JP3684026B2 - Manufacturing method of inorganic powder sintered body - Google Patents

Description

【００１５】
また、結合材のガスの除去速度ｆｉは等方的媒質中での拡散と見なせるので、結合材の濃度Ｃとの間には数２の拡散方程式が成り立つ。
【００１６】
【数２】

【００１７】
この結合材のガス化速度ｈｉがガス除去速度ｆｉを上回ると、ガス化して成形体中に発生した結合材のガスは除去されず、成形体の膨れや割れの原因となる。従って、常に、ｈｉ＜ｆｉとするためには、数３とする必要がある。
【００１８】
【数３】

【００１９】
この数３において、ｇｒａｄＴ＝ｖであり、成形体が均質に形成されているとすると、ｇｒａｄＣ≒ｘと見なしても構わないから、数４が成立する。
【００２０】
【数４】

【００２１】
この数４について、不等号をκ，ｋの係数で展開すると、数５となる。数５において、ｂ、ｄは任意の係数であり、ｄは、℃／ｈを単位としている。
【００２２】
【数５】

【００２３】
数５において、結合材の熱伝導係数κの逆数、すなわち１／κをａとし、結合材のガス拡散係数ｋをｃとすると、ｖ＝ａｌｎ（ｂ−ｃｘ）＋ｄとなり、成形体の肉厚ｘと加熱昇温速度ｖとの間で、請求項１の関係が成立する。ここで、ａは℃／ｈを単位とし、ｃは１／ｍｍを単位としている。
【００２４】
本発明者らが、これらのそれぞれの係数ａ，ｂ，ｃ，ｄを、不活性雰囲気中での実験によって鋭意検討により求めたところ、
２≦ａ≦６５
１．１３≦ｂ≦１８
０．０１≦ｃ≦５．４５
１．２≦ｄ≦５３．６
となった。ここで、ａ＜２、ｂ＜１．１３、ｃ＞５．４５、ｄ＜１．２の内のいずれかの条件に当てはまる場合には、加熱の昇温速度が遅すぎて結合材が気化、分解する前に液化して、成形体が変形する。又、さらにａ＞６５、ｂ＞１８、ｃ＜０．０１、ｄ＞５３．３の場合には、加熱昇温速度が速すぎ、気化や分解により発生した結合材のガスが成形体より除去されず、成形体に膨れや割れ等の不具合を生じる。
【００２５】
各係数は、２≦ａ≦６５、１．１３≦ｂ≦１８、０．０１≦ｃ≦５．４５、１．２≦ｄ≦５３．６としたが、２．１≦ａ≦６５．１、１．５≦ｂ≦１７、０．０５≦ｃ≦５．１２、１．５≦ｄ≦４３．６でも良く、より良くは２．５≦ａ≦５９、１．８≦ｂ≦１７、０．０５≦ｃ≦４．６７、３．６≦ｄ≦３８．１でも良く、特に２．８≦ａ≦５５、２．０≦ｂ≦１６、０．０５≦ｃ≦４．１１、４．９≦ｄ≦３７．５でも良く、いずれにおいても膨れや割れのない成形品とすることができる。
【００２６】
請求項２の発明は、無機物粉末と結合材を混合して成形した後、結合材を除去し、その後、焼結して無機物粉末焼結体とする方法において、 結合材の除去時の昇温速度をｖ（℃／ｈ）、成形後の成形体の肉厚をｘ（ｍｍ）、自然対数をｌｎとした場合、式 ｖ＝ａｌｎ（ｂ−ｃｘ）＋ｄ（式中、ａは結合材の熱伝導係数の逆数であり、℃／ｈを単位とし、ｂは任意の係数、ｃはガス化して除去される結合材のガス拡散係数であり、１／ｍｍを単位とし、ｄは℃／ｈを単位とした任意の係数である。又、５≦ａ≦７２、１．２≦ｂ≦２８、０．０１≦ｃ≦８．１２、１．５≦ｄ≦６２．４である。）上記式により昇温速度を特定する工程と、常圧の活性雰囲気中で前記工程で特定された昇温速度で加熱して結合材を除去することを特徴とする。
【００２７】
この方法は、常温の活性雰囲気中で結合材を除去するものであり、常温の活性雰囲気下においては、加熱昇温による結合材の気化、分解に加えて、活性ガスと結合材との反応による分解を考慮する必要がある。
【００２８】
本発明者らが、常温の活性雰囲気中でのそれぞれの係数ａ，ｂ，ｃ，ｄを、実験によって鋭意検討により求めたところ、
５≦ａ≦７２
１．２≦ｂ≦２８
０．０１≦ｃ≦８．１２
１．５≦ｄ≦６２．４
となった。ここで、ａ＜５、ｂ＜１．２、ｃ＞８．１２、ｄ＜１．５の内のいずれかの条件に当てはまる場合には、加熱の昇温速度が遅すぎて結合材が気化、分解する前に液化して、成形体が変形する。又、さらにａ＞７２、ｂ＞２８、ｃ＜０．０１、ｄ＞６２．４の場合には、加熱昇温速度が速すぎ、気化や分解により発生した結合材のガスが成形体より除去されず、成形体に膨れや割れ等の不具合を生じる。
【００２９】
各係数の範囲は、５≦ａ≦７２、１．２≦ｂ≦２８、０．０１≦ｃ≦８．１２、１．５≦ｄ≦６２．４としたが、５．８≦ａ≦６８、１．６≦ｂ≦２１、０．０３≦ｃ≦７．４４、１．５≦ｄ≦６１．３でも良く、より良くは６．１≦ａ≦６５、１．８≦ｂ≦１９、０．０５≦ｃ≦６．８９、３．２≦ｄ≦５８．７でも良く、特に７．３≦ａ≦５７、２．０≦ｂ≦１７、０．０５≦ｃ≦６．２２、３．５≦ｄ≦４５．１でも良い。
【００３０】
請求項３の発明は、無機物粉末と結合材を混合して成形した後、結合材を除去し、その後、焼結して無機物粉末焼結体とする方法において、結合材の除去時の昇温速度をｖ（℃／ｈ）、成形後の成形体の肉厚をｘ（ｍｍ）、自然対数をｌｎとした場合、式 ｖ＝ａｌｎ（ｂ−ｃｘ）＋ｄ（式中、ａは結合材の熱伝導係数の逆数であり、℃／ｈを単位とし、ｂは任意の係数、ｃはガス化して除去される結合材のガス拡散係数であり、１／ｍｍを単位とし、ｄは℃／ｈを単位とした任意の係数である。又、６≦ａ≦８１、１．５≦ｂ≦３２、０．０５≦ｃ≦８．９９、１．２≦ｄ≦７１．６である。）上記式により昇温速度を特定する工程と、減圧雰囲気中で前記工程で特定された昇温速度で加熱して結合材を除去することを特徴とする。
【００３１】
この方法は、減圧雰囲気中で加熱して結合材を除去するものであり、減圧雰囲気下においては、加熱昇温による結合材の気化、分解の他に減圧による結合材の昇華も考慮する必要がある。
【００３２】
本発明者らが、常温の活性雰囲気中でのそれぞれの係数ａ，ｂ，ｃ，ｄを、実験によって鋭意検討により求めたところ、
６≦ａ≦８１
１．５≦ｂ≦３２
０．０５≦ｃ≦８．９９
１．２≦ｄ≦７１．６
となった。ここで、ａ＜６、ｂ＜１．５、ｃ＞８．９９、ｄ＜１．２の内のいずれかの条件に当てはまる場合には、加熱の昇温速度が遅すぎて結合材が気化、分解する前に液化して、成形体が変形する。又、さらにａ＞８１、ｂ＞３２、ｃ＜０．０５、ｄ＞７１．６の場合には、加熱昇温速度が速すぎ、気化や分解により発生した結合材のガスが成形体より除去されず、成形体に膨れや割れ等の不具合を生じる。
【００３３】
