JP7473872B2 - Glass article manufacturing method and glass article manufacturing device - Google Patents

Description

The present invention relates to a method for manufacturing a glass article and an apparatus for manufacturing a glass article.

The method for manufacturing glass articles includes a transfer step in which the molten glass produced in the melting furnace is transferred to a forming device using a transfer device, and a forming step in which the molten glass is formed into a glass article such as a sheet glass using the forming device (see, for example, Patent Document 1).

The above-mentioned transfer device has a plurality of electrodes spaced apart from one another along the transfer path from the upstream side to the downstream side, and the molten glass transferred inside the transfer device is heated by passing a current between these electrodes (see, for example, Patent Documents 2 and 3). The transfer device includes, for example, a fining tank, a stirring tank, and a condition adjustment tank (pot).

JP 2016-88754 A JP 2012-101970 A JP 2012-116693 A

The stirring tank included in the transfer device has a main body portion with a bottom that extends in the vertical direction, and an outlet portion provided at the bottom of the side wall of the main body portion to transfer the molten glass in the main body portion to the next process.

In such a configuration, the fluidity of the molten glass becomes insufficient around the bottom of the main body, and a glass stagnation layer is likely to occur around the bottom of the main body. This glass stagnation layer may contain foreign glass with a different composition from the molten glass that flows normally inside the main body. If such foreign glass becomes mixed into the molten glass that flows normally, it may cause defects in the glass article that is manufactured. Therefore, from the perspective of manufacturing high-quality glass articles, it is desirable to suppress the occurrence of a glass stagnation layer around the bottom of the main body.

The objective of the present invention is to prevent the occurrence of a glass stagnation layer around the bottom of a bottomed main body portion that extends in the vertical direction.

The present invention, which was invented to solve the above problems, is a method for manufacturing glass articles that includes a transfer step in which molten glass is transferred using a transfer device, the transfer device includes a main body portion with a bottom that extends in the vertical direction, an outlet portion provided at the bottom of the side wall of the main body portion to transfer the molten glass in the main body portion to the next step, a discharge portion provided at the bottom of the main body portion to discharge the molten glass in the main body portion, a first electrode provided at the bottom, and a second electrode provided at the discharge portion, and is characterized in that in the transfer step, electricity is passed between the first electrode and the second electrode to heat the discharge portion.

In this way, the temperature of the molten glass around the bottom of the main body is increased by heating the discharge section. As a result, the fluidity of the molten glass around the bottom of the main body is improved, and the occurrence of a stagnant layer of glass around the bottom of the main body can be suppressed.

In the above configuration, it is preferable that the transport device further includes a third electrode provided on the main body portion upstream of the first electrode, and that in the transport process, electricity is passed between the first electrode and the third electrode to heat the main body portion.

In this way, the molten glass inside the main body can be adjusted to a suitable temperature by heating the main body.

In the above configuration, when the maximum value of the first AC current supplied to the discharge section is A, the maximum value of the second AC current supplied to the main body section is B, and the maximum value of the third AC current flowing through the first electrode by current supply to the transport device is C, it is preferable to adjust the phase difference between the first AC current and the second AC current so that the third AC current satisfies the relationship ( ^A2 + ^B2 + AB) ^1/2 ≦C.

By adjusting the phase difference between the first AC current and the second AC current in this manner, it is possible to easily and reliably increase the magnitude of the third AC current flowing through the first electrode (common electrode) that is used both when supplying the first AC current to the discharge section and when supplying the second AC current to the main body section. Then, by adjusting the phase difference between the first AC current and the second AC current so that the third AC current satisfies the relationship of the above formula, the third AC current flowing through the first electrode becomes large, and the molten glass around the first electrode can be efficiently heated. Therefore, the occurrence of a glass stagnation layer around the bottom of the main body section can be more reliably suppressed.

In the above configuration, the glass transfer device preferably further includes a fourth electrode provided at the outflow section, and in the transfer process, electricity is passed between the first electrode and the fourth electrode to heat the outflow section.

In this way, the temperature of the molten glass inside the outlet can be adjusted to a suitable level by heating the outlet.

