JP2004002998A - Press molding process for rare earth alloy powder and process for manufacturing rare earth alloy sintered body - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a vertical press molding process of a rare earth alloy powder which enables manufacturing of a sintered magnet having excellent magnetic properties. <P>SOLUTION: In the pressing process, a die formed from a non-magnetic material having a through-hole that forms a cavity and yokes located on both sides of the through-hole, is used. The process comprises steps wherein the rare earth alloy powder is prepared, filled into the cavity of the die and compressed employing a pair of pressing surfaces opposing each other. During the compression step, only after the powder inside the cavity achieves a predetermined apparent density corresponding to ≥47% of its true density, a pulse magnetic field almost perpendicular to the direction of compression is applied. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for press-molding a rare earth alloy powder and a method for producing a rare earth alloy sintered body.
[0002]
[Prior art]
Rare earth alloy sintered magnets (permanent magnets) are generally produced by pressing a rare earth alloy powder, sintering the resulting powder compact, and subjecting it to aging treatment. At present, two types of rare earth / cobalt magnets and rare earth / iron / boron magnets are widely used in various fields. Above all, rare earth / iron / boron magnets (hereinafter referred to as “R—Fe—B magnets.” R is a rare earth element containing Y, Fe is iron, and B is boron) are various magnets. It has the highest maximum magnetic energy product among them, and its price is relatively low, so it is actively used in various electronic devices.
[0003]
R-Fe-B based sintered magnets are mainly₂Fe₁₄It is composed of a main phase composed of a tetragonal compound of B, an R-rich phase composed of Nd or the like, and a B-rich phase. Note that a part of Fe may be substituted with a transition metal such as Co or Ni, and a part of boron (B) may be substituted with carbon (C). R-Fe-B-based sintered magnets to which the present invention is suitably applied are described in Patent Literature 1 and Patent Literature 2, for example.
[0004]
Conventionally, an ingot casting method has been used to produce an R-Fe-B-based alloy serving as such a magnet. According to a general ingot casting method, a rare earth metal, an electrolytic iron, and a ferroboron alloy, which are starting materials, are subjected to high-frequency melting, and the obtained molten metal is cooled relatively slowly in a mold to produce an alloy ingot.
[0005]
In recent years, the molten alloy has been cooled relatively quickly by contacting it with the inner surface of a single roll, twin roll, rotating disk, or rotating cylindrical mold, etc., and from the molten alloy, a solidified alloy ("alloy flake" A quenching method typified by a strip casting method and a centrifugal casting method for producing the quenching method has attracted attention. The thickness of the alloy piece produced by such a quenching method is generally in the range of about 0.03 mm or more and about 10 mm or less. According to the quenching method, the molten alloy begins to solidify from the surface in contact with the chill roll (roll contact surface), and crystals grow columnar from the roll contact surface in the thickness direction. As a result, the quenched alloy produced by the strip casting method or the like has an R size of about 0.1 μm to about 100 μm in the short axis direction and about 5 μm to about 500 μm in the long axis direction.₂Fe₁₄B crystal phase and R₂Fe₁₄It has a structure containing an R-rich phase dispersed and present at the grain boundaries of the B crystal phase. The R-rich phase is a non-magnetic phase in which the concentration of the rare-earth element R is relatively high, and its thickness (corresponding to the width of the grain boundary) is about 10 μm or less.
[0006]
The quenched alloy has a relatively short time (cooling rate: 10) as compared with an alloy (ingot alloy) produced by a conventional ingot casting method (die casting method).²° C / sec or more, 10⁴(° C./sec or less), the structure is refined and the crystal grain size is small. Further, since the area of the grain boundary is large and the R-rich phase is widely spread in the grain boundary, there is an advantage that the dispersibility of the R-rich phase is excellent. Because of these characteristics, a magnet having excellent magnetic properties can be manufactured by using a quenched alloy.
