Abstract
ABSTRACTIn this article, the shear degradation of lithium 12-hydroxy stearate grease will be measured using an in-house-developed Couette aging machine. In this device the shear rate is well defined. The aging is related to the generated entropy density as described in Rezasoltani and Khonsari's work (Tribology Letters, Vol. 56, No. 2, pp. 197–204, 2014). The rheological properties of the aged samples were evaluated using a parallel-plate rheometer. The results showed that there are two aging phases with different degradation rates: a progressive degradation phase at the early stage, followed by a rather slow deterioration afterwards. Based on this observation, an aging equation was formulated to describe the aging behavior of lithium-thickened grease. Atomic force microscopy results of the fresh and aged greases showed that the variation in thickener microstructure provides a good explanation for the lithium grease degradation mechanism: under shear, the original fibrous network is progressively destroyed and becomes fragmented, leading to the loss of consistency and a change in the rheological properties.
Highlights
Grease is a widely applied lubricant mostly used in rolling bearings
It was found that this grease loses its original consistency during aging and shows a two-phase aging behavior
The aging is dominated by the breakage of smaller fiber fragments, and the grease degrades at a much slower rate
Summary
Grease is a widely applied lubricant mostly used in rolling bearings. It is a multiphase system consisting of three parts: thickener (3–30%), base oil (70–90%), and additives (Lugt (1)). When subjected to the severe conditions within a rolling bearing, grease will undergo high shear, possibly causing deterioration. The degradation of this grease is usually reflected by the loss of its original consistency (softening), possibly yielding leakage from the bearing and, starvation. It may lead to continuous churning and high temperature Both cases result in a reduced life of the bearing (Lugt (1)). It is valuable to investigate the mechanism of grease degradation and to develop predictive models for this
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