In the above configuration, when the maximum value of the first AC current supplied to the discharge section is A, the maximum value of the second AC current supplied to the main body section is B, the maximum value of the third AC current flowing through the first electrode by current supply to the transport device is C, and the maximum value of the fourth AC current supplied to the discharge section is ^D , it is preferable to adjust the phase difference among the first AC current, the second AC current, and the fourth AC current so that the third AC current satisfies the relationship ( ^A2 + ^B2 + ^D2 + AB + 2AD + BD)1/2 ≦C.

By adjusting the phase difference between the first AC current, the second AC current, and the fourth AC current in this manner, it is possible to easily and reliably increase the magnitude of the third AC current flowing through the first electrode (common electrode) used when supplying the first AC current to the discharge section, when supplying the second AC current to the main body section, and when supplying the fourth AC current to the discharge section. Then, by adjusting the phase difference between the first AC current, the second AC current, and the fourth AC current so that the third AC current satisfies the relationship of the above formula, the third AC current flowing through the first electrode becomes large, and the molten glass around the first electrode can be efficiently heated. Therefore, the generation of a glass stagnation layer around the bottom of the main body section can be more reliably suppressed.

In the above configuration, it is preferable that the transfer device includes a mixing tank having a main body portion, a discharge portion, and an outflow portion.

The present invention, which was invented to solve the above problems, is a glass article manufacturing apparatus including a transfer device for transferring molten glass, the transfer device being characterized by including a main body portion with a bottom extending in the vertical direction, an outlet portion provided at the bottom of the side wall of the main body portion for transferring the molten glass in the main body portion to the next process, an outlet portion provided at the bottom of the main body portion for discharging the molten glass in the main body portion, a first electrode provided at the bottom portion, a second electrode provided at the outlet portion, and a power source that supplies current to the outlet portion located between the first electrode and the second electrode.

In this way, you can achieve the same effects as the corresponding configuration described above.

The present invention can suppress the occurrence of a glass stagnation layer around the bottom of the main body.

1 is a side view showing a glass article manufacturing apparatus according to a first embodiment of the present invention. 1 is a cross-sectional view showing the periphery of a stirring tank of a glass article manufacturing apparatus according to a first embodiment of the present invention. FIG. 5 is a cross-sectional view showing the periphery of a stirring tank of a glass article manufacturing apparatus according to a second embodiment of the present invention. FIG. 11 is a cross-sectional view showing the periphery of a stirring tank of a glass article manufacturing apparatus according to a third embodiment of the present invention. 13 is a graph showing a change in a third AC current according to an embodiment of the present invention.

Embodiments of the present invention will be described below with reference to the attached drawings. Note that in each embodiment, corresponding components are given the same reference numerals, and duplicated descriptions may be omitted. When only a portion of a configuration is described in each embodiment, the configuration of another embodiment previously described may be applied to the other portions of the configuration. In addition to the combinations of configurations explicitly stated in the description of each embodiment, configurations of multiple embodiments may be partially combined together even if not explicitly stated, provided that there is no particular problem with the combination.

First Embodiment
As shown in Fig. 1, the first embodiment illustrates an apparatus for manufacturing a glass article and a method for manufacturing a glass article. The apparatus for manufacturing a glass article according to this embodiment includes, in order from the upstream side to the downstream side in the transport direction of the molten glass Gm, a melting furnace 1, a transport device 2, and a molding device 3. The method for manufacturing a glass article according to this embodiment includes, in order, a melting process, a transport process, and a molding process. The method for manufacturing a glass article will be described together with the configuration of the apparatus for manufacturing a glass article.

The melting furnace 1 is used to carry out a melting process for continuously forming molten glass Gm. The heating method for the molten glass Gm (or glass raw material) in the melting furnace 1 can be, for example, a method of heating only by electrical heating (all-electric melting method), a method of heating only by combustion of gas fuel, or a method of heating using both electrical heating and combustion of gas fuel.

