Meeting Retailers’ Metal Detection Testing Requirements

By Rob Stevens, Market Manager, Mettler-Toledo Safeline Metal Detection

Retailers are increasingly including the requirement that food suppliers be able to prove regular testing of metal detection equipment as part of their codes of practice. Here we consider the tests that food manufacturers must undertake to comply.

For food companies operating metal detection systems for product inspection, it is imperative to understand both the capabilities of their equipment, and how these fit in with their retail customers’ requirements. Testing is a critical part of both aspects. Retailers are increasingly specifying the need for suppliers to undertake stringent testing of metal detectors and specifying that they have the data to prove it.

Frequent and appropriate testing of a metal detection system verifies that the system and its associated components, such as reject systems, beacons and fail-safes, continue to perform to the necessary standard. It is proof that best practice is being used.

On tunnel-type metal detectors there are three main tests, plus a fourth type of test that some retailers may also mandate. Each test should be carried out using ferrous, non-ferrous and stainless-steel test packs, inserted in that same order.

In the first of these, the Standard Test, metal detector operators insert the three test packs in sequence into the middle of normal operation of the system, with random numbers of clean packs between them, but with correct spacing maintained between packs (both clean and test). In a successful test, only the test packs should be rejected.

Sometimes, retailers will require that the reject mechanism of the detection system can cope with multiple contaminated products in succession. In this scenario, the Consecutive Test becomes appropriate. The operator introduces the test packs in the correct sequence one after the other, with normal pack spacing and at normal production speed, but without clean packs in between. If the test is successful, the metal detector will reject all three test packs.

The third test is an enhanced version of the Consecutive Test and is preferred by some retailers. The Memory Test introduces a clean pack between the test packs, which are again inserted in the ferrous/non-ferrous/stainless steel sequence. All packs should be correctly spaced. If successful, the test will see the three test packs rejected, and the two clean packs in between passed as good products.

Where companies are using metal detection equipment with a photogate side reject device, such as a pusher or air blast, a fourth type of test might be requested. This test checks that the reject timers on the systems are correctly set up. If they are not set up correctly, then contaminated packs might be missed by the reject system. Known as the “Large Metal Test”, this test requires the operator to place a large metal sample (often a 20-millimetre diameter ferrous ball) into the test pack. If the photogate timer is correctly set up, the reject mechanism will successfully divert the test pack into the reject bin. If it is not correctly set up, the mechanism may act too early or too late, and reject a good pack instead.

To ensure consistency, with each of the tests the ferrous test piece should be positioned at the front of the ferrous test pack, the non-ferrous test piece in the middle of its pack, and the stainless-steel test piece at the rear of its pack. The test pieces should also pass through the geometric centre of the detector’s aperture.

Codes of practice

Food manufacturers should get used to an increased focus on their commitment to these metal detector tests being enshrined in retailers’ codes of practice. Alongside the food safety imperatives, retailers are also embracing the move towards digital supply chain data that brings transparency and clarity to a food product’s origin and the processes it has been through on its journey to the supermarket.

Testing data is an important part of this desire for transparency, proving that best practice has been observed. It is part of the bigger picture that shows retailers are meeting the regulations and expectations imposed on them from government, industry and consumers.

Food manufacturers face a burden of proof, but they can benefit by retaining valued business and safeguarding their own brand reputation. They must keep records of their testing regime for product inspection equipment – not only for retailers but for auditors too. This is where the increasing sophistication of metal detection and other product inspection systems comes to the fore. The use of digital metal detector systems alongside ProdX™ data management software by Mettler-Toledo means that users can benefit from automatic prompting of compliant testing within prescribed intervals, electronic storage of test results, and smart optimisation of production and line operation.

Automation of many testing procedures for metal detection systems is therefore making the burden of proof much easier to bear for food manufacturers, in turn making compliance with retailer codes of practice simpler to maintain.

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About the Author:

Rob Stevens is the Market Manager for Mettler-Toledo Safeline Metal Detection, supporting a number of territories with the sales and service of metal detectors. Rob has a degree in Manufacturing Engineering and many years’ experience in working with various engineering companies including Siemens, Rolls-Royce and others around the world. Rob has worked in the food industry internationally, providing solutions to some of the world’s biggest food producers.