JP3933415B2

JP3933415B2 - Rare earth bonded magnets made from recycled magnet waste

Info

Publication number: JP3933415B2
Application number: JP2001177822A
Authority: JP
Inventors: 俊治鈴木; 憲一町田; 吟也足立
Original assignee: Japan Science and Technology Agency; National Institute of Japan Science and Technology Agency
Current assignee: Japan Science and Technology Agency; National Institute of Japan Science and Technology Agency
Priority date: 2001-06-12
Filing date: 2001-06-12
Publication date: 2007-06-20
Anticipated expiration: 2021-06-12
Also published as: JP2002367820A

Description

【０００１】
【発明の属する技術分野】
本発明は、焼結磁石廃材を再利用した省資源で安価、且つ高い磁気エネルギー積を有する希土類ボンド磁石に関する。
【０００２】
【従来の技術】
Ｎｄ−Ｆｅ−Ｂ系希土類ボンド磁石は、焼結磁石より磁気特性は劣るものの高寸法精度の円筒形状磁石が容易に製作できる。そのため、急冷法によって製造された磁粉を用いた等方性ボンド磁石は、ＨＤＤ用スピンドルモータや各種のステッピングモータに広く応用され生産量が増加している。また、水素処理をして異方性の結晶組織をもつ、所謂ＨＤＤＲ粉末と称するＮｄ−Ｆｅ−Ｂ系磁粉を用いた異方性ボンド磁石も、等方性より高い磁気特性が得られるために実用化され始めた。
【０００３】
一方、希土類焼結磁石の生産量も年々著しく増加しており、製造工程において発生する焼結不良品や研磨屑などの磁石廃材は磁石仕込み量の数十％に達し、年間数千トンに及んでいると推定される。この磁石廃材の中には希少資源である希土類元素が相当量含まれるために、その回収と再利用が求められている。
【０００４】
【発明が解決しようとする課題】
Ｎｄ−Ｆｅ−Ｂ系ボンド磁石は、ＭＱＩ社が製造販売する等方性磁粉にエポキシ樹脂を混合して圧縮成形または射出成形する方式が主流となっている。この磁石の磁気特性は成形体中の磁粉含有率の高低によってほぼ決まるが、磁気特性向上のための手段として第一に、平均粉末粒径を１００〜３００ミクロン程度に大きくし、磁石表面粗さの悪さを犠牲にして圧縮成形性を上げる、第二に、ダイスやパンチ類の消耗や欠損を考慮しつつ約１．５ＧＰａ迄の高圧力を加えて、粉末の充填性を上げる、第三に、ステアリン酸や窒化硼素などの潤滑剤を磁粉に混ぜるか金型に塗布して成形性を改善する、などの手段を採用しても磁気特性は９０〜１００ｋＪ／ｍ³程度である。
【０００５】
また、最近では、異方性のＨＤＤＲ磁粉を用いた異方性ボンド磁石も工業化の緒についたが、モータに多用される小径筒状磁石を製作する場合には本質的に磁界配向が充分に行われないため、角型ブロック磁石では容易に得られる１５０ｋＪ／ｍ³の特性が、１２０ｋＪ／ｍ³程度に止まってしまう。このように、いずれのボンド磁石においても、磁気特性を向上させることが容易ではなかった。
【０００６】
一方、近年の希土類磁石の生産量の増加に伴って資源再利用の必要性が唱えられている。ボンド磁石の製造工程は比較的短く、且つ成形後の機械加工がないために製品歩留まりは９８〜９９％であり、したがって、磁石廃材発生量は少ない。それに対して、Ｎｄ−Ｆｅ−Ｂ系焼結磁石は製造工程数が多く、主たる用途であるＨＤＤ向けＶＣＭ用磁石の場合には、大きなブロックを成形し、焼結した後に切断研磨する方式が採られているために、端材や研磨屑、あるいは特性不良品などの磁石廃材が多量に発生する。
【０００７】
この磁石廃材の中で、焼結片など数ｍｍの固形スクラップは再溶解して一次合金とした後に本溶解する事が一部実施されているが、メッキ被膜の剥離手間や不純物除去の困難性から採算的に問題がある。また、磁石の研磨屑は数ミクロン程度であるために表面が酸化して保磁力が著しく低下し、そのままでは焼結磁石に使用するのが困難である。従って、研磨屑は加熱焼成して完全な酸化物にして、イオン抽出法によりＮｄやＤｙなどを分離回収し合金原料とするが、工程管理が複雑で安定操業上その実施は限られている。
【０００８】
周知のように、Ｎｄ−Ｆｅ−Ｂ系焼結磁石は１ｍｍ以下の薄片や数十ミクロンの粉末形態では、核発生型の保磁力機構が故に保磁力が著しく低下し、従来は磁石として用いられることはなかった。
