Method of treating a glass ribbon and apparatus therefor

Abstract

A method and apparatus for forming and processing glass ribbons. The apparatus includes a processing roller and an edge roller that contacts an edge portion of a glass layer disposed on the processing roller. The edge roller cools the edge portion of the glass layer, and the cooled edge portion acquires increased viscosity compared to the central portion of the glass layer. Embodiments may include a second edge roller that contacts and cools opposing edge portions of the glass layer. The cooled edge portion can resist lateral shrinkage of the glass layer and the glass ribbon formed therefrom.

Description

Technical Field

[0001] This application claims priority to U.S. Provisional Application Serial No. 63 / 246,979, filed on September 22, 2021, the contents of which are incorporated herein by reference in their entirety.

[0002] This disclosure relates to a method for processing glass ribbons, and more specifically, to a method for reducing the shrinkage of glass ribbons in the width direction. An apparatus for carrying out this method is also disclosed. Prior Technology

[0003] One known method of processing molten glass involves passing molten glass over at least a portion of the circumference of a processing roller, during which a layer of molten glass on the roller is cooled and released. The molten glass layer can be drawn from the processing roller by a pull roller located below it, which applies downward tension to the molten glass to produce a glass ribbon of desired thickness. As the molten glass layer cools on and below the processing roller, the molten glass layer and the glass ribbon can shrink along the width direction of the glass, thereby reducing the total width of the glass ribbon and thus the usable width of the glass ribbon. Summary of the Invention

[0004] Figure 1 is a schematic diagram of a glass forming apparatus in which a stream of molten glass 10 is supplied from a container 12 configured to convey the molten glass to a processing roller 14. The molten glass stream is released from the processing roller and drawn downward by a pair of counter-rotating pull rollers 16. As the layer of molten glass in contact with the processing roller cools, contraction forces (e.g., surface tension) may cause the relative edges 18 and 22 of the glass stream to taper inward, as indicated by arrow 24, increasing the thickness of edges 18, 22 and reducing the overall width of the molten glass layer. This contraction can continue until the temperature of the glass ribbon becomes sufficiently low (and the edges of the glass ribbon are sufficiently hardened) so that no further contraction occurs. The thickened edge portions of the glass ribbon are unsuitable for sale and must be removed, further reducing the usable width 26 of the glass ribbon and the sheet of glass removed from it.

[0005] Therefore, a method for forming a glass ribbon while minimizing width shrinkage is disclosed. This method includes the following steps: flowing a molten glass stream on the outer surface of a processing roller, the processing roller rotating about a first rotation axis in a first rotation direction, the molten glass stream forming a molten glass layer on the outer surface of the processing roller; contacting an edge portion of the molten glass layer on the processing roller with a first edge roller, the first edge roller rotating about a second rotation axis in a second rotation direction opposite to the first rotation direction, the contact cooling the edge portion and increasing its viscosity, the molten glass layer leaving the processing roller as a molten glass ribbon. The first edge roller does not contact a central portion of the molten glass layer. The molten glass stream may, for example, flow from a forming body. In some embodiments, the forming body may include a slot from which the molten glass stream exits. In other embodiments, the forming body may include a forming wedge comprising a trough located in the upper surface of the forming body and a pair of inclined forming surfaces converging along the bottom edge of the forming wedge. Molten glass overflows from the trough, descends along the converging forming surfaces, and merges at the bottom edge to form a glass stream.

[0006] The method further includes drawing a molten glass ribbon from a processing roll along a stretching direction between a pair of pull rollers, the pull rollers engaging an edge portion on an opposite side below the processing roll of the glass ribbon. In various embodiments, the method may further include contacting the edge portion through a pair of edge rollers positioned between the processing roll and the pair of pull rollers, the pair of edge rollers further cooling the edge portion.

[0007] The surface of the first edge roller can be cooled by the flow of cooling fluid inside the edge roller.

[0008] The diameter of the processing roller can range from approximately 5 cm to approximately 31 cm. The length of the processing roller can range from approximately 25 cm to approximately 400 cm.

[0009] The diameter of the first edge roller can range from approximately 2.5 cm to approximately 8 cm. The length of the first edge roller can range from approximately 1 cm to approximately 26 cm.

[0010] The processing roller includes a top portion defined at an angular position of 0 degrees. A first edge roller may contact the edge portion at an angular position on the processing roller within the range of approximately 35 degrees to approximately 90 degrees in the direction of rotation of the processing roller relative to the 0-degree position.

[0011] The first edge roller can move along the second rotation axis.

[0012] The molten glass layer may include a first viscosity at a first point on an edge portion and a second viscosity at a center point of the molten glass layer on a horizontal line extending orthogonally to the stretching direction, and a viscosity ratio defined as between the viscosity of the molten glass layer at the first point and the viscosity of the molten glass layer at the center point may be in the range of about 1 to 100, for example in the range of about 1 to about 30, for example in the range of about 1 to about 16, for example in the range of about 5 to about 15.

[0013] A method for forming a glass ribbon is disclosed, comprising the steps of: flowing molten glass on the outer surface of a processing roller, the processing roller rotating about a first rotation axis in a first rotation direction via a first motor, the molten glass flow forming a molten glass layer on the outer surface of the processing roller; contacting an edge portion of the molten glass layer on the processing roller with a first edge roller, the first edge roller rotating about a second rotation axis in a second rotation direction opposite to the first rotation direction via a second motor, the contact cooling the edge portion and increasing its viscosity, the molten glass layer comprising a first viscosity at a first point on the edge portion and a second viscosity at a center point of the molten glass layer on a horizontal line extending orthogonal to a stretching direction, and a viscosity ratio defined as the ratio between the viscosity of the molten glass layer at the first point and the viscosity of the molten glass layer at the center point being in the range of about 1 to about 16, the molten glass layer leaving the processing roller as a molten glass ribbon. The method further comprises stretching the molten glass ribbon from the processing roller in a stretching direction between a pair of pull rollers, the pair of pull rollers engaging opposite edge portions of the glass ribbon below the processing roller. The first edge roller does not contact the center portion of the molten glass layer.

[0014] The processing roller can extend across the entire width of the molten glass layer in a direction orthogonal to the stretching direction.

[0015] The viscosity of the molten glass flow at the processing roll can range from about 10 9.9 poise to about 10 11.2 poise.

