ASTM D7420-23

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it may not be technically possible to adequately depict all changes accurately, ASTM recommends that users consult prior editions as appropriate. In all cases only the current version
of the standard as published by ASTM is to be considered the official document.
Designation: D7420 − 18 D7420 − 23
Standard Test Method for
Determining Tribomechanical Properties of Grease
Lubricated Plastic Socket Suspension Joints Using a High-
Frequency, Linear-Oscillation (SRV) Test Machine
This standard is issued under the fixed designation D7420; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (´) indicates an editorial change since the last revision or reapproval.
INTRODUCTION
This test method was originally published as bilingual company standard TRW 62 051 301 in June
2002. TRW Fahrwerksysteme transferred the copyright on Oct. 5, 2004 to standardization bodies. The
DIN 51834 working group has modified this standard by adding precision information based on round
robin tests.
1. Scope*
1.1 This test method covers a procedure for determining the friction and wear behavior of grease lubricated plastic socket
suspension joints, for validation of suspension joint greases and quality inspection for those greases under high-frequency
linear-oscillation motion using the SRV test machine.
1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.
1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility
of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of
regulatory limitations prior to use.
1.4 This international standard was developed in accordance with internationally recognized principles on standardization
established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued
by the World Trade Organization Technical Barriers to Trade (TBT) Committee.
2. Referenced Documents
2.1 ASTM Standards:
A295 Specification for High-Carbon Anti-Friction Bearing Steel
D217 Test Methods for Cone Penetration of Lubricating Grease
D4175 Terminology Relating to Petroleum Products, Liquid Fuels, and Lubricants
D5706 Test Method for Determining Extreme Pressure Properties of Lubricating Greases Using a High-Frequency, Linear-
Oscillation (SRV) Test Machine
This test method is under the jurisdiction of ASTM Committee D02 on Petroleum Products, Liquid Fuels, and Lubricants and is the direct responsibility of Subcommittee
D02.G0 on Lubricating Grease.
Current edition approved Dec. 1, 2018Nov. 1, 2023. Published January 2019December 2023. Originally approved in 2010. Last previous edition approved in 20172018
as D7420 – 17.D7420 – 18. DOI:10.1520/D7420–17.DOI:10.1520/D7420-23.
TRW Fahrwerksysteme (Chassis Systems), D-50543, Düsseldorf, Germany.
For referenced ASTM standards, visit the ASTM website, www.astm.org, or contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM Standards
volume information, refer to the standard’s Document Summary page on the ASTM website.
*A Summary of Changes section appears at the end of this standard
Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959. United States
D7420 − 23
E45 Test Methods for Determining the Inclusion Content of Steel
G40 Terminology Relating to Wear and Erosion
2.2 DIN Standards:
DIN EN ISO 683-17 Heat-treated steels, alloy steels and free-cutting steels—Part 17: Ball and roller bearing steels (replaces
DIN 17230-1980)
DIN EN ISO 13565-2: 1998 Geometrical Product Specifications (GPS)—Surface texture: Profile method—Surfaces having
stratified functional properties—Part 2: Height characterization using the linear material ratio curve
DIN EN 17022–4: 1998 Heat treatment of ferrous materials—Methods of heat treatment—Part 4: Nitriding and nitrocarburizing
(available in English)
3. Terminology
3.1 Definitions:
3.1.1 For definitions of terms used in this test method, refer to Terminology D4175.
3.1.2 break-in, n—in tribology, an initial transition process occurring in newly established wearing contacts, often accompanied
by transients in coefficient of friction or wear rate, or both, which are uncharacteristic of the given tribological system’s long-term
behavior. G40
3.1.3 coeffıcient of friction, μ or ƒ, n—in tribology, the dimensionless ratio of the friction force (F) between two bodies to the
normal force (N) pressing these bodies together. G40
3.1.4 lubricant, n—any material interposed between two surfaces that reduces the friction or wear between them. D4175
3.1.5 lubricating grease, n—a semi-fluid to solid product of a dispersion of a thickener in a liquid lubricant. D217
3.1.5.1 Discussion—
The dispersion of the thickener forms a two-phase system and immobilizes the liquid lubricant by surface tension and other
physical forces. Other ingredients are commonly included to impart special properties.
3.1.6 nitro-carburization, n—nitro-carburizing is not defined in the ASTM Dictionary of Engineering Science and Technology, but
is defined in DIN EN 17022-4:1998.
3.1.7 Ra (C.L.A.), n—in measuring surface finish, the arithmetic average of the absolute distances of all profile points from the
mean line for a given distance. Amstutz
3.1.8 Rpk, n—Reduced peak height according to DIN EN ISO 13565-2:1998. Rpk is the mean height of the peak sticking out above
the core profile section.
3.1.9 Rvk, n—Reduced valley height according to DIN EN ISO 13565-2:1998. Rvk is the mean depth of the valley reaching into
the material below the core profile section.
3.1.10 Rz (DIN), n—in measuring surface finish, the average of all Ry values (peak to valley heights) in the assessment length.
Amstutz
3.1.11 thickener, n—in lubricating grease, a substance composed of finely divided particles dispersed in a liquid lubricant to form
the product’s structure. D217
3.1.11.1 Discussion—
The thickener can be fibers (such as various metallic soaps) or plates or spheres (such as certain non-soap thickeners) which are
insoluble or, at most, only very slightly soluble in the liquid lubricant. The general requirements are that the solid particles be
extremely small, uniformly dispersed, and capable of forming a relatively stable, gel-like structure with the liquid lubricant.
