ISO 14635-3:2023
(Main)Gears — FZG test procedures — Part 3: FZG test method A/2,8/50 for relative scuffing load-carrying capacity and wear characteristics of semifluid gear greases
Gears — FZG test procedures — Part 3: FZG test method A/2,8/50 for relative scuffing load-carrying capacity and wear characteristics of semifluid gear greases
This document specifies a test method based on a FZG four-square test machine for determining the relative load-carrying capacity of semi-fluid gear greases defined by the gear surface damage known as scuffing. This method is useful for evaluating the scuffing load capacity potential of semi-fluid gear greases of NLGI classes 0 to 000, typically used with highly stressed gearing for enclosed gear drives. It can only be applied to greases giving a sufficient lubricant flow in the test gear box of the FZG test machine. NOTE The test method is technically equivalent to DIN Fachbericht 74.
Engrenages — Méthodes d'essai FZG — Partie 3: Méthode FZG A/2,8/50 pour évaluer la capacité de charge au grippage et les caractéristiques d'usure des graisses d'engrenages semi-fluides
L'ISO 14635-3:2005 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 de graisses d'engrenages semi-fluides, définie par une détérioration superficielle de l'engrenage appelée grippage. La présente méthode d'essai est utile pour évaluer la capacité de charge potentielle au grippage des graisses d'engrenages semi-fluides 0 à 000 de classes NLGI généralement utilisées pour des boîtes d'entraînement par engrenages soumis à de fortes contraintes.
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INTERNATIONAL ISO
STANDARD 14635-3
Second edition
2023-07
Gears — FZG test procedures —
Part 3:
FZG test method A/2,8/50 for relative
scuffing load-carrying capacity and
wear characteristics of semifluid gear
greases
Engrenages — Méthodes d'essai FZG —
Partie 3: Méthode FZG A/2,8/50 pour évaluer la capacité de charge
au grippage et les caractéristiques d'usure des graisses d'engrenages
semi-fluides
Reference number
ISO 14635-3:2023(E)
© ISO 2023
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ISO 14635-3:2023(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
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ISO 14635-3:2023(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Brief description of method . 4
4.1 General . 4
4.2 Precision . . . 4
5 Test materials . 4
5.1 Test gears . 4
5.2 Cleaning fluid . 4
6 Apparatus . 6
6.1 FZG spur gear test rig . 6
6.2 Heating device . 7
6.3 Revolution counter . 7
6.4 Weight measurement . 7
7 Preparation of apparatus .8
8 Test procedure .9
9 Reporting of results .10
Annex A (informative) Test report .12
Annex B (informative) Additional test procedure for the investigation of extended wear
characteristics of the lubricant .13
Annex C (informative) Checklist for maintenance of FZG gear test rig .15
Bibliography .20
iii
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ISO 14635-3:2023(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 14635-3:2005), 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;
— Table 1, description "pitch line velocity (v )" has been replaced by "circumferential velocity at the
w
pitch line" to harmonize the wording with the ISO 6336-series;
— Table 1, symbol for "specific sliding" has been corrected according to ISO 21771;
— Table 2, grinding: unit for "generating stroke drive" has been corrected;
— Table 3, information on the load coupling has been harmonized with ISO 14635-1;
— Clause 9, the reporting value of the specific weight loss has been corrected.
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 14635-3:2023(E)
Introduction
The types of gear failure which can be influenced by the lubricant are scuffing, low-speed wear and
the gear fatigue phenomena known as micro- and macropitting. In the gear design process, these
types of gear damage are taken into consideration by the use of specific lubricant and service-related
characteristic values. In order to provide a reasonable estimate of performance in service, adequate
2)
lubricant test procedures are required. The FZG test procedures described in ISO 14635-1, ISO 14635-2
and ISO 14635-3 can be regarded as tools for the determination of relative scuffing performance of
lubricants. Characteristic values can be introduced into the load-carrying capacity calculation of gears.
ISO 14635-1 FZG test method, A/8,3/90 for relative scuffing load-carrying capacity of oils, is useful for
the majority of applications in industrial and marine gears. ISO 14635-2, FZG step load test A10/16,
6R/120, is related to the relative scuffing load-carrying capacity of high extreme pressure (EP) oils
as used, e.g. for the lubrication of automotive driveline components such as manual transmissions.
ISO 14635-3 FZG test method A/2,8/50 describes a test procedure for the determination of the relative
scuffing load-carrying capacity and wear characteristics of semi-fluid greases used for enclosed gear
drives. Other FZG test procedures for the determination of low-speed wear, micro- and macropitting
load capacity of gears are currently being considered for standardization. They can be added later to
ISO 14635 as further parts.
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. It is the responsibility of the operator to ensure that all local
legislative and statutory requirements are met.
When the rig is running, there are long-loaded shafts and highly stressed test gears turning at high
speed and precaution needs to be taken to protect personnel. It is also necessary to provide protection
from noise.
2) FZG = Forschungsstelle für Zahnräder und Getriebebau, Technische Universität München (Gear Research
Centre, Technical University, Munich).
v
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INTERNATIONAL STANDARD ISO 14635-3:2023(E)
Gears — FZG test procedures —
Part 3:
FZG test method A/2,8/50 for relative scuffing load-
carrying capacity and wear characteristics of semifluid
gear greases
1 Scope
This document specifies a test method based on a FZG four-square test machine for determining the
relative load-carrying capacity of semi-fluid gear greases defined by the gear surface damage known as
scuffing.
