JP2004007960A

JP2004007960A - Polar anisotropic ring magnet

Info

Publication number: JP2004007960A
Application number: JP2003071550A
Authority: JP
Inventors: Yasuto Nozawa; 野澤　康人
Original assignee: Hitachi Metals Ltd
Current assignee: Proterial Ltd
Priority date: 2002-03-29
Filing date: 2003-03-17
Publication date: 2004-01-08
Anticipated expiration: 2023-03-17
Also published as: JP4320710B2

Abstract

<P>PROBLEM TO BE SOLVED: To provide a low-cost polar anisotropic ring magnet with less punctuation in intervals between magnetic poles and less cogging torque. <P>SOLUTION: The polar anisotropic ring magnet which is integrally molded with skew orientation comprises a plurality of magnetic poles parallel to an axis, with substantially no sintered body joint part after multi-stage molding. Specifically, the polar anisotropic ring magnet is integrally molded, and comprises magnetic poles which are parallel to the axis and magnetic poles which are spiral. The magnetic poles parallel to the axis and the spiral magnetic poles are continuously connected to the same pole. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、多段成形を行う必要のないらせん状の磁極部を有する高磁力の極異方性リング磁石に関する。
【０００２】
【従来の技術】
サーボモータ等の回転機にラジアル異方性リング磁石や極異方性リング磁石が多く使用されている。極異方性リング磁石を使用した場合、同一寸法のラジアルリング磁石に比べて高い表面磁束密度を得られ、小型でより高性能のモータを提供することができる。例えば特公平８−２８２９３号公報には極異方性を有するＲ−Ｆｅ−Ｂ系永久磁石の記載がある。
永久磁石を用いたモータにおいては、固定子と回転子との間の磁気抵抗が回転角によって変化するためにコギングが発生しやすい。特に磁石の磁極数が４〜８極と少ない場合にはコギングトルクが著しいものとなる。このコギングトルクは磁束密度の２乗に比例するので、コギングトルクを小さくするためには、ギャップ部の円周方向の磁束波形を滑らかにすることが必要である。ラジアル異方性リング磁石を使用する場合、着磁の際にスキュー着磁とすることによりコギングを抑制する手法が一般的である。
しかしながら表面磁束密度の高い極異方性リング磁石ではラジアルリング磁石と異なり、成形の配向時から着磁可能な方向が決まってしまう。配向は圧縮成形をしながら行うため成形体の磁極間のバラツキが出易く、また、着磁での調整を行うことができない。よってコギングを抑制するための対策が必要である。
例えば特公平８−２８２９３号公報には着磁極数Ｐが４〜８の極異方性リング磁石が記載され、また、各磁極部が軸線に対して一律に５°以上傾斜していることを特徴とする円筒状永久磁石の記載がある。しかしながら、この円筒状永久磁石を実際に製造すると、磁極部が軸に対して傾斜しているため、金型中で磁粉を配向しながら圧縮成形する際に、初期段階で配向した時の磁極部形状が圧縮されるにつれて形状を変えたり、磁極との磁気吸引力によって部分的に再度配向して配向が乱れるなどの問題があった。又、焼結時の収縮率のばらつきにより磁極同士の間隔およびスキュー角がばらつき、その結果モータのコギングトルクを一定にしづらいという欠点があった。
この対策として複数の極異方性磁石を用い、磁極をずらして軸方向に積層する例が見られる。特開平８−３４０６５２号には極異方性リング磁石を軸線方向に複数個に分割して磁極をずらしたあと着磁して、みかけのスキュー着磁をしたサーボモータの記載があるが、コギングトルクを小さくするためのずらし角度の制御に関する記載がない上、各々の磁石を固着する手間がかかる。極異方性リング磁石の個々での製造コストは安いがロータへの組み付け加工費が別途必要である。
また、特開平１１−８９６０号公報には、ずらし角度を制御するために磁界発生部の磁気センターを、複数個の治具間においてコギングトルクが逆位相になる角度だけずらした磁極ずらし治具を用いることによりずらし角度を制御している。この方式では治具から抜き出すときに磁石が回転しないように接着等の固定手段をとる必要があり生産性が悪い。
また、多段成形により極異方性リング磁石を製造するものを本発明者等により既に出願しており、その中で、多段成形時の第１の予備成形では通常の方法で極異方性に配向・成形した予備成形体を作成し、第２の予備成形において、この第１の予備成形とはことなる位置で磁極部を形成するように配向・成形し、みかけのスキュー着磁をした一体・長尺の極異方性リング磁石を提供している。しかしながら多段成形にて製造するため、成形歩留まりが悪化してコストが高くなるという問題があり、改善の余地を残していた。
【０００３】
【発明が解決しようとする課題】
よって本発明の課題は磁極同士の間隔のバラツキが少なくコギングトルクの小さいものを多段成形せず安価に得られる極異方性リング磁石を提供することである。
【０００４】
【課題を解決するための手段】
本発明者等は金型の磁気構造と成形の方法を工夫する事により、複数の磁石を一定角度ずらして接着するものと同じ効果を１個の磁石で再現性良く実現できる事を見出した。これにより高い表面磁束密度を保持しつつ、モータに組込んだときにコギングの小さい極異方性リング磁石を生産性の高い方法で再現性良く得る事が可能である。
つまり本発明は、スキュー配向された一体成形の極異方性リング磁石であって、軸に平行な磁極部を複数有し、かつ多段成形による接合部が実質的に存在しないことを特徴とする極異方性リング磁石を始めて製造可能としたものである。
ここで規定する多段成形による接合部があるか否かは軸方向に表面磁束密度を測定することで判別可能である。つまり一体成形であれば成形する際に磁粉の供給密度はほぼ一律になるため、焼結してもリング磁石の胴部分で密度が変わることがない。よって軸方向に磁極に沿って表面磁束密度を測定すると端部での表面磁束密度は落込むものの、胴部分で表面磁束密度が５％以上ばらつくことはない。多段成形になるとキャビティ中の磁粉がパンチにより複数回に分けて圧縮されるため、パンチにより押された部分と新たに磁粉が供給された部分で密度差が若干変わり、胴部分で表面磁束密度が５％以上さらには８％以上ばらつく。よってこの表面磁束密度を測定することによって多段成形か一体成形かの違いを判別可能である。
【０００５】
具体的な本発明の一形態として、一体成形された極異方性リング磁石であって、前記極異方性リング磁石は軸に平行な磁極部とらせん状の磁極部を具備し、前記軸に平行な磁極部とらせん状の磁極部は連続的に繋がっていることを特徴とするものである。
軸に平行な磁極部とらせん状の磁極部の組合せは様々なものが考えられ、特に限定されるものではないが、両端に軸に平行な磁極部が配置され、その間にらせん状の磁極部が配置されるものが最も製造するに好ましく、また顧客の要求特性を満足する上で好ましい。らせん状の磁極部（位後、らせん状磁極部とする）とは軸に対して平行ではなく、斜めに磁極部が配向された部分を指す。このらせん状磁極部の軸方向の幅はなるべく小さくすることが好ましく、平行な磁極部よりも短く配置するべきである。
また、配向ヨークのコイルの設置が容易であり、かつ高い配向磁束が得られるため配向度が高く表面磁束密度の高い極異方性リング磁石を得る事が可能である。特に配向度を高めても焼結割れが少ない希土類焼結磁石に有効である。また、ボンド磁石よりも成形圧縮率の高い粉末成形を行う焼結磁石に適用することで本発明の利点を最大限得る事ができる
【０００６】
ここで本発明の利点を図１、２および図７を用いて詳細に説明する。図２および図７中、１は金型、２は配向磁場を得るためのコイル、３は上パンチ、４は下パンチであり、上パンチ３、下パンチ４および金型１により囲まれたキャビティ内に成形材料５が充填している。また、図中６は成形時の配向による磁極と磁極の間を示す磁石中立線である。らせん状配向させた極異方性リング磁石を得る場合、従来の技術および図７で示したように軸に対して磁極部がほぼ一律傾斜するように配向すると、成形始めの段階（図７（ａ））では配向磁場に沿って成形材料５ａが配向されるが、上パンチ３と下パンチ４により成形材料５ａが圧縮された成形後の段階（図７（ｂ））では最初の配向磁場とは異なる角度に中立線６がひずむため、磁極間距離もこのひずみによりバラツキが出易い。成形材料が最終の成形品形状にまで圧縮させられた後に配向磁場をかけても成形材料は配向しない。逆に成形圧縮による磁極部のひずみを計算に入れて圧縮成形しようとすると、金型キャビティ内に入れる成形材料の量を厳密に制御する必要があり、工業生産上では実質困難である。
【０００７】
本発明の極異方性リング磁石では図１（模式的に円筒上で示す）に示すように、軸に平行な磁極部（以後、平行磁極部とする）ＡおよびＣを持つようにコイルが２ｂが金型内に具備される。これにより図２に示すように圧縮成形により成形材料が押し縮められても磁極部ＡおよびＣでの中立線の幅，方向は実質変わらず密度が向上するだけである。らせん状配向させた磁極部は従来に比べて僅かであり、磁極バラツキを抑制した極異方性リング磁石を製造可能である。
【０００８】
距離をあけずに相互の平行磁極部同士を接合すると、焼結時の収縮率による割れが発生しやすい。これを抑制するためにはある程度のらせん状配向させた磁極部の幅を設けることが好ましい。当然ながら磁極部は連続するように平行磁極部とらせん状磁極部を並べればこの焼結時の収縮率による割れをさらに低減できる。この際の配向コイルは図１に示す中立線６に重なるように金型内に巻線すればよく、極異方性リング磁石の端部から端部まで通して１磁極１つのコイルで構成可能である。
【０００９】
上記製法により図１に示すような磁極の位置および反転位置（中立線）が軸線方向に平行で、途中周方向に斜めに走る極異方性リング磁石が得られる。成形の際には、らせん状配向する位置の磁粉が金型に対して動かないようにキャビティ中の磁粉を両端から同じ距離だけ押しこむ圧縮成形をすることにより、配向の乱れが非常に小さい、一定のずれ角を有する一体型の極異方性磁石を得られる。
