JP4093041B2

JP4093041B2 - Iron-based powder mixture for powder metallurgy and method for producing the same

Info

Publication number: JP4093041B2
Application number: JP2002355702A
Authority: JP
Inventors: 由紀子尾崎; 繁宇波; 聡上ノ薗
Original assignee: JFE Steel Corp
Current assignee: JFE Steel Corp
Priority date: 2002-12-06
Filing date: 2002-12-06
Publication date: 2008-05-28
Anticipated expiration: 2022-12-06
Also published as: JP2004190051A

Description

【０００１】
【発明の属する技術分野】
本発明は、粉末冶金用鉄基粉末混合物およびその製造方法に関し、特に該鉄基粉末混合物の流動性および圧粉成形金型からの抜き出し性を改善すると共に、圧粉体密度の有利な向上を図ろうとするものである。
【０００２】
【従来の技術】
粉末冶金用鉄基粉末混合物は、鉄基粉末としての鉄粉に、銅粉や黒鉛粉、燐化鉄粉等の合金用粉末と、ステアリン酸亜鉛やステアリン酸アルミニウム等の潤滑剤とを混合し、さらに必要に応じてMnＳなどの切削性改善用粉末を混合して製造するのが一般的である。
【０００３】
しかしながら、このような粉末冶金用鉄基粉末混合物は、大きさ、形状および密度の異なる複数の粉末の混合体であるため、混合後の輸送、ホッパへの装入およびホッパからの排出、さらには金型充填時に、混合体の中で粉末が均一に分布しなくなり、偏析を生じ易いという問題があった。
このような偏析が生じた混合物を、加圧（圧縮）成形して成形体（以下、圧粉体という）とし、その圧粉体を焼結して最終製品にすると、製品毎に組成がばらつくだけでなく、寸法および強度が大きくばらつき、不良品が多発することになる。特に、鉄基粉末に混合する銅粉や黒鉛粉、燐化鉄粉等の合金用粉末は、いずれも鉄基粉末より微粉であるため、かような合金用粉末を混合した場合には、上記したばらつきの程度が一層大きくなる。
【０００４】
このような粉末冶金用鉄基粉末混合物の偏析を防止する技術として、鉄基粉末表面に合金用粉末などを付着させる技術（例えば、特許文献１，特許文献２，特許文献３参照）が、また遊離潤滑剤を混合する技術（例えば、特許文献４参照）が提案されている。
【０００５】
【特許文献１】
特開平１−219101号公報（特許請求の範囲）
【特許文献２】
特開平２−217403号公報（特許請求の範囲）
【特許文献３】
特開平３−162502号公報（特許請求の範囲）
【特許文献４】
特開平５−148505号公報（特許請求の範囲）
【０００６】
【発明が解決しようとする課題】
しかしながら、上記した従来技術で得られた鉄基粉末混合物はいずれも、流動性および金型からの抜き出し性に問題があっただけでなく、圧粉体密度の面でも改善の余地を残していた。
本発明は、上記の問題を有利に解決するもので、流動性が良く、また金型からの抜き出し力が小さく、しかも圧粉体密度の向上も図り得る粉末冶金用鉄基粉末混合物を、その有利な製造方法と共に提案することを目的とする。
【０００７】
【課題を解決するための手段】
さて、発明者らは、上記の問題を解決すべく鋭意研究を重ねた結果、鉄基粉末混合物の表面に予め黒鉛粒子と潤滑剤粒子を均一に付着させておくこと、さらに好適には鉄基粉末混合物に混合する遊離潤滑剤の粒度分布を適切に制御することによって、所期した目的が有利に達成されることの知見を得た。
本発明は、上記の知見に立脚するものである。
【０００８】
すなわち、本発明の要旨構成は次のとおりである。
１．鉄基粉末および副原料粉末からなる鉄基粉末混合物であって、該鉄基粉末および副原料粉末の表面がそれぞれ、粒径：0.01〜10μm の黒鉛粒子および粒径：0.01〜10μm の潤滑剤粒子の混合層で被覆されていることを特徴とする粉末冶金用鉄基粉末混合物。
【０００９】
２．上記１記載の鉄基粉末混合物中に、0.01〜2.0 mass％の遊離潤滑剤を混合した鉄基粉末混合物であって、該遊離潤滑剤の少なくとも20 vol％が、粒径：0.01〜80μm の一次粒子を凝集して造粒した粒径：10〜200 μm の二次粒子からなることを特徴とする粉末冶金用鉄基粉末混合物。
【００１０】
３．上記１または２において、前記副原料粉末が、銅粉末または酸化銅粉末のいずれかであることを特徴とする粉末冶金用鉄基粉末混合物。
【００１１】
４．上記１〜３のいずれかにおいて、前記鉄基粉末および副原料粉末の表面に被覆した混合層の厚みが 0.001〜5.0 μm であることを特徴とする粉末冶金用鉄基粉末混合物。
【００１２】
５．鉄基粉末と副原料粉末を混合した後、溶媒中に粒径：0.01〜10μm の黒鉛粒子および粒径：0.01〜10μm の潤滑剤粒子をそれぞれ乳化または分散させた処理液を噴霧して、該鉄基粉末および副原料粉末の表面を該処理液で覆い、ついで乾燥処理により該溶媒を揮散させて、該鉄基粉末および副原料粉末の表面に該黒鉛粒子および潤滑剤粒子の混合層を形成することを特徴とする粉末冶金用鉄基粉末混合物の製造方法。
【００１３】
