QC/Hygiene | IDM 9 2016 | international-dairy.com · 31 Table 1. Metal detectable bristle detection with and without the presence of food. without the presence of a dry (packed granulated white sugar) food product, and a wet (packed fresh chicken breast), as shown in Figure 1. Conclusion Metal detectable plastic bristles were not detectable in the presence of food and packaging, as shown in Table 1. Additionally, to achieve a similar detection to that of a ferrous ball with a spherical diameter of 1.5mm, metal wire lengths of between 3mm and 9mm would be required, as shown in Table 2. Currently brushes with metal detectable plastic bristles are only available with bristle diameters of 0.35mm, 0.50mm and 0.60mm, 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 Bristle cross-sectional diameter (mm) Bristle length (mm) Bristle orientation No food/packaging Packed sugar (dry) Packed chicken breast (wet) 0.35 100 --- I *1.8 N/D N/D 0.50 100 --- I *2.2 N/D N/D 0.60 100 --- I *2.5 N/D N/D 0.35 50 --- I N/D N/D N/D 0.50 50 --- I *1.8 N/D N/D 0.60 50 --- I *2.3 N/D N/D *Minimum threshold for detection (equivalent to a ferrous ball of the same diameter) N/D – Not Detected 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). Table and Graph 3a. 0.35 mm plastic (PBT) bristle strength and elongation. 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 highlighted in Table 1 above, a metal detectable bristle with a cross-sectional diameter of 0.50 mm and a length of 50 mm gives an equivalent detection to that of a 1.8 mm ferrous ball. Durability of metal detectable plastic bristles Tests to assess the break strength and elasticity of metal detectable and plastic bristles were performed by Zwick Roell, Germany, using a Zwicki 5kN bristle pull test apparatus, as shown in Figure 2. Results Plastic (PBT) bristles were 68% stronger and more than twice as elastic as metal detectable bristles, as shown in Tables and Graphs 3a & b. Figure 2. Zwicki 5kN bristle strength and elasticity assessment equipment (Zwick Roell, Germany) Fmax = Bristle Strength dL at Fmax = Bristle Elongation (elasticity) Load Cell: 200N HP Extensometer: Crosshead Grips: Pneumatic Grips - 8190 Newtons Jaws Insert: Oxidceramics Clamping Pressure: 4 bar Pre-Load: 1 Newtons Speed, Pre-load: 10 mm/min Test Speed: 20 mm/min Grip to Grip distance at start: 100 mm
IDM_09_2016
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