Assessment of the effect of temperature, shear rate and thickener content on the thixotropy of lithium lubricating greases

Abstract

As part of this research the thixotropy of lubricating greases based on mineral oil ORLEN OIL SN-400, thickened with lithium 12-hydroxystearate has been investigated. The investigations consisted in shearing grease samples in the rotational rheometer head for 1 h, followed by 24- h relaxation and again 1-h shearing, at a constant shear rate gradient. The increase in the structural viscosity of the grease, caused by the partial reconstruction of the lithium thickener microstructure between the two shearing stages, after 24- h relaxation, was studied. The studies have shown that there is a non-unique dependence between grease temperature T, shear rate gradient [Formula: see text], thickener percentage Sc and the intensity of grease microstructure reconstruction. In the adopted ranges of the input quantities: T (from −20 °C to + 80 °C), [Formula: see text] (from 8.1 to 48.6 s−1) and Sc (from 4% to 9%), the largest increment in structural viscosity was observed for the grease with thickener percentage Sc = 7.5%, sheared at shear rate gradient [Formula: see text] = 8.1 s−1 at temperature T = 28 °C. On the basis of the experimental studies, a mathematical relation for predicting the increment in the structural viscosity of lithium greases in different shearing conditions has been developed. The relation can find wide application in engineering practice in the design of machine lubrication systems and in the selection of lubricating media thickened with lithium soap.

Effect of grease thickener and surface material on rheological properties of boundary layer

“…Polyurea greases (about 5% of world production) form one of the largest groups among nonsoap greases [1]. Greases are rheologically complex non-Newtonian fluids with a diphase structure, showing thixotropic properties [2,3]. They are chemically and physically heterogeneous systems.…”

Effect of thermorheological properties on tribological behaviors of lubricating grease

“…Sánchez et al [2] found that as temperature increases, the soap fiber structure of lubricating grease becomes significantly thinner and the base oil is separated from the soap fiber structure, leading to reduced viscosity and better flowability of the lubricating grease. As observed by Paszkowski et al [3], the effects of temperature on the thixotropy of lubricating grease are closely related to the microscopic Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. soap fiber structure.…”

Effect of grease on bearing vibration performance caused by short-time high-temperature exposure

“…This clearly weakens the damping effect and reduces the anti-vibration effect. On the contrary, the LG has better heat flow and thixotropy performance [15,18], and the LG base oil has higher viscosity and better thermal tolerance, which result in an insignificant vibration rise. Further examining the vibration with WG shown in Fig.…”

“…Muller et al [16] and Delgado et al [17] studied the relationship between the microstructure and rheological properties of a lubricating grease at high temperature. Paszkowski et al [18] revealed that lithium grease softens, the apparent viscosity decreases, and chemical changes occur at the service limit temperature. With the increase in service limit temperature time, the grease solidified and the surface of soap crystals cracked, accompanied by the appearance of ketone and lipid oxidation products.…”