Measurement of lubricant film thickness of cylindrical roller bearing using ultrasound

The rollers and raceways in cylindrical roller bearings are separated by an extremely thin lubricant film in a narrow region, which is difficult to measure directly in actual working conditions. A cylindrical roller bearing oil film experiment platform is established in this study, and the method to measure the elastohydrodynamic lubrication film thickness in the contact area between the roller and outer raceway in actual working conditions is experimentally researched based on the principle of stiffness equivalence. The experiment platform is used to simulate the running states of a cylindrical roller bearing in actual working conditions, and a 50-MHz focus ultrasonic transducer is fixed on a micro-motion platform with 5-DOF so as to adjust the measuring position. A reflecting plate is pasted on the bearing cage to trigger the measurement so that the same roller can be measured at each time. A thermocouple is used to measure the bearing temperature. The maximum rotational speed that can be measured depends on the pulse repetition rate (PRR), and low PRR will cause measurement errors. The averaging effect of the transducer in its focal zone makes it hard to pick out the detail of the film thickness in the contact area. Oil films between 0.2 μm and 1.2 μm are measured in actual working conditions under a maximum speed 600 r/min and a maximum load 16 kN. Experimental results show that the thickness increases as the shaft speed increases, and decreases as the radial load increases. The correctness and effectiveness of the proposed method are proved through a comparison between the experimental results and theoretical values. © 2015, Editorial Office of Journal of Xi'an Jiaotong University. All right reserved.