Patent Application
20200161032
The present invention relates to a rare-earth sintered magnet and a sintered body for the rare-earth sintered magnet for use with the same, and a magnetic field applying device usable for manufacturing the same.
A linear motor is used in many devices such as industrial motors for manufacturing semiconductors and liquid crystals, shavers, and the like. For example, as described in JP 2004-297843A, a glass substrate is inspected using a stage on which an image processing device or the like is mounted in a manufacturing process for a liquid crystal display in some cases, and the linear motor capable of processing with high accuracy and at a high speed is used as driving means for this stage. This type of linear motor has a stator including a magnet unit including a plurality of permanent magnets disposed to face each other with a gap between them and a rotor including a three-phase coil in a magnetic gap, and is configured to obtain a driving force for driving the rotor to cause a driving current to flow though the three-phase coil.
In order to obtain a sufficient driving force in such a linear motor, it is necessary that the magnet has a sufficient magnetic force, in other words, that a surface magnetic flux density of a magnetic flux generated from the magnet is sufficiently large, but as a result, the magnet needs some degrees of a volume and a thickness. On the other hand, in order to drive the stage at a high speed, a size or a weight of the magnet unit needs to be reduced, and an increase in the volume or thickness of the magnet is not preferable. Moreover, a yoke for reducing a leakage magnetic flux by a magnetic circuit connecting one surfaces (principal surface) of the magnet in a thickness direction toward the rotor side and the other surface opposing to that is provided in the magnet unit in general, but there is a concern that the size or the weight of the magnet unit is increased by these yokes. Furthermore, in the aforementioned linear motor, for example, it is only necessary that the magnetic flux is generated in the one surface on which the rotor is disposed, and the magnetic flux generated on the other surface is basically unnecessary or rather can cause the leakage magnetic flux by the magnetic circuit, which is not preferable.
Patent Document 1: JP 2004-297843A
The present invention has been made in view of solving the above conventional problem in such a prior art, and an object thereof is to provide a rare-earth sintered magnet which can generate a magnetic flux having practically useful surface magnetic flux density only in one surface in a thickness direction or mainly in one surface in a thickness direction without increasing a size or a weight of a magnet unit, and a sintered body for the rare-earth sintered magnet for use with the same. In addition, another object thereof is to provide a magnetic field applying device usable for manufacturing same.
In order to solve the aforementioned problem, a rare-earth sintered magnet according to an aspect of the present invention is a rare-earth sintered magnet having a configuration in which a number of magnet material particles including a rare-earth substance and each having an easy magnetization axis are integrally sintered, the rare-earth sintered magnet having a three-dimensional shape with a width direction, a thickness direction, and a length direction and including a first surface and a second surface opposing each other in the thickness direction, in which in a plane in parallel with the width direction and the thickness direction, the magnet material particles are oriented such that, in a region extending from each of both end portions in the width direction toward the center portion in the width direction, the orientation direction of the easy magnetization axis is gradually changed, and a maximum surface magnetic flux density in the first surface and a maximum surface magnetic flux density in the second surface satisfy the relationship (D1/D2)≥4.
According to the rare-earth sintered magnet in this aspect, since the magnetic flux having practically useful surface magnetic flux density can be generated only in the first surface (one surface) of the magnet in the thickness direction or mainly in the one surface in the thickness direction, there is no need to provide many magnet materials on the second surface (the other surface) and there is no need to provide a yoke for catching a leakage magnetic flux leaking out of the magnetic circuit, or only a small quantity of the yoke needs to be provided, and as a result, a small-sized and light-weighted rare-earth sintered magnet can be provided.
According to the rare-earth sintered magnet in the above aspect, the orientation directions of the easy magnetization axes may be different between each of both end portions in the width direction and a center portion in the width direction by 90°±5° or 180°±5°.
Moreover, in the rare-earth sintered magnet in the above aspect, the orientation directions of the easy magnetization axes may be different between each of the both end portions in the width direction and the center portion in the width direction by 90°±5°, and only an N-pole or an S-pole is generated in the first surface.
Moreover, in the rare-earth sintered magnet in the above aspect, the orientation directions of the easy magnetization axes may be different between each of the both end portions in the width direction and the center portion in the width direction by 180°±5°, and the N-pole or the S-pole is generated on the one side in the width direction of the first surface, while the S-pole or the N-pole with polarity opposite to that on the one side is generated on the other side in the width direction of the first surface.
In the rare-earth sintered magnet in the above aspect, the maximum surface magnetic flux density on the first surface is preferably 0.25T or more.
By setting the maximum surface magnetic flux density in the first surface large, a useful surface magnetic flux density for driving of the linear motor and the like can be also obtained.
Moreover, in the rare-earth sintered magnet in the above aspect, the maximum surface magnetic flux density on the second surface is preferably 0.15T or less.
By setting the maximum surface magnetic flux density on the second surface small, a leakage magnetic flux can be reduced.
In the rare-earth sintered magnet in the above aspect, the maximum surface magnetic flux density per unit thickness obtained by dividing the maximum surface magnetic flux density in the first surface by a thickness dimension in the thickness direction between the first surface and the second surface is preferably 0.06T/mm or more.
As a result, the maximum surface magnetic flux density can be improved efficiently.
In the rare-earth sintered magnet in the above aspect, axial symmetry obtained by obtaining surface magnetic flux density distribution in the width direction at a plurality of positions in the length direction and by comparing the surface magnetic flux density distributions obtained at the plurality of positions with each other is preferably 0.7 or less.
By creating excellent symmetry, control of the linear motor or the like can be made easy and thrust fluctuation can be suppressed.
In the rare-earth sintered magnet in the above aspect, the thickness dimension in the thickness direction is preferably 10 mm or less.
If the thickness dimension is too large, a sufficient magnetic field cannot be applied to the rare-earth sintered magnet sintered body depending on a currently available magnetic field applying device and thus, the thickness dimension in the thickness direction is preferably limited to a certain size in order to obtain a desired surface magnetic flux density by sufficiently magnetizing the sintered body.
In the rare-earth sintered magnet in the above aspect, the width dimension in the width direction on the plane is preferably 40 mm or less.
If the width dimension is too large, a sufficient magnetic field cannot be applied to the rare-earth sintered magnet sintered body depending on a currently available magnetic field applying device and thus, the width dimension in the width direction is preferably limited to a certain size in order to obtain the desired surface magnetic flux density by sufficiently magnetizing the sintered body.
The rare-earth sintered magnet in the above aspect may have a cuboid shape.
In order to solve the above problem, a rare-earth sintered magnet sintered body according to an aspect of the present invention is a rare-earth sintered magnet sintered body having a configuration in which a large number of magnet material particles including the rare-earth substance and each having the easy magnetization axis are integrally sintered, the rare-earth sintered magnet sintered body having a three-dimensional shape with a width direction, a thickness direction, and a length direction and including a first surface and a second surface opposing each other in the thickness direction, in which in the plane in parallel with the width direction and the thickness direction, the magnet material particles are oriented such that the orientation direction of the easy magnetization axis is gradually changed in a region from each of the both end portions in the width direction toward the center portion in the width direction, and the magnet material particles are oriented so that the maximum surface magnetic flux density of the magnet material particles each having the easy magnetization axis oriented in a direction crossing the first surface on the first surface and the maximum surface magnetic flux density of the magnet material particles each having the easy magnetization axis oriented in a direction crossing the second surface on the second surface satisfy a relationship of (D1′/D2′)≥4.
According to the rare-earth sintered magnet sintered body in this aspect, since the magnetic flux having practically useful surface magnetic flux density can be generated only in the first surface (one surface) of the magnet in the thickness direction or mainly in the one surface in the thickness direction, there is no need to provide many magnet materials on the second surface (the other surface) and there is no need to provide a yoke for catching a leakage magnetic flux leaking out of the magnetic circuit, or only a small quantity of the yoke needs to be provided, and as a result, a small-sized and light-weighted rare-earth sintered magnet sintered body can be provided.
In the rare-earth sintered magnet sintered body in the above aspect, the orientation directions of the easy magnetization axes may be different between each of the both end portions in the width direction and the center portion in the width direction by 90°±5° or 180°±5°.
Moreover, in the rare-earth sintered magnet sintered body in the above aspect, the orientation directions of the easy magnetization axes may be different between each of the both end portions in the width direction and the center portion in the width direction by 90°±5°, and only the N-pole or the S-pole is generated in the first surface.
Moreover, in the rare-earth sintered magnet sintered body in the above aspect, the orientation direction of the easy magnetization axis may be different between each of the both end portions in the width direction and the center portion in the width direction by 180°±5°, and the N-pole or the S-pole is generated on the one side in the width direction of the first surface, while the S-pole or the N-pole with polarity opposite to that on the one side is generated on the other side in the width direction of the first surface.
In the rare-earth sintered magnet sintered body in the above aspect, a thickness dimension in the thickness direction is preferably 10 mm or less.
If the thickness dimension is too large, a sufficient magnetic field cannot be applied to the rare-earth sintered magnet sintered body depending on a currently available magnetic field applying device and thus, the thickness dimension in the thickness direction is preferably limited to a certain size in order to obtain the desired magnetic flux density by sufficiently magnetizing the sintered body.
