P&Q University Lesson 6- Off-Road Hauling

By |  July 19, 2015
Photo by Joe McCarthy

Photo by Joe McCarthy

In most aggregate operations, off-highway trucks provide the production link between the loading face in the pit and the primary crusher or processing plant. Efficient haulage is critical both to meeting production targets and to managing costs. Proper selection and sizing of trucks, efficient operation and timely maintenance, and well-designed and maintained haul roads are the keys to productive and low-cost haulage.

RIGID FRAME VERSUS ARTICULATED

There are two main kinds of haul trucks: Rigid frame and articulated. Though each type hauls material, the two different truck configurations have different strengths that suit the machines for most efficient operation in different site conditions. No matter what the choice of hauling system is, the machines must perform or participate in several functions: loading, hauling, dumping and returning. Each type of hauling unit has advantages in some parts of the cycle and disadvantages in others, depending on the site conditions.

All trucks require the use of a loading tool, and of course the loading machine and trucks must be matched carefully for fast, efficient and safe loading. For more information about the loading portion of the production cycle, see the additional discussion later in this chapter and in the excavating and loading chapter.

The hauling and returning segments of the cycle are most affected by truck attributes, but there are no hard-and-fast rules for selecting the right hauling system. Instead, the type of system must be selected to best handle the material, ground conditions, total resistance (grade and rolling resistance) and hauling distance.

The material type and consistency play roles in truck performance. Rigid-frame trucks can handle any material that an excavator, shovel or wheel loader can fill it with. Articulated trucks can work well with materials ranging from sand and gravel to well-shot rock. Articulated trucks are not suited for high impact loading, but they can handle rocky material or rocks as large as 18 inches.

The underfoot or ground conditions also affect productivity. Rigid-frame off-highway trucks work best when used on well-maintained surfaces, including the loading and dumping areas. Poor footing can make their use uneconomical, although features such as electronically governed traction-control systems can enhance the efficiency of rigid-frame trucks in variable conditions.

Articulated trucks, on the other hand, have high flotation and superior traction due to their comparatively light weight, large tire footprints and all-wheel-drive. Articulated trucks generally produce more than rigid frame trucks in adverse ground conditions. Of course lower ground pressure allows the three-axle articulated trucks to operate effectively in soft underfoot conditions.

The rolling resistance of the underfoot materials and the grades that a hauling machine must negotiate affect system economics as much as overall hauling distance. A rolling resistance of 3 percent – the resistance offered by a compacted dirt or gravel road – is optimal for hauling systems. For comparison, soft earth backfill generates about 8 percent rolling resistance. Each type of machine generates different rolling resistance, dependent on weight, load and tire size. But the ability to overcome the resistance and maintain high productivity relates directly to the machine’s rimpull characteristics.

The grades that hauling machines must traverse also figure into the productivity equation. Rigid-frame trucks are most efficient and productive when continuous grades are limited to 8 to 12 percent, but they can climb short grades as steep as 20 percent. Articulated trucks are the choice to handle steep grades, as they can work on grades as steep as 35 percent.

The distance that material must be hauled is another factor to be considered when selecting a hauling system. Rigid frame trucks take advantage of their high payload-to-weight ratio and high speeds on longer hauls. Such trucks can be effective on short hauls, but they are most effective when haul distances extend beyond one-half mile and haul roads are designed and maintained properly. Articulated trucks can be effective on shorter hauls.

The space available and the configuration of the loading and dumping sites can define equipment selection. If the loading or dumping area is particularly confined, articulated trucks can turn and maneuver more sharply than rigid-frame trucks.

Finally, rigid-frame trucks are available in larger sizes than articulated trucks, which currently are limited to about 50 tons payload. For high-volume crushed stone operations, large rigid-frame trucks operating on well-maintained haulage roads are usually the cost-effective choice.

NUMBER AND CONFIGURATION OF TRUCKS

Photo by Joe McCarthy

Photo by Joe McCarthy

The determining factor for the number of trucks needed is the production target. The goal is to have the right number of trucks and the right capacity to serve the crusher and/or stockpiles without making the loader wait or causing a line of trucks waiting on the loader. Both situations hurt productivity and drive up cost.

