Magnet maintenance for productivity and longer life

 

What causes
magnets to fail?

· Heat

 

Excessive Duty Cycle

 

External Heat

 

Exceeded Voltages

 

Shorted or Grounded Coil

· Moisture

· System failure

· Abuse

 
     

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

 

Operate within specified duty cycle ratings

 

Turn off magnets when not in use

 

Use magnets only for their intended purpose.

 

Reduce air gaps in loose material before lifting

 

Avoid lifting hot materials, if possible

 

Do not exceed recommended voltages

 

Inspect for shorted or grounded coils

 

Rotate hot magnets on a "buddy system"

 

Repair cracked casings and damaged connections

 

Correct or replace faulty controller components

 

Don't use the magnet as a drop ball or ram

 

Ensure magnet casings are water-tight

 

Store 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 heat.

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!


Contact Winkle for expert magnet service support.