Dry-pressed permanent magnetic ferrite and preparation method thereof

Abstract

The invention discloses a dry-pressed permanent magnetic ferrite and a preparation method thereof, and belongs to the technical field of magnetic materials. The method comprises the working procedures of ferrite pre-sintering material coarse powder preparation, fine grinding, concentration, drying, powder preparation, dry pressing magnetic field forming and sintering, wherein iron oxide red and strontium carbonate are weighed according to the molar ratio of 5.45-6.05, a proper amount of boric acid and light calcium carbonate are added, and coarse powder is prepared through multiple working procedures; 0.1%-1.5% dicalcium silicate is used for replacing a traditional additive in the fine grinding stage, a 45-85 DEG C three-stage low-temperature process is adopted for drying, pre-sintering waste heat is reused, and it is ensured that the water content of the magnetic powder is smaller than or equal to 0.5% in cooperation with 0.5-2% of a binder and 0.1-0.5% of a lubricant are added during powder preparation, and a finished product is obtained through magnetic field forming and sintering. The dicalcium silicate inhibits agglomeration through dual effects of charge neutralization and physical isolation, so that the repose angle of the prefabricated magnetic powder is less than or equal to 45 degrees, and the product performance reaches 96% or above of the wet-pressing performance.

Description

Technical Field

[0001] This invention belongs to the field of magnetic materials technology, specifically relating to a dry-pressed permanent magnet ferrite and its preparation method. Background Technology

[0002] Permanent magnet ferrites, with their advantages of low cost and high resistivity, are widely used in various fields such as electroacoustics, motors, and adsorption. Dry pressing is one of the mainstream manufacturing processes for permanent magnet ferrites. The preparation of dry-pressed permanent magnet ferrites generally uses iron oxide as raw material, with the addition of strontium carbonate or barium carbonate and other trace additives. Pre-calcined magnetic powder is synthesized through a solid-state reaction, followed by fine grinding, drying, dispersing, powdering, dry pressing in a magnetic field, and sintering to achieve densification and final product. Its advantages include low energy consumption, high molding efficiency, and strong environmental friendliness. Compared to wet pressing, it reduces water consumption by 60% and increases molding production efficiency by more than 30%. However, the magnetic powder used in dry pressing magnetic field molding often forms agglomerates due to electrostatic forces and van der Waals forces between particles, affecting the flowability of the powder (angle of repose ≥ 55°). This leads to low density of the molded blank and poor magnetic field orientation, resulting in low product performance. Generally, the performance of products prepared by dry pressing is only 90-92% of that prepared by wet pressing. Existing technologies often improve flowability by adding lubricants such as calcium stearate and zinc stearate, but this method can only reduce the coefficient of friction and cannot fundamentally break the agglomerate structure. While wet processes can optimize dispersibility, they have the drawbacks of high energy consumption and low molding efficiency.

[0003] Patent application CN 103848621A discloses a method for manufacturing dry-pressed anisotropic permanent magnet materials. The method involves drying fine powder at 100-700℃, then dispersing it using a high-efficiency powder mill, followed by the addition of calcium carbonate to ensure uniform dispersion. While adding calcium carbonate after drying avoids particle agglomeration caused by high-temperature decomposition of calcium carbonate, and vibratory milling helps to break up agglomerates, some materials in the finely ground magnetic powder contain small amounts of volatile or heat-soluble components (such as residual moisture and additives). High temperatures accelerate the migration of these components to the particle surface, forming a "sticky layer." Neither the high-efficiency powder mill nor the vibratory milling process can completely prevent particle agglomeration caused by melting, softening, or changes in surface composition of the finely ground magnetic powder during high-temperature drying. This leads to particle adhesion in the prepared dry-pressed magnetic powder, affecting its flowability.

[0004] Therefore, there is an urgent need for a new dry-pressed permanent magnet ferrite and its preparation method that is low-cost, easy to operate, and can effectively improve the flowability of magnetic powder, enhance the magnetic field orientation and product magnetic properties while maintaining the energy-saving and environmentally friendly advantages of the dry pressing process, and take into account process stability and cost control, so as to meet the continuous demand for high-performance permanent magnet ferrites in high-end application scenarios. Summary of the Invention

[0005] This invention provides a dry-pressed permanent magnet ferrite and its preparation method to solve the problems of poor flowability and low product performance of dry-pressed magnetic powder in the prior art.

