JP2006286859A - Manufacturing method for rare-earth magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain raw-material alloy fine powder having low oxygen contents for high magnetic characteristics while easily handling raw-material alloy fine powder (residual powder) remaining in a crushing system. <P>SOLUTION: In a manufacturing method for a rare-earth magnet, raw-material alloy coarse powder is air-current crushed in a closed circuit for the crushing system, and raw-material alloy fine powder is manufactured. In the manufacturing method, raw-material alloy coarse powder is air-current crushed under the state in which an oxygen concentration in the closed circuit is held at a value less than 0.2%, raw-material alloy fine powder is recovered, and the oxygen concentration in the closed circuit is held for a fixed time in 0.8 to 2.0%. The oxygen concentration in the closed circuit is held for the fixed time in 0.8 to 2.0%, and the closed circuit is opened to an atmospheric air. Alternatively, the oxygen concentration in the closed circuit is held for the fixed time in 0.8 to 2.0%, and the next raw-material alloy coarse powder is air-current crushed under the state in which the oxygen concentration in the closed circuit is held in 0.2 to 0.5% without opening the closed circuit to the atmospheric air. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a rare earth magnet in which raw material alloy coarse powder is air-flow pulverized in a closed circuit of a pulverization system to produce raw material alloy fine powder.

  For example, an R—T—B system such as an Nd—Fe—B magnet (R is at least one selected from Y and rare earth elements. T is essential for Fe, and other transition metal elements are added as necessary. In recent years, the demand for sintered magnets has been increasing due to the advantages such as excellent magnetic properties, Nd, which is a main component, and a relatively low price. It is in. Under these circumstances, research and development for improving the magnetic properties of RTB-based sintered magnets and improvement of manufacturing methods for manufacturing high-quality rare-earth sintered magnets have been promoted in various fields. ing.

  As a method for producing a rare earth sintered magnet, a powder metallurgy method is generally used, and a process including melting, casting, alloy lump coarse pulverization, fine pulverization, press molding, and sintering is widely applied. Specifically, the raw material alloy is coarsely pulverized and finely pulverized, then pressure-formed in a magnetic field, and sintered and heat-treated to obtain a magnet body.

  Of these, in the fine pulverization treatment, in order to reduce the activity of the powder and make it easy to handle, a small amount of oxygen is often introduced into the inert gas such as nitrogen as the pulverization gas.

As a pulverization apparatus for introducing oxygen gas into the system, for example, Patent Document 1 proposes a closed circuit pulverization apparatus that sets the oxygen concentration in the closed circuit to 0.5 to 2.0%. According to the invention of Patent Document 1, a layer having low combustion activity is formed in advance only on the surface of the object to be processed by mixing a component adjustment gas such as an oxygen-containing gas into the closed circuit, and the object to be processed is It is said that the object to be treated can be prevented from being oxidized or burned when taken out into the atmosphere.
JP-A-11-156224

  In recent years, there has been a demand for higher magnetic properties, and in order to cope with this, it is necessary to further reduce oxygen in the alloy powder used. As described in Patent Document 1, when oxygen gas is supplied and the alloy powder is oxidized, the magnetic properties are deteriorated. Therefore, in the future, the oxygen concentration in the closed circuit is not supplied in the closed circuit. It is desirable to perform pulverization in an atmosphere in which is approximately zero (for example, less than 0.2%). Since the powder obtained by pulverization is hardly oxidized, it is preferable in terms of obtaining a raw material alloy fine powder having high magnetic properties.

  However, the raw material alloy fine powder having a low oxygen content tends to adhere very much to the fine powder or to a pulverizer, a pipe wall, etc. inside the closed circuit because of its high activity. Moreover, if the raw material alloy fine powder having a low oxygen content adheres to a pulverizer, a piping wall, etc., it will be very difficult to drop off from the piping wall after that. Further, fine powder remains in a dead space such as a narrow portion or a bent portion of a pulverizer or a piping wall. For this reason, a small amount of raw material alloy fine powder remains in the closed circuit after pulverization and recovery. The raw material alloy fine powder (hereinafter referred to as residual powder) remaining in the system without being collected in a hopper or collection storage container has a low oxygen content and high activity. If the closed circuit is opened to the atmosphere immediately after completion of pulverization and collection for the purpose of replacement or manual removal of residual powder, etc., it may react with oxygen in the atmosphere and cause heat generation and ignition due to oxidation.

