JP4053277B2

JP4053277B2 - Electric furnace

Info

Publication number: JP4053277B2
Application number: JP2001339228A
Authority: JP
Inventors: 剛阿部; 正則中谷; 一代乾; 宏司大西; 利夫河波
Original assignee: Nikkato Corp
Current assignee: Nikkato Corp
Priority date: 2001-11-05
Filing date: 2001-11-05
Publication date: 2008-02-27
Anticipated expiration: 2021-11-05
Also published as: JP2003139472A

Description

【０００１】
【発明の属する技術分野】
本発明は、ランタンクロマイトを主成分とする円筒型の抵抗発熱体の内部を加熱室として利用する電気炉に関する。
【０００２】
【従来の技術】
ペロブスカイト型結晶構造を有するランタンクロマイト（ＬａＣｒＯ_３）を主成分とした、必要に応じてＬａの一部をＳｒ、Ｃａなどで、Ｃｒの一部をＣｏ、Ｎｉ、Ａｌ、Ｍｇなどで置換固溶した組成を有する発熱体（以下単にランタンクロマイト系という）は、１５００℃以上の高温酸化雰囲気において優れた安定性と長寿命をもつセラミックス抵抗発熱体として広く利用されている。
【０００３】
従来、一般に用いられている抵抗発熱体を使用した電気炉は、図１に示すように複数の棒状発熱体１２を用いて加熱室を加熱する構造になっているが、このような構造の電気炉では、装置の構造が複雑かつ大型化するなどの欠点があり、また熱効率が低く消費電力が高くなるため発熱体の使用温度及び昇温速度などの性能面及び寿命面にも限界があった。なお図１において、１３は断熱材、１４は炉心管を示す。
【０００４】
そこで図２に示すように発熱体１の構造を円筒型の一本の発熱体を用いて、中空部を加熱室とする構造にすることにより、電気炉の熱効率を向上し、使用温度及び昇温速度などの性能面及び寿命面を改善することが可能であり、炭化ケイ素（ＳｉＣ）のら管型、複ら管型発熱体などで一部実用化されている。なお、図２において、１５は発熱部、１６は電極、１７はリード線、１８は断熱材、１９は炉心管を示す。
【０００５】
しかしながら、従来より使用されている炭化ケイ素発熱体を大気中１５００℃以上の温度領域で用いる場合には、炭化ケイ素の酸化、及び炭化ケイ素の熱伝導率が高いことから、発熱体の寸法を長尺化し、端子部の温度を低下させること及び発熱部の気密性を高める必要があり、所望の温度とする有効加熱領域に対して発熱体が大型化し、ひいては電気炉が大型化してしまう問題がある。また、急速加熱冷却を繰り返すと短期で破断してしまうため寿命にも問題がある。このため、発熱体の材質だけをランタンクロマイトに変えるなどの対策も物理的には可能であるが、炭化ケイ素は熱膨張率が低く、熱伝導がよく、耐熱衝撃性に優れるのに対し、ランタンクロマイトはこれらに劣る一方、耐熱性、導電性の温度に対する安定性、耐久性が優れるなどの長所がある。そのため、炭化ケイ素製発熱体と同等の構造に使用することが不適当である。
【０００６】
【発明が解決しようとする課題】
本発明は、このような従来の問題点を解決し、小型でありながら発熱体の有効加熱領域が大きく、１９００℃まで急速加熱冷却が可能で長寿命のランタンクロマイト系発熱体からなるコンパクトな電気炉を提供することを目的とする。
【０００７】
【課題を解決するための手段】
本発明は、発熱体の端子部を一ケ所に集中することにより発熱体の長尺化を防ぎ、発熱体内部を有効加熱室として用いることにより電気炉を一体型化し、これらにより電気炉をコンパクト化すること、及び発熱体の形状及び材料の特性を適切な範囲に設定することにより前記目的を達成することができた。
【０００８】
【課題を解決するための手段】
本発明の第１は、発熱部と両端部からなる円筒型のランタンクロマイト系発熱体において、該発熱体材料の気孔率が５％未満でありかつ１０００℃における比抵抗が０．１Ωｃｍ以上であり、発熱体の下端面を２等分割する位置から垂直方向に２ケ所のスリットを設けることによって端子部を一方に集中し、該スリットの幅が１〜１０ｍｍ、端子部と発熱部の長さの合計とスリットの長さの比率（［スリットの長さＬ _３］／｛［端子部の長さＬ _１］＋［発熱部の長さＬ _２］｝）が０．８〜１．２の範囲にあり、該端子部に高温用金属電極を取り付けた発熱体と、該発熱体の外側に装着した断熱材と、該発熱体の中空部内に装着したセラミックス炉心管とを備え、該炉心管の中空部内を有効加熱室としたことを特徴とする電気炉に関する。
本発明の第２は、請求項１におけるランタンクロマイト系発熱体において、発熱部と端子部の外径の比率（［端子部外径］／［発熱部外径］）が１．１〜１．６の範囲にあり、発熱部と端子部の長さの比率（［端子部長さＬ_１］／［発熱部長さＬ_２］）が０．３〜１．０の範囲にあることを特徴とする請求項１記載の電気炉に関する。
【０００９】
以下に、図面を参照しつつ、本発明の電気炉について説明する。
【００１０】
図３および４は、本発明の電気炉の発熱体を示す図である。
即ち、図３は本発明電気炉の発熱体を正面からみた図、図４（Ａ）は本発明電気炉の発熱体を側面からみた図、図４（Ｂ）は図４（Ａ）のＡ−Ａ′断面図である。
【００１１】
図３において、発熱体１は、端子部２と発熱部３と上端部４からなる円筒型のランタンクロマイト系セラミックスからなり、発熱部３の外径を端子部２の外径未満として、さらに発熱体１の下端面を２等分割する位置から垂直方向に２ケ所のスリット５を設け、端子部電極を一方に集中して端子部２とし、該端子部２に高温用電極６及び金属リード部品７を取り付け、両端部間を発熱部３としたものである。かくして、電流は、一方の端子部→一方の発熱体→上端部→他方の発熱体→他方の端子部へと流れることとなる。
【００１２】
該発熱体１では、発熱部３と端子部２の外径の比率（［端子部外径］／［発熱部外径］）を１．１〜１．６の範囲とする必要がある。外径の比率が１．１未満の場合、発熱部３と端子部２の外径差がほとんどなくなり、端子部２の抵抗が発熱部３の抵抗とほぼ同じになるため、端子部電極が抵抗発熱を起こすため短寿命となる。また、外径の比率が１．６を超える場合、発熱部３と端子部２との外径差が大きすぎて発熱体１が不必要に大きくなるばかりでなく、消費電力の増大、端子部２への熱衝撃などにより発熱体が短寿命となり実用的でなくなる。このため、発熱部３と端子部２の外径の比率を１．１〜１．６の範囲とする必要があり、１．１５〜１．５の範囲とすることがより望ましい。
【００１３】
また、該発熱体１の発熱部３と端子部２の長さの比率（［端子部の長さＬ_１］／［発熱部の長さＬ_２］）が０．３〜１．０の範囲にある必要がある。長さの比率が０．３未満の場合、端子部２が短すぎるため端子部の冷却が十分にできず高温となり、端子部電極の劣化が速くなるため短寿命となり実用的でない。長さの比率が１．０を超える場合には端子部が不必要に長くなり消費電力が増大することにより寿命が短くなるだけでなく、発熱体の有効加熱領域に対して発熱体が大型化し、ひいては電気炉が大型化してしまい本発明の目的が達成されなくなる。このため発熱部と端子部の長さの比率が０．３〜１．０の範囲にある必要があり、０．６〜０．９５の範囲にあることがより望ましい。また、発熱部３と端子部２の長さは上記の条件の範囲内で適宜決めることができるが、スリットの長さと有効加熱領域とを考慮すると発熱体全長と端子部の長さの比率［（端子部の長さＬ_１＋発熱部の長さＬ_２＋上端部の長さ）／端子部の長さＬ_１］が２．０〜４．０の範囲にあることが望ましい。
