Apparatus and method for roll forming of high refractive index glass sheets

Abstract

A method of forming a glass sheet includes: (a) forming a glass ribbon from molten glass with a pair of forming rolls; (b) reducing a horizontal temperature variation of the glass ribbon to 10 °C or less over 80% of the entire width of the glass ribbon before the glass ribbon cools to the glass transition temperature; (c) controlling a cooling rate of the glass ribbon as the glass ribbon moves longitudinally downward in a solidification zone such that the glass ribbon has a first average cooling rate before the glass ribbon cools to the glass transition temperature and a second average cooling rate after the glass ribbon cools to the glass transition temperature, the first average cooling rate being less than the second average cooling rate; and (d) separating a glass sheet from the glass ribbon.

Description

[0001] This application claims priority to U.S. Provisional Patent Application Serial No. 63 / 113,507, filed November 13, 2020, pursuant to 35 USC §119(e), the entire contents of which are incorporated herein by reference. Background Technology

[0002] Augmented reality (AR) systems add computer-generated images to the real-world visual scene observed by the system user. AR systems typically include optical systems configured to add computer-generated images to directly observed real-world objects or scenes while allowing observation of those objects or scenes. The optical system may use light guides made of high-refractive-index glass to project the computer-generated images into the user's field of view. Deviations in the geometry of the light guide can degrade the quality of the image guided through it and presented to the user. For example, the total thickness variation and warpage of the light guide should be minimized to achieve a high-quality output image. Furthermore, sometimes a thinner light guide is specified.

[0003] One process for achieving optical guides with acceptable total thickness variation and warpage involves casting a pear-shaped piece of high-refractive-index glass, sawing the pear-shaped piece into multiple wafers, and grinding and polishing the wafers or reheating them to flatten them. However, these processes are expensive and time-consuming. Furthermore, reheating the wafers can cause the glass to devitrify.

[0004] In addition, fusion manufacturing processes are incompatible with high-refractive-index glass compositions because the liquidus viscosity associated with such compositions is too low (e.g., 1 to 100 poise). Furthermore, some processes cannot produce glass with the required thinness. Summary of the Invention

[0005] This disclosure addresses those problems by continuously rolling high-refractive-index glass into a glass ribbon (from which glass sheets are separated). The glass sheets can be segmented into the sizes required for augmented reality device applications. This process is not as expensive as the pear-to-wafer process described above.

[0006] However, another problem has been found: continuous roll forming of high-refractive-index glass ribbons can lead to ribbon breakage or separation of glass sheets with suboptimal total thickness variation and warping. This disclosure addresses this problem by: (a) reducing the horizontal temperature variation of the ribbon before cooling to the glass transition temperature; (b) one or more of the following: (i) reducing the longitudinal temperature drop rate of the ribbon before cooling to the glass transition temperature; and (ii) increasing the longitudinal temperature drop rate of the ribbon after cooling to the glass transition temperature; and (c) absorbing heat from one or both of the opposing rolls that form the molten glass ribbon. Reducing the horizontal temperature variation of the ribbon decreases the total thickness variation and warping of the glass sheets separated from the ribbon. As further explained below, one or more of (i) reducing the longitudinal temperature drop rate of the ribbon before cooling to the glass transition temperature and (ii) increasing the longitudinal temperature drop rate of the ribbon after cooling to the glass transition temperature result in a more linear longitudinal strain distribution of the ribbon. A more linear strain distribution reduces the likelihood of the glass ribbon breaking after the glass sheets separate, and also reduces the overall thickness variation and warping of the glass sheets. Furthermore, heat absorption from one or both of the opposing rollers reduces outward expansion at the roller center, which would otherwise result in a glass ribbon with thickness variations and warping.

[0007] This disclosure reduces the horizontal temperature variation of the glass ribbon by one or more of the following methods: (i) widening the width of the molten glass stream delivered to the gap between the opposing rollers forming the molten glass ribbon; (ii) increasing the heat loss of the glass ribbon relative to the transverse edges; (iii) reducing the heat loss of the central portion of the glass ribbon relative to the transverse edges; or (iv) increasing the puddle height of the molten glass in the gap between the forming rollers. This disclosure widens the width of the molten glass stream delivered to the gap by employing a distribution feed device to deliver the molten glass stream. This disclosure increases the heat loss of the glass ribbon relative to the central portion of the glass ribbon by one of the following methods: (i) blowing air onto the transverse edges; (ii) reducing the thickness of the transverse edges of the glass ribbon. This disclosure reduces the heat loss of the central portion of the glass ribbon relative to the transverse edges by such that the heat loss reduction element (e.g., a heat-insulating substrate, a heat-generating element, or a combination thereof) faces the central portion of the glass ribbon and not the transverse edges. This disclosure increases the height of the molten glass pit material in the gap between the forming rollers by using a lateral dam higher than the rollers to limit the lateral spread of the molten glass pit material.

[0008] This disclosure also reduces the longitudinal temperature drop rate of the glass ribbon before it cools to the glass transition temperature by using heat-reducing elements facing the center portion of the glass ribbon.

[0009] This disclosure increases the longitudinal temperature drop rate of the glass ribbon after it has been cooled to the glass transition temperature by either making the glass ribbon face the radiative cooling element or by blowing cooling fluid (e.g., air) onto the glass ribbon.

[0010] This disclosure extracts heat from at least one forming roll by: (i) employing a heat exchanger within the forming roll; (ii) spraying liquid onto the roll using a sprayer; (iii) bringing the roll into contact with a liquid-cooled metal brush; and / or (iv) bringing the roll opposite to a liquid-cooled slider.

[0011] In addition, continuous roll forming of high-refractive-index glass ribbons results in glass ribbons and the resulting separated glass samples being thicker than desired. This disclosure solves this problem by using forming rolls with an outer diameter of less than 80 mm (e.g., 20 mm to 80 mm).

[0012] According to a first aspect of this disclosure, a method for forming a glass sheet includes: (a) forming a glass ribbon from molten glass using a pair of forming rollers; (b) reducing the horizontal temperature variation of the glass ribbon over 80% of its entire width before cooling to the glass transition temperature to 10°C or less; (c) controlling the cooling rate of the glass ribbon as it moves longitudinally downward in the solidification zone such that the glass ribbon has a first average cooling rate before cooling to the glass transition temperature and a second average cooling rate after cooling to the glass transition temperature, the first average cooling rate being less than the second average cooling rate; and (d) separating the glass sheet from the glass ribbon.

[0013] According to another aspect of this disclosure, an apparatus for roll forming glass ribbons includes: (a) a pair of forming rolls separated by a gap, each roll in the pair having a shaft such that the shafts are parallel to each other, the gap having a minimum spacing along a horizontal plane extending through the two shafts, and a longitudinal plane extending through the gap parallel to the shafts; (b) a feed device for feeding molten glass stream into the gap, the feed device being arranged longitudinally above the horizontal plane extending through the shafts of the forming rolls, the feed device including: an inner chamber, a base plate, and a groove through the base plate providing a passage from the inner chamber; and (c) a pair of heat loss reduction elements, one heat loss reduction element being arranged on each side of the longitudinal plane extending through the gap between the forming rolls, each heat loss reduction element being arranged below the horizontal plane extending through the shafts of the forming rolls.

[0014] According to another aspect of this disclosure, an apparatus for roll forming a glass ribbon includes: (a) a pair of forming rollers, each forming roller having a shaft and an outer cylindrical surface, the pair of forming rollers being separated by a gap and the shafts being parallel to each other, the gap having a minimum spacing arranged along a horizontal plane extending through the two shafts; (b) a feed device for feeding a stream of molten glass into the gap, the feed device being arranged longitudinally above the horizontal plane extending through the shafts of the forming roller pair; (c) a first lateral edge cooling element and a second lateral edge cooling element, both arranged longitudinally below the horizontal plane, the first lateral edge cooling element being configured to reduce the temperature of a first lateral edge of the glass ribbon, and the second lateral edge cooling element being configured to reduce the temperature of a second lateral edge of the glass ribbon; and (d) a pair of dams arranged above the horizontal plane, which cooperate with the outer cylindrical surface to retain the molten glass, one or both dams in the pair being laterally movable relative to the other dam in the pair.

[0015] According to another aspect of this disclosure, a method of forming a glass ribbon includes: feeding molten glass into a gap separating a pair of forming rollers; wherein the viscosity of the molten glass is from 0.01 poise to 3000 poise; wherein each of the pair of forming rollers has an outer diameter; and wherein the outer diameter of the forming roller is from 20 mm to 80 mm.

[0016] Those skilled in the art will be able to further understand and appreciate these and other features, advantages and objects of the present invention by referring to the following description, claims and drawings. Attached Figure Description

[0017] Figure 1 This is a perspective view of the apparatus disclosed herein, showing a pair of forming rollers that form a glass ribbon from molten glass supplied by a feeding device;

[0018] Figure 2 yes Figure 1 A side view of the device shows: a horizontal plane extending through the shaft of the forming rollers, a longitudinal plane extending through the gap between the forming rollers, and a pair of elements for reducing heat loss (one element for reducing heat loss is arranged on each side of the longitudinal plane, below the horizontal plane).

[0019] Figure 3 yes Figure 2 An enlarged view of region III shows a first transverse edge cooling element in the form of clamping rollers arranged on each side of the longitudinal plane and below the horizontal plane;

[0020] Figure 4 yes Figure 1 The feeding device of the equipment is a dispensing feeding device having a trough and a heating element.

[0021] Figure 5 yes Figure 4A top-down cross-sectional view of the feed distribution device along line VV shows the bottom plate and sides that define the inner chamber communicating with the trough.