しかし、最近、焼結磁石表面にＺｎ被膜を形成して表面相の合金化反応を研究し、耐食性の向上についての報告がある（J. Alloys and Compound, 306(2000)253）。また、焼結磁石薄片にＡｕ，Ｔａ，Ｄｙなどのスパッタ被膜を形成して、保磁力回復の機構を研究した報告がある（Pro. of 16th Int. Workshop on Rare-earth Magnets and Their applications, Sendai, 2000, pp.257）。しかし、これらの報告は、いずれも、焼結磁石としての特性確保を目的とした研究に関するものであり、焼結磁石廃材を再利用する意図はみられない。
【０００９】
本発明は、希土類焼結磁石の製造工程において大量に発生する磁石廃材を、乾燥や粒度調整をしてそのまま用いるか、あるいは磁性回復等のための表面被膜形成処理を行ってボンド磁石用粉末として再利用することにより、省資源で安価、且つ高磁気特性のボンド磁石を提供することを目的とする。
【課題を解決するための手段】
【００１０】
本発明は、上記の目的を達成するために、希土類焼結磁石およびその加工屑から成る、平均粒径２〜４０ミクロンの磁石廃材粉末が６０質量％未満５質量％以上と、急冷法によって製作した平均粒径４０〜３００ミクロンの等方性Ｎｄ−Ｆｅ−Ｂ系粉末が４０質量％以上９５質量％未満とを、有機物樹脂で成形固化したことを特徴とする磁石廃材を再利用した等方性の希土類ボンド磁石を提供する。
【００１１】
また、希土類焼結磁石およびその加工屑から成る、平均粒径２〜４０ミクロンの磁石廃材粉末が６０質量％未満５質量％以上と、水素処理した平均粒径４０〜３００ミクロンの異方性Ｎｄ−Ｆｅ−Ｂ系粉末が４０質量％以上９５質量％未満とを、有機物樹脂で成形固化したことを特徴とする磁石廃材を再利用した異方性の希土類ボンド磁石を提供する。
【００１２】
さらに、上述の磁石廃材粉末として、その表面に０．０１〜３ミクロン厚の金属、合金、またはセラミックス被膜が形成されているものを用いたことを特徴とする磁石廃材を再利用した希土類ボンド磁石を提供する。
【００１３】
【作用】
本発明において、磁石廃材からなる粉末は、新規材磁粉の空隙を埋めることを意図しているために、その粒径は相対的に小さくなければならない。粒径の下限は２ミクロンとし、これより小さいと強酸化されているために保磁力の回復が実質的に困難であり、一方、４０ミクロンを超えると空隙を埋める作用が果たし得なくなる。
【００１４】
また、磁粉全体に占めるその混入量は、６０質量％未満までとすることが、充分な空隙充填効果を生み、従来の磁気特性を超えるために必要である。磁石廃材粉末は５質量％程度以上なるべく多く再利用した方が省資源上望ましいが、磁気特性を考慮すれば、好ましくは１０〜５０質量％、より好ましくは２０〜４０質量％とする。特に、異方性ボンド磁石においては、相対的に小さい磁石廃材粉末が磁界中成形時のＨＤＤＲ粉末粒子の回転を助長して、配向性を向上させる効果がある。
【００１５】
混合する磁石廃材粉末を微粉にするのに対して、新規材磁粉の平均粒径は高密度充填にとって有利なように大きくし、下限は４０ミクロンとする。これ以下の粒径では充填密度が著しく低下して所定の磁気特性が得られず、反対に３００ミクロンを超えると粉末粒子間の空隙が増加して密度が減少し、また、同時に磁石表面の粗さが大きくなって保護膜にピンホールができるので耐食性が低下する。
【００１６】
磁石廃材粉末の表面に金属、合金、またはセラミックス被膜を形成し粉末の表面を修復することにより保持力向上や耐酸化性を向上させることができる。これらの効果を得るには、被膜の膜厚は、少なくとも百原子層程度の０．０１ミクロンが必要であり、一方、３ミクロンを超えると被膜材質が非磁性であるために全体の磁性を薄めてしまうことになり、高磁気特性を得ることができなくなる
【００１７】
【発明の実施の形態】
本発明を製造工程に従って詳しく説明する。本発明で対象とする希土類ボンド磁石は、希土類元素をＲとし遷移元素をＴとした場合にＲ₂Ｔ₁₄Ｂ等で示される化合物を主相とし、一般にＮｄ−Ｆｅ−Ｂ系ボンド磁石と表現される。その合金成分中にはα−ＦｅやＦｅ₃Ｂ相を含有したり、あるいはＮｄ以外にＤｙやＰｒ等他の希土類元素や、Ｃｏ,Ｃｒ等の遷移元素を含有しても差し支えない。
【００１８】
ボンド磁石の結合材は成形方式によって選択され、圧縮成形ではエポキシやフェノール等の熱硬化性樹脂を、射出成形ではナイロンやＰＶＴ等の熱可塑性樹脂を、押し出し成形では加硫ゴムなどが用いられる。また、異方性磁石においては、８００〜２４００ｋＡ／ｍ程度の直流あるいはパルス磁界を所定の方向に印加させて成形を行う。得られた磁石は殆ど機械加工することなく、通常、錆び防止のために表面を樹脂で塗装し、最後に着磁をして磁石製品とする
【００１９】
