Views:23 Author:Site Editor Publish Time: 2019-09-17 Origin:Site
Application of metal detectors in food processing
Food packaging is an integral part of food products. It protects the food, prevents the damage of biological, chemical, and physical external factors during the circulation of the food from the factory to the consumer. It can also have the function of maintaining the stable quality of the food itself. Due to the increased attention to food safety and higher requirements, some countries have strengthened the regulation of food packaging. The implementation of nutritional standards and regulations, indirect additive regulations, etc. to promote degradable packaging, electronic scanning barcodes, etc., are promoting the new development of food packaging.
In the production process of different foods, potential physical hazards may exist in different production stages, and these hazards mainly come from four ways. First, raw materials: such as vaccination needles in meat, wire in wheat, mesh in powder, fish hooks in fish, small metal parts of machinery in vegetables, screws, etc. Second, human factors: such as buttons, pens, jewelry, coins, keys, watches and so on. Third, the maintenance process: such as wire, gadgets, welding slag, etc. generated during the cleaning and repair process. Fourth, the production equipment: such as the metal scrap generated by the crusher, the mixer, the slicer and the conveying system during the production process.
Food companies can eliminate the physical hazards caused by the above reasons through manual inspection, industrial filters, powerful magnetic bars or metal detectors. However, in order to reduce labor costs and obtain stable test results, metal detectors have become one of the widely used methods. It can help manufacturers to strictly abide by the regulations, timely discover metal foreign bodies in the production process, and discover potential hazards and dangerous external factors in time, including iron, non-ferrous and non-magnetic stainless steel.
The accuracy and reliability of a metal detector depends on the stability of the electromagnetic transmitter frequency and is typically used from 80 to 800 kHz. The lower the operating frequency, the better the detection performance of iron; the higher the operating frequency, the better the detection performance of high carbon steel. The sensitivity of the detector decreases as the detection range increases, and the magnitude of the induced signal depends on the size and conductivity of the metal particles.
Due to the pulsation of the current and the current filtering, the metal detector has a certain limit on the conveying speed of the detected articles. If the delivery speed exceeds a reasonable range, the sensitivity of the detector will decrease.
In order to ensure that the sensitivity does not drop, a suitable metal detector must be selected to accommodate the corresponding product being tested. In general, the detection range is controlled to a minimum as much as possible. For products with high frequency induction, the detector channel size should match the product size. The adjustment of the detection sensitivity is determined by referring to the center of the detection coil, and the induction at the center position is the lowest. The detected value of the product will change with the change of production conditions, such as temperature, product size, humidity, etc., which can be adjusted and compensated by the control function.
The ball is reproducible with minimal surface area and is the most difficult to detect for metal detectors. Therefore, the ball can be used as a reference sample for detection sensitivity. For non-spherical metals, the detection sensitivity depends largely on the position of the metal. Different locations have different cross-sectional areas and the detection effect is different. For example, iron is more sensitive when passing vertically, while high carbon steel and non-ferrous are less sensitive. When passing horizontally, iron is less sensitive, and high carbon steel and non-ferrous are more sensitive.
In the food industry, systems typically use higher operating frequencies. For foods such as cheese, the high frequency signal response is proportionally increased due to its inherent high frequency sensing performance. Moist fat or salt substances, such as bread, cheese, sausage, etc., have the same electrical conductivity as metals. In this case, in order to prevent the system from giving an error signal, the compensation signal must be adjusted to reduce the sensitivity.