In the rare-earth sintered magnet sintered body in the above aspect, the width dimension in the width direction is preferably 40 mm or less.
If the width dimension is too large, a sufficient magnetic field cannot be applied to the rare-earth sintered magnet sintered body depending on a currently available magnetic field applying device and thus, the width dimension in the width direction is preferably limited to a certain size in order to obtain the desired surface magnetic flux density by sufficiently magnetizing the sintered body.
In order to solve the above problem, the magnetic field applying device according to an aspect of the present invention includes a magnetic body yoke including a pair of yoke legs located at an interval in the width direction and a recess portion formed between the pair of yoke legs, and on a side adjacent to the recess portion on each of upper surfaces of the pair of yoke legs, a work placing portion across the recess portion of the magnetic body yoke is formed between the pair of yoke legs so that a work placing surface with a predetermined width is formed, and a magnetic field is applied to a work placed on the work placing portion, forming a magnetic field from one of the pair of yoke legs via a portion corresponding to the work placing surface on the upper surface of one of the yoke legs, passing through the work placed on the work placing portion in the width direction, via a portion corresponding to the work placing surface on the upper surface of the other of the pair of yoke legs and reaching the other yoke leg.
In the magnetic field applying device in the above aspect, a pair of non-magnetic body yokes disposed on the upper surfaces of the pair of yoke legs are further provided, each of the pair of non-magnetic body yokes is positioned on each of the upper surfaces of the pair of yoke legs with respect to the corresponding yoke legs so that the work placing surface with the predetermined width is left on a side adjacent to the recess portion of the magnetic body yoke, a work placing portion across the recess portion of the magnetic body yoke is formed between the pair of non-magnetic body yokes, and the magnetic field may be formed with respect to the work placed on the work placing portion, from one of the pair of yoke legs via a portion corresponding to the work placing surface on the upper surface of the one of yoke legs, passing through the work placed on the work placing portion in the width direction, via a portion corresponding to the work placing surface on the upper surface of the other of the pair of yoke legs and reaching the other yoke leg.
In the magnetic field applying device in the above aspect, the pair of yoke legs have a portion extending with the recess portion in a length direction orthogonal to both the width direction and the thickness direction of the recess portion, and the formed magnetic field is preferably formed by using a first conductor disposed on the recess portion along the length direction, a second conductor disposed along the length direction on a side opposite to the recess portion with respect to one of the pair of yoke legs in the width direction, and a third conductor disposed along the length direction on the side opposite to the recess portion with respect to the other of the pair of yoke legs in the width direction.
Moreover, in the magnetic field applying device in the above aspect, a direction of a current made to flow through the first conductor and a direction of the current made to flow through the second and third conductors are opposite to each other.
Furthermore, in the magnetic field applying device in the above aspect, the first conductor is made of a pair of conductors separated in the width direction, and it is preferable that one of the conductors in the pair of conductors disposed on a side closer to one of the pair of yoke legs in the width direction is connected to the second conductor, and the other conductor in the pair of conductors disposed on the side closer to the other of the pair of yoke legs in the width direction is connected to the third conductor.
In the magnetic field applying device in the above aspect, the magnetic body yoke further includes a plurality of additional yoke legs located at intervals from each other in the width direction between the pair of yoke legs and a recess portion formed between the pair of yoke legs and the plurality of additional yoke legs and between the plurality of additional yoke legs and between the plurality of additional yoke legs, and a first magnetic field toward the upper surface of one yoke leg in the pair of yoke legs adjacent to one yoke leg in the plurality of additional yoke legs and/or toward the upper surface of any of the other yoke legs in the plurality of additional yoke legs adjacent to the one yoke leg from the upper surface of the one yoke leg passing through the work placed on the work placing portion in the width direction and a second magnetic field from the upper surface of one yoke leg of the pair of yoke legs adjacent to the one yoke leg in the plurality of additional yoke legs and/or from the upper surface of any of the other yoke legs in the plurality of additional yoke legs adjacent to the one yoke leg toward the upper surface of the one yoke leg passing through the work placed on the work placing portion in the width direction may be formed alternately in the width direction between the pair of yoke legs and the plurality of additional yoke legs adjacent to each other.
Moreover, in the magnetic field applying device in the above aspect, the pair of yoke legs and the plurality of additional yoke legs have a portion extending with the recess portion in the length direction orthogonal to both the width direction and the thickness direction of the recess portion, and the first magnetic field and the second magnetic field may be formed by using a plurality of conductors disposed so as to sandwich each of the plurality of additional yoke legs in the width direction and disposed on the recess portion along the length direction.
Furthermore, in the magnetic field applying device in the above aspect, a direction of the current made to flow through the conductor disposed on the one side in the width direction and a direction of the current made to flow through the conductor disposed on the other side in the width direction are directions opposite to each other for each of the plurality of additional yoke legs.
Furthermore, in the magnetic field applying device in the above aspect, the conductor disposed on the one side in the width direction and the conductor disposed on the other side in the width direction are preferably connected to each other for each of the plurality of additional yoke legs.
According to the present invention, the rare-earth sintered magnet which can generate the magnetic flux having practically useful surface magnetic flux density only in the one surface in the thickness direction or mainly in the one surface in the thickness direction without increasing the size or the weight of the magnet unit, and the sintered body for the rare-earth sintered magnet for use with the same can be provided. Moreover, the magnetic field applying device which can be used for manufacturing them can be provided.
With reference to the accompanying drawings, the present invention will be described based on a preferred embodiment thereof. Although only a preferred embodiment of the present invention will be described below for the same of simplicity, it is to be understood that such an embodiment is not intended to limit the present invention.
In these rare-earth sintered magnets, a plurality of arrows depicted in a flat end surface in parallel with a width direction “α” and a thickness direction “β”, that is, in each of an end surface 14a of the rare-earth sintered magnet 1 in
The rare-earth sintered magnet 3 in
Moreover, the rare-earth sintered magnet 3 depicted in
Any of the rare-earth magnets 1 to 4 depicted in
A width dimension “W” in the width direction “α” of the rare-earth sintered magnets 1 to 4 is preferably small within a practical range, and when performances of a currently available magnetic field applying device are considered, it needs to be 10 mm or more and 40 mm or less, 30 mm or less is preferable, 20 mm or less is more preferable, and 10 mm or less is further preferable. If the width dimension “W” is too small or too large, since a sufficient magnetic field cannot be applied to the rare-earth sintered magnet sintered body depending on the currently available magnetic field applying device, the width dimension in the width direction is preferably limited to a certain size in order to obtain the desired surface magnetic flux density by sufficiently magnetizing the sintered body.
A thickness dimension “t” in the thickness direction “β” is preferably small within a practical range. By decreasing the thickness dimension, the size or the weight of the magnet unit can be reduced. However, if the thickness dimension is too small, sufficient surface magnetic flux density cannot be generated and thus, it needs to be at least 1 mm or more. On the other hand, if the thickness dimension is too large, since a sufficient magnetic field cannot be applied to the rare-earth sintered magnet sintered body, it needs to be 12 mm or less in order to sufficiently magnetize the sintered body by considering the performances of the currently available magnetic field applying device, 10 mm or less is preferable, 8 mm or less is more preferable, 6 mm or less is further preferable, and 4 mm or less is furthermore preferable. Moreover, as will be described later, if the thickness dimension is too large, since the maximum surface magnetic flux density cannot be improved efficiently, the thickness dimension in the thickness direction is preferably limited to a certain size while the maximum surface magnetic flux density is kept at a desired value also from a viewpoint that the maximum surface magnetic flux density is improved efficiently.
A length dimension “K” in the length direction “γ” can be determined relatively freely, but it is preferably 5 mm to 100 mm, more preferably 5 mm to 50 mm or further preferably 5 mm to 40 mm by considering the performances of the currently available magnetic field applying device.
Here, the surface magnetic flux density distribution is set so as to be substantially symmetrical by adjusting the orientation direction of the easy magnetization axis or the like.
As is obvious from
As is obvious from above, the rare-earth sintered magnet 1 generates the magnetic flux having the practically useful surface magnetic flux density particularly in the vicinity of the center portion (13c) in the width direction “α”, here, only in the one surface 11 in the thickness direction “β” or mainly in the one surface in the thickness direction.
As depicted in
In the rare-earth sintered magnet 2A depicted in
As is obvious from the above, the rare-earth sintered magnet 2 generates the magnetic flux having the practically useful surface magnetic flux density particularly at a position biased to the one side surface 23a or to the other side surface 23b rather than the center portion (23c) in the width direction “α”, here, only in the one surface 21 in the thickness direction “β” or mainly in the one surface in the thickness direction.
The magnetic forces generated in the side surfaces 23a and 23b located on the both end portions in the width direction “α” generate some or less repulsion to each other, but since the force is weak, a plurality of the rare-earth sintered magnets 2A and 2B can be also arrayed alternately in a state where their side surfaces 23a and 23b abut to each other as depicted in
As is obvious from
On the other hand, as is obvious from
As is obvious from the above, the rare-earth sintered magnets 3 and 4 generate the magnetic flux having the practically useful surface magnetic flux density only in the one surfaces 31 and 41 in the thickness direction “β” or mainly in the one surface in the thickness direction or particularly at the center portions (33c, 43c) in the width direction “α” and positions biased to the one surfaces 33a and 43a or to the other side surfaces 33b and 43b rather than the center portions (33c, 43c) in the width direction “α”, here.
