A processing technology for uniformly refining NdFeB grains

Abstract

The present invention relates to a processing technology for uniformly refining NdFeB grains in the production of permanent magnet NdFeB, and the technology can achieve the purpose of uniformly refining spherical grains. The technology is to crush alloy flakes into fine powder, add high boiling point organic matter and stir evenly, and obtain uniform spherical grains by heating, rapid solidification, and sieving and dispersing. The advantages of this new technology are: finer grains can be prepared, the grain size concentration is high, and the grain appearance is approximately spherical.

Description

Technical Field

[0001] The invention relates to a processing technology for uniformly refining NdFeB crystal grains, and belongs to the field of manufacturing technology of new material NdFeB magnets. Background Art

[0002] Problems with existing technologies: Currently, NdFeB manufacturers generally use refined alloy flake grains, and prepare fine powders of different grain sizes by adjusting the speed of the copper roller for cooling the casting and the speed of the airflow mill classifier. However, the grain size concentration is low and the appearance is irregular, which makes the surface defects of the prepared magnets more, increases the probability of reverse magnetization nucleation and reduces the microscopic scattered magnetic field, resulting in serious limitations in improving the coercive force. Therefore, the current production process cannot produce finer, more uniform and less defective grains. Summary of the invention

[0003] This technical solution solves the problem that the current grain refinement is limited by size, appearance and uniformity. It produces finer grains with high size concentration and spherical appearance. It can produce products with ultra-high coercivity. To achieve the above purpose, the present invention provides the following technical solution.

[0004] A processing technology for uniformly refining NdFeB grains consists of the following steps.

[0005] The first step: crush the NdFeB alloy sheet into powder by hydrogen crushing for the first time.

[0006] Step 2: subjecting the NdFeB alloy powder obtained after the first hydrogen crushing to a second hydrogen crushing and a first spheroidization treatment.

[0007] Step 3: Put the high boiling point organic mixture and the powder after the first spheroidization treatment into an atmosphere protection container, continuously stir and heat, and carry out the second spheroidization treatment. The insulation temperature is: 400~600℃, and the insulation time is 4~6 hours.

[0008] Step 4: After the insulation is completed, quickly cool to room temperature, put the powder into an atmosphere protection screening machine for screening and dispersion, the screen mesh size is 38 microns, and the refined NdFeB grains are obtained by screening and dispersion.

[0009] The first step is specifically: the first hydrogen crushing, heating the iron-boron alloy sheet to 200-400°C for incubation for 2 hours when the vacuum degree is ≤0.5Pa, while stirring the neodymium iron boron alloy sheet, hydrogen is introduced to quickly absorb hydrogen, and when the pressure drop rate is less than 10Pa per minute, the first hydrogen absorption is completed, and the neodymium iron boron alloy sheet after hydrogen absorption is heated to 900-1150°C for vacuum dehydrogenation, and when the vacuum degree is ≤0.5Pa, the outside of the hydrogen crushing tank is cooled to less than 50°C by spraying water, and the first dehydrogenation is completed, and the first hydrogen crushing is completed.

[0010] The second step is specifically: stirring the NdFeB alloy after the first dehydrogenation again, heating it to 300℃ for secondary incubation when the vacuum degree is ≤0.5Pa, introducing hydrogen gas to absorb hydrogen again, heating it to 900~1150℃ for dehydrogenation after the hydrogen absorption is saturated, and pouring water on the outside of the hydrogen crushing tank to cool it to less than 50℃ when the vacuum degree is ≤0.5Pa, completing the second hydrogen crushing. Because the surface energy of the exposed NdFeB grains in hydrogen crushing is large, the surface tension increases the pressure on the inside of the powder. At a lower temperature, the NdFeB grains are easy to melt, and the edges and corners of the grains are gradually melted, and the first spheroidization of the NdFeB powder is completed at the same time.

[0011] The third step is specifically: putting the high boiling point organic mixture and the crushed powder into an atmosphere protection container, continuously stirring and heating, the insulation temperature is: 400~600℃, the insulation time is 4~6 hours, and performing a second spheroidization treatment, the high boiling point organic mixture is a mixture of glycerol and ethanol, the weight ratio is 1:1~1:3, and the weight ratio of the organic mixture to the powder is 1:1000~2.5:1000.

