A high-density molded bonded samarium iron nitrogen magnet and its preparation method

Abstract

This invention belongs to the field of bonded permanent magnet materials technology, and discloses a high-density molded bonded samarium iron nitride (SMR) magnet and its preparation method. Addressing the shortcomings of existing molded magnets, such as low density, poor magnetic properties, and rapid mold wear, the magnet is made of 80%-95% SMR magnetic powder, binder, and other raw materials, achieving a density ≥7.3 g / cm³ and a maximum magnetic energy product ≥10.5 MGOe. A high-performance, detachable composite mold core, layered venting grooves, and a pressure mold with built-in magnetic field coils are employed. Combined with a preparation process of layered feeding, three-stage directional pressurization, and constant temperature pressure holding, the magnetic powder orientation and air expulsion are synchronized, improving magnet performance and mold life. This method is suitable for industrial mass production and can be applied in fields such as automotive motors and precision instruments.

Description

Technical Field

[0001] This invention belongs to the field of bonded permanent magnet technology, specifically relating to a high-density molded bonded samarium iron nitride magnet and its preparation method, and particularly to a bonding samarium iron nitride magnet preparation technology that achieves high density and high magnetic properties through a high-performance pressure mold and innovative pressing method. Background Technology

[0002] Samarium iron nitride (Samarium ferrite nitrogen) magnets, as a novel rare-earth permanent magnet material, possess advantages such as high magnetocrystalline anisotropy, high Curie temperature, low rare-earth content, and relatively low cost, making them promising for applications in consumer electronics, automotive motors, and precision instruments. Because Samarium ferrite nitrogen magnetic powder is prone to decomposition at temperatures above 180°C, it cannot be prepared using traditional high-temperature sintering processes; therefore, compression molding has become its primary forming method.

[0003] Currently, the preparation process of molded bonded samarium iron nitride magnets faces the following core technical challenges, which severely restrict the improvement of their density and magnetic properties, thus limiting their large-scale application:

[0004] Unreasonable mold structure: Most existing compression molds are single-cavity, fixed-core designs, resulting in poor venting of the mold cavity. During the pressing process, air in the mixture of magnetic powder and binder cannot be expelled in time, forming tiny cavities. This leads to low magnet density (usually below 6.8 g / cm³), with cavities accounting for more than 8% of the volume, which in turn creates magnetic resistance regions and reduces magnetic properties. At the same time, the frictional resistance between the mold core and the magnetic powder is high, making demolding difficult and easily causing damage to the magnet surface. Furthermore, the mold wears out quickly and has a short service life.

[0005] The pressing methods are not perfect: existing pressing processes mostly use single pressure pressing or simple two-step pressing, which have problems such as uneven pressure transmission, low magnetic powder orientation, and insufficient binder fluidity. Some processes use vacuum overflow or stepwise temperature pressing, but require additional vacuum equipment or multiple sets of molds, which makes the process complex, the production efficiency low, and cannot achieve simultaneous optimization of pressing and magnetic powder orientation, making it difficult to balance density and magnetic properties.

[0006] Poor compatibility: Existing molds and pressing methods are difficult to adapt to samarium iron nitrogen magnetic powders of different particle sizes. For surface-modified magnetic powders, problems such as insufficient bonding and uneven density are prone to occur, and the bridging effect between magnetic powder particles cannot be effectively solved, further reducing the density of the magnet.

[0007] In the prior art, the existing technology involving bonded samarium iron nitride magnets (such as the patent with publication number CN120126917A) mainly discloses that reducing the proportion of binder and combining it with high-pressure molding technology can solve the phenomenon of binder overflow under high pressure. When the binder content in the raw material of samarium iron nitride magnets is less than 1wt% by mass, the powder bridging effect is more obvious. In this case, the above-disclosed technical solution, by using ultra-high pressure rapid prototyping technology combined with vacuum overflow molding technology, can overcome the bridging effect of powder under this condition, effectively shorten the distance between micro powders in the bonded magnet, effectively increase the magnetization effect of micro powders and the interaction force after magnetization, and significantly improve the density of the magnet to 7.2g / cm, thus achieving the goal of significantly improving the magnetic properties of the magnet. However, the above technical solution does not make breakthrough innovations in the mold structure and pressing method for pressing the magnet, and cannot effectively solve the above-mentioned technical pain points. Therefore, designing a high-performance pressure mold and combining it with an innovative pressing method to achieve the efficient preparation of high-density, high-magnetic-performance bonded samarium iron nitrogen magnets has become a technical problem to be solved. Summary of the Invention

