JP2013189363A - Apparatus and method for molding glass tube - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an apparatus and method for molding a glass tube, which can mold a glass tube having excellent dimensional accuracy and a large diameter.SOLUTION: An apparatus for molding a glass tube by a Danner method includes: a sleeve for molding molten glass into a tubular shape; a drive means for rotating the sleeve; a tube drawing means for drawing the glass tube molded into the tubular shape from a tip of the sleeve; a gas supply means for supplying gas from the sleeve side to the inside of the glass tube; a pressure measuring means for measuring the pressure in the glass tube; cutting means arranged in an air pressure adjusting chamber where indoor air pressure is adjustable, which cuts the glass tube into a predetermined length; and a control means for controlling the pressure in the air pressure adjusting chamber according to a variation in pressure in the glass tube.

Description

  The present invention relates to a glass tube forming apparatus and a glass tube forming method by the Danner method, and more particularly, to a glass tube forming apparatus and a glass tube forming method capable of forming a glass tube having a large diameter.

  Various methods, such as the Danner method and the down draw method, have been proposed as glass tube forming methods. Among these methods, the Danner method can form a glass tube continuously and is excellent in productivity. For this reason, the Danner method is widely used for forming glass tubes.

  By the way, in recent years, a glass tube having a large diameter has been demanded. In order to increase the diameter of the glass tube, a method of increasing the amount of blown air supplied into the glass tube is conceivable. By increasing the amount of gas supply, the pressure in the glass tube can be increased, the action of the molten glass that is distant from the sleeve tip in an attempt to shrink in the radial direction can be suppressed, and the diameter of the glass tube can be increased.

  However, when the diameter of the glass tube is increased, the exhaust resistance in the glass tube is reduced, so that it is necessary to increase the flow rate of the blow air exponentially, and it becomes difficult to stabilize the pressure of the blow air. Further, when the flow rate of blow air is increased, the glass tube is rapidly cooled, so that the dimensions of the glass tube may become unstable. Therefore, it has been proposed to form a glass tube with a large diameter without increasing the flow rate of the blow air by arranging a cutting machine for cutting the glass tube and a blower for supplying the blow air in a pressurized pressure control chamber. (For example, refer to Patent Document 1).

  Further, in the Danner method, a phenomenon that the dimensions (outer diameter, inner diameter, wall thickness) of the glass tube fluctuate periodically occurs due to the unevenness of the molten glass wound around the sleeve. Therefore, in order to suppress this variation, it has been proposed to measure the dimensions of the glass tube to be molded and change the pressure of the blow air according to the measured value (see, for example, Patent Document 2).

JP-A-7-172853 JP-A-8-165128

  As described above, in recent years, a glass tube having a large diameter has been demanded. However, when a glass tube having a large diameter is formed, there is a problem that the dimensional accuracy of the glass tube is not stable because it is necessary to increase the flow rate of blow air as described above. In Patent Document 1, a glass tube having a large diameter is formed without increasing the flow rate of blow air by disposing a cutting machine for cutting glass tubes and a blower for supplying blow air in a pressurized air pressure control chamber. However, the problem that the dimensions of the glass tube fluctuate cannot be solved.

  Japanese Patent Application Laid-Open No. H10-228707 describes that the dimensional fluctuation of the glass tube is suppressed by changing the pressure of the blow air according to the outer diameter of the glass tube. However, when forming a glass tube with a large diameter, it is necessary to increase the flow rate of the blow air. Therefore, in order to suppress the dimensional fluctuation of the glass tube against the pressure of the blow air necessary to form a glass tube with a large diameter. The ratio of the pressure of the blow air necessary for this is relatively small. In other words, the pressure of the blow air necessary to suppress the dimensional fluctuation of the glass tube is very small compared to the pressure of the blow air necessary for forming the glass tube, so that it is very difficult to control the pressure of the blow air. Become.

  An object of the present invention is to provide a glass tube forming apparatus and a glass tube forming method capable of forming a large-diameter glass tube excellent in dimensional accuracy.

  The glass tube forming apparatus of the present invention is a glass tube forming apparatus by the Danner method, a sleeve for forming molten glass into a tubular shape, a driving means for rotating the sleeve, and a glass formed into a tubular shape from the tip of the sleeve. A tube pulling means for pulling the tube, a gas supply means for supplying gas from the sleeve side into the glass tube, a pressure measuring means for measuring the pressure in the glass tube, and a pressure adjusting chamber capable of adjusting the indoor pressure, and the glass tube And a control means for controlling the pressure in the atmospheric pressure adjustment chamber according to the fluctuation of the pressure in the glass tube.

