ISO 14635-2:2023
(Main)Gears — FZG test procedures — Part 2: FZG step load test A10/16, 6R/120 for relative scuffing load-carrying capacity of high EP oils
Gears — FZG test procedures — Part 2: FZG step load test A10/16, 6R/120 for relative scuffing load-carrying capacity of high EP oils
This document specifies a test method based on a FZG four-square test machine to determine the relative load-carrying capacity of high EP oils defined by the gear surface damage known as scuffing. This test method is useful for evaluating the scuffing load capacity potential of oils typically used with highly stressed cylindrical gearing found in many vehicle and stationary applications. It is not suitable for establishing the scuffing load capacity potential of oils used in highly loaded hypoid bevel gearing applications, for which purpose other methods are available in the industry. NOTE This method is technically equivalent to CEC L-84-02.
Engrenages — Méthodes d'essai FZG — Partie 2: Méthode FZG A10/16, 6R/120 à paliers de charge pour évaluer la capacité de charge au grippage des huiles à valeurs EP élevées
L'ISO 14635-2:2004 spécifie une méthode d'essai fondée sur une machine d'essai FZG à configuration quadrilatère ayant pour but de déterminer la capacité de charge relative d'huiles lubrifiantes pour valeurs EP élevées, définie par une détérioration superficielle de l'engrenage appelée grippage. Cette méthode d'essai est utile pour évaluer la capacité de charge potentielle au grippage des huiles utilisées pour des engrenages cylindriques soumis à de fortes contraintes qu'on trouve dans beaucoup d'applications mobiles ou stationnaires. Elle ne convient pas pour déterminer la capacité de charge potentielle au grippage des huiles utilisées dans des applications à engrenages coniques ou hypoïdes, pour lesquelles il existe au niveau industriel d'autres méthodes.
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INTERNATIONAL ISO
STANDARD 14635-2
Second edition
2023-07
Gears — FZG test procedures —
Part 2:
FZG step load test A10/16, 6R/120
for relative scuffing load-carrying
capacity of high EP oils
Engrenages — Méthodes d'essai FZG —
Partie 2: Méthode FZG A10/16, 6R/120 à paliers de charge pour
évaluer la capacité de charge au grippage des huiles à valeurs EP
élevées
Reference number
ISO 14635-2:2023(E)
© ISO 2023
---------------------- Page: 1 ----------------------
ISO 14635-2:2023(E)
COPYRIGHT PROTECTED DOCUMENT
© ISO 2023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this publication may
be reproduced or utilized otherwise in any form or by any means, electronic or mechanical, including photocopying, or posting on
the internet or an intranet, without prior written permission. Permission can be requested from either ISO at the address below
or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: +41 22 749 01 11
Email: copyright@iso.org
Website: www.iso.org
Published in Switzerland
ii
© ISO 2023 – All rights reserved
---------------------- Page: 2 ----------------------
ISO 14635-2:2023(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Failure criteria .2
5 Brief description of method . 4
5.1 General principle . 4
5.2 Precision . . . 4
6 Test materials . 4
6.1 Test gears . 4
6.2 Cleaning fluid . 4
7 Apparatus . 4
7.1 FZG spur-gear test rig. 4
7.2 Heating device . 6
7.3 Revolution counter . 6
7.4 Balance . 6
8 Preparation of apparatus .8
9 Test procedure .8
10 Reporting of results .9
Annex A (informative) FZG A10-type gear tooth face changes (flank damages) .11
Annex B (informative) Typical FZG test report sheet .13
Annex C (informative) Checklist for maintenance of FZG gear test rig .14
Bibliography .19
iii
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ISO 14635-2:2023(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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 60, Gears, Subcommittee SC 2, Gear
capacity calculation.
This second edition cancels and replaces the first edition (ISO 14635-2:2004), of which it constitutes a
minor revision. The changes are as follows:
1)
— ISO 1328-1:1995 has been dated as this document uses accuracy grade which is numerically
different than tolerance class in ISO 1328-1:2013;
— replacement of ISO 4287 which has been withdrawn and replaced by ISO 21920-2;
— replacement of ISO 4964 which has been withdrawn and similar information can be found in
ISO 18265;
— replacement of some bibliography entries which were withdrawn, and changes from dated to
undated references;
— subclause 6.2, wording harmonized with the ISO 14635 series;
— Table 2, description "pitch diameter circumferential speed (v )" has been replaced by "circumferential
w
velocity at the pitch line" to harmonize the wording with the ISO 6336 series;
— Table 5, insertion of line "Test lubrication volume" to conform to the information in the ISO 14635
series;
— Figure A.1, addition of the figure title.
A list of all parts in the ISO 14635 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
1) Cancelled and replaced by ISO 1328-1:2013.
iv
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ISO 14635-2:2023(E)
Introduction
The types of gear failures which can be influenced by the lubricant in use are scuffing, low-speed
wear and the gear-surface fatigue phenomena known as micro- and macropitting. In the gear design
process, these gear damages are taken into consideration by the use of specific lubricant and service-
related characteristic values. For an accurate, field-related selection of these values, adequate lubricant
2)
test procedures are required. The FZG test procedures specified in this document, ISO 14635-1 and
ISO 14635-3 can be regarded as tools for the determination of the lubricant-related characteristic
values to be introduced into the load-carrying capacity calculation of gears.
FZG test method A/8,3/90 for the relative scuffing load-carrying capacity of oils described in
ISO 14635-1 is typical for the majority of applications in industrial and marine gears. This document
is related to the relative scuffing load-carrying capacity of oils of very high extreme pressure (EP)
properties, as used for the lubrication of automotive driveline components. Other FZG test procedures
for the determination of low-speed wear, micro- and macropitting load-carrying capacity of gears are
intended to be added to the ISO 14635 series as further parts.
2) FZG = Forschungsstelle für Zahnräder und Getriebebau, Technische Universität München (Gear Research
Centre, Technical University, Munich).
v
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---------------------- Page: 5 ----------------------
INTERNATIONAL STANDARD ISO 14635-2:2023(E)
Gears — FZG test procedures —
Part 2:
FZG step load test A10/16, 6R/120 for relative scuffing
load-carrying capacity of high EP oils
1 Scope
This document specifies a test method based on a FZG four-square test machine to determine the
relative load-carrying capacity of high EP oils defined by the gear surface damage known as scuffing.