【００１０】
図１中の中間部分Ｂの軸方向の長さは磁極間のバラツキが出易いので短い方が好ましいが、あまりに短いと焼結時の収縮率による割れを抑制できなくなる。成形材料、配向度などにより適宜選択する必要がある。例えばＲ−Ｔ−Ｂ系磁石において、らせん状磁極部の軸方向に対する傾斜角度αは８５°以下が好ましい。好ましい傾斜角度は８０°以下、さらに好ましくは７０°以下である。軸方向の幅は０．３ｍｍ以上とすることが好ましい。
また、比較的焼結割れしやすいフェライト磁石において、傾斜角度αは６０°以下が好ましい。好ましい傾斜角度は５５°以下、さらに好ましくは４５°以下である。軸方向の幅は０．５ｍｍ以上とすることが好ましい。
多段成形のものと比較すると１つの成形機に対する単位時間での成形個数が大幅に向上し、多段成形品よりも磁極部のバラツキを抑制可能である。
【００１１】
ただし、ボンド磁石であれば成形後の効果工程を行っても収縮率による割れは発生しずらい。よって図８に示すような中立線をもつ極異方性リング磁石を得ることが可能である。また、配向磁場を低目にかけ、収縮割れを抑制することも可能である。これによりコギングトルクの小さい極異方性リング磁石を得ることができる。この方法であれば一体成形でありながららせん状磁極部が実質的に存在しない極異方性リング磁石が得られる。
【００１２】
本発明の極異方性を有するリング磁石は例えば以下の工程により製造される。
▲１▼焼結磁石：原料粉作製−給粉−配向−圧密化−焼結（必要により熱処理、加工、表面処理が追加される）
▲２▼ボンデッド磁石
（圧縮成形）：原料コンパウンド作製−給粉−配向−圧密化−硬化（必要により加工、表面処理が追加される）
（射出成形）：原料コンパウンド作製−射出（配向＋圧密化）−冷却（必要により加工、表面処理が追加される）
【００１３】
本発明の極異方性リング磁石を幾何学的に示す。図１に示したようにリング磁石の中心軸をｒ−θ−ｚ円筒座標系のｚ軸に一致させ、磁石の一端をｚ＝０平面に接触させ、前記リング磁石をｚ軸に垂直に仮想的に３分割しＺの小さい方からＡ，Ｂ，Ｃと名づけたとき、Ａの磁極部のθ成分がｚ軸方向にほぼ一定のθａで、反対端Ｃの対応する磁極部のθ成分がｚ軸方向にほぼ一定のθｃで、中間部分（らせん状磁極部）Ｂの磁化困難方向がθａからθｃに連続的に変化していることを特徴とするものである。また、前記ＡおよびＢの磁極部のθ成分の絶対値｜θｃ−θａ｜（ずらし角）がＡおよびＢの平均極間角度の５％以上５０％以下である。
【００１４】
前記リング磁石がＲ_２Ｔ_１４Ｂ金属間化合物（ＲはＹを含む希土類元素の少なくとも１種であり、ＴはＦｅ又はＦｅ及びＣｏである）を主相とする焼結磁石からなる場合に高い回転機特性になり実用性が高い。
前記リング磁石がＲ_２Ｔ_１４Ｂ金属間化合物またはＲ−Ｔ−Ｎ金属間化合物（ＲはＹを含む希土類元素の少なくとも１種であり、ＴはＦｅ又はＦｅ及びＣｏである）を主相とする異方性磁粉を結合剤で結合したボンデッド磁石からなる場合に焼結磁石よりも薄肉化が容易、加工が不要のためコストパフォーマンスが高い利点を有する。
又前記リング磁石がフェライト焼結磁石からなる場合にコストパフォーマンスのよい回転機を構成することができる。
又前記リング磁石がフェライトを主相とする異方性磁粉を結合剤で結合したボンデッド磁石からなる場合にコストパフォーマンスのよい回転機を構成することができる。
コギングを小さくするためには、らせん状磁極部の軸方向の長さが全長の１〜３０％以下であることが望ましく、Ｒ_２Ｔ_１４Ｂ金属間化合物（ＲはＹを含む希土類元素の少なくとも１種であり、ＴはＦｅ又はＦｅ及びＣｏである）を主相とする焼結磁石またはフェライト磁石に適用する事ができる。
【００１５】
【発明の実施の形態】
図２は本発明に用いる金型の断面模式図である（但し、磁粉の配向方向を示すためキャビティ部分は極異方性リング磁石の側面の配向状態を示す）。磁粉を円筒状の金型１内に給粉後、上パンチ３と下パンチ４を所定の位置に配置する。その後磁粉の外周面に接する金型側面に周方向に周期的にＮ極とＳ極を発生させる。このＮ極とＳ極は軸方向に対して傾斜が実質的に０°である平行磁極部とらせん状磁極部がある。コイル２ｂは極間の中立線上部に巻き回されるように金型内に配置されている。磁場の発生源としてはコイルに流すパルス電流、定常電流、また永久磁石などを利用する事ができる。それらの極が作り出す磁場の中で、磁粉はエネルギー的に安定な方向に回転、移動する。この操作により作り出された磁粉の配列パターンが一定方向に揃い配向される。配向された磁粉を上パンチ３および下パンチ４により軸方向に圧密化する事で成形工程が完了する。その際平行磁極部の互いの長さが一定の長さとなるように上パンチ３および下パンチ４の両方を同様に稼動させて、両方からパンチを押し込むように稼動させた。その後の取り扱いを容易にするために圧密化の後で弱い逆磁場を印加して脱磁した。
【００１６】
極異方性磁石の一例においては、磁極間の磁束は図３に示すように磁石中を円弧状に流れ、しかも磁気異方性をもった粒子が実質的に円弧に沿って配列される。極異方性磁石では配向により磁化されやすい方向が決まっており、着磁後の表面磁束密度を周方向に測定すると、磁束密度の周期的なピークが観察される。中立線は磁極が切り替わる位置をつないだ線として定義できる。この線はマグネットビューワを用いて製品着磁後に見る事ができる。また、着磁された微小磁石との吸引力測定、Ｘ線やカー効果を利用した観察により、製品着磁前の状態であっても中立線を測定可能である。
８極異方性Ｒ_２Ｔ_１４Ｂ焼結磁石の中立線を測定し、θ−ｚ座標に展開した結果を図４に示す。ｚ軸に平行な２本の線分の端面がｚ軸に平行でない線で連結されている。このような中立線は極数に等しい数存在する。屈曲点を通るθ軸に平行な２本の直線を引くことによりθの異なる３つの領域に分ける事ができる。ｚの小さいほうからＡ，Ｂ，Ｃと名づける。
Ａの領域ではθｍ＝θａ＋２πｍ÷ｎ（ｎは極数、ｍは０からｎまでの整数）
Ｃの領域ではθｍ＝θｃ＋２πｍ÷ｎ（ｎは極数、ｍは０からｎまでの整数）
で表現できる。らせん状磁極部Ｂの領域では平行磁極部ＡとＣの中間遷移状態である。
以下ｍ＝０の中立線のみ言及するが、それ以外のｍ値でも同様である。
θａ、θｃは生産上避けられないばらつきを含む事ができる。典型的なばらつきの値は極間角度の３％以内、さらには２％以内である。Ｂの領域では中立線がθａとθｃをつなぐように連続的に変化する。金型製作上は磁極が曲るところで巻線の太さに応じた滑らかな変化でつなぐ事が望ましい。
らせん状磁極部Ｂの軸方向の長さは全長の１％以上４０％以下である事が望ましい。らせん状磁極部Ｂが１％未満では磁化方向の変化が急すぎて、磁化容易方向と磁化困難方向の焼結工程における収縮率の差、焼結、熱処理の冷却時に磁化容易方向と磁化困難方向の熱膨張係数の差によって熱応力が発生し、クラックが入りやすい。らせん状磁極部Ｂが４０％を超えると、傾斜磁極の効果で配向を乱す割合が増えるために、コギングトルクがばらつきやすい。
らせん状磁極部Ｂの長さＨは以下のように簡易的に定義できる。マグネットビュワーシートを使用してらせん状磁極部Ｂの中立線と軸線の傾きαを求める。磁石の直径をＤ，極数をｎとすると極幅ｗは
ｗ＝πＤ÷ｎ
で表され、Ｈは以下の式で表される。
Ｈ＝ｗ÷ｔａｎα＝πＤ÷ｎ÷ｔａｎα
上記の方法によりらせん状磁極部Ｂの長さを知る事ができる。
両端の中立線の角度差（θｃ−θａ）の絶対値が平均極間角度の５％以上５０％以下に既定した理由は５％未満ではほとんどコギング低減効果がないためである。５０％以上ではモータートルクが８０％以下になり、実用に供し得ない。モータをゆっくり回転させたときのコギングトルクの波形はロータ極数ｎとステータ極数ｐの最小公倍数Ｍの山と同数の谷を有する事が多い。従って、望ましい中立線の角度差｜θｃ−θａ｜≦２π／Ｍとなる。
【００１７】
製品を着磁する時、弱い磁場を発生させる予備着磁と強い磁場を発生させる本着磁の２回に分ける事により、予備着磁でエネルギー的に安定な方向に磁石を回転させ、本着磁で十分に着磁する事が可能である。位置あわせマークをもとに着磁ヨークにセットするか、永久磁石を組込んで自発的に磁化容易方向に配置する着磁ヨークを使用すれば予備着磁を省略しても問題ない。
【００１８】
次に本発明のリング磁石の構成と数値の限定理由を説明する。以下単に％と記してあるのはｍａｓｓ％を意味するものとする。
本発明の極異方性リング磁石は例えばＲ_２Ｔ_１４Ｂ金属間化合物（ＲはＹを含む希土類元素の少なくとも１種であり、ＴはＦｅ又はＦｅ及びＣｏである）を主相とする焼結磁石またはボンデッド磁石である場合、主要成分のＲ、Ｔ及びＢの総計を１００％として、Ｒ：２７〜３４％、Ｂ：０．５〜２％、残部Ｔ（ＴはＦｅ又はＦｅ及びＣｏである）からなる組成が選択される。
Ｒ_２Ｔ_１４Ｂ金属間化合物で極異方性焼結リング磁石を製造する場合、リング磁石の質量を１００％としたとき、不可避的不純物として０．６％以下、好ましくは０．３％以下、より好ましくは０．２％未満の酸素、０．３％以下、好ましくは０．１％以下の炭素、０．０８％以下の窒素、０．０２％以下の水素、０．２％以下、好ましくは０．０５％以下、より好ましくは０．０２％以下のＣａの含有が許容される。
Ｒとして（Ｎｄ、Ｄｙ）、（Ｐｒ、Ｄｙ）、又は（Ｎｄ、Ｐｒ、Ｄｙ）の組合せが実用性が高い。又Ｒ量は２７〜３４％が好ましい。Ｄｙの一部をＴｂで置換しても良い。Ｒ量が２７％未満では固有保磁力ｉＨｃの低下が顕著になり、３４％超では残留磁束密度Ｂｒ、最大エネルギー積（ＢＨ）ｍａｘが大きく低下する。
Ｂ量は０．５〜２％が好ましく、０．８〜１．２％がより好ましい。Ｂ量が０．５％未満では実用に耐えるｉＨｃを得られず、２％超ではＢｒ、（ＢＨ）ｍａｘが大きく低下する。Ｂの一部がＣで置換可能な事は公知であり、本発明にも適用可能である。
表面磁束密度や耐食性を向上するために、Ｎｂ，Ａｌ，Ｃｏ，Ｇａ及びＣｕの群から選択される少なくとも１種の元素を適量含有することが好ましい。
Ｎｂの含有量は０．１〜２％が好ましい。Ｎｂの含有により焼結過程でＮｂのほう化物が生成し、結晶粒の異常粒成長が抑制できる。Ｎｂ含有量が０．１％未満では添加効果が認められず、２％超ではＮｂのほう化物の生成量が多くなりＢｒの低下が顕著になる。
Ａｌの含有量は０．０２〜２％が好ましい。Ａｌ含有量が０．０２％未満ではｉＨｃや耐食性の向上効果を得られず、２％超ではＢｒ、（ＢＨ）ｍａｘが顕著に低下する。
Ｃｏ含有量は０．３〜５％が好ましい。Ｃｏ含有量が０．３％未満ではキュリー点や耐食性を向上する効果が得られず、５％超ではＢｒ、ｉＨｃが共に大きく低下する。Ｇａ含有量は０．０１〜０．５％が好ましい。Ｇａ含有量が０．０１％未満ではｉＨｃの向上効果を得られず、０．５％超ではＢｒ、（ＢＨ）ｍａｘの低下が顕著になる。
Ｃｕ含有量は０．０１〜１％が好ましい。Ｃｕ含有量が０．０１％未満では耐食性やｉＨｃを向上する効果を得られず、１％超ではＢｒの低下が顕著になる。
Ｃｕ及びＣｏが前記特定量範囲で共に含有されるとき、第２次熱処理の許容温度幅が広がる効果を得られ好ましい。
