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Hey Prairie Dawg, “Let’s talk magnets in mining.”

Prairie Dawg Practical

by Tim Holmberg

Why in the world would I need a magnet in my mining or aggregate producing operation? Is this a spoof or something serious I need to look further into? What kind of magnet(s) would I be looking at to install? Where would I use such a thing and for what?

Okay, let’s get serious about magnets and how they can truly save thousands of dollars of valuable equipment from being damaged and, most importantly, valuable production downtime and contractual deadline penalties. Wow, I guess these “little” guys are somewhat valuable to an organization. But wait a minute – how do little magnets like those on my refrigerator also save my mining production equipment? Are the magnets we are referencing today really the little flat rectangular guys holding up the pictures or advertising the local pizza parlor? Although the magnetism concept is similar, that’s about it. The magnets we will be writing about are not ones you could even think about lifting by hand, let alone with a small-scale forklift.

Believe it or not, these bare, permanent magnets can weigh in at 1 to 5 tons and have to be suspended and anchored to keep them from swinging when they make contact with a piece of metal. Usually the magnet is suspended over a transition point, like the end of a conveyor, where the material is actually leaving contact of the head pulley zone. As the material free-falls, it’s easier and there are better odds the magnet will actually grab the metal that may otherwise get into delicate operating equipment, such as a cone crusher. Having what is referred to as an “uncrushable” going through a cone crusher will cause extreme damage each time it passes through.

Did I just say “uncrushable”? What exactly is an uncrushable piece of metal or tramp iron? An uncrushable item may be a loader tooth that has fallen off and was later realized to be missing. Imagine trying to figure out where the loader has been or how many different piles and places it scooped from during the day.

Oops, there it is – did you just here that clank? There it is again. I guess we now know where the loader tooth is – circulating through the crusher, making its seventh pass since it went missing off of the loader.

But back to the magnet. Now you can see that having a magnet grab and keep this dangerous object from wrecking your high dollar machine’s main bearings (or whatever other weakest part it hits first) is valuable.

Often there are many pieces of rogue metal, which is why having just one permanent magnet won’t ever be enough. The metal they collect eventually plugs up the magnet’s surface. Now, whatever makes its way by can no longer be grabbed if the static magnet is full. This is where the automation part of the magnet comes in – when you have more metal coming through the system than can logically be handled safely.

Having an added feature or upgrade is one in which you never need to worry about keeping the one clear of excessive metal plugging up the surface. It features a rotating conveyor belt with stainless steel paddles or cleats that carry the metal beyond the magnetic zone and then slings it away, off to the side of the conveyor belt.

These magnets are referred to as self-cleaning permanent magnets and are an absolute necessity if an operation is recycling concrete material with rebar imbedded within the concrete. I have watched these self-cleaning permanent magnets fill up a 20-foot scrap metal dumpster in under a day’s time. This is often a tangled mess of scrap metal that can otherwise create many customers a nightmare without this unique invention.

With all this automation and added magnetic strength being closely introduced to surrounding conveyor components, these areas could become problematic. But now knowing what we know, equipment manufacturers have learned how to evolve these zones by using stainless steel components so as not to compete with the magnet and what it needs to remain being good at – attracting fugitive metal from the product.

There is one more upgrade option to magnets: turning the permanent-style magnet into an energized magnet or self-cleaning electromagnet. These top-of-the-line magnets can be designed based on the burden depths of the material traveling over the conveyor system and still be strong enough to grab that nasty uncrushable item, bringing it up from deep within the material it was hidden in – once more saving a machine from major destruction or breakdown. So yes, these “little” magnets (in comparison to the size of the equipment they operate near) are extremely valuable in the duties they perform day in and day out. I hope by now, every time you see a little magnet holding up a picture or directing you to the local corner hangout, you’ll get a little chuckle thinking about how this concept is helping build and maintain our infrastructure around us.

If you enjoy these random aggregates and quarrying equipment-based subjects, tune back in for more topics to come. Send me a subject or topic you would like brought to light and any associated questions you would like to have discussed and I will gladly provide my best answer based upon my specific point of view and personal experience.

Questions or comments? Email Tim Holmberg at or visit .

Write me a letter and we will send you a T-shirt or ball cap:

Tim Holmberg / 2915 Idea Ave. / Aberdeen, SD 57401


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