TW201831409A - Glass article production method and glass substrate group - Google Patents

Abstract

This glass article production method comprises a fusion step for obtaining molten glass Gm by fusing, in a fusion furnace 1, a mixed raw material Gr obtained by mixing a glass raw material and cullet. In the fusion step, the range of fluctuation in foaming temperature of the cullet fed into the fusion furnace 1 is regulated.

Description

Glass article manufacturing method and glass substrate group

[0001] The present invention relates to a method of producing a glass article and a glass substrate group.

[0002] A method for producing a glass article such as flat glass includes a melting step of obtaining molten glass. In the melting step, the molten raw material is obtained by melting a mixed raw material in which cullet is applied to a glass raw material such as cerium oxide or feldspar in a melting furnace (see, for example, Patent Documents 1 and 2). . Here, the cullet is a recycled raw material obtained by breaking a glass article (including a defective glass article) produced by the melting step. [Prior Art Document] [Patent Document] [0003] Patent Document 1: JP-A-2016-037437 Patent Document 2: International Publication No. 2006/051953

[Summary of the Invention] [Problems to be Solved by the Invention] [0004] The melting step described above generates microbubbles in a furnace accompanied by melting of a mixed raw material including a glass raw material and cullet. The fine bubbles rise in the molten glass (in the liquid) by buoyancy as the bubble diameter of the heating increases, and a bubble layer is formed in the surface layer portion of the molten glass stored in the furnace. This bubble layer has an effect of preventing heat dissipation from the molten glass (insulation effect). [0005] However, when a molten glass is obtained using a mixed raw material, the range of the bubble layer is liable to become unstable. Therefore, there is a problem that the melting temperature in the furnace is unstable due to an increase or decrease in the heat insulating effect of the bubble layer. When the above problems occur, the quality of the glass article finally produced (for example, bubble quality or texture quality) may also have an adverse effect. [0006] The present invention is directed to stabilizing a melting temperature in a melting furnace when molten glass is obtained by melting a glass raw material and cullet, and obtaining a glass article having excellent quality. [Means for Solving the Problems] [0007] The present invention, which has been developed to solve the above problems, is a method for producing a glass article comprising a melting step of obtaining molten glass by melting a molten glass material and cullet in a furnace, characterized in that: The range of variation of the foaming temperature of the cullet of the furnace. [0008] The inventors of the present invention have focused on the results of research and efforts to obtain, for example, a melting furnace of a cullet having a composition, a color, and a particle size of a glass having a high level of management such as a glass substrate for a display, which makes the melting temperature in the furnace unstable. The variation of the bubble layer range is the knowledge generated by the broken glass. Specifically, the reason why the range mainly constituting the bubble layer is caused by the foaming temperature of the cullet. Here, it can be understood that the foaming temperature is a temperature at which microbubbles are generated from the cullet when the cullet is melted. This foaming temperature is greatly affected by the heat history of the melting step in the production of the glass article before the crushing based on the cullet. That is, although the cullet foaming temperature is substantially the same as long as the melting step through the same melting temperature, the cullet foaming temperature via the melting step of the different melting temperatures is also different. For this reason, if the foaming temperature of the cullet is not subjected to any management, that is, when the cullet is supplied to the furnace in the melting step, the probability of the foaming temperature of the cullet varies. When the fluctuation of the foaming temperature is increased, the bubble layer is formed or not formed at a predetermined temperature, so that the fluctuation of the bubble layer range is facilitated. Therefore, the present invention has the above configuration and limits the range of variation of the foaming temperature of the cullet supplied to the furnace. In this way, the temperature range generated by the bubble layer can be controlled, thereby stabilizing the bubble layer range. Therefore, it is possible to suppress the fluctuation of the heat insulating effect due to the bubble layer, and to stabilize the melting temperature in the furnace. In the above configuration, the foaming temperature of the cullet is preferably within a range of ±20 ° C of a predetermined reference value. As a result, the fluctuation range of the foaming temperature of the cullet is reduced, so that the fluctuation of the bubble layer range can be more reliably suppressed. [0010] In the above configuration, the reference value is preferably in the range of ±30 ° C of the melting temperature of the furnace. In this way, the formation range of the bubble layer is stabilized by the melting temperature, so that the bubble layer can enhance the heat insulation effect. As a result, since the amount of energy input required for temperature adjustment is stabilized, it is expected that energy-saving molten glass raw materials and cullet can be saved. [0011] 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, or a temperature of 180 dPa ‧ s or less. In this case, since the reference value is often the same as the temperature of the clarification chamber or lower than the melting temperature, the clarification can be effectively performed. [0012] In the above configuration, the cullet is preferably a first cullet comprising a first foaming temperature having a relatively low temperature and a second cullet having a second foaming temperature of a relatively high temperature. For example, the foaming temperature of the cullet of the two cullet mixed with the first cullet and the second cullet is affected by the foaming temperature of the first cullet and the second cullet, at the first foaming temperature and The temperature between the two foaming temperatures varies. Therefore, it becomes easy to control the foaming temperature of the cullet. [0013] In the above configuration, it is preferable to measure the foaming temperature of the cullet before the cullet is supplied to the furnace by the measuring step. In this way, the foaming temperature of the cullet supplied to the furnace is surely grasped in the melting step and can be managed. [0014] In the above configuration, the clarification step is provided, and the molten glass is clarified in the clarification chamber disposed on the downstream side of the furnace, and the foaming temperature is preferably equal to or lower than the clarification temperature of the clarification chamber. In this way, defoaming of the molten glass can be surely performed. [0015] In the above configuration, it is preferable that a portion not covered with the glass raw material and the cullet is formed in a portion of the liquid surface of the molten glass in the furnace. As a result, the melting temperature of the furnace is easily affected by the bubble layer as compared with the case where all of the liquid surface of the molten glass is covered with the glass raw material and the cullet, and therefore the effects of the present invention are more useful. [0016] The present invention, which has been developed to solve the above problems, is a glass substrate group composed of a plurality of glass substrates, and the difference between the maximum value and the minimum value of the foaming temperature is 40° C. or less. In the past, due to the unevenness of the foaming temperature of the cullet, the heat history of the melting step (the melting temperature in the melting furnace or the energy supplied to the furnace) became unstable, and as a result, the glass substrate was foamed. The temperature fluctuates, and there is a case where the difference between the maximum value and the minimum value of the foaming temperature exceeds 40 °C. According to the manufacturing method of the present invention, since the variation range of the foaming temperature of the cullet is restricted, the heat history of the melting step (the melting temperature in the furnace or the energy supplied to the furnace) can be stabilized, and the glass substrate can be foamed. The temperature changes below 40 °C. When the fluctuation of the foaming temperature of the glass substrate is 40° C. or less, it has excellent quality (for example, bubble quality or texture quality). In particular, when cullet is produced from a glass substrate, the surface temperature in the furnace can be stabilized by using this, and the bubble defects of the obtained product glass can be reduced. [Effect of the Invention] According to the present invention, since the meltable glass raw material and the cullet can stabilize the melting temperature in the furnace when the molten glass is obtained, a glass article excellent in quality can be obtained.

