Even if water has more favorable thermal characteristics than oil, its use in the realm of bearings is still restricted to some rare applications. Moreover, the presence of water in lubricating circuits is seen as not at all desirable. The contamination of oil by water results in dangerous effects on lubrication. In relation to this, the study of thermal enhancement that this contamination can provide is seen to be insignificant. The literature demonstrates the damaging effects of this type of contamination. However, the existing studies are commonly based on an analysis of the results obtained after a bearing failure. The present study evaluates the instantaneous effect of the water-oil mixture on hydrodynamic lubrication for significant levels of water concentration, up to 10% by mass. The aim of the work is to identify the conditions for which the presence of water is detrimental in lubrication. Such conditions could then be avoided and a new generation of lubrication circuits could be designed to be immune against water contamination. Moreover, any positive effects of water contamination on lubrication deserve to be studied, the possibility being that new lubricant concepts might emerge. Thus, the rheological behavior and thermal characteristics of the mixture (density, specific heat, and thermal conductivity) were numerically modeled and simulations of bearings operating with this mixture were performed. The lubrication characteristics were also measured on a tilting pad thrust bearing, similar effects to those obtained numerically being observed. The presence of water has a slight effect on lubrication, which is nevertheless recognized to amount to an improvement in the lubrication characteristics. In fact, it is found that pure oil could be replaced by a water-in-oil emulsion having the same viscosity. In this case, the film thickness and the friction coefficient will be weakly modified, whereas the bearing will run at a lower temperature. From the point of view of safety, this indicates a significant advantage in operating conditions.

Several studies have been carried out in order to describe the impact of water-contaminated lubricants on lubrication performance. One approach considers the water-contaminated oil as a homogeneous lubricant with physical characteristics varying with water concentration. The presented work is being achieved in order to experimentally validate this theory. First investigations showed that the variation of contaminated lubricant viscosity has the most significant effect on lubricating performance. Consequently, the lubricant viscosity is the only parameter taken into account in this study. Thus, based on the rheological measurements, water-in-oil emulsion viscosity has been modelled according to water concentration and temperature. Water concentration was considered relatively to total mass of oil: the mass concentration varied then from 0 to 7% and temperature from 10 to 80 • C. Viscosity modelling was then used to perform the numerical simulations of a hydrodynamic thrust bearing supplied with water contaminated oil. Finally, the experimental validation will be done by measuring various bearing characteristics like the film/pad temperature, the film thickness and the friction torque on a tilting pad thrust bearing test rig.

The effect of water contamination on the lubrication has been described in several studies. Water has been defined as a dangerous contaminant which has a very detrimental impact on bearing performance. Nevertheless, many of the previous studies are based on post-accidental analyses, made after the lubrication failure. Thus, these analyses do not take into account all the possible conditions of the presence of water in the oil that can describe the situation. For instance, the case of water-in-oil fine emulsion has never been considered neither the experimental study of the water effect in the case of bearings. Experiments presented in this study were carried out on an eight shoes tilting pad thrust bearing supplied with water-contaminated oil. The contamination rate reached 10% of water by mass while the mixture was a water-in-oil emulsion. Results show that the presence of water is not such detrimental as could have been expected for the cases studied and moreover, that the bearing could have an enhanced behaviour while operating with the presence of water in the oil.

No abstract

Burr formation is a significant problem during manufacturing and leads to a lack of geometrical quality through the appearance of undesired and undefined shapes on the workpiece. Thus, understanding the burr formation and elaborating of predictive models are helpful for process design in order to avoid or to reduce burrs and to optimize the strategies for eventual deburring. This study presents both an experimental approach and a model for the plane milling of openwork parts, where burrs are a significant factor. A large-scale analysis of relevant geometrical parameters and their interactions are performed. A phenomenological burr size model is established considering local parameters and the specificities of 3D cutting in milling. Based on local parameters, this article proposes a new methodology to simulate burr height along any part edge and for most face-milling trajectories. Simulations and validations during tool path exits, with changing local parameters, are presented. In addition to the quantitative approach, new 3D aspects of face milling in relation with exit order sequence (EOS) are developed.