Why a Stiff Operating Handle Means Less Magnetic Holding Force
As specialists in safe lifting, we regularly provide training on the safe use of lifting equipment, including lifting magnets. During these sessions, we often ask participants the following question:
"When using a manually operated lifting magnet, would you prefer the operating handle to move easily or require more force?"
The most common answer is: "More force, because it feels like the magnet is gripping the load more securely."
In reality, the opposite is true and here's why.
First, some background information. Lifting magnets may only be used to lift ferrous loads to a maximum height of 1.5 metres above ground level.
A typical application is lifting a steel component from a wooden packing crate where there is insufficient space to attach webbing slings. A lifting magnet allows the load to be lifted out of the crate first, after which slings can be attached for further handling.
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There are, of course, many other important safety considerations when using lifting magnets. These include the mandatory annual inspection, which checks for any reduction in the holding force of the permanent or electromagnetic system over time. Lifting round loads also requires special attention due to the reduced contact area and lower lifting capacity.
At Mennens, we're happy to advise you on the right lifting magnet and the safest solution for your specific application.
Light or Heavy?
With a manually operated lifting magnet, the load is secured by operating a lever. Contrary to what many people think, the easier the lever moves, the better. A light-operating lever indicates that the load is making good contact with the lifting magnet.
If the lever requires more force, it actually means there is greater resistance within the magnetic circuit and the magnet is making less effective contact with the load.
Consequences of Incorrect Operation
Incorrect use of lifting equipment, including lifting magnets, can cause a load to fall.
According to the Monitor Occupational Accidents 2021, incorrect operation of lifting equipment accounted for 10% of workplace accidents recorded in 2020 and 2021. Understanding how a lifting magnet works is therefore essential for safe lifting.
The Magnetic Field
Why does a lifting magnet hold less effectively when the operating lever feels heavy?
The answer lies in the magnetic field generated by the magnet. Every lifting magnet has a magnetic field with a specific depth and strength.
If the load—for example, a steel plate—is thinner than the effective depth of the magnetic field, part of the magnetic field extends beyond the material into the surrounding air. This reduces the available holding force, causing the magnet to grip the load less effectively and making the operating lever harder to move.
The Surface of the Load
The holding force of a lifting magnet also depends on the condition of the load surface.
A clean, flat surface provides maximum contact between the magnet and the load, allowing the full magnetic field to be utilised. In this situation, the operating lever moves easily.
If the surface is rough, uneven, or rusty, air gaps are created between the magnet and the load. Part of the magnetic field is then lost in these gaps, reducing the holding force and making the lever more difficult to operate.
Extra care is required when lifting round materials, as only a small portion of the magnetic field comes into contact with the load. For this reason, the Working Load Limit (WLL) for round loads is generally limited to 50% of the rated capacity shown on the lifting magnet.
Example: A 500 kg Lifting Magnet
Consider a lifting magnet with a Working Load Limit (WLL) of 500 kg.
This maximum capacity can only be achieved when the load has the correct thickness and a clean, flat surface. Under these conditions, the magnetic field is fully utilised and the magnet achieves maximum holding force.
However:
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If the load is thinner than the effective magnetic field depth, part of the magnetic field is lost through the air. In this case, the lifting capacity may be reduced from 500 kg to approximately 125 kg.
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If the load is thick enough but has a rough or uneven surface, the lifting capacity may be reduced from 500 kg to approximately 225 kg.
A surface is already considered rough or uneven when there is a height difference of only 0.5 mm between its highest and lowest points.
How Do You Know if the Load Is Safe?
One disadvantage of lifting magnets is that, unlike webbing slings or chain slings, you cannot immediately see whether the load is securely attached.
With a manual lifting magnet, the operating force of the lever provides a useful indication of the quality of the magnetic contact.
Electromagnetic lifting magnets, however, do not have a lever. They are simply switched on and off, providing no tactile feedback about the magnetic holding force.
Fortunately, there is no need to rely on guesswork.
Check the Specifications
Every lifting magnet is marked with its maximum Working Load Limit and the corresponding load dimensions for which that capacity applies.
The stated capacity is only achieved when the load dimensions fully utilise the magnetic field.
Use the Load Capacity Chart
Every lifting magnet is also supplied with a load capacity chart or performance graph.
If the load is thinner than specified or has a rough surface, this chart indicates the reduced lifting capacity of the magnet.
If the adjusted lifting capacity shown in the chart is lower than the weight of the load, a larger or more suitable lifting magnet should be selected.
Depending on the manufacturer, this information may be presented as a table, graph, or performance curve. Always consult the chart before lifting.
Knowledge file Safe Lifting
Use lifting equipment safely and correctly. Learn how to sling loads properly and how to inspect, examine, and certify lifting equipment to ensure safe and responsible lifting operations.
