SIST EN ISO 13691:2004

SLOVENSKI STANDARD
01-maj-2004
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SIST ISO 13691:2002
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Petroleum and natural gas industries - High-speed special-purpose gear units (ISO
13691:2001)
Erdöl- und Erdgasindustrie - Schnelllaufgetriebe für spezielle Anwendungen (ISO
13691:2001)
Industries du pétrole et du gaz naturel - Engrenages a grande vitesse pour applications
particulieres (ISO 13691:2001)
Ta slovenski standard je istoveten z: EN ISO 13691:2002
ICS:
21.200 Gonila Gears
75.180.20 Predelovalna oprema Processing equipment
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD
EN ISO 13691
NORME EUROPÉENNE
EUROPÄISCHE NORM
November 2002
ICS 21.200; 75.180.20
English version
Petroleum and natural gas industries - High-speed special-
purpose gear units (ISO 13691:2001)
Industries du pétrole et du gaz naturel - Engrenages à
grande vitesse pour applications particulières (ISO
13691:2001)
This European Standard was approved by CEN on 1 August 2002.
CEN members are bound to comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration. Up-to-date lists and bibliographical references concerning such national
standards may be obtained on application to the Management Centre or to any CEN member.
This European Standard exists in three official versions (English, French, German). A version in any other language made by translation
under the responsibility of a CEN member into its own language and notified to the Management Centre has the same status as the official
versions.
CEN members are the national standards bodies of Austria, Belgium, Czech Republic, Denmark, Finland, France, Germany, Greece,
Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway, Portugal, Spain, Sweden, Switzerland and United Kingdom.
EUROPEAN COMMITTEE FOR STANDARDIZATION
COMITÉ EUROPÉEN DE NORMALISATION
EUROPÄISCHES KOMITEE FÜR NORMUNG
Management Centre: rue de Stassart, 36  B-1050 Brussels
© 2002 CEN All rights of exploitation in any form and by any means reserved Ref. No. EN ISO 13691:2002 E
worldwide for CEN national Members.

Foreword
The text of ISO 13691:2001 has been prepared by Technical Committee ISO/TC 60 "Gears" of the
International Organization for Standardization (ISO) and has been taken over as EN ISO 13691:2002 by
Technical Committee CEN/TC 12 "Materials, equipment and offshore structures for petroleum and natural
gas industries", the secretariat of which is held by AFNOR.
This European Standard shall be given the status of a national standard, either by publication of an
identical text or by endorsement, at the latest by May 2003, and conflicting national standards shall be
withdrawn at the latest by May 2003.
According to the CEN/CENELEC Internal Regulations, the national standards organizations of the following
countries are bound to implement this European Standard: Austria, Belgium, Czech Republic, Denmark,
Finland, France, Germany, Greece, Iceland, Ireland, Italy, Luxembourg, Malta, Netherlands, Norway,
Portugal, Spain, Sweden, Switzerland and the United Kingdom.
Endorsement notice
The text of ISO 13691:2001 has been approved by CEN as EN ISO 13691:2002 without any modifications.
NOTE  Normative references to International Standards are listed in Annex ZA (normative).
Annex ZA
(normative)
Normative references to international publications with their relevant European
publications
This European Standard incorporates by dated or undated reference, provisions from other publications.
These normative references are cited at the appropriate places in the text and the publications are listed
hereafter. For dated references, subsequent amendments to or revisions of any of these publications apply
to this European Standard only when incorporated in it by amendment or revision. For undated references
the latest edition of the publication referred to applies (including amendments).
NOTE Where an International Publication has been modified by common modifications, indicated by
(mod.), the relevant EN/HD applies.
Publication Year Title EN Year
ISO 8501-1 1988 Preparation of steel substrates before EN ISO 8501-1 2001
application of paints and related
products - Visual assessment of surface
cleanliness - Part 1: Rust grades and
preparation grades of uncoated steel
substrates and of steel substrates after overall
removal of previous coatings
ISO 10441 1999 Petroleum and natural gas industries - Flexible EN ISO 10441 1999
couplings for mechanical power transmission -
Special purpose applications
INTERNATIONAL ISO
STANDARD 13691
First edition
2001-12-15
Petroleum and natural gas industries —
High-speed special-purpose gear units
Industries du pétrole et du gaz naturel — Engrenages à grande vitesse
pour applications particulières

