JP6115466B2 - Method for producing float glass sheet - Google Patents

Description

  The present invention relates to a method for producing plate glass by a float process.

The production of plate glass by the float process is generally performed by the method described below. After the glass raw material is heated and melted to obtain a molten glass, the molten glass is continuously supplied onto the surface of a molten metal such as molten tin accommodated in a float bath.
The glass ribbon is formed while transporting the molten glass along the surface of the molten metal from the upstream side to the downstream side, and the glass ribbon is drawn out from the float bath, slowly cooled, washed, and then cut to the desired size. Plate glass can be obtained.
This plate glass manufacturing method by float forming has high productivity, and the obtained plate glass is excellent in flatness. Therefore, plate glass by float forming is widely applied as plate glass for construction, plate glass for automobiles, plate glass for FPD (flat panel display) and the like.

The float bath is configured in a bathtub shape by laying a plurality of bottom bricks inside a metal bottom casing, and molten metal is stored in the bathtub. The upper space of the molten metal is surrounded by a roof structure made of a metal roof casing and a refractory brick installed on the inside thereof. The upper space of the molten metal is adjusted to an inert gas atmosphere containing hydrogen so as not to oxidize the molten metal.
A molten glass is supplied to the surface of the molten metal, and a glass ribbon having a desired thickness and width is formed by pulling both sides of the molten glass with a top roll while flowing from the upstream side to the downstream side of the float bath. This glass ribbon can be pulled out from the surface of the molten metal with a layer roll installed in a slow cooling furnace installed downstream of the float bath.

When the float bath has a double structure of the bottom casing and the bottom brick as described above, the molten metal intrudes into the joint portion of the bottom brick, and when the bottom casing is reached, the molten metal may be deformed or damaged. There is.
For this reason, conventionally, a configuration has been adopted in which cooling air is blown to the bottom outer surface of the bottom casing to cool the bottom casing and solidify the molten metal that has reached the vicinity of the bottom casing. Conventionally, as a device for cooling the bottom casing, a branch pipe provided with a plurality of jets on the bottom side of the bottom casing and a temperature sensor are provided, and the outer surface of the bottom casing is uniformly cooled while being measured by the temperature sensor. Patent Document 1 discloses a technique for controlling the outer surface temperature of the bottom casing to 4 ° C. or lower.
Moreover, the structure which installs a water cooling pipe | tube via the heat-transfer material on the outer surface of a bottom casing and cools a bottom casing is described in patent document 2, and it cools so that it may correspond to the joint part between refractory bricks in a bottom casing Patent Document 3 discloses a float bath in which a large number of air outlets are arranged.

International Publication No. 2012/060197 International Publication No. 2013/024649 JP 2012-036082 A

  In the float bath configured as described above, the bottom brick installed inside the bottom casing expands by receiving the heat of the molten metal, so if the bottom brick is installed at room temperature during the construction of the float bath, the thermal expansion is expected. The bottom brick is installed with a gap of about several mm between the bottom bricks. Therefore, when the molten metal is stored in the float bath, there are joint portions having a minute width between the plurality of bottom bricks, and the molten metal enters each joint portion. Since the bottom casing of the float bath is air-cooled from the outside, the temperature of the molten metal that has entered the joint portion decreases as it approaches the bottom casing, and the molten metal present in the portion near the bottom casing in the joint portion is It is solidified.

  When forming molten glass in a float bath, there is a phenomenon in which bubbles are generated from the bottom brick joint, this bubble comes into contact with the molten glass, entrains bubbles on the bottom side surface of the glass ribbon, and causes a problem of surface defects is there. This surface defect can be called BOS (bottom open seed).

  In particular, in recent years, when glass that is molded at a higher temperature than general soda-lime glass, such as non-alkali glass, is manufactured by the float process, BOS tends to be generated in the float bath, which improves the glass quality. It is a problem.

  The present invention has been made to solve the above-described problems, and is capable of producing a float plate glass capable of producing a high-quality plate glass having no defects without causing a defect involving bubbles in a float bath for forming molten glass. The purpose is to provide a method.

