JPH06219767A - Drawing method of glass base material for optical fiber - Google Patents

Abstract

(57) [Summary] [Purpose] The amount of gas used in the furnace can be reduced,
Further, the present invention provides a method for drawing a glass preform for optical fibers, which can prolong the life of the carbon core tube. [Structure] An optical fiber glass base material 4 is melted and drawn in a drawing furnace 1 in a furnace gas atmosphere, and then an optical fiber 5 obtained by drawing is placed in a clean box 11 adjacent to the drawing furnace 1. With clean air,
Next, in the drawing method of the glass base material 4 for an optical fiber which coats the resin, the optical fiber 5 in the clean box 11 is cooled at the boundary with the drawing furnace 1 in the clean box 11 in order from the boundary side. The in-furnace gas is caused to flow in the drawing furnace 1 direction, then the in-furnace gas is caused to flow in the direction opposite to the drawing furnace 1, and then clean air is caused to flow in the direction opposite to the drawing furnace 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for drawing a glass preform for optical fibers.

[0002]

2. Description of the Related Art An optical fiber is manufactured by inserting a rod-shaped glass base material for an optical fiber into a fixed tubular electric furnace at about 2000.degree.
It can be obtained by heating to, and drawing from the lower end. After the drawing, in order to protect the optical fiber, the outer peripheral surface of the optical fiber is coated with, for example, a plastic resin. By the way, in recent years, with the increase in the drawing speed of the optical fiber, when the plastic resin is coated online, the optical fiber is not sufficiently cooled and the surface temperature of the optical fiber increases, so that the coating is sufficiently performed. The problem of not having occurred. Therefore, a method has been used in which the drawing tower is raised to increase the distance between the electric furnace and the coating portion to perform natural cooling. However, this method could not sufficiently cool to a temperature at which coating was possible. For this reason, a forced cooling system that allows a gas that easily removes heat to flow near the surface of the optical fiber is required.
A method of flowing e-gas is generally used. However, since He gas is very expensive, as an alternative method, a gas other than He is blown from the nozzle onto the optical fiber to forcibly remove the high temperature gas on the surface of the optical fiber. . In the case of this method, blowing a heavy gas has a higher cooling effect, and for example, an excellent cooling effect is obtained by blowing inexpensive clean air (passed through an air filter or the like). Figure 2
It is a block diagram of the conventional optical fiber preform drawing apparatus. In the figure, 1 is a furnace body of an electric furnace, 2 is a carbon heater, 3 is a core tube, 4 is an optical fiber base material, 5 is an uncoated optical fiber, 6 is a gas supply line in the furnace, and 8 is downward clean air. Supply lines, 9 and 10 are upward clean air supply lines, 11 is a clean box, 12 is a resin coating die, 13 is a bellows tube, 14 is a curing furnace for curing the coated resin, for example, a UV lamp, 15 is A coated optical fiber core wire, 16 is an exhaust port provided in the clean box 11, and 18, 19 and 20 are cooling gas nozzles. The clean box 11 is connected to an electric furnace to prevent outside air from entering. In the clean box 11, in order from the top, clean air is supplied downward from the nozzle 18 by the clean air supply line 8 and clean air is supplied upward from the nozzles 19 and 20 by the clean air supply lines 9 and 10, respectively. Cool 5 Then, the optical fiber 5 is coated with an ultraviolet curable resin with a resin coating die 12 to form an optical fiber core wire 15, and then U
The UV curable resin is cured by the V lamp (ultraviolet irradiation lamp) 14.

[0003]

However, the method of blowing clean air to the optical fiber to cool it has the following problems. That is, 1) It is necessary to maintain a positive pressure in the clean box in order to prevent the outside air from being sucked in. In that case, the clean air in the clean box flows into the drawing furnace,
Carbon core tube is oxidized and deteriorated by oxygen of clean air, and its life is shortened. 2) If the inside of the clean box is filled with an inert gas such as Ar, the above problem can be solved, but then the original purpose of reducing the cooling cost cannot be achieved.

[0004]

DISCLOSURE OF THE INVENTION The present invention provides a method for drawing a glass preform for an optical fiber which solves the above-mentioned problems. The glass preform for an optical fiber is drawn in a drawing furnace in a furnace gas atmosphere. Glass fiber preform for optical fiber that melts and draws with, then cools the optical fiber obtained by drawing with clean air in a clean box adjacent to the drawing furnace, and then coats the outer peripheral surface of the optical fiber with resin In the drawing method, the optical fiber is cooled in the clean box at the boundary with the drawing furnace in the clean box, in order from the boundary side, first the furnace gas is caused to flow in the drawing furnace direction, and then the furnace gas is drawn. Is made to flow in the direction opposite to the drawing furnace, and then clean air is made to flow in the direction opposite to the drawing furnace.

