JPH04342425A - Protection of electrode - Google Patents

Abstract

PURPOSE:To prevent the oxidation and corrosion of electrodes by cylindrically covering the surface of each electrode portion not immersed in a molten glass in a glass melting furnace with a refractory protective cover. CONSTITUTION:Each rodlike electrode 1 made of e.g. Pt is vertically inserted through a penetrating hole 6 provided on the ceiling wall 4 of a working tank 3 and the lower portion of this electrode is immersed in a molten glass 5 in a furnace. The outside surface of the electrode 1 is cylindrically covered with a Al2O3 protective cover 2 so that the lower edge of cover is positioned onto a stopping collar 10, and the space between the cover 2 and the electrode 1 is fed with an inert gas at a flow rate of 0.5-3l/min through an inlet of the upper end holder 8, thereby preventing the volatiles in the glass from intrusion into the space. Thus, the electrode's wastage due to oxidation or corrosion is prevented in such operations as to inject current into the electrodes 1 in the melting furnace and the temperature of the glass is raised to melt it.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for protecting electrodes used in glass melting furnaces, and more particularly to a method for protecting heating electrodes that are immersed in molten glass from above in a working tank.

0002

2. Description of the Related Art Electric melting methods, in which electrodes are immersed in a glass melt and electricity is passed between the electrodes to generate Joule heat as a heat source, have been studied and put to practical use for a long time. The electrode material is required to not be eroded by the glass solution, and not to impair the quality of the glass even if it is slightly eroded and dissolved in the glass solution. Electrode materials currently in actual use that meet these requirements include molybdenum, platinum, platinum-rhodium alloys, and tin oxide.

[0003] Each of the above-mentioned electrodes has a high melting point and a high resistance to erosion by a glass solution. However, it has the drawback of being easily oxidized, sublimated, and consumed when exposed to a high-temperature oxidizing atmosphere.

[0004] For example, molybdenum electrodes are rapidly oxidized when exposed to high temperature air of about 600°C or higher. Therefore, when using molybdenum electrodes, it is recommended to cool the electrodes by directly spraying water on high-temperature areas exposed to the air, such as near through-holes in the furnace wall, or by attaching a water-cooled holder around the electrodes. The electrodes are protected by cooling.

Furthermore, there is also known a method of minimizing oxidation of the electrode by creating a vacuum in the space between the water-cooled holder and the electrode (see, for example, Japanese Patent Laid-Open No. 14142/1982).

[0006]

[Problems to be Solved by the Invention] However, in the electrode protection method using the cooling method described above, the surrounding area of the electrode that is heating the glass melt is also cooled more than necessary, which reduces the thermal efficiency of the melting furnace. The problem arises.

The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide a method for protecting electrodes that can effectively prevent oxidation and corrosion of electrodes.

[0008]

[Means for Solving the Problems] That is, the present invention is a method for protecting a heating electrode that penetrates the ceiling wall of a working tank of a glass melting furnace and is immersed in molten glass in the furnace, This method of protecting an electrode is characterized in that a protective cover made of a refractory material is arranged to cover the surface of the electrode portion that is not immersed in a cylindrical shape.

In the present invention, a gap is provided between the electrode and a protective cover made of refractory material that covers the electrode surface in a cylindrical shape, and a holder is fitted to cover the upper end of the protective cover. Preferably, an inert gas is introduced into the gap through the injection port. As the inert gas, N2
, Ar, or other gases can be used.

Further, in the present invention, it is preferable that the lower edge of the protective cover be located on a locking collar protruding from the electrode. Further, in the present invention, the material of the refractory protective cover that covers the electrode surface is not particularly limited, but it must have at least electrical insulation properties and do not change under high temperature conditions where the electrode is heated, that is, it must have heat resistance. The material must also have strain resistance, and in this respect, for example, low expansion glass and alumina are suitable materials.

[0011]

[Operation] According to the present invention, the surface of the part of the heating electrode in the furnace that is not immersed in the molten glass is covered with a cylindrical protective cover made of refractory material, so that the electrode material is generated by the volatile components in the molten glass. oxidation and erosion can be suppressed.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a diagram for explaining the present invention,
FIG. 3 is a longitudinal cross-sectional view of a working tank of a glass melting furnace.

