JPH11139833A - Production of glass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To decrease the number of microbubbles in product glass by defoaming molten glass under a reduced pressure and cooling the molten glass down to a temp. at which refoaming does not occur in the state of holding the pressure by executing the foam suppressing under the pressure exceeding the atm. pressure after the defoaming. SOLUTION: Glass raw material is melted at a temp. of about 1.5 to 2.5 the viscosity (log η) within a dissolving vessel, by which the molten glass is formed. The molten glass is stirred in a stirring vessel to microfoam the dissolved gas and to make the blank uniform. The molten glass contg. the very fine air bubbles is introduced by an introducing means, such as a riser, into a reduced pressure vessel where the molten glass is made into a viscosity of about 2.5 to 3.5 in a reduced pressure state of 1/20 to 1/3 atm. pressure. The very fine air bubbles float and break and the dissolved gas subjected to defoaming decreases. Then molten glass is introduced from the reduced pressure vessel to a storage tank by a leading-out means (downcomer) where the molten glass is pressurized to the pressure higher by about 0.2 to 0.5 than atm. pressure at about the viscosity 3.0 to 4.0 and is held under the pressure for >=30 to 60 minutes to execute the foam suppressing of the microfoam. The molten glass is then cooled down to the temp. (viscosity about 3.5 to 4.5) at which the refoaming does not occur. The molten glass is then sent to a molding stage and is molded to the glass products.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing glass by removing bubbles contained in molten glass.

[0002]

2. Description of the Related Art A fining step (defoaming step) at the time of melting glass is usually carried out by adding an appropriate fining agent in advance, and a typical example of this fining agent is sodium sulfate. Glauber's salt is decomposed at the refining temperature to generate SO ₃ bubbles, which mainly have a refining effect. In addition, for a substrate that is too viscous at the decomposition temperature of sodium sulfate and difficult to clarify with sodium sulfate, for example, As ₂ O ₃ or Sb ₂
O ₃ or the like is used. However, As ₂ O ₃ and Sb ₂ O ₃
When is used in the float molding method, it reacts with tin in the float bath and causes a drawback, which is not suitable for the float molding method.

As described above, a vacuum degassing method has been proposed for the purpose of refining glass that cannot be refined by a normal method.
An example of this is disclosed in JP-A-62-235222. In this vacuum degassing method, the clarification effect itself is high because the molten glass base is introduced into a vacuum chamber kept at atmospheric pressure or less,
It is not always suitable for a glass substrate having a composition containing a volatile component typified by B ₂ O ₃ because the volatile component volatilizes during fining.

[0004] In this respect, in the vacuum degassing apparatus of the type already proposed by the present applicant, the area exposed to the reduced pressure is limited only to the surface of the substrate, so that the volatilization of volatile components during fining can be suppressed. It has such an excellent feature. The technique of defoaming under reduced pressure as described above, which is further improved and improved is described in, for example, JP-A-2-1884.
No. 30, JP-A-2-221129, JP-A-3-330
No. 20, JP-A-5-58646, JP-A-5-2088
No. 30, etc.

[0005] Among them, for example, in the apparatus disclosed in Japanese Patent Application Laid-Open No. 3-33020, a method is adopted in which molten glass is successively led to a forming step through a melting tank, an ascending pipe, a vacuum degassing tank, a descending pipe and a storage tank. The equipment basically uses the principle of siphon, and guides the molten glass from the melting tank to a vacuum degassing tank, where it is defoamed to form a homogeneous molten glass, and then molded to form a glass with high homogeneity. Get the product.

[0006]

However, even when such a vacuum degassing apparatus is used, fine bubbles are difficult to float and may remain, and in recent years when increasingly high quality glass is required, Defoaming may not be sufficient.

[0007]

According to the present invention, the molten glass is defoamed under reduced pressure, and the bubbles remaining after defoaming are bubbled under a pressure exceeding atmospheric pressure, and the pressure is maintained. A method for producing glass, comprising a step of cooling to a temperature at which foaming does not occur again in a state.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the defoamed molten glass is pressurized and foamed, and cooled to a temperature at which refoaming is performed while maintaining the pressure. Can be very low.

