JP3556786B2 - Method and apparatus for producing anisotropic granulated powder - Google Patents
Method and apparatus for producing anisotropic granulated powder Download PDFInfo
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- JP3556786B2 JP3556786B2 JP31128596A JP31128596A JP3556786B2 JP 3556786 B2 JP3556786 B2 JP 3556786B2 JP 31128596 A JP31128596 A JP 31128596A JP 31128596 A JP31128596 A JP 31128596A JP 3556786 B2 JP3556786 B2 JP 3556786B2
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01F—MAGNETS; INDUCTANCES; TRANSFORMERS; SELECTION OF MATERIALS FOR THEIR MAGNETIC PROPERTIES
- H01F1/00—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties
- H01F1/01—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials
- H01F1/03—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity
- H01F1/032—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials
- H01F1/04—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys
- H01F1/06—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys in the form of particles, e.g. powder
- H01F1/061—Magnets or magnetic bodies characterised by the magnetic materials therefor; Selection of materials for their magnetic properties of inorganic materials characterised by their coercivity of hard-magnetic materials metals or alloys in the form of particles, e.g. powder with a protective layer
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- Engineering & Computer Science (AREA)
- Power Engineering (AREA)
- Glanulating (AREA)
- Powder Metallurgy (AREA)
- Hard Magnetic Materials (AREA)
Description
【０００１】
【発明の属する技術分野】
この発明は、Ｒ−Ｃｏ系磁石やＲ−Ｆｅ−Ｂ系磁石等の希土類焼結磁石の成形に用いる異方性造粒粉の製造方法に係り、該希土類焼結磁石の原料である希土類含有合金粉末を流動造粒法により造粒粉となす際に、希土類含有合金粉末を磁界配向された状態で固化させて異方性の造粒粉となすことにより、圧縮成形時の粉体の流動性を向上させて成形体の寸法精度の向上及び成形サイクルの短縮化を図り、かつ磁気特性の優れた希土類焼結磁石を製造できる異方性造粒粉の製造方法と製造装置に関する。
【０００２】
【従来の技術】
家電製品、コンピュータの周辺機器及び自動車等には多くのモーターやアクチュエーター等が用いられている。今日、これらの製品には、携帯性を高めるためあるいは省エネルギーを推進するため小型化、軽量化の要求が高まっている。それに伴い、モーターやアクチュエーター等に組み込まれる永久磁石材料には、より高性能でかつ小型形状、あるいは薄肉形状に対応できるものが求められている。
【０００３】
近年、上述の要求に答える材料として、焼結磁石に比べて形状の自由度が高いボンド磁石の生産量が増加している。しかし、ボンド磁石は樹脂を含有するため、ボンド磁石中に含まれる磁石粉末の占有率は焼結磁石の場合に比べてはるかに低く、そのため、ボンド磁石の最大エネルギー積は、同じ材料の焼結磁石の半分程度しか得られていないのが現状である。従って、小型形状や薄肉形状の磁石を、磁気特性の優れた焼結磁石で製造する技術が求められている。
【０００４】
現代の代表的な焼結磁石としては、Ｂａフェライト磁石、Ｓｒフェライト磁石、Ｒ−Ｃｏ系磁石、そして出願人が先に提案したＲ−Ｆｅ−Ｂ系磁石（特公昭６１−３４２４２号等）が挙げられる。Ｂａフェライト磁石やＳｒフェライト磁石等のフェライト磁石は、希土類磁石に比べ磁気特性は劣るものの、安価で軽量であることからモーターやアクチュエーター等に多用されている。また、Ｒ−Ｃｏ系磁石やＲ−Ｆｅ−Ｂ系磁石等の希土類磁石は、他の磁石材料に比べて磁気特性が格段に優れているため、各種用途に利用されている。
【０００５】
上記の希土類磁石において高い磁気特性を発現させるためには、所要組成からなる希土類含有合金粉末を微粉砕し、磁界中で成形後、焼結することが必要となる。磁界中成形前の希土類含有合金粉末の望ましい平均粒径は１〜１０μｍ程度であるが、希土類含有合金粉末をこのように微細に粉砕する理由は、粒径の大きな原料粉末を用いると焼結後の結晶粒径が粗大化し、実用的な保磁力が得られなくなるためである。
【０００６】
一方、希土類含有合金粉末の平均粒径を小さくすると粉末の流動性が低下するため、圧縮成形工程におけるダイス内への原料粉末の供給量のバラツキが大きくなり、成形体及び焼結体の寸法バラツキをもたらす。そこで、通常、ダイス内に原料粉末を一定量だけ自動的に供給するには、一定容積のキャビティー内に粉末を自然落下させる方法を用いている。
【０００７】
しかし、原料粉末の流動性が低い場合、粉体がキャビティー内で架橋現象を起こし易くなる。架橋現象とは、粉体が隔壁間に強固なアーチ構造を形成する現象であり、一旦架橋が形成されると、それより下の空間へは粉体が移動できなくなるため、架橋の上下で密度差が生じる。また、架橋現象はランダムに起こるため、圧縮成形の各サイクルで架橋の有無が生じ、原料粉末の供給量を一定に制御することが困難となる。
【０００８】
上述した架橋現象は、キャビティーの深さが深いほど、あるいはキャビティーの開口部の面積が小さいほど起こり易く、特にキャビティーの開口部が極めて小さい場合は、自然落下によってキャビティー内へ原料粉末を供給することは不可能となる。従って、寸法精度がよい小型形状の製品を工業的に製造するには、原料粉の流動性の改善が不可欠である。
【０００９】
従来から、粉体の流動性を改善する方法として造粒が行なわれている。しかし、通常の造粒法で得られる造粒粉は１次粒子の結晶方位がバラバラな等方性の造粒粉であるため、磁界中での配向性が悪く、成形時の配向磁界が低いと残留磁化や最大エネルギー積が低くなるという問題があった。
【００１０】
【発明が解決しようとする課題】
そこで、出願人は先に、Ｒ−Ｃｏ系合金やＲ−Ｆｅ−Ｂ系合金等の希土類含有合金からなる原料粉の流動性を改善し、なおかつ低い配向磁界でも高い磁気特性が得られる異方性造粒粉の製造方法を提案した（特開平８−２０８０１号）。この提案は、磁性粉末と溶媒とを混練してスラリー状となし、噴霧乾燥法により造粒粉となす際に、アトマイザー（微粒化装置）にスラリーを供給する配管に磁界を印加してスラリー中に含まれる磁性粉末を磁界配向したり、あるいは永久磁石を用いた磁気回路で構成される回転ディスク型アトマイザーにより噴霧される直前のスラリーに磁界を印加して磁性粉末を磁界配向することにより、１次粒子の結晶方位のよく揃った異方性造粒粉を得るものである。
【００１１】
さらに、出願人らは先に、より配向度の優れた異方性造粒粉を得る方法として、希土類含有合金粉末と溶媒とを混練してスラリー状となし、噴霧乾燥法により造粒粉となす際に、回転ディスク型やノズル型アトマイザーから噴出された液滴状のスラリーが通過する位置に磁界を発生させ、該液滴に磁界を印加して粉末を磁気配向させながら、同時に乾燥固化させる異方性造粒粉の製造方法とその装置を提案した（特願平８−１２６５２６号）。
【００１２】
これらの方法によって得られる異方性造粒粉は、等方性のものと異なり個々の２次粒子を構成する１次粒子の結晶方位が揃っていることが特徴で、このため、磁界中での配向性が向上し、高い残留磁化と最大エネルギー積を有する焼結磁石を得ることが可能となる。
【００１３】
しかし、上記の異方性造粒粉の製造方法には、以下のような問題点がある。すなわち、前者の提案においては、印加する磁界の強度をあまり強くするとスラリーを供給する配管やアトマイザー中にスラリーが閉塞し易くなる。また、後者の提案においては、永久磁石や電磁石で発生される磁界の強度を強くすると磁界強度に勾配が生じ易くなるため、スラリーが永久磁石や電磁石に補足されたり、あるいは磁極間にブリッジを形成してスラリーの飛行を妨げたりする。
【００１４】
このように、噴霧乾燥法による異方性造粒粉の製造方法においては、造粒粉の配向度を向上させるために配向磁界を高くすると、歩留まりや生産性が低下したり、場合によっては造粒が困難になるという問題があった。
【００１５】
この発明は、圧縮成形時の粉体の流動性が高く、成形体の寸法精度の向上および成形サイクルの短縮化が図られ、かつ造粒時に印加する磁界強度を高くすることができ、造粒粉に含まれる１次粒子の配向度が高いために、造粒粉を低配向磁界で成形しても磁気特性の優れた成形体および焼結体を製造できる希土類含有磁石用異方性造粒粉を、歩留まり良く製造できる方法および製造装置の提供を目的とする。
【００１６】
【課題を解決するための手段】
発明者らは、異方性造粒粉の新規な製造方法について種々検討した結果、粉体に流動層を形成させ、転動造粒作用を利用する流動造粒法において、希土類含有合金粉末に磁界を印加して配向するとともに、ガス流と攪拌羽根の回転によって流動層を形成させ、該粉末を流動層の転動造粒作用により造粒することにより、１次粒子の結晶方位の揃った異方性造粒粉を歩留まり良く製造でき、得られた異方性造粒粉が磁化中の配向性に極めて優れることを知見した。
【００１７】
また、発明者らは、希土類含有合金粉末を磁界中で配向しながら流動造粒する際に、印加磁界の強度を変化させることにより、１次粒子の配向度がさらに向上すると共に粒度分布がシャープで流動性に優れた異方性造粒粉が得られることを知見し、この発明を完成した。
【００１８】
すなわち、この発明は、
攪拌羽根とガス給気口及びガス排気口を有する流動槽と、該流動槽の周囲に配設されかつ槽内に磁界を印加するための磁気回路とからなる装置内に希土類含有合金粉末を装填し、該粉末に磁気回路による磁界を印加しながら、ガス給気口からのガス流と攪拌羽根の回転によって流動槽内に流動層を形成させた後、該流動層中にバインダー溶液を添加、混合し、該粉末を流動層の転動造粒作用により造粒することを特徴とする異方性造粒粉の製造方法である。
【００１９】
また、この発明は、
