High-performance thermal deformation permanent magnet and preparation method thereof

Abstract

The invention belongs to the technical field of permanent magnet production, particularly relates to the field of small-size neodymium iron boron permanent magnet production, and particularly relates to a high-performance thermal deformation permanent magnet and a preparation method. The magnet with the small overall dimension is manufactured in a powder extrusion mode, and the cross sectional area of the magnet can be as small as 25 mm < 2 >; one-time forming is achieved in a hot extrusion mode, the overall production process is short, and the problem that a thin and long mandrel forming an inner hole in an existing scheme is prone to damage is solved. The magnet produced by the invention has higher performance, and the magnetic field intensity of the circumferential surface is uniformly distributed after multi-pole magnetization. The number of poles reaches up to more than 20, the anisotropic field of the neodymium-iron-boron magnet at a higher temperature is reduced by heating during magnetizing, and higher magnetizing body performance can be obtained more easily under the condition that the magnetizing magnetic field intensity is limited due to the size. According to the technical scheme, in the structure of the prepared radial magnetic field magnet, the inter-pole difference does not exceed 10%, and the residual magnetism of the magnet is not lower than 10 kGs.

Description

Technical Field

[0001] The invention belongs to the technical field of permanent magnet production, in particular to the field of small-sized NdFeB permanent magnet production, and particularly relates to a high-performance thermal deformation permanent magnet and a preparation method thereof. Background Art

[0002] Smaller size (cross-section outer dimensions ≤ 100mm 2 , ≤50mm 2 Even ≤25mm 2 ) can be used in a variety of micro motors. Some of the applications are wearable devices, smart phones, etc. Therefore, it is hoped that permanent magnets can be developed in the direction of light, thin, short and small. Under the condition of limiting weight and volume, the magnets used in the above devices also have the requirement to further improve the magnetic properties.

[0003] In the prior art, there are several preparation schemes for multi-pole permanent magnets with small cross-sections:

[0004] 1. Mix isotropic magnetic powder and a binder and then perform molding or injection molding to obtain a molded / injection molded isotropic magnet.

[0005] 2. Anisotropic magnetic powder is mixed with a binder and then injection molded in a magnetic field to obtain an injection-molded anisotropic magnet.

[0006] 3. Use NdFeB rapid solidification casting sheets to make powder through HDDR and airflow milling, and use the obtained powder to further prepare sintered magnets. However, it is different from the usual sintered anisotropic NdFeB production method, but in the process of pressing the powder blank, there is no orientation, and after pressing, sintering is used to manufacture isotropic sintered NdFeB magnets.

[0007] 4. Use rapid quenching magnetic powder and hot pressing method to manufacture near-isotropic magnets.

[0008] 5. Use quick-quenching magnetic powder and other methods such as hot pressing / hot deformation, and use a mandrel-type mold to form an inner hole, and use positive extrusion or reverse extrusion to make anisotropic radial rings.

[0009] The above-mentioned multiple magnet preparation methods all have defects to varying degrees. For example, in method 1, the magnetic properties of the magnet product are diluted due to the addition of a binder. At the same time, because the magnet obtained by this processing scheme is an isotropic magnet, the upper limit of the magnetic properties of the final magnet is relatively low (the highest is about 12-13MGOe); in method 2, the magnet is injection molded in a magnetic field and oriented to a certain extent, but an adhesive is inevitably used in the raw material, and the upper limit of the magnetic properties of the final magnet is about 12-14MGOe; in methods 3-4, the production of outer cylindrical multi-pole magnets must be pre-sintered or hot-pressed into a block of isotropic magnets, and then cut out of shape by wire cutting or other methods. Since there is no non-magnetic binder to dilute the magnetic properties, the performance is improved compared to methods 1-2, but because it is still an isotropic magnet, the magnetic properties are still relatively low, and the upper limit of the magnetic properties is about 16-17MGOe. In method 5, because the required magnet size is extremely small, the strength and rigidity of the single-end fixed core shaft mold that forms the inner hole are difficult to withstand the relatively strong extrusion force and friction during extrusion, and it is very easy to be damaged or offset, making it difficult to effectively mass-produce qualified products.

