Note: Descriptions are shown in the official language in which they were submitted.
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In the conditioning and controlling o the tempexature
of molten glass flowing through a forehearth, it is typical that
such forehearths have a ~eries of gas burners arranged above the
level of the glass at either side. The burners have their flames
! directed just above the surface of the glass, the effect of which
is to control the amount of heat loss from the glass to the fore-
I hearth environment and atmosphere.
It is important that the glass temperature and vis-
cosity at the time that it issues from the forehearth be closely
con$rolled. The feeding of molten glass from the forehearth is
in a stream that is divided into gobs or charges of glass in
, glass container manufacturing. In the melting and feeding of
colored glass, it is much more difficult to control the tempe-
rature because the flame burning over the surface of the glass
does not penetrate by radiation and conduction as readily as
would be the case ln the feeding of clear or flint glass.
,' The glass entering the forehearth comes from a refiner
20, where its exit temperature is generally controlled so that the
temperature of the glass ad~acent the spout of the forehearth
may be predicted. On standard gas heated forehearths the glass
along the side of the channel runs colder than the glass in the
center of the channel. With colored glasses, this normally
would lead to a side temperature being 40 to 60 F. cooler than
the center line temperature. In some instances, these side-to-
center differences in temperature have been as high as 120 F.
This temperature imbalance has a marked effect on the glass
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distribution in the containers made from khs glass. As pro-
duction speeds are increased and the bottle weights are de-
creased, the amount of the temperature gradient that can be
tolerated becomes crucial.
Typically, thermocouples or other temperature measuring
devices immersed in the glass have been used at ~he refiner exit
or forehearth entrance. Furthermore, thermocouples have been
positioned at various points along the length of the forehearth.
The portion of the forehearth which is ; e~iately next to the
spout or fPeder is termed the "csnditioning section" of the
forehearth and it is to this section of the forehearth which the
; present invention is specifically addressed.
Electrical heating of glass forehearths, of course, is
not a new consideration and, as a recent example, reference may
be had to U.S~ Patent 4,227,909 dated October 14, 1980 and issued
in the name of ~ornyak, Jr., et al. This particular patent dis-
closes an arrangement for proviaing joule effect heating across
the ch~nnel of the forehearth by positioning of the electrodes
of opposite polarities on opposite sides of ~he forehearth. In
addition, the patent teaches an arrangement for assuring that all
of the electrodes in the forehearth are kept at the same
electrical potential relative to a counter-electrode immersed in
the glass melter.
Another patent recently issued, U.S. Patent No.
25! 4~247,733 to Sevenson dated January 27, 19~1, discloses an
electrically heated glass forehearth in which the electrodes
i appear to extend acro~s the full width of the forehearth, with
adjacent electrodes being of di~ferent polarity to provide a
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joule e~fect heating current therebetween These electrodes
are such as to divide the forehearth into a plurality of
individual zones under separa-te control.
The present invention provides apparatus for heat-
ing molten glass flowing through a conditioning section o
a forehearth comprising, a plurality of pairs of electrodes
e~tending through sidewalls of the forehearth with their
ends terminating adjacent the sidewalls thereof, circuit
means connected to the electrode pairs, the circuit means
being such as to cause joule effect heating of the glass
adjacent the sidewalls of the forehearth, a source of electri-
cal current connected to the circuit means, a first tempera-
ture sensing means positioned within the forehearth at the
center line thereof within the conditioning section adjacent
an end thereof, the first sensing means including a thermo-
couple immersed in the glass, a second temperature sensing
means extending into the forehearth adjacent one of the side-
walls thereof in alignment with the first sensing means,
a current controller in the circuit means, a settable, tempera-
ture override circuit connected to the circuit means, and
means connecting the second temperature sensing to the over-
ride circuit for adjusting the current to the electrodes
to bring the sidewall temperature to the selected set point
of the override circuit.