In FIG. 1, a through hole 6 is provided in a part of the ceiling wall 4 of the working tank 3 for vertically inserting a rod-shaped electrode 1 into the molten glass 5 in the furnace from above. As the material for the electrode 1, conventionally known materials such as molybdenum, platinum, platinum-rhodium alloy, or tin oxide can be selected.

Further, on the outside of the electrode 1, a protective cover 2 made of refractory material is disposed coaxially with the electrode 1 in a cylindrical shape. The electrode 1 covered with the protective cover 2 is connected to the ceiling wall 4.
The electrode 1 is inserted into the working tank 3 through a through hole 6, and the lower part of the electrode 1 is immersed in the molten glass 5.

FIG. 2 is an enlarged view of the main part of FIG. 1, and FIG. 3 is a sectional view taken along the line A--A in FIG. In FIG. 2, a gap 7 is provided between the electrode 1 and the protective cover 2, and a holder 8 is fitted to cover the upper end of the protective cover 2. The holder 8 also has an injection port 9 formed therein.
A nozzle (not shown) is attached to the injection port 9 so that inert gas can be continuously supplied to the gap 7.

FIG. 4 is a schematic plan view of the electrode 1 in FIG. 2 as viewed from the tip direction (downward in FIG. 2), and components other than the electrode 1 and the locking collar 10 are omitted. The locking collar 10 disposed on the electrode 1 is, for example, shown in FIG. 4(a) or (
The shape shown in b) can be applied. Further, the locking collar 10 may be integrally formed with the electrode 1 so as to project therefrom, or may be formed by welding a separate member to the electrode 1.

When inert gas is supplied to the gap 7 from the injection port 9 of the holder 8, the locking collar 10 is moved as shown in FIG.
It is preferable to have a shape like this. With the above shape, the inert gas flowing into the gap 7 can be discharged from the lower edge of the protective cover 2 into the working tank, preventing glass volatile components from entering the gap 7 and protecting the electrode. It is possible to do this effectively.

Furthermore, the inert gas supplied from the injection port 9 of the holder 8 to the gap 7 serves to protect the electrode 1 from the oxidizing atmosphere. For this reason, the supply flow rate of the inert gas is appropriately adjusted within a range that does not reduce the temperature of the area around the electrode in the working tank, and is approximately 0.5 to 3 liters at 20°C.
It is preferable to set it within the range of /min. If the flow rate is below the above range, there is a risk that glass volatile components will enter the gap 7 from between the locking collars 10 and corrode the electrode 1. On the other hand, if the flow rate exceeds the above range, the electrode protection effect will increase, but a large amount of inert gas will be discharged from the lower edge of the protective cover 2 into the working tank, and as a result, the temperature in the working tank will decrease by 10%. ℃
or more. By appropriately adjusting the inflow amount, the entire gap 7 is appropriately covered with inert gas, thereby blocking the intrusion of glass volatile components and improving the electrode protection effect.

Further, when inert gas is not allowed to flow into the gap 7, it is preferable that the locking collar 10 has the shape shown in FIG. 2(b). By adopting the above shape, intrusion of glass volatile components into the gap 7 is prevented, and since the gas present in the gap 7 hardly moves, the vapor pressure of the electrode material in the gap 7 is maintained close to the saturated vapor pressure. volatilization is less likely to occur.

Example 1 The outer surface of a platinum rod-shaped electrode with a protruding locking collar was
It was covered in a cylindrical shape with an alumina protective cover so that its lower edge was positioned above the locking collar. Then, the platinum electrode covered with the protective cover was inserted into the working tank through the through hole in the ceiling wall of the working tank.

To prevent the protective cover from touching the molten glass surface when the lower portion of the platinum electrode is immersed in the molten glass, the locking collar was adjusted to be approximately 20 mm above the molten glass surface.

The glass substrate crudely melted in the glass melting tank is led to a working tank, and in the working tank, electricity is applied between a platinum electrode and a platinum electrode electrically opposite thereto to bring the glass temperature to 130°C.
The mixture was heated and melted while maintaining the temperature at 0°C. Arsenic oxide was added to the molten glass as a refining agent.

As the molten glass was heated with electricity, arsenic was volatilized as a glass component from the surface of the molten glass. Then, the vaporized vapor was cooled and condensed near the ceiling wall in the work tank, and glass volatile components were deposited over the entire outer peripheral surface of the protective cover.

