【０００１】
【発明の属する技術分野】
この発明は，鉄の溶湯を測温する保護管を備えた金属溶湯測温用セラミック熱電対に関する。
【０００２】
【従来の技術】
従来，約１５００℃の鋳鉄溶湯を測温するための熱電対は，材料として比較的に融点が高く，大気中で安定であるＰｔ−Ｒｈを素線とし，該Ｐｔ−Ｒｈ素線をアルミナシリカファイバー製のパイプに固定した構造のものが使用されている。このような熱電対は，鋳鉄溶湯の測温を約１〜２回程度行った後に，正確な温度の測定が不能となり，廃棄しているのが現状であり，熱電対を多回数利用できずに熱電対そのものが極めて高価なものになっている。
【０００３】
また，シース型熱電対は，Ｗ−Ｒｅを素線とし，高温で使用される金属シース型部品の保護管として使用され，ステンレススチール（ＳＵＳ）等の金属で作製されたものが知られている。ＳＵＳシース型熱電対は，１０００℃以上の雰囲気で使用されるものがあり，その場合には，インコネル等の特殊耐熱合金で作製されている。或いは，熱電対として，保護管をサーメットで作製して，保護管の内部にＰｔ−Ｒｈを素線とした構造のものも知られている。
【０００４】
また，特開平６−１６０２００号公報には，気密端子付シース型熱電対が開示されている。該熱電対は，過渡的な温度変化等により，端子部に温度勾配が生じても測定誤差を生じさせないものであり，アルメル線とクロメル線の異種金属線からなる熱電対素線をステンレス製シース内に無機絶縁材と共に，相互に絶縁して収納し，シースの基端側を気密端子部により気密に封止する。気密端子部のセラミック端板に取り付けられた２本のコパール製の貫通パイプの内部に絶縁スリーブが挿入され，各熱電対素線はその内部を通って貫通パイプと直接接触せずに外部に引き出されている。
【０００５】
【発明が解決しようとする課題】
しかしながら．Ｐｔ−Ｒｈ熱電対は，不活性ガス雰囲気での使用はできず，大気中での使用可能温度は１５００℃が限界温度である。また，Ｗ−Ｒｅ熱電対は，大気中及び不活性ガス雰囲気中での使用が可能であり，大気中での使用可能温度は４００℃が限界温度であり，不活性ガス雰囲気中での使用可能温度は２３００℃が限界温度である。更に，Ｐｔ−Ｒｈ素線を用いたＰＲ熱電対について，ＰＲ熱電対の熱起電力は，ＣＡ熱電対の約１／１５であり，Ｗ−Ｒｅ熱電対の約１／７と小さいため，それらの熱電対に比較して測温の精度が劣り，応答性が悪いという問題を有している。そのため，現場においては，溶鉱炉の溶湯を測温するため，溶解炉の近傍で作業者が温度が安定するまでの約８秒間，その測定場所に居ることを余儀なくされる。
【０００６】
また，熱電対による溶湯の測温に際して，熱電対のＰｔ−Ｒｈ素線に鋳鉄が付着し，それを除去するための工程は煩雑になり，しかも現行品は寿命が２回程度の測温であり，熱電対の交換作業も手間がかかるという問題がある。また，熱電対におけるＷ−Ｒｅ素線は，大気中では酸化し易く，鋳鉄溶湯の温度測定には使用できないものである。しかも，外側の保護管には，鉄溶湯が付着し易いという問題を有している。
【０００７】
【課題を解決するための手段】
この発明の目的は，上記の課題を解決することであり，一対のタングステン−レニウム合金製素線の先端部を結合して測温点を構成し，これを多孔質セラミックスからなる充填部材を充填したセラミック製の第１保護管内にタングステン−レニウム合金製素線を配置し，更に前記第１保護管の測温端部をＭｏをベースとする第２保護管で覆い，それによって，金属溶湯と第２保護管との反応付着を阻止し，耐熱性，耐溶損性及び耐腐食性を向上させると共に，反復使用を可能にした金属溶湯測温用セラミック熱電対を提供することである。
【０００８】
この発明は，窒化ケイ素又はサイアロンから成る第１保護管，前記第１保護管内に配置され且つ先端部で結合された測温部を構成する異なる組成の一対のタングステン−レニウム合金製素線，前記第１保護管の内部で前記素線を埋設した状態で充填された多孔質窒化ケイ素系セラミックスから成る充填部材，前記第１保護管から開放端部が突出した状態で前記第１保護管の前記測温部の外側に配置され且つ耐溶損性のＭｏをベースにしたサーメットから成る第２保護管，及び前記第１保護管の端部を封止した緻密な耐熱部材と耐熱ガラスから成る封止部材から構成されている金属溶湯測温用セラミック熱電対に関する。
