WO2019074923A2

WO2019074923A2 - Methods for processing a pulling roll surface

Info

Publication number: WO2019074923A2
Application number: PCT/US2018/055010
Authority: WO
Inventors: Ji-Wan BAEK; Sung-Ryul Cho; Sang-Ho Lim; Moo-Seop Song; Gary Graham Squier
Original assignee: Corning Incorporated; Corning Precision Materials Co., Ltd
Priority date: 2017-10-10
Filing date: 2018-10-09
Publication date: 2019-04-18
Also published as: TW201922635A; JP2020536835A; CN111699160A; WO2019074923A3; KR20200055138A

Abstract

A method of processing a pulling roll for use in a glass making process includes contacting the pulling roll with a tramping roller with a predetermined force and rotating the pulling roll while the predetermined force is applied such that the tramping roller travels over the surface of the pulling roll. A contact surface of the pulling roll can be processed such that edges of the contact surface are radiused.

Description

METHODS FOR PROCESSING A PULLING ROLL SURFACE

RELATED APPLICATIONS

[0001] This application claims the benefit of priority of U.S. Provisional Application Serial No. 62/570,119 filed on October 10, 2017 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 disclosure relates generally to a glass making processes, and more particularly to methods for processing pulling rolls used to draw molten glass.

Technical Background

[0003] The manufacture of glass substrates, for example glass substrates used in the manufacture of lighting panels, liquid crystal displays and other electronic devices, typically involves drawing a glass ribbon from molten glass. In a drawing process, a glass ribbon can be drawn by pulling rolls - typically counter-rotating and opposed rolls that pinch edge portions of the glass ribbon and draw the glass from a forming body.

[0004] As the demand for an increasingly thinner nominal thickness of glass sheets increases, glass defects (flaws) placed into the surface of the glass ribbon from which such sheets may be derived represent a larger percentage of the total thickness of the ribbon. Additionally, as the ribbon becomes thinner, the ribbon is more prone to bending, or in some cases can be intentionally bent as part of the manufacturing process, thereby increasing surface tension on the glass ribbon. The stress induced into the surface of the glass ribbon, in the presence of flaws, can produce cracking and fracturing of the glass ribbon. Cracking of the ribbon is a main factor that results in frequent and premature changes of pulling rolls, especially pulling rolls used in the manufacture of thin glass, i.e., glass with a nominal thickness less than about 0.4 mm.

SUMMARY

[0005] The contact surfaces of pulling rolls in a glass making process can be in prolonged contact with high temperature glass, and are therefore typically comprised of high

temperature resistant refractory materials. Nonetheless, because of the harsh environment in which pulling rolls are employed, the expected lifetime of a pulling roll is relatively short. Accordingly, pulling rolls are changed frequently. For thin glass, i.e., glass with a thickness equal to or less than about 0.4 mm, cracking of the glass is a principal reason pulling rolls are changed earlier than their counterparts used with thicker glass especially producing thin glass less than 0.4 mm. The average pulling roll life at a thickness equal to or less than about 0.3 mm, for example, is less than 40% of the average life at a thickness in a range from about 0.5 mm to about 0.7 mm.

[0006] It has been found that as much as 65% of cracking failures for glass with a thickness equal to or less than about 0.4 mm occurs within 1 day after installation of new pulling rolls. Such failures have been traced to at least three principal attributes of the pulling rolls:

surface roughness, surface compliance and surface profile (roll shape).

[0007] Accordingly, in embodiments, a method for processing a pulling roll is disclosed comprising rotating the pulling roll about an axis of rotation and contacting a contact surface of the pulling roll with a tramping roller with a predetermined force F as the pulling roll rotates. The predetermined force F can be in a range from about 13 N to about 147 N, for example in a range from about 49 N to about 118 N. An average surface roughness Ra of the contact surface after the step of contacting can be equal to or less than 2 μπι after the contacting.

[0008] A distance traveled over the contact surface by the tramping roller during the contacting can be equal to or greater than a circumference of the contact surface, and can be, for example, equal to or greater than 5,000 cm, for example in a range from about 5,000 cm to about 70,000 cm.

[0009] In some embodiments, the contact surface can be joined to a chamfer surface of the pulling roll by a transition surface comprising a radius of curvature in a range from about 1.5 cm to about 7.6 cm.

[0010] The tramping roller may comprise alumina, although in other embodiments, the tramping roller can include stainless steel, for example a stainless-steel roller with a ceramic (e.g., alumina) layer disposed thereon. A diameter of the tramping roller is typically less than a diameter of the contact surface of the pulling roll.

[0011] In further embodiments, the method may also include mounting the pulling roll to a shaft of a pulling roll assembly. The pulling roll assembly can then be used to draw a glass ribbon. A thickness of the glass ribbon at a centerline thereof can equal to or less than about 0.7 mm after the drawing, for example equal to or less than about 0.4 mm.

[0012] In some embodiments, a plurality of tramping rollers can be employed. [0013] In other embodiments, a method of processing a pulling roll for a glass making process is described, comprising rotating the pulling roll about an axis of rotation and contacting a contact surface of the pulling roll with a tramping roller with a predetermined force F in a range from about 13 N to about 147 N as the pulling roll rotates, for example in a range from about 49 N to about 118 N, or in a range from about 78 N to about 118 N.

[0014] The contacting may be performed for a time in a range from greater than zero minutes to equal to or less than about 60 minutes, for example equal to or greater than about 5 minutes but equal to or less than about 15 minutes.

[0015] In some embodiments, the contacting can comprise contacting the contact surface with a plurality of tramping rollers.

[0016] In some embodiments, an average surface roughness Ra of the contact surface after the contacting can be equal to or less than about 2 μπι, for example equal to or less than about 1 μιη.

[0017] In embodiments, the contact surface may be joined to a chamfer surface of the pulling roll by a transition surface comprising a radius of curvature in a range from about 1.5 cm to about 7.6 cm.

[0018] The method may further comprise mounting the pulling roll to a shaft of a pulling roll assembly after the contacting. The pulling roll assembly can then be used to draw a glass ribbon after the mounting. A thickness of the glass ribbon at a centerline thereof after the drawing can equal to or less than about 0.7 mm, for example equal to or less than about 0.4 mm.

[0019] In still other embodiments, a method of processing a pulling roll for a glass making process is disclosed, comprising positioning a plurality of fired discs of a millboard material in a face-to-face relationship, axially compressing the plurality of fired discs, firing the axially compressed plurality of fired discs at a temperature and for a time sufficient to fuse at least a portion of the plurality of fired discs together to form a pulling roll, and milling an exterior surface of the pulling roll to a predetermined profile comprising a cylindrical portion including a cylindrical contact surface, and a chamfer portion comprising a chamfer portion surface, wherein a transition surface positioned between the cylindrical contact surface and the chamfer portion surface comprises a radius of curvature in a range from about 1.5 cm to about 7.6 cm.

[0020] The method may further comprise rotating the pulling roll about an axis of rotation and contacting a contact surface of the pulling roll with a tramping roller with a predetermined force F as the pulling roll rotates. The predetermined force F can be in a range from about 13 N to about 147 N, for example in a range from about 49 N to about 118 N, or in a range from about 78 N to about 118 N.

[0021] In some embodiments, a distance traveled over the contact surface by the tramping roller during the step of contacting can be equal to or greater than a circumference of the contact surface, such as equal to or greater than 5,000 cm, for example in a range from about 5,000 cm to about 70,000 cm.

[0022] The method may further comprise mounting the pulling roll to a shaft of a pulling roll assembly. The pulling roll assembly can then be used to draw a glass ribbon. A thickness of the glass ribbon at a centerline thereof can be equal to or less than about 0.4 mm.