  Further, even if the closed circuit is not immediately opened to the atmosphere after pulverization and recovery, the raw material alloy fine powder remaining in the pulverization system causes the following problems. Specifically, there is a problem when the high magnetic property material is pulverized and the normal magnetic property material having lower magnetic properties is sequentially pulverized. In this case, the raw material alloy fine powder obtained by pulverization under a medium oxygen concentration atmosphere (for example, 0.2% to 0.5%) is mixed with the raw material alloy coarse powder under a low oxygen concentration atmosphere (for example, less than 0.2%). Residual powder is mixed during grinding. Since the alloy powder pulverized in the above-mentioned medium oxygen concentration atmosphere is usually stable in the air, the forming process and the like are performed in the air. Therefore, if a low oxygen content alloy powder (residual powder) is mixed in this, it reacts with oxygen in the atmosphere, leading to heat generation and ignition due to oxidation of the compact or raw material alloy fine powder. The raw material alloy fine powder after heat generation and ignition has a markedly increased oxygen content, which adversely affects the magnetic properties of the rare earth magnet formed and sintered.

  The present invention has been proposed in view of such a conventional situation, and obtains a raw material alloy fine powder having a low oxygen content for high magnetic properties and a raw material alloy fine powder (residual powder) remaining in the grinding system. An object of the present invention is to provide a method for producing a rare earth magnet that can be easily handled.

  In order to solve the above-mentioned problems, a method for producing a rare earth magnet according to the present invention is a method for producing a rare earth magnet in which raw material alloy coarse powder is air-flow crushed in a closed circuit of a grinding system to produce raw material alloy fine powder. The raw material alloy coarse powder is air-flow pulverized and collected in a state where the oxygen concentration in the closed circuit is kept below 0.2%, and then the oxygen concentration in the atmosphere is set to 0.8% to 2.0%. It is characterized by holding time.

  In the method for producing a rare earth magnet as described above, after pulverization in a low oxygen concentration atmosphere of less than 0.2%, the raw material alloy fine powder having a low oxygen content obtained as a result of pulverization is recovered, and then the oxygen in the closed circuit is recovered. By setting the atmosphere to a high oxygen concentration concentration of 0.8% to 2.0%, for example, the raw material alloy fine powder (residual powder) that remains on the closed circuit after adhering to the piping wall or pulverizer, etc. is gradually oxidized and stabilized. Turn into. Therefore, even if the remaining raw material alloy fine powder (residual powder) is taken out into the atmosphere after that, the raw material alloy fine powder (residual powder) is stably present without heat generation and ignition due to oxidation.

  In addition, in the said patent document 1, the timing which introduce | transduces a component adjustment gas (oxygen containing gas) in a closed circuit is not considered at all, and the whole quantity of the raw material alloy powder which is a to-be-processed object is gradually oxidized. In this case, the amount of oxygen contained in the raw material alloy powder increases, and as a result, only rare earth magnets with low magnetic properties can be obtained.

  In contrast, in the present invention, most of the raw material alloy fine powder is collected before the slow oxidation, and the recovered raw material alloy fine powder is not brought into contact with a high oxygen concentration atmosphere of 0.8% to 2.0%. That is, only residual powder is gradually oxidized. Therefore, in most raw material alloy fine powders that are raw materials for rare earth magnets, a low oxygen content is maintained, and high magnetic properties are realized when used in magnets.

  According to the method for producing a rare earth magnet according to the present invention, it is possible to produce a rare earth magnet having high magnetic properties using a raw material alloy fine powder having a low oxygen content, and the raw material alloy fine powder (residual powder) remaining in the grinding system. Can be handled easily.

  Hereinafter, a method for producing a rare earth magnet to which the present invention is applied will be described in detail with reference to the drawings.

First, an outline of a rare earth magnet to be manufactured according to the present invention will be described.
Rare earth magnets, especially rare earth sintered magnets, are mainly composed of rare earth elements and transition metal elements. Here, the magnet composition (alloy composition) may be arbitrarily selected according to the purpose. For example, R-T-B (R is a concept including one or more rare earth elements, where the rare earth element includes Y. T is one or two of transition metal elements essential for Fe or Fe and Co. In order to obtain a rare earth sintered magnet having excellent magnetic properties, the rare earth element R is 20 to 20 in the magnet composition after sintering. It is preferable that the composition be 40 mass%, boron B is 0.5 to 4.5 mass%, and the balance is the transition metal element T. Here, R is one or more selected from rare earth elements, that is, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, and Lu. Especially, since Nd is abundant in resources and relatively inexpensive, the main component is preferably Nd. Further, the inclusion of Dy is effective in improving the coercive force Hcj because it increases the anisotropic magnetic field.

  Alternatively, the additive element M can be added to form an R-T-B-M rare earth sintered magnet. In this case, examples of the additive element M include Al, Cr, Mn, Mg, Si, Cu, C, Nb, Sn, W, V, Zr, Ti, Mo, Bi, and Ga. A seed | species or 2 or more types can be selected and added. The addition amount of these additive elements M is preferably 3% by mass or less in consideration of magnetic characteristics such as residual magnetic flux density. If the amount of additive element M added is too large, the magnetic properties may be deteriorated.

