JPS5934657B2 - glass electric melting furnace - Google Patents

Description

[Detailed description of the invention] The present invention relates to a vertical electric glass melting furnace.

In an electric glass melting furnace, in which electricity is applied directly to the glass from an electrode that is in contact with or immersed in the molten glass, and the glass is melted by the generated Joule heat, the molten glass is converted into glass raw material (glass batch) in order to effectively utilize thermal energy. The melting and refining of the glass proceeds in the depth direction of the furnace.

For this reason, a vertical furnace is usually used, which has an input section for glass raw materials at the top and a glass outlet (sometimes called a throat) through which the molten and clarified glass flows out at the bottom. ), and the electrodes are inserted into the side wall of the furnace body (tank), which has side walls arranged in a circular or polygonal shape such as a regular hexagon, so as to contact the molten glass.

In a vertical electric melting furnace, unlike an open hearth furnace, defoaming from the surface of the molten glass cannot be expected much, so semi-molten glass often progresses in the depth direction, which is a drawback.

Particularly in electric melting furnaces using rod-shaped electrodes, when a plurality of L/bevel electrodes are arranged, it is difficult to uniformly heat the plane of the furnace at each level, and thermal convection tends to occur unbalanced.

The unbalanced thermal convection causes the glass to flow downwards in the furnace, causing the return point of the convection (the point where the convection changes from descending to ascending) to proceed below the level of the lowest electrode. This may cause the three major defects of bubbles and streaks (heterogeneity) in the product glass.

The purpose of the present invention is to solve the above-mentioned difficulties in a vertical electric melting furnace, so that even glass such as pentasilicate glass, which has high electrical resistance and high viscosity and is difficult to melt and refine, can be sufficiently refined. The goal is to produce homogeneous glass.

Another object of the present invention is to provide a vertical electric melting furnace structure and electrode arrangement suitable for achieving the above object.

Still another object of the present invention is to provide a current distribution suitable for the temperature distribution in the electrode arrangement and a wiring system therefor.

According to the present invention, there is provided an electrode group which has a raw material input part at the top of the furnace, is immersed in molten glass from the side wall of the furnace, is arranged at a plurality of levels, and is used to melt and refine the glass by directly applying electricity to the molten glass. In a vertical glass electric melting furnace with a glass outlet at the bottom, the upper part of the furnace is equipped with a small group of electrodes arranged in an i/bevel arrangement to more intensely heat the glass in the periphery of the furnace. The melting and refining section is equipped with a melting and refining section, in which the glass raw materials are melted and the molten glass is mainly refined in the periphery of the furnace, and the lower part of the furnace is A rectifying and refining section is constructed with electrodes having a small cross-sectional area and arranged on at least one level to heat as uniformly as possible over the plane of the furnace, and in the rectifying and refining section the melting temperature is An electric glass melting furnace is provided which is characterized in that it is kept substantially free of convection by heating the glass as uniformly as possible over the plane of the furnace.

The first feature of the electric melting furnace according to the present invention is that the furnace body is structurally separated into two parts, namely, the upper part is a melting and refining part, and the lower part is a rectifying and refining part.

Functionally, the glass raw material charged in the melting and refining section is melted, and the molten glass is guided to the periphery of the furnace by convection, and most of the generated bubbles are defoamed in the periphery of the furnace, thereby clarifying the molten glass.

On the other hand, in the lower rectifying and clarifying section, a so-called "piston flow" state is maintained in which there is virtually no convection in the glass, and only a flow drawn out from the glass outlet exists. Further improve the clarity of the glass by allowing the bubbles to rise towards the melting and clarification zone.

In the melting and clarification section, the molten glass is guided to the periphery by convection and defoamed by igniting the periphery of the furnace, so the electrodes are arranged and wired so that the current covers the periphery of the furnace. Let's do it.

Specifically, a group of rod-shaped electrodes are penetrated through the furnace wall and arranged near the periphery of the furnace in a radial direction toward the center of the furnace. and the terminals of the power supply (transformer).

The electrode group is usually one stage (but is not necessarily limited to this).

On the other hand, in the rectifying and clarifying section, the electrodes are arranged and wired so that the plane on which the electrode group is arranged is heated as uniformly as possible.

The electrode groups are provided on at least one level, preferably on two levels.

The velocity of the remaining bubbles floating in the rectifying and clarifying section follows Tas's law, but it is preferable to keep this floating speed equal to or greater than the descending speed of the glass in the rectifying and clarifying section (velocity of the withdrawal flow). Therefore, assuming that the pull (glass production amount) is constant, the cross-sectional area, or inner diameter, of the rectifying and clarifying section is determined according to the required bubble quality level (minimum standards for number of bubbles and bubble size) of the product glass.

The inner diameter of the melt clarification section is one of the factors that determines the strength of convection toward the periphery, and is usually 1.1 to 2 of the inner diameter of the rectification and clarification section.
．． 0 times, preferably about 1.2 to 1.6 times.