[0023] Additional features and advantages of the embodiments disclosed herein will be set forth in the detailed description that 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.

[0024] 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 disclosed herein. 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

[0025] FIG. 1 is a schematic view of an exemplary glass making apparatus according to embodiments of the present disclosure;

[0026] FIG. 2 is a side cross sectional view of a portion of a forming apparatus;

[0027] FIG. 3 is a front view of a portion of the forming apparatus of FIG. 2;

[0028] FIG. 4 is a side view of an exemplary pulling roll sleeve;

[0029] FIG. 5 is a side view of another exemplary pulling roll sleeve;

[0030] FIG. 6 is a side view of an exemplary pulling roll cartridge;

[0031] FIG. 7 is a side view of at least a portion of a pulling roll assembly according to embodiments of the present disclosure; [0032] FIG. 8 is a front view of an exemplary apparatus for processing a contact surface of a pulling roll according to embodiments of the present disclosure;

[0033] FIG. 9 is a side view of the apparatus for processing a contact surface of a pulling roll shown in FIG. 8;

[0034] FIG. 10 is a front view of another exemplary apparatus for processing a contact surface of a pulling roll according to embodiments of the present disclosure;

[0035] FIG. 11 is a plot of three groups of data for glass strength, and pulling roll contact average surface roughness and hardness resulting from processing a contact surface of a pulling roll in accordance with embodiments of the present disclosure;

[0036] FIG. 12 illustrates two photographs representing a pulling roll (a) before tramping and (b) after tramping;

[0037] FIG. 13 is a plot showing glass strength for various conditions of pulling roll processing and deployment;

[0038] FIG. 14A is a top view of splayed pulling rolls with an arcuate transition surface between a contact surface and a chamfer portion surface.

[0039] FIG. 14B is a close-up view of the splayed pulling rolls of FIG. 14A;

[0040] FIG. 15A is a top view of splayed pulling rolls without an arcuate transition surface between a contact surface and a chamfer portion surface;

[0041] FIG. 15B is a close-up view of the splayed pulling rolls of FIG. 15 A.

DETAILED DESCRIPTION

[0042] Reference will now be made in detail to 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.

[0043] 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. [0044] Directional terms as might be 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.

[0045] Unless otherwise expressly stated, it is in no way 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 in no way 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.

[0046] As used herein, the singular forms "a," "an" and "the" include plural references 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.

[0047] The word "exemplary," "example," or various forms thereof are used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as "exemplary" or as an "example" is not necessarily to be construed as preferred or advantageous over other aspects or designs. Furthermore, examples are provided solely for purposes of clarity and understanding and are not meant to limit or restrict the disclosed subject matter or relevant portions of this disclosure in any manner. It is to be appreciated that a myriad of additional or alternate examples of varying scope could have been presented, but have been omitted for purposes of brevity.

[0048] As used herein, the terms "comprising" and "including", and variations thereof, shall be construed as synonymous and open-ended, unless otherwise indicated. A list of elements following the transitional phrases comprising or including is a non-exclusive list, such that elements in addition to those specifically recited in the list may also be present.

[0049] As used herein, "molten glass" shall be construed to mean a molten inorganic material which, upon cooling, can enter a glassy state. The term molten glass is used synonymously with the term "melt". The molten glass may form, for example, a majority silicate glass, although the present disclosure is not so limited.

[0050] As used herein, the term "fluid" shall denote any gas, mixture of gasses, liquid, gas and liquid mixtures, vapor, or combinations thereof.

[0051] As used herein, the term "refractory", or "refractory material" is used to denote non- metallic materials with chemical and physical properties that make them applicable for structures, or as components of systems, that are exposed to environments above 538°C, for example equal to or greater than about 700°C, such as equal to or greater than about 800°C.

[0052] As used herein, a "wt. %" or "weight percent" or "percent by weight" of a component, unless specifically stated to the contrary, is based on the total weight of the composition in which the component is included.

[0053] As used herein, the term "integral", unless otherwise indicated, refers to an article or body that is unified in construction, and not a collection of connected parts, e.g., monolithic.

[0054] As used herein, a contact surface of a pulling roll is a surface of the pulling roll intended and configured to contact a ribbon of viscous, visco-elastic or elastic material (e.g., a glass ribbon).

[0055] The manufacture of glass sheets by a dawn-draw process involves drawing molten glass from a forming body as a ribbon of indeterminate length. The ribbon comprises lateral edge portions and a central portion therebetween. The drawing process comprises pinching the lateral edge portions of the ribbon between pairs of counter-rotating pulling roll assemblies that exert a downward force on the ribbon that draws the molten glass away from the forming body. The glass ribbon cools to an elastic state, is cut into individual glass sheets, and the edge portions contacted by the pulling roll assemblies are removed.

[0056] Typically, pulling rolls themselves comprise refractory material and are mounted on metallic (e.g., steel) shafts. A pulling roll may be an integral body, or a body comprised of stacked refractory disks. In embodiments, a pulling roll may be in the form of a sleeve or a cartridge that facilitates easy attachment and removal from the shaft.

[0057] 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 that can include 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 and/or electrodes) configured to heat raw material and convert the raw material into molten glass. For example, melting furnace 14 may be an electrically-boosted melting vessel, wherein energy is added to the raw material through both combustion burners and by direct heating, wherein an electric current is passed through the raw material, the electric current thereby adding energy via Joule heating of the raw material. As used herein, an electrically-boosted melting vessel is a melting vessel that obtains heat energy from both Joule heating and above-surface combustion heating, and the amount of energy imparted to the raw material and/or melt via Joule heating is equal to or greater than about 20%. As used herein, an electrically-boosted melting vessel does not include submerged combustion processes. In some embodiments, the heat energy added to the molten material by Joule heating compared to the total heat energy added to the molten material via both above-surface combustion burners and Joule heating can be in a range from about 20% to about 80%, such as equal to or greater than 30%, equal to or greater than 40%, equal to or greater than 50%, equal to or greater than 60%, or equal to or greater than 70%.

[0058] In further embodiments, glass melting furnace 12 may include thermal management devices (e.g., insulation components) that reduce heat loss from the melting vessel. In still further embodiments, glass melting furnace 12 may include electronic devices and/or electromechanical devices that facilitate melting of the raw material into a glass melt. Still further, glass melting furnace 12 may include support structures (e.g., support chassis, support member, etc.) or other components.

[0059] Glass melting vessel 14 is typically formed from a refractory material, such as a refractory ceramic material, for example a refractory ceramic material comprising alumina or zirconia, although the refractory ceramic material may comprise other refractory materials, such as yttrium (e.g., yttria, yttria stabilized zirconia, yttrium phosphate), zircon (ZrSi0₄) or alumina-zirconia-silica or even chrome oxide, used either alternatively or in any combination. In some examples, glass melting vessel 14 may be constructed from refractory ceramic bricks.

[0060] In some embodiments, melting furnace 12 may be incorporated as a component of a glass manufacturing apparatus configured to fabricate a glass article, for example a glass ribbon of an indeterminate length, although in further embodiments, the glass manufacturing apparatus may be configured to form other glass articles without limitation, such as glass rods, glass tubes, glass envelopes (for example, glass envelopes for lighting devices, e.g., light bulbs) and glass lenses, although many other glass articles are contemplated. In some examples, the 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 (e.g., a fusion dawn-draw apparatus), an up-draw apparatus, a pressing apparatus, a rolling apparatus, a tube drawing apparatus or any other glass manufacturing apparatus that would benefit from the present disclosure. By way of example, FIG. 1 schematically illustrates glass melting furnace 12 as a component of a fusion dawn-draw glass manufacturing apparatus 10 for fusion drawing a glass ribbon for subsequent processing into individual glass sheets or rolling the glass ribbon onto a spool.

