JP4240988B2 - Rare earth alloy granulated powder manufacturing method, rare earth alloy granulated powder manufacturing apparatus, and rare earth alloy sintered body manufacturing method - Google Patents

Description

【０１０２】
また、表１には、それぞれのプレス用粉末の安息角をあわせて示す。安息角が大きい粉末は流動性が悪く、安息角が小さいものほど流動性が優れている。比較例１として示したように、原料粉末を造粒しないと安息角は約５２°と大きく、流動性が低い。これに対し、造粒を行った実施例１〜３、比較例２および３のいずれのプレス粉末も安息角は５０°未満まで低下している。特に、実施例１および２のプレス粉末は、比較例２のプレス粉末（造粒剤の添加量１質量％）よりも安息角が小さく、流動性が優れている。すなわち、残留磁化を利用することによって、従来よりも少ない造粒剤の添加によって、流動性が改善されることがわかる。なお、造粒剤の添加量が２質量％の実施例３および比較例３では、流動性に差が見られなった。
【０１０３】
表１に示したそれぞれのプレス用粉末を、上述したフィーダボックスを用いた方法で、縦２０ｍｍ、横１５ｍｍ、深さ１０ｍｍのキャビティ内に充填し、一軸プレス成形（９８ＭＰａ、配向磁界（０．８Ｔ）をプレス方向に直角に印加）を行った。この充填工程およびプレス成形工程は、全ての実施例および比較例について同じ条件で行った。なお、プレス条件を変えて成形体密度（グリーン密度）の異なる成形体を形成した。
【０１０４】
実施例１と比較例１のプレス成形体の質量ばらつき（％）と充填量ばらつき（σ）を評価した。成形体の質量ばらつきは、｛（最大質量−最小質量）／平均質量（ｎ＝５０）｝×１００（％）で求めた。また、充填量ばらつき（σ）は、５０個の成形体の質量分布の標準偏差を示している。実施例１の成形体の質量ばらつきは約４％であり、比較例１の質量ばらつき約１５％に比べて著しく改善されている。これは、充填量ばらつき（σ）についても同様で、比較例１の充填量ばらつき（σ）が約０．３３であるのに対し、実施例１の充填量ばらつき（σ）は０．１６と大きく改善されており、造粒によって流動性が改善されたことがわかる。勿論、造粒によって、成形性も同様に改善されており、成形体に欠けや割れが発生する割合も、比較例１に比べ著しく少なかった。これらの造粒の効果は、他の実施例についても確認された。
【０１０５】
得られた成形体をＡｒ雰囲気中で、１０６０℃にて約４時間焼結したあと、６００℃で１時間の時効処理を施し、焼結体を得た。さらに、この焼結体を２３８７ｋＡ／ｍの条件で着磁することによって、焼結磁石を得た。それぞれの実施例および比較例について、サンプル数は５０個とした。
【０１０６】
得られた焼結磁石の残留磁化Ｂｒ（Ｔ）を図４に示す。図４からわかるように、実施例１（図４中の黒丸）のＢｒは、比較例１（図４中の白丸）のＢｒと実質的な差異は認められず、優れた磁気特性を有している。造粒剤を添加した実施例２および実施例３のＢｒは、同量の造粒剤を添加し残留磁化を有していない原料粉末を用いた比較例２および比較例３のＢｒとほぼ同等であった。残留磁化を利用して造粒する場合においても、造粒剤はできるだけ少ない方が好ましい。
【０１０７】
上述したように、１次粒子の残留磁化による磁気的な凝集力を利用して造粒粉を作製することによって、造粒剤の結合力のみを用いて造粒粉を用いる場合に比べて、造粒剤の添加量を減らしても同等以上の流動性を得ることができるので、従来の同等以上の生産性で、従来よりも優れた磁気特性を有する焼結磁石を製造することができる。さらに、１次粒子の残留磁化のみを用いて造粒粉を作製すれば、磁気特性の低下を実質的に無くすことができる。
【０１０８】
【発明の効果】
本発明によると、流動性やプレス成形性に優れ、且つ、優れた磁気特性を有する磁石を製造することが可能な希土類合金の造粒粉の製造方法が提供される。この造粒粉を用いることによって、高品質の希土類合金焼結体を高い生産効率で製造する方法が提供される。
【０１０９】
本発明によると、磁気特性を低下させることなく、希土類合金粉末の流動性および成形性を改善することができるので、従来は磁気特性を犠牲にしていたプレス成形が困難な形状の焼結磁石の磁気特性を向上することができる。さらに、造粒時間の短縮や、脱バインダ工程の省略が可能となり、希土類焼結磁石の生産性を向上することができる。
【図面の簡単な説明】
【図１】（ａ）は、本発明の実施形態による造粒粉の構造を模式的に示す図であり、（ｂ）および（ｃ）は比較のための従来の造粒粉の構造を模式的に示す図である。
【図２】本発明による実施形態のＲ−Ｆｅ−Ｂ系合金造粒粉の製造に用いられる造粒装置１００を模式的に示す図である。
【図３】（ａ）および（ｂ）は、本発明の実施形態による造粒粉の製造方法における槽内の流気の状態（流量の時間変化）を模式的に示すグラフである。
【図４】本発明の実施例の造粒粉および比較例の造粒粉を用いて得られた焼結磁石の残留磁束密度Ｂｒを示すグラフである。
【符号の説明】
１０ａ、１０ｂ、１０ｃ １次粒子
２０ａ、２０ｂ、２０ｃ 造粒粉
１０ 槽（流動槽）
２０ 第１流路
２２ 調温装置
２４ 送風装置
２６、３６ 配管
２７、２８ バルブ
３０ 第２流路
３７、３８ バルブ
４０ 磁界発生装置
４２ 容器
４２ｂ 底板
４４ 排気管
４６ バルブ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a granulated powder of a rare earth alloy, an apparatus for producing a granulated powder of a rare earth alloy, and a method of producing a rare earth alloy sintered body.
[0002]
[Prior art]
Sintered rare earth alloy magnets (permanent magnets) are generally manufactured by press molding rare earth alloy powder, sintering the resulting powder compact, and aging treatment. Currently, rare earth / cobalt magnets and rare earth / iron / boron magnets are widely used in various fields. Among them, rare earth / iron / boron magnets (hereinafter referred to as “R—Fe—B magnets”, R is a rare earth element including Y, Fe is iron, and B is boron) are various magnets. Since it has the highest maximum magnetic energy product among them and its price is relatively low, it is actively used in various electronic devices.
[0003]
R-Fe-B sintered magnets are mainly R ₂ Fe ₁₄ The main phase is composed of a B tetragonal compound, an R rich phase composed of Nd, and the like, and a B rich phase. 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 Document 1 and Patent Document 2, for example.
[0004]
Conventionally, an ingot casting method has been used in order to produce an R—Fe—B alloy to be such a magnet. According to a general ingot casting method, a rare earth metal, electrolytic iron, and ferroboron alloy as starting materials are melted at a high frequency, and the resulting molten metal is cooled relatively slowly in a mold to produce an alloy ingot.
