JPS62260731A - Wire drawing furnace for optical fiber - Google Patents

Abstract

PURPOSE:To make it possible to maintain a small gap between a throttle plate and periphery of a preform and reduce fluctuation in wire diameter, by providing the throttle plate, having a gas blowing port and slidable in the direction perpendicular to the feed direction of a fiber preform on the top end of a wire drawing furnace. CONSTITUTION:A wire drawing furnace for an optical fiber capable of melting the tip part of an optical fiber preform 2 while heating and drawing the preform 2 into the optical fiber is formed from a throttle plate supporting member 5, provided at the top end part of a furnace body and having a gas feed port 12, the throttle plate 4 for passing the preform 2 therethrough and a gas inlet port 11 and blowing ports 14. The above-mentioned throttle plate 4 is contained in the interior of the above-mentioned support member 5 slidable to the direction perpendicular to the feed direction of the preform 2. The above-mentioned gas inlet port 11 is communicated to a gas feed port 12 of the above-mentioned support member 5. Gas F2 is evenly jetted from the above-mentioned blowing ports 14 on the outer peripheral surface of the preform 2.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to an optical fiber drawing furnace that maintains airtightness inside the furnace to obtain an optical fiber with less variation in wire diameter.

<Conventional technology> Optical fibers are manufactured using optical fiber matrices made of materials such as quartz.
The wire is inserted into the furnace from the upper part of the drawing furnace, the tip is heated and melted, and then pulled out from the lower part of the drawing furnace, and the diameter is reduced to the desired diameter. In this case 1. Foreign matter in the air, oxygen, water, nitrogen gas, metal ions, etc. that enter the drawing furnace cause a decrease in the strength and performance of the optical fiber, as well as a decrease in the life of the heater due to oxidation. It is necessary to constantly fill the furnace with inert raw gas to prevent the molten optical fiber preform from being exposed to air. Moreover, in order to reduce the variation in the diameter of the optical fiber due to the 7M1 degree fluctuation of the molten tip of the optical fiber preform, much effort has been made to stabilize the airflow in the drawing furnace. For example, the method shown in Japanese Patent Publication No. 59-30660 introduces potatoes and old gas into a drawing furnace, exhausts the gas in the furnace, controls the airflow in the sweeping furnace, and then The upper and lower openings are equipped with gas seals to prevent atmospheric air from entering from outside.

The fourth figure shows the structure of the upper part of such a conventional optical fiber drawing furnace.
As shown in the figure, a gas diffuser 1 is provided at the upper part of the drawing furnace 3 where the base material is inserted, and the gas ejected from the gas diffuser 1 is used to obtain a sealing effect within the drawing furnace 3.

<Problems to be solved by the invention> Generally, the inside of a drawing furnace is kept at a high temperature of nearly 2000°C in order to melt the optical fiber base material, so a strong upward air current is generated and there is no sufficient sole. In order to obtain the effect, a large amount of sealing gas must be supplied, which inevitably increases the cost of the product. On the other hand, attempts have been made to increase the gas pressure at the sealing part and improve the sealing effect by reducing the gap d between the gas diffuser l and the optical fiber base material 2 shown in FIG. 4, but in this case, Optical fiber base material 2
If the straightness of the optical fiber is not perfect or the operating accuracy of the machine is not perfect, the gas diffuser l and the optical fiber base material 2 will come into contact at the sealing part, damaging the optical fiber base material 2 and reducing the strength of the optical fiber. This may lead to a decrease in Therefore, the gap d between the gas diffuser 1 and the optical fiber base material 2
cannot be reduced below a certain point.

On the other hand, the gas ejected from the gas diffuser 1 collides with the rising air current in the furnace, and during the fourth cycle, turbulent flow as shown by the arrow occurs. For this reason, temperature unevenness occurs at the molten tip of the optical fiber preform 2, causing variations in the diameter of the optical fiber. In addition, as a result of air entering the furnace together with this inflowing gas, the furnace walls made of heat-resistant materials such as carbon and zirconia are worn out, and the generated dust damages the surface of the optical fiber base material, reducing the strength of the optical fiber. It was supposed to be lowered. This becomes more noticeable as the gas flow rate increases.

The present invention has been made in view of the problems of the prior art, and an object of the present invention is to provide an optical fiber drawing furnace that can improve the airtightness inside the furnace and draw an optical fiber without damaging the surface of the optical fiber base material. With the goal.

<Means for Solving the Problems> In the optical fiber drawing furnace according to the present invention, an optical fiber preform is fed into the inside, and the tip of the optical fiber preform is melted and drawn into an optical fiber. In an optical fiber drawing furnace, a diaphragm plate support member provided at the upper end of the furnace body and provided with a gas supply port, and a diaphragm plate support member provided inside the aperture plate support member in a direction perpendicular to the feeding direction of the optical fiber preform. a diaphragm plate that is slidably housed in the diaphragm plate and through which the optical fiber preform passes; a gas inlet that is formed in the diaphragm plate and communicates with the gas supply port of the diaphragm plate support part; The present invention is characterized in that it includes an outlet for evenly ejecting the high-pressure gas onto the outer circumferential surface of the optical fiber preform through the optical fiber base material.

The inside of the furnace is filled with gas in the small gap between the outer circumferential surface of the optical fiber base material and the inner circumferential surface of the aperture plate.

If the optical fiber base material and the aperture are misaligned, the pressure distribution of the sealing gas blown out from the outlet of the aperture plate towards the optical fiber base material will change, and the aperture should be adjusted so that this pressure distribution becomes uniform. The temporary slides within the aperture plate support member, and misalignment between the optical fiber preform and the aperture plate is automatically corrected, and the minute gap between the optical fiber preform and the aperture plate is kept constant.

<Embodiment> As shown in FIG. 1 showing the cross-sectional structure of the main part of an embodiment of the optical fiber drawing furnace according to the present invention, and FIG. 2 showing the cross-sectional shape in the direction of The aperture plate 4 is slidably held in the internal space 5a of the provided aperture plate support member 5. Further, the optical fiber preform 2 is inserted through the center of the temporary aperture 4 with a minute gap maintained. In addition, the diaphragm plate support member 5 has 2
A high-pressure gas supply port 12 is provided, and the restrictor 4 is provided with a high-pressure gas introduction port 11 that is constantly connected to this high-pressure gas supply port 12. Furthermore, an annular gas reservoir 13 is inserted into the high-pressure gas inlet 11 of the temporary diaphragm plate 4 and is inserted into the gas reservoir 13. A plurality of outlets 14 that uniformly eject high-pressure gas F2 are communicated around the fiber base material 2. Therefore, the high-pressure gas F2 is ejected from the high-pressure gas supply port 12 of the diaphragm plate support member 5 to the outer peripheral surface of the optical fiber preform 2 via the high-pressure gas inlet 1 of the diaphragm 4, the gas reservoir 13, and the outlet 14.

In this embodiment, eight outlets 14 are formed at equal intervals, and the pressure distribution at each outlet 14 may change.

For example, if the optical fiber base material 2 is misaligned with respect to the aperture plate 4, the pressure on the narrower side of the gap will increase, but as a result of acting on the aperture plate 4 so that these pressure distributions are in equilibrium, , the aperture plate 4 slides to a position where the gap between the inner circumferential surface of the aperture plate 4 and the outer circumferential surface of the optical fiber preform 2 becomes equal. Such a pivoting action of the restrictor 4 is based on the same principle as that of a so-called hydrostatic bearing.

As shown in FIG. 3, which shows the cross-sectional structure of the main part of another embodiment of the optical fiber drawing furnace according to the present invention, the aperture plate support member 5 is attached to the upper end of the furnace body of the optical fiber drawing furnace. ,
The optical fiber preform 2 to be fed into the optical fiber drawing furnace passes through the central portion. Further, inside the aperture plate support member 5, an aperture plate 4 through which the optical fiber preform 2 passes is arranged in the center. The aperture plate 4 is blown out by the gas F3 blown out from a large number of gas outlets (not shown) provided on the upper plate part 5a and the lower plate part 5b of the aperture plate support member 5 facing the aperture plate 4. , are supported so as to be able to slide very smoothly with respect to the lower plate portion 5b with minute gaps d, , d, respectively.

In addition, in the figure, the gaps d, , d are exaggerated for convenience of explanation.