[0012] The fourth step is specifically: after the heat preservation is completed, the powder is quickly cooled to room temperature, and the powder is placed in an atmosphere protection screening machine for screening and dispersion, the screen mesh aperture is 38 microns, and the powder after screening and dispersion is refined NdFeB grains.

[0013] In the crushing process of the present invention, the size of the alloy pieces ranges from 0.1 to 100 mm. After the alloy pieces are incubated in the early stage, hydrogen can quickly break through the surface barrier of the alloy pieces and enter the interior of the alloy pieces, accelerating the reaction between the rare earth neodymium in the grain boundary phase and hydrogen to generate neodymium hydride (Nd+H 2 =NdH 2 ), NdH 2 The volume increases, causing the grain boundary phase to peel off. When the hydrogen absorption reaches saturation, no more hydrogenated rare earth (NdH 2 ), and then rise to a high temperature of about 900~1150℃, the hydrogen is quickly removed, and a reversible reaction occurs again, generating the original grain boundary rare earth phase, making the grain boundary rare earth phase into ultrafine powder. This is the first crushing, preparing for the second hydrogen absorption. After the grain boundary rare earth phase is peeled off, the main phase of NdFeB is directly exposed. After incubation at a temperature of 300℃, Nd 2 Fe 14 B+2H 2 =2NdH 2 +12Fe+Fe 2 B reacts violently, NdH in the main phase 2The volume increases rapidly, directly destroying the main phase grains of NdFeB, breaking them into fine grains. When heated to 900~1150℃, the surface of the grains melts, causing the surface edges to melt and the appearance to become approximately spherical. However, a reversible dehydrogenation reaction occurs at the same time, and the hydrogen is quickly discharged to regenerate the main phase of NdFeB. After the second hydrogenation and the first spheroidization, the grains are composed of ultrafine powder of the grain boundary phase and broken grains of the main phase. The particle size of the ultrafine powder of the grain boundary phase is close to about 0.1 micron, and the broken grains of the main phase are about 0.5 micron, so the particle size of the generated grains is ≤1μm.

[0014] The second spheroidization of the present invention refers to the powder crystal grains that have been crushed for the second time and spheroidized for the first time, after adding a high boiling point organic mixture and mixing evenly, the surface of the powder crystal grains is fused with the additive, so that the surface of the rare earth phase ultrafine powder at the grain boundary is clustered, the presence of ultrafine powder is reduced, and the ultrafine powder is condensed into spherical crystal grains with uniform particle size, so that the concentration of the crystal grains is high, so the particle size of the generated crystal grains is ≤1μm, and no ultrafine powder exists. The formed spherical powder crystal grains are quickly shaped under rapid cooling conditions, and the powder crystal grains that have been spheroidized for the second time are then dispersed by screening, so that the spherical crystal grains that are clustered together are dispersed.

[0015] Compared with the prior art, the process for uniformly refining NdFeB grains adopted in the present invention can achieve the purpose of uniformly refining spherical grains. The process is to crush the alloy flakes into fine powder, add high-boiling point organic matter and stir evenly, and obtain uniform spherical grains by heating, rapid solidification, and sieving and dispersing. The advantages of this new process are: finer grains can be prepared, the grain size concentration is high, and the grain appearance is approximately spherical. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Example 1: A 500-fold scanning electron microscope photograph of NdFeB powder grains after being treated by the process of the present invention.

[0017] Figure 2 Example 4: 200 times scanning electron microscope photograph of NdFeB powder grains after being treated by the inventive process.

[0018] Figure 3 200x scanning electron microscope photo of NdFeB powder grains prepared by traditional process.

[0019] Figure 4 500x scanning electron microscope photograph of NdFeB powder grains prepared by traditional process.

[0020] Figure 5 Laser particle size distribution diagram of the powder particles of Example 1.

[0021] Figure 6 Laser particle size distribution diagram of the powder particles of Example 2.

[0022] Figure 7 Laser particle size distribution diagram of the powder particles of Example 3.

[0023] Figure 8 Laser particle size distribution diagram of the powder particles of Example 4.

[0024] Fig. 9 Laser particle size distribution of powder grains prepared by traditional process. DETAILED DESCRIPTION

[0025] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it is understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. If no specific technology or conditions are specified in the embodiments, the technology or conditions described in the literature in this area or the product specifications are used.