This test method is useful for evaluating the scuffing load capacity potential of oils typically used with
highly stressed cylindrical gearing found in many vehicle and stationary applications. It is not suitable
for establishing the scuffing load capacity potential of oils used in highly loaded hypoid bevel gearing
applications, for which purpose other methods are available in the industry.
NOTE This method is technically equivalent to CEC L-84-02.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
3)
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 14635-1, Gears — FZG test procedures — Part 1: FZG test method A/8,3/90 for relative scuffing load-
carrying capacity of oils
ISO 18265, Metallic materials — Conversion of hardness values
ISO 21920-2, Geometrical product specifications (GPS) — Surface texture: Profile — Part 2: Terms,
definitions and surface texture parameters
ASTM D 235, Standard Specification for Mineral Spirits (Petroleum Spirits) (Hydrocarbon Dry Cleaning
Solvent)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3) Cancelled and replaced by ISO 1328-1:2013.
1
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ISO 14635-2:2023(E)
3.1
scuffing
particularly severe form of gear tooth surface damage in which seizure or welding together of areas
of tooth surface occur, owing to the absence or breakdown of a lubricant film between the contacting
tooth flanks of mating gears, typically caused by high temperature and high pressure
Note 1 to entry: Scuffing is most likely when surface velocities are high. It can also occur at relatively low sliding
velocities when tooth surface pressures are high enough either generally or, because of uneven surface geometry
and loading, in discrete areas.
3.2
scuffing load-carrying capacity
〈of a lubricant〉 maximum load which can be sustained under a defined set of conditions
Note 1 to entry: It is the minimum load stage at which the failure criterion given in Clause 4 is reached. See
Table 1.
3.3
FZG test condition A10/16,6R/120
test condition where A10 is the particular tooth form of the test gears, according to Tables 2 and 3,
16,6 is the speed at the pitch circle, in metres per second, “R” indicates the reverse direction of rotation
(wheel drives pinion) and 120 is the initial oil temperature in degrees Celsius, from load stage 4 onward
in the oil sump
3.4
failure load stage
2
load stage reached when the sum of the damage to the 16 pinion teeth exceeds 100 mm in total area
damaged
Note 1 to entry: See Clause 4 and Table 1.
3.5
high EP oils
lubricants containing chemical additives appropriate for improving their scuffing load capacity
Note 1 to entry: EP = extreme pressure.
Note 2 to entry: These oils typically exceed the limits of the FZG test according to ISO 14635-1.
4 Failure criteria
Risk of scuffing damage varies with the properties of gear materials, the lubricant used, the surface
roughness of tooth flanks, the sliding velocities and the load. Consequences of scuffing include a
tendency to high levels of dynamic loading owing to an increase of vibrations, which usually leads to
further damage by scuffing, pitting or tooth breakage.
Because of the particular gear design and test loads used, an interference area typically results at the tip
of the pinion and root of the mating wheel. This area is usually about 1 mm in length (profile direction)
on the pinion and across the entire facewidth. Examples of various levels of distress occurring with
this test are shown in Annex A. The effect of the surface distress in these two regions is addressed as
follows.
a) For the purpose of the visual rating for scuffing, the top 1 mm near the tip of the pinion is not
included in the assessment until the damage extends below that level. The rated damage region
is then expressed as the total area scuffed over all 16 pinion teeth (see Figure 1). The failure load
2
stage is reached when the sum of the damage to the 16 pinion teeth exceeds 100 mm in total area
damaged.
b) For a valid test, the wheel shall be visually checked for signs of excessive wear after each pass load
stage, as this can alter the results of the test. If there is evidence of wear in the dedendum of the
wheel, then the gear shall be weighed to the nearest milligram (0,001 g) [see Annex A, Figure A.1 d)].
2
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ISO 14635-2:2023(E)
The test may be considered valid only if the loss in mass of the wheel is ≤ 20 mg: if the loss in mass
of the wheel exceeds 20 mg, the test shall not be considered valid.
See Table 1.
Table 1 — Test criteria
Pinion failure area Wheel wear
A Δm Result
2
mm mg
≤ 100 ≤ 20 PASS
a
≤ 100 > 20 INVALID
> 100 Not required FAIL
a
No statement on the scuffing load is possible.
Area in square millimetres
Key
1 exclusion zone (1 mm)
Figure 1 — Schematic of distress rating for pinion
3
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ISO 14635-2:2023(E)
5 Brief description of method
5.1 General principle
A set of test gears as defined in Tables 2 and 3 is run with the test lubricant at constant speed for a
fixed number of revolutions using dip-lubrication mode. Loading of the gear teeth is increased in steps
outlined in Table 4. Beginning with load stage 4, the initial oil temperature is controlled between 117 °C
and 123 °C. During the test run of each load stage, the oil temperature is allowed to rise freely. After
load stage 5, the pinion tooth flanks are inspected for surface damage at the end of each load stage and
any changes in appearance are noted. A test is considered complete when either the failure criteria
have been met or when load stage 10 has been completed without meeting the failure criteria.
It is the responsibility of the operator to ensure that all local legislative and statutory requirements are
met.
NOTE It has been assumed by the compilers of this test method that anyone using the method will either
be fully trained and familiar with all normal engineering and laboratory practice, or will be under the direct
supervision of such a person.
WARNING — When the rig is running, there are long loaded shafts and highly stressed test gears
turning at high speed and precaution shall be taken to protect personnel.
WARNING — Protection from noise is also highly recommended.
5.2 Precision
The precision of the method has been evaluated according to ISO 5725-2 with two reference oils. The
failure load stage of these oils covered the range 5 to 10 inclusive for the step load test.
Values of repeatability, r, and reproducibility, R, as defined in ISO 5725-2, for this test procedures are
r = 1 load stage,
R = 2 load stages.
6 Test materials
6.1 Test gears
A pair of type “A10” test gears with a specification according to Tables 2 and 3 shall be used for testing.
Each pair of test gears may be utilized twice for testing, using both tooth flanks as load-carrying flanks.
