JP7234182B2 - Drawing method for glass base material - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method of drawing a glass preform for an optical fiber, which heats the glass preform and pulls the end to form a drawn shape at the end.

A glass preform for an optical fiber is prepared so that the end portion of the preform is formed into a drawn shape as shown in FIG. 1 so that the drawing process can be carried out smoothly. The process of processing the edge of the base material in this way is called a "drawing" process.
In the drawing process, the drawing of the glass base material is started by heating and drawing down the drawn portion. It is preferable because it causes little loss of time and loss of the glass base material. For example, in the shape shown in FIG. 1, the taper length is often the distance C between the position A where the target outer diameter of the tip is obtained and the position B where the tapered portion starts. As the tip diameter, it is common to use the outer diameter D of the tip of the tapered portion. The position B where the tapered portion starts is generally a position where the outer diameter is 98% of the outer diameter of the straight body portion of the glass base material, but these often change as appropriate depending on the shape of the glass base material, the drawing method, and the like. . An example of the drawing method is disclosed in Patent Document 1.

Patent No. 6302833

An example of a drawing apparatus is shown in FIG. A glass base material 1 is suspended from a lifting device 4 via a connecting member 2 and a suspension shaft 3 . A heating furnace 5 is composed of a heater 6 , a heat insulating material 7 and a chamber 8 . A carbon heater is generally used as the heater 6 because a heater capable of heating to a high temperature of about 2000° C. is required to melt the glass base material 1 . Since carbon is oxidized and worn in the atmosphere at 500° C. or higher, the inside of the heating furnace 5 must be an atmosphere of an inert gas such as nitrogen. , an upper gas seal 9 and a lower gas seal 10 are provided. A take-off shaft 11 is connected to the lower part of the glass base material 1 , and the take-off shaft 11 is gripped by take-off rollers 12 .
Under such a configuration, by rotating the take-up roller 12 and pulling down the lower portion of the heated glass base material 1, the diameter of the heated portion is reduced, and drawing can be performed. Although not shown, the temperature of the heater 6 is measured by a radiation thermometer or the like.

A drawing method for a glass base material will be described with reference to FIG.
A drawing apparatus as shown in FIG. 2 is used as the drawing apparatus, but in FIG. there is
The glass base material 1 has an effective portion 13 effective as a base material and an ineffective portion 15 adjacent to the effective portion 13 . The end of the non-effective portion 15 is connected to the take-off shaft 11 and pulled down by rotating the take-off roller 12 . The glass base material 1 is set in the drawing device so that the boundary portion 14 between the effective portion 13 and the non-effective portion 15 is located approximately in the middle of the heater 6 in the height direction (see FIG. 3(a)).

Heating is started by the heater 6, and when the heating temperature rises to 2000° C. or higher, the temperature of the glass base material 1 rises and softens. Due to this temperature rise of the glass base material 1, the region between broken lines 16 and 17 in FIG. 3(b) can be deformed.
After heating in this manner, the take-up roller 12 is rotated to pull down the lower end (the end of the non-effective portion 15) of the glass base material 1 (see FIG. 3(c)). As a result, the boundary portion 14 moves to the lower portion of the heater 6 while decreasing in diameter, and a constricted portion having a constricted shape with the constricted boundary portion 14 as a constriction end is formed on the effective portion 13 side of the boundary portion 14 ( See Figure 3(d)). On the other hand, the non-effective portion 15 side from the boundary portion 14 is thermally fused and removed.

In this example, the lower end of the base material is pulled down by the take-up roller, but there is also a method of gripping the lower end of the base material with a chuck and pulling down the chuck itself. Further, in this example, the constricted portion is formed by pulling down the lower end of the glass base material while heating the lower part of the glass base material. Alternatively, the drawn portion may be formed on the upper end side of the base material by pulling up the upper end while heating the upper part of the base material.

