JP2004069199A

JP2004069199A - Vacuum container

Info

Publication number: JP2004069199A
Application number: JP2002229948A
Authority: JP
Inventors: Junichi Katsuki; 香月　淳一; Takashi Yamauchi; 山内　隆; Kenji Abiko; 安彦　兼次
Original assignee: Nisshin Steel Co Ltd
Current assignee: Nippon Steel Nisshin Co Ltd
Priority date: 2002-08-07
Filing date: 2002-08-07
Publication date: 2004-03-04

Abstract

<P>PROBLEM TO BE SOLVED: To prevent a leak of atmospheric air with a simple structure when evacuating a vacuum container for handling the melted metal. <P>SOLUTION: A part wherein a leak of the outside gas is generated in evacuation is covered with an Ar gas flow from the outside of the container to make the Ar gas leak in place of the atmospheric air. Especially, a cover is provided outside a fastened part of a closing part, and the Ar gas is supplied to a space surrounded by the cover and the container member, and the fastened part is covered with the Ar gas flow to provide a vacuum container. An Ar gas blow-off tube is provided near a part wherein a slide-contact part of a sliding part, of which bar-like member is to be brought in slide-contact with the container member, is exposed outside, and the exposed part of the slide-contact part is covered with the Ar gas flow blown off from the tube to form a vacuum container. <P>COPYRIGHT: (C)2004,JPO

