Production process of high-performance rare earth permanent magnet ferrite powder

Abstract

The application belongs to the technical field of magnetic material preparation, and particularly relates to a production process of high-performance rare earth permanent ferrite magnetic powder. The process comprises the following steps: preparing iron red and auxiliary materials, wherein the auxiliary materials comprise calcium carbonate, strontium carbonate, lanthanum oxide and cobalt oxide; mixing raw materials in proportion, then performing dry ball milling to obtain mixed materials; performing steam treatment on the obtained mixed materials to make the water content of the mixed materials reach 2-5%, then performing ripening, and the ripening time is at least 30 min, and the ripening process is completed in the screw conveyor; balling; pre-sintering; performing coarse crushing on the pre-sintered materials and sieving to obtain rare earth permanent ferrite magnetic powder. Through steam pretreatment and ripening, the strength and thermal stability of the ball materials are significantly improved, the ball materials remain complete in the kiln, the flowability is good, and the consistency and qualified rate of the product are improved.

Description

Technical Field

[0001] This invention belongs to the field of magnetic material preparation technology, specifically relating to a production process for high-performance rare-earth permanent magnet ferrite powder. Background Technology

[0002] La-Co (lanthanum-cobalt) added high-performance rare-earth permanent magnet ferrites are currently the mainstream high-end permanent magnet ferrite products. Their production process typically employs a dry process: raw material mixing, dry ball milling, pelletizing, rotary kiln pre-firing, and pulverization. In actual production, the inventors discovered that the sintering state within the rotary kiln is closely related to changes in ambient temperature. In summer, when temperatures are high, the kiln condition is good, and the pellets have good fluidity; however, in winter, when temperatures are low (especially when the maximum temperature is below 10℃), the kiln condition deteriorates, and "kiln caking" is highly likely to occur (e.g., ...). Figure 3 (As shown). Kiln caking manifests as a layer of material adhering to the kiln wall, which can detach and form large clumps in severe cases, leading to fluctuations in product performance. Once kiln caking occurs, it often requires shutdown for cleaning, which not only damages the refractory bricks inside the kiln and shortens the equipment's lifespan, but also causes significant energy waste and reduced production efficiency due to frequent start-ups and shutdowns.

[0003] In existing technologies, research on kiln caking problems mainly focuses on wet processes (such as CN116425523A) or on modifying kiln equipment (such as CN205537098U), or only on the influence of the formulation on magnetic properties (such as CN114249591A). However, for the dry production of rare earth permanent magnet ferrites, especially for the kiln caking problem unique to low-temperature winter environments, there are currently no effective process improvement solutions. Summary of the Invention

[0004] This invention aims to solve the technical problems of ball material cracking and rotary kiln clogging that easily occur in the production process of high-performance rare earth permanent magnet ferrite powder in low-temperature winter environments. It provides a production process of high-performance rare earth permanent magnet ferrite powder that is compatible with existing dry production equipment and can significantly improve production stability.

[0005] The technical solution adopted by this invention to solve its technical problem is:

[0006] A production process for high-performance rare-earth permanent magnet ferrite powder, the process comprising the following steps:

[0007] Step (1) Raw material preparation: Prepare iron oxide red and auxiliary materials, including calcium carbonate, strontium carbonate, lanthanum oxide and cobalt oxide;

[0008] Step (2) Dry ball milling densification: The raw materials from step (1) are mixed in proportion and then dry ball milled to obtain a mixture;

[0009] Step (3) Steam treatment and maturation: The mixture obtained in step (2) is steam treated to make the moisture content of the mixture reach 2-5%, and then maturation is carried out for at least 30 minutes. The maturation process is completed in the auger transfer.

[0010] Step (4) Pelletizing: The mixture after step (3) is fed into a pelletizing pan to produce pellets;

[0011] Step (5) Pre-firing: The pellets obtained in step (4) are fed into a rotary kiln for pre-firing;

[0012] Step (6) Crushing and sieving: The pre-calcined material is coarsely crushed and sieved to obtain rare earth permanent magnet ferrite powder.

[0013] Principle analysis of the invention:

[0014] Through long-term research, the inventors discovered that the fundamental reason for kiln caking at low temperatures in winter lies in the contradiction between the water-absorbing and exothermic properties of lanthanum oxide (La₂O₃) and the ambient temperature. Lanthanum oxide readily absorbs water to form lanthanum hydroxide, accompanied by exothermic reaction, which then reacts with CO₂ in the air to form lanthanum carbonate. In summer, when the ambient temperature is high, this reaction can be completed relatively quickly in the mixing and pre-pelleting stages. However, at low temperatures in winter (e.g., <10℃), the hydration kinetics of lanthanum oxide slows down, resulting in incomplete reaction before pelletizing.

