JPH0337129A - Production of optical glass fiber - Google Patents

Abstract

PURPOSE:To produce a good-quality multifiber having stable wire diameter by detecting tensile force in multifiber spinning, calculating temperature of neck down part of multifiber preform and controlling furnace temperature in a heating furnace to a prescribed value based on the calculated result. CONSTITUTION:A multifiber preform 1 is retained using a retaining tool 2 through plural load cells 4 on a feed table 3 and fed to the interior of an heating electric furnace 6 at a prescribed rate by a feed screw 5 and a multifiber 7 fed out while finely drawing from a neck down part 1a is drawn by rollers 8 to form the multifiber into a desired diameter. Diameter of the multifiber 7 spun in this time is measured by a measuring device 9 and output to a recorder 10 and control part 1 and simultaneously output from the load cells 4 is sent to the control part 11. In the control part 11, tensile force per unit cross-section in multifiber 7 spinning is calculated by output signal from the load cells and output signal of a diameter measuring device 9 and glass temperature of the neck down part 1a is calculated thereby to control temperature in the heating electric furnace 6 to proper temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a method for manufacturing optical glass fibers, and more particularly to a method for manufacturing flexible multi-fibers for image transmission used in endoscopes and the like.

(Prior Art) Flexible multi-fibers for image transmission, which are generally used in endoscopes, etc., are manufactured by an acid elution method as disclosed in U.S. Patent No. 3.004.368. .

Here, a general method for producing multi-fibers for image transmission using the acid elution method will be briefly explained.

A glass with a diameter of 500 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 covering the periphery.
A multi-fiber preform is prepared by arranging triple-structure single fibers with a length of 20 OIII μm in a mantle made of an acid-soluble glass pipe.

Next, one end of the mantle tube is sealed and the multi-fiber preform is fed into a heating electric furnace at a constant speed while exhausting the air inside the mantle tube.

The multi-fiber preform sent into the heating electric furnace is heated and softened, and by pulling out the softened lower end, a neck-down part where the diameter rapidly decreases is formed at the bottom of the multi-fiber preform. A thin multi-fiber is spun out from the bottom end of the down section.

A multifiber of a desired diameter is produced by pulling this thin multifiber with a roller.

Next, cut this multi-fiber to a certain length, coat both ends with a substance that does not dissolve in acid, immerse the middle part in an acid solution, and melt the mantle and acid-soluble glass in the middle part. A flexible multi-fiber for image transmission is installed (1).

(Problem to be Solved by the Invention) It is well known that when spinning a multi-fiber preform by heating it in a heating furnace, the furnace temperature of the heating furnace greatly affects the performance of the spun multi-fiber. It is being

Furthermore, the acid-soluble glass that constitutes the triple-layered single fiber has a drastic change in viscosity with respect to temperature, unlike optical glass or scientific glass.

The spinning temperature for multi-fibers is around the softening point of glass, and it is desirable to spin at as low a temperature as possible due to the properties of acid-soluble glass.

However, if the spinning temperature is too low, the viscosity of the glass increases and spinning becomes impossible. On the other hand, if it is too high, the viscosity of the acid-soluble glass becomes too low, causing problems such as the generation of bubbles and crystallization, which significantly impairs the performance of the spun multifiber.

Therefore, it is desirable to keep the furnace temperature of the heating furnace, especially the temperature of the neck-down portion where the multi-fibers come out, at an optimum value during spinning.

Further, it is desirable that the core glass, clad glass, and acid-soluble glass have the same viscosity at the spinning temperature.

However, it is very difficult to completely match the viscosity characteristics of the three types of glass, and as mentioned above, the viscosity of acid-soluble glass changes more drastically with respect to temperature than that of core glass and cladding glass. increases, and only the viscosity of acid-soluble glass becomes lower than that of core glass and clad glass.

As a result, the wire diameter of the spun multi-fiber becomes unstable, and the shape becomes oval rather than a perfect circle. In addition, air bubbles are generated in the acid-soluble glass, causing problems such as poor transmission characteristics. cause it to occur.

The present invention has been devised in view of the above circumstances, and an object of the present invention is to provide a method for producing optical glass fibers that can appropriately control the furnace temperature of a heating furnace and spin high-quality multi-fibers.

(Means for Solving the Problems) In order to achieve the above object, the present invention detects the tensile force during multi-fiber spinning, and determines the temperature of the neck-down portion of the multi-fiber nib form based on the detected tensile force. is calculated, and the furnace temperature of the heating furnace is controlled to a predetermined value based on the calculation result.

Another feature of the present invention is that, as the tensile force detected during multi-fiber spinning, a tensile force per unit word area calculated based on the wire diameter of the multi-fiber to be spun is used.