攪拌羽根、ガス給気口及びガス排気口を有する流動槽と、該流動槽の周囲に配設されかつ槽内に磁界を印加するための磁気回路とからなる装置内にバインダー溶液を添加、混合した希土類含有合金粉末を装填し、該粉末に磁界を印加しながら、ガス給気口からのガス流と攪拌羽根の回転によって流動槽内に流動層を形成させ、該粉末を流動層の転動造粒作用により造粒することを特徴とする異方性造粒粉の製造方法である。
【００２０】
さらに、この発明は、上記の製造方法において、
フェライト磁石原料粉末に予め疎水処理を施すこと、磁界強度を変化させながら印加することを合わせて提案する。
【００２１】
また、この発明は、
攪拌羽根、ガス給気口及びガス排気口を有する流動槽と、該流動槽の周囲に配設されかつ槽内に磁界を印加するための磁気回路とを有し、該磁気回路による流動槽内への磁界印加時に、該ガス給気口からのガス流と該攪拌羽根の回転とによる流動層の転動造粒作用を発生可能となして希土類含有合金粉末を異方性造粒粉となすことを特徴とする異方性造粒粉の製造装置である。
【００２２】
さらにこの発明は、上記の製造装置において、磁気回路の可変機構を備える異方性造粒粉の製造装置を合わせて提案する。
【００２３】
【発明の実施の形態】
この発明における異方性造粒粉の製造方法について以下に詳述する。
この発明において、対象とする希土類含有合金粉末は、結晶磁気異方性を有するものであればどのような粉末でも適用可能であるが、中でもＲ−Ｆｅ−Ｂ系合金粉末やＲ−Ｃｏ系合金粉末等が最も適している。希土類含有合金粉末としては、単一の所要組成からなる合金を粉砕した粉末や、異なる組成の合金を粉砕した後、混合して所要組成に調整した粉末、保磁力の向上や生産性を改善するために添加元素を加えたもの等、公知の希土類含有合金粉末を用いることができる。
【００２４】
希土類含有合金粉末の製造方法には、鋳造粉砕法、超急冷法、直接還元拡散法、水素含有崩壊法、アトマイズ法などの公知の方法を適宜選択することができる。また合金粉末の粒径も特に限定しないが、合金粉末の平均粒径が１μｍ未満では大気中の酸素あるいは溶媒と反応して酸化し易くなり、焼結後の磁気特性を低下させるため好ましくなく、また１０μｍを超える平均粒径では粒径が大き過ぎて焼結密度が低下するため好ましくない。よって、１〜１０μｍの平均粒径が好ましい範囲である。さらに好ましい範囲は１〜６μｍである。
【００２５】
この発明において、希土類含有合金粉末に添加するバインダー溶液を作製するために用いる溶媒としては、バインダーを容易に溶解することが可能で、かつ希土類含有合金粉末やバインダーと反応し難く、沸点が比較的低く、化学的に安定なものが好ましい。具体的には、水溶性バインダーを用いる場合には水が最も好ましく、その純度は特に限定しないが、希土類含有合金粉末の希土類成分との反応を極力制御するために、脱酸素処理した純水あるいは窒素などの不活性ガスでバブリング処理した水が好ましい。また、非水溶性バインダーを用いる場合には、エチルアルコール、イソプロピルアルコール、アセトン、メチルエチルケトン、ノルマルヘキサン、シクロヘキサン、トルエン、塩化メチレン、ジオキサン等の有機系の溶媒を用いることが好ましい。
【００２６】
この発明において、バインダー溶液の溶媒に水を用いる場合は、水溶性バインダーとして、メチルセルロース、ポリアクリルアミド、ポリビニルアルコールのうち少なくとも１種を用いることが好ましい。また、有機系の溶媒を用いる場合には、パラフィンワックス、ポリエチレングリコール（ＰＥＧ）、ポリビニルピロリドン（ＰＶＰ）、ヒドロキシプロピルセルロース（ＨＰＣ）、ヒドロキシプロピルメチルセルロース（ＨＰＭＣ）、エチルセルロース（ＥＣ）、アセチルセルロース、ニトロセルロース、酢酸ビニル樹脂などの使用する有機溶媒に溶解するバインダーの少なくとも１種を用いることができる。
【００２７】
この発明に用いるバインダー溶液の濃度は、５ｗｔ％未満では溶媒の乾燥に時間がかかり処理効率が低下し、また５０ｗｔ％を超えると希土類含有合金粉末との攪拌、混合が困難となるため、５〜５０ｗｔ％が好ましい。より好ましくは１０〜３０ｗｔ％である。
【００２８】
上記のバインダー溶液は、少量の添加で流動層の転動造粒作用を高めることができるとともに、乾燥後においても造粒粉中の粒子間に高い結合力を保持することができ、また、添加量が少量で十分なため、粉末中の残留酸素量、炭素量を低減することができる。さらに、バインダーを添加した場合、造粒粉がバインダーによって被覆されているため、大気中において酸化し難く、造粒粉の取り扱いが容易になるという利点がある。
【００２９】
バインダーを単独で用いる場合の含有量は、希土類含有合金粉末に対して０．０５ｗｔ％未満では造粒粉中の粒子間の結合力が弱く、成形前の給粉時に造粒粉が壊れて粉体の流動性が著しく低下し、また、０．５ｗｔ％を超えると焼結体の残留炭素量と酸素量が増加して保磁力が下がり磁気特性が劣化するので、０．０５〜０．５ｗｔ％の含有量がこれらの点で好ましい。また複合して用いる場合は、上記と同様な理由により、全てのバインダーの含有量の合計が０．０５〜０．４ｗｔ％の範囲であることが好ましい。
【００３０】
バインダーの添加方法には、流動造粒時にスプレー噴霧等によって添加する方法と、流動造粒前に予め希土類含有合金粉末にバインダーを添加しておく方法があり、また、両者を併用してもよい。
【００３１】
この発明において、希土類含有合金粉末を磁界配向するためには磁界を印加する必要がある。磁界の印加方法は、電磁石あるいは永久磁石のいずれによってもよい。希土類含有合金粉末に連続的に印加される磁界強度が０．５ｋＯｅ未満であると得られる異方性造粒粉の配向度が低くなり良好な磁界中配向性が得られないので好ましくなく、また、１０ｋＯｅを超えると希土類含有合金粉末が磁界中で固定され流動層の形成ができなくなるため、０．５〜１０ｋＯｅの範囲が好ましい。さらに好ましい範囲は１〜８ｋＯｅである。
【００３２】
この発明において、希土類含有合金粉末に印加する磁界強度を可変とし、高磁界と低磁界を交互に印加することも好ましい実施形態である。すなわち、流動層の形成を妨げない低い磁化強度で配向を行ないながら造粒を進行させ、非連続的に高い磁界強度を印加することにより、１次粒子の配向度が高く、かつ、粒度分布がシャープで流動性に優れた異方性造粒粉が製造できる。このように、非連続的に高磁界を印加するには、電磁石に流す電流を高くしたり、永久磁石と流動層との距離を近づけたりして容易に実施することができる。また、電磁石、永久磁石の他にソレノイドコイルを設け、パルス電流を流すことにより瞬間的にパルス磁界を印加するのも好ましい実施態様である。
【００３３】
この発明において、フェライト磁石原料粉末の流動層を形成させるために、後述する異方性造粒粉の製造装置のガス給気口から流動槽内に導入されるガスは、希土類含有合金粉末を攪拌して流動層を形成し、転動造粒作用をもたらすと共に、バインダー溶液の乾燥を行なう。希土類含有合金粉末の酸化を防止するために、窒素ガス、アルゴンガスなどの不活性ガスを用いることが好ましい。ガスの温度は、流動層の形成とバインダー溶液の添加時は０〜３０℃の範囲に抑え、添加後の乾燥時には６０〜１５０℃に短時間温度を上昇させて素早く乾燥させることが希土類含有合金粉末の酸化防止の観点から好ましい。
【００３４】
この発明において、希土類含有合金粉末にバインダー溶液を添加する前に予め有機金属化合物を混練、被覆させる疎水処理を行なうことは、希土類含有合金粉末とバインダー溶液中の溶媒との濡れ性を低下させ、希土類含有合金粉末と溶媒との反応による酸化を防止する効果を発揮し、また、乾燥工程における溶媒の離脱が容易になり乾燥時間が短縮でき、さらに、得られた造粒粉の流動性を向上させるため好ましい。
【００３５】
疎水処理用の有機金属化合物としては、ステアリン酸亜鉛のほか、ステアリン酸ニッケル、ステアリン酸カルシウム、ステアリン酸アルミニウム、ステアリン酸銅などの水に不溶の粉末を用いることができる。また、その添加量は、０．０１ｗｔ％未満では疎水処理の効果がなく、また、０．２ｗｔ％を超えると焼結磁石中に残留する金属成分の量が増加して、焼結体の機械的強度が低下し、また、非磁性相の増加により磁化が低下するので好ましくない。よって、疎水処理用の有機金属化合物の添加量は、０．０１〜０．２ｗｔ％が好ましい。なお、有機金属化合物の添加方法としては、希土類含有合金粉末の微粉砕後に添加するか、もしくは微粉砕の前に添加するなど適宜選択できる。
【００３６】
この発明において得られる異方性造粒粉の粒径は、バインダー溶液の濃度と添加量、印加磁界の強度、攪拌羽根の回転数、ガスの流量などの製造条件を調整することによって制御することができるが、造粒粉の平均粒径が２０μｍ未満では造粒紛の流動性がほとんど向上せず、また、平均粒径が４００μｍを超えると粒径が大き過ぎて成形時の金型内への充填密度が低下するとともに成形体密度も低下し、ひいては、焼結密度の低下を来たすことになるので好ましくない。よって、造粒粉の平均粒径は２０〜４００μｍが好ましい。さらに好ましい範囲は５０〜２００μｍである。
【００３７】
上述したこの発明の製造方法により得られた造粒粉は、着磁された状態となっているので、そのままでは、造粒粉同士が凝集して粉体の流動性が低下している。従って、成形前に該造粒粉の磁気を消磁する必要がある。
造粒粉の消磁には交番減衰磁界を用いるのが好ましい。交番減衰磁界とは、時間経過とともに磁界の向きが正方向と逆方向に交互に切り替わりながら、かつその最大強度が徐々に減少するような磁界である。交番減衰磁界を発生させるには、最も簡単にはコイル交番電流を流しながらその電流値を徐々に減少させるか、コイルと被消磁物との距離を徐々に長くするなどの方法を適宜用いることができる。
【００３８】
交番減衰磁界の最大強度が造粒時の磁界強度を超えると、印加磁界により異方性造粒粉が崩壊しやすくなるため、最大強度は造粒時の磁界を超えないことが好ましい。例えば、流動造粒装置中で希土類含有合金粉末を強度１．５ｋＯｅの一定な磁界で配向しながら造粒した場合には、消磁処理は最大強度が１．５ｋＯｅを超えない交番減衰磁界中で行なうのが、消磁磁界による造粒粉の崩壊を防止するために好ましい。
【００３９】
消磁処理に用いる交番減衰磁界の周波数は１Ｈｚ未満であると造粒粉の２次粒子の回転が起こり消磁ができず、また、１ｋＨｚを超えると１次粒子中の磁壁移動が不完全となり消磁ができないため、周波数は１Ｈｚ〜１ｋＨｚの範囲が好ましい。
また、交番減衰磁界の減衰速度について特に規定しないが、有効な消磁のためには最大磁界強度が見かけ上ゼロになるまでの時間が上記周波数に対応する周期の１０倍程度以上であることが好ましい。
【００４０】
この発明において、流動造粒と消磁を同一の装置で行なうことも好ましい実施形態である。例えば、造粒時に電磁石で磁界配向した場合には、同じ電磁石を用いて残磁を有する異方性造粒粉に交番減衰磁界を印加して消磁することができる。
【００４１】
この発明による消磁処理後の異方性造粒粉の残留磁化は１０Ｇ以下にすることが流動性の点から好ましい。このような低い残留磁化は、上述の有効な消磁処理を行なうことにより容易に達成することができる。
【００４２】
また、消磁後の造粒粉をふるいによってアンダーカット、オーバーカットすることにより、さらに極めて流動性に富んだ造粒粉を得ることができる。
さらに、得られた造粒粉にステアリン酸亜鉛、ステアリン酸マグネシウム、ステアリン酸カルシウム、ステアリン酸アルミニウム、ポリエチレングリコール等の潤滑剤を少量添加すると流動性をさらに向上させることができ有効である。
【００４３】
この発明による異方性造粒粉を用いて異方性焼結磁石を製造する工程、すなわち、成形、焼結、熱処理等の方法やその条件は、公知の粉末冶金的手段のいずれかを採用することができる。以下に好ましい条件の一例を示す。成形は、公知のいずれの成形方法も採用できるが、磁場中、圧縮成形で行なうことが最も好ましい。