However, in the method described in Patent Document 1, in order to make the outer diameter of the tip sufficiently thin, a very long pulling amount with a roller or a chuck is required, and from the point of view of device size, parts availability, cost, etc. Not realistic. Even if a sufficient amount of tension can be secured, the tapered portion also becomes long, so it is difficult to meet the requirements for the drawing shape that requires a tapered portion with a short length.
For this reason, in order to form a drawn portion that satisfies the customer's request, after drawing with a drawing machine, additional processing such as additional tip drawing with a glass lathe is performed. Due to this additional processing, the cost of workers, equipment, gas, etc., increases. This was one of the reasons for the increase in costs because it entailed dangers such as damage to equipment and injury to personnel.

The present invention has been made in view of such problems, and provides a drawing method for a glass base material that can form a tapered portion with a small tip diameter and a short length by a simple and inexpensive method. The purpose is to

In order to solve the above-described problems, the method for drawing a glass base material of the present invention is a method of drawing a glass base material by heating the glass base material with a heater and pulling the glass base material to form a drawn shape in a heating portion. A drawing method, comprising: a first drawing step of drawing the glass base material while heating the glass base material with the heater at a first heating temperature; and a second drawing step of heating the heater again at the second heating temperature to draw the glass base material.
Further, in the present invention , in the first drawing step of drawing the glass base material, the distance for drawing the glass base material is 0.5 to 2.5 times the outer diameter of the drawing target position of the glass base material. preferably.
In the present invention, it is preferable that the first heating temperature is 2000°C or higher, the cooling temperature is 1800°C or lower, and the second heating temperature is 1900°C or higher.
Furthermore, in the present invention, one or a plurality of additional cooling steps and additional drawing steps may be additionally provided following the second drawing step.

In the present invention, a first drawing step of drawing the glass base material while heating the glass base material with a heater at a first heating temperature, a cooling step of stopping the drawing and lowering the temperature of the heater to a predetermined cooling temperature, By heating the heater again at the second heating temperature and performing the second drawing step of drawing the glass base material, a tapered portion with a small tip diameter and a short length can be formed by a simple and inexpensive method.

It is a figure explaining an example of diaphragm shape. It is a schematic sectional drawing which shows the structural example of a drawing apparatus. It is the schematic which demonstrates a conventional drawing method in order later on. BRIEF DESCRIPTION OF THE DRAWINGS It is the schematic which demonstrates the drawing method of this invention in order later on.

As a result of intensive study, it was found that in the drawing method using the conventional drawing machine, the glass base material is heated not only at the target part of the drawing process but also in the vicinity of the target part because the surroundings are heated by a heater with heat insulation. are doing. Therefore, the viscosity of the glass base material is low not only in the target part of the drawing process, but also in the surrounding area. It turned out that there is
In order to raise the temperature of only the target part for drawing, it is possible to reduce the heat insulating material around the heater part so that the heating range is not widened, but in that case, the thermal efficiency will deteriorate and the cost will increase. In addition to the rise, adverse effects such as increased thermal damage to peripheral devices occur.

Therefore, in the present invention, as shown in FIG. 4, when the glass base material 1 is drawn while being heated by a heater, the boundary portion 14 between the effective portion 13 and the non-effective portion 15 of the glass base material 1 is It is set in the drawing device so as to be positioned approximately in the middle of the heater 6 in the height direction (see FIG. 4(a)).
After that, heating is started by the heater 6, and when the heating temperature rises to 2000° C. or higher, the temperature of the glass base material 1 rises, and the area between the broken lines 16 and 17 softens and becomes deformable (FIG. 4(b)). reference). The position of the dashed line 16 is the drawing target position at which drawing is started.
After that, the first squeezing step (see FIG. 4(c)) is performed while heating the heater at a high temperature of 2000 ° C or higher, and then the squeezing is temporarily stopped and the temperature of the heater is lowered to 1800 ° C or less. 4(d)) is performed, and the second squeezing step (see FIGS. 4(e) and 4(f)) is performed in which the heater is again heated to a high heating temperature for squeezing.
In the first drawing process, after a short drawing process is performed, the heater temperature is lowered to cool the glass base material, and then the glass base material is heated again. By heating intensively, it is possible to form a short tapered portion with a narrow tip, as shown in FIG. 4(g).