[0006] The objective of this invention can be achieved through the following technical solutions: In a first aspect, the present invention provides a method for preparing dry-pressed permanent magnet ferrite, comprising the following steps: S10. Preparation of ferrite pre-sintered material coarse powder: Iron oxide red and strontium carbonate are weighed in a molar ratio of 5.45-6.05, and 0.1-0.25% boric acid and 0.1-0.5% light calcium carbonate are added according to the total weight of iron oxide red and strontium carbonate. After being strongly mixed in a strong mixer, the mixture is densified in a densifier. After being pre-mixed with water, the densified material is pelletized in a pelletizer. The pellets are then transported to a rotary kiln for pre-sintering. After the pre-sintered pellets are cooled, they are crushed to obtain ferrite pre-sintered material coarse powder. S20, Fine grinding: Add 0.1%-1.5% dicalcium silicate to the above coarse powder to replace the traditional calcium carbonate and silica additives and grind it in a ball mill. S30. Concentration: After fine grinding, the slurry is filtered by a filter press and then dispersed to obtain a residue with a moisture content of no more than 15%. S40. Drying: The concentrated residue is dried in a belt dryer by "low temperature preheating, medium temperature drying, and low temperature cooling", and then broken up by a high-speed pulverizer to obtain dry-pressed magnetic powder with a moisture content of no more than 0.5%. S50. Powdering: Add 0.5-2% binder and 0.1-0.5% lubricant to the dry-pressed magnetic powder, mix it evenly with a strong mixer, and then break it apart with a high-speed pulverizer to obtain pre-made magnetic powder with excellent flowability. S60, Dry pressing magnetic field forming: Pre-made magnetic powder is pressed into shape under a magnetic field to form a green body; S70, Sintering: The green blank is sintered in air and cooled to obtain permanent magnet ferrite material.

[0007] According to the present invention, dicalcium silicate is introduced in the fine grinding stage to replace the traditionally used calcium carbonate or silicon dioxide. Utilizing the weakly alkaline nature of its surface (pH approximately 8-9), the Ca... 2+ Ions adsorb onto the surface of ferrite particles, neutralizing the negative charge formed on the particle surface due to the presence of hydroxyl groups and reducing the electrostatic attraction between particles. Simultaneously, dicalcium silicate forms a physical isolation layer on the particle surface, preventing direct contact between magnetic particles and weakening van der Waals forces, thereby inhibiting the formation of agglomerates. This technique differs from conventional methods that only reduce the coefficient of friction through lubricants, controlling powder dispersion behavior from two dimensions: the surface charge state and the physical spacing of the particles.

[0008] Furthermore, during the preparation of the ferrite pre-calcined material coarse powder in S10, 5-10% of pre-adjusted tap water with a pH value of 7-9 is added during the pre-water mixing process. The neutral to weakly alkaline water with a pH value of 7-9 can avoid the adverse effects of acidic and alkaline environments on the ferrite raw materials. The 5-10% water content ensures that the material obtains sufficient moisture to form stable spheres, while avoiding excessive moisture that could lead to insufficient sphere strength or difficulty in drying, thus ensuring the stability of the sphere-making process and the quality of the spheres.

[0009] Furthermore, during the preparation of the coarse powder of the ferrite pre-calcined material in S10, the pellets produced by the pelletizing machine have a diameter of 5-8 mm. If the pellet diameter is too small, the material will be easily carried away by the airflow during pre-calcination, and if the pellet diameter is too large, it will hinder the uniform transfer of heat and cause incomplete internal reaction.

[0010] Furthermore, during the preparation of the ferrite pre-calcined material coarse powder in S10, the rotary kiln pre-calcination temperature is 1170-1220℃; if the temperature is too low (<1170℃), the reaction will be incomplete, leaving unreacted substances; if the temperature is too high (>1220℃), the particles will be over-sintered, forming a dense structure that is difficult to break, and may also cause abnormal grain growth.

