Dry-pressed anisotropic ferrite multipole magnetic ring and method for manufacturing the same

Abstract

The application provides a preparation method of a dry-pressed hetero iron oxide multi-pole magnetic ring. The preparation method comprises the following steps: a) mixing pre-sintering materials and additives, and grinding to prepare a magnetic precursor; b) wet-pressing 70wt%-95wt% of the magnetic precursor, crushing, and preparing pre-magnetized dry-pressed powder; c) crushing the remaining magnetic precursor, and preparing non-pre-magnetized dry-pressed powder; and d) mixing the pre-magnetized dry-pressed powder and the non-pre-magnetized dry-pressed powder, dry-pressing, and sintering to obtain the dry-pressed hetero iron oxide multi-pole magnetic ring. The method solves the problem of low magnetic performance of the dry-pressed hetero iron oxide multi-pole magnetic ring prepared in the prior art, and is suitable for the field of magnetic material preparation.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of magnetic material preparation, in particular to a dry-pressed anisotropic ferrite multipole magnetic ring and a preparation method thereof. BACKGROUND

[0002] Traditional permanent ferrite manufacturing methods include dry pressing and wet pressing. Wet pressing has the characteristics of good orientation, high residual magnetism and other magnetic properties, and has been widely used after decades of production practice. Dry pressing has the characteristics of fast forming efficiency, high qualification rate, wide application range, and product shape diversification, and can be applied to many miniaturized and irregularly shaped products. However, the comprehensive magnetic properties of dry pressing are not as good as those of wet pressing, resulting in waste of magnetic properties. For anisotropic ferrite multipole magnetic rings, it is difficult to prepare them using the wet pressing method. Direct dry pressing of raw materials with the same formulation as the pre-magnetized powder for dry pressing results in a greater impact on the magnetic properties of the product. Further, dry pressing of raw materials with the same formulation as the pre-magnetized powder for anisotropic ferrite multipole magnetic rings can improve the magnetic properties of the product to some extent, but the loss of magnetic properties is still large, and the product is prone to cracking and other problems, resulting in a low yield.

[0003] In Chinese Patent Application CN101599333A, a manufacturing method for dry-pressed anisotropic multipole magnetic rings is disclosed, which uses crushed pre-magnetized particles for double-sided isostatic pressing to prepare anisotropic multipole magnetic rings after dry pressing and sintering. The residual magnetism of the prepared anisotropic multipole magnetic rings is only 83% of that of wet pressing, resulting in serious waste of magnetic properties.

[0004] In Chinese Patent Application CN109133900A, a high-surface magnetic flux density dry-pressed permanent ferrite magnet and a preparation method thereof are disclosed, which uses crushed pre-magnetized particles, lubricants and binders for dry pressing to prepare a permanent ferrite magnet after sintering. Since the crushed pre-magnetized particles are relatively coarse, the green density is small during dry pressing, and the residual magnetism is also not high. SUMMARY

[0005] The main purpose of the present application is to provide a dry-pressed anisotropic ferrite multipole magnetic ring and a preparation method thereof to solve the problem of low magnetic properties of the anisotropic dry-pressed ferrite multipole magnetic ring prepared in the prior art.

[0006] To achieve the above objectives, according to a first aspect of the present invention, a method for preparing anisotropic dry-pressed ferrite multipole magnetic ring is provided. The method includes: a) mixing pre-burned material and additives, and grinding to prepare a magnetic precursor; b) wet-pressing 70wt% to 95wt% of the magnetic precursor, crushing it, and preparing pre-magnetized dry-pressed powder; c) pulverizing the remaining magnetic precursor to prepare unpre-magnetized dry-pressed powder; d) mixing the pre-magnetized dry-pressed powder and the unpre-magnetized dry-pressed powder, dry-pressing, and sintering to obtain anisotropic dry-pressed ferrite multipole magnetic ring.

[0007] Further, the grinding in a) includes wet grinding; preferably, wet grinding includes wet ball milling; preferably, the grinding time of wet ball milling is 10-15 h; preferably, the rotation speed of wet ball milling is 20-40 rpm; preferably, the diameter of the ball milling pellets is 6-8 mm; preferably, the particle size of the magnetic precursor is 0.6-1.2 μm, more preferably 0.8-0.9 μm; preferably, the particle size of the pre-calcined material is 5-6 μm.

[0008] Further, the additives include one or more of silicon dioxide, calcium carbonate, or boric acid; preferably, the amount of silicon dioxide added is 0.2% to 0.5% of the mass of the pre-fired material; preferably, the amount of calcium carbonate added is 0.8% to 1% of the mass of the pre-fired material; preferably, the amount of boric acid added is 0.05% to 0.2% of the mass of the pre-fired material.

