Electrode Assembly for Molten Glass Forehearth

This invention relates to electrode holders, and deals more particularly with an electrode assembly adapted for use with an electrode passing through the sidewall of the furnace forehearth, which electrode comprises part of an electrical circuit for passing Joule effect heating current to the molten glass in the furnace.

Joule effect heating by the passage of electrical current through a body of molten glass is well known in the art of glass making, and is often used in the glass melting furnace, or in a furnace forehearth, either to supplement a gas or oil heating means, or to provide all the energy required for the melting or heating of the glass. Molybdenum is currently used for electrodes which must be immersed in the glass to achieve this Joule effect heating, and the electrode is usually inserted through an aperture in the refractory wall of the furnace such that a portion protrudes beyond the wall so as to be adapted for connection to a source of electrical power. While the glass material itself forms a suitable barrier around the molybdenum inside the forehearth channel, effectively preventing oxidation even at temperatures above 2,000.degree. F., oxidation has been encountered in the zone where these electrodes extend through the sidewall of the hot furnace and are in contact with air at a temperature in excess of 750.degree.. To avoid rapid oxidation present practice usually requires some type of forced fluid cooling to the electrode in this zone.

The general object of the present invention is to provide an electrode assembly for supporting an electrode in the sidewall of the furnace without the necessity for such cooling.

A more particular object of the present invention is to provide an electrode assembly of the type mentioned in the preceding paragraph wherein the molybdenum electrode is surrounded by a high temperature alloy steel sleeve spaced from the electrode, but sealed at each end of the sleeve. It has been found that certain elements, such as nickel tend to migrate into the molybdenum if there is physical contact between alloy steels and molybdenum at temperatures above 750.degree. F. Therefore, the present invention obviates this propensity for migration, and also obviates the oxidation formerly encountered with prior art designs when no cooling was applied to the zone of the electrode external to the refractory material in the furnace sidewall.

In the electrode assembly of the present invention a tubular sleeve of high temperature alloy steel is provided in radially spaced relationship to a generally cylindrical molybdenum electrode. The inner end of this sleeve is sealed by the hardening of the molten glass in this area and a high temperature ceramic spacer material supports the electrode at the inner end of the sleeve so that the spacer and the glass will support the electrode in spaced relation to this sleeve. The outer end of the sleeve is directly connected to the outer end of the electrode by a high temperature alloy steel plug, which plug also serves as an electrical connection between the electrical lead wire and the electrode itself.

Thus, the annular space between the sleeve and the electrode is effectively sealed from the atmosphere with the result that what little oxygen is allowed to remain in the annular space is quickly consumed by very slight initial oxidation of the molybdenum. The high temperature alloy steel sleeve has an annular flange associated with its exterior surface such that the entire electrode assembly can be clamped in place by thrust brackets associated with the outer end of the sleeve and exerting an inwardly directed thrust force on the entire assembly to maintain the electrode in the desired position relative to the furnace sidewall.

FIG. 1 is a vertical sectional view taken through the furnace forehearth at a point where the electrode assembly is mounted in the sidewall of the furnace and illustrates the elongated electrode in extended longitudinal relationship across the forehearth channel. Portions of the apparatus of FIG. 1 are shown broken away in order to reveal the construction of the electrode assembly.

FIG. 2 is a sectional view taken generally on the line 2--2 of FIG. 1.

FIG. 3 is a longitudinal sectional view through the electrode assembly of FIG. 1.

Turning now to the drawing in greater detail, FIG. 1 shows a molten glass forehearth channel 10 constructed of refractory material adapted to withstand the temperature of the molten glass (approximately 2,000.degree. to 2,400.degree. F.) and this channel serves to provide a conduit for the molten glass between the melting tank or furnace and a feeder bowl or other outlet means provided at the downstream end of the channel. The melting tank, the forehearth, and the feeder comprise conventional components which need not be described in detail herein.

The refractory forehearth channel defines a laterally extending aperture, or opening 10a, for receiving the elongated electrode 12, and its associated sleeve 14 to be described. The aperture 10a in the refractory channel sidewall comprises part of a somewhat larger aperture 16a provided in the insulated portion of the forehearth sidewall, and in axial alignment with the aperture 10a. The larger aperture 16a defined in the insulated portion 16 of the furnace forehearth sidewall, is more particularly defined by annular insulating blocks 16b, 16c, 16d and 16e. Forehearth constructions generally include both refractory material, where the molten glass contacts the structure itself, and insulating material, external to the refractory material, as well as a metal framework, such as indicated at 18 in FIG. 1. The metal framework retains both the insulation 16 and refractory components 10 in assembled relationship with one another.

By way of summary then, the furnace forehearth shown in FIG. 1 includes a sidewall which defines a stepped aperture or opening (16a and 10a) with the exterior of the refractory portion 10 defining an outwardly facing surface 10b to be referred to hereinafter in connection with the electrode assembly to be described.

