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Metal Detection: Essential Process Line Protection

Metal detectors are a common sight in today’s processing facilities, and for good reason. Metal detection offers protection. They protect processing equipment from damage caused by metal, they protect the products people consume, and they protect brand image against recalls that can arise from contaminated product.

By Robert Slauson, Assistant Sales Manager at Advanced Detection Systems

Robert Slauson, Assistant Sales Manager at Advanced Detection Systems

Robert Slauson, Assistant Sales Manager at Advanced Detection Systems

Most products, regardless of the industry, are in constant contact with metal machinery throughout the entire production process. Products are cut, shaped, mixed, packaged, and transported using equipment and components constructed primarily of metal.

Modern metal detectors come in many different sizes and configurations depending on the type of product they are inspecting and the methods used to convey the product through the detector. 

Regardless of the detector used in an application the questions of; why do I need a metal detector? how do I determine which detector to use? and how do I use the detector to meet my requirements? should all be considered to ensure your metal detector is being used in the most effective and efficient way possible. 

Why Should I Use Metal Detection? 

The goal of just about every metal detector in operation is the same, to detect metal within a product that shouldn’t have metal in it. The reasons why a company will use a metal detector varies.

In the food industry, metal detectors are a key component in many company’s HACCP (Hazard Analysis and Critical Control Point) Plans which are required to comply with food safety standards from governing bodies like GFSI (Global Food Safety Initiative), SQF (Safe Quality Food), and the BRC (British Retail Consortium). 

Many product retailers have their own food safety standards that require a higher level of contamination prevention and detection before a product can be sold on their shelves. If you want to sell your product on these retailer’s shelves, it will first need to be inspected for foreign contaminants by a metal detector or X-ray system. 

Outside of the food industry, metal detectors are often used to ensure product purity and to defend processing equipment from damage caused by metal contaminants. Depending on the product and process used to create it, a metal detector can be placed at the end of a production line to make sure there are no metal contaminants within the product.

A metal detector may also be placed in front of high-tolerance production equipment, like an injection mould or extruder, to protect them from damage. Metal contaminants pressed in a mould or forced through an extruder can damage those components and create imperfections in every subsequent product produced by that mould or extruder die. 

Metal Detection Pre-Purchase Considerations 

Metal detectors are a very important tool in safeguarding products, people, and equipment from metal contaminants. As with any tool, using the correct one for the job can be the difference between success and failure. 

The first things to look at when considering the purchase of a metal detector are your goals and requirements. Are you getting a metal detector to comply with safety standards? do you need a metal detector to prevent damage to processing equipment? or maybe both? 

The other main facet to metal detection is determining what steps to take if your metal detector does find a contaminant. Detecting the metal is the first step. Removing the contaminated product from the production line, documenting the occurrence, and determining how to prevent it from reoccurring are all subsequent steps that need to be taken into consideration. 

Sensitivity limits also need to be considered when deciding what type of metal detector is best for you. There are a lot of factors that determine the sensitivity of a metal detector but a good general rule of thumb: the larger the detector aperture is, the less sensitive the detector will be. A small detector will be able to find smaller pieces of metal than a large detector could when running the same product. 

The type of product being run through the detector and the environment it is in all factor into the detector’s sensitivity to metal. Most reputable metal detector manufacturers offer product testing services to determine what their detector’s sensitivity to metal within your specific product will be. 

Product testing generally involves sending samples of your products to a metal detector manufacturer who will then put them through metal detectors in their lab and report back to you with the sizes of metal they can detect within your products. 

Because there are so many variables that factor into determining a detector’s sensitivity within a single product, product testing is the only way a metal detector manufacturer can guarantee a specific detection level. 

Metal detection systems are generally configured in three different ways: conveyor mount, pipeline, and gravity drop. A quality metal detector manufacturer will work with you to determine which configuration is best suited for your application.

Each configuration of detector can also be broken down into three main components: the detector head which does the metal detecting; head support structure that supports the detector head and components; and a reject device to remove contaminated product from the production line. Regardless of what configuration is chosen; the functionality of each detector head will be the same, only the way it is constructed for your application changes. 

Max III Conveyor Sweep Arm Metal Detector

Conveyor: Packaged or bulk product is carried through the detector using a conveyor belt. Conveyor mount systems are the most prevalent configuration due to their versatility in working with both packaged and bulk goods. 

The metal detector and conveyor will be sized based on the dimensions of your product and the system can be designed with a multitude of reject devices depending on your needs. Common reject methods for packaged goods are stopping the belt upon detection for manual removal of the product or automatic sweep arms/rams that push the product off the belt without stopping production. 

Bulk goods are commonly rejected using a retracting pulley or flop gate to divert the product into a collection bin without stopping production. A conveyor mount metal detector should generally be sized 2 inches taller and 2 inches wider than your largest product. 

Max III Pipeline Metal Detector

Pipeline: These metal detectors inspect liquids and other viscous products that can be pumped through the detector. Pipeline units can be configured with an automatic reject device (commonly a 3-way ball valve) to divert contaminated product out of the product flow tube and into a reject receptacle without slowing down or stopping production. 