[0019] Hereinafter, an embodiment of a method for producing a glass article and a glass substrate group according to the present invention will be described with reference to the drawings. [0020] As shown in Fig. 1, the flat glass manufacturing apparatus used in the present manufacturing method includes the furnace 1, the clarification chamber 2, the homogenization chamber (stirring chamber) 3, the state adjustment chamber 4, and the molding apparatus in this order from the upstream side. 5 and the transfer pipes 6 to 9 connecting the parts. Here, the term "chamber" of the clarification chamber 2 or the like is a material having a groove-like structure or a material having a tubular structure. [0021] The furnace 1 is a space for performing a melting step of obtaining the molten glass Gm. The furnace 1 is connected to the clarification chamber 2 on the downstream side by a transfer pipe 6. [0022] The clarification chamber 2 is a space for clarifying the clarification step of the molten glass Gm supplied from the 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 the transfer pipe 7. [0023] The homogenization chamber 3 is a space for agitating the clarified molten glass Gm by the stirring blade 3a and performing a homogenization homogenization step. The homogenization chamber 3 is connected to the state adjustment chamber 4 on the downstream side by the transfer pipe 8. [0024] The state adjustment chamber 4 is a space for adjusting the molten glass Gm to a state adjustment step suitable for the molding state. The state adjustment chamber 4 is connected to the downstream molding device 5 by the transfer pipe 9. Further, the state adjustment chamber 4 may be omitted. [0025] The forming device 5 is a forming step for forming the molten glass Gm into a predetermined shape. In the present embodiment, the molding apparatus 5 forms the molten glass Gm into a plate shape by an overflow down-draw method. Specifically, the molding apparatus 5 has a cross-sectional shape (a cross-sectional shape orthogonal to the plane of the paper) and has a substantially oblique taper shape, 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 tank by the transfer pipe 9, the molten glass Gm is overflowed from the overflow tank, and flows along the side wall surfaces (the side surfaces on the front and back sides of the paper surface) on both sides of the forming apparatus 5. Further, the molten glass Gm which has flowed down is fused at the lower top portion of the side wall surface thereof, and is formed into a plate shape. The flat glass after the formation is, 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 used for a flat panel display such as a liquid crystal display or an organic EL display, an organic EL illumination, a solar cell, or the like. Substrate or shield. Further, the forming device 5 may perform another down-draw method such as a slit down-draw method. Further, the forming device 5 can also perform a float method. [0027] The transfer pipes 6 to 9 are formed, for example, of a cylindrical tube made of platinum or a platinum alloy, and the molten glass Gm is transferred in the lateral direction (substantially horizontal direction). The transfer pipes 6 to 9 are energized and heated as needed. [0028] As shown in Fig. 2, in the present embodiment, the furnace 1 is an electric melting furnace that electrically melts a mixed raw material Gr of a glass raw material and cullet to form a molten glass Gm. The furnace 1 is formed by, for example, a wall portion formed of heat-resistant bricks to form a molten space. In the bottom wall portion and/or the side wall portion of the furnace 1, a plurality of electrodes 10 are provided in a state of being immersed in the molten glass Gm. In the furnace 1, the heating means other than the electrode 10 is not provided, and only the raw material Gr is melted (all-electrically melted) by the electric heating (electric energy) of the electrode 10. Further, another heating means such as an electric heater may be provided above the liquid surface Gm1 of the molten glass Gm. Further, the furnace 1 may melt and mix the raw material Gr only by gas combustion, or may be melted by gas combustion and electric heating. In the present embodiment, the furnace 1 is a single melter having only one molten space of the mixed raw material Gr, but may be a composite melter that connects a plurality of molten spaces. [0030] The 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 part of the liquid surface Gm1 of the molten glass Gm forms a portion which is not covered with the mixed raw material (solid raw material) Gr. That is, the furnace 1 is a so-called semi-hot top type. Further, the furnace 1 may be a so-called cold-top type in which all of the liquid surface 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. [0031] The furnace 1 is provided with a flue 12 as a gas discharge path for discharging the gas in the furnace 1 to the outside. A fan 13 for supplying gas to the outside is provided in the flue 