JP4144326B2 - Iron-based powder mixture for powder metallurgy and method for producing the same - Google Patents
Iron-based powder mixture for powder metallurgy and method for producing the same Download PDFInfo
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- JP4144326B2 JP4144326B2 JP2002319890A JP2002319890A JP4144326B2 JP 4144326 B2 JP4144326 B2 JP 4144326B2 JP 2002319890 A JP2002319890 A JP 2002319890A JP 2002319890 A JP2002319890 A JP 2002319890A JP 4144326 B2 JP4144326 B2 JP 4144326B2
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- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 title claims description 131
- 239000000843 powder Substances 0.000 title claims description 102
- 229910052742 iron Inorganic materials 0.000 title claims description 61
- 239000000203 mixture Substances 0.000 title claims description 49
- 238000004663 powder metallurgy Methods 0.000 title claims description 18
- 238000004519 manufacturing process Methods 0.000 title claims description 8
- 239000000314 lubricant Substances 0.000 claims description 52
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 21
- 239000011163 secondary particle Substances 0.000 claims description 21
- 239000011230 binding agent Substances 0.000 claims description 20
- 239000002245 particle Substances 0.000 claims description 17
- 239000000956 alloy Substances 0.000 claims description 14
- 229910045601 alloy Inorganic materials 0.000 claims description 14
- 238000002156 mixing Methods 0.000 claims description 13
- 239000010439 graphite Substances 0.000 claims description 11
- 229910002804 graphite Inorganic materials 0.000 claims description 11
- 239000011164 primary particle Substances 0.000 claims description 9
- 238000002844 melting Methods 0.000 claims description 5
- 230000008018 melting Effects 0.000 claims description 5
- 230000002776 aggregation Effects 0.000 claims description 4
- 238000005054 agglomeration Methods 0.000 claims description 3
- 238000005469 granulation Methods 0.000 claims description 3
- 230000003179 granulation Effects 0.000 claims description 3
- 239000011361 granulated particle Substances 0.000 claims description 2
- 238000000605 extraction Methods 0.000 description 17
- 238000000034 method Methods 0.000 description 8
- 235000014113 dietary fatty acids Nutrition 0.000 description 6
- 239000000194 fatty acid Substances 0.000 description 6
- 229930195729 fatty acid Natural products 0.000 description 6
- 150000004665 fatty acids Chemical class 0.000 description 6
- 229910052751 metal Inorganic materials 0.000 description 6
- 239000002184 metal Substances 0.000 description 6
- 238000000465 moulding Methods 0.000 description 6
- 239000000344 soap Substances 0.000 description 6
- 229910000831 Steel Inorganic materials 0.000 description 5
- RKISUIUJZGSLEV-UHFFFAOYSA-N n-[2-(octadecanoylamino)ethyl]octadecanamide Chemical compound CCCCCCCCCCCCCCCCCC(=O)NCCNC(=O)CCCCCCCCCCCCCCCCC RKISUIUJZGSLEV-UHFFFAOYSA-N 0.000 description 5
- -1 polyethylene Polymers 0.000 description 5
- 239000010959 steel Substances 0.000 description 5
- 239000000374 eutectic mixture Substances 0.000 description 4