Reference number
ISO 13691:2001(E)
©
ISO 2001
ISO 13691:2001(E)
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ii © ISO 2001 – All rights reserved

ISO 13691:2001(E)
Contents Page
Foreword.iv
Introduction.v
1 Scope.1
2 Normative references.1
3 Terms and definitions .3
4 Symbols and abbreviated terms .6
5 Basic design.7
5.1 General.7
5.2 Gear rating.10
5.3 Gear elements.15
5.4 Casings.18
5.5 Casing connections.20
5.6 Dynamics.21
5.7 Bearings and bearing housings.24
5.8 Lubrication.26
5.9 Materials.26
5.10 Nameplates and rotation arrows.27
6 Accessories.28
6.1 General.28
6.2 Couplings and guards.28
6.3 Mounting plates.28
6.4 Controls and instrumentation .30
6.5 Piping and appurtenances.30
6.6 Special tools.31
7 Inspection, testing and preparation for shipment.31
7.1 General.31
7.2 Inspection.31
7.3 Testing.34
7.4 Preparation for shipment.37
8 Vendor's data.38
8.1 General.38
8.2 Proposals.39
8.3 Contract data.40
Annex A (informative) Special-purpose gear unit data sheets.42
Annex B (informative) Lateral critical speed map and mode shapes for typical rotor .47
Annex C (informative) Couplings for high-speed gear units.49
Annex D (informative) Vendor requirements regarding drawings and data .54
Annex E (informative) Gear tooth inspection.60
Annex F (informative) Inspector´s checklist.61
Annex G (informative) Relationship of tooth rating factors between ISO 13691, ISO 9084 and API 613.66
Bibliography.70

ISO 13691:2001(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 13691 was prepared by Technical Committee ISO/TC 60, Gears, Subcommittee SC 2, Gear capacity
calculation.
ISO 13691 is based on API 613 and is intended to give ratings similar to those found when using API 613.
Annexes A to G of this International Standard are for information only.

iv © ISO 2001 – All rights reserved

ISO 13691:2001(E)
Introduction
This International Standard is based on the accumulated knowledge and experience of manufacturers and users of
gear units. It has been developed to satisfy the requirements of the petroleum, petrochemical and natural gas
industries, but its use is not restricted to these industries.
The purpose of this International Standard is to establish minimum requirements for design and construction so
that the equipment is suitable for the purpose for which it is required.
Energy conservation and protection of the environment are matters of concern and are important in all aspects of
equipment design, application and operation. The manufacturers and users of equipment should aggressively
pursue alternative, innovative approaches which improve energy utilization and/or minimize the environmental
impact, without sacrificing safety or reliability. Such approaches should be thoroughly investigated and purchase
options should increasingly be based on the estimation of whole-life costs and the environmental consequences
rather than acquisition costs alone.
This International Standard requires the purchaser to specify certain details and features.
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.
A bullet (z) at the beginning of a paragraph indicates that either a decision is required or further information is to be
provided by the purchaser. This information should be indicated on the data sheets; otherwise it should be stated in
the quotation request or in the order.

INTERNATIONAL STANDARD ISO 13691:2001(E)

