【０００１】
【発明の属する技術分野】
本発明は、鋼材表面の測温方法及び測温装置に係わり、特に誘導加熱方式の加熱炉内に静置されたＳｉ含有量の大きい鋼材の表面温度を従来より正確に測定する技術に関する。
【０００２】
【従来の技術】
一般に、高温物体（以下、被測温物という）の表面温度を測定するには、非接触で連続測定が可能という利点があるので、放射温度計が用いられている。その原理は、高温にある被測温物が発する放射エネルギーの量（Ｌａ）を検出し、その放射エネルギー量を，図４に示すように、ある一定の放射率（εｉ）に固定して予め求めてある放射エネルギー量（Ｌｉ）と温度（Ｔｉ）との関係に照合して、温度（Ｔａ）を定めるものである。
【０００３】
ところが、被測温物の材質あるいは表面状態等によっては、放出される放射エネルギーの量が異なるので、この放射温度計で正確な（精度良く）測定をするには、放射率を適切な値（例えば、図４のεａに対応する線上にある）に補正する必要がある。特に、被測定物が例えば、１２００℃以上の温度に加熱される鋼材の場合には、以下のように表面状態の変化が避けられないので、放射率の補正は重要である。
【０００４】
▲１▼ 通常は還元性あるいは不活性ガスで炉内雰囲気が制御されている加熱炉内であっても、その雰囲気が乱れると、鋼材の表面にスケール（酸化鉄）が生成される。
【０００５】
▲２▼ 加熱炉に装入される前に生成されたスケールが加熱温度より低い融点を持つ場合には、加熱途中でスケールが溶け、放射温度計の視野内でスケール成分が一定でなくなる。この現象は、鋼材が珪素含有量の高い鋼種であるほど著しく、また表面状態が全体で不均一にもなる。
【０００６】
従って、被測温物が鋼材の場合、放射温度計で測定したその表面温度は、前記したように正確でなく、その後に施される熱間圧延で製造した鋼板等の製品に品質不良が発生するといった問題があった。
【０００７】
一方、放射率の補正を伴う測温技術については、従来より研究が行われ、公開されているものも多い。
【０００８】
例えば、被計測物から放射される熱放射線を計測する放射温度計と、前記被計測物の放射率を計測する放射率計測部と、前記放射温度計によるみかけの温度と放射率を用いて計測温度を算出する温度処理部とを有することを特徴とする温度計測装置が提案されている（特許文献１参照）。この温度計測装置は、新たに設けた前記放射率計測部で被計測物に放射線を照射し、その照射量、反射量、透過量及び吸収量に基づき該被計測物の放射率を求め、その放射率で放射温度計により別途測定したみかけの温度を補正するものである。
【０００９】
また、測定対象物に光を照射して反射光の強度から当該対象物の表面温度を測定する場合、複数の波長からなる光源を用いて、当該対象物の表面状態を表す放射率を算定した上で表面温度を演算することを特徴とする温度監視装置も開示されている（特許文献２参照）。この温度監視装置は、放射温度計を用いずに、光源より波長の異なる数種の光を被対象物に照射し、赤外線ＴＶカメラで受光した光の強度と被対象物の放射率との関係式を複数定め、それらの式より放射率を消去して被対象物の温度を演算で求めるようにしたものである。
【００１０】
【特許文献１】
前記特開昭６０−３８６２７号公報（２頁、右欄の１３行〜１８行）
【００１１】
【特許文献２】
特開昭６１−１６００２８号公報（１頁の右欄１８行〜２頁の右欄１８行）
しかしながら、前記特許文献１記載の温度計測装置は、被計測物が半導体薄板（ウエハ）であり、熱処理中に表面状態が変化するといっても、本発明の対象である鋼材より変化は少ない。また、前記特許文献２記載の温度監視装置は、被対象物が鋼材である場合にも適用できる。しかし、複雑な関係式を利用しており、実際に放射率を求めてその値で温度補正を行うものではないので、実用するには信頼性に欠ける。さらに、上記いずれの装置も、放射率を求めるのに赤外線を用いるので、設備が高価になるという問題もある。
