Classifications

• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B7/00—Distributors for the molten glass; Means for taking-off charges of molten glass; Producing the gob, e.g. controlling the gob shape, weight or delivery tact
  • C03B7/02—Forehearths, i.e. feeder channels
  • C03B7/06—Means for thermal conditioning or controlling the temperature of the glass
  • C03B7/07—Electric means
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B5/00—Melting in furnaces; Furnaces so far as specially adapted for glass manufacture
  • C03B5/16—Special features of the melting process; Auxiliary means specially adapted for glass-melting furnaces
  • C03B5/225—Refining
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B5/00—Melting in furnaces; Furnaces so far as specially adapted for glass manufacture
  • C03B5/16—Special features of the melting process; Auxiliary means specially adapted for glass-melting furnaces
  • C03B5/42—Details of construction of furnace walls, e.g. to prevent corrosion; Use of materials for furnace walls
• • C—CHEMISTRY; METALLURGY
  • C03—GLASS; MINERAL OR SLAG WOOL
  • C03B—MANUFACTURE, SHAPING, OR SUPPLEMENTARY PROCESSES
  • C03B5/00—Melting in furnaces; Furnaces so far as specially adapted for glass manufacture
  • C03B5/16—Special features of the melting process; Auxiliary means specially adapted for glass-melting furnaces
  • C03B5/42—Details of construction of furnace walls, e.g. to prevent corrosion; Use of materials for furnace walls
  • C03B5/43—Use of materials for furnace walls, e.g. fire-bricks
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
  • Y02P40/00—Technologies relating to the processing of minerals
  • Y02P40/50—Glass production, e.g. reusing waste heat during processing or shaping