６．上記５において、前記鉄基粉末および副原料粉末の表面に前記黒鉛粒子および潤滑剤粒子の混合層を形成したのち、さらに粒径：0.01〜80μm の一次粒子を凝集して造粒した粒径：10〜200 μm の二次粒子を少なくとも20 vol％含む遊離潤滑剤を、0.01〜2.0 mass％の範囲で添加し、ついで混合する際、該二次粒子が破壊しないせん断力で混合することを特徴とする粉末冶金用鉄基粉末混合物の製造方法。
【００１４】
７．上記５または６において、前記副原料粉末が、銅粉末または酸化銅粉末のいずれかであることを特徴とする粉末冶金用鉄基粉末混合物の製造方法。
【００１５】
【発明の実施の形態】
以下、本発明を具体的に説明する。
本発明において、基本粉末である鉄基粉末とは、純鉄粉純鉄粉を始めとして、FeにCr，Mn，Ni，Mo，Ｖ等を合金化させた完全合金化鋼粉や、Ti，Ni，Mo，Cu等を純鉄粉または完全合金化鋼粉に拡散接合させた部分合金化鋼粉などを含む。
【００１６】
また、本発明において、副原料粉末とは、銅粉、酸化銅粉、Ni基粉末、Mo基粉末等の合金化用粉末および／またはMnＳ粉末、ＢＮ粉末、CaＦ粉末、ヒドロキシアパタイト粉末等の切削性改善用粉末が、その代表である。
かかる副原料粉末は、粉末冶金において常識的な範囲の量を鉄基粉末に混合することができる。すなわち、ＢＮ粉末やMnＳ粉末等の比重の小さい粉末は 0.1〜20mass％を鉄基粉末に混合し、また銅粉（酸化銅粉を含む）、Ni基粉末、Mo基粉末等の金属粉末は 0.1〜50mass％を鉄基粉末に混合してすることができる。粉末冶金用副原料粉末の混合量（mass％）は、いずれも粉末冶金用鉄基粉末混合物全体における比率である。
【００１７】
さて、上記したような鉄基粉末および副原料粉末を混合したのち、溶媒中に粒径：0.01〜10μm の黒鉛粒子および粒径：0.01〜10μm の潤滑剤粒子をそれぞれ乳化または分散させた処理液を噴霧して、鉄基粉末および副原料粉末の表面を処理液で被覆する。
ここに、黒鉛粒子および潤滑剤粒子の粒径を0.01〜10μm の範囲に限定したのは、粒径が0.01μm 未満では、鉄基粉末表面に粒子が被覆されたのち溶媒を含有し易く、乾燥工程に長時間を要し、コスト高となり、一方10μm を超えると、鉄基粉末表面に黒鉛および潤滑剤粒子が付着し難くなり、被膜の形成が困難となるからである。
【００１８】
また、潤滑剤粒子の成分としては、ステアリン酸亜鉛、ステアリン酸カリウム、ステアリン酸リチウム、ヒドロキシステアリン酸リチウム等の金属石鹸およびその誘導体、あるいはオレイン酸、パルチミン酸等の脂肪酸、あるいはステアリン酸アミド、ステアリン酸ビスアミド、セバシン酸ビスアミド等のエチレンジアミンと脂肪酸との共重合生成物、あるいはポリオレフィン等の熱可塑性樹脂から選ばれる１種または２種以上が好ましい。
さらに、溶媒としては、エタノール、イソプロピルアルコール、トルエン、キシレン、メチルエチルケトンおよびブタノン等の有機溶媒、または水などが有利に適合する。溶媒乾燥後の処理を考えると、水を用いることが好適である。なお、水に不溶な潤滑剤であっても、界面活性剤を適切に選択することにより、水中に均一に分散させて使用することができる。
【００１９】
ついで、乾燥処理により溶媒を揮散させて、鉄基粉末および副原料粉末の表面に黒鉛粒子および潤滑剤粒子の混合層を形成する。
ここに、乾燥処理温度は、50〜120 ℃程度とするのが好ましい。というのは、処理温度が50℃に満たないと、溶媒の乾燥時間が増大し、一方 120℃を超えると、水等の溶媒使用時には鉄粉が腐食するという問題が生じるだけでなく、潤滑剤液滴が鉄基粉末の表面に十分に被覆される以前に溶媒が蒸発して、均一な被膜が形成されないという問題が生じるからである。
また、黒鉛粒子および潤滑剤粒子の表面に形成する混合層の厚みは、 0.001〜5.0 μm 程度とすることが有利である。というのは、層厚が 0.001μm に満たないと、製造された鉄基粉末混合物の成形を行う際に十分な潤滑効果を得ることができず、抜き出し力の増大を招き、一方 5.0μm を超えると、鉄基粉末の表面に分子間相互作用の大きい高分子有機物層が形成されるため、分子間相互作用が増大し、鉄基粉末混合物の流動性が悪化するという問題を生じるからである。
【００２０】
かくして、鉄基粉末および副原料粉末の表面が、黒鉛粒子および潤滑剤粒子の混合層で均一に覆われた鉄基粉末混合物を得られる。
かかる鉄基粉末混合物は、各粉末の表面が潤滑剤で均一に覆われているので、流動性が格段に向上する。また、黒鉛も各粉末の表面に均一に付着しているので、混合粉内で偏析したり、ばらつくこともない。さらに、潤滑効果が高まるので、従来に比べて潤滑剤の添加量を有利に低減させることができ、従って圧粉体密度の向上を図ることもできる。
【００２１】
さらに、本発明において、圧粉成形金型からの抜き出し性を一層向上させるには、粒度分布を適切に制御した遊離潤滑剤を添加することが有利である。
遊離潤滑剤は、添加する際には、微細粉（一次粒子）とこれらが凝集した粒径が大きい粉末（二次粒子）から構成される。従来は、かような一次粒子と二次粒子の比率については何ら考慮が払われてなく、鉄基粉末と潤滑剤とをできるだけ均一な状態に混合するのが好適と考えられていたので、混合する際には比較的大きなせん断力の下で混合が実施され、二次粒子を破壊していた。
しかしながら、発明者らの研究によれば、上記した混合の際のせん断力を適切に制御して、二次粒子をある程度以上の残存させることにより、金型からの抜き出し力が効果的に低減するだけでなく、圧粉体密度の有利な向上が達成されることが究明されたのである。
【００２２】
