JP3758745B2

JP3758745B2 - Air intrusion prevention device for sealed atmosphere heat treatment furnace

Info

Publication number: JP3758745B2
Application number: JP14951296A
Authority: JP
Inventors: 通田中
Original assignee: Nippon Sanso Holdings Corp
Current assignee: Nippon Sanso Holdings Corp
Priority date: 1996-06-11
Filing date: 1996-06-11
Publication date: 2006-03-22
Anticipated expiration: 2016-06-11
Also published as: JPH102681A

Description

【０００１】
【発明の属する技術分野】
本発明は、各種金属を高温で加熱処理する熱処理炉に関し、詳しくは空気以外の特殊な雰囲気ガス中で行われる密閉式雰囲気熱処理炉への空気の侵入を防止する装置に関するものである。
【０００２】
【従来の技術】
従来、各種金属品の熱処理の際、金属表面及びその近傍に強度や硬度または光輝性等の品質が要求される場合は、密閉式雰囲気熱処理炉を用いて空気以外の特殊な雰囲気ガス中で行われるのが一般的である。密閉式雰囲気熱処理炉内の圧力はほぼ大気圧に近く、大気と雰囲気ガスを遮断する扉等の密閉手段を有している。この密閉式雰囲気熱処理炉としては、密閉式バッチ炉や連続式トレープッシャー炉等が挙げられる。
特殊な雰囲気ガスとしては、吸熱性変成ガス（ＲＸガス）、発熱性変成ガス（ＤＸガス）、アンモニア分解ガス（ＡＸガス）等が広く使用されてきている。これら雰囲気ガスは、水素ガスや一酸化炭素ガス等の爆発可燃性ガスを含んでおり、その雰囲気発生には密閉式雰囲気熱処理炉とは別に設置された変成炉や分解炉を必要とする。例えばＲＸ変成炉では、メタン、プロパン、ブタン等の炭化水素ガスと空気を一定比率にして変成炉中の高温触媒に通してＲＸガスを発生させている。
【０００３】
図２は従来の二室式の密閉式雰囲気熱処理炉として密閉式浸炭焼き入れ炉の概略図を示す。この密閉式浸炭焼き入れ炉３０は、前扉１、前室２、中間扉３、加熱室４、油槽５とを主要な要素として備え、該油槽５の上部空間が前室２を構成している。中間扉３には、加熱室４と前室２を連通する雰囲気ガス通過用の開口穴３ａを有し、加熱室４内は電気ヒーターやガス燃焼式ラジアントチューブ等で高温に加熱される。また、油槽５内の焼き入れ用の油も５０〜１５０℃に加熱されていることが多い。
雰囲気ガスは図示略の雰囲気ガス供給源から、雰囲気ガス用配管６を通って加熱室４内に供給されファン７により撹拌される。これにより雰囲気ガスが加熱室内の温度と均一になり、被処理品８の雰囲気としての役割を果たす。
この雰囲気ガスは中間扉３の開口穴３ａを通って前室２に連続的に流れ、排気管９より炉外に排出され、排出されたガスはパイロットバーナ１０により燃焼され、排気ダクト１１により屋外に放出される。なお搬入テーブル１２上の被処理品８は搬入プッシャー等の搬入機構により前室２に搬入される。また前室２の被処理品８は搬出プーラー等の搬出機構により前室２から搬入テーブル１２に搬出される。また前扉１が開いたときフレームカーテン用ノズル１３に燃焼ガスが流れて燃焼し、前室２と外気との開口部を塞ぐようにフレームカーテンを構成し、炉内への空気の侵入を防げるようになっている。
【０００４】
このような密閉式浸炭焼き入れ炉３０にあっては、炉内の被処理品８の移動に伴い、炉内に圧力変動が生じる。この炉内の圧力変動について、図２を更に簡略化した図３を用いて被処理品８の動きとともに説明する。密閉式浸炭焼き入れバッチ処理は、搬入→昇温→浸炭→拡散→降温→均熱→油焼き入れ→油切り→搬出といった多くの工程を経て処理される。
【０００５】
「▲１▼搬入前」は、被処理品８はバスケット等に入れられ、搬入テーブル１２に置かれる。炉内は雰囲気ガスの連続的な供給により大気圧に対して５〜３０ｍｍＡｑの微正圧を保っている。その後、前扉１が開いてフレームカーテンが燃焼し、被処理品８は搬入プッシャー等により搬入テーブルから「▲２▼前室に搬送」されて前扉１が閉じ、炉内は密閉状態になる。そして搬入時のフレームカーテンの燃焼熱により加熱膨張された前室２内の雰囲気ガスは室温状態の被処理品８により収縮して弱負圧となる。炉内が負圧になると排気管９や前扉１の隙間から、周囲の空気が炉内に侵入してくる。
【０００６】
次に前扉１を小さく開き中間扉３を開いて、搬入プッシャー等により被処理品８を「▲３▼加熱室内に搬入」する。この時フレームカーテンは形成されない。その後中間扉３と前扉１を閉じて、再度密閉状態にする。この時も低温状態の被処理品８により加熱室４内の雰囲気ガスが収縮して、炉内は負圧になる。ただし、フレームカーテンによる加熱がないため負圧の程度は低く、一般的に弱い負圧にとどまる。
【０００７】
加熱室４内で被処理品８は高温に加熱されるが、昇温→浸炭→拡散→降温→均熱の一連の処理が終了すると、中間扉が開いて搬出プッシャー等により被処理品８は前室２に戻される（「▲４▼前室への搬出」）。この時高温状態の被処理品８により前室２の雰囲気ガスが加熱膨張して、炉内圧力は５０ｍｍＡｑを越える正圧となる。この時、前室２内の温度も急上昇する。そして中間扉３が閉じられる。
【０００８】
