Neodymium-iron-boron magnet and preparation method and application thereof

Abstract

The invention discloses a neodymium-iron-boron magnet and a preparation method and application thereof. The neodymium-iron-boron magnet is provided with a non-parallel magnetic circuit; the neodymium-iron-boron magnet is in a curved surface shape, and the cross section of the neodymium-iron-boron magnet is arc-shaped; wherein any position, except the center of the arc, of the same cross section meets the following formula: delta theta = alpha * (1-cos theta); wherein theta is a magnetic line angle, and theta is more than 0 degree and less than or equal to 90 degrees; delta theta is a numerical value corresponding to the magnetic declination in units of degrees, and 0 < Delta theta < = 10; alpha is selected from constants from 1 to 12. The neodymium-iron-boron magnet has a non-parallel magnetic circuit and also has low magnetic declination and high residual magnetism; after the motor is actually used for a permanent magnet motor, the motor efficiency can be improved, and the sound pressure level is reduced.

Description

Technical Field

[0001] This invention relates to a neodymium iron boron magnet, its preparation method, and its application. Background Technology

[0002] Non-parallel-oriented magnets are magnetic materials in which the magnetization direction or grain arrangement direction is not distributed along a single direction (such as parallel to a specific direction) during the manufacturing process. They possess the advantages of both radial magnetic rings and parallel-oriented magnets, while avoiding their disadvantages. These magnets typically exhibit anisotropy, meaning their magnetic properties differ in different directions, and are therefore widely used in motors, transformers, and other equipment requiring multi-directional magnetic properties.

[0003] However, existing non-parallel oriented magnets often have excessively high magnetic declination angles (up to 30° or more), which limits their practical application performance. For example, permanent magnet motors have relatively low energy conversion efficiency and high noise levels, and they are also difficult to manufacture.

[0004] Therefore, there is an urgent need for a non-parallel oriented magnet with low magnetic declination to produce high-performance non-parallel oriented magnetic steel. Summary of the Invention

[0005] To address the shortcomings of existing non-parallel oriented magnets, such as the difficulty in ensuring low magnetic declination, this invention provides a neodymium iron boron magnet, its preparation method, and its applications. This neodymium iron boron magnet possesses a non-parallel magnetic circuit while exhibiting low magnetic declination and high remanence (Br). When practically applied to permanent magnet motors, it can improve motor efficiency while reducing sound pressure levels. Furthermore, the preparation method is simple and easy to implement, allowing for large-scale production.

[0006] To achieve the above objectives, the present invention adopts the following technical solution.

[0007] This invention provides a neodymium iron boron magnet, which has a non-parallel magnetic circuit; and the neodymium iron boron magnet is curved with a circular arc cross-section; wherein, at any position on the same cross-section except at the center of the arc, the following formula is satisfied:

[0008] Δθ=α·(1-cosθ);

[0009] in,

[0010] θ is the angle of the magnetic field lines, and satisfies 0°<θ≤90°;

[0011] Δθ is the numerical value corresponding to the magnetic declination in °, and satisfies 0 < Δθ ≤ 10;

[0012] α is a constant selected from 1 to 12.

[0013] In this invention, the neodymium iron boron magnet can be considered to have a tile-like appearance. For the same cross-section, the theoretical direction of the magnetic field lines at any position can be considered to be perpendicular to the arc surface at that position. As in the formula above, θ can refer to the theoretical magnetic field line angle at any position on the same cross-section except for the center of the arc. When θ is infinitely close to 0°, the actual magnetic field line angle is infinitely close to 0°, and the magnetic declination is also infinitely close to 0°.

[0014] In this invention, the magnetic declination refers to the angle between the actual direction and the theoretical direction of the magnetic field lines at any position on the same cross section except at the center of the arc, and generally refers to the collection of all magnetic field lines at the corresponding position. Those skilled in the art will know its fixed meaning.

[0015] In this invention, the non-parallel magnetic circuit refers to a magnetic field line distributed in a divergent manner.