Many equipment dealers can assist in the truck selection process by using software supplied by manufacturers. The software asks for site configurations and conditions and calculates production and costs based on those inputs. The software enables quickly assessing a number of scenarios and equipment choices.

In addition to the right number of trucks, each truck body must be configured to work with the loading tool and provide a good loading target to allowing quick spotting and even load distribution within the body. Truck body rail height and width and length of the body are important in relation to the loading tool geometry.

For a rigid-frame truck, many different types of body designs and liners are available to configure the truck for the material and type of work the truck will be doing. For example, a truck that dumps into a hopper is best equipped with a flat-floor body, because the design allows metering the material into the hopper.  On the other hand, dual-slope bodies retain material better on steep grades.

For handling poorly fragmented rock, a heavy liner is needed to absorb impact and optimize the life of the body. But the liner adds weight, which reduces the payload that the truck is able to carry. Hardened steel bodies resist wear without the addition of liners. Steel liners and rubber liners are effective in reducing wear caused by abrasive materials, and rubber liners have the advantage of absorbing impact energy, which enhances truck operator comfort and absorbs sound.

Many different options are available on rigid-frame trucks. Perhaps the most critical for operations that periodically have slippery haul road conditions is a traction-assist feature on the rear axle.  The system improves control and handling and reduces tire wear. Two types are available: 1) Mechanical systems similar to automotive-type, limited-slip differentials; and 2) Electronic controls that monitor wheel rotation on each side independently and, when one exceeds the other by a set limit, applies the brakes, transferring torque to the tire with better traction. Electronic traction assist does not interfere with normal differential action and places no increased stress on the drive train.

COMPARING COSTS

Photo by Kevin Yanik

Photo by Kevin Yanik

Having determined production requirements and narrowed the field of candidate trucks, you can now compare costs of different trucks. Comparing costs across brands, unfortunately, is not as straightforward as it could be. There are two reasons for this:

1. Specs vary, so you will need to be careful in comparing features, performance, and ratings. This is especially true for body capacities, horsepower figures, torque curves, and related information.

2. Owning cost goes far beyond the initial purchase price. Over the life of the machine you have to add maintenance expenses-fuel, lubricants, antifreeze, belts, filters, etc. – plus parts and repairs. Seemingly minor variations in fuel consumption, payload and performance can make a substantial difference in total cost over the life of the truck.

This projected cost should be part of your truck selection criteria – along with requirements for routine maintenance. Routine truck service is facilitated by clustering of lube points, ground-level access to filters and fill points and modular components. In some machines, the time required for service can be significantly reduced when work can be done without removing major components.

The greater the maintenance requirement and the more difficult access to maintenance points and time needed for the work, the greater the long-term cost and risk maintenance will be overlooked. Increased equipment sophistication and high cost of service operations have prompted another trend: increased reliance on equipment dealers and maintenance contracts. Today’s equipment dealers offer a much broader variety of product-support choices than in the past.

Among these are:
■ Component rebuilding and replacement programs.
■ Plans to monitor machines on the job and schedule repair before failure.
■ Guaranteed maintenance contracts that assure product availability and put a lid on cost.

The aim, of course, is to keep machine availability and productivity up and eliminate unscheduled downtime.

TRUCK-LOADER MATCHING

The truck and loading machine match is critical to productivity and cost effectiveness. The trucks and loading machines are systems that must be considered together when configuring a mining operation and acquiring equipment.

The most important consideration when matching loaders and haulers is finding units with compatible capacities to get maximum loading efficiency. That requires an even number of bucket loads to fill the truck to capacity without overloading. It takes as long to load a half bucket of material as it does to load a full bucket of material. An even pass match is the key to loading efficiency.

Generally, filling the hauler in three passes is considered ideal. Four or five passes are considered acceptable, especially in high-capacity hauler loading.