[0022] Figure 6A yes Figure 1 An enlarged view of the device shows a first lateral edge cooling element and a second lateral edge cooling element arranged in the form of a pair of clamping rollers below the horizontal plane and laterally away from the heat insulation substrate;

[0023] Figure 6B yes Figure 1 An enlarged view of the device shows a first and a second transverse edge cooling element in the form of a pipe outlet for laterally inward blowing of cooling gas;

[0024] Figure 6C yes Figure 1 An enlarged view of the device shows a first lateral edge cooling element and a second lateral edge cooling element in the form of a radiation-absorbing element that performs thermal management via a cooling fluid;

[0025] Figure 7 yes Figure 6A A three-dimensional view of one of the clamping roller pairs;

[0026] Figure 8A It is used for Figure 1 A perspective view of a dam implementation of a device is shown, showing a dam that can be moved to a first position and a second position, can be moved away from the first position and the second position, and can be moved between the first position and the second position, with the dam being closer together at the second position than at the first position;

[0027] Figure 8B It is used for Figure 1 Another embodiment of the dam device shows a dam that can be slidably moved relative to the track;

[0028] Figure 9 yes Figure 1 An enlarged cross-sectional view of one of the forming rolls shows a heat exchanger introducing cooling fluid into the interior of the forming roll to cool the outer cylindrical surface of the forming roll;

[0029] Figure 10 It forms glass ribbons Figure 1 An enlarged view of the equipment shows a dispensing feeder (which supplies molten glass stream from the inner chamber through multiple orifices to the pit between the forming rollers), and the forming rollers that form glass ribbons from the pit.

[0030] Figure 11 yes Figure 10The side view shows a first set of clamping rollers in the form of a first transverse edge cooling element that reduces the thickness of the first transverse edge of the glass ribbon, and a glass ribbon extending through each of the opposing elements that reduce heat loss;

[0031] Figure 12 From Figure 1 A flowchart of a method for forming a glass sheet from a glass ribbon shows the following steps, wherein: (a) the horizontal temperature change of the glass ribbon is reduced; and (b) either (i) the longitudinal temperature drop rate of the glass ribbon is reduced before the glass ribbon is cooled to the glass transition temperature, or (b) the longitudinal temperature drop rate of the glass ribbon is increased after the glass ribbon is cooled to the glass transition temperature.

[0032] Figure 13 yes Figure 10 The enlarged view shows the glass sheet separated from the glass ribbon and the heat loss reduction element that reduces heat loss from the glass ribbon, located at: (i) the central portion of the glass ribbon and not at the lateral edge of the glass ribbon, and (ii) longitudinally between the horizontal plane and the solidification zone (partially located within the solidification zone), where the glass ribbon cools to the glass transition temperature.

[0033] Figure 14A yes Figure 10 The view shows a transverse edge cooling element in the form of a tube outlet that blows cooling gas onto the transverse edge of the glass strip;

[0034] Figure 14B yes Figure 10 The view shows a transverse edge cooling element arranged adjacent to the transverse edge of the glass strip and absorbing heat from the transverse edge of the glass strip.

[0035] Figure 15 yes Figure 10 The view shows the dam pairs that are closer together at a second location where the width of the pit material of the molten glass narrows;

[0036] Figure 16 The graph shows the relationship between the temperature of the glass ribbon in Comparative Example 2 and the horizontal position selected at two different horizontal positions as the glass ribbon cools longitudinally downwards. It shows the large horizontal temperature change across the entire glass ribbon without any active measures to reduce the horizontal temperature change.

[0037] Figure 17 This is a computer-modeled temperature diagram related to Comparative Example 2, showing the large temperature change within the glass ribbon caused by the molten wave flow as the single-tube feeder moves to the lateral edge;

[0038] Figure 18The fractured glass ribbon associated with Comparative Example 2 illustrates the effect of no active measures to reduce horizontal temperature changes and either: (i) reducing the longitudinal cooling rate before the glass ribbon cools to the glass transition temperature, or (ii) increasing the longitudinal cooling rate after the glass ribbon cools to the glass transition temperature (e.g., ...). Figure 12 (as described in the method), the glass ribbon tends to break after an attempt is made to separate the glass sheet from the glass ribbon;

[0039] Figure 19 The graph shows the relationship between the thickness of the glass ribbon in Comparative Example 3 and the horizontal position of the glass ribbon from one lateral edge to another, where no cooling was performed on the outer cylindrical surface of the forming roller, and the glass ribbon is thicker at the lateral edges than at its center.

[0040] Figure 20 The graph showing the relationship between the temperature and horizontal position of the glass strip in Comparative Example 4 illustrates the large horizontal temperature variation across the entire glass strip without any measures to actively reduce the horizontal temperature variation.

[0041] Figure 21 The graph shows the relationship between the temperature of the glass strip and its horizontal position in Example 5. It shows that the horizontal temperature change decreases on the right side of the glass strip, where cooling gas is blown through the tube outlet on the right horizontal side of the glass strip. In contrast, no such cooling gas is blown through the left side of the glass strip.

[0042] Figure 22 The graph shows the relationship between the temperature of the glass ribbon and its horizontal position in Example 6. It shows that the horizontal temperature change on the right side of the glass ribbon decreases. In this case, a set of clamping rollers reduces the thickness of the right lateral side of the glass ribbon. In contrast, no such set of clamping rollers is used on the left side of the glass ribbon.

[0043] Figure 23 The graph shows the relationship between the temperature of the glass strip in Comparative Example 7 and the horizontal position selected at two different longitudinal positions, demonstrating that there is no reduction in horizontal temperature change where no heat loss reduction element is used.

[0044] Figure 24 The graph shows the relationship between the temperature of the glass strip in Example 8 and the horizontal position selected at two different longitudinal positions. It shows that the horizontal temperature change is significantly reduced due to the heat loss-reducing elements (in the form of heat-insulating substrates) that are separated on each main surface of the glass strip at the center portion but not at the lateral edges.

[0045] Figure 25The glass ribbon shown in Example 8, along with the heat-reducing elements in the form of heat-insulating substrates facing both sides of the glass ribbon, demonstrates that because the heat-insulating substrates actively reduce horizontal temperature changes and the longitudinal cooling rate of the glass ribbon before it cools to the glass transition temperature, it is free from breakage.

[0046] Figure 26 The thermal imaging temperature distribution of the glass ribbon in Example 9 shows that: (i) when the dam is placed at a first position resulting in a shorter molten glass pit (“pit low”), the resulting glass ribbon has a higher horizontal temperature variation; (ii) when the dam is placed at a second position resulting in a higher molten glass pit (“pit medium”), the resulting glass ribbon has a lower horizontal temperature variation; and (iii) when the dam is placed at an even closer position resulting in an even higher molten glass pit (“pit high”), the resulting glass ribbon has a horizontal temperature variation greater than in the pit medium scenario but less extreme than in the pit low scenario.

[0047] Related to Example 10 Figure 27 The computer modeling of the relationship between strain and temperature of the glass ribbon as a function of longitudinal distance from the horizontal plane shows that if the cooling rate of the glass ribbon slows down in the solidification zone immediately before cooling to the glass transition temperature, and then accelerates in the solidification zone immediately after cooling to the glass transition temperature, the strain rate of change is relatively constant throughout the solidification zone, which means that the thermal stress decreases as the glass ribbon cools through the glass transition temperature.

[0048] Figure 28 This is a graph showing the temperature of the glass ribbon as a function of its longitudinal position for Comparative Example 11 (without a heat-loss-reducing element) and Example 12 (with a heat-loss-reducing element in the form of an insulating substrate). It shows that the insulating substrate used in Example 12 causes the glass ribbon to cool more slowly from position 1-2 and then more rapidly from position 2-3, which is closer to... Figure 27 The computer-modeled scenario of reduced thermal stress;

[0049] Related to Example 13 Figure 29 From according to Figure 12 Images of glass strips separated from glass produced by the method show that the glass strips are not broken or have perceptible warping.

[0050] Figure 30 yes Figure 29 The profile measurement instrument profile of the glass slide shows that the separated glass slide has minimized warpage and total thickness variation; and

[0051] Related to Example 14 Figure 31 It is shown that reducing the outer diameter of the forming roller reduces the thickness of the glass ribbon and thus the thickness of the glass sheet obtained by separation. Detailed Implementation

[0052] See now Figure 1-3 The apparatus 10 for roll forming glass strip 12 is shown and described herein. The apparatus 10 includes a pair of forming rollers 14. Each forming roller 14 has a pivot 16 and an outer cylindrical surface 18. The pivots 16 are parallel to each other. During operation of the apparatus 10, each forming roller 14 rotates about its pivot 16, as indicated by the arrow. The forming rollers 14 may be formed of steel. Each forming roller 14 has a width 20 parallel to its pivot 16. In embodiments, the width 20 of each forming roller 14 is from 100 mm to 500 mm, for example: 100 mm, 200 mm, 250 mm, 300 mm, 350 mm, 400 mm, or 500 mm, or any range including any two of those values ​​(e.g., 200 mm to 400 mm). The width 20 of the forming rollers 14 may be the same, but is not necessarily so. In embodiments, the outer cylindrical surface 18 has an outer diameter 22 ranging from 20 mm to 600 mm, for example: 20 mm, 25 mm, 50 mm, 60 mm, 80 mm, 100 mm, 110 mm, 200 mm, 300 mm, 400 mm, 500 mm, or 600 mm, or any range including any two of those values ​​(e.g., 20 mm to 80 mm, 50 mm to 110 mm, etc.). Unless otherwise stated, any range described herein includes the endpoint values ​​of the range. For example, "outer diameter 22 of 20 mm to 600 mm" means that the outer diameter 22 is greater than or equal to 20 mm and less than or equal to 600 mm (i.e., 20 mm ≤ outer diameter 22 ≤ 600 mm).

[0053] Gap 24 separates the pair of forming rollers 14. Gap 24 is the minimum distance 26 extending through the horizontal plane 28 of the two rotating shafts 16. Longitudinal plane 30 extends longitudinally through gap 24. Longitudinal plane 30 is oriented parallel to the rotating shafts 16 of the forming rollers 14. Thus, longitudinal plane 30 and horizontal plane 28 are orthogonal to each other and intersect in the gap 24 between the forming rollers 14, for example at the midpoint 32 of the minimum distance 26 of gap 24. Longitudinal plane 30 and horizontal plane 28 are not structural features of device 10, but rather conceptual guidelines to help explain the relative orientation of the structural features of device 10.

[0054] The apparatus 10 also includes a transfer system 34 and a feeding device 36 in communication with the transfer system 34. The feeding device 36 is arranged longitudinally above a horizontal plane 28 extending through the shaft 16 of the pair of forming rollers 14. In an embodiment, the transfer system 34 is a crucible. In an embodiment, the transfer system 34 is a continuous process. In an embodiment, the feeding device 36 is a distribution pipe (see, for example, see...). Figure 17 It can be made of platinum.