- 229910052750 molybdenum Inorganic materials 0.000 description 4
- XOOUIPVCVHRTMJ-UHFFFAOYSA-L zinc stearate Chemical compound [Zn+2].CCCCCCCCCCCCCCCCCC([O-])=O.CCCCCCCCCCCCCCCCCC([O-])=O XOOUIPVCVHRTMJ-UHFFFAOYSA-L 0.000 description 4
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 3
- 238000010438 heat treatment Methods 0.000 description 3
- LYRFLYHAGKPMFH-UHFFFAOYSA-N octadecanamide Chemical compound CCCCCCCCCCCCCCCCCC(N)=O LYRFLYHAGKPMFH-UHFFFAOYSA-N 0.000 description 3
- 239000000047 product Substances 0.000 description 3
- 238000005204 segregation Methods 0.000 description 3
- 238000010008 shearing Methods 0.000 description 3
- 238000003756 stirring Methods 0.000 description 3
- WRIDQFICGBMAFQ-UHFFFAOYSA-N (E)-8-Octadecenoic acid Natural products CCCCCCCCCC=CCCCCCCC(O)=O WRIDQFICGBMAFQ-UHFFFAOYSA-N 0.000 description 2
- LQJBNNIYVWPHFW-UHFFFAOYSA-N 20:1omega9c fatty acid Natural products CCCCCCCCCCC=CCCCCCCCC(O)=O LQJBNNIYVWPHFW-UHFFFAOYSA-N 0.000 description 2
- QSBYPNXLFMSGKH-UHFFFAOYSA-N 9-Heptadecensaeure Natural products CCCCCCCC=CCCCCCCCC(O)=O QSBYPNXLFMSGKH-UHFFFAOYSA-N 0.000 description 2
- 239000005642 Oleic acid Substances 0.000 description 2
- ZQPPMHVWECSIRJ-UHFFFAOYSA-N Oleic acid Natural products CCCCCCCCC=CCCCCCCCC(O)=O ZQPPMHVWECSIRJ-UHFFFAOYSA-N 0.000 description 2
- 239000004952 Polyamide Substances 0.000 description 2
- 239000004698 Polyethylene Substances 0.000 description 2
- 239000004743 Polypropylene Substances 0.000 description 2
- 239000004793 Polystyrene Substances 0.000 description 2
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 2
- 235000021355 Stearic acid Nutrition 0.000 description 2
- CJZGTCYPCWQAJB-UHFFFAOYSA-L calcium stearate Chemical compound [Ca+2].CCCCCCCCCCCCCCCCCC([O-])=O.CCCCCCCCCCCCCCCCCC([O-])=O CJZGTCYPCWQAJB-UHFFFAOYSA-L 0.000 description 2
- 239000008116 calcium stearate Substances 0.000 description 2
- 235000013539 calcium stearate Nutrition 0.000 description 2
- 229910052802 copper Inorganic materials 0.000 description 2
- 239000010949 copper Substances 0.000 description 2
- 238000007599 discharging Methods 0.000 description 2
- 230000000694 effects Effects 0.000 description 2
- 238000011049 filling Methods 0.000 description 2
- 239000012530 fluid Substances 0.000 description 2
- VAKIVKMUBMZANL-UHFFFAOYSA-N iron phosphide Chemical compound P.[Fe].[Fe].[Fe] VAKIVKMUBMZANL-UHFFFAOYSA-N 0.000 description 2
- QXJSBBXBKPUZAA-UHFFFAOYSA-N isooleic acid Natural products CCCCCCCC=CCCCCCCCCC(O)=O QXJSBBXBKPUZAA-UHFFFAOYSA-N 0.000 description 2
- HGPXWXLYXNVULB-UHFFFAOYSA-M lithium stearate Chemical compound [Li+].CCCCCCCCCCCCCCCCCC([O-])=O HGPXWXLYXNVULB-UHFFFAOYSA-M 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 238000010907 mechanical stirring Methods 0.000 description 2
- 229910052759 nickel Inorganic materials 0.000 description 2
- QIQXTHQIDYTFRH-UHFFFAOYSA-N octadecanoic acid Chemical compound CCCCCCCCCCCCCCCCCC(O)=O QIQXTHQIDYTFRH-UHFFFAOYSA-N 0.000 description 2
- OQCDKBAXFALNLD-UHFFFAOYSA-N octadecanoic acid Natural products CCCCCCCC(C)CCCCCCCCC(O)=O OQCDKBAXFALNLD-UHFFFAOYSA-N 0.000 description 2
- ZQPPMHVWECSIRJ-KTKRTIGZSA-N oleic acid Chemical compound CCCCCCCC\C=C/CCCCCCCC(O)=O ZQPPMHVWECSIRJ-KTKRTIGZSA-N 0.000 description 2