[0011] Furthermore, during the preparation of the ferrite pre-sintered material coarse powder in S10, the granular material is cooled by air cooling to obtain hot air at a temperature ≥150℃. After dust removal, this hot air is used as a heat source for the subsequent drying process. Air cooling can quickly lower the temperature and avoid excessive grain growth caused by residual heat. At the same time, the recovered hot air temperature of ≥150℃ is suitable as a drying heat source. This temperature meets the drying requirements while avoiding the melting of the particle surface that may be caused by high-temperature hot air. The waste heat recovery system realizes the cascade utilization of energy and significantly reduces production energy consumption.

[0012] Furthermore, the dicalcium silicate added in S20 is a 200-mesh sieve material with a purity ≥96%; the 200-mesh sieve material (particle size ≤74μm) ensures that the dicalcium silicate particles are small enough to be uniformly dispersed in the slurry; the high purity (≥96%) avoids impurities from interfering with the performance of ferrite.

[0013] Furthermore, the "low-temperature preheating, medium-temperature drying, and low-temperature cooling" method in S40 involves preheating at 45-60℃ for 1-2 hours, drying at 65-85℃ at 3-6 hours, and cooling at low temperature with natural wind for 0.5-1 hour. The heat source for the low-temperature preheating and medium-temperature drying is the hot air treated in the cooling section during the preparation of the ferrite pre-calcined powder, which is then adjusted to the required temperature by mixing with cold air. The hot air velocity is 1.2-1.8 m / s, and the humidity is ≤15% RH. The 45-60℃ low-temperature preheating slowly removes surface moisture, preventing the formation of a hard shell that hinders internal moisture evaporation. The 65-85℃ medium-temperature drying effectively removes internal moisture; this temperature range is sufficient to remove moisture without causing the particle surface to melt. The low-temperature cooling with natural wind avoids sudden temperature changes that could cause particle cracking. The 1.2-1.8 m / s wind velocity and ≤15% RH humidity ensure uniform moisture removal and prevent agglomeration caused by localized overheating.

[0014] Furthermore, the S40 belt dryer uses a 100-120 mesh mesh belt made of 316 stainless steel with a twill weave and a belt thickness of 0.8-1.2mm. Hot air can penetrate the mesh belt and act directly on the material layer. With an air velocity of 1.2-1.8m / s, it can reduce the phenomenon of "dry on top and wet on the bottom" and improve the uniformity of drying.

[0015] Furthermore, the dry-pressed magnetic powder prepared in S40 has a repose angle of 35-40° as determined by the funnel method (GB / T 1482-2010). This repose angle indicates that the powder has excellent flowability, which is due to the dual role of dicalcium silicate: its weak alkalinity neutralizes the negative charge on the particle surface and reduces electrostatic attraction; at the same time, it forms a physical isolation layer on the particle surface to reduce van der Waals forces.

[0016] Furthermore, in S50, the binder is water or camphor powder; the lubricant is zinc stearate to reduce the coefficient of friction between materials; water is environmentally friendly and economical as a binder, but its dosage needs to be controlled to avoid affecting subsequent drying; camphor powder, as an organic binder, can completely volatilize during sintering without leaving any impurities.

[0017] Furthermore, the pre-made magnetic powder prepared in S50 is measured by the funnel method (GB / T 1482-2010) to have a repose angle of 40-45°, excellent flowability, and product performance reaching more than 96% of wet pressing performance.

[0018] In some embodiments, the magnetic field strength in step S60 is not less than 5000 Oe, which is sufficient to orient the anisotropic ferrite particles along the magnetic field direction during the pressing process, thereby increasing the remanence and maximum magnetic energy product of the product.

[0019] In some embodiments, the sintering temperature in step S70 is 1200℃-1250℃ and the holding time is 1-2 hours. These process parameters can achieve sufficient densification of the green body while avoiding excessive grain growth that would lead to a decrease in coercivity.

[0020] In a second aspect, the present invention provides a dry-pressed permanent magnet ferrite, which is prepared by the preparation method described in any embodiment of the first aspect.