【００１４】
該発熱体１に設けられたスリット５の幅は１〜１０ｍｍとすることが必要である。スリット５の幅が１ｍｍ未満の場合には、長時間の使用による発熱体の変形によって接触、回路的短絡が発生する可能性があり、一方、スリット５の幅が１０ｍｍを超える場合には、スリット５からの熱のロスが大きくなるため消費電力が高くなり、さらにスリット５の幅が大きくなるために、発熱体の長時間使用による変形が大きくなり、発熱体が破損しやすくなるなど寿命面での問題があるばかりか、炉内温度分布が不均一となりやすく、発熱体として実用的ではない。このため、該発熱体１に設けられたスリット５の幅は１〜１０ｍｍとすることが必要であり、２〜６ｍｍの範囲にあることがより望ましい。
【００１５】
また、該発熱体１の端子部２と発熱部５の長さの合計とスリット５の長さの比率（［スリットの長さＬ_３］／｛［端子部の長さＬ_１］＋［発熱部の長さＬ_２］｝）が０．８〜１．２の範囲にあることが必要である。かかる比率が０．８未満の場合には、スリットの終端が肉薄である発熱部に位置するために強度的に弱く、発熱体の耐久性が低下する。また比率が１．２倍を超える場合には、上端部４にスリットが入ってくるために上端部の強度が低下し、発熱体の耐久性が低下する。このため、該発熱体１の端子部と発熱部の長さの合計とスリットの長さの比率（［スリットの長さＬ_３］／｛［端子部の長さＬ_１］＋［発熱部の長さＬ_２］｝）が０．８〜１．２の範囲にあることが必要であり、０．９〜１．０５倍の範囲にあることがより望ましい。
【００１６】
該発熱体１の材料として用いるランタンクロマイト系セラミックスは、気孔率が５％未満であることが必要であり、３％未満であることがより望ましい。気孔率を小さくすることにより繰り返しの熱衝撃に対する耐久性に優れた発熱体を得ることが可能となる。これに加えて、発熱体を形成するランタンクロマイト系セラミックスの１０００℃における比抵抗が０．１Ωｃｍ以上であることが必要である。比抵抗が０．１Ωｃｍ未満の場合は、抵抗特性が低く電流値が大きくなり端子部電極の劣化が速くなるため短寿命となる。また逆に比抵抗が高くなりすぎると、制御に必要な印加電圧値の範囲が大きくなり実用的でなくなるため、比抵抗が０．２〜２．０Ωｃｍの範囲にあることがより望ましい。これらの特性制御は適宜、Ｌａの一部をＳｒ、Ｃａなどで、Ｃｒの一部をＣｏ、Ｎｉ、Ａｌ、Ｍｇなどで置換固溶させることにより、上記特性を有する発熱体とすることができる。
【００１７】
図５は、本発明の電気炉の一例を示す断面図であり、発熱体１の中空部内には、セラミックス炉心管８を装着し、この中空部内を有効加熱室とする。セラミックス炉心管８は、この内部に被加熱物を置くことにより、発熱体１からの蒸発物によって被加熱物が汚染されることを防止できる。該セラミックス炉心管８の厚さ、長さ、及び外寸法は、電気炉の仕様に応じて適宜決めることができ、さらに、該セラミックス炉心管８は電気炉の仕様に応じて長さ方向に対して位置によって厚みや外寸法などを変化させてもよい。また、該セラミックス炉心管８は発熱体１と密着させても良いが、発熱部３では非接触とすることで、より一層被加熱物への汚染防止効果が向上する。図４に示した本発明の電気炉は、縦型で示されているが、縦型での使用は勿論のこと、横型での使用も全く問題なく可能であり、横型での使用の場合には、試料の出し入れが容易となる。また、本発明の電気炉において、セラミック炉心管８の上端部は、開放状態で使用されるが、密閉状態で使用することもできる。その場合、試料搬入口と試料搬出口は同一となる。
【００１８】
セラミックス炉心管８は、電気炉を使用する温度域に応じて、従来電気炉の炉心管として用いられている各種の公知のセラミックスを使用することができるが、特に、純度９５％以上、相対密度９３％以上のアルミナ、ムライト、スピネル、安定化ジルコニア（安定化剤も含めた純度が９５％以上）、マグネシア又はイットリアを使用することが望ましく、これらの材料を用いることにより、セラミックス炉心管８の耐熱性がさらに向上すると共に、発熱体１との反応も抑制され、被加熱物への汚染防止効果も向上する。
【００１９】
上記発熱体１の外側には、断熱材９を装着する。発熱体１の外側に断熱材９を装着することによって、電気炉の熱効率を上げることができる。断熱材の材質としては、耐火煉瓦、耐火断熱煉瓦、キャスタブル耐火物、セラミックファイバー成形体等の各種の公知の耐火物を使用できる。又、セラミックファイバー成形体を使用する場合には、断熱性に優れ、蓄熱量が小さいために、消費電力を低減することができ、発熱体１を更に長寿命化することが可能となる。また、断熱材の材質としてセラミックファイバー成形体を使用する場合、発熱体１と断熱材９との間に厚さ１〜３ｍｍ程度のセラミックス層を形成することにより、発熱体１と断熱材９との反応をより一層少なくすることができ、発熱体１をより一層長寿命化することが可能となる。
【００２０】
【実施例】
以下に本発明の実施例について下記に説明するが、本発明はこれらの実施例だけに限定するものではない。
【００２１】
実施例１
図５の電気炉において、発熱体１として、図３および図４（Ａ）（Ｂ）に示すように、表１に記載した形状および特性を有し、内径３２ｍｍ、端子部２及び上端部４の外径４４ｍｍ（端子部２の長さ５５ｍｍ、上端部４の長さ２５ｍｍ）、発熱部３の外径３６ｍｍ（有効発熱部の長さ７５ｍｍ）、全長１５５ｍｍの円筒型ランタンクロマイト系セラミックスを用い、端子部２の下端面を２等分割する位置から上端部に向かって垂直方向に２ケ所の幅３ｍｍ、長さ１３０ｍｍの溝を設けスリット５とし、端子部２の下端から２５ｍｍの位置までの部位（外周面及び端面）に白金ペーストを塗布し、１３００℃で焼き付けて、高温用電極６を形成したのち、ステンレス鋼ＳＵＳ３０４からなる金属リード部品７を取り付けた。この発熱体１の中空部内に純度９９．５％、相対密度９７％のアルミナセラミックス炉心管８（以下炉心管と呼ぶ）（外径３０ｍｍ×内径２４ｍｍ×長さ４００ｍｍ）を挿入し、発熱体１の外側に、純度９９．５％、相対密度９７％の円筒型のアルミナセラミックス１０（外径１０ａの大きさが５４ｍｍ、外径１０ｂの大きさが５０ｍｍ、内径１０が４６ｍｍ、全長１２０ｍｍ）を装着した。さらにその外側には断熱材９として、純度９５％のα−アルミナ材質からなる、かさ密度０．７ｇ／ｃｍ^３の成形体（セラミックファイバー成形体）を、中央部に４８ｍｍの貫通孔を有する形状に加工して配置し、その外部を、耐火材を内張りにした金属缶体で取り囲み固定することによって、電気炉を得た。
【００２２】
実施例２
図５の電気炉において、実施例１と同様の特性を有するランタンクロマイト系セラミックスを用いて、端子部２の外径５０ｍｍ、端子部２の長さ６０ｍｍ、全長１６０ｍｍ、スリットの長さ１３７ｍｍとして発熱体１を作製し、発熱体１の外側に、純度９９．５％、相対密度９７％の円筒型のアルミナセラミックス１０（外径１０ａの大きさが６０ｍｍ、外径１０ｂの大きさが５６ｍｍ、内径１０が５２ｍｍ、全長１２０ｍｍ）を装着したこと以外は、実施例１と同様にして電気炉を得た。
【００２３】
実施例３