[0009] Further, b) includes wet pressing 70wt% to 95wt% of the magnetic precursor, drying, crushing, and sieving to prepare pre-magnetized dry-pressed powder; preferably, the wet pressing process includes applying a magnetic field of 6000 to 10000 Oe along the pressing direction, and the pressing pressure is 2 to 5 MPa; preferably, the amount of magnetic precursor in b) is 80% to 90% of the total weight of the magnetic precursor; preferably, in b), drying is carried out at a first drying temperature of 60 to 100°C, more preferably 70 to 90°C, and even more preferably 80°C.

[0010] Furthermore, the moisture content of the pre-magnetized dry-pressed powder is 0.5-2%; preferably, the particle size of the pre-magnetized dry-pressed powder is 0.5-2 mm.

[0011] Further, c) includes drying, pulverizing, and sieving the remaining magnetic precursor to prepare unmagnetized dry-pressed powder; preferably, drying in c) is carried out at a second drying temperature of 60–100°C, more preferably 70–90°C, and even more preferably 80°C; preferably, the moisture content of the unmagnetized dry-pressed powder is 0.2–1%; preferably, the particle size of the unmagnetized dry-pressed powder is 0.8–1 μm, and the bulk density is 0.85–0.9 g / cm³. 3More preferably, the pulverization in c) includes two-stage or three-stage pulverization; even more preferably, the loose density of the unmagnetized dry-pressed powder after two-stage pulverization is 0.75–0.8 g / cm³. 3 More preferably, the loose density of the unmagnetized dry-pressed powder after three-stage grinding is 0.7–0.75 g / cm³. 3 .

[0012] Furthermore, the dry pressing process includes: applying a magnetic field of 6000-10000 Oe along the pressing direction, and a forming pressure of 2-5 MPa; preferably, the sintering temperature is 1200-1240℃; preferably, the sintering time is 1-2 h.

[0013] Furthermore, according to the above preparation method, the yield of the prepared anisotropic dry-pressed ferrite multipole magnetic ring is greater than 80%.

[0014] To achieve the above objectives, according to a second aspect of the present invention, an anisotropic dry-pressed ferrite multipole magnetic ring is provided, comprising anisotropic dry-pressed ferrite multipole magnetic ring prepared by the above-described preparation method.

[0015] Furthermore, under the same formulation, the anisotropic dry-pressed ferrite multipole magnetic ring does not crack compared to the multipole magnetic ring prepared by direct dry pressing; preferably, the magnetic properties of the anisotropic dry-pressed ferrite multipole magnetic ring are improved by 3 to 6% compared to the multipole magnetic ring prepared by direct pre-magnetization dry pressing.

[0016] By applying the technical solution of this invention, by adding a portion of unmagnetized dry-pressed powder to pre-magnetized dry-pressed powder, anisotropic dry-pressed permanent magnet ferrite multipole magnetic rings are prepared by dry pressing, thereby reducing magnetic performance loss and improving yield. Detailed Implementation

[0017] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other. The present invention will now be described in detail with reference to the embodiments.

[0018] Terminology Explanation:

[0019] Pre-magnetized dry-pressed powder: A magnetic precursor prepared by mixing and grinding pre-burned material and additives, then wet-pressing and crushing it to prepare powder.

[0020] Unmagnetized dry-pressed powder: A powder prepared by mixing and grinding pre-burned materials and additives to obtain a magnetic precursor, followed by drying and pulverizing.

[0021] As mentioned in the background section, multipole magnetic rings, as a branch of anisotropic ferrites, are widely used in variable frequency air conditioner motors, mahjong machines, washing machines, oil pump motors, servo motors, and stepper motors. Existing technologies contain anisotropic permanent magnet ferrite multipole magnetic rings, which are difficult to manufacture using wet pressing methods, while traditional dry pressing methods significantly affect the magnetic properties of the product and result in low yields. The inventors of this application have conducted in-depth research on the preparation methods of anisotropic permanent magnet ferrite multipole magnetic rings and proposed a method for preparing anisotropic dry-pressed ferrite multipole magnetic rings, as well as the resulting anisotropic dry-pressed ferrite multipole magnetic rings. This invention attempts to add a portion of unpre-magnetized dry-pressed powder to pre-magnetized dry-pressed powder, using dry pressing to prepare anisotropic dry-pressed permanent magnet ferrite multipole magnetic rings, thereby reducing magnetic property loss and improving yield.

[0022] Therefore, in this application, the inventors attempted to use the above-mentioned preparation method to dry-press anisotropic dry-pressed permanent magnet ferrite multipole magnetic rings, obtaining anisotropic dry-pressed permanent magnet ferrite multipole magnetic rings with low magnetic performance loss and high yield. Based on this, the applicant has proposed a series of protection schemes for this application.

[0023] In a first typical embodiment of this application, a method for preparing anisotropic dry-pressed ferrite multipole magnetic ring is provided. The method includes: a) mixing pre-burned material and additives, and grinding to prepare a magnetic precursor; b) wet-pressing 70wt% to 95wt% of the magnetic precursor, crushing it, and preparing pre-magnetized dry-pressed powder; c) pulverizing the remaining magnetic precursor to prepare unpre-magnetized dry-pressed powder; d) mixing the pre-magnetized dry-pressed powder and the unpre-magnetized dry-pressed powder, dry-pressing, and sintering to obtain anisotropic dry-pressed ferrite multipole magnetic ring.

[0024] Using the above preparation method, pre-calcined materials and additives are mixed and ground to prepare magnetic precursors. Additives are used to refine the grains, thereby achieving high intrinsic coercivity (Hcj) over a wider temperature range, increasing ferrite density, and improving the temperature coefficient. Most of the magnetic precursors are wet-pressed and crushed to prepare pre-magnetized dry-pressed powder, providing the magnetic properties for subsequent products. The remaining magnetic precursors are pulverized to prepare finer-particle-size unpre-magnetized dry-pressed powder. By adding finer-particle-size unpre-magnetized dry-pressed powder to the coarser-particle-size pre-magnetized dry-pressed powder, anisotropic dry-pressed ferrite multipole magnetic rings are prepared through dry pressing, improving both the magnetic properties of the dry-pressed product and the product yield.

[0025] In a preferred embodiment, the grinding in a) includes wet grinding; preferably, the wet grinding includes wet ball milling; preferably, the grinding time of the wet ball milling is 10-15 hours; preferably, the rotation speed of the wet ball milling is 20-40 rpm; preferably, the diameter of the balls used in the wet ball milling is 6-8 mm; preferably, the particle size of the magnetic precursor is 0.6-1.2 μm, more preferably 0.8-0.9 μm; preferably, the pre-calcined material includes DM4129, DM4240, or DM4748, etc.; preferably, the particle size of the pre-calcined material is 5-6 μm.

[0026] Wet grinding, preferably wet ball milling, is used to grind pre-calcined materials and additives. By flexibly adjusting grinding conditions such as grinding time, speed, and grinding balls, magnetic precursors with a particle size of 0.6–1.2 μm, preferably 0.8–0.9 μm, are prepared. The magnetic precursors prepared by wet ball milling exist in the form of a slurry. Pre-calcined materials include DM4129, DM4240, or DM4748. The preparation method for pre-calcined material DM4129 is as follows: iron oxide red and strontium ammonium carbonate are mixed in a molar ratio of 5.9–6.05, and 0.1–0.2 wt% of silica is added. Pre-calcination is carried out in a rotary kiln at 1270℃, and finally, dry ball milling is used to prepare a pre-calcined material with a particle size of 5–6 μm. Different types of pre-calcined materials are suitable for preparing heterogeneous dry-pressed ferrite multi-stage magnetic rings using this preparation method.

[0027] In a preferred embodiment, the additive includes one or more of silicon dioxide, calcium carbonate, or boric acid; preferably, the amount of silicon dioxide added is 0.2% to 0.5% of the mass of the pre-fired material; preferably, the amount of calcium carbonate added is 0.8% to 1% of the mass of the pre-fired material; preferably, the amount of boric acid added is 0.05% to 0.2% of the mass of the pre-fired material.

[0028] In the additives, calcium carbonate acts as a flux, producing low-melting-point products during subsequent sintering, lowering the reaction temperature, promoting solid-phase reactions, and increasing density and remanence. Silica reacts with calcium carbonate to form calcium silicate, which forms a liquid-phase glassy state enriched at grain boundaries, inhibiting grain growth, refining grains, and thus increasing Hcj. Using silica and boric acid, low-temperature co-firing conditions can be created, where the two can form a liquid-phase eutectic, inhibiting grain growth, appropriately lowering the pre-firing temperature, and forming fine-grained particles.