Furthermore, gas supply ports 12 are provided at a plurality of locations on the upper plate portion 5a and the lower temporary portion 5b of the aperture plate support member 5.
The aperture plate 4 located between a and 5b has a gas inlet 11 that faces the gas supply port 12 and has an opening larger than the opening.
is provided. In other words, the configuration is such that even if the cross-shaped cross section 4 slides within the aperture plate support member 5, the flow of the feed gas from the gas supply port 12 to the gas introduction port 11 will not be hindered. Further, an annular gas reservoir 13 is provided within the restrictor 4, and the high-pressure gas introduced from the gas inlet 11 is temporarily stored therein. The gas reservoir 13 is connected to an outlet 14 that opens at equal intervals on the inner peripheral surface of the diaphragm plate 4.
Therefore, the high-pressure gas stored in the gas reservoir 13 flows toward the outer peripheral surface of the optical fiber base material 2 in a high-pressure gas flow F2 with a uniform pressure.
It bursts out. In this case, if misalignment occurs between the optical fiber base material 2 and the diaphragm plate 4, the pressure on the narrower side of the gap increases as in the previous embodiment, but due to this imbalance in pressure distribution, the diaphragm plate 4 It slides and the misalignment is corrected so that the pressure distribution is uniform. Such centering action is similar to that of the embodiment shown in FIG.

In this embodiment, the diaphragm plate 4 is held by the gas flow F3 from the gas outlet provided in the upper and lower plate parts 5a and 5b of the diaphragm plate support member 5, so the sliding property is significantly improved. Since the followability is good, the aperture plate 4 will not come into contact with the optical fiber base material 2 and damage the optical fiber base material 2.

The gas inlet 11 of the diaphragm plate 4 and the gas supply port 12 of the diaphragm plate support member 5 are always in communication with each other at a constant rate of 2t! Since the gas of i is kept supplied, the blowing pressure of the high pressure gas does not fluctuate due to the sliding movement of the throttle plate 4.

Also, the gap d1°d2 between the aperture plate support member 5 and the aperture plate 4
Since the area is extremely narrow, the amount of gas flowing out from this area is extremely small and poses no problem. Furthermore, in this embodiment, the gas supply ports 12 provided in the aperture plate support member 5 are opposed to the upper and lower plate portions 5a and 5b of the aperture plate support member! Since the high-pressure gas is introduced from the upper and lower gas supply ports 12 to the gas inlet 11 of the throttle plate 4 evenly above and below, even if there is a fluctuation in the gas flow of the high-pressure gas, the gaps d, , d2 are maintained. does not change, and the influence of the gas flow F3 on the support of the diaphragm plate 4 can be completely ignored.

<Effects of the Invention> According to the optical fiber drawing furnace of the present invention, high-pressure gas is ejected onto the outer peripheral surface of the optical fiber preform from the aperture plate slidably supported by the aperture plate support member at the upper end of the furnace body. Due to the principle of pressure bearing, the temporary diaphragm can be maintained around the optical fiber base material without contacting it with a small gap.

Therefore, the inside of the furnace can be kept airtight from the atmosphere, keeping the atmosphere inside the furnace clean and suppressing fluctuations in the high-temperature rising air current inside the furnace, thereby preventing fluctuations in the temperature of the heated and melted part of the optical fiber base material tip. We were able to significantly reduce the variation in optical fiber diameter caused by this.

In addition, by effectively sealing the inside of the furnace from the atmosphere,
Impurities such as foreign matter, oxygen, water vapor, and metal ions in the atmosphere are not introduced into the furnace body, and this makes the optical fiber a
5. In addition to avoiding a decrease in optical strength, problems such as wear of parts in the furnace body and deterioration of the heater due to oxidation are eliminated, and excellent, high-quality optical fibers can be stably produced.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an embodiment of the gas seal portion of an optical fiber drawing furnace according to the present invention, FIG. 2 is a cross-sectional view taken along arrows -■, and FIG. A cross-sectional view of the gas seal portion, and FIG. 4 is a schematic view of the upper end of a conventional optical fiber drawing furnace. In the drawing, 2 is an optical fiber base material, 4 is an aperture plate, 5 is an aperture plate support member, 11 is a gas introduction port, 12 is a gas supply port, and 13
14 is a gas reservoir, and 14 is an outlet. Figure 1 Figure 3

Claims (1)

[Claims] In an optical fiber drawing furnace in which an optical fiber preform is fed into the interior and the tip of the optical fiber preform is heated and melted to draw the optical fiber, the furnace is provided at the upper end of the furnace body and is provided with a gas supply port. an aperture plate support member, an aperture plate that is slidably housed inside the support member in a direction perpendicular to the feeding direction of the optical fiber preform and through which the optical fiber preform passes; A gas inlet is formed and communicates with the gas supply port of the diaphragm plate support member, and a blow-off port is provided for evenly jetting the high-pressure gas onto the outer peripheral surface of the optical fiber preform through the gas inlet. An optical fiber drawing furnace featuring: