Optimized tribo-design of lubricants for power loss reduction in journal bearings used in process industry

The aim of the paper is to optimize the tribological characteristics of lubricating oils that are used in the process industry during machining. In several cases, the machines employed are organized in several “stands” forming “lines” and are equipped by several spindles supported by journal bearings, fed by the same oil. Typically, the spindles supported by the bearings rotate at increasing speeds from the feeding of the blank material to the outlet of the machined one. The power loss on the single spindle is different from the others, not only for the different rotational speed, but also because the oil with which the single bearing is fed has different temperature and, thus, different viscosity. At present, standard mineral oils for typical use are employed. Owing to the large power loss in these kinds of plants, an attractive idea for power saving is, therefore, to formulate a lubricating oil which, globally, along the entire line, has the best rheological characteristics depending on the actual rotational speed of all spindles. In this paper, the modelling of the line is presented, by using a TEHD (thermo-elasto-hydro-dynamic) model for the calculation of the power dissipated in each journal bearing and the lubricating oil characteristics are defined by means of a multivariate optimization on the parameters of viscosity, temperature and thickness of the oil film. Finally, the optimized dynamic viscosity curve is obtained and can be used for the formulation of an oil, not necessary of mineral origin, with suitable additives.