本発明がＲ_２Ｔ_１４Ｂ金属間化合物（ＲはＹを含む希土類元素の少なくとも１種であり、ＴはＦｅ又はＦｅ及びＣｏである）を主相とする異方性磁粉を結合剤で結合したボンデッド磁石である場合、平均結晶粒径０．０１〜０．５μｍであり、
熱間加工やＨＤＤＲ等の方法で異方性を付与した磁粉を用いる事が望ましい。結合材としては公知の材料である、ゴム、ナイロン、エポキシ、ＰＰＳ他のプラスチック材料または亜鉛や低融点合金を用いる事ができる。
本発明がＲ−Ｔ−Ｎ金属間化合物（ＲはＹを含む希土類元素の少なくとも１種であり、ＴはＦｅ又はＦｅ及びＣｏである）を主相とする異方性磁粉を結合剤で結合したボンデッド磁石である場合、Ｓｍ−Ｆｅ−Ｎで知られる金属間化合物であり、平均１から１０μｍ粉砕された異方性微粉を用いる事が望ましい。磁気特性を大幅に悪化させない添加物および不可避不純物は許容される。結合材としては公知の材料である、ゴム、ナイロン、エポキシ、ＰＰＳ他のプラスチック材料または亜鉛や低融点合金を用いる事ができる。
【００１９】
本発明の極異方性リング磁石を公知のフェライト磁石で作製すればコストパーフォーマンス上好ましい。
特に　（Ａ_１−ｘＲ’_ｘ）Ｏ・ｎ［（Ｆｅ_１−ｙＭ_ｙ）_２Ｏ_３］（原子比率）
（但し、ＡはＳｒ及び／又はＢａであり、Ｒ’はＹを含む希土類元素の少なくとも１種でありＬａを必ず含み、ＭはＣｏ又はＣｏ及びＺｎであり、ｘ，ｙ及びｎはそれぞれ下記条件：
５．０≦ｎ≦６．４
０．０１≦ｘ≦０．４，及び
０．００５≦ｙ≦０．０４
を満たす数字である。）により表される主要成分組成を有し、マグネトプランバイト型結晶構造を有する高性能フェライト磁石からなる焼結リング磁石を用いた場合に回転機性能を高められるので好ましい。
飽和磁化を高めるために、Ｒ’に占めるＬａの比率を、好ましくは５０原子％以上、より好ましくは７０原子％以上、特に好ましくは９９原子％以上とするのがよい。理想的には不可避的Ｒ’成分を除いてＲ’がＬａからなるのがよい。従って、Ｒ’元素供給原料として、Ｌａを５０原子％以上含み、残部がＰｒ、Ｎｄ及びＣｅの少なくとも１種並びに不可避的Ｒ’成分からなる安価なミッシュメタルの酸化物を用いるのが実用的である。その場合のＲ’はＬａとＮｄ、Ｐｒ及びＣｅの少なくとも１種と不可避的Ｒ’成分とで構成される。
モル比ｎは５．０〜６．４とする必要があり、５．５〜６．３がより好ましく、５．７〜６．２が特に好ましい。ｎが６．４超ではマグネトプランバイト相以外の異相（α−Ｆｅ_２Ｏ_３等）の存在によりｉＨｃが大きく低下し、ｎが５．０未満ではＢｒが大きく低下する。
ｘは０．０１〜０．４が好ましく、０．１〜０．３がより好ましく、０．１５〜０．２５が特に好ましい。ｘが０．０１未満では添加効果が認められず、０．４超では表面磁束密度が大きく低下する。
ｙとｘとの間には、電荷補償のために理想的には　ｙ＝ｘ／（２．０ｎ）　の関係が成立する必要があるが、ｙがｘ／（２．６ｎ）以上、ｘ／（１．６ｎ）以下であれば高いＢｒ及び高い減磁曲線の角形を具備するフェライト磁石を得られる。なお、ｙがｘ／（２．０ｎ）からずれた場合、Ｆｅ^２＋を含む場合があるが、何ら支障はない。典型的な例では、ｙの好ましい範囲は０．０４以下であり、特に０．００５〜０．０３である。
又、５．７≦ｎ≦６．２，０．２≦ｘ≦０．３及び１．０＜ｘ／２ｎｙ≦１．３　というＲ’過剰の主要成分組成を選択し、かつＣａＯ含有量が０．５〜１．５％及びＳｉＯ_２含有量が０．２５〜０．５５％のときに従来に比べて減磁曲線の角形を顕著に高めることができる。
緻密なフェライト焼結磁石を得るために焼結性を制御する添加物としてＳｉＯ_２及びＣａＯ（ＣａＣＯ_３）を所定量含有することが実用上重要である。
ＳｉＯ_２は焼結時の結晶粒成長を抑制する添加物であり、前記フェライト磁石の総ｍａｓｓを１００％としてＳｉＯ_２含有量を０．０５〜０．５５％にすることが好ましく、０．２５〜０．５５％がより好ましい。ＳｉＯ_２含有量が０．０５％未満では焼結時に結晶粒成長が過度に進行し保磁力が大きく低下し、０．５５％超では結晶粒成長が過度に抑制され結晶粒成長による配向度の改善が不十分となりＢｒが大きく低下する。
ＣａＯは結晶粒成長を促進する添加物であり、前記フェライト磁石の総ｍａｓｓを１００ｍａｓｓ％としてＣａＯ含有量は０．３５〜１．５％が好ましく、０．４〜１．５％がより好ましく、０．５〜１．５％が特に好ましい。ＣａＯ含有量が１．５％超では焼結時に結晶粒成長が過度に進行し、保磁力が大きく低下し、０．３５％未満では結晶粒成長が過度に抑制され、結晶粒成長による配向度の改善が不十分となりＢｒが大きく低下する。
本発明が公知のフェライトを主相とする異方性磁粉を結合剤で結合したボンデッド磁石である場合、コストパーフォーマンス上好ましい。
【００２０】
本発明の焼結リング磁石の成形は例えば図３の成形金型１（対称８極極異方性配向用）を備えたプレス機により行う。図３中、実線は図２（ｂ）でのＡ−Ａ断面、破線はＢ−Ｂ断面でのコイル位置である。成形金型１において、７は強磁性体からなるダイスであり、８はダイス７の環状空間内に同心状に配置された非磁性体からなる円形断面を有するコアである。ダイス７の円筒状内面には複数の溝１２が形成されており、各溝１２中に磁場発生用コイル２ｂが埋設されている。磁場発生用コイル２ｂは途中にらせん状磁極部を作るための屈曲部を有している。ダイス７の内周面上には溝１２を覆うようにしてコア８と相似形の円形断面を有する非磁性体製のスペーサ９が設けてある。スペーサ９とコア８との間がキャビティ１０である。各コイル２ｂに電流が通電されるとキャビティ１０に矢印で示される磁束が生じスペーサ９のコーナー部にＮ，Ｓ，Ｎ，Ｓ・・という交互の極性磁極が形成される。
次に図３の成形金型１により本発明の焼結リング磁石用成形体を成形する方法の一例を説明する。まず図２の上パンチ３を引き上げた状態で振動フィーダー等の供給手段により、キャビティ内に所定量の原料粉末又はスラリーを充填する。次いでコイル２ｂにパルス電流を通電し、焼結磁石用微粉末又はスラリーを配向させた状態としそのまま上パンチ３を下降させ、らせん状磁極部を中心に下パンチ４と対照となる位置まで下降させる。その後は下パンチ４と上パンチ３を同様のスピード、加圧力でキャビティ方向に加圧し、極異方性リング磁石の成形体を得る。また、上パンチ３の加圧の際、ダイスを上パンチ３の半分のスピードで下降させることで上記と同様に軸方向に左右対象な長さの平行磁極部を得る事が可能である。
印加する極異方性配向磁場強度は極力高くするのが好ましいが通常０．４〜２．０ＭＡ／ｍ（５〜２５ｋＯｅ）とされる。配向磁場強度が０．４ＭＡ／ｍ未満では配向が不十分になり、工業生産上２．０ＭＡ／ｍ超の高い配向磁場強度を確保するのは困難である。亀裂を抑制し、所定の配向度を得るために圧縮成形の圧力はＲ−Ｔ−Ｂ系焼結磁石用成形体の場合４９〜３９２ＭＰａ（５００〜４０００ｋｇ／ｃｍ^２）とし、フェライト磁石用成形体の場合２９〜３９ＭＰａ（３００〜４００　ｋｇ／ｃｍ^２）とするのが好ましい。
【００２１】
成形機がサーボモータを使用したサーボプレスである場合や、カムを使用したメカプレスである場合、もしくは数値制御された油圧シリンダを有する油圧プレスである場合、下パンチを上パンチの移動に対して逆方向に動かす、またはダイスを上パンチの移動に対して同方向に動かす事により、金型内の原料が上下方向に移動しない場所（以下ニュートラルラインと呼ぶ）を設定する事ができる。
本発明者は金型のらせん状配向部の中央と前記ニュートラルラインを一致させる制御を行う事により、らせん状配向部を成形する金型の位置で原料の上下移動を最小化する事ができる事を考案し、実験を行うことによって有効性を確認した。
【００２２】
さらに焼結磁石や圧縮成形によるボンド磁石の製造においてはアンダーフィル作動を組み合わせる事によりらせん状配向部で隔てられた平行磁極部Ａ，Ｃ部分とＢ部分の長さを変更できることも見出した。アンダーフィル作動とは原料をキャビティー内に充填した後、上パンチが加圧する前にダイスと下パンチの相対位置を動かして原料粉を金型内部に送り込む手法である。アンダーフィルによって磁石長さが異なる中間位置Ｂを磁石中央でない位置にもってくる事ができる。この事は同一金型を用いて総トルク重視かコギングトルク重視の調整が可能である事を意味する。
また、アンダーフィルの利用により同一のずらし角を有する軸方向の寸法が異なる磁石を作製可能である。
【００２３】
Ｒ−Ｔ−Ｂ系焼結磁石用成形体の場合は成形体密度：３．７〜４．６Ｍｇ／ｍ^３程度であり、フェライト焼結磁石用成形体の場合は成形体密度：２．６〜３．２Ｍｇ／ｍ^３程度に調整される。Ｒ−Ｔ−Ｂボンデッド磁石やＲ−Ｔ−Ｎボンデッド磁石の場合は、圧縮成形では５．５〜６．５Ｍｇ／ｍ^３程度に、射出成形では４．０〜５．７Ｍｇ／ｍ^３程度に調整される。フェライトボンデッド磁石の射出成形では２．６〜３．６Ｍｇ／ｍ^３程度に調整される。次に得られた本圧縮成形体を加圧した状態のままコイル５６に上記と逆方向のパルス電流を通電して脱磁する。ボンデッド磁石では磁粉付着が耐食性やコンタミネーション等の信頼性に影響するため脱磁と除粉が重要である。
【００２４】
本発明の焼結リング磁石の寸法は特に限定されないが、軸方向長さ（Ｌ）及び外径寸法（Ｄｏ）がそれぞれ、Ｌ＝５〜１００ｍｍ、好ましくはＬ＝８〜５０ｍｍでありかつ　　Ｄｏ＝３〜２００ｍｍ、好ましくはＤｏ＝７〜５０ｍｍのものの実用性が高い。Ｄｏ＜３ｍｍのものに極異方性を付与することは事実上困難であり、Ｄｏ＞２００ｍｍ　の焼結リング磁石は小型化のニーズに適合しない。又Ｌ＜５ｍｍでは中央の従来の１段成形品との有意差がなく、Ｌ＞１００ｍｍのものは小型化のニーズに適合しない。
本発明の焼結リング磁石の磁極数は特に限定されないが、外径面又は内径面の周方向に等間隔又は異なる間隔で４〜１００極、好ましくは４〜２４極形成するのが実用性が高い。コギングトルクのバラツキは２．５％以内とすることが可能である。
【００２５】
以下、実施例により本発明を詳細に説明するが、それら実施例により本発明が限定されるものではない。
（実施例１）
Ｎｄ：３０．５ｍａｓｓ％、Ｄｙ：１．５ｍａｓｓ％、Ｇａ：０．１ｍａｓｓ％、Ｂ：１．０ｍａｓｓ％、Ｆｅ：６４．８ｍａｓｓ％の主要成分組成を有する合金粗粉を不活性ガス雰囲気中でジェットミル微粉砕し、平均粒径４．５μｍ（Ｆ．Ｓ．Ｓ．Ｓ．）の焼結磁石用微粉を得た。この焼結磁石用微粉のかさ密度を測定したところ１．７Ｍｇ／ｍ^３であった。次に、図１に示すらせん状の磁極部配向が可能な図２の成形金型を用い、上ラムとダイスの動きを数値制御できるサーボプレスにより、まず上パンチを引き上げた状態でキャビティ内に所定量の前記微粉末を充填した。金型は８極異方性型でずらし角１１度である。充填された原料の中央が金型屈曲部に一致するようにアンダーフィル作動を行なった。キャビティに磁極あたり５．０ｋＡターンのパルス電流で極異方性磁場を間欠的に３回印加した状態としながら上パンチを下降させた。このときダイスを上パンチの半分の速度で下降させながら、圧縮成形を行い、下パンチを実質的にキャビティ方向へ加圧した状態とした。その後脱磁し、得られた本成形体の密度は４．２Ｍｇ／ｍ^３であった。
