TW201714840A - Apparatus and method for manufacturing glass sheet capable of uniformly heating the molten glass in a clarification tube without disturbing the flow of the gas in the gas phase space - Google Patents

Abstract

The present invention can uniformly heat the molten glass in a clarification tube without disturbing the flow of gas in the gas phase space. This invention provides a method for manufacturing a glass substrate, which comprises a clarification step to allow the molten glass flowing from the upstream side to the downstream side while heating the molten glass in a clarification tube arranged in a substantially horizontal direction, such that bubbles in the molten glass are discharged toward the gas phase space surrounded by the interface of the molten glass and the inner wall of the clarification tube. Being spaced from the lowermost portion and the uppermost portion of the inner wall of the clarification tube, a plate member is vertically arranged relative to the longitudinal direction of the clarification tube. In the clarification step, the flow amount and the flow rate of the molten glass flowing in the clarification tube are controlled so that the height of the interface of the molten glass is higher than the upper end portion of the plate member.

Description

Method for producing glass substrate and device for manufacturing glass substrate

The present invention relates to a method for producing a glass substrate and a device for producing a glass substrate.

The glass substrate is generally produced by a step of forming molten glass from a glass raw material and then forming the molten glass into a glass substrate. The above step includes a step of removing minute bubbles (hereinafter also referred to as clarification) contained in the molten glass. The clarification is carried out by heating the main body of the clarification pipe, and passing the molten glass prepared with the clarifying agent through the clarification pipe main body, and removing the bubbles in the molten glass by the redox reaction of the clarifying agent. More specifically, the temperature of the molten glass which is coarsely melted is further increased, and the clarifying agent functions to float and defoam the bubbles, and then the temperature is lowered, whereby the molten glass absorbs the relatively small amount of defoaming and remains relatively small. bubble. That is, the treatment including the treatment for floating and defoaming the bubbles (hereinafter also referred to as the defoaming treatment or the defoaming step) and the treatment of absorbing the small bubbles by the molten glass (hereinafter also referred to as an absorption treatment or absorption step) are clarified. The inner wall of the member that is in contact with the high-temperature molten glass before molding needs to contain an appropriate material depending on the temperature of the molten glass that is in contact with the member, the quality of the desired glass substrate, and the like. For example, it is known that a material constituting the clarification pipe main body is generally a simple substance or an alloy of a platinum group metal (Patent Document 1). The platinum group metal has a high melting point and is excellent in corrosion resistance to molten glass. [Prior Art Document] [Patent Document] [Patent Document 1] Japanese Patent Laid-Open Publication No. 2010-111533

[Problem to be Solved by the Invention] In the clarification step, the clarification tube is heated by energizing a clarification tube containing a simple substance or alloy of a platinum group metal, whereby the molten glass passing through the clarification tube is heated (heating heating). At this time, the temperature of the molten glass passing through the vicinity of the center of the clarification pipe becomes lower than the temperature of the molten glass in the vicinity of the inner wall of the clarification pipe. Further, since the speed of the molten glass passing through the clarification pipe has wall resistance, the speed near the center of the pipe becomes faster than the vicinity of the inner wall of the clarification pipe. Therefore, there is a problem that the clarification is insufficient by passing the clarification pipe through the molten glass near the center of the clarification pipe without sufficiently heating. On the other hand, if the heating amount of the clarification pipe is increased in order to increase the temperature of the molten glass near the center of the clarification pipe, the volatilization of the element or alloy of the platinum group metal constituting the clarification pipe is promoted by oxidation. If the volatilized platinum group oxide is reduced at a position where the temperature of the clarification tube is locally lowered, the reduced platinum group metal adheres to the inner wall surface of the clarification tube. The platinum group metal adhered to the inner wall surface is dropped and mixed into the molten glass in the defoaming step, and is mixed as a foreign matter into the glass substrate. In order to make the temperature of the molten glass in the clarification pipe uniform, it is also considered to provide a stirring mechanism for agitating the molten glass in the clarification pipe. However, if a stirring mechanism exists in the gas phase space in which the bubble is floated in the clarification pipe, there is a possibility that the flow of oxygen, CO ₂ , SO ₂ or the like contained in the bubble from the gas phase space to the outside of the clarification pipe is prevented. If the flow of the gas in the gas phase space is hindered, the reduced platinum group metal adheres to the inner wall surface of the clarification tube, falls and is mixed into the molten glass in the defoaming step, and is mixed as a foreign matter into the glass substrate. Hey. An object of the present invention is to provide a method for producing a glass substrate capable of uniformly agitating molten glass in a clarification tube without impeding the flow of a gas in a gas phase space, and a device for producing a glass substrate. [Technical means for solving the problem] The present invention encompasses the following various aspects. (1) A method for producing a glass substrate, comprising: a clarification step of flowing the molten glass from an upstream side to a downstream side while heating the molten glass in a clarification pipe disposed substantially in a horizontal direction; The bubbles in the molten glass are discharged toward a gas phase space surrounded by the interface between the molten glass and the inner wall of the clarification pipe, and the clarification pipe is spaced apart from the lowermost portion and the uppermost portion of the inner wall of the clarification pipe, and is opposed to each other. a plate member is vertically disposed in a longitudinal direction of the clarification pipe, and in the clarification step, the above-mentioned flow in the clarification pipe is controlled such that a height of an interface of the molten glass is higher than an upper end portion of the plate member The flow rate and flow rate of the molten glass. (2) The method for producing a glass substrate according to (1), wherein the flow rate and the flow rate of the molten glass flowing in the clarification pipe, that is, the position of the plate member in the longitudinal direction of the clarification pipe, are controlled as follows Dividing the flow rate of the molten glass flowing above the plate member by the flow path cross-sectional area above the plate member and the flow rate of the molten glass flowing below the plate member by The flow velocity obtained by the cross-sectional area of the flow path below the plate member becomes equal. (3) A method for producing a glass substrate, comprising: a clarification step of flowing the molten glass from an upstream side to a downstream side while heating the molten glass in a clarification pipe disposed substantially in a horizontal direction; The bubbles in the molten glass are discharged toward a gas phase space surrounded by the interface between the molten glass and the inner wall of the clarification pipe, and the clarification pipe is provided with a plurality of bubbles arranged perpendicularly to the longitudinal direction of the clarification pipe. The plate member group of the plate member, wherein the plate member group includes: a first plate member group, wherein the plurality of first plate members are arranged at intervals in a longitudinal direction of the clarification pipe, and the plurality of first plate members and The lowermost portion and the uppermost portion of the inner wall of the clarification pipe are disposed at a first height with a space therebetween; and the second plate member group is composed of a plurality of second plate members in a longitudinal direction of the clarification pipe and the first plate member Arranging alternately at intervals, the plurality of second plate members are disposed at an interval between a second height higher than the first height and an uppermost portion of the inner wall of the clarification pipe; and a plate member group in which a plurality of third plate members are alternately arranged at intervals from the first plate member in a longitudinal direction of the clarification pipe, and the plurality of third plate members are lower than the first height The third height is not spaced apart from the lowermost portion of the inner wall of the clarification pipe; and in the clarifying step, the height of the interface of the molten glass is higher than the highest position of the upper end of the plurality of plate members In a manner, the flow rate and flow rate of the molten glass are controlled. (4) The method for producing a glass substrate according to (3), wherein the flow rate and the flow rate of the molten glass flowing in the clarification pipe are controlled as follows, that is, at least one first in the longitudinal direction of the clarification pipe The position of the plate member is such that the flow rate of the molten glass flowing upward from the first plate member is divided by the flow path cross-sectional area above the first plate member, and the first plate member is to be compared with the first plate member. The flow rate of the molten glass flowing downward is divided by the flow velocity obtained by dividing the cross-sectional area of the flow path below the first plate member. (5) A method for producing a glass substrate, comprising: a clarification step of heating the molten glass from the upstream side to the downstream side while heating the molten glass, and directing the bubbles in the molten glass a gas phase space surrounded by the interface of the molten glass and the inner wall of the clarification pipe; and an interface position control step of controlling the flow into the clarification pipe so that the interface of the molten glass becomes a specific position a flow rate of the glass and the molten glass flowing out from the clarification pipe; the clarification pipe includes: a plate member disposed at a predetermined interval between the inner walls of the clarification pipe to suppress the flow of the molten glass; and an interface position measuring meter And measuring the position of the interface of the molten glass; and in the interface position control step, the position of the interface of the molten glass measured by the interface position meter is such that the height of the interface of the molten glass and the plate member are The flow rate of the molten glass is controlled in such a manner that the upper ends are uniform. (6) The method for producing a glass substrate according to (5), wherein the plate member is provided obliquely with respect to a longitudinal direction of the clarification pipe. (7) The method for producing a glass substrate according to (5) or (6), wherein, in the interface position control step, the inflow of the molten glass flowing into the clarification pipe by adjusting the step further upstream than the clarification step The amount, and/or the amount of the molten glass flowing out of the clarification pipe in the step further downstream than the clarification step, controls the position of the interface of the molten glass. (8) The method for producing a glass substrate according to any one of (5) to (7), wherein the clarification pipe is provided with an outer wall surface of the clarification pipe protruding to the outer side of the clarification pipe to cause the a vent pipe in which the gas phase space communicates with the outside atmosphere, and the interface position measuring instrument is introduced from the outer side of the clarification pipe through the vent pipe, and the position of the interface of the molten glass is measured. (9) A manufacturing apparatus for a glass substrate, comprising: a clarification pipe disposed in a substantially horizontal direction and for performing a clarification step of heating the molten glass to a downstream side from the upstream side while heating the molten glass a side, wherein the bubbles in the molten glass are discharged toward a gas phase space surrounded by an interface between the molten glass and an inner wall of the clarification pipe, and the clarification pipe is spaced apart from a lowermost portion and an uppermost portion of an inner wall of the clarification pipe a plate member is vertically disposed with respect to a longitudinal direction of the clarification pipe, and the molten glass flowing in the clarification pipe is controlled such that a height of an interface of the molten glass is higher than an upper end portion of the plate member Flow rate and flow rate. (10) A glass substrate manufacturing apparatus comprising a clarification tube disposed in a substantially horizontal direction and for performing a clarification step of heating the molten glass to the downstream side from the upstream side while heating the molten glass a side in which the air bubbles in the molten glass are discharged toward a gas phase space surrounded by the interface between the molten glass and the inner wall of the clarification pipe, and the clarification pipe is provided to be disposed perpendicularly to the longitudinal direction of the clarification pipe The plate member group of the plurality of plate members, wherein the plate member group includes: a first plate member group, wherein the plurality of first plate members are arranged at intervals in a longitudinal direction of the clarification pipe, and the plurality of first members The plate member is disposed at a first height from the lowermost portion and the uppermost portion of the inner wall of the clarification pipe, and the second plate member group is formed by the plurality of second plate members in the longitudinal direction of the clarification pipe and the first The one plate member is alternately arranged at intervals, and the plurality of second plate members are disposed at a height higher than the first height and spaced apart from an uppermost portion of the inner wall of the clarification pipe. a height of two; and a third plate member group, wherein the plurality of third plate members are alternately arranged at intervals from the first plate member in a longitudinal direction of the clarification pipe, and the plurality of third plate members are more The third height having the first low height is not spaced apart from the lowermost portion of the inner wall of the clarification pipe; and the height of the interface of the molten glass is higher than the highest position of the upper end portions of the plurality of plate members Control the flow rate and flow rate of the above molten glass. (11) A glass substrate manufacturing apparatus comprising a clarification tube for performing a clarification step of heating the molten glass while flowing the molten glass from an upstream side to a downstream side to cause the molten glass The bubble is discharged toward the gas phase space surrounded by the interface between the molten glass and the inner wall, and the clarification pipe includes a plate member which is provided at a predetermined interval on the inner wall of the clarification pipe to suppress the molten glass. a flow; and an interface position measuring device for measuring a position of the interface of the molten glass; and in the clarification tube, based on the position of the interface of the molten glass measured by the interface position measuring meter, to make the interface of the molten glass The flow rate of the molten glass is controlled in such a manner that the height coincides with the upper end portion of the above-mentioned plate member. [Effects of the Invention] According to the method for producing a glass sheet and the apparatus for producing a glass sheet according to the above aspect, the molten glass in the clarification tube can be uniformly stirred without interfering with the flow of the gas in the gas phase space.

