JPH0530773B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a pure quartz pipe having a uniform inner diameter.

Generally, an image guide is manufactured by gathering a large number of optical fibers in a pure quartz pipe, a so-called skin pipe, heating and drawing the fibers, and finishing the fibers to a predetermined diameter as a whole.

Conventionally, synthetic quartz skin pipes have been widely used as they have fewer bubbles and are stronger than natural quartz skin pipes, but they have large variations in inner diameter and lack sufficient dimensional accuracy. The problem was that it was difficult to obtain. For example, if there are variations in the inner diameter in the length direction, when optical fibers are assembled together, the optical fibers may become clogged at the small diameter portions, and if pushed in forcibly, the optical fibers may break. As a result of the fact that a gap remains between the optical fiber and the inner surface of the skin pipe at the portion where the fiber is drawn, problems such as the gas in the gap remain trapped when the fiber is drawn, causing bubble generation.

The present invention was made in view of the above circumstances, and its purpose is to fit a commercially available synthetic quartz pipe onto a carbon rod and perform collapsing to bring the inner surface of the pipe into close contact with the circumferential surface of the carbon rod. An object of the present invention is to provide a method for manufacturing a pure quartz pipe in which the inner diameter is made uniform.

The manufacturing method according to the present invention involves fitting and fixing a pure quartz pipe concentrically around a carbon rod, heating the outer circumferential surface while rotating the pipe together with the carbon rod around its axis, and bringing the inner circumferential surface into close contact with the circumferential surface of the carbon rod. The method is characterized by including a collapsing step.

The method of the present invention will be specifically explained below based on the drawings. Figure 1 is a cross-sectional view of a pipe including intermediate products from a commercially available pure quartz pipe to an intermediate product and finished product, a skin pipe. 2 is a pipe obtained by melting the inner surface of the original pipe (hereinafter referred to as the raw pipe),
2' is the diameter-expanded raw pipe, and 3 is the finished product, the skin pipe.

A step-by-step explanation will be given below. First, a raw tube 1 with few bubbles and no scratches is selected, and its inner surface is dissolved using a hydrofluoric acid solution (concentration of about 60%) to produce a raw tube 2 having a desired wall thickness. The inner diameter x of this raw pipe 2 is the outer diameter D _1p of the raw pipe 1 (also the outer diameter of the raw pipe 2), and the inner diameter
It is calculated according to the following formula based on D _1i , the inner diameter D _3i of the skin pipe, and the wall thickness t ₃ .

x=√ ₁₀ ² −4 ₃ ( ₃ + _3i ) ...(1) The basis for calculating the above formula is as follows. That is, since the cross-sectional area of the raw pipe: π/4 (D ₁₀ ² −X ² ) is equal to the cross-sectional area of the skin pipe: π/4 [(D _3i +2t ₃ ) ² −D _3i ² ] (Fig. (Reference) The following formula is obtained.

π/4(D ₁₀ ² −X ² ) =π/4 [(D _3i +2t ₃ ) ² −D _3i ² ]...(2) Equation (1) is derived from equation (2).

Note that there is no particular limitation on the specific method for dissolving the inner surface of the raw tube 1 with the hydrofluoric acid solution, and usually the raw tube 1 is filled with a hydrofluoric acid solution and the hydrofluoric acid solution is exchanged at regular intervals. This is carried out by repeating this process until a predetermined inner diameter is reached, but the dissolution may also be carried out by circulating the hydrofluoric acid solution inside the tube 1 at a low speed.

Next, the raw pipe 2 is cut to an effective length, and a separately prepared connecting pipe 2a having a smaller diameter than the raw pipe 2 is melted and connected to both ends of the raw pipe 2, and the inner surface is cleaned. Washing is performed, for example, by alternately passing methyl alcohol and pure water, and 10% hydrofluoric acid solution and pure water. Next, the blank tube 2 is fixed to chucks 4 and 5 of a glass lathe using a connecting tube as shown in FIG. One connecting pipe 2a has SPC
An air supply pipe (not shown) is connected using a joint, O ₂ is passed through the air supply pipe, and drying is performed while heating with a burner from the outside, so-called gas phase etching. For gas phase etching, operate the gas doping device to connect diluted O ₂ and CF ₄ to pipe 2a.
This process is repeated until the inside of the raw tube 2 becomes transparent and clean. Next, the inner diameter of the raw tube 2 is expanded. The diameter of the raw tube 2 is expanded by injecting an inert gas such as Ar into the raw tube through a pipe connected via an SPC joint to a connecting pipe 2a at one end of the raw tube 2, which is rotated around the axis on a glass lathe. The raw tube 2 is softened by heating the raw tube 2 from one end to the other end with a burner while increasing the internal pressure of the raw tube 2 through the heat exchanger. You will be forced to do so.

