JPH064493B2 - Method for producing optical glass fiber - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for producing an optical glass fiber, and more particularly to a method for producing a flexible multi-fiber for image transmission used in an endoscope or the like.

(Prior Art) A flexible multi-fiber for image transmission generally used for an endoscope or the like is manufactured by an acid elution method as disclosed in US Pat. No. 3,004,368.

Here, a general method for producing a multifiber for image transmission by the acid elution method will be briefly described.

A diameter of 500μ consisting of a core glass with a relatively high refractive index, a clad glass with a relatively low refractive index that covers the periphery, and an acid-soluble glass that covers the surroundings.
A triple-structured single fiber having a length of 200 mm and a length of 200 mm is aligned in a mantle made of an acid-soluble glass pipe to form a multi-fiber preform.

Next, the multi-fiber preform is fed into the heating electric furnace at a constant speed while sealing one end of the outer tube and discharging the air inside the outer 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 is formed at the bottom of the multi-fiber preform where the diameter is sharply reduced. Thin multi-fibers are spun out from the lower end of the down part.

A multi-fiber having a desired diameter is manufactured by pulling the multi-fiber having the small diameter with a roller.

Next, by cutting this multi-fiber into 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 outer tube and acid-soluble glass of the middle part. A multi-fiber for image transmission having flexibility is obtained.

(Problems to be Solved by the Invention) When spinning a multi-fiber preform by heating it in a heating furnace in this way, it is well known that the furnace temperature of the heating furnace greatly affects the performance of the spun multi-fiber. Has been.

Further, the acid-soluble glass constituting the triple-structured single fiber has a sharp change in the viscosity of the glass with respect to temperature, unlike general optical glass physicochemical glass.

The spinning temperature of the multi-fiber is a temperature near the softening point of the glass, and it is desirable to perform spinning at a temperature as low as possible due to the nature of the acid-soluble glass.

However, if the spinning temperature is too low, the viscosity of the glass becomes too high to allow spinning. On the other hand, if it is too high, the viscosity of the acid-soluble glass becomes too low, which causes problems such as the generation of bubbles and crystallization, resulting in a significant inhibition of 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-fiber comes out, at an optimum value for spinning.

The core glass, the clad glass and the acid-soluble glass preferably have the same viscosity at the spinning temperature.

However, it is very difficult to perfectly match the viscosity characteristics of the three types of glass. Further, as described above, the change in viscosity with respect to temperature of the acid-soluble glass is more severe than that of the core glass and the clad glass. It will be lower than that.

As a result, the wire diameter of the spun multifiber is not stable, the shape does not become a perfect circle and becomes an elliptical shape, bubbles occur in the acid-soluble glass, and the transmission characteristics deteriorate. It will cause.

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 an optical glass fiber capable of spinning a high quality multifiber by appropriately controlling the furnace temperature of a heating furnace.

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

Further, the present invention is characterized in that the tensile force per unit cross-sectional area calculated based on the wire diameter of the spun multifiber is used as the tensile force detected during multifiber spinning.

(Operation) During spinning of the multi-fiber, the tensile force acting on the multi-fiber is detected.

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 controlled. To a proper value.

As a result, a good quality multi-fiber having a stable wire diameter can be obtained.

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

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

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

Reference numeral 1 is a multi-fiber preform. The multi-fiber preform 1 comprises a core glass having a relatively high refractive index, a clad glass having a relatively low refractive index which covers the periphery thereof, and an acid-soluble material which further covers the periphery thereof. Diameter made of glass
A triple structure single fiber of 500 μm and length of 200 mm,
Approximately 10,000 in a mantle made of acid-soluble glass pipe
The book is arranged in line.

The upper part of the multi-fiber preform 1 is held by a holder 2 and is suspended, and the holder 2 is placed on a feed table 3 via a load cell 4.

The load cell 4 is for detecting the tensile force during spinning of the multi-fiber, and three load cells 4 are arranged between the feed base 3 and the holder 2 at equal intervals in the circumferential direction of the multi-fiber preform 1. There is.

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 the feed screw 5, and the multi-fiber preform 1 is fed into the heating electric furnace 6 at a predetermined speed by rotating the feed screw 5.

7 is a multifiber which is thinly extended from the neck-down portion 1a of the multifiber preform 1, and 8
Is a roller for pulling the multi-fiber 7, and the multi-fiber 7 having a desired diameter is spun by pulling by the roller 8.

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 a recorder 10.
Is connected to the control unit 11, and the recorder 10 records the diameter of the spun multi-fiber 7.

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 multifiber 7 based on the output signal from the load cell 4 and the output signal from the wire diameter measuring device 9. To do.

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 time lag between the tensile force and the wire diameter such that the multi-fiber 7 is spun from the neck-down portion 1a and moved to the wire diameter measuring device 9. Therefore, the tensile force per unit cross-sectional area at that time can be obtained by dividing the previous tensile force by the time of the shift using the current wire diameter.

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 at the time of spinning calculated by the control unit 11 is output to the recorder 10 and recorded.

