WO2023181772A1

WO2023181772A1 - Method for manufacturing r-t-b based sintered magnet

Info

Publication number: WO2023181772A1
Application number: PCT/JP2023/006577
Authority: WO
Inventors: 剛志村田
Original assignee: 株式会社プロテリアル
Priority date: 2022-03-22
Filing date: 2023-02-22
Publication date: 2023-09-28

Abstract

A method for manufacturing an R-T-B based sintered magnet according to the present disclosure comprises: a milling step for preparing a powder of an alloy for an R-T-B based sintered magnet; a molding step for fabricating a powder molded body using the powder; a cutting step for cutting and dividing the powder molded body into a plurality of molded body pieces; and a sintering step for sintering each of the plurality of molded body pieces to fabricate a plurality of sintered bodies. The cutting step includes a step for forming one or a plurality of cut surfaces including a curved surface, by cutting the powder molded body, submerged in a liquid, with a wire running in a horizontal direction, and by causing the wire to move in an arbitrary incising direction perpendicular to the running direction.

Description

Manufacturing method of RTB based sintered magnet

The present application relates to a method for manufacturing an RTB-based sintered magnet.

RTB system sintered magnet (R is a rare earth element and always contains at least one selected from the group consisting of Nd, Pr, and Ce, T is at least one transition metal and always contains Fe) , B is boron) is a compound formed by the main phase of a compound having a R ₂ Fe ₁₄ B type crystal structure, the grain boundary phase located at the grain boundary part of this main phase, and the influence of trace additive elements and impurities. It is composed of phases. RTB-based sintered magnets have a high residual magnetic flux density B _r (hereinafter sometimes simply referred to as “B _r ”) and a high coercive force H _cJ (hereinafter simply referred to as “H _cJ ”). It is known as the highest performance magnet among permanent magnets because of its excellent magnetic properties. For this reason, RTB-based sintered magnets are used in a wide variety of applications such as voice coil motors (VCMs) for hard disk drives, motors for electric vehicles (EV, HV, PHV), motors for industrial equipment, and home appliances. It is used for various purposes.

Such RTB-based sintered magnets are manufactured through, for example, a process of preparing alloy powder, a process of press-molding the alloy powder to produce a powder compact, and a process of sintering the powder compact. Ru. The alloy powder is produced, for example, by the following method.

First, an alloy is manufactured from molten metals of various raw materials by a method such as an ingot method or a strip casting method. The obtained alloy is subjected to a pulverization process to obtain an alloy powder having a predetermined particle size distribution. This pulverization process usually includes a coarse pulverization process and a fine pulverization process. be exposed.

The sintered body obtained by the step of sintering the powder compact is then subjected to mechanical processing such as grinding and cutting, and is separated into pieces having the desired shape and size. More specifically, first, R--Fe--B rare earth magnet powder is compression-molded using a press machine to produce a compact that is larger in size than the final magnet product. After the molded body is made into a sintered body through a sintering process, the sintered body is ground into a desired shape using, for example, a cemented carbide blade saw or a rotary grindstone. For example, after first producing a block-shaped sintered body, the sintered body is sliced with a blade saw or the like to cut out a plurality of plate-shaped sintered body parts.

However, the sintered bodies of rare earth alloy magnets such as R-Fe-B sintered magnets are extremely hard and brittle, and the processing load is large, so high-precision grinding is a difficult task and the processing time is long. It takes. Furthermore, some material parts are inevitably lost during processing. For this reason, the processing process has been a major cause of increased manufacturing costs.

For example, in order to solve the former problem, Patent Document 1 describes a technique of processing a magnet molded body using a wire saw before sintering. A wire saw is a processing technique in which a wire running in one direction or both directions is pressed against a molded body to be processed, and the molded body is ground or cut using abrasive grains between the wire and the molded body. According to this technique, since the powder compact is cut which is much softer and easier to process than the sintered body, the time required for the cutting process is significantly shortened.

JP2003-303728A

Patent Document 1 uses a wire saw having an outer diameter of 0.1 mm or more and 1.0 mm or less and abrasive grains fixed to this wire, and the oxygen concentration is 5% or more and 18% of the total in terms of molar ratio. The following discloses the processing of powder compacts in a controlled inert gas atmosphere. Performing wire saw processing in an inert atmosphere with a controlled oxygen concentration requires complicated equipment and management, and is poor in mass productivity.

Embodiments of the present disclosure provide a new method for manufacturing RTB-based sintered magnets that enables a wire saw process that does not require preparation of an inert atmosphere.

In an exemplary embodiment, the method for manufacturing an RTB-based sintered magnet of the present disclosure includes an RTB-based sintered magnet alloy (R is a rare earth element, consisting of Nd, Pr, and Ce). a pulverizing step of preparing a powder (which always contains at least one selected from the group consisting of: T is at least one transition metal and always includes Fe; and B is boron); and a powder compact using the powder. a cutting step of cutting the powder compact and dividing it into a plurality of compact pieces; and a sintering step of sintering each of the plurality of compact body pieces to produce a plurality of sintered bodies. process. In the cutting step, the powder compact submerged in the liquid is cut by a wire running in a horizontal direction, and the wire is moved in an arbitrary cutting direction perpendicular to the running direction to cut one or more curved surfaces. forming a cut surface.

In one embodiment, the cutting step includes dividing the horizontally running wire into a plurality of molded body pieces surrounded by the plurality of cut surfaces by moving the wire in an arbitrary cutting direction perpendicular to the running direction. including the step of

In one embodiment, in the cutting step, the maximum traveling speed of the wire is 300 m/min or more.

In one embodiment, in the cutting step, the tension of the wire is 29.4 N (3 kgf) or more.

In one embodiment, the moving speed of the wire in the cutting direction is 100 mm/min or more and 800 mm/min or less.

In one embodiment, the moving speed of the wire in the cutting direction when forming the curved surface is 100 mm/min or more and 600 mm/min or less.

