Continuous mining

TUNNEL-BORER

Following more than a year of discussions and planning, Falconbridge Ltd., Placer Dome and Boretec Inc. may be on the verge of launching a proposed $2-million venture to design and build a tunnel- boring machine that will drive drifts in Canadian hard-rock mines. At the time of this writing, the parties involved were in the midst of negotiations with prospective manufacturers, but nothing had been cast in stone. Besides the three companies already mentioned, the federal government and a Canadian manufacturer would be involved in the project. The proposed project stems from the test of a 7-ft, 2-inch diameter Jarva Mark 6 tunnel- boring machine (tbm) that was used in driving two drifts 4,500 ft in total length at Kiena Gold Mines in 1986. Current plans call for a far more powerful machine with a larger cutter head, more cutters and, most important, a more compact design for easier manoeuvring. The Jarva Mark 6, for example, delivered 280 to 290 tons of thrust. The machine on the drawing board would deliver at least 500 tons, roughly 20 to 25 tons for each of the 24 cutters on the machine. The head would rotate at 14.5 r.p.m., a good deal faster than the 11-12-r.p.m. rate of the earlier Kiena test vehicle.

However, the key word is compact, says Boretec President Lok Home. “We don’t want to go big. Although a bigger machine would achieve higher advance rates, it might swamp the mucking capacity of the mine,” he tells The Northern Miner Magazine. Under consideration now is a 7-ft, 6-inch-diameter borer that has been dubbed the Compact Underground Borer (cub).

It should be noted that the 7-ft, 2-inch-diameter Kiena test machine was just that: a pilot project that would set the parameters for a custom- designed hard-rock borer. Kiena and J. S. Redpath worked together on that project. It is believed that this was the first such test of a hard-rock tbm in Canada. Before undergoing modifications by Boretec, in preparation for the Kiena test, the Jarva Mark 6 had completed three tunnels for a total of 10,300 ft in civil-related work, according to a paper published by Daniel Vanin, a former production superintendent at Kiena. SHAFT-BORING MACHINE J. S. Redpath and Robbins Co. have developed a shaft-boring machine an d system that could well get its inaugural run at a Canadian mine this year. David Hansman, senior manager of development for Redpath, says his company is discussing a shaft-boring project in central Canada with the aim of having the project started before the year is out. He estimates that once the collar has been established and the machine set up, it should sink at the rate of 6 m to 8 m per day. Conventional shaft-sinking, under the best conditions, averages 3 m to 4 m per day, he says. Relative costs, however, are about identical, so the real advantage to the shaft-boring machine (sbm) is its speed.

The cutter head design employed on the Robbins machine is the same as that used on machines that bored lateral headings at the Mount Isa mine in Australia. According to literature on the device, the sbm employs disc cutting principles established in tunnel boring and mobile mining machines for horizontal or inclined development headings. Consisting of a cutter wheel with a horizontal axis mounted on a carriage with vertical travel, the entire assembly is positioned in the shaft by an upper and lower gripper system that grips the sides of the shaft. Walking cylinders, between the gripper assemblies, allow the machine to advance up or down the shaft in increments. The carriage is mounted on a slewing structure that rotates about the vertical axis of the shaft. A clam- type mucking unit is mounted opposite the cutting wheel on the slew structure and loads directly from the shaft bottom into a hopper. A conventional mine hoisting system allows muck buckets to be lowered into the sbm to transfer muck from the hopper to the surface.

The company says the system’s design complements the sbm’s performance potential while utilizing proven traditional shaft-sinking practices. This includes the surface plant as well as shaft lining and equipping facilities, laser beam and mechanical direction control devices, ground support installation facilities, water- handling and ventilation systems and simplified access for cutter changes and maintenance.

The cutter wheel is fitted with 28 disc cutters powered by two 350-h.p. motors. The cutter wheel diameter is 3.1 m and rotates at 13.6 r.p.m. All components of the machine will fit through a 2×2-m opening. The longest component is 5.5 m long. The heaviest individual component is 14 tonnes, while the unit as a whole weighs 181 tonnes. The mucking unit is a hydraulically actuated, boom-mounted clam with a half-cu-m capacity.

The shaft diameter can range from 6 m to 7.3 m. The minimum collar depth with upper grippers deployed is 8 m. ROADHEADER

When we first heard that Inco Ltd. was using a soft-rock roadheader at one of its Sudbury mines, we worried that maybe somebody up there had come unglued. The area is renowned for having some of the hardest rock in the country, and we knew that these roadheaders work fine in potash mines. But in Sudbury? Never. After a few inquiries, however, we learned that Inco had indeed incorporated a roadheader into its hard-rock operations at the Creighton mine in Sudbury. But the roadheader bores through cemented backfill in mined-out stopes to establish new drill horizons for vertical retreat mining.

