JP2968274B2 - Quartz glass tube decompression shaping method - Google Patents

Description

The present invention relates to a method for shaping the inner surface of a quartz glass tube. In particular, it is suitable for shaping quartz glass requiring high-precision dimensions.

<Prior Art> A conventional method for shaping the inner surface of a quartz glass tube is disclosed in
As shown in JP-A-31, insert a carbon mandrel finished to the desired surface accuracy into a quartz glass tube, and use an electric heating furnace or a flame such as oxyhydrogen / LP gas to form the quartz tube in the atmosphere. Was heated and softened together with the mandrel, and the quartz glass was brought into close contact with the mandrel by gravity or mechanical force to shape the inner surface of the quartz glass tube.

<Problems to be solved by the invention> In the conventional method of shaping the inner surface of a quartz glass tube in the atmosphere,
The carbon mandrel causes the surface roughness to deteriorate due to the chemical reaction of heat and oxygen in the atmosphere to shape the quartz glass tube, resulting in poor surface accuracy, and the inner surface accuracy of the quartz glass tube as desired after one or two uses. And it was uneconomical.
Also, in the method of shaping the quartz glass tube in close contact with the mandrel with mechanical force from the outer surface of the quartz glass tube, the mandrel is limited to a simple shape such as a cylinder, and in the shaping method by gravity, the quartz glass tube is shaped like a mandrel. In some cases, they did not adhere uniformly to each other and became elliptical.

In view of the above, the present invention prevents the deterioration of the surface accuracy of the mandrel and, regardless of the shape of the mandrel, the quartz glass tube uniformly adheres to the mandrel, and the quartz glass tube having a desired shape. It is an object of the present invention to provide a method for shaping the inner surface of a quartz glass tube, which can obtain the following.

<Means for Solving the Problems> In the method for shaping the inner surface of a quartz glass tube according to the present invention, a mandrel made of carbon having a predetermined shape is inserted into the quartz glass tube, and the atmosphere inside the quartz glass tube is inerted with argon, nitrogen, or the like. This is a quartz glass decompression shaping method in which the quartz glass tube and the mandrel are heated and a pressure difference from the atmospheric pressure is applied to make the quartz glass tube adhere to the mandrel.

In addition, the atmosphere inside the quartz glass tube is replaced with an inert gas such as argon or nitrogen and then exhausted to a reduced pressure state, thereby suppressing a chemical reaction between the carbon mandrel and oxygen in the atmosphere, and The surface accuracy is maintained, and the mandrel can be used repeatedly, which is economical.

As a result of repeating many experiments of the present invention, it was found that the atmosphere inside the quartz tube was replaced with an inert gas such as argon or nitrogen, and then the quartz tube was reduced in pressure from 7 × 10 ² Torr to 1 × 10 ^-6 Torr. The above problem was solved by shaping.

<Operation> By reducing the pressure in the quartz glass tube, the atmospheric pressure uniformly acts on the quartz glass tube from the surroundings, and the quartz glass tube adheres uniformly to the mandrel, so the inner surface of the quartz glass tube has the shape of a mandrel. Is accurately formatted. Also,
The inner surface of the quartz glass tube is shaped to a desired surface accuracy.

In the quartz glass decompression shaping method according to the present invention, regardless of the shape of the mandrel, the atmospheric pressure acts uniformly from the surroundings, so that the quartz tube is shaped into a polygonal prism including a cylindrical shape, as well as an elliptic cylinder. It is possible to shape a mandrel such as a shape, a shape combining a cylindrical shape and a prism, and the quartz tube can be shaped faithfully to the outer shape of the mandrel.

Also, after replacing the inside of the quartz glass tube with an inert gas,
By reducing the pressure, it is possible to prevent the carbon mandrel surface from being oxidized by reacting with oxygen in the atmospheric column, and to prevent the mandrel surface from being roughened.

<Embodiment> An embodiment of the quartz glass tube decompression shaping method of the present invention will be described as a first embodiment.
This will be described with reference to the process schematic diagrams of FIGS. (A), (b) and (c). FIG. 2 shows an inert gas replacement device.

