ISO 14635-1:2023

Gears - FZG test procedures - Part 1: FZG test method A/8,3/90 for relative scuffing load-carrying capacity of oils

This document specifies a test method based on a FZG four-square test machine to determine the relative load-carrying capacity of lubricating oils defined by the gear-surface damage known as scuffing. High surface temperatures due to high surface pressures and sliding velocities can initiate the breakdown of the lubricant films. This test method can be used to assess such lubricant breakdown under defined conditions of temperature, high sliding velocity and stepwise increased load. NOTE This method is technically equivalent to ASTM D 5182-19 and CEC L-07-A-95.

Engrenages — Méthodes d'essai FZG — Partie 1: Méthode FZG A/8,3/90 pour évaluer la capacité de charge au grippage des huiles

La présente partie de l'ISO 14635 spécifie une méthode d'essai fondée sur une machine d'essai FZG 2_ ayant pour but de déterminer la capacité de charge d'huiles lubrifiantes, de manière comparative, en ce qui concerne la résistance au grippage. Les températures superficielles élevées, dues à des pressions de contact et des vitesses de glissement élevées, peuvent entraîner la rupture du film lubrifiant. La présente méthode d'essai peut être utilisée pour évaluer des ruptures de lubrifiant sous des conditions définies de température, de vitesses de glissement élevées et de charge augmentant par palier. NOTE La présente méthode est techniquement équivalente aux normes ASTM D 5182 97, DIN 51354-1 et DIN 51354-2, IP 334/90 et CEC L-07-A-95.

General Information

• Status: Published
• Publication Date: 05-Jul-2023
• ICS: 21.200 - Gears
• Technical Committee: ISO/TC 60/SC 2 - Gear capacity calculation
• Drafting Committee: ISO/TC 60/SC 2 - Gear capacity calculation
• Current Stage: 6060 - International Standard published
• Start Date: 06-Jul-2023
• Due Date: 17-May-2024
• Completion Date: 06-Jul-2023

Relations

• Revises: ISO 14635-1:2000 - Gears - FZG test procedures - Part 1: FZG test method A/8,3/90 for relative scuffing load-carrying capacity of oils
• Effective Date: 19-Nov-2022

Overview

ISO 14635-1:2023 specifies the FZG test method A/8,3/90 for evaluating the relative scuffing load‑carrying capacity of lubricating oils. Using an FZG four‑square test machine, this standard defines a repeatable procedure to assess lubricant breakdown under high surface pressures, high sliding velocities and controlled temperatures that can cause gear-surface scuffing. The method is technically equivalent to ASTM D5182-19 and CEC L-07-A-95.

Key topics and requirements

• Test machine & setup: FZG four‑square (spur‑gear) rig, dip‑lubrication mode, heating device and revolution counter.
• Test condition A/8,3/90: Type A gear geometry; circumferential velocity at pitch line v = 8.3 m/s; initial oil temperature 90 °C (from load stage 5 onward).
• Test gears: Type “A” gears (module 4.5, pinion z = 16, wheel z = 24, effective tooth width = 20 mm), case‑hardened steel with specified composition, case depth 0.6–0.9 mm, surface hardness 60–62 HRC, accuracy grade Q5 (ISO 1328-1:1995).
• Load procedure: Stepwise increased load stages (see Table 3 in the standard); inspections of pinion tooth flanks after load stage 4 and after each subsequent stage.
• Failure criterion: Failure load stage is reached when the summed scuffing width on the 16 pinion teeth exceeds one gear‑tooth width (20 mm).
• Test materials & cleaning: Use petroleum spirit conforming to ASTM D235 for cleaning.
• Precision: Evaluated per ISO 5725-2. Repeatability r = 1 load stage; reproducibility R = 2 load stages (for failure stages 5–12).
• Safety: Warnings about rotating, loaded shafts and noise - operators must follow local safety regulations.

Applications and users

ISO 14635-1:2023 is intended for:

• Lubricant manufacturers validating anti‑scuffing and extreme‑pressure properties of oils.
• Tribologists and test laboratories performing standardized gear lubrication tests.
• Gear designers and OEMs (industrial, marine, and heavy machinery) who need lubricant characteristic values for gear load‑carrying capacity calculations.
• Quality and compliance teams comparing oil performance across standardized test methods (equivalent to ASTM/CEC methods).

Practical uses include oil product development, specification of lubricants for gearboxes, comparative benchmarking, and supporting gear life and reliability assessments.

Related standards

• ISO 14635 series (other parts for specific gear damage modes)
• ISO 1328-1 (gear accuracy)
• ISO 21920-2 (surface texture)
• ISO 18265 (hardness conversion)
• ASTM D5182-19; CEC L-07-A-95 (equivalent scuffing tests)
• ASTM D235 (cleaning fluid)

Keywords: ISO 14635-1, FZG test, A/8,3/90, scuffing, load-carrying capacity, lubricating oils, four-square test, gear scuffing, ASTM D5182.

