JP6011218B2 - Manufacturing method of transparent glass base material - Google Patents

Manufacturing method of transparent glass base material Download PDF

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JP6011218B2
JP6011218B2 JP2012221408A JP2012221408A JP6011218B2 JP 6011218 B2 JP6011218 B2 JP 6011218B2 JP 2012221408 A JP2012221408 A JP 2012221408A JP 2012221408 A JP2012221408 A JP 2012221408A JP 6011218 B2 JP6011218 B2 JP 6011218B2
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祐介 久保
祐介 久保
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Sumitomo Electric Industries Ltd
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Description

本発明は、透明ガラス母材の製造方法に関する。   The present invention relates to a method for producing a transparent glass base material.

例えば光ファイバ用の透明ガラス母材は、バーナの火炎中に生成したガラス微粒子を石英等からなるガラスロッドの外周あるいは下側に堆積させて多孔質ガラス母材を得て、この多孔質ガラス母材を脱水焼結炉内にて脱水・焼結して透明化させることにより製造される。このようにして得られた透明ガラス母材から、線引き設備にて線引きして細径化することにより、光ファイバが製造されている。   For example, a transparent glass preform for an optical fiber is obtained by depositing glass fine particles generated in a flame of a burner on the outer periphery or lower side of a glass rod made of quartz or the like to obtain a porous glass preform. It is manufactured by dehydrating and sintering the material in a dehydration sintering furnace to make it transparent. An optical fiber is manufactured from the transparent glass preform thus obtained by drawing with a drawing equipment to reduce the diameter.

円柱状の多孔質ガラス母材を焼結する際には、長手方向が鉛直方向を向くようにして焼結されている。この焼結時に粘度の低下したガラスが下側に移動し、透明ガラス母材の下方の径が大きな下膨れ形状に変形する場合がある。このように透明ガラス母材が下膨れ形状となると、例えば線引き加工する際に、透明ガラス母材の径が大きすぎて、線引き設備等の後工程用の設備に入らない不具合が生じることがある。   When the cylindrical porous glass base material is sintered, the sintering is performed such that the longitudinal direction is directed to the vertical direction. During this sintering, the glass having a lowered viscosity may move downward, and the transparent glass base material may be deformed into a downward swollen shape with a large lower diameter. When the transparent glass base material has a downward bulging shape as described above, for example, when drawing is performed, there is a case where the diameter of the transparent glass base material is too large to enter into a post-processing equipment such as a drawing equipment.

このため、特許文献１は多孔質ガラス母材の外径を下方から上方に向かって次第に大きくなるように形成し、多孔質ガラス母材の径の小さい箇所から先行して焼結することにより、下膨れ形状に変形することを防止している。また、特許文献２も下端部がテーパ形状となるように多孔質ガラス母材を形成することを提案している。   For this reason, Patent Document 1 forms the outer diameter of the porous glass base material so as to gradually increase from the lower side to the upper side, and is sintered in advance from the portion where the diameter of the porous glass base material is small. It is prevented from being deformed into a lower swollen shape. Patent Document 2 also proposes forming a porous glass base material so that the lower end is tapered.

特開２００７−２１０８６８号公報JP 2007-210868 A 特開２００９−０４０６６２号公報JP 2009-040661 A

しかし、特許文献１，２のように多孔質ガラス母材の外径を予め変えておいても、焼結での条件のずれなどによって想定した通りに外径が縮まないことがある。この場合、焼結が終了した後に外径が不均一であることが判明するため、外径を整えるために、焼結終了後に再度焼結プロセス（加熱）を実施することがある。また特許文献１，２のように、その長手方向に沿って外径が変わるようにガラス微粒子を堆積させて、多孔質ガラス母材を形成することは煩雑である。   However, even if the outer diameter of the porous glass base material is changed in advance as in Patent Documents 1 and 2, the outer diameter may not shrink as expected due to deviations in conditions during sintering. In this case, since the outer diameter is found to be non-uniform after the sintering is completed, the sintering process (heating) may be performed again after the sintering is completed in order to adjust the outer diameter. In addition, as in Patent Documents 1 and 2, it is complicated to form a porous glass base material by depositing glass fine particles so that the outer diameter changes along the longitudinal direction.

また、このように形成された多孔質ガラス母材を用いて透明ガラス母材を形成しても、線引き設備に透明ガラス母材が入らないことが判明した場合には、再び焼結炉に透明ガラス母材を投入して透明ガラス母材を変形させる必要がある。この場合には、焼結炉を再び加熱するためにコストが嵩み、また、焼結炉の稼働率が低下してしまう。   Also, even if a transparent glass base material is formed using the porous glass base material formed in this way, if it is found that the transparent glass base material does not enter the drawing equipment, it is again transparent in the sintering furnace. It is necessary to introduce a glass base material to deform the transparent glass base material. In this case, the cost increases because the sintering furnace is heated again, and the operating rate of the sintering furnace decreases.

