Modern Mining December 2024

MATERIALS HANDLING

A bifurcated Weba chute in an iron ore application, expertly designed to handle different material streams efficiently.

How chutes can deal with faster conveyor belt speeds It is common for a robust chute design to accommodate reasonable variations in material throughput, but raising the speed of the conveyor belt may require certain design adaptations to the chute. “O ur mining customers will often need to adjust the volumes of mined material they transfer to the plant, and our chutes are designed for these increases, within reason,” says Dewald Tintinger, Technical and modelling to measure the resultant velocity – the material’s speed after first impact – and to track how the material will move through the chute. When considering a change of material velocity, the impact point might change and the potential consequences of this then need investigation.

Manager at Weba Chute Systems. “Mines will vary the loading on their conveyors for operational reasons, as long as the increase is within the load specifications of the conveyor belt and system.” Tintinger explains that a chute’s design capacity is generally based on the width of the conveyor belt that feeds it, irrespective of the level to which the belt is loaded with material. There will therefore be variations and surges in the volumes, depending on the percentage loading. With the right design, he says, gravity will ensure material coming in faster will be discharged faster. However, when the speed of the conveyor belt is increased substantially, this can have a direct impact on the trajectory of material as it leaves the conveyor and enters the chute. While a relatively modest speed change from, say, 2,5 m/s to 3 m/s may not really be significant, the doubling of the speed will certainly create challenges. He highlights that, at twice the belt speed, the chute is also having to receive, and discharge double the volumes. “Weba is well known for our customised transfer point designs to suit each application, and the material trajectory is a very important part of this bespoke chute design,” he explains. “Working from the initial velocity of the material leaving the conveyor belt, we predict the location of the impact point on the inside wall of the chute.” The company’s design engineers then apply calculations

“For instance, if the impact angle approaches 90 degrees, the material flow could stall and start backing up, rather than travelling smoothly through the chute,” he says. “To address this, many chute suppliers try to design a bent trajectory using curved metal plates – but this can cause considerable wear, which in turn demands frequent maintenance.” Weba Chute Systems rather relies on a solid dead box design, which optimises the material-on-material flow to reduce wear on the chute itself. The dead-box is a highly effective way of reducing the impact and speed of incoming material, while also minimising the dust created. Tintinger emphasises that, with a higher speed conveyor, it is important to design a greater distance between the head pulley and the impact point. “Our designs allow us to create full cascade chutes with dead box sections reducing the impact and speed,” he says. “The key difference in our design is that we generally avoid bending the trajectory of the material; consider that the run-of-mine material could be travelling at 4-6 m/s, so this option creates a source of considerable wear and tear.” The dead-box principle is an important part of Weba Chute Systems’ designs, and the placement of the first dead-box in the chute – at the point of first impact – may change if the conveyor speed is increased significantly. This might require an addition lip

32  MODERN MINING  www.modernminingmagazine.co.za | DECEMBER 2024