JP2005268668A - Manufacturing method and apparatus of rare earth sintered magnet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable a stable cutting process with less amount of processing allowance without resulting in any damage on a molded body having completed the cutting process. <P>SOLUTION: On the occasion of molding a raw material alloy metal powder including a rare earth element and cutting the molded body into the predetermined shape, at least single-direction surface of the two-direction surfaces almost crossing at the right angle with the cutting surface of the molded body is compressively supported. For example, the molded body is pressed in the direction almost parallel to the cutting direction. The applied pressure should be set to 1% to 20% of the molding pressure of the molded body. The cutting process should be conducted, for example, through the wire processing. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method and an apparatus for manufacturing a rare earth sintered magnet containing a rare earth element, and more particularly to improvement of a cutting processing technique for a molded body.

  Rare earth sintered magnets, such as rare earth boron-based sintered magnets, have advantages such as excellent magnetic properties, and in recent years, their demand tends to increase more and more. Under such circumstances, research and development for improving the magnetic properties of rare earth boron-based sintered magnets and improvement of manufacturing methods for producing high-quality rare earth sintered magnets are being promoted in various fields.

  As a method for producing a rare earth sintered magnet, powder metallurgy is known and widely used because it can be produced at low cost. In the manufacturing method of rare earth sintered magnets by powder metallurgy, first, a raw material alloy ingot is roughly pulverized and finely pulverized to obtain a raw material alloy fine powder having a particle size of about several μm. The raw material alloy fine powder thus obtained is magnetically oriented in a static magnetic field, and is molded in a state where a magnetic field is applied. After molding in a magnetic field, the compact is sintered in a vacuum or in an inert gas atmosphere.

  In manufacturing the rare earth sintered magnet by the above-described powder metallurgy method, it is necessary to perform contour processing for making the obtained rare earth sintered magnet into a predetermined shape. Then, as a specific processing method, after pressing the raw material alloy fine powder to form a block and sintering the formed body, it is cut using a diamond grindstone or a cutter, etc., and then one block-shaped sintered body A method of cutting out a plurality of products from a product is known.

  However, when the said processing method is employ | adopted, there are many problems at the point of manufacturing cost. For example, a large amount of swarf is generated from the sintered body by contour processing, but since this swarf has already been sintered, it is extremely difficult to reuse, and depending on the processing method, the loss of the sintered body may occur. This increases the yield of the material. Since the material which comprises a rare earth sintered magnet is expensive, the fall of a material yield becomes a fatal defect with respect to cost. In addition, a sintered body of a rare earth sintered magnet is extremely hard and brittle and has a large processing load. Therefore, there is a problem that high-precision processing is difficult and a long processing time is required. Thus, the cost required for processing the sintered body is a major cause of an increase in manufacturing cost.

  Moreover, as a technique for solving the problems caused by processing the sintered body as described above, a press mold is designed so that the baked shape becomes a shape and size close to that of the final product, and a molded body using this is designed. A method of forming and sintering this can also be considered. In this case, the shape and dimensions of the final product can be finished by slight surface grinding, and only a small amount of chips are generated, and processing of the molded body is unnecessary.

  However, for example, when producing a molded body having an irregular shape such as a bow shape, if the molded body is produced so that the baked shape becomes a shape and size close to the final product, the material density inside the molded body is reduced due to the difference in compression ratio. There is a problem that variation occurs and cracks are formed in the molded body. When cracks occur, depending on the direction, most of the sintered body becomes defective and causes a significant reduction in yield. Further, there is a problem that a complicatedly shaped mold is expensive.

From the above situation, in the manufacturing process of the sintered body, it is considered to perform some processing at the stage of the molded body. For example, Patent Document 1 discloses a technique in which a chamfered portion is formed by a rotating grindstone or a rotating brush on an outer peripheral edge or an inner peripheral edge of an arcuate ferrite magnet molded body at the stage of the arcuate ferrite magnet molded body before firing. ing. In Patent Document 2, in order to prevent oxidation of a green body during green processing, a green body formed by molding fine powder for a rare earth sintered magnet is immersed in mineral oil, synthetic oil, or vegetable oil, and the molding in that state is performed. A technique of cutting a body with a rotating processing blade is disclosed. Patent Document 3 includes a step of producing a magnet powder compact, a step of processing the compact using a wire saw, and a step of sintering the compact in the production of a sintered magnet. Technology is disclosed.
JP-A-8-64451 JP-A-8-181028 JP 2003-303728 A