[0005]
In recent years, the molten alloy is cooled relatively quickly by bringing it into contact 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”) that is thinner than the ingot. The rapid cooling method typified by the strip casting method and the centrifugal casting method, which are used to produce the same), has attracted attention. The thickness of the alloy piece produced by such a rapid cooling method is generally in the range of about 0.03 mm to about 10 mm. According to the rapid cooling method, the molten alloy starts to solidify from the surface in contact with the cooling roll (roll contact surface), and crystals grow in a columnar shape from the roll contact surface in the thickness direction. As a result, the quenched alloy produced by the strip casting method has a short axis size of about 0.1 μm to about 100 μm and a long axis size of about 5 μm to about 500 μm. ₂ Fe ₁₄ B crystal phase and R ₂ Fe ₁₄ It has a structure containing an R-rich phase dispersed and present in the grain boundary of the B crystal phase. The R-rich phase is a nonmagnetic 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) compared with an alloy (ingot alloy) produced by a conventional ingot casting method (die casting method). ² ℃ / second or more, 10 ^Four (C / sec or less), the structure is refined and the crystal grain size is small. Further, since the area of the grain boundary is wide and the R-rich phase spreads widely within the grain boundary, there is an advantage that the dispersibility of the R-rich phase is also excellent. Because of these characteristics, a magnet having excellent magnetic properties can be produced by using a quenched alloy.
[0007]
A method called Ca reduction method (or reduction diffusion method) is also known. This 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 in a predetermined ratio, or an alloy powder of the above constituent elements Alternatively, metallic calcium (Ca) and calcium chloride (CaCl) are mixed with mixed powder containing a mixed oxide at a predetermined ratio, and 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 alloy solid.
[0008]
In this specification, the solid alloy ingot is referred to as “alloy ingot” and obtained by cooling a molten metal such as an alloy ingot obtained by a conventional ingot casting method or an alloy flake obtained by a rapid cooling method such as a strip cast method. In addition to the obtained solidified alloy, various types 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). The average particle size is 10 μm to 500 μm), for example, by fine pulverization by a dry pulverization method using a jet mill.
[0010]
The average particle diameter of the R—Fe—B alloy powder used for press molding is preferably in the range of 1.5 μm to 6 μm from the viewpoint of magnetic properties. Note that the “average particle size” of the powder refers to the FSSS particle size unless otherwise specified. However, when such a powder having a small average particle diameter is used, fluidity and press formability (including cavity filling and compressibility) are poor, and productivity is poor.
[0011]
As a method for solving this problem, it has been studied to cover the surface of alloy powder particles with a lubricant. For example, Patent Document 3 and Patent Document 4 include 0.02% by mass of a lubricant in which at least one fatty acid ester is liquefied in a coarse powder of an R—Fe—B alloy having an average particle size of 10 μm to 500 μm. Disclosed is a technique for producing a fine powder (for example, an average particle diameter of 1.5 μm to 5 μm) of an R—Fe—B alloy by jet milling using an inert gas after adding and mixing by ˜5.0 mass%. ing.
[0012]
The lubricant improves the fluidity and moldability (compressibility) of the powder and functions as a binder for imparting hardness (strength) to the compact, while remaining as residual carbon in the sintered compact and magnetically. Since it becomes a cause of deteriorating the characteristics, an excellent binder removal property is required. For example, Patent Document 5 discloses a depolymerized polymer, a mixture of a depolymerized polymer and a hydrocarbon-based solvent, and a mixture of a depolymerized polymer, a low-viscosity mineral oil, and a hydrocarbon-based solvent as lubricants having excellent binder removal properties. It is disclosed.
[0013]
However, according to the method using the above-described lubricant, although a certain improvement effect can be obtained, it is difficult to uniformly fill the cavity, and sufficient moldability cannot be obtained. In particular, a rapid cooling method such as a strip casting method (with a cooling rate of 10 ² Per second to 10 ^Four Compared with powders produced by the ingot method, the powder produced by (/ sec) is not only small in average particle size but also sharp in particle size distribution, so that the fluidity is particularly poor. Therefore, the amount of powder filled in the cavity varies beyond the allowable range, and the filling density in the cavity becomes non-uniform. As a result, the mass and dimensions of the molded body may vary beyond the allowable range, and the molded body may be chipped or cracked.
[0014]
Attempts have been made to use granulated powder as another method for improving the fluidity and formability of R-Fe-B alloy powders.
[0015]
For example, Patent Document 6 is obtained by adding 0.4 to 4.0% by mass of a mixture of a paraffin mixture and an aliphatic carboxylic acid in a liquid state at room temperature to the powder, kneading, and granulating. It is disclosed that the moldability can be improved by using the granulated powder. A method using PVA (polyvinyl alcohol) as a granulating agent is also known. Note that the granulating agent also functions as a binder for imparting strength to the molded body, like the lubricant.
[0016]
However, when the granulating agent disclosed in Patent Document 6 is used, the binder removal property is poor, and in the case of an R—Fe—B based sintered magnet, the magnetic properties are reduced due to carbon remaining in the sintered body. There is a problem of doing.
[0017]
On the other hand, the granulated powder produced by the spray dryer method using PVA has a strong binding force, so that the obtained granulated powder is too hard and the granulated powder is completely applied even when an external magnetic field is applied. Does not collapse. Therefore, there is a problem that primary particles cannot be sufficiently magnetically oriented, and as a result, a magnet having excellent magnetic properties cannot be obtained. PVA also has poor binder removal properties, and carbon derived from PVA tends to remain in the magnet. To solve this problem, there is a method of performing a binder removal treatment in a hydrogen atmosphere, but it is difficult to sufficiently remove carbon.
[0018]
In addition, in order to solve the problem that the granulated powder does not easily collapse due to the orientation magnetic field, the applicant of the present application forms individual particles (primary particles) magnetically oriented by granulating in a state where a static magnetic field is applied. A method for producing granulated powder combined with a granulating agent was proposed (see Patent Document 7). When this granulated powder is used, the magnetic properties are improved compared to the case of using a granulated powder in which primary particles that are not magnetically oriented are combined with a granulating agent, but the magnetic field is sufficiently oriented during press molding. Therefore, the magnetic properties are lower than in the case of using a non-granulated rare earth alloy powder.
[0019]
[Patent Document 1]
U.S. Pat. No. 4,770,723
[Patent Document 2]
U.S. Pat. No. 4,792,368
[Patent Document 3]
Japanese Patent Laid-Open No. 08-111308
[Patent Document 4]
US Pat. No. 5,666,635
[Patent Document 5]
JP 2000-306753 A
[Patent Document 6]
JP 63-237402 A
[Patent Document 7]
JP-A-10-140202
[0020]
[Problems to be solved by the invention]
As described above, various granulating agents and granulating methods have been studied so far, but rare earth alloys that are excellent in fluidity and press formability and that can produce magnets having excellent magnetic properties. No method has been developed yet for industrial production of granulated powder.
[0021]
On the other hand, there is an increasing need for magnets that are smaller, thinner, and higher in performance, and it is desired to develop a manufacturing method that can produce small or thin high-performance magnets with high production efficiency. In general, when a rare earth alloy sintered body (or a magnet magnetized with this) is machined, the magnetic characteristics are deteriorated due to the influence of processing strain, but this decrease in magnetic characteristics cannot be ignored in a small magnet. Therefore, it is strongly desired to produce a sintered body having a final shape to be used with a dimensional accuracy that does not require machining substantially for smaller magnets. Against this background, there is a growing demand for rare earth alloy powders excellent in fluidity and press formability, particularly R-Fe-B alloy powders.
[0022]
The present invention has been made in view of the above points, and a method for producing a granulated powder of a rare earth alloy capable of producing a magnet having excellent fluidity and press formability and having excellent magnetic properties. And a method for producing a high-quality rare earth alloy sintered body with high production efficiency.