Petroleum and natural gas industries — High-speed special-
purpose gear units
1 Scope
This International Standard specifies the minimum requirements for enclosed, precision, single and double helical,
−1
one- and two-stage speed increasers and reducers of parallel shaft design with pinion speeds of 3000 min or
greater, or pitch line velocities of 25 m/s or greater, for special purpose applications. Such applications will typically
be required to operate continuously for extended periods, without installed spare equipment and are critical to the
continued operation of the installation. By agreement this International Standard may be used for other services.
This International Standard also specifies a method of rating gears which meet the following criteria:
a) gear accuracy
 teeth accuracy: accuracy grade 4 or better as given in ISO 1328-1:1995, for both single pitch deviation, f ,
pt
and total cumulative pitch deviation, F ,
p
 total helix deviation F between the helices of the pinion and wheel: accuracy grade 4 or better as given in
β
ISO 1328-1:1995;
b) range of the transverse contact ratios: 1,2 < ε < 2,0;
α
c) overlap ratio ε W 1,0;
β
d) helix angle: 5 u β u 35°;
e) working flanks of the pinion or gear: provided with profile modifications to obtain a good conjugate tooth load
distribution along the path of contact;
f) working flanks of pinion or gear: modified as necessary to compensate for both torsional and bending
deflections and, when necessary for gears with pitch line velocities in excess of 100 m/s, also for thermal
distortions;
g) gear lubrication: straight mineral oil, viscosity grade VG-32 or VG-46 (see ISO 3448);
h) material of the gear teeth: quality MQ or better, in accordance with ISO 6336-5:1996.
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 7-1, Pipe threads where pressure-tight joints are made on the threads — Part 1: Dimensions, tolerances and
designation
ISO 261, ISO general-purpose metric screw threads — General plan
ISO 13691:2001(E)
ISO 262, ISO general-purpose metric screw threads — Selected sizes for screws, bolts and nuts
ISO 724, ISO general-purpose metric screw threads — Basic dimensions
ISO 965-1, ISO general-purpose metric screw threads — Tolerances — Part 1: Principles and basic data
ISO 965-2, ISO general- purpose metric screw threads — Tolerances — Part 2: Limits of sizes for general purpose
external and internal screw threads — Medium quality
ISO 965-3, ISO general-purpose metric screw threads — Tolerances — Part 3: Deviations for constructional screw
threads
ISO 1122-1, Vocabulary of gear terms — Part 1: Definitions related to geometry
ISO 1328-1:1995, Cylindrical gears — ISO system of accuracy — Part 1: Definitions and allowable values of
deviations relevant to corresponding flanks of gear teeth
ISO 1940-1:1986, Mechanical vibration — Balance quality requirements of rigid rotors — Part 1: Determination of
permissible residual unbalance
ISO 2953, Mechanical vibration — Balancing machines — Description and evaluation
ISO 3448:1992, Industrial liquid lubricants — ISO viscosity classification
ISO 6336-3, Calculation of load capacity of spur and helical gears — Part 3: Calculation of tooth bending strength
ISO 6336-5, Calculation of load capacity of spur and helical gears — Part 5: Strength and quality of materials
ISO 6743-6, Lubricants, industrial oils and related products (class L) — Classification — Part 6: Family C (Gears)
ISO 7005-1, Metallic flanges — Part 1: Steel flanges
ISO 7005-2, Metallic flanges — Part 2: Cast iron flanges
ISO 8501-1:1988, Preparation of steel substrates before application of paints and related products — Visual
assessment of surface cleanliness — Part 1: Rust grades and preparation grades of uncoated steel substrates and
of steel substrates after overall removal of previous coatings
ISO 8579-1, Acceptance code for gear units — Part 1: Test code for airborne sound
ISO 8821, Mechanical vibration — Balancing — Shaft and fitment key convention
ISO 9084:2000, Calculation of load capacity of spur and helical gears — Application to high speed gears and gears
of similar requirement
ISO/TR 10064-4, Cylindrical gears — Code of inspection practice — Part 4: Recommendations relative to surface
texture and tooth contact pattern checking
ISO 10438-1, Petroleum and natural gas industries — Lubrication, shaft-sealing and control-oil systems and
auxiliaries — Part 1: General requirements
ISO 10438-2, Petroleum and natural gas industries — Lubrication, shaft-sealing and control-oil systems and
auxiliaries — Part 2: Special-purpose oil systems
ISO 10438-3, Petroleum and natural gas industries — Lubrication, shaft-sealing and control-oil systems and
auxiliaries — Part 3: General-purpose oil systems
ISO 10441, Petroleum and natural gas industries — Flexible couplings for mechanical power transmission —
Special purpose applications
2 © ISO 2001 – All rights reserved

