CN114613585A

CN114613585A - Device and method for crushing/surface modifying sintered neodymium-iron-boron powder

Info

Publication number: CN114613585A
Application number: CN202011578132.4A
Authority: CN
Inventors: 永田浩; 刘仁辉; 武仁杰
Original assignee: Guorui Kechuang Rare Earth Functional Materials Ganzhou Co ltd; Jiangxi University of Science and Technology
Current assignee: Guorui Kechuang Rare Earth Functional Materials Ganzhou Co ltd; Jiangxi University of Science and Technology
Priority date: 2020-12-28
Filing date: 2020-12-28
Publication date: 2022-06-10

Abstract

The invention discloses a device and a method for crushing/surface modifying sintered neodymium iron boron powder. The invention changes the airflow direction of the airflow crushing device of the neodymium-iron-boron powder into the non-opposite direction, and finds that the invention can reduce sharp powder, make the powder approach to a spherical shape, simultaneously reduce the generation of fine powder, has good powder orientation degree, improves the magnetic permeability, further improves the yield, and improves the magnet performances such as coercive force, squareness, magnetization intensity and the like.

Description

Device and method for crushing/surface modifying sintered neodymium-iron-boron powder

Technical Field

The invention relates to the technical field of metal powder processing, in particular to processing of neodymium iron boron powder.

Background

Nd-Fe-B sintered permanent magnet materials are mostly prepared from Nd-Fe-B powder through a powder metallurgy process, pressing and sintering. Nd-Fe-B powder is mostly prepared by adopting a rapid hardening sheet (also called a strip casting method, a strip throwing method and the like, and SC) and hydrogen pulverization (HD) process at present. The neodymium iron boron SC alloy cast sheet becomes very brittle and fragile after hydrogen crushing treatment, and can be further crushed and refined.

The conventional jet milling method (JM) for pulverizing Nd-Fe-B powder is to use high-speed airflow to drive powder to collide, so as to crush coarse powder and obtain micro powder. Fig. 1 to 3 show an opposite type (also called opposite type/opposite type) pulverizing apparatus belonging to a common jet mill in the prior art, which includes a powder feeder 1 ', a powder pulverizing chamber 2 ', a rotary classifier 3 ', a jet classifier 4 ' and a product powder recovery container 5 '; the powder feeder 1 'feeds powder to be pulverized into the powder pulverizing chamber 2'; the powder crushing chamber 2 ' is provided with a plurality of nozzles 6 ', and the high-speed airflow sprayed by the nozzles 6 ' drives the powder to move and collide for crushing; the rotary classifier 3 'is arranged in the powder crushing chamber 2' and positioned above the nozzle 6 ', and the crushed powder with the grain diameter meeting the requirement is sent into the air flow classifier 4'; the air classifier 4 'separates the qualified powder from the unqualified powder through air flow separation, and sends the qualified powder into the product powder recovery container 5' or collects the qualified powder and sends the collected powder back to the crushing device for crushing. As shown in fig. 5, the collision type (also called impact type) pulverizing apparatus also includes a powder feeder 1 ", a powder pulverizing chamber 2", a rotary classifier 3 ", an air classifier 4" and a product powder recovery container 5 ", wherein a nozzle 6 is provided at the bottom of the powder pulverizing chamber 2", and a collision plate 7 is provided in the powder pulverizing chamber 2 ", and the powder collides with the collision plate 7" by ejecting air flow through the bottom nozzle 6 ", and the powder collides with each other, thereby increasing the pulverizing efficiency. For preventing oxidation, nitrogen, argon, helium, xenon (N) is generally used as the gas used in the powder pulverization chamber₂Ar, He, Xe), and the like. The grinding gas generally contains a small amount of oxygen, water, oil, and the like. The classified gas is recovered and compressed for reuse.

Most of the conventional JM methods are of an opposite type, that is, the nozzles of the powder pulverizing chamber are symmetrically arranged and opposite in direction, and the airflows ejected from the nozzles have a uniform intersection point, as shown in fig. 4 (a) to (e), each airflow has only one intersection point, and the airflows drive the powder to collide with each other in the forward direction at the intersection point. The pulverizing force of the opposed JM is very high, and the obtained Nd-Fe-B system fine powder is often sharp in shape with sharp edges and the number of fine sharp powder increases, resulting in deterioration of squareness and magnetic properties of the magnet.

Disclosure of Invention

The invention aims to overcome the defects of the prior art and provides a device and a method for crushing/surface modifying sintered neodymium-iron-boron powder. When the neodymium iron boron coarse powder which is prepared by the SC method and is subjected to hydrogen grinding is refined and ground, the counter-current (collision) type jet mill which is the mainstream in the prior art is improved, and a new grinding mode and a new grinding device are explored and developed.

