ISO 14635-2:2023

INTERNATIONAL ISO
STANDARD 14635-2
Second edition
2023-07
Gears — FZG test procedures —
Part 2:
FZG step load test A10/16, 6R/120
for relative scuffing load-carrying
capacity of high EP oils
Engrenages — Méthodes d'essai FZG —
Partie 2: Méthode FZG A10/16, 6R/120 à paliers de charge pour
évaluer la capacité de charge au grippage des huiles à valeurs EP
élevées
Reference number
© ISO 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 Failure criteria .2
5 Brief description of method . 4
5.1 General principle . 4
5.2 Precision . . . 4
6 Test materials . 4
6.1 Test gears . 4
6.2 Cleaning fluid . 4
7 Apparatus . 4
7.1 FZG spur-gear test rig. 4
7.2 Heating device . 6
7.3 Revolution counter . 6
7.4 Balance . 6
8 Preparation of apparatus .8
9 Test procedure .8
10 Reporting of results .9
Annex A (informative) FZG A10-type gear tooth face changes (flank damages) .11
Annex B (informative) Typical FZG test report sheet .13
Annex C (informative) Checklist for maintenance of FZG gear test rig .14
Bibliography .19
iii
Foreword
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electrotechnical standardization.
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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 14635-2:2004), of which it constitutes a
minor revision. The changes are as follows:
1)
— ISO 1328-1:1995 has been dated as this document uses accuracy grade which is numerically
different than tolerance class in ISO 1328-1:2013;
— replacement of ISO 4287 which has been withdrawn and replaced by ISO 21920-2;
— replacement of ISO 4964 which has been withdrawn and similar information can be found in
ISO 18265;
— replacement of some bibliography entries which were withdrawn, and changes from dated to
undated references;
— subclause 6.2, wording harmonized with the ISO 14635 series;
— Table 2, description "pitch diameter circumferential speed (v )" has been replaced by "circumferential
w
velocity at the pitch line" to harmonize the wording with the ISO 6336 series;
— Table 5, insertion of line "Test lubrication volume" to conform to the information in the ISO 14635
series;
— Figure A.1, addition of the figure title.
A list of all parts in the ISO 14635 series can be found on the ISO website.
Any feedback or questions on this document should be directed to the user’s national standards body. A
complete listing of these bodies can be found at www.iso.org/members.html.
1) Cancelled and replaced by ISO 1328-1:2013.
iv
Introduction
The types of gear failures which can be influenced by the lubricant in use are scuffing, low-speed
wear and the gear-surface fatigue phenomena known as micro- and macropitting. In the gear design
process, these gear damages are taken into consideration by the use of specific lubricant and service-
related characteristic values. For an accurate, field-related selection of these values, adequate lubricant
2)
test procedures are required. The FZG test procedures specified in this document, ISO 14635-1 and
ISO 14635-3 can be regarded as tools for the determination of the lubricant-related characteristic
values to be introduced into the load-carrying capacity calculation of gears.
FZG test method A/8,3/90 for the relative scuffing load-carrying capacity of oils described in
ISO 14635-1 is typical for the majority of applications in industrial and marine gears. This document
is related to the relative scuffing load-carrying capacity of oils of very high extreme pressure (EP)
properties, as used for the lubrication of automotive driveline components. Other FZG test procedures
for the determination of low-speed wear, micro- and macropitting load-carrying capacity of gears are
intended to be added to the ISO 14635 series as further parts.
2) FZG = Forschungsstelle für Zahnräder und Getriebebau, Technische Universität München (Gear Research
Centre, Technical University, Munich).
v
INTERNATIONAL STANDARD ISO 14635-2:2023(E)
Gears — FZG test procedures —
Part 2:
FZG step load test A10/16, 6R/120 for relative scuffing
load-carrying capacity of high EP oils
1 Scope
This document specifies a test method based on a FZG four-square test machine to determine the
relative load-carrying capacity of high EP oils defined by the gear surface damage known as scuffing.