Description

【０００１】
【発明の属する技術分野】
本発明は、中で溶融金属を取り扱う真空容器において、真空排気時に容器外部から内部への大気のリークを防止する技術に関する。
【０００２】
【従来の技術】
金属の溶解や鋳造、あるいは精錬は、しばしば真空容器中で行われる。その目的は様々であるが、主として以下のようなことが挙げられる。
▲１▼大気から溶融金属中への酸素や窒素の混入を防止する。
▲２▼湯面に酸化スケールが形成して鋳造性を損なうことを防止する。
▲３▼鋳造時にガスの巻き込みを防止する。
▲４▼溶融金属中のガス成分を効率よく除去する。
【０００３】
実験用あるいは小規模生産用の真空容器としては、その内部に、高周波誘導コイルを有する金属溶解用のルツボと鋳型を設置した「高周波真空溶解炉」が種々普及している。これらは、真空容器外部からの操作により溶解と簡単な精錬および鋳造が行えるようになっている。
【０００４】
大規模生産用の設備としては、鉄鋼製造ラインにおける真空脱ガス装置が挙げられる。例えば、ステンレス鋼製造ラインでは、粗脱炭および粗脱窒を行った溶鋼を取鍋のまま真空容器に装入し、真空排気しながら減圧下で酸素吹錬およびＡｒガス底吹き攪拌を行い、次いで０．５Ｔｏｒｒ程度の真空下でＡｒガス底吹き攪拌を行うことにより、効率よく脱炭・脱窒反応を進行させる精錬手法が採用されている（ＶＯＤ法）。
【０００５】
これらの溶融金属を取り扱う真空容器には、一部の実験用精密容器を除き、いくつかの共通的な特徴がある。まず、これらの容器は大径の蓋を備えている。真空溶解炉では原材料のセットや鋳型の出し入れが必要であり、ＶＯＤ法の真空脱ガス装置では取鍋の出し入れが必要であるため、これらの真空容器には径の大きな蓋が必要である。また、一般的に副原料の投入等が可能なハッチを備えている。さらに、測温・サンプリング用プローブ，酸素吹錬用ランスなどの摺動部材を備えている。
【０００６】
蓋やハッチは、操業中に迅速に開閉できるよう、一般的にガスケットを介した単純な閉じ合わせ構造になっている。測温・サンプリング用プローブ，酸素吹錬用ランス等は、操業中に溶融金属中に挿入するものであるから、それ自体が棒状の摺動部材を構成し、容器部材と摺接する構造になっている。真空排気を行ったとき、これらの閉じ合わせ部や摺動部は、その構造上、容器の外部から内部への気体の進入を完全に遮断することが難しく、通常、これらの部位から大気が内部へリークする。
【０００７】
このような大気のリークは、様々な金属の溶解・精錬において問題となりうる。なかでも、ＶＯＤ法によるステンレス鋼の精錬においては、現実に以下のような問題が生じている。
すなわち、ＶＯＤ法では真空精錬を行うことにより次の脱ガス反応を促進させ、効率的に脱炭・脱窒を行っている。
Ｃ＋Ｏ　→　ＣＯ（ガス）
２Ｎ　→　Ｎ_２（ガス）
（下線を付した元素は溶鋼中に溶解していることを意味する）。
もともとＶＯＤ法は極低Ｃ化，極低Ｎ化には有利な方法であるとされる。ところが、近年、品質向上，材料特性向上の要求が高まり、極低Ｃ，Ｎ化を図った材料を一層安定的かつ低コストで製造する必要が生じた。
【０００８】
極低Ｃ，Ｎ化を図るには、真空排気しながら気液反応界面積を増大させることが重要である。しかし、上記のとおり真空排気時には外部からの大気のリークが避けられないため、気液反応界面積を増大させると、真空容器内に侵入してきたＮ_２ガスの溶鋼中への「吸窒」が促進される。特に、Ｃｒ含有量の高い高耐食ステンレス鋼では、ＣｒとＮの相互作用によりＮの活量が小さくなり、吸窒量は増大しやすい。吸窒量を抑えるために溶鋼の攪拌力を下げると脱炭効率が低下してしまう。
【０００９】
従来、真空精錬中の大気のリークを防止する手段として、真空容器の閉じ合わせ部や摺動部を「二重シール構造」とする方法が提案されている（特開昭５０−９８４１７号）。これは、２つのガスケットを介して真空容器の内部と外部を隔てるものであり、その２つのガスケットの間に気密室を設け、ここにＡｒガスを２ｋｇ／ｃｍ^２程度に高めた状態でパージすることで内部への大気の侵入を防止しようというものである。
【００１０】
【発明が解決しようとする課題】
しかし、上記「二重シール構造」を既存の設備に適用するには大がかりな改造が必要である。また、特に摺動部においては構造が複雑になるため保守に手間がかかる。さらに、精錬用の真空容器には複数の閉じ合わせ部（フランジ部）や摺部があるため、これらすべてに二重シールを設けることは構造上容易でない。
【００１１】
そこで、本発明は、中で溶融金属を取り扱うための真空容器において、既存のシール構造がそのまま利用可能な簡便な手段により、真空排気時における容器内部への大気の侵入を効果的に防止する技術を提供することを目的とする。
【００１２】
【課題を解決するための手段】
発明者らは、種々検討した結果、真空排気時に大気のリークが生じる箇所を容器外部からＡｒガス流で覆うという簡便な手法を採用することで、当該真空容器中で溶融金属を処理して得られた鋳片には顕著な品質向上効果が認められることを知見し、本発明を完成するに至った。
【００１３】
すなわち、上記目的は、中で溶融金属を取り扱う真空容器において、真空排気時に外部気体のリークが生じる箇所を容器外部からＡｒガス流で覆うことにより、大気の代わりにＡｒガスをリークさせるようにした真空容器によって達成される。
ここで、「中で溶融金属を取り扱う」とは、真空容器の内部において、ｉ）　配合原料を溶解して溶融金属を作ること，ｉｉ）　溶融金属を精錬すること，ｉｉｉ）　溶融金属を鋳造すること、のうち１つ以上の処理を行うことをいう。
【００１４】
また、本発明では、真空排気時に外部気体のリークが生じやすい「閉じ合わせ部」と「摺動部」について、それぞれ大気の代わりにＡｒガスをリークさせる効果的な手段を採用した真空容器を提供する。
【００１５】
まず、閉じ合わせ部の改善を図った真空容器として、閉じ合わせ部の接合箇所外側にカバーを設け、そのカバーと容器部材とで囲まれた空間にＡｒガスを供給して、当該接合箇所をＡｒガス流で覆うことにより、大気の代わりにＡｒガスをリークさせるようにした真空容器を提供する。そのカバーは、閉じ合わせ部で係合する一方の部材に取り付けることにより、閉じ合わせ部の開閉動作を拘束しないようにすることができる。また、カバーと容器部材とで囲まれた空間内のガス圧が大気圧以上になるように、Ａｒガスの供給能力に応じて、当該空間からＡｒガスが逃げる隙間を小さくした真空容器を提供する。
