Method for manufacturing glass article, and glass melting apparatus

Abstract

To prevent a platinum foreign matter as much as possible from occurring as a defect in a glass article when manufacturing a glass article using a glass melting apparatus.SOLUTION: A method for manufacturing a glass article comprises: a supply step P1 of supplying a glass raw material 2 to a melting tank 9 of a glass melting apparatus 4; a melting step P2 heating and melting the glass raw material 2 while energizing and heating a molten glass 3 in the melting tank 9; a molding step P4 of molding a glass plate 7 from the molten glass 3; and an inspection step P5 of inspecting defects of the glass plate 7. The glass melting apparatus 4 includes a molybdenum ground electrode 12 contacting the molten glass 3 and an outflow pipe 14 or the like contacting the molten glass 3, and further includes a check step P6 of checking the occurrence of electric leakage through the molten glass 3 between the outflow pipe 14 or the like and the ground electrode 12 when platinum foreign matters are detected on the glass plate 7 in the inspection step P5.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a method for manufacturing glass articles, such as glass sheets, and a glass melting apparatus for melting glass raw materials to produce molten glass. [Background technology]

[0002] Glass articles such as glass plates, glass tubes, glass fibers, etc. are manufactured by melting glass raw materials to produce molten glass and then forming the molten glass into a predetermined shape. To produce the molten glass, as disclosed in Patent Document 1, a glass melting apparatus (referred to as a glass melting furnace in the document) of a type that electrically heats the molten glass may be used.

[0003] In this apparatus, glass raw materials are supplied to a melting tank, and the molten glass contained in the melting tank is heated and melted by electrically heating the glass raw materials. In this apparatus, heating by a burner is also used in addition to the above-mentioned electrically heating to heat the glass raw materials. The melting tank contains an electrically conducting electrode for electrically heating the molten glass while immersed in the molten glass, and a grounded electrode immersed in the molten glass. The melting tank also has an outlet for discharging the molten glass produced in the tank. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-31355 Summary of the Invention [Problem to be solved by the invention]

[0005] Although Patent Document 1 does not disclose the materials of the ground electrode and the extraction portion, for example, a molybdenum electrode can be used as the ground electrode. Furthermore, a platinum or platinum alloy pipe can be used as the extraction portion. When a glass melting apparatus having this configuration is used, platinum contaminants (for example, contaminants made of an alloy of platinum and molybdenum) containing platinum components can occur as defects in glass articles formed from molten glass. This has led to a problem in which the manufactured glass articles cannot be used as final products.

[0006] In view of the above circumstances, the problem to be solved is to prevent, as much as possible, the occurrence of platinum inclusions as defects in glass articles when the glass articles are produced using a glass melting apparatus. [Means for solving the problem]

[0007] As a result of extensive research, the inventors have found that, in producing a glass article using a glass melting apparatus of the type that performs electrical heating of molten glass, if an electric current flows between a molybdenum member and a platinum or platinum alloy member via the molten glass, platinum inclusions may be generated in the glass article, where the molybdenum member corresponds to the anode and the platinum or platinum alloy member corresponds to the cathode.

[0008] Based on the above findings, a first method for manufacturing a glass article for solving the above problems includes a supply step of supplying glass raw materials to a melting tank provided in a glass melting apparatus, a melting step of heating and melting the glass raw materials supplied to the melting tank while electrically heating the molten glass contained in the melting tank, a forming step of forming a glass article from the molten glass that has flowed out of the melting tank, and an inspection step of inspecting the glass article for defects, wherein the glass melting apparatus further includes a molybdenum member that contacts the molten glass and a platinum member that contacts the molten glass, and the method further includes a confirmation step of confirming the occurrence of leakage current through the molten glass between the platinum member and the molybdenum member if platinum foreign matter containing a platinum component is detected in the glass article in the inspection step.

[0009] Here, "molybdenum member" means a member made of molybdenum, and "platinum member" means a member made of platinum (including reinforced platinum) or a platinum alloy (including reinforced platinum alloy).

[0010] In the first glass article manufacturing method, if platinum contaminants are detected in the glass article during the inspection process, a confirmation process is performed to confirm the occurrence of a current leak through the molten glass between the platinum component and the molybdenum component. This allows the state to be repaired after the confirmation process, even if a current unintentionally flows between the platinum component and the molybdenum component through the molten glass. After repair, it is possible to prevent a current from flowing between the molybdenum component and the platinum component through the molten glass, thereby minimizing the occurrence of platinum contaminants in the glass article due to a current leak.