[0010] However, when using sintered anisotropic magnets to make extremely small magnetic rings, they cannot be effectively oriented directly into multi-pole or radial directions. When using conventional parallel-oriented magnets to make multi-poles, the magnetic properties of the poles that deviate from the orientation direction will be greatly reduced, and the magnetic induction intensity of the poles between different poles is too different, so they cannot be used in normal designs. Summary of the invention

[0011] The purpose of the present invention is to provide a high-performance thermal deformation permanent magnet and a preparation method thereof in view of the technical defects in the prior art that in the structure of preparing anisotropic magnets of extremely small size, it is impossible to simultaneously ensure high magnetic properties and a pole difference of a multi-pole magnet of no more than 10%.

[0012] In order to achieve the above object, the technical solution adopted by the present invention is:

[0013] A method for preparing a high-performance heat-deformed magnet comprises the following steps:

[0014] Step 1, prepare the raw materials according to the weight ratio, use uniform component powder or mix magnetic powders of multiple different components to obtain mixed magnetic powder for standby use;

[0015] Step 2, heating the uniform component powder or the mixed magnetic powder in step 1 to 600-800° C. in an atmosphere with an O2 content of no more than 0.1% to obtain preheated magnetic powder;

[0016] Step 3, extruding the preheated magnetic powder in step 2 through a mold cavity with a temperature range of 700-900° C., and hot extruding to obtain an anisotropic permanent magnet blank; the mold cavity is cylindrical, and the mold cavity includes an extrusion zone and a molding zone, and a variable cross-section area is provided between the extrusion zone and the molding zone;

[0017] Step 4, processing the magnet blank into a magnet of a specified size and shape; or further assembling the magnet blank with a shaft into a rotor assembly;

[0018] Step 5: magnetizing the magnet or rotor assembly in step 4 to obtain a multi-polar magnet or rotor assembly.

[0019] As a preferred embodiment of the present invention, in step 3, the cross-sectional area of ​​the mold cavity changes continuously in the variable cross-sectional area, and the angle between the section of the molding surface where the mold cavity contacts the magnetic powder and the central axis of the mold cavity is not higher than 60°.

[0020] In the technical solution of the present invention, the variable cross-section area is set in the internal space of the mold cavity, the purpose is to orient the magnetic powder during the extrusion process to obtain a radially anisotropic magnetic texture. The angle range between the tangent of the contour line of the variable cross-section area and the center axis of the mold is preferably not more than 60°, and the tangent here is understood as: the intersection formed by the contour line of the variable cross-section area and the contour line of the molding area, the angle between the tangent passing through the intersection and the center axis of the mold. It is further preferred to be 30°-60°. In this angle range, the extrusion of preheated magnetic powder has the best effect on the orientation of magnetic powder. When the angle is too small, although the compaction and deformation are slower and the effect is better, due to the long deformation process area, more materials are not formed into the final magnet product, and the economy of the process is reduced; the larger the angle, the faster the deformation, the greater the internal stress and rheological velocity gradient during deformation, the easier it is for the magnet to crack and other defects, and the yield rate is difficult to guarantee. In order to better balance the yield rate of the feed and ensure the yield rate of small-sized magnets, the angle of the variable cross-section is preferably 40°-55°.

[0021] Existing solutions such as graphite, molybdenum disulfide, etc. can be used for lubrication in the mold cavity, or a soft metal (such as copper, stainless steel) shell can be used to isolate the magnetic powder from the mold cavity.

[0022] Preferably, in step 3, the cross-sectional area of ​​the mold cavity molding zone is not greater than 100 mm 2 , further preferably, the cross-sectional area is not greater than 50 mm 2 The technical solution of the present invention is mainly used for preparing multi-pole permanent magnets with small cross-sections. The smaller the cross-sectional area of ​​the mold cavity molding zone is, the more obvious the process difference from the prior art is, and the better the effect is.

[0023] Preferably, the transverse cross-sections in the mold cavity are all circular.

[0024] Preferably, in the mold cavity, the cross-sectional area S1 located in the extrusion zone is larger than the cross-sectional area S2 of the molding zone, and 4≤S1 / S2≤12. S2 is determined according to the required magnet size, with a small amount of processing allowance reserved. The S1 / S2 ratio has a significant positive correlation with the magnetic properties of the obtained magnet. When the S1 / S2 ratio increases, the remanence of the magnet is higher and the coercive force is lower when other conditions remain unchanged. It is easier to magnetize, but it is easy to demagnetize after magnetization. Based on this, the appropriate S1 / S2 ratio in the aforementioned range can be selected according to the service characteristics of the magnet.

