The Ticket To Quality And Safety


Optimising your metal detection system

Siddharth Kachroo, Business Manager – Product Inspection & Global Key Accounts 

When dealing with products intended for human consumption, like foods and pharmaceuticals, every care must be taken to ensure that they meet the highest safety standards possible. It is simply not an area where brands can afford to take any risks, or gamble with their reputations. 

Due to their impact on consumer health, harm to brand reputation and the financial implications of legal proceedings, even minor quality shortcomings in the production process can be hugely damaging, perhaps irreversibly so for consumer brands. Product recalls are a particularly embarrassing and costly outcome for a producer to endure. The detection of hazardous foreign objects, such as ferrous metals, non-ferrous metals and stainless steels, is hence an area of massive importance.

The latest food and pharmaceutical industry trends show that consumers, whilst attracted by low prices in uncertain financial times, are nonetheless increasingly drawn to product safety and quality re-assurance .  It is vital that brands find a cost-effective way to meet these contemporary demands and advanced metal detection systems provide a solution.

A necessary process

“Every company needs to perform a hazard analysis for every product it produces to assess the risk of metal contamination in their products. If the hazard analysis shows there is a risk of metal contamination, then, a metal detector will be required.” British Retail Consortium (BRC) - Global Standard Guidelines 

An optimised metal detection programme is not a matter of choice for food and pharmaceutical producers – it is a matter of legal necessity.

To identify and remove contaminated products from the production line, metal detection solutions use either “balanced-coil” or “ferrous-in-foil” search heads.  Balanced coil heads can detect all types of metal contaminants, including ferrous, non-ferrous and stainless steels, in fresh and frozen foods, while ferrous-in-foil heads are used to detect ferrous metals and magnetic stainless steels within fresh or frozen products packed in aluminium foil wrapping. Balanced coil systems are by far the most common metal detectors in use. Systems of this type recognise any trace of metal through a three-coil arrangement that generates a high-frequency field, the voltage of which is disturbed by the presence of any metals in any material passing through it. Products can be inspected in the bulk processing phase or in their finished form, although a combination of the two is most effective. 

Producers faced with choosing a metal detection system must sort through numerous parameters that influence which system is ideal to handle the varied potential sources of contamination, so partnering with an experienced supplier is important to guarantee food safety. They must choose a supplier that can tailor solutions to their specific product and application needs, and provide the highest quality equipment and assistance without the burden of unnecessary cost.

Fitting the bill

The key to an effective metal detection programme is rooted in optimisation around certain key areas: product type, packaging used and the particular working environment. The array of available system options means that virtually any type of food, in any unusual shape or size, or any type of specialist package, can be inspected with equal rigour.  A top-level metal detection supplier will take all of these into account, working with the producer at all stages so that their requirements are fulfilled.

The product being inspected will govern the search head design and aperture which is the opening through which the product passes. Detectors with a “balanced coil” search head can inspect unwrapped or wrapped fresh or frozen products, even products wrapped in metallised film. Detectors utilising the latest multi- simultaneous frequency technology to push metal detector performance to another level. This technology incorporates a product signal suppression technique to effectively cancel out the product signal from difficult to inspect products. Cancelling these product signals or the effect of the package makes it easier to detect metal contaminants up to 50% smaller than previously possible.

For meeting local and global compliance needs, the processed food manufacturers are implementing data collection software which maximizes rigorous quality regimes and optimizes their production. It significantly reduces complexity and sources of error caused by multiple operating systems and proprietary machine software.

The choice of the most appropriate automatic rejection system to remove contaminated items also depends on the product and application and several options are available. A pneumatic air blast is ideal for light, single-file, discrete products running on a narrow belt, while a punch/pusher design suits light- to medium-weight discrete packs that are spaced and oriented on a narrow belt. A sweep or diverted arm is suitable for light- to medium-weight, discrete, random non-oriented products running on a narrow belt, typically up to 350mm wide. An end flap/dump suits random, small discrete items or loose bulk items (dry or sticky) running on a wide flat or dished inclined conveyor belt, while a retracting belt is reliable for most applications when more than one product passes in-line across the width of the conveyor. Lastly, for bulk loose, dry or sticky products, or multiple random items, a reverse belt is ideal.