It is known that the pressure of the molten glass reduces the bubble diameter (this is referred to herein as "bubbling"). In particular, it is considered that when the bubble diameter becomes smaller and the surface tension of the bubble becomes larger than the pressure inside the bubble, the bubble disappears in effect.

However, simply pressurizing the molten glass does not have a great effect on reducing bubbles because the original bubble diameter is too large.

On the other hand, in the present invention, the molten glass is depressurized once and then pressurized. In vacuum defoaming, the molten glass is placed in a reduced pressure state of, for example, 1/20 to 1/3 atm, so that large bubbles that easily float are removed. After defoaming under reduced pressure, the dissolved gas in the molten glass has been reduced. Since the gas in the bubble diffuses into the molten glass due to the pressure difference between the inside and the outside of the bubble, the reduction in the bubble diameter is accelerated when the amount of the dissolved gas in the molten glass is small. Therefore, if pressure is applied after defoaming under reduced pressure, the bubble diameter can be efficiently reduced, and the effect of reducing the number of bubbles is remarkable.

The method of the present invention will be described step by step.

First, the molten glass is defoamed under reduced pressure. This method can be performed by a known vacuum degassing method. That is, JP-A-62-235222, JP-A-3-33
020 and JP-A-5-208830. For example, Japanese Patent Application Laid-Open No. 3-3302
In the case of the method of No. 0, the following may be performed.

In the melting tank, the viscosity logη = 1.5 to
About 2.5 (1400 temperature with soda lime silica glass)
The glass raw material is melted at a temperature of about 1500 ° C. to obtain a molten glass.

Next, the molten glass is stirred by a stirrer in a stirring tank. By this stirring, the dissolved gas is microbubble, and the unevenness of the substrate generated when the raw material is dissolved is corrected.

Next, the molten glass containing such fine bubbles is introduced into a decompression tank by an introduction means such as a riser. The pressure inside the decompression tank is reduced to below atmospheric pressure, for example, 1/20 to 1
It is set to a reduced pressure of / 3 atm. The viscosity is logη =
It is preferable to set it to about 2.5 to 3.5 (about 1300 ° C. in soda lime silica glass). Under reduced pressure, the fine bubbles in the molten glass increase in bubble diameter and float to form a foam layer on the surface of the molten glass. When the foam layer breaks, the molten glass is defoamed, and the dissolved gas in the molten glass also decreases.

Next, the molten glass is drawn out of the decompression tank by a drawing-out means (downcomer), guided to a storage tank, and homogenized by auxiliary stirring with a stirrer in the storage tank.

Next, in the present invention, the molten glass is pressed. The pressure is suitably about 0.2 to 0.5 atm higher than the atmospheric pressure. And in that state, 30-6
Hold for at least 0 minutes. During that time, micro bubbles contained in the molten glass are foamed. As a pressurizing means, a method of pressurizing the entire system by pressure-feeding the molten glass to a closed container with a pump or the like,
There is a method in which the base channel is deepened so that the molten glass stays there for a certain time. Pressure treatment is performed with viscosity l
og η = approximately 3.0 to 4.0 (soda lime silica glass at a temperature of approximately 1200 ° C.).

Next, the mixture is cooled to a temperature at which it does not re-foam, for example, a viscosity logη = about 3.5 to 4.5 (about 1100 ° C. with soda lime silica glass). The cooling may be forced cooling or natural cooling. Methods of forced cooling include air cooling and insertion of a water pipe.

Next, the molten glass is sent to a forming step by a float method or the like, and is formed into various glass products having high homogeneity.

The method of the present invention can be applied to various glasses. For example, the present invention can be applied to soda lime silica glass, borosilicate glass, aluminosilicate glass, non-alkali glass, CRT panel, funnel or neck tube glass, lamp glass, bottle glass, and the like.

[0022]

As described above, according to the present invention, the number of microbubbles in the product glass can be greatly reduced by pressurizing the molten glass after defoaming under reduced pressure.

Claims (1)

[Claims] 1. Degassing of a molten glass under reduced pressure, further bubbling of bubbles remaining after degassing under a pressure exceeding atmospheric pressure, and cooling to a temperature at which refoaming is performed while maintaining the pressure. A method for producing glass, comprising the steps of: