JP4159775B2 - Rare earth magnet manufacturing method - Google Patents
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- JP4159775B2 JP4159775B2 JP2001375886A JP2001375886A JP4159775B2 JP 4159775 B2 JP4159775 B2 JP 4159775B2 JP 2001375886 A JP2001375886 A JP 2001375886A JP 2001375886 A JP2001375886 A JP 2001375886A JP 4159775 B2 JP4159775 B2 JP 4159775B2
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Description
【０００１】
【発明の属する技術分野】
本発明は、特にはＮｄ系、Ｓｍ系焼結磁石等を得る場合に好適とされる希土類磁石の製造方法に関する。
【０００２】
【従来の技術及び発明が解決しようとする課題】
希土類焼結磁石は、その高い磁気特性のために、フェライト等に比べて非常に高価であるにも関わらず近年高い需要を示している。Ｎｄ系磁石は磁気特性が高く、比較的価格も安いことから、ＨＤＤ用ＶＣＭや産業用モータ等広範な分野に使用されている。また、Ｓｍ系磁石は、温度特性に優れ、高温でも十分な保磁力及び磁化を有していることから、高温耐久性が必要となる産業用モータ、アクチュエーター等の分野に使用されている。
【０００３】
希土類磁石は、一般的に粉末冶金法を用いて製造され、以下のような工程を経る。即ち、所定の組成となるよう原料を配合し、高周波溶解炉等を用いて溶解し、鋳造することにより合金を作成でき、その合金を粉砕して平均粒径１〜２０μｍの微粉末を得、その微粉末を磁場中にて所望の形状に圧縮成形することにより磁性粉末の成形体が得られる。その後、焼結及び熱処理を施すことによって焼結磁石となる。
【０００４】
粉末冶金法を用いた製造方法では、微粉末を型の内部に充填して外部より高い圧力を印可し圧縮成形し、成形体を作製する必要がある。微粉末の充填方法としては、水、有機溶媒等の液体と微粉末を混合し、スラリー状にして型内に充填する方法や、乾いた微粉末を充填する方法がある。スラリーを用いる場合、型は排液性能を有する材料で作製されるか又は排液設備を有する金型を用いて圧縮成形を行う必要がある。そのため、磁石を製造するための磁場を印可する設備に加えて、常にスラリーが混合された状態でスラリーを維持、供給するための設備や、成形のための排水設備等を備えた複雑な成形設備が必要となるばかりでなく、成形中に排液工程も含まれることから、成形に必要な時間がかかる。成形後も完全には排液されておらず、更に真空引きなどを用いた脱液処理が不可欠となり、成形のみならず、その前後の工程も非常に複雑となる。
【０００５】
また、乾いた微粉末を圧縮成形する方法としては、ゴム型内に微粉末を充填し、静水圧を用いて等方的に圧縮する方法や、金型を用いて一軸加圧を行い、圧縮成形する方法があるが、ゴム型を用いた静水圧成形法は、等方的に圧縮成形されるため、成形体の密度を高くすることができる、成形体密度のばらつきを少なくすることができるなどのメリットがあるものの、成形体の末端部の形状がいびつになり、磁場による微粉末の配向と静水圧成形とを同時に行うことが非常に困難であり、更にクラック防止のためにゆっくり除圧する必要があり、成形に要する時間が長いなどのデメリットがある。
【０００６】
このため粉末冶金法による希土類磁石を製造するための磁場中圧縮成形法としては、乾いた微粉末と金型を用いた一軸加圧による圧縮成形が一般的に用いられている。金型成形では、金型の形状を所望する製品の形状に応じて設計することにより、任意の形状の製品を製造することが可能であり、製品の加工がいらない、又は仕上げ加工時のロスが最小限にとどめられるというメリットを有している。他方、微粉末を金型内で高圧を用いて圧縮成形する必要があるために、金型と微粉末或いは金型同士の摩擦が非常に大きく、金型に接する面では、金型との焼き付きが発生し、金型に傷が生じるために傷が成形体に転写され、所定の形状が得られない、傷を起点として成形体に微細なクラックが生じるなどの不都合が生じる場合がある。
【０００７】