[0007]
Further, a method called a Ca reduction method (or reduction diffusion method) is also known. The method includes the following steps. First, a mixed powder containing at least one of rare earth oxides, iron powder and pure boron powder, and at least one of ferroboron powder and boron oxide at a predetermined ratio, or an alloy powder of the above constituent elements Alternatively, calcium oxide (Ca) and calcium chloride (CaCl) are mixed with a mixed powder containing a mixed oxide at a predetermined ratio, and a reduction diffusion treatment is performed in an inert gas atmosphere. The obtained reaction product is slurried and treated with water to obtain an R-Fe-B-based alloy solid.
[0008]
In the present specification, a solid alloy mass is referred to as an “alloy mass”, and is obtained by cooling a molten metal such as an alloy ingot obtained by a conventional ingot casting method and an alloy flake obtained by a rapid cooling method such as a strip casting method. In addition to the solidified alloy obtained, various forms of solid alloys such as a solid alloy obtained by a Ca reduction method are included.
[0009]
The alloy powder to be subjected to press molding is obtained by pulverizing these alloy ingots by, for example, a hydrogen storage method and / or various mechanical pulverization methods (for example, a disk mill is used), and the obtained coarse powder (for example, (Average particle size of 10 μm to 500 μm) by, for example, fine pulverization by a dry pulverization method using a jet mill.
[0010]
The average particle size of the R-Fe-B-based alloy powder used for press molding is preferably in the range of 1.5 m to 6 m from the viewpoint of magnetic properties. The “average particle size” of the powder refers to a mass median diameter (MMD) unless otherwise specified. However, when powder having such a small average particle size is used, fluidity and press moldability (including cavity filling and compressibility) are poor, and productivity is poor.
[0011]
Particularly, a rapid cooling method such as a strip casting method (a cooling rate of 10²/ Sec-10⁴Powder produced by the ingot method is not only low in the average particle diameter but also sharp in the particle size distribution (steep), so that the fluidity is particularly poor. For this reason, the amount of the powder filled in the cavity may vary beyond an allowable range, and the filling density in the cavity may become uneven. As a result, the mass or size of the molded product may vary beyond the allowable range, or the molded product may be chipped or cracked. Furthermore, there was a problem that the orientation could not be sufficiently oriented by the orientation magnetic field, and the magnetic properties (for example, residual magnetic flux density) of the finally obtained sintered magnet were low.
[0012]
In addition, the method of press-forming a molded body for a magnet is roughly classified into two according to the direction of the orientation magnetic field. That is, there are a parallel pressing method in which an orientation magnetic field is applied in parallel with the pressing direction (compression direction) and a right-angle pressing method in which an orientation magnetic field is applied in a direction perpendicular to the pressing direction.
[0013]
With reference to FIGS. 1 (a) and 1 (b), a method for press-forming a formed body for an arcuate magnet will be described. The arrow B in FIG. 1A and the arrow B in FIG. 1B indicate the direction of the orientation magnetic field during press molding.
[0014]
The bow-shaped magnet 1a shown in FIG. 1A is manufactured by manufacturing the sintered body block 1b shown in FIG. 1B and cutting it from the viewpoint of productivity and magnetic properties. Conventionally, a formed body for obtaining the sintered body block 1b is formed using a right-angle pressing method. This is because the right-angle press method enables press-forming without losing the magnetic field orientation. Generally, magnets obtained by the right-angle press method have better magnetic properties than magnets obtained by the parallel press method. have.
[0015]
On the other hand, by arranging the yoke member in the vicinity of the through hole (die hole) for forming the cavity (within 15 cm in the alignment direction from the inner wall of the die hole) in the die formed of the non-magnetic material, the magnetic flux is concentrated in the cavity, Improving the strength of the alignment magnetic field has been performed. The higher the intensity of the orientation magnetic field in the cavity, the higher the residual magnetic flux density B of the finally obtained magnet._rIs improved. If the technique of increasing the strength of the orientation magnetic field in the cavity using such a yoke member is combined with the above-described right-angle pressing method, it becomes possible to manufacture a permanent magnet having more excellent characteristics. Such a technique is described in Patent Document 3, for example.
