Bolt Loading & Torque Variables

The purpose of Donhad’s R&D work, focused on bolt load and the correlating torque applied, is aimed primarily at reducing shutdown time associated with sag and ball mills. Bolting failures and torque integrity are contributing factors to shut down requirement; both to ensure liner life and performance, and mill shell integrity and seal. We aim to gather evidence from trials conducted at our Bassendean manufacturing plant, to enhance our technical expertise in recommendations, used to reduce on-site costs for the end user. Specific objectives are outlined below;

  • Reduce the variation from the mathematical calculation of torque required and actual, enabling less expensive equipment to be used for the torque process.
  • Reduce the variation of bolt load obtained within the same torque and process; creating certainty and consistency in bolt load achieved on site.
  • Preparation initiatives at point of manufacture, which reduce time on site
  • Potential to eliminate re-torque requirements

Trials were undertaken using both pneumatic and hydraulic torque equipment, exploring three different brands of lubricant on two different lengths, M48 oval head liner bolts. The R&D requires more depth in trials into the future; predominantly different diameter bolts and larger sample size in certain focus areas, however, initial findings have been an exciting insight to the opportunities for improved bolt load achievement. Some of which include;

  • The improved bolt load result through Donhad’s HT recess washer
  • The improved bolt load result through alternative lubrication utilised
  • The importance of procedural compliance

Thus far the combination of the above indicates a 47% improved result to what we understand the “norm” on site. The findings will certainly reduce cost, particularly for sites that experience bolt breakage problems, however also in the infrastructure required to perform the reline task. For more information please contact:

Brad McCracken; Technical Sales


John Mulholland; Forge Manager

A special thanks to Newcrest Telfer, in particular, Jason Harding for their strategic alliance in this project. We look forward to seeing Telfer realising the benefits, and further collaboration in the future.

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