JPH0251203A - Production of permanent magnet powder - Google Patents

Abstract

PURPOSE:To eliminate the scattering of a magnetic characteristic due to the differences of grain diameter of the powder and produce a magnetic powder superior in uniformity by allowing a purverized material of alloy melting by inactive gas jet to collide to a rotating rapid quench body. CONSTITUTION:Permanent magnetic alloy melting M having a specific component composition is produced in a high frequency fusion furnace 2 and passed out from an alloy melting nozzle 4 of the furnace bottom by the operation of a stopper 3. Slender alloy melting flow which flows down from the alloy melting nozzle 4 is pulverized and quenched by the dividing action of an inactive gas when it passes in an inactive gas jet nozzle 5 and the pulverized material collides with a conical cooling surface in which a lower rotating cooling body 6 is rotated fast. The powder collected in a lower powder collecting chamber 7 to collide with the rotating cooling body 6 has a good magnetic characteristic, its grain diameter is approximately 0.5-300mum, and the surface of grains has a clean surface state without oxidation, corrosion and other contamination.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for producing permanent magnet powder with improved magnetic properties.

[Conventional technology]

Demand for permanent magnet powder has been increasing recently as a raw material for resin magnets, sintered magnets, magnetic alloy layers of magnetic recording media, and the like.

Permanent magnet powder can be produced by (i) mechanically pulverizing a casting (ingot) of the alloy, compacting and sintering the pulverized product, and then mechanically pulverizing it into powder; (ii) ultra-quenching the molten alloy by a single-roll method, a twin-roll method, or a liquid quenching method such as centrifugation or cooling to form a ribbon-like or flake-like alloy ribbon;
Methods such as mechanically pulverizing the alloy ribbon into powder using a G-force are used.

In addition, as an improved method for producing permanent magnet powder in place of these methods, the applicant has developed a method of cooling the molten alloy by spraying a high-pressure jet stream of an inert gas (Ar, He, N2, etc.) onto the molten alloy stream. He proposed a method of pulverization (Patent Application 1986-2).
No. 18540).

[Problem to be solved by the invention]

The method of obtaining magnetic powder by re-pulverizing the compacted powder sintered body of the crushed ingot requires many steps from melting the alloy to obtaining the powder, and the manufacturing cost is extremely high. It is unavoidable that the quality of the powder deteriorates due to surface oxidation, corrosion, and other contamination.In addition, when producing rare earth-transition metal-boron permanent magnet powder with this method, the coercive force of the powder rapidly decreases as it is pulverized. There is a problem that the value decreases.

On the other hand, the method of pulverizing a ribbon-like or flake-like alloy ribbon obtained by liquid quenching a molten alloy is relatively expensive, even when the permanent magnet powder has an alloy composition containing rare earth elements. Although it is possible to obtain a powder having coercive force, it requires two steps: a liquid quenching step and a mechanical pulverization step, and contamination of the particle surface due to the mechanical pulverization is unavoidable.

On the other hand, the method of dividing and pulverizing the molten metal by spraying an inert gas jet onto the molten permanent magnet alloy flow does not require a mechanical pulverization process, but involves a single step of spraying inert gas onto the molten metal flow. It has the characteristic that magnetic powder with good magnetic properties can be obtained. However, spraying the inert gas flow onto the molten alloy requires a high-pressure jet flow of 50 kg/c111 or more in order to achieve a sufficient pulverization and quenching effect of the molten metal, and the jet flow also rapidly cools and pulverizes the molten metal. Fine particles are uneven, and while fine particles are given high magnetic properties due to the cooling effect, coarse particles have relatively low magnetic properties due to insufficient quenching effect, and the resulting magnetic powder is There is a problem in that variations in magnetic properties depending on the diameter are inevitable.

In view of the above, the present invention solves the above-mentioned characteristics of the method for producing magnetic powder using an inert gas jet stream, and produces magnetic powder with excellent homogeneity, with little variation in magnetic properties due to differences in powder particle size. This provides a method to do so.

[Means and effects for solving the problem] The method for producing permanent magnet powder of the present invention comprises flowing out a molten alloy prepared to have a predetermined composition from a nozzle, and blowing the molten metal flow with an inert gas jet stream. It is characterized by dividing and pulverizing it by attaching it and colliding the pulverized product against a rotating cooling body.

