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Abstract
SAG mill liner development draws primarily on practical experience from SAG milling operations supported by computer-based modeling of charge motion in SAG mills and on established good design practice. Liner design needs to respond to the process aspects of mill liner action that are critical to good SAG mill performance, i.e., the impact of shell liners on the grinding action and of grates and pulp lifters on pulp discharge. In recent years, the trend in large SAG mills has been to use wide-spaced shell lifters with large lifter face angles, primarily to reduce packing and ball/liner damage, and to use larger, hence fewer, mill liner parts to reduce downtime at liner change-outs.
Keywords: Comminution, Grinding, SAG mill, Mill liners
Introduction
Semi-autogenous grinding mills (S AG mills) are tumbling mills that most commonly have a shell diameter-to-length ratio of around two. With this high aspect ratio, SAG mills generate both thrown and cascading ball-milling actions with shell linings shaped to lift and to throw alloy steel grinding balls of up to 150 mm (6 in.) in diameter. These actions apply crushing, attrition and abrasion comminution processes to reduce primary-crushed ores down to ball-mill sized feed. Feed ore with a top size of up to 200 mm (8 in.) and water enter the feed end of a SAG mill through a feed chute; the ore is milled in the shell and milled product exits through grates and pulp lifters at the discharge end (Fig. 1). The discharge is screened and the undersize, typically less than 1 2 mm (0.5 in.), provides ball mill feed and the oversize is returned for further milling. To increase mill throughput, oversized "pebbles" may be crushed before return. Napier-Munn et al. (1996) and Wills and Napier-Munn (2006) describe the design and operation of SAG mills.
SAG mills are currently the technology of choice in hard rock milling operations for reducing primary-crushed ore to ball mill feed. In recent years, the trend has been towards larger-sized SAG mills with diameters of 10.4 m (34 ft) and above, with the largest being 12.2 m (40 ft) in diameter and drawing 20 to 22 MW (Jones, 2006).
Mill liners provide the replaceable wear-resistant surface within grinding mills; they also impart the grinding action...