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Stiffness of Loads Needs to be Considered When Selecting Lifting Magnets

Posted on June 26, 2017

In most cases, stiffness of loads is not a safety concern for operators when there is no bending of the load in a well-balanced lift. This generally happens when the load is thin and large in size so that weights of their overhanging sections are heavy enough to sag.

Metal too thin to be lifted by Armstrong Magnetics' plate lifting magnet PL-series 

To reach the maximum rated lifting capacity, the face of lifting magnets must be upright to the loads’ gravitational forces. When the overhanging sections of loads bend, the loads’ contacting section would then no longer be perpendicular to the faces of the magnets and lead to a peeling effect quickly separating the loads from the magnetic lifting devices. Operators should always keep in mind that the lifting strength is rated based on the contact surface conditions and the pull of loads. If one of these two conditions are imperfect, i.e. rough/dirty/painted/uneven surfaces of loads and/or face of magnets or the loads do not cover the entire poles of magnets, the lifting capacity would be de-rated and unable to overcome the peeling effect.

At our factory, we have tested the peeling effect against the thickness and weight of flat loads. Here’s the general guideline:

Length 4' 5' 6' 8' 10' 12'
Thickness >1/8" >3/16" >1/4" >5/16" >3/8" >1/2"

If the peeling effect is ignored during operation and the flat loads fall outside of the dimensional limitation, the result can be detrimental causing full release of the load when being lifted in air. When the lifting capacity cannot resist the pull force of loads’ bending portions, buyers and operators must consider applying spreader beams along with one or more extra lifting magnets to balance out the bending force and to minimize the overhanging lengths of plate loads. With the design of equalized magnetic forces, more loads’ weight would be perpendicular to the loads’ bottom pole faces and there would be less bouncing at the drooping portions during lifting and transferring.

If you have large but thin plates need to be lifted safely, please feel free to contact us for model and system design recommendations, and if necessary, we can manufacture custom lifting magnets to meet your lifting applications.  Your safety is our priority.