[0016]
[Patent Document 1]
U.S. Pat. No. 4,770,723
[Patent Document 2]
U.S. Pat. No. 4,792,368
[Patent Document 3]
JP 2002-47503 A
[0017]
[Problems to be solved by the invention]
In recent years, in order to reduce the grain size of the sintered magnet, fine powder having a particle size (FSSS particle size) of 6 μm or less has been used. In order to orient such fine powder particles, it is necessary to apply a stronger magnetic field than before. However, when the magnetic field strength in the cavity is increased by using the yoke member, the magnetic field strength distribution in the cavity is not uniform, and the magnetic field strength becomes higher near the end of the cavity in the orientation direction. Since the magnetic field strongly attracts the magnet powder in the cavity toward the yoke member, there is a problem that the apparent density of the magnet powder in the center of the cavity is lower than that in the end of the cavity. In particular, in the case of the conventional static magnetic field press, since the orientation magnetic field is applied from the initial stage of the compaction step (the stage where the powder density is small and the powder can move in the cavity), the bias of the powder tends to occur in the cavity. In such a case, the powder collected at the end of the cavity is pushed and moved toward the center of the cavity by the lowering and pressing of the upper punch, and at this time, the orientation is disturbed at both ends of the cavity. As described above, in the rectangular press using the yoke member, the degree of orientation and the density of the powder compact are likely to be non-uniform, and the uniformity of the magnet properties tends to be deteriorated. When the yoke member is arranged near the cavity, the magnetic flux itself tends to bend due to the concentration of the magnetic flux.
[0018]
The present invention has been made in view of the above-mentioned points, and a main object of the present invention is to provide a method for press-forming a rare-earth alloy powder that enables production of a sintered magnet having uniform magnetic properties. is there.
[0019]
[Means for Solving the Problems]
The method for pressing a rare earth alloy powder according to the present invention uses a die formed of a non-magnetic material, the die having a through hole for forming a cavity, and yokes arranged on both sides of the through hole. A method of pressing an alloy powder, wherein a step of preparing a rare earth alloy powder, a step of filling the rare earth alloy powder in a cavity of the die, and a pair of the rare earth alloy powders filled in the cavity are opposed to each other. And compressing the rare earth alloy powder in the cavity during the compression step only after the apparent density of the rare earth alloy powder in the cavity reaches a predetermined value of 47% or more of the true density. Applying a pulse magnetic field substantially perpendicular to the direction.
[0020]
It is preferable that the method further includes a step of applying vibration to the rare earth alloy powder before applying the pulse magnetic field during the compression step.
[0021]
In a preferred embodiment, the predetermined value is 3.55 g / cm.³This is set as above.
[0022]
In a preferred embodiment, the pulse magnetic field is an alternating damping magnetic field.
[0023]
In a preferred embodiment, the pulse magnetic field is a reverse pulse magnetic field.
[0024]
In a preferred embodiment, the vibration is supplied from at least one of the pair of pressure surfaces.
[0025]
In a preferred embodiment, the rare earth alloy powder is a powder produced using a quenching method.
[0026]
The method for producing a rare earth alloy sintered body according to the present invention includes a step of producing a molded body by any one of the above rare earth alloy powder press molding methods, and a step of sintering the molded body.
[0027]
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, compression molding of magnet powder is performed using a die formed of a non-magnetic material. The die used in the present invention has a through-hole (die hole) for forming a cavity, and a plurality of yoke members arranged on both sides of the die hole.
[0028]
According to various studies made by the present inventors, when a pulse magnetic field for orientation is applied so as to be perpendicular to the pressing direction, the apparent density of the alloy powder (referred to as “temporary compact (compacted compact) density”) In some cases, when a pulse magnetic field is applied at the stage when the value of the above-mentioned value becomes a predetermined value or more, a molded body having a high degree of orientation can be manufactured with high yield.
