JP2004131815A - Method and apparatus for manufacturing granulated powder of rare earth alloy, and method for manufacturing rare earth alloy sintered compact - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing granulated powder of rare earth alloy for manufacturing a magnet having excellent fluidity, press formability, and excellent magnetic characteristic. <P>SOLUTION: This method for manufacturing granulated powder of rare earth alloy comprises: a step of preparing powder of rare earth alloy having residual magnetization placed on a gas-permeable base plate 42b in a tank 10; a step of generating a first gas flow (a) flowing upward from a lower side with respect to the base plate 42b; a step of performing granulation under a substantially zero magnetic field by utilizing the coercive force by the residual magnetization of the powder and the rolling effect by the kinetic energy by giving the kinetic energy to the powder particles by the first gas flow; a step of generating a second gas flow (b) downward from an upper side with respect to the base plate 42b; and a step of forming a powder layer formed of the powder on the base plate and compressing the powder layer by the second air flow. In addition, at least a part of the step of generating the first air flow and the step of generating the second air flow is simultaneously performed. <P>COPYRIGHT: (C)2004,JPO

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]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing a rare earth alloy granulated powder, an apparatus for producing a rare earth alloy granulated 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 mainly ₂ Fe ₁₄ It 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 replaced with a transition metal such as Co or Ni, and a part of boron (B) may be replaced 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, 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 alloy melt has been 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 alloy melt, a solidified alloy thinner than an ingot ("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. ₂ Fe ₁₄ B crystal phase and R ₂ Fe ₁₄ It 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, 10 ⁴ (° 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 lump is referred to as an "alloy lump" 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 herein refers to the FSSS particle size 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]
As a method for solving this problem, covering the surface of the alloy powder particles with a lubricant has been studied. For example, Patent Literature 3 and Patent Literature 4 disclose that a lubricant in which at least one fatty acid ester is liquefied is added to a coarse powder of an R-Fe-B-based alloy having an average particle size of 10 µm to 500 µm by 0.02% by mass. A technique for producing a fine powder (for example, an average particle size of 1.5 μm to 5 μm) of an R—Fe—B-based alloy by performing jet mill pulverization using an inert gas after addition and mixing of up to 5.0 mass% is disclosed. ing.
[0012]
The lubricant improves the fluidity and moldability (compressibility) of the powder, and also functions as a binder for imparting hardness (strength) to the compact, while remaining as carbon remaining in the sintered compact and magnetically Excellent binder removal properties are required because they cause deterioration in characteristics. For example, Patent Literature 5 discloses that as a lubricant having excellent binder removal properties, a depolymerized polymer, a mixture of a depolymerized polymer and a hydrocarbon solvent, and a mixture of a depolymerized polymer, a low-viscosity mineral oil, and a hydrocarbon solvent are used. It has been disclosed.
[0013]
However, according to the above-described method using a lubricant, although a certain improvement effect can be obtained, it is difficult to uniformly fill the cavity, and sufficient moldability cannot be obtained. Particularly, a rapid cooling method such as a strip casting method (a cooling rate of 10 ² / Sec-10 ⁴ Powder 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.
[0014]
As another method for improving the flowability and the moldability of the R-Fe-B-based alloy powder, an attempt to use granulated powder has been made.
[0015]
For example, Patent Literature 6 discloses that a mixture of a paraffin mixture and an aliphatic carboxylic acid in a liquid state at room temperature is added to a powder in an amount of 0.4 to 4.0% by mass, kneaded, and then granulated. It is disclosed that the moldability can be improved by using the obtained 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, similarly to the lubricant.
[0016]
However, when the granulating agent disclosed in Patent Document 6 is used, since the binder removal property is poor, in the case of an R—Fe—B based sintered magnet, the magnetic properties are deteriorated 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, on the contrary, has a strong bonding force, so that the obtained granulated powder is too hard, and the granulated powder is completely formed even when an external magnetic field is applied. Does not collapse. Therefore, the primary particles cannot be sufficiently oriented in the magnetic field, and as a result, there is a problem that 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. In order to solve this problem, there is a method of performing a binder removal process 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 is hard to collapse due to the orientation magnetic field, the present applicant granulates in a state where a static magnetic field is applied, whereby individual particles (primary particles) oriented in the magnetic field are formed. A method for producing a granulated powder combined with a granulating agent has been proposed (see Patent Document 7). When this granulated powder is used, the magnetic properties are improved as compared with the case of using 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]
JP 08-111308 A
[Patent Document 4]
U.S. Pat. No. 5,666,635
[Patent Document 5]
JP 2000-306753 A
[Patent Document 6]
JP-A-63-237402
[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 which are excellent in fluidity and press formability and can produce magnets having excellent magnetic properties A method capable of industrially producing the granulated powder of the present invention has not yet been developed.
[0021]
On the other hand, there is an increasing need for downsizing, thinning, and high performance of magnets, and development of a manufacturing method capable of manufacturing small or thin high-performance magnets with high production efficiency is desired. In general, when a rare earth alloy sintered body (or a magnet magnetized thereof) is machined, its magnetic properties decrease due to the influence of processing strain. However, this decrease in magnetic properties cannot be ignored for small magnets. Therefore, it is strongly desired that a smaller magnet produce a sintered body having a final shape to be used with a dimensional accuracy that does not substantially require machining. Against this background, the demand for rare earth alloy powders excellent in fluidity and press formability, particularly R-Fe-B-based alloy powders, has become stronger.