[0016] In some implementations, the formula satisfies one or more of the following conditions:

[0017] (1) The θ satisfies 0°<θ≤30°;

[0018] (2) The Δθ satisfies 0<Δθ≤2;

[0019] (3) The α is selected from the constants of 8-12.

[0020] In some embodiments, the magnetic field lines in the neodymium iron boron magnet are arranged radially.

[0021] In some implementations, the magnetic declination gradually increases from the center of the arc to the edge of the arc in the same cross section; preferably, the difference between the magnetic declination of the center of the arc and the edge of the arc is not higher than 1.4°.

[0022] In some embodiments, the thickness of the NdFeB magnet at any location is 5-20 mm; preferably, the NdFeB magnet has a uniform thickness. Uniform thickness means that the thickness difference at different locations does not exceed 10% of the average thickness.

[0023] The present invention also provides a method for preparing a neodymium iron boron magnet, the method comprising the following steps:

[0024] Neodymium iron boron alloy sheets are produced by powdering, pressing, and sintering.

[0025] In some embodiments, the pressing molding apparatus has the following structure:

[0026] The forming device in the pressing process includes a first magnetic block and a second magnetic block. The first magnetic block includes an arc-shaped groove, and the second magnetic block includes a semi-circular protrusion located in the space formed by the arc-shaped groove.

[0027] An arc-shaped mold cavity is provided between the arc-shaped groove and the semi-circular protrusion;

[0028] Magnetic blocks are provided at both ends of the arc-shaped mold cavity.

[0029] In some preferred embodiments, in the first structure, the ratio of the radius of the semi-circular protrusion to the radius of the arc of the arc-shaped cavity on the side near the semi-circular protrusion is (0.8-0.95):1, more preferably (0.8-0.9):1, for example 0.85:1.

[0030] In some preferred embodiments, in the first structure, the ratio of the radius of the arc-shaped groove to the radius of the arc on the side of the arc-shaped mold cavity near the arc-shaped groove is (0.85-0.95):1, for example, 0.85:1.

[0031] In some preferred embodiments, in the first structure, the thickness of the gap formed between the arc-shaped groove and the semi-circular protrusion is greater than the thickness of the arc-shaped mold cavity.

[0032] The thickness of the gap formed between the arc-shaped groove and the semi-circular protrusion is preferably 5-20 mm, for example 15 mm.

[0033] The thickness of the arc-shaped mold cavity is preferably 5-20 mm.

[0034] Preferably, the distance between the arc of the arc-shaped mold cavity on the side closest to the semi-circular protrusion and the vertical distance between the semi-circular protrusion and the arc is 3-10mm, for example, 5mm.

[0035] Preferably, the vertical distance between the arc of the arc-shaped mold cavity on the side closest to the arc-shaped groove and the arc-shaped groove is 5-10mm, for example, 5mm.

[0036] In some preferred embodiments, in structure one, the relative permeability of the magnetic blocks is 1.02-10, for example 1.5; preferably, the relative permeability of the magnetic blocks at both ends is the same.

[0037] In some preferred embodiments, in structure one, the magnetic block is arc-shaped.

[0038] Preferably, the radii of the arcs of the magnetic block and the arc-shaped mold cavity near the arc-shaped groove are equal, and the radii of the arcs of the magnetic block and the arc-shaped mold cavity near the semi-circular protrusion are also equal.

[0039] Preferably, the percentage of the arc length of the magnetic block to the arc length of the arc-shaped mold cavity is 10%-20%, for example, 15%.

[0040] In some embodiments, the pressing molding apparatus has the following structure:

[0041] It includes a first magnetic block and a second magnetic block; the first magnetic block includes multiple parallel magnetic blocks with different relative permeabilities arranged in the horizontal direction, and the bottom of the multiple magnetic blocks forms an arc-shaped groove; the second magnetic block includes multiple parallel magnetic blocks with different relative permeabilities arranged in the horizontal direction, and the top of the multiple magnetic blocks forms a semi-circular protrusion; the semi-circular protrusion is located in the space formed by the arc-shaped groove;

[0042] An arc-shaped mold cavity is provided between the arc-shaped groove and the semi-circular protrusion.