【００１６】
次に、摺動部の改善を図った真空容器として、棒状部材が容器部材と摺接する摺動部の、摺接箇所が外部に露出している部位の近傍に、Ａｒガス吹き出し管を設け、その管から吹き出したＡｒガス流で前記摺接箇所の露出部位を覆うことにより、大気の代わりにＡｒガスをリークさせるようにした真空容器を提供する。特に、スリット状，孔状，またはノズル状のガス吹き出し口を有するＡｒガス吹き出し管を採用し、これを、棒状部材を取り巻くように配置し、摺接箇所の露出部位全体にＡｒガスが吹き掛かるようにした真空容器を提供する。
【００１７】
摺動部における別の改善手段を採用した真空容器として、棒状部材が容器部材と摺接する摺動部の、摺接箇所が外部に露出している部位の外側に、棒状部材の動作を拘束しないようにカバーを設け、そのカバーと容器部材と棒状部材とで囲まれた空間にＡｒガスを供給して、前記摺接箇所の露出部位をＡｒガス流で覆うことにより、大気の代わりにＡｒガスをリークさせるようにした真空容器を提供する。この場合、「容器部材」とは、容器を構成する部材のうち、摺動する棒状部材を除いたものをいう。また特に、カバーと容器部材と棒状部材とで囲まれた空間内のガス圧が大気圧以上になるように、Ａｒガスの供給能力に応じて、当該空間からＡｒガスが逃げる隙間を小さくした真空容器を提供する。
【００１８】
さらに本発明では、取鍋の出し入れができるように開放可能な上蓋と、副原料投入チャンバーと、上下動可能な酸素吹錬用ランスを備えた真空脱ガス精錬用の真空容器において、真空排気時に、上蓋閉じ合わせ部の接合箇所，副原料投入チャンバー閉じ合わせ部の接合箇所およびランス摺動部の摺接箇所を容器外部からＡｒガス流で覆うことにより、大気の代わりにＡｒガスをリークさせるようにした真空容器を提供する。
【００１９】
【発明の実施の形態】
上述のように、中で溶融金属を取り扱う一般的な真空容器は、構造上、真空排気中に閉じ合わせ部や摺動部などから大気のリークを生じる。このリークを防止するために容器の密閉性能を高めることは、技術的にも経済的にも多大の困難を伴い、操業現場への適用は現実的ではない。
本発明は、外部気体のリーク自体をくい止めるのではなく、リークする気体を大気からＡｒガスに変えるという思想により、既存の真空容器の性能に逆らうことなく効果的に大気の侵入を防止する。
【００２０】
Ａｒガスをリークさせるために、本発明では真空排気時に外部気体のリークが生じる箇所を容器外部からＡｒガス流で覆う手法を採る。Ａｒガス流で覆うとは、単にリーク箇所にＡｒガスを静的に存在させるのではなく、リーク箇所をＡｒガスの流れに曝し、その状態を維持することである。Ａｒガスの流れを形成することにより、周囲の大気が排除され、効率良くＡｒガスをリークさせることができる。
【００２１】
リーク箇所をＡｒガス流で覆う方法としては、▲１▼ノズル等から吹き出したＡｒガス流を連続的に直接リーク箇所にぶつける方法、▲２▼リーク箇所を囲うようにカバーを設け、そのカバーの内側にＡｒガスを連続供給してＡｒガスの流れを形成し、リーク箇所をその流れに曝す方法、などが挙げられる。
【００２２】
ここで、▲２▼のカバーを用いる方法においては、そのカバーの内側の空間を気密状態にするのではなく、カバー内側に供給したＡｒガスが外側に逃げるための隙間を設けておく。こうすることでカバー内側には常にＡｒガス流を形成することができる。カバー内側への大気の流入をできるだけ減らすには、Ａｒガス供給量とのバランスでカバー内側のガス圧が大気圧以上になるように、Ａｒガスが外側に逃げるための隙間を小さくすることが有効である。
以下、「閉じ合わせ部」と「摺動部」について、大気の代わりにＡｒガスをリークさせる手段を説明する。
【００２３】
図１には、真空容器のハッチの閉じ合わせ部において、蓋と容器本体の接合箇所の周囲に環状のカバーを設けた例を示す。真空容器本体２はハッチの開口部にフランジ部３を有し、蓋１とフランジ部３とが、ガスケット４を介して接合することにより、閉じ合わせ部を構成している。真空排気時にはガスケット４を介した接合箇所から外部気体のリークが生じる。この接合箇所を囲むように、フランジ部３および蓋１の外周全体にわたって環状のカバー５を設けてある。この図の例では、閉じ合わせ部で係合する蓋１とフランジ部３のうち、蓋１の方にカバー５を取り付けてあるので、閉じ合わせ部の開閉動作を拘束しない。
【００２４】
カバー５にはＡｒガス供給管６が設けられ、カバー５と容器部材（蓋１，ガスケット４，容器のフランジ部３）とで囲まれた空間２２には、真空排気時にＡｒガス供給管６から連続的にＡｒガスが供給される。ハッチ開口部が大きい場合にはＡｒガス供給管６を複数設けることが望ましい。カバー５と容器部材の間には隙間７があり、空間２２のＡｒガスは隙間７から外部に逃げるようになっている。Ａｒガスは、Ａｒガス供給管６→空間２２→隙間７の順に流動する。つまり、Ａｒガス供給管６からＡｒガスを供給しているとき、空間２２には常にＡｒガスの流れが生じており、ガスケット４を介した接合箇所は大気を排除したＡｒガス流に曝される。真空排気装置を作動させると当該接合箇所から大気の代わりにＡｒガスが容器内部にリークする。
【００２５】
空間２２への大気の流入をできるだけ避けるためには、Ａｒガス供給管６からの供給量と隙間７からの放出量および容器内部へのリーク量とのバランスにより、空間２２のガス圧が大気圧以上になるよう、隙間７を小さくすることが望ましい。例えば、カバー５を弾力性のある材料で作り、Ａｒガス供給前にはカバー５と容器部材とが隙間７の箇所で接するようにしておき、Ａｒガス供給時にその供給圧力によって最小限の隙間が自然に形成されるようにすれば、大気の流入を効果的に防止できる。
【００２６】
図２には、真空容器のハッチの閉じ合わせ部において、フランジ部と蓋全体をカバーで囲んだ例を示す。ガスケット４を介した接合箇所を含むようにフランジ部と蓋全体をカバー５で囲んである。ハッチ開口部が比較的小さい場合にはこのようなカバーを設けることが構造上簡便である。この場合も、Ａｒガスは、Ａｒガス供給管６→空間２２→隙間７の順に流動し、ガスケット４を介した接合箇所は大気を排除したＡｒガス流に曝される。真空排気時には当該接合箇所から大気の代わりにＡｒガスが容器内部にリークする。
【００２７】