[0016] The foregoing general description and the following detailed description are intended to present an overview or framework of embodiments for understanding the nature and characteristics 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 this disclosure and, together with the detailed description, explain their principles and operation. Simple Explanation of the Diagram

[0017] Figure 1 is a front view of an exemplary molten glass processing apparatus;

[0018] Figure 2 is a schematic diagram of an exemplary glass manufacturing apparatus according to an embodiment of the present disclosure;

[0019] Figure 3 is a front view of an exemplary molten glass forming and processing apparatus according to an embodiment of the present disclosure, wherein a stream of molten glass from a forming body is supplied to a processing roller, the forming body including grooves that can be used in the glass manufacturing apparatus of Figure 2;

[0020] Figure 4 is a front view of an exemplary molten glass forming and processing apparatus according to an embodiment of the present disclosure, wherein a stream of molten glass from a forming body is supplied to a processing roller, the forming body including a converging forming surface that can be used in the glass manufacturing apparatus of Figure 2;

[0021] Figure 5 is a front view of an exemplary molten glass processing apparatus;

[0022] Figure 6 is a cross-sectional view of an exemplary edge roller;

[0023] Figure 7 is a schematic diagram of an exemplary processing roller, showing the position of an edge roller configured to contact an edge portion of the molten glass layer disposed on the processing roller;

[0024] Figure 8 is a schematic diagram of a portion of the edge section, showing the edge roller movable along the rotation axis of the edge roller;

[0025] Figure 9 is a graph showing the modeling results, displaying the strip width in millimeters as a viscosity function from edge to center for five different glass ribbon center viscosities; and

[0026] Figure 10 is a graph showing the glass ribbon width as a function of the viscosity from the edge to the center of the glass ribbon. Implementation

[0027] The embodiments of this disclosure will now be described in detail with reference to examples shown in the accompanying drawings. Wherever possible, the same element symbols will be used in all drawings to indicate the same or similar parts. However, this disclosure may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein.

[0028] When used in this paper, the term approximate means that quantities, sizes, formulations, parameters, and other quantities and characteristics are not and need not be precise, but can be approximate and / or greater or smaller as necessary, reflecting similar factors such as tolerance, conversion factor, rounding, measurement error, and other factors known to those generally familiar with the technique.

[0029] The range may be expressed herein as from “about” one particular value, and / or “about” to another particular value. When expressing such a range, another embodiment includes going from one particular value to another. Similarly, the particular value will be understood to form another embodiment when the value is represented as an approximation by the use of the antecedent “about”. It should be further understood that the endpoints of each scope are significant with respect to the other endpoint as well as independently of the other endpoint.

[0030] The directional terms used in this paper—e.g., up, down, right, left, front, back, top, bottom—are made in reference only to the directions drawn and are not intended to imply absolute directions.

[0031] Unless expressly stated otherwise, any method articulated herein is in no way intended to be construed as requiring its steps to be performed in a particular order, nor is it imply that for any equipment a particular direction is required. Thus, if the method requisition does not actually state the sequence to be followed by its steps, or any equipment requisition does not actually state the order or direction of a single part, or the requisition or description does not otherwise specify that the steps should be restricted to a particular order, or is not noted for the particular order or direction of the parts of the equipment, it in no way means that the order or direction can be inferred in any respect. This applies to any possible non-explicit basis of interpretation, including logical lessons relating to step scheduling, operating flow, part sequence, or part orientation;simple implications derived from syntactic organization or punctuation, and;the number or type of embodiments described in the instructions.

[0032] When used herein, the singular forms “one,” “one,” and “the” contain plural references, unless the context otherwise expressly dictates. Thus, as an example, references to “one” part include states having two or more such parts unless the context otherwise explicitly indicates.

[0033] The terms "exemplary," "representative," or their various forms are used herein to denote examples, instances, or illustrations. Any form or design described herein as "exemplary" or "representative" should not be construed as preferred or superior to any other form or design. Furthermore, examples are provided solely for clarity and understanding and are not intended to limit or constrain the disclosed subject matter or any part thereof in any way. It should be understood that numerous additional or alternative examples with varying degrees of variation may have been presented, but have been omitted for the sake of brevity.

[0034] When used herein, unless otherwise stated, the terms "comprising" and "including" and their variations shall be interpreted as synonyms and open-ended. The list of elements following the transitional terms "comprising" or "including" is a non-exclusive list, allowing for the existence of elements other than those specifically described in the list.

[0035] The terms “substantially,” “substantially,” and variations thereof, as used herein, are intended to indicate that the described feature is equal to or approximately equal to a value or description. For example, a “substantially flat” surface is intended to mean a flat or approximately flat surface. Furthermore, “substantially” is intended to mean that two values ​​are equal or approximately equal. In some embodiments, “substantially” may mean values ​​that differ from each other by about 10%, such as about 5% or about 2%.

[0036] When used below, a distinction is made between molten glass stream (e.g., stream or glass flow), molten glass layer (e.g., glass layer), and glass ribbon (e.g., glass ribbon). As used herein, molten glass stream refers to the stream of molten glass from the forming body before contact with the downstream processing roll. The forming body can be the discharge end of a conduit or pipe, a narrow discharge groove, such as in a refractory or metal body, or a fused forming body from which molten glass overflows from a groove and flows down as a stream from the bottom edge of the body. For illustrative purposes, the molten glass will be referred to as a molten glass layer when in contact with the processing roll, but as a glass ribbon after being released from the surface of the processing roll. Thus, for illustrative purposes, three stages of molten glass are distinguished: after discharge from the forming body (glass stream, glass flow, molten glass stream, etc.), during contact with the processing roll (glass layer), and after being released from the processing roll (glass ribbon).

[0037] When used herein, unless otherwise stated, the terms "molten glass," "glass," and glass streams, glass layers, and glass ribbons refer to non-elastic viscous materials that can be cooled to form amorphous, elastic, glassy materials, such as silicate glass or other inorganic glass materials.

[0038] The method disclosed herein for manufacturing glass sheets having two opposing primary surfaces, at least one of which has a high surface quality, using roller surfaces to treat glass, is, though not limited, particularly suitable for such manufacturing on glass having a low liquidus viscosity, for example, glass having a liquidus viscosity below about 20,000 Pa·s. When used herein, the term "liquidus viscosity" refers to the viscosity of molten glass at its liquidus temperature, which is the temperature at which crystals first appear when the molten glass is cooled from its melting temperature, or the temperature at which the last crystals melt as the temperature increases from room temperature. Unless otherwise stated, the liquidus viscosity values ​​disclosed herein are determined by the following method: First, the liquidus temperature of the glass is measured according to ASTM C829-81 (2015), entitled "Standard Practice for Measuring the Liquidus Temperature of Glass by Gradient Furnace Method". Then, the viscosity of the glass at the liquidus temperature is measured according to ASTM C965-96 (2012), entitled "Standard Practice for Measuring the Viscosity of Glass Above its Softening Point".

[0039] The method disclosed herein may include the following steps: conveying a stream of molten glass as a molten glass layer onto a processing device (e.g., a processing roller); processing the molten glass layer with the processing device, the processing device being adapted to temporarily support the weight of the molten glass layer, increase its viscosity while accompanying the molten glass layer's descent, and maintain at least a central portion of one of its two principal surfaces so as not to contact the surface of the processing device; acting on a glass ribbon released from the processing device using appropriate means or mechanisms to control its movement speed and the width and / or thickness of the glass ribbon; and cooling the glass ribbon.