【００１２】
【発明が解決しようとする課題】
本発明は、かかる事情に鑑み、表面状態の変化が大きくても、従来より精度良く測温が可能な鋼材表面の測温方法及び測温装置を提供することを目的としている。
【００１３】
【課題を解決するための手段】
発明者は、上記目的を達成するため、従来装置の問題点を見直し、その成果を本発明に具現化した。
【００１４】
すなわち、本発明は、加熱炉内の鋼材の表面温度を、炉壁に設けた貫通孔を介して放射温度計で測定するに際して、前記鋼材表面に別の貫通孔を介して測温時に光を照射し、その反射映像を得て光量変化率を測定し、予め同種鋼材で定めておいた光量変化率と放射率との関係に照らして、前記光量変化率の測定値からこの測温時に対応した鋼材表面の放射率を求め、その放射率で前記放射温度計による測定温度を補正することを特徴とする鋼材表面の測温方法である。この場合、前記鋼材が珪素を３質量％以上含有する珪素鋼であったり、あるいは前記加熱炉が誘導コイルで加熱する方式であるのが好ましい。また、本発明は、加熱炉内の鋼材の表面温度を、炉壁に設けた貫通孔を介して測定する放射温度計を備えた鋼材表面の測温装置であって、前記貫通孔とは別の貫通孔を介して鋼材表面に光を照射する光源と、その反射光を、さらに別の貫通孔を介して鋼材の表面状態として観察、撮像するＣＣＤカメラと、該ＣＣＤカメラで得た映像から照射した光の光量変化率を演算し、予め同種鋼材で定めておいた光量変化率と放射率との関係に照らして鋼材表面の放射率を求めると共に、得られた放射率を用いて前記放射温度計の測定値を補正して真の鋼材表面温度を演算する演算器とを備えたことを特徴とする鋼材表面の測温装置である。
【００１５】
本発明では、被測温物である鋼材の表面を観察して、該表面で起きるスケールの変化状況を実際に確認すると共に、その映像を利用して鋼材表面からの放射率を正確に推定し、その放射率で放射温度計による測定値を補正できるようになる。その結果、表面状態の変化が大きい鋼材であっても、従来より精度良く測温が可能となる。
【００１６】
【発明の実施の形態】
以下、図面を参照して本発明の実施の形態を説明する。
【００１７】
まず、発明者は、以下のようにして、加熱中に鋼材表面で起きるスケールの変化と放射率との関係について調査した。
【００１８】
鋼種が３質量％Ｓｉの鋼材から１００ｍｍ四方で、且つ厚み２５ｍｍのサンプルを採取し、該サンプルを実験室規模の誘導コイルを備えた加熱炉に装入した。炉内の雰囲気は、窒素である。装入したサンプルを一定の昇温速度で加熱しながら、その表面状態を炉壁に設けた貫通孔より光を照射し、その反射光をＣＣＤカメラで撮像すると共に、別の貫通孔を介して放射温度計及びサンプルに予め取り付けておいた熱電対で表面温度を測定した。そして、別途設けてある演算器を用いて、サンプルの放射率（εｉ）を放射温度計の測定で得た見かけの温度（Ｔａ）と熱電対による真の温度（Ｔｓ）の比として求めると共に、前記ＣＣＤカメラで得た映像を演算器で解析して光量変化率（Ｍｉ）を求めた。この光量変化率を求めた理由は、サンプルの表面状態を評価するのに有効な指標になると考えたからであり、それは、サンプル表面から得たカメラ視野内の一定輝度（ＣＣＤカメラの受光量）を呈する面積が単位時間内に変化する割合、つまり一定の表面状態にある面積の変化率を表すものである。
【００１９】
調査結果の一例を、横軸を熱電対で測定したサンプルの真の表面温度、縦軸を前記のようにして求めた光量変化率及び放射率として、それぞれ図１（ａ）及び（ｂ）に整理した。これら図１（ａ）及び（ｂ）より、以下のことが明らかになる。
【００２０】
