High Pressure Grinding Rolls (HPGRs) is similar in principle to regular grinding rolls but material is subjected to much higher forces. HPGRs consists of a pair of counter rotating rolls, one fixed and the other floating. Material is fed between the rolls with the floating roll pressing against the material flow by means of hydraulic pressure in excess of 50 MPa. The resulting force causes the material to compact by inter particle breakage. Pressures and roll speeds are adjusted to obtain optimum grinding conditions. The roll faces are typically studded because of improved wear characteristics.
High pressure grinding rolls have the capability to fill the roll of secondary crushers and primary/secondary grinders. Often applied as a replacement for conventional SAG milling circuits, they result in lower energy consumption, lower grinding media consumption and lower operating costs. They also tend to have a smaller footprint with easier installation.
High pressure grinding roll is often referred to as HPGR, the ore is fed between two rollers which are pushed firmly together while their rotating motion pushes the ore through a small gap between them. Extreme pressure causes the rocks to fracture into finer particles and also causes micro-fracturing at the grain size level. HPGR is often considered as being more efficient than grinding mills, although they are not as common as grinding mills since they are a newer technology.