[0023]
[Means for Solving the Problems]
The method for producing a granulated powder of the rare earth alloy of the present invention comprises: (a) preparing a rare earth alloy powder having remanent magnetization in a tank in a state of being placed on a breathable base plate; ) Generating a first gas flow flowing from below the base plate in the tank; and (c) providing kinetic energy to the particles of the powder by the first gas flow and agglomerating due to residual magnetization of the powder. Using a force and for rolling by the kinetic energy, granulating under a substantially zero magnetic field; (d) a second gas flow directed from top to bottom with respect to the base plate; And (e) forming a powder layer made of the powder on the base plate, and compressing the powder layer by the second air flow, and including at least the step (d) Performing part and at least part of step (b) at the same time, The above-mentioned object can be achieved by the.
[0024]
In a preferred embodiment, the period in which step (d) and step (b) are performed simultaneously includes a period in which the flow rate of the second gas flow is increased while the flow rate of the first gas flow is decreased.
[0025]
In step (a), a rare earth alloy powder having no remanent magnetization is disposed in the tank, and a remanent magnetization is applied by applying a magnetic field to the powder disposed in the tank and having no remanent magnetization. And may include a step of. Alternatively, the step (a) may include a step of preparing a rare earth alloy powder having residual magnetization in advance and a step of placing the powder having residual magnetization in the vessel.
[0026]
In a preferred embodiment, step (b), step (c), step (d) and step (e) are repeated a plurality of times in this order.
[0027]
In a preferred embodiment, during the repetition, after at least one step (e), (f) temporarily stopping the first gas flow while generating the second gas flow, The powder layer formed on the base plate by generating the first gas flow having a flow rate exceeding the average flow rate of the first gas flow in the step (c) with the second gas flow stopped. Crushing.
[0028]
In a preferred embodiment, the rare earth alloy is an R—Fe—B alloy.
[0029]
In a preferred embodiment, the average particle size of the powder is in the range of 1.5 μm to 6 μm.
[0030]
In a preferred embodiment, a granulated powder having an average particle size in the range of 0.05 mm to 3.0 mm is produced.
[0031]
A method for producing a sintered rare earth alloy according to the present invention includes a step of producing a granulated powder using any one of the above-described methods for producing a granulated powder of a rare earth alloy, and applying a demagnetizing magnetic field to the granulated powder. Without filling the cavity with the rare earth alloy powder containing the granulated powder, and forming the compact by press molding in the state of applying an orientation magnetic field to the rare earth alloy powder containing the granulated powder And a step of sintering the molded body.
[0032]
The apparatus for producing granulated powder of rare earth alloy according to the present invention includes a tank provided with a base plate for receiving the rare earth alloy powder, and a first gas flow connected to the tank and flowing upward from below the base plate. A first flow path that can be generated in the tank, and a second flow path that is connected to the tank and that can generate a second gas flow that flows from the top to the bottom of the base plate in the tank. And the first flow path and the second flow path are connected to the tank independently of each other, thereby achieving the above object.
[0033]
It is preferable that a temperature control device and a blower device are further provided in the first flow path.
[0034]
It is good also as a structure further equipped with the buffer tank in the said 2nd flow path.
[0035]
It is preferable to have a thermometer that detects the temperature of the gas in the tank, and to include a control circuit that stops at least the operation of the blower when the detected temperature exceeds a predetermined temperature.
[0036]
It is preferable that the inside of the tank is maintained at a positive pressure during operation.
[0037]
It is good also as a structure further equipped with the magnetic field generation means which can apply a magnetic field to the said powder mounted on the said base plate.
[0038]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a method for producing granulated powder and a method for producing a rare earth alloy sintered body according to an embodiment of the present invention will be described with reference to the drawings. In the description of the following embodiments, the present invention is described by taking as an example a method for producing a sintered magnet using R-Fe-B alloy powder produced by a strip cast method, which is excellent in magnetic properties but low in fluidity. However, the present invention is not limited to this, and a rare earth alloy powder produced by another method may be used.
[0039]
The method for producing an R—Fe—B alloy sintered body according to an embodiment of the present invention produces an R—Fe—B alloy powder (hereinafter referred to as “raw material powder” or “primary particle powder”). Applying a magnetic field to the R-Fe-B alloy powder including the step, the step of imparting residual magnetization to the raw material powder, the step of granulating using the cohesive force due to the residual magnetization of the raw material powder, and the granulated powder It includes a step of forming a molded body by press molding in a state and a step of sintering the molded body. An R—Fe—B based sintered magnet is obtained by magnetizing the obtained sintered body by a known method. The magnetizing step is performed at an arbitrary time after sintering, and may be performed immediately before use, for example, by the user of the sintered magnet. Here, an unmagnetized magnet is also called a sintered magnet.
[0040]
In the manufacturing method of the R—Fe—B alloy sintered body according to the embodiment of the present invention, granulation is performed using the cohesive force due to the residual magnetization of the raw material powder. Therefore, the amount of granulating agent added can be reduced, or a binder having a lower binding strength than before can be used. Furthermore, it becomes possible to omit the addition of the granulating agent.
[0041]
With reference to FIG. 1 (a), (b) and (c), the manufacturing method of the granulated powder by embodiment of this invention and the characteristic of the obtained granulated powder are demonstrated. The left side of FIG. 1 is a diagram schematically showing the structure of the granulated powder, and the right side of FIG. 1 schematically shows the state of the granulated powder after an orientation magnetic field is applied in the cavity for press molding. FIG. 1A is a granulated powder 12a according to an embodiment of the present invention, FIG. 1B is a conventional granulated powder 12b using a granulating agent, and FIG. 1C is obtained by the method described in the above-mentioned Patent Document 7. The resulting granulated powder 12c is shown.
[0042]
As shown in FIG. 1A, in the granulated powder 12a of the present embodiment, primary particles 10a having residual magnetization are weakly coupled by magnetic cohesive force. Here, the case where a granulating agent is not used is illustrated. The primary particles 10a having remanent magnetization are magnetically coupled so as to form a magnetic closed circuit, and the remanent magnetization of the granulated powder 12a is slight (for example, about 0 mT or more and about 10 mT (millitesla) or less). Unlike the granulated powder 12c shown in FIG. 1C, the direction of the residual magnetization of the primary particles 10a in the granulated powder 12a is randomly oriented. For example, the average particle diameter of the primary particles 10a is 1.5 μm or more and 6.0 μm or less, and the average particle diameter of the granulated powder 12a is about 0.05 mm to 3.0 mm. The residual magnetization can be measured by inserting a gauss meter probe into the granulated powder.
[0043]
Since this granulated powder 12a has an appropriate particle size, it has excellent fluidity and low residual magnetization, so that the cavity can be easily and uniformly filled without causing bridging. Further, since the primary particles 10a are only bonded by magnetic cohesive force, as shown on the left side of FIG. 1A, the primary particles 10a can be surely applied by applying an orientation magnetic field (for example, 0.1T to 0.8T). The primary particles 10a collapse into primary particles 10a, and the primary particles 10a are magnetically oriented. Moreover, since the granulating agent is not included, the carbon content of the sintered body is not increased. A magnet obtained by magnetizing a sintered body produced using the granulated powder 12a is substantially the same as a magnet obtained without granulating raw material powder (residual magnetization is substantially zero). Have the same magnetic properties. That is, by using the granulated powder of the embodiment of the present invention, fluidity and moldability can be improved without deteriorating magnetic properties. Of course, a granulating agent may be added for the purpose of improving the strength of the molded body. Since the granulating agent is used as an auxiliary agent, a strong binding force is unnecessary, and the amount and type of the granulating agent may be selected so as not to deteriorate the magnetic characteristics.
