JPH0745543Y2 - Sealing structure of sintering furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to a sealing structure for a sintering furnace, and more particularly to a sealing structure for an upper part of a furnace core tube in a sintering furnace for an optical fiber preform.

(Prior Art) Optical fiber preform soot (porous glass fine particles such as SiO ₂ and GeO ₂ (dopant raw material)) by the VAD method is made into transparent glass by a resistance heating furnace or a high frequency heating furnace.

In this transparent vitrification step, a quartz core tube is used, and an inert gas (He or the like) and a dehydrating agent (Cl ₂ or the like) are used as atmosphere gases.

In FIG. 7 showing the conventional apparatus in the transparent vitrification step, 1 is a seed rod made of quartz glass, and the optical fiber preform soot 2 is formed at its tip in the step before the transparent vitrification step. The upper end of the seed rod 1 is held by a chuck mechanism 3, which is rotated by the chuck mechanism 3 and a slide mechanism (not shown).
It can be moved up and down by. Reference numeral 5 is a quartz furnace tube for sintering the optical fiber preform soot 2, and a flange portion 6 on which a split lid 8 is placed.
Are formed. A through hole 9 for inserting the seed rod 1 is formed in the split lid 8, and they are brought into contact with each other on a split surface 10 (FIG. 8). Reference numeral 12 denotes a support base for supporting the quartz furnace core tube 5. An exhaust pipe 13 is placed on the upper surface of the support base 12, atmospheric gas is exhausted from an exhaust port 14 of the exhaust pipe 13, and a scrubber (not shown). No.) and other exhaust gas treatment equipment. The atmospheric gas is supplied from the lower part of the quartz furnace core tube 5, rises in the quartz furnace core tube 5, and is introduced into the exhaust tube 13 through the gap between the seed rod 1 and the through hole 9.

The optical fiber base material soot 2 is formed by a gas phase reaction using SiCl ₄ , GeCl ₄ , O ₂ and H ₂ as glass raw materials, gas and combustion gas, but it is porous and opaque before sintering. It contains a lot of water.

In this transparent vitrification step, the porosity is vitrified and water is removed by a dehydrating agent (Cl ₂ or the like) to promote transparency.

(Problems of the prior art) The removal of water by the above-mentioned dehydrating agent (Cl ₂ etc.) is more effective when the partial pressure of Cl ₂ is higher. Therefore, in order to increase the transparency of the manufactured optical fiber and reduce the optical loss, , Seed stick 1
And the clearance between the through hole 9 and the Cl
_It is better to increase the partial pressure of ₂ as much as possible.

However, the split lid 8 is made of quartz glass in consideration of heat resistance and corrosion resistance, and it was difficult to bring the diameter of the through hole 9 close to the outer diameter of the seed rod 1 with high precision. It was also difficult to secure the degree. Increasing the partial pressure of Cl ₂ in other words, effectively increase the dewatering effect of Cl _2, it is difficult to increase the transparency of the optical fiber.

Further, when the optical fiber base material soot 2 is inserted and after the transparent vitrification step is completed, in order to take out the optical fiber base material 4 from the quartz furnace core tube 5, it is necessary to remove the split lid 8 from the flange portion 6. High temperature condition (for example, about 300 ℃)
Since it is performed at a temperature of up to 400 ° C. and the brittleness of glass often breaks the split lid 8, the split lid 8 is an expensive consumable item.

Moreover, when the split lid 8 is detached from the flange portion 6, a large amount of atmospheric air enters the quartz core tube 5 to cause a devitrification phenomenon on the inner wall of the quartz core tube 5. If this devitrification phenomenon progresses, the quartz core There is also a problem that a cracked portion occurs in the pipe 5 and gas leakage occurs.

(Means for Solving the Problems) In the present invention, in a sintering furnace for optical fiber preform soot, a lid member abutting on the upper surface of the furnace upper tube has a dividing surface passing near the center of the lid member and at least on the left and right sides. While being divided into two, a through hole is formed in the center, while a substantially annular center lid placed on the lid member near the through hole has an inner peripheral surface having a diameter smaller than the diameter of the through hole. Together with the outer peripheral surface having a diameter larger than the diameter of the through hole, the diameter of the through hole of the lid member is formed slightly larger than the outer diameter of the optical fiber preform after sintering, A sealing structure of a sintering furnace, wherein a diameter of an inner peripheral surface of the center lid is smaller than an outer diameter of the optical fiber preform after sintering.

