GLASS MAKING FURNACE APPARATUS

Abstract: A glass making furnace in which the ingredients are fed from a hopper (16) into a melting chamber (12) and heated in the presence of a pressurized gas supplied from a source (23) to collapse the bubbles in the melt. The chamber is heated to form melted glass which is expelled into a second chamber (14) for the removal of bubbles. The molten glass then flows from the second chamber through an outlet (102) with the flow rate being controlled by regulating the temperature of the nozzle. In the a second embodiment a homogenizer (136) is provided for removing bubbles from the molten glass.

Description: Title: Glass Making Furnace Apparatus Technical Field This invention relates to glass making furnace apparatus. Background.. Art To make glass, the constituent materials are mixed and heated until they become a viscous liquid. This liquid is normally contained in a clay pot or in a furnace lined with refractory brick. The glass making mixture is heated to the required temperature for an extended period of time sufficient for all chemical reactions to approach equilibrium and for the bubbles to rise to the surface. This process is called "fining" and the period, the "fining time". The properties of different types of glass are obtained by the selection and proportions of the various metallix oxides used. Furnace lining materials normally are also a mixture of metallic oxides. In spite of the fact that the lining composition is chosen so as to minimize its solubility in the glass, some dissolving occurs anyway. The erosion of the lining changes the glass composition and properties, creates inhomogeniety, corrodes and eventually destroys the lining. As the fining temperature is increased the glass viscosity decreases thereby allowing bubbles to rise faster and chemical reactions to proceed faster to allow the fining time to be reduced. Unfortunately the increased temperature also increases the erosion rate of the furnace lining to increase inhomogeniety and reduce furnace lift. These conflicting phenomena have forced a compromise in prior art glass making apparatus. The limitations imposed by erodable furnace wall materials can be eliminated by the use of a platinum (often alloyed with iridium or rhodium) crucible. Precision glass formulations are made this way but only small sized furnaces are feasible because of the cost of the platinum. Tungsten, rhenium and molybdenum are less expensive but oxidize at glass molting temperatures in the presence of oxygen, however, when submerged beneath liquid glass little or no oxida¬ tion or other chemical reaction takes place. Molybdenum is used routinely as an electrode material in glass tanks. Graphite, silicon carbide and silicon nitride are the other principal materials which are substanti¬ ally unreactive with glass and are used in such glass processing apparatus. Platinum is often used to prevent erosion only at certain key areas in the furnace or in special- ized apparatus. For example in U.S. Patent No. 3,401,536, issued September 17, 1968, to Glaser, a chamber or crucible as well as a feeder are fashioned of an alloy of platinum or other material capable of withsstanding the high temperature glass. In the appa- ratus of that patent a reservoir or holding chamber receives molten glass from a elter positioned above the crucible, with the melter receiving marbles of pre- fined glass from a hopper. The liquid glass passes a combination of baffles which reverse the direction of flow upwardly and over a baffle thus enhancing the removal of gases evolved from the glass. U.S. Patent No. 3,337,657, issued August 22, 1967, to Descarsin, discloses another apparatus uti¬ lizing noble metal crucibles, such as platinum. Another furnace apparatus is shown and described in U.S. Patent No. 3,358,066, issued December 12, 1967, to Tiede et al. This furnace is designed for producing elements of glass and is constructed of plati¬ num with bushing tips being provided for passage of the glass therethrough. The apparatus employs a stirrer or impeller for mixing the glass to provide a homogeneous mixture. Other apparatus used in manufacturing glass are shown in U.S. Patent No. 3,268,321, issued August 23, 1966, to Chapman and U.S. Patent No. 4,155,731, issued May 22, 1979, to Byrnes et al. After the constituent materials for glass have been .heated in a non-corroding chamber, there remains the next major step of removing the bubbles from the molten glass. One method of making bubble free glass is by the process of vacuum melting. This method involves heating a batch of glass-making materials under a vacuum while gradually raising the temperature to a maximum level. At that point the chamber is backfilled with an inert gas, such as argon or nitrogen, to collapse the bubbles and obtain a clear melt. However, this method is a batch process and in the past, has not provided a continuous supply of glass as is frequently necessary or desirable. In the above-mentioned Glaser patent struc¬ ture the feeder is provided with chambers of different volume with apertures through which the melted glass must pass for enabling the escape of bubbles. However,- certain types of glass, most notably pure cilica, remain sufficiently viscous even at temperatures as high as 2500°C that bubbles cannot be removed effec¬ tively. In previously used furnaces, the flow rate of molten glass from the furnace has been controlled primarily by the head of the furnace. In other words, the height of the molten glass pooled above the nozzle has regulated the pressure or force causing flow through the outlet. But the viscosities of the molten glass varies with the types of glass, therefore the head must be adjusted with each different glass. As described, the areas of the furnace above the molten pool are C.Y.PI Λ susceptible to erosion due to exposure to air and gases. Thus if the furnace is constructed to allow gre.at vari¬ ances of head, larger areas of the furnace are potenti¬ ally exposed to erosion. As a result, larger areas of the furnace would have to be lined with a precious metal thereby making the furnace