  Of course, it is needless to say that the present invention is not limited to these compositions, and can be applied to all known compositions as rare earth sintered magnets.

  Powder metallurgy is used to manufacture the aforementioned rare earth sintered magnet. The manufacturing process of rare earth sintered magnets by powder metallurgy is basically an alloying process, coarse pulverization process, fine pulverization process, magnetic field forming process, sintering process, aging process, processing process, and surface treatment process. Consists of. In order to prevent oxidation, most of the steps until aging are performed in a vacuum or in a non-oxidizing gas atmosphere (in a nitrogen atmosphere, an Ar atmosphere, etc.).

  In the alloying step, a raw material metal or alloy is blended in accordance with the magnet composition, melted in a vacuum or an inert gas, for example, Ar atmosphere, and cast into an alloy. As a casting method, a strip casting method (continuous casting method) in which molten high-temperature liquid metal is supplied onto a rotating roll and an alloy thin plate is continuously cast is preferable from the viewpoint of productivity and the like, but is not limited thereto. It is not a thing. As the raw material metal (alloy), pure rare earth elements, rare earth alloys, pure iron, ferroboron, and alloys thereof can be used.

  As the alloy, a single alloy having almost the final magnet composition may be used, or a plurality of types of alloys having different compositions may be mixed so as to have the final magnet composition. Mixing may be performed in any process of alloy, raw material coarse powder, and raw material fine powder.

  In the coarse pulverization step, first, a cast raw alloy sheet or ingot is pulverized to some extent to form an alloy lump and used for hydrogen storage. Although there is no restriction | limiting in particular in the dimension and shape of an alloy lump, It is preferable to set it as about 5-50 mm square. This pulverization may be performed by, for example, a jaw crusher.

  In the coarse pulverization step, hydrogen is occluded in the alloy lump and pulverization is performed. When hydrogen is occluded in the raw material alloy lump, the hydrogen occlusion amount differs depending on the phase, and pulverization proceeds from the surface in a self-destructive manner. In the coarse pulverization step, heat treatment is generally performed after the hydrogen storage treatment. Further, mechanical grinding such as a disk mill may be performed.

  After the coarse pulverization step is completed, a pulverization aid is usually added to the coarsely pulverized raw material alloy coarse powder. As the grinding aid, for example, additives such as fatty acid compounds such as zinc stearate and oleic acid amide or metal soap can be used. In particular, by using fatty acid amide as the grinding aid, good magnetic properties can be obtained. It is possible to obtain a rare earth sintered magnet having The addition amount of the grinding aid is preferably about 0.01 to 0.3% by mass. When the grinding aid is added within this range, the amount of residual carbon after sintering can be suppressed, which is effective in improving the magnetic properties of the rare earth sintered magnet.

  After the coarse pulverization step, a fine pulverization step is performed. The fine pulverization step is performed by airflow pulverization using an airflow pulverizer such as a jet mill in a pulverization system as described later. The conditions at the time of pulverization may be appropriately set according to the airflow pulverizer used, etc., but in the present invention, in order to obtain a raw material alloy fine powder having a low oxygen content for high magnetic properties, The oxygen concentration is controlled to less than 0.2%. The raw material alloy coarse powder is finely pulverized until the average particle size becomes about 1 to 10 μm, for example, 3 to 6 μm. The jet mill opens a high-pressure inert gas (for example, nitrogen gas) from a narrow nozzle to generate a high-speed gas flow, and the high-speed carrier gas flow accelerates the powder particles. This is a method of generating a collision and a collision with a collision plate or a container wall and crushing. Jet mills are generally classified according to an air flow generation method such as a jet mill using a fluidized bed or a jet mill using a vortex, or by an action or mechanism such as a jet mill using a collision plate. The pulverized particle size and the like are set and controlled according to the combination and conditions of the airflow generation method and the action substance.

  After the pulverization step, the raw material alloy fine powder is formed in the magnetic field in the magnetic field forming step. Specifically, the raw material alloy fine powder obtained in the fine pulverization step is filled in a mold in which an electromagnet is arranged, and is molded in a magnetic field in a state where crystal axes are oriented by applying a magnetic field. Forming in a magnetic field may be either longitudinal magnetic field shaping in which a parallel magnetic field is applied in the pressing direction or transverse magnetic field shaping in which a vertical magnetic field is applied in the pressing direction. The forming in the magnetic field may be performed at a pressure of about 50 to 260 MPa in a magnetic field of 400 to 1600 kA / m, for example. For the magnetic field orientation, a pulse magnetic field may be used, or a combination of a static magnetic field and a pulse magnetic field may be used. The pulse magnetic field is preferably 2400 kA / m or more.

  Since fine pulverization is performed by controlling the oxygen concentration in the atmosphere to less than 0.2%, the obtained raw material alloy fine powder has a low oxygen content and a high activity. Therefore, in the present invention, it is desirable to perform the forming step in a magnetic field in a low oxygen concentration atmosphere of, for example, less than 0.2%.

