Study on effects of ultrasonic vibration on sliding friction properties of PTFE composites/phosphor bronze under vacuum

This paper is a tribological problem extracted from the application of the ultrasonic motor under the vacuum. Nine frictional states were designed. Under the atmosphere and vacuum environment, the effects of longitudinal and torsional ultrasonic vibration modes on the sliding friction pair of phosphorus bronze and Polytetrafluoroethylene (PTFE) composites were studied. The results show that under vacuum, applying vertical or horizontal ultrasonic vibration can reduce the friction coefficient. However, comparing with sliding friction under ultrasonic vibration in atmosphere, the friction coefficient increases. With the increase of vacuum degree, the effect of friction reduction by ultrasonic vibration becomes weaker, which leads to the increases of the friction coefficient under high vacuum. The friction coefficient is almost no change under low excitation voltage. It is revealed that the increase of friction coefficient caused by ultrasonic vibration in vacuum is due to the decrease of air medium density, the reduction of acoustic levitation force and the increase of contact opportunity of friction pair.