US3345149A

US3345149A - Method of varying the thickness of a glass sheet while on a molten metal bath

Info

Publication number: US3345149A
Application number: US251848A
Authority: US
Inventors: Edmund R Michalik; George W Misson
Original assignee: Pittsburgh Plate Glass Co
Current assignee: PPG Industries Inc
Priority date: 1963-01-16
Filing date: 1963-01-16
Publication date: 1967-10-03
Anticipated expiration: 1984-10-03

Description

OC- 3. l967 E. R. MICHALIK ETAL 3,345,149

METHOD OF VARYING THE THICKNESS OF A GLASS SHEET WHILE ON A MOLTEN METAL BATH I Filed Jan. 16, 1963 6 Sheets-Sheet l Oct. 3, 1967 E. R. MICHALIK ETAL 3,345,149

METHOD OF VARYING THE THICKNESS OF A GLASS SHEET WHILE ON A MOLT'EN METAL BATH 6 Sheets-Sheet 2 Filed Jan. 16, 1963 FIG.3

FIG

INVENTORS fava/vo ,Q Mfr/MHK@ Bcfoeof n( CL 3, 1967 E. R. MICHALIK ETAL 3,345,149

METHOD OF VARYING THE THICKNESS OF A GLASS SHEET WHILE ON A MOLTEN METAL BATH Flled Jan 16, 1963 G Sheets-Sheet 5 Fia.

INVENTORS Hwa/m e www1/KQ? m6519265 W/W/ssQ/V OGL 3, 1967 E. R. MICHALIK ETAL 3,345,149

METHOD OF VARYI NG THE THICKNESS OF A GLASS SHEET WHILE ON A MOLTEN METAL BATH 6 Sheets-Sheet 4 Filed Jan. 16, 1963 vF'ICLS FGJO INVENTORS fMaA/a e wc/maxi( @meer #KM/ssa# #from/ff @CL 3, w67 E. R. MICHALIK ETAL 3,34549 METHOD OF VARYING THE THICKN'SS OF A GLASS SHEET WHILE ON A MOLTEN METAL BATH Filed Jan. le, 196s V e sheets-sheet 6 2W. N $0 Nrs E/S EWMM wif n a n E P wm E 0m. L E U GY w B .um M w u u R E P m U D o M /jM/llsm PRSSURE wm-sm FLOAT CHAwmER ATTORNEY United Statesv Patent O 3,345,149 METHOD F VARYING THE THICKNESS 0F A GLASS SHEET WHTLE 0N A MOLTEN METAL BATH Edmund R. Michalik, West Miliiin, and George W. Misson, Pittsburgh, Pa., assignors to Pittsburgh Plate Glass Company, Pittsburgh, Pa., a corporation of Pennsylvania Filed llan. 16, 1963, Ser. No. 251,848 l 4 Claims. (Cl. 65-99) This application relates to the manufacture of flat glass by floating glass on a liquidk bath, such as molten metal, so that the resultant flat glass has fire-finished surfaces requiring little or no additional surfacing for ultimate use.

lt has been proposed heretofore to produce flat glass by floating a ribbon or sheet of glass upon the surface of a bath of molten metal. The product produced by this process has surfaces which differ somewhat from each other. The top surface thereof, because of the heat involved, has a fire-finished surface. The bottom of the ribbon in contact With the molten metal is ilat and has a surface having a similar appearance to a fire-finished surface.

When producing oat glass of compositions approaching that of commercial plate and Window glass or similar soda-lime glasses and using a molten metal such as a bath of tin or tin alloy, molten glass poured directly onto the bath of metal ultimately will attain an equilibrium thickness of approximately 1A inch (hereinafter sometimes called equilibrium thickness), IEven a preformed ribbon of glass of a thickness different from the equilibrium thickness when remelted While supported on the molten metal, will nevertheless seek the equilibrium thickness. Heretofore, when thinner glasses were desired, it was considered necessary attenuate the ribbon of glass While in molten condition to produce thicknesses of glass differing from the equilibrium thickness or to subject a stiffened ribbon or sheet of dilferent dimension to only a surface melting treatment. To elfect attenuation, traction elements contacting the glass at its marginal edges to maintain ribbon width during attenuation are required. Considerable edge trim is thus required because of the necessary Width of the traction elements to chill the glass edges and maintain a substantially constant ribbon Width.

The need for glass of thicknesses different from the equilibrium thickness is great. For example, the majority of laminated glass assemblies useable in the automotive industry are constructed of two pieces of glass of a thickness less than the equilibrium thickness (usually of the order of 1)/16 or 1,@ inch) with a layer of plastic 4sandwiched therebetween. According to the invention described in the copending application of Edmund R. Michalik, Ser. No. 188,664, filed Apr. 19, 1962, now abandoned it has been found that glass of conventional plate and Window composition and of a desired thickness different from the described equilibrium thickness can be produced by floating a sheet or ribbon of glass on the surface of a molten bath of metal such as tin or tin alloy having a density greater than that of the glass and holding the glass at a melting temperature while modifying the apparent weight density of the glass with respect to the Weight density of the metal of the bath, e.g., by changing the degree of immersion `of the glass in the metal. Thus, it has now been found that when the glass displaces a greater quantity of metal than that usually displaced under normal atmospheric conditions, the molten glass tends to stabilize at a thinner thickness than the equilibrium thickness and vice versa. Thus, modifying the degree of immersion of the glass in the metal results in a modification of the amount of metal displaced by the glass which may be greater or less than For most purposes, it is found preferable to apply this different fluid pressure `only to a portion of the surface of the glass sheet and to leave a margin, generally a pairv of opposed margins, of the glass sheet exposed to another fluid pressure which rnay be the same as or different from that applied to the metal surface at the glass edge. As a result, of course, the margins diifer in thickness from the portion to which the dilferent fluid pressure is applied. In practice, assuming the glass is sufficiently hot to freely flow, and ignoring transient conditions, there need be no actual change in metal displacement. Rather, the metal level may remain the same but the mass of glass floating upon it, i.e., displacing it, Will be diminished because the glass exposed to the increased fluid pressure becomes thinner.

By selecting the magnitude of the pressure on the central areas of the glass and supplying a ribbon of desired thickness to the bath, the maintenance of this desired glass thickness is insured. If a ribbon of a thickness other than that which is desired is supplied to the metal bath, then, because of the character of molten glass to flow, a ribbon of the desired thickness can be produced by proper selection of the pressure which modifies the apparent densities of the glass with respect to the bath. Because of the temperature involved, the glass attains surfaces characteristic of lire-finished surfaces, so that little o-r no subsequent abrasive surfacing is required for ultimate use.

When the treated glass is cooled sufliciently, it is withdrawn from the metal bath without surface damage due to equipment contact, as by applying only a tractive force to the glass ribbon. Since attenuation of the glass becomes less important in accordance with the teachings of the aforesaid applicati-on, special apparatus within the contines of the metal bath or contiguous thereto to contact the glass surfaces is not required in contrast to previous processes.

The present invention is directed to improved methods and apparatus for producing glass according to the invention described and claimed in the aforesaid copending application. It is also directed to improved methods and apparatus for producing glass according to the inventiondescrbed and claimed in the copending application of Edmund R. Michalik and George W. Misson, Ser. No. 191,833, filed May 2, 1962, now Patent No. 3,241,937, which invention is directed to methods and apparatus for maintaining a diterent fluid pressure above separate portions of a floating glass ribbon.

According to an effective method of practicing the present invention, a ribbon of glass is presized as to thickness and width by convenient means, such as by passin-g molten glass through a slot or between sizing rolls and cooling the ribbon to stabilize its dimensions. This ribbon is then passed to a pool of molten metal having a greater density than that of the ribbon and the ribbon is oated on the surface of the metal during its movement thereacross. A super-atmospheric pressure is applied to the" upper surface of a central area of the ribbon while the temperature of the ribbon is raised to a melting temperature. After the surfaces of the ribbon have improved, i.e., smoothed out, and surface defects have been elimi- I nated or reduced in magnitude or number, the ribbon `is cooled to a stiffened state and is removed from the metal.

Such a super-atmospheric pressure may be applied through a large pressure chamber above the ribbon with adequate marginal seals to separate the pressure chamber from the atmosphere adjacent the ribbon edges and bath while allowing free movement of the ribbon beneath the chamber. An effective fluid seal can be achieved in accordance with the present invention by providing a plurality of separate, relatively small, fluid pressure zones around the periphery of the pressure chamber between the lower surface of the walls of the chamber and the underlying glass ribbon. Each zone is formed by an individual ow of gas from a reservoir under higher pressure, the flow being throttled between the reservoir and each zo-ne to restrict the passage of gas between the two. The gas may be throttled to different zones in a nonuniform manner to provide zones of dilerent pressures and thereby control the manner in which the seal functions. Within each zone, gas entering from the reservoir is diffused after throttling so as to avoid creation of localized jets normal to the glass ribbon. Provision may be made for the escape of the flow of gas emanating from each zone through passageways interspersed throughout the pressure bed.

Alternatively, the super-atmospheric pressure applied to the upper surface of a central area of the ribbon may be provided in its entirety by a plurality of separate, relatively small, fluid pressure zones created in close proximity to the ribbon throughout the central area. This arrangement not only eliminates the need for a separate edge seal surrounding the pressure area, but also allows the pressure exerted upon the upper surface of the ribbon to be varied both across the width and along the length thereof. It is thereby possible to quickly bring a ribbon to a desired thinner dimension by applying an initial pressure substantially in excess of that which would establish the desired thickness by supplying the zones adjacent the most recently formed portions of the ribbon with a greater pressure than zones positioned farther along the ribbon. It is also possible to produce a ribbon having a transverse wedge shape or other varying configuration with this arrangement. Thus, the pressure exerted upon the upper surface of the central area of the ribbon may be varied from one side to the other, either progressively or in stages, to create a corresponding thickness variation. In lieu of separate pressure zones, a po-r-ous plate through which gas under pressure may be emitted and having exhaust channels interspersed throughout can be used adjacent the upper surface of the oating ribbon to exert a fluid pressure.

The attendant advantages of this invention and the various embodiments thereof will be readily appreciated as the same become better understood by reference to the following detailed description when considered in connection with the accompanying drawings in which:

lFIG. 1 is a longitudinal section of an apparatus for producing glass according to the inventive process herein contemplated showing means for applying a super-atmospheric pressure to the top of a ribbon of glass supported on a molten metal bath and for dividing the apparatus into separate pressure chambers;

FIG. 2 is a horizontal, sectional view, with parts omitted, taken on line 2-2 of FIG. 1 looking in the direction of the arrows showing the means for providing a plurality of pressure zones between the glass ribbon and a wall separating a central pressure chamber from the surrounding portion of the apparatus',

FIG. 3 is a sectional view taken on line 3-3 of FIG. 1 and in the direction of the arrows partly showing a seal for separating the atmosphere within the apparatus from the surrounding atmosphere;

FIG. 4 is a sectional view taken on line 4-4 of FIG. 1 and in the direction of the arrows showing structure at the entrance end of the molten metal tank for controlling the level of the liquid metal.