- 229920002647 polyamide Polymers 0.000 description 2
- 229920000573 polyethylene Polymers 0.000 description 2
- 229920000098 polyolefin Polymers 0.000 description 2
- 229920001155 polypropylene Polymers 0.000 description 2
- 229920002223 polystyrene Polymers 0.000 description 2
- 239000011148 porous material Substances 0.000 description 2
- 239000008117 stearic acid Substances 0.000 description 2
- 229920005992 thermoplastic resin Polymers 0.000 description 2
- 229910010413 TiO 2 Inorganic materials 0.000 description 1
- 238000004220 aggregation Methods 0.000 description 1
- 238000013019 agitation Methods 0.000 description 1
- 238000005275 alloying Methods 0.000 description 1
- CEGOLXSVJUTHNZ-UHFFFAOYSA-K aluminium tristearate Chemical compound [Al+3].CCCCCCCCCCCCCCCCCC([O-])=O.CCCCCCCCCCCCCCCCCC([O-])=O.CCCCCCCCCCCCCCCCCC([O-])=O CEGOLXSVJUTHNZ-UHFFFAOYSA-K 0.000 description 1
- 229940063655 aluminum stearate Drugs 0.000 description 1
- 229910052804 chromium Inorganic materials 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 230000002950 deficient Effects 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 239000012467 final product Substances 0.000 description 1
- 230000005484 gravity Effects 0.000 description 1
- 230000001050 lubricating effect Effects 0.000 description 1
- 238000005461 lubrication Methods 0.000 description 1
- 229910052748 manganese Inorganic materials 0.000 description 1
- 229910052976 metal sulfide Inorganic materials 0.000 description 1
- 239000011812 mixed powder Substances 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 239000000377 silicon dioxide Substances 0.000 description 1
- 238000005245 sintering Methods 0.000 description 1
- 238000001694 spray drying Methods 0.000 description 1
- 239000000454 talc Substances 0.000 description 1
- 229910052623 talc Inorganic materials 0.000 description 1
Images
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、特に圧粉成形金型からの抜き出し力の低減と共に、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）、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、圧粉体密度が低いという欠点の他、金型からの抜き出し力の面でも問題を残していた。
本発明は、上記の問題を有利に解決するもので、金型からの抜き出し力が小さく、かつ圧粉体密度の向上を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．有機結合剤により黒鉛を付着させた鉄基粉末に、0.05〜0.6 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20mass％が、粒径：0.1〜80μm の一次粒子を凝集させて造粒した粒径：50〜200 μm（但し、 50 μ m および 150 μ m を除く）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。
【０００９】
２．前記鉄基粉末混合物中に、さらに合金用粉末および／または切削性改善用粉末を混合したことを特徴とする上記１記載の粉末冶金用鉄基粉末混合物。
【００１０】
３．鉄粉と黒鉛と有機結合剤を混合した鉄基粉末混合物を、該有機結合剤の融点以上に加熱して、該鉄粉の表面に黒鉛を付着させたのち、一次粒径が0.1〜80μmの潤滑剤が凝集して造粒された粒径：50〜200 μm（但し、 50 μ m および 150 μ m を除く）の二次粒子を、0.05〜0.6 mass％の範囲で添加し、かかる二次粒子が遊離潤滑剤全体に対して少なくとも20mass％の比率で含有するように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。
【００１１】
４．前記鉄基粉末混合物中に、さらに合金用粉末および／または切削性改善用粉末を混合したことを特徴とする上記３記載の粉末冶金用鉄基粉末混合物の製造方法。
【００１２】
【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、純鉄粉はもとより、CuやNi,Mo，Mn，Cr等を予め合金化したいわゆる予合金鋼粉およびNi，Mo，Cu等を鉄粉の表面に拡散付着させたいわゆる部分合金化鋼粉を含むものとする。
そして、かような鉄基粉末の表面に予め有機結合剤により黒鉛を付着させておくこととした。というのは、前述したとおり、黒鉛粉は鉄基粉末より微粉であるため、混合後の輸送時やホッパへの装入・排出時、さらには金型充填時に、混合体の中で偏析して、寸法や強度のばらつきを生じ易いのであるが、かような黒鉛粉を予め鉄基粉末の表面に付着させておけば、上記の偏析を有利に解消することができるからである。