図３には、摺動部にＡｒガス吹き出し管を設けた例を示す。測温プローブやランスなどの棒状部材１０が真空容器の内部と外部を貫通して容器部材と摺接している摺動部において、その摺接箇所１１が外部に露出している部位の近傍に、棒状部材１０を取り巻くように、Ａｒガス吹き出し管１２が設けてある。Ａｒガス吹き出し管１２にはスリット状または複数の孔状のガス吹き出し口１３があり、Ａｒガス吹き出し管１２に供給されたＡｒガスはガス吹き出し口１３から吹き出してＡｒガス流を形成し、そのＡｒガス流が前記摺接箇所の外部露出部位に直接ぶつかるようになっている。ガス吹き出し口１３は棒状部材１０の周囲にほぼ均等に設けてあるので、摺接箇所の外部露出部位の全体がＡｒガス流に曝される。真空排気装置を作動させると当該部位から大気の代わりにＡｒガスが容器内部にリークする。
【００２８】
図４は、図３と同様の摺動部にノズル状のガス吹き出し口１３を有するＡｒガス吹き出し管１２を設けた例を示す。棒状部材１０を取り巻くように複数のＡｒガス吹き出し管１２を配置することで摺接箇所の外部露出部位の全体をＡｒガス流に曝すことができる。
【００２９】
図５には、摺動部の摺接箇所外側をカバーで囲んだ例を示す。棒状部材１０が上記と同様に容器部材と摺接しており、その摺接箇所１１が外部に露出している部位の外側に環状のカバー５を設けてある。このカバー５は容器部材に取り付けてあり、棒状部材１０の動作を拘束しない。カバー５にはＡｒガス供給管６が設けられ、カバー５と容器部材と棒状部材１０とで囲まれた空間２３には、真空排気時にＡｒガス供給管６から連続的にＡｒガスが供給される。空間２３に供給されたＡｒガスは隙間７から外部に逃げるようになっている。Ａｒガスは、Ａｒガス供給管６→空間２３→隙間７の順に流動する。Ａｒガス供給管６からＡｒガスを供給しているとき、空間２３には常にＡｒガスの流れが生じており、摺接箇所の外部露出部位の全体がＡｒガス流に曝される。真空排気装置を作動させると当該部位から大気の代わりにＡｒガスが容器内部にリークする。
【００３０】
空間２３への大気の流入をできるだけ避けるためには、Ａｒガス供給管６からの供給量と隙間７からの放出量および容器内部へのリーク量とのバランスにより、空間２３のガス圧が大気圧以上になるよう、隙間７を小さくすることが望ましい。
【００３１】
【実施例】
ＶＯＤ法による真空脱ガス精錬用の真空容器において、真空排気時に、主たるリーク箇所から大気の代わりにＡｒガスをリークさせるようにして、ステンレス溶鋼の精錬を行い、極低Ｃ・極低Ｎ鋼の溶製を試みた。
【００３２】
図６に、真空脱ガス精錬用の真空容器の構造を模式的に示す。真空容器本体３０は取鍋３４を出し入れできるように上部に大きな開口部を有し、上蓋３１が閉じ合わせ部５０において本体３０と係合する。上蓋３１には、副原料投入チャンバー３６と酸素吹錬用ランス３８が備わる。副原料投入チャンバー３６の上部にはハッチ３７があり、閉じ合わせ部５１によって接合する。ランス３８は、先端が取鍋内の溶湯３２の中に浸漬できるように上下動可能になっており、摺動部５２において容器部材と摺接する。取鍋の底部にはポーラスプラグ３９があり、底吹きＡｒガスが供給される。容器本体３０には真空排気装置につながる排気口３５があり、真空排気装置を作動させると排気口３５から内部気体が排出されると同時に、閉じ合わせ部５０，５１および摺動部５２から外部気体がリークして真空容器内部に進入する。
【００３３】
この真空容器において、閉じ合わせ部５０，５１および摺動部５２の箇所にそれぞれ以下のように大気に代えてＡｒガスをリークさせる機構を設けた。
・上蓋閉じ合わせ部５０；　図１に示したタイプの環状のカバーを蓋側に取り付けた。Ａｒガス供給圧力：１．２ｋｇ／ｃｍ^２，Ａｒガス供給量：３００ＮＬ／ｍｉｎとした。
・ハッチ閉じ合わせ部５１；　図１に示したタイプの環状のカバーを蓋側に取り付けた。Ａｒガス供給圧力：１．２ｋｇ／ｃｍ^２，Ａｒガス供給量：３００ＮＬ／ｍｉｎとした。
・ランス摺動部５２；　図３に示したタイプのＡｒガス吹き付け管を摺接箇所の露出部位の近傍に設け、スリット状のガス吹き出し口から出たＡｒガス流が当該露出部位全体に直接ぶつかるようにセッティングした。Ａｒガス供給圧力：１．２ｋｇ／ｃｍ^２，Ａｒガス供給量：１５０ＮＬ／ｍｉｎとした。
【００３４】
Ｃｒ含有量が約１０〜３０質量％，Ｃ含有量が約４．５〜６．５質量％のＦｅ−Ｃｒ−Ｃ合金溶湯またはＦｅ−Ｃｒ−Ｎｉ−Ｃ合金溶湯約７０トンを、転炉にて酸素吹錬により粗脱炭・粗脱窒した後、取鍋に出湯し、その取鍋を上記の真空脱ガス精錬用真空容器にセットして精錬を行った。
【００３５】
各チャージとも、上蓋３１を閉じた後、閉じ合わせ部５０，５１および摺動部５２にリーク用Ａｒガスを上記の圧力および供給量にて供給開始した。その後、真空排気を行い、まず、取鍋中の溶鋼を底吹きＡｒガス（流量：１２ＮＬ／ｍｉｎ・ｔ）で攪拌しながらランス３８を溶湯３２に挿入して酸素吹錬を実施し、脱炭・脱窒を行った。Ｃ含有量が０．０１０〜０．０１３質量％に到達した後、酸素吹錬を止め、底吹きＡｒガスで攪拌しながら真空処理のみによる脱炭を行った。このときの真空度は０．５Ｔｏｒｒとした。この仕上げ脱炭・脱窒が終了した後、高塩基度フラックスを３０ｋｇ／ｔ−ｍｅｔａｌ添加して脱酸，脱硫等の仕上げ精錬を行った。その後、真空排気を止め、底吹きＡｒガス流量を３ＮＬ／ｍｉｎ・ｔに絞ったのち、容器内部に大気を導入し、リーク用Ａｒガスの供給も止めた。大気圧下で最終的な成分調整を行い、上蓋３１を開放して取鍋を取り出し、鋳造場に移送した。
なお、比較例として、リーク用Ａｒガスを供給しない従来の方法で同様の精錬を行った。
【００３６】
表１に、各チャージで得られた鋳造材のＣｒ，Ｎｉ，Ｃ，Ｎの含有量、およびＣ＋Ｎ量を示す。脱炭・脱窒の達成度の評価は、Ｃｒ含有量レベルに応じて以下のように判定した。
・Ｃｒ量が１５質量％未満の場合：　Ｃ＋Ｎ≦０．００６質量％を良好とする。
・Ｃｒ量が１５〜２０質量％の場合：　Ｃ＋Ｎ≦０．００８質量％を良好とする。
・Ｃｒ量が２０質量％を超える場合：　Ｃ＋Ｎ≦０．０１０質量％を良好とする。
表１からわかるように、真空排気時に大気の代わりにＡｒガスをリークさせた本発明例Ｎｏ．１〜６では、いずれのＣｒレベルにおいても脱炭・脱窒の達成度が「良好」と判定される極低Ｃ，Ｎ材が得られた。これに対し、大気のリークが生じる従来法を採用した比較例７〜１２では、「良好」と判定される極低Ｃ，Ｎ材は得られなかった。
【００３７】
【表１】

