JPH0558648A - Method for vitrifying porous glass preform - Google Patents

Abstract

PURPOSE:To facilitate degassing and prevent air bubbles from remaining by transparently vitrifying a rodlike porous glass preform while successively thermally melting the glass preform from the central position in the direction of both the axial ends. CONSTITUTION:The tip of a rodlike substrate 2 holding a porous glass preform 1 is connected to the first driving device, vertically held and pulled down to a prescribed position in a heating furnace. The upper heater 3 and the lower heater 4 are simultaneously moved to prescribed positions corresponding to the central part of the preform 1, which is then rotated at 0.1-10 r.p.m. speed. The second driving device is driven while heating the preform at 400-1600 deg.C with the heaters 3 and 4 and the preform 1 is heated and melted from the central position in the direction of the axial ends while moving the heater 3 in the direction of the upper shaft 1 at 0.5-10m/min speed and the heater 4 in the direction of lower shaft of the preform 1 at the same speed. Thereby, the objective preform 1 is transparently vitrified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for transparent vitrification by sequentially heating and melting a rod-shaped porous glass preform from a predetermined position, and particularly to a vertically held porous glass preform (hereinafter referred to as soot body). That is) to a transparent vitrification while heating and melting.

[0002]

2. Description of the Related Art Conventionally, SiCl ₄ or other silicon compounds are heated by an oxyhydrogen flame or other heat source, and soot-like silica fine particles produced by the flame hydrolysis reaction and high temperature thermal oxidation reaction are mixed with silica glass, alumina (Al A technique for producing a hollow rod-shaped soot body supported by a core body by uniformly laminating it on a heat resistant substrate such as ₂ O ₃ ) in the axial direction (JP-A-53-7044).
No. 9, et al., Hereinafter referred to as radial growth method) or a technique for producing a solid soot body by laminating the substrate along the axial direction from the axial end of the substrate (JP-A-52-143037 et al., Hereinafter referred to as axial growth method). ) To produce a soot body as a precursor of the synthetic quartz glass body, and then heating / sintering / melting the soot body in a vacuum or an inert gas atmosphere to obtain a transparent glass body. Methods for producing synthetic quartz glass bodies by phase are known.

[0003]

As a method of heating and melting the soot body to form a transparent glass, the entire length of the soot body is surrounded by a heater or housed in a heating furnace, and the entire length of the soot body is stretched at once. Although the method of heating was adopted, in such a method bubbles are often generated because the gas generated in the soot body is confined,
Not preferable.

For this reason, a method has been adopted in which the rod-shaped soot body is held vertically, and is heated sequentially from the shaft end side at the upper end or the lower end side to the shaft end side at the other side (JP-A-49-9).
523, Japanese Unexamined Patent Publication No. 52-143037 et al.), Even with such a method, as the soot body becomes longer and larger, the gas escape path from one shaft end of the melting start end to the other shaft end becomes unnecessarily long. In addition, since the escape rate is also delayed, the melting rate must be determined accordingly, and not only the productivity will inevitably decrease significantly, but even if the above method is adopted, the gas route Because of this, bubbles tend to remain in the central portion of the transparent glass.

When the gas remains in the central portion in this way, the central portion must be cut and used together with the shaft end even when manufacturing an optical fiber or a semiconductor manufacturing jig. The result is almost impossible.

In view of the above-mentioned drawbacks of the prior art, it is an object of the present invention to provide a vitrification method for a soot body which facilitates degassing during vitrification without lowering productivity. Another object of the present invention is that even if bubbles are generated, the generation of the bubbles is biased toward the shaft end side so that practical problems as a product do not occur.

[0007]

According to the present invention, the soot body is not heated and melted from the shaft end side, but rather the middle position of the soot body excluding the shaft end, more specifically, both shaft ends from substantially the center position. It is characterized by performing transparent vitrification while sequentially heating and melting in the direction.

In this case, the soot body is manufactured based on the radial growth method and is hollow rod-shaped body penetratingly supported by the heat-resistant substrate, or one end supported on the heat-resistant substrate is manufactured based on the axial growth method. Any of the solid rods described above can be applied. Further, the soot body moving means may be configured to move either one or both of the soot body itself and the heating and melting means.

[0009]

In the present invention, the soot body is heated and melted from the middle position excluding the shaft end, more specifically, from the substantially central position toward both shaft ends. The number of passages facing toward, and the gas vent passage length is 1
As a result, the degassing resistance is greatly reduced by the power of .alpha., So that even if the heating and melting rate is increased correspondingly, there is no possibility that bubbles will remain.

Further, according to the present invention, since heating is started from substantially the central portion of the soot body, there is no room for bubbles to remain in the central portion, and degassing is insufficient and even if bubbles remain, the remaining position is It becomes the shaft end side of the end of heating, and simply cutting that part will not cause any practical problems, and the product yield will be greatly improved.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT An embodiment of the present invention will be described in detail below as an example with reference to the drawings. However, unless otherwise specified, the dimensions, materials, shapes, relative positions, etc. of the components described in this embodiment are not intended to limit the scope of the present invention thereto, but are merely illustrative examples. Not too much.

FIG. 1 is a schematic diagram showing an apparatus for producing synthetic quartz glass according to an embodiment of the present invention. This apparatus holds a soot body 1 vertically in a high temperature heating furnace while rotating it about an axis. While surrounding the soot body 1 housed in the heating furnace via a first driving device 5 configured to be movable in the axial direction, a rotating device 6 connected to the driving device 5, and a furnace wall (not shown). It comprises a cylindrical lower heater 4 and an upper heater 3, and a driving device 7 for moving the both heaters in the axial direction of the soot body in a direction away from each other. The upper stage shown in FIG. A method of making the soot body 1 obtained by the above method transparent vitrification, and a lower stage shown in (b) show a method of making the soot body 1 obtained by the axial growth method transparent vitrification.

