JP2014224002A - Production method of glass plate, design method of dissolution tank, and dissolution tank - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method not generating a fusion loss by suppressing heat confinement of a foundation part of a dissolution tank, when forming molten glass having the electric resistivity of 160 Ω cm or higher at 1,550°C in the dissolution tank.SOLUTION: A heat insulation suppression structure of a bottom part is provided in a dissolution tank so that the temperature of the bottom part including a foundation part 124 of the dissolution tank is below a load softening point temperature of a refractory brick constituting the bottom part, when forming molten glass having the electric resistivity of 160 Ω cm or higher at 1,550°C by electric heating in the dissolution tank.

Description

  The present invention relates to a glass plate manufacturing method for manufacturing a glass plate, a melting tank used in the manufacturing method, and a method for designing the melting tank.

  In recent years, in the field of display panels, higher definition of pixels has been advanced in order to improve image quality. With the progress of this high definition, it is desired that the glass substrate used for the display panel is of high quality. For example, a glass substrate having a small thermal shrinkage is required so that a dimensional change hardly occurs in a glass substrate heat-treated at a high temperature during a panel manufacturing process.

  In general, it is known that the thermal contraction of a glass plate decreases as the strain point of the glass increases and as the annealing rate during the glass plate manufacturing process decreases. Therefore, even if the glass composition is the same, it is possible to reduce the thermal shrinkage to a required level by sufficiently reducing the slow cooling rate. In particular, when a glass plate is produced from molten glass by a float method, it is relatively easy to lengthen the slow cooling furnace and reduce the slow cooling rate, but when producing a glass plate using the downdraw method, It is difficult to lengthen from the point of view of equipment or operation. For this reason, in order to produce a glass plate that meets the requirements for thermal shrinkage by the downdraw method, a glass having a glass composition having a higher strain point than that of a conventional glass composition is used, in other words, a glass composition having a high temperature viscosity. Glass must be used. In general, a glass having such a glass composition tends to have a large electrical resistivity at the time of molten glass.

  Here, when making molten glass from a glass raw material, in the gas phase space in the melting tank, the temperature of the gas phase space is raised by burner heating to raise the temperature of the wall of the melting tank, and it is input by radiant heat from this wall. The melted glass raw material is melted and the molten glass formed by melting is heated by the radiant heat. Furthermore, the molten glass is made to have a desired viscosity by conducting current heating through an electrode pair provided in the liquid tank of the melting tank (paragraph 0015 of Patent Document 1).

JP 2012-517398 A

In the melting process for conducting heating of such molten glass, if the electrical resistivity of the molten glass is low, a large amount of current for heating must be passed, but on the other hand, if the electrical resistivity of the molten glass is high The current for heating may flow not only in the molten glass but also in the refractory bricks constituting the melting tank. The higher the electrical resistivity of the molten glass, the more current flows through the refractory brick. As such refractory bricks, zirconia (ZrO ₂ ) type electrocast refractory bricks with excellent erosion resistance of molten glass and high electrical resistivity and AZS electrocast refractory bricks containing Al ₂ O ₃ , ZrO ₂ and SiO ₂ are used. Even if it is used, in order to reduce the thermal shrinkage of the glass plate, when a glass composition having a high temperature viscosity and a high electrical resistivity is used, a current flows through the refractory brick, and the refractory brick is easily heated. For example, in the case of molten glass having an electrical resistivity at 1550 ° C. of 160 Ω · cm or more, the refractory brick of the melting tank is energized and heated, and the heat is accumulated in the refractory brick of the laying part constituting the bottom of the melting tank. However, it is difficult to ignore the heat that is partially higher than the surrounding area. In the case of a molten glass having an electrical resistivity at 1550 ° C. of 190 Ω · cm or more, the heat weight becomes significant. Due to the heat, the strength of the refractory brick is lowered and easily deformed. In some cases, the refractory brick may be melted. When the refractory bricks are melted, not only the production of the molten glass and thus the glass plate cannot be continued, but in some cases, serious equipment damage is caused.

As described above, when a glass sheet is improved by increasing the viscosity of the molten glass in response to a request for a glass substrate having a small thermal shrinkage, there is a possibility that the conventional melting tank may be damaged. In this respect, the design of the melting tank is important.
Further, since the molten glass having a high viscosity is hardly fusible, the liquid surface of the molten glass in the vicinity of the wall surface on the outlet side leading to the subsequent process has a foreign material (the concentration of SiO ₂ which is a hardly fusible component). In many cases, the substrate is higher than other places. When this heterogeneous substrate sinks to the bottom wall side of the melting tank and flows out to the subsequent process, the glass plate forms optically heterogeneous streak defects called striae. For this reason, it is also necessary to prevent the temperature of the molten glass near the wall on the outlet side in the melting tank from dropping too much compared to the temperature of the molten glass near the center.

  The present invention relates to a method for producing a glass plate that suppresses the heat trapping of the laying part of the melting tank and does not cause melting when the molten glass has an electric resistivity of 160 Ω · cm or more at 1550 ° C. in the melting tank. It aims at providing the design method and melting tank of a tank.

  One embodiment of the present invention is a method for producing a glass plate including a step of producing a molten glass having an electrical resistivity at 1550 ° C. of 160 Ω · cm or more by electric heating in a melting tank. At this time, the bottom heat retention suppressing structure is set in the melting tank so that the temperature of the bottom including the laying part of the melting tank is lower than the load softening point temperature of the refractory bricks constituting the bottom.

  In addition, a simulation calculation for making a molten glass using a melting tank model as a reference is performed to predict and calculate the temperature distribution of the bottom portion, and the bottom portion so that the maximum temperature of the temperature distribution is less than the load softening point temperature. It is preferable that a heat retention suppressing structure is set.

