NB/SH/T 0920-2016 Determination of the anti-fretting wear ability of lubricating grease under high Hertzian contact pressure High-frequency linear vibration testing machine method

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Card type: Test method

1. Method number / full name / English name / replacement relationship

• Standard number: NB/SH/T 0920—2016
• Chinese name: Determination of the anti-fretting wear ability of lubricating grease under high Hertzian contact pressure High-frequency linear vibration testing machine method
• English name: Standard test method for determining fretting wear resistance of lubricating greases under high Hertzian contact pressures using a high-frequency, linear-oscillation (SRV) test machine
• Replacement relationship: not provided in the available source (the foreword only states "adopted by modification using the redrafting method ASTM D7594-11", and does not mention replacing any previous version of the standard)
• Adoption relationship: adopted by modification using the redrafting method ASTM D7594-11
• Main technical differences from ASTM D7594-11 (foreword):
  • For ease of use, some referenced standards were changed to the corresponding national standards and industry standards of our country.
  • For the actual promotion and use of the standard, the cleaning solvent was changed to petroleum ether with a boiling range of 90℃~120℃ that complies with GB/T 15894.
  • To suit the national conditions of our country and for ease of actual use, the wear scar measurement result was modified to be accurate to 0.01mm.
• Publication/implementation: published on 2016-12-05, implemented on 2017-05-01; issued by the National Energy Administration
• Drafting organization: Sinopec Research Institute of Petroleum Processing; participating drafting organization: Sinopec Lubricant Chongqing Branch
• Main drafters: Yang He, Song Haiqing, Xue Ying, Tian Zhongli, Luo Yulan
• Custodianship: National Technical Committee for Standardization of Petroleum Products and Lubricants, Subcommittee on Petroleum Fuels and Lubricants (SAC/TC280/SC1)
• Proposed by: China Petrochemical Corporation

2. Scope of application and non-applicability

• This standard specifies a method for determining the lubricating performance of lubricating grease against fretting wear using a high-frequency linear vibration (SRV) testing machine or similar testing machine under conditions of high frequency, low stroke, high Hertzian contact pressure, and linear vibration.
• This standard is applicable to determining the anti-wear performance and coefficient of friction of lubricating grease under given temperature and load conditions.
• If another non-mandatory extreme pressure test is carried out according to SH/T 0784, the lubricating grease used in the test should be able to withstand a Hertzian contact pressure of at least 2200MPa without adhesive wear occurring.
• Method application (Chapter 5): applicable to determining the anti-fretting wear performance and coefficient of friction of lubricating grease under given temperature and load conditions, especially suitable for the case of long-duration high-speed vibration under low stroke and initial high Hertzian point contact pressure. It can be applied to screening tests of lubricating grease for rolling bearings, roller or ball screw drives or side shaft systems, and constant velocity joints. Users of this standard should determine whether its results are related to field performance or other applications.
• Non-applicability: no explicit "non-applicability" clause is provided in the available source.

3. Method principle

• 4.1 Using a SRV testing machine or similar testing machine, a test ball dipped in lubricating grease is reciprocated on a stationary test disk, with the movement frequency and applied load (the original text here has an unclear point at source-text extraction, requires confirmation against the source standard (source-text extraction)), and the stroke amplitude is short and constant, to determine the coefficient of friction and wear scar diameter.
• 4.2 Non-mandatory extreme pressure test (see Appendix A): the test load is increased in increments of 100N until seizure occurs (see SH/T 0784), and the load value immediately before seizure is recorded and reported. Note: the frequency, stroke, test temperature, and the materials of the test ball and test disk may differ from the requirements of this standard. The test ball usually produces a Hertzian point contact geometry. To obtain line or surface contact, specimens of different shapes may be used instead of the test ball.
• 4.3 The friction force is measured by a piezoelectric sensor integrated on the test disk. For I type and II type SRV testing machines, the coefficient of friction f is measured as a function of time; for III type and IV type SRV testing machines, the friction force or coefficient of friction for the entire test process can be displayed after the test ends, and the test data can be saved automatically.
• 4.4 After the test ends, the testing machine and chart recorder stop, and the wear scar on the test ball is measured. If a surface profilometer is available, additional wear information can also be obtained from the wear track on the test disk and the wear scar on the test ball (see Appendix A). The wear volume is in units of mm³, and the wear rate of the test disk and test ball is in units of mm³/(N·m).