  However, for example, when the technique described in Patent Document 1 is applied to a powder compact for a rare earth iron boron-based magnet having high oxidation reactivity, frictional heat is generated between the rotating grindstone or the rotating brush and the compact, Rare earth elements and iron in the molded body react rapidly with oxygen and moisture in the air atmosphere, and in the worst case, the molded body may ignite. Moreover, even if it does not fall into such a situation, the magnetic characteristics of the obtained magnet will deteriorate.

  On the other hand, in the technique described in Patent Document 2, a degreasing step for removing mineral oil and the like from the molded body after cutting and before sintering is indispensable. When degreasing is insufficient, carbon contained in the oil is sintered. It functions as an impurity and deteriorates the magnet characteristics. Moreover, in the processing method using the above blade saw, it is necessary to secure a large cutting allowance for the molded body, and there is a problem that the material yield is poor.

  Compared with these techniques, the wire processing by the wire saw described in Patent Document 3 has advantages such as less generation of frictional heat and less processing cost. However, it is not limited to this wire processing, but when the molded body is cut, how to support the molded body becomes a big problem.

  First, when the molded body after processing is thin, there is a problem that the molded bodies after cutting are overturned and damaged. Such a problem occurs regardless of whether the machining direction is parallel or perpendicular to the direction of gravity. In particular, for example, when it is cut in the horizontal direction as described in Patent Document 3, there is a problem that the thin plate-shaped molded body after processing falls due to gravity by the machining allowance at the end of processing. The invention does not consider this point at all. Further, even if cutting is stopped halfway so as not to fall, there is a risk of bending due to the weight of the molded body after processing, and processing into a thin and long shape is difficult.

  As an example of fixing a molded body at the time of processing, Patent Document 2 discloses an embodiment in which the molded body is fixed by a spacer. However, it is practically impossible to fix a brittle molded body having a low density only at the bottom surface.

  Furthermore, as described in Patent Document 3, it is conceivable to perform cutting processing in a casing-like case, but since the molded body is not fixed, it is possible to stably perform cutting processing. difficult. If the molded body is not fixed, for example, the molded body moves due to the processing force during processing, leading to an increase in machining allowance, that is, an increase in cutting waste. When the machining allowance increases and the amount of cutting waste increases, it becomes a factor of reducing the material yield.

  The present invention has been proposed in view of such a conventional situation, and rare earth sintering that can stably perform a cutting process with a small processing cost without damaging a formed body after the cutting process. It aims at providing the manufacturing method of a magnet, and also aims at providing the manufacturing apparatus which can implement | achieve such a cutting process.

  In order to achieve the above-mentioned object, the method for producing a rare earth sintered magnet according to the present invention forms a raw material alloy powder containing a rare earth element, and cuts the formed compact into a predetermined shape. It is characterized by pressure-supporting at least one of the two surfaces substantially orthogonal to the cut surface.

  At the time of cutting, by pressing and supporting at least one of the two directions substantially orthogonal to the cut surface, for example, when the formed body is cut into a thin plate shape, the thin plate-shaped formed body after cutting Is fixed, and the damage caused by falling or dropping is eliminated. Further, by performing the pressure support, the molded body is in a fixed state, the molded body does not move carelessly during the cutting process, a stable cutting process is realized, and the machining cost is reduced. Furthermore, the pressure support of the molded body brings about an improvement in the strength of the molded body. For example, by increasing the pressure to 1% to 20% of the molding pressure of the molded body, it is possible to improve the strength of the molded body during processing by pressing. Is done. It is known to increase the molding pressure in order to increase the strength of the molded body, but molding at a high pressure is not preferable because it causes galling and a decrease in the degree of orientation.

  On the other hand, the rare earth sintered magnet manufacturing apparatus of the present invention is an apparatus for manufacturing a rare earth sintered magnet used when a molded body formed by molding a raw material alloy powder containing rare earth elements is cut into a predetermined shape. The first support plate attached to the base in contact with one surface of the molded body and supporting the molded body under pressure, and the second support plate supporting the surface opposite to the surface in contact with the first support plate. And a slit is provided at a cutting position of the molded body of the first support plate, and a corresponding relief groove is provided in the second support plate. .

