Avoid Recalls with Magnetic Separation and Advanced Metal Detection Technology

Matching a magnetic separator with a metal detector can be a processor’s best defense against metal contamination

February 22, 2022

9 Min Read
Image courtesy of Eriez

Eric Confer, market manager for light industries, Eriez

While productivity is the end goal for any company involved in the food processing chain, there are considerable challenges to meet customers’ demands for product purity. Regulations coming from the FDA, the USDA, and a food manufacturer’s own hazard analysis and critical control point (HACCP) program are especially stringent regarding any type of metal contamination.

Product purity—ensuring your product is free of any metal contamination—is achieved by incorporating magnetic separators and metal detectors into the food manufacturing process. Matching a magnetic separator with a metal detector can be a processor’s best defense against any metal contamination and, therefore, product recalls.

Why install both? No magnetic separator is ever completely effective alone in removing metal contamination. Removing ferrous contamination first with a magnet means the metal detector will reject less frequently, reducing valuable product losses. The magnetic separator and metal detector working in combination can provide as close to a perfect product yield as possible.

Installing magnetic separators and metal detectors can also help avoid both material contamination and equipment damage in food processing. Magnetic separators come in a variety of configurations and divert ferrous materials, such as fines, shavings, abraded machine parts, screws, washers, and other pieces from the material process stream.


Metal detectors sense for and detect metal contaminants entering a specific field—a pipe, conveyor, or material chute—and then activate a rejection mechanism to remove the intruding metallic particle. The most sensitive metal detectors can detect ferrous and nonferrous metals down to submillimeter sizes.

Eliminating Contamination Early Stops Downtime

Metal contamination comes from a variety of sources and at various locations in the process. Any type of fine metal can come into a process with raw materials or find a way into ingredients because of processing equipment component wear or failure.

Objects from transportation vessels like truck beds, rail cars, barges, or ship holds may be involved. Or the contamination could originate in a loading station, silo, refinery, or from within the plant itself. For example, dry ingredients that are free-falling through a carbon steel or stainless steel chute can pick up contamination simply by scraping against the chute.

Then there is the human factor. Inevitably, coins, pens, bottle caps, and processing tools can fall into a material stream. By removing contamination early in the food production stage, the right magnetic separator installed prior to a metal detector can help prevent damage to grinders, ovens, screeners, and other vital equipment.

There are several types of magnetic separators and metal detectors that work well together in manufacturing. This dual approach is especially effective in eliminating metal from whole bulk foods such as almonds, coffee and cocoa beans, and raisins, as well as from more granular bulk items like sugar, flour crushed chili peppers, and various spices.

The magnet removes the ferrous contamination while the metal detector focuses on ferrous metals, as well as nonferrous metals such as aluminum, copper brass, and stainless steel, which are missed by the magnet.

Neither a magnetic separator nor a metal detector is going to catch every ferrous piece in the process stream, but the more metal separators and detectors a food manufacturing plant can afford and accommodate in the space, the better the product purity results.

Also, since the metal detector rejects valuable material with the metal — albeit it a small amount — when the reject mechanism detects a piece of metal, running material through a magnetic separator before the detector will help save material and avoid costly and time-consuming equipment damage down the process line

Magnetic Separators Purify Any Food Type

Magnetic separators are highly effective in applications where the goal is to extract ferrous and certain stainless steel before the food product is passed through metal detectors. The magnetic separation industry is constantly evolving to meet customer demands. Manufacturers work to improve their products by applying state-of-the-art material sciences, engineering developments, and manufacturing processes. Advancements in magnetic separators are made on a regular basis.

Magnetic separators perform just as their name implies—they remove ferrous materials including fines, shavings, machining pins, metallic flakes, screws, washers, and other contaminants from dry or liquid processing streams. Alnico and ceramic (Ferrite) were some of the first materials used in magnetic separators. Today, processors can choose magnets made from alloys of rare earth (RE) elements, which are substantially stronger than alnico or ceramic.

The RE magnet circuit is now incorporated into tubes, grates, plates, and liquid line traps. Newer models provide greater holding force and improved separation efficiency. This increased power has a direct and positive impact on product purity and plant productivity. These advanced magnets incorporate a balance between high-gauss and high-pull force to influence tramp metal trajectory and hold onto particulates, even during a wash-off process.

Assessing the material being processed is a key step in selecting the proper magnetic separator. Product generally falls into three distinct categories: dry, moist, or liquid. Within each of these groups a wide range of product variation exists. For example, dry products range from powder flowing down a chute to bulk food ingredients moving along a high-speed conveyor. These vastly dissimilar processes require different separation equipment.