[0025] Preferably, the contour of the longitudinal sectional view of the variable cross-section area is a trapezoidal shape, or the contour line of the longitudinal sectional view is an arc line.

[0026] Preferably, when the contour of the variable cross-section area of ​​the mold cavity is a trapezoidal shape, the angle between the contour line of the mold cavity and the central axis of the mold cavity is in the range of 30-60°;

[0027] When the contour line of the variable cross-section region of the mold cavity is a curve, the cross-sectional area of ​​the variable cross-section region from one end of the extrusion zone to one end of the molding zone decreases monotonically.

[0028] Preferably, an extrusion punch is provided in the mold cavity, the extrusion punch is a cylindrical structure, the diameter of the extrusion punch is adapted to the diameter of the extrusion zone of the mold cavity, and the extrusion punch extrude from the extrusion zone of the mold cavity toward the molding zone.

[0029] In the technical solution of the present invention, the extrusion die punch comprises an upper punch and a lower punch, the upper punch is arranged in the extrusion area of ​​the die cavity, and the lower punch is arranged in the forming area of ​​the die cavity. The upper punch and the lower punch cooperate with each other to complete the extrusion of the magnetic powder.

[0030] Preferably, the end of the upper punch contacting the magnet is a cylindrical structure, and the extrusion end point of the upper punch is the starting position of the variable cross-section area in the mold cavity, that is, the position where the cross-sectional area of ​​the variable cross-section area is the largest.

[0031] Preferably, in the mold of the present invention, an axial rod type core component for forming the inner hole of the magnet is not provided in the molding area. In the technical solution of the present invention, the mold is mainly used to prepare multi-pole permanent magnets with small cross-sections. In this case, the use of a core shaft poses a risk of mold damage, and can cause the magnet to bend during molding, thereby resulting in uneven magnet performance and increased pole fluctuations. Reduce the yield of the magnet. Therefore, in the technical solution of the present invention, the core shaft assembly in the prior art is discarded. The final magnet is a solid core column. It is subsequently further processed into a rotor-type component as needed.

[0032] Preferably, in step 5, when the magnet is magnetized, the temperature range of the magnet is 50-250°C.

[0033] Further preferably, the temperature range of the magnet during magnetization is 100°C-250°C. In the technical solution of the present application, since the size requirements of the magnet are relatively small, during the extrusion process, the coercive force of the small-sized magnet itself is higher than that of the large-sized extruded magnet structure, which further increases the difficulty of subsequent magnetization. At the same time, a larger number of magnetic poles corresponds to a smaller pole width, and it is difficult for the commonly designed magnetization fixture to fully magnetize it to a saturated state. In order to enable better magnetization, heating the magnet before magnetization is conducive to obtaining a higher degree of saturation at a lower field strength. Generally speaking, if other conditions remain unchanged, the higher the temperature of the magnet during magnetization (but it must be lower than the Curie temperature), the higher the surface magnetism of the magnet obtained after magnetization. However, too high a magnet temperature will make the operation inconvenient, and also place higher requirements on the temperature resistance of the magnetization fixture. In general, it is more appropriate when the magnet temperature is 50°C-250°C, and more preferably 100°C-200°C.

[0034] As a preferred technical solution of the present invention, the mixed magnetic powder is RTB magnetic powder, R represents a rare earth element, R includes any one or a combination of several of Nd, Pr, Dy, Tb, La, Ce, and Y; T includes any one or a combination of several of Fe, Co, Ga, Cu, Cr, and Al; and B is a boron element.

[0035] Preferably, the total rare earth element content is 27wt.% to 32wt.%.

[0036] As a preferred solution, the magnetic powder composition can be: Nd 20wt.%~24wt.%, Pr 6wt.%~10wt.%, Co 2wt.%~4.5wt.%, Ga 0.3wt.%~0.7wt.%, B 0.7wt.%~1wt.%, and the balance is Fe. Or: Nd 13wt.%~15wt.%, Pr 15wt.%~18wt.%, Co 2wt.%~4.5wt.%, Ga 0.3wt.%~0.7wt.%, B 0.7wt.%~1wt.%, and the balance is Fe. Usually, uniform composition powder (hot pressed magnetic powder) is made by rapid quenching process to obtain a small and uniform initial grain size, but other process means may also be used to achieve similar effects.