【０００９】
前記第２保護管の外周面には，熱膨張係数が小さく且つ鉄と反応し難いＺｒＢ２ 及び／又はＺｒＮを分散したＭｏをベースにした材料から成る被膜が形成されている。
【００１０】
前記第１保護管と前記第２保護管との隙間には，ＳｉＯ２ を主成分とするガラスから成る中間層が形成されている。
【００１１】
前記第１保護管内には，前記タングステン−レニウム合金製素線の酸化を防ぐため不活性ガスが封入されている。
【００１２】
前記第１保護管の端部から突出した前記第２保護管の前記開放端部内に存在する空気は，鉄溶湯中に浸した状態で前記開放端部内に密封され，前記開放端部内に鉄溶湯の侵入が阻止される。
【００１３】
この金属溶湯測温用セラミック熱電対は，測温領域の先端部を前記第１保護管と前記第１保護管の外側に配置した前記第２保護管の二重構造に構成し，前記先端部の熱容量と熱通過面積を可及的に小さく構成して前記第１保護管の後部への熱の伝達を低減したものである。
【００１４】
この金属溶湯測温用セラミック熱電対は，上記のように，窒化ケイ素又はサイアロンから成る第１保護管の測温領域を，Ｍｏをベースにしたサーメットから成る第２保護管で覆い，更に前記第２保護管の外周面を熱膨張係数が小さく且つ鉄と反応し難いＺｒＢ２ 及び／又はＺｒＮを分散したＭｏをベースにした材料から成る被膜で覆ったので，第１保護管のセラミックスが鉄溶湯と反応せず，耐熱性，耐溶損性を向上できる。しかも，前記第１保護管と前記第２保護管との間にはガラス層が配置されているので，たとえ前記第２保護管のサーメットに亀裂等が発生しても，該亀裂による隙間を前記耐熱ガラス層が埋め，しかもサーメットに熱衝撃による亀裂が発生しても，壊滅的な破壊が発生することがない。しかも．セラミックスの前記第１保護管が鉄の溶湯に直接接触せず，耐熱性，耐溶損性を向上できる。また，タングステン−レニウム合金製素線は不活性ガス中に封入されているので，Ｗ−Ｒｅ線の熱起電力が比較的に大きく，温度への応答性が良好になり，しかもＷ−Ｒｅ線の融点が３０００℃であり，鋳鉄溶湯中で溶けることはない。
【００１５】
【発明の実施の形態】
以下，図１を参照して，この発明による金属溶湯測温用セラミック熱電対の実施例を説明する。図１はこの金属溶湯測温用セラミック熱電対の実施例を示す断面図，図２は図１の金属溶湯測温用セラミック熱電対の先端部の拡大断面図，及び図３は本発明品と比較品との応答性を示すグラフである。
【００１６】
図１に示すように，この金属溶湯測温用セラミック熱電対は，測温領域の外側保護管として第１保護管１の測温領域を，第２保護管２で覆って耐熱性，耐溶損性を向上させたものである。タングステン−レニウム合金製素線（Ｗ−Ｒｅ素線）６，７は，Ｗ−５Ｒｅ素線６とＷ−２６Ｒｅ素線７から構成され，第１保護管１内に隔置して延びるように配置されている。タングステン−レニウム合金製素線６，７は，一端部が第１保護管１で測温部９を構成するように結線され，他端部が第１保護管１の端部から延び出した端子１２，１３に結線されている。Ｗ−Ｒｅ素線６，７の酸化腐食による断線を阻止するため，第１保護管１には，多孔質の窒化ケイ素系セラミックスから成る充填部材３が充填されている。
【００１７】
この金属溶湯測温用セラミック熱電対は，主として，第１保護管１，第１保護管１内に配置された異なる組成の一対のタングステン−レニウム合金製素線６，７，第１保護管１の内部でタングステン−レニウム合金製素線６，７を埋設した状態で充填された多孔質の窒化ケイ素系セラミックスから成る充填部材３，第１保護管１から開放端部１０が突出した状態で第１保護管１の測温部９の外側に配置され且つ耐溶損性のＭｏをベースにしたサーメットから成る第２保護管２，及び第１保護管１の端部を封止した緻密な耐熱部材と耐熱ガラスから成る封止部材８から構成されている。
【００１８】
