WO2017192478A1

WO2017192478A1 - Apparatus and method for mixing molten glass

Info

Publication number: WO2017192478A1
Application number: PCT/US2017/030493
Authority: WO
Inventors: Zagorka Dacic Gaeta; Martin Herbert Goller; Aaron Joshua Hade; Christopher Myron SMITH
Original assignee: Corning Inc
Current assignee: Corning Inc
Priority date: 2016-05-02
Filing date: 2017-05-02
Publication date: 2017-11-09
Anticipated expiration: 2018-11-02
Also published as: JP2019519362A; KR20180132967A; TW201742831A; CN109070029A

Abstract

A mixing apparatus including a mixing vessel and a stirrer rotatably mounted within the mixing vessel. The stirrer includes multiple sets of mixing impellers positioned along a shaft of the stirrer, each mixing impeller including a ribbon-like mixing blade arranged such that a major surface of the mixing blade is parallel to a longitudinal axis of the shaft. The mixing blade includes a distal end portion adjacent an inside wall surface of the mixing vessel, and side portions that attach to the shaft, and a radius of curvature of the distal end portion is different than radii of curvature of the side portions.

Description

APPARATUS AND METHOD FOR MIXING MOLTEN GLASS

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority of U. S. Provisional Application Serial No. 62/330,471 filed on May 2, 2016 the contents of which are relied upon and incorporated herein by reference in their entirety as if fully set forth below.

BACKGROUND Field

[0002] The present invention relates generally to apparatus and methods for homogenizing molten glass, and more particularly to a mixing vessel, including a mixing member positioned therein.

Technical Background

[0003] Large-scale commercial production of glass begins with the heating of raw materials to melt the raw materials and produce a molten mass. This molten mass, hereinafter molten glass or melt, can contain inhomogeneities of various types, including gaseous inclusions (e.g., blisters) and regions of thermal and/or chemical inhomogeneity. Gaseous inclusions may appear as bubbles in the finished glass article. Thermal and/or chemical inhomogeneities may impact other physical characteristics of the finished glass article. For example, the inhomogeneous regions may be stretched as the molten glass flows through downstream components of the glass making apparatus, producing what is referred to as cord. For example, in a drawing operation, such as a down draw glass making process, drawing the molten glass into sheets of glass can further stretch the cord into long filaments aligned along the draw direction. Cord arrayed at or near the surface of the glass article, for example a glass ribbon or glass sheet, can produce nanometer-scale raised regions on the glass surface that produce a readily discernible lensing effect. For some glass articles, for example glass substrates used in the manufacture of display devices, this visual defect is undesirable.

[0004] To produce homogeneous, defect-free glass articles, the molten glass is typically further processed subsequent to melting. For example, a refining process may be performed, wherein bubbles produced during the melting process are removed. Additionally, a mixing process may be conducted in which the molten glass is mixed, for example stirred, to reduce or eliminate thermal and/or chemical inhomogeneities. Stirring is typically conducted within a stirring vessel by a stirring member. However, the desire for high stirring effectiveness is usually tempered by the effect of high shear produced by the stirring member on the stirring vessel. High shear can erode the stirring vessel over time and result in contamination of the molten glass.

SUMMARY

[0005] During the manufacture of glass articles from molten glass, it is desirable to thoroughly mix the molten glass so as to minimize inhomogeneities (that may be present within the molten glass) from manifesting in the glass article produced therefrom. One such inhomogeneity is referred to as cord. For the purpose of the present disclosure, cord can originate as a region of chemical and/or thermal inhomogeneity in a body of molten glass resulting in small viscosity differences between the inhomogeneity and the surrounding molten glass. If the molten glass is drawn, the regions of inhomogeneity are stretched as well. Accordingly, cord may manifest as strings (filaments) of inhomogeneity extending in the draw direction of the drawn glass. When the glass cools, filaments of inhomogeneity near the surface of the glass can extend above the rest of the glass surface and produce slight thickness changes in the glass sheet, which can both visually and functionally affect the performance and perceived quality of a display device produced therefrom. For example, even small thickness changes on the surface of a glass sheet may affect deposition processes used to deposit electronic components on the glass sheet. Additionally, the resultant lensing effect produced by these raised areas can be visually apparent, particularly if the glass is formed into thin glass sheets that are used in the manufacture of visual display devices, such as but not limited to television and computer monitors.

[0006] Flowing the molten glass through a mixing process can significantly mitigate the effect of inhomogeneity in the molten glass supplied to the forming body by better homogenizing the molten glass. To that end, an improved mixing apparatus, including a mixing vessel and various mixing members (i.e., stirrers) mounted therein, are presented.

[0007] As described above, the mixing apparatus functions, inter alia, to homogenize the molten glass flowing therethrough. To accomplish this function, the mixing apparatus, and more specifically the mixing member, is designed to stretch and fold the viscous molten glass, much as a baker stretches and folds dough. Stretching the molten glass typically occurs between the inside wall of the mixing vessel and a distal end portion of a mixing blade attached to the mixing member shaft and extending outward therefrom. The distance between the mixing vessel inside wall surface and the distal end portion of the mixing blade is termed the coupling distance. Stretching of the molten glass occurs as a result of shear forces in the molten glass developed within the coupling distance as the mixing member rotates within the mixing vessel. However, high shear forces produced within small coupling distances can produce erosion of the mixing vessel and particulate contamination of the molten glass. On the other hand, increasing the coupling distance, or decreasing the coupling engagement (i.e., coupling area), which is the overall circumferential area of the mixing member that "couples" with the mixing vessel, decreases mixing efficiency. As used herein, the coupling area refers to the area of a mixing blade that is in close proximity to an inside wall of the mixing vessel.

[0008] Accordingly, a mixing apparatus is disclosed comprising a mixing vessel. The mixing apparatus comprises a mixing member rotatably positioned within the mixing vessel, the mixing member comprising a shaft and a first mixing impeller attached thereto and extending radially outward therefrom, the first mixing impeller including a mixing blade formed as a closed loop with the shaft, the mixing blade including a distal end portion comprising a first radius of curvature and first and second side portions adjacent to the distal end portion, the first and second side portions comprising a radius of curvature different than the first radius of curvature. The mixing apparatus still further comprises a first web portion and a second web portion spaced apart from the first web portion along a direction parallel with a longitudinal axis of the shaft, the first web portion and the second web portions attached to an inside major surface of the mixing blade along a captured edge of the first and second web portions.

