Compared to other suppliers, installation tension levels, measured with calibrated installation tools at 170,000 lbf, demonstrated superior performance. The shell reached 89% of the target tension, while the discharge end achieved 85%.

Following a shutdown in September 2022, ME Elecmetal conducted a thorough assessment and identified areas for improvement in the calibration processes of installation tools, torque application, and retorquing procedures at one of its client’s operations. The primary objective was to mitigate occurrences of bolt loosening and failures experienced during the February 2022 campaign, particularly affecting the SAG mill’s discharge end and shell. This included the total fracture of 10 bolts, leading to the detachment of two grates and subsequent economic losses due to unscheduled downtime, impacting the mill’s availability.


ME Elecmetal was dedicated to enhancing installation procedures and identified an opportunity to develop a comprehensive solution aimed at ensuring the reliability of liner fasteners on the shell and discharge end of SAG mills. This initiative was based on insights collected during the major shutdown in September 2022, when the online monitoring system was implemented.

The following recommendations were considered:

  • Implementing Valley Forge RidgeBack Grade B7 bolts on the discharge end and shell to improve the reliability of the SAG mill
  • Improving tension levels achieved during liner installation in SAG mills. Committing to suggesting a tightening and retorqueing procedure with specified tension values for each supplier
  • Improving the calibration process of the installation tools on the Skidmore test bench to ensure accurate tensioning
  • Utilizing monitoring system data to recommend re-tightening when bolt tension is low, mitigating failures associated with fastener loosening

For monitoring bolt tension, the installation of 73 sensors was proposed, with 38 allocated to SAG Mill 1 and 35 to SAG Mill 2.

The implementation and validation of Valley Forge bolts for SAG Mill 1 were carried out in both the shell and discharge end.

Valley Forge Ridgeback Bolt


Comparison between an oval bolt and a Valley Forge Ridgeback Bolt


Valley Forge Bolt Fastening Kit


Tracking and monitoring were implemented using the bolt tension monitoring system:

Operation of the Online Monitoring System

The implementation and validation process improved the bolt fastening system installation procedures emphasizing the selection of appropriate tools, ensuring correct assembly from each bolt supplier, implementing proper storage and protection measures for bolt and nut threads, optimizing bolt lubrication, and establishing a standardized bolt torque sequence.


End-of-Campaign Shell Tension


End-of-Campaign Tension Discharge End

  • ME Elecmetal leveraged its expertise to enhance calibration, torque application, and retorquing procedures. Consequently, the target tension in the discharge end was attained, marking an increase from 74% in the September 2022 campaign to 85% in the February 2023 campaign, along with significantly improved tension consistency.
  • Valley Forge bolts with Ridgeback technology attained higher installation tensions when used with installation tools calibrated at 170,000 lbf. In the shell, 89% of the target tension was reached, while in the discharge end, it reached 85%. These values surpass those offered by other suppliers, highlighting the superior performance of Valley Forge bolts.
  • Throughout the February 2023 campaign in SAG Mill 1, utilizing Valley Forge bolts, the rate of tension loss in the shell was notably lower compared to that of other suppliers. At the end of the campaign, the average tension remained at 120,000 lbf without requiring any retorquing.
  • Throughout the February 2023 campaign in SAG mill 1, with Valley Forge bolts, the rate of tension loss in the discharge end was lower than that of other suppliers, and at the end of the campaign, the average tension was 134,000 lbf without any retorquing.
  • Valley Forge bolts have been validated for use in both the shell and discharge end positions.


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