Standards Content (Sample)

INTERNATIONAL ISO
STANDARD 14635-1
Second edition
2023-07
Gears — FZG test procedures —
Part 1:
FZG test method A/8,3/90 for relative
scuffing load-carrying capacity of oils
Engrenages — Méthodes d'essai FZG —
Partie 1: Méthode FZG A/8,3/90 pour évaluer la capacité de charge
au grippage des huiles
Reference number
© 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: [phone]
Email: [e-mail]
Website: www.iso.org
Published in Switzerland
ii
Contents Page
Foreword .iv
Introduction .v
1 Scope . 1
2 Normative references . 1
3 Terms and definitions . 1
4 Brief description of method . 2
4.1 General principle . 2
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 . 8
6.3 Revolution counter . 8
7 Preparation of apparatus .8
8 Test procedure .9
9 Reporting of results .10
Annex A (informative) Typical FZG test report sheet .12
Annex B (informative) Checklist for maintenance of FZG gear test rig .13
Bibliography .18
iii
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 14635-1:2000), 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 5.2, wording harmonized with the ISO 14635 series;
— Table 1, description "pitch line circumferential speed (v )" has been replaced by "circumferential
w
velocity at the pitch line" to harmonize the wording with the ISO 6336 series;
— Table 4, insertion of lines "Direction of rotation" and "Test lubrication volume" to conform to the
information in the ISO 14635 series.
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
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 described in this document, ISO 14635-2 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 this
document is typical for the majority of applications in industrial and marine gears. ISO 14635-2 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
INTERNATIONAL STANDARD ISO 14635-1:2023(E)
Gears — FZG test procedures —
Part 1:
FZG test method A/8,3/90 for relative scuffing load-
carrying capacity of 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 lubricating oils defined by the gear-surface damage known as
scuffing. High surface temperatures due to high surface pressures and sliding velocities can initiate
the breakdown of the lubricant films. This test method can be used to assess such lubricant breakdown
under defined conditions of temperature, high sliding velocity and stepwise increased load.
NOTE This method is technically equivalent to ASTM D 5182-19 and CEC L-07-A-95.
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 : Definitions and allowable values of
deviations relevant to flanks of gear teeth
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/
3.1
scuffing load-carrying capacity
(of a lubricant) maximum load which can be sustained under a defined set of conditions
Note 1 to entry: For examples of failure see Figure 1.
3) Cancelled and replaced by ISO 1328-1:2013.
Note 2 to entry: Scuffing is a particularly severe form of damage to the gear-tooth surface in which seizure or
welding together of areas of tooth surface occur, due to absence or breakdown of a lubricant film between the
contacting tooth flanks of mating gears, typically caused by high temperature and high pressure. Scuffing is
most likely when surface velocities are high. Scuffing 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 3 to entry: 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 of high-speed
gears include a tendency to high levels of dynamic loading due to increase of vibrations, which usually leads to
further damage by scuffing, pitting or tooth breakage.
3.2
FZG test condition A/8,3/90
test condition where A is the particular tooth form of the test gears, according to Table 1, 8,3 is the
speed at the pitch circle, in metres per second, and 90 is the initial oil temperature in degrees Celsius,
from load stage 5 and onward in the oil sump
Note 1 to entry: The direction of the rotation of the gears is shown in Figure 3.
3.3
failure load stage
load stage in which 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: Examples of flank damages for the purpose of the test method are shown in Figure 1.
4 Brief description of method
4.1 General principle
A set of test gears as defined in Clause 5, Tables 1 and 2, 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 3. Beginning with load stage 5, the initial oil temperature is controlled between
(90 ± 3) °C. During the test run of each load stage, the oil temperature is allowed to rise freely. After
load stage 4, 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 has
been met or when load stage 12 is run 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 precautions shall be taken to protect personnel.
WARNING — Protection from noise is also highly recommended.
a) No failure marks b) No failure marks
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 1 This figure describes the typical pinion tooth flank changes occurring in FZG 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 2 The colours represented in the electronic file of this document can be neither viewed nor printed
as true representations. Only copies of this document printed by ISO can be guaranteed to represent the true
colours.
Figure 1 — FZG A-type gear-tooth face changes (flank damages)
4.2 Precision
The precision of the method has been evaluated according to ISO 5725-2 with three oils (two reference
oils and one oil from the market). The failure load stage of these oils covered the range 5 to 12 inclusive.
Values of repeatability, r, and reproducibility, R, as defined in ISO 5725-2, for this test procedure are:
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 Tables 1 and 2 shall be used for testing. Each
pair of test gears may be utilized twice for testing, using both tooth flanks as load-carrying flanks.
5.2 Cleaning fluid
Petroleum spirit conforming to ASTM D 235 shall be used.
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
wheel z 24
Profile-shift coefficient pinion x 0,853 2
wheel x - 0,50
Pressure angle α 20 °
Working pressure angle α 22,5 °
w
Circumferential velocity at the pitch line v 8,3 m/s
w
Addendum engagement pinion e 14,7 mm
a1
wheel e 3,3 mm
a2
Sliding speed at tooth tip pinion v 5,56 m/s
ga1
wheel v 1,25 m/s
ga2
Specific sliding at tooth tip pinion ζ 0,86
E1
wheel ζ 0,34
A2
Specific sliding at tooth root pinion ζ - 0,52
A1
wheel ζ - 5,96
E2
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
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 %
Material
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 %
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
...