図５の電気炉において、実施例１と同様の特性を有するランタンクロマイト系セラミックスを用いて、端子部２の長さ５０ｍｍ、発熱部３の外径３８ｍｍ、発熱部３の長さ８０ｍｍとして発熱体１を作製したこと以外は、実施例１と同様にして電気炉を得た。
【００２４】
実施例４
図５の電気炉において、実施例１と同様の特性を有するランタンクロマイト系セラミックスを用いて、発熱体１の内径２８ｍｍ、端子部２及び上端部４の外径４０ｍｍ（端子部２の長さ６５ｍｍ、上端部４の長さ２５ｍｍ）、発熱部３の外径３２ｍｍ、スリットの長さ１４０ｍｍとして発熱体１を作製したこと以外は、実施例１と同様にして電気炉を得た。
【００２５】
実施例５
図５の電気炉において、スリットの幅を５ｍｍ、発熱体１の全長１６０ｍｍ（上端部４の長さ３０ｍｍ）、スリットの長さを１３２ｍｍとして発熱体１を作製したこと以外は、実施例１と同様にして電気炉を得た。
【００２６】
実施例６
図５の電気炉において、実施例１と同様の特性を有するランタンクロマイト系セラミックスを用いて、発熱体１の内径１６ｍｍ、端子部２及び上端部４の外径２４ｍｍ（端子部２の長さ３５ｍｍ、上端部４の長さ１５ｍｍ）、発熱部３の外径２０ｍｍ（有効発熱部の長さ５０ｍｍ）、全長１００ｍｍ、スリットの幅２．５ｍｍ、スリットの長さ８０ｍｍとして発熱体１を作製し、発熱体１の中空部内に純度９９．５％、相対密度９７％のアルミナ炉心管（外径１５ｍｍ×内径１１ｍｍ×長さ２００ｍｍ）を挿入し、発熱体１の外側に、純度９９．５％、相対密度９７％の円筒型のアルミナセラミックス１０（外径１０ａの大きさが３６ｍｍ、外径１０ｂの大きさが３２ｍｍ、内径１０が２５ｍｍ、全長８０ｍｍ）を装着したこと以外は、実施例１と同様にして電気炉を得た。
【００２７】
実施例７
図５の電気炉において、実施例１と同様の特性を有するランタンクロマイト系セラミックスを用いて、発熱体１の内径８ｍｍ、端子部２及び上端部４の外径１５ｍｍ（端子部２の長さ２０ｍｍ、上端部４の長さ３０ｍｍ）、発熱部３の外径１１ｍｍ（有効発熱部の長さ３０ｍｍ）、全長６０ｍｍ、スリットの幅２ｍｍ、スリットの長さ５２ｍｍとして発熱体１を作製し、発熱体１の中空部内に純度９９．５％、相対密度９７％のアルミナ炉心管（外径６ｍｍ×内径４ｍｍ×長さ９０ｍｍ）を挿入し、発熱体１の外側に、純度９９．５％、相対密度９７％の円筒型のアルミナセラミックス１０（外径１０ａの大きさが２４ｍｍ、外径１０ｂの大きさが２０ｍｍ、内径１０が１６ｍｍ、全長７５ｍｍ）を装着したこと以外は、実施例１と同様にして電気炉を得た。
【００２８】
実施例８
図５の電気炉において、発熱体１の材料の比抵抗が０．５６Ωｃｍであるランタンクロマイト系セラミックスを用いて、発熱体１の内径４５ｍｍ、端子部２及び上端部４の外径６０ｍｍ（端子部２の長さ１００ｍｍ、上端部４の長さ４０ｍｍ）、発熱部３の外径５０ｍｍ（有効発熱部の長さ１６０ｍｍ）、全長３００ｍｍ、スリットの幅５ｍｍ、スリットの長さ２６０ｍｍとして発熱体１を作製し、発熱体１の中空部内に純度９９．５％、相対密度９７％のアルミナ炉心管（外径４２ｍｍ×内径３５ｍｍ×長さ４５０ｍｍ）を挿入し、発熱体１の外側に、純度９９．５％、相対密度９７％の円筒型のアルミナセラミックス１０（外径１０ａの大きさが８５ｍｍ、外径１０ｂの大きさが７５ｍｍ、内径１０が６５ｍｍ、全長２３０ｍｍ）を装着したこと以外は、実施例１と同様にして電気炉を得た。
【００２９】
比較例１
実施例１における図５の電気炉において、発熱部３の外径を４２ｍｍとして発熱体１を作製したこと以外は、実施例１と同様にして電気炉を得た。
【００３０】
比較例２
図５の電気炉において、実施例１と同様の特性を有するランタンクロマイト系セラミックスを用いて、発熱体１の内径１８ｍｍ、端子部２及び上端部４の外径５０ｍｍ、発熱部３の外径２２ｍｍ、スリットの幅２．５ｍｍとして発熱体１を作製し、発熱体１の中空部内に純度９９．５％、相対密度９７％のアルミナ炉心管（外径１５ｍｍ×内径１１ｍｍ×長さ４００ｍｍ）を挿入し、発熱体１の外側に、純度９９．５％、相対密度９７％の円筒型のアルミナセラミックス１０（外径１０ａの大きさが６０ｍｍ、外径１０ｂの大きさが５６ｍｍ、内径１０が５２ｍｍ、全長１２０ｍｍ）を装着したこと以外は、実施例１と同様にして電気炉を得た。
【００３１】
比較例３
実施例１における図５の電気炉において、発熱体１の内径３３ｍｍ、端子部２の長さ３５ｍｍ、発熱部３の長さ８５ｍｍ（全長１４５ｍｍ、スリットの長さ１２０ｍｍ）として発熱体１を作製したこと以外は、実施例１と同様にして電気炉を得た。
【００３２】
比較例４
図５の電気炉において、端子部２の長さを１００ｍｍ（全長２０５ｍｍ、スリットの長さ１８０ｍｍ）として発熱体１を作製したこと以外は、実施例１と同様にして電気炉を得た。
【００３３】
比較例５
図５の電気炉において、端子部２および上端部４の外径４２ｍｍ、発熱部３の外径３５ｍｍ、スリットの幅を０．５ｍｍとして発熱体１を作製したこと以外は、実施例１と同様にして電気炉を得た。
【００３４】
比較例６
図５の電気炉において、発熱体１の内径３０ｍｍ、スリットの幅を１２ｍｍ、全長１６０ｍｍとして発熱体１を作製したこと以外は、実施例１と同様にして電気炉を得た。
【００３５】
比較例７
実施例１における図５の電気炉において、端子部２及び上端部４の外径４６ｍｍ、発熱部３の外径３８ｍｍ、スリットの長さ１１０ｍｍとして発熱体１を作製し、発熱体１の外側に、純度９９．５％、相対密度９７％の円筒型のアルミナセラミックス１０（外径１０ａの大きさが５８ｍｍ、外径１０ｂの大きさが５４ｍｍ、内径１０が５０ｍｍ、全長１２０ｍｍ）を装着したこと以外は、実施例１と同様にして電気炉を得た。
【００３６】
比較例８
実施例１における図５の電気炉において、発熱体１の内径３３ｍｍ、スリットの長さ１４５ｍｍ、全長１６０ｍｍとして発熱体１を作製したこと以外は、実施例１と同様にして電気炉を得た。
【００３７】
比較例９
実施例８における図５の電気炉において、発熱体１の材料として気孔率７．２％のランタンクロマイト系セラミックスを用いて発熱体１を作製したこと以外は、実施例８と同様にして電気炉を得た。
【００３８】
比較例１０
実施例６における図５の電気炉において、発熱体１の材料の比抵抗が０．０８Ωｃｍであるランタンクロマイト系セラミックスを用いて、スリットの長さを８５ｍｍとして発熱体１を作製したこと以外は、実施例６と同様にして電気炉を得た。
【００３９】
試験例１
実施例１〜８及び比較例１〜１０のそれぞれの電気炉を、有効炉内中央での保持温度１８００℃、保持時間３０ｍｉｎ、昇降温速度６００℃／ｈで繰り返しサイクル通電試験を実施したときの、消費電力が最大となる保持温度到達時の電圧、電流、消費電力及び発熱体が破損するまでのサイクル回数を求めた。その結果を表２に示す。
【００４０】
表２から明らかなように、実施例１〜８の電気炉は、高い耐久性を示した。また比較例１〜１０の結果から明らかなように、本発明の要件を満足しないランタンクロマイト系発熱体を用いた電気炉は、耐久性に優れた電気炉とはならない。
【００４１】
試験例２
実施例１及び６〜８のそれぞれの電気炉を、有効炉内中央での保持温度１９００℃、保持時間３０ｍｉｎ、昇降温速度６００℃／ｈで通電試験を実施したときの、消費電力が最大となる保持温度到達時の電圧、電流、消費電力を求めた。その結果を表３に示す。
【００４２】
表３から明らかなように、本発明の電気炉は１９００℃までの急速加熱冷却が可能であった。
【表１】