[0043] In some preferred embodiments, in the second structure, the first magnetic block comprises 6-50 magnetic blocks.

[0044] Preferably, the relative permeability of the magnetic blocks disposed on the axis of the first magnetic block is lower than that of the magnetic blocks far from the axis of the first magnetic block.

[0045] Preferably, the relative permeability of the magnetic block increases in a gradient direction in the direction in which the axis of the first magnetic block extends to both ends.

[0046] In the first magnetically conductive block, the difference in relative permeability between adjacent magnetic blocks at both ends is preferably 40-333.

[0047] Preferably, the ratio of the relative permeability of the magnetic block located on the axis of the first magnetic block to the relative permeability of the magnetic block located away from the axis of the first magnetic block is 1.05:1.3.

[0048] In some preferred embodiments, in the second structure, the second magnetic block comprises 6-30 magnetic blocks.

[0049] Preferably, the relative permeability of the magnetic block disposed on the axis of the second magnetic block is lower than that of the magnetic block disposed away from the axis of the second magnetic block.

[0050] Preferably, the relative permeability of the magnetic block increases in a gradient direction in the direction in which the axis of the second magnetic block extends to both ends.

[0051] In the second magnetic block, the difference in relative permeability between adjacent magnetic blocks at both ends is preferably 66-333.

[0052] Preferably, the ratio of the relative permeability of the magnetic block located on the axis of the second magnetic block to the relative permeability of the magnetic block located away from the axis of the second magnetic block is 1.05:1.3.

[0053] In some preferred embodiments, in the second structure, the ratio of the radius of the semi-circular protrusion to the radius of the arc of the arc-shaped mold cavity on the side near the semi-circular protrusion is (0.8-0.95):1.

[0054] In some preferred embodiments, in the second structure, the ratio of the radius of the arc-shaped groove to the radius of the arc on the side of the arc-shaped mold cavity near the arc-shaped groove is (0.85-0.95):1.

[0055] In some preferred embodiments, in the second structure, the thickness of the gap formed between the arc-shaped groove and the semi-circular protrusion is greater than the thickness of the arc-shaped mold cavity.

[0056] The thickness of the gap formed between the arc-shaped groove and the semi-circular protrusion is preferably 5-20 mm.

[0057] The thickness of the arc-shaped mold cavity is preferably 5-20 mm.

[0058] Preferably, the vertical distance between the arc of the arc-shaped mold cavity on the side closest to the semi-circular protrusion and the semi-circular protrusion is 3-10mm.

[0059] Preferably, the vertical distance between the arc of the arc-shaped mold cavity on the side closest to the arc-shaped groove and the arc-shaped groove is 5-10mm.

[0060] In this invention, without considering specific formulations, non-parallel magnetic circuit NdFeB magnets can be produced using the above-described molding apparatus; specifically, after processing by the molding apparatus, low magnetic declination non-parallel magnetic circuit NdFeB magnets can be obtained by controlling the change of magnetic declination with the angle of magnetic field lines.

[0061] In some embodiments, the intensity of the magnetizing magnetic field used for pressing is 1.8-2.5t, for example 2.0t.

[0062] In some implementations, the molding pressure of the pressing is 4-8 MPa.

[0063] In some embodiments, the density of the pressed blank is 3.9-4.2 g / cm³. 3 For example, 4.14 g / cm³ 3 .

[0064] In this invention, the neodymium iron boron alloy sheet can be conventional in the art, for example, it can be obtained by melting and casting conventional neodymium iron boron raw materials, or it can be obtained from commercial products.

[0065] In this invention, the powder preparation and sintering operations are both conventional operations in the field.

[0066] In some embodiments, the particle size distribution of the powder obtained by the grinding process is in the range of 3.0-4.1 μm, for example 3.0-3.9 μm or 3.9-4.1 μm.

[0067] In some implementations, the sintering is performed under vacuum conditions.

[0068] In some embodiments, the sintering temperature is 1060-1090°C, for example 1080°C.