この理由については、まだ明確に解明されたわけではないが、遊離潤滑剤中に比較的粒径が大きい二次粒子を存在させると、この二次粒子は鉄基粉末間の空隙に効果的に侵入すると共に、これらの鉄基粉末混合物を圧粉成形金型に装入した場合、金型壁面とそれに接する鉄基粉末との空隙にも効果的に侵入し、加圧成形の際に凝集が解けて、鉄基粉末混合物の緻密化に伴い金型壁面接触面に発生する剪断力によって、金型壁面に押し広げられ、これにより潤滑効果が格段に向上して、金型からの抜き出し力の低減と圧粉体密度の向上が併せて達成されるものと考えられる。
【００２３】
ここに、一次粒子については、粒径を0.01〜80μm の範囲に制限する必要がある。というのは、一次粒子の粒径すなわち一次粒径が0.01μm に満たないと、粒子間結合力が強くなり、凝集して形成される二次粒子が鉄基粉末混合物成形時に解かれ難くなり、金型表面まで十分に分散しないため、潤滑効果が十分に発揮されないという問題が生じ、一方80μm を超えると、成形後、成形体中に残留し、焼結後の粗大空孔の原因となるからである。
また、二次粒子については、その粒径を10〜200 μm の範囲に制限する必要がある。というのは、二次粒子の粒径すなわち二次粒径が10μm に満たないと、鉄基粉末の粒子径に比べて極めて小さいため、鉄基粉末粒子の間隙に入って凝集が解かれ難くなるため、潤滑効果が十分に発揮されず、一方 200μm を超えると、二次粒子構造が解かれた後も一部凝集状態の二次粒子構造が残存し、成形体焼結後の粗大空孔の原因となるからである。
【００２４】
そして、上記した粒径が10〜200 μm の二次粒子を、遊離潤滑剤全体に対して少なくとも20 vol％の比率で含有させるのである。
というのは、二次粒子の比率が20 vol％に満たないと、鉄基粉末間の空隙や金型壁面とそれに接する鉄基粉末との空隙に侵入する二次粒子の量が少なすぎ、所期したほどの抜き出し力の低減および圧粉体密度の向上が望めないからである。
【００２５】
また、上記した遊離潤滑剤は、鉄基粉末混合物全体に対し0.01〜2.0 mass％の範囲で添加する必要がある。
というのは、鉄基粉末混合物全体に対する遊離潤滑剤の比率が0.01mass％に満たないと十分な潤滑効果が得られず，一方 2.0mass％を超えると鉄基粉末混合物中に占める潤滑剤の体積分率が高くなり、成形体密度の低下や焼結時の寸法収縮率の増大による焼結体の変形等の弊害を招くからである。
なお、上記した遊離潤滑剤としては、前述した混合層形成用の潤滑剤粒子と同じ成分で良い。
【００２６】
また、上記した造粒法を利用する場合には、遊離潤滑剤の二次粒子が破壊しない低せん断力で混合することが重要である。
混合手段として粉体混合機を使用する場合、粒径が10〜200 μm の二次粒子を少なくとも20 vol％残存させるために適当な粉体混合機としては、混合操作によって粉体に加えられる外力は小さい方が好ましい。混合機が混合操作によって粉体に与える外力については、例えば日本粉体工業技術協会編「粉体混合技術」（日刊工業新聞社，2001）によると、外力が小さい順に(1) 対流混合、(2) せん断混合、(3) 高せん断混合に分類される。この分類によれば、上記した(1), (2)程度の外力が好適である。
【００２７】
好適な混合機としては、容器回転式混合機、機械撹拌式混合機および流動撹拌式混合機などがあり、高速せん断式混合機や衝撃式混合機は適さない。
ここで、容器回転式混合機としては、Ｖ型混合機、二重円錐形混合機および円筒回転形混合機が、また機械撹拌式混合機としては、単軸リボン形混合機、回転鋤形混合機（レディゲミキサーなど）、円錐遊星スクリュー形混合機（ナウターミキサーなど）、高速底部回転式混合機（ヘンシェルミキサーなど）および傾斜回転パン形混合機（アイリッヒミルなど）が好適である。
なお、機械撹拌式混合機の場合、撹拌翼については、表面積が大きい形状や高回転数での撹拌は好ましくない。
【００２８】
【実施例】
実施例１
鉄基粉末、副原料粉末、黒鉛粉末、潤滑剤粒子および溶媒としては、それぞれ表１〜５に示すものを用いた。
さて、鉄基粉末に、副原料粉末を種々の割合で添加したのち、黒鉛粉末および潤滑剤粒子を溶媒に乳化または分散させた処理液を噴霧し、該鉄基粉末および副原料粉末の表面を該処理液で覆い、ついで同じく表６に示す温度で乾燥処理を施して溶媒を揮散させ、鉄基粉末および副原料粉末の表面に黒鉛粉末および潤滑剤粒子の混合層を形成した。
かくして得られた粉末冶金用鉄基粉末混合物の流動度、圧粉体密度および抜き出し性について調べた結果を表６に併記する。
【００２９】
また、比較のため、鉄基粉末、副原料粉末、黒鉛粉末、潤滑剤粒子の配合が同じで、これらをＶ型混合機で単純混合して作製した粉末冶金用鉄基粉末混合物の流動度、圧粉体密度および抜き出し性について調べた結果を表７に示す。なお、この時の潤滑剤粒子としては、溶媒に分散させる前の原料粉末を用いた。
【００３０】
なお、各特性は次のようにして評価した。
(1) 流動性
鉄基粉末混合物：100 ｇを、オリフィス径：2.63mmの容器に充填し、充填してから排出するまでの時間を測定して、流動度（ｓ／50ｇ）を求め、この流動度で評価した。
(2) 抜き出し性および圧粉体密度
抜き出し性は、日本粉末冶金工業会規格（JPMA P09, JPMA P13）に準拠して、686 MPa の圧力で圧縮し、直径：11.3mm、高さ：11mmの成形体を成形したのち、金型から成形体を抜き出し、その時の抜き出し力で評価した。
また、得られた成形体の密度を圧粉体密度とした。
【００３１】
【表１】