6.2 Cleaning fluid
Petroleum spirit conforming to ASTM D 235 shall be used.
7 Apparatus
7.1 FZG spur-gear test rig
7.1.1 The FZG spur-gear test machine utilizes a recirculating power loop principle, also known as a
four-square configuration, to provide a fixed torque (load) to a pair of precision test gears. A schematic
view of the test rig is shown in Figures 2 and 3. The slave gearbox and the test gearbox are connected
through two torsional shafts. Shaft 1 contains a load coupling used to apply the torque through the use
of known weights, defined in Table 4, hung on the loading arm.
4
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ISO 14635-2:2023(E)
7.1.2 The test gearbox contains heating elements to maintain and control the minimum temperature
of the oil. A temperature sensor located in the side of the test gearbox is used to control the heating
system as required by the test operating conditions.
7.1.3 The test machine is powered by an electric motor of minimum 7,4 kW at a speed of approximately
2 900 1/min. The direction of drive is reversed (anticlockwise when looking on the motor shaft),
i.e. wheel drives pinion, as shown in Figure 3. This is the opposite direction of rotation to that of
ISO 14635-1.
7.1.4 A check list for maintenance of FZG gear test rig is given for information in Annex C.
Table 2 — Details of FZG test gears type A10
Dimension Symbol Numerical value Unit
Shaft centre distance a 91,5 mm
Effective tooth width pinion b 10 mm
1
wheel b 20 mm
2
Working pitch diameter pinion d 73,2 mm
w1
wheel d 109,8 mm
w2
Tip diamet
...
ISO/FDIS 14635-2:2023(E)
ISO /TC 60/SC 2
Secretariat: DIN
Date: 2023-01-2503-03
Gears — FZG test procedures —
Part 2:
FZG step load test A10/16, 6R/120 for relative scuffing load-
carrying capacity of high EP oils
Engrenages — Méthodes d'essai FZG —
Partie 2: Méthode FZG A10/16, 6R/120 à paliers de charge pour évaluer la capacité de charge au grippage
des huiles à valeurs EP élevées
FDIS stage
© ISO 2023 – All rights reserved
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ISO/FDIS 14635-2:2023(E)
© ISO 2023
All rights reserved. Unless otherwise specified, or required in the context of its implementation, no part of this
publication may be reproduced or utilized otherwise in any form or by any means, electronic or mechanical,
including photocopying, or posting on the internet or an intranet, without prior written permission. Permission can
be requested from either ISO at the address below or ISO’s member body in the country of the requester.
ISO copyright office
CP 401 • Ch. de Blandonnet 8
CH-1214 Vernier, Geneva
Phone: + 41 22 749 01 11
EmailE-mail: copyright@iso.org
Website: www.iso.orgwww.iso.org
Published in Switzerland
ii © ISO 2023 – All rights reserved
---------------------- Page: 2 ----------------------
ISO/FDIS 14635-2:2023(E)
Contents
Foreword . v
Introduction .vi i
Part 2: FZG step load test A10/16, 6R/120 for relative scuffing load-carrying capacity of high EP oils . 1
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Failure criteria . 2
5 Brief description of method . 4
5.1 General principle . 4
5.2 Precision . 5
6 Test materials . 5
6.1 Test gears . 5
6.2 Cleaning fluid . 5
7 Apparatus . 5
7.1 FZG spur-gear test rig . 5
7.2 Heating device . 8
7.3 Revolution counter . 8
7.4 Balance . 8
8 Preparation of apparatus . 9
9 Test procedure . 10
10 Reporting of results. 11
Annex A (informative) FZG A10-type gear tooth face changes (flank damages) . 13
Annex B (informative) Typical FZG test report sheet . 15
Annex C (informative) Checklist for maintenance of FZG gear test rig. 17
Bibliography . 23
Foreword v
Introduction vii
1 Scope 1
2 Normative references 1
3 Terms and definitions 1
4 Failure criteria 2
5 Brief description of method 3
5.1 General principle 3
5.2 Precision 4
6 Test materials 4
6.1 Test gears 4
6.2 Cleaning fluid 4
7 Apparatus 4
7.1 FZG spur-gear test rig 4
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ISO/FDIS 14635-2:2023(E)
7.2 Heating device 6
7.3 Revolution counter 6
7.4 Balance 7
8 Preparation of apparatus 8
9 Test procedure 8
10 Reporting of results 9
Annex A (informative) FZG A10-type gear tooth face changes (flank damages) 11
Annex B (informative) Typical FZG test report sheet 13
Annex C (informative) Checklist for maintenance of FZG gear test rig 14
C.1 How to recognize malfunction 14
C.1.1 Distribution of scuffing marks 14
C.1.2 Tooth contact pattern 14
C.1.3 Tests with reference oil 14
C.1.4 Other indications 14
C.2 Parts that need maintenance 14
C.2.1 Test gear box 14
C.2.1.1 Shafts 14
C.2.1.2 Bearings 15
C.2.1.3 Keys 15
C.2.1.4 Spacer rings 15
C.2.1.5 Gear box and front cover 15
C.2.1.6 Seals 15
C.2.2 Connecting shafts and flanges 15
C.2.2.1 Load coupling 15
C.2.2.2 Torque-measuring device 15
C.2.2.3 Load coupling support bearing 15
C.2.2.4 Torsion shaft 16
C.2.2.5 Flanges 16
C.2.3 Slave gear box 16
C.2.3.1 Slave gears 16
C.2.3.2 Lubrication 16
C.2.4 Other parts 16
C.2.4.1 Heating 16
C.2.4.2 Flexible coupling 16
C.2.4.3 Motor 16
C.2.4.4 Approximate time intervals 16
Bibliography 18
iv © ISO 2023 – All rights reserved
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ISO/FDIS 14635-2:2023(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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Field Code Changed
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of any
patent rights identified during the development of the document will be in the Introduction and/or on
the ISO list of patent declarations received (see www.iso.org/patentswww.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to the World
Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.htmlwww.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 60, Gears, Subcommittee SC 2, Gear
capacity calculation.
