A method for improving the consistency of NdFeB

Abstract

The invention discloses a method for improving the consistency of NdFeB, relates to the technical field of NdFeB material preparation, and aims to solve the problem that powder in an NdFeB forming mold is difficult to be evenly distributed. The invention comprises the following steps: preparing a lubricant, an antioxidant, and a gasoline mixed solution; mixing NdFeB powder particles with the mixed solution and fully stirring the mixture to form a suspension; opening a plurality of holes at the bottom and around the mold cavity of the NdFeB forming mold, wherein the hole diameter is smaller than the particle diameter of the NdFeB powder particles; pouring the suspension into the mold cavity of the forming mold, and standing the mixture until the lubricant, antioxidant, and gasoline mixed solution are discharged from the holes; dividing the pressing height into four sections for pressing, and increasing the orientation magnetic field strength each time a new stage is reached during the pressing process, and finally pressing the formed blank into the molded blank, and subjecting the blank to isostatic pressing, sintering, and tempering to obtain a sintered NdFeB magnet. The invention can add NdFeB powder into the mold cavity in liquid form, and then discharge excess liquid, thereby easily achieving uniform distribution and improving the consistency of the magnet.

Description

Technical Field

[0001] The invention relates to the technical field of NdFeB material preparation, in particular to a method for improving the consistency of NdFeB. Background Art

[0002] Neodymium iron boron (NdFeB) permanent magnets, due to their excellent properties of high remanence, high coercivity, and high magnetic energy product, are widely used in permanent magnetic field devices and equipment, such as electroacoustic and telecommunications, motors, instrumentation, and nuclear magnetic resonance. The production process for sintered NdFeB includes steps such as batching, smelting, hydrogen explosion, pulverizing, molding, and sintering, resulting in billets with defined magnetic properties. These billets then undergo various grinding, cutting, and surface treatment processes before being manufactured into finished products. A single billet can often yield dozens, hundreds, or even thousands of finished products, so the consistency of the billet's performance impacts both product quality and yield.

[0003] The existing molding process is to pour NdFeB powder into the mold cavity for pressing. However, due to the poor fluidity of the powder, the powder will agglomerate and it is difficult for the powder to be evenly distributed in the mold cavity. There may even be a situation where there is no powder at the four corners of the bottom of the mold. The invention patent with the announcement number CN106971800B, entitled "Method for Preparing Compacts of Sintered NdFeB Magnets", records a method for measuring the molding hardness of NdFeB magnet powder before making the NdFeB magnet powder into compacts. It is believed that this method is helpful for qualitatively or quantitatively understanding certain characteristics of NdFeB powder and the relationship between the powder preparation process and the hardness of the powder molding, so as to continuously improve the powder making process and ensure the consistency and stability of the powder. However, in fact, this method is only an early trial production and does not contribute to how to solve the problem of difficult uniform distribution of powder in the specific process and improve product consistency. Therefore, a method for improving the consistency of NdFeB is urgently needed. Summary of the Invention

[0004] The object of the present invention is to provide a method for improving the consistency of NdFeB, so as to solve the problem that the powder in the NdFeB forming die cannot be evenly distributed.

[0005] To achieve the above object, the present invention provides the following technical solution: a method for improving the consistency of NdFeB, comprising the following specific contents:

[0006] S1. Prepare a mixed solution of lubricant, antioxidant and gasoline;

[0007] S2. The NdFeB powder particles are mixed with the mixed solution and stirred thoroughly to form a suspension;

[0008] S3. Open multiple holes at the bottom and around the NdFeB molding mold cavity, the pore size is smaller than the NdFeB powder particle size;

[0009] S4. The suspension is poured into the mold cavity of the molding mold and allowed to stand until the lubricant, antioxidant, and gasoline mixed solution are discharged from the hole;

[0010] S5. Divide the pressing height into 4 sections for pressing. During the pressing process, the orientation magnetic field strength is increased every time a new stage is reached, and the final pressing density is 4.0-4.5g / m 3 Forming blanks;

[0011] S6. The formed blank is subjected to isostatic pressing, sintering and tempering to obtain a sintered NdFeB magnet.

[0012] Preferably, in the above step S1, the lubricant is one or more of polyethylene glycol, zinc stearate, and sodium stearate; the antioxidant is one or more of 1-hexadecanol, triphenylmethanol, calcium stearate, and polyethylene glycol octane; and the gasoline is No. 90 gasoline.