(1) In the method for producing a float glass sheet according to the present invention, molten metal is stored in a float bath in which a plurality of bottom bricks are arranged in a metal bottom casing, and the molten glass is supplied onto the molten metal to form a glass ribbon. A method for producing a float sheet glass comprising a forming step,
The molten metal is put into the float bath, the molten metal is stored in the float bath in a state where the molten metal has entered the joints between the bottom bricks, the bottom casing is cooled, and the bottom outer surface temperature of the bottom casing Is maintained at a management temperature below the melting point of tin, when the molten glass is supplied onto the molten metal to form the glass ribbon,
After maintaining the bottom outer surface temperature of the bottom casing in a high temperature range higher than the control temperature by 15 ° C or more and 200 ° C or less, the bottom outer surface temperature of the bottom casing is lowered to the specific control temperature. The manufacturing method of the float glass plate provided with the process of shape | molding the said glass ribbon later.

(2) In the method for producing a float glass sheet according to the present invention, the molten metal is tin, and the bottom outer surface of the bottom casing is cooled to a temperature lower than the melting point of tin to solidify the molten tin on the joint portion bottom side. At the same time, it is preferable to reduce bubbles generated in the molten tin in the joint by controlling the temperature in the high temperature range.
(3) In the method for producing a float glass sheet according to the present invention, the float bath is covered with a roof structure to partition the upper space of the molten metal, and the upper space is filled with an inert gas containing hydrogen to generate bubbles. It is preferable to suppress.
(4) In the method for producing a float glass sheet according to the present invention, a blower pipe provided with a cooling gas jet is disposed on the bottom outer surface side of the bottom casing, and the bottom outer face of the bottom casing is passed from the blower through the blower pipe. When the cooling gas is sent to cool the bottom outer surface of the bottom casing, it is preferable to keep the temperature of the bottom casing bottom outer surface in a high temperature range by reducing the amount of air sent out from the blower.
(5) In the method for producing a float glass sheet according to the present invention, the flow of the circulating flow generated in the molten metal is changed by increasing the speed at which the glass ribbon is drawn out from the molten metal. A process for forcibly flowing the molten metal that has entered the joint between the bottom bricks is provided.

(6) In the method for producing a float glass sheet according to the present invention, the glass ribbon is generated in the molten metal by changing the plate thickness when the glass ribbon is pulled out from the molten metal to increase the drawing speed of the glass ribbon. The step of forcibly flowing the molten metal that has entered the joints between the spread bottom bricks by changing the flow of the circulating flow can be provided.
(7) In the method for producing a float glass sheet according to the present invention, the glass ribbon is generated in the molten metal by changing a plate width when the glass ribbon is pulled out from the molten metal to increase a drawing speed of the glass ribbon. The step of forcibly flowing the molten metal that has entered the joints between the spread bottom bricks by changing the flow of the circulating flow can be provided.
(8) In the method for producing a float glass sheet according to the present invention, it is preferable that vibration is applied to the bottom outer surface of the bottom casing.

(9) In the method for producing a float plate glass according to the present invention, an alkali-free glass having the following composition in terms of oxide-based mass percentage can be used as the molten glass.
_{SiO 2: 50~73%, Al 2} O 3: 10.5~24%, B 2 O 3: 0~12%, MgO: 0~10%, CaO: 0~14.5%, SrO: 0~ 24%, BaO: 0~13.5%, MgO + CaO + SrO + BaO: 8~29.5%, ZrO 2: 0~5%.
(10) In the method for producing a float glass sheet according to the present invention, it is preferable to use, as the molten glass, an alkali-free glass having the following composition in terms of oxide-based mass percentage.
_{SiO 2: 58~66%, Al 2} O 3: 15~22%, B 2 O 3: 5~12%, MgO: 0~8%, CaO: 0~9%, SrO: 3~12.5% BaO: 0-2%, MgO + CaO + SrO + BaO: 9-18%.
(11) In the method for producing a float glass sheet according to the present invention, it is preferable to use, as the molten glass, an alkali-free glass having the following composition in terms of oxide-based mass percentage.
_{SiO 2: 54~73%, Al 2} O 3: 10.5~22.5%, B 2 O 3: 0~5.5%, MgO: 0~10%, CaO: 0~9%, SrO: 0 to 16%, BaO: 0 to 2.5%, MgO + CaO + SrO + BaO: 8 to 26%.