[0022]
The present invention has been made in view of the above points, and is 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. Another object of the present invention is to provide 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 granulated powder of a rare earth alloy of the present invention comprises the steps of (a) preparing a rare earth alloy powder having remanent magnetization in a tank while being placed on a gas-permeable base plate; A) generating a first gas flow flowing from below to above the bed plate in the tank; and (c) imparting kinetic energy to the particles of the powder by the first gas flow to cause agglomeration of the powder due to residual magnetization. Granulating under a substantially zero magnetic field by using force and the rolling operation by the kinetic energy, and (d) forming a second gas flow from top to bottom with respect to the base plate. Forming in a vessel, and (e) forming a powder layer made of the powder on the base plate, and compressing the powder layer with the second flowing air, wherein at least the step (d) is performed. Characterized in that a part and at least a part of the step (b) are performed simultaneously, The above-mentioned object can be achieved by the.
[0024]
In a preferred embodiment, the period in which the steps (d) and (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 reduced.
[0025]
In the 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 having no remanent magnetization disposed in the tank. And the step of carrying out. Alternatively, the step (a) may include a step of preparing a rare earth alloy powder having residual magnetization in advance and a step of disposing the powder having residual magnetization in the tank.
[0026]
In a preferred embodiment, step (b), step (c), step (d) and step (e) are repeated multiple 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 an average flow rate of the first gas flow in step (c) in a state where the second gas flow is stopped. Pulverizing.
[0028]
In a preferred embodiment, the rare earth alloy is an R—Fe—B based 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 a range of 0.05 mm or more and 3.0 mm or less is produced.
[0031]
The method for producing a rare earth alloy sintered body according to the present invention includes a step of producing granulated powder using any one of the above-described methods for producing granulated powder of a rare earth alloy, and applying a demagnetizing magnetic field to the granulated powder. Filling a cavity with a rare earth alloy powder containing the granulated powder, and forming a compact by press-molding the rare earth alloy powder containing the granulated powder while an orientation magnetic field is applied to the cavity. And sintering the compact.
[0032]
An apparatus for producing granulated powder of a rare earth alloy according to the present invention comprises a tank provided with a base plate for receiving the powder of the rare earth alloy, 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 downward from above the base plate in the tank. Wherein the first flow path and the second flow path are connected to the tank independently of each other, whereby the object is achieved.
[0033]
It is preferable that a temperature controller and a blower are further provided in the first flow path.
[0034]
The second flow path may further include a buffer tank.
[0035]
It is preferable that a thermometer for detecting the temperature of the gas in the tank be provided, and a control circuit for stopping at least the operation of the blower when the detected temperature exceeds a predetermined temperature be provided.
[0036]
It is preferable that the inside of the tank is maintained at a positive pressure during operation.
[0037]
The apparatus may further include a magnetic field generating unit that can apply a magnetic field to the powder placed on the base plate.
[0038]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a method for manufacturing a granulated powder and a method for manufacturing a rare earth alloy sintered body according to an embodiment of the present invention will be described with reference to the drawings. In the following description of the embodiment, the present invention is exemplified by a method of manufacturing a sintered magnet using an R-Fe-B-based alloy powder manufactured by a strip casting method, which has excellent magnetic properties, but has particularly low fluidity. However, the present invention is not limited to this, and a rare earth alloy powder produced by another method may be used.
[0039]
In the method for producing an R-Fe-B-based alloy sintered body according to an embodiment of the present invention, powder of an R-Fe-B-based alloy (hereinafter, referred to as "raw material powder" or "primary particle powder") is produced. A step of imparting remanent magnetization to the raw material powder, a step of granulating utilizing cohesive force due to the residual magnetization of the raw material powder, and applying a magnetic field to the R-Fe-B-based alloy powder including the granulated powder The method includes a step of forming a molded body by press molding in a state, and a step of sintering the molded body. By magnetizing the obtained sintered body by a known method, an R—Fe—B based sintered magnet is obtained. The magnetizing step may be performed at any time after sintering, for example, by a user of the sintered magnet immediately before use. Here, the unmagnetized one is also called a sintered magnet.
[0040]
In the method of manufacturing an R-Fe-B-based alloy sintered body according to the embodiment of the present invention, granulation is performed using cohesion due to residual magnetization of the raw material powder. Therefore, the amount of the granulating agent to be added can be reduced, or a binder having a lower binding force than the conventional one can be used. Furthermore, it is even possible to omit the addition of the granulating agent.
[0041]
With reference to FIGS. 1 (a), 1 (b) and 1 (c), a method for producing a granulated powder according to an embodiment of the present invention and features of the obtained granulated powder will be described. 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 the application of the orientation magnetic field in the cavity for press molding. FIG. FIG. 1A shows a granulated powder 12a according to an embodiment of the present invention, FIG. 1B shows a conventional granulated powder 12b using a granulating agent, and FIG. 1C shows a granulated powder 12c obtained by a method described in Patent Document 7 described above. The obtained 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 bound by magnetic cohesion. Here, a case where a granulating agent is not used is illustrated. The primary particles 10a having residual magnetization are magnetically coupled so as to form a magnetic closed circuit, and the residual magnetization of the granulated powder 12a is slight (for example, more than 0 mT and 10 mT or less (millitesla)). The direction of the residual magnetization of the primary particles 10a in the granulated powder 12a is different from the direction of the granulated powder 12c shown in FIG. For example, the average particle size of the primary particles 10a is 1.5 μm or more and 6.0 μm or less, and the average particle size of the granulated powder 12a is about 0.05 mm to 3.0 mm. The remanent magnetization can be measured by inserting a Gauss meter probe into the granulated powder.