[0040] Molten glass streams can be generated without any contact after leaving the forming body and can be rapidly carried away before the glass stream becomes mechanically unstable, with a significant increase in viscosity. This instability can manifest in various forms, including variations in the width of the molten glass stream, lateral "walking" of the stream, separation of the stream into individual, distinct segments, and so on. The stream can be controlled and cooled to obtain a glass ribbon in which one of the main surfaces is not in contact with any surface, at least in its central portion.

[0041] As measured according to ASTM C829-81 (2015), the molten glass flow can be from about 5 Pa·s to about 5,000 Pa·s (about 50 poises to about 50,000 poises), for example, about 5, 7, 9, 10, 15, 20, 40, 50, 80, 100, 200, 400, 700, 1,000, 1,500, 2,000, 2,500, 3,000, 3,500, 4,000, 4,500 or 5,000 Pa·s, for example, in the range from about 10 Pa·s to 1,000 Pa·s (100 poises to 10,000 poises), for example, 10, 15, 20, 40, 50, 80, 100, 200, 400, 700 or 1,000 Pa·s.

[0042] The molten glass stream may have two main surfaces that do not contact any surface between the outlet of the conveying device and the processing device. When conveyed in this manner, the molten glass stream falls under the influence of gravity. The height of the molten glass stream's fall is limited because it should be carried away before becoming unstable. The acceptable fall height between the outlet of the glass stream conveying device and the processing device depends on the glass composition and its dimensions in question. Generally, the fall height does not exceed 150 millimeters (mm). For example, the fall height can be less than 60 millimeters. Given a specific glass composition and dimensions, those skilled in the art can generally optimize the fall height, for example, in implementing the conveying of molten glass. In an exemplary embodiment, for molten glass having a viscosity of about 100 Pa·s and wherein the thickness of the conveyed stream is about 3 mm, the maximum fall height can be about 10 mm.

[0043] According to the embodiments disclosed herein, the method may include processing a conveyed stream of molten glass. Before it becomes unstable, the molten glass stream can be carried away by the processing device under conditions that do not in themselves cause instability, and ensure that at least a central portion of one of the glass's main surfaces remains uncontacted with any other surface. This main surface may remain uncontacted or substantially uncontacted with another material. If any contact occurs, it can be confined to the edge portions of the stream. The glass may be processed such that at the end of the processing the molten glass is more viscous than when it was conveyed upstream, thereby stabilizing the stream.

[0044] The processing of the conveyed molten glass stream can include receiving the stream as a layer of molten glass on the surface of a processing roll, the processing roll having a suitable surface temperature and rotating in a suitable direction and at a suitable speed to accompany the movement of the molten glass layer, and the molten glass layer having no relative displacement with respect to the surface of the processing roll. The minimum permissible speed of the processing roll can be determined at least in part by the glass stream density and the distance between the exit point of the molten glass stream conveyed from the forming body and the top dead point (TDC) of the processing roll. For example, the minimum permissible rotational speed of the processing roll can be a rotational speed at the surface of the processing roll that results in a linear stretching rate of about 0.4 cm / min for the glass ribbon drawn from it. The upper limit of the stretching rate can be 250 cm / min or higher, or until the molten glass stream between the root and the processing roll becomes unstable.

[0045] The surface temperature of the processing roll can range from approximately 200°C to approximately 800°C and can vary depending on the thermal environment of the processing roll and the temperature of the molten glass layer. The processing roll can be associated with means or mechanisms for controlling the surface temperature of the processing roll and thus the temperature of the molten glass layer in contact with it. The processing roll can be appropriately positioned and driven to ensure contact with the molten glass layer and sufficient cooling of the molten glass layer, thereby achieving the desired viscosity increase, and the contact between the molten glass layer and the processing roll can be maintained without any relative displacement between them over a large portion of the roll's circumference.

[0046] The treated glass layer can be maintained such that at least the central portion of one main surface of the layer remains in contact with another surface, for example, by edge rollers and / or pull rollers.

[0047] When the glass stream comes into contact with a roller, such as a processing roller, an adhesion develops between the glass and the roller. The nature and magnitude of this adhesion can vary depending on the specific composition of the glass and the roller, as well as factors such as the surface texture of the roller material, the contact pressure of the glass layer on the roller surface, the contact time, and the temperature of the molten glass and the roller. Adhesion can result from Van der Waals-type interactions at the glass-roller interface. If the adhesion is too strong, the contacting glass cannot be released, or cannot be released without damaging either the glass or the roller. If the adhesion is too weak, the glass will slide relative to the roller surface, leading to variations in glass thickness and / or damage to the glass.

[0048] The adhesion between the roller and the molten glass layer can be used to compensate for the natural downward force of gravity on the molten glass layer during the manufacturing process. The adhesion between the molten glass layer and the roller can include one or more individual forces acting together. For example, in addition to the adhesion of the molten glass layer to the roller surface, orthogonal and / or tangential forces can act on the molten glass layer in the direction of adhesion. The adhesion force per unit area can be determined by those skilled in the art and is then used to determine the maximum orthogonal and / or tangential force that the glass layer can withstand without causing separation of the molten glass layer from the roller. For example, the determination of the tangential force can be made if the coefficient of static friction between the glass layer and the roller surface is known.

[0049] There is a relationship between the viscosity of the molten glass layer in contact with the roller and the potential adhesion between the molten glass layer and the roller after contact. Therefore, it is expected that the adhesion between the molten glass layer and the roller can be controlled by controlling the interface temperature between the molten glass layer and the roller.

[0050] The viscosity of the molten glass layer in contact with the roll (e.g., the processing roll) can vary depending on the glass composition and the method employed in a particular roll design. While not intended to be limiting, the viscosity of the molten glass layer in contact with the roll can generally be in the range of about 10⁸ Pa·s to about 10¹⁰ Pa·s, for example, about 1 x 10⁸, 5 x 10⁸, 1 x 10⁹, 5 x 10⁹, or 1 x 10¹⁰ Pa·s. Glass layers with a viscosity less than about 10⁸ Pa·s may exhibit irreversible adhesion between the molten glass layer and the roll. Glass layers with a viscosity of about 10⁹ Pa·s may exhibit moderate adhesion. Molten glass layers with a viscosity greater than about 10¹⁰ Pa·s may have no or substantially no adhesion between the molten glass layer and the roll.