The rare-earth sintered magnets 3 and 4 depicted in
As described above, since any of the rare-earth sintered magnets 1 to 4 depicted in
The rare-earth sintered magnets 1 to 4 depicted in
A rare-earth magnet-forming material serving as a basis for the rare-earth sintered magnet sintered body includes a magnet material containing a rare-earth substance. As the magnet material, it is possible to use, e.g., an Nd—Fe—B based magnet material. In this case, for example, the Nd—Fe—B based magnet material may contain, in terms of weight percent: R (R denotes one or more rare-earth elements including Y) in an amount of 27.0 to 40.0 wt %, preferably, 27.0 to 35 wt %; B in an amount of 0.6 to 2 wt %, preferably, 0.6 to 1.1 wt %; and Fe which is electrolytic iron in an amount of 60 to 75 wt %. Typically, the Nd—Fe—B based magnet material contains: Nd in an amount of 27 to 40 wt %; B in an amount of 0.8 to 2 wt % of B; and Fe in an amount of 60 to 70 wt %. With a view to improving magnetic properties, this magnet material may contain other element such as Dy, Tb, Co, Cu, Al, Si, Ga, Nb, V, Pr, Mo, Zr, Ta, Ti, W, Ag, Bi, Zn, or Mg, in a small amount.
The magnet material is comprised in the rare-earth magnet-forming material, in the form of fine magnet material particles. The rare-earth sintered magnets 1 to 4 and the rare-earth sintered magnet sintered body have a configuration in which these magnet material particles are integrally sintered, that is, a form in which the magnet material particles are connected to each other with a connection structure specific to the magnet and the sintered body at any position in these magnets or sintered bodies and thus, they have the configuration different from a magnet or a magnet forming sintered body obtained by cutting out a piece with a desired shape from a magnet or a sintered body and bonding a plurality of cut-out pieces to each other, for example.
Each of the magnet material particles has an easy magnetization axis oriented in a predetermined direction as depicted by arrows in
For example, an orientation direction of the easy magnetization axis in the rare-earth sintered magnet sintered body before the rare-earth sintered magnet 1 in
Similarly, the orientation direction of the easy magnetization axis in the rare-earth sintered magnet sintered body before the rare-earth sintered magnet 2 in
Moreover, the orientation direction of the easy magnetization axis in the rare-earth sintered magnet sintered body before the rare-earth sintered magnet 3 in
Furthermore, the orientation direction of the easy magnetization axis in the rare-earth sintered magnet sintered body before magnetizing the rare-earth sintered magnet 4 in
The easy magnetization axis usually does not have polarity, but since it becomes a vector having a polarity when the magnet material particles are magnetized, arrows giving directionality to the easy magnetization axes are depicted in
Respective meanings of terms relating to orientation will be described below.
The term “orientation angle” means an angle of the direction of the orientation axis of the easy magnetization axis of the magnet material particle with respect to a predetermined reference line.
The term “orientation axis angle” means a most frequently appearing orientation angle among orientation angles of the magnet material particles contained in a predetermined discrete area in a specific plane of a magnet. The area for determining the orientation axis angle is set as a rectangular area including at least 30, e.g., 200 to 300 magnet material particles, or a square area having a side length of 35 μm.
The “orientation axis angle” is an angle between these orientation axes denoted by arrows in
As depicted in
In an arbitrary rectangular area, a difference between the orientation axis angle and each of the orientation angles of the easy magnetization axes of all the sintered magnet material particles contained in the rectangular area is determined. Then, an angle value represented by a half width in a distribution of a deviation of the orientation angle with respect to the orientation axis angle is defined as an orientation angle deviation.
The orientation angle of the easy magnetization axis in each of the sintered magnet material particles P can be determined by an “Electron Back scatter Diffraction Analysis” (EBSD Analysis) based on a scanning electron microscopical (SEM) image. Examples of devices which can be used for the analysis are: JSM-70001F manufactured by Nihon Electron KK (JEOL Ltd.) having a head office in Akishima City, Tokyo, Japan, which is a scanning electron microscope equipped with an EBSD Detector (AZtecHKL EBSD NordlysNano Integrated) manufactured by Oxford Instruments, and SUPRA40VP manufactured by ZEISS, which is a scanning electron microscope equipped with an EBSD detector (Hikari High Speed EBSD Detector) manufactured by EDAX Inc. Further, examples of an entity who undertakes EBSD analysis as an outsourcing business include JFE Techno-Research Co., having a head office in Nihonbashi, Chuo-ku, Tokyo, Japan, and Nitto Analytical Techno-Center in Ibaraki City, Osaka, Japan. Through the EBSD analysis, it is possible to determine the orientation angles and the orientation axis angle regarding the easy magnetization axes of the sintered magnet material particles contained in a given area.
A manufacturing method according to an embodiment of the present invention which can be used for manufacturing the rare-earth sintered magnets 1 to 4 depicted in
The rare-earth magnet-forming material serving as a basis for the rare-earth sintered magnets 1 to 4 is prepared.
Subsequently, the coarsely-pulverized magnet material particles 115 are finely pulverized by a pulverization method such as a wet process using a bead mill 116, or a dry process using a jet mill. For example, in the fine pulverization based on the wet process using the bead mill 116, the coarsely-pulverized magnet material particles 115 are finely pulverized, in the solvent, to an average particle size falling within a given range, e.g., 0.1 μm to 5.0 μm to thereby disperse the resulting magnet material particles in the solvent (see
On the other hand, in the fine pulverization based on the dry process using the jet mill, the coarsely-pulverized magnet material particles 115 are finely pulverized by the jet mill, in (a) an atmosphere consisting inert gas such as nitrogen gas, Ar gas or He gas, wherein an oxygen content of the inert gas is 0.5% or less, preferably substantially 0%, or (b) an atmosphere consisting inert gas such as nitrogen gas, Ar gas or He gas, wherein an oxygen content of the inert gas is in the range of 0.001 to 0.5%, and pulverized into fine particles having an average particle size of 6.0 μm or less, or an average particle size falling within a given range, e.g., of 0.7 μm to 5.0 μm. Here, the term “the concentration of oxygen is substantially 0%” does not limitedly mean that the concentration of oxygen is absolutely 0%, but means that oxygen may be contained in an amount to an extent that it very slightly forms an oxide layer on surfaces of the fine particles. If hydrogen remains in the magnetic powder, an organic component is altered and thus, hydrogen is preferably removed from the pulverized magnetic powder. In order to remove hydrogen, the temperature may be raised from a room temperature to 120° C. or above in 0.5 hours, for example, and then, the temperature may be held for a predetermined period of time or one hour or more, for example.
Subsequently, the magnet material particles finely pulverized by the bead mill 116 or other pulverizing means are formed into a desired shape. For shaping of the magnet material particles, a mixture obtained by mixing the magnet material particles 115 finely pulverized in the above manner and a binder together, i.e., a composite material, is preliminarily prepared. As a resin material to be used as the binder, it is preferable to use a polymer containing no oxygen atom in its structure and having a depolymerization property. Further, it is preferable to use, as the resin material, a thermoplastic resin so as to enable a residue of the composite material of the magnet material particles and the binder, generated when the composite material is formed into a desired shape, to be reused, and enable magnetic field orientation to be performed under the condition that the resin material is softened by heating the composite material. More specifically, a polymer is suitably used which comprises one or more polymers or copolymers formed from a monomer represented by the following general formula (1):
(where each of R1 and R2 denotes one of a hydrogen atom, a lower alkyl group, a phenyl group and a vinyl group.)
Examples of a polymer satisfying the above conditions include: polyisobutylene (PIB) as a polymer of isobutylene; polyisoprene (isoprene rubber (IR)) as a polymer of isoprene; polypropylene, a poly(α-methylstyrene) polymerized resin as a polymer of α-methylstyrene; polyethylene; polybutadiene (butadiene rubber (BR)) as a polymer of 1,3-butadiene; polystyrene as a polymer of styrene; a styrene-isoprene-styrene block copolymer (SIS) as a copolymer of styrene and isoprene; butyl rubber (IIR) as a copolymer of isobutylene and isoprene; a styrene-butadiene-styrene block copolymer (SBS) as a copolymer of styrene and butadiene; a styrene-ethylene-butadiene-styrene copolymer (SEBS) as a copolymer of styrene, ethylene and butadiene; a styrene-ethylene-propylene-styrene copolymer (SEPS) as a copolymer of styrene, ethylene and propylene; an ethylene-propylene copolymer (EPM) as a copolymer of ethylene and propylene; EPDM obtained by copolymerizing diene monomers together with ethylene and propylene; a 2-methyl-1-pentene polymerized resin as a polymer of 2-methyl-1-pentene; and a 2-methyl-1-butene polymerized resin as a polymer of 2-methyl-1-butene. A resin to be used as the binder may have a composition containing a polymer or copolymer of monomers containing an oxygen atom and/or a nitrogen atom (e.g., poly(butyl methacrylate) or poly(methyl methacrylate)) in a small amount. Further, a monomer which does not meet the general formula (1) may be partially copolymerized. Even in such a situation, it is possible to achieve the object of the present invention.