[0021] The beneficial effects of this invention are: (1) The dry-pressed permanent magnet ferrite preparation method provided by the present invention achieves multiple technical advantages through precise raw material ratio and systematic process design. In terms of raw material matching, iron oxide red and strontium carbonate are weighed at a molar ratio of 5.45-6.05, and 0-0.25% of boric acid and 0-0.5% of light calcium carbonate are selectively added by weight of iron oxide red and strontium carbonate. The ferrite pre-calcined material coarse powder is prepared by strong mixing in a strong mixer, densification in a densifier, pre-water mixing and pelletizing, pre-firing in a rotary kiln and cooling and crushing, etc., laying a solid foundation for subsequent performance optimization; in the fine grinding stage, 0.1%-1.5% of dicalcium silicate is innovatively introduced to replace the traditional calcium carbonate and silicon dioxide additives. Utilizing its weakly alkaline surface properties, it can be used to pass through Ca 2+ Ion adsorption neutralizes the negative charge on the surface of ferrite particles caused by hydroxyl groups, reducing agglomeration caused by electrostatic effects. It can also form a physical isolation layer on the particle surface, blocking direct contact between magnetic particles and weakening the adsorption effect caused by van der Waals forces. This fundamentally improves the powder dispersion state, which is different from the traditional surface improvement approach that only relies on lubricants to reduce the coefficient of friction.

[0022] (2) In the process flow provided by the present invention, the finely ground slurry is filtered and concentrated by a filter press until the moisture content does not exceed 15%, and then processed by a three-stage low-temperature drying process and high-speed pulverization of a belt dryer. This effectively avoids material melting, softening and surface composition changes caused by high temperature, and reduces particle adhesion. At the same time, the drying process reuses the residual heat generated during the cooling process of the pre-burned material, eliminating the need for additional heat sources and achieving efficient energy utilization. Subsequently, by adding 0.5-2% binder and 0-0.5% lubricant, the pre-made magnetic powder is obtained through strong mixing and dispersion. Then, it is formed by magnetic field molding and air sintering to produce the finished product. The entire process does not require complex additional equipment and procedures, is easy to operate and is compatible with the existing production system. The excellent flowability of the magnetic powder can also significantly improve the magnetic field orientation effect during the molding process, effectively making up for the performance shortcomings of the traditional dry pressing process compared with the wet pressing process, and comprehensively improving the overall quality of the product. Detailed Implementation

[0023] The specific embodiments of the present invention will be described in detail below, but it should be understood that the scope of protection of the present invention is not limited to the specific embodiments.

[0024] Example 1

[0025] This embodiment provides a dry-pressed permanent magnet ferrite, which is prepared through the following steps: S10. Preparation of ferrite pre-sintered material coarse powder: Weigh 1 ton of material containing iron oxide red and strontium carbonate at a molar ratio of 5.75, and weigh 0.1% boric acid and 0.2% light calcium carbonate from 1 ton of total weight. Then, process the mixture through a 4m... 3 After being mixed for 20 minutes in a strong mixer, the material is densified by a 1.5×7 meter densifier. After being densified, the material is stirred evenly with 8% pre-adjusted tap water at pH 8. Then, it is pelletized in a ￠2.5m pelletizer to obtain 6-7mm pellets, which are then conveyed to a rotary kiln for pre-firing at 1190℃. After the pre-firing pellets are cooled, they are crushed to obtain 3-6μm ferrite pre-fired coarse powder. S20, Fine grinding: Weigh 1.5 tons of the above coarse powder and add 0.8% dicalcium silicate, and fine grind it in a 1.5T ball mill for 12 hours; S30, Concentration: After fine grinding, the slurry is filtered by a filter press and then dispersed to obtain a residue with a moisture content of 12%. S40. Drying: The concentrated residue is dried in a three-stage belt dryer, including preheating at 50℃ for 1.5 hours, drying at 75℃ for 4.5 hours, and cooling at low temperature by natural wind for 0.8 hours. The hot air velocity is 1.5 m / s and the humidity is 10%RH. After drying, the material is broken up by a 400-type high-speed pulverizer to obtain dry-pressed magnetic powder with a moisture content of 0.32%. S50, Powdering: Weigh 1 ton of dry-pressed magnetic powder and add 1.2% water and 0.3% zinc stearate, then process it through a 4m... 3 After mixing in a high-speed mixer for 20 minutes, the mixture is dispersed using a 400-type high-speed pulverizer to obtain pre-made magnetic powder (angle of repose 42.2°). S60, Dry pressing magnetic field forming: Pre-made magnetic powder is pressed into shape under a 5000Oe magnetic field to form a green body; S70, Sintering: The green blank is sintered in air at a temperature of 1220℃ for 1.5 hours. After cooling, the permanent magnet ferrite material is obtained.