[0011] The second method for manufacturing a glass article is the same as the first manufacturing method described above, except that the molybdenum member is a grounded electrode that is immersed in the molten glass in the melting tank and is earthed, and the method further includes a measurement process for measuring the current flowing through the grounded electrode, and if platinum foreign matter is detected in the glass article in the inspection process and the current measured in the measurement process increases, a confirmation process is carried out.

[0012] As in the second glass article manufacturing method, if the current measured in the measurement step (the current flowing through the ground electrode) increases after the measurement step, the occurrence of a leakage current through the molten glass between the platinum member and the molybdenum member is likely to be the cause of the platinum contaminants. Therefore, if a platinum contaminant is detected in the glass article in the inspection step and the current measured in the measurement step increases, the verification step can be performed to the greatest extent possible, thereby eliminating the waste of performing the verification step even when the above-mentioned leakage current does not actually occur.

[0013] The third method for manufacturing a glass article is the same as the second manufacturing method described above, except that an electric heating area is provided in the melting tank in which an electric electrode for electrically heating the molten glass is arranged, the glass melting apparatus further includes a transfer device for transferring the molten glass flowing out of the melting tank, and a ground electrode is arranged downstream of the electric heating area and upstream of the transfer device in the flow direction of the molten glass.

[0014] In the third method for producing a glass article, a ground electrode is disposed between the electrically heated region and the transfer device in the direction of molten glass flow, thereby preventing current from flowing from the molten glass in the melting tank to the molten glass in the transfer device, or conversely, preventing current from flowing from the molten glass in the transfer device to the molten glass in the melting tank.

[0015] A fourth method for manufacturing a glass article is any one of the first to third manufacturing methods described above, in which the molybdenum member is a grounded electrode that is immersed in the molten glass in the melting tank and is earthed, and a capacitor is provided on the current path connecting the molybdenum member and the earth.

[0016] As a result of extensive research, the inventors discovered that when a current flowing between a molybdenum member and a platinum member via molten glass is direct current rather than alternating current, platinum contaminants are generated in the glass article due to electrical leakage. Based on this discovery, the fourth method for producing a glass article is extremely advantageous in preventing the generation of platinum contaminants due to electrical leakage. This is because the provision of a capacitor can interrupt the direct current in the current path connecting the molybdenum member and ground, thereby preventing the flow of direct current between the molybdenum member and the platinum member via molten glass.

[0017] A fifth method for producing a glass article is any one of the first to fourth production methods described above, except that the glass raw material is a raw material for alkali-free glass.

[0018] A sixth method for producing a glass article is any one of the first to fifth methods described above, wherein the glass article is a glass substrate for a display.

[0019] In a glass substrate for a display, even the smallest amount of platinum foreign matter can render the substrate unusable as a product. Therefore, if the glass article is a glass substrate for a display, as in the sixth glass article manufacturing method, the aforementioned confirmation step can be carried out to preferably enjoy the effects of carrying out the step.

[0020] Based on the above findings, a first glass melting apparatus for solving the above problems comprises a melting tank that receives a supply of glass raw materials and contains molten glass formed by melting the glass raw materials, and an electric electrode that is immersed in the molten glass in the melting tank and electrically heats the molten glass, and is characterized by further comprising a molybdenum ground electrode that is immersed in the molten glass in the melting tank and is earthed, a platinum member that contacts the molten glass, and an ammeter that measures the current flowing through the ground electrode.

[0021] According to the first glass melting apparatus, it is possible to more accurately detect leakage current between the platinum member and the ground electrode through the molten glass based on an increase in current measured by an ammeter, and after the occurrence of leakage current is confirmed, the condition can be repaired. Therefore, it is possible to prevent platinum foreign matter from being generated in the glass article due to leakage current as much as possible.

[0022] Based on the above findings, a second glass melting apparatus for solving the above problems comprises a melting tank that receives a supply of glass raw materials and contains molten glass formed by melting the glass raw materials, and an electric electrode that is immersed in the molten glass in the melting tank and electrically heats the molten glass, and is characterized by further comprising a molybdenum ground electrode that is immersed in the molten glass in the melting tank and is earthed, a platinum member that contacts the molten glass, and a capacitor provided on a current path connecting the ground electrode and the earth.

