FEATURE MACHINE BUILDING, FRAMEWORKS & SAFETY


RAISING THE BAR... BUILDING A METAL DETECTION AND WEIGHING SOLUTION FOR DIET FOOD PRODUCTS


T


o save space, food and beverage industry manufacturers often want


to carry out metal detection and checkweighing on the same production line. Onemanufacturer, however, decided it wanted to screen its flow-wrapped bars for metal contamination prior to wrapping. The reason for this was the highest levels of detection sensitivity were needed as the bars, part of a diet product line, were wrapped in metallic film, which could confuse the metal detector. Checkweighing then needed to take place after the wrapping process had taken place. The customer had a number of


A custommetal detection and checkweighing installation met the demands


at speeds of up to 500ppm. However, the rejectmechanism


requirements. Given that weighing accuracy is imperative for diet products, which need to provide exactly the number of calories stated on the pack, the customer stipulated a target weight of 51g with a tolerance of ±1g. The customer also wanted the solution to provide speed and accuracy, specifying a metal detector and checkweigher capable of 400ppm. To meet the requirements, the company turned to Sparc Systems and Fortress Technology.


When a manufacturer of diet food needed a metal detection and


checkweighing solution, it turned to Sparc Systems and Fortress Technology


flow-wrapper, the two inspection systems ensure that every single bar leaves the line metal-free and compliant with its stated pack weight. Themain factor that limits inspection speed is


DETECTING AND WEIGHING Robustmachine construction, vibration-filtering software and a high-speed electric pusher reject are the threemain design elements utilised by Sparc to enable Fortress Technology’s Stealth metal detector and Sparc’s Sentinel checkweigher to inspect flow-wrapped bars at the required speeds of up to 400ppm, which equated tomore than six bars per second. Integrated within an entirely new cereal bar processing and packaging line, which includes ovens, cooling tunnels and a


the rejectmechanism, as Charlie Graham, sales manager at Fortress Technology and Sparc Systems, explains: “You can get a conventional air blast reject systemto reactmore quickly by using more compressed air, but the problem is that you’re never quite sure where the pack will end up – it can lift up or spin round and might end up missing the sensor. Most retailers require reject confirmation, and if a manufacturer can’t guarantee that rejected products are going to pass the sensor, they will have to stop the line.” To overcome this issue, Sparc supplied the


metal detector and checkweigher with an all-electric pusher reject, specified to reject


alone would not have been enough tomeet the customer’s speed requirements without other design concessions. One of the problems is that, at high speeds, vibrations affect the magnetic field of a metal detector, compromising detection sensitivity, and can affect checkweigher weighing performance. Sparc claims to be one of just a few machinery manufacturers in the 400ppm ballpark, and attributes this to the solid construction of its systems, coupled with its in-built software. Grahamexplained: “We use


stainless steel with aminimum thickness of 6mmfor the guarding and framework, which are all sheet metal, with no box sections, for maximum strength. This robust construction, coupled with software that filters out vibration, eliminates


interference, so that accurate performance is maintained at all times – even at very high speeds. In trials, the Stealthmetal detector was able to


detect samples as small as 0.6mm(ferrous), 0.7mm(non-ferrous) and 0.8mm(stainless steel) in diameter. Grahamadded: “This is one of those applications where X-ray would struggle because the density of the product would be similar to the density of the contaminants.” In operation since October 2020, the


solution has been running at a linear speed of 90m/min, with the checkweigher exceeding the customer’s expectations by achieving reliable weigh accuracy of ±0.25g, keeping the bars well within the e-mark rules.


Fortress Technology www.fortresstechnology.co.uk


More than six bars per second leave the line, with each beingmetal-free and compliant with its stated pack weight


1 DESIGN SOLUTIONS DECEMBER/JANUARY 2022 6


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