[0009] In some embodiments, the first web portion can be attached to a second mixing impeller adjacent the first mixing impeller.

[0010] In some embodiments, the second web portion can be attached to a third mixing impeller adjacent the first mixing impeller.

[0011] In some embodiments, a radius of curvature of at least one of the first and second side portions is infinite.

[0012] Each of the first web portion and the second web portion comprises a free edge. In some embodiments, the free edge comprises a linear edge portion, and in some embodiments the free edge comprises a concave curve.

[0013] In some embodiments, a line parallel with a longitudinal axis of the shaft and tangent to a free edge of the first web portion intersects the second web portion. In other embodiments, a line parallel with a longitudinal axis of the shaft and tangent to the free edge of the first web portion does not intersect the second web portion.

[0014] The mixing blade may further comprise first and second intermediate portions positioned between the distal end portion and the first and second side portions, respectively, wherein a radius of curvature of the distal end portion and the first and second intermediate portions is different than the radii of curvature of the first and second side portions.

[0015] In some embodiments, the radii of curvature of the first and second intermediate portions are less than the radii of curvature of the first and second side portions.

[0016] In some embodiments, the first radius of curvature is substantially the same as a radius of curvature of an inside wall surface of the mixing vessel adjacent the distal end portion.

[0017] The mixing apparatus may comprise a set of mixing impellers arranged about a first position on the shaft relative to a length of the shaft.

[0018] In some embodiments, the set of mixing impellers comprises at least 4 mixing impellers.

[0019] In some embodiments, the set of mixing impellers comprises at least 5 mixing impellers.

[0020] In some embodiments, the mixing apparatus comprises a plurality of sets of mixing impellers arranged at a plurality of positions on the shaft.

[0021] In still another embodiment, a mixing apparatus is described comprising a cylindrical mixing vessel, an inside wall of the mixing vessel comprising a radius of curvature, a mixing member rotatably positioned within the mixing vessel, the mixing member comprising: a shaft, and a first mixing impeller attached to the shaft and extending radially outward therefrom, the first mixing impeller including a mixing blade formed as a closed loop with the shaft and including a distal end portion comprising a first radius of curvature substantially equal to the radius of curvature of the inside wall of the mixing vessel, the first mixing impeller further comprising first and second web portions connected to the mixing blade.

[0022] The mixing blade may further comprise first and second adjacent side portions, the first and second side portions comprising radii of curvature different than the first radius of curvature.

[0023] In still another embodiment, a method of making glass is disclosed comprising: heating raw materials in a melting vessel to form a molten material, flowing the molten material into a mixing vessel, the missing vessel, and mixing the molten material with a mixing member rotatably positioned within the mixing vessel, the mixing member comprising a shaft and a first mixing impeller attached thereto and extending radially outward therefrom, the first mixing impeller including a mixing blade formed as a closed loop with the shaft, the mixing blade including a distal end portion comprising a first radius of curvature and side portions adjacent to the distal end portion, the side portions comprising a radii of curvature different than the first radius of curvature, the first mixing impeller further comprises first and second web portions connected to the mixing blade.

[0024] The method may further comprise mixing the molten material with a plurality of mixing impellers.

[0025] Additional features and advantages of the embodiments disclosed herein will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.

[0026] It is to be understood that both the foregoing general description and the following detailed description present embodiments intended to provide an overview or framework for understanding the nature and character of the embodiments. The accompanying drawings are included to provide further understanding, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments of the disclosure, and together with the description, serve to explain the principles and operations thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] FIG. 1 is a schematic view of an example fusion down draw glass making apparatus;

[0028] FIG. 2 is a side cross sectional view of a mixing apparatus suitable for use in the glass making apparatus of FIG. 1;

[0029] FIG. 3 is a side view of a mixing member suitable for use in the mixing apparatus of FIG. 2 according to embodiments of the present disclosure;

[0030] FIG. 4 is a perspective view of the mixing member of FIG. 3;

[0031] FIG. 5 is a plan view of the mixing member of FIG. 3 illustrating one set of a plurality of sets of impellers;

[0032] FIG. 6 is a partial plan view of the mixing member of FIG. 5;

[0033] FIG. 7 is a plan view of another embodiment of a mixing member according to the present disclosure wherein web members of the impellers comprises straight free edges; [0034] FIG. 8 is a plan view of still another embodiment of a mixing member according to the present disclosure, wherein web members of the impellers comprises curved free edges;

[0035] FIG. 9 is a plan view of another embodiment of a mixing member according to the present disclosure, wherein each set of impellers comprises a large number (greater than four) of impellers;

[0036] FIG. 10 is a plan view of another embodiment of a mixing member according to the present disclosure, each impeller having curved free edges with a radius of curvature such that molten glass can flow in a straight line through the impellers;

[0037] FIG. 11 A is a plan view of yet another embodiment of a mixing member according to the present disclosure, the mixing member comprising mixing blades with straight side portions and a distal end portion including a radius of curvature substantially the same as a radius of curvature of the cylindrical inside wall of the mixing vessel;

[0038] FIG. 11 B is a plan view of still another embodiment of a mixing member according to the present disclosure, the mixing member comprising mixing blades with straight side portions and a distal end portion including a radius of curvature less than a radius of curvature of the cylindrical inside wall of the mixing vessel.

DETAILED DESCRIPTION

[0039] Reference will now be made in detail to various embodiments of the present disclosure, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. However, this disclosure may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein.

[0040] 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 embodiment 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 embodiment. 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.