When matching capacities look at the weight the hauler can carry. Off-road trucks generally have a payload of about 10 percent over their nominal-rated load capacity, but significant overloading has many negative consequences, including compromised steering and braking. Divide the rated capacity of the hauler by the desired number of passes to fill it. The result will be the weight of material that must be carried in each bucket load.

Determine the density of materials the hauler will carry, and determine the number of cubic yards that constitutes the correct weight for an even number of passes to load the truck. When selecting a loading machine, remember that the rated capacity of the bucket may not be what you achieve at your operation. Bucket capacity is calculated on the basis of a 2-to-1 heap and a 100-percent fill factor. Buckets are not always 100-percent full when loaded. Bucket fill factor varies with changing conditions, the type of material loaded and the size of the blasted rock. A loader excavating shot rock may have a fill factor of 75 to 90 percent, while another working in sticky clay may have a much higher one.

Teeth, edge segments or other accessories on the bucket lip can increase bucket capacity significantly. To approximate how much each bucket load will contain, multiply the rated bucket capacity by the fill factor. By multiplying various bucket sizes by the probable fill factor for the material, the buyer identifies the correct size bucket and, therefore, the correct size loader.

A number of additional factors should also be considered when matching a wheel loader with a hauler. Compare the loader reach with the width of the hauler body. Loader reach is measured from the front of its front tires to the tip of the bucket cutting edge when the boom is fully raised and the bucket is dumped at 45 degrees. Comparing the loader reach to the width of the hauler bed ensures the loader can place a load to the far side of the hauler body.

Compare the width of the wheel loader bucket in relation to the length of the hauler body. Some equipment manufacturers recommend that bucket-width-to-body length should fall within a ratio of 1-to-1.4 or 1-to-1.5. The bucket should be wide enough to provide a degree of protection for the front tires but not so wide that it will be difficult for the operator to avoid bumping the back of the hauler cab or dumping material too close to the end of the hauler body. Rocks that land too close to the end of the body are likely to roll off the hauler the first time it goes up a grade.

Compare the wheel loader dump height in relation to the height of the hauler side. Compare both units the way they will be equipped in actual use. The teeth on a rock bucket, for example, can reduce dump height by as much as a foot. Also, adding sideboards or larger tires on a hauler can increase its height significantly. Making this comparison ensures the operator will not have to roll the bucket back to clear the side of the hauler, which increases cycle time.

BUILDING AND MAINTAINING HAUL ROADS

Photo by Zach Mentz

Photo by Zach Mentz

For rigid-frame haulers, especially, haul road design and maintenance has a huge impact on truck haulage cycle efficiency, costs and production. Proper road design is the first step in ensuring good truck productivity and low operating costs. Critical elements are grade, cross-slope and superelevation of curves. The goals are to maintain proper weight distribution of the load and to minimize lateral forces on tires. The same design that enhances truck productivity also reduces component wear and optimizes fuel burn, as the truck remains stable at optimum speeds.

The steeper the grade, the more weight bears on the rear tires. The goal is to keep the weight distribution at about one-third on the front tires and about two-thirds on the rear duals. Ideally, the grade would not exceed 8 percent. The grade should be constant and the road smooth to minimize rapid weight distribution changes, minimize transmission shifts and maintain higher average speed. Such a road also promotes smooth braking when trucks are returning to the loading area.

Optimum road design also helps to minimize spillage of rocks on the road. Approximately 75 percent of tire failures are caused by cuts from rocks and impacts with rocks.

Roads must also drain properly to reduce slippery conditions and to help minimize rolling resistance. On flat terrain, the minimum cross-slope maintains drainage for the expected rainfall at the mine. If conditions permit, consider a 2-percent constant cross-slope. Four-percent cross-slope can be used in rainy areas. Alternatively, the road should be crowned slightly to drain water to both sides of the road. On grades, minimal cross-slope or crowning is needed, because the grade itself helps direct water off the road.

Corners should have the maximum practical radius to help maintain speed and to minimize side force on tires. Side force generates heat in the tires and reduces casing life. High side forces scuff the tires and accelerate tread wear, too. Corners should be constant and smooth to reduce steering corrections, operator fatigue and component wear.

