A method for manufacturing an anisotropic permanent magnet ferrite magnet and the magnet itself.

Abstract

This invention discloses a method for manufacturing anisotropic permanent ferrite magnets and the magnet itself, belonging to the field of magnetic materials technology. The method for manufacturing anisotropic permanent ferrite magnets includes the following steps: wet ball milling of pre-calcined material and controlling the moisture content of the resulting pre-calcined slurry; orienting and pressing the pre-calcined slurry into magnetic blocks; processing the magnetic blocks into larger magnetic block particles; mixing the magnetic block particles with a surfactant; pulverizing the mixture to obtain smaller magnetic powder; dry pressing the magnetic powder to obtain a green body; and sintering the green body to obtain the magnet. This invention optimizes the manufacturing process of magnets with special shapes, sizes, and properties. This method has high production efficiency and low cost, and the resulting product is anisotropic permanent ferrite magnet, which is impossible to achieve with anisotropic wet orientation molding and whose magnetic properties cannot be achieved with isotropic product manufacturing processes.

Description

Technical Field

[0001] This invention belongs to the field of magnetic materials technology, specifically relating to a method for manufacturing an anisotropic permanent magnet ferrite magnet and the magnet itself. Background Technology

[0002] Permanent ferrite magnets are used in various industries, including automotive motors, audio microphones, home appliances, automatic control, and the information industry. These magnets vary in shape, size, and weight, and can be classified into isotropic and anisotropic types based on their magnetization method. However, both isotropic and anisotropic products have limitations in shape, size, and performance due to manufacturing constraints. Isotropic products have a lower performance ceiling (as defined in the industry standard SJ / T10410-2016 for permanent ferrite materials: Y8T, Br: 200~235mT, Hcb: 125~160KA / m, Hcj: 210~280KA / m, (BH)max: 6.5~9.5KJ / m3). Anisotropic permanent ferrite magnets, on the other hand, exhibit magnetic properties with a distinct directionality. Existing methods for manufacturing anisotropic permanent ferrite magnets typically employ wet pressing or bond pressing, as illustrated in patent application CN116313471A. While anisotropic products offer high performance limits, the molding process requires water extraction and orientation. For magnets with large aspect ratios, such as cylinders, prisms, and toroidal cylinders, as well as small sheet magnets, water extraction and orientation are difficult to achieve, resulting in low yield and low production efficiency. In actual production, larger products can be pressed during the molding process, sintered, and then cut and ground to produce smaller versions. However, this adds an extra step and increases the grinding amount, leading to higher final product costs. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a method for manufacturing an anisotropic permanent magnet ferrite magnet and the magnet itself.

[0004] To achieve the above objectives, the present invention provides a method for manufacturing an anisotropic permanent magnet ferrite magnet, comprising the following steps:

[0005] S1: Wet ball mill the pre-calcined material to 0.8-1.1 μm to obtain a pre-calcined slurry;

[0006] S2: After controlling the moisture content of the pre-fired slurry to 30-40%, the pre-fired slurry is oriented and pressed into magnetic blocks;

[0007] S3: Process the magnetic block into magnetic block particles with a size of Φ6~Φ8mm;

[0008] S4: Mix the magnetic block particles with a surfactant, and pulverize the mixture to obtain magnetic powder with a particle size of 0.9–1.1 μm;

[0009] S5: The magnetic powder is dry-pressed to obtain a green body;

[0010] S6: Sinter the green blank to obtain a magnet.

[0011] Preferably, in step S2, the moisture content of the slurry is controlled by a dewatering device, thereby regulating the rheological properties of the slurry and ensuring that the particles can respond to the magnetic field as fully as possible to oriented and align in the subsequent orientation pressing process.

[0012] Preferably, in step S2, the orientation magnetic field strength used to orient and press the pre-calcined slurry into magnetic blocks is 800–1000 kA / m, and the molding pressure is ≥300 kg / cm². 2 Sufficiently strong magnetization intensity can ensure that the ferrite particles in the pre-fired slurry are fully oriented, ensuring that the magnetic block has high orientation and initial magnetic properties. Sufficiently large molding pressure can ensure that the density and mechanical strength of the obtained magnetic block meet the expected indicators, so as not to crack or even collapse in subsequent steps.

[0013] Preferably, in step S3, the processing specifically involves slicing the magnetic block into magnetic block particles while maintaining the crystal orientation already obtained inside the particles.

