Submerged plate for selective diversion of molten metal flow in a glass forming chamber

A glass forming chamber wherein glass is formed while floating on the surface of a pool of molten metal is provided with a submerged plate in the pool of molten metal, which plate is contoured to divert the flow of molten metal in a central portion of the pool beneath an advancing layer of glass and to cause the flow of molten metal from the central portion into marginal portions of the pool or vice versa.

BACKGROUND OF THE INVENTION 
1. Field of the Invention: 
This invention relates to the art of manufacturing flat glass, wherein 
molten glass is delivered onto a surface of a pool of molten metal and 
formed while floating on the molten metal into a continuous sheet of 
glass. More particularly, this invention relates to devices positioned in 
the glass-supporting molten metal to control convection currents or flow 
of molten metal within the pool. 
2. Brief Description of the Prior Art: 
The use of dam barriers to influence thermal conditions within a 
glass-supporting pool of molten metal in a glass forming chamber has long 
been recognized. For example, U.S. Pat. No. 789,911 to Hitchcock discloses 
the use of a plurality of barriers to segregate a glass-supporting pool of 
molten metal into a plurality of pool segments, each of which could be 
selectively maintained at a desired temperature to permit the cooling and 
forming of glass as it passes over each segment of the pool during its 
travel through a forming chamber. 
Many patents, including U.S. Pat. No. 3,317,302 to Misson, U.S. Pat. No. 
3,584,475 to Galey and Sensi and U.S. Pat. No. 3,930,829 to Sensi, 
disclose dam barriers submerged in glass-supporting molten metal to alter 
or influence currents or flows in the molten metal. U.S. Pat. No. 
3,930,829 to Sensi discloses that dam barriers may be used in pairs of "V" 
configurations to divert metal flows outwardly from the central portion of 
a pool of glass-supporting molten metal into marginal portions of the 
pool. The purpose given by Sensi for such an arrangement is to make the 
thermal conditions within the forming chamber more uniform across the 
width of the chamber. 
U.S. Pat. No. 4,092,140 to Cerutti, Sensi and Henry discloses the use of 
triangular-shaped, closed loop heat pipes submerged in a glass-supporting 
pool of molten metal in a glass forming chamber. Such heat pipes would 
inherently divert flows of molten metal traveling in the direction of 
glass advance outwardly from the central portion of a forming chamber 
toward its marginal portions. 
Dam barriers inhibit molten metal flows primarily by providing impenetrable 
bodies through which molten metal cannot flow so that the metal flows 
generally perpendicularly against dam barriers and is thus slowed and 
diverted to the extent that flow is maintained. Only incidently do they 
influence molten metal flows by a viscous drag effect since a dam barrier 
generally does not have any large surface area in contact with metal 
flowing tangential to it. 
Modeling of glass forming processes has indicated that some short 
circuiting of molten metal flow over submerged dam barriers results in a 
fast flow of molten metal along with the advance of glass along its 
surface immediately adjacent the interface between the glass and the 
molten metal. This flow appears to reduce the effectiveness of submerged 
dam barriers. The present invention is therefore directed to an improved 
method and apparatus for the control of molten metal flows within the 
glass-supporting pool of molten metal. 
SUMMARY OF THE INVENTION 
A flat glass forming chamber which contains a pool of glass-supporting 
molten metal is provided with one or more flow-diverting plates which are 
submerged in the pool of molten metal. The forming chamber has associated 
with it other, conventional features such as a facility for delivering a 
continuous stream of molten glass onto the surface of the pool of molten 
metal; apparatus for advancing and applying forces to the glass to form it 
into a dimensionally stable, continuous sheet of glass of the desired 
width and thickness; coolers for removing heat from the glass (including 
means for transferring heat from the glass to and through the 
glass-supporting molten metal); and a facility for removing a formed, 
continuous sheet of flat glass from the surface of the pool of molten 
metal and from the forming chamber. 
The flow-diverting plate employed in the practice of this invention 
provides a large surface area along which there is generally tangential 
molten metal flow. Because of the tangential flow of molten metal, the 
plate surface imposes a viscous drag on the molten metal. Since the extent 
of viscous drag of a fluid upon a surface is directly dependent upon the 
viscosity of the fluid and the area and roughness of the surface, the 
plate may be appropriately sized for use in a glass forming chamber by 
proper consideration of the roughness of the plate surface to be used and 
the temperature of the molten metal at the location of intended placement 
of the plate in a forming chamber (viscosity being a function which varies 
with temperature variations). 