[0041] Directional terms as used herein - for example up, down, right, left, front, back, top, bottom - are made only with reference to the figures as drawn and are not intended to imply absolute orientation. [0042] Unless otherwise expressly stated, it is not intended that any method set forth herein be construed as requiring that its steps be performed in a specific order, nor that with any apparatus, specific orientations be required. Accordingly, where a method claim does not actually recite an order to be followed by its steps, or that any apparatus claim does not actually recite an order or orientation to individual components, or it is not otherwise specifically stated in the claims or description that the steps are to be limited to a specific order, or that a specific order or orientation to components of an apparatus is not recited, it is not intended that an order or orientation be inferred, in any respect. This holds for any possible non-express basis for interpretation, including: matters of logic with respect to arrangement of steps, operational flow, order of components, or orientation of components; plain meaning derived from grammatical organization or punctuation, and the number or type of embodiments described in the specification.

[0043] As used herein, the singular forms "a, " "an" and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to "a" component includes aspects having two or more such components, unless the context clearly indicates otherwise.

[0044] Shown in FIG. 1 is an exemplary glass manufacturing apparatus 10. In some embodiments, the glass manufacturing apparatus 10 can comprise a glass melting furnace 12 including a melting vessel 14. In addition to melting vessel 14, glass melting furnace 12 can optionally include one or more additional components such as heating elements (e.g., combustion burners or electrodes) that heat raw materials and convert the raw materials into molten glass. In further examples, glass melting furnace 12 may include thermal management devices (e.g., insulation components) that reduce heat loss from a vicinity of the melting vessel. In still further examples, glass melting furnace 12 may include electronic devices and/or electromechanical devices that facilitate melting the raw materials into molten glass. Still further, glass melting furnace 12 may include support structures (e.g., support chassis, support member, etc.) or other components.

[0045] Glass melting vessel 14 is typically comprised of refractory material, such as a refractory ceramic material, for example a refractory ceramic material comprising alumina or zirconia As used herein, a refractory material is defined as a non-metallic material having chemical and physical properties that make them applicable for structures, or as components of systems, that are exposed to environments above 538°C. In some examples, glass melting vessel 14 may be constructed from refractory ceramic bricks. [0046] In some examples, the glass melting furnace may be incorporated as a component of a glass manufacturing apparatus configured to fabricate a glass substrate, for example a glass ribbon of indeterminate length. In some examples, the glass melting furnace may be incorporated as a component of a glass manufacturing apparatus comprising a slot draw apparatus, a float bath apparatus, a down draw apparatus, an up draw apparatus, a press rolling apparatus, a tube drawing apparatus or any other glass manufacturing apparatus that would benefit from the aspects disclosed herein. By way of example, FIG. 1 schematically illustrates glass melting furnace 12 as a component of a fusion down draw glass manufacturing apparatus 10 for fusion drawing a glass ribbon for subsequent processing into individual glass substrates.

[0047] The glass manufacturing apparatus 10 (e.g. , fusion down-draw apparatus 10) can optionally include an upstream glass manufacturing apparatus 16 positioned upstream relative to glass melting vessel 14. As used herein, the terms upstream and downstream are to be construed relative to a flow direction of molten glass. In some examples, a portion of, or the entire upstream glass manufacturing apparatus 16, may be incorporated as part of glass melting furnace 12.

[0048] As shown in FIG. 1 , upstream glass manufacturing apparatus 16 can include a storage bin 18, a raw material delivery device 20 and a motor 22 connected to the raw material delivery device. Storage bin 18 may store a quantity of raw material 24 that can be fed into melting vessel 14 of glass melting furnace 12, as indicated by arrow 26. Raw material 24 typically comprises one or more glass forming metal oxides and one or more modifying agents. Raw material 24 may further comprise one or more additional constituents, for example one or more fining agents. In some examples, raw material delivery device 20 can be powered by motor 22 such that raw material delivery device delivers a predetermined amount of raw material 24 from the storage bin 18 to melting vessel 14. In further examples, motor 22 can power raw material delivery device 20 to introduce raw material 24 at a controlled rate based on a level of molten glass sensed downstream from melting vessel 14. Raw material 24 within melting vessel 14 can thereafter be heated to form molten glass 28.

[0049] Glass manufacturing apparatus 10 can optionally include a downstream glass manufacturing apparatus 30 positioned downstream of glass melting furnace 12. In some examples, a portion of downstream glass manufacturing apparatus 30 may be incorporated as part of glass melting furnace 12. However, in some embodiments, first connecting conduit 32, discussed below, or other portions of the downstream glass manufacturing apparatus 30, may be incorporated as part of the glass melting furnace 12. Elements of downstream glass manufacturing apparatus 30, including first connecting conduit 32, may be formed from a precious metal. Suitable precious metals include platinum group metals selected from the group of metals consisting of platinum, iridium, rhodium, osmium, ruthenium and palladium, or alloys thereof. For example, downstream components of the glass manufacturing apparatus may be formed from a platinum-rhodium alloy including from about 70 to about 90% by weight platinum and about 10% to about 30% by weight rhodium. However, other suitable metals can include molybdenum, rhenium, tantalum, titanium, tungsten and alloys thereof.

[0050] The downstream glass manufacturing apparatus 30 can include a first conditioning (i.e. processing) vessel, such as fining vessel 34, located downstream from melting vessel 14 and coupled to melting vessel 14 by way of the above-referenced first connecting conduit 32. In some embodiments, molten glass 28 may be gravity fed from melting vessel 14 to fining vessel 34 by way of first connecting conduit 32. For instance, gravity may drive molten glass 28 through an interior pathway of first connecting conduit 32 from melting vessel 14 to fining vessel 34. It should be understood, however, that other conditioning vessels may be positioned downstream of melting vessel 14, for example between melting vessel 14 and fining vessel 34. In some embodiments, a conditioning vessel may be employed between the melting vessel and the fining vessel wherein molten glass from a first, upstream melting vessel is further heated to continue the melting process, or cooled to a temperature lower than the temperature of the molten glass in the upstream melting vessel before entering the fining vessel.