In the float bath, the temperature of the bottom outer surface of the bottom casing is maintained at a high temperature range of 15 ° C. or higher and 200 ° C. or lower than the specific control temperature of the bottom outer surface of the bottom casing when molding molten glass. Then, the glass ribbon is formed after the temperature is lowered to a specific control temperature at the time of forming the glass ribbon. In this way, by holding the bottom outer surface of the bottom casing at a temperature higher than the control temperature at one end, it is possible to vent the molten metal that has entered the joints of the bottom brick. By forming the glass ribbon with the bottom outer surface of the bottom casing as a specific management temperature after degassing, it is possible to form a glass ribbon free from bubbles and free from defects due to bubbles.
In the float bath, air bubbles may be generated at the joints. By holding the bottom outer surface of the bottom casing at one end in a high temperature region, it is possible to degas from the molten tin at the joint. By forming the glass ribbon after degassing, it is possible to form a glass ribbon that is free of bubbles and has no defects caused by bubbles.

Sectional drawing which shows an example of the float plate glass manufacturing apparatus used in order to implement the manufacturing method which concerns on this invention. The top view which shows the state of the molten glass which flows on the molten metal of the float bath.

Hereinafter, although the manufacturing method of the float plate glass which concerns on this invention is demonstrated with reference to an accompanying drawing, this invention is not restrict | limited to embodiment described below.
As shown in FIG. 1, a float plate glass manufacturing apparatus 1 for carrying out the manufacturing method of the present embodiment includes molten tin (molten) contained in a float bath apparatus 2 with molten glass G supplied to the float bath apparatus 2. 3) an apparatus for forming a strip-like glass ribbon 5 by flowing along the surface of the metal 3 and spreading from both sides by the top roll 4 shown in FIG. 3 and flowing from the upstream side to the downstream side of the float bath apparatus 2. is there.

As shown in FIG. 1, the float bath apparatus 2 includes a float bath 2A and a roof structure 2B provided above the float bath 2A. A molten glass melting furnace is provided on the upstream side of the float bath apparatus 2, and the molten glass G is supplied from the melting furnace to the float bath 2A. The glass ribbon 5 formed in the float bath 2A is as shown in FIG. Are conveyed to a slow cooling furnace 8 through a chamber 7 provided on the downstream side of the float bath 2A. The glass ribbon 5 is pulled up from the surface of the molten metal 3 by a lift-out roll 9 provided in the chamber 7, transported to the slow cooling furnace 8 by a transport roll 10 provided in the slow cooling furnace 8, and gradually cooled.
As shown in FIG. 2, the molten glass G supplied to the float bath 2 </ b> A is adjusted to a necessary width and thickness by applying tension by the top rolls 4 that are obliquely arranged on both the left and right sides of the molten glass G. .

FIG. 1 is a longitudinal sectional view in which the float bath apparatus 2, the chamber 7, and the slow cooling furnace 8 are sectioned along the direction in which the glass ribbon 5 moves (the length direction of the glass ribbon 5).
As shown in FIG. 1, the glass ribbon 5 that has been transferred from the float bath 2 </ b> A to the slow cooling furnace 8 and cooled is washed in the next step, and then cut into a predetermined size by a cutting device to obtain a glass plate of a desired size. Is obtained.

In the float bath 2A of the present embodiment, the lip 13 provided at the terminal end of the supply passage 12 is the molten glass G sent from the melting furnace (not shown) through the supply passage 12 to the inlet portion 2a at the upstream end. It comes to be supplied through. A tween 14 for adjusting the flow of the molten glass G is installed in the supply passage 12 upstream of the lip 13. The supply passage 12 and the float bath 2A are each constructed by assembling a plurality of heat-resistant materials such as refractory bricks, but are simply illustrated in FIG.
In the float bath apparatus 2, the upper space of the flute bath 2A is surrounded by the roof structure 2B, the upper space of the molten metal 3 is blocked from the external atmosphere as much as possible, and the inside is a nitrogen gas atmosphere containing about 12% or less of hydrogen. Maintained in a reducing atmosphere.

