Condra is to manufacture a high-lift, high-speed, heavy-duty kibble (or bucket) hoist for a 15-ton pre-sink mining portal crane for a South African customer.
Lifting height will be 150m, which Condra said is unusually high and requires careful calculation of drum dimensions and winding sequence, while the Kibble hoist capacity will be 15 tons. Lifting speed will be 30m per minute, which Condra claimed is almost ten times faster than hoist lifting speeds found in standard mine workshop applications.
The ‘pre-sink’ phase in mining involves the sinking of a shaft or a well to access valuable underground resources.
Condra said the pre-sink design combines “rapid lifting speeds with optimised cross-travel via a crab-mounted hoist to transfer the loaded kibble to waiting dump trucks”. Rails allow the portal frame to move aside from the shaft during blasting. The high-speed, high-lift main hoist removes excavated spoil vertically by means of the kibble through an opening in the centre of the drilling stage incorporated as an integral part of the crane. The crab-mounted hoist then moves horizontally to waiting dump trucks. Separate stage-winders mounted on the portal frame are used to position the drilling stage within the shaft.
The configuration is different from the ‘level-luffing’ crane traditionally used for pre-sinking, where lifting speed is much lower, said Condra, and the crane’s jib – which remains level while lifting or lowering a load – is used to move the kibble to the trucks.
Condra cranes have previously completed shaft pre-sinking to depths of 100m in 120 days, work that usually takes up to 18 months, the company added.
Commenting on the new kibble hoist order, a Condra spokesman noted that the lifting height of 150m was just 4m short of the company’s high-lift record, held by an overhead crane servicing the Mohale Dam sluice gate in Lesotho.
“The challenge of this particular design was not its lift height… but more in the calculations we had to carry out to perfect the design of the hoist drum,” the spokesman explained.
“Shaft diameters meant that a wide drum to accept simple storage of rope windings for a full lift of 150m was not possible.
“The shafts restrict lateral movement of the hoist ropes within them, so design had to coordinate drum width with a dimension that would precisely control and restrict lateral movement of the four ropes moving vertically. All four ropes have to remain within the shaft at any point of the kibble’s lift without fouling the sides.”
The spokesman continued: “So, the design process was complex because the 18mm ropes wind onto or unwind from the drum in opposite directions as the drum rotates. At the same time, drum diameter had to be coordinated with motor design so that load placed on the electric motor will remain manageable throughout the non-stop nature of pre-sink work.”
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