JP2005233741A - Temperature-measuring part, heating furnace using the part, and furnace temperature control method of heating furnace - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a temperature-measuring part, a heating furnace using the part, and a furnace temperature control method capable of measuring the furnace temperature without fouling, a precursor for optical fiber manufacture to be subjected to heat treatment by metallic components. <P>SOLUTION: This temperature-measuring parts 43, 45 is provided insertably and drawably in a furnace tube 13 of the heating furnace 11 for performing heat treatment of the precursor for optical fiber manufacture. The temperature measuring parts 43, 45 have a constitution, wherein the periphery of a thermocouple 53 is covered with a carbon protection tube 57, and a control means 27 for controlling the operations of heaters 15a, 15b, 15c encircling the furnace tube 13 corrects operation control of the heaters 15a, 15b, 15c based on the temperature in the furnace tube 13 detected by the temperature measuring parts 43, 45. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

本発明は、光ファイバ製造用前駆体を加熱処理する際に用いて好適となる温度測定治具及び該温度測定治具を用いた加熱炉及び該加熱炉における炉内温度制御方法に関する。   The present invention relates to a temperature measurement jig suitable for use in heat-treating a precursor for optical fiber production, a heating furnace using the temperature measurement jig, and a furnace temperature control method in the heating furnace.

光ファイバ製造に当たっては、ＶＡＤ法（Vapor Phase Axial Deposiotion）等によって製造された多孔質母材を脱水焼結して透明母材とし、その透明母材を加熱延伸してプリフォームとし、プリフォームの端部を加熱溶融して光ファイバを線引きするといった方法が採られている。
ここで、多孔質母材を脱水焼結する工程、透明母材を加熱延伸する工程、プリフォームを線引きする工程では、それぞれ加熱処理が行われる。
これらの加熱処理に当たっては、通常、炉心管と炉心管の外周囲に配置したヒータとを備えた加熱炉が使用される。
ここでは、多孔質母材、透明母材、プリフォームを総称して光ファイバ製造用前駆体と称することとする。 In the production of optical fibers, a porous preform manufactured by the VAD method (Vapor Phase Axial Deposiotion) is dehydrated and sintered to form a transparent preform, and the transparent preform is heated and drawn into a preform. A method of drawing an optical fiber by heating and melting the end is employed.
Here, heat treatment is performed in each of the step of dehydrating and sintering the porous base material, the step of heating and stretching the transparent base material, and the step of drawing the preform.
In these heat treatments, a heating furnace including a furnace core tube and a heater arranged around the outer periphery of the furnace core tube is usually used.
Here, the porous base material, the transparent base material, and the preform are collectively referred to as an optical fiber manufacturing precursor.

炉心管内に収容される光ファイバ製造用前駆体の種類に応じて、加熱温度、加熱雰囲気、光ファイバ製造用前駆体に加えられる移動、回転、引張り等の機械的な操作は異なるが、炉心管内に収容した光ファイバ製造用前駆体を炉心管の外側に配置したヒータによって数百度以上の高温に加熱するという操作は共通である。また、いずれの場合も、加熱温度を制御するため、加熱炉の温度測定を行なっている。   Depending on the type of optical fiber manufacturing precursor contained in the core tube, the mechanical operation such as heating temperature, heating atmosphere, movement, rotation, and tension applied to the optical fiber manufacturing precursor is different. The operation of heating the optical fiber production precursor contained in the tube to a high temperature of several hundred degrees or more by a heater disposed outside the core tube is common. In either case, the temperature of the heating furnace is measured in order to control the heating temperature.

図７は、従来技術による加熱炉の主要部の断面図であって、温度測定の例を示すものである。図７において、１は炉体、２は炉心管、３はヒータ、４は断熱材、５は光ファイバ製造用前駆体、６は放射温度計、７は温度測定窓である。加熱処理の対象となる光ファイバ製造用前駆体５は、炉体１の内部に配置されたカーボン、石英等からなる炉心管２の内部に収容されて、炉心管２を周回するように配置されたカーボンからなるヒータ３によって加熱される。
ヒータ３は、電源９からの供給電力に応じた発熱をして、放射熱によって炉心管２内を加熱する。電源９の出力は、放射温度計６の測定値を監視している制御手段８によって制御される。 FIG. 7 is a cross-sectional view of a main part of a heating furnace according to the prior art and shows an example of temperature measurement. In FIG. 7, 1 is a furnace body, 2 is a furnace core tube, 3 is a heater, 4 is a heat insulating material, 5 is a precursor for manufacturing an optical fiber, 6 is a radiation thermometer, and 7 is a temperature measurement window. The optical fiber manufacturing precursor 5 to be heat-treated is accommodated in a core tube 2 made of carbon, quartz or the like disposed in the furnace body 1 and arranged to circulate around the core tube 2. Heated by a heater 3 made of carbon.
The heater 3 generates heat corresponding to the power supplied from the power source 9 and heats the inside of the core tube 2 by radiant heat. The output of the power source 9 is controlled by the control means 8 that monitors the measured value of the radiation thermometer 6.

なお、炉心管２とヒータ３は、炉体１内において断熱材４によって熱遮蔽されている。加熱炉の形式によっては炉心管の一部分が炉体の外側に出ているものもある。その場合でもヒータは、外気によって酸化消耗を起こさないように炉体で外気と遮断されている。   The core tube 2 and the heater 3 are thermally shielded by a heat insulating material 4 in the furnace body 1. Depending on the type of heating furnace, a part of the furnace core tube protrudes outside the furnace body. Even in that case, the heater is shut off from the outside air by the furnace body so as not to cause oxidative consumption by the outside air.

光ファイバ製造用前駆体の加熱処理において、光ファイバ製造用前駆体の温度を直接測定することは困難なので、通常は炉体１に取付けた温度測定窓７から炉体１の外側に設置した放射温度計６を使って、炉心管２の管表面又はヒータ３の外表面の温度を測定する（例えば、特許文献１参照）。   In the heat treatment of the optical fiber manufacturing precursor, it is difficult to directly measure the temperature of the optical fiber manufacturing precursor. Therefore, the radiation installed outside the furnace body 1 from the temperature measurement window 7 attached to the furnace body 1 is usually used. The temperature of the tube surface of the core tube 2 or the outer surface of the heater 3 is measured using the thermometer 6 (see, for example, Patent Document 1).

放射温度計６の測定した温度は、制御手段８に通知される。
制御手段８は、放射温度計６の検出した温度を基に炉心管内の温度又は光ファイバ製造用前駆体の温度を推定し、炉心管内の温度又は光ファイバ製造用前駆体の温度が適正温度に維持されるように、ヒータ３へ給電する電源９の出力を制御して、ヒータ３の温度制御を行なう。 The temperature measured by the radiation thermometer 6 is notified to the control means 8.
The control means 8 estimates the temperature in the furnace core tube or the temperature of the optical fiber manufacturing precursor based on the temperature detected by the radiation thermometer 6 so that the temperature in the core tube or the temperature of the optical fiber manufacturing precursor becomes an appropriate temperature. The temperature of the heater 3 is controlled by controlling the output of the power supply 9 that supplies power to the heater 3 so as to be maintained.

なお、図７は、放射温度計６によって炉心管２の管表面の温度を測定しているところを示す。図７では、ヒータ３及び断熱材４に隙間を設け、その隙間を通して炉心管２の管表面の温度を測定しているが、ヒータ３には隙間を設けず、ヒータの外表面の温度を測定する場合もある。   FIG. 7 shows that the temperature of the tube surface of the core tube 2 is measured by the radiation thermometer 6. In FIG. 7, a gap is provided in the heater 3 and the heat insulating material 4, and the temperature of the tube surface of the core tube 2 is measured through the gap. However, the heater 3 is not provided with a gap and the temperature of the outer surface of the heater is measured. There is also a case.