[0013] Preferably, in the suspension of step S2, the lubricant accounts for 1% to 2% of the weight of the NdFeB powder particles, the antioxidant accounts for 1.5% to 3% of the weight of the NdFeB powder particles, and the gasoline accounts for 30% to 36% of the weight of the NdFeB powder particles.

[0014] Preferably, the holes on the bottom and around the mold cavity of the NdFeB forming mold are distributed in an array and cover the entire bottom and around the mold cavity.

[0015] Preferably, the particle size of the NdFeB powder particles is 3-6 μm, and the diameter of the holes on the NdFeB forming mold is 2 μm.

[0016] Preferably, in the above step S4, after the suspension is poured into the mold cavity of the forming mold, it is left to stand for 10 minutes before starting the pressing.

[0017] Preferably, in the above step S5, when pressing down the first height, the initial pressing is performed under an orientation magnetic field greater than or equal to 1.0T to obtain a density of 2.5 to 2.8 g / m 3 When pressing the second height section, the pressing is carried out under an orientation magnetic field greater than or equal to 1.3T to obtain a density of 2.8 to 3.3 g / m 3 When pressing the third height section, the pressing is carried out under an orientation magnetic field greater than or equal to 1.7T to obtain a density of 3.3 to 3.8 g / m 3 When pressing the fourth height, the pressing is carried out under an orientation magnetic field greater than or equal to 2.0T to obtain a density of 4.0 to 4.5 g / m 3 Molding blank.

[0018] Preferably, the powder pressing is carried out under nitrogen protection, and the oxygen content is less than or equal to 50 ppm.

[0019] Preferably, in the above step S6, the isostatic pressure is greater than or equal to 210 MPa.

[0020] Preferably, in the above step S6, sintering and tempering are carried out in a vacuum sintering furnace, the sintering temperature is 1050-1090, the sintering time is 4-10 hours, and the tempering is two-stage tempering, the first tempering temperature is 820-960, the tempering time is 3-9 hours, and the second tempering temperature is 410-650, and the tempering time is 5-10 hours.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] 1. This method of improving the consistency of NdFeB magnets changes the state of the powder by making the bottom and sides of the mold porous. The powder is added to the mold in the form of a liquid with good fluidity, which can easily and completely fill the entire mold cavity. There is no agglomeration and porosity problem in the original mold-injection method. The liquid other than the powder is discharged through the holes. After a four-stage pressing process, the NdFeB magnet with uniform density and high overall performance consistency is obtained.

[0023] 2. This method of improving the consistency of NdFeB adopts a 4-stage pressing process. The powder particles undergo four magnetization treatments to fully orient the powder particles and ensure the consistency of the remanence at all positions of the magnet.

[0024] 3. The method for improving the consistency of NdFeB can be achieved by simply adding a few steps to the original process. The operation is not complicated and there is almost no additional consumption. It is suitable for application in the production of NdFeB magnets. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the top cross-sectional structure of the mold after the holes are opened in the present invention;

[0026] Figure 2 for Figure 1 Schematic diagram of the main structure of the mold shown. DETAILED DESCRIPTION

[0027] A method for improving the consistency of NdFeB, including the following specific contents:

[0028] S1. Prepare a mixed solution of lubricant, antioxidant and gasoline;

[0029] S2. The NdFeB powder particles are mixed with the mixed solution and stirred thoroughly to form a suspension;

[0030] S3. Open multiple holes at the bottom and around the cavity of the NdFeB forming mold, with the hole diameter smaller than the particle size of the NdFeB powder; Figure 1 and 2The holes opened at the bottom and around the mold cavity can be further distributed in an array and cover the entire bottom and around the mold cavity;

[0031] S4. Pour the suspension into the mold cavity of the molding die and let it stand until the lubricant, antioxidant, and gasoline mixed solution are discharged from the hole. For reference, let it stand for 10 minutes before starting to press. There is no need to worry about the solution not being completely discharged. The residual solution can be gradually discharged during the subsequent pressing process. In addition, since the main function of the mixed solution is to form a suspension with the NdFeB powder, the discharged mixed solution can also be collected and reused.