One of the technical schemes adopted by the invention for solving the technical problems is as follows:

a crushing/surface modification device for sintering neodymium iron boron powder comprises a powder crushing/surface modification chamber, wherein the powder crushing/surface modification chamber is provided with at least two nozzles; the at least two nozzles are arranged around a central point; a connecting line formed by the outlet of any nozzle and the central point forms an included angle with the flowing direction of the air flow sprayed by the nozzle, so that the air flows sprayed by the at least two nozzles do not meet at the central point; the gas flow is inert gas with the oxygen content of 5 ppm-500 ppm.

The nozzle structure of the powder crushing/surface modification chamber is of a non-opposite type (also called a non-collision type/non-opposite type), at least two nozzles are arranged around a central point, a connecting line formed by an outlet of any nozzle and the central point forms an included angle with the flowing direction of airflow sprayed by the nozzle, namely, the airflow sprayed by each nozzle flows towards the vicinity of the central point and is staggered with each other, so that the airflow sprayed by the at least two nozzles does not converge at the central point.

In one case, the center point may be a geometric center point of the outlets of the nozzles, such as a center of a circle in which the outlets of the nozzles are located in common, or a center of a sphere in which the outlets of the nozzles are located in common, or the like. In another case, the center point can also be understood as a point of uniform convergence of the air streams emitted from the nozzles in the opposed type pulverizing apparatus of the prior art.

In an embodiment, a connection line formed by the outlet of any one of the at least two nozzles and the central point forms an included angle of 2 ° to 30 °, for example, 2 °, 5 °, 8 °, 10 °, 15 °, 20 °, 25 °, or 30 °, with the flow direction of the air flow ejected by the nozzle.

In one embodiment, the air streams from the at least two nozzles interact near the center point to form a collective air stream that moves on a circumferential or spherical surface around the center point.

In one embodiment, the at least two nozzles are located on a plane perpendicular to the ground.

In one embodiment, the powder crushing/surface modification chamber is provided with at least three nozzles, and the air flows sprayed by the at least three nozzles do not have a uniform intersection point.

In one embodiment, the nozzles include a bottom nozzle and at least one side nozzle; the bottom nozzle is arranged at the center of the bottom of the powder crushing/surface modification chamber, and the at least one side nozzle is arranged on the side wall of the powder crushing/surface modification chamber.

In one embodiment, the number of the side nozzles is two, and the two side nozzles are oppositely arranged on the side wall of the powder crushing/surface modification chamber.

In one embodiment, the device further comprises a powder supply machine, a rotary classifier, an airflow classifier and a product powder recovery container; the powder feeder is communicated with the powder crushing/surface modification chamber; the rotary classifier is arranged in the powder crushing/surface modification chamber and is positioned above the at least two nozzles; the airflow classifier is connected with the rotary classifier; the product powder recovery container is connected with the airflow classifier.

In one embodiment, the powder pulverizing/surface modifying chamber is in the shape of an inverted truncated cone.

More preferably, the oxygen content in the jet stream for pulverization discharged from the nozzle is preferably 50ppm to 300 ppm.

The second technical scheme adopted by the invention for solving the technical problems is as follows:

a method for grinding/surface modifying sintered neodymium-iron-boron powder comprises the steps of crushing neodymium-iron-boron SC alloy cast sheets into coarse powder by hydrogen, and grinding the coarse powder in a non-opposite mode under the drive of at least two air flows to obtain micro powder with the average particle size of 1-10 mu m; the at least two air flows move towards a central point, but the at least two air flows do not meet at the central point; the gas flow is inert gas with the oxygen content of 5 ppm-500 ppm.

The fine powder having an average particle diameter of 1 to 10 μm obtained by the above method is molded by a magnetic field molding machine and sintered in a vacuum or inert gas to obtain an Nd-Fe-B sintered permanent magnet material (also called a sintered magnet or a sintered magnet).

In one embodiment, the at least two streams interact in the vicinity of the central point to move the neodymium iron boron powder on a circumferential or spherical surface around the central point.

In one embodiment, the meal is pulverized in a non-opposed manner in at least three air streams that do not have a uniform point of intersection.

In one embodiment, the raw material of the neodymium iron boron SC alloy cast piece comprises 5.0 at% to 5.8 at% of B. More preferably, the content of B in the raw materials of the NdFeB SC alloy cast sheet is in the range of 5.2 at% to 5.6 at%.

In one embodiment, the raw material of the neodymium iron boron SC alloy cast piece comprises 0.05 at% to 1.0 at% of Ga. More preferably, the content of Ga in the raw material of the Nd-Fe-B SC alloy cast piece is in the range of 0.1 at% to 0.8 at%.

More preferably, the oxygen content in the pulverizing gas stream is preferably 50ppm to 300 ppm.

In a preferred embodiment, the method may be carried out by means of a device for the comminution/surface modification of sintered neodymium iron boron powder as described above.

The invention develops a non-opposed (non-colliding) type pulverizing device and method different from the conventional one, which can perform pulverizing more stably and improve the performance and yield of a magnet obtained by molding and sintering a pulverized fine powder in a magnetic field. This is considered to be a composite effect due to a phenomenon of surface damage of the powder, a reduction in internal deformation of the powder, a reduction in lattice defects of the powder, spheroidization of the powder, a good degree of orientation of the powder, and a reduction in ultrafine powder.

The Nd-Fe-B sintered permanent magnet material of the present invention contains Nd, Fe, B as essential elements, 12 at% to 16 at% of Co, 3 at% or less of rare earth elements (including Y, La, Ce, Pr, Gd, Tb, Dy, Ho, etc.) mainly composed of Nd, 2 at% or less of Al, Cu, Ga, Si, Mn, Cr, Ge, Ni, 1 at% or less of Ti, Zr, Hf, W, V, Nb, Mo, Ta, Sn, Bi, Sb, at least 1 or more of the elements, 4 at% to 9 at% of B, and 1 at% or less of trace elements such as C, O, N, H, S, P. The neodymium iron boron powder is made into a sintered magnet by a powder metallurgy method, has a remanence of more than 13kGs and a coercive force of more than 10kOe, and is the magnet with the highest performance in the world.

Squareness Hk/Hcj (%) in a demagnetization curve of a magnet is an important practical index such as heat resistance and thermal demagnetization of the magnet.

After the neodymium iron boron SC alloy cast sheet is subjected to hydrogen crushing treatment, the coarse powder in a broken state is crushed in the powder crushing/surface modification chamber, and the crushing effect is actually achieved. In the embodiment of the present invention, the non-opposing, non-colliding, and smooth collision between the powders reduces lattice defects on the surface of the powders and inside the powders, and has a surface modification effect of the powder shape (spheroidization: turning sharp corners into spheroidization, etc.). Therefore, not only the pulverization but also the "surface improvement" is performed in the powder pulverization/surface modification chamber of the present invention.

The gas in the pulverizing step is an inert gas having an oxygen content of 5ppm to 500ppm, that is, mainly an inert gas and oxygen, but may contain unavoidable impurities such as a small amount of water, oil, an organic solvent, and an organic polymer. The inert gas in the present invention refers to an inert gas, typically nitrogen (N)₂) Argon (Ar), helium (He). In order to reduce the cost, the used inert gas may be recovered by filtering off residual powder, ultrafine powder, or the like.

The device of the present invention does not require special materials and materials. It is preferable to use SUS of ordinary gloss for piping and parts. In addition, the nozzle and the classifying wheel of the rotary classifier are easily worn, and therefore, it is preferable to use a hard material. In order to control the amount of oxygen, the connection portion of the pipe and the valve may be mostly provided with a rubber gasket and a sealant, and high sealability is preferred. In addition, it is preferable to use a wear-resistant material such as alumina or zirconia in a portion where wear is severe.

The equipment, reagents, processes, parameters and the like related to the invention are conventional equipment, reagents, processes, parameters and the like except for special description, and no embodiment is needed.

All ranges recited herein are intended to include all points within the range.

Compared with the background technology, the technical scheme has the following advantages:

1. the invention changes the airflow direction of the airflow crushing device for sintering neodymium-iron-boron powder into a non-opposite direction through the creative research, finds that sharp powder is reduced, the edge angle of the powder is rounded, the powder is close to a sphere, the generation of fine powder is reduced, the powder orientation degree is good, the magnetic conductivity is improved, the yield is improved, and the performance (coercive force, squareness and magnetization intensity) of the magnet is improved.

2. In the invention, the direction of the nozzle and the ejected air flow are not opposite, so that the powder is driven to rotate along the circumferential surface or the spherical surface, and the crushing efficiency is further improved.

3. When the contents of Ga and B contained in the Nd-Fe-B SC sheet alloy elements are in a certain range, the powder is further spheroidized, the powder orientation degree is good, the magnetic conductivity is improved, and the magnetic performance is further improved. This is considered to be due to the presence of many fine 6-13-1 phases in the grain boundaries.

