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PRESS RELEASE: Mine hoist manufacturer FLSmidth worked with Twiflex and its South African distribution partner, Tritec Sintered Products, on this installation. FLSmidth supplied a double drum Blair Multi-Rope (BMR) rock winder and a single drum BMR man / materials winder to the Nkana project. The BMR winder is a variation on the double-drum winder and is used in extremely deep shafts as the second drums cable is used to balance the primary load. The drums on both winders are identical; each measuring 5.7m in diameter, with two 1.8m wide rope compartments.
The double-drum BMR has a payload of 47.5 tonnes and operates at speeds up to 17.6 m/s in a 1,278 m deep shaft. A precision control system designed by FLSmidth is used to achieve synchronous braking of all the brake units.
Twiflex brakes are used for parking and holding each time the mine winders stop. In exceptional conditions (i.e. power failure), the brakes can be used to bring the load to rest whilst maintaining a maximum deceleration of 2.3m/s2.
To meet the hoists high rubbing speeds and provide greater thermal capacity, Twiflex engineers designed a new large pad version (174,700mm2 each pad) of its popular VMS3-SPS spring-applied, hydraulically-released brake, which is widely used on mine hoists around the world. Thermal capacity is a measure of the ability of the brake pad to absorb and dissipate heat. Known as the VMS3-VR the 16 off brakes (8 off on the fixed drum and 8 off on the clutched drum) operate on two 6,800mm diameter, 70 mm thick discs, producing a total braking torque of 12.2MNm.
For this application, each VMS3-VR is rated to 240 kN braking force (µ=0.4) using a 2mm air gap. At this braking force, the rated fatigue life is over two million braking cycles. To assist with maintenance, Twiflex brakes incorporate a monitoring system to signal brake pad wear and loss of braking force. The VMS3-VR brakes also include Twiflex’s unique ‘parked off’ feature: meaning they can be adjusted under hydraulic pressure so that when pressure is removed there is no stored energy.