【００１３】
ここに、上記した有機結合剤については、その種類が特に限定されるものではないが、次のものがとりわけ有利に適合する。
(1) 金属石鹸（ステアリン酸亜鉛、ステアリン酸リチウム、ステアリン酸カルシウムなど）
(2) 金属石鹸と脂肪酸の共融混合物（ステアリン酸、オレイン酸など）
(3) 脂肪酸アミド（ステアリン酸アミド、エチレンビスステアロアミドなど）
(4) 金属石鹸と脂肪酸アミドの共融混合物
(5) 熱可塑性樹脂（ポリエチレン、ポリプロピレンを含むポリオレフィン、ポリアミド、ポリスチレンなど）
なお、これらは単独で使用しても、また複合して使用してもよいのは言うまでもない。
【００１４】
さて、上記したような予め有機結合剤により黒鉛を付着させた鉄基粉末に対し、適正量の遊離潤滑剤を添加混合して粉末冶金用鉄基粉末混合物とするわけであるが、本発明において最も重要なことは、上記した遊離潤滑剤中に一次粒子が凝集して造粒された二次粒子をある程度以上残存させることである。
すなわち、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、少量の潤滑剤でも金型からの抜き出し力を効果的に低減させることができ、また潤滑剤量を少なくできるため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。
【００１５】
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、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、この二次粒子がほぐれること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が達成されるものと考えられる。
また、潤滑剤は、鉄基粉末に比べ比重が小さいため、少なくするほど圧粉体密度は向上する。
本発明では、少量の遊離潤滑剤で抜き出し力が低減するため、従来 0.8〜1.2mass％程度添加していた量を0.05〜0.6 mass％まで低減することができ、その分圧粉体密度の向上を図ることができた。
【００１６】
ここに、一次粒子については、粒径を 0.1〜80μm 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 0.1μm に満たないと、凝集力が強くなり、二次粒子が成形時にほぐれ難くなって抜き出し力が高くなり、一方80μm を超えると、成形体中に潤滑剤粒子に起因した粗大な空孔が残留して圧粉体密度の低下を招くからである。好ましくは１〜60μm である。
また、二次粒子については、その粒径を50〜200μm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50μm に満たないと、金型壁面と鉄基粉末との間に入り込む潤滑剤量が少なくなって、抜き出し力を十分に低下させることができず、一方 200μm を超えると、成形体中に潤滑剤粒子に起因した粗大な空孔が残留する結果、圧粉体密度の低下を招くからである。好ましくは50〜100 μm である。
なお、二次粒子への造粒は、スプレードライ法、マルメライザー等公知の方法を利用することができる。
【００１７】
そして、上記した粒径が50〜200 μm の二次粒子を、遊離潤滑剤全体に対して少なくとも20mass％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20mass％に満たないと、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が望めないからである。
【００１８】
また、上記した遊離潤滑剤は、鉄基粉末混合物全体に対し0.05〜0.6 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0.05mass％に満たないと十分な潤滑効果が得られず，一方 0.6mass％を超えると高い圧粉体密度が得られないという弊害を生じるからである。好ましくは 0.1〜0.4 mass％である。
【００１９】
なお、本発明の遊離潤滑剤としては、その種類が特に限定されるものではないが、次のものがとりわけ有利に適合する。
(1) 金属石鹸（ステアリン酸亜鉛、ステアリン酸リチウム、ステアリン酸カルシウムなど）
(2) 金属石鹸と脂肪酸の共融混合物（ステアリン酸、オレイン酸など）
(3) 脂肪酸アミド（ステアリン酸アミド、エチレンビスステアロアミドなど）
(4) 金属石鹸と脂肪酸アミドの共融混合物
(5) 熱可塑性樹脂（ポリエチレン、ポリプロピレンを含むポリオレフィン、ポリアミド、ポリスチレンなど）
その他、必要に応じてシリカやTiO2微粉等を混合しても良い。
【００２０】
図１に、従来の潤滑剤および本発明に従う有機結合剤および潤滑剤を用いた場合における潤滑剤総量（有機結合剤と潤滑剤の総量）と圧粉体密度との関係について調べた結果を、また図２には、潤滑剤総量と抜き出し力との関係について調べた結果を、さらに図３には、圧粉体密度と抜き出し力との関係について調べた結果を、それぞれ示す。
【００２１】
上記の実験に用いた鉄基粉末混合物は次のとおりである。
ａ．従来の鉄基粉末混合物（２％Ni−１％Mo部分合金化鋼粉に、黒鉛粉：0.6 mass％とステアリン酸亜鉛粉末（未造粒）：0.6 〜0.8 mass％を混合したもの）ｂ．本発明に従う鉄基粉末混合物（２％Ni−１％Mo部分合金化鋼粉に、有機結合剤（ステアリン酸アミドとエチレンビスステアロアミド）：0.1 ％で黒鉛粉：0.6 mass％を付着し、遊離潤滑剤（エチレンビスステアロアミド）：0.2 〜0.4 mass％を混合したもの）
上記の各粉末を用い、日本粉末冶金工業会規格（JPMA P09, JPMA P13）に準拠して、直径：11.3mm、高さ：11mmの圧粉体を 686 MPaの成形圧力で作製し、その時の圧粉体密度および抜き出し力を求めた。
【００２２】
図１，２から明らかなように、従来の鉄基粉末混合物ａを用いた場合には、潤滑剤の総量を少なくすれば圧粉体密度は向上するものの、一方で抜き出し力が大きくなり、0.6mass ％未満では事実上、成形が不可能であった。従って、総量で 0.6〜0.8 ％程度の潤滑剤を添加し、圧粉体密度は7.22 Mg/m3前後にすぎなかった。
これに対し、本発明に従う鉄基粉末混合物ｂを用いた場合には、潤滑剤の総量を 0.6％以下としても抜き出し力を効果的に低減することができ、また圧粉体密度も7.28 Mg/m3前後まで改善することができた。
特にそれらの特性を比較して示した図３によれば、本発明の潤滑剤を用いた場合は、抜き出し力の低減と圧粉体密度の向上を併せて達成できることが明白である。
【００２３】
また、この発明では、鉄基粉末混合物中に、さらに副原料粉末として合金用粉末や切削性改善用粉末を適宜混合させることができる。
ここに、合金用粉末としては、黒鉛粉、銅粉および各種合金元素粉などが、また切削性改善用粉末としては金属硫化物粉およびタルクなどが適合する。