In some embodiments, the surface of the wire is of metallic composition.

In one embodiment, the step of preparing the powder compact includes the step of compacting the powder by wet pressing.

In one embodiment, the method further includes a step of recovering the powder particles cut from the powder compact by the cutting step from the liquid.

According to the embodiment of the present disclosure, it is possible to cut with a wire saw without preparing an inert atmosphere, resulting in excellent mass productivity. Furthermore, it becomes possible to process the powder compact into a curved shape. According to the embodiment of the present disclosure, the degree of freedom in designing the shape of the powder compact is improved regardless of the shape of the mold of the press, so it is possible to reduce manufacturing costs while maintaining the characteristics of a high-performance magnet. becomes possible.

FIG. 1 is a flowchart showing the main steps of the manufacturing method in the embodiment of the present disclosure. FIG. 2 is a flowchart showing the details of the cutting process of the manufacturing method in the embodiment of the present disclosure. FIG. 3 is a perspective view schematically showing the configuration of a wire saw device used in an embodiment of the present disclosure. FIG. 4A is a front view for explaining the process of cutting a powder compact submerged in a liquid with a wire. FIG. 4B is a front view for explaining a process of cutting a powder compact submerged in a liquid with a metal wire. FIG. 5A is a side view for explaining a process of cutting a powder compact submerged in a liquid with a wire. FIG. 5B is a side view for explaining the process of cutting a powder compact submerged in a liquid with a wire. FIG. 6A is a side view for explaining a process of cutting a powder compact submerged in a liquid with a wire. FIG. 6B is a side view for explaining the process of cutting a powder compact submerged in a liquid with a wire. FIG. 7A is a diagram schematically showing a cut surface formed on the powder compact 10 by a wire saw. FIG. 7B is a diagram schematically showing a cut surface formed on the powder compact 10 by a wire saw. FIG. 7C is a diagram schematically showing a cut surface formed on the powder compact 10 by a wire saw. FIG. 8A is a diagram schematically showing another example of a cut surface formed on the powder compact 10 by a wire saw. FIG. 8B is a diagram schematically showing another example of a cut surface formed on the powder compact 10 by a wire saw. FIG. 8C is a diagram schematically showing another example of a cut surface formed on the powder compact 10 by a wire saw. FIG. 8D is a diagram schematically showing another example of a cut surface formed on the powder compact 10 by a wire saw. FIG. 8E is a diagram schematically showing another example of a cut surface formed on the powder compact 10 by a wire saw. FIG. 8F is a diagram schematically showing another example of a cut surface formed on the powder compact 10 by a wire saw. FIG. 9 is a graph showing how wire running speed and cutting speed affect the shape of a molded body piece. FIG. 10 is a graph showing how wire running speed and cutting speed affect the shape of a molded body piece. FIG. 11 is a graph showing how the wire traveling speed affects the shape of a molded body piece having a curved surface. FIG. 12 is a graph showing how the wire running speed affects the shape of a molded piece having a curved surface.

Hereinafter, embodiments of a method for manufacturing an RTB-based sintered magnet according to the present disclosure will be described. The method for manufacturing the RTB-based sintered magnet in this embodiment is as shown in the flowcharts of FIGS. 1 and 2.
・RTB system sintered magnet alloy (R is a rare earth element and always contains at least one selected from the group consisting of Nd, Pr and Ce, T is at least one transition metal and Fe and B is boron).
・A molding step (S20) of producing a powder compact using the powder obtained in the crushing step (S10);
- A cutting step (S30) of cutting the powder compact and dividing it into a plurality of compact pieces;
- A sintering step (S40) of producing a plurality of sintered bodies by sintering each of the plurality of molded body pieces;
including.

The cutting step (S30) includes a first processing step (S32) of cutting the powder compact submerged in the liquid with a running wire to form a first cut surface;
A powder compact submerged in a liquid that is the same as or different from the liquid is cut by a wire that is the same as or different from the running wire to form one or more second cut planes that intersect with the first cut plane. 2 processing step (S34).

In a preferred embodiment, such a cutting step (S30) is performed by cutting with a wire running horizontally and moving the wire in an arbitrary cutting direction perpendicular to the running direction, thereby cutting one or more surfaces including curved surfaces. It includes a step of forming a cut surface. The cutting step (S30) is a step of dividing the horizontally running wire into a plurality of molded body pieces surrounded by a plurality of cutting surfaces including curved surfaces by moving the wire in an arbitrary cutting direction perpendicular to the running direction. can include.

According to the method for manufacturing an RTB-based sintered magnet of the present disclosure, cutting is performed with a wire while the powder compact is submerged in a liquid, so there is no need to prepare an inert atmosphere. Examples of liquids that can be used in embodiments of the present disclosure are oils, such as mineral or synthetic oils.

Conventionally, in order to cut a powder compact using wire saw technology, it is necessary for hard abrasive grains fixed to the surface of the metal wires that make up the wire to come into contact with the powder compact and scrape off a portion of the powder compact through friction. It has been thought that. However, as a result of experiments conducted by the present inventor, when a traveling metal wire comes into contact with a powder compact submerged in a liquid, even the metal wire without abrasive grains can grind and cut the powder compact. I found out that it can be done. As a result of the inventor's study, a high-speed liquid flow (jet flow) is generated in the area where the powder compact is in contact with the metal wire running at a predetermined speed range, and in the vicinity thereof, which causes the powder compact to It was found that the powder particles that make up the material were scraped off. Some of the powder particles scraped off from the powder compact ride on the high-speed flowing liquid and are sandwiched between the metal wire and the powder compact, exhibiting a grinding function similar to that of free abrasive grains, and forming the powder compact. It is thought to promote the cleavage of Considering the mechanism by which the wire cuts the powder compact in the liquid, it is considered that the shape and form of the surface of the wire are not particularly limited. In other words, the surface of the wire may be smooth like normal piano wire.