【００４４】
成形時の磁場は、静磁場、パルス磁場、あるいはそれらの複合磁場、さらにそれらを交互に連続して印加する等の手段を採用することができ、磁場強度としては１０〜２０ｋＯｅが好ましい。特に、この発明により得られた異方性造粒粉は、個々の造粒粉中の希土類含有合金粉末が極めてよく配向されているため、磁界を印加して成形する場合、配向に必要な磁界強度は従来技術による造粒粉に比べて少なくてよい。例えば、小型モータ等に用いられる薄肉円筒形状で、回転中心から放射線方向に垂直に着磁して用いるいわゆるラジアルリング磁石を成形する場合、磁気回路上の制約から成形時の配向磁界強度は２〜３ｋＯｅしか印加することができないが、このような場合においても、この発明による異方性造粒粉は配向性が優れているため、配向度が高く、大きな表面磁束を有する磁石を作製することができる。さらに、通常の１０ｋＯｅ程度の配向磁界においてもこの発明による異方性造粒粉の磁界配向における優位性は明らかであり、原料粉をそのまま成形、焼結して作製した磁石と同等の残留磁化、最大エネルギー積を得ることができる。
なお、成形圧力は特に限定はしないが、０．３〜２．０ｔｏｎ／ｃｍ２が好ましい。
【００４５】
焼結前には、脱バインダー処理を行なうことが好ましく、脱バインダー処理法としては、真空中で加熱する一般的な方法のほか、水素流気中で１００〜２００℃／ｈで昇温し、３００〜６００℃で１〜２時間程度保持する等の方法を適宜選定することができる。脱バインダー処理を施すことにより成形体中のバインダー成分が抜け、焼結体中の残留炭素量を低減させることができ、磁気特性が向上する。
【００４６】
なお、希土類含有合金粉末は、水素を吸収し易いために水素流気中での脱バインダー処理後は脱水素処理を行なうことが好ましい。脱水素処理の条件としては、真空中で５０〜２００℃／ｈで昇温し、５００〜８００℃で１〜２時間程度保持することにより、吸蔵されていた水素はほぼ完全に除去される。
【００４７】
また、脱水素処理後は、引き続いて昇温加熱して焼結を行なうことが好ましく、５００℃を超えてからの昇温速度は任意に選定すればよく、例えば、１００〜３００℃／ｈなど、焼結に際してとられる公知の昇温条件を採用できる。
【００４８】
脱バインダー処理後の成形体の焼結、並びに焼結後の熱処理条件は、選定した希土類含有合金粉末の組成に応じて適宜選定されるが、例えば、焼結条件としては１０００〜１１８０℃で１〜２時間、熱処理条件としては４５０〜８００℃で１〜８時間程度が好ましい。
【００４９】
この発明における異方性造粒粉の製造装置の構成とその作用を図面に基づいて詳述する。図１はこの発明による異方性造粒粉の製造装置であって、希土類含有合金粉末に磁界を印加するための磁気回路を電磁石で構成した例を示す概略説明図である。また、図２は、この発明による異方性造粒粉の製造装置であって、希土類含有合金粉末に磁界を印加するための磁気回路を永久磁石で構成した例を示す概略説明図である。
【００５０】
図１に示すこの発明における異方性造粒粉の製造装置は、内部に攪拌羽根２、ガス給気口５、ガス排気口８、スプレーノズル６、バグフィルター７を具備する筒状の流動槽１と、該流動槽１の周囲に配置された電磁石９から構成される。
その動作を説明すると、まず、希土類含有合金粉末を攪拌羽根２の上に装填し、電磁石９によって磁界を印加して上下方向に配向する。それと同時に、ファンモーター３から送気されヒーター４によって加熱されたガスをガス給気口５より流動槽１内へ供給するとともに攪拌羽根２を回転させる。希土類含有合金粉末は磁界配向されたままガス気流と攪拌羽根の作用によって流動状態となって、流動槽１内で流動層を形成する。そしてその流動層中に、スプレーノズル６よりバインダー溶液を噴霧添加することにより、流動層の転動造粒作用により造粒が進行する。噴霧されたバインダー溶液中の溶媒は蒸発し、該ガスとともにバグフィルター７を通ってガス排気口８より外部へ排出される。
【００５１】
図２に示すこの発明における異方性造粒粉の製造装置は、基本構成は図１の装置と同じであり、電磁石に代わり永久磁石を配置した例である。永久磁石１０は、流動槽１の周囲に極性を交互に変えながら配置され、全体が攪拌羽根２の回転軸の上下方向に移動できるとともに、攪拌羽根２の回転方向と逆方向に回転できるように構成されており、該永久磁石１０を回転軸の上下方向に移動させることにより、印加磁界の強度を変化させることができる。
【００５２】
この発明において、造粒する希土類含有合金粉末は非常に酸化し易いために、使用するガスとしては、窒素ガス、アルゴンガスなどの不活性ガスが好ましい。また、流動槽は、その内部を不活性ガスなどで置換でき、かつその酸素濃度を常時３ｖｏｌ％以下に制御できる構造であることが好ましい。
【００５３】
また、小規模の装置では、不活性ガスを使い捨てすることも可能であるが、大規模な装置においては、不活性ガスの流れを閉回路にして繰り返し使用すると経済的である。この場合、流動槽を通過した不活性ガスは、バインダー溶液中の溶媒を含んでいるため、ガスを一旦冷却機などに通して溶媒を回収したのち、循環させることが好ましい。
【００５４】
バインダー溶液中の溶媒を蒸発させ、造粒された粉末を瞬時に乾燥固化させて、希土類含有合金粉末の酸化防止及び処理能率の向上を図るためには、供給する不活性ガスを加熱することが好ましい。加熱の手段は問わないが、例えば図１に示す如く、ガス給気口の手前にヒーターを設け、不活性ガスの温度を６０〜１５０℃の範囲で制御できることが好ましい。
【００５５】
また、ヒーターで加熱された不活性ガスの温度をそのまま維持しながら流動槽内へ送り込むために、ガス給気口の温度を６０〜１５０℃、特に好ましくは１００℃前後に加熱保持することも望ましい構成である。また、ガス給気口とガス排気口の温度差が小さい場合にも処理能率が低下する傾向があるため、ガス排気口の温度５０℃以下、より好ましくは４０℃以下あるいは常温に保持できる構成とすることも好ましい。
【００５６】
上述した製造装置を用いた異方性造粒粉の製造方法においては、攪拌羽根の回転数と不活性ガスの流量制御が重要であり、流動層の状態、特に希土類含有合金粉末の回転速度が変化し、転動造粒作用が変化するために、得られる造粒粉の２次粒子径が変化する。同じ粒度分布を持つ造粒粉を再現性よく製造するためには、これらを効率よく制御できる構成であることが望ましい。
【００５７】
この発明において、バインダー溶液を流動層中に添加する場合は、希土類含有合金粉末の量に見合った一定量を、流動槽内部に設けた注入口より添加するが、該注入口から直接バインダー溶液を添加するとバインダーの分布が極めて不均一となり、造粒粉の大きな塊が発生し易くなるため、該注入口の先にスプレーノズルを配置して、バインダー溶液を噴霧させて添加することが好ましい。スプレーノズルは、加圧ノズル、２流体ノズルなどを採用することができる。また、スプレーノズルの噴霧位置は、流動槽の上部から希土類含有合金粉末に向けて噴霧する方法と、希土類含有合金粉末の流動層の中に直接噴霧する方法とがあり、適宜選定できる。
【００５８】
この発明による異方性造粒粉の製造装置の特徴は、ガスと攪拌羽根によって流動層を形成した希土類含有合金粉末に磁界を印加する構成を有する点にあり、これにより、該粉末を磁気配向させながら、同時にバインダー溶液を蒸発させ、造粒粉を乾燥固化させて、異方性造粒粉を得るものである。
【００５９】
希土類含有合金粉末に磁界を印加するための磁気回路としては、図１に示す電磁石を用いたもの、または図２に示す永久磁石を用いたものが採用できる。永久磁石の場合、構造が簡単で電力を消費しないという利点を有するが、磁界強度を調整するために大掛かりな装置が必要になるという欠点を有する。それとは逆に電磁石の場合は、稼働中に磁界強度を簡単に調整できるという利点はあるが、電力を消費するという問題がある。いずれを採用するかは、製造規模や希土類含有合金粉末の種類などに応じて適宜選定することが望ましい。
【００６０】
また、磁気回路の磁界強度は１ｋＯｅ程度以上必要であるが、これを永久磁石で実現するためには、高磁気特性を有する希土類磁石などを用いることが好ましい。なお、磁気回路として電磁石、永久磁石のいずれの構成を採用するにしろ、希土類含有合金粉末の流動層が形成されている全ての位置に磁界を印加することができる構成であることが望ましい。
【００６１】
この発明において、磁気回路による配向磁界が強過ぎると、先述の如く希土類含有合金粉末が磁界中で固定され、流動層の形成が妨げられる。一方、配向度を高めるには磁界強度を十分に高くする方がよい。そこで、希土類含有合金粉末に印加する磁界強度を可変とし、高磁界と低磁界を交互に印加できるようにすることも好ましい装置構成である。すなわち、流動層の形成を妨げない低い磁界強度で配向を行ないながら造粒を進行させ、非連続的に高い磁界強度を印加することにより、１次粒子の配向度が高く、かつ粒度分布がシャープで流動性に優れた異方性造粒粉が製造できる。このように、非連続的に印加磁界強度を高くするには、電磁石に流す電流値を高くしたり、永久磁石と流動層との距離を近づけたりして容易に実施することができる。
【００６２】
また、電磁石、永久磁石の他に、ソレノイドコイルを設け、パルス電流を流すことにより瞬間的にパルス磁界を印加するのも好ましい構成である。
【００６３】
【実施例】
実施例１
Ｎｄ１３．６ａｔ％、Ｄｙ０．２８ａｔ％、Ｃｏ３．４ａｔ％、Ｂ６．５ａｔ％、残部Ｆｅ及び不可避的不純物からなる原料をアルゴンガス中で高周波溶解して希土類含有合金を溶製した。次に該合金を粗粉砕した後、ジョークラッシャー、ディスクミルにより４２０μｍ以下に粉砕し、ステアリン酸亜鉛を０．０５ｗｔ％添加、混合し、さらに、ジェットミルによって粉砕して平均粒径３μｍの希土類含有合金粉末を得た。
【００６４】
得られた希土類含有合金粉末を図１に示すこの発明による異方性造粒粉の製造装置に１ｋｇ装填し、ガス給気口から室温の窒素ガスを毎分０．５Ｎｍ３流しながら攪拌羽根を２００ｒｐｍで回転させ、該粉末の流動層を形成させ、さらに電磁石に通電し、２．０ｋＯｅの磁界を印加して該粉末を攪拌羽根の回転軸の上下方向に配向しながら、該粉末にポリビニルアルコールの２０ｗｔ％水溶液を一定速度で噴霧添加した。この状態では、粉末は針状に配向されながら、かつ流動槽内を激しく流動していた。
【００６５】
次に、希土類含有合金粉末に対するポリビニルアルコール溶質の割合が０．３ｗｔ％に達した時点で噴霧をやめ、窒素ガスの給気口温度を１００℃に上げ、５分間乾燥を行なった後、攪拌羽根の回転と電磁石の通電を止め、流動槽内を冷却した。この結果、針状に配向された粉末はバインダーによる固化、造粒と、攪拌による解砕を繰り返しながら、徐々葉巻状の異方性造粒粉に変化した。
【００６６】
次に、得られた異方性造粒粉を最大磁界２．０ｋＯｅの交番減衰磁界中に入れて消磁を行なった。そして、消磁後の造粒粉を目のひらきが２５０μｍのふるいにかけて粗粒子を除去し、また目のひらきが３２μｍのふるいにかけて微粒子を除去して、平均粒径１０５μｍの造粒粉を得た。この操作における歩留まりは９３ｗｔ％であった。また、この造粒粉の残留磁化は２．８Ｇであった。粒径選別した造粒粉の粉体流動性は、最小内径８ｍｍのロート状の管を１００ｇの粉体が自然落下して通過するまでに要する時間で測定した。その結果を表１のＮｏ．１に示す。
【００６７】