4. The invention is applied to the crushing of the sintered NdFeB SC cast sheet and is also applicable to the crushing of other brittle materials.

Drawings

Fig. 1 is a schematic side view of a prior art opposed type crushing apparatus.

Fig. 2 is a perspective view of a crushing apparatus of an opposed type in the related art.

Fig. 3 is a schematic sectional view of a prior art opposed type crushing apparatus.

Fig. 4 is a schematic view showing the direction of air flow in the prior art of the opposed type pulverization, wherein (a) is two air flows, (b) is three air flows, (c) is four air flows, (d) is five air flows, and (e) is six air flows.

Fig. 5 is a schematic cross-sectional view of a prior art collided crushing device.

FIG. 6 is a schematic side view of the non-opposing type pulverizing/surface modifying apparatus according to embodiments 1 to 4 of the present invention.

FIG. 7 is a schematic sectional view of the non-opposing type pulverizing/surface modifying apparatus according to examples 1 to 4 of the present invention.

FIG. 8 is one of the schematic gas flow directions of the non-opposing type pulverizing/surface modifying method of the present invention, wherein (a) is two gas flows, (b) is two gas flows, (c) is three gas flows, and (d) is four gas flows.

FIG. 9 is a second schematic view showing the direction of air flow in the non-opposing type pulverizing/surface modifying method of the present invention, wherein (a) is three air flows and (b) is four air flows; A1/A2/A3/A4 is an angle formed by a connecting line (indicated by a dot transverse line in the figure) formed by the outlet of the nozzle 6-1/6-2/6-3/6-4 and the central point M and a flowing direction (indicated by a dotted line in the figure) of the airflow jetted by the nozzle 6-1/6-2/6-3/6-4.

FIG. 10 is a schematic side view of a two-stage pulverizing apparatus using a prior art opposed pulverizing apparatus in combination with the non-opposed pulverizing/surface modifying apparatus of the present invention in example 5 of the present invention.

FIG. 11 is a schematic sectional view of an apparatus for two-stage pulverization using a prior art opposed-type pulverization apparatus in combination with the non-opposed-type pulverization/surface modification apparatus of the present invention in example 5 of the present invention.

Reference numerals:

the opposite type crushing device in the prior art comprises: a powder feeder 1 ', a powder pulverizing chamber 2', a rotary classifier 3 ', an air classifier 4', a product powder recovery container 5 ', and a nozzle 6';

of the colliding type crushing devices in the prior art: a powder feeder 1 ", a powder pulverizing chamber 2", a rotary classifier 3 ", an air classifier 4", a product powder recovery container 5 ", a nozzle 6", an impact plate 7 ";

the non-opposed type crushing/surface modification apparatus of the present invention comprises: a powder feeder 1, a powder crushing/surface modification chamber 2, a rotary classifier 3, an air classifier 4, a product powder recovery container 5 and a nozzle 6/6-1/6-2/6-3/6-4.

The direction of the gas flow is indicated by a dashed line.

Detailed Description

The invention is further illustrated by the following figures and examples.

Example 1

Referring to fig. 6 and 7, the non-opposing type crushing/surface modification apparatus for sintered neodymium iron boron powder of the present embodiment includes: a powder feeder 1, a powder crushing/surface modification chamber 2, a rotary classifier 3, an air classifier 4 and a product powder recovery container 5; the powder feeder 1 is communicated with the powder crushing/surface modification chamber 2, and the powder feeder 1 can feed the powder to be crushed into the powder crushing/surface modification chamber 2; the lower half part of the powder crushing/surface modification chamber 2 is in an inverted frustum shape and is provided with a plurality of nozzles 6, and high-speed airflow sprayed by the nozzles 6 drives powder to move and collide for crushing; the rotary classifier 3 is arranged in the powder crushing/surface modification chamber 2 and positioned above the plurality of nozzles 6, and the crushed powder with the particle size meeting the requirement is sent into the airflow classifier 4; the air classifier 4 is connected with the rotary classifier 3, the product powder recovery container 5 is connected with the air classifier 4, the air classifier 4 separates qualified and unqualified powder through air flow separation, and the qualified and unqualified powder is sent into the product powder recovery container 5 or collected to be sent back to the crushing device again for crushing.

