JP2004106035A - Electrode for heating sheet metal and sheet metal heating method using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide electrodes which can heat a sheet metal uniformly with no deformation. <P>SOLUTION: A plurality of freely movable electrodes with clamping mechanism are arranged to absorb thermal expansion in both length and width directions caused during heating of the sheet metal, and the surface of the electrode is provided with a layer of high electric resistance to enhance heat generation by electric current. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、金属薄板材をプレスなどで加工する場合に、あらかじめ通電加熱により薄板材を加熱する場合等の薄板材加熱用の通電加熱電極に関する。
【０００２】
【従来の技術】
シート状の金属は、自動車などのボディーや電化製品等日常の様々なものに使われ、その形状は複雑多岐にわたる。これらの製品は、通常鉄板やアルミおよびその合金などが使われるが、特に加工性や強度を持たせる場合には、シート状金属を一定温度以上に加熱してから加工を行う場合がある。
【０００３】
通常、シート状金属の加熱は、加熱炉でガスや重油用のバーナーを用いた燃焼ガスや電気ヒーターによる輻射加熱によることが多い。シート状金属は、酸化雰囲気で加熱されることが多く、あるいは、非酸化雰囲気で加熱していてもプレスなどの加工を行う場合には炉外へ出され大気にさらされた状態で加工を行うことになる。そのため、加工されるまでに加熱されたシート状金属は、放散熱によりシート内で温度偏差がつき、温度偏差によりシート内に強度のばらつきが生じるため加工精度を悪化させる原因の一つになっている。
【０００４】
また、高温で大気にさらされたシート状金属は、表面に酸化スケールが発生するため、スケール除去のための後処理が必要となり、スケール除去のための設備、処理費用、時間がかかる。
【０００５】
そのため、例えば、熱間加工する物体に不活性ガスを吹き付けて、酸化を防止する方法が公開されている（特許文献１参照）。また、鋼板表面にアルミをメッキし、鋼板の酸化を防止するとともに、高温に加熱した時にアルミが溶融しないように徐々に加熱し鉄との合金化を進める方法などが提案されている（特許文献２参照）。
【０００６】
【特許文献１】
特開平５−３０９４２６号公報
【特許文献２】
特開２０００−３８６４０号公報
【０００７】
しかし、前者の方法では不活性ガスを吹き付ける時、まわりの空気を巻き込むため酸素濃度を下げることができず、効果的な酸化防止にはならないという問題がある。また、加熱した金属をガスで冷やすことにもなり、加熱効果が薄れるとともに、温度偏差を増長し、加工精度の悪化にもつながる可能性がある。また、後者の方法では、メッキのための設備が必要であり製造コストの増加が避けられない。
【０００８】
また、上記方法における問題点を解決すべく、例えば、金型の近傍で通電加熱することが提唱されている（特許文献３参照）。
しかし、薄板材を通電加熱するときには、大きな２つの課題がある。その一つは、加熱により薄板材が膨張することにより薄板材が垂れてしまい、金型に接触しスパークしたり、垂れた被加熱材が電極に不安定接触してスパークが発生したりするという問題であり、もう一つは、電極近傍では被加熱材が薄いため電極により熱が奪われることにより、薄板内に大きな温度偏差が生じ熱応力が生じることと電極が薄板の幅方向の延びを拘束することにより、電極近傍にしわが入り薄板が変形を起こしてしまうことである。
【０００９】
前者の問題については、電極間で薄板材に張力を与えて伸ばすことが提唱されており（特許文献３および特許文献４参照）、また、後者の電極近傍の問題については、半径２０ｍｍ以下の球状電極で通電することにより、電極近傍の温度を上昇させる方法が提唱されている（特許文献５参照）。
【００１０】
【特許文献３】
特開２００２−１８５３１号公報
【特許文献４】
特開昭５３−１０９８０８号公報
【特許文献５】
特開２００２−１８５３１号公報
【００１１】
【発明が解決しようとする課題】
しかしながら、前者の加熱された薄板材の延びについては、電極間で張力を与えても、厚みが薄いので厚み方向の膨張は無視できるものの、熱膨張は電極間方向だけではなく平面的に一様に広がろうとするため、電極間方向だけに張力を与えても、しわ発生防止の解決にはならない。
【００１２】
