Maintaining magnets

Magnets are typically responsible for the heavy lifting at scrapyards, but their uses don’t stop there. Many yards will leverage these attachments to clean debris or unload railcars where traditional grapples may not fit.   

For a piece of equipment with such diverse applications, sizing and maintenance are relatively straightforward.   

“There’s not much maintenance on magnets, but there are a few basic things that can prolong the life of that magnet,” explains Kristian Knights, national sales manager at Boyne City, Michigan-based Walker Magnetics.   

In the following interview, Knights discusses scrap handling magnet sizing and shares maintenance tips.   

Recycling Today (RT): How do you properly size a magnet to a scrap handler, and what are the key factors you need to consider?  

Kristian Knights (KK): When sizing a magnet on a mobile piece of equipment at a scrapyard, like an excavator, you would need to consider the maximum weight that excavator can safely handle at its maximum reach—the max capacity. … That’s the upper limit.   

That’s not to say we wouldn’t go with a smaller magnet if it didn’t warrant them going with the maximum the mobile equipment can handle, but that’s just one parameter. What can the mobile piece of equipment handle?   

The other can be the size of the power source. These excavators often come with, for example, only a 15-kilowatt generator. Even if the weight of the magnet can be handled by the mobile piece of equipment, the power source isn’t large enough necessarily to max out the magnet size. A 15-kilowatt generator would only be able to power, say, a 57-inch magnet—that right there is your limit. Those are two examples or factors we would look into when sizing a magnet.  

RT: Is there a rule of thumb regarding how many magnets are needed at yards of certain sizes?  

KK: There’s no set rule of thumb. You look at a yard as an individual entity, as they all differ. Then you match up magnets wherever appropriate for the various applications at that specific yard. … But there are various applications that a yard could have. [For example,] a sweeping application, which uses the magnet as a cleanup item for rail cars, trucks, pathways, roads, etcetera. You’re not picking large loads of scrap, but you’re using it to clean.  

Some use a magnet to load and unload trucks and rail cars that grapples can’t fit into. … The ultimate question is: What are they handling? From there, you can determine how many magnets they would need.  

Some of these yards are a little more involved; they have auto shredding, [and] that right there is a whole new realm of magnets where you have magnet separators, such as magnetic drums, for processing the shredded automobiles, as well as cross belt separators [and] head pulleys. Eddy current magnets can be used to separate nonferrous material, like aluminum cans. There’s a whole list of magnets that are used in different applications, so, no rule of thumb.  

RT: What factors might affect a magnet’s lift capacity?  

KK: A magnet is going to act differently based on what [material it’s] handling. We often get the question, “How much can this magnet lift?” There’s not a simple answer. What are you trying to lift? It could lift 50 tons on a solid steel slab, but that same magnet could lift 3,000 pounds on Heavy Melt #1 scrap. That’s what affects it most. First and foremost, what material are they handling?  

Then [it’s] operator practices. Honestly, about 80 percent of all factors affecting the lift of a magnet can be attributed to proper operator use. More specifically, are they energizing the magnet too early as they come down on a load? Best practice is to use that magnet, leave it off as long as possible, and then use the weight of the magnet to compress and make a denser load. Then you energize it. [Some operators] are energizing too early, so [the magnet’s] already wanting to pick up scrap as it’s going down on the pile. Therefore, you have this very porous, airy load, because [the magnet] didn’t have an opportunity to compress [the pile]. You can lift almost double if you are patient [and] let it settle onto the pile [before energizing the magnet]. 

Then, [there’s] the condition of the magnet itself. The older a magnet gets, there’s going to be more … wear. Depending on the hardfacing, that type of wear is going to diminish the lifting performance of a magnet, as well as if it gets worn off and no longer protects the pole shoe surfaces.

Then there’s the temperature of the magnet. A magnet [is still subject to] the laws of physics. It’s going to lift more in the morning than it will at the end of the shift because a magnet performs most efficiently when it’s cool or at an ambient temperature. But as the operator uses it, it’s naturally going to heat up inside, and therefore [resulting in] a reduction in lift capacity.

RT: What magnet maintenance mistakes do you commonly see?  

KK: One mistake is … not maintaining the hardfacing on the pole shoes. The hard facing is there to protect the wear of the actual pole shoe itself.  

Not maintaining [the electrical] leads going to the magnet [is another mistake], because those can get severed or nicked, causing more problems down the line to the magnet itself. Not keeping up on proper lead care and not keeping the terminal box holes cleared, which … [can cause] a buildup of gunk, leading to issues. There’s not much maintenance on magnets, but there are a few basic things that can prolong the life of that magnet.  

RT: How should operators be handling magnets to prolong a magnet’s life?  

KK: [Operators should] adhere to the duty cycle of the magnet. Scrap magnets have typically a 75 percent duty cycle. As an example, say you have that magnet on for seven-and-a-half minutes, it would need to be off for two-and-a-half minutes to let it cool. When they exceed the duty cycle, that leads to an overheating of the internal temperature, therefore leading to a faster degradation of installation and a breakdown of compound and other materials, leading to an ultimate failure of a magnet.   

Another is keeping the magnet off the ground when not using it. … This allows more airflow for greater heat dissipation.   

You also want to keep it off the ground … so it’s not submerged in a puddle, because there’s tendencies for these welds [to] potentially crack. A hot magnet is going to suck up water into the magnet cavity, leading to shorts and expensive repairs. When you get water and electricity together, they don’t mix well.  

Don’t use the magnet for anything other than its intended purpose, which for a scrap magnet is to lift scrap. That’s to say, don’t use it to relocate rail cars, as a battering ram [or] to break up scrap. Just use it for what it was prescribed for.  

RT: Do you have any magnet maintenance tips?  

KK: Routine checks are very important. One of those would be electrical checks, which check the coil resistance and the ground resistance of that magnet. Those two electrical readings can determine the health of the magnet. … Electrically, check them at least once a month, not every day, and keep a running record of what those readings are. Then you get to see if the magnet is failing, and you can catch certain things early before an ultimate failure.   

There are also routine checks that should take place, [like] checking the welds underneath the magnet for cracks, checking the chains and chain pins for excessive wear.   

As I mentioned before, check the hardfacing for excessive wear. You can reapply hardfacing, but if you don’t, you’re starting to wear the actual pole shoes themselves. Those [checks] can happen more regularly, because it doesn’t take more than a couple minutes for an operator to lay eyes underneath the magnet.   

If anything needs repairing, contact your magnet supplier for proper procedures on how to repair. A lot of those repairs, if caught early, can be done on-site, versus an expensive, lengthy time without a magnet, sending it away to a certified magnet repair facility.