(Function) Detects the tensile force acting on the multi-fiber when spinning the multi-fiber.

Then, the temperature of the neck-down part of the multi-fiber preform is calculated from the detected tensile force, and the furnace temperature of the heating furnace is controlled to a predetermined value based on the calculation result, and the temperature of the neck-down part of the multi-fiber preform is Keep it at an appropriate value.

As a result, a high-quality multi-fiber with a stable wire diameter can be obtained.

In this case, the tensile force per unit area is calculated from the detected tensile force and the wire diameter of the spun fiber, and the temperature of the neck-down part of the multi-fiber preform is calculated from this tensile force per unit cross-sectional area. It is also possible.

(Example) Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a schematic diagram of an apparatus for explaining the manufacturing method according to the present invention.

1 is a multi-fiber preform, and the multi-fiber preform 1 consists 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 covering the periphery. It is constructed by arranging approximately 10,000 triple-structure single fibers made of glass with a diameter of 500 μm and a length of 20,011 mm in a mantle tube formed of an acid-soluble glass pipe.

The upper part of the multi-fiber preform l is held and suspended by a holder 2, and the holder 2 is placed on a feed table 3 via a load cell 4.

The load cells 4 detect the tensile force during spinning of multi-fibers, and three load cells 4 are arranged at equal intervals in the circumferential direction of the multi-fiber preform l between the feed table 3 and the holder 2. There is.

Furthermore, each load cell 4 can measure a load up to 50 kgf, and the total output of each load cell 4 is the sum of the weight of the multi-fiber preform 1, the weight of the holder 2, and the tensile force during spinning. .

The feed table 3 is screwed onto a feed screw 5, and as the feed screw 5 rotates, the multi-fiber preform 1 is fed into the heating electric furnace 6 at a predetermined speed.

7 is a multi-fiber stretched thinly from the neck-down part 1a of the multi-fiber preform l, 8
is a roller that pulls the multi-fiber 7, and by pulling the multi-fiber 7 with the roller 8, the multi-fiber 7 of a desired diameter is spun.

9 is a wire diameter measuring device for measuring the wire diameter of the spun multi-fiber 7, and the output of this wire diameter measuring device 9 is recorded by a recorder lO.
is connected to the control unit 11, and the recorder IO records the wire diameter of the multi-fiber 7 to be spun.

The control unit 11 controls the furnace temperature of the heating electric furnace 6, and calculates the tensile force per unit cross-sectional area during spinning of the multi-fiber 7 based on the output signal from the load cell 4 and the output signal from the wire diameter measuring device 9. calculate.

The tensile force per unit cross-sectional area is obtained by dividing the net tensile force obtained from the load cell 4 by the fiber cross-sectional area obtained from the wire diameter measuring device 9. There is a difference between the tensile force and the wire diameter by the amount of time required for the multi-fiber 7 to be spun from the neck-down portion 1a and moved to the wire diameter measuring device 9. Therefore, by dividing the previous tensile force by the time of the shift using the current wire diameter, the tensile force per unit cross-sectional area at that time can be obtained.

The temperature (viscosity) of the glass in the neck-down portion 1a of the multi-fiber preform 1 is calculated from this tensile force, and the temperature of the heating electric furnace 6 is controlled so that this temperature becomes an appropriate temperature (for example, 730° C.).

The data of the net tensile force during spinning calculated by the control unit 11 is output to the recorder IO and recorded.

Next, the operation of the apparatus having the above configuration and the method according to the embodiment will be described.

First, the feed screw 5 rotates, and the multi-fiber preform l supported on the feed table 3 is gradually fed into the heating electric furnace 6 and heated.

The multi-fibers 7 coming out of the neck-down part 1a of the heated and softened multi-fiber preform 1 are pulled by rollers 8, stretched into a thin fiber, and spun. At this time, the wire diameter of the multi-fiber 7 is constantly measured by the wire diameter measuring device 9.

When spinning the multi-fiber 7, the output of the load cell 4 is:
The value is the sum of the weights of the multi-fiber preform l and the holder 2, plus the tensile force by the rollers 8.

Therefore, by inputting the output signal of the load cell 4 during multi-fiber spinning into the control unit 11 and calculating it, the multi-fiber preform l can be obtained.

The net fiber bow tension can be determined by subtracting the weight of the retainer 2.

This net fiber tensile force represents the viscosity behavior of the glass in the neck-down portion 1a of the multi-fiber preform 1. That is, when the temperature is high and the viscosity of the glass is low, the multi-fiber 7 can be spun with a small tensile force. Furthermore, if the temperature is low and the glass has a high viscosity, spinning must be performed with a large tensile force.