4. Reagents and materials (purity / preparation)

• 7.1 Cleaning solvent: petroleum ether with a boiling range of 90℃~120℃ that complies with GB/T 15894. Warning: flammable, harmful to health.
• 7.2 Test ball: AISI 52100 steel (equivalent to GCr15 steel), Rockwell hardness HRC is 60±2 (the original text has an unclear point at source-text extraction, requires confirmation against the source standard (source-text extraction)), surface roughness Ra is 0.025μm±0.005μm, diameter is 10mm.
• 7.3 Test disk: the material is AISI 52100 steel produced by vacuum arc remelting (equivalent to GCr15 steel), with inclusion rating determined by ASTM E45 D method, ASTM A295/A295M as type A, and severity level as 0.5; or according to GB/T 28417, with total impurity content K≤10 and spherical carbides obtained by spheroidizing annealing, Rockwell hardness HRC is 60±2 (the original text has an unclear point at source-text extraction, requires confirmation against the source standard (source-text extraction)). The surface of the test disk should be ground but free of abrasive, the test disk diameter is 24mm, thickness is 7.85mm, and its four surface topography parameters should satisfy the following ranges:
  • 0.500μm < Rk < 0.650μm;
  • 0.035μm ≤ Rpk (C.L.A) < 0.050μm;
  • 0.020μm < Rvk < 0.035μm;
  • 0.050μm < Rwk < 0.075μm.
  • (Note: the original text has an unclear point in the topography parameter symbol source-text extraction, requires confirmation against the source standard (source-text extraction))

5. Instruments and equipment

• SRV Testing machine, schematic diagrams are shown in Figure 1 and Figure 2. Note: the left figure is III type, the right figure is I type (the original text has an unclear point at source-text extraction, requires confirmation against the source standard (source-text extraction)).
• Figure 2 Structural composition of the test chamber: 1— reciprocating vibration drive rod; 2— test ball holder; 3— loading rod; 4— test ball; 5— test disk; 6— resistance heater; 7— resistance thermometer; 8— test disk holder; 9— piezoelectric device; 10— base.
• Other equipment (scattered in various chapters): ultrasonic cleaner, microscope, surface profilometer, torque wrench, chart recorder (or computer), grease applicator (1mm high), scraper, laboratory paper towels, solvent-resistant gloves.

6. Recommended operating conditions

• 8.5 The frequency is set to 50Hz, and the time is 4h0min30s (as stated in the original text, requires confirmation against the source standard (source-text extraction)).
• 9.2.2 Apply a load of 50N and maintain it for 30s, then increase to 100N and maintain it for 240min.
• 9.2.3 The stroke amplitude is adjusted to 0.300mm (300μm).
• 9.2.1 Test temperature: preheat the test disk holder to 50℃; Note: other test temperatures may also be selected between 40℃~150℃ in increments of 10℃.
• 9.2.5 For III type and I type SRV testing machines, basic software input parameters: 50Hz; 0.300mm (300μm); 50℃; 50N load and maintain for 30s, then increase to 100N and maintain for 240min; fully tighten the test specimen holder, and operation should be carried out according to the instructions of the SRV testing machine software.
• 9.2.2 Tighten with a torque wrench to 2.2N·m~2.5N·m.
• 9.1.2 Install the test ball holder when the testing machine is not loaded (the load gauge reading indicates -13N or -14N).
• 8.1 Before the test, turn on the testing machine and recorder and preheat for 15min.
• 8.3 Turn the amplitude knob to "zero"; 8.4 Turn the stroke switch to the automatic position.
• 9.2.6 Terminating the test: when the predetermined time is reached, it stops automatically by the timer; if due to seizure, the coefficient of friction f exceeds a limit value, for example f=0.35 (see 3.14), the test should be stopped.

7. Sampling and specimen preparation

• 9.1.3 Place the grease applicator with a height of 1mm on a clean test disk, fill it with the grease sample, wipe off excess sample with a scraper, remove the grease applicator from above, and fasten the test disk with the fixture.
• 9.1.4 Install the cleaned test ball on top and place it in the middle of the lubricating grease sample, so that the lubricating grease forms a circularly symmetric uniform thin layer between the test ball and the test disk.
• 9.1.5 Tighten the fastening screw until resistance just appears.
• 9.1.1 Cleaning: wear solvent-resistant gloves, clean the test ball, test ball holder, and test disk, and wipe the surfaces of these parts with laboratory paper towels already dipped in cleaning solvent. Repeat wiping until no black residue appears on the paper towel. Immerse the test ball and test disk in a beaker containing cleaning solvent and oscillate with an ultrasonic cleaner for 10min. Air-dry the test ball holder. Dry the test ball and test disk with a clean paper towel, ensuring that no streaks appear on the surfaces.