[0023] According to the second glass melting apparatus, it is possible to obtain the same effects as those already described for the fourth method for producing a glass article. [Effects of the Invention]

[0024] According to the glass article manufacturing method and glass melting apparatus of the present disclosure, when a glass article is manufactured using the glass melting apparatus, it is possible to prevent as much as possible the occurrence of platinum foreign matter in the glass article due to electrical leakage. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a partial cross-sectional view showing a method for manufacturing a glass article and a glass melting apparatus. [Figure 2] FIG. 1 is a perspective view showing a method for manufacturing a glass article. [Figure 3] 1 is a partial cross-sectional view showing a method for manufacturing a glass article and a glass melting apparatus. [Figure 4] FIG. 1 is a cross-sectional view showing a test for confirming the generation of platinum foreign matter. DETAILED DESCRIPTION OF THE INVENTION

[0026] Hereinafter, embodiments of a method for manufacturing a glass article and a glass melting apparatus will be described with reference to the accompanying drawings. In the embodiments described below, a case where a glass substrate for a display is manufactured as a type of glass article will be exemplified. Note that the X direction, Y direction, and Z direction shown in some of the drawings referred to in the description of the embodiments are directions perpendicular to one another.

[0027] First Embodiment First, a manufacturing apparatus used in carrying out the method for manufacturing a glass article will be described.

[0028] As shown in Figures 1 and 2, the manufacturing apparatus 1 includes a glass melting device 4 for melting glass raw material 2 to produce molten glass 3, a forming device 6 for continuously forming a glass ribbon 5 (a glass plate that is long in one direction) from the molten glass 3, a cutting device (not shown) for cutting out a glass plate 7 that will become a glass substrate from the glass ribbon 5, and an inspection device 8 for inspecting the glass plate 7 for defects.

[0029] As shown in FIG. 1 , the glass melting apparatus 4 includes a melting tank 9 containing molten glass 3 produced from glass frits 2, a supply device 10 that supplies glass frits 2 onto the molten glass 3 in the melting tank 9, a plurality of current-carrying electrodes 11 that are immersed in the molten glass 3 in the melting tank 9 and electrically heat the molten glass 3, a molybdenum ground electrode 12 that is immersed in the molten glass 3 in the melting tank 9 and is earthed without receiving any power supply, an ammeter 13 that measures the current flowing through the ground electrode 12, a platinum alloy outlet pipe 14 that discharges the molten glass 3 from the melting tank 9 to the outside and is electrically insulated from the ground, and a transfer device 15 that transfers the molten glass 3 discharged from the melting tank 9 to the forming device 6.

[0030] Here, the ground electrode 12 corresponds to a molybdenum member that contacts the molten glass, and the outflow pipe 14 corresponds to a platinum member that contacts the molten glass.

[0031] Walls 19 of melting tank 9 include bottom wall 16, side walls 17, and ceiling wall 18. The portions of wall 19 that come into contact with molten glass 3 are made of refractory materials such as zirconia bricks or zircon bricks. The outer surfaces of wall 19 that come into contact with molten glass 3 (the outer wall surfaces of wall 19) are sufficiently cooled, as necessary, by air in contact with the outer surfaces or by cooling gas blown onto the outer surfaces. This ensures the insulation of wall 19 of melting tank 9.

[0032] The feeder 10 is disposed on a side wall 17 of a wall portion 19 of the melting tank 9, the side wall 17 being located at the upstream end in the flow direction (X direction) of the molten glass 3. As the feeder 10, for example, a screw feeder that feeds the glass raw material 2 into the melting tank 9, or a pusher that pushes the glass raw material 2 into the melting tank 9, or the like is used.

[0033] The glass raw material 2 continuously supplied by the supply device 10 is a raw material for alkali-free glass. Here, "alkali-free glass" refers to glass that does not substantially contain alkali components (alkali metal oxides), specifically glass having an alkali component weight ratio of 3000 ppm or less. The alkali component weight ratio is preferably 1000 ppm or less, more preferably 500 ppm or less, and most preferably 300 ppm or less.

