Method for manufacturing rare earth iron sintered magnets and apparatus for manufacturing rare earth iron sintered magnets

Abstract

To provide a manufacturing method of a rare earth iron-sintered magnet, the method materializing suppression of a coarse particle generated in an interface between rare earth iron-magnetic powders, the method thereby enabling improvement of the magnetic characteristics of the rare earth iron-sintered magnet.SOLUTION: A manufacturing method of a rare earth iron-sintered magnet according to an embodiment comprises the steps of: filling rare earth iron-magnetic powders made by means of super-rapid quenching into a metallic mold; setting the metallic mold in a sintering device, supplying a prescribed current from an electrode and pressurizing and heating the filled rare earth iron-magnetic powders to make a sintered magnet body; and magnetizing the sintered magnet body by a magnetization device. The metallic mold is constituted of: a hollow cylindrical die; a punch which is inserted into the die; and die supports which are formed of conductive materials and arranged on both axial ends of the die. The rare earth iron-magnetic powders are filled into a cavity formed by the die and the punch. The die includes: an inner die which is made of a non-conductive material; and an outer die which is made of the conductive material and arranged on the outside of the inner die. The inner periphery of the die support is in contact with the outer periphery of the outer die and the electrode is in contact with the die support.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing a rare earth iron-based sintered magnet, and Manufacturing equipment for rare earth iron-based sintered magnets Place Regarding. [Background technology]

[0002] As devices become smaller and more powerful, rare earth permanent magnets with high magnetic properties are increasingly being used in the motors within those devices. In recent years, there has also been an increase in demand for motors for in-vehicle use, requiring motors with heat resistance and environmental resistance.

[0003] On the other hand, common motor magnets are magnets (so-called bonded magnets) that are molded by mixing magnetic powder with resin. However, while bonded magnets offer flexibility in molding, they use organic resin as a binder, making them difficult to use in high-temperature environments such as engine compartments.

[0004] In contrast to this, there is a technology in which alloy flakes made from a molten rare earth-iron-based alloy are filled into a cavity formed by a punch and a die that serve as a pair of electrodes, and rare earth-iron-based permanent magnets are manufactured by spark plasma sintering without using a binder (see, for example, Patent Document 1).In the manufacturing method described in Patent Document 1, the punch that serves as a pair of electrodes is made of a conductive cemented carbide, and the die is made of a non-conductive sialon.

[0005] The rare earth iron-based permanent magnet described in Patent Document 1 is manufactured by spark plasma sintering without using a resin binder, making it possible to use it in high-temperature environments. Furthermore, based on the density ratio between rare earth iron-based magnetic powder (Nd-Fe-B magnetic powder) and a bonded magnet made of resin, the rare earth iron-based permanent magnet described in Patent Document 1 is expected to have magnetic properties that are approximately 20% better than those of a bonded magnet. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 4-96203 Summary of the Invention [Problem to be solved by the invention]

[0007] The rare earth iron-based permanent magnet manufactured as described above is then magnetized, but measurements of the surface magnetic flux density after magnetization showed that the improvement was only about 6%, not the expected 20% improvement compared to the bonded magnet.

[0008] For this reason, the inventors of the present invention observed the interfaces of the magnetic powders of rare earth iron-based permanent magnets using an electron microscope and, as a result of careful investigation, discovered that there were areas where the interfaces between the magnetic powders in contact with each other were unclear, and that in those areas the magnetic powders were fused together, giving the appearance of coarse grains. It is believed that these coarse grains caused the magnetic properties to deteriorate. In particular, when the permanent magnet is small, the proportion of coarse grains becomes relatively large, which is thought to have a correspondingly greater impact on the magnetic properties.