[0055] See also Figure 4 and 5 In this embodiment, the feeding device 36 is a dispensing feeding device 36. The dispensing feeding device 36 includes an inner chamber 38, a base plate 40 defining the inner chamber 38, and side panels 42 extending upward from the base plate 40. The dispensing feeding device 36 also includes a groove 44 passing through the base plate 40, which provides a passageway exiting the dispensing feeding device 36 from the inner chamber 38. The groove 44 is arranged along a width 46 parallel to the axis 16 of rotation of the pair of forming rollers 14. In this embodiment, the width 46 is 200 mm to 400 mm, for example: 200 mm, 250 mm, 300 mm, 350 mm, or 400 mm, or any range including any two of those values ​​(e.g., 250 mm to 350 mm). In other embodiments, the width 46 is greater than 400 mm.

[0056] In one embodiment, the dispensing feed device 36 includes a plurality of heating elements 48. The plurality of heating elements 48 are in thermal communication with an inner chamber 38. Each of the plurality of heating elements 48 has an independently controllable heat output, thereby heating the bottom plate 40 of the inner chamber 38 to different temperatures across all different heating zones 50. For example, heating element 48a can be independently controlled to generate a first heat output that heats the bottom plate 40 of the inner chamber 38 to a first temperature across the entire heating zone 50a. Simultaneously, heating element 48b can be independently controlled to generate a second heat output that heats the bottom plate 40 of the inner chamber 38 to a second temperature across the entire heating zone 50b. The plurality of heating elements 48 may generate heat via resistance and other options.

[0057] In one embodiment, the device 10 also includes a pair of elements 52 for reducing heat loss (see, for example, see...). Figure 2 and 3There is one heat loss reducing element 52 on each side of the longitudinal surface 30. Each heat loss reducing element 52 has a surface 54 (which may be flat) facing the longitudinal surface 30 extending through the gap 24 between the pair of forming rollers 14. Each heat loss reducing element 52 is arranged longitudinally below the horizontal surface 28 of the axis of rotation 16 extending through the pair of forming rollers 14. Each heat loss reducing element 52 has a width 56 parallel to the axis of rotation 16 of the pair of forming rollers 14. The width of each heat loss reducing element 52 is narrower than the width 20 of the pair of forming rollers 14. In an embodiment, the heat loss reducing element 52 is passive, such as a heat-insulating substrate. In an embodiment, the heat loss reducing element 52 is active and includes a heating element. In an embodiment, the heat loss reducing element 52 includes one or more heating elements 53, the heat output of each of which is independently controllable. In an embodiment, the plurality of heating elements 53 are arranged in a horizontal row. In an embodiment, the plurality of heating elements 53 are arranged in a longitudinal column. In an embodiment, the plurality of heating elements 53 are arranged in both horizontal rows and longitudinal columns.

[0058] See also Figures 6A-6C In one embodiment, the device 10 further includes a first lateral edge cooling element 58 and a second lateral edge cooling element 60. Both the first lateral edge cooling element 58 and the second lateral edge cooling element 60 are arranged longitudinally below the horizontal plane 28 extending through the shaft 16 of the pair of forming rollers 14. As will be explained below, the first lateral edge cooling element 58 and the second lateral edge cooling element 60 are positioned to cool the lateral edges of the glass strip 12. The first lateral edge cooling element 58 and the second lateral edge cooling element 60 can take various forms, as further described herein.

[0059] See also Figure 7 In one embodiment, the first lateral edge cooling element 58 includes a first pair of clamping rollers 62a-b (see...). Figure 6AThe first pair of clamping rollers 62a-b includes a second pair of clamping rollers 64a-b. One roller of the first pair of clamping rollers 62a-b is positioned on one side of a longitudinal surface 30 extending through the gap 24 between the pair of forming rollers 14, and the other roller of the first pair of clamping rollers 62a-b is positioned on the other side of the longitudinal surface 30. Similarly, one roller of the second pair of clamping rollers 64a-b is positioned on one side of the longitudinal surface 30, and the other roller of the second pair of clamping rollers 64a-b is positioned on the other side of the longitudinal surface 30. Roller 62a of the first pair of clamping rollers 62a-b includes a laterally extending axle 66a. A static support base 68a holds the axle 66a, allowing roller 62a to rotate about the axle 66a. Similarly, the other roller 62b of the first pair of clamping rollers 62a-b includes a laterally extending axle 66b. A movable support base 68b holds the axle 66b, allowing roller 62b to rotate about the axle 66b. The movable support base 68b is movable on a track 70, which extends parallel to a horizontal plane 28 extending through the axis 16 of the pair of forming rollers 14. The movable support base 68b is connected to a piston 72, which is braked by a brake 74. Actuating the brake 74 causes the movable support base 68b to move, thus causing the roller to be positioned closer to or further away from the other roller. The second pair of clamping rollers 64a-b can take the same general structure, only configured as a mirror image of the first pair of clamping rollers 62a-b. In an embodiment, the first pair of clamping rollers 62a-b and the second pair of clamping rollers 64a-b can be thermally controllable. In other words, the heat output can be controlled, for example, by a temperature setting. As will be explained further below, the first pair of clamping rollers 62a-b and the second pair of clamping rollers 64a-b apply clamping forces to the lateral edges of the glass ribbon 12, thereby reducing its thickness and cooling it.

[0060] In other implementations (see Figure 6B The first lateral edge cooling element 58 includes a first tube outlet 76, and the second lateral edge cooling element 60 includes a second tube outlet 78. The first tube outlet 76 is positioned to horizontally blow cooling gas 80 inwards parallel to the longitudinal surface 30 extending through the pair of forming rollers 14. The second tube outlet 78 is positioned to horizontally blow cooling gas 80 inwards parallel to the longitudinal surface 30 extending through the pair of forming rollers 14, but in the opposite direction to the first tube outlet 76. Both the first tube outlet 76 and the second tube outlet 78 are arranged below the horizontal plane 28 of the axis of rotation 16 extending through the pair of forming rollers 14. As will be explained below, the first tube outlet 76 and the second tube outlet 78 are positioned to cool the lateral edge of the glass ribbon 12 by blowing cooling gas 80 into it.

[0061] In other implementations (see Figure 6CThe first lateral edge cooling element 58 includes a first radiation-absorbing element 82, and the second lateral edge cooling element 60 includes a second radiation-absorbing element 84. The first radiation-absorbing element 82 is positioned adjacent to a longitudinal surface 30 extending through the gap 24 between the pair of forming rollers 14. The second radiation-absorbing element 84 is also positioned adjacent to the longitudinal surface 30, but opposite to the first radiation-absorbing element 82. In an embodiment, the first radiation-absorbing element 82 and the second radiation-absorbing element 84 receive a cooling fluid. The cooling fluid can be water or air, among other options. As will be explained further below, the first radiation-absorbing element 82 and the second radiation-absorbing element 84 are positioned to cool the lateral edges of the glass strip 12 by absorbing heat from the lateral edges. While this disclosure describes several forms that the first lateral edge cooling element 58 and the second lateral edge cooling element 60 can take, the forms described are not exclusive, and the first lateral edge cooling element 58 and the second lateral edge cooling element 60 include any other object configured and positioned to cool the lateral edges of the glass strip 12 near the horizontal surface 28.

[0062] See also Figure 8A and 8B In one embodiment, the device 10 further includes a pair of dams 86. These dams 86 are arranged above a horizontal plane 28 extending through the shaft 16 of the pair of forming rollers 14. One or both of the dams 86 can move laterally toward and away from the other dam. The dams 86 may have a first position 88, where a distance 90 separates them. The dams 86 can move to the first position 88 and a second position 92, move away from the first position 88 and the second position 92, and move between the first position 88 and the second position 92, wherein the distance separating the dams 86 is smaller than when the dams 86 are in the first position 88. As further detailed below, the dams 86 cooperate with the outer cylindrical surface 18 of the pair of forming rollers 14 to control the width and height of the molten glass introduced into the gap 24 between the pair of forming rollers 14.

[0063] In one embodiment, each dam 86 includes a first profile surface 94 and a second profile surface 96. The first profile surface 94 conforms to the outer cylindrical surface 18 of one of the pair of forming rollers 14. The second profile surface 96 conforms to the outer cylindrical surface 18 of the other of the pair of forming rollers 14. By "conforms," ​​this means that the first profile surface 94 is arched and has a constant radius of rotation 16 of the forming roller 14 facing from the first profile surface 94, and similarly, the second profile surface 96 is arched and has a constant radius of rotation 16 of the forming roller 14 facing from the second profile surface 96. Each dam 86 may also include a bottom edge 98, where the first profile surface 94 and the second profile surface 96 come closest to converge. In one embodiment, the bottom edge 98 separates the first profile surface 94 and the second profile surface 96 by 0.7 mm to 2.0 mm. Each of the pair of dams 86 includes an inwardly facing main surface 100. In one embodiment, the inwardly facing main surface 100 is flat and orthogonal to a longitudinal surface 30 extending through the gap 24 between the pair of forming rollers 14.

[0064] In this implementation, the dam 86 is suspended above a pair of positioning rods 124 (see [link]). Figure 8A The positioning rod 124 extends horizontally parallel to the axis 16 of rotation of the pair of forming rollers 14. Each dam 86 includes a pair of orifices 126, and a positioning rod 124 extends through each orifice 126. The lateral position of each dam 86 along the positioning rod 124 can be adjusted such that the dam moves to a first position 88 and a second position 92, moves away from the first position 88 and the second position 92, and moves between the first position 88 and the second position 92. In other embodiments, each dam 86 is mounted to a slider 128 (see...). Figure 8B The slider 128 is suspended in the track 130, in which the slider 128 is able to slide to allow the dam 86 to move to and away from the first position 88 and the second position 92.

[0065] In this embodiment, the outer cylindrical surface 18 of each forming roller 14 is cooled to reduce its temperature. As explained in further detail below in conjunction with Comparative Example 3, as the forming roller 14 contacts the molten glass, the outer cylindrical surface 18 of the forming roller 14 expands (the maximum expansion occurs at the middle of the width 20), thereby forming an outer arc shape that imprints a dog-bone shape in the glass ribbon 12. Active cooling (or complementary active heating) helps prevent or limit the expansion of the outer cylindrical surface 18 of the forming roller 14.