[0061] Glass manufacturing apparatus 10 (e.g., fusion dawn-draw apparatus 10) can optionally include an upstream glass manufacturing apparatus 16 positioned upstream relative to glass melting vessel 14. In some examples, a portion of, or the entire upstream glass manufacturing apparatus 16, may be incorporated as part of the glass melting furnace 12.

[0062] As shown in the embodiment illustrated in FIG. 1, the upstream glass manufacturing apparatus 16 can include a raw material storage bin 18, a raw material delivery device 20 and a motor 22 connected to the raw material delivery device. Raw material storage bin 18 may be configured to store a quantity of raw material 24 that can be fed into melting vessel 14 of glass melting furnace 12 through one or more feed ports, as indicated by arrow 26. Raw material 24 typically comprises one or more glass forming metal oxides and one or more modifying agents. In some examples, raw material delivery device 20 can be powered by motor 22 such that raw material delivery device 20 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 relative to a flow direction of the molten glass. Raw material 24 within melting vessel 14 can thereafter be heated to form molten glass 28. Typically, in an initial melting step, raw material is added to the melting vessel as particulate, for example as comprising various "sands". Raw material may also include scrap glass (i.e. cullet) from previous melting and/or forming operations. Combustion burners are typically used to begin the melting process. In an electrically boosted melting process, once the electrical resistance of the raw material is sufficiently reduced (e.g., when the raw materials begin liquefying), electric boost is begun by developing an electric potential between electrodes positioned in contact with the raw materials, thereby establishing an electric current through the raw material, the raw material typically entering, or in, a molten state.

[0063] Glass manufacturing apparatus 10 can also optionally include a downstream glass manufacturing apparatus 30 positioned downstream of glass melting furnace 12 relative to a flow direction of the molten glass 28. In some examples, a portion of downstream glass manufacturing apparatus 30 may be incorporated as part of glass melting furnace 12. However, in some instances, 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 the downstream glass manufacturing apparatus, including first connecting conduit 32, may be formed from a precious metal. Suitable precious metals include platinum group metals selected from the group 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 for forming downstream components of the glass manufacturing apparatus can include molybdenum, rhenium, tantalum, titanium, tungsten and alloys thereof.

[0064] 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 examples, 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 primary melting vessel is further heated in a secondary vessel to continue the melting process, or cooled to a temperature lower than the temperature of the molten glass in the primary melting vessel before entering the fining vessel.

[0065] As described previously, 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, although the use of arsenic and antimony may be discouraged for environmental reasons in some applications. 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 one or more fining agents included in the melt rise through the molten glass within the fining vessel, wherein gases in the molten glass produced in the melting furnace can coalesce or diffuse into the oxygen bubbles produced by the fining agent. The enlarged gas bubbles with increased buoyancy can then rise to a free surface of the molten glass within the fining vessel and thereafter be vented out of the fining vessel. The oxygen bubbles can further induce mechanical mixing of the molten glass in the fining vessel as they rise through the molten glass.

[0066] The downstream glass manufacturing apparatus 30 can further include another conditioning vessel, such as a mixing apparatus 36, for example a stirring vessel, for mixing the molten glass that flows downstream from fining vessel 34. Mixing apparatus 36 can be used to provide a homogenous glass melt composition, thereby reducing chemical or thermal inhomogeneities that may otherwise exist within the fined molten glass exiting the fining vessel. As shown, fining vessel 34 may be coupled to mixing apparatus 36 by way of a second connecting conduit 38. In some embodiments, 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. Typically, the molten glass within mixing apparatus 36 includes a free surface, with a free volume extending between the free surface and a top of the mixing apparatus. It should be noted that while mixing apparatus 36 is shown downstream of fining vessel 34 relative to a flow direction of the molten glass, mixing apparatus 36 may be positioned upstream from fining vessel 34 in other embodiments. 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. In some embodiments, one or more of the vessels and/or conduits may include static mixing vanes positioned therein to promote mixing and subsequent homogenization of the molten material.

[0067] 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. The molten glass within delivery vessel 40 can, in some embodiments, include a free surface, wherein a free volume extends upward from the free surface to a top of the delivery vessel. 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.

[0068] Downstream glass manufacturing apparatus 30 can further include forming apparatus 48 comprising the above-referenced forming body 42, 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 dawn-draw glass making apparatus can comprise a trough 52 positioned in an upper surface of the forming body and converging forming surfaces 54 (only one surface shown) that converge in a draw direction along a bottom edge (root) 56 of the forming body. Molten glass delivered to the forming body trough 52 via delivery vessel 40, exit conduit 44 and inlet conduit 50 overflows the walls of trough 52 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 root 56 to produce a single ribbon 58 of molten glass that is drawn from root 56 along a draw plane 59 (see FIG. 2) in a draw direction 60 by applying a downward tension to the glass ribbon, such as by gravity, edge rolls 62 and pulling roll assemblies 64, to control the dimensions of the glass ribbon as the molten glass cools and a viscosity of the material increases. Accordingly, glass ribbon 58 goes through a visco-elastic transition and acquires mechanical properties that give glass ribbon 58 stable dimensional characteristics. Glass ribbon 58 may in some embodiments be separated into individual glass sheets 68 by a glass separation apparatus (not shown) in an elastic region of the glass ribbon, while in further embodiments, the glass ribbon may be wound onto spools and stored for further processing.

[0069] FIGS. 2 and 3 show a side (edge) view and a front view, respectively, of at least a portion of forming apparatus 48, showing forming body 42, edge rolls 62 and pulling roll assemblies 64.

[0070] Pulling roll assemblies 64 can be assembled as modular components. Such modular components can, in various embodiments, be quickly replaced at the point of use to minimize downtime and costs associated with shipment and repair of pulling roll assemblies. In some embodiments, the modular components can include a sleeve of fired, compressed, heat resistant discs that have been at least partially fused together so the sleeve can be positioned on and removed from a pulling roll shaft as a single unit. In other embodiments, the modular component can comprise a cartridge configured to slide onto a pulling roll shaft. As used herein, the term pulling roll assembly refers to the assembly used to draw a glass ribbon. The pulling roll assembly comprises, a shaft, a pulling roll providing a contact surface that contacts the glass ribbon, a motor for rotating the shaft and thus the pulling roll, and various other hardware and software that might be needed, for example, to secure a pulling roll to the shaft, to control the pulling roll motor, etc. The term pulling roll comprises that portion of the pulling roll assembly that contacts the glass ribbon 58. Typically, the pulling roll comprises a sleeve of refractory material, for example heat resistant refractory discs, assembled face-to-face and fired to produce a sleeve. However, in other embodiments, a pulling roll can comprise a sleeve assembled onto a spool or other framework to produce a modular, replaceable cartridge that can be removably fitted to a shaft.

[0071] A pulling roll assembly can comprise one or more fittings positioned along a shaft. Such fittings can comprise a collar (fixed, movable and/or removable), a locking ring, a snap ring, a split retaining ring, or other device capable of securing one or more heat resistant discs in place on the shaft. Any device capable of applying an axial compressive force to the plurality of heat resistant discs mounted on a shaft can be used as a fitting.

[0072] Depending on the desired configuration of a given pulling roll assembly, one or more regions of heat resistant discs can be positioned along a shaft. In various embodiments, one, two, three, or more individual regions of heat resistant discs can be positioned along the shaft, wherein each of the regions comprises at least two fittings that can apply an axial compressive force to the heat resistant discs disposed therebetween.