各係数の範囲は、６≦ａ≦８１、１．５≦ｂ≦３２、０．０５≦ｃ≦８．９９、１．２≦ｄ≦７１．６としたが、６．３≦ａ≦７６、１．５≦ｂ≦２９、０．０６≦ｃ≦８．５１、１．４≦ｄ≦６８．７でも良く、より良くは６．８≦ａ≦６９、１．６≦ｂ≦２１、０．０８≦ｃ≦７．８９、２．５≦ｄ≦６２．１でも良く、特に７．０≦ａ≦５１、２．２≦ｂ≦１８、０．０８≦ｃ≦６．５４、２．８≦ｄ≦５８．３でも良い。
【００３４】
【発明の実施の形態】
（実施の形態１）
図１は、この実施の形態により成形された成形体１を示す。この成形体１は、金属粉末射出成形法（ＭＩＭ）により形成されたもので、平均粒径１２μｍのオーステナイト系ステンレス鋼（ＪＩＳ規格 ＳＵＳ３１６Ｌ）粉末 ９１．１ｗｔ％と、結合材としてポリスチレン（ＰＳ）４．１ｗｔ％、ポリメチルメタクリレート（アクリル、ＰＭＭＡ）３．５ｗｔ％、パラフィンワックス１．３ｗｔ％とを混合混練してコンパウンドとし、このコンパウンドを射出成形したものである。
【００３５】
成形体１は、矩形体部２の上部両端から耳部３が立設した一体的に形状となっている。図１における各寸法は、Ａが１２ｍｍ、Ｂが１２ｍｍ、Ｃが１６ｍｍ、Ｄが４ｍｍ、Ｅが１２ｍｍであり、これにより全幅２４ｍｍ、奥行き１２ｍｍ、高さ２４ｍｍの外形で、且つ中央に１６ｍｍ×１２ｍｍ×１２ｍｍの切欠きが形成されている。この成形体１は、矩形体部２が肉厚部となっている。
【００３６】
この成形体１を図示を省略した加熱炉に設置し、窒素雰囲気（不活性雰囲気）下で加熱昇温し、結合材を除去する。この時、各係数はそれぞれａ＝４．１、ｂ＝３．１、ｃ＝０．０６、ｄ＝１２．５となり、加熱昇温速度は、ｖ＝１６．１℃／ｈとなる。
【００３７】
この加熱昇温速度で４１０℃まで加熱し、４１０℃で３．５時間保持する。その後、加熱を終了し、結合材の除去の完了した成形体１を真空焼結炉に移送し、１０−４ｔｏｒｒ（１．３３×１０−２Ｐａ）の真空下、昇温速度３００℃／ｈで１３５０℃まで加熱し、１３５０℃で１時間保持した後、加熱を終了し、冷却後、焼結が完了した粉末焼結体となった成形体を取り出す。
【００３８】
本実施の形態によれば、結合材除去時の結合材のガス化すなわち加熱昇温で結合材が気化、分解したことによるガスの発生速度よりも、ガスの除去速度が上回るので、膨れや割れ等の不具合は発生しない。また、加熱昇温速度が結合材の液化を招くほど遅くないため、変形もしない。従って、膨れや割れ、変形を生じることなく、良好な金属粉末焼結体を成形することができる。
【００３９】
（実施の形態２）
図２は実施の形態２による成形体４を示し、シートプレス成形法により形成されている。すなわち、平均粒系１１μｍのステライト合金（Ｃｏ系合金）９５．４ｗｔ％と、結合材としてポリアミド（ＰＡ）４．６ｗｔ％とを混合混練し、シート状にし、このシート状の混合材をプレスにより図２に示す形状に成形している。
【００４０】
この成形体４は、外径Ｇの直径φが５ｍｍ、内径Ｈの直径φが４ｍｍ、高さＦが７ｍｍの円筒形を軸方向に縦に２分割した形状となっており、外径及び内径の間の０．５ｍｍの肉厚部となっている。
【００４１】
この成形体４を加熱炉に設置し、大気雰囲気（活性雰囲気）下で加熱昇温して結合材を除去する。この時、各係数はａ＝２７．１、ｂ＝１３．７、ｃ＝５．３５、ｄ＝１３．７となり、加熱昇温速度はｖ＝７８．７℃／ｈとなる。
【００４２】
この加熱昇温速度で３２５℃まで加熱し、３２５℃で２時間保持する。その後、加熱を終了し、結合材除去が完了した成形体を真空焼却炉に移送して、Ａｒ減圧雰囲気下５ｔｏｒｒ（６５．５Ｐａ）、昇温速度２５０℃／ｈで１２２０℃まで加熱し、１２２０℃で１時間保持した後、加熱を終了する。これにより焼結が終了し、その後、冷却し、粉末焼結体となった成形体を取り出す。
【００４３】
本実施の形態によれば、結合材除去時の結合材のガス化、すなわち加熱昇温で結合材が気化、分解に加え、活性雰囲気である大気雰囲気と結合材の反応分解にともなうガスの発生速度よりも、ガスの除去速度が上回るため、膨れや割れといった不具合は発生しない。また、加熱昇温速度が結合材の液化を招くほど遅くないため、変形することもない。従って、膨れや割れ、変形を生じることなく、良好な金属粉末焼結体を製造することができる。
【００４４】
（実施の形態３）
図３は、実施の形態３による成形体５を示し、セラミック粉末射出成形法（Ｃｅｒａｍｉｃ Ｉｎｊｅｃｔｉｏｎ Ｍｏｌｄｉｎｇ、ＣＩＭ ）によって成形されている。すなわち、平均粒系２μｍのアルミナ（Ａｌ２Ｏ３）粉末９３．２ｗｔ％と、結合材としてポリエチレン（ＰＥ）２．８ｗｔ％、アタックチックポリプロピレン（ＡＰＰ）２．８ｗｔ％、パラフィンワックス１．２ｗｔ％とを混合混練してコンパウンドとし、射出成形によって成形するものである。
【００４５】
この成形体５は、平板部６の両端の上下面から起立部７が一体的に立設した形状となっており、寸法Ｉ及びＪが５ｍｍ、Ｋが３ｍｍ、Ｍが４ｍｍとなっており、起立部７が３ｍｍの肉厚部となっている。
【００４６】
この成形体を加熱炉に設置し、１０−２ｔｏｒｒ（１．３３Ｐａ）の減圧雰囲気下で加熱昇温し、結合材を除去する。この時、各係数はａ＝８．７、ｂ＝１２．３、ｃ＝３．０８、ｄ＝２１．３となり、加熱昇温速度はｖ＝３１℃／ｈとなる。この加熱昇温速度で３５０℃まで加熱し、３５０℃で４時間保持する。
【００４７】
その後、加熱を終了し、結合材除去が完了した成形体を大気焼却炉に移送し、大気雰囲気下、２００℃／ｈの昇温速度で、１５００℃まで加熱し、１５００℃で３時間保持した後、加熱を終了して焼結した。そして、冷却後、焼結が完了して粉末焼結体となった成形体を取り出す。
【００４８】
本実施の形態によれば、結合材除去時の結合材のガス化、すなわち加熱昇温で結合材が気化、分解さらには減圧雰囲気下による結合材の昇華にともなうガスの発生速度よりも、ガスの除去速度が上回るため、膨れや割れ等の不具合は発生しない。また、加熱昇温速度が結合材の液化を招くほど遅くないため、変形することもない。従って、膨れや割れ、変形を生じることなく、良好なセラミック粉末焼結体を製造することができる。
【００４９】
以上の本発明は、以下の発明を包含するものである。
（１） 金属粉末と結合材を混合して成形した後、結合材を除去し、その後、焼結して焼結体とする方法において、
結合材の除去時の昇温速度をｖ（℃／ｈ）、成形後の成形体の肉厚をｘ（ｍｍ）、自然対数をｌｎとした場合、
式 ｖ＝ａｌｎ（ｂ−ｃｘ）＋ｄ