The present invention will be explained in detail below.

According to the present invention, a permanent magnet alloy molten metal having a predetermined composition is first melted in a high-frequency melting furnace or the like, and while flowing out from a nozzle, an inert gas (Ar
, He, Nz gas, etc.). The molten metal flow is divided and pulverized by spraying the inert gas, and then the 4) compound is made to collide with a rotating cooling body.

The molten metal powder separated by the inert gas jet has a particle size distribution ranging from minute to coarse (for example, a fraction of
micrometers to several hundred micrometers). Fine particles (approximately 20 μm or less) in the mixture have a high coercive force (i?(c)), but larger particles have a lower coercive force.

This is because fine particles with a large specific surface area are cooled rapidly, whereas particles with a large particle size have a slow cooling rate, and the quenching effect that each particle receives differs depending on the particle size. In the present invention, following the fragmentation of the molten metal by an inert gas jet stream, the pulverized material is caused to collide with a rotary cooling body in order to improve the rapid cooling effect due to the difference in particle size of the molten metal and pulverized material. This is to eliminate variations.

In other words, when the molten metal powder produced by the splitting action of the inert gas jet collides with the rotary cooling body, the fine particles have a high degree of cooling and solidification before colliding with the rotary cooling body, so they collide with the surface of the rotary cooling body. On the other hand, coarse particles with a large particle size and a low degree of solidification on cooling differ from fine particles when they impact the rotating cooling body surface, flattening slightly and maintaining contact with the cooling body surface, allowing conductive heat transfer. receives a cooling effect from The larger the particle size, the greater the rapid cooling effect provided by the rotary cooling body. In this way, particles with a large particle size are selectively compensated for the quenching effect due to contact with the rotary cooling body, and as a result, the molten metal powder has a large particle size distribution over its entire particle size, regardless of the broad particle size distribution. It is recovered as magnetic powder with uniform magnetic properties.

The conditions for spraying the inert gas jet stream onto the molten alloy flow are as follows:
It does not require much precision; for example, spraying requires a pressure of about 35~
50kg/cIIN, spraying to molten metal flow is the ratio of flow rate (
Inert gas flow/? By spraying at a rate of about 5 to 15 (8 molten liquid flow, weight ratio), it is possible to reduce the size to a fraction of a μm, which can be used as raw material for permanent magnets.
It can be divided and powdered into particles with a particle size of several hundred μm. Of course, higher pressure injection and higher flow rate ratios can be used, but even if the diameter of the molten metal particles to be separated is relatively coarse as described above, the rapid cooling effect is compensated by the rotating cooling body, so There is no need to set a higher pressure/high flow rate ratio. In addition, if the pressure/flow rate ratio is too high, a large amount of amorphous phase will be generated in the particles of the resulting powder, and the magnetic properties will tend to deteriorate. It is appropriate that the upper limit of the flow rate ratio for spraying is 80 kg/c++1 and about 20.

The rotating cooling body that collides the divided granules of the molten metal is a flat disk, cone, or cylinder (roll) having a cooling surface made of copper or other metal. The quenching effect of the powder that collides with the cooling surface of the rotary cooling body increases as the rotation speed increases;
The speed may be approximately 00 m/min.

Next, an embodiment of the method of the present invention will be explained with reference to FIG. 1. (2) is a high frequency melting furnace, (4) is a molten metal nozzle attached to the bottom of the furnace, and (5) is a molten metal nozzle (4). The inert gas injection nozzle (6) is placed directly under the chamber (1), and the rotary cooling body (6) is placed below it.
) is conjunctival within. (7) is a magnetic particle uncollected chamber provided at the lower part of the chamber (1). The chamber (1) and the unrecovered magnetic powder chamber (7) are replaced with an inert gas, so that a series of processing steps from alloy melting to magnetic powder recovery are performed in an inert atmosphere.

The nozzle hole diameter of the molten metal nozzle (4) is approximately 2 to 7 mm. The inert gas injection nozzle (5) directly below it is a multi-hole nozzle arranged in a circular manner so as to surround the molten alloy flow flowing down from the molten metal nozzle (4), and the inert gas injection nozzle (5) is approximately 30 to 50 kg/cffl with respect to the molten metal flow. Spraying injects inert gas under pressure. The flow rate ratio of spraying to the molten metal flow is approximately 5 to 15. The rotary cooling body (6) is a copper cone and rotates at high speed with its vertical rotation axis (61). The inclined surface of the cone has a sufficient area for collision of powdered molten metal particles. Its rotation speed is about 500Orpm
It is.

In the above-mentioned apparatus, a permanent magnet alloy molten metal (M) having a predetermined composition is melted in a high-frequency melting furnace (2), and is caused to flow out from a molten metal nozzle 4) at the bottom of the furnace by operating a stopper (3). The outflow of the molten metal from the molten metal nozzle (4) is a natural falling flow, but if necessary (for example, to make the molten metal flow out smoothly from the fine hole nozzle), an appropriate pressure may be applied to the surface of the molten metal in the furnace. In addition, it may be allowed to flow out.

The thin molten metal stream flowing down from the molten metal nozzle (4) is powdered and rapidly cooled by the splitting action of the inert gas jet flow when passing through the inert gas injection nozzle (5), and the powdered material continues to flow downward. It collides with the conical cooling surface of the rotary cooling body (6) which is rotating at high speed. Among the powdered products, particles with fine particle sizes and a high degree of solidification due to rapid cooling during powdering are repelled by the rotating cooling surface, while coarse particles with large particle sizes and a low degree of solidification are slightly crushed when they collide with the cooling surface. It is rapidly cooled instantly by flattening and maintaining contact with the cooling surface. Rotating cooling body (
The powder collided with 6) and collected into the powder collection chamber (7) below has good magnetic properties, and its particle size is approximately 0.
The particle size is 5 to 300 μm, and the grain surface has a clean surface condition free from oxidation, corrosion, and other contamination.

Incidentally, resin magnets, sintered magnets, magnetic recording media, etc. using the permanent magnet powder obtained by the method of the present invention as a raw material may be manufactured according to conventional methods. For example, when manufacturing a resin magnet, first surface treatment is performed with a coupling agent to improve the binding between the magnetic powder and the resin, and then the magnet is coated with a resin (for example, nylon 6 resin). , acrylic resin, etc.) and an appropriate ratio (for example, 85 to 95 by weight ratio:
15 to 5), add additives such as lubricants and stabilizers, knead, and then apply an appropriate pressure molding method (injection molding, extrusion molding, press molding, etc.) to improve magnetic properties. A resin magnet with excellent properties can be obtained.

〔Example〕

Permanent magnet powder is manufactured using the powder manufacturing apparatus shown in FIG.

Implementation ■ Soil (1) Manufacturing conditions of magnetic powder (1) Alloy molten metal composition: Nd+aFetsBe (at
%) (2) Molten metal nozzle hole diameter: 4IIlffl (3) Inert gas jet flow Conditions for spraying: Inert gas 2 Ar, pressure crab 40 kg/cIa, spraying flow 11 (Ar gas flow/molten metal flow, weight ratio) 28(4)
Rotary cooling body: copper cone (bottom diameter 30 cm), rotation speed 5000 rpm (linear velocity of the part where most of the powder collides is about 1500-4500 m / min).

(II) Characteristics of Magnetic Powder The obtained magnetic powder is a granular or flaky powder with an average particle size of 40 μm. Vibrating sample measurement method for powder in the final classification (
Intrinsic coercive force (jHc) measured by V, S, M, method)
) is 11KOe.

Furthermore, the magnetic powder is classified, and the specific coercive force of each is determined as V,
It was measured by the S, M, method, and the results shown in (a) in FIG. 2 were obtained.

In addition, as a comparative example, the collision treatment of the molten metal powder against the rotary cooling body was omitted, and instead, the inert gas jet stream was sprayed to increase the pressure to 80 kg/cffl to strengthen the pulverization and quenching effect of the molten metal, and other The conditions were set to be the same as in the above examples to produce magnetic powders with the same composition. Regarding the magnetic powder, the intrinsic coercive force was measured for each particle size in the same manner as above, and the results shown in (b) in FIG. 1 were obtained.