12. The fan 13 can also be omitted. Further, in the present embodiment, the gas in the furnace 1 is air, but is not limited thereto. Here, the production method is particularly useful when the glass raw material and the cullet (or the molten glass Gm) of the mixed raw material Gr are alkali-free glass. Further, the mixed raw material Gr is preferably a tin oxide-containing clarifying agent. The content of the tin oxide is preferably, for example, 0.01% by mass or more. Further, the particle diameter of the glass raw material and/or the cullet is preferably 0.5 to 50 mm, and more preferably 1 to 10 mm. The broken glass is crushed into a size of 1~10mm by crushing with a coarse crushing machine, a medium crusher and a mesh screening device. In addition, cullet of 0.5 mm or less may be mixed. Further, it can be classified by the method described in International Publication No. 2006/051953. Moreover, the ratio of the cullet in the mixed raw material Gr is, for example, 20% by mass or more. The symbol BL in FIG. 2 is a bubble layer which is generated by the melting of the mixed raw material Gr. The bubble layer BL is formed in the surface layer portion of the molten glass Gm. As long as the range of the bubble layer BL does not largely vary, the surface layer portion of the molten glass Gm may be a region where the bubble layer BL is not formed. [0034] Next, a method of manufacturing a glass article of the manufacturing apparatus configured as described above will be described. [0035] The production method includes the melting step, the clarification step, the homogenization step, the state adjustment step, and the molding step as described above. Further, the clarification step, the homogenization step, the state adjustment step, and the molding step are as described in the configuration of the above-described manufacturing apparatus, and the melting step will be described in detail below. [0036] As shown in FIG. 2, in the melting step, the molten glass Gm is obtained by melting the mixed raw material Gr composed of the glass raw material and the cullet in the furnace 1. At this time, the fluctuation range of the foaming temperature (also referred to as reboiling temperature) of the cullet contained in the mixed raw material Gr supplied to the furnace 1 is restricted. Specifically, the foaming temperature of the cullet is restricted to be within a range of ±20 ° C of a predetermined reference value. The foaming temperature of the cullet is preferably ±15 ° C of the reference value, and more preferably ± 10 ° C of the reference value. Here, the foaming temperature means a temperature at which the expansion of the microbubbles generated from the cullet is recognized when the cullet is melted. In the present embodiment, the foaming temperature of the cullet is a temperature at which the initial bubble diameter (for example, 70 to 80 μm) of the fine bubbles generated by the heating of the cullet is expanded to 1.5 times the diameter. [0037] The reference value is preferably in the range of ±30 ° C of the melting temperature of the furnace 1. In this way, the formation range of the bubble layer BL is stabilized by the melting temperature, so that the bubble layer BL can be used to enhance the heat insulating effect. Therefore, it can be expected that the mixed raw material Gr can be melted energy-saving. Here, the melting temperature of the furnace 1 is measured at the highest temperature in the furnace (for example, the temperature of the bottom surface 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 kPa s s or less, and most preferably a temperature range of 200 dPa ‧ s to 2000 dPa ‧ s. In this case, the reference value is the same as the temperature of the clarification chamber, or when it is more than the melting temperature, the clarification can be effectively performed. In the present embodiment, the reference value is preferably 1615 ° C or lower, more preferably 1600 ° C or lower, and most preferably 1400 ° C or higher and 1580 ° C or lower. [0039] The foaming temperature of the cullet is preferably clarified below the clarification temperature (heating temperature) of the clarification chamber 2. In this way, in the clarification chamber 2, since the bubbles are discharged from the cullet, the defoaming of the molten glass Gm can be surely performed. Here, the melting temperature of the furnace 1 is preferably, for example, a temperature at which the viscosity of the molten glass Gm is 210 dPa ‧ or less, for example, 1580 ° C or lower. The clarification temperature of the clarification chamber 2 is preferably, for example, a temperature range in which the viscosity of the molten glass is 210 to 70 dPa ‧ s, for example, 1580 to 1700 ° C. The viscosity of the glass decreases as the temperature rises. Therefore, in the above relationship of viscosity, the clarification temperature is higher than the melting temperature. The limitation of the range of variation of the foaming temperature of the cullet contained in the mixed