  The glass tube forming method of the present invention is a glass tube forming method by the Danner method, in which a molten glass is wound around a rotating sleeve and formed into a tubular shape, and the glass tube formed into a tubular shape from the tip of the sleeve is formed. A step of pulling, a step of supplying a gas from the sleeve side into the glass tube, a step of cutting the glass tube into a predetermined length in an atmospheric pressure adjustment chamber capable of adjusting the indoor atmospheric pressure, and an atmospheric pressure adjustment according to fluctuations in the pressure in the glass tube Controlling the pressure in the room.

  According to the present invention, a large-diameter glass tube having excellent dimensional accuracy can be formed.

It is a cross-sectional schematic diagram of the glass tube shaping | molding apparatus which concerns on 1st Embodiment. It is a cross-sectional schematic diagram of the shaping | molding apparatus of the glass tube which concerns on 2nd Embodiment.

(First embodiment)
FIG. 1 is a schematic cross-sectional view of a glass tube forming apparatus 100 according to the first embodiment. The glass tube forming apparatus 100 is an apparatus for forming a glass tube having a large diameter by the Danner method. More specifically, the glass tube forming apparatus 100 forms a glass tube S having a large diameter in which the inner diameter of the glass tube S to be formed is 1/10 or more of the outer diameter of the sleeve tip described later.

  As shown in FIG. 1, a glass tube forming apparatus 100 includes a forming mechanism 110, tube drawing mechanisms 120A and 120B, a pressure measuring mechanism 130, an inspection mechanism 140, a cutting cutter 150, an atmospheric pressure adjusting chamber 160, A control mechanism 170 and a transport mechanism 180 are provided.

(Configuration of molding mechanism 110)
The forming mechanism 110 includes a muffle furnace 111, a glass tube forming sleeve 112 (hereinafter referred to as a sleeve 112), a blow pipe 113, an air supply unit 114 (for example, a blower), and a rotating mechanism 115.

  The sleeve 112 is disposed in the muffle furnace 111 with the tip inclined downward. A molten glass G supplied from a nozzle (not shown) is wound around the outer peripheral surface of the sleeve 112 and formed into a glass tube S shape.

  The sleeve 112 is preferably made of a refractory material (for example, refractory brick). Further, it is more preferable to cover the surface of the sleeve 112 with a refractory metal (platinum (Pt) or a platinum alloy (for example, an alloy of platinum and rhodium (Rh))) as necessary.

The blow pipe 113 is inserted into a hole that penetrates the axis of the sleeve 112. An air supply machine 114 is connected to one end of the blow pipe. By sending air (air) at a constant flow rate from the air supply device 114, air is supplied from the tip of the blow pipe 113 into the glass tube S formed into a tubular shape. A gas other than air (for example, an inert gas such as Ar or N ₂ ) may be supplied from the blow pipe 113.

  The rotation mechanism 115 includes a motor (not shown) connected to the sleeve 112 and a motor driver (not shown) that controls the rotation speed of the motor. The rotation mechanism 115 rotates the sleeve 112 at a desired number of rotations.

(Configuration of pipe drawing mechanism 120A, 120B)
The tube drawing mechanisms 120A and 120B include first and second rollers 121 and 122, respectively. The first and second rollers 121 and 122 are rotationally driven by a motor (not shown) in contact with the glass tube S formed into a tubular shape, and draw the glass tube S at a desired speed.

(Configuration of pressure measuring mechanism 130)
The pressure measurement mechanism 130 is a pressure gauge. The pressure measurement mechanism 130 is provided at the tip of the sleeve 112 and measures the pressure in the glass tube S. The pressure measurement mechanism 130 outputs the measured pressure data to the control mechanism 170 described later. In addition, you may make it measure the pressure in the glass tube S through the hole which penetrates the axial center of the sleeve 112 which has inserted the blow pipe 113. FIG.

(Configuration of inspection mechanism 140)
The inspection mechanism 140 inspects for the appearance of the glass tube S (for example, cloudiness, scratches, bubbles). The inspection mechanism 140 is, for example, an image inspection device that includes an imaging device, a light source, and an image processing device.

(Configuration of cutting cutter 150)
The cutting cutter 150 cuts the glass tube S into a desired length.