【００３２】
【表２】

【００３３】
【表３】

【００３４】
【表４】

【００３５】
【表５】

【００３６】
【表６】

【００３７】
【表７】

【００３８】
表６および表７に、発明例１〜16と比較例１〜16それぞれを比較して示したところから明らかなように、同一配合の場合、黒鉛粉末と潤滑剤粒子を鉄基粉末の表面に被覆することにより、流動度が向上し、また高密度で低引き抜き力の成形が可能となる。
【００３９】
実施例２
実施例１と同様の方法で作製した表８に示す各種の鉄基粉末混合物に、表９に示す造粒構造の遊離潤滑剤を種々の範囲で添加したのち、Ｖ形混合機またはレディゲミキサーを用いて混合し、各種粉末冶金用鉄基混合粉末を作製した。
かくして得られた粉末冶金用鉄基混合粉末の流動度、圧粉体密度および抜き出し性について調べた結果を表10に示す。
また、比較のため、鉄基粉末、副原料粉末、黒鉛粉末、潤滑剤粒子の配合が同じで、これらをＶ型混合機で単純混合して作製した粉末冶金用鉄基粉末混合物の流動度、圧粉体密度および抜き出し性について調べた結果を表11に示す。
【００４０】
【表８】

【００４１】
【表９】

【００４２】
【表１０】

【００４３】
【表１１】

【００４４】
表10および表11に、発明例17〜32と比較例17〜32それぞれを比較して示したところから明らかなように、同一配合の場合、黒鉛粉末と潤滑剤の一部を予め鉄基粉末の表面に被覆し、潤滑剤の残部を造粒構造とすることにより、黒鉛粉末と潤滑剤粒子を鉄基粉末に単純に混合した場合に比べて、流動度は向上し、また高密度で低引き抜き力の成形が可能となった。
【００４５】
実施例３
実施例１および２で作製した試料の一部を 130℃に加熱し、流動度、圧粉体密度および抜き出し性を測定した。なお、圧粉体密度および抜き出し性の測定に際しては、 130℃に加熱した鉄基粉末混合物を 150℃に加熱した内径：11mmφの金型中に装入し、 686 MPaで成形した。
得られた結果を表12に示す。
【００４６】
【表１２】

