A primary crusher discharge chute had been a headache for a large Botswana diamond producer for many years. The crunch came when, after considerable capital expenditure, the new conventional chute needed maintenance just six weeks after installation.
“This could not continue and the mine needed a long term solution which is why we believe they came to us for a proposal,” says Hilton Buys, regional manager at Weba Chute Systems. “Senior experts from our company visited the site to take a careful look at the conditions the chute needed to deal with, and we took our conclusions back to our design office.”
Among the challenges were large lump sizes in the ore stream, contributing to build-up of material in the chute and regular choking, says Buys. Also, while Botswana’s dry season is long, the rain that does fall causes considerable problems to the flow dynamics. The kimberlite on the mine – depending on which part of the pit it comes from – can become very sticky in wet weather.
“We therefore had to pay particular attention to flow angles, and the design had to effectively accommodate both wet and dry conditions,” he says. The concept design – which included quick-release lips on dead boxes – was approved by the mine and the final design, manufacture and successful installation was conducted.
Adding to the complexity was that the feed end of the primary crusher was some eight metres below ground level, while the crusher itself stood about 10 metres tall. The chute had to be positioned below the rock box which stores the material from the crusher discharge, channelling the stream into the Weba chute at a transfer height of nine metres to the conveyor belt.
“The conventional chute also created excessive dust through uncontrolled rock velocity over this considerable transfer height,” he says. “By contrast, our chute’s controlled flow meant that the mine did not even have to apply its dust suppression system.”
After installation, Weba Chute Systems gave the customer a 12 month guarantee on this chute, as it does with all its new chutes. This, which comes with regular inspection reports, assures the customer that the performance will meet their expectations.
“These inspections allow us to monitor wear, so we can advise the customer on what action is required so that they can schedule maintenance and avoid unexpected downtime,” Buys says. Installed in 2017, the chute is still operating with little maintenance, having been delivered at a highly competitive price compared to the one it replaced.
“Designing a long lasting chute is not just about creating a box with some reinforcing where you think there will be wear,” he says. “It is an endeavour that must be scientific, based on in-depth analysis of material and flow conditions.”
Buys highlights the importance of asking a range of technical questions about the specific application so that the design answers those needs. The latest software and modelling tools are then applied by the Weba Chute Systems team to guide the most effective design.