(Configuration of atmospheric pressure adjustment chamber 160)
The atmospheric pressure adjustment chamber 160 is configured to maintain the internal pressure in a pressurized state (a state where the pressure is higher than the atmospheric pressure). A blower 161 (for example, a blower) is connected to the atmospheric pressure adjustment chamber 160. The air blower 161 sends air into the atmospheric pressure adjustment chamber 160 to place the atmospheric pressure adjustment chamber 160 in a pressurized state (a state where the atmospheric pressure is higher than the atmospheric pressure).

  In addition, an electromagnetic valve 162 is provided in the atmospheric pressure adjustment chamber 160, and the electromagnetic valve 162 opens / closes (opens / closes) based on an instruction from the control mechanism 170 described later, and the pressure in the atmospheric pressure adjustment chamber 160 is changed. Fluctuate. In the first embodiment, the electromagnetic valve 162 uses a normal close type valve. That is, the electromagnetic valve 162 is normally in a Closed state, and when instructed by the control mechanism 170, the Electromagnetic valve 162 is in an Open (opened) state, and the pressure in the atmospheric pressure adjustment chamber 160 is reduced.

(Configuration of control mechanism 170)
The control mechanism 170 is, for example, a computer, and includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), an NVRAM (Non Volatile RAM), and the like. The ROM stores a CPU operation program. The RAM provides a work area for the CPU. The NVRAM stores a threshold value.

  The control mechanism 170 opens and closes the electromagnetic valve 162 based on the pressure in the glass tube S measured by the pressure measurement mechanism 130, and controls the pressure in the atmospheric pressure adjustment chamber 160 so as to cancel the pressure fluctuation in the glass tube S. To do.

  Specifically, when the pressure output from the pressure measuring mechanism 130 that measures the pressure in the glass tube S exceeds the threshold value stored in the NVRAM, the control mechanism 170 opens the electromagnetic valve 162 and the atmospheric pressure adjustment chamber 160. The inside is depressurized. In addition, when the pressure output from the pressure measuring mechanism 130 that measures the pressure in the glass tube S is equal to or less than the threshold value stored in the NVRAM, the control mechanism 170 closes the electromagnetic valve 162 and the atmospheric pressure adjustment chamber. The pressure inside 160 is increased or kept constant.

  In the conventional method of changing the pressure of the blow air, the cooling of the glass tube S changes due to the change of the blow air, so that the viscous state of the glass tube S becomes unstable, and the dimensional accuracy of the glass tube S is not stable. However, in the glass tube forming apparatus 100 according to the first embodiment, the glass tube S is already cooled, and on the tube end side (downstream side) where there is no possibility that the size of the glass tube S changes due to a change in pressure. The pressure is adjusted. For this reason, the dimension of the glass tube S can be controlled while suppressing the influence on the cooling process of the glass tube S. As a result, the dimensional accuracy of the glass tube S can be improved. Therefore, there is little possibility that troubles, such as pipe bending, will occur.

  In addition, when decompressing the inside of the atmospheric pressure regulation chamber 160, in addition to opening the electromagnetic valve 162, the air volume of the blower 161 may be reduced. Further, when the pressure inside the atmospheric pressure adjustment chamber 160 is increased, in addition to closing the electromagnetic valve 162, the air volume of the blower 161 may be increased. The blower 161 may be controlled by the control mechanism 170.

(Configuration of the transport mechanism 180)
The transport mechanism 180 is, for example, a belt conveyor. The transport mechanism 180 carries out the glass tube S cut to a desired length by the cutting cutter 150 from the atmospheric pressure adjustment chamber 160.

  As described above, the glass tube forming apparatus 100 according to the first embodiment opens and closes the electromagnetic valve 162 based on the pressure in the glass tube S measured by the pressure measurement mechanism 130, and the glass tube S The pressure in the atmospheric pressure adjustment chamber 160 is controlled so as to cancel out the pressure fluctuation.

  In other words, the glass tube forming apparatus 100 adjusts the pressure on the tube end side (downstream side) where the glass tube S is already cooled and the size of the glass tube S is not likely to change due to a change in pressure. The dimension of the glass tube S can be controlled while suppressing the influence on the cooling process of the glass tube S. As a result, the dimensional accuracy of the glass tube S can be improved. In addition, since the influence on the cooling process of the glass tube S is suppressed, there is little possibility that a problem such as bending of the tube occurs due to a change in the cooling process of the glass tube S.

