ISO 14635-3:2023

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 2023
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ii
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
Foreword
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electrotechnical standardization.
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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
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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— replacement of ISO 4287 which has been withdrawn and replaced by ISO 21920-2;
— replacement of ISO 4964 which has been withdrawn and similar information can be found in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— replacement of some bibliography entries which were withdrawn, and changes from dated to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— Table 1, description "pitch line velocity (v )" has been replaced by "circumferential velocity at the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
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
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.
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
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)
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.
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 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
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
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
...