JP4820030B2 - Electromagnetic flowmeter for molten Pb-Bi - Google Patents

Electromagnetic flowmeter for molten Pb-Bi Download PDF

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JP4820030B2
JP4820030B2 JP2001262735A JP2001262735A JP4820030B2 JP 4820030 B2 JP4820030 B2 JP 4820030B2 JP 2001262735 A JP2001262735 A JP 2001262735A JP 2001262735 A JP2001262735 A JP 2001262735A JP 4820030 B2 JP4820030 B2 JP 4820030B2
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duct
molten
electrodes
magnetic poles
noble metal
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JP2003075215A (en
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邦明 三浦
達也 鬼沢
雄三 照山
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Sukegawa Electric Co Ltd
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Sukegawa Electric Co Ltd
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【０００１】
【産業上の利用分野】
本発明は、電磁誘導によりダクト内を移動する溶融Ｐｂ−Ｂｉ内に発生する起電力を測定することにより、その溶融Ｐｂ−Ｂｉの流量を計測する電磁流量計に関し、特に溶融Ｐｂ−Ｂｉに発生する起電力を電極へ安定して出力することが出来る溶融Ｐｂ−Ｂｉ用電磁流量計に関する。
【０００２】
【従来の技術】
Ｐｂ−Ｂｉを用いた高速増殖炉や消滅処理用配管内の溶融Ｐｂ−Ｂｉの流量を測定するためには電磁流量計を使用することが考えられる。
このような目的で使用される従来の電磁流量計の構成を図３に示す。溶融金属は、筒状のダクト１内を移動する。このダクト１を挟んで一対の磁極６、６がダクト１の中心軸と直交する方向に対向しており、この磁極６、６の間でダクト１内を移動する溶融金属をその移動の方向と直交する方向に切るよう磁束が形成される。さらに、ダクト１の中心軸及び前記磁極６、６が対向した方向と直交する方向に対向して一対の電極２、２が配置され、それら電極２、２の先端部４がダクト１内に臨んでいる。こられの電極２、２は、必要に応じて交換しやすいようにテーパ継手（例えば商標名「スエージロック」）５、５への押し込みにより密にダクト１に取り付けられている。この電極２、２にはダクト１内を移動する溶融金属に生じる電圧を測定するための電圧計７が接続されている。
【０００３】
このような溶融金属用電磁流量計では、磁極６、６の間に形成される磁束を切るようにダクト１内を溶融金属が流れるとき、いわゆるフレミングの右手の法則に従い、磁束の方向と溶融金属が流れる方向と直交する方向に溶融金属に起電力が生じる。この起電力の電圧の方向は前記電極２、２が対向した方向であり、且つその電圧値は理論上溶融金属の流速に比例する。従って、この電圧を電極２、２により出力し、電圧計７で測定することにより、溶融金属の流速が測定できる。磁極６、６間に形成される磁束が横切る部分のダクト１の断面積と前記溶融金属の流速との積が溶融金属の流量である。
このような従来の電磁流量計において、そのダクト１と電極２、２には、耐酸化特性と耐食性の良い非磁性のオーステナイト系ステンレス鋼が用いられていた。
【０００４】
【発明が解決しようとしている課題】
溶融Ｐｂ−Ｂｉは多量の酸素が大気中の精錬時に含まれてしまうので、溶融Ｐｂ−Ｂｉ中の酸素をＨ2 ガスバブリングや真空脱気等で除去しておかなければならない。こうしないと溶融Ｐｂ−Ｂｉをダクト内に充填するときにダクト表面に酸化膜が生じてしまう。ダクト内に溶融Ｐｂ−Ｂｉを充填する場合は、常にこの脱酸素ガス処理を行う必要がある。そこで以下の説明においては、この脱酸素ガス処理をした溶融Ｐｂ−Ｂｉを使う事を前提として説明をする。