  In the above description, the pressure in the atmospheric pressure adjustment chamber 160 is controlled based on the comparison between the pressure in the glass tube S and the threshold value stored in the NVRAM of the control mechanism 170. The correlation between the pressure change and the dimensional change of the glass tube S is examined in advance and stored in the VRAM of the control mechanism 170, and the dimensional change of the glass tube S based on the stored correlation and the pressure in the glass tube S. And the pressure in the atmospheric pressure adjustment chamber 160 may be controlled.

(Modification of the first embodiment)
In the glass tube forming apparatus 100 according to the first embodiment, in order to cancel the pressure fluctuation in the glass tube S, when the pressure in the glass tube S exceeds a threshold value, the electromagnetic valve 162 is opened, The pressure adjustment chamber 160 is depressurized. However, in order to cancel out the pressure fluctuation in the glass tube S, the inside of the atmospheric pressure adjustment chamber 160 may be increased or decreased when the pressure in the glass tube S falls outside the threshold range. In this case, what is necessary is just to increase / decrease the ventilation volume of the air blower 161, when the pressure in the glass tube S becomes out of the range of a threshold value. Specifically, it is possible to control the number of rotations of the blower 161 with an inverter or to variably control the opening area of the blower pipe between the blower 161 and the pressure adjustment chamber 160. Even if comprised in this way, the effect similar to the shaping | molding apparatus 100 of the glass tube which concerns on 1st Embodiment can be acquired.

(Second Embodiment)
FIG. 2 is a schematic cross-sectional view of a glass tube forming apparatus 200 according to the second embodiment. The glass tube forming apparatus 200 is an apparatus for forming a glass tube having a large diameter by the Danner method. More specifically, the glass tube forming apparatus 200 forms a glass tube S having a large diameter in which the inner diameter of the glass tube S to be formed is 1/10 or more of the outer diameter of the sleeve.

  In the second embodiment, a mode in which the electromagnetic valve 162 is opened / closed to cancel the pressure fluctuation in the glass tube S based on the outer diameter of the glass tube S will be described. The configuration of the glass tube forming apparatus 200 will be described below with reference to FIG. In addition, the same code | symbol is attached | subjected to the structure same as the glass tube shaping | molding apparatus 100 demonstrated with reference to FIG. 1, and the overlapping description is abbreviate | omitted.

  The glass tube forming apparatus 200 according to the second embodiment includes an outer diameter measuring mechanism 130 </ b> A that measures the outer diameter of the glass tube S instead of the pressure measuring mechanism 130. The outer diameter measuring mechanism 130A is, for example, a dimension measuring instrument (manufactured by Keyence Corporation: LS-7000 series or TM-3000 series). The outer diameter measuring mechanism 130A measures the outer diameter of the glass tube S. The outer diameter measuring mechanism 130A outputs the measured outer diameter data to the control mechanism 170 described later. The outer diameter measuring mechanism 130A is preferably arranged as close as possible to the catenary part of the glass tube S (the region in which the glass tube S hangs down due to gravity and draws a catenary curve). Specifically, it is preferable to arrange the glass tube S in a place where the temperature is below the strain point at which the shape does not change.

  The control mechanism 170 opens and closes the electromagnetic valve 162 based on the outer diameter of the glass tube S measured by the outer diameter measuring mechanism 130A, and controls the pressure in the atmospheric pressure adjustment chamber 160 so as to cancel the pressure fluctuation in the glass tube S. Control.

  The outer diameter of the glass tube S and the pressure in the glass tube S have a correlation. That is, when the pressure in the glass tube S is high, the outer diameter of the glass tube S is thick, and when the pressure in the glass tube S is low, the outer diameter of the glass tube S is thin. That is, by measuring the outer diameter of the glass tube S, the fluctuation of the pressure in the glass tube S can be known. In the second embodiment, using the correlation between the outer diameter of the glass tube S and the pressure in the glass tube S, the pressure in the atmospheric pressure adjustment chamber 160 is adjusted so as to cancel the pressure fluctuation in the glass tube S. Control.

  Specifically, the control mechanism 170 opens the electromagnetic valve 162 and adjusts the atmospheric pressure when the outer diameter output from the outer diameter measuring mechanism 130A that measures the outer diameter of the glass tube S exceeds the threshold stored in the NVRAM. The inside of the chamber 160 is depressurized. Further, when the outer diameter output from the outer diameter measuring mechanism 130A that measures the outer diameter of the glass tube S is equal to or less than the threshold value stored in the NVRAM, the control mechanism 170 closes the electromagnetic valve 162 to adjust the atmospheric pressure. The pressure in the adjustment chamber 160 is increased.