[0044]
On the other hand, as shown in FIG. 1B, the granulated powder 12b obtained by combining the primary particles 10b of the raw material powder with the granulating agent 14 does not sufficiently collapse in the orientation magnetic field, and is obtained as a result. The magnetic properties of the sintered magnet deteriorate. Compared to the case where the raw material powder is used without being granulated, for example, the residual magnetization is reduced by about 1% to 10%. In addition, since the primary particle 10b in the granulated powder 12b of FIG.1 (b) does not have a residual magnetization, the arrow is not described.
[0045]
Further, as shown in FIG. 1C, when the granulated powder 12c in which the primary particles 10c are bonded and fixed with the granulating agent 14 while the primary particles 10c are oriented in a static magnetic field, magnetic characteristics are obtained. However, since the granulated powder 12c does not completely collapse to the primary particles 10c, compared with the case where the raw material powder is used without granulation, for example, the residual magnetization is about 1% to several%. descend. Further, as schematically shown in FIG. 1C, the granulated powder 12c has an elongated shape along the direction of the magnetic pole, which is disadvantageous from the viewpoint of fluidity. Furthermore, since the granulated powder 12c has a relatively large residual magnetization, bridging occurs unless the magnet is once demagnetized (demagnetized), so that the cavity cannot be filled.
[0046]
On the other hand, the granulated powder 12a according to the embodiment of the present invention is nearly spherical and has a small residual magnetization, so that demagnetization is not required and the cavity can be easily and uniformly filled. Therefore, it is possible to employ a so-called metering and filling method in which granulated powder having a predetermined mass is weighed in advance and then filled into the cavity. As described above, the granulated powder 12a according to the embodiment of the present invention can produce a sintered magnet that is excellent in fluidity and filling ability into a cavity and that does not substantially deteriorate in magnetic properties.
[0047]
The granulated powder according to the embodiment of the present invention is obtained by a granulation method including a process in which kinetic energy is given to particles of raw material powder having remanent magnetization and the particles grow by rolling using the given kinetic energy. Moreover, you may add a granulating agent as needed.
[0048]
In the method for producing granulated powder according to the embodiment of the present invention, the step of imparting residual magnetization to the raw material powder may be performed before the raw material powder is filled in the tank (granulating tank) of the granulating apparatus. You may do it after loading in. However, since the primary particles 10a of the granulated powder 12a according to the present embodiment are coupled by a magnetic cohesive force due to residual magnetization, the granulated powder 12a collapses when a magnetic field is applied from the outside. Therefore, the grain growth process is performed under a substantially zero magnetic field. This is because in the method for producing the granulated powder 12c shown in FIG. 1C, a magnetic field is applied to orient the primary particles 10c until the granulated powder 12 is finally fixed by the granulating agent 14. In contrast to the need to continue. As used herein, “substantially zero magnetic field” refers to the degree to which a granulated powder in which a magnetic closed circuit is formed by the residual magnetization of the powder in the process of growing the particles by rolling operation and the powder This is a weak magnetic field that does not affect the residual magnetization.
[0049]
Various magnetic fields can be used as the magnetic field applied to impart the residual magnetization. In addition, since the residual magnetization which a primary particle has may be very small, it is preferable to use an alternating attenuation magnetic field. The magnetic field for imparting residual magnetization is not limited to an alternating attenuation magnetic field, and a monotonous attenuation magnetic field, another pulse magnetic field, or a static magnetic field may be used.
[0050]
Even if the residual magnetization is applied, if the coercive force of the raw material powder is small, it may be demagnetized until the final granulated powder is obtained, and the shape of the granulated powder may not be maintained. Accordingly, it is preferable that the raw material powder has a relatively high coercive force. Specifically, the raw material powder has a bulk density of 2.0 g / cm. ^Three When the coercive force value measured with a BH tracer is the apparent coercive force of the raw material powder, the raw material powder preferably has a coercive force of 70 kA / m or more, and 80 kA / m It is more preferable to have the above coercive force. For example, in the case of an R—Fe—B alloy, an alloy containing 2% by mass or more of Dy, 1% by mass or more of Tb, or 1% by mass or more of the total of Dy and Tb is preferable.
[0051]
As the R—Fe—B alloy powder used for press molding, it is preferable to use only the granulated powder produced as described above from the viewpoint of fluidity and moldability. A raw material powder (primary particle powder) can also be mixed and used. However, since the fluidity decreases as the proportion of the raw material powder increases, it is preferable to substantially use only the granulated powder in order to sufficiently obtain the effect of improving the fluidity by granulation. Moreover, when using raw material powder mixed with granulated powder, it is preferable that the particle | grain surface is coat | covered with the lubricant. By coating the surfaces of the primary particles with a lubricant, the flowability of the R—Fe—B based powder can be improved, and oxidation of the R—Fe—B based alloy can be prevented. In addition, the orientation in the magnetic field pressing process is also improved. In the specification of the present application, not only a powder of a rare earth alloy substantially (which may include an oxide layer on the surface), but also a powder used for press molding containing a granulating agent and a lubricant together with a rare earth alloy powder. Is also called rare earth alloy powder.
[0052]
The magnet manufacturing method using the R—Fe—B alloy sintered body of the embodiment according to the present invention will be described in the order of steps.
[0053]
First, R—Fe—B based alloy flakes are prepared using a strip casting method (see, for example, US Pat. No. 5,383,978). Specifically, an R—Fe—B alloy produced by a known method is made into a molten metal by high frequency melting. As the R—Fe—B alloy, in addition to the above, those having the compositions described in, for example, US Pat. No. 4,770,723 and US Pat. No. 4,792,368 are suitable. Can be used. In a typical composition of R—Fe—B rare earth alloy, Nd or Pr is mainly used as R, Fe may be partially substituted with a transition element (eg, Co), and B is C May be substituted.
[0054]
After maintaining the molten metal of this alloy at 1350 ° C., it is rapidly cooled on a single roll under conditions of a roll peripheral speed of about 1 m / sec, a cooling rate of 500 ° C./sec, and a supercooling degree of 200 ° C., and an alloy having a thickness of 0.3 mm Get flakes. This alloy flake is occluded with hydrogen and embrittled to obtain a coarse alloy powder. By pulverizing this alloy coarse powder in a nitrogen gas atmosphere using a jet mill apparatus, for example, the average particle diameter is 1.5 μm to 6 μm and the specific surface area by the BET method is about 0.45 m. ² / G to about 0.55m ² / G alloy powder (raw material powder) is obtained. The true density of this raw material powder is 7.5 g / cm. ^Three It is.
[0055]
Next, residual magnetization is imparted to the obtained raw material powder. Here, an alternating attenuation magnetic field having a peak magnetic field of 1.0 T is applied.
[0056]
Next, the raw material powder having remanent magnetization is granulated. Here, a fluidized bed granulation method is used. When the fluidized bed granulation method is used, a granulated powder having a shape close to a spherical shape can be obtained, and a granulated powder having an appropriate hardness can be obtained. When the granulated powder has a shape close to a sphere, the fluidity and moldability are excellent. The hardness of the granulated powder is also affected by the granulating agent, but as described above, it is inconvenient if it is too hard or too soft.
[0057]
In the conventional fluidized tank granulation method, a process (flow process) in which powder flows (also referred to as “rectification”) with a gas flow flowing from the bottom to the top in the tank and a gas flow flowing from the top to the bottom. The process of compressing the powder layer (consolidation process) was performed independently. For example, in a fluid compression apparatus described in Japanese Patent No. 3019953 (for example, FIG. 3), a gas flow for performing a flow process (hereinafter referred to as “first gas flow”) and a consolidation process are performed. Gas flow (hereinafter referred to as “second gas flow”) for switching between the two gas flows cannot be generated in the tank.