  In addition, the laying part is a laminated structure of a plurality of refractory bricks, and the setting of the heat insulation suppressing structure is that the thermal conductivity of the refractory bricks of the laying part is partially relative to the surroundings in at least one layer of the refractory bricks. It is preferable to include different.

  In addition, the laying part is a laminated structure of a plurality of refractory bricks, and the setting of the heat retention suppressing structure is such that at least one layer of the refractory brick is provided with a hole extending in the bottom surface of the laying part in the refractory brick of the laying part It is preferable to include.

  Or the setting of the said heat retention suppression structure is setting the position of any one opening among the drain port provided in the bottom part of the said melting tank, the opening for installation of a temperature sensor, and the gas introduction port for foam formation. It is also preferable to include.

The molten glass contains tin oxide, temperature at 10 ^2.5 poise may be 1580 ° C. or higher.

Another aspect of the present invention is a method for designing a melting tank in which molten glass having an electrical resistivity at 1550 ° C. of 160 Ω · cm or more is produced by electric heating. The method is
The temperature distribution of the bottom including the laying part of the melting tank is calculated by performing a simulation calculation of the heat conduction of the melting tank and the molten glass using a standard melting tank model, and the maximum temperature of the temperature distribution is the load softening point temperature. By setting the bottom of the melting tank model so as to be less than the minimum, a heat retention suppressing structure for the bottom of the melting tank is set.

Yet another embodiment of the present invention is a melting tank for producing molten glass. The melting tank is
A melting tank main body for storing molten glass having an electrical resistivity at 1550 ° C. of 160 Ω · cm or more;
An electrode pair for electrically heating the molten glass;
And a heat retention suppressing structure for the bottom portion that makes the temperature of the bottom portion including the laying portion of the melting tank lower than the load softening point temperature of the refractory brick that constitutes the bottom portion.

  According to the glass plate manufacturing method, the melting tank design method and the melting tank of the above embodiment, in the melting tank, when making molten glass having an electrical resistivity at 1550 ° C. of 160 Ω · cm or more, It can suppress heat turbulence and does not cause melting of the melting tank.

It is a figure which shows an example of the process of the manufacturing method of the glass plate of this embodiment. It is a figure which shows typically an example of the glass plate manufacturing apparatus which performs the melting process-cutting process in this embodiment. It is a perspective view explaining the outline of the structure of the melting tank main body of the melting tank of this embodiment, and its periphery. It is a figure explaining the cross section of the melting tank of this embodiment. It is sectional drawing along the longitudinal direction of the melting tank main body of this embodiment. (A) is the figure which showed an example of the cross-sectional structure of the reference melting tank model, (b) is the simulation calculation of the heat conduction of the melting tank and molten glass which have the structure shown to Fig.6 (a). It is a figure which shows an example of a result. (A) is the figure which showed an example of the cross-section of a melting tank model, (b) is an example of the result of the simulation calculation of the heat conduction of a melting tank and molten glass which has the structure shown to Fig.7 (a). FIG. (A) is the figure which showed another example of the cross-section of a melting tank model, (b) is the result of the simulation calculation of the heat conduction of a melting tank and molten glass which has the structure shown to Fig.8 (a). It is a figure which shows an example. It is a figure explaining the example of the convection of the molten glass in a melting tank. It is a figure explaining the example of the convection of the molten glass in the melting tank in this embodiment.

Hereinafter, the manufacturing method of the glass plate of this embodiment is demonstrated.
In the present embodiment, in order to suppress the above-described heat trap of the melting tank, the temperature of the bottom including the laying part of the melting tank is less than the load softening point temperature of the refractory bricks constituting the bottom of the melting tank. A heat retention suppressing structure is provided at the bottom of the melting tank.
For example, before making molten glass in the melting tank, the temperature distribution at the bottom of the melting tank is predicted and calculated by performing simulation calculation to make molten glass using the standard melting tank model, and the temperature distribution obtained by the prediction calculation The heat retention suppressing structure at the bottom of the melting tank is set so that the temperature of the refractory brick becomes less than the load softening point temperature of the refractory brick.
In addition, when the laying part has a laminated structure of a plurality of refractory bricks, the laying part refractory bricks have a thermal conductivity partially different from that of the surroundings in at least one layer of the refractory bricks of the laying part. Set the heat retention suppression structure of the part.
Alternatively, when the laying part has a laminated structure of a plurality of refractory bricks, at least one layer of the refractory bricks of the laying part is provided with a hole extending in the bottom surface of the laying part in the refractory brick of the laying part, thereby providing a heat retention suppressing structure Set.
Alternatively, the position of any one of the drain port provided at the bottom of the melting tank, the opening for installing the temperature sensor, and the gas inlet for foam formation is set, and the temperature of the bottom including the laying part of the melting tank However, it is made to become less than the load softening point temperature of the refractory brick which comprises a bottom part.

  Drawing 1 is a figure showing an example of a process of a manufacturing method of a glass plate of this embodiment.

(Overall overview of glass plate manufacturing method)
The glass plate manufacturing method includes a melting step (ST1), a refining step (ST2), a homogenizing step (ST3), a supplying step (ST4), a forming step (ST5), and a slow cooling step (ST6). And a cutting step (ST7). In addition, a plurality of glass plates that have a grinding process, a polishing process, a cleaning process, an inspection process, a packing process, and the like and are stacked in the packing process are conveyed to a supplier.