If truck speed exceeds 10 mph, the curve should be superelevated to negate centrifugal force that puts side loading on the truck. The amount of superelevation needed depends on curve radius and the speed at which it is negotiated. In addition to countering centrifugal forces, corners should be designed so that truck operators can see and avoid obstacles when traveling at normal speeds. The same consideration should be given to crests of hills. These calculations should use the worst-case scenarios: smallest obstacle, highest expected speeds, longest stopping distances, etc.

Road width is another factor that affects safe operating speeds and can help minimize tire contact with safety berms and spilled rocks. On one-way roads, road widths should be 2 to 2.5 times the width of the widest truck used at the site. On two-way roads, road width should be a minimum of 3 to 3.5 times the truck width on straight sections and 3.5 to 4 times in corners.

It’s important, too, to construct the road from material that will compact properly and will not become soft when wet. Quarry trucks create deep compaction forces; therefore, it’s important for the road base to compact well to maintain a solid road surface. Well-compacted roads also minimize rolling resistance, which promotes high productivity. In practice, a 5-percent increase in rolling resistance can result in a 10-percent decrease in production and a significant increase in production costs.

For reference, trucks using radial-ply tires experience approximately 1.5 percent rolling resistance on hard, well-maintained roads, and about 3 percent rolling resistance on firm, smooth, rolling roads. When tires penetrate 1 in., rolling resistance is approximately 4 percent, and 2-in. penetration means about 5 percent rolling resistance. Tire penetration of 100 mm means about 8 percent rolling resistance, and 200 mm penetration means 14 percent rolling resistance.

Photo by Joe McCarthy

Photo by Joe McCarthy

Frequently, high rolling resistance is associated with wet conditions. The road material becomes soft when wet. To avoid a saturated road base, adequate drainage structures should be built, such as ditches, to carry away the maximum expected rainfall. Properly sloping the roadway and carrying water away will help minimize water puddling, potholing and entry of water into the road base.

Remember, too, that the haulage road extends to the loading face and to the dump point. Bench widths should be adequate for a loaded truck to clear the loader under full acceleration and for an empty truck to avoid tight, high-speed turns. The minimum bench width should equal the machine turning radius plus space needed for the safety berm. Dump points should have enough space for the truck to align properly with a minimum of maneuvering.

OPERATING FOR LONG TIRE LIFE

Most truck tire failures are caused by contact with rocks spilled on the road, in the loading area or at the dump point. Machines to remove spillage and a communication system that promotes fast action are needed at every mine. But, in addition to good mine design, proper loading and operating techniques should reduce the need for cleaning up.

The loading machine operator plays a key role in getting long life from truck tires. Centering the load properly in the truck body and not overloading the truck allows the tires to work within their intended load limits. A correctly sized and properly placed load also is less likely to lose rocks onto the roadway.

Training motor grader operators in proper road construction and maintenance is important. Water truck operators should receive thorough training, too. Watering to suppress dust also helps maintain compaction in most climates. But too much water can create slippery conditions, and water can increase the likelihood of tire cuts from sharp rocks. Using intermittent watering patterns on slopes should reduce the risk of tire slippage.

To optimize truck productivity and truck tire life, do not overlook the dump areas. Dump areas should have a smooth floor that allows trucks to maintain speed until they reach the dump zone where they enter parallel to the edge or crusher opening and brake in a straight line before turning, stopping and reversing to the dump point.

DRIVER EDUCATION AND TRAINING

Photo by Kevin Yanik

Photo by Kevin Yanik

Frequently overlooked as a way of managing equipment costs, operator training can play an important role in cost effective fleet management. Driving a hauler is far different from driving a pickup truck, so new operators require training to be safe and efficient. Even the best operators can use a refresher course, an orientation to new equipment or an opportunity to unlearn bad habits. Poor operating habits, such as pulling away from dumps with the bed up or careless loading can quickly cancel out the steps you’ve taken to reduce cost per ton. Training is available from most dealers as well as independent companies specializing in equipment operator training.