粒径選別した造粒粉を磁界中プレス機に設置された給粉機に装填し、縦１０ｍｍ、横１５ｍｍ、深さ５０ｍｍ寸法のダイスのキャビティー内に造粒粉を自然落下により給粉し、次いで、１０ｍｍの辺に平行に０、３、５、８、１１ｋＯｅの磁界を印加して造粒粉を配向しながら、深さ方向に１．５Ｔｏｎ／ｃｍ２の圧力を加え成形した。得られた成形体を水素雰囲気中で室温から３００℃まで昇温速度１００℃／ｈで加熱する脱バインダー処理を行ない、引き続いて真空中で１１００℃まで昇温し１時間保持する焼結を行ない、さらに焼結完了後アルゴンガスを導入して７℃／ｍｉｎの速度で８００℃まで冷却した後、１００℃／ｈの速度で冷却して、５５０℃で２時間保持する時効処理を施して異方性の焼結磁石を得た。得られた焼結磁石には、ワレ、ヒビ、変形などは全く見られなかった。成形磁界と焼結磁石の磁気特性の関係を表１のＮｏ．１に示す。
【００６８】
比較例１
実施例１と同様の条件で電磁石に通電せずに等方性造粒粉を作製し、消磁処理を行なわずに実施例１と同一の粒径選別を行なった。この操作における歩留まりは９１ｗｔ％であった。また、粒径選別後の造粒粉の残留磁化は測定限界以下であった。粒径選別した造粒粉の粉体の流動性を表１のＮｏ．２に示す。
次に、粒径選別した造粒粉を実施例１と同じ方法によって磁界を変えながら成形した後、実施例１と同じ条件で脱バインダー処理、焼結及び時効処理を施して焼結磁石を得た。得られた焼結磁石には、ワレ、ヒビ、変形などは全く見られなかった。成形磁界と焼結磁石の磁気特性の関係を表１のＮｏ．２に示す。
【００６９】
比較例２
実施例１において、ジェットミル粉砕により得られた平均粒径３μｍの原料粉末を、造粒を行なわずに、実施例１と同じ方法によって磁界を変えながら成形した後、得られた成形体を真空中で１１００℃まで昇温し１時間保持する焼結を行ない、さらに焼結完了後、アルゴンガスを導入して７℃／ｍｉｎの速度で８００℃まで冷却した後、１００℃／ｈの速度で冷却して、５５０℃で２時間保持する時効処理を施して異方性の焼結磁石を得た。成形磁界と焼結磁石の磁気特性の関係を表１のＮｏ．３に示す。なお、ジェットミル粉砕後の粉体の流動性は、粉体が全く流れず測定不能であった。
【００７０】
【表１】
表１の測定結果から明らかなように、実施例１のこの発明による異方性造粒粉の流動性は、原料粉末に比べて非常に良好であり、また、磁界中での配向性が等方性造粒粉に比べて優れているため、原料粉末をそのまま成形、焼結した場合（比較例３）の磁気特性と同等の高い特性が全ての成形磁界で得られることが分かる。
【００７２】
実施例２
Ｓｍ１１．９ａｔ％、Ｃｕ８．８ａｔ％、Ｆｅ１２．６ａｔ％、Ｚｒ１．２ａｔ％、残部Ｃｏ及び不可避的不純物からなる原料をアルゴンガス中で高周波溶解して希土類含有合金を溶製した。次に該合金を粗粉砕した後、ジョークラッシャー、ディスクミルにより４２０μｍ以下に粉砕し、ステアリン酸亜鉛を０．０５ｗｔ％添加、混合し、さらに、ジェットミルによって粉砕して平均粒径３μｍの希土類含有合金粉末を得た。
【００７３】
得られた希土類含有合金粉末を図２に示すこの発明による異方性造粒粉の製造装置に１ｋｇ装填し、ガス給気口から室温の窒素ガスを毎分０．５Ｎｍ３流しながら攪拌羽根を２００ｒｐｍで回転させ、該粉末の流動層を形成させ、さらに流動層と同じ高さで永久磁石を攪拌羽根と逆方向に３０ｒｐｍで回転させ、１．５ｋＯｅの磁界を印加して該粉末を流動槽の壁面に垂直に配向しながら、該粉末にヒドロキシプロピルセルロースの２０ｗｔ％エタノール溶液を一定速度で噴霧添加した。この状態では、粉末は針状に配向されながら、かつ流動槽内を激しく流動していた。
【００７４】
次に、希土類含有合金粉末に対するバインダー溶質の割合が０．３ｗｔ％に達した時点で噴霧をやめ、窒素ガスの給気口温度を１００℃に上げ、５分間乾燥を行なった後攪拌羽根の回転を止め、永久磁石を流動槽の下方へ移動させて流動槽内を冷却した。この結果、針状に配向された粉末はバインダーによる固化、造粒と、攪拌による解砕を繰り返しながら、徐々葉巻状の異方性造粒粉に変化した。
【００７５】
次に、得られた異方性造粒粉を最大磁界１．５ｋＯｅの交番減衰磁界中に入れて消磁を行なった。そして、消磁後の造粒粉を目のひらきが２５０μｍのふるいにかけて粗粒子を除去し、また目のひらきが３２μｍのふるいにかけて微粒子を除去して、平均粒径１１０μｍの造粒粉を得た。この操作における歩留まりは９３ｗｔ％であった。また、この造粒粉の残留磁化は３．９Ｇであった。粒径選別した造粒粉の粉体流動性は、最小内径８ｍｍのロート状の管を１００ｇの粉体が自然落下して通過するまでに要する時間で測定した。その結果を表２のＮｏ．４に示す。
【００７６】
粒径選別した造粒粉を磁界中プレス機に設置された給粉機に装填し、縦１０ｍｍ、横１５ｍｍ、深さ５０ｍｍ寸法のダイスのキャビティー内に造粒粉を自然落下により給粉し、次いで磁界強度１０ｋＯｅ、１．５Ｔｏｎ／ｃｍ２の圧力を加え成形した。２０個の成形体を成形した時の成形体の重量と高さ方向の寸法の最大値と最小値を表２のＮｏ．４に示す。
【００７７】
得られた成形体を水素雰囲気中で室温から３００℃まで昇温速度１００℃／ｈで加熱する脱バインダー処理を行ない、引き続いて真空中で１２００℃まで昇温し１時間保持する焼結を行ない、さらに焼結完了後、１１６０℃にて溶体化処理を行ない、その後アルゴンガスを導入して８００℃から４００℃までの多段時効処理を施して異方性の焼結磁石を得た。得られた焼結磁石には、ワレ、ヒビ、変形などは全く見られなかった。得られた２０個の焼結磁石の磁気特性の平均値を表２のＮｏ．４に示す。
【００７８】
比較例３
永久磁石による磁界の印加をしない以外は実施例２と同様の条件で等方性造粒粉を作製し、消磁処理を行なわずに実施例２と同一の粒径選別を行なった。この操作における歩留まりは８９ｗｔ％であった。粒径選別した造粒粉の粉体の流動性を表２のＮｏ．５に示す。次に、粒径選別した造粒粉を実施例２と同じ方法で磁界中成形した。２０個の成形体を成形した時の成形体の重量と高さ方向の寸法の最大値と最小値を表２のＮｏ．５に示す。得られた成形体を実施例２と同じ条件で脱バインダー処理、焼結及び時効処理を施して焼結磁石を得た。得られた焼結磁石には、ワレ、ヒビ、変形などは全く見られなかった。得られた２０個の焼結磁石の磁気特性の平均値を表２のＮｏ．５に示す。
【００７９】
【表２】
表２の測定結果から明らかなように、実施例２のこの発明による異方性造粒粉の流動性及び成形体の寸法精度は、等方性造粒粉と同等であり、また、磁気特性は格段に優れていることが分かる。
【００８１】
実施例３
実施例１で作製した、消磁、粒径選別後の希土類含有合金粉末を用いて、該粉末を磁界中プレス機に設置された給粉機に装填し、外径１０ｍｍ、内径５ｍｍ、深さ３０ｍｍの寸法を持つ、円筒形のダイスのキャビティー内に造粒粉を自然落下により給粉し、次いで、円筒の肉厚の厚み方向（ラジアル方向）に２．５ｋＯｅの磁界を印加して造粒粉を配向し、深さ方向に１．５Ｔｏｎ／ｃｍ２の圧力を加えラジアルリング成形体を得た。２０個の成形体を成形した時の成形体の重量と、高さ方向の寸法の最大値と最小値を表３のＮｏ．６に示す。
【００８２】
得られた成形体を水素雰囲気中で室温から３００℃まで昇温速度１００℃／ｈで加熱する脱バインダー処理を行ない、引き続いて真空中で１１００℃まで昇温し１時間保持する焼結を行ない、さらに焼結完了後アルゴンガスを導入して７℃／ｍｉｎの速度で８００℃まで冷却した後、１００℃／ｈの速度で冷却して、５５０℃で２時間保持する時効処理を施して焼結磁石を得た。得られた焼結磁石には、ワレ、ヒビ、変形などは全く見られなかった。得られた２０個のラジアルリング磁石を着磁し、外周の表面磁束密度を測定した平均値を表３のＮｏ．６に示す。
【００８３】
比較例４
比較例１で作製した粒径選別後の等方性造粒粉を用いて、実施例３と同様の方法で成形を行なった。２０個の成形体を成形した時の成形体の重量と、高さ方向の寸法の最大値と最小値を表３のＮｏ．７に示す。得られた成形体を実施例３同じ条件で脱バインダー処理、焼結及び時効処理を施して焼結磁石を得た。得られた焼結磁石には、ワレ、ヒビ、変形などは全く見られなかった。得られた２０個のラジアルリング磁石を着磁し、外周の表面磁束密度を測定した平均値を表３のＮｏ．７に示す。
【００８４】
比較例５
実施例１において、ジェットミル粉砕により得られた平均粒径３μｍの原料粉末を、造粒を行なわずに、実施例３と同様の方法で成形を行なうことを試みた。しかし、給粉機から円筒形のダイスのキャビティー内に造粒粉を自然落下により給粉しようとしたが、粉体の流動性が悪いために原料粉がキャビティー内に全く落下せず、成形を行なうことができなかった。
【００８５】
【表３】
表３の結果から明らかなように、この発明による異方性造粒粉の流動性および成形時の寸法精度は非常に良好であるため、従来の原料粉では成形が困難かあるいは不可能であった薄物形状品、小物形状品等の成形を容易に行なうことが可能であり、また、磁界中での配向性が優れているため、ラジアルリングの成形のように、磁気回路上の制約から成形時の配向磁界強度が十分に高くできない場合にも、成形体の高い配向度を実現することができ、磁気特性と寸法精度がともに優れた焼結磁石を製造することができる。
【００８７】
【発明の効果】
この発明による異方性造粒粉の製造方法並びに製造装置によれば、圧縮成形時の粉体の流動性に優れる造粒粉を得ることができ、成形体の寸法精度の向上および成形サイクルの短縮化が図られ、かつ造粒時に印加する磁界強度を高くすることができ、造粒粉に含まれる１次粒子の配向度が高いために、造粒粉を低配向磁界で成形しても磁気特性の優れた成形体および焼結体を製造できる異方性造粒粉を歩留まり良く製造することができる。
【図面の簡単な説明】
【図１】この発明よる異方性造粒粉の製造装置において、磁気回路が電磁石で構成された一実施例を示す概略説明図である。
【図２】この発明よる異方性造粒粉の製造装置において、磁気回路が永久磁石で構成された一実施例を示す概略説明図である。
【符号の説明】
１ 流動槽
２ 攪拌羽根
３ ファンモーター
４ ヒーター
５ ガス給気口
６ スプレーノズル
７ バグフィルター
８ ガス排気口
９ 電磁石
１０ 永久磁石[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing anisotropic granulated powder used for molding a rare earth sintered magnet such as an R—Co based magnet or an R—Fe—B based magnet, and includes a rare earth containing magnet which is a raw material of the rare earth sintered magnet. When the alloy powder is formed into a granulated powder by the flow granulation method, the rare-earth-containing alloy powder is solidified in a magnetically oriented state to form an anisotropic granulated powder. The present invention relates to a method and an apparatus for producing anisotropic granulated powder capable of improving the dimensional accuracy of a compact and improving the compaction cycle by improving the resilience and producing a rare earth sintered magnet having excellent magnetic properties.