In the past, drill horizons were driven more conventionally by jack legs through ore below the mined-out stopes. According to a company official,the Alpine Miner roadheader has worked well. Unfortunately, ground conditions in the backfill are such that the machine can only advance about 6 to 8 ft at a time. Workers must then install square set timbers to support the drift walls and back. “The timbering slows us down,” the official says. Disposing the fill after the roadheader has completed its task is also time- consuming. Inco bought the roadheader as a used piece of equipment about three or four years ago. It drives a 12×12-ft drift (a 10 1/2-ft opening between timbers). MOBILE MINER

The Robbins Co. has successfully field-tested a boring machine that produces a smooth, rectangular heading in hard-rock mines. The machine, called the Mobile Miner, has driven a conveyor drift at the Mt. Isa Mine in northwest Queensland, Australia. The Mobile Miner comprises four main sub-assemblies: a crawler frame equipped with floor jacks and gripper system, a cutterhead boom and carriage, a cutterhead and a muck apron and conveyor. The machine employs a thin rotating wheel with multiple disc-cutters (designed to withstand continuous loads of 22 tonnes each) mounted on its periphery. The wheel is mounted to a boom, enabling it to sweep across the face parallel to its axis.

The Mobile Miner’s boring operation begins by bracing the jacks and gripper system against the floor and back of the drive. With the boom swung to one side of the heading, the rotating cutterwheel plunges about 100 mm into the rock. The operator then activates the boom swing cylinders and the boom traverses to the opposite side of the heading. The cutterwheel again plunges into the rock and the boom makes a reverse sweep. This cycle is repeated until the full 760-mm stroke of the propel cylinders is exhausted. Then, with grippers retracted, the machine crawls forward, the operator checks for line and grade using machine-mounted laser targets and boring begins again.

The cutting action of the Mobile Miner creates a nearly rectangular opening, with a flat floor, flat back and slightly arched ribs. The width of the opening can be adjusted from 7.4 m to 4.7 m by controlling the swing of the boom with limiting collars on the boom swing cylinder rods. The height of the opening is 3.7 m.

At Mt. Isa, the prototype machine bored a single 3.7×6.5-m decline, large enough to hold the conveyor and provide a servicing corridor. According to a report published by Robbins Co., the machine was delivered to Mt. Isa in mid-1984 and, after tranportation underground,
attained instantaneous penetration rates of up 1.5 m per hour. But dust control was a problem from the beginning. Traditional sealing systems used on tunnel-boring machines proved inadequate in the highly abrasive, highly concentrated silica dust. (Geologic studies had determined that the decline would stretch through basement rocks, 70% through very hard, abrasive quartzites — 110 to 270 MPa unconfined compressive strength, or 16,000 to 39,000 psi, and from 80% to 93% silica — and 30% through chloritic schists, or greenstone.) Conveyor tail pulley seals, drive motor and angle drive seals failed prematurely. All have been successfully modified. Redesigning the dust shields and increasing the capacity of the two scrubbers by 33% have greatly improved dust control.

Fines spillage from the conveyor and excessive decline groundwater (at 50degreesC) also caused delays until Mt. Isa introduced a fully sealed 10-ton-capacity transfer chain conveyor to accept water and fines for discharge by mud pump to decline sumps. Other design upratings and modifications involved the roof shield, drive motors, angle drives, cutter pads, reduction gearboxes, the boom, boom carriage and boom swing bearings.

Including all developmental and mine delays, the Mobile Miner averaged 42 m per month through May 17, 1986. This represents 17% utilization of total scheduled time. After major component rebuilds, however, utilization increased to more than 23% for the next 280 m and to 34% for the following 170 m (to July 28, 1986), still in quartzite. (In Mt. Isa’s hard quartzites, the Mobile Miner only needs to achieve 36% utilization to break even with drill and blast methods.)

Through July 28, some peak performances were: * Best Single Shift — 8 hours: 3.66 m in 5.3 hours cutting (66% utilization). * Best Three Consecutive Shifts — 24 hours: 9.11 m in 14.2 hours cutting (59% utilization). * Best Week — 136 hours: 28.5 m in 48.9 hours cutting (36% utilization). * Best Four Consecutive Weeks — 544 hours: 93.5 m in 174.1 hours cutting (32% utilization).

