types of magnetic separators

When they talk abouttypes of magnetic separators, they often start with a dry classification from a textbook - drum, suspended, roller... But in practice, when you are faced with a choice for a specific factory or quarry, everything looks different. The main question is usually not “what type exists?”, but “what type will survive here for six months?”. I have seen many times how they bought an expensive imported system with a bunch of automation, and after a month it was covered in sticky ore and clay and simply stopped rotating. Or vice versa - they placed a simple hanging magnet over the tape, and it caught 90% of the metal, because the installation location was correctly calculated. This is what I want to talk about - not about theory, but about how these types behave in real conditions, adjusted for wear and tear, the human factor and the economics of the process.

Drum separators: workhorses and their hidden problems

Perhaps the most common type for dry separation. It seems that everything is simple: a rotating drum, a magnetic system inside, material fed from above... But here are the nuances. If we are talking about a strong field for extracting ferromagnets, then a design with a fixed magnet inside is often used. The problem starts when the material is damp or dusty. It sticks to the drum, gets clogged in the gaps, and efficiency drops catastrophically. You have to either install scrapers, which adds a vulnerable unit, or organize regular manual cleaning - and this is simple.

One incident at a coal processing plant is well remembered. We installed a separator with a conventional ferrite system. Everything seemed to match according to the passport. But the local ore had a fine magnetic fraction, which created an abrasive “belt”. on the surface of the drum. The drum wore unevenly, the gap changed, and after eight months the pitch dropped by 30%. We switched to a system with rare earth magnets from the same manufacturer -LONGI Corporationoffers just such solutions - wear has decreased, but the cost, of course, is different. I had to consider what was more profitable: changing the drum more often or investing in a magnetic system once. As a result, we agreed on a hybrid version for different sections of the chain. Details of their designs can be viewed athttps://www.ljmagnet.ru— they have both drum and roller models, and with different types of magnetic cores.

Another point is the settling of dust inside the drum itself. Not all factories have an aspiration system, and magnetic dust gradually “short-circuits” field. I saw how technicians simply blew out the device with compressed air once a quarter, and the performance increased again. This is to the question that the type of separator is not only its design, but also the prescribed maintenance regulations, which are often ignored when purchasing.

Suspended separators (magnetic pulleys and plates): simplicity that requires intelligence

This is where a lot of misconceptions lie. It seems like hanging a magnet over a conveyor and the job is done. In fact, 80% of the efficiency here is determined by the distance from the magnetic surface to the layer of material and the speed of the belt. A standard mistake is to hang the magnet too high “so as not to interfere.” As a result, it only catches nails and large bolts, and allows small chips and scale to pass through, which then kills the crushers.

Worked with engineers fromLONGIon a project for a processing plant in Kazakhstan. The task was to protect the jaw crusher from metal. The original design proposed a powerful overhead separator directly above the feed conveyor. But we saw on the spot that the material was not coming in an even layer, but in ridges, plus there was vibration. A simple hanging magnet would not work well here. Changes were made: a magnetic pulley was installed as a drive drum at the end of the conveyor. This solution, by the way, is often overlooked. A pulley is the same separator, but built into the structure. The metal is attracted to its surface and thrown off the bottom side, and the clean product flies further along the trajectory. Efficiency jumped because the gap was minimal—actually the thickness of the tape.

Important practice tip: For suspended slabs, always look at the design of the relief system. There are self-discharging ones, and there are manual cleaning ones. If the material flow is continuous and there is a lot of metal, manual cleaning is the way to stop the line. Automation is needed here. But automatic ones also have their own problem - a stuck piece may not come off if it is “grabbed?” field along the entire length. You have to combine it: first, a powerful magnet catches everything, then the field is locally turned off to reset. Such systems are already closer to high-gradient separators in complexity.

Roller and roller separators: for fine separations

This is the next level, when it is necessary to separate not just “metal/non-metal”, but different magnetic minerals among themselves. For example, extracting magnetite from ilmenite or purifying quartz sands. The principle is based on the different magnetic susceptibility of particles. The accuracy of the settings is critical here: roll rotation speed, field strength, feed angle.

I remember the complex commissioning process at a glass raw material production plant. There was a multi-roller separator. The goal is to remove even traces of iron from the sand. According to the passport, everything should have worked. But at the exit every now and then “dirty” ones slipped through. parties. They began to figure it out. It turned out that the moisture content of the sand at the inlet fluctuated within 3-5%, which changed its flowability and the nature of its movement along the rolls. Dry sand was “bouncing”, wet sand was sticky. Not a single instruction took this into account. We had to empirically select the angle of inclination of the feeding tray and the rotation speed for different conditions on the spot. This is the case when the type of separator is chosen correctly, but its integration into the process chain requires fine tuning to a specific, often “non-ideal” one. material.

Companies that have been in the industry for a long time, likeLONGI Corporation, created back in 1993, usually have a bank of such solutions. Their specialists, who employ over 1,200 people, many with higher education, often face non-standard tasks. For example, when you need to design a separator for an existing cramped gallery, where there is no room for a standard design. Then hybrids are born - something between the drum and roller types.

High-gradient and magnetic fluid separators: when is purity needed down to the last particle?

This is already the major league, and the cost is appropriate. They are used where the price of the final product justifies the costs: in pharmaceuticals, in the production of high-purity powders, in the processing of electronic scrap for the extraction of rare metals. The principle is to create a non-uniform field of enormous intensity, which can trap even weakly magnetic or very small particles.

I worked with such a setup at a pilot site. Impressive, but maintenance is a science in itself. Magnetic systems are often based on superconductors; cryogenic systems are needed. Magnetic fluid separators require preparation of the carrier fluid itself. The slightest contamination and the separation efficiency drops. This is not “set it and forget it” equipment. This is a whole technological island with its own staff.

An interesting practical incident: such an expensive system can be killed... by ordinary dust. Not magnetic, but simply cement or coal. It clogs the matrices and channels through which the material passes. Therefore, preliminary preparation of the material (sifting, drying, sometimes even dust removal) for thesetypes of magnetic separatorsno less important than the choice of the device itself. Often a project fails precisely because this stage is underestimated.

What's the result? Selection criteria that are not written in catalogs

So, having gone through the main types, we can formulate several non-obvious selection rules. First: always analyze not only the material “as it ideally is?”, but also the material “as it will be on the line on Friday evening?”. With impurities, with humidity fluctuations, with wear and tear of upstream equipment.

Second: consider not the cost of the separator, but the cost of ownership. A cheap drum separator with ferrite magnets may require drum replacement once a year. Expensive with neodymium magnets - once every five years. But if the workshop is not able to carry out complex repairs, and you have to wait two weeks for specialists, then perhaps it is more profitable to replace it more often, but on your own.

Third, and most importantly: look for a manufacturer who will not just sell hardware, but will delve into the process. That's why they often turn to time-tested suppliers. The sameLONGI, with an area of 140,000 m2 and an annual production of approximately 4,000 units, is not just a factory. This is, in essence, an engineering center that can adapt a standard model to suit your conditions. They are the ones who will ask: “What is your source of metal mixing?” Is it common to get armor from an excavator? And based on this, he will recommend the type, power and even location.

Ultimately correcttype of magnetic separatoris the one that will solve your specific problem with minimal operational hassle. Sometimes it will be a monoblock, sometimes it will be a combination of a hanging magnet and a pulley. The theory provides a frame, but the house is completed on the spot, taking into account all the local ?but? and ?if?. It is this experience, full of cones at different objects, that is the most valuable when choosing.