Dry Magnetic Separator

When you hear “dry magnetic separator,” many people immediately think - well, a magnet and a drum, what’s so complicated about that? In fact, if you look into it, this is a whole story about granulometry, humidity, the trajectory of falling material, and even about how dust in a workshop can send the entire sorting scheme to hell. I myself worked with the installations for ten years, and I will say that the main misconception is that the separator supposedly works on its own. No, this is a system where every little thing affects the output concentrate. Especially in a dry process, where there is no water to smooth out flaws.

Where and why the dry method makes sense

Here, for example, are areas with water shortages - Kazakhstan, some parts of the Urals. Heredry magnetic separatornot just an option, but a necessity. But even there, not everything is clear. I remember that at one of the magnetite ore deposits they tried to install dry separation on material with a moisture content of about 4%. It would seem normal. But in winter, at subzero temperatures, this moisture was captured by an ice film on the particles, and the magnetic force simply slid without capturing. We had to fence off the supply air heating system - an emergency situation that will not be written about in the equipment passport.

Or another case is the processing of slag, where there are fine fractions, less than 0.5 mm. A dry separator based on such material begins to “dust” so that visibility in the workshop drops to zero, and efficiency drops along with it. Here we need not just separators, but entire complexes with aspiration and multi-stage separation. Sometimes saving on water turns into costs for a dust suppression and ventilation system. This is the very practical nuance that is often missed in theory.

By the way, about subtle factions. There is an opinion that the dry method is not suitable for them at all. Not really. I saw installations fromLONGI Corporation(their website, by the way, is https://www.ljmagnet.ru - you can look at the technical documentation there), which cope with a fraction of 0-1 mm. But there is a trick there - a special configuration of the magnetic system and the speed of rotation of the drum, which creates, as it were, an 'air cushion' for separation. But again, this only works with a perfectly uniform supply of material. Any blockage in nutrition - and that’s it, instead of concentrate you get a mixture.

Design: What's inside matters

If we take it apart, the key thing isdry magnetic separator- this is, of course, a magnetic system. Previously, there were many separators using ferrite magnets. Cheap, but the induction is rather weak, not an option for weakly magnetic ores. Now almost everywhere they have switched to rare earth magnets, neodymium-iron-boron. The force of attraction is different, you can work with a wider range of materials. But even here there is a pitfall - overheating. During prolonged operation at high speeds, the magnetic system may become demagnetized if cooling is not provided. I encountered this on one of the old samples; I had to introduce forced breaks in the cycle, which reduced the overall productivity of the line.

The drum is the second most important thing. Smooth or grooved? For large ore, from 5 mm, it is better to have a corrugated one - it better holds the material in the separation zone. But the corrugation is a place for small particles to stick; they must be constantly cleaned off, otherwise the efficiency decreases. For small fractions, as I already said, a smooth drum is preferable. And the drum coating material is not just “stainless steel”. Durability is important. On abrasive materials, ordinary steel wears out within a season. I saw solutions where special wear-resistant coatings were used, like those used in mining and processing equipment. The same LONGI in the descriptions on their website often emphasizes the materials used, and this is not without reason - they are specifically designed for mining equipment and know the specifics of wear.

And the third element, which is often underestimated, is the feed hopper and loading system. The material should be fed onto the drum in an even, thin layer. If the layer is thick, the magnetic field does not 'penetrate' it to the lower particles, and the valuable component goes into the tails. I adjusted the vibrating feeders myself to achieve this uniformity. Sometimes the problem was not even in the feeder, but in the material itself - if it is caked, in clumps, then no feeder will help. It was necessary to install an additional disintegrator in front of the separator. Each such addition means an increase in the cost of the circuit and new points of potential breakdowns.

Experience with specific brands and models

Worked with different equipment, both domestic and Chinese. From what I remember, the separators from the mentionedLONGI Corporation. The company, if we take their history (Shenyang Scientific Electromagnetic Company LONJI LLC was established in 1993), has been on the market for a long time, and this is felt in the approach. They don't just have hardware, but often components that are thought out to the smallest detail. For example, a system for quickly replacing magnetic drums on some of their industrial models. This is critical when switching to a different ore type or during routine maintenance. A downtime line is a direct loss.