【０００５】
しかしながら、このような溶融Ｐｂ−Ｂｉの脱酸素処理を行って、ダクト内に溶融Ｐｂ−Ｂｉを充填し、かつこの非磁性のオーステナイト系ステンレス鋼のダクト内表面の酸化膜を除去してあっても、溶融Ｐｂ−Ｂｉを充填するとき、非酸化ガスのＡｒやＮ2 の高温ガス雰囲に含まれるわずかな酸素により、その表面にＣｒ酸化膜が出来、溶融Ｐｂ−Ｂｉと濡れ性が損なわれる。このため、溶融Ｐｂ−Ｂｉの中に発生する起電力が低下したり、不安定となり、正確な流量測定が出来なくなってしまう。
【０００６】
これを改善するために雰囲気に還元ガスのＨ2 を４％程入れて酸化膜が出来ないようにするのが用いられてきた。しかし、このＨ2 ガスは４％以上空気中に存在すると爆発する危険性があり、高温の溶融金属を扱う溶融金属用電磁流量計では極めて危険である。
電磁流量計においては、ダクトや電極と溶融金属との濡れ性の低下に伴う接触抵抗の増加は、電圧出力の低下をもたらし、接触抵抗の不安定性は、電圧出力の不安定性をもたらす。
【０００７】
溶融Ｐｂ−Ｂｉは、化学的活性度の低い流体であることから、Ｎａ等のアルカリ金属のように化学的活性度の高い溶融金属に比べてダクトや電極の表面に出来た酸化膜を除去する作用も小さい。このため、溶融Ｐｂ−Ｂｉに対して耐食性の良いステンレス鋼の表面に出来た酸化膜を容易に除去出来ず、溶融Ｐｂ−Ｂｉとステンレス鋼との濡れ性が悪くなる。これにより、溶融Ｐｂ−Ｂｉとダクトや電極との間に接触抵抗が発生し、電磁流量計の出力低下を来す。これを計算式で表すと、式１で表される。
【０００８】
【式１】

Figure 0004820030
【０００９】
ここで、Ｅ＝電極を通して測定される出力（ｍＶ）、Ｂ＝ダクトを通過する磁束密度（Ｇａｕｓｓ）、ｖ＝ダクトを流れる流体の速度（ｃｍ／ｃ）、ｄ＝ダクト内径（ｃｍ）、Ｋ１＝磁極端末係数＝ｆ（磁極長さ＝Ｌ／ダクト外径）、Ｋ２＝ダクト短絡係数、Ｋ３＝磁石の温度による磁束低減係数＝ｆ（磁石温度）、Ｋ４＝ダクトの熱膨張補償係数＝１＋γ・ΔＴである。
【００１０】
前記の式１において、磁極端末係数Ｋ１は使用磁石の寸法が分かれば一義的に決まり、磁石の温度による磁束低減係数Ｋ３とダクトの熱膨張補償係数Ｋ４は磁石の温度とダクトの温度が決まればこれも一義的に決まる。他方、ダクト短絡係数Ｋ２は、次の式２で表される。ここで、Ｄ＝ダクト外径、τ＝接触抵抗（Ω−ｃｍ２）である。
【００１１】
【式２】
Figure 0004820030
【００１２】
このダクト短絡係数Ｋ２には、接触抵抗τを含む項があり、この接触抵抗τの増加によりダクト短絡係数Ｋ２が低下し、出力Ｅが低下することがわかる。このダクト短絡係数Ｋ２は接触抵抗τの増加で小さくなり、逆に接触抵抗τが小さくなるとダクト短絡係数Ｋ２は増加し、接触抵抗τが０となると、ダクト短絡係数Ｋ２はダクトの内径ｄ、ダクトの外径Ｄ、流体とダクトの材料の電気抵抗で決定される。
【００１３】
溶融金属とダクトや電極との接触抵抗をもたらす原因は、電極表面の酸化膜、酸化膜表面の吸着・吸蔵の酸素等のガス、さらに溶融金属中の酸化物が電極表面に付着することによって生じる。この中で一番問題なのは、電極表面に付いている、或いは加熱中に生じてしまう酸化膜である。
【００１４】
さらに、前述した従来の電磁流量計は、電極２、２がダクト１を貫通して取り付けられると共に、テーパ継手５で固定されているため、電極２、２の間で得られる出力が変動するようになったら、電極２、２を抜き、その先端を研磨して酸化膜を除去したうえで再取付して使用することができる。
【００１５】
このような電極２、２の取付構造は、電極２、２のメンテナンスが出来るという意味で非常に良い方式である。しかし、放射線が放射されるような場所では、そのようなメンテナンスは出来ない。
さらに電極２、２の交換等で電極２、２を密閉固定するテーパ継手５、５での電極２、２の締付不良を起こすと、溶融金属が漏洩することにもなる。
【００１６】
本発明は、前記従来の溶融金属用電磁流量計における電極の課題に鑑み、特に溶融Ｐｂ−Ｂｉ用電磁流量計において、ダクト内を移動する溶融Ｐｂ−Ｂｉとダクトの接触抵抗、とりわけダクトの内周面に付着或いは形成される酸化膜による接触抵抗の増大を防止し、電極間に発生する出力の低下やその変動を防止すると共に、溶融Ｐｂ−Ｂｉの漏洩を防止できるようにすることを目的とする。
【００１７】
【課題を解決するための手段】
本発明では、前記の目的を達成するため、ダクト１１の一対の電極１２、１２と一対の磁極１６、１６が対向した部分の内周面に、溶融Ｐｂ−Ｂｉへの溶融速度が或る数値以下の貴金属コーティング１４を施し、この貴金属コーティング１４を介して溶融Ｐｂ−Ｂｉ内に発生する起電力を電極１２、１２へ出力するようにした。
