Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02614867 2008-01-04
GLASS MELTING APPARATUS AND METHOD
RELATED APPLICATIONS
This is a divisional of Canadian Patent application No.
2,283, 020.
BACKGROUND OF THE INVENTION
This invention relates to certain improvements in apparatus
and methods for melting glass. More particularly, this
invention relates to apparatus and methods which control
the location of the "hot spot," i.e. area of highest
temperature in the liquid pool of melting or molten glass
in a glass melter so as to control the wear out of various
melter and discharge elements thereby reducing the number
of shutdowns needed for replacement or rebuild purposes.
Still further, this invention relates to unique methods and
apparatus for venting corrosive volatiles from the system.
Melters of various shapes and sizes which present glass
batch (usually in powdered ingredient form, with or without
cullet) often by floating the batch material as a
relatively thick layer on top of a molten pool of glass
being heated and melted beneath the batch, and thereafter
distributing the molten glass from the pool through a
discharge port in a side wall of the melter to a
conditioning zone (conditioner), and thereafter to a
forehearth array or other working area, are well known in
the art. Exemplary of such systems are conventional, in
line combinations of a melter, conditioner, and forehearth
used to distribute molten glass to an array of spinners for
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making fiberglass batts of insulation. Other uses for such
combinations are, of course, known, and the art, as a
whole, is generally represented by the following prior art
references: U.S. Pat. Nos. 3,498,779; 4,365,987; 3,897,234;
4,812,372; 4,001,001; 4,994,099; 4,017,294; 5,194,081;
4, 023, 950; and 5,616,994.
Generally speaking, and prior to my invention in the
aforesaid application Ser. No. 08/917,207, now U.S. Pat.
No. 5,961,686, the art of glass making accepted the problem
of multiple shutdowns due to the fact that the various
elements in conventional melters, except in very unusual
and unpredictable situations, wore out at different times.
In this respect, it is characteristic in the prior art
construction of melters to employ a cylindrical or
rectangular tank-like configuration in which the side and
bottom walls are formed of refractory material such as Cr,
Al--Zr--Si, or Al/Cr based compositions whose corrosion
rate usually increases with increased temperatures. Adding
to this problem is the fact that in such configurations one
or more discharge ports are either required or desired at
different locations within the tank, e.g. in the bottom
wall and in at least one location in the side wall of the
tank. Because the temperature of the glass can, and often
does, differ markedly between a "hot spot" volume in the
molten glass, usually in the center of the tank near the
bottom wall, and the remaining molten glass volume, e.g. at
the side walls, melter parts in the cooler areas wear out
less rapidly than parts located in or proximal the "hot
spot."
In a typical example of this problem, the melting tank is
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provided in its bottom wall with a discharge port for
draining the tank and a side discharge port for
distributing the molten glass to a conditioning zone. Such
discharge ports, whether in the bottom or side walls, are
normally formed of molybdenum or an alloy thereof which is
relatively corrosion resistant and thus is reasonably able
to withstand the high temperatures experienced in the
melter over a given period of time. Unfortunately, like the
refractory wall material, these molybdenum based ports have
a corrosion rate which increases with temperature.
In many melters it has also been conventional to cool the
walls by various techniques such as with a water-cooled
shell surrounding the melter. Such cooling of the bottom
and side walls, despite inherent currents of flow in the
molten glass, tend to isolate the "hot spot" and set up the
temperature differentials as discussed above, which then
lead to the differences in wear out rates of the various
parts and the need for expensive, time consuming, multiple
shutdowns otherwise unnecessary if all the parts were to
wear out at substantially the same time.
In a typical prior art melter, for example, usually of a
circular, cylindrical bottom, side wall configuration, the
furnace is open topped, side and bottom wall cooled, and is
provided with electrodes to melt the batch material. These
electrodes are usually located in the melter either above
the batch or in the molten pool of glass itself, often near
the bottom or inserted through the batch. Powdered batch
material is then "floated" on top of Lhe melting glass
beneath it, usually by a conventional, metered batch
delivery system located above the melt area and fed by
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gravity continuously to the batch layer as its underneath
surface melts into the molten volume of glass beneath it.
It is, of course, within this molten glass volume beneath
the batch layer that the aforesaid "hot spot" forms.
While convection currents created in the melting glass
serve to equalize, somewhat, the temperature of the molten
glass pool, it is very often an inherent characteristic of
such melters, particularly where bottom entry electrodes
are employed, that the bottom center of the melter is where
the "hot spot" forms. For example, a typical "hot spot"
may be from about 3150-3250 degrees F. By contrast, the
side walls will only then be, particularly if water-cooled,
at a significantly lower temperature, e.g. about 2500-2700
degrees F. Even if water-cooled, in certain instances, the
bottom wall will be so close to the "hot spot" that its
temperature in a localized area will, for all intents and
purposes, be that of the "hot spot," thus differing from
other areas of the bottom wall, as well as the side wall
and discharge port in the side wall. Since the drainage
port is conventionally located in the center of the bottom
wall, and thus at or proximal the usual "hot spot"
location, its corrosion rate differs markedly from that of
the side discharge port and side walls.
As exemplified by the above typical melter arrangement,
multiple melter shutdowns may thus become necessary. For
example, the discharge drain port and/or bottom wall may
have to be replaced, while the side walls and side
discharge port remain in acceptable operating condition,
only to have to replace one or more of these two latter
parts at a later time in a second shutdown, while the
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replaced bottom wall and/or drain discharge port are not
yet worn sufficiently to economically justify their
replacement.
In short, it would constitute a considerable advance in the
art of glass melting if a technique were developed which
could control the location of the aforesaid "hot spot" in a
glass melter so as to displace it (locate it) away from the
refractory walls and metallic discharge port tubes (side
and bottom) such that all of the elements in the melter
subject to corrosion and wear out therefrom were to wear
out at substantially the same time.
The term "at substantially the same time," as used herein,
means that the elements which are the subject of corrosive
wear out are in such a condition at the time that one
element is in the most advanced condition of wear out, that
it is economically justifiable to replace all the elements,
rather than to go through another shutdown to replace a
less worn out element when it completely wears out later in
time.
A significant advance toward reaching this goal and solving
this prior art problem was achieved, based upon the
acceptance of the inherent location of the "hot spot" in
the melter. By the use of a unique discharge port concept
located in the side wall of the melter, a sufficient
distance away from the "hot spot," coupled optionally with
side and bottom wall cooling means, the side discharge
ports and side walls could justifiably be replaced at the
same time. In addition, in certain embodiments, by relying
on convection currents and sufficient bottom wall cooling,
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the bottom wall and bottom discharge drain theoretically
could, at times, be controlled to wear out at substantially
the same time as the side wall and side discharge port.
Despite this significant advance in the art, it has now
been found that the "hot spot" (i.e. volume of highest
temperature) often exists, in certain furnaces, inherently
too close to the bottom and/or side walls of the melter
tank and that circulation currents, even with wall cooling,
are insufficient to keep the wear out rate of the bottom
wall and bottom discharge orifice truly substantially equal
to that of the side walls and side discharge orifice. Thus
there continues to be a need in the art for a still further
improvement which creates an even more equalized wear out
rate among the essential parts in the melter (e.g. the
refractory melter lining which makes up the melter walls,
side and bottom, and the various discharge ports in these
walls.
There is yet another problem which the art of glass melting
has had to face. In many glass melting operations, such as
in melting glass ultimately used to make fiberglass
insulation, it is necessary to employ batch ingredients
which create highly corrosive volatiles during the melting
and/or conditioning operation. These volatiles often end up
in the atmosphere above the glass and can thus rapidly
corrode walls, orifices and heater elements if not
effectively exhausted from the system. Such volatiles are
well known and include, for example, various sodium and
borate compounds.
In melting systems which do not employ, or need not employ,
the highly advantageous technique during glass melting of
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floating batch material in a relatively thick layer (e.g.
about 3"-4", or at times as high as 10") on top of the
molten glass, the corrosive volatiles can usually be
exhausted during melting by exhausting them from the melter
itself. However, when the more desirable batch technique of
floating the batch on top of a molten pooi of glass is
employed, the volatiles do not readily escape through the
batch, but rather are only released in the conditioner when
the molten glass is then freed from the batch material
being on top of it. This, then, gives rise to the need for
a new technique for effectively eliminating corrosive
volatiles from the glass in the conditioner, particularly
before they reach the forehearth.