【００３８】
【発明の効果】
本発明の真空容器は、以下のような優れた効果を有する。
（１）　真空排気時に大気のリークを大幅に防止できるので、中で取り扱う溶融金属の品質が向上する。
（２）　複雑なシール構造を必要としないので、既存の真空容器のシール構造をそのまま利用できる。
（３）　Ａｒガスをリークさせるための機構は簡易な構造で十分であるから改造も容易である。
（４）　実験用の小型真空溶解炉から営業生産用の大規模真空精錬装置に至るまで幅広く適用可能である。
このように、本発明は、簡便な手段により優れた効果を発揮するので、冶金分野における研究開発や営業生産に大きな利益をもたらす。
【図面の簡単な説明】
【図１】真空容器のハッチ部分について、蓋と容器本体の接合箇所の周囲に環状のカバーを設けた閉じ合わせ部の構造を模式的に示した断面図。
【図２】真空容器のハッチ部分について、フランジ部と蓋全体をカバーで囲んだ閉じ合わせ部の構造を模式的に示した断面図。
【図３】真空容器の内部と外部を貫通する棒状部材が容器部材と摺接する摺接箇所近傍にスリット状または複数の孔状のガス吹き出し口を有するＡｒガス吹き出し管を設けた摺動部の構造を模式的に示した断面図。
【図４】真空容器の内部と外部を貫通する棒状部材が容器部材と摺接する摺接箇所近傍に複数のノズル状のガス吹き出し口を有するＡｒガス吹き出し管を設けた摺動部の構造を模式的に示した断面図。
【図５】真空容器の内部と外部を貫通する棒状部材が容器部材と摺接する摺接箇所外側をカバーで囲んだ摺動部の構造を模式的に示した断面図。
【図６】真空脱ガス精錬用の真空容器の構造を模式的に示した断面図。
【符号の説明】
１　蓋
２　真空容器本体
３　フランジ部
４　ガスケット
５　カバー
６　Ａｒガス供給管
７　隙間
１０　棒状部材
１１　摺接箇所
１２　Ａｒガス吹き出し管
１３　ガス吹き出し口
２０　容器内部
２１　容器外部
２２　カバーと容器部材とで囲まれた空間
２３　カバーと容器部材と棒状部材とで囲まれた空間
３０　真空脱ガス精錬用の真空容器本体
３１　上蓋
３２　溶湯
３３　スラグ
３４　取鍋
３５　排気口
３６　副原料投入チャンバー
３７　ハッチ
３８　酸素吹錬用ランス
３９　ポーラスプラグ
５０　上蓋閉じ合わせ部
５１　ハッチ閉じ合わせ部
５２　ランス摺動部[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a technique for preventing a leak of air from the outside to the inside of a vacuum container handling molten metal during vacuum evacuation.
[0002]
[Prior art]
Melting, casting, or refining of metal is often performed in a vacuum vessel. Although the purpose is various, the following are mainly mentioned.
(1) Prevent oxygen and nitrogen from being mixed into the molten metal from the atmosphere.
{Circle around (2)} Prevents oxide scale from forming on the surface of the molten metal and impairing castability.
{Circle around (3)} Prevents entrainment of gas during casting.
(4) Efficiently remove gas components in the molten metal.
[0003]
As a vacuum vessel for experiments or small-scale production, various kinds of "high-frequency vacuum melting furnaces" in which a crucible for melting a metal having a high-frequency induction coil and a mold are installed therein are widely used. These can be melted and easily refined and cast by operations from outside the vacuum vessel.
[0004]
Equipment for large-scale production includes a vacuum degassing device in a steel production line. For example, in a stainless steel production line, the molten steel subjected to rough decarburization and rough denitrification is charged into a vacuum vessel as a ladle and subjected to oxygen blowing and Ar gas bottom blowing stirring under reduced pressure while evacuating, Then, a refining method is employed in which the decarburization / denitrification reaction is efficiently advanced by performing Ar gas bottom blowing and stirring under a vacuum of about 0.5 Torr (VOD method).
[0005]
Except for some experimental precision vessels, these vacuum vessels for handling molten metal have some common features. First, these containers have large-diameter lids. In a vacuum melting furnace, a set of raw materials and a mold must be taken in and out, and in a vacuum degassing apparatus of the VOD method, a ladle needs to be taken in and out. Therefore, these vacuum vessels require large-diameter lids. In addition, a hatch is generally provided so that auxiliary materials can be charged. Further, sliding members such as a probe for temperature measurement and sampling and a lance for oxygen blowing are provided.
[0006]
Lids and hatches are typically simple closed structures via gaskets so that they can be quickly opened and closed during operation. Probes for temperature measurement and sampling, lances for oxygen blowing, etc. are inserted into the molten metal during operation, so they themselves constitute a rod-shaped sliding member and have a structure that slides on the container member. I have. When evacuated, these closing parts and sliding parts are difficult to completely block the ingress of gas from the outside to the inside of the container due to their structure. Leaks to
[0007]
Such an air leak can be a problem in the melting and refining of various metals. Above all, the following problems actually occur in refining stainless steel by the VOD method.
That is, in the VOD method, the next degassing reaction is promoted by performing vacuum refining, and decarburization and denitrification are performed efficiently.
C + O → CO (gas)
2 N → N ₂ (gas)
(The underlined elements mean that they are dissolved in the molten steel).
Originally, the VOD method is considered to be an advantageous method for extremely low C and extremely low N. However, in recent years, there has been an increasing demand for quality improvement and material property improvement, and it has become necessary to produce more low-C and N-materials more stably and at lower cost.
[0008]
In order to achieve extremely low C and N, it is important to increase the gas-liquid reaction interface area while evacuating. However, as described above, leakage of atmospheric air from the outside is unavoidable during evacuation. Therefore, if the area of the gas-liquid reaction interface is increased, “nitrogen absorption” of N ₂ gas entering the vacuum vessel into molten steel will occur. Promoted. In particular, in a high corrosion resistant stainless steel having a high Cr content, the activity of N is reduced due to the interaction between Cr and N, and the nitrogen absorption is liable to increase. If the stirring power of the molten steel is reduced to suppress the amount of nitrogen absorption, the decarburization efficiency is reduced.
[0009]
Hitherto, as a means for preventing air from leaking during vacuum refining, a method has been proposed in which a closing portion and a sliding portion of a vacuum vessel have a "double seal structure" (Japanese Patent Laid-Open No. 50-98417). This is to separate the inside and the outside of the vacuum vessel through two gaskets. An airtight chamber is provided between the two gaskets, and the Ar gas is purged in this state with Ar gas being increased to about 2 kg / cm ^2. This is to prevent the intrusion of air into the interior.
[0010]
[Problems to be solved by the invention]
However, a major modification is required to apply the "double seal structure" to existing equipment. In addition, maintenance is troublesome because the structure is particularly complicated in the sliding portion. Furthermore, since the refining vacuum vessel has a plurality of closing portions (flange portions) and sliding portions, it is not structurally easy to provide a double seal for all of them.
[0011]
Therefore, the present invention provides a technology for effectively preventing the intrusion of the atmosphere into the inside of a vacuum container during vacuum evacuation by a simple means in which the existing sealing structure can be used as it is in a vacuum container for handling molten metal inside. The purpose is to provide.
[0012]
[Means for Solving the Problems]
As a result of various studies, the present inventors have adopted a simple method of covering a location where air leakage occurs during vacuum evacuation with an Ar gas flow from the outside of the container, thereby processing the molten metal in the vacuum container. The inventor found that a remarkable quality improving effect was recognized in the obtained cast slab, and completed the present invention.
[0013]
That is, the above object is to allow Ar gas to leak instead of air by covering a place where external gas leaks during vacuum evacuation with an Ar gas flow from outside of the container in a vacuum vessel handling molten metal therein. Achieved by a vacuum vessel.
Here, "handling the molten metal in" means i) dissolving the blended raw materials to produce a molten metal, ii) refining the molten metal, and iii) casting the molten metal inside the vacuum vessel. Means performing one or more processes.
[0014]
Further, the present invention provides a vacuum vessel which employs an effective means for leaking Ar gas instead of air for each of the "closed portion" and the "sliding portion" where leakage of external gas is likely to occur during vacuum evacuation. I do.
[0015]
First, as a vacuum container with an improved sealing portion, a cover is provided outside the joining portion of the sealing portion, and Ar gas is supplied to a space surrounded by the cover and the container member, and the joining portion is sealed with Ar gas. A vacuum vessel is provided which is covered with a gas flow so as to leak Ar gas instead of air. By attaching the cover to one of the members engaged by the closing portion, the opening and closing operation of the closing portion can be prevented. Further, according to the supply capacity of the Ar gas, there is provided a vacuum vessel in which a gap through which the Ar gas escapes from the space is reduced so that the gas pressure in the space surrounded by the cover and the container member becomes equal to or higher than the atmospheric pressure. .
[0016]
Next, as a vacuum container with an improved sliding portion, an Ar gas blowing pipe is provided near a portion where the rod-shaped member is in sliding contact with the container member, where the sliding contact portion is exposed to the outside, A vacuum vessel is provided in which the exposed portion of the sliding contact portion is covered with an Ar gas flow blown out from the pipe to leak Ar gas instead of air. In particular, an Ar gas blowing pipe having a slit-shaped, hole-shaped, or nozzle-shaped gas blowing port is employed, which is arranged so as to surround the rod-shaped member, and Ar gas is blown over the entire exposed portion of the sliding contact portion. A vacuum container is provided.
[0017]
As a vacuum container adopting another means for improving the sliding portion, the operation of the rod-shaped member is not restricted to the outside of the sliding portion where the rod-shaped member is in sliding contact with the container member, where the sliding contact portion is exposed to the outside. Ar gas is supplied to a space surrounded by the cover, the container member, and the rod-shaped member so that the exposed portion of the sliding contact portion is covered with an Ar gas flow, so that the Ar gas is used instead of the atmosphere. A vacuum vessel adapted to leak water. In this case, the “container member” refers to a member constituting the container except for a sliding rod-shaped member. Further, in particular, a vacuum in which a gap through which the Ar gas escapes from the space according to the supply capacity of the Ar gas is reduced so that the gas pressure in the space surrounded by the cover, the container member, and the rod-shaped member is equal to or higher than the atmospheric pressure. Provide a container.