This method is useful for evaluating the scuffing load capacity potential of semi-fluid gear greases of
NLGI classes 0 to 000, typically used with highly stressed gearing for enclosed gear drives. It can only
be applied to greases giving a sufficient lubricant flow in the test gear box of the FZG test machine.
NOTE The test method is technically equivalent to DIN Fachbericht 74.
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 flanks of gear teeth
ISO 6743-6, Lubricants, industrial oils and related products (class L) — Classification — Part 6: Family C
(Gears)
ISO 12925-1, Lubricants, industrial oils and related products (class L) — Family C (Gears) — Part 1:
Specifications for lubricants for enclosed gear systems
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, 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 14635-3:2023(E)
3.1
scuffing
particularly severe form of gear tooth surface damage in which seizure or welding together of areas of
tooth surface occurs, owing to insufficient or breakdown of lubricant film between the contacting tooth
flanks of mating gears, typically caused by a combination of high temperature, high pressure and other
factors
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.
Note 2 to entry: Care should be taken that scuffing does not occur and is polished away before ending the running
time at the higher load stages.
3.2
wear
continuous removal of material occurring when two surfaces roll and slide against one another
3.3
scuffing load-carrying capacity
〈of a lubricant〉 maximum load which can be sustained under a defined set of conditions
3.4
FZG test condition A/2,8/50
test condition where A is the particular tooth form of the test gears, according to Table 1, 2,8 is the
speed at the pitch circle in metres per second (m/s), and 50 is the initial lubricant temperature in
degrees Celsius, from load stage 4 onward in the lubricant sump
3.5
failure load stage
load stage reached when the summed total width of scuffing damage on the active flank area of the 16
pinion teeth exceeds one gear tooth width, i.e. 20 mm
Note 1 to entry: For examples of failure, see Figure 1. Examples of tooth flank changes due to continuous wear
are given in Figure 2. Continuous wear is not a failure criterion for the test.
2
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ISO 14635-3:2023(E)
a) Marks, no failure b) Marks, no failure
c) Approx. 5 mm failure marks d) Approx. 15 mm failure marks
e) 20 mm failure marks f) Approx. 2 mm failure marks
g) Approx. 6 mm failure marks h) 20 mm failure marks
NOTE This figure describes the typical pinion tooth flank changes occurring in FZG scuffing type tests.
Changes in the original surface condition (criss-cross grinding) can be described by their physical appearance.
One and the same type of flank damage can be described in different places in the world by using different
terminology (e.g. “scuffing”, “scoring” and “severe wear”). In order to avoid misinterpretation of the pinion tooth
flank changes occurring during the test, typical examples of non-failure and failure are given.
Figure 1 — FZG A-type gear tooth face changes (flank damages)
3
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ISO 14635-3:2023(E)
a) Light wear b) Medium wear c) Severe wear
Figure 2 — FZG A-type gear tooth flank changes due to continuous wear
4 Brief description of method
4.1 General
A set of test gears as defined in Clause 5, Tables 1 and 2, weighed to the nearest 0,001 g before the test, is
run with the test lubricant at constant speed for a fixed number of revolutions in dip lubrication mode.
Loading of the gear teeth is increased in the steps outlined in Table 3. Beginning with load stage 5, the
initial lubricant temperature is controlled between (50 ± 3) °C. During the test run of each load stage,
the lubricant temperature is allowed to rise freely. After load stage 4, the weight loss of the gear set is
determined to the nearest 0,001 g and the pinion tooth flanks are inspected for surface damage. For
each subsequent load stage, 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 criterion has been met or when load stage 12 is run without meeting the failure criterion. If load
stage 12 is reached without meeting the failure criterion, the gear set weight loss is determined to the
nearest 0,001 g.
4.2 Precision
Values of repeatability, r, and reproducibility, R, as defined in ISO 5725-2, are not valid for this test
procedure. However, experience suggests that similar methods (see ISO 14635-1) are expected to be
representative.
Values for ISO 14635-1 are indicated below.
r = 1 load stage
R = 2 load stages
NOTE The above precision results apply to the range of failure load stages 5 to 12.
5 Test materials
5.1 Test gears
A pair of type “A” gears with a specification according to Table 1 and Table 2 shall be used for testing.
Each pair of test gears may be used twice for testing, using both tooth flanks as load-carrying flanks.
5.2 Cleaning fluid
Petroleum spirits conforming to ASTM D 235 shall be used.
4
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ISO 14635-3:2023(E)
Table 1 — Details of FZG test gears type A
Dimension Symbol Numerical value Unit
Shaft centre distance a 91,5 mm
Effective tooth width b 20 mm
Working pitch diameter pinion d 73,2 mm
w1
wheel d 109,8 mm
w2
Tip diameter pinion d 88,77 mm
a1
wheel d 112,5 mm
a2
Module m 4,5 mm
Number of teeth pinion z 16
1
wheel z 24
2
Profile-shift coefficient pinion x 0,853 2
1
wheel x - 0,50
2
Pressure angle α 20 °
Working pressure angle α 22,5 °
w
Circumferential velocity at the pitch line v 2,8 m/s
w
Addendum engagement pinion e 14,7 mm
a1
wheel e 3,3 mm
a2
Sliding speed at tooth tip pinion v 1,85 m/s
ga1
wheel v 0,42 m/s
ga2
Specific sliding at tooth tip pinion ζ 1,86
E1
wheel ζ 0,34
A2
Specific sliding at tooth root pinion ζ - 0,52
A1
wheel ζ - 5,96
E2
2
a
Hertzian contact pressure p N/mm
14,7⋅ F
c
nt
a
F = normal tooth load in N (see Table 3).
