Magnetic drum screen

When you hear a “magnetic drum screen,” many people immediately imagine an ordinary separator where ore is poured into it, and a magnet pulls out the pieces of iron. But if you think like that, then you can make a big mistake when selecting or exploiting. In fact, this is a complex unit where screening and magnetic separation must work as one system, and not just coexist in one housing. A common mistake is to assume that the main thing is the strength of the magnet, and the rest is the shell. No, the design of the drum, the angle of inclination, the rotation speed, even the shape of the sieve cells - all this affects the final extraction. I myself saw how at one factory they installed a powerful magnet, but neglected to calibrate the gaps between the sieve and the drum - as a result, the small class was carried away with waste rock, although according to the passport the extraction should have been 95%. It’s these nuances that are not written in catalogs that I want to talk about.

Design: where the problems lie

If you take it apart, the key node is itselfmagnetic drum screen. Not just a shaft with a tensioned sieve, but a coaxial assembly, where the magnetic system is rigidly fixed inside, and the outer drum with the sieve rotates. The gap here is a delicate matter. Too small - the material sticks and clogs the cells. Too large - the magnetic field is 'sprayed', loses its gradient, and small ferromagnetic particles simply do not have time to be attracted. The optimal clearance is often selected empirically for a specific ore. I remember that for oxidized quartzites I had to increase it by 1.5 mm against the standard, otherwise the wet fine fraction would tightly seal the surface.

The sieve is a different story. The mesh is a classic, but for abrasive materials it wears out quickly. Molded polyurethane panels with slotted holes last longer, but are more difficult to clean if the material is sticky. It also happens that designers save on a system for washing or vibrating the sieve. Without it, especially when processing construction waste or slag, the cells become blind within a shift. You have to stop it and clean it manually - downtime, money down the drain.

And a magnetic system. Neodymium magnets are, of course, the standard now. But their arrangement - pole, multi-pole, in a checkerboard pattern - determines not just the strength, but the nature of the 'capture'. For rough cleaning of large scrap, a simple axial arrangement is suitable. But to extract finely dispersed magnetite from sand, you need a multi-pole field to create a rapidly changing field - the particles have time to remagnetize and 'bounce', separating from the flow. This is a fine tuning that not every manufacturer does well.

Application scenarios: beyond enrichment

The classic is, of course, mining. Pre-enrichment of iron ore, extraction of magnetite from tailings. But nowmagnetic drum screenI see it more and more often at other objects. Scrap metal recycling, for example. The task there is not just to pull out the iron, but to separate it from non-ferrous metals, plastic, and rubber. The drum works like a screen, sifting according to size, and at the same time the magnet pulls out the ferrous metal. An important point is the feed speed. If you fill it with a flow, the magnet will not have time to “grab” everything, and the screening becomes ineffective - the material simply flies by without being sifted.

Another direction is the cleaning of inert materials on construction sites. Crushed stone, sand, and ASG are often contaminated with reinforcing scale, bolts, and other metal debris. Here the device operates under more severe conditions, with a high load and often without preliminary screening. Wear is higher, but the requirements for product purity are lower. The main thing is to protect the magnetic system from vibration and shock. I have seen cases where, due to constant shaking, the magnet fastenings inside the drum became loose, they began to hit the casing - even to the point of destruction.

An interesting case was with the processing of slag. The material is complex, heterogeneous in size and moisture content. The standard screen became clogged, and the magnet became covered with a “fur coat” of small particles. The solution was found in a combination: a preliminary dewatering vibrating screen was installed, and only then the material was sent to a magnetic drum. And the drum itself was equipped with a constant self-cleaning system - a scraper that removed the adhering layer directly during operation. Productivity dropped, but performance stability and product purity increased significantly.

Experience with LONGI equipment

With equipmentLONGI Corporation (https://www.ljmagnet.ru) encountered more than once. A company that has been in the business since 1993, and you can feel it. Theirmagnetic drum screenseries, it seems, STV, is remembered for its modular design. The magnetic block could be removed for maintenance without disassembling the entire drum - a small thing, but in practice it saves hours. And the screen panels were attached not with bolts, but with clips - replacement in 15 minutes, not half a day.

But there were also negative experiences, to be honest. At one of the projects, their apparatus was installed to process recycled aluminum slag. The material turned out to be too dusty and electrostatically charged. Small non-magnetic particles 'stuck' to the drum due to static, clogging the screen. Magnetic separation worked perfectly, but screening did not. Together with their engineers, we had to modify it - we installed an ionizing bar to remove static and increased the vibration frequency of the sieve. It worked, but the commissioning time was behind schedule.

Overall, the impression from LONGI is that it is a solid, down-to-earth producer. They don’t chase super-innovations, but they work well on basic designs for different conditions. Their website shows that they cover the full cycle - from development to serial production of more than 4,000 units of equipment per year, with their own design bureau and production in Fushun. This is important: when the manufacturer does everything himself, from casting to assembly, it is easier to achieve consistency of components and quickly make changes if the project requires it.

Selection of parameters: what to ask the supplier

When you askmagnetic drum screen, it is not enough to simply say 'needed for ore'. You need to provide a technical specification with details. The first is the granulometric composition of the diet. Not just '0-50 mm', but preferably a distribution curve. If there is a lot of 'fines' below 5mm, pre-screening or a different screen configuration may be needed. The second is the content and nature of the magnetic fraction. Magnetite, hematite, steel scrap? The layout of the magnets and the field strength depend on this. Third, moisture and stickiness. For wet materials, a heated drum or a vibration system with shock pulses is often needed to prevent sticking.

Productivity is often forgotten. It is indicated for ideal conditions. In practice, you need to reserve at least 15-20%, especially if the food is unstable in composition. And be sure to clarify how the device behaves when overloaded. Some models simply “choke” - the material stops sifting and starts to drain. Others are more tolerant, but then the purity of the magnetic product suffers.

And the issue of service. How often should the sieves be changed? How to clean the magnetic system? Are there built-in diagnostic systems - bearing temperature sensors, vibration sensors? This is not a whim, but a matter of uninterrupted operation. In remote areas, downtime due to a failed bearing can cost tens of times more than the cost of the sensor.

Thinking out loud about technology development

I look at current trends, and it seems thatmagnetic drum screengradually becoming 'more intelligent'. Sensors are built in that analyze the composition of the tailings flow in real time and use it to adjust, for example, the rotation speed or inclination angle. This is no longer science fiction, but a serial option for some Western manufacturers. In our country, more often than not, everything is configured manually, based on the results of periodic testing.

Another direction is combined methods. I have seen prototypes where air classification or even an X-ray fluorescence analysis sensor is added to magnetic separation to filter out particles with certain elements. The result is not just a separator, but a multifunctional sorting complex. But it’s expensive and complicated, and it’s too early for the mass market.

What's really missing is more attention to energy efficiency. The drum drive, the vibration system, and sometimes the cooling of the magnetic system are all energy consumers. Small optimizations, for example, the use of frequency converters for soft starting and load regulation, can provide significant savings over the course of a year. But often when purchasing, they look only at capital costs, and operating costs fade into the background. In vain.

Finally, going back to the beginning:magnetic drum screen- a device that only seems simple. Its effectiveness consists of dozens of details, from the quality of the assembly to the technologist’s understanding of the process in which it is built. And experience, as always, is the best teacher - sometimes bitter, like that case with a clogged sieve, but invaluable for future projects. The main thing is not to be afraid to dig deep and ask uncomfortable questions to suppliers, even such trusted ones as LONGI. After all, the equipment must work, and not just sit in the workshop.