[0015] When "green pellets" containing a large amount of unreacted lanthanum oxide enter the tail of a rotary kiln (200-260℃), the high temperature triggers violent hydration and decomposition reactions, resulting in volume expansion and gas release, causing the pellets to crack and pulverize. The resulting fine powder easily adheres to the high-temperature kiln wall, eventually forming a blockage. Our team first tried adjusting the feed temperature at the kiln tail to extend the reaction time, but with little success. Subsequently, our team directly sprayed water droplets into the transfer auger, bringing the moisture content of the mixture to about 8%. The droplets, which were not absorbed by the mixture in time, adhered to the auger, causing blockage and ultimately leading to auger breakage.

[0016] This invention addresses the problem synergistically through the following means:

[0017] Steam pretreatment + maturation: This is the core step of the process in this invention. Before pelletizing, heat and moisture are introduced by steam to force the hydration reaction of lanthanum oxide in the mixture; and a maturation time of at least 30 minutes is set to ensure that the reaction is basically completed and the heat dissipates before entering the pelletizing pan. The resulting pellets have a dense structure and will not undergo violent reactions after entering the rotary kiln, thus avoiding cracking and kiln blockage. However, during the auger transfer process, the moisture content of the maturated material cannot be too high. If it is too high, it will adhere to the auger, causing transfer failure, blockage, and damage to the auger.

[0018] Preferably, the molar ratio n of the rare earth permanent magnet ferrite powder satisfies: n = (Fe+Co) / (La+Sr+Ca), where n is 5.3-6.0.

[0019] In step (1), preferably, the microstructure of the lanthanum oxide is a layered, stacked aggregate of particles (see...). Figure 2 And the particle size distribution satisfies 2.5μm≤X 50 ≤3.0μm, purity ≥99.5%; this specific morphology is beneficial for uniform dispersion, and the reaction is more uniform under vapor permeation conditions;

[0020] Preferably, the iron oxide red has an average particle size of 0.5-1.5 μm and a moisture content of ≤0.7%; based on the mass percentage of oxides, the iron oxide red contains ≤0.5% MnO, ≤0.08% SiO2, ≤0.08% Al2O3, ≤0.25% Cl, with the balance being Fe2O3;

[0021] Preferably, the cobalt oxide has a total cobalt content of 70-73% and an average particle size of 0.8-1.8 μm; the calcium carbonate has an average particle size of 0.8-1.2 μm and a purity of ≥97%; and the strontium carbonate has a purity of ≥97% and an average particle size of 0.8-1.8 μm.

[0022] As a preferred option, in step (4), water is added during the pelleting process to control the moisture content of the resulting pellets to be 13-16%.

[0023] The moisture content of the pellets is slightly higher than the conventional moisture content, which is 10-12%. In order to ensure the full reaction between lanthanum oxide and water, the moisture content is slightly increased. If it is lower than 13%, the possibility of kiln clogging will increase. If it is higher than 16%, it will not cause kiln sticking (because the moisture content of wet mixed feed is 18-22%), but it will lead to a significant increase in energy consumption.

[0024] Preferably, in step (5), the kiln tail temperature of the rotary kiln is controlled at 200-260℃; the maximum pre-firing temperature is 1240-1300℃, the holding time is 1-3h, and the total pre-firing time is 9-12h.

[0025] Preferably, in step (3), the maturation time is 30 min to 60 min.

[0026] Preferably, in step (4), water is added during the pelleting process to control the moisture content of the resulting pellets to be 13-14%.

[0027] In step (5), the kiln tail temperature of the rotary kiln is controlled at 200-240℃; more preferably 200-220℃.

[0028] The kiln tail temperature is controlled by induced draft. If the temperature is too high, the reaction between lanthanum oxide and moisture will be insufficient, leading to kiln clogging. If the temperature is too low, the kiln atmosphere will be abnormal, affecting the final performance. If the pre-firing process is too short, i.e., the feeding is too fast, the reaction between high lanthanum oxide and moisture will be insufficient, leading to kiln clogging again. The appropriate pre-firing process duration will result in reduced production efficiency, increased energy consumption, and increased costs.

[0029] Preferably, in step (6), the coarse crushing is carried out using a dry grinding mill, and the sieving is carried out using a 50-mesh sieve.

[0030] The beneficial effects of this invention are:

[0031] This method solves the problem of winter kiln caking in the dry process production of rare earth permanent magnet ferrite by means of a mechanism that does not require modification of large equipment, but can be achieved by adjusting process parameters and making minor improvements to the equipment.

[0032] Steam pretreatment and curing significantly improved the strength and thermal stability of the pellets, keeping them intact and fluid in the kiln, thus improving product consistency and yield.

[0033] It significantly reduced the number of shutdowns for cleaning due to kiln caking, protected the kiln's refractory materials, and saved energy and maintenance costs. Attached Figure Description

[0034] Figure 1 These are on-site photos of the rotary kiln without kiln crust during winter production in Example 1.

[0035] Figure 2 This is a SEM microstructure image (layered stacked agglomerated particles) of the lanthanum oxide raw material selected in this invention.

[0036] Figure 3 These are on-site photos of kiln clogging inside a rotary kiln during winter production, based on existing technology. Detailed Implementation

[0037] The technical solution of the present invention will be further described in detail below through specific embodiments. It should be understood that the implementation of the present invention is not limited to the following embodiments, and any modifications and / or alterations made to the present invention will fall within the protection scope of the present invention.

[0038] In this invention, unless otherwise specified, all parts and percentages are by weight, and the equipment and raw materials used are commercially available or commonly used in the art. Unless otherwise specified, the methods in the following embodiments are conventional methods in the art.

[0039] Unless otherwise specified, the reagents used in the following examples can be purchased from regular biochemical reagent stores. It should be noted that since the examples and comparative examples are all actual production cases, the raw material control is within the range.

[0040] It should be noted that Examples 1-3 represent production practices from the winter of 2024 to the present; Comparative Example 1 represents a traditional production process. During this period, it was observed at the production site that kilns producing products with a high lanthanum-cobalt ratio would experience kiln clogging if the temperature remained below 10°C for more than three consecutive days. Production was halted three times due to kiln clogging, with data collected from January to March 2023, totaling 40 production days. During production, small materials (calcium carbonate, strontium carbonate, cobalt oxide, and lanthanum oxide) were pre-mixed and stockpiled at the production site. Comparative Examples 2-4 represent trial production adjustments from December 2023 to November 2024, arranged chronologically. Comparative Example 2 underwent a total trial run of 33 days before kiln clogging caused production disruptions and shutdowns. Comparative Example 3 experienced feeding difficulties and no output was achieved. Comparative Example 4 began trial production on January 23, 2024, and continued until November 2024. Low temperatures led to minor kiln clogging, with a significant number of larger material clumps remaining, but the impact on continuous production was minimal.

[0041] Example 1

[0042] A production process for high-performance rare earth permanent magnet ferrite powder, the specific steps of which are as follows: (1) Raw material preparation: Iron oxide red with an average particle size of 0.5-1.5μm, as well as calcium carbonate, strontium carbonate, cobalt oxide and lanthanum oxide are selected. Among them, lanthanum oxide is selected as layered stacked agglomerated particles, and its loss on ignition is controlled to be 1.5%. Other raw material control conditions are as follows:

[0043] The average particle size of iron oxide red is 0.5-1.5 μm, and the moisture content is ≤0.7%. Based on the mass percentage of oxides, the iron oxide red contains ≤0.5% MnO, ≤0.08% SiO2, ≤0.08% Al2O3, and ≤0.25% Cl, with the balance being Fe2O3. The total cobalt content of cobalt oxide is 70-73%, and the average particle size is 0.8-1.8 μm. The average particle size of calcium carbonate is 0.8-1.2 μm, and the purity is ≥97%. The purity of strontium carbonate is ≥97%, and the average particle size is 0.8-1.8 μm.