特開２０００−１４６７００号公報JP 2000-146700 A

ところが、炉心管２は、通常、カーボン、石英等から形成されており、前駆体５の焼結処理時に前駆体５から放出される酸素などによる炉心管表面の酸化消耗や、カーボン微粉末の堆積によって、炉心管内面の状態変化が起こる。
そして、炉心管内面の消耗の進行に伴い、炉心管２を介しての前駆体５への加熱効率が変化していく。
そのため、放射温度計６が検出する炉心管２の管表面又はヒータ３の外表面の温度を基に制御手段８が前駆体５の温度を推定する従来の加熱炉では、炉心管表面の消耗の進行に伴う加熱効率の変化のために、推定温度と実際の前駆体５の温度との間の誤差が徐々に大きくなってしまい、結局、前駆体５に対して安定した加熱処理を長期に継続することが難しくなる。従って、安定した加熱処理を長期に渡って維持できる加熱炉の開発が望まれていた。 However, the core tube 2 is usually made of carbon, quartz or the like, and the oxidation consumption of the surface of the core tube due to oxygen released from the precursor 5 during the sintering process of the precursor 5 or the deposition of carbon fine powder. This causes a change in the state of the inner surface of the core tube.
And the heating efficiency to the precursor 5 through the core tube 2 changes with progress of exhaustion of the inner surface of the core tube.
Therefore, in the conventional heating furnace in which the control means 8 estimates the temperature of the precursor 5 based on the temperature of the tube surface of the core tube 2 detected by the radiation thermometer 6 or the outer surface of the heater 3, the consumption of the surface of the core tube is reduced. Due to the change in heating efficiency accompanying the progress, the error between the estimated temperature and the actual temperature of the precursor 5 gradually increases, and as a result, stable heat treatment for the precursor 5 is continued for a long time. It becomes difficult to do. Therefore, it has been desired to develop a heating furnace capable of maintaining stable heat treatment for a long time.

また、炉心管２内の前駆体５の実際の温度と推定温度との誤差を無くすために、間欠的に、炉心管２内に熱電対を挿入して、炉心管２内の温度を実測することも提案された。しかし、熱電対を直に高温の炉心管２内に挿入すると、熱電対の金属成分が炉心管２内に放出（揮散）して、前駆体５が熱電対の金属成分によって汚染されて、前駆体５における光ファイバ特性の低下を招く虞があった。   Further, in order to eliminate an error between the actual temperature of the precursor 5 in the core tube 2 and the estimated temperature, a thermocouple is intermittently inserted into the core tube 2 to actually measure the temperature in the core tube 2. It was also proposed. However, when the thermocouple is inserted directly into the high temperature core tube 2, the metal component of the thermocouple is released (volatilized) into the core tube 2, and the precursor 5 is contaminated by the metal component of the thermocouple, There was a possibility that the optical fiber characteristics of the body 5 would be deteriorated.

また、炉心管内面の消耗は、炉心管２内の温度分布の影響、或いは前駆体５のセット位置の影響のために、場所によって消耗速度が変わり、その結果、場所によって加熱効率にばらつきが生じるため、上記従来例のような一箇所の測定では、炉内の温度分布を正確に把握することができず、ヒータの動作制御による炉内温度の均一化が難しい。   Further, the consumption of the inner surface of the reactor core tube is affected by the temperature distribution in the reactor core tube 2 or the influence of the set position of the precursor 5, so that the consumption rate varies depending on the location. As a result, the heating efficiency varies depending on the location. Therefore, in the measurement at one place as in the conventional example, the temperature distribution in the furnace cannot be accurately grasped, and it is difficult to make the furnace temperature uniform by controlling the operation of the heater.

本発明の目的は、加熱処理する光ファイバ製造用前駆体を、金属成分によって汚損させずに炉内温度を実測でき、また、炉内温度を正確に所望温度に制御して、光ファイバ製造用前駆体に対する適正な加熱処理を長期に継続実施することができ、更には、ヒータの動作制御による炉内温度の均一化を実現して、高品位な光ファイバ母材を得るために適用される温度測定治具及び該治具を用いた加熱炉及び該加熱炉における炉内温度制御方法を提供することにある。   The object of the present invention is to measure the temperature inside the furnace without fouling the optical fiber precursor to be heat-treated by the metal component, and to accurately control the furnace temperature to the desired temperature to produce the optical fiber. Appropriate heat treatment for the precursor can be carried out over a long period of time. Furthermore, it is applied to obtain a high-quality optical fiber preform by realizing uniform furnace temperature by controlling the operation of the heater. A temperature measurement jig, a heating furnace using the jig, and a furnace temperature control method in the heating furnace are provided.

上記目的は下記構成により達成される。
上記目的を達成するために、本発明に係る請求項１記載の温度測定治具は、熱電対と、該熱電対を先端を部分的に露出させた状態で覆う短絡防止保護管と、前記熱電対の先端の露出部分を覆うカーボン保護管とを具備したことを特徴とする。 The above object is achieved by the following configuration.
In order to achieve the above object, a temperature measurement jig according to claim 1 of the present invention comprises a thermocouple, a short-circuit protection protective tube that covers the thermocouple with a tip partially exposed, and the thermocouple. And a carbon protective tube covering an exposed portion at the tip of the pair.

上記目的を達成するために、本発明に係る請求項２記載の加熱炉は、炉心管と、該炉心管の外周囲に配置したヒータと、該ヒータを外気から遮断するための炉体とを備える加熱炉であって、
前記炉心管内に挿抜可能に備えられて炉心管内の温度を検出する請求項１記載の温度測定治具を用いたことを特徴とする加熱炉。 In order to achieve the above object, a heating furnace according to claim 2 according to the present invention comprises a furnace core tube, a heater disposed on the outer periphery of the furnace core tube, and a furnace body for shielding the heater from outside air. A heating furnace comprising:
2. A heating furnace using the temperature measuring jig according to claim 1, wherein the temperature measuring jig is provided so as to be inserted into and removed from the furnace core tube and detects the temperature in the furnace core tube.

本発明に係る請求項３記載の加熱炉における炉内温度制御方法は、請求項２に記載の加熱炉において、前記温度測定治具及び加熱処理中に前記炉心管の表面温度を検出する温度検出手段により定期的に炉心管内外の温度を検出し、前記炉心管内の温度が所望温度になるように、前記温度測定治具及び温度検出手段により知見した炉心管内外の温度差に基づいて、前記ヒータの動作制御を行うことを特徴とする。   According to a third aspect of the present invention, there is provided a method for controlling the temperature in the furnace of the heating furnace according to the second aspect of the present invention, wherein in the heating furnace according to the second aspect, the temperature measurement tool detects the surface temperature of the core tube during the temperature measurement jig and heat treatment. Based on the temperature difference between the inside and outside of the core tube, which is found by the temperature measuring jig and the temperature detecting means, so that the temperature inside and outside the core tube is periodically detected by the means, and the temperature inside the core tube becomes a desired temperature, It is characterized by controlling the operation of the heater.

本発明に係る請求項４記載の加熱炉は、請求項２に記載の加熱炉において、前記炉心管の軸方向に位置をずらした複数の測定点で、温度検出を行うことを特徴とするとよい。   According to a fourth aspect of the present invention, there is provided the heating furnace according to the second aspect, wherein temperature detection is performed at a plurality of measurement points whose positions are shifted in the axial direction of the core tube. .

本発明に係る請求項５記載の加熱炉における炉内温度制御方法は、請求項４に記載の加熱炉において、前記温度測定治具及び温度検出手段により定期的に炉心管内外の複数点の温度を検出し、前記炉心管内の温度分布が所望温度分布になるように、前記温度測定治具及び温度検出手段により知見した炉心管内外の温度差分布に基づいて、前記ヒータの動作制御を行うことを特徴とするとよい。   According to a fifth aspect of the present invention, there is provided a method for controlling the temperature in the furnace of the heating furnace according to the fourth aspect, wherein the temperature measurement jig and the temperature detecting means are used to periodically control the temperature at a plurality of points inside and outside the core tube. And controlling the operation of the heater on the basis of the temperature difference distribution inside and outside the core tube found by the temperature measuring jig and the temperature detecting means so that the temperature distribution in the core tube becomes a desired temperature distribution. It is good to feature.

