Modern Quarrying Q1 2019

LOAD AND HAUL

The productivity of any surface mine hinges on the efficiency of its load and haul system.

Best loader-truck fleet combinations are generally regarded as the basis for optimal load and haul cycles.

three noteworthy delays that are not directly caused by the performance of the equipment, but rather due to load-haul equipment combinations. In many instances, idle or waiting time at the loading point is one of the enemies of optimal load and haul. What are the general causes of this and how can operations get the better of this setback? “Excessive waiting time at a loading point is normally due to the loading tool being too small or unproductive, therefore taking long to load the trucks,” says Castle. “It could also be affected by too many trucks or short haul distances where the trucks return quickly from dumping and, as a result, start lining up waiting to be loaded. The problem could be solved by matching the correct size loading tool to the truck and by ensuring that the loading tool can handle the number of trucks in the cycle,” adds Castle. To run a profitable aggregates operation, quarry managers need to identify relevant KPIs for the evalua- tion and identification of productivity improvement opportunities when it comes to load and haul. “The first visual indication of an inefficient load and haul process would be trucks waiting at either the loading or off- loading point. Solving this bottleneck would automatically improve produc- tivity. Also noticeable is the time that it takes for operations to resume after tea/lunch breaks and between shifts. If less time is wasted here productiv- ity would increase as well. This issue is solved by improved site manage- ment,” concludes Castle. l

In a load and haul operation, the capacities of the loading tool should be compatible with the capacities of the truck fleet.

in the combination are operating optimally and that waiting time is mini- mised,” says Castle. “While having the correct machine combinations allows for an overall efficient process, the site still requires efficient management for all of the processes to flow and achieve overall optimisation.” Traditionally, a key parameter in achieving the optimal match factor is the number of scoops a loading tool takes to fill the truck. What is the rule of thumb when it comes to the number of scoops a right-sized loading tool should achieve when loading a truck? Castle reasons that four to five scoops are ideal for a high production site where quicker turnaround times are required. “A four to five-scoop pairing also ensures that the loading tool is effective. With that being said, five to seven scoops are generally what is regarded as the norm at most of the sites across Africa,” says Castle. Enemies of optimal load and haul A key factor that is commonly ignored is the waiting time of a loader. ‘Waiting at dump’, ‘queuing’ and lastly ‘waiting time of loader’ are the

Fleetm@tic assissts in this regard,” says Castle. Loader-truck fleet combinations In a load and haul operation, the capacities of the loading tool should be compatible with the capacities of the truck fleet. According to a report published by the School of Mining Engineering of the University of Pretoria, in collab- oration with the Southern African Institute of Mining and Metallurgy, the equipment match factor between two interdependent pieces of equipment takes into account the total cycle time of the equip- ment. The equipment match factor refers to the ideal capacity and number of trucks that are paired in operation with a loader and how well they are suited to each other. Best loader-truck fleet combinations are generally regarded as the basis for optimal load and haul cycles. How does this affect the load and haul cycles and just how important is this to the overall optimisation of the pro- cess? “An efficient loader-truck com- bination ensures that both machines

24

MODERN QUARRYING QUARTER 1 - 2019