[0037] As a preferred technical solution of the present invention, the number of the magnetized poles can be up to 20 poles.

[0038] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0039] In the technical solution of the present invention, a magnet with a small outer dimension is obtained by powder extrusion, and the cross-sectional area of ​​the magnet can be as small as 25 mm 2; Through one-time molding by hot extrusion, the overall production process is short, and the problem of fragility of the slender core shaft forming the inner hole in the original solution is avoided. Compared with the existing common and feasible technical solutions, the magnets produced by the technical solution of the present invention have higher performance, the residual magnetism can reach more than 10kGs, and the circumferential surface magnetic field intensity is evenly distributed after multi-pole magnetization. Under the premise of a small cross-sectional area, the number of poles can be as high as 20 poles. Heating during magnetization reduces the anisotropy field of the NdFeB magnet at a higher temperature, making it easier to obtain higher magnet performance under the condition that the magnetization magnetic field intensity is limited due to size.

[0040] In the technical solution of the present invention, in the structure of the prepared radial magnetic field magnet, the difference between poles does not exceed 10%, and the residual magnetism of the magnet is not less than 10 kGs. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a schematic diagram of the mold structure of the first type in the present invention;

[0042] Figure 2 is a schematic cross-sectional structural diagram of a mold cavity of the first type of mold in the present invention;

[0043] Figure 3 is a schematic cross-sectional structural diagram of a mold cavity of the second type of mold in the present invention;

[0044] Figure 4 It is a schematic diagram of the process of hot extrusion of magnets by using the first type of mold in the present invention;

[0045] Icons: 1-die, 2-upper punch; 3-lower punch; 4-extrusion area; 5-forming area; 6-variable cross-section area; 7-magnetic powder to be processed; 8-densified magnetic powder; 9-blank. DETAILED DESCRIPTION

[0046] The present invention will be described in detail below in conjunction with the accompanying drawings.

[0047] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0048] Example 1

[0049] A method for preparing a high-performance radially oriented permanent magnet comprises the following steps:

[0050] Step 1: Prepare uniform magnetic powder with Nd 23wt.%, Pr 7.5wt.%, Co 4wt.%, Ga 0.45wt.%, B 0.9wt.%, and the remainder Fe by rapid quenching method;

[0051] Step 2, heat the uniform magnetic powder described in step 1 to 700±20°C in a normal pressure Ar atmosphere with an oxygen content not higher than 0.1% to obtain preheated magnetic powder; specifically, in step 2, the magnetic powder can be contained in a stainless steel container, and the stainless steel container together with the magnetic powder is placed in a resistive heating furnace in a closed operating chamber that can be evacuated and filled with a protective atmosphere. After the magnetic powder is heated to temperature, take the stainless steel container out of the heating furnace, and pour the magnetic powder in it into the mold cavity that is also placed in the aforementioned closed operating chamber. Figure 1-2 In the mold structure shown in FIG. 1 , when magnetic powder is added to the mold cavity of the mold (die 1), the upper punch 2 moves upward and leaves the mold cavity, and the upper end surface of the lower punch 3 is kept substantially flush with the boundary between the molding area 5 and the variable cross-section area 6, so that when magnetic powder is added, the magnetic powder 7 to be processed is mainly distributed in the extrusion area 4 and the variable cross-section area 6; for the specific extrusion process, see Figure 4 As shown;

[0052] Step 3, after the magnetic powder 7 to be processed in step 2 is kept warm in a mold at a temperature range of 800±20°C for 10s to 60s, the lower punch 3 is fixed, and the upper punch 2 is moved downward until the pressing pressure reaches 200MPa±10MPa to densify the magnetic powder; then the lower punch 3 is moved downward, and the upper punch 2 is immediately moved downward, and the densified magnetic powder 8 is hot-extruded to obtain an anisotropic permanent magnet blank 9; the mold cavity of the mold is cylindrical, and along the axial direction, the mold cavity sequentially includes an extrusion zone 4 and a molding zone 5, and a variable cross-section zone 6 is provided between the extrusion zone 4 and the molding zone 5; Figure 1 The figure shows the schematic diagram of the structure of the mold. In the mold structure used in this embodiment, the cross-sectional area S1 located in the extrusion zone is 314 mm 2 The cross-sectional area S2 located in the molding zone is 50 mm 2 ; The length of the variable cross-section area is 3.5 mm, the profile of the longitudinal cross-section view of the variable cross-section area is a trapezoidal shape, the contour line of the mold cavity is a straight line, and the angle between the contour line of the mold cavity and the central axis of the mold cavity is 60°;