【００１８】
すなわち、本発明による溶融Ｐｂ−Ｂｉ用電磁流量計は、溶融Ｐｂ−Ｂｉを移動させる筒状のダクト１１と、このダクト１１を挟んで対向し、ダクト１１内に磁束を形成する一対の磁極１６、１６と、ダクト１１を挟んで対向し、前記磁束を切る方向にダクト１１内を移動する溶融Ｐｂ−Ｂｉに生じる電圧を出力する一対の電極１２、１２とを有し、ダクト１１の電極１２、１２及び磁極１６、１６が対向した位置の内周面の全周にわたり、それら電極１２、１２と磁極１６、１６が対向した位置を中心としてダクト１１の軸方向に前記磁極１６、１６のダクト１１の軸方向の長さＬより短い長さｌの範囲にわたって貴金属コーティング１４を施したものである。
【００１９】
特に溶融金属が溶融Ｐｂ−Ｂｉである場合、貴金属コーティング１４は溶融Ｐｂ−Ｂｉへの溶融速度が１μｍ／ｓ以下の貴金属であるのがよく、そのような貴金属として例えばＲｈやＩｒをあげることができる。ダクト１１の内周面ににＲｈやＩｒをメッキによりコーティングする場合、ダクト１１の内周面に予めＡｕをアンダーコートし、その上にＲｈまたはＩｒをメッキする。
【００２０】
ダクト１１の内周面に酸化膜発生を防止するためにはあらかじめ、ダクト１１の内周面に貴金属をコーティングしておけば良いことになる。しかし、この貴金属のコーティングもＰｂ−Ｂｉに瞬間的に溶けてしまうＡｇ、Ａｕ、Ｐｔでは、酸化して酸化膜を発生させながらこれらの貴金属が瞬間的に溶けて行くので、発生する酸化膜がダクト内面に付着してしまう。ダクト系内に残留酸素が多ければなおさらである。
【００２１】
実験によれば、Ｐｔより溶融Ｐｂ−Ｂｉに溶けにくいＲｈやＩｒではゆっくり溶けるので、ＲｈやＩｒの表面にあった残留酸素によって酸化膜が発生してもＲｈやＩｒがゆっくり溶融Ｐｂ−Ｂｉに溶けてしまうので、酸化膜はダクト１１の内周面に付着せず、溶融Ｐｂ−Ｂｉ中に飛散してしまう。これによってダクト１１の内周面には酸化膜が付着しないので、溶融Ｐｂ−Ｂｉとダクト１１には、接触抵抗がほとんどない。このため、ダクト１１の外周面に電極１２、１２を直付けした構造でも、ダクト１１を介して電極１２、１２から安定して起電力が出力でき、これを測定することができる。
【００２２】
しかし、ダクト１１の外周面に接合した電極１２、１２の内側だけを局所的にＲｈやＩｒコートしただけだと、ダクト内周面と溶融Ｐｂ−Ｂｉとの接触抵抗がばらつき、この接触抵抗のばらつきで溶融Ｐｂ−Ｂｉ中に発生する起電力が変動し、ダクト１１の外周面の電極１２、１２を通して測定される出力が変動する。そのため、ダクト１１に内周面の溶融Ｐｂ−Ｂｉとの接触抵抗を均一する必要がある。
【００２３】
ダクト１１の内周面の接触抵抗を均一にするためには、ダクト１１の内周面全体にＲｈやＩｒコーティングし、かつＲｈやＩｒのコーティングをダクト１１の軸方向へも長くする必要がある。そこで、電極１２、１２と磁極１６、１６が対向した部分の全周にわたり、その対向した部分を中心にしてダクト１１の軸方向に前記磁極１６、１６のダクト１１の軸方向の長さＬより短い長さｌだけＲｈやＩｒのコーティングを施す。
【００２４】
【発明の実施の形態】
次に、図面を参照しながら、本発明の実施の形態について、具体的且つ詳細に説明する。
本発明の一実施形態による溶融Ｐｂ−Ｂｉ用電磁流量計の構成を図１と図２に示す。溶融金属は、筒状のダクト１１を通して流され、その流量は流速とダクト１１の流路断面積との積である。
【００２５】
このダクト１１を挟んで一対の磁極１６、１６がダクト１の中心軸と直交する方向に対向しており、この磁極１６、１６の間で前記ダクト１１内を流れる溶融金属の流れの方向と直交する方向に切るよう磁束が形成される。
さらに、ダクト１１の中心軸及び前記磁極１６、１６が対向したの方向と何れも直交する方向に対向して一対の電極１２、１２が配置され、それら電極１２、１２の先端部１３、１３がダクト１１の外周面に溶接により接続・固定されている。この電極１２、１２にはダクト１１内を移動する溶融金属に生じる起電力を測定するための電圧計１７が接続されている。
【００２６】
さらに、このダクト１１の内周面には、溶融Ｐｂ−Ｂｉとの濡れ性を改善するためにＲｈやＩｒ等の貴金属コーティング１４を施す。図２に示すように、この貴金属コーティング１４は、ダクト１１の内周面の電極１２、１２と磁極１６、１６が対向した位置の全周であって、且つそれら電極１２、１２と磁極１６、１６が対向した位置を中心としてダクト１１の軸方向に長さｌの範囲に亘って施す。図２では、磁極１６、１６のダクト１１の軸方向の長さＬに対して、貴金属コーティング１４の長さｌは、Ｌ＞ｌである。この長さｌは、対向した磁極１６、１６の間で、ほぼ均一な磁束密度の磁界が形成される範囲である。なお、これらＲｈ、Ｉｒの溶融Ｐｂ−Ｂｉへの溶解速度は１μｍ／ｓ以下と遅い。