As shown in FIG. 1 (a), one end of a quartz glass tube to be shaped is sealed, and a carbon mandrel 1 finished to a desired shape and surface accuracy is inserted into a quartz glass tube 2 to be processed. The other end is processed and squeezed, and an exhaust port 5 is provided.
The inert gas replacement device shown in FIG. 2 is connected to the exhaust port 5.

Next, the atmosphere inside the quartz tube 2 is replaced with an inert gas.
First, the inert gas flow control valve 7 is closed, the exhaust flow control valve 8 is opened, and the inside of the quartz glass tube 2 is evacuated by a vacuum pump (not shown) to a reduced pressure state.
Is closed, the inert gas flow control valve 7 is opened, and the quartz glass tube 2 is opened.
When the pressure gauge 9 indicates the atmospheric pressure, the inert gas flow control valve 7 is closed. Thus, the atmosphere inside the quartz tube 2 is replaced with an inert gas, but this operation is repeated several times as necessary to completely bring the inside of the quartz glass tube into an inert gas atmosphere.

After completion of the replacement operation, the opening degree of the inert gas flow control valve 7 and the exhaust flow control valve 8 is adjusted, and the pressure gauge 9 is adjusted to a predetermined value. At this time, if the pressure is 7 × 10 ² Torr or less, the atmospheric pressure can uniformly bring the quartz glass tube into close contact with the mandrel. Quartz glass tube 2 evacuated to reduce pressure
Is mounted on a glass lathe (not shown), and the quartz glass tube 2 is uniformly heated from the outer periphery to the softening temperature (1450 ° C. to 1750 ° C.) of the quartz glass by the oxyhydrogen flame 3 while rotating at a constant speed. Then, as shown in FIG. 1 (b), since the inside of the quartz glass tube 2 is depressurized, the atmospheric pressure acts on the quartz glass tube, and the quartz glass tube is uniformly pressed from the surroundings and closely adheres to the mandrel. become. Therefore, the gap 4 existing between the inner surface of the quartz glass tube 2 and the mandrel 1 is eliminated.

Next, the integrated quartz glass tube 2 and mandrel 1 are cooled. Since the coefficient of thermal expansion of carbon (about 1 × 10 ⁻⁶ / ° C.) is larger than the coefficient of thermal expansion of quartz glass (about 5 × 10 ⁻⁷ / ° C.), the quartz after cooling as shown in FIG. The mandrel 1 has a higher degree of shrinkage than the glass tube 2 and a slight gap 6 is generated. Then, the mandrel 1 can be pulled out of the quartz glass tube 2 by cutting the end face of the quartz glass tube 2 on the exhaust port 5 side.

As described above, the quartz glass tube 2 can be shaped to be exactly the shape of the mandrel 1, and the inner surface of the quartz glass tube 2 can be shaped to have the same surface accuracy as that of the mandrel 1.

The gap between the quartz glass and the carbon mandrel after cooling caused by the difference in expansion coefficient between the quartz glass and carbon is about 0.5 to 1% of the outer shape of the prepared mandrel. When the outer shape of the mandrel is the same as the desired inner diameter of the quartz glass, the inner diameter of the quartz glass becomes larger than the initially desired inner diameter after cooling due to the influence of the mandrel expansion due to heat when the quartz glass is brought into close contact. This cannot be ignored for industrial use. Therefore, the outer shape of the mandrel must be made smaller than the desired inner diameter of quartz glass by about 0.5 to 1% in consideration of thermal expansion when the quartz tube is brought into close contact.

The lower limit of the decompression range is suitably 1 × 10 ⁻⁶ Torr. This is because the quartz glass tube similarly adheres to the mandrel even at a low degree of pressure reduction, and a good result can be obtained. However, the degree of pressure reduction that can be easily obtained industrially is 1 × 10 ⁻⁶ Torr.

 Further, specific examples will be described below.

The desired inner diameter after shaping the quartz glass tube is 92.0 mm
± 0.1mm, minor axis 80.0 ± 0.1mm. A quartz tube having an inner diameter of 93.5 ± 1 mm, a thickness of 3 ± 0.5 mm, and a length of 1300 mm is prepared.

