1. CLARABELLE MILL CHALLENGES Vale’s Clarabelle Mill is a Ni-Cu sulfide concentrator located in Copper Cliff, Ontario, Canada. Since commissioning in 1971, Clarabelle Mill—originally a crushing and rod/ball mill circuit—experienced multiple reconfigurations to address the variability inherent in the Sudbury orebodies sourced from at least 5 underground mines. With increasing mine depth, a higher variability in ore competency, feed sizes and grades (declining), was expected. In 1990, a semi-autogenous grinding (SAG 32’x13.5’) mill was installed, and following the closure of the crushing plant in 2017 (care and maintenance), the operation relied solely on SAG milling. In 2020, Clarabelle Mill initiated the Vale Production System (VPS); an operational framework to align technical practices, drive continuous improvement and enhance standardization as part of the transformation toward a safer and more reliable operation. In 2021, a reliability study diagnosed that SAG mill maintenance strategy (scope and frequency of SAG mill relines) as a major opportunity to improve mill availability. Historically, liner-related failure modes—including packing, peening, pegging, breakage, and broken bolts—have negatively impacted mill uptime. In 2022, the SAG mill shell Hi-Lo liners failed causing significant mill downtime impact. To key to enhancing SAG mill availability and throughput lied in the development of a robust reliability-centered SAG reline strategy, which included liner design optimization, bolting technology, reline synchronization and liner condition-based maintenance. 2. SAG LINER DESIGN OPTIMIZATION When the SAG mill was installed, the shell liner configuration consisted of a “HiHi” lifter profile. In March 2021, this configuration was modified to a “Hi-Lo” lifter profile as part of an optimization effort to reduce the number of liner components to improve reline time and safety. However, on March 2022, the SAG mill shell liners experienced premature wear and cracks. Following the failure, the original “Hi-Hi” lifter was reinstated to restore operational stability. A comprehensive reliability analysis was conducted to determine the root cause of the liner failure. Using a structured approach—including Fault Tree Analysis (FTA), Failures Modes and Effects Analysis (FMEA), detailed wear profile assessments, and application of mechanical design guidelines, the liner optimization project was successfully completed, establishing a more robust and reliable configuration for future operations. 2.1 Hi-Lo Shell Liners Failure Investigation In March 2021, a 30-3 row “Hi-Lo” lifter with 27° face angle was installed. In March 2022, the SAG mill was shutdown initially due to the detection of full-sized grinding media escaping from the mill onto the pebble conveyor. During the internal inspection of the SAG, the deflector cone bolt failure had been identified and warranted immediate replacement. While in the process of the cone replacement, cracks and excessive wear on the discharge-end shell liners were also discovered (Figure 1). This initiated an emergency SAG liner replacement (all shell liners). This unplanned reline accounted for 217 hours, the original 60-3 row Hi-Hi lifter profile with 7° face angle was
RkJQdWJsaXNoZXIy MTM0Mzk2