Feeder conduits for a glass furnace with heating electrodes

A feeder conduit is disclosed for conveying molten glass from a forehearth of a glass furnace to a glass forming machine. The feeder conduit includes an elongated conduit which receives molten glass from the forehearth and delivers the molten glass to an inlet of a bowl-shaped container. The container has an orifice in its bottom for withdrawing the molten glass therefrom and a vertical cylinder disposed within the container and above the orifice. The cylinder and side wall of the container opposite the inlet of the container define a semi-annular channel therebetween and a first electrode is inserted in the molten glass upstream of said cylinder and a second electrode is inserted in the molten glass within the semi-annular channel. The first and second electrodes are offset from the centerline of the feeder conduit. As the molten glass flows through the inlet in the container, around the cylinder and through the semi-annular channel, an electric current passes between the electrodes to heat the molten glass.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to improvements in the feeder conduits for a glass 
furnace. 
2. Description of the Prior Art 
In manufacturing glass articles such as bottles, molten glass is conveyed 
from a glass furnace to a forehearth. The molten glass is delivered from 
the forehearth to several glass distribution conduits known as feeder 
conduits or "feeders". When needed, discrete gobs of molten glass or 
parisons are discharged from the downstream portion of each feeder to 
forming machines which produce the desired glass article. 
Usually, the feeder is an elongated conduit with its downstream portion 
terminating in a bowl-shaped container known as a bowl. The bottom of the 
bowl has openings for the discharge of the parisons. Molten glass flows 
from the forehearth, through the conduit, into the bowl, and out its 
openings. A rotatable vertical cylinder is located within the bowl above 
the openings. The cylinder is also movable along its axis from a low 
position to a high position. In its low position, the cylinder rests upon 
the bottom of the bowl to seal the openings and to prevent the molten 
glass from passing therethrough. In its high position, the molten glass is 
permitted to flow underneath the cylinder and through the openings. 
Plungers are movably positioned within the cylinder coaxial with the 
openings. When the cylinder is in its high position, the plungers assist 
in ejecting the molten glass through the openings from the bowl. 
The rotatable cylinder and the side wall of the bowl define a semi-annular 
channel in which the rotation of the cylinder causes a rotational 
circulation of the molten glass within the channel. Upon entering the 
bowl, the molten glass from the elongated conduit flows into the molten 
glass emerging from the semi-annular channel. Because the glass from the 
semi-annular channel is traveling in a direction opposite that of the 
glass entering from the elongated conduit, the flow rate of the glass 
decreases in the region where these two streams meet and the glass may 
stagnate. The temperature of the glass consequently reduces and 
devitrified zones of semi-hardened glass coagulate on the side wall of the 
bowl. 
Small fragments of the cooled material frequently detach from the wall of 
the bowl and pass with the parison through the bowl openings. As a result, 
the parison contains trailings of cold glass and does not have a uniform 
temperature. These thermal heterogeneities cause substantial variations in 
the physical and chemical properties of the pieces manufactured from such 
glass. For example, in the production of 600 g bottles, a variation in 
thickness of 0.2 to 1 mm has been detected, which makes it impossible for 
such bottles to meet their internal pressure specifications. 
SUMMARY OF THE INVENTION 
I have invented an improved feeder conduit which provides its forming 
machine with uniformly heated molten glass. The feeder conduit includes an 
elongated conduit having an inlet communicating with the forehearth to 
receive molten glass therefrom and an outlet. A bowl-shaped container has 
an inlet which communicates with the outlet of the elongated conduit to 
receive molten glass therefrom. The bottom of the container has an orifice 
for withdrawing the molten glass therefrom. A vertical cylinder is 
disposed within the container and above the orifice, and the cylinder and 
side wall of the container opposite the inlet of the container define a 
semi-annular channel therebetween. The cylinder is rotatable about its 
longitudinal axis for stirring the molten glass and producing a flow of 
glass through the semi-annular channel. A first electrode is inserted in 
the molten glass upstream of the cylinder and a second electrode is 
inserted in the molten glass within the semi-annular channel. Both 
electrodes substantially extend through the entire height of the molten 
glass. The first and second electrodes are offset from a vertical plane 
passing through the center of said elongated conduit and the center of 
said cylinder. The feeder conduit also includes means for energizing the 
first and second electrodes to produce an electric current flow through 
the molten glass between the electrodes to heat the molten glass flowing 
from said elongated conduit, past the cylinder and through the 
semi-annular channel. 
