Metalldetektion beim Förderband

Tunnel metal detectors are used for detecting all metals in the conveyor flow when material heights are high. MTF Technik primarily uses divisible tunnel metal detectors on conveyor belts. These have the advantage that they can be easily integrated into the conveyor belt design and, above all, the belts can be used as endless welded versions.

Closed tunnel detectors are particularly suitable when, for example, flat conveyor belts are to be pushed completely into the tunnel or when the conveyed material passes through the detector via chutes or in free fall. They have an even higher sensitivity than separable versions.

The sensitivity of the detectors depends primarily on the clear passage height. The smaller the clearance height, the higher the sensitivity. Steel parts are detected significantly better than, for example, parts made of stainless steel (rough guideline: factor 2) or other metals such as copper, aluminium, brass (here the factor is between 1.2 and 1.8).

Tunnel metal detectors require a special conveyor belt design with a metal-free zone tailored to the detector, i.e. in this area, the conveyor belt body, which is otherwise made of aluminium, is completely separated and replaced by a wooden structure. To ensure the best possible detection results, it is important to ensure that as little vibration as possible is transmitted to the detector. Influences from moisture, electromagnetic interference, etc. must also be taken into account.

As the tunnel detectors are very sensitive and also react to interference in the direction of the opening, it must be ensured that there are no electromagnetic interference fields too close to the detector (e.g. controls from other systems, motors and drives). Vibrations should also be avoided as far as possible (e.g. forklift traffic next to the device, falling objects onto the conveyor belt, etc.).

A magnetic drive roller is mounted at the outlet of the conveyor belt (pull drive). It separates ferro-magnetic parts from a continuous conveyor flow and transports them continuously.

Depending on the thickness of the conveyor flow, a combination of a magnetic drive roller and a plate magnet above the conveyor belt may also be useful.

In this way, the plate magnet pulls the foreign objects out of the upper product layers, while the magnetic drive roller separates the foreign objects from the lower layers of the product flow.

Plate magnets are used to separate small quantities of larger ferrous foreign objects from a continuous and easily permeable conveyor stream. They can be arranged above a conveyor belt, above or below chutes or in free fall. Depending on the task at hand, different magnetic materials can be used (ferrite or neodymium iron boron).

The advantage of this solution is its simplicity. Plate magnets do not require a power supply or evaluation electronics. They are therefore easy to integrate or install.

The disadvantage is that the plate magnet must be manually cleaned of any foreign objects that may have been attracted to it.