  Next, in the sintering process / aging process, sintering and aging treatment are performed. That is, in the sintering step, after the raw material alloy fine powder is formed in a magnetic field, the formed body is sintered in a vacuum or an inert gas atmosphere. Although it is necessary to adjust sintering temperature by various conditions, such as a composition, a grinding | pulverization method, and the difference of a particle size and a particle size distribution, for example, what is necessary is just to sinter at 1000-1150 degreeC for about 5 hours. After sintering, the obtained sintered body is preferably subjected to aging treatment. This aging step is an important step in controlling the coercive force Hcj of the obtained rare earth sintered magnet. For example, an aging treatment is performed in an inert gas atmosphere or in a vacuum. As the aging treatment, a two-stage aging treatment is preferable, and in the first aging treatment step, the temperature is maintained at a temperature of about 800 ° C. for 1 to 3 hours. Then, the 1st cooling process cooled to the range of room temperature-200 degreeC is provided. In the second stage aging treatment step, the temperature is maintained at about 550 ° C. for 1 to 3 hours. Next, a second cooling step for cooling to room temperature is provided. Since the coercive force Hcj is greatly increased by heat treatment at around 600 ° C., when aging treatment is performed in a single stage, it is advisable to perform aging treatment at around 600 ° C.

  After the sintering step and the aging step, a processing step and a surface treatment step are performed. The processing step is a step of mechanically processing the obtained sintered body into a desired shape by cutting, grinding, polishing, or the like. The surface treatment process is a process performed to suppress oxidation, cracking, cracking, etc. of the obtained rare earth sintered magnet, or to improve adhesiveness. For example, a plating film or a resin film is applied to the surface of the rare earth sintered magnet. To form. In addition, after the sintering step, a processing step may be performed, and an aging step and a surface treatment step may be performed.

  Hereinafter, the pulverization system used in the fine pulverization step will be described with reference to FIG.

  The pulverization system shown in FIG. 1 is a feeder (supply device) 10 for supplying raw material alloy coarse powder into a system (closed circuit) L of the pulverization system, and the raw material alloy coarse powder fed from the feeder 10 is conveyed by a carrier gas. Then, the pulverizer (airflow pulverizer) 20 for pulverization, and the raw material alloy fine powder (pulverized product) pulverized by the pulverizer 20 are recovered by the cyclone 30 and the cyclone 30 for recovering those having a particle diameter in a predetermined range. The hopper 40 for storing the raw material alloy fine powder, and the mixer for uniformly stirring and mixing the raw material alloy fine powder pulverized in the initial stage and the raw material alloy fine powder pulverized in the final stage after being accommodated in the hopper 40 50, a collection storage container 51 for taking out the raw material alloy fine powder stirred and mixed by the mixer 50 out of the system L, a bag filter for collecting the raw material alloy fine powder not recovered by the cyclone 30 ( Collecting device) 60 and after filter 61, is circulated back to the crusher 20 the carrier gas passed through the after-filter 61, a low-pressure tank 62 to the closed circuit system L, and a compressor 63 and a high pressure tank 64.

  The pulverization system includes an inert gas supply device 71 that supplies an inert gas such as nitrogen gas into the system L, an oxygen-containing gas supply device 72 that supplies oxygen gas into the system L, an inert gas and an oxygen-containing gas. And a gas mixer 73 for mixing the two. Note that each gas may be individually supplied into the system L by the inert gas supply device 71 and the oxygen-containing gas supply device 72 without providing the gas mixer 73. Further, the pulverization system includes an oxygen concentration meter 74 that measures the oxygen concentration in the gas mixer 73 and a gas recovery tank 75 that recovers the gas in the system L. Further, the pulverization system includes an on-line particle size distribution measuring device 80 for measuring the particle size distribution of the fine powder collected by the cyclone 30.

  The pulverizer 20 shown in FIG. 1 is a jet mill. The pulverizer 20 is a so-called vertical pulverizer, and includes an outer cylinder (container) 21 having an axial line in the vertical direction, an inner cylinder 22 provided along the axial direction of the outer cylinder 21, and an outer cylinder 21. An ejector nozzle (not shown) provided at the bottom and an impact plate 23 of the inner cylinder 22 attached to the inner diameter side of the inner cylinder 22 are provided. In the outer cylinder 21, a classification rotor 24 for classifying the pulverized raw material alloy fine powder is provided above the upper end portion of the inner cylinder 22. The classification rotor 24 has a cylindrical shape having an axis in a substantially horizontal direction (a direction substantially orthogonal to the flow of the raw material alloy fine powder in the pulverizer), and a plurality of slits having a predetermined width are formed on the outer peripheral surface thereof. A drive motor (not shown) provided outside the outer cylinder 21 is driven to rotate around its axis. Further, on the side of the classification rotor 24, there is provided a fine powder transport pipe (discharge unit) 25 that communicates with the internal space of the classification rotor 24 and feeds the classified raw material alloy fine powder to the cyclone 30.