Definitions

• the present disclosure relates generally to an apparatus for making glass, and in particular a molten glass delivery apparatus comprising a vessel including a wall with a thickness that varies circumferentially about a perimeter of the vessel
• molten glass The melting of raw materials to form a molten material, referred to hereinafter as molten glass requires the use of combustion gases and/or electrical energy during the melting process.
• the raw materials may then be conditioned and transported from the melting furnace to the forming apparatus.
• the molten glass is delivered to the forming apparatus via a precious metal delivery apparatus comprising various processing equipment.
• a precious metal delivery apparatus comprising various processing equipment.
• certain components of the delivery apparatus can be directly heated by producing an electric current in the components.
• the electric current heats the component, which in turn heats the molten glass therein.
• Different components of the delivery apparatus have varying energy requirements.
• the component with perhaps the highest power requirement in the delivery apparatus is the fining vessel, where the molten glass is conditioned to remove gases resulting from the melting process.
• the fining vessel is held at very high temperatures.
• the bubbles rise faster at lower viscosity, and solid inclusions dissolve faster at higher temperature.
• oxidation of the precious metal e.g. platinum and/or rhodium
• the rate at which oxidation occurs increases as a function of temperature and oxygen content.
• Precious metal oxidation leads to metal thinning.
• Oxidation is generally more severe at the top of the fining vessel for at least two reasons: 1) there is an air gap above a surface of the molten glass, and 2) the temperature is highest at the top of the fining vessel. Temperatures at the top of the fining vessel for some glasses can exceed 1700°C. Generally, temperatures at the top of the fining vessel can average 20°C higher than the temperature of the molten glass contained in the lower portion of the fining vessel. Because the higher temperature at the top of the fining vessel can lead to corrosion failure of the fining vessel, a reduction in fining vessel top temperature is needed.
• the fusion glass making process is capable of producing thin glass sheets of exceptional surface quality, making such glass sheets ideal for the manufacture of visual display products, such as televisions, cell phones, computer monitors and the like.
• raw materials referred to as batch
• the molten glass is subsequently conveyed through a delivery apparatus to a forming body.
• the forming body comprises a trough formed in the upper surface thereof, and exterior converging forming surfaces.
• the molten glass is received from the delivery apparatus by the trough, wherein the molten glass flows over and down the converging forming surfaces as separate flows. These separate flows join where the converging forming surfaces meet, forming a single glass ribbon, which, once cooled to an elastic solid, is cut into separate sheets of glass.
• the delivery apparatus that delivers the molten glass to the forming body is typically constructed using a high temperature metal, and in particular a high temperature metal that is resistant to oxidation.
• Suitable metals can be selected, for example, from the platinum group metals, i.e. platinum iridium, rhodium, palladium, osmium and ruthenium. Alloys of the foregoing platinum group metals may also be used.
• molten glass delivery apparatus are often constructed from platinum or an alloy of platinum, such as a platinum- rhodium alloy.
• the molten glass may be conditioned by passing the molten glass through a conditioning vessel such as a fining vessel where a de-gasification process takes place.
• a conditioning vessel such as a fining vessel where a de-gasification process takes place.
• gases are evolved. If left within the molten glass, these gases can produce bubbles in the finished glass article, such as the glass sheet from the fusion process.
• the temperature of the molten glass is raised in the fining vessel to a temperature greater than the melting temperature. Multivalent compounds included in the batch and present in the molten glass release oxygen during the increase in temperature and aid in sweeping the gases formed during the melting process from the molten glass.
• the gases are released into a vented volume of the fining vessel above a free surface of the molten glass.
• the temperature in the fining vessel can in some cases, for example in the production of glass sheets for the display industry, exceed 1650°C and even exceed 1700°C and approach the melting temperature of the fining vessel wall.
• One method of increasing the temperature in the fining vessel is to develop an electric current in the fining vessel, wherein the temperature is increased via the electrical resistance of the vessel's metal wall.
• Such direct heating may be referred to as Joule heating.
• electrodes also referred to as flanges, are attached to the fining vessel and serve as entrance and exit locations for the electric current.
• Monitoring of the fining vessel temperature at various locations on the fining vessel can be carried out by embedding thermocouples in the refractory insulating material that surrounds the fining vessel. Data from such monitoring has shown an increased temperature of the fining vessel where the gaseous atmosphere above the free surface of the molten glass is in contact with the fining vessel wall. This has been attributed to the reduced thermal conductivity of the gaseous atmosphere within the fining vessel relative to the thermal conductivity of the molten glass contained within the lower portion of the fining vessel. Autopsies performed on out-of-service fining vessels have shown excessive oxidation in the upper portions of the fining vessel not in contact with the molten glass, particularly where the flanges are joined to the fining vessel wall.
• embodiments disclosed herein are directed toward controlling the flow of current through the wall of the fining vessel to reduce the temperature of that portion of the wall in contact with the gaseous atmosphere within the fining vessel and over which molten glass does not flow.
• a delivery apparatus for molten glass comprising a fining vessel configured as a tube comprising a wall, the tube wall comprising a metal selected from the group consisting of platinum, rhodium, palladium, iridium, ruthenium, osmium and alloys thereof; a plurality of flanges encircling the tube and configured to conduct an electric current through the wall, the plurality of flanges comprising platinum, rhodium, palladium, iridium, ruthenium, osmium and alloys thereof. At least a portion of the wall between at least two consecutive flanges of the plurality of flanges comprises a thickness that varies circumferentially.
• the phrase "two consecutive flanges" is meant to indicate that, in a flow direction of the molten glass, the molten glass passes the two consecutive flanges in sequence, with no intervening flanges between the two consecutive flanges.
• the at least a portion of the wall may comprise a first wall portion and a second wall portion, and in a cross section of the at least a portion of the wall a thickness of the first wall portion may be less than a thickness of the second wall portion.
• the thickness of the first wall portion can be substantially uniform and the thickness of the second wall portion can be substantially uniform.
• the first wall portion is positioned at a top of the fining vessel and the second wall portion is positioned at the bottom of the fining vessel, below the first wall portion.