A pipeline detector will be sized based on the required diameter of the product flow tube used to move the product through the detector. Generally, the detector aperture is 1-2” larger in diameter than the product flow tube. One of the major benefits of a pipeline detection system is the ability to inspect large quantities of product using a small aperture. 

For instance, a company producing 10 gallons of chicken noodle soup would have poor detection level results using a large conveyor mount metal detector to inspect their final 10 gallon container of soup. A more appropriate solution would be to use a pipeline detector placed around the product flow tube that is filling their final container. 

That way the metal detector is only inspecting a small amount of product at once –as it flows though the detector­– instead of trying to inspect all 10 gallons at one time. In this situation the pipeline detector would be able to detect far smaller pieces of metal.

The detector itself would also be much less expensive, and if metal was detected, a small portion of the product could be diverted instead of all 10 gallons being wasted due to contamination. 

Max III Gravity Drop Metal Detector

Gravity Drop: Like pipeline metal detectors, gravity drop systems are configured to inspect flowing, bulk products such as powders or granules before they are packaged. Gravity Drop systems consist of the metal detector head, automatic reject valve, and a support stand. Gravity drop detectors are often used at the end of a production line, right before final packaging.

Just as with pipeline systems, large quantities of product can be inspected over a short time period. As opposed to inspecting all the final product at one time, after it is packaged. Some metal detector manufacturers offer ‘slim line’ gravity drop detectors for use in close proximity to form fill and seal machines. 

These slim line detectors are often used to inspect small quantities of product immediately before they are packaged in situations where the final package is made of metal or contains a metallic film that cannot be passed through a metal detector. 

The location of your metal detector on the production line is an important factor in meeting many safety regulations. If the primary goal of the metal detector is to ensure product purity and keep consumers safe, it should be placed near the end of production where there is little to no chance of metal contamination after the product has gone through the metal detector. 

If you are using a metal detector to protect processing equipment or inspect raw ingredients before value is added during processing, the detector should be placed just prior to the equipment it is supposed to protect form metal contaminants. 

Metal Detection Installation & Startup 

Metal Detectors are extremely sensitive instruments that need to be setup and installed properly to avoid difficulties during actual production. Metal Detectors are very susceptible to electrical interference generated by other equipment nearby or connected to the same power source. Most metal detector manufacturers will recommend a dedicated power line be ran to the metal detector to avoid interference or power dips/spikes generated by other equipment in the plant. If a dedicated line cannot be installed an inline power conditioner can be used to help create a clean power source for the detector. 

Once your metal detector has been installed, setting the system up for your product and training your employees on how to properly use the detector is paramount to the success of your inspection program. The functionality of a metal detector can be a difficult concept for many people to fully grasp because you cannot see what the metal detector is doing. 

The detector is creating an electromagnetic field and measuring the level of disturbance in that field as products pass through it, none of which is visible to the human eye. Every metal detector manufacturer has created their own way of adjusting and controlling their metal detectors, so it is important that your employees are trained by an expert on your brand of metal detector. 

That expert should walk you through every facet of your metal detector and make sure you are comfortable adjusting the system parameters. If your metal detector supplier does not offer on-site training, find a different supplier. 

Metal Detection Daily Use & Documentation 

One of the most important aspects of owning and operating a metal detector for the food industry is documentation. Due to the enormous number of factors that go into determining how well a metal detector will detect metal within a specific product, there is no straight-forward pass/fail rule to judge all metal detectors by. Instead, risk assessment documentation is used to demonstrate that your metal detector is being used as effectively as possible for the application. 

Daily Performance Validation is a routinely performed test of the metal detector’s functionality and accuracy done by employees during production. It involves purposely introducing metal contaminants (test pieces) into the product being produced and verifying that the detector is able to reliably detect the test-contaminants within the product. 

Validation tests are usually performed multiple times per day at prescheduled intervals, such as a shift change or product change. If the detector settings have been incorrectly adjusted or the system is not working properly, it will be discovered during the performance validation. Many food safety programs require a yearly Performance Certification visit by a 3rd party to certify that your daily performance validation tests are accurate. 

At its root these tests are no different than the performance validation tests your employees are doing on a daily basis, but they are being conducted by a qualified 3rd party such as the metal detector manufacture. 

Many modern metal detectors are capable of digitally recording and documenting metal detector usage and events. Be sure to speak with your metal detector manufacturer about how these features can be integrated into your production documentation systems. 


Metal Detectors offer protection. They protect your equipment from damage, they protect your product from contamination, and they protect your company image from recalls due to adulterated product. As metal detectors become more advanced the basic guiding principles stay the same. 

Knowing why you should use metal detection, what you need to consider before buying a machine, how to install and use the system, and what aspects of use you need to document will always be pertinent questions to ask. 

Every company’s metal detector needs and requirements will have unique aspects to be addressed, and a quality metal detector manufacturer will help you determine what those aspects are and design a metal detector to meet your needs.

Process Industry Informer

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