Long service

There are not too many original parts left on the frame – it bears the mudguards from a 793B, for example – but the truck is still hauling ore in a punishing copper operation. Even though this truck has more than 100,000 hours on the clock it still achieves more than 90% availability.The 793 that left the factory in 1991 had pride of place at Caterpillar’s recent Mine Site at Night show in Las Vegas.Good management has ensured the hauler – and five of its sisters – has lasted so long. Sierrita is a very low grade mine – at 0.26% it is probably the world’s lowest grade copper operation – so it has to run very lean to stay viable.The Sierrita operation is not an easy one either. It is a long haul up about 580 metres from the pit to the dump. Temperatures of 49C are not out of the question.A key to the 793’s longevity is the mine’s repair before failure philosophy. This means good condition monitoring and sound maintenance practices.Sierrita has been able to keep its maintenance team together – unusual for a mining operation. That stability has helped the team develop consistent maintenance processes.A Caterpillar product specialist told Australia’s Mining Monthly that the extremely good condition of the truck’s frame was a testament to the maintenance program.For one, the welds on cracks in the frame – over time these cracks happen to every frame – were small, indicating they were being picked up early.Sierrita’s maintenance program includes a component replacement plan, diligent condition monitoring procedures and strict contamination control. Haul road maintenance has been a priority too. These days haul road maintenance is mostly aimed at tyre preservation but the maintenance benefits go much further.Tyre management expert Tony Cutler said the cost of damage to the suspension, steering and chassis of a haul truck was usually three to four times the cost of tyre damage.To ensure its haul roads were as good as possible the mine put people in trucks and, using their engine monitoring systems, measured their responses to different haul road sections. It found that its haul roads were not quite as good as it thought. By reducing haul road grade variation Sierrita was able to increase the speed of the trucks and reduce the number of high-energy transmission shifts. This led to reduced rock spillage.Another part of the maintenance operation is the component rebuild program. This involves removing worn components and replacing them with ones rebuilt to Caterpillar standards.Those rebuilt parts come from Empire Machinery, the Caterpillar dealer in Arizona. Empire has been a key player in the truck’s longevity. Its project manager on the Sierrita site regularly attends the mine’s daily maintenance and operations department meetings.Sierrita and Empire have moved from using worked hours as the sole indicator of when a component should be replaced. They look at condition-based factors such as fuel burn as a better guide to the work an engine has experienced. Instead of replacing an engine once it has reached its hours-based target life, Empire will extend it for another 500 or 1000 hours – depending on its condition. It will monitor the filters, oil condition and consumption, and overall operating performance before making any engine replacement decisions.This puts a lot of emphasis on condition monitoring. The mine employs a dedicated team monitoring various equipment operating characteristics including temperatures, pressures and speeds. This helps support the fix-before-failure approach.Contamination control is also crucial. Lubricants are run through an off-board filtration system to remove contaminants. The areas where trucks are maintained are kept dust-free and closed to the outside.Keeping contaminants out of lubricants helps keep maintenance costs down. Those contaminants can knock metal off components they come into contact with. Those pieces of metal then repeat the favour. One piece of contamination quickly becomes two, becomes four and so on.While the truck may have started life as a 793A, a series of upgrades have made it closer in kind to a B-series truck – and that is not just in terms of body work. Among the upgrades are an electronic injection engine and the Vital Information Monitoring System. It does not have the four cup holders that operators of the F-Series Caterpillar trucks take for granted – yet.This column was originally published in the November edition of Australia’s Mining Monthly magazine.

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