新規材として用いる磁粉は、合金溶湯を回転するロール表面に噴出して急冷凝固させた等方性の急冷法によって製作した磁粉や、合金に水素を吸蔵放出させる過程で異方性の結晶組織を得た水素処理した（ＨＤＤＲ）磁粉が最も一般的であるが、その他にアトマイズや水中紡糸法による急冷法よっても所望の磁粉を得ることができる。これらの磁粉は、ボンド磁石内に高密度に充填させて高い磁気特性を得るために、適切な粒径を選択することが必要である。
【００２０】
一方、磁石廃材粉末の原料とする希土類焼結磁石およびその加工屑などの廃材としては、焼結工程で割れや亀裂を生じた不良品、メッキや樹脂塗装での外観不良品、検査工程での寸法や磁気特性不良品、切断時の欠けや端材、研磨工程での研磨屑などの加工屑、などが挙げられる。廃材として量的にはＮｄ−Ｆｅ−Ｂ系が圧倒的に多いがその約半分程度の量があるＳｍ−Ｃｏ系磁石廃材を対象の廃材として除外するものではない。
【００２１】
Ｓｍ−Ｃｏ系焼結磁石廃材は、Ｎｄ−Ｆｅ−Ｂ系磁石廃材と比較してＣｏを多量に含有するために酸化され難く、したがって、保持力の低下が少ない性質を持っている。また、Ｓｍ−Ｃｏ系焼結体の初期ＢＨｍａｘはＮｄ−Ｆｅ−Ｂ系より低いが、廃材ではＮｄ−Ｆｅ−Ｂ系より保持力の低下が小さいため、ボンド磁石に混合する廃材はどちらの系を用いてもかまわない。
【００２２】
これらの磁石廃材の内、大きさが１ｍｍ以上の欠けや不良品はクラッシャーによる粗粉砕後、ボールミルやジェットミルによる微粉砕を行って数〜数十ミクロンの粉末を製作する。また、研磨屑は通常数ミクロンの粉末となっており、粉末表面の酸化や形態的な荒れによって保磁力が著しく低下していることが多い。
【００２３】
保磁力を回復する場合、粉末粒子表面に各種の金属または合金薄膜を形成する。粒子表面に露出したＮｄ−Ｆｅ−Ｂ相は酸化によってＮｄが欠損しているために、ＮｄやＤｙ等の希土類金属を機械的に混合して成膜したり、気相蒸着あるいは物理蒸着法によって成膜する。
【００２４】
研磨屑は機械加工による内部歪と不規則な表面層をもつために、ＺｎやＡｌ等の比較的低融点の金属を蒸発成膜し、加熱によって粒子表面と固相反応を起こさせ、表面相の形態的修復を行う。なお、被膜材質はこの他に酸化防止効果のあるＮｉやＴａなどの金属または合金を用いることができる。さらには、酸化ケイ素などセラミックスをゾルゲル法などの湿式処理によって成膜しても、ボンド磁石の耐環境特性の向上に効果がある。
【００２５】
図３に、上記の磁石廃材粉末に各金属を被覆したときの、被膜の厚さと磁気特性の関係を示す。図３から明らかなように、磁石廃材粉末の表面にごく薄い被膜を形成することによって、保磁力（ＨcJ）と残留磁化（Ｂr）が著しく向上する。被膜厚が薄い場合の残留磁化の向上は保磁力の増加に伴う現象であり、被膜厚が厚過ぎる場合は非磁性の金属被膜の体積が増加するために、残留磁化は低下する。従って、本発明の磁石において用いる磁石廃材粉末の場合は、被膜厚は３ミクロン以下にすることが好ましい。
【００２６】
図３に示す磁石廃材粉末への成膜は、下記の方法によって行った。磁気エネルギー積が３３６ｋＪ／ｍ³のＮｄ−Ｄｙ−Ｆｅ−Ｃｏ−Ｂ系焼結磁石の研磨屑を回収・乾燥して、平均粒径７ミクロンの粉末を得た。この研磨屑は、粒子表面が酸化して２．１質量％の酸素を含有し、磁気特性のうち特に保磁力が著しく低下していたため、粒子表面の酸化層除去と凹凸解消の目的で金属被覆処理を行った。被覆処理は、研磨屑粉末に金属Ｚｎ，Ａｌ，またはＤｙの各粉末とアルミナボールを石英容器に装填し、真空引きした後に容器を回転させながら、４００〜６００℃で１〜６時間加熱することによった。
【００２７】
また、被膜の厚さ測定用として当該焼結磁石片を石英ポットに装填した。被膜の厚さはβ線測定器によって測定した。また、被覆しや粉末の磁気特性は、予め、パラフィン中に磁粉を混合して磁界中で配向固定し、４．８ＭＡ／ｍのパルス着磁をした後に振動試料型磁力計を用いて測定した。
【００２８】
【実施例】
以下、本発明を実施例に従って詳細に説明する。
実施例１
ＭＱＩ社製の急冷法によるＮｄ−Ｆｅ−Ｃｏ−Ｂ系磁粉（商品名：ＭＱＰＢ）を、窒素ガスを導入した衝撃式気流粉砕機を用いて粉砕刃の回転数を３０００ｒｐｍにセットして粉砕し、平均粒径１４０ミクロンの粗粉末を得た。一方、３３６ｋＪ／ｍ³の磁気エネルギー積をもつＮｄ−Ｄｙ−Ｆｅ−Ｃｏ−Ｂ系焼結磁石のアルミメッキ不良品を廃材として用いた。この磁石廃材から、塩酸によってメッキ膜を剥離乾燥した後に、粉砕機の回転数を６０００ｒｐｍに上げて粉砕をし、平均粒径２２ミクロンの微粉末を得た。
【００２９】
前者に、磁石廃材粉末を０，１０，２０，３０，４０，５０，６０，７０質量％の割合で混ぜた混合粉末と、質量比で２．５ｗｔ％のエポキシ樹脂とを混合・混練し、ＷＣ製金型を使用して無磁界中で１．２ＧＰａの圧力をかけて、１０×１０×７ｍｍの成形体を製作した。続いて、窒素雰囲気中、１２０℃で１時間の硬化処理を行って磁石試料とした。
【００３０】
