Compacted body transport system and method for manufacturing rare earth sintered magnet

Abstract

To make it possible to suppress oxidation of a powder compact of an alloy for a rare-earth sinter magnet with a reduced oxygen content after press forming and to prevent deformation of the rare-earth sinter magnet.SOLUTION: A compact conveyance system comprises: a compact lined-up chamber in which a container loaded with a powder compact is kept in an inert gas atmosphere; and a mobile that transports the container loaded with teh powder compact from the compact lined-up chamber to a sinter furnace. The mobile has: a storage chamber that accommodates the container loaded with the powder compact; and a cart that moves with the storage chamber placed thereon. The storage chamber has a door, and a gas inlet tube for introducing inert gas into the storage chamber. The compact lined-up chamber has a shutter, and an intermediate chamber surrounding the shutter. The intermediate chamber is configured to connect the compact lined-up chamber and the storage chamber by an inert gas atmosphere when the shutter and the door of the storage chamber are opened.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present disclosure relates to a compact transport system and a method for producing a rare earth sintered magnet using the compact transport system. [Background technology]

[0002] RTB sintered magnets (R is at least one rare earth element and always includes Nd, and T is at least one transition metal element and always includes Fe) are known as the highest performance permanent magnets, and are used in a wide variety of applications, including voice coil motors (VCM) for hard disk drives, motors for electric vehicles (EV, HV, PHV), motors for industrial equipment, and home appliances.

[0003] RTB sintered magnets are mainly R2T 14 It consists of a main phase made of B compounds and a grain boundary phase (two-particle grain boundary or multi-point grain boundary) located at the grain boundary of this main phase. 14 B compounds are ferromagnetic materials with high saturation magnetization and anisotropic magnetic field, and form the basis of the properties of RTB-based sintered magnets.

[0004] RTB sintered magnets are manufactured, for example, through the steps of preparing alloy powder, press-molding the alloy powder to produce a powder compact, and sintering the powder compact. The alloy powder is manufactured, for example, by the following method. First, an alloy is manufactured from a molten metal of various raw material metals using a method such as the ingot method or strip casting method. The obtained alloy is subjected to a pulverization process to obtain an alloy powder with a predetermined particle size distribution. The alloy powder is compressed in a press to produce a powder compact. The powder compact is then sintered in a sintering furnace to produce a rare earth sintered magnet.

[0005] Such RTB sintered magnets have a coercive force H cJ (Hereafter, simply "H cJ") decreases, and irreversible thermal demagnetization occurs. Therefore, when used in electric vehicle motors in particular, high H cJ To maintain a higher H cJ is required.

[0006] Conventionally, H cJ To improve the remanence, large amounts of heavy rare earth elements (mainly Dy) have been added to RTB sintered magnets. r (Hereafter, simply "B r Therefore, in recent years, heavy rare earth elements have been diffused from the surface to the interior of RTB sintered magnets to concentrate the heavy rare earth elements in the outer periphery of the main phase crystal grains, thereby reducing the B r While suppressing the decline of cJ A method has been adopted to obtain

[0007] However, heavy rare earth elements such as Dy are expensive and have problems such as price fluctuations. Therefore, it is necessary to minimize the amount of heavy rare earth elements such as Dy used to improve the H content of RTB sintered magnets. cJ There is a need for technologies to improve this.

[0008] Patent Document 1 discloses that the B content is lower than that of ordinary RTB alloys, and that R2T is achieved by including one or more metal elements M selected from Al, Ga, and Cu. 17 The R2T 17 Transition metal-rich phase (R6T 13 It is described that by ensuring a sufficient volume fraction of M, it is possible to obtain an RTB rare earth sintered magnet with high coercivity while suppressing the Dy content.

[0009] In addition, H other than the method described in Patent Document 1 cJ Techniques for improving performance include, for example, making the powder particles finer and reducing the oxygen content. In addition to improving performance, RTB sintered magnets are also required to be less expensive. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] International Publication No. 2013 / 008756 Summary of the Invention [Problem to be solved by the invention]

[0011] According to the investigations of the present inventors, it has been found that when powder compacts are produced using RTB-based sintered magnet alloy powders in which the powder particles have been refined and the oxygen content has been reduced, there is a problem in that the RTB-based sintered magnets suffer from deformation such as warping after the sintering process.

[0012] Further investigation by the present inventors has revealed that deformation of RTB sintered magnets occurs when a powder compact of an RTB sintered magnet alloy that has been refined and has a reduced oxygen content is partially oxidized after press molding.

[0013] The present invention provides a new compact transport system that can solve the above problems, and a method for producing a rare earth sintered magnet using the compact transport system. [Means for solving the problem]

[0014] In an exemplary embodiment, a compact transportation system according to the present disclosure is a compact transportation system for transporting powder compacts from a powder press to a sintering furnace, the system comprising: a compact arrangement chamber for receiving an empty container for the powder compact and allowing the container containing the powder compact produced by the powder press to wait in an inert gas atmosphere; and at least one mobile body for transporting the container containing the powder compact from the compact arrangement chamber to the sintering furnace. The at least one mobile body includes a storage chamber for accommodating the container containing the powder compact and a carriage for carrying and moving the storage chamber. The storage chamber has a door that opens and closes vertically or horizontally and a gas inlet tube for introducing an inert gas into the storage chamber. The compact arrangement chamber has a shutter that opens and closes vertically or horizontally and an intermediate chamber surrounding the shutter. The intermediate chamber is configured to communicate the compact arrangement chamber and the storage chamber through an inert gas atmosphere when the shutter and the door of the storage chamber are open.

