Vibrating Screens

Exciters that create the vibration for screens to work operate with very high "G" forces in the region of 3-5G. The bolts that hold these onto the structure are highly critical.

Our solutions have eliminated failures that were originally occurring every 3-4 weeks.

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Case Study: Vibrating Screens Exciter Bolts

Vibrating Screens Exciter Bolts

Vibrating screens provide a vital service in the mining industry, they are critical to operating efficiency. They operate with exciters that generate very high G-forces (typically 3-5G's), consequently the structural bolting needs to withstand these forces. We determine the root cause of any failures, eliminating the need for monthly re-torque or replacement maintenance strategies.

Vibrating screens

Causes

Torque tightening in perfect conditions is generally accepted as delivering a residual tension within +/- 25% of the target figure. This is compounded in this case by restricted access and uneven reaction surface.

Torque tightening

Pre-load too low

Our initial findings have shown that the residual tension from the initial torque tightening calculations on this application delivered 30-40% less tension than the OEM specification.

Consistency

The relationship between the applied torque and tension is always tenuous, we found that additional to the low average tension the variation bolt to bolt is another 30-40%.

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Our solutions

We use Ultrasonic bolt tension measurements too prove the achieved pre-load and then adjust the torque settings until the Tension meets the OEM specification.

The process we follow is:

Preparation – prior to work start

  • Calculate allowable tension for the Bolts

  • Determine allowable stresses for mating parts

  • Review the OEM requirements

  • Set up ultrasonic data files

  • Measure ultrasonic bolt reference lengths

During re-assembly

Apply the torque wrench whilst simultaneously measuring the residual tension STOP when the ideal tension is reached to ELIMINATE THE TORQUE VARIABLES.

Final Results

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Summary

This solution eliminated the failure of these bolts and allowed the mine to keep running between major planned shutdowns. This improved both productivity and safety. If you wish to know more please feel free to call or email us at:

Mobile: Trevor Robinson 0411 132784
Email: trevor.robinson@norbar.com.au

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