[0029]
According to the experiment of the present inventor, when a pulse magnetic field is applied in a state where the density of the temporary compact is low, there is a sufficient space around each powder particle, and the force for contacting the powder particles is relatively weak. Thus, the powder particles are oriented in the direction of the applied magnetic field. At this time, a phenomenon in which the powder in the die hole is attracted to the side where the yoke member is located, and the density of the end portion is increased as compared with the center portion of the die hole is also observed. Thereafter, when the temporary molded body is further pressed, the powder flows as the density of the temporary molded body increases, so that the orientation is disturbed. As a result, the degree of orientation of the powder particles in the finally obtained compact decreases.
[0030]
In order to solve such a problem, in the present invention, the pulse magnetic field is applied only after the density of the temporary compact reaches a predetermined value that is 47% or more of the true density. If a pulse magnetic field is applied after the density of the temporary compact reaches a certain level, the powder does not easily flow during the subsequent compression and compaction process, and the disorder of the orientation is suppressed.
[0031]
On the other hand, if the density of the temporary compact at the time of applying the pulse magnetic field is too high, the space formed around the individual powder particles is too small, and the powder particles are in contact with each other with a strong force. Even when a pulsed magnetic field is applied, the powder particles cannot change direction. If the density of the temporary formed body is too high beyond a certain value, it is difficult to obtain a magnet having excellent magnetic properties even when a strong pulse magnetic field is applied. It is desirable that the density of the temporary molded body is 53% or less of the true density.
[0032]
Even if the density of the temporary compact is the same, the frictional resistance between the alloy powders can be reduced by applying vibration. Therefore, it is preferable to apply an orientation magnetic field while the alloy powder is being vibrated. When vibration is applied to the alloy powder in the compression molding step, the magnetic field orientation can be sufficiently performed even after the density of the temporary compact increases.
[0033]
In addition, even if the density of the temporary compact is the same, the frictional resistance between the alloy powders can be reduced by applying the alternating damping pulse magnetic field, and the magnetic field can be sufficiently oriented even after the density of the temporary compact increases. Become.
[0034]
(Embodiment)
Hereinafter, an embodiment of a method for manufacturing a rare earth alloy sintered body according to the present invention will be described with reference to the drawings.
[0035]
First, the rare earth alloy powder used in the present embodiment will be described. Although there are various rare earth alloy powders that can be used in the present invention, R-Fe-B based rare earth alloys are preferably used. The composition and manufacturing method of the R-Fe-B-based rare earth alloy are described in, for example, U.S. Patent No. 4,770,723 and U.S. Patent No. 4,792,368.
[0036]
In a typical composition of an R-Fe-B rare earth alloy, Nd or Pr is mainly used as R, Fe may be partially substituted by a transition element (for example, Co), and B may be C. May be replaced by
[0037]
In the present embodiment, an Nd—Fe—B solidified alloy (with a density of 7.5 g / cm) manufactured by a quenching method is used.³)), And a powder having an average particle size in the range of 1.5 μm to 6 μm obtained by pulverizing is used. The surface of the alloy powder is preferably coated with a lubricant such as zinc stearate. Specifically, it can be manufactured as follows. First, the composition is Nd: 30% by mass, B: 1.0% by mass, Dy: 1.2% by mass, Al: 0.2% by mass, Co: 0.9% by mass, the balance being Fe and unavoidable impurities. The alloy is made into a molten metal by a high frequency melting method, and an alloy lump is produced by a strip casting method described in US Pat. No. 5,383,978. The obtained alloy ingot is roughly pulverized by a hydrogen storage method, and then finely pulverized by a jet mill to obtain an alloy powder having an average particle size of 3.5 μm (containing 0.3% by mass of zinc stearate as a lubricant). Obtainable.
[0038]
Next, the above powder is compression-molded using a press device. With reference to FIG. 2, a configuration of a press device suitably used in the present embodiment will be described.
