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CN-122025398-A - Preparation method of high-coercivity anisotropic bonded NdFeB magnetic powder

CN122025398ACN 122025398 ACN122025398 ACN 122025398ACN-122025398-A

Abstract

The invention discloses a preparation method of high-coercivity anisotropic bonded neodymium-iron-boron magnetic powder, which relates to the field of preparation of neodymium-iron-boron magnetic powder, and comprises the following steps of firstly soaking in pure water, secondly carrying out air floatation grading, namely sending the magnetic powder slurry into an air flow grader, and separating out magnetic powder in a target granularity range by adjusting air inlet pressure to 0.15-0.45MPa and grading wheel rotating speed to 800-3200rpm and utilizing the combination mass difference of wet magnetic powder and water, wherein the dispersity index of the target granularity range is less than or equal to 6.5, thirdly, dehydrating and drying, and fourthly, carrying out magnetic field orientation molding. According to the invention, through the innovative combination of pure water soaking and air floatation, the apparent density is reduced from 7.4g/cm 3 to 1.5-2.0g/cm 3 by utilizing the combination of water and magnetic powder, and meanwhile, the mass difference of particles with different particle sizes is amplified by increasing the wet mass, so that the technology breaks through the technical bottleneck of light mass, small inertia and difficult separation in the traditional dry method wind process.

Inventors

  • GUO BEI
  • ZHAO YUYUE
  • WAN YUNZHI
  • CHEN YINGPENG
  • TAO LIMING

Assignees

  • 江西江钨稀有金属新材料股份有限公司

Dates

Publication Date
20260512
Application Date
20260317

Claims (10)

  1. 1. The preparation method of the high-coercivity anisotropic bonded NdFeB magnetic powder is characterized by comprising the following steps of: Firstly, soaking by pure water, namely mixing the quick-quenched neodymium iron boron alloy powder with purified water according to the mass ratio of 1:1.5-2.0, and stirring to fully wet the magnetic powder to form magnetic powder slurry with the apparent density of 1.5-2.0g/cm 3 ; Step two, air floatation classification, namely feeding the magnetic powder slurry into an air classifier, and separating magnetic powder in a target granularity range by adjusting the air inlet pressure to be 0.15-0.45MPa and the rotation speed of a classifying wheel to be 800-3200rpm and utilizing the combination mass difference of wet magnetic powder and water, wherein the dispersity index of the target granularity range is less than or equal to 6.5; Step three, dehydrating and drying, namely dehydrating the separated magnetic powder with the target granularity to the water content of less than 0.1% to obtain dry magnetic powder; and fourthly, performing magnetic field orientation molding, namely mixing the dry magnetic powder with a binder, performing orientation molding under the condition that the magnetic field intensity is more than or equal to 2T, and curing to obtain the anisotropic bonded magnet.
  2. 2. The method for preparing high-coercivity anisotropic bonded NdFeB magnetic powder according to claim 1, wherein the conductivity of the purified water in the first step is less than or equal to 1 mu S/cm, the pH value is 6.5-7.5, the stirring speed is 150-300rpm, the stirring time is 5-30min, and the viscosity of the magnetic powder slurry is controlled to be 50-150 mPa.s.
  3. 3. The method for preparing high-coercivity anisotropic bonded NdFeB magnetic powder according to claim 1, wherein in the first step, 0.3-1.0 mass part of dispersing agent or 0.3-0.8 mass part of surface tension regulator is added into purified water, wherein the dispersing agent is polyethylene glycol or sodium silicate, and the surface tension regulator is isopropanol or ethanol.
  4. 4. The method for preparing the high-coercivity anisotropic bonded NdFeB magnetic powder according to claim 1, wherein the first step is ultrasonic-assisted soaking, the ultrasonic frequency is 20-60kHz, the power is 300-800W, and the ultrasonic time is 10-30min.
  5. 5. The preparation method of the high-coercivity anisotropic bonded NdFeB magnetic powder according to claim 1, wherein the target particle size range in the second step is 40-150 mu m, the air volume of the air classifier is controlled to be 8-25m 3 /min, and variable frequency speed regulation is adopted to realize stepless regulation of air speed.
  6. 6. The method for preparing the high-coercivity anisotropic bonded NdFeB magnetic powder according to claim 1, wherein the second step is two-stage serial air floatation: First-stage roughing, namely, the air inlet pressure is 0.20-0.30MPa, the rotating speed of a classifying wheel is 1000-1500rpm, and coarse particles with the diameter of more than 200 mu m are separated to be used as a furnace return material; And the second stage of fine selection, namely, separating out magnetic powder with the target granularity of 60-120 mu m, wherein the air inlet pressure is 0.35-0.50MPa, the rotating speed of a classification wheel is 2000-3000 rpm.
  7. 7. The method for preparing the high-coercivity anisotropic bonded NdFeB magnetic powder according to claim 1, wherein in the second step, a variable frequency speed regulation fan is adopted by the air classifier, the air quantity stepless regulation range is 8-25m 3 /min, and oversized particles with the particle diameter of more than 250 microns, target powder with the particle diameter of 40-80 microns and fine powder with the particle diameter of less than 40 microns are sequentially separated through a gradient speed increasing mode.
  8. 8. The method for preparing high coercivity anisotropic bonded NdFeB magnetic powder according to claim 1, wherein the step three is one of the following steps: Vacuum drying, wherein the temperature is 80-120 ℃, the vacuum degree is less than or equal to-0.08 MPa, and the time is 2-6h; or spray drying, wherein the inlet temperature is 160-200 ℃ and the outlet temperature is 80-100 ℃ to obtain hollow spherical magnetic powder; Or vacuum freeze drying, pre-freezing temperature is-30 to-50 ℃, vacuum sublimation time is 20-30h, and oxygen content is less than 300ppm.
  9. 9. The method for preparing high coercivity anisotropic bonded NdFeB magnetic powder according to claim 1, wherein the rapid quenching NdFeB alloy powder is double-alloy magnetic powder, and the method comprises the following steps: a main phase alloy Nd 12 Fe 80 B 8 for providing high magnetic energy product; Nd 60 Fe 40 of Nd-rich alloy, and optimizing a grain boundary phase; the mass ratio of the two is 9:1-8:2, and the average grain diameter after mixing and rapid quenching is 250-350 mu m.
  10. 10. The method for preparing high coercivity anisotropic bonded NdFeB magnetic powder according to claim 1, wherein the binder in the fourth step is epoxy resin, polyimide or silicone resin, and the dosage is 2-5% of the mass of the magnetic powder; The magnetic field intensity of the orientation molding is 2.5-3.5T, the molding pressure is 600-1000MPa, the curing temperature is 140-200 ℃, and the curing time is 2-6h.