It is a purpose of this invention to fulfill the above
needs in the art, as well as other needs which will become
apparent to the skilled artisan once given the following
disclosure.
SUMMARY OF THE INVENTION
Generally speaking, this invention fulfills at least one of
the above-described needs in the art by providing both a
method and an apparatus for melting glass which controls
the location of the "hot spot" so as to locate it within
the melt at a sufficient distance from the side and bottom
walls, as well as any discharge orifice therein, so that
the discharge orifices and walls (bottom and side) may be
replaced at substantially the same time.
In one embodiment of this invention this is accomplished by
providing in a melter for melting glass from batch material
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therein in which the batch material is floated on top of a
pool of molten glass and the batch is melted by heating
means so located as to form a finite volume of molten glass
within the pool of molten glass, which finite volume is at
a temperature substantially higher than the remainder of
the molten glass within said pool, the melter including a
side wall and a bottom wall and a discharge port located
within at least one of the walls, the improvement
comprising wherein:
the heating means are so located as to create this finite
volume of substantially higher temperature at a spaced
distance from the walls and any side discharge orifice
located in the walls whereby the walls and any side
discharge orifice wear out at substantially the same time
during melting of glass in the melter.
In certain preferred embodiments of this invention the
heating means comprises a plurality of electrodes in a
generally circular array located within the molten pool
beneath the batch material floating thereon, and including
a retaining structure for each electrode extending above
the batch, which retaining structure includes an adjustment
mechanism for adjusting the depth to which the electrode is
inserted into the molten pool, and also, preferably, for
adjusting the horizontal location of each electrode within
the pool, as well. By adjustment of the electrode array
both horizontally and vertically within the pool, the
optimal location for the inevitable "hot spot" can be
achieved for any particular size and/or configuration of
melter tank (furnace) extant to optimize the goal of
achieving substantially the same wear out time of the
various melter parts.
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In certain preferred embodiments, in this respect, the
melter may be one of an open top type, with a water-cooled
jacket or shell, whose batch feed, optionally, may be a
simple tube located above and in the center of the
electrode array. In still further preferred embodiments,
the melter is a cylindrical tank with a side discharge port
of the type disclosed in my aforesaid pending application
Ser. No. 08/917,207, now U.S. Pat. No. 5,961,686. A
particularly advantageous electrode array, in this respect,
consists essentially of six electrodes equally spaced in a
circular pattern about the center of the cylindrical tank,
the radius of the circle being about one-third the radius
of the inside diameter of the tank.
This invention further includes within its scope certain
unique methods for melting glass. Generally speaking, in
this respect, this invention includes in the method of
melting glass in a melter which includes a bottom wall, a
side wall and at least one discharge port located in a said
wall and comprised of a corrosion resistant material whose
corrosion rate increases with temperature, the steps
comprising, forming a molten pool of glass within the
melter, floating batch material on top of the molten pool,
melting the batch material so as to add further molten
glass to the pool, discharging molten glass from the melter
through a discharge port, and during the melting of the
glass batch material, creating within the pool a finite
volume of molten glass which is at a significantly higher
temperature than the remainder of the molten glass within
the pool, the improvement which comprises forming the
finite volume of the higher temperature molten glass at a
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location sufficiently removed from the walls and the
discharge port such that the walls and discharge port wear
out at substantially the same time.
This invention further includes within its scope certain
unique apparatus and methods for exhausting corrosion
causing volatiles from the overall system before they reach
the forehearth, thus fulfilling yet other needs in the art.
Generally speaking, the unique apparatus as contemplated
herein for exhausting volatiles during glass melting and
distribution includes, in the combination of a walled
melter, a walled conditioning system having at least one
heating element extending through an orifice in a wall
thereof and a forehearth, said melter being connected in
molten glass flow communication with said conditioning
system through a discharge port located in a wall of the
melter at a first end of the conditioning system and the
opposite end of the conditioning system being connected in
molten glass flow communication with the forehearth, the
improvement comprising at least one removable heating
element extending through the orifice in a wall of the
conditioning system and exhaust means proximal the orifice
for exhausting corrosive volatiles from above the molten
glass in the conditioning system through the orifice when
the removable heating element is removed therefrom.