【表２】

【表３】

【００４３】
【発明の効果】
本発明に係る電気炉においては、円筒型のランタンクロマイト系発熱体に２ケ所のスリットを設けることによって端子部を一方に集中しているため発熱体を従来よりも短尺化することができ、発熱体内部を有効加熱室として用いることにより電気炉を一体型化し、これらにより電気炉をコンパクト化することができる。また１９００℃まで急速加熱冷却が可能で長寿命となるほか、各種雰囲気制御を行うことが可能である。また本電気炉は、縦型での使用はもちろんのこと、横型での使用も全く問題なく可能であり、試料の出し入れが容易であるというメリットも持ちあわせている。
【図面の簡単な説明】
【図１】図１（Ａ）は従来の複数の発熱体を使用した管状型電気炉の縦断面図、図１（Ｂ）は従来の管状型電気炉の横断面図である。
【図２】図２（Ａ）は従来の一本の発熱体を使用した一体型の管状型電気炉の縦断面図、図２（Ｂ）は従来の一本の発熱体を使用した一体型の管状型電気炉の横断面図である。
【図３】図３は本発明電気炉の発熱体を正面から見た図である。
【図４】図４（Ａ）は本発明電気炉の発熱体を側面から見た図、図４（Ｂ）は図４（Ａ）のＡ−Ａ′断面図である。
【図５】図５は本発明電気炉の一例を示す縦断面図である。
【符号の説明】
１発熱体
２端子部
３発熱部
４上端部
５スリット
６電極
７金属リード部品
８セラミックス炉心管
９断熱材
１０セラミックス層
１０ａセラミックス層
１０ｂセラミックス層
１１金属缶体
１２棒状発熱体
１３断熱材
１４炉心管
１５発熱部
１６電極
１７リード線
１８断熱材
１９炉心管[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electric furnace that uses the inside of a cylindrical resistance heating element mainly composed of lanthanum chromite as a heating chamber.
[0002]
[Prior art]
Mainly composed of lanthanum chromite (LaCrO ₃ ) having a perovskite-type crystal structure. If necessary, part of La is replaced with Sr, Ca, etc., and part of Cr is replaced with Co, Ni, Al, Mg, etc. A heating element having the above composition (hereinafter simply referred to as a lanthanum chromite system) is widely used as a ceramic resistance heating element having excellent stability and long life in a high-temperature oxidizing atmosphere of 1500 ° C. or higher.
[0003]
Conventionally, an electric furnace using a resistance heating element generally used has a structure in which a heating chamber is heated using a plurality of rod-shaped heating elements 12 as shown in FIG. Furnace has drawbacks such as complicated and large equipment structure, and low heat efficiency and high power consumption, so there are limits to performance and life such as operating temperature and heating rate of the heating element. . In FIG. 1, reference numeral 13 denotes a heat insulating material, and 14 denotes a core tube.
[0004]
Therefore, as shown in FIG. 2, the structure of the heating element 1 is made of a cylindrical heating element with a hollow portion as a heating chamber, so that the thermal efficiency of the electric furnace is improved and the operating temperature and temperature rise are increased. It is possible to improve the performance and life such as the temperature rate, and some of them are put into practical use in a silicon carbide (SiC) tube type, a double tube type heating element, and the like. In FIG. 2, 15 is a heat generating part, 16 is an electrode, 17 is a lead wire, 18 is a heat insulating material, and 19 is a core tube.
[0005]
However, when the conventionally used silicon carbide heating element is used in the temperature range of 1500 ° C. or higher in the atmosphere, since the silicon carbide is oxidized and the thermal conductivity of silicon carbide is high, the size of the heating element is increased. It is necessary to reduce the temperature of the terminal part and increase the air tightness of the heat generating part, and there is a problem that the heating element becomes large and the electric furnace becomes large as compared with the effective heating area to be a desired temperature. is there. In addition, repeated rapid heating and cooling breaks in a short period of time, so there is a problem in life. For this reason, measures such as changing the material of the heating element only to lanthanum chromite are physically possible, but silicon carbide has a low coefficient of thermal expansion, good thermal conductivity, and excellent thermal shock resistance. While chromite is inferior to these, it has advantages such as heat resistance, conductivity stability against temperature and durability. Therefore, it is inappropriate to use the same structure as that of a silicon carbide heating element.
[0006]
[Problems to be solved by the invention]
The present invention solves such problems of the prior art, and is a compact electric power source composed of a lanthanum chromite-based heating element that has a large effective heating area of the heating element but can be rapidly heated and cooled to 1900 ° C. and has a long life. The purpose is to provide a furnace.
[0007]
[Means for Solving the Problems]
The present invention prevents the length of the heating element by concentrating the terminal portions of the heating element in one place, and integrates the electric furnace by using the inside of the heating element as an effective heating chamber, thereby making the electric furnace compact. It was possible to achieve the above-mentioned object by adjusting the shape of the heating element and the characteristics of the material to an appropriate range.
[0008]
[Means for Solving the Problems]
The first of the present invention is a cylindrical lanthanum chromite heating element comprising a heating part and both end parts, wherein the porosity of the heating element material is less than 5% and the specific resistance at 1000 ° C. is 0.1 Ωcm or more. The terminal part is concentrated on one side by providing two slits in the vertical direction from the position where the lower end surface of the heating element is divided into two equal parts, the width of the slit is 1 to 10 mm, and the length of the terminal part and the heating part is The ratio of the total to the slit length ([slit length L ₃ ] / {[terminal portion length L ₁ ] + [heat generating portion length L ₂ ]}) is in the range of 0.8 to 1.2. A heating element having a high-temperature metal electrode attached to the terminal, a heat insulating material attached to the outside of the heating element, and a ceramic core tube mounted in the hollow portion of the heating element. The present invention relates to an electric furnace characterized in that the inside of the hollow portion is an effective heating chamber .
According to a second aspect of the present invention, in the lanthanum chromite heating element according to claim 1, the ratio of the outer diameter of the heat generating portion to the terminal portion ([terminal portion outer diameter] / [heat generating portion outer diameter]) is 1.1 to 1. The ratio of the length of the heat generating portion to the terminal portion ([terminal portion length L ₁ ] / [heat generating portion length L ₂ ]) is in the range of 0.3 to 1.0. The electric furnace according to claim 1.
[0009]
The electric furnace of the present invention will be described below with reference to the drawings.
[0010]
3 and 4 are views showing a heating element of the electric furnace of the present invention.
3 is a front view of the heating element of the electric furnace of the present invention, FIG. 4A is a side view of the heating element of the electric furnace of the present invention, and FIG. 4B is A of FIG. 4A. It is -A 'sectional drawing.
[0011]
In FIG. 3, the heating element 1 is made of a cylindrical lanthanum chromite ceramic composed of a terminal part 2, a heating part 3, and an upper end part 4, and further generates heat by setting the outer diameter of the heating part 3 to be less than the outer diameter of the terminal part 2. Two slits 5 are provided in the vertical direction from the position at which the lower end surface of the body 1 is divided into two equal parts, and the terminal electrode is concentrated on one side to form the terminal portion 2, and the high temperature electrode 6 and the metal lead component are provided on the terminal portion 2. 7 is attached, and the heat generating part 3 is formed between both ends. Thus, the current flows from one terminal portion → one heating element → upper end → the other heating element → the other terminal portion.