本発明の目的は、確実に後工程の設備に入れることのできる透明ガラス母材を低コストで製造できる透明ガラス母材の製造方法を提供することにある。   The objective of this invention is providing the manufacturing method of the transparent glass base material which can manufacture the transparent glass base material which can be reliably put into the apparatus of a post process at low cost.

上記課題を解決することのできる本発明の透明ガラス母材の製造方法は、
ガラス微粒子が堆積されてなる多孔質ガラス母材をその中心軸が上下方向となるように焼結炉内で支持しながら、複数に分割されたヒータを前記多孔質ガラス母材が焼結する温度である目標温度まで上げて第一所定時間加熱し、前記多孔質ガラス母材の焼結を完了させて透明ガラス母材とし、
第一所定時間が経過した後、前記透明ガラス母材の中心位置より下部を加熱する前記ヒータの温度を前記目標温度、または前記目標温度より高く設定して第二所定時間保持し、前記透明ガラス母材を加熱することを特徴とする。 The method for producing the transparent glass base material of the present invention capable of solving the above problems is as follows.
The temperature at which the porous glass base material sinters the heater divided into a plurality of parts while supporting the porous glass base material on which the glass fine particles are deposited in the sintering furnace so that the central axis thereof is in the vertical direction. To a target temperature that is heated for a first predetermined time, to complete the sintering of the porous glass base material to be a transparent glass base material,
After the first predetermined time has elapsed, the temperature of the heater that heats the lower part from the center position of the transparent glass base material is set higher than the target temperature or the target temperature, and held for a second predetermined time, and the transparent glass It is characterized by heating the base material.

本発明の透明ガラス母材の製造方法において、
前記ヒータは、前記焼結炉内の中心温度より下部に位置する下ヒータと、前記下ヒータとは独立して温度を設定可能で前記焼結炉内の中心位置より上部に位置する上ヒータと、を有し、
前記第一所定時間が経過した後、前記上ヒータの温度を前記目標温度未満に設定して第三所定時間保持してもよい。 In the method for producing a transparent glass base material of the present invention,
The heater includes a lower heater located below the center temperature in the sintering furnace, an upper heater located above the center position in the sintering furnace, the temperature of which can be set independently of the lower heater, Have
After the first predetermined time has elapsed, the temperature of the upper heater may be set below the target temperature and held for a third predetermined time.

本発明の透明ガラス母材の製造方法によれば、焼結終了後に透明ガラス母材の中心位置より下部が下ヒータによって加熱されて透明ガラス母材の粘度が低下するため、加熱された透明ガラス母材の下部が下方に伸張してその径が小さくなり、透明ガラス母材の下膨れ形状が解消される。これにより、透明ガラス母材を、確実に次工程の線引き設備に入れることができる。また、焼結終了後にそのまま下部の加熱を続けるだけで下膨れ形状が解消されるので、焼結炉全体を再加熱する必要が無く、低コストで下膨れ形状を解消できる。   According to the method for producing a transparent glass base material of the present invention, the lower part of the transparent glass base material is heated by the lower heater after the completion of sintering, and the viscosity of the transparent glass base material is lowered. The lower part of the base material extends downward to reduce its diameter, and the bottom bulge shape of the transparent glass base material is eliminated. Thereby, a transparent glass base material can be reliably put into the drawing equipment of the next process. Further, since the lower swollen shape is eliminated by simply heating the lower part as it is after the sintering is completed, it is not necessary to reheat the entire sintering furnace, and the lower swollen shape can be eliminated at a low cost.

本実施形態に係る透明ガラス母材の製造方法において用いられる焼結炉の断面図である。It is sectional drawing of the sintering furnace used in the manufacturing method of the transparent glass base material which concerns on this embodiment. 本実施形態に係る透明ガラス母材の製造方法におけるヒータの温度パターンを示すグラフである。It is a graph which shows the temperature pattern of the heater in the manufacturing method of the transparent glass base material which concerns on this embodiment. 従来の透明ガラス母材の製造方法におけるヒータの温度パターンを示すグラフである。It is a graph which shows the temperature pattern of the heater in the manufacturing method of the conventional transparent glass base material.