In this embodiment, the molten glass Gm is made of alkali-free glass. The alkali-free glass contains, for example, in mass %, SiO ₂ 50-70%, Al ₂ O ₃ 12-25%, B ₂ O ₃ 0-12%, Li ₂ O + Na ₂ O + K ₂ O (total amount of Li ₂ O, Na ₂ O and K ₂ O) 0-less than 1%, MgO 0-8%, CaO 0-15%, SrO 0-12%, and BaO 0-15% as a glass composition. The electrical resistivity of the molten glass Gm made of alkali-free glass is generally high, and is, for example, 100 Ω·cm or more at a heating temperature of 1500° C. in the melting furnace 1.

The molten glass Gm is not limited to alkali-free glass, but may be, for example, soda glass, soda lime glass, borosilicate glass, aluminosilicate glass, alkali-containing glass, etc.

The transfer device 2 is used to carry out a transfer process in which the molten glass Gm is transferred from the melting furnace 1 to the forming device 3, and is composed of a transfer tube having an internal transfer path (space) for transferring the molten glass Gm. Here, the term transfer tube includes not only those having a tubular structure, but also those having a tank-like (container-like) structure.

In this embodiment, the transfer device 2 includes a fining tank 4, a stirring tank 5, a conditioning tank (pot) 6, and connecting pipes 7 to 10 that connect these components. In other words, the transfer process includes a fining process, a stirring process, and a conditioning process.

The fining tank 4 is used to carry out the fining process in which the molten glass Gm supplied from the melting furnace 1 is clarified (removed bubbles) by the action of a fining agent, etc.

The stirring tank 5 is used to carry out the homogenization process in which the molten glass Gm clarified in the fining tank 4 is stirred and homogenized using stirring blades (stirrer) 5a.

The condition adjustment tank 6 is used to carry out a condition adjustment process in which the molten glass Gm stirred in the stirring tank 5 is adjusted to a state suitable for forming. The condition adjustment tank 6 is a tank without mechanical stirring means such as stirring blades, and is located at the most downstream side when the transfer device 2 has multiple tanks as described above. In other words, the condition adjustment tank 6 is a tank that adjusts the flow rate, viscosity, etc. of the molten glass Gm immediately before the forming device 3.

The connecting pipes 7 to 10 are configured as tubular bodies (e.g., cylindrical bodies) made of, for example, platinum or a platinum alloy, and transfer the molten glass Gm in a lateral direction (approximately horizontal direction). In this embodiment, the connecting pipe 7 located at the most upstream part of the transfer device 2 and the connecting pipe 9 connecting the stirring tank 5 and the condition adjustment tank 6 are inclined so that the downstream side is located higher than the upstream side.

The forming device 3 is for carrying out a forming process in which the molten glass Gm transferred by the transfer device 2 is formed into a desired shape. In this embodiment, the forming device 3 is equipped with a forming body that continuously forms a glass ribbon G from the molten glass Gm by the overflow downdraw method.

The molding device 3 may also be a device that performs other known molding methods, such as the slot downdraw method, or the float method.

In the case of the overflow downdraw method, the molten glass Gm supplied to the forming device 3 overflows from a groove formed at the top of the forming device 3, flows along both sides of the wedge-shaped cross section of the forming device 3, and joins at the bottom end, thereby continuously forming a plate-shaped glass ribbon G. The formed glass ribbon G is gradually cooled (annealed) and cooled, and then cut to a predetermined size to produce plate glass as a glass product.

The produced sheet glass has a thickness of, for example, 0.01 to 10 mm (preferably 0.1 to 3 mm) and is used as a substrate or protective cover for panel displays such as liquid crystal displays and organic electroluminescence displays, organic electroluminescence lighting, solar cells, etc.

As shown in FIG. 2, the mixing tank 5 has a main body 11, an inlet 12, an outlet 13, and a discharge 14.

The main body 11 is a cylindrical body with a bottom that extends in the vertical direction and has an agitator blade 5a inside. The agitator blade 5a is configured to be able to agitate the molten glass Gm in the main body 11 by rotating it around its axis.

The main body 11 has an inlet 15 provided on the upper side wall, an outlet 16 provided on the lower side wall, and an outlet 17 provided at the bottom.

A cylindrical inlet 12 extending horizontally is connected to the inlet 15. A connecting pipe 8 is connected to the upstream end of the inlet 12. In other words, the molten glass Gm is transferred from the previous process (in this embodiment, the fining tank 4) into the main body 11 through the inlet 12.

