Abstract
PurposeThe purpose of this paper is to find a reason of a very high lubrication effectivity of a lithium grease filled with PTFE and copper powders when used as a lubricant between contacting steel surfaces under mixed friction conditions.Design/methodology/approachThe paper presents the results of the differential thermal analysis (DTA) of a lithium grease lubricant filled with 6 wt% PTFE and 6 wt% Cu and of a 1:1 mass mixture of PTFE and copper powders alone. The chemical composition analysis of post‐DTA residual substances was carried out using the x‐ray microanalysis. The same method was employed for the examination of the chemical composition of the post‐test friction area in the balls of a four‐ball apparatus. The balls were lubricated with three greases: without any fillers (the base 1S lithium grease), with one filler (6 wt% Cu), and with two fillers (6 wt% PTFE and 6 wt% Cu). For the latter compound, the load was 500 daN, for the remaining compositions, the load was 126 daN.FindingsThe results of the analyses done confirmed a thesis that the synergism of PTFE and Cu in the tested grease under mixed friction conditions is possible due to the thermal decomposition of PTFE and creation – as a result of a reaction of this decomposition products with an earlier formed platering layer – of new layers that are (to a high probability) complexes containing copper, fluorine, and sulphur.Practical implicationsPTFE and copper powders when used as fillers for a lithium grease form a very effective lubrication compound for steel sliding pairs. The application of this compound results in an overall reduction of friction and wear that is greater than a simple summation of gains obtained when using these two additives separately.Originality/valueIt was proved that a dominant factor contributing to the synergistic effect of PTFE and copper in a lithium grease when used for the lubrication of steel surfaces is the fluorine that originate from the thermal disintegration of PTFE and not sulphur from the base grease.
Subject
Surfaces, Coatings and Films,General Energy,Mechanical Engineering
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