[0051] The interface temperature between the molten glass layer and the roll can be controlled during the manufacturing process, thereby controlling adhesion. Specific glass manufacturing systems, particularly rolls such as those used for handling, can utilize any suitable method to control the surface temperature of the roll, thereby controlling the interface temperature and the viscosity of the resulting glass layer. This method includes any one or more of the methods described herein in various embodiments. The roll may include at least one channel within which a cooling fluid, such as air and / or water, can flow. As an additional or alternative to the cooling channel, other means and / or mechanisms can be used to control the surface temperature of the roll. For example, the roll may be hollow, allowing air and / or water to flow through, be sprayed, or otherwise applied to the inner wall of the roll. At least one set of external cooling nozzles can be used to control or partially control the surface temperature of the roll. Thermal control of the roll surface temperature can be achieved through radiation, convection, and / or conduction on at least a portion of the roll that is not in contact with the molten glass layer.

[0052] Therefore, the processing steps may include adjusting and controlling the temperature of a roller, such as a processing roller, before and / or simultaneously with contact with the molten glass layer, such that the molten glass layer in contact with the roller surface has a viscosity in the range of about 10⁸.9 Pa·s to about 10¹⁰.2 Pa·s, to achieve reversible adhesion between the processing roller and the molten glass layer. The adhesion should be reversible during the time period from the point where the molten glass stream first contacts the processing roller to the point where the glass layer is released from contact with the processing roller as a glass ribbon. The processing or processing steps may further optionally include adequately maintaining and / or reheating the contacting glass, thereby enabling any subsequent re-stretching (thinning) of the glass. The viscosity of the molten glass layer at the surface of the processing roller can first be determined by determining a viscosity versus temperature profile of the specific glass composition used. The temperature of the molten glass layer on the processing roller can then be measured, for example, using an optical pyrometer, and the viscosity of the molten glass can be calculated based on the previously determined viscosity versus temperature profile.

[0053] To effectively stabilize low liquidus viscosity glass, various techniques can be used to modify the tensile force applied between the roll and the molten glass layer in contact with it. In a first example, the surface area of ​​the interface between the roll and the molten glass layer in contact with it can be varied to provide cooling regulation. Accordingly, the surface of the roll can be roughened to have an average roughness (Ra) in the range of 0 to approximately 25 micrometers, determined using a surface photometer, where the average roughness is the arithmetic mean of the filter roughness profile determined by deviations around a centerline in the evaluation length. In a second example, the glass can be conveyed to different positions on the roll and / or from different directions. In a third example, tensile forces can be applied in different directions. For example, when the molten glass layer is released from the processing roll, pulling the roll and / or edge rolls can be used to prevent lateral shrinkage (tapering) of the glass belt. Each of these examples can be used individually or in any combination.

[0054] Figure 2 shows an exemplary glass manufacturing apparatus 100. The glass manufacturing apparatus 100 includes a glass furnace 102, which includes a melting vessel 104. In addition to the melting vessel 104, the glass furnace 102 may optionally include one or more additional components, such as heating elements (e.g., burners and / or electrodes) configured to heat the raw material and convert it into molten glass.

[0055] The glass furnace 102 may include other thermal management devices (e.g., insulation components) to reduce heat loss from the melting vessel. The glass furnace 102 may include electronic and / or electromechanical devices that facilitate melting raw materials into molten glass. The glass furnace 102 may include a support structure (e.g., a support chassis, support members, etc.) or other components.

[0056] The melting vessel 104 can be formed of a refractory material such as a refractory ceramic material, for example, a refractory ceramic material including alumina or zirconium oxide, although the refractory ceramic material may include other refractory materials, such as yttrium (e.g., yttrium oxide, yttrium oxide-stabilized zirconium oxide, yttrium phosphate), zircon (ZrSiO4), or alumina-zirconia-silica or even chromium oxide, which may be used alternately or in any combination. In some examples, the melting vessel 104 may be constructed of refractory ceramic bricks.

[0057] A glass furnace 102 may be incorporated as a component of a glass manufacturing apparatus configured to manufacture glass objects, such as glass ribbons. However, the glass manufacturing apparatus may also be configured to form other glass objects, such as glass rods, glass tubes, glass sleeves (e.g., glass sleeves for lighting devices, such as light bulbs), and glass lenses, although many other glass objects are also contemplated. The furnace may be included in a glass manufacturing apparatus, including slot draw equipment, float bath equipment, down-drawing equipment (e.g., fusion down-drawing equipment), up-drawing equipment, pressing equipment, rolling equipment, tube drawing equipment, or any other glass manufacturing apparatus that may benefit from this disclosure.

[0058] Glass manufacturing equipment 100 may optionally include upstream glass manufacturing equipment 106 located upstream of melting vessel 104. In some examples, a portion or all of upstream glass manufacturing equipment 106 may be incorporated as part of glass furnace 102.

[0059] As shown in Figure 2, the upstream glass manufacturing equipment 106 may include a raw material storage tank 108, a raw material conveying device 110, and a motor 112 connected to the raw material conveying device 110. The raw material storage tank 108 may be configured to store a predetermined amount of raw material 116, which may be fed into the melting vessel 104 of the glass furnace 102 via one or more inlets, as indicated by arrow 118. The raw material 116 typically contains one or more glass-forming metal oxides and one or more modifiers. In some examples, the raw material conveying device 110 may be powered by the motor 112 to convey a predetermined amount of raw material 116 from the raw material storage tank 108 to the melting vessel 104. In a further example, the motor 112 may power the raw material conveying device 110 to introduce the raw material 116 at a controlled rate based on a level of molten glass sensed downstream of the melting vessel 104 relative to the flow direction of the molten glass. The raw material 24 in the melting vessel 104 is then heated to form molten glass 120. Typically, in the initial melting step, raw material 116 is added to the melting vessel 104 in granular form, such as as various "sand grains". Raw material 116 may also include waste glass (i.e., sharded glass) from previous melting and / or forming operations. A burner is typically used to initiate the melting process. In the electro-assisted melting process, once the resistance of the raw material is sufficiently reduced, electro-assisted melting begins by generating a potential between the electrodes in contact with the raw material, thereby establishing a current through the raw material, which typically enters or is in a molten state. When used herein, the resulting molten material should be referred to as molten glass 120.

[0060] The glass manufacturing apparatus 100 may optionally include a downstream glass manufacturing device 122, which is positioned downstream of the glass furnace 102 relative to the flow direction of the molten glass 120. In some examples, a portion of the downstream glass manufacturing device 122 may be incorporated into the glass furnace 102. However, in some cases, the first connecting conduit 124 discussed below or other portions of the downstream glass manufacturing device 122 may be incorporated into the glass furnace 102.

[0061] Downstream glass manufacturing equipment 122 may include a first conditioning (i.e., processing) chamber, such as a refining vessel 126, located downstream of the melting vessel 104 and coupled to the melting vessel 104 via the aforementioned first connecting conduit 124. In some examples, molten glass 120 may be gravity-fed from the melting vessel 104 to the refining vessel 126 via the first connecting conduit 124. However, it should be understood that other conditioning chambers may be located downstream of the melting vessel 104, for example, between the melting vessel 104 and the refining chamber 126. Conditioning chambers may be used between the melting vessel and the refining chamber. For example, molten glass from the primary melting vessel may be further heated in a secondary melting (conditioning) vessel or cooled in the secondary melting vessel to a temperature lower than the temperature of the molten glass in the primary melting vessel before entering the refining vessel.