nt
5
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ISO 14635-3:2023(E)
Table 2 — Manufacturing details of FZG test gears type A
Material 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 %
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 %
S = 0,020 % to 0,035 % Cu = max. 0,30 %
Cr = 0,80 % to 1,30 %
Heat treatment 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:
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 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)
Pinion: Ra = 0,35 μm ± 0,1 μm
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
Grinding Maag criss-cross grinding (15° method), 154 1/min of generating stroke
drive
Flank modification None
6 Apparatus
6.1 FZG spur gear test rig
6.1.1 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 3 and 4. 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 3 hung on the loading arm at the 0,5 m notch.
6.1.2 The test gearb
...
ISO/FDIS 14635-3:2023(E)
ISO /TC 60/SC 2
Secretariat: DIN
Date: 2023-01-2502-28
Gears — FZG test procedures —
Part 3:
FZG test method A/2,8/50 for relative scuffing load-carrying
capacity and wear characteristics of semifluid gear greases
Engrenages — Méthodes d'essai FZG —
Partie 3: Méthode FZG A/2,8/50 pour évaluer la capacité de charge au grippage et les caractéristiques
d'usure des graisses d'engrenages semi-fluides
FDIS stage
© ISO 2023 – All rights reserved
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ISO/FDIS 14635-3:2023(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 14635-3:2023(E)
Contents
Foreword . v
Introduction .vi i
Part 3: FZG test method A/2,8/50 for relative scuffing load-carrying capacity and wear characteristics of
semifluid gear greases . 1
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Brief description of method . 5
4.1 General . 5
4.2 Precision . 5
5 Test materials . 5
5.1 Test gears . 5
5.2 Cleaning fluid . 6
6 Apparatus . 9
6.1 FZG spur gear test rig . 9
6.2 Heating device . 9
6.3 Revolution counter . 9
6.4 Weight measurement . 9
7 Preparation of apparatus . 11
8 Test procedure . 12
9 Reporting of results. 13
Annex A (informative) Test report . 15
Annex B (informative) Additional test procedure for the investigation of extended wear characteristics
of the lubricant . 17
Annex C (informative) Checklist for maintenance of FZG gear test rig. 18
Bibliography . 24
Foreword v
Introduction vii
1 Scope 1
2 Normative references 1
3 Terms and definitions 1
4 Brief description of method 4
4.1 General 4
4.2 Precision 4
5 Test materials 4
5.1 Test gears 4
5.2 Cleaning fluid 4
6 Apparatus 6
6.1 FZG spur gear test rig 6
6.2 Heating device 7
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ISO/FDIS 14635-3:2023(E)
6.3 Revolution counter 7
6.4 Weight measurement 7
7 Preparation of apparatus 8
8 Test procedure 9
9 Reporting of results 10
Annex A (informative) Test report 12
Annex B (informative) Additional test procedure for the investigation of extended wear characteristics
of the lubricant 13
B.1 General 13
B.2 Test procedure 13
B.3 Reporting results 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 15
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.3 Approximate time intervals 16
Bibliography 18
iv © ISO 2023 – All rights reserved
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ISO/FDIS 14635-3:2023(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 14635-3:2005), 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);;
— — Table 1,Table 1, description "pitch line velocity (v ))" has been replaced by "circumferential
w
velocity at the pitch line" to harmonize the wording with the ISO 6336-series;
— — Table 1,Table 1, symbol for "specific sliding" has been corrected according to ISO 21771;
1
Cancelled and replaced by ISO 1328-1:2013.
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ISO/FDIS 14635-3:2023(E)
— — Table 2,Table 2, grinding: unit for "generating stroke drive" has been corrected;
— — Table 3,Table 3, information on the load coupling has been harmonized with ISO 14635-1;
— — Clause 9,Clause 9, the reporting value of the specific weight loss has been corrected.
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 14635-3:2023(E)
Introduction
The types of gear failure which can be influenced by the lubricant are scuffing, low-speed wear and the
gear fatigue phenomena known as micro- and macropitting. In the gear design process, these types of
gear damage are taken into consideration by the use of specific lubricant and service-related
characteristic values. In order to provide a reasonable estimate of performance in service, adequate
2
lubricant test procedures are required. The FZG test procedures described in ISO 14635-1, ISO 14635-2
and ISO 14635-3 can be regarded as tools for the determination of relative scuffing performance of
lubricants. Characteristic values can be introduced into the load-carrying capacity calculation of gears.
ISO 14635-1 FZG test method, A/8,3/90 for relative scuffing load-carrying capacity of oils, is useful for
the majority of applications in industrial and marine gears. ISO 14635-2, FZG step load test A10/16,
6R/120, is related to the relative scuffing load-carrying capacity of high EP oils as used, e.g. for the
lubrication of automotive driveline components such as manual transmissions. ISO 14635-3 FZG test
method A/2,8/50 describes a test procedure for the determination of the relative scuffing load-carrying
capacity and wear characteristics of semi-fluid greases used for enclosed gear drives. Other FZG test
procedures for the determination of low-speed wear, micro- and macropitting load capacity of gears are
currently being considered for standardization. They can be added later to ISO 14635 as further parts.