[0015] In one embodiment, the molded body arrangement chamber has a connector connected to the gas inlet tube, and an inert gas is supplied into the storage chamber through the gas inlet tube.

[0016] In one embodiment, the storage chamber has a first oxygen sensor that measures the oxygen concentration in the storage chamber and a second oxygen sensor that measures the oxygen concentration in the intermediate chamber, and the door of the storage chamber is configured not to open when the oxygen concentration in the storage chamber exceeds a first predetermined value, and the shutter of the molded body arrangement chamber is configured not to open when the oxygen concentration in the intermediate chamber exceeds a second predetermined value.

[0017] In one embodiment, after the door of the storage chamber and the shutter of the compact arrangement chamber are opened, the container loaded with the powder compacts prepared in the compact arrangement chamber is moved from the compact arrangement chamber through the intermediate chamber into the storage chamber of the moving body.

[0018] In one embodiment, the at least one movable body includes a first movable body and a second movable body that move together, and the container loaded with the powder compact prepared in the compact arrangement chamber is moved from the compact arrangement chamber through the intermediate chamber into the storage chamber of the first movable body, and then an empty container is moved from the storage chamber of the second movable body through the intermediate chamber to the compact arrangement chamber.

[0019] In one embodiment, while the empty container is moved from the storage chamber of the second moving body through the intermediate chamber to the molded body arrangement chamber, an inert gas is supplied to the storage chamber of the first moving body through the gas introduction tube.

[0020] In one embodiment, the intermediate chamber and the storage chamber are in contact with each other via a buffer material and are connected to form a space closed off from the atmosphere.

[0021] In one embodiment, the storage chamber is surrounded by an outer wall made of a transparent material, allowing the interior to be viewed from the outside.

[0022] In one embodiment, the intermediate chamber has a frame fixed to the compact arranging chamber so as to surround a shutter of the compact arranging chamber, and a gas inlet for introducing an inert gas into the intermediate chamber.

[0023] In one embodiment, the powder compact is a compact of alloy powder for a rare earth sintered magnet.

[0024] In an exemplary embodiment, the method for manufacturing a rare earth sintered magnet of the present disclosure includes a step of transporting a powder compact of an alloy for a rare earth sintered magnet, produced in a powder press, from the powder press to a sintering furnace using any of the above-mentioned compact transport systems, and a step of sintering the powder compact in the sintering furnace to produce a rare earth sintered magnet. [Effects of the Invention]

[0025] According to the embodiments of the present disclosure, it is possible to provide a new compact transport system that can suppress oxidation of powder compacts of rare earth sintered magnet alloys with reduced oxygen content after press molding and prevent deformation such as warping of the rare earth sintered magnets, and a method for manufacturing a rare earth sintered magnet using the compact transport system. [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a diagram schematically illustrating a configuration example of a molded body transport system according to an embodiment of the present disclosure. [Figure 2] FIG. 1 is a perspective view schematically illustrating a configuration example of a moving body according to an embodiment of the present disclosure. [Figure 3] FIG. 2 is a perspective view schematically illustrating an example of the configuration of a molded body arranging chamber according to an embodiment of the present disclosure. [Figure 4] 1A to 1F are diagrams illustrating a molded body transport system including a plurality of moving bodies according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0027] Hereinafter, an embodiment of a molded body transport system according to the present disclosure will be described.

[0028] Please refer to Fig. 1. Fig. 1 is a diagram schematically showing an example of the configuration of a compact transport system in this embodiment. The compact transport system 1000 in this embodiment is a compact transport system that transports powder compacts 10 from a powder press machine 100 to a sintering furnace 200. The compact transport system 1000 includes a compact arrangement chamber 300 and at least one moving body 400.

[0029] The powder press 100 is a device that, for example, compresses powder filled in a cavity of a die using an upper punch and a lower punch to produce powder compacts of various shapes. The configuration of the powder press 100 is not particularly limited and can be any. It is preferable that the powder press 100 has a configuration that can appropriately mold alloy powder for rare earth sintered magnets with a reduced oxygen content without oxidizing it.

[0030] The compact arranging chamber 300 receives empty containers 20 transported by the moving body 400. The containers 20 are, for example, box-shaped metal containers. The moving body 400 is configured to move with a plurality of containers 20 stacked on trays. The compact arranging chamber 300 preferably includes a transport unit capable of receiving a plurality of containers 20 on a tray from the moving body 400. Such a transport unit may include, for example, a configuration in which a plurality of rollers are arranged, and may be configured to move the trays carrying the containers 20 from the moving body 400 by rotating the rollers. Such containers 20 are preferably made of a high-melting-point material that can be subjected to heat treatment for sintering in the sintering furnace 200 as is. For example, a molybdenum pack may be used as the container 20.