REDUCING NOISE IN THE CAB

For the average person, hearing loss begins in early adulthood. From this time forward, your hearing will continue to diminish as you grow older. It is extremely important to protect your hearing level.

The best way to reduce hearing loss is to protect your ears from extreme sound levels. What is considered to be extreme? Most regulatory agencies consider 85 dBA (decibels) for an eight-hour period to be an extreme sound. This noise level is equivalent to a vacuum cleaner. Interestingly, to most of us, this noise does not seem very loud. However, studies have shown that even moderate noise over long periods of time can wear down the sensitive components of the inner ear.

This can seem quite surprising to the average heavy equipment operator. After all, these operators are working around large diesel engines for long periods of time.

How to help protect against hearing loss:

■ Engineered controls: The concept here is to stop the sound from reaching the human ear. A muffler system is the perfect example. Also, by shrouding the engine compartment and shrouding the cab, noise from the engine and other mechanisms can be reduced significantly.
■ Administrative controls: These are work practice controls that help to protect employees. Examples are signs that read Hearing Protection Required. Training is another example.
■ Personal Protective Equipment (PPE): PPE is only employed when engineered and administrative controls have been applied and sound levels are still high. Earmuffs or earplugs are effective PPE.

When operating heavy equipment keep your ears in mind. Do you have to talk loudly to be heard? It is possible that you are working in an environment with excessive noise.

■ If possible, make sure the cab is sealed well and the windows are shut.
■ Keep a set of disposable earplugs with you.Employers typically supply these to employees for free. They are great at cutting down moderate noise.
■ Turn down the cab radio. Loud music is a big contributor to long term hearing loss.

Machine safety is the management of safety risks that can occur when operating a machine. Listed here are a few guidelines for everyday use:

■ Inspect the function of the doors / hinges, hydraulic hoses, nuts / bolts, condition of tires and other areas.
■ Verify lights, gauges, horns and other similar equipment are in working order; verify fluids are at required levels.
■ Ensure there are no obstructions or debris in the equipment before starting and the vehicle is free from leaks of any type.
■ Make sure the operating manual has been reviewed before operating any equipment.

Tier 4

Photo by Kevin Yanik

Photo by Kevin Yanik

Tier 4 refers to a generation of federal air emissions standards established by the U.S. Environmental Protection Agency (EPA) that apply to new diesel engines used in off-highway equipment. It requires manufacturers to reduce the levels of particulate matter and oxides of nitrogen (NOx) to a level that is 50 to 96 percent lower than the existing generation of diesel engines.

Tier 4 emissions requirements apply to new products only and do not apply retroactively to any existing machines or equipment. Off-road engines are responsible for 47 percent of particulate matter (PM) and 25 percent of NOx emissions from all mobile sources nationwide, according to the EPA. Diesel exhaust contains small carbon particles and other toxic substances that are created during an incomplete fuel burning process. When inhaled repeatedly, these small particles may aggravate asthma and allergies or cause other serious health problems.

TIER 4 INTERIM AND TIER 4 FINAL

Tier 4 regulations were introduced in two phases:

■ Tier 4 Interim began in 2011.
■ Tier 4 Final began in 2014.

EXISTING ENGINES

The Tier 4 requirements apply only to new engines – including those sold in California and all other states. There is no federal requirement to upgrade any existing engine to the new Tier 4 standards. California is pursuing separate state law requirements for the modernizing and upgrading of off-road machines and equipment in that state.

Although manufacturers will only be able to produce the Tier 4 engines after the established deadlines, equipment dealers may sell inventories of engines and equipment from the previous generation technology (Tier 3) until the inventory is depleted. Each engine and equipment OEM may have different technology and transition plans, so it will be important to understand these requirements for each machine. Under the EPA rules, manufacturers are provided with flexibility in meeting the requirements. Also, machines slated for export outside the U.S. are treated differently.

CEGR SYSTEMS

Many aftertreatment systems incorporate a three-fold approach: cooled exhaust gas recirculation (CEGR), a diesel oxidation catalyst (DOC) and a diesel particulate filter (DPF) with devices commonly combined in a single canister.