以下、本発明に係る透明ガラス母材の製造方法の実施の形態の例を、図面を参照して説明する。
図１は、本実施形態に係る透明ガラス母材の製造方法において用いられる焼結炉１の断面図である。図１に示される焼結炉１は、その内部に入れられた多孔質ガラス母材１０を焼結し透明化して透明ガラス母材１１を製造する為のものである。焼結炉１は、例えば、真空容器５内に、炉心管２、ヒータ３およびヒートシールド４を備えている。 Hereinafter, an example of an embodiment of a manufacturing method of a transparent glass base material concerning the present invention is explained with reference to drawings.
FIG. 1 is a sectional view of a sintering furnace 1 used in the method for producing a transparent glass base material according to this embodiment. A sintering furnace 1 shown in FIG. 1 is for producing a transparent glass base material 11 by sintering and transparentizing a porous glass base material 10 placed therein. The sintering furnace 1 includes, for example, a furnace core tube 2, a heater 3, and a heat shield 4 in a vacuum vessel 5.

炉心管２の外部に設けられたヒータ３は、焼結炉１の中心位置より下部に位置する下ヒータ３Ａと、焼結炉１の中心位置より上部に位置する上ヒータ３Ｂを有する。上ヒータ３Ｂと下ヒータ３Ａは、個別に目標温度を設定可能とされている。なお、以下の説明においては、下ヒータ３Ａと上ヒータ３Ｂとを区別せずに呼ぶ場合はヒータ３と呼ぶ。なお、焼結炉１の中心位置とは、上下方向（図１でいう縦方向）の中心位置をいう。   The heater 3 provided outside the furnace core tube 2 includes a lower heater 3 </ b> A located below the center position of the sintering furnace 1 and an upper heater 3 </ b> B located above the center position of the sintering furnace 1. The upper heater 3B and the lower heater 3A can individually set a target temperature. In the following description, when the lower heater 3A and the upper heater 3B are referred to without distinction, they are referred to as the heater 3. The center position of the sintering furnace 1 refers to the center position in the vertical direction (vertical direction in FIG. 1).

焼結炉１はさらに、排気用配管６、真空ポンプ７、ガス導入管８および圧力調整弁９を備えている。真空ポンプ７は、排気用配管６を介して真空容器５と接続されており、真空容器５の内部を排気する。ガス導入管８は、炉心管２と接続されており、ガス供給源（図示省略）から炉心管２の内部へ不活性ガスなどを導入する。圧力調整弁９は、排気用配管６の途中に設けられており、真空容器５の内部の圧力を調整する。   The sintering furnace 1 further includes an exhaust pipe 6, a vacuum pump 7, a gas introduction pipe 8, and a pressure adjustment valve 9. The vacuum pump 7 is connected to the vacuum vessel 5 through the exhaust pipe 6 and exhausts the inside of the vacuum vessel 5. The gas introduction tube 8 is connected to the core tube 2 and introduces an inert gas or the like into the core tube 2 from a gas supply source (not shown). The pressure adjustment valve 9 is provided in the middle of the exhaust pipe 6 and adjusts the pressure inside the vacuum vessel 5.

次に、本実施形態に係る透明ガラス母材の製造方法について説明する。
多孔質ガラス母材１０は、ＶＡＤ法やＯＶＤ法などにより石英ガラスなどの種棒にガラス微粒子を堆積させることで得られる。この多孔質ガラス母材１０を焼結することにより、透明ガラス母材１１を製造する。 Next, the manufacturing method of the transparent glass base material which concerns on this embodiment is demonstrated.
The porous glass base material 10 is obtained by depositing glass fine particles on a seed rod such as quartz glass by the VAD method or the OVD method. By sintering the porous glass base material 10, the transparent glass base material 11 is manufactured.

焼結炉１によって透明ガラス母材１１を製造する際には、多孔質ガラス母材１０を炉心管２の内部に入れ、不活性ガス（例えば、Ｈｅ，Ａｒ，Ｎ２等）の雰囲気下で、ヒータ３により加熱して製造する。 When the transparent glass base material 11 is manufactured by the sintering furnace 1, the porous glass base material 10 is placed inside the furnace core tube 2 and is in an atmosphere of an inert gas (for example, He, Ar, N 2 or the like). It is manufactured by heating with the heater 3.

図２の実線、点線は本実施形態のヒータ３の温度パターンを示す図である。実線（ａ）が下ヒータ３Ａの温度パターン、点線（ｂ）が上ヒータ３Ｂの温度パターンを示す。なお、図２の横軸は時間であり、縦軸はヒータの設定温度である。   A solid line and a dotted line in FIG. 2 are diagrams showing a temperature pattern of the heater 3 of the present embodiment. The solid line (a) shows the temperature pattern of the lower heater 3A, and the dotted line (b) shows the temperature pattern of the upper heater 3B. In FIG. 2, the horizontal axis represents time, and the vertical axis represents the set temperature of the heater.