[0044] According to the molecular formula Ca 1-x-z La x Sr z Co y Fe 2n-y O a, Ingredients, x=0.40, y=0.05, z=0.15, molar ratio n is 5.8; a=1+3n+0.5(xy). (2) Dry ball milling: Mix the raw materials and put them into a dry mill for ball milling until dense, to obtain a mixture. (3) Steam treatment and maturation: Steam is introduced into the mixture for treatment, and the moisture content of the mixture after treatment is controlled to be 3.5%. The material is maturated for 45 minutes during the auger transfer process to allow lanthanum oxide to fully pre-react. (4) Pelletizing: The maturated mixture is sent to a pelletizing pan, water is sprayed to form pellets, and the final moisture content of the pellets is controlled to be 14%. (5) Pre-firing: The pellets are sent to a rotary kiln. The kiln tail temperature is controlled at 220-240℃, the maximum sintering temperature is 1270℃, and the holding time is 2h. The total residence time of the material in the kiln is about 10h. The kiln tail temperature fluctuates in real time and can only be controlled by the kiln tail induced draft. In this embodiment, it is controlled at 220-240℃. The inspection is once / h. Under the premise that the equipment is normal, if the temperature of 5 consecutive points is not within the set range, it is considered abnormal. (6) Post-processing: After discharge, the material is coarsely crushed by a dry mill and passed through a 50-mesh sieve to obtain the finished magnetic powder, such as Figure 1 As shown, the kiln wall is clean, with only a few small clumps.

[0045] Example 2

[0046] The only difference from Example 1 is the adjustment of process parameters: In step (3), the moisture content of the mixture after steam treatment is 2.0%, and the maturation time is 30 min. In step (4), the moisture content of the pellets is 13%. In step (5), the kiln tail temperature is 200-220℃.

[0047] Example 3

[0048] The only difference from Example 1 is the adjustment of process parameters: In step (3), the moisture content of the mixture after steam treatment is 5.0%, and the maturation time is 60 min. In step (4), the moisture content of the pellets is 16%. In step (5), the kiln tail temperature is 240-260℃.

[0049] Comparative Example 1 (No steam treatment and aging)

[0050] Except for step (3), where steam treatment and aging are not performed, and the mixing and transfer time is about 10 minutes before directly entering the pelletizing tray for pelletizing, the other steps are the same as in Example 1; the microstructure of lanthanum oxide is not controlled in terms of raw materials. This is a traditional production process.

[0051] Comparative Example 2 (Kiln tail temperature too low)

[0052] Except for step (5), where the temperature at the kiln tail of the rotary kiln is controlled at 180-200℃, the other raw materials and steps are the same as in Comparative Example 1. This is the first adjustment.

[0053] Comparative Example 3 (mixture moisture content too low)

[0054] Except for step (3), in which water droplets were sprayed in to make the mixture moisture content reach about 8%, production could not proceed smoothly.

[0055] Comparative Example 4 (insufficient curing time)

[0056] Except for step (3), where steam treatment was changed and the feed auger speed was not adjusted, resulting in a transfer time of approximately 10 minutes, the other raw materials and steps are the same as in Example 1. This is the third adjustment. Figure 3 As shown, there is a small amount of caking inside the kiln wall, with large clumps of material.

[0057] Detection method:

[0058] Weigh out 400g of high-performance rare earth permanent magnet ferrite powder.

[0059] Examples 1-3 and Comparative Examples 1, 2 and 4 were formulated with the following secondary formulations based on the mass of coarse powder: 0.66% calcium carbonate, 0.3% silica, and 0.15% boric acid. The powder was wet-milled to an average particle size of 0.7 μm and pressed into 35.1 mm round cakes under a pressure of 63 t, with a density of 3.2 ± 0.05 g / cm³. 3 The sample was sintered at 1240℃ for 2 hours under the temperature of the measuring ring, and after surface grinding, the magnetic properties were measured by a BH magnetometer.

[0060] Performance standards: Br = 4250±50Gs, Hcj = 4800±200Oe.

[0061] Ball integrity rate test: After cooling, the pre-fired material is sampled and weighed (m0). Broken material is then sieved through a 6mm sieve to remove it, and the weight of intact balls (m1) is recorded. The ball integrity rate is calculated as: m1 / m0 × 100%.

[0062] Table 1

[0063]

[0064] Results analysis:

[0065] In Examples 1-3, after introducing steam treatment and sufficient maturation time, the integrity rate of the pellets was significantly improved, and no obvious kiln clogging phenomenon was observed during continuous production. This indicates that the process effectively solved the production problem under low temperature conditions in winter, and the overall performance was improved.

[0066] Comparative Example 1 employed a traditional steam-free treatment and curing process. Under low winter temperatures, the lanthanum oxide in the mixture failed to be fully hydrated beforehand. This resulted in violent hydration and decomposition reactions occurring at 200-260℃ after the green pellets entered the rotary kiln tail, causing the pellets to crack and pulverize, forming a large amount of fine powder adhering to the kiln wall, thus triggering kiln caking. Therefore, its pellet integrity rate was low, kiln caking occurred, and its magnetic properties (especially coercivity Hcj) were low.

