ferrite formula

When they say “ferrite formula?”, many people immediately imagine a dry chemical notation like FeO·Fe?O? or something like that. But in real production, especially when it comes to magnetic systems for mining equipment, this ?formula? - not just a line in a textbook. This is more of a starting point for much experimentation with doping, annealing and core geometry. A common mistake is to think that knowing the basic composition will already give you the desired magnetic properties. As if... In fact, the same ?formula? Ferrite, say, Mn-Zn grade, in different furnaces, with different cooling rates will give completely different values ​​of magnetic permeability and losses at the output. And this is where the fun begins.

Not just powder: what lies behind the chemical notation

Let's take, for example, the production of cores for separators. The same ones that are used for ore enrichment. Basic ferrite is, roughly speaking, pressed and sintered powder. But if you take raw materials of different dispersion, even with ideal molar ratios, the final density and uniformity of the granules will differ. And this directly affects the coercive force. I remember that at one of the old productions they tried to save money by using cheaper iron oxide with a large fraction. According to the ?formula? everything came together, but the finished core slabs heated up under load so much that the insulation began to melt. I had to return to a trusted supplier, although on paper there was no difference.

Or another nuance - alloying additives. Same ?formula? Ferrite often implies a basic composition. But to increase stability at high frequencies (and in modern switching power supplies for drilling rigs this is critical), nickel or cobalt is introduced into the charge. And their exact number, percentage ratio is no longer the same formula as in the reference book. This is the know-how of a specific manufacturer, the result of trial and error. For example, for a series of magnetic systems we supply, includingmining equipment, tested the addition of cobalt oxide to fractions of a percent in order to “catch?” minimal eddy current losses. Without this, the core would resonate in operation, creating an unpleasant whistle.

Therefore, when I see the request “ferrite formula?”, I always want to ask: what for? To calculate the theoretical saturation magnetization? Or in order to launch a pressing line in the workshop? These are different things. In the first case, a textbook will suffice. In the second, you need a technological map, which specifies not only the molar ratios, but also the pressing pressure, sintering temperature and time, and annealing parameters. And this map is the real, living “formula?” for an engineer.

From the laboratory to the assembly shop: where theory meets reality

Laboratory samples are one thing. They are almost always perfect: small toroids, slowly heated in an oven with a precise temperature profile. But try pressing a large plate for the magnetic separator system, say, 500x500 mm. Problems begin at the pressing stage. The non-uniformity of pressure over the area of ​​the mold leads to the fact that the density in the center and at the edges is different. And after sintering, this will result in different shrinkage and, as a result, internal stresses in the material. The magnetic properties of such a “pancake?” will be uneven, and the entire system will not reach its certified efficiency.

We encountered this about ten years ago, when we were developing a magnetic core for a new separator model. Lab tests were brilliant. And on the pilot batch from the workshop, the separation efficiency was 15% lower. We figured it out: it was the heterogeneity of the pressing that was to blame. We had to completely redo the design of the mold and introduce additional punches. And, what is important, we adjusted the preparation of the charge itself - we increased the granulation time to improve the flowability of the powder. This is the case when the ?formula? chemical composition remained unchanged, but the technological “formula” production was rewritten from scratch.

Another practical point is quality control after sintering. Microcracks. They can occur due to too rapid cooling or due to residual stresses. Visually, the slab may be intact, but when working in an alternating field, losses will be concentrated in these cracks. A standard magnetic permeability test will not always show the problem here. You have to selectively make microsections and look at the structure under a microscope. This is routine but necessary work. BLONGI CorporationFor example, at the site for testing magnetic materials there is just such equipment - both for ferrites and for hard magnetic alloys. Without this, it is simply impossible to guarantee the reliability of the final product, such as the enrichment separator, which must operate in difficult conditions for years.

Case from practice: when is it “correct?” ferrite didn't work

A good example is the story of the development of a power supply for the hydraulic control system of a roadheader. The customer needed a compact and reliable converter that could operate in conditions of strong vibration. We chose a seemingly ideal material - high-frequency ferrite on a nickel-zinc base with excellent loss parameters. According to all reference data and “formulas” he was coming.

We collected prototypes. At the stand, under normal conditions, everything worked flawlessly. But when the batch was sent for testing under conditions simulating real work at the mine face (vibration stand, temperature changes), failures began. The cores in the chokes were cracking. It turned out that the problem was the mechanical strength of this particular type of ferrite. He was fragile. Its magnetic ?formula? was impeccable, but its physical and mechanical properties were not suitable for this application.

The solution was not to change the chemical composition, but to do something else. We switched to ferrite with slightly worse magnetic characteristics, but more viscous and shock-resistant. And, most importantly, we changed the design of the core mounting unit in the body, adding damping pads. This case shows well that design is always a compromise. You can’t blindly follow the perfect numbers from a datasheet. You need to look at a complex of properties: magnetic, electrical, mechanical, thermal. And behind each group of properties there is its own, more complex than Fe?O?, “formula?” success.

The role of the manufacturer: from raw materials to the finished unit

This is where it matters who produces it and how. When an enterprise controls the entire cycle - from the purchase and testing of raw materials (those metal oxides) to final assemblymining equipment— it has much more leverage to ensure quality. You can quickly make adjustments to the technology based on problems identified at later stages of assembly.

Let's takeLONGI Corporation (https://www.ljmagnet.ru). The company, established back in 1993, is now a major manufacturer of mining equipment. Their profile is not just the sale of magnets or ferrite plates, but the creation of complex systems: magnetic separators, enrichment equipment. And what’s key is that they have their own facilities for processing magnetic materials. This means that their engineers, when developing, say, a new drum separator, can work closely with the technologists of the ferrite core production shop. They can say: “for this model we need to shift the Curie point 20 degrees higher to work in hot shops?”, and technologists will begin to experiment with alloying, selecting their own practical “formula”.

This integration is invaluable. Because when production is disrupted - ferrites are purchased from one supplier, machining from another, assembly from a third - it is almost impossible to achieve optimal results and quickly solve the problem. Everyone will refer to their own technical conditions. And when everything is in one place, as at the site in Fushun with a total area of ​​140,000 m2, issues are resolved faster. The experience accumulated since 1993 and more than 1,200 employees, most of whom are specialized experts, allow us to approach the issue comprehensively. The annual productivity of 4,000 pieces of equipment is not just a number, it is a streamlined process where thousands of nuances are taken into account, including those related to the notorious “ferrite formula”.

Instead of a conclusion: the formula is a process, not a dogma

So what is all this for? Moreover, what is the ?ferrite formula? - this is not a static truth. It is rather a living process of finding balance. A balance between raw material costs and final properties, between ideal laboratory conditions and shop floor realities, between magnetic efficiency and mechanical reliability.

For those just starting to work with these materials, my advice is: don't stop at the first line from the textbook. Study not only the chemical composition, but also the full technological cycle. Ask suppliers not only for datasheets, but also for recommendations on pressing and sintering. Best of all, find an opportunity to work hand in hand with an experienced manufacturer who has gone all the way from powder to complex machine. Like those who have been involved in development and production on site for years, seeing all the stages with their own eyes.

Ultimately, the correct ?formula? - this is the one that allows your equipment, be it a separator or a power supply, to work flawlessly for years under real, not ideal, conditions. And this formula is written not only in a laboratory journal, but also in the workshop, at the sintering furnace, and on a test bench that simulates the vibration of a quarry.