すなわち、光量変化率（Ｍｉ）は、熱伝対で測定した真の表面温度（Ｔｓ）でＴ１までは一定値（Ｍ１）であり、このとき放射率もε１で変わらない。そして、該光量変化率は、温度Ｔ１を超えるとスケールの状態が変わるため徐々に変化し、大きくなっていく。また、温度Ｔ２になると、光量変化率は、ピーク値（Ｍ２）に達し、それより温度が上昇しても、徐々に小さくなり、最終的にサンプルの表面状態は安定するためかほとんど変化しなくなった。さらに、上記の光量変化率の変化に対応して、放射率は、温度がＴ１〜Ｔ２間で徐々に小さくなり、Ｔ２以上においてはε２で安定することがわかった。つまり、任意の鋼材について光量変化率と放射率との関係を広い温度範囲にわたり定めることができる。
【００２１】
そこで、発明者は、これらの知見に基づき考察を行い、ＣＣＤカメラで撮像した鋼材の表面状態を光量変化率（Ｍｉ）で求めると共に、予めその鋼材での光量変化率（Ｍｉ）と放射率（εｉ）との関係が知られていれば、該鋼材の放射率が測定時の表面状態に応じて正確に推定でき、その放射率を用いて放射温度計による表面温度測定値の補正ができると結論し、本発明を完成させたのである。
【００２２】
つまり、加熱炉内の鋼材の表面温度を、炉壁に設けた貫通孔を介して放射温度計で測定するに際して、最初は放射温度計による測温と同時に前記鋼材表面に別の貫通孔を介して光を照射し、その反射映像から光量変化率を測定する。そして、引き続いて、該測定値を、予め同種鋼材で定めておいた光量変化率と放射率との関係に照らして、この測温時に対応した鋼材表面の放射率を求め、その放射率を用いて前記放射温度計による測定値を補正するようにしたのである。この場合、光量変化率と放射率との関係は、上記サンプル調査と同様にして、予め被測温物である鋼材と同種のサンプルで定めておけば良い。
【００２３】
次に、上記した本発明を実施する具体的な測温装置について説明すると、それは、図２に示すように、加熱炉１内の鋼材２の表面温度を、炉壁３に設けた貫通孔４を介して測定する放射温度計５を設けることを基本とする。その放射温度計５は、前記ＣＣＤカメラ６の光軸に対して前記光源７と対称となる角度に配置する。また、測温に必要な炉壁３に開けた貫通孔４は、耐熱性の良いパイプ（例えば、セラミック）を装着して保護するのが良い。
【００２４】
そして、該放射温度計５のための貫通孔４とは別に、同様な貫通孔８，８´を炉壁３に２箇所設け、それらを介して鋼材表面に光を照射する光源７と、その反射光を鋼材の表面状態として観察、撮像するＣＣＤカメラ６とをそれぞれ設ける。その光源７のパワーとしては、できるだけ高出力のものを選ぶのが好ましい。図２の例では、メタルハライド光源を使用している。また、該光源７からの光は、光ファイバ式ライトガイドを介して投光レンズ１０より照射させるのが良く、照射角度は、表面を鮮明に見ることの可能な角度を選ぶのが良い。ＣＣＤカメラ６には、レンズ１１及びフィルタ１２を設けるが、そのレンズ１１の種類はＣＣＤカメラ６と鋼材２との距離、観察したい範囲に応じて選定するのが好ましい。フィルタ１２は、鋼材２の表面温度が１２００℃以上と高いので、該鋼材２からの自発光を抑制できるものを選定する必要がある。また、ＣＣＤカメラ６の分光感度特性を考慮し、該カメラの感度の良い波長領域はできるだけ透過率を高くするのが良い。例えば、温度が１２００℃以上ならば、波長０．７μｍより長い波長の光をカットできる赤外カットフィルタを、カメラの感度が０．５〜０．６μｍにピークを持つ場合には、緑色のカラーフィルタを選定すると良い。
【００２５】
さらに、本発明では、そのようなＣＣＤカメラ６で得た映像から照射した光の光量変化率を演算し、予め同種鋼材で定めておいた光量変化率と放射率との関係に照らして鋼材表面からの放射率を求めると共に、得られた放射率を用いて前記放射温度計５の測定値を補正して真の鋼材表面温度を演算するために、演算器１３を設けるようにした。従って、該演算器１３には、ＣＣＤカメラ６で撮像した映像、放射温度計５で測定した温度信号及び予めオフラインでのサンプル実験で得た対象鋼材の光量変化率と放射率との関係が記憶される。そして、該演算器１３では、次の処理を行うことになる。
【００２６】
ａ．ＣＣＤカメラの映像から光量変化率Ｍｉをリアルタイムに計算する。
【００２７】
ｂ．光量変化率と放射率及び温度との関係（例えば、図１参照）を利用し、このＭｉに対する放射率εｉを求める。
【００２８】
ｃ．放射温度計からの放射率補正をしていない測定値Ｔａを取込み、前記εｉで補正して，真の表面温度Ｔｓを算出する。
【００２９】
なお，本発明に係る測温装置は、図３に示すように、放射温度計５とＣＣＤカメラ６とを同じ光軸上で使用する構成にしても良い。この場合、放射温度計５及びＣＣＤカメラ６の前面にハーフミラー１４を設ける必要がある。しかし、このような構成にすると、炉壁３の貫通孔数が減るばかりでなく、放射温度計５とＣＣＤカメラ６との視野合わせが不要となり、測温の作業性が良くなるという利点がある。
【００３０】
加えて、本発明は、被測温物が３質量％以上のＳｉを含有する鋼材２であると、非常に有効である。３質量％以上のＳｉを含み、表面状態の変化が激しくとも、放射率が正確に推定できるからである。さらに加えて、本発明を適用する加熱炉１としては、誘導コイルによる加熱を行う方式のものが好ましい。そのような炉では、鋼材２を静置して加熱することが多く、測温に都合が良いからである。
【００３１】
【実施例】
３質量％Ｓｉ含有の方向性電磁鋼板用スラブを１４００℃に加熱し、その後に熱間圧延し、以後通常工程により方向性電磁鋼板を製造した。使用した加熱炉１は、誘導加熱方式のものである。加熱炉に装入した鋼材は、表面温度が測定され、目標温度に達していない場合には、加熱温度を調整した。この表面温度の測定に、本発明に係る測温方法及び測温装置を採用した場合には、従来通りの放射温度計だけを用いた場合と比較して、得られた鋼板製品の加熱不足による特性不足又は過加熱によるトラブルは無くなり、安定製造及び歩留まり向上を達成できた。
【００３２】
【発明の効果】
以上述べたように、本発明により、表面状態の変化が大きい鋼材であっても、従来より精度良く測温が可能となった。
【図面の簡単な説明】
【図１】本発明の基礎となる鋼材の表面状態と放射率との関係を実験室規模で調査した結果を示す図であり、（ａ）は光量変化率と鋼材の真の表面温度との関係、（ｂ）は鋼材表面の放射率と真の温度との関係である。
【図２】本発明に係る鋼材表面の測温装置の一例を説明する図である。
【図３】本発明に係る鋼材表面の測温装置の別形態例を説明する図である。
【図４】一般的な被測温物の放射エネルギーと温度との関係を、放射率をパラメータとして示す図である。
【符号の説明】
１ 加熱炉
２ 鋼材
３ 炉壁
４ 貫通孔
５ 放射温度計
６ ＣＣＤカメラ
７ 光源
８、８´ 別の貫通孔
９ ライトガイド
１０ 投光レンズ
１１ レンズ
１２ フィルタ
１３ 演算器
１４ ハーフミラー[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method and an apparatus for measuring the temperature of a steel material surface, and more particularly to a technique for more accurately measuring the surface temperature of a steel material having a large Si content that is placed in an induction heating type heating furnace.