ISO 13691:2001(E)
ISO/TR 13593, Enclosed gear drives for industrial applications
ISO/TR 13989-1, Calculation of scuffing load capacity of cylindrical, bevel and hypoid gears — Part 1: Flash
temperature method
ISO/TR 13989-2, Calculation of scuffing load capacity of cylindrical, bevel and hypoid gears — Part 2: Integral
temperature method
IEC 60079-0, Electrical apparatus for explosive gas atmospheres — Part 0: General requirements
API 670, Vibration, axial position and bearing-temperature monitoring systems
ASME B16.11, Forged fittings, Socket-Welding and Threaded
ASME, Boiler and pressure vessel code — Section V
ASME, Boiler and pressure vessel code — Section VIII, Division 1
ASME Y 14.2 M, Line conventions and lettering
ASTM A956, Standard test method for Leeb hardness testing of steel products
ASTM E94, Standard guide for radiographic examination
ASTM E125, Standard reference photographs for magnetic particle indications on ferrous castings
ASTM E709, Standard guide for magnetic particle examination
3 Terms and definitions
For the purposes of this International Standard, the terms and definitions given in ISO 1122-1 and the following
apply.
NOTE The use of the word design in any term (such as design power, design pressure, design temperature, or design
speed) should be avoided in the purchaser’s specifications. This terminology should be used only by the equipment designer
and the manufacturer.
3.1
axially [horizontally] split casing joint
casing joint parallel to the shaft centreline
3.2
critical speed
shaft rotational speed at which the rotor-bearing-support system is in a state of resonance with any exciting
frequency associated with that speed
3.3
wheel
lower speed gear element in mesh
3.4
pinion
higher speed gear element in mesh
3.5
gear rated power
maximum power specified by the purchaser on the data sheet and stamped on the nameplate
cf. 5.2.1.
ISO 13691:2001(E)
3.6
normal transmitted power
power at which usual operation is expected and optimum efficiency is desired
NOTE The normal transmitted power may be equal to or less than the gear rated power.
3.7
mechanical rating
gear rated power (3.5) multiplied by the specified gear selection factor (3.17).
3.8
hunting tooth combination
·mating gearsÒ combination existing when a tooth on the pinion does not repeat contact with a tooth on the gear
until it has contacted all the other gear teeth
3.9
maximum allowable speed
highest rotational speed at which the manufacturer’s design will permit continuous operation
3.10
maximum continuous speed
·variable-speed unitÒ rotational speed at least equal to 105 % of the rated speed
3.11
maximum continuous speed
·constant-speed unitÒ rotational speed equal to the rated speed
3.12
minimum allowable speed
lowest rotational speed at which the manufacturer’s design will permit continuous operation
3.13
rated input speed
specified (or nominal) rated speed of the driver, as designated by the purchaser
3.14
rated output speed
specified (or nominal) rated speed of the driven equipment, as designated by the purchaser.
NOTE In selecting the number of teeth for the pinion and gear, it is often impracticable for the vendor to match exactly both
the rated input and the rated output speeds designated on the data sheets. The purchaser therefore indicates which of the two
is specified (that is, must be exactly adhered to by the vendor) and which is nominal (that is, permits some variation). The letter
S is used to indicate the specified speed, and the letter N to indicate the nominal speed. The purchaser also indicates on the
data sheets the allowable percentage of variation in the designed gear ratio.
3.15
contact stress number
σ
H
contact stress calculated based on the Hertzian contact pressure
3.16
bending stress number
σ
F
bending stress calculated from the resistance to fatigue cracking at the tooth root fillet
4 © ISO 2001 – All rights reserved

