Furnace electrode protector

A sealed connection for a sleeve and jacket for protecting a molybdenum electrode mounted through the wall of an electric glass furnace. Around the electrode in the wall is a stainless steel sleeve coated on the inside with a fused alumina and having an outwardly extending flange at its outer end which engages the outer wall or shoulder in the aperture in the wall through which the electrode extends. The flange has an axially outwardly extending rib of V-shaped radial cross-section which seats and centers in an annular V-shaped groove around the inner end of a water jacket that surrounds the electrode outside the furnace. Refractory sealing gaskets are placed between the flange and the wall of the furnace and in the cooperating grooves and ribs of the sleeve and water jacket. The sealed cylindrical annular space around the electrode between it and the sleeve and the jacket is filled with nitrogen to prevent oxidation of the molybdenum electrode. The water jacket and sleeve are urged together and against the outer wall of the furnace by an adjustable mounting. The electrode is separately and adjustably mounted so that as the electrode wears away inside the furnace, more of it can be easily fed into the furnace.

BACKGROUND OF THE INVENTION 
This invention is an improvement over applicants' assignee's U.S. Pat. No. 
3,634,588 issued Jan. 11, 1972 to Steitz et al and U.S. Pat. No. 3,777,040 
issued Dec. 4, 1973 to Gell et al. 
Although electrodes of this type with ceramic-coated metal sleeves and 
water jackets are known according to the above mentioned patents, neither 
of these patents include the specific improved coating, sealing and 
centering means for the sleeve and jacket invented and disclosed herein by 
applicants. 
SUMMARY OF THE INVENTION 
Generally speaking, this invention relates to the protection of molybdenum 
electrodes extending through the wall of a glass furnace for melting glass 
according to the joule effect. These electrodes may be mounted on 
adjustable jacks so they can be fed periodically into the furnace as the 
electrodes wear during operation of the furnace. 
Separately mounted and surrounding each molybdenum electrode to prevent its 
oxidation, is a protective sleeve and adjacent cooling jacket centered 
with each other and the electrode to provide an annular cylindrical space 
around the electrode in the furnace wall, which space can be maintained in 
an inert atmosphere, such as nitrogen. This sleeve is composed of 
stainless steel and is positioned inside the wall of the furnace extending 
toward the molten glass in the furnace. The other or outer end of this 
sleeve has an integral outwardly radially extending flange. Sealingly 
connected to this flange is the inner end of a jacket which also surrounds 
the electrode and which contains a labyrinth path for a cooling fluid. 
This flange on the sleeve is provided with a rib having tapered sides 
extending axially from the flange toward the outside of the furnace. This 
rib seats in a groove having tapered sides at the adjacent end of the 
cooling jacket. Thus, as the jacket is axially moved to engage the flange 
on the sleeve, the complimentary radially triangular cross-sections of the 
rib and groove center the jacket and sleeve with each other and the 
electrode. 
Between the flange and the wall of the furnace and between the rib and 
groove, there are provided refractory gaskets for sealing sleeve and 
jacket together and to the furnace wall as the jacket is urged against the 
flange of the sleeve. The inner end of the sleeve is sealed to the 
electrode by the molten glass in the furnace that flows into the aperture 
for the electrode. 
The inside of the stainless steel sleeve is fuse-coated with aluminum oxide 
to prevent the high temperature of the glass in the furnace from forming 
an alloy with the molybdenum in the electrode and thus welding the sleeve 
to the electrode. This fuse-coated alumina coating has a high wear and 
abrasion resistance of about ten times that of the uncoated metal sleeve 
and provides a thermal barrier for temperatures up to 2480.degree. C. In 
addition, this alumina coating has a high electrical resistance as well as 
a high corrosive resistance to resist action of oxides, acids and 
alkalies. Preferably in order to improve the adherence of this coating to 
the stainless steel sleeve, there may be a sub-or undercoating of a 
nickel-chrome alloy which also compensates for the difference in thermal 
expansion between the alumina coating and the stainless steel sleeve. 
Thus, the only seal at the inside of the electrode and sleeve will be the 
molten glass of the furnace that extends into the aperture in the furnace 
to the upper inner end of the metallic sleeve. 