[0014] Preferably, in step S4, the surfactant is β-Ni(OH)2 powder, and the amount of surfactant added is 0.2 to 0.4 wt%. β-Ni(OH)2 can coat the surface of magnetic powder particles, significantly reducing particle adhesion in subsequent processing and ensuring the loose flowability of magnetic powder.

[0015] Preferably, in step S5, the forming pressure used in the dry pressing is ≥300 kg / cm². 2 High pressure causes magnetic powder particles to pack tightly, and the magnetic moment of the oriented particles guides the adjacent disordered particles to achieve pressure orientation under pressure, thereby improving the overall orientation degree and final magnetic properties of the magnet.

[0016] Preferably, in step S6, the sintering specifically involves sintering at 1180–1220°C for 1–2 hours in an oxygen atmosphere. The oxygen atmosphere prevents the ferrite from losing oxygen and undergoing degeneration at high temperatures, which would lead to changes in its magnetic properties. Sintering at the specified temperature and time ensures that the grains are sufficiently densified while avoiding over-burning.

[0017] Preferably, the anisotropic permanent magnet ferrite magnet is cylindrical with an aspect ratio greater than 2 or has a volume less than 0.5 cm². 3 The sheet shape refers specifically to a geometric shape with a thickness-to-minimum-width ratio of less than 0.2. This invention breaks through conventional methods and has extremely high applicability to magnets of this special shape.

[0018] The present invention also proposes an anisotropic permanent magnet ferrite magnet, which is manufactured using the above-described manufacturing method.

[0019] Compared with existing technologies, this invention has the following advantages and effects: This invention optimizes the manufacturing process of anisotropic permanent ferrite magnets. Compared with the traditional isotropic dry pressing method, it uses a method where the oriented magnetic block is crushed into magnetic powder. The addition of surfactant β-Ni(OH)2 prevents the magnetic powder from sticking together. During molding, pressure naturally aligns the randomly arranged magnetic moment particles, concentrating them near the oriented particles, thus forming pressure orientation and improving magnetic properties. Compared with the traditional anisotropic wet pressing method, because this invention uses dry pressing, it achieves higher product yield, higher production efficiency, and lower costs for cylindrical magnets with large aspect ratios and small sheet magnets. Attached Figure Description

[0020] Figure 1 This is a flowchart of a method for manufacturing an anisotropic permanent magnet ferrite magnet according to the present invention.

[0021] Figure 2 This is a demagnetization curve of the magnet obtained in Embodiment 1 of the present invention.

[0022] Figure 3 This is a demagnetization curve of the magnet obtained in Embodiment 2 of the present invention.

[0023] Figure 4 This is a demagnetization curve of the magnet obtained in Embodiment 3 of the present invention.

[0024] Figure 5 This is a demagnetization curve of the magnet obtained in Comparative Example 1 of the present invention.

[0025] Figure 6 This is a demagnetization curve of the magnet obtained in Comparative Example 2 of the present invention.

[0026] Figure 7 This is a demagnetization curve of the magnet obtained in Comparative Example 3 of the present invention. Detailed Implementation

[0027] The technical solutions in the embodiments of the present invention will be clearly and completely described below. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0028] Example 1

[0029] like Figure 1 As shown, this embodiment provides a method for manufacturing an anisotropic permanent magnet ferrite magnet. The magnet is a cylinder with a diameter of approximately 28 mm and a height of approximately 10 mm. The method steps are as follows:

[0030] 1) Select BMS-12 grade permanent magnet ferrite pre-sintered material, and wet ball mill the pre-sintered material to 0.85μm;

[0031] 2) The slurry moisture content was controlled to 35% using a dewatering machine, and then magnetic blocks were formed using a strong magnetic field wet orientation molding process. The orientation magnetic field was 900 kA / m, and the resulting magnetic blocks had a density of 3.27 g / cm³. 3 ;

[0032] 3) Use a cutting machine to slice the magnetic block and cut it into magnetic block particles with a size of Φ6.9mm;

[0033] 4) Add 0.3wt% β-Ni(OH)2 powder to the magnetic block particles and pulverize it to 0.98μm magnetic powder using a high-speed pulverizer;

[0034] 5) The magnetic powder obtained by pulverization is pressed into a green body using a dry pressing machine at a pressure of 330 kg / cm². 2 ;

[0035] 6) The green body is sintered at 1200℃ for 1.5 hours, with oxygen continuously introduced during the sintering process;

[0036] 7) Finally, the magnet is ground to the required dimensions and its performance is tested.

