JP7090844B2 - Manufacturing method of glass articles and glass substrate group - Google Patents

Description

The present invention relates to a method for manufacturing a glass article and a group of glass substrates.

A method for manufacturing a glass article such as flat glass includes a melting step of obtaining molten glass. In this melting step, from the viewpoint of effective utilization of resources, it is common to melt a mixed raw material obtained by adding cullet to a glass raw material such as silica or slag in a melting furnace to obtain molten glass (for example, Patent Documents). See 1 and 2). Here, the cullet is a recycled raw material obtained by crushing a glass article (including a defective glass article) produced through a melting step.

Japanese Unexamined Patent Publication No. 2016-037437 International Publication No. 2006/051953

In the above melting step, fine bubbles are generated in the melting furnace as the mixed raw materials including the glass raw material and the cullet are melted. The fine bubbles rise in the molten glass (in the liquid) by buoyancy while the bubble diameter is expanded by heating, and form a bubble layer in the surface layer portion of the molten glass stored in the melting furnace. This foam layer has an effect of preventing heat dissipation from the molten glass (heat insulating effect).

However, when molten glass is obtained using a mixed raw material, the range of the foam layer tends to be unstable. Therefore, there is a problem that the heat insulating effect of the foam layer increases or decreases, and the melting temperature in the melting furnace is not stable. When such a problem occurs, the quality of the finally manufactured glass article (for example, foam grade or pulse grade) is also adversely affected.

An object of the present invention is to stabilize the melting temperature in a melting furnace when melting a glass raw material and a cullet to obtain molten glass, and to obtain a glass article of excellent quality.

The present invention, which was devised to solve the above problems, is a method for manufacturing a glass article including a melting step of melting a glass raw material and a cullet in a melting furnace to obtain molten glass, and the foaming temperature of the cullet supplied to the melting furnace. It is characterized by regulating the fluctuation range of.

As a result of diligent research, the inventor of the present application has found that even in a melting furnace using a cullet whose glass composition, chromaticity, and particle size are controlled at a high level, such as a glass substrate for a display, the melting temperature in the melting furnace is reached. It has been found that fluctuations in the foam layer range that destabilize can occur due to cullet. Specifically, the main cause of fluctuation in the foam layer range is the foaming temperature of the cullet. Here, the foaming temperature is a temperature at which expansion of fine bubbles generated from the cullet is recognized when the cullet is melted. This foaming temperature is greatly affected by the thermal history of the melting process during the production of the glass article before crushing, which is the source of the cullet. That is, the cullet that has undergone the melting steps of the same melting temperature has substantially the same foaming temperature, but the cullet that has undergone the melting steps of different melting temperatures has different foaming temperatures. Therefore, if the foaming temperature of the cullet is not controlled at all, there is a high possibility that the foaming temperature of the cullet will fluctuate each time the cullet is supplied to the melting furnace in the melting process. When the fluctuation of the foaming temperature becomes large, the foam layer may or may not be formed at a predetermined temperature, and the foam layer range tends to fluctuate. Therefore, in the present invention, as in the above configuration, the fluctuation range of the foaming temperature of the cullet supplied to the melting furnace is regulated. By doing so, the temperature range in which the foam layer is generated can be controlled, so that the foam layer range can be stabilized. Therefore, it is possible to suppress fluctuations in the heat insulating effect due to the foam layer and stabilize the melting temperature in the melting furnace.

In the above configuration, the foaming temperature of the cullet is preferably within the range of ± 20 ° C. of a predetermined reference value. By doing so, the fluctuation range of the foaming temperature of the cullet becomes small, so that the fluctuation of the foam layer range can be suppressed more reliably.

In the above configuration, the reference value is preferably within the range of ± 30 ° C. of the melting temperature in the melting furnace. By doing so, the formation range of the foam layer is stabilized at the melting temperature, so that the heat insulating effect of the foam layer can be enhanced. As a result, since the amount of energy input required for temperature adjustment is stable, it can be expected that the glass raw material and the cullet can be melted with energy saving.

In the above configuration, the reference value is preferably a temperature at which the viscosity of the molten glass is 150 dPa · s or less, and more preferably 180 dPa · s or less. By doing so, the reference value is often about the same as the temperature of the clarification chamber or lower than the melting temperature, and clarification can be effectively performed.