  In the manufacturing apparatus of the present invention having the above configuration, the molded body is pressure-supported by the first support plate and the second support plate, and the stable cutting process is easily realized. Moreover, since each support plate is provided with a slit, these support plates do not hinder cutting.

  In the present invention, by performing the cutting process at the stage of the formed body, the processing amount after sintering is greatly reduced, so that the processing time can be shortened and the manufacturing cost can be reduced. Further, since the molded body is supported at the time of cutting, it is possible to eliminate the damage due to falling over or dropping, and the processing cost can be reduced. In the present invention, since the density of the molded body can be improved and the strength can be increased without causing galling or a decrease in the degree of orientation, the occurrence of cracking or the like can be suppressed.

  Hereinafter, a method and apparatus for manufacturing a rare earth sintered magnet to which the present invention is applied will be described with reference to the drawings.

  First, the rare earth sintered magnet manufactured by the manufacturing method of the present invention will be described. Rare earth sintered magnets, especially rare earth boron-based sintered magnets, are basically composed of rare earth elements, transition metal elements and boron. What is necessary is just to select a magnet composition arbitrarily according to the objective.

For example, R-T-B (one or more of rare earth elements including R = Y, T = one or more of transition metal elements essential to Fe or Fe and Co, B = boron) system When a rare earth sintered magnet is used, in order to obtain a rare earth sintered magnet having excellent magnetic properties, the sintered magnet composition has a rare earth element R of 27.0 to 32.0 wt% and boron B of 0. It is preferable that the blending composition is 5 to 2.0% by weight and the balance is substantially the transition metal element T (for example, Fe). When the amount of the rare earth element R is less than 27.0% by weight, α-Fe or the like that is soft magnetic precipitates, and the coercive force decreases. Conversely, when the rare earth element R exceeds 32.0% by weight, the amount of the R-rich phase increases and the corrosion resistance deteriorates, and the volume ratio of the R ₂ T ₁₄ B crystal grains as the main phase decreases. The residual magnetic flux density is reduced. Further, when boron B is less than 0.5% by weight, a high coercive force cannot be obtained. Conversely, if boron B exceeds 2.0% by weight, the residual magnetic flux density tends to decrease.

Here, the rare earth element R is a rare earth element including Y, that is, one selected from Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Yb, and Lu, or 2 More than a seed. Among these, Nd and Pr are preferably Nd and Pr because the balance of magnetic properties is good and they are abundant and relatively inexpensive. Further, Dy ₂ Fe ₁₄ B and Tb ₂ Fe ₁₄ B compounds have a large anisotropic magnetic field, and adopting Dy or Tb as a substitution element for Nd is effective in improving the coercive force Hcj.

  Furthermore, the rare earth sintered magnet may be an R-TBM type rare earth sintered magnet by adding the additive element M. In this case, examples of the additive element M include Al, Cr, Mn, Mg, Si, Cu, C, Nb, Sn, W, V, Zr, Ti, and Mo. One or two of these may be used. The above can be selected and added. For example, the addition of Nb, Zr, W or the like, which is a refractory metal, has an effect of suppressing crystal grain growth. Of course, it is needless to say that the composition of the rare earth sintered magnet is not limited to these compositions and can be applied to all known compositions.

  In the rare earth sintered magnet described above, the oxygen content is preferably 2500 ppm or less. This is because when the oxygen content exceeds 2500 ppm, the amount of rare earth elements present as oxides increases, the magnetically effective rare earth elements to be present in the main phase and subphase decrease, and the coercive force decreases. The problem arises. Furthermore, the generated oxide is non-magnetic and causes a decrease in magnetization of the sintered body. The relationship between the amount of oxygen and the amount of oxide produced has a linear relationship according to the stoichiometric ratio of the compounds, but in order to satisfy the coercive force and magnetization required for high performance rare earth magnets in recent magnet applications. It is required to be 2500 ppm or less. In the present invention, the amount of oxygen contained in the raw material alloy powder is preferably 1000 ppm or less, particularly 400 ppm or less.