[0037] The demagnetization curve of the magnet obtained in this embodiment was detected as follows: Figure 2 The magnetic properties of the obtained magnet can be obtained by analyzing the demagnetization curve as follows:

[0038] Remanence Br = 437.6 mT; Coercivity Hc b =323.5KA / m; intrinsic coercivity Hc j =387.0KA / m; Maximum magnetic energy product (BH) max =38.24KJ / m 3 .

[0039] Example 2

[0040] This embodiment provides a method for manufacturing a ring-shaped permanent magnet ferrite sheet, requiring the following dimensions: outer diameter Φ38.5. ±1 mm, inner diameter 15.5 ±0.5 mm, thickness 30.0 ±0.1 mm.

[0041] The manufacturing method in this embodiment adopts the following steps:

[0042] 1) Select BMS-6 grade permanent magnet ferrite pre-sintered material, wet ball mill fine pulverization, and the particle size was measured to be 0.92μm;

[0043] 2) The moisture content of the slurry was controlled at 30-40% using a dewatering machine, and the measured moisture content was 34.7%. A rectangular magnet molding die (150×100×25.4mm) was used to press rectangular magnetic blocks into shape in an 800KA / m orientation magnetic field. The lowest measured density of the magnetic blocks was 3.34 g / cm³. 3 ;

[0044] 4) The magnetic blocks were sliced ​​and crushed into particles using an automatic slicer with a particle size of Φ7.4mm. 0.2wt% of β-Ni(OH)2 powder was added and then crushed into powder using a high-speed pulverizer. The particle size of the powder was measured to be 0.96μm.

[0045] 5) The powder is automatically pressed into 1000 green pieces using a dry pressing machine, with a pressing pressure of 310 kg / cm². 2 ;

[0046] 6) The green blanks are sintered at 1200℃ in an oxygen atmosphere for 1 hour, with oxygen continuously introduced during the sintering process;

[0047] 7) Grinding is used to achieve the required dimensional tolerances, and the magnet performance is tested.

[0048] The demagnetization curve of the magnet obtained in this embodiment was detected as follows: Figure 3 The magnetic properties of the obtained magnet can be obtained by analyzing the demagnetization curve as follows:

[0049] Remanence Br = 407.2 mT, coercivity Hcb = 287.5 kA / m, intrinsic coercivity Hcj = 307.7 kA / m, maximum energy product (BH). max =31.61KJ / m 3 Of the 1000 magnets produced using the above method, 78 were found to be defective and cracked.

[0050] Example 3

[0051] This embodiment provides a method for manufacturing a circular permanent magnet ferrite sheet, requiring an outer diameter of Φ7.2 mm. ±0.05 mm, thickness 1.1 ±0.05 mm;

[0052] The manufacturing method in this embodiment adopts the following steps:

[0053] 1) Select BMS-9 grade permanent magnet ferrite pre-sintered material, wet ball mill fine pulverization, and the particle size was measured to be 0.85μm;

[0054] 2) The moisture content of the slurry was controlled at 30-40% using a dewatering machine, and the measured moisture content was 36.3%.

[0055] 3) Using the same mold as in Example 3, rectangular magnetic blocks were pressed into a magnetic field of 900 kA / m. The lowest measured magnetic block density was 3.35 g / cm³. 3 ;

[0056] 4) The magnetic blocks were sliced ​​and crushed into particles using an automatic slicer with a particle size of Φ7.3mm. 0.3wt% of β-Ni(OH)2 powder was added and then crushed into powder using a high-speed pulverizer. The particle size of the powder was measured to be 0.95μm.

[0057] 5) The powder is automatically pressed into 1000 green pieces using a dry pressing machine, with a pressing pressure of 320 kg / cm². 2 ;

[0058] 6) Sinter the green blanks at 1190℃ and hold for 2 hours, continuously introducing oxygen during the sintering process;

[0059] 7) Grinding is used to achieve the required dimensional tolerances, and the magnet performance is tested.