第１保護管１は，窒化ケイ素（Ｓｉ３ Ｎ４ ）又はサイアロン（ｓｉａｌｏｎ），場合によっては炭化ケイ素（ＳｉＣ）から選択されるセラミックスによって作製されている。また，第２保護管２は，Ｍｏをベースにした炭化物系サーメント（Ｍｏ−ＺｒＯ２ ）から作製されている。また，第２保護管２の外周面には，ＺｒＮ及び／又はＺｒＢ２ が分散したＭｏをベースにした複合材で形成されている被膜４が溶射によって配置されている。
【００１９】
第１保護管１と第２保護管２との隙間には，ＳｉＯ２ を主成分とするガラスから成る中間層５が形成されている。それ故に，第２保護管２のサーメットに亀裂等が発生しても，該亀裂による隙間を中間層５のガラスが埋め，しかもサーメットに熱衝撃による亀裂が発生しても，壊滅的な破壊が発生することがない。
【００２０】
第１保護管１内には，タングステン−レニウム合金製素線６，７の酸化を防ぐため，Ａｒ，Ｎ２ 等の不活性ガスが封入されている。
【００２１】
第１保護管１の先端部１４から突出した第２保護管２の開放端部１０内に存在する空気は，鉄溶湯中に浸した状態で開放端部１０内に密封され，開放端部１０内に鉄溶湯の侵入が阻止される。
【００２２】
先端部の測温領域を，第１保護管１と第１保護管１の外側に配置した第２保護管２で二重構造に構成し，先端部１４の熱容量と熱通過面積を可及的に小さく構成して第１保護管１の後端部１５への熱の伝達を低減したものである。
【００２３】
この金属溶湯測温用セラミック熱電対において，特に，サーメットから作製された第２保護管２は，耐熱性，耐溶損性に優れ，しかも，熱衝撃で亀裂が発生しても緩やかに破壊に至り，例えば，従来のセラミックスから成る外殻のような壊滅的な破壊に至ることがない。第２保護管２内に封入された第１保護管１は，窒化ケイ素を主成分とするセラミックスから作製され，鉄溶湯に露出されると，窒化ケイ素は鉄と反応し，溶損が激しく，サーメットに比較して熱衝撃性が劣るが，この発明による第１保護管１は鉄の溶湯に直接接触することがないので，熱伝達率を小さくすることができ，従って，第１保護管１が熱衝撃で破損することが防止される。
【００２４】
この金属溶湯測温用セラミック熱電対は，第１保護管１，第２保護管２及び被膜４の合計の熱容量を小さく構成できるので，測温領域の先端部を二重構造に構成しても，温度測定の応答性を低下させることはない。更に，第１保護管１と第２保護管２との間には，ガラス層５が設けられている。従って，ガラス層５は，第１保護管１と第２保護管２との固定温度熱伝導性を向上させることができ，特に，第２保護管２に亀裂が発生した場合には，ガラスがその亀裂の部分へ浸入し，亀裂による隙間を埋める作用をし，第２保護管２の壊滅的な破壊を阻止することができる。
【００２５】
第１保護管１の後端部に設けられた封止部材８は，窒化ケイ素等の緻密な耐熱部材と耐熱部材に接して配置された耐熱ガラス部材から二重構造に構成されている。第１保護管１の内部には，充填部材３を充填して製造する時にＮ２ やＡｒの不活性ガスを封入し，第１保護管１の端部に封止部材８が嵌合して密閉状態に構成することができる。
【００２６】
また，第１保護管１内に充填された充填部材３は，Ｓｉ３ Ｎ４ 系反応焼結セラミックスから構成された多孔質構造に構成し，その熱伝導率が小さく構成されている。例えば，充填部材３は，空隙が多い構造に構成することによって熱伝導率を小さく構成することができる。従って，この金属溶湯測温用セラミック熱電対は，鉄等の金属の溶湯に入れられる第１保護管１が位置する測温領域の熱容量を小さく構成でき，該測温領域から後方の領域への熱の伝導を阻止できる。
【００２７】
−実施例−
実施例では，一対のＷ−Ｒｅ素線６，７は，互いに異なった組成を有するＷ−５ＲｅとＷ−２６Ｒｅからそれぞれ構成され，それぞれ線径が０．５ｍｍであり，長さが３００ｍｍであり，先端部が互いに溶接で結合されている結合部１６を備えている。Ｗ−Ｒｅ素線６，７を窒化ケイ素を主成分とする原料粉末で着肉した。一方，第１保護管１としては，外径が６．５ｍｍで長さが１２０〜１５０ｍｍであり，先端部１４が閉鎖され，後端部１５が開放した形状を有している窒化ケイ素製のものを使用した。上記の原料粉末が着肉したＷ−Ｒｅ素線６，７を，第１保護管１の開放した後端部１５から挿入して第１保護管１内に配置した。更に，第１保護管１内の隙間には，上記原料粉末を充填した。第１保護管１内に，ＡｒやＮ２ の不活性ガスを注入して第１保護管１の後端部１５を耐熱ガラスから成る封止部材８で密封した。
