The film thickness of a ball-on-disc contact lubricated with four greases of different formulations\nwas measured under different operating conditions until starvation. Two polymer-thickened\ngreases and two lithium-thickened greases, formulated with base oils of different nature and/or\nviscosity, were tested. The central film thickness was measured under constant operating conditions\n(load, temperature, slide-to-roll ratio) varying only the entrainment speed. In a separate test, the film\nthickness was measured over time with all operating conditions set to constant. Pictures of the\nfilm thickness profile across the contact area were also registered. The results were compared with\nthe fully flooded results. The coefficient of friction (COF) was measured in a ball-on-disc contact\nunder equal operating conditions and the results were correlated with the film thickness findings.\nThe different grease formulations and the influence of the operating conditions on the film thickness\nand COF were discussed. The polymer thickened the greases, promoting lower COF and higher film\nthickness, especially when there is thickener material crossing the contact which happens quite often\nfor these greases.
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