Dynamics monitoring, by the University of Queensland, of critical areas of the cutterwheel, boom, boom carriage, drive system and main frame has confirmed computer model predictions of very high imbalanced loads and fluctuating torques generated from the stepped cutterwheel. These irregularities have been the major cause of repetitive failure and low availability. A new cutterwheel, designed to rectify these problems, has recently been installed on the Mt. Isa machine. With this modification, it is reasonable to expect 50% utilization, with machine delays of 30% and mine delays of 20%. Anticipating higher utilization, Mt. Isa is using the Mobile Miner to bore another 850-m drive. TUNNEL-BORING MACHINE

Stillwater Mining Corp., a joint venture comprising Lac Minerals, Chevron Resources and Manville Corp., is using a 140-ton tunnel-boring machine (TBM), built by The Robbins Co., to drive adits at its platinum/ palladium mine near Billings, Mont. Mine Superintendent Cherie Tilley says the tunnel borer should advance at a rate of 14 ft per hour through nearly half a 24-hour shift. The machine can operate in rock with a compressive strength of 40,000 lb per sq inch.

The TBM, purchased second-hand from the city of Melbourne, Australia, at a cost of $2.5 million, has a drill diameter of 13 ft, six inches. The cutters are 15 1/2-inch high-capacity disc cutters. A Hagglund system will muck out behind the machine. A system of hydraulic clamps and legs propels the machine forward and grippers, or side clamps, anchor it while it cuts. It has retractable back legs and the front end rides on a “shoe” or skid. The end of a stroke at a single setting is 60 inches. The regripping cycle is less than two minutes.

The current mine plan calls for footwall laterals or adits to be driven at 200-ft intervals up both sides of the canyons where the Stillwater mine is located. These footwall laterals are driven parallel to the reef (ore zone) which extends along the Beartooth Mountain Range for about 26 miles. The Stillwater mine has mining claims for about three miles in each direction (east and west) from the river. In the mining plan, there are 160,000 ft of drifting at a size of 10×12-ft. This drifting will develop the platinum/ palladium resource for mining. In the mining plan, footwall lateral drifts are driven 100 ft south of, and parallel to, the reef zone. When the footwall laterals are completed, diamond drilling is conducted from the drift on 50-ft centres to delineate the ore zones that contain enough platinum and palladium to justify the economic extraction of the areas. The current experience at the mine is that about 40% of the footwall lateral is mineable. In considering a tunnel-boring machine, several items were addressed:

* Suitability of a machine to nego- tiate the curves necessary to drive the tunnel parallel to the ore zone.

* Borability of the rock.

* Portability of the machine, inasmuch as the mine plan calls for several adits between 5,000 and 8,000 ft long.

The Robbins Co. conducted rock tests on the Stillwater Complex and predicted that average penetration rates would range from 10 ft to 15 ft per hour. The expected utilization of the machine is 50% of available shift time for 24 hours. In addition, Boretec Inc. of Solon, Ohio, conducted tests for borability of the rock in conjunction with the Colorado School of Mines and reported unconfined compressive strengths ranging from 12,543 lb per sq inch to 23,968 lb per sq inch. Boretec predicted a utilization rate of 45% of the time, available in 24 hours and penetration rates ranging from 11.2 ft to 15.64 ft per hour.

Stillwater says it recognizes that previous attempts at applying TBMs to a mining environment have been unsuccessful. That was one of the reasons for buying a used machine. However, because of Stillwater’s 26-mi trend and the fairly long drives, the company believes the machine will prove successful. It is one of the most portable machines on the market. By limiting the trailing system to two backup decks and employing a Hagglund Shuttle Train System for muck haulage, the limiting factor and the turning radius of the machine is the length from the cutter to the end of the machine conveyor. The two decks in the trailing system are a hydraulic deck and an electrical deck.

The original machine, purchased from Melbourne, was modified in the following ways:

* The head power was increased to 1,110 hp from 750 hp.

* The head r.p.m. was increased to about 11.5 from 5.01.

* The machine was converted to electrical soft start.

* The hydraulic package was removed and replaced by surplus motors from a Thysen V-Mole machine used in Birmingham, Ala. This conversion changed the machine to 60-cycle electrics from 50-cycle and to water-cooled motors from air-cooled motors.

* Boretec designed and built a torque limiter in place of the Wichita air clutch system for engaging the head drive. Before the modifications, the propel force was 1.4 million lb. The final torque output was 497,569 ft-lb. The machine weighs 140 tons.