The melting step (ST1) is performed in a melting tank. In the melting tank, a glass raw material is charged into the liquid surface of the molten glass stored in the melting tank and heated to produce a molten glass having an electrical resistivity at 1550 ° C. of 160 Ω · cm or more. Furthermore, molten glass is poured toward the downstream process from the outlet provided in one bottom part of the inner side wall of the melting tank.
Heating of the molten glass in the melting tank is performed by supplying electricity to the molten glass itself, generating heat, and heating the glass, and supplementing a flame with a burner to melt the glass raw material. Specifically, the charged glass raw material is heated by heat radiation heat transfer from the wall surface of the gas phase space of the melting tank 101 or the flame of the burner, and is thermally decomposed and melted. The molten glass produced in this way is heated to a higher temperature. A clarifier is added to the glass raw material. SnO ₂ , As ₂ O ₃ , Sb ₂ O _{3 and the} like are known as fining agents, but are not particularly limited. However, SnO ₂ (tin oxide) can be used as a clarifying agent from the viewpoint of reducing environmental burden. In the melting tank, the glass raw material is completely melted so as not to cause striae in the glass plate, and a molten glass having a predetermined viscosity is produced by electric heating so that the subsequent process is appropriately performed.

The clarification step (ST2) is performed at least in the clarification tank. In the clarification process, when the molten glass in the clarification tank is heated, the bubbles containing O ₂ , CO ₂ or SO ₂ contained in the molten glass absorb O ₂ generated by the reductive reaction of the clarifier. As a result, the bubbles rise to the liquid surface of the molten glass and are discharged. Furthermore, in the clarification step, the reducing substance obtained by the reduction reaction of the clarifier undergoes an oxidation reaction by lowering the temperature of the molten glass. Thereby, gas components such as O ₂ in the foam remaining in the molten glass are reabsorbed in the molten glass, and the foam disappears. The oxidation reaction and reduction reaction by the fining agent are performed by controlling the temperature of the molten glass. In the clarification step, a clarification method using tin oxide as a clarifier can be used.

In the homogenization step (ST3), the glass components are homogenized by stirring the molten glass in the stirring tank supplied through the pipe extending from the clarification tank using a stirrer. Thereby, the composition unevenness of the glass which is a cause of striae or the like can be reduced.
In the supply step (ST4), the molten glass is supplied to the molding apparatus through a pipe extending from the stirring tank.

In the molding apparatus, a molding step (ST5) and a slow cooling step (ST6) are performed.
In the forming step (ST5), the molten glass is formed into a sheet glass to make a flow of the sheet glass. For forming, an overflow downdraw method is used.
In the slow cooling step (ST6), the sheet glass that has been formed and flowed is cooled to a desired thickness, so that internal distortion does not occur and warpage does not occur.
In a cutting process (ST7), a plate-shaped glass plate is obtained by cutting the sheet glass supplied from the forming device into a predetermined length in the cutting device. The cut glass plate is further cut into a predetermined size to produce a target size glass plate. After this, the end face of the glass plate is ground and polished, the glass plate is cleaned, and further, the presence of abnormal defects such as bubbles and striae is inspected. Will be packed as.

FIG. 2 is a diagram schematically illustrating an example of a glass plate manufacturing apparatus that performs the melting step (ST1) to the cutting step (ST7) in the present embodiment. As shown in FIG. 2, the apparatus mainly includes a melting apparatus 100, a forming apparatus 200, and a cutting apparatus 300. The melting apparatus 100 includes a melting tank 101, a clarification tank 102, a stirring tank 103, and glass supply pipes 104, 105, and 106.
In the melting apparatus 101 shown in FIG. 2, the glass raw material is charged using a bucket 101d, and the molten glass MG is heated so that the molten glass MG obtained by melting the glass raw material has a predetermined viscosity. In the clarification tank 102, the temperature of the molten glass MG is adjusted, and the clarification of the molten glass MG is performed using the oxidation-reduction reaction of the clarifier. Further, in the stirring vessel 103, the molten glass MG is stirred and homogenized by the stirrer 103a. In the forming apparatus 200, the sheet glass SG is formed from the molten glass MG by the overflow down draw method using the formed body 210. In the present embodiment, the bucket 101d is used as a glass raw material charging unit, but is not limited thereto. For example, a screw feeder can be used. The glass raw material charging method using the bucket 101d is a method of charging the liquid surface of the molten glass MG on the liquid surface on the raw material charging port side of the bucket 101d (charging in front), or charging the entire liquid surface (full charging). Include) method. In the present embodiment, as shown in FIG. 2, the glass raw material is charged by forward loading.

In such a glass plate manufacturing method and glass plate manufacturing apparatus, in order to produce a glass plate having a small thermal shrinkage, when glass having a glass composition having a high temperature viscosity is used, the melting tank 101 is not a glass having a high temperature viscosity. Compared to the above, it is necessary to heat by energizing by passing a large amount of current. However, in the glass having high viscosity at high temperature, the electrical resistivity in the molten state tends to increase, and the electrical resistivity of the molten glass is equivalent to the electrical resistivity of the refractory brick used for the side wall and the bottom wall of the melting tank 101. . For this reason, when an electric current is made to flow through the electrode pair provided on the side wall of the melting tank 101 and an electric current is made to flow through the molten glass, a part of the current that should originally flow through the molten glass is applied to the side wall and the bottom wall of the melting tank 101. The stream, the side walls and the bottom wall are heated. In particular, in the laying portion of the layer structure in which a plurality of layers of refractory bricks having excellent heat insulating properties are laid below the bottom wall of the melting tank 101, heat does not escape due to the heat insulating properties, and heat is partially accumulated, resulting in a high temperature. A heat turbulence occurs. Such a hot weight lowers the mechanical strength of the refractory bricks on the bottom wall and the laying part, causes thermal creep, and a part of the refractory bricks may be melted and the molten glass to be stored may flow out to the outside. There is also.
For this reason, in this embodiment, before making the molten glass whose electric resistivity in 1550 degreeC is 160 ohm * cm or more by electric heating, the temperature of the bottom part including the laying part of the melting tank 101 is the refractory brick which comprises a bottom part. The bottom heat retention suppressing structure is set so as to be lower than the load softening point temperature. In addition, the load softening point temperature of a refractory brick is prescribed | regulated by JISR2209: 2007. The load softening point temperature of the refractory brick in this embodiment is T2 (2% shrinkage) defined by the above JIS. A value obtained by subtracting a value within an allowable range (for example, 10 ° C. to 20 ° C.) from the value of T2 may be used as the load softening point temperature of the refractory brick. Hereinafter, the configuration of the melting tank will be described in more detail.