【００４７】
表12から明らかなように、本発明の鉄基粉末混合物によれば、抜き出し力の大きな上昇を伴うことなしに、さらに高密度の圧粉体を得ることが可能となる。
【００４８】
【発明の効果】
かくして、本発明によれば、流動性に優れ、また金型からの抜き出し力が小さく、しかも圧粉体密度が大きい、すなわち常温成形性および温間成形に優れた粉末冶金用鉄基粉末混合物を安定して得ることができる。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an iron-based powder mixture for powder metallurgy and a method for producing the same, and in particular, improves the fluidity of the iron-based powder mixture and the ability to withdraw from a compacting mold, and advantageously improves the density of the green compact. It is intended to be illustrated.
[0002]
[Prior art]
The iron-based powder mixture for powder metallurgy is obtained by mixing iron powder as iron-based powder with alloy powder such as copper powder, graphite powder and iron phosphide powder, and lubricant such as zinc stearate and aluminum stearate. Further, it is generally produced by mixing a machinability improving powder such as MnS as required.
[0003]
However, such an iron-based powder mixture for powder metallurgy is a mixture of a plurality of powders having different sizes, shapes, and densities, so that transportation after mixing, charging into the hopper and discharging from the hopper, When filling the mold, there is a problem that the powder is not uniformly distributed in the mixture and segregation is likely to occur.
When such a segregated mixture is pressed (compressed) to form a molded body (hereinafter referred to as a green compact), and the green compact is sintered into a final product, the composition varies from product to product. In addition, the size and strength vary greatly, and defective products frequently occur. In particular, alloy powders such as copper powder, graphite powder, and iron phosphide powder to be mixed with iron-based powder are all finer than iron-based powder, so when such alloy powder is mixed, The degree of variation is further increased.
[0004]
As a technique for preventing segregation of the iron-based powder mixture for powder metallurgy, a technique for attaching an alloy powder or the like to the surface of the iron-based powder (see, for example, Patent Document 1, Patent Document 2, and Patent Document 3) A technique for mixing a free lubricant (see, for example, Patent Document 4) has been proposed.
[0005]
[Patent Document 1]
JP-A-1-219101 (Claims)
[Patent Document 2]
JP-A-2-217403 (Claims)
[Patent Document 3]
JP-A-3-162502 (Claims)
[Patent Document 4]
JP-A-5-148505 (Claims)
[0006]
[Problems to be solved by the invention]
However, all of the iron-based powder mixtures obtained by the above-mentioned conventional techniques have problems in fluidity and moldability, and leave room for improvement in terms of green compact density. .
The present invention advantageously solves the above problems, and provides an iron-based powder mixture for powder metallurgy that has good fluidity, has a small extraction force from a mold, and can also improve the density of a green compact. The object is to propose with an advantageous manufacturing method.
[0007]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the inventors have previously uniformly adhered graphite particles and lubricant particles to the surface of the iron-based powder mixture, and more preferably iron-based powder. It has been found that the intended purpose can be advantageously achieved by appropriately controlling the particle size distribution of the free lubricant mixed in the powder mixture.
The present invention is based on the above findings.
[0008]
That is, the gist configuration of the present invention is as follows.
1. A iron-based powder mixture consisting of iron-based powder and the auxiliary raw material powder, each surface of the iron-base powder and the auxiliary raw material powder, grain size: 0.01 to 10 [mu] m graphite particles and particle size: 0.01 to 10 [mu] m of lubricant particles An iron-based powder mixture for powder metallurgy, characterized by being coated with a mixed layer.
[0009]
2. An iron-based powder mixture obtained by mixing 0.01 to 2.0 mass% of a free lubricant in the iron-based powder mixture described in 1 above, wherein at least 20 vol% of the free lubricant has a primary particle size of 0.01 to 80 μm. An iron-based powder mixture for powder metallurgy comprising secondary particles having a particle size of 10 to 200 μm formed by agglomerating particles.
[0010]
3. 3. The iron-based powder mixture for powder metallurgy according to 1 or 2, wherein the auxiliary raw material powder is either a copper powder or a copper oxide powder.
[0011]
4). 4. The iron-based powder mixture for powder metallurgy according to any one of 1 to 3, wherein the thickness of the mixed layer coated on the surfaces of the iron-based powder and the auxiliary raw material powder is 0.001 to 5.0 μm.
[0012]
5. After mixing the iron-based powder and the auxiliary raw material powder, a treatment liquid in which graphite particles having a particle size of 0.01 to 10 μm and lubricant particles having a particle size of 0.01 to 10 μm are emulsified or dispersed in a solvent is sprayed. Cover the surfaces of the iron-based powder and the auxiliary raw material powder with the treatment liquid, and then volatilize the solvent by a drying process to form a mixed layer of the graphite particles and the lubricant particles on the surface of the iron-based powder and the auxiliary raw material powder. A method for producing an iron-based powder mixture for powder metallurgy.
[0013]
6). In 5 above, after forming the mixed layer of the graphite particles and the lubricant particles on the surface of the iron-based powder and the auxiliary raw material powder, the primary particles having a particle size of 0.01 to 80 μm are further aggregated and granulated. A free lubricant containing at least 20 vol% of secondary particles of 10 to 200 μm is added in the range of 0.01 to 2.0 mass%, and then mixed with a shearing force that does not break the secondary particles when mixing. A method for producing an iron-based powder mixture for powder metallurgy.
[0014]
7). 5. The method for producing an iron-based powder mixture for powder metallurgy according to 5 or 6, wherein the auxiliary raw material powder is either copper powder or copper oxide powder.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be specifically described below.
In the present invention, the iron-based powder, which is a basic powder, includes a pure iron powder, a pure iron powder, a fully alloyed steel powder obtained by alloying Fe, Cr, Mn, Ni, Mo, V, etc., Ti, Includes partially alloyed steel powder that is diffusion-bonded to pure iron powder or fully alloyed steel powder.