A cylindrical outflow section 13 extending horizontally is connected to the outflow port 16. A connection pipe 9 is connected to the downstream end of the outflow section 13. In other words, the molten glass Gm in the main body section 11 is transferred to the next process (in this embodiment, the condition adjustment tank 6) through the outflow section 13.

A cylindrical discharge section (drain) 14 extending in the vertical direction is connected to the discharge port 17. When manufacturing a glass article, the discharge section 14 is blocked by solidified glass Gx that has solidified within the discharge section 14. On the other hand, when discharging the molten glass Gm, the solidified glass Gx within the discharge section 14 is heated to soften and flow, and the molten glass Gm within the main body section 11 is discharged to the outside through the discharge section 14.

A first electrode 18 is provided at the bottom (lower end) of the main body 11, and a second electrode 19 is provided at the lower end of the discharge section 14. The position of the second electrode 19 may be anywhere in the discharge section 14, so long as it is below the first electrode 18. However, from the viewpoint of expanding the area heated by energizing the discharge section 14, it is preferable to provide the second electrode 19 at the lower end of the discharge section 14.

Each electrode 18, 19 is made of a ring-shaped flange portion made of, for example, platinum or a platinum alloy, and is joined to the outer circumferential surface of the stirring tank 5 at a predetermined position by welding or the like. Although not shown in the figure, each electrode 18, 19 further includes an extraction electrode (made of, for example, platinum or a platinum alloy) for connecting a current supply path 20 described later, and a cooling mechanism (for example, water cooling).

Between the first electrode 18 and the second electrode 19, a first current supply path 20 is provided for passing electricity through the discharge portion 14 located between these electrodes 18, 19. The first current supply path 20 is provided with a first power source (voltage source) 21 that applies a voltage between the first electrode 18 and the second electrode 19. By applying a voltage from the first power source 21, a first AC current i1 is supplied to the discharge portion 14.

In this way, the temperature of the molten glass Gm around the bottom of the main body 11 is increased by electrically heating the discharge section 14. As a result, the fluidity of the molten glass Gm around the bottom of the main body 11 is improved, and the occurrence of a glass stagnation layer around the bottom of the main body 11 can be suppressed.

The discharge section 14 is electrically heated during the manufacture of such glass articles to the extent that the solidified glass Gx in the discharge section 14 does not soften and flow, that is, to the extent that the molten glass Gm does not flow out of the discharge section 14. For example, the solidified glass Gx in the discharge section 14 may be electrically heated so that its temperature is below its softening point. On the other hand, when the molten glass Gm in the main body section 11 is discharged to the outside through the discharge section 14, the first AC current i1 supplied by the first power source 21 is made larger than that during the manufacture of the glass article, causing the solidified glass Gx in the discharge section 14 to soften and flow.

Second Embodiment
3, the second embodiment illustrates a modified example of the stirring tank 5. Since the basic configuration of the stirring tank 5 is similar to that of the first embodiment, the following description will focus on the differences from the first embodiment.

In this embodiment, a third electrode 22 is provided at the upper end of the main body 11. The position of the third electrode 22 may be anywhere in the main body 11 as long as it is upstream of the first electrode 18. However, from the viewpoint of expanding the heating area by passing electricity through the main body 11, the position of the third electrode 22 is preferably above the liquid surface Gs of the molten glass Gm in the main body 11, and more preferably at the upper end of the main body 11.

Between the first electrode 18 and the third electrode 22, a second current supply path 23 is provided for passing electricity through the main body 11 located between these electrodes 18, 22. The second current supply path 23 is provided with a second power source (voltage source) 24 that applies a voltage between the first electrode 18 and the third electrode 22. By applying a voltage from the second power source 24, a second AC current i2 is supplied to the main body 11. The first electrode 18 is a common electrode used in both the first current supply path 20 and the second current supply path 23.

In this way, the molten glass Gm in the main body 11 can be adjusted to a suitable temperature by electrically heating the main body 11. Therefore, even if the magnitude of the first AC current i1 supplied to the discharge section 14 by the first power source 21 is reduced, the occurrence of a glass stagnation layer around the bottom of the main body 11 can be reliably suppressed.

