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Larger or More Lifting Magnets for Greater Strength?

Posted on July 24, 2017

lifting magnets connected by spreader beam

Imagine that you need to lift a 1” thick flat steel load weighing 1000 lbs. There are two options:

Option 1: Use a single NL-1320B permanent lifting magnet which meets the rated lifting capacity for this load. For 1” thickness, the lifting strength of this model would be derated to approximately 83% of its maximum value; in other words, its rated capacity for this load thickness is about 1095 lbs. The retail price for this lifting device is $695.

Option 2: Use two units of NL-660B permanent lifting magnets and a spreader beam FB-1320 connecting the two lifting devices. The lifting capacity of this model stays the same for 1” thickness as its maximum rated capacity. Total rated lifting capacity for this entire setup is 1320 lbs and the total price is $1,085.

It may seem that Option 1 is more economical and attaching it directly to a crane or hoist can well satisfy the lifting requirement. But a single large lifting magnet, NL-1320B in this case, would be unable to allot its magnetic attraction capacity over the entire load range. The single large sized magnetic lifter would yield a deep but concentrated magnetic field which cannot be distributed to the edges of the plate but can penetrate through thicker plates. To custom design a single magnetic lifting device with the required lifting capacity distributing wider magnetic field would be very cost and thus likely not be considered as an option during economical comparison.

Therefore, it is more efficient to apply more than one single magnet to cover more extensive load area. When we provide customers our recommendations, we take into consideration of the loads weight, shape and size and suggest the fewest amount magnets with highest efficiency. In this case, 3 units of NL-330B with spreader beam connections evenly distributed can also perform such job but operation would be slightly redundant. When designing the lifting magnet system, we also need to consider the crane’s support limitation. All attachments below the hook need to be accounted for and ensure the existing crane can uphold them, including the loads themselves, lifting magnets, linkages and spreader beams.

Loads can vary drastically from one to the other and when multiple lifting magnets are required, make sure the lifting beam and magnets do not extend passing the edges of the load. During operation, you must ensure every unit of magnetic lifting device satisfy its optimum lifting condition, or else their total lifting capacity would be de-rated. The same de-rating factors would apply to every single unit, such as surface conditions, percentage of contacts, carbon content in load material, etc. Sometimes, we may need to custom make a lifting beam based on the load size.
This industrial lifting magnets cannot be demagnetized while they are lifted, or the hoist rope is in tension.

If you have uniquely sized loads, feel free to contact us and our technical team can assist you along the entire process of setting up the best lifting magnet assembly.