raw material Gr is, for example, the following. [0042] First, before being supplied to the inside of the furnace 1, a part of the cullet contained in one batch is taken out, and the foaming temperature of the cullet after the extraction is measured (measurement step). This measuring step is, for example, to put the cullet into the quartz crucible and heat the electric to a predetermined temperature. By this heating process, the temperature (foaming temperature) at which the initial bubble diameter of the minute air bubbles enclosed by the melting of the cullet was expanded to 1.5 times the diameter was measured. At this time, the bubble diameter was measured by expanding the observation with a CCD camera at a high temperature. The residual cullet contained in the same batch as the extracted cullet is passed through a melting step which becomes the same melting temperature as the original glass article (plate glass or glass bottle), and thus can be regarded as having the same foaming temperature as the above measurement. Foaming temperature. Therefore, as long as the foaming temperature after the measurement is within the range of ±20 ° C of the reference value, it can be supplied into the furnace 1 in the state of residual cullet contained in the same batch. In order to confirm the melting of the cullet and the change of the bubble diameter, for example, a High Temperature Observation System manufactured by GLASS SERVICE Co., Ltd. can be used. Further, the method of measuring the foaming temperature of the cullet is an example, and other methods may be used. On the other hand, when the reference value is outside the range of ±20° C., the remaining cullet contained in the same batch is not supplied into the furnace 1 and the subsequent processing is performed. That is, in the measuring step, preparing: measuring the cullet having a low foaming temperature lower than the reference value (the first cullet having a relatively low temperature first foaming temperature), and measuring the cullet having a high foaming temperature than the reference value (Second cullet with a relatively high temperature second foaming temperature). At this time, it is preferable that the average particle diameter and the glass composition of the first cullet and the second cullet are the same. And, the first cullet and the second cullet are mixed. When mixing as described above, the foaming temperature of the cullet after mixing is affected by both the first cullet and the second cullet, and varies between the first foaming temperature and the second foaming temperature. For example, when the first foaming temperature and the second foaming temperature are mixed in the same amount of cullet of 1570 ° C and 1600 ° C, it is confirmed that the foaming temperature of the cullet after mixing is adjusted to 1585 ° C. Therefore, by mixing the first cullet and the second cullet, the foaming temperature can be adjusted to within ±20 ° C of the reference value. The mixing ratio of the first cullet to the second cullet is a temperature difference between the respective foaming temperatures and the reference value, and can be appropriately adjusted. That is, the amount of the first cullet may be larger than the amount of the second cullet, and the amount of the first cullet may be made smaller than the amount of the second cullet. [0044] Further, the adjustment of the foaming temperature of the cullet or the supply amount of the cullet can be ensured as follows. That is, cullet of three or more batches having different foaming temperatures may be mixed. It is also possible to mix only the cullet having a foaming temperature of a reference value or more, or to mix only cullet having a foaming temperature of a reference value or less. Further, cullet of two or more different batches in the range of ±20 ° C of the reference value may be mixed. As described above, the foaming temperature of the cullet which is sequentially supplied to the furnace 1 is managed within a range of ±20 ° C of the reference value, and the unevenness of the foaming temperature of the cullet can be suppressed. Thereby, the temperature range in which the bubble layer BL is generated can be controlled, and the range of the bubble layer BL can be stabilized. Therefore, the bubble layer BL can suppress the fluctuation of the heat insulating effect, and the melting temperature in the furnace 1 can be stabilized. Thereby, a glass substrate (glass article) having a stable quality such as a bubble quality or a pulse quality can be produced. Here, the glass substrate group composed of the plurality of glass substrates produced as described above has a difference between the maximum value and the minimum value of the foaming temperature, for example, 40° C. or less. The difference between the maximum value and the minimum value of the foaming temperature is preferably 30 ° C or less, and more preferably 20 ° C or less. The glass substrate group is composed of, for example, 100 to 500 glass substrates