In the above configuration, it is preferable that the cullet contains a first cullet having a relatively low first foaming temperature and a second cullet having a relatively high second foaming temperature. For example, the foaming temperature of a cullet, which is a mixture of two types of cullet, a first cullet and a second cullet, is affected by the foaming temperature of the first cullet and the second cullet, and is between the first foaming temperature and the second foaming temperature. Changes to. Therefore, it becomes easy to control the foaming temperature of the cullet.

In the above configuration, it is preferable to include a measuring step of measuring the foaming temperature of the cullet before supplying the cullet to the melting furnace. By doing so, it is possible to reliably grasp and control the foaming temperature of the cullet supplied to the melting furnace in the melting step.

In the above configuration, it is preferable that the clarification step for clarifying the molten glass in a clarification chamber arranged on the downstream side of the melting furnace is provided, and the foaming temperature is equal to or lower than the clarification temperature in the clarification chamber. By doing so, defoaming of the molten glass can be surely performed.

In the above configuration, in the melting furnace, it is preferable that a portion not covered with the glass raw material and the cullet is formed on a part of the liquid surface of the molten glass. By doing so, the melting temperature in the melting furnace is more easily affected by the foam layer as compared with the case where the entire liquid surface of the molten glass is covered with the glass raw material and the cullet, so that the effect of the present invention is more effective. It will be useful.

The present invention, which was devised to solve the above problems, is a glass substrate group composed of a plurality of glass substrates, and is characterized in that the difference between the maximum value and the minimum value of the foaming temperature is 40 ° C. or less. .. Conventionally, the thermal history of the melting process (melting temperature in the melting furnace and energy supplied to the furnace) becomes unstable due to the variation in the foaming temperature of the cullet, and as a result, the foaming temperature of the glass substrate fluctuates. In some cases, the difference between the maximum value and the minimum value of the foaming temperature exceeded 40 ° C. According to the manufacturing method of the present invention, since the fluctuation range of the foaming temperature of the cullet is regulated, the thermal history of the melting process (melting temperature in the melting furnace and energy supplied to the furnace) can be stabilized. The fluctuation of the foaming temperature of the glass substrate can be 40 ° C. or less. When the fluctuation of the foaming temperature of the glass substrate is 40 ° C. or less, the quality (for example, foam quality or pulse quality) is excellent. In particular, if a cullet is produced from a glass substrate and used, the surface temperature in the furnace can be stabilized and foam defects in the obtained product glass can be reduced.

According to the present invention, it is possible to stabilize the melting temperature in the melting furnace when melting the glass raw material and the cullet to obtain the molten glass, so that it is possible to obtain a glass article having excellent quality.

It is a side view which shows the manufacturing apparatus of a glass article. It is sectional drawing which shows the melting furnace of the manufacturing apparatus of the glass article of FIG. It is a graph which shows the result of the confirmation test of an Example. It is a graph which shows the result of the confirmation test of an Example.

Hereinafter, a method for manufacturing a glass article and an embodiment of a glass substrate group according to the present invention will be described with reference to the drawings.

As shown in FIG. 1, the plate glass manufacturing apparatus used in this manufacturing method includes a melting furnace 1, a clarification chamber 2, a homogenization chamber (stirring chamber) 3, a state adjustment chamber 4, and a molding apparatus in order from the upstream side. 5 and transfer pipes 6 to 9 connecting these parts are provided. Here, the term "chamber" such as the clarification chamber 2 includes those having a tank-like structure and those having a tubular structure.

The melting furnace 1 is a space for performing a melting step of obtaining molten glass Gm. The melting furnace 1 is connected to the clarification chamber 2 on the downstream side by a transfer pipe 6.

The clarification chamber 2 is a space for performing a clarification step of clarifying the molten glass Gm supplied from the melting furnace 1 by the action of a clarifying agent or the like. The clarification chamber 2 is connected to the homogenization chamber 3 on the downstream side by a transfer pipe 7.

The homogenization chamber 3 is a space for performing a homogenization step in which the clarified molten glass Gm is stirred by the stirring blade 3a and homogenized. The homogenization chamber 3 is connected to the state adjustment chamber 4 on the downstream side by a transfer pipe 8.

The state adjusting chamber 4 is a space for performing a state adjusting step of adjusting the molten glass Gm to a state suitable for molding. The state adjusting chamber 4 is connected to the molding device 5 on the downstream side by a transfer pipe 9. The state adjustment chamber 4 may be omitted.

The molding apparatus 5 is for performing a molding step of molding the molten glass Gm into a desired shape. In the present embodiment, the molding apparatus 5 forms the molten glass Gm into a plate shape by the overflow down draw method.

