JPH11302024A - Apparatus for production of float sheet glass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress the oxygen dissolution into a molten tin bath and the formation of tin oxide defects by providing a side sealing wall with a discharge through-hole disposed in a position lower than the central axis position of an assist roll and higher than the surface of the molten tin one piece or more. SOLUTION: Stretching force is applied by the assist roller 4 on a glass ribbon 1 floating on the molten tin 2 of the molten tin bath 7. The assist roll 4 is inserted into the side sealing wall 5. The discharge through-hole 6 is disposed in the position lower than the axial central position of the assist roll 4 and higher than the surface position of the molten tin 2. The diameter of the discharge through-hole 6 is specified to >=0.5 mm in order to suppress the diffusion and infiltration of the outdoor air by a venturi effect and is preferably specified to <=200 mm in order to maintain the upper space at a position pressure. If the discharge through-holes 5 are disposed at >=2 positions, the installation spacing therebetween is preferably confined to <=3000 mm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for producing sheet glass by a float method.

[0002]

2. Description of the Related Art A conventional float plate glass manufacturing apparatus includes a bath (hereinafter, referred to as a molten tin bath) filled with a molten metal (usually, molten tin or a molten tin alloy; hereinafter, the case of molten tin will be described). It comprises a molten tin upper structure (hereinafter referred to as an upper structure) for maintaining an atmosphere in contact with the molten tin in a reduced state, and a side sealing wall provided between the molten tin bath and the upper structure. The side sealing wall is usually composed of one or more blocks, and at least a part of the side sealing wall is removable.

[0003] In the production of sheet glass by the float method, molten glass is continuously poured into the float sheet glass production apparatus, and a stretching force is applied by one or more rolls (hereinafter referred to as assist rolls) inserted into side sealing walls. The molten glass is formed into a glass ribbon having a desired thickness and width. A reducing gas (usually a mixed gas of nitrogen gas and hydrogen gas) is supplied to the upper space of the molten tin bath surrounded by the upper structure of the molten tin and the side sealing wall to prevent oxidation of the molten tin. ing. The gas mainly composed of the reducing gas and existing in the upper space of the molten tin bath is hereinafter referred to as an atmosphere.

[0004] However, if oxygen enters through the side sealing wall or a clearance around it and the reducing action by the reducing gas is insufficient, the oxygen dissolves in the molten tin and contaminates the molten tin. When the oxygen concentration in the molten tin increases, tin oxide is likely to be generated, and as a result, tin oxide defects of the glass increase.

[0005] In order to prevent the oxidation of molten tin, conventionally, measures have been taken to prevent the intrusion of oxygen into the atmosphere above the molten tin and to eliminate the gap around the side sealing wall. Intrusion control is still inadequate. Also, the assist roll inserted to obtain the desired glass thickness and width is movable around the assist roll axis so that it can appropriately cope with production of various types.
It is virtually impossible to completely eliminate the gap near the assist roll shaft.

On the other hand, the atmosphere is kept reductive in order to prevent tin contamination by oxygen penetrating from the side sealing wall or a clearance around the side sealing wall. However, even if only a few ppm of oxygen is present in the atmosphere, the molten tin is easily contaminated, and it has been extremely difficult to completely eliminate the molten tin contamination due to invading oxygen.

[0007]

SUMMARY OF THE INVENTION The present invention can suppress the dissolution of oxygen into molten tin in a molten tin bath and the generation of tin oxide defects due to the intrusion of oxygen into the upper space, which could not be achieved by the prior art. An object of the present invention is to provide a float plate glass manufacturing apparatus.

[0008]

SUMMARY OF THE INVENTION The present invention provides a molten tin bath for holding molten tin, an upper structure, a side sealing wall provided between the molten tin bath and the upper structure, and a side sealing wall. A float sheet glass manufacturing apparatus provided with one or more inserted rolls (hereinafter, referred to as assist rolls), wherein an exhaust through-hole provided at a position lower than the assist roll axial center position and higher than a molten tin surface position is formed. Provided is an apparatus for manufacturing a float glass sheet having at least one piece on a sealing wall.

