In November, 2005, I wrote to the B30 Committee at the American Society of Mechanical Engineers (ASME). I had just completed my design for a new permanent magnetic lifter and wanted to make sure that in every respect, it met the standards as laid out in ASME's B30.20 "Close Proximity Operated Magnets."
As I poured through the details, I became concerned that the standard combined Manually Operated (Permanent) Lifting Magnets with Battery Operated (Electro) Magnetic Lifters and that the subject of test loads were based on the original "electro-magnetic" principle with a safety factor of 2:1 with little consideration for the disparity of air-gap performance between the two technologies.
In my letter, I provided scientific data to support the claim; in addition, I cited reference to the fact that the majority of manufacturers adopted a minimum 3:1 safety factor suggesting that the industry recognized the inadequacy of the standard. Indeed, for some of us even a 3:1 standard is not enough.
I received a "polite" response which thanked me for my concern. Five years later, the 2010 (ASME) standard for test loads remains unchanged at 2:1.
To my knowledge, all magnetic lifter manufacturers meet the ASME standard for Test Load, but not all manufacturers share the same concerns for safety. It follows, that a magnet that affords 30% less magnetic force for the same SWL is a lot cheaper to produce and likely more competitively priced.
It must be understood by the user that a lifting magnet's performance changes with the characteristics of the load. The material, the surface condition and geometry are all major factors not considering the application variables associated with lifting. The magnet producer can reference these limitations in the supporting documentation but is it reasonable for the user to fully appreciate the difference in performance between say, a hot-rolled finish versus a machined finish? What about the drop in force between lifting 1020 and 4140 steels? Let's face it; every manufacturer will undertake their test lifts in an "ideal" environment and not the typical conditions that you have in mind!
Taking the time to ask the supplier for information pertaining to the lifting magnet's test criteria and safety features will allow the buyer to make a more informed decision which can only benefit the welfare of all that use it.
The more clients know about this technology, the more they'll be convinced that magnets have a significant place in the management of steel.
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