Monday 19th Aug, 2019

Selecting the right electromagnet

Separation technology specialist, Eriez Magnetics, speaks to ABHR about what to look for when purchasing and installing a suspended electromagnet.

Separation technology specialist, Eriez Magnetics, speaks to ABHR about what to look for when purchasing and installing a suspended electromagnet.

Removing damaging tramp iron when conveying bulk materials is an important step to effectively increase plant availability, protect expensive downstream processing equipment and deliver a clean quality product to the customer.

The Suspended Electromagnet (SE) is widely used when handling bulk materials across a broad spectrum of industries. When installed and maintained correctly, an SE magnet can operate effectively and efficiently for years under the harshest of environments.

Both manual and self-cleaning SE magnets are typically mounted over a conveyor belt to remove large pieces of tramp iron such as rebar, nuts, bolts and other steel contamination that represent a hazard to downstream handling, loading and milling operations. They also remove sharp metal rods, also known as pokers that damage or tear conveyor belts, typically at transfer points.

Selecting and maintaining the right magnet for the job is key to help ensure long-term satisfaction.

Selecting and Positioning SE Magnets

SE magnets can be tailored for a number of applications, from static plants to bulk terminal loading/loadout facilities, ship loaders and even mobile equipment.

Key factors to keep in mind when selecting a magnet should be the burden depth, belt width, suspension height, position and tramp iron size and shape. Other factors are belt speed and incline, material density and maximum lump size.

SE magnets easily capture large pieces of tramp metal such as fencing wire, discarded machinery elements, or pipe fittings, and can be designed for smaller tramp like an M24 nut or bagging needles. The larger the mass, the easier to pick up even through a deep burden layer.

The required magnet strength increases as the belt width and burden depth increases. For example, a 1066-millimetre square SE magnet suspended at 330 millimetres can pull tramp iron through 280 millimetres of burden. A wider belt with an increased magnet height will require a bigger magnet to pull tramp through deeper burden depths, with magnet manufacturers such as Eriez Magnetics able to provide SE magnets for belt widths up to 2440 millimetres.

Standard vs. Custom Components

SE magnets consist of several standard components necessary to provide the magnetic force required to remove steel contaminants. These include the coil, core, back bar and steel enclosure.  Collectively, they comprise the magnetic circuit designed for the duty.

Fully immersing a coil in cooling oil helps to control heat and moisture – the greatest enemies of electromagnets – by keeping the coil relatively cool, maximising the magnet’s strength. Eriez is one of the only manufacturers to incorporate an expansion tank to ensure the coils are always completely submerged. 

Applications for Hazardous Areas

For hazardous applications, Eriez can supply SE oil cooled magnets to Zone 22 specification.

Some SE magnets are air-cooled which are most often used in hazardous areas. For these environments, permanent suspended magnets can be used where the strength and deep reach of an electromagnet is not required. 

Manual Clean vs. Self-Clean

Manual clean SE magnets work well on low frequency tramp occurrences. The magnet is moved away from the belt and the power is shut down to release the accumulated tramp into a skip.

A higher incidence of tramp typically requires a self-cleaning option to continually operate and propel accumulated tramp from the magnet face. Self-cleaners don’t require manual intervention.