Hereinafter, a method for producing a glass substrate and a device for producing a glass substrate of the present invention will be described. (Overall Outline of Manufacturing Method of Glass Substrate) Fig. 1 is a view showing an example of a procedure of a method for producing a glass substrate of the present embodiment. The manufacturing method of a glass substrate mainly has a melting step (ST1), a clarification step (ST2), a homogenization step (ST3), a supply step (ST4), a molding step (ST5), a slow cooling step (ST6), and a cutting step (ST7). ). Further, it may have a grinding step, a grinding step, a washing step, an inspection step, a packing step, and the like. The glass substrate to be produced is laminated by a packing step as needed, and is transported to the purchaser. In the melting step (ST1), molten glass is produced by heating the glass raw material. In the clarification step (ST2), by heating the molten glass, oxygen and CO contained in the molten glass are produced. ₂ Or SO ₂ Bubbles. The bubble is sucked (absorbed) by the oxygen generated by the reduction reaction of the clarifying agent (tin oxide or the like) contained in the molten glass, and is floated to the liquid surface of the molten glass to be released. Thereafter, in the clarification step, the reducing substance obtained by the reduction reaction of the clarifying agent is subjected to an oxidation reaction by lowering the temperature of the molten glass. Thereby, the gas component such as oxygen remaining in the bubbles of the molten glass is reabsorbed into the molten glass, and the bubbles disappear. The oxidation reaction and the reduction reaction using the clarifying agent are carried out by controlling the temperature of the molten glass. Further, in the clarification step, a vacuum defoaming method in which bubbles existing in the molten glass are grown in a reduced pressure environment and defoamed may be used. The vacuum defoaming mode is effective in not using a clarifying agent. However, the vacuum defoaming method complicates and enlarges the apparatus. Therefore, it is preferred to use a clarifying method using a clarifying agent to raise the temperature of the molten glass. In the homogenization step (ST3), the molten glass is stirred by using a stirrer to homogenize the glass component. Thereby, it is possible to reduce the compositional unevenness of the glass which is a cause of the pulse or the like. The homogenization step is carried out in the following agitation tank. In the supplying step (ST4), the molten glass after the stirring is supplied to the forming apparatus. The molding step (ST5) and the slow cooling step (ST6) are performed by a molding apparatus. In the molding step (ST5), the molten glass is formed into a sheet glass to produce a flow of the sheet glass. The forming system uses an overflow down-draw method. In the slow cooling step (ST6), the sheet glass which is formed and flowed has a desired thickness, and internal strain does not occur, and further, cooling is performed without causing warpage. In the cutting step (ST7), a plate-shaped glass substrate is obtained by cutting the slowly cooled sheet glass into a specific length. The cut glass substrate is then cut into a specific size to produce a glass substrate of a target size. Fig. 2 is a schematic view showing a manufacturing apparatus of a glass substrate in which a melting step (ST1) to a cutting step (ST7) are performed in the embodiment. As shown in FIG. 2, the manufacturing apparatus of a glass substrate mainly has the melting apparatus 100, the shaping apparatus 200, and the cutting apparatus 300. The melting apparatus 100 has a melting tank 101, a clarification pipe 120, a stirring tank 103, transfer pipes 104 and 105, and a glass supply pipe 106. A heating mechanism such as a burner (not shown) is provided in the melting tank 101 shown in Fig. 2 . A glass raw material to which a clarifying agent is added is introduced into the melting tank, and a melting step (ST1) is performed. The molten glass melted in the melting tank 101 is supplied to the clarification pipe 102 via the transfer pipe 104. In the clarification pipe 120, the temperature of the molten glass is adjusted, and the clarification step (ST2) of the molten glass is performed by the oxidation-reduction reaction of the clarifying agent. Specifically, by heating the molten glass in the clarification pipe 102, oxygen and CO contained in the molten glass are contained. ₂ Or SO ₂ The bubble is sucked in (absorbed) by the oxygen generated by the reduction reaction of the clarifying agent, and is floated to the liquid surface of the molten glass to be released into the gas phase space. Thereafter, the reducing substance obtained by the reduction reaction of the clarifying agent is subjected to an oxidation reaction by lowering the temperature of the molten glass. Thereby, the gas component such as oxygen remaining in the bubbles of the molten glass is reabsorbed into the molten glass, and the bubbles disappear. The clarified molten glass is supplied to the agitation vessel 103 via the transfer pipe 105. In the stirring tank 103, the molten glass is stirred by the stirring element 103a, and the homogenization process (ST3) is performed. The molten glass which has been homogenized by the agitation vessel 103 is supplied to the molding apparatus 200 via the glass supply pipe 106 (supply step ST4). In the molding apparatus 200, the sheet glass SG is formed from the molten glass by the overflow down-draw method (forming step ST5), and is gradually cooled (slow cooling step ST6). In the cutting device 300, a plate-shaped glass substrate cut out from the sheet glass SG is formed (cutting step ST7). In the manufacturing apparatus of such a glass substrate, the following clarification step or interface position control step is performed. (1) The clarification pipe 120 is spaced apart from the lowermost portion and the uppermost portion of the inner wall of the clarification pipe 120, and is provided with a plate member perpendicularly to the longitudinal direction of the clarification pipe 120, and in the clarification step, to make the molten glass The flow rate and flow rate of the molten glass flowing in the clarification pipe 120 are controlled in such a manner that the height of the interface is higher than the upper end of the plate member. (2) The clarification pipe 120 is provided with a plate member group including a plurality of plate members arranged perpendicularly to the longitudinal direction of the clarification pipe 120, and the plate member group includes: a first plate member group, which is composed of a plurality of first members The plate members 124 are disposed at intervals in the longitudinal direction of the clarification pipe 120, and the plurality of first plate members 124 are disposed at a first height spaced apart from the lowermost portion and the uppermost portion of the inner wall of the clarification pipe 120; The second plate member group is formed by alternately arranging a plurality of second plate members 125 at intervals from the first plate member 124 in the longitudinal direction of the clarification pipe 120, and the plurality of second plate members 125 are higher than the first height. The second height is provided at a distance from the uppermost portion of the inner wall of the clarification pipe 120; and the third plate member group is formed by the plurality of third plate members 126 in the longitudinal direction of the clarification pipe 120 and the first plate member 124. The plurality of third plate members 126 are disposed at intervals from the lowermost portion of the inner wall of the clarification pipe 120 at a third height lower than the first height. Further, in the clarification step, the flow rate and flow rate of the molten glass are controlled such that the height of the interface of the molten glass is higher than the highest position of the upper ends of the plurality of first to third plate members 124, 125, and 126. (3) The clarification pipe 120 is provided with a plate member which is provided at a predetermined interval between the inner walls of the clarification pipe 120 to suppress the flow of the molten glass, and an interface position measuring instrument which measures the position of the interface of the molten glass. Further, in the apparatus for manufacturing a glass substrate, an interface position control step of controlling the molten glass flowing into the clarification pipe 120 and flowing out from the clarification pipe 120 is performed in such a manner that the interface of the molten glass becomes a specific position. The flow of molten glass. In the interface position control step, the flow rate of the molten glass is controlled based on the position of the interface of the molten glass measured by the interface position meter so that the height of the interface of the molten glass coincides with the upper end portion of the plate member. Hereinafter, the first (1) to (3) embodiments will be described. (Configuration of the clarification pipe of the embodiment (1) and (2) Next, the configuration of the clarification pipe 120 in the form of (1) and (2) will be described with reference to Figs. 3 and 4 . Fig. 3 is a schematic perspective view showing the configuration of the clarification pipe 120 of the embodiment, and Fig. 4 is a vertical cross-sectional view of the clarification pipe 120 in the longitudinal direction. As shown in FIG. 3 and FIG. 4, electrodes 121a and 121b are provided on the outer peripheral surface of both ends of the clarification pipe 120 in the longitudinal direction, and are provided on the wall of the clarification pipe 120 that is in contact with the gas phase space 120a (see FIG. 4). There is an exhaust pipe 127. The body of the clarification tube 120, the electrodes 121a, 121b, and the exhaust pipe 127 contain a platinum group metal. In the present specification, the term "platinum group metal" means a metal containing a platinum group element, and is used as a term which includes not only a metal composed of a single platinum group element but also an alloy containing a platinum group element. Here, the platinum group element means six elements of platinum (Pt), palladium (Pd), rhodium (Rh), ruthenium (Ru), osmium (Os), and iridium (Ir). Although the platinum group metal is expensive, it has a high melting point and is excellent in corrosion resistance to molten glass MG. Further, in the present embodiment, the case where the clarification tube 120 contains a platinum group metal has been described as a specific example, but a part of the clarification tube 120 may also contain a refractory or other metal. The electrodes 121a and 121b are connected to the power supply device 122. The clarification tube 120 is electrically heated by applying a voltage between the electrodes 121a and 121b