This second edition cancels and replaces the first edition (ISO 14635-2:2004), of which it constitutes a
minor revision in accordance with ISO Directives, Part 1. The changes are as follows:
The main changes are as follows:
— — ISO 1328-1:1995, Cylindrical gears — ISO system of accuracy — Part 1: Definitions and allowable
1
values of deviations relevant to corresponding flanks of gear teeth has been dated as this document
still refers to accuracy grade;
— — replacement of ISO 4287, Geometrical Product Specifications (GPS) — Surface texture: Profile
method — Terms, definitions and surface texture parameters which has been withdrawn and replaced
by ISO 21920-2, Geometrical product specifications (GPS) — Surface texture: Profile — Part 2: Terms,
definitions and surface texture parameters;
— — replacement of ISO 4964, Steel — Hardness conversions which has been withdrawn and similar
information can be found in ISO 18265, Metallic materials — Conversion of hardness values;
— — updatingreplacement of some bibliography entries which were withdrawn, and changes from
dated to undated references where no specific reason requires the dated reference (see Bibliography
footnotes);;
— — Clause 6.2,subclause 6.2, wording harmonized withinwith the ISO 14635 series;
— — Table 2,Table 2, description "pitch diameter circumferential speed (vw))" has been replaced by
"circumferential velocity at the pitch line" to harmonize the wording with the ISO 6336- series;
1
Cancelled and replaced by ISO 1328-1:2013.
© ISO 2023 – All rights reserved v
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ISO/FDIS 14635-2:2023(E)
— — Table 5,Table 5, insertion of line "Test lubrication volume" to conform to be compliant withthe
information given withinin the ISO 14635 series;
— — Figure A.1,Figure A.1, addition of the figure title.
A list of all parts in the ISO 14635 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at
www.iso.org/members.htmlwww.iso.org/members.html.
vi © ISO 2023 – All rights reserved
---------------------- Page: 6 ----------------------
ISO/FDIS 14635-2:2023(E)
Introduction
The types of gear failures which can be influenced by the lubricant in use are scuffing, low-speed wear
and the gear-surface fatigue phenomena known as micro- and macropitting. In the gear design process,
these gear damages are taken into consideration by the use of specific lubricant and service-related
characteristic values. For an accurate, field-related selection of these values, adequate lubricant test
2
procedures are required. The FZG test procedures specified in this document and the other parts of
ISO 14635-1 and ISO 14635-3, can be regarded as tools for the determination of the lubricant-related
characteristic values to be introduced into the load-carrying capacity calculation of gears.
FZG test method A/8,3/90 for the relative scuffing load-carrying capacity of oils described in
ISO 14635-1 is typical for the majority of applications in industrial and marine gears. This document is
related to the relative scuffing load-carrying capacity of oils of very high EP properties, as used for the
lubrication of automotive driveline components. Other FZG test procedures for the determination of low-
speed wear, micro- and macropitting load-carrying capacity of gears are already in a late state of
development. They can intended to be added later to the ISO 14635 series as further parts.
2
FZG = Forschungsstelle für Zahnräder und Getriebebau, Technische Universität München (Gear Research Centre,
© ISO 2023 – All rights reserved vii
---------------------- Page: 7 ----------------------
ISO/FDIS 14635-2:2023(E)
Gears — FZG test procedures —
Part 2:
FZG step load test A10/16, 6R/120 for relative scuffing load-
carrying capacity of high EP oils
1 Scope
3
This document specifies a test method based on a FZG four-square test machine to determine the relative
load-carrying capacity of high EP oils defined by the gear surface damage known as scuffing. This test
method is useful for evaluating the scuffing load capacity potential of oils typically used with highly
stressed cylindrical gearing found in many vehicle and stationary applications. It is not suitable for
establishing the scuffing load capacity potential of oils used in highly loaded hypoid bevel gearing
applications, for which purpose other methods are available in the industry.
NOTE This method is technically equivalent to CEC L-84-02.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
4
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 5725-2, Accuracy (trueness and precision) of measurement methods and results — Part 2: Basic method
for the determination of repeatability and reproducibility of a standard measurement method
ISO 14635-1, Gears — FZG test procedures — Part 1: FZG test method A/8,3/90 for relative scuffing load-
carrying capacity of oils
ISO 18265, Metallic materials — Conversion of hardness values
ISO 21920-2, Geometrical product specifications (GPS) — Surface texture: Profile — Part 2: Terms,
definitions and surface texture parameters
ASTM D 235, Standard Specification for Mineral Spirits (Petroleum Spirits) (Hydrocarbon Dry Cleaning
Solvent)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
Field Code Changed
— IEC Electropedia: available at https://www.electropedia.org/https://www.electropedia.org/
3.1
scuffing
particularly severe form of gear tooth surface damage in which seizure or welding together of areas of
tooth surface occur, owing to the absence or breakdown of a lubricant film between the contacting tooth
flanks of mating gears, typically caused by high temperature and high pressure
3
FZG = Forschungsstelle für Zahnräder und Getriebebau, Technische Universität München (Gear Research
Centre, Technical University, Munich), Boltzmannstraße 15, D-85748 Garching, Germany.
4
Cancelled and replaced by ISO 1328-1:2013.
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ISO/FDIS 14635-2:2023(E)
Note 1 to entry: Scuffing is most likely when surface velocities are high. It can also occur at relatively low sliding
velocities when tooth surface pressures are high enough either generally or, because of uneven surface geometry
and loading, in discrete areas.
3.2
scuffing load-carrying capacity
〈of a lubricant〉 maximum load which can be sustained under a defined set of conditions
Note 1 to entry: It is the minimum load stage at which the failure criteriacriterion given in Clause 4Clause 4 is
reached. See Table 1.Table 1.
3.3
FZG test condition A10/16,6R/120
test condition where A10 is the particular tooth form of the test gears, according to Tables 2 and
3,Tables 2 and 3, 16,6 is the speed at the pitch circle, in metres per second, “R” indicates the reverse
direction of rotation (wheel drives pinion) and 120 is the initial oil temperature in degrees Celsius, from
load stage 4 onward in the oil sump
3.4
failure load stage
2
load stage reached when the sum of the damage to the 16 pinion teeth exceeds 100 mm in total area
damaged
Note 1 to entry: See Clause 4Clause 4 and Table 1.Table 1.