  Furthermore, the rare earth sintered magnet preferably has a carbon (C) content of 1500 ppm or less and a nitrogen (N) content of 200 to 1500 ppm. When the carbon content exceeds 1500 ppm, carbon forms a carbide with a part of the rare earth element, and the magnetically effective rare earth element is reduced and the coercive force is lowered. Further, by setting the nitrogen amount in the above range, both excellent corrosion resistance and high magnetic properties can be achieved.

  The rare earth sintered magnet described above is manufactured by powder metallurgy and is made into a sintered body by sintering. Hereinafter, a method for producing a rare earth sintered magnet by powder metallurgy will be described.

  FIG. 1 shows an example of a process for producing a rare earth sintered magnet by powder metallurgy. This manufacturing process basically includes an alloying step 1, a coarse pulverizing step 2, a fine pulverizing step 3, a magnetic field forming step 4, a molded body processing step 5, a sintering step 6, an aging step 7, a processing step 8, And the surface treatment step 9. In order to prevent oxidation, most of the steps after sintering are performed in a vacuum or in an inert gas atmosphere (in a nitrogen gas atmosphere, an Ar gas atmosphere, etc.).

  In the alloying step 1, a metal or alloy as a raw material is blended according to the magnet composition, dissolved in 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. As the raw material metal (alloy), pure rare earth elements, rare earth alloys, pure iron, ferroboron, and alloys thereof can be used. When cast as an ingot, solution treatment may be performed as necessary for the purpose of eliminating solidification segregation. As a condition for the solution treatment, for example, it is kept in a 700 to 1200 ° C. region for 1 hour or more under vacuum or Ar atmosphere.

  In the coarse pulverization step 2, the previously cast raw alloy thin plate, ingot or the like is pulverized until the particle size is about several hundreds of micrometers. As the pulverizing means, a stamp mill, a jaw crusher, a brown mill, or the like can be used. In order to improve the coarse pulverization property, it is effective to perform coarse pulverization after occlusion of hydrogen and embrittlement.

  After the aforementioned coarse pulverization step 2 is completed, a pulverization aid is usually added to the coarsely pulverized raw material alloy powder. As the grinding aid, for example, fatty acid compounds can be used. In particular, by using fatty acid amide as the grinding aid, a rare earth sintered magnet having good magnetic properties, particularly high orientation and high magnetization. Can be obtained. The addition amount of the grinding aid is preferably 0.03 to 0.4% by weight. If the addition amount of the grinding aid is less than 0.03% by weight, the effect on the magnetic properties of the lubricant cannot be sufficiently obtained. If the addition amount is 0.4% by weight or less, the residual after sintering The amount of carbon can be effectively reduced, which is effective in improving the magnetic properties of the rare earth sintered magnet.

  After the coarse pulverization step 2, a fine pulverization step 3 is performed. The fine pulverization step 3 is performed using, for example, an airflow pulverizer. The conditions for fine pulverization may be appropriately set according to the airflow pulverizer to be used, and the raw material alloy powder is finely pulverized until the average particle size becomes about 1 to 10 μm, for example, 3 to 6 μm. A jet mill or the like is suitable as the airflow pulverizer. A jet mill opens a high-pressure inert gas (for example, nitrogen gas) from a narrow nozzle to generate a high-speed gas flow, accelerates powder particles by this high-speed gas flow, and collides powder particles with each other. Or, it is a method of crushing by generating a collision with a collision plate or a container wall. Jet mills are generally classified into jet mills that use fluidized beds, jet mills that use vortex flow, jet mills that use impingement plates, and the like. Among these jet mills, a jet mill using a fluidized bed and a jet mill using a vortex are preferable, and a jet mill using a fluidized bed is particularly preferable. For example, the specific gravity of the raw material alloy powder and the grinding aid are greatly different, but in the fluidized bed and in the vortex, the grinding and mixing are performed well regardless of the difference in specific gravity. It is because it does not become.

  After the pulverizing step 3, in the forming step 4 in the magnetic field, the raw material alloy fine powder is formed in the magnetic field. Specifically, the raw material alloy fine powder obtained in the fine pulverization step 3 is filled in a mold in which an electromagnet is arranged, and is molded in a magnetic field with a crystal axis oriented by applying a magnetic field. The forming in the magnetic field may be either a vertical magnetic field forming in which the forming pressure and the magnetic field direction are parallel, or a horizontal magnetic field forming in which the forming pressure and the magnetic field direction are orthogonal to each other. Further, a pulse power source and an air-core coil can be employed as the magnetic field applying means. The forming in the magnetic field may be performed at a pressure of about 100 to 200 MPa in a magnetic field of 700 to 1300 kA / m, for example.