まず、多孔質ガラス母材１０を、その中心軸が上下方向を向くように焼結炉１の内部に支持する（図１参照）。この状態で、焼結炉１の内部を真空引きする。そして、時刻ｔ１にかけてヒータ３の温度を第一目標温度Ｔ１（後述）より低い温度まで徐々に上げていく。これにより、多孔質ガラス母材１０のガラス微粒子間の隙間にたまったガスを抜く。このとき、一気に温度を上げると多孔質ガラス母材１０が割れてしまうおそれがあるので、徐々に温度を上げる。   First, the porous glass base material 10 is supported inside the sintering furnace 1 so that the central axis thereof is directed in the vertical direction (see FIG. 1). In this state, the inside of the sintering furnace 1 is evacuated. Then, over time t1, the temperature of the heater 3 is gradually raised to a temperature lower than a first target temperature T1 (described later). Thereby, the gas accumulated in the gaps between the glass particles of the porous glass base material 10 is extracted. At this time, if the temperature is raised at once, the porous glass base material 10 may be broken, so the temperature is gradually raised.

次に、時刻ｔ２にかけてヒータ３の温度を、ガラス転移点より高い第一目標温度Ｔ１（目標温度：１４５０℃付近、下ヒータ温度Ｔ１Ａ、上ヒータ温度Ｔ１Ｂ）まで上昇させる。Ｔ１Ａ，Ｔ１Ｂは同じ温度でも、異なる温度であってもよい。さらにその後、時刻ｔ３にかけてヒータ３の温度を第一目標温度Ｔ１（Ｔ１Ａ，Ｔ１Ｂ）のまま維持し、多孔質ガラス母材１０の焼結を完了させて、透明ガラス母材１１とする。この工程では、ヒータ３を第一目標温度Ｔ１（Ｔ１Ａ，Ｔ１Ｂ）まで加熱し、多孔質ガラス母材１０を第一所定時間（ｔ３−ｔ２）加熱することにより、多孔質ガラス母材１０の焼結を完了させて透明ガラス母材１１を得る。第一目標温度Ｔ１および第一所定時間（ｔ３−ｔ２）は、多孔質ガラス母材１０の焼結が完了する範囲で適宜設定することができる。
なおこの際、ヒータ３（下ヒータ３Ａおよび上ヒータ３Ｂ）の温度を、焼結が完了する前に第一目標温度Ｔ１（Ｔ１Ａ，Ｔ１Ｂ）以上に上げてもよい。このようにすることにより、焼結時間を短くしたり、未焼結部分が残存しないようにすることができる。 Next, at time t2, the temperature of the heater 3 is raised to a first target temperature T1 (target temperature: around 1450 ° C., lower heater temperature T1A, upper heater temperature T1B) higher than the glass transition point. T1A and T1B may be the same temperature or different temperatures. Thereafter, the temperature of the heater 3 is maintained at the first target temperature T1 (T1A, T1B) until time t3, and the sintering of the porous glass base material 10 is completed to obtain the transparent glass base material 11. In this step, the heater 3 is heated to the first target temperature T1 (T1A, T1B), and the porous glass base material 10 is heated for the first predetermined time (t3-t2), whereby the porous glass base material 10 is baked. The transparent glass base material 11 is obtained by completing the ligation. The first target temperature T1 and the first predetermined time (t3-t2) can be appropriately set within a range where the sintering of the porous glass base material 10 is completed.
At this time, the temperature of the heater 3 (the lower heater 3A and the upper heater 3B) may be raised to the first target temperature T1 (T1A, T1B) or higher before the sintering is completed. By doing in this way, sintering time can be shortened or an unsintered part cannot remain.

本実施形態では、焼結が完了した後、下膨れ形状となるのを防止するために、時刻ｔ３から時刻ｔ４にかけて下ヒータ３Ａの温度を第一目標温度Ｔ１Ａより高い第二目標温度Ｔ２（約１５００℃）に上げている。   In this embodiment, after the sintering is completed, the temperature of the lower heater 3A is set to a second target temperature T2 (about 1500) higher than the first target temperature T1A from time t3 to time t4 in order to prevent a downward bulging shape. ℃).

下ヒータ３Ａについてはさらに、時刻ｔ４から時刻ｔ６にかけて、第二所定時間（ｔ６−ｔ４）の間、第一目標温度Ｔ１Ａよりも高い第二目標温度Ｔ２を維持する。これにより、透明ガラス母材１１の下部をガラス転移点以上の温度に維持する。   For the lower heater 3A, the second target temperature T2 higher than the first target temperature T1A is maintained from the time t4 to the time t6 for the second predetermined time (t6-t4). Thereby, the lower part of the transparent glass base material 11 is maintained at the temperature more than a glass transition point.