In the cutting process, it is preferable that the running speed of the wire is 300 m/min or more, and the tension of the wire at that time is preferably 3 kgf (29.4 N) or more, for example, 15 kgf (147 N) or less. If the running speed of the wire is less than 300 m/min, sufficient flow velocity necessary to cut the powder compact cannot be obtained, and if the tension of the wire is less than 3 kgf, the wire will bend and the flatness of the cut surface will deteriorate. may decrease. If the tension of the wire exceeds 15 kgf, a problem of breakage may occur. Further, in the cutting process, the cutting speed (workpiece feed speed) in the direction perpendicular to the running direction of the wire is preferably 100 mm/min or more. This is because if the cutting speed is less than 100 mm/min, the time required for the cutting process becomes longer and production efficiency decreases.

Note that when the diameter of the wire is 200 μm or more, the running speed of the wire can be 500 m/min or more. The higher the running speed of the wire, the higher the cutting speed can be. For example, if the wire diameter is 250 μm and the wire running speed is 500 m/min or more, the cutting speed can be 150 mm/min or more. Note that, as described later, the moving speed of the wire in the cutting direction when forming a curved surface is preferably 100 mm/min or more and 600 mm/min or less.

One of the advantages of cutting a powder compact in a liquid is that the temperature rise due to frictional heat at the part where the powder compact and wire come into contact is suppressed, and the generated heat is easily dissipated into the liquid. . In the atmosphere, the powder compact becomes hot due to the frictional heat generated and reacts with oxygen or water vapor in the atmosphere, resulting in an increase in the oxygen concentration in the final sintered magnet and deterioration of the magnetic properties. However, in this embodiment, such a problem can be avoided.

Another advantage of cutting the powder compact in a liquid is that the powder particles scraped from the powder compact by the wire settle in the liquid, making recovery easier. In a preferred embodiment, the step of preparing the powder compact includes the step of compacting the powder by wet pressing. In that case, wet pressing is preferably performed by adding the same type of liquid to the powder as the liquid used in the cutting process. This is because the powder particles cut from the powder compact in the cutting process can be easily recovered from the liquid and reused.

Furthermore, according to the method for manufacturing an RTB-based sintered magnet of the present disclosure, the surface of the powder compact is processed to make it flat in order to cut in the horizontal and lateral directions before cutting in the vertical and vertical directions. can do. At least a portion of the surface (for example, the upper surface) of the powder compact may have irregularities depending on the powder pressing process, and it has been necessary to cut or polish the surface after the sintering process. According to the embodiments of the present disclosure, such cutting or polishing steps can be omitted, so it is possible to reduce manufacturing costs while maintaining the characteristics of a high-performance magnet.

An example of the configuration of a wire saw device that can be used in the above manufacturing method will be described with reference to FIG. 3. FIG. 3 is a perspective view showing a configuration example of the wire saw device 100 in the embodiment of the present disclosure. For reference, the figure shows an X-axis, a Y-axis, and an X-axis that are orthogonal to each other. In this example, the XY plane is horizontal and the Z axis is oriented vertically.

The wire saw device 100 in FIG. 3 includes

rollers

30a, 30b, and 30c arranged so that their central axes of rotation are parallel to each other, and a single continuous wire 40. Each of the

rollers

30a, 30b, and 30c is rotatably supported by a support device 50. The support device 50 can be moved vertically and vertically (in the positive and negative directions of the Z axis) by a drive device (not shown). The drive device may obtain driving force from a hydraulic cylinder or may be operated by a motor. Further, in order to perform cutting along the horizontal lateral direction (X-axis direction), which will be described later, the support device 50 may move in the horizontal lateral direction.

The powder molded body 10 produced in the molding step (S20) is fixed to the fixing base 20 by a clamp portion (not shown), and placed inside the tank 70 that stores the liquid 60. In FIG. 3, the tank 70 is shown in dashed lines and the height of the surface of the liquid 60 is shown in dotted lines. In the example of FIG. 3, the entire powder compact 10 is immersed in the liquid 60. Note that instead of the support device 50 moving in the vertical and horizontal directions, the fixing base 20 may be configured to move in the vertical and horizontal directions.

A specific example of the process of producing the powder compact 10 will be described later. It should be noted here that the powder compact 10 is not a sintered body but a powder compact (green compact) before being sintered. The powder compact is an RTB-based sintered magnet alloy (R is a rare earth element and always contains at least one selected from the group consisting of Nd, Pr, and Ce, and T is at least one transition metal). It is obtained by molding a powder of (which always contains Fe and B is boron) by wet pressing or dry pressing in an orienting magnetic field.

The

rollers

30a, 30b, and 30c are arranged at a predetermined interval so that the rotation center axis is located at the vertex of the triangle when viewed from a direction parallel to the X-axis. A plurality of grooves are provided on each side surface of the rollers 31a, 31b, and 31c. The wire 40 is wound in order around a plurality of grooves of the

rollers

30a, 30b, and 30c. The center spacing (pitch) of the plurality of grooves defines the width of the element divided by wire saw cutting. Both ends of the wire 40 are wound around a collection bobbin (not shown), for example.

The wire 40 in the embodiment of the present disclosure is a metal wire to which no abrasive grains are adhered to the surface. In conventional wire saw technology, the wire includes a wire (core wire) and abrasive grains located on the outer peripheral surface of the wire. The average particle diameter of the abrasive grains is, for example, from several μm to several tens of μm. A typical example of such abrasive grains is artificial diamond, which has a hardness higher than that of rare earth alloys. Unlike the wire portion used in such conventional wire saw technology, the wire 40 in this embodiment is made of a metal material such as carbon steel, and is subjected to a tension of, for example, 3.0 kgf or more during the cutting process. Even if given, it can be used without expansion. The metal wire material that can be used for the wire 40 may be, for example, piano wire, high-tensile steel wire, or the like. The surface of the wire 40 may be plated. The diameter of the wire 40 is, for example, in the range of 100 μm or more and 350 μm, preferably in the range of 180 μm or more and 300 μm or less. If the diameter of the wire 40 is less than 100 μm, there is a problem in that the wire 40 stretches during cutting due to insufficient strength. The larger the diameter of the wire 40, the better is the ability to discharge chips, but the amount of chips increases, so the diameter is preferably 350 μm or less.