Specifically, in the molding apparatus 5, the cross-sectional shape (cross-sectional shape orthogonal to the paper surface) is substantially wedge-shaped, and an overflow groove (not shown) is formed in the upper portion of the molding apparatus 5. After the molten glass Gm is supplied to the overflow groove by the transfer pipe 9, the molten glass Gm overflows from the overflow groove and flows down along the side wall surfaces (side surfaces located on the front and back sides of the paper surface) on both sides of the molding apparatus 5. Let me. Then, the molten glass Gm that has flowed down is fused at the lower top of the side wall surface to form a plate. The molded plate glass has, for example, a thickness of 0.01 to 10 mm (preferably 0.05 to 3 mm, more preferably 0.1 to 1 mm), and is a flat panel display such as a liquid crystal display or an organic EL display, or organic. It is used for boards such as EL lighting and solar cells and protective covers. The molding apparatus 5 may execute another down-drawing method such as the slot down-drawing method. Further, the molding apparatus 5 may execute the float method.

The transfer tubes 6 to 9 are composed of, for example, a cylindrical tube made of platinum or a platinum alloy, and transfer the molten glass Gm in the lateral direction (substantially horizontal direction). The transfer pipes 6 to 9 are energized and heated as needed.

As shown in FIG. 2, in the present embodiment, the melting furnace 1 is an electric melting furnace that electrically melts a mixed raw material Gr of a glass raw material and a cullet to form a molten glass Gm. In the melting furnace 1, for example, a melting space is partitioned by a wall portion made of heat-resistant brick. A plurality of electrodes 10 are provided on the bottom wall portion and / or the side wall portion of the melting furnace 1 in a state of being immersed in the molten glass Gm. The melting furnace 1 is not provided with any heating means other than the electrode 10, and the mixed raw material Gr is melted (total electric melting) only by energization heating (electric energy) of the electrode 10. In addition, another heating means such as an electric heater may be provided above the liquid level Gm1 of the molten glass Gm. Further, the melting furnace 1 may melt the mixed raw material Gr only by gas combustion, or may melt the mixed raw material Gr by using gas combustion and electric heating in combination.

In the present embodiment, the melting furnace 1 is a single melter having only one melting space for the mixed raw material Gr, but may be a multi-melter in which a plurality of melting spaces are connected.

The melting furnace 1 is provided with a screw feeder 11 as a raw material supply means. The screw feeder 11 sequentially supplies the mixed raw material Gr so that a portion not covered with the mixed raw material (solid raw material) Gr is formed on a part of the liquid level Gm1 of the molten glass Gm. That is, the melting furnace 1 is a so-called semi-hot top type. The melting furnace 1 may be a so-called cold top type in which the entire liquid level Gm1 of the molten glass Gm is covered with the mixed raw material Gr. Further, the raw material supply means may be a vibration feeder or the like.

The melting furnace 1 is provided with a flue 12 as a gas discharge path for discharging the gas in the melting furnace 1 to the outside. A fan 13 for sending gas to the outside is provided in the flue 12. The fan 13 may be omitted. In the present embodiment, the gas in the melting furnace 1 is air, but the gas is not limited to this.

Here, this production method is particularly useful when the glass raw material and cullet (or molten glass Gm) contained in the mixed raw material Gr are non-alkali glass. Further, the mixed raw material Gr preferably contains tin oxide as a clarifying agent. The content of tin oxide is preferably, for example, 0.01% by mass or more. Further, the particle size of the glass raw material and / or the cullet is preferably 0.5 to 50 mm, more preferably 1 to 10 mm. The cullet is crushed to a size of 1 to 10 mm by repeating crushing with a coarse crusher and a medium crusher and classification with a mesh sieving device. A cullet of 0.5 mm or less may be mixed. Further, the classification may be carried out by the method described in International Publication No. 2006/051953. Further, the proportion of cullet in the mixed raw material Gr is, for example, 20% by mass or more.

Reference numeral BL in FIG. 2 is a foam layer generated by melting the mixed raw material Gr. The foam layer BL is formed on the surface layer portion of the molten glass Gm. As long as the range of the foam layer BL does not fluctuate significantly, there may be a region in the surface layer portion of the molten glass Gm where the foam layer BL is not formed.

Next, a method of manufacturing a glass article by the manufacturing apparatus configured as described above will be described.