(Embodiment) In FIGS. 1 to 4 showing an embodiment of the present invention, a seventh embodiment
The same reference numerals as those in the figure are corresponding parts, and only different points will be described below.

Reference numeral 20 denotes a two-divided lid placed on the flange portion 6 of the quartz furnace core tube 5 (Fig. 2), and a through hole 21 is formed in the central portion, and the diameter d _{1 of the through} hole 21 is the optical fiber preform. When the outer diameter of soot 2 before sintering is d ₂ and the outer diameter after sintering is d ₃ , d ₂ > d ₁
It is set to the relation of> d ₃ . Through hole 21 of this two-piece lid 20
A substantially annular center lid 23 is placed on the upper surface of the vicinity, and a leg portion 24 having an outer diameter matching the diameter d ₁ of the through hole 21 is inserted through the through hole 21. A through hole 25 is formed in the central portion of the central lid 23 so as to penetrate the leg portion 24 (FIG. 4). The outer diameter d5 of the central lid 23 is larger than the diameter d1 of the through hole 21, and the through hole 25
The diameter d ₆ is set to be slightly larger than the outer diameter d ₇ of the seed rod 1. The center lid 23 is integrally formed, and the diameter d ₆ can be accurately set, and can be formed to be approximately equal to the outer diameter d ₇ of the seed rod 1. And through hole 25
The gap between and is set to be as small as possible.

A carbon heater (not shown) is arranged so as to surround the quartz core tube 5 at a predetermined distance from the outer peripheral surface of the quartz core tube 5.

Next, the operation will be described. The diameter of the quartz furnace core tube 5 is, for example, about 90 mm, and the outer diameter d ₂ of the optical fiber preform soot ₂ is, for example,
It is about 60 to 65 mm, and in order to insert the optical fiber preform soot 2 formed on the seed rod 1 in the previous step into the quartz furnace core tube 5, it is necessary to remove the central lid 23 and the two-divided lid 20. After arranging the optical fiber preform soot 2 in the quartz core tube 5, the two-piece lid 20 is placed on the flange portion 6, and then the center lid 23 is placed on the upper surface near the through hole 21 of the two-piece lid 20. A carbon heater (not shown) is energized and the seed rod 1 is rotated while moving from the upper side to the lower side, and the optical fiber preform soot 2 is sintered in a He and Cl ₂ gas atmosphere to be a transparent glass. When this transparent vitrification is completed, the diameter
The diameter is reduced from d ₂ to d ₃ , and the optical fiber base material soot 4 becomes the optical fiber base material 4. In order to take out the optical fiber preform 4 from the quartz core tube 5, the seed rod 1 is moved upward. Since the diameter d ₃ of the optical fiber preform 4 is set to be smaller than the diameter d ₁ of the through hole 21 of the two-divided lid 20, the two-divided lid 20 has a flange 6 when the optical fiber preform 4 is taken out. No need to remove from. Also, the diameter of the through hole 25 of the center lid 23
Since d ₆ is set to be smaller than the diameter d _{3 of} the optical fiber preform 4, when the upper part of the optical fiber preform 4 comes into contact with the lower surface of the center cover 23 as the optical fiber preform 4 moves upward, The base material 4 moves the central lid 23 upward together, and only the central lid 23 is removed from the upper surface of the two-divided lid 20.

Therefore, the upper portion of the quartz furnace core tube 5 is not entirely exposed to the atmosphere, and a large amount of air does not flow into the quartz furnace core tube 5.

The optical fiber preform 4 that has undergone the transparent vitrification process is removed together with the seed rod 1, and a new optical fiber preform soot 2 is obtained.
Is set and the same process is repeated.

Another embodiment is shown in FIGS. 5 and 6, and in this embodiment a two-piece lid 28 having a structure similar to the two-piece lid 20.
Is placed on the upper surface of the two-divided lid 20, and the center lid 23 is placed on the upper surface of the two-divided lid 28. Split surface of the two-split lid 20
As shown in FIG. 6, 20a and the dividing surface 28a of the two-piece lid 28 are substantially
They are placed 90 degrees apart, and in such a configuration, 2
Atmosphere gas does not leak from the split lid 20a or the split surface 28a, and the partial pressure of Cl ₂ in the quartz furnace tube 5 in the transparent vitrification step can be increased more easily.

