On the film thickness behaviour of polymer greases at low and high speeds

Experimental batches of polymer thickened greases, as well as their base and bleed-oils were tribologically characterized through film thickness measurements over a wide range of entrainment speeds on a ball-on-disc test rig using optical interferometry. The results are in agreement with previous observations of several authors. Under fully flooded conditions and low speed it was observed that thickener lumps enter the contact producing a high film thickness plateau. The transition speed at which the film thickness increases with decreasing speed is dependent on the thickener content and operating temperature. At moderate to high speeds, all the tested greases show a film thickness much higher than the base and bleed-oils, even though the bleed-oil׳s film thickness is closer to the grease׳s.