続いてエレベータ等により被処理品８は油槽５内に浸漬されて、「▲５▼油槽焼き入れ」される。被処理品８が油槽５内に浸漬されることにより、被処理品８が有する熱が油槽５内の油に奪われる。これにより、前室２の雰囲気ガスの温度は低下し、前室２の雰囲気ガスは急速に収縮し、−５００ｍｍＡｑ以下の強い負圧となって、前室内に周囲の空気が侵入してくる。しばらくしてエレベータが上昇し、被処理品８は油槽５から引き上げられて前室２内に放置され、「▲６▼油切り」が行われる。以上の▲１▼〜▲６▼の間は、前扉１は閉止状態のままである。
【０００９】
油切りが終わると前扉１が開いてフレームカーテンが燃え、搬出プーラー等により搬入テーブル１２上に被処理品８が搬出され前扉１が閉じる。この後フレームカーテンにより加熱膨張された前室ガスが収縮して負圧となる（▲７▼搬出後）。
【００１０】
このような密閉式浸炭焼き入れバッチ炉３０の炉内に空気が侵入する機会としては、前扉１の解放時と炉内圧力が負圧時の２つが挙げられる。雰囲気ガスとしては、水素ガスや一酸化炭素ガス等の可燃性ガスが用いられるため、空気が有する酸素との混合による爆発の防止対策を講じる必要があり、密閉炉内への空気の侵入を極力少なくする必要がある。一般的に炉内酸素濃度が１％以下であれば、可燃性ガスの爆発に対して安全である。したがって、密閉式浸炭焼き入れバッチ炉３０の炉内への空気の侵入を防止するために、炉内に雰囲気ガスを流す必要があるが、雰囲気ガス量は短時間に変更できないため、空気の侵入に対応するため雰囲気ガスを最大量流し続けているのが現状である。
【００１１】
以上は二室式の密閉式浸炭焼き入れバッチ炉の従来技術について説明したが、トレープッシャー式連続炉の場合は二室式構造と異なり、後室が存在する。トレープッシャー式連続炉の場合、図３における「▲４▼前室への搬出」工程以降は前室を後室と呼びかえれば、炉内圧力変化等は二室式の密閉浸炭焼き入れバッチ炉の説明とほぼ同じになる。
【００１２】
【発明が解決しようとする課題】
前述した密閉式浸炭焼き入れバッチ炉３０への空気の侵入を防止する方法として、前扉１の解放信号に合わせて前室２に窒素ガス等の不活性ガスを流すスーパーパージと称される方法がある。また、特公平６−４７７１４号公報に開示されているように炉内の負圧時に排気管９からパイロットバーナ１０の燃焼ガスを逆流させたり、別途設置されたバーナの燃焼ガスを炉内に逆流させる方法がある。
【００１３】
しかしながら、特公平６−４７７１４号は、炉内が負圧時の必要な時だけバーナを燃焼させて炉内に燃焼ガスを供給する方法であるが、バーナの未着火や消炎の不安を解消することは本質的に困難である。
【００１４】
一方近年、窒素ベース熱処理法が普及してきている。この方法は窒素ガスをベースにメタノール、水素ガス、炭化水素ガス等を混合添加し、雰囲気ガスとして直接炉内に送入するものである。この窒素ベース熱処理法は変成炉や分解炉を必要としないため、雰囲気ガスの流量変更が容易という特徴を有している。またこの方法では窒素ガスを使用しているため、前記スーパーパージを実行しやすいという特徴を有している。
【００１５】
スーパーパージを採用している例としては、特開昭６１−１４７８６７号公報、特開平２−１５６０６４号公報を挙げることができる。このスーパーパージ法により、前扉１の解放時の空気侵入はかなり低減できる。また、炉内負圧時の空気侵入防止法として、従来は、前扉１が閉じた後、タイマーを利用して一定時間窒素ガス等のパージガスを流す方法が採られている。しかしこの方法だけでは、後述する実施例にあるように炉内酸素濃度を１％以下に維持することは困難である。また、炉内負圧を検知して負圧時にパージガスを流す方法が提案されている。例えば実公平２−３２６８２号公報は、前室２内の圧力を圧力計で検知して負圧時に電磁弁を開いて窒素ガスを油槽上部に吹き込む方法を採用している。しかしながら、雰囲気ガス量を削減した場合、この方法だけで炉内酸素濃度を１％以下にすることは難しく、また、電気的制御を採用しているため停電時や電気的故障時の作動に不安が残り、安全性が高いとは言い難い。
【００１６】
また、特開平３−１８０４５９号公報では、炉内の負圧時に窒素ガス送入に加え、前扉１の開時及び前室２の酸素濃度増加時に窒素ガスの送入とメタノールの増量送入を行う方法を提案している。この方法は３重の窒素送入システムであり安全性はかなり高くなるが、設備コストが嵩む不都合がある。
【００１７】
本発明は前記事情に鑑みてなされたもので、密閉式雰囲気ガス処理炉の炉内への空気の侵入を少なくして可燃性ガスの爆発の危険を少なくして安全性を高め、しかも空気侵入を防ぐ安全設備を低コストで提供することを課題としている。
【００１８】
【課題を解決するための手段】
本発明の請求項１に係る発明は、被処理品を高温で加熱処理する加熱室と、被処理品を加熱室に送り出す前室とを有し、該加熱室に雰囲気ガスを供給する供給ラインが接続され、該前室を扉により開閉する開閉手段を有する密閉式雰囲気熱処理炉の空気侵入防止装置であって、前記前室に、前記扉の開時に該扉の開信号により不活性ガスを送入するスーパーパージラインと、該扉の閉時に炉内が負圧時にのみガバナを介して不活性ガスを該炉内圧力が大気圧と等しくなるように該前室に送入するガバナラインを接続配置したことを特徴とする密閉式雰囲気熱処理炉の空気侵入防止装置である。
【００１９】
【発明の実施の形態】
図１は、本発明の密閉式雰囲気熱処理炉の空気侵入防止装置の概略図であり、従来例の説明で用いた汎用的な密閉式浸炭焼き入れバッチ炉に適用した場合を例示するものであって、この図１中の符号１から１３で示される同一の構成要素には同一符号を付してその説明を省略する。