Next, major axis 91.6 ± 0.05mm, minor axis 79.6 ± 0.05mm, length 1200
A mandrel made of carbon whose surface is polished with high precision of mm is inserted into a quartz glass tube, and an exhaust port is provided in the quartz tube. The inside of the quartz tube is evacuated from the exhaust port to maintain the degree of vacuum at 10 ^-5 Torr, and then uniformly heated to 1650 ° C. with an oxyhydrogen flame. Thereafter, the sealed end face was cooled and the mandrel was removed. The inner diameter of the quartz tube thus shaped is 92.0 mm
The short diameter is unified to 80.0 ± 0.1mm and the inner surface of the quartz glass tube is shaped to the surface accuracy of a polished carbon mandrel.

<Effects of the Invention> According to the quartz glass tube decompression shaping method, the quartz glass is faithfully shaped into the shape of the mandrel to be inserted, oxidation of the surface of the mandrel is suppressed, and surface roughening can be prevented. Can be used many times,
It is economical.

In addition, by using a mandrel with a combined shape of a cylinder and a square pillar, or a mandrel with a complex shape with a small diameter and a large diameter cylinder connected via a tapered part, in the manufacture of quartz glass products with complicated shapes, Conventionally, welding work that required advanced technology is no longer necessary, and industrial economic effects are great. As a specific example, as shown in FIG. 3 (b), the cross section of the quartz glass tube is shaped into an oval shape, and the upper circular portion is cut and removed, whereby a boat body of a semiconductor wafer can be manufactured. According to this method, conventionally, as shown in FIG. 3 (a), a member in which a quartz glass tube is divided into half and a quartz glass plate member is welded to form a boat is replaced with the quartz of the present invention. There is an enormous effect that the quartz glass tube shaped by the vacuum shaping method of the glass tube can be formed by a relatively simple technique of simply cutting.

Further, the quartz glass tube having a high inner surface precision shaped according to the present invention can be used for a quartz tube used in manufacturing an optical fiber preform manufactured by the MOVD method.

It goes without saying that it can be widely used in other fields.

[Brief description of the drawings]

1 (a), 1 (b) and 1 (c) are schematic views showing steps of an embodiment of a shaping method according to the present invention. FIG. 2 is a schematic view of an inert gas replacement apparatus, FIG. 3 (a) is an explanatory view of a conventional boat manufacturing method, and FIG. 3 (b) is an explanation of the case where the present invention is applied to boat manufacturing. FIG. DESCRIPTION OF SYMBOLS 1 ... Mandrel 2 ... Quartz tube 3 ... Oxy-hydrogen flame 4 ... Gap 5 ... Exhaust port 6 ... Gap 7 ... Inert gas flow control valve 8 ... Exhaust flow control valve 9 ... Pressure gauge

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-63-8321 (JP, A) JP-A-60-108330 (JP, A) JP-A-56-129621 (JP, A) 3014 (JP, B2) (58) Field surveyed (Int. Cl. ⁶ , DB name) C03B 23/08, 20/00

Claims (3)

(57) [Claims] In the heating and shaping of a quartz glass tube, a carbon mandrel having a predetermined shape is inserted into the quartz glass tube, and the atmosphere inside the quartz glass tube is replaced with an inert gas such as argon or nitrogen to reduce the pressure. A quartz glass tube depressurization shaping method in which a quartz glass tube and a mandrel are heated and a differential pressure from the atmospheric pressure is applied to bring the quartz glass tube into close contact with the mandrel. 2. The mandrel is made of carbon, the gap between the quartz glass tube and the mandrel is about 1 to 10 mm, and the outer diameter of the mandrel is 0.5 to 1% smaller than the inner diameter of the desired quartz pipe.
3. The method of claim 1, wherein the pressure is reduced to a certain extent. 3. A method for manufacturing a quartz glass boat, comprising: shaping a cross section of a quartz glass tube into an oval shape by the pressure reducing shaping method according to claim 1; and cutting an upper circular portion.