  In addition, when decompressing the inside of the atmospheric pressure adjustment chamber 160, not only the solenoid valve 162 is opened, but the air flow rate of the blower 161 may be reduced. Further, when the pressure inside the atmospheric pressure adjustment chamber 160 is increased, not only the electromagnetic valve 162 is closed, but the air flow rate of the blower 161 may be increased. The blower 161 may be controlled by the control mechanism 170.

  As described above, the glass tube forming apparatus 200 according to the second embodiment opens and closes the electromagnetic valve 162 based on the outer diameter of the glass tube S measured by the outer diameter measuring mechanism 130A, The pressure in the atmospheric pressure adjustment chamber 160 is controlled so as to cancel the pressure fluctuation. For this reason, the dimension of the glass tube S can be controlled while suppressing the influence on the cooling process of the glass tube S. As a result, the dimensional accuracy of the glass tube S can be improved. Other effects are the same as those of the glass tube forming apparatus 100 according to the first embodiment.

  In the above description, the pressure in the atmospheric pressure adjustment chamber 160 is controlled based on the comparison between the outer diameter in the glass tube S and the threshold value stored in the NVRAM of the control mechanism 170. The correlation between the pressure change of the glass tube S and the dimensional change of the glass tube S is examined in advance and stored in the VRAM of the control mechanism 170, and the size of the glass tube S is determined based on the stored correlation and the pressure in the glass tube S. A change may be predicted and the pressure in the atmospheric pressure adjustment chamber 160 may be controlled.

(Modification of the second embodiment)
In the glass tube forming apparatus 200 according to the second embodiment, in order to cancel the pressure fluctuation in the glass tube S, when the outer diameter of the glass tube S exceeds a threshold value, the electromagnetic valve 162 is opened, The pressure adjustment chamber 160 is depressurized. However, in order to cancel the pressure fluctuation in the glass tube S, the inside of the atmospheric pressure adjustment chamber 160 may be increased or decreased when the outer diameter of the glass tube S is out of the threshold range. In this case, what is necessary is just to increase / decrease the ventilation volume of the air blower 161, when the outer diameter of the glass tube S becomes out of the range of a threshold value. Specifically, it is possible to control the number of rotations of the blower 161 with an inverter or to variably control the opening area of the blower pipe between the blower 161 and the pressure adjustment chamber 160. Even if comprised in this way, the effect similar to the shaping | molding apparatus 200 of the glass tube which concerns on 2nd Embodiment can be acquired.

(Other embodiments)
As described above, the present invention has been described in detail based on the above specific examples. However, the present invention is not limited to the above specific examples, and various modifications and changes can be made without departing from the scope of the present invention. is there. For example, in the first and second embodiments, the pressure in the atmospheric pressure adjustment chamber 160 is controlled based on the pressure in the glass tube S and the outer diameter of the glass tube S, respectively. The pressure in the atmospheric pressure adjustment chamber 160 may be controlled based on the pressure and the outer diameter of the glass tube S.

  The glass tube forming apparatus and the forming method of the present invention can form a large-diameter glass tube excellent in dimensional accuracy.

  DESCRIPTION OF SYMBOLS 100,200 ... Glass tube shaping | molding apparatus, 110 ... Molding mechanism, 111 ... Muffle furnace, 112 ... Glass tube shaping | molding sleeve, 113 ... Blow pipe, 114 ... Air supply machine, 115 ... Rotation mechanism, 120A, 120B ... Pipe drawing Mechanism 121, 122 ... Roller 130 ... Pressure measuring mechanism 130A ... Outer diameter measuring mechanism 140 ... Inspection mechanism 150 ... Cutting cutter 160 ... Air pressure adjusting chamber 161 ... Air blower 162 ... Solenoid valve 170 ... Control mechanism , 180 ... conveying mechanism, G ... molten glass, S ... glass tube.