3.5
high EP oils
lubricants containing chemical additives appropriate for improving their scuffing load capacity
Note 1 to entry: EP = extreme pressure.
Note 2 to entry: These oils typically exceed the limits of the FZG test according to ISO 14635-1.
4 Failure criteria
Risk of scuffing damage varies with the properties of gear materials, the lubricant used, the surface
roughness of tooth flanks, the sliding velocities and the load. Consequences of scuffing include a tendency
to high levels of dynamic loading owing to an increase of vibrations, which usually leads to further
damage by scuffing, pitting or tooth breakage.
Because of the particular gear design and test loads used, an interference area typically results at the tip
of the pinion and root of the mating wheel. This area is usually about 1 mm in length (profile direction)
on the pinion and across the entire facewidth. Examples of various levels of distress occurring with this
test are shown in Annex A.Annex A. The effect of the surface distress in these two regions is addressed as
follows.
a) For the purpose of the visual rating for scuffing, the top 1 mm near the tip of the pinion is not included
in the assessment until the damage extends below that level. The rated damage region is then
expressed as the total area scuffed over all 16 pinion teeth (see Figure 1).Figure 1). The failure load
2
stage is reached when the sum of the damage to the 16 pinion teeth exceeds 100 mm in total area
damaged.
c)b) For a valid test, the wheel shall be visually checked for signs of excessive wear after each pass load
stage, as this couldcan alter the results of the test. If there is evidence of wear in the dedendum of the
wheel, then the gear shall be weighed to the nearest milligram (0,001 g) [see
Annex A, Figure A.1 d)].Annex A, Figure A.1 d)]. The test may be considered valid only if the loss in
mass of the wheel is ≤ 20 mg: if the loss in mass of the wheel exceeds 20 mg, the test shall not be
considered valid.
See Table 1.
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ISO/FDIS 14635-2:2023(E)
See Table 1.
Table 1 — Test criteria
Pinion failure area Wheel wear
A Δm Result
2
mm mg
≤ 100 ≤ 20 PASS
b a
≤ 100 > 20 20 INVALID
> 100 Not required FAIL
a
No statement on the scuffing load is possible.
Area in square millimetres
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ISO/FDIS 14635-2:2023(E)
Key
1 exclusion zone (1 mm)
Deleted Cells
Deleted Cells
Figure 1 — Schematic of distress rating for pinion
5 Brief description of method
5.1 General principle
A set of test gears as defined in Tables 2 and 3Tables 2 and 3 is run with the test lubricant at constant
speed for a fixed number of revolutions using dip-lubrication mode. Loading of the gear teeth is increased
in steps outlined in Table 4.Table 4. Beginning with load stage 4, the initial oil temperature is controlled
between 117 °C and 123 °C. During the test run of each load stage, the oil temperature is allowed to rise
freely. After load stage 5, the pinion tooth flanks are inspected for surface damage at the end of each load
stage and any changes in appearance are noted. A test is considered complete when either the failure
criteria have been met or when load stage 10 has been completed without having been metmeeting the
failure criteria having been met.
It is the responsibility of the operator to ensure that all local legislative and statutory requirements are
met.
NOTE It has been assumed by the compilers of this test method that anyone using the method will either be
fully trained and familiar with all normal engineering and laboratory practice, or will be under the direct
supervision of such a person.
WARNING — — When the rig is running, there are long loaded shafts and highly stressed test
gears turning at high speed and precaution shall be taken to protect personnel.
Protection from noise is also highly recommended.
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ISO/FDIS 14635-2:2023(E)
5.2 Precision
The precision of the method has been evaluated according to ISO 5725-2 with two reference oils. The
failure load stage of these oils covered the range 5 to 10 inclusive for the step load test.
Values of repeatability, r, and reproducibility, R, as defined in ISO 5725-2, for this test procedures are
r = 1 load stage,
R = 2 load stages.
6 Test materials
6.1 Test gears
A pair of type “A10” test gears with a specification according to Tables 2Tables 2 and 33 shall be used for
testing. Each pair of test gears may be used twice for testing, utilizingusing both tooth flanks as load-
carrying flanks.
6.2 Cleaning fluid
Petroleum spirit conforming to ASTM D 235 shall be used.
7 Apparatus
7.1 FZG spur-gear test rig
7.1.1 The FZG spur-gear test machine utilizes a recirculating power loop principle, also known as a
four-square configuration, to provide a fixed torque (load) to a pair of precision test gears. A schematic
view of the test rig is shown in Figures 2 and 3.Figures 2 and 3. The slave gearbox and the test gearbox
are connected through two torsional shafts. Shaft 1 contains a load coupling used to apply the torque
through the use of known weights, defined in Table 4,Table 4, hung on the loading arm.
7.1.2 The test gearbox contains heating elements to maintain and control the minimum temperature of
the oil. A temperature sensor located in the side of the test gearbox is used to control the heating system
as required by the test operating conditions.
7.1.3 The test machine is powered by an electric motor of minimum 7,4 kW at a speed of approximately
2 900 r/min. The direction of drive is reversed (anticlockwise when looking on the motor shaft), i.e. wheel
drives pinion, as shown in Figure 3.Figure 3. This is the opposite direction of rotation to that of
ISO 14635-1.
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ISO/FDIS 14635-2:2023(E)
7.1.4 A check list for maintenance of FZG gear test rig is given for information in Annex C.
Table 2 — Details of FZG test gears type A10
Dimension Symbol Numerical value Unit
Shaft centre distance a 91,5 mm
Effective tooth width pinion b1 10 mm
wheel b 20 mm
2
Working pitch diameter pinion dw1 73,2 mm
wheel dw2 109,8 mm
Tip diameter pinion d 88,77 mm
a1
wheel da2 112,5 mm
Module m 4,5 mm
Number of teeth pinion z1 16
wheel z2 24
Profile-shift coefficient pinion x 0,853 2
1
wheel x2 - 0,50
Pressure angle α 20 °
Working pressure angle αw 22,5 °
Circumferential velocity at the pitch line vw 8,316,6 m/s
Addendum engagement pinion e 14,7 mm
a1
wheel ea2 3,3 mm
Sliding speed at tooth tip pinion vga1 11,16 m/s
wheel v 2,50 m/s
ga2
Specific sliding at tooth tip pinion ζE1 0,86
wheel ζ 0,34
A2
Specific sliding at tooth root pinion ζA1 - 0,52
wheel ζE2 - 5,96
2
a
Hertzian contact pressure p N/mm
c 20,8∙�𝐹𝐹 ⋅�𝐹𝐹 P
nt nt
a
F = normal tooth load in N (see Table 3).Table 3).
