A mining regulator has places graders in the spotlight following reports of a number of incidents associated with the failure of grader stub axles. In the range of mining safety incidents, both drive and steering wheels have detached following the catastrophic failure of stub axles. Grader maintenance appears a significant contributor.
The regulator said ‘Recent incidents include: seven steering wheels detaching a driving wheel detaching. 
These incidents were injury free. In all cases there was temporary loss of control of the machine and the detached wheel rolled away in an uncontrolled manner.’
It said that ‘physical root causes and contributory factors in all these incidents were found to be similar.’
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Highlighting in its recent report to the industry the dangers of grader sub axles failure the regulator said that ‘The mass of a detached uncontrolled wheel assembly can typically range from 500 kg to 1,600 kg combined with a loss of grader steering control and rapid deceleration this type of incident has significant potential for harm. Coupled with the interference to mining operations from the disabled grader, detached wheel and recovery operation an incident could prove costly for mines.
Contributory issues on grader sub axle failures
It said that the contributory factors to the incident were the use of non-genuine parts fitted to shaft group assemblies.
The regulator has also focused attention on the management of fatigue in machine components highlighting that critical parts should be tracked for operating hours and fatigue of components in accordance with OEM operating procedure.
It said, “When parts are swapped between different machines or used stub axles are installed, information about operating hours should be transferred.”
Fundamentally the issues of training and guidance about material fatigue and its impact on safety could be a potential issue at mines. While not all the blame is on maintainers, the department said poor operating practices by grader operators could contribute to the failure of components.
These include: – mounting one front tyre on a dump pile and the other on the ground – running the front end directly into the pile – grading road verges and windrows – tyres mounting on windrows – operating on sharp turns and tight switch-backs – exceeding the oscillation stop limits of axles in rough terrain (total range of 32 degrees) – imposing excessive speed and shock loads to the grader front end (e.g. from excessive or sudden braking, or impacts with rocks and depressions in the road).
What can mines do to prevent sub axle failures?
Mining companies and their maintainers should ensure that stub axles are periodically inspected for surface cracks and other defects using OEM approved Non-Destructive Testing (NDT) methods, at the OEM recommended intervals and by competent inspection personnel.
It said ‘When defects are observed, apply OEM recommended discard criteria. Use only genuine (OEM approved) replacement parts for shaft group assemblies.’
Mines must also ensure maintenance management systems adequately track and manage fatigue limited components such as stub axles. Ensure maintenance management systems always capture, communicate and apply the latest guidance from OEM information bulletins.
Ensure up-to-date OEM manuals are readily available to maintenance personnel.
Ensure maintenance personnel have access to OEM dealership support whenever additional technical information, guidance or advice is required.
Ensure grader operators are adequately trained/assessed and fully aware of the performance limitations of their equipment and the types of operating practices that may contribute to premature failures.
Further information can be found on the DMIRS website
Images: DMIRS
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