It should be understood that other heat is applied
to the forehearth by gas combustion in the usual manner and
that the present invention, generallv speaking, could be
considered a front-end boosting by electric heat. In
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addition, the present invention provides a system in which
a set current level selected by the operator may be applied
ko elec-trodes positioned in the conditioning sectlon. These
electrodes and the setting will provide a certain degree
of boosting temperature to the sides of the forehearth. In
a preferred embodiment, tri-level thermocouples or thermo-
couples along the center line of the forehearth adjacent
the spout at three levels will monitor the temperature of
the glass at these three levels. The second temperature
sensing device provides a signal to the override circuit,
which has a settable temperature indicator which may be in
digital form. The operator may set the temperature desired
and the override circuit, in response to the sidewall tempera-
ture, will provide additional current to the system for bring-
ing the sidewall temperature up to the set point temperature.In this manner, sidewall temperature may be brought into
agreement with the center line temperature, thus providing
glass controlled to the optimum condition for glass container
forming.
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BRIEF DESCRIP~ION OF THE DRAWIN~S
EIG. 1 ls a schematic plan view oE the conditioning
section of a forehearth embodyin the present invention, with A
schematic electrical circuit arrangement and control therefor;
FIG. 2 is a cross-sectional view taken at line 2-2
o~ FIG. l; and
FIG 3 is a cross-sectional view taken at line 3-3 of
~IG. 1.
DETAILED DESCRIPTION OF THE DRAWINGS
With particular reference to FIG. 1, there is shown
the conditioning section of a forehearth. This section
of the forehearth comprises a ceramic channel 11 shown
in cross-section in FIG. 3. The channel 11 is
generally of parallel sidewall configuration extending from the
15- refiner until reaching a point 12 where the sidewalls begin to
converge toward each other. At the forwardmost end of the
channel 11, where the converging sidewalls reach their closest
extent, is where a feeder, or what is frequently termed a "spout"
13 is fixed. The spout 13 generally takes the form of a semi-
~O circular metal member 14 li~ed with heat resistant fire brick 15.The spout has a circular opening 16 in the bottom thereof. This
opening will be closed by a ceramic member 8 having downwardly
converging flow channels for providing one or more streams of
glass which may be cut into one or more discrete mold charges.
The member 8, closing the opening 16 is conventional in the art
and a detailed description thereof is not believed necessary.
Suffice it to say that this member termed in the art as a
"ceramic feeder orifice" is supported in an orifice pan normally
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15Z81
hinged to the f~eder bowl so as to be movable up into position or
away from the position of the opening 16.
Concentric above the opening 16 is a cyl~ndrical tube
17 termed a "feeder tube". This member is rotated about its
vertical axis and serves to circulate the glass around the out-
side thereof to equaiize the temperature of the glass in the
, feeder. Furthermore, the lower end of the tube 17 is positioned
relative to the upper edge of ~he opening 16 so as to control
I the flow rate of glass from the forehearth through the opening
10 ~ 16. In a typical forehearth where charges or gobs of glass are
formed for delivery to bottle forming machines, a vertical
plunger will be positioned within the tube 17 and the plunger
will be reciprocated vertically to, in effect, extrude the glass
I in one or more streams and upon raising of the plunger, have the
effect of stopping the flo~ of glass, at which time the extruded
glass is cut into a discrete charge with shears. This cycle
repeats itself so that discrete mold charges are fed from the
feeder 13 and then fall by gravity to the forming machine.
~, As shown in FIG 2, the feeder 13 may and typically
20 ' does have one or more gas burners 18 around the periphery there-
of for keeping the surface of the glass in the spout or feeder
at a stable temperature.
In forehearths of the type shown in PIGS. 1-3, the
forehearth channel 11 is covered by a ceramic roof 19 made of a
plurality of fire bricks 20. Mormally, this roo~ is uninter-
rupted; however, as can be seen in FI~S. 2 and 3, three access
~ holes 21, 22 and 23 are provided through the roof 19. Through
i each hole or openiny extends a te~perature sensing device 24.
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As can best be seen in FIG. 3, there are three ~uch devices,
as shown in E'IG. 2 and each tempera-ture sensin~ device i~
composed of a support member supporting three separate and
distinct thermocouples 26, 27 and 28.
S ~he upper thermocouple is
numbered 26, the middle thermocouple 27, and the bottom or
lowest thermocouple i5 designated 28. Each of the temperature
sensing devices is commonly referred to as a "tri-level thermo-
couple". However, basically, it is a temperature sensing
device having three vertically spaced thermocouples carried there-
by. While three couples are shown, obviously, more could be used
if desired.