[0053] Step 4, processing the anisotropic permanent magnet blank into a ring-shaped permanent magnet with an outer diameter of 7.8 mm, an inner diameter of 2 mm, and a height of 10 mm;

[0054] Step 5: magnetize the outer circle of the permanent magnet in step 4 to obtain a multi-pole permanent magnet. During the magnetization process, the temperature of the magnet is controlled at 200°C ± 10°C. The permanent magnet is marked as #1, and the number of poles of #1 is 10 poles in the outer circle.

[0055] Example 2

[0056] A method for preparing a high-performance radially oriented permanent magnet comprises the following steps:

[0057] Step 1: Prepare uniform powder with Nd 23wt.%, Pr 7.5wt.%, Co 4wt.%, Ga 0.45wt.%, B 0.9wt.%, and the balance Fe by rapid quenching method; marked as A magnetic powder;

[0058] Step 2, heat the magnetic powder described in step 1 to 700±20°C in an atmosphere with an oxygen content not higher than 0.1% to obtain preheated magnetic powder; specifically, the magnetic powder of step 2 can be contained in a stainless steel container, and the stainless steel container together with the magnetic powder is placed in a resistive heating furnace in a closed operating chamber that can be evacuated and filled with a protective atmosphere. After the magnetic powder is heated to temperature, take the stainless steel container out of the heating furnace, and pour the magnetic powder in it into the mold cavity that is also placed in the aforementioned closed operating chamber. When adding magnetic powder to the mold, the upper punch moves upward and leaves the mold cavity, and the upper end face of the lower punch is basically flush with the boundary of the molding area and the variable cross-section area, so that when the magnetic powder is added, the magnetic powder is mainly distributed in the extrusion area and the variable cross-section area;

[0059] Step 3, hot extruding the high temperature alloy magnetic powder in step 2 in a mold at a temperature range of 800±20°C to obtain an anisotropic permanent magnet blank; the mold cavity of the mold is cylindrical, and along the axial direction, the mold cavity sequentially includes an extrusion zone and a molding zone, and a variable cross-section area is provided between the extrusion zone and the molding zone; Figure 3 The figure shows the schematic diagram of the structure of the mold. In the mold structure used in this embodiment, the cross-sectional area S1 located in the extrusion zone is 314 mm 2 The cross-sectional area S2 located in the molding zone is 50 mm 2 ; The length of the variable cross-section area is 6mm, the contour line of the longitudinal section view of the variable cross-section area is a curve, and the cross-sectional area of ​​the variable cross-section area from one end of the extrusion zone to one end of the forming zone decreases monotonically; the longitudinal section view refers to Figure 3 As shown, when the contour line of the variable cross-section area is a curve, the included angle mainly refers to the angle α formed by the line connecting the intersection of the contour line of the variable cross-section area and the contour line of the molding area to the center axis of the mold cavity and the center axis of the mold cavity;

[0060] Step 4, processing the anisotropic permanent magnet blank into a ring-shaped permanent magnet with a diameter of 7.8 mm, an inner diameter of 2 mm, and a height of 10 mm;

[0061] Step 5: magnetize the permanent magnet in step 4 to obtain a multi-pole permanent magnet. During the magnetization process, the temperature of the magnet is controlled at 200° C.±10° C. The permanent magnet is marked as #2, and the number of poles of #2 is 10.

[0062] Example 3

[0063] Example 3 provides a method for preparing a high-performance radially oriented permanent magnet. The preparation method is described in reference to Example 1 or Example 2, except that the preparation process parameters are adjusted as shown in Table 1 below; the size of the mold is different from that of the mold in Example 1. Specifically, in the mold structure used in this embodiment, the cross-sectional area S1 located in the extrusion zone is 452 mm 2 The cross-sectional area S2 located in the molding zone is 100 mm 2 The length of the variable cross-section area is 3.5 mm, and the angle between the contour line of the mold cavity and the central axis of the mold cavity is 60°. The permanent magnet is marked as #3, and the number of poles of #3 is 24.

