[AIB Foreign Object Detection] Metal Out, Money In

Metal detection is a proven and reliable technology for product inspection in the food production and processing industry. But are manufacturers getting the best work from their systems? Experience shows that, rather than simply purchasing and installing a metal detector, plants that develop a complete metal detection program receive valuable benefits far beyond the mere removal of metal contamination. Such schemes will maximize product safety, ensure the protection of manufacturers’ brands, provide an optimum return on investment and, ultimately, increase profitability for the business. 

THE FUNDAMENTAL FUNCTION. The main purpose of a metal detector is, of course, to prevent metal contamination reaching consumers in a food product.

Metal contamination can originate from a number of sources, including contaminated raw ingredients, poor working practices during equipment installation and daily operations, or a lack of preventative maintenance procedures. All potential sources should be identified and addressed.

RAW MATERIALS. Inspecting raw materials when they arrive at the manufacturing facility offers the benefit of detection and removal of large contaminants before they are potentially broken into smaller pieces that are much more difficult to find later in the production process. Food manufacturers can and should, where possible, ensure that suppliers take full responsibility for the quality of their products by adhering to strict guidelines which may include the operation of an effective metal detection program similar to their own.

PRODUCTION PROCESS. The production process itself is another major source of potential metal contamination. Planned and preventative maintenance is essential to the effective operation of any metal detection program and can help to halt any contamination caused by malfunctioning equipment including broken or loose blades, swarf (bits of metal shavings), sieve wire, etc. Good engineering and manufacturing practices will ensure that defective equipment is repaired under controlled conditions so that potential problem areas are identified promptly. Retaining records of defective equipment and procedures carried out to correct non-conformance is crucial when reviewing the effectiveness of the planned maintenance program and incident resolution.

PERFECT POSITIONING. The optimum positioning of a metal detection system is important, as this can have an impact on inspection efficiency as well as delivering possible cost savings. HACCP techniques identify potential sources and types of contamination and pinpoint the necessary inspection points in the production process. Appropriate equipment should be located where it can identify and remove the contamination as early as possible. Where feasible, metal detectors should be integrated into the normal production flow to avoid possible confusion about which goods have been inspected. The factory environment plays a key role during the sitting process and must be assessed as it could have an adverse effect on operational performance — an element discussed further in this article.

At a minimum, the end of every production line should be viewed as a Critical Control Point. If products cannot be inspected immediately after packing, systems should be installed as close to that point as possible, immediately before packing. In situations where the nature of the product makes it impractical to carry out finished pack metal detection, such as canned foods, alternative control systems must be agreed upon with customers prior to installation. In this instance, the solution may include the installation of pipeline metal detectors in the process line just before the can filling takes place.

RELIABILITY AND SENSITIVITY. Attainable equipment sensitivity depends on many variables including product size, type and packaging material used, and should be determined following consultation with metal detector suppliers. For optimum consumer protection, systems should be set for the maximum sensitivity performance available while remaining stable and reliable.

Food retailers increasingly are establishing strict guidelines on operational sensitivity. Manufacturers should consider these as the minimum acceptable standards. If more stringent standards can be applied practically, processors will be able to offer a safer and higher standard of product to customers and consumers.

Sensitivity standards — expressed as minimum detectable ball sizes — can be established when specifying the equipment, ensuring that in-process stability is maintained in order to avoid instances of false rejection. Performance can be confirmed during commissioning trials. Maximum operating sensitivity performance will be balanced with the practicalities of implementation and enforcement. Figure 1 shows typical sensitivity standards demanded by major retailers.

THE IDEAL INSTALLATION. When installing and commissioning equipment, a number of points should be considered that may affect the long-term performance of inspection equipment. These include ensuring a “metal-free zone” is present around the detector, keeping its location free from excessive vibration or mechanical shock and, where possible, avoiding locations in proximity to sources of electromagnetic interference.

As part of the installation process, suppliers should provide an experienced engineer to ensure that any local relevant legislation is met, performance is optimized, operator training has been completed and the detector qualification process has been carried out correctly.

Once correctly installed, metal detectors should be audited and tested regularly, as defective equipment may allow contaminants to continue through the production process unidentified. As part of the preventative maintenance process, manufacturers can call on the experience of engineers and technicians who can quickly and easily identify potential equipment and/or program problems before they become an issue.

COMPLETE SYSTEM PERFORMANCE VALIDATION. After inspection equipment is installed and fully operational, regular validation of the whole system still is required. This will ensure compliance with product standards and the overall metal detection policy, and will also demonstrate due diligence. Validation tests are used to ensure that there has been no significant change in the detector sensitivity or settings since the previous validation test.

Best practice is to test equipment using three contaminant types — ferrous, non-ferrous and stainless steel — assuming these metals all are potential sources of contamination. If these tests are not practical, a compromise would be to focus testing for stainless steel on wet/conductive products and, in dry applications, for ferrous metals (and non-ferrous metals at higher frequencies). This regime will highlight any changes in sensitivity performance that can have an adverse effect on detection capability.

When conducting performance tests, samples should be positioned where they are least likely to be detected, offering the greatest challenge for the detection system. The importance of the correct positioning of the test piece should not be underestimated. Incorrect positioning may significantly impact the performance of the detector and reject device.

It is considered good practice to carry out testing at the beginning and end of each daily production shift. Validation tests should also be carried out following batch changes, machine setting adjustments and especially after periods of downtime. In addition to ensuring that the metal detector is performing to the required sensitivity standard, it is important to test that the reject device is functioning correctly.

Documentation of validation test results will demonstrate that all requirements of the validation procedure were met. If any validation or part of validation test fails, production should not restart until the cause of the contamination has been investigated and rectified. This not only guarantees equipment performance, but ensures the safety of products and the protection of the manufacturer’s reputation.

TO SUSPECT AND REJECT. If goods are rejected by the metal detection system during routine operations, they should be considered contaminated until proven otherwise. Evaluation of the suspect product should take place as soon as possible — but certainly before any product manufactured on the production line since the last successful test leaves the site.

To confirm contamination, the rejected product should be passed through the metal detector again, in multiple orientations. If, upon these further tests, no contamination is found, the suspect product can be considered acceptable. If the inspection system rejects the product again, manufacturers are advised to remove packaging materials and re-test the product itself. If the product is once again rejected and the metal contamination cannot be located visually, the product should be divided into smaller pieces and re-tested until the metal is found. This will allow the production team to identify any sources of contamination that may need attention.

It is vital that manufacturers have a clearly defined process for dealing with contaminated product, from the point of identification through to root cause investigation and final resolution. The results of this process, including details of the contamination, its source and actions taken, should be fully documented for future reference, ongoing analysis and regulatory compliance.

ANALYSIS AND IMPROVEMENT. The effectiveness of the facility’s inspection program can only be evaluated with efficient collection of data and trend analysis. Using this information over time will assess the value of the metal detector and be the first step in quantifying any savings or increased profit that has been generated.

In order to evaluate system effectiveness, plant’s must investigate all instances of contamination, rejected products and customer feedback. The number of rejects and complaints should be monitored over time to make sure improvements are being made and any underlying common causes are identified and eliminated.

SUMMARY. In today’s highly accountable business world, manufacturers need to optimize both the performance and value of their metal detectors. They can no longer be viewed simply as a means to remove metallic contamination; their role is far more important. A comprehensive and effective metal detection program will maximize safety, meet retailer standards, ensure regulatory compliance and protect the brands of food producers and their customers. Ultimately it will help to grow sales and profits. And no manufacturer would want to dismiss that opportunity.

The author is Marketing Manager, Mettler-Toledo Safeline.