The success of a mining operation has a lot to do with selecting the proper loading machine. Deciding on one machine over another is a complicated process. Hydraulic mining shovels combine the benefits of high digging forces with large capacity buckets. Electric rope shovels are the ideal loading tool for long-life mines. And large wheel loaders have grown in size over time to match the payloads of large mining trucks for a low-cost-per-ton loading solution.
The equipment that is best for the job depends on the characteristics of the site. But only one of these machines — the large wheel loader — can serve double duty, working as both a loader and a support machine for other loading tools on site. Thanks to their size, versatility and mobility, wheel loaders can keep production moving even when they’re not being used as the primary loading tool.
“Depending on the mine plan and the layout of the mine, as well as the ore deposits, the wheel loader can add a lot of value to the mining operation,” says Kent Clifton, a surface mining application specialist at Caterpillar. “And they add that value in a number of different ways.”
Serving as the primary loading tool
A number of mines have found large wheel loaders to be the ideal loader for their operations. They deliver consistent high bucket fill factors and are used effectively as primary loading tools where mobility is paramount.
“Larger wheel loaders, like the Cat® 994K, have the capability to load ultra-class trucks,” says Clifton. “They also traditionally deliver low owning and operating costs, which makes them very popular in mines worldwide.”
Conditions favorable to large wheel loaders include:
- Level, dry, smooth, firm floors
- Sufficient crossfall and drainage in wet areas to minimize tire damage
- Well-fragmented materials that minimize crowding time, particularly in the toe-area of the cut
- Lower face profile
- Multiple faces that require frequent tramming
Conditions that are not ideal for wheel loaders include underfoot conditions that are wet, soft or jagged; tight load areas; and poorly shot material.
The number one benefit of wheel loaders over other loading tools is their mobility. “If you have ore pockets that are spread out, the wheel loader is really valuable because it can travel at much higher speeds and much more effectively than a hydraulic shovel or electric rope shovel,” Clifton says. Wheel loaders can travel at speeds up to 38.6 kilometers per hour (24 miles per hour), more than 20 times faster than their loading counterparts.
This speed gives wheel loaders an advantage over other loading machines when:
- Moving out for a blast
- Moving to a new face
- Moving to a stockpile for a blending operation
- Loading the hopper and crusher
- Moving back to the service shop for maintenance
Adding value as a support machine
The mobility that makes wheel loaders so valuable as a primary loading tool also makes them ideal machines to support overall loading operations. “Mobility is a key attribute that allows the wheel loader to do multiple tasks throughout a mine site,” says Clifton.
Loaders are a valuable tool that ensures the primary loading tools can do their job. They can be used to keep loading floors clean, transport oversize material away from the loading area, touch up dumps, clean up around shovels and even tandem-load alongside shovels.
“Wheel loaders also add value because they can quickly take over loading duties if an electric rope shovel or hydraulic mining shovel is down for planned maintenance or for an unexpected repair,” says Clifton. “They can’t load at the same rate as a rope shovel, of course, but they keep production moving when loading operations would otherwise have to be stopped completely.”
Wheel loaders can also step in to support operations in case of a backup at the crusher. “You don’t want the trucks lined up waiting to dump,” says Clifton. “So one option that keeps production moving is to have the trucks dump their loads in a defined spot near the crusher, and then use the wheel loader to load and carry from the stockpile and dump directly into the crusher.”
Clifton says it takes some foresight and management from the mine to make sure wheel loaders are being used to their full potential as a support tool.
“Say you have the wheel loader working down in the pit and one of the shovels goes down, or there is a backup at the crusher,” says Clifton. “You have to remember that wheel loader is down there and call it back up to do these important jobs.”
Using the right tool for the job
No matter which loading tool you choose, it’s important to make sure you’re using it in the conditions that are ideal for that piece of equipment. “When you’re evaluating which machine will give you that low cost per ton you’re seeking, you have to break down the environment and the conditions it’s operating in,” Clifton says. “That will have the biggest impact on your costs.”
Clifton explains that each loading tool has a cost per ton of about 26 cents — when operated in the conditions for which it is intended. “Take the wheel loader, for example. If you’re putting it into extra hard, tough digging conditions with sharp-edged rock, you’re asking it to do something it’s not designed for. That’s very tough on the machine, plus your costs could go up 5 to 10 cents per ton.”
The same would be true for any loading machine. “If your application really calls for a wheel loader and you’re using a hydraulic shovel, and you’re requiring that shovel to shuttle and tram, the cost per ton for that shovel will increase 5 to 10 cents, too.”
The goal is to achieve the best results at the lowest cost. “At Caterpillar, we have first-hand knowledge and experience in analyzing field data and site conditions to make sure you’re getting that lowest cost,” Clifton says. “I recommend speaking to the experts when you’re evaluating this decision.”