This test method is useful for evaluating the scuffing load capacity potential of oils typically used with
highly stressed cylindrical gearing found in many vehicle and stationary applications. It is not suitable
for establishing the scuffing load capacity potential of oils used in highly loaded hypoid bevel gearing
applications, for which purpose other methods are available in the industry.
NOTE This method is technically equivalent to CEC L-84-02.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
3)
ISO 1328-1:1995 , Cylindrical gears — ISO system of accuracy — Part 1: Definitions and allowable values
of deviations relevant to corresponding flanks of gear teeth
ISO 14635-1, Gears — FZG test procedures — Part 1: FZG test method A/8,3/90 for relative scuffing load-
carrying capacity of oils
ISO 18265, Metallic materials — Conversion of hardness values
ISO 21920-2, Geometrical product specifications (GPS) — Surface texture: Profile — Part 2: Terms,
definitions and surface texture parameters
ASTM D 235, Standard Specification for Mineral Spirits (Petroleum Spirits) (Hydrocarbon Dry Cleaning
Solvent)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminology databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https:// www .iso .org/ obp
— IEC Electropedia: available at https:// www .electropedia .org/
3) Cancelled and replaced by ISO 1328-1:2013.
3.1
scuffing
particularly severe form of gear tooth surface damage in which seizure or welding together of areas
of tooth surface occur, owing to the absence or breakdown of a lubricant film between the contacting
tooth flanks of mating gears, typically caused by high temperature and high pressure
Note 1 to entry: Scuffing is most likely when surface velocities are high. It can also occur at relatively low sliding
velocities when tooth surface pressures are high enough either generally or, because of uneven surface geometry
and loading, in discrete areas.
3.2
scuffing load-carrying capacity
〈of a lubricant〉 maximum load which can be sustained under a defined set of conditions
Note 1 to entry: It is the minimum load stage at which the failure criterion given in Clause 4 is reached. See
Table 1.
3.3
FZG test condition A10/16,6R/120
test condition where A10 is the particular tooth form of the test gears, according to Tables 2 and 3,
16,6 is the speed at the pitch circle, in metres per second, “R” indicates the reverse direction of rotation
(wheel drives pinion) and 120 is the initial oil temperature in degrees Celsius, from load stage 4 onward
in the oil sump
3.4
failure load stage
load stage reached when the sum of the damage to the 16 pinion teeth exceeds 100 mm in total area
damaged
Note 1 to entry: See Clause 4 and Table 1.
3.5
high EP oils
lubricants containing chemical additives appropriate for improving their scuffing load capacity
Note 1 to entry: EP = extreme pressure.
Note 2 to entry: These oils typically exceed the limits of the FZG test according to ISO 14635-1.
4 Failure criteria
Risk of scuffing damage varies with the properties of gear materials, the lubricant used, the surface
roughness of tooth flanks, the sliding velocities and the load. Consequences of scuffing include a
tendency to high levels of dynamic loading owing to an increase of vibrations, which usually leads to
further damage by scuffing, pitting or tooth breakage.
Because of the particular gear design and test loads used, an interference area typically results at the tip
of the pinion and root of the mating wheel. This area is usually about 1 mm in length (profile direction)
on the pinion and across the entire facewidth. Examples of various levels of distress occurring with
this test are shown in Annex A. The effect of the surface distress in these two regions is addressed as
follows.
a) For the purpose of the visual rating for scuffing, the top 1 mm near the tip of the pinion is not
included in the assessment until the damage extends below that level. The rated damage region
is then expressed as the total area scuffed over all 16 pinion teeth (see Figure 1). The failure load
stage is reached when the sum of the damage to the 16 pinion teeth exceeds 100 mm in total area
damaged.
b) For a valid test, the wheel shall be visually checked for signs of excessive wear after each pass load
stage, as this can alter the results of the test. If there is evidence of wear in the dedendum of the
wheel, then the gear shall be weighed to the nearest milligram (0,001 g) [see Annex A, Figure A.1 d)].
