Weba Chute Systems has completed the complex design for ten chute systems comprising two for the tilt conveyors, four for the silo discharge and four for the crushing circuit at Assmang’s Black Rock Mine, about 80 kilometres north-west of Kuruman in the Northern Cape. The challenging design on an additional contract for four diverting chutes on top of the silos has also been completed. The tilt conveyor and silo discharge chutes have been approved for manufacture and will be delivered to the mine by the end of the third quarter of 2013.

Weba Chute Systems has a longstanding relationship with Black Rock Mine, having previously designed and manufactured 29 Weba Chute Systems at this mine. “We receive repeat business from our customer base for a number of reasons. Before any project is undertaken, we carefully and extensively consult with the customer regarding their specific needs,” says Mark Baller, managing director of M&J Engineering.

“It is important to factor in the direction of flow and velocity of the calculated volume and type of material in each application, while taking into account belt width, belt speed, material sizes, shape and throughput,” he continues.

“M&J Engineering provides designs and solutions that meet these needs and furthermore ensures that the finished product is of the highest possible quality to provide decreased downtime and wear, increased productivity and a favourable return on investment. Our team of highly experienced engineers is available at any stage, before and after installations, to discuss any issues or queries with the customer,” he adds.

Ted Cruickshank, projects manager, of M&J Engineering points out that the second contract required a unique design, as the transfer point had to cater for a tilting conveyor. Material is transferred from the tilting conveyors that feed the silo and the crushing circuits.

These two chutes are required for the material feed which comes from different sources.

One chute handles lump sizes up to minus 450 mm. These materials are conveyed and then transferred through the chute system. The capacity is 1 100 tph on an incoming 1 050 mm wide belt with speed of 1.85 m/s. The outgoing belt, which feeds the crushing circuit, is 900 mm wide and travels at 2 m/s. The second chute on the tilting conveyors moves material with a particle size of minus 150 mm, to the silo circuit on the identically-sized incoming and outgoing belts.

“We had to accurately determine the conveyor feed trajectory to eliminate spillage and at the same time minimise the wear and tear. During our discussions on the design with the mine personnel and their vendors, we utilised FEA (Finite Element Analysis) to ensure that the transfer point solution would optimally transfer material in line with the mine’s requirement,” Cruickshank states.

“It was critical at this point in the project to acquire not only approval on the verification of the design from the mine input, but also to constructively utilise their feedback on the process. While this portion of the contract was extremely onerous, it was also very fruitful and will ensure a benchmark transfer point for the mine,” Cruickshank says.

He says that the design on the four chutes on top of the silos was no less complicated. The silos are fed from the tilt conveyors with the material being transferred at a maximum lump size of minus 150 mm, with a throughput of 900 tph and a bulk density of 2.5. “We had to cater for reversible conveyors by using shuttle discharge boots to ensure that the material is discharged in the direction of the outgoing conveyor. As a specific requirement in this instance we had to ensure that the tolerances were exact. This required extensive design and engineering verification during the design process.”

The four chutes which form part of the upgrade on the crushing circuit will supply a grizzly feed chute, a grizzly oversize discharge chute to crusher, a fines discharge chute from the grizzly (undersize), and a crusher discharge chute.

“The maximum lump size feeding into the crushing circuit is minus 450 mm and the oversize maximum tonnage is 400 tph. The grizzly undersize chute is designed to cater for 500 tph, with a maximum lump size of 450 mm, while the oversize chute feeding the crusher is designed to accommodate 400 tph at minus 150 mm lump sizes. The crusher discharge chute was designed for ease of maintenance, without affecting the requisite 500 tph throughput of minus 150 mm crushed material,” Cruickshank continues.

“M&J Engineering embraces challenges such as the design on Black Rock Mine’s chutes. By stretching the capabilities of our engineers we are able to benefit customers on future projects through this extended knowledge and experience. Through the application of what the engineers have learned, we are then able to provide a chute system that is a plant enhancement, rather than a potential bottleneck,” Baller concludes.