[0005]

As described above, at the boundary between the optical fiber in the clean box and the drawing furnace in the clean box, first the furnace gas is flowed in the drawing furnace direction, and then the furnace gas is drawn. It is carried out by flowing in the direction opposite to the furnace and then flowing clean air in the direction opposite to the drawing furnace. Then, clean air does not flow into the drawing furnace from the clean box. Therefore, even if clean air is used, it is possible to prevent oxidative deterioration of the carbon core tube of the drawing furnace. Also, since the gas for the furnace is used only at the boundary with the drawing furnace in the clean box, and cheap clean air is flowed to other large volume parts excluding the boundary in the clean box, The amount of gas used can be reduced, and the cost of cooling the optical fiber can be reduced.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the embodiments shown in the drawings. FIG. 1 is an explanatory diagram of a method for drawing a glass preform for optical fibers according to the present invention. The reference numerals in the figure are the same as those used in the description of the prior art.
In this embodiment, the outer diameter is 100 mm and the parallel portion length is 500 mm.
0.78 mm / mi of the glass base material 4 for optical fiber in the furnace core tube 3 of the electric furnace for the wire drawing furnace, which has the carbon heater 2 with an inner diameter of 105 mm and is held in an Ar gas atmosphere.
Insert vertically at a speed of n. Then, the lower part of the glass base material 4 for optical fiber which is heated and softened and dropped is wound up at a linear speed of 500 m / min by a winder through a capstan to obtain a long diameter of 0.125 mm. To obtain the optical fiber 5. A resin coating die 12 is attached to the optical fiber 5.
Then, the UV curable resin was coated with and the UV curable resin was cured with the UV lamp 14 to obtain the optical fiber core wire 15.

The clean box 11 is hermetically connected to the lower part of the electric furnace in order to prevent outside air from entering. In the clean box 11, the nozzle 17 is used in order from the upper side at the boundary with the electric furnace, and the furnace gas supply lines 7a, 7
Ar gas is caused to flow in the electric furnace direction and the direction opposite to the electric furnace by b. A cooling gas nozzle 18 is provided in close contact with the lower side of the nozzle 17, and clean air is supplied from the clean air supply line 8 in the direction opposite to the electric furnace. Further, cooling gas nozzles 19 and 20 are provided below the cooling gas nozzle 18, and clean air is supplied upward by the clean air supply lines 9 and 10 to cool the optical fiber 5. By doing so, the clean air flowing upward from the clean air supply lines 9 and 10 is hindered by the Ar gas from the furnace gas supply 7b flowing downward and the clean air from the clean air supply line 8 and the electric furnace I can't go inside.

In this step, when the lower end of the glass preform 4 for an optical fiber is softened and dropped to start drawing the glass preform for optical fiber, Ar gas as a furnace gas is supplied at a flow rate of 15 (l / min). Flow from the line 6 into the core tube 3. Next, from the in-furnace gas supply lines 7a and 7b, 5
(L / min), 2 (l / min) Ar gas is flowed, and at the same time, the Ar gas flow rate from the furnace gas supply line 6 is set to 3
(L / min), and clean air was supplied from the clean air supply lines 8, 9, and 10 at a flow rate of 50 (l / min), respectively, to start drawing. On the other hand, for comparison, by the conventional method shown in FIG.
in) and the cooling gas nozzles 18, 19, 2
Wire drawing was performed by flowing 50 (l / min) each from 0. As a result of evaluating various characteristics of the optical fiber drawn by the method of this example and the optical fiber drawn by the method of the comparative example, it was found that there was no difference between the two. In this embodiment, since clean air is not entrained in the lower part of the electric furnace, it is considered that no problem will occur even if the Ar gas flow rate in the furnace is reduced. Further, when the life of the carbon core tube was compared, in this example, it was doubled as compared with the comparative example, and it was possible to reduce the cost of the drawing process together with the reduction of the amount of Ar gas used.

[0009]

As described above, according to the present invention, an optical fiber obtained by melting and drawing an optical fiber glass preform in a drawing furnace in a furnace gas atmosphere and then drawing In the drawing method of the glass preform for optical fibers, which is cooled by clean air in a clean box adjacent to the drawing furnace and then coated with resin on the outer peripheral surface of the optical fiber, the cooling of the optical fiber in the clean box is performed by the clean box. At the boundary with the drawing furnace, the furnace gas is flowed in the drawing furnace direction in order from the boundary side, then the furnace gas is flowed in the direction opposite to the drawing furnace, and then clean air is drawn. Since it is performed by flowing in the direction opposite to the furnace, the amount of gas used in the furnace can be reduced and the life of the carbon furnace tube can be extended. There is an excellent effect that.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an embodiment of a method for drawing a glass preform for optical fibers according to the present invention.

FIG. 2 is an explanatory diagram of a conventional method for drawing a glass preform for optical fibers.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 furnace body 2 carbon heater 3 core tube 4 optical fiber base material 5 optical fiber 6, 7a, 7b core gas supply line 8, 9, 10 clean air supply line 11 clean box 12 resin coating die 13 bellows tube 14 UV lamp 15 Optical fiber core 16 Exhaust port 17 Nozzle 18, 19, 20 Gas nozzle for cooling

Claims (1)

[Claims] 1. A glass preform for an optical fiber is melted and drawn in a drawing furnace in a furnace gas atmosphere, and then an optical fiber obtained by drawing is clean air in a clean box adjacent to the drawing furnace. Cooled by
In a method of drawing an optical fiber glass preform for coating a resin on an outer peripheral surface of an optical fiber, cooling of the optical fiber in the clean box is performed at a boundary with a drawing furnace in the clean box, in order from the boundary side, firstly, a furnace. The light is characterized in that the internal gas is caused to flow in the drawing furnace direction, then the furnace gas is caused to flow in the direction opposite to the drawing furnace, and then the clean air is caused to flow in the direction opposite to the drawing furnace. Drawing method of glass preform for fiber.