次に、本成形体を約０．０７Ｐａ（５×１０^−４Ｔｏｒｒ）の真空中、１１００℃で２時間焼結し、室温まで冷却した。次にＡｒ雰囲気中で５５０℃×２時間の第２次熱処理を行い室温まで冷却した。次に、端面及び外周面を加工（内径面は無加工）し、電着により熱硬化性樹脂（エポキシ樹脂）をコーティングし、外径１４ｍｍ、内径９ｍｍ、軸方向長さ１５ｍｍの対称８極極異方性リング磁石を得た。次に極異方性付与方向に沿って総磁束量が飽和する条件で着磁し、周方向に表面磁束密度を測定した。
測定場所は軸方向端面から２．５ｍｍステップで５箇所測定した。上の２箇所と下の２箇所のずらし角１１度に対応するデータを得た。波形形状を図５に示す。図４における平行磁極部（Ａ）では２箇所とも同様なほぼ正弦波の波形形状が、下の平行磁極部（Ｃ）では（Ａ）の波形形状と比較して１１度異相した以外は実質的に同等な波形形状が得られた。また、らせん状磁極部Ｂのデータは両者の中間であった。またらせん状磁極部Ｂの長さは３．０ｍｍで、全体の長さの２０％であった。この極異方性リング磁石のコギングトルクのバラツキを測定したところ、２％と非常に小さい値であった。コギングトルクのバラツキの測定は、極異方性リング磁石をロータコアと組み付け、そのロータに対応するステータに入れた後に１回転させた時の各コギング毎のトルクのバラツキを計り、それを試料数２０個のサンプルで行い平均値を取ったものである。
又、図１に示すように得られた対称８極極異方性リング磁石を図６に示すようにシャフト１上に固定し、回転子５を構成し、所定の回転機に組み込んだところ有用な回転機性能が得られた。
【００２６】
（比較例１）
前記らせん状磁極部の長さを殆ど取らずに検討を行った。外見上、複数の極異方性磁石をずらし角１１度で固着させたように製造し、（らせん状磁極部の長さ約０．１ｍｍ）の極異方性リング磁石の成形体を得た。前記成形体を１１００度にて２時間焼結したところ、このらせん状磁極部からひびが入り焼結割れを起してしまい使用に耐えなかった。
【００２７】
（比較例２）
前記らせん状磁極部の長さを各々の平行磁極部よりも長くして検討を行った。平行磁極部の長さを互いに４ｍｍづつ、らせん状磁極部を磁極部が平行磁極部と磁極が連続したらせん状磁極部として長さを７ｍｍとした。それ以外は実施例１と同様にして極異方性リング磁石を製造した。この極異方性リング磁石（Ｎ＝５０）のコギングトルクのバラツキを測定したところ、約１０％と大きい値であった。この極異方性リング磁石を実施例１と同様にしてシャフト１上に固定し、回転子５を構成し、所定の回転機に組み込むことは可能であるが、コギングトルクにバラツキがあると各回転機性能の差があるため、大量生産においては安定した製品化が目指せず顧客のニーズから外れてしまうことが解った。
【００２８】
（実施例２）
ＳｒＣＯ_３粉末（不純物としてＢａ，Ｃａを含む）及びα−Ｆｅ_２Ｏ_３粉末，　Ｌａ_２Ｏ_３粉末及びＣｏ_３Ｏ_４粉末を用いて、仮焼後に　（Ｓｒ_０．８０Ｌａ_０．２０）Ｏ・５．９５［（Ｆｅ_{０．９８３}Ｃｏ_{０．０１７}）_２Ｏ_３］で示される主要成分組成になるように湿式混合後、１２５０℃で２時間、大気中で仮焼した。仮焼物をローラーミルで乾式粗粉砕し粗粉を得た。次いで、アトライターにより湿式微粉砕し、平均粒径０．８μｍ（Ｆ．Ｓ．Ｓ．Ｓ．）の微粉砕粉を得、これを公知の手段で造粒した。微粉砕初期に、微粉砕に投入した粗粉に対するｍａｓｓ比でＬａ_２Ｏ_３粉末のみを０．６ｍａｓｓ％添加した。又微粉砕初期に焼結助剤としてＳｒＣＯ_３粉末，ＣａＣＯ_３粉末及びＳｉＯ_２粉末を微粉砕に投入した粗粉に対するｍａｓｓ比でそれぞれ０．１ｍａｓｓ％，１．０ｍａｓｓ％及び０．３ｍａｓｓ％添加した。
このフェライト磁石原料のかさ密度を測定したところ１．４Ｍｇ／ｍ^３であった。次に、図２の成形金型を備え、上ラムとダイスの動きを数値制御できるサーボプレスにより、まず上パンチを引き上げた状態でキャビティ４７内に所定量の前記微粉末を充填した。金型は８極異方性型でずらし角１１度である。充填された原料の中央が金型屈曲部に一致するようにアンダーフィル作動を行なった。キャビティに０．４ＭＡ／ｍ（５ｋＯｅ）のパルス電流で極異方性磁場を間欠的に３回印加した状態としながら上パンチを下降させた。このときダイスを上パンチの半分の速度で下降させながら、成形圧力：４４ＭＰａ（４５０ｋｇ／ｃｍ^２）で圧縮成形を行い、下パンチを実質的にキャビティ方向へ加圧した状態とした。その後脱磁し、得られた本成形体の密度は３．２Ｍｇ／ｍ^３であった。次いで１２００℃で２時間焼結し、下記の主要成分組成（Ｌａ過剰組成：Ｌａ／Ｃｏ＝１．２）を有する焼結体を得た。
（Ｓｒ_０．７６Ｌａ_０．２４）Ｏ・５．７２［（Ｆｅ_{０．９８３}Ｃｏ_{０．０１７}）_２Ｏ_３］
次に焼結体の端面及び外周面を加工（内径面は無加工）し、外径２０ｍｍ、内径１４ｍｍ、軸方向長さ３０ｍｍの対称８極極異方性リング磁石を得た。次に極異方性付与方向に沿って総磁束量が飽和する条件で着磁し、周方向に表面磁束密度を測定した。
測定場所は軸方向端面から５．０ｍｍステップで５箇所測定した。上の２箇所と下の２箇所はずらし角１１度に対応するデータを得た。またらせん状磁極部Ｂの長さは８．０ｍｍで、全体の長さの約２７％であった。この極異方性リング磁石（Ｎ＝５０）のコギングトルクのバラツキを測定したところ、２％と非常に小さい値であった。
又、図１に示すように得られた対称８極極異方性リング磁石を図６に示すようにシャフト１上に固定し、回転子を構成し、所定の回転機に組み込んだところ有用な回転機性能が得られた。
【００２９】
（比較例３）
前記らせん状磁極部の長さを短くして検討を行った。らせん状磁極部の長さが２．０ｍｍの極異方性リング磁石の成形体を得た。前記成形体を１１００度にて２時間焼結したところ、このらせん状磁極部からひびが入り焼結割れを起してしまい使用に耐えなかった。
【００３０】
（比較例４）
前記らせん状磁極部の長さを各々の平行磁極部よりも長くして検討を行った。平行磁極部の長さを互いに８ｍｍづつ、らせん状磁極部を磁極部が平行磁極部と磁極が連続したらせん状磁極部として長さを２２ｍｍとした。それ以外は実施例１と同様にして極異方性リング磁石を製造した。この極異方性リング磁石（Ｎ＝５０）のコギングトルクのバラツキを測定したところ、９％と大きい値であった。この極異方性リング磁石を実施例１と同様にしてシャフト１上に固定し、回転子５を構成し、所定の回転機に組み込むことは可能であるが、コギングトルクにバラツキがあると各回転機性能の差があるため、大量生産においては安定した製品化が目指せず顧客のニーズから外れてしまうことが解った。
【００３１】
（実施例３）
Ｎｄ：２９．２ｍａｓｓ％、Ｇａ：０．８ｍａｓｓ％、Ｂ：１．０ｍａｓｓ％、Ｃｏ：１０．５ｍａｓｓ％、残部Ｆｅの主要成分組成を有する合金を真空溶解し、ロール冷却を行って鋳造合金を得た。ロール冷却は銅製の単ロール法を用いており、板厚が３００〜５００μｍになるように作製した。冷却速度は約５×１０^２℃／ｓｅｃに相当する。この合金に均質化熱処理を施した後、室温で水素吸蔵させ、同温度で１０℃／ｓｅｃの昇温速度で８３０℃まで加熱した。この温度で２時間保持した後に１時間脱水素処理を行った。脱水素処理の終了後、炉内をアルゴン雰囲気に置換して冷却した。これにより得られた合金を３２〜１０６μｍに分級した。この合金粗粉とエポキシ樹脂を混合し原料とした。
次に、図１に示すらせん状の磁極部配向が可能な図２に記載の成形金型を用い、上ラムとダイスの動きを数値制御できるサーボプレスにより、まず上パンチを引き上げた状態でキャビティ内に所定量の前記微粉末を充填した。金型は１６極異方性型でずらし角３°とした。充填された原料の中央が金型屈曲部に一致するようにアンダーフィル作動を行なった。キャビティに磁極あたり５．０ｋＡターンのパルス電流で極異方性磁場を間欠的に３回印加した状態としながら上パンチを下降させた。
得られた成形体を熱処理して樹脂を硬化させてボンド磁石体である極異方性リング磁石を得た。電着により熱硬化性樹脂（エポキシ樹脂）をコーティングし、図１に示すような外径１４ｍｍ、内径１０ｍｍ、軸方向長さ１５ｍｍの対称８極極異方性リング磁石を得た。次に極異方性付与方向に沿って総磁束量が飽和する条件で着磁し、周方向に表面磁束密度を測定した。
測定場所は軸方向端面から２．５ｍｍステップで５箇所測定した。図１において上の平行磁極部（Ａ）２箇所では同様なほぼ正弦波の波形形状が、平行磁極部（Ｃ）では（Ａ）の波形形状と比較して１１度異相した波形形状が得られた。この極異方性リング磁石（Ｎ＝５０）のコギングトルクのバラツキを測定したところ、１．７％と非常に小さい値であった。
【００３２】
（実施例４）
実施例３と同様の原料を用いて極異方性リング磁石を製造した。
図８に示すら磁極部配向が可能な図７に記載の成形金型を用いて成形を行った。上ラムとダイスの動きを数値制御できるサーボプレスにより、まず上パンチを引き上げた状態でキャビティ内に所定量の前記原料を充填した。金型は１６極異方性型でずらし角３°とした。充填された原料の中央が金型屈曲部に一致するようにアンダーフィル作動を行なった。キャビティに磁極あたり４．０ｋＡターンのパルス電流で極異方性磁場を間欠的に３回印加した状態としながら上パンチを下降させた。得られた本成形体を熱処理して樹脂を硬化させてボンド磁石体である極異方性リング磁石を得た。電着により熱硬化性樹脂（エポキシ樹脂）をコーティングし、図８に示すような外径１４ｍｍ、内径８ｍｍ、軸方向長さ２０ｍｍの対称１６極極異方性リング磁石を得た。次に極異方性付与方向に沿って総磁束量が飽和する条件で着磁し、周方向に表面磁束密度を測定した。
測定場所は軸方向端面から４．０ｍｍステップで４箇所測定した。図８に平行磁極部（Ａ）と平行磁極部（Ｃ）では３度異相した波形形状が得られ、波形は実質的に同じものであった。この極異方性リング磁石（Ｎ＝５０）のコギングトルクのバラツキを測定したところ、２．２％と非常に小さい値であった。
【００３３】
【発明の効果】
以上記述の通り本発明によれば、従来にない形態である、軸に平行な磁極部を複数有し、かつ多段成形による焼結体接合部が実質的に存在しないという、一体で多段成形の必要がない長尺高磁力の極異方性リング磁石を提供することができた。
【図面の簡単な説明】
【図１】本発明の極異方性リング磁石の外観を示す模式図である。
【図２】本発明の極異方性リング磁石の成形に用いる金型構造の一例を示す図である。
【図３】図２の金型構造の軸断面を示す図である。
【図４】図１の極異方性リング磁石の側面の展開図である。
【図５】図１の極異方性リング磁石の表面磁束波形である。
【図６】本発明の極異方性リング磁石を用いたロータである。
【図７】本発明の極異方性リング磁石の成形に用いる金型構造の一例を示す図である。
【図８】本発明の極異方性リング磁石の外観を示す模式図である。
【図９】従来の極異方性リング磁石の成形に用いる金型構造を示す図である。
【符号の説明】
１　成形金型、２　コイル、３　上パンチ、４　下パンチ、５　極異方性リング磁石、６　中立線、７　ダイス、８　コア、９　スペーサ、１０キャビティ、１２　溝[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a high magnetic force polar anisotropic ring magnet having a helical magnetic pole that does not require multi-stage molding.
[0002]
[Prior art]
Radial anisotropic ring magnets and polar anisotropic ring magnets are often used in rotating machines such as servomotors. When a polar anisotropic ring magnet is used, a higher surface magnetic flux density can be obtained than a radial ring magnet having the same dimensions, and a small-sized and higher-performance motor can be provided. For example, Japanese Patent Publication No. 8-28293 describes an R-Fe-B-based permanent magnet having polar anisotropy.
In a motor using a permanent magnet, cogging is likely to occur because the magnetic resistance between the stator and the rotor changes according to the rotation angle. In particular, when the number of magnetic poles of the magnet is as small as 4 to 8 poles, the cogging torque becomes remarkable. Since this cogging torque is proportional to the square of the magnetic flux density, it is necessary to smooth the magnetic flux waveform in the circumferential direction of the gap in order to reduce the cogging torque. When a radial anisotropic ring magnet is used, a method of suppressing cogging by using skew magnetization when magnetizing is generally used.
However, in a polar anisotropic ring magnet having a high surface magnetic flux density, unlike a radial ring magnet, the direction in which magnetization can be performed is determined from the orientation of molding. Since the orientation is performed while performing compression molding, variations between the magnetic poles of the compact are likely to occur, and adjustment by magnetization cannot be performed. Therefore, measures for suppressing cogging are necessary.
For example, Japanese Patent Publication No. Hei 8-28293 describes a polar anisotropic ring magnet having a number of magnetized poles P of 4 to 8, and it is described that each magnetic pole portion is uniformly inclined at least 5 ° with respect to the axis. There is a description of a characteristic cylindrical permanent magnet. However, when this cylindrical permanent magnet is actually manufactured, the magnetic pole portion is inclined with respect to the axis. There have been problems such as the shape being changed as the shape is compressed, the orientation being partially reoriented by magnetic attraction with the magnetic pole, and the orientation being disturbed. Further, the interval between magnetic poles and the skew angle vary due to the variation in the shrinkage ratio during sintering, and as a result, there is a disadvantage that it is difficult to keep the cogging torque of the motor constant.
As a countermeasure, there is an example in which a plurality of polar anisotropic magnets are used and the magnetic poles are shifted and stacked in the axial direction. Japanese Patent Application Laid-Open No. 8-340652 describes a servomotor in which a polar anisotropic ring magnet is divided into a plurality of pieces in the axial direction, magnetized after shifting the magnetic poles, and magnetized to make apparent skew. There is no description about the control of the shift angle for reducing the torque, and it takes time and effort to fix each magnet. The production cost of the individual polar anisotropic ring magnet is low, but the assembly processing cost to the rotor is required separately.
Japanese Patent Application Laid-Open No. 11-8960 discloses a magnetic pole shifting jig in which the magnetic center of the magnetic field generating section is shifted by an angle at which the cogging torque has an opposite phase between a plurality of jigs in order to control the shifting angle. By using this, the shift angle is controlled. In this method, it is necessary to take a fixing means such as an adhesive so that the magnet does not rotate when the magnet is pulled out from the jig, and the productivity is poor.
In addition, the present inventors have already filed an application for manufacturing a polar anisotropic ring magnet by multi-stage molding, and among them, in the first preforming at the time of multi-stage molding, polar anisotropic ring magnet is formed by a usual method. An oriented and formed preformed body is prepared, and in the second preforming, the preformed body is oriented and formed so as to form a magnetic pole portion at a position different from the first preforming, and an apparent skew magnetized integrated body is formed.・ Provides long polar anisotropic ring magnets. However, since it is manufactured by multi-stage molding, there is a problem that the molding yield is deteriorated and the cost is increased, leaving room for improvement.
[0003]
[Problems to be solved by the invention]
Therefore, an object of the present invention is to provide a polar anisotropic ring magnet which can be obtained at low cost without forming a multi-stage magnet having a small variation in the interval between magnetic poles and a small cogging torque.
[0004]
[Means for Solving the Problems]
The present inventors have found that, by devising the magnetic structure of the mold and the method of molding, the same effect as that of bonding a plurality of magnets at a fixed angle can be realized with a single magnet with good reproducibility. This makes it possible to obtain a highly anisotropic ring magnet with small cogging when assembled into a motor with high reproducibility by a method with high productivity while maintaining a high surface magnetic flux density.
In other words, the present invention is an integrally molded polar anisotropic ring magnet with a skew orientation, having a plurality of magnetic pole portions parallel to the axis, and having substantially no joint by multi-stage molding. This is the first production of a polar anisotropic ring magnet.
Whether or not there is a joint formed by the multi-stage molding defined here can be determined by measuring the surface magnetic flux density in the axial direction. In other words, in the case of integral molding, the supply density of the magnetic powder during molding is substantially uniform, so that the density does not change at the body of the ring magnet even when sintered. Therefore, when the surface magnetic flux density is measured along the magnetic poles in the axial direction, the surface magnetic flux density at the end decreases but the surface magnetic flux density does not vary by 5% or more at the trunk portion. In the case of multi-stage molding, the magnetic powder in the cavity is compressed by the punch several times, so the density difference slightly changes between the part pressed by the punch and the part where the magnetic powder is newly supplied. 5% or more and further 8% or more. Therefore, by measuring the surface magnetic flux density, it is possible to determine the difference between multi-stage molding and integral molding.
[0005]
As a specific embodiment of the present invention, an integrally molded polar anisotropic ring magnet, wherein the polar anisotropic ring magnet includes a magnetic pole portion parallel to an axis and a helical magnetic pole portion; And the helical magnetic pole portion is continuously connected.
Various combinations of the magnetic pole part parallel to the axis and the helical magnetic pole part are conceivable and are not particularly limited, but the magnetic pole parts parallel to the axis are arranged at both ends, and the helical magnetic pole part is interposed therebetween. Is preferred for the most manufacture, and is more preferable for satisfying the characteristics required by customers. The helical magnetic pole portion (hereinafter referred to as a helical magnetic pole portion) refers to a portion in which the magnetic pole portion is not parallel to the axis but is obliquely oriented. The axial width of the helical magnetic pole portion is preferably as small as possible and should be shorter than the parallel magnetic pole portions.
In addition, it is easy to install the coil of the orientation yoke, and a high orientation magnetic flux can be obtained, so that a polar anisotropic ring magnet having a high degree of orientation and a high surface magnetic flux density can be obtained. In particular, the present invention is effective for rare earth sintered magnets with few sintering cracks even if the degree of orientation is increased. Further, by applying the present invention to a sintered magnet that performs powder molding having a higher molding compression ratio than a bonded magnet, the advantages of the present invention can be maximized.
[0006]
Here, the advantages of the present invention will be described in detail with reference to FIGS. 2 and 7, 1 is a mold, 2 is a coil for obtaining an alignment magnetic field, 3 is an upper punch, 4 is a lower punch, and a cavity surrounded by the upper punch 3, the lower punch 4, and the mold 1. Is filled with the molding material 5. In the figure, reference numeral 6 denotes a magnet neutral line between magnetic poles depending on the orientation at the time of molding. In order to obtain a helically oriented polar anisotropic ring magnet, if the magnetic pole portion is oriented so as to be substantially uniformly inclined with respect to the axis as shown in FIG. In a)), the molding material 5a is oriented along the orientation magnetic field, but in the stage after molding in which the molding material 5a is compressed by the upper punch 3 and the lower punch 4 (FIG. 7 (b)), the initial orientation magnetic field is reduced. Since the neutral line 6 is distorted at different angles, the distance between the magnetic poles tends to vary due to this distortion. Applying an orientation magnetic field after the molding material has been compressed to the final molded article shape does not orient the molding material. Conversely, if the compression molding is to be performed by taking into account the strain of the magnetic pole portion due to the molding compression, it is necessary to strictly control the amount of molding material to be put into the mold cavity, which is practically difficult in industrial production.
[0007]
In the polar anisotropic ring magnet of the present invention, as shown in FIG. 1 (schematically shown on a cylinder), the coil is formed so as to have magnetic pole portions A and C parallel to the axis (hereinafter referred to as parallel magnetic pole portions). 2b is provided in the mold. As a result, as shown in FIG. 2, even if the molding material is compressed by compression molding, the width and direction of the neutral line at the magnetic pole portions A and C are not substantially changed, and only the density is improved. The number of helically oriented magnetic pole portions is smaller than in the past, and a polar anisotropic ring magnet with reduced magnetic pole variation can be manufactured.
[0008]
If the parallel magnetic pole portions are joined to each other without leaving a distance, cracks due to shrinkage during sintering are likely to occur. In order to suppress this, it is preferable to provide a certain width of the magnetic pole portion which is spirally oriented. Naturally, if the parallel magnetic pole part and the helical magnetic pole part are arranged so that the magnetic pole part is continuous, the crack due to the shrinkage during sintering can be further reduced. In this case, the oriented coil may be wound in a mold so as to overlap the neutral line 6 shown in FIG. 1, and can be constituted by one coil with one magnetic pole passing from one end to the other of the polar anisotropic ring magnet. It is.
[0009]
By the above manufacturing method, a polar anisotropic ring magnet is obtained in which the positions of the magnetic poles and the reversal positions (neutral lines) are parallel to the axial direction and run obliquely in the circumferential direction on the way as shown in FIG. At the time of molding, compression molding is performed by pressing the magnetic powder in the cavity by the same distance from both ends so that the magnetic powder at the position of the spiral orientation does not move with respect to the mold, so that the disorder of the orientation is very small. An integrated polar anisotropic magnet having a certain shift angle can be obtained.
[0010]
The length of the intermediate portion B in FIG. 1 in the axial direction is preferably short because variations between magnetic poles are likely to occur, but if it is too short, cracks due to shrinkage during sintering cannot be suppressed. It is necessary to appropriately select the material depending on the molding material, the degree of orientation, and the like. For example, in the RTB-based magnet, the inclination angle α of the helical magnetic pole portion with respect to the axial direction is preferably 85 ° or less. The preferred angle of inclination is 80 ° or less, more preferably 70 ° or less. The width in the axial direction is preferably 0.3 mm or more.
In the case of a ferrite magnet which is relatively easily sintered and cracked, the inclination angle α is preferably 60 ° or less. The preferred inclination angle is 55 ° or less, and more preferably 45 ° or less. The width in the axial direction is preferably 0.5 mm or more.
Compared with a multi-stage molded product, the number of molded products in one molding machine per unit time is greatly improved, and the variation of the magnetic pole portion can be suppressed more than a multi-stage molded product.
[0011]
However, in the case of a bonded magnet, cracks due to shrinkage hardly occur even when the effecting step is performed after molding. Therefore, it is possible to obtain a polar anisotropic ring magnet having a neutral line as shown in FIG. It is also possible to apply a lower alignment magnetic field to suppress shrinkage cracking. Thereby, a polar anisotropic ring magnet with a small cogging torque can be obtained. According to this method, it is possible to obtain a polar anisotropic ring magnet which is formed integrally and substantially has no helical magnetic pole portion.
[0012]
The ring magnet having polar anisotropy of the present invention is manufactured, for example, by the following steps.
(1) Sintered magnet: raw material powder preparation-powder supply-orientation-consolidation-sintering (heat treatment, processing and surface treatment are added as necessary)
(2) Bonded magnet
(Compression molding): Preparation of raw material compound-powder supply-orientation-consolidation-curing (processing and surface treatment are added as necessary)
(Injection molding): Preparation of raw material compound-Injection (orientation + consolidation)-Cooling (processing and surface treatment are added if necessary)
[0013]
1 shows a polar anisotropic ring magnet of the present invention geometrically. As shown in FIG. 1, the center axis of the ring magnet coincides with the z-axis of the r-θ-z cylindrical coordinate system, one end of the magnet is brought into contact with the z = 0 plane, and the ring magnet is imagined perpendicular to the z-axis. When the components are divided into three and named as A, B, and C from the smaller Z, the θ component of the magnetic pole portion of A is substantially constant θa in the z-axis direction, and the θ component of the corresponding magnetic pole portion at the opposite end C is At a substantially constant θc in the z-axis direction, the hard magnetization direction of the intermediate portion (spiral magnetic pole portion) B continuously changes from θa to θc. The absolute value | θc−θa | (shift angle) of the θ component of the magnetic pole portions of A and B is 5% or more and 50% or less of the average pole angle of A and B.