[0016]
In the present invention, the auxiliary raw material powder is an alloying powder such as copper powder, copper oxide powder, Ni-based powder, and Mo-based powder and / or cutting such as MnS powder, BN powder, CaF powder, and hydroxyapatite powder. A typical example is a powder for improving property.
Such auxiliary raw material powders can be mixed with iron-based powders in an amount in a common sense range in powder metallurgy. That is, 0.1-20 mass% is mixed with iron-based powder for powders with small specific gravity such as BN powder and MnS powder, and metal powders such as copper powder (including copper oxide powder), Ni-based powder, and Mo-based powder are 0.1%. ~ 50 mass% can be mixed with iron-based powder. The mixing amount (mass%) of the auxiliary raw material powder for powder metallurgy is a ratio in the entire iron-based powder mixture for powder metallurgy.
[0017]
Now, after mixing the iron-based powder and the auxiliary raw material powder as described above, a processing liquid in which graphite particles having a particle size of 0.01 to 10 μm and lubricant particles having a particle size of 0.01 to 10 μm are emulsified or dispersed in a solvent, respectively. Is sprayed to coat the surfaces of the iron-based powder and the auxiliary raw material powder with the treatment liquid.
Here, the particle size of graphite particles and lubricant particles was limited to the range of 0.01 to 10 μm. If the particle size is less than 0.01 μm, it is easy to contain a solvent after the particles are coated on the surface of the iron-based powder. This is because the process takes a long time and the cost is high. On the other hand, when the thickness exceeds 10 μm, graphite and lubricant particles are difficult to adhere to the surface of the iron-based powder, making it difficult to form a film.
[0018]
In addition, the components of the lubricant particles include metal soaps such as zinc stearate, potassium stearate, lithium stearate, and lithium hydroxystearate and derivatives thereof, fatty acids such as oleic acid and palmitic acid, stearic acid amide, stearic acid One or two or more selected from a copolymerized product of ethylenediamine and a fatty acid such as acid bisamide or sebacic acid bisamide, or a thermoplastic resin such as polyolefin is preferred.
Further, as the solvent, organic solvents such as ethanol, isopropyl alcohol, toluene, xylene, methyl ethyl ketone and butanone, or water are advantageously suitable. Considering the treatment after the solvent drying, it is preferable to use water. Note that even a lubricant that is insoluble in water can be used by being uniformly dispersed in water by appropriately selecting a surfactant.
[0019]
Next, the solvent is volatilized by a drying treatment to form a mixed layer of graphite particles and lubricant particles on the surfaces of the iron-based powder and the auxiliary raw material powder.
Here, the drying treatment temperature is preferably about 50 to 120 ° C. This is because if the processing temperature is less than 50 ° C, the drying time of the solvent increases, while if it exceeds 120 ° C, not only the problem that iron powder corrodes when using a solvent such as water, but also a lubricant. This is because the solvent evaporates before the droplets are sufficiently coated on the surface of the iron-based powder, resulting in a problem that a uniform film is not formed.
The thickness of the mixed layer formed on the surfaces of the graphite particles and the lubricant particles is advantageously about 0.001 to 5.0 μm. This is because if the layer thickness is less than 0.001 μm, a sufficient lubrication effect cannot be obtained when the produced iron-based powder mixture is molded, leading to an increase in extraction force, while exceeding 5.0 μm. This is because a polymer organic material layer having a large intermolecular interaction is formed on the surface of the iron-based powder, so that the intermolecular interaction is increased and the fluidity of the iron-based powder mixture is deteriorated.
[0020]
Thus, an iron-based powder mixture is obtained in which the surfaces of the iron-based powder and the auxiliary raw material powder are uniformly covered with the mixed layer of graphite particles and lubricant particles.
In such an iron-based powder mixture, the surface of each powder is uniformly covered with a lubricant, so that the fluidity is remarkably improved. Further, since graphite is uniformly adhered to the surface of each powder, it does not segregate or vary in the mixed powder. Furthermore, since the lubricating effect is enhanced, the amount of lubricant added can be advantageously reduced as compared with the prior art, and therefore the green density can be improved.
[0021]
Furthermore, in the present invention, it is advantageous to add a free lubricant whose particle size distribution is appropriately controlled in order to further improve the drawability from the compacting mold.
When the free lubricant is added, the free lubricant is composed of fine powder (primary particles) and a powder (secondary particles) having a large particle size in which they are aggregated. Conventionally, no consideration has been given to the ratio of such primary particles to secondary particles, and it was considered preferable to mix the iron-based powder and the lubricant in as uniform a state as possible. In this case, mixing was performed under a relatively large shearing force, and the secondary particles were broken.
However, according to the research by the inventors, the extraction force from the mold is effectively reduced by appropriately controlling the shearing force during the above mixing and leaving the secondary particles to a certain extent. It has been found that an advantageous improvement in the green density is achieved as well.
[0022]
The reason for this has not been clearly clarified, but when secondary particles having a relatively large particle size are present in the free lubricant, the secondary particles effectively penetrate into the voids between the iron-based powders. In addition, when these iron-based powder mixtures are charged into a compacting mold, they effectively enter the gap between the mold wall surface and the iron-based powder in contact therewith, and the agglomeration is dissolved during pressure molding. In addition, the shear force generated on the mold wall contact surface as the iron-based powder mixture is densified causes the mold wall surface to be spread out, thereby greatly improving the lubrication effect and reducing the extraction force from the mold. It is thought that the improvement of the green compact density is achieved at the same time.