During cutting, the

rollers

30a, 30b, 30c and the collection bobbin rotate. The rotation direction of the

rollers

30a, 30b, and 30c depends on their arrangement and how the wire 40 is hung. In the wire saw device 100 shown in FIG. 3,

rollers

30a, 30b, and 30c rotate in the same direction.

Once a predetermined length of wire 40 has been wound onto one of the collection bobbins, the collection bobbin and

rollers

30a, 30b, and 30c are rotated in the opposite direction. This causes the wire 40 to move in the opposite direction, and by repeating this, the wire 40 can be reciprocated (moved).

In this embodiment, the step of cutting the powder compact 10 with the wire 40 is performed with the powder compact 10 submerged in the liquid 60. When the powder compact 10 is a powder compact formed by wet pressing, a preferable example of the liquid 60 is an oil agent of the same type as the dispersion medium such as an oil agent (mineral oil or synthetic oil) used in the wet press.

When processing the powder compact 10 with such a wire saw device 100, the powder particles constituting the powder compact 10 fall off as chips from the portion cut by the wire 40. These chips are powder particles constituting the powder compact 10 that have fallen off from the powder compact 10, and each particle has a rough fracture surface like metal chips (cutting waste). Not that there is. The shape and size of the particles constituting the chips scraped off by the wire from the powder compact before sintering are similar to the shape and size of the powder particles used to produce the powder compact 10. The inventor of this application considered reusing this cutting powder. When a hard sintered body obtained by sintering a powder compact is cut, the chips are particles whose grains have grown due to sintering or whose composition has changed due to a chemical reaction, or a combination of particles. Therefore, even if they are mixed with rare earth magnet powder and reused, the magnetic properties are likely to deteriorate. On the other hand, chips obtained from a powder compact before sintering have the same composition and size as other particles contained in the powder compact, and are therefore easier to reuse.

In addition, when the powder compact 10 is produced by wet pressing, if wire saw processing is performed in the same type of oil as the dispersant, the collected powder (chips) can be used as is in wet pressing, improving production efficiency. rises.

Hereinafter, the method for manufacturing the RTB-based sintered magnet of this embodiment will be explained in detail.

S10: Grinding Step In the grinding step (S10), powder of an RTB-based sintered magnet alloy is prepared. Below, the composition of the RTB-based sintered magnet alloy, the process for manufacturing the alloy, and the process for preparing the alloy powder will be explained in order.

<Composition of rare alloy for RTB-based sintered magnets>
R is a rare earth element and always contains at least one selected from the group consisting of Nd, Pr, and Ce. Preferably, Nd-Dy, Nd-Tb, Nd-Dy-Tb, Nd-Pr-Dy, Nd-Pr-Tb, Nd-Pr-Dy-Tb, Nd-Ce-Dy, Nd-Ce-Tb, Nd -Ce-Dy-Tb, Nd-Pr-Ce-Dy, Nd-Pr-Ce-Tb, and Nd-Pr-Ce-Dy-Tb combinations of rare earth elements are used.

Among R, Dy and Tb are particularly effective in improving H _cJ . In addition to the above elements, other rare earth elements such as La may be contained, and misch metal and didymium may also be used. Further, R may not be a pure element, and may contain impurities that are unavoidable in production within an industrially available range. The content is, for example, 27% by mass or more and 35% by mass or less. Preferably, the R content of the RTB-based sintered magnet is 31% by mass or less (27% by mass or more and 31% by mass or less, preferably 29% by mass or more and 31% by mass or less). By setting the R content of the RTB-based sintered magnet to 31% by mass or less and the oxygen content to 500 ppm or more and 3500 ppm or less (preferably 500 ppm or more and 3200 ppm or less, and more preferably 500 ppm or more and 2500 ppm or less). , higher magnetic properties can be obtained.

T contains iron (including cases where T consists essentially of iron), and 50% or less of it by mass ratio may be replaced with cobalt (Co) (T consists essentially of iron and cobalt). (including cases). Co is effective in improving temperature characteristics and corrosion resistance, and the alloy powder may contain 10% by mass or less of Co. The content of T may occupy the remainder of R and B, or R and B and M, which will be described later.

The content of B may be any known content, and for example, a preferable range is 0.9% by mass to 1.2% by mass. If it is less than 0.9% by mass, high H _cJ may not be obtained, and if it exceeds 1.2% by mass, _Br may decrease. Note that a part of B can be replaced with C (carbon).

In addition to the above elements, an M element can be added to improve H _cJ . The M element is one or more selected from the group consisting of Al, Si, Ti, V, Cr, Mn, Ni, Cu, Zn, Ga, Zr, Nb, Mo, In, Sn, Hf, Ta, and W. . The amount of the M element added is preferably 5.0% by mass or less. This is because if it exceeds 5.0% by mass, Br may decrease. Also, unavoidable impurities can be tolerated.

The content of N (nitrogen) in the RTB-based sintered magnet is preferably 50 ppm or more and 600 ppm or less. Further, the content of C (carbon) in the RTB-based sintered magnet is preferably 50 ppm or more and 1000 ppm or less.

<Production process of RTB alloy for sintered magnets>
The manufacturing process of an RTB alloy for sintered magnets will be exemplified. An alloy ingot can be obtained by an ingot casting method in which a metal or alloy that has been adjusted in advance to have the composition described above is melted and placed in a mold. In addition, molten metal is brought into contact with a single roll, twin rolls, rotating disk, or rotating cylindrical mold to rapidly cool it to produce a solidified alloy that is thinner than the alloy made by the ingot method, typically the strip casting method or centrifugal casting method. Alloy flakes can be produced by a rapid cooling method.