  The raw material alloy coarse powder fed from the feeder 10 through the pipe 11 and introduced into the outer cylinder 21 is ejected together with the carrier gas from the ejector nozzle, and hits the collision plate 23 and is pulverized. The raw material alloy fine powder obtained as a result of the pulverization rises with the flow of the carrier gas and is classified in the classification rotor 24. Only the raw material alloy fine powder of a predetermined size or less that has passed through the slit of the classification rotor 24 is sent to the cyclone 30 through the fine powder conveyance pipe 25, while the remaining raw material alloy fine powder passes through the gap between the outer cylinder 21 and the inner cylinder 22. It falls and circulates in the grinder 20 again.

  The raw material alloy fine powder obtained by pulverization by the pulverizer 20 is further collected in the cyclone 30 based on the weight, and further in a predetermined particle size range, and is collected by the hopper 40 via the pipe 31.

  A pipe 31 for supplying raw material alloy fine powder from the cyclone 30 to the hopper 40 is provided with a double damper 41 provided with a damper that can be opened and closed in two stages. By appropriately operating the double damper 41, the gas pressure in the system L and the hopper 40 can be shut off. Further, the pulverization system includes a valve 43 on the inlet side of the hopper 40, and the valve 43 can block the gas flow between the system L and the hopper 40. The raw material alloy fine powder collected in the hopper 40 is fed into the mixer 50 via the pipe 42.

  The raw material alloy fine powder stirred and mixed by the mixer 50 is sent to the recovery storage container 51, taken out of the system L by closing the valve of the recovery storage container 51, and supplied to the forming step in the magnetic field. When the raw material alloy fine powder fed into the collection storage container 51 is taken out from the system L, the valve of the pipe 42 is closed to prevent air from entering the system L and maintain the atmosphere of the system L at a predetermined oxygen concentration. be able to. The pulverization system includes a plurality of collection storage containers 51 and is configured to be able to replace the collection storage container 51 at an arbitrary timing (for example, for each lot). In FIG. 1, only one collection storage container 51 is illustrated.

  The pipe 31 is provided with a particle size distribution measuring device 80 for measuring the particle size distribution of the raw material alloy fine powder recovered by the cyclone 30. The particle size distribution measuring apparatus 80 irradiates a sampling tube (flow path) 81 connected to an opening (not shown) opened on the wall surface of the pipe 31 and a laser beam or the like into the sampling tube 81 to adjust the transmission degree. A measuring device main body (particle size distribution measuring meter) 82 that measures the particle size distribution based on this and a cyclone 83 that recovers the raw material alloy fine powder that has passed through the measuring device main body 82 are provided. The particle size distribution measuring apparatus 80 is not limited to the form in which the sampling pipe 81 is provided between the pipe 31 and the cyclone 83 as shown in FIG. 1, and any form can be used as long as the raw material alloy fine powder can be sampled. It may be. For example, the particle size distribution measuring device 80 may be in a form that branches from the fine powder conveyance pipe 25 and reaches the cyclone 30.

  A gas supply pipe 76 for supplying an inert gas mixed by the gas mixer 73 is connected to the pipe 65 connecting the low pressure tank 62 and the compressor 63. Gases respectively supplied from the inert gas supply device 71 and the oxygen-containing gas supply device 72 are adjusted to a desired oxygen content or the like by the gas mixer 73 and then passed through the gas supply pipe 76 to the pipe 65 (system L). Inside). The inert gas supply device 71 and the oxygen-containing gas supply device 72 may be directly supplied to the pipe 65 without providing the gas mixer 73. The oxygen concentration meter 74 measures the oxygen concentration in the gas mixer 73. In FIG. 1, an example in which the gas mixer 73 is provided with the oxygen concentration meter 74 is illustrated, but the pulverization system may be configured to include a plurality of oxygen concentration meters 74 in each part of the system L. By doing so, it becomes easy to confirm that the desired oxygen content is adjusted. The same applies to the case where the inert gas supply device 71 and the oxygen-containing gas supply device 72 are directly supplied to the pipe 65 without providing the gas mixer 73. Valves 77 and 78 are provided on the piping between the low-pressure tank 62 and the gas recovery tank 75 and between the high-pressure tank 64 and the gas recovery tank 75, respectively.

  In order to finely pulverize the raw material alloy coarse powder using the pulverization system having the above configuration, first, the gas supplied from the inert gas supply device 71, the oxygen-containing gas supply device 72, etc. is supplied from the feeder 10 as the carrier gas. The raw material alloy coarse powder is pulverized by airflow in a pulverizer 20. Thereafter, the raw material alloy fine powder having a predetermined particle size is recovered from the pulverized product via the classifying rotor 24 and the cyclone 30 and stored in the hopper 40 or the recovery storage container 51. During this pulverization step, the oxygen concentration of the atmosphere in the system L is kept below 0.2%.