上ヒータ３Ｂについては、時刻ｔ３から時刻ｔ５にかけて、第一目標温度Ｔ１Ｂよりも低い第三目標温度Ｔ３まで下げる。さらに時刻ｔ５から時刻ｔ６までの第三所定時間（ｔ６−ｔ５）、第一目標温度Ｔ１Ｂよりも低い第三目標温度Ｔ３のまま保持する。これにより、透明ガラス母材１１の上部をガラス転移点未満の温度に維持する。なお、上ヒータ３Ｂの温度は、時刻ｔ３から時刻ｔ６まで第一目標温度Ｔ１Ｂを維持していてもよいが、第一目標温度Ｔ１Ｂより下げることが好ましい。上ヒータ温度３Ｂの温度を第一目標温度Ｔ１Ｂより下げると、透明ガラス母材１１の上部の変形を防ぐことができる。   The upper heater 3B is lowered from time t3 to time t5 to a third target temperature T3 that is lower than the first target temperature T1B. Furthermore, the third target temperature T3 that is lower than the first target temperature T1B is held for the third predetermined time (t6-t5) from time t5 to time t6. Thereby, the upper part of the transparent glass base material 11 is maintained at the temperature below a glass transition point. The temperature of the upper heater 3B may be maintained at the first target temperature T1B from time t3 to time t6, but is preferably lower than the first target temperature T1B. When the temperature of the upper heater temperature 3B is lowered from the first target temperature T1B, deformation of the upper portion of the transparent glass base material 11 can be prevented.

第二目標温度Ｔ２および第二所定時間（ｔ６−ｔ４）は、透明ガラス母材の下膨れ形状が解消するために十分に高い温度および時間を設定することができる。
例えば、第二目標温度は１４００℃以上１６００℃以下、第二所定時間は２０分以上３０分以下に設定することができる。 The second target temperature T2 and the second predetermined time (t6-t4) can be set to a sufficiently high temperature and time so that the bottom bulging shape of the transparent glass base material is eliminated.
For example, the second target temperature can be set to 1400 ° C. to 1600 ° C., and the second predetermined time can be set to 20 minutes to 30 minutes.

このようにして、ヒータ３の加熱開始から時刻ｔ６が経過したら、ヒータ３による透明ガラス母材１１への加熱を停止し、焼結炉１の中から透明ガラス母材１１を取り出す。これにより、透明ガラス母材１１が得られる。この後は、例えば光ファイバを製造する場合には、後工程において線引き設備に透明ガラス母材１１を移し、透明ガラス母材１１から線引きして光ファイバを製造する。   Thus, when the time t6 has elapsed from the start of heating of the heater 3, heating of the transparent glass base material 11 by the heater 3 is stopped, and the transparent glass base material 11 is taken out from the sintering furnace 1. Thereby, the transparent glass base material 11 is obtained. Thereafter, for example, when manufacturing an optical fiber, the transparent glass preform 11 is transferred to a drawing facility in a subsequent process, and the optical fiber is manufactured by drawing from the transparent glass preform 11.

以上の本発明の実施形態に係る透明ガラス母材の製造方法によれば、第一目標温度Ｔ１で第一所定時間（ｔ３−ｔ２）、多孔質ガラス母材１０を加熱して、多孔質ガラス母材１０を焼結させて透明ガラス母材１１を得る。この後、透明ガラス母材１１の下部を加熱する下ヒータ３Ａの温度を第一目標温度Ｔ１以上の第二目標温度Ｔ２に設定して第二所定時間（ｔ６−ｔ４）維持し、透明ガラス母材１１の下部を加熱する。   According to the manufacturing method of the transparent glass base material which concerns on the above embodiment of this invention, the porous glass base material 10 is heated for 1st predetermined time (t3-t2) at 1st target temperature T1, and porous glass is used. The base material 10 is sintered to obtain the transparent glass base material 11. Thereafter, the temperature of the lower heater 3A that heats the lower portion of the transparent glass base material 11 is set to a second target temperature T2 that is equal to or higher than the first target temperature T1, and is maintained for a second predetermined time (t6-t4). The lower part of the material 11 is heated.