A front wall 15 is formed on the upstream end side of the float bath 2A, an inlet 2a is formed on the bottom side of the front wall 15, and a rear end wall 17 is formed on the downstream end side of the float bath 2A. An outlet 2c of the glass ribbon 5 is formed below the wall 17 at a position near the liquid level of the molten metal 3.
The float bath 2 </ b> A includes a front wall 15, a rear end wall 17, and a float bath roof 16 to constitute a roof structure 2 </ b> B. Further, in the roof structure 2B, a ceiling portion (not shown) is suspended and supported on the inside thereof, and a plurality of heaters are installed on the ceiling portion so that the temperature in the float bath 2A can be adjusted. . In addition, the gas which comprises the reducing atmosphere inside the float bath apparatus 2 flows out a little to the chamber 7 side from the exit part 2c from which the glass ribbon 5 is pulled out.

The chamber 7 provided on the downstream side of the float bath 2A includes a dross box 7A, a ceiling portion 7B, and a side wall (not shown). In this embodiment, three lift-out rolls 9 are provided inside the dross box 7A. Yes. The dross box 7A constitutes the bottom side of the chamber 7 so as to connect the float bath 2A and the slow cooling furnace 8.
In the dross box 7A, on the lower side of the lift-out roll 9, a wall-like pedestal 22 having a graphite seal block 21 at the upper portion is arranged to block the air flow between the float bath 2A and the slow cooling furnace 8. Has been.

The ceiling 7 </ b> B of the chamber 7 includes a hood 24 installed between the float bath 2 </ b> A and the slow cooling furnace 8, and a drape 25 suspended from the lower surface of the hood 24. The drape 25 is a plate-shaped partition member, and partitions the internal space of the chamber 7 into a plurality of space portions along the conveyance direction of the glass ribbon 5.
The slow cooling furnace 8 is configured as a passage type, and a plurality of transport rolls 10 are horizontally installed therein, and the glass ribbon 5 that has moved through the chamber 7 is slowly cooled while being transported by the plurality of transport rolls 10. Can do.

Next, the structure of the float bath 2A will be described in more detail.
The float bath 2 </ b> A of the present embodiment is formed by arranging a plurality of bottom bricks 31 in a shallow container-type metal bottom casing 30. The constituent material of the bottom brick 31 is preferably a material having low reactivity with respect to tin of the molten metal 3, or a material having no reactivity, and a material having high temperature and humidity resistance, such as alumina, sillimanite (silicite). In addition, materials such as clay can be used. The constituent material of the bottom casing 30 is not particularly limited, but is made of a metal material such as iron or stainless steel.

  Among the bottom bricks 31, the bottom bricks arranged at the outer peripheral edge of the bottom casing 30 are tall, and a plurality of short bottom bricks 31 are placed inside the tall bottom bricks with a slight gap between them ( It is installed via a joint part 32. A plurality of bottom bricks 31 are laid down, but even if the bottom brick 31 expands due to the heat of the molten metal 3, joint portions 32 having a distance of about several millimeters are formed between the adjacent bottom bricks 31, 31. Is formed.

A cooling device 33 for cooling the bottom casing 30 is provided below the bottom casing 30. The cooling device 33 includes a blower pipe 35 provided below the bottom casing 30, a blower 36 for sending air to the blower pipe 35, a plurality of temperature sensors 37 installed on the bottom outer surface of the bottom casing 30, and these temperatures. It is comprised from the control apparatus 38 which receives the temperature measurement result of the sensor 37, and controls the output of the air blower 36.
The blower pipe 35 includes a main pipe 35A extending along the length direction of the float bath 2A, and a plurality of branch pipes that branch out in a branch shape upward at a predetermined interval in the length direction of the main pipe 35A. 35B, and the jet outlets 35c formed at the tip of each branch pipe 35B are dispersedly arranged so as to face the bottom outer surface of the bottom casing 30. The blower pipe 35 serves as a passage for cooling air sent from the blower 36, and cooling air is blown from the respective outlets 35 c to the bottom outer surface side of the bottom casing 30.