• the molten glass delivery apparatus may further comprise a third wall portion positioned between the first wall portion and the second wall portion.
• a thickness of the third wall portion in the cross section may be greater than the thickness of the second wall portion.
• the second wall portion may be constructed to comprise a plurality of layers.
• the second wall portion may comprise a laminated structure comprising a plurality of metal plates.
• the at least a portion of the fining vessel wall may comprise a first wall portion and a second wall portion, wherein a thickness of the first wall portion is greater than a thickness of the second wall portion.
• the first wall portion is positioned at a top of the fining vessel, and the at least a portion of the wall may be positioned adjacent one of the two consecutive flanges.
• the thickness of the first and/or second wall portions may be substantially uniform.
• a length of the first wall portion when the first wall portion is thicker than the second wall portion maybe no greater than about 16 cm.
• the first wall portion, when the first wall portion is thicker than the second wall portion may comprise a plurality of metal layers.
• the first wall portion abuts a flange of the two consecutive flanges.
• the flange may be attached to an upper surface of the first wall portion, such as in a center portion of the first wall portion so that the first wall portion extends outward from the flange parallel with a longitudinal axis of the fining vessel.
• the first portion has a length along the longitudinal axis of the fining vessel of 16 cm, and the flange is attached to the first portion at the midpoint of the 16 cm length. It should be apparent from the foregoing that the length could be different than 16 cm, e.g. less than 16 cm, with the flange attached to the first wall portion at the midpoint of the first wall portion length.
• the at least a portion of the wall may comprise a first length portion, a second length portion spaced apart from the first length portion, and a third length portion positioned between the first and second length portions.
• a thickness of the first length portion may vary circumferentially
• a thickness of second length portion may vary circumferentially
• a thickness of the third length portion may be substantially constant.
• each of the first and second length portions may comprise a first wall portion and a second wall portion, and a thickness of the first wall portions of the first and second length portions are greater than a thickness of the second wall portions of the first and second length portions.
• the first wall portions of the first and second length portions are positioned at a top of the fining vessel.
• Each of the first and second length portions may be positioned adjacent one of the two consecutive flanges so that each of the first and second length portions abut a respective flange of the two consecutive flanges.
• the molten glass delivery apparatus may further comprise a fourth length portion positioned between the adjacent flanges, the fourth length portion comprising a first wall portion and a second wall portion, the first wall portion of the fourth length portion positioned at a top of the fining vessel.
• a thickness of the first wall portion of the fourth length portion can be greater than a thickness of the second wall portion of the fourth length portion.
• a method of forming glass comprising melting a batch material in a melting furnace, flowing the molten glass from the melting furnace through a metal fining vessel such that the molten glass comprises a free surface within the fining vessel and an atmosphere is positioned between the fining vessel and the free surface, the fining vessel comprising a wall comprising a first wall portion comprising a first thickness and a second wall portion comprising a second thickness such that in a cross section the first thickness is different than the second thickness.
• the flow of molten glass may then be controlled such that the flow of molten glass does not flow over a surface of the upper wall portion. Accordingly the first wall portion is positioned at the top of the fining vessel and the second wall portion is positioned at the bottom of the fining vessel.
• the first thickness may be less than the second thickness or the first thickness may be greater than the second thickness.
• the fining vessel may comprise a third wall portion positioned between the first wall portion and the second wall portion, the third wall portion comprising a third thickness in the cross section greater than the first and second thicknesses.
• the level of the molten glass in the fining vessel may be controlled such that the free surface intersects the third wall portion.
• a temperature of the first wall portion may, for example, be at least 5 degrees centigrade (°C) less than a temperature of the second wall portion.
• FIG. 1 is a elevational view of an example fusion downdraw glass making apparatus comprising a fining vessel according to embodiment described herein;
• FIG. 2 is a perspective view of a fining vessel of FIG. 1 ;
• FIG. 3 is a cross sectional view of a prior art fining vessel comprising a wall of circumferentially uniform thickness;
• FIG. 4 is a photograph of fining vessel wall corrosion failure
• FIG. 5 is a cross sectional view of a fining vessel according to embodiments described here, wherein the fining vessel wall thickness varies circumferentially;
• FIG. 6 is an electrical schematic illustrating the effects described in respect of FIG. 5;
• FIG. 7 is a cross sectional view of another fining vessel according to embodiments described here, wherein the fining vessel wall thickness varies circumferentially such that the upper wall portion is thinner than the lower wall portion, and the lower wall portion comprises layers;
• FIG. 8 is a cross sectional view of another fining vessel according to embodiments described here, wherein the fining vessel wall thickness varies circumferentially and an intermediate wall portion is positioned between the upper and lower wall portions;
• FIG. 9 is a side view of a fining vessel comprising both a thin portion and a thick portion in an upper portion of a fining vessel;
• FIG. 10 is a cross sectional view of the fining vessel of FIG. 9, wherein the cross section is taken at the thick portion of the upper wall portion;
• FIG. 1 1 is a cross sectional view of the fining vessel of FIG. 9, wherein the cross section is taken at the thin portion of the upper wall portion;
• FIG. 12 is an electrical schematic illustrating the effects of including both a thin upper wall portion and a thick upper wall portion in a fining vessel
• FIG. 13 is a side view of a fining vessel comprising a thin upper wall portion positioned between two thick upper wall portions;
• FIG. 14 is a side view of a fining vessel illustrating an upper wall portion, a lower wall portion, the upper and lower wall portions positioned between two consecutive flanges, wherein the upper wall portion is thinner than the lower wall portion, and wherein electrodes attached to the flanges extend upward from a vicinity of the upper portion of top of the fining vessel;
• FIG. 15 is a cross section of a fining vessel according to embodiments wherein flange electrodes extend downward from a position on the flanges nearest the flange bottom;
• FIG. 16 is a cross section of a fining vessel according to embodiments wherein flange electrodes extend downward from a position on the flanges nearest the flange bottom;
• FIG. 17 is a graph of modeled and actual temperature as a function of length along a fining vessel having a wall that is substantially circumferentiaUy uniform in thickness at cross sections of the fining vessel and showing a temperature at the top of the fining vessel that is generally greater than the temperature at other portions of the fining vessel;
