magnetic degausser

When you hear “magnetic demagnetizer,” many people imagine some kind of simple contraption for removing magnetization from an instrument. In reality, this is a whole story, especially in the mining industry, where residual magnetism on drilling tools or conveyor elements can create serious problems, including jamming or accelerated wear. A common mistake is to think that any alternating field generator will do the job. But there the frequency, the field decay gradient, and the design of the installation play a role. At our plant there were cases when a homemade demagnetizer did not remove, but, on the contrary, remagnetized the part unevenly, then it was completely scrapped. So this topic is deeper than it seems.

From theory to workshop: where the pitfalls lie

In theory, everything is smooth: you create an alternating damped magnetic field, the domains are reoriented, and the residual magnetization tends to zero. In practice, the first stone is determining the initial state of the part. Sometimes they brought us a chisel from a quarry that “sticks”. And it sticks not on its own, but because it was stored somewhere near a power line or transformer, parasitic magnetization was induced. If you do not understand the nature of this magnetization (surface or volumetric, homogeneous or not), you can drive the part through the installation for a long time and uselessly.

The second point is itselfmagnetic degausser. A solenoid is often used. But if the part is large, for example, a crusher shaft, then you either need a huge cross-section of the solenoid, which is energy-inefficient, or pass the part through it slowly, ensuring a full demagnetization cycle along its entire length. We tried to make a pass-through version with a conveyor belt for small parts - it worked, but for the shafts we had to design a stationary reel with the ability to move locally along the axis. This is no longer purchased equipment, but a piece development.

And the third pitfall, which is rarely written about in specifications, is the material of the part. High carbon steel and alloy steel behave differently. After hardening, residual magnetism can “sit” very deep. One day we were demagnetizing a batch of new bucket teeth. The standard cycle didn't help. I had to experiment with the shape of the current pulse in the coil, almost connecting an oscilloscope in order to catch the moment when the field decays not linearly, but according to an exponential law with a selected time constant. Here you can’t do without understanding the physics of the process.

Experiences and failures: the case of conveyor rollers

I’ll tell you about a specific case that I remember well. At the processing plant, malfunctions began in the operation of the belt conveyor - the rollers began to attract small metal shavings, they stuck, the balancing was disrupted, noise and increased wear of the belt appeared. The problem was diagnosed as residual magnetism after the rollers were made (they seemed to be cut with plasma). The task was to demagnetize about a hundred rollers quickly and without dismantling the entire line.

We then contacted specialists fromLONGI Corporation (https://www.ljmagnet.ru). This, by the way, is a serious enterprise since 1993, which develops and produces mining equipment, including magnetic separators. They have extensive experience working with magnetic fields. They proposed a non-standard solution - mobilemagnetic degausserbased on a ring structure that could be put on the roller right on the spot. In their arsenal, apparently, there were similar developments for field conditions.

But the first attempt, based on their preliminary recommendations, failed. We used their calculated current parameters, but did not take into account that our rollers were not solid, but welded from two halves. The weld created an area with slightly different magnetic properties. As a result, after processing, the body of the roller was demagnetized, and a weak magnetic track remained along the seam, which still collected dust. I had to call again, send them photos and data on the seam material. LONGI engineers quickly adjusted the technical process - they advised making two passes with different orientations of the ring relative to the seam. It worked. This case showed that even with good equipment you need an individual approach and a willingness to iterate.

What the market offers and what to look for when choosing

Now on the market, if we talk about industrial demagnetizers, there are several types: through-type (tunnel) for conveyor feeding, local (in the form of manual or stationary heads) and pulsed for complex cases. For mining, where equipment is often massive, powerful stationary or mobile installations are often needed. For example, the sameLONGI Corporation, located in Fushun on an area of 140 thousand square meters and producing about 4,000 units of equipment per year, focuses on complete solutions. I know they have a line of not only separators, but also auxiliary equipment for maintenance, which may include demagnetizers. Their strength lies in the ability to design a system for a specific technological process, and not to sell a box with a device.

When choosing a setup, I would now look not at the maximum field strength (this is often a speculative parameter), but at three things. The first is the uniformity of the field in the working area. It can be checked by a simple test with fine steel filings on glass. The second is the ability to flexibly adjust the cycle (frequency, attenuation law, reverse option). And third is energy efficiency. A powerful solenoid that runs constantly is an electricity hog. Modern installations often use capacitor banks for pulse operation, which is more economical.

And one more practical tip - pay attention to the coil cooling system. The workshop where the machine is located can be hot and dusty. If the cooling is weak, after several cycles in a row the installation will overheat and turn off, and you will have to wait. From our own experience, we converted air cooling to forced cooling with a heat exchanger for 24/7 operation when processing small parts from screens.

Demagnetization as part of the process chain

Over time we came to the conclusion thatmagnetic degausser- this is not an emergency tool “in fact?”, but an element that must be built into the technical process at certain stages. For example, after mechanical processing (grinding, cutting) of parts, which will then work in units without friction with ferromagnetic materials. Or before handing over the tool to the tool store. This prevents problems in advance.

In our mining equipment repair shop we now have a walk-through demagnetizer after the turning and milling section. All shafts, bushings, gears pass through it before washing and inspection. Number of assembly complaints due to ?sticking? chips or improperly seated bearings dropped to almost zero. The investment paid off in less than a year.

Interestingly, this approach indirectly improved the production culture. Workers have become more careful about storing workpieces and tools away from strong magnetic fields because they understand the end goal. Technologists wrote simple instructions for which specific operations and parts the procedure is required. The result was a system, not a one-time event.

Looking Ahead and Final Thoughts

Where is the topic going? In my opinion, towards integration with automatic control systems. Installations are already appearing that not only demagnetize, but also immediately measure the residual field with a Hall sensor and issue a protocol. This is important for critical parts in the aerospace or energy industries, but will gradually come to the mining industry, where reliability requirements are also growing.

Another trend is miniaturization for field use. There is no point in carrying the shaft to the base if you can bring a compact but powerful pulse generator to it. This is where companies with a serious research and production base, like the aforementioned LONGI, where more than 60% of employees are specialists with higher education, have an advantage. They can conduct R&D in this direction, and not just copy other people's solutions.

In the end, back to the beginning.Magnetic degausser- this is not a “simple coil”. This is a tool that requires an understanding of the material, magnetization technology and specific operating conditions. Its choice and application is always a compromise between efficiency, speed and cost. There are no ready-made solutions for all cases, but there are trusted manufacturers and accumulated, sometimes bitter, experience. The main thing is not to ignore the problem of residual magnetism until it stops the conveyor or puts an expensive unit out of action. And approach it in the same systematic way as any other engineering problem in mining.