GB/T 12583-1998 Determination of extreme pressure properties of lubricants — Four-ball method

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GB/T 12583-1998, Determination of extreme pressure properties of lubricants — Four-ball method, specifies three tests for the extreme pressure properties of lubricants: load-wear index (LWI), weld point (P_D) and maximum non-seizure load (P_B).

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 methods for determining the extreme pressure properties of lubricants and covers the following three tests: 1.1.1 load-wear index LWI; 1.1.2 weld point P_D; 1.1.3 maximum non-seizure load P_B. 1.2 This standard is applicable to lubricants. 1.3 This standard involves certain hazardous materials, operations and equipment, but it is not the intent to address all safety issues associated with them. Users should therefore establish appropriate safety and protective measures and determine applicable management rules before using this standard. 1.4 This standard uses legal units of measurement, with the customary non-legal units given in parentheses. Not applicable: the available material does not provide an explicit non-applicability clause.

Principle: One top ball of the four-ball machine rotates under an applied load against three stationary balls in an oil cup. The sample in the oil cup immerses the three test steel balls. The spindle speed is 1 760 r/min ± 40 r/min. The sample temperature is 18 °C to 35 °C. Loads are applied stepwise as specified in this standard and a series of 10 s tests is run until welding occurs. Ten tests are run before the weld point. If fewer than ten tests are made between the maximum non-seizure load and the weld point, and the wear scar diameter before the maximum non-seizure load is within 5 % of the wear scar diameter on the corresponding compensation line (portion AB in Figure 1), these tests need not be run, and their corrected loads can be obtained from Table 3; in that case it may be assumed that the wear scar diameters produced at the maximum non-seizure load and before it are equal to the compensation diameter, so that a total of ten tests is reached by extrapolation. The assumed wear scar diameters are given in Table 1. The curves for the maximum non-seizure load and the weld point are shown in Figure 1.

Apparatus: Four-ball extreme pressure test machine: either hydraulic or lever type; the spindle speed shall meet the upper limit required by the test conditions, and the load shall be not less than 7 845 N (800 kgf). The four-ball oil cup assembly is shown in Figure 2. NOTE 1: It is important to use the four-ball EP test machine and the four-ball wear test machine separately. The four-ball EP test machine is suitable for extreme pressure tests but has poorer accuracy and is not suitable for wear tests. NOTE 2: The four-ball EP test machine should be calibrated every year with reference oils, and the reliability of its compensation line should be checked. 6.2 Microscope: a direct-reading microscope fitted with a micrometer, or an automatic precision measuring instrument. Readings accurate to 0.01 mm. 6.3 Timer: accurate to 0.1 s. 6.4 Friction force recorder.

Reagents and reference materials: Petroleum ether: 60 to 90 °C, conforming to the NY-90 requirement of GB 1922. 7.2 Solvent naphtha: conforming to the NY-190 requirement of GB 1922. 7.3 Test steel balls: test steel balls specially for the four-ball machine. High-quality chrome alloy bearing steel GCr15A, ball diameter 12.7 mm, hardness HRC 64 to 66. NOTE (8.1): Do not clean with carbon tetrachloride or other solvents having load-carrying properties, as this would affect the test results.

Key conditions: Spindle speed: 1 760 r/min ± 40 r/min (see Clause 4, 8.2). Sample temperature: 18 to 35 °C (see Clause 4, 9.4). Test duration: 10 s ± 0.2 s (see 9.6). Load stages: the load stages listed in Table 1 (59 N (6 kgf) to 7 845 N (800 kgf) etc., see column 2 of Table 1). Starting load for weld point determination: generally starts at 784 N (80 kgf) (see 9.10). Oil cup nut torque (NOTE, 9.1): 68 N·m ± 7 N·m (6.93 kgf·m ± 0.71 kgf·m) improves repeatability; when a torque of approximately 136 N·m (13.87 kgf·m) is applied, the weld point is markedly lower.