各試料の密度はアルキメデス法により、また、磁気特性は４．８ＭＡ／ｍのパルス磁界を加えた後、２ＭＡ／ｍの磁界中でＢＨトレーサによって測定した。得られた試料の、混合比に対する密度と磁気特性との関係を図１に示す。図から明らかなように、ＭＱＰＢ粉末に粒子サイズの小さな磁石廃材粉末を混合することによって、密度が向上し、その結果として磁気特性が向上した。ただし、磁石廃材粉末の混合率が６０質量％以上では微粉末量が過剰となるために、ＭＱＰＢ磁粉単独の場合より密度が低下して磁気特性も低下する。
【００３１】
実施例２
ＭＱＰＢ粉末を粉砕せずに振動ふるい機によって篩い分けし、平均粒径が２８，４７，７４，１１０，１６４，２７４，３５５みくろんの各粉末を得た。この粉末に、実施例１で用いた平均粒径２２ミクロンの磁石廃材微粉末を２０質量％の割合で混合し、エポキシ樹脂とを添加混合してボンド磁石を製作し、本発明試料１〜５、および比較例試料２〜３とした。また、上記の本発明試料３の１１０ミクロンの粉末を使用して、磁石廃材粉末を混合しない磁石試料を比較例１として製作した。表１に、各試料の密度と磁気特性を示す。
【００３２】
【表１】

【００３３】
ＭＱＰＢ粉末の粒径が小さ過ぎる比較例２と大き過ぎる比較例試料３は、磁石廃材粉末を混合しない比較例試料１より、密度も磁気特性共に低下した。この理由は、比較例２の試料では粒径が小さ過ぎるために、磁石廃材粉末がＭＱＰＢの粒子間の空隙に充填されずに密度が得られなかったためで、比較例３の試料では粒径が大き過ぎるため上記空隙を埋めるに充分な磁石廃材粉末が供給されずに密度が低下したためである。一方、本発明試料１〜５は密度が向上して、高い磁気特性が得られた。
【００３４】
実施例３
水素処理によって製作されたＮｄ−Ｄｙ−Ｆｅ−Ｚｒ−Ｂ系のＨＤＤＲ磁粉を粉砕した平均粒径１４０ミクロンの粉末に、実施例１で用いた平均粒径２２ミクロンの磁石廃材からなる微粉末を、０，１０，２０，３０，４０，５０，６０，７０質量％の割合で混合した。この混合粉末に、質量比で２．２％のエポキシ樹脂と０．１％のオレイン酸を添加混合し、１．６ＭＡ／ｍの磁界中で１ＧＰａの圧力を加えて１０×１０×７ｍｍの成形体を製作し、硬化処理を行って異方性の磁石試料を得た。
【００３５】
図２に、磁石廃材粉末の混合比に対する密度と磁気特性との関係を示す。この結果、磁石廃材粉末を混合させることによって密度と磁気特性が向上することがわかった。但し、混合率が６０質量％以上では微粉末量が過剰となり磁気特性が低下する。
【００３６】
実施例４
磁気エネルギー積が３３６ｋＪ／ｍ³のＮｄ−Ｄｙ−Ｆｅ−Ｃｏ−Ｂ系焼結磁石の研磨屑を回収・乾燥して、平均粒径７ミクロンの粉末を得た。この研磨屑粉末と金属Ｚｎ粉末とアルミナボールを石英容器に装填し、真空引きした後に容器を回転させながら、５００℃で１時間加熱し厚さ０.０８ミクロンのＺｎ被膜粉末を得た。このＺｎ被膜粉末２０質量％を平均粒径１００ミクロンに粉砕したＨＤＤＲ磁粉に混合した。この混合粉末にシランカップリング処理をして１２ナイロン樹脂を６質量％混合し、加熱押し出しをして成形用ペレットを製作した。次に、極配向用金型を用いて２８０℃で射出成形をし、外形２４ｍｍ、内径２０ｍｍ、高さ４ｍｍの極異方配向した本発明試料を得た。
【００３７】
また、比較例として、ＨＤＤＲ単独粉を用いて射出成形した磁石を合わせて製作した。これら磁石を着磁ヨークに装填し、約２ＭＡ／ｍのパルス磁界を加えて外周２４極に着磁をし、ガウスメータによって表面磁束密度を測定した。その結果、比較例の表面磁束密度が３２２ｍＴであるのに対して本発明試料のそれは３４０ｍＴの値を示し、研磨廃材を用いているにもかかわらず高い磁気特性が得られることがわかった。
【００３８】
【発明の効果】
本発明によれば、希土類ボンド磁石において、焼結磁石の廃材を磁石粉として再利用し、従来、ボンド磁石に用いていた磁粉より粒径を小さくして、磁石中の磁粉充填率を従来より高めて磁気特性の高い希土類ボンド磁石ができる。また、磁石廃材粉末の表面に被膜を形成して保磁力を回復させること、耐環境特性を向上させることもでき、優れた特性を有し、省資源で安価なボンド磁石の供給が可能になる。
【図面の簡単な説明】
【図１】図１は、ＭＱＰＢ粉末と磁石廃材粉末の混合比に対する、ボンド磁石の密度と磁気特性との関係を示すグラフである。
【図２】図２は、ＨＤＤＲ粉末と磁石廃材粉末の混合比に対する、ボンド磁石の密度と磁気特性との関係を示すグラフである。
【図３】図３は、磁石廃材粉末への各金属の被覆膜厚と、磁気特性の関係を示すグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a rare earth bonded magnet having a high magnetic energy product, which is resource-saving, inexpensive, and reuses a sintered magnet waste material.
