Whether it is loading or hauling, optimising production through smart equipment choices and top technology can make a real difference.
By Mark S. Kuhar
Surface excavation and hauling are where the rubber meets the road in mining operations. Optimising both of these areas through best practices and the latest technology makes the job of digging deeper a lot easier and more profitable.
The foundation of a good excavation and hauling plan is to have effective haul roads. When haul roads are kept in top condition, trucks run faster and more safely, cycle times improve and more ore is produced. Good road conditions also reduce truck maintenance, lower fuel costs and reduce tire damage.
According to Caterpillar, in its Viewpoints magazine, there are nine things you can do to ensure your haul roads are your site’s greatest asset, instead of your greatest liability.
- Design them right. The best haul roads have crowned straight sections, superelevated curves, safety berms and drainage ditches on both sides.
- Ensure proper grade. The ideal grade is between 8% and 10% with low rolling resistance of 2% or less.
- Watch bench and dump areas. In the load zone, ensure the floor is smooth, debris is cleared away so trucks don’t drive over rocks, and that trucks are able to leave under full, continuous acceleration. In the dump zone, ensure the floor is smooth and that trucks are able to enter at high speed and reverse to dump.
- Pay attention to road width. Roads should be three times the width of the widest truck, so tires aren’t bumping into the safety berms or dropping into ditches.
- Use the proper material to prepare and maintain the road bed. If the surface under the haul road is soft or moist, rolling resistance is high and tires are allowed to sink – which slows production and can wear away the rubber from the tires.
- Keep them clean. Making sure haul roads are free from rocks and other debris should be a top priority on every mine site. Haul road should be free of puddles, potholes, ruts and gullies, and spillage should be removed quickly to save tires and allow trucks to travel at their expected speeds.
- Keep them watered. It’s important to keep dust down to improve safety and allow trucks to run at the desired speed. However, watch for excess water because it increases rolling resistance, which slows down the machine and is hard on tires.
- Educate operators. Motor grader operators need training in how to properly maintain haul roads. Truck operators need to be aware of how their driving habits have an impact on cycle times and tires. Operators should be trained to watch loads and speeds, check tire pressures, be aware of rocks and debris, and be careful on turns.
- Make the investment. Haul road maintenance sometimes takes a back seat to moving material. But if poorly maintained roads lead to damaged tires, damaged trucks or reduced cycle times, the result is lost production.
As stated mine haulage represents the highest cost component of any mining operation, meaning optimisation of mine haulage fleet is paramount. HAULSIM and Discrete Event Simulation from RPMGlobal drive down operating costs through prediction of production, allowing users to take control of uncertainty in their mining operations, according to the company.
Providing more insight than ever before, users can control uncertainty in their mining operations with the use of HAULSIM to model and visualise every aspect of their haulage system in 3D. The impact of changes to mine haulage systems can be simulated and quantified rapidly, giving users confidence in their planning and design improvement decisions.
HAULSIM brings simulation in house, reducing reliance on costly specialist consultants. HAULSIM is fast to set up and easy to use – users can build models in a drag and drop environment and generate simulations rapidly. This means multiple scenarios can be explored at any given time. Minor incremental adjustments or major changes can be made with ease, and the visible impact of these changes is available within minutes.
HAULSIM models incorporate real operational constraints and parameters including:
- Current fleet usage statistics such as breakdowns and rosters.
- Modelling of congestion and queuing at sources and destinations.
- Truck speed (calibrated using GPS data).
- Road rules.
- Haulage networks and road conditions.
- Other infrastructure such as crushers, stockpiles and ore passes.
With a holistic focus on the haulage network, HAULSIM features a 3D user interface for users to identify bottlenecks, congestion, and other areas of improvement quickly and easily.
With a focus on operational efficiency, both large and small decisions can be made with confidence using tested assumptions. Users can also calibrate models to form accurate predictions on future performance.
Eliminate the cost and risk of real world testing using HAULSIM to visualise the effects of “what-if” scenarios such as:
- Adding, removing or modifying equipment.
- Variations to equipment task assignment.
- Improvement of maintenance practices.
- Haulage route and speed limit changes.
- Changes in truck or loader allocation.
- Production versus cost.
- Change in configuration of ore passes, crushers and stockpiles and analyse the timing of interactions between different pieces of equipment.
- Congestion and bottleneck improvement strategies.
