuring station. Special enclosure features, such as noise reduction, windage reduction or vacuum (which may be required to spin bladed rotors at balancing speed), are not covered by this part of ISO 21940.
Vibrations mécaniques — Équilibrage des rotors — Partie 23: Enceintes et autres mesures de protection pour le poste de mesurage des machines à équilibrer
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Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 21940-23
First edition
2012-06-01
Mechanical vibration — Rotor balancing —
Part 23:
Enclosures and other protective
measures for the measuring station of
balancing machines
Vibrations mécaniques — Équilibrage des rotors —
Partie 23: Enceintes et autres mesures de protection pour le poste de
mesurage des machines à équilibrer
Reference number
ISO 21940-23:2012(E)
©
ISO 2012
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ISO 21940-23:2012(E)
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ii © ISO 2012 – All rights reserved
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ISO 21940-23:2012(E)
Contents Page
Foreword .iv
Introduction .vi
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 List of significant hazards . 1
4.1 General . 1
4.2 Risk assessment . 1
4.3 Access to balancing machine . 3
5 Safety requirements and protective measures . 3
5.1 General requirements . 3
5.2 Specific requirements . 5
6 Verification of safety requirements and protective measures . 5
7 Information for use . 9
7.1 General requirements . 9
7.2 Instruction handbook . 9
7.3 Marking . 9
Annex A (normative) Class C enclosure selection . 11
Annex B (informative) Equipment for impact tests .19
Annex C (informative) Examples of protective devices .20
Bibliography .23
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ISO 21940-23:2012(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.
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 21940-23 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 cancels and replaces ISO 7475:2002, which has been technically revised. The main change
is deletion of protection class 0.
ISO 21940 consists of the following parts, under the general title Mechanical vibration — Rotor balancing:
1)
— Part 1: Introduction
2)
— Part 2: Vocabulary
3)
— Part 11: Procedures and tolerances for rotors with rigid behaviour
4)
— Part 12: Procedures and tolerances for rotors with flexible behaviour
5)
— Part 13: Criteria and safeguards for the in-situ balancing of medium and large rotors
6)
— Part 14: Procedures for assessing balance errors
7)
— Part 21: Description and evaluation of balancing machines
8)
— Part 23: Enclosures and other protective measures for the measuring station of balancing machines
1) Revision of ISO 19499:2007, Mechanical vibration — Balancing — Guidance on the use and application of balancing
standards
2) Revision of ISO 1925:2001, Mechanical vibration — Balancing — Vocabulary
3) Revision of ISO 1940-1:2003 + Cor.1:2005, Mechanical vibration — Balance quality requirements for rotors in a constant
(rigid) state — Part 1: Specification and verification of balance tolerances
4) Revision of ISO 11342:1998 + Cor.1:2000, Mechanical vibration — Methods and criteria for the mechanical balancing
of flexible rotors
5) Revision of ISO 20806:2009, Mechanical vibration — Criteria and safeguards for the in-situ balancing of medium and
large rotors
6) Revision of ISO 1940-2:1997, Mechanical vibration — Balance quality requirements of rigid rotors — Part 2: Balance
errors
7) Revision of ISO 2953:1999, Mechanical vibration — Balancing machines — Description and evaluation
8) Revision of ISO 7475:2002, Mechanical vibration — Balancing machines — Enclosures and other protective measures
for the measuring station
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ISO 21940-23:2012(E)
9)
— Part 31: Susceptibility and sensitivity of machines to unbalance
10)
— Part 32: Shaft and fitment key convention
9) Revision of ISO 10814:1996, Mechanical vibration — Susceptibility and sensitivity of machines to unbalance
10) Revision of ISO 8821:1989, Mechanical vibration — Balancing — Shaft and fitment key convention
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ISO 21940-23:2012(E)
Introduction
In designing and operating balancing machines, efforts already are made to minimize hazards arising from the
use of the machines themselves. Rising demand for still greater safety in the working environment, however,
requires additional protective measures, especially with respect to the rotor to be balanced. Potential hazards
to the balancing machine operator or the surrounding workshop area can exist, e.g. by personnel coming into
contact with machine components or the rotor, by rotor components or unbalance correction masses detaching
and flying off or by the rotor lifting from the supports or disintegrating.
Special-purpose balancing machines, e.g. those used in the mass production automotive industry, normally
incorporate all necessary protective measures because the workpiece, as well as the operating conditions of the
machine, are known and can be taken into account by the machine manufacturer. For multipurpose balancing
machines, however, where the workpieces to be balanced are generally unknown to the machine manufacturer,
and are thus beyond his control, basic protective measures are limited to obvious hazards, e.g. from end-drive
or belt-drive systems. However, the balancing machine manufacturer has to provide sufficient information for
the user to assess possible hazards originating from a rotor when in the balancing machine, and from the
intended use of the balancing machine. Together with this information, the user of the balancing machine has
to state the possible hazards originating in his rotors in order to allow the balancing machine manufacturer to
supply equivalent protective measures or the user has to provide adequate protective measures on his own.
When the rotors are not known in advance, e.g. in service and repair, a good estimation is needed. Table A.2
states typical values for different balancing machine sizes. But for each individual type of rotor to be balanced,
the user of the balancing machine needs to check if the protective measures cover all hazards.
Most local regulations require certain minimum protective measures to be taken. Observance of such
requirements in conjunction with the recommendations contained in this part of ISO 21940 will generally provide
an adequate measure of protection to the balancing machine operator and surrounding workshop personnel.
There may be applications, however, in which the recommended enclosures or other protective measures are
so costly, or their use so time-consuming, that other protective precautions have to be considered, such as
vacating the surrounding area for a sufficient distance, remote control of the balancing machine or work outside
normal hours.
The consideration of accident probability can be important if a rotor needs to be balanced or spin-tested at or
above its service speed, where major rotor failure cannot be excluded with as much certainty as during low-
speed balancing.
On the other hand, a rotor being balanced at low speed may consist of an assembly of several components,
such as a bladed turbine wheel. It is then important to consider whether an enclosure for low-speed balancing
should withstand penetration of a turbine blade or whether it is sufficient to protect against unbalance correction
masses that might fly off during balancing. If the probability of blade separation is practically non-existent, a
light enclosure, which just protects against correction masses, may be sufficient.
Since this part of ISO 21940 deals with balancing machines and protective measures in general, no details
of the risk can be stated for specific rotor types and balancing machines. Individual investigations, based on
actual rotor parameters, will probably be required in each specific case. In this connection, risk analysis of
possible accidents should include the characteristics of the balancing machine itself. For the extent of the
ensuing damages, it may be of decisive importance to know how much unbalance can be endured by its
supports and bearings due to partial rotor failure, e.g. rotor components becoming detached.
The significant hazards covered by this part of ISO 21940 are listed in Clause 4. The safety requirements
and protective measures to prevent or minimize those hazards are identified in Clause 5, and procedures for
verification of these requirements and protective measures are found in Clause 6.
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INTERNATIONAL STANDARD ISO 21940-23:2012(E)
Mechanical vibration — Rotor balancing —
Part 23:
Enclosures and other protective measures for the measuring
station of balancing machines
1 Scope
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 applicability for each class of protection.
Devices for adjusting the mass distribution of a rotor and devices to transfer the rotor are not covered by this
part of ISO 21940, even if they are combined with the measuring station.
Special enclosure features, such as noise reduction, windage reduction or vacuum (which may be required to
spin bladed rotors at balancing speed), are not covered by this part of ISO 21940.
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.
11)
ISO 1925, Mechanical vibration — Balancing — Vocabulary
ISO 4849, Personal eye-protectors — Specifications
3 Terms and definitions
For the purposes of this document, the terms and definitions given in ISO 1925 apply.
4 List of significant hazards
4.1 General
Significant hazards identified at measuring stations of centrifugal (rotational) balancing machines are listed in
Table 1 together with examples of associated hazardous situations, activities and danger zones.