[0008] To address the shortcomings of existing molded bonded samarium iron nitride magnets, such as low density, poor magnetic properties, rapid mold wear, and low pressing efficiency, this invention provides a high-density molded bonded samarium iron nitride magnet and its preparation method. By designing a high-performance pressure mold and an innovative pressing process, the magnet density and magnetic properties are simultaneously improved, while extending the mold's service life and increasing production efficiency, thus filling a gap in existing technologies.

[0009] The magnet is made from the following raw materials in the indicated mass percentages: 80%-95% samarium iron nitrogen magnetic powder, 3%-18% binder, 0.5%-1.5% coupling agent, and 0.3%-1.0% lubricant; the magnet has a density ≥7.3 g / cm³, a hole volume ratio ≤2%, a maximum magnetic energy product ≥10.5 MGOe, and a coercivity ≥1200 kA / m.

[0010] Preferably, the samarium iron nitrogen magnetic powder is a surface-modified magnetic powder, coated with a titanate coupling agent, with a particle size of 5-50 μm; the binder is a compound system of epoxy resin and polyamide resin (mass ratio 1:0.3-0.8), which has both thermosetting and flowability properties; the lubricant is a compound system of zinc stearate and graphite (mass ratio 2:1), which can simultaneously reduce the frictional resistance between magnetic powders and between magnetic powders and mold.

[0011] The high-performance pressure mold used to prepare the above-mentioned high-density molded bonded samarium iron nitrogen magnets includes an upper mold base, a lower mold base, a mold core, a mold sleeve, and a guiding mechanism. Its innovation lies in:

[0012] The mold core is a detachable composite mold core, consisting of an inner wear-resistant core and an outer elastic buffer layer. The inner wear-resistant core is made of hard alloy (WC-Co alloy) with a nitrided surface and a hardness ≥HRC65, effectively reducing wear. The outer elastic buffer layer is made of high-temperature resistant silicone rubber that can withstand ≥140℃, with a thickness of 0.5-1.5mm. It can generate elastic deformation during the pressing process, achieving uniform pressure transmission and avoiding excessive local pressure that could lead to magnetic powder breakage.

[0013] The inner wall of the mold sleeve is provided with annular layered venting grooves. The venting grooves are evenly distributed in 3-5 layers along the height direction of the mold sleeve. The width of each layer of venting groove is 0.1-0.3mm and the depth is 0.2-0.5mm. The distance between two adjacent layers of venting grooves is 5-10mm. One end of the venting groove is connected to the venting hole at the top of the mold sleeve. The venting hole is connected to a negative pressure adsorption device, which can discharge the air and excess adhesive in the mold cavity in real time during the pressing process, completely solving the void problem and avoiding magnetic defects caused by adhesive overflow.

[0014] Both the upper and lower mold bases have built-in annular magnetic field coils. The magnetic field coils are connected to an external magnetic field controller and can generate a directional magnetic field of 0.8-1.2T to achieve synchronous orientation of samarium iron nitrogen magnetic powder during the pressing process and improve the magnetic properties of the magnet. The magnetic field coils are wrapped with a high-temperature resistant insulation layer that can withstand ≥140℃ to avoid the high temperature affecting the coil performance during the pressing process.

[0015] The guiding mechanism adopts a structure of ball bearing guide post and guide sleeve. The surface of the guide post is coated with high-temperature resistant grease that can withstand ≥140℃ to ensure smooth up and down movement of the upper mold base and avoid magnetic size deviation caused by mold offset. The fit clearance between the guide sleeve and the guide post is 0.01-0.03mm, which improves the positioning accuracy of the mold.