金型との摩擦の軽減及び傷を防止するために、金型の内面を鏡面研摩したり、超硬などの硬い金属を金型材料として用いたりするが、いずれも十分ではなく、１ショット或いは数ショット毎に金型内面に付着した微粉末を除去するなどの処置を施す必要があり、非常に生産効率が悪い。
【０００８】
予め微粉末の潤滑性を向上させるために潤滑効果を有する有機化合物などを微粉末に混合する方法もあるが、微粉末と金型の潤滑効果は認められるものの、金型同士の潤滑には寄与せず、また潤滑効果を高めるために微粉末への有機化合物の添加量を増加させると、潤滑剤中に存在する炭素の磁石中に残留する量が増加することによって、結果として保磁力が減少する、角形性が悪化するなどの磁気特性に問題が生じる。
【０００９】
このように、粉末冶金法による希土類磁石の磁場中圧縮成形に用いられる金型を用いた一軸加圧による圧縮成形の際に、金型と微粉末の焼き付きによる金型内面での傷の発生に伴い、所定の形状が得られなく、成形体に微細なクラックが発生し、金型内面の掃除に伴う生産効率の悪化、微粉に添加する有機化合物による磁気特性に問題があった。
【００１０】
本発明は、上記従来の希土類磁石の製造にかかわる問題点に鑑みなされたもので、効率よく、実用上十分の保磁力を有し、高い残留磁化を有する高性能希土類磁石の製造方法を提供することを目的とする。
【００１１】
【課題を解決するための手段及び発明の実施の形態】
本発明者らは、かかる課題を解決するために、希土類磁石の製造条件、特に金型を用いた一軸加圧による磁場中成形工程を詳細に検討した結果、金型内面に直接潤滑効果を有する液体を塗布することで潤滑性を保持させることに着目し、種々の液状有機化合物を金型内面にスプレー或いは布、不織布又はスポンジで塗布することによる金型潤滑方法を試みたところ、成形時に生ずる金型と微粉末或いは金型同士の摩擦が減少し、金型内面の傷の発生が抑制されることを見出した。即ち、沸点が１５０℃以上３５０℃以下で、室温での動粘度が０．１ｃＳｔ以上１００ｃＳｔ以下である液状有機化合物を金型内面に上記いずれかの方法で塗布することにより、金型内面の傷の発生や成形体のクラックが抑制され、かつ必要上十分な保磁力及び角形性を有する希土類磁石を製造することが可能となって、本発明を完成させた。
【００１２】
従って、本発明は、希土類磁石用合金粉末を磁場中において一軸加圧により金型で乾式成形し、その後焼結して希土類焼結磁石を製造する方法において、磁場中で金型成形する際に用いられる金型潤滑剤として、脂肪酸及びそのエステル並びに高級アルコールから選ばれる炭素数５〜２０であって、沸点が１５０℃以上３５０℃以下で、動粘度が０．１ｃＳｔ以上１００ｃＳｔ以下である液状有機化合物を用い、この液状有機化合物を内面に塗布した金型に上記希土類磁石用合金粉末を充填し、磁場中で成形し、焼結することを特徴とする希土類磁石の製造方法を提供する。
【００１３】
以下、本発明を詳細に説明する。
本発明が適用される希土類永久磁石は、特にＮｄ系希土類磁石、Ｓｍ系希土類磁石が好ましく、ジェットミル等で最終粉砕された好ましくは平均粒径１〜２０μｍの希土類磁石用合金微粉末を磁場中で金型を用いて成形する際に、沸点が１５０℃以上３５０℃以下で、室温での動粘度が０．１ｃＳｔ以上１００ｃＳｔ以下である物理的性質を有する液状の有機化合物を金型の潤滑剤として用いる。
【００１４】
液状の有機化合物としては、脂肪酸又はそのエステル、高級アルコールから選ばれる炭素数５〜２０の有機化合物であり、単独或いはその混合物など、種々の種類及び組み合わせが考えられるが、基本的には液状であって、混合物の場合は少なくともその１種以上の有機化合物が上記の物理的性質を有している必要がある。なお、必要により溶媒としてエタノール等のアルコール、フロン等を配合し、溶媒で希釈して調整して潤滑剤として用いることもできる。この場合、広範囲に塗布する際に塗布性を向上させるために、約３０重量％以上液状有機化合物を含有するように溶媒で希釈して用いることが好ましい。
【００１５】
金型の潤滑剤として用いられる液状有機化合物の沸点が１５０℃未満では、室温中においても揮発するため、金型壁面に残留する量が減少するので、使用量を多くする必要があるため好ましくなく、３５０℃を超えると、成形体表面に残留した金型潤滑用の液状有機化合物を完全に脱脂することができず、結果として磁石中に炭素として残留し磁気特性、形状等に悪影響を及ぼすため好ましくない。より好ましくは、２００℃以上３００℃以下の沸点を有する液状有機化合物がよい。
