Open-Pit Mining: What’s New CONVEYING POWER

One of Canada’s foremost technology watchdogs has predicted that the surface mines of the 1990s will be so dependent on computer-based technology that manpower will be reduced to one-third of current levels.

Addressing the Minexpo ’88 mining convention in Chicago, Ill., in April, Dr Raj Singhal of the Canada Centre for Mineral and Energy Technology (canmet) reviewed some of the recent trends in open-pit mining technology. “The most visible change in the industry is the greater application of conveyor transportation technology,” said Singhal, who is group leader of advanced mining technology for canmet’s Coal Laboratory in Devon, Alta. “The manufacturers of off- highway trucks are facing competition from high-speed belt conveyors and, during the past few years, have lost some ground to conveyors.

“High-speed belt conveyors with the present technology can achieve speeds of up to 7.5 m per second, depending on the length of the belt and the material being transported. Such conveyors can be powered by six 2,000-kw units.

“A new competitive addition to conventional long belt conveyors is the cable belt conveyor. This system is by no means new in origin, but over time it has undergone substantial design changes and consequent improvement in performance, reliability and operating cost. Cable belts separate the driving medium from the material- carrying medium. In conventional systems, the belt must be capable not only of carrying the material load; it must also be able to transmit the driving tension.”

Several cable belt installations are operating in North America, but the longest is in Western Australia, Singhal said. Worsley Alumina, an Australian subsidiary of Billiton of The Netherlands, has built two long conveyors in Western Australia to transport bauxite ore more than 50 km from the company’s mine to its new refinery. One conveyor is 30 km long and the other is 21 km long.

Conveyor belts are also being used to climb steep slopes. “Compared with trucks, high-angle conveyors are more efficient energy-users,” Singhal said. “Trucks deliver their payloads plus their own dead weight, which can range up to 45% of the total gross weight hauled. In a high-angle conveyor, a higher percentage of the energy goes toward elevating the material.”

High-angle conveyors can be built with belt widths of up to 3 m to carry up to 9,000 tons per hour, provide a lift of more than 300 m with steel cord belt and at angles of up to 60 degrees . (See separate story on vertical conveyors in the Underground Equipment section on page b b .)

But off-highway truck-manufacturers are not taking the competition from conveyors lying down. Several developments dominate. Trolley- assisted trucks have gained renewed interest in the industry because of the savings in diesel fuel consumption, higher speeds on ramps and lower engine maintenance, Singhal said. “Trolley assistance gives, conservatively, a 25% increase in both wheel motor armature life and engine life,” he estimated.

Suitable transmissions are also available now for very large mechanical-drive trucks. “Mechanical-drive trucks are easier to service and maintain,” Singhal said. “And they do not require highly-skilled maintenance personnel.”

Besides conveying, the development in surface mining which has received most of the attention worldwide has been in-pit crushers. “Three years ago a portable crushing unit was erected by Krupp Canada at the Island Copper mine of Utah Mines, on Vancouver Island. Island Copper is a 3,600-ton-per-day truck-and-shovel operation. The 155-ton trucks were loaded with 11.5-cu-m cable shovels. The trucks dump ore into a 240-cu-m apron feeder in the pit, which feeds into a 1.35×1.85-m gyratory crusher and then on to a discharge conveyor 2.1 m wide. Another large semi- mobile in-pit crushing plant, a 1.52×2.26-m gyratory, has been installed at the Highland Valley mine in British Columbia (see “Cost-cutter” in our December, 1987, issue for details). Computerized truck dispatching, too, is making truck haulage more efficient.

Elsewhere in the pit, front-end loaders are being increasingly used as load- and-carry machines, performing both excavation and face haulage functions. But in loading, electric cable shovels are still the work horse of the hard- rock industry. Reliability and mechanical availability are two important reasons.

“All classes of conventional loading equipment have undergone design changes,” Singhal said. “These include improved electrics and the incorporation of health-monitoring and diagnostic systems, resulting in increased reliability and improved performance. This, in turn, has resulted in lower unit cost of production.