But not everything is perfect for them either. Once they installed a separator for the enrichment of iron ore concentrate. According to the passport - productivity is 15 tons per hour. In practice, we reached 12, and even then with a stretch. Why? The material was wetter than the raw material supplier had stated and it began to stick inside the hopper. I had to modify it myself - install additional vibrators on the walls of the bunker. The representatives of the plant themselves, when contacted, said: 'Yes, for material with a moisture content above 2%, modification of the feeder is necessary.' It is this moment - knowledge of the boundary conditions of equipment operation - that distinguishes just a supplier from a normal manufacturer. It’s good that they at least honestly admitted this and made recommendations.

Another point regarding brands is the availability of spare parts. With equipment from large, but purely Chinese manufacturers, of which there are many on the market, there is a problem: a bearing assembly of a non-standard size breaks, and you wait a month for delivery. Companies with history and representative offices like LONGI (they, by the way, have a total production area of ​​140,000 m2 and more than 1,200 employees) often have a spare parts warehouse, if not in the country, then in the region. This reduces the risk of prolonged downtime. For production, where every ton of concentrate counts, this is a powerful argument.

Typical errors during operation and installation

The most common mistake is incorrect installation relative to other units.Dry Magnetic Separatoroften placed at the end of the technological chain, after crushers and screens. But if it is installed without taking dust into account, all this dust will settle on neighboring equipment, which can lead to breakdowns. I saw a workshop where the separator was located close to the control panels - after six months, all the electronics failed due to metallized dust.

The second mistake is saving on the foundation. A rotating drum separator creates vibration. If you place it on a light base, over time it will loosen itself, backlashes will appear, and the alignment of the shafts will be disrupted. There will be noise, increased wear, and eventually the drum will rupture. When installing, you should always look at the manufacturer's recommendations for the weight of the foundation. For serious companies that develop and produce mining equipment as their main profile, this data is always clearly stated in the manual.

Third, neglect of staff training. The operator must do more than simply press buttons. He must determine by the sound and appearance of the product that comes out that the process has gone wrong. For example, if clearly magnetic particles appear in the tails (they can be seen by the characteristic “brush”), it means that either the speed of the drum has decreased, or the gap has become clogged, or the magnetic system has weakened. A trained person will notice this immediately and correct it. No - the marriage will be driven away for weeks. By the way, companies with a large staff of engineers (like LONGI, where over 60% of the staff have higher education) often have installation supervision and training services, and they should not be neglected.

Where technology is heading: a view from the shop floor

Nowadays there is a lot of talk about 'smart' separators, with sensors and automatic adjustment of parameters. I have seen prototypes where optical sensors analyze the composition of the tails and change the rotation speed or feed angle in real time. It sounds great, but in the conditions of a mining and processing plant, where there is an eternal suspension of dust in the air, such optical systems quickly fail. Reliability is still poor. It seems that the near future does not lie in complete robotization, but in improving self-cleaning systems for drums and magnetic systems, as well as in increasing maintainability. So that key components change in hours, not days.

Another trend is hybrid solutions. Not just a dry separator, but a combination, for example, of air classification and magnetic separation in one housing. This allows particles to be more clearly separated not only by magnetic properties, but also by density and size. For complex, difficult-to-process ores, this could be a breakthrough. But again, the complexity of the design increases significantly, and hence the price and maintenance requirements.

In the end, back to the beginning.Dry Magnetic Separator- This is far from a primitive unit. This is a tool whose effectiveness is 30% determined by the quality of manufacturing and 70% by the correct integration into the technological process, taking into account all the little things like humidity, granulometry and dust suppression. And when choosing it, you should look not only at the numbers in the passport, but also at how much the manufacturer understands these nuances and is ready to support not just sales, but the solution of real production problems. Like those who have been in this business since '93 and make 4,000 pieces of equipment a year, they usually have something to say other than the price tag.