JP3623036B2

JP3623036B2 - Method for firing MnZn-based ferrite core and continuous firing furnace

Info

Publication number: JP3623036B2
Application number: JP01666196A
Authority: JP
Inventors: 英明小日置; 聡志後藤; 貴史河野; 清詩有江; 慎一来島
Original assignee: JFE Chemical Corp
Current assignee: JFE Chemical Corp
Priority date: 1995-02-01
Filing date: 1996-02-01
Publication date: 2005-02-23
Anticipated expiration: 2016-02-01
Also published as: JPH08268749A

Description

【０００１】
【発明の属する技術分野】
本発明は、ＭｎＺｎ系フェライトコアの焼成方法及び連続焼成炉に関し、例えば、連続焼成トンネル炉を用いて該フェライトコアを焼成するに際し、その冷却工程での雰囲気及び温度を制御する技術に係わる。
【０００２】
【従来の技術】
ＭｎＺｎ系フェライトコアは、各種通信機器、電源等のコイル、トランス材料として広く用いられ、近年の電子機器の小型化に大きく貢献しており、さらに高特性のＭｎＺｎ系フェライトコアを安定かつ効率的に製造することが強く望まれている。
【０００３】
ところで、磁気特性の優れたＭｎＺｎ系フェライトコアを得るためには、日本金属学会報の第２４巻、第４号（１９８５年）、２８８頁の論文「ソフトフェライト」（平賀貞太郎著）に記載されているように、昇温・最高温度保持・冷却の各段階においてそれらの温度と雰囲気中の酸素量とを精密に制御しながら焼成することが必須であると言われている。特に、冷却過程における該ＭｎＺｎフェライトコアの酸化状態の変化が磁気特性に大きな影響を及ぼすことも周知であった。
【０００４】
そこで、従来の連続焼成炉（通常、トンネル炉を使用）は、ＭｎＺｎ系フェライト焼成体の酸化を防止するために、その冷却帯における酸素分圧を極力低減して窒素雰囲気にすると共に、急速な冷却を行っている。そのため、多量の窒素ガスを冷却帯に導入して、その圧力を高く保持していた。
例えば、特公平４−７７２３４号公報は、低酸素分圧室を設けたローラ・ハース式連続焼成トンネル炉を提案し、その低酸素分圧室の酸素濃度を数ｐｐｍ〜１００ｐｐｍ程度に低減したことを開示している。また、特公平６−７６２５７号公報は、ＭｎＺｎ系フェライトコアを２０時間未満とこの分野では従来に比較し非常に短い時間で焼成する技術を開示している。つまり、短時間高能率生産が実現しているのである。
【０００５】
しかしながら、前記特公平４−７７２３４号公報記載のローラ・ハース式連続焼成炉を用いた場合、形状及び大きさの異なるフェライトコアを、異なる積載量及び荷姿で台板上に載置して移動させつつ連続的に焼成するに際し、磁気特性の劣化やばらつきが発生し、製造の安定性の面で大きな問題となっていた。
【０００６】
【発明が解決しようとする課題】
本発明は、かかる事情を鑑み、連続焼成炉を用いた焼成で磁気特性の優れたＭｎＺｎ系フェライトコアを安定して多量生産できる技術を提供することを目的としている。
【０００７】
【課題を解決するための手段】
発明者は、上記目的を達成するため、フェライトコアの形状、大きさ、台板上への積載量、荷姿等による冷却工程での温度変動、あるいは焼成による磁気特性の劣化やばらつきの原因を鋭意研究した。
その結果、従来の連続焼成トンネル炉では冷却工程の窒素雰囲気室に電気ヒータ等の加熱源による温度制御装置を備えていないため、後述する実施例に示すように、焼成台板上に積載されたフェライト焼成体の形状、大きさ、積載量及び荷姿等の変化によって冷却状態が変わり、冷却工程の温度パターンが大きく変動しており、特に、酸素分圧制御雰囲気室とそれに続く窒素雰囲気室との境界部の温度変動が、磁気特性の劣化やばらつきの最大の原因となっていることが明らかになった。さらに、ＭｎＺｎ系フェライトコアの酸化状態を示すＦｅ^２＋の含有量を分析した結果、境界部の温度の変動に応じてＦｅ^２＋の含有量が変動しており、ＭｎＺｎ系フェライトコアの磁気特性を大きく左右する酸化状態が変化させられていることが明らかとなった。
【０００８】
上記のような現象は、台板の送りが速いローラ・ハース式連続焼成トンネル炉で顕著となり、特公平６−７６２５７号公報にて開示されている焼成時間が２０時間未満の短時間焼成では特に顕著であった。また、プッシャ式連続焼成トンネル炉でも同様の現象が磁気特性の劣化やばらつきの原因となっていることが明らかとなった。なお、ここで、焼成時間とは、室温から昇温、保持冷却を経て、１５０℃となるまでに要する時間を言う。
【０００９】
そこで、発明者は、冷却工程の酸素分圧制御雰囲気帯とそれに続く窒素雰囲気帯との境界部温度を最適値とし、且つその変動を小さく制御することが、高特性のＭｎＺｎ系フェライトコアを安定して得る手段になると考え、本発明を着想するに至った。しかし、連続焼成トンネル炉においては、この境界部前後の上記雰囲気帯の温度や雰囲気を独立に制御する必要があるため、該境界部の開口を極力小さくしなければならない等の制約があり、そこに電気ヒータ等の加熱源と温度制御装置を配置することは実質的には困難であった。それゆえ、本発明では、境界部前後の上記雰囲気帯の温度を電気ヒータ等の加熱源と温度制御装置により精密に制御することで、該境界部の温度を制御するようにした。
【００１０】
すなわち、本発明は、昇温、最高温度保持及び冷却の工程を順次経てＭｎＺｎ系フェライトコアを焼成するに際し、上記冷却工程に酸素分圧制御雰囲気帯とそれに続く窒素雰囲気帯とを設け、該酸素分圧制御雰囲気帯と該窒素雰囲気帯との境界部の温度範囲を１０００〜１２００℃とし、且つ該境界部温度を±２５℃以下の変動幅で制御して焼成することを特徴とするＭｎＺｎ系フェライトコアの焼成方法である。また、本発明は、上記境界部の温度を制御するため、前記酸素分圧制御雰囲気帯及び窒素雰囲気帯の温度を、それぞれ１０５０〜１３００℃及び８５０〜１１５０℃としたり、あるいは前記酸素分圧制御雰囲気帯及び窒素雰囲気帯にそれぞれ加熱源を配置し、該加熱源でそれぞれの温度を制御することを特徴とするＭｎＺｎ系フェライトコアの焼成方法である。さらに、本発明は、前記酸素分圧制御雰囲気帯及び窒素雰囲気帯の酸素分圧をそれぞれ０．１〜５体積％及び０．１体積％以下としたり、あるいは室温から最高温度に昇温し、その温度から１５０℃まで冷却するのに要する焼成時間を２０時間未満とすることを特徴とするＭｎＺｎ系フェライトコアの焼成方法でもある。
【００１１】
加えて、上記方法を実施する装置に関しても発明をなし、それは、昇温、最高温度保持及び冷却の３つの領域で形成するＭｎＺｎ系フェライトコアの連続焼成炉において、上記冷却領域に酸素分圧制御雰囲気室とそれに続く窒素雰囲気室とを設け、該酸素分圧制御雰囲気室及び該窒素雰囲気室には、温度センサと、加熱源と、酸素分圧を測定する酸素センサと、雰囲気ガス噴出弁とをそれぞれ配設し、且つ該温度センサにより測定した温度を目標値に一致するよう該加熱源の出力を調整する温度制御装置と、該酸素センサにより測定した酸素分圧を目標値に一致するよう該雰囲気ガス吐出弁を調整する酸素分圧制御装置とを配設すると共に、上記酸素分圧制御雰囲気室と窒素雰囲気室との境界部に上記温度制御装置につながる温度センサを追設したことを特徴とするＭｎＺｎ系フェライトコアの連続焼成炉である。さらに加えて、本発明は、炉体をローラ・ハ−ス式としたことを特徴とするＭｎＺｎ系フェライトコアの連続焼成炉でもある。