また、後者の電極近傍の問題についても解決が困難である。すなわち、小電極にしても電極の接触面積が小さくなり電極近傍は、電流密度が高くなるため容易に薄板材の温度が上昇するが、電極近傍のみが加熱され過加熱となりやすく時には溶断する場合があること、電極が球であるため、加熱で延びた薄板材が電極面と不安定接触することによりスパークが発生しやすくなるなどの問題が生じる。また、電極が幅方向に広がろうとするのを拘束することによる薄板材の変形を防止することはできない。
本発明は、上記課題を解決し金属薄板材を変形や温度偏差無く加熱できる電極を提供することを目的とする。
【００１３】
【課題を解決するための手段】
本発明の要旨は、以下の通りである。
（１）金属薄板を挟持可能な一対のクランプ電極が、電源を介して対向して設置され、該対向する電極が並列に２系列以上設置され、さらに各電極が任意の方向に可動自在としてなることを特徴とする金属薄板用加熱電極。
（２）少なくとも被加熱物と接触する面が、電極母材の電気抵抗より大きな材質からなることを特徴とする電極部材。
（３）電極母材から被加熱物と接触する面まで、順に電気抵抗が大きくなる様に複数の層を設けたことを特徴とする電極部材。
（４）前記（２）または（３）に記載の電極部材を用い、被加熱物である金属薄板を挟持可能とする一対のクランプ電極が、電源を介して対向して設置され、該対向する電極が並列に２系列以上設置され、さらに各電極が任意の方向に可動自在であることを特徴とする金属薄板用加熱電極。
（５）前記（１）または（４）に記載の金属薄板用加熱電極を用いて、金属薄板を挟持しながら通電して加熱し、加熱に伴う金属薄板の熱膨張によるしわや延びを吸収する様に各電極を移動させることを特徴とする金属薄板加熱方法。
【００１４】
【発明の実施の形態】
以下に、本発明を図面に基いて詳細に説明する。
図１は、加熱前後金属薄板材の変化を説明する図である。金属薄板材とは通常鋼板であるが、アルミ等の他の金属でも良い。図１の点線で示す薄板材ＡＢＣＤを加熱し、拘束無く自由に平面上で膨張させた場合、金属薄板材（以降は薄板材と記載する）は細線Ａ’Ｂ’Ｃ’Ｄ’の様に広がろうとする。しかし、電極が両端で薄板材を拘束することにより、電極間方向の熱膨張による延びは、薄板材を水平にして加熱する場合には重力により下方に垂れることで応力の発生を吸収しようとする。
【００１５】
一方、幅方向の延びは、板中央付近は自由に延びることができるものの、両端は電極で拘束されるため延びることができず、しわを発生させ、図中の実線ＡＥＦＢＣＧＨＤの様な形状になろうとする。電極は、通常冷却されていることもあり、加熱された薄板材と電極部間では熱応力も加わり、容易に座屈し、薄板材両端に変形を与えてしまう。この様な変形は、薄板材が加熱後プレスされる様な場合には、重大な欠陥となってしまう。
【００１６】
そこで、この様な変形を生じさせず、板内の温度偏差を最小とするための電極について検討を行った。まず、加熱により生じる熱膨張については、従来の様に電極間方向の延びは、電極間方向に張力を加えるように電極を動かすことで解消できるが、それだけでは不十分で幅方向の延びも考慮しなければならない。そのため、本発明では、電極間に薄板を挟むクランプ電極とし、熱膨張に合わせ電極間方向だけではなく幅方向にも移動できる電極とした。
【００１７】
図２、図３で、本発明による電極について説明する。図２は、本発明による電極の作用を説明する模式図であり、図３は、本発明による電極構造例を説明する模式図である。被加熱材である薄板１は、電源４に導電部材５、電流分配器６で接続された一方の電極２，２’と、同じく電源４に導電部材５、電流分配器７で接続された対向するもう一方の電極３，３’間で、電流を通じジュール加熱される。
【００１８】
薄板１は、先に述べた様に図１の加熱前ＡＢＣＤが、加熱されるとＡ’Ｂ’Ｃ’Ｄ’になろうとする。従来の電極は、板幅一杯に拘束する構造であるため辺ＡＤ、ＢＣが拘束されてしまうが、本発明例である図２では、片方の電極を２つとし、薄板１の４隅近傍をクランプして通電することから、薄板１が拘束されるのはこの４隅の電極だけとなり、他は自由に膨張しようとする。膨張すると薄板１は垂れようとすることから、電極２を図１のＡからＡ’の方向へ、電極２’を図１のＤからＤ’の方向へ，電極３を図１のＢからＢ’の方向へ、電極３’を図１のからＣ’の方向へ移動させると、薄板１は、垂れることなく、また、しわを発生することなく加熱することができる。
【００１９】
電極構造としては、例えば図３に示すように、薄板１の電極による圧下と開放は、電極支持機構８’の内部に電動シリンダや油圧シリンダ、エアシリンダなどの圧下機構を持たせ、この圧下機構に先端に上下の電極２’がついたアーム１０を接続し、前記圧下機構のシリンダの移動で行う。電極２’は、アーム１０と絶縁板および絶縁ボルトで接合され、圧下機構とは電気的に絶縁する。
【００２０】
電極の材質は、薄板と接触する表面の材質は溶着しにくく酸化のしにくいセラミックスやサーメットを溶射などで設けるのが望ましく、内部の材質は電流による発熱を抑えるため電気抵抗が小さく、比透磁率の小さな銅や銅の合金を用いるのが望ましい。また、水冷等により電極全体が発熱するのを防止することも必要である。
【００２１】