[0058]
As a result of various experiments conducted by the inventor, the first gas flow for carrying out the flow process and the second gas flow for carrying out the consolidation process are simultaneously present in the tank, so that the granulated powder of the rare earth alloy can be further improved. It turned out that it can manufacture efficiently.
[0059]
This is because the true specific gravity of the rare earth alloy is 7.5 g / cm. ^Three It is considered that the granulated powder is produced by using a relatively large force and / or a relatively weak force of residual magnetization. If the binder is not used, the production yield of the granulated powder decreases unless the compaction process is performed after the first gas flow and the second gas flow coexist in the tank. On the other hand, when a binder is used, it is based on the experimental fact that the superiority difference from the conventional method was not confirmed. However, it is not well understood why the production efficiency of the granulated powder is improved by the coexistence of the first gas flow and the second gas flow.
[0060]
The granulated powder production method and production apparatus according to the embodiment of the present invention will be described in detail with reference to FIGS.
[0061]
FIG. 2 is a diagram schematically showing the structure of a granulated powder production apparatus 100 that is preferably used in the method for producing granulated powder according to an embodiment of the present invention, and FIGS. It is a graph which shows typically the state (time change of flow rate) of the in-tank in the manufacturing method of the granulated powder by the embodiment of the present invention.
[0062]
The granulated powder manufacturing apparatus 100 shown in FIG. 2 has a tank (fluid tank) 10 and a first flow path that is connected to the tank 10 and can generate a first gas flow flowing from below to above in the tank 10. 20 (a) and a second flow path 30 (b) that is connected to the tank 10 and that can generate a second gas flow that flows from the top to the bottom in the tank 10. (A) and the 2nd flow path 30 (b) are mutually connected with respect to the tank 10 independently. Reference numerals 20 and 30 are used when mainly referring to physical structures constituting the first flow path and the second flow path, respectively, and reference signs a and b are the first flow path and the second flow path, respectively. Used mainly when referring to the path of gas flow in a channel.
[0063]
The tank 10 has a structure for receiving a container 42 filled with rare earth alloy powder at the bottom. The bottom plate (base plate) 42b of the container 42 has air permeability, and can be formed of, for example, a net or cloth. From the viewpoint of workability, it is preferable to use the container 42 as described above, but other structures may be used as long as the tank 10 has a breathable base plate.
[0064]
The rare earth alloy powder placed on the bottom plate 42b of the container 42 is fluidized by being given kinetic energy by the first gas flow flowing from the bottom to the top with respect to the bottom plate 42b. At this time, the granulation process is performed under a substantially zero magnetic field by using the cohesive force due to the residual magnetization of the rare earth alloy powder and the rolling action by the kinetic energy given to the powder by the first gas flow. . Further, a powder layer is formed on the bottom plate 42b by the weight of the powder and / or the second gas flow, and the compaction process is performed by compressing the powder layer by the second air flow.
[0065]
The first flow path 20 includes a temperature control device 22, a blower (for example, a blower for blowing) 24 and a pipe 26, and is connected (connected) to the tank 10 by valves 27 and 28, A first flow path a to be circulated is formed (see arrows A1 and A2 in FIG. 2). In order to suppress oxidation of the rare earth alloy powder, it is preferable to use an inert gas (rare gas or nitrogen gas), and here, nitrogen gas is used. The volume fraction of oxygen gas contained in the gas is preferably controlled to 0.1% or less.
[0066]
Further, if the temperature of the rare earth alloy powder becomes too high, the coercive force is lowered and the cohesive force of the powder is lowered. As a result, it becomes difficult to form granulated powder and / or the oxidation of the rare earth alloy powder is suppressed. Therefore, it is preferable to control the temperature of the gas within a range of 10 ° C. or more and 40 ° C. or less, and it is more preferable to control the temperature within a range of 20 ° C. or more and 30 ° C. or less. Of course, if necessary, a humidity control device may be provided to remove moisture from the gas.
[0067]
The air blower 24 generates the first gas flow using the gas whose temperature is controlled by the temperature controller 22. The flow rate of the first gas flow generated in the tank 10 is performed by adjusting the output of the blower 24 and / or the opening of the valve 27.
[0068]
The second flow path 30 has a buffer tank 32 and a pipe 36 and is connected (coupled) to the tank 10 by valves 37 and 38 to form a second flow path b for circulating the gas in the tank 10. (See arrows B1 and B2 in FIG. 2). The buffer tank 32 is connected to an original pipe (for example, a factory nitrogen gas pipe) 34 via a regulator 33. The pressure of the nitrogen gas supplied to the main pipe 34 is, for example, about 7 kg / cm ² Several kg / cm by the regulator 33 ² Has been stepped down. The flow rate of the second gas flow generated in the tank 10 is performed by adjusting the opening degree of the valves 37 and 38.
[0069]
Both ends of the first flow path 20 and the second flow path 30 are connected to the tank 10, respectively, and the gas flow path is substantially closed. Accordingly, the state (temperature / humidity) of the nitrogen gas in the tank 10 can be controlled efficiently, and the consumption of nitrogen gas can be reduced. However, since it is difficult to adjust the gas flow in a completely closed system, a configuration in which the exhaust pipe 44 is connected to the tank 10 via the valve 46 and the nitrogen gas in the tank 10 is exhausted with a predetermined resistance is adopted. Is preferred. At this time, it is preferable to adjust the resistance of the exhaust pipe 44 so that the pressure in the tank 10 is maintained higher than the pressure (atmospheric pressure) of the atmosphere outside the tank 10 at least during operation.
[0070]
Furthermore, since rare earth alloy powders are easily oxidized, there is even an explosion risk if the temperature rises abnormally. Therefore, a thermometer 18 for detecting the temperature in the tank 10 is provided, and when the temperature in the tank 10 exceeds a predetermined temperature, at least a control circuit for stopping the operation of the blower 24 is provided. preferable. Of course, the valves 27, 28, 37, 38 and 46 may be constituted by electromagnetic valves, and may be controlled so as to close when a predetermined temperature is exceeded. From various experiences, when an R—Fe—B alloy is used, since the possibility of rapid oxidation (which may be accompanied by ignition or explosion) increases when the temperature exceeds 50 ° C., the above stop operation is started. The temperature is preferably set to 50 ° C.
[0071]
The tank 10 has different inner diameters at the bottom portion that receives the container 42 and the vicinity thereof, and the body portion that is positioned above the bottom portion. As shown in FIG. 2, the inner diameter D1 of the bottom of the tank 10 is smaller than the inner diameter D2 of the body part, and becomes larger as it approaches the body part. When the tank 10 having such a structure is used, the flow rate of the first air generated in the tank 10 by the first flow path 20 decreases as it goes upward, so that it is floated by the first air. Can be efficiently dropped. The length (height) of the bottom portion having an inner diameter smaller than the inner diameter D2 of the trunk portion is, for example, about 20% of the entire length of the tank 10, and the minimum value of the inner diameter D1 of the bottom portion (the portion where the bottom plate 42b is located). ) Is, for example, about 50% of D2.
[0072]
The granulated powder production apparatus 100 further includes a magnetic field generating means 40 capable of applying a magnetic field to the rare earth alloy powder filled in the container 42. The magnetic field generation means 40 is preferably an electromagnet having a coil and a yoke, for example, and can generate an alternating attenuation magnetic field. Of course, the magnetic field generating means 40 can be omitted in the case of using a rare earth alloy powder which has been given a remanent magnetization outside the vessel 10.
