Note: Descriptions are shown in the official language in which they were submitted.
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D E S C R I P T I O N
ELECTRIC MELTING OF SOLIDIFIED
GLASS lN MELTING UNITS
TECHNICAL FIELD
This invention is a method and electrode
arrangement for electrically melting solidified glass in
15 difficult to reach regions of a glass melting furnace not
readily accessible with fossil fuel heating means and more
particularly to electrical heating of solidified glass in
regions such as a submerged outlet throat between a furnace
melter section and the ri;er through which the glass i5
20 supplied in production.
During periods of curtailment of furnace
operations in the production of glass, the practice has
been to maintain the upper region of the melter section and
the outlet throat at a low temperature by supplying a low
25 level of heat thereto. Upon decision to restart the
furnace, the start-up time can thus be minimized as well as
the thermal shock and mechanical stress of startup of the
furnace.
The cost of energy for maintaining furnaces in a
30 heated condition over such an extended period, for example,
in the order o~ months, hDwever, is an extre~ely costly
non-productive burden. To eliminate such high cost, two
alternate approaches are possible, one being to drain the
furnace co~pletely upon shut-down, and the second is to
35 allow the glass to completely solidify in the furnace.
When a glass melting furnace is completely
drained during down times, restart procedures correspond
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1 much to those of start-up of a new furnace. Restart of a
completely drained furnace, however, has the disadvantage
that spalling of refractory and cracking under thermal
stress can result in areas of previous wear of the furnace.
Restart of a furnace with solidified glass of the
previous melt therein is often found more desirable in that
it reduces the thermal shock difficulties. Where a
submerged throat exists in the outlet end of the furnace,
however, remelting of the solid glass in the thr~at is
lO extremely difficùlt to accomplish because of its
inaccessability to external sources of heat in addition to
remoteness of heat of the melt.
Accordingly, it is a general object of the
present invention to provide a method and means for melting
15 solidified glass in the difficult to reach regions of a
glass melting furnace.
More particularly, it is an object of the present
invention to provide a method and means for electrically
melting solidified glass in a submerged throat between the0 melter and the riser sections of a glass melting furnace.
BACKGROUND ART
During periods of curtailment or reduction of
usage of glass melting furnaces, it has been the practice
to maintain the glass in a submerged throat in a molten
25 state by use of electrodes as disclosed in Maddux, U.S.
Patent 3,997,710. This becomes extremely uneconomical as
the length of out-of-service time increases. Methods have
been developed to remelt glass in a melter section by
combustion heating means as disclosed in Froberg et al,
30 U.S. Patent 3,842,180. This method, relying on combustion
heating, will not work in areas which are inaccessible to
fossil fuel combustion such as a submerged throat. Similar
methods of remelting glass in a forehearth by means of
combustion gas has been disclosed by Nuzum, 1n U.S. Patent
3,1g8,619. Again, combustion gases cannot be used in the
present invention. The only other non-combustion gas means
for melting glass in an inaccessible region is through
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1 Radio Frequency heating such as disclosed by Ferguson, U.S.
Patent 2,186,718. The ph~sical size of the submerged
throat makes this method impractical. The present
invention using Joule effect heating elements and
5 sequencing the power between selected pairs of electrodes
overcomes the problems associated with the prior art.
DISCLOSURE nF THE INVENTION
Solidified glass in a submerged throat of a glass
melting furnace is melted according to the invention by the
10 step by step thawing or melting of glass between each
adjacent pair of a series of electrodes spaced apart from
each other in a path extending from a position just before
the entry to the throat to a position at the riser. The
spacing of the electrodes in the series is such that when
15 power is applied between any two adjacent electrodes when
molten material exists about one of the electrodes, a Ooule
effect conductive path is provided to the next adjacent
electrode. Under such condition, glass between the two
electrodes can be melted by supply of electric energy
20 between the two adjacent electrodes. Molten glass is then,
in turn, provided about the second electrode to permit
Joule effect heating of glass between it and the next
succeeding electrode of th~ series as well as between such
next electrode and the first electrode. Thus, solidified
25 glass between each succes;ive adjacent pair of electrodes
can be melted step-by-step to provide a continuous molten
path through the throat to the riser whereupon the glass
can be supplied for production and conventional heating of
the glass can be relied upon.
