ISO 14691:1999

INTERNATIONAL ISO
STANDARD 14691
First edition
1999-11-01
Petroleum and natural gas industries —
Flexible couplings for mechanical power
transmission — General purpose
applications
Industries du pétrole et du gaz naturel — Accouplements flexibles pour
transmission de puissance mécanique — Applications d'usage général
A
Reference number
Contents
Foreword.iii
Introduction.iv
1 Scope .1
2 Normative references .1
3 Terms and definitions .2
4 Purchaser’s specification .8
5 Coupling selection and rating .9
6 Constructional requirements.11
7 Balance .14
8 Materials .16
9 Accessories.16
10 Manufacturing quality, inspection, testing and preparation for shipment .16
11 Vendor’s data .17
Annex A (informative) Data sheet .19
Annex B (informative) Potential unbalance .21
Annex C (informative) Types of misalignment .24
Bibliography.26
©  ISO 1999
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form or by any means, electronic
or mechanical, including photocopying and microfilm, without permission in writing from the publisher.
International Organization for Standardization
Case postale 56 • CH-1211 Genève 20 • Switzerland
Internet iso@iso.ch
Printed in Switzerland
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ISO
Foreword
ISO (the International Organization for Standardization) is a world-wide 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.
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.
International Standard ISO 14691 was prepared by Technical Committee ISO/TC 67, Materials, equipment and
offshore structures for the petroleum and natural gas industries, Subcommittee SC 6, Processing equipment and
systems.
Annexes A, B and C of this International Standard are for information only.
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Introduction
This International Standard is based on the accumulated knowledge and experience of manufacturers and users of
power transmission couplings in the petroleum and natural gas industries, but its use is not restricted to these
industries.
Users of this International Standard should be aware that further or differing requirements may be needed for
individual applications. This International Standard is not intended to inhibit a vendor from offering, or the purchaser
from accepting, alternative equipment or engineering solutions for the individual application. This may be particularly
appropriate where there is innovative or developing technology. Where an alternative is offered, the vendor should
identify any variations from this International Standard and provide details.
This International Standard requires the purchaser to specify certain details and features.
A bullet (l) at the beginning of a clause, subclause or paragraph indicates that either a decision is required or
further information is to be provided by the purchaser. This information or decision should be indicated on the data
sheets; otherwise it should be stated in the quotation request (enquiry) or in the order.
iv
INTERNATIONAL STANDARD  © ISO 14691:1999(E)
ISO
Petroleum and natural gas industries — Flexible couplings
for mechanical power transmission — General purpose
applications
1 Scope
1.1  This International Standard specifies the requirements for couplings for the transmission of power between the
rotating shafts of two machines for general purpose applications in the petroleum and natural gas industries. Such
applications typically require couplings to transmit power at speeds not exceeding 4 000 r/min, between machines in
which the first lateral critical speed is above the running speed range (stiff-shaft machines). It may, by agreement,
be used for applications outside these limits.
This International Standard is applicable to couplings designed to accommodate parallel (or lateral) offset,
1.2
angular misalignment and axial displacement of the shafts without imposing excessive mechanical loading on the
coupled machines. Couplings covered include gear (and other mechanical contact types), metallic flexible-element
and various elastomeric types. Special types such as clutch, hydraulic, eddy-current, rigid, radial spline and
universal joint types, are not covered.
1.3  This International Standard covers design, materials of construction, inspection and testing of couplings and
methods of attachment of the coupling to the shafts (including tapered sleeve and other proprietary devices). This
International Standard does not define criteria for the selection of coupling types for specific applications.
1.4  It is recommended that, when users fit new couplings to existing equipment which are different from those
originally fitted, they consult the manufacturers of the driving or driven equipment.
NOTE 1 In many cases, couplings covered by this International Standard are manufacturer’s catalogue items.
NOTE 2 For the following applications, the use of ISO 10441 is recommended :
 large or high-speed machines that may be required to operate continuously for extended periods, are often unspared and
are critical to the continued operation of the installation (special purpose applications);
 machines in which the first lateral critical speed is less than the maximum required operating speed (flexible-shaft
machines);
 machines where the rotor dynamics are particularly sensitive to coupling unbalance.
