JPS603014B2 - Manufacturing method of quartz glass tube with high axial symmetry - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a quartz glass tube having high axial symmetry from a quartz glass blank.

In recent years, the internal CVD method (internal chemical deposition method) and the rod-in-tube method have been applied to the production of silica glass preforms used, for example, in the production of optical communication fibers, and are being put into practical use.

In the internal CVD method, a gas containing silicon tetrachloride, a refractive index modifier such as germanium tetrachloride, and oxygen is introduced into a quartz glass tube with a diameter of about 2 m wide, and the inner wall of the tube is heated. This is a method of obtaining a quartz glass base material by forming a quartz glass layer on the tube, then increasing the temperature further and crushing the quartz glass tube to eliminate the space inside the tube and making it into a solid rod shape.

The rod-in-tube method is a method in which a quartz glass glass tube with a relatively high refractive index is inserted into a quartz glass tube with a low refractive index, and the two are bonded together to obtain a quartz glass base material.

The important conditions for the quartz glass tube used in each of the above methods are that the cross section of the tube is a perfect circle, and that the inner diameter, outer diameter, and wall thickness of the tube are constant along the longitudinal direction.

In other words, if the accuracy of the roundness and diameter of the quartz glass tube is poor, the dimensional accuracy of the optical fiber obtained by drawing the quartz glass base material manufactured using the quartz glass tube will also be poor. , transmission loss in optical communication increases, leading to a reduction in transmission capacity, and also making it difficult to connect optical fibers to each other. Therefore, a quartz glass tube is required that has a diameter of 1% or less and a roundness (minimum diameter/maximum diameter x 100) of 99% or more. Normally, quartz glass tubes are manufactured by being pulled out by their own weight from the bottom hole of a molten rubbo with a plug, and therefore their dimensional accuracy is 95% roundness, 2-3% ridge accuracy, and 10% wall thickness accuracy. ``It is necessary to further process it to improve its accuracy.

Therefore, in order to satisfy the above requirements, a material such as carbon, which has a higher melting point than a quartz glass tube, is inserted into a general quartz glass tube, and the quartz glass tube is melted and collapsed by heating. The method consists of bringing the birch material into close contact with the outer circumferential surface of the birch material, then grinding the outer circumferential surface of the quartz glass tube using the center of the birch material as an axis, and then pulling out the birch material based on the difference in thermal expansion between the quartz glass tube and the birch material. A method for manufacturing a quartz glass tube has been proposed (see, for example, Tokokukan Sho 52-134623).

However, the above method has the following problems. In other words, when melting and collapsing the quartz glass tube and bringing it into close contact with the offering material, it must be heated to a high temperature of 1800m or higher using an oxyhydrogen burner or the like.
Si02 that makes up the quartz glass tube is thermally dissociated,
Oxygen is released together with volatile SiO, which tends to cause bubbles and grain weakening in the quartz glass tube.Also, the outer surface of the bamboo wood is susceptible to oxidative damage, making it difficult to maintain dimensional accuracy and requiring repeated use. There are inconveniences such as making it difficult to use.
There are problems such as a decrease in processing accuracy and yield. From the above-mentioned point of view, this invention provides a method for manufacturing a quartz glass tube with high axial symmetry, which suppresses disturbances caused by volatile Si0 and oxygen due to thermal dissociation of quartz glass, and ensures further stabilization of each process. A thermally stable material having a higher melting point than the quartz glass tube made of molybdenum and molybdenum-based alloys, tantalum and tantalum-based alloys, tungsten and tungsten-based alloys is placed in the silica glass base tube. After inserting a cylindrical material molded from metal and having a predetermined size with high axial symmetry, the degree of vacuum inside the quartz glass tube is maintained at lton or less by sealing it while drawing a vacuum. The quartz glass base tube containing the material is heated to a relatively low temperature of 120 to 1500 oo under a relatively low pressure of hydrostatic pressure above normal pressure to form the quartz glass tube on the outer peripheral surface of the bamboo material. The inner diameter of the quartz glass tube is determined by softening and adhering without thermal dissociation, and the inner diameter is made highly symmetrical.Subsequently, while rotating the bamboo material as rattan, The outer circumferential surface of the quartz glass Aoi tube is ground to define its outer protrusion dimensions, and its outer diameter is made to be highly symmetrical.Finally, the main process of pulling out the birch material is to form the quartz glass Aoi tube. This method is characterized by producing a quartz glass tube with high axial symmetry and high dimensional accuracy in both the inner diameter and outer diameter.