Next, the method according to the embodiment will be described together with the operation of the apparatus configured as described above.

First, the feed screw 5 rotates, and the multi-fiber preform 1 supported on the feed base 3 is gradually fed into the heating electric furnace 6 and heated.

Then, the multifibers 7 coming out from the neck-down portion 1a of the heated and softened multifiber preform 1 are pulled by the roller 8, stretched finely 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 obtained by adding the tensile force by the roller 8 to the sum of the weights of the multi-fiber preform 1 and the holder 2.

Therefore, by inputting the output signal of the load cell 4 at the time of multi-fiber spinning to the control unit 11 and calculating it, the net fiber pulling force from which the weights of the multi-fiber preform 1 and the holder 2 are subtracted can be obtained. .

This net fiber pulling force represents the viscosity of the glass of 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. Also, when the temperature is low and the viscosity of the glass is high, spinning must be performed with a large tensile force.

This means that the glass temperature of the neck-down portion 1a can be indirectly obtained by calculating the net fiber pulling force. 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 makes it possible to spin a good-quality multi-fiber 7 having a stable circular diameter and free from bubbles in the acid-soluble glass.

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

In the figure, the tensile force is the net fiber tensile force obtained by subtracting the weight of the multi-fiber preform 1 and the weight of the holder 2.

As the multifiber 7 is spun, the weight of the multifiber preform 1 gradually decreases. Therefore, the load subtracted from the output of the load cell 4 needs to be changed with the passage of time.

For the load to be subtracted, the output of the load cell 4 immediately before spinning is usually used, and thereafter, the value obtained by calculation from the spinning speed is added.

In this case, the net fiber pulling force is from a few Kg to a dozen Kg.
And the decrease of the multi-fiber preform 1 due to spinning is a value of 100 g to several hundred g, the above method is sufficient.

The net fiber pulling force shows a change similar to the change in wire diameter, as is apparent from FIG.

Further, at the start of spinning, the time is shifted by the time during which the spun multifiber 7 moves from the neck-down portion 1a of the multifiber preform 1 to the wire diameter measuring device 9.

The net fiber pulling force is proportional to the viscosity of the glass when it is stretched in the neck-down portion 1a and the amount of glass to be pulled.

Therefore, if the wire diameter is large, a large pulling force is required in order to stretch more glass. This can be confirmed from the fact that the tensile force per unit cross-sectional area of the multifiber 7 is calculated from the data shown in FIG.

On the other hand, when the temperature of the heating electrification furnace 6 is raised to perform spinning, the tensile force becomes small. On the contrary, when the temperature is lowered, the tensile force becomes large, and finally the spinning becomes impossible.

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

When the furnace temperature is raised to 740 ° C by 10 ° C and spinning is performed, the tensile force is 2
It decreased to Kgf, and spun multifibers caused blemishes, etc., and the quality deteriorated.

Thus, a slight increase in temperature has a great influence on the performance of the spun multi-fiber 7.

In this example, by controlling the temperature of the heating electric furnace 6 so that the tensile force was always 5 Kgf or more, the good quality multi-fibers 7 could always be spun.

In the present embodiment, the case where the wire diameter of the multifiber 7 is measured by the wire diameter measuring device 9 has been described. However, if the manufacturing device is configured so that the multifiber 7 is spun with a constant wire diameter in advance, it is simply pulled. It is also possible to calculate the temperature of the neck-down portion 1a from the force.

Further, the present invention can be applied not only to spinning of the multi-fiber 7 by the acid elution method, but also to spinning of silica glass fiber used for optical communication, and spinning of optical glass fiber by a general rod-in-tube method.

(Effects of the Invention) As described above, according to the method for producing an optical glass fiber of the present invention, a high-quality multifiber having a stable wire diameter can be spun.

[Brief description of drawings]

FIG. 1 is a schematic view of an apparatus for explaining the present invention, and FIG. 2 is an explanatory view showing an example of recording wire diameter and tensile force in this embodiment. In the figure, 1 is a multi-fiber preform, 1a is a neck-down part, 2 is a holder, 3 is a feed table, 4 is a load cell, 5 is a feed screw, 6 is a heating electric furnace, 7 is a multi-fiber, and 8 is a roller. , 9 is a wire diameter measuring device, 10 is a recorder,
Reference numeral 11 is a control unit.

Claims (2)

[Claims] 1. An optical glass in which a multifiber preform is fed into a heating furnace, and the multifibers coming out from a neck-down portion of the heated and softened multifiber preform are stretched by a tensile force to be thinly drawn and spun into a desired diameter. In the fiber manufacturing method, the tensile force during multi-fiber spinning is detected, the temperature of the neck-down portion of the multi-fiber preform is calculated based on the detected tensile force, and the heating furnace is based on this calculation result. The method for producing an optical glass fiber is characterized in that the furnace temperature is controlled to a predetermined value. 2. The method for producing an optical glass fiber according to claim 1, wherein the tensile force detected during multifiber spinning is a tensile force per unit cross-sectional area calculated based on the wire diameter of the spun multifiber.