[0014]
The ring magnet is R ₂ T ₁₄ When a sintered magnet having a main phase of a B intermetallic compound (R is at least one kind of rare earth element containing Y and T is Fe or Fe and Co) is used, high rotating machine characteristics are obtained and practicality is improved. high.
The ring magnet is R ₂ T ₁₄ An anisotropic magnetic powder having a main phase of a B intermetallic compound or an RTN intermetallic compound (R is at least one kind of rare earth element containing Y and T is Fe or Fe and Co) is used as a binder. In the case where the bonded magnet is formed by a bonded magnet, there is an advantage that the thickness can be easily reduced compared to the sintered magnet and processing is unnecessary, so that cost performance is high.
When the ring magnet is made of a sintered ferrite magnet, a rotating machine with good cost performance can be constituted.
In addition, when the ring magnet is formed of a bonded magnet in which anisotropic magnetic powder having ferrite as a main phase is bound by a binder, a rotary machine with good cost performance can be constituted.
In order to reduce cogging, the axial length of the helical magnetic pole portion is desirably 1 to 30% or less of the entire length. ₂ T ₁₄ The present invention can be applied to a sintered magnet or a ferrite magnet having a B intermetallic compound (R is at least one kind of rare earth element including Y and T is Fe or Fe and Co) as a main phase.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 2 is a schematic cross-sectional view of the mold used in the present invention (however, the cavity portion shows the orientation state of the side surface of the polar anisotropic ring magnet in order to show the orientation direction of the magnetic powder). After the magnetic powder is supplied into the cylindrical mold 1, the upper punch 3 and the lower punch 4 are arranged at predetermined positions. Thereafter, N poles and S poles are periodically generated in the circumferential direction on the mold side surface in contact with the outer peripheral surface of the magnetic powder. The N pole and the S pole include a parallel magnetic pole portion and a helical magnetic pole portion whose inclination with respect to the axial direction is substantially 0 °. The coil 2b is disposed in the mold so as to be wound above the neutral line between the poles. As a source of the magnetic field, a pulse current, a steady current, a permanent magnet, or the like can be used. In the magnetic field created by these poles, the magnetic particles rotate and move in an energetically stable direction. The arrangement pattern of the magnetic powder created by this operation is aligned in a certain direction. The compacting process is completed by consolidating the oriented magnetic powder in the axial direction by the upper punch 3 and the lower punch 4. At this time, both the upper punch 3 and the lower punch 4 were operated in the same manner so that the lengths of the parallel magnetic pole portions were constant, and the punches were operated from both. After consolidation, a weak reverse magnetic field was applied to facilitate de-magnetization to facilitate subsequent handling.
[0016]
In an example of a polar anisotropic magnet, the magnetic flux between the magnetic poles flows in an arc shape in the magnet as shown in FIG. 3, and particles having magnetic anisotropy are arranged substantially along the arc. In the polar anisotropic magnet, the direction in which the magnet is easily magnetized is determined by the orientation. When the surface magnetic flux density after magnetization is measured in the circumferential direction, a periodic peak of the magnetic flux density is observed. The neutral line can be defined as a line connecting the positions where the magnetic poles switch. This line can be seen after magnetizing the product using a magnet viewer. Further, the neutral line can be measured even before the product is magnetized by measuring the attractive force with the magnetized magnet and observing using the X-ray and the Kerr effect.
8-pole anisotropy R ₂ T ₁₄ FIG. 4 shows the result of measuring the neutral line of the sintered B magnet and developing the neutral line into θ-z coordinates. End faces of two line segments parallel to the z-axis are connected by a line not parallel to the z-axis. There are a number of such neutral lines equal to the number of poles. By drawing two straight lines parallel to the θ axis passing through the inflection point, it can be divided into three regions having different θ. Named as A, B, C from the smaller z.
In the region A, θm = θa + 2πm ÷ n (n is the number of poles, m is an integer from 0 to n)
In the region C, θm = θc + 2πm ÷ n (n is the number of poles, m is an integer from 0 to n)
Can be expressed by In the region of the helical magnetic pole B, the transition state is an intermediate transition between the parallel magnetic poles A and C.
Hereinafter, only the neutral line of m = 0 will be mentioned, but the same applies to other m values.
θa and θc can include unavoidable variations in production. Typical variation values are within 3%, or even 2%, of the gap angle. In the region B, the neutral line changes continuously so as to connect θa and θc. From the viewpoint of mold production, it is desirable that the connection be made with a smooth change corresponding to the thickness of the winding where the magnetic pole bends.
The axial length of the helical magnetic pole portion B is desirably 1% or more and 40% or less of the entire length. If the helical magnetic pole portion B is less than 1%, the change in the magnetization direction is too steep, and the difference in shrinkage in the sintering step between the easy magnetization direction and the hard magnetization direction, the easy magnetization direction and the hard magnetization direction during sintering and heat treatment cooling. Thermal stress is generated due to the difference in thermal expansion coefficient between them, and cracks are likely to occur. When the helical magnetic pole portion B exceeds 40%, the rate of disturbing the orientation due to the effect of the inclined magnetic pole increases, so that the cogging torque tends to vary.
The length H of the helical magnetic pole B can be simply defined as follows. The inclination α between the neutral line and the axis of the helical magnetic pole portion B is determined using a magnet viewer sheet. If the diameter of the magnet is D and the number of poles is n, the pole width w is
w = πD ÷ n
And H is represented by the following equation.
H = w ÷ tanα = πD ÷ n ÷ tanα
The length of the helical magnetic pole portion B can be known by the above method.
The reason why the absolute value of the angle difference (θc−θa) between the neutral lines at both ends is specified to be 5% or more and 50% or less of the average gap angle is that if it is less than 5%, there is almost no cogging reduction effect. If it is 50% or more, the motor torque becomes 80% or less, which is not practical. The waveform of the cogging torque when the motor is slowly rotated often has the same number of valleys as the number of peaks of the least common multiple M of the number n of the rotor poles and the number p of the stator poles. Therefore, a desirable neutral line angle difference | θc−θa | ≦ 2π / M is satisfied.
[0017]
When the product is magnetized, it is divided into premagnetization, which generates a weak magnetic field, and main magnetization, which generates a strong magnetic field. It is possible to sufficiently magnetize with magnetism. If the magnetizing yoke is set on the magnetizing yoke based on the alignment mark, or a magnetizing yoke which incorporates a permanent magnet and is spontaneously arranged in the direction of easy magnetization is used, there is no problem even if the preliminary magnetizing is omitted.
[0018]
Next, the configuration of the ring magnet of the present invention and the reasons for limiting the numerical values will be described. Hereinafter, the expression “%” means mass%.
The polar anisotropic ring magnet of the present invention is, for example, R ₂ T ₁₄ In the case of a sintered magnet or a bonded magnet having a main phase of B intermetallic compound (R is at least one kind of rare earth element including Y and T is Fe or Fe and Co), R, T And the total of B is 100%, a composition consisting of R: 27 to 34%, B: 0.5 to 2%, and the balance T (T is Fe or Fe and Co) is selected.
R ₂ T ₁₄ When manufacturing a polar anisotropic sintered ring magnet with the B intermetallic compound, when the mass of the ring magnet is set to 100%, as an inevitable impurity, 0.6% or less, preferably 0.3% or less, more preferably 0.3% or less. Less than 0.2% oxygen, 0.3% or less, preferably 0.1% or less carbon, 0.08% or less nitrogen, 0.02% or less hydrogen, 0.2% or less, preferably 0.1% or less. A content of Ca of not more than 05%, more preferably not more than 0.02% is acceptable.
A combination of (Nd, Dy), (Pr, Dy), or (Nd, Pr, Dy) as R has high practicality. The R amount is preferably 27 to 34%. Part of Dy may be replaced with Tb. If the R amount is less than 27%, the specific coercive force iHc is significantly reduced, and if it is more than 34%, the residual magnetic flux density Br and the maximum energy product (BH) max are significantly reduced.
B content is preferably 0.5 to 2%, more preferably 0.8 to 1.2%. If the amount of B is less than 0.5%, iHc that can withstand practical use cannot be obtained. If the amount of B exceeds 2%, Br and (BH) max are greatly reduced. It is known that a part of B can be replaced by C, and is applicable to the present invention.
In order to improve the surface magnetic flux density and corrosion resistance, it is preferable to contain an appropriate amount of at least one element selected from the group consisting of Nb, Al, Co, Ga and Cu.
The content of Nb is preferably 0.1 to 2%. By containing Nb, a boride of Nb is generated during the sintering process, and abnormal grain growth of crystal grains can be suppressed. When the Nb content is less than 0.1%, the effect of addition is not recognized. When the Nb content is more than 2%, the amount of Nb boride generated increases and the reduction of Br becomes remarkable.
The content of Al is preferably 0.02 to 2%. If the Al content is less than 0.02%, the effect of improving iHc and corrosion resistance cannot be obtained, and if it exceeds 2%, Br and (BH) max are significantly reduced.
The Co content is preferably from 0.3 to 5%. If the Co content is less than 0.3%, the effect of improving the Curie point and corrosion resistance cannot be obtained, and if it exceeds 5%, both Br and iHc are greatly reduced. The Ga content is preferably 0.01 to 0.5%. If the Ga content is less than 0.01%, the effect of improving iHc cannot be obtained. If the Ga content exceeds 0.5%, the reduction of Br and (BH) max becomes remarkable.
The Cu content is preferably 0.01 to 1%. If the Cu content is less than 0.01%, the effect of improving the corrosion resistance and iHc cannot be obtained, and if it exceeds 1%, the decrease in Br becomes remarkable.
When both Cu and Co are contained in the above-mentioned specific amount range, the effect of widening the allowable temperature range of the second heat treatment is preferably obtained.
The present invention relates to R ₂ T ₁₄ In the case of a bonded magnet in which an anisotropic magnetic powder having a main phase of a B intermetallic compound (R is at least one kind of rare earth element including Y and T is Fe or Fe and Co) is bonded by a binder, Average grain size of 0.01 to 0.5 μm,
It is desirable to use magnetic powder having anisotropy by a method such as hot working or HDDR. As the binder, a known material such as rubber, nylon, epoxy, PPS or other plastic material, or zinc or a low melting point alloy can be used.
The present invention combines an anisotropic magnetic powder having an RTN intermetallic compound (R is at least one kind of rare earth element including Y and T is Fe or Fe and Co) with a binder. In the case of a bonded magnet, it is preferable to use an anisotropic fine powder which is an intermetallic compound known as Sm-Fe-N and is pulverized on average from 1 to 10 μm. Additives and unavoidable impurities that do not significantly degrade the magnetic properties are acceptable. As the binder, a known material such as rubber, nylon, epoxy, PPS or other plastic material, or zinc or a low melting point alloy can be used.
[0019]
It is preferable in terms of cost performance to produce the polar anisotropic ring magnet of the present invention with a known ferrite magnet.
Especially (A _1-x R ' _x ) On [(Fe _1-y M _y ) ₂ O ₃ ] (Atomic ratio)
(However, A is Sr and / or Ba, R 'is at least one kind of rare earth element including Y and always contains La, M is Co or Co and Zn, and x, y and n are conditions:
5.0 ≦ n ≦ 6.4
0.01 ≦ x ≦ 0.4, and
0.005 ≦ y ≦ 0.04
Is a number that satisfies The use of a sintered ring magnet composed of a high-performance ferrite magnet having a main component composition represented by the formula (1) and having a magnetoplumbite type crystal structure is preferable because the rotating machine performance can be improved.
In order to increase the saturation magnetization, the ratio of La in R ′ is preferably at least 50 atomic%, more preferably at least 70 atomic%, particularly preferably at least 99 atomic%. Ideally, R 'should consist of La except for the unavoidable R' component. Therefore, it is practical to use an inexpensive misch metal oxide containing 50 atomic% or more of La and a balance of at least one of Pr, Nd and Ce and an unavoidable R 'component as the R' element supply material. is there. In this case, R ′ is composed of La, at least one of Nd, Pr and Ce, and an unavoidable R ′ component.
The molar ratio n needs to be 5.0 to 6.4, preferably 5.5 to 6.3, and particularly preferably 5.7 to 6.2. When n exceeds 6.4, a phase other than the magnetoplumbite phase (α-Fe ₂ O ₃ IHc) is greatly reduced by the presence of (e.g.), and when n is less than 5.0, Br is greatly reduced.
x is preferably 0.01 to 0.4, more preferably 0.1 to 0.3, and particularly preferably 0.15 to 0.25. When x is less than 0.01, the effect of addition is not recognized, and when it exceeds 0.4, the surface magnetic flux density is greatly reduced.
Ideally, the relationship of y = x / (2.0n) must be established between y and x for charge compensation. However, when y is equal to or more than x / (2.6n), x / x If it is not more than (1.6 n), a ferrite magnet having a high Br and a high demagnetization curve square can be obtained. When y deviates from x / (2.0n), Fe ²⁺ May be included, but there is no problem. In a typical example, the preferred range of y is 0.04 or less, especially 0.005 to 0.03.
Further, a main component composition in which R ′ is excessive such that 5.7 ≦ n ≦ 6.2, 0.2 ≦ x ≦ 0.3 and 1.0 <x / 2ny ≦ 1.3 is selected, and the CaO content is reduced. 0.5-1.5% and SiO ₂ When the content is 0.25 to 0.55%, the square shape of the demagnetization curve can be significantly increased as compared with the conventional case.
SiO as an additive to control sinterability to obtain a dense sintered ferrite magnet ₂ And CaO (CaCO ₃ Is important in practical use.
SiO ₂ Is an additive that suppresses the growth of crystal grains during sintering. ₂ Preferably, the content is 0.05 to 0.55%, more preferably 0.25 to 0.55%. SiO ₂ If the content is less than 0.05%, the crystal grain growth proceeds excessively during sintering, and the coercive force greatly decreases. If the content exceeds 0.55%, the crystal grain growth is excessively suppressed, and the degree of orientation due to the crystal grain growth is improved. Insufficiently, Br is greatly reduced.
CaO is an additive that promotes crystal grain growth, and the total mass of the ferrite magnet is preferably 100 mass%, and the CaO content is preferably 0.35 to 1.5%, more preferably 0.4 to 1.5%, 0.5-1.5% is particularly preferred. When the CaO content is more than 1.5%, the crystal grain growth proceeds excessively during sintering, and the coercive force greatly decreases. When the CaO content is less than 0.35%, the crystal grain growth is excessively suppressed, and the degree of orientation due to the crystal grain growth is increased. Is insufficiently improved and Br is greatly reduced.
When the present invention is a bonded magnet in which a known anisotropic magnetic powder having ferrite as a main phase is bound with a binder, it is preferable in terms of cost performance.
[0020]
The molding of the sintered ring magnet of the present invention is performed by, for example, a press equipped with a molding die 1 (for symmetric 8-pole anisotropic orientation) shown in FIG. In FIG. 3, the solid line is the AA cross section in FIG. 2B, and the dashed line is the coil position in the BB cross section. In the molding die 1, reference numeral 7 denotes a die made of a ferromagnetic material, and reference numeral 8 denotes a core having a circular cross section made of a nonmagnetic material and arranged concentrically in the annular space of the die 7. A plurality of grooves 12 are formed in the cylindrical inner surface of the die 7, and a magnetic field generating coil 2 b is embedded in each groove 12. The magnetic field generating coil 2b has a bent portion for forming a helical magnetic pole portion in the middle. A nonmagnetic spacer 9 having a circular cross section similar to the core 8 is provided on the inner peripheral surface of the die 7 so as to cover the groove 12. A cavity 10 is provided between the spacer 9 and the core 8. When a current is applied to each coil 2b, a magnetic flux indicated by an arrow is generated in the cavity 10, and alternating polarity magnetic poles of N, S, N, S...
Next, an example of a method for molding the molded body for a sintered ring magnet of the present invention using the molding die 1 of FIG. 3 will be described. First, a predetermined amount of raw material powder or slurry is filled in the cavity by a supply means such as a vibrating feeder with the upper punch 3 of FIG. 2 pulled up. Next, a pulse current is applied to the coil 2b to lower the upper punch 3 as it is in a state in which the fine powder or slurry for the sintered magnet is oriented, and lowers the helical magnetic pole portion to a position that is in contrast to the lower punch 4. . Thereafter, the lower punch 4 and the upper punch 3 are pressed in the cavity direction at the same speed and pressure to obtain a molded body of a polar anisotropic ring magnet. When the upper punch 3 is pressurized, the dice are lowered at half the speed of the upper punch 3, so that a parallel magnetic pole portion having a length symmetrical in the axial direction can be obtained in the same manner as described above.
The applied polar anisotropic orientation magnetic field strength is preferably as high as possible, but is usually 0.4 to 2.0 MA / m (5 to 25 kOe). When the orientation magnetic field strength is less than 0.4 MA / m, the orientation becomes insufficient, and it is difficult to secure a high orientation magnetic field strength exceeding 2.0 MA / m in industrial production. In order to suppress cracks and obtain a predetermined degree of orientation, the compression molding pressure is 49 to 392 MPa (500 to 4000 kg / cm) in the case of a molded body for an RTB based sintered magnet. ² ), And 29 to 39 MPa (300 to 400 kg / cm) in the case of a molded body for a ferrite magnet. ² ) Is preferable.
[0021]
When the molding machine is a servo press using a servo motor, a mechanical press using a cam, or a hydraulic press having a numerically controlled hydraulic cylinder, the lower punch is reversed with respect to the movement of the upper punch. By moving the die in the same direction or by moving the die in the same direction with respect to the movement of the upper punch, it is possible to set a place where the material in the mold does not move in the vertical direction (hereinafter referred to as a neutral line).
The inventor can minimize the up-and-down movement of the raw material at the position of the mold for forming the spirally oriented portion by controlling the center of the spirally oriented portion of the mold to coincide with the neutral line. Was devised and its effectiveness was confirmed by conducting experiments.
[0022]
Furthermore, in the production of a sintered magnet or a bonded magnet by compression molding, it has been found that the length of the parallel magnetic pole portions A, C and B portions separated by the helical orientation portion can be changed by combining the underfill operation. The underfill operation is a method of moving the relative position between the die and the lower punch and feeding the raw material powder into the mold before the upper punch pressurizes after filling the raw material into the cavity. An intermediate position B having a different magnet length can be brought to a position other than the center of the magnet due to the underfill. This means that it is possible to adjust the total torque or the cogging torque using the same mold.
Further, by using an underfill, it is possible to produce magnets having the same shift angle but different axial dimensions.
[0023]
In the case of a molded body for an RTB-based sintered magnet, the molded body density is 3.7 to 4.6 Mg / m. ³ In the case of a molded body for a sintered ferrite magnet, the molded body density is 2.6 to 3.2 Mg / m. ³ Adjusted to the extent. In the case of an RTB bonded magnet or an RTN bonded magnet, 5.5 to 6.5 Mg / m by compression molding. ³ To the extent, 4.0 to 5.7 Mg / m by injection molding ³ Adjusted to the extent. 2.6 to 3.6 Mg / m for injection molding of ferrite bonded magnet ³ Adjusted to the extent. Next, a pulse current in the opposite direction to that described above is applied to the coil 56 while the obtained compression molded body is kept in a pressurized state, and demagnetized. In a bonded magnet, demagnetization and powder removal are important because adhesion of magnetic powder affects reliability such as corrosion resistance and contamination.
[0024]
Although the dimensions of the sintered ring magnet of the present invention are not particularly limited, the axial length (L) and the outer diameter dimension (Do) are respectively L = 5 to 100 mm, preferably L = 8 to 50 mm, and Do = Those having a thickness of 3 to 200 mm, preferably Do = 7 to 50 mm, are highly practical. It is practically difficult to impart polar anisotropy to those with Do <3 mm, and sintered ring magnets with Do> 200 mm do not meet the needs for miniaturization. When L <5 mm, there is no significant difference from the conventional one-stage molded product at the center, and when L> 100 mm, it does not meet the needs for miniaturization.
Although the number of magnetic poles of the sintered ring magnet of the present invention is not particularly limited, it is practical to form 4 to 100 poles, preferably 4 to 24 poles at equal or different intervals in the circumferential direction of the outer or inner diameter surface. high. The variation in cogging torque can be within 2.5%.
[0025]
Hereinafter, the present invention will be described in detail with reference to examples, but the present invention is not limited to the examples.
(Example 1)
An alloy coarse powder having a main component composition of Nd: 30.5 mass%, Dy: 1.5 mass%, Ga: 0.1 mass%, B: 1.0 mass%, and Fe: 64.8 mass% in an inert gas atmosphere. Jet mill pulverization was performed to obtain a fine powder for sintered magnets having an average particle size of 4.5 μm (FSSS). When the bulk density of this sintered magnet fine powder was measured, it was 1.7 Mg / m. ³ Met. Next, using the molding die shown in FIG. 2 that allows the helical magnetic pole portion orientation shown in FIG. 1, a servo press capable of numerically controlling the movement of the upper ram and the die is used to first pull up the upper punch into the cavity. A predetermined amount of the fine powder was filled. The mold is an 8-pole anisotropic mold with a shift angle of 11 degrees. An underfill operation was performed so that the center of the filled raw material coincided with the bent portion of the mold. The upper punch was lowered while the polar anisotropic magnetic field was intermittently applied to the cavity three times with a pulse current of 5.0 kA turns per magnetic pole. At this time, compression molding was performed while lowering the die at half the speed of the upper punch, and the lower punch was pressed substantially in the cavity direction. Thereafter, demagnetization was performed, and the density of the obtained molded article was 4.2 Mg / m. ³ Met.
Next, the molded product was placed in a pressure of about 0.07 Pa (5 × 10 ^-4 Sintered at 1100 ° C. for 2 hours in a vacuum of Torr) and cooled to room temperature. Next, a second heat treatment was performed at 550 ° C. × 2 hours in an Ar atmosphere to cool to room temperature. Next, the end surface and the outer peripheral surface are processed (the inner diameter surface is not processed), and a thermosetting resin (epoxy resin) is coated by electrodeposition, and the outer diameter is 14 mm, the inner diameter is 9 mm, and the axial length is 15 mm. An isotropic ring magnet was obtained. Next, magnetization was performed under the condition that the total magnetic flux was saturated along the direction of polar anisotropy, and the surface magnetic flux density was measured in the circumferential direction.
The measurement was performed at five locations in 2.5 mm steps from the axial end face. Data corresponding to a shift angle of 11 degrees between the upper two places and the lower two places was obtained. The waveform is shown in FIG. In the parallel magnetic pole portion (A) in FIG. 4, substantially the same sine wave waveform shape is substantially the same at both locations, but the lower parallel magnetic pole portion (C) is substantially 11 ° out of phase with the waveform shape of FIG. A waveform shape equivalent to the above was obtained. The data of the helical magnetic pole portion B was intermediate between the two. The length of the helical magnetic pole portion B was 3.0 mm, which was 20% of the entire length. When the variation of the cogging torque of this polar anisotropic ring magnet was measured, it was a very small value of 2%. The variation of the cogging torque was measured by assembling a polar anisotropic ring magnet with a rotor core, measuring the variation of the torque for each cogging when the rotor was rotated once after being put in a stator corresponding to the rotor, and measuring the number of samples by 20. The average value was obtained for each sample.
Further, the symmetrical octupole-pole anisotropic ring magnet obtained as shown in FIG. 1 is fixed on the shaft 1 as shown in FIG. 6, and the rotor 5 is constructed and assembled into a predetermined rotating machine. Rotating machine performance was obtained.
[0026]
(Comparative Example 1)
The study was carried out with almost no length of the spiral magnetic pole part. Apparently, a plurality of polar anisotropic magnets were manufactured so as to be fixed at a staggered angle of 11 ° to obtain a molded article of a polar anisotropic ring magnet having a length of about 0.1 mm of a helical magnetic pole. . When the molded body was sintered at 1100 ° C. for 2 hours, cracks occurred in the helical magnetic pole portion to cause sintering cracks, and the product was not usable.
[0027]
(Comparative Example 2)
The study was conducted by making the length of the helical magnetic pole part longer than each parallel magnetic pole part. The length of the parallel magnetic pole portions was 4 mm each, and the length of the spiral magnetic pole portion was 7 mm, with the magnetic pole portion being a spiral magnetic pole portion where the parallel magnetic pole portion and the magnetic pole were continuous. Otherwise, a polar anisotropic ring magnet was manufactured in the same manner as in Example 1. When the variation of the cogging torque of the polar anisotropic ring magnet (N = 50) was measured, it was a large value of about 10%. It is possible to fix the polar anisotropic ring magnet on the shaft 1 in the same manner as in the first embodiment to form a rotor 5 and incorporate it into a predetermined rotating machine. It was found that due to differences in rotating machine performance, stable commercialization was not aimed at in mass production, deviating from customer needs.