[0002]
[Prior art]
Nd-Fe-B rare earth bonded magnets can be easily manufactured as cylindrical magnets with high dimensional accuracy, although magnetic properties are inferior to sintered magnets. For this reason, isotropic bonded magnets using magnetic powder produced by a rapid cooling method are widely applied to HDD spindle motors and various stepping motors, and their production volume is increasing. In addition, anisotropic bonded magnets using Nd-Fe-B based magnetic powders called so-called HDDR powders, which have an anisotropic crystal structure after hydrogen treatment, also have magnetic properties higher than isotropic properties. Began practical use.
[0003]
On the other hand, the production volume of rare earth sintered magnets has increased remarkably year by year, and magnet waste materials such as poorly sintered products and abrasive scraps generated in the manufacturing process have reached several tens of percent of the amount of magnets charged, reaching several thousand tons per year. It is estimated that Since this magnet waste material contains a considerable amount of rare earth elements, which are rare resources, recovery and reuse are required.
[0004]
[Problems to be solved by the invention]
Nd—Fe—B based bonded magnets are mainly produced by compression molding or injection molding by mixing an isotropic magnetic powder manufactured and sold by MQI with an epoxy resin. The magnetic properties of this magnet are almost determined by the level of magnetic powder content in the compact, but as a means for improving the magnetic properties, first, the average powder particle size is increased to about 100 to 300 microns, and the magnet surface roughness is increased. Improve compression moldability at the expense of poorness. Second, increase the powder filling by applying high pressure up to about 1.5 GPa while considering the consumption and chipping of dies and punches. Even if means such as a lubricant such as stearic acid or boron nitride is mixed with magnetic powder or applied to a mold to improve the moldability, the magnetic properties are about 90 to 100 kJ / m ³ .
[0005]
Recently, anisotropic bonded magnets using anisotropic HDDR magnetic powder have begun to be industrialized. However, when manufacturing small-diameter cylindrical magnets frequently used in motors, the magnetic field orientation is essentially sufficient. Since it is not performed, the characteristic of 150 kJ / m ³ easily obtained with the square block magnet is limited to about 120 kJ / m ³ . As described above, it is not easy to improve the magnetic characteristics of any bonded magnet.
[0006]
On the other hand, the necessity of resource reuse is advocated with the recent increase in production of rare earth magnets. The manufacturing process of the bonded magnet is relatively short, and since there is no machining after molding, the product yield is 98 to 99%. Therefore, the amount of magnet waste generated is small. On the other hand, Nd-Fe-B sintered magnets have a large number of manufacturing processes, and in the case of VCM magnets for HDD, which is the main application, a method of forming a large block, sintering and then cutting and polishing is adopted. For this reason, a large amount of scrap magnets, scraps, or magnet waste materials such as defective properties are generated.
[0007]
In this magnet waste material, solid scraps of several mm, such as sintered pieces, have been partially melted and made into a primary alloy and then partially melted. However, it is difficult to remove the plating film and remove impurities. There is a problem with profitability. Further, since the polishing scrap of the magnet is about several microns, the surface is oxidized and the coercive force is remarkably lowered, so that it is difficult to use it as it is for a sintered magnet. Accordingly, polishing scraps are heated and fired to form complete oxides, and Nd, Dy, and the like are separated and recovered by an ion extraction method and used as alloy raw materials. However, the process management is complicated and its implementation is limited for stable operation.
[0008]
As is well known, Nd-Fe-B sintered magnets have a remarkably reduced coercive force when used in the form of flakes of 1 mm or less or powders of several tens of microns due to the nucleation type coercive force mechanism, and are conventionally used as magnets. It never happened.
Recently, however, a Zn coating is formed on the surface of a sintered magnet to study the alloying reaction of the surface phase, and there is a report on improving the corrosion resistance (J. Alloys and Compound, 306 (2000) 253). In addition, there is a report that studied the mechanism of coercive force recovery by forming a sputtered film of Au, Ta, Dy, etc. on sintered magnet flakes (Pro. Of 16th Int. Workshop on Rare-earth Magnets and Their applications, Sendai , 2000, pp.257). However, all of these reports relate to research aimed at securing characteristics as a sintered magnet, and there is no intention to reuse the sintered magnet waste.
[0009]
The present invention uses the waste magnet material generated in a large amount in the manufacturing process of the rare earth sintered magnet as it is after drying and particle size adjustment, or by performing a surface film forming treatment for magnetic recovery or the like as a powder for a bond magnet. An object of the present invention is to provide a bond magnet that is resource-saving, inexpensive, and has high magnetic properties by being reused.
[Means for Solving the Problems]
[0010]
In order to achieve the above object, the present invention produces a magnet waste material powder having an average particle diameter of 2 to 40 microns consisting of a rare earth sintered magnet and its processing scraps by less than 60% by mass and 5% by mass or more by a rapid cooling method. Isotropic Nd-Fe-B powder having an average particle size of 40 to 300 microns, which is 40% by mass or more and less than 95% by mass, solidified with an organic resin, isotropically reusing waste magnetic material The rare earth bonded magnet is provided.
