Abstract
The paper presents the rheological behavior of a MP multifunctional grease (additived, for EP, containing Li and Ca soaps– for general use), experimentally obtained on the THERMO-HAAKE Viscotester VT550, as correlations, at different temperatures, between 15-60<sup>o</sup>C. It results a strong non-Newtonian behavior, with threshold, time depending (tixotropy or rheopexy, depending on the operating conditions). With the aid of the rheological parameters, obtained from the experiments, it is analyzed the influence on a ball bearing frictional coefficient in the contact zone ball-inner ring, in the case of the elasto-hydrodynamic-lubrication (EHL).
Highlights
Adequate lubrication is one of the key elements of the maintenance success; in most of the applications it is an optimum correlation between lubrication and safety
Characterization of lubricant rheological behavior can be done by rheological measurements resulting rheograms, viscosity variation with temperature, time dependent behavior, which give accurate results about grease behavior in service
Empirical relationships for the bearings frictional coefficient [6,7,8,9]. From our experiments it results that it doesn’t matter so much the equation we choose for frictional coefficient in the contact zone ball-inner ring, in comparison with the influence of the working conditions, manifested by temperature and shear rate on grease behavior
Summary
Adequate lubrication is one of the key elements of the maintenance success; in most of the applications it is an optimum correlation between lubrication and safety. Even failures, could have origin in lubrication deficiencies so this topic is of a great interest among the maintenance problems. The lubrication can be done: - with dedicated substances: fluids (oils), semi solids (greases) or gases, upon the technical parameters of the application; - with the working fluid (in some special cases when the contamination with lubricants is forbidden – often encountered in the food or chemical industries, for example). Characterization of lubricant rheological behavior can be done by rheological measurements resulting rheograms, viscosity variation with temperature, time dependent behavior, which give accurate results about grease behavior in service. Greases can show tixotropy or rheopexy, characterized by the fact that the loading and the unloading curves are not identically, the loading curve is above the unloading curve in tixotropy case and vice versa in the case of rheopexy. Previous experimental researches of the authors were done on other types of greases [2, 3], and the results were in concordance with the literature [4,5,6,7,8,9]
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