[0069] The present invention also provides a neodymium iron boron magnet, which is prepared by the method for preparing neodymium iron boron magnets as described above.

[0070] The present invention also provides an application of neodymium iron boron magnets in magnetic steel as described above.

[0071] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0072] The reagents and raw materials used in this invention are all commercially available.

[0073] The positive and progressive effects of this invention are as follows:

[0074] The neodymium iron boron magnet of this invention, in the case of a non-parallel magnetic circuit, can simultaneously achieve low magnetic declination and high remanence by controlling the change of magnetic declination with the angle of magnetic field lines. It is applicable to different raw material formulations and preparation processes, and can also significantly reduce the cracking rate. When practically applied to permanent magnet motors, it can effectively improve motor efficiency while reducing its sound pressure level. Furthermore, the entire preparation method is simple and easy to implement, and can be used for large-scale production. Attached Figure Description

[0075] Figure 1 This is a schematic diagram of the structure of the neodymium iron boron magnets obtained in the embodiments and comparative examples of the present invention.

[0076] Figure 2 This is a schematic diagram of the molding device used in Embodiment 1 of the present invention.

[0077] Figure 3 This is a schematic diagram of the feeder used in Comparative Example 1 of the present invention.

[0078] Figure 4 This is a schematic diagram of the molding apparatus used in Comparative Example 1 of the present invention.

[0079] Figure 5 This is a schematic diagram of the structure of the ring-shaped neodymium iron boron magnet used in the test of Example 2 of the present invention.

[0080] The attached figures are labeled as follows:

[0081] 1-First magnetic conductive block; 2-Second magnetic conductive block; 3-Arc-shaped mold cavity; 4-Magnetic block. Detailed Implementation

[0082] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0083] In the following embodiments and comparative examples, unless otherwise specified, the neodymium iron boron magnets are all arc-shaped magnets, and their structural schematic diagrams are shown below. Figure 1 As shown, starting from the edge (the center of the seam), the deflection angle of the entire arc is 60°, and different areas are divided according to different deflection angles, as shown in Table 1.

[0084] Table 1

[0085]

[0086] Based on the above magnet structure, the corresponding parameters are explained in detail below:

[0087] (1) Angle of magnetic field lines (referring to the theoretical angle of magnetic field lines):

[0088] The center of any arc in the cross-section of a neodymium iron boron magnet is taken as the 30° position. Using the center of the magnet as the base point, rotate 10° clockwise along the same cross-section from this position to get the 20° position, or rotate 10° counterclockwise to get the 40° position, and so on, to obtain the positions of 0°, 5°, 10°, 20°, 30°, 40°, 50°, 55° and 60° respectively. These angles are taken as the physical position angles. At the physical position angle of 30°, the magnetic field line angle is considered to be 0°, at the physical position angle of 10°, the magnetic field line angle is considered to be 20°, at the physical position angle of 40°, the magnetic field line angle is considered to be 10°, and so on, to obtain the magnetic field line angles of different physical positions.

[0089] (2) Magnetic declination

[0090] According to the different regions defined above, a thin slice is placed in a magnetic declination tester to measure the magnetic declination in each region. Specifically, referring to GB / T 43266-2023 "Method for Measurement of Magnetic Declination of Permanent Magnets", the component magnetic moments in the X, Y, and Z directions are measured using a magnetic declination tester. Then, the total magnetic moment is synthesized, and the magnetic declination in the corresponding region can be calculated using the magnetic declination calculation formula.

[0091] Example 1

[0092] The neodymium iron boron magnets of this embodiment were prepared according to the following steps:

[0093] 1. Take neodymium iron boron alloy sheets and add 0.1wt% lubricant (zinc stearate) to grind them into powder to obtain powder with a particle size distribution range of 3.9-4.1μm.

[0094] The specific formula of the alloy sheet is as follows (by mass percentage): PrNd: 29.5%; Al: 0.2%; Cu: 0.15%; Co: 0.4%; Ga: 0.2%; Zr: 0.18%; B: 0.95%; the remainder is Fe.