[0023]
Here, for primary particles, it is necessary to limit the particle size to a range of 0.01 to 80 μm. This is because when the primary particle size, that is, the primary particle size is less than 0.01 μm, the interparticle bonding force becomes strong, and the secondary particles formed by aggregation become difficult to be unraveled at the time of forming the iron-based powder mixture, Since it does not sufficiently disperse to the mold surface, there is a problem that the lubrication effect is not sufficiently exhibited.On the other hand, if it exceeds 80 μm, it will remain in the molded body after molding and cause coarse pores after sintering. It is.
For secondary particles, the particle size must be limited to a range of 10 to 200 μm. The reason is that if the particle size of the secondary particles, that is, the secondary particle size is less than 10 μm, the particle size of the iron-based powder is extremely small compared to the particle size of the iron-based powder, so that it is difficult for the agglomeration to be solved by entering the gap between the iron-based powder particles. Therefore, the lubrication effect is not fully exhibited.On the other hand, if it exceeds 200 μm, the secondary particle structure remains partially agglomerated even after the secondary particle structure is unraveled, and the coarse pores after the sintered compact remains. It is a cause.
[0024]
The secondary particles having a particle size of 10 to 200 μm are contained at a ratio of at least 20 vol% with respect to the entire free lubricant.
This is because if the ratio of the secondary particles is less than 20 vol%, the amount of secondary particles entering the voids between the iron-based powders and the voids between the mold wall and the iron-based powders in contact therewith is too small. This is because it is not possible to reduce the extraction force as much as expected and to improve the green density.
[0025]
Moreover, it is necessary to add the above-mentioned free lubricant in the range of 0.01 to 2.0 mass% with respect to the entire iron-based powder mixture.
This is because if the ratio of the free lubricant to the entire iron-based powder mixture is less than 0.01 mass%, sufficient lubrication effect cannot be obtained, while if it exceeds 2.0 mass%, the volume of lubricant in the iron-based powder mixture This is because the fraction is increased, which causes adverse effects such as a decrease in the density of the molded body and deformation of the sintered body due to an increase in the dimensional shrinkage rate during sintering.
The above-mentioned free lubricant may be the same component as the above-described lubricant particles for forming the mixed layer.
[0026]
Moreover, when utilizing the above-mentioned granulation method, it is important to mix with a low shear force that does not break the secondary particles of the free lubricant.
When a powder mixer is used as a mixing means, an appropriate external force applied to the powder by the mixing operation is used as a suitable powder mixer in order to leave at least 20 vol% of secondary particles having a particle size of 10 to 200 μm. Is preferably smaller. For example, according to the “Powder Mixing Technology” (Nikkan Kogyo Shimbun, 2001) edited by the Japan Powder Industry Technical Association, the external force applied to the powder by the mixing operation is as follows: (1) Convective mixing, 2) Shear mixing, (3) High shear mixing. According to this classification, the external force of the above (1) and (2) is preferable.
[0027]
Suitable mixers include a container rotating mixer, a mechanical stirring mixer, and a fluid stirring mixer, and a high-speed shearing mixer and an impact mixer are not suitable.
Here, as a container rotary mixer, a V-type mixer, a double cone mixer and a cylindrical rotary mixer are used. As a mechanical stirring mixer, a single-shaft ribbon mixer, a rotary bowl mixer, and the like. A machine (such as a Redige mixer), a conical planetary screw-type mixer (such as a Nauter mixer), a high-speed bottom rotary mixer (such as a Henschel mixer), and an inclined rotary pan-type mixer (such as an Eirich mill) are suitable.
In the case of a mechanical stirring mixer, stirring with a shape having a large surface area or high rotational speed is not preferable for the stirring blade.
[0028]
【Example】
Example 1
As the iron-based powder, auxiliary material powder, graphite powder, lubricant particles and solvent, those shown in Tables 1 to 5 were used.
Now, after adding the auxiliary raw material powder in various proportions to the iron-based powder, a treatment liquid in which graphite powder and lubricant particles are emulsified or dispersed in a solvent is sprayed, and the surfaces of the iron-based powder and auxiliary raw material powder are sprayed. The mixture was covered with the treatment liquid, and then dried at the temperature shown in Table 6 to volatilize the solvent, thereby forming a mixed layer of graphite powder and lubricant particles on the surfaces of the iron-based powder and the auxiliary raw material powder.
Table 6 also shows the results of examining the fluidity, the green density, and the extractability of the iron-based powder mixture for powder metallurgy thus obtained.
[0029]
For comparison, the fluidity of the iron-based powder mixture for powder metallurgy prepared by simply mixing the iron-based powder, auxiliary raw material powder, graphite powder, and lubricant particles with a V-type mixer, Table 7 shows the results of examining the green compact density and the extractability. Note that the raw material powder before being dispersed in a solvent was used as the lubricant particles at this time.
[0030]
Each characteristic was evaluated as follows.
(1) Flowable iron-based powder mixture: 100 g is filled into a container with an orifice diameter of 2.63 mm, and the time from filling to discharging is measured to determine the fluidity (s / 50 g). The fluidity was evaluated.
(2) Pull-out property and green compact density The pull-out property is compressed at a pressure of 686 MPa in accordance with the Japan Powder Metallurgy Industry Association Standard (JPMA P09, JPMA P13), diameter: 11.3 mm, height: 11 mm. After molding the molded body, the molded body was extracted from the mold and evaluated by the extraction force at that time.
Moreover, the density of the obtained molded object was made into the green compact density.
[0031]
[Table 1]