[0016] Furthermore, a demolding ejector pin is provided at the bottom of the mold core. The demolding ejector pin is connected to the hydraulic drive mechanism in the lower mold base, which can realize the smooth demolding of the magnet and avoid damage to the surface of the magnet during the demolding process. The top of the demolding ejector pin is flush with the upper surface of the mold core, so as not to affect the molding accuracy of the magnet.

[0017] The method for preparing high-density molded bonded samarium iron nitride magnets using the above-mentioned high-performance pressure mold includes the following steps:

[0018] Raw material pretreatment: Place the samarium iron nitrogen magnetic powder in a vacuum drying oven and dry it at 80-100℃ for 2-3 hours to remove surface moisture; dissolve the coupling agent in anhydrous ethanol to prepare a coupling agent solution with a mass concentration of 5%-10%, mix it with the dried samarium iron nitrogen magnetic powder, stir at 40-60℃ for 30-60 minutes, and vacuum dry to remove the solvent to obtain surface-modified samarium iron nitrogen magnetic powder;

[0019] Mixing: Add surface-modified samarium iron nitrogen magnetic powder, binder, and lubricant to a high-speed mixer and mix for 20-30 minutes at a speed of 1000-1500 r / min and a temperature of 60-80℃ to obtain a uniform mixture; the mixture is then crushed and passed through an 80-120 mesh sieve to remove agglomerated particles.

[0020] Mold preheating and adjustment: Install the high-performance pressure mold on the hydraulic press, and preheat the mold core and mold sleeve to 100-140℃ (adapted to the softening temperature of the adhesive) through the mold's built-in heating device; adjust the magnetic field controller to generate a directional magnetic field of 0.8-1.2T and maintain magnetic field stability; start the negative pressure adsorption device to expel the air in the exhaust groove, so that a slight negative pressure (pressure of -0.02~-0.05MPa) is formed in the mold cavity.

[0021] Layered feeding and pre-compression: Add the mixture into the mold cavity in 2-3 layers, and pre-compress after each layer. The pre-compression pressure is 100-150MPa and the holding time is 5-10s. Layered feeding can avoid uneven accumulation of the mixture, and pre-compression can initially remove air in the mixture and reduce voids in the subsequent pressing process.

[0022] Directional pressurization and constant temperature pressure holding: Start the hydraulic press, the upper mold base moves downward, and directional pressurizes the mixture in the mold cavity. The pressurization pressure is gradually increased to 600-800MPa (in 3 stages: 200MPa→400MPa→600-800MPa), and the pressure is held for 3-5 seconds after each stage. During the pressurization process, the magnetic field coil continuously generates a directional magnetic field to achieve synchronous orientation of the magnetic powder. At the same time, the mold temperature is maintained at 100-140℃, and constant temperature pressure is held for 15-25 seconds to fully soften and flow the binder, fill the gaps between the magnetic powder particles, and completely eliminate voids. During the pressurization process, the air and excess binder in the mold cavity are discharged by the negative pressure adsorption device through the venting groove and venting hole.

[0023] Pressure relief and demolding: After the pressure holding period, gradually reduce the pressure to normal pressure (pressure relief rate is 50-100MPa / min) to avoid sudden pressure drop that could cause the magnet to crack; turn off the magnetic field controller and negative pressure adsorption device, start the hydraulic drive mechanism, and use the demolding ejector pins to smoothly eject the green magnet from the mold cavity;

[0024] Curing and post-treatment: The green magnet blank is placed in a curing oven and a stepped curing process is adopted: first, it is kept at 80-100℃ for 1-2 hours to eliminate the pressure stress; then the temperature is raised to 160-180℃ and kept for 3-4 hours to completely cure the adhesive; after curing, the magnet is ground, polished and coated to obtain a high-density molded bonded samarium iron nitride magnet.