Assuming generally invariant temperature and viscosity for molten metal in 
any transverse location extending across a forming chamber with an 
insignificant longitudinal dimension, a plate of uniform width and length 
will provide a viscous drag that is uniform across the width and length of 
the portion of the forming chamber under consideration. However, it is a 
primary object of this invention to provide for diversion of molten metal 
flows and a non-uniform viscous drag is the immediate force to be employed 
for accomplishing that objective. Thus, the submerged plate employed in 
this invention has a surface that increases in width at successive 
locations along the length of the plate in the direction of glass advance 
through a forming chamber. 
The plate may have a surface with diverging or converging edges. It may, 
therefore, have an edge or edges facing the inlet end of a forming chamber 
that are either convex or concave when viewing the plate in a plan view. 
The edge (or combination of edges) facing the inlet end of a forming 
chamber is, for convenience, called the leading edge of a plate. The 
leading edge may be a continuous curve, for example a "U" or inverted "U" 
shape. The leading edge may be made up of a plurality of straight edges, 
for example a "V" or an inverted "V" shape. 
By using a plate having an increasing surface area at successive locations 
along its length extending in the direction of glass advance, molten metal 
flowing over its surface in the direction of glass advance encounters a 
non-uniform viscous drag effect. There is not only an increasing viscous 
drag in a longitudinal dimension, but a greater rate of increase of 
viscous drag in selected longitudinally extending regions at some 
transverse locations relative to others. For example, a plate having a 
leading edge that is a "U" or "V" shape with the apex facing the inlet end 
of a forming chamber provides for a greater rate of viscous drag increase 
in a central portion of a chamber relative ro marginal portions of the 
chamber. Such a plate causes molten metal flows to diverge outwardly. On 
the other hand, a plate having a leading edge that is an inverted "U" or 
inverted "V" shape with the apex facing away from the inlet end of a 
forming chamber provides for a greater rate of viscous drag increase in 
marginal portions of a chamber relative to a central portion of the 
chamber. Such a plate causes molten metal flows to converge inwardly. 
The submerged flow-diverting plate is preferably triangular or "V" shaped. 
It is placed in a forming chamber with an angle pointed upstream toward 
the inlet end of the forming chamber and toward the facility for 
delivering molten glass to the chamber with the point or tip on the angle 
on or near the center line of the chamber. The plate has an upper surface 
that is usually flat but which may be bowed or dished slightly. The upper 
surface lies generally in a horizontal plane, although in some embodiments 
of the invention it lies in a sloped plane that is lower toward the 
upstream end of the chamber and higher toward the downstream end of the 
chamber. In general, the plane of the upper surface of the plate is at a 
depth beneath the upper surface of the pool of glass-supporting molten 
metal that is from 3 percent to 25 percent of the depth of the pool where 
the plate is located. 
The submerged flow-diverting plate may be mounted on the bottom of a 
forming chamber and supported by legs to which it is fixed. Alternatively, 
the plate may be sufficiently dense to sink in the molten metal and merely 
rest on legs. It is also possible to provide a flow-diverting plate that 
has a neutral buoyancy by having an effective density that is equal or 
nearly equal to that of the molten metal. A neutral, buoyant plate may be 
provided with a sufficiently dense upstream tip so that it tends to sink 
completely and be mounted at its downstream corners to the sides of the 
forming chamber in which it is placed. The dense upstream tip serves to 
hold the plate beneath the glass-supporting surface of the molten metal 
pool and the side mountings serve to hold the plate above the bottom of 
the pool and in a desired orientation to establish outwardly diverging 
flows of molten metal over the plate. 
The submerged flow-diverting plate may be a triangular plate or a 
"V"-shaped plate. For either shape, the angle of the tip or point of the 
plate to be oriented in an upstream direction facing the molten glass 
delivery facility is an angle of from 45 to 120 degrees, preferably from 
60 to 90 degrees. The increase of plate surface area encountered by molten 
metal flowing over the plate in a downstream direction is effective to 
cause outward flow divergence by virtue of conservation of mass of the 
molten metal. The surface may be smooth or roughened. 
The submerged flow-diverting plate is preferably sufficiently thin so that 
it is effective as a flow diverter primarily due to drag of the tangential 
flow of molten metal over the generally horizontal surfaces of the plate 
rather than by a blocking of flow due to the thickness of the plate. Thus, 
the thickness of the plate is much less than the width of the surface of 
the plate measured transverse to the forming chamber. The thickness should 
be less than 1 percent of the average width of the plate. The preferred 
thickness for a flow-diverting plate is from 1/16 to 1/4 the depth of the 
molten metal pool in which it is submerged. In a conventional glass 
forming chamber, a plate having a thickness of from 1/8 inch to 1 inch 
(0.3 to 2.5 centimeters) is satisfactory. 