[0018]
Further, according to the present invention, a vacuum vessel for vacuum degassing and refining equipped with an upper lid that can be opened and removed so that a ladle can be taken in and out, an auxiliary material charging chamber, and a vertically movable lance for oxygen blowing can be used for vacuum evacuation. By covering the joint of the upper lid closing part, the joint of the auxiliary material input chamber closing part, and the sliding contact of the lance sliding part with an Ar gas flow from outside the container, Ar gas is leaked instead of air. A vacuum container is provided.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
As described above, a general vacuum vessel handling molten metal therein leaks air from a closing portion, a sliding portion, and the like during the evacuation due to its structure. Enhancing the sealing performance of the container in order to prevent this leakage involves a great deal of technical and economical difficulties, and is not practically applicable to operation sites.
The present invention effectively prevents the invasion of the atmosphere without deteriorating the performance of the existing vacuum vessel, based on the idea of changing the leaked gas from the atmosphere to the Ar gas, instead of stopping the leak of the external gas itself.
[0020]
In order to leak Ar gas, the present invention employs a method of covering a location where external gas leaks during evacuation with an Ar gas flow from outside the container. To cover with the Ar gas flow means not to make the Ar gas statically exist at the leak location, but to expose the leak location to the flow of the Ar gas and maintain the state. By forming the flow of the Ar gas, the surrounding atmosphere is removed, and the Ar gas can be efficiently leaked.
[0021]
As a method of covering the leak location with the Ar gas flow, (1) a method in which the Ar gas flow blown out from the nozzle or the like is continuously and directly hitting the leak location, (2) a cover is provided so as to surround the leak location, and A method of continuously supplying Ar gas to the inside to form a flow of Ar gas, and exposing a leak location to the flow, and the like.
[0022]
Here, in the method using the cover of (2), the space inside the cover is not made airtight, but a gap is provided for the Ar gas supplied inside the cover to escape outside. By doing so, an Ar gas flow can always be formed inside the cover. In order to reduce the inflow of air into the inside of the cover as much as possible, it is effective to reduce the gap for the Ar gas to escape to the outside so that the gas pressure inside the cover becomes higher than the atmospheric pressure in balance with the supply amount of Ar gas. It is.
Hereinafter, means for leaking Ar gas instead of air for the “closer” and “slider” will be described.
[0023]
FIG. 1 shows an example in which an annular cover is provided around a joint between a lid and a container body at a closing portion of a hatch of a vacuum container. The vacuum vessel main body 2 has a flange portion 3 at the opening of the hatch, and the lid 1 and the flange portion 3 are joined via a gasket 4 to form a closing portion. At the time of evacuation, leakage of the external gas occurs from the joint via the gasket 4. An annular cover 5 is provided over the entire outer periphery of the flange portion 3 and the lid 1 so as to surround the joint. In the example of this figure, the cover 5 is attached to the lid 1 of the lid 1 and the flange 3 that are engaged with each other at the closing portion, so that the opening / closing operation of the closing portion is not restricted.
[0024]
An Ar gas supply pipe 6 is provided on the cover 5, and a space 22 surrounded by the cover 5 and the container member (the lid 1, the gasket 4, and the flange portion 3 of the container) is provided from the Ar gas supply pipe 6 during evacuation. Ar gas is continuously supplied. When the hatch opening is large, it is desirable to provide a plurality of Ar gas supply pipes 6. There is a gap 7 between the cover 5 and the container member, and Ar gas in the space 22 escapes from the gap 7 to the outside. The Ar gas flows in the order of the Ar gas supply pipe 6 → the space 22 → the gap 7. That is, when the Ar gas is supplied from the Ar gas supply pipe 6, the flow of the Ar gas is always generated in the space 22, and the joint portion via the gasket 4 is exposed to the Ar gas flow excluding the atmosphere. . When the evacuation device is activated, Ar gas leaks from the joint to the inside of the container instead of the air.
[0025]
In order to avoid the inflow of the atmosphere into the space 22 as much as possible, the gas pressure in the space 22 is reduced to the atmospheric pressure by the balance between the supply amount from the Ar gas supply pipe 6, the release amount from the gap 7, and the leak amount into the container. As described above, it is desirable to reduce the gap 7. For example, the cover 5 is made of a resilient material, and the cover 5 and the container member are brought into contact with each other at the gap 7 before the supply of the Ar gas. If it is formed naturally, the inflow of air can be effectively prevented.
[0026]
FIG. 2 shows an example in which the flange portion and the entire lid are surrounded by a cover at the closing portion of the hatch of the vacuum vessel. The flange and the entire lid are surrounded by a cover 5 so as to include a joint portion via the gasket 4. When the hatch opening is relatively small, providing such a cover is structurally simple. Also in this case, the Ar gas flows in the order of the Ar gas supply pipe 6 → the space 22 → the gap 7, and the joint via the gasket 4 is exposed to the Ar gas flow excluding the atmosphere. At the time of vacuum evacuation, Ar gas leaks into the container instead of the air from the joint portion.
[0027]
FIG. 3 shows an example in which an Ar gas blowing pipe is provided in the sliding portion. In a sliding portion in which a rod-shaped member 10 such as a temperature measuring probe or a lance penetrates the inside and outside of the vacuum container and is in sliding contact with the container member, in the vicinity of a portion where the sliding contact portion 11 is exposed to the outside, An Ar gas blowing pipe 12 is provided so as to surround the rod-shaped member 10. The Ar gas blowing pipe 12 has a slit-shaped or a plurality of hole-shaped gas blowing ports 13, and Ar gas supplied to the Ar gas blowing pipe 12 is blown out from the gas blowing port 13 to form an Ar gas flow, and the Ar gas flow is formed. The gas flow directly hits the externally exposed portion of the sliding contact portion. Since the gas outlet 13 is provided substantially uniformly around the rod-shaped member 10, the entire externally exposed portion of the sliding contact portion is exposed to the Ar gas flow. When the evacuation device is operated, Ar gas leaks from the portion instead of the air into the container.
[0028]
FIG. 4 shows an example in which an Ar gas blowing pipe 12 having a nozzle-shaped gas blowing port 13 is provided on the same sliding portion as in FIG. By arranging a plurality of Ar gas blowing pipes 12 so as to surround the rod-shaped member 10, the entire externally exposed portion of the sliding contact portion can be exposed to the Ar gas flow.
[0029]
FIG. 5 shows an example in which the sliding portion outside the sliding portion is surrounded by a cover. The rod-shaped member 10 is in sliding contact with the container member in the same manner as described above, and the annular cover 5 is provided outside a portion where the sliding contact portion 11 is exposed to the outside. The cover 5 is attached to the container member and does not restrict the operation of the rod-shaped member 10. An Ar gas supply pipe 6 is provided on the cover 5, and an Ar gas is continuously supplied from the Ar gas supply pipe 6 to the space 23 surrounded by the cover 5, the container member, and the rod-shaped member 10 during evacuation. . The Ar gas supplied to the space 23 escapes from the gap 7 to the outside. The Ar gas flows in the order of the Ar gas supply pipe 6 → the space 23 → the gap 7. When the Ar gas is supplied from the Ar gas supply pipe 6, a flow of the Ar gas is always generated in the space 23, and the entire externally exposed portion of the sliding contact portion is exposed to the Ar gas flow. When the evacuation device is operated, Ar gas leaks from the portion instead of the air into the container.
[0030]
In order to minimize the inflow of the atmosphere into the space 23, the gas pressure in the space 23 is reduced to the atmospheric pressure by the balance between the supply amount from the Ar gas supply pipe 6, the release amount from the gap 7, and the leakage amount into the container. As described above, it is desirable to reduce the gap 7.
[0031]
【Example】
In a vacuum vessel for vacuum degassing and refining by the VOD method, at the time of vacuum evacuation, a stainless steel molten steel is refined by leaking Ar gas instead of air from a main leak point, and ultra-low C / ultra-low N steel is produced. Attempted smelting.
[0032]
FIG. 6 schematically shows the structure of a vacuum vessel for vacuum degassing and refining. The vacuum vessel main body 30 has a large opening at the top so that the ladle 34 can be taken in and out, and the upper lid 31 is engaged with the main body 30 at the closing portion 50. The upper lid 31 is provided with an auxiliary raw material charging chamber 36 and an oxygen blowing lance 38. A hatch 37 is provided at an upper portion of the auxiliary material input chamber 36 and is joined by a closing portion 51. The lance 38 can be moved up and down so that the tip can be immersed in the molten metal 32 in the ladle, and slidably contacts the container member at the sliding portion 52. A porous plug 39 is provided at the bottom of the ladle, and bottom blown Ar gas is supplied. The container body 30 has an exhaust port 35 connected to the vacuum exhaust device. When the vacuum exhaust device is operated, the internal gas is exhausted from the exhaust port 35 and, at the same time, the external gas is exhausted from the closing