  In the molding process 4 in the magnetic field, the molded body is cut and contoured in the molded body machining process 5 to be described later. Therefore, it is not necessary to set the shape and size so that the molded body shape substantially matches the final product. . For example, when manufacturing a fan-shaped rare earth sintered magnet is considered, the molded body need not be formed into a fan shape, and may be a simplified rectangular parallelepiped shape, for example.

  Next, in the molded body processing step 5, the molded body is processed into an arbitrary shape. For example, it is cut into a predetermined thickness with a wire saw and further cut into a fan shape. FIG. 2 shows an example of processing on the rectangular parallelepiped shaped body 11, which is sliced to a predetermined thickness along the cutting line S and contoured along the cutting line R.

  Here, for example, when cutting to a predetermined thickness by the cutting line S, when the thickness is particularly reduced, there is a risk that the molded bodies 11 after being cut will fall over each other and may be damaged or bent. Moreover, if the molded object 11 is not fixed, the molded object 11 will move with process force, and a machining cost will increase. Therefore, in the present invention, for example, when cutting with a wire saw, the molded body 11 is pressure-supported to prevent the above-described collapse and bending, and an increase in pressure allowance due to movement of the molded body 11 is prevented. I will do it.

  At the time of pressure support, at least one of the two directions substantially orthogonal to the cut surface of the molded body 11 may be supported by pressure, but the long side of the cut surface of these two directions is supported. If the surface to be pressed (that is, the wider surface) is pressure-supported, it can be stably supported. Further, it is preferable to press and support a surface in a direction orthogonal to the cutting direction and press the formed body in a direction substantially parallel to the cutting direction.

  Specifically, when the molded body 11 shown in FIG. 2 is cut along the cutting line S by advancing a wire saw in the arrow W direction, the upper surface 11a of the molded body 11 is pressure-supported. Actually, the bottom surface 11b of the molded body 11 is supported by the base, for example, by placing the molded body 11 on the base, and the upper surface 11a is supported by pressing the upper surface 11a of the molded body 11 as described above. A pressing force is applied between the bottom surface 11b in parallel with the cutting direction of the wire saw.

  At this time, the applied pressure is preferably 1% to 20% of the molding pressure of the molded body 11. Usually, since the molding pressure is 80 MPa to 150 MPa, the preferable pressure range is 0.8 MPa to 30 MPa. By applying the pressure, it is possible to support the molded body 11 reliably and stably, and it is also possible to improve the strength of the molded body by the applied pressure and prevent cracking. However, if the applied pressure exceeds 20% of the molding pressure, the cut molded body 11 may be damaged by the applied pressure. If the applied pressure is less than 1% of the molding pressure, stable and reliable fixing becomes difficult, and the effect of improving density cannot be expected.

  Of course, the optimum pressing force varies depending on the thickness and the processing length of the molded body 11 after the cutting process, and it may be desirable to set a small value such as 1% to 15% or 1% to 7%. The thinner the thickness after cutting, the longer the processing length, the smaller the pressure applied.

  As described above, the surface to be pressed and supported is optimally the upper surface 11a and the bottom surface 11b of the molded body 11 that pressurizes the molded body in a direction substantially parallel to the cutting direction (arrow W direction). Not only this but the side surfaces 11c and 11d of the molded object 11 can also be pressure-supported. In particular, when the widths of the side surfaces 11c and 11d are wider than the top surface 11a and the bottom surface 11b, it is advantageous to press and support the side surfaces 11c and 11d.

  Furthermore, you may make it press-support both the upper surface 11a and the bottom face 11b of the molded object 11, and the side surfaces 11c and 11d. In that case, it is preferable that the pressure applied to the side surfaces 11c and 11d is smaller than the pressure applied in a direction substantially parallel to the cutting direction, that is, the pressure applied to the upper surface 11a. About the front surface 11e and the back surface 11f of the molded body 11, if the pressure support is performed in this direction, the cut molded body 11 is pushed in as much as the cutting allowance, which causes bending and breakage.