ISO 13691:2001(E)
3.17
gear selection factor
K
SL
factor applied to the calculated contact stress number and the calculated bending stress number, depending on the
characteristics of the driver and the driven equipment, to account for potential overload, shock load and/or
continuous oscillatory torque characteristics
3.18
trip speed
rotational speed at which the independent emergency overspeed device operates to shut down a prime mover
NOTE 1 For fixed-frequency alternating current motor drives, the trip speed is taken to be the speed corresponding to the
synchronous speed of the motor at the highest supply frequency.
NOTE 2 For steam turbines and reciprocating engines, the trip speed is at least 110 % of the maximum continuous speed.
For gas turbines, the trip speed is at least 105 % of the maximum continuous speed.
3.19
special-purpose application
application for which the equipment is designed for uninterrupted, continuous operation in critical service and for
which there is usually no spare equipment
3.20
total indicated runout
total indicator reading
TIR
runout of a diameter or face determined by measurement with a dial indicator
NOTE The indicator reading implies an out-of-squareness equal to the reading or an eccentricity equal to half the reading.
3.21
Gauss level
magnetic field level of a component measured with a “Hall effect” probe with no interference from adjacent
magnetic parts or structures
3.22
unit responsibility
responsibility for coordinating the technical aspects of the equipment and all auxiliary systems included in the
scope of the order
NOTE Responsibility for such factors as the power requirements, speed, rotation, general arrangement, couplings,
dynamics, noise, lubrication, sealing system, material test reports, instrumentation, piping, and testing of components is
included.
3.23
purchaser
individual or organization that issues the order and specification to the vendor
NOTE The purchaser may be the owner of the plant in which the equipment is to be installed, or the owner´s agent (often
the vendor of the equipment to be driven by the gear).
3.24
vendor
organization that supplies the equipment
NOTE The vendor may be the manufacturer of the equipment or the manufacturer´s agent and is normally responsible for
service support.
ISO 13691:2001(E)
4 Symbols and abbreviated terms
See Table 1.
Table 1
Symbol Meaning or term Unit
a centre distance mm
b facewidth mm
b facewidth of one helix on a double helical gear mm
B
B total facewidth of a double helical gear including the gap width mm
d reference diameter of pinion, wheel mm
1,2
D shaft diameter at coupling of pinion, wheel mm
1,2
f single pitch deviation µm
pt
F total cumulative pitch deviation µm
p
F (nominal) transverse tangential force at reference cylinder N
t
F external force (coupling) N
R
F total helix deviation µm
β
HBW Brinell hardness —
HRC Rockwell hardness number (C scale) —
K dynamic factor —
v
K face load factor (root stress) —
F
β
K face load factor (contact stress) —
H
β
K selection factor —
SL
m normal module mm
n
−1
n rotational speed of pinion, of wheel, nominal min
1,2
P gear rated power kW
Ra arithmetic average roughness value µm
u gear ratio z /z W 1 —
2 1
v pitch line velocity at reference cylinder m/s
Υ form factor —
F
Y stress correction factor —
S
Y helix angle factor (root stress) —
β
z , z number of teeth of pinion, of wheel —
1 2
Z elasticity factor N/mm²
E
Z zone factor —
H
Z helix angle factor (contact stress) —
β
Z contact ratio factor (contact stress) —
ε
α normal pressure angle °
n
α transverse pressure angle °
t
α pressure angle at the pitch cylinder °
wt
β helix angle at the reference cylinder °
β base helix angle °
b
6 © ISO 2001 – All rights reserved

ISO 13691:2001(E)
Table 1 (continued)
Symbol Meaning or term Unit
ε transverse contact ratio —
α
ε overlap ratio —
β
σ calculated bending stress number N/mm
F
σ allowable design bending stress number N/mm
FAD
σ calculated contact stress number N/mm
H
σ allowable design contact stress number N/mm
HAD
5 Basic design
5.1 General
5.1.1 The equipment (including auxiliaries) covered by this International Standard shall be designed and
constructed for a minimum service life of 20 years and at least three years of uninterrupted operation. It is
recognized that this is a design criterion.
5.1.2 The vendor shall assume responsibility for the engineering coordination of the equipment and all auxiliary
systems included in the scope of the order.
z 5.1.3 Control of the sound pressure level (SPL) of all equipment furnished shall be a joint effort of the purchaser
and the vendor. Unless otherwise specified, the equipment furnished by the vendor shall conform to the
requirements of ISO 8579-1 and to the maximum allowable sound pressure level specified by the purchaser.
5.1.4 Equipment shall be designed to run safely to the trip speed setting. Unless otherwise agreed, rotors for
turbine driven gear units shall be designed to operate safely at momentary speeds up to 130 %of the rated speed.
5.1.5 The arrangement of the equipment, including piping and auxiliaries, shall be developed jointly by the
purchaser and the vendor. The arrangement shall provide adequate clearance areas and safe access for operation
and maintenance.
z 5.1.6 Electrical components and installations shall be suitable for the area classification (class, group and
division) specified and shall comply with the requirements of IEC 60079-0 and with any local codes specified and
furnished by the purchaser.
5.1.7 Oil reservoirs and housings that enclose moving lubricated parts (such as bearings, shaft seals), highly
polished parts, instruments and control elements, shall be designed to minimize contamination by moisture, dust
and other foreign matter during periods of operation and idleness.
5.1.8 The gear shall perform on the test stand and on its permanent foundation within the specified acceptance
criteria. After installation, the performance of the combined units shall be the joint responsibility of the purchaser
and the vendor who has unit responsibility.
z 5.1.9 Many factors (such as piping loads, alignment at operating conditions, supporting structure, handling
during shipment, and handling and assembly at the site) may adversely affect site performance. To minimize the
influence of these factors, the vendor shall review and comment on the purchaser’s baseplate and foundation
drawings. In addition, the vendor’s representative may be requested to check alignment at the operating
temperature and may be requested to be present during the initial alignment check and the tooth contact check.
z 5.1.10 The purchaser shall specify whether the installation is indoors (heated or unheated) or outdoors (with or
without a roof) as well as the weather and environmental conditions in which the equipment must operate (including
maximum and minimum temperatures, unusual humidity and dusty or corrosive conditions).
5.1.11 Unless otherwise agreed, gear units shall not require a running-in period at reduced speed and load in the
field.
ISO 13691:2001(E)
It is recognized that under certain conditions a running-in period may be requested. If a running-in period is
required, the vendor shall specify in the proposal the required load, speed and duration of the period. The vendor
shall also specify in the proposal any additional field inspection and commissioning required during the break-in
period.
z 5.1.12 The gearing shall be designed to withstand all internal and external loads inherent to geared, rotating
machinery systems. The gearing shall be capable of withstanding the specified external loads (thrust, lube-oil
piping, and so forth) while the unit is operating at the gear rated power specified by the purchaser.
5.1.13 All equipment shall be designed to permit rapid and economical maintenance. Major parts such as casing
components and bearing housings shall be designed (shouldered or cylindrical dowelled) and manufactured to
ensure accurate alignment on reassembly. Where practical, components should be dowelled, keyed or shouldered
asymmetrically to prevent incorrect assembly.
5.1.14 Spare parts for the machine and all furnished auxiliaries shall meet all the criteria of this International
Standard.
z 5.1.15 The purchaser shall specify the appropriate shaft assembly designation selected from the combinations
listed in Table 2 and illustrated in Figure 1. The purchaser may alternatively circle one or more of the assembly
designations on a copy of Figure 1 and submit the copy with the quotation request. If the shaft arrangement has not
been finalized at the time of the quotation request, the purchaser shall designate all of the combinations under
consideration.
Table 2 — Shaft assembly combinations
High-speed shaft Low-speed shaft
L R
R L
L L
R R
R LR
L LR
LR L
LR R
LR LR
NOTE  L = left; R = right. The letters refer to the number and direction
of shaft extensions (see Figure 1).