At the outer end of the cooling jacket, there is provided a gasket for 
sealing the cooler parts of the electrode and jacket together. Thus a 
closed annular cylindrical space is provided for the inert gas adjacent 
the heated parts of the electrode. An adjustable bracket is provided for 
urging and holding the jacket against the sleeve and the sleeve against 
the furnace once they are in position, which bracket may be connected to 
the support for the furnance. 
Although water is generally employed for circulating through the cooling 
jacket, other cooling liquids may be employed without departing from the 
scope of this invention. Furthermore, if additional cooling is required, 
jets of air may be applied to the outside of the jacket and electrode 
outside the furnace. 
OBJECTS AND ADVANTAGES 
An object of this invention is to provide an improved, simple, efficient, 
effective and economic means of centering, aligning and sealing a jacket 
and sleeve for surrounding and protecting an electrode in a furnace. 
Another object is to provide an interfitting structure between a cooling 
jacket and a sleeve that surrounds and protects an electrode extending 
through an aperture in a furnace wall which permits a greater degree of 
sealing, reliability and proper positioning of the jacket and sleeve 
around such an electrode. 
Another object is to provide a sealed inert atmosphere around an electrode 
to prevent its reaction with a protective sleeve and jacket around the 
electrode, particularly at the higher temperature closer to the inside of 
the furnace, thereby preventing sticking of the sleeve to the electrode 
and/or jacket. 
A further object is to provide a high temperature, abrasion, wear, 
electrical, and corrosion resistant coating on the inside of the metal 
sleeve that surrounds the electrode in the wall of the furnace, thereby 
further protecting the electrode, particularly if the electrode becomes 
chemically reactive at its operating temperature.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
Referring first to FIG. 1, there is shown a section of part of an electric 
glass furnace 10 having a bottom wall 12 and side wall 14 filled with 
molten glass 16, on the top of which molten glass is a layer of unmelted 
glass particles 18. Projecting through the bottom wall 12 is an aperture 
13 which herein is shown to have an outward enlarged portion 15 providing 
a shoulder 17. However, it is to be understood that the shoulder 17 may 
comprise the outer surface of the wall 12, or another shoulder 19 shown in 
FIG. 2. 
Projecting through the aperture 13 and 15 there is shown an electrode 20 
which may be composed of a high refractory electrical conducting material, 
such as graphite, molybdenum, or the like. The length of the electrode is 
preferably longer than the portion that is exposed into the molten glass 
16. The outer end of this electrode is mounted on a jack 22 so that is can 
be gradually fed into the molten glass 16 in the furnace as its upper ends 
wears away due to the high temperature and electrolysis in the furnace. 
Referring now more specifically to FIG. 2, there is shown a stainless steel 
sleeve 30 which may be composed of a high temperature resistant steel such 
as Inconel 600, which is a nickel-chromium-iron alloy. 
The inside of the hollow cylindrical sleeve 30 is fused-coated with 
aluminum oxide 31 so that at its inner end adjacent the molten glass 16, 
it will not tend to melt and form an alloy with the molybdenum in the 
electrode 20 by welding or sticking thereto, and thus resist adjustment of 
the electrode. This aluminum oxide coating is flame-sprayed on the inside 
of the tube, such as by an oxygen acetylene flame in a spray gun backed up 
by air pressure to blow out the melted particles of the aluminum oxide at 
a speed of about 180 meters per second. Then melted alumina particles are 
deposited and integrally adhere to the inside of the sleeve 30. This pure 
aluminum oxide coating has a wear and abrasion resistance of about 20 
times that of the metal sleeve per se, and provides a thermal barrier to 
temperatures up to 2480.degree. C. Furthermore, since this is an electric 
furnace, this coating has a high electrical resistance, as well as a high 
corrosion resistance to oxides, acids and alkalis. The relative thickness 
of this aluminum oxide coating ranges between about 0.25 and 0.635 
millimeters and preferably between about 0.35 and 0.40 millimeters. 
Furthermore, in order to improve the adherence of this coating 31 to the 
stainless steel sleeve 30, there may be provided a thin subcoating under 
the aluminum oxide on the inside of the tube 30, such as of a 
nickel-chromium alloy which also may be sprayed on the inside of the tube 
30. This undergoing reduces the difference in thermal expansion between 
that of the ceramic aluminum oxide coating 31 and that of the stainless 
steel sleeve 30. The thickness of this undercoating usually ranges between 
about 0.025 and 0.125 millimeters, and preferably between about 0.05 and 
0.075 millimeters. 