[0002]
[Prior art]
2. Description of the Related Art Many motors and actuators are used in home electric appliances, computer peripheral devices, automobiles, and the like. Today, there is an increasing demand for miniaturization and weight reduction of these products in order to enhance portability or promote energy saving. Along with this, there is a demand for permanent magnet materials incorporated in motors, actuators, and the like, which have higher performance and can cope with small-sized or thin-walled shapes.
[0003]
In recent years, as a material that meets the above-mentioned requirements, the production of bonded magnets having a higher degree of freedom in shape than sintered magnets has been increasing. However, since the bonded magnet contains resin, the occupation ratio of the magnet powder contained in the bonded magnet is much lower than that of the sintered magnet, so that the maximum energy product of the bonded magnet is the same as that of the sintered material. At present, only about half of magnets are obtained. Therefore, there is a need for a technique for manufacturing a small-sized or thin-walled magnet with a sintered magnet having excellent magnetic properties.
[0004]
As typical sintered magnets of the present day, Ba ferrite magnets, Sr ferrite magnets, R-Co magnets, and R-Fe-B magnets previously proposed by the applicant (Japanese Patent Publication No. 61-34242, etc.). No. Ferrite magnets, such as Ba ferrite magnets and Sr ferrite magnets, are inferior in magnetic properties to rare earth magnets, but are inexpensive and lightweight, and are widely used in motors and actuators. Rare-earth magnets such as R-Co-based magnets and R-Fe-B-based magnets are used in various applications because their magnetic properties are much better than other magnet materials.
[0005]
In order to exhibit high magnetic properties in the rare-earth magnet, it is necessary to pulverize a rare-earth-containing alloy powder having a required composition, compact it in a magnetic field, and then sinter it. The desirable average particle size of the rare earth-containing alloy powder before compaction in a magnetic field is about 1 to 10 μm. The reason why the rare earth-containing alloy powder is finely pulverized in this way is that when a raw material powder having a large particle size is used, sintering occurs. This is because the crystal grain size becomes coarse and a practical coercive force cannot be obtained.
[0006]
On the other hand, if the average particle size of the rare earth-containing alloy powder is reduced, the fluidity of the powder is reduced, so that the variation in the supply amount of the raw material powder into the die in the compression molding process is increased, and the dimensional variation of the compact and the sintered body is increased. Bring. Therefore, in order to automatically supply a fixed amount of the raw material powder into the die, a method of naturally dropping the powder into a cavity having a fixed volume is used.
[0007]
However, when the flowability of the raw material powder is low, the powder is likely to cause a crosslinking phenomenon in the cavity. The cross-linking phenomenon is a phenomenon in which the powder forms a strong arch structure between the partition walls. Once the cross-link is formed, the powder cannot move to a space below the cross-link. There is a difference. Further, since the crosslinking phenomenon occurs randomly, the presence or absence of crosslinking occurs in each cycle of the compression molding, and it becomes difficult to control the supply amount of the raw material powder to a constant.
[0008]
The cross-linking phenomenon described above is more likely to occur as the depth of the cavity is deeper or as the area of the opening of the cavity is smaller. Particularly, when the opening of the cavity is extremely small, the raw material powder is dropped into the cavity by gravity. Will be impossible to supply. Therefore, in order to industrially produce small-sized products with good dimensional accuracy, it is essential to improve the fluidity of the raw material powder.
[0009]
Conventionally, granulation has been performed as a method for improving the fluidity of powder. However, the granulated powder obtained by the usual granulation method is an isotropic granulated powder in which the crystal orientation of the primary particles is different, so that the orientation in a magnetic field is poor and the orientation magnetic field during molding is low. There is a problem that the residual magnetization and the maximum energy product are reduced.
[0010]
[Problems to be solved by the invention]
In view of this, the present applicant has previously improved the fluidity of a raw material powder composed of a rare earth-containing alloy such as an R-Co-based alloy or an R-Fe-B-based alloy, and obtained an anisotropic material capable of obtaining high magnetic properties even with a low orientation magnetic field. A method for producing a granulated powder was proposed (Japanese Patent Application Laid-Open No. Hei 8-20801). This proposal proposes that when a magnetic powder and a solvent are kneaded to form a slurry, and then formed into a granulated powder by a spray drying method, a magnetic field is applied to a pipe for supplying the slurry to an atomizer (atomizer), thereby forming a slurry. The magnetic powder contained in the magnetic powder is magnetically oriented, or the magnetic powder is magnetically oriented by applying a magnetic field to the slurry immediately before being sprayed by a rotating disk atomizer composed of a magnetic circuit using a permanent magnet. The purpose is to obtain anisotropic granulated powder in which the crystal orientation of the secondary particles is well-aligned.
[0011]
Furthermore, the applicants previously kneaded rare earth-containing alloy powder and a solvent into a slurry to obtain an anisotropic granulated powder having a higher degree of orientation, and formed a granulated powder by spray drying. During the process, a magnetic field is generated at a position where the slurry in the form of droplets ejected from the rotary disk type or the nozzle type atomizer passes, and the magnetic field is applied to the droplets to magnetically orient the powder and simultaneously dry and solidify the powder. A method and an apparatus for producing anisotropic granulated powder have been proposed (Japanese Patent Application No. 8-126526).
[0012]
The anisotropic granulated powder obtained by these methods is characterized by the fact that the primary particles constituting the individual secondary particles have the same crystal orientation, unlike isotropic powders. Is improved, and a sintered magnet having a high remanent magnetization and a maximum energy product can be obtained.
[0013]
However, the above-mentioned method for producing anisotropic granulated powder has the following problems. That is, in the former proposal, if the intensity of the applied magnetic field is too high, the slurry is likely to be clogged in a pipe for supplying the slurry or an atomizer. Also, in the latter proposal, if the strength of the magnetic field generated by the permanent magnet or the electromagnet is increased, the gradient tends to be generated in the magnetic field strength. And hinder the flight of the slurry.
[0014]
As described above, in the method for producing anisotropic granulated powder by the spray drying method, if the orientation magnetic field is increased to improve the degree of orientation of the granulated powder, the yield and productivity may decrease, and in some cases, There was a problem that the grains became difficult.
[0015]
According to the present invention, the fluidity of the powder during compression molding is high, the dimensional accuracy of the compact is improved, the compacting cycle is shortened, and the magnetic field intensity applied during granulation can be increased. Since the degree of orientation of the primary particles contained in the powder is high, anisotropic granulation for rare earth-containing magnets can produce compacts and sintered compacts having excellent magnetic properties even when the granulated powder is compacted with a low orientation magnetic field. It is an object of the present invention to provide a method and a production apparatus capable of producing powder with a high yield.
[0016]
[Means for Solving the Problems]
The present inventors have conducted various studies on a novel method for producing anisotropic granulated powder, and found that a fluidized bed was formed on the powder, and in a fluid granulation method utilizing a rolling granulation effect, the rare earth-containing alloy powder was used. By applying a magnetic field and orienting, the fluidized bed is formed by the rotation of the gas flow and the stirring blade, and the powder is granulated by the rolling granulation action of the fluidized bed, so that the crystal orientation of the primary particles is uniform. It has been found that anisotropic granulated powder can be produced with good yield, and that the obtained anisotropic granulated powder has extremely excellent orientation during magnetization.
[0017]
In addition, the present inventors, when performing fluidized granulation while orienting the rare earth-containing alloy powder in a magnetic field, change the intensity of the applied magnetic field to further improve the degree of orientation of the primary particles and sharpen the particle size distribution. It was found that anisotropic granulated powder having excellent fluidity could be obtained by the method described above, and the present invention was completed.
[0018]
That is, the present invention
A rare-earth-containing alloy powder is loaded into an apparatus including a stirring vessel, a fluidized tank having a gas inlet and a gas outlet, and a magnetic circuit disposed around the fluidized tank and for applying a magnetic field to the vessel. Then, while applying a magnetic field by a magnetic circuit to the powder, after forming a fluidized bed in the fluidized bed by the rotation of the gas flow from the gas supply port and the stirring blade, a binder solution is added to the fluidized bed, A method for producing anisotropic granulated powder, comprising mixing and granulating the powder by the tumbling granulation action of a fluidized bed.
[0019]
In addition, the present invention
A binder solution is added and mixed in a device comprising a fluidizing tank having a stirring blade, a gas supply port and a gas exhaust port, and a magnetic circuit arranged around the fluidizing tank and for applying a magnetic field to the vessel. The rare-earth-containing alloy powder is charged, and while applying a magnetic field to the powder, a fluidized bed is formed in the fluidized vessel by the gas flow from the gas supply port and the rotation of the stirring blade, and the powder is rolled. This is a method for producing an anisotropic granulated powder, wherein granulation is performed by a granulating action.
[0020]
Further, the present invention provides the above-mentioned production method,
It is proposed that the raw material powder of the ferrite magnet be subjected to hydrophobic treatment in advance, and that the magnetic powder be applied while changing the magnetic field strength.
[0021]
In addition, the present invention
A fluidized tank having a stirring blade, a gas supply port and a gas exhaust port, and a magnetic circuit arranged around the fluidized tank and for applying a magnetic field to the vessel, wherein At the time of applying a magnetic field to the fluidized bed, the rolling granulation action of the fluidized bed by the gas flow from the gas supply port and the rotation of the stirring blades can be generated, thereby forming the rare earth-containing alloy powder into anisotropic granulated powder. An apparatus for producing anisotropic granulated powder, characterized in that:
[0022]
Further, the present invention proposes an apparatus for producing anisotropic granulated powder having a variable mechanism of a magnetic circuit in the above-mentioned production apparatus.
[0023]
BEST MODE FOR CARRYING OUT THE INVENTION
The method for producing anisotropic granulated powder in the present invention will be described in detail below.
In the present invention, as the target rare earth-containing alloy powder, any powder having a crystal magnetic anisotropy can be applied, and among them, R-Fe-B-based alloy powder and R-Co-based alloy Powders and the like are most suitable. As the rare earth-containing alloy powder, a powder obtained by crushing an alloy having a single required composition or a powder obtained by crushing an alloy having a different composition and then mixing and adjusting the required composition, improving coercive force and improving productivity For this purpose, known rare earth-containing alloy powders such as those to which additional elements are added can be used.
