Magnet maintenance for productivity and longer life
What causes magnets to fail?
Excessive Duty Cycle
Shorted or Grounded Coil
· System failure
Lifting magnets are important revenue
generators for scrap metal yards and, for steel production
facilities, magnets are a critical link in primary processes.
But few users of industrial magnets are actually getting their
money's worth from their magnet system!
Magnets are one of the most poorly understood pieces of material
handling equipment. They can be incredibly reliable and potentially
last for many, many years of service. Instead, we find that
working magnets chronically underperform and are often a costly
maintenance item. To get your full value out of a magnet,
you first have to recognize it as a valuable piece of equipment
and treat it with that kind of respect.
"Just cool it!" to reduce maintenance costs
Heat is the number one factor in premature magnet failure. Moisture, electrical system faults and simple abuse can also compromise magnet performance, but heat is by far the most important factor.
As a magnet heats up to its operating temperature (220°F-270°F), it loses 22%-25% of lifting capacity and 25%-28% of current.
The first place to look for heat-related magnet problems is in the magnet's duty cycle. The length of time that the magnet is powered up during the lifting cycle is critical. Think of it this way: an average toaster produces 800 watts of heat during its work cycle. A typical 66" to 68" magnet produces nearly 20,000 watts! That's a lot of heat and, unlike the toaster, magnet casings aren't vented.
Winkle recommends that operators stay well within the recommended
duty cycle rating. Operators often power up magnets too early
in the lift cycle, allowing too much "on" time for
the unit to heat up. A hot magnet, running around 270o
F, loses up to 25% of its lifting capacity. In scrap handling
applications, for instance, it’s best to waiting till
2 or 3 seconds before the magnet reaches the pile. This will
help to keep the heat down and actually increase the amount
of material the magnet picks up. To pick up loose material,
set the magnet right down on the pile and let it crush out
some of the air gaps before you actuate it, so you can improve
the lift per cycle even more.
Check list for magnet performance
within specified duty cycle ratings
off magnets when not in use
Use magnets only for their intended purpose.
air gaps in loose material before lifting
Avoid lifting hot materials, if possible
Do not exceed recommended voltages
for shorted or grounded coils
hot magnets on a "buddy system"
cracked casings and damaged connections
or replace faulty controller components
use the magnet as a drop ball or ram
magnet casings are water-tight
magnets off the ground
More hot spots
External sources of heat can be another factor in magnet performance, including the temperature of ambient air and of the material being lifted. This factor is especially important in steel mills and foundries where air temperatures and material temperatures are most extreme. Magnets in these applications must be designed specifically for hot surface work.
Over-powering the magnet is one common cause of excessive
magnet heat that can be prevented. In most cases, magnets
are designed to run at 230 volts DC. A small difference in
voltage makes a big difference to the amperage running through
the coils and the amount of heat it generates. Over-powering
by just 20 volts can generate thousands of watts of damaging
Improper magnet use is costly in several ways. Abuse and heat not only wear out the magnet faster, they can undercut your entire material handling capacity for a long time before the magnet finally fails. That means your crane is underperforming, and whatever it's feeding is under capacity, too.
Better magnet maintenance can really pay off for every part of your operation!