to cause a current to flow to the clarification tube 120 between the electrodes 121a and 121b. By the electric heating, the maximum temperature of the main body of the clarification pipe 120 is, for example, 1600 ° C to 1750 ° C, more preferably 1630 ° C to 1750 ° C, and the highest molten glass MG supplied from the transfer pipe 104 is supplied. The temperature is heated to a temperature suitable for defoaming, for example, 1600 ° C to 1720 ° C, more preferably 1620 ° C to 1720 ° C. Moreover, by controlling the temperature of the molten glass MG by the electric heating, the viscosity of the molten glass MG can be adjusted, whereby the flow velocity of the molten glass MG passing through the clarification pipe 120 can be adjusted. Further, a temperature measuring device (such as a thermocouple) (not shown) may be provided on the electrodes 121a and 121b. The temperature measuring device measures the temperatures of the electrodes 121a and 121b, and outputs the measured results to the control device 123. The control device 123 controls the amount of current that the power source device 122 energizes the clarification tube 120, thereby controlling the temperature and flow rate of the molten glass MG passing through the clarification tube 120. The control device 123 is a computer including a CPU (Central Processing Unit), a memory, and the like. An exhaust pipe 127 is provided in the wall of the clarification pipe 120 that is in contact with the gas phase space. The exhaust pipe 127 is disposed above the gas phase space 120a. The exhaust pipe 127 is preferably disposed between the upstream end portion and the downstream end portion in the flow direction of the molten glass MG in the clarification pipe 120. The exhaust pipe 127 may also have a shape protruding from the outer wall surface of the main body of the clarification pipe 120 toward the outer chimney. The exhaust pipe 127 communicates the gas phase space 120a (refer to FIG. 4) with the outer space of the clarification pipe 120. The oxygen released from the molten glass MG in the clarification pipe 120 can be discharged by discharging the gas in the gas phase space 120a from the exhaust pipe 127. Thereby, it is possible to suppress oxidation of the platinum group metal and volatilization, and to reduce the amount of precipitation of the platinum group metal due to reduction of the volatilized platinum group metal. In the present embodiment, as shown in FIG. 4, the clarification pipe 120 is disposed to extend in a substantially horizontal direction. The substantially horizontal direction refers to the direction of inclination within a range of 5 degrees with respect to the horizontal plane. Inside the clarification pipe 120, a plate member group including a plurality of plate members 124, 125, 126 is provided. The plate member group includes a first plate member group including a plurality of first plate members 124, a second plate member group including a plurality of second plate members 125, and a third plate member group including a plurality of third plate members 126. The first plate member 124, the second plate member 125, and the third plate member 126 contain a platinum group metal similarly to the main body of the clarification pipe 120. The first plate member 124, the second plate member 125, and the third plate member 126 are disposed perpendicular to the longitudinal direction of the clarification pipe 120. In other words, the first plate member 124, the second plate member 125, and the third plate member 126 are provided such that the widest flat surfaces (main surfaces) of the respective plate members are oriented in the longitudinal direction of the clarification pipe 120. The plurality of first plate members 124 are provided at a first height and spaced apart from the lowermost portion and the uppermost portion of the inner wall of the clarification pipe 120. The plurality of first plate members 124 are disposed at intervals in the longitudinal direction of the clarification pipe 120. The first plate member 124 blocks the flow of the molten glass MG flowing in the longitudinal direction of the clarification pipe 120 near the center of the clarification pipe 120 so as to be closer to the upper side than the first plate member 124 and lower than the first plate member 124. Branch. The plurality of second plate members 125 are provided at a second height higher than the height (first height) of the first plate member 124, and are spaced apart from the uppermost portion of the inner wall of the clarification pipe 120. The plurality of second plate members 125 are alternately arranged at intervals from the plurality of first plate members 124 in the longitudinal direction of the clarification pipe 120. The second plate member 125 prevents the flow of the molten glass MG flowing in the longitudinal direction of the clarification pipe 120 in the vicinity of the interface of the molten glass MG in the clarification pipe 120, and causes the flow of the molten glass MG to be lower than the second plate member 125 ( Near the center of the clarification tube). The plurality of third plate members 126 are disposed at a third height lower than the height (first height) of the first plate member 124, and are not spaced apart from the lowermost portion of the inner wall of the clarification pipe 120. The plurality of third plate members 126 are alternately arranged at intervals from the plurality of first plate members 124 in the longitudinal direction of the clarification pipe 120. The third plate member 126 blocks the flow of the molten glass MG flowing in the longitudinal direction of the clarification pipe 120 at the lowermost portion of the molten glass MG in the clarification pipe 120, and the flow of the molten glass MG is directed upward of the third plate member 126 (clarification) Near the center of the tube). By providing the first plate member 124, the second plate member 125, and the third plate member 126, the molten glass MG in the clarification pipe 120 flows not only along the longitudinal direction of the clarification pipe 120 but also along the molten glass MG. Since the method of moving in the vertical direction is changed, the molten glass MG is uniformly stirred in the clarification pipe 120, and the temperature of the molten glass MG can be made uniform. Further, as shown in FIG. 4, the second plate member 125 and the third plate member 126 may be located at the same position in the longitudinal direction of the clarification pipe 120. That is, the third plate member 126 may be provided below the second plate member 125. Here, it is preferable to control the flow rate and flow rate of the molten glass MG flowing through the clarification pipe 120 in such a manner that the molten glass flowing on the upper side of the first plate member 124 is placed at the position of the first plate member 124. The flow rate of the MG is divided by (removed) the flow velocity obtained by the cross-sectional area of the flow path on the upper side of the first plate member 124, and the flow rate of the molten glass MG flowing on the lower side of the first plate member 124 is divided (removed) by the first plate. The flow velocity obtained by the cross-sectional area of the flow path on the lower side of the member 124 becomes equal. By making the flow velocity of the molten glass MG flowing on the upper side of the first plate member 124 equal to the flow velocity of the molten glass MG flowing on the lower side of the first plate member 124, the molten glass MG can be uniformly stirred in the clarification pipe 120. The flow velocity of the molten glass MG flowing on the upper side of the first plate member 124 and the flow rate of the molten glass MG flowing on the lower side of the first plate member 124 can be adjusted by the heating amount by the clarification pipe 120. For example, by increasing the amount of heating of the clarification pipe 120, the temperature of the molten glass MG which is close to the inner wall of the clarification pipe 120 and flows down the lower side of the first plate member 124 is increased to lower the viscosity, thereby improving the viscosity. The flow rate of the molten glass MG flowing on the lower side of the first plate member 124. On the other hand, by reducing the amount of heating of the clarification pipe 120, the temperature of the molten glass MG which is close to the inner wall of the clarification pipe 120 and flows down the lower side of the first plate member 124 is lowered to increase the viscosity. The flow rate of the molten glass MG flowing on the lower side of the first plate member 124 is lowered. Further, since the molten glass MG flowing on the upper side of the first plate member 124 is far from the inner wall of the clarification pipe 120, the amount of change in temperature caused by the change in the heating amount of the clarification pipe 120 is smaller than that in the first plate member 124. The molten glass MG flowing on the lower side. In the present embodiment, the height of the interface of the molten glass MG in the clarification pipe 120 is controlled to be higher than the highest position of the upper end portions of the first plate member 124, the second plate member 125, and the third plate member 126. Flow and flow rate of glass MG. In other words, the first plate member 124, the second plate member 125, and the third plate member 126 are all located in the molten glass MG, and the first plate member 124, the second plate member 125, and the third plate are not present in the vapor phase space 120a. The height of the interface of the molten glass MG in the clarification pipe 120 is adjusted in the manner of the member 126. When the height of the interface of the molten glass MG is changed, it is only necessary to change the flow rate of the molten glass MG which flows in the transfer pipes 104 and 105. For example, the flow rate of the molten glass MG flowing from the transfer pipe 104 toward the clarification pipe 120 is larger than the flow rate of the molten glass MG flowing out of the clarification pipe 120 by the transfer pipe 105, whereby the interface of the molten glass MG in the clarification pipe 120 can be increased. height. On the other hand, the flow rate of the molten glass MG flowing into the clarification pipe 120 from the transfer pipe 104 is smaller than the flow rate of the molten glass MG flowing out of the clarification pipe 120 by the transfer pipe 105, so that the molten glass MG in the clarification pipe 120 can be lowered. The height of the interface. When the flow rate of the molten glass MG in the transfer pipes 104 and 105 is controlled, the viscosity of the molten glass MG may be adjusted by changing the temperature of the molten glass MG flowing through the transfer pipes 104 and 105. For example, by increasing the temperature of the molten glass MG, the viscosity