[0009] The present invention has been made in view of the above, and provides a method and an apparatus for producing a rare earth / iron-based sintered magnet that can suppress the generation of coarse grains at the interfaces between rare earth / iron-based permanent magnet powders and improve magnetic properties. Place The purpose is to provide. [Means for solving the problem]

[0010] In order to solve the above-mentioned problems and achieve the object, one aspect of the present invention provides a method for producing a rare earth-iron-based sintered magnet, which comprises the steps of: filling a mold with rare earth-iron-based magnetic powder produced by a rapid cooling method; setting the mold in a sintering machine, supplying a predetermined current from electrodes, and pressurizing and heating the filled rare earth-iron-based magnetic powder to produce a sintered magnet body; and magnetizing the sintered magnet body with a magnetizing machine. includeThe die includes a hollow cylindrical die, a punch inserted into the die, die supports made of a conductive material and disposed on both axial ends of the die, Contains The cavity formed by the die and punch is filled with rare earth iron-based magnet powder. The die comprises an inner die made of a non-conductive material, an outer die made of a conductive material and disposed outside the inner die, and Contains composition is. The inner peripheral surface of the die support contacts the outer peripheral surface of the outer die, and the electrode contacts the die support.

[0011] A method for producing a rare earth-iron-based sintered magnet according to one aspect of the present invention can suppress the generation of coarse grains at the interfaces between rare earth-iron-based permanent magnet powder particles, thereby improving magnetic properties. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a flowchart showing an example of steps in a method for producing a rare earth iron-based sintered magnet according to one embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing a state in which rare earth iron-based (Nd—Fe—B-based) magnet powder is filled into the die as magnet powder, and an upper punch is set. [Figure 3] FIG. 3 is a cross-sectional view showing a state in which an upper insulating plate and an upper die support are set on the upper punch. [Figure 4] FIG. 4 is a cross-sectional view showing a state in which the mold is set in the sintering device. [Figure 5] FIG. 5 is a perspective view of the sintered magnet body. [Figure 6] FIG. 6 shows examples of measurement results of surface magnetic flux density of a bonded magnet, a sintered magnet produced by a conventional manufacturing method, and a sintered magnet produced by the manufacturing method of the embodiment. [Figure 7] FIG. 7 is an electron microscope view of the crystal structures of a sintered magnet produced by a conventional production method and a sintered magnet produced by the production method of the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0013] Hereinafter, a method for producing a rare earth-iron-based sintered magnet, an apparatus for producing a rare earth-iron-based sintered magnet, and a rare earth-iron-based sintered magnet according to embodiments will be described with reference to the drawings. Note that the present invention is not limited to these embodiments. Furthermore, the dimensional relationships and ratios of elements in the drawings may differ from reality. The dimensional relationships and ratios may differ between the drawings. Furthermore, the content described in one embodiment or variant applies, in principle, to other embodiments or variants as well.

[0014] 1 is a flowchart showing an example of steps in a method for producing a rare earth iron-based sintered magnet according to one embodiment. Note that the steps in the production method described below may be performed manually by an operator, by a robot mechanism or the like operating under the control of a control device (computer device), or by a combination of both.

[0015] In FIG. 1, an operator or a control device first prepares magnet powder (step S1). Here, as a rare earth iron-based magnet, an RTB (boron)-based magnet is as follows: RTB-based magnets are ternary tetragonal compounds, R2T 14 B phase (e.g. NdFe 14The RTB magnet contains a rare earth element (Nd, B-type compound phase) as the main phase. Furthermore, RTB magnets usually further contain an R-rich phase. R represents rare earth elements including Nd and / or Pr. In other words, R contains Nd and / or Pr as essential components. Examples of rare earth elements include neodymium (Nd) and praseodymium (Pr), as well as scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). The rare earth elements other than Nd and Pr may be used singly or in combination. Specifically, only Nd may be used as R, only Pr may be used, or only Nd and Pr may be used. Furthermore, Nd and a rare earth element other than Nd and Pr may be used, Pr and a rare earth element other than Nd and Pr may be used, or Nd and Pr and a rare earth element other than Nd and Pr may be used. It is preferable that at least Nd is used as R. T represents Fe, or Fe and Co. As such, T may be only Fe, or a portion of T may be substituted with Co. When the total amount of T is 100 atomic %, it is preferable that Fe is contained in an amount of 50 atomic % or more.