[0029] In a preferred embodiment, b) includes wet pressing a portion of the magnetic precursor, drying, crushing, and sieving to prepare a pre-magnetized dry-pressed powder; preferably, the wet pressing process includes applying a magnetic field of 6000-10000 Oe along the pressing direction and a pressing pressure of 2-5 MPa; preferably, the amount of magnetic precursor in b) is 80%-90% of the total weight of the magnetic precursor; preferably, in b), drying is carried out at a first drying temperature of 60-100°C, more preferably 70-90°C, and even more preferably 80°C.

[0030] In a preferred embodiment, the moisture content of the pre-magnetized dry-pressed powder is 0.5-2%; preferably, the particle size of the pre-magnetized dry-pressed powder is 0.5-2 mm.

[0031] 70wt%–95wt% of magnetic precursors are wet-pressed, dried, crushed, and sieved to prepare pre-magnetized dry-pressed powder, providing a magnetic performance basis for the subsequent preparation of anisotropic dry-pressed ferrite multipole magnetic rings. To further improve the magnetic performance of the prepared anisotropic dry-pressed ferrite multipole magnetic rings, 80wt%–90wt% of magnetic precursors are wet-pressed to prepare pre-magnetized dry-pressed powder. After wet pressing and before crushing and preparing the pre-magnetized dry-pressed powder, drying is performed at a first drying temperature of 60–100°C, more preferably 70–90°C, and even more preferably 80°C. After drying, crushing is performed, and the resulting pre-magnetized dry-pressed powder has a moisture content of 0.5–2% and a particle size of 0.5–2 mm, preferably 1.0–1.5 mm. By flexibly adjusting the drying temperature and drying time, the moisture content of the pre-magnetized dry-pressed powder can be controlled to prevent the moisture content from being too high. In the subsequent sintering process, the moisture will be heated into a gaseous state, forming pores in the material and reducing the density, performance, and strength of the anisotropic dry-pressed ferrite multipole magnetic ring product.

[0032] In a preferred embodiment, c) includes drying, pulverizing, and sieving the remaining magnetic precursor to prepare unmagnetized dry-pressed powder; preferably, drying in c) is carried out at a second drying temperature of 60–100°C, more preferably 70–90°C, and even more preferably 80°C; preferably, the moisture content of the unmagnetized dry-pressed powder is 0.2–1%; preferably, the particle size of the unmagnetized dry-pressed powder is 0.8–1 μm; preferably, the bulk density of the unmagnetized dry-pressed powder is 0.85–0.9 g / cm³. 3 More preferably, the pulverization in c) includes two-stage or three-stage pulverization; even more preferably, the loose density of the unmagnetized dry-pressed powder after two-stage pulverization is 0.75–0.8 g / cm³. 3 More preferably, the loose density of the unmagnetized dry-pressed powder after three-stage grinding is 0.7–0.75 g / cm³. 3 .

[0033] Residual magnetic precursors that have not undergone wet pressing are dried, pulverized, and sieved to prepare finer-particle-size unmagnetized dry-pressed powder, which increases the yield of dry-pressed products. Two-stage or three-stage pulverization produces more uniform unmagnetized dry-pressed powder, improving its orientation and enhancing the overall magnetic properties of the dry-pressed product. Increasing the number of pulverization stages only alters the bulk density of the powder, not the particle size. By flexibly adjusting the drying temperature and time, the moisture content of the unmagnetized dry-pressed powder can be controlled to prevent excessive moisture from being heated into a gaseous state during subsequent sintering, forming pores in the material and reducing the density, performance, and strength of the anisotropic dry-pressed ferrite multipole magnetic ring product.

[0034] In a preferred embodiment, the dry pressing process includes: applying a magnetic field of 6000-10000 Oe along the pressing direction, and a forming pressure of 2-5 MPa; preferably, the sintering temperature is 1200-1240℃; preferably, the sintering time is 1-2 h.

[0035] By mixing the above-mentioned pre-magnetized dry-pressed powder and non-pre-magnetized dry-pressed powder, and flexibly adjusting the dry-pressing parameters according to the type of dry-pressed powder and the performance requirements of the target product, the high-temperature sintering after dry pressing can eliminate the internal stress of the anisotropic dry-pressed ferrite multipole magnetic ring, which is conducive to improving the product yield.

[0036] In a preferred embodiment, the yield of the anisotropic dry-pressed ferrite multipole magnetic ring is greater than 80%. Using the above preparation method, the anisotropic dry-pressed ferrite multipole magnetic ring has a high yield and is less prone to cracking or other problems that affect the product's yield and appearance.

[0037] In a second typical embodiment of this application, an anisotropic dry-pressed ferrite multipole magnetic ring is provided, which includes anisotropic dry-pressed ferrite multipole magnetic rings prepared using the above-described preparation method.

[0038] In a preferred embodiment, under the same formulation, the anisotropic dry-pressed ferrite multipole magnetic ring does not crack compared to the multipole magnetic ring prepared by direct dry pressing; preferably, the magnetic properties (surface magnetic properties) of the anisotropic dry-pressed ferrite multipole magnetic ring are improved by 3% to 6% compared to the multipole magnetic ring prepared by direct pre-magnetized dry pressing.

[0039] Products prepared by wet pressing exhibit higher remanence than those prepared by dry pressing of the same material. Therefore, the remanence ratio between wet and dry pressing is calculated to measure the magnetic property (remanence) loss in products prepared by dry pressing. In existing processes for preparing anisotropic ferrite multipole magnetic rings, the large size of the wet pressing mold makes it impossible to apply complex magnetic field orientations to the smaller multipole rings, thus hindering the use of wet pressing. Furthermore, when preparing anisotropic dry-pressed ferrite multipole magnetic rings using the same raw material as the unmagnetized dry-pressed powder, the yield is very low, and the products frequently crack or even fail to form. Therefore, existing multipole magnetic rings are primarily prepared by pre-magnetizing dry-pressed powder, resulting in directly pre-magnetized dry-pressed multipole magnetic rings. However, the pre-magnetized powder has a coarser particle size, so its remanence is typically only about 85% of that of wet-pressed products, resulting in significant performance waste.

[0040] The anisotropic dry-pressed ferrite multipole magnetic ring prepared using the method of this application achieves approximately 90% of the remanence of wet-pressed rings, with a magnetic performance loss of 10%. Compared to the 15% magnetic performance loss of multipole magnetic rings prepared by direct pre-magnetization dry pressing, this represents a 33% reduction in magnetic performance loss. Furthermore, since wet pressing, which eliminates magnetic performance loss, cannot be used to prepare anisotropic ferrite multipole magnetic rings, a loss-free preparation process does not exist; only dry pressing can be used. The anisotropic dry-pressed ferrite multipole magnetic ring prepared by the method of this application, while ensuring a high yield, achieves magnetic performance close to that of dry-pressed powder without pre-magnetization.

[0041] The beneficial effects of this application will be explained in more detail below with reference to specific embodiments.

[0042] Example 1:

[0043] Dry pressing for magnet production:

[0044] 1. DM4129 pre-fired material was selected, with an average particle size of 5.5μm. 0.2wt% silica, 0.8wt% calcium carbonate, and 0.2wt% boric acid were added twice. The wet ball milling speed was 27 rpm, the ball diameter was 6.3mm, and the grinding time was 13 hours. The average particle size of the slurry was 0.8μm.

[0045] 2. Take 10wt% of the slurry from step 1 and place it in an oven to dry at 80℃ until the moisture content is 0.2%. Place the dried material into a high-speed pulverizer and pulverize it in three stages using 20-mesh, 40-mesh, and 80-mesh sieves to obtain a loose density of 0.73 g / cm³. 3 Unmagnetized dry-pressed powder;

[0046] 3. The remaining slurry from step 1 is wet-pressed into a magnetic field and dried at 80°C. Then it is crushed and passed through a 20-mesh sieve to obtain pre-magnetized dry-pressed powder with a particle size of 0.86 mm.

[0047] 4. The unmagnetized dry-pressed powder from step 2 and the premagnetized powder from step 3 were thoroughly mixed, dry-pressed, and sintered at 1210℃ for 1 hour. The magnetic field of the dry-pressing was 8000 Oe and the pressure was 4 MPa. Magnets with a diameter of 43.2 mm and a height of 12 mm were prepared and tested. The test results are shown in Table 1.

[0048] Wet pressing for magnet preparation:

[0049] 1. DM4129 pre-fired material was selected, with an average particle size of 5.5μm. 0.2wt% silica, 0.8wt% calcium carbonate, and 0.2wt% boric acid were added twice. The wet ball milling speed was 27 rpm, the ball diameter was 6.3mm, and the grinding time was 13 hours. The average particle size of the slurry was 0.8μm.

[0050] 2. The slurry was wet-pressed and sintered at 1210℃ for 1 hour. The wet-pressing conditions were a magnetic field of 8000 Oe and a pressure of 4 MPa. Magnets with a diameter of 43.2 mm and a height of 12 mm were prepared and tested. The test results are shown in Table 1.