CEGR works by recycling a portion of the exhaust gas with fresh air, thereby reducing oxygen levels in the combustion chamber, which helps to reduce NOx formation. The challenge with CEGR is that particulate matter is not reduced to satisfactory levels within the engine and an aftertreatment is needed such as the DOC and the DPF.

Since the DPF is typically a ceramic wall flow filtration system that further separates the particulate matter from the exhaust, it will require periodic regeneration to reduce the particulate matter into ash using the high temperatures of the exhaust to burn off the accumulated particulate matter. The timing of the regeneration varies based on fuel usage and engine load.

Passive regeneration occurs during machine usage, allowing the machine to continue operation. However, manual regeneration is initiated by the operator from the control console and requires the machine to sit idle and be parked until the regeneration cycle is complete.

At approximately 3,000 to 4,000 hours, depending on the specific manufacturer’s recommendations, the accumulated ash from regeneration must be removed from the DPF. Typically, this involves the removal of the DPF from the machine for cleaning and/or refurbishing. “DPF maintenance greatly depends on the machine’s prolonged idle time. Lower-rpm operation will increase the frequency of service,” says Chad Ellis, Doosan product manager.

Depending on the manufacturer and the machine, DPF replacement can typically be completed in two hours or less, and the cleaning procedure requires roughly one hour. Because the accumulated ash is considered hazardous material, Ellis recommends that service only be performed by the dealer or an authorized DPF service provider.

SCR SYSTEMS

A second system is the selective catalyst reduction (SCR) aftertreatment technology. SCR systems are used in conjunction with engines that have been optimized to reduce PM. The use of SCR reduces NOx using an additional liquid called diesel exhaust fluid (DEF) consisting of water and ammonia for the aftertreatment of the exhaust gases.

Ellis says that for every 100 gallons of diesel fuel consumed by the engine, approximately 5 gallons of DEF will be used. For example, if a DEF tank capacity is 15 gallons, the DEF will need to be refilled after about 300 gallons of diesel fuel, so operators will typically want to top off the DEF in conjunction with refueling.

According to Aaron Kleingartner, Doosan segment application marketing manager, since DEF is a water-based solution, special precautions should be taken in cold climates. “The DEF will begin to crystallize and freeze at about 12 degrees, but the systems and EPA regulations are designed to accommodate that,” Kleingartner says.

He also points out that DEF with the approved urea content of 32.5 percent will allow the solution to freeze and thaw at the same rate, ensuring the consistent ratio required by the SCR system. Additionally, all SCR systems are configured to allow machine operation until the DEF thaws, and DEF storage tanks are designed to allow for expansion as the solution freezes.

FUEL AND OIL

All machines using the CEGR + DOC/DPF technologies require ultra-low sulfur diesel (ULSD). Sulfur is a significant contributor to pollutants that exist in diesel engine exhaust, and the catalyst system used with Tier 4i engines is dependent on ULSD, which has significantly less sulfur compared to prior diesel fuels (15 ppm versus 500 ppm). Higher amounts of sulfur than what is contained in ULSD will reduce the service life of the catalyst, requiring it to be replaced – a costly repair to the exhaust system.

All machines using the CEGR + DOC/DPF technologies require the use of American Petroleum Institute (API)-rated CJ-4 (sometimes referred to as low-ash oil) to help reduce the amount of particulate matter in the DPF. While not specific to Tier 4 Interim-compliant diesel engines, this high-performance engine oil has superior soot-viscosity control, reduced low-temperature sludge buildup and reduced high-temperature deposits – and helps maintain viscosity in severe temperature service.

MECHANIC TRAINING

Photo by Zach Mentz

Photo by Zach Mentz

Reducing emissions down to near-zero levels introduces a number of changes in engine and equipment design, and each manufacturer has determined its own product-compliance strategy. These changes could include devices such as particulate filters, oxidation catalysts, lean-NOx traps or SCR that are integrated into the existing exhaust and muffler systems.

Technicians need to have a general familiarity with electronically controlled engines, exhaust aftertreatment control devices, the concept and practice of measuring backpressure, along with general exhaust equipment maintenance and operation. New operator warning lights and dashboard indicators have been introduced by some manufacturers to denote levels/conditions of new diesel exhaust fluid, or the indication of an active particulate filter regeneration event that might require special attention.

Some Tier 4 engines may use particulate filter technology that could require periodic maintenance and cleaning and/or removal. This may also involve some new equipment in a service facility such as an oven or cleaning cabinet to fully service the filters. Some of these functions can be performed by vendors off site.

For manufacturers that use SCR technology, service employees will need to be trained in the general aspects of SCR technology, including the basic SCR components on the machine (SCR catalyst, storage tank, spray nozzle and plumbing systems), fluid flows and pressures, and troubleshooting. Training on the safe handling, storage, disposal and dispensing of diesel exhaust fluid, including its material safety data sheet (MSDS) is also strongly suggested.

Selecting an ADT

When you’re considering the purchase of a new articulated dump truck (ADT), you need confidence that the investment you’re making will help you achieve your business goals. You want to know that your ADT can quickly and efficiently haul high volumes of material over rugged terrain for long distances at the lowest possible cost of ownership. Industry experts say that’s not too much to ask.

Today’s ADTs provide more power, productivity and stability, resulting in shorter haul cycles than previous generations. They also offer a number of off-road performance advantages over rigid frame trucks in most mining and quarry applications, says Doosan ADT Product Specialist Brian Bereika.

Owing to their articulated design, ADTs are able to withstand conditions even at the earliest stages of mine-site preparation and excavation. They can be operated in areas where there are no roads or only poorly maintained pathways. Generally, ADTs are designed for moving material over distances as great as two miles, with volumes as large as 35 cu. yd., and when the ground is soft, slippery or hilly.

Since an ADT’s capabilities can be very different from other pieces of hauling equipment, it’s important that models be compatible with the specific tasks being performed. “The first step is to identify the tasks the mine needs to perform, and then determine what ADT design is best for those jobs.

“If the tasks are routine and regular, owners will most likely purchase the ADTs. If the tasks are performed only on a periodic basis, it may be more advantageous to rent them as needed. You’ll also want to pair them with properly sized loading equipment for the best results, and find dedicated dealer support to help you sustain their performance and decrease ownership costs,” Bereika says.

He offers the following five factors to consider when specifying an ADT to perform mining and quarry work.

1. Match the machine to the task: ADTs are commonly tasked with removing overburden – such as surface rocks and soil – in the early stages of a mine’s development. Other common chores include cleaning out holding ponds, hauling material to crushers and hoppers, and stockpiling aggregate. Articulated trucks are available in 25-ton to 40-ton class sizes and can carry up to 46-ton payloads. Since an ADT’s body is its revenue generator, size and payload are critical specifications and involve several additional factors. Therefore, accurately estimating productivity before purchasing for a particular task in mining environments needs to be specific and comprehensive.

“It may be necessary to measure the haul roads and accurately calculate gradients to arrive at sound production estimates. The hardest estimation can be rolling resistance, as it is subjective and can change quickly,” Bereika says.

For greater productivity with all tasks, some ADT manufacturers offer body designs that enhance the stability of the machine during transport. For better dumping performance on ground, over banks and into hoppers, some trucks are engineered with lower centers of gravity for faster dumping rates. Since ADTs perform well in half-mile to two-mile applications, look for advanced transmission systems and other component advantages that contribute to reduced fuel consumption. On longer hauls, possible overheating of transmissions, cooling systems and tires must be considered, which may result in necessary cooling-down periods. This may slow production, so manufacturers should be consulted for recommendations on a particular application.

Other task-related issues that should be considered are whether tailgates will be an advantage or a disadvantage for your operation. For instance, large boulders or stumps can contact the tailgate during dumping and cause safety concerns. Also, determine early in the process if your ADT will need a body liner to minimize impact damage from loading larger rock or if materials to be hauled are abrasive and will cause shorter body life. Body liners are generally steel but can be plastic or polyethylene if very sticky materials are to be hauled. Other options in cold climates can include heated bodies and cold weather engine starting aids.