In this embodiment, the powder pulverization/surface modification chamber 2 is provided with three nozzles 6 including a bottom nozzle and two side nozzles, and the three nozzles 6 are located on the same plane perpendicular to the ground. The bottom nozzle is arranged at the center of the bottom of the powder crushing/surface modification chamber, but the airflow jet direction of the bottom nozzle is not vertically upward but slightly inclined, for example, an included angle of 2-30 degrees is formed between the airflow jet direction and the vertical direction; the two side nozzles are oppositely arranged on the side wall of the powder crushing/surface modification chamber 2, but the two side nozzles are not arranged in a mirror symmetry manner, but are slightly inclined and staggered, for example, on the basis of mirror symmetry, one side nozzle is slightly inclined upwards, and the other side nozzle is slightly inclined downwards. The inclination angle of the two side nozzles can be referred to the angle between the air flow jet direction of the bottom nozzle and the vertical direction, i.e. the three nozzles 6 can be arranged centrosymmetrically. Thus, the three streams from the bottom nozzle and the two side nozzles do not have a uniform intersection.

The nozzle structure of the device of the present embodiment is a non-opposing type, that is, the three nozzles 6 are arranged around a central point, but a connecting line formed by the outlet of any one nozzle 6 and the central point forms an angle with the flow direction of the air flow ejected from the nozzle 6, that is, the air flows ejected from each nozzle 6 flow towards the vicinity of the central point and are staggered with each other, so that the air flows ejected from the three nozzles 6 do not meet at the central point, and the air flows ejected from the three nozzles 6 do not have a uniform meeting point, but interact near the central point, so that the formed meeting air flow moves on a circumferential surface or a spherical surface around the central point.

The method for crushing/surface modifying sintered neodymium iron boron powder by using the device of the embodiment comprises the following steps: crushing the neodymium iron boron SC alloy cast sheet into coarse powder by hydrogen, and sending the coarse powder into a powder crushing/surface modification chamber 2 by a powder feeder 1; since the airflows from the three nozzles 6 do not have a uniform intersection point but interact with each other near the center point, and the formed integrated airflows move on the circumferential surface or the spherical surface around the center point, the coarse powder moves on the circumferential surface or the spherical surface around the center point under the drive of the non-opposing airflows, and the coarse powder is collided and crushed with each other to be refined, and the fine powder with the average particle size of 1 to 10 μm is obtained.

In the present embodiment, the number of nozzles 6 is three, and thus the number of air flows is three. But not limited thereto. As shown in fig. 8 (a) to (d), the air flow may be two, three, four, or more. The nozzles may or may not all be distributed in the same plane. As long as the directions of the air flows do not meet at the central point, or even do not have a uniform meeting point, a corresponding crushing effect can be achieved.

As shown in fig. 9 (a), there are three nozzles 6-1/6-2/6-3, generating three streams of air. The outlets of the three nozzles 6-1/6-2/6-3 are on the same circle, and the center of the circle is the center point M. However, since the nozzle 6-1/6-2/6-3 is inclined, that is, the extension line of the axis of the nozzle 6-1/6-2/6-3 does not pass through the center of the circle, so that the direction of the ejected air flow does not pass through the center of the circle, the connecting line of each of the three nozzles 6-1/6-2/6-3 and the center point M forms an included angle A1/A2/A3 of 2-30 degrees with the flowing direction of the air flow ejected by the nozzle 6-1/6-2/6-3. The included angles a1, a2, A3 are preferably the same or may be different.

As shown in fig. 9 (b), there are four nozzles 6-1/6-2/6-3/6-4, generating four streams of air. The outlets of the four nozzles 6-1/6-2/6-3/6-4 are on the same circle, and the center point of the circle is the center point M. The connecting line formed by the four nozzles 6-1/6-2/6-3/6-4 and the central point M and the flowing direction of the airflow sprayed out by the nozzles 6-1/6-2/6-3/6-4 form an included angle A1/A2/A3/A4 of 2-30 degrees. The included angles A1, A2, A3 and A4 are preferably the same or different.

Example 2

The raw materials for preparing the neodymium iron boron SC alloy cast sheet of the embodiment are as follows: Pr-Nd-14 at%, B-5 at%, Ga-0.3 at%, Al-0.3 at%, Cu-0.3 at%, Co-0.8 at%, Mn-0.1 at%, Cr-0.1 at%, and the balance of Fe and inevitable impurities.