As a resin to be used as the binder, it is desirable, from a viewpoint of adequately performing magnetic field orientation, to use a thermoplastic resin capable of being softened at a temperature of 250° C. or less, more specifically a thermoplastic resin having a glass-transition temperature or flow start temperature of 250° C. or less.
In order to disperse the magnet material particles over the thermoplastic resin, it is desirable to add an orientation lubricant in an appropriate amount. As the orientation lubricant, it is desirable to add at least one selected from the group consisting of alcohol, carboxylic acid, ketone, ether, ester, amine, imine, imide, amide, cyanogen, phosphorous functional group, sulfonic acid, a composite material having an unsaturated bond such as a double bond or a triple bond, and a liquid, saturated hydrocarbon composite material. Two or more of them may be used in the form of a mixture. Further, in applying a magnetic field to the mixture of the magnet material particles and the binder, i.e., the composite material, to thereby magnetically orient the magnet material particles, as described later, the mixture is heated to allow such magnetic field orientation treatment to be performed under the condition that the binder component is softened.
By using a binder satisfying the above conditions to serve as the binder to be mixed with the magnet material particles, it is possible to reduce an amount of carbon and an amount of oxygen remaining in a sintered body after sintering. Specifically, the amount of carbon remaining in the sintered body after sintering may be reduced to 2000 ppm or less, preferably 1000 ppm or less. Further, the amount of oxygen remaining in the sintered body after sintering may be reduced to 5000 ppm or less, preferably 2000 ppm or less.
An addition amount of the binder is set to a value capable of, when shaping a slurry-form or heated and melted composite material, filling gaps among the magnet material particles so as to provide improved thickness accuracy to a shaped body obtained as a result of the shaping. For example, the ratio of the binder to a total amount of the magnet material particles and the binder is preferably set in the range of 1 wt % to 40 wt %, more preferably 2 wt % to 30 wt %, still more preferably 3 wt % to 20 wt %, particularly preferably 5 wt % to 15 wt %. Further, the ratio of the resin material to be used in the binder to a total amount of the magnet material particles and the resin material is preferably set in the range of 1 wt % to 30 wt %, more preferably in the range of 2 wt % to 20 wt %, still more preferably in the range of 3 wt % to 15 wt %, particularly preferably in the range of 3.5 wt % to 12 wt %.
In the following embodiments, the mixture of the magnet material particles and the binder, i.e., a composite material 117, is once formed into a sheet-like green shaped body (hereinafter referred to as “green sheet”), and then further formed into a shape for the orientation treatment. For forming the composite material, particularly, into a sheet shape, it is possible to employ: a forming method using, for example, a hot-melt coating process which comprises heating the composite material 117 as the mixture of the mixture of the magnet material particles and the binder, and then forming the melt into a sheet shape: a process which comprises putting the composite material 117 as the mixture of the magnet material particles and the binder into a forming die, and heating the composite material 117 while applying a pressure thereto, to thereby form the composite material into a sheet shape; a process which comprises extruding the composite material by an extruder to thereby form the composite material into a sheet shape; or a slurry coating process which comprises coating a slurry containing the magnet material particles, the binder and an organic solvent, on a substrate, to thereby form the slurry into a sheet shape.
In the following description, description will be made about formation of the green sheet using, particularly, the hot-melt coating process. However, the present invention is not limited to such a specific shaping process. For example, the composite material 117 may be put in a shaping die and shaped under a pressure of 0.1 to 100 MPa while heating at a temperature of room temperature to 300° C. More specifically, in this case, it is possible to employ a process which comprises applying an injection pressure to the composite material 117 heated to a softening temperature, so as to press and charge the composite material 117 into a die, to thereby form the composite material 117 into a sheet shape.
As previously mentioned, a binder is mixed with the magnet material particles finely pulverized using the bead mill 116 or the like to produce a clayey mixture of the magnet material particles and the binder, i.e., the composite material 117. Here, it is possible to use, as the binder, a mixture of a resin and an orientation lubricant, as mentioned above. As one example of the binder, it is preferable to use a thermoplastic resin comprising a polymer containing no oxygen atom in its structure and having a depolymerization property. Further, as the orientation lubricant, it is preferable to add at least one selected from the group consisting of alcohol, carboxylic acid, ketone, ether, ester, amine, imine, imide, amide, cyanogen, phosphorous functional group, sulfonic acid, and a compound having an unsaturated bond such as a double bond or a triple bond.
Among them, it is preferable to use a compound having an unsaturated bond. Examples of this type of compound include a compound having a double bond or a triple bond. Particularly, a compound having a triple bond is preferable, from a viewpoint of being capable of promising an effect of reducing crack in the sintered body.
As the compound having a triple bond, it is preferable to use a compound capable of being easily removed in the aftermentioned calcination treatment. Therefore, the compound to be used is preferably a compound having no hetero atom, particularly preferably a compound consisting only of hydrocarbon. Further, in order to enable stronger interaction with the surfaces of the magnet material particles to thereby bring out a higher orientation lubricating effect, the compound having a triple bond preferably has the triple bond at the end.
With regard to the compound having a triple bond, from a viewpoint of raising the boiling point thereof to facilitate handling, the number of carbon as a constituent element of the compound is preferably 10 or more, more preferably 14 or more, further preferably 16 or more, particularly preferably 18 or more. Although the upper limit of the carbon number is not particularly limited, it may be set to, e.g., 30 or less.
With regard to the compound having a double bond, from a viewpoint of enabling stronger interaction with surfaces of the magnet material particles to bring out a higher orientation lubricating effect, it is preferable to use a compound having a functional group with a hetero atom, and more preferably a compound having a functional group with a hetero atom at the end.
The number of carbon constituting the compound having a double bond is preferably 6 or more, more preferably 10 or more, further preferably 12 or more, particularly preferably 14 or more. Although the upper limit of the carbon number is not particularly limited, it may be set to, e.g., 30 or less.
Further, the compounds having a triple bond and the compound having a double bond may be used in combination.
As previously mentioned, the addition amount of the binder is set such that the ratio of the binder to a total amount of the magnet material particles and the binder in the composite material 117 after the addition is preferably set in the range of 1 wt % to 40 wt %, more preferably 2 wt % to 30 wt %, still more preferably 3 wt % to 20 wt %, particularly preferably 5 wt % to 15 wt %. Further, the ratio of a resin material to be used in the binder to a total amount of the resin material and the magnet material particles is preferably set in the range of 1 wt % to 30 wt %, more preferably 2 wt % to 20 wt %, still more preferably 3 wt % to 15 wt %, particularly preferably 3.5 wt % to 12 wt %.
Here, an addition amount of the orientation lubricant is preferably determined depending on a particle size of the magnet material particles, and it is recommended to increase the addition amount as the particle size of the magnet material particles becomes smaller. Specifically, the addition amount may be set in the range of 0.01 weight parts to 20 weight parts, preferably in the range of 0.3 weight parts to 10 weight parts, more preferably in the range of 0.5 weight parts to 5 weight parts, particularly preferably in the range of 0.8 weight parts to 3 weight parts, with respect to 100 weight parts of the magnet material particles. If the addition amount is excessively small, a dispersion effect becomes poor, possibly leading to deterioration in orientation property. On the other hand, if the addition amount is excessively large, the lubricant is likely to contaminate the magnet material particles. The orientation lubricant added to the magnet material particles adheres onto surfaces of the magnet material particles, and acts to facilitate dispersion of the magnet material particles to provide the clayey mixture, and to assist turning of the magnet material particles in the aftermentioned magnetic field orientation treatment. As a result, it becomes possible to facilitate orientation during application of a magnetic field so as to uniformize respective directions of the easy magnetization axes of the magnet material particles, into approximately the same direction, resulting in an increase in the degree of orientation. Particularly, in the case where the binder is mixed with the magnet material particles, the binder tends to be present around the surfaces of the magnet material particles, so that a frictional force against the magnet material particles during the magnetic field orientation treatment is increased, thereby possibly leading to deterioration in orientation property of the magnet material particles. Thus, the effect arising from addition of the orientation lubricant becomes more important.
Preferably, the mixing of the magnet material particles and the binder is performed in an atmosphere of inert gas such as nitrogen gas, Ar gas or He gas. The mixing of the magnet material particles and the binder is performed, for example, by charging the magnet material particles and the binder into a stirring machine and stirring them using the stirring machine. In this case, with a view to enhancing kneading performance, heating-stirring (stirring under heating) may be performed. It is also desirable to perform the mixing of the magnet material particles and the binder, in an atmosphere of inert gas such as nitrogen gas, Ar gas or He gas. Particularly, in the case where the coarsely-pulverized magnet material particles are finely pulverized by a wet process, the composite material 117 may be obtained by adding the binder to a solvent used for pulverization, without extracting the magnet material particles from the solvent, and, after kneading the resulting mixture, volatilizing the solvent.
Subsequently, the composite material 117 is formed into a sheet shape to prepare the aforementioned green sheet. Specifically, in case of employing the hot-melt coating process, the composite material 117 is heated and melted to have flowability, and then coated on a support substrate 118. Subsequently, the composite material 117 is solidified by heat dissipation to form an elongated strip-shaped green sheet 119 on the support substrate 118 (see
Here, as a coating system for the melted composite material 117, it is preferable to use a system having excellent layer thickness controllability, such as a slot-die system or a calender roll system. Particularly, in order to realize high thickness accuracy, it is desirable to use a die system or a comma coating system which is a system having particularly excellent layer thickness controllability, i.e., a system capable of coating a layer having a highly-accurate thickness, on a surface of a substrate. For example, in the slot-die system, the composite material 117 after being heated to have flowability is pressure-fed from a gear pump into a die, and discharged from the die to perform coating. On the other hand, in the calender roll system, the composite material 117 is fed into a nip gap between two heated rolls, in a controlled amount, and the rolls are rotated to coat the composite material 117 melted by heat of the rolls, onto the support substrate 118. As one example of the support substrate 118, it is preferable to use a silicone-treated polyester film. Further, it is preferable to use a defoaming agent or perform vacuum heating defoaming to sufficiently defoam a layer of the coated and developed composite material 117 so as to prevent gas bubbles from remaining in the layer. Alternatively, the melted composite material 117 may be extruded onto the support substrate 118 while being formed into a sheet shape, by an extrusion forming or injection forming, instead of being coated on the support substrate 118, to thereby form the green sheet 119 on the support substrate 118.
In the embodiment depicted in
Preferably, the thickness of the green sheet 119 is set in the range of 0.05 mm to 20 mm. If the thickness is reduced to 0.05 mm or less, it becomes necessary to laminate a plurality of layers so as to achieve a required magnet thickness, resulting in reduced productivity.
Last of all, the green sheet 119 formed on the support substrate 118 by the hot-melt coating process is cut into a size corresponding to a desired magnet size to form a processing sheet piece. The processing sheet piece can be deemed as one example of the rare-earth magnet-forming material, because it will subsequently be set in a sintering die, and serves as a basis for the rare-earth sintered magnet. Further, the green sheet 119 serves as a raw material or a precursor member for the processing sheet piece, i.e., as a basis for the rare-earth sintered magnet. Thus, it is to be understood that the green sheet 119 falls into the concept of the rare-earth magnet-forming material. Further, it is possible to use, as the rare-earth magnet-forming material, not only a shaped body produced by the aforementioned green sheet forming method, but also a shaped body produced by a powder compacting method. This will be specifically described later.
The shape of the processing sheet piece when it is cut out from the green sheet 119 is determined while taking into account the shape of the rare-earth sintered magnets 1 to 4 as a final product, and an actual size of the processing sheet piece just after the cutting-out is determined while taking into account dimensional shrinkage in a pressing direction (pressure application direction) in a sintering step, so as to obtain a given magnet size after the sintering step. The sintering step is performed by pressure-sintering, as described later. Thus, although shrinkage occurs in the processing sheet piece in the pressing direction (the length direction “γ” in
The processing sheet piece is heated, and the gradually changing magnetic field is applied along the direction of the arrow schematically depicted in
Although a temperature and a time period for heating the processing sheet piece varies depending on the type and amount of the binder used, they may be set, e.g., in range of 40 to 250° C. and in the range of 0.1 to 60 minutes, respectively. In either case, in order to soften the binder comprised in the processing sheet piece, the heating temperature needs to be set to a value equal to or greater than a glass-transition temperature or a flow start temperature of the binder used. Examples of means to heat the processing sheet piece include a heating system using a hot plate, and a system using, as a heat source, a heating medium such as silicone oil. A magnetic field intensity during the magnetic field application may be set in the range of 5000 [Oe] to 150000 [Oe], preferably 10000 [Oe] to 120000 [Oe], particularly preferably 25000 [Oe] to 70000 [Oe]. As a result, the easy magnetization axes of the magnet material particles comprised in the processing sheet piece are oriented along the direction of the magnetic field. This magnetic field application step may be configured such that a magnetic field is simultaneously applied to a plurality of the processing sheet pieces. In this case, the magnetic field may be simultaneously applied, using a die having a plurality of cavities, or a plurality of dies arranged side-by-side. The step of applying a magnetic field to the processing sheet piece may be performed in concurrence with the heating step, or during a period after completion of the heating step and before solidification of the binder of the processing sheet piece.
The oriented processing sheet piece in which the easy magnetization axes are oriented is subjected to calcination treatment in a non-oxidizing atmosphere adjusted at an atmospheric pressure, or a pressure greater or less than the atmospheric pressure such as 0.1 MPa to 70 MPa, preferably 1.0 Pa or 1.0 MPa, under a decomposition temperature of the binder, for a holding time of at least 2 hours or more or preferably several hours to several ten hours, e.g., 5 hours. In this treatment, it is recommended to use a hydrogen atmosphere or a mixed gas atmosphere of hydrogen and inert gas. In the case where the calcination treatment is performed in a hydrogen atmosphere, a supply amount of hydrogen during the calcination is set to 2 to 6 L/min, e.g., 5 L/min, but it can be changed as appropriate by a size of a furnace for calcination or a filling amount of the processing sheet piece. The calcination treatment makes it possible to remove the binder, i.e., an organic compound comprised in the composite material obtained by mixing the magnet material particles with the thermoplastic resin, by decomposing the organic compound to monomers through a depolymerization reaction or other reaction, and releasing the monomers. That is, decarbonizing which is treatment for reducing the amount of carbon remaining in the processing sheet piece is performed. Further, it is preferable to perform the calcination treatment under conditions which enable the amount of carbon remaining in the processing sheet piece to become 2000 ppm or less, preferably 1000 ppm or less. This makes it possible to densely sinter the entire processing sheet piece through subsequent sintering treatment to thereby suppress deteriorations in residual magnetic flux density and coercivity. Here, in the case where a pressurization condition during the calcination treatment is set to a pressure greater than atmospheric pressure, it is desirable to set the pressure to 15 MPa or less. Further, the pressurization condition may be set to a pressure greater than atmospheric pressure, more specifically, 0.2 MPa or more. In this case, an effect of reducing the amount of residual carbon can be particularly expected. Although a calcination temperature varies depending on the type of binder, the temperature may be set in the range of 250° C. to 600° C., preferably 300° C. to 550° C., such as 450° C.
In the above calcination treatment, it is preferable to set a temperature rise rate to a smaller value, as compared to typical sintering treatment of a rare-earth sintered magnet. Specifically, the temperature rise rate may be set to 2° C./min or less, e.g., 1.5° C./min to obtain a preferable result. Thus, the calcination treatment is performed such that the calcination temperature is raised at a given temperature rise rate of 2° C./min or less, as depicted in
Deoiling treatment may be performed before the calcination treatment for dissipating oil contents such as the orientation lubricant, plasticizer, etc. A temperature during the deoiling treatment varies depending on the type of oil contained, the temperature may be set in the range of 60° C. to 120° C., preferably in the range of 80° C. to 100° C. In the deoiling treatment, a preferably result can be obtained by setting the temperature rise rate to 5° C./min or less, e.g., 0.7° C./min. A more preferable result can be obtained by performing the deoiling treatment in an atmosphere at a reduced pressure, preferably of 0.01 Pa to 20 Pa, more preferably of 0.1 Pa to 10 Pa. Here, the magnetic properties of the rare-earth sintered magnet as a final product do not vary depending on whether or not the deoiling treatment is performed.
The sintering process is performed in a state in which the processing sheet piece is set inside a preliminarily-prepared sintering die (not depicted) comprising a pair of a male die half and a female die half. The sintering die has a cavity with a shape corresponding to that of the rare-earth sintered magnet as a final product, e.g., a cavity having a cross-section corresponding to that of the processing sheet piece. The processing sheet piece is set inside the sintering die, in a state in which each of the easy magnetization axes thereof is oriented in one plane, i.e., is oriented in one plane defined by the width direction “α” and the thickness direction “β” in
In the sintering treatment “A”, the calcined processing sheet piece is heated and sintered, while a pressing force is applied thereto by clamping the processing sheet piece between the male die half and the female die half to load a press pressure thereon, that is, the calcined processing sheet piece is subjected to pressure sintering. The pressing direction is set to a direction (the length direction “γ” in
Raising of the pressure is initiated when the temperature reaches, e.g., 300° C. (in the example depicted in
After reaching the pressure-raising initiation temperature, the processing sheet piece 3 is heated at the constant temperature rise rate, until the temperature reaches a predetermined first maximum achieving temperature. Preferably, the first maximum achieving temperature is set to greater than 900° C., e.g., in a reduced-pressure atmosphere at several Pa or less. If the first maximum achieving temperature is set to 900° C. or less, a void is generated in the processing sheet piece 3, and, when the high-temperature heat treatment “B” is subsequently performed, shrinkage of the processing sheet piece 3 occurs not only in the pressing direction but also in all directions, leading to difficulty in controlling a shape or the like of the magnet as a final product. By setting the first maximum achieving temperature to greater than 900° C., it becomes possible to facilitate control of the shape. Preferably, the first maximum achieving temperature is determined while taking into account an average particle size and a composition of the magnet material particles forming the processing sheet piece 3. Generally, when the average particle size is relatively large, the first maximum achieving temperature needs to be set to a higher value. Further, when the content of a rare-earth substance is relatively small, the first maximum achieving temperature needs to be set to a higher value. Further, it is preferable that the pressure reaches the ultimately achieving load before the temperature reaches the first maximum achieving temperature.