[0032]
[Table 2]

[0033]
[Table 3]

[0034]
[Table 4]

[0035]
[Table 5]

[0036]
[Table 6]

[0037]
[Table 7]

[0038]
Tables 6 and 7 clearly show that Comparative Examples 1 to 16 and Inventive Examples 1 to 16 are compared, and in the case of the same composition, graphite powder and lubricant particles are placed on the surface of the iron-based powder. By coating, the fluidity is improved, and the molding with high density and low pulling force becomes possible.
[0039]
Example 2
A free lubricant having a granulated structure shown in Table 9 was added in various ranges to various iron-based powder mixtures shown in Table 8 prepared by the same method as in Example 1, and then a V-shaped mixer or a Redige mixer. Were used to prepare various iron-based mixed powders for powder metallurgy.
Table 10 shows the results of examining the fluidity, green density, and extractability of the iron-based mixed powder for powder metallurgy thus obtained.
For comparison, the fluidity of the iron-based powder mixture for powder metallurgy prepared by simply mixing the iron-based powder, auxiliary raw material powder, graphite powder, and lubricant particles with a V-type mixer, Table 11 shows the results of examining the green compact density and the extractability.
[0040]
[Table 8]

[0041]
[Table 9]

[0042]
[Table 10]

[0043]
[Table 11]

[0044]
In Table 10 and Table 11, it is clear from the comparison between Inventive Examples 17-32 and Comparative Examples 17-32 that, in the case of the same composition, graphite powder and a part of the lubricant are previously iron-based powder. As a result, the flow rate is improved compared to the case where graphite powder and lubricant particles are simply mixed with iron-based powder, and the density is low. The drawing force can be formed.
[0045]
Example 3
A part of the sample prepared in Examples 1 and 2 was heated to 130 ° C., and the fluidity, the green density, and the drawability were measured. In the measurement of the green compact density and the extractability, the iron-based powder mixture heated to 130 ° C. was placed in a mold having an inner diameter of 11 mmφ heated to 150 ° C. and molded at 686 MPa.
The results obtained are shown in Table 12.
[0046]
[Table 12]

[0047]
As is apparent from Table 12, according to the iron-based powder mixture of the present invention, it is possible to obtain a green compact with a higher density without a significant increase in the extraction force.
[0048]
【The invention's effect】
Thus, according to the present invention, an iron-based powder mixture for powder metallurgy that is excellent in fluidity, has a small extraction force from a mold, and has a large green compact density, that is, excellent in room temperature formability and warm forming. It can be obtained stably.

Claims

A iron-based powder mixture consisting of iron-based powder and the auxiliary raw material powder, each surface of the iron-base powder and the auxiliary raw material powder, grain size: 0.01 to 10 [mu] m graphite particles and particle size: 0.01 to 10 [mu] m of lubricant particles An iron-based powder mixture for powder metallurgy, characterized by being coated with a mixed layer.

An iron-based powder mixture in which 0.01 to 2.0 mass% of a free lubricant is mixed in the iron-based powder mixture according to claim 1, wherein at least 20 vol% of the free lubricant has a particle size of 0.01 to 80 µm. An iron-based powder mixture for powder metallurgy comprising secondary particles having a particle size of 10 to 200 μm formed by agglomerating primary particles.

3. The iron-based powder mixture for powder metallurgy according to claim 1 or 2, wherein the auxiliary raw material powder is either a copper powder or a copper oxide powder.

The iron-based powder mixture for powder metallurgy according to any one of claims 1 to 3, wherein the thickness of the mixed layer coated on the surfaces of the iron-based powder and the auxiliary raw material powder is 0.001 to 5.0 µm.

After mixing the iron-based powder and the auxiliary raw material powder, a treatment liquid in which graphite particles having a particle size of 0.01 to 10 μm and lubricant particles having a particle size of 0.01 to 10 μm are emulsified or dispersed in a solvent is sprayed. Cover the surfaces of the iron-based powder and the auxiliary raw material powder with the treatment liquid, and then volatilize the solvent by a drying process to form a mixed layer of the graphite particles and the lubricant particles on the surface of the iron-based powder and the auxiliary raw material powder. A method for producing an iron-based powder mixture for powder metallurgy.

6. The particle size according to claim 5, wherein a mixed layer of the graphite particles and lubricant particles is formed on the surface of the iron-based powder and the auxiliary raw material powder, and further, primary particles having a particle size of 0.01 to 80 μm are aggregated and granulated. : Add a free lubricant containing at least 20 vol% of secondary particles of 10-200 μm in the range of 0.01-2.0 mass%, and then mix with a shearing force that does not break the secondary particles when mixing. A method for producing an iron-based powder mixture for powder metallurgy.

7. The method for producing an iron-based powder mixture for powder metallurgy according to claim 5 or 6, wherein the auxiliary raw material powder is either copper powder or copper oxide powder.