[0011]
Further, a magnet waste material powder having an average particle diameter of 2 to 40 microns composed of a rare earth sintered magnet and its processing waste is less than 60 mass% and 5 mass% or more, and an anisotropic Nd having an average particle diameter of 40 to 300 microns treated with hydrogen. Provided is an anisotropic rare-earth bonded magnet that reuses a magnet waste material, in which an Fe-B-based powder is molded and solidified with an organic resin at 40 mass% or more and less than 95 mass%.
[0012]
Furthermore, as the above-mentioned magnet waste material powder, a rare earth bonded magnet that reuses the magnet waste material, wherein the surface is formed with a metal, alloy, or ceramic film having a thickness of 0.01 to 3 microns. I will provide a.
[0013]
[Action]
In the present invention, the powder made of magnet waste material is intended to fill the voids of the new magnetic material powder, so its particle size must be relatively small. The lower limit of the particle size is 2 microns, and if it is smaller than this, it is substantially difficult to recover the coercive force because it is strongly oxidized. On the other hand, if it exceeds 40 microns, the effect of filling the voids cannot be achieved.
[0014]
Further, the mixing amount in the whole magnetic powder is required to be less than 60% by mass in order to produce a sufficient gap filling effect and to exceed conventional magnetic characteristics. It is desirable in terms of resource saving to reuse as much as possible about 5% by mass or more of the magnet waste material powder, but preferably 10 to 50% by mass, more preferably 20 to 40% by mass considering the magnetic properties. In particular, in an anisotropic bonded magnet, relatively small magnet waste material powder has an effect of promoting the rotation of HDDR powder particles during molding in a magnetic field and improving the orientation.
[0015]
While the magnet waste material powder to be mixed is made fine, the average particle size of the new material magnetic powder is made large so as to be advantageous for high-density filling, and the lower limit is made 40 microns. If the particle size is smaller than this, the packing density is remarkably lowered and a predetermined magnetic property cannot be obtained. Conversely, if the particle diameter exceeds 300 microns, the gap between the powder particles is increased and the density is decreased. As the thickness increases, pinholes are formed in the protective film, which reduces the corrosion resistance.
[0016]
By forming a metal, alloy, or ceramic film on the surface of the magnet waste material powder and repairing the surface of the powder, it is possible to improve the holding power and the oxidation resistance. In order to obtain these effects, the film thickness needs to be at least 0.01 micron of about 100 atomic layers. On the other hand, if it exceeds 3 microns, the film material is non-magnetic, so the whole magnetism is reduced. As a result, high magnetic properties cannot be obtained.
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described in detail according to the manufacturing process. The rare earth bonded magnet which is the subject of the present invention has a compound represented by R ₂ T ₁₄ B or the like as a main phase when R is a rare earth element and T is a transition element, and is generally expressed as an Nd—Fe—B based bonded magnet. Is done. The alloy component may contain an α-Fe or Fe ₃ B phase, or may contain other rare earth elements such as Dy and Pr, and transition elements such as Co and Cr in addition to Nd.
[0018]
The bonding material of the bond magnet is selected according to the molding method, and a thermosetting resin such as epoxy or phenol is used for compression molding, a thermoplastic resin such as nylon or PVT is used for injection molding, and a vulcanized rubber is used for extrusion molding. An anisotropic magnet is formed by applying a direct current or pulsed magnetic field of about 800 to 2400 kA / m in a predetermined direction. The obtained magnet is hardly machined and is usually coated with a resin to prevent rust, and finally magnetized to obtain a magnet product.
Magnetic powder used as a new material is produced by isotropic quenching method in which molten alloy is jetted onto the rotating roll surface and rapidly solidified, and anisotropic crystal structure is produced in the process of absorbing and releasing hydrogen into the alloy. The obtained hydrogen-treated (HDDR) magnetic powder is the most common, but the desired magnetic powder can also be obtained by the rapid cooling method by atomization or underwater spinning. It is necessary to select an appropriate particle size in order to obtain high magnetic properties by filling these magnetic powders in a bonded magnet with high density.
[0020]
On the other hand, rare earth sintered magnets that are used as raw materials for magnet waste powder and scraps such as processing scraps include defective products that have cracked or cracked in the sintering process, defective appearance in plating and resin coating, and inspection processes. Dimensional and magnetic property defective products, chips and end materials at the time of cutting, processing scraps such as polishing scraps in the polishing process, and the like. Sm-Co-based magnet waste materials, which are predominantly Nd-Fe-B-based in terms of quantity but are about half that amount, are not excluded as target waste materials.
[0021]
The Sm—Co based sintered magnet waste material is less oxidized because it contains a large amount of Co as compared with the Nd—Fe—B based magnet waste material. In addition, the initial BHmax of the Sm—Co-based sintered body is lower than that of the Nd—Fe—B system, but the waste material has a smaller decrease in holding power than the Nd—Fe—B system. May be used.
[0022]
Of these magnet waste materials, chips and defectives with a size of 1 mm or more are coarsely pulverized by a crusher and then finely pulverized by a ball mill or a jet mill to produce a powder of several to several tens of microns. In addition, the polishing dust is usually a powder of several microns, and the coercive force is often significantly reduced due to oxidation and morphological roughness of the powder surface.