[0060] The demagnetization curve of the magnet obtained in this embodiment was detected as follows: Figure 4 The magnetic properties of the obtained magnet can be obtained by analyzing the demagnetization curve as follows:

[0061] Remanence Br = 427.1 mT, coercivity Hcb = 304.85 kA / m, intrinsic coercivity Hcj = 386.1 kA / m, maximum energy product (BH). max =33.72KJ / m 3 Of the 1,000 magnets produced using the above method, 89 were found to be defective and cracked.

[0062] Comparative Example 1

[0063] This comparative example provides a method for manufacturing a toroidal permanent magnet ferrite sheet, requiring the following dimensions: outer diameter Φ38.5. ±1 mm, inner diameter 15.5 ±0.5 mm, thickness 30.0 ±0.1 mm; produced using the following steps:

[0064] 1) Select BMS-6 grade permanent magnet ferrite pre-sintered material, wet ball mill fine pulverization, and the particle size was measured to be 0.91μm;

[0065] 2) The moisture content of the slurry was controlled at 30-40% using a dewatering machine, and the measured moisture content was 34.6%.

[0066] 3) 1000 green blanks were pressed using a wet pressing machine in an 800KA / m orientation magnetic field;

[0067] 4) Sinter the green blank at 1200℃ in an oxygen atmosphere for 1 hour (test the temperature before sintering).

[0068] 5) Grinding is used to achieve the required dimensional tolerances, and the magnet performance is tested.

[0069] The demagnetization curve of the magnet obtained in this comparative example is as follows: Figure 5 The magnetic properties of the obtained magnet can be obtained by analyzing the demagnetization curve as follows:

[0070] Remanence Br = 410.2 mT, coercivity Hcb = 285.2 kA / m, intrinsic coercivity Hcj = 305.0 kA / m, maximum energy product (BH). max =31.59KJ / m 3 Of the 1000 magnets produced using the above method, 316 were found to be defective and cracked.

[0071] Comparative Example 2

[0072] This comparative example provides a method for manufacturing a circular permanent magnet ferrite sheet, requiring the following dimensions: outer diameter Φ7.2. ±0.0.5 mm, thickness 1.1 ±0.05 mm; produced using the following steps:

[0073] 1) Select BMS-9 grade permanent magnet ferrite pre-sintered material, wet ball mill fine pulverization, and the particle size was measured to be 0.85μm;

[0074] 2) The moisture content of the slurry was controlled at 30-40% using a dewatering machine, and the measured moisture content was 35.9%.

[0075] 3) Using the same mold as in Example 3, rectangular magnetic blocks were pressed into a magnetic field of 900 kA / m. The lowest measured magnetic block density was 3.36 g / cm³. 3 ;

[0076] 4) The magnetic blocks were sliced ​​and crushed into particles using an automatic slicer with a particle size of Φ7.3mm. The particles were then pulverized into powder using a high-speed pulverizer, and the particle size of the powder was measured to be 0.94μm.

[0077] 5) Press 1000 green pieces of powder using a dry pressing machine, with a forming pressure of 320 kg / cm². 2 ;

[0078] 6) Sinter the green blanks at 1190℃ and hold for 2 hours;

[0079] 7) Grinding is used to achieve the required dimensional tolerances, and the magnet performance is tested.

[0080] The demagnetization curve of the magnet obtained in this comparative example is as follows: Figure 6The magnetic properties of the obtained magnet can be obtained by analyzing the demagnetization curve as follows:

[0081] Remanence Br = 408.7 mT, coercivity Hc b =299.2KA / m, intrinsic coercivity Hc j =366.8KA / m, maximum magnetic energy product (BH) max =32.06KJ / m 3 Of the 1000 magnets produced using the above method, 91 were found to be defective and cracked.

[0082] Comparative Example 3

[0083] The required dimensions for the magnet are: outer diameter Φ7.2. ±0.0.5 mm, thickness 1.1 ±0.05 mm; produced using the following steps:

[0084] 1) Select BMS-9 grade permanent magnet ferrite pre-sintered material, wet ball mill fine pulverization, and the particle size was measured to be 0.85μm;

[0085] 2) After drying the slurry, add 8% calcium stearate binder to form 0.6-0.9mm particles;

[0086] 3) 1000 green pieces were pressed using a dry pressing machine in a 900KA / m orientation magnetic field, with a forming pressure of 320kg / cm². 2 ;

[0087] 6) Sinter the green blanks at 1190℃ and hold for 2 hours;

[0088] 7) Grinding is used to achieve the required dimensional tolerances, and the magnet performance is tested.

