Effects of Contamination on Selected Rheological and Tribological Properties of Lubricating Greases Working in Underground Mines

Abstract

This study examines the effect of mining pollutants and wear products on the rheological and tribological properties of a lubricating grease working in the microclimate of the Polkowice-Sieroszowice mine belonging to the KGHM Polska Miedź Group (Polkowice, Poland). The material under investigation is a commercial lubricating grease thickened with complex lithium soap, based on mineral oil with a molybdenum disulfide (MoS2) addition. A sample of the grease was taken from one of the friction junctions of a self-propelled drilling jumbo operated in the mine. Comparative tests of the fresh grease and the spent grease were carried out. For the two greases, rheological tests, i.e., dynamic oscillation tests and tests in steady flow conditions, were carried out at a constant shear rate. The rheological tests were conducted using a rotational rheometer. Moreover, the tribological characteristics of the tested greases under different friction junction loads were carried out using a ball-on-disc tribometer. Besides friction resistance, the lubrication ability of the two greases was also evaluated through an analysis of the wear of the steel disks after the friction process. Contour and topographic maps of the wear traces of the discs together with their wear profiles were compared.

Energy Dissipation in Tribological Stressed Greases

“…A more detailed investigation in [18] provided conditions for the initiation of instability. Several dissipation mechanisms were considered and, among others, a criterion with ∂γ critic ∂ϵ < 0 and ∂F f ∂ϵ > 0 (5) was found. This means that, with decreasing critical deformations γ critic at increasing ϵ and simultaneously increasing fragmentation rate F f of the agglomerates, there is a possibility of instability occurring.…”

“…The general lubricating grease behavior under frictional load, i.e., in the presence of a shearing process, has been investigated and documented in many studies, e.g., [1][2][3][4][5].…”