本発明の温度測定治具及び該治具を用いた加熱炉及び該加熱炉における炉内温度制御方法によれば、炉心管内に挿入されて炉心管内の温度を検出できる温度測定治具を装備しているため、例えば、定期的に温度測定治具によって炉内温度の測定を実施し、加熱処理中に炉心管の表面又はヒータの外表面の温度を検出する温度検出手段の測定値と前記温度測定治具の測定値とを比較することによって、炉心管内面の消耗に起因した炉心管の加熱効率の変化や、この加熱効率の変化に起因した実際の前駆体の温度と推定温度との間の誤差を検知することができる。
従って、加熱効率の変化に起因した実際の前駆体の温度と推定温度との間の誤差が所定以下になるように、制御手段によるヒータの動作制御を補正することで、炉心管内面の消耗の進行に伴う加熱効率の変化に拘わらず、炉心内を正確に所望温度に維持して、光ファイバ製造用前駆体に対する適正な加熱処理を長期に継続実施することができる。
また、炉心管内の温度の測定を行う温度測定治具は、温度測定に使用される熱電対の周囲がカーボン保護管で覆われているため、熱電対がヒータによる加熱で高温に昇温しても熱電対の金属成分が炉内に放出されることを防止できる。従って、加熱処理する光ファイバ製造用前駆体や炉心管内を金属成分によって汚損させずに炉内温度を実測することができる。 According to the temperature measurement jig of the present invention, the heating furnace using the jig, and the furnace temperature control method in the heating furnace, the temperature measurement jig that is inserted into the furnace core tube and can detect the temperature in the furnace core tube is equipped. Therefore, for example, the temperature in the furnace is periodically measured with a temperature measuring jig, and the temperature detection means for detecting the temperature of the surface of the core tube or the outer surface of the heater during the heat treatment and the temperature By comparing the measured value of the measurement jig, the change in the heating efficiency of the core tube due to the exhaustion of the inner surface of the core tube, and the actual precursor temperature and the estimated temperature due to this change in heating efficiency Error can be detected.
Therefore, by correcting the heater operation control by the control means so that the error between the actual precursor temperature and the estimated temperature due to the change in the heating efficiency is less than a predetermined value, the consumption of the inner surface of the core tube is reduced. Regardless of the change in the heating efficiency with the progress, the inside of the core can be accurately maintained at a desired temperature, and an appropriate heat treatment for the optical fiber production precursor can be continued for a long time.
In addition, the temperature measurement jig that measures the temperature inside the core tube is covered with a carbon protective tube around the thermocouple used for temperature measurement. Also, the metal component of the thermocouple can be prevented from being released into the furnace. Therefore, it is possible to actually measure the furnace temperature without fouling the precursor for manufacturing an optical fiber to be heat-treated or the furnace core tube with a metal component.

以下、本発明に係る温度測定治具及び該治具を用いた加熱炉及び該加熱炉における炉内温度制御方法の好適な実施の形態について、図面を参照して詳細に説明する。
図１は、本発明に係る加熱炉の一実施の形態を示したものである。 DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of a temperature measurement jig, a heating furnace using the jig, and a furnace temperature control method in the heating furnace according to the present invention will be described in detail with reference to the drawings.
FIG. 1 shows an embodiment of a heating furnace according to the present invention.

この一実施の形態の加熱炉１１は、光ファイバの原料となる多孔質母材、透明母材、プリフォーム等の光ファイバ製造用前駆体を加熱処理するもので、カーボン、石英等で筒状に形成されて略中心軸線に沿って加熱処理対象の光ファイバ製造用前駆体が挿入される炉心管１３と、該炉心管１３の外周囲に配置した複数個のヒータ１５ａ，１５ｂ，１５ｃと、これらの各ヒータ１５ａ，１５ｂ，１５ｃへ給電する電源１７と、上記の各ヒータ１５ａ，１５ｂ，１５ｃを外気から遮断する炉体１９と、加熱処理中に炉心管１３の表面（外周面）１３ａ又はヒータ１５ａ，１５ｂ，１５ｃの外表面の温度を検出する複数個の温度検出手段２３ａ，２３ｂ，２３ｃと、炉心管１３内に挿抜可能に炉体１９の上部に取り付けられて炉心管１３内の温度測定に使用される温度測定治具４３，４５と、各温度検出手段２３ａ，２３ｂ，２３ｃの検出値を監視して、ヒータ１５ａ，１５ｂ，１５ｃの加熱動作を制御する制御手段２７とを備えて、炉心管１３内に設置された光ファイバ製造用前駆体に対して所定の加熱処理を行う。   The heating furnace 11 of this embodiment heats a precursor for manufacturing an optical fiber such as a porous base material, a transparent base material, and a preform that is a raw material for an optical fiber, and is tubular with carbon, quartz, or the like. A core tube 13 in which a precursor for manufacturing an optical fiber to be heat-treated is inserted along a substantially central axis, and a plurality of heaters 15a, 15b, 15c arranged on the outer periphery of the core tube 13, A power source 17 for supplying power to each of these heaters 15a, 15b, 15c, a furnace body 19 for shutting off each of the heaters 15a, 15b, 15c from the outside air, and a surface (outer peripheral surface) 13a of the furnace core tube 13 during the heat treatment or A plurality of temperature detecting means 23 a, 23 b, 23 c for detecting the temperature of the outer surface of the heaters 15 a, 15 b, 15 c, and the temperature inside the core tube 13 attached to the upper part of the furnace body 19 so as to be insertable / removable into the core tube 13. Measurement Temperature measuring jigs 43 and 45, and control means 27 for monitoring the detection values of the temperature detecting means 23a, 23b and 23c and controlling the heating operation of the heaters 15a, 15b and 15c, Predetermined heat treatment is performed on the optical fiber manufacturing precursor installed in the core tube 13.

ヒータ１５ａ，１５ｂ，１５ｃは、カーボンから形成されていて、電源１７からの供給電力に応じた発熱をして、放射熱によって炉心管１３内を加熱する。
各ヒータ１５ａ，１５ｂ，１５ｃは、炉心管１３の軸方向に位置をずらして配備されている。
なお、図示はしていないが、ヒータ１５ａ，１５ｂ，１５ｃと炉体１９と間には、断熱材壁が装備されて、ヒータ１５ａ，１５ｂ，１５ｃの発熱が炉体１９側に逃げないように、熱遮蔽されている。 The heaters 15a, 15b, and 15c are made of carbon, generate heat according to the power supplied from the power source 17, and heat the inside of the core tube 13 by radiant heat.
The heaters 15a, 15b, and 15c are arranged with their positions shifted in the axial direction of the core tube 13.
Although not shown, a heat insulating wall is provided between the heaters 15a, 15b, 15c and the furnace body 19 so that the heat generated by the heaters 15a, 15b, 15c does not escape to the furnace body 19 side. , Is heat shield.

電源１７は、各ヒータ１５ａ，１５ｂ，１５ｃへの供給電力を各ヒータ毎に個別に調整可能なもので、供給電力の増減が制御手段２７によって制御される。   The power source 17 can adjust the power supplied to the heaters 15 a, 15 b, and 15 c individually for each heater, and the control means 27 controls the increase or decrease in the power supplied.

温度検出手段２３ａ，２３ｂ，２３ｃは、放射温度計で、炉体１９の外側に装備されている。
各温度検出手段２３ａ，２３ｂ，２３ｃは、ヒータ１５ａ，１５ｂ，１５ｃの装備位置に対応して設けられている。そして、炉体１９の内側には、放射温度計の測定光の通路となる温度測定管３１ａ，３１ｂ，３１ｃが装備されている。各温度測定管３１ａ，３１ｂ，３１ｃは、ヒータ１５ａ，１５ｂ，１５ｃを貫通して炉心管１３の表面１３ａに到達している。
各温度検出手段２３ａ，２３ｂ，２３ｃは、炉心管１３の表面温度を常時検出して、制御手段２７に通知する。 The temperature detection means 23 a, 23 b, and 23 c are radiation thermometers and are provided outside the furnace body 19.
Each temperature detection means 23a, 23b, 23c is provided corresponding to the installation position of the heaters 15a, 15b, 15c. Inside the furnace body 19, temperature measuring tubes 31a, 31b, and 31c serving as a measurement light path of the radiation thermometer are provided. Each temperature measuring tube 31a, 31b, 31c passes through the heaters 15a, 15b, 15c and reaches the surface 13a of the core tube 13.
Each temperature detection means 23 a, 23 b, 23 c constantly detects the surface temperature of the core tube 13 and notifies the control means 27.