prohibitively expensive. Glassmakers have studied.and experimented with bubble removal for centuries. It is possible that the concept of a bubble sieve has been considered and tried. To be effective, however, the holes must be as small as the smallest bubbles, about 0.1 mm diameter. Holes that small are difficult to make and if they were made very little glass will pass through them. The answer lies in slits of the same width having many meters in length. The lack of suitable materials and fabrication technology has apparently prevented the evolution of such a bubble separator. All continuous refining of glass is done at relatively low temperatures at which the glass is very viscous, so viscous that fining takes many hours, often days. A furnace with non-erodible walls can operate at a much higher temperature at which the glass can be fined in minutes. By using elevated pressure the operating temperature and flow rate can be increased still further. Note that existing furnaces operate at atmospheric pressure and that one atmosphere of pressure over the glass is equivalent to 4.63 meters of head at atmospheric pressure of borosilicate glass. Another area of concern with present furnaces is energy consumption. With greater heads and more molten glass in the accumulator, there is more radi¬ ating area with the resulting heat loss. With increased energy costs, such furnaces are expensive to operate. It is an object of the present invention to provide a new and improved glass making furnace apparatus. It is still another object of the present invention to provide a new and improved glass making apparatus in which only insoluble chamber walls con- fine the melt. It is another object of the present invention to provide a new and improved glass making furnace appa¬ ratus for a vacuum melting process on a batch or con¬ tinuous production basis. It is still another object of the present invention to provide a new and improved method and apparatus for removing bubbles from viscous and thixo- tropic liquids. It is still another object of the present invention to provide a new and improved method and apparatus utilizing an on-off fluid valve to obtain from a batch process apparatus a continuous glass output. It is still another object of the present invention to provide a new and improved method and apparatus utilizing a combination of gas pressure and temperature regulation to control the output of a glass producing process. It is still a further object of the present invention to provide a new and improved support system for a glass melting furnace. Summary of the Invention In a first embodiment, a sealed vibratory hopper is provided for feeding particulate glass making materials or the like to a first vacuum melting chamber having a downwardly depending tube through which molten glass flows to a second chamber having a downwardly depending tube terminating in a control valve and extrusion nozzle formed .of inert material. The hopper and melting chamber are sealed and provided with a pressure control system. The connecting tube between the first and second chambers is closed by a valve. To start the melting cycle the fluid on-off valve must be closed when the vacuum pump is energized. The mixed raw materials are fed from the hopper into the first chamber and heat is applied until the maximum desired temperature is maintained long enough for the melt to approach equilibrium. The vacuum is then shut off, the chamber is backfilled with an inert gas such as argon to collapse the bubbles, and the batch is drained into the second chamber having a dispensing nozzle for extruding the glass in the form of rod, tubing or fiber. While the extruding is taking place the on-off valve is closed and a new melting cycle started in the first chamber thereby making this furnace function as a con¬ tinuous process melter. The second embodiment of the invention oper¬ ates continuously and incorporates a static device for homogenizing and removing bubbles from the glass. The feed hopper and first chamber are sealed and operated at elevated pressures created by an inert gas which flows from the melt chamber and, if desired, bubbles through the molten glass to carry carbon dioxide .or other undesirable gases out. Operating at elevated pressures extends the boiling point of highly volatile materials and reduces the tendencies to boil off thereby stabilizing the composition of the molten liquid. The molten glass flows through a connecting section into a second chamber housing the homogenizer which consists of a structure of many rings stacked vertically in spaced relationship to form narrow slits through which the glass must flow. Bubbles less than about one-tenth millimeter in diameter are unstable thereby causing the gas bubbles to diffuse into the glass and disappear. Larger bubbles cannot pass through the slits and float to the top. The flow rate through the homogenizer to an extrusion nozzle is controlled primarily by regu¬ lating the pressure in the furnace. Both embodiments of the invention utilize a gas-tight chamber into which the glass ingredients are fed for mixing and heating to form molten glass. Cor¬ rosion of the chamber is minimized by controlling to the extent possible the atmosphere contacting the chamber walls. Also along the chamber walls at or near the level of the liquid glass platinum sheeting or foil is used to eliminate erosion that otherwise can often not be avoided. Formation of bubbles- in the molten glass is minimized by regulation of the pressure within ' the chamber. Inert gases are bubbled up through the molten glass to promote circulation and mixing, to pre¬ vent bridging of the incoming glass ingredients and to carry off the evolved gases. The ability to vary pres¬ sure between say one one-hundredth and fifty newtons per square centimeter though obviously desirable, has not been feasible until the availability of this compact apparatus designed for pressure operation. Brief Description of the Drawings FIG. 1 is a cross-sectional view of furnace apparatus incorporating a first embodiment of the invention; FIG. 2 is an enlarged cross-sectional view