【００１２】
なお、この場合、温度の変動幅とは、平均温度にたいする最大偏差の範囲をいい、境界部を通過するフェライト成形体の形状、大きさ、積載量及び荷姿等により空間的ないし時間的に変動する許容温度範囲である。また、酸素分圧制御雰囲気室及び窒素雰囲気室以外の冷却工程における雰囲気は従来通りでよい。
以上の本発明をＭｎＺｎフェライトコアの焼成に採用するようにしたので、連続焼成炉を用いた焼成であっても磁気特性の優れたＭｎＺｎ系フェライトコアが安定して多量に生産できるようになった。
【００１３】
次に、本発明で採用した焼成条件の限定理由について説明する。
まず、酸素分圧制御雰囲気とそれに続く窒素雰囲気との境界部の温度を１０００〜１２００℃とし、この温度の変動幅を±２５℃以下に限定した理由及びこの２つの雰囲気温度と酸素分圧を限定した理由について以下に説明する。
境界部の最適温度は、ＭｎＺｎ系フェライトコアの材質によって異なり、フェライトの結晶粒界成分が液相から固相に変態する温度、他の微量成分が該結晶粒界に析出する温度、該粒界における酸素の拡散が遅くなる温度等が考えられ、この温度より高温側では温度に応じた酸素分圧の制御によりＭｎＺｎ系フェライトの酸化状態を安定に制御し、低温側では窒素雰囲気中において冷却することにより酸化を防止できると考え、酸素分圧制御雰囲気と窒素雰囲気に分割し制御することとした。
【００１４】
本発明者らが数種類の材質について実験を繰り返して検討した結果、上記境界部の温度は、材質によって異なるが、１０００〜１２００℃が適切であり、好ましくは１０５０〜１１５０℃とするべきであることが判明したので、そのように限定した。
該境界部温度の変動幅は、材質によって定まる上記最適温度より±２５℃を超えて外れると、製品の磁気特性が劣化したり、ばらつきが大きくなるので、そのように限定したが、磁気特性をほぼ一定にするには、該変動幅を±１０℃以下とするのが一層好ましい。
【００１５】
また、酸素分圧制御雰囲気帯及び窒素雰囲気帯の温度は、上記境界部の温度を最適値にするような組み合わせとなるが、後者の窒素雰囲気帯温度はフェライト焼成体の酸化を防止するため、８５０〜１１５０℃の範囲が望ましい。一方、酸素分圧制御雰囲気帯の温度は、そこでの冷却速度を小さくすることがフェライトの特性発現に好ましいことから、１０５０〜１３００℃の範囲とした。
【００１６】
さらに、酸素分圧制御雰囲気帯では、温度に応じて酸素分圧を制御することが、ＭｎＺｎフェライトの酸化状態の制御においてより好ましいため、酸素分圧を０．１〜５％とした。窒素雰囲気帯では、フェライトコアの酸化を防止するために、酸素分圧０．１％以下の窒素雰囲気とした。また、この窒素雰囲気帯に続く８５０℃未満の冷却工程も窒素雰囲気とすることが好ましい。但し、ここで言う窒素雰囲気は、不活性ガスであればよく、アルゴンガス等で代替できるが、工業的には窒素ガスが好ましい。
【００１７】
なお、本発明では、限定条件にしていないが、窒素雰囲気帯に設ける電気ヒータ等の加熱源は、上記境界部の近傍にのみ設け、８５０℃以下の低温域には加熱源を配置しない方がよい。８５０℃以下の低温域では、窒素雰囲気で急冷することにより酸化の影響を小さくできるためであるが、加熱源の設置による炉体の開口部からの外気の流入が窒素雰囲気の酸素分圧を上昇させることを避けるためでもある。
【００１８】
加熱源は、酸素分圧制御雰囲気及び窒素雰囲気中で加熱可能で、かつこの２つの雰囲気の酸素分圧を変動させない形態であれば良く、例えば、電気ヒータ等による抵抗加熱、赤外線ランプ等による赤外線加熱、高周波加熱、加熱した雰囲気ガスによるガス加熱等が加熱源として採用可能である。
また、使用される連続焼成トンネル炉は、本発明の条件が満たされる焼成ができればいかなる方式のものであっても良いが、例えば、すでに特公平４−７７２３４号公報で提案したローラ・ハース式連続焼成トンネル炉において、図１に示すような窒素雰囲気室の８５０〜１１５０℃の領域まで電気ヒータ等の加熱源を配置したものを用いることが、製品の磁気特性及び生産効率の両面で推奨される。ローラ・ハース式連続焼成トンネル炉は、台板の送りを速くすることができ、フェライト製造の高能率化に大きく貢献できるが、それゆえ、フェライト焼成体の積載量及び荷姿等の影響による温度の変動が大きく、本発明の効果が大きく発揮される。
【００１９】
さらに、本発明に係る焼成方法が適用されるＭｎＺｎ系フェライトとしては、主成分にＦｅ_２Ｏ_３、ＭｎＯ及びＺｎＯを含んだものであるが、製品の各種特性を改善するため、ＣｏＯ、ＮｉＯ、ＭｇＯ、ＣｕＯ等が添加されたり、あるいはＳｉＯ_２、ＣａＯ、Ｖ_２Ｏ_５、Ｎｂ_２Ｏ_５、Ｔａ_２Ｏ_５、ＳｎＯ_２、ＴｉＯ_２、ＺｒＯ_２、Ｉｎ_２Ｏ_３、Ｂｉ_２Ｏ_３、Ｓｂ_２Ｏ_３，ＧｅＯ_２等が微量添加されたものであっても良い。なお、これらのＭｎＺｎ系フェライトコアを焼成する時、最高温度は１１５０〜１４００℃の範囲でそれぞれの材質に適した温度とする。
【００２０】
【発明の実施の形態】
まず、図１に本発明に係る焼成方法を実施した連続焼成炉の１例を示す。図１はローラ・ハース式の例であるが、そこでは連続焼成トンネル炉のうちの昇温工程部分を省略して台板９に載置した焼成体８を最高温度に保持する所謂保持工程部分の後半と、冷却工程を示している。
【００２１】
本発明に係る焼成炉の重要ポイントは、上記冷却領域の一部に酸素分圧制御雰囲気室とそれに続く窒素雰囲気室とを設け、その境界部１２を仕切壁で分け、該酸素分圧制御雰囲気室、該窒素雰囲気室及び境界部１２には、温度センサ３と加熱源２とをそれぞれ別個に設けたことである。そして、そこで測定された温度が、前記した本発明の温度条件（目標値）を満足するよう加熱源２の出力が調整される。その調整のため、公知の温度制御装置１０が炉壁外に配置されている。また、酸素分圧を測定する酸素センサ６と、該測定値を所望の値に調整する公知の酸素分圧制御装置１１も設置されている。
【００２２】
次に、図１の上記連続焼成炉を用いて、具体的にＭｎＺｎ系フェライトコアを本発明に係る焼成方法で製造した例を説明する。
［実施例１］
Ｆｅ_２Ｏ_３：５３．２モル％、ＭｎＯ：３５．６モル％及びＺｎＯ：１１．２モル％からなる原料混合物を９５０℃で仮焼した後、湿式ボールミルで粉砕し，平均粒径１．２μｍの粉末とした。この粉砕時に微量成分としてＳｉＯ_２、ＣａＣＯ_３、Ｔａ_２Ｏ_５及びＺｒＯ_２をそれぞれ１００、１２００、４００及び２００ｐｐｍだけ同時に添加した。ついで，該粉砕粉に，バインダとしてポリビニルアルコールを添加して造粒した後、外径３６ｍｍ、内径２４ｍｍ、高さ１２ｍｍのリング状に成形した。
【００２３】
ＪＩＳに規定されたＦＥ１６〜ＦＥ５０のＥ形フェライトコアを２〜５ｋｇ積載した台板上に，上記のリング状のフェライトコアを３段積みで２セット（計６個）積載し、それらを、無作為な順序で、窒素雰囲気室に電気ヒータを配置した場合としない場合のローラ・ハース式連続焼成トンネル炉に通炉して焼成した。その際、焼成の最高温度を１３２０℃とし、焼成時間は１１時間とした。さらに、酸素分圧制御雰囲気室の温度及び酸素分圧を表１に示すように変え、各条件で１０台板分のリング状のフェライトコア６０個を焼成した。
【００２４】
得られた焼成体について、周波数：１００ｋＨｚ、最大磁束密度：０．２Ｔ、温度１００℃におけるコアロスを、交流Ｂ−Ｈループトレーサを用いて測定した。その結果得られたコアロスの平均値、最小値及び最大値を表１に併せて示す。また、酸素分圧制御雰囲気室を温度１１６０℃、酸素分圧１．２体積％に固定し、酸素分圧０．０３体積％の窒素雰囲気室の温度を変えることにより、両室の境界部温度を変動幅±１０℃で制御して１０００〜１２００の範囲で変化させ、得られた焼成体のコアロスの値を図２に示す。
【００２５】
【表１】