The diameter of the raw pipe 2 is further reduced by this diameter expansion, and the inner diameter becomes such that it can be fitted onto a carbon rod used in collapsing to make the inner diameter uniform.
When the diameter expansion of the raw pipe is completed, it is washed again using the same washing liquid as described above, and collapsing as shown in FIG. 3 is performed. FIG. 3 is a schematic diagram showing a state in which collapsing is being carried out, in which the proximal end of a carbon rod 6 is fixed to one chuck 4 of the glass lathe, and a base tube 2 with an enlarged diameter is fixed to the other chuck 5. ' is fitted onto the carbon rod 6, and the tip is positioned concentrically with the carbon rod 6 with its tip abutting against the diameter-expanding tapered portion 6a of the carbon rod 6 and fixed. The carbon rod 6 is fixed in advance on a glass lathe and its surface is polished with abrasive paper. After that, the surface is cleaned with soft paper or cloth impregnated with acetone, and then heated with a burner to evaporate the moisture on the surface. let Once the lathe is stopped, the raw tube 2 is fitted onto the carbon rod 6, and its tip is butted against the tapered portion 6a of the carbon rod 6, crushed with a burner so that it comes into close contact with the carbon rod 6a, and placed concentrically with the chuck 5. Fix it.

The outer peripheral surface of the raw tube 2' is heated with a burner while passing an inert gas such as N ₂ between the carbon rod 6 and the raw tube 2', and when the raw tube 2' approaches the melting temperature, the inert gas is heated. At the same time as stopping the supply, this is conversely sucked to apply negative pressure inside the raw tube 2', and using burner pressure, the inner surface of the raw tube 2' is successively brought into close contact with the circumferential surface of the carbon rod 6 from the tip side. , performs what is called collapsing. During this time, the carbon rod 6 is heated using a sub-burner (not shown), and its thermal expansion is used to bring it into close contact with the inner surface of the raw tube 2'.
The restraining force on the raw pipe 2' is increased. When the collapsing is completed and the carbon rod 6 has cooled down, the carbon rod 6 separates from the skin pipe 3 because the coefficient of thermal expansion of the carbon rod 6 is greater than that of the skin pipe 3, so the skin pipe 3 is removed.

In addition, although the above-mentioned example includes a step of heating and inflating the raw tube 2 and then fitting it onto the carbon rod 6, this may not necessarily be necessary depending on the carbon rod 6 used, and the process may be moved immediately to the collapsing step. It's okay. Of course, if the original tube is clean, it may be directly transferred to the collapsing process.

In the case of using the method of the present invention as described above, the wall thickness is
It became possible to easily obtain skin pipes of about 0.5 mm. Of course, it is possible to make the wall even thinner, but there is a problem that cracks are likely to occur when connecting a connecting pipe to this during wire drawing, resulting in a lower yield. By using the above-mentioned skin pipe with a wall thickness of 0.5 mm, the wall thickness of the skin pipe after wire drawing is 15 μm, compared to the conventional 80 to 150 μm.
It has become possible to reduce the thickness to approximately 40 μm. As a result of the flexibility test (i.e., the minimum diameter of a circle without breakage when the image guide is wrapped around a circle with a predetermined diameter), the results were as follows: 6000 bare fibers, diameter 1.0
With a mm image guide, it is now possible to reduce the distance to 100 mm or less. By the way, the conventional image guide
It was about 250mm.

As described above, in the method of the present invention, the diameter of the pure quartz pipe is reduced using a carbon rod for regulating the inner surface so that the inner surface touches the carbon rod, so that the obtained skin pipe has a uniform inner diameter. The optical fiber does not break when it is pushed into the skin pipe, and when it is drawn, air bubbles are not trapped in the gap between the optical fiber and the inner surface of the skin pipe, resulting in a significant improvement in product quality. The present invention exhibits excellent effects, such as significant improvements.

[Brief explanation of the drawing]

Figures 1A to 2 are cross-sectional views of the original pipe, raw pipe, and skin pipe, and Figure 2 is a schematic diagram showing the expanded diameter state of the raw pipe.
FIG. 3 is a schematic diagram showing the collapsing process. 1...Original pipe, 2, 2'...Main pipe, 3...Skin pipe, 4,5...Chick, 6...Carbon rod.

Claims (1)

[Claims] 1 A pure quartz pipe is fitted concentrically around a carbon rod, an inert gas is passed between the two, the outer circumferential surface is heated while the pipe is rotated around the axis along with the carbon rod, and the inner circumferential surface is heated. A method for manufacturing a pure quartz pipe with a uniform inner diameter, characterized by including a collapsing process in which the pipe is brought into close contact with the circumferential surface of a carbon rod.