showing the support for the chambers of the furnace of FIG. 1; • FIG. 3 is an enlarged cross-sectional view of the extrusion nozzle assembly of the apparatus of FIG. 1; FIG. 4 is a cross-sectional view of a ' furnace apparatus made in accordance with a second embodiment of the invention; FIG. 4A is a cross-sectional view along the line 4A-4A of ' FIG. 4; • - OMPI ' FIGS. 5, 5A and 6 are enlarged cross-sec¬ tional views of the homogenizer used in the apparatus of FIG. 4; and FIGS. 7 and 8 are cross-sectional views similar to FIG. 5 of an alternate homogenizer configu¬ ration. Description of the Preferred Embodiments In FIG. 1 there is shown a two-stage glass- making apparatus 10 comprising a vibratory hopper 16 for feeding batches of premixed material 17 into a vacuum melting first chamber 12 which drains into a second chamber 14 for continually feeding an extrusion nozzle 90. The hopper 16 receives the constituent materials 17 and is provided with a suitable cover 18 which is closed during the glass-making process. The cover is provided with a seal (not shown) and a vacuum pump 20 connects with a tube 22 passing through.to the upper interior of the hopper 16 for evacuating the system for vacuum melting purposes and to evacuate and backfill the system at the time of startup. This hopper can also be pressurized from a pressured gas source 23. The pressure in the hopper is regulated by control of the pressure control valve 21. The hopper also has a downwardly extending spout 24 posi- tioned at the center of the sloping bottom wall and connected through a flexible coupling 26 to an inlet tube 28. Preferably the hopper includes a vibrator (not shown) to agitate and feed the material therein. The bellows or flexible coupling 26 serves as fibration isolation means to minimize the transmission of the vibration from the hopper to the furnace apparatus 10. The external structure of the furnace appa¬ ratus 10 is generally water-cooled, particularly at the joints and seals. A cover plate 30 forms a top wall through which the inlet tube 28 extends. A water- -. cooled steel plate 32 having a similar cross-sectional configuration as the cover plate is suitably fastened in abutting relation thereto with a vacuum seal 34 sandwiched therebetween in a circumferential groove. 5 Depending downwardly from the periphery of the water- cooled plate 32 is a cylindrical outer shell or side wall 36 which is supported at the bottom end by a second generally disc-shaped cover plate 38. The shell 36 preferably is secured to 'the end plates by 10 welding or the like and is filled with insulation to limit heat loss from the enclosed chamber structure. A second water-cooled plate 40 having the same general shape as the steel plate 38 is secured in the abutting relationship therewith. This plate 40 includes water- 15 cooling tubes (not shown), and a vacuum seal 42. A second cylindrical shell 44 is affixed to the under surface of the water-cooled plate.4.0 in coaxial relationship to the shell 36 and enclosed at the oppo¬ site end thereof by a bottom cover plate 46. Each of 20 the end plates 30, 32, 38, 40 and 4.6- is formed of stainless steel or the like. Assembled within the interior of the cylindri¬ cal shell 36 is the first or melting chamber 12- which is generally circular in cross-section and coaxially 25 positioned with the cylindrical shell 36. This chamber is provided with an upwardly extending inlet 48 and a downwardly depending outlet tube 50. The tube 50 provides a flow path into the reservoir or second chamber 14 and serves as a valve in a manner to be 30 described later. The chamber 12 is formed of tungsten or molyb- ( denum, strong materials particularly at high temperatures but which exhibit brittle tendencies at room temperature. Tungsten or molybdenum have the capability of with- 35 standing the high temperatures normally encountered in . Oft-PI glass melting while also being generally nonreactive with the liquid glass. The chamber 12, including the inlet 48 and the outlet 50.are fabricated as a unitary assembly having a main cylindrical body portion 52 with the . inlet portion 48 being configured as an inverted funnel and the outlet 50 likewise being configured as an upright funnel forming a collecting basin. A cylindrical tungsten heater member 54 is positioned in close thermal relation to the main body portion 52 of the melting chamber 12. Surrounding the heater 54 is a plurality of cylindrical concentric sleeves or heat shields 56 preferably formed of tungsten or molybdenum. Also a gas inlet 53 and outlet 53A connect with the chamber 63 surrounding the outlet tube 50. When cool- ing gas is introduced through the gas inlet, the tube 50 is cooled in a manner to be explained later. The melting chamber is supported on the .end plate 38 and the lower chamber 14 is supported in a similar manner on the cover plate 46. . The details .of these supports will be described later. The water-cooled plates 38 and 40 are provided with suitable openings through which extends the fluid valve tube 50 connecting the chambers. The tube 50 is surrounded by a second tungsten heater 60 enclosed by a tubular heat shield pack 62 formed of layers of tungsten or molybdenum. The heat shield pack 62 extends from the bottom wall 58 of the hea shield 56 to a top wall 64 having a .central aperture through which the tube 50 extends. The combination of.the tube 50, the heater .60 and the cooling gas system forms a control¬ lable on-off valve 61 for regulating the flow of molten glass from the first to the second chamber. If the heater is energized, the valve is open, i.e. molten glass or other material will readily flow through the conduit. To close the valve the heater is deenergized oy-pi and cooling gas is caused to flow into the inlet 53 and out the passage 53A cooling the tube 50 suffi¬ ciently to cause a buildup of solidified glass starting at the tube walls and finally closing the flow passage. In this manner, an on-off valve is supplied to control the passage of viscous fluid from the first chamber to the second chamber with no moving parts. The second chamber 14 is insulated by