【００２６】
表１より、実験Ｎｏ．７のように、酸素分圧制御室及び窒素雰囲気室に電気ヒータ等の加熱源による温度制御がなくとも、酸素分圧制御室及び窒素雰囲気室の境界部温度が１０００〜１２００℃で、その変動幅が±２５℃であれば、コアロスは小さく、そのバラツキも小さいことがわかる。これは、フェライトコア焼成体の形状、積載量及び荷姿を一定の範囲内に限定することにより実現される。これに対し、実験Ｎｏ．１５のように両室に加熱源がない場合、実験Ｎｏ．１３、１４のように酸素分圧制御室に電気ヒータを備え、窒素雰囲気室に電気ヒータが無い場合、あるいは実験Ｎｏ．１１、１２のように酸素分圧制御室及び窒素雰囲気室の両方に電気ヒータを備えているが、境界部の温度及び変動幅が上記条件を満足しない場合は、コアロスの値及びそのバラツキは大きくなる。
【００２７】
一方、実験Ｎｏ．１〜８の結果で明らかなように、酸素分圧制御室及び窒素雰囲気室の両方に電気ヒータを備えるようにすると、該境界部の温度変動幅は±１０℃以下に抑えることができ、コアロス及びそのバラツキは一層小さくなった。なお、表１の実験Ｎｏ．１〜６の結果及び図２で明らかなように、本実施例の材質に適した境界部温度は１１２０℃であるが、境界部温度が１１２０℃から低温及び高温にずれると共に、コアロスは増加し、かつそのばらつきも増加している。これは、従来の窒素雰囲気室に温度制御装置のないローラ・ハース式連続焼成トンネル炉における境界部温度のばらつきが±約４０℃である時、コアロスのばらつきが約１３０ｋＷ／ｍ^３と大きくなることをよく説明し、従来の焼成方法におけるコアロスの劣化やばらつきの原因が境界部温度の変動によることを証明している。
【００２８】
本発明を適用して境界部の温度を最適温度に設定し、その変動幅を±２５℃以下に制御すると、コアロスの平均値は２６５ｋＷ／ｍ^３、そのばらつきは±２０ｋＷ／ｍ^３以下となり、高特性のＭｎＺｎフェライト焼成体を安定に得ることができた。
［実施例２］
Ｆｅ_２Ｏ_３：５２．２モル％、ＭｎＯ：２６．２モル％及びＺｎＯ：２１．６モル％からなる原料混合物を９５０℃で仮焼した後、湿式ボールミルで粉砕し、平均粒径１．２μｍの粉末とした。その粉砕時に、微量成分としてＳｉＯ_２、ＣａＣＯ_３、Ｎｂ_２Ｏ_５及びＢｉ_２Ｏ_３をそれぞれ５０、３５０、１５０及び２００ｐｐｍだけ添加した。ついで、この粉砕粉に、バインダとしてポリビニルアルコールを添加造粒した後、外径３６ｍｍ、内径２４ｍｍ、高さ１２ｍｍのリング状に成形した。
【００２９】
ＪＩＳに規定されたＦＯＲ１３〜ＦＯＲ４５のリング状フェライトコアを２〜６ｋｇ積載した台板上に、上記のリング状フェライトコアを３段積みで２セット（計６個）積載し、前記同様にローラ・ハース式連続焼成トンネル炉に通炉して焼成した。その際、焼成の最高温度は１３４０℃とし、焼成時間は１３時間とした。さらに、酸素分圧制御雰囲気室とそれに続く窒素雰囲気室の温度及び酸素濃度を上記同様に表２に示すよう変えて、各条件で１０台分の台板上フェライトコアを焼成した。得られた焼成体の周波数：１ｋＨｚ、且つ室温における初透磁率を、インピーダンス・アナライザを用いて測定した。その結果得られた初透磁率の平均値、最小値及び最大値を表２に併せて示す。
【００３０】
【表２】