[0043]
Since the granulated powder 12a has an appropriate particle size, it has excellent fluidity and low residual magnetization, so that it can be easily and uniformly filled into the cavity without causing bridging. Furthermore, since the primary particles 10a are only bonded by magnetic cohesion, as shown on the left side of FIG. 1A, the application of an alignment magnetic field (for example, 0.1T to 0.8T) ensures that the primary particles 10a are reliably applied. The primary particles 10a collapse into primary particles 10a, and the primary particles 10a are magnetically oriented. Further, since no granulating agent is contained, the carbon content of the sintered body does not increase. A magnet obtained by magnetizing a sintered body manufactured using the granulated powder 12a is substantially different from a magnet obtained by using a raw material powder (having substantially no residual magnetization) without granulating. Have the same magnetic properties. That is, by using the granulated powder of the embodiment of the present invention, the fluidity and the moldability can be improved without lowering the 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, a strong bonding force is not required, and the amount and type of the granulating agent may be selected so as not to deteriorate the magnetic properties.
[0044]
On the other hand, as shown in FIG. 1B, the granulated powder 12b in which the primary particles 10b of the raw material powder are bound by the granulating agent 14 does not sufficiently collapse in the orientation magnetic field, and as a result, is obtained. The magnetic properties of the sintered magnet decrease. For example, the residual magnetization is reduced by about 1% to 10% as compared with the case where the raw material powder is used without being granulated. In addition, since the primary particles 10b in the granulated powder 12b of FIG. 1B do not have residual magnetization, arrows are not described.
[0045]
Further, as shown in FIG. 1 (c), when the primary particles 10c are bonded and fixed by the granulating agent 14 while the primary particles 10c are oriented in a static magnetic field, the magnetic characteristics can be improved. However, since the granulated powder 12c does not completely collapse to the primary particles 10c, the residual magnetization is, for example, about 1% to several% as compared with the case where the raw material powder is not used for granulation. 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, if it is not demagnetized (demagnetized), bridging occurs, 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 it does not require demagnetization and can be easily and uniformly filled in the cavity. Therefore, it is possible to employ a so-called metering and filling method in which granulated powder having a predetermined mass is measured in advance and then charged 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 fillability into a cavity and has substantially no decrease in magnetic properties.
[0047]
The granulated powder according to the embodiment of the present invention is obtained by a granulation method including a process of giving kinetic energy to particles of a raw material powder having remanent magnetization and growing the particles by a rolling operation using the applied kinetic energy. Further, a granulating agent may be added as necessary.
[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 filling the raw material powder into a tank (granulation tank) of the granulating apparatus, It may be performed after loading inside. However, since the primary particles 10a of the granulated powder 12a according to the present embodiment are bonded by magnetic cohesion due to residual magnetization, the granulated powder 12a collapses when a magnetic field is applied from the outside. Therefore, the particle growth process is performed under a substantially zero magnetic field. This is because in the manufacturing method of 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 having to keep doing. The term “substantially zero magnetic field” as used herein refers to the degree to which the granulated powder having a magnetically closed circuit formed by the residual magnetization of the powder is obtained in the process of growing the particles by the rolling operation and the powder. 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 of the primary particles may be slight, it is preferable to use an alternating damping magnetic field. The magnetic field for imparting the residual magnetization is not limited to the alternating attenuation magnetic field, but may be a monotonic attenuation magnetic field, another pulse magnetic field, or a static magnetic field.
[0050]
If the coercive force of the raw material powder is small even if the residual magnetization is applied, the raw material powder may be demagnetized before the final granulated powder is obtained, and the shape of the granulated powder may not be maintained. Therefore, it is preferable that the raw material powder has a relatively high coercive force. Specifically, the bulk density of the raw material powder is 2.0 g / cm. ³ When the value of the coercive force measured by a BH tracer is defined as 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-based 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]
From the viewpoint of fluidity and moldability, it is preferable to use only the granulated powder produced as described above as the R-Fe-B-based alloy powder to be subjected to press molding. Raw material powders (primary particle powders) can be mixed and used. However, when the proportion of the raw material powder increases, the fluidity decreases. Therefore, in order to sufficiently obtain the effect of improving the fluidity by granulation, it is preferable to use substantially only the granulated powder. When the raw material powder is used by being mixed with the granulated powder, it is preferable that the particle surface is coated with a lubricant. By coating the surface 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. Further, the orientation in the magnetic field pressing step is also improved. In the specification of the present application, not only a powder of substantially a rare earth alloy (which may include an oxide layer on the surface) but also a powder to be subjected to press molding containing a granulating agent and a lubricant together with the powder of the rare earth alloy. Are also referred to as rare earth alloy powders.
