Bunting, Redditch, UK, has won an order to supply a large electro overband magnet to a gold mine in northern Finland. Over a 12 month operating period, the overband magnet – the largest yet to be built at the Redditch facility – will lift and separate damaging tramp metal from conveyed ore, protecting crushers, screens and other upstream process plant.

In operation, the large electro overband magnet will be suspended in a crossbelt orientation across the non-magnetic head pulley of a conveyor transporting mined ore.  Any tramp ferrous metal entering the deep and strong magnetic field is attracted to the face of the electro magnet and lifted up and on to the surface of a continuously moving self-cleaning rubber belt.  Reinforced and heavy-duty rubber wipers on the belt catch the captured metal, transferring it to the side and away from the conveyed ore.  As the wipers move the ferrous metal out of the magnet’s magnetic field, it drops under gravity into a collection area.

This latest electro overband magnet forms part of a major plant expansion and upgrade at the Kittila mine. When initially contacted, Bunting engineers worked closely with the mine operator to design a bespoke overband magnet for this difficult application.  Design considerations included the width of the conveyor, the volume of conveyed ore, and the size and shape of the tramp ferrous metal.  With these details, Bunting’s design team calculated the minimum magnetic field and force density for optimum separation using an in-house developed program. These criteria provided the basis for the design of the electromagnetic coil by the Bunting-Redditch engineering team.

The final design is a model 205 OCW50 crossbelt electro overband magnet.  The 17kW electromagnetic coil, generating the strong magnetic field, is cooled using recirculated oil.  Efficient cooling of the electromagnet is critical as the magnetic force decreases proportionally to the rising temperature of the coil.  The overband magnet weighs just over 13t. The conveyed ore has a particle size range of between 70 and 400mm, varying in conveyed capacity between 450 and 765t/h (equating to 2.7 million tonnes/yr). The tramp iron ranges widely in size and nature and includes steel rebar (2400 x 20mm diameter), cable bolts (600 x 15mm), steel mesh, and broken drill bits. www.mastermagnets.com
 

The finished Bunting crossbelt electro overband magnet

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