[0026] Example 1

[0027] Step 1: The first hydrogen crushing, add the NdFeB alloy sheet into the hydrogen crushing furnace, when the vacuum degree is 0.5Pa, heat it to 200℃ and incubate it for two hours, start the stirring button of the hydrogen crushing furnace, and introduce hydrogen to quickly absorb hydrogen. When the pressure drop rate is 7Pa per minute, the first hydrogen absorption is completed, start the vacuum pump, turn off the stirring button, heat the NdFeB alloy sheet after hydrogen absorption to 900℃ and continue to vacuum dehydrogenation. When the vacuum degree is 0.5Pa, sprinkle water on the outside of the hydrogen crushing tank to cool it to 48℃, turn off the vacuum pump, and the first dehydrogenation is completed.

[0028] Step 2: Start the equipment, heat the NdFeB grains after the first dehydrogenation to 300℃ and incubate for 1 hour, turn on the stirring button, and introduce hydrogen to absorb hydrogen again. When the pressure drop rate is 8Pa per minute, the second hydrogen absorption is completed, start the vacuum pump, turn off the stirring button, heat the NdFeB alloy powder after the second hydrogen absorption to 900℃, and complete the second dehydrogenation at a vacuum degree of 0.5Pa. Because the surface energy of the exposed NdFeB grains in hydrogen crushing is large, the surface tension increases the pressure inside the powder. At a lower temperature, the NdFeB grains are easy to melt, and the edges and corners of the grains are gradually melted, completing the first spheroidization of the NdFeB powder, and cooling it to 48℃ by pouring water on the outside of the hydrogen crushing tank to prepare grains with a particle size of ≤1μm.

[0029] Step 3: Put the high boiling point organic mixture and the crushed powder into an atmosphere protection container, continuously stir and heat, the insulation temperature is 400°C, the insulation time is 4 hours, and perform a second spheroidization treatment. The high boiling point organic mixture is a mixture of glycerol and ethanol, the weight ratio is 1:1, and the weight ratio of the organic mixture to the powder is 1:1000.

[0030] Step 4: After the insulation is completed, quickly cool to 30°C, put the powder into an atmosphere protection screening machine for screening and dispersion, the screen aperture is 38 microns, and the powder after screening and dispersion is refined NdFeB grains.

[0031] Example 2

[0032] Step 1: The first hydrogen crushing, add the NdFeB alloy sheet into the hydrogen crushing furnace, when the vacuum degree is 0.5Pa, heat it to 250℃ and incubate it for two hours, start the stirring button of the hydrogen crushing furnace, and introduce hydrogen to absorb hydrogen quickly. When the pressure drop rate is 6Pa per minute, the first hydrogen absorption is completed, start the vacuum pump, turn off the stirring button, heat the NdFeB alloy sheet after hydrogen absorption to 1000℃ and continue to vacuum dehydrogenation. When the vacuum degree is 0.4Pa, sprinkle water on the outside of the hydrogen crushing tank and cool it to 45℃, turn off the vacuum pump, and the first dehydrogenation is completed.

[0033] Step 2: Start the equipment, heat the NdFeB grains after the first dehydrogenation to 300℃ for 1 hour, turn on the stirring button, and introduce hydrogen to absorb hydrogen again. When the pressure drop rate is less than 10Pa per minute, the second hydrogen absorption is completed, start the vacuum pump, turn off the stirring button, and heat the NdFeB alloy powder after the second hydrogen absorption to 1000℃. Because the surface energy of the exposed NdFeB grains in hydrogen crushing is large, the surface tension increases the pressure inside the powder. At a lower temperature, the NdFeB grains are easy to melt, and the edges and corners of the grains gradually melt, completing the first spheroidization of the NdFeB powder. After dehydrogenation, at a vacuum degree of 0.5Pa, water is poured on the outside of the hydrogen crushing tank to cool to 45℃ to prepare grains with a particle size of ≤1μm.

[0034] Step 3: Place the high boiling point organic mixture and the crushed powder into an atmosphere protection container, continuously stir and heat, the insulation temperature is 450°C, the insulation time is 4.5 hours, and perform a second spheroidization treatment. The high boiling point organic mixture is a mixture of glycerol and ethanol, the weight ratio is 1:2, and the weight ratio of the organic mixture to the powder is 1.5:1000.