Furthermore, in this embodiment, the stirring tank 5 is provided with a phase adjustment unit 25 that adjusts the phase difference θ between the first AC current i1 and the second AC current i2. The phase adjustment unit 25 is connected to the first power source 21 and the second power source 24. The first power source 21, the second power source 24, and the phase adjustment unit 25 are configured, for example, by a three-phase AC power source. In the case of a three-phase AC power source, the phase difference θ between the first AC current i1 and the second AC current i2 can be adjusted by appropriately changing the connection terminals (for example, TR, RT, RS, SR, etc.).

For example, when the maximum value of the first AC current i1 is A, the maximum value of the second AC current i2 is B, and the maximum value of the third AC current i3 flowing through the first electrode 18 by the supply of the first AC current i1 and the second AC current i2 is C, the phase adjustment unit 25 is configured to adjust the phase difference θ between the first AC current i1 and the second AC current i2 so that the third AC current i3 satisfies the relationship in the following formula (1). That is, in the manufacturing method of a glass article, in the transporting step (in this embodiment, the stirring step included in the transporting step), the phase difference θ between the first AC current i1 and the second AC current i2 is adjusted so that the third AC current i3 satisfies the relationship in the following formula (1).
( ^A2 + ^B2 +AB) ^1/2 ≦C... (1)

Here, i1 = A sin(ωt + θ), i2 = B sinωt, and i3 = i2 - i1. Here, ω is the angular velocity, t is the time, and θ is the phase difference of the first AC current i1 relative to the second AC current i2. The phase difference θ is based on the phase of the second AC current i2, but is not limited to this. Since the direction of each current is defined in FIG. 3, if the base of the first electrode 18 (the junction with the main body 11) is considered to be the branch point, the current flowing into the branch point is i2, and the current flowing out from the branch point is i1 and i3. Therefore, according to Kirchhoff's law, the third AC current i3 is expressed as "i2 - i1" as above.

In this case, the third AC current i3 can be expressed by the following equation (2) according to the addition theorem of trigonometric functions.
i3 = B sin ωt - A sin (ωt + θ)
= (B - A cos θ) sin ωt - A sin θ cos ωt ... (2)

Furthermore, the formula (2) can be expressed as the following formula (2)' using the composition formula of trigonometric functions.
i3 = {(B - A cos θ) ² + A ² sin ² θ} ^1/2 sin (ωt - α)
= (A ² + B ² - 2AB cos θ) ^1/2 sin (ωt - α) ... (2)'
Here, sin α=A sin θ/(A ² +B ² −2AB cos θ) ^1/2 , and cos α=(B−A cos θ)/(A ² +B ² −2AB cos θ) ^1/2 .

Since −1≦sin(ωt−α)≦1, formula (2)′ indicates a maximum value when sin(ωt−α) = 1. That is, the maximum value C of the third AC current i3 is expressed by the following formula (3).
C = (A ² + B ² - 2AB cos θ) ^1/2 ... (3)

In this way, by adjusting the phase difference θ between the first AC current i1 and the second AC current i2, the magnitude of the third AC current i3 flowing through the first electrode 18 can be easily and reliably adjusted. If the phase difference θ between the first AC current i1 and the second AC current i2 is adjusted so that the third AC current i3 satisfies the relationship of the above formula (1), the third AC current i3 flowing through the first electrode 18 becomes large, and the first electrode 18 and the bottom periphery of the main body 11 can be efficiently heated. This improves the flow of molten glass Gm around the bottom of the main body 11. In other words, the occurrence of a glass stagnation layer around the bottom of the main body 11 can be more reliably suppressed.

The phase adjustment unit 25 is preferably configured to adjust the phase difference θ between the first AC current i1 and the second AC current i2 so as to satisfy the relationship of the following equation (4).
A + B = C ... (4)

Here, the phase difference θ is preferably 120° to 240° (or -120° to -240°), and more preferably 180° (or -180°). Note that the left side of equation (1) is the value of equation (3) when θ = 120° (or -120°), and the left side of equation (4) is the value of equation (3) when θ = 180° (or -180°).