[0002]
[Prior art]
In general, a radiation thermometer is used for measuring the surface temperature of a high-temperature object (hereinafter, referred to as an object to be measured) because it has an advantage that it can be continuously measured without contact. The principle is to detect the amount of radiant energy (La) emitted from the object to be measured at a high temperature and fix the amount of radiant energy to a certain constant emissivity (ε i ) as shown in FIG. The temperature (Ta) is determined by checking the relationship between the radiant energy (Li) and the temperature (Ti) obtained in advance.
[0003]
However, since the amount of emitted radiant energy varies depending on the material or surface condition of the object to be measured, an accurate (accurate) measurement of the emissivity requires an appropriate value ( for example, it is necessary to correct to a) on the line corresponding to the epsilon a in FIG. In particular, when the object to be measured is, for example, a steel material heated to a temperature of 1200 ° C. or more, the correction of the emissivity is important because a change in the surface state is inevitable as described below.
[0004]
{Circle around (1)} Even in a heating furnace where the furnace atmosphere is normally controlled by a reducing or inert gas, if the atmosphere is disturbed, scale (iron oxide) is generated on the surface of the steel material.
[0005]
{Circle around (2)} When the scale formed before being charged into the heating furnace has a melting point lower than the heating temperature, the scale melts during heating, and the scale component becomes inconsistent within the visual field of the radiation thermometer. This phenomenon is more remarkable as the steel material is a steel type having a higher silicon content, and the surface state becomes uneven as a whole.
[0006]
Therefore, when the object to be measured is a steel material, the surface temperature measured by the radiation thermometer is not accurate as described above, and quality defects occur in products such as a steel plate manufactured by hot rolling performed thereafter. There was a problem of doing.
[0007]
On the other hand, temperature measurement techniques with correction of emissivity have been studied and many of them have been published.
[0008]
For example, a radiation thermometer that measures thermal radiation radiated from an object to be measured, an emissivity measurement unit that measures the emissivity of the object to be measured, and measurement using an apparent temperature and emissivity by the radiation thermometer A temperature measuring device having a temperature processing unit for calculating a temperature has been proposed (see Patent Document 1). This temperature measurement device irradiates the object to be measured with the newly provided emissivity measurement unit, and obtains the emissivity of the object based on the amount of irradiation, the amount of reflection, the amount of transmission, and the amount of absorption. It corrects the apparent temperature separately measured by a radiation thermometer using the emissivity.
[0009]
When measuring the surface temperature of the object from the intensity of the reflected light by irradiating light to the object to be measured, using a light source having a plurality of wavelengths, the emissivity representing the surface state of the object was calculated. A temperature monitoring device that calculates the surface temperature above is also disclosed (see Patent Document 2). This temperature monitoring device irradiates an object with several types of light having different wavelengths from a light source without using a radiation thermometer, and the relationship between the intensity of light received by an infrared TV camera and the emissivity of the object. A plurality of equations are determined, the emissivity is eliminated from the equations, and the temperature of the object is calculated by calculation.
[0010]
[Patent Document 1]
JP-A-60-38627 (page 2, right column, lines 13 to 18)
[0011]
[Patent Document 2]
JP-A-61-160028 (page 18, right column, line 18 to page 2, right column, line 18)
However, in the temperature measurement device described in Patent Document 1, even though the object to be measured is a semiconductor thin plate (wafer) and the surface state changes during the heat treatment, the change is smaller than that of the steel material to which the present invention is applied. Further, the temperature monitoring device described in Patent Document 2 can also be applied to a case where the object is a steel material. However, since a complicated relational expression is used, and the emissivity is not actually obtained and the temperature is corrected with the value, the reliability is lacking for practical use. Furthermore, all of the above-mentioned devices use infrared rays to determine the emissivity, so that there is a problem that the equipment becomes expensive.