[0034] The multiple current-carrying electrodes 11 are arranged in the X and Y directions with a gap between them. The multiple current-carrying electrodes 11 include multiple pairs of electrodes. When viewed from a plan view (Z direction) of the melting furnace 9, the current-carrying heating zone S in which the multiple current-carrying electrodes 11 are arranged corresponds to the region in the X and Y directions in which the multiple current-carrying electrodes 11 are arranged. Each current-carrying electrode 11 is made of, for example, molybdenum, platinum, or a platinum alloy. Each current-carrying electrode 11 is inserted into the melting furnace 9 through the bottom wall 16 of the melting furnace 9 while being electrically insulated from the bottom wall 16. In this embodiment, a power source (not shown) that supplies power to the current-carrying electrodes 11 is an AC power source. When the molten glass 3 is electrically heated by the multiple current-carrying electrodes 11, the glass frit 2 on the molten glass 3 is heated and melted accordingly.

[0035] Ground electrode 12 is located downstream of electrical heating zone S and upstream of outlet pipe 14 in the flow direction (X direction) of molten glass 3. Ground electrode 12 is inserted into melting tank 9 through bottom wall 16. Unlike current-carrying electrode 11, ground electrode 12 is not intentionally supplied with power from a power source or the like and is not supplied with power from outside melting tank 9. Ground electrode 12 can reduce the potential of molten glass 3 around the electrode relative to the ground as much as possible (to approach 0 V). This minimizes the flow of unintended current from components in melting tank 9 (e.g., current-carrying electrode 11) to components in transfer device 15 via molten glass 3, or from components in transfer device 15 to components in melting tank 9. This prevents unintended current from flowing through molten glass 3 to components in melting tank 9.

[0036] The ammeter 13 is disposed on a current path connecting the ground electrode 12 and the earth. The ammeter 13 may be for DC, for AC, or may be a combination of DC and AC. From the viewpoint of detecting leakage current that may cause platinum foreign matter, it is preferable to include a DC ammeter 13.

[0037] Outlet pipe 14 is disposed so as to penetrate sidewall 17, which is located at the downstream end of wall portion 19 of melting tank 9 in the flow direction (X direction) of molten glass 3. In this embodiment, outlet pipe 14 uses a platinum-rhodium alloy as the platinum alloy, but may be made of a platinum alloy other than a platinum-rhodium alloy, or may be made of platinum (pure platinum). Outlet pipe 14 is ensured to be in a state of being out of contact with other conductors. Outlet pipe 14 may be equipped with equipment for electrically heating the pipe, and the pipe may be electrically heated.

[0038] Transfer device 15 includes, in order from the upstream side in the flow direction of molten glass 3, a fining tank 20 for fining molten glass 3 (removing bubbles from molten glass 3), a stirring tank 21 (installed in two locations in the illustrated example) for stirring and homogenizing molten glass 3 with a stirrer (not shown), and a conditioning tank 22 for adjusting the temperature (viscosity) and flow rate of molten glass 3 to a temperature and flow rate suitable for forming glass ribbon 5. Transfer device 15 also includes pipes 23-28 for connecting the above-mentioned equipment 20-22. In the following description, each of equipment 20-22 and pipes 23-28 may be referred to as component E of transfer device 15.

[0039] Each of the multiple components E (equipment 20-22 and pipes 23-28) included in the transfer device 15 is made of platinum or a platinum alloy (here, a platinum-rhodium alloy), and at least some of the multiple components E are equipped with equipment for electrically heating the element. The transfer device 15 is divided into multiple units U1-U3 (three in the illustrated example) separated by boundaries B1, B2, and B3 shown in FIG. 1. Adjacent units are electrically insulated from each other by insulators interposed between the units. Furthermore, of the units U1-U3, unit U1 is electrically insulated from the outflow pipe 14 by an insulator interposed between them.

[0040] In each of the multiple units U1 to U3, a refractory material (e.g., zirconia bricks, zircon bricks, alumina bricks, castable refractories, etc.) is arranged in the area surrounded by the dashed line in FIG. 1 to cover the constituent element E of the transfer device 15 while being in contact with the element. The outer surface of the refractory material is sufficiently cooled, as necessary, by air in contact with the outer surface or by cooling gas blown onto the outer surface. This ensures the insulating properties of the refractory material and prevents electrical leakage through the refractory material. Furthermore, each constituent element E of the transfer device 15 is kept out of contact with other conductors.