[0035] Step 4: After the insulation is completed, quickly cool to room temperature, put the powder into an atmosphere protection screening machine for screening and dispersion, the screen mesh aperture is 38 microns, and the powder after screening and dispersion is refined NdFeB grains.

[0036] Example 3

[0037] Step 1: The first hydrogen crushing, add the NdFeB alloy sheet into the hydrogen crushing furnace, when the vacuum degree is 0.5Pa, heat it to 300℃ and incubate it for two hours, start the stirring button of the hydrogen crushing furnace, and introduce hydrogen to absorb hydrogen quickly. When the pressure drop rate is 5Pa per minute, the first hydrogen absorption is completed, start the vacuum pump, turn off the stirring button, heat the NdFeB alloy sheet after hydrogen absorption to 1100℃ and continue to vacuum dehydrogenation. When the vacuum degree is 0.45Pa, spray water on the outside of the hydrogen crushing tank and cool it to 48℃, turn off the vacuum pump, and the first dehydrogenation is completed.

[0038] Step 2: Start the equipment, heat the NdFeB grains after the first dehydrogenation to 300℃ for 1 hour, turn on the stirring button, and introduce hydrogen to absorb hydrogen again. When the pressure drop rate is 5Pa per minute, the second hydrogen absorption is completed, start the vacuum pump, turn off the stirring button, heat the NdFeB alloy powder after the second hydrogen absorption to 1100℃, and complete the second dehydrogenation at a vacuum degree of 0.5Pa. Because the surface energy of the exposed NdFeB grains of hydrogen crushing is large, the surface tension increases the pressure inside the powder. At a lower temperature, the NdFeB grains are easy to melt, and the edges and corners of the grains gradually melt, completing the first spheroidization of the NdFeB powder. Cool the outside of the hydrogen crushing tank to 48℃ by pouring water to prepare grains with a particle size of ≤1μm.

[0039] The third step is specifically: putting the high boiling point organic mixture and the crushed powder into an atmosphere protection container, continuously stirring and heating, the insulation temperature is: 500°C, the insulation time is 5 hours, and the second spheroidization treatment is carried out. The high boiling point organic mixture is a mixture of glycerol and ethanol, the weight ratio is 1:2.5, and the weight ratio of the organic mixture to the powder is 2:1000.

[0040] Step 4: After the insulation is completed, quickly cool to room temperature, put the powder into an atmosphere protection screening machine for screening and dispersion, the screen mesh aperture is 38 microns, and the powder after screening and dispersion is refined NdFeB grains.

[0041] Example 4

[0042] Step 1: The first hydrogen crushing, add the NdFeB alloy sheet into the hydrogen crushing furnace, when the vacuum degree is 0.5Pa, heat it to 400℃ and incubate it for two hours, start the stirring button of the hydrogen crushing furnace, and introduce hydrogen to absorb hydrogen quickly. When the pressure drop rate is 8Pa per minute, the first hydrogen absorption is completed, start the vacuum pump, turn off the stirring button, heat the NdFeB alloy sheet after hydrogen absorption to 1100℃ and continue to vacuum dehydrogenation. When the vacuum degree is 0.1Pa, spray water on the outside of the hydrogen crushing tank to cool it to 49℃, turn off the vacuum pump, and the first dehydrogenation is completed.

[0043] Step 2: Start the equipment, heat the NdFeB grains after the first dehydrogenation to 300℃ for 1 hour, turn on the stirring button, and introduce hydrogen to absorb hydrogen again. When the pressure drop rate is 9Pa per minute, the second hydrogen absorption is completed, start the vacuum pump, turn off the stirring button, heat the NdFeB alloy powder after the second hydrogen absorption to 1150℃, and complete the second dehydrogenation at a vacuum degree of 0.5Pa. Because the surface energy of the exposed NdFeB grains in hydrogen crushing is large, the surface tension increases the pressure inside the powder. At a lower temperature, the NdFeB grains are easy to melt, and the edges and corners of the grains are gradually melted, completing the first spheroidization of the NdFeB powder, and cooling it to 49℃ by pouring water on the outside of the hydrogen crushing tank to prepare grains with a particle size of ≤1μm.