The test may be considered valid only if the loss in mass of the wheel is ≤ 20 mg: if the loss in mass
of the wheel exceeds 20 mg, the test shall not be considered valid.
See Table 1.
Table 1 — Test criteria
Pinion failure area Wheel wear
A Δm Result
mm mg
≤ 100 ≤ 20 PASS
a
≤ 100 > 20 INVALID
> 100 Not required FAIL
a
No statement on the scuffing load is possible.
Area in square millimetres
Key
1 exclusion zone (1 mm)
Figure 1 — Schematic of distress rating for pinion
5 Brief description of method
5.1 General principle
A set of test gears as defined in Tables 2 and 3 is run with the test lubricant at constant speed for a
fixed number of revolutions using dip-lubrication mode. Loading of the gear teeth is increased in steps
outlined in Table 4. Beginning with load stage 4, the initial oil temperature is controlled between 117 °C
and 123 °C. During the test run of each load stage, the oil temperature is allowed to rise freely. After
load stage 5, the pinion tooth flanks are inspected for surface damage at the end of each load stage and
any changes in appearance are noted. A test is considered complete when either the failure criteria
have been met or when load stage 10 has been completed without meeting the failure criteria.
It is the responsibility of the operator to ensure that all local legislative and statutory requirements are
met.
NOTE It has been assumed by the compilers of this test method that anyone using the method will either
be fully trained and familiar with all normal engineering and laboratory practice, or will be under the direct
supervision of such a person.
WARNING — When the rig is running, there are long loaded shafts and highly stressed test gears
turning at high speed and precaution shall be taken to protect personnel.
WARNING — Protection from noise is also highly recommended.
5.2 Precision
The precision of the method has been evaluated according to ISO 5725-2 with two reference oils. The
failure load stage of these oils covered the range 5 to 10 inclusive for the step load test.
Values of repeatability, r, and reproducibility, R, as defined in ISO 5725-2, for this test procedures are
r = 1 load stage,
R = 2 load stages.
6 Test materials
6.1 Test gears
A pair of type “A10” test gears with a specification according to Tables 2 and 3 shall be used for testing.
Each pair of test gears may be utilized twice for testing, using both tooth flanks as load-carrying flanks.
6.2 Cleaning fluid
Petroleum spirit conforming to ASTM D 235 shall be used.
7 Apparatus
7.1 FZG spur-gear test rig
7.1.1 The FZG spur-gear test machine utilizes a recirculating power loop principle, also known as a
four-square configuration, to provide a fixed torque (load) to a pair of precision test gears. A schematic
view of the test rig is shown in Figures 2 and 3. The slave gearbox and the test gearbox are connected
through two torsional shafts. Shaft 1 contains a load coupling used to apply the torque through the use
of known weights, defined in Table 4, hung on the loading arm.
7.1.2 The test gearbox contains heating elements to maintain and control the minimum temperature
of the oil. A temperature sensor located in the side of the test gearbox is used to control the heating
system as required by the test operating conditions.
7.1.3 The test machine is powered by an electric motor of minimum 7,4 kW at a speed of approximately
2 900 1/min. The direction of drive is reversed (anticlockwise when looking on the motor shaft),
i.e. wheel drives pinion, as shown in Figure 3. This is the opposite direction of rotation to that of
ISO 14635-1.
7.1.4 A check list for maintenance of FZG gear test rig is given for information in Annex C.
Table 2 — Details of FZG test gears type A10
Dimension Symbol Numerical value Unit
Shaft centre distance a 91,5 mm
Effective tooth width pinion b 10 mm
wheel b 20 mm
Working pitch diameter pinion d 73,2 mm
w1
wheel d 109,8 mm
w2
Tip diamet
...