Metal contamination detection

Metal is a potential hazard in all types of food products. The hazard can be reduce greatly by proper equipment and an effective programme to manage tramp metal.

Although the necessity for the control of metal contamination in food products has been practiced by conscientious food producers for many years, never before has the application of quality control inspection been practiced to such high standards.

An ever increasing awareness of potential metal physical hazards present in food products has raised the expectation that a better detection strategy be used, and en expectation being reinforced in an increasingly demanding nature by the regulatory agency.

Metal contamination normally arises form any four sources:
*Raw materials: metal tags, screen wire in powder, etc
*Personal effects: paper clips, jewelry, hair clips, etc
*Maintenance: welding swarf, wore off cuts, shavings, etc
*In plant processing: small parts or shavings form mills, blenders, slicers, etc

In essence a metal detection loop consists of three basic components: product transfer, the metal detection system and reject system.

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.

To maximize the effectiveness of metal detection, the appropriate device should be installed as close as possible to the finished product fill station or all finished and closed packages should pass through a detector.

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.

A metal detector by itself will not provide assurance that all metal will be detected and removed. For best results, the metal detector should be part of a quality assurance program specifically designed for each product.

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 basic principle of metal detection is based on the transmission and reception of electrical impulse, much like radio waves. All metal have characteristics that will cause an alteration in transmitted signal, because of their conductivity and magnetic properties.

The test by quality assurance 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 recognizing 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.
Metal contamination detection