これにより、多孔質ガラス母材１０の焼結後、透明ガラス母材１１の下部が下ヒータ３Ａによって加熱されてガラス転移点以上の温度に維持され、透明ガラス母材１１の下部の粘度が部分的に低下する。粘度が低下した透明ガラス母材１１の下部は、重力によって下方に引っ張られて、下方に伸張しその分径が小さくなる。このように重力によって多孔質ガラス母材１０の下部を部分的に変形させることにより、透明ガラス母材１１の下膨れ形状が解消される。   Thereby, after the porous glass base material 10 is sintered, the lower part of the transparent glass base material 11 is heated by the lower heater 3 </ b> A and is maintained at a temperature equal to or higher than the glass transition point. Decline. The lower part of the transparent glass base material 11 having a reduced viscosity is pulled downward by gravity, and extends downward to decrease the diameter. In this way, by partially deforming the lower portion of the porous glass base material 10 by gravity, the lower bulging shape of the transparent glass base material 11 is eliminated.

このように、本実施形態に係る透明ガラス母材１１の製造方法によれば、透明ガラス母材１１を、線引き設備等の後工程の設備に入れる前に、透明ガラス母材１１の下膨れ形状が解消される。したがって、確実に透明ガラス母材１１を後工程の設備に入れることができる。   Thus, according to the manufacturing method of the transparent glass base material 11 which concerns on this embodiment, before putting the transparent glass base material 11 in the facilities of post processes, such as a drawing equipment, the bottom swelling shape of the transparent glass base material 11 is. It will be resolved. Therefore, the transparent glass base material 11 can be reliably put into the equipment of a post process.

なお、従来のように、製造方法の最後に透明ガラス母材の下部を加熱しガラス転移点以上の温度に維持する工程が無い場合は、後工程の設備に入れるときに透明ガラス母材１１が後工程の設備に入らないことが判明したら、焼結炉を再び加熱して透明ガラス母材１１を変形させていた。この場合と比べて、本実施形態に係る透明ガラス母材１１の製造方法は、焼結炉１全体を再加熱する必要がない。このため、低コストで確実に後工程の設備に入れることのできる透明ガラス母材１１を提供することができる。   In addition, when there is no process of heating the lower part of a transparent glass base material at the end of a manufacturing method and maintaining it at the temperature more than a glass transition point like the past, when the transparent glass base material 11 is put into the apparatus of a post process, If it turned out that it would not enter into a post-process equipment, the sintering furnace was heated again and the transparent glass base material 11 was deformed. Compared to this case, the method for manufacturing the transparent glass base material 11 according to this embodiment does not require reheating the entire sintering furnace 1. For this reason, the transparent glass preform | base_material 11 which can be reliably put into the apparatus of a post process at low cost can be provided.

また、本発明の実施形態に係る透明ガラス母材の製造方法によれば、多孔質ガラス母材１０の焼結を完了させた後、下ヒータ３Ａを第二目標温度Ｔ２に設定する一方、上ヒータ３Ｂを第一目標温度Ｔ１未満の第三目標温度Ｔ３に設定して第三所定時間（ｔ６−ｔ５）保持している。これにより、下ヒータ３Ａによって透明ガラス母材１１の下部を加熱する際に、透明ガラス母材１１の上部が加熱されて，上部が軟化するのを防止できる。したがって、透明ガラス母材１１の下膨れ形状を解消する際に、上部の変形を防ぎ、より効果的に下膨れ形状を解消することができる。   In addition, according to the method for manufacturing a transparent glass base material according to the embodiment of the present invention, after the sintering of the porous glass base material 10 is completed, the lower heater 3A is set to the second target temperature T2, while the upper The heater 3B is set to a third target temperature T3 lower than the first target temperature T1, and is held for a third predetermined time (t6-t5). Thereby, when the lower part of the transparent glass base material 11 is heated by the lower heater 3A, it is possible to prevent the upper part of the transparent glass base material 11 from being heated and the upper part from being softened. Therefore, when the lower bulge shape of the transparent glass base material 11 is eliminated, the upper bulge shape can be prevented and the lower bulge shape can be more effectively eliminated.

なお、本発明の透明ガラス母材の製造方法は、前述した実施形態に限定されるものでなく、適宜な変形，改良等が可能である。   In addition, the manufacturing method of the transparent glass base material of this invention is not limited to embodiment mentioned above, A suitable deformation | transformation, improvement, etc. are possible.

また、上述した実施形態においては、上下に独立した二つのヒータ３Ａ，３Ｂを有する焼結炉１を例に挙げて説明したが、本発明はこの例に限られない。例えば、焼結炉として、一つあるいは三つ以上の独立したヒータを有するもの、可動式の一つのヒータを備えたもの、を採用することができる。   Moreover, in embodiment mentioned above, although demonstrated taking the case of the sintering furnace 1 which has the two heaters 3A and 3B independent up and down, this invention is not limited to this example. For example, as a sintering furnace, one having one or three or more independent heaters, or one having a movable heater can be adopted.