【００２７】
コーティング手段はダクト１１の内周面にＲｈやＩｒをメッキによりコーティングするのが実用的である。但し、ＲｈやＩｒは硬い材料であり、ＳＵＳ３１６等のオーステナイト系ステンレス鋼にこれらをメッキする場合、予め下地として１μ以下の厚さのＡｕメッキを施すのがよい。
【００２８】
このような溶融Ｐｂ−Ｂｉ用電磁流量計では、磁極１６、１６の間に形成される磁束を切るようにダクト１１内を溶融金属が流れるとき、いわゆるフレミングの右手の法則に従い、磁束の方向と溶融金属が流れる方向と直交する方向に溶融金属に起電力が発生する。この起電力による電圧の方向は前記電極１２、１２が対向した方向であり、且つその電圧値は理論上溶融金属の流速に比例する。このため、この電圧をダクト１１を介して電極１２、１２から出力し、電圧計１７で測定することにより、溶融金属の流速が測定できる。既に述べた通り、磁極１６、１６間に形成される磁束が横切る部分のダクト１１の断面積と前記溶融金属の流速との積が溶融金属の流量であり、これにより溶融金属の流量が測定される。
【００２９】
この場合において、前記ダクト１１の内周面に施したＲｈ、Ｉｒ等の貴金属コーティング１４は、溶融Ｐｂ−Ｂｉへの溶解速度が１μｍ／ｓ以下と遅い。このため、、ＲｈやＩｒの表面に存在する酸素と溶融金属とが酸化膜を短時間に作っても、ＲｈやＩｒのコーティング膜が溶融Ｐｂ−Ｂｉ中へ徐々に溶融していくので、酸化膜が溶融Ｐｂ−Ｂｉの中に飛散していき、ダクト１１の内周面に酸化膜が殆ど残らない。また、多少の酸化膜が残っても、残りの大半の部分でダクト１１の内周面と溶融Ｐｂ−Ｂｉが酸化膜を介さずに接触し、接触抵抗が無い状態で接続している。このため、ダクト１１の内周面と溶融Ｐｂ−Ｂｉとの間の接触抵抗が無く、溶融Ｐｂ−Ｂｉの中に発生する起電力を電極１２、１２に確実に出力することができる。また、ダクト１１の内周面と溶融Ｐｂ−Ｂｉとの間の酸化膜による接触抵抗が無いので、温度変動等に伴う酸化膜の抵抗値の変動等の影響も受けず、出力変動も小さい。
【００３０】
【発明の効果】
以上説明した通り、本発明による溶融Ｐｂ−Ｂｉ用電磁流量計では、ダクト１１内を移動する溶融Ｐｂ−Ｂｉと接触するダクト１１の内周面の接触抵抗、とりわけダクト１１の内周面に付着或いは形成される酸化膜による接触抵抗の増大を防止し、ダクト１１を介して電極１２、１２に出力される起電力の低下やその変動を防止することが出来る。これにより、ダクト１１内を流れる溶融Ｐｂ−Ｂｉの流速、流量を正確に測定出来るようになる。
【図面の簡単な説明】
【図１】本発明の一実施形態による溶融Ｐｂ−Ｂｉ用電磁流量計を示す電極及び磁極部分の縦断端面図である。
【図２】同実施形態による溶融Ｐｂ−Ｂｉ用電磁流量計を示す電極及び磁極部分の縦断側面図である。
【図３】従来例である溶融Ｐｂ−Ｂｉ用電磁流量計を示す電極及び磁極部分のダクトの縦断端面図である。
【符号の説明】
１１ ダクト
１２ 電極
１４ 貴金属コーティング
１６ 磁極[0001]
[Industrial application fields]
The present invention relates to an electromagnetic flowmeter that measures the flow rate of molten Pb-Bi by measuring an electromotive force generated in molten Pb-Bi that moves in a duct by electromagnetic induction, and in particular, generated in molten Pb-Bi. The present invention relates to an electromagnetic flow meter for molten Pb-Bi that can stably output an electromotive force to an electrode.
[0002]
[Prior art]
In order to measure the flow rate of molten Pb-Bi in the fast breeder reactor using Pb-Bi or the extinguishing treatment pipe, it is conceivable to use an electromagnetic flow meter.
