A Guide to Magnetic Separators

Some common questions about magnetic separation

Magnetic separators and metal separators play a vital role in protecting key manufacturing processes from potentially harmful and costly metal particle contamination. A product recall could potentially cost the manufacture huge sums of money, not to mention damage to brand confidence.

magnetic separators used in contaminated flour

What are Magnetic Separators?

A magnetic separator applies basic magnetic principles to remove ferrous based and paramagnetic metals from a range of substances including powders, granules, liquids, pellets or pastes. They are usually installed within the product stream at key HACCP or inspection points.

magnetic separators - product flow

How does Magnetic Separation work?

In summary, the raw material or finished product is fed either by gravity, air, pumped or conveyor belt where it passes through or over a magnetic rod, grid, grate or plate.

The magnetic field captures the ferrous contamination by attracting it to the magnetic tube or plate. The non-magnetic clean product continues through the process.

grid magnet

What types of Magnetic Separator are available?

There are various types of magnetic separator, the choice is dependent on the feed method and the substance being fed. 

They are typically split into 2 groups – primary magnetic separators and secondary magnetic separators.

Primary separators are used to prevent machinery damage and remove larger ‘tramp’ type contamination such as nails, screws, bolts. They are usually installed around bulk intake points or in applications where the bulk materials are flakes or pellets (non-powder).

Various options exist such as magnetic strips, bands or plates which sit over or under conveyors. Or rotating magnetic drums or chutes which fit into gravity free fall processes.

Secondary separators guarantee product purity and quality by removing ultra-fine particle ferrous contamination such as natural process machinery wear.

Usually located in mid or end of process, options include simple magnetic rods, magnetic grids or grates, housed grids, high pressure grids, rotating grids or housed rod assemblies and multi row self-cleaning grids.

magnetic separation used in spice production

What substances do magnetic separators typically protect?   

Magnetic separators are effective in any sector which has risk of ferrous particle ingress. Safety critical processes such as food, pharmaceuticals and chemicals use both primary and secondary separators to protect powders, granulates and liquids. Typical examples being flour, starch, sugar, chocolate, tea and cereal.

In other industries such as recycling and construction materials primary separation may be adequate, typical examples include cement, aggregates, wood chips, plastic or glass recycling.   

Is the magnet type important when it comes to select the right magnetic separators?

Different magnet materials have different properties, so the choice is very important. The latest high intensity magnetic separators use Neodymium (NdFeB) (also known as Rare Earth) magnets. This is the strongest magnet material and is effective in extracting the finest ferrous and paramagnetic particles.

Depending on the intensity required for the application, Neodymium magnets are available in strengths typically between 7,000 and 12,000 Gauss, the higher the Gauss number the stronger the magnetic force. Samarium Cobalt and Ferrite (Ceramic) magnet materials are also available often for applications where the particle size is larger, or the magnetic field needs to be projected further. These materials typically have a weaker magnetic strength (circa 3000 Gauss) but can withstand higher temperatures and exposure to corrosive elements.

These are not recommended for safety critical applications such as food or pharmaceutical. In a magnetic separator the magnet is contained in tube or cover. When specifying the magnetic strength, it is important to check with the manufacturer that the Gauss reading is taken on the outside of the tube or cover as this will be a true measure of the magnets’ effectiveness.

Eclipse Magnetics double row housed grid magnetic separator

Where can magnetic separators be installed?

Magnetic separators are ideal for many different installation points on gravity, free-fall, pneumatic, pumped or conveyor feed processing lines. Either at raw materials intake to check incoming ingredients, mid-production at HACCP points or protecting finished product at the end of the process on bulk discharge.

Typical installation points include gravity-fed chutes, pre and post sifting, bulk tanker discharge, ingredient sieving, pre and post mixers, vacuum or pneumatically lines, grain tips, sack rip and tip stations, above or below transfer conveyors or vibratory feeders.

Are magnetic separators effective with Stainless Steel or Paramagnetic materials?

As most process equipment is made from 304 or 316 stainless steel we are often asked whether the magnets are effective in removing minute process wear fragments which become detached from machinery and equipment.

The answer is yes, in fine particle form i.e. (< 0.1-3mm) 304 and 316 Stainless Steel change properties to become paramagnetic. Exposure to a strong magnetic field induces a magnetic response magnetic in the same direction of the magnetic force being applied. This means that fine 304 and 316 Stainless Steel particles can be extracted by high intensity magnets such as Neodymium.