• FIG. 18 is a side view of the fining vessel modeled by the curves of FIG. 17;
• FIG. 19 is a graph of modeled current density as a function of length along the fining vessel of FIG. 17 and FIG. 18;
• FIG. 20 is a graph illustrating modeled temperature as a function of length along a fining vessel comprising an upper wall portion, a lower wall portion, and wherein a thickness of the upper wall portion is less than a thickness of the lower wall portion;
• FIG. 21 is a graph illustrating modeled current density as a function of length for the fining vessel of FIG. 20.
• Ranges can be expressed herein as from “about” one particular value, and/ or to "about” another particular value. When such a range is expressed, another aspect includes from the one particular value and/or to the other particular value. Similarly, when values are expressed as approximations, by use of the antecedent "about,” it will be understood that the particular value forms another aspect. It will be further understood that the endpoints of each of the ranges are significant both in relation to the other endpoint, and independently of the other endpoint. When ranges are expressed as "between" one value and another value, the one value and the other value represent the endpoints of the range and are included within the range.
• circumferential is to be construed generally as pertaining to angular location about a perimeter of a cross section and is not limited to circular cross sections, thus the phrasing wherein a thickness varies circumferentiaUy means that the thickness of a cross section of a wall of the article (e.g. fining vessel) varies as angular position changes about the fining vessel relative to a longitudinal axis, and is not limited to circular (cylindrical) fining vessels.
• an angle subtended by an arc, line, or other curve is an angle whose two rays pass through the endpoints of the arc.
• the term "vessel” should be construed to include tanks, conduits, tubes or other structures in which a molten glass may be contained or flowed through.
• molten glass 16 is dependent on the particular glass composition, but for glasses suitable for use as substrates for liquid crystal displays T i can be in excess of 1500°C.
• the molten glass flows from melting furnace 14 through connecting conduit 18 to fining vessel 20. From fining vessel 20 the glass flows to stirring vessel 22 through connecting conduit 24, wherein the molten glass is mixed and homogenized, and from stirring vessel 22 through connecting conduit 26 to delivery vessel 28, and thereafter through exit conduit 30 to forming body inlet conduit 32. The molten glass can then be directed from inlet conduit 32 to forming body 34.
• the molten glass delivered to forming body 34 flows over converging forming surfaces 36, where the separate flows are joined together, or fused, at the location where the converging forming surfaces meet, referred to as root 38, to form ribbon of glass 40.
• the ribbon may then be cooled and separated to form individual glass sheets.
• the molten glass is heated to a second temperature T 2 higher than Ti .
• the heating of fining vessel 20 can be accomplished, for example, by establishing an electric potential across at least a portion of the length of the fining vessel via flanges 42 coupled to the fining vessel. Flanges 42 are in turn connected to a suitable power source (not shown). Fining vessel 20 comprises at least two flanges 42. The electric potential is responsible for producing an electric current that heats the fining vessel. Additional flanges may also be connected to connecting conduit 18 for similar direct heating of the connecting conduit to heat the molten glass flowing therethrough to the fining temperature T 2 .
• T2 can be at least 100°C greater than ⁇
• the relatively high temperature T 2 reduces the viscosity of the molten glass, thereby allowing bubbles in the molten material to be eliminated from the molten glass more easily.
• the higher temperature releases oxygen contained in fining agents (e.g., multivalent oxide materials) that entered the molten glass through the batch.
• the released oxygen forms bubbles in the molten glass that can serve as nucleating sites for other gases.
• dissolved gasses in the molten glass migrate into the oxygen bubbles, growing the bubbles.
• the increased buoyancy resulting from the bubble growth speeds removal of the bubbles from the molten glass through a free surface of the molten glass. Additionally, as the bubbles rise through the molten glass, some localized mechanical stirring of the glass also occurs, which further stimulates the extraction of gasses.
• melting furnace 14 typically comprises a refractory ceramic material (e.g. ceramic bricks or large monolithic ceramic blocks)
• a refractory ceramic material e.g. ceramic bricks or large monolithic ceramic blocks
• Such components include connecting conduits 18, 24, 30, fining vessel 20, stirring vessel 22, delivery vessel 28, exit conduit 30 and inlet 32.
• the molten glass is at an elevated temperature, and therefore a "high temperature" material, e.g. a material capable of withstanding temperatures in excess of at least 1500°C for prolonged time periods, is needed for the delivery apparatus components.
• a "high temperature” material e.g. a material capable of withstanding temperatures in excess of at least 1500°C for prolonged time periods.
• the material should be resistant to oxidation, which can be accelerated by high temperature in the presence of oxygen.
• molten glass can be fairly corrosive, so the material should be relatively resistant to attack from the molten glass that can result in contamination of the resultant glass article by the vessel material.
• Metals comprising the periodic table platinum group metals - platinum, rhodium, iridium, palladium, ruthenium, osmium and alloys thereof - are particularly useful for this purpose, and because platinum can be more easily worked than other platinum group metals, many high temperature processes utilize platinum or platinum alloy vessels.
• One common platinum alloy is a platinum - rhodium alloy. However, because such precious metals are expensive, every effort is made to minimize the size of these vessels to reduce the weight of metal used.
• the molten glass is raised to the fining temperature T 2 .
• Heating of the molten glass may begin within connecting conduit 18 between melting furnace 14 and fining vessel 20 such that the molten glass is at or near the fining temperature as it enters the fining vessel.
• the current can be an alternating current (AC) or a direct current (DC).
• Direct heating of both the connecting conduit and the fining vessel may be employed, and thus both the connecting conduit and the fining vessel may comprise flanges 42.
• care is exercised in the design and attachment of flanges 42 to the fining vessel. Nevertheless, hot spots within the fining vessel wall have been monitored within an upper portion of the fining vessel wall.
• FIG. 2 illustrates a perspective view of at least a portion 43 of a fining vessel 20 having a nominally cylindrical cross sectional shape and a length L, and including several flanges 42 shown attached to and in electrical contact with the fining vessel, shown in FIG. 2 as the endpoints of the at least a portion.
• cross sectional shape or more simply “cross section” refers to the shape of the outer wall 44 of the fining vessel as cut by a plane 46 perpendicular to the longitudinal axis 48 of the fining vessel unless otherwise specified.
• Electrodes 49 are in electrical contact with flanges 42 and serve to connect the flanges to an electric power source through cables, buss bars or other electrical conductors.
