Jul 28, 2020 High-pressure grinding rolls (HPGRs) have struggled for acceptance into the hard-rock mining sector. CRITICAL HPGR PARAMETERS. HPGR roll diameters typically range from 0.5 m to 2.8 m, depending on the supplies, and roll widths vary from 0.2 m to 1.8 m. The aspect ratio of the rolls also varies as a function of manufacturer