FIG. 5 is a sectional view taken on line 5-5 of FIG. 1

and in the direction of the arrows showing the surfacing zone, tank wall construction, and a Huid seal constructed in accordance with the present invention for separating a pressure zone above a central portion of a floating ribbon from the surrounding zone within the apparatus;

FIG. 6 is a sectional view taken on line 6-6 of FIG. 1 and in the direction of the arrows showing the molten metal level control structure at the exit end of the molten metal tank;

FIG. 7 is a sectional view taken on line 7-7 of FIG. 1 looking in the direction of the arrows showing the exit seal of the molten ymetal tank;

FIG. 8 is an enlarged view, partly in section, of the uid pressure seal arrangement taken along line 8-8 of FIG. 2 looking in the direction of the arrows and schematically indicating the principal flows of gas;

FIG. 9 is a partial horizontal view of the pressure seal arrangement taken along the line 9 9 of FIG. 8 looking in the direction of the arrows;

FIG. 10 is an enlarged view similar to FIG. 8 but showing a second embodiment of a uid pressure seal arrangement and schematically indicating the principal flows of gas;

FIG. 11 is a partial horizontal View of the uid pressure seal embodiment of FIG. 10 taken along the line 11-11 of FIG. 10 looking in the direction of the arrows;

FIG. 12 is a longitudinal section of another apparatus for changing the thickness of a oating glass ribbon showing means for selectively applying a super-atmospheric pressure to the top of a ribbon of glass using a plurality of closely adjacent uid pressure zones above the ribbon;

FIG. 13 is a horizontal, sectional view taken along the line 13-13 of FIG. 12 looking in the direction of the arrows, schematically showing in phantom the individual chmaber means in modular arrangement for applying a super-atmospheric pressure to the top of a floating ribbon;

FIG. 14 is a view partly in section taken along the line 14-14 of FIG. 12 showing in end elevation a modular arrangement of pressure chambers and a plenum for supplying gas thereto positioned above a floating ribbon of glass;

FIG. 15 is a horizontal view taken along the line 15-15 of FIG. 14 looking in the direction of the arrows showing in detail the modular arrangement of chambers for producing pressure zones above the glass ribbon;

FIG. 16 is a sectional view of the chambers taken along the line 16-16 of FIG. 15 looking in the direction of the arrows, schematically showing the ow of gas from the chambers to the upper surface of a oating ribbon and includes a diagrammatic pressure graph;

FIG. 17 is a bottom plan view similar to FIG. 15 but showing a different embodiment including a porous plate and exhaust passageways therethrough for providing a uid pressure above a floating ribbon of glass; and

FIG. 18 is a view partly in section of the apparatus shown in FIG. 17 taken along the line 18-18 and looking in the direction of the arrows and schematically indicating the ow of gas.

With particular reference to the drawings, in FIG. 1 there is shown a pair of forming rolls 12 at the delivery end of a glass melting furnace of conventional construction (not shown) to form a ribbon of glass 14 which is delivered onto an apron arrangement 15 and thence onto the surface of a bath of molten metal 16 contained within a tank 18. The molten metal has a density greater than the glass ribbon 14, so that the ribbon oats on the surface of the molten metal. The metal may be tin, an alloy of tin, or the like.

In order to maintain the metal of the bath 16 in molten condition, thermal regulating means, such as electrodes 20 may be located in the floor of the tank 18, as illustrated, or may be submerged within the molten metal, so as to affect the temperature of the bath. The electrodes 20 are connected to a suitable source of power (not shown) in a conventional manner. Each electrode may be individually energized and controlled, so as to provide a desired thermal gradient within the various sections of the tank 18, as will be described. The glass ribbon 14, after treatment within the tank 18, is withdrawn from the tank without injury to its surfaces by traction or pinch rolls 22 onto a roller conveyor 24.

The tank 18 is constructed of a refractory bottom portion 26 and a refractory top portion 28, joined and sealed together, except for an entrance 18a and an exit 18h, by a suitable sealing means 29 (FIG. 3). The sealing means illustrated is of a bellows type and permits the top portion 28 of the tank to be raised from the bottom portion 26 for repairs, etc., without the necessity of removing refractory parts and the subsequent repair of removal parts. The bottom portion 26 contains the molten metal 16 and is subdivided into an entrance zone 26a, a heating zone 26b, a surfacing zone 26e and a cooling zone 26d. These zones are defined by submerged walls or baffles 38a, 30h, and 30e, so built to materially reduce convection currents inthe molten metal between the various zones. Other submerged baflles 32 are in the cooling zone to control convection currents in that zone. The level of the metal of the bath is controlled by level control weir 34 at the entrance end of the tank 18, a level control weir 36 at the exit end of the tank, and by an inlet 38. Preferably, the metal level is always maintained so that the glass ribbon being treated remains free of contact with any submerged wall or bafiie within the tank 18. The inlet 38 (see FIG. 5) is located through a Wall of the tank 18 and is connected to a suitable source of molten metal to supply molten metal to the tank 18.

VThe space between the top portion 28 and the surface of the metal pool is divided into two

vchambers

28a and 28b by the front side of a circumferential wall 40. This wall depends from the roof 28 and has its side sections spaced from the walls of tank 18, thereby providing a gas space 28e along each side of the tank. This gas space 28C may in effect be a continuation or extension of chamber 28a.

A gas which is inert to the components of the bath, such as nitrogen or the like, is introduced, under pressure, into each gas chamber or pressure zone, through conduits 42 and 44, each connected to a suitable source of the pressurized gas (not shown). The gas is preferably heated, so as to eliminate chilling of the zones and the glass being treated. The pressure at which the gas is introduced into the

zones

28a and 28C is different from the pressure of the gas introduced into the zone 28h, as will be later described in detail. The pressure zone 28b may be further subdivided by Walls or baffles 46a, 46b, 46c and 46d for temperature control purposes.

Radiant heaters 48 are located adjacent the roof of the tank 18 to maintain the desired glass temperature between the exit and entrance ends of the tank. These radiant heaters 48, located in both pressure zones, as illustrated, are connected in a conventional manner to a source of electric power (not shown) and may be individually controlled for temperature :gradient control. The control means is any conventional control means and need not be ldescribed and shown in detail. If necessary, cooling means can be located above the cooling zone to insure the proper temperature of the glass being removed from the bath.

In order to prevent the leakage of the inert gas from the zones Within tank 18 to the outside atmosphere,

pressure seal arrangements

50 and 52, as disclosed in the aforementioned copending application Ser. No. 191,- 833, are provided at the entrance and exit ends, respectively, of the tank 18. Each includes a plurality of grooves 66 (FIGS. 2 and 3) and inert gas is supplied to the upper seals through pipes 62 and to the lower seals through plenum chambers 70 (see FIGS. 1 and 3), both having a plurality of orifices, not shown in the pipes but indicated at 72 inthe plenum chamber, for emitting inert gas upgler pressure. The discharged gas, flowing across the lands and grooves minimizes the transfer of gas be- 6 tween the chambers in the top 28 of tank 18 and the outside atmosphere.