• FIG. 3 shows an example fining vessel in cross section, the fining vessel comprising a longitudinally closed wall 44 enclosing a longitudinally extending volume therein.
• the cross section of FIG. 3 is shown containing molten glass 16 having a free surface 50 in contact with a gaseous atmosphere 52 above the free surface.
• Wall 44 includes an inner surface 54 and an outer surface 56, wherein the inner surface 54 faces the interior volume of the fining vessel enclosed by the wall and the outer surface 56 is exposed to an ambient environment outside the fining vessel.
• FIG. 3 shows the relative thickness of wall 44 extending between the inner and outer surfaces about a circumference of the fining vessel, which, in the illustrated fining vessel, is substantially constant. That is, the thickness "t" of the fining vessel wall cross section illustrated in FIG. 3 at any angular location about the circumference of the fining vessel is substantially the same, varying only within normal manufacturing tolerances and at joints and/or welds.
• the fining vessel can be surrounded by one or more layers of a refractory insulating material (not shown), and thermocouples embedded within this refractory jacket may be used to monitor the temperature of the fining vessel at or near the location of the thermocouple. As previously described, such monitoring has shown an elevated temperature of the fining vessel wall at locations where inside surface 54 of the wall is in contact with the contained gaseous atmosphere 52 rather than portions of the wall in contact with the molten glass. Autopsies performed on out-of-service fining vessels have shown increased oxidation corrosion of the metal in portions of the fining vessel where the inside surface 54 is not in contact with the molten glass flowing through the fining vessel. This localized corrosion prematurely thins the wall.
• the wall thinning can increase the current density in that localized portion of the wall, which can further increase the temperature.
• corrosion e.g. oxidation
• FIG. 4 A photograph of such corrosion failure is shown in FIG. 4, where the illustrated region 58 includes a breach of the fining vessel wall.
• cracking produced by the corrosion can extend around the fining vessel, and in extreme instances, cracks can meet and completely separate one section of the fining vessel from another section.
• the corrosion process described above is typically a localized event, and depends at least on the local current density and oxygen concentration. To wit, this corrosion does not occur uniformly over the entire wall surface, even when considering only that portion of the fining vessel wall in contact with the gaseous atmosphere above the molten glass free surface. And, since the oxygen concentration can be difficult to control on a localized basis, one direction is to control current density and thus the temperature of the fining vessel wall.
• fining vessel 20 is configured to have a cross sectional shape such that the wall thickness varies circumferentially about the fining vessel in at least one portion of the fining vessel, and in some embodiments, the wall thickness may vary over the entire length of the fining vessel. That is, when viewing a cross section of the fining vessel, the thickness of the fining vessel wall may vary angularly as one views the cross sectional around the circumference of cross section. In other embodiments the wall thickness may vary in one cross section of the fining vessel and not vary in another cross section. FIG.
• FIG. 5 shows a cross section of a fining vessel 20 according to one embodiment where the fining vessel comprises an upper, or first wall portion 44a that forms a first arc, and a lower, or second wall portion 44b that forms a second arc, wherein the first and second wall portions comprise the overall fining vessel wall 44.
• Each of the first and second wall portions comprise a wall thickness, t a and tb respectively, and, in accordance with the present embodiment, 3 ⁇ 4 is greater than t a when the fining vessel is viewed in cross section. That is, the wall thickness t a of upper wall portion 44a in cross section is less than the wall thickness 3 ⁇ 4 of the lower, or second wall portion 44b in cross section.
• free surface 50 of molten glass 16 intersects second wall portion 44b so that molten glass 16 does not flow over upper wall portion 44a of fining vessel 20.
• the angle ⁇ subtended by the first arc of the upper wall portion can be in a range from about 10 degrees to about 180 degrees, and thus in some embodiments the upper wall portion may comprise the entire top half of the fining vessel, or in other embodiments only a portion of the top half of the vessel.
• the complimentary angle ⁇ subtended by the second arc of the lower, or second wall portion can be in a range from about 180 degrees to about 350 degrees.
• the thicker lower second wall portion 44b can present a reduced resistance to electric current in the fining vessel compared to the resistance of the upper portion.
• the lower current in the first wall portion can produce a decreased temperature in the first wall portion when compared with the current in the second wall portion. This can be better understood with the aid of FIG. 6.
• FIG. 6 illustrates an electrical schematic of a first resistive element RE a and a second resistive element REb.
• Resistive element RE a comprising a length L a , a cross sectional area A a and a resistivity p a .
• Resistive element RE b comprises a length L b , a cross sectional area A b and a resistivity p b .
• Each resistive element may be imagined, for example, as a cylindrical, solid and homogenous wire.
• resistive elements RE a and REb are connected in parallel between two buss bars 64 and 66, and an electric potential E is imposed between the two buss bars.
• RE a may be used to represent the upper wall portion 44a of fining vessel 20 and resistive element RE b may be used to represent lower, or second wall portion 44b of fining vessel 20.
• both resistive elements have identical resistance, i.e. the electrical resistance of resistive element RE a , R a , equals the electrical resistance R b of resistive element REb (where generically resistivity p is equal to resistance R times area A divided by length L). Consequently, the current I a through RE a is equal to the current 3 ⁇ 4 through RE b (neglecting other transmission losses).
• resistive element RE a was identical to resistive element REb.
• resistive element RE a is the same wire as in the preceding example, only thinner. This is equivalent, for example, to reducing the thickness of upper wall portion 44a.
• R a > R b , and I a ⁇ 3 ⁇ 4 Using the values from the preceding example, assume the resistance R a of resistive element RE a is now 6 ohms and the resistance R b of resistive element REb is 5 ohms.
• RE a and RE b can be used to represent the upper and lower portions of the fining vessel wall, 44a and 44b, respectively.
• a reduced power into the glass from the fining vessel into the glass can result in a reduced overall glass temperature.
• cooling of the glass to a temperature less than the initial, base case is not desirable, as one would like to keep the same process conditions for the molten glass.
• the power into the molten glass should be maintained constant, which can be achieved, for example, with an increase in the voltage E across the buss bars, in this instance to approximately 10.44 volts to again obtain a power of 40 watts.
• I a is now approximately 1.74 amps and 3 ⁇ 4, is approximately 2.089 amps.