nt
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ISO/FDIS 14635-2:2023(E)
Table 3 — Manufacturing details of FZG test gears type A10
Case-hardening steel with restricted hardenability to 2/3 of the lower
scatter band. Material composition:
C = 0,13 % to 0,20 % Mo = max. 0,12 %
Material
Si = max. 0,40 % Ni = max. 0,30 %
Mn = 1,00 % to 1,30 % Al = 0,02 % to 0,05 %
P = max. 0,025 % B = 0,001 % to 0,003 %
Case-hardening steel with restricted Cu = max. 0,30 %
Inserted Cells
hardenability to 2/3 of the lower
scatter band. Material composition:
C = 0,13 % to 0,20 %
Mo = max. 0,12 %
Si = max. 0,40 %
Ni = max. 0,30 %
Material
Merged Cells
Mn = 1,00 % to 1,30 %
Al = 0,02 % to 0,05 %
P = max. 0,025 %
B = 0,001 % to 0,003 %
S = 0,020 % to 0,035 %
Cu = max. 0,30 %
Cr = 0,80 % to 1,30 %
Cr = 0,80 % to 1,30 %
The test gears are carburized and case hardened. The case depth at a
hardness of 550 HV10 shall be 0,6 mm to 0,9 mm. The surface hardness
after tempering: 60 HRC to 62 HRC, core strength in tooth root centre:
Heat treatment
2 2
1 000 N/mm to 1 250 N/mm (determined in accordance with ISO 18265
based on Brinell hardness).
Retained austenite should be nominally 20 %.
Gear accuracy grade Q5 according to ISO 1328-1:1995
Arithmetic roughness of flanks Ra Ra is separately determined for left and right flanks, measured each at
three flanks per gear across the centre of the tooth parallel to the pitch line;
measuring parameters according to ISO 21920-2
measured length l = 4,8 mm,
t
:cut-off length λc = 0,8 mm;
velocity vt = 0,5 mm/s, using a skid.
measured length l = 4,8 mm;
t
cut-off length λ = 0,8 mm;
c
velocity v = 0,5 mm/s, using a skid.
t
Average roughness (relating to manufacture batches of a minimum of a 100
gear sets).
Average roughness (relating to manufacture
batches of a minimum of a 100 gear sets)
Pinion:
Inserted Cells
Pinion: Ra = 0,35 μm ± 0,1 μm
Gear:
Inserted Cells
Gear: Ra = 0,30 μm ± 0,1 μm
Maximum roughness (average of three measurements according to the
described method and valid for 95 of 100 tested gears).
Pinion and gear: Ra = 0,5 μm
Pinion and gear: Ra = 0,5 μm
Maag criss-cross grinding (15° method), 154 r/min of generating stroke
Grinding
drive
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ISO/FDIS 14635-2:2023(E)
Flank modification None
7.37.2 Heating device
A suitable oven or heating device is required to warm the test gears to 60 °C to 80 °C for assembling on
the shafts.
7.47.3 Revolution counter
A suitable counter shall be used to control the number of revolutions (cycles) during each load stage of
the test. The counter should be capable of shutting down the test machine at the appropriate number of
revolutions.
7.57.4 Balance
A suitable balance of a minimum weighing capacity 1,3 kg and with accuracy to the nearest to 0,001 g
shall be used to determine the mass of the test wheel.
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Key
1 6
Testtest wheel Drivedrive motor
2 7
Viewview A Loadload coupling
3 8
Testtest pinion Shaft 1shaft 1 (two pieces)
4 Torquetorque measuring coupling 9 Slaveslave gears
5 Shaft 2shaft 2 (torsion shaft) 10 torsion shaft outer tube
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ISO/FDIS 14635-2:2023(E)
Figure 2 — Schematic section of the FZG gear test machine
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Key
1
Testtest wheel
Deleted Cells
2
Testtest pinion
Deleted Cells
3
Activeactive tooth flank
Figure 3 — Mounting of the FZG test gears of type A10 (view A of Figure 2)Figure 2)
8 Preparation of apparatus
8.1 Flush the test gear case twice with petroleum spirit, ensuring that the bearings are cleared of any
previous oil, and air dry with a clean, water-free air line.
8.2 Clean the test gears in petroleum spirit and air dry, using protective gloves.
8.3 Visually inspect the test gears for corrosion, rust or any other damage. Reject the gears if so
damaged.
8.4 Weigh the wheel to the nearest 0,001 g.
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ISO/FDIS 14635-2:2023(E)
8.5 For easier mounting, heat both test gears and bearing races to between 60 °C and 80 °C with the
heating device.
8.6 Assemble the test gear box (except the top cover) with the test pinion on shaft 1 (right-hand side)
and the test wheel on shaft 2 (left-hand side) as shown in Figure 3.Figure 3.
8.7 Switch drain cock to the CLOSED position.
8.8 Fill the test gear box with nominal 1,25 litrel of test oil.
8.9 Plug in the h
...
FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 14635-2
ISO/TC 60/SC 2
Gears — FZG test procedures —
Secretariat: DIN
Voting begins on:
Part 2:
2023-03-17
FZG step load test A10/16, 6R/120
Voting terminates on:
for relative scuffing load-carrying
2023-05-12
capacity of high EP oils
Engrenages — Méthodes d'essai FZG —
Partie 2: Méthode FZG A10/16, 6R/120 à paliers de charge pour
évaluer la capacité de charge au grippage des huiles à valeurs EP
élevées
RECIPIENTS OF THIS DRAFT ARE INVITED TO
SUBMIT, WITH THEIR COMMENTS, NOTIFICATION
OF ANY RELEVANT PATENT RIGHTS OF WHICH
THEY ARE AWARE AND TO PROVIDE SUPPOR TING
DOCUMENTATION.