In the above embodiment, the two-part lid 20 and the two-part lid 28 are each divided into two parts on the left and right, but the number of parts is not limited to two, and it may be divided into three or four. Is also possible. In yet another embodiment, the two-divided lid 20 having the same structure as the two-divided lid 20 may be placed in a triple or quadruple structure (not shown). In addition to the quartz glass, the two-divided lids 20 and 28 and the central lid 23 are
It may be formed of ceramic or the like.

(Effects of the Invention) In the sintering furnace sealing structure according to the present invention, in the sintering furnace for the optical fiber preform soot 2, the lid member 20 (28) contacting the upper surface of the furnace core tube 5 is the center of the lid member 20 (28). It has a split surface 20a (28a) passing through the vicinity and is divided into at least two parts on the left and right sides, and a through hole 21 is formed in the central portion, while a substantially annular shape placed on the lid member 20 in the vicinity of the through hole 21. The central lid 23 is a through hole
It has an inner peripheral surface with a diameter smaller than that of 21 and has a through hole.
It has an outer peripheral surface with a diameter larger than that of 21 and the center lid 23
Since they are integrated, the diameter of the inner peripheral surface of the central lid 23 can be accurately set to a value close to the outer diameter of the seed rod 1. Therefore, the partial pressure of Cl ₂ or the like as the dehydrating agent in the quartz furnace tube 5 in the transparent vitrification step of the optical fiber preform soot 2 can be more easily increased, and the dehydration effect can be enhanced, resulting in high transparency and light loss. A small number of excellent optical fiber preforms 4 can be easily manufactured. Moreover, the optical fiber base material 4
When removing from the quartz furnace core tube 5, only the central lid 23 needs to be removed, and it is not necessary to remove the two-part lid 20.
The probability that the item will be damaged can be extremely reduced, making it expensive.
It is possible to prevent the split lid 20 from becoming a consumable item.
Further, when removing the optical fiber preform 4 from the quartz furnace core tube 5, only the central lid 23 needs to be removed, and it is not necessary to remove the two-divided lid 20.
Even when the quartz furnace core tube 5 is removed, the problem that a large amount of air flows into the quartz furnace core tube 5 does not occur, and the problem that the quartz furnace core tube 5 devitrifies can be eliminated.

[Brief description of drawings]

FIG. 1 is a vertical sectional side view showing an embodiment of the present invention, and FIG.
FIG. 3 is a plan view of a split lid, FIG. 3 is a plan view of a central lid, FIG. 4 is a vertical side view, FIG. 5 is a vertical side view of a main portion showing another embodiment, FIG. FIG. 8 is a partially omitted vertical side view showing a conventional example, and FIG. 8 is a plan view of a two-divided lid. 2 …… Optical fiber base material soot, 4 …… Optical fiber base material, 5 …… Quartz core tube, 20, 28 …… 2 split lid, 21 …… Through hole, 23 …… Center lid, 20a …… Divided surface, d1 ...... Diameter of through hole, d
3 …… Outer diameter of optical fiber base material, d5 …… Outer diameter of center lid, d
6 …… Inner diameter of the center lid

Claims (2)

[Scope of utility model registration request] 1. In a sintering furnace for the optical fiber preform soot 2, a lid member 20 abutting on the upper surface of the furnace core tube 5 has a dividing surface 20a passing near the center of the lid member 20 and is at least divided into two parts on the left and right sides. Together with the through hole 21 is formed in the center,
A substantially annular center lid 23 placed on the lid member 20 in the vicinity of the through hole 21 has an inner peripheral surface having a diameter d ₆ smaller than the diameter d _{1 of the through} hole 21, and the diameter d of the through hole 21. Diameter d ₅ greater than ₁
While the diameter d ₁ of the through hole 21 of the lid member 20 is formed to be slightly larger than the outer diameter d ₃ of the optical fiber preform 4 after sintering, A sealing structure for a sintering furnace, wherein a diameter d _{6 of} an inner peripheral surface is formed smaller than an outer diameter d ₃ of the optical fiber preform 4 after sintering. 2. The lid members 20 and 28 are formed into at least two upper and lower halves, and the lid members 20 and 28 are divided into left and right portions in a state where the dividing surfaces 20a and 28a are different from each other. The sintering furnace sealing structure according to claim 1, wherein 20,28 are placed on the upper surface of the furnace core tube 5.