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 286-2, ISO system of limits and fits — Part 2: Tables of standard tolerance grades, and limit deviations for
holes and shafts.
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ISO 1940-1:1986, Mechanical vibration — Balance quality requirements of rigid rotors — Part 1: Determination of
permissible residual unbalance.
ISO 8821, Mechanical vibration — Balancing — Shaft and fitment key convention.
ISO 10441, Petroleum and natural gas industries — Flexible couplings for mechanical power transmission —
Special purpose applications.
AGMA 9002 - A86, March 1986, Bores and keyways for flexible couplings (Inch series) Annex A.
3 Terms and definitions
For the purposes of this International Standard, the following terms and definitions apply.
3.1 Definitions of coupling types
3.1.1
mechanical contact coupling
coupling designed to transmit torque by direct mechanical contact between mating parts and accommodate
misalignment and axial displacement by relative rocking and sliding motion between the parts in contact
NOTE 1 The contacting parts may be metallic or may be made of self-lubricating non-metallic material.
NOTE 2 This category includes gear couplings (see 3.1.1.1).
3.1.1.1
gear coupling
coupling designed to transmit torque and accommodate angular misalignment, parallel offset and axial displacement
by relative rocking and sliding motion between mating profiled gears
3.1.2
metallic flexible-element coupling
coupling that obtains its flexibility from the flexing of thin metallic discs, diaphragms or links
NOTE This category includes the two types given in 3.1.2.1 and 3.1.2.2.
3.1.2.1
metallic diaphragm coupling
coupling consisting of one or more metallic flexible elements in the form of thin circular plates that are attached to
one part of the coupling at their outer diameter and the other part at their inner diameter
3.1.2.2
metallic disc coupling
coupling consisting of one or more metallic flexible elements that are alternately attached to the two parts of the
coupling, the attachment points being essentially the same distance from the centreline
3.1.3
elastomeric flexible-element coupling
a coupling in which the torque is transmitted through one or several elastomeric elements
NOTE This category includes elastomeric shear (3.1.3.1) and elastomeric compression (3.1.3.2) couplings.
3.1.3.1
elastomeric shear coupling
coupling in which the torque is transmitted through an elastomeric element which is principally loaded in shear
NOTE The element may be in the form of a tyre, a bellows (with one or more convolutions) or a diaphragm. A single such
elastomeric element is usually able to accommodate angular misalignment, parallel offset and axial displacement.
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3.1.3.2
elastomeric compression coupling
coupling in which elastomeric inserts, often in the form of bushes or wedges or one single insert, are located
between adjacent parts of the driving and driven halves of the coupling and are principally loaded in compression
NOTE The ability of such couplings to accommodate misalignment, particularly of the parallel offset type, is limited.
3.1.4
double-engagement coupling
coupling with two planes of flexure
NOTE This arrangement enables couplings of certain types, notably gear and metallic flexible-element types, which cannot
normally accommodate parallel (or lateral) offset, to do so.
3.1.5
single-engagement coupling
coupling with only one plane of flexure
NOTE Single-engagement couplings of some types, notably gear and metallic flexible-element types, will not normally
accommodate parallel (or lateral) offset misalignment.
3.2 Terms relating to coupling rating
3.2.1
coupling axial reaction force
axial force developed within the coupling resulting from the imposed operating conditions
NOTE 1 Examples of imposed operating conditions are axial deflection, misalignment, speed, temperature, etc.
NOTE 2 The force is a function of the shape and stiffness of the flexible-elements or the sliding friction between the elements
of a mechanical contact coupling.
3.2.2
coupling continuous rated torque
T
c
coupling manufacturer's declared maximum torque that the coupling will transmit continuously for not less than
25 000 h
NOTE 1 It is expressed either as a single value at the coupling rated speed, when simultaneously subjected to the coupling
rated maximum continuous misalignment (both angular misalignment and parallel or lateral offset) and the coupling rated
maximum continuous axial displacement, or as an interrelated function of speed, misalignment and axial displacement.
NOTE 2 For certain types of coupling, particularly those with elastomeric elements or inserts, the coupling continuous rated
torque may also be a function of the operating temperature.
3.2.3
coupling rated maximum continuous misalignment
maximum misalignment (both angular misalignment and parallel or lateral offset) the coupling is able to tolerate
continuously for not less than 25 000 h at the coupling rated speed, when transmitting the coupling continuous rated
torque and simultaneously subjected to the coupling rated maximum continuous axial displacement
3.2.4
coupling rated maximum continuous axial displacement
maximum axial displacement the coupling is able to tolerate continuously for not less than 25 000 h at the coupling
rated speed, when transmitting the coupling continuous rated torque and simultaneously subjected to the coupling
rated maximum continuous misalignment
3.2.5
coupling rated speed
maximum speed at which the coupling is capable of continuously transmitting the coupling continuous rated torque
when simultaneously subjected to the coupling rated maximum continuous misalignment and the coupling rated
maximum continuous axial displacement
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3.2.6
maximum allowable speed
highest rotational speed at which the coupling design will permit transient operation
3.3 Terms relating to coupling duty
3.3.1
application factor
K
a
factor by which the machine rated torque is increased to allow for the fact that the torque required to be transmitted
with certain types of driving or driven machines is not constant but varies in a cyclic manner
NOTE Examples of application are with reciprocating engines or compressors.
3.3.2
confidence factor
K
c
factor by which the machine rated torque is increased to allow for uncertainties in the determination of the machine
rated torque and possible future changes to the application
3.3.3
machine rated torque
T
m
maximum mean torque required to be transmitted continuously by the coupling
NOTE Mean torque is the short-time average torque and does not include cyclic variations such as those associated with
reciprocating machines.
3.3.4
machine rated speed
highest rotational speed at which the machine rated torque is required to be transmitted continuously by the
coupling
3.3.5
maximum continuous speed
maximum rotational speed at which the coupling is required to operate continuously but not necessarily transmitting
the machine rated torque
NOTE In most cases, the machine rated speed and the maximum continuous speed are the same. In some applications,
however, the coupling may be required to operate at speeds above the speed at which it is required to transmit its rated torque.
3.3.6
trip speed
rotational speed of the coupling corresponding to the speed at which the independent emergency overspeed device
operates to shut down a variable-speed prime mover
NOTE Where the term is used in relation to a machine train driven by a constant-speed, alternating-current electric motor,
the trip speed is assumed to be the coupling speed corresponding to the motor synchronous speed at the maximum supply
frequency.
3.4 General terms
3.4.1
angular misalignment
minor angle between the centrelines of two shafts that intersect at a point or, where the shafts do not intersect, the
minor angle between the centreline of one shaft and an intersecting line parallel to the centreline of the other shaft
See Figure C.2.
NOTE With double-engagement couplings, the term also applies to the minor angle between the centreline of one shaft
and the effective centreline of the floating shaft (3.4.6).
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3.4.2
axial displacement
change in the relative axial position of the adjacent shaft ends of two coupled machines
3.4.3
axial reference point
axial position on the shaft of the driving or driven machine (normally the extreme end of the shaft) from which axial
distances are measured
3.4.4
electrically insulated coupling
coupling designed to prevent the flow of electrical current from one shaft to the other through the coupling
3.4.5
flexing length
axial distance between the effective flexing planes of a double-engagement coupling
3.4.6
floating shaft
floating part, or assembly, of a double-engagement coupling that connects and is flexibly supported from the shaft
mounted assemblies and through which the power is transmitted
NOTE The floating shaft may include the spacer or may be only part of the spacer.
3.4.7
hub
part of a coupling mounted directly onto the shaft of the driving or driven machine
3.4.8
lateral offset
lateral distance between the centrelines of two coupled shafts that are not parallel, measured at the axial reference
point of the driving machine shaft
See Figures C.3 and C.4.
3.4.9
limited-end-float coupling
coupling designed to limit the axial movement of the coupled shaft ends with respect to each other and transmit an
axial force of a prescribed magnitude
3.4.10
manufacturer
body responsible for the design and manufacture of the coupling
NOTE The manufacturer is not necessarily the vendor.
3.4.11
maximum allowable temperature
maximum temperature, in the immediate vicinity of the coupling, for which the manufacturer has designed the
coupling
3.4.12
maximum continuous temperature
maximum temperature, in the immediate vicinity of the coupling, at which the coupling will continuously transmit the
coupling continuous rated torque at the specified operating conditions of speed and misalignment
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3.4.13
minimum operating temperature
lowest temperature, in the immediate vicinity of the coupling, at which the coupling is required to transmit torque
and/or accommodate misalignment or axial displacement
3.4.14
parallel offset
lateral distance between the centrelines of two coupled shafts that are parallel but not in the same straight line
See Figure C.1.
3.4.15
purchaser
body that issues the order and the specification to the vendor
NOTE The purchaser may be the end user or the end user’s agent or the vendor of the driving or driven machine.
3.4.16
potential unbalance
maximum probable net unbalance of a complete coupling after installation
NOTE 1 Potential unbalance results from a combination of the residual unbalance of individual components and
subassemblies and possible eccentricity of the components and subassemblies due to run-out and tolerances of the various
locating surfaces and registers.
NOTE 2 The numerical value of the potential unbalance is the square root of the sum of the squares of all the contributory
unbalances. Typical contributory unbalances are:
 the measured residual unbalance of each component or subassembly;
 errors in the balance of each component or subassembly resulting from eccentricity in the fixture used to mount the
component or subassembly in the balancing machine;
 the unbalance of each component or subassembly due to eccentricity resulting from clearance or run-out of the relevant
registers or fits.
NOTE 3 The concept of potential unbalance is explained more fully and a worked example is given in annex B.
3.4.17
residual unbalance
level of unbalance remaining in a component or assembly after it has been balanced either to the limit of the
capability of the balancing machine or in accordance with the relevant standard
3.4.18
shaft-mounted assembly
total assembly of parts rigidly connected to the shaft of the driving or driven machine, including the hub, where
supplied, and all other components up to the flexible-element(s) of a metallic or elastomeric flexible-element
coupling or one of the pair of contacting parts in a mechanical contact type coupling
3.4.19
spacer
part of a coupling that is removable to provide space and give access for the use of tools to remove the coupling
hubs or for other purposes
NOTE The spacer may be a single component or an assembly.
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3.4.20
spacer gap length
axial length of the free gap, after the removal of the spacer assembly, that is available for the use of tools to remove
the hubs or for other purposes
NOTE The spacer gap length may be less than the distance between the shaft ends.
3.4.21
torsional stiffness
torque required to produce unit angular displacement between the coupled shafts
NOTE Couplings with elastomeric flexible-elements may exhibit a dynamic torsional stiffness which is significantly different
from the static value.
3.4.22
unit responsibility
responsibility for coordinating the technical aspects of the complete machine train and the associated auxiliary
systems
NOTE 1 The technical aspects to be considered include, but are not limited to, such factors as the power requirements,
speed, rotation, general arrangement, couplings and coupling guards, dynamics, noise, lubrication, sealing system,
instrumentation, piping, conformance to specifications and testing of components.
NOTE 2 Unit responsibility normally resides with the vendor of the driven machine.
3.4.23
vendor
body that supplies the coupling in reponse to an order from the purchaser
NOTE The vendor may be the manufacturer of the coupling or the manufacturer’s agent and is normally responsible for
service support.
3.5 Terms relating to gear couplings
The terms defined in 3.5.1 and 3.5.2 are applicable only to gear-type couplings.
3.5.1
batch-lubricated coupling
coupling designed to be lubricated by a periodically changed charge of oil or grease
3.5.2
neutral state
state when the meshing pairs of gear teeth are axially centrally located with respect to each other,
that is with equal scope for axial displacement in each direction
3.6 Terms relating to flexible-element couplings
The terms defined in 3.6.1 and 3.6.2 are applicable to metallic flexible-element couplings and elastomeric flexible-
element couplings.
3.6.1
axial natural frequency
natural frequency of the mass of the spacer assembly supported by the flexible elements acting as axial springs
NOTE 1 The spring rate of certain designs of flexible elements may be non-linear, varying in relation to the axial deflection.
With such designs, a range of axial natural frequencies exists within a band corresponding to deflection amplitudes from zero
to the maximum allowable.
NOTE 2 Some types of coupling which have significantly non-linear axial stiffness and/or internal damping may not exhibit an
axial natural frequency.