[0073]
Next, referring to FIGS. 3A and 3B, the state of air flow in the tank 10 in the method for producing granulated powder in the embodiment of the present invention will be described. FIG. 3A shows a series of steps (one cycle) from the start of operation, and FIG. 3B shows a series of steps (one cycle) including a crushing step.
[0074]
First, with reference to FIG. 3A, the state of air flow in the tank 10 after the container 42 filled with the rare-earth alloy powder having residual magnetization is set at a predetermined position of the apparatus 100 will be described.
[0075]
Immediately after the container 42 is set, the flow rate a of the first air flow a ₀ And the second flow rate b ₀ Are all zero. The operation of the temperature control device 22 and the blower device 24 is started, the valves 27 and 28 are opened, and the first air flow a is generated in the tank 10. The flow rate of the first air flow a gradually increases, and the steady state flow rate a ₁ To reach. In this state, the powder is granulated by the cohesive force due to residual magnetization while undergoing a rolling operation in the tank 10. During this time, the powder (including particles in the granulation process) existing near the center of the tank 10 is suspended against the gravity by the first air flow a, and the powder near the inner wall of the weak tank 10 having a low flow velocity is caused by its own weight. Fall.
[0076]
With the flow rate of the first air flow a maintained substantially constant for a predetermined time (for example, about 20 minutes), the valves 37 and 38 are opened to start the generation of the second air flow b (the flow rate b1 at the starting point). . The flow rate of the second flow b is gradually increased so that the steady flow b ₂ Before reaching the flow rate, the flow rate of the first flow a is decreased (the flow rate at the decrease start point is a ₂ ). That is, a period in which the flow rate of the second flow b is increased while the flow rate of the first flow a is decreased (a in FIG. 3A). ₂ ~ B ₂ Period). Thus, the existence of a period in which the first air flow a and the second air flow b are simultaneously present in the tank 10 makes it possible to more efficiently produce a rare earth alloy granulated powder. The reason for this is not necessarily clear, but if the first flow a is stopped abruptly, or if the flow rate of the second flow b is too large with respect to the flow rate of the first flow a, the granulated powder suddenly increases. This is because the granulated powder is destroyed by impact. Moreover, if the production | generation of the 2nd air flow b is started after the 1st air flow a is stopped completely, since the inside of the tank 10 will become a negative pressure and control of a pressure will become difficult, it is unpreferable.
[0077]
As described above, when the flow rate of the second air b is increased while gradually decreasing the flow rate of the first air a, the granulated powder is not destroyed by an impact when falling on the bottom plate 42b. The powder layer is formed, and then compressed by the second air b, so that the powder layer is consolidated. This consolidation process increases the hardness of the granulated powder.
[0078]
By repeating the cycle shown in FIG. 3A, a granulated powder having an appropriate hardness can be obtained. However, as shown in FIG. 3A, the flow rate of the first air flow a at the start of the second and subsequent cycles is zero (a ₀ The flow rate a at the end of the cycle shown in FIG. _Three It may be.
[0079]
By simply repeating the cycle shown in FIG. 3A, the powder layer compressed on the bottom plate 42b cannot be sufficiently crushed, and coarse particles may be generated. Therefore, in order to more reliably disintegrate the powder layer, it is preferable to execute the cycle shown in FIG.
[0080]
Point b in FIG. ₁ 'I will explain from the following steps. Here, the point b in FIG. ₁ Up to ', the point b in FIG. ₁ A case will be described in which the steps up to and including step (b) of FIG. 3 are subsequently performed.
[0081]
In the same manner as described above, the generation of the second flow b is started (the flow rate b at the start time). ₁ ') And the flow rate of the second flow b is the steady flow rate b. ₂ Before reaching ', the flow rate of the first flow a begins to decrease (the flow rate a at the start of the decrease). ₂ '). Thereafter, the valves 27 and 28 are closed, and the state where the first air flow a is stopped is maintained (point a in FIG. 3A). _Three '~ Point a _Four ': Α minutes). If the air blower 24 is continuously operated during this time, the gas pressure in the pipe 26 from the air blower 24 to the valve 27 increases. In other words, the valve 27 is closed until a predetermined pressure for crushing the powder layer is obtained. Thereafter, the valves 37 and 38 are closed to stop the second air flow b (point b in FIG. 3B). ₀ ') And the valves 27 and 28 are opened to generate the first air flow a (point a in FIG. 3B). ₀ '). At this time, the flow rate a of the first air flow a generated in the tank 10 ₀ 'Is the flow rate a of the stationary first gas flow a in FIG. ₁ (= A ₂ ) And the powder layer can be efficiently crushed. The flow rate of the first flow a for obtaining the rolling action is typically substantially constant as shown in FIG. ₁ = A ₂ ) But may vary. In this case, it is preferable that the flow rate of the first flow a for pulverizing the powder layer is larger than the average flow rate of the first flow a for obtaining the rolling action.
[0082]
In the above example, by operating the valves 37 and 38, the diversion a ₀ The first flow a is generated, but the flow rate of the first flow a may be adjusted by controlling the blowing capacity of the blower 24, or may be combined with the valve operation. Note that the flow rate a in FIG. ₁ 'And flow rate a ₂ 'Is the flow rate a in FIG. ₁ And flow rate a ₂ May be the same.
[0083]
When the granulated powder formed using the remanent magnetization becomes a certain size, a magnetic closed circuit is formed, so that the magnetic attractive force acting between the granulated powders is weakened. The crushing cycle shown in Fig. 1 is no longer necessary. Therefore, for example, in a process in which a predetermined granulated powder is obtained by repeating the basic cycle shown in FIG. 3A and the crushing cycle shown in FIG. In the first 20 cycles, it is preferable to include 5 to 10 cycles for crushing.
[0084]
In addition, when the raw material powder having residual magnetization is used, a desired granulated powder can be obtained in a shorter time (for example, about half the time) than when the raw material powder having no residual magnetization is used. This is presumably because when a raw material powder having residual magnetization is used, nuclei for generating granulated powder are easily generated by magnetic cohesion between primary particles.
[0085]
The average particle diameter of the granulated powder is preferably in the range of 0.05 mm to 3.0 mm. In general, the primary particles contained in the granulated powder are very few, and there are very few higher-order granulated powders of tertiary particles or more, so the average particle size of the secondary particles is substantially the average of the granulated powder. It can be treated as representative of particle size. Here, the average particle diameter of the secondary particles obtained by microscopic observation is used as the average particle diameter of the granulated powder. When the average particle diameter of the granulated powder is smaller than 0.05 mm, the effect of improving the fluidity is low, and it is difficult to obtain a uniform molded body with sufficient density. On the other hand, when the average particle diameter of the granulated powder is larger than 3 mm, the filling property into the cavity is lowered, and it is difficult to obtain a uniform compact with a sufficient density. The average particle diameter of the granulated powder is more preferably in the range of 0.1 mm to 2.0 mm.
[0086]
Next, a molded body is formed by press molding the obtained granulated powder. Here, a compact is formed using only the granulated powder. A known press molding apparatus can be used for the press molding, and typically, a uniaxial press molding apparatus that presses the powder in the cavity (die hole) of the mold with upper and lower punches is used. The granulated powder is transferred for each batch, for example, in a state in which nitrogen gas is filled or flowed in a highly airtight container.