[0012]
[Problems to be solved by the invention]
In view of such circumstances, an object of the present invention is to provide a temperature measuring method and a temperature measuring device for a steel material surface capable of measuring the temperature more accurately than in the past, even if the change in the surface state is large.
[0013]
[Means for Solving the Problems]
In order to achieve the above object, the inventor reviewed the problems of the conventional device, and embodied the results in the present invention.
[0014]
That is, according to the present invention, when measuring the surface temperature of a steel material in a heating furnace with a radiation thermometer through a through hole provided in a furnace wall, light is emitted at the time of temperature measurement through another through hole on the steel material surface. Irradiate, obtain the reflection image, measure the light quantity change rate, and illuminate the relationship between the light quantity change rate and the emissivity determined in advance with the same type of steel material, and respond to this temperature measurement from the measured value of the light quantity change rate. A method for measuring the temperature of a steel material surface, wherein the emissivity of the steel material surface obtained is obtained, and the temperature measured by the radiation thermometer is corrected by the emissivity. In this case, it is preferable that the steel material is silicon steel containing 3% by mass or more of silicon, or that the heating furnace is heated by an induction coil. Further, the present invention is a temperature measuring device for a steel material surface provided with a radiation thermometer for measuring the surface temperature of the steel material in the heating furnace through a through hole provided in the furnace wall, wherein the temperature measuring device is different from the through hole. A light source that irradiates the surface of the steel material with light through the through-hole, a reflected light thereof is observed and imaged as a surface state of the steel material through another through-hole, and a CCD camera that captures images from the image obtained by the CCD camera. Calculate the rate of change in the amount of light of the irradiated light, determine the emissivity of the steel material surface in light of the relationship between the rate of change of light and the emissivity predetermined for the same type of steel, and use the obtained emissivity to obtain the emissivity. And a calculator for calculating a true steel surface temperature by correcting a measurement value of the thermometer.
[0015]
In the present invention, while observing the surface of a steel material, which is a temperature measuring object, and actually confirming the scale change occurring on the surface, the emissivity from the steel material surface is accurately estimated using the image. The emissivity allows the value measured by the radiation thermometer to be corrected. As a result, even if the steel material has a large change in the surface state, the temperature can be measured more accurately than in the past.
[0016]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[0017]
First, the inventors investigated the relationship between the change in scale occurring on the surface of a steel material during heating and the emissivity as follows.
[0018]
A sample of 100 mm square and 25 mm thick was taken from a steel material having a steel type of 3 mass% Si, and the sample was placed in a heating furnace equipped with a laboratory scale induction coil. The atmosphere in the furnace is nitrogen. While heating the loaded sample at a constant heating rate, the surface state is irradiated with light from a through-hole provided in the furnace wall, and the reflected light is imaged by a CCD camera, and is passed through another through-hole. The surface temperature was measured with a radiation thermometer and a thermocouple previously attached to the sample. Then, the emissivity (ε i ) of the sample is obtained as a ratio between the apparent temperature (Ta) obtained by the measurement of the radiation thermometer and the true temperature (Ts) obtained by the thermocouple using a separately provided arithmetic unit. Then, the image obtained by the CCD camera was analyzed by an arithmetic unit to determine a light amount change rate (Mi). The reason for determining the light amount change rate is that it is considered to be an effective index for evaluating the surface state of the sample. It is based on the fact that the constant luminance (light reception amount of the CCD camera) in the camera field of view obtained from the sample surface is obtained. It indicates the rate at which the presented area changes within a unit time, that is, the rate of change of the area in a constant surface state.