3.2 Definitions of Terms Specific to This Standard:
Available from Beuth Verlag GmbH (DIN-- DIN Deutsches Institut fur Normung e.V.), Burggrafenstrasse 6, 10787, Berlin, Germany, http://www.en.din.de.
Amstutz, Hu, “Surface Texture: The Parameters,” Bulletin MI-TP-003-0785, Sheffield Measurement Division, Warner and Swasey, 1985, p. 21
Amstutz, Hu, “Surface Texture: The Parameters”, Bulletin MI-TP-003-0785, Sheffield Measurement Division, Warner and Swasey, 1985, pp. 29–31.
D7420 − 23
3.2.1 linear wear, n—the change in length of each pin prior and after tribological test.
3.2.2 metal specimen, n—represented by the lower specimen. Ball stud or ball pins are also used as common synonym.
3.2.3 plastic socket, n—represented by the upper polymeric disk specimen. Plastic seat or beating is also used as common
synonym.
3.2.4 seizure, n—localized fusion of metal between the rubbing surfaces of the test pieces. D5706
3.2.4.1 Discussion—
In this test method, seizure is indicated by a sharp rise in the coefficient of friction, over steady state, of greater than 0.2 for over
20 s. In severe cases, a stoppage in the motor will occur (for example, see Test Method D5706).
3.3 Abbreviations:
3.3.1 SRV, n—Schwingung, Reibung, Verschleiß (German); oscillating, friction, wear (English translation).
4. Summary of Test Method
4.1 This test method is performed on SRV test machine using a polymeric disk having three flat pins oscillating at 50 Hz 50 Hz
against a steel test disk with lubricant (grease) between them. Test load is fixed to 2000 N using a test temperature of 50 °C and
a stroke of 1.5 mm during a test time of 2 h.
NOTE 1—Test frequency, stroke length, temperature, and polymeric disk and disk material can be varied to simulate field conditions. The polymeric disk
having three flat pins yields surface-on-flat contact geometry.
NOTE 2—This test can not be executed with SRV I and SRV II models, as they are limited to 1200 N and 1400 N, respectively. The SRV III and SRV
IV models are from the test chamber and operating conditions identical, but the SRV IV model allows to tilt and rotate the test chamber. Both are fully
computer controlled. This test runs in the SRV IV and 5 models horizontally and untilted. SRV III test machines after 1995 reach 2000 N. SRV 4 and
SRV 5 models can be equipped with a maximum test load unit of 2500 N.
5. Significance and Use
5.1 This test method can be used to quickly determine the lubricating ability of greases lubricating automotive plastic socket
suspension joints. This test method has found wide application in qualifying greases used in chassis systems. This test method is
a material and application oriented approach based on inputs from field experiences for characterizing the tribological behavior
(friction and wear) using random, discrete, and constant parameter combinations. Users of this test method should determine
whether results correlate with field performance or other applications prior to commercialization.
6. Apparatus
6.1 SRV Test Machine, —illustrated in Figs. 1-4.
7. Reagents and Materials
+0.2
7.1 Polymeric Test Disk with Three Pins, Ø = 18.2 -mm diameter. Each pin has a diameter of Ø = 3.0-mm (see Fig. X1.1). The
plastic specimen should represent characteristic items of an inner plastic socket surface. Specimens are molded from original
socket material; functional surfaces shall be free from scratches and any surface damages.
7.2 Lower Test Disk —Vacuum arc remelted (VAR) AISI 52100 steel with a inclusion rating using Method D, Type A, as severity
level number of 0.5 according to Test Methods E45 and Specification A295 or a inclusion sum value K1 ≤ 10 according to DIN
EN ISO 683-17 and spherodized annealed to obtain globular carbide, 62 6 1 HRC hardness, the surfaces of the disk being lapped
and free of lapping raw materials. The topography of the disk will be determined by four values:
0.5 μm < Rz (DIN) <0.650 μm
0.35 μm < C.L.A. (Ra) < 0.050 μm
The sole source of supply of the apparatus known to the committee at this time is Optimol Instruments GmbH, Flößergasse 3, D-81369 Munich, Germany. If you are
aware of alternative suppliers, please provide this information to ASTM International Headquarters. Your comments will receive careful consideration at a meeting of the
responsible technical committee, which you may attend.
D7420 − 23
FIG. 1 SRV Model III Test Machine
1. Oscillation drive rod 6. Electrical Resistance Heater
2. Test Ball Holder 7. Resistance Thermometer
3. Load Rod 8. Test Disk Holder
4. Test Ball 9. Piezoelectric Measuring Device
4. Three Pin Specimen 9. Piezoelectric Measuring Device
5. Test Disk 10. Receiving Block
FIG. 2 Test Chamber Elements (Schematic) of SRV Model III Test Machine
0.020 μm 0.050 μm < Rvk < 0.075 μm (24 mm 6 0.5 mm diameter by 7.8 mm 6 0.1 mm thick)
If other surface roughnesses are applied, they have to be measured and stated in the report. The type of coating and/or
thermomechanical treatment has to be reported.
NOTE 3—The steel 41CrS4 (DIN 1.7039; SAE 5140H) is also used in practice. The test disks should be polished to R 1-1.5 μm and can be carbo-nitrided.
Z
7.3 Grease, Store in a sealed container prior to testing. (Different greases have different characteristics for storage stability and
shelf life and users should be guided by their own knowledge of the material to be tested, or by the recommendation of the
supplier.)
7.4 Cleaning Solvent, the test disks have to be cleaned by a liquid solvent (non-chlorinated, non-film forming).
D7420 − 23
FIG. 3 SRV Model 4 Test Machine
8. Preparation of Apparatus
8.1 SRV Ma
...