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3.6.2
neutral state
state in which there is no net axial force imposed on the coupling
4 Purchaser’s specification
4.1  It is recommended that the information required to be specified by the purchaser be entered on a suitable data
sheet, a typical form of which is given in annex A. Where appropriate, the information required should be provided in
the form of sketches or diagrams.
l4.2  The purchaser may require the vendor to select the coupling based on the information provided or may select
the coupling from the vendor’s catalogue. In the latter case, the purchaser may require the vendor to confirm the
suitability of the coupling selected.
l4.3  The purchaser shall provide the following information:
a) the make and type of driving and driven machine, and a description of the whole machine train if this comprises
more than two coupled units;
b) the type of coupling (gear, flexible-element, etc.) required and the method of attachment to the shafts (7.2);
c) the machine rated speed (3.3.4), the equipment's operating speed range and the trip speed (3.3.6);
The machine rated speed should normally be the maximum continuous speed.
d) the machine rated torque (3.3.3);
The machine rated torque should be not less than the maximum continuous torque required to be transmitted
under any operating conditions. Where one single machine is driven from a driver, the machine rated torque
should generally be the maximum continuous torque of the driver. Where two or more machines are driven
from one driver, either in tandem, through a multishaft gearbox or from both ends of the driver, care should be
taken in determining the machine rated torque for each coupling. Generally this should be based on the most
adverse possible split of power consumption between the driven machines.
e) the environment in which the coupling is required to operate, including the maximum and minimum
temperatures and the presence of atmospheric contaminants likely to attack the components of the coupling.
l4.4  If the coupling vendor is required to select the coupling, in addition to the information required by 4.3, the
purchaser shall provide the following information:
a) the value to be used for the application factor ( ) as defined in 3.3.1.
K
a
The value of the application factor (K ) should be selected to allow for cyclic variation in the continuous torque
a
to be transmitted. Where the purchaser has no reason to use a specific value, the manufacturer’s catalogue
values should be used. In no case, when the prime mover is a turbine or an induction (asynchronous) electric
motor, should the value of K be less than the values in Table 1.
a
Table 1 — Application factors for electric motor
and turbine prime movers
Driven machine Value of K
a
Generator 1,0
Centrifugal pump or compressor 1,2
Fan or screw compressor 1,5
Reciprocating pump or compressor with 4 or more cylinders 1,75
Reciprocating pump or compressor with less than 4 cylinders 2,5
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When the prime mover is a reciprocating machine, a frequently started synchronous motor or a variable speed
electric motor, the value of K to be used shall be agreed between purchaser and vendor.
a
b) the value to be used for the confidence factor (K ) as defined in 3.3.2;
c
The value of the confidence factor (K ) should normally be 1,0. A value greater than 1,0 may be specified if the
c
torque required to be transmitted is uncertain or the purchaser wishes to provide an uprating capability. In no
case should the value of K be less than 1,0.
c
c) the required misalignment capability, in terms of the angular misalignment and the parallel or lateral offset, and
the axial displacement the coupling is required to accommodate;
d) the expected magnitude, nature and number of occurrences of torsional transients which the coupling is
required to tolerate in service, without damage.
Torsional transients should include start-up and shut-down effects, particularly those associated with
synchronous motors and variable-frequency drive systems.
4.5  If the purchaser makes his own selection from the vendor’s catalogue, he should specify the type and size of
coupling required taking into account suitable values for K , K and the required misalignment and axial deflection
a c
capability.
l4.6  The purchaser may specify the axial distance between the ends of the shafts of the two machines to be
coupled, in the cold static condition, and precisely the point on each shaft from which this distance is measured (the
axial reference points). If the purchaser fails to define the axial reference points, the vendor shall assume that they
are the extreme ends of the shafts. Alternatively, the purchaser may accept the vendor’s standard or proposed
coupling length.
l4.7  If relevant, the purchaser should also specify the expected magnitude of momentary torques, resulting from
fault conditions, which the coupling is required to survive but possibly with some damage.
NOTE It is recognized that, after such an event, the coupling should be inspected and components replaced as necessary.
l4.8  The purchaser may state if any properties of the coupling are considered important from consideration of the
rotor dynamics of the driving or driven machines, or for any other reason, and may specify the range of acceptable
values. For example:
 overhung mass,
 torsional stiffness,
 coupling axial reaction force,
 coupling transverse stiffness,
 coupling angular stiffness.