[0024]
As a method for producing the rare earth-containing alloy powder, a known method such as a casting and pulverizing method, a super-quenching method, a direct reduction diffusion method, a hydrogen-containing disintegration method, and an atomizing method can be appropriately selected. Also, the particle size of the alloy powder is not particularly limited, but if the average particle size of the alloy powder is less than 1 μm, it easily reacts with oxygen or a solvent in the air to be easily oxidized, and deteriorates the magnetic properties after sintering. On the other hand, an average particle size exceeding 10 μm is not preferable because the particle size is too large and the sintered density decreases. Therefore, an average particle size of 1 to 10 μm is a preferable range. A more preferred range is 1 to 6 μm.
[0025]
In the present invention, as a solvent used for preparing a binder solution to be added to the rare earth-containing alloy powder, the binder can be easily dissolved, and hardly reacts with the rare earth-containing alloy powder or the binder, and the boiling point is relatively high. Low and chemically stable ones are preferred. Specifically, when a water-soluble binder is used, water is most preferable, and the purity thereof is not particularly limited, but in order to control the reaction of the rare earth-containing alloy powder with the rare earth component as much as possible, deoxygenated pure water or Water subjected to bubbling treatment with an inert gas such as nitrogen is preferable. When a water-insoluble binder is used, it is preferable to use an organic solvent such as ethyl alcohol, isopropyl alcohol, acetone, methyl ethyl ketone, normal hexane, cyclohexane, toluene, methylene chloride, and dioxane.
[0026]
In the present invention, when water is used as the solvent of the binder solution, it is preferable to use at least one of methyl cellulose, polyacrylamide, and polyvinyl alcohol as the water-soluble binder. When an organic solvent is used, paraffin wax, polyethylene glycol (PEG), polyvinylpyrrolidone (PVP), hydroxypropylcellulose (HPC), hydroxypropylmethylcellulose (HPMC), ethylcellulose (EC), acetylcellulose, nitrocellulose At least one kind of binder soluble in an organic solvent to be used such as cellulose and vinyl acetate resin can be used.
[0027]
If the concentration of the binder solution used in the present invention is less than 5 wt%, it takes a long time to dry the solvent and the treatment efficiency is reduced, and if it exceeds 50 wt%, stirring and mixing with the rare earth-containing alloy powder become difficult. 50 wt% is preferred. More preferably, it is 10 to 30 wt%.
[0028]
The above-mentioned binder solution can enhance the tumbling granulation action of the fluidized bed with a small amount of addition, can maintain a high bonding force between the particles in the granulated powder even after drying, and Since a small amount is sufficient, the amount of residual oxygen and carbon in the powder can be reduced. Furthermore, when a binder is added, the granulated powder is covered with the binder, so that it is not easily oxidized in the air, and there is an advantage that the granulated powder is easily handled.
[0029]
When the content of the binder alone is less than 0.05 wt% with respect to the rare earth-containing alloy powder, the bonding force between the particles in the granulated powder is weak, and the granulated powder is broken at the time of powder supply before compaction. If the fluidity of the sintered body is significantly reduced, and if it exceeds 0.5 wt%, the residual carbon content and the oxygen content of the sintered body increase, the coercive force decreases, and the magnetic characteristics deteriorate. % Is preferred in these respects. When used in combination, the total content of all binders is preferably in the range of 0.05 to 0.4 wt% for the same reason as described above.
[0030]
The method of adding the binder includes a method of adding the binder by spraying or the like during fluid granulation, and a method of adding a binder to the rare earth-containing alloy powder before fluid granulation, or both may be used in combination. .
[0031]
In the present invention, it is necessary to apply a magnetic field to orient the rare earth-containing alloy powder in a magnetic field. The method of applying the magnetic field may be either an electromagnet or a permanent magnet. If the magnetic field strength continuously applied to the rare earth-containing alloy powder is less than 0.5 kOe, the degree of orientation of the obtained anisotropic granulated powder is lowered, and good orientation in a magnetic field cannot be obtained. If it exceeds 10 kOe, the rare earth-containing alloy powder is fixed in a magnetic field and a fluidized bed cannot be formed, so the range of 0.5 to 10 kOe is preferable. A more preferred range is 1 to 8 kOe.
[0032]
In a preferred embodiment of the present invention, the intensity of the magnetic field applied to the rare earth-containing alloy powder is made variable, and a high magnetic field and a low magnetic field are alternately applied. That is, by performing granulation while performing orientation with a low magnetization intensity that does not hinder the formation of the fluidized bed, and by applying a high magnetic field strength discontinuously, the degree of orientation of the primary particles is high, and the particle size distribution is high. A sharp, anisotropic granulated powder with excellent fluidity can be produced. As described above, the application of a high magnetic field discontinuously can be easily performed by increasing the current flowing through the electromagnet or shortening the distance between the permanent magnet and the fluidized bed. In a preferred embodiment, a solenoid coil is provided in addition to the electromagnet and the permanent magnet, and a pulse magnetic field is applied instantaneously by passing a pulse current.
[0033]
In the present invention, in order to form a fluidized bed of the raw material powder of ferrite magnet, a gas introduced into a fluidized tank from a gas supply port of an apparatus for producing anisotropic granulated powder, which will be described later, stirs the rare earth-containing alloy powder. To form a fluidized bed, to provide a rolling granulation effect, and to dry the binder solution. In order to prevent oxidation of the rare earth-containing alloy powder, it is preferable to use an inert gas such as a nitrogen gas or an argon gas. The rare earth-containing alloy is that the temperature of the gas is kept within the range of 0 to 30 ° C. during the formation of the fluidized bed and the binder solution is added, and the temperature is raised to 60 to 150 ° C. for a short time during the drying after the addition to quickly dry the alloy. It is preferable from the viewpoint of preventing oxidation of the powder.
[0034]
In the present invention, before adding the binder solution to the rare earth-containing alloy powder, kneading the organometallic compound in advance and performing a hydrophobic treatment for coating reduces the wettability between the rare earth-containing alloy powder and the solvent in the binder solution, Exhibits the effect of preventing oxidation due to the reaction between the rare earth-containing alloy powder and the solvent, facilitates the removal of the solvent in the drying process, shortens the drying time, and improves the fluidity of the obtained granulated powder Is preferred.
[0035]
As the organic metal compound for the hydrophobic treatment, in addition to zinc stearate, water-insoluble powders such as nickel stearate, calcium stearate, aluminum stearate, and copper stearate can be used. If the addition amount is less than 0.01 wt%, the effect of the hydrophobic treatment is not obtained, and if it exceeds 0.2 wt%, the amount of the metal component remaining in the sintered magnet increases, and the mechanical properties of the sintered body are increased. This is not preferred because the magnetic strength decreases and the magnetization decreases due to an increase in the nonmagnetic phase. Therefore, the addition amount of the organometallic compound for hydrophobic treatment is preferably 0.01 to 0.2 wt%. The method of adding the organometallic compound can be appropriately selected, for example, after the pulverization of the rare earth-containing alloy powder, or before the pulverization.
[0036]
The particle size of the anisotropic granulated powder obtained in the present invention is controlled by adjusting the production conditions such as the concentration and amount of the binder solution, the intensity of the applied magnetic field, the rotation speed of the stirring blade, and the gas flow rate. However, if the average particle size of the granulated powder is less than 20 μm, the fluidity of the granulated powder is hardly improved, and if the average particle size exceeds 400 μm, the particle size is too large and enters the mold during molding. Is not preferred because the packing density decreases and the compact density also decreases, resulting in a decrease in sintered density. Therefore, the average particle size of the granulated powder is preferably 20 to 400 μm. A more preferred range is 50 to 200 μm.
[0037]
Since the granulated powder obtained by the above-described production method of the present invention is in a magnetized state, the granulated powder is aggregated and the fluidity of the powder is reduced as it is. Therefore, it is necessary to demagnetize the granulated powder before molding.
It is preferable to use an alternating attenuation magnetic field for demagnetizing the granulated powder. The alternating attenuating magnetic field is a magnetic field in which the direction of the magnetic field is alternately switched in a forward direction and a reverse direction with the passage of time, and the maximum intensity thereof gradually decreases. The simplest way to generate an alternating attenuating magnetic field is to use a method such as gradually decreasing the current value while flowing the coil alternating current, or gradually increasing the distance between the coil and the degaussing object. it can.
[0038]
If the maximum strength of the alternating attenuation magnetic field exceeds the magnetic field strength at the time of granulation, the applied magnetic field tends to cause the anisotropic granulated powder to collapse. Therefore, it is preferable that the maximum strength does not exceed the magnetic field at the time of granulation. For example, when the rare-earth-containing alloy powder is granulated in a fluidized-granulation apparatus while orienting the rare-earth-containing alloy powder with a constant magnetic field of 1.5 kOe, the demagnetization treatment is performed in an alternating damping magnetic field whose maximum strength does not exceed 1.5 kOe. This is preferable in order to prevent the granulated powder from collapsing due to the demagnetizing magnetic field.
[0039]
If the frequency of the alternating attenuating magnetic field used for the demagnetization process is less than 1 Hz, the secondary particles of the granulated powder rotate and cannot be demagnetized, and if it exceeds 1 kHz, the domain wall movement in the primary particles becomes incomplete and demagnetization occurs. Therefore, the frequency is preferably in the range of 1 Hz to 1 kHz.
Although the attenuation rate of the alternating attenuation magnetic field is not particularly defined, it is preferable that the time required for the maximum magnetic field strength to become apparently zero is about 10 times or more the period corresponding to the frequency for effective demagnetization. .
[0040]
In the present invention, it is also a preferred embodiment that fluid granulation and demagnetization are performed by the same apparatus. For example, when the magnetic field is oriented by an electromagnet during granulation, the same electromagnet can be used to apply an alternating attenuating magnetic field to anisotropic granulated powder having remanence to demagnetize the powder.
[0041]
The residual magnetization of the anisotropic granulated powder after the demagnetization treatment according to the present invention is preferably 10 G or less from the viewpoint of fluidity. Such a low residual magnetization can be easily achieved by performing the above-described effective demagnetization processing.
[0042]
Further, by subjecting the demagnetized granulated powder to undercut and overcut by sieving, it is possible to obtain granulated powder having extremely high fluidity.
Further, when a small amount of a lubricant such as zinc stearate, magnesium stearate, calcium stearate, aluminum stearate, or polyethylene glycol is added to the obtained granulated powder, the fluidity can be further improved, which is effective.
[0043]
The step of manufacturing an anisotropic sintered magnet using the anisotropic granulated powder according to the present invention, that is, the method of molding, sintering, heat treatment and the like, employs any of known powder metallurgy means. can do. An example of preferable conditions is shown below. The molding can be performed by any known molding method, but is most preferably performed by compression molding in a magnetic field.
[0044]
As the magnetic field at the time of molding, a means such as a static magnetic field, a pulsed magnetic field, or a composite magnetic field thereof, and a method of alternately and continuously applying them can be adopted. The magnetic field strength is preferably 10 to 20 kOe. In particular, in the anisotropic granulated powder obtained according to the present invention, since the rare earth-containing alloy powder in each of the granulated powders is extremely well-oriented, the magnetic field necessary for the orientation is required when molding by applying a magnetic field. The strength may be lower compared to the granulated powder according to the prior art. For example, when forming a so-called radial ring magnet used in a thin cylindrical shape used for a small motor or the like and magnetized in a direction perpendicular to the radiation direction from the center of rotation, the orientation magnetic field strength during molding is 2 to 2 due to restrictions on the magnetic circuit. Although only 3 kOe can be applied, even in such a case, since the anisotropic granulated powder according to the present invention has excellent orientation, it is possible to produce a magnet having a high degree of orientation and a large surface magnetic flux. it can. Further, even in a normal orientation magnetic field of about 10 kOe, the superiority in the magnetic field orientation of the anisotropic granulated powder according to the present invention is evident. The maximum energy product can be obtained.