The apron arrangement 15 may take several forms without departing from the spirit of the invention. For example, it many include a conventional series of rollers, as illustrated in United States Patent No. 1,954,077 to Gelstharp, or it may be a slip table, as illustrated in United States Patent No. 1,657,212 to Hitchcock.

Means are provided for controlling the level of the molten metal in the bath 16 and may include, as illustrated, the

weirs

34 and 36 and the inlet 38. The

weirs

34 and 36 are plates of a refractory material slideable within slots formed in the tank refractory parts. The weirs are vertically adjustable by suitable means, as

screws

34a and 36a, respectively (FIGS. 4 and 6), so as to adjust the molten metal level, depending upon the thickness of glass being produced. Each Weir defines one side of a trough 34b and 36h, respectively, the other sides and bottoms of the troughs being defined by walls of the tank or other suitable refractory material. Conduits 74 and 76 pass through the walls of the tank 18 and communicate at one end with the troughs 34h and 36h, respectively. Each conduit is connected to discharge molten metal into a sump (not shown) for regeneration and reheating and from which molten metal is pumped to the tank 18 through the inlet 38. Each conduit 74 and 76 is provided with a trap, i.e., a U-bend in the conduit, so as to prevent the entrance of atmospheric air into the tank 18 which would cause oxidation of the metal of the bath.

Referring now to FIGS. 2, 5, 8 and 9, there is shown means for providing a very effective fluid pressure seal between the lower surface of circumferential wall 40 and the upper surface of the ribbon of glass 14. The purpose of this seal is to restrict the flow of gas from chamber 2812 to chambers 28C, which are at a lower pressure. The more effective the seal is, the more uniform is the pressure applied to the central area of the ribbon. This is because any flow of gas from within chamber 2812 to chambers 28e reduces the static pressure exerted upon the glass. Thus, if leakage occurs, the pressure profile across the ribbon decreases from the center to the margins and becomes bell-shaped rather than square, notwithstanding the fact that the volume ofl gas exerting the pressure within chamber 28b may be maintained constant by continually replacing escaped gas.

In order to achieve an effective seal, a plurality of individually supplied pressure zones are provided directly beneath wall 40. To this end, a fiat, modular bed of chambers 80, each chamber or module being small with respect to the length and width of the dividing wall and in close juxtaposition, each to the other, is provided beneath wall 40. In the embodiment of FIGS. 5, 8 and 9 all modules 80 have their lower termini of rectangular configuration and lying in a common plane. The modules 80 are arranged in successive rows crossing the intended path of travel of the ribbon and extending along the wall 40. Preferably the rows are at an angle from the direction of ribbon travel, as illustrated in FIGS. 2 and 9. Each module shown is subdivided into

separate chambers

88a, 80b, 80C and 80d, each individually supplied with gas through orifices 82.

Each module 80 has a hollow stem 84 of smaller cross sectional area that the outer terminus and each opens into a plenum chamber positioned above the module bed and acting as a support therefor. Each module of this embodiment is substantially enclosed, except for the lower, open end, and separated from other modules by an eX- haust zone 86 communicating with larger exhaust channels 87 between the module stems. Communication between the exhaust Zones 85 and the pressure chamber 28h is prevented by barrier plate 83 along the inside row of modules 80. Barriers 88 separate the plenum chamber into independent sections and inert gas, such as nitrogen, is fed to the independent sections through pipes 89 from a source not shown. The modules and plenum chamber are in most cases made of metal or refractory material that will withstand high operating temperatures.

The embodiment shown in FIGS. 10 and 1l may also be used to create a plurality of independent pressure zones beneath wall 40. A plurality of modules 90 are provided, contiguous with each other and each supplied through a separate orifice 92 in direct communication with a plenum chamber 94. In this embodiment, no exhaust passages are provided between adjacent modules.

In the operation of this device illustrated a ribbon of glass is formed by passage of molten glass between a pair of forming rolls 12 from a source thereof, such as a conventional glass melting tank, and the ribbon 14 is delivered to the front section of the tank 18 passing through the front or entrance seal 50.

Gas which is inert to the metal is fed into a pipe 62 and flows downwardly impinging against the glass and thereby isolates the interior of the tank 18 from the outside atmosphere. A similar gas is supplied to the plenum chamber 70 under pressure high enough to cause the gas in this chamber to flow through the orifices into the grooves 66 and to hold the ribbon away from the solid parts of the tank.

In general, this gas is preheated by means not shown to a temperature suciently high to prevent undue cooling of the glass. Normally, the temperature of the gas supplied to pipe 62 and chamber 70 will be above 500 to 1000 F. and often in the range of 1400 F. up to a melting temperature of the glass.

After the ribbon 14 has entered chamber 28a it is laid upon the surface of the molten metal and is led through the modular fluid pressure seal into chamber 28b which is at a higher pressure than chambers 28a and 23C.

As shown in the drawings, the ribbon 14 has a width greater than that enclosed by the wall 40, thus providing a narrow margin which extends beyond the edges of the wall 40 into the chambers 28C. Sealing gas is delivered from

modules

80 or 90, the outer termini of which are narrowly spaced from the upper surface of the ribbon. The spacings contemplated herein are on the order of 0.001 inch to 0.10 inch or greater. Gas emitted from the modules is caused to impinge against the edge portion of the ribbon 14 that is immedaitely below the walls 40, thereby separating the chamber 28b from 28e by a gaseous curtain. The gas is supplied at a pressure sufiicient to maintain the pressure differential between the chambers.

