JPS6121169B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a direct current heating melting furnace for glass and a method for melting the same. In particular, the present invention relates to a directly energized glass melting furnace of the cold-top type having electrically opposed rod-shaped electrodes vertically inserted into the molten glass in the furnace from the hearth, and a method for melting the glass.

As is known, as glass becomes hotter, its electrical resistance decreases and it becomes a good conductor. By directly passing electricity through an electrode, the molten glass itself becomes an electrical resistance heating element, and the generated Joule heat is utilized. A method of melting and refining glass raw materials has been conventionally used. Recently, the so-called cold-top type melting system, in which the upper surface of the molten glass in the melting tank is covered with a glass raw material batch, has been attracting attention because of its advantages such as high thermal efficiency and low environmental pollution.

This cold-top type glass melting method by direct current heating is based on the method of supplying electric power to the molten glass in the melting furnace. A method of supplying electric power between electrically opposing rod-shaped electrodes inserted horizontally into the molten glass in the furnace from the wall, and a furnace as disclosed in Japanese Patent Publication No. 28-994 or Japanese Patent Publication No. 43-12886. A typical method is to supply power between electrically opposing rod-shaped electrodes inserted vertically into the molten glass in the furnace from the floor.

By the way, in the latter type of electrification heating and melting using a rod-shaped electrode inserted vertically into the molten glass in the furnace from the hearth, intense convection of the molten glass in the vertical direction centering on the electrode occurs due to the Joule heat generated. Convection propagates heat to the frit batch layer on the top surface of the molten glass and refines the molten glass. This is a major feature as well as an advantage.

However, one of the problems with the latter method of melting furnaces is that the glass must be melted while maintaining a layer of frit powder with a constant thickness on the top surface of the molten glass to prevent the dissipation of heat and harmful gases. For the molten layer, there are optimal conditions for the height of the rod-shaped electrode inserted perpendicularly from the hearth, the amount of power supplied, and the amount of molten glass pulled up, so if these are removed, several problems will occur. This can be mentioned. This problem can be solved if the amount of molten glass pulled up is always kept constant, but in actual production, the amount of pulled up must be changed every time the molded product is changed. In order to change the pulling amount from the melting furnace, in principle, it is sufficient to increase the amount of power supplied as the pulling amount increases, or decrease it as the pulling amount decreases.
In reality, the permissible range is narrow at best for the following reasons.
It is about 20-30%. In other words, if the power supply is increased as the amount of pull is increased, the curve c in Figure 4
As shown in , the vertical temperature distribution of the molten glass in the melting tank at that time is generally higher than the temperature distribution curve b in the case of the optimum pulling amount, and the temperature increase in the high temperature range significantly accelerates the melting of the furnace material. especially throat 10
This results in erosion of the furnace material and shortens the life of the furnace.

On the other hand, if the power supply is reduced as the pulling amount decreases, the temperature distribution curve as shown in curve a in Figure 4 will inevitably cause a decrease in the temperature of the entire molten glass in the furnace, resulting in a decrease in fining. On the other hand, if the power supply amount is increased in order to prevent the deterioration of this fining effect, the thickness of the frit batch layer on the upper surface of the molten glass becomes thinner, resulting in a significant decrease in thermal efficiency.

As a method for solving the above-mentioned problems caused by variations in the amount of molten glass pulled up, as disclosed in Japanese Patent Publication No. 28-994, the insertion height of a rod-shaped electrode inserted perpendicularly from the hearth can be adjusted appropriately. There are several methods of adjusting or positioning several groups of vertical electrodes with their upper ends at different levels in the molten glass, which maintain a sliding fit between the electrode insertion holes in the hearth and the insertion electrodes. It is extremely difficult to do so, and it is difficult to control the temperature of the molten glass in layers from the hearth, so no satisfactory solution has been found, and as a result, the only way to solve this problem is to maintain a constant pulling amount, as mentioned above. The inability to reduce fluctuations in the pulling amount, especially the inability to reduce the fluctuation, has been a major drawback of direct current heating melting furnaces of the cold top type with vertical electrode insertion.

The present invention provides a directly energized glass melting furnace and a method for melting glass, which solves the above-mentioned problems.

Already, the present invention relates to a cold-top glass direct current heating melting furnace, in which a large number of electrodes are inserted perpendicularly into the molten glass in the furnace from the hearth of the melting tank into a plurality of electrode groups each having a different height. At the same time, each electrode group is constructed so that the substantial electrode portions do not overlap in the vertical direction, and the vertical temperature distribution of the molten glass in the melting tank is controlled at each height without losing the convection effect of the rod-shaped electrodes. This allows for free control by adjusting the amount of power supplied to the rod-shaped electrode.

Hereinafter, the present invention will be explained in detail according to embodiments shown in the drawings.

Embodiment As shown in FIG. 1, a melting furnace 1 includes a melting tank 9 for melting and clarifying batches of frit, a working tank 11 for drawing out molten glass 6, a throat 10 connecting these at the bottom, and a lower rod-shaped electrode 3 inserted vertically from the hearth 2 of the tank 9;
Similarly, a rod-shaped electrode 4 at a higher level is inserted perpendicularly from the hearth 2, and the rod-shaped electrode 4 forming this higher-level electrode group corresponds to the electrode portion _l1 of the rod-shaped electrode 3 forming the lower electrode group. are electrically insulated by a fireproof insulator 8, and the upper part ( _l2 =l- _l1 ) thereof substantially constitutes an electrode.