【００２８】
また，第２保護管２を，ＭｏをベースにしたＺｒＯ２ から成るサーメットによって内径７ｍｍのサイズに形成した。第２保護管２の外周面に，ＺｒＮ及び／又はＺｒＢ２ を分散させたＭｏをベースにした複合材から成る被膜４として溶射によって形成した。被膜４を溶射した第２保護管２に，第１保護管１を挿入した。この時，第２保護管２は，その端部１０が第１保護管１の先端部１４から突き出し，開放した空気室１１が形成される状態に配置した。次いで，第１保護管１と第２保護管２との隙間に，耐熱ガラスから成るガラス層５を充填して両者を固定し，端部をガラスを用いて固定封止処理を行った。
【００２９】
上記のように構成した金属溶湯測温用セラミック熱電対（本発明品）を使用して，約１４５０℃の鋳鉄溶湯の測温を行ったところ，原料粉末が焼成され，安定化するまでの時間は約８秒かかったが，鉄溶湯の測温を５００サイクル繰り返した。第２保護管２には，亀裂が認められたが，鉄溶湯の測温性能には問題がなく，その状態で更に鉄溶湯の測温を１０００回以上の鋳鉄溶湯の測温を行ったが，金属溶湯測温用セラミック熱電対の起電力の変化はなく，安定して測温することができた。
【００３０】
また，鋳鉄溶湯の測温とは別に，上記の金属溶湯測温用セラミック熱電対を使用して，約１５００℃の金属溶湯の連続測温を行ったところ，５００時間以上経過した時点においても，この金属溶湯測温用セラミック熱電対の起電力の変化等の異常は確認できなかった。即ち，この金属溶湯測温用セラミック熱電対は，耐熱性，耐溶損性が良好であることが分かった。
【００３１】
この金属溶湯測温用セラミック熱電対（本発明品）を別の熱電対と比較するため，比較例として，窒化ケイ素から成る内径７ｍｍの保護管内に，上記の原料粉末が着肉したＷ−Ｒｅ素線を挿入した構造を持つ熱電対（比較品）を作製した。比較品の応答性，鉄溶湯の付着性，及び耐久性の評価を行ったところ，本発明品に比較して．図３に示すように応答性が悪く，また，鉄が窒化ケイ素性保護管に付着し易いことが分かった。
【００３２】
【発明の効果】
この発明による金属溶湯測温用セラミック熱電対は，上記のように，窒化ケイ素製第１保護管がＭｏをベースにしたサーメット等の複合材から成る第２保護管で保護されているので，耐熱性，耐溶損性を向上でき，反復使用しても，鉄溶湯等の金属溶湯の温度を高精度に且つ迅速に測定でき，その寿命を向上させることができる。しかも，第２保護管の表面に，熱膨張係数が小さく且つ鉄と反応し難いＺｒＢ２ 及び／又はＺｒＮを分散したＭｏをベースにした材料から成る被膜を形成することによって，更に性能をアップできる。また，測温領域の温度は，第１保護管内の多孔質セラミックスから成る充填部材によってその領域が制限され，前記第１保護管内を通じて後方へ熱が逃げ難くなり，測温領域の熱容量を小さく構成でき，熱電対の測温応答性を向上させることができる。
【図面の簡単な説明】
【図１】この発明による金属溶湯測温用セラミック熱電対の実施例を示す断面図である。
【図２】図１の金属溶湯測温用セラミック熱電対の先端部の拡大断面図である。
【図３】本発明品と比較品との応答性を示すグラフである。
【符号の説明】
１ 第１保護管
２ 第２保護管
３ 充填部材
４ 被膜
５ ガラス層
６，７ タングステン−レニウム合金製素線
８ 封止部材
９ 測温部
１０ 開放端部
１１ 空気室
１２，１３ 端子
１４ 先端部
１５ 後端部
１６ 接合部[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a ceramic thermocouple for measuring the temperature of molten metal provided with a protective tube for measuring the temperature of molten iron.