この空気侵入防止装置４０は、密閉式浸炭焼き入れバッチ炉３０の前扉１の開時に該前扉１の開信号により不活性ガスを送入するスーパーパージラインＡと、該前扉１の閉時に炉内が負圧時にのみガバナ２２を介して不活性ガスを該炉内圧力が大気圧と等しくなるように前室２に送入するガバナラインＢとを備えて構成されている。
【００２０】
前記スーパーパージラインＡは、窒素、二酸化炭素、アルゴンなどの不活性ガスを貯留する不活性ガス容器１４に一端を接続し、フィルタ１５、一次減圧弁１６、圧力スイッチ１７を介して前室２に接続される不活性ガス供給ラインをなしており、前記圧力スイッチ１７の下流側に、流量スイッチ１８、流量調整弁１９、電磁弁２０を順に介して前室２に接続されている。
【００２１】
前記ガバナラインＢは、スーパーパージラインＡの圧力スイッチ１７配設位置と流量スイッチ１８配設位置との間に一端を接続し、他端はスーパーパージラインＡと合流して前室２に接続された分岐ラインである。このガバナラインＢの途中には、ガバナ２２が設けられている。このガバナ２２は、電気的な制御システムを全く使用せずに、機械的な圧力制御によって二次側（炉内）の負圧を補償するように一次側のガスを送給可能なものが好適に使用される。この種のガバナ２２としては市販の各種のガバナ装置のうちから選択して使用することができ、例えば伊藤工機（株）製のガバナなどが使用される。この種のガバナ２２によれば、ガバナ２２の作動圧力調整によって炉内が負圧時にのみガバナ２２のガス流路が開となり、不活性ガスを送入するように調整しておくことにより、数ｍｍＡｑ単位でガバナ２２の二次圧力の設定値を正確に決めることが可能である。これにより、炉内圧力が大気圧以上（０ｍｍＡｑ以上）の時はガバナ２２から不活性ガスが流れることはなく、不活性ガスの無駄な使用を抑えるための別段の操作は必要としない。
【００２２】
不活性ガス容器１４からの不活性ガスは、フィルター１４（またはストレーナ）を通り、一次減圧弁１６で減圧される。この一次減圧弁１６の二次圧は、その下流側のガバナ２２の一次圧力に適合する圧力（通常3500mmAq以下）に減圧調整される。また該一次圧力弁１６の下流側には圧力スイッチ１７が設けられている。この圧力スイッチ１７は一次側から二次側に不活性ガスが供給されていることを検知するとともに、一次減圧弁１６の二次圧を検知して、設定圧以上であれば警報等の認識手段を作動させるためのものである。
圧力スイッチ１７の下流側で該不活性ガス流路は、流路Ａと流路Ｂの２つの流路に分岐されている。一方の流路Ａは、流量スイッチ１８、流量調節弁１９、電磁弁２０を介して密閉式浸炭焼き入れバッチ炉３０の前室２に接続されている。この流路Ａに用いられる機器類は、前扉１の解放信号に合わせて前室２内に窒素ガス等の不活性ガスを流すために設けられたもので、従来のスーパーパージの方法において用いられるものとほぼ同じである。この流路Ａを設けたことによって、図３における被処理品８の「▲２▼前室へ搬入」、「▲３▼加熱室への搬入」、「▲７▼搬出」の各工程では、前扉１を開にする開信号によって電磁弁２０が開き、流量調節弁１９によって流量が調節された不活性ガスが前室２に送入され、前扉１の開時に炉内への空気の侵入が抑制される。不活性ガスが流れると流量スイッチ１８がＯＮになり、不活性ガスが流れた信号を発する。この信号により、不活性ガスが流れない時は、炉３０の前扉１が開かないようにインターロックをかけて制御を行うことも可能である。
【００２３】
前扉１を閉じて前扉の開信号がＯＦＦになると、電磁弁２０が閉となる。この電磁弁２０は、通電時に閉となるノーマルオープン型のものが使用される。その使用によって、この電磁弁２０は停電時には自動的に開となり、前室２に不活性ガスが送入されるようになっており、安全性が高まる。なお、流量スイッチ１８、流量調節弁１９、電磁弁２０は、必ずしもこの順序に接続する必要はない。
また、炉内が負圧状態になった場合にのみ、他方の流路Ｂに設けられた低圧用の圧力調整器であるガバナ２２から不活性ガスが自動的に前室２に流れるようになっている。すなわち、ガバナ２２の作動圧力調整によって炉内が負圧時にのみガバナ２２のガス流路が開となり、不活性ガスを送入するように調整しておくことにより、数ｍｍＡｑ単位でガバナ２２の二次圧力の設定値を正確に決めることが可能である。これにより、炉内圧力が大気圧以上（０ｍｍＡｑ以上）の時はガバナ２２から不活性ガスが流れることはなく、不活性ガスの無駄な使用を抑えるための別段の操作は必要としない。しかも、このガバナ２２からの炉内への窒素ガスの送入は、電気的な制御システムを全く使用せずに行うことができる。このガバナ２２からの不活性ガスの送入により、負圧状態となった炉内への空気の侵入を防ぐことができ、炉内の酸素濃度を１％以下に維持することができる。
【００２４】
このように本発明では、スーパーパージライン（流路Ａ）と、ガバナライン（流路Ｂ）を併用したことによって、炉３０内への空気の侵入を効果的に防止でき、炉３０内の酸素濃度を１％以下に維持して一連の熱処理操作を実施することができる。
また、上記各ラインの併用によって、不活性ガスの有効利用ができ、不活性ガスの使用量を減少させることができる。
更に、ガバナ２２を用いたことによって初期調整の後は調整操作が不要であり、停電時や電気的故障が生じた際に安全である。
【００２５】