laminated on one tray. The measurement of the foaming temperature of the glass substrate group is performed, for example, below. First, five glass substrates were taken from the glass substrate group. Next, each of the taken glass substrates was crushed into a predetermined size to obtain cullet. Then, the foaming temperature of each cullet was measured, and the maximum value, the minimum value, and the difference were calculated. [0048] The glass substrate is preferably a glass substrate formed by an overflow method. [0049] The glass substrate is 50 to 70% by mass of SiO ₂ , 12 to 25% of Al ₂ O ₃ , 0 to 12% of B ₂ O ₃ , and Li ₂ O+Na ₂ O+K ₂ O (Li ₂ O, The total amount of Na ₂ O and K ₂ O is preferably less than 0 to 1%, MgO 0 to 8%, CaO 0 to 15%, SrO 0 to 12%, and BaO 0 to 15% of alkali-free glass. [Examples] [0050] A confirmation test was conducted to investigate the influence of the foaming temperature of the cullet. The cullet is carried out by OA-11, an alkali-free glass of Nippon Electric Glass Co., Ltd. The melting of the glass is carried out in a furnace equipped with an oxygen burner and a molybdenum electrode. The results are shown in Figs. 3 and 4. Fig. 3 is a graph showing how the foaming temperature and the like of the glass article produced by the melting step change when the temperature in the top of the furnace is changed (when the energy supplied to the furnace is changed), and Fig. 4 is a view showing how the foaming temperature of the glass article produced by the melting step is changed. The energy supplied to the furnace is maintained under a certain state, and when the foaming temperature of the broken glass is changed, the temperature at the top of the furnace is changed. As shown in FIG. 3, as the approximate straight line indicated by the dotted line is directed to the right shoulder, the temperature at the top of the furnace (melting temperature) of the melting step becomes higher, and the foaming temperature of the glass article also becomes higher. This means that the foaming temperature of the cullet obtained by pulverizing the glass article becomes higher in proportion to the melting temperature at the time of production of the original glass article. That is, the lower the melting temperature at the time of manufacture of the original glass article, the lower the foaming temperature of the cullet obtained from the glass article, and the higher the melting temperature at the time of manufacture of the original glass article, the glass article The foaming temperature of the obtained cullet tends to be higher. Therefore, it is predicted that the foaming temperature of the cullet obtained from the glass article becomes a certain degree according to the melting temperature at the time of manufacture of the original glass article. On the other hand, as shown in FIG. 4, it can be seen that even if the energy source supplied to the furnace is the same, when the foaming temperature of the used cullet is changed, the furnace top temperature (melting temperature) of the melting step is large. change. In detail, the approximate straight line indicated by the dotted line goes downward to the right shoulder, and as the foaming temperature of the cullet becomes higher, the temperature at the top of the furnace becomes lower. This is because the formation of the bubble layer becomes difficult as the foaming temperature of the cullet becomes higher, and the heat insulating effect of the bubble layer is lowered. From the results as described above, it has been confirmed that the present invention which appropriately manages the foaming temperature of the cullet which is sequentially supplied to the furnace to stabilize the bubble layer range becomes useful. Further, the present invention is not limited to the configuration of the above embodiment, and is not limited to the above-described operational effects. Various changes can be made without departing from the spirit and scope of the invention. [0054] The above embodiment has been described in the case where the measurement step is performed before the cullet is supplied to the furnace 1, but the measurement step may be omitted. That is, the melting temperature of the melting step in the production of the cullet and the glass article which is the base material of the cullet can be pre-marked and recorded, and the foaming temperature of the cullet can be roughly grasped without performing the measurement step. That is, the method of limiting the range of variation of the foaming temperature of the cullet is not limited to the method of directly measuring the foaming temperature of the cullet, but also the method of indirectly grasping the foaming temperature of the cullet. In the above embodiment, the case where the glass article formed by the molding device 5 is a flat glass is described, but the invention is not limited thereto. For example, the glass article formed by the molding device 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 any shape.