[0032] S5. Divide the pressing height into 4 sections for pressing. During the pressing process, the orientation magnetic field strength is increased every time a new stage is reached, and the final pressing density is 4.0-4.5g / m 3 The forming blank is mainly pressed in 4 sections with progressive orientation magnetic field strength. The specific parameter selection can be adjusted according to the actual situation. For reference, when pressing the first section height, the initial pressing is carried out under an orientation magnetic field greater than or equal to 1.0T, and the density is 2.5~2.8g / m 3 When pressing the second height section, the pressing is carried out under an orientation magnetic field greater than or equal to 1.3T to obtain a density of 2.8 to 3.3 g / m 3 When pressing the third height section, the pressing is carried out under an orientation magnetic field greater than or equal to 1.7T to obtain a density of 3.3 to 3.8 g / m 3 When pressing the fourth height, the pressing is carried out under an orientation magnetic field greater than or equal to 2.0T to obtain a density of 4.0 to 4.5 g / m 3 Forming blanks;

[0033] S6. The formed blank is subjected to isostatic pressing, sintering and tempering to obtain a sintered NdFeB magnet; wherein the isostatic pressing pressure can be further preferably greater than or equal to 210 MPa; sintering and tempering can further preferably use a vacuum sintering furnace. In an optional embodiment, the sintering temperature is 1050-1090, the sintering time is 4-10 hours, and the tempering adopts two-stage tempering, the first tempering temperature is 820-960, the tempering time is 3-9 hours, and the second tempering temperature is 410-650, and the tempering time is 5-10 hours.

[0034] For reference, among the raw materials of the mixed solution, the lubricant can be one or more of polyethylene glycol, zinc stearate, sodium stearate, etc.; the antioxidant can be one or more of 1-hexadecanol, triphenylmethanol, calcium stearate, polyethylene glycol octane, etc.; gasoline can use No. 90 gasoline, etc.

[0035] In a preferred embodiment, the lubricant in the suspension is preferably 1% to 2% of the weight of the NdFeB powder particles, the antioxidant is preferably 1.5% to 3% of the weight of the NdFeB powder particles, and the gasoline is preferably 30% to 36% of the weight of the NdFeB powder particles.

[0036] In addition, powder pressing is the same as conventional pressing, generally carried out under nitrogen protection, and the oxygen content should be less than or equal to 50ppm.

[0037] Example:

[0038] An R-Fe-MB alloy is prepared by a conventional process, wherein R is Nd with an R content of 30.5 wt%, B content is 0.94%, M is Ga, Co, Al, Cu, Zr, Nb with an M content of 3.0%, and the rest is Fe.

[0039] The alloy is melted, hydrogen-exploded and pulverized to obtain fine particles with a particle size of 3-6 μm.

[0040] Polyethylene glycol, polyethylene glycol octane and No. 90 gasoline were selected as raw materials for the lubricant antioxidant gasoline mixed solution; the lubricant antioxidant gasoline mixed solution was prepared according to the ratio of lubricant to powder weight 1%, antioxidant to powder weight 1.5%, and gasoline to powder weight 30%, and NdFeB powder particles were added. The mixture was stirred in a blender for 3 hours, and the resulting suspension was poured into the mold cavity of a forming mold (the mold was as shown in FIG. Figure 1 and 2 As shown, the bottom and surrounding openings of the mold cavity are distributed in an array, with a pore diameter of 2um. After standing for 10 minutes until most of the mixed solution flows out of the holes, the pressing height is evenly divided into 4 sections for pressing. When pressing the first section height, the initial pressing is carried out under an orientation magnetic field greater than or equal to 1.0T to obtain a density of 2.5 to 2.8g / m 3 When pressing the second height section, the pressing is carried out under an orientation magnetic field greater than or equal to 1.3T to obtain a density of 2.8 to 3.3 g / m 3 When pressing the third height section, the pressing is carried out under an orientation magnetic field greater than or equal to 1.7T to obtain a density of 3.3 to 3.8 g / m 3 When pressing the fourth height, the pressing is carried out under an orientation magnetic field greater than or equal to 2.0T to obtain a density of 4.0 to 4.5 g / m 3The powder is pressed under nitrogen protection, with an oxygen content of less than or equal to 50ppm. The formed blank is isostatically pressed to a pressure greater than or equal to 210MPa, then placed in a vacuum sintering furnace for sintering and tempering. The sintering temperature is 1050-1090°C, the sintering time is 4-10 hours, and the tempering is performed twice. The first tempering temperature is 820-960°C, the tempering time is 3-9 hours, and the second tempering temperature is 410-650°C, the tempering time is 5-10 hours, and finally a sintered NdFeB magnet is obtained. The magnet is evenly divided into several 10mm*10mm small squares. The performance of the small squares at different positions is tested as follows:

[0041] Table 1: Performance test results of various parts of NdFeB magnets in Example

[0042] Location Br(KGs) Hcb(KOe) Hcj(KOe) (BH)max(MGOe) <![CDATA[P(g / cm 3 )]]> upper left corner 12.64 12.18 20.12 38.86 7.585 lower left corner 12.62 12.15 20.19 38.14 7.586 upper right corner 12.61 12.13 20.15 38.65 7.582 lower right corner 12.63 12.19 20.23 38.32 7.583 middle 12.59 12.05 20.31 38.02 7.584

[0043] Comparative Example 1:

[0044] The R-Fe-MB alloy in the above embodiment was melted, hydrogen-exploded, and pulverized to obtain fine particles with a particle size of 3-6 μm. 1% of polyethylene glycol by weight, 1.5% of polyethylene glycol octane by weight, and 2% of No. 90 gasoline by weight were directly added to the powder tank and stirred for 3 hours. The powder was poured into the mold cavity of the forming mold, and the pressing height was evenly divided into 4 sections for pressing. When pressing the first section, the initial pressing was performed under an orientation magnetic field of greater than or equal to 1.0 T to obtain a density of 2.5 to 2.8 g / m 3 When pressing the second height section, the pressing is carried out under an orientation magnetic field greater than or equal to 1.3T to obtain a density of 2.8 to 3.3 g / m 3 When pressing the third height section, the pressing is carried out under an orientation magnetic field greater than or equal to 1.7T to obtain a density of 3.3 to 3.8 g / m 3 When pressing the fourth height, the pressing is carried out under an orientation magnetic field greater than or equal to 2.0T to obtain a density of 4.0 to 4.5 g / m 3 The powder is pressed under nitrogen protection, with an oxygen content of less than or equal to 50ppm. The formed blank is isostatically pressed to a pressure greater than or equal to 210MPa, then placed in a vacuum sintering furnace for sintering and tempering. The sintering temperature is 1050-1090°C, the sintering time is 4-10 hours, and the tempering is performed twice. The first tempering temperature is 820-960°C, the tempering time is 3-9 hours, and the second tempering temperature is 410-650°C, the tempering time is 5-10 hours, and finally a sintered NdFeB magnet is obtained. The magnet is evenly divided into several 10mm*10mm small squares. The performance of the small squares at different positions is tested as follows:

[0045] Table 2: Performance test results of NdFeB magnets in Comparative Example 1

[0046] Location Br(KGs) Hcb(KOe) Hcj(KOe) (BH)max(MGOe) <![CDATA[P(g / cm 3 )]]> upper left corner 12.64 11.98 19.87 37.25 7.586 lower left corner 12.37 11.85 20.32 38.74 7.579 upper right corner 12.31 12.05 20.27 38.25 7.570 lower right corner 12.53 12.01 20.08 37.98 7.581 middle 12.15 11.29 20.91 37.72 7.563

[0047] Comparative Example 2:

[0048] The R-Fe-MB alloy in the above embodiment was melted, hydrogen-exploded, and pulverized to obtain fine particles with a particle size of 3-6 μm. 1% of polyethylene glycol by weight, 1.5% of polyethylene glycol octane by weight, and 2% of No. 90 gasoline by weight were directly added to the powder tank and stirred for 3 hours. The powder was poured into the mold cavity of the forming mold and pressed under an oriented magnetic field of greater than or equal to 2.0 T to obtain a density of 4-4.5 g / m 3 The powder is pressed under nitrogen protection, with an oxygen content of less than or equal to 50ppm. The formed blank is isostatically pressed to a pressure greater than or equal to 210MPa, then placed in a vacuum sintering furnace for sintering and tempering. The sintering temperature is 1050-1090°C for 4 hours, the sintering temperature is 410-650°C for 5-10 hours, and the tempering time is 5-10 hours. Finally, sintered NdFeB magnets are obtained. The magnet is evenly divided into several 10mm*10mm small squares. The performance of the small squares at different positions is tested as follows:

[0049] Table 3: Performance test results of NdFeB magnets in comparative example 2