[0041] As described above, each component E of the outflow pipe 14 and the transfer device 15 is, in principle, kept out of contact with other conductors. However, there are exceptions, such as when a thermocouple (thermometer) is attached to the outer surface of the outflow pipe 14 and / or the component E of the transfer device 15 to measure the temperature of the outflow pipe 14 and / or the component E. The thermocouple contains a conductor (platinum, platinum alloy, etc.), but is placed inside a protective tube with a closed tip. Therefore, in principle, it does not come into direct contact with the outflow pipe 14 or the component E, but comes into contact with the outflow pipe 14 or the component E via the protective tube. This protective tube is made of an insulator (e.g., alumina).

[0042] Here, each of the components E of the transfer device 15 (each of the equipment 20 to 22 and the pipes 23 to 28) corresponds to a platinum member that comes into contact with the molten glass.

[0043] As shown in Fig. 1, the forming apparatus 6 includes a forming body 29 into which the molten glass 3 flowing out of the conditioning tank 22 flows. The forming body 29 of this embodiment is a forming body for use in an overflow downdraw method. Alternatively, the forming body 29 may be a forming body for use in a slot downdraw method. The glass ribbon 5 formed by the forming body 29 is formed so as to be long in one direction (Z direction), and ear portions that are thicker than other portions are formed on both ends of the glass ribbon 5 in the width direction (X direction).

[0044] A refractory material is arranged around the molded body 29 (the area surrounded by the dashed line in FIG. 1) so as to surround the molded body 29.

[0045] The cutting device not shown in the figure includes a first cutting device for cutting the glass ribbon 5 in the width direction (X direction) to cut out glass plates with edge portions from the glass ribbon 5, and a second cutting device for cutting and removing the edge portions from the glass plates with edge portions to obtain glass plates 7.

[0046] As shown in Figure 2, the inspection device 8 includes a conveying device 30 that conveys the glass plate 7 while holding it in a vertical position, and a defect detection device 31 that is arranged on the conveying path of the glass plate 7 and detects defects in the glass plate 7.

[0047] The defect detection device 31 has a light source 32 that emits a long line of light in the vertical direction, and a line sensor 34 with multiple cameras 33 arranged in the vertical direction. In this defect detection device 31, light is irradiated from the light source 32 toward the glass plate 7 being transported, and is received by the line sensor 34 on the opposite side of the glass plate 7, and the presence or absence of a defect is detected based on a change in the amount of light received.

[0048] A method for manufacturing a glass article using the above manufacturing apparatus 1 will now be described.

[0049] This manufacturing method includes a supplying step P1, a melting step P2, a measuring step P3, and a molding step P4 shown in FIG. 1, a cutting step (not shown), and an inspection step P5 shown in FIG.

[0050] In the supplying process P1, glass frits 2 are continuously supplied from a supplying device 10 to a melting tank 9 provided in a glass melting apparatus 4. In the melting process P2, the molten glass 3 contained in the melting tank 9 is heated by applying electricity through a plurality of current-carrying electrodes 11, while the glass frits 2 supplied to the melting tank 9 are heated and melted. In the measuring process P3, the current flowing through the grounding electrode 12 is measured using an ammeter 13. In the forming process P4, a glass ribbon 5 is formed from the molten glass 3 that has flowed out of the melting tank 9 and been refined, stirred, and conditioned in a refining tank 20, a stirring tank 21, and a conditioning tank 22. In the cutting process, a glass sheet 7 is obtained from the glass ribbon 5 using a cutting device (first and second cutting devices). In the inspection process P5, defects in the glass sheet 7 are inspected using an inspection device 8 (a conveying device 30 and a defect detection device 31). More specifically, in the inspection process P5, defects in the glass sheet 7 are detected and their locations are identified using the inspection device 8 (a conveying device 30 and a defect detection device 31). The detected defects are then observed using a microscope inspection device or chemically analyzed using an analytical device to identify the type of defect (for example, bubbles, platinum foreign matter, etc.).

[0051] Furthermore, in this manufacturing method, if platinum contaminants (e.g., contaminants composed of a platinum-molybdenum alloy) containing platinum components are detected in the glass plate 7 in the inspection step P5 and the current measured in the measurement step P3 is higher than the reference value, the confirmation step P6 is performed. In the confirmation step P6, the occurrence of leakage current through the molten glass between the platinum and molybdenum components is confirmed. For example, the electrical insulation between the outflow pipe 14 and other conductors, the electrical insulation between the component E of the transfer device 15 and other conductors, and the electrical insulation between the ground electrode 12 and other conductors are confirmed. That is, the presence of insulation defects in the platinum and molybdenum components is confirmed. If insulation is confirmed, it can be confirmed that no leakage current has occurred. If insulation is not confirmed, the occurrence of leakage current may be confirmed. If insulation is not confirmed, a repair step is performed to restore insulation.