In certain preferred embodiments of this invention the
melter, conditioning system and forehearth are all located
in substantially the same horizontal plane. In certain
other preferred embodiments, of course, this invention
employs as its melter the aforesaid unique melter which
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controls the "hot spot" so that its various elements wear
out at substantially the same time.
Still further, and generally speaking, the unique methods
associated with this novel exhaust technique include in the
method of melting, conditioning and distributing molten
glass wherein the method includes the steps of providing in
serial flow communication, a melter, a walled conditioner
and a forehearth array, melting glass in the melter,
delivering molten glass from the melter to the conditioner,
providing at least one heating means located in an orifice
in a wall of the conditioner, delivering the molten glass
from the conditioner to the forehearth and distributing the
molten glass from the forehearth, wherein the method
further includes the step of removing a substantial portion
of the corrosive volatiles from the atmosphere above the
glass before they reach the forehearth, the improvement
comprising, removing at least one of the heating means from
its respective orifice thereby providing an open orifice in
a wall of the conditioner, providing an exhaust means in
exhaust functioning communication with respect to the open
orifice, and exhausting corrosive volatiles from the
conditioner through the open orifice.
In certain preferred embodiments the method as above set
forth further includes the step of providing batch material
on top of the molten glass in the melter.
This invention will now be described with respect to
certain embodiments thereof accompanied by various
illustrations.
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BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partial side sectional view of one embodiment
of this invention.
FIG. 1A is a partial top view of the embodiment of FIG. 1,
with the molten glass and batch only partially shown so as
to illustrate the inside bottom wall of the melter.
FIG. 2 is a partial side sectional view of the embodiment
of FIG. 1.
FIG. 3 is a schematic outline of the current pattern among
the electrodes in the embodiment of FIG. 1.
FIG. 4 is a partial side sectional view of the side
discharge port and vent chamber of the embodiment of FIG.
I.
FIG. 5 is an end sectional view of the cooling means and
side discharge tube of FIG. 1.
FIG. 6 is a side sectional view of a conditioner cooling
means used in the practice of an embodiment of this
invention.
DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS
With reference initially to FIG. 1, there is illustrated
therein an apparatus for melting glass according to this
invention. The apparatus as illustrated includes a melter
1, a conditioner 3, and, as partially shown, a forehearth
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5. Forehearth 5 is conventional and, for example, may be of
the type provided with multiple orifices along its
elongated bottom wall (not shown for convenience) for
distributing molten, conditioned glass at an appropriate
temperature to a conventional spinner array for making
fiberglass insulation batts (also not shown for
convenience). Orifice 7, as illustrated, is an air-cooled
drain orifice in this embodiment used to drain the system
during shutdown, the distribution orifices leading to
fiberglass spinners being further downstream.
In the embodiment of FIG. 1 the three zones of operation,
i.e. melter 1, conditioner 3, and forehearth 5 are
preferably all located in substantially the same horizontal
plane. This eliminates a known use of the location of the
forehearth on a level (e.g. on a separate floor of the
plant) below the conditioner, called the "drop area", which
heretofore was advantageously used to exhaust volatiles
from the system. In this way, the need to build into the
plant facility a separate level or floor is eliminated and
its considerable cost saved. However, this eliminates the
aforesaid advantageous drop area between the exit end of
conditioner 3 and entrance end 6 of forehearth 5 which was
used to vent (exhaust) corrosive volatiles. This, in turn,
gives rise to the unique venting system of this invention
discussed above and described more fully below.
Turning now to a more detailed description of melter 1,
attention is directed, in addition to FIG. 1, to FIGS. 1A,
2 and 3. The mechanism illustrated is one embodiment of a
mechanism as contemplated by this invention for selecting
the location of, and controlling the size of, "hot spot" 9
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created in molten glass pool 11 during the melting
operation. As illustrated schematically in FIGS. 1, 1A, and
3 in dotted lines, by using an array of heating electrodes
13, and here preferably six, arranged in a substantially
circular fashion below the layer of batch material 15
floating on pool 11, "hot spot" 9 is generally confined to
a finite, generally hexagonal or circular cylindrically
shaped volume of glass below batch 15, whose central
vertical axis "C" corresponds with the central vertical
axis of cylindrical melter tank 1. FIG. 3 is a schematic
whose full lines illustrate the theoretical paths of
heating current extending among the electrodes and whose
dotted lines illustrate a top view of "hot spot" 9.