In an embodiment of the present invention, the second electrode includes an 
arcuate plate member immersed in the molten glass and having a 
configuration corresponding to the configuration of the side wall of the 
container adjacent the second electrode. An electrode holder shaft is 
connected to said plate member and the plate member is energized through 
the holder shaft. A protective tube encircles the electrode holder shaft 
and rests upon the upper surface of the arcuate plate member.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
FIGS. 1 and 2 illustrate the downstream portion of a feeder 10 having an 
elongated conduit 11 and a tapered channel 12, a semi-cylindrical bowl 14, 
and a cylinder 20 which are typical of the prior art, and electrodes 28, 
28', 30 and 30' which are positioned and utilized in accordance with my 
invention. Channel 12 connects the main portion of feeder 10 to bowl 14 
and tapers in the direction of the bowl. Channel 12 thereby serves as the 
inlet to bowl 14. The bottom of bowl 14 has an opening at its center which 
is covered by a discharge washer 16. To permit the discharge of parisons, 
discharge washer 16 has orifices 18 passing therethrough. 
Vertical cylinder 20 is disposed above discharge washer 16 and is 
substantially coaxial with the side wall of bowl 14 and defines with the 
side wall opposite tapered channel 12 a semi-annular channel 24 
therebetween. Cylinder 20 is rotated about its longitudinal axis by drive 
means (not shown). In addition to its rotational motion, cylinder 20 is 
movable along its axis between a high position (FIG. 2) which allows the 
molten glass contained in bowl 14 to flow through orifices 18, and a low 
position in which the lower end of cylinder 20 rests upon the bottom of 
bowl 14 and thereby prevents the molten glass from flowing through the 
orifices. 
To assist in expelling the molten glass through orifices 18 when cylinder 
20 is at its high position, plungers 22 are slidably positioned within 
cylinder 20 in line with orifices 18. The plungers move up and down to 
push the glass through the orifices. 
Molten glass flows through feeder 10, past tapered channel 12 and into bowl 
14. As tube 20 rotates clockwise, some of the molten glass enters portion 
27 of bowl 14, passes through semi-annular channel 24 and encounters at 29 
the molten glass passing along tapered channel 12. Prior to the present 
invention, the molten glass in the colliding streams stagnates and its 
temperature decreases. The cooled glass coagulates on the side walls of 
bowl 14 at 26 and forms lumps of devitrified material. As previously 
described, the cooled material would inadvantageously pass with the 
parisons to the forming machines. 
To avoid this cooling, an auxiliary quantity of energy is supplied by the 
present invention to the molten glass in the downstream portion of feeder 
10 via electrodes 28, 28' and 30, 30'. Illustratively, two electrodes 28 
and 28' are placed in the molten glass at tapered channel 12, and two 
electrodes 30 and 30' are placed in the molten glass at semi-annular 
channel 24. Electrodes 28 and 30 are placed on one side of a vertical 
plane passing through the center of elongated conduit 11 and the center of 
the cylinder. Electrodes 28' and 30' are positioned on the other side of 
the plane. As shown in FIG. 1, electrodes 28 and 28' are connected in 
parallel to one terminal of a secondary coil 31 of a variable transformer 
32 and electrodes 30 and 30' are connected in parallel to the other 
terminal. A primary coil 33 of transformer 32 is connected to a source of 
suitable voltage. 
According to the present invention (FIG. 1), a voltage potential is applied 
across electrodes 28, 28' and 30, 30' to produce a current therebetween. 