[0050] Location Br(KGs) Hcb(KOe) Hcj(KOe) (BH)max(MGOe) <![CDATA[P(g / cm 3 )]]> upper left corner 12.60 12.14 20.18 38.56 7.577 lower left corner 12.47 11.89 20.06 37.94 7.586 upper right corner 12.58 12.05 20.32 38.25 7.580 lower right corner 12.63 12.23 20.08 37.98 7.579 middle 12.35 11.69 20.51 38.72 7.565

[0051] By comparing the performance test results of the above embodiment and the two comparative examples, it is not difficult to see that under the conditions of the same pressing components, comparative example 1 adopts the same multi-stage pressing as the embodiment, but adopts a conventional molding method, and the distribution of the obtained magnets is obviously uneven, and the performance of each part is uneven. The pressing and molding of comparative example 2 are different from those of the embodiment, and the consistency of the obtained magnets is also poor. Obviously, the embodiment improves the uniformity of the magnet density and the consistency of the overall performance of the magnet by improving the molding and pressing process.

[0052] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by a person skilled in the art within the technical scope disclosed in the present invention should be included in the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be based on the scope of protection defined by the claims.

[0053] Any matters not described in detail in the present invention are well-known technologies to those skilled in the art.

Claims

1. A method for improving the consistency of NdFeB, characterized in that: Including the following specific contents: S1. Prepare a mixed solution of lubricant, antioxidant and gasoline; S2. Mixing the NdFeB powder particles with the mixed solution and stirring thoroughly to form a suspension, wherein the lubricant in the suspension is 1% to 2% by weight of the NdFeB powder particles, the antioxidant is 1.5% to 3% by weight of the NdFeB powder particles, and the gasoline is 30% to 36% by weight of the NdFeB powder particles; S3. Open multiple holes at the bottom and around the NdFeB molding mold cavity, the pore size is smaller than the NdFeB powder particle size; S4. The suspension is poured into the mold cavity of the molding mold and allowed to stand until the lubricant, antioxidant, and gasoline mixed solution are discharged from the hole; S5. Divide the pressing height into 4 sections for pressing. During the pressing process, the orientation magnetic field strength is increased every time a new stage is reached. When pressing the first section height, the initial pressing is performed under an orientation magnetic field greater than or equal to 1.0T to obtain a density of 2.5 to 2.8 g / m 3 When pressing the second height section, the pressing is carried out under an orientation magnetic field greater than or equal to 1.3T to obtain a density of 2.8 to 3.3 g / m 3 When pressing the third height section, the pressing is carried out under an orientation magnetic field greater than or equal to 1.7T to obtain a density of 3.3 to 3.8 g / m 3 When pressing the fourth height, the pressing is carried out under an orientation magnetic field greater than or equal to 2.0T to obtain a density of 4.0 to 4.5 g / m 3 Forming blanks; S6. The formed blank is subjected to isostatic pressing, sintering and tempering to obtain a sintered NdFeB magnet.

2. A method for improving the consistency of NdFeB according to claim 1, characterized in that: In step S1, the lubricant is one or more of polyethylene glycol, zinc stearate, and sodium stearate; the antioxidant is one or more of 1-hexadecanol, triphenylmethanol, calcium stearate, and polyethylene glycol octane; and the gasoline is No. 90 gasoline.

3. The method for improving the consistency of NdFeB according to claim 1, wherein: The holes on the bottom and around the mold cavity of the NdFeB forming mold are distributed in an array and cover the entire bottom and around the mold cavity.

4. The method for improving the consistency of NdFeB according to claim 1, wherein: The particle size of the NdFeB powder particles is 3-6 μm, and the diameter of the holes on the NdFeB forming mold is 2 μm.

5. The method for improving the consistency of NdFeB according to claim 1, wherein: In step S4, after the suspension is poured into the mold cavity of the forming mold, it is left to stand for 10 minutes before starting the pressing.

6. The method for improving the consistency of NdFeB according to claim 1, wherein: The powder pressing is carried out under nitrogen protection, and the oxygen content is less than or equal to 50ppm.

7. The method for improving the consistency of NdFeB according to claim 1, characterized in that: In step S6, the isostatic pressure is greater than or equal to 210 MPa.

8. The method for improving the consistency of NdFeB according to claim 1, wherein: In step S6, sintering and tempering are performed in a vacuum sintering furnace, the sintering temperature is 1050-1090, the sintering time is 4-10 hours, and the tempering is performed in two stages, the first tempering temperature is 820-960, the tempering time is 3-9 hours, and the second tempering temperature is 410-650, and the tempering time is 5-10 hours.

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