なお、図１においては、スーパーパージラインＡとガバナラインＢを合流させて前室２に接続しているが、これらのラインは合流させずに別個に前室２に接続させても良い。また不活性ガス配管の炉内への接続位置は特に限定されない。例えば、前室２と加熱室４の炉内圧力はほぼ同様に変化するので、ガバナラインＢを加熱室４に接続することも可能である。ただし、この場合には不活性ガス送入により加熱室４内の雰囲気ガスが多量に排出されるので、次の処理のための雰囲気形成に時間がかかり、本実施の形態における密閉式浸炭焼き入れバッチ炉ではガバナラインＢを前室２に接続することが好ましい。また、トレープッシャー炉では、ガバナラインを前室と後室の両方に接続することが好ましい。
【００２６】
【実施例】
図１の空気侵入防止装置４０を組み立てて、以下の試験を行った。ここで使用した密閉式浸炭炉の標準的雰囲気ガス量は、吸熱性変成ガス（ＲＸガス）で１０ｍ³／ｈである。
【００２７】
（実施例１）
雰囲気ガスとして窒素ガスのみを５ｍ³／ｈ加熱室に送入した。そしてダミー材にて前述の浸炭パターンを実行した。すなわちスーパーパージラインＡとガバナラインＢの両方を作動させて前室２への窒素ガスの供給を行った。なお、前室２の扉開時のスーパーパージガス量は１５ｍ³／ｈに設定した。スーパーパージが行われる時間は１処理中に１〜３分程度であり、実際に使用されるスーパーパージガス量はわずかである。この実施例１における前室２の炉内圧力と酸素濃度の測定を行った。その結果を表１に示す。表１における炉内圧力と酸素濃度は、各工程で測定された最大負圧と最高酸素濃度を記したものである。
【００２８】
（比較例１）
実施例１と同じ雰囲気ガス量５ｍ³／ｈの条件で、同様な処理を行った。ただし、スーパーパージラインＡとガバナラインＢの両方を作動させずに行った。すなわち前室２への窒素ガスの送入を全く行わなかった。その結果を表１に示す。
【００２９】
（比較例２）
実施例１と同じ雰囲気ガス量５ｍ³／ｈの条件で、同様な処理を行った。ただし、前室２への窒素ガスの送入を前扉１の開時にスーパーパージのみとし、ガバナ２２は強制的に作動させずに行った。その結果を表１に示す。
【００３０】
【表１】

【００３１】
以上の実施例１と比較例１，２において、雰囲気ガスとして窒素ガスのみを使用しているので、侵入した空気の酸素分はそのまま酸素濃度として測定されることにより高めの値となる。また、「▲２▼前室への搬入」と「▲３▼加熱室搬入」の間は、５〜１０分間と比較的短時間であるので、「▲２▼前室への搬入」工程で侵入した酸素が充分パージされず、「▲３▼加熱室搬入」工程での酸素濃度を高めている。実施例１と比較例１，２を比べると、前扉１の開時のスーパーパージのみでは、特に「▲５▼油槽焼き入れ」工程の空気の侵入防止にはほとんど役立たないことが分かる。そして、表１の実施例１に示したように、ガバナラインによる負圧制御を行うことにより、「▲５▼油槽焼き入れ」工程の酸素濃度は１％以下に劇的に減少することがわかる。
【００３２】
（実施例２）
窒素／メタノールを雰囲気ガスとして、５ｍ³／ｈを加熱室に送入した。そしてＳＣＭ４２０Ｈ鋼の浸炭部品にてスーパーパージラインＡとガバナラインＢを併用して浸炭処理を行った。なお、前室２の前扉１開時のスーパーパージガス量は、実施例１と同様に１５ｍ³／ｈに設定した。また、浸炭部品６個の平均浸炭深さとして、０．９１ｍｍが得られた。この実施例２における前室２の炉内圧力と酸素濃度の測定を行った。その結果を表２に示す。表２における炉内圧力と酸素濃度は、各工程で測定された最大負圧と最高酸素濃度を記したものである。
【００３３】
（比較例３）
実施例２と同じ雰囲気ガス量５ｍ³／ｈの条件で、同様な処理を行った。ただし、ガバナ２２は強制的に作動させずに行った。すなわち比較例２と同様に前室２への窒素ガスの送入を前扉１の開時におけるスーパーパージのみとした。その結果を表２に示す。
【００３４】
【表２】

【００３５】
表１と表２の比較により、窒素／メタノールの可燃性雰囲気では、前扉１の開時の炉内酸素は燃焼に費やされ、炉内酸素濃度はかなり低下する。また、ガバナ２２を作動させた実施例２により、炉内酸素濃度は全処理工程に亘って１％以下に維持され、安全である。
【００３６】
【発明の効果】
以上説明したように、本発明による密閉式雰囲気熱処理炉の空気侵入防止装置は、扉開時に炉内に不活性ガスを送入するスーパーパージラインと扉閉時の炉内負圧時に不活性ガスを炉内に送入するガバナラインを設けたものなので、全処理工程を通じて炉内酸素濃度を１％以下に維持でき、炉内に雰囲気ガスとしての可燃性ガスを送入しても爆発の危険がなく安全性を高めることができる。
【図面の簡単な説明】
【図１】図１は本発明による密閉式雰囲気熱処理炉の空気侵入防止装置の一形態を示す概略構成図である。
【図２】図２は従来の密閉式雰囲気熱処理炉を例示する概略構成図である。
【図３】図３は密閉式雰囲気熱処理炉を用いた被処理物の処理工程と圧力変動を説明する概略図である。
【符号の説明】
１……前扉、２……前室、４……加熱室、１４……不活性ガス容器、２２……ガバナ、３０……密閉式浸炭焼き入れ炉、４０……空気侵入防止装置、Ａ……スーパーパージライン、Ｂ……ガバナライン。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a heat treatment furnace that heat-treats various metals at a high temperature, and more particularly to an apparatus that prevents air from entering a closed atmosphere heat treatment furnace that is performed in a special atmosphere gas other than air.