[0051] Within fining vessel 34, bubbles may be removed from molten glass 28 by various techniques. For example, raw material 24 may include multivalent compounds (i.e. fining agents) such as tin oxide that, when heated, undergo a chemical reduction reaction and release oxygen. Other suitable fining agents include without limitation arsenic, antimony, iron and cerium. Fining vessel 34 is heated to a temperature greater than the melting vessel temperature, thereby heating the fining agent. Oxygen bubbles produced by the temperature- induced chemical reduction of the fining agent(s) rise through the molten glass within the fining vessel, wherein gases in the melt produced in the melting furnace can coalesce into the oxygen bubbles produced by the fining agent. The enlarged gas bubbles can then rise to a free surface of the molten glass in the fining vessel and thereafter be vented from the fining vessel. The oxygen bubbles can further induce mechanical mixing of the molten glass in the fining vessel. [0052] Downstream glass manufacturing apparatus 30 can further include another conditioning vessel such as mixing apparatus 36, for mixing the molten glass. Mixing apparatus 36 may be located downstream from the fining vessel 34. The glass melt mixing apparatus 36 can be used to provide a homogenous molten glass composition, thereby reducing chemical or thermal inhomogeneity that may otherwise exist within the fined molten glass exiting fining vessel 34. As shown, fining vessel 34 may be coupled to molten glass mixing apparatus 36 by way of a second connecting conduit 38. In some examples, molten glass 28 may be gravity fed from the fining vessel 34 to mixing apparatus 36 by way of second connecting conduit 38. For instance, gravity may drive molten glass 28 through an interior pathway of second connecting conduit 38 from fining vessel 34 to mixing apparatus 36. It should be noted that while mixing apparatus 36 is shown downstream of fining vessel 34, mixing apparatus 36 may in further embodiments be positioned upstream from fining vessel 34. In some embodiments, downstream glass manufacturing apparatus 30 may include multiple mixing apparatus, for example a mixing apparatus upstream from fining vessel 34 and a mixing apparatus downstream from fining vessel 34. These multiple mixing apparatus may be of the same design, or they may be of a different design from one another. For example, in some embodiments, a mixing apparatus may comprise static elements, such as vanes or other fixed objects that redirect the flow direction of molten glass. In some embodiments, a mixing apparatus may include active elements, such as stirring elements that actively redirect the flow direction of the molten glass. In still other embodiments, mixing apparatus according to the present disclosure may include both static and active elements for redirecting the flow direction of molten glass.

[0053] Downstream glass manufacturing apparatus 30 can further include another conditioning vessel such as delivery vessel 40 that may be located downstream from mixing apparatus 36. Delivery vessel 40 may condition molten glass 28 to be fed into a downstream forming device. For instance, delivery vessel 40 can act as an accumulator and/or flow controller to adjust and provide a consistent flow of molten glass 28 to forming body 42 by way of exit conduit 44. As shown, mixing apparatus 36 may be coupled to delivery vessel 40 by way of third connecting conduit 46. In some examples, molten glass 28 may be gravity fed from mixing apparatus 36 to delivery vessel 40 by way of third connecting conduit 46. For instance, gravity may drive molten glass 28 through an interior pathway of third connecting conduit 46 from mixing apparatus 36 to delivery vessel 40.

[0054] Downstream glass manufacturing apparatus 30 can further include forming apparatus 48 comprising the above-referenced forming body 42 and including inlet conduit 50. Exit conduit 44 can be positioned to deliver molten glass 28 from delivery vessel 40 to inlet conduit 50 of forming apparatus 48. Forming body 42 in a fusion down draw glass making apparatus can comprise a trough 52 positioned in an upper surface of the forming body and a pair of converging forming surfaces 54 that converge in a draw direction along a bottom edge 56 of the forming body. Molten glass delivered to the forming body trough via delivery vessel 40, exit conduit 44 and inlet conduit 50 overflows the walls of the trough and descends along the converging forming surfaces 54 as separate flows of molten glass. The separate flows of molten glass join below and along the bottom edge 56 to produce a single ribbon of glass 58 that is drawn in a draw direction 60 from bottom edge 56 by applying tension to the glass ribbon, such as by one or more of gravity, edge rolls and pulling rolls (not shown), to control the dimensions of the glass ribbon as the glass cools and a viscosity of the glass increases. Accordingly, as glass ribbon 58 cools, the glass goes through a visco-elastic transition and acquires mechanical properties that give the glass ribbon 58 stable dimensional characteristics. Glass ribbon 58 may, in some embodiments, be separated into individual glass sheets 62 by a glass separation apparatus (not shown) in an elastic region of the glass ribbon, although in further embodiments the glass ribbon may be rolled onto spools.

[0055] FIG. 2 is a schematic view of an exemplary mixing apparatus 36 including mixing vessel 100 and mixing member 102 rotatably positioned within mixing vessel 100. Mixing vessel 100 includes an inside wall 104, that may, for example, be cylindrical in shape.

Mixing vessel 100 and mixing member 102 may be formed from platinum or an alloy thereof. For example, mixing vessel 100 and mixing member 102 may be formed from a platinum- rhodium alloy. However, either one of mixing vessel 100 and/or mixing member 102 may comprise different metals, alternatively or in addition to platinum and/or rhodium. For example mixing member 102 may include other platinum group metals, including iridium, palladium, osmium, and ruthenium, or other high temperature metals such as molybdenum. The metals may be alloys, non-alloys, or both. For example, in some embodiments, one or more portions of mixing member 102 may be formed with platinum or a platinum alloy (e.g., a platinum rhodium alloy or a platinum iridium alloy), or include an external cladding material, for example an iridium cladding.

[0056] Mixing member 102 may be connected to a motor (not shown) that rotates mixing member 102 within mixing vessel 100. Mixing member 102 may be connected to the motor by any suitable means, for example by a belt, chain or gear train Mixing vessel 100 is shown in FIG. 2 comprising an inlet conduit, e.g. , second conduit 38, positioned at a top half of the mixing vessel, and an outlet conduit, e.g., third connecting conduit 46, positioned at a bottom half of the mixing vessel. Such an arrangement facilitates gravity flow of molten glass through the mixing vessel. While FIG. 2 illustrates ingress (arrow 106) and egress (arrow 108) of the molten glass from a side of the mixing vessel, in some embodiments, egress of the molten glass may occur through a floor of the mixing vessel. In some embodiments, the molten glass flows from the top of the mixing vessel in a generally downward flow direction 109 to the outlet conduit as shown, however in other embodiments, the ingress and egress locations may be reversed such that the molten glass flows in a generally upward direction through the mixing vessel.

