Recent developments aimed at increasing the life and performance of porous metal bearings have included a double layer bearing of low permeability, porous aluminium for better heat conductivity, ultrasonic cleaning of the porous surface, and the possible use of synthetic oils for improved oxidation resistance. The interactions between the porosity and the oil in terms of the surface tension, the effects of gas content on viscosity and permeability, and the rate of oil loss and reabsorption, are discussed in relation to these developments. A better understanding of the mechanisms involved leads to a practical design criterion for the limit of hydrodynamic lubrication of porous bearings of finite L/d ratio based on an eccentricity ratio of 0.8 and the difficulties of determining the appropriate value of permeability required for a more rigorous design procedure are outlined, together with suggested work for overcoming them.
Discussion: “Hydrodynamic Lubrication of Narrow Press-Fitted Porous Metal Bearings” (Rouleau, W. T., 1963, ASME J. Basic Eng., 85, pp. 123–128)