By performing the above sintering treatment “A”, it is possible to suppress variation in shrinkage arising during the sintering to obtain a rare-earth sintered magnet-forming sintered body (called a sintered body “1A”, for convenience) having a desired shape. Here, the rare-earth sintered magnets 1 to 4 as a final product have the same size and shape as those of the sintered body 1A. Thus, the rare-earth sintered magnets 1 to 4 depicted in
As a pressing-sintering technique to be used in the sintering treatment “A”, it is possible to employ any heretofore-known technique such as hot press sintering, hot isostatic press (HIP) sintering, ultrahigh pressure synthesis sintering, gas pressure sintering, or spark plasma sintering (SPS). In particular, it is preferable to employ an inner-heat pressure sintering apparatus in which a heat source is installed inside a sintering furnace capable of applying a pressure in a uniaxial direction.
The sintered body 1A after being subjected to the sintering treatment “A” is cooled to room temperature, and heated to a given temperature again in the subsequent high-temperature heat treatment “B”. The cooling to room temperature may be natural cooling. The heating is performed in a reduced-pressure atmosphere, more specifically, under a pressure at least lower than the pressing force in the sintering treatment “A”. However, as long as the heating is performed in an atmosphere of inert gas such as argon gas, nitrogen gas, or helium gas, this atmosphere needs not be a reduced-pressure atmosphere. In the high-temperature heat treatment “B”, the temperature of the sintered body 1A is raised to a second maximum achieving temperature preliminarily set for the high-temperature heat treatment, within a given period of time, e.g., within 10 hours, preferably within 5 hours, more preferably within 2 hours. The second maximum achieving temperature for the high-temperature heat treatment is set in the range of greater than 900° C. to 1100° C. Further, the second maximum achieving temperature is set such that a difference from the first maximum achieving temperature reachable in the sintering treatment “A” is within 250° C., preferably within 150° C., more preferably within 100° C. By setting the difference from the first maximum achieving temperature reachable in the sintering treatment “A” to fall within the above range, it is possible to achieve both an increase in density after the sintering and an improvement in magnetic properties by the high-temperature heat treatment “B”. After reaching the second maximum achieving temperature, the second maximum achieving temperature is held for a given period of time (interval (b) depicted in
−1.13x+1173≥y≥−1.2x+1166(where 1100° C.≥x≥900° C.)
, where x (° C.) denotes the second maximum achieving temperature, and y (hour) denotes the holding time at a temperature around the second maximum achieving temperature.
The setting of the second maximum achieving temperature is also influenced by an average particle size of the magnet material particles after the fine pulverization. For example, when the average particle size is 1 μm, the second maximum achieving temperature is preferably set to greater than 900° C., and, when the average particle size is 5 μm, the second maximum achieving temperature is preferably set to 1100° C. or less. The average particle size is measured using a laser diffraction/scattering particle size distribution measuring device (device name: LA950; manufactured by Horiba Ltd.). Specifically, the magnet material particles after the fine pulverization are slowly oxidized at a relatively low oxidation rate. Then, a few hundred mg of the slowly-oxidized powder is uniformly mixed with silicone oil (product name: KF-9611-1 million cs; manufactured by Shin-Etsu Chemical Co., Ltd.) to form a paste-like mixture. Then, the paste-like mixture is clamped between quartz glass plates to obtain a test sample. (HORIBA paste method). In a graph presenting a particle size distribution (volume %), a value of D50 is defined as the average particle size. In a case where the particle size distribution has a double peak shape, D50 is calculated only with respect to a smaller peak of a particle size to obtain the average particle size.
A sintered body (called a sintered body “1B”, for convenience) after being subjected to the high-temperature heat treatment “B” is cooled again to room temperature, and heated to a given temperature again in the subsequent low-temperature heat treatment “C”. The cooling to room temperature may be natural cooling. The heating is performed in a reduced-pressure atmosphere, as with the high-temperature heat treatment “B”. However, as long as the heating is performed in an atmosphere of inert gas such as argon gas, nitrogen gas, or helium gas, this atmosphere needs not be a reduced-pressure atmosphere. In the low-temperature heat treatment “C”, the temperature of the sintered body 1B is raised to a third maximum achieving temperature preliminarily set for the low-temperature heat treatment, within a given period of time, e.g., within 10 hours, preferably within 5 hours, more preferably within 2 hours. The third maximum achieving temperature for the low-temperature heat treatment is set to a temperature less than the second maximum achieving temperature for the high-temperature heat treatment, e.g., in the range of 350° C. to 650° C., preferably 450° C. to 600° C., more preferably 450° C. to 550° C. After reaching the third maximum achieving temperature, the third maximum achieving temperature is held for a given period of time (interval (c) depicted in
A sintered body (called a sintered body “1C”, for convenience) after being subjected to the low-temperature heat treatment can be magnetized by using the magnetic field applying device 5 which will be described below, for example. However, the magnetic field applying device 5 does not necessarily have to be used, but currently available other general magnetic field applying devices may be also used. Via the magnetization step, the sintered body 1C becomes the rare-earth sintered magnet 1. The magnetized rare-earth sintered magnet 1 is installed on a linear motor, for example, after that.
The easy magnetization axes of the magnet material particles can be oriented by using the magnetic field applying device 5, and by applying the magnetic field to a work, e.g. a processing sheet piece which is an example of the material for forming the rare-earth magnet. In addition, the rare-earth sintered magnet 2 can be manufactured by magnetizing the rare-earth sintered magnet sintered body by using this device 5. Not only the orientation but also the orientation direction of the easy magnetization axis and the magnetization direction or in other words, the directions of magnetization of the rare-earth sintered magnets 1 to 4 can be easily matched by using the device 5 at magnetization, and the magnetization can be performed with higher accuracy. However, the device 5 does not necessarily have to be used for the orientation and the magnetization.
The magnetic field applying device 5 has a symmetrical shape in the width direction “α” and includes a magnetic body yoke 60 extending in the length direction “γ” and a non-magnetic body yoke 51 comprising a pair of non-magnetic body yokes 51A and 51B extending in the length direction “γ”.
The magnetic body yoke 60 includes a pair of yoke legs 61A and 61B extending in the length direction “γ” and a recess portion 62 formed between the pair of yoke legs 61A and 61B and extending in the length direction “γ”. The pair of yoke legs 61A and 61B has flat upper surfaces 61a and 61b, respectively, and is positioned at an interval “w3” in the width direction “α”.
Each of the pair of non-magnetic body yokes 51A and 51B is disposed on each of the upper surfaces 61a and 61b of the pair of yoke legs 61A and 61B, respectively, and is positioned with respect to the corresponding yoke legs 61A and 61B so that work placing surfaces 61a1 and 61b1 are left with a predetermined width “w2” on a side adjacent to the recess portion 62 of the magnetic body yoke 60 on each of the upper surfaces 61a and 61b of the pair of yoke legs 61A and 61B.
A work placing portion 67 having a cavity with a shape corresponding to a work is formed in order to place the work, e.g. a processing sheet piece and a rare-earth sintered magnet sintered body. The work placing portion 67 is formed in a state across the recess portion 62 of the magnetic body yoke 60 between the pair of non-magnetic body yokes 51A and 51B in the width direction “α”. A die 70 for applying the magnetic field in which the work is accommodated may be installed on the work placing portion 67. The die 70 is specified by a bottom portion 72, side walls 73a and 73b separated from each other in the width direction “α”, and a front wall 73c and a rear wall 73d (not shown) separated from each other in the length direction “γ”. An access opening is provided on an upper part 71 of the die 70 in order to accommodate the work. However, the die 70 is not necessarily needed.
A coil having a substantially linear portion may be used for forming a magnetic field for the work placed on the work placing portion 67. These coils include a first conductor 81 (81A, 81B), a second conductor 82A, and a third conductor 82B, a part of which is disposed along the length direction “γ”, for example. The first conductor 81 is disposed on the recess portion 62, the second conductor 82A is disposed on a side opposite to the recess portion 62 with respect to the yoke leg 61A in the width direction “α”, and the third conductor 82B is disposed on the side opposite to the recess portion 62 with respect to the yoke leg 61B in the width direction “α”. The first conductor 81 may be made of a pair of conductors 81A and 81B separated in the width direction “α”. A direction of a current made to flow through the conductor 81 and a direction of a current made to flow through the conductors 82A and 82B are assumed to be opposite to each other. In this case, the conductor 81A disposed on a side close to the yoke leg 61A in the width direction “α” may be connected to the second conductor 82A through a loop portion 83A, for example, and the conductor 81B disposed on the side close to the yoke 61B in the width direction “α” may be connected to the third conductor 82B through a loop portion 83B, for example. By connecting the conductors, the currents in the opposite directions to each other can be made to flow through these conductors at a time. It is needless to say that a diameter of the conductor is not particularly limited, but the one with a diameter of 1.4 mm can be used, here, from a viewpoint of stabilizing the magnetic field and the like.
