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MEI Online: Sizing & Classification: Latest News: March 19th 2007


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:: Local Company Builds Largest Trommel Ever for U.S. Customer

Multotec Manufacturing has completed the largest trommel it has ever built, an order it received from FFE Minerals. “This is probably the largest trommel ever built in southern Africa," remarks Anthony Yell, product manager - screening, Multotec Manufacturing.

The trommel has an internal diameter of 5.1 metres and is 5.4 metres in length, with a mass of 25 tons. After the steelwork was completed, the trommel was taken by road to DCD-DORBYL in Vereeniging for stress-relieving, whereafter the frame was shotblast and prepared for rubber lining. The trommel flange was machined and rubber lining completed before the screen panels were installed.

The trommel was despatched to Lumwana Copper Mine in Zambia, and will be attached to a 11.6 metre diameter by 5.5 metre long SAG mill supplied by FFE Minerals. The SAG mill will have a 3 600 tph capacity, and will be driven by an 18 MW motor.

The trommel incorporates hand-cast polyurethane panels, each measuring 785 mm wide by 1 350 mm long x 44 mm thick with 12 mm x 38 mm slotted apertures. Multotec’s toolroom had to make up a special mould to cast these panels. After casting, the panels were trimmed and then rolled to the correct radius of the trommel.

Trommel screens are still considered a wear component in smaller mills. However, technological advances over the past decade have resulted in frames designed to last for many years. The structure is rubber-lined to prevent erosion of the steelwork, while the surfaces are now equipped with replaceable screen media.

Flanges are machined to ensure seamless contact with the mill trunnion flange to prevent undue stress in the joint. In actual fact, trommel screens are complex steel structures that have to cater for uneven loads discharged from mills and scrubbers.

As the units rotate, the product discharges through an arc of no more than 25° of the circumference, creating a preferential load-bearing zone, and keeping the frame under constant stress.

Over the years, Multotec has developed methods of designing trommels in-house to cater for these requirements with the assistance of finite element analysis.

With the advent of large SAG and ball milling processes, trommel screens have become more prominent in processing plants. Mills have increased in size to cater for higher throughputs, significantly increasing the size and complexity of trommel screens as well.




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