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. It is the responsibility of the operator to ensure that all local legislative and
statutory requirements are met.
When the rig is running, there are long-loaded shafts and highly stressed test gears turning at high speed
and precaution mustneeds to be taken to protect personnel. It is also necessary to provide protection
from noise.
2
FZG = Forschungsstelle für Zahnräder und Getriebebau, Technische Universität München (Gear Research Centre,
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ISO/FDIS 14635-3:2023(E)
Gears — FZG test procedures —
Part 3:
FZG test method A/2,8/50 for relative scuffing load-carrying
capacity and wear characteristics of semifluid gear greasegreases
1 Scope
3
This document specifies a test method based on a FZG four-square test machine for determining the
relative load-carrying capacity of semi-fluid gear greases defined by the gear surface damage known as
scuffing.
This method is useful for evaluating the scuffing load capacity potential of semi-fluid gear greases of NLGI
classes 0 to 000, typically used with highly stressed gearing for enclosed gear drives. It can only be applied
to greases giving a sufficient lubricant flow in the test gear box of the FZG test machine.
NOTE The test method is technically equivalent to DIN Fachbericht 74.
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 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 6743-6, Lubricants, industrial oils and related products (class L) — Classification — Part 6: Family C
(Gears)
ISO 12925-1, Lubricants, industrial oils and related products (class L) — Family C (Gears) — Part 1:
Specifications for lubricants for enclosed gear systems
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, Specification for Mineral Spirits (Petroleum Spirits) (Hydrocarbon Dry Cleaning Solvent)
DIN 51818, Lubricants; consistency classification of lubricating greases; NLGI grades
43 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
3
FZG = Forschungsstelle für Zahnräder und Getriebebau, Technische Universität München (Gear Research Centre,
Technical University, Munich).
4
Cancelled and replaced by ISO 1328-1:2013.
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ISO/FDIS 14635-3:2023(E)
— IEC Electropedia: available at https://www.electropedia.org/
Field Code Changed
3.1
scuffing
particularly severe form of gear tooth surface damage in which seizure or welding together of areas of
tooth surface occurs, owing to insufficient or breakdown of lubricant film between the contacting tooth
flanks of mating gears, typically caused by a combination of high temperature, high pressure and other
factors
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.
Note 2 to entry: Care should be taken that scuffing does not occur and is polished away before ending the running
time at the higher load stages.
3.2
wear
continuous removal of material occurring when two surfaces roll and slide against one another
3.3
scuffing load-carrying capacity
〈of a lubricant〉 maximum load which can be sustained under a defined set of conditions
3.4
FZG test condition A/2,8/50
test condition where A is the particular tooth form of the test gears, according to Table 1, 2.Table 1, 2,8 is
the speed at the pitch circle in metres per second (m/s), and 50 is the initial lubricant temperature in
degrees Celsius, from load stage 4 onward in the lubricant sump
3.5
failure load stage
load stage reached when the summed total width of scuffing damage on the active flank area of the 16
pinion teeth exceeds one gear tooth width, i.e. 20 mm.
Note 1 to entry: For examples of failure, see Figure 1.Figure 1. Examples of tooth flank changes due to continuous
wear are given in Figure 2.Figure 2. Continuous wear is not a failure criteriacriterion for the test.
2 © ISO 2023 – All rights reserved
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ISO/FDIS 14635-3:2023(E)
The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location.
The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location.
a) Marks, no failure b) Marks, no failure
The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location.
The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location.
c) Approx. 5 mm failure marks d) Approx. 15 mm failure marks
© ISO 2023 – All rights reserved 3
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ISO/FDIS 14635-3:2023(E)
The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location.
The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location.
e) 20 mm failure marks f) Approx. 2 mm failure marks
The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location.
The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location.
g) Approx. 6 mm failure marks h) 20 mm failure marks
NOTE This figure describes the typical pinion tooth flank changes occurring in FZG scuffing type tests.
Changes in the original surface condition (criss-cross grinding) can be described by their physical
appearance. One and the same type of flank damage can be described in different places in the world by
using different terminology (e.g. “scuffing”, “scoring” and “severe wear”). In order to avoid
misinterpretation of the pinion tooth flank changes occurring during the test, typical examples of non-
failure and failure are given.
NOTE This figure describes the typical pinion tooth flank changes occurring in FZG scuffing type tests. Changes
in the original surface condition (criss-cross grinding) can be described by their physical appearance. One and the
same type of flank damage can be described in different places in the world by using different terminology (e.g.
“scuffing”, “scoring” and “severe wear”). In order to avoid misinterpretation of the pinion tooth flank changes
occurring during the test, typical examples of non-failure and failure are given.
Figure 1 — FZG A-type gear tooth face changes (flank damages)
4 © ISO 2023 – All rights reserved
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ISO/FDIS 14635-3:2023(E)
The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location. The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location. The linked image cannot be displayed. The file may have been moved, renamed, or deleted. Verify that the link points to the correct file and location.
a) Light wear b) Medium wear c) Severe wear
Figure 2 — FZG A-type gear tooth flank changes due to continuous wear
54 Brief description of method
5.14.1 General
A set of test gears as defined in Clause 5, Tables 1Clause 5, Tables 1 and 2,2, weighed to the nearest
0,001 g before the test, is run with the test lubricant at constant speed for a fixed number of revolutions
in dip lubrication mode. Loading of the gear teeth is increased in the steps outlined in Table 3.Table 3.