• the preceding simple example illustrates that making the thickness of the upper wall portion of fining vessel 20, i.e. that portion of the fining vessel wall in contact with the gaseous atmosphere above the free surface of the molten glass, less thick relative to the lower wall portion, i.e. that portion of the fining vessel wall in contact with the molten glass, can reduce the current in the upper wall portion of the fining vessel and thereby also reduce the temperature of the upper wall portion. A reduced temperature of even several degrees centigrade can result in a significant extension of serviceable lifetime for the fining vessel. Because the increase in current in the lower portion is distributed over a much larger cross sectional area (the lower portion being considerably larger and thicker than the upper portion), the current increase in the lower portion may have only a negligible effect (only a negligible increase in current density).
• a thickness of the upper, or first wall portion 44a can be made less than a thickness of the lower wall portion by laminating the lower, or second wall portion 44b with additional material as shown in FIG. 7.
• a second metal plate of arbitrary thickness can be rolled into a second cylindrically-shaped plate and joined to the first plate, such as by welding, thereby increasing the thickness of the first plate by at least the thickness of the second plate.
• the second layer may be the same material or a different material than the first layer.
• the addition of one or more layers may increase the overall cost of the fining vessel, as it requires additional material to be used (which in the case of platinum group metals can be significant).
• the amount by which the thickness of the upper portion can be decreased is limited by having a fining vessel structure capable of maintaining its shape during extended periods of time at a temperature very near the melting point of the metal, while alternatively increasing the thickness of the lower portion is limited primarily by cost.
• the initial increased cost may be outweighed by the gain in longevity of the fining vessel.
• fining vessel 20 may further comprise third wall portions 44c positioned between first and second wall portions 44a,b.
• Third wall portions 44c comprise a third thickness t c greater than tb. Because the thickness t c of third wall portions 44c is greater than the thickness of either wall thicknesses t a and/or tb, cracks that may form in first wall portion 44a, such as those produced by oxidation-based thinning, can be prevented from propagating into lower, or second wall portion 44b of the fining vessel by the increased thickness of wall portions 44c. As shown in FIG.
• the level of molten glass within fining vessel 20 can be controlled such that free surface 50 of molten glass 16 intersects second wall portion 44b, and may, in some embodiments, intersect third wall portions 44c.
• Methods of controlling the level of molten glass in a glass making system are known and not further discussed herein.
• FIG. 9 depicts a fining vessel 20 and shows a locally thickened section of upper wall portion 44a adjacent a flange 42.
• the increased thickness of a short (localized) section along the longitudinal axis of the fining vessel of the upper, or first wall portion 44a relative to upper, or second wall portion 44b can reduce the current density within the localized portion of the upper wall portion of the fining vessel. This can be especially effective when the localized thickening of upper wall portion 44a is positioned at a location abutting a flange 42.
• upper wall portion 44a between two consecutive flanges 42 may include a first length portion 44ai and a second length portion 44a 2 , wherein second length portion 44a 2 is located adjacent to and abutting a flange 42, and wherein a thickness t a2 of the upper wall portion of second length portion 44a 2 is greater than a thickness t a i of the upper wall portion of first length portion 44a 1 ; as shown in the cross sections of FIGS. 10 and 11.
• consecutive flanges what is meant is that no additional flange lies between the subject flanges.
• second wall portion 44b can comprise a thickness equal to or greater than a thickness of the first, or upper wall portion of first length portion 44 a i (i.e. 3 ⁇ 4 > t a i). Second wall portion 44b may further comprise a thickness equal to or greater than a thickness of the upper, or first wall portion of second length portion 44a 2 ( ⁇ t a 2).
• the following additional simple illustration shown in FIG. 12 will aid in understanding the effect of thickening at least a portion of the upper portion of the fining vessel.
• FIG. 6 illustrates an electrical schematic of first resistive element RE a and second resistive element RE b .
• Resistive element RE a comprises a length L a , a cross sectional area A a and a resistivity p a .
• Resistive element REb comprises a length L , a cross sectional area A b and a resistivity b .
• Each resistive element may be, for example, a wire.
• resistive elements RE a and REb are connected in parallel between two buss bars 64 and 66. An electric potential E is imposed between the two buss bars.
• RE a represents the upper wall portion 44a of fining vessel 20
• resistive element REb represents lower, or second wall portion 44b of fining vessel 20.
• the current I a through RE a is equal to the current lb through REb (neglecting other transmission losses).
• the total current I t is I a + 3 ⁇ 4 or E/(R a Rt (R a +Rb)).
• resistive element RE a was identical to resistive element REb.
• resistive element RE a comprises two resistive element segments, first resistive element segment RE a i and second resistive element segment RE a 2.
• RE a i comprises a length Lai, a cross sectional area A a i, a resistivity p a i and a resistance R a i .
• RE a2 comprises a length L a2 , a cross sectional area A a2 , a resistivity p a2 , and a resistance R a2 .
• length Lai of first resistive element segment RE a i is much greater than length L a2 of second resistive element segment RE a2
• the cross sectional area A a2 of second resistive element segment RE a2 is greater than the cross sectional area A a i of first resistive element segment RE a i .
• first resistive element RE a is comprised of two segments arranged end to end in series, where the thickness of the second segment is greater than the thickness of the first segment, but wherein the length of the first segment is much longer than the second segment.
• the resistance of RE a i may dominate the overall resistance of RE a (as a numerical example, consider that for two resistive elements in series, wherein one resistive element has a resistance of 100 ohms and the second resistive element has a resistance of 5 ohms, a total resistance of the two series resistive elements is 105 ohms, not significantly different than the resistance of the 100 ohm resistive element).
• 3 ⁇ 4 E/Rb.
• the current I a in the leg represented by segments RE a i and RE a 2, that is, resistive element RE a will be approximately determined by E/R al .
• the current 3 ⁇ 4 will be the same as the current 3 ⁇ 4 related to FIG. 6.
• current I a of the present embodiment will be distributed over a cross sectional area A a 2 in second resistive element segment RE a 2 that is greater than the cross sectional area A a i of first resistive element segment RE a i.
• the heating of second resistive element segment RE a2 will be less than the heating of first resistive element segment RE a i and, accordingly, the temperature of second resistive element segment RE a 2 will be less than the temperature of first resistive element segment RE a i.
• this has the effect of reducing the temperature of the fining vessel at the location of the flanges, where the current enters and/or leaves the fining vessel and the current density tends to be greatest.
• upper wall portion 44a of the at least a portion of the fining vessel may include three length segments, first length portion 44a ! and second length portion 44a 2 as previously described, and a third length portion 44a 3 .