（式中、ａは結合材の熱伝導係数の逆数であり、℃／ｈを単位とし、ｂは任意の係数、ｃはガス化して除去される結合材のガス拡散係数であり、１／ｍｍを単位とし、ｄは℃／ｈを単位とした任意の係数である。又、２≦ａ≦６５、１．１３≦ｂ≦１８、０．０１≦ｃ≦５．４５、１．２≦ｄ≦５３．６である。）
を満たし、且つ常圧の不活性雰囲気中で加熱して結合材を除去することを特徴とする製造方法。
（２） 金属物粉末と結合材を混合して成形した後、結合材を除去し、その後、焼結して焼結体とする方法において、
結合材の除去時の昇温速度をｖ（℃／ｈ）、成形後の成形体の肉厚をｘ（ｍｍ）、自然対数をｌｎとした場合、
式 ｖ＝ａｌｎ（ｂ−ｃｘ）＋ｄ
（式中、ａは結合材の熱伝導係数の逆数であり、℃／ｈを単位とし、ｂは任意の係数、ｃはガス化して除去される結合材のガス拡散係数であり、１／ｍｍを単位とし、ｄは℃／ｈを単位とした任意の係数である。又、５≦ａ≦７２、１．２≦ｂ≦２８、０．０１≦ｃ≦８．１２、１．５≦ｄ≦６２．４である。）
を満たし、且つ常圧の活性雰囲気中で加熱して結合材を除去することを特徴とする製造方法。
（３） 金属物粉末と結合材を混合して成形した後、結合材を除去し、その後、焼結して焼結体とする方法において、
結合材の除去時の昇温速度をｖ（℃／ｈ）、成形後の成形体の肉厚をｘ（ｍｍ）、自然対数をｌｎとした場合、
式 ｖ＝ａｌｎ（ｂ−ｃｘ）＋ｄ
（式中、ａは結合材の熱伝導係数の逆数であり、℃／ｈを単位とし、ｂは任意の係数、ｃはガス化して除去される結合材のガス拡散係数であり、１／ｍｍを単位とし、ｄは℃／ｈを単位とした任意の係数である。又、６≦ａ≦８１、１．５≦ｂ≦３２、０．０５≦ｃ≦８．９９、１．２≦ｄ≦７１．６である。）
を満たし、且つ減圧雰囲気中で加熱して結合材を除去することを特徴とする製造方法。
（４） セラミックス粉末と結合材を混合して成形した後、結合材を除去し、その後、焼結して焼結体とする方法において、
結合材の除去時の昇温速度をｖ（℃／ｈ）、成形後の成形体の肉厚をｘ（ｍｍ）、自然対数をｌｎとした場合、
式 ｖ＝ａｌｎ（ｂ−ｃｘ）＋ｄ
（式中、ａは結合材の熱伝導係数の逆数であり、℃／ｈを単位とし、ｂは任意の係数、ｃはガス化して除去される結合材のガス拡散係数であり、１／ｍｍを単位とし、ｄは℃／ｈを単位とした任意の係数である。又、２≦ａ≦６５、１．１３≦ｂ≦１８、０．０１≦ｃ≦５．４５、１．２≦ｄ≦５３．６である。）
を満たし、且つ常圧の不活性雰囲気中で加熱して結合材を除去することを特徴とする製造方法。
（５） セラミックス粉末と結合材を混合して成形した後、結合材を除去し、その後、焼結して焼結体とする方法において、
結合材の除去時の昇温速度をｖ（℃／ｈ）、成形後の成形体の肉厚をｘ（ｍｍ）、自然対数をｌｎとした場合、
式 ｖ＝ａｌｎ（ｂ−ｃｘ）＋ｄ
（式中、ａは結合材の熱伝導係数の逆数であり、℃／ｈを単位とし、ｂは任意の係数、ｃはガス化して除去される結合材のガス拡散係数であり、１／ｍｍを単位とし、ｄは℃／ｈを単位とした任意の係数である。又、５≦ａ≦７２、１．２≦ｂ≦２８、０．０１≦ｃ≦８．１２、１．５≦ｄ≦６２．４である。）
を満たし、且つ常圧の活性雰囲気中で加熱して結合材を除去することを特徴とする製造方法。
（６） セラミックス粉末と結合材を混合して成形した後、結合材を除去し、その後、焼結して焼結体とする方法において、
結合材の除去時の昇温速度をｖ（℃／ｈ）、成形後の成形体の肉厚をｘ（ｍｍ）、自然対数をｌｎとした場合、
式 ｖ＝ａｌｎ（ｂ−ｃｘ）＋ｄ
（式中、ａは結合材の熱伝導係数の逆数であり、℃／ｈを単位とし、ｂは任意の係数、ｃはガス化して除去される結合材のガス拡散係数であり、１／ｍｍを単位とし、ｄは℃／ｈを単位とした任意の係数である。又、６≦ａ≦８１、１．５≦ｂ≦３２、０．０５≦ｃ≦８．９９、１．２≦ｄ≦７１．６である。）
を満たし、且つ減圧雰囲気中で加熱して結合材を除去することを特徴とする製造方法。
【００５０】
【発明の効果】
以上説明したように、本発明の製造方法によれば、不活性雰囲気、常圧の活性雰囲気、減圧雰囲気のいずれの雰囲気においても、膨れや割れが生じることのない状態で結合材を除去することができる。このため、変形のない成形体を製造することができる。
【図面の簡単な説明】
【図１】実施の形態１によって成形される成形体の斜視図である。
【図２】実施の形態２によって成形される成形体の斜視図である。
【図３】実施の形態３によって成形される成形体の斜視図である。
【符号の説明】
１ ４ ５ 成形体[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing an inorganic powder sintered body.
[0002]
[Prior art]
After mixing and kneading an inorganic powder made of metal powder or ceramic powder and a binder (organic binder), the mixture is molded by injection molding, casting molding, compacting, etc. to a desired shape, and then bonded. A manufacturing method for obtaining a final inorganic powder sintered body by removing the material and then sintering it has been attracting attention.
[0003]