5.1.16 The rotational direction of high-speed and low-speed shafts is either clockwise (CW) or counterclockwise
(CCW) as viewed from the coupling ends of the respective shaft.
5.1.16.1 On the data sheets and in drawings and tables, the shaft rotational direction shall be designated by the
abbreviations CW or CCW, as indicated by the circular arrows in Figure 2.
z 5.1.16.2 The purchaser shall specify the rotational direction of both the high-speed and the low-speed shafts.
When either or both shafts have an extension at each end, the purchaser may alternatively indicate the rotational
directions on the appropriate assembly designation (see Figure 1) and submit a copy of the figure with the
quotation request.
z 5.1.16.3 In finalizing the data for purchase, the purchaser shall prepare a sketch that shows the direction of rotation
of each item in the train.
8 © ISO 2001 – All rights reserved

ISO 13691:2001(E)
Key
1 Low-speed shaft
2 High-speed shaft
NOTE 1 L = left; R = right
NOTE 2 Arrows indicate the line of sight used to determine the direction of the shaft extensions. (The figure depicts plan
views.)
NOTE 3 The letter(s) before the hyphen refer to the number and direction of high-speed shaft extensions; the letter(s) after
the hyphen refer to the number and direction of low speed shaft extensions.
NOTE 4 The material for this figure was extracted from AGMA 6010-F97 with permission of the publisher.
Figure 1 — Shaft assembly designations (for parallel-shaft, single- and double-helical one- and two-stage
speed increasers and reducers)
CW CCW
Figure 2 — Shaft rotation designations
ISO 13691:2001(E)
5.2 Gear rating
5.2.1 General
The rating method to be used for gears which are not within the limits in clause 1 a) to h) shall be subject to
agreement between purchaser and vendor.
It is recognized that special cases will exist in which it may be desirable or even mandatory to deviate from the
rating rules specified in 5.2.1 through 5.2.9. The vendor shall describe and justify such deviations in the proposal.
5.2.2 Gear rated power, P
z The required gear rated power P shall be specified by the purchaser. All modes of normal and abnormal operation
should be considered. Modes of operation should include the number of starts per unit of time, reduced load,
reversed load (if possible), reduced speed, overload and overspeed conditions. For electric motor drives, the gear
rated power will be the motor manufacturer's name plate rating multiplied by the motor service factor.
For gear units located next to a single-ended driver, the required gear rated power should be the maximum
installed power capability of the driver.
For gear units located between two items of driven equipment, or where the drive is taken from both ends of the
driver, the required rated power of the gear should be not less than item a) or b) below, whichever is greater:
a) 110 % of the maximum power required by the equipment driven by the gear;
b) the maximum power of the driver pro-rated between the driven equipment, based on normal power demands.
If the maximum transmitted torque occurs at an operating speed other than the maximum continuous speed, this
torque and its corresponding speed should be specified by the purchaser and should be the basis for sizing the
gear.
5.2.3 Rating criteria
For each gear mesh of the unit, the stress numbers shall be calculated with regard to
 surface durability (pitting),
 tooth-bending strength.
The calculated stress numbers shall not exceed the allowable design stress numbers as shown in Table 3.
In addition, scuffing resistance should be considered.
The rating factors used assume that the working flanks of pinion and gear have been modified as necessary to
compensate for both torsional and bending deflections and, when necessary for gears with pitch line velocities in
excess of 100 m/s, also for thermal distortions.
10 © ISO 2001 – All rights reserved