(Melting tank)
FIG. 3 is a perspective view for explaining the outline of the melting tank main body of the melting tank 101 and its peripheral structure, and FIG. 4 is a diagram for explaining the section of the melting tank 101 in a simplified manner. When the direction from the raw material inlet to the outlet that flows to the subsequent step of the molten glass is referred to as the longitudinal direction of the melting tank 101, the cross section shown in FIG. 4 is a cross section at the longitudinal position where the electrode 114 shown in FIG. is there. FIG. 5 is a cross-sectional view along the longitudinal direction of the melting tank body.

  In the present embodiment, the melting tank 101 mainly has a melting tank main body 110, a burner 112, an electrode pair 114, and a compression portion 118.

  The melting tank main body 110 has a gas phase space in the upper part and stores molten glass in the lower part, and stores molten glass having an electrical resistivity at 1550 ° C. of 160 Ω · cm or more.

  Three burners 112 are provided on both walls facing each other at different positions in the longitudinal direction on the gas phase space partition wall 116 surrounding the gas phase space of the melting tank main body 110. At this time, the burners 112 are not provided at positions facing each other, but are provided alternately. Note that three burners 112 may be provided on one wall, not on both walls facing each other. In FIG. 3, only the burner 112 provided on the inner wall of the melting tank main body 110 is shown. The burner 112 emits a flame by burning a combustion gas in which fuel and oxygen are mixed. In FIG. 4, two burners 112 are shown to be provided at opposing positions on the opposing walls, but the two burners 112 shown in FIG. 4 are provided at different positions in the direction perpendicular to the paper surface of FIG. ing.

  Three pairs of the electrode pairs 114 are provided at three different positions in the longitudinal direction of the side wall portion of the melting tank main body 110 so as to energize and heat the molten glass so as to face each other with the molten glass interposed therebetween. In FIG. 3, only the electrode provided in the side wall part of the near side of the melting tank main body 110 is shown. For the electrode pair 114, for example, a conductive material having heat resistance such as tin oxide or molybdenum is used. The electrode pair 114 is connected to the control unit 120 and receives a controlled current supply from the control unit 120. The control unit 120 is connected to the computer 122, and the current flowing through the electrode pair 114 is controlled by a control signal from the computer 122. The computer 122 generates a control signal so that a predetermined current flows through the electrode pair 114 such that the temperature of the bottom of the melting tank 101 is lower than the load softening point temperature of the refractory bricks constituting the bottom.

  The gas phase space partition wall 116 is a part of the melting tank main body 110 and is a wall provided on the upper part of the molten glass storage portion. A burner 112 is provided on this wall. Further, the gas-phase space partition wall 116 is provided with a raw material inlet 101f that can be freely opened and closed, and a bucket 101d (see FIG. 2) in which glass raw materials are loaded enters and exits through the raw material inlet 101f. Glass material is thrown into the liquid level of the molten glass stored in the melting tank main body 110 by the bucket 101d. An outflow port 104a is provided in the vicinity of the bottom of the side wall facing the raw material charging port 101f of the melting tank main body 110. The melting tank 101 flows the molten glass from the outlet 104a toward the subsequent process.

The compression portion 118 is a ceiling wall that closes the gas phase space of the melting tank 101. FIG. 4 shows the compression portion 118 in detail. A temperature sensor 118 a is provided on the top of the compression portion 118.
As the melting tank main body 110, the gas phase space partition wall 116, and the compression portion 118, those having heat resistance with respect to the temperature of the molten glass are used. For example, zirconia electrocast refractory bricks having high electric resistance and corrosion resistance are used. Used. Further, AZS (Al ₂ O ₃ —ZrO ₂ —SiO ₂ ) may be used for the partition wall and the close portion 118.

  At the lower part of the melting tank main body 110, a laying portion 124 having a laminated structure made of refractory bricks is provided. The laying part 124 has a heat insulating layer having a four-layer structure. A refractory brick having a higher load softening point temperature than the refractory brick used for the laying portion 124 is used for the bottom wall 110a of the melting tank 101. Since the refractory brick having a high load softening point temperature is a dense refractory brick having a low porosity, the thermal conductivity is relatively high. For this reason, in the laying part 124, a refractory brick having a low thermal conductivity and a high heat insulating property is used compared to the refractory brick used for the bottom wall 110a. Since the refractory brick with low thermal conductivity is a refractory brick with high porosity, the load softening point temperature is low. Such a layer structure is generally used for the melting tank 110. In the present embodiment, the part including the bottom wall 110 a and the laying part 124 of the melting tank main body 110 is referred to as the bottom part 126 of the melting tank 110.