IN ADDITION TO THEIR EVALUATION AS
Reference number
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/FDIS 14635-2:2023(E)
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN-
DARDS TO WHICH REFERENCE MAY BE MADE IN
NATIONAL REGULATIONS. © ISO 2023
---------------------- Page: 1 ----------------------
ISO/FDIS 14635-2:2023(E)
FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 14635-2
ISO/TC 60/SC 2
Gears — FZG test procedures —
Secretariat: DIN
Voting begins on:
Part 2:
FZG step load test A10/16, 6R/120
Voting terminates on:
for relative scuffing load-carrying
capacity of high EP oils
Engrenages — Méthodes d'essai FZG —
Partie 2: Méthode FZG A10/16, 6R/120 à paliers de charge pour
évaluer la capacité de charge au grippage des huiles à valeurs EP
élevées
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or ISO’s member body in the country of the requester.
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DOCUMENTATION.
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IN ADDITION TO THEIR EVALUATION AS
Reference number
Email: copyright@iso.org
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/FDIS 14635-2:2023(E)
Website: www.iso.org
LOGICAL, COMMERCIAL AND USER PURPOSES,
DRAFT INTERNATIONAL STANDARDS MAY ON
Published in Switzerland
OCCASION HAVE TO BE CONSIDERED IN THE
LIGHT OF THEIR POTENTIAL TO BECOME STAN-
DARDS TO WHICH REFERENCE MAY BE MADE IN
ii
© ISO 2023 – All rights reserved
NATIONAL REGULATIONS. © ISO 2023
---------------------- Page: 2 ----------------------
ISO/FDIS 14635-2:2023(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Failure criteria .2
5 Brief description of method . 4
5.1 General principle . 4
5.2 Precision . . . 4
6 Test materials . 4
6.1 Test gears . 4
6.2 Cleaning fluid . 4
7 Apparatus . 4
7.1 FZG spur-gear test rig. 4
7.2 Heating device . 6
7.3 Revolution counter . 6
7.4 Balance . 6
8 Preparation of apparatus .8
9 Test procedure .8
10 Reporting of results .9
Annex A (informative) FZG A10-type gear tooth face changes (flank damages) .11
Annex B (informative) Typical FZG test report sheet .13
Annex C (informative) Checklist for maintenance of FZG gear test rig .15
Bibliography .20
iii
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ISO/FDIS 14635-2:2023(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.
The procedures used to develop this document and those intended for its further maintenance are
described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the
different types of ISO documents should be noted. This document was drafted in accordance with the
editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. ISO shall not be held responsible for identifying any or all such patent rights. Details of
any patent rights identified during the development of the document will be in the Introduction and/or
on the ISO list of patent declarations received (see www.iso.org/patents).
Any trade name used in this document is information given for the convenience of users and does not
constitute an endorsement.
For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and
expressions related to conformity assessment, as well as information about ISO's adherence to
the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see
www.iso.org/iso/foreword.html.
This document was prepared by Technical Committee ISO/TC 60, Gears, Subcommittee SC 2, Gear
capacity calculation.
This second edition cancels and replaces the first edition (ISO 14635-2:2004), of which it constitutes a
minor revision. The changes are as follows:
1)
— ISO 1328-1:1995 has been dated as this document still refers to accuracy grade;
— replacement of ISO 4287 which has been withdrawn and replaced by ISO 21920-2;
— replacement of ISO 4964 which has been withdrawn and similar information can be found in
ISO 18265;
— replacement of some bibliography entries which were withdrawn, and changes from dated to
undated references;
— subclause 6.2, wording harmonized with the ISO 14635 series;
— Table 2, description "pitch diameter circumferential speed (v )" has been replaced by "circumferential
w
velocity at the pitch line" to harmonize the wording with the ISO 6336 series;
— Table 5, insertion of line "Test lubrication volume" to conform to the information in the ISO 14635
series;
— Figure A.1, addition of the figure title.
A list of all parts in the ISO 14635 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
1) Cancelled and replaced by ISO 1328-1:2013.
iv
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ISO/FDIS 14635-2:2023(E)
Introduction
The types of gear failures which can be influenced by the lubricant in use are scuffing, low-speed wear
and the gear-surface fatigue phenomena known as micro- and macropitting. In the gear design process,
these gear damages are taken into consideration by the use of specific lubricant and service-related
characteristic values. For an accurate, field-related selection of these values, adequate lubricant test
2)
procedures are required. The FZG test procedures specified in this document and ISO 14635-1 and
ISO 14635-3, can be regarded as tools for the determination of the lubricant-related characteristic
values to be introduced into the load-carrying capacity calculation of gears.
FZG test method A/8,3/90 for the relative scuffing load-carrying capacity of oils described in
ISO 14635-1 is typical for the majority of applications in industrial and marine gears. This document is
related to the relative scuffing load-carrying capacity of oils of very high EP properties, as used for the
lubrication of automotive driveline components. Other FZG test procedures for the determination of
low-speed wear, micro- and macropitting load-carrying capacity of gears are intended to be added to
the ISO 14635 series as further parts.
2) FZG = Forschungsstelle für Zahnräder und Getriebebau, Technische Universität München (Gear Research
Centre,
v
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FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 14635-2:2023(E)
Gears — FZG test procedures —
Part 2:
FZG step load test A10/16, 6R/120 for relative scuffing
load-carrying capacity of high EP oils
1 Scope
This document specifies a test method based on a FZG four-square test machine to determine the
relative load-carrying capacity of high EP oils defined by the gear surface damage known as scuffing.
This test method is useful for evaluating the scuffing load capacity potential of oils typically used with
highly stressed cylindrical gearing found in many vehicle and stationary applications. It is not suitable
for establishing the scuffing load capacity potential of oils used in highly loaded hypoid bevel gearing
applications, for which purpose other methods are available in the industry.
NOTE This method is technically equivalent to CEC L-84-02.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
3)
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 14635-1, Gears — FZG test procedures — Part 1: FZG test method A/8,3/90 for relative scuffing load-
carrying capacity of oils
ISO 18265, Metallic materials — Conversion of hardness values
ISO 21920-2, Geometrical product specifications (GPS) — Surface texture: Profile — Part 2: Terms,
definitions and surface texture parameters
ASTM D 235, Standard Specification for Mineral Spirits (Petroleum Spirits) (Hydrocarbon Dry Cleaning
Solvent)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3) Cancelled and replaced by ISO 1328-1:2013.