The depth of the melt refining section (distance between the glass level and the bottom) is such that the generated convection can sufficiently penetrate into the peripheral area of the furnace, and is usually 0.2 to 0.5 times the inner diameter.

On the other hand, the depth of the rectifying and clarifying section varies depending on the quality level of the filter glass required, and should be about 1 to 1.5 times the inner diameter, but if the purpose is to produce higher quality glass, it can be as deep as about twice. It is preferable to do so.

The cross sections of the melt clarification section and the rectification clarification section in the plane direction are as follows.

Since it is normal to have a circular or polygonal shape and use C3-phase alternating current as a power source, it is preferable to assemble the side walls to form a 3n-gon with n=2 or more, particularly a regular 9-gon or a regular 12-gon.

The glass raw material inlet at the top of the melting and clarification section is located around the furnace. It is preferable to provide a cover tile or lid with an opening in the center that constitutes an inlet to prevent heat radiation from the periphery of the furnace and to form a mirror surface free of frit to promote defoaming.

Embodiments of the invention will now be described with reference to the accompanying drawings.

FIG. 1 shows a plan view of an electric melting furnace according to the present invention, and FIG.
The figure shows a section taken along the line II--n in FIG. 1 and a section of a part of the upper passageway and the fluoroceum following the furnace, respectively.

In the figure, -110 indicates a melting and refining section constituting the upper part of the furnace body, and below it, an elongated rectifying and refining section 20 having a smaller cross-sectional area and constituting the lower part of the furnace body.

A glass outlet 30, usually called a throat, is provided at the bottom of the rectifying and clarifying section, and the molten glass exits the glass outlet and is guided through an upper channel 31, usually called a riser, that extends upward, and then into a forehole that extends horizontally. From the berth 32, it is led to a molding machine (not shown).

Regarding the melt refining section 10, 1 indicates a frit input section provided at the top of the furnace, and 2 indicates a layer of unmelted frit introduced, which is suspended in a layer on the molten glass 3 below. Then, they are sequentially melted and vitrified from the interface between the two.

4 is a step around the top of the furnace (square opening 5 in the center)
The opening 5 serves as an inlet for glass raw material.

This cover tile 4 is covered with a frit layer and is
℃・Reduce heat radiation from the molten glass surface around the furnace.

Further, a protrusion 6 extending downward to the molten glass surface is provided near the opening 5 of the cover tile 4 so as to serve to hold the frit layer 2 in the center of the furnace.

In addition, 7 indicates a small diameter hole provided in the cover tile 4, which is used to discharge gas (mostly carbon dioxide gas) generated by defoaming the molten glass to the outside of the furnace. , a plurality of them are provided adjacent to the side wall of the furnace.

In this example, the side wall 11 of the melt refining section 10 is assembled to form a regular dodecagon.

Penetrating each side wall, one bar electrode 12 is immersed in the molten glass radially toward the center of the furnace.

The rod-shaped electrode 12 extends from the side wall to 1/3 to 1/3 of the radius of the melt clarification part.
It is preferable to extend it to about 1/4 and immerse it in the molten glass, so that the electric current is distributed around the molten clarified part and this part is strongly heated.

On the other hand, the side wall 21 of the rectification and clarification section 20 is similarly assembled into a regular dodecagon, but its diameter is smaller than that of the melt and clarification section, and it has a more elongated shape.

Passing through each side wall 21 of the upper part of the rectifying and clarifying section, there are two levels, each radially arranged at ℃ towards the center of the furnace.
Two groups of rod-shaped electrodes 220 and a group of 12 rod-shaped electrodes 230 similarly arranged below the two groups of rod-shaped electrodes 220 are provided.

In these electrode groups, it is preferable to extend the electrodes from the side wall to about 173 to 1/2 of the radius of the rectifying and clarifying section and immerse them in the glass. The current is distributed as uniformly as possible over the area.

When the electrode groups are installed at two levels, as in this example, a larger amount of power is applied to the upper level to prevent rising convection from occurring in this area.

By maintaining the highest temperature area (hot spot) at the level where the electrode group at the top of the rectification and clarification section is arranged, and by keeping the temperature gradually decreasing downward, the temperature can be maintained over almost the entire length of the rectification and clarification section. This prevents convection from occurring, so that only a downwardly directed extraction flow is actually present.

In this way, the clarity of the molten glass can be further improved by preventing unrefined or unmelted glass from flowing down and entering the rectifying and refining section from the melt refining section above, and by raising any remaining air bubbles.

By maintaining the temperature distribution conditions as described above, a circulating convection occurs in the melt refining section that ascends in the center of the furnace and descends in the periphery as shown by the arrow, and the molten glass containing unmelted raw materials and bubbles is It is melted and degassed in the surrounding area, which is kept at a high temperature.

The molten glass, which has been sufficiently degassed in this circulation convection, becomes a drawing flow and flows down to the rectifying and clarifying section below, where it is further clarified and homogenized, and then flows out from the glass outlet.