この電極全体を移動させる手段としては、例えば図３ではベース１３を土台に固定し、その上に長手方向、板幅方向に電極支持機構８’全体を移動させるためのモーター１１，１２を設ければ良い。電極の移動量は、薄板１の温度に応じた熱膨張量を計算しておきその計算値に合わせ移動させても良いし、あるいは薄板の温度に応じ薄板が塑性変形しない様にトルクを測定しながら移動させる方法でも良い。
【００２２】
本例では、モーターを用いて電極を移動させる例を示したが、油圧シリンダやエアシリンダなどでも構わない。
【００２３】
以上は、比較的通電電流量が小さく電極近傍の発熱が問題にならない場合には、極めて有効であるが、通電電流量が多い場合には、片側電極２個では電極近傍の電流密度が高く発熱が問題になる場合がある。この様な場合、煩雑になるため電源との接続は省略してあるが、図４の様に電極を複数（２，２’，３，３’，１４〜１９）に分け、各々の電極が上記同様自在に可動できるようにしておけば、熱膨張を吸収させることができる。
ここで、図中２０〜２５は電極支持機構を示す。
【００２４】
この場合、片側電極が偶数個でも奇数個のどちらでも良いが、偶数個と奇数個とでは電極の動きが多少異なる。具体的には、奇数個の場合には、板幅中央に設置する電極は、電極間方向にのみ引っ張る様にし、この中央に設置した電極の両側の電極は、薄板の延びに合わせて板幅方向と電極間方向に動き結果的には斜めの方向に引っ張るようにすれば良いし、偶数個の場合には、同様に板幅中央を挟んで薄板の延び方向に斜めに引っ張るようにするのが望ましい。
【００２５】
次に、電極による薄板からの抜熱による薄板の変形防止法について説明する。
薄板は、厚みが薄いことから容易に電極から抜熱され、温度偏差が生じやすい。温度偏差が生じ、電極の拘束があると容易に変形し座屈してしまう場合が多い。電極からの抜熱を防止するためには、薄板と接触する電極表面温度が加熱された薄板の温度に近ければ良い。電極表面温度を高温にするために、本発明では図５の様に抵抗の小さな電極母材２６（例えば銅など）を電極フォルダー３３にロウづけした水冷銅パイプ３１，３２で冷却する一方、少なくとも電極表面には抵抗の大きい材質（例えばニクロムなど）の層３０を設け、電極から薄板へ流れる電流により電極表面部を発熱させる。このことで、上記薄板と電極との温度偏差を小さくする、あるいはなくすことができる。
【００２６】
この場合、母材から表面部までの間は徐々に抵抗が大きくなるように複数の層（本例では層２７，２８，２９）にすると良好な場合が多い。すなわち、抵抗の大きな材質は、一般に熱伝導率も小さく、熱膨張率も大きいという性質を有することから、物性値の傾斜をつけることで熱膨張差による層間剥離等のトラブルを回避することができるためである。
【００２７】
抗層の設け方は、溶射が施工しやすく物性値変化もつけやすい。その他としてはメッキや焼きばめなども有効である。この様にして、電極表面を加熱することにより、加熱された薄板から電極への伝熱量が小さくなるため、当然のことながら薄板内の温度偏差も小さくなり熱応力が生じにくくなり、座屈の発生を防止することができる。
【００２８】
【実施例】
本発明による効果を実験で確認した。実験は、厚さ０．１８ｍｍ、幅３００ｍｍ、長さ６００ｍｍの冷延鋼板を室温から８００℃まで加熱し、加熱中の鋼板の変形ならびに加熱終了後の鋼板の変形状態について、本発明による電極と比較例として固定電極を用いた場合について比較した。
【００２９】
本発明による電極は、電極全体が鋼板長手方向、幅方向に移動可能な様にリニアガイド上にエアシリンダで、任意の方向へ移動できるようにし、鋼板のクランプも、エアシリンダにより行う様にした。用いた電極は、水冷した銅母材の電極（幅５０ｍｍ、奥行き４０ｍｍ）の表面にクロムカーバイドのニッケルクロムサーメットを２５０μｍ溶射したものを片側２個用い、幅方向、長手方向に加熱に合わせて移動させた場合（実施例１）、片側の電極３個を用い幅方向、長手方向に加熱に合わせて移動させた場合（実施例２）、電極表面にニクロムをワイヤー溶射で１ｍｍ施工し片側３個の電極を用い、幅方向、長手方向に加熱に合わせて移動させた場合（実施例３）と、比較例として幅４００ｍｍの水冷銅電極用い、電極を固定した場合（比較例１）、比較例１と同様にしながら電極を長手方向に移動させた場合（比較例２）で比較を行った。電源は、５０Ｖ／８０００Ａのサイリスタ制御盤を用いた。
【００３０】
結果を表１に示す。本発明による実施例１では、鋼板の両端４隅に電極を配置し４隅を引っ張るように電極を動かしたことから、電極近傍は電流密度が高くなり、電極部だけがやや高温になったものの、鋼板は平面を保とうとし鋼板形状の不良は加熱中、加熱後も見られなかった。
【００３１】
実施例２は、実施例１で電極近傍の電流密度が高かったことから、電流密度を低減する目的で幅方向中央に電極を１つ増やし電極数を３個としたもので、端の電極は長手方向幅方向ともに動かし、中央の電極は長手方向に引っ張る様に移動させたものであるが、極めて小さく実用上問題無いレベルではあるが、中央の電極近傍に小さなしわが加熱中に発生し、冷却後もわずかなしわが残ったものの、電極近傍の温度偏差は緩和され８０℃が４０℃に低減した。
【００３２】