[0031] In the compact arranging chamber 300, for example, a robot arm places the powder compacts 10 produced by the powder press 100 onto an empty container 20. In the compact arranging chamber 300, the container 20 loaded with the powder compacts 10 waits in an inert gas atmosphere. A typical example of the inert gas is nitrogen.

[0032] The mobile body 400 receives the container 20 loaded with the powder compacts 10 from the compact arrangement chamber 300 and transports it to the sintering furnace 200. The mobile body 400 may be a vehicle that is moved by being pushed by a person, or may be an automatic guided vehicle (AGV). Note that the term "unmanned" means that no person is required to steer the vehicle, and does not exclude the case where an automatic guided vehicle moves with a "person (e.g., someone who loads and unloads luggage)" on board. The AGV may be a tracked vehicle or a non-tracked vehicle.

[0033] 1 schematically shows a moving body 400 carrying a container 20 containing a powder compact 10 moving from a compact arranging chamber 300 toward a sintering furnace 200. FIG. 1 also schematically shows a moving body 400 carrying a plurality of empty containers 20 moving toward the compact arranging chamber 300. While FIG. 1 shows one moving body 400 moving, the compact transport system 1000 may have a plurality of moving bodies 400. Furthermore, the compact transport system 1000 may be configured to transport a compact from any one of a plurality of compact arranging chambers 300 to any one of a plurality of sintering furnaces 200.

[0034] Next, configuration examples of the moving body 400 and the molded body arranging chamber 300 will be described with reference to Figures 2 and 3. Figure 2 is a perspective view that schematically shows a configuration example of the moving body 400. Figure 3 is a perspective view that schematically shows a configuration example of the molded body arranging chamber 300. For reference, the figures show an X-axis, a Y-axis, and a Z-axis that are orthogonal to each other.

[0035] 2, the moving body 400 has a storage chamber 40 and a carriage 42 that moves while carrying the storage chamber 40. The storage chamber 40 has a shape and size that can accommodate the container 20 that has the powder compact 10 loaded therein. The storage chamber 40 has a door 44 that opens and closes vertically or horizontally, and a gas inlet tube 46 for introducing an inert gas into the storage chamber 40.

[0036] In a preferred embodiment, the storage chamber 40 is surrounded by an outer wall made of a transparent material, allowing the interior to be seen from the outside. For example, the storage chamber 40 may be made of a transparent synthetic resin plate such as an acrylic plate, or a glass plate. In the example of FIG. 2, the door 44 is configured to be able to open the front portion of the storage chamber 40 by moving it downward. The up and down movement of the door 44 may be driven, for example, by air pressure or an electric motor.

[0037] The compact arranging chamber 300 has a shutter 32 that opens and closes vertically or horizontally, and an intermediate chamber 34 that surrounds the shutter 32. In the example of Fig. 3, when the shutter 32 moves upward, the compact arranging chamber 300 is in an "open state," and when the shutter 32 moves downward, it is in a "closed state." In the example of Fig. 3, one compact arranging chamber 300 has two compact removal ports, each of which is provided with a shutter 32 that moves up and down. However, for ease of understanding, the left-side intermediate chamber 34 is omitted, and only the right-side intermediate chamber 34 is shown.

[0038] The intermediate chamber 34 is configured to communicate the compact arranging chamber 300 and the storage chamber 40 through an inert gas atmosphere when the shutter 32 and the door 44 of the storage chamber 40 are open. FIG. 1 also shows a state in which the movable body 400 is connected to the compact arranging chamber 300 via the intermediate chamber 34. In this state, when the shutter 32 of the compact arranging chamber 300 is opened and the door 44 of the storage chamber 40 of the movable body 400 is opened, the interior of the intermediate chamber 34 is kept isolated from the atmosphere. As a result, the inflow of oxygen-containing atmosphere into both the compact arranging chamber 300 and the storage chamber 40 of the movable body 400 is suppressed.

[0039] In a preferred embodiment, the compact arranging chamber 300 has a connector 35 that connects to a gas inlet tube 46. The compact arranging chamber 300 can supply an inert gas to the inside of the storage chamber 40 through the gas inlet tube 46.

[0040] It is preferable to have a first oxygen sensor 40S that measures the oxygen concentration inside the storage chamber 40 and a second oxygen sensor 34S that measures the oxygen concentration inside the intermediate chamber 34. The door 44 of the storage chamber 40 is configured not to be opened when the oxygen concentration inside the storage chamber 40 exceeds a first predetermined value. Furthermore, the shutter 32 of the compact arrangement chamber 300 is configured not to be opened when the oxygen concentration inside the intermediate chamber 34 exceeds a second predetermined value. The predetermined values ​​of the oxygen concentrations are, for example, 150 ppm or less in both cases.

[0041] When the moving body 400 is connected to the compact arrangement chamber 300 via the intermediate chamber 34, if the oxygen concentrations measured by the first oxygen sensor 40S and the second oxygen sensor 34S exceed the predetermined values, an inert gas such as nitrogen is supplied to the storage chamber 40 and / or the intermediate chamber 34. When the measured oxygen concentrations fall below the predetermined values, the shutter 32 and the door 44 are opened. For example, if 200 liters of nitrogen gas is supplied per minute, sufficient replacement with nitrogen gas can be completed within a few minutes, and the oxygen concentration can fall below the predetermined value. The supply rate of the inert gas can be appropriately determined depending on the volume of the space to which the gas is supplied.

