Effects of sliding speed, periodic pauses, and atmospheric moisture content on the wear of graphite against cast iron

The effects of sliding speed, periodic pauses in sliding, and atmospheric humidity on the sliding wear of graphite against cast iron were investigated. Each variable was changed while maintaining the others constant. The geometry of the wear test involved two rings in tangential contact, in which there was oscillatory rotation of the axes of the rings to produce reciprocating contact. This "twin-ring tribometer" was operated in an atmospherecontrolled chamber. As relative humidity increased, the wear rate of the graphite decreased due to an acceleration of the severe-to-mild wear transition. Non-friction time exceeding 10 s in duration owing to the pause after each sliding movement led to early onset of mild wear, which resulted in a reduction of the total wear. As the sliding speed decreased, the wear of graphite decreased with a corresponding change in the wear mode from severe to mild. This behavior is explained in terms of the friction that occurs during instances of relative motion within the real area of contact. When the contact period was long, as was associated with low sliding speed, small wear particles were generated leading to an acceleration of the severe-mild wear transition.