The submerged flow-diverting plate may be made of an iron or stainless 
steel plate covered with a wrapping or covering of ceramic, porcelain, 
carbon or graphite or other material suited for protecting iron from 
attack by molten tin which is the principal constituent of a molten metal 
for use in a glass forming chamber. A plate may be suitably constructed of 
a dense metal material, such as molybdenum, tungsten or alloys of such 
metals. No covering or other protection against molten metal attack is 
needed with such materials, although it is useful to provide a graphite or 
carbon cover to facilitate glass slippage over the plate in the event of 
glass contact with its upper surface. To construct a neutral, buoyant 
plate an appropriate combination of the suggested materials of 
construction may be employed. To construct a plate having an upstream tip 
that will readily submerge more deeply than its downstream portion, it is 
possible to use an iron plate with a tip plate of tungsten-molybdenum 
alloy mounted on it. 
The submerged flow-diverting plate may be used alone or with other 
flow-diverting plates or together with submerged dam barriers. Plates 
having "V" shapes may be nested together to accumulate the effect of a 
plurality of flow diversions. Plates may be used effectively in the hotter 
portions of a forming chamber near its glass inlet end as well as in 
cooler portions of a forming chamber. They may be used with dam barriers 
aligned at least partially with the direction of glass advance through the 
chamber. All of the suggested arrangements are suited for establishing 
desired transverse uniformity of thermal conditions in the forming 
chamber. 
This invention may be further appreciated with reference to the 
accompanying drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIGS. 1 and 2, there is shown a glassmaking apparatus 
comprising a glassmaking furnace or tank 11 connected through a molten 
glass delivery facility 13 to a glass forming chamber 15. The forming 
chamber 15 is, in turn, connected to a glass lift-out and removal facility 
17. The glassmaking furnace 11 includes a furnace bottom 19, side walls 
21, a front facing wall 23, an upper front wall 25, and a crown or roof 26 
extending between the side walls. The glassmaking furnace 11 includes a 
melter (not shown) in addition to the conditioner which has its downstream 
or discharge end illustrated. The glassmaking furnace 11 serves to melt 
and refine glass and to condition the glass for delivery to the forming 
chamber 15. 
The molten glass delivery facility 13 includes a canal bottom 29 and canal 
side walls 31 which, together, form a channel or canal through which 
molten glass can flow from the furnace 11 to the forming chamber 15. The 
canal bottom 29 may be mounted on a structure 33 which includes a cooler. 
The canal bottom 29 terminates with a lip 35 which is shown mounted above 
and extending over a pool of molten metal in the forming chamber. The 
molten glass delivery facility 13 further includes a roof 37 having 
openings through it for receiving metering members or tweels. An operating 
tweel 39 is mounted by means (not shown) for raising and lowering the 
tweel 39 to provide an opening of controlled size defined by the operating 
tweel 39, the canal bottom 29 and canal side walls 31 in order to meter or 
control the flow of molten glass from the furnace 11 through the canal to 
the forming chamber 15. A backup tweel 41 is also provided. It is mounted 
in a manner similar to the mounting for the operating tweel 39. It is 
employed to control the flow of molten glass during periods when the 
operating tweel is being replaced or under repair, and it is used to close 
off the flow of molten glass entirely during periods of maintenance on the 
forming chamber 15 or maintenance or replacement of the lip 35. A cover 
block or tile 43 may be provided over the opening for receiving the backup 
tweel 41 when the backup tweel 41 is removed from the canal. 
A lip extension piece 45 may be mounted on the lip 35 to extend the surface 
which supports molten glass during its delivery. The surface which 
supports molten glass during its delivery can be positioned to contact a 
pool of molten metal in the forming chamber onto which molten glass is to 
be delivered. 
The forming chamber 15 includes a bottom casing 47 and an upper casing 49 
which, together, provide an enclosure for the chamber. Mounted within the 
bottom casing 47 is a bottom liner 51 of refractory material. Fixed across 
the inlet or upstream end of the forming chamber 15 is an end wall 53. 