[0026] Example 2

[0027] The difference between this embodiment and Embodiment 1 is that "the molar ratio of iron oxide red to strontium carbonate is 5.75" is changed to "the molar ratio of iron oxide red to strontium carbonate is 5.45", "the pre-firing temperature of the rotary kiln is 1190℃" is changed to "the pre-firing temperature of the rotary kiln is 1170℃", and "drying at 75℃ for 4.5 hours in the drying process" is changed to "drying at 72℃ for 5 hours in the drying process".

[0028] The remaining raw materials and preparation process are the same as in Example 1.

[0029] Example 3

[0030] The difference between this embodiment and Embodiment 1 is that "the molar ratio of iron oxide red to strontium carbonate is 5.75" is changed to "the molar ratio of iron oxide red to strontium carbonate is 6.05", "the pre-firing temperature of the rotary kiln is 1190℃" is changed to "the pre-firing temperature of the rotary kiln is 1220℃", and "drying at 75℃ for 4.5 hours in the drying process" is changed to "drying at 81℃ for 3.5 hours in the drying process".

[0031] The remaining raw materials and preparation process are the same as in Example 1.

[0032] Example 4

[0033] The difference between this embodiment and Embodiment 1 is that "the molar ratio of iron oxide red to strontium carbonate is 5.75" is changed to "the molar ratio of iron oxide red to strontium carbonate is 5.60", and "drying at a medium temperature of 75°C for 4.5 hours in the drying process" is changed to "drying at a medium temperature of 69°C for 5.5 hours in the drying process".

[0034] The remaining raw materials and preparation process are the same as in Example 1.

[0035] Example 5

[0036] The difference between this embodiment and Embodiment 1 is that "0.8% dicalcium silicate addition" is changed to "0.1% dicalcium silicate addition".

[0037] The remaining raw materials and preparation process are the same as in Example 1.

[0038] Example 6

[0039] The difference between this embodiment and Embodiment 1 is that "0.8% dicalcium silicate addition" is changed to "1.5% dicalcium silicate addition".

[0040] The remaining raw materials and preparation process are the same as in Example 1.

[0041] Example 7

[0042] The difference between this embodiment and Embodiment 1 is that "adding 1.2% water and 0.3% zinc stearate during powder preparation" is changed to "adding 0.5% water and 0.5% zinc stearate during powder preparation".

[0043] The remaining raw materials and preparation process are the same as in Example 1.

[0044] Example 8

[0045] The difference between this embodiment and Embodiment 1 is that "adding 1.2% water during powder preparation" is changed to "adding 2.0% camphor powder during powder preparation".

[0046] The remaining raw materials and preparation process are the same as in Example 1.

[0047] Comparative Example 1

[0048] The difference between this comparative example and Example 1 is that dicalcium silicate is not added during fine grinding; instead, calcium carbonate and silica powder (0.5% calcium carbonate and 0.3% silica) in equal mass proportions are added. The specific implementation steps are as follows: During the fine grinding stage, 0.5% calcium carbonate and 0.3% silica powder are added to 1.5 tons of ferrite pre-calcined coarse powder to replace the 0.8% dicalcium silicate in Example 1, and the powder is finely ground in a 1.5T ball mill for 12 hours.

[0049] The remaining raw materials and preparation process are the same as in Example 1.

[0050] Comparative Example 2

[0051] The difference between this comparative example and Example 1 is that dicalcium silicate is not added during fine grinding. Instead, calcium carbonate and silica powder (0.6% calcium carbonate and 0.2% silica) in equal mass proportions are added. The specific implementation steps are as follows: During the fine grinding stage, 0.6% calcium carbonate and 0.2% silica powder are added to 1.5 tons of ferrite pre-calcined coarse powder to replace 0.8% dicalcium silicate in Example 1, and the mixture is finely ground in a 1.5T ball mill for 12 hours.

[0052] The remaining raw materials and preparation process are the same as in Example 1.

