SH/T 0762-2005 Determination of Friction Coefficient of Lubricating Oils (Four-Ball Method)

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Card type: Test method

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

• Standard number: SH/T 0762—2005
• Chinese title: Determination of Friction Coefficient of Lubricating Oils (Four-Ball Method)
• English title: The test method for determination of the coefficient of friction of lubricants using the four-ball wear test machine
• Replacement relationship: not provided in the available source (the foreword states "this standard is first published")
• Adoption relationship: modified adoption of ASTM D5183-95 (1999) "Standard Test Method for Determination of Friction Coefficient of Lubricating Oils Using a Four-Ball Wear Test Machine", redrafted according to ASTM D5183-95 (1999)
• Publication/implementation: published on 2005-04-11, implemented on 2005-09-01
• Issuing body: National Development and Reform Commission of the People's Republic of China
• Custodian: Sinopec Research Institute of Petroleum Processing
• Main drafting organization: Lanzhou Lubricating Oil Research and Development Center of PetroChina Company Limited
• Main drafters: Cai Jiyuan, Dai Lixia, Zhang Kuande, Ding Fangling

2. Scope of application and non-applicability

• 1.1 This standard specifies a test method for determining the friction coefficient of lubricating oils using a four-ball wear test machine.
• 1.2 This standard is applicable to the determination of the friction coefficient of lubricating oils.
• 1.3 The numerical values in this standard use International System of Units (SI) units, but some equipment conforming to this standard uses cm-kgf, so cm-kgf units are retained.
• 1.4 This standard involves certain hazardous materials, operations and equipment, but it is not intended to address all safety issues associated with them. Users should establish appropriate safety and protective measures before using this standard, and determine management systems with applicability.
• Non-applicability: no explicit "non-applicability" clause is provided in the available source (Appendix A notes that "the above data cannot be used for rolling four-ball tests").

3. Method principle

• 4.1 Three steel balls with a diameter of 12.7mm (0.5in) are clamped together, and 10mL of break-in oil is added. Another steel ball with a diameter of 12.7mm (0.5in) serves as the upper steel ball and makes three-point contact with the three clamped steel balls, and a load of 392N (40kgf) is applied. The lubricating oil test temperature is 75℃ (165℉), and the upper steel ball runs at a speed of 600r/min for 60min.
• 4.2 Pour off the break-in oil and clean the steel balls. Measure the wear scar diameter of each of the three lower steel balls. If the average wear scar value is 0.65mm±0.05mm (0.026in±0.002in), use the run-in test balls and add 10mL of test oil to the oil cup. The test oil temperature is 75℃ (167℉), and the upper steel ball runs at a speed of 600r/min for 10min under a load of 98.1N (10kgf).
• 4.3 Increase the load by 98.1N (10kgf) every 10min, and record the friction coefficient once every 10min, until the friction force recorder begins to show jumping.
• 5 Significance and use: This test method can be used to determine the friction coefficient of lubricating oils under specified test conditions. Users of this test method may examine whether the results obtained by the test method correlate with actual application performance or other bench tests.

4. Reagents and materials (purity / preparation)

• 7.1 Reagent purity: Analytical reagent grade reagents should be used in all tests to ensure that the reagents have sufficiently high purity so as not to reduce the precision of the test.
• 7.2 Break-in oil: industrial white oil conforming to SH/T 0006, with a viscosity at 40℃ of 24.3mm²/s~26.1mm²/s. It should be filtered through activated alumina to remove residual impurities.
• 7.3 Acetone: conforming to GB 686 standard. Note: flammable and harmful to health.
• 7.4 n-Heptane. Note: flammable and harmful to health.
• 7.5 Methyl ethyl ketone. Note: flammable and harmful to health.
• 7.6 Nitrogen: purity not lower than 99.9%.
• Differences from ASTM D5183-95 (1999) (foreword): Chapter 7 adds a purity requirement for nitrogen; Chapter 7 deletes the pyridine reagent.

5. Apparatus and equipment

• 6.1 Four-ball test machine: use a four-ball wear test machine, see Figure 1 (schematic diagram of four-ball contact), Figure 2 (four-ball wear test machine), Figure 3 (multifunctional friction and wear test machine). Note: First, a four-ball extreme pressure test machine and a four-ball wear test machine must be distinguished (see test methods SH/T 0189). The four-ball extreme pressure test machine is designed for tests under heavy loads and lacks the necessary sensitivity for wear tests.
• 6.2 Microscope: capable of measuring the wear scar diameters formed on the surfaces of the three steel balls without removing them from the oil cup, with an accuracy requirement of 0.01mm.
• 6.3 Test steel balls: steel balls specially used for four-ball machines conforming to the requirements of GB 308, material GCr15, diameter 12.7mm (0.5in), hardness between HRC64~66.
• Others: ultrasonic cleaner (see 10.1), heater, temperature controller, automatic clock controller (see 8.3), friction force recorder (see 4.3, 10.17), pressure calibrator (see 8.4).

