839 charge motion and optimize power consumption. The SAG mill operational control was also determined. Liner material compositions were reviewed, and it was decided to maintain the chromium-molybdenum steel alloy and same total liner weight in order to not compromise the SAG mill power and integrity capacity. Optimized Hi-Hi Shell Liner The new customized shell liner configuration was a 40-2 row Hi-Hi lifter with 35° face angle. As shown in Figure 6, mill charge trajectory simulations, designed for 30% of total volumetric charge (18% of ore and 12% grinding media), indicated that the SAG mill should be initially operated with an upper limit of 10.4 rpm (note: SAG operates at variable speed; min: 8 rpm / max: 10.8 rpm). To maintain the optimal charge lift and trajectory throughout the wear cycle, the operating speed should be incrementally increased to 10.8 rpm over the liner life cycle. In addition, the new liner set was designed with larger pieces, decreasing the number for shell liner pieces from 180 to 80. This reduction further decreased reline time (25 hours) and permitted safer installation. Figure 6 – 40-2 row Hi-Hi with 35° face angle, Bradken’s MILLSIM charge trajectory simulation @ 10.4 rpm, and liner packing mitigation. Feed End Liner To address the pegging, the pinch points between the top of the side rib and the main lifter were reduced by shortening the sides of the rib to eliminate gaps where balls were previously trapped. To extend liner life, the lifter height was increased by 38mm, and the leading face angle was modified from 4° to 25° to reduce peening thereby minimizing direct high-energy impact on the liner face. To reduce reline time, the total number of components was reduced from 42 to 36 by integrating two liner segments into a single larger casting, consolidating the wear zone and enabling replacement of one liner instead of multiple smaller pieces. Discharge End Liner During the shell liner failure investigation, it was determined that chronic breakage to the DE intermediate liners were related to the poor shell liner design (which promoted increased media/ore impact onto DE liners). Poor discharge-end liner face angles also can contribute to discharge end impacts by throwing material onto itself. To reduce peening, the face angle was increased from 1° to 10°. To extend liner life, the lifter height was increased by 31 mm. The grates were modified to curved ribs; slot size maintained at 2” as well as the total grate slot/open area. These dimensions were used to keep the mill’s overall volume consistent with the original design.
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