Ultrasonic resonance approach to measure rolling element bearing raceway films in-situ: A practical approach

The lubricant film adhering to a bearing raceway is the primary contributor to developing an adequate inlet meniscus to avoid starvation and thus premature wear. This paper shows that lubricant films adhering to the raceways of rolling element bearings are measurable via an in-situ ultrasonic resonance technique, that is applicable to fully metallic bearings. This work first validates the measurement of free-surface oil films on bearing steel using the ultrasonic resonance method before applying to a fully metallic, cylindrical roller bearing. Practical considerations are discussed to optimise the measurement range and accuracy, and limitations are highlighted. Quantifying a dynamic raceway film into single thickness measurements is discussed, and two oils with a magnitude difference in viscosity are compared. • Ultrasonic resonant frequency governed by oil free-film thickness. • Lubricant films on fully metallic bearing raceway measured in-situ. • Observable raceway film thickness distribution across inlet to roller contact. • Contact centre has thinner film, creating ‘U’ shape distribution.