Are all Rare Earth Magnetic Separators the Same?

2nd of 10 Magnetic Separator Myths

A client has a metal contamination problem and needs to install the most suitable magnetic separation.  The metal is small and so they believe that a Magnetic Separator with Rare Earth Magnets is what they need as this produces the strongest magnetic field.  So he picks up the phone and orders a Rare Earth Magnetic Separator and his problem is solved.

Or is it?

Bunting Europe at PRE 2015-2520

Unfortunately, the term ‘Rare Earth Magnet’ is pretty unspecific.  It’s the same as ordering a car instead of specifying a specific model like a Ford Mondeo or BMW 5 series.  This blog will help explain.

Rare Earth Magnets are strong permanent magnets made from alloys of rare earth elements such as Neodymium Iron Boron. Developed in the 1970s and ’80s, Rare Earth Magnets are the strongest type of permanent magnets made, producing significantly stronger magnetic fields than other types such as ferrite or alnico magnets.  The magnetic field typically produced by rare-earth magnets can be in excess of 1.4 Tesla, whereas ferrite or ceramic magnets typically exhibit fields of 0.5 to 1 tesla. There are two types of Rare Earth Magnet:

The use of the different types of Rare Earth Magnets depends on the application and the following is a general guide:

  1. Neodynium Iron Boron (Nd2Fe14B) – Unfortunately, life is never that straight forward and there are two distinct types of Neodymium Magnet:
    • Sintered – These are produced using a high temperature process to produce a strong even and uniform bond of the material. This is the highest grade of Neodynium Iron Boron Rare Earth Magnet, producing surface fields of between 1 and 1.4 Tesla.  Due to the higher specification, these are higher in cost;
    • Bonded – These are weaker in terms of their magnetic properties. The materials are mixed and bonded using a synthetic resin or polymer.  However, due to the manufacturing process the magnetic strength is lower (0.6 to 0.7 Tesla) and they are physically weaker.  Bonded Neodynium Iron Boron is cheaper than sintered versions;
  2. Samarium Cobalt (SmCo5) – All Samarium Cobalt magnets are sintered and the magnetic fields produced range from 0.8 to 1.15 Tesla.  However, these magnets are significantly more expensive than Neodymium Iron Boron, but they are ideal for very high temperature applications.  Whereas standard Neodynium Iron Boron magnets are suitable for applications up to 80° C, Samarium Cobalt and high temperature Neodynmium Iron Boron magnets maintain their magnetic strength at higher temperatures;

In industry, the most common Rare Earth Magnets are Neodynium Iron Boron, but it is worth asking whether the magnets inside the Cartridge or Tube Magnet or Plate Magnet are sintered or bonded.  The vast majority of magnetic separators use the sintered Rare Earth Material as it is physically better and produces a higher magnetic field, but we recommend asking the question to ensure that what is supplied is true value for money and best suited for the application.

Other Magnetic Myths in this series published so far are:

Should you always use the strongest Magnet?

For more information or a site review by our trained sales engineers, please contact us on:

Phone: 01442875081


Via the website

What is an Axial and Radial Magnetic Field?

Explaining Magnetic Separation

Rotary Magnetic Separators, such as the Bunting Drum Magnet and Magnetic Separation Pulley, are designed with a specific type of magnetic field.  The type of magnetic field has to be considered when looking at any application and when deciding which design will achieve a customer’s separation objective.

So what is an Axial or Radial Magnetic Field and why is it so important?

Axial Magnetic Field

Axial Magnetic Field Bunting Magnetics- Figure 1 – Axial Magnetic Field

This is when the magnetic field stretches across the width of the rotary Magnetic Separator.  Magnetically susceptible material entering into the field is attracted to the point of highest magnetic intensity (the pole) but is then dragged through an area of weaker field (between the poles) and onto another pole by the motion of the conveyor or drum.

This type of magnetic field is ideal when there could be a high level of entrapped non-magnetic material captured by the Magnetic Separator.  The motion of moving between the poles results in non-magnetic material being released as the magnetic item ‘tumbles’ in the field.  However, with this type of magnetic field there can be a reduced separation performance.

Radial Magnetic Field

Radial Magnetic Field Bunting MagneticsFigure 2 – Radial Magnetic Field

The Radial Magnetic Field has poles running in the same direction as the rotation of the conveyor or drum and with the flow of the material.  Magnetically susceptible material is attracted to the points of highest magnetic intensity (the poles) and held until it is dragged out of the magnetic field underneath the conveyor or Drum.

