JPH08283031A - Production of glass tube - Google Patents

Abstract

PURPOSE: To decrease bubbles and to improve workability by adjusting the steam partial pressure in a muffle furnace by a steam supplying mechanism at the time of forming a glass tube by a Danner method. CONSTITUTION: Fused glass G is allowed to flow down in a ribbon form from a trough 10, is wound around the root part of a rotary sleeve 13 by a motor 11 for the sleeve, is gradually lowered downward and is pulled by an automatic pipe pulling machine 14 in the Danner method glass tube making method for supplying the fused glass onto the sleeve rotating in the muffle furnace 12 and pulling the glass to the glass pulling machine while blowing blow air into the fused glass through the sleeve shaft disposed at the central axis of the sleeve. The blow air is supplied from a blow air generating machine 16 to the sleeve shaft 15. A pipe 19 having a front end aperture 19a disposed in the muffle furnace 12 is connected to this steam generating machine 18. The steam partial pressure in the muffle furnace 12 is adjusted by operating the steam generating machine 18 at the time of production, by which the steam concn. in the glass is increased and the bubbles, softening point and distortion point are lowered.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a glass tube by the Danner method.

[0002]

2. Description of the Related Art The Danner method, which is one of the methods for manufacturing glass tubes, supplies molten glass onto a sleeve that rotates in a muffle furnace, and blow air generated from a blow air generator is used as a molding machine. The glass tube is formed by pulling the glass with a tube pulling machine while blowing it into the molten glass through a sleeve shaft provided on the central axis of the glass, and then cutting the glass tube into a predetermined length with a cutting machine.

[0003]

By the way, in the production of glass, the viscosity and the infrared absorptivity of the glass are likely to vary depending on the melting conditions thereof, and these characteristics will affect the workability after glass forming. For example, in the case of a glass tube, various bending processes are performed depending on the application, but if the viscosity is high during glass processing or the infrared absorptivity is low, a large amount of heat is required when processing the glass tube. This will lead to higher costs.

As described above, a major cause of fluctuations in the viscosity and infrared absorptivity during the processing of glass depending on the melting conditions is that the concentration of water in the molten glass tends to change due to the influence of the melting atmosphere and the like. According to Henry's law, water molecules easily enter and leave the molten glass, and the water in the glass has a network structure of glass.

[0005]

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Breaking the bond,

[0007]

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In the form of the above, the structural change causes fluctuations in viscosity and infrared absorptivity during processing of glass. That is, the higher the concentration of water in the molten glass, the lower the viscosity of the glass and the higher the infrared absorptivity, which facilitates processing.

However, even if a large amount of water is dissolved in the glass melting furnace, the dissolved water molecules are unfavorably separated from the glass in a low temperature portion such as the glass molding portion, and bubbles are easily formed.

An object of the present invention is to provide a method capable of suppressing the generation of bubbles when manufacturing a glass tube by the Dunner method, maintaining a low viscosity during the processing of glass, and maintaining a high infrared absorption rate. Is to provide.

[0011]

According to the method of manufacturing a glass tube of the present invention, molten glass is supplied onto a sleeve rotating in a muffle furnace, and blow air generated from a blow air generator is fed to a central axis of the sleeve. When forming a glass tube by pulling the glass with a tube drawing machine while blowing it into the inside of the molten glass through a sleeve shaft provided in, a steam supply mechanism is used to adjust the partial pressure of steam in the muffle furnace. .

The steam supply mechanism used in the present invention comprises a steam generator for generating steam or a mixed gas of steam and air, and a pipe for supplying such a gas into the muffle furnace. As a steam generator,
For example, a boiler can be used, which is decompressed and then mixed with air adjusted to an appropriate pressure to obtain a mixed gas of water vapor and air. Further, if the boiler and the muffle furnace are connected by a pipe and a valve is provided in the middle of this pipe, steam or a mixed gas of this and air will be supplied into the muffle furnace when the valve is opened.

The water vapor partial pressure may be adjusted within the range of 0 to 1 atm. That is, when the concentration of water in the molten glass is sufficiently high, it is not necessary to operate the water vapor supply mechanism, while when the concentration of water in the molten glass is low, it is necessary to operate the water vapor supply mechanism. Even at the maximum, it is sufficient to set the water vapor partial pressure to 1 atm.

