JP7243698B2 - Method for producing RTB based sintered magnet - Google Patents

Description

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

RTB based 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 the main phase of a compound having a R ₂ Fe ₁₄ B-type crystal structure, the grain boundary phase located in the grain boundary portion of this main phase, and the compound produced by the influence of trace elements and impurities phase. The RTB sintered magnet has 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 a magnet with the highest performance among permanent magnets due to its excellent magnetic properties. For this reason, RTB sintered magnets are used in a wide variety of motors such as voice coil motors (VCM) for hard disk drives, motors for electric vehicles (EV, HV, PHV), motors for industrial equipment, and home appliances. used for various purposes.

Such an RTB based sintered magnet is manufactured through, for example, a step of preparing an alloy powder, a step of press-molding the alloy powder to produce a powder compact, and a step of sintering the powder compact. be. The alloy powder is produced, for example, by the following method.

First, an alloy is produced 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. The former uses, for example, the hydrogen embrittlement phenomenon, and the latter uses, for example, a jet mill. will be

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

However, 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. It takes. In addition, some material parts are inevitably lost due to processing. Therefore, the processing steps have been a major cause of increased manufacturing costs.

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

Japanese Patent Application Laid-Open No. 2003-303728

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 the wire, and the oxygen concentration is 5% or more and 18% of the whole in terms of molar ratio. Disclosed below is the processing of powder compacts in a controlled inert gas atmosphere. Performing wire sawing in an inert atmosphere in which the oxygen concentration is controlled in this manner complicates equipment and management, and is inferior in mass productivity.

Embodiments of the present disclosure provide a novel RTB-based sintered magnet manufacturing method that enables a wire sawing process that does not require the preparation of an inert atmosphere.

In an exemplary embodiment of the method for producing an RTB based sintered magnet of the present disclosure, an RTB based sintered magnet alloy (R is a rare earth element, consisting of Nd, Pr and Ce always contains at least one selected from the group, T is at least one transition metal, must contain Fe, and B is boron), and a powder compact using the powder a cutting step of cutting the powder compact to divide it into a plurality of compact pieces; and a sintering step of sintering each of the plurality of compact pieces to produce a plurality of sintered bodies. wherein the cutting step comprises a first processing step of cutting the powder compact immersed in a liquid with a traveling wire saw to form a first cut surface; and a second processing step of cutting the submerged powder compact with a wire saw that is the same as or different from the traveling wire saw to form one or more second cut planes intersecting with the first cut plane.

In one embodiment, the first cutting plane is parallel to a horizontal plane, and the second cutting plane is perpendicular to the first cutting plane.

In one embodiment, in the cutting step, the wire saw travels at a speed of 300 m/min or higher.

In one embodiment, the tension of the wire saw is 3 kgf or more in the cutting step.

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

In one embodiment, the wet pressing is performed by adding the same type of liquid to the powder as the liquid in the cutting step.

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

In one embodiment, the wire saw used in the first treatment step is different from the wire saw used in the second treatment step, and the wire saw used in the second treatment step includes a plurality of metal wires running in parallel.

According to the embodiments of the present disclosure, cutting with a wire saw is possible without preparing an inert atmosphere, which is excellent in mass productivity. Furthermore, it becomes possible to process the surface of the powder compact to make it flat. At least part of the surface (for example, the upper surface) of the powder compact may have unevenness depending on the powder pressing process, and it has been necessary to cut or polish it by processing after the sintering process. According to the embodiments of the present disclosure, such a step of cutting or polishing can be omitted, so it is possible to reduce manufacturing costs while maintaining the characteristics of high-performance magnets.