WHEEL DOZERS HELP MINES INCREASE EFFICIENCY
Mining companies are always chasing productivity. How quickly can we drill, blast and gain access to the ore? How much rock can we load in a shift? How many tons can we move in a year?
Trucks and loaders are the heroes on the surface mine site, where they are responsible for moving precious material. But sites that remember the importance of support machines like dozers, motor graders and wheel dozers will find their productivity – and profitability – increase as these machines make it possible for the loading and hauling equipment to do their jobs more efficiently.
From constructing and maintaining haul roads to cleaning up the loading and dumping areas, support machines have a direct impact on productivity. There are several types of equipment that do similar jobs, and it’s important to understand their differences to ensure they are being used in the right application to deliver their full value.
Caterpillar’s Kent Clifton, senior marketing professional for surface mining, helps miners understand the best applications for support machines and how to optimize them once they’re on site. He recently shared his insight regarding wheel dozers.
UNDERSTANDING WHEEL DOZERS
Wheel dozers combine the production capabilities of track-type tractors with the mobility and versatility of wheel loaders. Cat Wheel Dozers are based on Cat Wheel Loaders – designed for mining applications, with structures and a powertrain designed for dozing.
They can be found in a variety of applications, such as:
- Loading area cleanup.
- Dump area maintenance.
- Haul road construction and maintenance.
- Safety berm construction and maintenance.
- Blasting area cleanup.
“You’re really looking to take advantage of its versatility,” said Clifton. “They really deliver a lot of value when they’re working with hydraulic mining shovels, backhoes and electric rope shovels. They just make that process more efficient.”
COMPARING TRACK AND WHEEL DOZERS
Track-type dozers are the traditionally the machine of choice for mine site support. They’re durable and reliable, and have the weight-to-horsepower ratios to push large loads. But when mobility, speed and versatility are the most important aspects of an application, Clifton suggests looking at a wheel dozer.
If properly applied in the right applications, wheel dozers can deliver lower fuel costs, lower undercarriage costs and save mines money by reducing the amount of support equipment required on site.
“A good rule of thumb that I use is, if you’re going to be pushing 70% to 110% blade load all the time and you don’t need mobility, you need to be looking at a track-type tractor,” said Clifton. “If you need mobility and are pushing zero to 70% blade load, you need to be mobile, and to be quick to get out of the truck’s way, then you want to be looking at the wheel dozer.”
To help its customers understand and compare machines and their applications, Caterpillar produces the Caterpillar Performance Handbook. The handbook offers these considerations when deciding between a track or wheeled dozer for a mining application:
- Speed. Wheel dozers travel at speeds up to three times faster than track dozers.
- Maneuverability. Articulated steering and good visibility give wheel tractors high maneuverability.
- Utility. Mobility, maneuverability and good speed suit wheel dozers for yard and stockpile work and for clean-up around shovels. Lower maintenance costs may be realized in certain soils that can be highly abrasive to track-type undercarriages.
- Coal pile. Wheel dozers are recommended in this application when following conditions are present:
– Long push distances.
– Need for good material spread.
– High degree of compaction desired.
- Production Dozing. A wheel dozer should be considered in the following conditions:
– Long push distances.
– Loose soils, little or no rock.
– Level or downhill work.
– Good underfoot conditions.
- Pushloadiing Scrapers. A wheel dozer should be considered in the following conditions:
– Thin scraper cut.
– Good underfoot conditions – no rock.
– Higher push speeds.
Clifton encourages miners to look carefully at their site-specific conditions to determine the right equipment. For example, if the truck dump is fully burdened and a dozer will be dedicated full time to cleanup at that location, the track-type tractor is ideal. “It’s going to deliver better value in this application because you don’t need to be mobile with that tractor. It’s going to stay on that dedicated dump throughout the day.
If a site has dumps scattered throughout the site, however, a wheel dozer is a better choice. “If I have two or three dumps and I’m not fully utilizing them, but I need to maintain them, the wheel dozer is going to get from spot to spot much, much quicker,” he said.
USING A WHEEL DOZER ON HAUL ROADS
There’s no doubt that motor graders are the best tool for haul road repair and maintenance. They help create and maintain constant grade and proper draining, and ensure the floor is smooth in the loading and dumping zones. But there are times when a wheel dozer is an ideal support machine for the grader.