【００３１】
表２より、電気ヒータ等の温度制御装置がないローラ・ハース式連続焼成トンネル炉では、酸素分圧制御雰囲気室とそれに続く窒素雰囲気室との境界部温度の変動幅が±３１〜５３℃にもなり、初透磁率のばらつきも最大最小の差で１１３０〜１８２０であった。それに対して、本発明を適用して、例えば実験ＮＯ．２３のように境界部温度を最適値１０７５℃に設定し、その変動幅を±２５℃以下に制御すると、初透磁率の平均値は、７８７０と従来より高くなる。また、実験ＮＯ．２１〜２６を通じて、初透磁率のばらつきは、平均値に対し±５００以下と小さく、高透磁率のＭｎＺｎ系フェライトコア焼成体を安定に得ることができた。
【００３２】
【発明の効果】
以上述べたように、本発明により、従来よりも優れた磁気特性を有するＭｎＺｎ系フェライトコアを安定して製造することができるようになった。
【図面の簡単な説明】
【図１】本発明に係る連続焼成炉を示す平面図である。
【図２】本発明に係る焼成方法の実施で得た境界部温度と製品のコアロスとの関係を示す図である。
【符号の説明】
１炉体
２加熱源（電気ヒータ）
３温度センサ
４酸素分圧制御の雰囲気ガス噴出路
５窒素ガス噴出路
６酸素センサ
７ハース・ローラ
８フェライトコア（焼成体）
９台板
１０温度制御装置
１１酸素分圧制御装置
１２境界部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for firing a MnZn-based ferrite core and a continuous firing furnace, for example, to a technique for controlling the atmosphere and temperature in the cooling step when firing the ferrite core using a continuous firing tunnel furnace.
[0002]
[Prior art]
MnZn-based ferrite cores are widely used as various communication devices, power supply coils, and transformer materials, and have greatly contributed to the miniaturization of electronic devices in recent years. There is a strong desire to manufacture.
[0003]
By the way, in order to obtain a MnZn ferrite core with excellent magnetic properties, it is described in the 24th, 4th (1985), 288 pages, "Soft Ferrite" (written by Sadataro Hiraga), Journal of the Japan Institute of Metals. As described above, it is said that it is essential to perform firing while precisely controlling the temperature and the amount of oxygen in the atmosphere at each stage of raising temperature, maintaining the maximum temperature, and cooling. In particular, it has been well known that the change in the oxidation state of the MnZn ferrite core during the cooling process has a great influence on the magnetic properties.
[0004]
Therefore, the conventional continuous firing furnace (usually using a tunnel furnace) reduces the oxygen partial pressure in the cooling zone as much as possible to prevent the oxidation of the MnZn-based ferrite fired body to a nitrogen atmosphere, and rapidly Cooling is in progress. Therefore, a large amount of nitrogen gas was introduced into the cooling zone to keep the pressure high.
For example, Japanese Patent Publication No. 4-77234 proposes a roller-hearth type continuous firing tunnel furnace provided with a low oxygen partial pressure chamber, and the oxygen concentration in the low oxygen partial pressure chamber is reduced to several ppm to about 100 ppm. Is disclosed. Japanese Examined Patent Publication No. 6-76257 discloses a technique for firing an MnZn-based ferrite core in less than 20 hours in this field in a very short time compared to the conventional technique. In short, high-efficiency production in a short time has been realized.
[0005]
However, when the roller hearth type continuous firing furnace described in the above Japanese Patent Publication No. 4-77234 is used, ferrite cores having different shapes and sizes are placed on the base plate with different loading amounts and packing forms and moved. In continuous firing, the magnetic characteristics deteriorated and varied, which was a big problem in terms of manufacturing stability.
[0006]
[Problems to be solved by the invention]
In view of such circumstances, an object of the present invention is to provide a technique capable of stably mass-producing a MnZn-based ferrite core having excellent magnetic properties by firing using a continuous firing furnace.
[0007]
[Means for Solving the Problems]
In order to achieve the above-mentioned object, the inventor has found the cause of the temperature variation in the cooling process due to the shape and size of the ferrite core, the load on the base plate, the package shape, etc., or the deterioration or variation in magnetic properties due to firing. Researched earnestly.
As a result, the conventional continuous firing tunnel furnace is not equipped with a temperature control device using a heating source such as an electric heater in the nitrogen atmosphere chamber of the cooling process, so that it was loaded on the firing base plate as shown in the examples described later. The cooling state has changed due to changes in the shape, size, loading capacity, and packing of the ferrite fired body, and the temperature pattern of the cooling process has fluctuated greatly. Especially, the oxygen partial pressure control atmosphere chamber and the nitrogen atmosphere chamber that follows it It became clear that temperature fluctuations at the boundary of the magnetic field caused the greatest deterioration of magnetic properties and variations. Furthermore, analysis of the content of Fe ²⁺ indicating the oxidation state of MnZn ferrite core, the content of Fe ²⁺ in response to variations in the temperature of the boundary portion is changed, increasing the magnetic properties of MnZn ferrite core It became clear that the oxidation state which influences was changed.
[0008]
The above phenomenon becomes remarkable in the roller-hearth type continuous firing tunnel furnace in which the feed of the base plate is fast, and particularly in the short-time firing in which the firing time is less than 20 hours disclosed in Japanese Patent Publication No. 6-76257. It was remarkable. In addition, it has been clarified that the same phenomenon causes the deterioration and dispersion of the magnetic characteristics in the pusher-type continuous firing tunnel furnace. Here, the firing time refers to the time required for the temperature to rise to 150 ° C. from room temperature through temperature rise and holding cooling.
[0009]
Therefore, the inventor makes the boundary temperature between the oxygen partial pressure control atmosphere zone in the cooling process and the nitrogen atmosphere zone that follows the optimum value and controls the fluctuation small to stabilize a high-performance MnZn ferrite core. Thus, the present invention has been conceived. However, in a continuous firing tunnel furnace, it is necessary to independently control the temperature and atmosphere of the atmosphere zone before and after the boundary, and there is a restriction that the opening of the boundary must be as small as possible. It has been substantially difficult to dispose a heating source such as an electric heater and a temperature control device. Therefore, in the present invention, the temperature of the boundary zone is controlled by precisely controlling the temperature of the atmosphere zone before and after the boundary by a heating source such as an electric heater and a temperature control device.
[0010]
That is, the present invention provides an oxygen partial pressure control atmosphere zone and a nitrogen atmosphere zone that follows the oxygen cooling zone when the MnZn-based ferrite core is fired through the steps of temperature increase, maximum temperature holding and cooling in sequence. A MnZn system characterized in that the temperature range of the boundary part between the partial pressure control atmosphere zone and the nitrogen atmosphere zone is 1000 to 1200 ° C., and the boundary temperature is controlled with a fluctuation range of ± 25 ° C. or less. This is a method for firing a ferrite core. Further, in the present invention, in order to control the temperature of the boundary portion, the temperatures of the oxygen partial pressure control atmosphere zone and the nitrogen atmosphere zone are set to 1050 to 1300 ° C. and 850 to 1150 ° C., respectively, or the oxygen partial pressure control is performed. A method for firing a MnZn-based ferrite core, characterized in that a heating source is arranged in each of an atmosphere zone and a nitrogen atmosphere zone, and each temperature is controlled by the heating source. Further, in the present invention, the oxygen partial pressure in the oxygen partial pressure control atmosphere zone and the nitrogen atmosphere zone is 0.1 to 5% by volume and 0.1% by volume or less, respectively, or the temperature is raised from room temperature to the maximum temperature, It is also a method for firing a MnZn-based ferrite core, characterized in that the firing time required for cooling from that temperature to 150 ° C. is less than 20 hours.
[0011]
In addition, the invention for the apparatus for carrying out the above method has also been invented, which is the oxygen partial pressure control in the cooling region in the continuous firing furnace of MnZn based ferrite core formed in three regions of temperature rising, maximum temperature holding and cooling. An atmosphere chamber and a nitrogen atmosphere chamber subsequent thereto are provided, and the oxygen partial pressure control atmosphere chamber and the nitrogen atmosphere chamber include a temperature sensor, a heating source, an oxygen sensor for measuring the oxygen partial pressure, and an atmosphere gas ejection valve. And a temperature control device that adjusts the output of the heating source so that the temperature measured by the temperature sensor matches the target value, and the oxygen partial pressure measured by the oxygen sensor matches the target value. with disposing the oxygen partial pressure control device for adjusting the atmospheric gas discharge valve, a temperature sensor connected to the temperature controller at the boundary between the oxygen partial pressure control atmosphere chamber and a nitrogen atmosphere chamber additionally It is a continuous firing furnace MnZn ferrite cores, characterized in that the. In addition, the present invention is also a continuous firing furnace for MnZn-based ferrite cores characterized in that the furnace body is of a roller- hearth type.
[0012]
