JPS61101429A - Production of glass tube - Google Patents

Abstract

PURPOSE:In depositing glass fine particles on a mandrel, to produce a quartz glass tube having low water content and a smooth inner wall face, by using the mandrel made of ZrO2, and specifying bulk density of the deposited material. CONSTITUTION:As the mandrel 3 is rotated, the glass fine particles 8 in a soot state are jetted to the mandrel by the oxyhydrogen flame 6, to form the deposited material 9. In the operation, the mandrel 3 is made of ZrO2, and the bulk density of the deposited material is adjusted to =0.2g/cm<3>-=0.7g/cm<3>. Then, the deposited material 9 is extracted from the mandrel 3, dehydrated, and calcined. Consequently, a high-quality quartz glass tube having a smooth inner face and low water content is obtained and it is used as a clad material for optical fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a method for manufacturing a high-quality glass tube, and more particularly to a method for manufacturing a silica-based glass tube that contains a small amount of water and has a smooth inner wall. The glass produced by the method of the present invention can be suitably used as a cladding glass for an optical fiber, and further can be suitably used as a cladding glass for a single mode fiber which requires an extremely low water content/water content.

(Prior Art) Conventionally, as a method for manufacturing a base material for a quartz-based glass tube or an optical fiber, there is a so-called external method as shown in Japanese Patent Application Laid-Open No. 48-75522.

In this method, particulate glass (soot) such as sto produced by a flame hydrolysis reaction of a glass raw material such as 5ICt4 is placed on the outside of a rotating refractory starting material such as carbon, quartz glass, or alumina (referred to as a mandrel). After a predetermined amount has been deposited, the deposition is stopped and the mandrel is pulled out. The obtained pipe-shaped soot body is sintered in a high-temperature electric furnace to melt and vitrify it to obtain pipe-shaped glass.

(Problems to be Solved by the Invention) A drawback of the above-mentioned external mounting method is that the inner wall of the soot is easily scratched after the mandrel is pulled out, and therefore the inner wall of the glass tube after sintering is smooth. Sometimes it is difficult to obtain something with a positive aspect.

In addition, in order to prevent the inner wall of the soot pipe from being scratched,
In the process of depositing soot, the flame temperature is set high,
If the bulk density of the soot body is increased and the soot body is deposited, it becomes difficult to remove the mandrel, and it also becomes difficult to perform sufficient dehydration in the subsequent sintering process.

The purpose of the present invention is to improve the conventional external fitting method, eliminate the above-mentioned drawbacks, and create a high-quality glass tube with a smooth inner wall, easy mandrel drawing, and extremely low moisture content. The object of the present invention is to provide a method for manufacturing a glass tube.

(Means for solving the problem) The present inventors used zirconia (zirconium oxide Zr01), which was not previously known as a mandrel, and
Moreover, it has been found that the above object can be achieved by depositing soot to have a specific bulk density.

That is, in the present invention, fine particulate glass produced by a flame hydrolysis reaction of a raw material for forming a vapor phase glass is deposited on a starting material to obtain a deposited body, and then, after the starting material is extracted from the deposited body, , a method of dehydrating and sintering the deposit, using zirconia as the starting material, and depositing the deposit at a bulk density of 0.2 f/aw" or more and α71/as" or less. A method for manufacturing a tube is provided.

The manufacturing method of the present invention will be explained below with reference to the drawings.

FIG. 1 is a diagram schematically explaining one embodiment of the present invention, in which 1 is a chuck of a pulling machine, 2 is a dummy rod, and 5 is a diagram schematically explaining one embodiment of the present invention.
4 is a hole for mechanically connecting the dummy rod 2 and the mandrel 3. A pin is inserted into this hole 4 to fix the mandrel 5. 4 is a sleeve made of quartz glass, and 6 is an oxyhydrogen burner, into which gas phase raw materials for glass synthesis such as "C4,01", "N", etc. are introduced. 7 is a flame, inside which soot 8 is generated,
Soot 8 is deposited on the mandrel 3 in a semi-sintered state. 9 is a soot deposit. At this time, mandrel 3
is rotated by chuck 1 and pulled up at a constant speed.

The first feature of the method of the present invention is that a zirconia tube is used as the mandrel 3. Zirconia is difficult to wet with glass, and it is difficult for them to react with each other even at very high temperatures. Furthermore, since the coefficient of expansion of zirconia is larger than that of other refractories such as alumina and carbon, the mandrel contracts greatly during the cooling process after soot is deposited using flame, making it easier to pull out the mandrel. Furthermore, zirconia is relatively stable even in oxidizing or reducing atmospheres, so
No material deterioration occurs during soot synthesis. Furthermore, since the vapor pressure of zirconia itself is low, it does not cause contamination, which is preferable.

The shape of the zirconia used as the mandrel is preferably tubular because it is difficult to crack due to its thermal history.

The second feature of the present invention is that the bulk density during soot deposition is adjusted within a certain range. In the present invention, the bulk density of soot deposited on a zirconia mandrel is α7t.
/a13 or less α2t/country 3 or more is preferable, particularly preferably 0.5t, /am” or less α2 f/ax
"That's all. When the bulk density exceeds 0.7flα1,
Even without using a zirconia mandrel, scratches or cracks on the soot inner wall when the mandrel is pulled out can be reduced, but it becomes difficult to perform sufficient dehydration in the subsequent sintering process. Note that the bulk density herein refers to an average value in a layer having a thickness of about 11 mm in the vicinity of the mandrel.

In the method of the present invention, a soot body can be formed with a relatively small soot bulk density of αyy/at" or less, so the above-mentioned dehydration can be carried out sufficiently, so that high quality glass can be obtained. Can be done.

On the other hand, the bulk density of soot is CL 2 f / am ”
It is not preferable to deposit soot in an improper manner because cracks are likely to occur in the soot body during the deposition process. The bulk density of the soot can be adjusted by adjusting the temperature of the flame during flame hydrolysis or the relative position between the flame and the soot body.

(Example) Example 1 According to the configuration shown in Figure 1, the outer diameter is 20 mm and the wall thickness is 2 m! 11,
A zirconia mandrel with a length of 500 ms was held in a chuck, and while rotating at 10 rpm, the tip of the oxyhydrogen flame burner was set at a position 5 am lateral to the core. The raw materials shown in Table 1 below were charged into the oxyhydrogen flame burner.

Table 1 810 generated in the flame. While soot was being deposited onto the indrel, the mandrel was pulled up at a constant rate of 55 I/hr. When the length of the soot body reached 401 mm, the supply of raw materials was stopped, and after being left at room temperature for more than 1 hour, the mandrel was pulled out by applying force between the mandrel and the quartz glass sleeve. When the bulk density of this soot body was measured, it was found that CL5f/ax"
Met.

By adding fluorine, dehydrating and sintering the obtained tubular soot body in an electric furnace under the conditions shown in Table 2 below,
A fluoridated transparent glass tube was obtained.

Table 5 Regarding the glass tube obtained above, the amount of residual OH groups was measured by measuring the absorbance at a wavelength of 2.7 pm using an infrared spectrophotometer.
It was found that the amount of OH groups was less than ppm, which was less than the detection sensitivity of the device.

Furthermore, the inner wall of the obtained glass tube had few scratches, and when a separately prepared optical fiber core material (high-purity quartz glass) was inserted into the tube and the combined body was heated and melted to join, the interface A glass base material for optical fiber could be produced without any formation of bubbles. When a single mode fiber was made from this base material, the light absorption loss due to residual moisture at a wavelength of 1.38 μm was relatively low at 10 (iB/km).

Example 2 A single mode fiber was produced in the same manner as in Example 1, except that the bulk density during deposition of the soot body was set to [L5f/ex''. The wavelength of the obtained fiber was 1. Absorption loss at 38 μm: 15 dE/k
It was m.

Comparative Examples 1 to 6 The same procedure as in Example 1 was carried out, except that the mandrel material and the bulk density conditions during deposition of the soot body were as shown in Table 3.
A glass for cladding was synthesized, and a fiber was also created in the same manner. These results and the results of Example 1.2 are summarized in Table 3.

Note that - in the table means that the fiber could not be created.

Table 3 In the above examples and comparative examples, pure silica glass is used as the core material, but the core material is quartz glass containing additives such as Go01 and the cladding is silica glass. It goes without saying that the method of the present invention can also be used in the case of silica glass containing additives.

(Effects of the Invention) As is clear from the above explanation and the results of Examples and Comparative Examples, the method of the present invention allows for easy pulling out of the mandrel, less occurrence of scratches, smooth tube inner surface, and water-containing tubes. It is possible to obtain high-quality quartz-based glass tubes in small quantities. Furthermore, by using the glass tube obtained by the method of the present invention as an optical fiber cladding material, an optical fiber with low absorption loss due to OH groups can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating one embodiment of the method for manufacturing a glass tube of the present invention.

Claims (1)

[Claims] After depositing particulate glass produced by flame hydrolysis reaction of a vapor-phase glass-forming raw material on a starting material to obtain a deposit, and then extracting the starting material from the deposit,
In the method of dehydrating and sintering the deposit, zirconia is used as the starting material, and the bulk density of the deposit is 0.
A method for manufacturing a glass tube, characterized by depositing at 2 g/cm^3 or more and 0.7 g/cm^3 or less.