The temperature sensors 37 are devices that measure the bottom outer surface temperature of the bottom casing 30, and a plurality of the temperature sensors 37 are attached to the bottom outer surface of the bottom casing 30 at a predetermined interval.
The cooling device 33 measures the temperature of the bottom outer surface of the bottom casing 30 by a plurality of temperature sensors 37, adjusts the output of the blower 36 by the control device 38 based on the temperature measurement result, and the temperature of the bottom outer surface of the bottom casing 30. It has a function to control as uniform as possible.

In order to form the glass ribbon 5 according to the float method using the float glass manufacturing apparatus 1 having the above-described configuration, after the float bath apparatus 2 is constructed, the molten metal 3 is stored in the float bath 2A. Further, the blower 36 is operated to send air from the outlet 35c of each branch pipe 35B to the outer bottom surface side of the bottom casing 30 to cool the outer bottom surface of the bottom casing 30.
When constructing the float bath apparatus 2, a plurality of bottom bricks 31 are installed on the bottom casing 30 at predetermined intervals, so that even if the bottom bricks 31 are expanded by receiving the heat of the molten metal 3, they are arranged side by side. A joint portion 32 of about several mm is formed between the plurality of bottom bricks 31. For this reason, in a state where the molten metal 3 is stored in the float bath 2 </ b> A, a part of the molten metal 3 enters the joint portion 32.

Here, when the molten glass G is caused to flow from the inlet portion 2 a to the surface of the molten metal 3 and the forming of the molten glass G is started, cooling air is blown from the ejection port 35 c using the cooling capacity of the cooling device 33. The manufacturing condition of the glass ribbon 5 is to form the molten glass G while maintaining the temperature of the bottom outer surface side of the bottom casing 30 at a predetermined control temperature not higher than the melting point of tin.
On the other hand, in the present embodiment, the temperature of the bottom outer surface of the bottom casing 30 is a high temperature region that is 15 ° C. or more higher than the specific management temperature, and the temperature of the bottom outer surface of the bottom casing 30 is 200 ° C. or less. Keep in the area. As an example of the high temperature region, it is more preferable to select a temperature region that is higher by, for example, 40 ° C. than the specific management temperature.
Although the time to hold | maintain is not specifically limited, The range of several hours-several hundred hours can be selected. In order to maintain the temperature in the above-described high temperature region, the blowing force from the jet outlet 35c that cools the bottom outer surface of the bottom casing 30 may be reduced by a predetermined rate.

As an example, when the management temperature of the bottom outer surface of the bottom casing 30 when forming the glass ribbon 5 is 85 ° C., a temperature that is 15-60 ° C. higher than this temperature, for example, a range of 100-145 ° C. is selected. Thus, it is preferable to keep this temperature range. Similarly, when the control temperature of the bottom outer surface of the bottom casing 30 is 100 ° C., a temperature that is 15 to 60 ° C. higher than this temperature, for example, a range of 115 to 160 ° C. is selected and held in this temperature range. It is preferable. Similarly, when the management temperature of the bottom outer surface of the bottom casing 30 is 70 ° C., a temperature higher by 15 to 60 ° C. than this temperature, for example, a range of 85 to 130 ° C. is selected and held in this temperature range. It is preferable.
In addition, the high temperature range which is 40 degreeC or more higher than the said management temperature is an illustration as a preferable high temperature range, and when the management temperature is 85 degreeC, you may select between 100-200 degreeC, and when the management temperature is 100 degreeC May select between 115-200 degreeC, and when the management temperature is 70 degreeC, you may select between 85-200 degreeC. The management temperature can be set to any temperature below the melting point of tin.

By maintaining the temperature of the outer surface of the bottom part of the bottom casing in the above-described high temperature range, bubbles are generated from the joint part, the bubbles B rise, float on the liquid surface of the molten metal 3, and break the foam. 32 can remove bubbles.
If air bubbles are sufficiently promoted by maintaining the temperature in the high temperature range for a necessary time, the external surface temperature of the bottom casing 30 is returned to the temperature control below the melting point of tin. In order to return the temperature, the blower output of the blower 36 that cools the outer bottom surface of the bottom casing 30 may be increased to increase the amount of air blown from the jet outlet 35c.

