Metal Detector - Removing Foreign Bodies

Section summary
1. Metal Detection
2. Rejection
3. Design

Metal detectors are totally different than simple magnets. They are not going to trap metals but will detect metal presence in a product stream and possibly reject it.

1. How is the detection performed ?

When metal is passing through the metal detector, it will change the magnetic field that is applied by the metal detector. This disruption will allow the detection of the presence of metal.

2. Rejection

Metal detectors can be equipped with a rejection. It takes most often the shape of a flap that is opened as soon as the metal detector spots the presence of metal in the product flow.
Each time a diversion occurs, some product is lost, it is important not to have false detection otherwise a lot of losses will be generated.

3. Chosing the right metal detector

The following parameters must be taken into account when chosing a metal detector : the product throughput to handle, the location of the metal detector and the sensitivity targetted

Table 1 : Metal Detector design criteria

Design parameter Consideration to keep in mind
Detection limit Metal Detector Diameters
Minimum powder speed Distance powder point of chute - entry of metal detector
Powder max throughput Ensure that the powder flow is roughly dosed
Metal detector Diameter
Performance check Access to Metal Detector entry - introduction of test balls / rods

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