In this case, the temperature fluctuation range refers to the range of the maximum deviation with respect to the average temperature, and varies spatially or temporally depending on the shape, size, loading capacity, and packing form of the ferrite compact passing through the boundary. This is the allowable temperature range. Further, the atmosphere in the cooling process other than the oxygen partial pressure control atmosphere chamber and the nitrogen atmosphere chamber may be the same as in the past.
Since the present invention has been adopted for firing MnZn ferrite cores, MnZn ferrite cores having excellent magnetic properties can be stably produced in large quantities even when firing using a continuous firing furnace. .
[0013]
Next, the reason for limiting the firing conditions employed in the present invention will be described.
First, the temperature at the boundary between the oxygen partial pressure control atmosphere and the subsequent nitrogen atmosphere is set to 1000 to 1200 ° C., the reason why the fluctuation range of this temperature is limited to ± 25 ° C. or less, and the two atmosphere temperatures and the oxygen partial pressure are set as follows. The reason for the limitation will be described below.
The optimum temperature at the boundary varies depending on the material of the MnZn ferrite core, the temperature at which the ferrite grain boundary component transforms from the liquid phase to the solid phase, the temperature at which other trace components precipitate at the grain boundary, the grain boundary The temperature at which the diffusion of oxygen is slowed is considered, and the oxidation state of the MnZn ferrite is stably controlled by controlling the oxygen partial pressure according to the temperature at a temperature higher than this temperature, and cooled in a nitrogen atmosphere at the lower temperature. Therefore, it was decided that the oxygen partial pressure control atmosphere and the nitrogen atmosphere were divided and controlled.
[0014]
As a result of the present inventors repeatedly examining experiments on several kinds of materials, the temperature of the boundary portion varies depending on the materials, but 1000 to 1200 ° C. is appropriate, and preferably 1050 to 1150 ° C. As it turned out, it was limited to that.
The variation range of the boundary temperature is deviated by more than ± 25 ° C from the above optimum temperature determined by the material, so that the magnetic characteristics of the product deteriorates or the variation becomes large. In order to make it substantially constant, it is more preferable that the fluctuation range is ± 10 ° C. or less.
[0015]
Further, the temperature of the oxygen partial pressure control atmosphere zone and the nitrogen atmosphere zone is a combination that optimizes the temperature of the boundary portion, but the latter nitrogen atmosphere zone temperature prevents oxidation of the ferrite sintered body, A range of 850 to 1150 ° C is desirable. On the other hand, the temperature of the oxygen partial pressure control atmosphere zone is set to the range of 1050 to 1300 ° C., since it is preferable to reduce the cooling rate therefor in order to develop the ferrite characteristics.
[0016]
Furthermore, in the oxygen partial pressure control atmosphere zone, it is more preferable in controlling the oxidation state of MnZn ferrite to control the oxygen partial pressure according to the temperature, so the oxygen partial pressure is set to 0.1 to 5%. In the nitrogen atmosphere zone, a nitrogen atmosphere with an oxygen partial pressure of 0.1% or less was used to prevent oxidation of the ferrite core. Further, it is preferable that the cooling step below 850 ° C. following the nitrogen atmosphere zone is also a nitrogen atmosphere. However, the nitrogen atmosphere here may be an inert gas and can be replaced by argon gas or the like, but industrially nitrogen gas is preferred.
[0017]
In the present invention, although not a limiting condition, a heating source such as an electric heater provided in the nitrogen atmosphere zone is provided only in the vicinity of the boundary portion, and a heating source is not disposed in a low temperature region of 850 ° C. or lower. Good. This is because the influence of oxidation can be reduced by quenching in a nitrogen atmosphere at a low temperature range of 850 ° C. or lower, but the inflow of outside air from the opening of the furnace body due to the installation of the heating source increases the oxygen partial pressure of the nitrogen atmosphere. It is also to avoid making it.
[0018]
The heating source may be of any form that can be heated in an oxygen partial pressure controlled atmosphere and a nitrogen atmosphere and that does not change the oxygen partial pressures of the two atmospheres. For example, resistance heating by an electric heater or the like, infrared rays by an infrared lamp, or the like Heating, high-frequency heating, gas heating with heated atmospheric gas, and the like can be employed as the heating source.
Further, the continuous firing tunnel furnace used may be of any type as long as the conditions of the present invention can be satisfied. For example, the roller-hearth type continuous furnace already proposed in Japanese Patent Publication No. 4-77234 In the firing tunnel furnace, it is recommended to use a heating source such as an electric heater up to a range of 850 to 1150 ° C. in a nitrogen atmosphere chamber as shown in FIG. 1 in terms of both the magnetic characteristics of the product and the production efficiency. . The roller-hearth-type continuous firing tunnel furnace can speed up the feeding of the base plate and can greatly contribute to the improvement of the efficiency of ferrite production. The effect of the present invention is greatly exhibited.
[0019]
Furthermore, the MnZn-based ferrite to which the firing method according to the present invention is applied includes Fe ₂ O ₃ , MnO and ZnO as main components, but in order to improve various properties of the product, CoO, NiO, MgO, CuO or the like is added, or SiO ₂ , CaO, V ₂ O ₅ , Nb ₂ O ₅ , Ta ₂ O ₅ , SnO ₂ , TiO ₂ , ZrO ₂ , In ₂ O ₃ , Bi ₂ O ₃ , Sb ₂ O ₃ , GeO ₂ or the like may be added in a small amount. When these MnZn-based ferrite cores are fired, the maximum temperature is set in a range of 1150 to 1400 ° C. and suitable for each material.
[0020]
DETAILED DESCRIPTION OF THE INVENTION
First, FIG. 1 shows an example of a continuous firing furnace in which the firing method according to the present invention is performed. FIG. 1 shows an example of a roller-hearth type, in which a so-called holding process part in which the heating process part of the continuous firing tunnel furnace is omitted and the fired body 8 placed on the base plate 9 is held at the maximum temperature. The latter half and the cooling process are shown.
[0021]
An important point of the firing furnace according to the present invention is that an oxygen partial pressure control atmosphere chamber and a nitrogen atmosphere chamber subsequent thereto are provided in a part of the cooling region, the boundary portion 12 is divided by a partition wall, and the oxygen partial pressure control atmosphere is provided. The temperature sensor 3 and the heating source 2 are separately provided in the chamber, the nitrogen atmosphere chamber, and the boundary portion 12. And the output of the heating source 2 is adjusted so that the temperature measured there satisfies the above-described temperature condition (target value) of the present invention. For the adjustment, a known temperature control device 10 is arranged outside the furnace wall. An oxygen sensor 6 for measuring the oxygen partial pressure and a known oxygen partial pressure control device 11 for adjusting the measured value to a desired value are also installed.
[0022]
Next, an example in which a MnZn-based ferrite core is specifically manufactured by the firing method according to the present invention using the continuous firing furnace of FIG. 1 will be described.
[Example 1]
A raw material mixture composed of Fe ₂ O ₃ : 53.2 mol%, MnO: 35.6 mol% and ZnO: 11.2 mol% was calcined at 950 ° C. and then pulverized by a wet ball mill. The powder was 2 μm. This as a minor component during milling _{_{_{SiO 2, CaCO 3, Ta 2}}} O 5 and ZrO ₂ only each 100,1200,400 and 200ppm were added simultaneously. Next, the pulverized powder was granulated by adding polyvinyl alcohol as a binder, and then formed into a ring shape having an outer diameter of 36 mm, an inner diameter of 24 mm, and a height of 12 mm.
[0023]
Two sets (6 in total) of the above ring-shaped ferrite cores are loaded on a base plate on which 2 to 5 kg of E-type ferrite cores of FE16 to FE50 specified in JIS are loaded. In a work order, firing was conducted through a roller-hearth continuous firing tunnel furnace with and without an electric heater in the nitrogen atmosphere chamber. At that time, the maximum firing temperature was 1320 ° C., and the firing time was 11 hours. Further, the temperature and oxygen partial pressure in the oxygen partial pressure control atmosphere chamber were changed as shown in Table 1, and 60 ring-shaped ferrite cores for 10 plates were fired under each condition.
[0024]
About the obtained sintered body, the core loss at a frequency: 100 kHz, a maximum magnetic flux density: 0.2 T, and a temperature of 100 ° C. was measured using an AC BH loop tracer. The average value, minimum value, and maximum value of the core loss obtained as a result are also shown in Table 1. In addition, by fixing the oxygen partial pressure control atmosphere chamber at a temperature of 1160 ° C. and an oxygen partial pressure of 1.2% by volume, and changing the temperature of the nitrogen atmosphere chamber with an oxygen partial pressure of 0.03% by volume, the boundary temperature between the two chambers FIG. 2 shows the core loss value of the fired body obtained by controlling the variation within a range of 1000 to 1200 by controlling the fluctuation width at ± 10 ° C.
[0025]
[Table 1]