a cylindrical heat shield pack 66 secured between the periphery of a heat shield pack 64 and a bottom wall 68 generally closing the other end of the heat shield chamber. Supported within this heat shield chamber is the second chamber 14 which is generally cylindrical in cross-section and includes a downwardly sloping bottom wall 68 having an opening therein for passage of liquid glass.. Surrounding the main body portion of the second chamber is a third tungsten heater 70 in heat exchange relationship with the side walls of the chamber and positioned within the outer heat shield sleeve 66. In FIG. 2 is shown the support for the chamber 12 which is generally identical to the support for the chamber 14. The tube 50, as previously described, is funnel-shaped with a main tubular portion 73 and an upwardly tapered wall 72. A support collar 74 in the form of an annular ring is sandwiched between the tapered wall 72 of the tube 50 and a generally planar portion 80 of a conical support 82, the lower ends of which rest on an annular ledge 84 formed on the bottom wall 38. Thus the lower end of the support 82 is cooled by the water-cooled plate 38 whereas the top of the cone is essentially at the temperature of the chamber 12. With this construction tungsten or molyb¬ denum can be utilized for the chamber 12 as well as the reservoir 14 with the bottom portions thereof coacting with the small diameter support collar 74, which in O.V.Pl turn coacts with the large diameter of the support 82. By utilization of the conical expansion structure 82 as a support, the large thermal gradients are trans¬ ferred uniformly about the surface of the support thereby providing stability to the overall structure. A dditionally the relatively long radius of the conical structure 82 provides a large area for dissipating heat conducted from the attached chamber wall. Although not shown, the volume 37 and 45 within the cylindrical shields 36 and 44 and the respective components therein are filled with insulation. Referring now to FIG. 3, the extrusion nozzle assembly 90 includes a rubular portion 92 for receiving therein the upper end of the tube 94 for ducting glass from above. Around the spout 94 is a tungsten mesh heater 96 surrounded by a heat shield pack 98. The sleeve 92 is suitably secured to an inverted conical shaped flange 98 having the extending end thereof secured to the lower water-cooled end plate 46. The extrusion nozzle 92 preferably is formed of platinum, silicon nitride, silicon carbide or iridium with ' the conical flange 98 being brazed to th : end plate 46. The conical flange compensates the large theremal gradient between the glass reservoir and the water- cooled cover plate 46. The nozzle assembly 90 is one of the few components which must be made of precious metal with the balance of the furnace being formed of steel, tungsten or molybdenum. The glass makes no contact with clay or fire- brick in this furnace but contacts only unreactive metals or materials such as platinum, iridium, tungsten, molybdenum, silicon nitride or silicon carbide. Due to the high cost of platinum and iridium, these materials are used only in the areas that are exposed to the atmosphere, whereas the internal structures which are immersed by liquid glass or an inert atmosphere need be made only of tungsten or molybdenum. This design allows the furnace to operate at much higher temper¬ atures without the adverse side effects of erosion. The higher operating temperatures allow the glass making process to be completed in a much shorter time. For a given production capacity the furnace is much smaller, with the area of the furnace walls being easier to insulate to increase the fuel efficiency. As examples of temperatures the furnace must with¬ stand, the highest fining temperature necessary is for glass of pure silicon dioxide, 2600° to 3000° centi¬ grade,,with the working temperature being nearly 1800° centigrade. Soda lime glass, however, is fined at 1700° to 2100° and extruded at 700° to 1000° centi¬ grade. The outside area of this type of furnace is typically one-fiftieth to one-five hundredth the size of the present production furnaces with equal pro¬ duction capacity. Thus the more efficient insulation of the. furnace effects a great savings in fuel costs. At the extrusion outlet the glass is exposed to the atmosphere for the first time and is therefore extruded through a platinum nozzle or, if the glass is pure silica, the nozzle may be made of iridium. Three basic types of outlet nozzles can be used - a plain round one for making rod or gobs, one containing con¬ centric tubes for making glass tubing or a bushing with many small holes which is normally used to make fiber¬ glass. Referring further to FIG. 1, a more detailed description of the operation of the furnace follows. The.vibratory hopper 16 contains enough premixed material for many batches of glass. This hopper is connected to the vacuum pump 20 and is designed to withstand the compressive forces resulting from the vacuum as well as modest internal pressures- (1 to 50 newtons per square centimeter) to collapse bubbles. The vacuum pump is connected to the region surrounding chamber 12 as well as to the inside and to the hopper. At one start of each cycle a load of raw material is fed into the first chamber. This chamber is evacuated and heated by the tungsten heater 54 capable of achiev¬ ing the necessary melting temperatures. When the glass materials are melted the molten glass may have bubbles in it because the vacuum has been present during the entire cycle. After enough time has elapsed to thor¬ oughly melt the glass, an inert gas such as-argon is fed into the furnace at atmospheric pressure or above. At this time, the heater 60 is turned on and the glass plug in the tube 50 melts so the molten glass can flow down from" the first chamber to the second or lower chamber 14 * . As soon as the glass begins to flow, the heater 60 is deenergized and the draining glass from the first chamber begins to cool as the gas jets are turned on to cause solidifying glass to block the tube 50. Naturally the proportions (diameter