of the molten glass MG is lowered, and the flow rate and flow rate of the molten glass MG can be increased. On the other hand, by lowering the temperature of the molten glass MG, the viscosity of the molten glass MG is improved, and the flow rate and flow rate of the molten glass MG can be lowered. By adjusting the height of the interface of the molten glass MG in the clarification pipe 120, the first plate member 124, the second plate member 125, and the third plate member 126 can be prevented from being exposed to the gas phase space 120a. Therefore, the first plate member 124, the second plate member 125, and the third plate member 126 do not hinder the release of oxygen and CO into the gas phase space 120a. ₂ , SO ₂ The gas flows toward the exhaust pipe 127. Further, the first plate member 124, the second plate member 125, the third plate member 126, and the oxygen and CO discharged into the gas phase space 120a are prevented. ₂ , SO ₂ The contact with the gas can prevent the platinum group metal constituting the first plate member 124, the second plate member 125, and the third plate member 126 from being volatilized by oxidation. (Configuration of the clarification pipe of the (3) embodiment) Next, the configuration of the clarification pipe 120 will be described with reference to Figs. 5 and 6 . Fig. 5 is a schematic perspective view showing the configuration of the clarification pipe 120 of the above (3) embodiment, and Fig. 6 is a vertical cross-sectional view of the clarification pipe 120 of the third embodiment. As shown in FIG. 5 and FIG. 6, the electrodes 121a and 121b are provided on the outer peripheral surface of the both ends of the clarification pipe 120 in the longitudinal direction, and are provided on the wall of the clarification pipe 120 that is in contact with the gas phase space 120a (see FIG. 6). There is an exhaust pipe 127. Further, an interface position measuring instrument 128 is provided in the clarification pipe 120, and the sensor portion of the interface position measuring instrument 128 is introduced into the clarification pipe 120 through the exhaust pipe 127, and the interface position of the molten glass MG is measured. The body of the clarification tube 120, the electrodes 121a, 121b, and the exhaust pipe 127 contain a platinum group metal. In addition, in FIGS. 5 and 6, the case where the clarification tube 120 contains a platinum group metal will be described as a specific example, but one part of the clarification tube 120 may also contain a refractory or other metal. The electrodes 121a and 121b are connected to the power supply device 122. The clarification tube 120 is electrically heated by applying a voltage between the electrodes 121a and 121b to cause a current to flow to the clarification tube 120 between the electrodes 121a and 121b. By the electric heating, the maximum temperature of the main body of the clarification pipe 120 is, for example, 1600 ° C to 1750 ° C, more preferably 1630 ° C to 1750 ° C, and the highest molten glass MG supplied from the transfer pipe 104 is supplied. The temperature is heated to a temperature suitable for defoaming, for example, 1600 ° C to 1720 ° C, more preferably 1620 ° C to 1720 ° C. Moreover, by controlling the temperature of the molten glass MG by the electric heating, the viscosity of the molten glass MG can be adjusted, whereby the flow velocity of the molten glass MG passing through the clarification pipe 120 can be adjusted. Further, a temperature measuring device (such as a thermocouple) (not shown) may be provided on the electrodes 121a and 121b. The temperature measuring device measures the temperatures of the electrodes 121a and 121b, and outputs the measured results to the control device 123. The control device 123 controls the amount of current that the power source device 122 energizes the clarification tube 120, thereby controlling the temperature and flow rate of the molten glass MG passing through the clarification tube 120. The control device 123 is a computer including a CPU, a memory, and the like. An exhaust pipe 127 is provided in the wall of the clarification pipe 120 that is in contact with the gas phase space. The exhaust pipe 127 is disposed above the gas phase space 120a. The exhaust pipe 127 is preferably disposed between the upstream end portion and the downstream end portion in the flow direction of the molten glass MG in the clarification pipe 120. The exhaust pipe 127 may also have a shape protruding from the outer wall surface of the main body of the clarification pipe 120 toward the outer chimney. The exhaust pipe 127 communicates the gas phase space 120a (refer to FIG. 4) with the outer space of the clarification pipe 120. The oxygen released from the molten glass MG in the clarification pipe 120 can be discharged by discharging the gas in the gas phase space 120a from the exhaust pipe 127. Thereby, it is possible to suppress oxidation of the platinum group metal and volatilization, and to reduce the amount of precipitation of the platinum group metal due to reduction of the volatilized platinum group metal. The interface position measuring device 128 includes a sensor portion that detects an interface position of the molten glass MG in the clarification tube 120, and a measuring portion that measures an interface position based on a signal (data) detected by the sensor portion. Here, the interface position is the boundary region between the liquid phase region in which the molten glass MG in the clarification pipe 120 flows and the gas phase region (gas phase space) in which the bubbles in the molten glass MG are discharged, and is the uppermost position of the liquid phase region. The lowest position of the gas phase region. The sensor portion of the interface position measuring device 128 is introduced into the clarification pipe 120 through the exhaust pipe 127 to detect the interface position of the molten glass MG in the clarification pipe 120. The measuring unit is connected to the sensor unit, and measures the interface position of the molten glass MG in the clarification pipe 120 based on a signal (data) transmitted from the sensor unit. In the present embodiment, the interface position of the molten glass MG in the clarification pipe 120 is measured by the interface position measuring instrument 128 so that the height of the interface of the molten glass MG matches the upper end portion of the second plate member 125 described later. The flow rate of the molten glass MG. In the present embodiment, as shown in FIG. 6, the clarification pipe 120 is disposed to extend in a substantially horizontal direction. The substantially horizontal direction refers to the direction of inclination within a range of 5 degrees with respect to the horizontal plane. Inside the clarification pipe 120, a plate member group including a plurality of plate members 124, 125, 126 is provided. The plate member group includes a first plate member group including a plurality of first plate members 124, a second plate member group including a plurality of second plate members 125, and a third plate member group including a plurality of third plate members 126. The first plate member 124, the second plate member 125, and the third plate member 126 contain a platinum group metal similarly to the main body of the clarification pipe 120. The plurality of first plate members 124 are spaced apart from the lowermost portion and the uppermost portion of the inner wall of the clarification pipe 120 at a first height. The plurality of first plate members 124 are disposed at intervals in the longitudinal direction of the clarification pipe 120. The first plate member 124 blocks the flow of the molten glass MG flowing in the longitudinal direction of the clarification pipe 120 near the center of the clarification pipe 120 so as to be closer to the upper side than the first plate member 124 and lower than the first plate member 124. Branch. The first plate member 124 is disposed perpendicular to the longitudinal direction of the clarification pipe 120. That is, the widest plane (main surface) of the first plate member 124 faces the longitudinal direction of the clarification pipe 120. The plurality of second plate members 125 are provided at a second height higher than the height (first height) of the first plate member 124, and are spaced apart from the uppermost portion of the inner wall of the clarification pipe 120. The plurality of second plate members 125 are alternately arranged at intervals from the plurality of first plate members 124 in the longitudinal direction of the clarification pipe 120. The second plate member 125 prevents the flow of the molten glass MG flowing in the longitudinal direction of the clarification pipe 120 in the vicinity of the interface of the molten glass MG in the clarification pipe 120, and causes the flow of the molten glass MG to be lower than the second plate member 125 ( Near the center of the clarification tube). The plurality of second plate members 125 are disposed obliquely with respect to the longitudinal direction of the clarification pipe 120. Specifically, the second plate member 125 is inclined so as to face upward (the uppermost side of the inner wall) in the direction of the downstream side in the flow direction of the molten glass MG in the longitudinal direction of the clarification pipe 120. The inclination angle A1 (the inclination angle with respect to the longitudinal direction of the clarification pipe 125) of the plurality of second plate members 125 is, for example, in the range of 20 to 70 degrees, more preferably 30 to 60 degrees. When the second plate member 125 is provided in the clarification pipe 120, the flow of the molten glass MG that has collided with the second plate member 125 is temporarily stagnated, and a heterogeneous glass may be generated. However, since the second plate member 125 can increase the shear rate, the molten glass MG can be further stretched (stirred). The shear velocity is a derivative of a fluid velocity distribution obtained by differentiating a fluid velocity distribution in a direction orthogonal to a flow direction of a fluid in the above-described orthogonal direction. The flow characteristics of the molten glass MG were calculated by calculating the shear rate of the molten glass MG. The larger the shear rate, the larger the flow velocity difference between the adjacent molten glass MG, and the higher the stirring effect, the more the molten glass MG can be homogenized. On the other hand, the smaller the shear rate, the smaller the flow velocity difference between the adjacent molten glass MGs, and the lower the stirring effect. Therefore, by providing the second plate member 125, the shear rate is increased, and the shear rate of the molten glass MG flowing through the clarification pipe 120 is improved, thereby improving the stirring efficiency. In addition, when impurities such as bubbles having a small size are present in the molten glass MG, the impurities are floated up to the interface (surface) of the molten glass MG, and are not stirred by the plurality of first plate members 124, and flow to the downstream side. There is a case where the impurity affects the quality of the glass. Therefore, by providing a plurality of second plate members 125 at a specific angle, the shear rate is increased, and the plurality of second plate members 125 are stirred by the molten glass MG, and the time for staying in the clarification pipe 120 can be extended. Thereby promoting defoaming treatment. At the lower end portion of the second plate member 125, the molten glass MG that has collided with the second plate member 125 flows downward along the second plate member 125 (in the direction of the bottom of the clarification pipe 120) to generate eddy current. The molten glass MG is stirred by the vortex. At the upper end portion of the second plate member 125, the molten glass MG that has collided with the second plate member 125 flows upward along the second plate member 125 (the interface direction of the molten glass MG). Since the flow rate of the molten glass MG is controlled such that the height position of the interface of the molten glass MG matches the position of the upper end of the second plate member 125, the molten glass MG flowing upward along the first plate member 124 is the second plate member. 