JPH026348A - Optical fiber drawing furnace - Google Patents

Abstract

PURPOSE:To prevent the intrusion of air into a furnace for drawing a glass preform in an inert gas atmosphere under heating and softening, to prolong the life of the heat source and to prevent the contamination of the fiber with impurities by forming a shielded chamber forming a flow channel of an inert gas in the main body of the drawing furnace. CONSTITUTION:A furnace main body 10 holding a carbon furnace core tube 2 and a carbon resistance heater 3 has a double-walled structure composed of an outer wall 11 and an inner wall 12. A shielding chamber 13 encircling the whole furnace is formed between the walls. A gas inlet part 14 for introducing an inert gas into the shielding chamber 13 is formed at the top of the furnace main body 10. An inert gas such as N2 or Ar introduced through the inlet part 14 is passed through the shielding chamber 13 and discharged through an exhaustion port 15 of the furnace main body 10 together with an inert gas introduced into the furnace core tube 2. A shielding layer is formed in the shielding chamber 13 by this process to separate the inside of the furnace main body 10 from the outside.

Description

[Detailed Description of the Invention] <Public Expenses for Industrial Use> The present invention relates to an optical fiber drawing furnace that prevents outside air from entering the furnace to prevent oxidative deterioration of the heating source.

<Prior Art> Optical fibers are generally drawn by heating and softening a rod-shaped glass preform for optical fibers in a furnace and drawing them. Carbon resistance furnaces are often used to manufacture such optical fibers.

An example of a conventional drawing furnace is shown in FIG. As shown in the figure, the furnace body 1 includes a carbon furnace core jv! as a heating source. :2 and a carbon resistance heater 3 are provided, and the optical fiber glass preform (hereinafter simply referred to as preform) 4 pushed into the furnace core tube 2 is heated and softened in the furnace core tube 2. The optical fiber 5 is drawn. In this type of drawing furnace, in order to prevent oxidation deterioration of the furnace core tube 2 and heater 3,
The furnace body 1 has an airtight structure, and an inert gas is introduced into the furnace core v: 2 from the gas introduction part 6 at the upper part toward the lower part, and a preform support rod 7 is installed at the inlet of the preform 4. A shutter 8 is provided which is in close contact with the housing to maintain airtightness.

<Problems to be Solved by the Invention> However, even in the cotton drawing furnace having the structure described above, air gradually enters from the outside, causing oxidative deterioration of the carbon furnace core tube 2 and the carbon resistance heater 3, resulting in The problem is that the lifespan is shortened. In addition, the furnace core tube 2
There is also the problem that carbon tends to fall off from the preform, and the carbon adheres to the molten part of the preform, resulting in low strength of the optical fiber.

In view of these circumstances, an object of the present invention is to provide a hollow optical fiber drawing furnace that completely prevents air from entering from outside the furnace.

Means for Solving the Problems> An optical fiber drawing furnace according to the present invention that achieves the above object draws an optical fiber by stretching a glass base material for an optical fiber while heating and softening it in an inert gas atmosphere. In an optical fiber drawing furnace having a furnace body, there is a cutoff chamber that surrounds the furnace body and serves as a flow path for inert gas, and a cutoff layer made of inert gas that allows inert gas to flow into the cutoff chamber. It is characterized by having a gas introduction means for forming.

Function> The furnace body for drawing optical fiber is surrounded by a cutoff chamber, and when an inert gas is poured into the cutoff chamber by a gas inflow means, a cutoff layer made of inert gas is formed, and this cutoff layer causes the furnace to close. The inside and outside of the main body are isolated.

<Embodiment> FIG. 1 shows the configuration of an optical fiber drawing furnace according to a preferred embodiment of the present invention. It should be noted that the same members as those in the conventional FIG.

As shown in FIG. 1, in this embodiment, a furnace body 10 holding a carbon furnace core tube 2 and a carbon resistance heater 3 is attached to an outer wall 1.
1 and an inner wall 12, a cutoff chamber 13 that surrounds the entire furnace is formed between the outer wall 11 and the inner wall 12, and a gas for introducing inert gas into the cutoff chamber 13 is formed in the upper part of the furnace body 10. The structure is such that an introduction section 14 is provided. From this gas introduction part 14, N2. Ar.

When an inert gas such as He is introduced, the inert gas flows through the cutoff chamber 13 and is discharged from the gas outlet 1 formed in the furnace body.
5, the gas is discharged together with the inert gas introduced into the furnace core tube 2. That is, a barrier layer is formed in the barrier chamber 13 by the flow of inert gas, and the furnace body 10 is
The inside and outside are separated by a barrier layer.

In addition, by constantly introducing inert gas from the gas introduction part 14, there is no direct contact with air as in the conventional case, so air can gradually penetrate into the furnace. lost. Therefore, it is possible to extend the life of the carbon component by preventing oxidative deterioration of carbon, and it is also possible to effectively prevent the strength of the optical fiber from decreasing due to carbon deterioration.

When the optical fiber was drawn for 120 hours with the temperature of the core tube 2 of the drawing furnace of the above example at 2200°C, the average breaking strength of the optical fiber at this point was maintained at a high strength of 5.9 kg. Ta. Furthermore, when I continued to draw the line,
It was only after 1000 hours that some carbon loss began to be seen.

For comparison, according to the conventional drawing furnace shown in Figure 2, if drawing was continued for 120 hours under the same conditions, significant carbon loss would be observed, and the average breaking strength of the optical fiber at this point would be The weight dropped significantly to 3 kg).

<Effects of the Invention> As explained above, according to the optical fiber drawing furnace according to the present invention, it is possible to prevent air from entering the furnace, so parts that are easily oxidized such as carbon parts can be used as round heating sources. Even during use, its oxidation is prevented and its lifespan can be extended. Moreover, it is possible to prevent a decrease in the strength of the optical fiber due to impurities that are caused by deterioration of the components getting mixed into the fiber.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an optical fiber drawing process according to an embodiment of the present invention, and FIG. 2 is a block diagram showing an optical fiber drawing furnace according to the prior art. In the drawing, 2 is a carbon furnace core tube, 3 is a carbon resistance heater, 4 is a glass base material for optical fiber, 5 is an optical fiber, 6 is a gas introduction part, 10 is a furnace body, 11 is an outer wall, 12 is an inner wall, 13 is a cutoff chamber, 14 is a gas inlet, and 15 is an outlet.

Claims (1)

[Claims] In an optical fiber drawing furnace that has a furnace body that heats and softens a glass base material for optical fiber in an inert gas atmosphere and draws it into an optical fiber, it surrounds the furnace body and serves as a flow path for the inert gas. An optical fiber drawing furnace comprising a blocking chamber and a gas introducing means for flowing an inert gas into the blocking chamber to form a blocking layer made of the inert gas within the blocking chamber.