[0052] As described above, if platinum contaminants are detected in the inspection step P5 and the current measured in the measurement step P3 is higher than the reference value, there is a high probability that the outflow pipe 14 or component E of the transfer device 15 unintentionally came into contact with another conductor, causing the current flowing through that conductor to leak to the platinum component, and further causing current to flow from the platinum component to the molybdenum component via the molten glass. The reason for this is as follows: As a result of the inventor's extensive research, it has been found that if another current-carrying conductor (e.g., a thermocouple) comes into unintentional direct contact with the platinum alloy outflow pipe 14 due to wear of the protective tube, current flows between the molybdenum ground electrode 12 and the platinum alloy outflow pipe 14 via the molten glass 3, which can result in the formation of platinum contaminants on the glass sheet 7. For this reason, it is effective to perform the confirmation step P6.

[0053] The reference value of the current in the measurement step P3 is set to be greater than the maximum value (e.g., 0.1 A) of the current (current measured by the ammeter 13) that can flow through the ground electrode 12 when the above-mentioned leakage current does not occur.

[0054] In addition to the wear of the thermocouple protective tube, specific examples of cases where the above-mentioned insulation failure occurs include a case where part of the outflow pipe 14 is damaged, causing the molten glass 3 leaking from the damaged area to come into contact with other conductors. When an insulation failure is confirmed in the confirmation step P6 as in this case, work is carried out in the repair step to eliminate the cause of the insulation failure.

[0055] Second Embodiment The second embodiment will be described below with reference to Fig. 3. Note that only the differences between the second embodiment and the first embodiment will be described.

[0056] The second embodiment differs from the first embodiment in that a capacitor 35 is disposed on the current path connecting the ground electrode 12 and the earth. In this embodiment, the capacitor 35 is disposed closer to the earth than the ammeter 13, but the capacitor 35 may be disposed on the opposite side, closer to the ground electrode 12 than the ammeter 13. In the latter case, it is preferable to use an ammeter 13 for AC current.

[0057] The provision of the capacitor 35 makes it possible to block DC current on the current path connecting the ground electrode 12 and the earth. This makes it possible to prevent DC current from flowing through the molten glass 3 between the molybdenum ground electrode 12 and the platinum alloy outflow pipe 14, or between the molybdenum ground electrode 12 and the platinum alloy component E.

[0058] The test for confirming the generation of platinum foreign matter will be described below with reference to FIG.

[0059] This test was conducted to confirm that insulation failure occurs in platinum components such as the outflow pipe 14 and component E and / or molybdenum components such as the ground electrode 12, causing current to flow between the platinum and molybdenum components via the molten glass 3, which may result in the generation of platinum foreign matter.

[0060] The equipment used in this test includes a crucible 36 containing molten glass 3, and a pair of electrodes 37 (anode) made of molybdenum and 38 (cathode) made of a platinum-rhodium alloy. The molten glass 3 is molten glass for an alkali-free glass substrate (product name: OA-11) manufactured by Nippon Electric Glass Co., Ltd. The crucible 36 is made of a refractory material (dense zircon). The electrodes 37 and 38 are connected to a DC power supply (1 V) and inserted into the crucible 36 so as to be immersed in the molten glass 3.

[0061] In this test, a state in which a current flows between electrode 37 and electrode 38 via molten glass 3 is created. This state reproduces a state in which a current flows between the platinum member and the molybdenum member via molten glass 3 due to poor insulation of the platinum member or the molybdenum member.

[0062] Using the above equipment, current was passed between electrode 37 and electrode 38 for 24 hours with molten glass 3 at a temperature of 1550°C, and platinum foreign matter (foreign matter made of an alloy of platinum and molybdenum) was produced around electrode 38 (cathode). Note that when the anode and cathode were interchanged, with electrode 37 made of a platinum-rhodium alloy serving as the anode and electrode 38 made of molybdenum serving as the cathode, when both the anode and cathode were made of a platinum-rhodium alloy, or when an AC power supply was used instead of a DC power supply, no platinum foreign matter was produced.