[0052]
A method of manufacturing a magnet using an R-Fe-B-based alloy sintered body according to an embodiment of the present invention will be described in the order of steps.
[0053]
First, R-Fe-B-based alloy flakes are prepared by a strip casting method (see, for example, U.S. Pat. No. 5,383,978). Specifically, an R-Fe-B alloy produced by a known method is melted by high frequency melting. As the R-Fe-B-based alloy, in addition to the above, for example, those having compositions described in U.S. Pat. No. 4,770,723 and U.S. Pat. No. 4,792,368 are preferable. Can be used. 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
[0054]
After keeping the melt of this alloy at 1350 ° C, the alloy was rapidly cooled on a single roll under the 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. Get the flakes. The alloy flakes are made to absorb hydrogen and embrittle them to obtain a coarse alloy powder. This alloy coarse powder is finely pulverized in a nitrogen gas atmosphere by using a jet mill, for example, to have an average particle diameter of 1.5 μm to 6 μm and a specific surface area of about 0.45 m by a BET method. ² / G to about 0.55m ² / G of alloy powder (raw material powder). The true density of this raw material powder is 7.5 g / cm ³ It is.
[0055]
Next, residual magnetization is given to the obtained raw material powder. Here, an alternating attenuation magnetic field having a peak magnetic field of 1.0T is applied.
[0056]
Next, the raw material powder having residual 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 spherical shape, the fluidity and the moldability are excellent. Further, the hardness of the granulated powder is also affected by the granulating agent, but as described above, inconvenience occurs if it is too hard or too soft.
[0057]
In the conventional fluidized-bed granulation method, a process (fluidization process) of flowing powder (also referred to as “rectification”) by a gas flow flowing from bottom to top in the tank, and a gas flow flowing from top to bottom. The step of compacting the powder layer (consolidation process) has been performed independently. For example, in the fluid compression device described in Japanese Patent No. 3019953 (for example, FIG. 3), a gas flow (hereinafter, referred to as “first gas flow”) for performing a flow process and a consolidation process are performed. Gas flow (hereinafter referred to as a "second gas flow") for switching the gas flow, and it was not possible to generate both gas flows in the tank.
[0058]
As a result of various experiments performed by the present inventors, the first gas flow for performing the flow process and the second gas flow for performing the consolidation process are simultaneously present in the tank, so that the granulated powder of the rare-earth alloy can be further reduced. It turned out that it can be manufactured efficiently.
[0059]
This is because the true specific gravity of the rare earth alloy is 7.5 g / cm. ³ It is considered that the granulated powder is manufactured using a relatively weak force of remanent magnetization. This is because when the binder is not used, the first gas stream and the second gas stream coexist in the vessel, and then the compaction process is not performed unless the production yield of the granulated powder is reduced. On the other hand, when a binder was used, it was based on the experimental fact that a superior difference from the conventional method was not confirmed. However, the reason why the production efficiency of granulated powder is improved by the coexistence of the first gas stream and the second gas stream is not well understood.
[0060]
A method and an apparatus for producing granulated powder according to an 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 manufacturing apparatus 100 suitably used in the granulated powder manufacturing method according to the embodiment of the present invention, and FIGS. 3 (a) and 3 (b) It is a graph which shows typically the state of the airflow in a tank (time change of flow volume) in the manufacturing method of the granulated powder by embodiment of this invention.
[0062]
The apparatus 100 for producing granulated powder shown in FIG. 2 includes a tank (fluidized tank) 10 and a first flow path connected to the tank 10 and capable of generating a first gas flow flowing from bottom to top in the tank 10. 20 (a), and a second flow path 30 (b) connected to the tank 10 and capable of generating a second gas flow flowing from top to bottom in the tank 10 and having the first flow path 20 (b). (A) and the second flow path 30 (b) are connected to the tank 10 independently of each other. Reference numerals 20 and 30 are used when mainly referring to a physical structure constituting the first flow path and the second flow path, respectively, and reference signs a and b are respectively used for the first flow path and the second flow path. Used when mainly indicating the path of gas flow in a road.
[0063]
The tank 10 has a structure for receiving a container 42 filled with rare earth alloy powder at the bottom thereof. The bottom plate (base plate) 42b of the container 42 has air permeability, and may 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 gas-permeable base plate.
[0064]
The rare earth alloy powder placed on the bottom plate 42b of the container 42 is given kinetic energy by the first gas flow flowing from bottom to top with respect to the bottom plate 42b, and is fluidized. At this time, the granulation process is performed under a substantially zero magnetic field using the cohesive force due to the residual magnetization of the rare earth alloy powder and the rolling operation due to 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 flow.