8. Analytical procedure

• 9.1 Test preparation (see Section 7 Sampling and specimen preparation).
• 9.2 Test run:
  • 9.2.1 At the start of the test run, turn on the heater and wait until the temperature reaches the test temperature and remains stable (the original text has an unclear point at source-text extraction, requires confirmation against the source standard (source-text extraction)). Note: the initial hardness HRC of AISI 52100 steel at room temperature is 62.5; after being held at a temperature of 149℃ for 100h, the Rockwell hardness HRC will decrease to 61; after heating beyond (the original text here has an unclear point at source-text extraction, requires confirmation against the source standard (source-text extraction)) Rockwell hardness HRC will remain at 60.
  • 9.2.2 Apply 50N load, preheat the test disk fixture to 50℃. Wait for 10min to allow the test disk and grease (original source-text extraction unclear in the source text, requires confirmation against the source standard (source-text extraction)). Tighten with a torque wrench to 2.2N·m~2.5N·m.
  • 9.2.3 When the temperature has stabilized, turn on the recorder paper feed switch (or computer), press down the recording pen, press down the toggle switch until the timer starts counting, adjust the stroke amplitude knob to 0.300mm (300μm). Note: The stroke should be checked periodically, which can be done by measuring the difference between the wear scar length on the test disk and the wear scar diameter on the test ball; the difference should be less than the set stroke (original source-text extraction unclear in the source text, requires confirmation against the source standard (source-text extraction)).
  • 9.2.4 When the timer reaches 30s, the test load is increased to 100N and run for 4h (original source-text extraction unclear in the source text, requires confirmation against the source standard (source-text extraction)).
  • 9.2.5 For III type and I type SRV testing machines, only the following parameters need to be entered in the basic software: 50Hz; 0.300mm (300μm); 50℃; 50N load and maintain for 30s, then increase to 100N and maintain for 240min; fully tighten the test specimen fixture, and operate according to the instructions of the SRV testing machine software.
  • 9.2.6 Terminate the test as specified below:
    • When the predetermined time is reached, the test can be automatically stopped by the timer, and the machine will automatically shut down. Note 1: At the end of the test, the power will be automatically cut off. Note 2: If due to seizure, the friction coefficient f exceeds a limit value such as f=0.35 (see 3.14), the test should be stopped. If the machine cannot stop automatically at this point, stop it manually.
    • At the end of the test, turn off the heating controller. Reconnect the load power supply, reduce the load to -13N or -14N for disassembly (original source-text extraction unclear in the source text, requires confirmation against the source standard (source-text extraction)).
  • 9.2.7 Disassemble and clean the test ball and test disk according to 9.1.1.
• 9.3 Measurement:
  • 9.3.1 Place the cleaned test ball on a suitable fixture, and use a microscope to measure the wear scar width in the sliding direction (d₁) and the wear scar width perpendicular to the sliding direction (d₂), accurate to 0.01mm (10μm). The average wear scar diameter (WSD) is the average of these two measured values (WSD=…, original formula source-text extraction missing, requires confirmation against the source standard (source-text extraction)). If the wear scar diameter is less than 1.1 times the Hertzian contact diameter, the wear scar profile can be measured at the center of the wear scar to calculate the wear volume. If the wear scar diameter is greater than 1.1 times the Hertzian contact diameter, only report the wear scar diameter (see NB/SH/T 0847). The wear volume w of the test ball should be expressed in cubic millimeters. Note: Measuring the wear volume is an optional (original source-text extraction unclear in the source text, requires confirmation against the source standard (source-text extraction)) method. For methods of measuring the wear profile and calculating the wear volume, see ASTM D7755.
  • 9.3.2 Although no specific procedure has been established, when wear analysis is required, the wear scar surface profile on the test disk can be analyzed according to the surface profilometer instructions (see ASTM D7755).
  • 9.3.3 From the recorder or (original source-text extraction unclear in the source text, requires confirmation against the source standard (source-text extraction)), obtain the minimum friction coefficient and maximum friction coefficient (fmin, fmax) and the friction coefficients at 15min, 30min, 45min, 60min within each hour (f15, f30, f45, f60), accurate to 0.001.
  • 9.3.4 If there is strong fluctuation (amplitude width ≥0.005) near the friction coefficient point measured by the recorder or other output device (original source-text extraction unclear in the source text, requires confirmation against the source standard (source-text extraction)), record the average value and fluctuation value at that point (see NB/SH/T 0847, original source-text extraction unclear in the source text, requires confirmation against the source standard (source-text extraction)).
  • 9.3.5 At the end of the test, the load-carrying capacity of the test ball can also be reported by the geometric contact pressure P, which can be calculated according to formula (1):
    • Formula (1): Parm = F / Wx (original formula source-text extraction incomplete, requires confirmation against the source standard (source-text extraction))
    • Where: Parm— geometric contact pressure, in newtons per square millimeter (N/mm²); F— normal force (test load), in newtons (N); Wx— average wear scar (original source-text extraction unclear in the source text, requires confirmation against the source standard (source-text extraction)), in millimeters (mm).
    • Note 1: Geometric contact pressure (original source-text extraction unclear in the source text, requires confirmation against the source standard (source-text extraction)) than Hertzian contact pressure.
    • Note 2: Before evaluating the anti-wear ability of grease under fretting conditions, two extreme pressure tests can be completed according to the method of SH/T 0784, both at a temperature of 50℃, with strokes of 1mm and 2mm respectively (see Appendix A), but this is not mandatory.
    • Note 3: When the test load is equal to 100N, the initial Hertzian wear scar diameter of the test ball is 0.296mm (the initial diameter of the test ball is 10mm), Hertzian contact (original source-text extraction unclear in the source text, requires confirmation against the source standard (source-text extraction)); when the test load is equal to 50N, the initial Hertzian wear scar diameter of the test ball is 0.236mm (the initial diameter of the test ball is 10mm).

