The investigation of oil film thickness in heavily-loaded contact

An experimental study of the shape and thickness of the oil film during rolling in a thrust ball bearing has been carried out by the interference method.The experimental results showed good agreement with theory. Oil film thickness was affected mainly by the rolling velocity, viscosity of oil and maximum Hertzian stress. The groove radius had no effect on the film thickness. With increase of rolling velocity the film thickness increases and then reduces sharply owing to temperature rise and the non-Newtonian properties of the lubricant. A qualitative similarity was derived from the experimentally observed dimensionless shapes of the film and of the dimensionless theoretical shapes of the oil film for the lubricant in the non-Newtonian state. The flat “squashed” contact area diminished and disappeared with rise in velocity, which agreed with theoretical predictions.Good agreement was found between the theoretical and the experimental values of the oil film thickness and the friction coefficients for a ball sliding on a plane. Values of relaxation time for oil agree with values observed by the vibration method.The interference method is proposed to estimate the relation of the relaxation time for lubricants to the pressure and temperature up to maximum Hertzian pressures of 14,000 kg/cm². Experimental studies by the interference method and the solution of the non-isothermal hydrodynamic contact problem for liquids both in the Newtonian and non-Newtonian state provide a method of calculation of the friction coefficient.