[0073] It should be appreciated that a variety of pulling roll configurations exist in the literature and are suitable for use in the manufacture of sheet glass. For example, US Pat. 6,896,646 describes methods of producing a pulling roll from millboard materials. The present disclosure is not limited to a particular pulling roll configuration or arrangement, and one of skill in the art could readily choose an appropriate pulling roll configuration.

[0074] In embodiments, a pulling roll assembly can comprise a configuration including a single region of heat resistant discs extending over the length of a shaft, or a portion thereof. Such a pulling roll assembly can include one or more portions specifically adapted for contacting a glass sheet, wherein the outer perimeter of heat resistant discs in that portion extend a farther distance from the shaft than do surrounding heat resistant discs. Such a configuration can reduce the possibility of particles from a pulling roll becoming deposited on the glass sheet as "onclusions" (e.g., surface particles). In a full roll configuration, a single region of heat resistant discs comprises two portions adapted to contact a glass ribbon at different locations, for example, at opposite edges of the glass ribbon. In other embodiments, a pulling roll assembly can comprise a bare shaft configuration, wherein two or more regions of heat resistant discs adapted to contact a glass ribbon, for example at opposite edge portions, are separated by a region of the shaft comprising no discs. Each of the individual regions can have fittings to secure the heat resistant discs in place and to provide an axial compressive force to those heat resistant discs disposed therebetween.

[0075] In a stub pulling roll assembly 64, shown in FIG. 3, a single region of heat resistant discs mounted to a shaft is adapted to contact one edge portion of a glass sheet, and a separate stub pulling roll assembly 64 (comprising a separate shaft) can be used to contact an opposite edge of the glass sheet. That is, in a stub roll configuration, one shaft does not extend across an entire width of the glass ribbon.

[0076] The axial compressive force used to compress a portion of a pulling roll and achieve a particular hardness of the contact surface can vary. In various embodiments, the force can range from about 31,376 Newtons to about 134,467 Newtons (N), from about 44,822 N to about 89,644 N, or from about 35,858 N to about 58,269 N. In other embodiments, the force can be less than about 31,376 N or greater than about 134,467 N. The axial compressive force should be sufficient to cause, upon heating, at least a portion of the heat resistant fired discs to fuse together.

[0077] An exemplary pulling roll comprises a plurality of heat resistant planar discs (optionally fired), positioned on a shaft in face-to-face orientation, and compressed such that the exterior edge of each disc of the plurality of discs forms an exterior surface of the pulling roll capable of contacting a glass ribbon. The specific shape, size, and composition of any one or more of the plurality of heat resistant discs can vary depending on, for example, the intended application and operating conditions of the resulting pulling roll. At least a portion of the exterior surface of the pulling roll can be configured to contact the glass sheet.

[0078] The composition of any one or more of the heat resistant discs can vary depending on the desired properties of the pulling roll. In embodiments, one or more discs can be formed from a millboard material. In some embodiments, one or more discs can comprise a silicate, clay, refractory ceramic fiber, or a combination thereof. In some embodiments, one or more discs can comprise a commercially available millboard material, such as, for example, Nichias SD-115 (available from Nichias Corporation, Tokyo, Japan). While certain components and concentration ranges are recited herein for specific millboard materials, these are exemplary and not intended to be limiting in respect of any particular millboard material, components, and/or concentration ranges.

[0079] In some embodiments, the millboard from which at least a portion of the heat resistant discs is formed can comprise an asbestos-free, shot-free refractory composition, such as that described in U.S. Patent No. US7507194B2. In various exemplary embodiments, such a millboard can comprise, on a dry weight basis, from about 5 weight percent to about 30 weight percent refractory ceramic fiber, from about 1 weight percent to about 10 weight percent organic fiber, such as, for example, cellulose, from about 10 weight percent to about 40 weight percent magnesium silicate, such as, for example, Forsterite, from about 5 weight percent to about 32 weight percent mica, from about 10 weight percent to about 35 weight percent kaolin clay, less than about 0.5 weight percent crystalline silica, and less than about 0.8 weight percent titanium dioxide.

[0080] Ceramic fibers for use in such a millboard material can comprise naturally occurring materials and/or man-made ceramic fibers produced from kaolinite and silica. Useful ceramic fibers can comprise fibers of various fiber grades, such grades being determined by production methods, shot (non-fibrous) content, lubrication and the like. One of skill in the art, in possession of this disclosure, could readily select appropriate ceramic fiber materials. In some embodiments, such ceramic fibers can have fiber lengths up to about 5 micrometers, diameters up to about 3 micrometers, and aspect ratios of greater than about 5: 1. It should be noted that these values are exemplary and other fibers can be used depending on the desired properties of the resulting pulling roll. In embodiments, a ceramic fiber material for pulling rolls should not melt at temperatures below about 1,760°C, and should retain physical and chemical integrity when subjected to continuous temperatures up to about 1,260°C.

[0081] An organic fiber, if used, can be any organic fiber suitable for use in a millboard material or pulling roll application. An organic fiber can comprise cellulose for example. In some embodiments, the cellulose can comprise an unbleached, semi-bleached, or bleached wood pulp. In other embodiments, the millboard composition does not comprise an organic fiber.

[0082] An inorganic binder, if present, can comprise one or more inorganic compounds including, for example, clay, gypsum, fly ash, and alkaline ionic silicates such as silicates of sodium, potassium, or magnesium. For example, an inorganic binder can comprise from about 10 to about 30 weight percent kaolin clay and from about 10 to about 40 weight percent magnesium silicate, based on the total dry weight of the millboard composition.

[0083] In some embodiments, an aqueous slurry of the millboard components can be prepared, a flocculent can optionally be added, and the resulting slurry formed into a sheet by, for example, depositing the slurry onto a rotating screened cylinder. [0084] The millboard sheet can be compressed, during and/or after formation, to provide a uniform or substantially uniform thickness. Any residual moisture in a formed millboard sheet can be removed, for example, by heating.

[0085] A heat resistant disc and/or the material from which one or more heat resistant discs are cut can be fired prior to assembly to form a pulling roll so that the heat resistant discs exhibit substantially no compositional or dimensional changes when exposed to the temperatures at which the rolls operate. For example, heat resistant discs can be heated in a firing step at a temperature of from about 650°C to about 1,000°C, or from about 760°C to about 1,000°C, or from about 900°C to about 1,000°C, and held for a period of at least two hours. The heat resistant discs can then be cooled to ambient temperature and assembled to form a pulling roll, or a modular component as described herein. A modular component may be, for example, a sleeve formed of fired, compressed, heat resistant discs that have been at least partially fused together, or a cartridge having heat resistant material disposed thereon, for example a sleeve.

[0086] A sleeve can be prepared from a plurality of heat resistant discs, for example, of a millboard material that can become rigid and at least partially fused together when compressed and heated. A sleeve can be prepared and/or configured to a desired dimension prior to delivery to a point of use to further minimize downtime and the effort required to repair a pulling roll.

[0087] A sleeve can be prepared, for example, by punching or cutting a plurality of discs from one or more sheets of a millboard material. The discs can then be fired for a time and at a temperature sufficient to dry the discs and remove volatile and/or combustible components from the discs. The discs can be fired such that after firing they exhibit substantially no weight loss (e.g., < 1.5 weight percent) when exposed to the temperatures associated with a pulling roll during use and will thus be dimensionally stable under operating conditions. For example, discs can be fired by heating the discs at a temperature from about 650°C to about 1,000°C, or from about 760°C to about 1,000°C, or from about 900°C to about 1,000°C, and held at that temperature for a period of at least two hours, and then cooled back to room temperature before assembly onto a shaft to form the sleeve.