The maximum value A of the first AC current i1 and the maximum value B of the second AC current i2 may be the same value, but are preferably different values (e.g., B>A). In addition, at least one of the maximum value A of the first AC current i1 and the maximum value B of the second AC current i2 may be adjusted together with the phase difference θ so as to satisfy the relationship of the above formula (1) or (4).

Third Embodiment
4, the third embodiment illustrates a modified example of the stirring tank 5. Since the basic configuration of the stirring tank 5 is similar to that of the second embodiment, the following description will focus on the differences from the second embodiment.

In this embodiment, a fourth electrode 26 is provided at the outflow section 13 (in the illustrated example, at the downstream end of the outflow section 13).

Between the first electrode 18 and the fourth electrode 26, a third current supply path 27 is provided for passing electricity through the outflow portion 13 located between these electrodes 18, 26. The third current supply path 27 is provided with a third power source (voltage source) 28 that applies a voltage between the first electrode 18 and the fourth electrode 26. By applying a voltage from the third power source 28, a fourth AC current i4 is supplied to the outflow portion 13. The first electrode 18 is a common electrode used in all of the first current supply path 20, the second current supply path 23, and the third current supply path 27.

In this way, the molten glass Gm in the outflow section 13 can be adjusted to a suitable temperature by electrically heating the outflow section 13. Therefore, even if the magnitude of the first AC current i1 supplied to the outflow section 14 by the first power source 21 is reduced, the occurrence of a glass stagnation layer around the bottom of the main body section 11 can be reliably suppressed.

Furthermore, in this embodiment, the phase adjustment unit 25 is connected to the first power source 21, the second power source 24, and the third power source 28, and is configured to adjust the phase difference θ1 between the first AC current i1 and the second AC current i2, and the phase difference θ2 between the second AC current i2 and the fourth AC current i4. The first power source 21, the second power source 24, the third power source 28, and the phase adjustment unit 25 are configured, for example, by a three-phase AC power source.

For example, the phase adjustment unit 25 is configured to adjust the phase difference θ1 between the first AC current i1 and the second AC current i2 and the phase difference θ2 between the second AC current i2 and the fourth AC current i4 so that the third AC current i3 satisfies the relationship of the following formula (5) when the maximum value of the first AC current i1 is A, the maximum value of the second AC current i2 is B, the maximum value of the third AC current i3 is C, and the maximum value of the fourth AC current i4 is D. That is, in the manufacturing method of a glass article, in the transport step (in the present embodiment, the stirring step included in the transport step), the phase difference θ1 between the first AC current i1 and the second AC current i2 and the phase difference θ2 between the second AC current i2 and the fourth AC current i4 are adjusted so that the third AC current i3 satisfies the relationship of the following formula (5).
( ^A2 + ^B2 + ^D2 +AB+2AD+BD) ^1/2 ≦C... (5)

Here, i1 = A sin(ωt + θ1), i2 = B sinωt, i4 = D sin(ωt + θ2), and i3 = i2 - i1 - i4. Note that ω is the angular velocity, t is time, θ1 is the phase difference of the first AC current i1 relative to the second AC current i2, and θ2 is the phase difference of the fourth AC current i4 relative to the second AC current i2. The phase differences θ1 and θ2 are based on the phase of the second AC current i2, but are not limited to this. The third AC current i3 is a current that flows through the first electrode 18 due to the supply of the first AC current i1, the second AC current i2, and the fourth AC current i4.

In this case, the third AC current i3 can be expressed by the following equation (6) according to the addition theorem of trigonometric functions.
i3 = B sin ωt - A sin (ωt + θ1) - D sin (ωt + θ2)
= (B - A cos θ1 - D cos θ2) sin ωt
−(A sin θ1 + D sin θ2) cos ωt ... (6)

Furthermore, the formula (6) can be expressed as the following formula (6)' using the composition formula of trigonometric functions.
i3 = {(B - A cos θ1 - D cos θ2) ²
+(A sin θ1 + D sin θ2) ² } ^1/2 sin(ωt-α) ... (6)'
However, if r = {(B - A cos θ1 - D cos θ2) ² + (A sin θ1 + D sin θ2) ² } ^1/2 , then sin α = (A sin θ1 + D sin θ2)/r and cos α = (B - A cos θ1 - D cos θ2)/r.