The bottom wall of the melting tank main body 110 is provided with a temperature sensor installation opening 126a, a drain port 126b, and a hole 126c. In this embodiment, the temperature sensor installation opening 126a, the drain port 126b, and the hole 126c are provided, but any one or two of the temperature sensor installation opening 126a, the drain port 126b, and the hole 126c may be provided. Moreover, the number of each of the temperature sensor installation openings 126a and the holes 126c is not limited to one and may be plural.
The temperature sensor installation opening 126a is an opening provided in the bottom wall of the melting tank main body 110 in order to install a temperature sensor that measures the temperature in the bottom wall portion of the molten glass MG, for example, a thermocouple. This opening is connected to a hole formed in the refractory brick of the bottom wall 110a and the laying portion 124. Therefore, the holes connected to the openings are suppressed from keeping the holes and the periphery of the holes so as to prevent the molten glass MG from leaking out of the holes by increasing the viscosity of the molten glass MG.
The drain port 126b is an outflow port 104a that flows out of the glass plate manufacturing apparatus without flowing the molten glass MG in a subsequent process. The molten glass MG stored in the melting tank main body 110 may be completely extracted from the melting tank main body 110 in order to repair the melting tank 101 or the melting apparatus 100. In addition, the drain port 126b can also be provided in the side wall in which the outflow port 104a is provided.
Moreover, in order to grow the bubble in the molten glass MG in the melting tank main body 110, and to make it easy to clarify in a clarification process of a post process, a bubble may be introduce | transduced into molten glass MG. In this case, a bubble forming gas inlet for introducing bubbles into the molten glass MG is provided on the bottom wall of the melting tank main body 110. In the embodiment shown in FIGS. 3 to 5, the bubble forming gas inlet is not provided. This gas inlet is also connected to a hole made in the refractory brick of the bottom wall 110a and the laying part 124. Therefore, the holes connected to the bubble forming gas introduction port are also kept at a low temperature so as to prevent the molten glass MG from leaking out of the holes by increasing the viscosity of the molten glass MG.
The hole 126c is a hole provided in at least one layer of the refractory brick and extending from the refractory brick to the bottom surface 124a of the laying portion 124. In the example shown in FIG. 5, a hole 126c is provided between the second brick layer from the bottom of the laying portion 124 and the bottom surface 124a. The hole 126c may be a hole extending from at least one layer of the refractory brick to the bottom surface 124a, and the starting position of the hole 126c is not particularly limited except for the surface of the bottom wall of the melting tank 101. By providing the hole 126c, the refractory brick surrounding the hole 126c has a large area in contact with the outside air, so that it is easy to radiate heat. For this reason, the heat insulation of the refractory bricks around the hole 126c is suppressed.
As described above, providing the temperature sensor installation opening 126a, the drain port 126b, the bubble forming gas introduction port for introducing bubbles into the molten glass MG, or the hole 126c corresponds to providing a heat retention suppressing structure. Then, the temperature sensor installation opening 126a, the drain port 126b, the bubble forming gas introduction port for introducing bubbles into the molten glass MG, or the position of the hole 126c is appropriately provided so that the refractory bricks constituting the bottom 126 are formed. It can be made to become less than a load softening point temperature.

  In such a melting tank 101, in order to set the viscosity of the molten glass to a predetermined viscosity, an electric current is passed through the molten glass to heat it, so that a molten glass having an electrical resistivity at 1550 ° C. of 160 Ω · cm or more is used. As described above, heat is likely to be generated in a part of the bottom portion 126. For this reason, the bottom 126 is provided with a heat retention suppressing structure for the bottom 126 that makes the temperature of the bottom 126 less than the load softening point temperature of the refractory bricks constituting the bottom 126. In addition, although the part in which a heat cloud generate | occur | produces changes according to the electric current given to each position of the electrode pair 114, and the shape of the melting tank main body 110, the part in which a heat fog generate | occur | produces is roughly, It is often located between the center in the longitudinal direction and a position shifted from this center toward the outlet 104a.

  For example, a structure in which the thermal conductivity of the refractory brick of the laying portion 124 is partially different from that of the same layer in at least one of the refractory bricks of the laying portion 124 can be used as the heat insulation suppressing structure. More specifically, when the laying portion 124 is not provided with a heat retention suppressing structure, the temperature at the position where the temperature of the refractory brick becomes the highest and which is equal to or higher than the load softening point temperature of the refractory brick is melted. It is found by measuring the temperature distribution of the tank 101 or by thermal simulation calculation using a computer. When the found portion is exposed to a temperature equal to or higher than the load softening point temperature for a long period of time, thermal creep occurs due to the weight of the molten glass MG or the weight of the melting bath 101, and further, There is a risk of melting and damaging the melting tank 101. For this reason, in order to suppress the above-mentioned heat bulging, the refractory brick of the laying portion 124 where the heat bulging occurs is changed to a refractory brick with higher thermal conductivity as a heat retention suppressing structure. Therefore, in this case, the heat retention suppressing structure is a structure in which the thermal conductivity of the refractory brick of the laying portion 124 is partially different from that of the same layer in at least one refractory brick of the laying portion 124. For example, in the central part of 30.5% to 69.5% of the width of the bottom wall of the melting tank 101 across the center line in the width direction perpendicular to the longitudinal direction of the melting tank 101, compared to both sides of this central part It is preferable to use a refractory brick having a high thermal conductivity, that is, a high heat dissipation effect. The thermal simulation calculation may be performed before the molten glass for actually producing the glass plate is made or after the start of the operation for producing the molten glass for producing the glass plate.

As a heat retention suppressing structure, any one of a drain port 126b provided at the bottom of the melting tank 101, a temperature sensor installation opening 126a, and a bubble forming gas introduction port is provided in the portion where the heat is generated. It is also possible to use a structure in which the position is set. The drain port 126b, the temperature sensor installation opening 126a, and the bubble forming gas introduction port are connected to holes formed in the refractory bricks of the bottom wall 110a and the laying portion 124, and have a structure that suppresses heat retention. Therefore, heat insulation is low and heat dissipation is easy. For this reason, the heat insulation is suppressed by setting the position of any one of the drain port 126b, the temperature sensor installation opening 126a, and the bubble forming gas introduction port in the specified portion of the thermal mass. can do.
Moreover, the structure which set the hole 126c provided in the bottom part of the melting tank 101 can also be used for the part in which the said heat dust generate | occur | produces as a heat retention suppression structure. The hole 126c is a hole opened in the refractory brick of the laying portion 124, and has a structure that suppresses heat retention. Therefore, the heat insulating property is low and it is easy to radiate heat. For this reason, heat retention can be suppressed by providing the hole 126c in the specified portion of the heat sink.

