Observation of lubrication conditions using an ultrasonic technique

Abstract

AbstractEvaluation of lubrication conditions for a real frictional surface, such as a steel bearing, becomes an important issue for safe operation of a machine. In this paper, an application of ultrasonic technique is attempted for a purpose of evaluating the lubrication conditions. Ultrasonic waves emitted towards a hydrodynamic lubrication interface are reflected multiple times in oil film, and an echo height of reflected waves from the boundary is dependent on film thickness. The results of this study indicated that the ultrasonic technique is able to measure film thickness of approximately 50 nm in the case of a standstill surface having extremely small surface roughness. Furthermore, a potential for estimating the oil film thickness between a piston ring and cylinder is also indicated. In addition, in the case of a ball bearing, quantitative measurement of a size of dent, which forms the origin of flaking, is important for an evaluation of lubrication conditions. This becomes possible with an observation of a change in the echo height reflected from a boundary surface between a housing and an outer ring of the ball bearing. In this study, quantitative measurement of an indentation having 0.32 mm width on a raceway surface of an inner ring was achieved. Copyright © 2009 John Wiley & Sons, Ltd.