FIG. 1 is a flow chart showing main steps of a manufacturing method in an embodiment of the present disclosure. FIG. 2 is a flow chart showing the details of the cutting process of the manufacturing method according to the embodiment of the present disclosure. FIG. 3 is a perspective view schematically showing the configuration of the wire saw device used in the embodiment of the present disclosure. FIG. 4A is a front view for explaining a step of cutting a powder compact immersed in liquid with a wire saw. FIG. 4B is a front view for explaining a step of cutting a powder compact submerged in a liquid with a metal wire saw. FIG. 5A is a side view for explaining a step of cutting a powder compact immersed in liquid with a wire saw. FIG. 5B is a side view for explaining the step of cutting the powder compact immersed in liquid with a wire saw. FIG. 6A is a side view for explaining a step of cutting a powder compact immersed in liquid with a wire saw. FIG. 6B is a side view for explaining the step of cutting the powder compact immersed in liquid with a wire saw. 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. 8 is a graph showing how the wire running speed and the cutting speed affect the shape of the compact piece. FIG. 9 is a graph showing how the wire running speed and the cutting speed affect the shape of the compact piece.

An embodiment of a method for producing an RTB based sintered magnet according to the present disclosure will be described below. As shown in the flow charts of FIGS. 1 and 2, the method for producing an RTB based sintered magnet according to the present embodiment includes:
・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, T is at least one transition metal and Fe and B is boron);
- A forming step (S20) for producing a powder compact using the powder obtained in the pulverizing 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 sintering each of the plurality of molded body pieces to produce a plurality of sintered bodies;
including
The cutting step (S30) includes a first processing step (S32) of cutting the powder compact immersed in liquid with a traveling wire saw to form a first cut surface;
The powder compact immersed in a liquid that is the same as or different from the liquid is cut by a wire saw that is the same as or different from the traveling wire saw to form one or more second cut planes that intersect the first cut plane. and a processing step (S34).

According to the manufacturing method of the RTB based sintered magnet of the present disclosure, since cutting is performed with a wire saw while the powder compact is submerged in liquid, it is not necessary to prepare an inert atmosphere. Examples of liquids that can be used with embodiments of the present disclosure are oils such as mineral oils or synthetic oils.

Conventionally, in order to cut a powder compact with a wire saw, hard abrasive grains adhered to the surface of the metal wires that make up the wire saw come into contact with the powder compact, and it is necessary to scrape off a part of the powder compact by friction. It has been thought that there is. However, as a result of experiments by the present inventors, when a running metal wire comes into contact with a powder compact immersed in a liquid, the powder compact can be ground and cut even with only the metal wire to which no abrasive grains are fixed. It turns out you can. As a result of studies by the inventors, it was found that a high-speed liquid flow (jet flow) is generated in a region where the metal wire traveling at a speed within a predetermined range and the powder compact are in contact with each other and in the vicinity thereof, thereby generating a powder compact. It was found that the powder particles that make up the Some of the powder particles scraped off from the powder compact are sandwiched between the metal wire and the powder compact by riding on the liquid flowing at high speed, and exhibit the same grinding function as free abrasive grains to form the powder compact. is thought to promote the cleavage of It is considered that the shape and form of the surface of the wire are not particularly limited because of the mechanism by which the wire cuts the powder compact in the liquid. In other words, the surface of the wire may be smooth like normal piano wire.

In the cutting step, the wire running speed is preferably 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, a sufficient flow speed necessary for cutting 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 be poor. is likely to decline. If the tension of the wire exceeds 15 kgf, there may be a problem of breakage. Moreover, in the cutting step, the cutting speed (work feed speed) in the direction orthogonal to the wire traveling direction 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 long and the production efficiency decreases.

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 wire running speed, the higher the cutting speed. For example, if the diameter of the wire is 250 μm and the running speed of the wire is 500 m/min or more, the cutting speed can be 150 mm/min or more.

One of the advantages of cutting a powder compact in a liquid is that the temperature rise due to frictional heat at the contact point between the powder compact and the wire saw is suppressed, and the generated heat is easily dissipated into the liquid. . If it is in the air, the powder compact heated to a high temperature by the generated frictional heat reacts with oxygen or water vapor in the air, increasing the oxygen concentration in the final sintered magnet and degrading the magnetic properties. However, in this embodiment, such a problem can be avoided.

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

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

A configuration example of a wire saw device that can be used in the above manufacturing method will be described with reference to FIG. FIG. 3 is a perspective view showing a configuration example of the wire saw device 100 according to the embodiment of the present disclosure. For reference, the figure shows X, Y, and X axes 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 of FIG. 3 has rollers 30 a , 30 b , 30 c arranged so that their central axes of rotation are parallel to each other, and a single continuous wire 40 . Each of the rollers 30 a , 30 b , 30 c is rotatably supported by a support device 50 . The support device 50 can be moved vertically and longitudinally (positive and negative directions of the Z-axis) by a driving device (not shown). The driving device may obtain driving force from a hydraulic cylinder, or may be operated by a motor. In addition, the support device 50 may move in the horizontal and lateral direction in order to perform cutting along the horizontal and lateral direction (X-axis direction), which will be described later.

The powder compact 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. As shown in FIG. In FIG. 3, the tank 70 is indicated by a dashed line, and the height of the surface of the liquid 60 is indicated by a dashed line. In the example of FIG. 3, the entire powder compact 10 is immersed in the liquid 60 . Instead of the support device 50 moving vertically and horizontally, the fixing base 20 may move vertically and horizontally.

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, always contains at least one selected from the group consisting of Nd, Pr and Ce, and T is at least one transition metal. and contains Fe and B is boron) by wet pressing or dry pressing in an oriented magnetic field.

The rollers 30a, 30b, and 30c are arranged at predetermined intervals so that the axis of the center of rotation is positioned at the vertex of the triangle when viewed from the direction parallel to the X-axis. A plurality of grooves are provided on each side surface of the rollers 31a, 31b, and 31c. A wire 40 is sequentially wound around a plurality of grooves of the rollers 30a, 30b, and 30c. The center-to-center spacing (pitch) of the grooves defines the width of the elements separated by the wire saw cut. Both ends of the wire 40 are wound around, for example, recovery bobbins (not shown).

The wire 40 in the embodiment of the present disclosure is a metal wire with no abrasive grains adhered to the surface. In conventional wire saw technology, a wire comprises a wire (core wire) and abrasive grains located on the outer peripheral surface of the wire. The average grain size of the abrasive grains is, for example, several micrometers to several tens of micrometers. A typical example of such abrasive grains is synthetic diamond, which has a hardness higher than that of rare earth alloys. Unlike such a conventional wire, the wire 40 in this embodiment is made of a metal material such as carbon steel, and can be stretched even if a tension of 3.0 kgf or more is applied during the cutting process. can be used without Metal wire materials that can be used for the wire 40 can be, for example, piano wire, high-strength steel wire, and 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 to 350 μm, preferably in the range of 200 μm to 300 μm. If the diameter of the wire 40 is less than 100 μm, there is a problem that the wire 40 extends during cutting due to insufficient strength. The larger the diameter of the wire 40, the better the discharge performance of chips, but the amount of chips increases.

During cutting, the rollers 30a, 30b, 30c and the collection bobbins rotate. The direction of rotation of the rollers 30a, 30b, and 30c depends on their arrangement and how the wire 40 is wound. In the wire saw device 100 shown in FIG. 3, the rollers 30a, 30b, 30c rotate in the same direction.

After the predetermined length of wire 40 is wound on one of the collection bobbins, the collection bobbins and rollers 30a, 30b, 30c are rotated in opposite directions. As a result, the wire 40 moves 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 while the powder compact 10 is submerged in the liquid 60 . When the powder compact 10 is a powder compact formed by wet pressing, a preferred example of the liquid 60 is the same type of oil as the dispersion medium such as the oil (mineral oil or synthetic oil) used in the wet pressing.

When the powder compact 10 is processed by such a wire saw device 100, the powder particles forming the powder compact 10 fall off from the portion cut by the wire 40 as shavings. These shavings are the powder particles that make up the powder compact 10 falling off from the powder compact 10, and each particle has a rough fractured surface like metal shavings (cutting waste). It doesn't mean there is. The shape and size of the particles that constitute the shavings scraped off from the powder compact before sintering with a wire are the same as the shape and size of the powder particles used to produce the powder compact 10 . The inventors of the present application have considered reusing the chips. When a hard sintered body obtained by sintering a powder compact is cut, the shavings are particles or a combination of particles whose grains have grown due to sintering or whose composition has changed due to chemical reactions. Therefore, even if they are mixed with rare earth magnet powder and reused, there is a high possibility that the magnetic properties will deteriorate. On the other hand, shavings obtained from a powder compact before sintering are similar in composition and size to other particles contained in the powder compact, and are therefore easy to reuse.

Further, when the powder compact 10 is produced by wet pressing, if wire saw processing is performed in the same kind of oil as the dispersant, the collected powder (cutting dust) can be used as it is for wet pressing, resulting in production efficiency. rises.

The method for manufacturing the RTB based sintered magnet of this embodiment will be described in detail below.

S10: Pulverization Step In the pulverization step (S10), a powder of RTB based sintered magnet alloy is prepared. Hereinafter, the composition of the RTB based sintered magnet alloy, the manufacturing process of the alloy, and the process of preparing the alloy powder will be described in order.

<Composition of rare alloy for RTB sintered magnet>
R is a rare earth element and necessarily 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 are used.

Of R, Dy and Tb are particularly effective in improving _HcJ . In addition to the above elements, other rare earth elements such as La may be contained, and misch metal and didymium can also be used. Moreover, R may not be a pure element, and may contain impurities that are unavoidable in manufacturing 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 mass % or less (27 mass % or more and 31 mass % or less, preferably 29 mass % or more and 31 mass % or less). By setting the R content of the RTB sintered magnet to 31% by mass or less and the oxygen content to be 500 ppm or more and 3500 ppm or less (preferably 500 ppm or more and 3200 ppm or less, more preferably 500 ppm or more and 2500 ppm or less). , higher magnetic properties can be obtained.

T contains iron (including the case where T consists essentially of iron), and 50% or less of it in 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 Co in an amount of 10% by mass or less. The content of T may account for the remainder of R and B or R and B and M described later.

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

In addition to the above elements, M element can be added to improve _HcJ . 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 M element to be added is preferably 5.0% by mass or less. This is because if the content exceeds 5.0% by mass, Br may decrease. In addition, unavoidable impurities can also be allowed.

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

<Manufacturing process of RTB based sintered magnet alloy>
An example of the manufacturing process of an RTB based sintered magnet alloy will be described. An alloy ingot can be obtained by an ingot casting method in which metals or alloys preliminarily prepared to have the composition described above are melted and put into a mold. In addition, it is represented by the strip casting method or centrifugal casting method in which the molten metal is brought into contact with a single roll, twin rolls, a rotating disk, or a rotating cylindrical mold, etc. and rapidly cooled to produce a solidified alloy that is thinner than the alloy made by the ingot method. Alloy flakes can be produced by a quenching method.

Materials manufactured by either the ingot method or the quenching method can be used in the embodiments of the present disclosure, but are preferably manufactured by a quenching method such as strip casting. The thickness of the quenched alloy produced by the quenching method is usually in the range of 0.03 mm to 1 mm and is in the form of flakes. The molten alloy begins to solidify from the surface in contact with the chill roll (roll contact surface), and crystals grow in a columnar shape from the roll contact surface in the thickness direction. The quenched alloy is cooled in a shorter time than the alloy (ingot alloy) produced by the conventional ingot casting method (die casting method), so the structure is refined and the crystal grain size is small. In addition, the area of the grain boundary is wide. Since the R-rich phase spreads widely within the grain boundary, the rapid cooling method is excellent in the dispersibility of the R-rich phase. Therefore, it is easy to break at the grain boundary by the hydrogen pulverization method. By hydrogen-pulverizing the quenched alloy, 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 pulverized, for example, by a jet mill.

<Step of preparing powder of alloy for RTB sintered magnet>
Rare earth alloy powders for RTB sintered magnets are active and easily oxidized. For this reason, the gas used in the jet mill is nitrogen, argon, helium, etc., in order to avoid the risk of heat generation and ignition and to reduce the oxygen content as an impurity to improve the performance of the magnet. An inert gas is used.

The object to be pulverized (coarsely pulverized powder) fed into the 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 captured by a cyclone. will be moved to the collector. Cyclone collectors are used to separate powder from the air stream that carries it. Specifically, the coarsely pulverized powder of the RTB sintered magnet alloy is pulverized by the preceding jet mill, and the fine powder produced by the pulverization is sent to the cyclone collector together with the gas used for the pulverization. supplied. A mixture of inert gas (pulverization gas) and pulverized fine powder forms a high-speed air stream and is sent to the cyclone collector. Cyclone collectors are utilized to separate these grinding gases and fines. Fine powder separated from the grinding gas is collected in a powder collector.