In the embodiments of the present disclosure, materials manufactured by either the ingot method or the quenching method can be used, but it is preferable to manufacture by a quenching method such as a strip casting method. The thickness of the rapidly solidified alloy produced by the rapid cooling method is usually in the range of 0.03 mm to 1 mm, and has a flake shape. The molten alloy begins to solidify from the surface in contact with the cooling roll (roll contact surface), and crystals grow in columnar shapes in the thickness direction from the roll contact surface. Rapidly solidified alloys are cooled in a shorter time than alloys (ingot alloys) produced by conventional ingot casting methods (mold casting methods), so they have finer structures and smaller crystal grain sizes. Also, the area of grain boundaries is wide. Since the R-rich phase widely spreads within the grain boundaries, the rapid cooling method has excellent dispersibility of the R-rich phase. For this reason, it is easy to fracture at grain boundaries by hydrogen pulverization. By subjecting the rapidly solidified alloy to hydrogen pulverization, the size of the hydrogen pulverized powder (coarsely pulverized powder) can be reduced to, for example, 1.0 mm or less. The coarsely pulverized powder thus obtained is finely pulverized using, for example, a jet mill.

<Process of preparing powder of RTB-based sintered magnet alloy>
The rare earth alloy powder for RTB sintered magnets is active and easily oxidized. For this reason, gases used in jet mills include nitrogen, argon, helium, etc., in order to avoid the risk of heat generation and ignition, and to reduce the oxygen content as an impurity and improve the performance of the magnet. An inert gas is used.

The material to be pulverized (coarsely pulverized powder) fed into a jet mill is, for example, pulverized into a fine powder having a particle size distribution with an average particle size (median diameter: d50) of 2.0 μm or more and 4.5 μm or less, and then is captured in a cyclone. It will be moved to a collection device. Cyclone collectors are used to separate powder from the airflow that carries it. Specifically, coarsely pulverized powder of RTB-based sintered magnet alloy is pulverized in a jet mill in the previous stage, and the fine powder generated by pulverization is sent to a cyclone collection device along with the gas used for pulverization. Supplied. A mixture of inert gas (grinding gas) and pulverized fine powder forms a high-speed airflow and is sent to a cyclone collector. A cyclone collector is used to separate these grinding gases and fine powders. The fine powder separated from the grinding gas is collected by a powder collector.

S20: Molding process In the molding process (S20), a powder compact is produced using the powder obtained in the pulverizing process (S10).

In this embodiment, a powder compact is produced from the above powder by pressing in a magnetic field. In pressing in a magnetic field, from the viewpoint of suppressing oxidation, it is preferable to form a powder compact by pressing in an inert gas atmosphere or wet pressing. In particular, in wet pressing, the surfaces of the particles constituting the powder compact are coated with a dispersant such as an oil agent to suppress contact with oxygen and water vapor in the atmosphere. Therefore, it is possible to prevent or suppress the particles from being oxidized by the atmosphere before, during or after the pressing process.

When performing wet pressing in a magnetic field, a slurry of fine powder mixed with a dispersion medium is prepared, and the slurry is supplied to a cavity in a mold of a wet pressing device and press-molded in a magnetic field. The powder compact thus formed has a density of, for example, 4 g/cm ³ or more and 5 g/cm ³ or less.

- Dispersion medium A dispersion medium is a liquid in which a slurry can be obtained by dispersing alloy powder.

Mineral oil or synthetic oil can be mentioned as a preferred dispersion medium used in the present disclosure. The type of mineral oil or synthetic oil is not specified, but if the kinematic viscosity at room temperature exceeds 10 cSt, the increased viscosity will strengthen the bonding force between the alloy powders, which will affect the orientation of the alloy powder during wet compaction in a magnetic field. may have a negative impact. Therefore, the kinematic viscosity of the mineral oil or synthetic oil at room temperature is preferably 10 cSt or less. Furthermore, if the fractionation point of mineral oil or synthetic oil exceeds 400° C., it becomes difficult to remove oil after obtaining a molded body, and the amount of residual carbon in the sintered body may increase, resulting in a decrease in magnetic properties. Therefore, the fractionation point of mineral oil or synthetic oil is preferably 400°C or lower. Furthermore, vegetable oil may be used as a dispersion medium. Vegetable oil refers to oil extracted from plants, and the type of plant is not limited to a specific plant.

- Preparation of slurry A slurry can be obtained by mixing the obtained alloy powder and a dispersion medium.

Although the mixing ratio of the alloy powder and the dispersion medium is not particularly limited, the concentration of the alloy powder in the slurry is preferably 70% or more (ie, 70% by mass or more) in terms of mass ratio. This is because at a flow rate of 20 to 600 cm ³ /sec, the alloy powder can be efficiently supplied into the cavity and excellent magnetic properties can be obtained. The concentration of the alloy powder in the slurry is preferably 90% or less in terms of mass ratio. The method of mixing the alloy powder and the dispersion medium is not particularly limited. The alloy powder and the dispersion medium may be prepared separately, and a predetermined amount of both may be weighed and mixed together. In addition, when obtaining alloy powder by dry-pulverizing coarsely ground powder with a jet mill or the like, a container containing a dispersion medium is placed at the alloy powder outlet of the jet mill or other grinding device, and the alloy powder obtained by pulverizing may be collected directly into a dispersion medium in a container to obtain a slurry. In this case, it is preferable that the atmosphere in the container is also made of nitrogen gas and/or argon gas, and the obtained alloy powder is directly collected into a dispersion medium without being exposed to the atmosphere to form a slurry. Furthermore, it is also possible to obtain a slurry consisting of the alloy powder and the dispersion medium by wet-pulverizing the coarsely pulverized powder while it is held in a dispersion medium using a vibration mill, a ball mill, an attritor, or the like.