In the case of a metal injection molding method (Metal Injection Molding, MIM) which is a kind of this manufacturing method, a compound (feedstock) is prepared by mixing and kneading a metal powder having an average particle size of about 10 μm and a wax or a thermoplastic resin as a binder. This compound is injection-molded to form an injection-molded body (green body, green body, green part), and then the binder is removed from the injection-molded body (degreasing, dewaxing, debinder) and the removed body (degreasing) Body, brown body, brown body, brown parts). Thereafter, the removed body is sintered to obtain a final inorganic powder sintered body (sinter body, sinter body, sinter part). In this MIM, it is possible to accurately mold a three-dimensional complex shape.
[0004]
However, in such a manufacturing method, there is a problem that in the removing step of removing the binder by heating, the heating rate is high, and the molded body swells or breaks when rapidly heated. This is because, in the binder removal process, the binder is vaporized or decomposed to generate gas, and the generated gas stays inside the molded body and expands in volume in the molded body.
[0005]
For this reason, Japanese Patent Publication No. 6-89369 discloses a binder with good removability having a composition for preventing expansion and cracking of a molded body. By using this binder, Damage to the molded body is prevented.
[0006]
[Problems to be solved by the invention]
However, in actual manufacturing, even when a binder having good removability is used, heating of a thick molded body requires a long heating time. Even if the binder has a slight problem in removability, if the thickness of the molded body is sufficiently thin, even if the heating rate is increased, swelling and cracking are less likely to occur. This suggests that defects such as swelling and cracking of the molded product when removing the binder are not determined solely by the removal characteristics of the binder, but are more influenced by the thickness of the molded product. is there.
[0007]
As described above, the heating temperature increase rate at the time of removing the binder is greatly influenced by the thickness of the molded body. For this reason, conventionally, try and error were repeated several times to determine the optimum heating rate for removing the binder from the molded body.
[0008]
In actual production, it is known that the heating atmosphere greatly affects the removal of the binding material by heating and heating. That is, when the heating atmosphere is an inert atmosphere, only the vaporization and decomposition of the binder due to the heating temperature increase occurs, and the heating temperature rising rate is easily determined by considering only the thermal characteristics of the bonding material. it can.
[0009]
On the other hand, when the heating atmosphere is an active atmosphere, it is necessary to consider decomposition due to reaction with the active atmosphere in addition to vaporization and decomposition of the binder due to heating and heating. This is also a factor that increases try and error.