そして、これらの合金用粉末および切削性改善用粉末の添加量は、混合物全体に対し 0.1〜5.0 mass％程度とすることが好ましい。
【００２４】
次に、本発明の製造条件について説明する。
まず、本発明では、鉄基粉末の表面に有機結合剤により黒鉛を付着させる。そのためには、鉄基粉末中に適量の有機結合剤と黒鉛粉とを混合した鉄基粉末混合物を、有機結合剤の融点以上に加熱して、該鉄粉の表面に黒鉛を付着させる。
なお、この際、必要であれば、合金用粉末や切削性改善用粉末も鉄基粉末混合物中に併せて混合しておく。
ここに、有機結合剤の添加量は、鉄基粉末混合物全体に対して0.05〜0.3 mass％程度、また黒鉛粉の添加量は 0.1〜1.2 mass％程度が好適である。
また、加熱温度は有機結合剤の種類によって異なるけれども、有機結合剤としてエチレンビスステアロアミド（融点：148 ℃）を用いた場合には、 150〜160℃程度で十分である。
【００２５】
ついで、上記のようにして得た鉄基粉末の表面に黒鉛粉等を付着させた鉄基粉末混合物中に、遊離潤滑剤を適量添加したのち、遊離潤滑剤の二次粒子が破壊しないせん断力の混合機を使用して混合を実施する。
かような混合機としては、容器回転式、機械撹拌式、流動撹拌式および無撹拌式等の、混合粉体に与えるせん断力が小さい混合機が好適である。容器回転式混合機では、水平円筒型、傾斜円筒型、Ｖ型、二重円錐型および連続Ｖ型が好ましく、撹拌羽が内蔵されている混合機も好適に使用できる。機械撹拌式混合機では、リボン型、スクリュー型、複軸パドル型、円錐形スクリュー型および回転円板型が好ましい。流動撹拌式混合機では、流動床式、旋回流動式、ジェットポンプ式が好ましい。
【００２６】
混合機の条件は、例えば、上記したＶ型容器回転式混合機を使用する場合、粒径が50〜200μmの二次粒子を少なくとも20mass％残存させるためには、２リットルの容器の回転数を10〜100 rpm とすることが好適である。ただし、混合条件は、上記の範囲に限定されるものではなく、遊離潤滑剤の二次粒子の凝集強度に応じて、適宜決定されるものである。
【００２７】
成形方法については、公知の方法いずれもが適合する。
例えば、鉄基粉末混合物を室温とし、金型を50〜70℃に加熱する方法は、粉末の取り扱いが容易で、圧粉体密度がさらに向上するため好適である。
また、粉末、金型ともに 120〜130 ℃に加熱する温間成形も使用することができる。さらに、その後の焼結および熱処理についても公知の方法を使用すれば良い。
【００２８】
【実施例】
実施例１
鉄基粉末、有機結合剤、遊離潤滑剤および合金用・切削性改善用粉末（副原料粉末）として、それぞれ表１〜４に示すものを用いた。
これらを素材として、表５〜７に示す割合で混合し、各有機結合剤の融点以上に加熱して鉄粉の表面に黒鉛を付着させたのち、さらに遊離潤滑剤を添加してＶ型混合機に入れ、せん断力を制御しつつ混合した。
得られた鉄基粉末混合物中における遊離潤滑剤の二次粒子の比率について調べた結果を表５に併記する。
ついで得られた鉄基粉末混合物を、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の圧粉成形体を作製した。
かくして得られた圧粉体の密度および成形金型からの抜き出し力について調べた結果を表５〜７に併記する。
【００２９】
【表１】
【表２】
【表３】
【表４】
【表５】
【表６】
【表７】
表５〜７から明らかなように、発明例はいずれも、潤滑剤使用量の低減の下で、高い圧粉体密度と低い抜き出し力の両者が併せて達成されている。
【００３７】
また、図４には、本発明に従う潤滑剤の顕微鏡写真を示す。
同図に示したとおり、遊離潤滑剤の一次粒子および二次粒子が分布していることが分かる。
【００３８】
【発明の効果】
かくして、本発明によれば、金型からの抜き出し力が小さく、かつ圧粉体密度が大きいすなわち常温成形性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。
【図面の簡単な説明】
【図１】 従来の潤滑剤および本発明に従う潤滑剤を用いた場合における潤滑剤総量と圧粉体密度との関係を示したグラフである。
【図２】 従来の潤滑剤および本発明に従う潤滑剤を用いた場合における潤滑剤総量と抜き出し力との関係を示したグラフである。
【図３】 圧粉体密度と抜き出し力との関係を示したグラフである。
【図４】 本発明に従う潤滑剤の顕微鏡写真である。[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 particularly to reduce the pulling force from a compacting mold and to improve the compact density advantageously.
[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), or liberation A technique for mixing a 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-described prior art have a problem in terms of the extraction force from the mold in addition to the disadvantage that the green compact density is low.
The present invention advantageously solves the above problems, and proposes an iron-based powder mixture for powder metallurgy that has a small extraction force from the mold and can improve the density of the green compact, together with its advantageous production method. The purpose is to do.
[0007]
[Means for Solving the Problems]
Now, as a result of intensive studies to solve the above problems, the inventors have achieved the intended purpose advantageously by appropriately controlling the particle size distribution of the free lubricant mixed in the iron-based powder mixture. Gained the knowledge of being.
The present invention is based on the above findings.
[0008]
That is, the gist configuration of the present invention is as follows.