[0066] For this, please refer to the following: Figure 9In one embodiment, the device 10 further includes a heat exchanger 102 disposed in one or both of the forming rollers 14, providing a channel for cooling fluid 110 in thermal communication with the outer cylindrical surface 18 of the forming roller 14. For example, the forming roller 14 includes transverse shafts 104a-b that define a pivot 16. The forming roller 14 also includes a distributor 106 having a plurality of orifices 108 arranged from the outer cylindrical surface 18 inward toward the pivot 16. Cooling fluid 110 (e.g., water, air, and water mist) or other suitable cooling fluid 110 is pressurized and fed into the distributor 106. The cooling fluid 110 is sprayed from the orifices 108 through the distributor 106 onto the inner cylindrical surface 112 of the forming roller 14, thereby cooling the inner cylindrical surface 112. Cooling of the inner cylindrical surface 112 is similarly achieved by conduction to cool the outer cylindrical surface 18. The heated cooling fluid 110 is removed from the interior of the forming roller 14 through the annular gap 114 between the distributor 106 and the transverse shaft 104b. The holes 108 can be arranged in any desired pattern to achieve the desired cooling effect.

[0067] In one embodiment, device 10 also includes a sprayer 116 (see, for example, see...). Figure 2 and 3 The sprayer 116 is positioned and configured to spray a fluid 118 (i.e., liquid or gas) (at a temperature lower than the outer cylindrical surface 18 of the forming roller 14) onto the outer cylindrical surface 18. The fluid 118 can be water or air, among other options. As the forming roller 14 rotates, the fluid 118 sprayed onto the outer cylindrical surface 18 by the sprayer 116 absorbs heat from the outer cylindrical surface 18 of the forming roller 14, thereby lowering the temperature and thus reducing its outer arc.

[0068] In other embodiments, device 10 further includes a liquid-cooled metal brush 120. The liquid may be water. The metal may be copper or some other metal having a high thermal conductivity and a sufficiently high melting point to withstand operating conditions. The liquid is in thermal contact with the metal brush 120. The metal brush 120 contacts and absorbs heat from the outer cylindrical surface 18 of the forming roller 14 as the forming roller 14 rotates. The liquid in thermal contact with the metal brush 120 absorbs the absorbed heat from the metal brush 120.

[0069] In other embodiments, device 10 further includes one or more liquid-cooled sliders 122. The liquid may be water. Each slider 122 may have a metal surface facing the outer cylindrical surface 18 of the forming roller 14. The metal may be copper or some other metal with a high thermal conductivity and a sufficiently high melting point to withstand the operating conditions. The metal surface absorbs heat from the outer cylindrical surface 18 of the forming roller 14. The liquid is in thermal communication with the metal surface and absorbs the absorbed heat from the metal surface.

[0070] In one embodiment, the apparatus further includes a convection cooling element 123. One convection cooling element 123 may be arranged on each side of the longitudinal surface 30 to guide cooling fluid (liquid or gas, such as air) toward the longitudinal surface 30. The convection cooling element 123 is arranged below the heat loss reduction element 52 (if included). As will be discussed further below, the convection cooling element 123 can increase the cooling rate of the glass ribbon 12 after it has cooled to the glass transition temperature and before the glass sheet 154 separates from the glass ribbon 12.

[0071] See also Figure 10 and 11 In use, the feed device 36 supplies a stream 132 of molten glass 134 downward into the gap 24 between the pair of forming rollers 14. The feed device 36 receives the molten glass 134 from a transfer system 34 (which may be a batch system supplying a certain volume of molten glass 134, or a continuous system supplying molten glass 134 for several days, months, or even years). In embodiments of the device 10 where the feed device 36 is a dispensing feed device 36, the molten glass 134 in the inner chamber 38 exits the inner chamber 38 as the stream 132 of molten glass 134 through the trough 44. In such embodiments, the molten glass 134 in the inner chamber 38 of the dispensing feed device 36 preferably has a viscosity of 5 poise to 8 poise. Glass substrates with high refractive indices typically have low liquidus viscosities within this range. In one embodiment, the stream 132 of molten glass 134 has a width 136 of 25 mm to 4000 mm parallel to the axis 16 of the forming roller 14, for example: 25 mm, 50 mm, 100 mm, 200 mm, 250 mm, 300 mm, 350 mm, 400 mm, 500 mm, 750 mm, 1000 mm, 2000 mm, 3000 mm, or 4000 mm, or any range including any two of those values ​​(e.g., 250 mm to 3000 mm). In other embodiments, the stream 132 of molten glass 134 exiting the dispensing feeder 36 is a single stream and has a generally cylindrical shape.

[0072] The flow 132 of molten glass 134 deposited between the pair of forming rollers 14 forms a puddle 138 of the molten glass 134 in contact with the pair of forming rollers 14 within the gap 24. In an embodiment of the device 10 including a pair of dams 86, the dams 86 cooperate with the outer cylindrical surfaces 18 of the pair of forming rollers 14 to define the puddle retention volume. In other words, the dams 86 limit the width of the puddle 138 of the molten glass 134, and the puddle 138 of the molten glass 134 contacts the outer cylindrical surfaces 18 of the pair of forming rollers 14 at a height 142 above a horizontal plane 28 extending through the pivot 16 of the pair of forming rollers 14.

[0073] As the pair of forming rollers 14 rotate toward each other above the horizontal plane 28, they draw the molten glass 134 into the pit 138 and downward through the gap 24, thereby forming a glass ribbon 12 extending longitudinally downward from the horizontal plane 28. The glass ribbon 12 has two main surfaces 144. These two main surfaces 144 face approximately in opposite directions. These two main surfaces 144 are approximately parallel to the longitudinal plane 30. The glass ribbon 12 has a thickness 146 between these two main surfaces 144.

[0074] While forming the molten glass 134 into a glass strip 12, the forming rollers 14 may cause the molten glass 134 to spread. This is as follows: Figure 10 The width 148 of the glass ribbon 12, parallel to the axis 16 of the pair of forming rollers 14, is wider than the width 140 of the pit 138 of the molten glass 134. In an embodiment, the width 148 of the glass ribbon 12 may be approximately equal to the width 140 of the pit 138 of the molten glass 134. The width 148 extends between a first lateral edge 150a and a second lateral edge 150b (extending generally longitudinally). Furthermore, the pair of forming rollers 14 cools the glass so that the viscosity of the pit 138 of the molten glass 134 is sufficiently high to support the glass ribbon 12 without the weight of the glass ribbon 12 causing the glass ribbon 12 to separate from the pit 138 of the molten glass 134 below the horizontal plane 28.

[0075] A portion of each main surface 144 of the glass strip 12 faces one of the heat loss reduction elements 52. In other words, the heat loss reduction element 52 sandwiches the glass strip 12 between them. In one embodiment, the heat loss reduction element 52 does not contact the glass strip 12, while in other embodiments, the heat loss reduction element 52 does contact the glass strip 12. In one embodiment, the width 56 of each heat loss reduction element 52 is narrower than the width 148 of the glass strip 12. In one embodiment, where the heat loss reduction element 52 includes a heating element 53, the heating element 53 is independently controlled to generate heating adjacent to the glass strip 12.

[0076] As mentioned above, the outer diameter 22 of the outer cylindrical surface 18 of the forming roller 14 is between 20 mm and 600 mm. Choosing a smaller outer diameter 22 within this range can improve the distribution of the molten glass 134 in the pits 138 and achieve a reduced flow rate. In this embodiment, the outer diameter 22 of the forming roller 14 is between 20 mm and 80 mm. As shown in Examples 1 and 14 below, the improved distribution of the molten glass 138 due to the smaller outer diameter 22 of the forming roller 14 can produce a glass ribbon 12 with a generally wider width 148 and a thinner thickness 146 (compared to the forming roller 14 with a larger outer diameter 22).

[0077] When the viscosity of the molten glass 134 is between 0.1 poise and 3000 poise, using a forming roller 14 with a smaller outer diameter 22 is particularly useful. At these viscosities, gravity effectively distributes the molten glass 134 horizontally into pits 138 before the glass is formed into the glass ribbon 12, even when the feed device 36 is a distribution pipe. The less viscous the molten glass 134, the wider the horizontal distribution of the pits 138. The wider the pits 138, the wider the resulting glass ribbon 12 width 148. Viscosities above 3000 poise may prevent gravity from distributing the molten glass 134 into a wide range of pits 138.

[0078] For any given rotational speed, the smaller outer diameter 22 reduces the amount of time that the molten glass 134 pit 138 contacts the forming roller 14. This reduction in time decreases heat transfer from the molten glass 134 pit 138 to the forming roller 14. This reduction in heat transfer means that the forming roller 14 forms the glass ribbon 12 at a relatively higher temperature, which results in a relatively thinner glass ribbon 12 with a thickness 146.

[0079] Furthermore, for any given longitudinal spacing relative to the horizontal plane, the horizontal spacing between the forming rollers 14 above the horizontal plane 28 increases as the outer diameter 22 of the forming rollers 14 decreases. In other words, as the outer diameter 22 of the forming rollers 14 decreases, the area of ​​the top surface of the pit 138 of the molten glass 134 increases. This increased area increases the pressure that pushes the pit 138 wider along the axis of rotation 16 of the forming rollers 14, resulting in a wider glass ribbon 12 with a wider width 148.

[0080] See also Figure 12 and 13 This document describes a method 152 for forming a glass sheet 154 from a glass ribbon 12. After the pair of forming rollers 14 have formed the glass ribbon 12 from the pit 138 of the molten glass 134 (step 156), method 152 includes: (a) reducing the horizontal temperature change of the glass ribbon 12 before it cools to the glass transition temperature, and (b) one or more of the following: (i) reducing the longitudinal temperature drop rate of the glass ribbon 12 before it cools to the glass transition temperature, and (ii) increasing the longitudinal temperature drop rate of the glass ribbon 12 after it cools to the glass transition temperature. In this embodiment, the viscosity of the glass ribbon 12 slightly below the horizontal plane 28 is approximately 10. 7Poiseuille. This viscosity allows the glass ribbon 12 to support itself longitudinally downward from the pair of forming rollers 14 while simultaneously providing sufficient time to manipulate horizontal temperature changes and longitudinal cooling rates, according to method 152, as described below. If the glass ribbon 12 had a much lower viscosity at this point, it would stretch under its own weight, increasing the difficulty of controlling the glass ribbon 12 near the glass transition temperature. If the glass ribbon 12 had a much higher viscosity, it would experience pressure checks (i.e., surface defects in the glass ribbon 12) and residual stress. Furthermore, at this viscosity order, the transverse edges 150a-b of the glass ribbon 12 are sufficiently cooled to limit rounding due to surface tension that has not yet been cooled, thereby suppressing further cooling of the transverse edges 150a-b relative to the central portion 158 of the glass ribbon 12, thus reducing horizontal temperature changes before cooling to the glass transition temperature.

[0081] As the pair of forming rollers 14 transforms the pit 138 of molten glass 134 into glass ribbon 12, the temperature of the glass ribbon 12 may vary as a function of its horizontal position along the width 148 of the glass ribbon 12. For example, assuming at the same horizontal position (i.e., at the same distance from the horizontal plane 28 extending through the axis 16 of the pair of forming rollers 14), the temperature of the glass ribbon 12 at its lateral edges 150a-b may be higher than the temperature of the glass ribbon 12 at its central portion 158.

[0082] Furthermore, as the pair of forming rollers 14 transforms the molten glass 134 from the pit 138 into the glass ribbon 12, the temperature of the glass ribbon 12, as a function of the distance from the horizontal plane 28, decreases from top to bottom. For example, the temperature of the glass ribbon 12 at the longitudinal position 160 is higher than that at the lower longitudinal position 162, and these two longitudinal positions 160, 162 are approximately equidistant from the lateral edges 150a, 150b of the glass ribbon 12. Ultimately, the temperature of the glass ribbon 12 cools to the glass transition temperature in the solidification zone 164, which may occur after a distance of 166 from the horizontal plane 28.

[0083] After the glass ribbon 12 has cooled below its glass transition temperature, it continues to cool. Method 152 also includes step 168 separating the glass sheet 154 from the glass ribbon 12. Multiple glass sheets 154 can be separated from the glass ribbon 12 during the same batch.

[0084] This disclosure specifically reveals that if: (a) the horizontal temperature change of the glass ribbon 12 is not reduced before the glass ribbon 12 is cooled to the glass transition temperature in the solidification zone 164, and (b) either: (i) the rate of temperature decrease of the glass ribbon 12 is not reduced before the glass ribbon 12 is cooled to the glass transition temperature in the solidification zone 164, or (ii) the rate of temperature decrease of the glass ribbon 12 is not increased after the glass ribbon 12 is cooled to the glass transition temperature, then it is impossible to separate the glass sheet 154 from the glass ribbon 12 without causing the glass sheet 154 and the glass ribbon 12 to break, or if the glass sheet 154 is successfully separated from the glass ribbon 12 without breaking, the glass sheet 154 has a suboptimal warpage and / or total thickness variation. This concept is illustrated in Comparative Example 2 below. In other words, it was found that if: (a) the horizontal temperature change of the glass strip 12 is sufficiently reduced before the glass strip 12 is cooled to the glass transition temperature, and (b) either: (i) the rate of temperature decrease of the glass strip 12 is sufficiently reduced before the glass strip 12 is cooled to the glass transition temperature, or (ii) the rate of temperature decrease of the glass strip 12 is sufficiently increased after the glass strip 12 is cooled to the glass transition temperature, then the glass sheet 154 can be separated from the glass strip 12 without breakage and the glass sheet 154 can have acceptable warpage and total thickness variation, even when the glass composition results in the glass sheet 154 having a low liquidus viscosity.

[0085] Without being bound by theory, it is hypothesized that the tendency of the glass strip 12 to fracture is a function of the internal stress level of the glass strip 12, as are the warpage level and total thickness variation of the glass sheet 154 separated from the glass strip 12. As the internal stress of the glass strip 12 increases, the step 168 of separating the glass sheet 154 from the glass strip 12 becomes more likely to cause both to fracture, and if the glass sheet 154 is separated without fracture, the warpage and total thickness variation will be even greater.

[0086] Furthermore, it is hypothesized that the internal stress of glass strip 12 is a function of the horizontal temperature change, and either (i) the rate of temperature decrease of glass strip 12 before it cools to the glass transition temperature in solidification zone 164, or (ii) the rate of temperature decrease of glass strip 12 after it cools to the glass transition temperature. Horizontal temperature fluctuations increase internal stress: the greater the fluctuation, the greater the stress. For the longitudinal rate of temperature decrease, it is hypothesized that a constant rate of change of thermal strain along the downward direction of glass strip 12 results in no thermal stress caused by thermal strain, and therefore no warping. Assuming the horizontal temperature change is close to zero and the longitudinal rate of change of thermal strain is relatively constant, the Laplace operator of thermal strain is also close to zero, and there is no thermal stress caused by thermal strain. However, since thermal strain is a function of the coefficient of thermal expansion of the glass material, this increases complexity. Furthermore, the coefficient of thermal expansion of glass strip 12 is higher when its temperature is above the glass transition temperature than when its temperature is below the glass transition temperature. Therefore, in order to achieve a constant rate of thermal strain change along the glass ribbon 12 downwards (particularly in the solidification zone 164, where the glass ribbon 12 enters at a temperature higher than the glass transition temperature and leaves at a temperature lower than the glass transition temperature), the glass ribbon 12 cools more slowly when the temperature is above the glass transition temperature (compared to when the temperature is below the glass transition temperature). In other words, to achieve the desired constant rate of thermal strain change along the direction of the glass ribbon 12 downwards, it is particularly important to achieve a slower cooling before reaching the glass transition temperature (e.g., + / - 50°C) (within the solidification zone 164) and a faster cooling after reaching the glass transition temperature. This concept is further explained below in conjunction with Example 10. This can be achieved by either (i) actively reducing the rate of temperature drop of the glass ribbon 12 before reaching the glass transition temperature, or (ii) actively increasing the rate of temperature drop of the glass ribbon 12 after reaching the glass transition temperature, or both (i) and (ii).

[0087] The internal stress of the glass strip 12 can be reduced by taking proactive measures to reduce horizontal temperature changes and either (i) reducing the longitudinal cooling rate of the glass strip 12 before it reaches the glass transition temperature in the solidification zone 164, or (ii) increasing the longitudinal cooling rate of the glass strip 12 after it reaches the glass transition temperature (or both (i) and (ii)).

[0088] In one embodiment, in step 170, method 152 further includes: feeding molten glass 134 into the inner chamber 38 of the distribution feeder 36 before the pair of forming rollers 14 form glass strip 12 from the pit 138 of molten glass 134.

[0089] Following this, in step 172, method 152 further includes: supplying molten glass 134 from the inner chamber 38 through multiple orifices 44 of the dispensing feed device 36 and into the gap 24 separating the pair of forming rollers 14, thereby forming the pit 138 of the molten glass 134. As will be further demonstrated below in conjunction with Comparative Example 2, supplying molten glass 134 with a single outlet pipe results in a higher temperature change on the glass ribbon 12 immediately after the pair of forming rollers 14 form the glass ribbon 12. With a single outlet pipe, the newly supplied molten glass 134 flows laterally away from the existing pit 138 of the molten glass 134 above the forming rollers 14 and has less cooling time before forming the lateral edges 150a-b of the glass ribbon 12 (compared to the molten glass 134 in the central portion of the pit 138 forming the central portion 158 of the glass ribbon 12). A feed stream 132 (groove 44 having a width of 46) for molten glass 134 is supplied using a distribution feed device 36, resulting in a wider mass distribution of the newly supplied molten glass 134 on the feed 138. The molten glass 134 is supplied across the entire width 46 of the groove 44, leading to a wider distribution of the molten glass 134 to the pair of forming rollers 14 compared to a single outlet pipe. This wider distribution results in a more uniform cooling time before the forming rollers 14 draw the feed 138 of the molten glass 134 downwards to form the glass ribbon 12. This more uniform cooling time in the horizontal direction on the feed 138 of the molten glass 134 results in a glass ribbon 12 with reduced horizontal temperature variations.

[0090] In one implementation, in step 174, method 152 further includes independently controlling the heat output of each of the plurality of heating elements 48 of the dispensing feeder 36. During the formation of the glass ribbon 12, horizontal temperature variations of the glass ribbon 12 can be monitored. When the use of the dispensing feeder 36 results in a glass ribbon 12 with suboptimal horizontal temperature variations, the heat output of each of the plurality of heating elements 48 can be independently controlled to compensate for these suboptimal horizontal temperature variations. For example, if the lateral edges 150a-b of the glass ribbon 12 have a higher temperature than the central portion 158 or the area between the lateral edges 150a-b and the central portion 158, heating elements 48 corresponding approximately to the lower temperature region of the glass ribbon 12 can be activated to increase the temperature of the molten glass 134 flowing through the region of the groove 44. This reduces the horizontal temperature variations of the subsequently formed glass ribbon 12.

[0091] In an embodiment, in step 176, method 152 further includes absorbing heat from one or both of the pair of forming rollers 14 after the glass ribbon 12 has been formed from the molten glass 134 from the pit 138. As the temperature of the forming rollers 14 increases, the outer diameter 22 of the forming rollers 14 experiences a maximum increase at the midpoint of the width 20 of the forming rollers 14. The increase in the outer diameter 22 of the forming rollers 14 gradually decreases from the midpoint of the width 20 of the forming rollers 14 in a laterally outward manner. Regardless of the degree of horizontal temperature change of the glass ribbon 12 or the rate at which the glass ribbon 12 cools to the glass transition temperature, this outward arc of the forming rollers 14 solidifies in the glass ribbon 12 to form a dog-bone shape. Cooling the outer cylindrical surface 18 reduces the arc, thereby reducing or eliminating the dog-bone shape.