A configuration of a conventional electromagnetic flow meter used for such a purpose is shown in FIG. Molten metal moves in the cylindrical duct 1. A pair of magnetic poles 6 and 6 are opposed to each other in a direction orthogonal to the central axis of the duct 1 across the duct 1, and the molten metal moving in the duct 1 between the magnetic poles 6 and 6 is defined as the direction of movement. Magnetic flux is formed so as to cut in the orthogonal direction. Furthermore, a pair of electrodes 2 and 2 are arranged in a direction orthogonal to the direction in which the central axis of the duct 1 and the magnetic poles 6 and 6 face each other, and the tips 4 of the electrodes 2 and 2 face the duct 1. It is out. These electrodes 2 and 2 are tightly attached to the duct 1 by being pushed into tapered joints (for example, trade name “Swagelok”) 5 and 5 so as to be easily exchanged as necessary. The electrodes 2 and 2 are connected to a voltmeter 7 for measuring a voltage generated in the molten metal moving in the duct 1.
[0003]
In such an electromagnetic flowmeter for molten metal, when the molten metal flows through the duct 1 so as to cut the magnetic flux formed between the magnetic poles 6 and 6, the direction of the magnetic flux and the molten metal are obeyed according to the so-called Fleming's right hand rule. An electromotive force is generated in the molten metal in a direction perpendicular to the direction in which the metal flows. The direction of the voltage of the electromotive force is the direction in which the electrodes 2 and 2 face each other, and the voltage value is theoretically proportional to the flow rate of the molten metal. Therefore, by outputting this voltage through the electrodes 2 and 2 and measuring it with the voltmeter 7, the flow rate of the molten metal can be measured. The product of the cross-sectional area of the duct 1 where the magnetic flux formed between the magnetic poles 6 and 6 crosses and the flow velocity of the molten metal is the flow rate of the molten metal.
In such a conventional electromagnetic flow meter, non-magnetic austenitic stainless steel having good oxidation resistance and corrosion resistance is used for the duct 1 and the electrodes 2 and 2.
[0004]
[Problems to be solved by the invention]
Since the molten Pb-Bi contains a large amount of oxygen during refining in the atmosphere, the oxygen in the molten Pb-Bi must be removed by H 2 gas bubbling or vacuum degassing. Otherwise, an oxide film is formed on the duct surface when the molten Pb-Bi is filled in the duct. When filling the duct with molten Pb-Bi, it is necessary to always perform this deoxygenation gas treatment. Therefore, in the following explanation, explanation will be made on the assumption that this deoxidized gas-treated molten Pb-Bi is used.
[0005]
However, such a deoxidation treatment of the molten Pb-Bi is performed to fill the duct with the molten Pb-Bi, and to remove the oxide film on the inner surface of the duct of this nonmagnetic austenitic stainless steel. However, when filling with molten Pb-Bi, a slight amount of oxygen contained in the high-temperature gas atmosphere of non-oxidizing gas Ar or N 2 forms a Cr oxide film on the surface, impairing the wettability with molten Pb-Bi. It is. For this reason, the electromotive force generated in the molten Pb-Bi decreases or becomes unstable, and accurate flow rate measurement cannot be performed.
[0006]
In order to improve this, it has been used to prevent the formation of an oxide film by introducing about 4% of the reducing gas H 2 into the atmosphere. However, if this H 2 gas is present in the air in an amount of 4% or more, there is a risk of explosion, and it is extremely dangerous in an electromagnetic flowmeter for molten metal that handles high-temperature molten metal.
In an electromagnetic flow meter, an increase in contact resistance accompanying a decrease in wettability between ducts or electrodes and molten metal results in a decrease in voltage output, and instability in contact resistance results in instability in voltage output.
[0007]
Molten Pb-Bi is a fluid having a low chemical activity, and therefore removes oxide films formed on the surfaces of ducts and electrodes as compared with a molten metal having a high chemical activity such as an alkali metal such as Na. Small effect. For this reason, the oxide film formed on the surface of the stainless steel having good corrosion resistance against the molten Pb-Bi cannot be easily removed, and the wettability between the molten Pb-Bi and the stainless steel is deteriorated. As a result, a contact resistance is generated between the molten Pb-Bi and the duct or electrode, resulting in a decrease in the output of the electromagnetic flow meter. When this is expressed by a calculation formula, it is expressed by Formula 1.
[0008]
[Formula 1]
Figure 0004820030
[0009]
Where E = output measured through the electrode (mV), B = flux density through the duct (Gauss), v = velocity of fluid flowing through the duct (cm / c), d = duct inner diameter (cm), K1 = Magnetic pole terminal coefficient = f (magnetic pole length = L / duct outer diameter), K2 = duct short circuit coefficient, K3 = magnetic flux reduction coefficient due to magnet temperature = f (magnet temperature), K4 = thermal expansion compensation coefficient of duct = 1 + γ ΔT.
[0010]
In Equation 1, the magnetic pole terminal coefficient K1 is uniquely determined if the size of the magnet used is known, and the magnetic flux reduction coefficient K3 and the duct thermal expansion compensation coefficient K4 are determined if the magnet temperature and the duct temperature are determined. This is also determined uniquely. On the other hand, the duct short circuit coefficient K2 is expressed by the following equation 2. Here, D = outer diameter of the duct and τ = contact resistance (Ω-cm 2).