  In the cutting process described above, the processing method is not particularly limited. For example, it may be a cutting process using the above-mentioned wire saw, or a cutting process using a cutting blade such as a blade saw. Further, the processing atmosphere at the time of cutting is not limited, but since it is processing of the compacted rare earth alloy powder 11 that is easily oxidized, it may be performed in an inert gas atmosphere such as nitrogen gas or in a non-oxidizing atmosphere such as oil. preferable. When it is performed in the air, it is preferably performed while spraying oil or an organic solvent on the processed part.

  In order to perform cutting while supporting the molded body 11 under pressure as described above, for example, an apparatus as shown in FIG. 3 may be used. Hereinafter, this manufacturing apparatus will be described.

  The manufacturing apparatus shown in FIG. 3 is for smoothly proceeding with cutting while supporting the compact 11 under pressure. The configuration includes a pressure cover 12 that covers and presses the molded body 11 and a base plate 15 that supports the bottom surface 11b of the molded body 11, and between these, the upper surface 11a and the bottom surface 11b of the molded body 11 are provided. Is supported under pressure.

  The pressure cover 12 is formed, for example, by bending a metal plate or the like, and has an upper surface plate 12a that contacts and supports the upper surface 11a of the molded body 11. Further, it is connected to both sides of the upper surface plate 12a, is bent at a right angle with respect to the upper surface plate 12a, is supported at the side surface support plate 12b for supporting the side surfaces 11c and 11d of the molded body 11, and is further bent at a right angle outward from the side surface support plate 12b. The upper plate 12a and a mounting plate 12c parallel to the upper plate 12a are provided.

  The upper surface plate 12a and the side surface support plate 12b of the pressure cover 12 are formed with slits 13 at a pitch corresponding to the thickness to be cut and, for example, do not hinder the progress of the wire when cutting with a wire saw. It is like that. The depth of the slit 13 is set so as to exceed the thickness of the molded body 11, but is formed so as not to reach the mounting plate 12c, and the connection state of the pressure cover 12 is maintained. ing.

  The mounting plate 12c of the pressure cover 12 is provided with pressure support points 12d at four corners, and the pressure support points 12d are supported by pressing with a pressure cylinder 14 such as a hydraulic cylinder or a pneumatic cylinder. Thus, the compact 11 is pressure-supported between the pressure cover 12 and the base plate 15.

  On the other hand, the base plate 15 is also provided with relief grooves 16 corresponding to the slits 13. Therefore, when the wire saw reaches the escape groove 16, the molded body 11 can be sliced to a predetermined thickness.

  FIG. 4 shows a pressure support state of the molded body 11 by the pressure cover 12 and the base plate 15. When the molded body 11 is pressed and supported, the base plate 15 is placed on the base 17 and the molded body 11 is placed thereon. Further, a pressure cover 12 is attached so as to cover the molded body 11, and the pressure cover 12 is pressure-fixed to the base 17 by the pressure cylinder 14.

  At this time, if the height from the base 17 of the side support plate 12b mounting plate 12c of the pressure cover 12 is set slightly smaller than the sum of the thickness of the molded body 11 and the thickness of the base plate 15, The compact 11 is pressed by the upper surface plate 12 a of the pressure cover 12 by the pressure applied by the pressure cylinder 14. It is also possible to control the pressure applied to the molded body 11 by adjusting the pressure applied by the pressure cylinder 14.

  After the molded body 11 is pressed and supported by the pressure cover 12 and the base plate 15 as described above, the molded body 11 is cut into a predetermined thickness by, for example, a wire saw 18 as shown in FIG. The wire saw 18 includes a cutting wire 18a and a pair of guide rollers 18b and 18c provided with a guide groove for stable running of each wire 18a. The body 11) is cut.

  In this example, the cutting | disconnection by the wire 18a advances toward the downward direction from the upper surface 11a of the molded object 11. FIG. At this time, the molded body 11 is pressure-supported by the pressure cover 12 substantially in parallel with the traveling direction of the wire 18a.

  After the molded body processing step 5 described above, a sintering process is performed on the molded body processed into a predetermined shape in the sintering step 6. That is, the molded body processed into a desired shape with a high-pressure fluid as described above is sintered in a vacuum or an inert gas atmosphere (such as a nitrogen gas atmosphere or an Ar gas atmosphere).