Turning now to a more complete description of the electrode 12 and its associated sleeve 14, it will be apparent that the electrode 12 is in contact with the molten glass for a substantial portion of its length, and more particularly throughout its entire inner portion which extends across the forehearth channel as shown in FIG. 1. It is characteristic of such electrodes, particularly those which are made from a molybdenum material, that molybdenum tends to oxidize at the elevated temperatures characteristic of molten glass generally, but that the molten glass prevents such oxidation where the electrode is surrounded by molten glass rather than air, or some other oxidizing atmospheric environment. It is a feature of the present invention that the molybdenum electrode 12 is surrounded by a high temperature alloy steel sleeve 14 which sleeve is mounted in spaced relationship to the electrode as best shown in FIG. 3 in order to provide an annular space between the sleeve 14 and the electrode 12. This annular space is formed or defined by a high temperature rope ceramic material, such as FIBERFRAX, made by The Carborundum Company, as indicated generally at 20, adjacent the inner end of the sleeve 14, and is made airtight in this area by the hardened molten glass which will penetrate this material 20 to some extent. The outer end of the sleeve is supported by the plug 22 as best shown in FIG. 3. The annular space between the steel sleeve 14 and the electrode not only isolates that atmosphere surrounding the electrode 12, to prevent excessive oxidation of the molybdenum electrode itself, but also serves to keep the sleeve out of contact with the molybdenum electrode 12 especially that portion of the electrode 12 likely to be at an elevated temperature and subjected to migration of contaminants from the high temperature alloy steel sleeve 14 to the surface of the molybdenum electrode 12. It is noted that only in the extreme outer end portion of the electrode 12 does the electrode come in contact with the high temperature alloy steel plug material, and at this point on the electrode 12 the temperature will normally be well below the 750.degree. temperature at which migration of contaminant materials into molybdenum is likely to occur.

Still with reference to the high temperature alloy steel sleeve 14, an annular flange 24 is provided outside the sleeve 14 and this flange is preferably fitted with a gasket of heat resistant material, similar to the material used to pack the space between the inner end of the sleeve 14 and the electrode 12 as referred to above at 20. FIG. 1 shows an annular gasket 26 of this material, and also illustrates this high temperature resistant material 26 in contact with the molten glass in the forehearth channel, which molten glass will have hardened in the space between the outside of the sleeve 14 and the inside wall of the aperture 10a of the refractory 10 during normal operation of the furnace forehearth.

As best shown in FIG. 1 the high temperature alloy steel sleeve 14 has diametrically opposed flange defining means 14a and 14b welded to the exterior wall of the sleeve 14 in order to provide a convenient connection with the mounting means for the electrode assembly, such that the electrode assembly can be thrust inwardly of the furnace in order that the gasket 26 will achieve an effective seal between the annular flange 24 and the stepped shoulder portion 10b of the aperture in the furnace sidewall.

Turning next to a more complete description of the means for so mounting the electrode assembly to the furnace framework 18, FIG. 1 shows two threaded studs 28, 28 having their head portions welded to the steel framework 18 of the furnace in spaced relationship to the aperture 16a in the furnace sidewall referred to previously. These threaded studs 28, 28 are adapted to receive openings in electrical insulator blocks 30, 30 which blocks have their inner ends bolted to the projecting ears 14a, and 14b by fasteners indicated generally at 32 in FIG. 1. As so constructed and arranged, the electrode assembly can be effectively clamped into the stepped aperture in the sidewall of the forehearth so as to thrust the sleeve 14 inwardly of the furnace and achieve a seal between the flange 24 and the refractory sidewall portion 10b.

Turning next to a more complete description of the high temperature alloy steel plug 22 and referring particularly to FIG. 3, it will be apparent that this plug 22 contacts the molybdenum electrode 12 only in the area of the threaded connection 34 therebetween. The plug 22 defines a female threaded opening to receive the threaded end portion of the molybdenum electrode 12, and the plug 22 further includes an annular portion 22a also defining a female threaded portion so as to threadably receive the end portion of the high temperature alloy steel sleeve 14. The male thread of sleeve 14 is preferably provided with a high temperature thread sealant such as NEVER-SEEZ made by a company of the same name located in Broadview, Ill. 60155. An asbestos gasket 23 is provided between the end of the sleeve 14 and the plug 22.

This construction affords an effective airtight seal between the sleeve 14 and the electrode 12 with the result that any trapped air between the sleeve 14 and the electrode 12 will have its oxygen quickly used up during initial operation of the electrode assembly in a furnace. Oxidation will be prevented by virture of the fact that airtight seals are afforded by the plug 22 at the outer end of the electrode assembly, and by the congealed glass at the inner end of the sleeve 14, in an improved construction which also avoids any migration of the nickel in the high temperature alloy steel sleeve 14 to the relatively high temperature portion of the electrode 12.

Still with reference to the plug 22 an outwardly open threaded aperture 22b is provided for receiving a threaded electrical connector screw 36 associated with the lead wire 38. This configuration provides a path for the electrical energy to the electrode 12 passing through the high temperature alloy steel plug 22 from the electrical connector screw 36 to the outer end of the electrode 12. Thus, the high temperature alloy steel plug 22 serves to support the electrode and the sleeve 14 in spaced relationship to one another, and to seal the annular space between these elements at least at the outer end thereof, and also serves to provide an electrical series connector between the screw 36 and the electrode itself.