This curtain or fluid pressure seal is comprised of a plurality of individually supplied pressure zones that function independently from one another. The independent functioning is assured by supplying each separate charnber from a separate orifice. FIGS. 8 and l0 schematically indicate the principal ows of gas. The relatively small size of

orifices

82 or 92 provides a drop in gas pressure from the plenum to the interior of the modules. Not only are slight variations in plenum pressure minimized thereby, but also the gap between the lower terminus of each module and the upper surface of the glass ribbon becomes self-adjusting to a uniform spacing about the entire periphery of each module or, if divided, each submodule. This occurs because any decrease in the gap results in a buildup of pressure within the module cavity, thereby exerting the necessary force, as great as the plenum pressure, if necessary, to move the ribbon away from the module, As this occurs, the gap becomes larger and the pressure within the module cavity is reduced by the escape of gas through the larger gap. To be responsive to localized changes in spacing that do not occur along the entire ribbon margin, it is necessary that the modules be relatively small with respect to the length and width of the wall 40. For this reason small chambers, such as 80a, 8017, 80C and 80d function extremely effectively. However, as long as the module size is kept small, on the order of one to two inches across, it is generally not necesary that they be subdivided. Various module designs and their construction suitable for providing the pressure seal contemplated herein are disclosed in the -copending application of James C. Fredley and George E. Sleighter, Ser. No. 139,901, filed Sept. 22, 1961, now abandoned and the copending application of George W. Misson, Ser. No. 236,- 036, tiled Nov. 7, 1962, now Patent No. 3,223,500.

Internal pressure within chamber 28b may be most effectively maintained, particularly in the absence of eX- haust zones within the fluid curtain as in the embodiment of FIGS. l0 and l1, by varying the pressure in the module chambers across the width of the pressure seal. That is, if the modules positioned most closely adjacent the interior of pressure chamber 28 exert an inward pressure approximating that within the chamber, there will be no outward flow of gas from chamber 28b. If the modules toward the outer portion of Wall 40 exert progressively less pressure, the tlow of gas from the pressure seal will be substantially entirely outward of pressure chamber 28b A substantially static condition within chamber 28b is thereby achieved completely across the width to the very inside edge of the fluid pressure seal and the pressure upon the entire -portion of the ribbon beneath chamber 28b remains constant. Of course, this would not be possible if the spacing between the ribbon and the modules could not be maintained constant, as in the manner facilitated by the self-adjusting feature of the modules.

The pressures exerted by the various modules may be conveniently varied in whatever manner desired by varying the size of the

orifices

82 or 92. Thus, for greater pressure in those modules at the inner edge of wall 40, the

orifices

82 or 92 should be relatively large. However, the pressure in the modules must be kept below plenum pressure if the ability to automatically adjust the spacing between the module and the ribbon is to be retained. The inlet orifices to the modules along the outer edge of wall 40 may be decreased in size to effect a greater pressure drop between the module pressure and the common plenum pressure. Such a decrease in pressure facilitates the outward flow of gas from the curtain where exhaust passages are not provided around each module.

The temperature of the gas supplied to the front and side sections of wall 40 in front of baffle 46a generally should approximate a melting temperature of the glass or at least should be high enough to avoid cooling the ribbon edges below a melting temperature.

The ribbon 14, while floating on the metal surface, advances through the chamber 28b and finally is withdrawn from the tank 18 passing through the seal 52. It is pulled from the tank between the traction rolls 22 which may, if desired or if necessary, exact enough tension upon the ribbon to keep it moving. Enough tension may be applied by these rolls to cause the ribbon to attenuate or stretch to a thinner ribbon if desired.

As the ribbon passes through the chamber 28b, the temperature is maintained high enough to cause the ribbon to become molten during a substantial distance of its path, During this time the surfaces of the ribbon smooth out and the ribbon seeks an equilibrium thickness the magnitude of which is dependent upon the pressure established within chamber 28b.

The pressure required in the chamber 28b depends upon the thickness desired and the external pressure, i.e., the pressure in the chamber 28e to which the edges of the ribbon extend. Where it is desired to produce a ribbon thinner than the aforesaid equilibrium thickness of about 0.27 inch, the pressure in the chamber 28b should be above, normally at least 0.01 ounce per square inch above, that pressure at the edges of the molten ribbon, e.g., in the chamber 28C.

For example, the ribbon tends to stabilize at a thickness et/1G inch when the pressure differential is 0.11 ounce per square inch.

The degree of stabilization is a function of time. Con sequently, it is readily possible to produce glass 0.125 inch in thickness simply by sizing the thickness of the ribbon at this thickness or slightly lower, subjecting the sized ribbon to the treatment herein contemplated at a suitable pressure of about 0.2 ounce per square inch, which includes improving its surfaces, and removing the sheet before its thickness can grow unduly.

In general, the pressure differential established between the chamber 28h and that at the edge of the sheet or ribbon ranges from 0.01 to 2 ounces per square inch. High differential pressures normally are unnecessary and may :be diiicult to maintain. They should be in no event be so high as to cause the ribbon to break and rarely are above 5 to 10 ounces per square inch.

The temperature established in the forepart of the chamber 28b is a melting temperature of the glass of the ribbon. Toward the end, i.e., beyond baille 46a, the temperature is reduced low enough to ensure delivery of a stable ribbon which is not marred by contact with rolls to the discharge end of the tank, for example 600 to 800 F or below.

The rate of movement of the ribbon over the pool is controlled so as to ensure a smoothing of the surfaces of the ribbon and in general this is best accomplished by bringing a section of the ribbon to molten state.

Example I A ribbon of glass of convenient width, for example 12 inches or more, having a composition, :by weight, of 71.38 percent SiO2, 13.26 percent NaZO-l-KZO, 11.76 percent CaO, 2.54 percent MgO, 0.75 percent Na2SO4. 0.15 percent A1203, 0.11 percent Fe203, and 0.06 percent NaCl, and a weight density of 2.542 grams per cubic centimeter is formed by a pair of rolls to a thickness of substantially 0.125 inch and delivered at 1400 F. and floated upon the surface of a molten bath of metal of 100 percent tin having a weight density of 6.52 grams per cubic centimeter at 1800 F. The tank of molten metal is of the construction illustrated in the drawing and is longitudinally divided into three sections, an entrance section, the metal of which is maintained at a temperature of 1500 F., a melting section, the metal of which is maintained at a temperature of 1900 F., and a cooling section in which the metal is at a temperature ranging from 1900 F. to 1000 F. The space above the metal is subdivided into two pressure chambers and pressurized gas is fed to each chamber. The gas is preheated to 1900 F. for this supply. The first chamber 28a is maintained at slightly above atmospheric pressure while the second chamber 28hl is maintained Iat 0.5 ounce per square inch gauge pressure, so that a pressure differential of 0.2 ounce per square inch existed between the two chambers.