In the sintering process 6, a degreasing process is performed prior to sintering as necessary. The degreasing treatment is performed, for example, by maintaining at a temperature of 100 to 500 ° C. and a pressure of 10 ⁻¹ Torr or less for 30 minutes or more. By this treatment, fluids such as organic solvent and oil remaining in the processing waste can be sufficiently removed. The holding temperature does not need to be fixed at one point in the temperature range of 100 to 500 ° C., and may be held at two or more different temperatures. Further, for example, the same effect as the above treatment can be obtained by setting the rate of temperature increase from room temperature to 500 ° C. at 10 ° C./min or less, preferably 5 ° C./min or less under a pressure of 10 ⁻¹ Torr or less. be able to.

  The sintering temperature needs to be adjusted according to various conditions such as composition, pulverization method, difference in particle size and particle size distribution, etc. For example, sintering may be performed at 1000 to 1150 ° C. for about 5 hours, and rapid cooling after sintering. Is preferred.

  After sintering, in the aging step 7, it is preferable to subject the obtained sintered body to an aging treatment. This aging treatment is an important step in controlling the coercive force Hcj of the obtained rare earth sintered magnet. For example, the 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. Next, a first quenching step is provided for quenching to room temperature to 200 ° C. In the second stage aging treatment step, the temperature is maintained at about 550 ° C. for 1 to 3 hours. Next, a second quenching step for quenching 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 preferable to perform aging treatment at around 600 ° C.

  After the aging step 7, a processing step 8 and a surface treatment step 9 are performed. The processing step 8 is a step of mechanically forming into a desired shape, but in the present invention, the formed body is processed in advance into a shape close to the product shape by high-pressure fluid processing, and may be omitted. Even when the processing step 8 is performed, the amount of processing after sintering and the load on the processing jig used for processing after sintering can be greatly reduced as compared with the conventional method. The surface treatment step 9 is a step performed to suppress oxidation of the obtained rare earth sintered magnet. For example, a plating film or a resin film is formed on the surface of the rare earth sintered magnet.

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

<Pressure processing>
A metal or alloy as a raw material was blended so as to have a predetermined composition, and an alloy melted by high frequency melting in an alumina crucible was made into a thin plate alloy having a thickness of 1 mm or less by a strip casting method. The alloy composition is Nd 30.7 wt%, Dy 1.5 wt%, Cu 0.3 wt%, Al 0.1 wt%, B 1.02 wt%, and Fe balance.

  The thin plate-like alloy was dehydrogenated by Ar flow or evacuation in a fully evacuated furnace by occlusion and embrittlement of hydrogen at around room temperature, followed by heating. The embrittled thin plate alloy was coarsely pulverized to several hundred μm by mechanical pulverization in a nitrogen atmosphere, and further finely pulverized to a mean particle size of 4 μm by a jet mill in a nitrogen stream.

  The pulverized raw material alloy fine powder was subjected to a forming process while oxygen was blocked. In the forming step, a green compact (formed product) in which the crystal directions of the particles of the raw material alloy fine powder obtained by the magnetic field were aligned was obtained using a magnetic field forming machine. Also in the molding process, the amount of oxygen in the atmosphere was strictly controlled to 500 ppm or less. The shape of the molded body was a rectangular parallelepiped shape of 20 mm × 50 mm × 120 mm. The molding pressure is 120 MPa.

  Next, using a device shown in FIGS. 3 to 5 in an atmosphere in which the amount of oxygen is controlled, as shown by a line S in FIG. 2, a rectangular parallelepiped shaped body is cut into a thin plate with the thickness shown in Table 1. did. Here, Examples 1 to 3 were performed so as to support the pressure in the same direction (parallel direction) as the cutting direction by the wire saw. In Example 4, pressure was also applied in the perpendicular direction in addition to the parallel direction. In the comparative example, cutting was performed without applying pressure to the molded body. Table 1 shows the applied pressure, crack crack occurrence rate, post-processing thickness, and processing allowance in each example and comparative example.

  In the comparative example in which no pressure was applied, crack cracks occurred nearly 10% despite the relatively thick thickness after processing of 4.5 mm. Moreover, since a blur occurs at the time of cutting, the machining cost is large. On the other hand, in each Example to which a pressing force was applied, even when cut to a thickness of half or less, almost no cracks occurred. The machining allowance is also small compared to the comparative example.