[0062] As described above, gases can be removed from the molten glass 120 using various techniques. For example, raw material 116 may include a multivalent compound such as tin oxide (i.e., a clarifying agent), which undergoes a chemical reduction reaction upon heating and releases oxygen. Other suitable clarifying agents may include, but are not limited to, arsenic, antimony, iron, and / or cerium, although the use of arsenic and antimony may be discouraged for environmental reasons in some applications due to their toxicity. The clarifying container 126 is heated to a temperature, for example, above the internal temperature of the molten container, thereby heating the clarifying agent. Oxygen generated by the chemical reduction induced by the temperature of one or more clarifying agents contained in the molten glass diffuses into the bubbles generated during melting. The enlarged bubbles, with increased buoyancy, then rise to the free surface of the molten glass within the clarifying container and are discharged from the clarifying container.

[0063] The downstream glass manufacturing apparatus 122 may further include another regulating chamber, such as a stirring vessel, like a mixing device 130, for mixing the molten glass flowing downstream from the clarifying vessel 126. The mixing device 130 can be used to provide a homogeneous glass melt composition, thereby reducing chemical or thermal inhomogeneities that may be present in the molten glass leaving the clarifying vessel. As shown, the clarifying vessel 126 may be connected to the mixing device 130 via a second connecting conduit 132. In some embodiments, the molten glass 120 may be gravity-fed from the clarifying vessel 126 into the mixing device 130 via the second connecting conduit 132. Typically, the molten glass within the mixing device 130 comprises a free surface and has a free (e.g., gaseous) volume extending between the free surface and the top of the mixing device. Although the mixing device 130 is shown downstream of the clarifying vessel 126 relative to the flow direction of the molten glass, the mixing device 130 may be positioned upstream of the clarifying vessel 126. In some embodiments, the downstream glass manufacturing apparatus 122 may include multiple mixing devices, such as a mixing device upstream of the clarifying vessel 126 and a mixing device downstream of the clarifying vessel 126. When in use, multiple mixing devices may have the same design, or they may have different designs from each other. In some embodiments, one or more containers and / or conduits may include static mixing blades located therein to facilitate mixing and subsequent homogenization of the molten material.

[0064] Downstream glass manufacturing equipment 122 may further include another regulating chamber, such as a delivery container 134 located downstream of mixing equipment 130. Delivery container 134 can regulate the molten glass 120 to be fed into downstream forming apparatus. For example, delivery container 134 may act as an accumulator and / or flow controller to regulate and / or provide a consistent flow rate of molten glass 120 to downstream forming and processing equipment 142 via delivery conduit 140. In some embodiments, the molten glass within delivery container 134 may include a free surface, wherein the free volume extends upward from the free surface to the top of the delivery container. As shown, mixing equipment 130 may be coupled to delivery container 134 via a third connecting conduit 136.

[0065] As described above, the downstream glass manufacturing apparatus 122 may further include forming and processing equipment 142, wherein molten glass 120 is formed into a molten glass stream and conveyed to a processing roller. As shown in FIG3, a conveying conduit 140 may be positioned to convey molten glass 120 from a conveying container 134 to a forming body 143, which forms part of the forming and processing apparatus 142. In some embodiments shown in FIG3, the forming body 143 may be a groove stretching device, wherein the forming body includes a container having grooves along the bottom surface of the container from which molten glass exits the container. Thus, the forming body 143 conveys the molten glass stream 144 from the grooves to the processing roller 146, wherein the molten glass stream 144 is deposited as a glass layer 150 on the circumferential (outer) surface 148 of the processing roller. Although the processing roller 146 may be formed of other suitable metals, the processing roller 146 may be a metal roller formed of a corrosion-resistant metal, such as a stainless steel roller. In various embodiments, the processing roller 146 may be hollow and supplied with a cooling fluid such as air or water. For example, the processing roller 146 may include one or more internal channels configured to convey cooling fluid through the processing roller and / or the cooling fluid may be sprayed onto the inner surface of the processing roller. The molten glass stream 144 may impinge on the processing roller 146 at the 12 o'clock position (0 degrees, i.e., top dead center (TDC)) and form a glass layer 150 on the processing roller, and then be released as a glass ribbon 152 at the 3 o'clock position (90 degrees). However, the glass ribbon 152 may be released from the processing roller 146 at different angular positions, for example, in the range from approximately 0 degrees to approximately 100 degrees, depending on the adhesion of the molten glass to the processing roller and / or the rotational speed of the processing roller. Furthermore, the molten glass stream 144 may impinge on the processing roller at positions other than the 12 o'clock position. For example, one or both of the stream 144 or the processing roller 146 may be moved such that the stream impinges on the processing roller in a position range from approximately 10 o'clock to approximately 2 o'clock (e.g., from approximately -30 to approximately 60 degrees relative to the TDC).

[0066] The glass ribbon 152 can be separated into individual glass sheets by a downstream glass separation device (not shown). However, the glass ribbon can optionally be wound onto a reel and stored for further processing. The glass ribbon 152 can be pulled downward from the processing roller 146 by a plurality of counter-rotating pull roller assemblies 154 positioned below the processing roller 146. The pull roller assemblies 154 (e.g., a pair of counter-rotating pull rollers) contact the glass ribbon 152 along its edge portions 156a and 156b without contacting the center portion 158 of the glass ribbon (see FIG. 5), with the center portion 158 extending between the edge portions 156a and 156b. The thickness 160 of the glass ribbon 152 along its longitudinal centerline 162 can be defined between the first main surface 164 and the second main surface 166 of the glass ribbon 152. The thickness 160 can be less than or equal to about 4 mm, less than or equal to about 3 mm, less than or equal to about 2 mm, less than or equal to 1 mm, less than or equal to about 0.7 mm, less than or equal to about 0.5 mm, less than or equal to about 0.1 mm, or less than or equal to about 500 micrometers (μm), for example, less than or equal to about 300 μm, for example, less than or equal to about 200 μm, or for example, less than or equal to about 100 μm, but other thicknesses are also possible. Furthermore, the glass ribbon 152 can be formed from a variety of glass compositions, including but not limited to soda-lime glass, borosilicate glass, aluminoborosilicate glass, alkali-containing glass such as alkali metal aluminoborosilicate glass, or alkali-free glass.

