ISO 7475:2002
(Main)Mechanical vibration — Balancing machines — Enclosures and other protective measures for the measuring station
Mechanical vibration — Balancing machines — Enclosures and other protective measures for the measuring station
This International Standard 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 International Standard 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 International Standard, 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 International Standard.
Vibrations mécaniques — Machines à équilibrer — Enceintes et autres mesures de protection pour le poste de mesurage
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Standards Content (Sample)
INTERNATIONAL ISO
STANDARD 7475
Second edition
2002-03-01
Mechanical vibration — Balancing
machines — Enclosures and other
protective measures for the measuring
station
Vibrations mécaniques — Machines à équilibrer — Enceintes et autres
mesures de protection pour le poste de mesurage
Reference number
ISO 7475:2002(E)
©
ISO 2002
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ISO 7475:2002(E)
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ii © ISO 2002 – All rights reserved
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ISO 7475:2002(E)
Contents Page
Foreword.iv
Introduction.v
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 .2
5 Safety requirements and/or protective measures.2
5.1 General requirements.2
5.2 Specific requirements.5
6 Verification of safety requirements and/or protective measures .5
7 Information for use .8
7.1 General requirements.8
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 protection classes .20
Bibliography.23
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ISO 7475:2002(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 3.
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 International Standard may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights.
ISO 7475 was prepared by Technical Committee ISO/TC 108, Mechanical vibration and shock, Subcommittee
SC 1, Balancing, including balancing machines.
This second edition cancels and replaces the first edition (ISO 7475:1984) and the technical corrigendum, of which
it constitutes a technical revision.
Major chances to the previous edition are
expanding the permissible particle velocity range,
using the area-specific energy of a particle as criterion for the capability of the enclosure material to hold a
particle which leaves the rotor,
taking the absolute energy of a particle as criterion for the strength of the fastening of the whole enclosure or
of its components,
considering the impulse of a particle when it hits a free-standing enclosure, and
adding other safety aspects that are intrinsic to balancing machines and are related to the integrity of the
operator.
This International Standard follows the rules for drafting and presentation of a machinery-related safety standard as
they are mandatory in European Standards, and gives verification procedures for the safety requirements.
Annex A constitutes a normative part of this International Standard. Annexes B and C are for information only.
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ISO 7475:2002(E)
Introduction
In designing and using balancing machines, efforts 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 protection, especially with respect to the rotor to be balanced. Potential hazards to the balancing
machine operator or the surrounding workshop area may exist, for example, 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. These potential hazards may theoretically increase with rotor
size and balancing speed, but they are generally minimized by appropriate rotor design and balancing instructions.
Special-purpose balancing machines, for example 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, for example end-drive
coupling and/or drive belt covers. Therefore 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 these 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 rotor to be balanced, the user
should 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 International Standard will generally provide an
adequate measure of protection to the balancing machine operator and surrounding workshop personnel. There
may be applications, however, where the recommended enclosures or other protective measures are so costly, or
their use so time-consuming, that other protective precautions, such as vacating the surrounding area for a
sufficient distance, remote control of the balancing facility, or work outside normal hours, etc., have to be
considered.
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. Maximum service and spin-test speeds are generally well below the speed where major rotor failure can
be expected.
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 International Standard deals with balancing machines and protective measures in general, no details of
the risk can be stated for specific rotor types and balancing facilities. 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, for example rotor components becoming detached.
The significant hazards covered by this International Standard are those listed in clause 4. The safety requirements
and/or protective measures to prevent or minimize those hazards identified in Table 1 and procedures for
verification of these requirements or protective measures are found in clause 5.
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INTERNATIONAL STANDARD ISO 7475:2002(E)
Mechanical vibration — Balancing machines — Enclosures and
other protective measures for the measuring station
1 Scope
This International Standard 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 International Standard 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
International Standard, 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 International Standard.
2 Normative references
The following normative documents contain provisions which, through reference in this text, constitute provisions of
this International Standard. For dated references, subsequent amendments to, or revisions of, any of these
publications do not apply. However, parties to agreements based on this International Standard are encouraged to
investigate the possibility of applying the most recent editions of the normative documents indicated below. For
undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC
maintain registers of currently valid International Standards.
ISO 1925, Mechanical vibration — Balancing — Vocabulary
ISO 2041, Vibration and shock — Vocabulary
ISO 2806, Industrial automation systems — Numerical control of machines — Vocabulary
ISO 4849, Personal eye-protectors — Specifications
3 Terms and definitions
For the purposes of this International Standard, the terms and definitions given in ISO 1925 and ISO 2041 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 International Standard (i.e. the user, designer, manufacturer or supplier) shall conduct a risk
assessment. As part of the risk assessment, the user of this International Standard 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
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ISO 7475:2002(E)
International Standard shall also verify whether the list of hazards in Table 1 is exhaustive and applicable to the
balancing machine under consideration.
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/or 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 whilst opening or closing.
During operation of a balancing machine, various potential hazards to the balancing machine operator or the
surrounding workshop area can exist, for example,
from personnel coming into contact with moving machine components or the rotor,
from rotor components or unbalance correction masses detaching and flying off, and
from the rotor lifting from the supports or disintegrating.
General safety requirements therefore have to cover two areas: protection against contacts with hazardous
movements (mainly the rotating workpiece) and protection against particles or parts flying off the rotor.
5.1.2 Protection against contact
Many rotors represent a hazard during balancing due to the surface (e.g. bladed rotors) or due to the rotational
energy stored. For that reason the work zone of a dynamic balancing machine shall be protected by guards
(barriers, fences) to protect people from contacting the rotating workpiece and drive.
Such guards are not needed in special cases, provided that all of the following criteria apply.
a) The surface of the rotor shall be so smooth that contact is not dangerous.
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 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 drive torque shall be be low to ensure that the circumferential forces stay below 100 N at all
relevant radii [for moments of inertia, see f)].
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 7475:2002(E)
Table 1 — List of significant specific hazards and examples of hazard sources associated with the
measuring station in balancing machines
Item Specific hazard Examples of hazard source Associated activity Related danger zone
1 Mechanical
1.1 Crushing workpiece moving loading the workpiece between rotor and pedestal
1.2 Shearing workpiece rotating check of belt drive around drive shaft and
rotor/guide rollers
workpiece rotating lubrication of rollers between journal and roller
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
1.3 Impact of mass ejection of rotor protective bracket not area around machine and
closed, large unbalances, remote, depending on speed
high balancing speed and energy of masses
parts loose, excessive
ejection of rotor parts
balancing speed
ejection of correction masses masses insufficiently fixed
1.4 Stabbing or end drive not coupled to rotor start of drive around end drive
puncture and drive actuated
rotor with protruding parts checking set-up while rotor
at rotor
rotating running
1.5 Entanglement belt drive running check of belt drive between belt and rotor/guide
rollers
rotor with protruding parts checking set-up while rotor
at rotor
rotating running
1.6 Slip, trip and fall ejection of lubricant from during operation of machine floor area around machine
sleeve bearing
2 Electrical
2.1 High voltage contact to live parts
2.2 Drive power automatic re-start after power during set-up of rotor around rotor and drive
loss
loss of speed control during between rotor and clamping
indexing of rotor
indexing activity device
3 Excessive noise balancing bladed rotors, balancing run near machine
air-drive
4 Neglecting ergonomic principles
4.1 lifting and reaching while during loading/ unloading load/unload position;
handling workpiece and and maintenance maintenance action points
Unhealthy postures
machine parts
or excessive efforts
4.2 inadequate consideration of while operating the workplace
(repetitive strain)
human hand-arm or foot-leg balancing machine
anatomy
4.3 Inadequate local judgement and accuracy of during loading and set-up at drive elements, pedestals
lighting manual actions during set-up and load/unload position
and loading
5 Human errors inadvertent operation of measuring unbalance during around rotor
controls, misuse of guard- set-up
controls
NOTE This list should not be considered complete.
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ISO 7475:2002(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 protection [see A.2.1 and equation (A.1)]. The particle or part shall not penetrate or
escape from the protection.
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
protection [see A.3.1 and equation (A.6)]. The protection shall not disintegrate so that a particle or part cannot
escape from the protection.
c) Impulse
This criterion is based on the case that the impulse of a particle or part is transmitted to the protection [see
A.5.1 and equation (A.10)]. The protection 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 may fly off the rotor; and
the need for a guard (e.g. barrier, fence) for the balancing machine (see Table 2).