A feature of the invention is that it allows
curtailment of glass production by complete shutdown of a
furnace without requiring full drainage of the glass or
requiring that it be main~ained hot during the shutdown
period.
Another feature of the invention is that it
maximizes production for the energy input regardless of
fluctuating demands for output.
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~R I EF DESCR I PTI ON OF T~IE ~RAW I NGS
FIGURE 1 is a broken away plan view illustrating
an electric glass melting furnace with a submerged throat
and riser in its exit end leading to a forehearth from
5 which molten glass is supplied for production of products
such as glass fibers.
FIGURE 2 is a cross sectional view taken on line
2^2 of the throat portion of the electric furnace
represented in FIGURE 1.
FIG~RE 3 illustrates in perspective the submerged
throat represented in cross section in FIGURE 2 showing the
electrodes inserted in the submerqed channel for melting
solidified glass therein.
BEST MnDE F~R CARRYING OUT THE I_VENTION
Referring to the drawings in greater detail,
FIGURE 1 illustrates a plan view of an electric furnace lU
having a melting region 11 heated by electric power
supplied by way of electrodes 20 located in the four
corners of the furnace. The furnace here illustrated is of
20 the cold top type in which the batch is supplied to the top
of the molten mass within the furnace, such batch being
melted at its interface with the underlying molten pool of
glass. As the molten glass is heated by the power supplied
at the electrodes 20, it is withdrawn for use in production
25 of products through a recessed channel or slot 12 located
at the mid-region of one wall of the furnace. Thus glass
is flowed through an outlèt throat 15 to a riser 16
connected to the furnace forehearth 17 for the supply of
glass to units for production of products such as glass
fibers.
In supplying glass from the furnace through a
submerged throat, as illustrated, it is conventional to
provide supplementary heat by way of electrodes 30 and 40
located in the slot 12 leading to the throat 15 and at the
35 exit from the throat in the region of the riser 16,
respectively. Thus, the glass flowing from the melting
region can be controlled in temperature by supply of the
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1 supplementary heat before its introduction into the
forehearth. This arrangement is quite advantageous in
assuriny proper and stable temperature of the glàss output
from the melting region upon its introduction into the
S forehearth for use in production.
As hereinabove described, production at times is
required to be curtailed, usually for economic reasons, and
the downtime can continue for extended periods such as d
matter of weeks or even months. Whereas it has been a
lO practice to maintain such furnaces in a heated condition
under low power supplied from electrodes 2~, because of the
high cost of drainage and restart of an empty furnace, it
is more desirable to shut down the furnace with a full load
of glass contained therein. Such shutdown of the furnace,
15 however, has a disadvantage in that certain regions of the
furnace, such as the submerged throat, when loaded with
solidified glass is extremely difficult Dr practically
impossible to melt by conventional means for reinitiation
of the flow of glass output.
According to the present invention, one or more
auxiliary or supplementary electrodes are specially
inserted or permanently provided in the difficult to reach
regions, such as the submerged throat 15. In the
arrangement illustrated, a series of electrodes 35a, 35b,
35c, 3sd and 35e are pro~ided in spaced relation within the
throat 15 between the main power supply electrodes 30 and
40 located at the entry and exit ends of the throat
respectively. In normal operation of the furnace, glass
flows from the melting region 11 into the recessed channel
30 or slot 12 and upon passage through the throat 15 to the
riser 16 and forehearth 17, it is controlled in temperature
by supply of additional heat by ~oule effect current flow
between the electrodes 3~ and 40. The power of electrodes
30 and 40 is supplied frc,m transformer 50 which has a
35 primary 51 and d secondary 52 connected to the electrodes
30 and 4U. However, when the furnace is shut down and the
glass is allowed to solicify in the melting region 11 and
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l the throat 15 these electrodes are ineffective to melt the
solidified glass because of the non-conductivity of the
glass in its solidified condition.