[0092] Heat can be absorbed from one or both of the pair of forming rollers 14 in a variety of ways. In one embodiment, heat is absorbed from one or both of the pair of forming rollers 14 in one or more of the following ways: (i) by transferring heat exchange cooling fluid 110 into the forming roller 14 and by thermally communicating the heat exchange cooling fluid 110 with the outer cylindrical surface 18 of the forming roller 14; (ii) by spraying fluid 118 with a temperature lower than that of the outer cylindrical surface 18 of the forming roller 14 onto the outer cylindrical surface 18, for example by sprayer 116; (iii) by bringing the forming roller 14 into contact with the liquid-cooled metal brush 120; and (iv) by positioning the forming roller 14 opposite the liquid-cooled slider 122, but not limited thereto. In one embodiment, more heat is absorbed near the midpoint of the width 20 of the forming roller 14 compared to the edges of the forming roller 14.

[0093] As mentioned above, in step 156, method 152 includes reducing the horizontal temperature variation of the glass ribbon 12 before it cools to the glass transition temperature. In an embodiment, step 156 of reducing the temperature variation includes increasing the heat loss of the lateral edges 150a-b of the glass ribbon 12 relative to the central portion 158 of the glass ribbon 12. In other words, to reduce the horizontal temperature variation, the focus can be on making the cooling of the lateral edges 150a-b greater than that of the central portion 158 of the glass ribbon 12.

[0094] As mentioned above, the molten glass 134 forming the glass ribbon 12 tends to have a higher temperature at the transverse edges 150a-b compared to the central portion 158. This is one aspect of the horizontal temperature variation of the glass ribbon 12. Without being bound by theory, it is believed that this temperature inconsistency leads to inconsistency in surface tension (specifically, an increased surface tension at the transverse edges 150a-b). The greater surface tension at the transverse edges 150a-b pulls the adjacent molten glass 134 towards the transverse edges 150a-b, thereby increasing the thickness 146 of the glass ribbon 12 at the transverse edges 150a-b. This increased thickness 146 at the transverse edges 150a-b results in a decrease in the surface-to-volume ratio at the transverse edges 150a-b, and thus further reduces the cooling rate relative to the rest of the glass ribbon 12, further amplifying the horizontal temperature variation. Therefore, actively reducing the thickness 146 and / or temperature of the glass ribbon 12 at the transverse edges 150a-b before cooling to the glass transition temperature compensates for the aforementioned effects and thereby improves the horizontal temperature variation. Externally, actively reducing the thickness 146 of the glass strip 12 at the transverse edges 150a-b directly reduces the total thickness variation of the glass strip 12.

[0095] See also Figure 14A In an embodiment, increasing the heat loss of the transverse edges 150a-b of the glass ribbon 12 relative to the central portion 158 of the glass ribbon 12 includes blowing cooling gas 80 onto the transverse edges 150a-b. For example, a first pipe outlet 76 is positioned to blow cooling gas 80 onto the transverse edge 150a of the glass ribbon 12 parallel to the longitudinal plane 30, and a second pipe outlet 78 is positioned to blow cooling gas 80 onto the second transverse edge 150b of the glass ribbon 12, which is also parallel to the longitudinal plane 30. The cooling gas 80 can be air. Because the cooling gas 80 is blown onto the transverse edges 150a-b of the glass ribbon 12 parallel to the longitudinal plane 30, the contact between the cooling gas 80 and the transverse edges 150a-b is prior to and greater than that with the central portion 158 of the glass ribbon 12. Therefore, the increase in heat loss of the cooling gas 80 relative to the transverse edges 150a-b of the glass ribbon 12 is greater than that with the central portion 158 of the glass ribbon 12. This concept is illustrated in Comparative Example 4 and Embodiment 5 below. Care should be taken when selecting the flow rate of the cooling gas 80, because as the flow rate increases, the probability of the cooling gas 80 introducing warping into the glass ribbon 12 increases.

[0096] See also Figure 14BIn other embodiments, increasing the heat loss of the lateral edges 150a-b of the glass ribbon 12 relative to the central portion 158 of the glass ribbon 12 includes a first lateral edge cooling element 58 that reduces the temperature of the first lateral edge 150a of the glass ribbon 12 and a second lateral edge cooling element 60 that reduces the temperature of the second lateral edge 150b of the glass ribbon 12. As mentioned above, the first lateral edge cooling element 58 and the second lateral edge cooling element 60 may respectively include a first radiation absorbing element 82 and a second radiation absorbing element 84. The first radiation absorbing element 82 faces the first lateral edge 150a of the glass ribbon 12. The second radiation absorbing element 84 faces the second lateral edge 150b of the glass ribbon 12. Adjusting the flow rate of the cooling fluid flowing through the first radiation absorbing element 82 and the second radiation absorbing element 84 alters the heat absorbed from the first lateral edge 150a and the second lateral edge 150b of the glass ribbon 12, respectively.

[0097] Come back and see Figure 10 and 11In one embodiment, increasing the heat loss of the lateral edges 150a-b of the glass ribbon 12 relative to the central portion 158 of the glass ribbon 12 includes reducing the thickness 146 of the glass ribbon 12 at its lateral edges 150a-b. For example, the first pair of clamping rollers 62a-b are configured to reduce the thickness 146 of the glass ribbon 12 at its first lateral edge 150a. One roller of the first pair of clamping rollers 62a-b contacts one of the main surfaces 114 of the glass ribbon 12 at the first lateral edge 150a. The other roller of the first pair of clamping rollers 62a-b contacts another main surface 144 of the glass ribbon 12 at the first lateral edge 150a. The rollers of the first pair of clamping rollers 62a-b apply a clamping force on the first lateral edge 150a of the glass ribbon 12. Therefore, as the first pair of clamping rollers 62a-b rotates and thus pulls the glass ribbon 12 between them, the rollers of the first pair of clamping rollers 62a-b reduce the thickness 146 of the glass ribbon 12. The second pair of clamping rollers 64a-b is configured to reduce the thickness 146 of the glass ribbon 12 at the second lateral edge 150b in a similar manner. The second pair of clamping rollers 64a-b contacts and pulls the second lateral edge 150b of the glass ribbon 12 through the second pair of clamping rollers 64a-b, reducing the thickness 146 at the second lateral edge 150b. The rotational speed of the first pair of clamping rollers 62a-b and the second pair of clamping rollers 64a-b can be faster than the speed at which the glass ribbon 12 moves forward through the first pair of clamping rollers 62a-b and the second pair of clamping rollers 64a-b. The faster rotation of the clamping rollers 62a-b and 64a-b prevents the glass ribbon 12 from sticking and reduces out-of-round variation (i.e., the variation induced by the clamping rollers 62a-b and 64a-b not rotating in a perfect circle around their respective axles 66).

[0098] Furthermore, in this embodiment, the first pair of clamping rollers 62a-b and the second pair of clamping rollers 64a-b can be thermally controlled to actively control the heat absorbed from the lateral edges 150a-b of the glass ribbon 12. This heat absorption from the lateral edges 150a-b can improve the horizontal temperature variation on the glass ribbon 12. In other words, in this embodiment, increasing the heat loss of the lateral edges 150a-b of the glass ribbon 12 relative to the central portion 158 includes bringing the lateral edges 150a-b of the glass ribbon 12 into contact with the opposing rollers 62a-b, 64a-b that absorb heat from the lateral edges 150a-b of the glass ribbon 12.

[0099] As further illustrated in Embodiment 6 below, both the first pair of clamping rollers 62a-b and the second pair of clamping rollers 64a-b can reduce horizontal temperature variations on the glass ribbon 12 (improving warping, overall thickness variations, and the ability to separate the glass sheet 154 without breakage) and directly reduce the thickness variation of the lateral edges 150a-b of the glass ribbon 12 relative to the central portion 158. In this embodiment, before the thickness 146 of the glass ribbon 12 at the lateral edges 150a-b is reduced, the thickness 146 of the glass ribbon 12 at the lateral edges 150a-b is at least 0.5 mm greater than the thickness 146 of the glass ribbon 12 at the central portion 158. In this embodiment, after the thickness 146 of the glass ribbon 12 at the lateral edges 150a-b is reduced, the thickness 146 of the glass ribbon 12 at the lateral edges 150a-b is less than 0.1 mm greater than the thickness 146 of the glass ribbon 12 at the central portion 158.

[0100] In this embodiment, reducing the horizontal temperature variation of the glass ribbon 12 before it cools to the glass transition temperature includes reducing the heat loss of the central portion 158 of the glass ribbon 12 relative to the lateral edges 150a-b. As described above, one approach to reducing the horizontal temperature variation of the glass ribbon 12 is to reduce the temperature of the lateral edges 150a-b relative to the central portion 158. Another approach is to reduce the heat loss of the central portion 158 relative to the lateral edges 150a-b. This approach achieves cooling of the lateral edges 150a-b without assistance while slowing the cooling rate of the central portion 158. As the glass ribbon 12 approaches the glass transition temperature, the faster cooling of the hotter lateral edges 150a-b and the slower cooling of the central portion 158 allow the horizontal temperature variation to decrease as the glass ribbon 12 moves downward.

[0101] In this embodiment, reducing heat loss of the central portion 158 of the glass strip 12 relative to the lateral edges 150a-b of the glass strip 12 involves oriented the central portion 158 of the glass strip 12 toward the heat-reducing element 52 (while the lateral edges 150a-b of the glass strip 12 are not). As described above, the width 56 of each heat-reducing element 52 is narrower than the width 148 of the glass strip 12. Assuming that each heat-reducing element 52 is centered relative to the glass strip 12, each heat-reducing element 52 is opposite to one of the main surfaces 144 at the central portion 158 of the glass strip 12 but not opposite to the lateral edges 150a-b of the glass 12. Thus, the heat-reducing element 52 (which, as mentioned, may be an insulating substrate, an active heating element, or both) reduces the rate at which the central portion 158 of the glass strip 12 cools but does not reduce the rate at which the lateral edges 150a-b of the glass strip 12 cool. As the glass ribbon 12 moves downward from the horizontal plane 28 and cools toward the glass transition temperature, the cooler lateral edges 150a-b cool faster than the central portion 158 opposite the heat loss reduction element 52, thus reducing the horizontal temperature variation. This aspect is further explained in Comparative Examples 7 and 8 below. When an active heating element is used as the heat loss reduction element 52, the heating element 53 can be controlled such that the temperature of the surface 54 of the heat loss reduction element 52, which is affected by the heating element 53 and faces the glass ribbon 12, contributes to the balance of the horizontal temperature variation of the glass ribbon 12. In some cases, the temperature of the surface 54 of the heat loss reduction element 52 is lower than the temperature of the region of the glass ribbon 12 closest to the surface 54. In other cases, the temperature of the surface 54 of the heat loss reduction element 52 is higher than the temperature of the region of the glass ribbon 12 closest to the surface 54.