炉体１９の上面の中心には、ゲート弁３３によって開閉可能な開口部３５が装備されると共に、この開口部３５に連通して予備室４６が装備されている。この予備室４６は、隔壁４７によって炉体１９の上に密閉空間を画成する。   An opening 35 that can be opened and closed by a gate valve 33 is provided at the center of the upper surface of the furnace body 19, and a spare chamber 46 is provided in communication with the opening 35. The preliminary chamber 46 defines a sealed space on the furnace body 19 by the partition wall 47.

予備室４６内には、炉心管１３の中心軸線上を昇降可能に配置されたロッド４１と、該ロッド４１の先端に吊持された略棒状の測定部４３と、ゲート弁３３が開いた時にゲート弁３３の代わりに炉心管１３の上部開口を塞ぐ上蓋４４と、この上蓋が下端に連結された上蓋昇降用架台４５とを備えている。なお、本明細書中において、上記の測定部４３及び上蓋昇降用架台４５を含んで温度測定治具と呼ぶ。   In the spare chamber 46, when the rod 41 arranged so as to be movable up and down on the central axis of the core tube 13, the substantially rod-shaped measuring portion 43 suspended at the tip of the rod 41, and the gate valve 33 are opened. Instead of the gate valve 33, an upper lid 44 for closing the upper opening of the core tube 13 and an upper lid raising / lowering base 45 connected to the lower end of the upper lid are provided. In the present specification, the measurement unit 43 and the upper lid lifting platform 45 are referred to as a temperature measurement jig.

ロッド４１は、所定の下限位置まで降下すると、降下が停止される。また、ロッド４１は、上昇時の上限位置が、図示略のストッパ又は近接スイッチによって規制される。
ロッド４１が最下限位置まで降下した時に、後述の図４に示すように、測定部４３は最も深く炉心管１３内に挿入された状態になる。 When the rod 41 is lowered to a predetermined lower limit position, the lowering is stopped. Further, the upper limit position of the rod 41 when it is raised is regulated by a stopper or a proximity switch (not shown).
When the rod 41 is lowered to the lowest limit position, the measuring unit 43 is most deeply inserted into the core tube 13 as shown in FIG.

測定部４３は、図２及び図３に示すように、温度測定用の熱電対５３の周囲をアルミナ製の短絡防止保護管５５及びカーボン保護管５７で覆った構成を成して、挿入された炉心管１３内の温度を熱電対５３により検出する。
短絡防止保護管５５は、熱電対５３の短絡防止を果たすもので、熱電対５３を挿通させる一対の挿通孔５５ａをアルミナ製の円柱体に貫通させた構造を成し、先端側に熱電対５３の測定端５３ａが部分的に露出する。
カーボン保護管５７は、熱電対５３の昇温によって熱電対５３の金属成分が炉心管１３内に放出（揮散）されることを防止するためのもので、短絡防止保護管５５の外周から熱電対５３の測定端５３ａまでを覆う有底筒状を成している。
以上の測定部４３は、上端部がロッド４１に接続されることで、ロッド４１の下端に吊持された状態になり、ロッド４１の昇降によって炉心管１３内に挿抜される。 As shown in FIGS. 2 and 3, the measurement unit 43 is inserted so as to cover the temperature measurement thermocouple 53 with an alumina short circuit protection tube 55 and a carbon protection tube 57. The temperature inside the core tube 13 is detected by a thermocouple 53.
The short-circuit prevention protective tube 55 serves to prevent the thermocouple 53 from being short-circuited, and has a structure in which a pair of insertion holes 55a through which the thermocouple 53 is inserted is passed through an alumina cylinder, and the thermocouple 53 is provided at the tip side. The measurement end 53a is partially exposed.
The carbon protective tube 57 is for preventing the metal component of the thermocouple 53 from being released (evaporated) into the core tube 13 due to the temperature rise of the thermocouple 53. It has a bottomed cylindrical shape that covers up to 53 measurement ends 53a.
The measuring unit 43 is connected to the rod 41 at the upper end, and is suspended from the lower end of the rod 41. The measuring unit 43 is inserted into and removed from the reactor core tube 13 by raising and lowering the rod 41.

測定部４３の熱電対５３は、隔壁４７の外部に配置されたレコーダ６１と補償導線６３を介して接続されていて、熱電対５３により検出される温度データがレコーダ６１に収集・記録される。   The thermocouple 53 of the measurement unit 43 is connected to the recorder 61 disposed outside the partition wall 47 via the compensation lead wire 63, and temperature data detected by the thermocouple 53 is collected and recorded in the recorder 61.

上蓋昇降用架台４５は、ロッド４１に上下動可能に嵌合すると共に、その上端面が予備室４６の内部上面に近接した所定の上限位置に配置されることによって、上方への移動が拘束される。上蓋昇降用架台４５の下端面中心部には、測定部４３を挿通可能にする開口が設けられている。   The upper lid lifting platform 45 is fitted to the rod 41 so as to be movable up and down, and its upper end surface is disposed at a predetermined upper limit position close to the inner upper surface of the spare chamber 46, thereby restraining the upward movement. The An opening that allows the measurement unit 43 to be inserted is provided at the center of the lower end surface of the upper lid lifting platform 45.

ロッド４１の降下時、上蓋昇降用架台４５は、上蓋４４が図４及び図５に示すように炉心管１３の上端の段差部１３ｂに着座するまでは、ロッド４１と一緒に降下する。そして、上蓋４４が炉心管１３の上端の段差部１３ｂに着座した時点で、上蓋昇降用架台４５の降下は停止し、それより下には下がらない。ロッド４１自体は、図４に示すように、所定の最下限位置の高さに到達するまで降下可能で、ロッド４１が最下限位置まで降下した時には、ロッド４１の下端は図４に示すように、上蓋４４に近接する位置に到達する。   When the rod 41 is lowered, the upper lid lifting platform 45 is lowered together with the rod 41 until the upper lid 44 is seated on the stepped portion 13b at the upper end of the core tube 13 as shown in FIGS. When the upper lid 44 is seated on the stepped portion 13b at the upper end of the core tube 13, the lowering of the upper lid raising / lowering platform 45 stops and does not lower below it. As shown in FIG. 4, the rod 41 itself can be lowered until it reaches the height of the predetermined lower limit position. When the rod 41 is lowered to the lower limit position, the lower end of the rod 41 is as shown in FIG. The position near the upper lid 44 is reached.

測定部４３は、炉心管１３内への挿入量を調整することで、測定端５３ａの位置を炉心管１３内の任意の高さにすることができ、例えば、ロッド４１の降下動作を間欠的にして、測定端５３ａ（図２参照）の位置を各ヒータ１５ａ，１５ｂ，１５ｃの位置で一次停止させて温度測定することにより、各ヒータ１５ａ，１５ｂ，１５ｃの位置に対応した炉内温度を実測することができる。
図４に示した符号Ｐ１，Ｐ２，Ｐ３は、ヒータ１５ａ，１５ｂ，１５ｃの位置に対応した炉内温度を実測する場合の測定点で、これらの各測定点Ｐ１，Ｐ２，Ｐ３が、熱電対５３の測定端５３ａを停止させる位置となる。 The measuring unit 43 can adjust the amount of insertion into the core tube 13 to set the position of the measurement end 53a to an arbitrary height in the core tube 13. For example, the lowering operation of the rod 41 is intermittent. Then, the position of the measurement end 53a (see FIG. 2) is temporarily stopped at the position of each heater 15a, 15b, 15c, and the temperature is measured, whereby the furnace temperature corresponding to the position of each heater 15a, 15b, 15c is obtained. It can be measured.
Symbols P1, P2, and P3 shown in FIG. 4 are measurement points when the furnace temperature corresponding to the positions of the heaters 15a, 15b, and 15c is actually measured. These measurement points P1, P2, and P3 are thermocouples. This is the position at which the measurement end 53a of 53 is stopped.