[0051]

[0052] Example 2:

[0053] Dry pressing for magnet production:

[0054] 1. DM4129 pre-calcined material was selected, with an average particle size of 5.5μm. 0.2wt% silica, 0.8wt% calcium carbonate and 0.2wt% boric acid were added twice. The wet ball milling speed was 27 rpm, the ball diameter was 6.3mm and the grinding time was 11 hours. The average particle size of the slurry was 0.9μm.

[0055] 2. Take 20wt% of the slurry from step 1 and place it in an oven to dry at 150℃ until the moisture content is 0.2%. The dried material is then placed in a high-speed pulverizer and subjected to three stages of pulverization using 20-mesh, 40-mesh, and 80-mesh sieves, resulting in a bulk density of 0.75 g / cm³. 3 Unmagnetized dry-pressed powder;

[0056] 3. The remaining slurry from step 1 is wet-pressed into a magnetic field and dried at 150°C. Then it is crushed and passed through a 20-mesh sieve to obtain pre-magnetized dry-pressed powder with a particle size of 0.9 mm.

[0057] 4. The fine powder from step 2 and the pre-magnetized powder from step 3 were thoroughly mixed, dry-pressed, and sintered at 1210℃ for 1 hour. The dry-pressing magnetic field was 10000 Oe and the pressure was 5 MPa. Magnets with a diameter of 43.2 mm and a height of 12 mm were prepared and tested. The test results are shown in Table 1.

[0058] Wet pressing for magnet preparation:

[0059] 1. DM4129 pre-calcined material was selected, with an average particle size of 5.5μm. 0.2wt% silica, 0.8wt% calcium carbonate and 0.2wt% boric acid were added twice. The wet ball milling speed was 27 rpm, the ball diameter was 6.3mm and the grinding time was 11 hours. The average particle size of the slurry was 0.9μm.

[0060] 2. The slurry was wet-pressed and sintered at 1210℃ for 1 hour with a magnetic field of 10000 Oe and a pressure of 5 MPa to prepare a magnet with a diameter of 43.2 mm and a height of 12 mm. The test results are shown in Table 1.

[0061] Example 3:

[0062] Preparation of 8-level magnetic rings

[0063] 1. DM4129 pre-fired material was selected, with an average particle size of 5.5μm. 0.2wt% silica, 0.8wt% calcium carbonate, and 0.2wt% boric acid were added twice. The wet ball milling speed was 27 rpm, the ball diameter was 6.3mm, and the grinding time was 15 hours. The average particle size of the slurry was 0.76μm.

[0064] 2. Take 20wt% of the slurry from step 1 and place it in an oven to dry at 80℃ until the moisture content is 0.2%. Place the dried material into a high-speed pulverizer and pulverize it in three stages using 20-mesh, 40-mesh, and 80-mesh sieves to obtain a loose density of 0.71 g / cm³. 3 Unmagnetized dry-pressed powder;

[0065] 3. The remaining slurry from step 1 is wet-pressed into a magnetic field and dried at 80°C. Then it is crushed and passed through a 10-mesh sieve to obtain pre-magnetized dry-pressed powder with a particle size of 1.1 mm.

[0066] 4. Thoroughly mix the fine powder from step 2 and the pre-magnetized powder from step 3, dry press them into a magnetic ring blank, and sinter at 1210℃ for 1 hour to obtain a magnetic ring with an outer diameter of 24mm, an inner diameter of 19mm, and a height of [missing information]. The magnets were tested, and the test results are shown in Table 2.

[0067] Comparative Example 1:

[0068] Dry pressing for magnet production:

[0069] 1. DM4129 pre-calcined material was selected, with an average particle size of 5.5μm. 0.2wt% silica, 0.8wt% calcium carbonate, and 0.2wt% boric acid were added twice. The wet ball milling speed was 27 rpm, the ball diameter was 6.3mm, and the grinding time was 14 hours. The average particle size of the slurry was 0.78μm.

[0070] 2. The above slurry is wet-pressed into a magnetic field and dried at 80°C. Then it is crushed and passed through a 20-mesh sieve to obtain pre-magnetized dry-pressed powder with a particle size of 0.88 mm.

[0071] 3. The magnet was dry-pressed and sintered at 1210℃ for 1 hour. The dry-pressing magnetic field was 8000 Oe and the pressure was 3 MPa. The magnet with a diameter of 43.2 mm and a height of 12 mm was prepared and tested. The test results are shown in Table 1.