実施例３は、実施例２と同様の電極配置、移動をさせたもので、電極のみ表面が抵抗の高い材質としたものであるが、電極近傍では加熱中も加熱後も形状の異常は見られないとともに、温度偏差も極めて小さなものであった。
【００３３】
それに対し、従来の固定電極で加熱した比較例１では鋼板に大きなしわと垂れが発生し、このしわはそのまま冷却後にも残ってしまった。また、熱膨張による延びを吸収する目的で提唱されている電極間で鋼板を引っ張る比較例２では、垂れは無くなりしわの幅が若干改善されるものの、やはり大きなしわが残ってしまった。
この様に、本発明の電極を用いれば、品質の良い薄板の加熱を可能とすることができた。
【００３４】
【表１】

【００３５】
【発明の効果】
本発明の電極を用いれば、形状悪化しやすい薄板の加熱であっても、形状不良を発生することなく品質の良い加熱が可能となるため、特に形状が問題になる熱間プレスなどに本加熱電極を用いて薄板を通電加熱すれば、温度偏差も小さく強度ばらつきの無い状態でプレスができるため、精度の良い製品を製造することができるとともに、歩留まり生の低下もなく生産性も向上させることができる。
【図面の簡単な説明】
【図１】薄板の静止加熱を説明する模式図である。
【図２】本発明による、２つの自在に移動可能な電極を使う例を示す平面模式図である。
【図３】本発明による、電極の構造例を説明する断面模式図である。
【図４】本発明による、複数の自在に移動可能な電極を使う例を示す平面模式図である。
【図５】本発明による、電極構造を説明する断面模式図である。
【符号の説明】
１：薄板
２，２’：電極
３，３’：電極
４：電源
５：導電部材
６：電流分配器
７：電流分配器
８，８’：電極支持機構
９，９’：電極支持機構
１０：アーム
１１：モーター
１２：モーター
１３：ベース
１４：電極
１５：電極
１６：電極
１７：電極
１８：電極
１９：電極
２０：電極支持機構
２１：電極支持機構
２２：電極支持機構
２３：電極支持機構
２４：電極支持機構
２５：電極支持機構
２６：電極母材
２７：高抵抗層
２８：高抵抗層
２９：高抵抗層
３０：表面高抵抗層
３１：水冷パイプ
３２：水冷パイプ
３３：電極フォルダー[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a current-carrying heating electrode for heating a thin sheet material such as a case where a thin sheet material is previously heated by current heating when a metal sheet material is processed by a press or the like.
[0002]
[Prior art]
Sheet-shaped metal is used for various everyday objects such as bodies of automobiles and electric appliances, and the shapes thereof are complex and varied. For these products, iron plates, aluminum and alloys thereof are usually used. In particular, when workability and strength are required, the sheet metal may be heated to a certain temperature or more before working.
[0003]
Usually, the heating of the sheet-like metal is often performed by combustion gas using a burner for gas or heavy oil in a heating furnace or radiant heating by an electric heater. Sheet metal is often heated in an oxidizing atmosphere, or even when heated in a non-oxidizing atmosphere, when processing such as pressing, it is taken out of the furnace and processed in the atmosphere. Will be. Therefore, the sheet metal heated before being processed has a temperature deviation in the sheet due to heat dissipation, and the temperature deviation causes a variation in strength in the sheet, which is one of the causes of deteriorating the processing accuracy. I have.
