Abstract
Percussive rock drills operate by repeated blows of a pneumatically operated piston striking a bit with cemented tungsten carbide inserts on its wear faces. In order to investigate the mechanism of wear on the faces of these inserts, bits worn in actual field operation were studied and, in addition, laboratory experiments simulating rock drilling were carried out where the wearing process could be observed. All of the experimental evidence indicates that the chief wear mechanism is a fatigue microspalling of the carbide surface related to the blows. The contribution of sliding wear, and therefore the effects of sliding velocity and hold-down force, were found to be minor. The surface fatigue wear rate is equal to the product of the average volume of a spall, the number of sites of possible spall formation and a probability factor giving the proportion of these sites that receive sufficient energy to produce a spall. From the wear data obtai, the number of sites of possible spall formation is small, sometimes less than one per insert per blow, while the probability factor is large, almost unity. This indicates that when a site becomes properly conditioned, little additional energy is required to complete the formation of a spall.
Published Version
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