JPH01308842A - Drawing furnace for optical fiber - Google Patents

Abstract

PURPOSE:To prevent disturbance of an atmosphere in a furnace and contamination of the outside air into the furnace by providing a gas curtain device for blowing an inert gas on the outer peripheral surface of a preform near a preform inlet of an optical fiber drawing furnace body, outside diameter measuring instrument for measuring the outside diameter of the preform and flow controller of the afore-mentioned gas. CONSTITUTION:A drawing furnace body 1 for an optical fiber is provided with a gas curtain device 5 and an outside diameter measuring instrument 11. The outside diameter of a preform 2, etc., is measured by the outside diameter measuring instrument 11 with laser beams to send a signal to an arithmetic unit 13, which takes a deviation from the standard outside diameter 14 inputted separately from measured data to control a flow controller 12 so as to provide a gas flow rate corresponding to the changed outside diameter thereof. Thereby, effects of the gas curtain device 5 are kept constant.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application> The present invention relates to an optical fiber drawing furnace capable of producing optical fibers with less variation in wire diameter and less decrease in strength.

<Conventional technology> Conventionally, optical fiber base material (referred to as preform)
In an optical fiber drawing furnace that heats and melts and draws optical fibers, it is possible to prevent disturbances in the atmosphere inside the drawing furnace to produce optical fibers with no diameter variation, and to prevent outside air from entering the drawing furnace. In order to prevent oxidative deterioration of the heater and the like due to contamination, a gas curtain is formed at the entrance of the preform to the drawing furnace, or a heating furnace containing the heater is sealed.

An example of a drawing furnace capable of forming such a gas curtain is shown in FIG. As shown in the figure, the drawing furnace main body 1 has a furnace core tube 3 into which the preform 2 is introduced and a heater 4. An annular gas curtain device 5 having an inner diameter approximately the same as the inner diameter of the gas curtain device 5 is provided. A groove-shaped gas outlet 5a is formed in the inner peripheral surface of the gas curtain device 5 in the circumferential direction, and an inert gas 6 introduced from the outside is passed through the gas outlet 5a to form a preform. It is configured to eject toward the outer circumferential surface of No. 2. Such a gas curtain device 5
An inert gas 6 such as nitrogen gas is ejected from the gas ejection port 5a of the preform 2, and after being blown onto the outer peripheral surface of the preform 2, it is distributed in the vertical direction, and the gas directed toward the inside of the furnace passes through the inside of the furnace. Forms a flow of gas that is discharged from the lower part of the furnace. This creates a constant flow of atmospheric gas within the furnace and prevents outside air from flowing into the furnace. Note that the preform 2 is welded to a dummy rod 7 and inserted into the furnace by a base material insertion device 8.

<Problems to be Solved by the Invention> In the above-mentioned drawing furnace, normally, due to the difference in the outer diameter between the introduced preform 2 and the dummy rod 7, a wire diameter variation occurs in the drawn optical fiber. There is a problem in that outside air is mixed into the furnace, causing oxidative deterioration of the furnace core tube 3 and the like.

Such problems also occur due to differences in outer diameter between preforms or differences in outer diameter in the longitudinal direction of the preforms.

In view of these circumstances, it is an object of the present invention to provide an optical fiber drawing furnace that can prevent changes in the outer diameter of the optical fiber caused by changes in the outer diameter of the preform and prevent entry of outside air. .

Means for Solving the Problems〉 The optical fiber drawing furnace of the present invention that achieves the above object is an optical fiber drawing furnace that has a drawing furnace body that heats and melts an optical fiber preform to draw the wire. A gas curtain device that sprays an inert gas onto the outer peripheral surface of the base material near the base material inlet of the drawing furnace body to prevent outside air from flowing into the wire drawing furnace body; an outer diameter measuring device for measuring the outer diameter of the base material; and a control means for controlling the flow rate of the inert gas blown out from the gas curtain device according to the outer diameter of the base material measured by the outer diameter measuring device. It is characterized by having the following.

Function> The inert gas blown out from the gas curtain device hits the outer circumferential surface of the optical fiber preform and then flows toward the inside of the furnace and toward the outside of the furnace along the axial direction of the outer circumferential surface of the preform. When the outer diameter of the optical fiber preform changes, the flow rate of the inert gas is controlled accordingly, so that the flow rate of the inert gas flowing toward the inside of the furnace is controlled to be constant, and the atmosphere inside the furnace is maintained constant.

Embodiment A preferred embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of the optical fiber drawing furnace according to this embodiment, but the same members as those in the conventional drawing furnace shown in FIG. .

As shown in FIG. 1, the optical fiber drawing furnace of this embodiment is equipped with an outer diameter measuring device 11 above a gas curtain device 5 provided in a drawing furnace main body 1. As shown in FIG. This outer diameter measuring device 11 measures the outer diameter of the preform 2 or the dummy rod 7 using 1 (8-Ne laser, etc.), and this measurement data is based on the flow rate of the inert gas 6 sent to the gas curtain device 5. The data is input to a computing unit 13, which serves as a control means for controlling a gas flow rate regulator 12, which is composed of an electromagnetic valve or the like that can adjust the flow rate.