As described above, this manufacturing method includes a melting step, a clarification step, a homogenization step, a state adjusting step, and a molding step. Since the clarification step, the homogenization step, the state adjustment step, and the molding step are as described in accordance with the above-mentioned configuration of the manufacturing apparatus, the melting step will be described in detail below.

As shown in FIG. 2, in the melting step, the mixed raw material Gr composed of the glass raw material and the cullet is melted in the melting furnace 1 to obtain molten glass Gm. At this time, the fluctuation range of the foaming temperature (also referred to as the reboiling temperature) of the cullet contained in the mixing raw material Gr supplied to the melting furnace 1 is regulated. Specifically, the foaming temperature of the cullet is regulated to be within the range of ± 20 ° C. of a predetermined reference value. The foaming temperature of the cullet is preferably ± 15 ° C., which is a reference value, and more preferably ± 10 ° C., which is a reference value. Here, the foaming temperature means a temperature at which expansion of fine bubbles generated from the cullet is recognized when the cullet is melted. In the present embodiment, the foaming temperature of the cullet is the temperature at which the initial bubble diameter (for example, 70 to 80 μm) of the fine bubbles generated by heating the cullet is expanded to 1.5 times the diameter.

The reference value is preferably within the range of ± 30 ° C. of the melting temperature in the melting furnace 1. By doing so, the formation range of the foam layer BL is stabilized at the melting temperature, so that the heat insulating effect of the foam layer BL can be enhanced. Therefore, it can be expected that the mixed raw material Gr can be melted with energy saving. Here, the melting temperature in the melting furnace 1 is measured at the maximum temperature in the furnace (for example, the bottom temperature in the furnace).

The reference value is preferably a temperature at which the viscosity of the molten glass Gm is 150 dPa · s or less, more preferably 180 dPa · s or less, and a temperature range of 200 dPa · s to 2000 dPa · s. Is even more preferable. By doing so, the reference value is often about the same as the temperature of the clarification chamber or lower than the melting temperature, and clarification can be effectively performed. In the present embodiment, the reference value is, for example, preferably 1615 ° C. or lower, more preferably 1600 ° C. or lower, and further preferably 1400 ° C. or higher and 1580 ° C. or lower.

The foaming temperature of the cullet is preferably equal to or lower than the clarification temperature (heating temperature) in the clarification chamber 2. By doing so, in the clarification chamber 2, bubbles are generated from the cullet, so that the molten glass Gm can be reliably defoamed.

Here, the melting temperature in the melting furnace 1 is preferably, for example, a temperature at which the viscosity of the molten glass Gm is 210 dPa · s or less, and is, for example, 1580 ° C. or less. The clarification temperature in the clarification chamber 2 is preferably in a temperature range in which the viscosity of the molten glass is, for example, 210 to 70 dPa · s, and is, for example, 1580 to 1700 ° C. Since the viscosity of glass decreases with increasing temperature, the clarification temperature is higher than the melting temperature in relation to the above viscosity.

The regulation of the fluctuation range of the foaming temperature of the cullet contained in the mixed raw material Gr is performed as follows, for example.

First, before supplying to the inside of the melting furnace 1, a part of the cullet contained in one lot is extracted, and the foaming temperature of the extracted cullet is measured (measurement step). In this measuring step, for example, a cullet is put into a quartz crucible and electrically heated to a predetermined temperature. In this heating process, the temperature (foaming temperature) when the initial bubble diameter of the minute air bubbles entrained by the melting of the cullet is expanded to 1.5 times the diameter is measured. At this time, the bubble diameter is measured by magnifying observation with a high temperature CCD camera. The remaining cullet contained in the same lot as the extracted cullet has the same foaming temperature as the above-measured foaming temperature because the original glass article (plate glass or glass bottle) has undergone the same melting process. Can be regarded as. Therefore, if the measured foaming temperature is within the range of ± 20 ° C. of the reference value, the remaining cullet contained in the same lot is supplied to the melting furnace 1 as it is. For example, the High Temperature Observation System manufactured by GLASS SERVICE Co., Ltd. can be used to confirm the melting of the cullet and the change in the bubble diameter. The method for measuring the foaming temperature of the cullet is an example, and other methods may be used.