The width of the ribbon is greater than the width of the second chamber so that the margins of the ribbon extend laterally beyond the outer side edge of the chamber. The glass is heated from above to ya temperature of 1900 F. in the second chamber to remelt the ribbon throughout its entire thickness in a section across the entire width of the ribbon under the chamber and is then cooled to 1000 F. at the exit of the molten metal tank after which it is withdrawn from metal contact. The ribbon thickness remains at substantially 0.125 inch and the surfaces are fire-finished and at except for the edges which are bulbed.

The interior of chamber 281; is separated from

chambers

28a and 28c yby a gas pressure seal or curtain in the manner shown in FIG. 8 of the drawings` Gas is supplied to the plenum chamber 85 at a pressure of 10 ounces per square inch gauge. Orices in the modules 80 reduce the pressure by a factor of approximately twenty times with the glass ribbon spaced approximately 0.020 inch from the outer terminal of the modules, providing a curtain or seal pressure of 0.5 ounce per square inch gauge against the ribbon. Exhaust zones 86 and channels 87 allow the ow of gas from the curtain to escape to chamber 28C.

Various other embodiment of the process may be practiced. For example, the ribbon may be supplied substantially at melting temperature to the molten metal, held molten for a period and then gradually cooled. Pressure zones forming the uid pressure seal may be formed by other modules or nozzles than those depicted herein while not departing from the principle disclosed. The fluid curtain may vary in width from `one or two pressure zones to ve or more. The entrance and exit seals to tank 18 may be constructed in the same manner as the pressure seal beneath wall 40 where improved sealing is desired. As indicated in phantom in FIG. 2 of the drawings, the central chamber 28b may be tapered to a narrower width toward the withdrawal end of the tank to maintain the fluid pressure seals in proper relationship with the marginal edges of the ribbon in those pvocesses wherein the ribbon is attenuated to, in part, reduce the thickness. Such attenuation results in a narrowing, as well as a thinning, of the ribbon.

Referring now to FIGS. 12-16, apparatus is shown for applying a super-atmospheric pressure to the upper surface of a oating ribbon of glass with a plurality of relatively small Huid pressure zones. The tank construction of this embodiment being the same as in the embodiment shown in FIG. 1, all like parts are designated with the same reference numerals and need not be again described.

ln place of the circumferential wall 40 and uid pressure seal of modules separating the upper chamber 28 of tank 18 into the separate chambers of the embodiment shown in FIG. 1, a super-atmospheric pressure is applied to the central area of the ribbon 14 by a bed of modules 80 overlying, in close proximity, the entire width of the ribbon, except for the marginal edges along each side, and most of the length of the lloat tank including the heating zone, surfacing zone and at least the lirst portion of the cooling zone. Plenum chamber is supported above the ribbon in the top 28 of tank 18 by cross beams .suitably fastened to the sides of tank 18. Inert gas under pressure is supplied to each module 80 from an associated plenum chamber 85 subdivided into independent subplenums by barrier 88'. Each subplenum is supplied with inert gas, such as nitrogen under pressure, through pipes 89 from a source, not shown. The gas is preheated to approximately the temperature of the glass before being introduced to the plenum chamber and radiant heaters 48 maintain the temperature.

Each module is small with respect to the length and width of the ribbon and is close to, but spaced from, the next adjacent m-odules. In the embodiment shown, all modules 80 have their lower termini of rectangular configuration and lying in a common plane. The modules 80 are arranged in successive rows crossing the intended path of travel of the ribbon. Preferably, the rows are at an angle from the direction of ribbon travel, as illustrated in FIG. 13. Each module is subdivided into a plurality of separate chambers 80a', 80b, 80C', and 80d', each individually supplied with gas through orices 82.

Each module 80 has a hollow stem 84 of smaller cross sectional area than the outer terminus and each opens into a plenum chamber 85 positioned above the module bed and acting as a support therefor. Each module 80' is substantially enclosed, except .for the lower, open end, and separated from other modules by an exhaust zone 86 communicating with larger exhaust channels 87 between the module stems. Tubes communicate between exhaust channels 87 and the surrounding atmosphere and prevent a pressure build-up in the exhaust spaces. Exhaust gases also ilow laterally along channels 87 to the marginal edges of the plenum chambers.

In operation, the individually supplied pressure zones function independently from one another in the same manner as in the aforedescribed fluid pressure seal. Thus, the combination of the small orifices 82 and the Iclose spacing, generally 0.001 to 0.10 inch, between the lower termini of the module walls and the glass ribbon provides a self-adjusting gap therebetween that assures the existence of a uniform pressure over the entire ribbon beneath the module bed and hence a uniform thickness.

Exhaust zones such as those provided by passageways 86 between adjacent pressure zones beneath modules 80 are necessary to prevent a build-up of pressure centrally of the ribbon. Such a build-up is caused when gas must flow laterally across the ribbon to exhaust at the marginal edges. A nonuniform pressure of this type would cause the ribbon to be thin in the center and progressively thicker toward the sides. The uniform pressure beneath each module and the overall flatness of the pressure profile beneath the entire module bed is diagrammatically indicated by the graphs accompanying FIG. 16. Uniformity of treatment is further assu-red by skewing the module rows relative to the path of ribbon travel. With such an arrangement no one portion of the ribbon travels under an exhaust zone for any appreciable distance, and any variations in pressure or temperature are averaged throughout the ribbon.

Where desired, the transversely extending subplenums may be supplied with gas at different pressures. Thus, a high initial pressure may be desirable to rapidly bring the glass ribbon to a proper thickness while a lower pressure thereafter will maintain this thickness. Adequate exhaust space between adjacent modules allows purposely created differential pressures to exist throughout the module bed by essentially isolating one pressure zone from the next.