[0016] RTB magnets may contain other elements. Examples of such elements include titanium (Ti), zirconium (Zr), niobium (Nb), molybdenum (Mo), hafnium (Hf), tantalum (Ta), and tungsten (W). One or more of these elements may be used alone, or two or more may be used in combination. In RTB magnets, R is preferably contained in an amount of 12 atomic % to 16 atomic %. B is preferably contained in an amount of 6 atomic % to 8 atomic %. Furthermore, when the above-mentioned other elements are contained, the total amount of the other elements is preferably greater than 0 atomic % and less than 3 atomic %. Here, the remainder is the total amount of T and unavoidably contained elements.

[0017] Here, as an RTB magnet, for example, NdFe 14 Taking an Nd-Fe-B based magnet, which uses an Nd-Fe-B based alloy with B as the main phase, as an example, rare earth iron based magnet powder for that purpose is used.

[0018] The operator or the control device produces rare earth iron-based magnet powder, for example, by the ultra-rapid cooling method (melt-spun method). Specifically, the operator or the control device melts an Nd-Fe-B-based alloy by high-frequency induction heating under reduced pressure or in an argon atmosphere. Next, the molten alloy is sprayed onto a rotating roll and ultra-rapidly cooled (cooled at high speed) to produce ribbon-shaped thin strips. Next, the thin strips are pulverized. For example, the thin strips are preferably broken into pieces of several millimeters to several tens of millimeters, and then pulverized using a pulverizer or the like. The thin strips are pulverized to obtain pulverized powder.

[0019] Next, an operator or a control device pulverizes the ribbon-shaped thin strip to obtain powder, which is then heat-treated to obtain rare earth iron-based magnet powder. At this stage, the easy axis of magnetization of each crystal grain of the powder is not aligned in one direction, so it is magnetically isotropic. Note that instead of actually producing rare earth iron-based magnet powder, pre-manufactured rare earth iron-based magnet powder can be used. For example, Magnequench offers magnetically isotropic Nd-Fe-B rare earth iron-based magnet powder that is produced by a rapid quenching method and then pulverized.

[0020] Next, an operator or a control device prepares the mold 110 (step S2). As shown in FIGS. 2 to 4, the mold 110 includes a hollow cylindrical outer die 121 and an inner die 122, cylindrical upper punch 141 and lower punch 142 inserted inside the inner die 122, and a columnar core 131 inserted inside the upper punch 141 and the lower punch 142. The mold 110 also includes a hollow cylindrical upper die support 161 and a lower die support 162, each of which has a closed end and fits onto the outside of the outer die 121. A disc-shaped upper insulating plate 151 is interposed between the upper punch 141 and the upper die support 161, and a disc-shaped lower insulating plate 152 is interposed between the lower punch 142 and the lower die support 162.

[0021] The upper punch 141, the lower punch 142, and the core 131 are made of a conductive cemented carbide, the outer die 121 is made of a conductive material (e.g., graphite, cemented carbide, etc.), and the inner die 122 is made of a non-conductive material (e.g., silicon nitride, sialon, etc.). The upper die support 161 and the lower die support 162 are made of a conductive material (e.g., graphite, cemented carbide, etc.), and the upper insulating plate 151 and the lower insulating plate 152 are made of a non-conductive material (e.g., a boron nitride sheet or a silicon nitride plate, which are electrically insulating and heat-resistant).

[0022] Next, returning to FIG. 1, the operator or the control device fills the mold 110 with magnet powder, sets the mold 110 in the sintering apparatus 100 for sintering, and removes the sintered magnet body from the mold 110 (step S3).

[0023] Fig. 2 is a cross-sectional view showing a state in which rare earth iron-based (Nd-Fe-B-based) magnet powder 201 has been filled as magnet powder into the mold 110, and the upper punch 141 has been set in place. That is, Fig. 2 shows the state in which the rare earth iron-based (Nd-Fe-B-based) magnet powder 201 has been filled into the cavity formed by the upper punch 141, the lower punch 142, the inner die 122, and the core 131. Fig. 3 is a cross-sectional view showing a state in which an upper insulating plate 151 and an upper die support 161 have been set in the upper punch 141 from the state shown in Fig. 2.