125 stirring. By matching the height position of the interface of the molten glass MG with the position of the upper end portion of the second plate member 125, impurities such as bubbles in the molten glass MG and the molten glass MG do not flow above the upper end portion of the second plate member 125. And it is stirred by the 2nd plate member 125. Thereby, the defoaming process can be promoted. The interval D1 between the second plate members 125 is, for example, in the range of 100 mm to 500 mm, more preferably in the range of 200 mm to 400 mm. When the distance D1 between the second plate members 125 is too wide, the molten glass MG is not stirred by the second plate member 125, but flows from the upstream side to the downstream side, so that the defoaming treatment is not promoted, and the second plate is made When the distance between the members 125 and the distance D1 is too narrow, the flow of the molten glass MG is stagnated by the second plate member 125, and impurities such as bubbles in the molten glass MG float up to the interface (surface) of the molten glass MG without being stirred. Will have an impact on the quality of the glass. Therefore, by providing a plurality of second plate members 125 such that the distance D1 between the second plate members 125 is at a predetermined interval, the shear rate is increased and the molten glass MG is stirred, whereby the defoaming process can be promoted. The plurality of third plate members 126 are disposed at a third height lower than the height (first height) of the first plate member 124, and are not spaced apart from the lowermost portion of the inner wall of the clarification pipe 120. That is, the third plate member 126 is connected to the lowermost portion of the inner wall of the clarification pipe 120. The plurality of third plate members 126 are alternately arranged at intervals from the plurality of first plate members 124 in the longitudinal direction of the clarification pipe 120. The third plate member 126 blocks the flow of the molten glass MG flowing in the longitudinal direction of the clarification pipe 120 at the lowermost portion of the molten glass MG in the clarification pipe 120, and the flow of the molten glass MG is directed upward of the third plate member 126 (clarification) Near the center of the tube). A plurality of third plate members 126 are disposed obliquely with respect to the longitudinal direction of the clarification pipe 120. Specifically, the third plate member 126 is inclined so as to face downward (the bottom direction of the inner wall) in the direction of the downstream side in the flow direction of the molten glass MG in the longitudinal direction of the clarification pipe 120. The inclination angle B1 of the plurality of third plate members 126 is, for example, 20 to 70 degrees, more preferably 30 to 60 degrees. Further, the third plate members 126 are spaced apart from each other by, for example, 100 mm to 500 mm, more preferably 200 mm to 400 mm. Fig. 7 is a view showing a shear speed obtained by simulation of a vertical section in the longitudinal direction of the clarification pipe 120, and Fig. 7(a) shows a shearing speed in the case where the second plate member 125 is not provided. 7(b) shows that the height position of the interface of the molten glass MG coincides with the position of the upper end portion of the second plate member 125, and the second plate member 125 and the third plate member 126 are obliquely disposed in the manner shown in FIG. A plot of the shear rate in the case of the situation. As shown in Fig. 7(a), when the second plate member 125 is not provided, the shearing speed is increased and the mixture is stirred in the vicinity of the first plate member 124 (the center portion of the clarification pipe 120). The vicinity of the interface of the glass MG and the vicinity of the bottom of the clarification pipe 120 have different shear rates, and the stirring unevenness of the molten glass MG occurs. Further, the molten glass MG flows in the vicinity of the interface of the molten glass MG which is above the upper end portion of the first plate member 124, and the flow velocity of the molten glass MG becomes faster than that of the other regions. Since the second plate member 125 is not present, the molten glass MG is not stirred and flows from the upstream side to the downstream side. Therefore, the time for staying in the clarification pipe 120 is shortened, and the defoaming treatment is not promoted. On the other hand, as shown in Fig. 7(b), when the height position of the interface of the molten glass MG coincides with the position of the upper end portion of the second plate member 125, the molten glass MG is stirred by the second plate member 125, and sheared. The speed becomes higher. Further, in the vicinity of the interface of the molten glass MG and the vicinity of the bottom of the clarification pipe 120, the shear rate is uniform, and the molten glass MG is uniformly stirred in the clarification pipe 120. In addition, the molten glass MG that has collided with the second plate member 125 and the third plate member 126 flows to the lower end side of the second plate member 125 and the upper end side of the third plate member 126, and becomes a vortex. Therefore, the molten glass MG is allowed to flow from the upstream side to the downstream side while being agitated by the second plate member 125 and the third plate member 126, and the time for staying in the clarification pipe 120 becomes long, and the defoaming treatment is promoted. By providing the first plate member 124, the second plate member 125, and the third plate member 126, the molten glass MG in the clarification pipe 120 flows not only along the longitudinal direction of the clarification pipe 120 but also along the molten glass MG. Since the method of moving in the vertical direction is changed, the molten glass MG is uniformly stirred in the clarification pipe 120, and the temperature of the molten glass MG can be made uniform. Further, as shown in FIG. 6, the second plate member 125 and the third plate member 126 may be provided at the same position in the longitudinal direction of the clarification pipe 120. That is, the third plate member 126 may be provided below the second plate member 125. Here, it is preferable to control the flow rate and flow rate of the molten glass MG flowing through the clarification pipe 120 in such a manner that the molten glass flowing on the upper side of the first plate member 124 is placed at the position of the first plate member 124. The flow rate of the MG is divided by (removed) the flow velocity obtained by the cross-sectional area of the flow path on the upper side of the first plate member 124, and the flow rate of the molten glass MG flowing on the lower side of the first plate member 124 is divided (removed) by the first plate. The flow velocity obtained by the cross-sectional area of the flow path on the lower side of the member 124 becomes equal. By making the flow velocity of the molten glass MG flowing on the upper side of the first plate member 124 equal to the flow velocity of the molten glass MG flowing on the lower side of the first plate member 124, the molten glass MG can be uniformly stirred in the clarification pipe 120. The flow velocity of the molten glass MG flowing on the upper side of the first plate member 124 and the flow rate of the molten glass MG flowing on the lower side of the first plate member 124 can be adjusted by the heating amount by the clarification pipe 120. For example, by increasing the amount of heating of the clarification pipe 120, the temperature of the molten glass MG which is close to the inner wall of the clarification pipe 120 and flows down the lower side of the first plate member 124 is increased to lower the viscosity, thereby improving the viscosity. The flow rate of the molten glass MG flowing on the lower side of the first plate member 124. On the other hand, by reducing the amount of heating of the clarification pipe 120, the temperature of the molten glass MG which is close to the inner wall of the clarification pipe 120 and flows down the lower side of the first plate member 124 is lowered to increase the viscosity. The flow rate of the molten glass MG flowing on the lower side of the first plate member 124 is lowered. Further, since the molten glass MG flowing on the upper side of the first plate member 124 is far from the inner wall of the clarification pipe 120, the amount of change in temperature caused by the change in the heating amount of the clarification pipe 120 is smaller than that in the first plate member 124. The molten glass MG flowing on the lower side. In the third embodiment, the flow rate and the flow velocity of the molten glass MG are controlled so that the height of the interface of the molten glass MG in the clarification pipe 120 coincides with the highest position of the upper end portion of the second plate member 125. In other words, the first plate member 124, the second plate member 125, and the third plate member 126 are all located in the molten glass MG, and the first plate member 124, the second plate member 125, and the third plate are not present in the vapor phase space 120a. The height of the interface of the molten glass MG in the clarification pipe 120 is adjusted in the manner of the member 126. When the first plate member 