Scheffer magnet lifting systems
Magnets for rolled profile transportation
Transporting rolled profiles calls for the use of narrow magnet and crossbeam solutions. This is the only way that the operator can move freely in the profile webs and/or between the rows of stacked profiles. As well as transporting the materials faster and more reliably, other benefits for the operator include the absence of pathways between the stacked profiles and no need for intermediate layers for the fastening of chains or belts, therefore creating a much higher packing density within the storage area.
How material becomes magnetised:
when ferromagnetic steel (e.g. 42CrMO4) is transported magnetically, the material still has a high level of residual magnetism after the magnetic field has been switched off. This is due to the orientation of magnetic domains known as ‘Weiss domains’. If these domains have the same orientation, the material is measurably magnetic.
This magnetic field has a major impact on the further processing of the material:
- Metal chips and grinding dust stick to the workpiece;
- Sintered tools wear out faster;
- Downtimes for robots/automatic feeding systems due to parts sticking together;
- Magnetic field sensors are activated by mistake;
- Measurement errors generated by highly sensitive measuring instruments;
- Defective weld seams;
- Defective electron beam welding;
- Uneven thickness of hard chromium or titanium nitride coatings;
- Edges break off during wire EDM;
Demagnetisation during switch-off.
Scheffer magnet systems feature a demagnetisation function that can be selected to prevent these negative effects of ‘residual magnetism’. When this function is selected, the material is exposed to a strong alternating magnetic field (polarity reversal of + and -) when the magnets are switched off. The strength of this field is consistently reduced to zero. By measuring the current quickly, the duration can be reduced to a minimum. The homogeneous orientation of the ‘Weiss domains’ is destroyed and the magnetic effect reduced externally.
Once the demagnetisation process is complete, the crane’s hoisting unit is enabled once again and the material can be processed without any disruptive magnetic effects.
The current and thus the field of the magnets on the Scheffer magnet system can be infinitely adjusted by using Siemens DCM converters.
One converter is used per magnet group.
The magnetic force in partial-load operation can be controlled in the following ways:
- As a fixed value
- As step switching with binary signals or as a BCD code
- As infinitely variable pre-selection using a potentiometer or decimal value
In full-load operation, it is not possible to manually adjust the magnetic force.
However, in two-handed operation, it is possible to return to partial-load operation. Then, the magnetic force can be adjusted as described above.
Magnets for rolled profile transportation:
When transporting shaped steel, the use of ‘multipolar magnets’ offers advantages when picking up wide, but especially also narrow profiles.
Unlike the conventional use of double-sided pole plates, in this solution several poles are arranged along the centre line of the magnet. This creates a central magnetic field between these ‘multipolar poles’.
The narrow design of the poles means that even small beams can be picked up in the middle of the web. The narrow overall design of the magnets, without side contours, makes it possible to work with precision, even between high stacks of materials or in stakes.
When picking up wide profiles, the magnets can be rotated by up to 90° to prevent the material from tilting around its longitudinal axis.
These tried-and-tested advantages of multipolar magnets therefore offer an efficient and reliable solution for transporting shaped steel profiles.