[0024] FIG. 4 is a cross-sectional view showing the mold 110 set in the sintering apparatus 100. Specifically, an upper electrode 171 is disposed on the upper end of the upper die support 161, and a lower electrode 172 is disposed on the lower end of the lower die support 162. The upper electrode 171 and the lower electrode 172 are formed of a conductive material (e.g., graphite, cemented carbide, etc.). The sintering apparatus 100 includes a power supply device and a control device that apply a predetermined voltage between the upper electrode 171 and the lower electrode 172 to supply a predetermined current. Note that an SPS apparatus (spark plasma sintering apparatus) is used as the sintering apparatus 100, but in this embodiment, spark plasma sintering is not performed between the magnet powder particles, and sintering is performed only by Joule heat. Sintering is preferably performed under reduced pressure or in an inert atmosphere, such as nitrogen or argon.

[0025] 4, rare earth-iron-based magnetic powder 201 filled in the cavity of die 110 is pressed by upper punch 141 and lower punch 142 due to the pressure applied between upper electrode 171 and lower electrode 172. The powder is also heated by Joule heat generated by current flowing through the path upper electrode 171 → upper die support 161 → outer die 121 → lower die support 162 → lower electrode 172. For example, the rare earth-iron-based magnetic powder is heated to 600 to 700°C while being pressed at 30 to 50 MPa.

[0026] After heating, the current is cut off and the body is cooled. After cooling to a predetermined temperature, the mold 110 is removed from the sintering apparatus 100, and the ring-shaped sintered magnet body 202 formed by sintering the rare earth-iron-based magnet powder 201 is removed from the mold 110. FIG. 5 is a perspective view of the sintered magnet body 202.

[0027] In conventional spark plasma sintering apparatuses, such as those described in Patent Document 1, the rare-earth iron-based magnetic powder serves as a current path, heating the rare-earth iron-based magnetic powder through the discharge plasma and Joule heat. In contrast, in this embodiment, the rare-earth iron-based magnetic powder 201 does not serve as a current path and is heated solely by Joule heat from the current-carrying areas. Furthermore, the upper punch 141, lower punch 142, and core 131, which contact the rare-earth iron-based magnetic powder 201, are insulated by the upper insulating plate 151, lower insulating plate 152, and inner die 122, which is made of a non-conductive (insulating) material, and therefore do not directly contact the current path. Therefore, in this embodiment, the generation of coarse grains between the rare-earth iron-based magnetic powder particles in the permanent magnet due to the discharge plasma is suppressed, thereby improving magnetic properties. While atmospheric heating and high-frequency heating are methods for sintering by simple heating, these methods are inefficient because they heat a wide area and are prone to generating coarse grains due to the long heating time. Therefore, the apparatus configuration of this embodiment is more advantageous.

[0028] Returning to FIG. 1, the operator or a control device then forms an anti-corrosion film on the sintered magnet body 202 removed from the mold 110, if necessary (step S4).

[0029] Next, the operator or a control device magnetizes the sintered magnet body 202 (step S5). That is, the operator or a control device magnetizes the sintered magnet body 202 with a predetermined number of poles using a magnetizing device (not shown), thereby obtaining a rare earth sintered magnet.

[0030] FIG. 6 shows examples of measurement results for the surface magnetic flux density of a bonded magnet, a sintered magnet produced by a conventional manufacturing method, and a sintered magnet produced by the manufacturing method of this embodiment. For each case, the average maximum value of the surface magnetic flux density was calculated for a ring-shaped magnet magnetized with 10 poles. Three magnets each were evaluated using the conventional manufacturing method, the manufacturing method of this embodiment, and the bonded magnet. The surface magnetic flux was measured using a 50 μm square Hall element, with the distance between the magnet and the Hall element fixed at 0.14 mm. The shape of the ring-shaped magnet is an outer diameter of 1.6 mm, an inner diameter of 0.6 mm, and a height of 3.5 mm. The density [g / cm] of each magnet was 3 ] is about 6.0 [g / cm 3 ], and the sintered magnet produced by the conventional manufacturing method is approximately 7.5 [g / cm 3 ], and the sintered magnet produced by the manufacturing method of this embodiment has a density of about 7.5 [g / cm 3 ].