[0019]
FIGS. 1 (a) and 1 (b) show an example of the survey results, where the horizontal axis represents the true surface temperature of the sample measured with a thermocouple, and the vertical axis represents the light intensity change rate and emissivity obtained as described above. Tidy. From FIGS. 1A and 1B, the following becomes clear.
[0020]
That is, the light quantity change rate (Mi) is a constant value (M 1 ) up to T 1 at the true surface temperature (Ts) measured by the thermocouple, and the emissivity does not change at ε 1 at this time. Then, the light amount change rate is gradually changed for the scale of state changes exceeds the temperature T 1, increases. Further, at a temperature T 2, the light amount change rate is the peak value reached (M 2), be higher than the temperature it gradually decreases, the surface state of the final sample or nearly to stabilize changed No longer. Further, in response to changes in the light amount change rate of the emissivity, the temperature is gradually reduced between T 1 through T 2, the T 2 or more were found to be stable at epsilon 2. That is, the relationship between the light quantity change rate and the emissivity can be determined for a given steel material over a wide temperature range.
[0021]
Therefore, the inventor considers based on these findings, obtains the surface state of the steel material imaged by the CCD camera by the light amount change rate (Mi), and also previously determines the light amount change rate (Mi) and the emissivity (Mi) of the steel material. If the relationship with ε i ) is known, the emissivity of the steel material can be accurately estimated according to the surface state at the time of measurement, and the emissivity can be used to correct the measured surface temperature by the radiation thermometer. Thus, the present invention has been completed.
[0022]
In other words, when measuring the surface temperature of the steel material in the heating furnace with a radiation thermometer through a through hole provided in the furnace wall, first, at the same time as the temperature measurement by the radiation thermometer, through another through hole in the steel material surface. And irradiates the light, and the light amount change rate is measured from the reflected image. Then, subsequently, the measured value is compared with the relationship between the light amount change rate and the emissivity previously determined for the same type of steel, the emissivity of the steel material surface corresponding to the temperature measurement is obtained, and the emissivity is used. Thus, the value measured by the radiation thermometer is corrected. In this case, the relationship between the light quantity change rate and the emissivity may be determined in advance in the same manner as in the above-described sample investigation, using a sample of the same type as the steel material to be measured.
[0023]
Next, a specific temperature measuring device for carrying out the present invention will be described. As shown in FIG. 2, the surface temperature of a steel material 2 in a heating furnace 1 is measured by a through hole 4 provided in a furnace wall 3. Is basically provided with a radiation thermometer 5 for measuring via a. The radiation thermometer 5 is arranged at an angle symmetrical to the light source 7 with respect to the optical axis of the CCD camera 6. The through-hole 4 formed in the furnace wall 3 required for temperature measurement is preferably protected by attaching a pipe having good heat resistance (for example, ceramic).
[0024]
In addition to the through hole 4 for the radiation thermometer 5, similar through holes 8, 8 'are provided at two places on the furnace wall 3, and a light source 7 for irradiating the steel material surface with light therethrough, A CCD camera 6 for observing and imaging the reflected light as the surface state of the steel material is provided. As the power of the light source 7, it is preferable to select a power as high as possible. In the example of FIG. 2, a metal halide light source is used. The light from the light source 7 is preferably emitted from the light projecting lens 10 through an optical fiber type light guide, and the irradiation angle is preferably selected so that the surface can be clearly seen. The CCD camera 6 is provided with a lens 11 and a filter 12, and the type of the lens 11 is preferably selected according to the distance between the CCD camera 6 and the steel material 2 and the range to be observed. Since the surface temperature of the steel material 2 is as high as 1200 ° C. or more, it is necessary to select a filter that can suppress self-emission from the steel material 2. In addition, in consideration of the spectral sensitivity characteristics of the CCD camera 6, it is preferable that the transmittance of the wavelength region where the sensitivity of the camera is good is as high as possible. For example, if the temperature is 1200 ° C. or higher, an infrared cut filter that can cut light having a wavelength longer than 0.7 μm is used. If the camera sensitivity has a peak at 0.5 to 0.6 μm, a green color filter is used. Select a filter.