Description

Preparation method of high-coercivity anisotropic bonded NdFeB magnetic powder Technical Field The invention relates to the technical field of preparation of neodymium iron boron magnetic powder, in particular to a preparation method of high-coercivity anisotropic bonded neodymium iron boron magnetic powder. Background The bonded NdFeB magnet is a permanent magnet material prepared by mixing quick quenching NdFeB magnetic powder with a high polymer binder, and performing magnetic field orientation and compression molding/injection molding. Compared with sintered NdFeB, the bonded magnet has the advantages of high shape freedom degree, good dimensional accuracy, no need of subsequent processing and the like, and is widely applied to the fields of automobile motors, hard disk drives, household appliances, precise instruments and the like. With the rapid development of new energy automobiles, 5G communication and Internet of things equipment, the performance requirements on bonded magnets are continuously improved, and particularly, an anisotropic bonded magnet with high coercivity (high temperature stability) and high magnetic energy product (high magnetic output) is required. The size distribution and morphology of the magnetic powder directly affect the magnetic properties and formability of the bonded magnet. At present, dry mechanical screening or dry air classification is mainly adopted in industry to carry out particle size classification on the quick-quenched magnetic powder, but the following prominent problems exist: 1. The dry air separation precision is low, the true density of the quick quenching neodymium iron boron magnetic powder is about 7.4g/cm 3, but the particles are fine (the average particle diameter is 50-300 mu m), the shape is irregular, agglomeration is easy to occur among the particles during the dry air separation, the inertia is small due to light weight, and the quick quenching neodymium iron boron magnetic powder is difficult to accurately separate according to the particle size in air flow. The wind speed regulation precision of the traditional winnowing machine is limited (generally only 3-5 grades), stepless and accurate control of particles with different masses cannot be realized, the phenomenon of 'the remained and blown away' often appears, the particle size distribution is wide (dispersity index D90/D10> 8), the surface of a magnet is rough due to the inclusion of large particles, and the orientation degree is reduced due to excessive fine powder; 2. the dry sieving efficiency is low, for fine powder with the particle size of less than 100 mu m, the sieve is easy to be blocked by the dry sieving, and the sieving efficiency is less than 60% due to electrostatic adsorption, so that the continuous production requirement can not be met; 3. Oxidation and pollution, namely fully contacting magnetic powder with air in the dry classification process, and easily oxidizing to reduce coercive force; 4. the traditional process can only obtain wider particle size distribution, if the magnetic powder with narrow distribution is prepared, multiple sieving or winnowing is needed, the process is complicated, the yield is low, and the oxidation is aggravated by multiple treatments. Therefore, the preparation method of the high-coercivity anisotropic bonded NdFeB magnetic powder solves the problems. Disclosure of Invention Aiming at the problems in the prior art, the invention provides a preparation method of high-coercivity anisotropic bonded NdFeB magnetic powder, which breaks through the barrier of the traditional technology and realizes high-precision particle size classification. In order to achieve the above purpose, the preparation method of the high-coercivity anisotropic bonded NdFeB magnetic powder adopted by the invention comprises the following steps: Firstly, soaking by pure water, namely mixing the quick-quenched neodymium iron boron alloy powder with purified water according to the mass ratio of 1:1.5-2.0, and stirring to fully wet the magnetic powder to form magnetic powder slurry with the apparent density of 1.5-2.0g/cm 3; Step two, air floatation classification, namely feeding the magnetic powder slurry into an air classifier, and separating magnetic powder in a target granularity range by adjusting the air inlet pressure to be 0.15-0.45MPa and the rotation speed of a classifying wheel to be 800-3200rpm and utilizing the combination mass difference of wet magnetic powder and water, wherein the dispersity index of the target granularity range is less than or equal to 6.5; Step three, dehydrating and drying, namely dehydrating the separated magnetic powder with the target granularity to the water content of less than 0.1% to obtain dry magnetic powder; and fourthly, performing magnetic field orientation molding, namely mixing the dry magnetic powder with a binder, performing orientation molding under the condition that the magnetic field intensity is more than or equal to 2T