The method for drawing a glass base material according to the present invention will be described in more detail below.
The following embodiments are examples, and the invention according to the claims is not limited to these embodiments, and various aspects are possible. Furthermore, not all combinations of features described in the following embodiments are essential to the means for solving the problems.

FIG. 2 shows an example of a drawing apparatus used for drawing the glass base material of this embodiment.
A glass base material 1 is suspended from a lifting device 4 via a connecting member 2 and a suspension shaft 3 . A take-off shaft 11 is connected to the lower part of the glass base material 1 , and the take-off shaft 11 is gripped by take-off rollers 12 . Under such a configuration, drawing can be performed by rotating the take-up roller 12 and pulling down the lower portion of the glass rod 1 heated by the heater 6 .

In FIG. 4, the lower part of the glass base material 1 and the heater 6 are extracted from the overall structure of the drawing apparatus shown in FIG. 2, and the rest is omitted. The glass base material 1 has an effective portion 13 and an ineffective portion 15 adjacent to the effective portion 13, and the boundary portion 14 between the effective portion 13 and the ineffective portion 15 is positioned approximately in the middle of the heater 6 in the height direction. It is set in the drawing machine.

After setting the glass base material 1 at a predetermined position, heating by the heater 6 is started to raise the heating temperature to 2150° C. as the first drawing step. After the glass base material 1 is softened, the take-up roller 12 is rotated to pull down the lower end of the glass base material 1 . In this case, the lowering amount of the lower end of the glass base material 1 in the first drawing step is preferably 0.5 times or more and 2.5 times or less as large as the outer diameter of the drawing target position of the glass base material 1 . This is because if the amount of drawing down is too small, the necessary diameter reduction cannot be achieved in the first drawing process, but if the amount of drawing down is too large, the diameter will be excessively reduced and the taper length will become too long. be.

After the first drawing process, as a cooling process, the heating of the heater 6 and the rotation of the take-up roller 12 are stopped, and the heating temperature by the heater 6 is lowered to 1800° C. or less. As a result, the diameter-reduced portion formed in the first drawing step is solidified and is less likely to deform.
After the cooling step, as the second drawing step, heating by the heater 6 is restarted to raise the heating temperature to 2000° C., and when the diameter-reduced portion formed in the previous first drawing step is softened, the take-up roller 12 is moved. By rotating again, the lower end of the glass base material 1 is pulled down. In this case, the amount of lowering the lower end of the glass base material 1 in the second drawing process may be such that the boundary between the lower end of the take-up shaft 11 and the glass base material 1 approaches the take-up roller 12 and the drawing is no longer possible. Around 1000mm is a standard.

In this way, the glass base material is heated to form a short diameter-reduced portion once, cooled, and then the heating temperature is raised again and drawing is performed again. Since the material softens exponentially, drawing can be performed by concentrating only on the central portion of the short diameter-reduced portion, making it possible to shorten the taper length and narrow the tip diameter.
Such a drawing process may be performed continuously after the drawing process of the glass base material. Moreover, the same effect can be exhibited even if it is carried out not at the lower end of the glass base material but at the upper end or the central portion. Further, the position of the glass base material may be changed between the first drawing process and the second drawing process.
In addition, by stopping the drawing down in the second drawing step in the present invention, cooling and reheating, the same effect can be exhibited even if additional drawing steps such as the third and fourth are performed, and the taper length can be shorter.

A glass base material 1 having an outer diameter of 150 mm was drawn using the drawing apparatus shown in FIG. The outer diameter of the glass base material 1 at the drawing target position was 150 mm. A carbon heater having an inner diameter of 250 mm and a height of 210 mm was used as the heater 6 . The glass base material 1 was set in the drawing apparatus so that the boundary portion 14 between the effective portion 13 and the non-effective portion 15 was located substantially in the middle of the heater in the height direction.