By molding the slurry thus obtained using a known wet press device, a powder compact having a predetermined size and shape can be obtained. Conventionally, this powder compact is usually sintered to obtain a sintered body, but in this embodiment, the powder compact is divided by a wire saw device before sintering, as described below.

S30: Cutting process In the cutting process (S30), the powder compact is cut and divided into a plurality of compact pieces.

First, a method for forming a planar cut surface by making vertical or horizontal cuts will be explained, and then a method for forming a cut surface that spreads diagonally or a curved surface will be explained.

The cutting of the powder compact in this step is performed by, for example, a wire saw device shown in FIG. 3. 4A and 4B are front views for explaining the process of cutting the powder compact 10 submerged in the liquid 60 with the wire 40, respectively. FIG. 4A shows the state before the cutting process starts, and FIG. 4B shows the state in the middle of the cutting process. A broken line inside the powder compact 10 shown in FIG. 4B schematically indicates the position of the wire 40 while cutting the powder compact 10. When the position of the wire 40 indicated by the broken line moves downward from the top surface of the powder compact 10 and reaches the bottom surface of the powder compact 10, the powder compact 10 is divided into a plurality of compact pieces.

In the illustrated example, the wire 40 moves in a direction perpendicular to the running direction of the wire 40 (negative direction of the Z-axis) while running at a predetermined speed in the Y-axis direction. The direction perpendicular to the running direction of the wire 40 is the cutting direction, and the speed in this direction (cutting speed) is set to, for example, 100 mm/min or more. In the example shown in FIG. 4B, the running wire 40 is moving in the negative direction of the Z-axis with respect to the powder compact 10 in a stationary state, but the powder compact 10 is moving along the Z-axis together with the fixing base 20. may be lifted in the positive direction.

FIGS. 5A and 5B are side views for explaining the process of cutting the powder compact 10 submerged in the liquid 60 with the wire 40, respectively. FIG. 5A shows the state before the cutting process starts, and FIG. 5B shows the state during the cutting process. In the illustrated example, one powder compact 10 is divided into eight compact pieces.

The diameter of the wire 40 is, for example, 100 μm or more and 350 μm or less. The running speed of the wire 40 (wire linear speed) may be set, for example, in a range of 100 m/min or more and 800 m/min or less. On the other hand, the cutting speed (the feeding speed of the wire with respect to the powder compact 10 in the negative direction of the Z axis in FIG. 3) may be set, for example, in a range of 100 mm/min or more and 600 mm/min or less. The tension applied to the wire 40 is, for example, 3 kgf or more and 15 kgf or less. The tension can be adjusted, for example, by adjusting the distance of roller 30c with respect to

rollers

30a and 30b. By cutting with a wire saw, the powder compact 10 can be divided into compact pieces having a thickness of about 1 to 10 mm, for example. The thickness of the compact piece is determined by the spacing of the wires 40 and the diameter of the wires 40, as shown in FIG. 5B.

Performing wire saw processing in liquid also has the advantage of facilitating the discharge of cutting chips. In addition, as described above, cutting can be performed while the powder compact 10 is immersed in the dispersion medium (mineral oil or synthetic oil) used when producing the powder compact 10 by wet pressing (cutting in oil). , the powder particles precipitated in the liquid during wire saw processing can be recovered, and the recovered powder particles can be reused as they are in the molding process.

FIGS. 6A and 6B are side views for explaining the process of horizontally cutting the powder compact 10 submerged in the liquid 60 with the wire 40. In the illustrated example, the

rollers

30a, 30b, and 30c are moving in the horizontal direction (in the direction of the rotation axis of each roller) relative to the powder compact 10 during the cutting process. Before performing the steps described with reference to FIGS. 4A to 5B, the surface of the powder compact 10 can be made flat by making horizontal incisions using the wire 40. At least a portion of the surface (for example, the upper surface) of the powder compact 10 may have irregularities depending on the powder pressing process. For example, after filling powder into the die hole of a powder press machine and before pressing the powder with a punch, a "filter cloth" is placed between the punch and the powder, and a dispersant (oil agent) is passed through the filter cloth. may be discharged. In that case, irregularities may be formed on the upper surface of the obtained powder compact by the filter cloth.

In the embodiment of the present disclosure, since such an uneven surface is cut off with a wire before the sintering process, the process of cutting or polishing for flattening after the sintering process can be omitted.

FIGS. 7A to 7C are diagrams schematically showing cut surfaces formed on the powder compact 10 by a wire saw. By the step (first treatment step) described with reference to FIGS. 6A and 6B, the running wire 40 moves along the broken line 11c in FIG. 7A with respect to the powder compact 10 submerged in the liquid 60. , the rough surface region 10T of the powder compact 10 is cut thinly to form a first cut surface 11 perpendicular to the Z-axis direction. Thereafter, by performing the step (second treatment step) described with reference to FIGS. 5A and 5B, a plurality of second cut surfaces 12 that intersect with the first cut surface 11 are formed. In the second processing step, the second cut surface 12 is formed by moving the running wire along the broken line 12c. The first treatment step and the second treatment step may be performed using the same wire saw device or different wire saw devices. In other words, in the second treatment step, the powder compact may be cut by the same wire while being submerged in the same liquid as that in which it was submerged in the first treatment step, or it may be cut by the same wire while the powder compact is submerged in the same liquid as the one in the first treatment step. The wires may be cut by different wires while the wires are in the same state.

In the example shown in FIGS. 7A to 7C, the first cutting surface 11 is parallel to the horizontal plane, and the second cutting surface 12 is perpendicular to the first cutting surface 11. The respective orientations of the first cut surface 11 and the second cut surface 12 are not limited to this example.

The second cutting speed is preferably, for example, 100 mm/min or more and 800 mm/min or less.

The technical effect of performing the first processing step of cutting the powder compact in the liquid horizontally and laterally before performing the second processing step of cutting the powder compact in the vertical and vertical directions is that It can be obtained not only when using a wire but also when using a wire in which abrasive grains are fixed to the surface of a metal wire. However, when cutting a powder compact in a liquid, it is preferable to cut with a metal wire to which no abrasive grains are attached, since problems caused by abrasive grains falling off can be avoided.

8A to 8F show that the powder compact 10 submerged in the liquid 60 is surrounded by a plurality of cut surfaces including curved surfaces by moving the wire 40 in an arbitrary cutting direction perpendicular to the running direction. FIG. 3 is a diagram for explaining a step of dividing the molded product into a plurality of pieces. In the illustrated example, during the cutting process, the

rollers

30a, 30b, 30c that rotate the wire 40 and the support device 50 can move simultaneously in both the Z-axis direction and the X-axis direction.

In the process of changing from the state shown in FIG. 8A to the state shown in FIG. 8B, the wire 40 moves horizontally in the negative direction of the X-axis. As a result, a horizontal cut surface is formed in the powder compact 10.

Next, in the process of changing from the state shown in FIG. 8B to the state shown in FIG. 8C, the wire 40 moves perpendicularly to the negative direction of the Z-axis. As a result, a vertical cut surface is formed in the powder compact 10.

Furthermore, in the process of changing from the state shown in FIG. 8C to the state shown in FIG. 8D, the wire 40 moves in the negative direction of the Z-axis while moving in the positive direction of the X-axis. As a result, a downwardly convex curved cut surface is formed in the powder compact 10. At this time, for example, if the moving speed in the X-axis direction is kept constant, an arbitrary curved surface can be formed by gradually changing the moving speed in the Z-axis direction.

In the process of changing from the state shown in FIG. 8D to the state shown in FIG. 8E, the wire 40 moves in the positive direction of the Z-axis while moving in the positive direction of the X-axis. As a result, a downwardly convex curved cut surface is formed in the powder compact 10.

Finally, in the process of changing from the state in FIG. 8E to the state in FIG. 8F, the wire 40 moves perpendicularly to the positive direction of the Z-axis. As a result, a vertical cut surface is formed in the powder compact 10, and finally a downwardly convex, semi-cylindrical shaped compact piece is obtained.

In the example shown in FIGS. 8A to 8F, one compact piece is formed from one powder compact 10, but the present invention is not limited to this example. By controlling the movement of the wire 40, a plurality of molded body pieces can be formed from one powder molded body 10. Further, the shape and size of the molded body piece to be formed are not limited to the illustrated example.

S40: Sintering process In the sintering process (S40), each of the plurality of molded body pieces is sintered to produce a plurality of sintered bodies. That is, the individual molded body pieces cut by the above-mentioned wire saw process are sintered to obtain an RTB type sintered magnet (sintered body). The sintering process of the molded body piece is performed at a temperature of, for example, 1000°C to 1150°C under a pressure of, for example, 0.13 Pa (10 ^-3 Torr) or less, preferably 0.07 Pa (5.0 × 10 ^-4 Torr) or less. This can be done within the range of To prevent oxidation due to sintering, residual gases in the atmosphere may be replaced by inert gases such as helium, argon, etc. It is preferable to perform additional heat treatment such as aging treatment on the obtained sintered body. Such heat treatment can improve magnetic properties. Heat treatment conditions such as heat treatment temperature and heat treatment time can employ known conditions. The thus obtained RTB-based sintered magnet is subjected to a grinding/polishing process, a surface treatment process, and a magnetization process, as necessary, to produce the final RTB-based sintered magnet. The magnet is completed.

In a preferred embodiment, the method for manufacturing an RTB-based sintered magnet of the present disclosure includes introducing a heavy rare earth element RH (RH is at least one of Tb, Dy, and Ho) from the surface of the sintered body into the inside. The method further includes a step of diffusing. By diffusing the heavy rare earth element RH from the surface of the sintered body into the interior, the coercive force can be efficiently increased. The method of the diffusion step is not particularly limited. A known method can be adopted.

(Example)
Nd: 22.6%, Pr: 7.8%, B: 0.9%, Co: 0.5%, Al: 0.1%, Cu: 0.2%, Ga: 0.4% (both The raw materials of each element were weighed so as to have a composition with the balance being Fe (% by mass), and the balance was Fe, and an alloy was produced by a strip casting method. The obtained alloy was subjected to hydrogen pulverization to obtain coarsely pulverized powder.

Next, 0.04% by mass of zinc stearate was added as a lubricant to the obtained coarsely pulverized powder based on 100% by mass of the coarsely pulverized powder, and after mixing, dry pulverization was carried out in a nitrogen stream using a jet mill. A finely pulverized powder (alloy powder) having a particle size D50 of 4 μm was obtained. The finely pulverized material was immersed in mineral oil having a fractionation point of 250° C. and a kinematic viscosity of 2 cSt at room temperature in a nitrogen atmosphere to prepare a slurry. The slurry concentration was 85% by mass. The obtained slurry was molded in a magnetic field (wet molding) to produce a powder compact. The size of the powder compact was 80 mm x 45 mm x 60 mm.

The powder compact was divided into eight compact pieces using a wire (metal wire made of piano wire) having a diameter of 250 μm. Cutting with a wire saw was performed while the powder compact was submerged in a liquid (the same liquid as the mineral oil used during molding was used). Each powder compact was cut with eight wires (multi-wire) running in parallel. The tension applied to the wire during cutting was 10 kg, and the roller spacing was 250 mm.

FIG. 9 is a graph showing how the wire running speed and cutting speed affect the shape of the molded body piece. The horizontal axis of the graph is the wire running speed [m/min], and the vertical axis is the cutting speed [mm/min]. The "x" shown in this graph means that a "crack" has occurred in a part of the molded body piece divided by wire saw cutting, and the "〇" means that such a crack has occurred in the molded body piece. This means that the molded product could be divided into good-shaped pieces without any occurrence.

