Design Aspects Of A New Material Wear Tester

Abstract

Most material frictionhear testers are variations of the BOCLE@ tester. It uses a rotating or oscillating spindle, loaded down with a weight. The spindle has one or more 0.5 inch diameter balls at its end rubbing over a flat test sample. Wear depends on the inaterlal properties of contacting surfaces: ball(s) and flat test sample. The flat test sample is fixed inside a cup filled with lubricant. The ratio of drag force to contact force provides the friction coefficient. Wear is reported for either material, as weight loss rate, or rate of groove width increase. Wear depends on contact surfaces physical properties, contact pressure, velocity, lubricant and contact temperature. Problems associated with the BOCLE@ tester are vibrations caused by the rotating or oscillating weight on the spindle, d~fficulty in changing the spindle load and rapid changes in ball contact area and thus pressure. Two new material-wear testers have been developed at WVU. The first one was for testing bearing materials submerged in methanol. The second to test bearing materials submerged in liquid zinc. The sample geometry was selected for low cost, ease of wear measurement, and self-centering. A l-inch balllhemisphere was mounted at end of rotating spindle. The fixed sample has a narrow seat making a 45-degree contact angle with ball. It is mounted inside a three-inch diameter cup, filled with molten zinc. The cup is suspended from a disc floating on ball bearmgs to facilitate self-alignment between ball and seat and to measure friction torque. The assembly is supported on a rubber inner tube, to dampen vibrations and maintain constant load The load is adjusted by lowering the spindle. Only at very heavy loads, inertia weights are added to the cup holder to dampen rotational vibrations. This design provides constant pressure wear testing. The seat wear rate is measured optically. Transactions on Engineering Sciences vol 43, © 2003 WIT Press, www.witpress.com, ISSN 1743-3533