Tag Archives: Bunting

Bunting ups the design ante with new Permanent Crossbelt Overband Magnet optionality

Comminution of minerals, Mining equipment, Mining services, Sustainable mining, , , , , ,

Bunting says it has developed three designs of Permanent Crossbelt Overband Magnet (PCB), with different magnetic polarity, to suit an ever-expanding range of applications.

Overband Magnets are mounted over conveyors to separate ferrous metal from non-magnetic material and are commonly used in industries, including mining.

The magnetic field of a Permanent Crossbelt Overband Magnet (PCB) is generated by charging ferrite or rare earth magnet blocks mounted inside a stainless steel box with a steel back bar. The steel bar back forces the magnetic field to propagate through and out of the bottom of the magnet box, which would be down towards a conveyor transporting bulk materials. Although all three designs operate under this basic principle, that is where the similarities cease.

The magnetic field of the three designs of PCBs is defined as being either a ‘Single Pole’, ‘Twin Pole’ or ‘Tri-Pole’.

The Single Pole design (PCB Single Pole) is the simplest and most common design of PCB. Constructed with a single magnet block and steel back bar, the north pole sits on the back bar with the south pole at the bottom of the block. The field runs vertical, from north to south, projecting out from the south pole and into material being transported on a conveyor. The Single Pole design removes general tramp metal from a range of products in various applications.

A Twin Pole (PCB Twin Pole) configuration uses two separate magnet boxes, mounted side by side on a single steel back bar, each with a different magnetic pole. The magnetic field flows from south to north (from one box to the other) producing a deep magnetic field that projects away and down from the magnet faces.

The enhanced separation performance of the PCB Twin Pole enables capture of smaller ferrous particles. The twin pole configuration has the advantage of lifting longer and thinner tramp ferrous metal, typically steel rebar, in a flat orientation which aids discharge and reduces belt wear. This characteristic of the Twin Pole occurs due to the different poles of the two magnet boxes attracting opposite ends of the ferrous metal rod, forcing it to remain flat in the field. The Single Pole design attracts one end, resulting in one end striking the belt or face of the magnet box.

The Tri-Pole Permanent Crossbelt Overband Magnet (PCB Tri-Pole) has two additional steel side poles mounted either side, with a gap, of a single central magnet box. Each of the side poles has a magnetic north pole, with the centre of the box being south pole (ie three poles). This generates two magnetic fields running from the box to the steel sidepoles. The sidepoles reduce flux leakage and concentrate the magnetic field downwards toward the product.

The greater depth of magnetic field generated by the PCB Tri-Pole results in a higher suspension height of the Overband Magnet, which is ideal for deeper troughed conveyors and higher burdens of material, Bunting says. The Tri-Pole model captures smaller ferrous metals that are difficult to separate with a PCB Single Pole.

An added advantage is that the shape and direction of the magnetic field limits any magnetisation of the Overband Magnet frame.

Bunting offers up armour for Overband Magnet applications

Bulk handling, Equipment maintenance, Mineral processing, Mining equipment, , ,

The highest wear part on an Overband Magnet is the belt that transfers the separated metal away from the conveyor and into a collection area. In order to reduce such wear in applications from mining to recycling to biomass power plants, Bunting has developed a special lightweight armouring for the rubber belt.

In operation, an Overband Magnet sits over a conveyor transporting materials such as mined ore. The magnetic field of the Overband Magnet, generated by either a permanent magnet or an electromagnetic block, attracts ferrous metal from the conveyed material up and onto the revolving self-cleaning belt. Rubber upstands on the belt catch the lifted metal, transporting it away from the conveyed material into a separate collection area.

The force of the ferrous metal striking against the self-cleaning rubber belt is significant due to the magnetic attractive energy of the permanent or electromagnetic block increasing as the metal moves closer to the face. This means the metal is accelerating into the belt. The moving belt becomes sandwiched between the lifted metal and the magnetic block momentarily, until the upstand catches and drags the item away and out of the magnetic field.