9. Qualitative and Quantitative and Calculation Formulas

• Average wear scar diameter (WSD): the average of the wear scar width in the sliding direction (d₁) and the wear scar width in the perpendicular direction (d₂) (original formula source-text extraction missing, requires confirmation against the source standard (source-text extraction)).
• Geometric contact pressure calculation formula (Formula 1): Parm = F / Wx (original formula source-text extraction incomplete, requires confirmation against the source standard (source-text extraction)); where Parm— geometric contact pressure (N/mm²); F— normal force (test load) (N); Wx— average wear scar (requires confirmation against the source standard (source-text extraction)) (mm).
• Wear volume: in units of mm³; the wear rate of the test disk and test ball is in units of mm³/(N·m).
• Friction coefficient: minimum friction coefficient fmin, maximum friction coefficient fmax, and f15, f30, f45, f60, accurate to 0.001.
• Seizure judgment (3.14): The friction coefficient has a sharp increase beyond the steady state, the friction coefficient increases by 0.2 compared to the steady-state value and (original source-text extraction unclear in the source text, requires confirmation against the source standard (source-text extraction)) exceeds 20s, or the friction coefficient is greater than 0.35, or judged according to the examples given in ASTM D5706-05 and NB/SH/T 0882. If any of the above occurs, it indicates that the test is invalid.

10. Precision

• 11.1 Precision: 16 laboratories conducted round-robin tests on six greases in 2009 under 50℃ conditions. The precision determined from the statistical test results (original source-text extraction unclear in the source text, requires confirmation against the source standard (source-text extraction)).
• 11.1.1 Precision of wear scar diameter (WSD):
  • 11.1.1.1 Repeatability r: The difference between two consecutive test results obtained by the same operator, in the same laboratory, using the same instrument, on the same test sample should not be greater than 0.051mm.
  • 11.1.1.2 Reproducibility R: The difference between two single, independent test results obtained by different operators, in different laboratories, using different instruments, according to the same method, on the same test sample should not be greater than 0.207mm.
• 11.1.2 Precision of friction coefficient:
  • 11.1.2.1 Repeatability r: The difference between two consecutive test results obtained by the same operator, in the same laboratory, using the same instrument, on the same test sample should not be greater than 0.009.
  • 11.1.2.2 Reproducibility R: The difference between two single, independent test results obtained by different operators, in different laboratories, using different instruments, according to the same method, on the same test sample should not be greater than 0.0234.
• 11.2 Bias: Since the friction coefficient and wear scar diameter (WSD) of this standard are defined according to this test method, the bias of this standard for evaluating the friction and wear characteristics of grease cannot be determined.

