A century of expertise delivers state-of-art shaft conveyance
Northern Ontario-based mining supplier, Wabi Iron & Steel Corp., has recently designed and manufactured a unique mine shaft conveyance for an underground facility in the United States. Of major significance is the fact that this is the first conveyance worldwide to be fitted with an emergency braking system able to operate effectively with steel shaft guides. The system would arrest the uncontrolled fall of a cage in a vertical mine shaft.
In most North America mining jurisdictions, the relevant governing agencies require, with the suspension of shaft conveyances from a single hoist rope, the use of a safety arrest mechanism capable of both decelerating and also supporting a fully loaded conveyance in the event of rope severance. It is the deceleration performance requirement that has caused difficulties for conveyance manufacturers to comply with the request from mine designers for steel-guided shaft compartments.
Until now, commercially available arrest systems capable of operating with steel guides, were incapable of producing controlled deceleration rates during the arrest of free-falling shaft conveyances. Not only are these systems incapable of producing controlled deceleration rates, most are “instant-on” systems whereby an occupant inside a conveyance being arrested would be subjected to a ten-fold increase in gravitational force (10 g’s). Being saved from hitting the shaft bottom under such circumstances may not necessarily be beneficial to the conveyance occupants.
The emergency braking system supplied by Wabi is an optional extra feature provided by the Levelok holding system, which was originally developed to overcome the problems associated with cage movement caused by rope stretch when loading conveyances in deep vertical shafts.
This recently supplied shaft conveyance contained more than one unique feature. Aside from the Levelok emergency braking system, the system also provided conveyance-holding functions during the loading/unloading of the conveyance decks. The variable positioning of the two decks when aligning with the shaft station levels was easily addressed as the holding system is “conveyance-mounted”. This self-contained mounting greatly simplified shaft furnishings at the shaft station levels. The conveyance was equipped with vertical lift equipment doors that could be operated pneumatically from a remote location, or manually at the conveyance. The conveyance was arranged to permit holding functions and door opening/closing functions to occur from a remote location with no intervention from a person at the conveyance. The traditional hands-on approach for these functions was also possible via override features.
The manufacturer is three years short of celebrating its 100th birthday. “Wabi has thrived for the last 100 years because a culture of being in the forefront of technology is deeply entrenched in the company psyche,” comments general sales manager Steve Hill. Wabi currently exports around 40% of its sales to the United States.
“The system was originally developed in South Africa, where vertical shafts can be up to 3,000 m in depth,” comments Hill. Wabi is the exclusive North American distributor of this product. “By holding a conveyance in a shaft during loading or off-loading, both safety and productivity are increased,” Hill says. Systems have been developed for use with both cages and skips. “In addition to completely removing spillage caused by rope stretch with mine skips, case studies in South Africa have shown the system to contribute significantly to an improvement in rope life–in some cases around 25%,” he notes. These holding systems are being safely used on a daily basis in a number of Canadian and South African mines, and mines around the world.
With the introduction of the Levelok emergency braking system, design engineers can now be assured that an emergency braking system has become available for use with steel guides. This was not previously the case, so it was a restricting factor in designing vertical shafts with the more cost-effective steel guides.
“Deceleration rates provided by the Levelok system are superior to those provided by the traditional ‘safety dog’ used with timber guides,” Hill claims. “The original designs of the safety dogs date back to around 1948. One must seriously consider whether it is now time that the design and use of safety dogs be thoroughly investigated once more, for safety sake,” he comments.