• the upper wall portion of first length portion 44ai in cross section comprises a thickness t a i
• the upper wall portion of second length portion 44a 2 in cross section comprises a thickness ta 2 , and t a2 > t al .
• Third length portion 44a 3 in cross section comprises a thickness t a3 greater than t al and equal to or substantially equal to t a2 .
• First length portion 44a ! is positioned between second length portion 44a 2 and third length portion 44a 3 . Either one or both of second length portion 44a 2 or third length portion 44a 3 may be positioned abutting a flange 42.
• flanges typically include a tab or electrode that extends from the flange and connects to cables or buss bars that feed current to the flange.
• FIG. 14 illustrates a side view of a fining vessel comprising a wall with a thickness that varies circumferentially.
• An electrode 49 is positioned at flange 42 nearest to the upper, or first wall portion 44a of fining vessel wall 44 such that current (e.g. current density) in the upper portion of the fining vessel wall is greatest within a region of the wall 44 that is line with electrode 49. That is, the current density at the top of the fining vessel, closest to electrode 49, may be higher than can be tolerated by the material of the upper wall portion 44a of the fining vessel, thereby potentially leading to increased heating of the upper portion of the fining vessel that is in contact with atmosphere 52.
• FIG. 15 illustrating a cross section of the fining vessel of FIG. 14 at one of the flanges 42.
• the current producing the high current density is represented by arrows 60, and the region of high current density is the region labeled Za
• the electrodes 49 may be positioned such that the electrodes are nearest the lower, or second wall portion 44b of the fining vessel as shown in FIG. 16 so that the high current density occurs in the fining vessel where the fining vessel wall 44 is in contact with the molten glass, region Zb, That is, the electrodes 49 may be positioned at and extending in a downward from the bottom of flanges 42. This is particularly helpful when the thickness of the lower wall portion is greater than the thickness of the upper wall portion.
• FIG. 17 illustrates a graph of temperature along the length of a fining vessel comprising a cross sectional wall thickness that is circumferentially substantially uniform.
• the fining vessel further comprises a thickness band 75 positioned between the flanges, adjacent to and abutting the second flange (the flange farthest right in the figure) and extending longitudinally along the fining vessel for a distance of approximately 1 1 cm.
• the thickness band encircles the fining vessel and is greater than a thickness of the remainder of the fining vessel wall but the thickness of the thickness band is itself substantially uniform.
• Flanges are located at positions A and B.
• Curves 70, 72 and 74 represent modeled data generated with the aid of Fluent® software, and the circle and triangles represent actual data on a fining vessel obtained via thermocouples embedded in refractory insulating material surrounding the fining vessel.
• the graph shows that the actual data generally mimics the modeled data, helping to substantiate the viability of the model for representing temperature along the length of the fining vessel.
• Curve 70 represents temperature at the top of the fining vessel as a function of normalized length
• curve 72 represents temperature along the bottom of the fining vessel as a function of normalized length
• curve 74 represents the temperature of the fining vessel as a function of length along a side thereof, midway between the top and bottom of the fining vessel.
• the data show that the temperature along the top of the fining vessel is approximately 15 to 20 degrees centigrade hotter than the temperature at the sides and bottom of the fining vessel.
• the presence of a wall portion thicker than another wall portion can reduce the current density at the location of the thicker wall portion, and that is borne out by the modeling, which shows a drop in temperature just prior to the flange at B (viewing FIG. 17 from left to right).
• the lack of a thickness difference elsewhere along the fining vessel e.g. a circumferential thickness variation
• the drop in temperature at the flanges, and in particular the flange at B is due to the heat dissipation capacity of the flanges.
• each flange functions at least in part as a fin that dissipates heat conductively and radiatively.
• the flanges were modeled as being actively cooled by a cooling coil positioned around the perimeter of each flange through which a cooling fluid is flowed.
• FIG. 19 is a graph illustrating the modeled current density in amps/square millimeter (A/mm 2 ) for the conditions of FIG. 17, where curve 76 represents the current density in the upper wall portion as a function of normalized length, curve 78 represents the current density in the lower wall portion as a function of normalized length, and curve 80 represents the current density as a function of length at the sides of the fining vessel midway between the top and the bottom of the fining vessel.
• the data show an increase in current density just prior to the thickness band (again, when viewing FIG. 19 from left to right), with a steep decrease in current density at the thickness band.
• FIG. 20 illustrates a graph of temperature along the length of a fining vessel comprising an upper wall portion and a lower wall portion, wherein a cross sectional wall thickness of the upper wall portion is less than a cross sectional thickness of the lower wall portion, e.g. the fining vessel of FIG. 5.
• the fining vessel of FIG. 20 does not include a thickness band. Length is shown as a normalized length, and temperature is shown in degrees centigrade (°C).
• Curves 80, 82 and 84 represent modeled data generated with the aid of Fluent® software.
• Curve 80 represents temperature at the top of the fining vessel as a function of normalized length
• curve 82 represents temperature along the bottom of the fining vessel as a function of normalized length
• curve 84 represents temperature of the fining vessel along a side thereof as a function of normalized length, midway between the top and bottom of the fining vessel.
• a first flange is located at A and a second flange is located at B.
• the data show that the temperature along a majority of the top of the fining vessel is approximately 5 to 10 degrees centigrade less than the temperature at the sides and bottom of the fining vessel except at a position close to the flange at position B, where the temperature is shown to increase over the bottom temperature.
• FIG. 21 is a graph illustrating the modeled current density in amps/square millimeter for the conditions of FIG. 20. Curves 86, 88 and 90 represent modeled data generated with the aid of Fluent® software.
• Curve 86 represents current density at the top of the fining vessel as a function of normalized length
• curve 88 represents current density along the bottom of the fining vessel as a function of normalized length
• curve 90 represents current density in the fining vessel along a side thereof as a function of normalized length, midway between the top and bottom of the fining vessel.
• the graph shows a generally uniform current density around a circumference of the fining vessel (as indicated by current densities at top, bottom and midpoint) as a result of the varying circumferential thickness within the mid-length of the fining vessel between the two flanges, but also shows the increase in current density at the flanges due to the presence of the flanges, as the flanges serve to direct all current in the fining vessel into or out of the fining vessel.
• the flanges can be viewed as collection or distribution nodes.