11. Report

• 10.1 Report the average wear scar diameter of the test ball (WSD) and the friction coefficient when no seizure occurs at the end of the test. When there are specific requirements, also report (original source-text extraction unclear in the source text, requires confirmation against the source standard (source-text extraction)).
• 10.2 Report content (original source-text extraction unclear in the source text, requires confirmation against the source standard (source-text extraction)): test disk material and sample number (original listed before 10.1, source-text extraction order unclear in the source text, requires confirmation against the source standard (source-text extraction)).
• Appendix A (Informative Appendix) Complete summary of anti-fretting wear characteristics results:
  • Table A.1 Summary of results of anti-wear tribological characteristics of grease samples under fretting friction conditions, including: maximum test load without seizure/N (maximum geometric contact pressure Parm/MPa) (temperature 50°, frequency 50Hz, test method SH/T 0784); wear rate/(10⁻⁹mm³/(N·m)) (temperature 50℃, load 100N, stroke 0.3mm, time 4h); test ball wear scar diameter/mm; friction coefficient. Example data: grease sample first time 4.4, 0.8, 0.38/0.39, 0.077; second time 4.9, 0.8, 0.39/0.40, 0.078; maximum test load 2000N (5907MPa).
  • Figure A.1 Example graph of friction coefficient and linear wear versus time for grease samples. Note 1: The upper two figures plot friction coefficient versus time, and the lower two figures plot linear wear versus time; test conditions are Fw=100N; T=50℃; v=50Hz; Δx=300μm; t≤8h. Note 2: A decrease in linear wear rate is a favorable phenomenon.
  • Figure A.2 Example diagram of wear profile measurement results for a grease sample. The upper figure is a schematic diagram of the trajectory of the vertical probe of the profilometer passing through the center of the wear scar on the test disk in the sliding direction; the two figures below are wear curves, in which the parabola is the shape of the ball before wear and before loading, and the wear of the flat surface is in units of μm³. Tribological quantities (according to ASTM): sample 1 average wear scar diameter is 0.385mm; ball wear volume: 191×10⁻⁶mm³; ball wear rate: 4.4×10⁻⁹mm³/(N·m); disk wear rate: 16.5×10⁻⁹mm³/(N·m) (original text source-text extraction unclear in the source text, requires confirmation against the source standard (source-text extraction)).
  • Figure A.3 Example diagram of extreme pressure test results for a grease sample. According to test method SH/T 0784, the maximum load at which seizure did not occur (pass/OK load value) is 2000N (maximum geometric contact pressure P is 5907MPa), stroke is 2mm.

12. Normative references

• GB/T 269 Determination of cone penetration of lubricating greases and petrolatum
• GB/T 15894 Chemical reagent Petroleum ether
• GB/T 17754—2012 Tribology terminology
• GB/T 18778.2 Geometrical product specifications (GPS) Surface texture Profile method Surfaces having stratified functional properties Part 2: Characterization of height properties using a linearized material ratio curve
• GB/T 28417 Carbon bearing steel
• SH/T 0784 Determination of extreme pressure properties of lubricating greases (high-frequency linear vibration test machine method)
• NB/SH/T 0847 Determination of friction and wear properties of extreme pressure lubricating oils SRV test machine method
• NB/SH/T 0882 Determination of extreme pressure properties of lubricating oils SRV test machine method
• ASTM A295/A295M Specification for high-carbon anti-friction bearing steel (Specification for High-Carbon Anti-Friction Bearing Steel)
• ASTM D5706-05 Determination of extreme pressure properties of lubricating greases (high-frequency linear vibration test machine method) (Standard Test Method for Determining Extreme Pressure Properties of Lubricating Greases Using a High-Frequency, Linear-Oscillation (SRV) Test Machine)
• ASTM D7755 Determination method for wear volume of standard test specimens for high-frequency linear vibration (SRV) (Standard Practice for Determining the Wear Volume on Standard Test Pieces Used by High-Frequency, Linear-Oscillation (SRV) Test Machine)
• ASTM E45 Determination method for impurity content in steel (Test Methods for Determining the Inclusion Content of Steel)
• Drafting basis: GB/T 1.1—2009

13. Source and verification

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14. Quick reference for questions and answers