Next, an experimental example based on this structure will be described in detail. First, the soot body 1 (outer diameter 150 mm, length 1.5 m, weight 11 K obtained by known manufacturing means)
g) is pulled down to a predetermined position in the heating furnace in a state where the upper end of the rod-shaped substrate 2 is connected to the first driving device and held vertically.
Next, the upper heater 3 (inner diameter 200 mm, length 10 mm)
Then, the lower heater 4 (inner diameter 200 mm, length 10 mm) is moved to a predetermined position corresponding to substantially the central portion of the soot body 1 and then the vitrification step is performed.

Next, the soot body 1 is set to 0.1 to 10 rpm.
While rotating with, the upper heater 3 and the lower heater 4
While heating to 400 to 1600 ° C., the second heater drives the upper heater 3 in the upper axis direction of the soot body 1 and the lower heater 4 in the lower axis of the soot body 1 at a speed of 0.5 to 10 mm / min. The soot body 1 was heated and melted in the axial end direction from the central portion while being moved in the direction away from each other, and vitrification was performed.

In order to confirm the effect of the embodiment of the present invention, the upper heater 3 and the lower heater 4 are integrated and the soot body 1 is formed.
Comparative transparent glass body which was made into transparent vitreous by moving from the lower axis direction to the upper axis direction A glass body manufactured according to the above-mentioned example was manufactured. Incidentally, in the comparative example, the moving speed of the heater was set to 1/2 of that in the above-mentioned example, and the vitrification time was set to be twice that in the example.

Then, when two glass bodies each produced by the above-mentioned production procedure were compared and inspected, a glass body having an outer diameter of 80 mm, a length of 1.5 m and a weight of 11 kg was obtained. It was confirmed that air bubbles remained in the central portion of the comparative transparent glass, but the glass body of this example was transparent without the presence of air bubbles.

FIG. 1 (b) shows a method for producing the soot body 1 obtained by the axial growth method. When the transparent glass body produced by the same production procedure as described above was visually confirmed, the glass body was also confirmed. The presence of bubbles was not recognized.

2 and 3 show another manufacturing method. In FIG. 2, the upper heater 3 is fixed and the soot body 1 is lowered at an α speed, while the lower heater 4 is moved at a speed of 2α which is twice the speed. Manufacturing procedure for transparent vitrification while descending, or FIG.
Contrary to the above, while the lower heater 4 is fixed and the soot body 1 is raised at the α speed, the upper heater 3 is doubled by 2α.
The manufacturing procedure for performing transparent vitrification while increasing the speed is shown. (A) shows the vitrification method of the soot body 1 manufactured based on the radial growth method and (b) shows the vitrification method. When the transparent glass body produced by the production procedure was visually inspected, the presence of air bubbles was not observed in the glass body.

[0019]

As described above, according to the present invention, the degassing resistance of the present invention is significantly reduced as compared with the prior art in which heating is performed from the axial direction of one side of the soot body, and accordingly, the heating and melting rate is correspondingly increased. However, there is no risk of bubbles remaining. Further, in the present invention, since heating is started from the substantially central portion of the soot body 1, there is no room for air bubbles to remain in the central portion, and even if air bubbles remain, the remaining position is on the axial end side of the heating end end. In addition, the air bubbles do not remain in the central portion, the product yield is improved, and the time required for transparent vitrification can be greatly shortened as described above, so that the productivity is also improved. And so on.

[Brief description of drawings]

FIG. 1 is a vitrification method for a porous glass preform according to an embodiment of the present invention in which vitrification is performed with the soot body fixed, (a) is a method for producing a soot body obtained by a radial growth method. , (B) a method for producing a soot body obtained by an axial growth method,

FIG. 2 is a vitrification method for a porous glass preform according to an embodiment of the present invention in which vitrification is performed with an upper heater fixed, and (a) is a method for producing a soot body obtained by a radial growth method. , (B) a method for producing a soot body obtained by an axial growth method,

FIG. 3 is a vitrification method for a porous glass preform according to an embodiment of the present invention in which vitrification is performed with a lower heater fixed, and (a) is a method for producing a soot body obtained by a radial growth method. , (B) a method for producing a soot body obtained by an axial growth method,

[Explanation of symbols]

 1 porous glass base material 2 rod-shaped substrate 3 upper heater 4 lower heater

Claims (4)

[Claims] 1. In a method of performing transparent vitrification while sequentially heating and melting a rod-shaped porous glass base material from a predetermined position, the heating start position of the base material is set to an intermediate position excluding the shaft end of the base material, A vitrification method for a porous glass preform characterized by performing transparent vitrification while sequentially heating and melting from the middle position toward both axial ends. 2. The vitrification method for a porous glass base material according to claim 1, wherein the heating start position of the base material is set to a substantially central position of the base material. 3. The method for vitrifying a porous glass preform according to claim 1, wherein the rod-shaped porous glass preform is a hollow rod-shaped body or a solid rod-shaped body supported by a core body. 4. The vitrification method for a porous glass preform according to claim 1, wherein one or both of the rod-shaped porous glass preform and the heating / melting means are sequentially heated and melted while moving in the axial direction of the preform.