[0011]
[Formula 2]
Figure 0004820030
[0012]
The duct short circuit coefficient K2 includes a term including the contact resistance τ, and it can be seen that the increase in the contact resistance τ decreases the duct short circuit coefficient K2 and decreases the output E. The duct short-circuit coefficient K2 decreases as the contact resistance τ increases. Conversely, when the contact resistance τ decreases, the duct short-circuit coefficient K2 increases. When the contact resistance τ becomes 0, the duct short-circuit coefficient K2 increases the inner diameter d of the duct, the duct Is determined by the electrical resistance of the fluid and the material of the duct.
[0013]
The cause of contact resistance between the molten metal and the duct or electrode is caused by the oxide film on the electrode surface, gas such as oxygen adsorbed and occluded on the oxide film surface, and oxides in the molten metal adhering to the electrode surface. . Of these, the most problematic is the oxide film attached to the electrode surface or formed during heating.
[0014]
Further, in the conventional electromagnetic flow meter described above, since the electrodes 2 and 2 are attached through the duct 1 and are fixed by the taper joint 5, the output obtained between the electrodes 2 and 2 varies. In this case, the electrodes 2 and 2 can be removed and the tip can be polished to remove the oxide film, and then reattached for use.
[0015]
Such an attachment structure of the electrodes 2 and 2 is a very good system in the sense that the electrodes 2 and 2 can be maintained. However, such maintenance is not possible in places where radiation is emitted.
Furthermore, if the fastening failure of the electrodes 2 and 2 at the taper joints 5 and 5 that hermetically fix the electrodes 2 and 2 is caused by exchanging the electrodes 2 and 2, the molten metal leaks.
[0016]
In view of the problem of the electrodes in the conventional electromagnetic flowmeter for molten metal, the present invention is a contact resistance between molten Pb-Bi moving in the duct and the duct, particularly in the duct, particularly in the electromagnetic flowmeter for molten Pb-Bi. An object of the present invention is to prevent an increase in contact resistance due to an oxide film adhering to or formed on a peripheral surface, to prevent a decrease in output generated between electrodes and fluctuations thereof, and to prevent leakage of molten Pb-Bi. And
[0017]
[Means for Solving the Problems]
In the present invention, in order to achieve the above-described object, the melting rate to the molten Pb-Bi is a certain numerical value on the inner peripheral surface of the portion of the duct 11 where the pair of electrodes 12, 12 and the pair of magnetic poles 16, 16 face each other. The following noble metal coating 14 was applied, and an electromotive force generated in the molten Pb-Bi via this noble metal coating 14 was output to the electrodes 12 and 12.
[0018]
That is, the electromagnetic flowmeter for molten Pb-Bi according to the present invention has a cylindrical duct 11 that moves molten Pb-Bi and a pair of magnetic poles 16 that face each other across the duct 11 and form a magnetic flux in the duct 11. , 16 and a pair of electrodes 12, 12 that output a voltage generated in the melted Pb-Bi that moves in the duct 11 in a direction to cut the magnetic flux across the duct 11, and the electrode 12 of the duct 11. , 12 and the magnetic poles 16, 16 over the entire circumference of the inner peripheral surface thereof, the ducts of the magnetic poles 16, 16 in the axial direction of the duct 11 around the positions where the electrodes 12, 12 and the magnetic poles 16, 16 face each other. Noble metal coating 14 is applied over a range of length l shorter than 11 axial length L.
[0019]
In particular, when the molten metal is molten Pb-Bi, the noble metal coating 14 is preferably a noble metal having a melting rate of 1 μm / s or less to the molten Pb-Bi, and examples of such noble metals include Rh and Ir. it can. When the inner peripheral surface of the duct 11 is coated with Rh or Ir by plating, Au is previously undercoated on the inner peripheral surface of the duct 11 and then Rh or Ir is plated thereon.
[0020]
In order to prevent the generation of an oxide film on the inner peripheral surface of the duct 11, it is only necessary to coat a noble metal on the inner peripheral surface of the duct 11 in advance. However, in Ag, Au, and Pt, where the noble metal coating also dissolves instantaneously in Pb-Bi, these noble metals are instantaneously dissolved while being oxidized to generate an oxide film. It will adhere to the inside of the duct. This is even more so if there is more residual oxygen in the duct system.
[0021]
According to experiments, Rh and Ir, which are less soluble in molten Pb-Bi than Pt, dissolve slowly, so even if an oxide film is generated due to residual oxygen on the surface of Rh or Ir, Rh or Ir slowly becomes molten Pb-Bi. Since it melts, the oxide film does not adhere to the inner peripheral surface of the duct 11 and scatters in the molten Pb-Bi. As a result, no oxide film adheres to the inner peripheral surface of the duct 11, so that there is almost no contact resistance between the molten Pb-Bi and the duct 11. For this reason, even in the structure in which the electrodes 12 and 12 are directly attached to the outer peripheral surface of the duct 11, the electromotive force can be stably output from the electrodes 12 and 12 via the duct 11, and this can be measured.