When glass in a furnace is allowed to solidify or
5 otherwise approach solidity in an area such as the melting
region, it can ordinarily be remelted such as with a
combustion burner to melt the desired solidified regions.
In the case of an electrit furnace 10, the glass surface in
the regions of the electrodes can be selectively melted to
10 establish a conductive path between electrodes 20 of
opposite potential and, thereafter, melting can continue by
application of power to the electrodes to promote the flow
of Joule effect current and thus progressively reestablish
a molten pool.
Solidified glass in the throat 15 of the furnace,
however, cannot be so reathed with a combustion burner and,
accordingly, reestablishment of flow through the throat by
such means is usually practically impossiblP. Although the
glass about the electrode 3û might be melted, no conductive
20 path is provided through the throat because of the
non-conductive solidified glass therein between the
electrodes 30 and 40. Thus, where electrodes 35a to 35e
are not permanently in place, a series of such electrodes
can be installed by drilling through the refractory
25 underlying the throat 15 for insertion of as many
electrodes 35 as are necessary for progressive melting of
the glass between the electrode 30 to the electrode 40.
Ilore specifically, molten glass of the melting
region is present about the electrode 30 after conventional
30 heating of the glass in the melting region 11. The molten
glass about the electrode 30 then allows establishment of
an electrically conductive path between it and the adjacent
electrode 35a. Thus, when the power output of the
transformer 50 is applied between electrode 30 and 35a,
35 glass can be melted between these two electrodes. In
addition, glass can be melted in the region about the
electrode 35a in sufficient amount to perm~t establishment
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1 of a conductive path between electrodes 35a and 35b. The
secondary lead 56 of the transformer ~0 can then be removed
from the electrode 35a and connected in turn to `electrode
35b to establish a Joule effect conductive path between the
5 electrodes 30 and 35b. The glass about the electrode 35b
can thereupon be melted to permit subsequent flow of
current between 35b and 35c by connection of the
transforrn~r lead 56 to electrode 35c. The solidified glass
in the throat 15 can thus be progressively melted by
10 successive connection of the transformer secondary lead 56
to each of the electrodes 35a to 35e, one at a time until a
complete conductive path of molten glass is established
between electrodes 30 and 40, whereupon conventional
heating of the throat glass can be resorted to by steady
15 supply of power thereto.
As a variation of this procedure, a voltage can
be established between electrodes 30 and 40 to maintain a
potential difference thereb2tween during the sequential
application of voltage in advancing relation from electrode
20 3~ to 35a, 35b, 35c, etc., by moving the jumper 56 of
secondary 52 of the transformer 50 to each succeeding
electrode as the melt is advanced through the throat.
Thus, the voltage between electrodes 30 and 40 will take
over as soon as the mass of glass in the throat is
25 sufficiently conductive to effect a generation of heat.
As still another variation of the described
arrangeménts, the electrodes 35a to 3~e can be permanently
installed with a sequencing circuit designed to both
provide heat when necessary during operation of the furnace
30 and to automatically advance application of power to the
melt in the throat from a cold start without need for
manually connecting jumpers from one electrode to another
as the glass is melted therein. In addition, electrodes in
the throat may be grouped and sequenced or might be aligned
35 with different spacing in staggered relation through the
throat.
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Thus, while certain arrangments of the present
invention have been described, it will be apparent to those
skilled in the art that various changes and modifications
may be made therein without departing from the spirit and
5 scope of the invention as claimed.
INDUSTRIAL APPLIC~BILITY
The present inv~ntion pertains to glass melting
furnaces~ This invention overcomes the problem of having to
completely drain a glass melting furnace prior to shutdown
10 conditions.