and length) of this tube are important and must be selected so that the cooling glass will block the tube to complete the valve closing action but only after the first chamber has drained. When a fresh load of glass from the first chamber 12 enters the second chamber 14, the level of the glass rises substantially, however, the chamber is sufficient to maintain the flow from the extrusion nozzle 90 between cycles. The argon pressure within the second chamber is controlled to compensate for the changes in head pressure thereby assuring a uniform rate of flow. Regulation of the pressures and temper¬ atures within the furnace preferably is done with a . mini computer because of the interdependency of the various regulated parameters of the process. O. PI Tungsten and molybdenum are strong but at room temperature very brittle metals and are hard to fabricate. Both chambers must be supported by the novel arrangements described wherein the rings 74 rest on the conical discs 82 and 83 which are silver brazed to the water-cooled end plates 38 and 46, respectively. The design of the extrusion nozzle assembly 90 has also been given special consideration. Preferably it is gold brazed to the water-cooled end plate number 46. The conical flange 98 between the braze and the nozzle tube itself must handle the large thermal gradient between the glass and the cooler end plate. A special startup procedure is required • primarily to coat the inner metal walls with glass to protect them from oxidation. A load of prerefined glass is placed in the vibratory hopper and the hopper is sealed. A temporary cover with a gas inlet is placed over the extrusion nozzle 92. An inert gas con¬ taining approximately 2% to 5% hydrogen is flushed through the apparatus and exhausted through the hopper in the normal way. Pumping a vacuum and backfilling can speed up this process. Powdered.glass is fed from the hopper and melted until the desired glass levels in each chamber are reached. The feed hopper then is emptied and filled with the mixed glass-making material, the lid is closed and sealed and the inert gas lines opened to the normal pressure and flow rates. The glass is drained leaving enough glass in the on- off valve to form the necessary plug. .The vacuum pump is started and the batch material 17 is fed into the vacuum chamber 12 for initiating the normal glass- making process. The material 17 enters from the hopper through the flexible coupling 26 to the interior of. the chamber 12 and the heater 54 is energized.to create a liquid glass level shown generally by line 100. At the completion of the melting cycle the vacuum pump is turned off and an inert gas such as argon is fed into the chamber 12 until the pressure is equalized with that in the chamber 14, the heater 60 is then energized. Liquid glass flows through the fluid valve 61 to the reservoir 14 for passage through the extru¬ sion nozzle assembly 90 to form a glass rod 102 extruding from the bottom thereof. This process is repeated with the level within the reservoir or chamber 14 varying in accordance with the rate of flow from the nozzle assembly 90. In this manner, a vacuum melting may be accomplished within the chamber 12 for removal of bubbles, while permitting the discharge of glass from chamber 14 to form the end product 102 on a con¬ tinuous process basis, particularly advantageous when making quartz fiber of quartz tubing. In FIGS. 4 and 4A is shown a second embodiment of the. onvention wherein inventive features are incorpo- rated in a continuous process furnace. This furnace, like the furnace of the first embodiment, employs a first chamber 110 and a second chamber 111 mounted, coaxially with the first chamber being above the second for a gravity feed therebetween. The overall heated portions of the furnace are enclosed in an outer shell 112 with the ends closed by a top or end plate 114 and a bottom or end plate 115. These end plates are water- cooled in the manner described relative to the first embodiment. A hopper 116 feeds materials through a feed tube 117 to the first chamber. While not shown, this hopper has a variable sp esd vibrator which agi¬ tates the material for an even and controllable flow. A variety of feeding methods can be used. The feed tube preferably includes a bellows or vibration isolater (not shown) and passes through an opening 119 OMPI in the top wall 114 of the furnace. The hopper is sealed by a top lid (not shown) which can be opened for refilling the hopper. Pressure within the hopper is controlled by a pressure control 113. In the same 5 manner previously described, energization of the vibrator will cause a gravity flow of the feed material into the first chamber. The first chamber is formed of a top wall 122 and side walls 124. Inside the chamber is located 10 a tungsten heater 125. The top wall 122 is platinum " „ ' foil lined to prevent corrosion at the liquid gas inter¬ face. Corrosion results from oxygen which occurs un¬ avoidably during the fining process- The top wall 122 slopes in a conical configuration upwards towards the 15 center and extends below the liquid le^-el such that escaping gas bubbles will break up any tendency of incoming material to bridge across. Extending to to the first chamber is an inert gas infeed line 126. With the infeed of material pref- 20 erably to the level of the dotted line 123A and the tungsten heater 125 energized, the glass material will melt " to a molten state. As argon gas is fed through the inlet tube 126, bubbling will occur up through the molten mass in a direction generally counter to the 25 downward flow of the viscous fluid within the cylindri¬ cal baffle 123. After the flow passes the bottom of the baffle 123 it is turned upward by the wall 127 to flow upward along the second baffle 128 and over the top of this wall to again flow downward along the 30 cylindrically configured tungsten heater 125. The bub¬ bling gas will improve the mixing and tend to carry from the molten mass any gas bubbles which naturally -form in the fluid. Generally speaking, the liquid level of the molten mass will be near the dotted line 35 