Melter 1 is of a conventional tank-like, cylindrical
construction having conventional side wall 19, and bottom
wall 23, each lined with refractory linings 21 and 25,
respectively. Such refractory linings 21 and 25 may be
formed of conventionally used refractory material such as a
chromium based material which is known for its corrosion
resistance, but whose corrosion rate increases with
temperature. In a typical example, lining 21 may be 90% or
more by weight Cr, while linings 19, 23, and 25 may have
less Cr, e.g. about 30-50% by weight. Melter 1 further
includes in conventional fashion drain discharge port 31
located centrally of melter 1. Discharge port 31 is
conventionally formed of a corrosion resistant metallic
tube 33 inserted through an orifice in shell 29, bed
material 35, wall 23 and liner 25. Port 31 is principally
used for draining glass from melter 1 preparatory to
shutdown.
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As further illustrated in FIG. 1, but better shown in FIG.
2, batch material 15 is floated on pool 11 of molten glass
such that the underside surface of batch material 15 is
constantly being melted while the batch layer is being
added to as it is consumed by a conventional metered batch
system whose exit end tube is shown at 37. As best
illustrated in FIGS. 1, 1A, powdered batch 15 is fed by
gravity to the substantial center of the circle having a
radius R, whose circumference is subscribed by the location
of the six electrodes 13 as points on the circle and whose
center is contiguous vertical axis "C".
As best illustrated in FIG. 2, the depth "D" of molten pool
11 is the distance from the inner surface of lining 25 to
the under surface of batch material layer 15. Distance "D"
varies, of course, given the drainage slope in the bottom
wall structure of melter tank 1. As shown in FIG. lA, in
one embodiment of such a melter 1, radius R2 may be about
7-8 feet, radius Rl, about 1/4-1/3 of R2, e.g. about 2-3
feet, while depth "D" at the side wall 19 may be about 13-
15 inches and the thickness "T" of the powdered to semi-
molten batch layer may be about 3-5 inches or more (e.g. up
to 10").
With further reference to FIG. 1 and FIG. 4 more
particularly, melter 1 is provided with a side discharge
port generally at 39 for distributing molten glass from
pool 11 to conditioner 3. In preferred embodiments of this
invention side discharge port 39 is constructed according
to my aforesaid application Ser. No. 08/917,207, now U.S.
Pat. No. 5,961,686. As disclosed therein and as illustrated
here, discharge port 39 includes a corrosion resistant
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metallic tube 41 (e.g. of molybdenum or an alloy thereof
and usually of the same metal which makes up drain tube 33)
extending through the side wall structure of tank 1 in flow
communication with the entrance end of conditioner 3. As
shown in FIGS. 1 and 5, tube 41 is thicker at its top than
bottom circumference, and is cooled by circulating water or
other fluid through surrounding shell 43 in the direction
of the arrows (FIG. 5).
The purpose of making the top of tube 41 thicker is
because, for some reason not fully understood, and despite
the fact that tube 41 is fully submerged in molten glass
theoretically protecting it throughout its circumference
from oxidation, the top of tube 41 wears out more rapidly
than its bottom portion. Thus it has been found in practice
to be advantageous for longer wear life to, for example,
with a discharge tube of about 6 inches (O.D.), use a 4
inch (ID) orifice created by a 1/2 inch offset from center.
While not fully understood, this uneven wear pattern may be
explainable by the phenomenon known as "upward drilling" in
a refractory material as it is corroded by corrosive
materials in the glass.