This type of magnetic field is ideal when the maximum level of separation is required, but there can be some carryover of non-magnetic material.  The fact that the captured magnetics always remain on the pole of highest magnetic intensity means that they are far more likely to be removed and, therefore, the radial design provides the best level of separation.

These types of Magnetic Fields are used in Magnetic Separators such as Magnetic Drums and Magnetic Pulleys.

For further details on the Bunting range of Metal Separation Equipment, please contact our technical sales team on:


Metal Contaminated Metal Scare

Food Safety Scare with Metal Contaminated Meat in USA

One single metal fragment has resulted in the recall of 30 tonnes of ground beef in Texas, USA, reports Food Safety News.

The cost of that single metal fragment is significant.  Not only are there the direct costs, loss of profits and any damages costs payable to their customers, but there is also the negative impact of bad press on the company’s reputation and image with the potential loss of orders and customers.  All this due to the presence of one single item of metal.

Sadly, reports about metal contaminated food frequently hit the headlines and this latest Food Safety scare follows:

Can Metal Contamination Be Prevented?

Metal is both removed and detected during the food manufacturing process using a combination of Magnetic Separators and Metal Detectors.  Some food manufacturers also use Infra-Red and X-Ray to check for any item of foreign body contamination including plastic and metal.

Plate Magnets Bunting Magnetics-9797

However, the vast majority of food processing plants use Magnetic Separator and Metal Detectors.  Unfortunately, having the right equipment does not always mean that the best solution is in place.  The location and the maintenance of the Magnetic Separator and Metal Detector are vital to maintain optimum performance.  Annual reviews for preventing metal contamination are positive ways of ensuring that equipment is checked, assessing the functionality of the Magnetic Separator and Metal Detector as well as the location.  Questions can be asked.  Has there been a change in the process? How frequently are the Magnetic Separators cleaned?  Has the sensitivity of any of the Metal Detectors being changed?

To help in assessing the best way to prevent metal contamination, we have produced a series of installation guides, assessing typical plant layouts for specific food types and identifying both the location and the type of Magnetic Separator and Metal Detector.  These include:

Additional installation guides for other foods will be released in the coming months.

Metal contamination can be prevented and for further information or a free on site review, please contact the Bunting team on:

Phone: +44 (0) 1442 875081



Misconception About the Rotor Strength of Eddy Current Separator

5th of 5 Eddy Current Separator Misconceptions Focusing on Rotor Strength

This is the 5th and final installment in a short series of blogs discussing misconceptions about Eddy Current Separation.  are used extensively throughout the recycling industry to separate non-ferrous metal (e.g. aluminium beverage cans, shredded aluminium and copper etc) from non-metallic materials.

How Important is Magnetic Rotor Strength?

Stronger is better, or is it?  Also, what does ‘stronger’ actually mean?

The principle of eddy current separation is based around a rotating magnetic field with changing polarity.  In accordance with Faraday’s Law of induction, electric currents are induced with conductors entering the rotating field (eg non-ferrous metals such as aluminium).  By Lenz’s Law, the induced eddy currents create a magnetic field that opposes the magnetic field that created it, thus resulting in the conductor being repelled away from the magnetic source.

Therefore, if the rotating magnetic field is stronger, then the repulsive effect must be greater.  Unfortunately, in operation, separation is not as simple as that.

In theory, stronger magnetic rotors producing better levels of separation could be true, but in practice the manufacturing and design process means that there are limits to any magnetic rotor.  All Eddy Current Magnetic Rotors are constructed from permanent magnets attached to a carrier pulley.  The size of the permanent magnet (both in length around the rotor and thickness) dictates the throw of magnetic field.  Longer and thicker magnets produce deeper magnetic fields than shorter and thinner magnets.

Irrespective of whether the magnet is long or short, the maximum magnetic intensity is on the pole (surface) of the magnet.  Therefore, in practice, there has already been a loss of magnetic intensity by the time the field reaches the surface of the feed conveyor belt as it has to pass through:

  • A non-metallic shell;
  • An air gap between the shell and the magnetic rotor;
  • The belt;

If very short magnets are used a very shallow magnetic field is produced and this may only just reach the surface of the belt.  In contrast, longer magnets throw a deeper magnetic field.