On the other hand, if the temperature is outside the range of ± 20 ° C. of the reference value, the remaining cullet contained in the same lot is not supplied to the melting furnace 1 as it is, and the following processing is performed. That is, in the measurement step, the cullet whose foaming temperature was measured to be lower than the reference value (the first cullet having a relatively low first foaming temperature) and the cullet whose foaming temperature was measured to be higher than the reference value. (A second cullet having a relatively high second foaming temperature) is prepared. At this time, it is preferable that the average particle size and the glass composition of the first cullet and the second cullet are about the same. Then, these first cullet and the second cullet are mixed. When mixed in this way, the foaming temperature of the cullet after mixing is affected by both the first cullet and the second cullet and changes between the first foaming temperature and the second foaming temperature. For example, when the same amount of cullet having a first foaming temperature and a second foaming temperature of 1570 ° C. and 1600 ° C. was mixed, it was confirmed that the foaming temperature of the cullet after mixing was adjusted to 1585 ° C. Therefore, by mixing the first cullet and the second cullet, the foaming temperature can be adjusted within the range of ± 20 ° C. of the reference value. The mixing ratio of the first cullet and the second cullet can be appropriately adjusted in consideration of the temperature difference between each foaming temperature and the reference value. That is, the amount of the first cullet may be larger than the amount of the second cullet, or the amount of the first cullet may be smaller than the amount of the second cullet.

The following may be used to adjust the foaming temperature of the cullet and secure the supply amount of the cullet. That is, cullet of three or more kinds of lots having different foaming temperatures may be mixed. Further, only the cullet having the foaming temperature of the reference value or more may be mixed, or only the cullet having the foaming temperature of the reference value or less may be mixed. Further, two or more different lots of cullet within the range of ± 20 ° C. of the reference value may be mixed.

As described above, if the foaming temperature of the cullet sequentially supplied into the melting furnace 1 is controlled within the range of ± 20 ° C. of the reference value, the variation in the foaming temperature of the cullet can be suppressed. As a result, the temperature range in which the foam layer BL is generated can be controlled, so that the range of the foam layer BL can be stabilized. Therefore, it is possible to suppress fluctuations in the heat insulating effect due to the foam layer BL and stabilize the melting temperature in the melting furnace 1. Therefore, it is possible to manufacture a glass substrate (glass article) having stable quality such as foam quality and pulse quality.

Here, in the glass substrate group composed of the plurality of glass substrates manufactured in this manner, for example, the difference between the maximum value and the minimum value of the foaming temperature is 40 ° C. or less. The difference between the maximum value and the minimum value of the foaming temperature is preferably 30 ° C. or lower, more preferably 20 ° C. or lower. The glass substrate group consists of, for example, 100 to 500 glass substrates laminated on one pallet.

The foaming temperature of the glass substrate group is measured, for example, as follows. First, five glass substrates are collected from the glass substrate group. Next, each of the collected glass substrates is crushed to a predetermined size to obtain cullet. Then, the foaming temperature of each cullet is measured, and the minimum value, the maximum value, and the difference are obtained.

The glass substrate is preferably a glass substrate formed by the overflow method.

The glass substrate is made of SiO ₂ 50 to 70%, Al ₂ O ₃ 12 to 25%, B ₂ O ₃₀ to 12%, Li ₂ O + Na ₂ O + K ₂ O (Li ₂ O, Na ₂ O and K) in terms of mass%. (Mixed amount of _2O ) It is preferable to use non-alkali glass containing 0 to less than 1%, MgO 0 to 8%, CaO 0 to 15%, SrO 0 to 12%, and BaO 0 to 15%.

A confirmation test was conducted to investigate the effect of cullet foaming temperature. The cullet was performed with OA-11, which is a non-alkali glass manufactured by Nippon Electric Glass Co., Ltd. The glass was melted in a melting furnace equipped with an oxygen burner and a molybdenum electrode. The results are shown in FIGS. 3 and 4. FIG. 3 shows how the foaming temperature of the glass article manufactured through the melting process changes when the ceiling temperature inside the melting furnace is changed (when the energy supplied to the melting furnace is changed). FIG. 4 is a graph showing how the ceiling temperature in the furnace changes when the foaming temperature of the cullet used is changed while the energy supplied to the melting furnace is maintained almost constant. It is a graph which shows.

As shown in FIG. 3, as the approximate straight line shown by the dotted line rises to the right, the higher the ceiling temperature (melting temperature) in the furnace in the melting step, the higher the foaming temperature of the glass article. This means that the foaming temperature of the cullet obtained by crushing the glass article also increases in proportion to the melting temperature at the time of manufacturing the original glass article. That is, if the melting temperature at the time of manufacturing the original glass article is low, the foaming temperature of the cullet obtained from the glass article is also low, and if the melting temperature at the time of manufacturing the original glass article is high, the cullet obtained from the glass article is also low. The foaming temperature of the glass also tends to be high. Therefore, the foaming temperature of the cullet obtained from the glass article can be predicted to some extent based on the melting temperature at the time of manufacturing the original glass article.