S20: Molding Step In the molding step (S20), the powder obtained in the pulverization step (S10) is used to produce a powder compact.

In this embodiment, a powder compact is produced from the above powder by pressing in a magnetic field. In magnetic field pressing, the powder compact is preferably formed by pressing in an inert gas atmosphere or wet pressing from the viewpoint of suppressing oxidation. Particularly in wet pressing, the surfaces of the particles constituting the powder compact are coated with a dispersant such as an oil to prevent 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 wet pressing is performed in a magnetic field, a slurry is prepared by mixing a fine powder with a dispersion medium, 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 The dispersion medium is a liquid in which the alloy powder can be dispersed to obtain a slurry.

Mineral or synthetic oils can be mentioned as preferred dispersion media for use in the present disclosure. The type of mineral oil or synthetic oil is not specified, but if the kinematic viscosity at normal temperature exceeds 10 cSt, the increase in viscosity will strengthen the bonding force between the alloy powders, and the orientation of the alloy powders during wet compaction in a magnetic field. may adversely affect Therefore, the kinematic viscosity of the mineral oil or synthetic oil at room temperature is preferably 10 cSt or less. If the fraction point of the mineral oil or synthetic oil exceeds 400° C., it becomes difficult to remove the oil after obtaining the molded body, and the amount of residual carbon in the sintered body increases, which may reduce the magnetic properties. Therefore, the fraction point of mineral oil or synthetic oil is preferably 400° C. or less. Moreover, you may use vegetable oil as a dispersion medium. Vegetable oil refers to oil extracted from a plant, 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.

The mixing ratio of the alloy powder and the dispersion medium is not particularly limited, but the concentration of the alloy powder in the slurry is preferably 70% or more (that is, 70% or more by mass) by mass. 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 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 separately prepared, weighed in predetermined amounts, and mixed. Also, when coarsely pulverized powder is dry pulverized with a jet mill or the like to obtain alloy powder, the alloy powder obtained by placing a container containing a dispersion medium at the alloy powder outlet of the pulverizer such as a jet mill and pulverizing it. may be collected directly into the dispersion medium in the container to obtain a slurry. In this case, it is preferable that the inside of the vessel is also filled with an atmosphere of nitrogen gas and/or argon gas, and the obtained alloy powder is recovered directly into the dispersion medium without exposing it to the atmosphere to form a slurry. Further, it is also possible to wet-pulverize the coarsely pulverized powder in a dispersion medium using a vibrating mill, a ball mill, an attritor, or the like to obtain a slurry composed of the alloy powder and the dispersion medium.

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

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

The cutting of the powder compact in this step is performed, for example, by a wire saw device shown in FIG. 4A and 4B are respectively front views for explaining the process of cutting the powder compact 10 submerged in the liquid 60 with the wire 40. FIG. FIG. 4A shows the state before the cutting process starts, and FIG. 4B shows the state during the cutting process. A dashed line in the powder compact 10 shown in FIG. 4B schematically indicates the position of the wire 40 during cutting of the powder compact 10 . When the position indicated by the broken line of the wire 40 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 traveling direction of the wire 40 (negative direction of the Z-axis) while traveling in the Y-axis direction at a predetermined speed. The direction orthogonal to the running direction of the wire 40 is the cutting direction, and the speed in this direction (cutting speed) is set at, for example, 100 mm/min or more. In the example shown in FIG. 4B, the running wire 40 moves in the negative direction of the Z-axis with respect to the stationary powder compact 10. may be lifted in the positive direction of

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. FIG. 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 wire 40 has a diameter of, for example, 100 μm or more and 350 μm or less. The running speed of the wire 40 (wire wire speed) can be set, for example, in the range of 100 m/min or more and 800 m/min or less. On the other hand, the cutting speed (the feed speed of the wire with respect to the powder compact 10 in the negative direction of the Z-axis in FIG. 3) can be set, for example, within the 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. Tension can be adjusted, for example, by adjusting the distance of roller 30c relative to rollers 30a and 30b. By wire saw cutting, 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.

