Summary • The amount of alternating current and direct current has no effect on the friction values during a dynamic tribo- testing
• Lubricants containing ZDDP show significantly higher ECR values than ZDDP-free formulations.
• Increasing the AC current through the oils formulated with ZDDP can strongly affect the wear scar starting from 10 mA
Figure 5: Wear scare areas and depths for oil 1 ZDDP at different AC current intensities.
Higher wear area and dept are measured generally by adding DC currents during the Tribo-testing with SRV®
• Under DC, ZDDP-containing oils cause more severe wear than under AC, especially above 100 mA.
• Some similar trends are observed in DC and AC, but the insulation effect of the ZDDP-induced tribo-film is more pronounced in oils than in greases.
. Highly significant is the high wear scare value at 200 mA DC, as shown in Figure 6.
Long-term test of rolling friction of greases and measurement of ECR The rolling friction values of two greases (Grease 1 containing ZDDP and Grease 2 not containing ZDDP) were tested in accordance with the ASTM D8317-23 standard. The electrical contact resistance (ECR) was measured over a 19-hour test period at 100 °C during the rolling friction test with the addition of 200 mA AC.
Figure 6: Wear scar areas and depths for oil 1 at different DC current intensities.
In case of both greases for both current types of changes in the wear scare, the values were not significant.
Exemplary the results for grease 2 for DC current is illustrated in Figure 7.
Figure 7: Wear scar areas and depths for grease 2 at different DC current intensities.
Figure 8: ECR values of two greases under 200 mA, AC at rolling movement.
Although the two greases show very similar rolling friction values, their ECR behaviour was very different.
20 LUBE MAGAZINE NO.190 DECEMBER 2025
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