Quality control for metal contamination detection
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Although the necessity for the control of metal contamination in food products has been practised by conscientious food producers for many years, never before has the application of quality control inspection been practised to such high standards. The verification of these quality control practices is assured by independent inspectors such as the European Food Safety Inspection Service (Efsis) and British Retail Corporation (BRC).
While food producers have been directly responsible for the implementation of improved quality assurance, it should be recognised that a major factor has been the demand from the main supermarket companies for the enforcement of such quality controls. These have been enforced through a ‘code of practice for the prevention of metal contamination in food products’, drafted by each of the major supermarkets and issued to all of their suppliers of food products.
The implementation of quality assurance practices has been driven by the research and development involved in the manufacture of metal detection equipment, providing microprocessor-controlled machines incorporating software programs to assist and ensure due diligence.
Today the metal detection system has a minimum requirement to reject a contaminated product from the production line while providing accurate confirmation of the rejection. This is dependent on accurate timing and speed control devices to ensure that the precise product is rejected, especially on ever increasing high-speed production lines. The introduction of inverter controls integrated into the main power supply of the metal detector ensures that this is carried out with due diligence, as it enables the reject timing to be automatically determined by the metal detector, even if the line speed is raised or lowered remotely or manually.
Quality assurance of an accurately calibrated metal detector has to be verified through constant calibrated checks by qualified quality control staff, who must conduct regular sensitivity tests, the timing of which is guaranteed by a programmable demand from the metal detector. The test involves sensitivity checks with samples of various magnetic, non-magnetic and inoxydable metals, and this testing programme is itself verified. This verification is controlled by the metal detector recognising and confirming that the metal test samples employed are of the correct metal type, dimension and electromagnetic conductivity, as required for the actual product being inspected.
The latest editions of the code of practice issued by the supermarkets include even stricter quality control practices. This includes the request for the various test samples of ferrous, non-ferrous and stainless steel to be passed through the metal detector in consecutive test products, ensuring that the electromagnetic field is totally stable and capable of full recovery from disturbance by one metal contaminate prior to the immediate introduction of another metal contaminate.
Obviously the primary requirement is for a reliable metal detector generating a stable and perfectly balanced electromagnetic field. The new mechanised production techniques employed have contributed to a major transformation in the design and performance of metal detection equipment to ensure field stability.
In recent years, this has led to major investment by Ceia, a leading manufacturer, to move away from the traditional hand built methods to automated production techniques, thus ensuring that the metal detector is accurately assembled with reliable repeatability and perfectly formed coil assemblies which do not require pre-balancing during manufacture or re-balancing when installed in the food processing line. The introduction of programmable laser profiling machines, programmable case bending machines to control internal stresses, automated case alignment and programmable welding machines have all enhanced the performance and reliability of modern metal detectors.
Author
Leslie Hunt, Constant Instruments Ltd
Further information
Constant Instruments Ltd
Tel: +44 1903 739333
Fax: +44 1903 739222
Email: sales@constant-ceia.com
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