[0012]
In the heating element 1, the ratio of the outer diameter of the heat generating part 3 and the terminal part 2 ([terminal part outer diameter] / [heat generating part outer diameter]) needs to be in the range of 1.1 to 1.6. When the ratio of the outer diameter is less than 1.1, the difference between the outer diameters of the heat generating part 3 and the terminal part 2 is almost eliminated, and the resistance of the terminal part 2 becomes almost the same as the resistance of the heat generating part 3, so Short life due to heat generation. Further, when the ratio of the outer diameter exceeds 1.6, not only the outer diameter difference between the heat generating portion 3 and the terminal portion 2 is too large, the heating element 1 becomes unnecessarily large, but also the power consumption increases, the terminal portion Due to thermal shock to 2 and the like, the heating element has a short life and becomes impractical. For this reason, it is necessary to make the ratio of the outer diameter of the heat generating part 3 and the terminal part 2 into the range of 1.1-1.6, and it is more desirable to set it as the range of 1.15-1.5.
[0013]
Further, the ratio of the length of the heat generating portion 3 and the terminal portion 2 of the heat generating element 1 ([terminal portion length L ₁ ] / [heat generating portion length L ₂ ]) is in the range of 0.3 to 1.0. Need to be in. When the length ratio is less than 0.3, the terminal portion 2 is too short, so that the terminal portion cannot be sufficiently cooled and becomes high temperature, and the terminal electrode is rapidly deteriorated. When the length ratio exceeds 1.0, the terminal part becomes unnecessarily long and power consumption increases, so that not only the life is shortened, but also the heating element becomes larger than the effective heating area of the heating element. As a result, the electric furnace becomes large, and the object of the present invention cannot be achieved. For this reason, the ratio of the length of the heat generating portion and the terminal portion needs to be in the range of 0.3 to 1.0, and more preferably in the range of 0.6 to 0.95. The lengths of the heat generating portion 3 and the terminal portion 2 can be determined as appropriate within the range of the above conditions. However, when the length of the slit and the effective heating area are taken into consideration, the ratio of the length of the heating element to the length of the terminal portion [ It is desirable that (the length L _{1 of the} terminal portion + the length L _{2 of the} heat generating portion + the length of the upper end portion) / the length L _{1 of the} terminal portion] is in the range of 2.0 to 4.0.
[0014]
The width of the slit 5 provided in the heating element 1 needs to be 1 to 10 mm. If the width of the slit 5 is less than 1 mm, contact and circuit short circuit may occur due to deformation of the heating element due to long-term use. On the other hand, if the width of the slit 5 exceeds 10 mm, the slit Since the heat loss from 5 increases, the power consumption increases, and the width of the slit 5 increases, so that the deformation of the heating element increases due to long-term use, and the heating element tends to be damaged. In addition to the above problems, the temperature distribution in the furnace tends to be non-uniform and is not practical as a heating element. For this reason, the width | variety of the slit 5 provided in this heat generating body 1 needs to be 1-10 mm, and it is more desirable to exist in the range of 2-6 mm.
[0015]
Further, the ratio of the total length of the terminal portion 2 and the heat generating portion 5 of the heat generating element 1 to the length of the slit 5 ([slit length L ₃ ] / {[terminal length L ₁ ] + [heat generation] The length L ₂ ]}) of the part needs to be in the range of 0.8 to 1.2. When such a ratio is less than 0.8, the end of the slit is located in the thin heat generating portion, so that the strength is weak and the durability of the heat generating element is lowered. On the other hand, when the ratio exceeds 1.2 times, a slit enters the upper end portion 4, so that the strength of the upper end portion is lowered and the durability of the heating element is lowered. For this reason, the ratio of the total length of the terminal portion and the heat generating portion of the heat generating element 1 to the length of the slit ([slit length L ₃ ] / {[terminal length L ₁ ] + [heat generating portion The length L ₂ ]}) needs to be in the range of 0.8 to 1.2, and more preferably in the range of 0.9 to 1.05 times.
[0016]
The lanthanum chromite ceramic used as the material of the heating element 1 is required to have a porosity of less than 5%, and more preferably less than 3%. By reducing the porosity, it is possible to obtain a heating element having excellent durability against repeated thermal shocks. In addition to this, it is necessary that the specific resistance at 1000 ° C. of the lanthanum chromite ceramic forming the heating element is 0.1 Ωcm or more. When the specific resistance is less than 0.1 Ωcm, the resistance characteristic is low, the current value is large, and the terminal electrode is rapidly deteriorated, resulting in a short life. On the other hand, if the specific resistance is too high, the range of the applied voltage necessary for control becomes large and becomes impractical, and therefore the specific resistance is more preferably in the range of 0.2 to 2.0 Ωcm. These characteristics can be appropriately controlled by substituting and dissolving a part of La with Sr, Ca, etc. and a part of Cr with Co, Ni, Al, Mg, etc. to obtain a heating element having the above characteristics. .
[0017]
FIG. 5 is a cross-sectional view showing an example of an electric furnace according to the present invention. A ceramic furnace core tube 8 is mounted in the hollow portion of the heating element 1, and this hollow portion is used as an effective heating chamber. The ceramic furnace core tube 8 can prevent the heated object from being contaminated by the evaporated material from the heating element 1 by placing the heated object therein. The thickness, length, and external dimensions of the ceramic furnace core tube 8 can be determined as appropriate according to the specifications of the electric furnace. Further, the ceramic core tube 8 can be arranged in the length direction according to the specifications of the electric furnace. Depending on the position, the thickness and outer dimensions may be changed. Further, the ceramic core tube 8 may be brought into close contact with the heating element 1, but if the heating part 3 is not in contact, the effect of preventing contamination of the object to be heated is further improved. The electric furnace of the present invention shown in FIG. 4 is shown in a vertical type, but it can be used in a horizontal type as well as in a vertical type as well as in a vertical type. The sample can be easily taken in and out. In the electric furnace of the present invention, the upper end portion of the ceramic core tube 8 is used in an open state, but can also be used in a sealed state. In that case, the sample carry-in port and the sample carry-out port are the same.