For special purposes, it may be desirable to vary the pressure transversely of the ribbon and thereby vary the thickness at which various portions of the ribbon stabilize. This can be accomplished by subdividing the plenum chamber 85 longitudinally of the ribbon travel into as many subplenums as desired. It may also be accomplished by varying the size of lthe orifices 82 in the manner described in connection with the fluid pressure seal formed with modules 80. By progressively varying the pressure across the width of the ribbon, a ribbon of glass wedge shaped in transverse cross section can be produced. This can also be achieved by progressively varying the spacing between the lower extremities of Ithe modules and the ribbon, as by slightly tilting the module bed transversely of the ribbon. Of course, the variation in thickness across the width need not be progressive but can abruptly change in stages to produce a series of contiguous strips of different thicknesses, each strip being a constant thickness. Other variations will occur to those skilled in the art. Such glass would find use as an architectural product.

The embodiment shown in FIGS. 17 and 18 may also be used to apply a super-atmospheric pressure above the oating ribbon 14. A porous plate 102 forms the bottom of a plenum chamber 104 and extends above and closely spaced from ribbon 14 in -the same manner as the bed of modules 80'. The porous plate 102 may be made of porous stainless steel or other heat resistant foraminous material. By virtue of the large number of small, randomly located passageways through plate 102, the plenum pressure is reduced and the flow of gas diffused to provide a uniform pressure on the ribbon. Tubes 106 open through the porous plate 102 and extend through the plenum chamber 104, opening to the atmosphere above, thereby providing exhaust channels for the flow of gas emitted through the pores of plate 102. This prevents a build-up of pressure centrally of the ribbon and assures a uniform pressure profile across the width of the ribbon. Such a plenum chamber having a porous wall and exhaust passages is disclosed and claimed in the copending application of George W. Misson, Ser. No. 251,851, filed Jan. 16, 1963, now Patent No. 3,300,290.

Example II A ribbon of glass of convenient width, for example 12 inches or more, having a composition, by weight, of 71.38 percent SiOZ, 13.26 percent Na2O-l-K2O, 11.76 percent CaO, 2.54 percent MgO, 0.75 percent Na2SO4, 0.15 percent A1203, 0.11 percent Fe203, and 0.06 percent NaCl, and a weight density of 2.542 grams per cubic centimeter is formed by a pair of rolls to a thickness of substantially 0.125 inch and delivered at 1400 F. and floated upon the surface of a molten bath of metal of 100 percent tin having a weight density of 6.52 grams per cubic centimeter at 1800 F. The tank of molten metal is of the construction illustrated in the drawing and is longitudinally divided into three zones: an entrance zone, the metal of which is maintained at a temperature of 1500 F.; a heating zone, the metal of which is maintained at a temperature of 1900" F.; and a cooling zone in which the metal is at a temperature ranging from 1900 F. to 1000 F. The chamber above the metal is maintained at a pressure slightly above atmospheric by introducing an inert gas at a slight positive pressure of about 0.2 ounce per square inch and preheated to 1900 F.

A module bed is disposed above the ribbon with the lower termini of the modules spaced from the ribbon a distance of approximately 0.020 inch. Inert gas preheated to a temperature of 1900 F. is supplied under pressure to the plenum chambers in the subplenums overlying the heating surfacing zones and is preheated to a temperature of about 1400 F. for the subplenum overlying the first portion of the cooling zone. The gas is supplied to all subplenums at a pressure of 10 ounces per square inch gauge. Orifices in the modules reduce the pressure by a factor of approximately twenty times with the underlying glass spaced from the module walls a distance of about 0.020 inch. A pressure of approximately 0.50 ounce per square inch gauge is uniformly applied above that portion of the ribbon underlying the module bed.

The width of the ribbon is slightly greater than the Width of the module bed so that the margins of the ribbon extend laterally beyond the bed. The glass is heated from above by the hot gas from the modules and from radiant heat to a temperature of 1900 F. in the heating and surfacing zone to reheat the ribbon to a flowing condition throughout its entire thickness in a section across the entire width of the ribbon beneath the module bed. The ribbon is then cooled to 1000 F. in the cooling zone at the exit end of the molten metal tank, after which it is withdrawn from metal contact. The ribbon thickness remains at substantially 0.125 inch and the surfaces are fire-finished and at except for the edges which are bulbed.

Although the present invention has been described with reference to certain specific details, it is not intended that such details shall be regarded as limitations upon the scope of the invention except insofar as included in the accompanying claims.

We claim:

1. In a process of producing glass sheet wherein the glass is deposited upon and supported on a liquid having a density greater than that of the glass and the glass when 4molten and allowed to How freely on said liquid tends to naturally attain an equilibrium thickness, the improvement which comprises,

floating a layer of glass at a temperature at which it flows on said liquid, flowing a pressurized gas from a plurality of spaced and separate pressure zones onto laterally spaced areas of the upper surface of the glass beneath said zones located above each of said areas and within the edges thereof, flowing the gas at different pressures from different zones above each said area, maintaining the pressure of the zones above the most Closely adjacent portions of said laterally spaced areas at a first pressure which is substantially the same as the pressure between said laterally spaced areas, maintaining the pressure of the zones above the most remote portions of said laterally spaced areas at a second pressure which is substantially the same as the pressure beyond said laterally spaced areas and above said supporting liquid, and

maintaining a gradient in the pressures provided by the laterally spaced pressure zones located between each pair of said pressure zones providing said rst and second pressure,

whereby to subject liquid outside and in contact with the glass to a iiuid pressure of different magnitude than that of said gas between said laterally spaced areas to control the thickness of the glass within the edges thereof so as to be different from said equilibrium thickness.