[0025] Preferably, in step (5), during the directional pressurization process, the elastic buffer layer of the mold core undergoes an elastic deformation of 0.1-0.3 mm, so that the pressure is evenly transmitted to all parts of the mixture, avoiding excessive local pressure that could cause the magnetic powder to break, while improving the density uniformity of the magnet.

[0026] Preferably, in step (7), the coating treatment uses an electrophoretic epoxy coating with a thickness of 10-20 μm, which can improve the corrosion resistance and surface smoothness of the magnet.

[0027] Compared with the prior art, the present invention has the following outstanding advantages:

[0028] Outstanding novelty: The designed high-performance pressure mold adopts an integrated structure of "detachable composite mold core + layered venting groove + built-in magnetic field coil", which solves the problems of poor venting, uneven pressure transmission, asynchronous magnetic powder orientation, difficult demolding, and rapid wear of existing molds; the innovative pressing method of layered feeding + three-stage directional pressing + constant temperature pressure holding realizes the simultaneous process of air venting, magnetic powder orientation and binder flow, which is significantly different from the existing single pressing and step-by-step pressing process and has not been disclosed in existing technology.

[0029] Significant Innovative Aspects: This invention effectively solves the bridging effect between magnetic powder particles through synergistic innovation in mold structure and pressing method, increasing the magnet density to over 7.3 g / cm³, reducing the void volume ratio to below 2%, and achieving a maximum magnetic energy product ≥ 10.5 MGOe. Compared to existing technologies (density ≤ 6.8 g / cm³, maximum magnetic energy product ≤ 7.0 MGOe), the magnetic performance is significantly improved. Simultaneously, the detachable mold core extends the mold's lifespan (by over 50%), and the integrated pressing process increases production efficiency by over 30%. The technical effects are remarkable and not obvious to those skilled in the art.

[0030] Highly practical: The mold structure is simple and easy to assemble and disassemble, and it can be adapted to samarium iron nitrogen magnetic powders of different particle sizes, making it suitable for industrial mass production; the preparation method is simple and the parameters are easy to control, eliminating the need for complex vacuum equipment and reducing production costs; the prepared magnets have high density, excellent magnetic properties, and good surface quality, and can be widely used in automotive motors, precision instruments, consumer electronics and other fields.

[0031] Good compatibility: It adopts a compound binder and lubricant system, which is compatible with surface-modified samarium iron nitrogen magnetic powder. It has a good bonding effect, which can effectively avoid magnetic powder agglomeration and further improve the density and magnetic properties of the magnet. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to specific embodiments. These embodiments are only used to explain the present invention and do not constitute a limitation on the scope of protection of the present invention. Example 1

[0033] A high-density molded bonded samarium iron nitrogen magnet, comprising the following raw material mass percentages: 90% samarium iron nitrogen magnetic powder, 4% epoxy resin, 3% polyamide resin, 1% titanate coupling agent, 0.6% zinc stearate, and 0.4% graphite; wherein the samarium iron nitrogen magnetic powder is a surface-modified magnetic powder with a particle size of 10-30 μm; and the mass ratio of epoxy resin to polyamide resin is 1:0.75.

[0034] Parameters of high-performance pressure mold: The inner wear-resistant core of the mold core is made of WC-Co alloy with surface nitriding treatment and a hardness of HRC68; the outer elastic buffer layer is made of high-temperature resistant silicone rubber that can withstand ≥140℃, with a thickness of 1.0mm; the inner wall of the mold sleeve has 3 layers of annular venting grooves, each venting groove is 0.2mm wide and 0.3mm deep, and the distance between adjacent layers is 8mm; the directional magnetic field strength generated by the magnetic field coil is 1.0T; the fitting clearance of the guide mechanism is 0.02mm.