Next, with reference to FIGS. 3 and 4, a connection system between the electrode groups installed in the melting and refining section 10 and the rectifying and refining section 20 and the power source will be explained.

In Fig. 3, 41, 42, 43, and 44 indicate a three-phase AC transformer in which both the primary and secondary coils are connected in a △ (delta) shape, and R, S, and T are the two-phase transformers of each phase. The next terminals are shown respectively.

In this case, each electrode is connected to a phase terminal having a phase different from that of adjacent electrodes.

That is, 12 electrodes R1, Sl, T1. R2, S2. T
2. R3, S3. T3゜R4, s4j 'r4 all have a different phase from the electrodes adjacent on both sides, so for example, from electrode R1, adjacent electrodes S1 and T
1 produces an equal current distribution through the molten glass, and similarly, electrode S1 produces an equal current distribution between electrode R1 and electrode T1.

Therefore, as shown in the figure, in the melting and refining section, the area around the furnace covered by the electrodes is mainly heated by °C.

Similarly, in FIG. 4, 51, 52, 53, and 54 each indicate a three-phase AC transformer with a Δ connection.

In this case, the electrode R1 connected to the R phase terminal of the transformer 51
are the electrodes S connected to the S-phase terminal and the T-phase terminal, respectively.
The same is true for transformers 52-54, which are arranged in point symmetry about the center of the furnace at an angle of 120 degrees with respect to T1.

Thus, there are a total of four electrodes R1tR2tR37R4 connected to the R phase terminals in clockwise order from the electrode R1, and then electrodes S1... connected to the S phase terminals. S2. S3゜S4 Then the electrode T1.S4 is connected to the T-phase terminal. T2゜'r
They are arranged sequentially at equal angles of 3F'r4 or 30.

In such a wiring system, for example, the electrode R2 generates a current between the electrodes of different phases, namely S, ~S4, T1~T4.

Similarly, electrode R8 flows between electrodes S1-S4 and T1-T4, and electrode R4 flows between electrodes S1-S4 and T1-T4.

Since any one electrode produces a current between eight electrodes having different phases and distributed at 30 equal angles with respect to the center of the furnace, for a total of 240 angles, the rectifying and clarifying section 20
In this case, the entire surface of the molten glass is heated almost uniformly at the level where the electrode group is arranged.

[Brief explanation of the drawing]

FIG. 1 shows a plan view of the main body of the electric melting furnace according to the present invention,
FIG. 2 shows a cross section taken along line II-II in FIG. FIG. 3 and FIG. 4 respectively explain the connection system between the electrodes and the power source in the melting and refining section and the rectification and refining section. 1... Glass raw material input section, 2... Glass raw material layer, 3... Molten glass, 4... Cover tile, 10... Melting Clearing Department, 11...
...Side wall, 12...Electrode, 20...--
Rectification and clarification section, 21...Side wall, 22...
Electrode, 23... Electrode, 30... Glass outlet, 31... Upper channel, 32... Foreverse, 41, 42° 43.44. ...Three-phase AC transformer, 51,52゜53.54...Three-phase AC transformer.

Claims (1)

[Scope of Claims] 1. A furnace having a raw material inputting part 1 at the top, immersing molten glass from the side wall of the furnace, melting and refining the glass by directly applying current to the r & molten glass arranged at multiple levels. In a vertical glass electric melting furnace with a group of electrodes and a glass outlet 30 at the bottom, the upper part of the furnace has electrodes arranged on at least one level to heat the glass in the periphery of the furnace more intensely. A melting and refining section 10 is provided with a group, and the melting and refining section melts the glass raw materials and mainly refines the molten glass in the peripheral area of the furnace, and the lower part of the furnace has a smaller cross-sectional area than the melt and refining section. The rectifying and refining section 20 has a depth of 1 to 2 times the inner diameter and includes at least one level-disposed electrode group so as to heat the molten glass as uniformly as possible over the plane of the furnace. An electric glass melting furnace characterized in that, in the rectifying and clarifying section, the molten glass is heated as uniformly as possible over the plane of the furnace in a state in which convection is not substantially generated.2. The electric melting furnace according to claim 1, wherein the inner diameter of the melt clarification section is 1.1 to 2.01 times the inner diameter of the rectification and clarification section.3 The side walls of the melt clarification section and the rectification and clarification section are n. - The electric melting furnace according to claim 1 or 2, which is assembled into two or more regular n-gons. 4. The top of the melting and refining section is covered with a cover tie/L/4 having an opening in the center. 5. The electric latent melting furnace according to claim 1, wherein electrode groups are arranged at two levels in the upper part of the melting fdt section. Furnace. 6. The envelope melting furnace according to claim 3, wherein the electrodes are inserted radially from each side wall of the furnace toward the center of the furnace and are placed so as to be immersed in the molten glass in the furnace.