[0102] In one embodiment, reducing the horizontal temperature variation of the glass ribbon 12 before it cools to the glass transition temperature includes increasing the height 142 of the pit 138 of the molten glass 134 relative to the horizontal plane 28. In another embodiment, increasing the height 142 of the pit 138 of the molten glass 134 includes increasing the flow rate of the molten glass 134 feed stream 132 from the feed device 36. It was found that the temperature of the transverse edges 150a-b of the glass ribbon 12 (and thus the horizontal temperature variation of the glass ribbon 12) is a function of the height 142 of the pit 138 of the molten glass 134. More specifically, the lower the height 142 of the pit 138 of the molten glass 134, the higher the temperature of the transverse edges 150a-b of the molten glass 134 and the greater the horizontal temperature variation. Experiments have confirmed that for every millimeter increase in the height 142 of the pit 138 of the molten glass 134, the temperature at the transverse edges 150a-b of the glass ribbon 12 decreases by approximately 6°C. Unrestricted by theory, it is believed that increasing the height 142 of the pit 138 of the molten glass 134 increases the amount of time that the molten glass 134 contacts the outer cylindrical surface 18 of the forming roller 14, and the increase in contact time further reduces the temperature of the molten glass 134 before forming the glass ribbon 12.

[0103] See also Figure 15 As mentioned above, the device 10 may include a pair of laterally movable dams 86 that can move closer to each other, and the dams 86 and the outer cylindrical surface 18 of the forming roller 14 define a pit material retention volume. As at least one of the pair of dams 86 moves from a first position 88 (see, for example, [link to previous text]). Figure 10 Move to the second position 92 (see, for example) Figure 15 The width 140 of the pit 138 of the molten glass 134 narrows and the height of the pit 138 of the molten glass 134 increases. This causes the dams 86 to move closer to each other, increasing the height 142 of the pit 138 of the molten glass 134. In an embodiment, increasing the height 142 of the pit 138 of the molten glass 134 relative to the horizontal plane 28 includes moving one or both of the movable dams 86 closer to the other of the movable dams 86. The movable dams 86 additionally provide a constant height 142 of the pit 138 of the molten glass 134 in response to changes in the flow rate of the molten glass 134 from the feed device 36. In an embodiment, the dams 86 are thermally controllable, thereby absorbing heat from the sides of the molten glass 134, which can help reduce horizontal temperature variations in the glass ribbon 12. The relationship between the height 142 of the pit 138 and the horizontal temperature variations of the glass ribbon is further illustrated in Embodiment 9 below.

[0104] In an embodiment, the horizontal temperature change of the glass strip 12 before it is cooled to the glass transition temperature results in a horizontal temperature change of 10°C or less, or 8°C or less, or 5°C or less, or 2°C or less, or 1°C or less across the entire width of the glass strip 12, for example: 10°C, 9°C, 8°C, 7°C, 6°C, 5°C, 4°C, 3°C, 2°C, 1°C, 0.5°C, or 0.1°C, or any range including any two of those values ​​(e.g., 0.1°C to 5°C). In an embodiment, the temperature change is at 60%, 65%, 70%, 75%, 80%, 95%, 90%, 95%, or 99% of the entire width of the glass strip 12. Therefore, the horizontal temperature variation of the glass strip 12 over 80% of the entire width of the glass, for example, could be 10°C or less, or 8°C or less, or 5°C or less, or 2°C or less, or 1°C or less. In another example, the horizontal temperature variation of the glass strip 12 over 90% of the entire width of the glass could be 10°C or less, or 8°C or less, or 5°C or less, or 2°C or less, or 1°C or less. The horizontal temperature variation is the difference between the maximum and minimum temperatures of a portion of the glass strip 12 selected at the same horizontal position. It can be measured via an infrared camera. The measurement is taken before the glass strip 12 cools to the glass transition temperature, for example, when the difference between the minimum temperature and the glass transition temperature is within 50°C.

[0105] In addition to reducing the horizontal temperature change of the glass ribbon 12, method 152 further includes one or more of the following: (i) reducing the longitudinal temperature drop rate of the glass ribbon 12 before it cools to the glass transition temperature; and (ii) increasing the longitudinal temperature drop rate of the glass ribbon 12 after it cools to the glass transition temperature. As described above, one aspect of longitudinal temperature control is achieving a constant rate of change of thermal strain through the solidification zone 164 as the glass ribbon 12 cools to and through the glass transition temperature. A constant rate of change of thermal strain reduces thermal stress. This concept is further explained below in conjunction with Example 10. Reducing thermal strain results in the ability to separate the glass sheet 154 from the glass ribbon 12 without breakage, and the glass sheet 154 having acceptable warpage and total thickness variation. In the embodiment, (i) the glass ribbon 12 is cooled at a first average cooling rate from 50°C above the glass transition temperature to the glass transition temperature; (ii) the glass ribbon 12 is cooled at a second average cooling rate from the glass transition temperature to 50°C below the glass transition temperature; and (iii) the first average cooling rate is slower than the second average cooling rate. In other words, the glass ribbon 12 is cooled at a first average cooling rate before it reaches the glass transition temperature, which is slower than the second average cooling rate at which the glass ribbon 12 is cooled after it reaches the glass transition temperature. The average cooling rate discussed herein refers to the average cooling rate of the glass ribbon 12 along the length of the glass within the solidification zone 164.

[0106] In this implementation, the glass strip is cooled to its glass transition temperature within a 24-inch range from the horizontal plane, for example: within 5 inches, 6 inches, 7 inches, 8 inches, 9 inches, 10 inches, 11 inches, 12 inches, 13 inches, 14 inches, 15 inches, 16 inches, 17 inches, 18 inches, 19 inches, 20 inches, 21 inches, 22 inches, 23 inches, or 24 inches, or any range including any two of those values ​​(e.g., 8 to 18 inches). Thus, step 156, which reduces horizontal temperature variation, is performed within this span (and, if combined, slows the longitudinal cooling rate along the glass strip 12).

[0107] In one embodiment, reducing the longitudinal temperature drop rate of the glass ribbon 12 before it cools to the glass transition temperature involves oriented the main surface 144 of the glass ribbon 12 toward the element 52 for reducing heat loss. In an embodiment where the element 52 for reducing heat loss is an insulating substrate, the insulating substrate reduces heat transfer from the glass ribbon 12 to the external environment, which reduces the temperature drop rate of the glass ribbon 12. To effectively reduce heat transfer from the glass ribbon 12, the insulating substrate should be approximately 1 mm away from the glass ribbon 12. In an embodiment where the element 52 for reducing heat loss includes a heating element 53, the heat output of the heating element 53 can be controlled to reduce the longitudinal temperature drop rate of the glass ribbon 12 (compared to the case without the element 52 for reducing heat loss). The rows of heating elements 53 can be configured such that their heat output is reduced as a function of the longitudinal distance relative to the horizontal plane 28.

[0108] Then, after the glass ribbon 12 cools to the glass transition temperature and before the glass sheet 154 is separated from the glass ribbon 12, the main surface 144 of the glass ribbon 12 no longer faces the heat loss reduction element 52. In other words, the heat loss reduction element 52 faces the glass ribbon 12 before the temperature of the glass ribbon 12 is above the glass transition temperature, but after the temperature of the glass ribbon 12 cools to below the glass transition temperature (e.g., when the temperature of the glass ribbon 12 is 25°C, or 50°C, or 25°C to 50°C below the glass transition temperature), the heat loss reduction element 52 no longer faces the glass ribbon 12. These aspects are further illustrated below in conjunction with Comparative Example 11 and Example 12.

[0109] In one embodiment, increasing the longitudinal temperature drop rate of the glass ribbon 12 after it has cooled to the glass transition temperature includes purging cooling fluid onto one or more main surfaces 144 of the glass ribbon 12. In another embodiment, a convection cooling element 123 can direct cooling fluid to the main surfaces 144 of the glass ribbon 12. In yet another embodiment, the convection cooling element 123 directs cooling fluid to the main surfaces 144 of the glass ribbon 12 while the glass ribbon 12 is in the solidification zone 164 (but after the glass ribbon 12 has cooled to the glass transition temperature).

[0110] As mentioned, the aforementioned apparatus 10 and method 152 are particularly advantageous for manufacturing glass sheets 154 with high refractive indices. The refractive index used herein is the refractive index at room temperature and with respect to electromagnetic radiation with a wavelength of approximately 589 nm. For "high refractive index," this means that the glass sheet 154 has a refractive index of 1.65 or greater, for example: 1.65, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3.0, 3.1, 3.2, 3.3, or any range including any two of those values ​​(e.g., 1.7 to 3.0, 1.7 to 2.1, etc.). For example, a composition providing a refractive index of 1.8 (at a wavelength of 633 nm) comprises (in mole percent): 40.1 SiO2, 11.3 Li2O, 3.8 ZrO2, 4.8 Nb2O5, 2.4 B2O3, 22.9 CaO, 5.4 La2O3, and 9.3 TiO2. In weight percent, the composition comprises: 28.5 SiO2, 4.00 Li2O, 5.5 ZrO2, 15 Nb2O5, 2.0 B2O3, 15.2 CaO, 21 La2O3, and 8.8 TiO2. While method 152 is particularly advantageous for producing glass sheets 154 with high refractive indices, method 152 can produce glass sheets 154 with any refractive index.