124, the second plate member 125, and the third plate member 126 are exposed to the vapor phase space 120a, the flow of the gas in the gas phase space is hindered, and as a result, the volatile component of the platinum group metal is present. It is agglomerated and adhered to the inner wall surface of the clarification pipe, dropped and mixed into the molten glass MG in the defoaming step, and mixed as a foreign matter into the glass substrate. When the height of the interface of the molten glass MG is changed, it is only necessary to change the flow rate of the molten glass MG which flows in the transfer pipes 104 and 105. By homogenizing the step from the earlier step of the clarification step, that is, the step of melting to the clarification step, that is, the inflow amount of the molten glass MG flowing into the clarification tube, and/or the step of flowing out from the clarification step to the downstream of the clarification step, that is, homogenization The chemical step, the supply step, and the forming step, that is, the outflow amount of the molten glass MG flowing out of the clarification tube, controls the position of the interface of the molten glass MG. For example, the flow rate of the molten glass MG flowing from the transfer pipe 104 to the clarification pipe 120 is made larger than the flow rate of the molten glass MG flowing out of the clarification pipe 120 by the transfer pipe 105, whereby the interface of the molten glass MG in the clarification pipe 120 can be increased. height. When the flow rate of the molten glass MG in the transfer pipes 104 and 105 is controlled, the viscosity of the molten glass MG may be adjusted by changing the temperature of the molten glass MG flowing through the transfer pipes 104 and 105. For example, by increasing the temperature of the molten glass MG, the viscosity of the molten glass MG is lowered, and the flow rate and flow rate of the molten glass MG can be increased. On the other hand, by lowering the temperature of the molten glass MG, the viscosity of the molten glass MG is improved, and the flow rate and flow rate of the molten glass MG can be lowered. The flow rate of the molten glass MG can be arbitrarily changed, for example, in the range of 0.05 kg/s to 0.3 kg/s, preferably 0.07 kg/s to 0.28 kg/s, more preferably 0.1 kg/s to 0.25 kg/s. The average flow velocity of the molten glass MG can be arbitrarily changed, for example, in the range of 0.25 mm/s to 1.4 mm/s, preferably 0.27 mm/s to 1.38 mm/s, more preferably 0.3 mm/s to 1.35 mm/s. . In order to increase the height of the interface of the molten glass MG in the clarification pipe 120, the time interval for inputting the glass raw material to the melting tank 101 is shortened, and more specifically, the input time interval is set to 2 minutes and 1 minute from 3 minutes. In addition, the amount of input of the glass raw material is increased by one time, and more specifically, the input amount of one time is set to 200 kg and 300 kg from 100 kg. Thereby, the height of the interface of the molten glass MG in the clarification pipe 120 can be raised. On the other hand, the flow rate of the molten glass MG flowing from the transfer pipe 104 to the clarification pipe 120 is smaller than the flow rate of the molten glass MG flowing out of the clarification pipe 120 by the transfer pipe 105, whereby the molten glass MG in the clarification pipe 120 can be lowered. The height of the interface. In order to reduce the height of the interface of the molten glass MG in the clarification pipe 120, the time interval for putting the glass raw material into the melting tank 101 is increased, and more specifically, the input time interval is set to 4 minutes and 5 minutes from 3 minutes. In addition, the amount of input of the glass raw material is reduced by one time, and more specifically, the input amount of one time is set to 80 kg and 50 kg from 100 kg. Thereby, the height of the interface of the molten glass MG in the clarification pipe 120 can be reduced. The time interval and the input amount of the glass raw material can be arbitrarily changed within the range in which the glass raw material can be melted in the melting tank 101. Further, the flow rate of the molten glass MG flowing out of the clarification pipe 120 is made smaller than the flow rate of the molten glass MG flowing into the clarification pipe 120, whereby the height of the interface of the molten glass MG can be increased. In order to increase the height of the interface of the molten glass MG in the clarification pipe 120, the temperature of the molten glass MG flowing in the glass supply pipe 106 located downstream of the clarification pipe 120 is lowered, and more specifically, the temperature of the molten glass MG is from 1000 ° C. Set to 980 ° C, 950 ° C. By suppressing the flow rate of the molten glass MG flowing through the glass supply pipe 106, the flow rate of the molten glass MG flowing out of the clarification pipe 120 is suppressed, so that the height of the interface of the molten glass MG in the clarification pipe 120 can be increased. On the other hand, the height of the interface of the molten glass MG can be lowered by causing the flow rate of the molten glass MG flowing out of the clarification pipe 120 to be larger than the flow rate of the molten glass MG flowing into the clarification pipe 120. In order to lower the height of the interface of the molten glass MG in the clarification pipe 120, the temperature of the molten glass MG flowing to the glass supply pipe 106 located downstream of the clarification pipe 120 is increased, and more specifically, the temperature of the molten glass MG is from 1000 ° C. Set to 1020 ° C, 1050 ° C. By increasing the flow rate of the molten glass MG flowing through the glass supply pipe 106, the flow rate of the molten glass MG flowing out of the clarification pipe 120 is increased, so that the height of the interface of the molten glass MG in the clarification pipe 120 can be lowered. The temperature of the molten glass MG in the glass supply pipe 106 and the position at which the temperature of the molten glass MG is changed can be arbitrarily changed within the range in which the sheet glass SG can be formed in the molding apparatus 200. By adjusting the height of the interface of the molten glass MG in the clarification pipe 120, the first plate member 124, the second plate member 125, and the third plate member 126 can be prevented from being exposed to the gas phase space 120a. Therefore, the first plate member can be prevented. 124. The second plate member 125 and the third plate member 126 do not hinder the release of oxygen and CO into the gas phase space 120a. ₂ , SO ₂ The gas flows toward the exhaust pipe 127. Further, the first plate member 124, the second plate member 125, the third plate member 126, and the oxygen and CO discharged into the gas phase space 120a are prevented. ₂ , SO ₂ The contact with the gas can prevent the platinum group metal constituting the first plate member 124, the second plate member 125, and the third plate member 126 from being volatilized by oxidation. Further, by temporarily increasing the flow rate of the molten glass MG, the height of the interface of the molten glass MG in the clarification pipe 120 is higher than the upper end portion of the second plate member 125, and the small impurities existing in the molten glass MG can be removed. . When the amount of the molten glass MG is continuously controlled so that the height of the interface of the molten glass MG coincides with the upper end portion of the second plate member 125, the impurity may float up to the molten glass MG in the case of a small impurity. The interface (surface) gradually accumulates in the vicinity of the second plate member 125, and is not agitated by the second plate member 125 to flow to the downstream side, and this impurity affects the quality of the glass. Therefore, by temporarily increasing the flow rate of the molten glass MG, impurities accumulated in the vicinity of the second plate member 125 are extruded to the downstream. Since the impurities accumulated in a fixed amount continue to flow in the vicinity of the interface of the molten glass MG, they are removed in the stirring tank 103 for performing the homogenization step (ST3), whereby impurities can be efficiently removed. In the above, the glass substrate manufacturing method and the glass substrate manufacturing apparatus of the present invention have been described in detail. However, the present invention is not limited to the above-described embodiments, and various modifications may be made without departing from the spirit and scope of the invention. Or change. The glass substrate produced by the method for producing a glass substrate of the present embodiment is an alkali-free boron-aluminum silicate glass or a glass containing a small amount of alkali which has a high strain point or a slow cooling point and has good dimensional stability. The glass substrate to which the present embodiment is applied contains, for example, an alkali-free glass having the following composition. SiO ₂ : 56 to 65 mass% Al ₂ O ₃ : 15 to 19% by mass B ₂ O ₃ : 8 to 13% by mass MgO: 1 to 3 mass% CaO: 4 to 7 mass% SrO: 1 to 4 mass% BaO: 0 to 2 mass% Na ₂ O: 0 to 1 mass% K ₂ O: 0 to 1 mass% As ₂ O ₃ :0 to 1 mass% Sb ₂ O ₃ :0 to 1 mass% SnO ₂ :0 to 1 mass% Fe ₂ O ₃ :0 to 1 mass% ZrO ₂ 0 to 1% by mass The glass substrate produced by the present embodiment is applied to a glass substrate for a display including a glass substrate for a flat panel display. A glass substrate for an oxide semiconductor display using an oxide semiconductor such as IGZO (Indium gallium zinc oxide) (indium gallium zinc oxide) (indium, gallium, zinc, or oxygen) and a LTPS (Low Temperature Poly-Silicon) semiconductor A glass substrate for LTPS displays. Further, the glass substrate produced by the present embodiment is suitably used for a glass substrate for a liquid crystal display having a very small content of an alkali metal oxide. Moreover, it is also applicable to a glass substrate for an organic EL (electroluminescence) display. In other words, the method for producing a glass substrate of the present embodiment is suitable for the production of a glass substrate for a display, and is particularly suitable for the production of a glass substrate for a liquid crystal display. Further, it can also be used as a cover glass for a mobile terminal device or the like, a cover glass for a casing, a glass substrate for a solar cell, or a cover glass. In particular, it is suitable for a glass substrate for a liquid crystal display using a polycrystalline silicon TFT (Thin Film Transistor). Further, the glass substrate produced by the present embodiment can also be applied to a cover glass, a glass for a disk, a glass substrate for a solar cell, or the like.