[0064] Example 4

[0065] This embodiment provides a method for preparing a high-performance radially oriented permanent magnet. The preparation method is described in Example 1 or Example 2, except that the preparation process parameters are adjusted as shown in Table 1 below. In the mold structure used in this embodiment, the cross-sectional area S2 located in the molding zone is 80 mm 2 The angle between the contour line of the mold cavity and the center axis of the mold cavity is 60°. The permanent magnet is marked as #4, and the number of poles of #4 is 16.

[0066] Example 5

[0067] This embodiment provides a method for preparing a high-performance radially oriented permanent magnet. The preparation method is described in reference to Embodiment 1 or Embodiment 2, except that the preparation process parameters are adjusted as shown in Table 1 below. In this embodiment, the cross-sectional area of ​​the hot extrusion is 60 mm 2 The angle between the contour line of the mold cavity and the central axis of the mold cavity is 55°. The permanent magnet is marked as #5, and the number of poles of #5 is 14.

[0068] Example 6

[0069] The present embodiment provides a method for preparing a high-performance radially oriented permanent magnet. The preparation method is described in reference to the description of embodiment 1 or embodiment 2, except that the magnetic powder composition is adjusted to Nd 12.5wt.%, Pr 18wt.%, Co 3.5wt.%, Ga 0.5wt.%, B 0.9wt.%, and the balance is Fe, and the uniform composition is marked as B magnetic powder, and the preparation process parameters are adjusted, see Table 1 below; in this embodiment, the raw material ratio is different, the angle between the contour line of the mold cavity and the central axis of the mold cavity is 40°, and the cross-sectional area of ​​the hot extrusion is 25mm 2 , the permanent magnet is marked as #6, and the number of poles of #6 is 8.

[0070] Example 7

[0071] This embodiment provides a method for preparing a high-performance radially oriented permanent magnet. The preparation method is described in reference to Embodiment 1 or Embodiment 2, except that the preparation process parameters are adjusted as shown in Table 1 below. In this embodiment, the raw material ratio is different, the angle between the contour line of the mold cavity and the central axis of the mold cavity is 52°, and the cross-sectional area of ​​the hot extrusion is 25 mm. 2 , the permanent magnet is marked as #7, and the number of poles of #7 is 10.

[0072] Example 8

[0073] This embodiment provides a method for preparing a high-performance radially oriented permanent magnet. The preparation method is described in reference to Embodiment 1 or Embodiment 2, except that the preparation process parameters are adjusted as shown in Table 1 below. In this embodiment, the raw material ratio is different, the angle between the contour line of the mold cavity and the central axis of the mold cavity is 60°, and the cross-sectional area of ​​the hot extrusion is 25 mm. 2 , the permanent magnet is marked as #8, and the number of poles of #8 is 14.

[0074] Comparative Example 1

[0075] This comparative example 1 provides a method for preparing a small-section multi-pole permanent magnet, which is basically the same as the steps described in Example 5, except that in this comparative example 1, a core shaft with an outer diameter of 1.54 mm is provided in the mold cavity for forming an inner hole during the molding process, and the core shaft is made of high-temperature alloy or cemented carbide; because the core shaft is quite slender, there is a lateral swing phenomenon when it is subjected to force during molding, which makes the coaxiality of the inner hole and the outer periphery deteriorate on the one hand, so that more processing allowance needs to be reserved to make the coaxiality of the inner hole and the outer periphery after processing meet the use requirements, and at the same time, due to the uneven circumferential deformation, the performance consistency of different poles of the magnet deteriorates. From the performance test results, it can be compared that after adding the core shaft, the fluctuation amplitude of the surface magnetism is large, and the mold damage rate is high, which is not suitable for batch production practice.

[0076] Comparative Example 2

[0077] Comparative Example 2 provides a method for preparing a small-section multi-pole permanent magnet, which is basically the same as the steps described in Example 8, with the difference that, in Comparative Example 2, a core shaft with an outer diameter of 0.98 mm is provided in the mold cavity for forming an inner hole during the molding process; because the core shaft is too slender and cannot withstand the force during molding, the core shaft breaks during molding, and effective production cannot be achieved.

