Canadian Crane & Hoist Manufacturing Ltd has designed and fabricated three bridge cranes that have been installed inside an underground copper mine, minimising the need for costly excavation.

Canadian Crane was contacted in the summer of 2001 by major minerals producer Falconbridge to quote for three bridge cranes for use 1,500m underground in its Kidd Creek mine near Timmins, Ontario in Canada. The cranes are needed firstly to construct and then to service the access elevators. Two of the cranes have a safe working load of 45t (49 US ton), while the third is rated at 35t.

However, to reduce underground excavation costs, Falconbridge requested an alternative low headroom crane configuration. The client also requested spans of 13m or 14m on the 45t cranes, despite the fact that anything longer than 9.2m could not be shipped underground due to the limited size of the access ramp at the mine.

Offering a re-configured hoist, Canadian Crane was able to reduce the headroom dimension from 2,505mm to 1,600mm, reducing the amount of underground excavation that was required in each crane bay.

Due to the limited size of the mine ramp being used to transport the crane underground, the bridge girders (together with service platform) were spliced, allowing shipping of each girder in two smaller pieces which would fit the ramp. For the splice to work at this capacity, some 750 holes were precision drilled in the web, flanges and splice plates.

Canadian Crane’s proposal and drawings were sent to Hatch Engineering for third party technical review and approval. The plan was approved. And the order was secured.

Operations manager Foad Sabet says: “The contract was awarded to us based on the extremely high quality of our products, the complete range of engineering services that we provide, and our competitive pricing. We are especially proud of this order since we were competing with crane manufacturers from around the world.” Two of the three cranes have been installed, while the third is ready and set to be shipped in February. Although the cranes were specially engineered, they were fundamentally based on Canadian Crane’s proven design standards, with hoists supplied by Kuli of Germany, whose factory Falconbridge visited.

In addition to the standard features such as rope guides, thermistor protection inside the lifting motors, live axle drive connections and an electro-mechanical load limiting device, the cranes were also equipped with specially designed and fabricated end stops, allowing hook approach dimensions as low as 740mm.

Motors were specially impregnated with resin during their manufacture. Resin was applied by hand while applying low voltage to the winding. This gives better impregnation and so improves motor protection and resistance to start-up shock. To reduce wear and tear from cold-starts, all gearboxes were grease packed rather than oil filled, eliminating the possibility of the lubricant settling inside the gearbox after a period of inactivity. Furthermore, grease-packed gearboxes cannot develop leaks, and as a result, are less maintenance intensive, Sabet says.

Variable frequency drives (VFDs) were used on the bridge and trolley motions, allowing both bridge and trolley to operate at infinitely variable speeds. The VFDs not only result in greater operator precision, but also in less impact on the mechanical components during start and stop functions. Special provisions were made for cooling of the VFD units, due to the dusty and confined underground environment.

To increase the safety and flexibility of the operation, radio remote controls were supplied on the cranes. A local pendant on a floating cable system was provided as a back up unit, and can be selected via a control panel mounted toggle switch.

All bridge and trolley motions were supplied with two-stage ‘end-of-the-line’ position limit switches, designed to slow the bridge/trolley automatically to creep speed near the end of its travel, and automatically stop the unit just before it reaches the end of its travel, preventing a collision with the end stop.

Most of the lifts will be less than 10t in capacity, therefore for each of the 45t cranes Falconbridge specified a smaller auxiliary hoist on an independent trolley. These auxiliary hoists are 11t rated, according to FEM Group 3m (heavy duty), and will be used for the majority of lifts. An anti-collision system based on photo-electric sensors protects the main and auxiliary trolleys.

For serviceability, the customer specified a service platform on the bridge. Because of the splice on the bridge girders, the service platform was specially designed with its own splice, allowing the girders with the platform to be shipped into the mine through the narrow ramp.

Quick disconnects (pin connectors) were incorporated so that the cranes could easily be disassembled and re-assembled after testing at Canadian Crane’s facility, ensuring all wires and other electrical connections were installed properly, and reducing the chance of human error during re-assembly in the mine.