[0056]

1‧‧‧furnace

2‧‧‧Clarification room

3‧‧‧Homogenization Room

3a‧‧‧Agitating wing

4‧‧‧State Adjustment Room

5‧‧‧Forming device

6~9‧‧‧Transfer tube

10‧‧‧ electrodes

11‧‧‧Spiral feeder

12‧‧‧ flue

13‧‧‧Fan

BL‧‧‧ bubble layer

Gm‧‧‧ molten glass

Gr‧‧‧ mixed raw materials (glass raw materials and broken glass)

[0018] FIG. 1 is a side view showing a manufacturing apparatus of a glass article. Fig. 2 is a cross-sectional view showing a furnace of the apparatus for manufacturing a glass article of Fig. 1. Fig. 3 is a graph showing the results of the confirmation test of the examples. Fig. 4 is a graph showing the results of the confirmation test of the examples.

Claims (10)

A method for producing a glass article, which is a method for producing a glass article comprising a molten glass raw material and a cullet in a melting furnace to obtain a melting step of molten glass, characterized by: limiting a foaming temperature of the cullet supplied to the furnace The scope of the change. The method for producing a glass article according to the first aspect of the invention, wherein the foaming temperature of the cullet is within a range of ±20 ° C of a predetermined reference value. The method for producing a glass article according to the second aspect of the invention, wherein the reference value is within a range of ± 30 ° C of a melting temperature of the furnace. The method for producing a glass article according to the second or third aspect of the invention, wherein the reference value is a temperature at which the viscosity of the molten glass is not more than 150 dPa ‧ s. The method for producing a glass article according to the fourth aspect of the invention, wherein the reference value is a temperature at which the viscosity of the molten glass is not more than 180 dPa ‧ s. The method for producing a glass article according to any one of claims 1 to 5, wherein the cullet comprises: a first cullet having a relatively low temperature first foaming temperature, and having a relative A second cullet of a second temperature at a higher temperature. The method for producing a glass article according to any one of claims 1 to 6, further comprising a measuring step of measuring a foaming temperature of the cullet before supplying the cullet to the furnace. The method for producing a glass article according to any one of the preceding claims, wherein the method of producing a glass article includes a clarification step of clarifying the molten glass in a clarification chamber disposed on a downstream side of the furnace, and the foaming The temperature is below the clarification temperature of the above clarification chamber. The method for producing a glass article according to any one of the first aspect of the present invention, wherein, in the furnace, a portion of the liquid surface of the molten glass is not formed with the glass material and Part of the broken glass. A glass substrate group which is a glass substrate group composed of a plurality of glass substrates, wherein a difference between a maximum value and a minimum value of a foaming temperature is 40° C. or less.