JPS5951501B2 - Optical fiber drawing furnace - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a drawing furnace for heating and softening an optical fiber base material and drawing it into an optical fiber using a carbon resistor as a heating element.

Conventionally, as this type of resistance heating wire drawing furnace, one constructed as shown in FIG. 1 is known. That is, in FIG. 1, 1 is a base material for an optical fiber, 2 is a drawing furnace body, 3 is a heat insulating material, 4 is a resistance heating element, 5 is an optical fiber, and 6 is a heating element electrode. However, in such a structure, in order to provide the heating element 4 with a required resistance value, a slit parallel or spiral to the axial direction of the heating element 4 is required. For this reason, in the central portion of the heating element 4, the heat received from the heating element 4 of the base material 1 is not uniform in the circumferential direction of the base material 1. That is, heat transfer by radiation becomes discontinuous at the slit portion of the heating element 4. In addition, an inert gas is flowed into the furnace to prevent oxidation and consumption of carbon, but the atmospheric gas in the furnace enters and exits at the slit, causing turbulence in the gas flow at the center of the heating element 4. As a result, the heat conduction through the gas is unstable, and the temperature of the heated portion of the base material 1 fluctuates, resulting in a fluctuation in the fiber diameter. The turbulence of the atmospheric gas is also significantly affected by its inflow amount, and the fiber outer diameter also varies greatly due to temperature fluctuations caused by the gas turbulence. Furthermore, when drawing base materials having various outside diameters, it is necessary to use a heating element suitable for each diameter, which has the disadvantage of extremely reducing work efficiency. The present invention has been made in view of the above points, and provides an extremely good optical fiber that can uniformly heat the base material and eliminate temperature fluctuations by inserting a carbon cylinder inside the heating element. The purpose is to provide wire drawing furnaces.

An embodiment of the present invention will be described in detail below with reference to the drawings.

That is, in FIG. 2, 1 is a fiber base material, J2 is a furnace body, 3 is a heat insulating material, 4 is a heating element, 5 is an optical fiber, 6 is a heating element electrode, and 7 is a carbon cylindrical heat-uniforming layer.

In order to draw a fiber using the drawing furnace configured as described above, the fiber base material 1 is inserted from the upper part of the furnace body 2, and the fiber base material 1 is inserted into the central part of the heating element 4 using a carbon resistor. The base material 1 is softened by heating and drawn into a fiber. At this time, the base material 1 is not directly heated by the heating element 4, but a carbon cylinder 5 interposed between the heating element 4 and the base material 1. A feature of the present invention is that heating is performed indirectly by the heat-uniforming layer 7.

Next, the above embodiment will be specifically illustrated.

A heating element 4 with an inner diameter of 50 mmφ was used, and a carbon cylinder with an inner diameter×outer diameter of 38×44 mmφ was inserted as a heat-uniforming layer 7 inside the heating element 4. As a result, when a quartz fiber base material 1 with an outer diameter of 25 mmφ is drawn into a fiber with an outer diameter of 125 μmφ, at a drawing speed of 30 to 60 m/min, the outer diameter of the fiber fluctuates within ±1.5 μm with respect to 125 μmφ. It was hot. Comparing this result with the case without the heat-uniforming layer under the same conditions, the outer diameter variation is ±5μ without the heat-uniforming layer.
It was more than m. Furthermore, in order to make the ratio of the outer diameter of the base material/the diameter of the heating element the same as in the example, the heating element 4 was replaced with one having an inner diameter of 40 mm and wire drawing was performed. In this case as well, the variation in the outer diameter is approximately ±2 μm, which is clearly smaller in the case where the heat-uniforming layer 7 is provided, and it is clear that the variation is more effective. On the other hand, variations in the fiber outer diameter are also affected by the flow rate of atmospheric gas flowing into the furnace to keep it inert.

Therefore, in the embodiment described above, the gas flow rate is set with a focus on reducing the variation in the outer diameter, but it is preferable to take the following consideration into preventing wear of the heating element 4. That is, it is effective to maintain airtightness between the inside of the two-layer soaking layer 7 and the side of the heating element 4, and to control the flow rates of each separately. In this case, a heating element 4 and a heat equalizing layer 7 having the same dimensions as those in the above embodiment are provided, and a gas seal is created between the inside of the heat equalizing layer 7 and the atmosphere on the side of the heating element 4 and 2 using a gasket made of carbon felt, for example. good. Thereby, the variation in the outer diameter of the fiber can be controlled by the flow rate of the gas flowing into the inside of the heat-uniforming layer 7. When wire is drawn under the same conditions as in the above embodiment, the outer diameter variation is ±1 μm when the flow rate of argon gas flowing into the heat absorbing layer 7 is in the range of 4 to 81/min.
decreased to a certain extent. On the other hand, on the heating element 4 side, by setting the mixed gas of argon/nitrogen to 121/min,
The life of heating element 4 was over 500 hours. That is, by interposing the heat-uniforming layer 7 between the heating element 4 and the base metal 1, discontinuities in the base material circumferential direction of radiant heat transfer due to the slits of the heating element 4 and the flow of gas in the furnace atmosphere are prevented. It is possible to eliminate uneven heat transfer caused by turbulence. Therefore, the fiber base material can be heated uniformly within the heat-uniforming layer and the temperature can be kept stable. Furthermore, since the fiber base material is heated uniformly and at a constant temperature, it is possible to eliminate fluctuations in the fiber outer diameter due to temperature fluctuations.

As explained above, the optical fiber drawing furnace according to the present invention can eliminate fiber diameter fluctuations caused by temperature fluctuations, and can stably draw long fibers with a uniform diameter, including automatic control of the drawing speed. It has the advantage of being able to

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional resistance heating drawing furnace, and FIG. 2 is a block diagram showing an embodiment of an optical fiber drawing furnace according to the present invention. DESCRIPTION OF SYMBOLS 1... Optical fiber base material, 2... Wire drawing furnace body, 3... Heat insulating material, 4... Resistance heating element, 5... ... Optical fiber 6 ... Heating element electrode, 7 ... Carbon cylindrical heat equalizing layer.

Claims (1)

[Claims] 1. In an optical fiber drawing furnace that heats and softens an optical fiber base material with a heating element made of a carbon resistor provided inside the furnace and draws it into an optical fiber having a predetermined outer diameter, the heating element and the optical fiber base material are An optical fiber drawing furnace characterized by having a carbon cylindrical heat-uniforming layer interposed between the fiber and the fiber.