[0039]
The illustrated press forming apparatus 10 includes a base plate 12, which is supported by a plurality of legs 14. A die 16 is arranged above the base plate 12. The lower surface of the die 16 is connected to the connecting plate 20 via a pair of guide posts 18 penetrating the base plate 12. The connection plate 20 is connected to a lower hydraulic cylinder (not shown) via a cylinder rod 22. Therefore, the die 16 can be moved vertically by the lower hydraulic cylinder.
[0040]
A die hole (through hole) 24 penetrating in the vertical direction is formed at a substantially central portion of the die 16, and a lower punch 26 is inserted into the die hole 24 from below, and a cavity 28 is formed in the die hole 24.
[0041]
As shown in FIG. 3, the die 16 has a pair of yoke members 16a and 16b facing each other so as to sandwich the die hole 24 along the direction of the alignment magnetic field (X direction). The yoke members 16a and 16b are formed of a material having high magnetic permeability such as carbon steel, and are formed of, for example, permendur. Further, in consideration of productivity, it is preferable to use a material having a low saturation magnetic flux density Bs in order to achieve both the prevention of heat generation due to eddy current and the alignment direction at the time of pressing. On the other hand, the die 16 is formed of a non-magnetic material, and a concave portion in which the yoke members 16a and 16b are fitted is formed on a side surface of the die 16. In this specification, “non-magnetic material” refers to a material having a saturation magnetization of 0.2 Tesla (T) or less.
[0042]
Further, as shown in FIG. 3, the length 16c of the yoke is set equal to or longer than the length 24a of the cavity to be sandwiched (120%). By doing so, the directions of the lines of magnetic force to be oriented can be made more parallel.
[0043]
FIG. 1 is referred to again.
[0044]
The lower punch 26 is disposed on the vibration device 30, and the vibration device 30 is disposed on the die plate 12. Therefore, although the lower punch 26 is fixed on the base plate 12, the lower punch 26 can be vibrated in the vertical direction, that is, in the pressing direction by the vibration device 30. As the vibration device 30, for example, a vibration device manufactured by Daiichi Co., Ltd. can be used.
[0045]
An upper punch plate 32 is arranged above the die 16. An upper punch 34 is provided on a lower surface of the upper punch plate 32 at a position where the upper punch 34 can be inserted into the cavity 28. A cylinder rod 36 is provided on the upper surface of the upper punch plate 32. An upper hydraulic cylinder (not shown) is connected to the cylinder rod 36. A pair of guide posts 38 provided in the vertical direction are inserted near both ends of the upper punch plate 32, and the lower ends of the guide posts 38 are connected to the upper surface of the die 16.
[0046]
The upper punch plate 32 is vertically movable by an upper hydraulic cylinder while being guided by the guide post 38, so that the upper punch 34 is vertically movable and is inserted into the cavity 28.
[0047]
During press molding, the powder is compressed by the lower punch 26 and the upper punch 34 in the cavity 28 to form a compact.
[0048]
A magnetic field generator 40 for orienting the powder in the cavity 28 is provided near the die 16. The magnetic field generator 40 has a pair of yokes 42a and 42b symmetrically arranged so as to sandwich the die 16 from both sides. Similarly to the yoke members 16a and 16b of the die 16, the yokes 42a and 42b are formed of a material having high magnetic permeability such as carbon steel. Coils 44a and 44b are wound around the yokes 42a and 42b, respectively, and a pulse magnetic field is formed in a direction indicated by an arrow X by energization to orient the powder in the cavity 28. In this specification, a pulse magnetic field refers to a magnetic field in which the period during which the magnetic field intensity is 90% or more of the peak value is 0.2 seconds or less.
[0049]
According to the press device 10, the press direction and the direction of the orientation magnetic field are in a right angle relationship, and the applied magnetic field intensity shows, for example, 3T at the center of the cavity.
[0050]
The illustrated press device 10 is a withdrawal-type press device that moves the die 16 up and down, but a double-press type press device that moves both the upper punch 34 and the lower punch 26 may be used.
[0051]
As shown in FIG. 2, after the cavity 24 is formed by the die hole 28 of the die 16 and the upper surface (pressing surface) of the lower punch 26, the cavity 24 is filled with the above-described alloy powder.