[0057] FIG. 3 is an elevational view of an example mixing member 102 showing shaft 1 10 including a longitudinal axis 1 12, which is also an axis of rotation of the mixing member, and a plurality of sets 114 of mixing impellers 116. Shaft 1 10 may, in some embodiments, be a hollow shaft, for example a hollow cylindrical tube. Shaft 1 10 may comprise multiple tube segments joined along a circumference of the ends of adj acent tube segments. Shaft 1 10 may include multiple concentric layers for a tube-within-tube structure.

[0058] FIG. 3 illustrates four sets 114 of mixing impellers 116, including, as an example, from top to bottom, set 114a, 1 14b, 114c and 1 14d. Further embodiments may have more or fewer sets of mixing impellers depending on need. The sets of mixing impellers are arranged in a spaced-apart relationship along a length of shaft 1 10 in a direction parallel with longitudinal axis 1 12. That is, each set of mixing impellers represents a separate position along shaft 110 along a length of the shaft (i.e., parallel with longitudinal axis 1 12). As seen in FIG. 3, each set 1 14 (e.g. 114a - 1 14d) of mixing impellers 116 is separated and spaced apart from another set 114 of mixing impellers 1 16 by a gap G measured from the top of one set of mixing impellers to the bottom of an adjacent set of mixing impellers at their closest point. Gap G may be the same between the adjacent sets of mixing impellers, or gap G may vary between adjacent sets of mixing impellers. For example, the gap G between impeller set 1 14a and 1 14b may be the same or different than the gap between mixing impeller sets 1 14b and 1 14c, or any other sets of mixing impellers, adjacent or not. Each set of mixing impellers may be aligned such that the mixing impellers in one mixing impeller set are directly and identically opposed to the mixing impellers in an adjacent set, i.e., where any one set of mixing impellers is aligned in a direction parallel with longitudinal axis 1 12 with the mixing impellers of any other set of mixing impellers on the shaft. However, in other embodiments, one set of impellers may be rotated on the shaft relative to an adjacent set of impellers so that the impellers from the one set are not aligned with the impellers of an adjacent set. [0059] Turning now to FIG. 4, which is a perspective view of the example mixing member 102 of FIG. 3, each mixing impeller 116 in a set of mixing impellers includes a mixing blade 118 and a pair of web members 120, 122. Each mixing blade 118 is of a generally flat form with two major surfaces, an inside major surface 124 and an outside major surface 126. The inside major surface 124 and the outside major surface 126 may be generally parallel. The mixing blade is thus generally ribbon shaped and forms a closed loop with shaft 1 10, wherein the ends of the ribbon-shaped mixing blade are attached to shaft 110, and with major surfaces 124, 126 of the mixing blade parallel to longitudinal axis 112.

[0060] FIG. 5 illustrates a plurality of mixing impellers 116 (i.e., mixing impellers 116a - 116d) of a set (i.e., set 114a) of mixing impellers 116, the set of mixing impellers 116 including mixing blades 118a - 118d. The following description will center on impeller 116a comprising mixing blade 118a to avoid unnecessary confusion, with the understanding that the mixing impellers and mixing blades of the same or another set of mixing impellers may follow a similar pattern. Indeed, all mixing blades of each mixing impeller and set of mixing impellers disclosed herein may be identical in pattern and construction for a given mixing member.

[0061] As is evident from FIGS. 5 and 6, mixing blade 118a of impeller 116a of impeller set 114a comprises a distal end portion 128a and side portions 130a, 132a, wherein side portions 130a, 132a are positioned between distal end portion 128a and shaft 1 10. Side portions 130a, 132a may connect, either directly or indirectly, with shaft 110. As is further evident, distal end portion 128a and side portions 130a, 132a may be curved. For example, distal end portion 128a may comprise a first radius of curvature and each of side portions 130a, 132a can comprise a different curvature than the curvature of distal end portion 128a. The radius of curvature of side portion 130a may be the same radius of curvature as the curvature of side portion 132a or the curvature of side portion 130a may be different than the radius of curvature of side portion 132a. In some embodiments, the radius of curvature of the distal end portion may be substantially equal to the radius of curvature of inside wall 104 of mixing vessel 100, thereby maximizing the coupling area of the blade. In other

embodiments, the first radius of curvature may be less than the radius of curvature of inside wall 104 of mixing vessel 100. The radii of curvature of side portions 130a, 132a in some embodiments may be infinite. That is, in some embodiments, one or both side portions 130a, 132a may be straight (e.g., planar) segments.

[0062] In some embodiments, as best seen in FIG. 6, mixing blade 118a may include a pair of intermediate portions 134a, 136a positioned between distal end portion 128a and side portions 130a, 132a, wherein intermediate portions 134a, 136a comprise a radius of curvature different from the radii of curvatures of the distal end portion and the side portions, for example a radius of curvature less than any of the radii of curvatures of the distal end portion or the side portions.

[0063] Mixing blade 118a may, in the alternative, be viewed as, in conjunction with shaft 1 10, comprising a closed loop, wherein mixing blade 118a includes a varying radius of curvature (wherein the radius of curvature is not constant along the entire loop), and wherein in some embodiments the radius of curvature of the distal end portion is substantially equal to the radius of curvature of the inside wall of the mixing vessel, while in other embodiments, the radius of curvature of the distal end portion is less than the radius of curvature of the inside wall of the mixing vessel.