[0087]
Fill the mold cavity of the uniaxial press molding machine with granulated powder. The step of filling the granulated powder into the cavity is, for example, a filling method using a sieve, Japanese Examined Patent Publication No. 59-40560, Japanese Unexamined Patent Publication No. 10-58198, Japanese Unexamined Utility Model Publication No. 63-110521, or Japanese Unexamined Patent Publication No. 2000-. It can be executed by using a filling method using a feeder box as disclosed in Japanese Patent No. 248301 (these may be collectively referred to as “dropping method”).
[0088]
In particular, when forming a small molded body, it is preferable to measure the amount of granulated powder corresponding to the internal volume of the cavity using the cavity. For example, a feeder box having an opening below is moved over the cavity, the granulated powder is dropped by gravity (natural fall), and then the excess granulated powder supplied to the cavity is ground to make it relatively uniform. In addition, a predetermined amount of granulated powder can be filled. Of course, the granulated powder weighed separately may be filled into the cavity using a funnel or the like.
[0089]
After filling the cavity with the granulated powder, the upper punch of the uniaxial press apparatus is lowered, and an orientation magnetic field is applied in a state where the opening of the cavity is closed, and the granulated powder is collapsed into primary particles. Next particles are magnetically oriented. The granulated powder according to the embodiment of the present invention surely collapses into primary particles in a relatively weak magnetic field of 0.1T to 0.8T. However, considering a sufficient degree of orientation, about 0.5T to 1.5T is desirable. The direction of the magnetic field is, for example, a direction perpendicular to the pressing direction. While applying the magnetic field in this way, the powder is uniaxially pressed with an upper and lower punch, for example, at a pressure of 98 MPa. As a result, a molded body having a relative density (molded body density / true density) of 0.5 to 0.7 is obtained. The direction of the magnetic field may be parallel to the press direction as necessary.
[0090]
Next, the obtained molded body is sintered in a vacuum or an inert gas atmosphere at a temperature of, for example, about 1000 ° C. to about 1180 ° C. for about 1 hour to 6 hours. Since the granulated powder of this embodiment does not contain a granulating agent or contains only a granulating agent that can be substantially removed during the sintering process, it is not necessary to provide a separate binder removal step. The conventional typical binder removal step is performed at a temperature of about 200 ° C. to 800 ° C. in an inert gas atmosphere at a pressure of about 2 Pa for about 3 hours to about 6 hours.
[0091]
By subjecting the obtained sintered body to an aging treatment at a temperature of about 450 ° C. to about 800 ° C. for about 1 hour to 8 hours, an R—Fe—B based sintered magnet is obtained. Thereafter, the R—Fe—B sintered magnet is finally completed by magnetizing at an arbitrary stage.
[0092]
According to the present invention, since the granulated powder having excellent fluidity and moldability is used as described above, there is little variation in the filling amount, and the cavity is uniformly filled. Therefore, there is little variation in the mass and dimensions of the molded body obtained by press molding. Further, the molded body is less likely to be chipped or cracked.
[0093]
Furthermore, since the primary particles of the granulated powder of this embodiment are substantially bonded by the magnetic cohesive force of residual magnetization, the primary particles are surely collapsed into primary particles by application of an orientation magnetic field. Therefore, the degree of orientation of primary particles does not decrease. Moreover, since the deterioration of the magnetic characteristics due to the carbon of the granulating agent remaining in the sintered body is suppressed to a minimum, a sintered magnet having excellent magnetic characteristics can be obtained. Thus, according to the present invention, a high-quality R—Fe—B alloy sintered magnet can be produced with high production efficiency.
[0094]
【Example】
Examples of the present invention will be described below.
[0095]
An R—Fe—B alloy powder was prepared as follows. A molten alloy was prepared using electrolytic iron having a purity of 99.9%, a ferroboron alloy containing 19.8% B, and Nd and Dy having a purity of 99.7% or more as starting materials. From this molten alloy, flakes of an R—Fe—B alloy having a composition of 30.0% by mass Nd, 5.0% by mass Dy, 64.0% by mass Fe and 1.0% by mass B were obtained by strip casting. . This is used with a jet mill and an inert gas (for example, N ₂ Gas, gas pressure 58.8 MPa) to obtain a raw material powder having an average particle diameter of about 3 μm.
[0096]
Next, an alternating decay magnetic field (peak magnetic field: 1.0 T) was applied to the raw material powder for the examples to impart residual magnetization.
[0097]
Next, granulated powder was manufactured using the manufacturing apparatus 100 described above.
[0098]
The internal diameter (D2) of the tank 10 is 300 mm, and the internal volume is about 7 × 10. ^Four cm ^Three , The flow rate a in FIGS. 3 (a) and 3 (b) ₁ = A ₂ = A ₁ '= A ₂ 'Is about 1m ^Three / Min, flow rate a ₀ 'Is about 2.0m ^Three / Min, flow rate b ₂ = B _Three = B ₂ '= B _Three 'Is about 0.75m ^Three / Min. The input amount of the rare earth alloy raw material powder was about 5 kg, and the temperature of the nitrogen gas was controlled at about 30 ° C.
[0099]
In the production of the granulated powders of Examples 2 to 3 and Comparative Examples 2 and 3, polybutene and isoparaffin described in Japanese Patent Application No. 2001-96572 by the applicants of the present application were used as granulating agents.
[0100]
In both the examples and the comparative examples, the conditions were set so that the average particle diameter of the granulated powder was 0.5 mm. The obtained granulated powder had a residual magnetization of about 0.2 mT. The granulation process of Examples 1 to 3 took about 15 minutes, and the granulation process of Comparative Examples 2 and 3 took about 30 minutes. In Comparative Example 1, the raw material powder (not applied with a magnetic field) was used without granulation. Table 1 summarizes the preparation conditions of the pressing powders in Examples 1 to 3 and Comparative Examples 1 to 3, respectively.
[0101]
[Table 1]

[0102]
Table 1 also shows the angle of repose of each press powder. A powder having a large angle of repose has poor fluidity, and a powder having a small angle of repose is excellent in fluidity. As shown in Comparative Example 1, if the raw material powder is not granulated, the angle of repose is as large as about 52 ° and the fluidity is low. On the other hand, the angle of repose of all the pressed powders of Examples 1 to 3 and Comparative Examples 2 and 3 subjected to granulation is reduced to less than 50 °. In particular, the press powders of Examples 1 and 2 have a smaller angle of repose and excellent fluidity than the press powder of Comparative Example 2 (addition amount of granulating agent 1% by mass). That is, it can be seen that by using the remanent magnetization, the fluidity is improved by adding less granulating agent than before. In Example 3 and Comparative Example 3 in which the addition amount of the granulating agent was 2% by mass, there was no difference in fluidity.
[0103]
Each press powder shown in Table 1 was filled into a cavity having a length of 20 mm, a width of 15 mm, and a depth of 10 mm by the method using the feeder box described above, and uniaxial press molding (98 MPa, orientation magnetic field (0.8 T ) Was applied at right angles to the pressing direction. This filling step and press molding step were performed under the same conditions for all examples and comparative examples. In addition, the press body was changed and the molded object from which a molded object density (green density) differs was formed.