6. Recommended operating conditions

• The test conditions are shown in Table 1.

Table 1 Test conditions for determining the friction coefficient of lubricating oils

Note: Increase the load by 98.1N (10kgf) every 10min, until an abnormality appears on the friction force recorder (the friction force exceeds the stable value and suddenly increases).

• 8.1 Set the test machine speed to 600r/min±30r/min.
• 8.2 Set the test oil temperature on the temperature controller to 75℃±2℃ (167℉±4℉).
• 8.3 If an automatic clock controller is selected to terminate the test, its precision must be checked; the error at 60min shall not exceed 1min, and the error at 10min shall not exceed 10s.
• 8.4 After the test specimen is assembled and the test oil is added, the loading mechanical system should be balanced to zero. To check whether the test machine has suitable precision, verification may be carried out by increasing or decreasing the load by 2.0N (0.2kg) under the balanced state; at this time, an obvious imbalance should occur. When the load is at 147N and 392N (15kgf and 40kgf), it is often difficult to determine its precision; careful measurement of the force arm ratio and weight is required, or a pressure calibrator combined with the piston diameter is used to determine its precision. Note: Because test equipment may differ in structure, the manufacturer's recommendations should be considered in the adjustment and operation of the test machine.
• 10.17 The test is divided into ten stages in total, starting from 98.1N, increasing the load by 98.1N every 10min, with a maximum load of 981N. Shutdown is not allowed during the whole test process; when the friction torque suddenly increases, stop the test.

7. Sampling and specimen preparation

• No independent sampling and specimen preparation chapter is provided in the available source. Sample amounts: break-in oil 10mL (4.1, 10.4); test oil 10mL (4.2, 10.14).
• For cleaning and preparation of steel balls, see 10.1, 10.1.1, 10.11, 10.12, 10.13.

8. Analytical procedure

• 10.1 Soak the four test steel balls, the upper and lower ball holders and the oil cup in n-heptane for 1min, then clean with an ultrasonic cleaner for 10s. Replace with fresh n-heptane and rinse.
• 10.1.1 Repeat the step in 10.1 with acetone, and blow dry with nitrogen.
• 10.2 Install a clean test steel ball on the spindle of the test machine.
• 10.3 Install three clean test steel balls in the oil cup and clamp them with the holder.
• 10.4 Pour 10mL of break-in oil into the oil cup so that the break-in oil fills the gaps in the oil cup and covers the tops of the steel balls by at least 3mm. After the break-in oil fills the gaps in the oil cup, observe whether the oil level still maintains its original level.
• 10.5 Install the oil cup on the test machine (at this time the loading system should be balanced to zero). Slowly apply the test load to 392N, avoiding impact.
• 10.6 Turn on the heater switch to heat the test oil.
• 10.7 After reaching the test temperature, start the motor to drive the upper steel ball to rotate at 600r/min±30r/min. For test machines with an automatic start function, a temperature controller is used; it will start when the temperature is below the set temperature, and the corresponding value should be set so that the test machine starts when the temperature is 2℃ (4℉) below the set temperature.
• 10.8 After the test has run for 60min±1min, turn off the heater and spindle motor, and remove the oil cup.
• 10.9 Pour off the break-in oil in the oil cup and wipe the area near the wear scars with silk.
• 10.10 Pour off the test oil in the oil cup and wipe the area near the wear scars with silk, and place the oil cup holding the three steel balls on a microscope base designed according to the requirements. Each wear scar is measured twice, once along the radial line direction of the holder center, and the other at an angle of 90° to the previous measurement. If the wear scar is elliptical, measure once along the direction of the wear scar and once perpendicular to the wear scar. During measurement, the line of sight should be kept perpendicular to the surface being measured. Report the average wear scar diameter of the six measurements. If the average wear scar diameter is 0.65mm±0.05mm, proceed with the test according to the following steps; otherwise, replace the test balls and repeat the break-in procedure from 10.1 to 10.10. (For different test machines, the break-in wear scar may exceed this range, but the deviation of repeated results should be ±0.05mm; users should first determine the average break-in wear scar diameter of that test machine.)
• 10.11 Add n-heptane to the oil cup and soak for 1min while shaking continuously, then pour off the n-heptane. Use a rubber bulb to draw up n-heptane and rinse the residual lubricating oil inside the oil cup. Repeat this step twice. Finally, use a rubber bulb to draw up acetone and clean the inside of the oil cup twice, and blow dry with nitrogen.
• 10.12 Wipe the surfaces of the upper steel ball and the upper steel ball holder with clean silk moistened with n-heptane and acetone respectively, and blow dry with nitrogen.
• 10.13 Wipe the wear scars of the three steel balls and the wear track of the upper steel ball with clean silk moistened with methyl ethyl ketone.
• 10.14 Add test oil to the oil cup; after the test oil fills the gaps in the oil cup, it is required to cover the tops of the steel balls by at least 3mm. Observe whether the liquid level still maintains its original level after the test oil fills the gaps in the oil cup.
• 10.15 Install the oil cup onto the testing machine, slowly apply the 98.1N test load, and avoid load impact.
• 10.16 Turn on the heater switch, set the temperature to 75℃±2℃, and heat the test oil.
• 10.17 After the oil temperature reaches the test temperature, start the motor to drive the spindle at 600r/min±30r/min rotational speed for 10min, and record the torque value at 10min. The test is divided into ten stages in total, starting from 98.1N, increasing the load by 98.1N every 10min, with a maximum load of 981N. Shutdown is not allowed during the entire test; when the friction torque suddenly increases, stop the test.
• 10.18 Sequentially turn off the heater and the power switch. Measure the wear scar diameters of the lower three balls as described in 10.10, to an accuracy of 0.01mm, and observe the wear scar morphology.
• Differences from ASTM D5183-95 (1999) (foreword): in clause 4.2 and chapter 10, the acceptable range for the running-in wear scar diameter is changed from 0.67mm±0.03mm to 0.65mm±0.05mm.