[0088] The fired discs can then be positioned onto a shaft in a face-to-face orientation. Throughout this disclosure, for ease in description, when the discs are referred to simply as "discs", it is with the understanding that they may be either fired or not fired prior to assembly onto a shaft to form the modular component of the pulling roll assembly. On the other hand, "fired discs" specifically refer to discs that have been heated to dry them and remove any volatile and/or combustible components in the discs, as described above. In various embodiments, the shaft used to prepare the sleeve can be a pulling roll shaft or a model shaft for use solely in preparing such a sleeve. When the shaft is a pulling roll shaft, it may or may not also be subsequently used as the pulling roll shaft of a pulling roll assembly later used to produce sheet glass.

[0089] In embodiments, the shaft may be configured such that the positioned discs can be compressed in an axial manner. For example, in various embodiments at least one end of the shaft can comprise a fixed collar or back plate to prevent movement of the discs along the length of the shaft. In some embodiments, at least one end of the shaft can comprise a fitting for securing, compressing, and/or preventing movement of the plurality of discs along the length of the shaft.

[0090] In some embodiments, a removable collar, locking ring, or other fittings for securing and compressing the plurality of discs can be positioned either at the opposing end of the shaft and/or at one or more positions along the length of the shaft. For example, a shaft can comprise a fixed collar positioned on one end of the shaft. In such an embodiment, a plurality of fired discs can be positioned in face-to-face orientation along the shaft, abutting the fixed collar. After positioning the plurality of fired discs on the shaft, a removable collar can be positioned on the opposing end of the shaft and adjusted to provide a compressive axial force to the plurality of fired discs.

[0091] After positioning and compressing the plurality of fired discs, all or a portion of the discs can optionally be milled (e.g., cut, ground, sanded, etc.) to a desired dimension. For example, a pulling roll assembly can be configured such that a portion of the pulling roll contacts a glass sheet. Thus, the exterior surface of the assembly of compressed fired discs can be milled or otherwise dimensioned to provide a desired profile. The fired discs can be milled, for example, to provide a sleeve capable of fitting any of a variety of roll shapes and/or configurations.

[0092] The compressed assembly of fired discs can then be fired at a temperature and for a time sufficient to fuse the plurality of discs together. For example, the compressed assembly of fired discs can be heated at a temperature of at least about 925°C for a period of at least about 24 hours, such as at least about 950°C for at least about 48 hours. Such a heating step can be performed in a kiln, for example.

[0093] The specific compression, as well as time and temperature conditions for firing a compressed assembly of fired discs, can vary, and the present disclosure is not intended to be limited to any particular set of conditions as long as the conditions are sufficient to fuse the compressed assembly of fired discs together to form a sleeve. In some embodiments, the firing time and temperature may also be sufficient to form a mullite layer on at least a portion of the contact surface of the pulling roll (the surface of the pulling roll that contacts the glass). A mullite layer can reduce and/or eliminate dust generation, and can result in increased hardness of the contact surface of the pulling roll (e.g., Shore D hardness), thus making the resulting pulling roll more resistant to process damage. In some embodiments, the firing time and temperature can be sufficient to form a cristobalite layer on at least a portion of the surface of the pulling roll.

[0094] After firing the assembly of compressed fired discs, the assembly can be removed from the shaft as a sleeve. It is desirable that the shaft and fittings, for example collars, be designed such that the sleeve is not damaged upon removal from the shaft. A shaft for preparing a sleeve can be designed such that the sleeve length can be controlled, for example, to match the desired length of heat resistant material for a particular pulling roll shaft onto which the sleeve will be installed. The surface of the shaft should be sufficiently smooth and free from burrs, welds, or rough areas to allow easy removal of the sleeve.

[0095] In some embodiments, the assembly of compressed fired discs can be shaped to a predetermined profile, for example by cutting, sanding, filing, scrapping, grinding or any other suitable method or combination of methods, prior to firing to form the sleeve. In other embodiments, the sleeve can be shaped after firing the compressed assembly of fired discs. Various other dimensioning steps can be performed both prior to and after firing the compressed assembly of fired discs. For example, FIG. 4 illustrates a plurality of compressed fired discs after firing, in which example the cutting has been performed after the firing, the dashed line 70 indicating an outline of material removed to produce shaped sleeve 72.

[0096] As shown in FIG. 4, sleeve 72 of fired discs can be shaped (e.g., milled) such that an outside surface of the sleeve comprises a cylindrical portion 74 including a contact surface 76 and a chamfer portion 78 comprising a chamfered portion surface 80. In embodiments, cylindrical portion 74 is positioned between two chamfered portions 78. Accordingly, contact surface 76 is positioned between a pair of chamfered portion surfaces 80. An outer perimeter of the sleeve at the contact surface extends a farther distance from the longitudinal axis 82 than do the chamfer portion surfaces. An angle a of a chamfer portion surface 80 relative to contact surface 76 can be within a range from about 16 to 20 degrees. Sleeve 72 further comprises a bore 84 extending along the longitudinal axis 82, which is a center of the sleeve and contains an axis of rotation. [0097] In further embodiments, and as shown in FIG. 5, an arcuate transition surface 86 can be formed between cylindrical contact surface 76 and chamfer portion surfaces 80. Each arcuate transition surface can comprise a radius of curvature in a range from about 1.5 cm to about 7.6 cm, although in further embodiments, the radius of curvature of the transition surfaces can be less than 1.5 cm or greater than 7.6 cm depending on need.

[0098] Sleeves can be prepared and distributed in a variety of shapes, sizes, and configurations tailored to the specific needs of customers and process lines. An inventory of such sleeves can be maintained to enable quick repair of pulling roll assemblies and thus, minimize process downtime.

[0099] In some embodiments, the present disclosure can provide a modular pulling roll, wherein the modular component is a cartridge comprising a spool and a heat resistant material disposed thereon. The heat resistant material may be a sleeve 72 formed from a compressed assembly of heat resistant discs. The heat resistant material may be formed as a compressed assembly of discs. Such a cartridge comprising compressed discs can be shaped to a desired profile. In various embodiments, the heat resistant material of a cartridge can be shaped prior to assembly, after assembly, and/or at the point of use. For example, a cartridge can be produced to a desired preliminary profile, and shipped to a point of use for final shaping and installation on a pulling roll shaft.

[00100] In embodiments, a cartridge can be prepared by cutting and/or punching discs from one or more sheets of a millboard material. The discs can then be fired for a time and at a temperature sufficient to dry the discs and remove any volatile and/or combustible components in the discs. For example, the discs can be fired such that they exhibit substantially no weight loss (e.g., < 1.5 weight percent) when exposed to the temperatures associated with a pulling roll during use and will thus be dimensionally stable under operating conditions. For example, discs can be heated at a temperature of from about 650°C to about 1,000°C, or from about 760°C to about 1,000°C, or preferably from about 900°C to about 1,000°C, and held at that temperature for a period of at least two hours, and then cooled back to room temperature before assembly into a cartridge by disposing the discs (e.g., sleeve) on a spool.

[00101] A spool of the present disclosure can be of any suitable material and/or design for use with a pulling roll. In some embodiments, a spool may comprise a ceramic material. In some embodiments, a spool can comprise a metal. In yet other embodiments, a spool comprises a material that can withstand the temperatures typically incurred during glass production and pulling roll use. In still other embodiments, a spool may comprise a material resistant or substantially resistant to oxidation or chemical attack. In other embodiments, a coefficient of thermal expansion of the spool can be matched or substantially matched (selected to be equal to or substantially equal) to at least one of the pulling roll shaft or the heat resistant discs. A suitable spool may meet any one or combination of the preceding attributes.

