Lube-Tech
Figure 4: Profilogram displayed on a screen and taken perpendicularly in the centre of the wear track on a SRV®
test disk
It can be noted that the higher values of COF do not always result in an increased wear volume value. This is more pronounced in case of greases where many phenomena such as structure or depletion of thickener molecules, characteristic of the base oil, contribute to the complexity of the tribo-system.
To interpret the measured data for the six greases, the following aspects were considered: A) Impact of viscosity at the applied temperature B) Impact of the thickener system C) Impact of the concentration of the additives (only for BO 600 based greases; Grease C and F)
3.1 SRV tests on the greases based on BO 150 Figure 5 shows the COF values of four different formulated greases based on BO 150 (Grease A and Grease D).
PUBLISHED BY LUBE: THE EUROPEAN LUBRICANTS INDUSTRY MAGAZINE
No.136 page 5
complex), and b) the Lithium complex grease runs at a lower COF than the lithium grease.
Furthermore, when considering the wear volume on the disk and the ball and finally the total wear, the differences between the formulations are significant, Figure 6.
Figure 6: Wear volumes of different formulated greases based on BO 150
However, Figure 6 suggests that in the case of additivated lithium grease, the wear scar diameter remains unchanged, but the wear volume on disc shows a significant increase which cannot be explained. Hence, a separate investigation is required in order to find a possible reason.
3.2 Tribological tests on the greases based on BO 400 Figure 7 presents the COF results for four different formulated greases based on BO 400 (Grease B and Grease E).
Figure 5: Friction Coefficient for the Greases based on BO 150
Figure 5 suggests that a) the friction coefficient is lower for the additivated greases when comparing different thickener systems (lithium vs lithium
Figure 7: Friction Coefficient for the Greases based on BO 400
Figure 7 demonstrates the positive effect of the additive on COF for both thickener systems.
LUBE MAGAZINE NO.165 OCTOBER 2021 33
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