[0042] To prevent atmospheric oxygen from entering the interior of the intermediate chamber 34 and the storage chamber 40, the intermediate chamber 34 and the storage chamber 40 are preferably connected to each other via a resilient buffer material such as rubber to form a space closed off from the atmosphere.

[0043] In the example shown in the figure, the intermediate chamber 34 has a frame 37 fixed to the molded body arranging chamber 300 so as to surround the shutter 32 of the molded body arranging chamber 300, and a gas inlet 38 for introducing an inert gas into the intermediate chamber 34.

[0044] After the door 44 of the storage chamber 40 and the shutter 32 of the compact arrangement chamber 300 are opened, the container 20 loaded with the powder compacts 10 prepared in the compact arrangement chamber 300 is moved from the compact arrangement chamber 300 through the intermediate chamber 34 into the storage chamber 40 of the moving body 400.

[0045] As shown in FIG. 1 , the moving body 400 carries the container 20 containing the powder compacts 10 and moves from in front of the compact arrangement chamber 300 to the position of the sintering furnace 200. It is desirable that the storage chamber 40 be airtight so that oxygen is sufficiently prevented from entering the inside of the storage chamber 40 of the moving body 400 from the atmosphere during the movement. The time required for the movement from the compact arrangement chamber 300 to the sintering furnace 200 may be, for example, about 5 to 30 minutes. If the oxygen concentration in the storage chamber 40 increases above a predetermined value during the movement, an inert gas may be supplied into the storage chamber 40 using a gas inlet tube 46 from an inert gas supply device installed in the factory.

[0046] Next, with reference to FIG. 4, an embodiment of a molded body transport system 1000 including a plurality of moving bodies 400 will be described.

[0047] In this embodiment, the plurality of moving bodies 400 includes a first moving body 400A and a second moving body 400B that move together.

[0048] In the example shown in Figure 4(a), a first movable body 400A not carrying a container 20 is positioned in front of the intended intermediate chamber 34 of the compact arranging chamber 300 in order to receive a container 20 carrying a powder compact 10 that has been prepared in the compact arranging chamber 300.

[0049] Next, as shown in Figure 4(b), the storage chamber 40 of the first movable body 400A is connected to the compact arranging chamber 300 via the intermediate chamber 34. An inert gas is supplied to the storage chamber 40 from the compact arranging chamber 300 through a gas inlet tube 46. Similarly, an inert gas is supplied to the interior of the intermediate chamber 34. When the oxygen concentrations measured by the first oxygen sensor 40S and the second oxygen sensor 34S respectively fall below a predetermined value, the shutter 32 and the door 44 are opened.

[0050] Next, as shown in Figure 4(c), the container 20 loaded with the powder compacts 10 prepared in the compact arranging chamber 300 is moved from the compact arranging chamber 300 through the intermediate chamber 34 into the storage chamber 40 of the first moving body 400A.

[0051] Next, as shown in FIG. 4(d), the container 20 containing the powder compacts 10 is moved from the compact arranging chamber 300 through the intermediate chamber 34 into the storage chamber 40 of the first mover 400A, and then the first mover 400A moves aside. The storage chamber 40 of the second mover 400B is then connected to the compact arranging chamber 300 via the intermediate chamber 34. Although not shown for simplicity, at this time, inert gas is supplied from the compact arranging chamber 300 through the gas inlet tube 46 to the storage chamber 40 of the second mover 400B. Inert gas is also supplied to the interior of the intermediate chamber 34. When the oxygen concentrations measured by the first oxygen sensor 40S and the second oxygen sensor 34S, respectively, fall below a predetermined value, the shutter 32 and the door 44 are opened.

[0052] 4(e) and 4(f), the empty container 20 is moved from the storage chamber 40 of the second mover 400B through the intermediate chamber 34 to the compact arrangement chamber 300. In this embodiment, while the empty container 20 is moved from the storage chamber 40 of the second mover 400B through the intermediate chamber 34 to the compact arrangement chamber 300, an inert gas is supplied to the storage chamber 40 of the first mover 400A through the gas introduction tube 46.

[0053] Thereafter, second moving body 400B becomes capable of receiving container 20 containing powder molded bodies 10 from molded body arranging chamber 300 in the same manner as first moving body 400A.

[0054] In FIG. 4, the left shutter of the molded body arranging chamber 300 is not in use, but as shown in FIG. 1, empty containers may be moved from the second moving body 400B through the left shutter.

[0055] The gas introduction tube 46 may also be provided in the compact arranging chamber 300. In that case, a connector is provided in the moving body 400 instead of the gas introduction tube 46. Both the compact arranging chamber 300 and the moving body 400 may be provided with the gas introduction tube 46. In that case, both gas introduction tubes 46 can be connected.

[0056] According to this embodiment, it is possible to prevent the powder compact from being partially oxidized during the process of conveying the powder compact, and to solve the problem of deformation during the sintering process.

[0057] <Manufacturing method for rare earth sintered magnets> Hereinafter, an embodiment of a method for producing an RTB based sintered magnet will be described as an embodiment of a method for producing a rare earth sintered magnet according to the present disclosure.