[0072] Wet pressing for magnet preparation:

[0073] 1. DM4129 pre-calcined material was selected, with an average particle size of 5.5μm. 0.2wt% silica, 0.8wt% calcium carbonate, and 0.2wt% boric acid were added twice. The wet ball milling speed was 27 rpm, the ball diameter was 6.3mm, and the grinding time was 14 hours. The average particle size of the slurry was 0.78μm.

[0074] 2. The slurry was wet-pressed and sintered at 1210℃ for 1 hour. The wet-pressing magnetic field was 8000 Oe and the pressure was 3 MPa. Magnets with a diameter of 43.2 mm and a height of 12 mm were prepared and tested. The test results are shown in Table 1.

[0075] Comparative Example 2:

[0076] Dry pressing for magnet production:

[0077] 1. DM4129 pre-calcined material was selected, with an average particle size of 5.5μm. 0.2wt% silica, 0.8wt% calcium carbonate, and 0.2wt% boric acid were added twice. The wet ball milling speed was 27 rpm, the ball diameter was 6.3mm, and the grinding time was 10 hours. The average particle size of the slurry was 0.93μm.

[0078] 2. Place the above slurry in an oven and dry it at 150℃ until the moisture content is 0.2%. Then, place the dried material into a high-speed pulverizer and pulverize it in three stages using 20-mesh, 40-mesh, and 80-mesh sieves to obtain a loose density of 0.73 g / cm³. 3 ;

[0079] 3. The fine powder was dry-pressed and sintered at 1210℃ for 1 hour. The dry-pressing magnetic field was 10000 Oe and the pressure was 5 MPa. Magnets with a diameter of 43.2 mm and a height of 12 mm were prepared and tested. The test results are shown in Table 1.

[0080] Wet pressing for magnet preparation:

[0081] 1. DM4129 pre-calcined material was selected, with an average particle size of 5.5μm. 0.2wt% silica, 0.8wt% calcium carbonate, and 0.2wt% boric acid were added twice. The wet ball milling speed was 27 rpm, the ball diameter was 6.3mm, and the grinding time was 10 hours. The average particle size of the slurry was 0.93μm.

[0082] 2. The slurry was wet-pressed and sintered at 1210℃ for 1 hour. The wet-pressing magnetic field was 10000 Oe and the pressure was 5 MPa. Magnets with a diameter of 43.2 mm and a height of 12 mm were prepared and tested. The test results are shown in Table 1.

[0083] Comparative Example 3:

[0084] Preparation of 8-level magnetic rings

[0085] 1. DM4129 pre-fired material was selected, with an average particle size of 5.5μm. 0.2wt% silica, 0.8wt% calcium carbonate, and 0.2wt% boric acid were added twice. The wet ball milling speed was 27 rpm, the ball diameter was 6.3mm, and the grinding time was 15 hours. The average particle size of the slurry was 0.76μm.

[0086] 2. The slurry from step 1 is wet-pressed into a magnetic field and dried at 80°C. Then it is crushed and passed through a 10-mesh sieve to obtain pre-magnetized dry-pressed powder with a particle size of 1.12 mm.

[0087] 3. The pre-magnetized powder from step 2 is dry-pressed into a magnetic ring blank and sintered at 1210℃ for 1 hour to prepare the magnetic ring blank. The magnets were tested, and the test results are shown in Table 2.

[0088] Table 1

[0089]

[0090]

[0091] Note: Br is the remanence, Hcb is the magnetic coercivity, Hcj is the intrinsic coercivity, and (BH)max is the maximum energy product.

[0092] Table 2

[0093]

[0094] As can be seen from the above description, the above embodiments of the present invention achieve the following technical effects: The present invention adds a portion of unmagnetized dry-pressed powder to pre-magnetized dry-pressed powder, and uses dry pressing to prepare heterogeneous dry-pressed permanent magnet ferrite multipole magnetic rings, thereby reducing the magnetic performance loss of heterogeneous dry-pressed permanent magnet ferrite multipole magnetic rings and improving the product yield.

[0095] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing anisotropic dry-pressed ferrite multipole magnetic ring, characterized in that, The preparation method includes: a) Mix pre-calcined materials and additives, and grind them to prepare magnetic precursors; b) Wet pressing and crushing of 70 wt% to 95 wt% of the magnetic precursor to prepare pre-magnetized dry-pressed powder; the wet pressing process includes: applying a magnetic field of 6000 to 10000 Oe along the pressing direction, and the pressing pressure is 2 to 5 MPa; c) Crush the remaining magnetic precursor to prepare unmagnetized dry-pressed powder; d) Mix the pre-magnetized dry-pressed powder and the unpre-magnetized dry-pressed powder, dry-press them, and sinter them to obtain the heterogeneous dry-pressed ferrite multipole magnetic ring.