[0004]
In addition, the sheet metal exposed to the atmosphere at a high temperature generates oxide scale on the surface, so that a post-treatment for removing the scale is required, and equipment for removing the scale, processing cost, and time are required.
[0005]
Therefore, for example, a method has been disclosed in which an inert gas is blown onto an object to be hot worked to prevent oxidation (see Patent Document 1). Also, a method has been proposed in which aluminum is plated on the surface of a steel sheet to prevent oxidation of the steel sheet, and gradually heated so that the aluminum does not melt when heated to a high temperature to promote alloying with iron (Patent Documents) 2).
[0006]
[Patent Document 1]
JP-A-5-309426 [Patent Document 2]
JP 2000-38640 A
However, in the former method, when the inert gas is blown, the surrounding air is entrained, so that the oxygen concentration cannot be reduced, and there is a problem that effective oxidation is not prevented. In addition, since the heated metal is cooled by the gas, the heating effect is reduced, the temperature deviation is increased, and the processing accuracy may be deteriorated. Also, the latter method requires equipment for plating, and inevitably increases the manufacturing cost.
[0008]
Further, in order to solve the problems in the above method, for example, it has been proposed to energize and heat near a mold (see Patent Document 3).
However, there are two major problems when electrically heating a thin plate. One of them is that the thin sheet material expands due to heating, and the thin sheet material hangs down, sparks when it comes into contact with the mold, and the hanging material to be heated comes into unstable contact with the electrode to generate sparks. Another problem is that since the material to be heated is thin near the electrode, heat is taken away by the electrode, causing a large temperature deviation in the thin plate, causing thermal stress and causing the electrode to extend in the width direction of the thin plate. The restraint causes wrinkles near the electrodes and deformation of the thin plate.
[0009]
Regarding the former problem, it has been proposed to stretch the thin plate material by applying tension between the electrodes (see Patent Literature 3 and Patent Literature 4). Regarding the latter problem near the electrode, a spherical material having a radius of 20 mm or less is proposed. There has been proposed a method of increasing the temperature in the vicinity of an electrode by energizing the electrode (see Patent Document 5).
[0010]
[Patent Document 3]
JP 2002-18531 A [Patent Document 4]
JP-A-53-109808 [Patent Document 5]
JP 2002-18531 A
[Problems to be solved by the invention]
However, with regard to the former extension of the heated thin plate material, even if tension is applied between the electrodes, the thickness is small, so the expansion in the thickness direction can be ignored, but the thermal expansion is uniform not only in the direction between the electrodes but also in a plane. Therefore, applying tension only in the direction between the electrodes does not solve the problem of preventing wrinkles.
[0012]
It is also difficult to solve the latter problem near the electrode. In other words, even with a small electrode, the contact area of the electrode is small, and the current density is high in the vicinity of the electrode, so that the temperature of the thin plate material easily rises. In addition, since the electrode is a sphere, there arises a problem that a thin plate material extended by heating comes into unstable contact with the electrode surface to easily cause a spark. Further, it is impossible to prevent the deformation of the thin plate material due to restraining the electrode from trying to spread in the width direction.
An object of the present invention is to solve the above problems and to provide an electrode capable of heating a thin metal sheet without deformation or temperature deviation.
[0013]
[Means for Solving the Problems]
The gist of the present invention is as follows.
(1) A pair of clamp electrodes capable of sandwiching a thin metal plate are installed facing each other via a power supply, the opposed electrodes are installed in two or more lines in parallel, and each electrode is movable in any direction. A heating electrode for a metal sheet.
(2) An electrode member characterized in that at least a surface that comes into contact with an object to be heated is made of a material larger than an electric resistance of an electrode base material.
(3) An electrode member comprising a plurality of layers provided so that the electric resistance increases in order from the electrode base material to the surface in contact with the object to be heated.
(4) Using the electrode member according to (2) or (3), a pair of clamp electrodes capable of sandwiching a metal thin plate as an object to be heated are installed facing each other via a power supply, and are opposed to each other. A heating electrode for a metal sheet, wherein two or more electrodes are arranged in parallel and each electrode is movable in an arbitrary direction.