The magnetic field applying device 5A has a symmetric shape in the width direction “α” and includes a magnetic body yoke 60B extending in the length direction “y. The magnetic body yoke 60B includes a pair of yoke legs 61A and 61B extending in the length direction “γ” similarly to the device 5 depicted in
In order to place the work, the work placing portion 67 having a cavity with a shape corresponding to the work is provided on the magnetic body yoke 60B. The work placing portion 67 is formed across the additional yoke legs 61C to 61E and the recess portions 62A, 62B, 62D, and 62E between the pair of magnetic body yokes 61A and 61B in the width direction “α”. The work may be placed on the work placing portion 67 in a state accommodated in a case 68 or the like, for example. However, the case is not necessarily needed.
A substantially linear conductor may be used for forming a magnetic field for the work placed on the work placing portion 67. These conductors may form conductor pairs 8A to 8C, and a part of the conductors forming each of the conductor pairs 8A to 8C is disposed on the recess portions 62A, 62B, 62D, and 62E along the length direction “γ”. The conductor pair 8A is disposed across the recess portions 62A and 62D so as to sandwich the yoke leg 61D from one side and the other side in the width direction “α”, the conductor pair 8C is disposed across the recess portions 62D and 62E so as to sandwich the yoke leg 61C from one side and the other side in the width direction “α”, and the conductor pair 8B is disposed across the recess portions 62E and 62B so as to sandwich the yoke leg 61E from one side and the other side in the width direction “α”. A direction of the current made to flow through the one conductors 81A to 81C forming each of the conductor pairs 8A to 8C and the direction of the current made to flow through the other conductors 82A to 82C are opposite to each other. The conductors forming these conductor pairs 8A to 8C preferably form a loop connected to each other as depicted in the aforementioned
The pulse magnetic field is applied in a state where a pressure is applied in the thickness direction “β” by pressing an upper portion of the work 6 by the rectangular case 68, for example, as depicted in
Particularly in the example depicted in
With respect to the rare-earth sintered magnet 2A depicted in
This is a value “D1” (T) of the surface magnetic flux density which becomes the maximum at a position away from the one surface 21 in a direction opposite to the other surface 22 only by 1 mm in the thickness direction “β”. Moreover, this is a value “D2” (T) of the surface magnetic flux density which becomes the maximum at a position away from the other surface 22 in a direction opposite to the one surface 21 only by 1 mm in the thickness direction “β”. In general, the surface magnetic flux density “D1” is preferably larger, while the surface magnetic flux density “D2” is preferably smaller. As a result, the leakage magnetic flux by the magnetic circuit connecting the one surface of the magnet and the other surface faced with that can be reduced. The value of the surface magnetic flux density is a component in parallel with a normal line direction with respect to the surface 21. In the measurement, a three-dimensional magnetic-field vector distribution measuring device (MTX-5R) by IMS was used.
This is a ratio (D1/D2) between the maximum surface magnetic flux density “D1” on the one surface 21 and the maximum surface magnetic flux density “D2” on the other surface 22 acquired in the above (1). If the magnetic flux density ratio is larger than 1, it means that the maximum surface magnetic flux density on the one surface 21 is larger than the maximum surface magnetic flux density on the other surface 22. When the magnetic flux density ratio has a large value, it has an effect that the yoke is not necessary on the other surface, and for that purpose, the value needs to be at least 3 or more and preferably 4 or more.
This is a value obtained by dividing the maximum surface magnetic flux density “D1” (T) on the one surface 21 acquired in the above (1) by the thickness dimension “t” (mm) in the thickness direction “β” between the one surface 21 and the other surface 22. This value can be an index for specifying a thickness dimension of the rare-earth sintered magnet from a viewpoint of efficient improvement of the maximum surface magnetic flux density “D1”, and the value is preferably larger. Since the maximum surface magnetic flux density becomes larger as its thickness increases, the thickness should be made larger from a viewpoint of increasing the maximum surface magnetic flux density, but since the maximum surface magnetic flux density per unit thickness becomes smaller as the thickness increases, the thickness should not be made much larger from a viewpoint of the efficient improvement of the maximum surface magnetic flux density D1 on the first surface. An optimal thickness dimension can be determined by using this index in order to efficiently improve the maximum surface magnetic flux density while the maximum surface magnetic flux density is held at a desired value.
This is a characteristic obtained by acquiring the surface magnetic flux density distribution in the width direction “α” at a plurality of positions in the length direction “γ” and by comparing the surface magnetic flux density distributions acquired at the plurality of positions with each other. If the value of axial symmetry is small, it means that the symmetry is excellent. Control of the linear motor or the like can be facilitated, and thrust fluctuation can be suppressed, for example, by improving symmetry.
In order to acquire the axial symmetry, as a preparation stage, first, FIG. 24 corresponding to
Subsequently, a value of axial symmetry was acquired by digitalizing a rate of concordance between the surface magnetic flux density on the line 2a and the surface magnetic flux density on the line 2c by using a residual sum of squares for each distance at the 0.004-mm interval from the end portion “d1” in the width direction “α”. The following equation was used for the digitization:
where N denotes the total sum of sampling, n denotes the n-th sampling, Xn denotes a distance from the end portion “d1” at the n-th sampling or in more detail, 0.004×n (mm), a function Fa (Xn) is a value of the surface magnetic flux density at Xn on the line 2a or in more detail, a value of the surface magnetic flux density at a position away from the end portion “d1” only by “Xn”, and similarly, a function Fb (Xn) is a value of the surface magnetic flux density at Xn on the line 2c or in more detail, a value of the surface magnetic flux density at a position away from the end portion “d1” only by “Xn”, respectively.
An analysis result is depicted in the following Table 1:
The rare-earth sintered magnet 2A depicted in
At room temperature, hydrogen was adsorbed onto an alloy obtained by a strip casting process, and the resulting alloy was held under a pressure of 0.85 MPa for one day. Subsequently, the resulting alloy was further held under a pressure of 0.2 MPa for one day, while being cooled by liquefied Ar, thereby inducing hydrogen cracking. The alloy had a composition “comprising Nd: 25.25 wt %, Pr: 6.75 wt %, B: 1.01 wt %, Ga: 0.13 wt %, Nb: 0.2 wt %, Co: 2.0 wt %, Cu: 0.13 wt %, Al: 0.1 wt %, a remainder including Fe, and other unavoidable impurities”.
1 weight part of methyl caproate was mixed with 100 weight parts of the coarsely-pulverized coarse alloy powder, and the resulting mixture was fed to a helium jet mill pulverizer (device name: PJM-80HE, manufactured by Nippon Pneumatic Mfg. Co., Ltd. (NPK)) to pulverize the hydrogen-cracked coarse alloy powder. The resulting pulverized alloy particles were separated and collected by a cyclone system, and an ultrafine powder was removed. During the pulverization, a feed rate of the mixture was set to 4.3 kg/h, and an introduction pressure and a flow rate of He gas were set, respectively, to 0.6 MPa and 1.3 m3/min. Further, an oxygen concentration was 1 ppm or less, and a dew point was −75° C. or less. The pulverized fine particles had an average particle size of about 3 μm.
The magnetic powder was dehydrogenated by raising a temperature of the magnetic powder subjected to the fine pulverization under a reduced pressure from a room temperature to 180° C. in 0.5 hours and then, by holding it for 5 hours.
With respect to 100 weight parts of the dehydrogenated magnetic powder, 4 weight parts of an SIS resin (Quintac 3390: by Zeon Corporation) which is a styrene-isoprene block copolymer, 1.5 weight parts of 1-octadecyne, and 4.5 weight parts of 1-octadecene were mixed and kneaded so as to obtain a work (processing sheet) in which the magnetic powder and an organic substance were mixed.
The work was filled in a die having a cavity of a width of 19 mm, a thickness of 4 mm, and a length of 14 mm and molded by being held at 80° C. for 3 minutes and by being pressurized at 3 MPa.
The orientation processing was executed by installing the molded work in the magnetic field applying device (orientation instrument) 5 depicted in
Decarbonization processing was executed to the work after the pulse magnetic field was applied under a hydrogen pressurized atmosphere of 0.8 MPa. The temperature was raised from the room temperature to 500° C. in 8 h at a temperature rise speed of approximately 1° C./min and was held for 2 h. A hydrogen flowrate was 2 to 3 L/min.
A sample after the decarbonization step was contained in a sintering die made of graphite. The sintering die made of graphite had a hole formed for sliding so as to enable pressure application in a length direction of the sample, and a pressing pin made of graphite for pressure application contained in the hole for sliding was inserted thereinto.
The sample contained in the sintering die made of graphite was subjected to sintering by a pressure sintering device in the length direction of the sample under a reduced pressure atmosphere by applying pressure to the graphite pin for pressing. As sintering conditions, pressure sintering was performed such that temperature was raised from the room temperature to 700° C. in 35 minutes while a load of 0.7 MPa was applied under the reduced pressure atmosphere and then, the temperature was raised to 950° C. in 13 minutes while a load of 6.6 MPa was applied and held in that state for 15 minutes.
