Degausser

When you hear “demagnetizer,” many people immediately imagine a simple device for removing magnetization from an instrument. But in the mining industry, especially in beneficiation, everything is much more complicated. A common mistake is to think that the main thing is to create an alternating field and everything will resolve itself. In fact, if you do not take into account the type of ore, its humidity, particle size distribution and even the temperature in the workshop, you can get the opposite effect - not demagnetize, but magnetize the material even more strongly. I went through this myself.

From theory to workshop: where the pitfalls lie

The institutes teach basic principles: a damped alternating field destroys the domain structure. But you arrive at the factory, and there is a conveyor belt with wet magnetite ore, on which, after crushing and separation, small ferromagnetic particles remain. They create problems - they stick to the rollers, wear out the belt, and clog the sieves. Theoreticaldegausserfrom the textbook is often useless here. It is necessary to select not only the amplitude and frequency, but also the shape of the pulse and the angle of installation of the coil relative to the flow of material. Sometimes it is not a standard sine wave that is more effective, but a specially generated pulse signal.

I remember one incident at a plant in Kuzbass. We installed a standard demagnetization device after the drum separator. Everything seems to be according to the instructions: the power is sufficient, the gap is maintained. But the effect is negligible. They began to figure it out. It turned out that the ore after wet magnetic separation retained its residual magnetization non-uniformly - large grains were almost neutral, and the small fraction, the same “magnetic dust”, turned out to be highly charged. The standard field did not “take” it. It was necessary to develop a two-stage system: first, a powerful pulse to knock down the main domains in large particles, then a gradually decaying field for fine purification of the fine fraction. It was not a finished product off the shelf, but actually a piece of work.

Another nuance is cooling. When the device operates at full power 24/7, the coil heats up mercilessly. Overheating leads not only to insulation failure, but also to a drift of magnetic field parameters. As a result, by the end of the shift, the efficiency of the installation may drop by 20-30%. Just installing a fan is not enough. In the dusty conditions of processing plants, this is death for equipment. A well-thought-out closed liquid cooling system is needed, but it also requires regular maintenance, otherwise salts from the water will clog the heat exchanger. The balance between reliability, efficiency and maintenance complexity is a constant quest.

LONGI equipment: an inside look at the practice

When we talk about serious industrial equipment, we cannot fail to mention proven manufacturers with deep expertise. Here, for example, is the LONGI corporation (official website:https://www.ljmagnet.ru). This company is not a newcomer, it has been operating since 1993 and has grown into the largest enterprise in the development and production of mining equipment. Their Fushun plant has 140,000 m2 of space and more than 1,200 employees, most of whom are engineers and technologists. The scale is impressive: up to 4,000 pieces of equipment per year. This is not a garage production.

What's important about their approach? They don't just sell a ?box? calleddegausser. Their engineers first deeply analyze the customer's process chain. I had experience interacting with their specialists on a project for an apatite-nepheline ore processing plant. They sent a technologist who spent a week studying our process: from the installation location of the future apparatus to the chemical composition of the pulp. As a result, they proposed a non-standard solution - a demagnetizer with an adaptive field adjustment system depending on the current electrical conductivity of the pulp, which fluctuated greatly in our case. This was a level of customization that not everyone is ready for.

Of course, not everything is always perfect for them either. Once we ordered a batch of devices from them for demagnetizing steel balls in mills. Everything was clear in the specification. But when we received it and started it up, we discovered that the mounting brackets were not designed to withstand vibration from a running mill—a month later, cracks appeared. We had to urgently strengthen the structure on site. LONGI representatives responded quickly, sending reinforced parts and updating drawings for future orders. This case shows that even large and experienced manufacturers have room for improvements based on actual use. Theory and bench tests are one thing, but the conditions in the workshop are completely different.

Non-obvious aspects: what is not written in the passport

The effectiveness of demagnetization often depends on the preparation of the material. Let's say you need to demagnetize steel filings for remelting. If the chips are pressed into dense lumps, then the external field will weaken in the upper layer, and the core will remain magnetized. You have to either loosen the material first (which is not always possible), or use a combined method - for example, combining the influence of an alternating field with mechanical vibration of the tray itself. It's not easy anymoredegausser, but a whole technological unit.

Another subtle point is the residual magnetization of the device itself. It would seem like a paradox: the demagnetization device itself can become magnetized over time, especially its core and body elements. This gradually distorts the created field. Therefore, in high-quality industrial models, like the same LONGI, a periodic “zeroing” procedure is incorporated. own magnetic elements using an additional external circuit. But this procedure is often forgotten or ignored in the maintenance schedule, which then results in an incomprehensible drop in productivity.

In terms of energy consumption, there is also something to think about. A constantly running powerful coil is a big expense. Modern trends are intelligent systems that, based on a material flow sensor or its magnetic properties, turn on at full power only when necessary. But the introduction of such automation means an increase in complexity and price. For many businesses, this calculation (capital costs vs. savings on electricity) turns out to be negative, and they prefer the good old “always on” ones. devices. Choice is always a compromise.

Failures and lessons: when the demagnetizer did not help

I had a sad experience at a scrap recycling plant. The goal is to demagnetize large steel forgings before automatically sorting them. Installed a powerful stationarydegausserportal type. We skip the forging - everything seems to be clean. But the sensors on the sorting line still went off. It turned out that due to the large mass and complex shape of the product, eddy currents arose inside it, which themselves created a secondary magnetic field, and it screened part of the external influence. In fact, only the surface was demagnetized. It was not possible to overcome this phenomenon using standard methods - it was necessary to change the entire technological chain and heat the forgings before processing in order to increase the electrical resistance of the steel and reduce the effect of eddy currents. Expensive and ineffective. Sometimes the task is beyond the capabilities of standard equipment, and we must admit that there is no universal solution.

Another case is when trying to use a degausser to protect measuring equipment from interference. We placed the apparatus on a conveyor that feeds ore into the crusher. The interference from magnetized pieces has indeed decreased, but a new problem has appeared: fine metal dust, which previously settled in the bunkers, has lost its “stickiness” after demagnetization. and began to rise into the air, worsening working conditions. We had to additionally design the aspiration system. It turned out that they solved one problem and created another. This is a classic story for any technologist - any intervention in the process has a chain reaction of consequences.

It is from such failures that real understanding is born. Now, before recommending the installation of a demagnetizer, I always ask a bunch of clarifying questions: not only about the material, but also about what happens to it before and after in the technological chain. Sometimes the right solution is not to install an additional apparatus, but to modify the previous stage - for example, replacing the crusher lining material or changing the magnetic separation mode in order to minimize the problem of residual magnetization itself. Prevention is often cheaper and more reliable than dealing with the consequences.

Looking to the Future: Where Technology is Heading

Now I see an interesting direction - combining functions. The same LONGI, judging by some of their developments, is experimenting with devices that can work bothdegausser, and as a low-field magnetic separator, depending on the settings. This is logical: one hardware, two different tasks. But the complexity of managing and configuring such hybrids increases by an order of magnitude. Operators of completely different qualifications will be required, not just “turn on and off”, but capable of working with the software interface and understanding the physics of the process.

Another trend is miniaturization and specialization for robotics. In automated warehouses where manipulators work with metal workpieces, even weak magnetization can lead to parts doubling or inaccurate positioning. We need compact, built-in demagnetizing heads, possibly based on high-frequency fields. This is no longer about the mining industry, but there is a market, and it is growing.

Ultimately, at least the operating principledemagnetizerand has not changed since Faraday, its embodiment is constantly evolving. The main driver is not abstract technical progress, but specific requests and production problems. Whether it's extending the life of conveyor belts at a mining and processing plant or ensuring the cleanliness of silicon wafers at a microelectronics plant. Therefore, the most important skill for an engineer in this field is not the ability to read specifications, but the ability to understand what the customer actually needs, often even contrary to his original technical specifications. And sometimes the correct answer is: “You don’t just need a degausser, you need to reconsider this entire area?” But this is only said by those who have themselves gone through similar situations and are not afraid to get their hands dirty with machine oil and ore dust.