JPH0143382Y2 - - Google Patents

Description

[Detailed Description of the Invention] a. Technical Field The present invention relates to a heating furnace for spinning an optical fiber bundle for image transmission produced by an acid elution method.

b. Prior Art and its Problems First, a general method for manufacturing an optical fiber bundle for image transmission, which is manufactured by an acid elution method, will be briefly explained.

A triple structure single with a diameter of 500 μm and a length of 200 mm, consisting of a core glass with a relatively high refractive index, a clad glass with a relatively low refractive index surrounding it, and an acid-soluble glass surrounding it. A multi-fiber preform is produced by arranging the fibers in a mantle made of an acid-soluble glass pipe, and sealing one end of the mantle and exhausting the air inside the mantle while forming the multi-fiber preform. is fed into a heating electric furnace at a constant speed, and the multifibers that come out from the bottom of the heating electric furnace are spun with rollers to produce multifibers. This multi-fiber is cut to a certain length, both ends are coated with a substance that is insoluble in acid, and the middle part is immersed in an acid solution to dissolve the mantle tube in the middle part, making it flexible. Optical fiber bundles for image transmission can be manufactured.

It is well known that when spinning a multifiber preform by heating it in an electric heating furnace, the temperature of the heating electric furnace and the temperature distribution within the furnace greatly affect the performance of the spun multifiber. .

Ideally, as shown in Figure 4, the temperature distribution in the furnace is such that the temperature is high only from the point where the multifiber preform begins to deform to the point where the deformation ends, and the temperature is low before and after that. A heated furnace is preferable.

However, in an actual heating furnace, the temperature distribution is significantly different from such a temperature distribution.

In other words, the size of the heating furnace required varies depending on the outer diameter of the multi-fiber preform, but in general, the heating furnace required for spinning a multi-fiber preform with an outer diameter of approximately φ40 mm In the case of a furnace, the hot plate holding the heating element in the furnace needs to have an inner diameter of 150 to 200 mm and a height of about 120 to 150 mm.

When the temperature distribution in the vertical direction of such a heating furnace is measured, as shown in FIG. 5, the range of high temperatures becomes quite wide, which is quite different from the ideal temperature distribution shown in FIG.

When the range of high temperatures becomes wider in this way, it becomes one of the causes of the following disadvantages.

(1) If multifiber preforms and spun multifibers are exposed to high temperatures for long periods of time, there is a risk of crystallization, so it is not recommended to leave multifibers in such high temperature areas for long periods of time. do not have.

(2) Also, since the fused portion becomes longer, it becomes easier to trap air bubbles between the multifibers. In other words, when a multi-fiber preform is gradually fed into a furnace from above, the temperature generally increases as it goes downwards, so fusing starts from below, but if the high-temperature area is wide, the melting starts from below. Sometimes it happens that the parts do not fuse and instead fuse from the top first.
When this happens, air bubbles are trapped between the multifibers, and if the air bubbles trapped between the multifibers are exposed to high temperatures for a long time,
During that time, it expands and becomes larger, causing blemishes. If the high temperature area is narrow, the multifiber preform is cooled to a low temperature before the bubbles expand, so the bubbles do not grow and do not cause blemishing.

Therefore, special heating furnaces have been devised to solve the above-mentioned problems. For example, an elliptical or parabolic reflector is placed inside the furnace to concentrate heat in a narrow area and the high-temperature area is narrowed, or a heating element such as carbon that can generate a large amount of heat is used. There are furnaces that narrow the high-temperature area by shortening the length. However, these furnaces have drawbacks such as a complicated structure and the need to create an inert atmosphere when using a carbon heater.

c Purpose Therefore, the present invention solves the above problems by arranging a cold pipe in the upper part of the heating furnace through which cooling water can flow, and has a simple structure and a wide high temperature range. The purpose of the present invention is to provide a heating furnace capable of spinning a narrow and good multi-fiber.

d. Configuration of Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view of a heating furnace showing a first embodiment of the present invention. The electric heating furnace 1 has a hollow cylindrical shape, and has openings on its upper and lower surfaces for passing a multi-fiber preform. A section is formed. Further, on the circumferential wall of the heating furnace 1, a hollow cylindrical hot plate 2 holding a heating element 3 wound in stages is provided.
is located.

Further, a water-cooled pipe 4 shown in FIG. 3 is disposed at the upper opening of the electric heating furnace 1, and the water-cooled pipe is
A hollow cylindrical part 4a formed of a metal with good thermal conductivity such as copper, through which the multi-fiber preform passes, and a disc-shaped part for supporting the hollow cylindrical part 4a in the opening of the electric heating furnace 1. It consists of a collar portion 4b and a copper pipe 5 wound around the outer periphery of the hollow cylindrical portion 4a in multiple layers and through which cooling water flows.

