JPH0478570B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] 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 vertically within 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 base material 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 heating furnace, the optical fiber base material 3 is heated by the heater 4, and a gas supply port 8A is provided in the lower part of the furnace core tube 2 through the gas supply line 8 provided in the furnace body 1. The optical fiber 9 was manufactured by flowing an inert gas into the upper part of the furnace core tube 2 to prevent air from entering the furnace core tube 2, and drawing the optical fiber base material 3 under such conditions.

Particularly, when the inert gas is flowed 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, since the shutter lid 7 has an optical fiber passage hole 7B, the gas supply port 8A is connected to the furnace body 1.
The gas supplied inside the furnace does not necessarily all flow upward as shown in FIG. 3, but a portion leaks out of the furnace through the optical fiber passage hole 7B of the shutter lid 7 located at the bottom. 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 base material 3 becomes unstable. A problem has arisen in that the instability of this flow causes variations in the outer diameter of the optical fiber 9 being drawn.

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. For example, the shutter blade 7 shown in FIGS.
A shutter lid 7 made of A is proposed. In this type of heating furnace, when the optical fiber 9 is first pulled out from the optical fiber base material 3, a glass weight 10 having an outer diameter of about 15 mm is placed on the lower end of the optical fiber member 3, as shown in FIG. Since the optical fiber 9 is attached to the furnace and the optical fiber 9 is pulled out of the furnace by its gravity to start drawing, it is possible to create a structure in which it is divided into two parts as shown in Figure 5, or a diaphragm structure as shown in Figure 6. 10, the shutter blade 7A is opened and closed after passing.

However, both of these methods do not provide perfect sealing, so as an improvement plan, a diffuser block is provided at the optical fiber outlet, as described in Japanese Patent Laid-Open No. 62-36039, and the optical fiber passage hole is closed. A method has been proposed in which gas is blown out from the surrounding surface 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 provided close to 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 exited, 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 wire drawing has become faster and faster, the amount of gas leaking out of the furnace due to the traveling optical fiber 9 tends to increase.
This problem is becoming more and 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 manufacture optical fibers with less variation in outer diameter. Our goal is to provide the following.

[Means for Solving the Problems] To explain the configuration of the present invention for achieving the above object, the present invention has a gas supply port provided at the lower part of the furnace body, and the 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 base material in a heating furnace main body in which a gas is flowed, the above-mentioned light is supplied to the optical fiber outlet in the lower part of the heating furnace main body. The nozzle diameter is smaller than the weight when the fiber is drawn out, and the length in the axial direction is 10 times the nozzle diameter.
It is characterized in that a lower outlet nozzle whose size is more than twice as large is provided below the position of the gas supply port.

[Function] When such a lower outlet nozzle is provided, the length of the lower outlet nozzle is more than 10 times the nozzle diameter, so the fluid resistance inside the nozzle increases and the flow from the gas supply port to the furnace increases. The leakage of gas supplied into the furnace to the outside 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 wire-based 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 opening the optical fiber 9 at the optical fiber outlet 6 in the lower part of the heating furnace main body 5, and a nozzle length in the axial direction. A lower outlet nozzle 12 in which L is 10 times or more the nozzle diameter D.
is connected below the position of the gas supply port 8A.

Since such a lower outlet nozzle 12 has a nozzle length L that is at least 10 times the diameter D of the nozzle, the fluid resistance inside the lower outlet nozzle 12 increases and the amount of gas leaking out of the furnace is reduced. As a result, the flow inside the furnace can be stabilized, and fluctuations in the outer diameter of the optical fiber 9 can be reduced. The nozzle diameter D is, for example, 3 mm, and the nozzle length L is, for example, 75 mm. This nozzle length L needs to be increased as the linear velocity increases. For example, when the linear speed is 600 m/min, the nozzle length L is increased to about 200 mm.

FIG. 2 shows the relationship between the nozzle diameter D and the nozzle length L. In the figure, ◯ indicates no fiber diameter variation, and △ 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 D is smaller than the weight at the time of outlet is that if the nozzle diameter is larger than this,
This is because the nozzle length L becomes extremely large, which is not practical. Further, as a matter of course, by making the nozzle diameter D smaller than the weight, in the case of the present invention, the lower outlet nozzle is of a type divided 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 it may be a so-called tapered shape in which the inner diameter decreases toward the bottom. In this case, the nozzle length L may be 10 times the average inner diameter of the tapered 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 preventing contact between the inner surface of the nozzle and the traveling optical fiber can be expected.

[Effects of the Invention] As explained above, the optical fiber heating furnace according to the present invention has an optical fiber outlet at 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 smaller diameter than the fiber outlet weight and an axial length that is at least 10 times the nozzle diameter, it is possible to reduce the leakage of gas inside the furnace, and to prevent gas leakage from outside the furnace. 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 fluctuations.

[Brief explanation of the drawing]

FIG. 1 is a vertical cross-sectional view showing an embodiment of the optical fiber heating furnace according to the present invention, FIG. 3 and 4 are longitudinal cross-sectional views of a conventional heating furnace and a vertical cross-sectional view of the state when a weight passes through the furnace, and FIGS. 5 and 6 are plan views showing the 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 line, 8A...
Gas supply port, 9...optical fiber, 10...weight,
12...Lower outlet nozzle.

Claims (1)

[Claims] 1 A gas supply port is provided in the lower part of the furnace body, and the gas supply port allows gas to flow from the lower part of the furnace body to the upper part of the furnace body.The optical fiber base material is heated and drawn to produce optical fiber. In the optical fiber wire-based heating furnace, the optical fiber outlet in the lower part of the heating furnace main body has a nozzle diameter smaller than the weight when the optical fiber is drawn out, and the length in the axial direction is at least 10 times the nozzle diameter. 1. A fiber optic heating furnace, characterized in that a lower outlet nozzle having the shape of 1 is provided below the position of the gas supply port.