[0067] Comparative Example 2 attempted to lower the kiln tail temperature based on the traditional process, but failed to change the fundamental problem of "reaction delay" of lanthanum oxide in the mixture. Although the lower temperature slowed down the reaction rate to some extent, the unreacted lanthanum oxide would still undergo adverse reactions during the subsequent heating process in the kiln. Therefore, the kiln clogging problem was only slightly alleviated but not eliminated, and although the integrity rate of the pellets was improved, it was still not ideal.

[0068] Comparative Example 3 attempted to promote the reaction by increasing the moisture content through direct water spraying, but the excessively high moisture content (8%) resulted in the generation of free water droplets that were not absorbed by the material in time. This caused the mixed material to adhere and clump on the conveyor auger, eventually leading to serious malfunctions such as material blockage or even breakage of the equipment (auger), making production impossible.

[0069] Comparative Example 4 introduced steam treatment, but the curing time was insufficient (only about 10 minutes of transfer time). This caused the hydration reaction of lanthanum oxide to start but not complete. Some of the "semi-raw" material continued to react after entering the kiln, still producing a certain degree of cracking and fine powder, resulting in slight kiln caking and the formation of larger lumps. Although its pellet integrity and magnetic properties were better than those of the traditional process, its stability was not as good as the fully cured example.

[0070] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to in the method section.

[0071] The production process of a high-performance rare-earth permanent magnet ferrite powder provided by this invention has been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. It should be noted that those skilled in the art can make several improvements and modifications to this invention without departing from the principles of this invention, and these improvements and modifications also fall within the protection scope of the claims of this invention.

Claims

1. A production process for high-performance rare-earth permanent magnet ferrite powder, characterized in that, The process includes the following steps: Step (1) Raw material preparation: Prepare iron oxide red and auxiliary materials, including calcium carbonate, strontium carbonate, lanthanum oxide and cobalt oxide; Step (2) Dry ball milling densification: The raw materials from step (1) are mixed in proportion and then dry ball milled to obtain a mixture; Step (3) Steam treatment and maturation: The mixture obtained in step (2) is steam treated to make the moisture content of the mixture reach 2-5%, and then maturation is carried out for at least 30 minutes. Step (4) Pelletizing: The mixture after step (3) is fed into a pelletizing pan to produce pellets; Step (5) Pre-firing: The pellets obtained in step (4) are fed into a rotary kiln for pre-firing; Step (6) Crushing and sieving: The pre-calcined material is coarsely crushed and sieved to obtain rare earth permanent magnet ferrite powder.

2. The production process according to claim 1, characterized in that, The molar ratio n of the rare earth permanent magnet ferrite powder satisfies: n = (Fe+Co) / (La+Sr+Ca), where n is 5.3-6.

0.

3. The production process according to claim 1, characterized in that, In step (1), The lanthanum oxide has a microstructure of layered, stacked aggregates with a particle size distribution satisfying 2.5 μm ≤ X. 50 ≤3.0μm, purity ≥99.5%; The iron oxide red has an average particle size of 0.5-1.5 μm and a moisture content of ≤0.7%; based on the mass percentage of oxides, the iron oxide red contains ≤0.5% MnO, ≤0.08% SiO2, ≤0.08% Al2O3, ≤0.25% Cl, with the balance being Fe2O3; The cobalt oxide has a total cobalt content of 70-73% and an average particle size of 0.8-1.8 μm; the calcium carbonate has an average particle size of 0.8-1.2 μm and a purity of ≥97%; the strontium carbonate has a purity of ≥97% and an average particle size of 0.8-1.8 μm.

4. The production process according to claim 1, characterized in that, In step (4), water is added during the pelleting process to control the moisture content of the resulting pellets to be 13-16%.

5. The production process according to claim 1, characterized in that, In step (5), the kiln tail temperature of the rotary kiln is controlled at 200-260℃; the maximum pre-firing temperature is 1240-1300℃, the holding time is 1-3h, and the total pre-firing time is 9-12h.

6. The production process according to claim 1, characterized in that, In step (6), the coarse crushing is carried out using a dry grinding mill, and the sieving is carried out using a 50-mesh sieve.

7. The production process according to claim 1, characterized in that, In step (3), the maturation time is 30 to 60 minutes.

8. The production process according to claim 1, characterized in that, In step (4), water is added during the pelleting process to control the moisture content of the resulting pellets to be 13-14%. In step (5), the kiln tail temperature of the rotary kiln is controlled to be 200-240℃.

Images