After defoaming as described above, the glass ribbon 5 is formed using the float glass manufacturing apparatus 1 while flowing the molten glass G from the upstream end inlet portion 2a to the downstream end outlet portion 2c side of the float bath 2A. To do. Then, the glass ribbon 5 is pulled up from the molten metal 3 by the lift-out roll 9 and conveyed to the chamber 7 side, and subsequently cooled to the slow cooling furnace 8 side by the conveyance roll 10 to obtain the glass ribbon 5.
Moreover, the glass plate of the target width | variety and length can be obtained by cut | disconnecting with the washing | cleaning apparatus and cutting device which are provided in the downstream of the slow cooling furnace 8.

As the glass applied to the molding of the glass ribbon 5 described above, alkali-free glass shown in the following composition examples can be applied.
As a first example, an alkali-free glass having the following composition in terms of oxide-based mass percentage can be used.
_{SiO 2: 50~73%, Al 2} O 3: 10.5~24%, B 2 O 3: 0~12%, MgO: 0~10%, CaO: 0~14.5%, SrO: 0~ 24%, BaO: 0~13.5%, MgO + CaO + SrO + BaO: 8~29.5%, ZrO 2: 0~5%.

As a second example, an alkali-free glass having the following composition in terms of oxide-based mass percentage can be used.
_{SiO 2: 58~66%, Al 2} O 3: 15~22%, B 2 O 3: 5~12%, MgO: 0~8%, CaO: 0~9%, SrO: 3~12.5% BaO: 0-2%, MgO + CaO + SrO + BaO: 9-18%.

As a third example, an alkali-free glass having the following composition in terms of oxide-based mass percentage can be used.
_{SiO 2: 54~73%, Al 2} O 3: 10.5~22.5%, B 2 O 3: 0~5.5%, MgO: 0~10%, CaO: 0~9%, SrO: 0 to 16%, BaO: 0 to 2.5%, MgO + CaO + SrO + BaO: 8 to 26%.
Examples of the plate glass produced by the float process using these alkali-free glasses include plate glass having a thickness of 0.7 mm to 0.1 mm, a vertical width of 2500 mm, a horizontal width of 2200 mm, and the like.

  Since the molding temperature of the alkali-free glass having the above composition is higher than that of a conventional general soda lime glass, the above-described foam removal operation at the joint is important. If the foaming of the joint portion 32 of the float bath 2A is sufficiently performed, even a plate glass made of alkali-free glass having the above-described composition can produce a high-quality plate glass having no bubble defect.

By the way, when the glass ribbon 5 is formed by the manufacturing method, the thickness of the glass ribbon 5 when the glass ribbon 5 is pulled out from the molten metal 3 is made thinner than the thickness of the glass ribbon that has been manufactured so far. A step of increasing the speed when pulling out the ribbon 5 may be provided.
When the speed at which the glass ribbon 5 is drawn out from the molten metal 3 is increased, the state of the circulating flow indicated by arrows a, b and c in FIG. 3 generated in the molten metal 3 is changed, and the joint portion of the float bath 2A is changed. It is possible to force the molten metal 3 that has entered 32 to flow. By this operation, the foam of the joint portion 32 can be removed.

Moreover, the process of raising the speed | rate which draws out the glass ribbon 5 from the molten metal 3 by making the width | variety at the time of pulling out the glass ribbon 5 from the molten metal 3 narrower than the width | variety of the glass ribbon 5 manufactured until then. You may prepare.
Furthermore, when defoaming the joint portion 32, a step of applying an impact or vibration to the bottom portion of the bottom casing 30 may be provided.
By performing the step of applying an impact or vibration to the bottom of the bottom casing 30, the generation of bubbles in the joint portion 32 can be promoted, and the foam removal of the joint portion 32 can be promoted by this operation.