[0067] Figure 4 shows another forming and processing apparatus 142, in which a delivery conduit 140 (not shown in Figure 4) delivers molten glass 120 to another forming body 143. According to the forming body of Figure 4, the forming body includes a groove 168 located in the upper surface of the forming body, and also includes converging forming surfaces 170a and 170b converging along the bottom edge 172 of the forming body 143. Molten glass 120 overflows the walls of the groove and flows downward over the converging forming surfaces. The separate molten glass flows converge along the bottom edge 172 to form a molten glass flow 144, which is then deposited as a glass layer 150 on a processing roller 146. Thereafter, the embodiment of Figure 4 is operated according to the embodiment of Figure 3.

[0068] Components of the downstream glass manufacturing apparatus 122, including any one or more of connecting conduits 124, 132, 138, clarifying vessel 126, mixing device 130, conveying vessel 134, conveying conduit 140, or forming body 143, may be formed of precious metals. Suitable precious metals include platinum group metals or alloys thereof selected from the group consisting of platinum, iridium, rhodium, osmium, ruthenium, and palladium. For example, downstream components of the glass manufacturing apparatus may be formed of a platinum-rhodium alloy comprising about 70% to about 90% by weight of platinum and about 10% to about 30% by weight of rhodium. However, other suitable metals for forming downstream components of the glass manufacturing apparatus may include molybdenum, rhenium, tantalum, titanium, tungsten, or alloys thereof. In the embodiment of FIG. 4, forming body 143 may include a refractory material, such as a ceramic refractory.

[0069] Edge rollers 174 can be used to contact glass layer 150 at its lateral edge portion, cooling the glass at the lateral edge portion and helping to mitigate shrinkage of the glass layer and / or glass strip stretched from the processing rollers. Accordingly, these functions can be performed while the glass layer resides on the processing roller 146, or, if the edge rollers are included below the processing rollers, on the glass strip. For example, a pair of edge rollers 174 can be used, which capture (e.g., squeeze) the glass layer 150 in the gap 176 between the edge rollers and the processing rollers. Although other suitable metals can be used, edge rollers are typically metal, such as corrosion-resistant metals like stainless steel.

[0070] Figure 5 is a front view of a processing roller 146 rotatable about a first rotation axis 178, a first edge roller 174a rotatable about a second rotation axis 180a, and a second edge roller 174b rotatable about a third rotation axis 180b. The first and second edge rollers 174a and 174b are spaced apart to contact opposing edge portions 156a and 156b, respectively, and the second rotation axis 180a is coaxial with the third rotation axis 180b. The first and second edge rollers 174a and 174b are spaced apart from the processing roller 146 such that a gap 176 exists between the first and second edge rollers and the processing roller, the gap 176 being sized to receive the first edge portion 156a and the second edge portion 156b, respectively. The first and second edge rollers 174a and 174b contact the glass layer 150 that is in contact with the processing roller 146. The edge rollers cool the edge portions and increase their viscosity, thereby reducing the lateral shrinkage of the glass layer 150. The first edge roller 174a and the second edge roller 174b can be coupled to corresponding motors 182a, 182b, which are configured to rotate the respective edge rollers in a direction opposite to the rotation direction of the processing roller 146. As shown, the first edge roller 174a and the second edge roller 174b can be smaller than the processing roller 146. For example, the diameter 184 of the first and second edge rollers 174a, 174b can be in the range of about 2.5 cm to about 8 cm, for example, in the range of about 3 cm to about 7 cm, in the range of about 3.5 cm to about 6.5 cm, or in the range of about 4 cm to about 6 cm, including all ranges and subranges therein. For comparison, the diameter 186 of the processing roller 146 can be in the range of approximately 5 cm to approximately 31 cm, in the range of approximately 5 cm to approximately 26 cm, in the range of approximately 5 cm to approximately 21 cm, in the range of approximately 5 cm to approximately 15 cm, in the range of approximately 5 cm to approximately 10 cm, in the range of approximately 31 cm to approximately 10 cm, in the range of approximately 31 cm to approximately 15 cm, in the range of approximately 31 cm to approximately 15 cm, in the range of approximately 31 cm to approximately 20 cm, or in the range of approximately 31 cm to approximately 25 cm, including all ranges and sub-ranges therein. However, the diameter 184 of the first and second edge rollers 174a, 174b can be equal to or greater than the diameter 186 of the processing roller 146.

[0071] The length 188 of the first and second edge rollers 174a, 174b can range from about 1 cm to about 26 cm, for example, from about 1 cm to about 20 cm, from about 1 cm to about 15 cm, from about 1 cm to about 10 cm, from about 1 cm to about 5 cm, from about 10 cm to about 26 cm, from about 15 cm to about 26 cm, and from about 20 cm to about 26 cm, including all ranges and sub-ranges therein. The first and second edge rollers 174a, 174b are configured and arranged to contact the edge portions 156a, 156b of the glass layer 150, respectively, but not the central portion 158 of at least one exposed (outward) surface of the glass layer 150 (e.g., the second main surface 166) located on the processing roller 146. In contrast, the entire width of the first main surface 164 of the glass layer 150 contacts a portion of the processing roller 146. The processing roller 146 may have a length 188, which is in the range of about 25 cm to about 400 cm, for example, in the range of about 50 cm to about 400 cm, in the range of about 75 cm to about 400 cm, in the range of about 100 cm to about 400 cm, in the range of about 125 cm to about 400 cm, in the range of about 150 cm to about 400 cm, in the range of about 175 cm to about 400 cm, in the range of about 200 cm to about 400 cm, and in the range of about 225 cm to about 400 cm. Within the range of approximately 250cm to approximately 400cm, within the range of approximately 275cm to approximately 400cm, within the range of approximately 300cm to approximately 400cm, within the range of approximately 25cm to approximately 350cm, within the range of approximately 25cm to approximately 300cm, within the range of approximately 25cm to approximately 250cm, within the range of approximately 25cm to approximately 200cm, within the range of approximately 25cm to approximately 150cm, within the range of approximately 25cm to approximately 100cm, or within the range of approximately 25cm to approximately 75cm, including all ranges and subranges therein.

[0072] The first and second edge rollers 174a and 174b can have various outer and circumferential surface finishes. For example, in some embodiments, the first edge roller 174a and the second edge roller 174b can have smooth outer surfaces, while in other embodiments, the outer circumferential surfaces of the first edge roller 174a and the second edge roller 174b can be rough, and in some embodiments, the outer surfaces can be knurled.

[0073] The first and second edge rollers 174a and 174b can be cooled. For example, the first edge roller 174a and the second edge roller 174b may be hollow or include one or more channels through which cooling fluid can flow. By way of example and not limitation, FIG6 shows a cross-sectional view of an exemplary edge roller 174, which includes an edge roller body 300 containing an internal cavity 302. A shaft 304 including an internal channel 306 couples the edge roller body to a motor (not shown). A cooling fluid supply line 308 extends into the cavity 302 via the channel 306 defined within the shaft 304. Cooling fluid 310 is supplied from a coolant source (not shown) to the coolant supply line and exits the coolant supply line within the cavity 302, wherein the coolant contacts the inner surface of the edge roller body, thereby cooling the edge roller body. The edge roller 174 may have a smooth outer contact surface 312 (the surface that contacts the molten glass or glass ribbon) or a knurled or other patterned outer surface.

