ferrite alloy

When they say “ferrite alloy?”, many people immediately imagine a permanent magnet from a speaker or a toy. But this, of course, is superficial. In fact, this is a whole class of materials where the properties depend not so much on the formula, but on how exactly you prepared this alloy. Here the composition of the charge, the sintering mode, and even how it was cooled - everything leaves a trace. A common mistake is to chase the maximum residual induction Br, forgetting about the coercive force Hc. But in practice, especially in mining equipment, where there are vibrations, shocks and temperature changes, resistance to demagnetization is often more important than “strength?” on paper. I went through this myself.

From powder to product: where the devil lies

It all starts with the powder. You can take, conditionally, standard Y30, but if you slightly change the granulometric composition, pressing will go differently, the density of the green workpiece will be uneven. And this will then come back to haunt you during sintering - warping or internal cracks. I used to think that the main thing was to maintain the temperature in the oven. It turned out that the heating rate to 900 degrees is no less critical. If you rush, the ligament does not have time to go away evenly, the pores remain. It turns out fragile.

One of our orders forLONGI CorporationI was just talking about magnets for separators. What was required was not just stability, but resistance to abrasive dust in the conditions of processing plants. Standard ferrite was not suitable - it wore out. I had to experiment with additives that do not affect the magnetic properties, but change the microstructure. It was a long process of testing, some of the batches were rejected. On the websitehttps://www.ljmagnet.ruThey indicate that they produce about 4,000 units of equipment per year - which means that each unit must work flawlessly, and our magnet was only a small part, but a failure in it could stop the entire line.

This is where you understand that laboratory characteristics are one thing, but work in the field is completely different. The temperature in the enrichment shop can be high, plus vibration from the crushers. We then made several test batches with different cobalt contents - not to increase Br, but to improve the temperature coefficient Hc. The result was average, but the experience has settled down: sometimes a small adjustment of the recipe for specific operating conditions gives more than choosing the “most powerful” one. according to the alloy catalog.

Quality control: don't trust, check

It would seem that sintering has passed, the geometry is within tolerance. But the most insidious stage is monitoring the magnetic parameters after magnetization. We had a case where a batch of magnets for a motor showed ideal Br and Hc on the measuring setup, but produced increased noise in the assembled unit. It turned out that the problem was the inhomogeneity of the magnetic field over the surface - somewhere there were microscopic zones with reduced coercivity. This was not caught on the standard test.

An additional sampling method had to be developed using a Hall effect sensor and a rotary table to scan the surface. This added time, but made it possible to weed out hidden defects. For such a large manufacturer asLONGI, where the staff includes more than 1,200 people and over 60% are specialists with higher education, such nuances, I am sure, are well known. Their engineers always look at the complete assembly rather than individual certifications.

A simple conclusion follows from this: specifications forferrite alloyshould be not only according to standard points (Br, Hc, BHmax), but also, possibly, according to additional parameters, for example, homogeneity. But registering this in the technical specifications is half the battle. It is also necessary that production can provide this stably. And this is a question of the culture of the workshop and the accuracy of the equipment.

Practical scenarios and why theory sometimes lags behind

In mining equipment, which is precisely its specializationLONGI, magnets work in harsh conditions. I remember discussing one project for a magnetic separator for wet enrichment. The environment there is pulp, alkaline or acidic. The customer initially requested standard barium ferrite. But we knew that with prolonged contact with certain reagents, surface corrosion could begin, which, although it would not eat the magnet immediately, would gradually reduce its effectiveness.

They offered an option with a protective coating. But not just paint, but a combined layer: phosphating plus an epoxy coating of a certain thickness. This increased the cost, but extended the service life significantly. Interestingly, at the testing stage, a non-obvious thing became clear: the coating itself, if applied in too thick a layer, could affect the heat dissipation during operation of the separator, which in the long term also led to degradation. I had to find a balance.

Such situations are not described in textbooks. This is knowledge that is collected bit by bit from project to project. When you see that the company, located in Fushun on an area of ​​140,000 m2, has been developing production for years, it becomes clear that their success is built on attention to such details. Their equipment is not just a matter of assembling components, but a deep understanding of how each component, including our humbleferritic alloy, will behave after five years of continuous operation.

Economics of material: when cheaper - more expensive

In production there is always a question of cost. Ferrites are relatively inexpensive materials, especially compared to rare earth magnets. Hence the temptation to save on something: on the purity of the starting oxides, on the accuracy of the dosage, on cheaper but less durable protection. In the short term this provides benefits.

But we once faced the consequences of such “savings”. For one series of drives, we purchased a batch of magnets from an alternative supplier at a price 15% lower. The geometry and passport data matched. Six months later, a complaint report arrived: a drop in torque was observed in several dozen drives. Disassembly showed partial demagnetization. Analysis of the material showed an increased content of impurities, which reduced the temperature stability of Hc. The equipment operated in workshops with elevated temperatures, and this was enough.

Direct losses from replacement and downtime outweighed the initial savings many times over. This lesson well illustrates the approach that I think a serious player should have: reliability is more important than short-term gain. Production capacityLONGI Corporation, their scale - 4,000 units of equipment per year - suggests that they are in business for the long term. And suppliers of materials for them, accordingly, are selected according to the same principle.

Looking to the future: evolution, not revolution

There is a lot of talk now about new magnetic materials. Butferrite alloywon't go anywhere. Its market share is huge, and for many high-volume applications, especially where corrosion resistance and stability over a wide temperature range are needed without huge costs, it will remain uncontested. The question is not to replace it, but to continuously improve it.

The directions are visible: increasing the uniformity of properties from batch to batch, developing more effective protective coatings for aggressive environments, optimizing the geometry of products for specific applications in order to use the material to the fullest extent possible. For example, in the same separators fromLONGIThe shape of the magnetic system is constantly improving, which means that the requirements for the shape and magnetization of individual ferrite elements may also change.

For me personally, ferrite is not just “good old” material. This is a living example of how a deep understanding of technology, from pressing to control, allows year after year to squeeze out new facets of reliability and efficiency from a seemingly well-known formula. And when you see the final equipment operating at a mining and processing plant, you understand that your small part of the work - that same magnet - also contributes to this large and complex process. And this is the main professional satisfaction.