Big diggers

Oct. 11, 2007
Giant-size mining projects depend on massive machines.

Kenneth J. Korane Managing Editor

From precious metals to copper and coal, the increasing demand for basic commodities has driven up prices and spurred a global mining boom.

For example, one of the most exciting mining ventures in North America centers on oil sands in northern Alberta. Estimated to contain about 180 billion barrels of recoverable oil using current technology, more than 80 projects are underway or on the drawing boards. They are expected to extract nearly three million barrels of crude oil per day by 2010.

To get to the oil-bearing material, however, millions of tons of soil and rock up to 75-ft thick have to be moved first. One key to making such projects economically viable is quickly removing the massive volumes of overburden. Mining with large excavators that fill haul trucks as fast as possible is the preferred approach. It’s productive, readily adapts to changing mine operations and, compared with draglines and bucketwheels, disturbs less of the surface and returns land to its natural state years sooner.

Massive machines
To meet these demands, mining OEMs are developing a new generation of supersized machines that are fast, efficient, and reliable. For instance, the RH 340B mining excavator from Terex O&K, Dortmund, Germany, was introduced at the recent Bauma Fair in Munich and weighs 625 tons, has a cab nearly 30 ft off the ground, can reach 62 ft, and dig more than 29 ft deep. Its standard bucket capacity is 45.5 yd3. That translates into a payload of 60 tons, letting it fill widely used 240-ton haul trucks in only four passes.

Not one, but dual turbocharged diesel engines — either two Cummins QSK 45s or Caterpillar 3512Cs — generate a combined 3,000 hp to power the machine. The twin-engine design permits uninterrupted work should one engine fail, maintaining maximum digging force while still operating at 55 to 60% speed.

Steel plates up to 10-in. thick and castings — some weighing more than 10 tons — are welded together into the structural framework necessary to carry such large loads. Booms and sticks, for instance, have a torsion- resistant, welded-box construction using high-tensile steel with large steel castings at pivot areas.

Extensive finite-element modeling plays a key role in maximizing structural integrity while keeping overall weight within reason. For instance, FEA lets engineers analyze booms and sticks for superfluous weight, permitting thinner plates in certain sections. A stronger structure and less deadweight translates into higher payloads in the bucket. Engineers also moved welding seams away from high-stress areas for added durability.

Terex O&K’s TriPower mechanism — in essence a rotating, triangular steel plate on each side of the front-shovel boom — provides kinematic assistance to the hydraulics on face-shovel versions of the machine. Mechanical lever action lets cylinders generate greater digging and lifting forces through the entire range of motion. It also keeps the bucket at a constant angle regardless of lifting height, and prevents spills out the back of the bucket.

Hefty hydraulics
Another gargantuan aspect of the RH 340-B is its hydraulics. The five-circuit system includes four main swash-plate double pumps, delivering a combined 1,372 gpm at 4,460 psi for attachments and 5,220 psi for the track drive. And four additional swash-plate pumps, each generating 93 gpm at 5,080 psi, power hydraulic motors that swing the unit from side to side. The system holds about 2,500 gallons of hydraulic oil, with a tank capacity of 1,876 gallons.

The hydraulic cooling system, fully independent of the main hydraulics, uses four gear pumps, each sending 129 gpm of low-pressure oil to the radiators. A microprocessor controls the speed of four hydraulically driven radiator fans, letting the system deliver maximum cooling even when the engine is idling.

An electrohydraulic servosystem gives operators responsive joystick control of pump flow and bucket position, according to company officials. A key component is the electronic pumpmanagement system. It communicates with the engine controller to precisely match hydraulic power to application demands while limiting fuel consumption. For example, it cuts engine speed and throttles pump flow to zero when there is no demand.

The system also offers loadlimit control, reduces pump flow should hydraulic fluid temperature range above or below set values, and adjusts the hydraulics when only one engine is running. A myriad of sensors throughout the excavator continuously sends diagnostic data to a large in-cab display and immediately warns of irregularities.

Fuel efficiency
Talking about fuel economy in machines that consume nearly 100 gallons of fuel/hr might seem out of place. But when a fill-up can take upwards of 3,000 gallons, operating efficiency becomes a significant concern.

Komatsu America, Vernon Hills, Ill., recently released the 200-ton class PC2000-8 excavator. It features several systems that, according to company officials, cut fuel consumption 10%, compared to the previous model doing the same work. The machine is powered by a 12-cylinder, 956-hp Komatsu SAA12V140E engine that meets Tier 2 emission standards.

The unit’s Total Power Management system, for example, is said to minimize power losses in the hydraulics, cooling fan, and PTO. To do this, it bases pump horsepower and engine output on actual demand. And it controls fan speed at the oil coolers and radiator according to hydraulic fluid and coolant temperatures, and varies engine output according to fan speed.

Two different working modes, power and economy, let operators tailor productivity and fuel efficiency to working conditions. An additional heavy-lift mode delivers all-out power to increase boom force, beneficial for handling heavy rocks.