[0089] The demagnetization curve of the magnet obtained in this comparative example is as follows: Figure 7 The magnetic properties of the obtained magnet can be obtained by analyzing the demagnetization curve as follows:

[0090] Remanence Br = 389.4 mT, coercivity Hc b =292.7KA / m, intrinsic coercivity Hc j =349.2KA / m, maximum magnetic energy product (BH) max =30.28KJ / m 3 Of the 1000 magnets produced using the above method, 92 were defective and cracked.

[0091] The difference between Comparative Example 1 and Example 2 is that Comparative Example 1 used wet pressing orientation molding to press the green blank. The magnetic properties of the final magnets were similar, but Comparative Example 1 had 238 more crack defects. This is because wet pressing orientation molding requires water removal, and the magnet has a large aspect ratio, which leads to incomplete water removal in the middle part of the green blank, resulting in a large number of crack defects after sintering.

[0092] The difference between Comparative Example 2 and Example 3 is that Comparative Example 2 did not add surfactant β-Ni(OH)2. The final magnet performance of Comparative Example 2 was lower than that of Example 4. This is because some of the magnetic powder will stick together after being crushed. During molding, the sticky magnetic powder is not completely oriented under pressure orientation, resulting in the lower final magnet performance. The present invention proposes to add surfactant β-Ni(OH)2 to the magnetic powder, which can effectively solve this problem.

[0093] The difference between Comparative Example 3 and Example 3 is that Comparative Example 3 used traditional dry pressing orientation molding to press the green blank. The number of crack defects in the final magnet was about the same. However, when using the same pre-fired material, the magnetic properties achieved by Comparative Example 3 were only about 90% of those of Example 4. This is because dry pressing orientation molding requires drying the ball-milled material and then adding a binder to make particles. The orientation degree is not high during dry pressing orientation molding, which leads to lower performance.

[0094] This invention optimizes the manufacturing process of anisotropic permanent magnet ferrite magnets, resulting in high production efficiency and low cost, and achieving superior magnetic properties in magnets of special sizes.

[0095] Although embodiments of the invention have been shown and described, those skilled in the art will recognize that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and concept of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method of manufacturing an anisotropic permanent ferrite magnet, characterized by, The method comprises the following steps: S1: wet ball milling the pre-sintered material to 0.8-1.1 μm to obtain a pre-sintered material slurry; S2: controlling the water content of the pre-sintered material slurry to 30-40%, and then orientally pressing the pre-sintered material slurry into a magnetic block; the orienting magnetic field strength used in the step of orientally pressing the pre-sintered material slurry into a magnetic block is 800-1000 KA / m; S3: processing the magnetic block into a magnetic block particle with a size of Φ6-Φ8 mm; S4: mixing the magnetic block particle with a surfactant, and crushing the mixture to obtain a magnetic powder with a size of 0.9-1.1 μm; the surfactant is β-Ni(OH)2 powder, and the addition amount of the surfactant is 0.2-0.4 wt%; S5: dry-pressing the magnetic powder to obtain a green body without applying an external magnetic field; S6: sintering the green body to obtain a magnet; The anisotropic permanent ferrite magnet has a shape of a columnar shape with an aspect ratio greater than 2 or a tab shape with a volume less than 0.5 cm 3 .

2. The method of producing an anisotropic permanent ferrite magnet according to claim 1, characterized by, In step S2, the water content of the slurry is controlled by a dehydration device.

3. The method of producing an anisotropic permanent ferrite magnet according to claim 1, characterized by, In step S2, the forming pressure used in the step of orientally pressing the pre-sintered material slurry into a magnetic block is ≥300 kg / cm2.

4. The method of producing an anisotropic permanent ferrite magnet according to claim 1, characterized by In step S3, the tool used for machining is a cutter for slicing the magnetic block into magnetic block particles.

5. The method of producing an anisotropic permanent ferrite magnet according to claim 1, characterized by In step S5, the forming pressure used in the dry compression molding is ≥ 300 kg / cm 2 .

6. The method of producing an anisotropic permanent ferrite magnet according to claim 1, characterized by In step S6, the sintering is specifically sintering at 1180-1220 °C for 1-2 hours in an oxygen atmosphere.

7. An anisotropic permanent ferrite magnet, characterized by, The magnet is prepared by the manufacturing method in any one of claims 1-6.

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