This means that you could have a magnetic rotor with short exceptionally strong Rare Earth Magnets that produce a weaker magnetic field at the point of separation (ie on the surface of the conveyor belt) than one constructed from longer standard strength Ferrite Magnets.  This also makes it very difficult to classify any magnetic rotor as being ‘strong’ or ‘weak’ as this definition is totally dependent on where the measurement to support that decription is taken.  For example:

Rotor design On the surface of the belt 10mm above the surface of the belt
Rotor 1 Short, exceptionally strong Rare Earth Magnets with a shallow field Strongest Weakest
Rotor 2 Long, standard strength Ferrite Magnets with a deep field Weakest Strongest

The key to magnetic rotor selection need to be based on what needs to be separated.  If the non-ferrous particle is large (eg an aluminium can) and you want the magnetic field projected into the centre of that particle for maximum separation effect, then a deep magnetic field with longer magnets is required.  For small non-ferrous metal particles (eg as found in plastics) then a shallow magnetic field with shorter magnets will produce the best separation.

Understanding these principles is vitally important when considering which design and type of Eddy Current Separators to purchase.  Simply being advised that the actual strength of the magnetic field is the ‘strongest on the market’ will not determine if that Eddy Current Separator design is right for a particular application.

Other blogs in this series on Misconceptions about Eddy Current Separation include:

1 of 5 Rotor Speed

2 of 5 Belt Speed

3 of 5 Belt Length

4 of 5 Ferrous Metal Removal

For further details on the Bunting range of Eddy Current Separators, Magnetic Separators and Metal Detectors please contact Carlton Hicks ( or our technical sales team on:

Bunting Metal Separation System Recapture Plastics-4

Metal Found in Chocolate Eclairs

Sainsbury and Morrisons Remove Metal Contaminated Products from Shop Shelves

The announcement of a Food Safety issue at any major supermarket is always cause for concern.  The latest ‘metal in food’ safety announcement relates to chilled desert products, such as chocolate eclairs and profiteroles, supplied by Bakkavor to Sainsbury and Morrisons in the UK.

During the food manufacturing, it is widely accepted that metal will be introduced into the process.  The metal can arise from processing equipment (eg a broken screen, damaged pump) or from accidental introduction.  The metal can be ferrous, stainless steel or non-ferrous.

Ensuring that the metal is removed during the process or detected and removed as part of the final product is achieved by installing a series of Magnetic Separators and Metal Detectors.  Magnetic Separators are able to magnetically attract and hold ferrous metal and abraded stainless steel.  Stainless steel becomes weakly magnetic when work hardened (eg from wear) and can be attracted and held by strong Rare Earth Magnets in the form of Tube Magnets, Grate Magnets and Plate Magnets.

Tube Cartridge Magnets Bunting Magnetics-5

Commonly, Magnetic Separators are installed as the food is being processed and Metal Detectors are used towards the end of the process, often just before and after packing the food product.

As processes and products change, a regular review of the plant is required to check that the Magnetic Separators and Metal Detectors are located in the optimum position to capture any problematic metal.  This is often Magnetic Separation Audit with the findings recorded as part of the Quality and Safety Management procedure.

Other news articles discussing Metal Contamination in food include:

For further information on Magnetic Separators and Metal Detectors used to separate and detect metal in foodstuffs, please contact us on:

Phone: +44 (0) 1442 875081


Should You Always Use the Strongest Magnet?

 1st of 10 Magnetic Separator Myths

Strongest is always best, or is it?  Commonly, companies will call and request a quote for a Magnetic Separator with the strongest magnet.  But is that actually what they need?

Magnetic Pull Test Kit Bunting Magnetics

The strongest magnetic fields are produced by specialist Superconducting Magnets and are used in industrial and medical applications.  However, their use in industry is very specific due to the high capital cost and you would not find a Superconducting Magnet installed in a food processing line removing nuts and bolt.  So, immediately the term ‘strongest’ has lost some relevance.

Also, the wide range and varied designs of Magnetic Separator means that comparing one with another on the basis of magnetic strength alone is impossible.  If they are the same type of magnetic separator (e.g. a Cartridge or Tube Magnet), then you have a chance, but even then strongest magnet is not necessarily the best solution for the specific metal separation issue.

Before quoting for any magnetic separator, it is vitally important for us to understand the application and there are a number of key questions that we ask.  They include:

  1. What is the metal that needs be magnetically separated? How big?  How magnetic?
  2. From what is the metal to be magnetically separated?
  3. Why does the metal need to be removed? Is it to protect some down-line processing equipment?  Is it to recover the metal?
  4. How is the material being transported? Is it on a conveyor or as a slurry in a pipeline?
  5. What is the budget?

Armed with this information, the application can then be assessed by experienced engineers and a suitable design and strength of magnetic separation will be proposed.

