JPH02188430A - Production of glass - Google Patents

Abstract

PURPOSE:To highly remove bubbles and to improve homogeneity by stirring molten glass freed of bubbles under a reduced pressure and molding the resulting homogenized molten glass. CONSTITUTION:Molten glass having 10<2>-10<3>P viscosity is freed of bubbles by holding under a reduced pressure of 1/20-1/3atm for 30-90min. The viscosity of the molten glass is then regulated to 10<2.5>-10<3.5> P and the molten glass is homogenized by stirring at 0.5-1.5m/min peripheral speed for 10-30min and molded into a desired shape.

Description

[Detailed description of the invention] (Industrial application field) The present invention relates to a method for manufacturing glass.

(Prior Art) When molten glass that has been refined is stirred, air bubbles are generated in the molten glass, and these air bubbles are mixed into the product. Therefore, the manufacturing method for glass with a high degree of air bubble removal is to stir molten glass to homogenize it, hold the homogenized molten glass at high temperature for a long time, and float and remove air bubbles generated in the glass. A method of molding this into a predetermined shape is adopted.

However, this method has a problem in that the molten glass becomes non-uniform during the process of removing air bubbles, and although the air bubbles are removed to a high degree, a product with reduced homogeneity is obtained.

(Problems to be Solved by the Invention) It is an object of the present invention to solve the above-mentioned problems that the conventional techniques had, and to provide a method for producing glass in which air bubbles are removed to a high degree and the glass is excellent in homogeneity.

(Means for Solving the Problems) The present invention is a method for producing glass, which includes defoaming molten glass under reduced pressure, stirring the defoamed molten glass to homogenize it, and molding the homogenized glass into a predetermined shape. It provides:

Although the composition of the glass in the present invention is not particularly limited, it is particularly suitable for glass in which the temperature in the clear region, that is, when the viscosity reaches 10" to 101 voids, is relatively high and homogeneity is required. Such glasses include low-alkali glass containing little alkali metal, alkali-free glass containing no alkali metal, SrO, B
Examples include glass for panels of color cathode ray tubes containing a relatively large amount of aO.

In the present invention, defoaming of the molten glass under reduced pressure is preferably carried out when the viscosity of the molten glass is 10' to 10'' voice.

If the viscosity is greater than 103 Boise, it is undesirable because it takes a long time for defoaming or defoaming is not substantially performed. On the other hand, if the viscosity is less than 10" Boise, defoaming is performed in a short time. Although this is possible, it requires a large amount of heat energy, which is not preferable in terms of energy conservation.

Furthermore, as for the pressure at that time, if the pressure is too high, the defoaming effect will be reduced, and if it is too low, the equipment for reducing the pressure will be complicated and the energy required to obtain the reduced pressure will be extremely large, so neither is preferable. The preferred pressure is l/20~
It is in the range of 1/3 atmospheric pressure.

Furthermore, the time for holding under such reduced pressure is 30 minutes to
90 minutes is preferred. If this holding time is shorter than 30 minutes, a sufficient defoaming effect cannot be obtained, and if it exceeds 90 minutes, glass productivity decreases, which is not preferable.

The defoamed glass is stirred and homogenized. Such stirring is usually carried out under atmospheric pressure, but can also be carried out under reduced pressure.

Such stirring is performed when the viscosity of the glass is IQl, S ~ 103.6
It is preferable to do this for things within the Boise range.
The reason is as follows. That is, the viscosity of glass is 10
If the viscosity of the glass is larger than 10"°.6 voids, it is undesirable because it takes time to obtain a homogenized glass. If the viscosity of the glass is smaller than 10"°6 voids, it is undesirable because a lot of thermal energy is consumed. More preferably, stirring is carried out while the viscosity of the glass is within the range of 101 to 103 S voids.

For stirring, a wide range of commonly used materials can be used. For example, by providing blades radially to the rotating shaft,
A type that stirs the molten glass by immersing it in the molten glass and rotating it, with a plurality of protruding members,
An example is a type in which the convex member is immersed in the molten glass and moved back and forth to stir the molten glass.

Too strong stirring is not preferred because it tends to cause the following drawbacks. That is, new bubbles are likely to be generated around the blades due to the cavitation phenomenon. Additionally, there is a risk that air may be drawn in from above the glass substrate.

Too weak stirring is not preferred because homogenization will be insufficient.

Preferably, in the former type, the circumferential speed of the blade is 0.
It ranges from 5 to 1.5 rmI minutes. On the other hand, in the latter type, it is preferable that the speed of the convex member is in the range of 1 to 2 m/min.

In addition, the stirring time is preferably 10 to 30 minutes; if the stirring time is shorter than 10 minutes, homogenization tends to be insufficient (so it is undesirable), and if it is longer than 30 minutes, the productivity of glass decreases, which is undesirable. .

(Thus, the homogenized molten glass is then formed into a desired shape, such as a plate shape.

In the present invention, each of the above steps may be provided in the flow path of the glass, such as in a continuous melting tank, and the above treatments may be performed while the glass is flowing. It can also be carried out by so-called batch processing in which the steps are repeated.

(Example) A batch or cullet prepared to have the target composition shown in the table was weighed, placed in a platinum crucible, and heated to obtain molten glass. When heating, the viscosity of glass is approximately 10
``I held it at the temperature where it became voiced until the gravel and bubbles disappeared.

This molten glass was then held under reduced pressure to defoam. The viscosity, pressure, and holding time of the glass at this time are listed in the same table.

The glass was then brought to a viscosity of about 1Os and stirred.

As for the stirring method, a stirrer with 20×50 mm square blades was inserted into the glass, and
It was carried out for 10 to 30 minutes at a rotation speed of m.

Next, this glass was formed into a plate shape, and then the air bubbles were measured. The results are also listed in the same table. In the same table, the case without vacuum treatment is a comparative example, in which glass was melted and clarified under the same conditions and stirred under the same conditions without vacuum treatment, then formed into a plate shape, and the glass was measured.

As is clear from the figure, bubbles that had previously disappeared due to fining are generated by stirring, but according to the present invention, the generation of such bubbles is extremely small.

Further, although not shown in the figure, in the glass according to the present invention, almost no striae can be seen with the naked eye, but in the glass that was not stirred, a large amount of striae was found.

(Effects of the Invention) According to the present invention, a glass with excellent homogeneity and no bubbles can be obtained, and the yield can be improved.

The above-mentioned effect is particularly great for panel glass for color cathode ray tubes, etc., which require strict quality in terms of homogeneity and bubble point.

Furthermore, since stirring can be performed in a region with higher viscosity than in conventional methods, the stirring process can be easily controlled and thermal energy can be saved.

Claims (1)

[Claims] A method for manufacturing glass, which includes defoaming molten glass under reduced pressure, stirring and homogenizing the defoamed molten glass, and molding the homogenized glass into a predetermined shape.