An in-cab monitor warns operators when the engine idles for more than 5 min, helping prevent unnecessary fuel consumption. And an Eco-gauge on the monitor tracks cumulative fuel consumption and compares it with predetermined target values, helping operators work efficiently.

The PC2000-8 also uses fewer components than previous models, adding to reliability, say company officials. For instance, it has a single engine, larger hydraulic pumps, and simpler hydraulic circuits than prior versions. A larger oil-cooler keeps hydraulic temperatures down and helps the fluid last longer. And heat-resistant elastomer seals in pumps and cylinders are said to significantly increase component durability and life.

Data management
Another shows topper at Bauma was the giant EX5500 mining excavator from Hitachi Construction Machinery, Moline, Ill. The unit weighs more than 1.1 million lb, generates digging forces exceeding 300,000 lb, and its bucket capacity is 38 yd3. As investments in such machines can run several million dollars, accurately tracking performance is critical to productivity, maintenance, and profits.

Hitachi’s Machine Information Center, an onboard data logger, captures and stores up to 10,000 hr of information on construction- size excavators and 2,000 hr on mining machines. It records data such as engine speeds, hydraulic and coolant temperatures, pump pressures, alarms and faults, hours of operation, and the time spent traveling, swinging, and idling.

Technicians download the data with a Palm Pilot through a simple Hotsync operation, then transfer it to a PC. Proprietary software summarizes the data and generates performance reports and graphs that highlight machine use.

Mine operators use the MIC system to improve efficiency by tracking how often a machine sits idle and whether it is properly sized for the job. And knowing how many hours the machine travels, how hard the engine and pumps work, and when alarms and faults occur, it can track component life and decrease unscheduled downtime.

Another electronic watchdog, Komatsu’s Vehicle Health Monitoring System (VHMS) scrutinizes major systems and enables remote analysis of machines and operations. The system monitors the engine, transmission, and numerous other major components, and records information such as faults, payload, and operating history.

Company specialists download data via a PC or satellite link, and analyze and monitor trends in the machine’s conditions. Thus, VHMS helps spot abnormalities, possibly heading off catastrophic failures. Scheduling preventive maintenance before minor nuisances escalate into major headaches ultimately reduces maintenance costs and extends machine up-time.

VHMS can be used with Web- CARE, a company Web-site database that stores diagnostic data such as oil and wear analyses. It provides a comprehensive look at machine health and operating efficiency. WebCARE e-mails reports that help job-site managers more readily gauge machine use and performance and, ultimately, lower operating costs.

Make Contact:
Bosch Rexroth,
Komatsu America,
Hitachi Construction Machinery,
Terex O&K,

Fluid power

A general trend among newer mining excavators, according to officials at Bosch Rexroth, Bethlehem, Pa., is toward higher-capacity hydraulic systems. And increasingly, OEMs control flow the via pump stroke, rather than metering it across spool valves. Thus, OEMs are moving away from traditional load-sensing systems. Although it matches pump flow to demand and is rather efficient, load sensing still requires control valves that generate a several-hundredpounds/ square inch pressure drop. In systems running at over a thousand gallons/minute, this results in significant energy losses and produces a lot of heat. Eliminating valve losses results in more-efficient systems, and less heat tends to prolong the life of hydraulic fluid and system components.

For example, powerful, high-flow hydraulics that produce quick working cycles are reportedly key features on two recently introduced machines from Liebherr, Newport News, Va.: the 250-ton R 9250 and 300-ton R 9350 mining excavators. The latter, powered by a 1,500-hp Cummins QSK 45, is equipped with a 32-ft gooseneck boom, a 19-ft stick, and a 23.5 yd3 bucket. Together, the digging implements weigh more than 70 tons and demand immense hydraulic components to move them about. For instance, the two hoist cylinders measure more than 15-ft long and nearly 2 ft in diameter, and weigh 8,380 lb each.

Four variable-flow, axial-piston pumps send about 800 gpm of oil at 4,640 psi to power the shovel. They also supply the travel drive — two axial piston motors per side that turn planetary reduction gears and move the unit at speeds to 1.86 mph.

Separate pumps running at 5,076 psi deliver 200 gpm to axial-piston motors that drive the swing-drive’s planetary reduction gears and, in turn, the swing ring gear. Swing torque is an impressive 826,000 lb-ft at up to 3.7 rpm. Each machine function has independent electrohydraulic proportional control, and accumulators provides emergency control of all attachments should the engine stop.

Terex O&K’s RH 340-B mining excavator has a 45.5 yd3 bucket capacity, letting it fill 240-ton haul trucks in only four passes.

Hitachi EX5500 mining excavators have an operating weight of 1,142,000 lb. Two 1,350-hp twin-turbo diesel engines power the machine at speeds to 1.86 mph.

The Liebherr R 9250 is a 250-ton machine powered by a 12-cylinder Cummins turbo-diesel engine rated at 1,290 hp. Standard versions of this large excavator are equipped with either a backhoe or bottomdump bucket, each with a capacity of 19.6 yd3.

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