Overloading of ADTs can easily occur and will shorten the life of components, so understand and abide by weight limitations for best results. On-board weighing systems can be a good investment if each load can’t be weighed on a site’s truck scale.

2. Partner with the right loading equipment: One of the best ways to achieve maximum efficiency is to match an ADT to its loading equipment, so that neither the loader operator nor the ADT operator will have long waits between loads. Over 95 percent of ADTs are loaded by excavators, while large wheel loaders, conveyor belts, or hoppers are used in many mining or quarry operations.

For most material hauling sites with good production, the industry consensus is that it typically takes between six and 10 passes to fill an average ADT with an excavator and four to six passes with a wheel loader. For maximum production, the number of passes to load should be between three and five. “Many of the largest ADTs available are similar in size to the smallest rigid-frame truck commonly used in mining, so it’s easy to mismatch equipment,” Bereika says.

3. Identify jobsite restrictions: Are there any width, height or maneuverability restrictions that may impact an ADT’s ability to fully perform? Loading under a hopper, for example, will usually mean there are width and height restrictions, and some larger ADTs may not physically fit in the space. Built for maximum maneuverability, ADTs are designed to adapt to uneven terrain through use of a hinge connecting the cab to the body, which allows the truck to flex. This feature also assists in keeping all six wheels in constant contact with the ground while traveling over loose or compacted soil, banks, material pilings or rocks common in mining or quarry jobsites.

Due to their massive size, mining and quarry projects can involve long drives on congested haul roads and operations in confined staging and dump areas. Select an ADT with a tight turning radius, which can help decrease the time it takes for operators to position the trucks for loading and unloading.

4. Choose tires carefully: “Tires are always a concern in quarries and mines because of the risk of sidewall damage and lower tread life due to operation on hard-packed surfaces,” Bereika says, “so choose tires carefully to minimize costs.” The right tires contribute significantly to an ADT’s tractive force, which is determined by the tread design, remaining tread life and tire inflation, along with the ground conditions at the site.

One of the most important tire decisions is whether to use E3 or E4 tires. The most common ADT tires are two-star E3 radial tires; however, E4 tires offer better sidewall protection for sites that have sharp rocks and may serve as an upgrade in those environments. Hard-packed roads cause shorter life for all tires, but individual tire manufacturers can inform users about which rubber compounds will provide longer life.

5. Extend ADT life with dealer support: Finally, make sure you understand all of your ownership costs and the expected lifetime of ADT components, as they may be different from equipment you currently own. Since ADTs are used off-road and are subject to severe duty, component lifetimes may be different than typical mining equipment. This is why educated and dependable product support is critical. Before purchasing an ADT, choose a dealer that has product specialization and trained mechanics, offers great response times and has good parts stock.

“I would advise sitting down with an ADT dealer and having a discussion about the type of work you’ll be performing, required scheduled maintenance, a preventive maintenance program and major component rebuilding,” Bereika says, “because the cost of downtime is usually the most expensive component of any maintenance or repair, so it must be minimized.”

When properly evaluated and matched to the type of work you’re performing, the return on an ADT investment will be proven out in daily performance, lower ownership costs and longer life.

Sources

Contributors to this chapter include the following, in alphabetical order:

Case Construction Equipment

Caterpillar Inc.

Cummins Inc.

Diesel Technology Forum

Doosan Infracore

John Deere

Komatsu America Corp.

Debbie McClung
Technical Writer
Two Rivers Marketing

Volvo Construction Equipment


Lesson 6 Quiz

1. Regardless of whether a rigid frame or articulated haul truck is used, what are its four main functions?

2. What does Tier 4 mean?

3. Which type of truck offers larger sizes: rigid frame or articulated?

4. What causes most haul truck tire failures?

5. When operating a haul truck, what are some measures to restrict hearing loss?

6. What is the three-fold system that most Tier 4 after-treatment systems incorporate?

7. How does selective catalyst reduction (SCR) aftertreatment technology reduce NOx?

8. What are the five factors to consider when specifying an articulated dump truck (ADT) to perform mining and quarry work?

 

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