On the other hand, as shown in FIG. 4, it can be seen that even if the energy supplied to the inside of the furnace is the same, the ceiling temperature inside the furnace (melting temperature) in the melting step greatly changes when the foaming temperature of the cullet used changes. .. In detail, the ceiling temperature in the furnace decreases as the foaming temperature of the cullet increases, so that the approximate straight line shown by the dotted line decreases to the right. It is considered that this is because the foam layer becomes difficult to form as the foaming temperature of the cullet increases, and the heat insulating effect of the foam layer decreases. From such a result, it can be confirmed that the present invention capable of appropriately controlling the foaming temperature of the cullet sequentially supplied into the furnace and stabilizing the foam layer range is useful.

The present invention is not limited to the configuration of the above embodiment, and is not limited to the above-mentioned action and effect. The present invention can be modified in various ways without departing from the gist of the present invention.

In the above embodiment, the case where the measurement step is performed before supplying the cullet to the melting furnace 1 has been described, but the measurement step may be omitted. That is, if the cullet and the melting temperature in the melting process at the time of manufacturing the glass article that is the source of the cullet are linked and recorded in advance, the foaming temperature of the cullet can be roughly grasped without performing the measurement process. be able to. That is, the method of regulating the fluctuation range of the cullet foaming temperature is not limited to the method of directly measuring the cullet foaming temperature, but also includes the method of indirectly grasping the cullet foaming temperature.

In the above embodiment, the case where the glass article molded by the molding apparatus 5 is flat glass has been described, but the present invention is not limited to this. For example, the glass article molded by the molding apparatus 5 may be, for example, an optical glass component, a glass tube, a glass block, a glass fiber, a glass roll, or the like, or may have an arbitrary shape.

1 Melting furnace 2 Clarification chamber 3 Homogenization chamber 3a Stirring blade 4 Condition adjustment chamber 5 Molding equipment 6-9 Transfer pipe 10 Electrode 11 Screw feeder 12 Flue 13 Fan BL Foam layer Gm Molten glass Gr Mixed raw material (glass raw material and cullet)

Claims (10)

In a method for manufacturing a glass article, which comprises a melting step of melting a glass raw material and cullet in a melting furnace to obtain molten glass.
A method for manufacturing a glass article, which regulates a fluctuation range of the foaming temperature of the cullet supplied to the melting furnace. The method for producing a glass article according to claim 1, wherein the foaming temperature of the cullet is within a range of ± 20 ° C. of a predetermined reference value. The method for manufacturing a glass article according to claim 2, wherein the reference value is within a range of ± 30 ° C. of the melting temperature in the melting furnace. The method for producing a glass article according to claim 2 or 3, wherein the reference value is at least a temperature at which the viscosity of the molten glass becomes 150 dPa · s. The method for producing a glass article according to claim 4, wherein the reference value is at least a temperature at which the viscosity of the molten glass becomes 180 dPa · s. Any of claims 1 to 5, wherein the cullet comprises a first cullet having a relatively low first foaming temperature and a second cullet having a relatively high second foaming temperature. The method for manufacturing a glass article according to item 1. The method for producing a glass article according to any one of claims 1 to 6, further comprising a measuring step of measuring the foaming temperature of the cullet before supplying the cullet to the melting furnace. A clarification step for clarifying the molten glass in a clarification chamber arranged on the downstream side of the melting furnace is provided.
The method for producing a glass article according to any one of claims 1 to 7, wherein the foaming temperature is equal to or lower than the clarification temperature in the clarification chamber. The invention according to any one of claims 1 to 7, wherein in the melting furnace, a portion not covered with the glass raw material and the cullet is formed on a part of the liquid surface of the molten glass. How to manufacture glass articles. A group of glass substrates consisting of multiple glass substrates,
The glass substrate has a foaming temperature derived from the cullet used as a raw material and has a foaming temperature.
When the foaming temperature is defined as the temperature at which expansion of fine bubbles generated from the crushed glass substrate is observed when the glass substrate is crushed and melted.
A group of glass substrates characterized in that the difference between the maximum value and the minimum value of the foaming temperature is 40 ° C. or less.

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