[0010]
Furthermore, when the heating atmosphere is a reduced-pressure atmosphere, it is necessary to consider the sublimation of the binder under reduced pressure in addition to the vaporization and decomposition of the binder due to heating and heating.
[0011]
The present invention has been made in consideration of such circumstances, and causes swelling and cracking when removing the binder in each of an inert atmosphere, an active atmosphere, and a reduced pressure atmosphere. The aim is to provide a method without any problem.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, the invention of claim 1 is a method in which an inorganic powder and a binder are mixed and molded, then the binder is removed, and then sintered to form an inorganic powder sintered body. Assuming that the heating rate at the time of removal is v (° C./h), the thickness of the molded body after molding is x (mm), and the natural logarithm is ln, the formula v = aln (b−cx) + d (wherein , A is the reciprocal of the thermal conductivity coefficient of the binder, in units of ° C./h, b is an arbitrary coefficient, c is the diffusion coefficient of the gas of the binder removed by gasification, and is in units of 1 / mm D is an arbitrary coefficient in units of ° C./h, and 2 ≦ a ≦ 65, 1.13 ≦ b ≦ 18, 0.01 ≦ c ≦ 5.45, 1.2 ≦ d ≦ 53 6) The step of specifying the heating rate according to the above formula , and heating at the heating rate specified in the above step in an inert atmosphere at normal pressure, It is characterized by removing.
[0013]
In this method, the binder is gasified and decomposed by heating and heating to gasify, and is removed from the surface of the molded body by this gasification. Since the gasification rate hi of this binding material depends on thermal energy, Equation 1 is established according to the thermal energy conservation law.
[0014]
[Expression 1]

[0015]
Further, since the gas removal rate fi of the binding material can be regarded as diffusion in an isotropic medium, the diffusion equation of Formula 2 is established between the concentration C of the binding material.
[0016]
[Expression 2]

[0017]
When the gasification rate hi of the binder exceeds the gas removal rate fi, the gas of the binder generated by gasification and generated in the molded body is not removed, which causes swelling and cracking of the molded body. Therefore, in order to always satisfy hi <fi, it is necessary to satisfy Equation 3.
[0018]
[Equation 3]

[0019]
In Equation 3, if gradT = v and the molded body is uniformly formed, Equation 4 can be established because gradC≈x may be considered.
[0020]
[Expression 4]

[0021]
When the inequality sign is expanded with the coefficients of κ and k with respect to Equation 4, Equation 5 is obtained. In Equation 5, b and d are arbitrary coefficients, and d is in units of ° C./h.
[0022]
[Equation 5]

[0023]
In Equation 5, when the reciprocal of the thermal conductivity coefficient κ of the binder, that is, 1 / κ is a, and the gas diffusion coefficient k of the binder is c, v = aln (b−cx) + d, and the thickness of the molded body The relationship of claim 1 is established between x and the heating temperature increase rate v. Here, a is in units of ° C./h, and c is in units of 1 / mm.
[0024]
When the present inventors obtained these coefficients a, b, c, and d by earnest examination through experiments in an inert atmosphere,
2 ≦ a ≦ 65
1.13 ≦ b ≦ 18
0.01 ≦ c ≦ 5.45
1.2 ≦ d ≦ 53.6
It became. Here, when any of the conditions a <2, b <1.13, c> 5.45, and d <1.2 is satisfied, the heating rate of heating is too slow and the binder is vaporized. The product is liquefied before being decomposed, and the molded body is deformed. Further, when a> 65, b> 18, c <0.01, and d> 53.3, the heating temperature rise rate is too high, and the binder gas generated by vaporization and decomposition is removed from the molded body. This causes problems such as swelling and cracking in the molded body.
[0025]
The coefficients are 2 ≦ a ≦ 65, 1.13 ≦ b ≦ 18, 0.01 ≦ c ≦ 5.45, 1.2 ≦ d ≦ 53.6, but 2.1 ≦ a ≦ 65.1. 1.5 ≦ b ≦ 17, 0.05 ≦ c ≦ 5.12, 1.5 ≦ d ≦ 43.6, and more preferably 2.5 ≦ a ≦ 59, 1.8 ≦ b ≦ 17, 0.05 ≦ c ≦ 4.67, 3.6 ≦ d ≦ 38.1 may be acceptable, and in particular, 2.8 ≦ a ≦ 55, 2.0 ≦ b ≦ 16, 0.05 ≦ c ≦ 4.11, 4 .9 ≦ d ≦ 37.5 may be satisfied, and in any case, a molded article free from swelling or cracking can be obtained.
[0026]
The invention of claim 2 is a method in which the inorganic powder and the binder are mixed and molded, then the binder is removed, and then sintered to form an inorganic powder sintered body. When the speed is v (° C./h), the thickness of the molded body after molding is x (mm), and the natural logarithm is ln, the formula v = aln (b−cx) + d (where a is the binding material) The reciprocal of the thermal conductivity coefficient, in units of ° C / h, b is an arbitrary coefficient, c is the gas diffusion coefficient of the binder removed by gasification, 1 / mm is the unit, d is ° C / h which is the arbitrary coefficient in units. Moreover, it is 5 ≦ a ≦ 72,1.2 ≦ b ≦ 28,0.01 ≦ c ≦ 8.12,1.5 ≦ d ≦ 62.4.) above identifying a heating rate by the equation, and removing the binder by heating at specified heating rate in the step in the normal pressure inert atmosphere.
[0027]
This method is to remove the binder in an active atmosphere at room temperature, and in the active atmosphere at room temperature, in addition to vaporization and decomposition of the binder by heating and heating, it is due to the reaction between the active gas and the binder. Decomposition needs to be considered.
[0028]
When the present inventors obtained the coefficients a, b, c, and d in the active atmosphere at room temperature through earnest examination through experiments,
5 ≦ a ≦ 72
1.2 ≦ b ≦ 28
0.01 ≦ c ≦ 8.12
1.5 ≦ d ≦ 62.4
It became. Here, if any of the conditions a <5, b <1.2, c> 8.12, and d <1.5 is satisfied, the heating rate of heating is too slow and the binder is vaporized. The product is liquefied before being decomposed, and the molded body is deformed. Further, when a> 72, b> 28, c <0.01, and d> 62.4, the heating temperature rise rate is too high, and the binder gas generated by vaporization and decomposition is removed from the molded body. This causes problems such as swelling and cracking in the molded body.