[0058] The RTB sintered magnet produced in this embodiment has an oxygen content of, for example, 500 ppm to 4000 ppm by mass. To obtain even better magnetic properties, the oxygen content of the RTB sintered magnet is preferably, for example, 500 ppm to 3000 ppm, and more preferably 500 ppm to 2500 ppm.

[0059] The preferred compositions of the RTB based sintered magnet are shown below.

[0060] R is a rare earth element and must include at least one selected from the group consisting of Nd, Pr, and Ce. Preferably, a combination of rare earth elements represented by Nd-Dy, Nd-Tb, Nd-Dy-Tb, Nd-Pr-Dy, Nd-Pr-Tb, or Nd-Pr-Dy-Tb is used.

[0061] Among R, Dy and Tb are particularly cJThis is effective in improving the properties of the magnet. In addition to the above elements, other rare earth elements such as La may be contained, and misch metal or didymium may also be used. Furthermore, R does not have to be a pure element, and may contain impurities unavoidable during production within the industrially available range. The R content is, for example, from 27% to 35% by mass. Preferably, the R content of the RTB based sintered magnet is 31% by mass or less (from 27% to 31% by mass, preferably from 29% to 31% by mass).

[0062] T contains iron (including when T consists essentially of iron), and up to 50% by mass of iron may be replaced with cobalt (Co) (including when T consists essentially of iron and cobalt). Co is effective in improving temperature characteristics and corrosion resistance, and the alloy powder may contain up to 10% by mass of Co. The content of T may account for the remainder of R and B, or R, B, and M, which will be described later.

[0063] The content of B may be a known content, and for example, a preferred range is 0.9% by mass to 1.2% by mass. If it is less than 0.9% by mass, high H cJ If it exceeds 1.2 mass%, B may not be obtained. r A part of B can be substituted with C (carbon). The content is more preferably 1.0 mass % or less, and even more preferably 0.96 mass % or less.

[0064] In addition to the above elements, H cJ To improve the strength, an M element can be added. 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 M element added is preferably 5.0 mass% or less. If it exceeds 5.0 mass%, B r In addition, unavoidable impurities can be tolerated.

[0065] In the R-T-B sintered magnet, the nitrogen (N) content is preferably 50 ppm or more and 600 ppm or less in terms of mass ratio. It is possible to suppress the deterioration of magnetic properties due to nitridation. The nitrogen content is more preferably 50 ppm or more and 400 ppm or less, and most preferably 100 ppm or more and 300 ppm or less. This is because it is possible to suppress the deterioration of the magnetic properties of the R-T-B sintered magnet due to nitridation while improving the pulverizability. Further, in the R-T-B sintered magnet, the carbon (C) content is preferably 80 ppm or more and 1500 ppm or less in terms of mass ratio, and more preferably 80 ppm or more and 1000 ppm or less. Furthermore, the lower limit of the C content can be 500 ppm, and can also be 800 ppm or more.

[0066] R2T which is the main phase of the R-T-B sintered magnet in the present embodiment 14 The average crystal grain size of the B phase is 2.5 μm or more and 8.0 μm or less. The average crystal grain size can be obtained by the number average of the equivalent circle diameters of crystal grains (5000 or more) evaluated by EBSD (Electron BackScatter Diffractiom).

[0067] <Example of the step of preparing the coarse pulverized powder of the alloy for the R-T-B sintered magnet> In the present embodiment, the step of preparing the coarse pulverized powder of the alloy for the R-T-B sintered magnet with an average particle size of 10 μm or more and 500 μm or less includes the step of preparing the alloy for the R-T-B sintered magnet and the step of coarsely pulverizing this alloy by, for example, the hydrogen pulverization method.

[0068] An example of the manufacturing method of the alloy for the R-T-B sintered magnet is illustrated. An alloy ingot can be obtained by the ingot casting method in which a metal or alloy previously adjusted to have the above-described composition is melted and put into a mold. Further, the molten metal is brought into contact with a single roll, double roll, rotating disk or rotating cylindrical mold, etc. and rapidly cooled, and alloy flakes can be manufactured by a rapid cooling method typified by the strip casting method or centrifugal casting method for producing a solidified alloy thinner than the alloy made by the ingot method.

[0069] In the embodiments of the present disclosure, materials produced by either the ingot method or the quenching method can be used, but production by a quenching method such as strip casting is preferred. The thickness of a quenched alloy produced by the quenching method is typically 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 that contacts the chill roll (the roll contact surface), and crystals grow columnarly from the roll contact surface in the thickness direction. Compared to alloys (ingot alloys) produced by conventional ingot casting (mold casting), quenched alloys are cooled in a shorter time, resulting in a finer structure and smaller crystal grain size. Furthermore, the grain boundary area is larger. Because the R-rich phase spreads widely within the grain boundaries, the quenching method provides excellent dispersibility of the R-rich phase. Therefore, hydrogen pulverization easily causes fracture at the grain boundaries. 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 obtained in this manner is pulverized using a jet mill.