[0002]
[Prior art]
Conventionally, when heat treatment of various metal products requires quality such as strength, hardness, or luster on the metal surface and its vicinity, it is performed in a special atmosphere gas other than air using a sealed atmosphere heat treatment furnace. It is common. The pressure in the closed atmosphere heat treatment furnace is close to atmospheric pressure, and has a sealing means such as a door for shutting off air and atmospheric gas. Examples of the closed atmosphere heat treatment furnace include a closed batch furnace and a continuous tray pusher furnace.
As the special atmosphere gas, endothermic modified gas (RX gas), exothermic modified gas (DX gas), ammonia decomposition gas (AX gas) and the like have been widely used. These atmospheric gases contain explosive flammable gases such as hydrogen gas and carbon monoxide gas, and in order to generate the atmosphere, a transformation furnace and a cracking furnace installed separately from the sealed atmosphere heat treatment furnace are required. For example, in an RX shift furnace, RX gas is generated by passing a hydrocarbon gas such as methane, propane, or butane and air at a constant ratio through a high-temperature catalyst in the shift furnace.
[0003]
FIG. 2 is a schematic view of a closed carburizing and quenching furnace as a conventional two-chamber closed-type atmosphere heat treatment furnace. The closed carburizing and quenching furnace 30 includes a front door 1, a front chamber 2, an intermediate door 3, a heating chamber 4, and an oil tank 5 as main elements, and the upper space of the oil tank 5 constitutes the front chamber 2. Yes. The intermediate door 3 has an opening 3a for passing atmospheric gas that connects the heating chamber 4 and the front chamber 2, and the inside of the heating chamber 4 is heated to a high temperature by an electric heater, a gas combustion type radiant tube or the like. Moreover, the oil for quenching in the oil tank 5 is often heated to 50 to 150 ° C.
The atmospheric gas is supplied from an atmospheric gas supply source (not shown) through the atmospheric gas pipe 6 into the heating chamber 4 and stirred by the fan 7. As a result, the atmospheric gas becomes uniform with the temperature in the heating chamber, and serves as an atmosphere of the article 8 to be processed.
This atmospheric gas continuously flows into the front chamber 2 through the opening hole 3a of the intermediate door 3 and is discharged out of the furnace through the exhaust pipe 9. The discharged gas is combusted by the pilot burner 10 and outdoors by the exhaust duct 11. To be released. The article 8 to be processed on the carry-in table 12 is carried into the front chamber 2 by a carry-in mechanism such as a carry-in pusher. Further, the article 8 to be processed in the front chamber 2 is unloaded from the front chamber 2 to the loading table 12 by a unloading mechanism such as a unloading puller. Further, when the front door 1 is opened, combustion gas flows into the frame curtain nozzle 13 and burns, and the frame curtain is configured so as to close the opening between the front chamber 2 and the outside air, thereby preventing air from entering the furnace. It is like that.
[0004]
In such a closed carburizing and quenching furnace 30, pressure fluctuations occur in the furnace as the article to be processed 8 moves in the furnace. The pressure fluctuation in the furnace will be described together with the movement of the workpiece 8 with reference to FIG. 3 which is a simplified version of FIG. The closed-type carburizing and quenching batch process is processed through a number of processes including carry-in → temperature rise → carburization → diffusion → temperature drop → temperature equalization → oil quenching → oil removal → carry-out.
[0005]
In “{circle around (1)]”, the article 8 to be processed is placed in a basket or the like and placed on the carry-in table 12. The inside of the furnace maintains a slight positive pressure of 5 to 30 mmAq with respect to atmospheric pressure by continuous supply of atmospheric gas. Thereafter, the front door 1 is opened and the frame curtain is combusted, and the article 8 to be processed is conveyed from the carry-in table by the carry-in pusher or the like “(2) Transported to the front chamber”, the front door 1 is closed, and the furnace is hermetically sealed. . Then, the atmospheric gas in the front chamber 2 heated and expanded by the combustion heat of the frame curtain at the time of carrying in is contracted by the article 8 to be processed at room temperature and becomes a weak negative pressure. When the pressure in the furnace becomes negative, ambient air enters the furnace through the gap between the exhaust pipe 9 and the front door 1.
[0006]
Next, the front door 1 is opened small, the intermediate door 3 is opened, and the article 8 to be processed is “carrying into the heating chamber” by a carry-in pusher or the like. At this time, the frame curtain is not formed. Thereafter, the intermediate door 3 and the front door 1 are closed and sealed again. Also at this time, the atmosphere gas in the heating chamber 4 is contracted by the article 8 to be processed at a low temperature, and the pressure in the furnace becomes negative. However, since there is no heating by the frame curtain, the degree of negative pressure is low, and generally it remains at a weak negative pressure.
[0007]
The article 8 to be processed is heated to a high temperature in the heating chamber 4, but when the series of processes of raising temperature → carburizing → diffusion → falling temperature → soaking is completed, the intermediate door is opened and the article 8 to be treated is removed by a carry-out pusher or the like. It is returned to the front chamber 2 (“(4) carrying out to the front chamber”). At this time, the atmosphere gas in the front chamber 2 is heated and expanded by the article 8 to be processed at a high temperature, and the pressure in the furnace becomes a positive pressure exceeding 50 mmAq. At this time, the temperature in the front chamber 2 also rises rapidly. Then, the intermediate door 3 is closed.
[0008]
Subsequently, the article to be treated 8 is immersed in the oil tank 5 by an elevator or the like, and “(5) oil tank quenching” is performed. By immersing the article to be treated 8 in the oil tank 5, the heat of the article to be treated 8 is taken away by the oil in the oil tank 5. As a result, the temperature of the atmospheric gas in the front chamber 2 is reduced, the atmospheric gas in the front chamber 2 is rapidly contracted, and a strong negative pressure of −500 mmAq or less is generated, so that ambient air enters the front chamber. After a while, the elevator rises, and the article 8 to be processed is pulled up from the oil tank 5 and left in the front chamber 2 to perform “(6) oil draining”. Between the above (1) to (6), the front door 1 remains closed.