4.2 Risk assessment
The user of this part of ISO 21940 (i.e. the balancing machine user, designer, manufacturer or supplier) shall
conduct a risk assessment. As part of the risk assessment, the user of this part of ISO 21940 shall describe the
intended use of the balancing machine including manual tool loading, workpiece set-up, maintenance, repair
and cleaning, together with reasonably foreseeable misuse of the machine. As part of the risk assessment,
the user of this part of ISO 21940 shall also verify whether the list of hazards in Table 1 is applicable to the
balancing machine under consideration.
11) To become ISO 21940-2 when revised.
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ISO 21940-23:2012(E)
Table 1 — List of significant specific hazards and examples of hazard sources
associated with the measuring station of balancing machines
Item Specific hazard Example of hazard source Associated activity Related danger zone
1 Mechanical
1.1 Crushing workpiece moving loading the workpiece between rotor and pedestal
around drive shaft and rotor/
check of belt drive
guide rollers
workpiece rotating
lubrication of rollers between journal and roller
1.2 Shearing
workpiece moving in axial between rotor and pedestal,
during process control
direction when rotating access area around machine
power operation of clamping between rotor and clamping
loading of rotor
device device
protective bracket not closed,
ejection of rotor large unbalances, high
balancing speed
area around machine and
1.3 Impact of mass remote, depending on speed
ejection of rotor parts
parts loose, excessive
and energy of masses
balancing speed
rotor bursting
ejection of correction masses masses insufficiently fixed
end drive not coupled to rotor
start of drive around end drive
and drive actuated
Stabbing or
1.4
puncture
rotor with protruding parts checking set-up while rotor
at rotor
rotating running
between belt and rotor/guide
belt drive running check of belt drive
rollers
1.5 Entanglement
rotor with protruding parts checking set-up while rotor
at rotor
rotating running
ejection of lubricant from sleeve
1.6 Slip, trip and fall during operation of machine floor area around machine
bearing
area around machine and
mechanical vibration caused by balancing at high speeds,
1.7 Excessive vibration remote, depending on
unbalances and bending modes overspeeding
vibration magnitude
2 Electrical
2.1 High voltage contact to live parts
automatic restart after power
during set-up of rotor around rotor and drive
loss
2.2 Drive power
loss of speed control during between rotor and clamping
indexing of rotor
indexing activity device
balancing bladed rotors,
3 Excessive noise balancing run near machine
air-drive
4 Neglecting ergonomic principles
lifting and reaching while
during loading or unloading load and unload positions,
handling workpiece and
and maintenance maintenance action points
Unhealthy postures
machine parts
4.1 or excessive efforts
inadequate consideration of
(repetitive strain)
while operating the balancing
human hand–arm or foot–leg workplace
machine
anatomy
judgement and accuracy of
Inadequate local at drive elements, pedestals,
4.2 manual actions during set-up during loading and set-up
lighting and load and unload positions
and loading
inadvertent operation of
measuring unbalance, during
5 Human error controls, misuse of guard- around rotor
set-up
controls
NOTE This list should not be considered complete.
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ISO 21940-23:2012(E)
4.3 Access to balancing machine
The risk assessment shall assume foreseeable access to the balancing machine from all directions. Risks to
both the operator(s) and other persons who may have access to the danger zones shall be identified, taking
into account all hazards which may occur during the lifetime of the balancing machine. The assessment shall
include an analysis of the effect of failure(s) of protective functions in the control system.
5 Safety requirements and protective measures
5.1 General requirements
5.1.1 General considerations
The balancing machine shall be securely attached to the foundation (or the floor) in such a way as to safely
withstand all loads occurring from the rotor mass, the unbalance, particles or parts flying off the rotor, and the
necessary movements of the enclosure while opening or closing.
During operation of a balancing machine, various potential hazards to the balancing machine operator or the
surrounding workshop area can exist, e.g.:
— from personnel coming into contact with moving machine components or the rotor;
— from rotor components or unbalance correction masses detaching and flying off;
— from the rotor lifting from the supports or disintegrating.
General safety requirements therefore have to cover two areas: protection against contact with hazardous
movements (mainly the rotating workpiece) and protection against particles or parts flying off the rotor.