Landscapes

• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Materials Engineering (AREA)
• Organic Chemistry (AREA)
• Physics & Mathematics (AREA)
• Thermal Sciences (AREA)
• Glass Melting And Manufacturing (AREA)
• Waste-Gas Treatment And Other Accessory Devices For Furnaces (AREA)

Priority Applications (4)

Applications Claiming Priority (2)

Publications (1)

Family

ID=52828595

Family Applications (1)

Country Status (5)

Cited By (4)

Families Citing this family (6)

Citations (5)

Family Cites Families (14)

• 2014
  • 2014-10-14 KR KR1020217007566A patent/KR102288421B1/ko active IP Right Grant
  • 2014-10-14 CN CN201911192726.9A patent/CN110803857B/zh not_active Expired - Fee Related
  • 2014-10-14 JP JP2016524125A patent/JP6533221B2/ja not_active Expired - Fee Related
  • 2014-10-14 WO PCT/US2014/060398 patent/WO2015057646A1/en active Application Filing
  • 2014-10-14 KR KR1020167012394A patent/KR102230177B1/ko active IP Right Grant
  • 2014-10-14 CN CN201480069200.0A patent/CN105829253B/zh not_active Expired - Fee Related
  • 2014-10-15 TW TW103135687A patent/TWI633072B/zh not_active IP Right Cessation
• 2019
  • 2019-05-23 JP JP2019096676A patent/JP6754469B2/ja not_active Expired - Fee Related

Patent Citations (5)

Also Published As

Similar Documents

Legal Events