[0064] Returning to FIG. 5, mixing impeller 1 16a also includes a pair of web members 120a, 122a connected thereto. For example, as shown in FIG. 5, web member 120a is connected to and thereby captured by inside major surface 124a of mixing blade 118a along one edge of web member 120a, the connected edge of web member 120a following the curvature or curvatures of inside major surface 124a of mixing blade 118a. For example, web member 120a may be welded to inside major surface 124a of mixing blade 118a, such as along a median line between top and bottom edges of side portion 130a Web member 120a may additionally be connected to outside major surface 126b of a mixing blade (e.g., mixing blade 118b) of an adjacent mixing impeller (e.g., mixing impeller 116b). For example, web member 120a is shown attached to the inside major surface 124a of mixing blade 118a, and also attached to outside major surface 126b of mixing blade 118b of adjacent mixing impeller 1 16b along line 1 17b so that web member 120a is shared between mixing blade 118a and mixing blade 118b. Similarly, web member 122a is connected to and thereby captured by inside major surface 124a of mixing blade 118a along an edge of web member 122a, the connected edge following the curvature or curvatures of inside major surface 124a of side portion 132a. For example, web member 122a may be welded to inside maj or surface 124a of mixing blade 1 18a (e.g., side portion 132a). Web member 122a may additionally be connected to inside major surface 126d of a mixing blade (e.g. , mixing blade 1 18d) of an adjacent mixing impeller (e.g., mixing impeller 116d). For example, web member 122a is shown attached to the inside major surface 124a of mixing blade 1 18a, and, although not visible in FIGS. 5 and 6, is also attached to outside major surface 126d of mixing blade 118d of adjacent mixing impeller 116d (as shown in FIG. 6, web member 122a extends "below" a portion of web member 120d in the figure to connect with mixing blade 1 18d). Additionally, each web member may be further attached to shaft 1 10, for example by welding. Web members 120a and 122a may be perpendicular to mixing blade 118a, and may further be perpendicular to adjacent mixing blades 1 18b and 1 18d, and mixing blade 1 18c, which mixing blades surfaces may in turn be parallel with mixing blade 1 18a. In accordance with some embodiments, web members 120a, 120b, 120c and 120d may be coplanar and web members 122a, 122b, 122c and 122d may be coplanar, although web members 120 a - d are spaced apart from web members 122a - d in a direction parallel with longitudinal axis 112.

[0065] Free edge 144a of web member 120a, which is the edge opposite the connected edge attached to mixing blade 1 18a, may be a straight edge (infinite radius of curvature), or free edge 144a may comprise a radius of curvature less than infinity (i.e., free edge 144a may be curved). Similarly, free edge 146a of web member 122a (shown as a phantom line in FIG. 5), which is the edge opposite the connected edge attached to side portion 132a, may be a straight edge (infinite radius of curvature), or free edge 146a may comprise a radius of curvature less than infinity. It should be noted that free edge 146a shown in FIG. 5 is not a continuation of free edge 144d of web member 120d. Also, described above, web members 120a, 122a can be displaced from each other along a length of the shaft (i.e., in a direction parallel with longitudinal axis 1 12) such that when mixing member 102 is positioned within mixing apparatus 36 in a vertical orientation, web member 120a is spaced vertically apart from web member 122a

[0066] It should be apparent with the aid of FIG. 6 that mixing blade 118a includes two opposing curvatures. Accordingly, opposing web members 120a, 122a are attached to the same mixing blade, with one web member (e.g., web member 120a) also attached to a mixing blade (e.g., mixing blade 118d) of a first adjacent mixing impeller (e.g. , mixing impeller 1 16d) and the opposing web member (e.g., web member 122a) also attached to a mixing blade (e.g., mixing blade 118b) of a second adjacent mixing impeller (e.g., mixing impeller 1 16b). Regardless of a direction of rotation of the mixing member, each mixing blade comprises two portions, a leading portion and a trailing portion relative to the direction of rotation. The leading portion and the trailing portions are offset in a direction of longitudinal axis 1 12. The leading portion and the trailing portions are connected in the distal end portion 128 such that the distal end portion comprises an "S" or "Z" shape, as best seen with the aid of FIG. 3. The opposing curvatures of the mixing blade means that for any direction of rotation (i.e., clockwise or counterclockwise) one portion of the impeller (e.g., the outside major surface of one portion of the mixing blade) either "pushes" or "pulls" the molten glass, while a web member folds cord over a free edge thereof. [0067] FIG. 7 is a plan view of a portion of a mixing member 202 according to another embodiment of the present disclosure. Similar to the preceding embodiment, mixing member 202 comprises a shaft 210 with a longitudinal axis 212 that is also an axis of rotation of the mixing member (shown extending into the drawing sheet) and a plurality of sets of mixing impellers 216 arranged along a longitudinal axis of the shaft, each set of mixing impellers spaced apart from adjacent sets of mixing impellers. Each set of mixing impellers 216 comprises a plurality of mixing impellers arranged around shaft 210. For example, FIG. 7 illustrates one set of mixing impellers comprising four mixing impellers, e.g., mixing impellers 216a, 216b, 216c, 216d. However, it should be understood that each set of mixing impellers may have fewer than four mixing impellers, or, alternatively, more than four mixing impellers, for example five mixing impellers. The following description will center on impeller 216a comprising mixing blade 218a to avoid unnecessary confusion, with the understanding that the impellers and mixing blades of the same or another set of impellers may follow a similar pattern. Indeed, all mixing blades of each impeller and set of impellers may, in some embodiments, be identical in pattern and construction.

[0068] As is evident from FIG. 7, mixing blade 218a of impeller 216a of impeller set 214a comprises a distal end portion 228a and side portions 230a, 232a, wherein side portions 230a, 232a connect with shaft 210 at one end of the side portions, and connect, either directly or indirectly, with distal end portion 228a at the opposite ends of the side portions. That is, side portions 230a and 232a are positioned between and coupled to distal end portion 228a and shaft 210. As is further evident, distal end portion 228a and side portions 230a, 232a may be curved. For example, distal end portion 228a may comprise a first radius of curvature and each of side portions 230a, 232a can comprise a radius of curvature different from the first radius of curvature. In certain embodiments, the first radius of curvature may be substantially equal to the radius of curvature of inside wall 104 of mixing vessel 100, thereby maximizing the coupling area of the mixing blade. In other embodiments, the first radius of curvature may be less than the radius of curvature of inside wall 104 of mixing vessel 100. The radii curvature of side portions 230a and 232a in some embodiments may be infinite. That is, in some embodiments, side portions 230a, 232a may be straight (e.g. , planar) segments. In some embodiments, side portions 230a and 232a may comprises different radii of curvature, such that the radius of curvature of side portions 230a is different than the radius of curvature of side portion 232a, although in further embodiments the radii of curvature of the side portions are equal. In some embodiments, the radii of curvature of the side portions vary, but are numerically equal but opposite in direction. That is, in some embodiments, the side portions may be mirror duplicates in shape and/or size.