This calculator 13 calculates the deviation between the measured data and the separately input reference outer diameter 14, controls the flow rate regulator 12 so that the gas flow rate corresponds to the changed outer diameter, and controls the gas flow rate of the gas curtain device 5. The curtain effect is always constant. At this time, the calculator 13 simultaneously determines that the current outer diameter measurement portion enters the gas curtain device 5 based on the distance between the outer diameter measurement position and the air curtain device 5 and the preform feed rate by the base material insertion device 8 at that time. The time is determined and the flow rate regulator 12 is controlled accordingly.

That is, when the outer diameter of the brifome 2 changes within the gas curtain device S, the gas flow rate is adjusted in accordance with the changing outer diameter.

The operation of the drawing furnace of this embodiment will be explained.

If the actual preform diameter is smaller than the reference outer diameter 14, if the gas flow rate is kept constant, the gas will flow inward (downward) into the drawing furnace after hitting the outer peripheral surface of the preform 2. The flow of the flowing inert gas 6 becomes smaller and the gas curtain effect is weakened, but in the drawing furnace of this embodiment, the preform diameter is small (when the small part enters the gas curtain device 5, the gas flow rate is Since the preform is adjusted so that it increases according to the diameter, the gas flow rate toward the inside of the drawing furnace is kept constant.On the other hand, when the preform diameter increases, the gas flow rate remains constant. As a result, the flow of the inert gas 6 flowing toward the inside of the drawing furnace increases, but in the drawing furnace of this embodiment, when the portion of the preform with a large diameter enters the gas curtain device 5, the gas The flow rate of the gas flowing into the drawing furnace remains constant since the flow rate is adjusted to decrease depending on its diameter.

In this way, in the drawing furnace of this embodiment, even if the diameter of the preform 2 or the dummy rod 7 changes, the gas blows out from the gas curtain device 5, hits the outer peripheral surface of the preform 2, etc., and then heads into the drawing furnace. Since the flow rate of the gas flowing through the furnace is kept constant and the gas curtain effect is constant, disturbances in the atmosphere inside the furnace are prevented, and outside air does not get mixed into the furnace.

<Test Example> In the drawing furnace of the above example, wire was drawn using a preform whose outer diameter varied from 26 mmφ to 23 mmφ in the longitudinal direction. The reference outer diameter was set to 25 φ, the inert gas (N2) flow rate at this time was 101/min, and the gas flow rate was set to change by 11/min for a preform outer diameter difference of 1+mφ. That is, the preform outer diameter is 1f.
The gas flow rate was set so that when flφ increased, the gas flow rate decreased by 11/min, and when the preform outer diameter decreased by 1 mmφ, the gas flow rate increased by lj/min.

When we measured the gas flow rate flowing out from the bottom of the furnace during this wire drawing, we found that it was 6! even if the preform diameter changed. The diameter variation of the drawn optical fiber was as small as 125±0.5 μm, and no decrease in strength was detected.

On the other hand, for comparison, we used a conventional drawing furnace as shown in Fig. 2 to draw a preform with a diameter varying from 26 to 23 φ at a constant gas flow rate of 101/min. The gas flow rate flowing out from the bottom of the fiber varies between 717 min and 41 min, and the diameter variation of the optical fiber is 125 ± 1.0μ.
It has become about twice as large as m. Furthermore, when the gas flowing out from the lower part of the furnace reached 417 minutes, air was mixed in from the lower part of the furnace, and the materials constituting the furnace were oxidized.

<Effects of the Invention> As explained above, according to the optical fiber drawing furnace of the present invention, even if the preform diameter changes, the amount of inert gas flowing into the drawing furnace can be kept constant. At the same time, the mixing of outside air is also prevented, which prevents an increase in diameter variation and a decrease in strength of the optical fiber being drawn, and improves productivity.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an optical fiber drawing furnace 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 drawings, 1 is the drawing furnace body, 2 is the preform (optical fiber base material), 3 is the furnace core tube, 4 is the heater, 5 is the gas curtain device, 7 is the dummy rod, 8 is the base material insertion device, 11 is an outer diameter measuring device, 12 is a flow rate regulator, and 13 is a computing unit.

Claims (1)

[Claims] In an optical fiber drawing furnace having a drawing furnace body that heats and melts an optical fiber preform to draw the fiber, an inert gas is blown onto the outer circumferential surface of the preform near the inlet of the preform in the drawing furnace main body. A gas curtain device that prevents outside air from entering the drawing furnace body, an outer diameter measuring device that measures the outer diameter of the base material introduced into the drawing furnace body, and an outer diameter measuring device that measures the outer diameter of the base material introduced into the drawing furnace body. An optical fiber drawing furnace comprising: a control means for controlling the flow rate of the inert gas blown out from the gas curtain device according to the outer diameter of the base material.