JPH07110966B2 - Manufacturing method of rare earth magnet alloy particles - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing rare earth magnet alloy particles, more specifically, a rare earth magnet alloy melt is produced by, for example, an induction melting method, kept in a protective atmosphere and containing a low temperature liquid such as liquid argon. Injected into the chamber, the melt stream is atomized, for example, by jetting with an inert gas jet to form droplets, which are then cooled, solidified and collected by dropping them into a cooling medium at the bottom of the chamber. The present invention relates to a method for producing rare earth magnet alloy particles taken out from a chamber.

[0002]

It is well known to produce permanent magnets containing at least one rare earth element as an important alloy constituent. It is also known that these elements may be, for example, samarium, praseodymium, neodymium, lanthanum, cerium, yttrium or mischmetal.

Conventionally, these magnets are manufactured by vacuum induction melting a prealloyed charge to produce a melt of the desired magnet alloy component composition. The melt is cast into an ingot mold and solidifies. The solidified ingot is prepared by a method in which a ball mill or a jet mill is used to obtain a final particle size of 2 to 2 after the first crushing operation.
Grinded to a fine powder on the order of 5 microns. The powder so produced may be sintered after cold pressing, or the magnet mold desired by either a plastic binder in which the magnet powder is embedded to form the magnet mold, or a low melting point material suitable as a binder. Is molded into.

Due to the relatively slow solidification rate of powdered ingots, the ingot and its powder are not uniform due to segregation that occurs in the ingot during cooling. In addition, the surface of the fine powder is oxidized during the grinding operation. Further, during the milling operation, the associated machining causes stresses and strains in the powder, similar to defects in the powder caused by the milling media. These various factors in the conventional method of manufacturing rare earth permanent magnets contribute not only to the resulting non-uniformity of the magnet mold but also to the non-uniformity of the composition of the magnet mold. Affect the characteristics.

[0005]

SUMMARY OF THE INVENTION The present invention provides a process for the production of rare earth magnet alloy particles from which a magnet mold is produced which is characterized by excellent compositional uniformity and absence of defects and impurities. It is an issue. More specifically, it is to provide a method for producing a powder which can be produced in the form of a permanent magnet which is essentially uniform in composition and free of impurities and defects.

[0006]

The method of the present invention is a well-known method, for example, by induction melting,
A process for producing a melt of a preferred rare earth magnet alloy and pouring a molten fluid into a chamber having a bottom containing a cryogenic liquid, such as liquid argon, kept in a protective atmosphere while holding the melt in a protective atmosphere. And the process.

The melt stream impinges on the cryogenic liquid, or
Or it will impinge on a bottom plate which is cooled by a cryogenic liquid or other suitable cooling medium. The melt stream is then cooled to a solidified body, which solidified body is removed from the chamber. Due to the rapid solidification of the melt of the rare earth magnet alloy, the composition becomes relatively uniform, which helps to improve the magnetic properties of the manufactured magnet. This is in contrast to crushed conventional cast ingots with relatively slow cooling rates and segregation distributed throughout the solidified ingot.

Another implementation of the present invention involves forming a droplet of molten alloy body flow as it enters the chamber, with a spray medium such as argon gas, to form a droplet. Alternatively, it is cooled, solidified and collected either in a bottom plate cooled by a cryogenic liquid or other suitable cooling medium. The resulting powder is removed from the chamber and used to mold the magnet. The melt stream may be atomized by a jet of an inert fluid such as argon gas.

The method of the present invention, which is generally applicable to rare earth permanent magnet alloys, as detailed below, includes 35 to 38 wt% neodymium, 60 to 64.8 wt% iron, and boron.
It is particularly effective for rare earth magnet alloys having a composition range of 0.2 to 2% by weight. With respect to this alloy, neodymium as referred to in the detailed description of the invention and in the claims refers to "effective neodymium", because effective neodymium forms Nd ₂ O ₃ from all neodymium. The oxygen content of is obtained by subtracting the reacting portion, and the amount of this neodymium is determined as follows. % Nd (effective) =% Nd (overall) −6 ×% O ₂ For example, a 35% neodymium-containing alloy containing 0.121% oxygen has an effective neodymium of 34.28%.