[0104]
The mass variation (%) and filling amount variation (σ) of the press-formed bodies of Example 1 and Comparative Example 1 were evaluated. The mass variation of the molded body was determined by {(maximum mass−minimum mass) / average mass (n = 50)} × 100 (%). Further, the filling amount variation (σ) indicates the standard deviation of the mass distribution of 50 molded bodies. The mass variation of the molded body of Example 1 is about 4%, which is remarkably improved as compared with the mass variation of Comparative Example 1 of about 15%. This is the same for the filling amount variation (σ). The filling amount variation (σ) of Comparative Example 1 is about 0.33, whereas the filling amount variation (σ) of Example 1 is 0.16. It can be seen that the fluidity has been improved by granulation. Of course, the formability was improved by granulation as well, and the proportion of chipping and cracking in the molded product was significantly lower than in Comparative Example 1. These granulation effects were confirmed for other examples.
[0105]
The obtained molded body was sintered at 1060 ° C. for about 4 hours in an Ar atmosphere, and then subjected to an aging treatment at 600 ° C. for 1 hour to obtain a sintered body. Further, this sintered body was magnetized under the condition of 2387 kA / m to obtain a sintered magnet. For each example and comparative example, the number of samples was 50.
[0106]
FIG. 4 shows the residual magnetization Br (T) of the obtained sintered magnet. As can be seen from FIG. 4, the Br of Example 1 (black circle in FIG. 4) has no significant difference from the Br of Comparative Example 1 (white circle in FIG. 4), and has excellent magnetic properties. ing. The Br of Example 2 and Example 3 to which the granulating agent was added was almost equivalent to the Br of Comparative Example 2 and Comparative Example 3 in which the same amount of granulating agent was added and the raw material powder having no residual magnetization was used. Met. Even in the case of granulating using the residual magnetization, it is preferable that the granulating agent is as small as possible.
[0107]
As described above, by producing the granulated powder using the magnetic cohesive force due to the residual magnetization of the primary particles, compared to the case of using the granulated powder only using the binding force of the granulating agent, Even if the addition amount of the granulating agent is reduced, the fluidity equal to or higher than that can be obtained, so that a sintered magnet having magnetic properties superior to those of the conventional one can be manufactured with the productivity equivalent to or higher than the conventional one. Furthermore, if the granulated powder is produced using only the remanent magnetization of the primary particles, the deterioration of the magnetic properties can be substantially eliminated.
[0108]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the granulated powder of the rare earth alloy which can manufacture the magnet which is excellent in fluidity | liquidity and press moldability, and has the outstanding magnetic characteristic is provided. By using this granulated powder, a method for producing a high-quality rare earth alloy sintered body with high production efficiency is provided.
[0109]
According to the present invention, the fluidity and formability of the rare earth alloy powder can be improved without deteriorating the magnetic properties. Magnetic characteristics can be improved. Further, the granulation time can be shortened and the binder removal step can be omitted, and the productivity of the rare earth sintered magnet can be improved.
[Brief description of the drawings]
1A is a diagram schematically showing the structure of a granulated powder according to an embodiment of the present invention, and FIGS. 1B and 1C are diagrams schematically showing the structure of a conventional granulated powder for comparison. FIG.
FIG. 2 is a diagram schematically showing a granulating apparatus 100 used for producing an R—Fe—B based alloy granulated powder according to an embodiment of the present invention.
FIGS. 3A and 3B are graphs schematically showing the state of air flow (change in flow rate with time) in a tank in the method for producing granulated powder according to the embodiment of the present invention.
FIG. 4 is a graph showing the residual magnetic flux density Br of sintered magnets obtained using the granulated powder of the example of the present invention and the granulated powder of the comparative example.
[Explanation of symbols]
10a, 10b, 10c primary particles
20a, 20b, 20c Granulated powder
10 tanks (fluidized tank)
20 First flow path
22 Temperature controller
24 Blower
26, 36 piping
27, 28 Valve
30 Second channel
37, 38 valves
40 Magnetic field generator
42 containers
42b Bottom plate
44 exhaust pipe
46 Valve

Claims (16)

(A) preparing a rare earth alloy powder having remanent magnetization in a tank in a state of being placed on a base plate having air permeability;
(B) generating a first gas flow flowing from below the base plate in the tank;
(C) Giving kinetic energy to the particles of the powder by the first gas flow, and using the cohesive force due to the residual magnetization of the powder and the rolling action by the kinetic energy without applying a magnetic field from the outside , comprising the steps of granulating,
(D) generating a second gas flow in the tank from the top to the bottom with respect to the base plate;
(E) forming a powder layer made of the powder on the base plate, and compressing the powder layer by the second air flow;
Including
A method for producing a granulated powder of a rare earth alloy, wherein at least a part of the step (d) and at least a part of the step (b) are simultaneously performed.   The granulation according to claim 1, wherein the period in which step (d) and step (b) are simultaneously performed includes a period in which the flow rate of the second gas flow is increased while the flow rate of the first gas flow is decreased. Powder manufacturing method.   In step (a), a rare earth alloy powder having no remanent magnetization is disposed in the tank, and a remanent magnetization is applied by applying a magnetic field to the powder disposed in the tank and having no remanent magnetization. The manufacturing method of the granulated powder of Claim 1 or 2 including the process to do.   The rare earth alloy according to claim 1 or 2, wherein the step (a) includes a step of preparing a rare earth alloy powder having residual magnetization in advance and a step of placing the powder having residual magnetization in the vessel. Of granulated powder.   The method for producing granulated powder according to any one of claims 1 to 4, wherein the step (b), the step (c), the step (d) and the step (e) are repeated a plurality of times in this order. During the repetition, after at least one step (e),
(F) The average of the first gas flow in the step (c) in a state where the first gas flow is temporarily stopped in a state where the second gas flow is generated and then the second gas flow is stopped. Crushing the powder layer formed on the base plate by generating the first gas flow having a flow rate exceeding the flow rate;
The manufacturing method of the granulated powder of Claim 5 containing this.   The method for producing granulated powder of a rare earth alloy according to any one of claims 1 to 6, wherein the rare earth alloy is an R-Fe-B alloy.   The method for producing a granulated powder of a rare earth alloy according to any one of claims 1 to 7, wherein an average particle diameter of the powder is in a range of 1.5 µm to 6 µm.   The method for producing a granulated powder of a rare earth alloy according to any one of claims 1 to 8, wherein a granulated powder having an average particle size in the range of 0.05 mm to 3.0 mm is produced. A step of producing a granulated powder using the method for producing a granulated powder of a rare earth alloy according to any one of claims 1 to 9,
Filling a cavity with a rare earth alloy powder containing the granulated powder without applying a demagnetizing magnetic field to the granulated powder;
Forming a molded body by press-molding a rare earth alloy powder containing the granulated powder while applying an orientation magnetic field; and
Sintering the molded body;
The manufacturing method of the rare earth alloy sintered compact containing this. A tank provided with a base plate for receiving rare earth alloy powder;
A first flow path connected to the tank and capable of generating a first gas flow in the tank flowing from below the base plate;
A second flow path connected to the tank and capable of generating a second gas flow in the tank flowing from the top to the bottom of the base plate;
Have
The apparatus for producing granulated powder of rare earth alloy, wherein the first flow path and the second flow path are independently connected to the tank. The manufacturing apparatus according to claim 11 , further comprising a temperature controller and a blower in the first flow path.   The manufacturing apparatus according to claim 11, further comprising a buffer tank in the second flow path.   The thermometer which detects the temperature of the gas in the said tank, and when the detected temperature exceeds predetermined | prescribed temperature, the control circuit which stops the operation | movement of the said air blower at least is provided. The manufacturing apparatus as described.   The manufacturing apparatus according to claim 11, wherein the inside of the tank is maintained at a positive pressure during operation.   The manufacturing apparatus according to any one of claims 11 to 15, further comprising magnetic field generating means capable of applying a magnetic field to the powder placed on the base plate.

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