  By the way, it is desirable that the entire amount of the raw material alloy coarse powder charged into the system L from the feeder 10 is recovered as the raw material alloy fine powder in the recovery storage container 51, but actually, in the pulverization system after the recovery operation (for example, the system L Some amount of the raw material alloy fine powder remains as residual powder on the piping wall, the inside of the crusher 20, the inside of the cyclone 30, and the like. Since the oxygen concentration in the system L is less than 0.2%, the oxygen content of the residual powder is very low, and when taken out into the atmosphere, it reacts violently with the oxygen in the atmosphere and oxidizes, generating heat. ·set a fire.

  Therefore, in the present invention, for the purpose of suppressing heat generation and ignition when the residual powder in the system L is taken out, the oxygen concentration in the system L is maintained at 0.8% to 2.0% for a predetermined time, Slow oxidation. Specifically, after collecting most of the raw material alloy fine powder from the system L in the recovery storage container 51, the flow of gas to the recovery storage container 51 is blocked by closing the pipe 42 or the valve of the recovery storage container 51. State. Further, by closing the valve 43 on the inlet side of the hopper 40, the gas flow to the hopper 40, the mixer 50, and the collection storage container 51 may be blocked. In this state, by operating the inert gas supply device 71, the oxygen-containing gas supply device 72, and the gas mixer 73, the oxygen concentration in the system L is increased to 0.8% to 2.0% and held for a predetermined time. To do. By this operation, the residual powder in the system L is gradually oxidized and stabilized, and the handling in the atmosphere becomes easy.

  On the other hand, most of the raw material alloy fine powder collected earlier is contained in a space (recovery storage container 51) that is shut off from the system L by closing the valve 43 and the valve of the recovery storage container 51. No contact with 0.8% to 2.0% atmosphere. That is, most of the raw material alloy fine powder maintains a low oxygen content without being gradually oxidized. Therefore, a rare earth magnet exhibiting high magnetic properties can be produced by using the raw material alloy fine powder collected in the collection storage container 51 as the raw material powder of the rare earth magnet.

  In order to gradually oxidize the residual powder in the system L, it is necessary to increase the oxygen concentration in the atmosphere in the system L to 0.8% to 2.0%. When the amount is less than the above range, there is a problem that it takes a long time to slowly oxidize the residual powder, or the gradual oxidation of the residual powder becomes insufficient, which causes oxidation in the atmosphere, heat generation and ignition. On the other hand, when the above range is exceeded, there is a risk that the oxidation reaction of the residual powder proceeds rapidly in the system L and heat generation / ignition occurs. Also, when the oxygen concentration of the slow oxidation exceeds the above range, when reducing the oxygen concentration in the system L for the purpose of performing the next pulverization, it takes a long time to reduce to the desired oxygen concentration, and the production efficiency is reduced. There is a risk of lowering.

  The time for maintaining the oxygen concentration in the atmosphere in the system L at 0.8% to 2.0% may be set to a time during which the residual powder is oxidized to the extent that the residual powder does not generate heat or ignite in the atmosphere. For example, it can be 20 minutes to 180 minutes. Although depending on the scale of the system L, it may be about 20 minutes to 150 minutes if the atmosphere is set to efficient gradual oxidation conditions.

  The system L may be opened to the atmosphere after the residual powder is gradually oxidized as described above. Heat generation and ignition of residual powder in the atmosphere are suppressed, so system L such as inspection work and parts replacement work of each part of the grinding system or mechanical removal work of residual powder in system L is opened to the atmosphere. The work to be performed can be easily performed without requiring special safety equipment.

  Further, after the residual powder is gradually oxidized as described above, the next raw material alloy coarse powder may be finely pulverized using a pulverization system without opening the system L to the atmosphere. If the residual powder is gradually oxidized before the next fine pulverization, the pulverization of the material for high magnetic properties (the oxygen concentration in the atmosphere is less than 0.2%) and the next raw material alloy coarse powder by one pulverization system Even when the material for normal magnetic properties is continuously pulverized (oxygen concentration in atmosphere is 0.2% to 0.5%), the raw material alloy fine powder resulting from the mixing of low oxygen residual powder or Heat generation and ignition of the molded body can be suppressed.

  Since the oxygen content of the gradually oxidized residual powder is about 3000 ppm to 6000 ppm, a raw material alloy for pulverization in a medium oxygen concentration atmosphere (for example, 0.2% to 0.5%) mixed with the residual powder after the slow oxidation. Even when a rare earth magnet is manufactured using fine powder, a decrease in magnetic properties hardly poses a problem.