The inner end of this sleeve 30 is sealed to the furnace 12 and the 
electrode 20 by the molten glass 16 as more clearly shown in FIG. 2. 
The outer end of this sleeve 30 is provided with an integral radially 
outwardly extending flange 32, which flange contains an axially extending 
annular rib 34 toward the outside of the furnace 10. This rib 34 has a 
general triangular radial cross-section; that is, a rib with tapered sides 
35. The lower end of the sleeve 30 is sealed to the outer wall of the 
furnace, particularly herein to the shoulder 17, by a gasket 36 which is 
squeezed between the flange 32 and shoulder 17 of the outer side of the 
wall 12 of the furnace 10. Also surrounding the electrode 20 and toward 
the outside of the furnace wall 12 is provided a cooling jacket or water 
box 40 which in FIG. 2 is shown to have a partial concentric internal 
partition 42 to provide a labyrinth path for the introduction of the 
cooling fluid, such as water, from pipe 44 regulated by a valve 46. The 
fluid or water flows from intake pipe 44 adjacent and around the inner 
wall of the jacket 40, then around the inner end of the partition 42 and 
around the inside of the outer wall of the jacket 40 to the outlet duct 
48. The inner end of the jacket 40 is provided with a ring 41 having an 
annular groove 43 with tapered sides 45 which are parallel to the tapered 
sides 35 of the rib 34 on the sleeve 30. The congruence of the tapered 
sides 35 of the rib 34 and the tapered sides 45 of the groove 43 are so 
located with respect to each other and the electrode 20 so when they are 
fitted together from the position shown in FIG. 3 to that shown in FIGS. 2 
and 4, the sleeve 30 and jacket 40 are coaxially aligned and centered 
around the electrode 20 and its centerline. This positioning provides an 
enclosed continuous annular cylindrical space 50 around the electrode 20, 
and between it and the sleeve 30 and the jacket 40. This annular 
cylindrical space 50 is filled with an inert gas such as nitrogen, which 
is introduced thereinto from the closing ring 49 at the outer end of the 
jacket 40. In order to maintain an inert atmosphere in the cylindrical 
space 50, there is a connection 52 through the ring 49 to the space 50 
from an inert gas supply. The particular cooperating shapes of the rib 34 
and groove 43 insure the centering and uniformity of the spaces 50. Since 
the outside of the lower end of the jacket 40 is not at a high 
temperature, the outer seal 53 between the jacket 40 and the electrode 20 
may be a normal pressable gasket urged into place by an additional ring 55 
and bolts 56. Attached to the outside of the jacket 40 are brackets 58 
through which the jacket is held in place as shown in FIGS. 2 and 4. These 
brackets 58 may be adjustably anchored to a beam 59 (see FIG. 1), which 
beam also may be a support for the furnace 10. 
In the bottom of the groove 43 there is provided a refractory gasket 60 for 
sealing the connection between the sleeve 30 and jacket 40. In addition to 
the gasket 60, or as an integral part thereof, there is an additional 
gasket 62 in the groove formed between the inner edge of the groove 43 and 
the groove formed between the sleeve and the rib 34 for providing a second 
seal between the sleeve 30 and jacket 40. These gaskets 36, 60 and 62 are 
of a refractory material which can withstand temperatures up to 
2300.degree. F., such as for example Fiberfrax 970 comprised primarily of 
aluminum and silica fibers. 
If additional cooling is required, an air jet 64 (see FIG. 2) may also be 
directed onto the outside of the jacket 40 and adjacent electrode 20. 
Although specific compositions have been described for the electrode 20, 
sleeve 30, inert gas, gaskets 36, 60 and 62, and cooling fluids for the 
jacket 40, and jet 64, it should be clearly understood that other 
materials may be used for the parts for the protection of the electrodes 
20 without departing from the scope of this invention. 
While there is described above the principles of this invention in 
connection with specific apparatus, it is to be clearly understood that 
this description is made only by way of example and not as a limitation to 
the scope of this invention.