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Lube-Tech


The cut-off criteria of (the moment that seizure occurred) is defined in this standard ASTM D5706 B (COF > 0.0,2 for 20 s).


Based on the result obtained from this test, there is a tendency that the greases with lower viscosity and subsequently higher thickener content, show a better response to additive package I. Greases C and F, with the higher concentration of the extreme pressure agent (additive package II), do not show any increase in the load carrying capacity as expected.


PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE


No.136 page 8


scar diameters for the two greases is within the repeatability of the test. Furthermore, the significantly lower thickener content in Grease D has no negative impact on the wear scar or on the weld load.


b) The additive package I performs differently in lithium and lithium greases; i. In lithium complex greases significantly higher weld load is obtained.


ii. In the case of wear scar diameter, the additive package performs worst in Lithium complex grease based on BO 150 (Sample # 7) and best in lithium grease based on the same base oil (Sample # 2), an increase by almost 38 percent.


Table 5: Results of load carrying capacity tests measured by SRV® 5


3.5 Four-ball tests according to ASTM D 2266 and ASTM D 2596


Beside linear oscillating movement of ball on disk with SRV®


, four-ball tests according to ASTM D 2266 (wear scar test) and ASTM D 2596 (weld load test) have been conducted on all greases. It is inviable to highlight the major differences between the four ball tests and SRV tests; for example in the case of four-ball tests we have point contact and rotational condition while in the case of the SRV tests, used in this study, ball on plain surface and oscillatory movement.


The obtained results are summerised in Table 7.


a) Comparing two neat lithium greases (Sample # 1 & 6); an increase of the weld load by 25 percent probably has to be attributed to the viscosity of the base oil (BO 600). The difference in wear


36 LUBE MAGAZINE NO.165 OCTOBER 2021


c) The impact of additive package II in lithium and lithium complex greases based on BO 600 (Sample # 5 & 10); in the case of lithium greases (sample # 4 & 5), significantly higher load and lower wear scare diameter are measured which is in line with the expectations, however this could not be found in the case of lithium complex greases (sample # 9 and 10). Regardless of the reason behind this, it can be concluded that a higher concentration of the extreme pressure additive that is involved in package II, contributes to a more expensive formulation. This finding verifies the earlier observation that was found by SRV measurements, Table 5.


Table 7: Results of load carrying capacity and wear tests measured by four-ball machine.


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