(5) Using the metal sheet heating electrode according to (1) or (4), the metal sheet is heated while being energized while being sandwiched, thereby absorbing wrinkles and elongation due to thermal expansion of the metal sheet caused by heating. A metal sheet heating method, wherein each electrode is moved as described above.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram illustrating a change in a metal sheet material before and after heating. The metal sheet material is usually a steel sheet, but may be another metal such as aluminum. When the thin sheet material ABCD shown by the dotted line in FIG. 1 is heated and freely expanded on a flat surface without restriction, the metal sheet material (hereinafter referred to as a thin sheet material) becomes like a thin line A′B′C′D ′. Try to spread. However, since the electrodes restrain the sheet material at both ends, the extension due to thermal expansion in the direction between the electrodes tends to absorb the generation of stress by dropping downward due to gravity when heating the sheet material horizontally. .
[0015]
On the other hand, the extension in the width direction can freely extend in the vicinity of the center of the plate, but cannot extend because both ends are restrained by the electrodes, causing wrinkles, resulting in a shape like a solid line AEFBCGHD in the figure. Try to. Since the electrode is usually cooled, thermal stress is also applied between the heated thin plate material and the electrode portion, and the electrode easily buckles and deforms both ends of the thin plate material. Such a deformation becomes a serious defect when the sheet material is pressed after heating.
[0016]
Therefore, an electrode for minimizing the temperature deviation in the plate without causing such deformation was studied. First, regarding the thermal expansion caused by heating, the extension in the direction between the electrodes as in the past can be eliminated by moving the electrodes so as to apply tension in the direction between the electrodes, but this alone is insufficient and the extension in the width direction is also considered. Must. For this reason, in the present invention, a clamp electrode is used in which a thin plate is sandwiched between the electrodes, and the electrode can move not only in the direction between the electrodes but also in the width direction in accordance with thermal expansion.
[0017]
2 and 3, the electrode according to the present invention will be described. FIG. 2 is a schematic diagram illustrating the operation of the electrode according to the present invention, and FIG. 3 is a schematic diagram illustrating an example of the electrode structure according to the present invention. The thin plate 1 which is a material to be heated is opposed to one of the electrodes 2 and 2 ′ connected to the power source 4 by the conductive member 5 and the current distributor 6, and is also connected to the power source 4 by the conductive member 5 and the current distributor 7. Joule heating is performed by passing an electric current between the other electrodes 3 and 3 ′.
[0018]
As described above, when the ABCD before heating of FIG. 1 is heated, the thin plate 1 tends to become A′B′C′D ′. Since the conventional electrode has a structure in which the width of the sheet is constrained, the sides AD and BC are constrained. However, in FIG. Since current is applied by clamping, the thin plate 1 is restricted only at these four corner electrodes, and the other members are free to expand. When the thin plate 1 expands, the thin plate 1 tends to hang, so that the electrode 2 is moved in the direction from A to A 'in FIG. 1, the electrode 2' is moved in the direction from D to D 'in FIG. 1, and the electrode 3 is moved from B to B in FIG. When the electrode 3 ′ is moved in the direction of ′ in the direction of C ′ from FIG. 1, the thin plate 1 can be heated without sagging and without wrinkling.
[0019]
As the electrode structure, for example, as shown in FIG. 3, the pressing and opening by the electrode of the thin plate 1 is performed by providing a pressing mechanism such as an electric cylinder, a hydraulic cylinder, or an air cylinder inside the electrode support mechanism 8 '. Is connected to an arm 10 having upper and lower electrodes 2 'at the ends, and the cylinder of the pressure-lowering mechanism is moved. The electrode 2 'is joined to the arm 10 by an insulating plate and an insulating bolt, and is electrically insulated from the pressing-down mechanism.
[0020]
As for the material of the electrode, it is desirable that the material of the surface in contact with the thin plate is formed by spraying ceramics or cermet which is not easily welded and hardly oxidized.The inner material has low electric resistance to suppress heat generation due to electric current, and the relative magnetic permeability It is desirable to use copper or a copper alloy having a small diameter. It is also necessary to prevent the entire electrode from generating heat due to water cooling or the like.
[0021]
As means for moving the entire electrode, for example, in FIG. 3, a base 13 is fixed to a base, and motors 11 and 12 for moving the entire electrode supporting mechanism 8 'in the longitudinal direction and the plate width direction are provided thereon. Good. The amount of movement of the electrode may be calculated by calculating the amount of thermal expansion according to the temperature of the thin plate 1 and moving it in accordance with the calculated value, or by measuring the torque so that the thin plate does not undergo plastic deformation according to the temperature of the thin plate. It may be a method of moving while moving.
[0022]
In this example, an example in which the electrodes are moved using a motor has been described, but a hydraulic cylinder or an air cylinder may be used.
[0023]
The above is extremely effective when the amount of flowing current is relatively small and heat generation near the electrodes is not a problem. However, when the amount of flowing current is large, the current density near the electrodes is high for two electrodes on one side and the heat generation is high. May be a problem. In such a case, the connection to the power supply is omitted because it becomes complicated, but the electrodes are divided into a plurality (2, 2 ', 3, 3', 14 to 19) as shown in FIG. If it can be freely moved as described above, thermal expansion can be absorbed.