[0029]
The range of each coefficient is 5 ≦ a ≦ 72, 1.2 ≦ b ≦ 28, 0.01 ≦ c ≦ 8.12, 1.5 ≦ d ≦ 62.4, but 5.8 ≦ a ≦ 68. 1.6 ≦ b ≦ 21, 0.03 ≦ c ≦ 7.44, 1.5 ≦ d ≦ 61.3, and more preferably 6.1 ≦ a ≦ 65, 1.8 ≦ b ≦ 19, It may be 0.05 ≦ c ≦ 6.89, 3.2 ≦ d ≦ 58.7, especially 7.3 ≦ a ≦ 57, 2.0 ≦ b ≦ 17, 0.05 ≦ c ≦ 6.22, .5 ≦ d ≦ 45.1 may be acceptable.
[0030]
The invention of claim 3 is a method in which the inorganic powder and the binder are mixed and molded, then the binder is removed, and then sintered to obtain an inorganic powder sintered body. When the speed is v (° C./h), the thickness of the molded body after molding is x (mm), and the natural logarithm is ln, the formula v = aln (b−cx) + d (where a is the binding material) The reciprocal of the thermal conductivity coefficient, in units of ° C / h, b is an arbitrary coefficient, c is the gas diffusion coefficient of the binder removed by gasification, 1 / mm is the unit, d is ° C / h which is the arbitrary coefficient in units. Moreover, it is 6 ≦ a ≦ 81,1.5 ≦ b ≦ 32,0.05 ≦ c ≦ 8.99,1.2 ≦ d ≦ 71.6.) above identifying a heating rate by the equation, and removing the binder by heating at a Atsushi Nobori rate specified by said step in a reduced pressure atmosphere.
[0031]
In this method, the binder is removed by heating in a reduced-pressure atmosphere. In the reduced-pressure atmosphere, it is necessary to consider sublimation of the binder due to reduced pressure in addition to vaporization and decomposition of the binder by heating and heating. is there.
[0032]
When the present inventors obtained the coefficients a, b, c, and d in the active atmosphere at room temperature through earnest examination through experiments,
6 ≦ a ≦ 81
1.5 ≦ b ≦ 32
0.05 ≦ c ≦ 8.99
1.2 ≦ d ≦ 71.6
It became. Here, when any of the conditions of a <6, b <1.5, c> 8.99, and d <1.2 is satisfied, the heating rate of heating is too slow and the binder is vaporized. The product is liquefied before being decomposed, and the molded body is deformed. Further, when a> 81, b> 32, c <0.05, and d> 71.6, the heating temperature rise rate is too high, and the binder gas generated by vaporization and decomposition is removed from the molded body. This causes problems such as swelling and cracking in the molded body.
[0033]
The range of each coefficient is 6 ≦ a ≦ 81, 1.5 ≦ b ≦ 32, 0.05 ≦ c ≦ 8.99, 1.2 ≦ d ≦ 71.6, but 6.3 ≦ a ≦ 76. 1.5 ≦ b ≦ 29, 0.06 ≦ c ≦ 8.51, 1.4 ≦ d ≦ 68.7, and more preferably 6.8 ≦ a ≦ 69, 1.6 ≦ b ≦ 21, It may be 0.08 ≦ c ≦ 7.89 and 2.5 ≦ d ≦ 62.1, especially 7.0 ≦ a ≦ 51, 2.2 ≦ b ≦ 18, 0.08 ≦ c ≦ 6.54, .8 ≦ d ≦ 58.3 may be acceptable.
[0034]
DETAILED DESCRIPTION OF THE INVENTION
(Embodiment 1)
FIG. 1 shows a molded body 1 molded according to this embodiment. This molded body 1 is formed by a metal powder injection molding method (MIM), 91.1 wt% austenitic stainless steel (JIS standard SUS316L) powder having an average particle size of 12 μm, and polystyrene (PS) 4 as a binder. 0.1 wt%, polymethyl methacrylate (acrylic, PMMA) 3.5 wt%, and paraffin wax 1.3 wt% are mixed and kneaded to form a compound, and the compound is injection molded.
[0035]
The molded body 1 has an integrally formed shape in which ears 3 are erected from both upper ends of the rectangular body 2. Each dimension in FIG. 1 is 12 mm for A, 12 mm for B, 16 mm for C, 4 mm for D, and 12 mm for E, so that the outer shape has a total width of 24 mm, a depth of 12 mm, and a height of 24 mm, and 16 mm × 12 mm in the center. A notch of × 12 mm is formed. The molded body 1 has a rectangular body portion 2 which is a thick portion.
[0036]
The molded body 1 is placed in a heating furnace (not shown), and heated and heated in a nitrogen atmosphere (inert atmosphere) to remove the binder. At this time, the coefficients are a = 4.1, b = 3.1, c = 0.06, d = 12.5, respectively, and the heating temperature rise rate is v = 16.1 ° C./h.
[0037]
Heat to 410 ° C. at this heating rate and hold at 410 ° C. for 3.5 hours. Thereafter, the heating was finished, and the molded body 1 from which the binder had been removed was transferred to a vacuum sintering furnace, and heated at a rate of heating of 300 ° C./h under a vacuum of 10 −4 torr (1.33 × 10 −2 Pa). After heating to 1350 ° C. and holding at 1350 ° C. for 1 hour, the heating is finished, and after cooling, the compact that has become a sintered powder body that has been sintered is taken out.
[0038]
According to the present embodiment, since the gas removal rate exceeds the gas generation rate due to the gasification and decomposition of the binder during heating and heating, the gas removal rate exceeds the gasification rate of the binder during removal of the binder. Such problems do not occur. Further, since the heating temperature rise rate is not so slow as to cause liquefaction of the binder, it is not deformed. Therefore, a good metal powder sintered body can be formed without causing swelling, cracking or deformation.