100‧‧‧melting device
101‧‧‧melting tank
102‧‧‧clarification tube
103‧‧‧Stirring tank
103a‧‧‧ stirrer
104‧‧‧Transfer tube
105‧‧‧Transfer tube
106‧‧‧Glass supply tube
120‧‧‧clarification tube
120a‧‧‧ gas phase space
121a‧‧‧electrode
121b‧‧‧electrode
122‧‧‧Power supply unit
123‧‧‧Control device
124‧‧‧1st plate member
125‧‧‧2nd plate member
126‧‧‧3rd plate member
127‧‧‧Exhaust pipe
128‧‧‧Interface position measuring instrument
200‧‧‧Forming device
300‧‧‧ cutting device
A1‧‧‧ tilt angle
B1‧‧‧ Tilt angle
D1‧‧‧ interval
MG‧‧‧ molten glass
SG‧‧‧Flake glass
ST1~ST7‧‧‧ steps

Fig. 1 is a view showing the flow of the manufacturing method of the embodiment. 2 is a schematic view showing a manufacturing apparatus of a glass substrate. Fig. 3 is a schematic view showing an embodiment of a clarification pipe shown in Fig. 2; Figure 4 is a vertical cross-sectional view of the embodiment of the clarification tube shown in Figure 2 in the longitudinal direction. Fig. 5 is a schematic view showing another embodiment of the clarification pipe shown in Fig. 2; Fig. 6 is a vertical cross-sectional view showing another embodiment of the clarification pipe in the longitudinal direction. Figure 7 is a graph showing the shear rate obtained by simulation of the vertical section in the longitudinal direction of the clarification pipe, and Figure 7 (a) shows the shear rate in the case where the second plate member is not provided in the clarification pipe. 7(b) shows a case where the height position of the interface of the molten glass coincides with the position of the upper end portion of the second plate member, and the second plate member and the third plate member are obliquely provided (the embodiment). The map of speed.