[0022]
However, if only the inside of the electrodes 12 and 12 joined to the outer peripheral surface of the duct 11 is locally Rh or Ir coated, the contact resistance between the inner peripheral surface of the duct and the molten Pb-Bi varies, and this contact resistance Due to the variation, the electromotive force generated in the molten Pb-Bi varies, and the output measured through the electrodes 12 and 12 on the outer peripheral surface of the duct 11 varies. Therefore, it is necessary for the duct 11 to have uniform contact resistance with the molten Pb-Bi on the inner peripheral surface.
[0023]
In order to make the contact resistance of the inner peripheral surface of the duct 11 uniform, it is necessary to coat the entire inner peripheral surface of the duct 11 with Rh and Ir, and to extend the coating of Rh and Ir in the axial direction of the duct 11 as well. . Therefore, over the entire circumference of the portion where the electrodes 12 and 12 and the magnetic poles 16 and 16 are opposed , the axial length of the duct 11 of the magnetic poles 16 and 16 is longer than the axial length L of the duct 11 around the opposed portion. Apply Rh or Ir coating for a short length l .
[0024]
DETAILED DESCRIPTION OF THE INVENTION
Next, embodiments of the present invention will be described specifically and in detail with reference to the drawings.
The configuration of an electromagnetic flow meter for molten Pb-Bi according to an embodiment of the present invention is shown in FIGS. Molten metal is flowed through the cylindrical duct 11, and the flow rate is the product of the flow velocity and the flow path cross-sectional area of the duct 11.
[0025]
A pair of magnetic poles 16, 16 are opposed in a direction orthogonal to the central axis of the duct 1 across the duct 11, and are orthogonal to the direction of the molten metal flowing through the duct 11 between the magnetic poles 16, 16. A magnetic flux is formed so as to cut in the direction of the movement.
Further, a pair of electrodes 12 and 12 are arranged so as to face each other in a direction orthogonal to the central axis of the duct 11 and the direction in which the magnetic poles 16 and 16 face each other, and the tip portions 13 and 13 of the electrodes 12 and 12 are arranged. It is connected and fixed to the outer peripheral surface of the duct 11 by welding. A voltmeter 17 for measuring an electromotive force generated in the molten metal moving in the duct 11 is connected to the electrodes 12 and 12.
[0026]
Further, a noble metal coating 14 such as Rh or Ir is applied to the inner peripheral surface of the duct 11 in order to improve wettability with molten Pb-Bi. As shown in FIG. 2, this noble metal coating 14 is the entire circumference of the position where the electrodes 12, 12 and the magnetic poles 16, 16 on the inner peripheral surface of the duct 11 face each other, and the electrodes 12, 12 and the magnetic poles 16, 16. It is applied over a range of length l in the axial direction of the duct 11 with the position at which 16 is opposed. In FIG. 2, the length l of the noble metal coating 14 is L> l with respect to the axial length L of the duct 11 of the magnetic poles 16 and 16. This length l is a range in which a magnetic field having a substantially uniform magnetic flux density is formed between the opposing magnetic poles 16 and 16. The dissolution rate of these Rh and Ir in molten Pb—Bi is as low as 1 μm / s or less.
[0027]
As a coating means, it is practical to coat Rh or Ir on the inner peripheral surface of the duct 11 by plating. However, Rh and Ir are hard materials, and when these are plated on austenitic stainless steel such as SUS316, it is preferable to perform Au plating with a thickness of 1 μm or less as a base in advance.
[0028]
In such an electromagnetic flow meter for molten Pb-Bi, when the molten metal flows through the duct 11 so as to cut the magnetic flux formed between the magnetic poles 16 and 16, the direction of the magnetic flux is determined according to the so-called Fleming's right-hand rule. An electromotive force is generated in the molten metal in a direction orthogonal to the direction in which the molten metal flows. The direction of the voltage due to the electromotive force is the direction in which the electrodes 12 are opposed to each other, and the voltage value is theoretically proportional to the flow rate of the molten metal. For this reason, the flow rate of the molten metal can be measured by outputting this voltage from the electrodes 12 and 12 through the duct 11 and measuring the voltage with the voltmeter 17. As already described, the product of the cross-sectional area of the duct 11 where the magnetic flux formed between the magnetic poles 16 and 16 crosses and the flow velocity of the molten metal is the flow rate of the molten metal, whereby the flow rate of the molten metal is measured. The
[0029]
In this case, the precious metal coating 14 such as Rh or Ir applied to the inner peripheral surface of the duct 11 has a slow dissolution rate in molten Pb—Bi of 1 μm / s or less. For this reason, even if oxygen and molten metal existing on the surface of Rh or Ir make an oxide film in a short time, the coating film of Rh or Ir gradually melts into the molten Pb-Bi. The film scatters into the molten Pb-Bi, and almost no oxide film remains on the inner peripheral surface of the duct 11. Even if some oxide film remains, the inner peripheral surface of the duct 11 and the molten Pb-Bi are in contact with each other through the oxide film in most of the remaining portion, and are connected without contact resistance. For this reason, there is no contact resistance between the inner peripheral surface of the duct 11 and the molten Pb-Bi, and an electromotive force generated in the molten Pb-Bi can be reliably output to the electrodes 12 and 12. Further, since there is no contact resistance due to the oxide film between the inner peripheral surface of the duct 11 and the molten Pb-Bi, the output fluctuation is small without being affected by the fluctuation of the resistance value of the oxide film due to the temperature fluctuation or the like.