Beginning with load stage 5, the initial lubricant temperature is controlled between (50 ± 3) °C. During
the test run of each load stage, the lubricant temperature is allowed to rise freely. After load stage 4, the
weight loss of the gear set is determined to the nearest 0,001 g and the pinion tooth flanks are inspected
for surface damage. For each subsequent load stage, 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 criteriacriterion has been met or when load stage 12 is run without
meeting the failure criteriacriterion. If load stage 12 is reached without meeting the failure
criteriacriterion, the gear set weight loss is determined to the nearest 0,001 g.
5.24.2 Precision
Values of repeatability, r, and reproducibility, R, as defined in ISO 5725-2, are not valid for this test
procedure. However, experience suggests that similar methods (see ISO 14635-1) are expected to be
representative.
Values for ISO 14635-1 are indicated below.
r = 1 load stage
R = 2 load stages
NOTE The above precision results apply to the range of failure load stages 5 to 12.
65 Test materials
6.15.1 Test gears
A pair of type “A” gears with a specification according to Table 1Table 1 and Table 2Table 2 shall be used
for testing. Each pair of test gears may be used twice for testing, utilizingusing both tooth flanks as load-
carrying flanks.
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ISO/FDIS 14635-3:2023(E)
6.25.2 Cleaning fluid
Petroleum spirits conforming to ASTM D 235 shall be used.
6 © ISO 2023 – All rights reserved
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ISO/FDIS 14635-3:2023(E)
Table 1 — Details of FZG test gears type A
Dimension Symbol Numerical value Unit
Shaft centre distance a 91,5 mm
Effective tooth width b 20 mm
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 z 16
1
wheel z2 24
Profile-shift coefficient pinion x 0,853 2
1
wheel x2 - 0,50
Pressure angle α 20 °
Working pressure angle α 22,5 °
w
Circumferential velocity at the pitch line vw 2,8 m/s
Addendum engagement pinion e 14,7 mm
a1
wheel ea2 3,3 mm
Sliding speed at tooth tip pinion vga1 1,85 m/s
wheel v 0,42 m/s
ga2
Specific sliding at tooth tip pinion ζE1 1,86
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 14,7∙�𝐹𝐹 ⋅�𝐹𝐹 P
nt nt
a
Fnt = normal tooth load in N (see Table 3).Table 3).
© ISO 2023 – All rights reserved 7
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ISO/FDIS 14635-3:2023(E)
Table 2 — Manufacturing details of FZG test gears type A
Material 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 %
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 %
Material Case-hardening steel with Cu = max. 0,30 %
Inserted Cells
restricted hardenability to 2/3 of
Merged Cells
the lower scatter band. Material
composition:
C = 0,13 % to 0,20 %
Mo = max. 0,12 %
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 %
S = 0,020 % to 0,035 %
Cu = max. 0,30 %
Cr = 0,80 % to 1,30 %
Cr = 0,80 % to 1,30 %
Heat treatment 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:
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 lt = 4,8 mm,
cut-off length λc = 0,8 mm;
velocity vt = 0,5 mm/s, using a skid.
measured length lt = 4,8 mm,
cut-off length λc = 0,8 mm;
velocity vt = 0,5 mm/s, using a skid.
Average roughness (relating to manufacture batches of a minimum of a 100
gear sets)
Pinion: Ra = 0,35 μm ± 0,1 μm
Gear: Ra = 0,30 μm ± 0,1 μm
Pinion: Ra = 0,35 μm ± 0,1 μm
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
8 © ISO 2023 – All rights reserved
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ISO/FDIS 14635-3:2023(E)
Grinding Maag criss-cross grinding (15° method), 154 r/min of generating stroke
drive
Flank modification None
86 Apparatus
8.16.1 FZG spur gear test rig
6.1.1 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 3 and 4.Figures 3 and 4. 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 3Table 3 hung on the loading arm at the 0,5 m notch.
6.1.2 The test gearbox contains heating elements for maintaining and controlling the minimum
temperature of the lubricant. 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.
2 2
NOTE The heating elements typically have a maximum heat density of 3 W/cm to 5 W/cm for minimizing
thermal degradation of the test lubricant.
6.1.3 The test machine is driven at 500 r/min ± 3 % by an electric motor giving sufficient torque to
carry out the test.
6.1.4 A check list for maintenance of the FZG gear test rig is given for information in Annex B.Annex B.
8.26.2 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.
8.36.3 Revolution counter
A suitable counter shall be used to control the number of revolutions during each load stage of the test.
The counter should be capable of shutting down the test machine at the appropriate number of
revolutio
...
FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 14635-3
ISO/TC 60/SC 2
Gears — FZG test procedures —
Secretariat: DIN
Voting begins on:
Part 3:
2023-03-14
FZG test method A/2,8/50 for relative
Voting terminates on:
scuffing load-carrying capacity and
2023-05-09
wear characteristics of semifluid gear
greases
Engrenages — Méthodes d'essai FZG —
Partie 3: Méthode FZG A/2,8/50 pour évaluer la capacité de charge
au grippage et les caractéristiques d'usure des graisses d'engrenages
semi-fluides
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 14635-3:2023(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 14635-3:2023(E)
FINAL
INTERNATIONAL ISO/FDIS
DRAFT
STANDARD 14635-3
ISO/TC 60/SC 2
Gears — FZG test procedures —
Secretariat: DIN
Voting begins on:
Part 3:
FZG test method A/2,8/50 for relative
Voting terminates on:
scuffing load-carrying capacity and
wear characteristics of semifluid gear
greases
Engrenages — Méthodes d'essai FZG —
Partie 3: Méthode FZG A/2,8/50 pour évaluer la capacité de charge
au grippage et les caractéristiques d'usure des graisses d'engrenages
semi-fluides
COPYRIGHT PROTECTED DOCUMENT
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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.
RECIPIENTS OF THIS DRAFT ARE INVITED TO
ISO copyright office
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OF ANY RELEVANT PATENT RIGHTS OF WHICH
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DOCUMENTATION.
Phone: +41 22 749 01 11
IN ADDITION TO THEIR EVALUATION AS
Reference number
Email: copyright@iso.org
BEING ACCEPTABLE FOR INDUSTRIAL, TECHNO-
ISO/FDIS 14635-3:2023(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 14635-3:2023(E)
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Brief description of method . 4
4.1 General . 4
4.2 Precision . . . 4
5 Test materials . 4
5.1 Test gears . 4
5.2 Cleaning fluid . 4
6 Apparatus . 6
6.1 FZG spur gear test rig . 6
6.2 Heating device . 6
6.3 Revolution counter . 6
6.4 Weight measurement . 7
7 Preparation of apparatus .8
8 Test procedure .9
9 Reporting of results .10
Annex A (informative) Test report.12
Annex B (informative) Additional test procedure for the investigation of extended wear
characteristics of the lubricant .13
Annex C (informative) Checklist for maintenance of FZG gear test rig .15
Bibliography .20
iii
© ISO 2023 – All rights reserved
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ISO/FDIS 14635-3:2023(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 14635-3:2005), 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;
— Table 1, description "pitch line velocity (v )" has been replaced by "circumferential velocity at the
w
pitch line" to harmonize the wording with the ISO 6336-series;
— Table 1, symbol for "specific sliding" has been corrected according to ISO 21771;
— Table 2, grinding: unit for "generating stroke drive" has been corrected;
— Table 3, information on the load coupling has been harmonized with ISO 14635-1;
— Clause 9, the reporting value of the specific weight loss has been corrected.
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 14635-3:2023(E)
Introduction
The types of gear failure which can be influenced by the lubricant are scuffing, low-speed wear and
the gear fatigue phenomena known as micro- and macropitting. In the gear design process, these
types of gear damage are taken into consideration by the use of specific lubricant and service-related
characteristic values. In order to provide a reasonable estimate of performance in service, adequate
2)
lubricant test procedures are required. The FZG test procedures described in ISO 14635-1, ISO 14635-2
and ISO 14635-3 can be regarded as tools for the determination of relative scuffing performance of
lubricants. Characteristic values can be introduced into the load-carrying capacity calculation of gears.
ISO 14635-1 FZG test method, A/8,3/90 for relative scuffing load-carrying capacity of oils, is useful for
the majority of applications in industrial and marine gears. ISO 14635-2, FZG step load test A10/16,
6R/120, is related to the relative scuffing load-carrying capacity of high EP oils as used, e.g. for the
lubrication of automotive driveline components such as manual transmissions. ISO 14635-3 FZG test
method A/2,8/50 describes a test procedure for the determination of the relative scuffing load-carrying
capacity and wear characteristics of semi-fluid greases used for enclosed gear drives. Other FZG test
procedures for the determination of low-speed wear, micro- and macropitting load capacity of gears
are currently being considered for standardization. They can be added later to ISO 14635 as further
parts.
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. It is the responsibility of the operator to ensure that all local
legislative and statutory requirements are met.
When the rig is running, there are long-loaded shafts and highly stressed test gears turning at high
speed and precaution needs to be taken to protect personnel. It is also necessary to provide protection
from noise.
2) FZG = Forschungsstelle für Zahnräder und Getriebebau, Technische Universität München (Gear Research
Centre,
v
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FINAL DRAFT INTERNATIONAL STANDARD ISO/FDIS 14635-3:2023(E)
Gears — FZG test procedures —
Part 3:
FZG test method A/2,8/50 for relative scuffing load-
carrying capacity and wear characteristics of semifluid
gear greases
1 Scope
This document specifies a test method based on a FZG four-square test machine for determining the
relative load-carrying capacity of semi-fluid gear greases defined by the gear surface damage known as
scuffing.
This method is useful for evaluating the scuffing load capacity potential of semi-fluid gear greases of
NLGI classes 0 to 000, typically used with highly stressed gearing for enclosed gear drives. It can only
be applied to greases giving a sufficient lubricant flow in the test gear box of the FZG test machine.
NOTE The test method is technically equivalent to DIN Fachbericht 74.
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 flanks of gear teeth
ISO 6743-6, Lubricants, industrial oils and related products (class L) — Classification — Part 6: Family C
(Gears)
ISO 12925-1, Lubricants, industrial oils and related products (class L) — Family C (Gears) — Part 1:
Specifications for lubricants for enclosed gear systems
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, 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
© ISO 2023 – All rights reserved
---------------------- Page: 6 ----------------------
ISO/FDIS 14635-3:2023(E)
3.1
scuffing
particularly severe form of gear tooth surface damage in which seizure or welding together of areas of
tooth surface occurs, owing to insufficient or breakdown of lubricant film between the contacting tooth
flanks of mating gears, typically caused by a combination of high temperature, high pressure and other
factors
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.