[00102] A spool can comprise any geometry suitable for use with a pulling roll. In embodiments, as shown in FIG. 6, a spool 88 can comprise a hollow tube 90 and a flange 92, and a locking collar, or other fittings attached to one end of tube 90 that limits movement of the heat resistant discs along tube 90. The fittings used to assemble a cartridge, and/or to locate a cartridge on a pulling roll shaft, may be like those described above relating to sleeves. In some embodiments, the locking collar, flange, or other fitting positioned on the tube 90 may include an opening in registration with the hollow portion of the tube, such that the tube can at least partially slide over a pulling roll shaft.

[00103] The discs can then be positioned onto tube 90 in a face-to-face orientation. The positioned discs can be compressed and held in place with any suitable fittings as described herein, such as, for example, a snap ring or removable collar. In some embodiments, the discs can be held in place with a snap ring and a groove for receiving and positioning such a snap ring. For example, the groove can be cut into a circumference of tube 90. After assembling and positioning the discs, the assembly can optionally be fired to remove any remaining water, volatile, and/or combustible components from the heat resistant material.

[00104] After positioning the discs on the spool 88, the discs can be axially compressed along the tube. Such a compression step can comprise any suitable technique, such as, for example, a hydraulic press. After compression, any device or means suitable for securing the discs and maintaining the compression thereof can be positioned on the spool. For example, a second flange 92 can be positioned on tube 90 and a snap ring can be positioned in a pre-cut groove on the tube to secure the second flange 92 on tube 90 and maintain compression of the discs on the spool.

[00105] Once positioned and compressed on spool 88, the discs can optionally be shaped (e.g., milled) to a desired profile. At least one of the locking collar or removable collar of a spool can optionally comprise a raised area, textured area, cones, or other means to prevent independent rotation of the heat resistant discs about the tube. Together the spool and the discs (e.g., sleeve) form a cartridge 94 that may be readily positioned on a shaft. Alternatively, instead of positioning and compressing individual discs on spool 88, a sleeve 72 may be positioned on spool 88. Accordingly, further cartridge discussion will be based on a pulling roll comprising a spool 88 including a sleeve 72 mounted thereon.

[00106] In some embodiments, a cartridge comprising a sleeve 72 can be fired and shaped to a desired dimension just prior to use as described in respect of the foregoing sleeve. In some embodiments, a cartridge can be put into service such that the operational temperatures to which the cartridge is exposed during use provide the desired hardness of the contact surface. For example, the sleeve may have or can develop a mullite layer on at least a portion of an exterior surface (e.g., contact surface) of the cartridge. In other embodiments, the sleeve may have or can develop a cristobalite layer on at least a portion of the exterior surface of the cartridge sleeve.

[00107] Referring now to FIG. 7, installation of a pulling roll 96 (e.g., cartridge 94 or, individually, sleeve 72) onto a pulling roll shaft 98 can comprise sliding pulling roll 96 onto the pulling roll shaft 98. Either one of the shaft 98 or an interior surface of tube 90 can comprise matching keys and keyways to prevent independent rotation of the cartridge or sleeve on the shaft. A retaining ring, locking collar, or other fitting or device (not shown) can then be used to keep the cartridge on the shaft and minimize movement and/or slippage. In some embodiments, fittings may be used on both ends of a pulling roll to hold it in a desired axial position on the pulling roll shaft. In other embodiments, a thread can be positioned on the pulling roll shaft whereby a threaded nut can be secured to the shaft via the threads. The threads should have a sufficiently low thread pitch (e.g., threads per inch) to prevent seizure with the retaining ring.

[00108] It has been found that the lifetime of a pulling roll assembly, and in particular a pulling roll employed in the drawing of thin glass ribbons, for example glass ribbons with a thickness equal to or less than about 0.4 millimeters, for example equal to or less than about 0.3 mm, such as equal to or less than about 0.2 millimeters, such as equal to or less than about 1 millimeter, is considerably less when compared with pulling roll assemblies used with thicker glass ribbons. In some cases, this reduction in lifetime can be greater than 60%. This reduced lifetime can lead to more frequent pulling roll changes. However, it has further been found that many of the breaks in thin glass ribbons occur within 1 day of a new pulling roll installation. Factors leading to flaw introduction into the glass ribbon by the pulling rolls can include contact pressure on the glass and roughness of the contact surface of the pulling roll.

[00109] Shown in FIGS. 8 and 9 is an apparatus 100 for processing a cylindrical contact surface 76 of a pulling roll 96 (e.g., pulling roll cartridge 94). Apparatus 100 comprises a drive assembly 102 including a drive motor 104 coupled to a spindle 106, for example through a reducing gear assembly 108, spindle 106 configured to receive pulling roll 96. For example, spindle 106 may be sized to fit within hollow tube 90. Pulling roll 96 can be mounted on spindle 106, wherein drive motor 104 rotates spindle 106, and pulling roll 96, at a predetermined rotational rate. In some embodiments, apparatus 100 may include a backing plate 110 mounted on spindle 106 and against which pulling roll 96 can be engaged. In some embodiments, backing plate 110 may be fixed to spindle 106 such that backing plate 110 turns with spindle 106 as spindle 106 rotates, although in other embodiments, backing plate may be free torn rotate on spindle 106. A compression plate 112 can then be slid over spindle 106 and urged against pulling roll 96 by a threaded nut 114 or other suitable fastening device, thereby securing pulling roll 96 to spindle 106 and against backing plate 110. Pulling roll 96 can be rotated about an axis of rotation by drive motor 104 at any suitable rotation rate, for example a rotation rate in a range from about 5 revolutions per minute to about 50 revolutions per minute (RPM), for example in a range from about 10 RPM to about 40 RPM, from about 15 RPM to about 35 RPM, for example in a range from about 20 RPM to about 30 RPM.

[00110] Apparatus 100 further comprises a tramping device 116 comprising at least one tramping roller 118 configured to be pressed against contact surface 76 with a predetermined force F along a line 119 perpendicular to contact surface 76. As used herein, "tramping" refers generally to the repeated pressing of a surface, and more specifically to the pressing of the surface of a pulling roll by a roller with a predetermined force as the tramping roller rolls over the contact surface of the pulling roll. Tramping roller 118 may be rotatably mounted in a frame 120 positioned such that tramping roller 118 can be urged against (engaged with) contact surface 76 with a predetermined force as pulling roll 96 is rotated by drive assembly 102. Tramping roller 118 can be formed from a ceramic material, for example alumina. However, in other embodiments, tramping roller 118 can be a metal roller, for example a stainless steel roller. In still other embodiments, tramping roller 188 can comprise a stainless steel roller with a ceramic (e.g., alumina) coating or layer applied thereto. During operation of apparatus 100, tramping roller 118 can be forced against contact surface 76 with a predetermined force F as pulling roll 96 is rotated. For example, in some embodiments, frame 120 may be coupled to a spring 122 that urges frame 120, and tramping roller 118, in a direction toward pulling roll 96. Alternatively, or in addition, a pneumatic or hydraulic cylinder (not shown) may be used to supply predetermined force F. In some embodiments, predetermined force F can be in a range from about 10 N to about 100 N, for example in a range from about 15 N to about 100 N, such as in a range from about 20 N to 100 N, in a range from about 30 N to about 100 N, in a range from about 40 N to about 100 N, in a range from about 50 N to about 100 N, in a range from about 60 N to about 100 N, in a range from about 70 N to about 100 N, in a range from about 80 N to about 100 N, or in a range from about 90 N to about 100 N, including all ranges and subranges therebetween.