5.1.2 Protection against contact
All rotors represent a hazard during balancing. For that reason, the work zone of a centrifugal (rotational)
balancing machine shall be protected by guards (barriers, fences, enclosures and covers) to protect people
from contacting the rotating workpiece and drive.
Such guards are not needed in special cases, provided that all of the criteria a) to f) apply.
a) The surface of the rotor shall be so smooth that contact is not dangerous, and entanglement is not possible.
b) The correction method shall be such that no particles can become detached (normally material removal).
c) The maximum rotor speed shall be such that major rotor failure is not expected.
d) The rotor shall be prevented from lifting out of the balancing machine bearings by provisions such as
those mentioned in Table 3 (item 1.3) or the rotor mass and the rotational energy of the rotor at maximum
balancing speed shall be so small that no damage is possible if the rotor lifts out of the machine.
e) The maximum available drive torque shall be such that the circumferential forces required to stop rotation
at all relevant radii shall be less than 100 N.
f) The kinetic energy of the rotor plus drive (if coupled without the ability to slip) shall be below 20 N⋅m at
balancing speed. For rotors with large diameter (e.g. automotive wheels), higher values may be permitted
if entanglement with operator’s clothes is not possible.
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ISO 21940-23:2012(E)
5.1.3 Protection against particles or parts
According to the mass and velocity of particles or parts flying off the rotor, different protective measures
are needed, from personal eye-protectors (spectacles, goggles or face-shields), over machine enclosures, to
burst-proof protections. In general three different criteria shall be considered.
a) Area-specific energy
This criterion is based on the case that the kinetic energy of a particle or part is concentrated with its
smallest possible area on the protective device (see A.2.1). The particle or part shall not penetrate or
escape from the protective device.
b) Absolute energy
This criterion is based on the case that the kinetic energy of a particle or part is loading the structure of the
protective device (see A.3.1). The protective device shall not disintegrate so that a particle or part cannot
escape from the protective device.
c) Impulse
This criterion is based on the case that the impulse of a particle or part is transmitted to the protective device
(see A.5.1). The protective device shall not turn over and its displacement shall be reasonably limited.
5.1.4 System of protection classes
The system of protection classes on a balancing machine, as given in Table 2, can be described by two criteria:
— the area-specific energy, absolute energy, and impulse of a part which could fly off the rotor; and
— the need for a guard (e.g. barrier, fence, enclosures, and covers) for the balancing machine.
Table 2 — Balancing machine protection classes
Necessity for
guards on the No Yes
balancing machine
Area-specific energy
up to approximately
2
Minimum protection
340 mN⋅m/mm
required to avoid Area-specific energy,
Spectacles, goggles Absolute energy up to
physical contact with absolute energy or
Criteria or face-shields approximately
rotating parts and impulse values above
needed 2 000 N⋅m
no particles shall be the class C criteria
Impulse up to
released
approximately
200 kg⋅m/s
Protection class A B C D
In some cases it may be advisable to combine classes A and B, e.g. if a rotor is dangerous to contact and only
small particles with limited energy can be ejected during balancing.
5.1.5 Mode of operation
If the machine is equipped with guards around the work zone, it shall have two modes of operation. These
modes are a) and b).
a) Mode 1: Normal (production) operation: Rotation of the workpiece under manual or numerical control to
achieve sequential operation with the enclosure closed and/or protective devices active (e.g. guard lock,
pressure-sensitive protective device, electro-sensitive protection equipment).
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ISO 21940-23:2012(E)
b) Mode 2: Setting mode of operation: Rotation of the workpiece under manual or numerical control to validate
the set-up with work zone enclosure open and the interlocks suspended.
Mode 2 shall only be provided when details of the intended application and required skill level of operators are
defined in the instructions for use. Reduced balancing speed is a significant factor in the risk reduction for this
mode and the maximum speed permitted shall be carefully considered and determined by a risk assessment.
The selection of the mode shall be by a key switch, access code or equally lockable means, and shall only be
permitted from outside the work zone and shall not initiate start-up. For application of the modes, see Table 3.
The selected mode shall be clearly indicated.