[0095] 2. The obtained powder is processed using methods such as... Figure 2 The molding apparatus shown is used to press the material under a magnetic field of 2.0t and a molding pressure of 4-8MPa to obtain a density of 3.9g / cm³. 3 The blank; where, due to the influence of actual operation, the forming pressure here will fluctuate within a certain range.

[0096] The molding device has the following specific structure: it includes a first magnetically conductive block 1 and a second magnetically conductive block 2. The first magnetically conductive block 1 includes an arc-shaped groove, and the second magnetically conductive block 2 includes a semi-circular protrusion located in the space formed by the arc-shaped groove. An arc-shaped mold cavity 3 is provided between the arc-shaped groove and the semi-circular protrusion. The ratio of the radius of the semi-circular protrusion to the radius of the arc of the arc-shaped mold cavity 3 near the semi-circular protrusion is 0.85:1. Magnetic blocks 4 are respectively provided at both ends of the arc-shaped mold cavity 3, and the relative permeability of the magnetic blocks 4 is 1.5. The percentage of the arc radius of the arc-shaped groove of the first magnetically conductive block 1 to the outer arc radius of the mold cavity is 0.85:1. The thickness of the gap formed between the arc-shaped groove and the semi-circular protrusion is 15mm; the thickness of the arc-shaped mold cavity 3 is 5mm. The vertical distance between the arc of the arc-shaped cavity 3 near the semi-circular protrusion and the semi-circular protrusion is 5mm. The vertical distance between the arc of the arc of the arc-shaped cavity 3 near the arc-shaped groove and the arc-shaped groove is 5mm. The magnetic block is arc-shaped, and the radius of the arc of the magnetic block and the arc of the arc-shaped cavity 3 near the arc-shaped groove are equal. The radius of the arc of the magnetic block and the arc of the arc-shaped cavity 3 near the semi-circular protrusion are also equal. The arc length of the magnetic block accounts for 15% of the arc length of the arc-shaped cavity 3.

[0097] A feeder is connected to the outside of the arc-shaped mold cavity 3. Figure 2 (Not shown in the diagram, but its shape is similar to the arc-shaped mold cavity 3, i.e., both are arc-shaped). The feeder is used to deliver raw materials into the arc-shaped mold cavity 3. A small cylinder is designed at the front end of the feeder, and a pin with a size close to that of the mold cavity is mounted on the cylinder. After the feeder is filled with half of the powder, it retracts a certain distance, the feeder cylinder moves downward, and the pin enters the powder in the mold cavity to solve the problem of bridging inside the powder.

[0098] 3. The pressed blank is sintered in a vacuum environment at 1080℃ to obtain the final product.

[0099] The angles of the magnetic field lines and the magnetic declination at different positions of the obtained neodymium iron boron magnets are shown in Table 2.

[0100] Example 2

[0101] Compared to Example 1, the only difference is the formulation of the NdFeB alloy sheet, specifically:

[0102] PrNd: 30.5%; Al: 0.15%; Cu: 0.2%; Co: 0.5%; Ga: 0.2%; Zr: 0.2%; B: 0.96%, with the remainder being Fe.

[0103] The angles of the magnetic field lines and the magnetic declination at different positions of the obtained neodymium iron boron magnets are shown in Table 2.

[0104] Example 3

[0105] Compared to Example 1, the only difference is the process parameters, specifically:

[0106] The particle size distribution of the powder obtained from milling ranges from 3.0 to 3.9 μm, and the density of the pressed green body is 4.14 g / cm³. 3 .

[0107] The angles of the magnetic field lines and the magnetic declination at different positions of the obtained neodymium iron boron magnets are shown in Table 2.

[0108] Comparative Example 1

[0109] The fabrication process of the neodymium iron boron magnet in this comparative example is as follows:

[0110] 1. Perform powder preparation according to step 1 in Example 1 to obtain powder with a particle size distribution range of 3.0-3.9μm.

[0111] 2. The obtained powder is pressed using a conventional feeder and conventional molding device under a magnetic field of 2.0t and a molding pressure of 4-8MPa to obtain a density of 4.15g / cm³. 3 The blank.

[0112] The feeder uses a conventional diamond-shaped feeder, as shown in the schematic diagram below. Figure 3 As shown.

[0113] The structure of the molding device is as follows: Figure 4 As shown, the structural difference between the molding device used in Example 1 and that in Example 2 is only: (1) no magnetic block is provided in the arc-shaped mold cavity 3; (2) the ratio of the radius of the semi-circular protrusion to the radius of the arc on the side of the arc-shaped mold cavity 3 near the semi-circular protrusion is 1:1.

[0114] 3. The pressed blank is sintered in a vacuum environment at 1080℃ to obtain the final product.

[0115] 4. The angles of the magnetic field lines and the magnetic declination at different positions of the obtained neodymium iron boron magnets are shown in Table 2.

[0116] The magnetic field lines in the obtained magnet cannot diverge in the intended direction. Specifically, the divergence angle is inconsistent and the magnetic field lines are severely deflected. Furthermore, the uniformity of the magnetic field strength inside the cavity is extremely poor. The powder is redistributed in the cavity under the action of the magnetic field force, resulting in extremely uneven density of the blank and cracking.

[0117] Example 1

[0118] The remanence of the neodymium iron boron magnets obtained in Examples 1-3 and Comparative Example 1 was tested at different locations. The specific testing methods are as follows:

[0119] A φ10*5mm small circular piece was cut along the vertical direction of the arc for measurement, and tested using an NIM62000TB magnetic property measuring instrument.

[0120] The results are shown in Table 2.

[0121] Table 2

[0122]

[0123] As shown in Table 2, the following formula can be satisfied at any position on the same cross-section of the neodymium iron boron magnet obtained by the present invention, except at the center of the arc:

[0124] Δθ=α·(1-cosθ);

[0125] in,

[0126] θ is the (theoretical) magnetic field line angle, and satisfies 0°<θ≤90°; Δθ is the value corresponding to the magnetic declination in °, and satisfies 0<Δθ≤10; α is a constant selected from 1-12.

[0127] Furthermore, the thickness of the NdFeB magnets obtained in Examples 1-3 can be guaranteed to be within the range of 5-20 mm at any location, and the thickness is uniform. Uniform thickness means that the thickness difference at different locations does not exceed 10% of the average thickness.

[0128] In Comparative Example 1, α is 36.3-102.7, which does not satisfy the above formula.

[0129] Example 2

[0130] 1. Sound pressure level test

[0131] Six equal portions of the neodymium iron boron magnets obtained in Examples 1-3 and Comparative Example 1 were taken respectively, and... Figure 5 The assembly method shown yields a ring-shaped neodymium iron boron magnet, which is used in a permanent magnet motor. The sound pressure level is tested in accordance with ISO 3745 / GB / T 10069.1 "Semi-anechoic chamber testing". The testing instrument is a Class 1 or Class 2 accuracy sound level meter conforming to IEC 61672-1 standard.

[0132] 2. Crack ratio test

[0133] Each of the following methods were used to obtain the same number of NdFeB magnets: one for each of the examples 1-3 and the other for Comparative Example 1. Each magnet was observed visually using an industrial electronic magnifying glass. If a magnet had a crack, it was recorded as a cracked magnet. The cracking ratio was calculated as the number of cracked magnets divided by the total number of magnets.

[0134] The results are shown in Table 3.

[0135] Table 3

[0136] serial number Crack rate (%) Sound pressure level dB(A) Example 1 0.23 59 Example 2 0.29 58 Example 3 0.27 61 Comparative Example 1 3.5 66

[0137] As shown above, the neodymium iron boron magnet obtained in the embodiments of the present invention has a non-parallel magnetic circuit while ensuring that the magnetic declination angle is less than 2°, the remanence is as high as 1.37-1.42T, and the cracking ratio is low. When actually used in permanent magnet motors, it can improve the motor efficiency while reducing its sound pressure level (not higher than 61A).