[0002]
[Prior art]
Conventionally, a thermocouple for measuring the temperature of a cast iron melt at about 1500 ° C. uses a Pt-Rh wire that is relatively high in melting point and is stable in the air as a material, and uses the Pt-Rh wire as an alumina silica. A structure fixed to a fiber pipe is used. After measuring the temperature of the molten cast iron about 1-2 times, such thermocouples cannot be accurately measured and are now discarded, and the thermocouple cannot be used many times. In addition, thermocouples themselves are extremely expensive.
[0003]
In addition, a sheath-type thermocouple using W-Re as a strand, used as a protective tube for a metal sheath-type component used at a high temperature, and made of a metal such as stainless steel (SUS) is known. . Some SUS sheathed thermocouples are used in an atmosphere of 1000 ° C. or higher, and in such a case, are made of a special heat-resistant alloy such as Inconel. Alternatively, a thermocouple having a structure in which a protection tube is made of cermet and Pt-Rh is used as a wire inside the protection tube is also known.
[0004]
Japanese Patent Application Laid-Open No. 6-160200 discloses a sheath-type thermocouple with an airtight terminal. The thermocouple does not cause a measurement error even if a temperature gradient occurs at the terminal due to a transient temperature change or the like. A thermocouple wire composed of a dissimilar metal wire of an alumel wire and a chromel wire is connected to a stainless steel sheath. The sheath is housed together with the inorganic insulating material while being insulated from each other, and the base end side of the sheath is hermetically sealed by the hermetic terminal portion. Insulation sleeves are inserted into the two through-hole pipes made of Kopearl attached to the ceramic end plate of the hermetic terminal, and each thermocouple wire is drawn out without passing through the inside thereof and directly contacting the through-hole pipe. Have been.
[0005]
[Problems to be solved by the invention]
However. The Pt-Rh thermocouple cannot be used in an inert gas atmosphere, and its usable temperature in the atmosphere is 1500 ° C. as a limit temperature. In addition, the W-Re thermocouple can be used in the atmosphere and in an inert gas atmosphere. The usable temperature in the atmosphere is 400 ° C., which is the limit temperature. The limit temperature is 2300 ° C. Further, regarding the PR thermocouple using the Pt-Rh strand, the thermoelectromotive force of the PR thermocouple is about 1/15 of that of the CA thermocouple and about 1/7 of that of the W-Re thermocouple. However, there is a problem that the accuracy of temperature measurement is inferior to that of the thermocouple and the response is poor. Therefore, at the site, in order to measure the temperature of the molten metal in the blast furnace, the operator is forced to stay at the measuring place for about 8 seconds until the temperature stabilizes near the blast furnace.
[0006]
In addition, when measuring the temperature of the molten metal with a thermocouple, the cast iron adheres to the Pt-Rh strand of the thermocouple, and the process for removing the cast iron becomes complicated. In addition, there is a problem that the work of replacing the thermocouple is troublesome. Further, the W-Re element wire in the thermocouple is easily oxidized in the atmosphere and cannot be used for measuring the temperature of the molten cast iron. In addition, there is a problem that the molten iron easily adheres to the outer protective tube.
[0007]
[Means for Solving the Problems]
SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems. A pair of tungsten-rhenium alloy strands is joined to form a temperature measuring point, which is filled with a filling member made of porous ceramics. A tungsten-rhenium alloy wire is placed in the first ceramic protection tube thus obtained, and the temperature measuring end of the first protection tube is covered with a second protection tube based on Mo. An object of the present invention is to provide a ceramic thermocouple for measuring the temperature of a molten metal, which prevents reaction adhesion to a second protective tube, improves heat resistance, erosion resistance and corrosion resistance, and enables repeated use.