[0009]
When the oil draining is finished, the front door 1 is opened, the frame curtain is burned, the article 8 to be processed is carried out onto the carry-in table 12 by a carry-out puller or the like, and the front door 1 is closed. Thereafter, the front chamber gas heated and expanded by the frame curtain contracts and becomes negative pressure (after 7).
[0010]
There are two opportunities for air to enter the furnace of such a closed type carburizing and quenching batch furnace 30 when the front door 1 is released and when the pressure in the furnace is negative. As the atmosphere gas, a flammable gas such as hydrogen gas or carbon monoxide gas is used, so it is necessary to take measures to prevent explosions due to mixing with oxygen in the air, and to prevent air from entering the sealed furnace as much as possible. There is a need to reduce it. Generally, if the in-furnace oxygen concentration is 1% or less, it is safe against explosion of combustible gas. Therefore, in order to prevent the intrusion of air into the furnace of the sealed carburizing and quenching batch furnace 30, it is necessary to flow the atmospheric gas into the furnace, but the amount of atmospheric gas cannot be changed in a short time, so that the intrusion of air The current situation is that the maximum amount of atmospheric gas is allowed to flow.
[0011]
The prior art of the two-chamber closed carburizing and quenching batch furnace has been described above, but in the case of the tray pusher type continuous furnace, unlike the two-chamber structure, there is a rear chamber. In the case of a tray pusher type continuous furnace, if the front chamber is called the rear chamber after the step “4) Carrying out to the front chamber” in FIG. 3, the pressure change in the furnace is a two-chamber closed carburizing and quenching batch furnace. It becomes almost the same as the explanation.
[0012]
[Problems to be solved by the invention]
As a method for preventing the intrusion of air into the above-described closed carburizing and quenching batch furnace 30, a method called super purge in which an inert gas such as nitrogen gas is allowed to flow in the front chamber 2 in accordance with the release signal of the front door 1. There is. Further, as disclosed in Japanese Patent Publication No. 6-47714, the combustion gas of the pilot burner 10 is caused to flow backward from the exhaust pipe 9 at the negative pressure in the furnace, or the combustion gas of a separately installed burner is caused to flow backward into the furnace. There is a way to make it.
[0013]
However, Japanese Patent Publication No. 6-47714 is a method in which the burner is burned and the combustion gas is supplied into the furnace only when the inside of the furnace is at a negative pressure, but the concern about unignition and extinguishing of the burner is eliminated. That is inherently difficult.
[0014]
On the other hand, a nitrogen-based heat treatment method has become widespread in recent years. In this method, methanol, hydrogen gas, hydrocarbon gas, or the like is mixed and added based on nitrogen gas, and is directly fed into the furnace as atmospheric gas. Since this nitrogen-based heat treatment method does not require a shift furnace or a cracking furnace, it has a feature that it is easy to change the flow rate of the atmospheric gas. Further, since this method uses nitrogen gas, it has a feature that the super purge is easily performed.
[0015]
Examples of employing the super purge include JP-A Nos. 61-147867 and 2-15664. By this super purge method, air intrusion when the front door 1 is released can be considerably reduced. Further, as a method for preventing air intrusion at the time of negative pressure in the furnace, conventionally, after the front door 1 is closed, a method of flowing a purge gas such as nitrogen gas for a predetermined time using a timer is employed. However, with this method alone, it is difficult to maintain the in-furnace oxygen concentration at 1% or less as in the examples described later. Further, a method for detecting a negative pressure in the furnace and flowing a purge gas at the negative pressure has been proposed. For example, Japanese Utility Model Publication No. 2-332682 employs a method in which the pressure in the front chamber 2 is detected by a pressure gauge and the electromagnetic valve is opened at the time of negative pressure to blow nitrogen gas into the upper part of the oil tank. However, when the amount of atmospheric gas is reduced, it is difficult to reduce the oxygen concentration in the furnace to 1% or less by this method alone, and since electric control is adopted, there is anxiety about the operation at the time of power failure or electrical failure. However, it is hard to say that safety is high.
[0016]
Further, in Japanese Patent Laid-Open No. 3-180459, in addition to nitrogen gas feeding at a negative pressure in the furnace, nitrogen gas feeding and methanol feeding in addition when the front door 1 is opened and the oxygen concentration in the front chamber 2 is increased. Proposes a way to do. This method is a triple nitrogen feed system, which is considerably safer, but has the disadvantage of increasing the equipment cost.
[0017]
The present invention has been made in view of the above circumstances, and reduces the intrusion of air into the furnace of a closed atmosphere gas processing furnace to reduce the risk of an explosion of combustible gas, and enhances safety. It is an issue to provide safety equipment at low cost.
[0018]
[Means for Solving the Problems]
The invention according to claim 1 of the present invention has a heating chamber for heat-treating the article to be treated at a high temperature, and a front chamber for sending the article to be treated to the heating chamber, and supplies an atmosphere gas to the heating chamber. And an air intrusion prevention device for a closed atmosphere heat treatment furnace having an opening / closing means for opening and closing the front chamber by a door, wherein an inert gas is supplied to the front chamber by an open signal of the door when the door is opened. A super-purge line for sending in and a governor line for sending inert gas into the front chamber through the governor only when the inside of the furnace is negative when the door is closed so that the pressure inside the furnace becomes equal to the atmospheric pressure. An air intrusion prevention device for a closed atmosphere heat treatment furnace, characterized in that it is connected and arranged.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic view of an air intrusion prevention apparatus for a sealed atmosphere heat treatment furnace according to the present invention, and illustrates a case where the apparatus is applied to a general-purpose sealed carburizing and quenching batch furnace used in the description of the conventional example. The same constituent elements shown by reference numerals 1 to 13 in FIG.