As is clear from the comparison between (a) and (b) in Figure 1, the magnetic powder (b) obtained only by pulverization and quenching of the molten metal using an inert gas jet has a variation in coercive force depending on the particle size. The coercive force of particles larger than approximately 40 (tm), which account for most of the powder, remains at a low level of 2 to 3 KOe, whereas the powder quenching treatment using an inert gas jet flow and rotational cooling Magnetic powder (a) of the invention example subjected to quenching treatment by a body
It can be seen that the material has a high coercive force exceeding 9 KOe over the entire grain size, and has excellent uniformity of magnetic properties.

Implementation t2 (1) Production of magnetic powder For molten alloys of various compositions, magnetic powder (1) was prepared under the same conditions as in Example 1, except that the inert gas injection was performed by changing the pressure and the rotation speed of the rotary cooling body. -(4) were manufactured.

(It) Characteristics of Magnetic Powder The coercive force of each sample magnetic powder was measured using the V, S, and M methods, and the results shown in Table 1 were obtained. Both have high coercive force, which is desired as a permanent magnet powder. As a comparative example, magnetic powder (11) was obtained by mechanically pulverizing an alloy ribbon using an attritor using a liquid quenching method, which is a typical manufacturing method for conventional rare earth magnetic powder (alloy composition: (same as magnetic powder (1)). Magnetic powders (1) to (1) of examples of the present invention
It can be seen that 4) has a coercive force equivalent to or higher than this.

(Reference example: Manufacture of resin magnet) N(lz, FetsBe magnetic powder (1
) and (11) are sieved to 200 mesh under, surface treated with a coupling agent, mixed with resin powder, added with a lubricant, stabilizer, etc., heated and kneaded at 250°C to obtain raw materials. A compound was prepared, and this was then subjected to injection molding to obtain resin magnet A (using 1 magnetic powder) and resin magnet B (using 1 inch magnetic powder).

Compounding ratio Ferromagnetic powder 90 parts by weight Nylon 6 resin 9 parts by weight Coupling agent (silane rA-1100J Japan Unicar trout agent)
...0.5 parts by weight Lubricant (zinc stearate) ...0.5 parts by weight V, S, M for each of the above resin magnets A and B.

The coercive force (t Hc ) was measured by the method and the following results were obtained.

Hc Resin magnet A (magnetic powder 1) 12.9 Resin magnet B (magnetic powder 11) 12.8 [Effects of the invention] According to the present invention, (i) Rotating the powdered molten alloy by an inert gas jet flow Permanent magnet powder with excellent magnetic properties can be obtained through a single process of colliding with a quenched body. Therefore, manufacturing costs are significantly reduced compared to conventional manufacturing methods that require multiple steps including mechanical crushing steps.

(ii) Even though the obtained magnetic powder has a broad particle size distribution, it has a high coercive force over the entire particle size and has excellent homogeneity.

(iii) The particle size distribution of the resulting magnetic powder can be changed by changing the conditions for spraying the inert gas jet onto the molten alloy flow.

(iv) Since the resulting magnetic powder has a spherical or flat shape, it has excellent moldability in the permanent magnet manufacturing process, unlike magnetic powder obtained through a conventional mechanical crushing process.

As described above, the method of the present invention enables the production of permanent magnet powder with excellent magnetic properties and handling properties at low cost through a simple process, and also has excellent mass productivity, and its industrial value is extremely high. It's large.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing a specific example of the method for producing permanent magnet powder according to the present invention, and FIG. 2 is a graph showing the intrinsic coercive force of magnetic powder according to particle size. l: Chamber, 2: High frequency melting furnace, 4: Molten metal nozzle, 5
: Inert gas injection nozzle, 6: Rotary cooling body, 7: Powder recovery chamber.

Claims (2)

[Claims] 1. A method for producing permanent magnet powder, which comprises: flowing the molten permanent magnet alloy from a nozzle, dividing the molten metal flow into powder by spraying an inert gas jet flow, and colliding the powder with a rotating cooling body. . 2. 2. The method for producing permanent magnet powder according to claim 1, wherein the permanent magnet alloy is a rare earth element-transition metal element-boron alloy.