portions

50 and 51 and the sliding portion 52. Leaks into the vacuum chamber.
[0033]
In this vacuum vessel, a mechanism for leaking Ar gas instead of the atmosphere was provided at each of the closing

portions

50 and 51 and the sliding portion 52 as described below.
-Upper lid closing part 50: An annular cover of the type shown in Fig. 1 was attached to the lid side. Ar gas supply pressure: 1.2 kg / cm ² , Ar gas supply: 300 NL / min.
Hatch closing portion 51: An annular cover of the type shown in FIG. 1 was attached to the lid side. Ar gas supply pressure: 1.2 kg / cm ² , Ar gas supply: 300 NL / min.
A lance sliding portion 52; an Ar gas blowing pipe of the type shown in FIG. 3 is provided in the vicinity of the exposed portion of the sliding contact portion, and the Ar gas flow coming out of the slit-shaped gas outlet directly hits the entire exposed portion. It was set as follows. Ar gas supply pressure: 1.2 kg / cm ² , Ar gas supply: 150 NL / min.
[0034]
About 70 tons of molten Fe—Cr—C alloy or molten Fe—Cr—Ni—C alloy having a Cr content of about 10 to 30% by mass and a C content of about 4.5 to 6.5% by weight After decarburization and denitrification by oxygen blowing, the hot water was poured into a ladle, and the ladle was set in the vacuum vessel for vacuum degassing and refining to perform refining.
[0035]
In each charge, after the upper lid 31 was closed, the supply of the Ar gas for leakage to the