[0053] Comparative Example 3

[0054] Compared with Example 1, the difference in this comparative example is that a high-temperature environment is used for drying. The specific implementation steps are as follows: During the drying stage, the concentrated residue is dried at a high temperature of 120°C in the drying equipment, and the drying time is shortened to 2 hours, so that the moisture content of the residue is controlled within 0.28%. Because the drying temperature is too high, the required temperature cannot be reached by using only residual heat, so an independent heat source needs to be added for heating, and the three-stage drying process of "low temperature preheating, medium temperature drying, and low temperature cooling" is cancelled.

[0055] The remaining raw materials and preparation process are the same as in Example 1.

[0056] Comparative Example 4

[0057] Compared with Example 1, the difference in this comparative example is that a high-temperature environment is used for drying. The specific implementation steps are as follows: During the drying stage, the concentrated residue is dried at a high temperature of 350°C in the drying equipment, and the drying time is shortened to 1 hour, so that the moisture content of the residue is controlled within 0.25%. Because the drying temperature is too high, the required temperature cannot be reached by using only residual heat, so an independent heat source needs to be added for heating, and the three-stage drying process of "low temperature preheating, medium temperature drying, and low temperature cooling" is cancelled.

[0058] The remaining raw materials and preparation process are the same as in Example 1.

[0059] Comparative Example 5

[0060] Compared with Example 1, the difference in this comparative example is that a high-temperature environment is used for drying. The specific implementation steps are as follows: During the drying stage, the concentrated residue is dried at a high temperature of 500°C in the drying equipment, and the drying time is shortened to 0.8 hours, so that the moisture content of the residue is controlled within 0.26%. Because the drying temperature is too high, the required temperature cannot be reached by using only residual heat, so an independent heat source needs to be added for heating, and the three-stage drying process of "low temperature preheating, medium temperature drying, and low temperature cooling" is cancelled.

[0061] The remaining raw materials and preparation process are the same as in Example 1.

[0062] Comparative Example 6

[0063] The difference between this comparative example and Example 1 is that the hot air velocity during drying is adjusted to 1.0 m / s. The specific implementation steps are as follows: during the drying stage, the hot air velocity of the three-section belt dryer is set to 1.0 m / s, and the other drying process parameters (temperature, time, humidity) are the same as those in Example 1.

[0064] The remaining raw materials and preparation process are the same as in Example 1.

[0065] Comparative Example 7

[0066] The difference between this comparative example and Example 1 is that a conventional preparation method is used, the additives are replaced during fine grinding, and a high-temperature environment is used during drying. The specific implementation steps are as follows: 1. In the fine grinding stage, 0.5% calcium carbonate and 0.3% silica powder are added to 1.5 tons of ferrite pre-calcined material coarse powder to replace 0.8% dicalcium silicate in Example 1, and fine grinding is carried out in a 1.5T ball mill for 12 hours; 2. In the drying stage, the concentrated slag is dried at a high temperature of 350℃ in a drying equipment, and the drying time is shortened to 1 hour, so that the moisture content of the slag is controlled within 0.27%. An independent heat source is required for heating, and the three-stage drying process is eliminated.

[0067] The remaining raw materials and preparation process are the same as in Example 1.

[0068] Comparative Example 8

[0069] The difference between this comparative example and Example 1 lies in the use of a conventional method, the replacement of additives during fine grinding, and the use of a high-temperature environment during drying. The specific implementation steps are as follows: 1. In the fine grinding stage, 0.6% calcium carbonate and 0.2% silica powder are added to 1.5 tons of ferrite pre-calcined material coarse powder, replacing the 0.8% dicalcium silicate in Example 1, and finely ground in a 1.5T ball mill for 12 hours; 2. In the drying stage, the concentrated slag is dried at 500℃ in a drying device, shortening the drying time to 0.8 hours, controlling the moisture content of the slag to within 0.25%. An independent heat source is required, and the three-stage drying process is eliminated. The remaining raw materials and preparation process remain the same as in Example 1.

[0070] Performance testing

[0071] 1. Magnetic performance indicators (Br remanence, Hcb magnetic coercivity, Hcj intrinsic coercivity, BHmax maximum energy product, Hk / Hcj coercivity ratio): performed in accordance with GB / T 3217-2013 "Test Methods for Magnetic Properties of Permanent Magnet (Hard Magnet) Materials".