[0026]
From Table 1, Experiment No. As shown in FIG. 7, even if the oxygen partial pressure control chamber and the nitrogen atmosphere chamber are not controlled by a heating source such as an electric heater, the boundary temperature between the oxygen partial pressure control chamber and the nitrogen atmosphere chamber is 1000 to 1200 ° C. If the width is ± 25 ° C., the core loss is small and the variation is small. This is realized by limiting the shape, loading amount and packing form of the ferrite core fired body within a certain range. In contrast, Experiment No. When there is no heating source in both chambers as in Experiment 15, When the oxygen partial pressure control chamber has an electric heater and the nitrogen atmosphere chamber does not have an electric heater as shown in FIGS. 11 and 12, both the oxygen partial pressure control chamber and the nitrogen atmosphere chamber are equipped with electric heaters. However, if the boundary temperature and fluctuation range do not satisfy the above conditions, the value of core loss and its variation are large. Become.
[0027]
On the other hand, Experiment No. As is apparent from the results of 1 to 8, when both the oxygen partial pressure control chamber and the nitrogen atmosphere chamber are provided with electric heaters, the temperature fluctuation width of the boundary portion can be suppressed to ± 10 ° C. or less, and the core loss is reduced. And the variation was even smaller. In addition, the experiment No. As is clear from the results of 1 to 6 and FIG. 2, the boundary temperature suitable for the material of this example is 1120 ° C. However, the core temperature increases as the boundary temperature shifts from 1120 ° C. to low and high temperatures. And the variation is also increasing. This is because when the temperature variation at the boundary in a conventional roller-hearth-type continuous firing tunnel furnace without a temperature control device in a nitrogen atmosphere chamber is ± about 40 ° C., the core loss variation becomes as large as about 130 kW / m ^3. It is proved that the cause of the deterioration and variation of the core loss in the conventional firing method is due to the fluctuation of the boundary temperature.
[0028]
When the boundary temperature is set to the optimum temperature by applying the present invention and the fluctuation range is controlled to be ± 25 ° C. or less, the average value of the core loss is 265 kW / m ³ , and the variation is ± 20 kW / m ³ or less. A high-quality MnZn ferrite fired body could be obtained stably.
[Example 2]
A raw material mixture composed of Fe ₂ O ₃ : 52.2 mol%, MnO: 26.2 mol% and ZnO: 21.6 mol% was calcined at 950 ° C., and then pulverized by a wet ball mill. The powder was 2 μm. At the time of the pulverization, SiO ₂ , CaCO ₃ , Nb ₂ O ₅ and Bi ₂ O ₃ were added as trace components by 50, 350, 150 and 200 ppm, respectively. Subsequently, after adding and granulating polyvinyl alcohol as a binder to this pulverized powder, it was formed into a ring shape having an outer diameter of 36 mm, an inner diameter of 24 mm, and a height of 12 mm.
[0029]
Two sets of the above-mentioned ring-shaped ferrite cores (three in total) are loaded on a base plate on which 2 to 6 kg of the ring-shaped ferrite cores of FOR13 to FOR45 specified in JIS are loaded. Fired through a hearth continuous firing tunnel furnace. At that time, the maximum temperature of baking was 1340 ° C., and the baking time was 13 hours. Further, the temperature and oxygen concentration of the oxygen partial pressure control atmosphere chamber and the subsequent nitrogen atmosphere chamber were changed as shown in Table 2 in the same manner as described above, and 10 ferrite cores on the base plate were fired under each condition. The frequency of the obtained fired body: 1 kHz, and the initial magnetic permeability at room temperature were measured using an impedance analyzer. Table 2 shows the average value, minimum value, and maximum value of the initial permeability obtained as a result.
[0030]
[Table 2]

[0031]
From Table 2, in the roller hearth type continuous firing tunnel furnace without a temperature control device such as an electric heater, the fluctuation range of the boundary temperature between the oxygen partial pressure control atmosphere chamber and the nitrogen atmosphere chamber following it is ± 31 to 53 ° C. Also, the variation in initial permeability was 1130 to 1820 with a maximum and minimum difference. On the other hand, the present invention is applied to, for example, experiment NO. When the boundary temperature is set to an optimum value of 1075 ° C. and the fluctuation range is controlled to be ± 25 ° C. or less as in 23, the average value of the initial magnetic permeability is 7870, which is higher than the conventional value. Experiment NO. Through 21 to 26, the dispersion of the initial permeability was as small as ± 500 or less with respect to the average value, and a high permeability MnZn ferrite core fired body could be obtained stably.
[0032]
【The invention's effect】
As described above, according to the present invention, it has become possible to stably manufacture a MnZn ferrite core having magnetic properties superior to those of the prior art.
[Brief description of the drawings]
FIG. 1 is a plan view showing a continuous firing furnace according to the present invention.
FIG. 2 is a diagram showing the relationship between the boundary temperature obtained by the firing method according to the present invention and the core loss of the product.
[Explanation of symbols]
1 Furnace 2 Heating source (electric heater)
3 Temperature sensor 4 Oxygen partial pressure control atmosphere gas ejection path 5 Nitrogen gas ejection path 6 Oxygen sensor 7 Hearth roller 8 Ferrite core (fired body)
9 Base plate 10 Temperature control device 11 Oxygen partial pressure control device 12 Boundary part