Side walls 55 extend along the length of the forming chamber inside both 
the lower and upper casings. An exit end lip 57 extends across the exit 
end of the forming chamber and is mounted within an exit lip casing or 
plate 49. A pool of molten metal 61, preferably tin or an alloy of tin, is 
contained inside the forming chamber in a container formed by the bottom 
liner 51, the hot end wall 53, the side walls 55 and the exit lip 57. A 
space called a headspace overlies the pool of molten metal 61 between the 
side walls of the forming chamber. A lintel 63 extends across the inlet of 
the forming chamber above the lip 35 and inside the upper casing 49. A 
ceiling or roof 65 extends from the lintel between the side walls 55 along 
the length of the forming chamber and separates the headspace from a 
plenum or service space 67 located above the roof 65 but within the upper 
casing 49. 
The glass lift-out and removal facility 17 includes a canopy 69 which is 
provided with thermal insulation 71. The canopy 69 serves to support a 
plurality of drapes or curtains 73 which extend transversely across a path 
for glass removal and into close proximity to a conveyer for glass in 
order to seal the headspace of the forming chamber from the outside 
environment. The lift-out facility 17 further includes a support 75 with 
lift-out rolls 77 mounted on it. The lift-out rolls 77 may be provided 
with seals 79. 
During operation, a pool of molten glass 80 is maintained within the 
furnace 11. A stream of molten glass 82 is withdrawn from the furnace 11 
and flows through the delivery facility 13 beneath the operating tweel 39 
and over the lip 35 with extension piece 45 directly onto the surface of 
the pool of molten metal 61 in the forming chamber. A pair of diverging 
guides 83 is preferably provided to confine the delivered molten glass and 
to establish a body of molten glass on the surface of the pool of molten 
metal 61 of desired width for forming into a continuous sheet of flat 
glass. After the glass advances from between the diverging guides 83, it 
may be engaged along its marginal portions by edge rolls 85 which impose 
tractive and attenuating forces to the glass and serve to maintain or 
control its width as it is attenuated to a desired thickness as a 
dimensionally stable, continuous sheet or ribbon of glass 86. The 
continuous sheet of glass 86 is then removed from the pool of molten metal 
and from the forming chamber for further processing and use. The diverging 
guides 83 are preferably made of a material such as silica or alumina 
which is wetted by glass, and each guide includes a diverging piece 89 as 
well as an end piece 91 to establish the width of the advancing glass. 
Preferably, the width of the glass advancing from between the guides is 
established as the width of the ribbon or sheet of glass 86 produced in 
the process. 
Submerged in the pool of molten metal 61 is a flow-diverting plate 93. As 
seen in FIG. 3, the preferred flow-diverting plate 93 comprises a dense 
plate 95 (e.g. iron, stainless steel, molybdenum, tungsten, an alloy or a 
composite) resting on legs 97. The dense plate 95 may be provided with a 
covering 99 (e.g. asbestos, silica cloth, graphite or carbon or the like). 
The flow-diverting plate has an upstream tip "A" located at or near the 
center line of the chamber and pointing upstream. It has downstream 
corners "B" located near the sides of the chamber. The upstream angle of 
the plate may be a shallow angle as shown in FIG. 1 or may be a sharp 
angle. The elevation of the plate at the upstream tip "A" may be slightly 
below the generally common elevation of the downstream corners "B" in 
order to enhance the outward divergence of molten metal flows over the 
plate. 
A submerged dam barrier 101 may be employed in conjunction with the 
flow-diverting plate 93 to further diminish longitudinal flow of molten 
metal beneath glass advancing along the molten metal surface. 
In FIG. 4 there is shown another embodiment of this invention. A "V"-shaped 
flow-diverting plate 103 is provided. It includes a plate 105 and legs 
107. 
Referring back to FIGS. 1 and 2, there is shown a plate 109 having a 
leading edge that is an inverted "V" shape that is convex as it faces the 
inlet end of the chamber. It rests on legs 111 and serves to cause 
inwardly converging flows of molten metal. 
Simulated model studies of a glass forming chamber employing water as a 
molten metal simulant and using dye to trace the flow of the molten metal 
simulant indicates that outwardly diverging surface flows may be 
established beneath an advancing layer of glass in the glass forming 
chamber through the use of submerged flow-diverting plates such as 
disclosed here. Outwardly diverging surface flows of molten metal are 
expected to provide a more uniform distribution of heat than usual 
throughout a glass-supporting pool of molten metal so that as glass is 
advanced and formed while being supported on such a pool of molten metal, 
it will be formed with minimal temperature deviations across its width 
which could give rise to optical distortion in the finished sheet of flat 
glass produced in such a forming chamber. 
While this invention has been described with reference to particularly 
preferred embodiments, those skilled in the art of flat glass manufacture 
will appreciate that other embodiments of the invention may be devised 
which are within the spirit of this disclosure and within the scope of the 
appended claims.