scope:

A common cause for damaged belt conveyors and other continuous material handling equipment and associated components are metal parts conveyed with the bulk material, leading to faults in regular operation. These parts can be present in the bulk material during exploitation or inadvertently contaminate the bulk material during transport or handling.

The contaminants can also result in faults or damage in systems downstream of the continuous handling equipment, e.g. at transfer points, crushers, mills or other equipment.

Metal contamination can also have a negative impact on the conveyed material's quality (e.g. in plastic granulates, feedingstuffs and foodstuffs).

To protect the conveyor equipment and the system as a whole, these contaminants shall be separated as early as possible to avoid adverse consequences. Immediate detection and/or separation using automatic separation equipment must be used if such parts frequently are contained in the bulk material and if stopping the conveyor must be prevented.

If contaminants are detected rarely, marking and manual sorting can be sufficient. However, this requires the conveyor to be stopped and an operator to be summoned.

The application of individual processes is influenced by:

• conveyor's technical data

• conveyed material's mass flow

• bulk material properties

• shape, size and quantity of metallic items to be separated

In all applications, it is advantageous to firstly ensure equal blending of the bulk material and to limit the material's height on the conveyor.

Detection and/or separation can be performed using different processes (Table 1).

The information in Table 1 and Table 2 require the following:

• selection of the system best suited for the relevant conditions

• no under-dimensioning or over-dimensioning of the system

Due to the multitude of parameter, the separation rates described are reference values only that can deviate upwards or downwards.

To correctly design a magnet system, the manufacturer needs at least the following information:

• type of continuous handling equipment

• conveyor width

• conveying speed

• conveyed material's layer height

• conveyed material

• conveyed material's bulk density

• conveyed material's mass flow

• shape, size and expected quantities of metal parts to be separated

• peculiarities, e.g. material compounds

• intended magnet arrangement