【００１６】
また、室温での動粘度が０．１ｃＳｔ未満では、十分に金型同士或いは金型と微粉末との潤滑性を維持することが困難であるので好ましくなく、１００ｃＳｔを超えると粘性が増し、微粉末を巻き込み、微粉末と液状有機化合物の混合状態となってしまい、かえって金型に傷を付ける要因となってしまう場合があるために好ましくなく、１〜１０ｃＳｔの液状有機化合物を用いることが更に好ましい。なお、動粘度の数値は、測定時の環境温度が室温での測定結果を用いることが望ましいが、一般的には室温近傍の４０℃前後で測定が行われることが多く、その測定値は室温での結果とほぼ同等と考えることができるので、それらの数値を室温の動粘度として用いることができる。
【００１７】
本発明においては、特にＮｄ系又はＳｍ系焼結磁石の製造に好適であるが、Ｎｄ系或いはＳｍ系焼結磁石は、Ｎｄ−Ｆｅ−Ｂ系、Ｓｍ−Ｃｏ系、Ｓｍ−Ｆｅ−Ｎ系等が挙げられ、通常、合金溶解、粗粉砕、微粉砕、磁場中成形、焼結、熱処理の工程を経て製造されるが、磁場中成形工程時に金型内面に沸点が１５０℃以上３５０℃以下で、室温での動粘度が０．１ｃＳｔ以上１００ｃＳｔ以下である物理的性質を有する液状の有機化合物をスプレー又は上記液体を含浸させた布、不織布或いはスポンジ等でおおよそ１×１０-4〜５×１０-3ｃｃ／ｃｍ2金型に塗布することにより、成形圧力印可時の微粉末と金型、或いは上パンチとダイ、下パンチとダイ同士の摩擦が軽減される結果、金型内面の傷の発生やそれに伴う形状不良、成形体のクラックが抑制され、健全な形状を有した成形体をより簡便に製造することができ、かつ成形体表面の金型潤滑材料の付着による磁石中の炭素含有量の増加に伴う磁気特性の悪化、特には保磁力の著しい減少もなく、必要上十分な保磁力を有する希土類磁石を製造することが可能となる。
【００１８】
希土類磁石用合金の製造方法は、まず、Ｎｄ系磁石及びＳｍ系磁石のどちらの場合も、目標の組成となるように原材料を配合し、真空中或いは不活性ガス雰囲気中にて高周波溶解炉等を用いて溶解し、溶湯を鋳造して合金を作製する。溶湯を鋳型に流し込むことによって鋳造してもよいし、単ロール、双ロール等を用いてストリップキャスティングを行い、鋳造してもよい。また、得られた合金は、合金組織の均質化を目的として、必要に応じて合金の融点以下の温度で溶体化処理を施してもよい。次に、作製した合金を不活性ガス雰囲気中にてジョウクラッシャー、ブラウンミル、ピンミル等を用いて機械的に粗粉砕を行い、所用合金の粗粉を得る。粗粉砕の方法として、当該合金の水素吸蔵放出特性を用い、水素の吸蔵に伴う内部応力を利用して合金にクラックを生じさせることで粗粉砕を行い、合金の粗粉を得ることもできる。得られた粗粉末を更にアトライターミル、ジェットミル等を用いて微粉砕を行い、平均粒径１〜２０μｍの微粉末を得る。
【００１９】
その後、本発明の特徴である、沸点が１５０℃以上３５０℃以下で、室温での動粘度が０．１ｃＳｔ以上１００ｃＳｔ以下である物理的性質を有する液状の有機化合物を金型内面にスプレー、又は上記液体を含浸させた布、不織布或いはスポンジ等で適量、好ましくは１×１０-4〜５×１０-3ｃｃ／ｃｍ2を塗布した後、該金型に平均粒径１〜２０μｍの上記微粉末を充填し、通常１０ｋＯｅ以上の磁場中にて０．１〜２ｔｏｎ／ｃｍ2の圧力にて成形し、密度が３〜５ｇ／ｃｃの成形体を得ることができる。なお、金型としては、公知のものが使用できる。
【００２０】
以上のようにして得られた成形体は、Ｎｄ系磁石の場合、１０００〜１１５０℃の真空中或いはアルゴン等の不活性ガス雰囲気中で０．１〜１０時間焼結を行い、冷却した後、４００〜１０００℃で０．１〜１０時間の熱処理を１回以上行い、Ｎｄ系磁石とする。Ｓｍ系磁石の場合、１１００〜１２５０℃の真空中或いは不活性ガス雰囲気中で０．１〜１０時間焼結を行い、冷却した後、１０００〜焼結温度以下の真空中或いは不活性ガス雰囲気中で０．１〜１０時間熱処理を行い、冷却する。その後、６００〜９５０℃の真空中或いは不活性ガス雰囲気中で０．５〜５０時間保持した後、０．１〜１０℃／ｍｉｎの速度で４００℃以下まで冷却する熱処理を１回以上行い、Ｓｍ系磁石とする。
【００２１】
なお、焼結の前に、塗布した金型潤滑剤を積極的に除去する目的で５００℃以下の温度で真空中、或いは不活性ガス気流中にて０．５〜１０時間保持、又は５００℃まで１〜１０℃／ｍｉｎの範囲で昇温を行って、脱脂することができる。
【００２２】