[0074] For example, the cooling of the first edge roller 174a and the second edge roller 174b can be controlled by controlling the flow rate and temperature of the cooling fluid. Suitable cooling fluids may include water or air. The cooled first and second edge rollers 174a, 174b then cool the edge portions 156a, 156b, increasing the viscosity of the edge portions. The harder edge portions (as a result of the increased viscosity) resist the shrinkage of the molten glass layer. Subsequently, the molten glass layer is released as a glass ribbon from the outer circumferential surface of the processing roller, wherein the increased viscosity of the edge portions 156a, 156b due to contact with the first and second edge rollers 174a, 174b further reduces the shrinkage of the glass ribbon 152 descending from the processing roller 146. The viscosity of the glass ribbon 152 at the release point from the processing roller 146 can be in the range of about 10 3 Pa·s to about 10 6 Pa·s (10 4 poise to 10 7 poise), for example, about 10 3 Pa·s, 10 4 Pa·s, 10 5 Pa·s or 10 6 Pa·s.

[0075] The first and second edge rollers 174a and 174b can move toward or away from the processing roller 146 in the vertical and / or horizontal directions, thereby positioning the first and second edge rollers 174a and 174b along an arc 190, as shown in FIG. 7. The arc 190 can be concentric with the outer surface of the processing roller 146. The first and second edge rollers can be positioned along the arc 190 at an angle ranging from greater than 0 degrees to approximately 90 degrees (relative to the TDC). Accordingly, the first edge roller 174a and the second edge roller 174b can contact the glass layer 150 at any angular position along the arc 190. Movement toward or away from the processing roller 146 in a horizontal position can also be used to increase or decrease the gap 176 between the edge rollers and the processing roller 146. Furthermore, the first and second edge rollers 174a and 174b can move horizontally in directions along the rotation axes 180a and 180b, respectively, as shown in FIG. 8 (showing the movement of the first edge roller 174a along the second rotation axis 180a).

[0076] Additional edge rollers 192 can be applied to the glass ribbon 152 downstream of the processing roller 146. These additional edge rollers can act on edge portions 156a, 156b such that the second main surface 166 facing outwards from the center portion 158 of the glass ribbon 152 remains uncontacted. These additional edge rollers can act on opposite edge portions of the glass ribbon in pairs with opposite rotation. Accordingly, FIG5 also shows a set of additional edge rollers 192 located downstream of the processing roller 146; a pair of opposing, oppositely rotating first additional edge rollers 192a arranged along the first edge portion 156a, and a pair of opposing, oppositely rotating second additional edge rollers 192b arranged along the second edge portion 156b. The opposing edge rollers of each pair of additional edge rollers 192a, 192b are positioned along their respective edge portions adjacent to the opposing first and second main surfaces 164, 166 of the glass ribbon 152. The additional edge roller pairs 192a and 192b of the additional edge roller 192 are configured to contact the first and second edge portions 156a and 156b without contacting the center portion 158 of the glass ribbon 152. The additional edge roller pairs 192a and 192b can move vertically toward or away from the processing roller 146. The additional edge roller pairs 192a and 192b can also move horizontally along their respective axes of rotation. The additional edge roller 192 can be a driven edge roller. For example, at least one edge roller in each additional edge roller pair can be coupled to a motor 194. In other examples, each edge roller in each additional edge roller pair can be coupled to a drive motor 194. However, in other cases, neither edge roller in each additional edge roller pair can be driven. The edge roller 192 can be structurally identical to the edge roller 174.

[0077] The pull roller assembly 154 can be used to stretch the glass ribbon 152 from the processing roller 146. For example, the pull roller assembly 154 may include a pair of pull roller assemblies 154a and 154b, each pull roller assembly including a first pair of 154a pull rollers 196a that rotates opposite to each other and in opposite directions, and a second pair of 154b pull rollers 196b that rotates opposite to each other and in opposite directions. The pull roller pairs 196a and 196b apply downward tension to the glass ribbon 152 to control the travel speed of the glass ribbon 152 and the width and thickness of the glass ribbon. The pull roller pairs 196a and 196b can be of any suitable design, but the individual pull rollers can be made of compressed refractory material, such as a plurality of fiber ceramic discs arranged face-to-face, compressed and mounted on a shaft. One or both pull rollers in each pull roller pair can be driven, for example, coupled to a motor 198.

[0078] As the glass ribbon descends below the pull roller, the glass ribbon 152 can continue to be cooled. Any known methods and techniques for cooling formed glass ribbons can be used, provided that the glass ribbon and / or at least one side of the glass ribbon remains undamaged.

[0079] Figure 9 is a graph showing the modeled strip width, displayed as a viscosity function from edge to center in millimeters, including five different glass strip center viscosities (viscosity at the centerline of the glass strip at the starting point of the processing roller): 60 kpoise (6 kPa·s), 80 kpoise (8 kPa·s), 100 kpoise (10 kPa·s), 160 kpoise (16 kPa·s), and 200 kpoise (20 kPa·s). The data shows that the glass strip width increases with increasing edge-to-center viscosity ratio. For the case considered in Figure 9, a glass strip width of approximately 200 mm can be obtained by increasing the edge-to-center viscosity ratio by approximately 15 times (15x). This 15-fold change in viscosity ratio is feasible by significantly cooling the strip edges using the contact heat conduction mechanism disclosed herein.

[0080] Figure 10 is another graph showing the effect of temperature drop and edge roll length at the starting point on the glass ribbon width using modeled data. The simulation assumes a processing roll length of 205 cm. As can be seen from Figure 10, the first and second edge rolls can increase the glass ribbon width from approximately 1.83 meters to approximately 1.93 meters (an increase of 5–6%). It can also be observed that temperature drop is the primary driver of the glass ribbon width gain. The edge roll length has a moderate effect on the glass ribbon width but can significantly affect the pull force. The dashed line in Figure 10 represents the upper limit of pull force, defined by the pulling machine system and the glass viscosity. For a given pulling machine with a pull force exceeding the upper limit (as indicated by the arrows in Figure 10), stretching the ribbon with higher forces may be impractical. For example, in the case where the presented edge roll length is approximately 50 mm, the ribbon width gain is greatest for a given pull force limit. Furthermore, the edge roll length affects the cooling effect of the edge roll. The shorter the edge roll length, the less heat is extracted from the molten glass.

[0081] It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments disclosed herein without departing from the spirit and scope of this disclosure. Therefore, this disclosure is intended to cover such modifications and variations as long as they fall within the scope of the appended claims and their equivalents.