[0070] <Example of a process for obtaining fine powder> The material to be pulverized is supplied to a jet mill and subjected to the pulverization process. The material to be pulverized is a coarsely pulverized powder of an alloy for an RTB-based sintered magnet, with an average particle size of 10 μm to 500 μm. The average particle size (d50) in this disclosure can be measured by an airflow dispersion laser diffraction method (in accordance with JIS Z 8825: 2013 revised edition). In other words, in this specification, the average particle size refers to the particle size (median diameter) at which the cumulative particle size distribution (volume basis) from the small particle size side is 50%.

[0071] The average particle size (d50) in the embodiments of the present disclosure refers to the d50 measured using a particle size distribution analyzer "HELOS&RODOS" manufactured by Sympatec under the following conditions: dispersion pressure: 4 bar, measurement range: R2, calculation mode: HRLD.

[0072] Alloy powder for RTB sintered magnets is active and easily oxidized. For this reason, the gas used in jet mills is generally a dry (high-purity) inert gas such as nitrogen, argon, or helium with a dew point of -60°C or below, in order to avoid the risk of heat generation and fire and to reduce the oxygen content as an impurity, thereby improving the performance of the magnet. Milling can also be carried out in a humidified state by intentionally introducing moisture into such an inert gas.

[0073] Examples of inert gases include nitrogen, argon, and helium, with nitrogen being the most preferred because it is available as a highly pure gas at low cost.

[0074] In the process of producing a powder compact using a press, for example, wet pressing in a magnetic field or magnetic pressing in an inert gas atmosphere can be performed to reduce oxygen, and the resulting compact can then be sintered. The average particle size of the fine powder used in the process of obtaining the fine powder is 2.0 μm or more and 6.0 μm or less. If it is less than 2.0 μm, the crushed particle size of the fine powder may be too small to prevent a decrease in crushing efficiency during jet mill crushing, while if it exceeds 6.0 μm, high magnetic properties may not be obtained. It is more preferable that the crushed particle size of the fine powder is 2.0 μm or more and 5.0 μm or less. By reducing the average particle size, it is possible to improve the magnetic properties.

[0075] <Example of powder compact manufacturing process> In a preferred embodiment, the process for producing a sintered body of fine powder includes a process for producing a powder compact from the fine powder by pressing in a magnetic field and a process for sintering the powder compact. When using a magnetic field, it is preferable to form the powder compact by pressing in an inert gas atmosphere or by wet pressing, from the viewpoint of suppressing oxidation. In particular, wet pressing coats the surfaces of the particles constituting the powder compact with a dispersant such as an oil, thereby suppressing contact with oxygen and water vapor in the atmosphere. This prevents or suppresses oxidation of the particles by the atmosphere before, during, or after the pressing process.

[0076] When wet pressing in a magnetic field is performed, a slurry is prepared by mixing a dispersion medium with fine powder, and the slurry is supplied to a cavity in a mold of a wet pressing device and press-molded in a magnetic field.

[0077] ·Dispersion medium The dispersion medium is a liquid in which the alloy powder can be dispersed to obtain a slurry.

[0078] Preferred dispersion media used in the present disclosure include mineral oils and synthetic oils. While the type of mineral oil or synthetic oil is not limited, if the kinematic viscosity at room temperature exceeds 10 cSt, the increased viscosity may strengthen the bonding strength between the alloy powders, adversely affecting the orientation of the alloy powder during wet compaction in a magnetic field. For this reason, the kinematic viscosity of the mineral oil or synthetic oil at room temperature is preferably 10 cSt or less. Furthermore, if the distillation point of the mineral oil or synthetic oil exceeds 400°C, deoiling after obtaining a compact becomes difficult, resulting in increased residual carbon in the sintered compact and possibly degrading the magnetic properties. Therefore, the distillation point of the mineral oil or synthetic oil is preferably 400°C or less. Vegetable oil may also be used as the dispersion media. Vegetable oil refers to oil extracted from plants, and the type of plant is not limited to a specific plant.

[0079] Slurry preparation The obtained alloy powder is mixed with a dispersion medium to obtain a slurry.

[0080] 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 (i.e., 70% by mass or more) in terms of mass ratio. 3This is because a flow rate of 1 / sec allows the alloy powder to be efficiently supplied into the cavity and excellent magnetic properties to be obtained. The concentration of the alloy powder in the slurry is preferably 90% or less by mass. The method for mixing the alloy powder and the dispersion medium is not particularly limited. The alloy powder and the dispersion medium may be prepared separately, and then weighed and mixed in predetermined amounts. Alternatively, when dry-pulverizing coarsely pulverized powder using a jet mill or the like to obtain alloy powder, a container containing the dispersion medium may be placed at the alloy powder outlet of the jet mill or other grinding device, and the pulverized alloy powder may be directly recovered in the dispersion medium in the container to obtain a slurry. In this case, the container is preferably also filled with a nitrogen and / or argon gas atmosphere, and the obtained alloy powder is directly recovered in the dispersion medium without being exposed to the air to form a slurry. Furthermore, it is also possible to wet-pulverize the coarsely pulverized powder in the dispersion medium using a vibrating mill, ball mill, attritor, or the like to obtain a slurry consisting of the alloy powder and the dispersion medium.

[0081] The slurry thus obtained is molded in a known wet press to obtain a molded body having a predetermined size and shape.

