About Grinding Mills

Grinding mills are a key piece of equipment widely used in the mining industry for grinding crushed materials during the ore dressing stage. This process separates valuable minerals from their ore. As the process is very arduous, mills are lined with steel or rubber liners, these are re-lined regularly to prevent damage to the main shell. As part of the mill re-lining process, the mill liner bolts are normally retorqued 24 to 48 hours after going back online. Due to the large number of bolts, the re-torquing process is time consuming, and costs of lost production are extremely high. However, if re-torquing is not done, there is an increased chance of unplanned down-time due to bolt failure.

The Boltsress Ultrasonics Technical Services Approach – Know Your Problem

At Boltstress, we champion doing this job once, and eliminating the need to do a re-torque. We have applied our experience and knowledge to develop a mill liner re-torquing process that is accurate and efficient. The key to developing our trusted service has been in identifying and understanding the root causes of bolt failures.

The Root Cause of Bolt Failures

Liner bolts fail (break or loosen off) for several reasons, but our extensive experience demonstrates that these can be eliminated if the pre-load is correct. Fatigue failure is the most common failure; this is almost invariably due to pre-load that is too low. The reasons for this can be divided into three groups: inadequate original tension, inconsistent tension, and high relaxation.

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