Conditioner 3 is principally used to lower the glass
exiting melter 1 to an appropriate temperature for
distribution to the forehearth. For example, in a typical
operation, glass "G" may exit side discharge tube 41 at a
temperature of about 2560 degrees F, and be lowered to
about 2230 degrees F (e.g. a drop of greater than 200
degrees F) as it enters forehearth 5 beneath submerged
block (dam) 45 which functions along with dam 47 to isolate
molten glass in conditioner 3 from glass in forehearth 5
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during shutdown. Dam 45 further serves to isolate the
relatively volatile free atmosphere of forehearth 5 from
the atmosphere of conditioner 3. In a similar manner, of
course, dam 49 isolates molten glass in conditioner 3 from
melter 1 and exhaust area "E" (described below) during a
shutdown. Drain port 51 is provided in bottom wall 53
(which may be water-cooled) to drain glass from conditioner
3 prior to shutdown or when otherwise needed.
Provided in top wall 55 of conditioner 3 is a cooling
baffle structure 57 (more than one can be optionally added,
if desired) for circulating cooling water or air
therethrough. Baffle 57 is a unique concept to this
invention. Without baffle(s) 57, there would be formed a
stream of higher temperature glass on the surface of flow,
potentially causing lower glass to crystallize. Baffle(s)
57 divert hot glass downwardly, thereby preventing this
problem from occurring and creating better homogeniety of
temperature in the glass and a lack of stagnant glass in
the bottom of conditioner 3.
In addition, top wall 55 is provided with removable burners
59a-e located in their respective orifices extending
through wall 55. During start-up of the system, in
conventional fashion, burners 59a-e are employed to heat
the refractory walls so that molten glass flowing from
melter 1 and exiting tube 41 will remain molten, and
continue to flow through conditioner 3, rather than
solidify when it contacts the refractory walls.
After start-up and filling conditioner 3 to the depth
desired with molten glass (not shown for convenience), the
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molten glass must then be cooled to the required exit
temperature as aforesaid. For this purpose, one or more of
the removable burners 59a-e are removed (thus vacating
their respective orifice 60a, b, c, d, or e) and replaced
by water-cooled tubes such as a cooling tube 61 shown in
FIG. 6, which is inserted into a vacated orifice made open
by removal of a burner 59 therefrom. As shown in FIG. 6,
cooling tube 61 is a simple rectangular or circular shell
63 (depending on the conforming shape of the vacated
orifice it is inserted in). Shell 63 has located in its
wall, water outlet port 65. Within shell 63 there is
located an internal tube 67 for providing cooling water (or
other fluid) to shell 63 in the direction of the arrows.
Cooling tubes 61 are metallic and may be made of a
corrosion resistant metal such as molybdenum, if desired.
Tubes 61 can be provided with a simple mechanism for
controlling their depth of emersion into the molten glass.
This, in turn, can be used to ultimately control the outlet
temperature of the glass at the entrance 6 of forehearth 5.
In this respect, orifice 64 is used for a thermocouple (not
shown) to sense the temperature of the glass that is
entering forehearth 5.
To cool the glass, cooling air may be used instead of, or
alternatively with, cooling tubes 61. For example, in a
typical operation which cools the molten glass from about
2560 degrees F to 2230 degrees F in conditioner 3, orifice
59a may have cooling air blown through it, as may orifice
59e. This also forces an atmosphere changeover to
continuously rid the atmosphere of volatiles. Then, cooling
tubes 61 may be inserted into orifices 59b and c. This
leaves orifice 59d open for use in a unique exhaust system
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as contemplated by this invention and as described below.
It is understood, of course, that orifices 59a-e may have
other combinations of air flow and/or cooling tubes
employed, including all cooling tubes 61 or all cooling air
flow if desired. It is, however, an important feature of a
preferred embodiment of this invention that at least one of
these vacated orifices, preferably either orifice 59d or
59e, and most preferably 59d, be employed to exhaust
corrosive volatiles from the atmosphere above the molten
glass in conditioner 3.
As illustrated in FIG. 1 in phantom dotted lines, an
exhaust system 69 is provided at orifice 59d which may be
turned on after burner 59d is removed, thus exhausting
volatiles from conditioner 3 before they reach forehearth
5. As a further part of a preferred exhaust system, a
further permanent exhaust port 71 is provided at the
initial entrance end of area "E" in conditioner 3 where an
initial portion of the volatiles may first be removed from
the atmosphere above the molten glass immediately as it
exits side discharge tube 41.
Turning now, more particularly, to the electrode melting
apparatus illustrated in FIGS. 1-3, there is presented a
unique apparatus and method for controlling the size and
location of "hot spot" 9 which can otherwise be so
detrimental to wear out, and which, if not controlled, can
cause unnecessary multiple shutdowns of the system as
described above.
