Lifting Magnets

Permanent lifting magnets do not always deliver their rated capacity, as the actual holding force varies depending on the characteristics of the workpiece. Technicians must understand these factors in order to accurately determine a safe lifting capacity

Specifically, the actual lifting capacity is given by the relation:

Actual Lifting Capacity= T × F × M × Magnet Rated Capacity

Where:

• T: Factor based on material thickness (T – Thickness)
• F: Factor based on surface roughness / surface quality (F – Face roughness)
• M: Factor based on material quality / carbon content (M – Material quality)
• Magnet Rated Capacity: The maximum rated lifting capacity.

The above factors are given approximately by the following tables:

T – Thickness

The thinner the object is, the lower magnetic penetration can be achieved. This significantly reduces the actual holding force.

F – Face roughness

Roughness of the contact surface reduces the magnetic flux, leading to reduced holding force.

M – Material quality

Higher carbon content = poorer magnetic conductivity.

Basic rules:

• Small thickness = low performance
• Rough surface = reduced contact
• High-carbon material = lower magnetic permeability
• The three factors are multiplied — one poor characteristic can dramatically reduce the capacity.

Lifting magnets are manufactured with high safety factors, typically 3.0 to 3.5 times the stated lifting capacity. This means that the actual magnet force is multiple times the rated value. Nevertheless, this value should not be taken into account when selecting the magnet.

In addition, the geometry of the workpiece to be lifted also plays a decisive role in the magnet’s performance. Each model provides a different rated capacity for flat and for cylindrical surfaces. For round workpieces, the actual lifting capacity typically ranges at 40–60% of the rated value achieved on a flat square or rectangular workpiece. This parameter must always be checked.

The Earth-Chain table shows the differences in strength due to geometry for its models