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Electromagnets vs. Permanent Magnets: Application Pros & Cons in Overhead Magnetic Separators

Overhead Magnetic Separators

For many conveyed material applications ferrous metal contaminants can be problematic. Whether it’s the damage they can cause to your processing equipment or a reduction in the purity of your product stream, they must be removed. One of the most effective ways to do this is with an overhead magnetic separator

Overhead magnetic separators, when properly positioned over the conveyor belt or head pulley, draw the ferrous impurities out of your product. Magnetic separators can use either electromagnets or permanent magnets in their construction. Depending on the application, each type has its own benefits and drawbacks.

Types of Magnets use in Magnetic Separators

Permanent Magnets

Permanent magnets are made from materials that are magnetically charged to create their own persistent magnetic field. Once these materials are charged they will always have a magnetic field and display attractive behavior. They only lose their magnetic field if they are exposed to a demagnetizing field, extreme heat, or physical damage caused by breakage or corrosion.

Industrial permanent magnets are often constructed of:

  • Ceramic or “Ferrite” materials: a mixture of iron oxide and strontium carbonate
  • Alnico: a combination of aluminum, nickel and cobalt
  • Rare earths: including samarium cobalt and neodymium.

While rare earth magnets are generally stronger than ceramic or Alnico varieties, they can also be more susceptible to corrosion. Neodymium is particularly susceptible and may not be suitable for some magnetic separation applications.

Permanent Ceramic Block Magnets
Permanent Ceramic/Ferrite Magnetic Material

Electromagnets

An electromagnet is made of a coil of conductive wire or strap that is wound around an iron or steel core. When an electrical charge is passed through this coil, it creates a magnetic field that flows through the center of the core along its longitudinal axis and circles back around the outside of the coil creating a toroidal shaped field (See image below).

Magnetic Field Produced by Electromagnet

As long as the electrical current is passing through the coil of the electromagnet, it will behave like a magnet. When the electricity stops flowing, the coil stops producing the magnetic field and any material bound to the magnet will be released.

Permanent Magnets vs. Electromagnets in Magnetic Separation Applications

Benefits of Permanent Magnets

One of the main benefits of using permanent magnets in a magnetic separator is that they always produce a magnetic field and don’t require any outside energy to produce it. Permanent magnets also require less space than electromagnets due to the lack of a coil structure or cooling oil. This smaller size makes them ideal for applications where space is limited like in portable plants.

Permanent Magnet Magnetic Separator
Permanent Overhead Magnetic Separator on a Portable Plant

Drawbacks of Permanent Magnets

While the permanence of the magnetic field is a benefit, in some magnetic separation applications it can also be a detriment because ferrous materials must be removed either manually or by use of a self-cleaning belt or other removal mechanism.

Magnetic Field of Electromagnet vs Permanent Magnet

Benefits of Electromagnets

Electromagnets have greater control over the magnetic field.  By simply cutting the power ferrous material will be released giving an electromagnet an advantage over the use of a permanent magnet in some metal separation applications. The deep toroidal shape of the magnetic field produced by an electromagnet accommodates the burden depth and lump size of material conveyed in troughed belts well. This can make it the magnet of choice for those applications.

Electromagnet Magnetic Separator
Overhead Electromagnetic Separator with Durabelt

Drawbacks of Electromagnets

The main drawback of electromagnets is that they require electricity to operate which is an added expense. This also necessitates running an electrical supply up to the magnets location which may not be possible in some applications. Another potential drawback of using an electromagnet in your magnetic separator is the of the shape of the magnetic field it produces. In some metal separation applications, where sharp tramp metal is common, the toroidal shape of the field holds the ferrous material vertically against the magnet’s body or self-cleaning belt. This may require the use of a protective mechanism like the Dings “Durabelt” to defend the underlying rubber belt.

Stationary vs. Self-Cleaning Magnetic Separators

Once the type of magnet has been determined to fit the application, the next question is whether a stationary or self-cleaning magnetic separator is a better option. If tramp metal is prevalent in the process, a self-cleaning model might be best. A self-cleaning magnet automatically discharges the ferrous contaminants saving time and labor costs. If tramp metal is rare in the process but intolerable, a stationary magnet can be an optimal choice. Without having to accommodate for the sag of a self-cleaning belt in the suspension height, a smaller more economical magnetic separator may be possible.

Which Magnet Separator is Best for Your Process? Dings Can Help.

Dings Company Magnetic Group engineering and sales staff work together from our Milwaukee, WI factory to provide outstanding customer service from experts in magnetic separation. We listen to our customers to gain an understanding of their needs and apply our experience in their trade to provide magnetic separation equipment that is sized and positioned for the best possible performance in their specific application. Contact Us at magsales@dingsco.com or call us at (414)672-7830.