The practice of this invention to produce rare earth magnets and the powders used to make the magnets, especially with respect to the composition of the particular alloy, induces in particular magnetic properties.
ction) and coercive force were drastically improved. The coercive force is improved by the uniformity of the powder grains. Therefore, magnets are made from the viewpoint of both metallurgical composition and defect-free, and the finer the powder, the smaller the change in composition within the crystal grains.

Since the powders produced by the practice of this invention have improved homogeneity over the powders produced by conventional methods, the homogeneity of the component composition within the crystal grains has reached its maximum limit by the present invention. , Induction is improved as a result of the finer grain size associated with the relative reduction of crystals within each grain. This allows maximum orientation to maximize induction. As will be shown below, the practice of this invention improves upon the attendant disadvantages of increased stress and strain as a result of the large amount of machining during milling, and without the consequent increase in defects. It is possible to produce the desired powder for induction.

The present invention will be specifically described below with reference to examples. [Example] FIG. 1 is a schematic view of a specific apparatus used in the method of the present invention. As shown in FIG. 1, molten alloy is injected into a tundish 4 from a tiltable furnace 2. The tundish and furnace are placed in an enclosure 6 to create a protective atmosphere. The molten alloy shown as 8 is made from a prealloyed rare earth permanent magnet alloy. Tundish 4
In the bottom view there is a nozzle 10 through which the metal enters in the form of a molten metal stream 12 from a tundish into a chamber 14 kept in a protective atmosphere. Molten metal stream 12 is atomized by a jet 16 that directs a nebulized gas stream 18 into the molten metal stream, forming droplets 20. The droplets drop to the bottom of the chamber, cool in the cryogenic liquid 22, solidify and are ejected. The solidification rate of the spray powder according to the invention will be on the order of 1000 ° C to 1000000 ° C per second, depending on the particle size distribution. This extremely rapid solidification rate prevents variability in powder composition resulting from cooling.

The invention described above comprises at least one rare earth element consisting of samarium, neodymium, braseodymium, lanthanum, cerium, yttrium and mischmetal,
For example, it is suitable to use a general rare earth magnet alloy containing 20 to 40%. The balance of the alloy may be at least one transition metal such as cobalt, iron or nickel, or copper. It may also contain up to about 2% by weight boron, as well as up to about 10% by weight aluminum.

In order to show by one detailed example the homogeneity of the powder produced by the practice of this invention as compared to conventional powders which were vacuum induction melted, ingot cast and crushed, the following composition of components was used: Vacuum melted. Neodymium 32.58 wt% Iron 66.44 wt% Boron 0.98 wt% This alloy was conventional ingot cast and ground to the grain sizes shown in Table I. Separately, in accordance with the practice of this invention, it was sprayed with an argon gas jet and quenched in liquid argon.
Quenched as-is powders were screened through the particle size classifications shown in Table I and tested by Curie temperature measurements to determine the metallurgical phase. The results obtained are shown in Table I.

[0015]

[Table 1]

As can be seen from Table I, conventional ingot casting alloys have two phases, namely tetragonal Nd ₁₅ Fe ₈₀ B.
₅ and Fe ₂ B phases were present in each case. Only the former phase was present in the powders produced according to the invention, showing complete homogeneity.

Improved magnetic properties, ie induction ratio (Br / Bs), for conventional ingot casting and vacuum induction melting rare earth magnet alloys of the following composition made by this invention of atomization and liquid argon quenching: Table of coercive force
Shown in II. The composition of the alloy is as follows. Neodymium 32.58% by weight Iron 66.44% by weight Boron 0.98% by weight

[0018]

[Table 2]

The coercivity of the present invention with particle sizes smaller than 74 microns is much finer than that produced by conventional methods.2.
It will be seen that the values are similar to the 8 micron particle size. Coercive force and induction ratio of rare earth magnet alloy powder (Br / Bs
) Values show a dramatic improvement at particle sizes between 88 and 74 microns.

The data in Table III are for SmCo ₅ alloys
Shows the improvement in coercive force achieved by the present invention,
This same alloy is compared with a conventional method of ingot casting and crushing to form a powder for producing a permanent magnet. In this test, both the powder produced according to the invention and the powder produced by the conventional method were used, the powder was filled in the die space and a magnetic field was applied so that it had the same orientation with respect to the powder. The powder was then compression molded while applying a magnetic field. The cold-pressed compact has a temperature of 1122 ° C (20
Sintered at a temperature of 50 ° F., followed by 954.4 ° C. (17
Heat treated at 50 ° F. for 3 hours.

[0021]

[Table 3]

As can be seen from Table III, for powders in all particle size ranges, the coercivity values achieved by the practice of this invention have been dramatically improved over those achieved by the conventional method. The spray powder produced by the present invention was divided into the particle size classifications reported by the sieving operation, and used for the production of the magnet body without further pulverization.

In the practice of this invention, neodymium is 35 to 38% by weight, iron is 60 to 64.8% by weight and boron is 0.2 to 2% by weight.
If a rare earth magnet alloy having the above-described composition is used, a drastic improvement in energy product (BHmax) of at least the order of 30,000,000 Gauss Oersted can be achieved. To demonstrate this, rare earth magnet alloys with the compositional compositions of Table IV were manufactured for testing. The composition of these rare earth magnet alloys was used to make the powder for making the permanent magnet bodies of this invention by argon gas atomization and liquid argon quenching.

[0024]

[Table 4]

As can be seen in FIG. 2, the maximum energy product values are achieved in the range of about 35 to 38 wt% neodymium, and as can also be seen in FIG. 3, the optimum coercive force of 1000 Oersteds or more is , Achieved within this same neodymium range. As a result, the method of the present invention finds it particularly advantageous to use alloys in the range of 35-38 wt% neodymium, 60-64.8 wt% iron and 0.2-2 wt% boron. .

[0026]

The method for producing rare earth magnet alloy particles according to the method of the present invention does not require a step of pulverizing the particles as in the conventional method, and the obtained particles have a uniform component composition. The magnetic properties of the magnets made are superior to those of magnets made by conventional methods.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an apparatus used in the present invention.

FIG. 2 is a graph showing the relationship between the neodymium content of the rare earth magnet alloy produced according to the present invention and the maximum energy product of the alloy.

FIG. 3 is a graph showing the relationship between the neodymium content of the rare earth magnet alloy produced according to the present invention and the coercive force of the alloy.

[Explanation of symbols]

 2 furnace 4 tundish 6 enclosure device 10 nozzle 14 chamber 20 droplet 22 low temperature liquid

Front Page Continuation (72) Inventor Edward J. A. Deuris, Pennsylvania, USA 15230 Pittsburgh, Hastings Millroad 1775 (56) References JP-A-60-189901 (JP, A) JP-A-59-219904 ( JP, A)

Claims (7)

[Claims] 1. A method for producing particles having uniform components for use in the production of rare earth permanent magnets, the method comprising: producing a melt of a rare earth magnet alloy; maintaining the melt in a protective atmosphere. Introducing the melt stream into a chamber that is a protective atmosphere and has a cooling medium at the bottom; atomizing the melt stream to create droplets; at the bottom of the chamber to create particles A method of making particles comprising rapidly cooling and collecting the droplets and removing the particles from the chamber. 2. The method according to claim 1, wherein the melt of the rare earth magnet alloy is manufactured by vacuum induction melting. 3. The cooling medium is a cryogen liquid.
Manufacturing method. 4. The method of claim 3 wherein the cryogen liquid is liquid argon and the chamber has an argon atmosphere. 5. The melt stream is adapted for use with an inert fluid.
The production method according to claim 1, which is further atomized. 6. The contract wherein the inert fluid is argon gas.
The manufacturing method of claim 5. 7. The rare earth magnet alloy is 35 to 35% by weight.
38% Neodymium, 60-64.8% Iron and 0.2-2%
2. The method according to claim 1, wherein the composition contains the boron.