GB/T 3142-2019 Determination of load-carrying capacity of lubricants — Four-ball method

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GB/T 3142-2019, Determination of load-carrying capacity of lubricants — Four-ball method, specifies the determination of maximum non-seizure load (P_B), weld load (P_D) and comprehensive wear value (ZMZ) on a four-ball extreme-pressure tester.

Evidence note: The content of this page was compiled from the original text of this standard held in the Origin Standard library (where marked [to be verified], the source is [source unclear]); for individual values and the current status, please refer to the original standard page and the product certificate.

Scope: This standard specifies the method for determining the load-carrying capacity of lubricants using a four-ball extreme-pressure tester, including the determination of three indices: maximum non-seizure load (P_B), weld load (P_D) and comprehensive wear value (ZMZ). This standard is applicable to lubricants. In practice, different evaluation indices may be selected according to the different applications of the lubricant. Not applicable: the available material does not provide an explicit non-applicability clause.

Principle: Four steel balls are arranged in a regular tetrahedron. The upper ball rotates at 1 450 r/min ± 50 r/min, and the three lower balls are held together in an oil cup; load is applied to the balls from below through a lever or hydraulic system. During the test the contact points of the four steel balls are all immersed in the lubricant. Each test lasts 10 s, and after the test the wear scar diameter of any one of the balls in the oil cup is measured. Tests are repeated according to the specified procedure until the evaluation index representing the load-carrying capacity of the lubricant is obtained.

Apparatus: Four-ball extreme-pressure test machine: a) the core part is shown in Figure 2; b) spindle speed 0 r/min to 3 000 r/min, load range 59 N to 9 810 N; c) it shall have a rigid, vibration-resistant structure. The radial runout of the friction assembly (upper steel ball) of the four-ball machine, measured at 3.5 mm from the lowest point of the steel ball, shall not exceed 0.02 mm. The four-ball extreme-pressure test machine shall be calibrated every year with reference grease (see Annex A), and the reliability of its compensation line checked (see Annex B). NOTE: It is preferable not to carry out both extreme-pressure tests and wear tests on the same four-ball machine, so as not to affect the sensitivity of the wear tests. Microscope: a direct-reading microscope fitted with a micrometer, or an automatic precision measuring instrument. Readings accurate to 0.01 mm. Timer: accurate to 0.1 s. Friction force recorder: an instrument capable of directly recording changes in friction force.

Reagents and reference materials: 4.1 Reagents Cleaning agent: No. 1 solvent naphtha conforming to GB 1922—2006. Warning — flammable, harmful to health. Petroleum ether: petroleum ether with a boiling range of 60 °C to 90 °C conforming to GB/T 15894—2008. Warning — flammable, harmful to health. 4.2 Materials Steel balls: test steel balls specially for the four-ball machine. Material conforming to E-52100 chrome alloy steel balls in the American ANSI standard, or high-carbon chromium bearing steel balls conforming to GB/T 308.1—2013, diameter 12.7 mm, hardness HRC 61 to 66. Reference grease: specification requirements see Table A.1 in Annex A.

Key conditions: Room temperature: 25 °C ± 5 °C. Spindle speed: 1 450 r/min ± 50 r/min. Idling time: start the motor and idle for 2 min to 3 min. Test duration: 10 s each time. Load range: 59 N to 9 810 N. Load stages: Table 1 lists stages 1 to 23, corresponding to loads P/N of 59, 78, 98, 128, 157, 196, 235, 314, 392, 491, 618, 785, 981, 1 236, 1 570, 1 962, 2 453, 3 090, 3 924, 4 905, 6 082, 7 848, 9 810 (NOTE: for doubtful values in [source unclear] see Clause 13). When determining the weld load, the oil cup shall be tightened to a torque of at least 85 N to ensure that the lower balls do not roll during the test.

Calculation and results: Calculation of Hertzian diameter D_H (equation 1): D_H = 4.08×10⁻³ P_m^(1/3) where: D_H — Hertzian diameter, in millimetres (mm); P_m — static load, in newtons (N). Calculation of corrected load P_corr (equation 2): P_corr = P · D_H / D where: P — actual load. For a lever-type four-ball machine, P is the total weight applied (weights and weight pan) multiplied by the lever arm ratio, in newtons (N); D_H — Hertzian diameter, in millimetres (mm); D — measured wear scar diameter, in millimetres (mm). Calculation of comprehensive wear value ZMZ (equation 3): ZMZ = (A₁ + A₂ + B/2) / (A + B/2) (NOTE: the formula appears in [source unclear] as “ZMZ-1+B/2_A, +A, +B/2”, apparently containing noise, [to be verified] ([source unclear])) where: A — when P_D is greater than 3 924 N, A is the sum of the corrected loads of 3 090 N and the 9 stages below 3 090 N; when P_D is less than or equal to 3 924 N, A is the sum of the corrected loads of 10 stages; B — when P_D is greater than 3 924 N, B is the arithmetic mean of the corrected loads of the stages from 3 924 N up to but not including the weld load; when P_D is less than or equal to 3 924 N, B is 0; A₁ — the sum of the corrected loads before the P_B point, i.e. the part on the compensation line; A₂ — the sum of the corrected loads after the P_B point and before 3 090 N. Reporting of results: Maximum non-seizure load: report the value of P_B, in newtons (N). Weld load: report the value of P_D, in newtons (N). Comprehensive wear value: calculate according to equation (3) and report ZMZ, in newtons (N). Report: take the arithmetic mean of two replicate determinations as the determination result.

Quality control: General: if the test results conform to the compensation line, judge the reliability of the results as specified below (95 % confidence level). 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 sample shall not be greater than the following values: a) P_B — 15 % of the mean; b) P_D — one load stage; c) ZMZ — 10 % of the mean. Reproducibility R: the difference between two single, independent test results obtained by different operators, in different laboratories, using different instruments and following the same method on the same sample shall not be greater than the following values: a) P_B — 30 % of the mean; b) P_D — one load stage; c) ZMZ — 25 % of the mean. NOTE: This standard does not establish precision for lubricants that do not follow the mean compensation line (the whole load-wear curve lying above the mean compensation line). Bias: since the maximum non-seizure load, weld load and comprehensive wear value in this standard are all defined by this standard, the method in this standard has no bias.

Normative references: GB/T 308.1—2013 Rolling bearings — Balls — Part 1: Steel balls GB 1922—2006 Solvent naphtha for paints and cleaning GB/T 15894—2008 Chemical reagent — Petroleum ether GB/T 1.1—2009 (mentioned in the foreword, rules for drafting standards)

Verification note: [To be verified] and [source unclear] mark points that still need to be checked against the original standard text; they do not mean the values have been verified. Do not use these values or procedures directly as a basis for work.

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