測定部４３は、通常は図１に示すように予備室４６内に待機した状態にされているが、定期的に、図４に示すように炉心管１３内に挿入されて、炉内温度の検出を行う。
測定部４３により炉内温度を検出する場合は、炉体１９内は通常の待機時と同様の真空状態、昇温状態（例えば、８００℃）に整え、更に、予備室４６も炉体１９内と同様の真空状態に整えた後にゲート弁３３を開いて、予備室４６を炉心管１３に連通した状態にし、その後、ロッド４１の降下動作によって、測定部４３を炉心管１３内に挿入する。
ロッド４１の降下は、熱電対５３の測定端５３ａが予め設定した測定点Ｐ１，Ｐ２，Ｐ３の何れかで停止するように、制御される。 The measurement unit 43 is normally in a standby state in the auxiliary chamber 46 as shown in FIG. 1, but is periodically inserted into the core tube 13 as shown in FIG. Perform detection.
When the temperature in the furnace is detected by the measuring unit 43, the inside of the furnace body 19 is adjusted to a vacuum state and a temperature rising state (for example, 800 ° C.) similar to those during normal standby, and the preliminary chamber 46 is also placed in the furnace body 19. After the vacuum state is adjusted, the gate valve 33 is opened, the spare chamber 46 is communicated with the core tube 13, and then the measuring unit 43 is inserted into the core tube 13 by the lowering operation of the rod 41.
The lowering of the rod 41 is controlled so that the measurement end 53a of the thermocouple 53 stops at any of the preset measurement points P1, P2, and P3.

そして、熱電対５３による温度測定時には、炉心管１３内は、通常の加熱処理時と同様に炉心管１３内が光ファイバ製造用前駆体の熱処理に必要な温度（例えば、１２００℃程度）となるように、ヒータ１５ａ，１５ｂ，１５ｃを作動させる。
そして、炉心管１３内の温度が、設定温度の±１０℃以内に安定後、１時間以上その加熱状態をキープして、その間に熱電対５３による温度測定を行う。
炉内温度の検出が終了したら、図５に示すように、測定部４３はロッド４１の上昇によって予備室４６内に退避した状態に戻す。そして、図６に示すように、測定部４３及び上蓋４４及び上蓋昇降用架台４５が完全に予備室４６内に退避したら、ゲート弁３３を閉じて、予備室４６を炉心管１３側と切り離す。 When the temperature is measured by the thermocouple 53, the temperature inside the core tube 13 becomes a temperature necessary for heat treatment of the optical fiber manufacturing precursor (for example, about 1200 ° C.) in the same manner as in the normal heat treatment. Thus, the heaters 15a, 15b, and 15c are operated.
Then, after the temperature in the core tube 13 is stabilized within ± 10 ° C. of the set temperature, the heating state is kept for one hour or more, and the temperature is measured by the thermocouple 53 during that time.
When the detection of the in-furnace temperature is completed, the measuring unit 43 returns to the state retracted into the preliminary chamber 46 by the ascent of the rod 41 as shown in FIG. As shown in FIG. 6, when the measuring unit 43, the upper lid 44, and the upper lid raising / lowering base 45 are completely retracted into the spare chamber 46, the gate valve 33 is closed and the spare chamber 46 is separated from the core tube 13 side.

制御手段２７は、定期的に温度測定治具４３，４５により検出される炉心管１３内の温度をレコーダ６１を介して監視する一方、各温度検出手段２３ａ，２３ｂ，２３ｃの検出した炉心管１３の表面温度を常時監視している。
そして、制御手段２７は、各温度検出手段２３ａ，２３ｂ，２３ｃの検出値と予め設定された炉心管１３の加熱効率とに基づいて炉心管１３内部の温度分布を推定する機能を有しており、推定した炉内温度が、光ファイバ製造用前駆体に対して適正な加熱温度となるように、電源１７の出力を制御することで各ヒータ１５ａ，１５ｂ，１５ｃの発熱動作を制御する。 The control means 27 periodically monitors the temperature in the core tube 13 detected by the temperature measuring jigs 43 and 45 via the recorder 61, while the core tube 13 detected by each temperature detection means 23a, 23b and 23c. The surface temperature is constantly monitored.
And the control means 27 has a function which estimates the temperature distribution inside the core tube 13 based on the detected value of each temperature detection means 23a, 23b, 23c and the preset heating efficiency of the core tube 13. The heating operation of each of the heaters 15a, 15b, and 15c is controlled by controlling the output of the power supply 17 so that the estimated furnace temperature becomes an appropriate heating temperature for the optical fiber manufacturing precursor.

更に、制御手段２７は、推定した温度と温度測定治具の測定部４３によって検出された実際の炉内の温度とを比較し、両者の誤差が一定以上の場合には、炉心管１３の内面の消耗によって加熱効率が変化し、その結果当初の加熱性能が得られなくなったと見なして、温度測定治具の測定部４３による実測温度が光ファイバ製造用前駆体に対して適正な加熱温度となるように、各ヒータ１５ａ，１５ｂ，１５ｃの発熱動作を補正する。   Furthermore, the control means 27 compares the estimated temperature with the actual temperature in the furnace detected by the measuring unit 43 of the temperature measuring jig, and if the error between the two is more than a certain value, the inner surface of the furnace core tube 13 is compared. It is assumed that the heating efficiency has changed due to the consumption of heat, and as a result, the initial heating performance can no longer be obtained, and the actual temperature measured by the measuring unit 43 of the temperature measuring jig becomes an appropriate heating temperature for the optical fiber manufacturing precursor. As described above, the heating operation of each heater 15a, 15b, 15c is corrected.

即ち、上記の加熱炉１１において光ファイバ製造用前駆体を加熱処理する場合に、制御手段２７は、温度検出手段２３ａ，２３ｂ，２３ｃにより定期的に炉心管１３内外の温度を検出し、炉心管１３内の温度が所望温度になるように、温度検出手段２３ａ，２３ｂ，２３ｃ及び温度測定治具４３，４５により知見した炉心管１３内外の温度差に基づいて、ヒータ１５ａ，１５ｂ，１５ｃの動作制御を補正する。   That is, when the optical fiber production precursor is heat-treated in the heating furnace 11 described above, the control means 27 periodically detects the temperature inside and outside the core tube 13 by means of the temperature detection means 23a, 23b, 23c, and the furnace core tube. The operation of the heaters 15a, 15b, 15c is based on the temperature difference between the inside and outside of the core tube 13 found by the temperature detecting means 23a, 23b, 23c and the temperature measuring jigs 43, 45 so that the temperature in the inside 13 becomes a desired temperature. Correct the control.

なお、上記実施の形態の場合は、図４に示したように、温度測定治具４３，４５は、熱電対５３の測定端５３ａの降下位置を、各測定点Ｐ１，Ｐ２，Ｐ３に順にずらして測定を実施することで、炉心管１３内の３箇所の温度を測定し、炉内温度分布を検知することができる。
制御手段２７は、温度検出手段２３ａ，２３ｂ，２３ｃによって検出される炉心管１３の表面の温度分布と、温度測定治具４３，４５によって検出した炉内の温度分布とを比較することによって、炉心管１３内における加熱効率のばらつきを検知することができ、このような加熱効率のばらつきがなくなるように、各ヒータ１５ａ，１５ｂ，１５ｃの動作制御を補正することで、炉内の温度のばらつきを無くすことができる。 In the case of the above embodiment, as shown in FIG. 4, the temperature measurement jigs 43 and 45 shift the descending position of the measurement end 53a of the thermocouple 53 to the measurement points P1, P2, and P3 in order. By carrying out the measurement, it is possible to measure the temperature at three locations in the core tube 13 and detect the temperature distribution in the furnace.
The control means 27 compares the temperature distribution on the surface of the core tube 13 detected by the temperature detection means 23a, 23b, and 23c with the temperature distribution in the furnace detected by the temperature measuring jigs 43 and 45, thereby making the core Variations in the heating efficiency in the tube 13 can be detected, and the variations in the temperature in the furnace are corrected by correcting the operation control of the heaters 15a, 15b, and 15c so as to eliminate such variations in the heating efficiency. It can be lost.

