Experimental Study on Mechanism of Lubrication in Porous Journal Bearings : Oil Film Formed in Bearing Clearance

An oil film formed in a bearing clearance is experimentally investigated to explicate the mechanism of lubrication in porous journal bearings. To visualize the oil film, a porous bronze bearing impregnated with a fluorescent-dyed oil is used for the test bearing, and the oil film is rendered visible by a pair of ultraviolet lamps. It is observed that the oil film is formed in the loaded part of the bearing and, in particular, it extends over a wide range for the relatively small static load and high oil-feed pressure. However, even under hydrodynamic lubrication conditions, the angular extent of the oil film for the porous journal bearing is significantly small as compared to that for the solid journal bearing. This suggests that the previous postulate for the solid journal bearings, i. e., the half-film condition known as the Gumbel or half-Sommerfeld condition, is not applicable to the theoretical analysis of the porous journal bearings, unless an unlimited amount of oil is supplied to the bearing gap through the oil-feed hole.