[0078] Table 1 is a summary table of parameters and performance of the permanent magnet products in Examples 1-8 and Comparative Examples 1-2

[0079]

[0080]

[0081] It can be seen from the above table that in the technical solution of the present invention, by changing the cross-sectional area of ​​the magnet in the molding area and conducting magnetization experiments with different pole numbers, it is found that in the permanent magnet product finally obtained by the technical solution of the present invention, the residual magnetism can be maintained above 10kGs. On this basis, the fluctuation of the surface magnetism is small, not exceeding 5%.

[0082] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a high-performance thermally deformed permanent magnet, characterized in that: The following steps are involved: Step 1, prepare the raw materials according to the weight ratio, use uniform component powder or mix magnetic powders of multiple different components to obtain mixed magnetic powder for standby use; Step 2, heating the uniform component powder or mixed magnetic powder in step 1 to 600-800° C. in an atmosphere with an oxygen content of no more than 0.1% to obtain preheated magnetic powder; Step 3, hot extruding the preheated magnetic powder in step 2 in a mold at a temperature range of 700-900° C. to obtain an anisotropic permanent magnet blank; the mold cavity of the mold is cylindrical, and along the axial direction, the mold cavity sequentially includes an extrusion zone and a molding zone, and a variable cross-section area is provided between the extrusion zone and the molding zone; Step 4, processing the anisotropic permanent magnet blank into a permanent magnet of specified size and shape; Step 5: magnetize the permanent magnet in step 4 to obtain a multi-pole permanent magnet.

2. The method for preparing a high performance thermal deformation permanent magnet according to claim 1, characterized in that: In the mold cavity, the cross-sectional area S1 in the extrusion zone is larger than the cross-sectional area S2 in the molding zone, and 4≤S1 / S2≤12.

3. The method for preparing a high performance thermal deformation permanent magnet according to claim 1, characterized in that: The profile of the transverse cross-sectional view of the variable cross-sectional area is a trapezoidal shape, or the profile line of the transverse cross-sectional view is an arc line.

4. The method for preparing a high performance thermal deformation permanent magnet according to claim 3, characterized in that: When the contour of the variable cross-section area of ​​the mold cavity is a trapezoidal shape, the angle between the contour line of the mold cavity and the central axis of the mold cavity is in the range of 30-60°; When the contour line of the variable cross-section region of the mold cavity is a curve, the cross-sectional area of ​​the variable cross-section region from one end of the extrusion zone to one end of the molding zone decreases monotonically.

5. The method for preparing a high performance thermal deformation permanent magnet according to claim 3, characterized in that: An extrusion punch is arranged in the mold cavity, the end of the extrusion punch contacting the magnet is a cylindrical structure, the diameter of the extrusion punch is adapted to the diameter of the extrusion zone of the mold cavity, and the extrusion punch extrude from the extrusion zone of the mold cavity toward the molding zone.

6. The method for preparing a high performance thermal deformation permanent magnet according to claim 1, characterized in that: In step 5, when the magnet is magnetized, the temperature range of the magnet is 50-250°C.

7. The method for preparing a high performance thermally deformed permanent magnet according to claim 6, characterized in that: During the magnetization process, the temperature of the magnet is controlled at 100-250°C.

8. The method for preparing a high performance thermal deformation permanent magnet according to claim 1, characterized in that: The mixed magnetic powder is RTB magnetic powder, R represents a rare earth element, R includes any one or a combination of several of Nd, Pr, Dy, Tb, La, Ce, and Y; T includes any one or a combination of several of Fe, Co, Ga, Cu, Cr, and Al; and B represents a boron element.

9. A high performance thermal deformation permanent magnet, characterized in that: The thermal deformation permanent magnet is prepared according to the method for preparing a high-performance thermal deformation permanent magnet according to any one of claims 1 to 8.

10. The high performance thermal deformation permanent magnet according to claim 9, characterized in that: The remanence of the permanent magnet is not less than 10 kGs; the permanent magnet is a cylindrical multi-pole permanent magnet, and the outer cross-sectional area of ​​the permanent magnet does not exceed 100 mm 2 ; The difference in magnetic properties between the poles of the permanent magnet does not exceed 10%.

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