Since −1≦sin(ωt−α)≦1, equation (6)′ indicates a maximum value when sin(ωt−α) = 1. That is, the maximum value C of the third AC current i3 is expressed by the following equation (7).
C = {(B - A cos θ1 - D cos θ2) ²
+ (A sin θ1 + D sin θ2) ² } ^1/2 ... (7)

In this way, by adjusting the phase differences θ1, θ2 between the first AC current i1, the second AC current i2, and the fourth AC current i4, the magnitude of the third AC current i3 flowing through the first electrode 18 can be easily and reliably adjusted. If the phase differences θ1, θ2 between the first AC current i1, the second AC current i2, and the fourth AC current i4 are adjusted so that the third AC current i3 satisfies the relationship of the above formula (5), the third AC current i3 flowing through the first electrode 18 becomes large, and the first electrode 18 and the bottom periphery of the main body 11 can be efficiently heated. This makes it possible to more reliably suppress the generation of a glass stagnation layer around the bottom periphery of the main body 11.

It is preferable that the phase adjustment unit 25 is configured to adjust the phase differences θ1, θ2 between the first AC current i1, the second AC current i2, and the fourth AC current i4 so as to satisfy the relationship of the following equation (8).
A + B + D = C ... (8)

Here, the phase differences θ1 and θ2 are preferably 120°≦θ≦240° (or -120°≧θ≧-240°), and more preferably 180° (or -180°). Note that the left side of equation (5) is the value of equation (7) when θ1=θ2=120° (or -120°), and the left side of equation (8) is the value of equation (7) when θ1=θ2=180° (or -180°).

The maximum value A of the first AC current i1, the maximum value B of the second AC current i2, and the maximum value D of the fourth AC current i4 may be the same value, but are preferably different values (e.g., B>D>A). In addition, at least one of the maximum value A of the first AC current i1, the maximum value B of the second AC current i2, and the maximum value D of the fourth AC current i4, together with the phase differences θ1 and θ2, may be adjusted so as to satisfy the relationship of the above formula (5) or (8).

The present invention is not limited to the configuration of the above embodiment, nor is it limited to the above-mentioned effects. Various modifications of the present invention are possible without departing from the gist of the present invention.

The electric heating method described in the above embodiment can also be applied to a mixing vessel having multiple body parts connected together. In this case, it is preferable to connect the upper part of one of two adjacent body parts to the lower part of the other with a connecting tube.

In the above embodiment, an electrode may be further provided at the inlet of the mixing vessel, and electricity may be further passed between the electrode at the inlet and a third electrode at the main body. In this way, heating of the inlet and the upper end of the main body is promoted.

The electrical heating method described in the above embodiment can be similarly applied to parts of the transfer device other than the mixing tank.

In the above embodiment, the glass article formed by the forming device is a plate glass, but the present invention is not limited to this. The glass article formed by the forming device may be, for example, a glass roll in which a glass film is wound into a roll, an optical glass part, a glass tube, a glass block, glass fiber, etc., and may be of any shape.

The following describes an embodiment of the present invention, but the present invention is not limited to this embodiment.

In this example, the third AC current i3 and its maximum value C change when the phase difference θ1 between the first AC current i1 and the second AC current i2 and the phase difference θ2 between the second AC current i2 and the fourth AC current i4 are changed in the stirring tank 5 shown in FIG. 4. The maximum value A of the first AC current i1 is 500 A, the maximum value B of the second AC current i2 is 3000 A, and the maximum value D of the fourth AC current i4 is 2000 A. The third AC current i3 and its maximum value C in this case can be calculated from the above formulas (6) and (7). The results are shown in FIG. 5 and Table 1.

5 and Table 1, if the phase difference θ1 between the first AC current i1 and the second AC current i2 and the phase difference θ2 between the second AC current i2 and the fourth AC current i4 are not properly managed, the maximum value C of the third AC current i3 will be small as in Examples 4 and 5, and the heating efficiency of the first electrode 18 and its surroundings will decrease. In contrast, if the phase difference θ1 between the first AC current i1 and the second AC current i2 and the phase difference θ2 between the second AC current i2 and the fourth AC current i4 are properly managed, the maximum value C of the third AC current i1 will be large as in Examples 1 to 3, and the first electrode 18 and its surroundings can be efficiently heated. Here, in Examples 1 and 2, the maximum value C of the third AC current i1 satisfies the relationship of the above formula (5), and in Example 3, the maximum value C of the third AC current i1 satisfies the relationship of the above formula (8).

