• 03 APR 18

    How to Eliminate Irregular-shaped Metal Shards from Your Production Line

    Metal contaminants come in all shapes and sizes. Irregular-shaped contaminants are the most likely to cause recalls as these are potentially the most difficult to detect. As well as posing a major safety hazard for consumers, the negative publicity that will inevitably result from the discovery of metal fragments in food or medicines also has the potential to cause serious brand damage.

    Food and pharmaceutical manufacturers rely on automated, high-speed processing systems to increase productivity in order to keep up with growing demand for their products. However, this can cause greater risk of irregular-shaped metal fragments such as wire, slivers of metal and “swarf”, due to broken processing equipment or foreign bodies that have entered the production line with the raw ingredients.

    Common irregular-shaped metal fragments detected by Safeline metal detectors.

    Irregular-shaped contaminants such as wires and swarf can be difficult to detect due to something called “orientation effect”. This is observed when the thickness of the contaminant is less than the spherical operating sensitivity of the metal detector in question. When it comes to detectability, a wire type contaminant will have a most favorable and least favorable orientation when passing through the detector search head depending on the metal type in question. Ferrous contaminants are easier to detect when they are presented parallel to the direction of travel, but more difficult to detect in other orientations. Stainless Steels and non-ferrous contaminants are more readily detected when they are at 90 degrees to the direction of travel, and more difficult to detect in other orientations. Of course, it isn’t possible to control the orientation of metal contaminants as they pass through the detector. For this reason, ball bearings are used as a measure of metal detector performance and supplied as metal detector test pieces, as they don’t possess any orientation effect; and are therefore a reliable and repeatable means of measuring that a detector is working at a known specification.

    To minimize the orientation effect, the best solution is to operate the metal detection system at the highest possible spherical sensitivity and a 0.1mm improvement in spherical sensitivity will dramatically improve the length of wire detectable. Therefore, careful consideration must be given to the installation location, frequency, aperture size and most importantly the type of the metal detector. The results of a Hazard Analysis and Critical Control Point (HACCP) audit will help determine these factors.

    One possible solution to conquering the orientation effect in food manufacturing is to use multiple metal detector search heads on the same production line, which are set at different angles to the conveyor. This maximizes the likelihood of detection as the orientation of the contaminant relative to each detector changes. It is vitally important when employing this type of solution that any additional metal detector heads do not operate at a lower spherical sensitivity than the main metal detector head. This would negate the improvement gained from utilizing angled metal detectors and actually reduce, not increase, detection levels.

    A UK-based meat production company uses three metal detector heads to combat orientation effect on its production line.

    Often manufacturers know the size of contaminant they are trying to detect. In the pharmaceutical industry, for example, one of the greatest contamination risk comes from broken sieve wires. Manufacturers who are aware of the diameter of the wire used in the sieves on their production lines can specify a minimum level of metal detector sensitivity when commissioning a new metal detection system. The metal detector can then be tested to check it is capable of detecting the specific sieve wire type even in its most challenging orientation.

    To protect their business and brands from the cost and damage of recalls, manufacturers must be able to trust the processing systems and product inspection technology on their production lines. To minimize the risk of metal contamination recalls, it is crucial that inspection systems are capable of detecting both regular and irregular-shaped contaminants.

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