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The two South African equipment providers created a solution that could reduce mill wear and other processing challenges caused by the uncontrolled flow of mined material into the mills.
The joint design also had to be able to deal with frequent large-size material, as the mine has no crushing stage before the milling circuit.
According to Weba Chute Systems technical advisor Alec Bond, the over-feeding of material through the existing manually operated chutes was causing regular "mill vomit" in the mine's four mills. The inconsistent feed exacerbated wear on mill bearings as the material's weight shifted forwards and backwards inside the mill, he explained.
The waves of material causing the ‘vomit' also carried insufficiently milled material out of the mill, including large chunks of rock. This led to problems for the downstream mineral processing facilities, including inefficient recovery in flotation cells and even blockages in pumps, Bond said.
"The challenge starts with the existing chutes needing constant supervision and control by operators, being opened and closed with a chain block device," he added. "Our solution was to design a robust, self-controlling chute and feeder system that would ensure an even flow of material into the mills."
He added that the mine's existing system had no means of closing the silo outlet; any maintenance at the chute area required the emptying of the silo and the stoppage of the mill.
"We therefore added a spile bar arrangement which seals off the silo," said Weba Chute Systems designer Wesley Hunkin. "The Weba chute, which is choke fed, is placed under this installation. This allows the feed rate to be controlled by the Kwatani feeder, which has been integrated into the chute design."
The vibrating action of the feeder can control the tonnage and feed rate to the mill, keeping the flow constant. New mounting structures have been designed to accommodate each chute and feeder. There will also be civils works below the silo to provide a solid foundation that absorbs vibrations from the feeder.