closing portions

50 and 51 and the sliding portion 52 at the above-described pressure and supply amount was started. Thereafter, vacuum evacuation is performed, and first, the lance 38 is inserted into the molten metal 32 while the molten steel in the ladle is stirred with bottom-blown Ar gas (flow rate: 12 NL / min · t) to perform oxygen blowing and decarburization.・ Denitrification was performed. After the C content reached 0.010 to 0.013 mass%, oxygen blowing was stopped, and decarburization was performed only by vacuum treatment while stirring with bottom-blown Ar gas. At this time, the degree of vacuum was 0.5 Torr. After the finishing decarburization / denitrification was completed, a high basicity flux was added at 30 kg / t-metal to perform finishing refining such as deoxidation and desulfurization. Thereafter, the evacuation was stopped, the flow rate of the bottom-blown Ar gas was reduced to 3 NL / min · t, and then the atmosphere was introduced into the container, and the supply of the Ar gas for leakage was stopped. The final components were adjusted under atmospheric pressure, the upper lid 31 was opened, the ladle was taken out, and transferred to the foundry.
As a comparative example, the same refining was performed by the conventional method without supplying the leak Ar gas.
[0036]
Table 1 shows the contents of Cr, Ni, C, and N and the amount of C + N of the cast material obtained by each charge. The evaluation of the degree of achievement of decarburization / denitrification was determined as follows according to the Cr content level.
When the amount of Cr is less than 15% by mass: C + N ≦ 0.006% by mass is determined to be good.
When the amount of Cr is 15 to 20% by mass: C + N ≦ 0.008% by mass is determined to be good.
When the amount of Cr exceeds 20% by mass: C + N ≦ 0.010% by mass is regarded as good.
As can be seen from Table 1, Example No. 1 of the present invention in which Ar gas was leaked instead of air during vacuum evacuation. In Nos. 1 to 6, extremely low C and N materials in which the degree of achievement of decarburization / denitrification was determined to be “good” at any Cr level were obtained. On the other hand, in Comparative Examples 7 to 12 employing the conventional method in which the air leaks, very low C and N materials judged to be “good” were not obtained.
[0037]
[Table 1]

[0038]
【The invention's effect】
The vacuum vessel of the present invention has the following excellent effects.
(1) Since air leakage can be largely prevented at the time of evacuation, the quality of the molten metal handled therein is improved.
(2) Since a complicated sealing structure is not required, the existing sealing structure of the vacuum vessel can be used as it is.
(3) Since a simple structure is sufficient for the mechanism for leaking Ar gas, the remodeling is easy.
(4) It can be widely applied from small vacuum melting furnaces for experiments to large-scale vacuum refining equipment for commercial production.
As described above, the present invention exerts excellent effects by simple means, and thus brings great benefits to R & D and commercial production in the field of metallurgy.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view schematically showing the structure of a closing portion in which a hatch portion of a vacuum container is provided with an annular cover around a joint between a lid and a container body.
FIG. 2 is a cross-sectional view schematically showing a structure of a closing portion in which a hatch portion of the vacuum vessel surrounds a flange portion and a lid with a cover.
FIG. 3 shows a sliding portion provided with an Ar gas blowing pipe having a slit-shaped or a plurality of hole-shaped gas blowing ports in the vicinity of a sliding contact point where a rod-shaped member penetrating the inside and outside of the vacuum container is in sliding contact with the container member. Sectional drawing which showed the structure typically.
FIG. 4 schematically shows a structure of a sliding portion provided with an Ar gas blowing pipe having a plurality of nozzle-shaped gas blowing ports near a sliding contact point where a rod-shaped member penetrating through the inside and outside of the vacuum vessel slides on the vessel member. FIG.
FIG. 5 is a cross-sectional view schematically illustrating a structure of a sliding portion in which a rod-shaped member penetrating through the inside and outside of the vacuum vessel is in sliding contact with the vessel member and the outside of a sliding contact portion is surrounded by a cover.
FIG. 6 is a sectional view schematically showing the structure of a vacuum vessel for vacuum degassing and refining.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Lid 2 Vacuum container main body 3 Flange part 4 Gasket 5 Cover 6 Ar gas supply pipe 7 Gap 10 Bar-shaped member 11 Sliding contact point 12 Ar gas blowing pipe 13 Gas blowing port 20 Inside of container 21 Outside of container 22 Surrounded by cover and container member Space 23 surrounded by cover, container member and rod-shaped member 30 vacuum container body 31 for vacuum degassing and refining upper lid 32 molten metal 33 slag 34 ladle 35 exhaust port 36 auxiliary material charging chamber 37 hatch 38 oxygen blowing Lance 39 Porous plug 50 Top lid closing part 51 Hatch closing part 52 Lance sliding part

Claims

A vacuum vessel for handling molten metal in a vacuum vessel, wherein an Ar gas flow from the outside of the vessel is covered with an Ar gas flow from a location where an external gas leaks during vacuum evacuation, thereby allowing Ar gas to leak instead of air.

In a vacuum vessel handling molten metal in the inside, a cover is provided outside the joint portion of the closing part where leakage of external gas occurs during evacuation, and Ar gas is supplied to a space surrounded by the cover and the container member, A vacuum vessel in which the joint is covered with an Ar gas flow to leak Ar gas instead of air.

3. The vacuum vessel according to claim 2, wherein a cover is attached to one of the members engaged with the closing portion so as not to restrict the opening / closing operation of the closing portion.

4. The vacuum container according to claim 2, wherein a gap for escaping Ar gas from the space is reduced so that a gas pressure in a space surrounded by the cover and the container member is equal to or higher than the atmospheric pressure.

In a vacuum vessel handling molten metal in the inside, Ar gas is placed in the vicinity of a portion of the sliding portion where the rod-shaped member comes into sliding contact with the container member and the external gas leaks during vacuum evacuation, where the sliding contact portion is exposed to the outside. A vacuum vessel provided with a blow-out tube and covering an exposed portion of the sliding contact portion with an Ar gas flow blown out from the tube, thereby allowing Ar gas to leak instead of air.

An Ar gas blowing pipe having a slit-shaped, hole-shaped or nozzle-shaped gas blowing port is arranged so as to surround the rod-shaped member, and Ar gas is blown over the entire exposed portion of the sliding contact portion. The vacuum vessel as described.

In a vacuum vessel that handles molten metal inside, a rod-shaped member slides out of the sliding part where the rod-shaped member comes into sliding contact with the container member and an external gas leaks during evacuation, where the sliding contact point is exposed to the outside. A cover is provided so as not to restrict the operation of the above, and Ar gas is supplied to a space surrounded by the cover, the container member, and the rod-shaped member, and the exposed portion of the sliding contact portion is covered with an Ar gas flow, so that Vacuum container in which Ar gas is leaked instead of.

8. The vacuum vessel according to claim 7, wherein a gap in which the Ar gas escapes from the space surrounded by the cover, the container member, and the rod-shaped member is reduced so that a gas pressure in the space is equal to or higher than the atmospheric pressure.

In a vacuum vessel for vacuum degassing and refining equipped with an upper lid that can be opened and removed so that the ladle can be taken in and out, an auxiliary material charging chamber, and a vertically movable oxygen blowing lance, the upper lid closing part A vacuum vessel in which an Ar gas is leaked instead of the atmosphere by covering the joint of the above, the joint of the closing portion of the auxiliary material input chamber, and the sliding contact of the lance sliding part with an Ar gas flow from outside the container.