次に、上述した実施形態に係る透明ガラス母材の製造方法を適用した実施例と、本発明とは異なる製造方法を適用した比較例について説明する。以下の実施例では、直径１３０〜１８０［ｍｍ］、軸方向長さ１０００〜２０００［ｍｍ］の純シリカ製の多孔質ガラス母材について、以下の温度パターンに基づいてヒータで加熱した。   Next, the Example which applied the manufacturing method of the transparent glass base material which concerns on embodiment mentioned above, and the comparative example which applied the manufacturing method different from this invention are demonstrated. In the following examples, a porous glass preform made of pure silica having a diameter of 130 to 180 [mm] and an axial length of 1000 to 2000 [mm] was heated with a heater based on the following temperature pattern.

実施例として、図２に示すヒータ３の温度パターンにしたがって焼結を実施する。   As an example, sintering is performed according to the temperature pattern of the heater 3 shown in FIG.

ヒータ３を昇温させて、脱気処理などが終わった後、多孔質ガラス母材１１を焼結させるため、下ヒータ３Ａの温度を１４８０℃（目標温度Ｔ１Ａ）、上ヒータ３Ｂの温度を１４６０℃（目標温度Ｔ１Ｂ）に上昇させる。続いて上ヒータ３Ｂを１４６０℃、下ヒータ３Ａの温度をそれぞれ１４８０℃のままとして９０分間（第一所定時間（ｔ３−ｔ２））維持する。   After the heater 3 is heated and the deaeration process is completed, the temperature of the lower heater 3A is 1480 ° C. (target temperature T1A) and the temperature of the upper heater 3B is 1460 in order to sinter the porous glass base material 11. The temperature is raised to ° C. (target temperature T1B). Subsequently, the upper heater 3B is maintained at 1460 ° C. and the temperature of the lower heater 3A is maintained at 1480 ° C. for 90 minutes (first predetermined time (t3-t2)).

ｔ３の時点で多孔質ガラス母材１１の焼結が完了し、透明な透明ガラス母材が得られる。その後、３分間かけて、下ヒータ３Ａの温度を１５３０℃に上昇させる。   Sintering of the porous glass base material 11 is completed at time t3, and a transparent transparent glass base material is obtained. Thereafter, the temperature of the lower heater 3A is increased to 1530 ° C. over 3 minutes.

一方、上ヒータ３Ｂの温度は、ｔ３からｔ５まで８分間かけて１３５０℃（第三目標温度Ｔ３）に下げ、１８分間（第三所定時間（ｔ６−ｔ５））維持する。下ヒータ３Ａの温度は１５３０℃のまま、２３分間（第二所定時間（ｔ６−ｔ４））維持する。これにより、透明ガラス母材の上部が軟化するのを防止しつつ、透明ガラス母材の下部を加熱して下膨れ形状を解消する。この後、透明ガラス母材を焼結炉から取り出す。   On the other hand, the temperature of the upper heater 3B is lowered to 1350 ° C. (third target temperature T3) from t3 to t5 over 8 minutes and maintained for 18 minutes (third predetermined time (t6-t5)). The temperature of the lower heater 3A is maintained at 1530 ° C. for 23 minutes (second predetermined time (t6-t4)). Thereby, while preventing the upper part of a transparent glass preform | base_material from softening, the lower part of a transparent glass preform | base_material is heated and a bottom swelling shape is eliminated. Thereafter, the transparent glass base material is taken out from the sintering furnace.

比較例として、図３に示すヒータの温度パターンで焼結を実施する例を説明する。ヒータを昇温させて脱気処理などを終えた後、多孔質ガラス母材を焼結するために上ヒータ３Ｂの温度を１４６０℃（Ｔ１Ａ）、下ヒータ３Ａの温度を１４８０℃（Ｔ２Ａ）として、焼結を完了させるまでは、上述した実施例と同様である。この後、透明ガラス母材を焼結炉から取り出す。   As a comparative example, an example in which sintering is performed with the temperature pattern of the heater shown in FIG. 3 will be described. After finishing the deaeration process by raising the temperature of the heater, the temperature of the upper heater 3B is set to 1460 ° C. (T1A) and the temperature of the lower heater 3A is set to 1480 ° C. (T2A) in order to sinter the porous glass base material. Until the sintering is completed, it is the same as the above-described embodiment. Thereafter, the transparent glass base material is taken out from the sintering furnace.