Here, reference numerals 20 to 25 in the figure denote electrode support mechanisms.
[0024]
In this case, the number of electrodes on one side may be either an even number or an odd number, but the movement of the electrodes is slightly different between the even number and the odd number. Specifically, in the case of an odd number, the electrode placed in the center of the plate width should be pulled only in the direction between the electrodes, and the electrodes on both sides of the electrode placed in the center should have a width corresponding to the extension of the thin plate. In the case of an even number of pieces, similarly, the sheet may be pulled obliquely in the extending direction of the thin plate across the center of the sheet width. Is desirable.
[0025]
Next, a method of preventing deformation of a thin plate due to heat removal from the thin plate by an electrode will be described.
Since the thin plate has a small thickness, heat is easily removed from the electrode, and a temperature deviation is likely to occur. In many cases, a temperature deviation occurs, and if the electrode is restricted, the electrode easily deforms and buckles in many cases. In order to prevent heat removal from the electrode, the temperature of the electrode surface in contact with the thin plate should be close to the temperature of the heated thin plate. In order to increase the electrode surface temperature, in the present invention, the electrode base material 26 (for example, copper or the like) having a small resistance is cooled by water-cooled copper pipes 31 and 32 brazed to an electrode folder 33 as shown in FIG. A layer 30 of a material having a large resistance (for example, nichrome) is provided on the electrode surface, and a current flowing from the electrode to the thin plate causes the electrode surface to generate heat. Thus, the temperature deviation between the thin plate and the electrode can be reduced or eliminated.
[0026]
In this case, it is often preferable to provide a plurality of layers (layers 27, 28, and 29 in this example) so that the resistance from the base material to the surface portion gradually increases. That is, since a material having a large resistance generally has a property that the thermal conductivity is small and the coefficient of thermal expansion is large, it is possible to avoid a trouble such as delamination due to a difference in thermal expansion by giving a slope of the property value. That's why.
[0027]
In the method of providing the barrier layer, thermal spraying is easy to apply, and physical property values can be easily changed. In addition, plating and shrink fit are also effective. In this way, by heating the electrode surface, the amount of heat transfer from the heated thin plate to the electrode is reduced, so that the temperature deviation in the thin plate is naturally reduced, so that thermal stress is less likely to occur, and buckling occurs. Occurrence can be prevented.
[0028]
【Example】
The effect of the present invention was confirmed by experiments. The experiment was conducted by heating a cold-rolled steel sheet having a thickness of 0.18 mm, a width of 300 mm, and a length of 600 mm from room temperature to 800 ° C., and examining the deformation of the steel sheet during heating and the deformation state of the steel sheet after heating, with the electrode according to the present invention. As a comparative example, comparison was made for a case where a fixed electrode was used.
[0029]
The electrode according to the present invention is configured such that the entire electrode can be moved in any direction by an air cylinder on a linear guide so as to be movable in the longitudinal direction and the width direction of the steel sheet, and the steel plate is also clamped by the air cylinder. . The electrode used was a water-cooled copper base metal electrode (50 mm wide, 40 mm deep) sprayed with 250 μm of nickel chrome cermet of chromium carbide on each side, using two pieces on one side, and moving in the width direction and longitudinal direction according to the heating. In the case where three electrodes on one side are used (Example 1), and the electrodes are moved in the width direction and the longitudinal direction in accordance with the heating (Example 2), 1 mm of nichrome is applied to the electrode surface by wire spraying, and three electrodes are used on one side. When the electrode was moved in accordance with the heating in the width direction and the longitudinal direction using the electrode (Example 3), and when a water-cooled copper electrode having a width of 400 mm was used as the comparative example and the electrode was fixed (Comparative Example 1), the comparative example Comparison was made in the case where the electrode was moved in the longitudinal direction while performing the same operation as in Example 1 (Comparative Example 2). The power supply used was a 50 V / 8000 A thyristor control panel.
[0030]
Table 1 shows the results. In Example 1 according to the present invention, the electrodes were arranged at the four corners at both ends of the steel plate, and the electrodes were moved so as to pull the four corners. Therefore, the current density increased near the electrodes, and only the electrode portions became slightly hot. However, the steel sheet tried to keep its flat surface, and no defect in the shape of the steel sheet was observed during and after heating.
[0031]
In Example 2, since the current density near the electrodes was high in Example 1, one electrode was added at the center in the width direction to reduce the current density, and the number of electrodes was set to three. The center electrode was moved so as to be pulled in the longitudinal direction while moving both in the longitudinal width direction, but at a level that is extremely small and has no practical problem, small wrinkles near the center electrode occurred during heating, Although slight wrinkles remained after cooling, the temperature deviation in the vicinity of the electrode was alleviated and 80 ° C. was reduced to 40 ° C.