In the melting configuration as illustrated there are
provided six conventional electrode melters 13 which are
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conventionally water-cooled by entrance line 73 and exit
line 75. Other configurations using lesser numbers of, or
more, electrodes may be used. Electrode 13, including its
current-carrying shaft 79, may be formed of molybdenum as
is the actual electrode melter portion 81. Water-cooled
shell 77 may be formed of stainless steel. As illustrated
schematically in FIG. 2 and more realistically in FIG. 1,
electrode portion 81 is immersed in the molten glass 11 to
the depth required, while molybdenum shaft 79 is
protectively cooled by cooling shell 77.
Electrode 13 is supported by horizontal shaft 83 which
carries electric current and the cooling water to and from
the electrode. In turn, shaft 83 is connected to an
adjusting mechanism 85 which includes a central shaft 87
which retains, in vertical position, outer shaft 89.
Rotating mechanism 91 allows shafts 89, and thus shaft 83
attached thereto, to be angularly adjusted in the
horizontal plane by rotating the shaft on ball bearing 93
and securing the shaft at the desired angle by a
conventional locking mechanism 95 when the desired angle is
reached.
In addition to this horizontal adjustment, the vertical
position of electrode 13 within molten pool 11 is
accomplished by gear rachet mechanism 97 which, via screw
threaded rod 99 attached to shaft (sleeve) 89, slidable in
retaining tube 101, may be activated to vertically adjust
the height of shaft 83 above melter 1 and thus that of
electrode 13 with respect to pool 11. Protective bellows
103 extends between slidable shaft 89 and upper nonslidable
shaft 105 to which rachet mechanism 97 is attached, to
CA 02614867 2008-01-04
protect that portion of shaft 87 on which shaft 89 slides
during vertical adjustment, from dust and other
contamination.
As can be seen, the adjusting mechanism 85 provides an
effective mechanism for adjusting both the horizontal and
vertical positions of each electrode 13 with respect to the
molten bath. Since it is the electrode array which
ultimately defines and limits the finite volume of "hot
spot" 9 (e.g. typically at 3150-3250 degrees F), the unique
apparatus illustrated here presents, by its precise
adjustability, the ability to control the location, size
and, indeed, in certain instances, the general shape of the
"hot spot" 9. Thus, by proper adjustment, the "hot spot"
may be controlled at a preselected location within melter 1
(i.e. within pool 11) sufficiently removed from the
sensitive refractory and metallic parts, so that these
elements wear out at substantially the same time, thus
minimizing the number of shutdowns needed for repair.
In a typical operation of the above-described system,
electrodes 13 are adjusted so as to be equally spaced (as
illustrated in FIG. 1A) about vertical axis "C" of tank 1.
Electrode melter portion 81 of each electrode 13 may be
approximately 6 inches in diameter and about 61/2 inches in
height and may be operated at about 4000 amps. Given a side
height "D" within the aforesaid range, and a radius R2 of
about 8 feet and a radius Rl of about 3 feet, with an
adjusted depth of about 9-12 inches between the bottom of
electrodes 13 and the top surface of bottom wall liner 25
for each of the six electrodes employed in the array as
shown, a "hot spot" 9 as illustrated in FIGS. 1, IA is
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sufficiently controlled and confined to a finite volume
within the electrode array such that the "hot spot",
usually at about 3150-3250 degrees F is substantially
removed from the refractory walls and discharge ports,
while such walls and ports are located nearest the coolest
glass as cooled by the cooling water in cooling shell 29
and as affected by glass flow currents shown by the
circulating arrows in FIG. 1. In this way, and by proper
adjustment of the electrode array for any given
configuration of melting tank, arrived at by routine
experimentation well within the skill of the artisan once
given this disclosure, a unique technique for substantially
equalizing wear out of the melting tank parts may be
accomplished, thus minimizing the number of shutdowns
required for replacement of parts.
Once given the above disclosure, many other features,
modifications and improvements will become apparent to the
skilled artisan. Such features, modifications and
improvements are, therefore, considered a part of this
invention, the scope of which is to be determined by the
following claims.
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