[0072] 2. Angle of repose of pre-made magnetic powder (flowability test): Performed in accordance with GB / T 1482-2022 "Standard funnel method (Hall flowmeter method) for determination of flowability of metal powders".

[0073] 3. Moisture content of dry-pressed magnetic powder: The moisture content was determined by drying at 105℃ to constant weight using the loss on drying method.

[0074] The results are shown in Table 1: Table 1

[0075] As can be seen from Table 1, the repose angle of the pre-made magnetic powder in all embodiments (1-8) is concentrated between 41.5° and 44.8°, and is ≤45°, which fully meets the technical goal of "excellent flowability". In the comparative examples, Comparative Examples 1-2 and 7-8, which did not use dicalcium silicate but instead used traditional calcium carbonate + silicon dioxide, all had an angle of repose ≥48.8°, with Comparative Example 7-8 reaching an even higher angle of repose of 55.8°-56.2°, indicating extremely poor fluidity. This directly demonstrates that replacing traditional additives with dicalcium silicate is the core to improving the dispersibility of magnetic powder and inhibiting agglomeration. Comparative Examples 3-5, which were dried at high temperatures of 120°C-500°C, had an angle of repose of 50.3°-51.8°, significantly higher than the low-temperature drying group in the examples, confirming the technical pain point that high temperatures can cause particle melting and adhesion, exacerbating agglomeration. Comparative Example 6, with a drying wind speed of less than 1.0 m / s, had an angle of repose of 47.5%, and the moisture content of the dry-pressed magnetic powder increased to 0.62%, indicating that when the wind speed is lower than the 1.2-1.8 m / s specified in the claims, it will cause uneven drying and excessive moisture content, thereby weakening the fluidity of the magnetic powder.

[0076] Regarding the magnetic properties of the products, the core indicators of the embodiments are comprehensively superior to those of the comparative examples, achieving a significant approximation of the performance of dry pressing to that of wet pressing. The dry pressing Br:wet pressing Br ratio of all embodiments is between 96.2% and 97.6%, far exceeding the 90%-92% of the traditional dry pressing process. Among them, the ratio of 97.6% in embodiment 6 is the best among all groups, indicating that after dicalcium silicate improves the fluidity, the magnetic field orientation of the magnetic powder during the molding process is significantly improved, effectively making up for the performance shortcomings of the dry pressing process. The remanent magnetism Br of the embodiments is concentrated between 3945Gs and 4002Gs, the maximum magnetic energy product BHmax is between 3.81 and 3.96MGoe, the intrinsic coercivity Hcj is between 3297Oe and 3355Oe, and Hk / Hcj is ≥0.935, demonstrating stable and excellent magnetic properties and magnetic stability. In the comparative examples, Comparative Examples 1-2 and 7-8, which did not use dicalcium silicate, had a dry-pressed Br:wet-pressed Br ratio of only 91.7%-93.6% and a BHmax ≤ 3.80 MGoe, significantly lower than the examples. Comparative Examples 3-5, which were dried at high temperature, had a ratio of 92.1%-92.6% and a BHmax ≤ 3.78 MGoe, proving that particle agglomeration caused by high temperature directly leads to a decrease in magnetic properties. Comparative Example 6, which had insufficient drying air velocity, had a ratio of 94.1% and a BHmax of 3.84 MGoe, indicating that slight deviations in the drying process can be transmitted to the final performance. Comparative Examples 7-8, which used the conventional method, had the worst performance, with a dry-pressed Br:wet-pressed Br ratio of only 91.7%-91.8% and a BHmax as low as 3.65-3.69 MGoe, forming a stark contrast with the examples and highlighting the inventive advantages of the technical solution of this invention.

[0077] The above-disclosed embodiments are merely a few specific examples of the present invention. However, the embodiments of the present invention are not limited thereto, and any variations that can be conceived by those skilled in the art should fall within the protection scope of the present invention.