Note 2 to entry: Care should be taken that scuffing does not occur and is polished away before ending the running
time at the higher load stages.
3.2
wear
continuous removal of material occurring when two surfaces roll and slide against one another
3.3
scuffing load-carrying capacity
〈of a lubricant〉 maximum load which can be sustained under a defined set of conditions
3.4
FZG test condition A/2,8/50
test condition where A is the particular tooth form of the test gears, according to Table 1, 2,8 is the
speed at the pitch circle in metres per second (m/s), and 50 is the initial lubricant temperature in
degrees Celsius, from load stage 4 onward in the lubricant sump
3.5
failure load stage
load stage reached when the summed total width of scuffing damage on the active flank area of the 16
pinion teeth exceeds one gear tooth width, i.e. 20 mm
Note 1 to entry: For examples of failure, see Figure 1. Examples of tooth flank changes due to continuous wear
are given in Figure 2. Continuous wear is not a failure criterion for the test.
a) Marks, no failure b) Marks, no failure
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ISO/FDIS 14635-3:2023(E)
c) Approx. 5 mm failure marks d) Approx. 15 mm failure marks
e) 20 mm failure marks f) Approx. 2 mm failure marks
g) Approx. 6 mm failure marks h) 20 mm failure marks
NOTE This figure describes the typical pinion tooth flank changes occurring in FZG scuffing type
tests. Changes in the original surface condition (criss-cross grinding) can be described by their phys-
ical appearance. One and the same type of flank damage can be described in different places in the
world by using different terminology (e.g. “scuffing”, “scoring” and “severe wear”). In order to avoid
misinterpretation of the pinion tooth flank changes occurring during the test, typical examples of
non-failure and failure are given.
Figure 1 — FZG A-type gear tooth face changes (flank damages)
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ISO/FDIS 14635-3:2023(E)
a) Light wear b) Medium wear c) Severe wear
Figure 2 — FZG A-type gear tooth flank changes due to continuous wear
4 Brief description of method
4.1 General
A set of test gears as defined in Clause 5, Tables 1 and 2, weighed to the nearest 0,001 g before the test, is
run with the test lubricant at constant speed for a fixed number of revolutions in dip lubrication mode.
Loading of the gear teeth is increased in the steps outlined in Table 3. Beginning with load stage 5, the
initial lubricant temperature is controlled between (50 ± 3) °C. During the test run of each load stage,
the lubricant temperature is allowed to rise freely. After load stage 4, the weight loss of the gear set is
determined to the nearest 0,001 g and the pinion tooth flanks are inspected for surface damage. For
each subsequent load stage, 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 criterion has been met or when load stage 12 is run without meeting the failure criterion. If load
stage 12 is reached without meeting the failure criterion, the gear set weight loss is determined to the
nearest 0,001 g.
4.2 Precision
Values of repeatability, r, and reproducibility, R, as defined in ISO 5725-2, are not valid for this test
procedure. However, experience suggests that similar methods (see ISO 14635-1) are expected to be
representative.
Values for ISO 14635-1 are indicated below.
r = 1 load stage
R = 2 load stages
NOTE The above precision results apply to the range of failure load stages 5 to 12.
5 Test materials
5.1 Test gears
A pair of type “A” gears with a specification according to Table 1 and Table 2 shall be used for testing.
Each pair of test gears may be used twice for testing, using both tooth flanks as load-carrying flanks.
5.2 Cleaning fluid
Petroleum spirits conforming to ASTM D 235 shall be used.
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ISO/FDIS 14635-3:2023(E)
Table 1 — Details of FZG test gears type A
Dimension Symbol Numerical value Unit
Shaft centre distance a 91,5 mm
Effective tooth width b 20 mm
Working pitch diameter pinion d 73,2 mm
w1
wheel d 109,8 mm
w2
Tip diameter pinion d 88,77 mm
a1
wheel d 112,5 mm
a2
Module m 4,5 mm
Number of teeth pinion z 16
1
wheel z 24
2
Profile-shift coefficient pinion x 0,853 2
1
wheel x - 0,50
2
Pressure angle α 20 °
Working pressure angle α 22,5 °
w
Circumferential velocity at the pitch line v 2,8 m/s
w
Addendum engagement pinion e 14,7 mm
a1
wheel e 3,3 mm
a2
Sliding speed at tooth tip pinion v 1,85 m/s
ga1
wheel v 0,42 m/s
ga2
Specific sliding at tooth tip pinion ζ 1,86
E1
wheel ζ 0,34
A2
Specific sliding at tooth root pinion ζ - 0,52
A1
wheel ζ - 5,96
E2
2
a
Hertzian contact pressure p N/mm
14,7⋅ F
c
nt
a
F = normal tooth load in N (see Table 3).
nt
Table 2 — Manufacturing details of FZG test gears type A
Material 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 %
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 %
S = 0,020 % to 0,035 % Cu = max. 0,30 %
Cr = 0,80 % to 1,30 %
Heat treatment 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:
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
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ISO/FDIS 14635-3:2023(E)
TTabablele 2 2 ((ccoonnttiinnueuedd))
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 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)
Pinion: Ra = 0,35 μm ± 0,1 μm
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
Grinding Maag criss-cross grinding (15° method), 154 r/min of generating stroke
drive
Flank modification None
6 Apparatus
6.1 FZG spur gear test rig
6.1.1 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 3 and 4. 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 3 hung on the loading arm at the 0,5 m notch.