5.1.6 Controls
The safety-related parts of control systems for interlocking, monitoring, reduced speed(s), and enabling
device(s) shall be designed so that a single fault in the control shall not lead to loss of the protective function(s),
and wherever reasonably practicable, the single fault shall be detected at or before the next demand upon the
protective function.
Monitoring may be achieved by separate channels, automatic monitoring or other appropriate means.
An enabling device may be a two-position device in conjunction with an emergency stop device, or a three-
position device.
5.2 Specific requirements
Each machine shall be designed and safeguarded in accordance with the specific requirements and protective
measures listed in Table 3.
6 Verification of safety requirements and protective measures
Safety requirements and protective measures implemented in accordance with Clause 5 shall be verified using
the procedures given in Table 3, rightmost column.
Table 3 — List of safety requirements and protective measures and their verification procedures
Item Hazard source Safety requirement and protective measure Verification
1 Mechanical
An enclosure around the universal joint shaft shall prevent the
Disengagement or By visual
whipping around of the shaft if not coupled to a rotor. Alternative
1.1 failure of the end- inspection or
interlocking devices shall prevent the start of the motor if the shaft
drive coupling functional test
is not coupled
Axial rotor On belt drive machines, axial thrust stops shall prevent axial By visual
1.2 movement off the movement of the rotor. On end-drive machines, the drive shaft inspection or
machine supports shall be able to transmit the axial load to the drive thrust bearing measurement
The machine shall be equipped with closed bearings or hold-down
brackets.
By visual
Rotor lifting out
inspection and
If, when balancing cardan shafts, one or all clamping devices
1.3 of the machine’s
(if necessary)
fail, the rotor as a whole shall be caught by protective catches.
open bearings
by calculation
Fragments of the clamping devices shall be caught by a protective
device of an appropriate protection class
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ISO 21940-23:2012(E)
Table 3 (continued)
Item Hazard source Safety requirement and protective measure Verification
Work zones shall be guarded using fixed and/or interlocked
movable guards or fences designed to prevent access to the
work zone by the operator. Guard interlocking shall incorporate
redundancy and monitoring. Redundancy may be by two separate
switches or by a guard-closed switch and detection of guard-lock
Operator coming
position. Measures to minimize possible defeat of interlocking shall
into contact with
By visual
be taken.
any part of the
1.4 inspection and
spinning rotor or
In some applications, only part of the rotor needs to be protected,
practical checks
rotor-specific drive
because other parts of the rotor fall into protection class A. In such
elements
cases, it is sufficient to prevent contact only with the dangerous
surface(s) of the rotor (e.g. low-speed wheel balancing machines
where only the clamping mechanism shall be protected or
designed in such a way that entanglement of operator’s clothes is
not possible)
Examination of
circuit diagrams
In mode 1 [see 5.1.5 a)], machine movements shall only be
and practical
possible when the guards are closed and/or the protective devices
checks. Check to
are active. If in this mode, it is possible to open an interlocking
ensure that the
movable guard, this shall cause the hazardous movements to
1.4.1
hazardous moving
cease and be inhibited.
parts are not
If opening of the interlocking guard gives access to hazards 1.1 to
accessible when
1.6 of Table 1, guard locking shall be provided
the interlocking
guard is opened
In mode 2 [see 5.1.5 b)], powered machine movements shall be
possible only when all of the following conditions are satisfied:
a) Key or code access to this mode with program execution
limited to a single block or fixed/canned cycle (see
Examination of
ISO 2806).
circuit diagrams
1.4.2 b) Machine movements initiated by cycle start control in
and practical
conjunction with an enabling device.
checks
c) The selection of mode 1 shall automatically reinstate all
appropriate safeguarding (e.g. interlocking functions).
d) Machine movements in the reinstated mode 1 shall not be
possible until the cycle start control is operated
Personal eye-protectors (spectacles, goggles or face-shields) shall
By calculation and
be used, unless the impact energy of particles separating from
Ejection of very check of personal
1.5 the rotor exceeds the limits set by ISO 4849 or local regulations,
small particles eye-protector
in which case enclosures or other protective
...
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