[0138] Compared to Example 1, when using a conventional feeder and a conventional molding device for pressing, the magnetic declination of the neodymium iron boron magnets obtained in Comparative Example 1 was significantly increased at the corresponding positions; after being actually used in a permanent magnet motor, the sound pressure level was still as high as 66A.

Claims

1. A neodymium iron boron magnet, characterized in that, The neodymium iron boron magnet has a non-parallel magnetic circuit; and the neodymium iron boron magnet is curved with a circular arc cross-section; wherein, at any position on the same cross-section except at the center of the arc, the following formula is satisfied: Δθ=α·(1-cosθ); in, θ is the angle of the magnetic field lines, and satisfies 0°<θ≤90°; Δθ is the numerical value corresponding to the magnetic declination in °, and satisfies 0 < Δθ ≤ 10; α is a constant selected from 1 to 12.

2. The neodymium iron boron magnet as described in claim 1, characterized in that, The formula satisfies one or more of the following conditions: (1) The θ satisfies 0°<θ≤30°; (2) The Δθ satisfies 0<Δθ≤2; (3) The α is selected from the constants of 8-12.

3. The neodymium iron boron magnet as described in claim 1, characterized in that, In the neodymium iron boron magnet, the magnetic field lines are arranged radially.

4. The neodymium iron boron magnet as described in claim 1, characterized in that, In the same cross-section, the magnetic declination gradually increases from the center of the arc to the edge of the arc; And / or, the difference in magnetic declination between the center and edge of the arc is not higher than 1.4°.

5. The neodymium iron boron magnet as described in claim 1, characterized in that, The thickness of the neodymium iron boron magnet at any position is 5-20 mm; preferably, the neodymium iron boron magnet has a uniform thickness.

6. A method for preparing a neodymium iron boron magnet as described in any one of claims 1-5, characterized in that, The method for preparing the neodymium iron boron magnet includes the following steps: Neodymium iron boron alloy sheets are produced by powdering, pressing, and sintering.

7. The method for preparing a neodymium iron boron magnet as described in claim 6, characterized in that, The forming device in the pressing process includes a first magnetic block and a second magnetic block. The first magnetic block includes an arc-shaped groove, and the second magnetic block includes a semi-circular protrusion located in the space formed by the arc-shaped groove. An arc-shaped mold cavity is provided between the arc-shaped groove and the semi-circular protrusion; Magnetic blocks are provided at both ends of the arc-shaped mold cavity; Preferably, the molding apparatus also satisfies one or more of the following conditions: (1) The ratio of the radius of the semi-circular protrusion to the radius of the arc of the arc-shaped mold cavity on the side near the semi-circular protrusion is (0.8-0.95):1, preferably (0.8-0.9):1, for example 0.85:1; (2) The ratio of the radius of the arc-shaped groove to the radius of the arc on the side of the arc-shaped mold cavity near the arc-shaped groove is (0.85-0.95):1, for example, 0.85:1; (3) The thickness of the gap formed between the arc-shaped groove and the semi-circular protrusion is greater than the thickness of the arc-shaped mold cavity; The thickness of the gap formed between the arc-shaped groove and the semi-circular protrusion is preferably 5-20 mm, for example 15 mm; The thickness of the arc-shaped mold cavity is preferably 5-20 mm; Preferably, the vertical distance between the arc of the arc-shaped mold cavity on the side near the semi-circular protrusion and the semi-circular protrusion is 3-10mm, for example, 5mm. Preferably, the vertical distance between the arc of the arc-shaped mold cavity on the side closest to the arc-shaped groove and the arc-shaped groove is 5-10mm, for example, 5mm; (4) The relative permeability of the magnetic blocks is 1.02-10, for example 1.5; preferably, the relative permeability of the magnetic blocks at both ends is the same; (5) The magnetic block is arc-shaped; Preferably, the radii of the arcs of the magnetic block and the arc-shaped mold cavity near the arc-shaped groove are equal, and the radii of the arcs of the magnetic block and the arc-shaped mold cavity near the semi-circular protrusion are equal. Preferably, the percentage of the arc length of the magnetic block to the arc length of the arc-shaped mold cavity is 10%-20%, for example, 15%.