[0025]
Further, in the present invention, the light amount change rate of the irradiated light is calculated from the image obtained by such a CCD camera 6, and the surface of the steel material is illuminated based on the relationship between the light amount change rate and the emissivity determined in advance for the same kind of steel material. A calculator 13 is provided to calculate the true steel material surface temperature by calculating the emissivity from, and correcting the measurement value of the radiation thermometer 5 using the obtained emissivity. Therefore, the arithmetic unit 13 stores the image taken by the CCD camera 6, the temperature signal measured by the radiation thermometer 5, and the relationship between the light quantity change rate and the emissivity of the target steel material obtained in advance in an off-line sample experiment. Is done. Then, the arithmetic unit 13 performs the following processing.
[0026]
a. The light amount change rate Mi is calculated in real time from the image of the CCD camera.
[0027]
b. The emissivity εi for this Mi is determined using the relationship between the light quantity change rate, the emissivity, and the temperature (for example, see FIG. 1).
[0028]
c. The measured value Ta from which the emissivity has not been corrected from the radiation thermometer is taken and corrected by the aforementioned εi to calculate the true surface temperature Ts.
[0029]
The temperature measuring device according to the present invention may be configured such that the radiation thermometer 5 and the CCD camera 6 are used on the same optical axis as shown in FIG. In this case, it is necessary to provide a half mirror 14 in front of the radiation thermometer 5 and the CCD camera 6. However, such a configuration not only reduces the number of through-holes in the furnace wall 3 but also eliminates the need to match the field of view between the radiation thermometer 5 and the CCD camera 6, thereby improving the workability of temperature measurement. .
[0030]
In addition, the present invention is very effective when the temperature measurement target is a steel material 2 containing 3% by mass or more of Si. This is because the emissivity can be accurately estimated even when the content of Si is 3% by mass or more and the surface state changes greatly. In addition, as the heating furnace 1 to which the present invention is applied, a heating furnace using an induction coil is preferable. In such a furnace, the steel material 2 is often left standing and heated, which is convenient for temperature measurement.
[0031]
【Example】
A slab for a grain-oriented electrical steel sheet containing 3% by mass of Si was heated to 1400 ° C., and then hot-rolled, and thereafter, a grain-oriented electrical steel sheet was manufactured by a normal process. The heating furnace 1 used is of the induction heating type. The surface temperature of the steel material charged into the heating furnace was measured, and when the temperature did not reach the target temperature, the heating temperature was adjusted. In the measurement of the surface temperature, when the temperature measuring method and the temperature measuring device according to the present invention are employed, compared with the case where only the conventional radiation thermometer is used, due to insufficient heating of the obtained steel sheet product. Trouble due to insufficient characteristics or overheating was eliminated, and stable production and improved yield were achieved.
[0032]
【The invention's effect】
As described above, according to the present invention, it is possible to more accurately measure the temperature of a steel material having a large surface state change than in the past.
[Brief description of the drawings]
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing the results of an examination on a laboratory scale of the relationship between the surface state and emissivity of a steel material on which the present invention is based, and FIG. The relationship (b) is the relationship between the emissivity of the steel surface and the true temperature.
FIG. 2 is a diagram illustrating an example of a temperature measuring device for a steel material surface according to the present invention.
FIG. 3 is a view for explaining another embodiment of the temperature measuring device for steel surface according to the present invention.
FIG. 4 is a diagram showing a relationship between radiant energy and temperature of a general temperature measuring object using emissivity as a parameter.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Heating furnace 2 Steel material 3 Furnace wall 4 Through hole 5 Radiation thermometer 6 CCD camera 7 Light source 8, 8 'Separate through hole 9 Light guide 10 Light emitting lens 11 Lens 12 Filter 13 Computing unit 14 Half mirror