Reference Signs List 1 Melting furnace 2 Transport device 3 Molding device 4 Refining tank 5 Stirring tank 6 Conditioning tank 11 Main body 12 Inlet section 13 Outlet section 14 Discharge section 18 First electrode 19 Second electrode 20 First current supply path 21 First power source 22 Third electrode 23 Second current supply path 24 Second power source 25 Phase adjustment section 26 Fourth electrode 27 Third current supply path 28 Third power source G Glass ribbon Gm Molten glass i1 First AC current i2 Second AC current i3 Third AC current i4 Fourth AC current

Claims (7)

A method for manufacturing a glass article, comprising a transfer step of transferring molten glass using a transfer device, the transfer device comprising: a main body portion with a bottom extending in a vertical direction; an outlet portion provided in a lower portion of a side wall of the main body portion for transferring the molten glass in the main body portion to a next step; a discharge portion provided in a bottom portion of the main body portion for discharging the molten glass in the main body portion; a first electrode provided in the bottom portion; and a second electrode provided in the discharge portion,
The method for manufacturing a glass article, characterized in that in the transporting step, a current is applied between the first electrode and the second electrode to heat the discharge portion , thereby increasing the temperature of the molten glass at the bottom portion . the transport device further includes a third electrode provided on the main body portion upstream of the first electrode;
The method for manufacturing a glass article according to claim 1 , wherein in the transporting step, a current is applied between the first electrode and the third electrode to heat the main body portion. When a maximum value of a first AC current supplied to a portion of the discharge portion located between the first electrode and the second electrode is A, a maximum value of a second AC current supplied to a portion of the main body portion located between the first electrode and the third electrode is B, and a maximum value of a third AC current flowing through the first electrode due to a current supply to the transport device is C,
The third alternating current is
( ^A2 + ^B2 +AB) ^1/2 ≦C
The method for manufacturing a glass article according to claim 2 , further comprising adjusting a phase difference between the first AC current and the second AC current so as to satisfy the following relationship: The transport device further includes a fourth electrode provided at the outlet portion,
The method for manufacturing a glass article according to claim 2 , wherein in the transporting step, a current is applied between the first electrode and the fourth electrode to heat the outflow portion. Let A be the maximum value of a first AC current supplied to a portion of the discharge portion located between the first electrode and the second electrode , B be the maximum value of a second AC current supplied to a portion of the main body portion located between the first electrode and the third electrode , C be the maximum value of a third AC current flowing through the first electrode due to current supply to the transport device, and D be the maximum value of a fourth AC current supplied to a portion of the outlet portion located between the first electrode and the fourth electrode ,
The third alternating current is
( ^A2 + ^B2 + ^D2 +AB+2AD+BD) ^1/2 ≦C
The method for producing a glass article according to claim 4 , further comprising adjusting a phase difference between the first AC current, the second AC current, and the fourth AC current so as to satisfy the following relationship: The method for manufacturing a glass article according to any one of claims 1 to 5, wherein the transfer device comprises a stirring tank having the main body, the discharge section, and the outflow section. A glass article manufacturing apparatus including a transfer device that transfers molten glass,
The transfer device includes:
A main body portion with a bottom extending in the vertical direction;
an outflow portion provided at a lower portion of a side wall of the main body portion for transporting the molten glass in the main body portion to a next process;
a discharge portion provided at a bottom of the main body portion for discharging the molten glass in the main body portion;
An electric heating device is provided,
The electric heating device includes a first electrode provided on the bottom portion, a second electrode provided on the discharge portion, and a power source that supplies current to a portion of the discharge portion located between the first electrode and the second electrode ,
The glass article manufacturing apparatus is characterized in that the electric heating device is configured to pass electric current between the first electrode and the second electrode to heat the discharge section, thereby raising the temperature of the molten glass at the bottom.

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