[0052]
The filling of the alloy powder is performed by various known methods. For example, a method of filling the alloy powder using its own weight using a feeder box is simple and preferable. Using this method, an appropriate apparent density (for example, 1.7 g / cm) can be obtained in the cavity.³~ 2.5g / cm³) Can be filled with the alloy powder. After the cavity is filled with the alloy powder, the amount of the alloy powder to be filled into the cavity 28 can be made substantially constant by, for example, moving a cutting bar or the like along the surface of the die 16. For example, a powder feeding method described in JP-A-2001-9595 can be suitably used.
[0053]
Next, the alloy powder in the cavity 28 is uniaxially pressed by moving the upper punch 34 and / or the lower punch 26 up and down. Typically, the upper punch 34 is lowered, but the upper punch 34 may be lowered and the lower punch 26 may be raised.
[0054]
In the present embodiment, vibration (mechanical vibration) is applied to the alloy powder filled in the cavity 28 during the uniaxial pressing process. By giving vibrations to the alloy powder, the bridge structure between the powder particles is broken, and the powder particles are easily moved. This situation will be described with reference to FIGS.
[0055]
As shown in FIG. 4B, in the alloy powder that has been filled in the cavity, the particles 2 are in contact with each other to form a bridge structure. Therefore, the total space 3 existing between the particles 2 is large, but the space 3 is unevenly distributed. By applying vibration to the alloy powder in such a state, the bridge structure formed by the particles 2 in contact with each other is broken, and the unevenly distributed spaces 3 are evenly distributed as shown in FIG. become. As a result, although the sum of the spaces 3 existing between the particles 2 is reduced and the apparent density is increased, the spaces 2 are distributed substantially evenly around the individual particles 2 so that the particles 2 move (ie, the magnetic field orientation). With the rotation). Of course, the density distribution of the alloy powder in the cavity becomes uniform. Furthermore, even if the apparent density is the same, the alloy powder is in a state of being more easily moved when vibration is applied than when no vibration is applied, and is easily oriented according to the orientation magnetic field. It is considered that by giving vibration to the alloy powder, the friction between the alloy powders changes from static friction to dynamic friction, and the friction resistance decreases.
[0056]
Preferably, the vibration is applied from the pressing surface (ie, the bottom surface of the upper punch and / or the top surface of the lower punch). In particular, when the lower punch is mechanically vibrated, kinetic energy can be efficiently applied to the alloy powder, and the structure of the press device can be simplified.
[0057]
The amplitude of the vibration is preferably 0.001 mm or more and 0.2 mm or less. If the amplitude of the vibration is less than 0.001 mm, the bridge structure of the powder particles may not be sufficiently broken, and if it exceeds 0.2 mm, the powder particles may easily bite into the gap between the die and the lower punch, for example. This causes damage to the die and the lower punch.
[0058]
The frequency of the vibration is preferably 5 Hz or more and 1000 Hz or less. If the frequency of vibration is less than 5 Hz, the bridge structure of the powder particles may not be sufficiently broken. On the other hand, if the frequency of vibration exceeds 1000 Hz, a device for generating vibration is too costly to be practical.
[0059]
When a pulse magnetic field is applied to the alloy powder in the cavity, vibration is applied so that the state shown in FIG. 2B is obtained. The vibration may stop when the apparent density reaches a predetermined value due to compression, or may continue after reaching the desired value.
[0060]
In order to reliably perform the operation of applying the pulse magnetic field when the density of the temporary formed body is within the predetermined range, the stroke of the upper punch and / or the lower punch is controlled, and the temporary formed body having the predetermined density is formed. It is preferable to stop the stroke of the upper punch and / or the lower punch once obtained. An orientation magnetic field is applied during this stop period, and then the pressing step for obtaining a final molded body may be restarted.