このようにして得られた磁石は、成形体中及び焼結体中に傷或いはクラック等が見受けられず、健全な形状を有する。また、金型内面にも傷の発生はほとんど認められず、金型掃除等のメンテナンス作業軽減の伴う生産効率の改善に非常に効果を有する。更に、金型潤滑剤の成形体への残留に伴う磁気特性の劣化も見受けられない等、本発明によりＮｄ系磁石などの希土類磁石の生産性を著しく向上させる効果を有する。
【００２３】
このように、本発明は、特に乾いた微粉末を用い、粉末冶金法による希土類磁石を製造するための、金型を用いた磁場中圧縮成形において、圧縮成形時の金型と微粉末或いは金型同士での摩擦に起因する金型面上の傷の発生と、その傷に伴う成形体の形状不良、成形体のクラックの発生などを生産効率を下げることなく、また磁気特性を低下させることなく防止することができる。
【００２４】
即ち、室温での動粘度が０．１ｃＳｔ以上１００ｃＳｔ以下である物理的性質を有する液状有機化合物を潤滑剤に用いることにより、金型内面に直接スプレー、又は上記液体を含浸させた布、不織布或いはスポンジ等で適量塗布することにより、生産性を犠牲にすることなく金型潤滑剤の塗布を行うことができる。また、液状有機化合物の沸点が１５０℃以上３５０℃以下である物理的性質を有することにより、焼結工程の昇温時、或いは積極的な熱処理除去によって、磁石微粉末と反応することなく蒸発するため、金型潤滑剤に起因する磁石中に残留する炭素がないか、非常にわずかとなって、磁気特性に悪影響を及ぼさないものと考えられる。
【００２５】
【実施例】
以下、本発明の具体的実施態様を実施例を挙げて説明するが、本発明はこれらに限定されるものではない。
【００２９】
［実施例１、比較例１］
組成式Ｓｍ１２．０、Ｆｅ１７．５、Ｃｏ６３．３、Ｃｕ５．０、Ｚｒ２．２（数値はａｔ％）となる合金を、純度９９．９％以上の各原料を誘導加熱高周波溶解炉にてＡｒガス雰囲気中で溶解し、鋳造して、インゴットとして作製した。この合金インゴットをＡｒガス雰囲気中でジョウクラッシャー、及びブラウンミルを用いて粗粉砕し、その後ジェットミルを用いて微粉砕を行い、平均粒径で３．５μｍの微粉末を得た。金型内面に成形時に毎回、動粘度約６ｃＳｔで沸点が２４０℃である有機化合物カプリル酸と、エタノールを１：２の割合で混合したものをスプレーにて１×１０-3ｃｍ3／ｃｍ2直接塗布したのち、該金型にこの微粉末を充填し、粉末の方位をそろえるために印可した約１５ｋＯｅの磁場中で、磁場に対して垂直な方向に約１．５ｔｏｎ／ｃｍ2の圧力にて加圧成形して、成形体密度４．６ｇ／ｃｃの成形体を得た。金型に生じた傷、成形体の欠け、クラックの有無を評価するため、連続して成形を行った。これらの成形体をＡｒガス気流中で４００℃まで１０℃／ｍｉｎの速度で昇温したのち、引き続き真空中にて１２００℃で６０分焼結を行い、その後１１５０℃で６０分熱処理後冷却して、焼結体を得た。このようにして得られた焼結体を、不活性ガス中で８００℃で４時間保持したのち、１℃／ｍｉｎで室温まで冷却する処理を２回施して、Ｓｍ系磁石の実施例とした。
【００３０】
成形時に金型内面に全く何も塗布しない以外は実施例と同様に行って得られた同一組成の成形体に、実施例と同一の焼結及び熱処理を施した試料をＳｍ系磁石の比較例とした。
【００３１】
各試料の連続成形可能個数、残留磁束密度（Ｂｒ）、保磁力（Ｈｃｉ）、最大エネルギー積（ＢＨｍａｘ）を求めた結果は表１に示す通りである。表中、連続成形個数ごとに成形体の状態を目視にて観察した結果を記号にて表してある。○は目視にて成形体が健全な状態であることを表し、△は成形体に傷が生じている状態を表し、×は成形体にクラック或いは欠けが発生した状態を表す。
【００３２】
【表１】
表１から明らかなように本発明の方法によれば、成形体に傷、欠け、或いはクラックを生じさせることなく３００個以上の成形体を連続して作製することが可能である。また、本発明の方法によって磁気特性の悪化は見られなかった。
【００３４】
【発明の効果】
本発明の製造方法により、生産性の向上に伴い、安定して高品質で安価な希土類永久磁石を提供することができ、産業上その効果は極めて高い。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a rare earth magnet particularly suitable for obtaining Nd-based, Sm-based sintered magnets, and the like.