133. The level of the feed material and possibly the __OMPI _ liquid level can be observed through the optic system 129 comprising a tube extending through the upper wall 114. Additionally the temperature of the furnace interior can be measured through various pyrometric devices (not shown) by viewing the interior through tubes extending through the furnace side wall. Prefer¬ ably these tubes are made of tungsten and lead to a pyrometric sensor (not shown) positioned outside the furnace. As the viscous glass liquid is formed in the first chamber ' 110, it will be pulled by gravity into the second chamber 111. The chamber 111 is provided primarily as an accumulator and to house a homogenizer 136. A second tungsten heater 137 is positioned co- axial with and adjacent to the chamber wall. The chamber is formed of side walls 138 and a bottom end wall 139. A baffle 140 is positioned around the homogenizer to cause the molten glass to flow downward along the heater 137 and then reverse direction to flow upward along the outer surface of the homogenizer. The purpose for th homogenizer is to thoroughly mix the viscous glass liquid and to remove any bubbles having a diameter generally greater than 0.1 millimeters. The homogenizer consists of a cylinder having an outside wall including many slits which are approximately 0.1 millimeters wide. As the viscous fluid passes from external this cylinder to the inside, bubbles are separated therefrom and a high shear mixing of the glass is achieved as the glass moves through the slits. Preferably the homogenizer is built of a plurality of tungsten or molybdenum rings 141 (FIGS. 5 and 6) separated by precision spacers 142 which control the width of the slits therebetween and hold together by several rods 143 passing through aligned openings in the rings. As shown in the drawings in diagrammatic OMPI form, the preferred design for the homogenizer incorpo¬ rates between 100 and 300 rings 141 between 8 and 30 centimeters in diameter and having a thickness of approxi¬ mately 2.5 to 4.0 millimeters. The spacers 142 between adjacent rings are approximately 0.05 to 0.2 millimeters thick and are intermittent to allow the viscous fluid to flow therebetween. In FIG. 6, the rings are shown in enlarged detail with the viscous fluid flowing as shown in the direction of the arrow 144 while the bubbles 145 are too large or have a tendency not to flow horizon¬ tally into the space between the rings. Thus the bubbles rise vertically along the outer face 146 of the rings and flow in the direction of the arrow 147. Preferably this face is beveled in the manner shown with the smaller diameter positioned lower so as to encourage flow of the bubbles vertically along the homogenizer and also require a horizontal flow of the molten glass passing between the rings. Because the bubbles natu¬ rally rise, they tend to flow upward and not be carried horizontally by the molten glass. The bubbles separated from the molten glass rise and strike the bottom surface of the wall 127 of the baffle. This wall is of an inverted conical con¬ figuration so as to encourage the flow of the bubbles radially outward therealong to subsequently pass through openings 127A in the wall 127 within the confines of the baffle 140 and rise through the ' downward flowing molten glass. . This gas and the inert gas from the nozzle 126 is expelled through an outlet (not shown) in the hopper. The outlet can include a filter if desired. The second chamber 111 is supported on an annular ring 151 fixed to an inverted conical flange 152 in the same manner as in the first embodiment. Such structure will withstand the temperature and provide sufficient heat dissipation to compensate for the temperature gradient between the water-cooled wall of the furnace and the chamber wall. The bottom wall 154 of the chamber 111 is funnel-shaped and connects with a vertical tube 155 leading to an extrusion nozzle (not shown). Extending around the tube 155 are gas manifolds 156 and a series cf heaters 157. Cooling gas is pumped in through the conduits 158 (see FIGS. 4 and 4A) to be distributed along the length of the tube 155 by the manifolds 156. Openings 159 face the tube 155 and cause a high velocity gas flow on the tube exterior wall for cooling. The gas is then retrieved through the tube 160 connecting to a heat exchanger and pump (not shown) for recycling. Thus the temperature of the molten glass passing through the exit tube 155 is regulated closely for controlling the rate of flow there¬ through. The rate of flow through this tube is also regulated by controlling the internal pressures within the furnace. These internal gas pressures allow control not only of the flow of molten glass through the exit tube but also the flow of glass from the first chamber through the second chamber, which is in the second embodi¬ ment includes the homogenizer. By providing for both cooling and heating of the glass as it is extruded from the furnace, a close control over the temperature of the glass is achieved. For instance, in some glass making processes it is known that the exterior of the tube or gob cools more quickly than desired. By the apparatus shown, the exterior layer of the rod can be heated during extrusion to compensate for subsequent surface cooling to improve the ultimate glass product. Insulation around the furnace is provided first by the heat shield 138 which preferably comprises 10 to 12 wrappings of 0.03 to 0-5 millimeters thick sheet tungsten or molybdenum which has been dimpled so _ O H as to keep the layers slightly separated. Preferably ' the spacing between layers is 0.6 millimeters or more so that a heat shield of ten layers is approximately 6 millimeters thick. Next to the heat shield is the quartz chamber wall 124.. Experience .shows that if the fining process is operating at 2000° .centigrade, the outer heat shield operates at approximately 800°C to 900°C and the gradient through the quartz wall is small, probably less than 50° centigrade. To prevent leakage, silica is plasma sprayed around .the pyrometric sensing tubes and the electrical terminals that enter the melt