Eddy current sorter

When you hear “eddy current sorter,” many people immediately think of a powerful magnet that pulls pieces of metal out of the waste stream. This, of course, is the basis, but if you delve into it, everything is much more subtle. A common mistake is to assume that the main thing here is the strength of the magnetic field. In fact, it is the frequency, tuning and understanding of what kind of material you are working with that is critical. You can install the most expensive unit, but if you don’t feel the material, the sorting will be so-so, and the rotor wear will be colossal.

From theory to workshop: where the pitfalls lie

In theory, everything is smooth: an alternating magnetic field induces eddy currents in conducting particles (nonferrous metals - aluminum, copper), which create their own field, are repelled from the rotor and fly off from the flow. But in practice, say, on an electronic scrap recycling line or an automobile shredder, the composition of the stream is always a surprise. Heterogeneity of sizes, humidity, the presence of films or contaminants on the surface - all this affects the effectiveness of repulsion.

I remember at one of the facilities they tried to isolate pure aluminum from a complex mixture after crushing engines. The sorter seemed to be working, but the yield of the target product was low. They began to figure it out. It turned out that the particles were not clean, but covered with a layer of oxides and varnishes - the conductivity decreased, the repulsive force was insufficient. I had to experiment with pre-drying and even a little abrasive treatment of the flow in order to “bare” it. metal. This is not a textbook thing, this is technological savvy.

Another point is adjusting the gap between the rotor and the conveyor belt. It would seem like a small thing. But if the gap is too large, the magnetic field weakens and small aluminum particles simply do not “feel” it. push. Too small - there is a risk of clogging, increased wear and the line stops altogether. You need to set this up not according to your passport, but on the spot, looking at a specific faction. Sometimes you literally remove it millimeter by millimeter until you see a clear, beautiful release into a separate bunker.

Equipment at work: selection and adaptation

There are many offers on the market, from European brands to Asian ones. Here it is important to look not at the beautiful numbers in the catalog, but at the rotor design, cooling system and maintainability. The rotor is the heart of the system. There are prefabricated ones, and there are monolithic ones. Prefabricated ones, in my opinion, are more convenient for maintenance - you can replace individual magnet segments without removing the entire axis. But even monolithic ones, if made with high quality, last for years.

By the way, about quality. For example, Chinese manufacturers. Previously, there were many questions about them, but now some companies have reached a very decent level. I'll take it as an exampleLONGI Corporation (https://www.ljmagnet.ru). ThisShenyang Scientific Electromagnetic Company LONGJI, founded back in 1993, has long been more than just a collector. They have their own serious production base in Fushun, more than 1,200 employees, most of whom are engineers and technologists. They don’t just copy, but actually develop equipment, including for the mining industry, where conditions are harsh. When you see their sorters in operation, it is noticeable that aspects such as dust protection, ease of replacing drive belts, and access to sensors have been taken into account. This speaks to the experience gained over years of real projects.

We implemented them somehoweddy current separatorat the solid waste processing site. The task is to remove aluminum cans and small non-ferrous metals from the flow after the drum screen. The equipment arrived complete, but the instructions were... standard. We had to select the optimal rotor speed ourselves for our specific waste composition (there were a lot of wet organic residues). At first they set low frequencies - there was not enough strength to throw away the stuck cans. They picked it up - small particles began to “jump over?” too far, past the bunker. We spent a week on calibration, but the result was worth it - the purity of the isolated aluminum increased to 92-94%. This is a good indicator for such a ?dirty? incoming flow.

Practical nuances and common mistakes

One of the most common mistakes during operation is ignoring the condition of the conveyor belt. If the belt sags or its tension is uneven, the distance to the rotor “walks”. The efficiency of separation drops catastrophically, and the operator may not immediately notice it. It is necessary to introduce into the regulations a shift check not only of the separator itself, but also of the supply path.

The second mistake is working without taking temperature into account. Inductors get hot, especially on intense lines. Overheating leads to a decrease in magnetic properties, and in the long term - to failure of the insulation. Good modern models, including the one mentionedLONGI, have built-in temperature sensors and an air or even water cooling system. But this does not eliminate the need to monitor the ventilation grilles - they simply become clogged with dust. I saw a case where, because of this, the sorter went into emergency shutdown in the middle of the shift until it was cleaned.

And thirdly, underestimating the preparation of the material.Eddy current separator- not a magic wand. If at the entrance there is an unclassified mixture from clay to large pieces of concrete, you should not expect a miracle. Preliminary classification by size (screening) and, preferably, drying are required. For small fractions (less than 5 mm), the efficiency of the eddy current method decreases sharply - here you need to look towards other technologies. This is a matter of building the entire technological chain, and not just purchasing one device.

Process economics: when is it really profitable?

The introduction of such equipment is always an investment. And you need to consider not only the cost of the device, but also the costs of electricity (especially when working around the clock), maintenance, and possible downtime. Payback directly depends on two factors: the volume of processed material and the cost of recovered secondary raw materials. If you have a flow of 5 tons per hour and you extract pure aluminum, which can be sold at a profit, then the machine will recover in a year and a half.

But there is also a hidden benefit. For example, improving the quality of other factions. By removing non-ferrous metal from the cullet or plastic stream, you increase the cost of these materials, as they become cleaner and more suitable for deeper processing. In addition, abrasive wear of the following equipment on the line (crushers, shredders) is reduced - metal inclusions are destructive for them.

The important point is versatility. goodeddy current sortermust have an adjustable rotor speed and, preferably, the ability to quickly replace the rotor itself with a model with a different pattern of magnetic poles. This allows you to adapt one installation for different types of raw materials: today we process a car shredder, tomorrow - construction waste, the day after tomorrow - electronic scrap. Flexibility is money.

Looking ahead: what can change

Technology does not stand still. Combined solutions are now appearing, where eddy current separation is combined, for example, with optical sorting or with sensors based on X-ray fluorescence analysis (XRF). This makes it possible not only to separate non-ferrous metals from non-magnetic materials, but also to separate the non-ferrous metals themselves - copper from aluminum, brass from zinc. While this is an expensive solution, it is already beginning to be used for high-margin flows, such as electronic scrap.

Another direction is intelligent control systems. Simple frequency converters are giving way to systems that automatically adjust operating parameters based on output sensors (say, the metal content in the sorted fraction). This reduces dependence on the human factor. But, frankly, it’s too early to completely trust automation - the eye and experience of the operator, who sees how the particles fly, is irreplaceable.

Overall,eddy current sorterFrom the exotic of 20 years ago, it has turned into a standard, almost obligatory element of a modern line for processing solid waste and secondary resources. The main thing is to approach its selection and operation without illusions, with an understanding of its real capabilities and limitations. This is a tool, and like any tool, it requires skillful hands and head. And when these conditions are met, it brings both real savings and a feeling of satisfaction from a well-established technological process.