Claims

1. A method for preparing dry-pressed permanent magnet ferrite, characterized in that, Includes the following steps: S10. Preparation of ferrite pre-sintered material coarse powder: Iron oxide red and strontium carbonate are weighed in a molar ratio of 5.45-6.05, and 0.1-0.25% boric acid and 0.1-0.5% light calcium carbonate are added according to the total weight of iron oxide red and strontium carbonate. After being strongly mixed in a strong mixer, the mixture is densified in a densifier. After being pre-mixed with water, the densified material is pelletized in a pelletizer. The pellets are then transported to a rotary kiln for pre-sintering. After the pre-sintered pellets are cooled, they are crushed to obtain ferrite pre-sintered material coarse powder. S20, Fine grinding: Add 0.1%-1.5% dicalcium silicate to the above coarse powder to replace the traditional calcium carbonate and silica additives and grind it in a ball mill. S30. Concentration: After fine grinding, the slurry is filtered by a filter press and then dispersed to obtain a residue with a moisture content of no more than 15%. S40. Drying: The concentrated residue is dried in a belt dryer by "low temperature preheating, medium temperature drying, and low temperature cooling", and then broken up by a high-speed pulverizer to obtain dry-pressed magnetic powder with a moisture content of no more than 0.5%. S50. Powdering: Add 0.5-2% binder and 0.1-0.5% lubricant to the dry-pressed magnetic powder, mix it evenly with a strong mixer, and then break it apart with a high-speed pulverizer to obtain pre-made magnetic powder with excellent flowability. S60, Dry pressing magnetic field forming: Pre-made magnetic powder is pressed into shape under a magnetic field to form a green body; S70, Sintering: The green blank is sintered in air and cooled to obtain permanent magnet ferrite material.

2. The method for preparing dry-pressed permanent magnet ferrite according to claim 1, characterized in that, When preparing the coarse powder of the ferrite pre-sintered material in S10, 5-10% of pre-adjusted tap water with a pH value of 7-9 is added during the pre-water mixing process; when preparing the coarse powder of the ferrite pre-sintered material in S10, the pellets produced by the pelletizing machine have a diameter of 5-8mm.

3. The method for preparing dry-pressed permanent magnet ferrite according to claim 1, characterized in that, When preparing the coarse powder of the ferrite pre-calcined material in S10, the pre-calcination temperature of the rotary kiln is 1170-1220℃. When preparing the coarse powder of the ferrite pre-calcined material in S10, the granules are cooled by air cooling to obtain hot air with a temperature ≥150℃, which is then used as a heat source for the subsequent drying process after dust removal.

4. The method for preparing dry-pressed permanent magnet ferrite according to claim 1, characterized in that, The dicalcium silicate added in S20 is a material that passes through a 200-mesh sieve and has a purity of ≥96%.

5. The method for preparing dry-pressed permanent magnet ferrite according to claim 1, characterized in that, The "low-temperature preheating, medium-temperature drying, and low-temperature cooling" method in S40 is as follows: low-temperature preheating at 45-60℃ for 1-2 hours, medium-temperature drying at 65-85℃ for 3-6 hours, and low-temperature cooling by natural wind for 0.5-1 hours. The heat source used for low-temperature preheating and medium-temperature drying is the hot air after cooling treatment during the preparation of ferrite pre-calcined material coarse powder, which is adjusted to the required temperature by combining with cold air. The hot air velocity is 1.2-1.8 m / s, and the humidity is ≤15% RH.

6. The method for preparing dry-pressed permanent magnet ferrite according to claim 1, characterized in that, The S40 belt dryer uses a 100-120 mesh twill woven belt made of 316 stainless steel with a belt thickness of 0.8-1.2mm.

7. The method for preparing dry-pressed permanent magnet ferrite according to claim 1, characterized in that, The dry-pressed magnetic powder prepared in S40 has a repose angle of 35-40° as determined by the funnel method; the pre-made magnetic powder prepared in S50 has a repose angle of 40-45° as determined by the funnel method.

8. The method for preparing dry-pressed permanent magnet ferrite according to claim 1, characterized in that, The adhesive in S50 is water or camphor powder; the lubricant is zinc stearate.

9. The method for preparing dry-pressed permanent magnet ferrite according to claim 1, characterized in that, In step S60, the magnetic field strength is not less than 5000 Oe; in step S70, the sintering temperature is 1200℃-1250℃, and the holding time is 1-2 hours.

10. A dry-pressed permanent magnet ferrite, characterized in that, It is prepared by the method for preparing dry-pressed permanent magnet ferrite according to any one of claims 1-9.

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