Effects of Side Leakage in 120-Degree Centrally Supported Journal Bearings

Abstract

Abstract Theoretical treatment of journal-bearing lubrication, based on the assumption that the bearing is infinitely wide, and hence has no oil flow from the sides of the film, has been brought to a high degree of development during recent years. Less is known, however, of the various phenomena that occur in an actual oil film. Experiments, necessarily on a bearing of finite proportions and from which oil is leaking at the sides of the film, show results entirely different from those predicted by the theory which takes no account of side leakage. From the viewpoint of bearing design, it is highly desirable to have further information for applying the excellent theoretical charts now available. The most important work on this problem has been done by A. G. M. Michell (4) and Albert Kingsbury (5). In 1905, Mr. Michell published a mathematical solution for a plane slide block of finite width. In all cases considered, he assumed the film thickness at the entering edge to be twice that at the trailing edge. The oil viscosity was assumed constant throughout the film. In 1931, Mr. Kingsbury published a method of investigating any film form regardless of shape, viscosity variation, or boundary conditions. In a later publication (6), Mr. Kingsbury introduced the idea of optimum bearing conditions and pointed out that in the case of a plane rectangular slide block the best results at finite and infinite widths are not found with the same film form. By means of the method developed and used by Mr. Kingsbury, the present paper undertakes an analysis of this problem in the case of 120-deg centrally supported journal bearings. The effect of side leakage is found to vary not only with the bearing dimensions of length and width, but also with the load carried by a bearing of given proportions. Results are given in tabular form and also by curves, and from these, optimum operating conditions are apparent. The problem of the best bearing for a given minimum film thickness, load, speed, and journal diameter is treated, the only assumption being a desired average oil viscosity in the film.