Maintenance LIFELINE OF THE MINE

Last fall, 20 senior supervisors from Noranda Inc.’s operations across the country went through an intensive hoist maintenance course. For three days in Toronto and another day in Montreal, the group learned about the installation of hoists and their commissioning, operation, testing, servicing and repair. They were also brought up to date on the latest wrinkles in hoist design. That kind of forum for debate, discussion, and learning is a must, for in new mines and old, the hoist is the single most expensive item of equipment in all underground operations. That fact alone would merit it special attention. But the hoist is also the lifeline of a mine, and the security of its components is paramount.

The hoist itself consists of ropes, sheaves, conveyances, a headframe, and a shaft. Each hoist has a different operating duty, but the maintenance requirements are basically similar. Provincial regulations are specific as to the need for regular inspections and tests, and inspectors closely monitor compliance. On top of all this though, maintenance supervisors are being challenged in several ways. They must keep up with the pace of equipment development. They have to keep in mind that engineering is assuming more importance in over- all maintenance actions, and that diagnostic ability in interpreting failures increasingly depends on analysis that is only possible with an intimate knowledge of the equipment.

This applies especially to much of the newer electronic equipment that is increasingly more reliable and less prone to failure, like the latest hoist drive systems. The dc hoist drive gives adjustable speed with manual or automatic control. It will continue to be in greatest demand, with static conversion taking increasing precedence over the motor-generator set. A big attraction of the static converter is delivery. Hoist installations, always on the critical path, can be commissioned faster.

There are two basic types of mine hoists available:

* the drum hoist — on which the hoist rope is stored during the hoisting cycle, and

* the friction hoist — which merely passes the rope over the wheel during hoisting, using the tension differential between the point where the rope enters the wheel and the point where it leaves. Friction hoists are designed to use a tail rope. That is, a friction hoisting system using skips in balance has the same out-of-balance presented to the motor on either side of the hoist.

It is usually best to hoist the largest skip load possible at the lowest rope speed. For any given tonnage, the result is lower energy consumption per ton hoisted. The limiting factor in using large skiploads is rope safety.

The rope is the most important component of the mechanical system. Three types are in use. The most versatile, round-strand ropes are also the most widely used. Abrasion resistance in flattened-strand ropes is excellent because a greater number of wires is exposed to external friction and movement. Lock coil is non- twisting, which has definite advantages for friction hoists.

Used hoists are constantly in demand, sometimes even those that are third- and fourth-hand. During their lifetime, they invariably receive the care warranted as a lifeline. Regular inspections and tests of the components are imposed by law.

The foregoing is something of a primer on hoists. For maintenance people, learning as much as possible about hoists and their ancillary equipment is important. The Noranda seminar made that clear, because each participant was able to talk with some of the best engineers in the country. Visits were made to manufacturers and each plant visit covered a different area of hoist maintenance: J. T. Hepburn Ltd. (mechanical components); cge (electrical drive systems); Wire Rope Industries, Siemens Electric Limited and asea (electronic control). There was a visit to Peacock Inc., which repairs hoists and other industrial machinery, and a tour of the Ontario government laboratory where the hoist rope samples, taken as part of regulations, are tested to destruction.

Lectures were given: Largo Albert, Senior Hoisting Specialist, Inco Ltd. on conveyances, safety controls and rope maintenance; Tiley and Associates on selection and upgrading of used hoists; Dynatec Mining on specifications of a hoisting system; Secord Inc. on friction and drum hoist selection; and J. S. Redpath Ltd. on hoist installation, start-up and training.

That kind of comprehensive seminar is hard to beat. Everyone involved gained experience and useful contacts for future reference. As one participant noted: “Having the opportunity to share common problems and solutions gives immediate benefits, and identifying the various maintenance personnel at each property throughout the Noranda Mineral’s group helps for future reference when tackling problems.”

The seminar was organized by David Griffiths, Noranda’s director of plant engineering and maintenance. This is the third seminar in the program set up by Griffiths. Keith Bowley is a Toronto-based maintenance consultant.