Conducting the wire sawing process in a liquid also has the advantage of facilitating the discharge of shavings. Further, as described above, the powder compact 10 is immersed in the dispersion medium (mineral oil or synthetic oil) used when the powder compact 10 is produced by wet pressing (cutting in oil). , the powder particles that have precipitated in the liquid during the wire sawing process can be recovered, and the recovered powder particles can be reused as they are in the molding process.

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. FIG. In the illustrated example, the rollers 30a, 30b, and 30c are moved relatively to the powder compact 10 in the horizontal direction (rotating axis direction of each roller) during the cutting process. The surface of the powder compact 10 can be flattened by cutting in the horizontal direction with the wire 40 before performing the steps described with reference to FIGS. 4A to 5B. At least part 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 holes of a die of a powder pressing device, 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. can be performed. In that case, unevenness may be formed by the filter cloth on the upper surface of the obtained powder compact.

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

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

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

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

Note that the technical effect of performing the first processing step of cutting the powder compact in the liquid in the horizontal and horizontal direction before performing the second processing step of cutting the powder compact in the vertical direction is the It can be obtained not only when using a wire saw, but also when using a wire saw in which abrasive grains are fixed to the surface of a metal wire. However, when a powder compact is cut in a liquid, it is preferable to use a metal wire to which abrasive grains are not adhered, because the problem of abrasive grain falling off can be avoided.

S40: Sintering Step In the sintering step (S40), each of the plurality of compact pieces is sintered to produce a plurality of sintered bodies. That is, the RTB system sintered magnet (sintered body) is obtained by sintering the individual compact pieces cut by the wire saw process. The step of sintering the compact pieces is performed, for example, at a pressure of 0.13 Pa (10 ⁻³ Torr) or less, preferably 0.07 Pa (5.0×10 ⁻⁴ Torr) or less, at a temperature of 1000° C. to 1150° C. can be done in the range of Residual gases in the atmosphere may be replaced by inert gases such as helium, argon, etc. to prevent oxidation due to sintering. It is preferable to subject the obtained sintered body to additional heat treatment such as aging treatment. Magnetic properties can be improved by such heat treatment. As heat treatment conditions such as heat treatment temperature and heat treatment time, known conditions can be adopted. The RTB system sintered magnet thus obtained is subjected to a grinding/polishing process, a surface treatment process, and a magnetization process, as required, to obtain the final RTB system sintered magnet. magnet is complete.

In a preferred embodiment, the method for producing a RTB based sintered magnet of the present disclosure includes adding a heavy rare earth element RH (RH is at least one of Tb, Dy, and Ho) from the surface of the sintered body to the inside. Further includes a diffusing 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 diffusion process method 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% (any % by mass), and the raw materials of each element were weighed so that the balance was Fe, and an alloy was produced by a strip casting method. The obtained alloy was hydrogen pulverized to obtain a coarsely pulverized powder.

Next, 0.04% by mass of zinc stearate as a lubricant is added to the coarsely ground powder with respect to 100% by mass of the coarsely ground powder, mixed, and then dry pulverized in a nitrogen stream using a jet mill. Then, a finely pulverized powder (alloy powder) having a particle size D50 of 4 μm was obtained. A slurry was prepared by immersing the pulverized portion in a mineral oil having a fractionation point of 250° C. and a kinematic viscosity of 2 cSt at room temperature in a nitrogen atmosphere. The slurry concentration was 85% by mass. The resulting slurry was compacted (wet compacted) in a magnetic field 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 with a wire saw (metal wires made of piano wires) having a diameter of 250 μm. Cutting with a wire saw was performed in a state where the powder compact was submerged in a liquid (the liquid used was the same mineral oil as used in the molding). 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. 8 is a graph showing how the wire running speed and the cutting speed affect the shape of the compact piece. The horizontal axis of the graph is the wire running speed [m/min], and the vertical axis is the cutting speed [mm/min]. "X" shown in this graph means that a "crack" occurred in a part of the molded piece cut by the wire saw, and "○" indicates that such a crack occurred in the molded piece. This means that no cracks occurred and that the molded body pieces could be divided into good-shaped pieces.