chambers. .. The capacity or production rate of this furnace is limited only by the rate of flow through ' the homogenizer. That in turn is limited by its operating temperature. This may be set at any point up to the boiling point of the glass. The rate is then controlled only by the pressure over the melt. This pressure may be increased until the flow rate becomes limited by the heating capacity of heaters 125 and "137. The boiling point, pressure, flow rate and heater capacity are all interrelated. A computer programmed to recognize these interrelationships is therefore preferable to control the apparatus. Tungsten melts at 3400°, however,the operating temperature should not exceed 3000° to get reasonable heater life. Using tungsten heaters the furnace capacity is approximately proportional to the. working area of the heaters. The liquid level is maintained by controlling the feed rate of the raw material by adjusting the speed of the vibrator. The liquid level may be observed either visually or by closed circuit television (not shown) but automatic control is based on one or more temperature sensors located near the liquid level. A computer program is preferably provided which relates this input with the observed liquid level and accord¬ ingly controls the vibratory feeder. To the extent that this feed material is preheated and predried, ^ the load on the heaters is reduced. The hot gas coming from the bubbles system contributes to this cause as it flows through the bellows to the material-in the hopper and on through it to the filter and pressure control outlet valve. In the manner just described there is pro¬ vided a continuous process glass furnace incorporating the inventive features of the first embodiment but substituting the homogenizer for removing the bubbles from molten glass. Other embodiments of the homoge- nizer are feasible to take advantage of the concept. For instance, the homogenizer can be configured as shown in FIG. 7 having " a truncated cone shape. In this embodiment the rings are manufactured from molyb¬ denum or tungsten material. While lesser flow area is provided near the top of the homogenizer, the reverse or upward flow of the molten glass or other liquid generally causes less liquid to reach the top area anyway. The conical configuration causes the verti¬ cally rising bubbles to separate more readily from the homogenizer wall also. Alternatively the homogenizer may be constructed from a helicoidally wound coil (not shown) having a cross-section the same as the thickness of the discs used previously and being separated by spacers of a desired thickness. It should be realized that while the homoge¬ nizer described for removing gas bubbles from molten glass only, it can be used in many other applications and with many other materials to mix materials and separate bubbles therefrom. Additionally the furnace embodiment may have uses other than for the making of glass. _ OM?I

Claims: Claims 1. A furnace for making glass.and the like from constituent materials, comprising: a first chamber formed of walls insoluble in molten glass; a second chamber formed of walls insoluble in molten glass; an outlet from said second chamber; a flow passage connecting said first and second chamber; heating means for heating said first and second chambers to melt said constituent materials in the first chamber into a liquid; a hopper for feeding constituen material ■ to said first chamber; means to mix said constituent materials and separate out gas bubbles from said fluid; and means to prevent corrosion of said chambers while said materials are being heated. 2. A furnace as defined in Claim 1 wherein said means to prevent corrosion includes means to draw a vacuum in said first chamber while the material is being heated. 3. A furnace as defined in Claim 1 wherein said means to prevent corrosion includes means to intro¬ duce an inert gas into said first chamber. 4. A furnace as defined in Claim 3 wherein said gas is introduced into the bottom of said first chamber so as to bubble up through said liquid. 5. A furnace as defined in Claim 2 including a valve in said flow passage for controlling flow of liquid from the first chamber to the second chamber. "BUREAU OΛ'PI 6. A furnace as defined in Claim 1 wherein said means to separate out gas bubbles comprises a homogenizer having a wall member with small slits therethrough to allow fluid to flow therethrough while preventing the passage of gas bubbles. 7. A furnace.as defined in. laim 6 wherein said slits are between .05 and 0.2 millimeters across. 8. A furnace as defined in Claim.1 wherein the portion of said first chamber at and above the liquid level is lined with a noble metal to limit cor¬ rosion due to the presence of said heated liquid. .9. A furnace as defined in Claim 6 wherein said homogenizer is comprised of a plurality of rings stacked together with spacers therebetween to form said slits. 10. A furnace as defined in Claim 9 wherein said rings.are made of one of the metals from the group of tungsten and molybdenum. 11. A furnace as defined in Claim 4 including a baffle structure forming flow passages in said first chamber through which the liquid must flow .to reach said flow passage with at least a portion of said flow passage including the path of said gas bubbles to enhance the flow of liquid. 12. Apparatus for .homogenizing and separating bubbles from a liquid, said apparatus comprising: a wall member forming a plurality of slits of a width less than the size of the bubbles; means to create a pressure differential across said wall member; and means to direct the liquid along one side of said wall member whereby said liquid will flow through said slits and said bubbles will be excluded from said flow. 13. Apparatus as defined in Claim 12 wherein said wall member comprises a plurality of annular rings stacked one on the other with spacers therebetween to form said slits between said rings. 14. Apparatus as defined in Claim 12 wherein said means directs the liquid to flow upward along said wall member. 