In some cases it may be advisable to combine classes A and B, for example if a rotor is dangerous to contact and
only small particles with limited energy can be ejected during balancing.
Table 2 — Protection classes, specified by the necessity for guards for the balancing machine and
resistance against particles or parts
Necessity for guards
No Yes
(barriers, fences)
above class B,
Area-specific
2
energy up to ≈ 340 mN⋅m/mm
below the below the
spectacles, above class B,
Resistance to necessity for necessity for above the
goggles or
Absolute energy up to
particles or spectacles, spectacles,
values of
face-shields
≈ 2 000 N⋅m
parts goggles or goggles or class C
needed
face-shields face-shields
above class B,
up to
Impulse
≈ 200 kg⋅m/s
Protection class 0 A B C D
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ISO 7475:2002(E)
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 as follows.
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 protection device, electro-sensitive protection equipment).
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 needs to be carefully considered and determined by risk assessment.
The selection of the mode shall be by either 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/or protective
measures listed in Table 3.
6 Verification of safety requirements and/or protective measures
Safety requirements and/or protective measures implemented in accordance with clause 5 shall be verified using
the recommended procedures given in Table 3, last column.
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ISO 7475:2002(E)
Table 3 — List of safety requirements and/or protective measures and their verification procedures
Item Hazard sources Safety requirements and/or protective measures Verification
1 Mechanical
1.1 Disengagement or An enclosure around the universal joint shaft shall prevent the whipping By visual inspection
failure of the end- around of the shaft if not coupled to a rotor. Alternative interlocking
drive coupling devices shall prevent the start of the rotor if the shaft is not coupled.
1.2 Axial rotor On belt drive machines, axial thrust stops should prevent axial movement By visual inspection
movement off the of the rotor. On end-drive machines, the drive shaft should be able to
machine supports carry the axial load.
1.3 Rotor lifting out of The machine should be equipped with closed bearings or hold-down By visual inspection
the machine’s open brackets (see also note). and (if necessary)
bearings by calculation
Work zones shall be guarded using fixed and/or interlocked movable
1.4 Operator coming By visual and
guards or fences designed to prevent access to the work zone by the
into contact with any practical checks
part of the spinning operator. Guard interlocking shall incorporate redundancy and
rotor or rotor
monitoring. Redundancy may be by two separate switches or by a
specific drive
guard-closed switch and detection of guard-lock position. Measures to
elements
minimize possible defeat of interlocking shall be taken.
In some applications, only part of the rotor has to be protected, because
other parts of the rotor fall into protection class 0. In such cases, it is
sufficient to prevent contact only with the dangerous surface(s) of the
rotor. (For example, 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.)
In mode 1 [see 5.1.5 a)], machine movements shall only be possible
1.4.1 Examination of
when the guards are closed and/or the protective devices are active. If in
circuit diagrams
this mode, it is possible to open an interlocking movable guard, this shall and practical
checks. Check to
cause the hazardous movements to cease and be inhibited.
ensure that the
hazardous moving
If opening of the interlocking guard gives access to hazards 1.1 to 1.6 of
parts are not
Table 1, guard locking shall be provided.
accessible when
the interlocking
guard is opened.
In mode 2 [see 5.1.5 b)], powered machine movements shall be possible
1.4.2 Examination of
only when all of the following conditions are satisfied.
circuit diagrams
and practical
a) Key or code access to this mode with program execution limited to a
checks
single block or fixed/canned cycle (see ISO 2806).
b) Machine movements initiated by cycle start control in conjunction
with an enabling device.
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.
1.5 Ejection of very If the impact energy of the largest possible particle separating from the By visual inspection
small particles rotor is not negligible but does not exceed the limits set by ISO 4849 or and check of
local regulations, personal eye-protectors (spectacles, goggles or personal eye-
face- shields) shall be used to protect the operator. protector
specification
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ISO 7475:2002(E)
Hazard sources Safety requirements and/or protective measures Verification
Item
1.6 Ejection of particles The rotor components, from which particles may separat
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