[0065]
The first flow path 20 has a temperature control device 22, a blower (for example, a blower for blowing) 24, and a pipe 26, and is connected (coupled) 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 (a rare gas or a nitrogen gas), and here, a 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 is too high, the coercive force is reduced, and the cohesive force of the powder is reduced. As a result, it is difficult to form granulated powder, and / or the oxidation of the rare earth alloy powder is suppressed. For this reason, it is preferable to control the temperature of the gas within the range of 10 ° C. or more and 40 ° C. or less, and it is more preferable to control the gas temperature within the 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 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 adjusted 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, is connected (coupled) to the tank 10 by valves 37 and 38, and forms a second flow path b for circulating gas in the tank 10. (See arrows B1 and B2 in FIG. 2). The buffer tank 32 is connected to a main pipe (for example, a nitrogen gas pipe for a factory) 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 And several kg / cm by the regulator 33 ² Has been lowered. The flow rate of the second gas flow generated in the tank 10 is adjusted by adjusting the degree of opening 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. Therefore, the state (temperature and humidity) of the nitrogen gas in the tank 10 can be efficiently controlled, and the consumption of the nitrogen gas can be reduced. However, in the case of a completely closed system, it is difficult to control the gas flow. Therefore, a configuration in which the exhaust pipe 44 is connected to the tank 10 through 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]
In addition, rare earth alloy powders are easily oxidized, and there is even a risk of explosion if the temperature rises abnormally. Therefore, it is possible to provide a thermometer 18 for detecting the temperature in the tank 10 and to provide a control circuit for stopping at least the operation of the blower 24 when the temperature in the tank 10 exceeds a predetermined temperature. 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 the temperature exceeds a predetermined temperature. From various experiences, when using an R-Fe-B-based alloy, if the temperature exceeds 50 ° C, the possibility of rapid oxidation (which may be accompanied by ignition or explosion) increases, so that the above-mentioned stopping operation is started. Preferably, the temperature is set at 50 ° C.
[0071]
The inside diameter of the tank 10 is different between the bottom part for receiving the container 42 and the vicinity thereof, and the body part located at the upper part thereof. As shown in FIG. 2, the inside diameter D1 at the bottom of the tank 10 is smaller than the inside diameter D2 of the body, and becomes larger as approaching the body. When the tank 10 having such a structure is used, the flow velocity of the first flow generated in the tank 10 by the first flow path 20 decreases as going upward, so that the first flow is suspended by the first flow. Powder can be efficiently dropped. The length (height) of the bottom having an inner diameter smaller than the inner diameter D2 of the body 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 (the part where the bottom plate 42b is located) Is, for example, about 50% of D2.
[0072]
The granulated powder manufacturing apparatus 100 further includes a magnetic field generating unit 40 that can apply a magnetic field to the rare earth alloy powder filled in the container 42. The magnetic field generating means 40 is, for example, an electromagnet having a coil and a yoke, and preferably generates an alternating attenuated magnetic field. Of course, when a rare earth alloy powder having a residual magnetization is used outside the tank 10, the magnetic field generating means 40 can be omitted.
[0073]
Next, the state of air flow in the tank 10 in the method for producing granulated powder according to the embodiment of the present invention will be described with reference to FIGS. 3 (a) and 3 (b). 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 the airflow 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 ₀ And the flow rate b of the second stream ₀ Are both zero. The operation of the temperature control device 22 and the blowing device 24 is started, the valves 27 and 28 are opened, and the first flow a is generated in the tank 10. The flow rate of the first stream a gradually rises, and the flow rate a ₁ To reach. In this state, the powder is granulated by cohesive force due to residual magnetization while undergoing a rolling operation in the tank 10. During this time, the powder (including particles in the process of granulation) existing near the center of the tank 10 is suspended by the first air stream a against the gravity, and the powder near the inner wall of the weak tank 10 having a low flow velocity is reduced by its own weight. Fall.
[0076]
While maintaining the flow rate of the first flow a 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 flow b (flow rate b1 at the start point). . The flow rate of the second flow b is gradually increased, and the steady flow rate b ₂ Before reaching the flow rate, the flow rate of the first flow a is reduced (the flow rate at the reduction start point is set to 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 reduced (a period in FIG. 3A). ₂ ~ B ₂ ). As described above, the presence of the period in which the first stream a and the second stream b are simultaneously present in the tank 10 makes it possible to more efficiently produce the rare earth alloy granulated powder. The reason for this is not necessarily clear, but if the first flow a is suddenly stopped, or if the flow rate of the second flow b becomes too large relative to the flow rate of the first flow a, the granulated powder will rapidly It is considered that the granulated powder is destroyed by the impact. Further, if the generation of the second flow b is started after the first flow a is completely stopped, the inside of the tank 10 becomes a negative pressure, and it becomes difficult to control the pressure, which is not preferable.
[0077]
As described above, when the flow rate of the second stream b is increased while gradually decreasing the flow rate of the first stream a, the granulated powder is not broken by an impact when dropped on the bottom plate 42b. , A powder layer is formed, and then compressed by the second air stream b to consolidate the powder layer. This compaction process increases the hardness of the granulated powder.
[0078]
By repeating the cycle shown in FIG. 3A, granulated powder having an appropriate hardness can be obtained. However, the flow rate of the first flow a at the start of the second and subsequent cycles is zero (a) as shown in FIG. ₀ ), And the flow rate a at the end of the cycle shown in FIG. ₃ It may be.
[0079]
By merely repeating the cycle shown in FIG. 3A, the powder layer compressed on the bottom plate 42b may not 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. 3 (b) ₁ 'The following steps will be described. Here, the point b in FIG. ₁ Up to the point b in FIG. ₁ Steps up to and including the step shown in FIG. 3B will be described.