  By the way, in the system L after the residual powder is gradually oxidized as described above, a gas having a high oxygen concentration (0.8% to 2.0%) used in the slow oxidation is filled. Therefore, when the next raw material alloy coarse powder is finely pulverized without opening the system L to the atmosphere, first, the inside of the system L needs to be reduced to a desired oxygen concentration (0.2% to 0.5%). There is. However, simply supplying an inert gas having an oxygen concentration in the above range to the system L is advantageous in terms of cost, but it takes a long time to reduce the oxygen concentration to a desired level, resulting in deterioration in production efficiency. Invite.

  Therefore, from the viewpoint of setting the system L to a desired oxygen concentration in a short time, it is desirable to supply a high-purity inert gas into the system L for a short time. The high purity inert gas used here is preferably as high as possible, and the oxygen concentration is preferably 0.002% or less, for example. The oxygen concentration of so-called pure nitrogen gas (for example, pure nitrogen gas having a purity of 99.999% or more) used industrially is about 0.5 ppm (0.00005%). On the other hand, considering the cost and the like, the purity will be lowered, but from the viewpoint of rapidly reducing the oxygen concentration in the system L, the oxygen concentration is preferably 0.002% or less. Although it depends on the scale of the system L, the supply time may be set to a pressure and a flow rate substantially the same as those during pulverization for 1 to 10 minutes. The oxygen concentration in the system L can be quickly lowered by increasing the pressure of the inert gas supply or increasing the flow rate.

  Further, as a technique for reducing the inside of the system L to a desired oxygen concentration in a short time, the valves 77 and / or 78 provided in the high-pressure tank 64 and / or the low-pressure tank 62 are opened, and the high-pressure tank 64 and / or the low-pressure tank are opened. It is also effective to discard the high oxygen concentration gas in the tank 62 to the gas recovery tank 75. Both the supply of the high purity inert gas and the disposal of the high oxygen concentration gas in the tank may be performed or may be performed independently. For example, when it is intended to reduce the oxygen concentration in the system L from 1.4% to 0.4%, when the conventional method is performed, that is, the supply of the high purity inert gas and the high oxygen concentration gas in the tank It took approximately 120 minutes when the grinding system was idled (carrier gas was allowed to flow through the system L for a predetermined time) without performing both disposals. On the other hand, when the high oxygen concentration gas in the tank is discarded and then idle operation is performed, it can be achieved in about 20 minutes. Further, when the high purity inert gas is supplied into the system L, it can be achieved in about 3 minutes.

  Furthermore, after the residual powder is gradually oxidized, the residual powder may be collected in the hopper 40 or the collection storage container 51 without opening the system L to the atmosphere. When the residual powder is gradually oxidized, the activity of the surface is lowered, and the residual powder is easily removed from the piping wall and the like. Therefore, the residual powder can be efficiently removed out of the system L by a simple operation of applying impact to the piping to drop off the residual powder and then storing it in the collection storage container 51. By removing the residual powder after the slow oxidation out of the system L, when the powder is pulverized in a medium oxygen concentration atmosphere (for example, 0.2% to 0.5%), the residual powder in the obtained raw material alloy fine powder Mixing can be suppressed. As a result, it is possible to suppress the heat generation and ignition of the raw material alloy fine powder due to the mixing of the residual powder. Moreover, when there is much quantity of the residual powder collect | recovered by the hopper 40, it mixes with the raw material alloy fine powder of medium oxygen concentration atmosphere (for example, 0.2%-0.5%) grinding | pulverization, and a composition of raw material alloy fine powder Although it may cause fluctuations, and in turn, causes fluctuations in the magnetic properties, mechanical characteristics, corrosion resistance, etc. of rare earth sintered magnets produced using this as a raw material, since residual powder can be efficiently removed outside the system L, These problems can be solved.

  The embodiment of the method for producing a rare earth magnet of the present invention has been described above by taking the production of an R-T-B rare earth sintered magnet as an example, but it goes without saying that the present invention is not limited to this embodiment. Yes. For example, the target raw material alloy powder is not limited to the R—T—B type alloy powder, but can be applied to, for example, an SmCo type alloy powder. However, in that case, it is necessary to set the oxygen concentration in the inert gas within an appropriate range according to the type of alloy powder to be applied.

  Hereinafter, specific examples of the present invention will be described based on experimental results.