104‧‧‧Transfer tube

120‧‧‧clarification tube

120a‧‧‧ gas phase space

121a‧‧‧electrode

121b‧‧‧electrode

124‧‧‧1st plate member

125‧‧‧2nd plate member

126‧‧‧3rd plate member

127‧‧‧Exhaust pipe

MG‧‧‧ molten glass

Claims (11)

A method for producing a glass substrate, comprising: a clarification step in which a molten glass is heated from the clarified glass disposed in a substantially horizontal direction, and the molten glass is heated from the upstream side to the downstream side to cause the molten glass The bubble is discharged toward the gas phase space surrounded by the interface between the molten glass and the inner wall of the clarification pipe, and the clarification pipe is spaced apart from the lowermost portion and the uppermost portion of the inner wall of the clarification pipe, and is clarified with respect to the clarification a plate member is vertically disposed in a longitudinal direction of the tube, and in the clarification step, the molten glass flowing in the clarification pipe is controlled such that a height of an interface of the molten glass is higher than an upper end portion of the plate member Flow rate and flow rate. The method for producing a glass substrate according to claim 1, wherein the flow rate and the flow rate of the molten glass flowing in the clarification pipe, that is, the position of the plate member in the longitudinal direction of the clarification pipe, are controlled as follows The flow rate of the molten glass flowing above the plate member is divided by the flow velocity obtained by the cross-sectional area of the flow path above the plate member, and the flow rate of the molten glass flowing downward from the plate member is divided by the plate member The flow rates obtained by the cross-sectional area of the flow path below become equal. A method for producing a glass substrate, comprising: a clarification step in which a molten glass is heated from the clarified glass disposed in a substantially horizontal direction, and the molten glass is heated from the upstream side to the downstream side to cause the molten glass The bubble is discharged toward the gas phase space surrounded by the interface between the molten glass and the inner wall of the clarification pipe, and the clarification pipe is provided with a plurality of plate members arranged perpendicularly to the longitudinal direction of the clarification pipe. The plate member group includes: a first plate member group in which a plurality of first plate members are arranged at intervals in a longitudinal direction of the clarification pipe, and the plurality of first plate members and the clarification pipe The lowermost portion and the uppermost portion of the inner wall are disposed at a first height with a space therebetween; and the second plate member group is spaced apart from the first plate member by a plurality of second plate members in a longitudinal direction of the clarification pipe Arranging alternately, the plurality of second plate members are disposed at an interval between a second height higher than the first height and an uppermost portion of the inner wall of the clarification pipe; and a plate member group in which a plurality of third plate members are alternately arranged at intervals from the first plate member in a longitudinal direction of the clarification pipe, and the plurality of third plate members are lower than the first height The third height is not spaced apart from the lowermost portion of the inner wall of the clarification pipe; and in the clarifying step, the height of the interface of the molten glass is higher than the highest position of the upper end of the plurality of plate members In a manner, the flow rate and flow rate of the molten glass are controlled. The method for producing a glass substrate according to claim 3, wherein the flow rate and flow rate of the molten glass flowing in the clarification pipe are controlled as follows, that is, at least one first plate member in a longitudinal direction of the clarification pipe The flow rate obtained by dividing the flow rate of the molten glass flowing upward from the first plate member by the cross-sectional area of the flow path above the first plate member and melting the flow below the first plate member The flow rate of the glass is divided by the flow velocity obtained by dividing the cross-sectional area of the flow path below the first plate member. A method for producing a glass substrate, comprising: a clarification step of heating the molten glass from the upstream side to the downstream side while heating the molten glass, and directing the bubbles in the molten glass toward the melting The interface between the glass and the gas phase space surrounded by the inner wall of the clarification pipe is discharged; and the interface position control step is to control the molten glass flowing into the clarification pipe and the self to make the interface of the molten glass a specific position a flow rate of the molten glass flowing out of the clarification pipe; the clarification pipe includes: a plate member provided at an interval between the inner walls of the clarification pipe to suppress flow of the molten glass; and an interface position measuring instrument a position of the interface of the molten glass; and in the interface position control step, the position of the interface of the molten glass measured by the interface position meter is such that the height of the interface of the molten glass and the upper end of the plate member In a consistent manner, the flow rate of the molten glass described above is controlled. The method of producing a glass substrate according to claim 5, wherein the plate member is disposed obliquely with respect to a longitudinal direction of the clarification tube. The method for producing a glass substrate according to claim 5 or 6, wherein in the interface position control step, the inflow amount of the molten glass flowing into the clarification tube by adjusting a step further upstream than the clarification step, and/or The position of the interface of the molten glass is controlled by the outflow amount of the molten glass flowing out from the clarification pipe in the step further downstream than the clarification step. The method for producing a glass substrate according to any one of claims 5 to 7, wherein the clarification pipe is provided with an outer wall surface of the clarification pipe protruding to the outer side of the clarification pipe to connect the gas phase space to the external atmosphere. a vent pipe, wherein the interface position measuring instrument is introduced from the outer side of the clarification pipe through the vent pipe, and the position of the interface of the molten glass is measured. A glass substrate manufacturing apparatus comprising a clarification tube disposed in a substantially horizontal direction and for performing a clarification step of heating the molten glass to flow from the upstream side to the downstream side The bubbles in the molten glass are discharged toward a gas phase space surrounded by the interface between the molten glass and the inner wall of the clarification pipe, and the clarification pipe is spaced apart from the lowermost portion and the uppermost portion of the inner wall of the clarification pipe, and is opposed to each other. a plate member is vertically disposed in a longitudinal direction of the clarification pipe, and a flow rate and a flow rate of the molten glass flowing in the clarification pipe are controlled such that a height of an interface of the molten glass is higher than an upper end portion of the plate member . A glass substrate manufacturing apparatus comprising a clarification tube disposed in a substantially horizontal direction and for performing a clarification step of heating the molten glass to flow from the upstream side to the downstream side The bubbles in the molten glass are discharged toward a gas phase space surrounded by the interface between the molten glass and the inner wall of the clarification pipe, and the clarification pipe is provided with a plurality of bubbles arranged perpendicularly to the longitudinal direction of the clarification pipe. The plate member group of the plate member, wherein the plate member group includes: a first plate member group, wherein the plurality of first plate members are arranged at intervals in a longitudinal direction of the clarification pipe, and the plurality of first plate members and The lowermost portion and the uppermost portion of the inner wall of the clarification pipe are disposed at a first height with a space therebetween; and the second plate member group is composed of a plurality of second plate members in a longitudinal direction of the clarification pipe and the first plate member Arranged alternately at intervals, the plurality of second plate members are disposed at a second interval higher than the first height and spaced apart from an uppermost portion of the inner wall of the clarification pipe And a third plate member group, wherein the plurality of third plate members are alternately arranged at intervals from the first plate member in a longitudinal direction of the clarification pipe, and the plurality of third plate members are more a third height having a low height is not spaced apart from a lowermost portion of the inner wall of the clarification pipe; and a height of an interface of the molten glass is higher than a highest position of an upper end portion of the plurality of plate members, The flow rate and flow rate of the above molten glass are controlled. A manufacturing apparatus for a glass substrate, comprising: a clarification tube for performing a clarification step of heating the molten glass while flowing the molten glass from an upstream side to a downstream side to cause bubbles in the molten glass The clarification pipe is provided with a plate member that is provided at a predetermined interval between the inner wall of the clarification pipe to prevent the flow of the molten glass; and An interface position measuring device for measuring a position of an interface of the molten glass; and, in the clarification tube, a position of an interface of the molten glass measured by the interface position measuring meter to make a height of an interface of the molten glass and the above The flow rate of the molten glass is controlled in such a manner that the upper ends of the plate members are uniform.