The air intrusion prevention device 40 includes a super purge line A for sending an inert gas in response to an opening signal of the front door 1 when the front door 1 of the sealed carburizing and quenching batch furnace 30 is opened, and closing of the front door 1. In some cases, a governor line B is provided for feeding an inert gas into the front chamber 2 through the governor 22 only when the pressure in the furnace is negative, so that the pressure in the furnace becomes equal to the atmospheric pressure.
[0020]
The super purge line A has one end connected to an inert gas container 14 that stores an inert gas such as nitrogen, carbon dioxide, and argon, and is connected to the front chamber 2 via a filter 15, a primary pressure reducing valve 16, and a pressure switch 17. An inert gas supply line to be connected is formed, and is connected to the front chamber 2 on the downstream side of the pressure switch 17 through a flow rate switch 18, a flow rate adjustment valve 19, and an electromagnetic valve 20 in this order.
[0021]
The governor line B has one end connected between the pressure switch 17 and the flow rate switch 18 on the super purge line A, and the other end joined to the super purge line A and connected to the front chamber 2. Branch line. In the middle of the governor line B, a governor 22 is provided. The governor 22 is preferably capable of supplying the gas on the primary side so as to compensate the negative pressure on the secondary side (inside the furnace) by mechanical pressure control without using any electrical control system. Used for. As this kind of governor 22, it can select and use from various commercially available governor apparatuses, for example, the governor by Ito Koki Co., Ltd. is used. According to this type of governor 22, by adjusting the operating pressure of the governor 22, the gas flow path of the governor 22 is opened only when the inside of the furnace is negative pressure, and by adjusting so that an inert gas is fed, It is possible to accurately determine the set value of the secondary pressure of the governor 22 in units of mmAq. Thereby, when the pressure in the furnace is equal to or higher than atmospheric pressure (0 mmAq or higher), the inert gas does not flow from the governor 22, and a separate operation for suppressing wasteful use of the inert gas is not required.
[0022]
The inert gas from the inert gas container 14 passes through the filter 14 (or strainer) and is depressurized by the primary pressure reducing valve 16. The secondary pressure of the primary pressure reducing valve 16 is adjusted to be reduced to a pressure (usually 3500 mmAq or less) that matches the primary pressure of the governor 22 on the downstream side. A pressure switch 17 is provided on the downstream side of the primary pressure valve 16. The pressure switch 17 detects that the inert gas is supplied from the primary side to the secondary side, and detects the secondary pressure of the primary pressure reducing valve 16 and recognizes an alarm or the like if the pressure is higher than the set pressure. It is for operating.
On the downstream side of the pressure switch 17, the inert gas flow path is branched into two flow paths, a flow path A and a flow path B. One flow path A is connected to the front chamber 2 of the sealed carburizing and quenching batch furnace 30 via a flow switch 18, a flow control valve 19, and a solenoid valve 20. The equipment used in the flow path A is provided for flowing an inert gas such as nitrogen gas in the front chamber 2 in accordance with the release signal of the front door 1, and is used in the conventional super purge method. Is almost the same as By providing this flow path A, in each step of “(2) Carrying into the front chamber”, “(3) Carrying into the heating chamber”, and “(7) Carrying out” of the article 8 in FIG. The electromagnetic valve 20 is opened by the opening signal for opening the front door 1, the inert gas whose flow rate is adjusted by the flow control valve 19 is sent into the front chamber 2, and the air into the furnace is opened when the front door 1 is opened. Intrusion is suppressed. When the inert gas flows, the flow switch 18 is turned ON, and a signal indicating that the inert gas has flowed is generated. By this signal, when the inert gas does not flow, it is possible to perform control by interlocking so that the front door 1 of the furnace 30 is not opened.
[0023]
When the front door 1 is closed and the opening signal of the front door is turned OFF, the solenoid valve 20 is closed. The solenoid valve 20 is a normally open type that closes when energized. Due to its use, the solenoid valve 20 is automatically opened at the time of a power failure, and an inert gas is fed into the front chamber 2, which increases safety. The flow rate switch 18, the flow rate adjustment valve 19, and the solenoid valve 20 do not necessarily need to be connected in this order.
Further, only when the inside of the furnace is in a negative pressure state, the inert gas automatically flows into the front chamber 2 from the governor 22 which is a pressure regulator for low pressure provided in the other flow path B. ing. That is, by adjusting the operating pressure of the governor 22, the gas flow path of the governor 22 is opened only when the pressure in the furnace is negative, and the inert gas is fed in, so that the governor 22 is adjusted in units of several mmAq. It is possible to accurately determine the set value of the secondary pressure. Thereby, when the pressure in the furnace is equal to or higher than atmospheric pressure (0 mmAq or higher), the inert gas does not flow from the governor 22, and a separate operation for suppressing wasteful use of the inert gas is not required. Moreover, the nitrogen gas can be fed from the governor 22 into the furnace without using any electrical control system. By feeding the inert gas from the governor 22, it is possible to prevent air from entering the furnace in a negative pressure state, and to maintain the oxygen concentration in the furnace at 1% or less.
[0024]
As described above, in the present invention, by using the super purge line (flow path A) and the governor line (flow path B) in combination, air can be effectively prevented from entering the furnace 30, and oxygen in the furnace 30 can be prevented. A series of heat treatment operations can be performed while maintaining the concentration at 1% or less.
In addition, the combined use of the above-mentioned lines makes it possible to effectively use the inert gas and reduce the amount of inert gas used.
Further, since the governor 22 is used, no adjustment operation is required after the initial adjustment, and it is safe at the time of a power failure or an electrical failure.
[0025]
In FIG. 1, the super purge line A and the governor line B are joined and connected to the front chamber 2, but these lines may be connected separately to the front chamber 2 without being joined. Further, the connection position of the inert gas pipe into the furnace is not particularly limited. For example, since the furnace pressures of the front chamber 2 and the heating chamber 4 change in substantially the same manner, the governor line B can be connected to the heating chamber 4. However, in this case, since the atmosphere gas in the heating chamber 4 is exhausted in a large amount by feeding the inert gas, it takes time to form the atmosphere for the next treatment, and the sealed carburizing and quenching in the present embodiment In the batch furnace, the governor line B is preferably connected to the front chamber 2. Further, in the tray pusher furnace, it is preferable to connect the governor line to both the front chamber and the rear chamber.
[0026]
【Example】
The air intrusion prevention device 40 of FIG. 1 was assembled and the following tests were performed. The standard atmospheric gas amount of the sealed carburizing furnace used here is 10 m ³ / h of endothermic metamorphic gas (RX gas).
[0027]
Example 1
Only nitrogen gas was fed into the 5 m ³ / h heating chamber as the atmospheric gas. And the above-mentioned carburizing pattern was performed with the dummy material. That is, both the super purge line A and the governor line B were operated to supply nitrogen gas to the front chamber 2. The amount of super purge gas when the door of the front chamber 2 was opened was set to 15 m ³ / h. The super purge is performed for about 1 to 3 minutes during one process, and the amount of super purge gas actually used is small. The in-furnace pressure and oxygen concentration of the front chamber 2 in Example 1 were measured. The results are shown in Table 1. The furnace pressure and oxygen concentration in Table 1 are the maximum negative pressure and maximum oxygen concentration measured in each step.
[0028]
(Comparative Example 1)
The same treatment was performed under the same atmospheric gas amount of 5 m ³ / h as in Example 1. However, the operation was performed without operating both the super purge line A and the governor line B. That is, no nitrogen gas was fed into the front chamber 2 at all. The results are shown in Table 1.
[0029]
(Comparative Example 2)
The same treatment was performed under the same atmospheric gas amount of 5 m ³ / h as in Example 1. However, nitrogen gas was fed into the front chamber 2 only when the front door 1 was opened, and only the super purge was performed, and the governor 22 was not forcedly operated. The results are shown in Table 1.
[0030]
[Table 1]

[0031]
In Example 1 and Comparative Examples 1 and 2 described above, since only nitrogen gas is used as the atmospheric gas, the oxygen content of the intruded air becomes a higher value by being directly measured as the oxygen concentration. Also, the time between “(2) Loading into the front chamber” and “(3) Loading into the heating chamber” is a relatively short time of 5 to 10 minutes. The invading oxygen is not sufficiently purged, and the oxygen concentration in the “(3) heating chamber loading” step is increased. Comparing Example 1 with Comparative Examples 1 and 2, it can be seen that only the super purge when the front door 1 is opened is hardly useful for preventing air intrusion particularly in the “(5) oil tank quenching” process. And as shown in Example 1 of Table 1, by performing negative pressure control by the governor line, it can be seen that the oxygen concentration in the “(5) oil tank quenching” step is dramatically reduced to 1% or less. .
[0032]
(Example 2)
Nitrogen / methanol was used as an atmospheric gas, and 5 m ³ / h was fed into the heating chamber. Then, carburizing treatment was performed using a super purge line A and a governor line B in combination with carburized parts of SCM420H steel. The amount of super purge gas when the front door 1 of the front chamber 2 was opened was set to 15 m ³ / h as in the first embodiment. Moreover, 0.91 mm was obtained as an average carburizing depth of six carburized parts. The pressure in the furnace and the oxygen concentration in the front chamber 2 in Example 2 were measured. The results are shown in Table 2. The furnace pressure and oxygen concentration in Table 2 describe the maximum negative pressure and the maximum oxygen concentration measured in each step.
[0033]
(Comparative Example 3)
The same treatment was performed under the same atmospheric gas amount of 5 m ³ / h as in Example 2. However, the governor 22 was not operated forcibly. That is, as in Comparative Example 2, the nitrogen gas was fed into the front chamber 2 only by super purge when the front door 1 was opened. The results are shown in Table 2.
[0034]
[Table 2]

[0035]
According to the comparison between Table 1 and Table 2, in the flammable atmosphere of nitrogen / methanol, the oxygen in the furnace when the front door 1 is opened is consumed for combustion, and the oxygen concentration in the furnace is considerably reduced. Further, according to Example 2 in which the governor 22 was operated, the in-furnace oxygen concentration was maintained at 1% or less throughout the entire treatment process, which is safe.
[0036]
【The invention's effect】
As described above, the air intrusion prevention apparatus for a closed atmosphere heat treatment furnace according to the present invention includes the super purge line that feeds the inert gas into the furnace when the door is open and the inert gas when the pressure is negative in the furnace when the door is closed. Because it has a governor line to feed the gas into the furnace, the oxygen concentration in the furnace can be maintained at 1% or less throughout the entire treatment process, and there is a risk of explosion even if combustible gas is sent into the furnace as atmospheric gas. It is possible to improve safety.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an embodiment of an air intrusion prevention apparatus for a closed atmosphere heat treatment furnace according to the present invention.
FIG. 2 is a schematic configuration diagram illustrating a conventional sealed atmosphere heat treatment furnace.
FIG. 3 is a schematic diagram for explaining the treatment process of an object to be treated and the pressure fluctuation using a sealed atmosphere heat treatment furnace.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Front door, 2 ... Front chamber, 4 ... Heating chamber, 14 ... Inert gas container, 22 ... Governor, 30 ... Sealed carburizing and quenching furnace, 40 ... Air intrusion prevention device, A ...... Super purge line, B ... Governor line.

Claims

A heating chamber for heat-treating the product to be processed at a high temperature and a front chamber for sending the product to be processed to the heating chamber are connected to a supply line for supplying atmospheric gas to the heating chamber, and the front chamber is opened and closed by a door. An air intrusion prevention device for a closed atmosphere heat treatment furnace having an opening / closing means for performing,
A super purge line for sending an inert gas to the front chamber when the door is opened by an open signal of the door, and the inert gas is supplied to the furnace via a governor only when the inside of the furnace is under a negative pressure when the door is closed. An air intrusion prevention apparatus for a sealed atmosphere heat treatment furnace, wherein a governor line for feeding into the front chamber is connected and arranged so that the internal pressure becomes equal to the atmospheric pressure.