The molten glass MG produced in the melting tank 101 contains tin oxide and suppresses the occurrence of thermal creep of the melting tank main body 110 and the bottom 126 even when the temperature at 10 ^2.5 poise is 1580 ° C. or higher. It is possible to suppress refractory bricks from melting. That is, containing tin oxide, when using a high melting glass having high temperature viscosity temperature is above 1580 ° C. when a 10 ^2.5 poise, the effect of the present invention is increased.
Moreover, in this embodiment, it can apply also to the molten glass whose electrical resistivity in 1550 degreeC is 190 ohm * cm or more.

Such a melting tank 110, that is, a melting tank for producing a molten glass having an electrical resistivity at 1550 ° C. of 160 Ω · cm or more by current heating can be designed by the following design method.
First, the temperature distribution of the bottom 126 including the laying part 124 of the melting tank 101 is obtained by performing a simulation calculation of the heat conduction of the molten glass MG using the melting tank 101 using a melting tank model (not shown) as a reference. When the maximum temperature of the obtained temperature distribution is equal to or higher than the load softening point temperature, the heat retention suppressing structure of the bottom portion 126 of the melting tank 101 is modified by correcting the heat retention suppressing structure of the above-described melting tank model so as to be lower than the load softening point temperature. To decide.
Such a design method can be realized by executing software using a computer having an arithmetic processing unit and a memory.

Thus, when providing a heat retention suppression structure in the bottom part 126 of the melting tank 101, it is preferable not to provide a heat retention suppression structure in the part of the bottom part 126 connected with the downstream side wall 101b in which the outflow port 104a of the molten glass MG is provided. . If a heat retention suppressing structure is used for this part, the temperature of the molten glass MG in the vicinity of the downstream side wall 101b is lowered, so that the liquid surface of the molten glass MG in the vicinity of the downstream side wall 101b has a foreign material (SiO ₂ which is a hardly fusible component). The substrate whose concentration is higher than other places is likely to accumulate. This heterogeneous substrate sinks below the molten glass MG, flows out from the outlet 104a, and flows to the subsequent process, thereby forming striae. In order to suppress such outflow of the heterogeneous substrate, it is necessary to prevent the temperature of the molten glass MG in the vicinity of the downstream side wall 101b from being excessively lowered. From this point, it is preferable not to provide the above-described heat retention suppressing structure in the portion of the bottom portion 126 connected to the downstream side wall 101b of the melting tank 101.

Next, the temperature distribution of the melting tank using the simulation calculation of the heat conduction between the melting tank 101 and the molten glass MG will be described.
Fig.6 (a) is the figure which showed an example of the cross-sectional structure of the melting tank model used as a reference | standard. Fig.6 (a) has shown the figure which cut | disconnected the melting tank model by the vertical plane along the longitudinal direction through the center position of the width direction orthogonal to a longitudinal direction. The melting tank model 101M includes a melting tank main body model 110M and a laying part model 124M. The laying part model 124M is configured by a four-layer brick layer model. As the thermal conductivity of the melting tank main body model 110M and the laying part model 124M, the values of the thermal conductivity of the melting tank main body 110 and the laying part 124 of the actual actual melting tank 101 were used. The thermal conductivity of the part corresponding to the wall of the melting tank main body model 110M is (3.18799 × 10 ⁻¹² T ⁴ −1.8239798 × 10 ⁻⁸ T ³ + 4.0884149 × 10 ⁻⁵ T ² −0.0384005T + 13.677581) [W / ( m · K)] (T: temperature [K]), and the thermal conductivity of the four-layer laying part model 124M is, in order from the upper layer,
・ (3.18799 × 10 ⁻¹² T ⁴ −1.8239798 × 10 ⁻⁸ T ³ + 4.0884149 × 10 ⁻⁵ T ² −0.0384005T + 13.677581) [W / (m · K)] (T: temperature [K]),
3.605 [W / (m · K)],
-2.093 [W / (mK)],
・ (3.05869 × 10 ^-4 T-0.159519) [W / (m ・ K)] (T: Temperature [K]),
It was.
FIG.6 (b) is a figure which shows an example of the result of the simulation calculation of the heat conduction of the melting tank 101 and molten glass MG which have the structure shown to Fig.6 (a). As the heat conduction simulation calculation, the fluid element simulating the molten glass MG is filled in the melting tank main body model 110M, and the temperature of the radiant heat transfer boundary condition (emissivity 0.7, reference temperature 1580 ° C.) on the liquid surface of the fluid element. Boundary conditions are applied, and heating is performed on the fluid elements under conditions of (flow rate 6 tons / day, inflow temperature 1500 ° C, three electrodes, 114 amperes, 125 amperes, 138 amperes in order from the input side). Then, the simulation calculation of the temperature distribution by the heat conduction of the molten glass MG and the melting tank 101 was performed.
According to FIG. 6B, the temperature is the highest in the portion of the bottom model 126 </ b> M corresponding to the bottom 126. This maximum temperature was 1713 ° C. The position of the maximum temperature in the longitudinal direction is a position that is closer to the side where the outflow port 104a is reproduced from the longitudinal center portion of the melting tank model 101M.

  Fig.7 (a) is a figure which shows an example of a structure of the melting tank model 101M which provided the drain port model 126bM in the position which became the maximum temperature 1713 degreeC shown in FIG.6 (b). In this case, the brick model surrounding the drain port model 126bM is a brick model surrounding the brick model so that the heat dissipation by the drain port model 126bM does not become extremely large. The thermal conductivity is set so that the thermal conductivity is lower than that of (higher heat retention). FIG.7 (b) is a figure which shows an example of the result of the simulation calculation of the heat conduction of the melting tank and molten glass of the structure shown to Fig.7 (a). In the simulation calculation of heat conduction, except for the brick model surrounding the drain port model 126bM, the same simulation calculation as in FIG. 6A is used, using the same value of thermal conductivity as in FIG. Went. The thermal conductivity of the brick model surrounding the drain port model 126bM was 1.744 [W / (m · K)]. According to FIG.7 (b), the position of the highest temperature of the bottom model 126M including the laying part model 124M which reproduced the bottom 126 moved to the glass raw material supply side of a longitudinal direction, and the highest temperature fell to 1696 degreeC. .