[0063] The results of this test show that when a current flows between a platinum member and a molybdenum member through molten glass, platinum inclusions can be generated.

[0064] Here, the following modifications can also be applied to the above embodiment.

[0065] In the above embodiment, the confirmation step P6 is executed when platinum contaminants are detected in the inspection step P5 and the current measured in the measurement step P3 is greater than the reference value. However, this is not limited to this, and the current measured in the measurement step P3 does not necessarily need to be taken into consideration when executing the confirmation step P6. In other words, the confirmation step P6 may be executed only when platinum contaminants are detected in the inspection step P5.

[0066] In the above embodiment, the case where the outflow pipe 14 or the component E of the transfer device 15 unintentionally comes into contact with another conductor has been described as an example, but this is not limited thereto. For example, a platinum or platinum alloy layer may be formed on the inner wall surface of the wall portion 19 of the melting tank 9 at a location that comes into contact with the molten glass 3, and this layer may unintentionally come into contact with another conductor. The method for manufacturing a glass article of the present disclosure may be applied to this layer as a platinum member. The platinum or platinum alloy layer may be formed, for example, from a thermal spray coating or a plate material. [Explanation of symbols]

[0067] 2. Glass raw materials 3 Molten Glass 4. Glass melting equipment 5. Glass Ribbon 7 Glass Plate 9 Dissolution tank 11 Current-carrying electrode 12 Ground electrode 13 Ammeter 14 Outlet Pipe 15 Transfer device 35 Capacitor E. Components of the transport device P1 Supply process P2 Melting process P3 Measurement process P4 Molding process P5 Inspection process P6 Confirmation process S Current heating area

Claims

1. a supply step of supplying glass raw materials to a melting tank provided in the glass melting apparatus; a melting step of heating and melting the glass raw materials supplied to the melting tank while electrically heating the molten glass contained in the melting tank; a forming step of forming a glass article from the molten glass that has flowed out of the melting tank; an inspection step of inspecting the glass article for defects; A method for manufacturing a glass article comprising: the glass melting apparatus further includes a molybdenum member in contact with the molten glass and a platinum member in contact with the molten glass; A method for manufacturing a glass article, characterized in that it further includes a confirmation step of confirming the occurrence of leakage current through the molten glass between the platinum member and the molybdenum member when platinum foreign matter containing a platinum component is detected in the glass article in the inspection step.

2. the molybdenum member is a ground electrode that is immersed in the molten glass in the melting tank and is grounded; further comprising a measuring step of measuring a current flowing through the ground electrode; 2. The method for manufacturing a glass article according to claim 1, wherein the confirmation step is carried out when platinum foreign matter is detected in the glass article in the inspection step and the current measured in the measurement step increases.

3. an electric heating region in which an electric electrode for electrically heating the molten glass is disposed is provided in the melting tank; the glass melting apparatus further includes a transfer device that transfers the molten glass flowed out of the melting tank; The method for manufacturing a glass article according to claim 2, wherein the ground electrode is disposed downstream of the electrically heated region and upstream of the transfer device in the flow direction of the molten glass.

4. the molybdenum member is a ground electrode that is immersed in the molten glass in the melting tank and is grounded; 2. The method for manufacturing a glass article according to claim 1, further comprising providing a capacitor on a current path connecting the molybdenum member to the ground.

5. 5. The method for producing a glass article according to claim 1, wherein the glass raw material is a raw material for alkali-free glass.

6. 5. The method for producing a glass article according to claim 1, wherein the glass article is a glass substrate for a display.

7. a melting tank that receives glass raw materials and contains molten glass obtained by melting the glass raw materials; a current-carrying electrode immersed in the molten glass in the melting tank and electrically heating the molten glass; A glass melting apparatus comprising: a molybdenum ground electrode immersed in the molten glass in the melting tank and grounded; a platinum member in contact with the molten glass; an ammeter for measuring a current flowing through the ground electrode; The glass melting apparatus further comprises:

8. a melting tank that receives glass raw materials and contains molten glass obtained by melting the glass raw materials; a current-carrying electrode immersed in the molten glass in the melting tank and electrically heating the molten glass; A glass melting apparatus comprising: a molybdenum ground electrode immersed in the molten glass in the melting tank and grounded; a platinum member in contact with the molten glass; a capacitor provided on a current path connecting the ground electrode and earth; The glass melting apparatus further comprises:

Images