JPH04198036A - Heating furnace for wire drawing of optical fiber - Google Patents

Abstract

PURPOSE:To prevent cracking from occurring due to thermal stress in a base material during wire drawing and enable production of optical fiber without any strain by providing the upper side of a wire drawing heater of a wire drawing heating furnace for the optical fiber with an annealing heater. CONSTITUTION:When a wire drawing heating furnace (1A) is used to heat a base material 11 for optical fiber and carry out wire drawing, the base material 11 is initially heated at a high heating temperature than the glass strain point and a lower temperature than the softening point with a built-in annealing heater 5 to remove the strain remaining in the base material. The tip of the base material 11 is melted with a wire drawing heater 2 and drawn into a wire.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a drawing heating furnace used for drawing optical fibers.

[Conventional technology]

FIG. 2 is a schematic cross-sectional view of a wire heating furnace used for drawing optical fibers. a carbon muffle 3 for preventing adhesion to the optical fiber base material used to draw the optical fiber;
It is composed of a heat insulating material 4 for increasing the thermal efficiency of the line heater 2. In the figure, 11 is an optical fiber base material, and 12 is a drawn optical fiber.

Incidentally, when drawing an optical fiber, helium, argon,
While flowing an inert gas such as nitrogen gas or a mixture thereof, the optical fiber base material 11 is sequentially heated from one end to 2.
The optical fiber 12 is manufactured by heating it to 000° C. or more and pulling it down in the axial direction.

[Problem to be solved by the invention]

As is well known, the base material for optical fiber is obtained as a transparent glass base material by heating a porous base material to transparently vitrify and solidify it, but when solidifying, it is not always cooled and solidified uniformly. The surface of this transparent base material for optical fiber is flame polished to make the surface smooth and then wire is drawn, but the softening and solidification of the surface by heating at this time is not always uniform, and as a result, stress strain may occur in the base material. remain. When such a base material is drawn, there is a problem in that it may crack or become an optical fiber with residual distortion.

[Means to solve the problem]

The present invention has been made in order to solve the above-mentioned problems, and in an optical fiber line heating furnace with a built-in line drawing heater, a heating temperature higher than that of the line drawing heater is provided on the upper side of the line drawing heater. This is a line heating furnace having a built-in annealing heater with a low heating temperature, that is, higher than the strain point of glass and lower than its softening point.

[Effect]

When a base material is heated and drawn using the drawing heating furnace having the structure of the present invention as described above, the base material is first heated by an annealing heater, and the temperature thereof is higher than the glass strain point and lower than the softening point. Therefore, residual strain in the base material is removed.

Since the tip of the base material is melted and drawn by the wire drawing heater, the base material does not crack during drawing or become an optical fiber with residual distortion.

〔Example〕

FIG. 1 is a schematic cross-sectional view of a line heating furnace according to the present invention, in which the same part numbers and symbols are used as in FIG. , Ayu-Relay heater 5 arranged on the upper side, Carbon Matsufuru 3
and a heat insulating material 4. Although the heating temperature of the line heater 2 is 2000°C or higher, the heating temperature of the annealing heater 5 is set so that the heating temperature G of the line heater 2 is higher than the strain point of 1100°C and lower than the softening point of 1300°C. Set it lower than the heating temperature.

When drawing an optical fiber, it is drawn while flowing an inert gas in the heating furnace IA as in the conventional example, but the optical fiber base material 11 is first heated in the annealing heater 5.
When heated to 00 to 1,300°C, the strain in the base material is removed, and the base material 11 is gradually fed downward, and the tip is heated by the wire drawing heater 2 to melt it and draw the wire downward. An optical fiber 12 (without distortion) is obtained. No cracks in the base material were observed during drawing.

〔Effect of the invention〕

If the optical fiber is drawn using the optical fiber drawing heating furnace according to the present invention (A), the strain in the base material will be eliminated before drawing, so cracks will not occur in the base material during drawing due to thermal stress. In addition, it is possible to manufacture optical fibers without distortion.

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view of an optical fiber line heating furnace according to the present invention, and FIG. 2 is a schematic sectional view of a conventional optical fiber line heating furnace. 1. IA: heating furnace, 2: line drawing heater, 5 near annealing heater.

Claims (1)

[Claims] 1. In an optical fiber line heating furnace with a built-in line heater, an annealing heater with a heating temperature higher than the strain point of the glass and lower than its softening point is built into the upper side of the line heater. Features: Optical fiber line heating furnace.