[0032]
In the third embodiment, the electrodes are arranged and moved in the same manner as in the second embodiment, and only the electrodes are made of a material having a high resistance. In addition, the temperature deviation was extremely small.
[0033]
On the other hand, in Comparative Example 1 heated by the conventional fixed electrode, large wrinkles and sagging occurred in the steel sheet, and the wrinkles remained after cooling as they were. In Comparative Example 2, in which the steel plate was pulled between the electrodes proposed to absorb the elongation due to thermal expansion, the sagging was eliminated and the width of the wrinkles was slightly improved, but large wrinkles remained.
Thus, the use of the electrode of the present invention made it possible to heat a thin plate of good quality.
[0034]
[Table 1]

[0035]
【The invention's effect】
The use of the electrode of the present invention enables high-quality heating without causing shape defects, even when heating a thin plate that easily deteriorates in shape. If the thin plate is heated by electricity using electrodes, it can be pressed in a state where the temperature deviation is small and there is no variation in strength, so that it is possible to manufacture a product with high accuracy, and to improve productivity without lowering the yield. Can be.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating static heating of a thin plate.
FIG. 2 is a schematic plan view showing an example of using two freely movable electrodes according to the present invention.
FIG. 3 is a schematic sectional view illustrating a structural example of an electrode according to the present invention.
FIG. 4 is a schematic plan view showing an example of using a plurality of freely movable electrodes according to the present invention.
FIG. 5 is a schematic sectional view illustrating an electrode structure according to the present invention.
[Explanation of symbols]
1: Thin plates 2, 2 ': Electrodes 3, 3': Electrodes 4: Power supply 5: Conductive member 6: Current distributor 7: Current distributors 8, 8 ': Electrode support mechanisms 9, 9': Electrode support mechanisms 10: Arm 11: Motor 12: Motor 13: Base 14: Electrode 15: Electrode 16: Electrode 17: Electrode 18: Electrode 19: Electrode 20: Electrode support mechanism 21: Electrode support mechanism 22: Electrode support mechanism 23: Electrode support mechanism 24: Electrode support mechanism 25: Electrode support mechanism 26: Electrode base material 27: High resistance layer 28: High resistance layer 29: High resistance layer 30: Surface high resistance layer 31: Water cooling pipe 32: Water cooling pipe 33: Electrode folder

Claims (5)

金属薄板を挟持可能な一対のクランプ電極が、電源を介して対向して設置され、該対向する電極が並列に２系列以上設置され、さらに各電極が任意の方向に可動自在としてなることを特徴とする金属薄板用加熱電極。A pair of clamp electrodes capable of sandwiching a metal thin plate are installed facing each other via a power supply, the opposed electrodes are installed in two or more lines in parallel, and each electrode is movable in any direction. Heating electrode for metal sheet. 少なくとも被加熱物と接触する面が、電極母材の電気抵抗より大きな材質からなることを特徴とする電極部材。An electrode member characterized in that at least a surface in contact with an object to be heated is made of a material larger than an electric resistance of an electrode base material. 電極母材から被加熱物と接触する面まで、順に電気抵抗が大きくなる様に複数の層を設けたことを特徴とする電極部材。An electrode member, comprising a plurality of layers provided so as to sequentially increase electric resistance from an electrode base material to a surface in contact with an object to be heated. 請求項２または３に記載の電極部材を用い、被加熱物である金属薄板を挟持可能とする一対のクランプ電極が、電源を介して対向して設置され、該対向する電極が並列に２系列以上設置され、さらに各電極が任意の方向に可動自在であることを特徴とする金属薄板用静止加熱電極。A pair of clamp electrodes capable of sandwiching a thin metal plate to be heated by using the electrode member according to claim 2 or 3 are installed facing each other via a power supply, and the opposed electrodes are arranged in two lines in parallel. A stationary heating electrode for a thin metal plate, which is installed as described above, and wherein each electrode is movable in an arbitrary direction. 請求項１または４に記載の金属薄板用加熱電極を用いて、金属薄板を挟持しながら通電して加熱し、加熱に伴う金属薄板の熱膨張によるしわや延びを吸収する様に各電極を移動させることを特徴とする金属薄板加熱方法。Using the heating electrode for a metal sheet according to claim 1, the metal sheet is heated while being energized while sandwiching the metal sheet, and each electrode is moved so as to absorb wrinkles and extensions due to thermal expansion of the metal sheet accompanying the heating. A method for heating a thin metal plate.

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