Further, both ends of the copper pipe 5 are connected to the flange portion 4b.
The cooling water passes through holes 9a and 9b provided in the copper pipe 5 and is connected to a cooling water tank (not shown), and the cooling water is circulated within the copper pipe by a pump or the like.
and the cylindrical portion 4a are bonded together by brazing 7 so that cooling by the cooling water is sufficiently transmitted to the cylindrical portion 4a.

FIG. 6 shows a water-cooled pipe 1 showing a second embodiment of the present invention.
1 is a perspective view of FIG.

This water cooling pipe 11 is composed of a cylindrical portion 4a, a collar 4b, a jacket 10, and copper pipes 5a and 5b.

The inside of the jacket 10 is hollow, and cooling water can be stored therein. Cooling water enters through a copper pipe 5a, and the tip of the copper pipe 5a forms a ring around the cylindrical portion 4 in the jacket 10.

The ring part of the copper pipe 5a has 10 to 15 holes 12 for blowing out cooling water downward, and the cooling water flowing through the copper pipe 5a flows through the holes 12 into the jacket 10. It is filled. The cooling water in the jacket 10 exits to the outside through the other outlet, the copper pipe 5b.

As the cooling water passes through the jacket 10, the cylindrical portion 4a is uniformly cooled, and a temperature distribution in the furnace having a sharp peak as shown in FIG. 2 is obtained.

Since the jacket 10 of the water cooling pipe 11 is uniformly filled with cooling water, the cylindrical portion 4a is cooled uniformly. As a result, compared to the water-cooled tube of the first embodiment in which the copper pipe 5 is wound, the temperature distribution in the circumferential direction is more uniform.

e Effect of the Example When measuring the temperature distribution inside the furnace in which the water-cooled pipes 4 and 11 are not installed at the top of the furnace, as shown in Fig. 5, the upper end of the furnace is also high temperature, and the preform becomes thinner. However, the temperature rises gently until it reaches its maximum temperature, and then slowly decreases toward the bottom of the furnace.

On the other hand, when we measured the temperature distribution in the vertical direction at the center of the heating furnace 1 with the water-cooled pipes 4 and 11 installed at the top of the furnace, we found that the inside of the water-cooled pipes 4 and 11 was relatively The temperature is low, and the temperature begins to rise around the time it exits the water-cooled tube 4, forming a sharp peak, and then slowly decreases.

Compared to the temperature distribution in a furnace without the water cooling pipes 4 and 11 installed, the shape is closer to the ideal temperature distribution in the furnace shown in FIG.

f Effects In the present invention, as configured as described above, the temperature distribution in the furnace starts to rise suddenly from the vicinity of exiting the water-cooled tube, so that a sharp peak is formed.

As a result, when the preform is spun, it is placed inside the water-cooled tube before it is deformed into a thinner material, so it is not exposed to high temperatures, reducing undesirable effects such as glass crystallization. can do.

Furthermore, since the temperature is rising sharply, the range in which fusion starts is shortened, and it is possible to eliminate the problem of trapping bubbles that would otherwise occur if the fusion start portion was long.

By installing the water-cooled pipe, the range of the high-temperature section moves downward, thereby shortening the length of the high-temperature section as a whole. As a result, the spun fibers are quickly taken out of the furnace and are less exposed to the high temperature section for a long time. Therefore, the trapped air bubbles are less likely to expand due to high temperatures and cause blemishes.

As a result, a good multi-fiber without blemish can be spun.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of a heating furnace showing the first embodiment of the present invention, Fig. 2 is a temperature distribution diagram in the furnace when the present invention is implemented, and Fig. 3 is a water-cooled pipe of the first embodiment. FIG. 4 is a diagram of temperature distribution in an ideal multi-fiber spinning heating furnace, FIG. 5 is a diagram of temperature distribution in a furnace without water-cooled tubes, and FIG. FIG. 7, a perspective view of the water-cooled pipe, is a sectional view of the water-cooled pipe of the second embodiment. 1... Heating furnace, 2... Hot plate, 3... Heating element, 4
...water-cooled pipe, 5 ... copper pipe, 6 ... preform, 7 ... wax, 8 ... spun fiber,
10...jacket.

Claims (1)

[Claims for Utility Model Registration] A heating furnace for spinning optical fibers with an optical fiber preform rod disposed at the center of a heating element, a water-cooled pipe arranged above the heating furnace to surround the optical fiber preform rod. A heating furnace for optical fiber spinning, characterized in that a heating furnace is provided with.