WHITE PAPER Method - Detectability In collaboration with Mettler Toledo, food industry standard metal detectable bristles were investigated with regard to their detectability using a Profile Advantage multi-frequency Metal Detector, with and without the presence of a dry (packed granulated white sugar), and a wet (packed fresh chicken breast) food product, as shown in Figure 5. Transport Speed: 18 m/m, Aperture Size: 350 x 175 mm. Conclusion - Detectability Metal detectable plastic bristles were not detectable in the presence of food and packaging, as shown in Table 1. Discussion – Detectability Previous studies (Lock, 1990) have shown that to achieve a similar detection to that of a ferrous (iron) ball with a spherical diameter of 1.5 mm, metal wire lengths of between 3 mm and 9 mm would be required, as shown in Table 2. Table 2: Lengths of metal wire required to obtain a similar level of metal detection to that of a 1.5 mm spherical diameter ferrous ball. (Lock, 1990) Ferrous ball (spherical diameter) Pure steel paper clip (ferrous) 0.95 mm cross-sectional diameter Pure copper wire (nonferrous) 0.91 mm cross-sectional diameter Pure stainless steel wire EN 58/ AISI 304L (part ferrous) 1.16 mm cross-sectional diameter 1.5 mm 3 mm long 9 mm long 8 mm long Figure 5. A Profile Advantage multi-frequency Metal Detector (Mettler Toledo, Denmark) Results - Detectability Table 1 shows the detectability of different sizes and lengths of metal detectable plastic brush bristles, when positioned in different orientations, with and without the presence of food. Currently brushes with metal detectable plastic bristles are only available with bristle diameters of 0.35 mm, 0.50 mm and 0.60 mm, i.e. much thinner than the metal wires assessed in Table 2. It can be concluded therefore that even longer lengths of metal detectable plastic bristles would be required to achieve the same level of detection. For example, using the data highlighted in Table 1, to achieve an Table 1: Metal detectable bristle detection with and without the presence of food Bristle cross-sectional diameter (mm) 0.35 0.50 0.60 0.35 0.50 0.60 Bristle length (mm) 100 100 100 50 50 50 Bristle orientation | __ | __ | __ | __ | __ | __ No food/packaging *1.8 *2.2 *2.5 N/D *1.8 *2.3 Packed sugar (dry) N/D N/D N/D N/D N/D N/D Packed chicken breast (wet) N/D N/D N/D N/D N/D N/D N/D – Not Detected. *Minimum threshold for detection (equivalent to a ferrous sphere of the same diameter) Vikan A/S - Department of Research & Development 4 Copyright © 2021 Vikan A/S · All Rights Reserved
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