[0023]
When recovering the coercive force, various metal or alloy thin films are formed on the surface of the powder particles. Since the Nd-Fe-B phase exposed on the particle surface lacks Nd due to oxidation, it is formed by mechanically mixing rare earth metals such as Nd and Dy, or by vapor deposition or physical vapor deposition. Form a film.
[0024]
Since the polishing scraps have internal strain due to machining and an irregular surface layer, a relatively low melting point metal such as Zn or Al is evaporated to form a solid phase reaction with the particle surface by heating. Perform morphological repair. In addition, the coating material may be a metal or alloy such as Ni or Ta that has an antioxidant effect. Furthermore, even if a ceramic film such as silicon oxide is formed by a wet process such as a sol-gel method, it is effective in improving the environmental resistance characteristics of the bonded magnet.
[0025]
FIG. 3 shows the relationship between the thickness of the coating and the magnetic properties when each metal is coated on the magnet waste material powder. As is clear from FIG. 3, the coercive force (HcJ) and the residual magnetization (Br) are remarkably improved by forming a very thin film on the surface of the magnet waste material powder. Improvement of the remanent magnetization when the film thickness is thin is a phenomenon associated with an increase in coercive force. When the film thickness is too thick, the volume of the nonmagnetic metal film increases, and the remanent magnetization decreases. Therefore, in the case of the magnet waste material powder used in the magnet of the present invention, the film thickness is preferably 3 microns or less.
[0026]
Film formation on the magnet waste material powder shown in FIG. 3 was performed by the following method. The polishing scraps of the Nd—Dy—Fe—Co—B based sintered magnet having a magnetic energy product of 336 kJ / m ³ were recovered and dried to obtain a powder having an average particle diameter of 7 microns. This polishing scrap contains 2.1% by mass of oxygen as a result of oxidation of the particle surface, and the coercive force is particularly low among the magnetic properties. Therefore, it is coated with metal for the purpose of removing the oxide layer on the particle surface and eliminating irregularities. Processed. In the coating treatment, each powder of metal Zn, Al, or Dy and alumina balls and abrasive balls are loaded into a quartz container and heated at 400 to 600 ° C. for 1 to 6 hours while rotating the container after evacuation. According.
[0027]
The sintered magnet piece was loaded into a quartz pot for measuring the thickness of the coating. The thickness of the coating was measured with a β-ray measuring device. The magnetic properties of the coating and powder were measured using a vibrating sample magnetometer after mixing magnetic powder in paraffin and fixing the orientation in a magnetic field and performing pulse magnetization of 4.8 MA / m in advance. .
[0028]
【Example】
Hereinafter, the present invention will be described in detail according to examples.
Example 1
Nd-Fe-Co-B type magnetic powder (trade name: MQPB) produced by MQI by rapid cooling method is pulverized using an impact airflow pulverizer into which nitrogen gas has been introduced and the rotational speed of the pulverizing blade set to 3000 rpm. A coarse powder having an average particle size of 140 microns was obtained. On the other hand, defective aluminum plating of Nd—Dy—Fe—Co—B based sintered magnet having a magnetic energy product of 336 kJ / m ³ was used as a waste material. From this magnet waste material, the plating film was peeled and dried with hydrochloric acid, and then pulverized by increasing the rotational speed of the pulverizer to 6000 rpm to obtain a fine powder having an average particle size of 22 microns.
[0029]
In the former, mixed powder obtained by mixing magnet waste material powder at a ratio of 0, 10, 20, 30, 40, 50, 60, 70 mass% and epoxy resin having a mass ratio of 2.5 wt% are mixed and kneaded, Using a WC mold, a pressure of 1.2 GPa was applied in the absence of a magnetic field to produce a 10 × 10 × 7 mm compact. Subsequently, a magnet sample was obtained by performing a curing treatment at 120 ° C. for 1 hour in a nitrogen atmosphere.
[0030]
The density of each sample was measured by the Archimedes method, and the magnetic characteristics were measured by a BH tracer in a magnetic field of 2 MA / m after applying a pulse magnetic field of 4.8 MA / m. FIG. 1 shows the relationship between the density and the magnetic characteristics of the obtained sample with respect to the mixing ratio. As is apparent from the figure, the density was improved by mixing the magnet waste material powder having a small particle size with the MQPB powder, and as a result, the magnetic properties were improved. However, when the mixing ratio of the magnet waste material powder is 60% by mass or more, the amount of fine powder becomes excessive, so that the density is lowered and the magnetic characteristics are also lowered as compared with the case of MQPB magnetic powder alone.
[0031]
Example 2
The MQPB powder was sieved by a vibrating sieve without pulverization, and each powder having an average particle size of 28, 47, 74, 110, 164, 274, 355 was obtained. The magnet waste material fine powder having an average particle size of 22 microns used in Example 1 was mixed with this powder at a ratio of 20% by mass, and an epoxy resin was added and mixed to produce a bonded magnet. And Comparative Samples 2-3. In addition, a magnet sample in which the waste magnet powder was not mixed using the 110-micron powder of Sample 3 of the present invention was manufactured as Comparative Example 1. Table 1 shows the density and magnetic properties of each sample.
[0032]
[Table 1]

[0033]
The comparative example 2 in which the particle size of the MQPB powder is too small and the comparative example sample 3 in which the particle size is too large are lower in both density and magnetic properties than the comparative example sample 1 in which the magnet waste material powder is not mixed. This is because the particle size of the sample of Comparative Example 2 is too small, and the magnet waste material powder is not filled in the voids between the MQPB particles, and the density cannot be obtained. This is because, since it is too large, the magnet waste material powder sufficient to fill the gap is not supplied and the density is lowered. On the other hand, the inventive samples 1 to 5 were improved in density, and high magnetic properties were obtained.