The molding pressure is not particularly limited, but 0.3 to 2.0 ton / cm. 2 Is preferred.
[0045]
Before sintering, it is preferable to perform a binder removal treatment. As a binder removal treatment method, in addition to a general method of heating in a vacuum, the temperature is raised at 100 to 200 ° C./h in a stream of hydrogen, A method such as holding at 300 to 600 ° C. for about 1 to 2 hours can be appropriately selected. By performing the binder removal treatment, the binder component in the compact is removed, the amount of residual carbon in the sintered body can be reduced, and the magnetic properties are improved.
[0046]
In addition, since the rare earth-containing alloy powder easily absorbs hydrogen, it is preferable to perform dehydrogenation after debinding in a hydrogen stream. As conditions for the dehydrogenation treatment, the stored hydrogen is almost completely removed by raising the temperature in a vacuum at 50 to 200 ° C./h and maintaining the temperature at 500 to 800 ° C. for about 1 to 2 hours.
[0047]
In addition, after the dehydrogenation treatment, it is preferable to perform sintering by heating and heating continuously, and the heating rate after exceeding 500 ° C. may be arbitrarily selected, such as 100 to 300 ° C./h. Well-known temperature raising conditions used for sintering can be adopted.
[0048]
The sintering of the molded body after the binder removal treatment and the heat treatment conditions after the sintering are appropriately selected according to the selected composition of the rare earth-containing alloy powder. The heat treatment is preferably performed at 450 to 800 ° C. for about 1 to 8 hours.
[0049]
The structure and operation of the anisotropic granulated powder production apparatus according to the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic explanatory view showing an example of an apparatus for producing anisotropic granulated powder according to the present invention, in which a magnetic circuit for applying a magnetic field to a rare earth-containing alloy powder is constituted by an electromagnet. FIG. 2 is a schematic explanatory view showing an example of an apparatus for producing anisotropic granulated powder according to the present invention, in which a magnetic circuit for applying a magnetic field to rare earth-containing alloy powder is constituted by permanent magnets.
[0050]
The apparatus for producing anisotropic granulated powder according to the present invention shown in FIG. 1 has a cylindrical fluidized tank having a
Explaining the operation, first, the rare earth-containing alloy powder is loaded on the
[0051]
The apparatus for producing anisotropic granulated powder according to the present invention shown in FIG. 2 has the same basic configuration as the apparatus shown in FIG. 1, and is an example in which permanent magnets are arranged instead of electromagnets. The
[0052]
In the present invention, since the rare earth-containing alloy powder to be granulated is very easily oxidized, an inert gas such as a nitrogen gas or an argon gas is preferably used as the gas. Further, it is preferable that the fluidized tank has a structure in which the inside can be replaced with an inert gas or the like and the oxygen concentration can be constantly controlled to 3 vol% or less.
[0053]
In a small-scale device, the inert gas can be disposable. However, in a large-scale device, it is economical to repeatedly use the inert gas in a closed circuit. In this case, since the inert gas that has passed through the fluidized tank contains the solvent in the binder solution, it is preferable that the gas is once passed through a cooler or the like to recover the solvent, and then circulated.
[0054]
In order to evaporate the solvent in the binder solution and instantaneously dry and solidify the granulated powder to prevent oxidation of the rare earth-containing alloy powder and improve the processing efficiency, it is necessary to heat the inert gas to be supplied. preferable. The heating means is not limited, but it is preferable that a heater is provided in front of the gas supply port to control the temperature of the inert gas in the range of 60 to 150 ° C., as shown in FIG.
[0055]
Further, in order to feed the inert gas heated by the heater into the fluidized vessel while maintaining the temperature of the inert gas as it is, it is also desirable to heat and maintain the temperature of the gas supply port at 60 to 150 ° C, particularly preferably around 100 ° C. Configuration. Further, even when the temperature difference between the gas supply port and the gas exhaust port is small, the processing efficiency tends to decrease, so that the temperature of the gas exhaust port is maintained at 50 ° C. or lower, more preferably 40 ° C. or lower, or room temperature. It is also preferable to do so.
[0056]
In the method of manufacturing anisotropic granulated powder using the above-described manufacturing apparatus, it is important to control the rotation speed of the stirring blade and the flow rate of the inert gas, and the state of the fluidized bed, particularly, the rotation speed of the rare earth-containing alloy powder, Therefore, the secondary particle diameter of the obtained granulated powder changes. In order to produce granulated powders having the same particle size distribution with good reproducibility, it is desirable that the composition be such that these can be efficiently controlled.
[0057]
In the present invention, when the binder solution is added to the fluidized bed, a fixed amount corresponding to the amount of the rare-earth-containing alloy powder is added from an injection port provided inside the fluidized tank. When added, the distribution of the binder becomes extremely non-uniform, and large lumps of granulated powder are likely to be generated. Therefore, it is preferable that a spray nozzle is disposed in front of the injection port to spray and add the binder solution. As the spray nozzle, a pressure nozzle, a two-fluid nozzle, or the like can be employed. Further, the spray position of the spray nozzle can be appropriately selected from a method of spraying the rare earth-containing alloy powder from the upper part of the fluidizing tank toward the rare earth-containing alloy powder and a method of directly spraying the rare earth-containing alloy powder into the fluidized bed.
[0058]
The feature of the apparatus for producing anisotropic granulated powder according to the present invention is that it has a configuration in which a magnetic field is applied to a rare earth-containing alloy powder in which a fluidized bed is formed by gas and stirring blades. Simultaneously, the binder solution is evaporated and the granulated powder is dried and solidified to obtain an anisotropic granulated powder.
[0059]
As a magnetic circuit for applying a magnetic field to the rare earth-containing alloy powder, one using an electromagnet shown in FIG. 1 or one using a permanent magnet shown in FIG. 2 can be employed. The permanent magnet has an advantage that the structure is simple and consumes no electric power, but has a disadvantage that a large-scale device is required to adjust the magnetic field strength. Conversely, an electromagnet has the advantage of being able to easily adjust the magnetic field strength during operation, but has the problem of consuming power. It is desirable to appropriately select which one to use depending on the production scale, the type of the rare earth-containing alloy powder, and the like.
[0060]
Further, the magnetic field strength of the magnetic circuit needs to be about 1 kOe or more, but in order to realize this with a permanent magnet, it is preferable to use a rare earth magnet or the like having high magnetic properties. Regardless of whether an electromagnet or a permanent magnet is employed as the magnetic circuit, it is desirable that the magnetic circuit be capable of applying a magnetic field to all positions where the fluidized bed of the rare earth-containing alloy powder is formed.
[0061]
In the present invention, if the orientation magnetic field by the magnetic circuit is too strong, the rare earth-containing alloy powder is fixed in the magnetic field as described above, and the formation of a fluidized bed is prevented. On the other hand, it is better to increase the magnetic field strength sufficiently to increase the degree of orientation. Therefore, it is also a preferable device configuration that the magnetic field intensity applied to the rare earth-containing alloy powder is made variable so that a high magnetic field and a low magnetic field can be alternately applied. That is, granulation proceeds while performing orientation at a low magnetic field strength that does not hinder the formation of a fluidized bed, and a high degree of magnetic field is applied discontinuously, whereby the degree of primary particle orientation is high and the particle size distribution is sharp. And anisotropic granulated powder having excellent fluidity can be produced. In this way, the intensity of the applied magnetic field can be increased discontinuously by increasing the value of the current flowing through the electromagnet or by shortening the distance between the permanent magnet and the fluidized bed.
[0062]
It is also preferable that a solenoid coil is provided in addition to the electromagnet and the permanent magnet, and a pulse magnetic field is applied instantaneously by passing a pulse current.
[0063]
【Example】
Example 1
A rare-earth-containing alloy was produced by high-frequency melting a raw material comprising 13.6 at% of Nd, 0.28 at% of Dy, 3.4 at% of Co, 6.5 at% of B, balance Fe and unavoidable impurities in argon gas. Next, after coarsely pulverizing the alloy, pulverize it to 420 μm or less with a jaw crusher and a disc mill, add and mix 0.05 wt% of zinc stearate, and further pulverize with a jet mill to contain a rare earth element having an average particle diameter of 3 μm. An alloy powder was obtained.
[0064]
1 kg of the obtained rare earth-containing alloy powder was loaded into the apparatus for producing anisotropic granulated powder according to the present invention shown in FIG. 1, and nitrogen gas at room temperature was supplied at a rate of 0.5 Nm / min. 3 While stirring, the stirring blade was rotated at 200 rpm to form a fluidized bed of the powder, and a current was applied to the electromagnet to apply a magnetic field of 2.0 kOe to orient the powder in the vertical direction of the rotation axis of the stirring blade. A 20 wt% aqueous solution of polyvinyl alcohol was spray-added to the powder at a constant rate. In this state, the powder was vigorously flowing in the fluidizing tank while being oriented in a needle shape.
[0065]
Next, when the ratio of the polyvinyl alcohol solute to the rare earth-containing alloy powder reaches 0.3 wt%, the spraying is stopped, the temperature of the nitrogen gas supply port is increased to 100 ° C., and drying is performed for 5 minutes. The rotation of and the energization of the electromagnet were stopped, and the inside of the fluidized tank was cooled. As a result, the needle-oriented powder gradually changed to a cigar-shaped anisotropic granulated powder while repeatedly solidifying with a binder, granulating, and crushing by stirring.
[0066]
Next, the obtained anisotropic granulated powder was placed in an alternating attenuating magnetic field having a maximum magnetic field of 2.0 kOe to be demagnetized. Then, the granulated powder after demagnetization was passed through a sieve having an opening of 250 μm to remove coarse particles and fine particles were passed through a sieve having an opening of 32 μm to obtain granulated powder having an average particle diameter of 105 μm. The yield in this operation was 93% by weight. The remanent magnetization of the granulated powder was 2.8 G. The powder flowability of the granulated powder whose particle size was selected was measured by the time required for 100 g of the powder to naturally fall and pass through a funnel-shaped tube having a minimum inner diameter of 8 mm. The results are shown in Table 1. It is shown in FIG.
[0067]
The granulated powder having the selected particle size is loaded into a powder feeding machine installed in a press in a magnetic field, and the granulated powder is naturally dropped into a cavity of a 10 mm long, 15 mm wide and 50 mm deep die. Then, while applying a magnetic field of 0, 3, 5, 8, and 11 kOe in parallel to the 10 mm side to orient the granulated powder, 1.5 Ton / cm in the depth direction. 2 , And molded. The obtained molded body is subjected to a binder removal treatment of heating from room temperature to 300 ° C. in a hydrogen atmosphere at a heating rate of 100 ° C./h, followed by sintering in which the temperature is raised to 1100 ° C. in vacuum and held for 1 hour. After completion of sintering, argon gas is introduced and cooled at a rate of 7 ° C./min to 800 ° C., then cooled at a rate of 100 ° C./h, and subjected to an aging treatment of holding at 550 ° C. for 2 hours. An isotropic sintered magnet was obtained. No cracks, cracks, deformations, etc. were observed in the obtained sintered magnet. Table 1 shows the relationship between the molding magnetic field and the magnetic properties of the sintered magnet. It is shown in FIG.
[0068]
Comparative Example 1
Under the same conditions as in Example 1, an isotropic granulated powder was produced without supplying electricity to the electromagnet, and the same particle size sorting as in Example 1 was performed without performing the demagnetizing treatment. The yield in this operation was 91% by weight. Further, the residual magnetization of the granulated powder after the particle size selection was below the measurement limit. The fluidity of the powder of the granulated powder having been subjected to particle size selection is shown in Table 1 as No. 1. It is shown in FIG.