[0069] In some embodiments, mixing blade 218a may include a pair of intermediate portions positioned between distal end portion 228a and side portions 230a, 232a, wherein the intermediate portions comprise a radius of curvature different from the radius of curvature of the distal end portion and different than one or both of the radii of curvature of the side portions, for example a radius of curvature less than any one or all of the radius of curvature of the distal end portion or the radii of curvature of the side portions.

[0070] Mixing blade 218a may, in the alternative, be viewed as, in conjunction with shaft 210, comprising a closed loop, wherein mixing blade 218a includes a varying radius of curvature (wherein the radius of curvature is not constant along the entire loop), and wherein in some embodiments the radius of curvature of the distal end portion is substantially equal to the radius of curvature of the inside wall of the mixing vessel, while in other embodiments, the radius of curvature of the distal end portion is less than the radius of curvature of the inside wall of the mixing vessel.

[0071] Mixing impeller 216a also includes a pair of web members 220a, 222a connected thereto. For example, as shown in FIG. 7, web member 220a (shown in Crosshatch) is connected to and thereby captured by inside major surface 224a of mixing blade 218a along one edge of web member 220a, the connected edge following the curvature or curvatures of inside major surface 224a of mixing blade 218a. For example, web member 220a may be welded to inside major surface 224a of mixing blade 218a, such as along a median line between top and bottom edges of the mixing blade. Web member 220a may additionally be connected to shaft 210, for example by welding. Similarly, web member 222a is connected to and thereby captured by inside major surface 224a of mixing blade 218a along an edge of web member 222a, the connected edge following the curvature or curvatures of inside major surface 224a of mixing blade 218a Web member 222a may additionally be connected to shaft 210, for example by welding. Major surfaces of web members 220a and 222a may be perpendicular to the major surfaces of mixing blade 218a, and may further be perpendicular to the major surfaces of adjacent mixing blades 218b and 218d, and mixing blade 218c, which mixing blades may in turn comprise major surfaces in parallel with the major surfaces of mixing blade 218a. In accordance with the present embodiment, the major surfaces of the web members of each impeller overlaps, as shown by the crosshatched area 250 of impeller 216c depicted in FIG. 7. As in the previous embodiments, web members 220a and 222a are spaced apart in a direction of the longitudinal axis 212. [0072] Free edge 244a of web member 220a, which is the edge opposite the connected edge attached to mixing blade 218a, may comprise a linear edge (infinite radius of curvature), or free edge 244a may comprise a radius of curvature less than infinity (i.e., wherein free edge 244a may curve). Similarly, free edge 246a of web member 222a, which is the edge opposite the connected edge attached to mixing blade 218a, may comprise a linear edge (infinite radius of curvature), or free edge 244a may comprise a radius of curvature less than infinity (see FIG. 8). Web members 220a, 222a can be displaced from each other along a length of shaft 210 (i.e., in a direction parallel with longitudinal axis 212) such that when mixing member 202 is positioned within mixing apparatus 36 in a vertical orientation, web member 220a is spaced vertically apart from web member 222a.

[0073] It should be apparent with the aid of FIG. 7 that mixing blade 218a includes two opposing curvatures regardless of a direction of rotation of the mixing member, each mixing blade comprises two portions, a leading portion and a trailing portion relative to the direction of rotation. The leading portion and the trailing portions are offset in a direction of longitudinal axis 212 (offset axially). The leading portion and the trailing portions are connected at distal end portion 228 such that the distal end portion comprises an "S" or "Z" shape, as best seen with the aid of FIG. 3. The opposing curvatures of each mixing blade means that for any direction of rotation (i. e. , clockwise or counterclockwise) one portion of the impeller (e.g. , the outside major surface of one portion of the mixing blade) "pushes" the molten glass, while the other portion of the impeller (a free edge of a web member) folds cord over the free edge of the web member.

[0074] In the embodiment of FIG. 7, neither web member 220a, 222a connects

significantly or, or in some embodiments, at all, with an adjacent mixing blade, thus allowing more compact impeller designs and an increase in the number of impellers. In some embodiments, a mixing blade does not contact an adjacent mixing blade. In the mixing member design of FIG. 9, a mixing member 302 is shown illustrating one of a plurality of sets of impellers, where, as depicted, each set of impellers comprises five impellers. Thus, any number of impellers can be arranged within each set of impellers, for example two impellers, three impellers, four impellers, five impellers, six impellers, seven impellers, and so on, the number of impellers limited by the strength of the impeller connection to the shaft and the amount of flow through available for molten glass (i.e., the percentage of cross sectional area of the mixing vessel interior not covered by impellers, and especially not covered by the web members of the impellers) to flow through the mixing vessel. As should be apparent, as the number of impellers increases, the connection area with the shaft (e.g., shaft 310) decreases. Additionally, as the number of mixing impellers increases, the cross sectional area of the mixing vessel covered by the mixing impellers may increase (depending on the surface area of the web members).

[0075] Each set of mixing impellers according to mixing member 102, 202 or 302 may be aligned with one or more other sets of mixing impellers arranged along respective shafts. For example, for a vertically arranged shaft, a mixing impeller of any set of mixing impellers connected to the shaft may be vertically aligned with a respective impeller of another set of impellers on the shaft. Thus, a straight flow path for molten glass may exist between the aligned impellers. However, in other examples, the impellers may not be aligned, such that only a tortuous (non-straight) path exists between the impellers along a flow direction through the mixing vessel. In still other examples, e.g., mixing member 202 of FIG. 10, the curvature of the free edges of each web member of a given mixing impeller may be sufficiently large that there is an area within the mixing impeller where the web members do not overlap and molten glass may flow in a straight line through the mixing impeller, as evidenced by the crosshatched area 260 of FIG. 9.