When this platinum electrode was extracted and the surface condition was visually observed, almost no corrosion by volatile components was observed. Furthermore, the amount of platinum volatilization was measured. As a result, the amount of platinum volatilized from the electrode surface was 0.2 μg/cm 2 ·h per unit area. This amount of volatilization is 1/30 of the amount of volatilization per unit area of the platinum electrode when no protective cover is used, which is 6.0 μg/cm2・h, and this example reduces the weight loss of the platinum electrode material. This was confirmed.

Example 2 As in Example 1, the outer surface of a platinum rod-shaped electrode was covered in a cylindrical shape with an alumina protective cover, and a holder was fitted onto the upper end of the protective cover to cover the platinum electrode. was inserted into the working tank through a hole in the ceiling wall of the working tank. Electricity was applied between the platinum electrodes, and the glass temperature was maintained at 1300° C. to heat and melt the glass. Arsenic oxide was added to the molten glass as a refining agent.

[0026] Then, electrical current is applied between the platinum electrodes to heat the space between them, and nitrogen gas is injected into the gap between the platinum electrode and the protective cover covering the electrode surface from the injection port of the holder at a rate of 1°C at 20°C.
It was supplied at a flow rate of 1/min. The nitrogen gas supplied to the gap passed through the gap and was discharged into the working tank from the gap between the lower edge of the protective cover and the locking collar.

[0027] Arsenic volatilized from the surface of the molten glass base material due to electrical heating was cooled and condensed near the ceiling wall in the working tank, and adhered to the entire outer peripheral surface of the protective cover.

When this platinum electrode was taken out and the surface condition was visually observed, no corrosion due to volatile components was observed. Furthermore, when we measured the amount of platinum volatilization, we found that the amount of platinum volatilized from the electrode surface was 0.0 per unit area.
It was 3 μg/cm2·h. The amount of volatilization per unit area of the platinum electrode when a protective cover is not used is 6.
It is 1/200 compared to 0 μg/cm2・h, and it is also about 1/7 compared to the case of Example 1 in which inert gas is not allowed to flow into the gap. As a result of flowing an inert gas into the gap with the flow rate adjusted appropriately, it was confirmed that weight loss was further reduced significantly.

[0029]

Effects of the Invention As detailed above, according to the electrode protection method of the present invention, refractory protection is applied to the surface of the heating electrode in the furnace that is exposed to high temperatures and is not immersed in molten glass. Since the cover is arranged coaxially in a cylindrical shape, it is possible to suppress wear and tear on the electrode material due to oxidation and erosion.

Furthermore, since the lower edge of the protective cover is positioned on the locking collar protruding from the electrode, volatile components in the molten glass enter the gap between the lower edge of the protective cover and the electrode. can prevent oxidation and erosion of the electrode material. Furthermore, by flowing inert gas into the gap between the electrode and the protective cover from the inlet of the holder fitted over the top of the protective cover, it is possible to block the intrusion of high-temperature oxidizing atmosphere, preventing oxidation of the electrode material. Erosion can be prevented more effectively.

[0031]

[Brief explanation of drawings]

[Fig. 1] A longitudinal cross-sectional view of a working tank of a glass melting furnace suitable for carrying out the present invention.

[Figure 2] Enlarged view of the main parts of Figure 1

[Figure 3] Cross-sectional view along line A-A in Figure 2

[Figure 4]
(a) and (b) are schematic plan views seen from the direction of the electrode tip in Figure 2.

[Explanation of symbols]

1 Electrode 2 Protective cover 3 Work tank 4 Ceiling wall 5. Molten glass 6 Through hole 7 Gap 8 Holder 9 Inlet 10 Locking collar

Claims (2)

[Claims] 1. A method for protecting a heating electrode that penetrates the ceiling wall of a working tank of a glass melting furnace and is immersed in molten glass in the furnace, the method comprising: protecting the surface of the electrode portion that is not immersed in the molten glass; A method for protecting an electrode, characterized by arranging a protective cover made of refractory over the cylindrical shape. 2. A gap is provided between the electrode and the protective cover, a holder is fitted to cover the upper end of the protective cover, and an inert gas is flowed into the gap from an injection port of the holder. 1. The method for protecting an electrode according to 1.