[0044] Step 3: Place the high boiling point organic mixture and the crushed powder into an atmosphere protection container, continuously stir and heat, the insulation temperature is 500°C, the insulation time is 5 hours, and perform a second spheroidization treatment. The high boiling point organic mixture is a mixture of glycerol and ethanol, the weight ratio is 1:3, and the weight ratio of the organic mixture to the powder is 2.5:1000.

[0045] Step 4: After the insulation is completed, quickly cool to room temperature, put the powder into an atmosphere protection screening machine for screening and dispersion, the screen mesh aperture is 38 microns, and the powder after screening and dispersion is refined NdFeB grains.

[0046] Comparative Example 1 is a conventional process, which has only one hydrogen absorption and desorption, and no subsequent second hydrogen absorption and desorption crushing and first spheroidization, and second spheroidization process. The alloy grains produced by the conventional process are observed by scanning electron microscopy, and the powder grains are irregular angular alloy particles, such as Figure 3 and 4 The powder particles of Examples 1 and 4 of the present invention are spherical or quasi-spherical in shape. Figure 1 and 2 shown.

[0047] The powder crystals obtained in Examples 1-4 were subjected to laser particle size analysis, and the powder particle size distribution was as follows: Figure 5 , 6 , 7, and 8 show that the particle size of the powder produced by the traditional process is Fig. 9 The distribution of NdFeB grains processed by conventional processes is between 0 and 10 microns, while the distribution of NdFeB grains processed by the process of the present invention is narrowed to between 0.2 and 1 micron, thus solving the problem of low grain size concentration in conventional processes.

[0048] Table 1.

[0049]

[0050] The four embodiments of the present invention are compared in detail with the prior art comparative example 1, as shown in Table 1.

[0051] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited to the specific details of the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0052] It should also be noted that the various technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further explain various possible combinations.

Claims

1. A process for uniformly refining NdFeB grains, characterized by: The following steps are involved: The first step: crush the NdFeB alloy sheet into powder by hydrogen crushing for the first time; Step 2: The NdFeB alloy powder obtained after the first hydrogen crushing is subjected to a second hydrogen crushing and a first spheroidization treatment; Step 3: Put the high boiling point organic mixture and the powder after the first spheroidization treatment into an atmosphere protection container, continuously stir and heat, and perform the second spheroidization treatment at a holding temperature of 400-600°C for 4-6 hours; Step 4: After the heat preservation is completed, the powder is quickly cooled to room temperature, and the powder is placed in an atmosphere protection screening machine for screening and dispersion. The sieve aperture is 38 microns, and the fine NdFeB grains are obtained by screening and dispersion; The first hydrogen crushing process of NdFeB alloy sheet into powder is as follows: when the vacuum degree is ≤0.5Pa, the iron boron alloy sheet is heated to 200~400℃ for incubation for 2 hours, while the NdFeB alloy sheet is stirred, hydrogen is introduced to quickly absorb hydrogen, and when the pressure drop rate is less than 10Pa per minute, the first hydrogen absorption is completed, and the NdFeB alloy sheet after hydrogen absorption is heated to 900~1150℃ for vacuum dehydrogenation, and when the vacuum degree is ≤0.5Pa, the outside of the hydrogen crushing tank is cooled to less than 50℃ by water spraying, and the first hydrogen crushing is completed. The NdFeB alloy powder obtained after the first hydrogen crushing is subjected to the second hydrogen crushing and the first spheroidization treatment process as follows: the NdFeB alloy after the first dehydrogenation is stirred again, and when the vacuum degree is ≤0.5Pa, it is heated to 300℃ for secondary incubation, and hydrogen is introduced again to absorb hydrogen. After the hydrogen absorption is saturated, it is heated to 900~1150℃ for dehydrogenation. When the vacuum degree is ≤0.5Pa, water is poured on the outside of the hydrogen crushing tank to cool it to less than 50℃, and the second hydrogen crushing is completed, and the first spheroidization of the NdFeB powder is completed at the same time.

2. The process for uniformly refining NdFeB grains according to claim 1, characterized in that: The high boiling point organic mixture is a mixture of glycerol and ethanol in a weight ratio of 1:1 to 1:

3.

3. The process for uniformly refining NdFeB grains according to claim 1 is characterized by: The weight ratio of the high boiling point organic mixture to the powder after the first spheroidization treatment is 1:1000~2.5:1000.

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