9. Qualitative and Quantitative Determination and Calculation Formulas

• 11.1 Determine the friction coefficient using formula (1) or formula (2):

μ = 0.0023 · fL/P …… (1)

Where:

• μ—— friction coefficient;
• f—— friction force, g;
• L—— friction arm length, cm;
• P—— test load, kg.

Note: For a testing machine with an arm length of 7.62cm (3in), when the friction force is displayed in units of gram-force, use μ=0.0170f/P.

μ = 0.00227 · fL/P …… (2)

Where:

• μ—— friction coefficient;
• f—— friction force, N;
• L—— friction arm length, cm;
• P—— test load, kg.

Note 1: For a testing machine with an arm length of 7.62cm (3in), when the friction force is displayed in units of newton, use μ=1.73f/P. Note 2: For a testing machine that directly reads the friction force, users may refer to its operating manual to determine the calculation formula.

• Appendix A (informative appendix) friction coefficient calculation: provides a schematic diagram for friction coefficient calculation (Figure A.1) and formulas (A.1) to (A.6). Contact angle = 35.2644°, friction radius = 3.66175mm (metric) / 0.14434in (imperial); P=cos(35.2644°)N=0.8164965N, N=1.224745P. Note: all dimensions marked in Figure A.1 are metric; the above data cannot be used for the rolling four-ball test. Meanings of formula variables in Appendix A: μ—— friction coefficient; T—— friction torque; L—— test arm length; P—— test load; N—— total contact load on the three steel balls; f—— total contact friction force. (The formula details in Appendix A are doubtful due to source-text extraction noise and require confirmation against the source standard (source-text extraction))

10. Precision

• 13 The precision of this test method is obtained by statistical calculation from test data of multiple laboratories (95% confidence level).
• 13.1 Repeatability (r): Under constant operating conditions, using the same test material, with correct operation according to the test method requirements, and conducting consecutive tests by the same operator on the same testing machine, the difference between the two results obtained shall not exceed the value calculated by the following formula.

r = 0.20 × X …… (3)

Where: X—— the average of the two repeat test results.

• 13.2 Reproducibility (R): Using the same test material, two test results independently obtained by two operators in different laboratories shall not differ by more than the value calculated by the following formula.

R = 0.49 × X …… (4)

Where: X—— the average of the two test results.

Note: Under a load of 40kg, test steel balls are arbitrarily selected, and the friction coefficients obtained according to this test method are listed as precision calculation data.

• 13.3 Bias: The bias of this standard has not yet been determined.

11. Report

• 12.1 Report the following contents:
• 12.1.1 Average running-in wear scar diameter, mm.
• 12.1.2 Friction coefficient for each increase of 98.1N load.
• 12.1.3 Failure load, N.
• 12.1.4 Final average wear scar diameter, mm.

12. Referenced Documents

• GB 308 Steel balls
• GB 686 Acetone
• SH/T 0006 Industrial white oil
• SH/T 0189 Determination of anti-wear properties of lubricating oils (four-ball machine method)
• ASTM D5183-95 (1999) (the original standard modified and adopted)
• Foreword note: deleted standards in ASTM D5183-95 (1999) that are not directly cited by this standard; the cited standards adopt the corresponding current standards of our country.

13. Source and verification

This page is an AI translation of the available Chinese method card. Human verification is pending. It is not an official translation of the standard. Check the source standard and product certificate before use.

14. Quick Reference Q&A