[0034]
Example 3
The fine powder composed of the waste magnet material having an average particle size of 22 microns used in Example 1 was added to the powder having an average particle size of 140 microns obtained by pulverizing the NDDR-Dy-Fe-Zr-B type HDDR magnetic powder produced by the hydrogen treatment. , 0, 10, 20, 30, 40, 50, 60, 70 mass%. To this mixed powder, 2.2% by weight of epoxy resin and 0.1% oleic acid are added and mixed, and a pressure of 1 GPa is applied in a magnetic field of 1.6 MA / m to form 10 × 10 × 7 mm. The body was manufactured and cured to obtain an anisotropic magnet sample.
[0035]
FIG. 2 shows the relationship between the density and the magnetic characteristics with respect to the mixing ratio of the magnet waste material powder. As a result, it was found that the density and magnetic properties were improved by mixing the magnet waste material powder. However, if the mixing ratio is 60% by mass or more, the amount of fine powder becomes excessive and the magnetic properties are deteriorated.
[0036]
Example 4
The polishing scraps of the Nd—Dy—Fe—Co—B based sintered magnet having a magnetic energy product of 336 kJ / m ³ were recovered and dried to obtain a powder having an average particle diameter of 7 microns. This polishing scrap powder, metal Zn powder, and alumina ball were loaded into a quartz container, and after vacuuming, the container was rotated and heated at 500 ° C. for 1 hour to obtain a 0.08 micron thick Zn coating powder. 20% by mass of this Zn coating powder was mixed with HDDR magnetic powder pulverized to an average particle size of 100 microns. This mixed powder was subjected to silane coupling treatment, mixed with 6% by mass of 12 nylon resin, and heated to produce a pellet for molding. Next, injection molding was performed at 280 ° C. using a polar orientation mold, and a sample of the present invention having an outer shape of 24 mm, an inner diameter of 20 mm, and a height of 4 mm was obtained.
[0037]
Further, as a comparative example, a magnet molded by injection molding using HDDR single powder was also produced. These magnets were loaded into a magnetized yoke, a pulse magnetic field of about 2 MA / m was applied to magnetize the outer 24 poles, and the surface magnetic flux density was measured with a gauss meter. As a result, the surface magnetic flux density of the comparative example was 322 mT, whereas that of the sample of the present invention showed a value of 340 mT, and it was found that high magnetic properties were obtained despite using the polishing waste material.
[0038]
【The invention's effect】
According to the present invention, in the rare earth bonded magnet, the waste material of the sintered magnet is reused as the magnet powder, the particle size is made smaller than the magnetic powder conventionally used in the bonded magnet, and the magnetic powder filling rate in the magnet is conventionally increased. A rare earth bonded magnet with high magnetic properties can be produced. In addition, it is possible to recover the coercive force by forming a film on the surface of the magnet waste material powder and to improve the environmental resistance, and it is possible to supply a bond magnet that has excellent characteristics, is resource-saving, and is inexpensive. .
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the density and magnetic properties of a bonded magnet with respect to the mixing ratio of MQPB powder and magnet waste material powder.
FIG. 2 is a graph showing the relationship between the density of a bonded magnet and the magnetic characteristics with respect to the mixing ratio of HDDR powder and magnet waste material powder.
FIG. 3 is a graph showing the relationship between the coating thickness of each metal on the magnet waste material powder and the magnetic characteristics.

Claims

Nd-Fe-B or Sm-Co rare earth sintered magnets with cracks or cracks in the sintering process, defective appearance with plating or resin coating, defective dimensions or magnetic properties in the inspection process, Among scraped magnets and scraps at the time of cutting, those having a size of 1 mm or more are pulverized into powder, or composed of abrasive scraps of the rare earth sintered magnet and having an average particle size of 2 to 40 microns Magnet waste material powder is less than 50 % by mass and 20 % by mass or more, and isotropic Nd—Fe—B type powder having an average particle size of 40 to 300 microns manufactured by a rapid cooling method is 50 % by mass or more and less than 80 % by mass. Ri formed by molding solidified in resin, (BH) max 88.0kJ / m 3 or more der rare earth bonded magnet of isotropic Rukoto reusing the magnet waste characterized by.

Nd-Fe-B or Sm-Co rare earth sintered magnets with cracks or cracks in the sintering process, defective appearance with plating or resin coating, defective dimensions or magnetic properties in the inspection process, Among scraped magnets and scraps at the time of cutting, those having a size of 1 mm or more are pulverized into powder, or composed of abrasive scraps of the rare earth sintered magnet and having an average particle size of 2 to 40 microns a magnet scrap powder 10 mass% or more and less than 50 wt%, the anisotropy Nd-Fe-B powders having an average particle size of 40 to 300 microns which is hydrogen treatment and less than 50 wt% 90 wt%, with organic resin by molding solidified Ri formed, (BH) max 140kJ / m 3 or more der Rukoto anisotropic rare earth bonded magnet which reuse magnets waste characterized by.

The magnet waste material according to claim 1 or 2, wherein the magnet waste material powder has a surface on which a metal, alloy, or ceramic film having a thickness of 0.01 to 3 microns is formed. Recycled rare earth bonded magnet.