Calculation and results: Maximum non-seizure load P_B: determine and report the maximum non-seizure load P_B as specified in 9.9, in N (kgf). 10.2 Weld point P_D: determine and report the weld point P_D as specified in 9.10, in N (kgf). 10.3 Load-wear index LWI: 10.3.1 Calculate and report the load-wear index LWI in N (kgf) according to equation (3): Equation (3): LWI = (A₁ + A₂) / 10 (the formula in the original is [source unclear] and illegible, [to be verified] ([source unclear])) where: A₁ — sum of the corrected loads of the ten tests before the weld point, N (kgf); A₂ — sum of the corrected loads on the compensation line, N (kgf); A₂ — sum of the corrected loads after the maximum non-seizure load, N (kgf). (NOTE: the symbols A₁ and A₂ here are [source unclear] duplicated/ambiguous in the original, [to be verified] ([source unclear])) NOTE: If the test results conform to the compensation line, A may be defined as the sum of the sum of the corrected loads on the compensation line before the weld point, A₁, and the sum of the corrected loads off the compensation line, A₂, making ten load stages in total. 10.3.2 Corrected load P_J: the corrected load P_J of each test between the maximum non-seizure load and the weld point, N (kgf), is calculated according to equation (4): Equation (4): P_J = L·D_h / x (the formula in the original is [source unclear] and illegible, [to be verified] ([source unclear])) where: L — test load. For a lever-type four-ball machine, L is the total gravity of the weights and weight pan multiplied by the lever arm ratio, N (kgf); D_h — Hertzian diameter, mm; x — average wear scar diameter measured in the test, mm. If the wear scar diameters at and below the maximum non-seizure load are within 5 % of the compensation line, they may be assumed to be equivalent to the compensation diameter. These tests therefore need not be carried out, and their corrected loads can be found from Table 3 at the intersection of the maximum non-seizure load and the weld point. For example, if the maximum non-seizure load of a sample is 510 N (52 kgf), and tests are then run at loads of 618, 784, 981, 1 236 and 1 569 N (63, 80, 100, 126 and 160 kgf) and the weld point is 1 961 N (200 kgf), Table 3 gives 1 457 N (148.6 kgf) at the intersection of P_B 490 N and P_D 1 961 N (50 kgf and 200 kgf). This value is the sum of the corrected loads on the compensation line; it is obtained by using the compensation line to determine the wear scar diameters at loads of 490, 392, 314, 235 and 196 N (50, 40, 32, 24 and 20 kgf) respectively and summing the corrected loads at each stage. Corrected loads for the part off the compensation line are calculated stage by stage according to equation (4). Related calculation formulae for terms: 3.4 Hertzian diameter D_h: D_h = 4.08×10⁻² P^(1/3) … (1), where P — static load, N; D_h — Hertzian diameter, mm. If the static load is expressed in kgf, equation (1) is written: D_h = 8.73×10⁻² P^(1/3) … (2) Annex A (informative) Rapid calculation of the load-wear index (LWI): A1 Scope: this method is applicable to the rapid calculation of the load-wear index LWI of lubricants, especially for screening large numbers of samples. A2 Test procedure: A2.1 determine the maximum non-seizure load P_B as specified in 9.9 of this standard. A2.2 determine the weld point P_D as specified in 9.10 of this standard. A3 LWI calculation: calculate LWI according to the following formulae, first taking into account the stage difference between P_B and P_D. A3.1 When the stage difference between P_B and P_D is ≤2: LWI = 0.230 P_B + 0.130 P_D … (A1) A3.2 When P_D ≥ 9.8×620 N or the stage difference between P_B and P_D is ≥8: LWI = 0.184 P_B + 0.092 P_D + 4.9 … (A2) A3.3 When P_D ≤ 9.8×160 N: LWI = 0.1160 (P_B + P_D) … (A3) A3.4 When 9.8×200 N ≤ P_D ≤ 9.8×500 N: LWI = 0.116 (P_B + P_D) + 3.6 … (A4)

Quality control: Precision and bias: if the test results conform to the compensation line, judge the reliability of the test results as follows (95 % confidence level). 11.1 Repeatability: the difference between the results of two consecutive tests by the same operator, using the same equipment and the same sample under the specified conditions, shall not exceed the following values: maximum non-seizure load: 15 % of the mean; weld point: one load stage; load-wear index: 17 % of the mean. 11.2 Reproducibility: the difference between independent test results from two laboratories, obtained by different operators, in different laboratories, using the same sample under the specified conditions, shall not exceed the following values: maximum non-seizure load: 30 % of the mean; weld point: one load stage; load-wear index: 44 % of the mean. 11.3 This standard does not establish precision for samples with a weld point greater than 3 922 N (400 kgf) or for samples whose test results do not conform to the compensation line. 11.4 Bias: since no suitable data are available for this standard, its bias has not been determined.

Normative references: GB 1922 Solvent naphtha

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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