6.1.2 The test gearbox contains heating elements for maintaining and controlling the minimum
temperature of the lubricant. 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.
2 2
NOTE The heating elements typically have a maximum heat density of 3 W/cm to 5 W/cm for minimizing
thermal degradation of the test lubricant.
6.1.3 The test machine is driven at 500 r/min ±3 % by an electric motor giving sufficient torque to
carry out the test.
6.1.4 A check list for maintenance of the FZG gear test rig is given for information in Annex B.
6.2 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.
6.3 Revolution counter
A suitable counter shall be used to control the number of revolutions during each load stage of the
test. The counter should be capable of shutting down the test machine at the appropriate number of
revolutions of the pinion.
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ISO/FDIS 14635-3:2023(E)
6.4 Weight measurement
A suitable balance of 1,3 kg min. weight capacity with reading to the nearest 0,001 g shall be used to
determine the weight of the test wheel.
Key
1 test wheel 6 drive motor
2 view A 7 load coupling
3 test pinion 8 shaft 1 (two pieces)
4 torque measuring coupling 9 slave gears
5 shaft 2 (torsion shaft) 10 torsion shaft outer tube
Figure 3 — Schematic section of the FZG gear test machine
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ISO/FDIS 14635-3:2023(E)
Key
1 test wheel
2 test pinion
3 active tooth flank
Figure 4 — Mounting of the FZG test gears type A (view A of Figure 3)
7 Preparation of apparatus
7.1 Flush the test gear case twice with petroleum spirit, ensuring that the bearings are clean of any
previous lubricant, and air dry with a water-free air line.
If the previous lubricant tested contained any solid lubricant particles such as graphite or MoS , the test
2
machine shall be completely disassembled and cleaned carefully.
7.2 Mark the test pinion and test wheel as shown in Figure 4.
7.3 Clean the test gears in petroleum spirit and air dry. After cleaning, use gloves to handle gears.
7.4 With the unaided eye, inspect the gears for corrosion, rust or any other damage. Reject the gears
if so damaged.
7.5 Weigh the pinion and the wheel each to the nearest 0,001 g.
7.6 Heat both the gears to between 60 °C and max. 80 °C using an appropriate heating device.
7.7 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. Ensure the test pinion and test
wheel are correctly aligned, i.e. no offset. Also ensure that the locating marks are positioned as shown
in Figure 4.
7.8 Switch drain cock in the CLOSED position.
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ISO/FDIS 14635-3:2023(E)
7.9 Fill the test gear box with a nominal 1,25 l of test lubricant.
7.10 Plug in the heater.
7.11 Fit top cover to the test gear box.
7.12 Apply load stage 12 using the 0,5 m radius position (see Table 3) for 2 min to 3 min, without
running the motor, in order to bring the test gears and the clearances in the system into correct working
position.
8 Test procedure
8.1 Apply load corresponding to stage 1 (see Table 3). Start the motor, switch on the heater and run
for 21 700 revolutions of the motor (approximately 45 min), according to Table 4.
8.2 Stop the motor and apply the load for stage 2. Restart and run according to Table 4 for 21 700
revolutions of the motor. Repeat for load stage 3 and load stage 4.
8.3 At the end of load stage 4, remove the lubricant from the unit and save. Visually inspect the pinion
for damage. Record the tooth condition, using the examples in Figure 1 as a guide.
8.4 Disassemble and weigh the pinion and the wheel, each to the nearest 0,001 g.
8.5 Re-assemble the test gear box according to 7.7 to 7.12. Ensure that the pinion teeth are immersed
in the test lubricant. If needed, add a small amount of the same lubricant.
8.6 Before starting the next higher load stage, ensure that the lubricant temperature in the test
gearbox is (50 ± 3) °C. This can be accomplished through the use of cooling water or by using the
procedure given in 8.8.2. When the temperature reaches (50 ± 3) °C turn off the cooling water and
continue the test. The cooling water shall be turned off during the test.
8.7 Continue the test with the next load stages (see Table 3). Visually inspect all the pinion teeth after
each stage, ensuring the lubricant temperature is (50 ± 3) °C before applying the next higher load stage.
Continue the test until the failure load stage according to 3.5 is reached. If the failure criterion is not
reached, terminate the test at the end of load stage 12.
8.8 Determine the failure load stage by summing the flank damages on all the test pinion teeth.
8.8.1 If the failure criterion is not reached, continue the test with the next higher load stage up to a
maximum of load stage 12.
8.8.2 If the machine is shut down at the end of a load stage beyond load stage 4 for a period of time
before the test is completed and the test oil temperature drops below 47 °C, carry out the following
before resuming the test.
a) Apply load stage 1, start the motor, switch on the heater and run until the lubricant temperature
reaches (50 ± 3) °C.
b) Stop the motor, switch off the heater and apply the next load stage in the text sequence. Continue
the test according to 8.6 and 8.7, respectively.
8.9 If the test is terminated after load stage 12 without reaching the failure criterion, weigh the test
pinion and the test wheel each to the nearest 0,001 g and determine the weight losses during the test.
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