[0031] As is clear from FIG. 6, the surface magnetic flux density of the rare earth-iron-based sintered magnet produced using the conventional manufacturing method is only increased by about 6% compared to the bonded magnet, but the surface magnetic flux density of the rare earth-iron-based sintered magnet produced using the manufacturing method of this embodiment achieves an increase of about 20% compared to the bonded magnet, as expected from the density ratio.

[0032] If the volumetric ratio of coarse particles after sintering is 0%, the increase in magnet density and the increase in surface magnetic flux density are the same. Therefore, we defined the amount of coarse particles as the difference between the measured surface magnetic flux density after sintering and the theoretical value, and calculated the amount of coarse particles by manufacturing method. Here, coarse particles are components that do not contribute to the surface magnetic flux density. Converted to a volumetric ratio, the coarse particles are 0% for bonded magnets, 13% to 17% for sintered magnets manufactured using conventional manufacturing methods, and less than 2% for sintered magnets manufactured using conventional manufacturing methods. Since the weight of a motor using a permanent magnet increases with the increase in permanent magnet density, a smaller amount of coarse particles, which do not contribute to the increase in the permanent magnet's magnetic force, is preferable for motor performance. Therefore, from the perspective of improving motor performance and weight increase, it is preferable to keep the volumetric ratio of coarse particles to 10% or less, and more preferably to 5% or less.

[0033] Figure 7 shows electron microscope images of the crystalline structures of a sintered magnet produced by a conventional manufacturing method and a sintered magnet produced by the manufacturing method of this embodiment. Figure 7 shows that the crystalline structure of the rare earth-iron-based sintered magnet produced by the conventional manufacturing method has unclear interfaces between the rare earth-iron-based magnetic powder particles, and the formation of apparent coarse grains and traces of the effects of the discharge plasma can be seen. On the other hand, the crystalline structure of the rare earth-iron-based sintered magnet produced by the manufacturing method of this embodiment has clear interfaces between the rare earth-iron-based magnetic powder particles, so the formation of coarse grains is not evident and almost no traces of the effects of current flow are found.

[0034] Although the above description has been given of a case where a ring-shaped sintered magnet body 202 is obtained, the sintered magnet body may also be disk-shaped. In this case, for example, the core 131 in Figures 2 to 4 is not necessary, and the upper punch 141 and lower punch 142 are cylindrical.

[0035] Furthermore, the upper punch 141 and the lower punch 142 may be formed from the same non-conductive material as the inner die 122. In this case, the upper insulating plate 151 and the lower insulating plate 152 interposed between the upper punch 141 and the lower punch 142 and the upper die support 161 and the lower die support 162 are not necessary. Note that, since the non-conductive material used for the upper punch 141 and the lower punch 142 is limited in terms of strength and thermal expansion coefficient, cemented carbide, which is a conductive material in terms of strength and thermal expansion coefficient, is preferred.

[0036] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present invention.

[0037] As described above, the method for producing a rare earth-iron-based sintered magnet according to the embodiment comprises the steps of filling a mold with rare earth-iron-based magnetic powder produced by a rapid cooling method, setting the mold in a sintering apparatus, supplying a predetermined current from electrodes, and pressurizing and heating the filled rare earth-iron-based magnetic powder to produce a sintered magnet body, and magnetizing the sintered magnet body with a magnetizing apparatus. The mold comprises a hollow cylindrical die, a punch inserted into the die, and die supports made of a conductive material and disposed on both axial ends of the die. The rare earth-iron-based magnetic powder is filled into a cavity formed by the die and the punch. The die comprises an inner die made of a non-conductive material and an outer die made of a conductive material and disposed on the outside of the inner die. The inner peripheral surface of the die support contacts the outer peripheral surface of the outer die, and the electrodes contact the die support. This prevents the formation of coarse particles at the interfaces between the rare earth magnet powder particles in the permanent magnet, thereby improving the magnetic properties.

[0038] Furthermore, an insulating plate is interposed between the punch and the die support, which makes it possible to prevent the punch from becoming a current path even if the punch is made of a conductive material.