The molten glass between the electrodes acts as a resistive medium for 
generating heat, and the temperature of the glass increases. The auxiliary 
energy advantageously prevents the glass from cooling and forming 
devitrified lumps of material at 26. 
Referring to FIG. 3, there is shown another method according to the present 
invention for connecting the electrodes to a power source. Electrodes 28 
and 30 are connected in parallel to one terminal of a power source U and 
electrodes 28' and 30' are connected in parallel to the other terminal of 
power source U. As in the case of the electrode connections of FIG. 1, 
this arrangement also can be used to raise the temperature of the molten 
glass. 
Referring to FIG. 4, there is shown an enlarged view of electrode 28'. 
Illustratively, electrodes 28 and 28' are of the type described in U.S. 
application Ser. No. 772,023 filed Feb. 25, 1977, which is incorporated 
herein by reference. Each electrode comprises a cylindrical electrode 
proper 34 made of molybdenum which is screwed onto an electrode holder 
shaft 36 made of refractory steel. Shaft 36 is protected on the outside by 
a protective tube 38 which is made of refractory material. 
Referring to FIG. 5, there is shown an enlarged perspective view of 
electrode 30'. Illustratively, electrodes 30 and 30' comprise an arcuate 
plate 40 immersed in molten glass and having a curvature similar to that 
of the side wall of bowl 14. Two semi-cylindrical rods 42 and 44 bracket 
plate 40 and are secured to the plate by rivets 46. One of the 
semi-cylindrical rods extends above plate 40 to form a threaded end part 
48 which is screwed onto an electrode holder shaft 50 made of refractory 
steel. Shaft 50 is protected on the outside by a protective tube 52 made 
of refractory material. Tube 52 is shown in a raised position; but, in 
operation, its lower end rests upon the top of plate 40. 
The auxiliary energy supplied by the electric current according to the 
present invention prevents the formation of zones of cold devitrified 
glass on the side wall of bowl 14. The parisons obtained by utilizing the 
present invention are free of cold glass trailings and the objects 
produced from the glass have more uniform physical characteristics, such 
as thickness. 
More particularly, in the production of 600 g bottles, according to the 
present invention, an improvement of 2 to 4 bars has been observed in the 
resistance of the bottles to internal pressure. Further, in a feeder 
provided with two sets of electrodes and energized by 10 kw power, gas 
burner heating requirements are reduced by more than 45 therms per hour. 
Finally, the use of electrodes 28,28', 30, 30' makes it possible to save 
approximately one quarter hour per replacement of discharge washer 16. 
This is a substantial time savings because discharge washer 16 is subject 
to internal corrosion and must be changed frequently. More particularly, 
discharge washer 16 is changed by placing rotating tube 20 in its low 
position to stop the glass flow through orifices 18. The washer is then 
replaced and glass flow is resumed by lifting the rotating tube to its 
high position. As a result of the interruption in its flow, the molten 
glass in the bowl inadvantageously cools. Prior to the present invention, 
it was necessary to reheat the glass by intense gas heating before the 
parison could be ejected from the feeder. According to the present 
invention, the electrodes are energized with an increased voltage to 
prevent cooling of the glass as discharge washer 16 is replaced. The 
feeder therefore may be utilized sooner than previously possible. 
While the invention has been described in conjunction with certain 
embodiments, it is understood that various modifications and changes may 
be made without departing from the spirit and scope of the invention. For 
example, electrodes 28 and 28' may be replaced by a single electrode 
and/or electrodes 30 and 30' may be replaced by another single electrode. 
Electrodes 28 and 28' or its single replacement electrode may be 
positioned before bowl 14 and offset from a vertical plane passing through 
the center of elongated channel 10 and the center of cylinder 20. 
Electrodes 30 and 30' or its replacement electrode need not be arcuately 
configured and may be positioned within semi-annular channel 24 and offset 
from the vertical plane.