[00111] FIG. 10 illustrates another embodiment of a tramping device 216 that may be used in conjunction with drive assembly 102, tramping device 216 comprising a frame 220 configured to press a plurality of tramping rollers 218 against contact surface 76 of pulling roll 96.

[00112] For example, tramping rollers 218 may be rotatably mounted in frame 220 and positioned such that tramping rollers 218 can be urged against (engaged with) contact surface 76 of pulling roll 96 as pulling roll 96 is rotated about an axis of rotation by drive assembly 102. As in the previous embodiment, tramping rollers 218 can be formed from a ceramic material, for example alumina. However, in other embodiments, tramping rollers 218 can be metal rollers, for example stainless steel rollers. In still other embodiments, tramping rollers 218 can be stainless steel rollers with a ceramic (e.g., alumina) layer or coating. In some embodiments, frame 220 may be coupled to a spring 222 that urges frame 220 forward with a predetermined force Fl, such that tramping rollers 218 are forced against contact surface 76 with predetermined force F as pulling roll 96 rotates, where predetermined force F is the force applied to contact surface 76 by a tramping roller 218 along a line perpendicular to contact surface 76. Alternatively, or in addition, a pneumatic or hydraulic cylinder (not shown) may be used to apply force Fl . In some embodiments, predetermined force F can be in a range from about 10 N to about 100 N, for example in a range from about 15 N to about 100 N, such as in a range from about 20 N to 100 N, in a range from about 30 N to about 100 N, in a range from about 40 N to about 100 N, in a range from about 50 N to about 100 N, in a range from about 60 N to about 100 N, in a range from about 70 N to about 100 N, in a range from about 80 N to about 100 N, or in a range from about 90 N to about 100 N, including all ranges and subranges therebetween.

[00113] It should be apparent that any number of tramping rollers can be urged against the contact surface of pulling roll 96, and the present disclosure is not limited by the number of tramping rollers illustrated.

[00114] FIG. 11 illustrates three groups of data for a sintered pulling roll including two line plots represented by curves 300 (squares) and 302 (triangles), and bar plots, for 5 different tramping times: no tramping (0 minutes), tramping for 5 minutes, tramping for 10 minutes, tramping for 15 minutes, and tramping for 60 minutes. The pulling roll comprised rounded transition surfaces with a radius of curvature of about 1.5 cm positioned between the contact surface and the chamfered portion surfaces. All tramping in FIG. 11 was performed with an apparatus like the tramping device shown in FIG. 10, wherein total force Fl was 98 N (and wherein the individual perpendicular force applied by each tramping roller against the pulling roll was 86.4 N), and pulling roll 96 was rotated at a speed of 24 RPM. Curve 300 depicts changes in hardness of contact surface 72 (plotted against the left vertical axis) as measured using a Shore indenter. The data show a small increase in hardness of the pulling roll contact surface after 60 minutes of tramping, indicating nearly stable hardness, although the small increase suggests longer tramping times may provide greater hardness gains. On the other hand, average surface roughness, represented by curve 302, showed a substantial decrease, wherein the average surface roughness Ra decreased from about 225 μιη with no tramping to about 1 μιη after 60 minutes of tramping. Ra represents the arithmetic average value of a filtered roughness profile determined from deviations about a center line within an evaluation length. Average roughness was measured using a Mitutoyo Surftest SJ-301 surface roughness tester. The data further indicate that tramping in excess of about 10 minutes yielded lesser improvement, suggesting that although additional improvement in average roughness (e.g., about 2x) can be obtained by tramping for greater than 10 minutes, if time is a consideration, then acceptable benefit may be obtainable within a shorter period of time, for example less than about a 10 minute tramping interval, and in some embodiments, less than about a 5 minute tramping interval. It should be noted that the preceding results are predicated on the conditions under which testing was conducted, and that variations in results may be obtained under different conditions.

[00115] In embodiments, one or more tramping rollers may be urged against contact surface 76 over a circumferential distance on the contact surface of equal to or greater than a one circumference of the contact surface as the pulling roll is rotated. In some embodiments, the circumferential distance over which the tramping roller(s) travel on the contact surface can be at least 5000 cm. However, it should be noted that the circumferential distance over which a tramping roller should be applied against a pulling roll contact surface is dependent upon at least the material of the pulling roll, the size (e.g., diameter) of the pulling roll contact surface, and the predetermined force F applied against the pulling roll contact surface by the tramping roller. Accordingly, in some embodiments, a minimum circumferential distance can be less than 5000 cm, whereas in other embodiments, the minimum

circumferential distance can be more than 5,000 cm, for example equal to or greater than 8,000 cm, equal to or greater than 10,000 cm, or equal to or greater than 15,000 cm equal to or greater than 20,000 cm, equal to or greater than 40,000 cm, or even equal to or greater than 60,000 cm, for example in a range from about 5,000 cm to about 100,000 cm, including all ranges and subranges therebetween. For example, a tramping roller applied against a pulling roll contact surface with a circumference of 44 cm rotated at a rate of 24 RPM for 60 minutes will have traveled a circumferential distance greater than 63,000 cm (approximately 63,360 cm).

[00116] The bar plot of FIG. 11 depicts the failure stress of glass samples based on a ring- on-ring test. Testing was performed as follows. Samples of Corning® Eagle XG® glass measuring 2.5 cm x 2.5 cm were prepared and held against a rotating pulling roll with a force of 49 Newtons for a period of 0.2 seconds. The samples were then tested for failure strength using a ring-on-ring measurement in accordance with ASTM C1499-09. The data show an almost 200% increase in failure strength when samples exposed to an un-tramped pulling roll are compared to an identical pulling roll that was tramped for 5 minutes (120.2 MPa vs. about 210 MPa), with only small variations for tramping times thereafter. Overall, the data from FIG. 11 show that tramping improves average surface roughness of a refractory pulling roll thereby decreasing the occurrence of sharp surface protrusions that might damage the glass, and further, increasing the strength of the glass surface contacted by the pulling roll contact surface. FIG. 12 illustrates two photographs of a pulling roll (a) before tramping, and (b) after tramping, highlighting an increased uniformity of the surface evident from the more linear interface between the contact surface and the adjoining chamfer portion surface.

[00117] FIG. 13 depicts a bar plot showing the results of strength testing indicated by the average failure stress for a glass sample applied against a pulling roll as in the testing for FIG. 11, without tramping (non-treated, and without arcuate transition surfaces), a pulling roll without tramping (and without an arcuate transition surfaces) and with a simulated splay angle a in a horizontal direction orthogonal to the draw direction 60 (i.e., wherein a rotational axis of the pulling roll was angled to the plane of the glass sample by 5 degrees), a pulling roll (including an arcuate transition surfaces comprising a radius of curvature of 1.5 cm) positioned between the contact surface of the pulling roll and the chamfer portion surface) that had been tramped for 60 minutes, a pulling roll (including arcuate transition surfaces comprising a radius of curvature of 1.5 cm) that had been tramped for 60 minutes, and which included a 5 degree splay angle a relative to the glass sample surface, and a pulling roll (including arcuate transition surfaces comprising a radius of curvature of 1.5 cm) positioned between the contact surface of the pulling roll and the chamfer portion surface. FIG. 14A depicts, by way of example, a top view of a pair of pulling roll assemblies 64 pinching a glass ribbon therebetween, the pulling roll assemblies exhibiting splay. It should be clear that splay can cause edges of the pulling rolls 96 (e.g., transition surfaces 86) to bear directly on the glass surfaces. A close-up view of the contact region, labeled as region "A" in FIG. 14 A, is shown in FIG. 14B. The use of an arcuate transition surface avoids a sharp interface between contact surface 76 and chamfer portion surface 80 that can result in an increased risk of damage to the glass ribbon 58. In the absence of arcuate transition surfaces, that is, if the interface between a contact surface and a chamfer surface is a sharp edge (see for example, FIG. 15 A), damage to the glass can be incurred, especially if an average surface roughness is large, e.g., greater than about 9 μιη. A close-up view of the contact region, labeled as region "B" in FIG. 15 A, is shown in FIG. 15B.