[0039]
(Embodiment 2)
FIG. 2 shows a molded body 4 according to Embodiment 2, which is formed by a sheet press molding method. That is, 95.4 wt% of a stellite alloy (Co alloy) having an average grain size of 11 μm and 4.6 wt% of polyamide (PA) as a binder are mixed and kneaded to form a sheet, and this sheet-like mixed material is pressed by a press. It is formed into the shape shown in FIG.
[0040]
This molded body 4 has a shape in which a cylindrical shape having an outer diameter G of 5 mm, an inner diameter H of 4 mm, and a height F of 7 mm is vertically divided into two in the axial direction. It is a 0.5mm thick part between.
[0041]
The molded body 4 is placed in a heating furnace, and heated and heated in an air atmosphere (active atmosphere) to remove the binder. At this time, the coefficients are a = 27.1, b = 13.7, c = 5.35, d = 13.7, and the heating temperature rise rate is v = 78.7 ° C./h.
[0042]
Heat to 325 ° C. at this heating rate and hold at 325 ° C. for 2 hours. Thereafter, the heating was finished, and the molded body after the removal of the binder was transferred to a vacuum incinerator and heated to 1220 ° C. at 5 torr (65.5 Pa) under a reduced pressure Ar atmosphere at a heating rate of 250 ° C./h. After holding at 0 ° C. for 1 hour, heating is terminated. As a result, the sintering is completed, and then cooled, and the molded body that has become a powder sintered body is taken out.
[0043]
According to the present embodiment, the gasification of the binder during the removal of the binder, that is, the generation of gas accompanying the reactive decomposition of the active atmosphere to the atmosphere and the binder in addition to the vaporization and decomposition of the binder by heating and heating. Since the gas removal speed exceeds the speed, problems such as swelling and cracking do not occur. Further, since the heating temperature rise rate is not so slow as to cause liquefaction of the binder, it is not deformed. Therefore, a good metal powder sintered body can be produced without causing swelling, cracking or deformation.
[0044]
(Embodiment 3)
FIG. 3 shows a molded body 5 according to Embodiment 3, which is molded by a ceramic powder injection molding method (CIM). That is, 93.2 wt% of alumina (Al 2 O 3) powder having an average grain size of 2 μm, 2.8 wt% of polyethylene (PE) as a binder, 2.8 wt% of attack polypropylene (APP), and 1.2 wt% of paraffin wax are mixed. It is kneaded into a compound and molded by injection molding.
[0045]
This molded body 5 has a shape in which upright portions 7 are integrally erected from the upper and lower surfaces of both ends of the flat plate portion 6, the dimensions I and J are 5 mm, K is 3 mm, and M is 4 mm. The standing part 7 is a 3 mm thick part.
[0046]
The molded body is placed in a heating furnace, heated and heated in a reduced pressure atmosphere of 10-2 torr (1.33 Pa) to remove the binder. At this time, the coefficients are a = 8.7, b = 12.3, c = 3.08, d = 21.3, and the heating temperature rise rate is v = 31 ° C./h. Heat to 350 ° C. at this heating rate and hold at 350 ° C. for 4 hours.
[0047]
Thereafter, the heating was finished, and the molded body from which the binder was removed was transferred to an atmospheric incinerator, heated to 1500 ° C. at a temperature increase rate of 200 ° C./h in an atmospheric atmosphere, and held at 1500 ° C. for 3 hours. Thereafter, heating was terminated and sintering was performed. Then, after cooling, the compact that has been sintered and becomes a powder sintered body is taken out.
[0048]
According to the present embodiment, the gasification of the binder during the removal of the binder, i.e., the gasification of the binder by heating and heating, decomposition, and further the gas generation rate due to the sublimation of the binder in a reduced-pressure atmosphere. Since the removal speed of the is higher, problems such as swelling and cracking do not occur. Further, since the heating temperature rise rate is not so slow as to cause liquefaction of the binder, it is not deformed. Therefore, a good ceramic powder sintered body can be produced without causing swelling, cracking or deformation.
[0049]
The present invention described above includes the following inventions.
(1) In a method in which a metal powder and a binder are mixed and molded, the binder is removed, and then sintered to form a sintered body.
When the heating rate at the time of removing the binder is v (° C./h), the thickness of the molded body after molding is x (mm), and the natural logarithm is ln,
Formula v = aln (b−cx) + d
(Wherein, a is the reciprocal of the thermal conductivity coefficient of the binder, in units of ° C./h, b is an arbitrary coefficient, c is the gas diffusion coefficient of the binder removed by gasification, 1 / mm Where d is an arbitrary coefficient in units of ° C./h, and 2 ≦ a ≦ 65, 1.13 ≦ b ≦ 18, 0.01 ≦ c ≦ 5.45, 1.2 ≦ d ≦ 53.6.)
And a binder is removed by heating in an inert atmosphere at normal pressure.
(2) After mixing and molding the metal powder and the binder, the binder is removed, and then sintered to form a sintered body.
When the heating rate at the time of removing the binder is v (° C./h), the thickness of the molded body after molding is x (mm), and the natural logarithm is ln,
Formula v = aln (b−cx) + d
(Wherein, a is the reciprocal of the thermal conductivity coefficient of the binder, in units of ° C./h, b is an arbitrary coefficient, c is the gas diffusion coefficient of the binder removed by gasification, 1 / mm Where d is an arbitrary coefficient in units of ° C./h, and 5 ≦ a ≦ 72, 1.2 ≦ b ≦ 28, 0.01 ≦ c ≦ 8.12, 1.5 ≦ d. ≦ 62.4.)
And a binder is removed by heating in an active atmosphere at normal pressure.
(3) In a method in which a metal powder and a binder are mixed and molded, then the binder is removed, and then sintered to form a sintered body.
When the heating rate at the time of removing the binder is v (° C./h), the thickness of the molded body after molding is x (mm), and the natural logarithm is ln,
Formula v = aln (b−cx) + d
(Wherein, a is the reciprocal of the thermal conductivity coefficient of the binder, in units of ° C./h, b is an arbitrary coefficient, c is the gas diffusion coefficient of the binder removed by gasification, 1 / mm Where d is an arbitrary coefficient in units of ° C./h, and 6 ≦ a ≦ 81, 1.5 ≦ b ≦ 32, 0.05 ≦ c ≦ 8.99, 1.2 ≦ d ≦ 71.6.)