1
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ISO/FDIS 14635-2:2023(E)
3.1
scuffing
particularly severe form of gear tooth surface damage in which seizure or welding together of areas
of tooth surface occur, owing to the absence or breakdown of a lubricant film between the contacting
tooth flanks of mating gears, typically caused by high temperature and high pressure
Note 1 to entry: Scuffing is most likely when surface velocities are high. It can also occur at relatively low sliding
velocities when tooth surface pressures are high enough either generally or, because of uneven surface geometry
and loading, in discrete areas.
3.2
scuffing load-carrying capacity
〈of a lubricant〉 maximum load which can be sustained under a defined set of conditions
Note 1 to entry: It is the minimum load stage at which the failure criterion given in Clause 4 is reached. See
Table 1.
3.3
FZG test condition A10/16,6R/120
test condition where A10 is the particular tooth form of the test gears, according to Tables 2 and 3,
16,6 is the speed at the pitch circle, in metres per second, “R” indicates the reverse direction of rotation
(wheel drives pinion) and 120 is the initial oil temperature in degrees Celsius, from load stage 4 onward
in the oil sump
3.4
failure load stage
2
load stage reached when the sum of the damage to the 16 pinion teeth exceeds 100 mm in total area
damaged
Note 1 to entry: See Clause 4 and Table 1.
3.5
high EP oils
lubricants containing chemical additives appropriate for improving their scuffing load capacity
Note 1 to entry: EP = extreme pressure.
Note 2 to entry: These oils typically exceed the limits of the FZG test according to ISO 14635-1.
4 Failure criteria
Risk of scuffing damage varies with the properties of gear materials, the lubricant used, the surface
roughness of tooth flanks, the sliding velocities and the load. Consequences of scuffing include a
tendency to high levels of dynamic loading owing to an increase of vibrations, which usually leads to
further damage by scuffing, pitting or tooth breakage.
Because of the particular gear design and test loads used, an interference area typically results at the tip
of the pinion and root of the mating wheel. This area is usually about 1 mm in length (profile direction)
on the pinion and across the entire facewidth. Examples of various levels of distress occurring with
this test are shown in Annex A. The effect of the surface distress in these two regions is addressed as
follows.
a) For the purpose of the visual rating for scuffing, the top 1 mm near the tip of the pinion is not
included in the assessment until the damage extends below that level. The rated damage region
is then expressed as the total area scuffed over all 16 pinion teeth (see Figure 1). The failure load
2
stage is reached when the sum of the damage to the 16 pinion teeth exceeds 100 mm in total area
damaged.
b) For a valid test, the wheel shall be visually checked for signs of excessive wear after each pass load
stage, as this can alter the results of the test. If there is evidence of wear in the dedendum of the
wheel, then the gear shall be weighed to the nearest milligram (0,001 g) [see Annex A, Figure A.1 d)].
2
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ISO/FDIS 14635-2:2023(E)
The test may be considered valid only if the loss in mass of the wheel is ≤ 20 mg: if the loss in mass
of the wheel exceeds 20 mg, the test shall not be considered valid.
See Table 1.
Table 1 — Test criteria
Pinion failure area Wheel wear
A Δm Result
2
mm mg
≤ 100 ≤ 20 PASS
a
≤ 100 > 20 INVALID
> 100 Not required FAIL
a
No statement on the scuffing load is possible.
Area in square millimetres
Key
1 exclusion zone (1 mm)
Figure 1 — Schematic of distress rating for pinion
3
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ISO/FDIS 14635-2:2023(E)
5 Brief description of method
5.1 General principle
A set of test gears as defined in Tables 2 and 3 is run with the test lubricant at constant speed for a
fixed number of revolutions using dip-lubrication mode. Loading of the gear teeth is increased in steps
outlined in Table 4. Beginning with load stage 4, the initial oil temperature is controlled between 117 °C
and 123 °C. During the test run of each load stage, the oil temperature is allowed to rise freely. After
load stage 5, the pinion tooth flanks are inspected for surface damage at the end of each load stage and
any changes in appearance are noted. A test is considered complete when either the failure criteria
have been met or when load stage 10 has been completed without meeting the failure criteria.
It is the responsibility of the operator to ensure that all local legislative and statutory requirements are
met.
NOTE It has been assumed by the compilers of this test method that anyone using the method will either
be fully trained and familiar with all normal engineering and laboratory practice, or will be under the direct
supervision of such a person.
WARNING — When the rig is running, there are long loaded shafts and highly stressed test gears
turning at high speed and precaution shall be taken to protect personnel.
Protection from noise is also highly recommended.
5.2 Precision
The precision of the method has been evaluated according to ISO 5725-2 with two reference oils. The
failure load stage of these oils covered the range 5 to 10 inclusive for the step load test.
Values of repeatability, r, and reproducibility, R, as defined in ISO 5725-2, for this test procedures are
r = 1 load stage,
R = 2 load stages.
6 Test materials
6.1 Test gears
A pair of type “A10” test gears with a specification according to Tables 2 and 3 shall be used for testing.
Each pair of test gears may be used twice for testing, using both tooth flanks as load-carrying flanks.
6.2 Cleaning fluid
Petroleum spirit conforming to ASTM D 235 shall be used.
7 Apparatus
7.1 FZG spur-gear test rig
7.1.1 The FZG spur-gear test machine utilizes a recirculating power loop principle, also known as a
four-square configuration, to provide a fixed torque (load) to a pair of precision test gears. A schematic
view of the test rig is shown in Figures 2 and 3. The slave gearbox and the test gearbox are connected
through two torsional shafts. Shaft 1 contains a load coupling used to apply the torque through the use
of known weights, defined in Table 4, hung on the loading arm.
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ISO/FDIS 14635-2:2023(E)
7.1.2 The test gearbox contains heating elements to maintain and control the minimum temperature
of the oil. A temperature sensor located in the side of the test gearbox is used to control the heating
system as required by the test operating con
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