[0039] Furthermore, the current supplied to the electrodes forms a current path between the electrodes, the die support, and the outer die, which ensures that the discharge plasma does not cause the rare earth-iron-based magnet powder to produce coarse particles.

[0040] The present invention also provides a manufacturing apparatus for rare earth-iron-based sintered magnets, comprising a mold, a sintering apparatus, and a magnetizing apparatus, wherein the mold comprises a hollow cylindrical die, a punch inserted into the die, and die supports made of conductive material and disposed on both axial ends of the die, the cavity formed by the die and the punch being filled with rare earth-iron-based magnetic powder produced by an ultra-rapid cooling method, the die comprises an inner die made of a non-conductive material and an outer die made of a conductive material and disposed outside the inner die, the inner peripheral surface of the die support contacts the outer peripheral surface of the outer die, electrodes of the sintering apparatus contact the die supports of the mold set in the sintering apparatus, and a predetermined current is supplied from the electrodes to pressurize and heat the filled rare earth-iron-based magnetic powder to produce a sintered magnet body, and the magnetizing apparatus magnetizes the sintered magnet body.

[0041] Furthermore, it is possible to produce a rare earth iron-based sintered magnet in which the volume ratio of coarse grains within the sintered magnet is 10% or less, thereby obtaining a magnet with excellent magnetic properties that can be used at high temperatures.

[0042] Furthermore, the present invention is not limited to the above-described embodiments. Configurations in which the above-described components are appropriately combined are also included in the present invention. Furthermore, further effects and modifications can be easily derived by those skilled in the art. Therefore, the broader aspects of the present invention are not limited to the above-described embodiments, and various modifications are possible. [Explanation of symbols]

[0043] 100 Sintering device, 110 Mold, 121 Outer die, 122 Inner die, 131 Core, 141 Upper punch, 142 Lower punch, 151 Upper insulating plate, 152 Lower insulating plate, 161 Upper die support, 162 Lower die support, 171 Upper electrode, 172 Lower electrode, 201 Rare earth iron-based magnet powder, 202 Sintered magnet body

Claims

1. a step of filling a mold with rare earth iron-based magnet powder produced by the rapid cooling method; a step of setting the mold in a sintering machine, supplying a predetermined current from electrodes, and pressurizing and heating the filled rare earth-iron-based magnet powder to produce a sintered magnet body; a step of magnetizing the sintered magnet body using a magnetizing device; A method for producing a rare earth iron-based sintered magnet, comprising: the die includes a hollow cylindrical die, a punch inserted into the die, and die supports formed of a conductive material and disposed on both axial ends of the die, Filling the cavity formed by the die and punch with the rare earth iron-based magnet powder, the die includes an inner die made of a non-conductive material and an outer die made of a conductive material disposed outside the inner die; an inner peripheral surface of the die support contacts an outer peripheral surface of the outer die; the electrode contacts the die support; A method for manufacturing rare earth iron-based sintered magnets.

2. an insulating plate is interposed between the punch and the die support; A method for producing the rare earth iron-based sintered magnet according to claim 1.

3. The current supplied to the electrode forms a current path through the electrode, the die support, and the outer die. The method for producing the rare earth iron-based sintered magnet according to claim 1 or 2.

4. The apparatus includes a mold, a sintering device, and a magnetizing device, the die includes a hollow cylindrical die, a punch inserted into the die, and die supports formed of a conductive material and disposed on both axial ends of the die, A cavity formed by the die and the punch is filled with rare earth iron-based magnet powder produced by a rapid cooling method, the die includes an inner die made of a non-conductive material and an outer die made of a conductive material disposed outside the inner die; an inner peripheral surface of the die support contacts an outer peripheral surface of the outer die; an electrode of the sintering apparatus contacts the die support of the mold set in the sintering apparatus, and a predetermined current is supplied from the electrode to pressurize and heat the filled rare earth-iron-based magnet powder to produce a sintered magnet body; a magnetizing device for magnetizing the sintered magnet body; Manufacturing equipment for rare earth iron-based sintered magnets.

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