Dry Free-Flowing, Granular-Type Products

If the material is small and free-flowing, a grate magnet provides the best opportunity for the ferrous contamination to contact a magnet directly. Grates can be cleaned best for vertical product flows, while plate magnets will work well if the material is cascading down a chute. These cleaning methods require that the product flow be stopped when removing collected iron from the magnet.


Dry Product with Some Bridging

While grates provide for efficient removal of fine metallic contamination, they do not work if the material cannot cascade between the magnetic tubes. Plate magnets do not restrict the flow of material and will not contribute to the bridging (building up of material) problem if installed beneath a sloped chute. Magnetic humps are available for less than free-flowing products if the material will cascade down a sloped chute.

Moist, Starchy or Lumpy Products

These products do not flow through grate assemblies because of bridging, nor chutes because of a high angle of repose. The best options include a deep reach separator. The deep reach separator’s inherent design allows materials to flow through the unit without bridging.


Liquid or Slurry Products

Products in a liquid or slurry state require the use of a magnetic trap. Traps are available in grate or plate type configurations. Many traps are built similarly to grates in that tube magnets are arranged perpendicular to the flow inside the body of a casting to “trap” any ferrous materials passing through. A U-trap employs a flat plate magnet in a shallow body to minimize damage to the product flowing past. U-traps are ideal for chunky-flow applications.

Metal Detectors Enhance Food Safety

Once dry material passes through the magnets, the next stop should be for it to pass through a metal detector to “reject” any magnetic and nonmagnetic metal contamination. Metal detectors are available in washdown or non-washdown designs, depending upon the hygienic nature of a food processing operation and sanity conditions.

Today’s metal detection products combine a precision mechanical design with state-of-the-art electronics, multiple-frequency range, vibration immunity, and complex algorithms to detect the smallest metals in difficult products. Industrial metal detectors are also designed for harsh wash-down environments.

In a survey, field representatives and food processors determined what they sought in terms of today’s metal detection systems. Here is a brief report:

* Customers seek metal detection systems for demanding applications. They must work in extremely low and high-temperatures and be able to withstand severe high-pressure washdown/environments.

* In a world where contamination results in recalls, processors stress the importance for monitoring, recordkeeping, and sophisticated electronics.

* Food processors want to detect the smallest contaminant possible, while minimizing the number of false rejects.

New metal detection systems can find smaller metal contaminants than previous metal detectors, even in difficult applications. This is due to metal detector technology that has advanced throughout the years. For example, metal detectors now ship with factory presets for various materials based on actual testing and the provided application date.

A tunnel-style metal detector, for example, can be strategically placed during the processing stage when bulk food material is transported on a conveyor belt and before final packaging. These conveyor-system metal detectors are available in various belt widths and aperture heights and can be calibrated for different food material sensitivities.

With an enhanced metal detection system’s software and graphical interface, customers can detect contaminants at levels never possible. With typical metal detection technology, these contaminants went undetected. Be certain to evaluate the software when you compare metal detectors before making a final decision.

Remote Monitoring and Record Keeping are Critical

Government guidelines drive companies to create policies, procedures, and protocols to ensure food safety. New metal detector systems provide user and reject log monitoring along with remote notifications to processors when a problem exists. Both are critical when it comes to safety and existing food safety regulations.

Today, it is critical to have records as confirmation and regular reporting. Even 24/7 monitoring from remote locations is possible. It is vital to monitor product purity from the time the product enters the plant until the time it leaves the shipping department. This continual data logging is imperative to accommodate corrective actions and auditing.

Investigative Food Safety Training and Services

Magnetic separation and metal detection equipment manufacturers can help food processors with their toughest metal contamination challenges. A number of manufacturers—like Eriez®—are on the front line when serious metal fine problems appear.  As part of the purchase, customers not only receive high-performance magnetic separators, and metal detectors, but they also have access to training.

Training takes several forms, including in-plant training, webinars, and mobile training units. In increased cases, manufacturers provide tutorial videos, case studies, product literature, installation and operation manuals (IOM), and start-up installation support.


There are many reasons why new high-powered rare earth magnetic separators, metal detectors, and smart manufacturing techniques have raised the bar when it comes to product purity and equipment protection. Each day, diligent food processing companies avoid recalls and damaged reputations. Companies must look at technology to be certain they are achieving the highest product purity possible.

Proper support and training enhance value beyond the price of the purchased equipment for years to come. Look for manufacturers who have developed a highly skilled worldwide representative network that is ready to meet any processing and production challenges. Reduce the chance for tramp metal contamination, improve product purity, and educate employees. Following these recommendations will help processors avoid product recalls, damaged equipment, and lost productivity.

Eric Confer is Eriez market manager for light industries. In this role, he is responsible for the strategic growth of products sold in the food, pharmaceutical, chemical, plastics, wood, glass, rubber, and textile markets. He can be reached at [email protected]. For more information on Eriez, visit www.eriez.com.


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