[Comparative Example 1]
First, as Comparative Example 1, the heater 6 heated to 2150° C. at a rate of temperature increase of 60° C./min. After reaching 2150° C., the lower end of the glass base material 1 was lowered by 1000 mm while maintaining the temperature to form a drawn portion.

[Example 1]
In Example 1, the heater 6 heated to 2150° C. at a rate of 60° C./min. After reaching 2150° C., the lower end of the glass base material 1 was lowered by 50 mm while maintaining the temperature. After that, the temperature maintenance of the heater 6 was stopped and the temperature was lowered to 1650°C. Again, the heater 6 heated up to 2000° C. at a rate of temperature increase of 60° C./min. After reaching 2000° C., the temperature was maintained and the lower end of the glass rod 1 was lowered by 1000 mm to form a constricted portion.

[Example 2]
In Example 2, the heater 6 heated up to 2150° C. at a rate of 60° C./min. After reaching 2150° C., the lower end of the glass base material 1 was lowered by 400 mm while maintaining the temperature. After that, the temperature maintenance of the heater 6 was stopped and the temperature was lowered to 1650°C. Again, the heater 6 heated up to 2000° C. at a rate of temperature increase of 60° C./min. After reaching 2000° C., the lower end of the glass rod 1 was lowered by 1000 mm while maintaining the temperature to form a constricted portion.

[Example 3]
In Example 3, the heater 6 heated up to 1950° C. at a rate of 60° C./min. After reaching 1950° C., the lower end of the glass base material 1 was pulled down by 200 mm while holding the temperature to draw, but the glass base material 1 was not softened and could not be pulled down.

[Example 4]
In Example 4, the heater 6 heated up to 2150° C. at a rate of 60° C./min. After reaching 2150° C., the lower end of the glass base material 1 was lowered by 200 mm while maintaining the temperature. After that, the temperature maintenance of the heater 6 was stopped and the temperature was lowered to 1750°C. Again, the heater 6 heated up to 2000° C. at a rate of temperature increase of 60° C./min. After reaching 2000° C., the temperature was maintained and the lower end of the glass rod 1 was lowered by 1000 mm to form a constricted portion.

[Example 5]
In Example 5, the heater 6 heated up to 2150° C. at a rate of 60° C./min. After reaching 2150° C., the lower end of the glass base material 1 was lowered by 200 mm while maintaining the temperature. After that, the temperature maintenance of the heater 6 was stopped and the temperature was lowered to 1650°C. Again, the heater 6 heated up to 1880° C. at a heating rate of 60° C./min. After reaching 1880° C., drawing was attempted by lowering the lower end of the glass rod 1 by 1000 mm while maintaining the temperature, but the glass base material 1 was not softened and could not be lowered.

[Example 6]
In Example 6, the heater 6 heated up to 2150° C. at a rate of 60° C./min. After reaching 2150° C., the lower end of the glass base material 1 was lowered by 200 mm while maintaining the temperature. After that, the temperature maintenance of the heater 6 was stopped and the temperature was lowered to 1650°C. Again, the heater 6 heated up to 2000° C. at a rate of temperature increase of 60° C./min. After reaching 2000° C., the temperature was maintained and the lower end of the glass rod 1 was lowered by 1000 mm to form a constricted portion.

[Example 7]
In Example 7, the heater 6 heated up to 2150° C. at a rate of 60° C./min. After reaching 2150° C., the lower end of the glass base material 1 was lowered by 200 mm while maintaining the temperature. After that, the temperature maintenance of the heater 6 was stopped and the temperature was lowered to 1650°C. Again, the heater 6 heated up to 2000° C. at a rate of temperature increase of 60° C./min. After reaching 2000° C., the lower end of the glass rod 1 was lowered by 200 mm while maintaining the temperature. After that, the temperature maintenance of the heater 6 was stopped and the temperature was lowered to 1650°C. Further, the heater 6 heated up to 2000° C. at a heating rate of 60° C./min. After reaching 2000° C., the lower end of the glass rod 1 was lowered by 1000 mm while maintaining the temperature to form a constricted portion.