NOTE It is not expected that this will be necessary for the majority of general purpose applications.
l4.9  The purchaser may indicate a preference, or a requirement, for a coupling design that either maintains or
disconnects the drive in the event of failure of the flexing elements.
5 Coupling selection and rating
l5.1  Where the vendor has been required to select the coupling, the coupling selection shall be submitted for the
purchaser's approval. Alternatively, where the purchaser has selected a coupling (type and size) from the vendor’s
catalogue, if required, the vendor shall confirm that the coupling selected is suitable for the application in
accordance with the information provided by the purchaser.
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5.2  The vendor shall state the coupling continuous rated torque. The coupling continuous rated torque shall be not
less than the value determined by equation (1).
T = T { K { K (1)
c m a c
where
T is the coupling continuous rated torque (3.2.2);
c
T is the machine rated torque [3.3.3 and 4.2 d)];
m
K is the application factor [3.3.1 and 4.3 a)];
a
K is the confidence factor [3.3.2 and 4.3 b)].
c
Should the purchaser fail to specify values for and , the vendor may, for the purpose of initial selection of a
K K
a c
coupling, assume a value of 1,0 for K and a value for K in accordance with 4.4 a). The vendor shall clearly state
c a
his assumed values in his proposal.
5.3  The vendor shall state the maximum allowable speed. This shall not be less than the trip speed.
5.4  All couplings shall be capable of accepting some degree of parallel or lateral offset. This generally requires that
certain types of coupling be of the double-engagement type.
5.5  The vendor shall state the coupling rated maximum continuous misalignment, both angular misalignment and
parallel offset (3.2.3). The vendor shall also state the maximum acceptable short-term misalignment if different from
this.
5.6  Unless otherwise agreed, the coupling shall be designed/selected such that its neutral state (3.5.2 or 3.6.2) is
the cold static condition.
5.7  The vendor shall state the coupling rated maximum continuous axial displacement (3.2.4) from the neutral
state in each direction. The vendor shall also state the maximum acceptable short-term axial displacement if
different from this.
5.8  The vendor shall state the relationship between the coupling continuous torque, the coupling continuous
misalignment and the coupling continuous axial displacement if the rated maximum values of each cannot be
accepted simultaneously.
NOTE With some types of coupling, particularly those with elastomeric elements or inserts, this relationship may also be a
function of temperature.
5.9  The capability of the coupling to accept misalignment and axial displacement, whilst transmitting the machine
rated torque multiplied by the factors K and K , at the machine rated speed, shall be not less than the required
a c
misalignment and axial displacement capability specified by the purchaser [4.4 c)].
When the purchaser has failed to specify the required misalignment and axial displacement capability, the coupling
shall be capable of accepting the following misalignments and axial displacement simultaneously whilst transmitting
the machine rated torque multiplied by the factors K and K , at the machine rated speed:
a c
 angular misalignment (as defined in 3.4.1): 0,1°;
 lateral offset (as defined in 3.4.8):  0,5 % of the diameter of the driving or driven machine shaft, whichever is
larger, but not less than 0,25 mm;
 axial displacement (as defined in 3.4.2): 1,5 % of the diameter of the driving or driven machine shaft,
whichever is larger, but not less than 1 mm.
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The most severe combination of angular misalignment and lateral offset shall be assumed.
NOTE For double-engagement couplings the most severe combination normally occurs when the two forms of
misalignment are in the same plane and in the same direction. (Figure C.3).
5.10  The coupling shall be capable of transmitting 115 % of the purchaser-specified maximum transient torque as
specified in 4.4 d), for sufficient duration and frequency to satisfy the operational requirements as specified in 4.4 d),
without damage. If the purchaser has failed to specify the expected transients, the coupling shall be capable of
transmitting, without damage, a cyclic torque of amplitude (zero to maximum) equal to 2,5 times the specified
machine rated torque (T ) for not less than 10 cycles.
m
l5.11  The coupling shall be strong enough to survive the momentary fault condition torques specified in accordance
with 4.7, albeit with some damage. Alternatively, when specified, the coupling shall incorporate an agreed type of
torque-limiting feature to prevent damage to the coupling or to the coupled equipment.
6 Construction requirements
6.1 General
l6.1.1  When specified, the coupling design shall be such that the flexible element or elements or inserts, and/or the
components carrying the gear teeth or other wearing parts can be removed and replaced in situ without the need to
move either the driving or driven machine or otherwise disturb the alignment.
l6.1.2  When specified, the design shall be such that the coupling can be completely dismantled and removed,
including hubs, to facilitate the maintenance of adjacent bearings and/or seals, without removal of either shaft or
disturbance of the equipment alignment. The purchaser shall specify the minimum spacer gap length (3.4.20)
required.
l6.1.3  When specified, the coupling shall be of the limited-end-float design. The purchaser shall specify the end-
float required and the maximum axial force the coupling is required to transmit.
NOTE The most common situation in which a limited-end-float coupling is required is with a sleeve bearing motor without
an axial bearing. In such cases, a positive-stop, limited-end-float design may not be necessary with flexible-element couplings
provided the axial stiffness (spring rate) of the coupling is sufficient to hold the motor rotor within its axial limits during normal
operation, start-up and shut-down.
6.1.4  The vendor shall state the maximum coupling axial reaction force (see 3.2.1). In the case of gear couplings
and other mechanical contact types, this shall be based on the friction between the teeth or other elements under
the coupling rated torque, and the vendor shall state the assumed value of the friction factor. In the case of flexible-
element couplings, the vendor shall provide a curve of axial force vs. displacement and shall state the maximum
acceptable axial displacement.
l6.1.5  For double-engagement couplings, the vendor shall ensure that the first lateral resonant frequency of the
floating shaft (3.4.6), is not less than 200 % of the maximum speed at which the coupling will be required to operate
(normally the maximum continuous speed), or shall notify the purchaser of the actual value. Details of the method
used to determine the first lateral resonant frequency shall be made available for review by the purchaser if
required.
6.1.6  All major parts (hubs, spacers, etc. but excluding flexible elements and fasteners) shall be indelibly marked
such that they can be uniquely identified.
6.2 Coupling hubs
l6.2.1  The purchaser shall specify the method to be used for attaching the coupling hubs to the machine shaft ends
and shall allocate responsibility for the final machining of the hub bores.
l6.2.2  The purchaser shall specify if the coupling hubs are required to be fitted to the shafts with proprietary
clamping devices, and may specify the make and type of such devices. Acceptable clamping devices include
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ISO
tapered bushes, frictional locking assemblies and shrink discs. The body responsible for the final machining of the
hub bores shall select a suitable rating/size device to suit the coupling and the application.
Care shall be exercised in the selection of these devices, as some are not inherently self-centring and may
introduce eccentricity and unbalance into the coupling assembly. The eccentricity and unbalance effect must be
evaluated and allowed for when determining the coupling potential unbalance.
l6.2.3  Where the hubs are to be keyed to the shafts, the purchaser shall specify the number and configuration of
the keys and keyways. Where the purchaser has failed to specify the number and configuration of the keys, a single
key shall be assumed.
6.2.4  Coupling hubs not provided with proprietary clamping devices shall be fitted to the shaft with an interference
fit.
6.2.5  Unless otherwise specified, cylindrical shafts shall be assumed to comply with AGMA 9002 - A86 and the
coupling hubs shall be bored to the following tolerances:
 for shafts of 50 mm diameter and smaller: ISO 286-2, Grade N7;
 for shafts larger than 50 mm diameter: ISO 286-2, Grade N8.
Unless otherwise specified, keys and keyways and their tolerances shall be in accordance with AGMA 9002 - A86,
normal fit.
6.2.6  Unless otherwise specified, tapered shaft ends not intended for hydraulic fitting of hubs, and their keys, shall
be assumed to be 1/10 conical shaft ends, long series, in accordance with AGMA 9002 - A86, except that the
keyways shall be assumed to be machined parallel to the taper. The keyway clearance and the dimensional
tolerances of keys and keyways shall be in accordance with AGMA 9002 - A86, normal fit.
The bore taper shall be checked using a suitable plug gauge. A light coat of blueing shall be used for the check and
the bore shall indicate at least a 70 % blued fit (surface contact) to the plug gauge. By agreement, an alternative
method of demonstrating the correct fit may be used.
l6.2.7  The taper of tapered bores, for hydraulically fitted hubs, shall be specified by the purchaser and agreed by
the vendor. The bore shall be checked by using a plug gauge furnished by the purchaser, from a matched plug and
ring gauge set. A light coat of blueing shall be used for the check and the bore shall indicate at least an 85 % blued
fit (surface contact) to the plug gauge. By agreement, an alternative method of demonstrating the correct fit may be
used.
l6.2.8  Where the coupling is retained on the shaft by a shaft end nut or bolt, the coupling design shall provide
adequate clearance for a suitable wrench. The purchaser shall provide details of the nut (or bolt) and the wrench to
be used and specify the required clearance.
6.2.9  The surface finish of the bore of keyed hubs shall be 3,2 mm arithmetic average roughness (R ) or smoother.
a
The surface finish of the bore of hydraulically fitted hubs shall be 1,6 mm arithmetic average roughness (R ) or
a
smoother.
Keyed coupling hubs shall be provided with suitable threaded puller holes or other agreed facilities for hub
6.2.10
removal.
6.2.11  When the coupling vendor supplies coupling hubs to be finished bored by others, the hubs shall be provided
with suitable reference surfaces with respect to which the concentricity of the finished bores can be verified.
6.3 Bolting
6.3.1  All fasteners shall be in accordance with a recognized national or International Standard and grade. The
values of the mechanical properties of the fasteners, used for coupling design purposes, shall be in accordance with
the relevant standard.
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ISO
6.3.2  For connections which may need to be dismantled in the field, the coupling vendor shall specify the bolt
tension required, and how this is to be achieved and controlled. Where this is to be achieved by control of the
tightening torque, the vendor shall specify whether this is in a dry or lubricated condition.
6.3.3  Bolts shall be held within tolerances, on both dimensions and mass, sufficient to permit both interchange
within the same set of bolts and substitution of a spare set of bolts without affecting the coupling integrity or
resulting in the balance being outside the prescribed limits. (See also clause 8 and annex B.)
6.4 Electrical insulation
l6.4.1  When specified, the coupling shall be electrically insulated. The method of insulation and the materials used
shall be subject to the purchaser's approval.
l6.4.2  When electrical insulation is required, or when specified, and where the coupling design is such that contact
between the two halves of the coupling is only through elastomeric elements or inserts, the vendor shall state the
electrical resistance of the coupling and the extent to which this can be varied by the use of different elastomer
formulations.
6.5 Alignment provision
Couplings shall be provided with suitable reference surfaces for alignment purposes, machined with sufficient
accuracy appropriate to the misalignment capability of the coupling, and provision shall be made for the attachment
of alignment equipment to the coupling shaft-mounted assemblies, without the need to remove the spacer or
dismantle the coupling in any way.
By agreement, this requirement may be relaxed when a method of alignment has been specified or agreed that
makes it unnecessary.
6.6 Rotor dynamic data
lWhen requested, the vendor shall furnish all the necessary data to the purchaser, or, by agreement, the vendor
having unit responsibility (where different), to enable the required lateral and torsional dynamic analyses of the
coupled machines and of the whole train to be performed.
NOTE It is not expected that it will be necessary to request this data for the majority of general purpose applications.
6.7 Non-horizontal applications
lThe requirements of this International Standard have been developed primarily for couplings to be used between
horizontal shafts. The purchaser shall specify if the coupling is to be used in a non-horizontal position.
6.8 Additional requirements for gear couplings
l6.8.1  The purchaser may specify if the coupling is to have the external teeth on the hub or on the spacer.
NOTE General purpose gear couplings usually have the external teeth on the hub. A coupling may have a different
arrangement of teeth at the two ends.
6.8.2  The design and materials of the teeth shall be such that the axial length of the teeth expected to suffer the
most rapid wear shall be less than the axial length of the mating teeth.
6.8.3  Gear couplings shall be designed for batch lubrication unless otherwise specified. The vendor shall state the
type of lubricant and the method and frequency of replenishment.
NOTE If batch lubrication is not considered accep
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