  FIG. 8A is a diagram showing another example of the configuration of the melting tank model in which the drain port 126bM is provided in the portion where the maximum temperature is 1713 ° C. shown in FIG. 6B. In this case, three hole models 126cM are provided in the region showing the maximum temperature shown in FIG. 7B, and one hole model 126cM is provided on the side corresponding to the outlet in the longitudinal direction with respect to the drain port 126bM. Provided. Further, in the second brick layer model from the bottom among the brick layer models corresponding to the four brick layers of the laying part 124, the brick in the center portion across the center line in the width direction orthogonal to the longitudinal direction of the melting tank 101. The thermal conductivity of the layer model is made higher than the thermal conductivity of the brick layer model on the outer side in the width direction across this central portion, and this brick layer model with high thermal conductivity is used as the longitudinal axis of the melting tank model 101M. It was configured to extend in the direction. The thermal conductivity of the central brick layer model was 2.093 [W / (m · K)]. The heat conductivity of the brick layer model other than this used the heat conductivity similar to the example shown to Fig.7 (a). That is, the model reproduces that the thermal conductivity of the refractory brick of the laying portion 124 is partially different from the surrounding in at least one refractory brick layer. The brick layer model of the laying part 124 other than this used the value of thermal conductivity similar to the example shown in FIG.

  FIG.8 (b) is a figure which shows an example of the result of the simulation calculation of the heat conduction of the melting tank and molten glass of the structure shown to Fig.8 (a). In the simulation calculation of heat conduction, the same simulation calculation as in the example shown in FIG. According to FIG. 8B, the position of the maximum temperature of the bottom model 126M has moved to the molten glass outlet 104a side in the longitudinal direction, and the maximum temperature has decreased to 1664 ° C.

  From the result of such a simulation calculation, the configuration of the brick layer of the laying portion 124 is adjusted to adjust the position of the drain port 126b, and the position of the hole 126c is set to provide the hole 126c, thereby providing a melting tank. The temperature of the bottom 126 of the 101 can be reduced. Since the load softening point temperature of the refractory brick used for the bottom portion 126 is, for example, around 1700 ° C., the temperature of the refractory brick of the bottom portion 126 is made lower than the load softening point temperature by adopting the above-described structure for suppressing heat retention. It becomes possible to do.

Referring to the temperature distribution of the molten glass as a result of the simulation calculation shown in FIG. 6B, the position of the maximum temperature of the bottom 126 is located on the outlet side from the longitudinal central portion of the widthwise central portion of the melting tank. Also in the bottom wall of the melting tank 101, the temperature is highest at the position (position A) in the longitudinal direction of the maximum temperature of the bottom 126. For this reason, as shown in FIG. 9, convection in which molten glass MG rises from position A toward the liquid surface is likely to occur in melting tank 101. FIG. 9 is a diagram for explaining an example of convection of the molten glass MG in the melting tank 101. When such convection of the molten glass MG occurs, the heterogeneous substrate 101c, which is a substrate in which the concentration of SiO ₂ , which is a hardly soluble component in the glass raw material 101a, is higher than that in other locations is caused to flow out in the longitudinal direction by convection. In many cases, the liquid level is accumulated on the side of 104a. This heterogeneous substrate 101c rides on the flow of convection B and sinks on the bottom wall side of the melting tank 101 and flows out to the subsequent process, and the glass plate may form optically heterogeneous streak defects called striae. There is. For this reason, in order not to generate the convection as shown in FIG. 9, the temperature T ₃ of the molten glass near the wall surface on the outlet 104 a side in the melting tank 101 is compared with the temperature T ₂ of the molten glass MG at the position A. Smallness is not preferable. In this regard, the result of the simulation calculation shown in FIG. 6B is an undesirable result because an optically heterogeneous streak defect called striae is formed in the glass plate to be manufactured. In the simulation calculation result shown in FIG. 7B, the difference between the temperature T ₃ and the temperature T ₂ is smaller than the simulation calculation result shown in FIG. 6B.

On the other hand, in the simulation calculation result shown in FIG. 8B, the temperature of the molten glass MG in the vicinity of the groove bottom of the melting tank 101 is the temperature at the center in the longitudinal direction with respect to the temperature T ₃ on the side wall on the outlet 104a side. T ₂ is low. Furthermore, the temperature T ₁ on the side wall on the raw material input side is lower than the temperature T ₂ . Moreover, the temperature T ₄ of the surface layer of the molten glass MG at the glass raw material charging position is lower than the temperature T ₃ . For this reason, as shown in FIG. 10, in the melting tank 101, counterclockwise convection is generated in the molten glass MG. FIG. 10 is a diagram for explaining an example of a preferable convection of the molten glass MG in the melting tank 101. A part of the molten glass MG that did not flow from the outlet 104a rises toward the liquid level along the side wall of the melting tank 101, and a part of the molten glass MG that has risen to the liquid level enters the raw material input side along the liquid level. Flows toward the side wall of the melting tank 101, descends from the liquid level along the side wall of the melting tank 101 on the raw material charging side, and further flows from the raw material charging side toward the discharge port along the bottom wall. For this reason, the heterogeneous substrate 101b does not drift near the side wall on the outlet 104a side. Furthermore, since the flow of the molten glass MG flows from the bottom wall toward the liquid level on the side wall on the outlet 104a side, the heterogeneous substrate 101b does not sink. For this reason, optically heterogeneous streak defects called striae are not formed in the manufactured glass plate. Thus, adopting the above-described heat retention suppressing structure can improve the convection of the molten glass MG in the melting tank 101 and prevent the glass plate from generating striae.