<Example 1>
Nd-Fe-B system having a composition of Nd30.3%, Dy1.0%, B1.0%, Zr0.15%, Co0.5%, Al0.2%, Cu0.07%, balance Fe in mass percentage The raw material alloy coarse powder (passed through a sieve having a 2 mm opening) was used for fine pulverization using the pulverization system shown in FIG. Fine pulverization was performed by airflow pulverization until the average particle size became 4.1 μm using pure nitrogen gas having an oxygen concentration of 0.5 ppm as a carrier gas. Thereafter, the raw material alloy fine powder having a predetermined particle size was recovered in a recovery storage container. The mass of the raw material alloy fine powder accommodated in the collection storage container was 785 kg with respect to the input mass of the raw material alloy coarse powder of 800 kg. If the mass of finer powder collected by the bag filter and after filter is also subtracted, the mass of the raw material alloy fine powder (residual powder) remaining in the system of the pulverization system is estimated to be 4.5 kg. Since the oxygen in the system was adsorbed by the fine powder during pulverization, the oxygen concentration in the pulverization system after the recovery was substantially 0%.

  Next, shut off the collection storage container and piping after containing the raw material alloy fine powder, then increase the oxygen concentration in the system by mixing and supplying the gas from the inert gas supply device and oxygen-containing gas supply device I let you. Specifically, the oxygen concentration in the system was increased from 0% to 1.3% over about 50 minutes. Thereafter, the state of 1.3% oxygen in the system was maintained for 60 minutes. The total time for maintaining the oxygen concentration in the system at 0.8% or more was 85 minutes.

  Thereafter, the piping was vibrated to collect residual powder in another collection storage container of the pulverization system. The recovered residual powder was 3.7 kg. When the recovered residual powder was taken out into the atmosphere, no heat or ignition of the residual powder occurred. Moreover, it was 5500 ppm as a result of measuring the oxygen content of the collect | recovered residual powder. This oxygen content is a value that does not cause a problem as a raw material alloy fine powder of a rare earth magnet, and it is sufficient to mix an appropriate amount of the raw material alloy fine powder in a medium oxygen concentration atmosphere (for example, 0.2% to 0.5%). It was a usable value. Although it depends on the amount of residual powder recovered, it was a value that could be used even if it was mixed with the raw material alloy fine powder in a low oxygen concentration atmosphere (less than 0.2%) if the mixing ratio of the residual powder was very small.

  From the above experimental results, by supplying an inert gas with an appropriate oxygen concentration into the closed circuit of the pulverization system after pulverization at a low oxygen concentration, no heat generation or ignition occurs when taken out to the atmosphere. Moreover, it was confirmed that the residual powder in the system can be oxidized to the extent that the magnetic properties are not affected when the raw material after the slow oxidation is used as the raw material for the rare earth magnet. Further, by supplying an inert gas having an appropriate oxygen concentration after pulverization at a low oxygen concentration, 3.7 kg of the residual powder of 4.5 kg could be recovered without opening the system L.

It is a figure which shows typically the grinding | pulverization system used for the manufacturing method of the rare earth magnet of this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Feeder, 20 Crusher, 30 Cyclone, 40 Hopper, 50 Mixer, 51 Collection storage container, 60 Bag filter, 71 Inert gas supply device, 72 Oxygen-containing gas supply device 73 Gas mixer, 74 Oxygen meter, 75 gas Recovery tank, 77, 78 valve, 80 Particle size distribution measuring device

Claims (6)

A method for producing a rare earth magnet in which a raw material alloy coarse powder is air-flow crushed in a closed circuit of a grinding system to produce a raw material alloy fine powder,
The raw material alloy coarse powder is air-flow pulverized while the oxygen concentration in the closed circuit is kept below 0.2%, and the raw material alloy fine powder is collected. A method for producing a rare earth magnet, which is maintained at 0% for a predetermined time.   2. The method for producing a rare earth magnet according to claim 1, wherein after the oxygen concentration in the closed circuit is maintained at 0.8% to 2.0% for a predetermined time, the closed circuit is opened to the atmosphere.   After maintaining the oxygen concentration in the closed circuit at 0.8% to 2.0% for a predetermined time, the oxygen concentration in the closed circuit is set to 0.2% to 0.00% without opening the closed circuit to the atmosphere. 2. The method for producing a rare earth magnet according to claim 1, wherein the next raw material alloy coarse powder is air-flow pulverized in a state of being maintained at 5%. The closed circuit comprises a tank for compressing and storing gas circulating in the closed circuit;
After maintaining the oxygen concentration in the closed circuit at 0.8% to 2.0% for a predetermined time, and before maintaining the oxygen concentration in the closed circuit at 0.2% to 0.5%, The method for producing a rare earth magnet according to claim 3, wherein the gas in the tank is disposed outside the closed circuit.   After maintaining the oxygen concentration in the closed circuit at 0.8% to 2.0% for a predetermined time, and before maintaining the oxygen concentration in the closed circuit at 0.2% to 0.5%, The method for producing a rare earth magnet according to claim 3 or 4, wherein an inert gas having an oxygen concentration of 0.002% or less is supplied into the closed circuit.   The method for producing a rare earth magnet according to claim 1, wherein the predetermined time is 20 minutes to 180 minutes.

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