2. The preparation method according to claim 1, characterized in that, The grinding described in a) includes wet grinding.

3. The preparation method according to claim 2, characterized in that, The wet grinding process includes wet ball milling.

4. The preparation method according to claim 3, characterized in that, The grinding time for the wet ball mill is 10-15 hours.

5. The preparation method according to claim 3, characterized in that, The rotational speed of the wet ball mill is 20~40 rpm.

6. The preparation method according to claim 3, characterized in that, The diameter of the ball milling stones used in the wet ball milling process is 6-8 mm.

7. The preparation method according to claim 1, characterized in that, The magnetic precursor has a particle size of 0.6~1.2μm.

8. The preparation method according to claim 1, characterized in that, The particle size of the magnetic precursor is 0.8~0.9μm.

9. The preparation method according to claim 1, characterized in that, The pre-burned material has a particle size of 5~6μm.

10. The preparation method according to claim 2, characterized in that, The additives include one or more of silicon dioxide, calcium carbonate, or boric acid.

11. The preparation method according to claim 10, characterized in that, The amount of silica added is 0.2% to 0.5% of the mass of the pre-burned material.

12. The preparation method according to claim 10, characterized in that, The amount of calcium carbonate added is 0.8% to 1% of the mass of the pre-burned material.

13. The preparation method according to claim 10, characterized in that, The amount of boric acid added is 0.05~0.2% of the mass of the pre-burned material.

14. The preparation method according to claim 1, characterized in that, b) This includes wet pressing 70 wt% to 95 wt% of the magnetic precursor, drying, crushing, and sieving to prepare pre-magnetized dry-pressed powder.

15. The preparation method according to claim 14, characterized in that, The amount of the magnetic precursor used in b) is 80% to 90% of the total weight of the magnetic precursor.

16. The preparation method according to claim 14, characterized in that, In b), drying is performed at a first drying temperature of 60~100℃.

17. The preparation method according to claim 16, characterized in that, The first drying temperature is 70~90℃.

18. The preparation method according to claim 16, characterized in that, The first drying temperature is 80℃.

19. The preparation method according to claim 14, characterized in that, The moisture content of the pre-magnetized dry-pressed powder is 0.5-2%.

20. The preparation method according to claim 14, characterized in that, The particle size of the pre-magnetized dry-pressed powder is 0.5~2 mm.

21. The preparation method according to claim 1, characterized in that, c) This includes drying, pulverizing, and sieving the remaining magnetic precursor to prepare unmagnetized dry-pressed powder.

22. The preparation method according to claim 21, characterized in that, c) is dried at a second drying temperature of 60~100℃.

23. The preparation method according to claim 22, characterized in that, The second drying temperature is 70~90℃.

24. The preparation method according to claim 22, characterized in that, The second drying temperature is 80°C.

25. The preparation method according to claim 21, characterized in that, The moisture content of the unmagnetized dry-pressed powder is 0.2-1%.

26. The preparation method according to claim 21, characterized in that, The particle size of the unmagnetized dry-pressed powder is 0.8~1μm.

27. The preparation method according to claim 21, characterized in that, The loose density of the unmagnetized dry-pressed powder is 0.85–0.9 g / cm³. 3 .

28. The preparation method according to claim 21, characterized in that, The pulverization described in c) includes two-stage pulverization or three-stage pulverization.

29. The preparation method according to claim 28, characterized in that, The loose density of the unmagnetized dry-pressed powder after secondary crushing is 0.75–0.8 g / cm³. 3 .

30. The preparation method according to claim 28, characterized in that, The loose density of the unmagnetized dry-pressed powder after the three-stage crushing is 0.7–0.75 g / cm³. 3 .

31. The preparation method according to claim 1, characterized in that, The dry pressing process includes: applying a magnetic field of 6000~10000 Oe along the pressing direction, and a molding pressure of 2~5 MPa.

32. The preparation method according to claim 1, characterized in that, The sintering temperature is 1200~1240℃.

33. The preparation method according to claim 1, characterized in that, The sintering time is 1-2 hours.

34. A heterogeneous dry-pressed ferrite multipole magnetic ring, characterized in that, The heterogeneous dry-pressed ferrite multipole magnetic ring includes the heterogeneous dry-pressed ferrite multipole magnetic ring prepared by the preparation method according to any one of claims 1 to 33.

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