Next, the reason why the degree of vacuum, pressurizing pressure, and heating temperature are limited as described above in the method of the present invention will be explained.

'a} If the degree of vacuum exceeds the degree of vacuum ltom, the outer circumferential surface of the birch material may oxidize due to residual gas during the softening and adhesion process of the quartz glass tube, or the outer circumferential surface of the birch material may oxidize at a relatively low pressure. Since it would be difficult to adhere to the surface, a high degree of vacuum of less than ltorr was set.

'b,' Pressure pressure As mentioned above, since the degree of vacuum inside the silica glass tube is lto less than r, even if the pressurization pressure is normal pressure, there will be a considerable pressure difference between the inside and outside of the quartz glass tube. The pressurizing pressure was set to be higher than normal pressure because it allows the quartz glass tube to be brought into close contact with the outer peripheral surface of the equipment.

'c- Heating temperature If the heating temperature is less than 1200°C, the quartz glass base tube will not be sufficiently softened in the softening and adhesion process;
When the heating temperature exceeds qo, S
Since thermal dissociation of i02 occurs, the heating temperature was set at 1200 to 1500 qo.

Next, the method of the present invention will be explained by way of examples with reference to the drawings.

Example 1 As shown in the longitudinal cross-sectional view in FIG.
A high-purity synthetic quartz glass tube with a bottom at one end, which has an inner circumference of 13.5±0.3 ribs, an outer circularity of 95%, and an inner circumferential circularity of 96%, is prepared. For this purpose, we prepared a piece of tantalum material that was formed using a lathe to a length of 90 mm, a diameter of 11.9 mm, and a roundness of 99.8%. At each end, there is a protrusion piece 3 as a detachment mark to prevent the quartz glass tube from rotating.
At the same time, a cutting notch 2a was attached.

First, as shown in FIG. 1, the quartz glass material 2 is inserted from one end of the quartz glass tube 1 through the entrance, and then the quartz glass tube is sealed while evacuating the inside of the quartz glass tube 1. The degree of vacuum inside the raw tube 1 was maintained at 1 rr, and then the quartz glass mill tube 1 with the bulges 2 enclosed was placed in an annular furnace (argon gas The quartz glass tube 1 is uniformly softened and brought into close contact with the outer peripheral surface of the bamboo material 3 by passing it through a graphite heater furnace with a cover at a rate of 4 rods per minute, as shown in the vertical cross-sectional view in FIG. I let it happen.

Next, a cut was made in the quartz glass tube 1 outside the rotation stopper part of the shank material 2 with a cutter, and both ends thereof were removed as shown in the vertical cross-sectional view in FIG. 3.

Subsequently, the birch material 2 is mounted on a glass lathe using both ends exposed from the quartz glass mill tube as grippers, and the outer circumferential surface of the quartz glass raw tube 1 is ground while rotating with the birch material 2 as an axis. to make it uniform in thickness.

Next, both ends of the twill material 2 are removed so that the anti-rotation part is fully protruded, and the state shown in the vertical cross-sectional view in FIG. I pulled out 2.

The resulting quartz glass tube has a length of 8130 ribs, an outer diameter of 18.0 mm, and an inner diameter of 12.0 mm. As for its accuracy, the obtained quartz glass tube was cut at approximately every 6th cape and measured, and the outer diameter ±0.07 side and the inner diameter ±0.04. The roundness of the outer circumference of the ribs was 99.2%, and the circularity of the inner circumference was 99.3%.

Note that no abnormality was observed on the surface of the bamboo wood after use. Example 2 A quartz glass tube with a length of 1000 ribs and an outer diameter of 20.0
Soil 0.5 side, inner diameter 15.5±0.5, outer circumference roundness 95
A quartz glass tube obtained by melting natural bK crystal with a dimensional accuracy of % and inner circumference roundness was prepared, and a metal molybdenum material was used as a bamboo material with a length of 800 ribs and a small diameter end face diameter. 13
．． Outer side, large diameter end face diameter 14.5, small diameter side roundness 99.
It is molded into a twill material with a bulge having a dimensional accuracy of 5% and a roundness of 99.6% on the Oyo side, and the ends of this molybdenum shank are formed around the quartz glass base tube as in Example 1. A stop was added.

Next, the softening and adhesion process of the quartz glass tube to the molybdenum birch material was carried out at a vacuum degree of 0.1 within the quartz glass tube.
tom, and a hydrostatic heating furnace (Hotlsostatic
A quartz glass tube was manufactured using the same process as in Example 1 except that the process was carried out using a Press furnace (abbreviated as mP) in an argon gas atmosphere of 12 atmospheric pressures at a temperature of 125 mm for 3 hours.

The dimensions and accuracy of the resulting quartz glass tube are such that the length has no unevenness, the center outer diameter is 16.5 ± 0.07, the small diameter side has an inner diameter of 13.1, and the large diameter side has an inner diameter of 14.6. The circularity of the outer circumference was 99.1%, the circularity of the inner circumference on the small side was 99.2%, and the circularity of the inner circumference on the large side was 99.2%.

Further, as in Example 1, no abnormality was observed in the bamboo wood after use. The heating means for softening and adhering the quartz glass tube to the bar material may be a normal external heating method or a high frequency concessional heating method utilizing the fact that the quartz glass material is made of metal. The entire Qin tube may be heated, or the heating zone may be moved along the longitudinal direction from the end of the quartz glass blank tube in the manner of zone melting.

Furthermore, when using a particularly expensive high-purity quartz glass tube as the quartz glass base tube, as mentioned above, the wear and tear caused by removing the quartz glass tube at the Kabamura end is uneconomical. It is better to perform the operation by adding cheaper quartz glass tube pieces to both ends of the glass tube.

As is clear from the above description, according to the method of the present invention, it is possible to reliably produce a quartz glass tube with high axial symmetry without thermal dissociation of Si02, and the twill material can be repeatedly used without damage. This brings about industrially useful effects such as ease of use.

[Brief explanation of the drawing]

FIG. 1, FIG. 2, FIG. 3, and FIG. 4 are schematic vertical cross-sectional views showing each implementation step of the present invention. In the figure, 1... quartz glass glass, 2...
・Bamboo material, 2a...Cutting notch, 3...Protrusion piece, 1'...Quartz glass tube. Younger brother' figure 2 figure 3 figure 4

Claims (1)

[Claims] 1. A quartz glass tube is molded from a metal having a higher melting point than the quartz glass tube, which is molybdenum and molybdenum-based alloys, tantalum and tantalum-based alloys, tungsten and tungsten-based alloys, and is axially symmetrical. After inserting a high bar of a predetermined size, the degree of vacuum inside the quartz glass tube is maintained at 1 torr by sealing while drawing a vacuum, and then the quartz glass tube containing the bar is heated to a pressure higher than normal pressure. The quartz glass tube is heated to a temperature of 1200° C. to 1500° C. under hydrostatic pressure to soften and adhere to the outer circumferential surface of the bar, and then the quartz glass tube is heated while rotating around the bar as an axis. A quartz glass having high axial symmetry, which comprises the main steps of grinding the outer circumferential surface of a tube to define its outer diameter dimension, imparting high axial symmetry, and finally pulling out the bar. Method of manufacturing tubes.