8. The method for preparing a neodymium iron boron magnet as described in claim 6, characterized in that, The forming device in the pressing process includes a first magnetic block and a second magnetic block; the first magnetic block includes multiple parallel magnetic blocks with different relative permeabilities arranged in the horizontal direction, and the bottom of the multiple magnetic blocks forms an arc-shaped groove; the second magnetic block includes multiple parallel magnetic blocks with different relative permeabilities arranged in the horizontal direction, and the top of the multiple magnetic blocks forms a semi-circular protrusion; the semi-circular protrusion is located in the space formed by the arc-shaped groove; An arc-shaped mold cavity is provided between the arc-shaped groove and the semi-circular protrusion; Preferably, the molding apparatus also satisfies one or more of the following conditions: (1) The first magnetic block comprises 6-50 magnetic blocks; Preferably, the relative permeability of the magnetic blocks disposed on the axis of the first magnetic block is lower than that of the magnetic blocks far from the axis of the first magnetic block. Preferably, the relative permeability of the magnetic block increases in a gradient direction in the direction in which the axis of the first magnetic block extends to both ends; In the first magnetically conductive block, the difference in relative permeability between adjacent magnetic blocks at both ends is preferably 40-333. Preferably, the ratio of the relative permeability of the magnetic blocks disposed on the axis of the first magnetic block to the relative permeability of the magnetic blocks far from the axis of the first magnetic block is 1.05:1.

3. (2) The second magnetic block comprises 6-30 magnetic blocks; Preferably, the relative permeability of the magnetic blocks disposed along the axis of the second magnetic block is lower than the relative permeability of the magnetic blocks disposed away from the axis of the second magnetic block. Preferably, the relative permeability of the magnetic block increases in a gradient direction in the direction in which the axis of the second magnetic block extends to both ends; In the second magnetic block, the difference in relative permeability between the magnetic blocks at adjacent ends is preferably 66-333. Preferably, the ratio of the relative permeability of the magnetic blocks disposed on the axis of the second magnetic block to the relative permeability of the magnetic blocks far from the axis of the second magnetic block is 1.05:1.

3. (3) The ratio of the radius of the semi-circular protrusion to the radius of the arc of the arc-shaped mold cavity on the side near the semi-circular protrusion is (0.8-0.95):1; (4) The ratio of the radius of the arc-shaped groove to the radius of the arc on the side of the arc-shaped mold cavity closest to the arc-shaped groove is (0.85-0.95):1; (5) The thickness of the gap formed between the arc-shaped groove and the semi-circular protrusion is greater than the thickness of the arc-shaped mold cavity; The thickness of the gap formed between the arc-shaped groove and the semi-circular protrusion is preferably 5-20 mm. The thickness of the arc-shaped mold cavity is preferably 5-20 mm; The distance between the arc of the arc-shaped mold cavity on the side closest to the semi-circular protrusion and the vertical distance between the semi-circular protrusion and the arc is preferably 3-10mm. Preferably, the vertical distance between the arc of the arc-shaped mold cavity on the side closest to the arc-shaped groove and the arc-shaped groove is 5-10mm.

9. The method for preparing a neodymium iron boron magnet as described in claim 6, characterized in that, The method for preparing the neodymium iron boron magnet satisfies one or more of the following conditions: (1) The particle size distribution range of the powder obtained by the powder preparation is 3.0-4.1μm, for example 3.0-3.9μm or 3.9-4.1μm; (2) The strength of the magnetizing magnetic field used for pressing is 1.8-2.5t, for example 2.0t; (3) The molding pressure of the pressing is 4-8 MPa; (4) The density of the pressed blank is 3.9-4.2 g / cm³. 3 For example, 4.14 g / cm³ 3 ; (5) The sintering is carried out under vacuum conditions; (6) The sintering temperature is 1060-1090℃, for example 1080℃.

10. An application of a neodymium iron boron magnet as described in any one of claims 1-5 in magnetic steel.

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