[0028]
(Example 2)
SrCO ₃ Powder (containing Ba and Ca as impurities) and α-Fe ₂ O ₃ Powder, La ₂ O ₃ Powder and Co ₃ O ₄ After calcination using powder (Sr _0.80 La _0.20 ) O.5.95 [(Fe _0.983 Co _0.017 ) ₂ O ₃ And then calcined in air at 1250 ° C. for 2 hours. The calcined product was subjected to dry coarse pulverization with a roller mill to obtain coarse powder. Next, wet pulverization was performed with an attritor to obtain a finely pulverized powder having an average particle size of 0.8 μm (FSSS), which was granulated by a known means. In the initial stage of the fine pulverization, the mass ratio of La to the coarse powder put into the fine pulverization is La. ₂ O ₃ 0.6 mass% of powder alone was added. SrCO is used as a sintering aid in the early stage of pulverization. ₃ Powder, CaCO ₃ Powder and SiO ₂ The powder was added in a mass ratio of 0.1 mass%, 1.0 mass%, and 0.3 mass% to the coarse powder charged in the fine pulverization.
When the bulk density of this ferrite magnet raw material was measured, it was 1.4 Mg / m. ³ Met. Next, a predetermined amount of the fine powder was filled into the cavity 47 in a state where the upper punch was pulled up by a servo press having the molding die of FIG. 2 and capable of numerically controlling the movement of the upper ram and the die. The mold is an 8-pole anisotropic mold with a shift angle of 11 degrees. An underfill operation was performed so that the center of the filled raw material coincided with the bent portion of the mold. The upper punch was lowered while a polar anisotropic magnetic field was intermittently applied to the cavity three times with a pulse current of 0.4 MA / m (5 kOe). At this time, the molding pressure: 44 MPa (450 kg / cm) while lowering the die at half the speed of the upper punch. ² ), The lower punch was pressed substantially in the cavity direction. Thereafter, the magnet was demagnetized, and the density of the obtained molded article was 3.2 Mg / m. ³ Met. Subsequently, sintering was performed at 1200 ° C. for 2 hours to obtain a sintered body having the following main component composition (La excess composition: La / Co = 1.2).
(Sr _0.76 La _0.24 ) O.5.72 [(Fe _0.983 Co _0.017 ) ₂ O ₃ ]
Next, the end surface and the outer peripheral surface of the sintered body were processed (the inner surface was not processed) to obtain a symmetric 8-pole anisotropic ring magnet having an outer diameter of 20 mm, an inner diameter of 14 mm, and an axial length of 30 mm. Next, magnetization was performed under the condition that the total magnetic flux was saturated along the direction of polar anisotropy, and the surface magnetic flux density was measured in the circumferential direction.
The measurement was performed at five locations in 5.0 mm steps from the axial end face. Data corresponding to a shift angle of 11 degrees was obtained for the upper two places and the lower two places. The length of the helical magnetic pole portion B was 8.0 mm, which was about 27% of the entire length. When the variation of the cogging torque of this polar anisotropic ring magnet (N = 50) was measured, it was a very small value of 2%.
Also, the symmetrical 8-pole anisotropic ring magnet obtained as shown in FIG. 1 is fixed on the shaft 1 as shown in FIG. 6, a rotor is formed, and the rotor is assembled into a predetermined rotating machine. Machine performance was obtained.
[0029]
(Comparative Example 3)
The study was conducted by shortening the length of the spiral magnetic pole portion. A molded product of a polar anisotropic ring magnet having a helical magnetic pole portion length of 2.0 mm was obtained. When the molded body was sintered at 1100 ° C. for 2 hours, cracks occurred in the helical magnetic pole portion to cause sintering cracks, and the product was not usable.
[0030]
(Comparative Example 4)
The study was conducted by making the length of the helical magnetic pole part longer than each parallel magnetic pole part. The length of the parallel magnetic pole portions was 8 mm each, and the helical magnetic pole portion was a spiral magnetic pole portion in which the magnetic pole portion was continuous with the parallel magnetic pole portion and the length was 22 mm. Otherwise, a polar anisotropic ring magnet was manufactured in the same manner as in Example 1. When the variation of the cogging torque of this polar anisotropic ring magnet (N = 50) was measured, it was as large as 9%. It is possible to fix the polar anisotropic ring magnet on the shaft 1 in the same manner as in the first embodiment to form a rotor 5 and incorporate it into a predetermined rotating machine. It was found that due to differences in rotating machine performance, stable commercialization was not aimed at in mass production, deviating from customer needs.
[0031]
(Example 3)
Nd: 29.2 mass%, Ga: 0.8 mass%, B: 1.0 mass%, Co: 10.5 mass%, the alloy having the main component composition of Fe is vacuum melted and roll-cooled to cast alloy. Obtained. Roll cooling was performed using a single roll method made of copper, and the plate was manufactured such that the plate thickness became 300 to 500 μm. Cooling rate is about 5 × 10 ² C / sec. After the alloy was subjected to a homogenizing heat treatment, hydrogen was absorbed at room temperature and heated to 830 ° C. at the same temperature at a rate of 10 ° C./sec. After maintaining at this temperature for 2 hours, a dehydrogenation treatment was performed for 1 hour. After the completion of the dehydrogenation treatment, the inside of the furnace was replaced with an argon atmosphere and cooled. The alloy thus obtained was classified into 32 to 106 μm. The alloy coarse powder and the epoxy resin were mixed to obtain a raw material.
Next, using the molding die shown in FIG. 2 capable of orienting the helical magnetic pole portion shown in FIG. 1, a servo press capable of numerically controlling the movement of the upper ram and the die is used. Was filled with a predetermined amount of the fine powder. The mold was a 16-pole anisotropic mold with a shift angle of 3 °. An underfill operation was performed so that the center of the filled raw material coincided with the bent portion of the mold. The upper punch was lowered while the polar anisotropic magnetic field was intermittently applied to the cavity three times with a pulse current of 5.0 kA turns per magnetic pole.
The obtained molded body was heat-treated to cure the resin to obtain a polar anisotropic ring magnet as a bonded magnet body. A thermosetting resin (epoxy resin) was coated by electrodeposition to obtain a symmetric 8-pole anisotropic ring magnet having an outer diameter of 14 mm, an inner diameter of 10 mm, and an axial length of 15 mm as shown in FIG. Next, magnetization was performed under the condition that the total magnetic flux was saturated along the direction of polar anisotropy, and the surface magnetic flux density was measured in the circumferential direction.
The measurement was performed at five locations in 2.5 mm steps from the axial end face. In FIG. 1, a similar substantially sinusoidal waveform shape is obtained at the two upper parallel magnetic pole portions (A), and a waveform shape that is 11 degrees out of phase with the parallel magnetic pole portion (C) is obtained. Was. When the variation of the cogging torque of this polar anisotropic ring magnet (N = 50) was measured, it was a very small value of 1.7%.
[0032]
(Example 4)
A polar anisotropic ring magnet was manufactured using the same raw materials as in Example 3.
As shown in FIG. 8, molding was performed using a molding die shown in FIG. 7 capable of magnetic pole orientation. First, a predetermined amount of the raw material was filled in the cavity with the upper punch pulled up by a servo press capable of numerically controlling the movement of the upper ram and the die. The mold was a 16-pole anisotropic mold with a shift angle of 3 °. An underfill operation was performed so that the center of the filled raw material coincided with the bent portion of the mold. The upper punch was lowered while the polar anisotropic magnetic field was intermittently applied to the cavity three times with a pulse current of 4.0 kA turns per magnetic pole. The obtained main body was heat-treated to cure the resin, thereby obtaining a polar anisotropic ring magnet as a bonded magnet body. A thermosetting resin (epoxy resin) was coated by electrodeposition to obtain a symmetric 16-pole anisotropic ring magnet having an outer diameter of 14 mm, an inner diameter of 8 mm, and an axial length of 20 mm as shown in FIG. Next, magnetization was performed under the condition that the total magnetic flux was saturated along the direction of polar anisotropy, and the surface magnetic flux density was measured in the circumferential direction.
The measurement was performed at four locations in 4.0 mm steps from the axial end face. In FIG. 8, the parallel magnetic pole part (A) and the parallel magnetic pole part (C) had waveforms that were three times out of phase, and the waveforms were substantially the same. When the variation of the cogging torque of this polar anisotropic ring magnet (N = 50) was measured, it was a very small value of 2.2%.
[0033]
【The invention's effect】
As described above, according to the present invention, an unconventional form, having a plurality of magnetic pole portions parallel to the axis, and substantially not having a sintered body joint by multi-stage molding, an integrated multi-stage molding It is possible to provide a long, high magnetic polar anisotropic ring magnet that is unnecessary.
[Brief description of the drawings]
FIG. 1 is a schematic view showing the appearance of a polar anisotropic ring magnet of the present invention.
FIG. 2 is a diagram showing an example of a mold structure used for molding the polar anisotropic ring magnet of the present invention.
FIG. 3 is a view showing an axial cross section of the mold structure of FIG. 2;
FIG. 4 is a development view of a side surface of the polar anisotropic ring magnet of FIG. 1;
FIG. 5 is a surface magnetic flux waveform of the polar anisotropic ring magnet of FIG. 1;
FIG. 6 is a rotor using the polar anisotropic ring magnet of the present invention.
FIG. 7 is a view showing an example of a mold structure used for molding the polar anisotropic ring magnet of the present invention.
FIG. 8 is a schematic view showing an appearance of a polar anisotropic ring magnet of the present invention.
FIG. 9 is a view showing a mold structure used for molding a conventional polar anisotropic ring magnet.
[Explanation of symbols]
1 Mold, 2 coils, 3 upper punch, 4 lower punch, 5 pole anisotropic ring magnet, 6 neutral wire, 7 dies, 8 cores, 9 spacer, 10 cavities, 12 grooves

Claims

A skew-oriented integrally molded polar anisotropic ring magnet, having a plurality of magnetic pole portions parallel to the axis, and having substantially no sintered body joint by multi-stage molding. Isotropic ring magnet.

An integrally formed polar anisotropic ring magnet, wherein the polar anisotropic ring magnet includes a magnetic pole portion parallel to an axis and a helical magnetic pole portion, and a magnetic pole portion parallel to the axis and a helical magnetic pole. The polar anisotropic ring magnet characterized in that the parts are continuously connected to the same pole.

The polar anisotropic ring magnet according to claim 2, wherein magnetic pole portions parallel to the axis are disposed at both ends of the polar anisotropic ring magnet, and a helical magnetic pole portion is disposed therebetween.

The polar anisotropic ring magnet according to claim 2, wherein the helical magnetic pole portion has a shorter axial width than a magnetic pole portion parallel to the axis.

The polar anisotropic ring magnet is a rare earth sintered magnet, and an inclination angle α of the helical magnetic pole portion when the outer peripheral surface of the polar anisotropic ring magnet is developed on a plane is 85 ° or less. Item 5. The polar anisotropic ring magnet according to any one of Items 2 to 4.

The polar anisotropic ring magnet is a sintered ferrite magnet, and an inclination angle α of the helical magnetic pole portion when the outer peripheral surface of the polar anisotropic ring magnet is developed on a plane is 60 ° or less. The polar anisotropic ring magnet according to claim 2.

An integrally formed polar anisotropic ring magnet, wherein a center axis of the ring magnet coincides with a z-axis of an r-θ-z cylindrical coordinate system, and one end of the magnet is brought into contact with a z = 0 plane, When a magnet is virtually divided into three parts perpendicular to the z-axis and named as A, B, and C from the smaller Z, the θ component of the magnetic pole portion of A is substantially constant θa in the z-axis direction and the opposite end C The θ component of the same magnetic pole portion corresponding to the above is substantially constant θc (≠ θa) in the z-axis direction, and the θ component of the same magnetic pole portion of the intermediate portion B continuously changes from θa to θc. A polar anisotropic ring magnet, characterized in that:

The absolute value | θc−θa | of the θ component of the magnetic pole portions of A and C is not more than 50% (not including 0%) of the average inter-pole angle (360 ° / number of magnetic poles) of A and C. The polar anisotropic ring magnet according to claim 7, wherein