FIG. 3 shows a power supply device, which is provided so that alternating current power can be distributed between opposing electrodes as appropriate power by transformers 20 and 20'. It goes without saying that by operating the switches 21 and 22, it is possible to supply power to either or both of the lower electrodes 3 and 3' or the higher electrodes 4 and 4'.

Next, a method for melting glass in the melting furnace 1 according to the present invention will be explained.

The frit batch is flatly thrown onto the upper surface of the molten glass from the upper opening of the melting tank 9 following the amount of the molten glass 6 pulled up, thereby forming the frit batch layer 7 . When the amount of molten glass 6 pulled up is the average optimum amount for the melting capacity of the melting tank 9, approximately the same amount of power is supplied between the lower electrodes 3 and 3' and between the higher electrodes 4 and 4'. be done. The temperature distribution in the vertical direction in the melting tank at this time is like the temperature curve d shown in FIG. 5 (equal to the curve b in FIG. 4).

Regarding the case where the amount of molten glass 6 pulled up is reduced due to production reasons, in this case the amount of glass raw material batch input naturally decreases. At this time, if power is continued to be supplied under the same conditions as above, the temperature of the molten glass in the melting tank 9 will rise and the thickness of the frit batch layer 7 will decrease. Therefore, in order to prevent this, the amount of power supplied between the higher electrodes 4 and 4' is reduced, and the thickness of the frit batch layer 7 is maintained constant so as not to increase the temperature of the upper part of the molten glass. At this time, the vertical temperature distribution of the molten glass in the melting tank 9 is as shown in the temperature curve e shown in FIG. At this time, if a problem arises in clarification due to a drop in the temperature at the upper part of the melting tank 9, complete clarification is maintained by increasing the amount of power supplied between the lower electrodes 3 and 3'.

On the other hand, when the amount of molten glass 6 to be pulled up increases due to production reasons, the amount of frit batches added increases accordingly, which lowers the temperature of the molten glass in the melting tank 9 and lowers the temperature of the frit batch layer 7. Thickness increases and fining problems arise. In order to prevent this, the amount of power supplied between the higher electrodes 4 and 4' is increased.

Therefore, although the temperature in the upper layer of the melting tank 9 increases, the amount of power supplied between the lower electrodes 3 and 3' can be reduced to a level that does not cause problems with fining, and the amount of power supplied can be reduced. By increasing the temperature, the temperature reaches the lower part of the melting tank 9 as shown by the curve b in FIG. 4, and there is no fear that the furnace material, especially the throat 10 material, will be significantly invaded as in the conventional method. At this time, the temperature distribution of the molten glass in the melting tank 9 in the vertical direction is as shown by a temperature curve f shown in FIG.

With the above operating method, the conventional method using a rod-shaped electrode of a constant height could only reduce the fluctuation of glass melting amount by 25%, but in the example of the present invention, even when the fluctuation was reduced by 40%, it was completely reduced. We were able to pull up the clarified molten glass.

As explained above, the glass direct current heating melting furnace and its melting method of the present invention are capable of keeping the thickness of the frit batch layer on the top surface of the molten glass constant even when the amount of molten glass pulled up varies. It is easy to use, it is possible to suppress the rise in temperature of molten glass, it is possible to widen the range of variation in the amount of pulled glass without deteriorating the quality of pulled glass, and it is possible to suppress the rise in temperature of molten glass. It has outstanding effects such as extending life.

In the above embodiment, the electrodes were divided into two groups, high and low, but if necessary,
It goes without saying that a multi-tiered electrode group can be constructed with rod-shaped electrodes whose upper portions substantially constitute electrodes except for the middle or lower substantial electrode portions that have different heights.

[Brief explanation of the drawing]

Fig. 1 is an explanatory longitudinal cross-sectional view of a direct current heating melting furnace for glass according to the present invention, Fig. 2 is an explanatory cross sectional view taken along line A-A' in Fig. 1, and Fig. 3 is a direct current heating melting furnace for glass according to the present invention. Explanatory diagram of the power supply device for the 4th
This figure shows the vertical temperature distribution of the molten glass in the melting tank in the conventional apparatus, and FIG. 5 shows the vertical temperature distribution of the molten glass in the melting tank in the apparatus of the present invention. 1... Melting furnace, 2... Hearth, 3, 3'... Lower electrode, 4, 4'... Higher electrode, 6... Molten glass, 7... Glass raw material batch layer, 8... Fireproofing Insulator.

Claims (1)

[Scope of Claims] 1. In a cold-top glass direct current heating melting furnace having a large number of electrodes inserted vertically from the hearth of the melting tank, the electrodes are divided into a plurality of electrode groups having different heights. In addition, the electrode groups except the lowest one are provided so that the portion below the height of the next lowest electrode is covered with insulation, and the electrode groups are configured so that the substantial electrode portions of each electrode group do not overlap in the vertical direction. Features a direct current heating and melting furnace for glass. 2. A large number of electrodes inserted vertically from the hearth of the melting tank are divided into multiple electrode groups with different heights, and in the electrode groups except the lowest one, the part below the next lowest electrode height is covered with insulation. In a directly energized heating and melting furnace for glass, the temperature gradient in the vertical direction inside the tank can be gradually increased or decreased from the hearth to the furnace top by independently supplying power to these multiple electrode groups. A method for melting glass, characterized in that a method can be selected within a range.