ISO 13691:2001(E)
Table 3 — Allowable design stress numbers σ , σ — Maximum (L/d) ratios of pinion
HAD FAD
Allowable design stress number Maximum L/d ratio of pinion
of contact of bending
Tooth
Material
hardness σ σ
HAD FAD
double helical single helical
N/mm
Through-hardened steels 302 HBW 525 250 2,2 1,6
321 HBW 542 256 2,2 1,6
341 HBW 560 263 2,2 1,6
363 HBW 580 270 2,2 1,6
Carburized and case-
58 HRC 760 350 2,0 1,6
hardened steels
Nitrided steels 58 HRC 660 270 2,2 1,6
NOTE 1 HBW = Brinell hardness number, HRC = Rockwell “C” hardness number.
NOTE 2 L = b (for single-helical gear); L = B (for double-helical gear); d = pinion operating pitch diameter, in millimetres.
NOTE 3 For gears which are subject to full load reversal in each load cycle, the values of σ shall be multiplied by a factor 0,7.
FAD
5.2.4 Surface durability
The surface stress of the gear teeth is based on the Hertzian contact pressure theory. The following equation has
been derived from the method in ISO 9084, see annex G.
F u +1
t
s = 426 ◊ K (1)
HSL
db u
(for a double-helical gear, b = 2b )
B
The value of the factor K in the above equation shall be determined in accordance with 5.2.8. The symbols are
SL
defined in clause 4.
The relation between the calculated contact stress number σ and the allowable design contact stress number
H
σ is:
HAD
s u s (2)
H HAD
(see Table 3).
5.2.5 Tooth-bending strength
The bending strength of a gear is a measure of the resistance to fatigue cracking at the tooth root fillet. The
calculated bending stress number σ shall be determined separately for the pinion and the gear. For an explanation
F
of the factors used, see annex G. The following equation has been derived from the method in ISO 9084, see
annex G.
F
t
s =KY◊◊1, 55 ◊Y◊Y◊ (3)
FSL F S β
mb
n
The values of the factors in the above equation shall be determined in accordance with 5.2.8 and 5.2.9. For double-
helical gears, b = 2b .
B
ISO 13691:2001(E)
The relation between calculated bending stress number σ and the allowable design bending stress number σ
F FAD
is:
s u s (4)
F FAD
(see Table 3).
5.2.6 Allowable design stress numbers σ , σ
HAD FAD
5.2.6.1 General
Table 3 presents allowable design contact stress numbers σ (for surface durability) and allowable design
HAD
bending stress numbers σ (for bending strength) and also maximum length-to-diameter (L/d) ratios of pinion for
FAD
several materials in current use (see 7.2.2.6.3).
The L/d values shown in Table 3 apply to helical gears when designed to transmit the rated power.
When a L/d ratio higher than tabulated in Table 3 is proposed, the gear vendor shall submit justification in the
proposal for using a higher L/d ratio. Purchaser’s approval is required when L/d ratios exceed those in Table 3.
When operating conditions other than the gear rated power are specified by the purchaser, such as the normal
transmitted power, the gear vendor shall consider in the analysis the length of time and load range at which the
gear unit will operate at each condition, so that the correct helix modification can be determined. When modified
helices are to be furnished, purchaser and vendor shall agree on the tooth contact patterns obtained in the
checking stand, housing or test stand.
For thro
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