[0061]
In the present embodiment, a pulse magnetic field (maximum magnetic field intensity: 2 to 5 T, pulse width: 0.05 seconds) is applied, and vibration (amplitude: 0.01 to 0.03 mm, frequency: 40) is applied because of the magnetic field orientation. 〜80 Hz) from the lower punch. Vibration was caused by filling the alloy powder and forming a cavity by dropping the upper punch, resulting in a molding density of 3.55 g / cm.³~ 3.90 g / cm³It is preferable to give until. Further, it is preferable that the pulse magnetic field is applied while the upper and lower punches are stopped and vibration is applied. Thereafter, in the present embodiment, the density of the final molded body is 4.0 g / cm.³~ 4.4 g / cm³Pressurize again so that The size of the molded body can be, for example, 60 mm × 40 mm × 20 mm.
[0062]
For example, after performing a sintering process at about 1000 to 1200 ° C. for 2 to 6 hours in an Ar atmosphere, the aging treatment is performed at about 400 to 600 ° C. for 1 to 3 hours in an Ar atmosphere. By performing the above, a sintered body can be obtained.
[0063]
The timing of applying the pulse magnetic field is determined by the density of the preliminarily formed body being 3.55 g / cm.³When set at the time when the above-mentioned predetermined value is reached, the residual magnetic flux density further increases by applying vibration. The timing of applying the pulse magnetic field is such that the density of the preliminarily formed body is 3.6 g / cm.³It is preferable to set the time when the above-mentioned predetermined value is reached.³Even with the above settings, a sufficient effect can be obtained. However, the application of the pulse magnetic field was performed when the density of the preliminarily formed body was 4.0 g / cm.³, The residual magnetic flux density tends to decrease, and it is known that the powder particles are not sufficiently oriented. From the above, the density of the temporary formed body was 3.55 g / cm.³Above 3.9 g / cm³When in the following range, it is preferable to apply a pulsed magnetic field. The lower limit of the more preferable density range is 3.6 g / cm.³The lower limit of the more preferable density range is 3.7 g / cm.³It is.
[0064]
A pulse magnetic field may be applied a plurality of times or a static magnetic field may be applied together with the pulse magnetic field to the temporary molded body within the above-mentioned predetermined density range.
[0065]
According to the present embodiment, even when the magnetic field distribution in the cavity is not uniform due to the yoke member provided near the die hole, the degree of orientation can be made uniform by adjusting the application timing of the pulse magnetic field.
[0066]
The same can be said for the case where an alternating decay pulse is applied. The magnetic powder is rotated by the magnetic field whose direction is reversed, and the bridge structure formed by the alloy powder filled in the cavity can be broken. Such destruction of the bridge structure can be performed not only by the application of the alternating decay pulse but also by the application of the inversion pulse.
[0067]
(Example)
A sintered body was produced in the same manner as in the above embodiment. Specifically, a sintered body was produced under the following conditions.
[0068]
Raw material powder: composition: Nd: 30% by mass, B: 1.0% by mass, Dy: 1.2% by mass, Al: 0.2% by mass, Co: 0.9% by mass, balance Fe and inevitable impurities The powder of the alloy was roughly pulverized by hydrogen pulverization and then finely pulverized by a jet mill.
[0069]
Forming method: {circle around (2)} Using the apparatus shown in FIG. 2, compression molding was performed by applying a pulse magnetic field (pulse width: 0.05 seconds) having a peak intensity of 3T as an orientation magnetic field.
[0070]
At the start of application of the orientation magnetic field: density 3.6 g / cm³
Shape and size of molded product: $ 60mm x 40mm x 20mm
Sintering conditions: After performing a sintering treatment at about 1050 ° C. for 5.5 hours in an Ar atmosphere, aging treatment was performed at about 500 ° C. for 3 hours in an Ar atmosphere.
[0071]
(Comparative example)
A sintered body was produced in the same manner as in the example except that a static magnetic field of 1 T was applied as the orientation magnetic field.
