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Lube-Tech


4 Summary Within the frame of this study, three lithium and three lithium complex greases were produced based on various naphthenic base oils. The use of naphthenic base oils has kept the thickener content low, however, a direct correlation between the viscosity of these naphthenic base oils and the thickener content was found; the higher the viscosity the lower thickener content.


The tribological investigations have proven to be crucial when optimising the grease formulation for specific tribological contacts. However, the most interesting differences between the two different thickener systems have been observed in additivated greases;


a) The additivated lithium greases based on BO 150 and BO 400 showed higher wear values than the non-additivated greases. While same package reduced significantly the wear values of disk when used in lithium complex greases, Figure 6 and 8.


b) The “Additive package II” (which contains an extra dosage of extreme pressure additive) performed differently in different test rigs; - SRV tests; an increase of the wear values regardless the thickener type for the greases based on BO 600 has been observed, Figure 10.


- Four-ball tests; positive impacts (both on the wear scar diameter and load carry capacity) have been observed for the lithium grease. In the case of the lithium complex grease (Sample # 10) this positive effect was only monitored on the load carrying capacity in Table 7.


c) The thickener content of a grease seems to affect the tribological performance which, in turn, is dominated by the characteristics of the base oil, e.g. its polarity, degree of solvency and viscosity.


PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE


No.136 page 9


d) The conditions in SRV and four-ball rigs are different which can explain the different outputs. This also emphasises the necessity of selection of relevant test methods that may supposed to simulate the actual conditions of applications in the fields, otherwise the obtained data may lead to the wrong conclusions.


In complex systems, such as lithium and lithium complex greases, the components involved may sometimes interfere with each other, hence, in order to formulate a high-performance grease, the use of tribological tests, as demonstrated in this study, could be of valuable assistance.


Acknowledgment


The authors would like to thank Dr. George Dodos at Eldon’s for the four-ball measurements.


Reference: [1] G. Patzer, Evaluation of High-Performance Lubricating Greases on the what does this mean? Tranlatory Oscillation Tribometer, Materials Performance & Characterization, ASTM International, Voil.7, No.3, 2018, p. 340 – 354.


[2] M. Fathi-Najafi et.al, The impact of high viscous naphthenic oils in various thickener systems, Eurogrease 3, July-August-September 2018


LINK www.nynas.com


LUBE MAGAZINE NO.165 OCTOBER 2021


37


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