1. An iron-based powder mixture in which 0.05 to 0.6 mass% of a free lubricant is mixed with iron-based powder to which graphite is adhered by an organic binder, and at least 20 mass% of the free lubricant has a particle size of 0.1 to 80 μm. primary particles by agglomeration granulation and particle size: 50 to 200 [mu] m (where, 50 mu m and 0.99 mu excluding m) for powder metallurgy iron-based powder mixture, characterized in that it consists of secondary particles of.
[0009]
2. 2. The iron-based powder mixture for powder metallurgy according to the above 1, wherein an alloy powder and / or a machinability improving powder are further mixed in the iron-based powder mixture.
[0010]
3. An iron-based powder mixture obtained by mixing iron powder, graphite, and an organic binder is heated to a temperature equal to or higher than the melting point of the organic binder to adhere graphite to the surface of the iron powder, and then has a primary particle size of 0.1 to 80 μm. lubricant is aggregated granulated particle size: 50 to 200 [mu] m (excluding the 50 mu m and 0.99 mu m) of the secondary particles of, is added in a range of 0.05 to 0.6 mass%, such secondary A method for producing an iron-based powder mixture for powder metallurgy, characterized in that the particles are mixed so as to contain at a ratio of at least 20 mass% with respect to the entire free lubricant.
[0011]
4). 4. The method for producing an iron-based powder mixture for powder metallurgy according to 3 above, wherein an alloy powder and / or a machinability improving powder are further mixed in the iron-based powder mixture.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be specifically described below.
In the present invention, the basic powder, iron-based powder, is not only pure iron powder but also so-called pre-alloyed steel powder obtained by pre-alloying Cu, Ni, Mo, Mn, Cr, etc., and Ni, Mo, Cu, etc. as iron powder. So-called partially alloyed steel powder diffused and adhered to the surface of the steel.
And it was decided to make graphite adhere to the surface of such iron-based powder beforehand with an organic binder. This is because, as mentioned above, graphite powder is finer than iron-based powder, so it segregates in the mixture during transportation after mixing, during charging / discharging into the hopper, and during mold filling. This is because variations in size and strength are likely to occur. However, if such graphite powder is previously attached to the surface of the iron-based powder, the above segregation can be advantageously eliminated.
[0013]
Here, the kind of the organic binder described above is not particularly limited, but the following are particularly advantageously adapted.
(1) Metal soap (zinc stearate, lithium stearate, calcium stearate, etc.)
(2) Eutectic mixture of metal soap and fatty acid (stearic acid, oleic acid, etc.)
(3) Fatty acid amides (stearic acid amide, ethylenebisstearamide, etc.)
(4) Eutectic mixture of metal soap and fatty acid amide
(5) Thermoplastic resin (polyolefin including polyethylene, polypropylene, polyamide, polystyrene, etc.)
Needless to say, these may be used alone or in combination.
[0014]
Now, to the iron-based powder to which graphite is previously attached by the organic binder as described above, an appropriate amount of free lubricant is added and mixed to obtain an iron-based powder mixture for powder metallurgy. The most important thing is that the secondary particles formed by agglomeration of primary particles in the above-described free lubricant remain to some extent.
That is, according to the study by the inventors, by appropriately controlling the shearing force at the time of mixing described above and leaving the secondary particles to a certain extent or more, even with a small amount of lubricant, the extraction force from the mold can be increased. It has been determined that an advantageous improvement in green density can be achieved because it can be effectively reduced and the amount of lubricant can be reduced.
[0015]
The reason for this is not yet clearly understood, but when secondary particles having a relatively large particle size are present in the free lubricant, when the iron-based powder mixture is charged into a compacting mold, Effectively penetrates into the gap between the mold wall and the iron-based powder in contact with it, and the secondary particles are loosened, so that the lubrication effect is greatly improved and the extraction force from the mold is reduced. it is conceivable that.
Further, since the specific gravity of the lubricant is smaller than that of the iron-based powder, the green density increases as the lubricant is decreased.
In the present invention, since the extraction force is reduced with a small amount of free lubricant, the amount conventionally added about 0.8 to 1.2 mass% can be reduced to 0.05 to 0.6 mass%, and the partial pressure powder density is improved. We were able to plan.
[0016]
Here, for primary particles, it is necessary to limit the particle size to a range of 0.1 to 80 μm. This is because if the particle size of the primary particles, that is, the primary particle size is less than 0.1 μm, the cohesive force becomes strong, the secondary particles are difficult to loosen during molding, and the extraction force increases, while if the particle size exceeds 80 μm, This is because coarse pores resulting from the lubricant particles remain in the body, leading to a reduction in the density of the green compact. Preferably it is 1-60 micrometers.
Also, the secondary particles, it is necessary to restrict the particle size in the range of 50 ~200μm. This is because if the particle size of the secondary particles, that is, the secondary particle size is less than 50 μm, the amount of lubricant entering between the mold wall surface and the iron-based powder is reduced, and the extraction force is sufficiently reduced. On the other hand, if it exceeds 200 μm, coarse pores resulting from the lubricant particles remain in the molded body, resulting in a reduction in the green compact density. Preferably it is 50-100 micrometers.