As described above, in the present embodiment, the temperature of the bottom portion 126 including the laying portion 124 of the melting tank 101 is less than the load softening point temperature of the refractory bricks constituting the bottom portion 126, and the heat retention of the bottom portion 126 is suppressed in the melting tank 101. A structure is provided. For this reason, the heat obscuration of the bottom 126 is suppressed, and the melting tank is not damaged.
In the present embodiment, before making the molten glass, a simulation calculation for making the molten glass is performed using the reference melting tank model to predict and calculate the temperature distribution of the bottom 126, and the maximum temperature of the temperature distribution is the load softening point temperature. The heat retention suppressing structure of the bottom 126 is set so as to be less than the value. For this reason, since the temperature of the refractory brick at the bottom 126 can be predicted by numerical calculation instead of the trial and error experiment using the melting tank, the heat retention at the bottom 126 is suppressed, and the heat retention is suppressed without causing melting of the melting tank. The structure can be found efficiently.
In the present embodiment, the setting of the heat retention suppressing structure of the bottom portion 126 includes, in at least one layer of the refractory bricks of the bottom portion 126, partially changing the thermal conductivity of the refractory bricks of the laying portion 124 with respect to the surroundings. By simply changing the type of refractory bricks, heat conduction can be increased and heat traps can be easily suppressed.
In addition, the setting of the heat retention suppressing structure of the bottom portion 126 includes providing a hole extending in the bottom surface of the laying portion 126 in the refractory brick of the laying portion 124 in at least one layer of the refractory brick of the laying portion 124, so that heat dissipation is easily increased. It is possible to suppress heat accumulation.
Moreover, the setting of the heat retention suppression structure of the bottom 126 is to set the position of any one of a drain port provided at the bottom of the melting tank 101, a temperature sensor installation opening, and a bubble forming gas introduction port. Therefore, it is possible to increase heat dissipation and easily suppress heat turbulence.
Note that the molten glass contains tin oxide, and even when the temperature at 10 ^2.5 poise is 1580 ° C. or higher, the temperature of the bottom 126 can be set by setting the heat retention suppressing structure of this embodiment. Since it can be made to be lower than the load softening point temperature of the refractory brick constituting the bottom portion 126, compared with the case where the heat retention suppressing structure of the present embodiment is not adopted, the suppression of the heat weight and the melting of the melting tank are performed. The effect of suppressing is increased.

  As mentioned above, although the manufacturing method of the glass plate of this invention, the design method of the melting tank, and the melting tank were demonstrated in detail, this invention is not limited to the said embodiment, In the range which does not deviate from the main point of this invention, it is various improvement. Of course, you may make changes.

DESCRIPTION OF SYMBOLS 100 Melting apparatus 101 Melting tank 101a Glass raw material 101b Downstream side wall 101c Heterogeneous base 101d Bucket 101f Raw material inlet 102 Clarification tank 103 Stirring tank 103a Stirrer 104,105,106 Glass supply pipe 104a Outlet 110 Melting tank main body 112 Burner 114 Electrode pair 116 Gas phase space partition wall 118 Strain section 120 Control unit 122 Computer 124 Laying section 126 Bottom section 200 Molding apparatus 210 Molded body 300 Cutting apparatus 101M Melting tank model 110M Melting tank body model 124M Laying section model 126M Bottom section model 126bM Drain port model 126cM Hole model

Claims (8)

In a melting tank, a method for producing a glass plate comprising a step of producing a molten glass having an electrical resistivity at 1550 ° C. of 160 Ω · cm or more by electric heating,
The bottom of the melting tank is provided with a heat retention suppressing structure so that the temperature of the bottom including the laying part of the melting tank is lower than the load softening point temperature of the refractory bricks constituting the bottom. A method for manufacturing a glass plate.   Perform a simulation calculation to make a molten glass using a melting tank model as a reference to predict and calculate the temperature distribution of the bottom, and keep the temperature of the bottom so that the maximum temperature of the temperature distribution is less than the load softening point temperature. The manufacturing method of the glass plate of Claim 1 with which a suppression structure is set. The laying part is a laminated structure of a plurality of refractory bricks,
3. The glass plate according to claim 1, wherein the setting of the heat retention suppressing structure includes partially changing the thermal conductivity of the refractory brick of the laying part with respect to the surroundings in at least one layer of the refractory brick. Manufacturing method. The laying part is a laminated structure of a plurality of refractory bricks,
The setting of the said heat retention suppression structure includes providing the hole extended in the bottom face of the said laying part in the refractory brick of the said laying part in at least one layer of the said refractory bricks. Manufacturing method of glass plate.   The setting of the heat retention suppressing structure includes setting the position of any one of a drain port provided at the bottom of the melting tank, an opening for installing a temperature sensor, and a bubble forming gas inlet. The manufacturing method of the glass plate of any one of Claims 1-4. The molten glass contains tin oxide, temperature at 10 ^2.5 poise is 1580 ° C. or more, a manufacturing method of a glass plate according to any one of claims 1 to 5. A method for designing a melting tank in which a molten glass having an electrical resistivity at 1550 ° C. of 160 Ω · cm or more is produced by electric heating,
The temperature distribution of the bottom including the laying part of the melting tank is calculated by performing a simulation calculation of the heat conduction of the melting tank and the molten glass using a standard melting tank model, and the maximum temperature of the temperature distribution is the load softening point temperature. The method for designing a melting tank is characterized by setting a heat retention suppressing structure at the bottom of the melting tank by correcting the bottom of the melting tank model so as to be less than the value. A melting tank for making molten glass,
A melting tank main body for storing molten glass having an electrical resistivity at 1550 ° C. of 160 Ω · cm or more;
An electrode pair for electrically heating the molten glass;
A melting tank comprising: a bottom temperature keeping structure for lowering a temperature of a bottom portion including a laying portion of the melting tank to be lower than a load softening point temperature of a refractory brick constituting the bottom portion.

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