The productivity of any surface mine hinges on the efficiency of its load and haul system. Yet, loading and hauling run of mine material represents a very significant component of the total operating cost. Consequently, the incentive to reduce cost in this area remains high.
The current aggregates business climate is characterised by price volatility, high labour costs, shrinking margins and increasing operational costs. This is exacerbated by a steady decline in the growth of aggregates demand due to the lack of meaningful construction projects. For quarries to survive and mine profitably, they need to capitalise on the opportunity to improve their productivity and focus on one factor they can control: operational efficiency.
Increasing productivity is one of the key drivers to counter diminishing profit margins as it effectively reduces operating costs. However, the emphasis should not only be on increasing output with the same input, but increasing the output while decreasing the input, and ultimately adding optimum value to current resources. Research shows that an increase in production will ultimately decrease the operation’s unit cost, especially fixed costs.
Load and haul is probably the biggest cost driver for any quarry. Yet, if properly implemented, a load and haul optimisation programme can identify significant opportunities for operational improvement. Brad Castle, Product Marketing Manager at Bell Equipment, estimates the cost percentage of load and haul in the whole production equation at a typical quarrying operation to be between 25-30% based on the whole operation cost, including site personnel and vehicle costs.
So, how can quarry owners reduce their operation’s unit cost related to load and haul? A reduction in the unit cost of loading and hauling can been achieved, on one hand, by applying new and innovative mining equipment and methods, and on the other hand, by optimising the use of existing equipment.
What should a load and haul fleet optimisation programme entail? Castle says it is important to ensure that the machinery is correctly matched to the site and application, as well as the timing of cycles compared to the number of trucks.
“While this is so important, however, none of it will work unless the site is managed correctly. I would therefore say that site management is as important as the equipment on site. Bell has made this easier for customers by developing an innovatively designed fleet management system, Fleetm@tic®. Machine productivity, machine utilisation and machine condition can all be accessed from the owner’s computer, tablet or mobile phone. Customers can therefore be rest assured that their investments are earning a maximum return. Machine breakdowns are also detrimental to an operation, therefore, managing preventative maintenance schedules is vitally important and Fleetm@tic® assists with this,” 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 collaboration 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 equipment. 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 process? “An efficient loader-truck combination ensures that both machines in the combination are operating optimally and that waiting time is minimised,” says Castle. “While having the correct machine combinations allows for an overall efficient process, the site still requires efficient site 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 normally what is generally 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 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 evaluation 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 offloading point. Solving this bottleneck would automatically improve productivity. 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 productivity would increase as well. This issue is solved by improved site management,” concludes Castle.