実施例に係る温度パターンを実行して得られた透明ガラス母材、および、比較例に係る温度パターンを実行して得られた透明ガラス母材について、それぞれ後工程として線引き加工を施した。   The transparent glass base material obtained by executing the temperature pattern according to the example and the transparent glass base material obtained by executing the temperature pattern according to the comparative example were each subjected to a drawing process as a subsequent process.

このとき、実施例に係る温度パターンを実行して得られた透明ガラス母材について、後工程の線引き設備に入らなかったガラス母材は、全体の５％であった。これに対して、比較例に係る温度パターンを実行して得られた透明ガラス母材について、線引き設備に入らなかったガラス母材は、全体の２０％であった。このように、本実施形態に係る透明ガラス母材の製造方法によれば、線引き設備に入れることのできる透明ガラス母材を安定して提供することができる。   At this time, about the transparent glass preform | base_material obtained by performing the temperature pattern which concerns on an Example, the glass preform | base_material which did not enter into the drawing equipment of a post process was 5% of the whole. On the other hand, about the transparent glass base material obtained by performing the temperature pattern which concerns on a comparative example, the glass base material which did not enter drawing equipment was 20% of the whole. Thus, according to the manufacturing method of the transparent glass base material which concerns on this embodiment, the transparent glass base material which can be put into a drawing equipment can be provided stably.

１：焼結炉、２：炉心管、３：ヒータ、３Ａ：下ヒータ、３Ｂ：上ヒータ、４：ヒートシールド、５：真空容器、６：排気用配管、７：真空ポンプ、８：ガス導入管、９：圧力調整弁、１０：多孔質ガラス母材、１１：透明ガラス母材
Ｔ１：第一目標温度（目標温度）、Ｔ２：第二目標温度、Ｔ３：第三目標温度、ｔ３−ｔ２：第一所定時間、ｔ６−ｔ４：第二所定時間、ｔ６−ｔ５：第三所定時間 1: sintering furnace, 2: furnace core tube, 3: heater, 3A: lower heater, 3B: upper heater, 4: heat shield, 5: vacuum vessel, 6: exhaust pipe, 7: vacuum pump, 8: gas introduction Tube, 9: Pressure adjusting valve, 10: Porous glass base material, 11: Transparent glass base material, T1: First target temperature (target temperature), T2: Second target temperature, T3: Third target temperature, t3-t2 : First predetermined time, t6-t4: second predetermined time, t6-t5: third predetermined time

Claims (2)

ガラス微粒子が堆積されてなる多孔質ガラス母材をその中心軸が上下方向となるように焼結炉内で支持しながら、複数に分割されたヒータを前記多孔質ガラス母材が焼結する温度である目標温度まで上げて第一所定時間加熱し、前記多孔質ガラス母材の焼結を完了させて透明ガラス母材とし、
前記第一所定時間が経過した後、前記透明ガラス母材の中心位置より下部を加熱する前記ヒータの温度を前記目標温度、または前記目標温度より高く設定して第二所定時間保持し、前記第二所定時間の間は前記透明ガラス母材の中心位置より上部を加熱する前記ヒータの設定温度を前記透明ガラス母材の中心位置より下部を加熱する前記ヒータの設定温度より低く設定し、前記透明ガラス母材を加熱することを特徴とする透明ガラス母材の製造方法。 The temperature at which the porous glass base material sinters the heater divided into a plurality of parts while supporting the porous glass base material on which the glass fine particles are deposited in the sintering furnace so that the central axis thereof is in the vertical direction. To a target temperature that is heated for a first predetermined time, to complete the sintering of the porous glass base material to be a transparent glass base material,
After the first predetermined time has elapsed, the temperature of the heater that heats the lower part from the center position of the transparent glass base material is set higher than the target temperature or the target temperature, and is held for a second predetermined time . For two predetermined periods of time, the set temperature of the heater that heats the upper part from the center position of the transparent glass base material is set lower than the set temperature of the heater that heats the lower part from the center position of the transparent glass base material, and the transparent A method for producing a transparent glass base material, comprising heating the glass base material. 前記ヒータは、前記焼結炉内の中心位置より下部に位置する下ヒータと、前記下ヒータとは独立して温度を設定可能で前記焼結炉内の中心位置より上部に位置する上ヒータと、を有し、
前記第一所定時間が経過した後、前記上ヒータの温度を前記目標温度未満に設定して第三所定時間保持することを特徴とする請求項１に記載の透明ガラス母材の製造方法。 The heater includes a lower heater located below the center position in the sintering furnace, an upper heater located above the center position in the sintering furnace, capable of setting the temperature independently of the lower heater, Have
The method for producing a transparent glass base material according to claim 1, wherein after the first predetermined time has elapsed, the temperature of the upper heater is set to be lower than the target temperature and held for a third predetermined time.
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