[0082] 10: Molten glass flow 12: Container 14: Processing Roller 16: Pull the roller 18: Edge 22: Edge 24: Arrow 26: Available width 100: Glass manufacturing equipment 102: Glass Furnace 104: Melting container 106: Upstream glass manufacturing equipment 108: Raw material storage box 110: Raw material conveying device 112: Motor 116: Raw materials 118: Arrow 120: Molten Glass 122: Downstream glass manufacturing equipment 124: First connecting catheter / connecting catheter 126: Clarifying container 130: Mixing equipment 132: Second connecting catheter / connecting catheter 134: Conveying Container 138: Connecting catheter 140: Delivery tubing 142: Forming and processing equipment 143: Forming Main Body 144: Molten glass flow / flow 146: Processing Roller 148: Circumferential surface 150: Glass layer 152: Glass ribbon 154: Pulling roller assembly 154a: First pair / pull roller assembly 154b: Second pair / pull roller assembly 156a: First edge portion / edge portion 156b: Second edge portion / edge portion 158: Central Part 160: Thickness 162: Longitudinal centerline 164: First Primary Surface 166: Second primary surface 168: Groove 170a, 170b: Converging and forming surfaces 172: Bottom edge 174: Edge Roller 174a: First edge roller 174b: Second edge roller 176: Gap 178: First axis of rotation 180a: Second axis of rotation / axis of rotation 180b: Third axis of rotation / axis of rotation 182a, 182b: Motors 184, 186: Diameter 188: Length 190: Curve 192: Edge Roller / Additional Edge Roller 192a: First additional edge roll pair / Additional edge roll pair 192b: Second Additional Edge Roll Pair / Additional Edge Roll Pair 194: Motor / Drive Motor 196a, 196b: Pulling roller pair 300: Edge roller body 302: Internal cavity / cavity 304: Shaft 306: Internal passageway 308: Cooling fluid supply line 310: Cooling fluid 312: External contact surface

[0083] Domestic storage information (please note in order of storage institution, date, and number) none Overseas storage information (please note in the order of storage country, institution, date, and number) none

Claims

1. A method of forming a glass ribbon, comprising the steps of: flowing a molten glass stream on an outer surface of a processing roller, the processing roller rotating about a first rotation axis in a first rotation direction, the molten glass stream forming a molten glass layer located on the outer surface of the processing roller; contacting an edge portion of the molten glass layer on the processing roller with a first edge roller, the contact cooling the edge portion and increasing its viscosity, wherein the first edge roller contacts the edge portion of the molten glass layer on the processing roller but not a central portion of the molten glass layer on the processing roller, the molten glass layer leaving the processing roller to form a molten glass ribbon; drawing the molten glass ribbon from the processing roller in a stretching direction between a pair of pull rollers located below the processing roller, the pair of pull rollers engaging the edge portion on opposite sides of the glass ribbon.

2. The method as described in claim 1, further comprising contacting the edge portion through a pair of downstream edge rollers located between the processing roller and the pair of pull rollers.

3. The method as described in claim 1, further comprising cooling the first edge roller by contacting an inner surface of the first edge roller with a cooling liquid.

4. The method as described in claim 1, further comprising cooling the processing roller by contacting an inner surface of the processing roller with a cooling liquid.

5. The method as claimed in claim 1, wherein the processing roller includes a top defined at an angular position of 0 degrees, and the first edge roller contacts the molten glass layer on the processing roller at an angular position ranging from approximately 35 degrees to approximately 90 degrees in the direction of rotation of the processing roller relative to the 0-degree position.

6. The method of any one of claims 1 to 5, wherein the molten glass layer includes a first viscosity at a first point on the edge portion and a second viscosity at a center point of the molten glass layer on a horizontal line extending orthogonally to the stretching direction, and a viscosity ratio defined as between the viscosity of the molten glass layer at the first point and the viscosity of the molten glass layer at the center point is in the range of about 1 to about 16.

7. A method of forming a glass ribbon, comprising the steps of: causing a molten glass stream to flow on an outer surface of a processing roller, the processing roller being rotated about a first rotation axis in a first rotation direction by a first motor, the molten glass stream forming a molten glass layer located on the outer surface of the processing roller; An edge portion of the molten glass layer on the processing roller is brought into contact with a first edge roller, which is rotated about a second axis of rotation in a second rotation direction opposite to the first rotation direction by a second motor. This contact cools the edge portion and increases its viscosity. The first edge roller contacts the edge portion of the molten glass layer on the processing roller but not a central portion of the molten glass layer on the processing roller. The molten glass layer includes a first viscosity at a first point on the edge portion and a second viscosity at a central point on a horizontal line extending orthogonal to a stretching direction. A viscosity ratio is defined as the ratio between the viscosity of the molten glass layer at the first point and the viscosity of the molten glass layer at the central point, which is in the range of about 1 to about 16. The molten glass layer leaves the processing roller as a molten glass strip, wherein the entire width of a main surface of the molten glass layer contacts a portion of the processing roller. The molten glass strip is stretched from the processing roller along the stretching direction between a pair of pull rollers, which engage opposite sides of the glass strip below the processing roller.

8. An apparatus for processing glass ribbons, comprising: A conveying device configured to convey a stream of molten glass; A processing roller, arranged below the conveying device and positioned to receive the molten glass stream as a molten glass layer and release the molten glass layer as a glass ribbon, the molten glass layer being located on the outer surface of the processing roller; and a first set of edge rollers, arranged adjacent to the processing roller, the first set of edge rollers including a first edge roller and a second edge roller, the first edge roller being positioned to contact the molten glass layer at a first transverse edge portion on the processing roller but not at a central portion on the processing roller, and the first edge roller being configured to press the first transverse edge portion against the surface of the processing roller, the second edge roller being positioned to contact the molten glass layer at a second transverse edge portion on the processing roller relative to the first transverse edge portion but not at the central portion on the processing roller, and the second edge roller being configured to press the second transverse edge portion against the surface of the processing roller.

9. The apparatus of claim 8, further comprising a set of pull rollers positioned below the processing roller, the set of pull rollers including a first pair of pull rollers arranged to capture the glass strip at a first edge portion of the glass strip and a second pair of pull rollers arranged to capture the glass strip at a second edge portion of the glass strip, a first pull roller of the first pair of pull rollers coupled to a first motor configured to rotate the first pull roller, and a second pull roller of the second pair of pull rollers coupled to a second motor configured to rotate the second pull roller.

10. The apparatus as claimed in claim 8 or 9, further comprising a set of downstream edge rollers positioned between the processing roller and the set of pull rollers, the set of downstream edge rollers including a first pair of downstream edge rollers and a second pair of downstream edge rollers, the first pair of downstream edge rollers being arranged to capture the glass strip at a first edge portion of the glass strip between them, and the second pair of downstream edge rollers being arranged to capture the glass strip at a second edge portion of the glass strip between them.

Images