In addition, the granulation to a secondary particle can utilize well-known methods, such as a spray-dry method and a malmerizer.
[0017]
The secondary particles having a particle size of 50 to 200 μm are contained at a ratio of at least 20 mass% with respect to the entire free lubricant.
This is because if the ratio of secondary particles is less than 20 mass%, the amount of secondary particles entering the gap between the mold wall and the iron-based powder in contact with it is too small, reducing the extraction force as expected. Because I can not hope.
[0018]
Moreover, it is necessary to add the above-mentioned free lubricant in the range of 0.05 to 0.6 mass% with respect to the entire iron-based powder mixture.
This is because a sufficient lubricating effect cannot be obtained unless the ratio of the free lubricant to the entire iron-based powder mixture is less than 0.05 mass%, while a high green compact density cannot be obtained if the ratio exceeds 0.6 mass%. It is because it produces. Preferably it is 0.1-0.4 mass%.
[0019]
The type of the free lubricant of the present invention is not particularly limited, but the following are particularly advantageous.
(1) Metal soap (zinc stearate, lithium stearate, calcium stearate, etc.)
(2) Eutectic mixture of metal soap and fatty acid (stearic acid, oleic acid, etc.)
(3) Fatty acid amides (stearic acid amide, ethylenebisstearamide, etc.)
(4) Eutectic mixture of metal soap and fatty acid amide
(5) Thermoplastic resin (polyolefin including polyethylene, polypropylene, polyamide, polystyrene, etc.)
In addition, silica or TiO 2 fine powder may be mixed as necessary.
[0020]
FIG. 1 shows the results of investigating the relationship between the total amount of lubricant (total amount of organic binder and lubricant) and the green density when using the conventional lubricant and the organic binder and lubricant according to the present invention. FIG. 2 shows the results of examining the relationship between the total amount of the lubricant and the extracting force, and FIG. 3 shows the results of examining the relationship between the green compact density and the extracting force.
[0021]
The iron-based powder mixture used in the above experiment is as follows.
a. Conventional iron-based powder mixture (mixed 2% Ni-1% Mo partially alloyed steel powder with graphite powder: 0.6 mass% and zinc stearate powder (ungranulated): 0.6-0.8 mass%) b. Iron-based powder mixture according to the present invention (2% Ni-1% Mo partially alloyed steel powder, organic binder (stearic amide and ethylene bisstearamide): 0.1% and graphite powder: 0.6 mass% adhered, Free lubricant (ethylene bisstearamide): 0.2 to 0.4 mass% mixed)
Using each of the above powders, in accordance with the Japan Powder Metallurgy Industry Association Standard (JPMA P09, JPMA P13), a green compact with a diameter of 11.3 mm and a height of 11 mm was produced at a molding pressure of 686 MPa. The green density and extraction force were determined.
[0022]
As is apparent from FIGS. 1 and 2, when the conventional iron-based powder mixture a is used, the density of the green compact is improved if the total amount of the lubricant is reduced, but on the other hand, the extraction force is increased, and 0.6 If it is less than mass%, molding was practically impossible. Therefore, a total amount of about 0.6 to 0.8% of lubricant was added, and the green density was only around 7.22 Mg / m 3 .
On the other hand, when the iron-based powder mixture b according to the present invention is used, the extraction force can be effectively reduced even if the total amount of the lubricant is 0.6% or less, and the green compact density is 7.28 Mg / m 3 was able to be improved to the front and rear.
In particular, FIG. 3 showing a comparison of these characteristics clearly shows that when the lubricant of the present invention is used, a reduction in extraction force and an improvement in green density can be achieved.
[0023]
Moreover, in this invention, the powder for alloys and the powder for improving machinability can be appropriately mixed as an auxiliary material powder in the iron-based powder mixture.
Here, graphite powder, copper powder and various alloy element powders are suitable as the alloy powder, and metal sulfide powder and talc are suitable as the machinability improving powder.
The amount of the alloy powder and the machinability improving powder added is preferably about 0.1 to 5.0 mass% with respect to the entire mixture.
[0024]
Next, the manufacturing conditions of the present invention will be described.
First, in the present invention, graphite is adhered to the surface of the iron-based powder by an organic binder. For this purpose, an iron-based powder mixture obtained by mixing an appropriate amount of an organic binder and graphite powder in an iron-based powder is heated to a temperature equal to or higher than the melting point of the organic binder to adhere graphite to the surface of the iron powder.
At this time, if necessary, alloy powder and machinability improving powder are also mixed in the iron-based powder mixture.
Here, the addition amount of the organic binder is preferably about 0.05 to 0.3 mass% with respect to the entire iron-based powder mixture, and the addition amount of the graphite powder is preferably about 0.1 to 1.2 mass%.