Efficiency has also been improved by advances in equipment design, fabrication and construction. The weight and strength of materials used to fabricate major components of machines, and the design and materials used in cutting elements and improved hydraulics have all contributed to machine reliability and availability. Equipment size mix has also changed to make the loading equipment more compatible with the hauling equipment.” Jack of All Trades

Wiseda of Cardin, Okla., is marketing a hefty, manoeuvrable jack for lifting the biggest haulers, scrapers, loaders, tractors, drills and other pieces of heavy, open pit equipment. Rated at 80 tons, the Super Jack iii can support the load in a mechanically locked position without tipping.

The jack is safer and faster to use than other jacks, overhead cranes and other methods, the company says.

The jack is available with electric, air, gasoline or diesel power. A single workman can manoeuvre the jack precisely into position. A wide stance provides adequate load distribution. Wheel Loaders

John Deere has introduced three new, e-series 4-wheel-drive loaders.

They are said to provide better loading performance, more stability, easier serviceability and greater operator comfort than the company’s d-series which they replace. The e-series loaders are available in three sizes: the 95-hp 444E, the 115-hp 544E and the 160-hp 644E.

Bucket capacities are 1.75 cu yd, 2.5 cu yd and 3.5 cu yd respectively and bucket breakout forces are 18,298 lb, 22,524 lb and 36,274 lb respectively.

Features include longer wheelbases and wider treads for improved transport and loading stability and higher tipping loads. Also featured are z-bar linkage that increases bucket breakout force, dump speed, and bucket ro llback for faster cycle times and greater productivity. Versatile Loader

Mannesmann Demag has come up with a dual-attachment design for the company’s H135 hydraulic excavator.

The feature allows operators to choose one of three bucket attachments for the most efficient excavation and loading. Bucket options include 11.2 cu yd, 12.4 cu yd and 13.6 cu yd.

The h135 has a breakout force of 132,300 lb, a single 800-hp diesel engine, three main pumps, a novel hydraulic power system and a service weight of 291,000 lb.

The machine made its debut at the Minexpo ’88 mining convention in Chicago in April. A Powerful Scraper

Caterpillar has introduced a new 198-kw scraper. With a payload capacity of 12.2 cu m, the new 615C bridges the gap between the utility of the 613C and the production-oriented 623E, the company reports.

A new torque converter impeller on the machine provides 6.5% more rim-pull in direct drive and 14.5% more in torque converter drive than previous models.

Features include improved elevator hydraulics, a redesigned hydraulic system for easier service, a new wiring system providing a diagnostic connector in the cab and a new fixed hood design with hinged doors for easy access to the engine compartment.

For the operator, there is more leg room, better line of sight and vibration adsorption mounts for the engine and transmission. Redesigned Tractor

Caterpillar has redesigned the D4C track-type tractor for improved performance.

Improvements include a more powerful, 58.2-kw engine, a foot pedal decelerator, refined hydraulic blade control, improved oil-cooled steering clutches and brake performance, more wear-resistant undercarriage, and increased operator comfort.

The blade features more wear- resistant pins, stronger angle cylinder brackets and a mechanical linkage between c-frame and blade for greater blade stability, the company reports.

Operators will enjoy standard suspension seats with longer and wider arm rests, a contoured transmission lever and a redesigned brake pedal. Tireless Tires

Bridgestone Canada has made what it calls the most important breakthrough in truck tires in several decades.

The company has applied a new approach to restraining fatigue in the truck tire by deriving the optimum shape of a truck tire around a structure which controls cord tension and relieves stress on various sections of a fully-inflated, load-bearing tire in motion.

The most significant improvement has come in durability — up 20%. This was achieved by relieving the strain on the tire carcass by redistributing tension throughout the tire, the company reports. Bridgestone has filed for five patents on the new design. Soil Compactor

Teledyne Canada is marketing a new machine which can compact sand, clay and other loose materials with 6,135 kg of impulse force, 2,000 cycles per minute of vibration, plus boom down-pressure from a backhoe.

The 1500 A compactor weighs 468 kg and requires 114 l of oil per min at 120-155 bar for peak performance. The unit is designed to be mounted on large backhoes and excavators. The area compacted is 0.62 sq m. An optional swivel attachment that permits the compactor to rotate 180 degrees on the end of the excavator boom is also available. — 30 —