Claims (16)

A glass tube molding apparatus using the Danner method,
A sleeve for forming molten glass into a tubular shape;
Drive means for rotating the sleeve;
A pulling means for pulling a glass tube formed into a tubular shape from the tip of the sleeve;
Gas supply means for supplying gas from the sleeve side into the glass tube;
Pressure measuring means for measuring the pressure in the glass tube;
A cutting means arranged in a pressure adjusting chamber capable of adjusting the indoor pressure, and cutting the glass tube into a predetermined length;
Control means for controlling the pressure in the atmospheric pressure adjustment chamber according to the fluctuation of the pressure in the glass tube;
An apparatus for forming a glass tube, comprising:   2. The glass tube forming apparatus according to claim 1, wherein an inner diameter of the glass tube is one tenth or more of an outer diameter of a tip of the sleeve. The control means includes
The apparatus for forming a glass tube according to claim 1 or 2, wherein when the pressure in the glass tube exceeds a predetermined value, the pressure in the atmospheric pressure adjusting chamber is lowered. The control means includes
The apparatus for forming a glass tube according to any one of claims 1 to 3, wherein when the pressure in the glass tube is equal to or lower than a predetermined value, the pressure in the atmospheric pressure adjustment chamber is increased. A glass tube molding apparatus using the Danner method,
A sleeve for forming molten glass into a tubular shape;
Drive means for rotating the sleeve;
A pulling means for pulling a glass tube formed into a tubular shape from the tip of the sleeve;
Gas supply means for supplying gas from the sleeve side into the glass tube;
An outer diameter measuring means for measuring the outer diameter of the glass tube;
A cutting means arranged in a pressure adjusting chamber capable of adjusting the indoor pressure, and cutting the glass tube into a predetermined length;
Control means for controlling the pressure in the atmospheric pressure adjustment chamber according to the fluctuation of the outer diameter of the glass tube;
An apparatus for forming a glass tube, comprising:   6. The glass tube forming apparatus according to claim 5, wherein an inner diameter of the glass tube is one tenth or more of an outer diameter of a tip of the sleeve. The control means includes
The glass tube forming apparatus according to claim 5 or 6, wherein when the outer diameter of the glass tube exceeds a predetermined value or less, the pressure in the atmospheric pressure adjusting chamber is lowered. The control means includes
The apparatus for forming a glass tube according to any one of claims 5 to 7, wherein when the outer diameter of the glass tube is equal to or less than a predetermined value, the pressure in the atmospheric pressure adjustment chamber is increased. A glass tube forming method by the Danner method,
Wrapping molten glass around a rotating sleeve and forming it into a tubular shape;
Drawing a glass tube formed into a tubular shape from the tip of the sleeve;
Supplying gas from the sleeve side into the glass tube;
Cutting the glass tube into a predetermined length in a pressure control chamber capable of adjusting the indoor pressure;
A step of controlling the pressure in the atmospheric pressure adjustment chamber according to the fluctuation of the pressure in the glass tube;
A method of forming a glass tube, comprising:   The glass tube forming method according to claim 9, wherein an inner diameter of the glass tube is one tenth or more of an outer diameter of a tip of the sleeve. The step of controlling the pressure includes
The method for forming a glass tube according to claim 9 or 10, wherein when the pressure in the glass tube exceeds a predetermined value, the pressure in the atmospheric pressure adjustment chamber is lowered. The step of controlling the pressure includes
The method for forming a glass tube according to any one of claims 9 to 11, wherein when the pressure in the glass tube is equal to or lower than a predetermined value, the pressure in the atmospheric pressure adjustment chamber is increased. A glass tube forming method by the Danner method,
Wrapping molten glass around a rotating sleeve and forming it into a tubular shape;
Drawing a glass tube formed into a tubular shape from the tip of the sleeve;
Supplying gas from the sleeve side into the glass tube;
Cutting the glass tube into a predetermined length in a pressure control chamber capable of adjusting the indoor pressure;
A step of controlling the pressure in the atmospheric pressure adjustment chamber according to a change in the outer diameter of the glass tube;
A method of forming a glass tube, comprising:   The method for forming a glass tube according to claim 13, wherein an inner diameter of the glass tube is one tenth or more of an outer diameter of a tip of the sleeve. The step of controlling the pressure includes
The method for forming a glass tube according to claim 13 or 14, wherein when the outer diameter of the glass tube exceeds a predetermined value, the pressure in the atmospheric pressure adjusting chamber is lowered. The step of controlling the pressure includes
The method for forming a glass tube according to any one of claims 13 to 15, wherein the pressure in the atmospheric pressure adjusting chamber is increased when the outer diameter of the glass tube is equal to or less than a predetermined value.

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