The float glass manufacturing apparatus having the configuration shown in FIGS. 1 and 2 is used to form a float having a width of several meters and a length of several tens of meters. In the bath, molten tin was stored as molten metal. A molten glass having the following composition was supplied onto the molten tin to form a glass ribbon. The atmosphere on the molten tin in the float bath was a nitrogen gas atmosphere containing 8% hydrogen.
The composition of the molten glass used was SiO ₂ : 55%, Al ₂ O ₃ : 13%, B ₂ O ₃ : 4%, MgO: 4%, CaO: 6%, SrO: 10%, BaO: 6%, ZrO ₂ : 2%.

Before supplying the molten metal to the float bath and supplying the molten glass, after adjusting the air flow rate of the blower to control the bottom outer surface temperature of the bottom casing of the float bath to a temperature described later, the molten glass having the composition Was supplied onto the molten tin to form a glass ribbon.
Note that the temperature of the molten tin is maintained by adjusting the heater output, and in this state, molten glass is poured to form a glass ribbon.

After throwing tin into the float bath, the maximum temperature-minimum temperature difference of the bottom casing for one month and the subsequent number of bubbles generated (number of BOS / m ² ) were measured. In addition, since the temperature in a float bath changes with the flow directions of molten tin, and also differs in a composition, the management temperature of a bottom casing was shown by the maximum temperature-minimum temperature difference.
The case No. 1 in Table 1 shown below is a high temperature range higher than the management temperature, the case adjusted to a temperature difference of 21 ° C., and the case No. 2 is a high temperature range higher than the management temperature. The case adjusted to a temperature difference of 55 ° C., the case of No. 3 is a high temperature region higher than the management temperature, and the case adjusted to a temperature difference of 16 ° C., the case of No. 4 is higher than the management temperature. This is a case where the temperature is adjusted to a high temperature range of 47 ° C. In each case, after the molten glass was put into the float bath, the number of bubbles generated (BOS number / m ² ) after 20 days and the number of bubbles generated after 40 days were measured.
In either case, after controlling the temperature around the maximum temperature for about 10 days, gradually decrease the temperature toward the target management temperature over about 5 days, and maintain the management temperature corresponding to the above temperature difference. Was measured.
The number of bubbles generated (the number of BOS / m ² ) was measured by observing the surface of the obtained glass with a lens.

From the results shown in Table 1, it can be seen that the number of bubbles generated decreases as the number of days elapses by adding the temperature difference in the range of 16 to 55 ° C.
In addition, since the temperature increase allowance for the cases No. 2 and 4 is larger than the temperature increase allowance for the cases No. 1 and 3, the larger the temperature increase allowance is, the faster the BOS decay rate. I know that there is.

From the results of Table 1, it can be seen that when the bottom outer surface temperature of the bottom casing is maintained at a temperature higher than the bottom outer surface temperature of the bottom casing at the time of glass ribbon production, the effect can be obtained if the temperature is 15 ° C. or higher. This effect was confirmed up to an example of 55 ° C.
From these comparisons, a higher temperature difference seems to be effective in reducing the number of bubbles generated. For this reason, it seems that 20 degreeC or more is more preferable. Of course, it is possible to raise the temperature exceeding 55 ° C., and there is no problem from the structure of the bottom casing until the temperature of the bottom casing is about 200 ° C. Therefore, the temperature of the bottom outer surface of the bottom casing is raised to 200 ° C. Things are also possible. However, if the temperature exceeds 200 ° C., it approaches the melting point of molten tin, and therefore 200 ° C. is preferably set as the upper limit of temperature control.

  DESCRIPTION OF SYMBOLS 2 ... Float bath apparatus, 2A ... Float bath, 2a ... Inlet part, 2c ... Outlet part, 3 ... Molten metal, 3a ... Solid part, B ... Foam, G ... Molten glass, 4 ... Top roll, 5 ... Glass ribbon, 6 ... chamber, 6A ... dross box, 7 ... chamber, 8 ... slow cooling furnace, 9 ... lift-out roll, 10 ... transport roll, 30 ... bottom casing, 31 ... bottom brick, 32 ... joint, 33 ... cooling device, 35 ... Blow pipe, 35A ... main pipe, 35B ... branch pipe, 35c ... jet outlet, 36 ... blower, 37 ... temperature sensor, 38 ... control device.