Applications in which self-cleaning belts experience high levels of wear include:

  • When there are high amounts of ferrous metal present in the conveyed material;
  • When the ferrous metal is large and heavy;
  • When there are nails or thin and sharp ferrous metals; and
  • When the magnetic block has additional magnetic force, as with the ElectroMax and ElectroMax-Plus models.

To combat the excessive wear and extend the life of a self-cleaning belt, Bunting’s engineers designed a lightweight but heavy-duty armouring for the belt. There were other options, including special wear-resistant belt coatings and other types of rubber belt, however the armouring provided unrivalled protection, significantly lengthening belt life, Bunting says.

The armouring on the rubber belt is comprised of high-density polyethylene (HDPE) slats. Each slat is 100-mm wide and 10-mm thick, with a length to suit the model of overband magnet. The slats are fastened to the belt using special 304 stainless steel elevator bucket bolts and nyloc nuts.

“The introduction of this design of armoured belt has proven very popular,” Adrian Coleman, Bunting’s Technical Director, says. “Other types of belt armouring have proven unsuccessful, but the HDPE has worked exceptionally well.”

Bunting develops UK’s ‘largest DC impulse industrial magnetiser’ at Redditch facility

Comminution of minerals, Mineral processing, Mining equipment, Mining services, Steel and iron ore, , , ,

To meet the increased demand for magnetic separators following a sustained period of sales growth, Bunting has redesigned and refurbished the industrial magnetiser at its Redditch manufacturing facility in the United Kingdom. The enhancements make this DC impulse industrial magnetiser the largest in the UK, outside of academia, it claims.

Bunting is a leading designer and manufacturer of magnetic separators, eddy current separators, metal detectors and electrostatic separators. The Bunting European manufacturing facilities are in Redditch, just outside Birmingham, and Berkhamsted, both in the UK.

At the Redditch manufacturing operation, Bunting’s industrial magnetiser charges permanent magnet assemblies used in overband magnets, drum magnets and pulley magnets. The magnet assemblies are built in an uncharged state and then placed within the magnetiser for charging to create a focused and specific shape of magnetic field. The nature of this created magnetic field dictates how the magnetic separator will separate ferrous metals and magnetically susceptible materials from non-metallic materials as in the recycling, mining and quarrying sectors.

Bunting’s operations team continually review manufacturing processes for improvement opportunities and highlighted key benefits of upgrading the industrial magnetiser. These included significant operating efficiency improvements, which would support the continued sales growth.

The extensive refurbishment involved a complete mechanical and electrical overhaul. However, production demands dictated the time allowed for the refurbishment was limited to a maximum of 10 days.

The Redditch impulse industrial magnetiser is rated at 50 kW, drawing a continuous amount of DC current from the mains power. Each energising phase lasts for only 10 seconds and generates approximately 500 kJ of energy. The 12 t magnetiser stands 1.5-m tall on a 3 x 2-m footprint.

Since the upgrade, magnetisation of a magnet assembly requires significantly less ‘magnetic hits’, reducing the energy consumed by the magnetiser by over 30%, Bunting explains. The quicker magnetising process results in freeing production resource, accommodating the extra demand creating through sales growth. The size scope of chargeable magnet assemblies has also increased up to 2,000 x 1,400 x 400 mm, weighing approximately 5 t.

Adrian Coleman, Bunting’s European Engineering Manager, said: “Magnetising is a key stage within our manufacturing process and with the magnetiser refurbishment we are able to magnetise quicker and more efficiently than previously. The result is increased manufacturing capability and the ability to magnetise larger magnet assemblies.”

Bunting on the importance of Permanent Overband Magnet selection for mineral separation

Comminution of minerals, Mineral processing, Mining equipment, Mining services, Steel and iron ore, , ,

Permanent Overband Magnets are commonplace in mines and quarries, removing tramp ferrous metal and protecting crushers, screens and conveyors against damage. However, there are many different designs of Permanent Overband Magnet, developed to suit specific applications, with an understanding of installation being key to selecting the right one.