And a binder is removed by heating in a reduced pressure atmosphere.
(4) After the ceramic powder and the binder are mixed and molded, the binder is removed, and then sintered to form a sintered body.
When the heating rate at the time of removing the binder is v (° C./h), the thickness of the molded body after molding is x (mm), and the natural logarithm is ln,
Formula v = aln (b−cx) + d
(Wherein, a is the reciprocal of the thermal conductivity coefficient of the binder, in units of ° C./h, b is an arbitrary coefficient, c is the gas diffusion coefficient of the binder removed by gasification, 1 / mm Where d is an arbitrary coefficient in units of ° C./h, and 2 ≦ a ≦ 65, 1.13 ≦ b ≦ 18, 0.01 ≦ c ≦ 5.45, 1.2 ≦ d ≦ 53.6.)
And a binder is removed by heating in an inert atmosphere at normal pressure.
(5) After the ceramic powder and the binder are mixed and molded, the binder is removed, and then sintered to form a sintered body.
When the heating rate at the time of removing the binder is v (° C./h), the thickness of the molded body after molding is x (mm), and the natural logarithm is ln,
Formula v = aln (b−cx) + d
(Wherein, a is the reciprocal of the thermal conductivity coefficient of the binder, in units of ° C./h, b is an arbitrary coefficient, c is the gas diffusion coefficient of the binder removed by gasification, 1 / mm Where d is an arbitrary coefficient in units of ° C./h, and 5 ≦ a ≦ 72, 1.2 ≦ b ≦ 28, 0.01 ≦ c ≦ 8.12, 1.5 ≦ d. ≦ 62.4.)
And a binder is removed by heating in an active atmosphere at normal pressure.
(6) In the method in which the ceramic powder and the binder are mixed and molded, the binder is removed, and then sintered to form a sintered body.
When the heating rate at the time of removing the binder is v (° C./h), the thickness of the molded body after molding is x (mm), and the natural logarithm is ln,
Formula v = aln (b−cx) + d
(Wherein, a is the reciprocal of the thermal conductivity coefficient of the binder, in units of ° C./h, b is an arbitrary coefficient, c is the gas diffusion coefficient of the binder removed by gasification, 1 / mm Where d is an arbitrary coefficient in units of ° C./h, and 6 ≦ a ≦ 81, 1.5 ≦ b ≦ 32, 0.05 ≦ c ≦ 8.99, 1.2 ≦ d ≦ 71.6.)
And a binder is removed by heating in a reduced pressure atmosphere.
[0050]
【The invention's effect】
As described above, according to the manufacturing method of the present invention, the binder is removed in a state in which no expansion or cracking occurs in any of the inert atmosphere, the normal pressure active atmosphere, and the reduced pressure atmosphere. Can do. For this reason, the molded object without a deformation | transformation can be manufactured.
[Brief description of the drawings]
FIG. 1 is a perspective view of a molded body molded according to Embodiment 1. FIG.
FIG. 2 is a perspective view of a molded body molded according to the second embodiment.
3 is a perspective view of a molded body molded according to Embodiment 3. FIG.
[Explanation of symbols]
1 4 5 Molded body

Claims (3)

After mixing and molding the inorganic powder and the binder, the binder is removed, and then sintered to form an inorganic powder sintered body.
When the heating rate at the time of removing the binder is v (° C./h), the thickness of the molded body after molding is x (mm), and the natural logarithm is ln,
Formula v = aln (b−cx) + d
(Wherein, a is the reciprocal of the thermal conductivity coefficient of the binder, in units of ° C./h, b is an arbitrary coefficient, c is the gas diffusion coefficient of the binder removed by gasification, 1 / mm Where d is an arbitrary coefficient in units of ° C./h, and 2 ≦ a ≦ 65, 1.13 ≦ b ≦ 18, 0.01 ≦ c ≦ 5.45, 1.2 ≦ d ≦ 53.6.)
A step of specifying a temperature increase rate by the above formula;
A method for producing an inorganic powder sintered body, wherein the binder is removed by heating at an elevated temperature specified in the above step in an inert atmosphere at normal pressure. After mixing and molding the inorganic powder and the binder, the binder is removed, and then sintered to form an inorganic powder sintered body.
When the heating rate at the time of removing the binder is v (° C./h), the thickness of the molded body after molding is x (mm), and the natural logarithm is ln, the formula v = aln (b−cx) + d
(Wherein, a is the reciprocal of the thermal conductivity coefficient of the binder, in units of ° C./h, b is an arbitrary coefficient, c is the gas diffusion coefficient of the binder removed by gasification, 1 / mm Where d is an arbitrary coefficient in units of ° C./h, and 5 ≦ a ≦ 72, 1.2 ≦ b ≦ 28, 0.01 ≦ c ≦ 8.12, 1.5 ≦ d. ≦ 62.4.)
A step of specifying a temperature increase rate by the above formula;
A method for producing an inorganic powder sintered body, wherein the binder is removed by heating at an elevated temperature specified in the above step in an atmospheric pressure active atmosphere. After mixing and molding the inorganic powder and the binder, the binder is removed, and then sintered to form an inorganic powder sintered body.
When the heating rate at the time of removing the binder is v (° C./h), the thickness of the molded body after molding is x (mm), and the natural logarithm is ln,
Formula v = aln (b−cx) + d
(Wherein, a is the reciprocal of the thermal conductivity coefficient of the binder, in units of ° C./h, b is an arbitrary coefficient, c is the gas diffusion coefficient of the binder removed by gasification, 1 / mm Where d is an arbitrary coefficient in units of ° C./h, and 6 ≦ a ≦ 81, 1.5 ≦ b ≦ 32, 0.05 ≦ c ≦ 8.99, 1.2 ≦ d ≦ 71.6.)
A step of specifying a temperature increase rate by the above formula;
A method for producing an inorganic powder sintered body, wherein the binder is removed by heating at a temperature increase rate specified in the above step in a reduced-pressure atmosphere.

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