[0008]
The present invention relates to a first protective tube made of silicon nitride or sialon, a pair of tungsten-rhenium alloy wires of different compositions constituting a temperature measuring unit disposed in the first protective tube and connected at a tip end thereof, A filling member made of porous silicon nitride-based ceramic filled with the wires buried inside the first protection tube, and a filling member of the first protection tube with an open end protruding from the first protection tube; A second protection tube, which is disposed outside the temperature measuring unit and is made of a cermet based on erosion resistance Mo, and a sealing made of a dense heat-resistant member sealing the end of the first protection tube and heat-resistant glass; The present invention relates to a ceramic thermocouple for measuring the temperature of a molten metal made of a member.
[0009]
Wherein the outer circumferential surface of the second protective tube, coating of a Mo coefficient of thermal expansion was dispersed small and iron react with hardly ZrB 2 and / or ZrN from a material based is formed.
[0010]
An intermediate layer made of glass containing SiO 2 as a main component is formed in a gap between the first protection tube and the second protection tube.
[0011]
An inert gas is sealed in the first protection tube to prevent oxidation of the tungsten-rhenium alloy strand.
[0012]
Air present in the open end of the second protective tube protruding from the end of the first protective tube is sealed in the open end while being immersed in the molten iron, and the molten iron is contained in the open end. Is prevented.
[0013]
The ceramic thermocouple for measuring molten metal temperature has a dual structure of the first protective tube and the second protective tube disposed outside the first protective tube at the distal end of the temperature measuring region, The heat capacity and heat passage area of the first protective tube are made as small as possible to reduce the transmission of heat to the rear part of the first protective tube.
[0014]
As described above, this ceramic thermocouple for measuring molten metal temperature covers the temperature measuring region of the first protective tube made of silicon nitride or sialon with the second protective tube made of a cermet based on Mo. (2) Since the outer peripheral surface of the protection tube is covered with a coating made of a Mo-based material in which ZrB 2 and / or ZrN dispersed with a small coefficient of thermal expansion and hardly reacts with iron, the ceramic of the first protection tube is made of molten iron. And does not react with it, improving heat resistance and erosion resistance. In addition, since the glass layer is disposed between the first protection tube and the second protection tube, even if a crack or the like occurs in the cermet of the second protection tube, the gap caused by the crack is reduced. Even if the heat-resistant glass layer is filled and the cermet is cracked by thermal shock, catastrophic destruction does not occur. Moreover. The first protective tube made of ceramics does not directly contact the molten iron, so that heat resistance and erosion resistance can be improved. In addition, since the tungsten-rhenium alloy wire is sealed in an inert gas, the thermoelectric power of the W-Re wire is relatively large, the responsiveness to temperature is improved, and the W-Re wire is improved. Has a melting point of 3000 ° C. and does not melt in molten cast iron.
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, an embodiment of a ceramic thermocouple for measuring molten metal temperature according to the present invention will be described with reference to FIG. FIG. 1 is a sectional view showing an embodiment of the ceramic thermocouple for measuring molten metal temperature, FIG. 2 is an enlarged sectional view of a tip portion of the ceramic thermocouple for measuring molten metal temperature in FIG. 1, and FIG. It is a graph which shows the responsiveness with a comparative product.
[0016]
As shown in FIG. 1, this ceramic thermocouple for measuring the temperature of a molten metal is formed by covering a temperature measuring region of a first protective tube 1 with a second protective tube 2 as an outer protective tube of the temperature measuring region. It is the one with improved characteristics. The tungsten-rhenium alloy wires (W-Re wires) 6, 7 are composed of a W-5Re wire 6 and a W-26Re wire 7, and extend so as to be spaced apart in the first protection tube 1. Are located. One end of each of the tungsten-rhenium alloy wires 6 and 7 is connected to the first protective tube 1 so as to constitute the temperature measuring section 9, and the other end thereof extends from the end of the first protective tube 1. 12 and 13 are connected. The first protective tube 1 is filled with a filling member 3 made of porous silicon nitride ceramics in order to prevent disconnection of the W-Re wires 6 and 7 due to oxidative corrosion.
[0017]
The ceramic thermocouple for measuring molten metal temperature is mainly composed of a pair of tungsten-rhenium alloy strands 6 and 7 having different compositions arranged in the first protective tube 1 and the first protective tube 1. A filling member 3 made of porous silicon nitride-based ceramics filled with tungsten-rhenium alloy wires 6 and 7 buried therein, and a first protective tube 1 with an open end 10 protruding therefrom. (1) A second heat protection tube (2), which is disposed outside the temperature measuring section (9) of the heat protection tube (1) and is made of a cermet based on erosion resistance Mo and a dense heat-resistant member sealing the end of the heat protection tube (1) And a sealing member 8 made of heat-resistant glass.
