JPH0292838A - Heating furnace for drawing optical fiber - Google Patents

Abstract

PURPOSE:To stabilize the flow of a gas in a furnace and suppress the fluctuation in outside diameter of an optical fiber by providing the bottom outlet nozzle of a special shape under a gas feed port at an outlet for the optical fiber of the heating furnace in using the heating furnace having the gas feed port at the bottom and drawing an optical fiber preform. CONSTITUTION:A gas feed port (8A) is provided in the bottom of a furnace body 1 and a gas is fed from the gas feed port (8A) to draw an optical fiber preform 3 while passing the gas from the lower to the upper parts of the furnace body 1 and heating the optical fiber preform 3 in the heating furnace body 5. Thereby, an optical fiber is produced. In the process, a bottom outlet nozzle 12, having a smaller nozzle caliber than the diameter of a weight for end picking of the optical fiber and the length thereof in the axial direction of >=10 times based on the nozzle caliber is provided at the outlet 6 for the optical fiber at the bottom of the heating furnace body 5 and under the position of the gas feed port (8A). As a result, leakage of the gas in the furnace body 1 can be reduced to prevent entry of air from the outside of the furnace.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to an optical fiber drawing heating furnace used for drawing optical fiber.

[Prior Art] Conventionally, as shown in FIG. 3, optical fibers are drawn using a furnace body 1, a furnace core tube 2 disposed above and below the furnace body 1, and a furnace core tube 2 disposed on the outer periphery of the furnace core tube 2. It consists of a heating furnace main body 5 consisting of a heater 4 made of carbon or the like that heats the optical fiber preform 3 in the furnace core tube 2, and a shutter lid 7 that seals the optical fiber outlet 6 of the heating furnace main body 5. Using an optical fiber line heating furnace, the optical fiber preform 3 is heated with the heater 4, and the furnace core tube 2 is heated through the gas supply line 8 provided in the furnace body 1.
Inside, inert gas is flowed from the lower gas supply port 8A to the upper part to prevent air from entering the furnace core tube 2, and in this state, the optical fiber fnU3 is drawn to form the optical fiber 9.
was manufacturing.

Particularly, by flowing the inert gas from the bottom to the top within the furnace core tube 2, dust can be discharged upward, so that the optical fiber 9 is not covered with dust and the strength of the optical fiber 9 is improved.

However, the shutter M7 has an optical fiber passage hole 7B.
Therefore, the gas supplied into the furnace body 1 from the gas supply port 8A does not necessarily all flow upwards as shown in FIG. leaks out of the furnace. As a result, the flow of gas leaking out of the furnace collides with the flow of rising air 11 entering from outside the furnace into the furnace through the optical fiber passage hole 7B.
The flow becomes unsteady, and the flow near the so-called optical fiber forming part where the optical fiber 9 is drawn from the optical fiber preform 3 becomes unstable. A problem has arisen in that the outer diameter of the optical fiber 9 being drawn varies due to the instability of this flow.

Therefore, in order to suppress the intrusion of air from outside the furnace, it is desired to improve the sealing performance at the optical fiber outlet 6, and for example, a shutter lid 7 consisting of shutter blades 7A as shown in FIGS. 5 and 6 has been proposed. There is. These are the heating furnaces of this type.
When first pulling out the optical fiber 9 from the optical fiber base material 3, a glass weight 10 with an outer diameter of about 15 InIIl is attached to the lower end of the optical fiber member 3 as shown in FIG. Since the weight 9 is pulled out of the furnace to start drawing, the shutter blade 7A is opened when the weight 10 passes by using a two-part structure as shown in Fig. 5 or a constriction structure as shown in Fig. 6. , it is supposed to be closed after passing.

However, both of these methods do not provide perfect sealing, so as an improvement plan, as described in JP-A-62-36039, a diffuser block is provided at the optical fiber exit, and the optical fiber passage hole is closed. A method has been proposed that blows gas out of the furnace to prevent air from entering from outside the furnace.

[Problems to be Solved by the Invention] In this conventional method, the gas supply port is installed near the optical fiber passage hole, that is, close to the atmosphere, and the gas is blown out. There was a problem in that a large amount of gas went out, and as a result, an unsteady flow was created that was separate from the upward airflow 11 indicated by the arrow in FIG. 3, and this caused a change in the outer diameter of the optical fiber 9. . Moreover, as drawing speeds have become even faster these days, the amount of gas leaking out of the furnace along with the traveling optical fiber 9 tends to increase, making this problem even more serious.

An object of the present invention is to provide an optical fiber wire heating furnace that can minimize the amount of gas leaking into the atmosphere from the lower outlet of the furnace, stabilize the flow of gas in the furnace, and thereby manufacture optical fibers with less variation in outer diameter. It is about providing.