Under the conditions of Comparative Example 1 and Examples 1 to 7, the glass base material 1 was drawn, and the taper length was measured. The taper length was the length from the position where the outer diameter was 97% of the outer diameter of the original glass base material of 150 mm to the position where the tip diameter was 20 mm. Further, for Examples 3 and 5 in which the pull-down could not be completed, the process could not be completed. These results are summarized in Table 1.

Comparative Example 1 was produced by a conventional drawing method, and the taper length was as long as 552 mm, requiring additional machining with a lathe or the like.
The taper lengths of Examples 1 and 2 were 445 mm and 413 mm respectively, which were shorter than those of Comparative Example 1, but were slightly longer. In both cases, after performing the first drawing process, the second drawing process is performed after the cooling process. Therefore, the effect of the present invention was not sufficiently exhibited. Therefore, the drawing distance in the first drawing step is preferably 0.5 to 2.5 times the outer diameter of the drawing target position of the glass base material, thereby shortening the taper length.

In Example 3, the heating temperature in the first drawing process is 1950 ° C., which is lower than 2150 ° C. in other examples. Since the temperature was lower than 2000° C., the glass base material was not sufficiently softened and the drawing process could not be completed. Therefore, the heating temperature in the first drawing step is preferably 2000° C. or higher, and the heating temperature in the second drawing step is preferably 1900° C. or higher. can be done.

In Example 4, the temperature in the cooling process was 1750° C., which was higher than 1650° C. in other examples, and the glass base material could not be sufficiently solidified. Although the length was shorter than 552 mm in Comparative Example 1, it was slightly longer at 392 mm. Therefore, when the cooling temperature in the cooling process is 1700° C. or less, it was found that the present invention can appropriately exhibit the effect and shorten the taper length.

In Example 6, the heater temperatures in the first drawing process, the cooling process, and the second drawing process were respectively 2150° C., 1650° C., and 2000° C., and the drawing distance in the first drawing process was 200 mm, all of which were appropriate. , the taper length could be sufficiently shortened to 285 mm.
In Example 7, after the first drawing process, cooling process, and second drawing process, an additional cooling process and an additional drawing process (third drawing process) were performed. It was possible to shorten the taper length to a short 280 mm.
It should be noted that the present invention is not limited to the above-described embodiments, and can be freely modified and improved as appropriate.

A: Target tip outer diameter,
B: the position where the tapered portion starts,
C: taper length,
D: the outer diameter of the tip of the tapered portion,
1: glass base material,
2: connecting member,
3: shaft,
4: lifting device,
5: heating furnace,
6: heater,
7: thermal insulation,
8: chamber,
9: top gas seal,
10: lower gas seal,
11: take-up shaft,
12: take-up roller,
13: effective part,
14: Boundary,
15: non-effective portion,
16, 17: dashed lines.

Claims (4)

A method for drawing a glass base material, wherein a drawn shape is formed in a heating portion by pulling the glass base material while heating the glass base material with a heater, wherein the glass base material is heated to a first heating temperature with the heater. a cooling step of stopping the drawing and lowering the temperature of the heater to a predetermined cooling temperature; heating the heater again at the second heating temperature to heat the glass base material; A drawing method for a glass base material, comprising: a second drawing step of drawing the base material. 2. The method according to claim 1, wherein in the first drawing step of drawing the glass base material, the distance for drawing the glass base material is 0.5 times or more and 2.5 times or less of the outer diameter of the drawing target position of the glass base material. A drawing method for the glass base material described. 2. The method for drawing a glass base material according to claim 1, wherein the first heating temperature is 2000[deg.] C. or higher, the cooling temperature is 1800[deg.] C. or lower, and the second heating temperature is 1900[deg.] C. or higher. 2. The method for drawing a glass base material according to claim 1, further comprising one or more additional cooling steps and additional drawing steps following the second drawing step.

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