When a wire with a diameter of 250 μm was used, at a traveling speed of 300 m/min, a crack-free molded piece could be obtained at a cutting speed of 100 to 150 mm/min. Furthermore, at a running speed of 500 m/min, a crack-free compact 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 a molded piece without cracks could be obtained.

It should be noted that when a wire with a diameter of 160 μm was used, good formation pieces could be separated when both the running speed and the cutting speed were relatively low. As the diameter of the wire becomes smaller, the wire tends to stretch and bend more easily. Therefore, if a high tension is applied and the wire is run at a high speed, cracks and chips are likely to occur when the powder compact is cut. Therefore, it is preferable that the wire (metal wire) has a diameter of 200 μm or more. As the diameter of the wire increases, the cutting margin increases, but normal cutting is possible.

For comparison, even if an attempt was made to cut a powder compact placed in the air only with a metal wire, the cutting could not be performed normally, and the contact between the running metal wire and the powder compact was caused by a liquid (preferably oil) was found to be necessary.

FIG. 9 shows experimental results when the upper surface region of the powder compact was cut horizontally in oil with a single wire as shown in FIGS. 6A and 6B. "Lateral feed" is the cutting speed in the horizontal lateral direction, and "line speed" is the running speed of the wire. When a wire with a diameter of 250 μm was used, a molded piece without cracks could be obtained at a running speed of 300 m/min and a cutting speed of 100 to 300 mm/min. Furthermore, at a running speed of 500 m/min, a molded piece without cracks could be obtained at a cutting speed of 300 mm to 500/min. Furthermore, even at a running speed of 700 m/min, a molded piece without cracks could be obtained at a cutting speed of 500 mm/min.

In order to cut off the vicinity of the upper surface of the powder compact by "traverse feeding", it is preferable that the powder compact has sufficient "hardness". The hardness of the powder compact can be evaluated, for example, by compacting 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 , the cut surface becomes uneven. Therefore, it is preferable that the density of the powder compact is 4 g/cm ³ or more.

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

Claims (9)

RTB based sintered magnet alloy (R is a rare earth element, 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 and B is boron);
A molding step of producing a powder compact using the powder;
a cutting step of cutting the powder compact to divide it into a plurality of compact pieces;
a sintering step of sintering each of the plurality of molded body pieces to produce a plurality of sintered bodies;
including
a first treatment step of cutting the powder compact immersed in an oil by running a metal wire having no abrasive grains adhered to the surface to form a first cut surface;
The powder compact immersed in an oil solution that is the same as or different from the oil solution is cut by a metal wire that is the same as or different from the running metal wire , and one or a plurality of second cut surfaces that intersect the first cut surface. a second treatment step of forming a cut surface;
A method for producing an RTB-based sintered magnet, comprising: The first cut plane is parallel to the horizontal plane,
2. The method for producing a RTB based sintered magnet according to claim 1, wherein said second cut plane is orthogonal to said first cut plane. 3. The method for producing a RTB based sintered magnet according to claim 1, wherein in said cutting step, said metal wire travels at a speed of 300 m/min or more. 4. The method for producing a RTB based sintered magnet according to claim 1, wherein in said cutting step, the tension of said metal wire is 29.4 N or more . The RTB system sintering according to any one of claims 1 to 4, wherein the cutting speed in the direction perpendicular to the running direction of the metal wire is 100 mm / min or more and 800 mm / min or less. Method of manufacturing magnets. 6. The method for producing a RTB based sintered magnet according to claim 1 , wherein the step of preparing the powder compact includes a step of compacting the powder by wet pressing. 7. The method for producing a RTB based sintered magnet according to claim 6 , wherein said wet pressing is carried out by mixing said powder with the same kind of oil as said oil in said cutting step. The RTB based sintered magnet according to any one of claims 1 to 7 , further comprising a step of recovering particles of said powder scraped from said powder compact in said cutting step from said oil solution . manufacturing method. The metal wire used in the first treatment step and the metal wire used in the second treatment step are different,
9. The method for producing a RTB based sintered magnet according to claim 1, wherein said metal wires used in said second treatment step run in parallel.

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