2. In a process of producing glass sheet wherein the glass is deposited upon and supported on a liquid having a density greater than that of the glass and the glass when molten and allowed to flow freely on said liquid tends to naturally attain an equilibrium thickness, the improvement which comprises,

oating a layer of glass at a temperature at which it flows on said liquid, flowing pressurized gas at a uniform pressure upon the area of the glass supported on said liquid from a plurality of spaced and separate pressure zones arranged in a row extending transverse to the length of the glass sheet at a location closely adjacent that at which said glass is deposited upon said supporting liquid, flowing pressurized gas upon the area of the glass supported on said liquid from each of the transversely arranged zones in each of a plurality of rows of zones arranged sequentially lengthwise of said glass sheet and beyond said first-named row, maintaining the pressure of the gas uniform in each of the transversely arranged pressure zones in each row,

maintaining the pressure of the gas from each such row at a value less than that of the preceding row,

maintaining the pressure of the gas from the row of transversely arranged zones most remote from the location at which said glass is deposited on said supporting liquid at a value suicient to maintain said glass at a predetermined thickness,

maintaining pressurized gas over the supporting liquid outside and in contact with the glass to provide a gas pressure thereover of a different magnitude than that of said gas between said pressure zones and the surface of the glass therebelow,

whereby said glass deposited on said supporting liquid rapidly reaches its predetermined thickness provided for by said diiference in magnitude of the gas pressures over said glass and said liquid outside and in contact with said glass. 3. In a process of producing glass sheet wherein the glass is deposited upon and supported on a liquid having a density greater than that of the glass and the glass when molten and allowed to flow freely on said liquid tends to naturally attain and equilibrium thickness, the improvement which comprises,

floating a layer of glass at a temperature at which it flows on said liquid, owing pressurized gas upon the area of the glass supported on said liquid from a plurality of rows of spaced and separate pressure zones extending transversely to the length of the glass sheet, said rows of said zones being arranged adjacent to one another and extending lengthwise of said glass sheet,

maintaining the pressure of the gas from pressure zones lying on one axis extending lengthwise of said glass sheet at a Value different than that from pressure zones lying on a second axis extending lengthwise of said glass sheet and spaced laterally from said rstnamed axis, and

maintaining pressurized gas over the liquid outside and in contact with the glass to provide a gas pressure thereover of a different magnitude than that of said gas between said pressure zones and the surface of the glass therebelow,

whereby to produce a glass sheet having laterally spaced zones of different thickness extending lengthwise of said sheet.

4. The process of claim 3 wherein the pressure of the gas owing from each separate pressure zone is uniformly and transversely, progressively less in each row of said zones transversely of said glass sheet,

whereby to produce a glass sheet having a wedgeshaped cross section extending transversely of the lengthwise direction of said glass sheet.

References Cited UNITED STATES PATENTS 2,911,759 11/ 1959 Pilkington et al. n- 65-182 3,048,383 S/l962 Champlin 65-182 3,223,501 12/ 1965 Fredley et al 65-182 3,241,939 3/ 1966 Michalik 65-99 FOREIGN PATENTS 732,043 2/ 1943 Germany.

DONALL H. SYLVESTER, Primary Examiner. D. CRUPAIN, G. R. MYERS, Assistant Examiners.

UNITED STATES PATENT OFFICE CERTIFICATE 0F CORRECTION Patent No. 5,345,149 october 3, 1967 Edmund R. Mchalik et al.

It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 13, line 8, for "pressure" read pressures column 14, line 7, for "and" read an Signed and sealed this 19th day of November 1968.

(SEAL) Attest:

EDWARD J. BRENNER Edward M. Fletcher, Jr.

Commissioner of Patents Attesting Officer

Claims

1. IN A PROCESS OF PRODUCING GLASS SHEET WHEREIN THE GLASS IS DEPOSITED UPON AND SUPPORTED ON A LIQUID HAVING A DENSITY GREATER THAN THAT OF THE GLASS AND THE GLASS WHEN MOLTEN AND ALLOWED TO FLOW FREELY ON SAID LIQUID TENDS TO NATURALLY ATTAIN AN EQUILIBRIUM THICKNESS, THE IMPROVEMENT WHICH COMPRISES, FLOATING A LAYER OF GLASS AT A TEMPERATURE AT WHICH IT FLOWS ON SAID LIQUID, FLOWING A PRESSURIZED GAS FROM A PLURALITY OF SPACED AND SEPARATE PRESSURE ZONES ONTO LATERALLY SPACED AREAS OF THE UPPER SURFACE OF THE GLASS BENEATH SAID ZONES LOCATED ABOVE EACH OF SAID AREAS AND WITHIN THE EDGES THEREOF, FLOWING THE GAS AT DIFFERENT PRESSURES FROM DIFFERENT ZONES ABOVE EACH SAID AREA, MAINTAINING THE PRESSURE OF THE ZONES ABOVE THE MOST CLOSELY ADJACENT PORTIONS OF SAID LATERALLY SPACED AREAS AT A FIRST PRESSURE WHICH IS SUBSTANTIALLY THE SAME AS THE PRESSURE BETWEEN SAID LATERALLY SPACED AREAS, MAINTAINING THE PRESSURE OF THE ZONES ABOVE THE MOST REMOTE PORTIONS OF SAID LATERALLY SPACED AREAS AT A SECOND PRESSURE WHICH IS SUBSTANTIALLY THE SAME AS THE PRESSURE BEYOND SAID LATERALLY SPACED AREAS AND ABOVE SAID SUPPORTING LIQUID, AND MAINTAINING A GRADIENT IN THE PRESSURES PROVIDED BY THE LATERALLY SPACED PRESSURE ZONES LOCATED BETWEEN EACH PAIR OF SAID PRESSUE ZONES PROVIDING SAID FIRST AND SECOND PRESSURE, WHEREBY TO SUBJECT LIQUID OUTSIDE AND IN CONTACT WITH THE GLASS TO A FLUID PRESSURE OF DIFFERENT MAGNITUDE THAN THAT OF SAID GAS BETWEEN SAID LATERALLY SPACED AREAS TO CONTROL THE THICKNESS OF THE GLASS WITHIN THE EDGES THEREOF SO AS TO BE DIFFERENT FROM SAID EQUILIBRIUM THICKNESS.