[0072]
When the surface magnetic flux density was measured at two places (center and end) along the direction of the orientation magnetic field, the difference in the surface magnetic flux density was 10% in the example, but the difference in the surface magnetic flux density in the comparative example was 10%. 4%.
[0073]
In the above-described embodiment, the Nd-Fe-B-based alloy powder produced by the strip casting method is used although the magnetic properties are excellent, but the flowability is particularly low, but the rare-earth alloy powder produced by another method is used. However, it goes without saying that the effects of the present invention can be obtained.
[0074]
In the above embodiment, the alloy powder is used after being subjected to a surface treatment with a lubricant. However, another surface treatment may be performed, and further, a granulated powder may be used. Since the granulated powder can be disintegrated using vibration and / or an orientation magnetic field, a sufficient degree of orientation can be obtained.
[0075]
【The invention's effect】
According to the present invention, there is provided a method for right-angle press forming rare earth alloy powder, which enables production of a sintered magnet having excellent magnetic properties. Since the compact obtained by the press molding method of the present invention has a sufficiently high compact density and a sufficiently high degree of orientation of the alloy particles, a sintered magnet having excellent magnetic properties can be obtained. According to the present invention, the productivity of sintered magnets having different shapes can be significantly improved.
[Brief description of the drawings]
FIG. 1A is a schematic diagram showing an arcuate magnet, and FIG. 1B is a schematic diagram of a sintered body block for producing an arcuate magnet.
FIG. 2 is a schematic diagram showing a configuration of a press device suitably used for press molding of an embodiment according to the present invention.
FIG. 3 is a perspective view showing a configuration example of a die used for press molding of the embodiment according to the present invention.
FIG. 4A is a view schematically showing a state of powder particles subjected to vibration in the press molding method according to the present invention, and FIG. 4B is a view showing a state of powder particles before vibration is applied. It is a figure which shows typically.
[Explanation of symbols]
1a bow magnet
1b sintered block
2 alloy powder particles
3 space
10mm press machine
12mm base plate
14 legs
16 die
16a yoke member
16b yoke member
16c Length of yoke member
18 guide post
20mm connecting plate
22 cylinder rod
24 die hole (through hole)
24a cavity length
26mm lower punch (yoke)
28 cavity
30 vibration device
34mm upper punch
32 upper punch plate 32
36 cylinder rod
38 guide post
40 ° magnetic field generator
42a @ yoke
42b @ yoke
44a coil
44b coil
X direction of pulsed magnetic field
P @ breath direction

Claims (8)

A die formed from a non-magnetic material, a through hole for forming a cavity, a method of pressing a rare earth alloy powder using a die having a yoke member disposed on both sides of the through hole,
A step of preparing a rare earth alloy powder,
Filling the die cavity with the rare earth alloy powder,
Compressing the rare earth alloy powder filled in the cavity with a pair of pressing surfaces facing each other,
Within the period of the compression step,
A step of applying a pulse magnetic field substantially perpendicular to the compression direction only after the apparent density of the rare earth alloy powder in the cavity reaches a predetermined value that is 47% or more of the true density. Press molding method. The method of press-forming a rare-earth alloy powder according to claim 1, further comprising a step of applying vibration to the rare-earth alloy powder before applying the pulse magnetic field during the compression step. The method according to claim 1, wherein the predetermined value is set to 3.55 g / cm ³ or more. The method of press-forming a rare-earth alloy powder according to any one of claims 1 to 3, wherein the pulse magnetic field is an alternating attenuation magnetic field. The method for press-molding a rare-earth alloy powder according to claim 1, wherein the pulse magnetic field is a reversal pulse magnetic field. The method of press-molding a rare-earth alloy powder according to claim 1, wherein the vibration is supplied from at least one of the pair of pressing surfaces. The method of press-molding a rare-earth alloy powder according to claim 1, wherein the rare-earth alloy powder is a powder produced by using a quenching method. A step of producing a compact by a method of press-molding a rare earth alloy powder according to any one of claims 1 to 7,
Sintering the compact,
A method for producing a rare earth alloy sintered body, comprising:

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