Claims (11)

A float plate glass manufacturing method comprising a step of storing molten metal in a float bath in which a plurality of bottom bricks are arranged in a metal bottom casing, and supplying molten glass onto the molten metal to form a glass ribbon. ,
The molten metal is put into the float bath, the molten metal is stored in the float bath in a state where the molten metal has entered the joints between the bottom bricks, the bottom casing is cooled, and the bottom outer surface temperature of the bottom casing Is maintained at a management temperature below the melting point of tin, when the molten glass is supplied onto the molten metal to form the glass ribbon,
After the bottom outer surface temperature of the bottom casing is maintained in a high temperature region that is 15 ° C. or more higher than the management temperature and is 200 ° C. or less, the bottom outer surface temperature of the bottom casing is lowered to the specific management temperature. The manufacturing method of the float glass plate provided with the process of shape | molding the said glass ribbon later.   The molten metal is tin, the bottom casing bottom outer surface is cooled to solidify the molten tin on the joint bottom side, and the bubbles generated from the joint are reduced by controlling the temperature in the high temperature range. The method for producing a float glass sheet according to claim 1.   The method for producing a float glass sheet according to claim 2, wherein the float bath is covered with a roof structure to partition the upper space of the molten metal, and the upper space is filled with an inert gas containing hydrogen to suppress generation of bubbles.   A blower pipe having a cooling gas jet port is disposed on the bottom outer surface side of the bottom casing, and a cooling gas is sent from the blower to the bottom outer surface of the bottom casing via the blower pipe so that the bottom outer surface of the bottom casing is The method for producing a float sheet glass according to any one of claims 1 to 3, wherein when cooling, the amount of air sent out from the blower is reduced to keep the temperature of the bottom outer surface of the bottom casing in a high temperature range.   By increasing the speed at which the glass ribbon is drawn out from the molten metal, the flow of the circulating flow generated in the molten metal is changed to force the molten metal that has entered the joints between the bottom bricks laid down. The manufacturing method of the float plate glass as described in any one of Claims 1-4 provided with the process made to flow in.   By changing the plate thickness when drawing the glass ribbon from the molten metal and increasing the drawing speed of the glass ribbon, the flow of the circulating flow generated in the molten metal is changed and the spread bottom The manufacturing method of the float plate glass as described in any one of Claims 1-4 provided with the process of forcedly flowing the molten metal which permeated into the joint part of bricks.   By changing the plate width when pulling out the glass ribbon from the molten metal and increasing the drawing speed of the glass ribbon, the flow of the circulating flow generated in the molten metal is changed and the spread bottom The manufacturing method of the float plate glass as described in any one of Claims 1-4 provided with the process of forcedly flowing the molten metal which permeated into the joint part of bricks.   The manufacturing method of the float glass plate as described in any one of Claims 1-7 which provides a vibration to the bottom part outer surface of the said bottom casing. The manufacturing method of the float plate glass as described in any one of Claims 1-8 which uses the alkali free glass which has the following composition by the mass percentage display of an oxide basis as the said molten glass.
_{SiO 2: 50~73%, Al 2} O 3: 10.5~24%, B 2 O 3: 0~12%, MgO: 0~10%, CaO: 0~14.5%, SrO: 0~ 24%, BaO: 0~13.5%, MgO + CaO + SrO + BaO: 8~29.5%, ZrO 2: 0~5%. The manufacturing method of the float plate glass as described in any one of Claims 1-8 which uses the alkali free glass which has the following composition by the mass percentage display of an oxide basis as the said molten glass.
_{SiO 2: 58~66%, Al 2} O 3: 15~22%, B 2 O 3: 5~12%, MgO: 0~8%, CaO: 0~9%, SrO: 3~12.5% BaO: 0-2%, MgO + CaO + SrO + BaO: 9-18%. The manufacturing method of the float plate glass as described in any one of Claims 1-8 which uses the alkali free glass which has the following composition by the mass percentage display of an oxide basis as the said molten glass.
_{SiO 2: 54~73%, Al 2} O 3: 10.5~22.5%, B 2 O 3: 0~5.5%, MgO: 0~10%, CaO: 0~9%, SrO: 0 to 16%, BaO: 0 to 2.5%, MgO + CaO + SrO + BaO: 8 to 26%.

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