When using a wire with a diameter of 250 μm, at a running speed of 300 m/min, it was possible to obtain a crack-free molded piece at a cutting speed of 100 to 150 mm/min. Furthermore, at a running speed of 500 m/min, a crack-free molded piece could be obtained at a cutting speed of 250 mm/min. Furthermore, at a running speed of 700 m/min, even at a cutting speed of 400 mm/min, the wire did not bend during cutting, and it was possible to obtain molded pieces without cracks. Therefore, the maximum running speed of the wire is preferably 300 m/min or more.

Note that when a wire with a diameter of 160 μm was used, it was possible to divide the molded product into good pieces when both the running speed and cutting speed were relatively low. The smaller the diameter of the wire, the easier it is to stretch and bend, so if a high tension is applied and the wire runs at a high speed, it is thought that cracks and chips are more likely to occur when cutting the powder compact. Therefore, the diameter of the wire (metal wire) is preferably 200 μm or more. Note that as the diameter of the wire increases, the cutting margin increases, but normal cutting is possible.

For comparison, even if you try to cut a powder compact placed in the atmosphere with just a metal wire, the cutting will not work properly, and the contact between the traveling metal wire and the powder compact will be caused by liquid (preferably It was confirmed that it was necessary to conduct the test in oil).

FIG. 10 shows the experimental results when the upper surface area of the powder compact was cut horizontally in oil using a single wire as shown in FIGS. 6A and 6B. "Transverse feed" is the cutting speed in the horizontal lateral direction, and "linear speed" is the running speed of the wire. When a wire with a diameter of 250 μm was used, a crack-free molded piece could be obtained at a cutting speed of 100 to 300 mm/min at a running speed of 300 m/min. Further, at a running speed of 500 m/min, it was possible to obtain molded pieces without cracks at cutting speeds of 300 mm to 500/min. Furthermore, even at a running speed of 700 m/min, a crack-free molded piece could be obtained at a cutting speed of 500 mm/min.

In order to cut off the vicinity of the top surface of the powder compact by "transverse feeding", it is preferable that the powder compact has sufficient "hardness". The hardness of a powder compact can be evaluated based on, for example, the compaction pressure or density during powder compaction. It has been found that when the density of the powder compact in air is less than 4 g/cm ³ , there is a problem in that the cut surface is not smooth. For this reason, it is preferable that the density of the powder compact is 4 g/cm ³ or more.

FIGS. 11 and 12 are graphs showing how the speed of wire movement in the cutting direction affects the shape of a molded piece having a curved surface when forming a molded piece having a semi-cylindrical shape. . The data in FIG. 11 was obtained when the wire tension was 9 kgf (88.2 N), and the data in FIG. 12 was obtained when the wire tension was 12 kgf (117.6 N). The diameter of the wire is 250 μm. In this example, when cutting the curved surface, the incision made by the wire was advanced in the direction of increasing the position (coordinate) in the X-axis direction. It can be seen that the position of the cut plane deviates from the target position in the latter half of the cut. The cause of this is the bending of the wire.

According to the inventor's study, it was found that when the wire moving speed in the cutting direction is 100 mm/min or more and 600 mm/min or less, the desired curved shape can be cut with a high yield by adjusting the wire tension. The tension is preferably 9 kgf (88.2 N) or more. Further, it is preferable that the wire moving speed in the cutting direction is 540 mm/min or less.

DESCRIPTION OF SYMBOLS 10... Powder compact, 20... Fixing base, 30a, 30b, 30c... Roller, 40... Wire, 50... Support device, 60... Liquid, 70... Tank , 100... wire saw device

Claims

RTB alloy for sintered magnets (R is a rare earth element and always contains at least one selected from the group consisting of Nd, Pr and Ce, T is at least one transition metal and contains Fe) a pulverizing step of preparing a powder of
a molding step of producing a powder compact using the powder;
a cutting step of cutting the powder compact and dividing it into a plurality of compact pieces;
a sintering step of producing a plurality of sintered bodies by sintering each of the plurality of molded body pieces;
including;
The cutting step includes:
The powder compact submerged in the liquid is cut by a wire running in a horizontal direction, and the wire is moved in an arbitrary cutting direction perpendicular to the running direction to form one or more cut surfaces including curved surfaces. A method for producing an RTB-based sintered magnet, including the step of:
The cutting step includes a step of dividing the wire running in a horizontal direction into a plurality of molded body pieces surrounded by the plurality of cutting surfaces by moving the wire in an arbitrary cutting direction perpendicular to the running direction. A method for manufacturing an RTB based sintered magnet according to claim 1.
The method for manufacturing an RTB-based sintered magnet according to claim 1 or 2, wherein in the cutting step, the maximum traveling speed of the wire is 300 m/min or more.
The method for manufacturing an RTB-based sintered magnet according to any one of claims 1 to 3, wherein in the cutting step, the tension of the wire is 29.4 N (3 kgf) or more.
The method for manufacturing an RTB-based sintered magnet according to any one of claims 1 to 4, wherein the moving speed of the wire in the cutting direction is 100 mm/min or more and 800 mm/min or less.
The method for manufacturing an RTB-based sintered magnet according to claim 5, wherein the moving speed of the wire in the cutting direction when forming the curved surface is 100 mm/min or more and 600 mm/min or less.
The method for manufacturing an RTB-based sintered magnet according to any one of claims 1 to 6, wherein the surface of the wire has a metallic composition.
The method for manufacturing an RTB-based sintered magnet according to any one of claims 1 to 7, wherein the step of preparing the powder compact includes a step of compacting the powder by wet pressing.
The RTB based sintered magnet according to any one of claims 1 to 8, further comprising a step of recovering from the liquid the particles of the powder cut from the powder compact by the cutting step. manufacturing method.