During the manufacturing process, products come under threat of contamination from numerous sources, from the processing of raw materials through to in-house filling and packaging. For instance, mince meat products are at risk of metal contamination from metal tags in the raw material stage, from personal effects such as jewellery and buttons in handling, and metal fragments from in-house milling machines. An appropriate metal detection solution must be devised to take account of these factors – finding the right balance between in-process and finished product inspection.

The manufacturing environment is no less important in dictating the specific detection solution required. In some plants, the slightest temperature variation or vibrations from motors and pulleys can induce false rejection of a perfectly safe product when inferior metal detectors are used. Microscopic movements of the coils relative to each other as small as one micron can cause a signal sufficient to result in a false rejection. One way to negate this problem is by “potting” the detector case - filling it with an appropriate material, the weight of which prevents relative movement of the coils. Similarly, temperature changes, build-up of product in the aperture, ageing of electric components and slow changes in the mechanical structure will also contribute to an out-of-balance voltage. This can be eliminated by electronic techniques such as Automatic Balance Control or quartz crystal control, which enable the detector to permanently maintain this sensitivity without operator attention and without the generation of false rejects. 

One feature that all metal detection systems must observe is a metal free zone (MFZ) in the area immediately adjacent to the detector head. The MFZ is necessary to negate the magnetic field leaking from the detector's metal case through the aperture. It is therefore necessary to have an area containing no metals around the opening. Technological expertise and experience are required to find the absolute optimum size for the MFZ.  Also, producers with limited space are now able to install a compact unit utilising “zero metal free zone” technology, where the MFZ is much smaller.

To ensure that a reject device is operating properly, that contaminated packs are accurately rejected and the metal detection system is operating effectively, additional devices can be included. These customized features may include a container or rejected product bin to collect contaminated product, failsafe systems and alarms to indicate the occurrence of faults in the detector or rejection device or reject confirmation systems to confirm that the correct product has been rejected from the production line. Producers also have the option of adding further features such as high level warning beacons or audible alarms that can signal when a problem occurs. These additional features allow food producers wide scope in customizing their setup – taking account of product type and, crucially, available budget. 

Clearly, manufacturers must consider every last detail in order to optimise the performance of their metal detection programme. They must be able to rely on experienced, reliable and flexible machinery suppliers to ensure all specific criteria are met – whether dealing with fresh or frozen, wrapped or unwrapped products.

Keeping standards high

Technological innovation and efficiency optimisation are all well and good; but without proof of due diligence and regulatory compliance, they count for very little. Plant inspections require that safety standards are met at all stages, and the penalties of any deviation can be severe. Metal detection equipment must have features such as condition monitoring, record keeping and traceability to support compliance.  

When a contaminant is found, current metal detection systems allow highly accurate record keeping and traceability. Metal detection systems allow preventive action to be implemented rather than having a dependence on reactive maintenance and frequent verification testing. The detection process is therefore constantly refined. Similarly, the latest metal detectors are designed with general hygiene in mind, constructed using materials that be easily cleaned and re-assembled without excessive downtime. Sealing standards to prevent water ingress to electronic components and enclosures is also very important, particularly in harsh aggressive environments.

The full package

Perhaps surprisingly, stringent safety standards do not have to come at the expense of line efficiency. The eradication of potential threats posed by stray metal through the introduction of a sophisticated metal detection programme actually pays huge dividends to those companies who seek to put the long-term success of their business ahead of ill-advised corner cutting.

Wise investment provides peace-of-mind, strengthens consumer trust and protects brands from complications arising from failed plant inspections. There is no better method for complying with food safety trends and regulations than through the installation of a reliable, consistent metal detection programme.

Siddharth Kachroo, Business Manager – Product Inspection & Global Key Accounts
Mettler-Toledo India Pvt Ltd
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