Hoisting: Engineers and legislators face off

It’s a very rare event in underground mines. But it couldn’t have happened at a worse time, in terms of public relations, for Placer Dome.

As 500 delegates from around the world began checking into the Sheraton Centre in downtown Toronto last week for five days of technical talk on trends in mine hoisting and safety, the wire rope which hoists ore and development rock from the Dome mine in Timmins, Ont., broke, sending an unloaded skip plummeting 5,000 ft to the bottom of the main, No 8 production shaft.

The Dome mine produces about 132,000 oz of gold a year — accounting for 17% of Placer Dome’s total gold output.

The incident began when the skip door failed to close after dumping its load at surface, General Manager Robert Perry tells The Northern Miner. When the skip started back down the shaft, it jammed and slack rope paid out on top of the skip.

When the skip unjammed itself, it fell freely, snapping the rope once the slack was taken up. Four men were in the mine at the time but no one was injured.

For many delegates, some of whom came from as far away as China to attend the conference, the incident gave some immediacy to the issues of technological advances in hoisting. “This is exactly the kind of thing we want to avoid,” conference chairman Robert Dengler says.

(For Placer Dome, production from the Dome mine will be affected for an undetermined period of time. At presstime, shaft inspection crews were making their way slowly down the shaft, assessing the damage done by the falling skip. Ore can be hoisted from the mine through the old No 3 shaft, but at a rate of only 2,100 tons per day compared with 4,200 tons per day through the No 8.)

The last time a wire rope on a skip broke in an Ontario mine was in 1984. In fact, there have been only six such accidents in Ontario since 1980, accounting for only 1% of the total number of hoisting accidents during that period, according to the Ontario Ministry of Labour.

Spillage of muck or other items down a mine shaft is the most common accident in this, the country’s largest mining province, accounting for 17% of the total number of accidents. Technical failures (components and equipment) were the second most common type of hoisting accident, accounting for about 16% of the total.

There are 169 mine hoisting plants in Ontario and more than 400 in all of Canada.

Despite the proliferation of mine hoists, the technology of hoisting does not vary much from mine to mine. Nor has it changed much over the years.

In his opening plenary session speech Jim Redpath, known in the industry as “Mr. Headframe,” painted a picture for delegates of what hoisting might look like 25 years from now. His imaginative vision includes such things as 3,660-m shafts with long, cylindrical aerodynamic conveyances moving at speeds approaching 40 m per sec and breaking on a cushion of air at the bottom of the shaft.

One of the advances necessary to make such a dream a reality is an increase in the ratio of strength-to- weight of a wire rope. This has advanced very little in 40 years, plenary session chairman V. B. Cook points out. That fact alone has restrained engineers to hoisting from depths of only 2,100 m and at speeds or only 18 m per sec.

“If wire ropes were to receive the research attention they deserve and warrant,” Cooke says, “a 20% increase in this strength-to-weight ratio would mean billions of dollars for mining companies worldwide.”

It is this kind of break-out thinking this conference has generated among hoisting engineers and operators.

The most dramatic change in recent years has been the drive to hoist larger loads from greater depths and to cut costs in underground mining operations.

Several shaft-deepening projects are under way in Canada, including one at Brunswick Mining & Smelting’s No 3 shaft in Bathurst, N.B. That 690-ft project will extend the shaft to the 4,300-ft level and allow the company to hoist lead/zinc/ copper/silver ore at a much faster rate of 3,000 ft per min.

“Everything is expected to be in operation by the end of October,” says Peter Blight of BM&S.

Cost-cutting has been achieved in some mines, such as Inco Ltd.’s Copper Cliff North mine in Sudbury, Ont., where the hoist has been fully automating for about a year now, according to E. Henderson of Inco.

The hoisting conference was organized by the maintenance and engineering division of the Canadian Institute of Mining and Metallurgy to present hoist manufacturers and designers with a broad spectrum of ideas for future developments in the industry — a future in which hoisting people would like to see government legislators worldwide working closely with engineers to incorporate new technologies safely into the hoisting process.

The proliferation of hoisting regulations around the world make it very difficult for manufacturers like Canadian General Electric to sell equipment to other countries, says P. deH. Eastcott.

“The Canadian Standards Association is attempting to write a modern, practical hoisting standard. If this was adopted as a model to generate a world class hoisting standard, many advantages would result,” Eastcott says.