unaffected, and the wear scar diameter decreased for one grease. The wear volumes were more discriminative, confirming the wear trends and the different behaviours. Thus, an amperage step can either increase the wear protection or reduce the wear protection offered by a grease.
Figure 4: Wear scar diameters (WSD) and wear volumes of balls in a DC amperage step test using electrified ASTM D2266 mod. (100°C, FN= 392 N, 1.5 V DC, DC; t= 105 minutes).
Figure 5 shows the morphology of representative wear scars for the tests with the “Clay thickened, polyolester, NLGI 2“. In the case from the electrified test, wear increased and the wear scar revealed abrasive wear. This effect could have resulted from arcing that destroyed the tribofilm formation from functional additives or enhanced the built-up of iron oxides (Fe2
O3 , Fe3 O4
2.3 Loss of EP Protection Existing scuffing tests (O.K./pass load) determine the “last non-seizure load” by an increase (a) of load steps (by weight) and/or (b) in constant increments of Hertzian contact pressure. A third option to generate scuffing is by arcing with a constant amperage ramp rate. We saw an increase in wear in the amperage ramps-up and ramps-down by using a modified D2266 for the grease “clay thickened, polyolester, NLGI 2”. We then used this grease to test another methodology by running D2266 at a constant amperage, e.g. 1 A. The results are shown in Figure 6. For the wear scar diameter of 0.44 mm from a test at 1 A, the current density through the three tribo-contacts is 2.19 A/mm² under a geometric contact pressure P0 of 1,050 MPa. This result indicates considerable resistance to amperage, because the wear didn´t increase when compared to no amperage. This conclusion is also supported by the fact that the wear scar morphology was the same under 0 A and 1 A. As a consequence, the “loss of wear protection under amperage” seen in the step tests occurred above 1 A. Tests at constant current of 2 A or 3 A may be performed in the future to determine if wear protection is lost at higher current densities.
) on AISI 52100 steel, which also
protected against scuffing. Iron oxides have sufficient hardness to offer wear resistance, but their values differ from single crystals to nano-crystalline scales (Fe2
O3 , 5-6 Mohs hardness or 360-630 HV and Fe3 O4
5.5-6.5 Mohs hardness or 480-800 HV). This will be the subject of future studies.
0 Ampére
Ramped 0-3 A up and 3-0 A down
Figure 6: Impact of DC current at 75°C (4-ball, D2266 mod., FN= 392 N, 60 minutes; 1 A with 1.5 V DC).
Conclusions ,
Lubricants have a mature functional profile to reduce friction and protect against wear and scuffing. Amperage can make tribologically effective additives and formulations ineffective or may in fact be beneficial. To evaluate this effect, new electrified tribometric methodologies are being developed to reveal the positive or negative impacts of amperages on wear resistance as tools for lubrication engineers and formulators. This excerpt from the test programme showed that it is possible to identify existing formulations that respond well to amperage.
Figure 5: Morphology of wear scars on balls (Clay thickened, polyolester, NLGI 2; D2266 mod., 100°C, 0-3 A up, 3-0 A down, 1.5 V DC; t= 105 minutes).
LUBE MAGAZINE NO.190 DECEMBER 2025
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