Massive trommel for Lumwana

Multotec Manufacturing has completed the largest trommel it has ever built, under an order it received from FFE Minerals. Anthony Yell, Product Manager – Screening, Multotec Manufacturing: "This is probably the largest trommel ever built in southern Africa." It has an internal diameter of 5.1 m and is 5.4 m in length, with a mass of 25 t. After the steelwork was completed, the trommel was taken by road to DCD-DORBYL in Vereeniging, South Africa, 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 Equinox Minerals’ Lumwana copper mine in Zambia, and will be attached to an 11.6 m diameter by 5.5 m long SAG mill supplied by FFE Minerals. The SAG mill will have a 3,600 t/h 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 had to make 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. www.multotec.com; www.equinoxminerals.com