[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 stream b is a steady state flow rate b ₂ Before the flow rate reaches the first flow rate a (the flow rate a at the start of the decrease). ₂ '). Thereafter, the valves 27 and 28 are closed to maintain the state in which the first flow a is stopped (point a in FIG. 3A). ₃ '~ Point a ₄ ': Α minutes). If the blower 24 is continuously operated during this time, the gas pressure in the pipe 26 from the blower 24 to the valve 27 increases. Conversely, the valve 27 is kept closed until a predetermined pressure for crushing the powder layer is obtained. Thereafter, the valves 37 and 38 are closed to stop the second flow b (point b in FIG. 3B). ₀ ′) And open the valves 27 and 28 to generate the first flow a (point a in FIG. 3B). ₀ '). At this time, the flow rate a of the first flow a generated in the tank 10 ₀ 'Is the flow rate a of the steady first gas flow a in FIG. ₁ (= A ₂ ), And the powder layer can be efficiently disintegrated. Typically, the flow rate of the first flow a for obtaining the rolling operation is substantially constant (a) as shown in FIG. ₁ = A ₂ ), But may fluctuate. In this case, it is preferable that the flow rate of the first flow a for crushing the powder layer is larger than the average flow rate of the first flow a for obtaining the rolling operation.
[0082]
In the above example, by operating the valves 37 and 38, the diversion a ₀ Although the first flow a was generated, 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 a valve operation. The flow rate a in FIG. ₁ 'And flow rate a ₂ 'Indicates the flow rate a in FIG. ₁ And flow rate a ₂ May be the same as
[0083]
When the granulated powder formed by using the remanent magnetization becomes a certain moderately large size, it forms a magnetically closed circuit, so that the magnetic attraction acting between the granulated powders is weakened. The necessity of the crushing cycle described in (1) is eliminated. Therefore, for example, in a process in which a predetermined granulated powder is obtained by repeating a basic cycle shown in FIG. 3A and a crushing cycle shown in FIG. Preferably, the first 20 cycles include 5 to 10 crushing cycles.
[0084]
In addition, when the raw material powder having the residual magnetization is used, a desired granulated powder can be obtained in a shorter time (for example, about half time) than when the raw material powder having no residual magnetization is used. This is presumed to be because, when the raw material powder having residual magnetization is used, nuclei for generating granulated powder are easily generated by magnetic cohesion between the primary particles.
[0085]
The average particle size of the granulated powder is preferably in the range of 0.05 mm to 3.0 mm. Generally, the amount of primary particles contained in the granulated powder is very small, and the amount of high-order granulated powder of tertiary particles or more is very small. It can be treated as a representative of the particle size. Here, the average particle size of the secondary particles obtained by microscopic observation is used as the average particle size of the granulated powder. If the average particle size 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 compact with sufficient density. On the other hand, if the average particle size of the granulated powder is larger than 3 mm, the filling property into the cavity is reduced, and it is difficult to obtain a uniform compact with sufficient density. The average particle size of the granulated powder is more preferably in the range of 0.1 mm to 2.0 mm.
[0086]
Next, a compact is formed by press-molding the obtained granulated powder. Here, a compact is formed using only granulated powder. A known press molding apparatus can be used for press molding. Typically, a uniaxial press molding apparatus that presses powder in a cavity (die hole) of a mold with upper and lower punches is used. The transfer of the granulated powder is performed for each batch, for example, in a state in which a highly airtight container is filled with or flushed with nitrogen gas.
[0087]
The granulated powder is filled in the cavity of the mold of the uniaxial press molding machine. The step of filling the granulated powder into the cavity may be performed, for example, by a filling method using a sieve, Japanese Patent Publication No. 59-40560, Japanese Patent Application Laid-Open No. 10-58198, Japanese Utility Model Application Laid-Open No. 63-110521, and It can be performed using a filling method using a feeder box as disclosed in Japanese Patent Publication No. 248301 (these may be collectively referred to as a “dropping method”).
[0088]
In particular, when forming a small compact, 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 onto a cavity, and the granulated powder is dropped by gravity (natural fall), and then the excess granulated powder supplied to the cavity is scrubbed to be relatively uniform. Can be filled with a predetermined amount of granulated powder. Of course, separately measured granulated powder may be filled into the cavity using a funnel or the like.
[0089]
After filling the granulated powder into the cavity, the upper punch is lowered by a uniaxial pressing device, and an orientation magnetic field is applied while closing the opening of the cavity to disintegrate the granulated powder into primary particles. The secondary particles are magnetically oriented. The granulated powder according to the embodiment of the present invention reliably disintegrates into primary particles with a relatively weak magnetic field of 0.1T to 0.8T. However, in consideration of 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. The powder is uniaxially pressed with the upper and lower punches at a pressure of, for example, 98 MPa while applying a magnetic field in this manner. As a result, a compact having a relative density (compact density / true density) of 0.5 to 0.7 is obtained. The direction of the magnetic field may be parallel to the pressing direction if 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 to 6 hours. Since the granulated powder of the present embodiment does not contain a granulating agent or contains only a granulating agent that can be substantially removed in the sintering step, it is not necessary to separately provide a binder removing step. The conventional typical binder removal process 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]
The obtained sintered body is aged at a temperature of, for example, about 450 ° C. to about 800 ° C. for about 1 to 8 hours to obtain an R—Fe—B based sintered magnet. Thereafter, the R-Fe-B based 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, the variation in the filling amount is small and the cavity is uniformly filled. Therefore, there is little variation in the mass and dimensions of the compact obtained by press molding. Further, chipping or cracking of the molded body is less likely to occur.
[0093]
Furthermore, since the primary particles of the granulated powder of the present embodiment are substantially bound by the magnetic cohesion of the remanent magnetization, the primary particles are surely disintegrated by application of the orientation magnetic field. Therefore, the degree of orientation of the primary particles does not decrease. In addition, since a decrease in magnetic properties due to the carbon of the granulating agent remaining in the sintered body is suppressed to a minimum, a sintered magnet having excellent magnetic properties can be obtained. As described above, according to the present invention, a high quality R—Fe—B based alloy sintered magnet can be manufactured with high production efficiency.
[0094]
【Example】
Hereinafter, examples of the present invention will be described.
[0095]
An R-Fe-B-based alloy powder was produced as follows. A molten alloy was prepared using, as starting materials, electrolytic iron having a purity of 99.9%, a ferroboron alloy containing 19.8% of B, and Nd and Dy having a purity of 99.7% or more. 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 from the molten alloy by a strip casting method. . Using a jet mill, this is inert gas (for example, N2). ₂ The mixture was finely pulverized in a gas at a gas pressure of 58.8 MPa) to obtain a raw material powder having an average particle size of about 3 μm.
[0096]
Next, an alternating attenuating magnetic field (1.0 T peak magnetic field) was applied to the raw material powder for the example to impart residual magnetization.
[0097]
Next, granulated powder was manufactured using the manufacturing apparatus 100 described above.
[0098]
The inside diameter (D2) of the tank 10 is 300 mm, and the internal volume is about 7 × 10 ⁴ cm ³ , Flow rate a in FIGS. 3 (a) and (b) ₁ = A ₂ = A ₁ '= A ₂ 'Is about 1m ³ / Min, flow rate a ₀ 'Is about 2.0m ³ / Min, flow rate b ₂ = B ₃ = B ₂ '= B ₃ 'Is about 0.75m ³ / 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 present applicant were used as granulating agents.
[0100]
In each of the examples and the comparative examples, conditions were set such that the average particle size of the granulated powder was 0.5 mm. The residual magnetization of the obtained granulated powder was about 0.2 mT. The granulation steps of Examples 1 to 3 took about 15 minutes, and the granulation steps of Comparative Examples 2 and 3 required about 30 minutes. In Comparative Example 1, the raw material powder (without applying a magnetic field) was used without granulation. Table 1 summarizes the preparation conditions of the powder for pressing in each of Examples 1 to 3 and Comparative Examples 1 to 3.
[0101]
[Table 1]

[0102]
Table 1 also shows the angle of repose of each pressing powder. A powder having a large angle of repose has poor fluidity, and a powder having a small angle of repose has excellent 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. In contrast, the angle of repose of each of the pressed powders of Examples 1 to 3 and Comparative Examples 2 and 3 in which the granulation was performed is reduced to less than 50 °. In particular, the pressed powders of Examples 1 and 2 have a smaller angle of repose than the pressed powder of Comparative Example 2 (addition amount of the granulating agent: 1% by mass), and are excellent in fluidity. In other words, it can be seen that by using the residual magnetization, the flowability is improved by adding a smaller amount of a granulating agent than in the past. In addition, in Example 3 and Comparative Example 3 in which the addition amount of the granulating agent was 2% by mass, no difference was observed in the fluidity.
[0103]
Each pressing 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 a method using the above-described feeder box, and was subjected to uniaxial press molding (98 MPa, orientation magnetic field (0.8 T). ) Was applied at right angles to the pressing direction). The filling step and the press molding step were performed under the same conditions for all Examples and Comparative Examples. In addition, molded articles having different molded article densities (green densities) were formed by changing the pressing conditions.
[0104]
The press molded bodies of Example 1 and Comparative Example 1 were evaluated for variation in mass (%) and variation in filling amount (σ). The mass variation of the molded body was determined by {(maximum mass−minimum mass) / average mass (n = 50)} × 100 (%). In addition, the filling amount variation (σ) indicates the standard deviation of the mass distribution of 50 compacts. The mass variation of the molded product of Example 1 was about 4%, which is significantly improved as compared with the mass variation of Comparative Example 1 of about 15%. The same applies to the variation in the filling amount (σ). The variation in the filling amount (σ) in Comparative Example 1 is about 0.33, while the variation in the filling amount (σ) in Example 1 is 0.16. It is greatly improved, indicating that the fluidity was improved by granulation. Of course, the formability was also improved by the granulation, and the ratio of occurrence of chipping or cracking in the molded product was significantly smaller than that of Comparative Example 1. The effects of these granulations were also confirmed for other examples.
[0105]
After sintering the obtained molded body at 1060 ° C. for about 4 hours in an Ar atmosphere, aging treatment was performed at 600 ° C. for 1 hour to obtain a sintered body. Further, the sintered body was magnetized under the condition of 2387 kA / m to obtain a sintered magnet. The number of samples was 50 for each of the examples and comparative examples.
[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 circles in FIG. 4) has no substantial difference from the Br of Comparative Example 1 (white circles 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 the same as the Br of Comparative Example 2 and Comparative Example 3 using the same amount of the granulating agent and the raw material powder having no residual magnetization. Met. Even in the case of granulation utilizing residual magnetization, it is preferable that the amount of granulating agent is as small as possible.
[0107]
As described above, by making the granulated powder using the magnetic cohesion caused by the residual magnetization of the primary particles, compared to the case of using the granulated powder using only the binding force of the granulating agent, Even if the added amount of the granulating agent is reduced, the same or more fluidity can be obtained, so that it is possible to produce a sintered magnet having superior magnetic properties with the same or higher productivity as before. Furthermore, if the granulated powder is produced using only the residual magnetization of the primary particles, it is possible to substantially eliminate the deterioration of the magnetic properties.
[0108]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the granulated powder of a rare earth alloy which is excellent in fluidity and press moldability, and can manufacture the magnet which has excellent magnetic characteristics 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, it is possible to improve the fluidity and moldability of the rare-earth alloy powder without lowering the magnetic properties, so that a sintered magnet having a shape that is difficult to press-form, which has conventionally sacrificed magnetic properties, can be obtained. Magnetic properties 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]
FIG. 1A is a diagram schematically showing a structure of a granulated powder according to an embodiment of the present invention, and FIGS. 1B and 1C are diagrams schematically showing a structure of a conventional granulated powder for comparison. FIG.
FIG. 2 is a view 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. 3 (a) and (b) are graphs schematically showing the state of air flow in a tank (time change of flow rate) in a method for producing granulated powder according to an embodiment of the present invention.
FIG. 4 is a graph showing 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 tanks)
20 First flow path
22 Temperature control device
24 Blower
26, 36 piping
27, 28 valve
30 Second flow path
37, 38 valve
40 Magnetic field generator
42 containers
42b bottom plate
44 Exhaust pipe
46 valve

Claims (16)

(A) a step of preparing a rare earth alloy powder having remanent magnetization in a tank while being placed on a gas-permeable base plate;
(B) generating a first gas flow flowing from below to above the bed plate in the tank;
(C) imparting kinetic energy to the particles of the powder by the first gas flow, and forming the particles under substantially zero magnetic field by utilizing the cohesive force due to the residual magnetization of the powder and the rolling operation due to the kinetic energy. A step of granulating,
(D) generating a second gas flow in the vessel from top to 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 with the second stream;
, And
A method for producing 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 the steps (d) and (b) are simultaneously performed includes a period in which the flow rate of the second gas stream is increased while the flow rate of the first gas stream is decreased. Powder manufacturing method. In the step (a), a rare earth alloy powder having no remanent magnetization is arranged in the tank, and a remanent magnetization is applied by applying a magnetic field to the powder having no remanent magnet arranged in the tank. The method for producing a granulated powder according to claim 1 or 2, further comprising the step of: 3. The rare earth alloy according to claim 1, wherein the step (a) includes a step of preparing a rare earth alloy powder having a remanent magnetization in advance and a step of disposing the powder having the remanent magnetization in the tank. 4. Production method of granulated powder. The method for producing a granulated powder according to any one of claims 1 to 4, wherein step (b), step (c), step (d), and step (e) are repeated a plurality of times in this order. During said iteration, after at least one step (e),
(F) temporarily stopping the first gas flow while the second gas flow is being generated, and then averaging the first gas flow in step (c) while the second gas flow is stopped. Crushing the powder layer formed on the base plate by generating the first gas flow at a flow rate exceeding the flow rate;
The method for producing a granulated powder according to claim 5, comprising: The method for producing a rare earth alloy granulated powder according to any one of claims 1 to 6, wherein the rare earth alloy is an R-Fe-B-based alloy. The method for producing a rare earth alloy granulated powder according to any one of claims 1 to 7, wherein the average particle diameter of the powder is in a range of 1.5 µm to 6 µm. The method for producing a rare earth alloy granulated powder according to any one of claims 1 to 8, wherein a granulated powder having an average particle size in a range of 0.05 mm or more and 3.0 mm or less is produced. A step of producing granulated powder by using the method of producing a rare earth alloy granulated powder according to any one of claims 1 to 9,
Filling the cavity with rare earth alloy powder containing the granulated powder without applying a demagnetizing magnetic field to the granulated powder,
A step of forming a compact by press-molding the rare earth alloy powder including the granulated powder while applying an orientation magnetic field,
Sintering the compact,
A method for producing a rare earth alloy sintered body, comprising: 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 flowing from below to above the base plate in the tank;
A second flow path connected to the tank and capable of generating a second gas flow flowing from top to bottom of the base plate in the tank;
Has,
The manufacturing apparatus of the rare earth alloy granulated powder, wherein the first flow path and the second flow path are independently connected to the tank. The manufacturing apparatus according to claim 10, further comprising a temperature control device and a blowing device in the first flow path. The manufacturing apparatus according to claim 11, further comprising a buffer tank in the second flow path. The thermometer according to any one of claims 11 to 13, further comprising: a thermometer configured to detect a temperature of the gas in the tank, and a control circuit configured to stop at least an operation of the blower when the detected temperature exceeds a predetermined temperature. Manufacturing apparatus according to the above. The manufacturing apparatus according to any one of claims 11 to 14, 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 a magnetic field generating means capable of applying a magnetic field to the powder placed on the base plate.

Images