Further, although the heating temperature varies depending on the type of the organic binder, when ethylene bisstearamide (melting point: 148 ° C.) is used as the organic binder, about 150 to 160 ° C. is sufficient.
[0025]
Then, after adding an appropriate amount of free lubricant to the iron-based powder mixture in which graphite powder or the like is adhered to the surface of the iron-based powder obtained as described above, the shear force that does not break the secondary particles of the free lubricant Mixing is carried out using a mixer.
As such a mixer, a mixer having a small shearing force applied to the mixed powder, such as a container rotating type, a mechanical stirring type, a flow stirring type and a non-stirring type, is preferable. In the container rotation type mixer, a horizontal cylinder type, an inclined cylinder type, a V type, a double cone type and a continuous V type are preferable, and a mixer having a built-in stirring blade can also be suitably used. In the mechanical stirring mixer, a ribbon type, a screw type, a biaxial paddle type, a conical screw type and a rotating disk type are preferable. In the fluid agitation mixer, a fluid bed type, a swirl type, and a jet pump type are preferable.
[0026]
The condition of the mixer is, for example, when using the above-mentioned V-shaped container rotary mixer, in order to leave at least 20 mass% of secondary particles having a particle size of 50 to 200 μm, the rotational speed of a 2 liter container must be set. It is suitable to set it as 10-100 rpm. However, the mixing conditions are not limited to the above range, and are appropriately determined according to the aggregation strength of the secondary particles of the free lubricant.
[0027]
Any known method is suitable for the molding method.
For example, a method in which the iron-based powder mixture is brought to room temperature and the mold is heated to 50 to 70 ° C. is preferable because the powder can be easily handled and the green density is further improved.
Also, warm molding in which both the powder and the mold are heated to 120 to 130 ° C. can be used. Furthermore, a known method may be used for the subsequent sintering and heat treatment.
[0028]
【Example】
Example 1
As iron-based powder, organic binder, free lubricant, and alloy / cutting ability improving powder (sub-material powder), those shown in Tables 1 to 4 were used.
Using these as raw materials, mixing at the ratios shown in Tables 5-7, heating to above the melting point of each organic binder to adhere graphite to the surface of the iron powder, then adding free lubricant and V-type mixing The mixture was mixed and the shearing force was controlled.
The results of examining the ratio of secondary particles of the free lubricant in the obtained iron-based powder mixture are also shown in Table 5.
The resulting iron-based powder mixture was then compressed at a pressure of 686 MPa in accordance with the Japan Powder Metallurgy Industry Association Standard (JPMA P09, JPMA P13), and the compacted body with a diameter of 11.3 mm and a height of 11 mm. Was made.
The results of examining the density of the green compact thus obtained and the extraction force from the molding die are also shown in Tables 5-7.
[0029]
[Table 1]
[Table 2]
[Table 3]
[Table 4]
[Table 5]
[Table 6]
[Table 7]
As is clear from Tables 5 to 7, in all of the inventive examples, both a high green compact density and a low extraction force are achieved under a reduction in the amount of lubricant used.
[0037]
FIG. 4 shows a photomicrograph of the lubricant according to the present invention.
As shown in the figure, it can be seen that the primary particles and secondary particles of the free lubricant are distributed.
[0038]
【The invention's effect】
Thus, according to the present invention, it is possible to stably obtain an iron-based powder mixture for powder metallurgy having a small extraction force from a mold and a high density of a green compact, that is, excellent in room temperature formability.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between the total amount of lubricant and the green density when a conventional lubricant and a lubricant according to the present invention are used.
FIG. 2 is a graph showing the relationship between the total amount of lubricant and the extraction force when a conventional lubricant and a lubricant according to the present invention are used.
FIG. 3 is a graph showing the relationship between the green compact density and the extraction force.
FIG. 4 is a photomicrograph of a lubricant according to the present invention.
Claims (4)
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| JP2002319890A Expired - Fee Related JP4144326B2 (en) | 2002-11-01 | 2002-11-01 | Iron-based powder mixture for powder metallurgy and method for producing the same |
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Families Citing this family (5)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2010007176A (en) * | 2008-05-27 | 2010-01-14 | Jfe Steel Corp | Iron-based powdery mixture for powder metallurgy |
| JP5223547B2 (en) * | 2008-09-05 | 2013-06-26 | Ｊｆｅスチール株式会社 | Iron-based mixed powder for powder metallurgy |
| WO2014103287A1 (en) * | 2012-12-28 | 2014-07-03 | Ｊｆｅスチール株式会社 | Iron-based powder for powder metallurgy |
| JP6227903B2 (en) * | 2013-06-07 | 2017-11-08 | Ｊｆｅスチール株式会社 | Alloy steel powder for powder metallurgy and method for producing iron-based sintered body |
| PL3253512T3 (en) * | 2015-02-03 | 2023-06-12 | Höganäs Ab (Publ) | Powder metal composition for easy machining |
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