Bunting is a leading designer and manufacturer of magnetic separators, eddy current separators, metal detectors and electrostatic separators. The Bunting European manufacturing facilities are in Redditch, just outside Birmingham, and Berkhamsted, both in the United Kingdom.

Bunting designed and built the first Permanent Overband Magnets in the early 1980s and has since supplied thousands to companies operating across the world, it says. Although the basic technology has not changed, advances in magnet materials and manufacturing techniques have significantly enhanced the ferrous metal separation performance.

Overband Magnets lift and automatically remove tramp ferrous metal from conveyed mined or quarried rock. The permanent design features a magnet block mounted in a frame, with two or four pulleys, and a revolving self-cleaning rubber belt.

In operation, mined or quarried rock is conveyed underneath the Overband Magnet, which attracts, lifts and then removes damaging tramp ferrous metal. The size and type of magnetic system (Permanent or Electro) is dictated by the conveyor width, depth of material on the conveyor and the nature of the tramp ferrous metal.

Permanent Overband Magnets are commonly found on mobile plant such as crushers and screens.

Bunting’s range of Permanent Overband Magnets includes four different models to suit different installations. The heavy-duty PCB model suits quarry and small mining operations, operating at suspension heights of up to 400 mm on conveyors between 300 mm and 2,000 mm wide.

The PCB-C compact and lightweight model suits mobile plant installations, such as crushers and screens, and operations where space is limited. The PCB-C operates at suspension heights up to 250 mm, above 600 mm to 1,500 mm wide conveyors.

For installations where the Overband Magnet is located in a difficult location for regular maintenance, Bunting designed the QBC quick-belt change model. As the model implies, the self-cleaning belt is easy and quick to change, reducing downtime. This model operates at suspension heights up to 300 mm on conveyors between 600 mm and 1,500 mm.

The Tri-Polar Overband Magnet produces a different shaped magnetic field with increased power. Although commonly heavier, the deeper magnetic field means that the suspension height of the Tri-Pole is higher, up to 400 mm. The shape and depth of the magnetic field makes this model better suited for the separation of smaller or long and thin tramp ferrous metal.

Bunting concluded: “Selecting the correct Overband Magnet, in terms of permanent or electro and the specific model, is dictated by the application. Bunting’s applications engineers assess the ferrous metal separation objective (ie the plant being protected); the nature of the tramp ferrous metal (ie shape, size, etc); and the conveyed rock (ie size range, burden depth). These criteria assist the team in selecting the optimum Overband Magnet for any given application.”

Bunting ups the Electro Overband Magnet stakes for Agnico’s Kittilä gold mine

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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.”

Bunting expands Permanent Overband Magnet range

Mineral processing, Mining equipment, Mining services, , , , ,

Bunting has released a new model Permanent Overband Magnet that, it says, is specifically developed for use on mobile plant such as crushers and screens used in mining, quarrying and recycling.

The PMax model is a lighter and more compact design that meets specific requirements of reduced maintenance time and lighter weights, it said. It has been released alongside the Easibelt Permanent Overband Magnet for recycling and bulk handling terminal applications. These models come on top of the classic PCB model in the Overband range.

The design of the Overband Magnet is simple with two pulleys mounted on a frame either side of a permanent magnetic block, according to Bunting. It is positioned above a conveyor, either over the head pulley, or more commonly across the belt. In operation, conveyed material passes under the Overband where the strong magnetic field attracts, lifts and then automatically discards tramp ferrous metal.

The PMax is 15% lighter than the standard PCB model across the range and 12% shorter in length, according to Bunting. These reductions result in a 14% higher magnetic force to weight ratio. It operates at a maximum working height of 300 mm (above the conveyor) on belts with widths between 600 and 1,500 mm.

The reduction in weight and size is achieved through adopting new manufacturing processes, including investing in new production plant, the company said. The new design release was in response to customer requests across Europe, it added.

Adrian Coleman, the General Manager of Bunting-Redditch, said: “Our PCB model has been an industry-standard for several decades and remains the optimum design for many applications. However, the PMax is specifically designed as a lower weight option for mobile plant, whilst the Easibelt offers significantly reduced maintenance time.”