HENNING KNAPP1, STEPHAN HANNOT1, & FRANK VAN DER MEER1
ABSTRACT
High pressure grinding rolls (HPGR) are an energy efficient solution for comminution of industrial minerals and metal ores. The technology is successfully applied in an expanding field of applications throughout the minerals industry. HPGRs compress and grind the particle bed in the operating gap between two counter-rotating rolls. The equipment provides a high capacity, low energy alternative for applications with conventional tertiary and quaternary crushing and grinding, with size reduction reaching from 100 mm feed down to 25 microns product.
In this process, maintaining a controlled and evenly distributed operating pressure between the rolls is very important. Due to feed segregation, the pressure distribution along the roll’s surface can become uneven, resulting in a coarser product. This paper will show that the pressure distribution can become severely uneven. As it is difficult to eliminate feed segregation, the HPGR design should compensate and adapt for the uneven pressure distribution as much as possible. This paper will present that the best approach to compensate and adapt for the uneven pressure is to allow the rolls to skew relative to each other. This will be further supported by operating data from operational HPGR installations. Coarser products are also caused by an inadequate pressure distribution: the much-discussed edge effect. To minimize the consequence of the edge effect, an optimized ratio for the roll length to roll diameter will be calculated. Furthermore, the design philosophy behind application of cheek plates will be detailed. This cheek plate is used to retain the material between the rolls, reducing the edge effect while still allowing roll skew. Together these design considerations help optimize HPGR’s performance.
Keywords
High pressure grinding rolls, HPGR, roll skew, pressure distribution, edge effect, cheek plate, feed segregation, HPGR design