Claims

When firing the MnZn-based ferrite core sequentially through the steps of temperature raising, maximum temperature holding and cooling,
The cooling step is provided with an oxygen partial pressure control atmosphere zone and a nitrogen atmosphere zone that follows, and the temperature range of the boundary portion between the oxygen partial pressure control atmosphere zone and the nitrogen atmosphere zone is 1000 to 1200 ° C., and the boundary portion A method for firing a MnZn-based ferrite core, characterized in that the firing is performed while controlling the temperature within a fluctuation range of ± 25 ° C. or less.

The method for firing a MnZn ferrite core according to claim 1, wherein the oxygen partial pressure control atmosphere zone and the nitrogen atmosphere zone are set to 1050 to 1300 ° C and 850 to 1150 ° C, respectively.

3. The MnZn ferrite core according to claim 1, wherein the oxygen partial pressure in the oxygen partial pressure control atmosphere zone and the nitrogen atmosphere zone is 0.1 to 5% by volume and 0.1% by volume or less, respectively. Firing method.

4. The MnZn-based ferrite core according to claim 1, wherein a heating source is disposed in each of the oxygen partial pressure control atmosphere zone and the nitrogen atmosphere zone, and each temperature is controlled by the heating source. Firing method.

The firing of the MnZn-based ferrite core according to any one of claims 1 to 4, wherein a firing time required for raising the temperature from room temperature to the maximum temperature and cooling from the temperature to 150 ° C is less than 20 hours. Method.

In a continuous firing furnace of MnZn-based ferrite core formed in three regions of temperature rise, maximum temperature holding and cooling,
An oxygen partial pressure control atmosphere chamber and a subsequent nitrogen atmosphere chamber are provided in the cooling region, and the oxygen partial pressure control atmosphere chamber and the nitrogen atmosphere chamber are provided with a temperature sensor, a heating source, and oxygen for measuring the oxygen partial pressure. A temperature control device that adjusts the output of the heating source so that the temperature measured by the temperature sensor matches a target value, and the oxygen content measured by the oxygen sensor. An oxygen partial pressure control device that adjusts the atmospheric gas discharge valve to adjust the pressure to a target value is disposed, and is connected to the temperature control device at the boundary between the oxygen partial pressure control atmosphere chamber and the nitrogen atmosphere chamber A continuous firing furnace for MnZn-based ferrite cores, wherein a temperature sensor is additionally provided .

7. The continuous firing furnace for MnZn ferrite cores according to claim 6, wherein the furnace body is a roller-Haas type.