In the present situation, where the glass in the fore-
hearth enters the conditioning section at approximately six
inches in depth, the individual thermocouples or sensing elements
of the "tri-level" may be at one inch, three inches and five
i inches,respectively,from the bottom of the channel. Thus lt can
be seen that the thermocouples all are immersed in the molten
~ stream of glass and will sense the actual temperature of the
glass at the position thereof.
It has been applicants' experience that, in the
operation of a forehearth, it is desirable to have the center
line "tri-level" thermocouple sensing elements all at as close
to the same temperature as is possible. ~he control to achieve
such a condition, by and large, must be effected by adjusting the
temperature of the glass issuing from the refiner, with any
additional heat, due to surface radiation, being prevented or
compensated for by the firing of the gas burners along the sides
of the channel prior to the glass arriving at the conditioning
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152~1
section of the forehearth. In some cases, the glass may be
runniny too hot at the bottom of the center line which may
necessitate cooling the bottom glass of the forehearth.
Obviously, anytime it is necessary to provide extra cooling in
the forehearth in order to achieve a temperature balance, some
fuel is being wasted. The ideal condition would be the arrival
of the glass at the tri-level thermocouple with all three couples
registering the same ideal temperature for the glass composition
being melted.
10 ' As previously stated, it is well known that the glass
along the sides of the forehearth channel at the conditioning
section tends to be 20 to 40 cooler than the glass at the
center line of the forehearth. With this in mind, a plurality of
electrodes 29 extending through the sidewall of the channel ll
,. ,
are provided and have their ends immersed in the molten glass to
approximately three inches~ As can be seen, the adjacent elect-
¦ rodes are of opposite polarity, while opposed electrodes are ofthe same polarity, thus the major portion of the current flows
between adjacent electrodes and only a minor portion will flow
20 1 across the channel to any significant degree. Joule effect heat-
ing then occurs principally along the sidewall and only in the
; conditioning section in advance of the feeder or spout. The
exact ratio of current flowing between adjacent electrodes versus
opposite electrodes is a function of the relative spacing.
The electrodes are connected to a transformer 30 which
in turn is connected to a current control device 31 and thence to
a source of current. The current control device 31 is of the
type that may be preset by the operator to some preselected
current level. The current level chosen will be that believed
to be sufficient to maintain the sidewall temperature and the
centerline at a fairly close level.
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15281
All of the thermocouples 26, 27 and 2~ in the center of
the temperature ~ensing device 24 are connected by a lead 32 to
a temperature indicator 33. Likewise, the three thermocouple
associated with the right side thermo~ouple mounted in the hole
5, 23 are connected by a lead 34 to the lndicator 33. Ind~cator 33
may be a multi-channel temperature mea~uring deviae such a~ a
Doric digital ~eadout device sold by Do~ic In~trument Company.
This instrument may provide visual readings of all of the thermo-
couples and, if desired, may provide recordings of these readings
over a period of time. The readings given by the indicator 33
may influence the setting of the current control 31 by the
operator and al50 provide a tool for the operator to use in sett-
ing up the glass temperature as it enters the forehearth.
The temperature sensing device mounted in the hole 21
to the left siae, as viewed in FIG. 3, has its middle thermo-
couple connected by a lead 25 to an override circuit 36. The
override circuit 36 is provided ~ith a set point temperature
scale 37 that may be selected by the operator and typically would
be selecte~ to be the s~me t~mperature reading as that of the
ce~ter line of the forehearth. The o~erride circuit, in response
to deviations o~ the sidewall thermocouple readings~will provide
current adju~tment to the current to the transformer 30 and this
control is automatic. Thus, the overriae circuit will adjust the
current to the electrodes so as to bring the sidewall temperature
25j of the forehearth up to the center line tem~erature, or the
'~ temperature which is placed in the ~et point temperature scale 37
In this manner the temperature imbalance, which has a marked
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effect on glass distribution in bottles foxmed by the glass from
the forehearth, i8 obviated and the system will provide fxont
end boosting of the temperature and resulk in incxeased job
efficiency and improved quality o~ ware.
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