[0035] The preparation method is as follows:

[0036] Raw material pretreatment: Samarium iron nitrogen magnetic powder was vacuum dried at 90℃ for 2.5h; titanate coupling agent was dissolved in anhydrous ethanol to prepare an 8% solution, mixed with magnetic powder, stirred at 50℃ for 45min, and vacuum dried to remove solvent to obtain surface modified magnetic powder;

[0037] Mixing: Add surface-modified magnetic powder, epoxy resin, polyamide resin, zinc stearate and graphite to a high-speed mixer and mix at 1200 r / min and 70℃ for 25 min. After crushing, pass through a 100-mesh sieve.

[0038] Mold preheating and adjustment: Install the mold on the hydraulic press and preheat it to 120℃; adjust the magnetic field controller to stabilize the magnetic field strength at 1.0T; start the negative pressure adsorption device to make the pressure inside the mold cavity -0.03MPa;

[0039] Layered feeding and pre-compression: The mixture is added in two layers, with each layer pre-compressed at 120MPa and held for 8 seconds;

[0040] Directional pressurization and constant temperature pressure holding: pressurize in three stages to 700MPa (200MPa→400MPa→700MPa), holding pressure for 4 seconds at each stage; maintain mold temperature at 120℃ and hold pressure for 20 seconds.

[0041] Pressure relief and demolding: Depressurize to atmospheric pressure at a rate of 80 MPa / min, activate the demolding ejector pin, and eject the green magnet blank;

[0042] Curing and post-treatment: The green blank is placed in a curing oven and kept at 80℃ for 1.5h, then heated to 170℃ and kept at 3.5h; after curing, it is ground and polished, and an electrophoretic epoxy coating (15μm thick) is applied to obtain the finished magnet.

[0043] Finished magnet performance testing: density 7.4 g / cm³, void volume ratio 1.8%, maximum magnetic energy product 10.8 MGOe, coercivity 1250 kA / m, surface flatness ≤0.01 mm, no obvious defects. Example 2

[0044] A high-density molded bonded samarium iron nitrogen magnet, comprising the following raw material mass percentages: 85% samarium iron nitrogen magnetic powder, 6% epoxy resin, 5% polyamide resin, 1.2% titanate coupling agent, 0.5% zinc stearate, and 0.3% graphite; wherein the samarium iron nitrogen magnetic powder is a surface-modified magnetic powder with a particle size of 5-20 μm; and the mass ratio of epoxy resin to polyamide resin is 1:0.8.

[0045] Parameters of high-performance pressure mold: The inner wear-resistant core of the mold core is made of WC-Co alloy with surface nitriding treatment and a hardness of HRC65; the outer elastic buffer layer is made of high-temperature resistant silicone rubber that can withstand ≥140℃, with a thickness of 0.8mm; the inner wall of the mold sleeve has 4 layers of annular venting grooves, each venting groove is 0.15mm wide and 0.4mm deep, with a spacing of 6mm between adjacent layers; the directional magnetic field strength generated by the magnetic field coil is 1.1T; the fitting clearance of the guide mechanism is 0.015mm.

[0046] The preparation method is basically the same as that in Example 1, except that: in step (4), the material is added in 3 layers, the pre-pressure is 100MPa, and the pressure is maintained for 5s; in step (5), the pressure is increased to 750MPa in three stages, and the constant temperature pressure is maintained for 22s; in step (7), the curing process is to keep the temperature at 90℃ for 1h and at 175℃ for 3h.

[0047] Finished magnet performance testing: density 7.3 g / cm³, hole volume ratio 1.9%, maximum magnetic energy product 10.6 MGOe, coercivity 1220 kA / m, and good surface quality. Example 3

[0048] A high-density molded bonded samarium iron nitrogen magnet, comprising the following raw material mass percentages: 92% samarium iron nitrogen magnetic powder, 3% epoxy resin, 3% polyamide resin, 0.8% titanate coupling agent, 0.7% zinc stearate, and 0.3% graphite; wherein the samarium iron nitrogen magnetic powder is a surface-modified magnetic powder with a particle size of 20-50 μm; and the mass ratio of epoxy resin to polyamide resin is 1:0.5.

[0049] Parameters of high-performance pressure mold: The inner wear-resistant core of the mold core is made of WC-Co alloy with surface nitriding treatment and a hardness of HRC70; the outer elastic buffer layer is made of high-temperature resistant silicone rubber that can withstand ≥140℃, with a thickness of 1.2mm; the inner wall of the mold sleeve has 5 layers of annular venting grooves, each venting groove is 0.25mm wide and 0.2mm deep, and the distance between adjacent layers is 10mm; the directional magnetic field strength generated by the magnetic field coil is 0.9T; the fitting clearance of the guide mechanism is 0.025mm.

[0050] The preparation method is basically the same as that in Example 1, except that: in step (4), the material is added in two layers, the pre-pressure is 150MPa, and the pressure is maintained for 10s; in step (5), the pressure is increased to 650MPa in three stages, and the constant temperature pressure is maintained for 18s; in step (7), the curing process is to keep the temperature at 100℃ for 1h and at 165℃ for 4h.

[0051] Finished magnet performance testing: density 7.5 g / cm³, hole volume ratio 1.5%, maximum magnetic energy product 11.0 MGOe, coercivity 1280 kA / m, and good surface quality. Comparative Example 1

[0052] Using existing conventional molds (single mold cavity, no venting groove, no built-in magnetic field coil) and a single pressure pressing method, with the same raw material composition as in Example 1, bonded samarium iron nitrogen magnets were prepared.

[0053] Finished magnet performance testing: density 6.6 g / cm³, void volume ratio 8.5%, maximum magnetic energy product 6.8 MGOe, coercivity 1050 kA / m, slight surface defects, and significant wear on the mold after 1000 uses.

[0054] The comparison shows that the magnets prepared by this invention through high-performance pressure molds and innovative pressing methods have significantly better density and magnetic properties than existing technologies, and the molds have a longer service life and higher production efficiency, demonstrating significant technical advantages.

[0055] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0056] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A high-density molded bonded samarium iron nitride magnet, characterized in that, It is prepared from the following raw materials in the indicated mass percentages: 80%-95% samarium iron nitrogen magnetic powder, 3%-18% binder, 0.5%-1.5% coupling agent, and 0.3%-1.0% lubricant; the magnet has a density ≥7.3 g / cm³, a hole volume ratio ≤2%, a maximum magnetic energy product ≥10.5 MGOe, and a coercivity ≥1200 kA / m; the binder is a compound system of epoxy resin and polyamide resin in a mass ratio of 1:0.3-0.8; the lubricant is a compound system of zinc stearate and graphite in a mass ratio of 2:

1. The high-performance pressure mold used to prepare the high-density molded bonded samarium iron nitrogen magnet includes an upper mold base, a lower mold base, a mold core, a mold sleeve, and a guide mechanism. The mold core is a detachable composite mold core, which consists of an inner wear-resistant core and an outer elastic buffer layer. The inner wall of the mold sleeve is provided with annular layered exhaust grooves. The exhaust grooves are evenly distributed in 3-5 layers along the height direction of the mold sleeve. The width of each exhaust groove is 0.1-0.3mm and the depth is 0.2-0.5mm. The distance between two adjacent exhaust grooves is 5-10mm. One end of the exhaust groove is connected to the exhaust hole at the top of the mold sleeve. The exhaust hole is connected to a negative pressure adsorption device. Both the upper and lower mold bases have built-in annular magnetic field coils, which are connected to an external magnetic field controller and can generate a directional magnetic field of 0.8-1.2T. The method for preparing the high-density molded bonded samarium iron nitrogen magnet includes the following steps: raw material pretreatment, mixing, mold preheating and debugging, layered feeding and pre-pressing, directional pressurization and constant temperature holding, pressure release and demolding, curing and post-treatment.

2. The high-density molded bonded samarium iron nitride magnet according to claim 1, characterized in that, The samarium iron nitrogen magnetic powder is a surface-modified magnetic powder, which is coated with a titanate coupling agent and has a particle size of 5-50 μm.

3. The high-density molded bonded samarium iron nitride magnet according to claim 1, characterized in that, The guiding mechanism of the high-performance pressure mold adopts a matching structure of ball guide post and guide sleeve. The surface of the guide post is coated with high-temperature resistant grease that can withstand ≥140℃. The matching clearance between the guide sleeve and the guide post is 0.01-0.03mm. The inner wear-resistant core is made of WC-Co alloy material, and the surface is nitrided, with a hardness ≥HRC65; the outer elastic buffer layer is made of high-temperature resistant silicone rubber material that can withstand ≥140℃, with a thickness of 0.5-1.5mm. The magnetic field coil is wrapped with a high-temperature resistant insulation layer that can withstand temperatures of ≥140℃.

4. The high-density molded bonded samarium iron nitride magnet according to claim 1, characterized in that, The high-performance pressure mold has a demolding ejector pin at the bottom of the mold core. The demolding ejector pin is connected to a hydraulic drive mechanism in the lower mold base, and the top of the demolding ejector pin is flush with the upper surface of the mold core.

5. The high-density molded bonded samarium iron nitride magnet according to claim 1, characterized in that, The specific steps of the method for preparing the high-density molded bonded samarium iron nitride magnet are as follows: (1) Raw material pretreatment: Vacuum dry samarium iron nitrogen magnetic powder at 80-100℃ for 2-3h; Dissolve coupling agent in anhydrous ethanol to prepare a 5%-10% solution, mix with magnetic powder, stir at 40-60℃ for 30-60min, vacuum dry to remove solvent, and obtain surface modified samarium iron nitrogen magnetic powder. (2) Mixing: Add surface-modified samarium iron nitrogen magnetic powder, binder and lubricant to a high-speed mixer and mix for 20-30 minutes at a speed of 1000-1500 r / min and a temperature of 60-80℃. After crushing, pass through an 80-120 mesh sieve to obtain the mixture. (3) Mold preheating and debugging: Install the high-performance pressure mold on the hydraulic press and preheat it to 100-140℃; debug the magnetic field controller to generate a directional magnetic field of 0.8-1.2T in the magnetic field coil; start the negative pressure adsorption device to form a micro negative pressure of -0.02~-0.05MPa in the mold cavity; (4) Layered feeding and pre-compression: Add the mixture into the mold cavity in 2-3 layers, and pre-compress after each layer is added. The pre-compression pressure is 100-150MPa and the holding time is 5-10s; (5) Directional pressurization and constant temperature pressure holding: A three-stage pressurization method is adopted to gradually increase the pressure to 600-800MPa, and the pressure is held for 3-5s after each pressurization. During the pressurization process, the magnetic field coil continuously generates a directional magnetic field to maintain the mold temperature at 100-140℃ and hold the pressure for 15-25s. The air and excess adhesive in the mold cavity are discharged by the negative pressure adsorption device through the exhaust groove and exhaust hole. (6) Depressurization and demolding: Depressurize to normal pressure at a rate of 50-100MPa / min, turn off the magnetic field controller and negative pressure adsorption device, start the hydraulic drive mechanism, and eject the magnet blank through the demolding ejector pin; (7) Curing and post-treatment: The green magnet blank is placed in a curing oven and a stepped curing process is adopted: keep it at 80-100℃ for 1-2 hours, and then raise the temperature to 160-180℃ and keep it for 3-4 hours; after curing, it is ground, polished and coated to obtain the finished magnet.

6. The high-density molded bonded samarium iron nitride magnet according to claim 5, characterized in that, In step (5) of the method for preparing the high-density molded bonded samarium iron nitrogen magnet, during the directional pressurization process, the elastic buffer layer of the mold core undergoes an elastic deformation of 0.1-0.3 mm.

7. The high-density molded bonded samarium iron nitride magnet according to claim 5, characterized in that, In step (7) of the method for preparing the high-density molded bonded samarium iron nitrogen magnet, the coating treatment adopts an electrophoretic epoxy coating with a coating thickness of 10-20 μm.