<Examination of applied pressure>
Next, the pressure was changed, and the molded body was cut and processed in the same manner as in Examples 1 to 3 above. The thickness after processing is 3.1 mm. Since the molding pressure of the molded body is 120 MPa, the relationship between the percentage with respect to the molding pressure and the applied pressure is as shown in Table 2. Table 3 shows the pressurizing force, crack crack occurrence rate, post-processing thickness, and processing allowance in Examples 5 to 9.

  A larger applied pressure results in fewer cracks and a smaller cutting allowance. For example, compared with Example 5 in which the applied pressure is less than 1% of the molding pressure, Examples 6 to 9 in which the applied pressure is 1% or more of the molding pressure have fewer cracks and a smaller cutting allowance. However, as in Example 9, when the applied pressure exceeded 20% of the molding pressure and became too large, damage due to the applied pressure occurred.

It is a flowchart which shows an example of the manufacturing process of the rare earth sintered magnet of this invention. It is a perspective view which shows the cutting line and outline processing line in a rectangular parallelepiped shaped molded object. It is a disassembled perspective view which shows an example of the manufacturing apparatus of this invention. It shows the pressure support state of the molded body, (a) is a sectional view seen from the front, (b) is a side view. It is a perspective view which shows the cutting process by a wire saw.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Alloying process, 2 Coarse grinding | pulverization process, 3 Fine grinding | pulverization process, 4 Forming process in a magnetic field, 5 Molded body processing process, 6 Sintering process, 7 Aging process, 8 Processing process, 9 Surface treatment process, 11 Molded body, 11a Top surface, 11b Bottom surface, 11c, 11d Side surface, 12 Pressure cover, 13 Slit, 14 Pressure cylinder, 15 Base plate, 16 Escape groove, 18 Wire saw

Claims (10)

  When forming a raw material alloy powder containing a rare earth element and cutting the formed compact into a predetermined shape, at least one of the two directions substantially orthogonal to the cut surface of the compact is supported by pressure. A method for producing a rare earth sintered magnet.   2. The method of manufacturing a rare earth sintered magnet according to claim 1, wherein a surface corresponding to the long side of the cut surface is pressed and supported among the surfaces in the two directions.   The method for producing a rare earth sintered magnet according to claim 1, wherein a surface in a direction orthogonal to the cutting direction is pressed and supported, and the formed body is pressed in a direction substantially parallel to the cutting direction.   Both the surfaces in two directions substantially orthogonal to the cut surface of the molded body are supported by pressure, and the applied pressure in a direction substantially parallel to the cutting direction is larger than the applied force in the direction orthogonal thereto. The method for producing a rare earth sintered magnet according to claim 1.   The method for producing a rare earth sintered magnet according to any one of claims 1 to 4, wherein the applied pressure is 1% to 20% of the molding pressure at the time of forming the molded body.   The method for producing a rare earth sintered magnet according to any one of claims 1 to 5, wherein the cutting process is a slicing process of cutting a molded body with a predetermined thickness.   The method for producing a rare earth sintered magnet according to claim 6, wherein the cutting is performed by wire saw processing. An apparatus for producing a rare earth sintered magnet used when a formed body formed by molding a raw material alloy powder containing a rare earth element is cut into a predetermined shape,
A first support plate that is attached to the base in contact with one surface of the molded body and supports the molded body under pressure, and a second support plate that supports a surface opposite to the surface in contact with the first support plate And
A rare earth sintered magnet according to claim 1, wherein a slit is provided at a cutting position of the molded body of the first support plate, and a clearance groove is provided in the second support plate correspondingly. apparatus. The first support plate includes a first surface in contact with one surface of the molded body, second and third surfaces along both side surfaces substantially orthogonal to the first surface of the molded body, and the second surface. , 4th and 5th surfaces that are bent outward substantially perpendicular to the third surface and have a mounting portion to the base,
9. The rare earth sintered magnet manufacturing apparatus according to claim 8, wherein a slit having a depth corresponding to the thickness of the molded body is provided on the second and third surfaces.   The apparatus for producing a rare earth sintered magnet according to claim 8 or 9, further comprising a wire saw for performing the cutting process.

Images