[0018]
The ceramic furnace tube 8 can use various known ceramics conventionally used as a furnace tube of an electric furnace depending on the temperature range in which the electric furnace is used. It is desirable to use 93% or more of alumina, mullite, spinel, stabilized zirconia (purity including a stabilizer of 95% or more), magnesia or yttria. By using these materials, the ceramic core tube 8 The heat resistance is further improved, the reaction with the heating element 1 is suppressed, and the effect of preventing contamination of the object to be heated is also improved.
[0019]
A heat insulating material 9 is attached to the outside of the heating element 1. By mounting the heat insulating material 9 on the outside of the heating element 1, the thermal efficiency of the electric furnace can be increased. As a material of the heat insulating material, various known refractory materials such as refractory bricks, refractory heat insulating bricks, castable refractories and ceramic fiber molded bodies can be used. Further, when the ceramic fiber molded body is used, since the heat insulation is excellent and the heat storage amount is small, the power consumption can be reduced and the life of the heating element 1 can be further extended. Further, when a ceramic fiber molded body is used as the material of the heat insulating material, by forming a ceramic layer having a thickness of about 1 to 3 mm between the heat generating body 1 and the heat insulating material 9, the heat generating body 1 and the heat insulating material 9 It is possible to further reduce the reaction, and it is possible to further extend the life of the heating element 1.
[0020]
【Example】
Examples of the present invention will be described below, but the present invention is not limited to these examples.
[0021]
Example 1
In the electric furnace of FIG. 5, the heating element 1 has the shape and characteristics described in Table 1 as shown in FIGS. 3 and 4A and 4B, an inner diameter of 32 mm, a terminal portion 2 and an upper end portion 4. The cylindrical lanthanum chromite ceramics having an outer diameter of 44 mm (55 mm of the terminal portion 2 and 25 mm of the upper end portion 4), an outer diameter of the heating portion 3 of 36 mm (effective heating portion length of 75 mm), and a total length of 155 mm are used. The lower end surface of the terminal part 2 is divided into two equal parts from the position where the lower end surface is divided into two in the vertical direction toward the upper end part to form a slit 5 with a groove having a width of 3 mm and a length of 130 mm, from the lower end of the terminal part 2 to a position of 25 mm. A platinum paste was applied to the portions (outer peripheral surface and end surface) and baked at 1300 ° C. to form the high-temperature electrode 6, and then a metal lead component 7 made of stainless steel SUS304 was attached. An alumina ceramic core tube 8 (hereinafter referred to as a core tube) (outer diameter 30 mm × inner diameter 24 mm × length 400 mm) having a purity of 99.5% and a relative density of 97% is inserted into the hollow portion of the heating element 1. A cylindrical alumina ceramic 10 having a purity of 99.5% and a relative density of 97% (the outer diameter 10a is 54 mm, the outer diameter 10b is 50 mm, the inner diameter 10 is 46 mm, and the total length is 120 mm) is mounted outside. did. Further, on the outside, as a heat insulating material 9, a molded body (ceramic fiber molded body) made of an α-alumina material having a purity of 95% and having a bulk density of 0.7 g / cm ³ and a through-hole of 48 mm in the center part is formed. An electric furnace was obtained by surrounding and fixing the outside with a metal can body lined with a refractory material.
[0022]
Example 2
In the electric furnace shown in FIG. 5, the lanthanum chromite ceramic having the same characteristics as in Example 1 was used to generate heat with an outer diameter of the terminal portion 2 of 50 mm, a length of the terminal portion 2 of 60 mm, an overall length of 160 mm, and a slit length of 137 mm. The body 1 is manufactured, and the cylindrical alumina ceramic 10 having a purity of 99.5% and a relative density of 97% is formed outside the heating element 1 (the outer diameter 10a is 60 mm, the outer diameter 10b is 56 mm, the inner diameter is An electric furnace was obtained in the same manner as in Example 1 except that 10 was 52 mm and the total length was 120 mm.
[0023]
Example 3
In the electric furnace shown in FIG. 5, a lanthanum chromite ceramic having the same characteristics as in Example 1 is used, and the heating element has a terminal part 2 length of 50 mm, a heat generating part 3 outer diameter of 38 mm, and a heat generating part 3 length of 80 mm. An electric furnace was obtained in the same manner as in Example 1 except that No. 1 was produced.
[0024]
Example 4
In the electric furnace of FIG. 5, the lanthanum chromite ceramics having the same characteristics as in Example 1 are used, and the inner diameter of the heating element 1 is 28 mm, the outer diameter of the terminal portion 2 and the upper end portion 4 is 40 mm (the length of the terminal portion 2 is 65 mm). An electric furnace was obtained in the same manner as in Example 1 except that the heating element 1 was manufactured with the length of the upper end 4 being 25 mm), the outer diameter of the heating part 3 being 32 mm, and the length of the slit being 140 mm.
[0025]
Example 5
In the electric furnace of FIG. 5, except that the heating element 1 was manufactured with the slit width of 5 mm, the entire length of the heating element 1 of 160 mm (the length of the upper end 4 is 30 mm), and the slit length of 132 mm. An electric furnace was obtained in the same manner.
[0026]
Example 6
In the electric furnace of FIG. 5, the lanthanum chromite ceramic having the same characteristics as in Example 1 is used, the inner diameter of the heating element 16 is 16 mm, the outer diameter of the terminal portion 2 and the upper end portion 4 is 24 mm (the length of the terminal portion 2 is 35 mm). The heating element 1 is manufactured with a length of the upper end 4 of 15 mm), an outer diameter of the heating part 3 of 20 mm (an effective heating part length of 50 mm), a total length of 100 mm, a slit width of 2.5 mm, and a slit length of 80 mm. An alumina core tube (outer diameter 15 mm × inner diameter 11 mm × length 200 mm) having a purity of 99.5% and a relative density of 97% is inserted into the hollow portion of the heating element 1, and a purity of 99.5% Example except that cylindrical alumina ceramic 10 having a relative density of 97% (the outer diameter 10a is 36 mm, the outer diameter 10b is 32 mm, the inner diameter 10 is 25 mm, and the total length is 80 mm) An electric furnace was obtained in the same manner as in 1.
[0027]
Example 7