[0076] FIGS. 1 1 A and 1 IB illustrate plan views of mixing members 402 and 502, respectively, each mixing member comprising a plurality of sets of mixing impellers 216 arranged along a length of their respective shafts 410 and 510, wherein each set of impellers comprises six impellers 416 and 516, respectively, including two web members each, 420, 422 and 520, 522, respectively, wherein web members of a given mixing impeller are spaced apart in a direction parallel with a longitudinal axis of the shaft. In the embodiment of FIG. 1 1 A, each mixing impeller 416 comprises a mixing blade 418 including a distal end portion 428 and side portions 430 and 432. Each distal end portion 428 in the illustrated embodiment comprises an identical first radius of curvature, and each side portion is a straight side portion (infinite radius of curvature), and the first radius of curvature is substantially the same as the radius of curvature of the cylindrical mixing vessel wall 102. The hatched area 434 represents the area of overlap between web members. Such overlap can exist for each mixing impeller. In the embodiment of FIG. 1 I B, each mixing impeller 516 comprises a mixing blade 518 including a distal end portion 528 and side portions 530, 532. Each distal end portion 528 in the illustrated embodiment comprises an identical first radius of curvature, and each side portion is a straight side portion (infinite radius of curvature), and the first radius of curvature of the distal end portion 528 is different than the radius of curvature of the cylindrical mixing vessel wall 102, and as depicted, less than the radius of curvature of the mixing vessel wall. The hatched area 534 represents the area of overlap between web members. Such overlap can exist for each mixing impeller.

[0077] It will be apparent to those skilled in the art that various modifications and variations can be made to embodiment of the present disclosure without departing from the spirit and scope of the disclosure. Thus it is intended that the present disclosure cover such modifications and variations provided they come within the scope of the appended claims and their equivalents.

Claims

What is claimed is:

1. A mixing apparatus comprising:

a mixing vessel;

a mixing member rotatably positioned within the mixing vessel, the mixing member comprising a shaft and a first mixing impeller attached thereto and extending radially outward therefrom, the first mixing impeller including a mixing blade formed as a closed loop with the shaft, the mixing blade including a distal end portion comprising a first radius of curvature and first and second side portions adjacent to the distal end portion, the first and second side portions comprising a radius of curvature different than the first radius of curvature; and

a first web portion and a second web portion spaced apart from the first web portion along a direction parallel with a longitudinal axis of the shaft, the first web portion and the second web portions attached to an inside major surface of the mixing blade along a captured edge of the first and second web portions.

2. The mixing apparatus according to claim 1 , wherein the first web portion is attached to a second mixing impeller adjacent the first mixing impeller.

3. The mixing apparatus according to claim 2, wherein the second web portion is attached to a third mixing impeller adjacent the first mixing impeller.

4. The mixing apparatus according to claim 1 , wherein a radius of curvature of at least one of the first and second side portions is infinite.

5. The mixing apparatus according to claim 1 , wherein each of the first web portion and the second web portion comprises a free edge.

6. The mixing apparatus according to claim 5, wherein the free edge comprises a linear edge portion.

7. The mixing apparatus according to claim 6, wherein along a line parallel with a longitudinal axis of the shaft, and tangent to the free edge of the first web portion, the line intersects the second web portion.

8. The mixing apparatus according to claim 5, wherein the free edge comprises a concave curve.

9. The mixing apparatus according to claim 8, wherein along a line parallel with a longitudinal axis of the shaft and tangent to the free edge of the first web portion, the line does not intersect the second web portion.

10. The mixing apparatus according to claim 1, wherein the mixing blade further comprises first and second intermediate portions positioned between the distal end portion and the first and second side portions, respectively, and a radius of curvature of the distal end portion and the first and second intermediate portions is different than the radii of curvature of the first and second side portions.

11. The mixing apparatus according to claim 10, wherein the radii of curvature of the first and second intermediate portions are less than the radii of curvature of the first and second side portions.

12. The mixing apparatus according to claim 1, wherein the first radius of curvature is substantially the same as a radius of curvature of an inside wall surface of the mixing vessel adjacent the distal end portion.

13. The mixing apparatus according to claim 1, wherein the mixing apparatus comprises a set of mixing impellers arranged about a first position on the shaft relative to a length of the shaft.

14. The mixing apparatus according to claim 13, wherein the set of mixing impellers comprises at least 4 mixing impellers.

15. The mixing apparatus according to claim 14, wherein the set of mixing impellers comprises at least 5 mixing impellers.

16. The mixing apparatus according to claim 13, the mixing apparatus further comprising a plurality of sets of mixing impellers arranged at a plurality of positions on the shaft.

17. A mixing apparatus comprising:

a cylindrical mixing vessel, an inside wall of the mixing vessel comprising a radius of curvature;

a mixing member rotatably positioned within the mixing vessel, the mixing member comprising:

a shaft; and

a first mixing impeller attached to the shaft and extending radially outward therefrom, the first mixing impeller including a mixing blade formed as a closed loop with the shaft and including a distal end portion comprising a first radius of curvature substantially equal to the radius of curvature of the inside wall of the mixing vessel, the first mixing impeller further comprising first and second web portions connected to the mixing blade.

18. The mixing apparatus according to claim 17, wherein the mixing blade further comprises first and second adjacent side portions, the first and second side portions comprising radii of curvature different than the first radius of curvature.

19. A method of making glass comprising:

heating raw materials in a melting vessel to form a molten material;

flowing the molten material into a mixing vessel, the missing vessel; and

mixing the molten material with a mixing member rotatably positioned within the mixing vessel, the mixing member comprising a shaft and a first mixing impeller attached thereto and extending radially outward therefrom, the first mixing impeller including a mixing blade formed as a closed loop with the shaft, the mixing blade including a distal end portion comprising a first radius of curvature and side portions adjacent to the distal end portion, the side portions comprising a radii of curvature different than the first radius of curvature, the first mixing impeller further comprises first and second web portions connected to the mixing blade.

20. The method according to claim 19, further comprising mixing the molten material with a plurality of mixing impellers.