The raw materials are smelted by adopting an intermediate frequency induction rapid hardening furnace to obtain the neodymium iron boron SC alloy cast sheet with the average thickness of 0.3 mm. The cast Nd-Fe-B SC alloy sheet is put into a hydrogen crushing device, treated in a hydrogen atmosphere of 0.09MPa to crush the cast alloy sheet, and then subjected to dehydrogenation treatment at 550 ℃ for 4 hours. The hydrogen-pulverized raw material was roughly divided into 3 equal parts, and 1 part was charged into the non-opposed pulverization/surface modification apparatus of example 1. The remaining two portions were fed into a conventional opposed type pulverizer (see fig. 1 to 3) and an opposed type pulverizer (see fig. 5), respectively. The nitrogen pressure of each nozzle was 6kg/cm²The nitrogen gas contained oxygen in an amount of 5ppm, 50ppm, 100ppm, 200ppm, 300ppm, 500ppm on average, and was pulverized to obtain a fine powder.

The powders having different oxygen contents obtained by the respective pulverizing apparatuses were compacted under an oriented magnetic field of 2T (Tesla) at 0.2ton/cm²Pressure ofThe pressure was applied to form a block of 30mm by 30 mm. Then, each square block is sintered for 3 hours at 980-1080 ℃ in a vacuum sintering furnace, heat treated for 1 hour at 800 ℃, heat treated for 1 hour at 650 ℃ and heat treated for 1 hour at 500 ℃. Then, each magnet was processed into a 10mm cube, and the magnet performance was evaluated by a BH magnet performance apparatus, and the performance of the powder obtained by each pulverizing method is shown in table 1 by comparison.

TABLE 1 comparison of the properties of the powders obtained in example 2 by the respective comminution methods

Note: FSSS particle size: average particle size evaluation by Fisher-Sub-Sieve-Sizer method.

The examples of the present invention are not limited to the average particle diameter, the magnet performance. This is a comparison between the non-frontal collision and non-collision type pulverizing methods, and provides a basis for the reduction of collision impact capability of powder pulverization, the reduction of crystal defects occurring in the surface of powder particles, the generation of nuclear generation type remanence generating mechanism, and the improvement of the properties, especially remanence and squareness value, of the Nd-Fe-B system sintered magnet. In addition, the magnet of the present invention having a large average grain size has a larger Br value according to the principle of magnetic moment of magnetic field orientation.

In addition, regarding the average oxygen content in pulverization, the opposed type and the clash type of comparative examples, the particle diameter after pulverization and the magnet performance were not greatly affected. This means that the impact force at the time of pulverization is very strong, and the particle diameter after pulverization actually dominates the magnet performance. On the other hand, in the non-opposed, non-colliding type of the present invention, the pulverized particle size and the magnet performance are strongly affected by the average oxygen amount during pulverization, and the magnet performance is improved in the case where the average oxygen amount is 500 ppm. This is a novel insight of the present invention.

Further, even in the apparatus of the present invention, when the amount of oxygen contained is 1000ppm, the effect of promoting the pulverizability by the surface oxidation of the powder is reduced.

Further, it was confirmed that oxidation due to an increase in the average oxygen content in the magnet leads to a decrease in magnet performance, and no good effect was obtained.

Example 3

The raw materials for preparing the neodymium iron boron SC alloy cast sheet of the embodiment are as follows: nd-13 at%, B-4.8 at% -6.0 at% (4.8 at%, 5.0 at%, 5.2 at%, 5.4 at%, 5.6 at%, 5.8 at%, 6.0 at%), Ga-0.1 at%, Al-1 at%, Cu-0.1 at%, Co-2 at%, Mn-0.05 at%, Cr-0.05 at%, Si-0.1 at%, and the balance of Fe and unavoidable impurities.

The raw materials are smelted by adopting a medium-frequency induction rapid hardening furnace to obtain the neodymium iron boron SC alloy cast sheet with the average thickness of 0.2 mm. The cast Nd-Fe-B SC alloy sheet is put into a hydrogen crushing device, treated in a hydrogen atmosphere of 0.08MPa to crush the cast alloy sheet, and then subjected to dehydrogenation treatment at a temperature of 450 ℃ for 4 hours. The hydrogen-pulverized raw material was roughly divided into 3 equal parts, and 1 part was charged into the non-opposed pulverization/surface modification apparatus of example 1. The remaining two portions were fed into a conventional opposed type pulverizer (see fig. 1 to 3) and an opposed type pulverizer (see fig. 5), respectively. The nitrogen pressure of each nozzle was 5kg/cm²The nitrogen gas contained an average amount of 200ppm of oxygen, and was pulverized to obtain fine powder.