In the electric furnace of FIG. 5, the inner diameter of the heating element 1 is 8 mm, the outer diameter of the terminal portion 2 and the upper end portion 4 is 15 mm (the length of the terminal portion 2 is 20 mm) using lanthanum chromite ceramics having the same characteristics as in the first embodiment. The heating element 1 was prepared with a length of the upper end 4 of 30 mm, an outer diameter of the heating part 3 of 11 mm (an effective heating part length of 30 mm), a total length of 60 mm, a slit width of 2 mm, and a slit length of 52 mm. An alumina core tube (outer diameter 6 mm × inner diameter 4 mm × length 90 mm) having a purity of 99.5% and a relative density of 97% is inserted into the hollow portion 1, and a purity of 99.5% and a relative density are placed outside the heating element 1. Except that 97% cylindrical alumina ceramics 10 (the outer diameter 10a is 24 mm, the outer diameter 10b is 20 mm, the inner diameter 10 is 16 mm, and the total length is 75 mm) is the same as in Example 1. An electric furnace was obtained.
[0028]
Example 8
In the electric furnace shown in FIG. 5, the lanthanum chromite ceramic having a specific resistance of the heating element 1 of 0.56 Ωcm is used, the inner diameter of the heating element 45 is 45 mm, the outer diameter of the terminal portion 2 and the upper end portion 4 is 60 mm (terminal portion). 2 with a length of 100 mm, a length of the upper end 4 of 40 mm), an outer diameter of the heat generating portion 3 of 50 mm (effective heat generating portion length of 160 mm), a total length of 300 mm, a slit width of 5 mm, and a slit length of 260 mm. The alumina core tube (outer diameter 42 mm × inner diameter 35 mm × length 450 mm) having a purity of 99.5% and a relative density of 97% is inserted into the hollow portion of the heating element 1. 5%, 97% relative density cylindrical alumina ceramic 10 (outer diameter 10a size is 85mm, outer diameter 10b size is 75mm, inner diameter 10 is 65mm, total length 230mm) Except that, to obtain an electric furnace in the same manner as in Example 1.
[0029]
Comparative Example 1
In the electric furnace of FIG. 5 in Example 1, an electric furnace was obtained in the same manner as in Example 1 except that the heating element 1 was produced with the outer diameter of the heat generating part 3 being 42 mm.
[0030]
Comparative Example 2
In the electric furnace shown in FIG. 5, the lanthanum chromite ceramic having the same characteristics as in Example 1 is used, the inner diameter of the heating element 1 is 18 mm, the outer diameter of the terminal part 2 and the upper end part 4 is 50 mm, and the outer diameter of the heating part 3 is 22 mm. The heating element 1 is manufactured with a slit width of 2.5 mm, and an alumina core tube (outer diameter 15 mm × inner diameter 11 mm × length 400 mm) having a purity of 99.5% and a relative density of 97% is inserted into the hollow portion of the heating element 1. On the outside of the heating element 1, a cylindrical alumina ceramic 10 having a purity of 99.5% and a relative density of 97% (the outer diameter 10a is 60 mm, the outer diameter 10b is 56 mm, the inner diameter 10 is 52 mm, An electric furnace was obtained in the same manner as in Example 1 except that a total length of 120 mm) was attached.
[0031]
Comparative Example 3
In the electric furnace of FIG. 5 in Example 1, the heating element 1 was produced with the inner diameter of the heating element 1 of 33 mm, the length of the terminal part 2 of 35 mm, and the length of the heating part 3 of 85 mm (total length 145 mm, slit length 120 mm). An electric furnace was obtained in the same manner as in Example 1 except that.
[0032]
Comparative Example 4
In the electric furnace shown in FIG. 5, an electric furnace was obtained in the same manner as in Example 1 except that the heating element 1 was prepared with the terminal portion 2 having a length of 100 mm (total length 205 mm, slit length 180 mm).
[0033]
Comparative Example 5
In the electric furnace of FIG. 5, the same as in Example 1 except that the heating element 1 was manufactured with the outer diameter of the terminal portion 2 and the upper end portion 42 being 42 mm, the outer diameter of the heating portion 3 being 35 mm, and the slit width being 0.5 mm. An electric furnace was obtained.
[0034]
Comparative Example 6
An electric furnace was obtained in the same manner as in Example 1 except that the heating element 1 was produced with an inner diameter of the heating element 1 of 30 mm, a slit width of 12 mm, and a total length of 160 mm.
[0035]
Comparative Example 7
In the electric furnace of FIG. 5 in Example 1, the heating element 1 was prepared with the outer diameter of the terminal part 2 and the upper end part 46 being 46 mm, the outer diameter of the heating part 3 being 38 mm, and the slit length being 110 mm. Other than mounting cylindrical alumina ceramic 10 (outer diameter 10a size is 58mm, outer diameter 10b size is 54mm, inner diameter 10 is 50mm, total length 120mm) with purity 99.5% and relative density 97% Obtained an electric furnace in the same manner as in Example 1.
[0036]
Comparative Example 8
In the electric furnace of FIG. 5 in Example 1, an electric furnace was obtained in the same manner as in Example 1 except that the heating element 1 was manufactured with an inner diameter of 33 mm, a slit length of 145 mm, and a total length of 160 mm.
[0037]
Comparative Example 9
In the electric furnace shown in FIG. 5 in Example 8, the electric furnace was manufactured in the same manner as in Example 8 except that the heating element 1 was produced using lanthanum chromite ceramic having a porosity of 7.2% as the material of the heating element 1. Got.
[0038]
Comparative Example 10
In the electric furnace of FIG. 5 in Example 6, using the lanthanum chromite ceramic with a specific resistance of the material of the heating element 1 of 0.08 Ωcm, except that the heating element 1 was made with a slit length of 85 mm, An electric furnace was obtained in the same manner as in Example 6.
[0039]
Test example 1
When each of the electric furnaces of Examples 1 to 8 and Comparative Examples 1 to 10 was repeatedly subjected to a cycle current test at a holding temperature of 1800 ° C., a holding time of 30 min, and a temperature raising / lowering speed of 600 ° C./h in the center of the effective furnace. The voltage, current, power consumption, and the number of cycles until the heating element was damaged when the holding temperature reached the maximum power consumption were obtained. The results are shown in Table 2.
[0040]
As is clear from Table 2, the electric furnaces of Examples 1 to 8 showed high durability. Further, as is apparent from the results of Comparative Examples 1 to 10, an electric furnace using a lanthanum chromite heating element that does not satisfy the requirements of the present invention is not an electric furnace having excellent durability.
[0041]
Test example 2
When each of the electric furnaces of Examples 1 and 6 to 8 was subjected to an energization test at a holding temperature of 1900 ° C. in the center of the effective furnace, a holding time of 30 minutes, and a heating / cooling rate of 600 ° C./h, the power consumption was maximum. The voltage, current, and power consumption when the holding temperature was reached were obtained. The results are shown in Table 3.
[0042]
As is clear from Table 3, the electric furnace of the present invention was capable of rapid heating and cooling to 1900 ° C.
[Table 1]

