Modern Mining June 2021

traditionally-designed banana screens were too high, leading to poor screening performance,” he concludes. “With Kwatani’s depth of technical under- standing and experience, we were able to consider geometrical and mechanical factors such as drive angle, operating speed and stroke to find an optimal design for the existing screen.” He notes that the research has also contrib- uted to the ongoing evolution of Kwatani’s screen design capabilities, which are invested in its custom- designed screens to match each customer’s specific requirements and operating conditions. 

carry-over forced the mine to limit the feed-rate to about 250 t/h per screen. It was therefore crucial to improve the dewatering efficiency of the screen if higher throughput was to be achieved. He notes that the changes had to be made without altering the chute work, the motor base position, the available power or the support structure. “The solution was to increase the drive angle to 50° to improve the dewatering ability of the screen,” says Mayhew-Ridgers. “Any higher than this would have reduced the discharge material velocity too much.” The feed-end slope and position were kept the same but shortened, so that the top deck remained the same height as the feed chute. The second slope was also short, with its main purpose being to transi- tion the material from the steep feed-end slope to a long decline slope of 3°. This last slope reduced the speed of the material for better dewatering. Given the load on the 3,66 m wide screen, circular hollow sections were used to provide improved strength properties in comparison to the H-profile deck beams often used in these applications. After the modifications were made, the mine’s plant manager reported that the feed rate had been pushed up to 500 t/h with very little water carry-over allowing the plant to produce a record throughput. “The numerical analysis was therefore very valuable in highlighting how material velocities on

Banana screens undergoing final testing before dispatching to an end user in the coal sector.

Key takeaways  By applying research findings on the performance of multi-slope or ‘banana-type’ vibrating screens, Kwatani has improved the design to dou- ble the throughput on a customer’s dewatering machine  The research was conducted by PW Cleary, JW Fernandez, MD Sinott and RD Morrison from Australia’s Commonwealth Scientific and Industrial Research Organisation (CSIRO) and the University of Queensland  Using mainly numerical simulation methods such as discrete element mod- elling (DEM) and smoothed particle hydrodynamics (SPH), they modelled the granular behaviour of solid particles as well as the fluid-like behaviour of water and slurry mixtures  An interesting finding from the simulation research was that the mass flow rate of the fluid through the first few slopes was actually better when the screen was stationary than when it was excited

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