ASTM D2596 for measurement of extreme-pressure properties of lubricating grease
ASTM D2596 for standard test method for measurement of extreme-pressure properties of lubricating grease (Four-Ball method)
10. Calculations and Reports
10.1 Corrected Load - Calculate and record (Table 1, Column 5) for each applied load between the last nonseizure load and weld point using the equation:
Corrected load, kgf = LD(h)/X
where:
L = applied load, kgf, that is, total weight applied (tray and weights) multiplied by lever arm ratio,
D(h) = Hertz scar diameter, mm, and
X = average scar diameter, mm.
10.2 Load-Wear Index - Calculate and report the Load-Wear Index (formerly Mean-Hertz Load) in kilograms-force using the equation:
Load - Wear Index, kgf = A/10
where:
A = sum of the corrected loads determined for the ten applied loads immediately preceding the weld point (Note 6).
NOTE 6 - If tests applied to the lubricant indicate it follows the compensation line, then A may be defined as:
A = sum of corrected loads plus compensation line corrected loads, for the ten applied loads immediately preceding the weld point.
For convenience, Table 2 has been constructed to give the compensation line corrected load for any portion of the compensation line. This value is obtained by noting the intersection of the last nonseizure load and weld load values. For example: the last nonseizure load of a lubricant was found to be 490 N (50 kgf). Subsequent runs in the seizure portion of the curve were made at 618, 784, 981, 1236, and 1569-N (63, 80, 100, 126, and 160-kgf) loads with weld-point found to be 1961 N (200 kgf). Table 2 notes the value at intersection of 490 and 1961 N (50 and 200 kgf) to be 1456 N (148.6 kgf). This value, the compensation line corrected load, was obtained by correcting loads of 490, 392, 314, 235, and 196 N (50, 40, 32, 24, and 20 kgf) using compensation line scar diameters. This fulfills the definition of Load-Wear Index, that a total of twelve runs be made, the eleventh run causing welding of the test balls and the twelfth to verify the weld point. If the tests applied to the lubricant indicate the wear scars do not follow the compensation line, then Table 2 cannot be applied and actual determinations must be made for all ten applied loads preceding the weld point.
10.3 Weld Point - Report the verified weld point as found in 8.11.
11. Precision and Bias
11.1 The precision of this test method as determined by statistical examination of interlaboratory results is as follows:
11.1.1 Load Wear Index (Formerly Mean-Hertz Load):
11.1.1.1 Repeatability - The difference between two test results, obtained by the same operator with the same apparatus under constant operating conditions on identical test material, would in the long run, in the normal and correct operation of the test method, exceed the following values only in one case in twenty:
0.14 (X)
where:
X = average of two test results.
11.1.1.2 Reproducibility - The difference between two single and independent results obtained by different operators working in different laboratories on identical test material would, in the long run, in the normal and correct operation of the test method, exceed the following values only in one case in twenty:
0.44 (X)
where:
X = average of the two test results.
11.1.2 Weld Point - Precision data were determined on samples having weld points up to a maximum of 6080 N (620 kgf).
11.1.2.1 Repeatability - The difference between two tests results, obtained by the same operator with the same apparatus under constant operating conditions on identical test material, would in the long run, in the normal and correct operation of the test method, exceed one increment loading only in one case in twenty.
11.1.2.2 Reproducibility - The difference between two single and independent results obtained by different operators working in different laboratories on identical test material would, in the long run, in the normal and correct operation of the test method, exceed one increment loading only in one case in twenty.
11.2 Last Non-Seizure Load:
Repeatability = 0.35 (X)
Reproducibility = 0.78 (X)
where:
X = average of the two test results.
11.3 Bias - The procedure in this test method has no bias because the value of extreme-pressure can be defined only in terms of a test method.
12. Keywords
12.1 extreme pressure; four-ball EP; grease; Hertz line; load-wear index; lubricating grease; weld point