[0030]
【The invention's effect】
As described above, the molten Pb-Bi electromagnetic flowmeter according to the present invention adheres to the contact resistance of the inner peripheral surface of the duct 11 that contacts the molten Pb-Bi moving in the duct 11, particularly to the inner peripheral surface of the duct 11. Alternatively, it is possible to prevent an increase in contact resistance due to the formed oxide film, and it is possible to prevent a decrease in electromotive force output to the electrodes 12 and 12 via the duct 11 and fluctuations thereof. Thereby, the flow velocity and flow rate of the molten Pb-Bi flowing in the duct 11 can be accurately measured.
[Brief description of the drawings]
FIG. 1 is a longitudinal end view of electrodes and magnetic pole portions showing an electromagnetic flowmeter for molten Pb-Bi according to an embodiment of the present invention.
FIG. 2 is a longitudinal side view of an electrode and a magnetic pole portion showing an electromagnetic flowmeter for molten Pb-Bi according to the same embodiment.
FIG. 3 is a longitudinal end view of a duct of an electrode and a magnetic pole part showing a conventional electromagnetic flowmeter for molten Pb-Bi.
[Explanation of symbols]
11 Duct 12 Electrode 14 Precious metal coating 16 Magnetic pole

Claims (5)

溶融Ｐｂ−Ｂｉを移動させる筒状のダクト（１１）と、このダクト（１１）を挟んで対向し、ダクト（１１）内に磁束を形成する一対の磁極（１６）、（１６）と、ダクト（１１）を挟んで対向し、前記磁束を切る方向にダクト（１１）内を移動する溶融Ｐｂ−Ｂｉに生じる電圧を出力する一対の電極（１２）、（１２）とを有する溶融Ｐｂ−Ｂｉ用電磁流量計において、ダクト（１１）の電極（１２）、（１２）及び磁極（１６）、（１６）が対向した位置の内周面の全周にわたり、それら電極（１２）、（１２）と磁極（１６）、（１６）が対向した位置を中心としてダクト（１１）の軸方向に前記磁極（１６）、（１６）のダクト（１１）の軸方向の長さＬより短い長さｌの範囲にわたって貴金属コーティング（１４）を施したことを特徴とする溶融Ｐｂ−Ｂｉ用電磁流量計。A cylindrical duct (11) that moves the molten Pb-Bi, a pair of magnetic poles (16), (16) that are opposed to each other with the duct (11) interposed therebetween and that form a magnetic flux in the duct (11), and the duct A molten Pb-Bi having a pair of electrodes (12) and (12) that output a voltage generated in the molten Pb-Bi that is opposed to each other with (11) and moves in the duct (11) in the direction of cutting the magnetic flux. In the electromagnetic flow meter for use, the electrodes (12), (12) are formed over the entire circumference of the inner peripheral surface at the position where the electrodes (12), (12) and the magnetic poles (16), (16) of the duct (11) face each other. And a length l shorter than the axial length L of the duct (11) of the magnetic poles (16) and (16) in the axial direction of the duct (11) with the position where the magnetic poles (16) and (16) face each other. that subjected to noble metal coating (14) over a range of The magnetic flow molten Pb-Bi to symptoms. 貴金属コーティング（１４）が溶融Ｐｂ−Ｂｉへの溶融速度が１μｍ／ｓ以下の貴金属からなることを特徴とする請求項１に記載の溶融Ｐｂ−Ｂｉ用電磁流量計。2. The electromagnetic flow meter for molten Pb-Bi according to claim 1, wherein the noble metal coating (14) is made of a noble metal having a melting rate of 1 μm / s or less to the molten Pb-Bi. 貴金属コーティング（１４）がＲｈまたはＩｒであることを特徴とする請求項２に記載の溶融Ｐｂ−Ｂｉ用電磁流量計。The electromagnetic flowmeter for molten Pb-Bi according to claim 2, wherein the noble metal coating (14) is Rh or Ir. 貴金属コーティング（１４）の下にＡｕがアンダーコートされ、その上にＲｈまたはＩｒがメッキされていることを特徴とする請求項３に記載の溶融Ｐｂ−Ｂｉ用電磁流量計。The molten Pb-Bi electromagnetic flowmeter according to claim 3, wherein Au is undercoated under the noble metal coating (14), and Rh or Ir is plated thereon. 電極（１２）、（１２）はダクト（１１）の外周に直に取り付けられていることを特徴とする請求項１〜４の何れかに記載の溶融Ｐｂ−Ｂｉ用電磁流量計。Electrode (12), (12) is directly attached to the outer periphery of a duct (11), The molten Pb-Bi electromagnetic flowmeter in any one of Claims 1-4 characterized by the above-mentioned.
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