ferrite steel

When they talk aboutferrite steel, many people immediately think of laboratory samples or electronics. But in our business - the production of heavy mining equipment - everything is different. Here this material works under conditions that few people imagine: vibration, shock loads, temperature changes and constant exposure to abrasive dust. A common mistake is to assume that the main thing isferrite steel- this is the maximum magnetic induction. Yes, it is important, but if the material does not withstand mechanical loads, the entire system fails. On ourLONGI CorporationThere was a case when a batch of magnetic separators showed excellent results on a test bench, but after three months of work at the enrichment plant, problems began. It turned out that at low temperatures in the quarry, the ferrite structure became brittle. We had to revise the entire heat treatment technology.

From theory to practice: why composition is just the beginning

Everything is beautiful in the textbooks: I determined the chemical composition, carried out heat treatment, and obtained the necessary magnetic properties. In reality, at our plant in Fushun, even two melts with the same nominal composition after rolling and annealing can behave differently. It all comes down to details, which are often not specified in the standards. For example, the cooling rate after homogenization. For a long time we could not achieve consistency in batches for drum separators. The coercive force indicators jumped by 10-15%. They began to figure it out and track each stage. It turned out that the problem was uneven cooling of large-section workpieces in the workshop - one side cooled faster due to a draft. It would seem like a small thing. But it is precisely because of such little things that the difference between a good and a defective magnetic core arises.

Another point is the influence of mechanical processing. Cutting, drilling, milling - all this introduces internal stresses into the surface layerferrite steel. These stresses can locally change magnetic permeability. We noticed this when we tested cores for new powerful electromagnets for lifting devices. After mechanical assembly, the performance dropped. It was necessary to introduce an additional operation - low-temperature annealing after all mechanical operations. This increased the cost, but it ensured that each unit assembled atLONGI Corporation, will work at the passport values.

People often ask why we don't switch to more modern amorphous or nanocrystalline alloys for all equipment. The answer is economics and reliability. For 90% of applications in mining equipment - in the same separators or magnetic traps - properly processedferrite steelprovides an optimal balance of cost, durability and maintainability. Our engineering department, where more than 60% of employees have higher education, is constantly researching new materials, but a massive transition is often not justified. The new material must not only perform better in the laboratory, it must survive a -40°C quarry and be compatible with existing repair infrastructure.

Case from the workshop: a failure that taught more than success

I would like to talk about one specific project that almost failed due to underestimation of the material. The discussion was about the development of a high-intensity magnetic separator for wet enrichment. The design required the creation of a powerful and compact magnetic field. We chose one of the grades of electrical steel with seemingly ideal loss characteristics. A prototype was made. In factory tests, it showed fantastic efficiency - 20% higher than its analogues.

But when the separator was sent for testing to an operating enterprise - an enrichment plant in Kemerovo - problems began. After two weeks of continuous work 24/7, operators began to complain about a drop in efficiency. The unit was disassembled. It turned out that in the aggressive environment of the pulp (a mixture of water, ore and reagents) intense corrosion began on the surface of the magnetic system. The protective coating, which worked perfectly in dry separators, did not hold up here. The corrosion layer created an additional non-magnetic gap, which sharply reduced the field strength. This was a classic case of focusing on magnetic propertiesferrite steel, but forgot about corrosion resistance in a specific environment.

A solution was found, but it turned out to be complex. It was necessary not only to change the grade of steel to a more resistant one (which increased the cost), but also to completely revise the design of the unit in order to minimize contact with the pulp, and to develop a new multi-layer protection system. This experience is now a mandatory training case for our young engineers. It clearly shows that a material is not just numbers in a specification, it is behavior in real, often non-ideal conditions. Now any of our new projects for wet environments undergo mandatory long-term corrosion tests not only in salt spray, but also in a real pulp simulator.

Interaction with other components: a system, not a part

Magnetic material never works on its own. Its characteristics directly depend on how it is assembled, on the design of the yoke, on the quality of the insulation between the packages, even on the method of fastening. In our production area of ​​140,000 m2, we produce more than 4,000 pieces of equipment per year, and each magnetic unit is always a compromise.

For example, to reduce eddy currents, we assemble magnetic cores from sheets insulated from each otherferrite steel. It would seem that the thinner the sheet, the less loss. But in practice, for powerful lifting electromagnets that lift multi-ton pieces of ore, a sheet that is too thin (less than 0.3 mm) creates problems with the rigidity of the entire structure. With frequent switching on/off and shock loads, micro-mobility of the package begins, which leads to abrasion of the insulation and, ultimately, to short-circuited turns and overheating. We had to empirically find the optimal thickness for each type of equipment. For some tasks it is 0.35 mm, for others it is 0.5 mm. No theory will give this, only experience and, sometimes, analysis of failed units.

A separate story is the aging of the material. Yes, ferromagnetic steels can change properties over time, especially when working under conditions of variable mechanical loads. We keep statistics on key components that are returned for scheduled repairs. We notice certain trends. For example, in magnetic systems of vibrating feeders, after several years of operation, a slight increase in coercive force is observed - the material seems to “get tired” of constant vibration. This is taken into account during the design - we initially set up slightly different magnetization modes, so that after five years the equipment will still operate within the design parameters. This approach to long-term reliability is one of the reasons why technologyLONGI Corporationvalued at many mining and processing plants.

The future and conservatism of the industry

Where is the industry heading? Requests for energy efficiency are growing, which means that demands for reducing losses in magnetic systems are also growing. This pushes us to search for new solutions. We are experimenting with alloying, with new laser cutting modes that minimize the heat-affected zone on the edge, with improved insulating coatings.

But the mining industry is conservative. Any change in material or technology must not only be better, but also proven to last in long-term use. Introduction of a new rangeferrite steelis always a big risk. It is necessary to rebuild technological chains, retrain personnel, and conduct a full cycle of tests. Therefore, changes occur evolutionarily. For example, a transition from one grade of steel to another, with specific losses improved by 5%, can last for a year and a half only at the stage of testing and adjusting all production regulations.

Ultimately, what is the most important thing when working with ferritic steels for applications like ours? This is not blind adherence to standards, but a deep understanding of the physics of the processes occurring in the material under load. This is the ability to see a material as part of a complex system and anticipate its behavior not on a test bench, but in the harsh conditions of a quarry or processing plant. It is this practical experience, often gained through trial and error, that distinguishes a simple product from reliable industrial equipment that must work for years without failure. And this, perhaps, is our main task as a manufacturer.