Selecting the best magnetic separator for an application can be a challenge. Certain products and applications have their own requirements, and at times the advice you may receive from one magnet supplier can be different to another!

This aim of this blog post is to provide information and advice on choosing the right magnetic separator for food processing applications.

Firstly though, we need to emphasise that 100% metal separation cannot be guaranteed. No magnet supplier can truthfully make claims regarding control of work hardened stainless fragments due to the variation in magnetic susceptibility. It is critical to ensure that the magnet meets relevant design standards for food safety and can meet the demands of each specific duty.

It is also very important to know that just because a magnet is strong, it does not mean it is effective in its purpose. There are several factors which can influence a magnet’s effectiveness and should be taken into consideration when choosing a magnetic separator. These include:

Product stream coverage

A magnet needs to have adequate product stream coverage to be effective in collecting metal fragments from the process. You must ensure that the product flow is covering the effective working area on the magnet. Product that is not covering the high strength pole centres is allowing the contamination to escape the magnet.

Careful consideration is required at the design stage to ensure that minimum product coverage requirements are met without posing an unacceptable risk of restricting the product flow.

Magnet coverage will vary greatly depending on particle size / density / flowrate / speed / direction of flow. If coverage is poor, the contamination will flow past and continue downstream.

Installation

To add to the previous point of product stream coverage, properly installing the magnetic separator is crucial.

The magnet should be installed so that the product is concentrated on the high strength pole centres for maximum separation efficiency.  This is why the magnet configuration for a horizontal line differs from a sloping or vertical orientation magnet.

Modifying a magnet should not be done without consulting a magnet supplier or getting the magnet validated! For example, removing bars from grate magnets to prevent blockage may introduce a new risk that compromises separation. By speaking to a trusted magnet supplier, you will be aware of any risks to product safety such as reduced product stream coverage and can take appropriate measures.

Product contamination levels

Certain products have higher levels of contamination, while others have lower levels. Choosing a magnet that is designed to cope with high levels of fragments is very important. This means ensuring the magnet has an adequate area for safe retention of contaminants out of the impact of the product flow.

Products that typically contain more metal are usually abrasive, such as nuts, cereals, rendered meat and bone meal, and rice, and products that have fewer metal fragments are usually salad mixes and vegetables.

Cleaning

Cleaning magnetic separators plays an important role in their effectiveness. When a magnet becomes overloaded with magnetic fragments, it can become ineffective in collecting any more contaminants. This means that those fragments will continue downstream and remain in the product! Magnets should be cleaned prior to becoming overloaded to reduce the risk of shorting out.

You must ensure that there is no risk of contaminants re-entering the product stream while cleaning takes place. Magnet cleaning must take place away from the opening of the product flow area.   While the magnet is removed, the product stream is vulnerable to re-contamination and a good magnet design should minimize this risk or measures should be put in place to avoid re-contamination.

There can be issues with some quick-clean magnet designs as a final control. Some of these designs allow operators to quickly action the cleaning with one swift movement, however, there is a risk that some contaminants can get caught on seals or moving parts and become dislodged when the magnet is returned. There is also a risk that contaminants can remain hidden and not detected by the operator, which masks the true level of contamination.

The magnet design should allow operators to thoroughly inspect the entire surface of the magnet.   This is why sleeved magnets are unhygienic and not recommended. As per the magnet standard for food safety, sleeved magnets are excluded for use in final magnet applications.

Design

Additionally to the above issue with magnet sleeves, poor magnet designs can be frustrating for operators to deal with and can pose a risk to magnetic fragments remaining in or contaminating the product.

There are many magnet designs suited to many different industries and built for different purposes.

Whether it is machine protection or product purity, it is important to make a well-informed decision and research what you are buying prior to purchase.

For example, when working with sensitive, hygienic product and applications such as dairy powders or pharmaceuticals, having dairy-grade equipment is a must. This means that the equipment has no cracks or grooves where sensitive product can build up, and the magnet housing is smooth and polished.

Magnets that are handled with care can last a very long time. Magnets that are bent, have dints, corrosion, or rust, are not going to keep their strength like well looked-after magnets would. At times, magnets can become a source of contamination and a risk to product security. This is why it is important to have magnets thoroughly inspected annually.

You should look out for signs of galvanic reaction on the surface of the magnet. This could lead to pitting and eventual deterioration. Other deteriorating factors may arise out of moisture ingress internally. This is the leading cause of internal corrosion that leads to swelling, splitting and strength loss.

Ensure that you are always handling magnetic separation equipment with care and are not dropping or banging magnets.

Temperature

The temperature of the product can have a huge impact on separation efficiency and should be considered when selecting magnetic separation equipment. Certain magnets are designed to withstand higher temperatures and should be selected for high-temp product.

Retention

A magnetic separator needs to have the ability to collect and retain metal fragments in the location and product it is installed in. If it is a high-velocity process, then the magnet needs to be designed to perform well in those conditions.

Taking all these aspects into consideration when choosing a magnetic separator is crucial. You can find out if your existing magnets are effective and well-suited to your processing lines by having them validated using traceable, calibrated instruments employed by an accredited technician.

The AMR Magnet Validation reports include a lot more than just recording magnetic strength. Verifying design specification with each magnet validation is important, especially if a magnet has been relocated or modified. Other essential aspects of magnet validations are product stream coverage, retention, location requirements, cleaning, physical condition, installation, and more.

Find out more about magnet validations and the validation process.

Have any questions? Get in touch with our friendly team today.