[Means for Solving the Problems] To explain in detail the present invention for achieving the above object, the present invention includes a gas supply port provided in the lower part of the furnace body, and this gas supply port allows the supply of gas from the lower part of the furnace body to the upper part. In an optical fiber drawing heating furnace that manufactures an optical fiber by heating and drawing an optical fiber preform in a heating furnace main body in which a gas is flowed, the light is A lower outlet nozzle, which has a nozzle diameter smaller than the weight when the fiber is drawn out and whose length in the axial direction is 10 times or more the nozzle diameter, is provided below the position of the gas supply port. It is characterized by

[Effect 1] When such a lower outlet nozzle is provided, since the lower outlet nozzle has a strength more than 10 times the nozzle diameter, the fluid resistance inside the nozzle increases, and the flow from the gas supply port to the inside of the furnace increases. Leakage of supplied gas to the outside of the furnace can be reduced.

As a result, the flow of gas in the furnace (in this case, upward flow) is stabilized, and fluctuations in the outer diameter of the optical fiber are extremely small.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to FIG. Note that parts corresponding to those in FIGS. 3 and 4 described above are designated by the same reference numerals.

The optical fiber line heating furnace of this embodiment has a nozzle having a diameter smaller than that of the weight 10 (see FIG. 2) at the time of leading out the optical fiber 9 and a nozzle length in the axial direction. However, the lower outlet nozzle 12, which has a diameter more than 10 times the nozzle diameter, is connected below the position of the gas supply port 8A.

Since such a lower outlet nozzle 12 has a nozzle length that is more than 10 times the diameter of the nozzle, the fluid resistance inside the lower outlet nozzle 12 increases and gas leaks to the outside of the furnace. The amount can be reduced, and as a result, the flow in the furnace can be stabilized, thereby making it possible to reduce fluctuations in the outer diameter of the optical fiber 9.

The nozzle diameter is, for example, 3s, and the nozzle length is, for example, 755m. This nozzle length L needs to be increased as the linear velocity increases.

For example, when the linear velocity is 600771/min, the nozzle quality L is set to about 200M.

FIG. 2 shows the relationship between nozzle diameter and nozzle length. In the figure, the O symbol indicates no fiber diameter variation, and the Δ symbol indicates fiber diameter variation. As is clear from the figure, when L/D≧10, no fiber diameter variation occurs.

The reason why the nozzle diameter is made smaller than the weight at the time of outlet is that if it is made larger than this, the nozzle length becomes very large, which is not practical. Also,
Naturally, by making the nozzle diameter smaller than the weight, in the case of the present invention, the lower outlet nozzle is split into two in the axial direction.

Further, in the above embodiments, only the shape of the nozzle is shown in which the inner diameter is constant from the nozzle inlet to the outlet, but a so-called tapered shape, in which the inner diameter decreases toward the bottom, may also be used. In this case, the nozzle length may be 10 times the average inner diameter of the Taber nozzle.

Furthermore, if the solidified formation position of the optical fiber 9, that is, the position where the outer diameter is approximately the final one, is placed in the nozzle of the lower outlet nozzle 12, the flow of gas around the molten part of the optical fiber 9 becomes stable. For this reason, it is more effective in suppressing outer diameter fluctuations.

In addition, according to the present invention, it is only necessary to make the nozzle diameter smaller than the weight, and sufficient effects can be expected even if the nozzle diameter is not made extremely small. Therefore, effects such as being able to prevent contact between the inner surface of the nozzle and the running optical fiber can be expected.

[Effects of the Invention] As explained above, the optical fiber line heating furnace according to the present invention has an optical fiber at the outlet of the optical fiber in the lower part of the heating furnace main body and further below the gas supply port into the furnace. By providing a lower outlet nozzle with a diameter smaller than the fiber outlet weight and with an axial length of at least 10 times the nozzle diameter, leakage of gas inside the furnace can be reduced, and gas leakage from outside the furnace can be reduced. Since it is also possible to prevent air from entering, it is possible to stabilize the flow of gas within the furnace. As a result, it is possible to manufacture an optical fiber with extremely small outer diameter variations.

[Brief explanation of drawings]

FIG. 1 is a vertical cross-sectional view showing an embodiment of the optical fiber line heating furnace according to the present invention, and FIG. 2 is a relationship between the nozzle diameter and nozzle length showing the effect of the lower outlet nozzle in this embodiment.
FIGS. 3 and 4 are a vertical cross-sectional view of a conventional heating furnace and a 5tti plane view of the state when a weight passes through the furnace, and FIGS. 5 and 6 are plan views showing a conventional shutter lid in an open state. DESCRIPTION OF SYMBOLS 1... Furnace body, 2... Furnace core tube, 3... Optical fiber base material, 4... Heater, 5... Heating furnace main body, 6... Optical fiber outlet, 8... Gas supply system path, 8A... Gas supply port, 9... Optical fiber, 10... Weight, 12.
...Lower outlet nozzle. fart

Claims (1)

[Claims] A gas supply port is provided at the bottom of the furnace body, and gas is flowed from the bottom of the furnace body to the top through the heating furnace body. An optical fiber preform is heated and drawn to produce an optical fiber. In the optical fiber line heating furnace, the optical fiber outlet in the lower part of the heating furnace body has a nozzle diameter smaller than the weight at the time of leading out the optical fiber, and the length in the axial direction is 10 times or more the nozzle diameter. 1. An optical fiber heating furnace characterized in that a lower outlet nozzle is provided below the position of the gas supply port.