以上に説明した加熱炉１１における炉内温度制御方法によれば、加熱炉１１自体に、炉心管１３内に挿入されて炉心管１３内の温度を実測する温度測定治具４３，４５を装備しているため、例えば、定期的に温度測定治具４３，４５によって炉内温度の測定を実施し、加熱処理中に炉心管１３の表面又はヒータ１５ａ，１５ｂ，１５ｃの外表面の温度を検出する温度検出手段２３ａ，２３ｂ，２３ｃの測定値と温度測定治具４３，４５の測定値とを比較することによって、炉心管１３内面の消耗に起因した炉心管１３の加熱効率の変化や、この加熱効率の変化に起因した実際の前駆体の温度と推定温度との間の誤差を検知することができる。
従って、加熱効率の変化に起因した実際の前駆体の温度と推定温度との間の誤差が所定以下になるように、制御手段２７によるヒータ１５ａ，１５ｂ，１５ｃの動作制御を補正することで、炉心管１３内面の消耗の進行に伴う加熱効率の変化に拘わらず、炉心内を正確に所望温度に維持して、光ファイバ製造用前駆体に対する適正な加熱処理を長期に継続実施することができる。 According to the in-furnace temperature control method in the heating furnace 11 described above, the heating furnace 11 itself is equipped with temperature measuring jigs 43 and 45 that are inserted into the core tube 13 and actually measure the temperature in the core tube 13. Therefore, for example, the temperature in the furnace is periodically measured by the temperature measuring jigs 43 and 45, and the temperature of the surface of the core tube 13 or the outer surface of the heaters 15a, 15b, and 15c is detected during the heat treatment. By comparing the measured values of the temperature detecting means 23a, 23b, and 23c with the measured values of the temperature measuring jigs 43 and 45, the change in the heating efficiency of the core tube 13 due to the exhaustion of the inner surface of the core tube 13, and the heating An error between the actual precursor temperature and the estimated temperature due to the change in efficiency can be detected.
Therefore, by correcting the operation control of the heaters 15a, 15b, and 15c by the control means 27 so that the error between the actual precursor temperature and the estimated temperature due to the change in heating efficiency is equal to or less than a predetermined value, Regardless of the change in the heating efficiency accompanying the progress of the exhaustion of the inner surface of the core tube 13, it is possible to maintain the inside of the core accurately at a desired temperature and to continue the appropriate heat treatment for the optical fiber manufacturing precursor for a long time. .

また、炉心管１３内の温度の測定を行う温度測定治具４３，４５は、温度測定に使用される熱電対５３の周囲がカーボン保護管５７で覆われているため、熱電対５３がヒータ１５ａ，１５ｂ，１５ｃによる加熱で高温に昇温しても熱電対５３の金属成分が炉内に放出されることを防止できる。従って、加熱処理する光ファイバ製造用前駆体や炉心管１３内を金属成分によって汚損させずに炉内温度を実測することができる。   Further, the temperature measuring jigs 43 and 45 for measuring the temperature in the core tube 13 are covered with the carbon protective tube 57 around the thermocouple 53 used for temperature measurement, so that the thermocouple 53 is the heater 15a. , 15b, 15c, the metal component of the thermocouple 53 can be prevented from being released into the furnace even when the temperature is raised to a high temperature. Therefore, the temperature in the furnace can be measured without polluting the precursor for manufacturing an optical fiber to be heat-treated or the furnace core tube 13 with a metal component.

更に、炉心管１３の軸方向に位置をずらした複数の測定点で、温度測定治具４３，４５及び温度検出手段２３ａ，２３ｂ，２３ｃによりそれぞれ炉心管１３内外の温度を検出することで、炉心管１３内外における温度分布を正確に実測でき、その実測結果を分析することによって炉心管１３内面各部における消耗の程度差を検知することができ、炉心管１３内面各部における消耗の程度差に応じてヒータ１５ａ，１５ｂ，１５ｃの動作制御を補正することことで、炉心管１３の内面各部における消耗の程度差に拘わらず、ヒータ１５ａ，１５ｂ，１５ｃの動作制御による炉内温度の均一化を実現して、高品位な光ファイバ母材を得ることができる。   Further, the temperature inside and outside the core tube 13 is detected by the temperature measuring jigs 43 and 45 and the temperature detecting means 23a, 23b and 23c at a plurality of measurement points shifted in the axial direction of the core tube 13, respectively. The temperature distribution inside and outside the tube 13 can be accurately measured, and by analyzing the measured results, differences in the degree of wear at each inner surface of the core tube 13 can be detected. By correcting the operation control of the heaters 15a, 15b, and 15c, the furnace temperature can be made uniform by controlling the operation of the heaters 15a, 15b, and 15c, regardless of the difference in the degree of wear in each part of the inner surface of the core tube 13. Thus, a high-quality optical fiber preform can be obtained.

更に上記実施の形態の具体的な実施例を、以下に示す。   Furthermore, specific examples of the above embodiment are shown below.

上記図１に示した加熱炉１１を用い、上記の炉内温度制御方法を実施した。
温度測定治具４３，４５による炉内温度の測定は、１０回の加熱処理作業につき１回の割合で定期的に行うこととした。そして、測定部４３による炉内温度測定箇所は、図４に示した各測定点Ｐ１，Ｐ２，Ｐ３について実施して、炉内温度分布を求めた。
また、炉心管１３の表面温度分布を、温度検出手段２３ａ，２３ｂ，２３ｃにより、測定した。
そして、炉内温度分布と表面温度分布とを比較して、炉心管１３の内外での温度差を算出し、その算出結果に基づいて、各測定時及び各測定点で「炉内温度を所望の値に保つための炉心管外面温度」を算出し、炉心管外面温度設定値に補正をかけ、光ファイバ製造用前駆体の焼結を行った。
その結果、連続的に、安定して、光ファイバ製造用前駆体の透明ガラス化に成功した。
また、この方法で得た前躯体から線引処理によって得た光ファイバの伝播ロスも良好であった。 The above furnace temperature control method was carried out using the heating furnace 11 shown in FIG.
The measurement of the temperature in the furnace by the temperature measuring jigs 43 and 45 was performed periodically at a rate of once per 10 heat treatment operations. And the furnace temperature measurement location by the measurement part 43 was implemented about each measurement point P1, P2, P3 shown in FIG. 4, and the furnace temperature distribution was calculated | required.
Further, the surface temperature distribution of the core tube 13 was measured by the temperature detection means 23a, 23b, 23c.
Then, the temperature distribution inside and outside the furnace core tube 13 is calculated by comparing the temperature distribution inside the furnace and the surface temperature distribution. Based on the calculation result, the “internal furnace temperature is desired at each measurement point and at each measurement point”. The core temperature of the core of the core for maintaining the above value was calculated, the core tube outer surface temperature set value was corrected, and the precursor for optical fiber production was sintered.
As a result, the glass fiber precursor was successfully vitrified continuously and stably.
Moreover, the propagation loss of the optical fiber obtained by drawing from the precursor obtained by this method was also good.

実施例１との対比のために、下記の比較例１〜３を実施した。それぞれ、下記に示す結果となり、上記実施の形態の構成が極めて有効であることが確認できた。
〈比較例１〉……炉内温度未測定の場合である。
図１に示した温度測定治具４３，４５を使用せずに、連続して光ファイバ製造用前駆体の透明ガラス化を行った。
この時、「炉内実際温度」を推定するために、放射温度計を用いて測定した「炉心管外面温度」を使用した。そして、炉心管外面温度が一定となるように、ヒータの加熱動作を調整しながら、連続して複数本の光ファイバ製造用前駆体の加熱処理を行い、透明ガラス化を試みた。
しかし、３５本目の加熱処理を行った時に、光ファイバ製造用前駆体の透明化不足が発生した。その光ファイバ製造用前駆体は、再度加熱処理を行って、透明化する必要があった。また、以降の処理では、透明化不足となる光ファイバ製造用前駆体が頻発した。
また、５２本目の焼結を行ったところ、光ファイバ製造用前駆体に焼結不良（割れ）が発生した。その光ファイバ製造用前駆体は、廃棄処分となった。以降、焼結不良（割れ）となる光ファイバ製造用前駆体が頻発した。
調査の結果、炉内の温度分布に偏りが生じたためと判明した。 For comparison with Example 1, the following Comparative Examples 1 to 3 were performed. The following results were obtained, respectively, and it was confirmed that the configuration of the above embodiment was extremely effective.
<Comparative example 1> ...... In this case, the temperature in the furnace is not measured.
Without using the temperature measuring jigs 43 and 45 shown in FIG. 1, the precursor for optical fiber production was continuously made into a transparent glass.
At this time, in order to estimate the “actual temperature in the furnace”, the “outer core tube outer surface temperature” measured using a radiation thermometer was used. Then, while adjusting the heating operation of the heater so that the temperature of the outer surface of the core tube becomes constant, a plurality of optical fiber manufacturing precursors were continuously heat-treated to attempt transparent vitrification.
However, when the 35th heat treatment was performed, insufficient transparency of the precursor for optical fiber production occurred. The optical fiber manufacturing precursor had to be heat treated again to be transparent. Further, in the subsequent processing, a precursor for producing an optical fiber that becomes insufficiently transparent frequently occurred.
Moreover, when the 52nd sintering was performed, the sintering failure (crack) generate | occur | produced in the precursor for optical fiber manufacture. The optical fiber manufacturing precursor was discarded. Thereafter, a precursor for producing an optical fiber that was poorly sintered (cracked) frequently occurred.
The investigation revealed that the temperature distribution in the furnace was uneven.

〈比較例２〉……炉内温度は定期的に測定するが、炉内温度を測定する熱電対の周囲を覆うカーボン保護管が無く、且つ、炉内の温度測定箇所が１箇所のみの場合である。
炉内の温度を熱電対で直接的に測定するため、熱電対として白金−ロジウム熱電対を使用し、１０回の焼結作業につき１回の割合で定期的に炉内温度と炉心管外面温度とを測定した。
そして、温度測定時には、炉内の実測温度と炉心管外面温度との差を算出し、その算出結果に基づき、各測定時において「炉内実際温度を一定に保つための炉心管外面温度」を算出し、定期的に炉心管外面温度設定値に補正をかけ、光ファイバ製造用前駆体の焼結を行った。
結果は、光ファイバ製造用前駆体が金属成分による汚染を受けており、この方法で得た前躯体から線引処理によって得た光ファイバの特性を確認したところ、伝播ロスが高く、製品として使用できないものがあった。
また、７５本目の加熱処理を行ったところ、光ファイバ製造用前駆体の焼結不良（割れ）が発生した。その光ファイバ製造用前駆体は、廃棄処分となった。以降、焼結不良（割れ）となる光ファイバ製造用前駆体が頻発した。調査の結果、炉内の温度分布に偏りが生じたためと判明した。 <Comparative example 2> ...... In-furnace temperature is measured periodically, but there is no carbon protective tube covering the periphery of the thermocouple for measuring the in-furnace temperature, and there is only one temperature measurement point in the furnace It is.
In order to directly measure the temperature in the furnace using a thermocouple, a platinum-rhodium thermocouple is used as the thermocouple, and the furnace temperature and the outer surface temperature of the core tube are periodically measured at a rate of once per 10 sintering operations. And measured.
At the time of temperature measurement, the difference between the actually measured temperature in the furnace and the outer surface temperature of the core tube is calculated. Based on the calculation result, the `` outer core tube outer surface temperature for keeping the actual furnace temperature constant '' is calculated at each measurement time. Calculation was performed, the furnace core tube outer surface temperature set value was periodically corrected, and the precursor for optical fiber production was sintered.
As a result, the precursor for optical fiber production has been contaminated with metal components, and the characteristics of the optical fiber obtained by drawing from the precursor obtained by this method were confirmed. There was something I couldn't do.
Moreover, when the 75th heat processing was performed, the sintering failure (crack) of the precursor for optical fiber manufacture generate | occur | produced. The optical fiber manufacturing precursor was discarded. Thereafter, a precursor for producing an optical fiber that was poorly sintered (cracked) frequently occurred. The investigation revealed that the temperature distribution in the furnace was uneven.

〈比較例３〉……図１に示した構造の温度測定治具４３，４５で炉内温度を測定するが、炉内の温度測定箇所が１箇所のみの場合である。
図１に示す加熱炉１１を使用し、温度測定治具４３，４５による炉内温度の測定を１０回の加熱処理作業につき１回の割合で定期的に行うこととした。そして、測定部４３による炉内温度測定箇所は、図４に示した各測定点Ｐ１，Ｐ２，Ｐ３の内の１箇所のみを選択して行った。
また、炉内温度の測定時には、同時に、炉心管外面温度の測定も実施した。
そして、温度測定時には、炉内の実測温度と炉心管外面温度との差を算出し、その算出結果に基づき、各測定時において「炉内実際温度を一定に保つための炉心管外面温度」を算出し、定期的に炉心管外面温度設定値に補正をかけ、光ファイバ製造用前駆体の焼結を行った。
結果は、上記加熱処理で得た前躯体から線引処理によって得た光ファイバの特性を確認したところ、伝播ロスは良好であった。
しかし、７３本目の加熱処理を行ったところ、光ファイバ製造用前駆体の焼結不良（割れ）が発生した。その光ファイバ製造用前駆体は、廃棄処分となった。以降、焼結不良（割れ）となる光ファイバ製造用前駆体が頻発した。調査の結果、炉内の温度分布に偏りが生じたためと判明した。 <Comparative Example 3> The temperature in the furnace is measured by the temperature measuring jigs 43 and 45 having the structure shown in FIG. 1, but only one temperature measurement place is provided in the furnace.
The heating furnace 11 shown in FIG. 1 was used, and the temperature in the furnace was measured periodically by the temperature measuring jigs 43 and 45 at a rate of once per 10 heat treatment operations. And the furnace temperature measurement location by the measurement part 43 selected and performed only one location among each measurement point P1, P2, P3 shown in FIG.
At the same time, the outer surface temperature of the core tube was also measured.
At the time of temperature measurement, the difference between the actually measured temperature in the furnace and the outer surface temperature of the core tube is calculated, and based on the calculation result, the `` outer core tube outer surface temperature for keeping the actual furnace temperature constant '' is calculated at each measurement time. Calculation was performed, the furnace core tube outer surface temperature set value was periodically corrected, and the precursor for optical fiber production was sintered.
As a result, when the characteristics of the optical fiber obtained by drawing from the precursor obtained by the heat treatment were confirmed, the propagation loss was good.
However, when the 73rd heat treatment was performed, sintering failure (cracking) of the precursor for optical fiber production occurred. The optical fiber manufacturing precursor was discarded. Thereafter, a precursor for producing an optical fiber that was poorly sintered (cracked) frequently occurred. The investigation revealed that the temperature distribution in the furnace was uneven.

以上の各比較例１〜３からも判るように、光ファイバ製造用前駆体に焼結不良（割れ）が発生することを防止するためには、炉心管内外の温度測定を複数箇所として、炉心管の内外の温度分布を求め、温度分布に偏りが生じないように、各温度検出手段２３ａ，２３ｂ，２３ｃの動作制御をすることが極めて重要なことが判る。   As can be seen from each of the above Comparative Examples 1 to 3, in order to prevent the occurrence of poor sintering (cracking) in the optical fiber production precursor, temperature measurement inside and outside the core tube is performed at a plurality of locations. It can be seen that it is extremely important to obtain the temperature distribution inside and outside the tube and to control the operation of each temperature detecting means 23a, 23b, 23c so that the temperature distribution is not biased.

なお、上記実施の形態における温度測定治具４３，４５は、測定部４３内に１組の熱電対５３しか装備していない。そのため、炉心管内に複数点の測定点を設定して、それらの各測定点において温度測定を行う場合には、ロッド４１の降下量を調節することで、測定部４３の測定端５３ａの位置を各測定点に移動させて、測定を繰り返す必要があった。
しかし、もし、測定部４３内に、予め、測定端の位置をずらした複数組の熱電対を装備しておけば、一度に複数の測定点において、温度測定することが可能になる。
従って、温度測定治具の測定部４３には、複数組の熱電対を測定端の位置をずらして装備しておくことが望ましい。 Note that the temperature measurement jigs 43 and 45 in the above embodiment are equipped with only one set of thermocouples 53 in the measurement unit 43. Therefore, when a plurality of measurement points are set in the furnace core tube and the temperature measurement is performed at each of these measurement points, the position of the measurement end 53a of the measurement unit 43 is adjusted by adjusting the amount of descent of the rod 41. It was necessary to move to each measurement point and repeat the measurement.
However, if a plurality of sets of thermocouples whose measurement ends are shifted in advance are provided in the measurement unit 43, it is possible to measure temperature at a plurality of measurement points at once.
Therefore, it is desirable to equip the measurement unit 43 of the temperature measurement jig with a plurality of sets of thermocouples with the measurement end position shifted.

また、上記実施の形態では、温度検出手段２３ａ，２３ｂ，２３ｃとして使用された放射温度計は、炉心管内の温度を推定するために、炉心管の外面の温度を検出したが、炉心管の外面の温度を検出する代わりに、ヒータ外表面の温度を測定するようにしても良い。   Moreover, in the said embodiment, although the radiation thermometer used as temperature detection means 23a, 23b, 23c detected the temperature of the outer surface of a reactor core tube, in order to estimate the temperature in a reactor core tube, the outer surface of a reactor core tube Instead of detecting the temperature of the heater, the temperature of the outer surface of the heater may be measured.

本発明に係る加熱炉及び該加熱炉の一実施の形態の縦断面図である。1 is a longitudinal sectional view of an embodiment of a heating furnace according to the present invention and the heating furnace. 本発明に係る温度測定治具の概略構成を示す透視斜視図である。It is a see-through | perspective perspective view which shows schematic structure of the temperature measurement jig | tool which concerns on this invention. 図２に示した温度測定治具の縦断面図である。It is a longitudinal cross-sectional view of the temperature measurement jig | tool shown in FIG. 本発明の第１の実施の形態の加熱炉において炉内温度の検出時の状態を示す縦断面図である。It is a longitudinal cross-sectional view which shows the state at the time of the detection of the furnace temperature in the heating furnace of the 1st Embodiment of this invention. 本発明の第１の実施の形態の加熱炉において炉内温度の検出後に温度測定治具を炉外に退避させる動作時の縦断面図である。It is a longitudinal cross-sectional view at the time of the operation | movement which retracts | saves a temperature measurement jig | tool outside a furnace after the detection of the furnace temperature in the heating furnace of the 1st Embodiment of this invention. 本発明の第１の実施の形態の加熱炉において、光ファイバ製造用前駆体を加熱処理する時の温度測定治具の退避状態を示す縦断面図である。It is a longitudinal cross-sectional view which shows the retracted state of the temperature measurement jig | tool when heat-processing the precursor for optical fiber manufacture in the heating furnace of the 1st Embodiment of this invention. 従来の加熱炉及び該加熱炉における炉内温度制御方法を示す縦断面図である。It is a longitudinal cross-sectional view which shows the conventional heating furnace and the furnace temperature control method in this heating furnace.

符号の説明Explanation of symbols

１１ 加熱炉
１３ 炉心管
１３ａ 表面
１５ａ，１５ｂ，１５ｃ ヒータ
１７ 電源
１９ 炉体
２３ａ，２３ｂ，２３ｃ 温度検出手段
２７ 制御手段
３３ ゲート弁
３５ 開口部
４１ ロッド
４１ａ 位置検出部
４２ 吊りジョイント
４３ 測定部
４４ 上蓋
４５ 上蓋昇降用架台
４６ 予備室
４７ 隔壁
５１ 下限近接スイッチ
５３ 熱電対
５３ａ 測定端
５５ 短絡防止保護管
５７ カーボン保護管
６１ レコーダ
６３ 補償導線 DESCRIPTION OF SYMBOLS 11 Heating furnace 13 Core tube 13a Surface 15a, 15b, 15c Heater 17 Power supply 19 Furnace body 23a, 23b, 23c Temperature detection means 27 Control means 33 Gate valve 35 Opening part 41 Rod 41a Position detection part 42 Hanging joint 43 Measurement part 44 Upper cover 45 Upper lid lifting platform 46 Preliminary chamber 47 Bulkhead 51 Lower limit proximity switch 53 Thermocouple 53a Measuring end 55 Short-circuit prevention protective tube 57 Carbon protective tube 61 Recorder 63 Compensation conductor

Claims (5)

熱電対と、該熱電対を先端を部分的に露出させた状態で覆う短絡防止保護管と、前記熱電対の先端の露出部分を覆うカーボン保護管とを具備したことを特徴とする温度測定治具。   A temperature measurement treatment comprising: a thermocouple; a short-circuit-preventing protective tube that covers the thermocouple with the tip partially exposed; and a carbon protective tube that covers the exposed portion of the tip of the thermocouple. Ingredients. 炉心管と、該炉心管の外周囲に配置したヒータと、該ヒータを外気から遮断するための炉体とを備える加熱炉であって、
前記炉心管内に挿抜可能に備えられて炉心管内の温度を検出する請求項１記載の温度測定治具を用いたことを特徴とする加熱炉。 A heating furnace comprising a furnace core tube, a heater disposed on the outer periphery of the furnace core tube, and a furnace body for blocking the heater from outside air,
2. A heating furnace using the temperature measuring jig according to claim 1, wherein the temperature measuring jig is provided so as to be inserted into and removed from the furnace core tube and detects the temperature in the furnace core tube. 請求項２に記載の加熱炉において、前記温度測定治具及び加熱処理中に前記炉心管の表面温度を検出する温度検出手段により定期的に炉心管内外の温度を検出し、前記炉心管内の温度が所望温度になるように、前記温度測定治具及び温度検出手段により知見した炉心管内外の温度差に基づいて、前記ヒータの動作制御を行うことを特徴とする加熱炉における炉内温度制御方法。   3. The heating furnace according to claim 2, wherein temperature inside and outside the core tube is periodically detected by the temperature measuring jig and temperature detecting means for detecting a surface temperature of the core tube during heat treatment, and the temperature inside the core tube. The furnace temperature control method in the heating furnace is characterized in that operation control of the heater is performed based on a temperature difference between the inside and outside of the furnace core tube found by the temperature measuring jig and the temperature detecting means so that the temperature becomes a desired temperature. . 前記温度測定治具及び温度検出手段は、前記炉心管の軸方向に位置をずらした複数の測定点で、温度検出を行うことを特徴とする請求項２に記載の加熱炉。   The heating furnace according to claim 2, wherein the temperature measurement jig and the temperature detection means perform temperature detection at a plurality of measurement points shifted in the axial direction of the furnace core tube. 請求項４に記載の加熱炉において、前記温度測定治具及び温度検出手段により定期的に炉心管内外の複数点の温度を検出し、前記炉心管内の温度分布が所望温度分布になるように、前記温度測定治具及び温度検出手段により知見した炉心管内外の温度差分布に基づいて、前記ヒータの動作制御を行うことを特徴とする加熱炉における炉内温度制御方法。

In the heating furnace according to claim 4, by periodically detecting the temperature of a plurality of points inside and outside the furnace core tube by the temperature measurement jig and temperature detection means, so that the temperature distribution in the furnace core tube becomes a desired temperature distribution, An in-furnace temperature control method in a heating furnace, wherein operation control of the heater is performed based on a temperature difference distribution inside and outside the furnace core tube found by the temperature measuring jig and temperature detecting means.