[Table 2]

[Table 3]

[0043]
【The invention's effect】
In the electric furnace according to the present invention, since the terminal portions are concentrated on one side by providing two slits in the cylindrical lanthanum chromite heating element, the heating element can be made shorter than before, By using the inside of the body as an effective heating chamber, the electric furnace can be integrated, and thus the electric furnace can be made compact. In addition to rapid heating and cooling to 1900 ° C. and a long life, various atmosphere controls can be performed. In addition, the electric furnace can be used not only in a vertical type but also in a horizontal type without any problem, and has the merit that the sample can be taken in and out easily.
[Brief description of the drawings]
FIG. 1A is a longitudinal sectional view of a conventional tubular electric furnace using a plurality of heating elements, and FIG. 1B is a transverse sectional view of a conventional tubular electric furnace.
FIG. 2A is a longitudinal sectional view of an integrated tubular electric furnace using a conventional heating element, and FIG. 2B is an integrated type using a conventional heating element. It is a cross-sectional view of the tubular electric furnace.
FIG. 3 is a front view of a heating element of the electric furnace of the present invention.
4A is a side view of a heating element of the electric furnace of the present invention, and FIG. 4B is a cross-sectional view taken along the line AA ′ of FIG. 4A.
FIG. 5 is a longitudinal sectional view showing an example of the electric furnace of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Heat generating body 2 Terminal part 3 Heat generating part 4 Upper end part 5 Slit 6 Electrode 7 Metal lead component 8 Ceramic furnace core tube 9 Heat insulating material 10 Ceramic layer

10a Ceramic layer

10b Ceramic layer 11 Metal can body 12 Rod-shaped heating element 13 Heat insulating material 14 Core tube 15 Heating part 16 Electrode 17 Lead wire 18 Heat insulating material 19 Core tube

Claims

In a cylindrical lanthanum chromite heating element composed of a heating part and both ends, the porosity of the heating element material is less than 5% and the specific resistance at 1000 ° C. is 0.1 Ωcm or more. By providing two slits in the vertical direction from the position of dividing into two equal parts, the terminal part is concentrated on one side, the width of the slit is 1 to 10 mm, the total length of the terminal part and the heat generating part, and the length of the slit The ratio ([slit length L ₃ ] / {[terminal portion length L ₁ ] + [heat generating portion length L ₂ ]}) is in the range of 0.8 to 1.2. A heating element having a high-temperature metal electrode attached thereto, a heat insulating material mounted on the outside of the heating element, and a ceramic core tube mounted in a hollow portion of the heating element, and an effective heating chamber in the hollow portion of the core tube An electric furnace characterized by that.

The lanthanum chromite heating element according to claim 1, wherein the ratio of the outer diameter of the heat generating portion to the terminal portion ([terminal portion outer diameter] / [heat generating portion outer diameter]) is in the range of 1.1 to 1.6. _2. The electric furnace according to claim 1, wherein the ratio of the length of the terminal portion to the terminal portion ([terminal portion length L ₁ ] / [heat generating portion length L ₂ ]) is in the range of 0.3 to 1.0. .