[00118] The test setup used to generate the data for FIG. 13 was the same as used to generate the data for FIG. 11 : The pulling roll had a 13.2 cm diameter contact surface and was rotated as a rate of 24 RPM during tramping. The force Fl applied to the frame

(comprising two tramping rollers) during tramping was 98 N. After tramping, glass samples were held against the pulling roll (still rotating at a rate of 24 RPM) with a force of 49 N for 0.2 seconds. The glass samples were subsequently tested using a ring-on-ring testing procedure.

[00119] The data from FIG. 13 show that without arcuate transition surfaces (e.g., rounded edges), a 5 degree splay wherein the glass samples were exposed to the non-rounded edges at the junction between the contact surface and the chamfer portion surfaces resulted in a decline in failure stress (decline in glass strength).

[00120] It will be apparent to those skilled in the art that various modifications and variations can be made to embodiments of the present disclosure without departing from the spirit and scope of the disclosure. For example, while the methods described herein have been discussed in the context of glass ribbons with a centerline thickness of equal to or less than 0.4 mm, it should be readily apparent that benefits described herein can be applicable to glass ribbons with a greater thickness, for example in a range from greater than 0.4 mm to equal to or less than 0.5 mm, in a range from greater than 0.4 mm to equal to or less than 0.6 mm, in a range from greater than 0.4 mm to equal to or less than 0.7 mm, in a range from greater than 0.4 mm to equal to or less than 0.8 mm, or even greater, such as in a range from greater than 0.4 mm to at least 2 mm. 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 method of processing a pulling roll for a glass manufacturing process comprising: rotating the pulling roll about an axis of rotation; and

during the rotating, contacting a contact surface of the pulling roll with a tramping roller with a predetermined force F.

2. The method according to claim 1, wherein a circumferential distance traveled over the contact surface by the tramping roller during the contacting is equal to or greater than a circumference of the contact surface.

3. The method according to claim 2, wherein the circumferential distance traveled over the contact surface by the tramping roller is equal to or greater than about 5,000 cm.

4. The method according to claim 2 or claim 3, wherein the circumferential distance traveled over the contact surface by the tramping roller is in a range from about 5,000 cm to about 70,000 cm.

5. The method according to any one of claims 1 to 4, wherein the contact surface is joined to a chamfer surface of the pulling roll by a transition surface, the transition surface comprising a radius of curvature in a range from about 1.5 cm to about 7.6 cm.

6. The method according to any one of claims 1 to 5, wherein the predetermined force F is in a range from about 13 N to about 147 N.

7. The method according to claim 6, wherein the predetermined force F is in a range from about 49 N to about 118 N.

8. The method according to any one of claims 1 to 7, wherein after the contacting, an average surface roughness Ra of the contact surface is equal to or less than 2 μιη.

9. The method according to any one of claims 1 to 8, wherein the tramping roller comprises alumina.

10. The method according to any one of claims 1 to 9, wherein a diameter of the tramping roller is less than a diameter of the contact surface.

11. The method according to any one of claims 1 to 10, further comprising mounting the pulling roll to a shaft of a pulling roll assembly after the contacting.

12. The method according to claim 11, further comprising drawing a glass ribbon with the pulling roll assembly after the mounting.

13. The method according to claim 12, wherein a thickness of the glass ribbon at a centerline of the glass ribbon is equal to or less than 0.7 mm.

14. The method according to claim 13, wherein the thickness is equal to or less than 0.4 mm.

15. The method according to any one of claims 1 to 14, wherein the contacting comprises a contacting the contact surface of the pulling roll with plurality of tramping rollers.

16. A method of processing a pulling roll for a glass manufacturing process comprising: rotating the pulling roll about an axis of rotation; and

during the rotating, contacting a contact surface of the pulling roll with a tramping roller with a predetermined force F in a range from about 13 N to about 147 N.

17. The method according to claim 16, wherein the predetermined force F is in a range from about 49 N to about 118 N.

18. The method according to claim 16, wherein the predetermined force F is in a range from about 78 N to about 118 N.

19. The method according to any one of claims 16 to 18, wherein the contacting is performed for greater than zero minutes but equal to or less than about 60 minutes.

20. The method according to any one of claims 16 to 19, wherein the contacting is performed for equal to or greater than 5 minutes but equal to or less than about 15 minutes.

21. The method according to any one of claims 16 to 20, wherein the contacting comprises contacting the contact surface with a plurality of tramping rollers.

22. The method according to claim 16, wherein after the contacting, an average surface roughness Ra of the contact surface is equal to or less than 2 μιη.

23. The method according to claim 16, wherein after the contacting, an average surface roughness Ra of the contact surface is equal to or less than 1 μιη.

24. The method according to any one of claims 16 to 23, wherein the contact surface is joined to a chamfer surface of the pulling roll by a transition surface comprising a radius of curvature in a range from about 1.5 cm to about 7.6 cm.

25. The method according to any one of claims 16 to 24, further comprising mounting the pulling roll to a shaft of a pulling roll assembly after the contacting.

26. The method according to claim 25, further comprising drawing a glass ribbon with the pulling roll assembly after the mounting.

27. The method according to claim 26, wherein a thickness of the glass ribbon at a centerline of the glass ribbon is equal to or less than about 0.7 mm.

28. The method according to claim 27, wherein the thickness is equal to or less than about 0.4 mm.

29. A method of processing a pulling roll for a glass making process, comprising:

positioning a plurality of fired discs of a millboard material in a face-to-face

relationship;

axially compressing the plurality of fired discs;

firing the axially compressed plurality of fired discs to fuse at least a portion of the plurality of fired discs together to form a pulling roll; and milling an exterior surface of the pulling roll to a predetermined profile comprising a cylindrical portion including a cylindrical contact surface, and a chamfer portion comprising a chamfer portion surface, wherein a transition surface positioned between the cylindrical contact surface and the chamfer portion surface comprises a radius of curvature in a range from about 1.5 cm to about 7.6 cm.

30. The method according to claim 29, further comprising:

rotating the pulling roll about an axis of rotation;

31. The method according to claim 30, wherein the predetermined force F is in a range from about 13 N to about 147 N.

32. The method according to claim 30 or claim 31, wherein a circumferential distance traveled over the contact surface by the tramping roller during the contacting is equal to or greater than a circumference of the contact surface.

33. The method according to claim 30 or claim 31, wherein a circumferential distance traveled over the contact surface by the tramping roller during the contacting is greater than 5,000 cm.

34. The method according to any one of claims 29 to 33, further comprising mounting the pulling roll to a shaft of a pulling roll assembly after the contacting.

35. The method according to claim 34, further comprising drawing a glass ribbon with the pulling roll assembly after the mounting.

36. The method according to claim 35, wherein a thickness of the glass ribbon at a centerline of the glass ribbon is equal to or less than about 0.4 mm.