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Designing Lifting Magnets with Highest Safety Factor

Posted on June 8, 2017

Armstrong Magnetics' brand new NL-B Permanent Lifting Magnets 

All Armstrong’s lifting magnets for sale are designed and manufactured meeting or exceeding the provisions of ASME B30.20.

Based on the ASME B30.20, each magnetic lifting device must be attached with a label containing information on company name, model, rated lifting capacity. Such tag shall be designed to bring operator’s attention and be placed in a convenient position to be easily read. For instance, all of our NL-B series lifting magnets have breakaway force 3 times greater than of their corresponding rated lifting capacity under “perfect condition”. “Perfect condition” is defined as an unused magnetic device being vertically pulled away a clean, flat, low carbon steel plate that is at least 3-inch thick. So why should the operators strictly lift ferrous plates weighing no more than the magnet’s holding limit value?

Required by ASME, design factor is minimum 2:1, or 3:1 for most of our permanent magnetic lifter. New NL-2200B permanent lifting magnets with 2200 lbs of rated lifting capacity has a breakaway force equal or more than 6600 lbs. Our safety label affixed clearly state the working load limit value of 2200 lbs. Working environment is always changing and almost never “perfect”. There are many factors that can affect and decrease lifting values, including air gap caused by dust, coating or worn magnet face, vibration during transportation, extreme temperature outside of working temperature range, and more. Before we process any orders on our lifting magnets, we try to obtain accurate information on customer’s lifting operation, factor in all conditions and provide recommendations with highest safety factor. In many cases, our customers would need to lift a range of steel loads. Our labels tabulate the de-rated lifting capacity against thickness of flat load and air gap to conveniently allow operators estimate the safety factor for each specific hoisting action. However, if there is any uncertain, operators must pulse the job, consult either internal expert or contact us.