Truck spillage is one example. “I don’t want to be picking the blade up on a motor grader to bring it over to a switchback or a change in the grade on a road to clean up a little bit of spillage that came from the truck,” said Clifton. “So I can get on the radio and call the wheel dozer. It’s going to be extremely quick to get out and clean up that little bit of spillage, push it off to the side of the road, and then go do some of the other activities on the mine site.”
CHOOSING THE RIGHT SIZE MACHINE
Clifton stresses the importance of choosing a wheel dozer that is sized appropriately for the production machines. Caterpillar offers several sizes of wheel dozers – the 844 and 854 models – that are designed for ultra-class mines, where trucks range from 227 to 363 tonnes (250 to 400 ton) payload capacity. Mid-sized operations, working with hydraulic shovels like the Cat 6020, 6030 and 6040, should consider an 834-size wheel dozer.
“It really depends on the size of the trucks you’re going to be working with and the size of the loading tools,” said Clifton. “For example, one of the keys when you’re working on a truck dump is that you need to keep up with the trucks. So when you start looking at sizing your machine, you know that within a couple of passes there will be another truck coming in. You want to make sure that you can get that material pushed off in time. A smaller machine may not have the capacity to do that type of cleanup work. It’s the same under a shovel.”
“The truck is what’s really ringing the cash register,” he continued. “You don’t want to get a machine that’s so big that you’re obstructing the trucks running on the haul road. You want to get them back as quickly as you can to the loading tool. So you have to size the wheel dozer accordingly.”
SIZING THE BLADE
Once the right size dozer has been selected, it’s important to select the right blade for the application. Caterpillar offers several different types of blades, from straight blades to u-shaped, semi-u shaped and coal blades.
“The narrower the blade, the more aggressive it’s going to be. You’re going to have more horsepower per inch of cutting edge,” Clifton explained. “The wider the blade, the less aggressive it’s going to be.”
Wide, U-shaped blades are ideal for cleanup work. “Those wings are going to help retain material,” said Clifton. “So if you’re doing a lot of cleanup work, like underneath a shovel, it’s going to take fewer passes with a big wide blade and having the wings on the front. The wings actually help roll that material into the middle of the blade and you’re not going to lose it out around the toes.”
On the other hand, wide, curved blades are not the best choice for harder material. “If you have to get real aggressive, the narrower blade is going to allow better penetration to tear out some of that harder material. But it’s not going to retain as much in front.”
RECOGNIZING THE VALUE
In recent years, as mining companies face capital reductions and are continually looking for new ways to control costs, investing in a wheel dozer may seem like an unnecessary expense. Clifton stresses that the exact opposite is true.
“When it comes to a wheel dozer, you may see it as one of those ‘nice-to-have’ things,” he said. “When you look at it from a capital standpoint, it gets to be a fairly pricey machine. But what I encourage people to do is take the cost of that machine and look at the value that it’s adding.”
He uses truck exchange times as an example. “Say the dozer operator’s goal is to come in and make two cleanup passes and get out of the way,” he explained. “You’re not going to be able to do that with a track-type tractor. You’re going to be looking at over a minute to do one cleanup pass. That wheel dozer can do it in about 30 seconds.” Once the area is cleaned, the truck is back on its way to being productive.
“You have to take that credit – the value the wheel dozer is adding in exchanging out the trucks – and give that credit right back to that wheel dozer,” said Clifton. “If I can put the wheel dozer in there and reduce my truck exchange time to 40 seconds, that’s two more trucks an hour ... times three or four loading tools. At the end of the year it’s millions of dollars.”
“When you start off-setting it in that way, it’s really easy to justify the value of that wheel dozer,” he said.
HERE COMES A FULLY MOBILE SURGE LOADER
Mining Machinery Developments (MMD) is a world leader in the design, manufacture and supply of mineral processing solutions and associated machinery serving the mining, quarry and recycling industries.
The company is introducing the world’s first fully mobile Surge Loader. This revolutionary concept is based on proven innovative MMD technology that has already been tried and tested on projects in Colombia and China. The Surge Loader has been designed to transform the way mines operate their truck-and-shovel fleets.
MMD’s manufacturing commitment for this project has been handled by several of the group’s facilities worldwide, with parts coming from the United Kingdom, South Africa, India, China, Australia and the United States.
The Surge Loader is expected to deliver increased shovel utilisation of nearly 95%, reduce OPEX costs and improved operator safety.