However, do not be surprised if it isn’t the strongest magnet.

For more information or a site review by our trained sales engineers, please contact us on:

Call us on 01442875081


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Misconception of Ferrous Metal Removal before an Eddy Current Separator

4th of 5 Misconceptions About Eddy Current Separation

This is the 4th in a short series of blogs discussing misconceptions about Eddy Current Separation.  Eddy Current Separators are used extensively throughout the recycling industry to separate non-ferrous metal (e.g. aluminium beverage cans, shredded aluminium and copper etc) from non-metallic materials.

Bunting Eddy Current Separator-5

All Ferrous Metal Need to be Removed

Despite the Eddy Current Separator being a separation system based on magnetic principles, there is often a question about whether it should be used to also remove ferrous metals.

In its simplest form, the Eddy Current Separator is a conveyor with a magnetic rotor acting as a magnetic head pulley.  Due to the laws of physics, the Magnetic Rotor will attract ferrous metal and so could be used to separate magnetically susceptible materials.  However, there are some limitations:

  1. With Eddy Current Separators that have Concentric Magnetic Rotors (ie the magnetic rotor spins uniformly within an outer non-magnetic shell), it can be difficult to discharge magnetic material from the belt. Due to the high speed rotating magnetic field, magnetic material that has not been discharged and remains vibrating at the bottom of the rotor can get hot and, when the conveyor belt stops, can burn through the plastic of the belt.  This can then damage the shell and the magnetic rotor;
  2. The Eccentric Magnetic Rotor design is more forgiving as the rotor sits in a corner quadrant of the non-metallic shell and so magnetic material leaves the magnetic field as it is pulley around by the conveyor. This ferrous metal is discharged underneath and often into the non-metallic fraction;

Successful metal recovery and separation is achieved by focusing on specific materials at key points in the process and this means removing as much ferrous metal prior to the Eddy Current Separator as possible.  This then leaves the Eddy Current to focus on separating non-ferrous metals from non-metallic materials.

Typically ferrous metals are removed and recovered prior to the Eddy Current Separators with:

Other blogs in this series on Misconceptions about Eddy Current Separation include:

For further details on the Bunting range of Eddy Current Separators, Magnetic Separators and Metal Detectors please contact Carlton Hicks ( or our technical sales team on:

Bunting Secures Record Export Order for Magnetic Separators

Bunting Magnetics Europe Ltd has secured their largest single export order from a German processing plant designer and builder.  The record order is to manufacture and supply 63, high-strength, Rare Earth Plate Magnets, which will be installed in a tobacco manufacturing operation in Indonesia.

Bunting Plate Magnets
Plate Magnets designed and manufactured by Bunting Magnetics for use in a tobacco processing plant overseas

The Plate Magnets are used to remove metal from the shredded tobacco.  Metal enters the tobacco process at various points, including at source, with the raw material infeed, and during the slicing and cutting of the leaves.  The Plate Magnets attract and hold the magnetically susceptible particles, including abraded stainless steel.  This prevents damage to delicate processing equipment such as the cutting blades as well as maintaining the quality of the end product.

The recent order in June 2016 was for 63 Rare Earth Plate Magnets and followed an earlier order for 26 placed in February 2016.  Another large Export order for Plate Magnets was secured in 2015.

Two different models of Plate Magnet are being supplied, with 34 having a magnetic face width of 609mm and a 125mm deep magnetic field and 29 with a face width of 508mm projecting a 90mm deep magnetic field.

A Plate Magnet comprises of a stainless steel box or housing into which high strength Rare Earth blocks are positioned.  The type of Rare Earth block and configuration of the blocks within the housing dictate the shape, strength, and depth of the magnetic field.  A deep magnetic field was important in this application.

Head of Sales, Dave Hills, explained the importance of the order:

“Developing export business is vital for our continued growth in the UK.  This is our single largest order for Magnetic Separators on record and is the result of a prolonged focus on developing business overseas.  On this project we worked closely with the German client and had several meetings in Germany to understand their requirements before we proposed the best metal separation solution.  This is a very exciting development for Bunting Magnetics in Europe.”

The Plate Magnets will be manufactured and supplied in batches in specially designed transportation boxes and are due to be despatched between June and August 2016.

For further details on the Bunting range of Magnetic Separators and Metal Detectors please contact our technical sales team on:

Bunting Plate Magnets
Plate Magnets designed and manufactured by Bunting Magnetics for use in a tobacco processing plant overseas