The present inventors have earnestly studied oxygen intrusion into the upper space and have obtained the following findings.
Usually, since the assist roll is cooled, a downward flow occurs near the assist roll. Therefore, the outside air (containing about 20% of oxygen) entering from near the assist roll shaft rides on the downward flow, is guided from the inner surface of the side wall to the molten tin surface, and is dissolved in the molten tin, thereby rapidly contaminating the molten tin. I do. Therefore, in order to forcibly discharge oxygen that has entered from the outside to the outside without contacting the molten tin, an exhaust through hole is installed at a position lower than the center position of the assist roll on the side wall and higher than the surface position of the molten tin. However, it was found that it is essential that the invading oxygen be discharged in an airflow that is forcibly discharged to the outside before the oxygen enters the molten tin surface by flowing down the atmosphere.

The upper space is usually filled with a reducing gas and has a positive pressure with respect to the atmospheric pressure. But,
Even if the upper space is maintained at a positive pressure, if there is a minute gap on the side wall, especially if there is a gap of 0.5 mm or less, invasion of outside air by the venturi effect cannot be avoided. It is virtually impossible to eliminate a gap of 5 mm or less over the entire side wall. Therefore, it is useful to install the exhaust through-hole even in the side wall portion without the assist roll, and the lower the installation height, the more effective. However, it is sufficiently effective to install it at a position lower than the position of the center of the assist roll which is generally installed.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The exhaust through hole according to the present invention is installed at a position lower than the assist roll axis center position on the side wall and higher than the molten tin surface position. It is preferable to install as close to the molten tin surface as possible.

The diameter of the exhaust through-hole is preferably 0.5 mm or more in order to suppress the invasion of the outside air due to the Venturi effect. In order to keep the upper space at a positive pressure, the diameter of the exhaust through hole is preferably 200 mm or less.

The interval between the exhaust through holes is preferably 3000 mm or less in order to exhibit the effect over the entire area of the float plate glass manufacturing apparatus of the present invention. The installation interval here is the distance between the centers of the exhaust through holes.
The smaller the installation interval is, the better, but the lower limit is about the diameter of the exhaust through hole + 50 mm in view of the space required for installation.

The diameter, installation interval and number of the exhaust through-holes must be determined within a range where the upper space can be maintained at a positive pressure with respect to the atmospheric pressure. That is, it must be determined that the total flow rate of the gas discharged from the exhaust through hole is smaller than the flow rate of the reducing gas supplied to the upper space.

The exhaust through-holes have a diameter of 10 to 50 mm, and the intervals between the exhaust through-holes are 300 to 1000 mm. It is preferable to install. The material constituting the exhaust through-hole is not particularly limited, and a generally used heat-resistant metal material or heat-resistant ceramic material can be used.

Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a partial cross-sectional view of a float glass manufacturing apparatus according to an embodiment of the present invention. FIG. 2 is a partial side view thereof. In FIG. 2, the details of the side sealing wall are omitted.

A stretching force is applied to the glass ribbon 1 (only the edge portion is shown in the figure) floating on the molten tin 2 of the molten tin bath 7 by the assist roll 4. The assist roll 4 is inserted into the side sealing wall 5. The exhaust through-hole 6 is provided at a position lower than the axial center position of the assist roll 4 and higher than the surface position of the molten tin 2.

[0018]

According to the present invention, the atmosphere near the surface of molten tin can be discharged to the outside. In other words, even when the outside air enters from the side wall and rides on the downflow of the atmosphere, the atmosphere near the surface of the molten tin can be discharged by the airflow that is forcibly discharged to the outside. Oxygen dissolution in tin can be suppressed. As a result, it is possible to suppress the generation of defects due to the adhesion of tin oxide to the glass ribbon.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view in a width direction of a molten tin bath according to an embodiment of the present invention.

FIG. 2 is a partial side view of the embodiment of the present invention.

[Explanation of symbols]

 1: glass ribbon 2: molten tin 3: upper structure 4: assist roll 5: side sealing wall 6: exhaust through hole 7: molten tin bath

Claims (3)

[Claims] 1. A molten tin bath for holding molten tin, an upper structure, a side sealing wall provided between the molten tin bath and the upper structure, and one or more rolls inserted into the side sealing wall (hereinafter, referred to as a roll). Float glass manufacturing apparatus comprising: a float having at least one exhaust through hole provided in a side sealing wall at a position lower than the assist roll axis position and higher than the molten tin surface position. Flat glass manufacturing equipment. 2. A float glass manufacturing apparatus according to claim 1, wherein the diameter of the exhaust through hole is 0.5 to 200 mm. 3. The float glass manufacturing apparatus according to claim 1, wherein the apparatus has two or more exhaust through holes, and a distance between centers of adjacent exhaust through holes is 3000 mm or less.