Friction measurement on Ni-Hard 4 during high pressure crushing of silica

A novel high pressure shear cell has been used to study friction phenomena between crushed silica and Ni-Hard 4 at surface stresses commonly experienc ed in ore crushers. Surface normal loads of more than 300 MPa were used, to gether with tangential loads sufficient to initiate and maintain slip at th e crushing surface. Under these load conditions, the friction coefficient i ncreased with sliding distance, rising from an initial value of less than 0 .1 and leveling off to a plateau value of about 0.4-0.6 in the first few mi llimeters of shear displacement. The variation of friction coefficient with shear displacement could be divided into three stages: the first dominated by particle rearrangement in the abrasive bed, a second transition stage w here particle rearrangement and particle crushing occurred together, and a third dominated by a slowly evolving layer of fine powder adjacent to the c rushing surface. This last stage was characterized by a relatively stable ( plateau) value for the friction coefficient. This plateau was a weak functi on of the normal load. Analytical and experimental results showed that larger abrasive particles p referentially penetrate the surface and, as a result, cause the most extens ive ploughing damage. Thus, if fine particles are concentrated at the crush ing surface they can protect that surface from penetration and ploughing by larger particles. a feature also observed experimentally. An energy analysis of the crushing and wear event revealed that interpartic le friction and particle fracture occurring within the bed of abrasive mate rial contributes significantly to the energy consumed as a result of shear displacement. (C) 2001 Elsevier Science B.V. All rights reserved.