[0018]
The first protection tube 1 is made of ceramics selected from silicon nitride (Si 3 N 4 ), sialon, and in some cases, silicon carbide (SiC). Further, the second protection tube 2 is made of a carbide-based comment (Mo-ZrO 2 ) based on Mo. Further, a coating 4 made of a composite material based on Mo in which ZrN and / or ZrB 2 is dispersed is disposed on the outer peripheral surface of the second protective tube 2 by thermal spraying.
[0019]
An intermediate layer 5 made of glass containing SiO 2 as a main component is formed in a gap between the first protection tube 1 and the second protection tube 2. Therefore, even if a crack or the like occurs in the cermet of the second protective tube 2, the gap of the crack is filled with the glass of the intermediate layer 5, and even if the cermet is cracked by a thermal shock, catastrophic destruction occurs. Does not occur.
[0020]
An inert gas such as Ar or N 2 is sealed in the first protection tube 1 in order to prevent oxidation of the tungsten-rhenium alloy wires 6 and 7.
[0021]
The air existing in the open end 10 of the second protective tube 2 protruding from the distal end 14 of the first protective tube 1 is sealed in the open end 10 while being immersed in the molten iron, and the open end 10 is closed. The intrusion of molten iron into the interior is prevented.
[0022]
The temperature measurement area at the tip is formed in a double structure by the first protection tube 1 and the second protection tube 2 disposed outside the first protection tube 1, and the heat capacity and the heat passage area of the tip 14 are as small as possible. The heat transfer to the rear end 15 of the first protection tube 1 is reduced.
[0023]
In this ceramic thermocouple for measuring molten metal, particularly, the second protective tube 2 made of cermet is excellent in heat resistance and erosion resistance, and even if cracks are generated by a thermal shock, it gradually breaks. For example, it does not lead to catastrophic destruction like the outer shell made of conventional ceramics. The first protective tube 1 enclosed in the second protective tube 2 is made of a ceramic containing silicon nitride as a main component, and when exposed to a molten iron, silicon nitride reacts with iron and is severely melted. Although the thermal shock resistance is inferior to that of cermet, the first protective tube 1 according to the present invention does not come into direct contact with the molten iron, so that the heat transfer coefficient can be reduced. Is prevented from being damaged by thermal shock.
[0024]
The ceramic thermocouple for measuring molten metal temperature can reduce the total heat capacity of the first protective tube 1, the second protective tube 2 and the coating 4, so that the tip of the temperature measuring region is configured to have a double structure. However, the response of the temperature measurement is not reduced. Further, a glass layer 5 is provided between the first protection tube 1 and the second protection tube 2. Therefore, the glass layer 5 can improve the fixed-temperature thermal conductivity between the first protective tube 1 and the second protective tube 2, and particularly, when the second protective tube 2 is cracked, the glass is It penetrates into the crack and acts to fill the gap caused by the crack, thereby preventing the catastrophic destruction of the second protective tube 2.
[0025]
The sealing member 8 provided at the rear end of the first protection tube 1 has a dual structure of a dense heat-resistant member such as silicon nitride and a heat-resistant glass member arranged in contact with the heat-resistant member. An inert gas such as N 2 or Ar is filled in the inside of the first protective tube 1 when the filling member 3 is filled and manufactured, and a sealing member 8 is fitted to an end of the first protective tube 1. It can be configured in a sealed state.
[0026]
The filling member 3 filled in the first protective tube 1 has a porous structure made of Si 3 N 4 reactive sintered ceramics, and has a small thermal conductivity. For example, the filling member 3 can be configured to have a low thermal conductivity by forming a structure having many voids. Therefore, this ceramic thermocouple for measuring the temperature of the molten metal can reduce the heat capacity of the temperature measuring area where the first protective tube 1 to be put in the molten metal of iron or the like is located. Heat conduction can be prevented.