Further, in order to achieve the intended purpose of the present invention, it is necessary to prevent excess air from entering the muffle furnace from the outside, and the pressure inside the muffle furnace is higher than the pressure outside the furnace. The amount of water vapor and the mixed gas of this and air must be adjusted so that it becomes higher, and the outlet of the glass tube which is the opening opening of the muffle furnace must be made as small as possible.

[0015]

In the production of the glass tube by the Dunner method, the molten glass supplied onto the sleeve has a slow flow, so that the contact time with the atmospheric gas is long and the surface area in contact with the atmospheric gas per unit weight is large. for that reason,
It is considered that this molten glass reaches the equilibrium of melting and desorption based on Henry's law with the atmospheric gas, and as a result, the molten glass on the sleeve is adjusted by adjusting the partial pressure of water vapor in the muffle furnace. It is possible to adjust the concentration of water in the water.

[0016]

EXAMPLES The method for producing a glass tube of the present invention will be described in detail below with reference to examples.

FIG. 1 is an explanatory view showing an apparatus for carrying out the glass tube manufacturing method of the present invention.

In the figure, the molten glass G flowing down from the trough 10 in a ribbon shape is wrapped around the base of the sleeve 13 rotating in the muffle furnace 12 by the sleeve motor 11 and gradually moves downward. The molten glass G reaching the tip of the sleeve 13 is pulled by the automatic pipe drawing machine 14 at an appropriate speed while rotating with the rotation of the sleeve 13, and blown onto the sleeve shaft 15 penetrating the axial center of the sleeve 13. Blow air having an appropriate pressure is supplied from a generator 16 to form a glass tube T having a predetermined size, and then a cutting machine 17 cuts the glass tube T into a predetermined length.

In this apparatus, a steam generator 18 is provided outside the muffle furnace 12, and this steam generator 1
A heat-resistant steel pipe 19 leads from 8 to the muffle furnace 12. This pipe 19 is about 2 m inside the muffle furnace 12.
It is provided so as to crawl, and the tip end opening portion 19a is
It is directed to the molten glass G wrapped around the base of the sleeve 13.

It should be noted that about 2 pipes 19 are placed in the muffle furnace 12.
The reason for crawling in mm is to prevent the molten glass G from partially cooling by making the mixed gas equal to the room temperature in the muffle furnace 12.

Using such a device, silica-lead-
When a potassium-soda glass tube was manufactured, the water concentration in the glass when the steam generator 18 was not activated was 50 ppm, but the steam generator 18 was activated,
A mixed gas of water vapor and air is introduced into the tip opening portion 1 of the pipe 19.
When it is blown out from 9a, the concentration of water in the glass gradually increases, and when the partial pressure of water vapor in the muffle furnace 12 is finally adjusted to 0.5 atm, the concentration of water in the glass becomes 250 ppm. After that, it kept an almost constant value.

In order to examine the workability of the glass tube before and after operating the steam generator 18, the softening point and the strain point were examined. The former glass tube had a softening point of 615 ° C.,
While the strain point was 395 ° C, the softening point of the latter glass tube was 603 ° C and the strain point was 378 ° C. As the softening point and strain point are lower, it is possible to bend the glass tube with a smaller amount of heat. Therefore, it is clear that the latter glass tube has better workability than the former glass tube. is there.

The water concentration in the above glass is measured based on the infrared transmittance curve.

[0024]

As described above, according to the method of the present invention, the concentration of water in the glass can be increased without dissolving a large amount of water in the glass melting furnace. It is possible to manufacture a glass tube having excellent properties.

[Brief description of drawings]

FIG. 1 is an explanatory view showing an apparatus for carrying out the glass tube manufacturing method of the present invention.

[Explanation of symbols]

 12 Muffle furnace 13 Sleeve 15 Srib shaft 18 Steam generator 19 Pipe

Claims (1)

[Claims] 1. While supplying molten glass onto a sleeve that rotates in a muffle furnace and blowing blow air generated from a blow air generator into the inside of the molten glass through a sleeve shaft provided on the central axis of the sleeve. A method for producing a glass tube, which comprises adjusting a partial pressure of water vapor in a muffle furnace by a water vapor supply mechanism when the glass tube is formed by pulling the glass with a tube drawing machine.