The temperature of the sintered body cooled to the room temperature was raised from the room temperature to 1000° C. in 1.5 hours and held for 4 hours. After that, after being cooled to the room temperature, the temperature was raised again to 500° C. in 0.5 hours and then, held at 500° C. for 1 hour and quenched for annealing. The annealing step was performed under the reduced pressure atmosphere.
The annealed sintered body was shaped by a polishing machine to have a sintered body with a dimension of a width of 19 mm, a thickness of 4 mm, and a length of 6.8 mm.
The pulse magnetic field was applied once to the polished sintered body by using the magnetic field applying device 5 used for the magnetic field orientation so as to perform magnetization and to have a bipolar rectangular anisotropic rare-earth sintered magnet. The application of the pulse magnetic field was performed under conditions of the capacitor capacity of 1000 μF and the charge voltage of 1300 V. The maximum current value at that time was 13 kA and the pulse width were 1.5 ms.
With regard to the rare-earth sintered magnet fabricated with the conditions above, the results of sampling with the same procedures as the procedures described in the above “(4) Axial symmetry” were plotted, and the result depicted in the aforementioned
When a linear motor used as industrial motors for manufacturing a semiconductor and a liquid crystal, a shaver and the like is to be driven, for example, the surface magnetic flux density on the one surface (principal surface) needs to be 0.2T or more at the minimum, preferably 0.25T or more, more preferably 0.3T or more and further preferably 0.4T or more. According to Inventive Example 1, the maximum surface magnetic flux density on the one surface (principal surface) 21 or in more detail, a maximum value (absolute value) D1 of the surface magnetic flux density at a center (line 2b in
Moreover, when this type of linear motor is to be driven, the surface magnetic flux density on the other surface needs to be, though depending on the surface magnetic flux density on the principal surface, 0.2T or less at the maximum, preferably 0.15T or less, more preferably 0.1T or less or further preferably 0.095T or less. According to Inventive Example 1, the maximum value (absolute value) D2 of the maximum surface magnetic flux density on the other surface (second surface) is 0.095T, and the surface magnetic flux density sufficiently below 0.2T was obtained.
Moreover, since the magnetic flux density ratio acquired by using them was 5.0 (≈0.473/0.095), it can be considered that the magnetic flux having practically useful surface magnetic flux density is concentrated only in one surface or mainly in one surface in this rare-earth sintered magnet. Therefore, the leakage magnetic flux is small, and there is no need to provide a yoke on the other surface.
The maximum surface magnetic flux density per unit thickness is considered to be practically needed to be at least 0.04 T/mm or more, preferably 0.06 T/mm or more, more preferably 0.08 T/mm or more, further preferably 0.1 T/mm or more, furthermore preferably 0.12 T/mm or more, and an upper limit is not particularly limited, but it can be 0.5 T/mm or less, for example. According to Inventive Example 1, the maximum surface magnetic flux density per unit thickness was 0.12 (≈0.473/4) T/mm, which is a sufficient value from the viewpoint of efficient improvement of the maximum surface magnetic flux density “D1”.
The axial symmetry is preferably 0.7 or less, more preferably 0.6 or less, further preferably 0.5 or less, and furthermore preferably 0.3 or less. According to Inventive Example 1, the axial symmetry was 0.11, which is a value sufficiently below 0.7 and sufficiently symmetric in the length direction “γ”. This can be considered to be because orientation accuracy could be improved by realizing the pulse magnetic field orientation with respect to the work, and a sintering operation can be performed by pressure sintering, while holding the work.
The same operation as that in Inventive Example 1 was performed except that the conditions described in Table 1 were changed. Particularly in Inventive Examples 2 to 5, the conditions were all the same except that the thickness of the rare-earth sintered magnet was changed.
With regard to the rare-earth sintered magnet with the thickness of 3 mm fabricated in accordance with Inventive Example 2, the maximum surface magnetic flux density D1 on the first surface was 0.434 (T), the maximum value (absolute value) D2 of the maximum surface magnetic flux density on the second surface was 0.083 (T), the magnetic flux density ratio was 5.2, and the maximum surface magnetic flux density per unit thickness was 0.14 (T/mm), and the result of these values was as good as that of Inventive Example 1. The axial symmetry was 0.58 and was slightly poorer in the axial symmetry in the length direction “γ” as compared with Inventive Example 1.
Moreover, with regard to the rare-earth sintered magnet with the thickness of 2 mm fabricated in accordance with Inventive Example 3, the maximum surface magnetic flux density D1 on the first surface was 0.337 (T), the maximum value (absolute value) D2 of the maximum surface magnetic flux density on the second surface was 0.073 (T), the magnetic flux density ratio was 4.6, and the maximum surface magnetic flux density per unit thickness was 0.17 (T/mm), and the result of these values was as good as that of Inventive Example 1 similarly to Inventive Example 2. The axial symmetry was 0.26 and was slightly poorer in the axial symmetry in the length direction “γ” as compared with Inventive Example 1.
With regard to the rare-earth sintered magnet with the thickness of 6 mm fabricated in accordance with Inventive Example 4, the maximum surface magnetic flux density D1 on the first surface was 0.547 (T), the maximum value (absolute value) D2 of the maximum surface magnetic flux density on the second surface was 0.071 (T), the magnetic flux density ratio was 7.7, and the maximum surface magnetic flux density per unit thickness was 0.09 (T/mm).
With regard to the rare-earth sintered magnet with the thickness of 10 mm fabricated in accordance with Inventive Example 5, the maximum surface magnetic flux density D1 on the first surface was 0.591 (T), the maximum value (absolute value) D2 of the maximum surface magnetic flux density on the second surface was 0.051 (T), the magnetic flux density ratio was 11.6, and the maximum surface magnetic flux density per unit thickness was 0.06 (T/mm).
As is also obvious from these results, the maximum surface magnetic flux density per unit thickness becomes smaller as the thickness becomes larger, while the maximum surface magnetic flux density becomes larger as the thickness becomes larger. By considering a balance between the maximum surface magnetic flux density per unit thickness and the maximum surface magnetic flux density, the thickness of the rare-earth sintered magnet is preferably 10 mm or less and more preferably 8 mm or less. If the thickness of the rare-earth sintered magnet is larger than 10 mm (Inventive Example 5), the maximum surface magnetic flux density D1 on the first surface becomes larger, but the maximum surface magnetic flux density per unit thickness becomes smaller than 0.04 T/mm and as a result, it is likely that efficient improvement of the maximum surface magnetic flux density D1 on the first surface becomes difficult.
As is obvious from the results of these Inventive Examples 1 to 5, the magnetic flux having practically useful surface magnetic flux density is concentrated only in the one surface 21 in the thickness direction “δ” or mainly in the one surface in the thickness direction in the rare-earth sintered magnets 1 to 5 of the present invention, while the magnetic flux is scarce on the other surface 22, and at least the relationship of the magnetic flux density ratio (D1/D2)≥4 is satisfied between the maximum surface magnetic flux density “D1” on the one surface 21 and the maximum surface magnetic flux density “D2” 22 on the other surface. Though the upper limit of this magnetic flux density ratio is not particularly limited, but it can be 8 or more or 10 or more, and it is known from the results of Inventive Examples that the upper limit can be increased to at least approximately 12.
Though detailed results are not particularly shown for the rare-earth sintered magnet sintered body before magnetization, the rare-earth sintered magnet sintered body can be considered to be similar to the rare-earth sintered magnet. In more detail, the rare-earth sintered magnet sintered body has not been magnetized yet, but with regard to the magnet material particles contained in that, the magnet material particles having the easy magnetization axes oriented in the direction crossing the one surfaces 11 and 21 in the thickness direction “β” and the magnet material particles having the easy magnetization axes oriented in the direction crossing the other surfaces 12 and 22 in the thickness direction “β” generate the magnetic flux having a predetermined surface magnetic flux density through the magnetic field orientation, and since it is obvious that the ratio of these surface magnetic flux densities corresponds to that of the rare-earth sintered magnet, at least the relationship of (D1′/D2′)≥4 is satisfied between the maximum surface magnetic flux density (D1′) of the magnet material particles having the easy magnetization axes oriented in the direction crossing the one surface 11 in the one surface 11 and the maximum surface magnetic flux density (D2′) of the magnet material particles having the easy magnetization axes oriented in the direction crossing the other surface 12 in the other surface 12 similarly to the rare-earth sintered magnet.
The present invention is not limited to the aforementioned embodiments but is capable of other various changes. Therefore, the drawings and the description are only exemplification and are not binding.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2017-092487 | May 2017 | JP | national |
This application claims the priority of Japanese Patent Application No. 2017-092487, filed on May 8, 2017 in the JPO (Japanese Patent Office). Further, this application is the National Phase Application of International Application No. PCT/JP2018/017794, filed on May 8, 2018, which designates the United States and was published in Japan. Both of the priority documents are hereby incorporated by reference in their entireties.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2018/017794 | 5/8/2018 | WO | 00 |