[0082] <Powder compact transport process> The powder compact is transported to a sintering furnace using the aforementioned embodiment of the compact transport system. According to the embodiment of the compact transport system of the present disclosure, it is possible to suppress the increase in oxygen content of the RTB based sintered magnet from the process of producing the powder compact to the sintering process to, for example, 150 ppm or less by mass, more typically 100 ppm or less.

[0083] <Sintering process> Next, the compact is sintered to obtain a rare earth sintered magnet body (sintered body).

[0084] The compact is preferably sintered at a pressure of 0.13 Pa (10 -3 Torr) or less, preferably 0.07 Pa (5.0 × 10 -4The sintering process is carried out at a temperature between 1000°C and 1150°C under a pressure of 1000 Torr or less. To prevent oxidation during sintering, residual gas in the atmosphere can be replaced with an inert gas such as helium or argon. The resulting sintered body is preferably subjected to heat treatment, which can improve its magnetic properties. Known conditions can be used for the heat treatment, such as the heat treatment temperature and time. The rare earth sintered magnet body thus obtained is then subjected to grinding and polishing, surface treatment, and magnetization, as necessary, to produce the final rare earth sintered magnet.

[0085] In a preferred embodiment, a diffusion step may be carried out in which a heavy rare-earth element RH (RH is at least one of Tb, Dy, and Ho) is diffused from the surface of the sintered body to the interior thereof. Diffusion of the heavy rare-earth element RH from the surface of the sintered body to the interior thereof can efficiently increase the coercive force.

[0086] According to this embodiment, it is possible to suppress oxidation of a powder compact of an alloy for a rare earth sintered magnet, which has a reduced oxygen content, after press molding, and to prevent deformation of the rare earth sintered magnet. [Explanation of symbols]

[0087] 10. Powder compact 20...container 32. Shutter 37...Frame body 34. Intermediate chamber 34S··Second oxygen sensor 35···Connector 38 Gas inlet 40 Storage Chamber 40S··First oxygen sensor 44 doors 46 Gas inlet tube 100···Press machine 200···Sintering furnace 300 Molded body arrangement chamber 400...Mobile 400A··First moving body 400B Second moving body

Claims

1. A compact transport system for transporting powder compacts from a powder press to a sintering furnace, comprising: a compact arrangement chamber that receives an empty container for placing the powder compact therein and keeps the container with the powder compact produced by the powder press therein waiting in an inert gas atmosphere; at least one moving body that transports the container with the powder compacts loaded therein from the compact arrangement chamber to the sintering furnace, The at least one moving body a storage chamber that accommodates the container in which the powder compact is placed; a carriage that carries the storage chamber and moves; The storage chamber has a door that opens and closes vertically or horizontally, and a gas introduction tube for introducing an inert gas into the storage chamber, The molded body arranging chamber is A shutter that opens and closes vertically or horizontally; an intermediate chamber surrounding the shutter; the intermediate chamber is configured to communicate the molded body arrangement chamber and the storage chamber with an inert gas atmosphere when the shutter and the door of the storage chamber are open, The compact arranging chamber has a connector connected to the gas inlet tube, and an inert gas is supplied into the storage chamber through the gas inlet tube.

2. A compact transport system for transporting powder compacts from a powder press to a sintering furnace, comprising: a compact arrangement chamber that receives an empty container for placing the powder compact therein and keeps the container with the powder compact produced by the powder press therein waiting in an inert gas atmosphere; at least one moving body that transports the container with the powder compacts loaded therein from the compact arrangement chamber to the sintering furnace, The at least one moving body a storage chamber that accommodates the container in which the powder compact is placed; a carriage that carries the storage chamber and moves; The storage chamber has a door that opens and closes vertically or horizontally, and a gas introduction tube for introducing an inert gas into the storage chamber, The molded body arranging chamber is A shutter that opens and closes vertically or horizontally; an intermediate chamber surrounding the shutter; the intermediate chamber is configured to communicate the molded body arrangement chamber and the storage chamber with an inert gas atmosphere when the shutter and the door of the storage chamber are open, a first oxygen sensor for measuring an oxygen concentration within the storage chamber; a second oxygen sensor that measures the oxygen concentration in the intermediate chamber; the door of the storage chamber is configured not to be opened when the oxygen concentration in the storage chamber exceeds a first predetermined value; The molded body transport system is configured so that the shutter of the molded body arranging chamber will not open when the oxygen concentration in the intermediate chamber exceeds a second predetermined value.

3. A compact transport system for transporting powder compacts from a powder press to a sintering furnace, comprising: a compact arrangement chamber that receives an empty container for placing the powder compact therein and keeps the container with the powder compact produced by the powder press therein waiting in an inert gas atmosphere; at least one moving body that transports the container with the powder compacts loaded therein from the compact arrangement chamber to the sintering furnace, The at least one moving body a storage chamber that accommodates the container in which the powder compact is placed; a carriage that carries the storage chamber and moves; The storage chamber has a door that opens and closes vertically or horizontally, and a gas introduction tube for introducing an inert gas into the storage chamber, The molded body arranging chamber is A shutter that opens and closes vertically or horizontally; an intermediate chamber surrounding the shutter; the intermediate chamber is configured to communicate the molded body arrangement chamber and the storage chamber with an inert gas atmosphere when the shutter and the door of the storage chamber are open, A molded body transport system in which, after the door of the storage chamber and the shutter of the molded body arrangement chamber are opened, the container loaded with the powder molded body prepared in the molded body arrangement chamber is moved from the molded body arrangement chamber through the intermediate chamber and into the storage chamber of the moving body.

4. A compact transport system for transporting powder compacts from a powder press to a sintering furnace, comprising: a compact arrangement chamber that receives an empty container for placing the powder compact therein and keeps the container with the powder compact produced by the powder press therein waiting in an inert gas atmosphere; at least one moving body that transports the container with the powder compacts loaded therein from the compact arrangement chamber to the sintering furnace, The at least one moving body a storage chamber that accommodates the container in which the powder compact is placed; a carriage that carries the storage chamber and moves; The storage chamber has a door that opens and closes vertically or horizontally, and a gas introduction tube for introducing an inert gas into the storage chamber, The molded body arranging chamber is A shutter that opens and closes vertically or horizontally; an intermediate chamber surrounding the shutter; the intermediate chamber is configured to communicate the molded body arrangement chamber and the storage chamber with an inert gas atmosphere when the shutter and the door of the storage chamber are open, the at least one moving body includes a first moving body and a second moving body that move together; After the container loaded with the powder compacts prepared in the compact arranging chamber is moved from the compact arranging chamber through the intermediate chamber into the storage chamber of the first moving body, A molded body transport system, wherein empty containers are moved from the storage chamber of the second moving body through the intermediate chamber to the molded body arranging chamber.

5. 5. The molded body transport system according to claim 4, wherein an inert gas is supplied to the storage chamber of the first movable body through the gas inlet tube while the empty container is moved from the storage chamber of the second movable body through the intermediate chamber to the molded body arrangement chamber.

6. A compact transport system for transporting powder compacts from a powder press to a sintering furnace, comprising: a compact arrangement chamber that receives an empty container for placing the powder compact therein and keeps the container with the powder compact produced by the powder press therein waiting in an inert gas atmosphere; at least one moving body that transports the container with the powder compacts loaded therein from the compact arrangement chamber to the sintering furnace, The at least one moving body a storage chamber that accommodates the container in which the powder compact is placed; a carriage that carries the storage chamber and moves; The storage chamber has a door that opens and closes vertically or horizontally, and a gas introduction tube for introducing an inert gas into the storage chamber, The molded body arranging chamber is A shutter that opens and closes vertically or horizontally; an intermediate chamber surrounding the shutter; the intermediate chamber is configured to communicate the molded body arrangement chamber and the storage chamber with an inert gas atmosphere when the shutter and the door of the storage chamber are open, A molded body transport system, wherein the intermediate chamber and the storage chamber are in contact with each other via a buffer material and are connected to form a space closed off from the atmosphere.

7. A compact transport system for transporting powder compacts from a powder press to a sintering furnace, comprising: a compact arrangement chamber that receives an empty container for placing the powder compact therein and keeps the container with the powder compact produced by the powder press therein waiting in an inert gas atmosphere; at least one moving body that transports the container with the powder compacts loaded therein from the compact arrangement chamber to the sintering furnace, The at least one moving body a storage chamber that accommodates the container in which the powder compact is placed; a carriage that carries the storage chamber and moves; The storage chamber has a door that opens and closes vertically or horizontally, and a gas introduction tube for introducing an inert gas into the storage chamber, The molded body arranging chamber is A shutter that opens and closes vertically or horizontally; an intermediate chamber surrounding the shutter; the intermediate chamber is configured to communicate the molded body arrangement chamber and the storage chamber with an inert gas atmosphere when the shutter and the door of the storage chamber are open, The storage chamber is surrounded by an outer wall made of a transparent material, making it possible to see the inside of the storage chamber from the outside.

8. A compact transport system for transporting powder compacts from a powder press to a sintering furnace, comprising: a compact arrangement chamber that receives an empty container for placing the powder compact therein and keeps the container with the powder compact produced by the powder press therein waiting in an inert gas atmosphere; at least one moving body that transports the container with the powder compacts loaded therein from the compact arrangement chamber to the sintering furnace, The at least one moving body a storage chamber that accommodates the container in which the powder compact is placed; a carriage that carries the storage chamber and moves; The storage chamber has a door that opens and closes vertically or horizontally, and a gas introduction tube for introducing an inert gas into the storage chamber, The molded body arranging chamber is A shutter that opens and closes vertically or horizontally; an intermediate chamber surrounding the shutter; the intermediate chamber is configured to communicate the molded body arrangement chamber and the storage chamber with an inert gas atmosphere when the shutter and the door of the storage chamber are open, The intermediate chamber is a frame fixed to the compact arranging chamber so as to surround the shutter of the compact arranging chamber; a gas inlet for introducing an inert gas into the intermediate chamber; A compact transport system comprising:

9. The compact transport system according to claim 1 , wherein the powder compact is a compact of alloy powder for a rare earth sintered magnet.

10. a step of transporting a powder compact of an alloy for a rare earth sintered magnet, produced by a powder press, from the powder press to a sintering furnace by using the compact transport system according to any one of claims 1 to 9; sintering the powder compact in the sintering furnace to produce a rare earth sintered magnet; A method for producing a rare earth sintered magnet, comprising:

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