The powders having different oxygen contents obtained by the respective pulverizing apparatuses were compacted in an oriented magnetic field of 2.4T (Tesla) at 0.25ton/cm²The pressure of (2) was pressed into a block of 30mm by 30 mm. Then, each square block is sintered at 980-1080 ℃ for 3 hours, heat treated at 900 ℃ for 1 hour, heat treated at 700 ℃ for 1 hour and heat treated at 460 ℃ for 1 hour in a vacuum sintering furnace. Then, each magnet was processed into a 10mm cube, and the magnet performance was evaluated by a BH magnet performance apparatus, and the performance of the powder obtained by each pulverizing method is shown in table 2 by comparison.

TABLE 2 comparison of the properties of the powders obtained in example 3 by the respective comminution methods

The pulverizing apparatus and the pulverizing method of the present invention have a great dependence on the B content in the magnet alloy. This is considered to be because the magnet alloy is easily pulverized due to the B content, and has subtle dependence. Specifically, the amount of precipitation and the state of precipitation of the 2-17 phase, the 6-13-1 phase and the Nd-rich amorphous phase other than the 2-14-1 type main phase were changed by the change in the B content in the SC alloy, and the pulverizability was greatly affected. It is considered that the B content affects the surface state and lattice defects of the powder.

The examples of the present invention are not limited to the average particle diameter, the magnet performance. This is a comparison of the non-frontal collision and non-collision type pulverization methods, and the reduction of the impact force upon powder pulverization and the reduction of the lattice defects occurring on the surface of the powder particles, and the ideal powder particles can improve the remanence and squareness of the magnet according to the nucleation field theory of the Nd-Fe-B system sintered magnet. In addition, it can be analyzed and understood that the magnet of the present invention having a large average grain size has a larger Br value than the principle of magnetic moment orientation by a magnetic field.

On the other hand, in the opposite/head-on type pulverization method, the pulverization property is not affected by the B component due to the strong impact force. The powder is affected by deterioration of properties due to lattice defects, and magnetic properties are reduced. In addition, since the powder is fine and sharp in shape, the magnetic field orientation is not sufficient, and the magnetic properties are further degraded.

Example 4

The raw materials for preparing the neodymium iron boron SC alloy cast sheet of the embodiment are as follows: nd-13.5 at%, B-5.4 at%, Ga-0.02 at% -1.2 at% (0.02 at%, 0.05 at%, 0.1 at%, 0.2 at%, 0.4 at%, 0.6 at%, 0.8 at%, 1.0 at%, 1.2 at%), Al-0.5 at%, Cu-0.3 at%, Co-0.5 at%, Mn-0.1 at%, Cr-0.03 at%, Si-0.05 at%, and the balance of Fe and unavoidable impurities.

600kg of raw materials are smelted by adopting a medium-frequency induction rapid hardening furnace to obtain the neodymium iron boron SC alloy cast sheet with the average thickness of 0.18 mm. The cast Nd-Fe-B SC alloy sheet was put into a hydrogen pulverizer, treated in a hydrogen atmosphere of 0.095MPa to crush the cast alloy sheet, and then subjected to dehydrogenation treatment at 600 ℃ for 4 hours. The hydrogen-pulverized raw material was roughly divided into 3 equal parts, and 1 part was charged into the non-opposed pulverization/surface modification apparatus of example 1. The remaining two portions are fed into a counter-type pulverizing apparatus of the prior art (see the figure)1-3), a colliding-type pulverizing device (as shown in fig. 5). The nitrogen pressure of each nozzle was 4.5kg/cm²The nitrogen gas contained 300ppm of oxygen on average, and the fine powder was obtained by pulverizing.

The pulverized powder of each pulverizer was pressed at an orientation strength of 2.2T (Tesla) of 0.2ton/cm²The pressure of (3) was applied to a square of 30mm by 30 mm. Then, each square is sintered for 3 hours at 960-1080 ℃ in vacuum, heat-treated for 1 hour at 900 ℃, heat-treated for 1 hour at 650 ℃ and heat-treated for 1 hour at 500 ℃. Then, each magnet was processed into a 10mm cube, and the magnet performance was evaluated by a BH magnet performance apparatus, and the performance of the powder obtained by each pulverization method is shown in table 3 by comparison.

TABLE 3 comparison of the properties of the powders obtained in example 4 by the respective comminution methods

The pulverizing apparatus and the pulverizing method of the present invention have a great dependence on the Ga content in the magnet alloy. This is considered to be because the magnet alloy contains a small amount of Ga, is easily pulverized, and has subtle dependence. Specifically, depending on the change in the Ga content in the SC alloy, Ga preferentially precipitates in the grain boundaries, and actively precipitates in the B-rich phase, 2-17 phase, 6-13-1 phase, and Nd-rich amorphous phase in addition to the 2-14-1 type main phase. The precipitation state of grain boundaries, which are starting points of pulverization, changes, and the pulverization performance is greatly affected by the Ga content.

On the other hand, in the opposite/head-on type pulverizing method, the pulverizing property is not affected by Ga component due to strong impact force. The powder is affected by deterioration in properties caused by lattice defects, and the magnet properties are reduced. In addition, since the powder is fine and sharp in shape, the magnetic field orientation is not sufficient, and the magnetic properties are further degraded.

Example 5

As shown in fig. 10 and 11, the crushing apparatus of the present invention can be used in the final crushing process of the 2 nd and 3 rd stage crushing of the prior art. Coarse pulverization is carried out in the former step (for example, a counter type pulverizer as shown in fig. 10 and 11, or a collision type pulverizer or other pulverizer may be used), and final pulverization is carried out in the apparatus of the present invention. The pulverizing apparatus of the present invention has the ability to produce a powder with few lattice defects and a high-performance powder with spheroidization, and therefore, when used in the final pulverizing stage, the powder has a high degree of orientation and improved magnetic permeability, and the best magnet performance can be obtained.

The above description is only a preferred embodiment of the present invention, and therefore should not be taken as limiting the scope of the invention, which is defined by the appended claims and their equivalents.

Claims

1. A crushing/surface modification device for sintering neodymium iron boron powder is characterized in that: the device comprises a powder crushing/surface modification chamber, wherein the powder crushing/surface modification chamber is provided with at least two nozzles; the at least two nozzles are arranged around a center point; a connecting line formed by the outlet of any nozzle and the central point forms an included angle with the flowing direction of the air flow sprayed by the nozzle, so that the air flows sprayed by the at least two nozzles do not meet at the central point; the gas flow is inert gas with the oxygen content of 5 ppm-500 ppm.

2. The apparatus of claim 1, wherein: and in the at least two nozzles, a connecting line formed by the outlet of any nozzle and the central point forms an included angle of 2-30 degrees with the flowing direction of the airflow sprayed by the nozzle.

3. The apparatus of claim 1, wherein: the air flows sprayed by the at least two nozzles interact near the central point to form a converged air flow, and the converged air flow moves on a circumferential surface or a spherical surface surrounding the central point.

4. The apparatus of claim 1, wherein: the at least two nozzles are located on a plane perpendicular to the ground.

5. The apparatus of claim 1, wherein: the powder crushing/surface modification chamber is provided with at least three nozzles, and the air flows sprayed by the at least three nozzles do not have uniform intersection points.

6. The apparatus of claim 1, wherein: the nozzles comprise a bottom nozzle and at least one side nozzle; the bottom nozzle is arranged at the center of the bottom of the powder crushing/surface modification chamber, and the at least one side nozzle is arranged on the side wall of the powder crushing/surface modification chamber.

7. The apparatus of claim 6, wherein: the two side nozzles are oppositely arranged on the side wall of the powder crushing/surface modification chamber.

8. The apparatus of claim 1, wherein: the device also comprises a powder feeder, a rotary classifier, an airflow classifier and a product powder recovery container; the powder feeder is communicated with the powder crushing/surface modification chamber; the rotary classifier is arranged in the powder crushing/surface modification chamber and is positioned above the at least two nozzles; the airflow classifier is connected with the rotary classifier; and the product powder recovery container is connected with the airflow classifier.

9. The apparatus of claim 1, wherein: the powder crushing/surface modification chamber is in an inverted cone frustum shape.

10. A method for pulverization/surface modification of sintered neodymium iron boron powder, characterized by: crushing the neodymium iron boron SC alloy cast sheet into coarse powder by hydrogen, and crushing the coarse powder in a non-opposite mode under the drive of at least two air flows to obtain micro powder with the average particle size of 1-10 mu m; the at least two air streams move in the direction of a central point, but the at least two air streams do not meet at the central point; the gas flow is inert gas with the oxygen content of 5 ppm-500 ppm.

11. The method of claim 10, wherein: the at least two air streams interact near the center point to move the neodymium iron boron powder on a circumferential or spherical surface around the center point.

12. The method of claim 10, wherein: the coarse meal is comminuted in a non-opposed manner in at least three gas streams which do not have a uniform point of intersection.

13. The method of claim 10, wherein: the raw material of the neodymium iron boron SC alloy casting sheet comprises 5.0 at% to 5.8 at% of B.

14. The method of claim 10, wherein: the raw material of the neodymium iron boron SC alloy cast sheet contains 0.05 at% to 1.0 at% of Ga.