15. . Apparatus as defined in Claim 13 wherein said rings on the edge facing outward from said wall . member are cut on a bevel with the greater diameter side being positioned above -the smaller diameter side to direct the separated bubbles away from said wall member. 16. A furnace for making glass and the like from constituent material comprising: a first chamber having top, side and bottom walls forming a first cavity; means to introduce constituent material into said first cavity; a first heater energizeable to heat said material in said first cavity to cause it to melt and form a viscous liquid; an outlet port in said first chamber; a.second chamber having top, side and bottom walls forming a second cavity; an inlet port in said second chamber; a first conduit connecting said first chamber outlet port to said second chamber inlet port; an outlet port in said second chamber; means to. introduce an inert gas into said chambers to limit erosion of said chamber walls; and control means to cause energization of said first heater to cause melting of said material and to regulate the inert gas pressure in said chambers to change the flow of said melted liquid from said first chamber into said second chamber. 17. A furnace as defined in Claim 16 wherein said inert gas is introduced into said chambers so as to flow upward through said melted liquid to assist in mixing said material. 18. A furnace as defined in Claim 17 includ¬ ing a second heater for heating said second chamber. 19. A furnace as defined in Claim 18 includ¬ ing means for cooling the outlet port of said second chamber. 20. A furnace as defined in Claim 19 in¬ cluding means for heating the outlet port of said second chamber. 21. A glass making furnace comprising: a gas tight first chamber; means to introduce glass making con¬ stituents into said first chamber; * means to heat said first chamber to melt the constituents into a viscous liquid; an outlet nozzle connecting with said first chamber through which the viscous liquids can flow; and means to introduce a gas into said first chamber to regulate the rate said viscous liquid flows through said outlet nozzle. 22. A glass making furnace as defined in Claim 21 including means to separate gas bubbles from said viscous liquid. 23. A glass making furnace as defined in Claim 21 including a second chamber positioned to receive flow of viscous liquid from said first chamber and to supply viscous liquid to said outlet nozzle. 24. A glass making furnace as defined in Claim 23 including a flow passage connecting said first and second chambers through which said viscous liquid can flow. Bϋ O.Y:PI . ■■ 25. A glass making furnace as defined in Claim 24 including a flow control valve in said flow passage. 26. A glass making furnace as defined in Claim 23 including a homogenizer in said second chamber to separate gas bubbles from said viscous liquid. 27. A glass making furnace as defined in Claim 26 including means to heat said outlet nozzle to regulate the temperature of the viscous liquid flowing therethrough. 28. A glass making furnace as defined in Claim 26 including means to cool said outlet nozzle to regulate the temperature of the viscous liquid flowing therethrough. 29. A glass making furnace as defined in Claim 21 wherein said means to introduce gas intro¬ duces said gas at a location to cause bubbling up through said viscous liquid to mix said liquid. 30. A glass making furnace as defined in Claim 29 wherein said gas is introduced to bubble through and prevent bridging of said constituents. 31. A glass making furnace comprising: a melting chamber formed of walls that do not chemically reset with molten glass; means for .introducing the ingredients of glass into said chamber; means to heat said chamber; means to introduce a gas into said chamber; means to control the gas pressure in said chamber; and an outlet nozzle for expelling molten glass from the chamber. O.V.FI 32. A glass making furnace as defined in Claim 31 wherein said means for introducing the ingred¬ ients for glass includes a gas tight storage hopper connected to said chamber by a feeder pipe. 33. A glass making furnace as defined in- Claim 32 including a baffle mounted in said melting chamber and positioned to cause said glass to flow upwards and over to separate gas bubbles therefrom. 34. A glass making furnace as defined in Claim 33 including means to expel bubbles of gas into said chamber in a position to travel upwards with said molten glass to promote the flow of and mixing of said molten glass. 35. A glass making furnace as defined in Claim 31 wherein said means to heat said chamber is a refractory metal heater immersed in the glass ingredients. 36. A glass making furnace as defined in Claim 31 including means to remove bubbles from said molten glass prior to expulsion through said outlet nozzle. 37. A glass making furnace as defined in Claim 36 wherein said means to remove bubbles com¬ prises a wall member including a plurality of slits sufficiently large to permit molten glass to flow through but small enough to prevent the flow of at least the largest bubbles. 37. A glass making furnace as defined in Claim 37 wherein said wall member is made of a plur¬ ality of stacked rings spaced apart to form the slits therebetween. 39. A glass making furnace as defined in Claim 31 wherein said nozzle includes means to cool said molten glass prior to expulsion therefrom. 40. A glass making furnace as defined in Claim 31 wherein said nozzle includes means to heat said molten glass passing therethrough. 41. A glass making furnace as defined in Claim 31 including: a second chamber to store molten glass and maintain a continuous flow to said outlet nozzle; a flow passage connecting said melting chamber and said second chamber; and a valve in said flow passage for con¬ trolling liquid flow through said passage. 42. A glass making furnace as defined in Claim 41 wherein said valve includes means to cool and heat molten glass flowing through said passage to block and open said passage.

Inventors: CARMAN JUSTICE N, CARMAN, JUSTICE, N.
Applicants: CARMAN JUSTICE N, CARMAN, JUSTICE, N.
Application year: 1981
Main classification: C03B3
IPC codes: C03B3, C03B5