[0027]
-Example-
In the embodiment, the pair of W-Re wires 6 and 7 are respectively composed of W-5Re and W-26Re having different compositions, each having a wire diameter of 0.5 mm and a length of 300 mm. And a connecting portion 16 whose distal ends are connected to each other by welding. W-Re wires 6 and 7 were filled with a raw material powder containing silicon nitride as a main component. On the other hand, the first protective tube 1 is made of silicon nitride having an outer diameter of 6.5 mm, a length of 120 to 150 mm, a closed front end 14 and an open rear end 15. One used. The W-Re wires 6 and 7 to which the above-mentioned raw material powders were attached were inserted from the opened rear end 15 of the first protective tube 1 and placed in the first protective tube 1. Further, the raw material powder was filled in the gap in the first protection tube 1. The first protective tube 1 was sealed rear end portion 15 of the first protection pipe 1 by injecting an inert gas of Ar and N 2 with a sealing member 8 made of heat-resistant glass.
[0028]
The second protective tube 2 was formed with a cermet made of ZrO 2 based on Mo to have a 7 mm inner diameter. A coating 4 made of a composite material based on Mo in which ZrN and / or ZrB 2 is dispersed was formed on the outer peripheral surface of the second protection tube 2 by thermal spraying. The first protective tube 1 was inserted into the second protective tube 2 on which the coating 4 was sprayed. At this time, the second protective tube 2 was arranged such that the end portion 10 thereof protruded from the distal end portion 14 of the first protective tube 1 to form an open air chamber 11. Next, a glass layer 5 made of heat-resistant glass was filled in the gap between the first protective tube 1 and the second protective tube 2 to fix them, and the ends were fixed and sealed using glass.
[0029]
When the temperature of the cast iron melt was measured at about 1450 ° C. using the ceramic thermocouple for measuring the temperature of the molten metal (product of the present invention) configured as described above, the time until the raw material powder was fired and stabilized was measured. Took about 8 seconds, but the temperature measurement of the molten iron was repeated 500 cycles. Although cracks were found in the second protective tube 2, there was no problem with the temperature measurement performance of the molten iron. In this state, the temperature of the molten iron was measured 1000 times or more. In addition, there was no change in the electromotive force of the ceramic thermocouple for measuring the temperature of the molten metal, and the temperature could be measured stably.
[0030]
In addition to measuring the temperature of the molten cast iron, the temperature of the molten metal at about 1500 ° C. was continuously measured using the above-mentioned ceramic thermocouple for measuring the temperature of the molten metal. No abnormality such as a change in electromotive force of the ceramic thermocouple for measuring molten metal temperature could be confirmed. That is, it was found that this ceramic thermocouple for measuring molten metal temperature had good heat resistance and erosion resistance.
[0031]
In order to compare this ceramic thermocouple for measuring the molten metal temperature (the present invention) with another thermocouple, as a comparative example, a W-Re having the above-mentioned raw material powder deposited in a protective tube made of silicon nitride having an inner diameter of 7 mm was used. A thermocouple (comparative product) having a structure in which the wires were inserted was manufactured. The responsiveness, adhesion of the molten iron, and durability of the comparative product were evaluated. As shown in FIG. 3, it was found that the response was poor and that iron easily adhered to the silicon nitride protective tube.
[0032]
【The invention's effect】
In the ceramic thermocouple for measuring molten metal temperature according to the present invention, as described above, the first protective tube made of silicon nitride is protected by the second protective tube made of a composite material such as a cermet based on Mo. Performance and erosion resistance, and even when used repeatedly, the temperature of molten metal such as molten iron can be measured with high precision and speed, and the life thereof can be improved. In addition, the performance can be further improved by forming a coating made of a material based on Mo in which ZrB 2 and / or ZrN are dispersed, which has a small coefficient of thermal expansion and does not easily react with iron, on the surface of the second protection tube. . Further, the temperature of the temperature measuring area is limited by the filling member made of porous ceramic in the first protective tube, so that it is difficult for heat to escape backward through the first protective tube and the heat capacity of the temperature measuring area is reduced. Temperature response of the thermocouple can be improved.
[Brief description of the drawings]
FIG. 1 is a sectional view showing an embodiment of a ceramic thermocouple for measuring molten metal temperature according to the present invention.
FIG. 2 is an enlarged sectional view of a distal end portion of the ceramic thermocouple for measuring molten metal temperature in FIG. 1;
FIG. 3 is a graph showing the responsiveness of the product of the present invention and a comparative product.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 1st protection tube 2 2nd protection tube 3 Filling member 4 Coating 5 Glass layer 6,7 Tungsten-rhenium alloy strand 8 Sealing member 9 Temperature measuring part 10 Open end part 11 Air chamber 12,13 Terminal 14 Tip part 15 Rear end 16 Joint
