The largest Electro Overband Magnet ever built at the Bunting manufacturing plant in Redditch, England, is destined for installation at the Agnico Eagle-owned Kittilä gold mine, in northern Finland.
Over a 12-month operating period, the Overband Magnet will lift and separate damaging tramp metal from around 2.7 Mt of conveyed ore, protecting crushers, screens and other up-stream process plant, according to Bunting.
One of the world’s leading designers and manufacturers of magnetic separators for the recycling and waste industries, Bunting has European manufacturing facilities in Redditch, just outside Birmingham, and Berkhamsted, both in the UK.
The Electro Overband Magnet uses high-strength magnetic forces to lift and then automatically discard tramp ferrous metal present in conveyed ore, Bunting says.
“In operation, the large Electro Overband Magnet is suspended in a crossbelt orientation across the non-magnetic head pulley of a conveyor transporting mined ore,” the company explains. “Any tramp ferrous metal entering the deep and strong magnetic field is attracted to the face of the electromagnet and lifted up and onto 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 Overband Magnet’s magnetic field, it drops under gravity into a collection area.”
This latest Electro Overband Magnet is part of a major plant expansion and upgrade at Kittilä, Bunting said. This will see ore production go from 1.6 Mt/y to 2 Mt/y, with gold output expected to rise by 50,000 oz/y to 70,000 oz/y when completed.
When initially contacted, Bunting engineers worked closely with the mine operator to design a bespoke Overband Magnet for the difficult application, it said. 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, the Bunting design team calculated the minimum magnetic field and force density for optimum separation using an in-house developed Electro Overband Magnet Selection 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, with the 17 kW electromagnetic coil, generating the strong magnetic field, cooled using recirculated oil. Efficient cooling of the electromagnet is critical as the magnetic force decreases proportionally to the rising temperature of the coil, Bunting said.
The Overband Magnet is 4.2 m long, 3 m wide and 2.2 m high, and weighs just over 13 t.
The Electro Overband Magnet is designed for positioning in a crossbelt orientation over the non-magnetic head pulley of a 1,600 mm wide conveyor, inclined at 12° and travelling at 0.75 m/s. The conveyed ore has a particle size range of between 70-400 mm, Bunting said, varying in conveyed capacity between 450-765 t/h (equating to 2.7 Mt/y).
“The tramp iron ranges widely in size and nature and includes steel rebar (2,400 x 20 mm diameter), cable bolts (600 x 15 mm diameter), steel mesh, and broken drill bits,” Bunting said. “With a maximum working gap of 600 mm (distance between the magnet face and the bottom of the ore conveyor), the Electro Overband Magnet is designed to lift and separate the tramp metal through a splayed burden of up to 500 mm. This requires a substantially deep and strong magnetic field and related force density.”
Adrian Coleman, General Manager of Bunting’s Redditch facility, said large mining projects, such as this, often require bespoke solutions.
“Over 40 years, we have gained considerable experience in designing and building large Electro Overband Magnets,” he said.
“However, this was the largest we have ever manufactured at Redditch, presenting many challenges, which were overcome. And the design and manufacturing process all took place during the COVID-19 crisis.”