[0002]
[Prior art and problems to be solved by the invention]
Rare earth sintered magnets have shown high demand in recent years due to their high magnetic properties, despite being very expensive compared to ferrite and the like. Nd-based magnets are used in a wide range of fields such as HDD VCMs and industrial motors because of their high magnetic properties and relatively low prices. Sm-based magnets are excellent in temperature characteristics and have sufficient coercive force and magnetization even at high temperatures, so that they are used in fields such as industrial motors and actuators that require high-temperature durability.
[0003]
Rare earth magnets are generally manufactured using powder metallurgy and go through the following steps. That is, the raw materials are blended so as to have a predetermined composition, melted using a high-frequency melting furnace or the like, and an alloy can be created by casting, and the alloy is pulverized to obtain a fine powder having an average particle diameter of 1 to 20 μm. A compact of the magnetic powder is obtained by compressing the fine powder into a desired shape in a magnetic field. Then, it becomes a sintered magnet by performing sintering and heat treatment.
[0004]
In the production method using the powder metallurgy method, it is necessary to fill a fine powder into a mold, apply a pressure higher than the outside, and perform compression molding to produce a molded body. As a filling method of the fine powder, there are a method of mixing a liquid such as water or an organic solvent and a fine powder, making the slurry into a mold, and a method of filling a dry fine powder. When using a slurry, the mold must be made of a material having drainage performance or compression molded using a mold having drainage equipment. Therefore, in addition to equipment that applies a magnetic field to manufacture magnets, complex molding equipment equipped with equipment for maintaining and supplying slurry in a state where the slurry is always mixed, drainage equipment for molding, etc. Not only is necessary, but also a drainage step is included in the molding, and therefore it takes time necessary for the molding. The liquid is not completely drained after the molding, and it is indispensable to perform a draining process using vacuuming or the like. Not only the molding but also the processes before and after the molding become very complicated.
[0005]
In addition, as a method of compression molding dry fine powder, the powder is filled in a rubber mold and compressed isotropically using hydrostatic pressure, or uniaxial pressure is applied using a mold and compression is performed. Although there is a method of molding, the hydrostatic pressure molding method using a rubber mold is isotropically compression-molded, so that the density of the molded body can be increased, and variations in the density of the molded body can be reduced. However, it is very difficult to simultaneously orient the fine powder by the magnetic field and isostatic pressing, and remove the pressure slowly to prevent cracks. There is a demerit such as a long time required for molding.
[0006]
For this reason, as a compression molding method in a magnetic field for producing a rare earth magnet by powder metallurgy, compression molding by uniaxial pressing using a dry fine powder and a mold is generally used. In mold forming, it is possible to manufacture a product of any shape by designing the shape of the mold according to the shape of the desired product. It has the advantage of being kept to a minimum. On the other hand, since it is necessary to compress and mold the fine powder using high pressure in the mold, the friction between the mold and the fine powder or the mold is very large, and the surface in contact with the mold is seized with the mold. In some cases, the mold is scratched and the scratch is transferred to the molded body, a predetermined shape cannot be obtained, and a fine crack is generated in the molded body starting from the scratch.
[0007]
In order to reduce friction with the mold and prevent scratches, the inner surface of the mold is mirror-polished, or a hard metal such as carbide is used as the mold material. It is necessary to take measures such as removing the fine powder adhering to the inner surface of the mold every few shots, and the production efficiency is very poor.
[0008]
In order to improve the lubricity of fine powder in advance, there is a method of mixing organic compounds having a lubricating effect into fine powder, but although the lubricating effect of fine powder and mold is recognized, it contributes to lubrication between molds Without increasing the amount of organic compound added to the fine powder to enhance the lubrication effect, the amount of carbon remaining in the lubricant increases, resulting in a decrease in coercivity. This causes problems in magnetic properties such as deterioration of squareness.
[0009]
In this way, during compression molding by uniaxial pressing using a mold used for magnetic field compression of rare earth magnets by powder metallurgy, scratches on the inner surface of the mold due to seizure of the mold and fine powder As a result, a predetermined shape could not be obtained, fine cracks were generated in the molded body, the production efficiency was deteriorated due to the cleaning of the inner surface of the mold, and there were problems with the magnetic properties due to the organic compound added to the fine powder.
[0010]
The present invention has been made in view of the problems associated with the production of the above-mentioned conventional rare earth magnets, and provides a method for producing a high performance rare earth magnet having high coercive force and practically sufficient coercive force and high residual magnetization. For the purpose.
[0011]
Means for Solving the Problem and Embodiment of the Invention
In order to solve such problems, the present inventors have studied in detail the manufacturing conditions of rare earth magnets, particularly the molding process in a magnetic field by uniaxial pressing using a mold, and as a result, the inner surface of the mold has a direct lubrication effect. Focusing on maintaining lubricity by applying a liquid, and trying a mold lubrication method by applying various liquid organic compounds to the inner surface of the mold with a spray, cloth, nonwoven fabric or sponge, it occurs during molding. It has been found that the friction between the mold and fine powder or between the molds is reduced, and the occurrence of scratches on the inner surface of the mold is suppressed. That is, by applying a liquid organic compound having a boiling point of 150 ° C. or more and 350 ° C. or less and a kinematic viscosity at room temperature of 0.1 cSt or more and 100 cSt or less to the inner surface of the mold by any of the above methods, It was possible to produce a rare earth magnet with suppressed coercive force and squareness, and the generation of the present invention was completed.
[0012]
Accordingly, the present invention provides a method for producing a rare earth sintered magnet by dry molding a rare earth magnet alloy powder in a magnetic field by uniaxial pressing in a magnetic field and then sintering the alloy powder. The mold lubricant used is a liquid organic material having 5 to 20 carbon atoms selected from fatty acids and esters thereof and higher alcohols, having a boiling point of 150 ° C. or higher and 350 ° C. or lower and a kinematic viscosity of 0.1 cSt or higher and 100 cSt or lower. There is provided a method for producing a rare earth magnet comprising using a compound, filling a mold having the liquid organic compound coated on the inner surface thereof with the alloy powder for a rare earth magnet, molding in a magnetic field, and sintering.
[0013]
Hereinafter, the present invention will be described in detail.
The rare earth permanent magnet to which the present invention is applied is particularly preferably an Nd-based rare earth magnet or an Sm-based rare earth magnet, and a rare earth magnet alloy fine powder having an average particle size of 1 to 20 μm, which has been finally pulverized by a jet mill or the like, in a magnetic field. When a mold is used to mold a liquid organic compound having a physical property of having a boiling point of 150 ° C. or higher and 350 ° C. or lower and a kinematic viscosity at room temperature of 0.1 cSt or higher and 100 cSt or lower. Used as
[0014]
The liquid organic compound, a fatty acid or an ester thereof, an organic compound of 5-20 carbon atoms selected from higher alcohols, either alone or including mixtures thereof, various types and combinations are conceivable, in principle in a liquid form In the case of a mixture, it is necessary that at least one organic compound has the above physical properties. If necessary, an alcohol such as ethanol, chlorofluorocarbon or the like may be blended as a solvent, diluted with a solvent, adjusted, and used as a lubricant. In this case, in order to improve applicability when applying over a wide range, it is preferable to dilute with a solvent so as to contain about 30% by weight or more of a liquid organic compound.
[0015]
If the boiling point of the liquid organic compound used as the lubricant for the mold is less than 150 ° C., it will volatilize even at room temperature, and the amount remaining on the mold wall surface will decrease, which is not preferable because it is necessary to increase the amount used. If the temperature exceeds 350 ° C, the liquid organic compound for mold lubrication remaining on the surface of the molded body cannot be completely degreased, and as a result, it remains as carbon in the magnet and adversely affects the magnetic properties, shape, etc. It is not preferable. More preferably, a liquid organic compound having a boiling point of 200 ° C. or higher and 300 ° C. or lower is preferable.
[0016]
Also, if the kinematic viscosity at room temperature is less than 0.1 cSt, it is difficult to maintain sufficient lubricity between the molds or between the mold and the fine powder, and this is not preferable, and if it exceeds 100 cSt, the viscosity increases. Undesirably, the powder is entrained, resulting in a mixed state of the fine powder and the liquid organic compound, which may cause damage to the mold, and it is not preferable to use a liquid organic compound of 1 to 10 cSt. preferable. In addition, although it is desirable to use the measurement result when the environmental temperature at the time of measurement is room temperature, the value of kinematic viscosity is generally measured at around 40 ° C. near room temperature. Therefore, these values can be used as the kinematic viscosity at room temperature.
[0017]
In the present invention, it is particularly suitable for production of Nd-based or Sm-based sintered magnets. Nd-based or Sm-based sintered magnets are Nd-Fe-B-based, Sm-Co-based, Sm-Fe-N-based. Usually, it is manufactured through the steps of alloy melting, coarse pulverization, fine pulverization, forming in a magnetic field, sintering, heat treatment, but the boiling point on the inner surface of the mold is 150 ° C. or higher and 350 ° C. or lower during the forming step in the magnetic field. And about 1 × 10 −4 to 5 × by spraying a liquid organic compound having a physical property having a kinematic viscosity at room temperature of 0.1 cSt or more and 100 cSt or less, or a cloth, nonwoven fabric or sponge impregnated with the liquid. By applying to a 10 -3 cc / cm 2 mold, the fine powder and mold at the time of molding pressure application, or the upper punch and die, and the lower punch and die are reduced in friction, resulting in damage to the inner surface of the mold. Occurrence, shape defects associated with the Deterioration of magnetic properties due to increased carbon content in the magnet due to adhesion of mold lubricant on the surface of the molded body In particular, it is possible to produce a rare earth magnet having a necessary and sufficient coercive force without a significant decrease in coercive force.
[0018]
The method for producing an alloy for a rare earth magnet is as follows. First, the raw materials are blended so as to achieve the target composition in both the Nd-based magnet and the Sm-based magnet, and a high-frequency melting furnace or the like in a vacuum or in an inert gas atmosphere. Is melted and casted to produce an alloy. Casting may be performed by pouring the molten metal into a mold, or strip casting may be performed using a single roll, a twin roll, or the like. Further, the obtained alloy may be subjected to a solution treatment at a temperature equal to or lower than the melting point of the alloy as necessary for the purpose of homogenizing the alloy structure. Next, the produced alloy is mechanically coarsely pulverized in an inert gas atmosphere using a jaw crusher, a brown mill, a pin mill or the like to obtain a coarse powder of a desired alloy. As a method of coarse pulverization, coarse pulverization can be performed by using the hydrogen storage / release characteristics of the alloy and generating cracks in the alloy by utilizing internal stress associated with the storage of hydrogen. The obtained coarse powder is further finely pulverized using an attritor mill, a jet mill or the like to obtain fine powder having an average particle diameter of 1 to 20 μm.
[0019]
Thereafter, a liquid organic compound having a physical property having a boiling point of 150 ° C. or more and 350 ° C. or less and a kinematic viscosity at room temperature of 0.1 cSt or more and 100 cSt or less, which is a feature of the present invention, is sprayed on the inner surface of the mold, or After applying an appropriate amount, preferably 1 × 10 −4 to 5 × 10 −3 cc / cm 2 , with the cloth, nonwoven fabric or sponge impregnated with the liquid, the fine particles having an average particle diameter of 1 to 20 μm are applied to the mold. Filled with powder, and molded at a pressure of 0.1 to 2 ton / cm 2 in a magnetic field of usually 10 kOe or more, a molded product having a density of 3 to 5 g / cc can be obtained. In addition, a well-known thing can be used as a metal mold | die.
[0020]
In the case of an Nd-based magnet, the molded body obtained as described above is sintered for 0.1 to 10 hours in a vacuum of 1000 to 1150 ° C. or in an inert gas atmosphere such as argon, and cooled. Heat treatment is performed at 400 to 1000 ° C. for 0.1 to 10 hours at least once to obtain an Nd magnet. In the case of Sm-based magnets, sintering is performed in a vacuum of 1100 to 1250 ° C. or in an inert gas atmosphere for 0.1 to 10 hours, and after cooling, in a vacuum of 1000 to a sintering temperature or lower or in an inert gas atmosphere And heat treatment for 0.1 to 10 hours. Then, after holding in a vacuum at 600 to 950 ° C. or in an inert gas atmosphere for 0.5 to 50 hours, heat treatment is performed at least once at a rate of 0.1 to 10 ° C./min to cool to 400 ° C. or less, Sm magnets are used.
[0021]
In addition, before sintering, in order to positively remove the applied mold lubricant, it is kept at a temperature of 500 ° C. or lower in vacuum or in an inert gas stream for 0.5 to 10 hours, or 500 ° C. It is possible to degrease by raising the temperature in the range of 1 to 10 ° C./min.
[0022]
The magnet thus obtained has a sound shape with no scratches or cracks observed in the molded body and the sintered body. In addition, scars are hardly observed on the inner surface of the mold, which is very effective in improving production efficiency accompanied by reduction of maintenance work such as mold cleaning. Furthermore, the present invention has the effect of remarkably improving the productivity of rare earth magnets such as Nd-based magnets, such as no deterioration of the magnetic properties due to the remaining of the mold lubricant in the molded body.
[0023]
Thus, in the present invention, in the compression molding in a magnetic field using a mold for producing a rare earth magnet by a powder metallurgy method using a dry fine powder, the mold and the fine powder or the metal at the time of compression molding are used. Decrease magnetic properties without reducing production efficiency due to generation of scratches on the mold surface due to friction between molds, shape defects of the molded body due to the scratches, cracks in the molded body, etc. Can be prevented.
[0024]
That is, by using a liquid organic compound having a physical property having a kinematic viscosity at room temperature of 0.1 cSt or more and 100 cSt or less as a lubricant, the inner surface of the mold is directly sprayed, or the cloth, nonwoven fabric or By applying an appropriate amount with a sponge or the like, the mold lubricant can be applied without sacrificing productivity. In addition, since the liquid organic compound has a physical property that the boiling point is 150 ° C. or higher and 350 ° C. or lower, it evaporates without reacting with the magnetic fine powder at the time of temperature rise in the sintering process or by aggressive heat treatment removal. Therefore, it is considered that there is no or very little carbon remaining in the magnet due to the mold lubricant, and the magnetic properties are not adversely affected.
[0025]
【Example】
Hereinafter, specific embodiments of the present invention will be described with reference to examples, but the present invention is not limited thereto.
[0029]
[Example 1 and Comparative Example 1 ]
An alloy having composition formula Sm12.0, Fe17.5, Co63.3, Cu5.0, Zr2.2 (numerical values are at%), each raw material having a purity of 99.9% or more is heated in an induction heating high-frequency melting furnace with Ar. It melt | dissolved in the gas atmosphere, casted, and produced as an ingot. This alloy ingot was coarsely pulverized using a jaw crusher and a brown mill in an Ar gas atmosphere, and then finely pulverized using a jet mill to obtain a fine powder having an average particle size of 3.5 μm. Each time it is molded on the inner surface of the mold, a mixture of an organic compound caprylic acid having a kinematic viscosity of about 6 cSt and a boiling point of 240 ° C. and ethanol in a ratio of 1: 2 is sprayed at 1 × 10 −3 cm 3 / cm 2. After direct application, the mold is filled with this fine powder, and the pressure is about 1.5 ton / cm 2 in a direction perpendicular to the magnetic field in a magnetic field of about 15 kOe applied to align the orientation of the powder. To obtain a molded body having a molded body density of 4.6 g / cc. In order to evaluate the presence or absence of scratches on the mold, chipping of the molded product, and cracks, molding was continuously performed. These molded bodies were heated to 400 ° C. at a rate of 10 ° C./min in an Ar gas stream, then sintered in a vacuum at 1200 ° C. for 60 minutes, and then cooled after heat treatment at 1150 ° C. for 60 minutes. Thus, a sintered body was obtained. The sintered body thus obtained was held in an inert gas at 800 ° C. for 4 hours, and then subjected to a treatment of cooling to room temperature at 1 ° C./min twice to obtain an example of an Sm-based magnet. .
[0030]
A comparative example of an Sm-based magnet obtained by performing the same sintering and heat treatment on a molded body having the same composition obtained in the same manner as in the example except that nothing was applied to the inner surface of the mold at the time of molding. It was.
[0031]
Table 1 shows the results of obtaining the number of continuously moldable samples, residual magnetic flux density (Br), coercive force (Hci), and maximum energy product (BHmax). In the table, the result of visual observation of the state of the molded body for each continuous molding number is represented by symbols. ○ represents that the molded body is in a healthy state by visual observation, Δ represents a state in which the molded body is flawed, and x represents a state in which the molded body is cracked or chipped.
[0032]
[Table 1]
As apparent from Table 1, according to the method of the present invention, it is possible to continuously produce 300 or more molded bodies without causing scratches, chips or cracks in the molded body. Moreover, no deterioration of the magnetic properties was observed by the method of the present invention.
[0034]
【The invention's effect】
With the production method of the present invention, it is possible to provide a rare earth permanent magnet that is stable, high-quality and inexpensive, as productivity increases, and the effect is extremely high in the industry.
Claims (6)
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| JP5942922B2 (en) * | 2013-05-08 | 2016-06-29 | 信越化学工業株式会社 | Manufacturing method of rare earth sintered magnet |
| WO2016152778A1 (en) * | 2015-03-20 | 2016-09-29 | 日立化成株式会社 | Method for forming molded article by press molding |
| JP2017011158A (en) * | 2015-06-24 | 2017-01-12 | 株式会社ジェイテクト | Magnet manufacturing method and magnet |
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