This means that by calculating the net fiber tensile force, the temperature of the glass in the necked-down portion 1a can be determined indirectly. Then, the temperature obtained from the calculation result is compared with the set value, and the temperature of the heating electric furnace 6 is controlled so that the deviation becomes zero. This results in a perfectly circular wire with a stable diameter.

Moreover, it becomes possible to spin a high-quality multi-fiber 7 without generating bubbles in the acid-soluble glass.

An example of the wire diameter and tensile force recorded by the recorder 10 is shown in FIG.

In the figure, the tensile force is the net fiber tensile force after subtracting the weight of the multifiber preform l and the weight of the holder 2.

As the multi-fiber 7 is spun, the weight of the multi-fiber preform 1 gradually decreases, so the load subtracted from the output of the load cell 4 needs to be changed over time.

The load to be subtracted is usually the output of the load cell 4 immediately before spinning, and thereafter a value calculated from the spinning speed is added.

In this case, the net fiber tensile force is from viKg to a few tens of g, and the decrease in the multi-fiber preform l due to spinning is from a hundred g to several hundred g, so one or more methods are sufficient. be.

The net fiber tensile force shows a similar variation as the wire diameter as seen in FIG.

Further, at the start of spinning, the time axis is shifted from the time axis by the time required for the spun multi-fiber 7 to move from the neck-down portion 1a of the multi-fiber preform 1 to the wire diameter measuring device 9.

The net fiber tensile force is proportional to the viscosity and the amount of glass being pulled when the glass is stretched at the neckdown section la.

Therefore, the larger the wire diameter, the greater the tensile force needed to stretch the glass. This can be confirmed by the fact that when the tensile force per unit cross-sectional area of the multi-fiber 7 is calculated from the data in Figure 2, it remains almost constant over time.6 On the other hand, by increasing the temperature of the heating electric furnace 6, When this is done, the tensile force becomes smaller; on the other hand, when the temperature is lowered, the tensile force becomes larger, and eventually spinning becomes impossible.

In the case of this example, the tensile force was 7 gf when the temperature of the heating electric furnace 6 was 730°C. At this temperature, high quality multi-fiber 7 could be spun.

At this point, the furnace temperature is raised by 10°C to 740°C for spinning.

The tensile force decreased to 2 Kgf, and premits etc. were generated in the spun multi-fiber, resulting in deterioration of quality.

In this way, a slight increase in temperature greatly affects the performance of the spun multifiber 7.

In this practical example, by controlling the temperature of the heating electric furnace 6 so that the tensile force was always above 5 Kgfg, it was possible to always spin a high-quality multi-fiber 7.

In this embodiment, the wire diameter of the multi-fiber 7 is measured by the wire diameter measuring device 9. However, if the manufacturing device is configured to spin the multi-fiber 7 in advance to a constant wire diameter, the wire diameter of the multi-fiber 7 can be simply It is also possible to calculate the temperature of the neck-down portion 1a from the force.

Furthermore, the present invention is applicable not only to the spinning of the multi-fiber 7 by the U elution method, but also to the spinning of quartz glass fibers used in optical communications, and the spinning of optical glass fibers, etc., by the general rod-in-tube method.

(Effects of the Invention) As described above, according to the method for producing optical glass fiber according to the present invention! It is possible to spin high-quality multi-fibers with a stable I diameter.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an apparatus for explaining the present invention, and FIG. 2 is an explanatory diagram showing an example of recording the wire diameter and tensile force in this embodiment. In the figure, ■ is the multi-fiber preform, la is the neck-down part, 2 is the holder, 3 is the feed stand, 4 is the load cell, 5 is the feed screw, 6 is the heating electric furnace, 7 is the multi-fiber, and 8 is the roller. , 9 is a wire diameter measuring device, IO is a recorder,
11 is the system (wholesale department).

Claims (2)

[Claims] (1) A multi-fiber preform is sent into a heating furnace, and a tensile force is applied to the multi-fibers that come out of the neck-down part of the heated and softened multi-fiber preform to thin them and spin them into a desired diameter. In the manufacturing method, the tensile force during multi-fiber spinning is detected, the temperature of the neck-down part of the multi-fiber preform is calculated based on the detected tensile force, and the temperature of the neck-down part of the heating furnace is calculated based on the calculation result. A method for producing optical glass fiber, characterized in that the temperature is controlled to a predetermined value. (2) The method for producing optical glass fiber according to claim 1, wherein the tensile force detected during multi-fiber spinning is a tensile force per unit cross-sectional area calculated based on the wire diameter of the multi-fiber to be spun.