Next, the granulated powder whose particle size has been selected is formed while changing the magnetic field by the same method as in Example 1, and then subjected to debinding, sintering and aging under the same conditions as in Example 1 to obtain a sintered magnet. Was. No cracks, cracks, deformations, etc. were observed in the obtained sintered magnet. Table 1 shows the relationship between the molding magnetic field and the magnetic properties of the sintered magnet. It is shown in FIG.
[0069]
Comparative Example 2
In Example 1, a raw material powder having an average particle size of 3 μm obtained by jet mill pulverization was molded without changing the magnetic field by the same method as in Example 1 without performing granulation. In the sintering, the temperature was raised to 1100 ° C. and held for 1 hour, and after completion of sintering, argon gas was introduced and cooled to 800 ° C. at a rate of 7 ° C./min, and then at a rate of 100 ° C./h. After cooling, aging treatment was performed at 550 ° C. for 2 hours to obtain an anisotropic sintered magnet. Table 1 shows the relationship between the molding magnetic field and the magnetic properties of the sintered magnet. 3 is shown. In addition, the fluidity of the powder after jet mill pulverization could not be measured because the powder did not flow at all.
[0070]
[Table 1]
As is clear from the measurement results in Table 1, the fluidity of the anisotropic granulated powder according to the present invention of Example 1 is much better than that of the raw material powder, and the orientation in a magnetic field is equal. Since it is superior to the isotropic granulated powder, it can be seen that high properties equivalent to the magnetic properties when the raw material powder is directly molded and sintered (Comparative Example 3) can be obtained in all the molding magnetic fields.
[0072]
Example 2
A raw material comprising Sm 11.9 at%, Cu 8.8 at%, Fe 12.6 at%, Zr 1.2 at%, balance Co and unavoidable impurities was subjected to high frequency melting in an argon gas to produce a rare earth-containing alloy. Next, after coarsely pulverizing the alloy, pulverize it to 420 μm or less with a jaw crusher and a disc mill, add and mix 0.05 wt% of zinc stearate, and further pulverize with a jet mill to contain a rare earth element having an average particle diameter of 3 μm. An alloy powder was obtained.
[0073]
1 kg of the obtained rare earth-containing alloy powder was loaded into the apparatus for producing anisotropic granulated powder according to the present invention shown in FIG. 2 and nitrogen gas at room temperature was supplied at a rate of 0.5 Nm / min. 3 The stirring blade was rotated at 200 rpm while flowing to form a fluidized bed of the powder, and the permanent magnet was rotated at the same height as the fluidized bed at 30 rpm in the opposite direction to the stirring blade, and a magnetic field of 1.5 kOe was applied. A 20 wt% ethanol solution of hydroxypropylcellulose was spray-added to the powder at a constant rate while vertically orienting the powder on the wall surface of the fluidized vessel. In this state, the powder was vigorously flowing in the fluidizing tank while being oriented in a needle shape.
[0074]
Next, when the ratio of the binder solute to the rare earth-containing alloy powder reaches 0.3 wt%, the spraying is stopped, the temperature of the nitrogen gas supply port is raised to 100 ° C., and drying is performed for 5 minutes. Was stopped and the permanent magnet was moved below the fluidized vessel to cool the inside of the fluidized vessel. As a result, the needle-oriented powder gradually changed to a cigar-shaped anisotropic granulated powder while repeatedly solidifying with a binder, granulating, and crushing by stirring.
[0075]
Next, the obtained anisotropic granulated powder was placed in an alternating attenuating magnetic field having a maximum magnetic field of 1.5 kOe to be demagnetized. Then, the granulated powder after demagnetization was sifted through a sieve having an opening of 250 μm to remove coarse particles, and fine particles were removed by sifting through a 32 μm opening to obtain granulated powder having an average particle diameter of 110 μm. The yield in this operation was 93% by weight. The remanent magnetization of the granulated powder was 3.9G. The powder flowability of the granulated powder whose particle size was selected was measured by the time required for 100 g of the powder to naturally fall and pass through a funnel-shaped tube having a minimum inner diameter of 8 mm. The results are shown in Table 2. It is shown in FIG.
[0076]
The granulated powder having the selected particle size is loaded into a powder feeding machine installed in a press in a magnetic field, and the granulated powder is naturally dropped into a cavity of a 10 mm long, 15 mm wide and 50 mm deep die. , Then a magnetic field strength of 10 kOe and 1.5 Ton / cm 2 , And molded. Table 20 shows the maximum and minimum values of the weight and height dimension of the molded bodies when 20 molded bodies were molded. It is shown in FIG.
[0077]
The obtained compact is subjected to a binder removal treatment in a hydrogen atmosphere from room temperature to 300 ° C. at a heating rate of 100 ° C./h, followed by sintering to raise the temperature to 1200 ° C. in vacuum and hold for 1 hour. After completion of sintering, a solution treatment was performed at 1160 ° C., and then an argon gas was introduced to perform a multi-stage aging treatment from 800 ° C. to 400 ° C. to obtain an anisotropic sintered magnet. No cracks, cracks, deformations, etc. were observed in the obtained sintered magnet. The average value of the magnetic properties of the obtained 20 sintered magnets was designated as No. It is shown in FIG.
[0078]
Comparative Example 3
An isotropic granulated powder was prepared under the same conditions as in Example 2 except that no magnetic field was applied by a permanent magnet, and the same particle size sorting as in Example 2 was performed without demagnetizing treatment. The yield in this operation was 89% by weight. The fluidity of the granulated powder having the selected particle size is shown in Table 2 as No. It is shown in FIG. Next, the granulated powder whose particle size was selected was molded in a magnetic field in the same manner as in Example 2. Table 20 shows the maximum and minimum values of the weight and height dimension of the molded bodies when 20 molded bodies were molded. It is shown in FIG. The obtained compact was subjected to binder removal treatment, sintering and aging treatment under the same conditions as in Example 2 to obtain a sintered magnet. No cracks, cracks, deformations, etc. were observed in the obtained sintered magnet. The average value of the magnetic properties of the obtained 20 sintered magnets was designated as No. It is shown in FIG.
[0079]
[Table 2]
As is evident from the measurement results in Table 2, the fluidity of the anisotropic granulated powder according to the present invention of Example 2 and the dimensional accuracy of the compact are equivalent to those of the isotropic granulated powder, and the magnetic properties Is much better.
[0081]
Example 3
Using the rare earth-containing alloy powder after demagnetization and particle size selection prepared in Example 1, the powder was loaded into a powder feeder installed in a press in a magnetic field, and the outer diameter was 10 mm, the inner diameter was 5 mm, and the depth was 30 mm. The granulated powder is supplied by gravity into the cavity of a cylindrical die having the following dimensions, and then a magnetic field of 2.5 kOe is applied in the thickness direction (radial direction) of the thickness of the cylinder to perform granulation. Orient the powder, 1.5 Ton / cm in the depth direction 2 Was applied to obtain a radial ring molded body. Table 3 shows the weights of the molded bodies and the maximum and minimum values of the dimension in the height direction when 20 molded bodies were molded. It is shown in FIG.
[0082]
The obtained molded body is subjected to a binder removal treatment of heating from room temperature to 300 ° C. in a hydrogen atmosphere at a heating rate of 100 ° C./h, followed by sintering in which the temperature is raised to 1100 ° C. in vacuum and held for 1 hour. After completion of sintering, argon gas is introduced and cooled at a rate of 7 ° C./min to 800 ° C., then cooled at a rate of 100 ° C./h, and subjected to an aging treatment of holding at 550 ° C. for 2 hours. A magnet was obtained. No cracks, cracks, deformations, etc. were observed in the obtained sintered magnet. The obtained 20 radial ring magnets were magnetized, and the average value of the surface magnetic flux densities on the outer periphery was measured. It is shown in FIG.
[0083]
Comparative Example 4
Using the isotropic granulated powder produced in Comparative Example 1 after the particle size selection, molding was performed in the same manner as in Example 3. Table 3 shows the weights of the molded bodies and the maximum and minimum values of the dimension in the height direction when 20 molded bodies were molded. It is shown in FIG. The obtained compact was subjected to binder removal treatment, sintering and aging treatment under the same conditions as in Example 3 to obtain a sintered magnet. No cracks, cracks, deformations, etc. were observed in the obtained sintered magnet. The obtained 20 radial ring magnets were magnetized, and the average value of the surface magnetic flux densities on the outer periphery was measured. It is shown in FIG.
[0084]
Comparative Example 5
In Example 1, an attempt was made to mold a raw material powder having an average particle diameter of 3 μm obtained by jet mill pulverization in the same manner as in Example 3 without performing granulation. However, the granulation powder was spontaneously dropped into the cavity of the cylindrical die from the powder feeder, but the raw material powder did not fall into the cavity at all because of the poor fluidity of the powder. Molding could not be performed.
[0085]
[Table 3]
As is evident from the results in Table 3, the fluidity of the anisotropic granulated powder according to the present invention and the dimensional accuracy at the time of molding are very good, so that molding is difficult or impossible with conventional raw material powder. Thin and small-sized products can be easily formed, and because of their excellent orientation in a magnetic field, they can be formed due to restrictions on magnetic circuits, such as the formation of radial rings. Even when the orientation magnetic field strength cannot be increased sufficiently, a high degree of orientation of the molded body can be realized, and a sintered magnet excellent in both magnetic properties and dimensional accuracy can be manufactured.
[0087]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to the manufacturing method and manufacturing apparatus of an anisotropic granulated powder according to the present invention, it is possible to obtain a granulated powder excellent in fluidity of the powder at the time of compression molding, to improve the dimensional accuracy of the compact and to improve the molding cycle Shortening can be achieved, and the magnetic field intensity applied at the time of granulation can be increased, and the degree of orientation of the primary particles contained in the granulated powder is high. Anisotropic granulated powder capable of producing a compact and a sintered body having excellent magnetic properties can be produced with good yield.
[Brief description of the drawings]
FIG. 1 is a schematic explanatory view showing an embodiment in which a magnetic circuit is constituted by electromagnets in an apparatus for producing anisotropic granulated powder according to the present invention.
FIG. 2 is a schematic explanatory view showing one embodiment in which a magnetic circuit is constituted by a permanent magnet in the apparatus for producing anisotropic granulated powder according to the present invention.
[Explanation of symbols]
1 fluidized tank
2 stirring blades
3 fan motor
4 heater
5 Gas inlet
6 spray nozzle
7 Bag Filter
8 Gas outlet
9 Electromagnet
10 permanent magnet
Claims (6)
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP31128596A JP3556786B2 (en) | 1996-11-06 | 1996-11-06 | Method and apparatus for producing anisotropic granulated powder |
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| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP31128596A JP3556786B2 (en) | 1996-11-06 | 1996-11-06 | Method and apparatus for producing anisotropic granulated powder |
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| JPH10140202A JPH10140202A (en) | 1998-05-26 |
| JP3556786B2 true JP3556786B2 (en) | 2004-08-25 |
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| US7622010B2 (en) | 2001-11-28 | 2009-11-24 | Hitachi Metals, Ltd. | Method and apparatus for producing granulated powder of rare earth alloy and method for producing rare earth alloy sintered compact |
| JP4609644B2 (en) * | 2005-02-23 | 2011-01-12 | Ｔｄｋ株式会社 | Manufacturing method of rare earth sintered magnet |
| JP4839899B2 (en) * | 2006-03-13 | 2011-12-21 | 住友金属鉱山株式会社 | Resin-bonded magnet composition, magnetic anisotropic bonded magnet using the same, and method for producing the same |
| JP4900121B2 (en) * | 2007-03-29 | 2012-03-21 | 日立化成工業株式会社 | Fluoride coat film forming treatment liquid and fluoride coat film forming method |
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