[0111] In some embodiments, the glassware (based on oxides, total weight percentages summed to 100%) comprises the following components:

[0112] SiO2, 5-55% by weight;

[0113] ZrO2, 5-10% by weight;

[0114] CaO, 3.5-18% by weight;

[0115] La2O3, 0.2% to 30% by weight;

[0116] Nb2O5, 0.5 wt% to 20 wt%;

[0117] TiO2, 5-20% by weight;

[0118] As₂O₃, 0% to 0.2% by weight; and

[0119] Er₂O₃, 0.05% to 0.9% by weight (and preferably 0.1% to 0.9% by weight, for example, 0.1% to 0.8% by weight) and / or Pr₂O₃, 0.05% to 1% by weight; or Nd₂O₃, 0.05% to 1% by weight; or Ho₂O₃, 0.05% to 1% by weight; or oxides of Ce (CeO₂) 0.05% to 1% by weight.

[0120] In this embodiment, the glass composition comprises (based on oxides, with total weight percentages summed to 100%):

[0121] SiO2, 5-60% by weight;

[0122] ZrO2, 5-10% by weight;

[0123] CaO, 3.5-18% by weight;

[0124] La2O3, 0.2% to 30% by weight;

[0125] Nb2O5, 0.5 wt% to 20 wt%;

[0126] TiO2, 5-20% by weight;

[0127] As2O3, 0% to 0.2% by weight;

[0128] Er2O3, 0.01% to 0.5% by weight (e.g., 0.05% to 0.5% by weight, or 0.1% to 0.5% by weight);

[0129] Na2O, 2-5% by weight;

[0130] K2O5, 0-9% by weight;

[0131] SrO, up to 1% by weight;

[0132] BaO, 0-20% by weight;

[0133] F, 0-1% by weight; and

[0134] B2O3, 0-20% by weight.

[0135] Because pure silicon dioxide has a refractive index of approximately 1.5, adding higher refractive index dopants while maintaining the SiO2 content at 55% or lower (e.g., 7-45 wt%) allows the glass to become a high-refractive-index glass with high transparency and no noticeable coloration. If the SiO2 content increases to above 60%, it may be necessary to add higher refractive index dopants or constituent components, which could result in colored rather than transparent glass. According to some embodiments, the total amount of Er2O3, Nd2O3, Ho2O3, Ce oxides, and Pr2O3 in the glass is less than 1.5 wt%, which helps maintain the glass's transparency and high transmittance at the desired wavelengths.

[0136] Step 168 of method 152 includes separating glass sheets 154 from the glass belt 12. It should be understood that multiple glass sheets 154 can be separated from the glass belt 12, and the feeding device 36 delivers a constant supply of molten glass 134 from the transfer system 34 to the forming rollers 14, which continuously reforms the glass belt 12. This achieves continuous formation of the glass belt 12 and the resulting glass sheets 154, at least until all the molten glass 134 from the transfer system 34 is exhausted.

[0137] Step 168 includes any process for separating the glass sheet 154 from the glass ribbon 12. In an embodiment, separating the glass sheet 154 includes first scribing the glass ribbon 12, applying tensile stress to the scribing to create a crack, and then driving the crack through the thickness 26 of the glass ribbon 12. The scribing can be formed by any conventional method. For example, the scribing can be created by causing the glass ribbon 12 to be scribed with a scribing element 177 (e.g., a scribing wheel, scribing tool, or abrasive element that causes damage on a main surface 144). The subsequent tensile stress is applied by bending the glass ribbon 12 in a direction that puts it under tension on the scribing side (on the scribing line). The tension then drives the crack formed at the scribing point through the thickness 146 of the glass ribbon 12. Preferably, the scribing is formed in the central portion 158 of the glass ribbon 12, that is, on the width 148 of the glass ribbon 12 between the lateral edges 150a-b.

[0138] In other embodiments, the scribing element 177 is a laser and an optional cooling device that brings the glass strip 12 into contact with a cooling fluid (e.g., a cooling gas, liquid, or a combination thereof (fog)). The laser heats the glass strip 12 along the target scribing path with a laser beam, which heats a narrow region of the glass strip 12 after impact. The heated path is then cooled with the cooling fluid, resulting in a large tension in the glass strip 12 that produces the scribing.

[0139] In this implementation, the glass sheet 154 is separated from the glass strip 12 at a distance of 15 to 100 inches from the horizontal plane 28, for example: 15 inches, 20 inches, 25 inches, 30 inches, 35 inches, 40 inches, 45 inches, 50 inches, 55 inches, 60 inches, 65 inches, 70 inches, 75 inches, 80 inches, 85 inches, 90 inches, 95 inches, or 100 inches, or any range including any two of those values ​​(e.g., 25 inches to 50 inches). Method 152, which achieves cooling the glass strip 12 below its glass transition temperature and separating the glass sheet 154 from the glass strip 12 at a span of 100 inches or less from the horizontal plane 28, is a significantly different and advantageous result compared to using a slow annealing process to minimize stress. Method 152 results in the glass strip 12 cooling at an average rate of 5°C / s to 25°C / s, which is a much faster average cooling rate than a slow and lengthy annealing process. Therefore, method 152 advantageously requires less space compared to a slow annealing process. A slow annealing process would require the glass strip 12 to make one or more horizontal turns to meet longitudinal building restrictions. The method 152 described herein requires less than 12 feet of longitudinal height (or even less than 5 feet) for the glass strip 12 before separating it from the glass strip 154, and therefore does not require the glass strip 12 to make horizontal turns.

[0140] Therefore, the glass sheet 154 manufactured according to method 152 has a higher hypothetical temperature than the glass sheet 154 manufactured by a slow annealing process. "Hypothetical temperature" is a concept used to describe the structural state of the glass. Glass that is rapidly cooled from a high temperature is considered to have a higher hypothetical temperature because it is "solidified" in a higher temperature structure. Glass that is cooled more slowly or held near its annealing point for a period of time is considered to have a lower hypothetical temperature.

[0141] Compression (also known as thermal stability or dimensional change) is an irreversible dimensional change (shrinkage) in a glass substrate. A glass sheet 154 manufactured according to method 152 may have greater compression than a glass sheet 154 manufactured from a slowly annealed glass ribbon 12.

[0142] Glass plate 154 has a thickness of 178 (see...) Figure 13The distance 180 between the two main surfaces 180 of the glass sheet 154 is defined as the distance between them, which may be slightly smaller than the distance between the glass strip 12 from which the glass sheet 154 is separated due to compression. The ability to form a glass strip 12 with the desired thickness 146 and thus a glass sheet 154 with the desired thickness 178 depends on the rotational speed of the pair of forming rollers 14. In an embodiment, the glass sheet 154 has a thickness 178 of 0.1 mm to 8.5 mm, for example: 0.1 mm, 0.11 mm, 0.25 mm, 0.5 mm, 0.6 mm, 0.7 mm, 0.8 mm, 0.9 mm, 1.0 mm, 1.1 mm, 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, 1.6 mm, 1.7 mm, 1.8 mm, 1.9 mm, 2.0 mm, 2.1 mm, 2.2 mm. Thicknesses of 178 mm can be measured using a diameter gauge. The range of thicknesses is 2.3 mm, 2.4 mm, 2.5 mm, 2.6 mm, 2.7 mm, 2.8 mm, 2.9 mm, 3.0 mm, 3.5 mm, 4.0 mm, 4.5 mm, 5.0 mm, 5.5 mm, 6.0 mm, 6.5 mm, 7.0 mm, 7.5 mm, 8.0 mm, 8.5 mm, or any range including any two of those values ​​(e.g., 0.7 mm to 2.0 mm, 0.1 mm to 3.0 mm, etc.).

[0143] In one embodiment, a forming roller 14 having an outer diameter 22 of 20 mm to 80 mm results in a glass strip 12 (from which a glass sheet 154 is separated), and the thickness 178 of the glass sheet 154 is 0.1 mm to 3.0 mm (e.g., 0.1 mm to 1.0 mm).

[0144] The glass sheet 154 produced according to method 152 has acceptable low warpage and total thickness variation. In an embodiment, the glass sheet 154 has a warpage of 100 μm or less, for example: 50 μm or less, 25 μm or less, 15 μm or less, 0.01 to 100 μm, 0.01 μm to 50 μm, 0.01 μm to 25 μm, 0.01 μm to 15 μm, or 0.01 μm, 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm or 15 μm, 25 μm, 50 μm, 100 μm, or any range including any two of those values ​​(e.g., 1 μm to 50 μm). As described in ASTM F1390, “warping” refers to the difference between the maximum and minimum distances between the mid-plane and the reference plane. As taught in ASTM F1390, the mid-plane is a “fictitious” plane within the glass sheet 154, which is assumed to be equidistant from the main surface 180 of the glass sheet 154. ASTM F1390 is incorporated herein by reference.

[0145] In an embodiment, the glass sheet 154 has a total thickness variation of 100 μm or less, for example: 50 μm or less, 25 μm or less, 0.01 μm to 100 μm, 0.01 μm to 50 μm, 0.01 μm to 25 μm, or 0.1 μm, 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, 50 μm, 100 μm, or any range including any two of those values ​​(e.g., 4 μm to 50 μm). As used in this article, “total thickness variation” refers to the difference between the maximum and minimum thickness of the glass sheet 154 in a free and unclamped state.

[0146] In this embodiment, the width 182 of the glass sheet 154 is between the lateral edges and ranges from 15 mm to 500 mm, for example: 15 mm, 25 mm, 50 mm, 100 mm, 110 mm, 120 mm, 130 mm, 140 mm, 150 mm, 160 mm, 170 mm, 180 mm, 190 mm, 200 mm, 210 mm, 220 mm, 230 mm, 240 mm, 250 mm, 260 mm, 270 mm, 280 mm, 290 mm, 300 mm, 310 mm, 320 mm, 330 mm, 340 mm, 350 mm, 375 mm, 400 mm, 425 mm, 450 mm, 475 mm, 500 mm, or any range including any two of those values ​​(e.g., 50 mm to 400 mm). In this embodiment, the lateral edges are parallel and extend for a length 184.

[0147] Example

[0148] Example 1: For Example 1, two different settings of forming rollers were used to form two types of glass ribbons: the first setting had an outer diameter of 4 inches (approximately 101 mm), and the second setting had an outer diameter of 2 inches (approximately 51 mm). A single-tube outlet feed device was used to supply the molten glass stream to the gap between the forming roller sets to form the molten glass pits. The molten glass was passed to each forming roller set at the same flow rate. No dams were used to adjust the width or height of the molten glass pits.

[0149] For a forming roll assembly with a 4-inch outer diameter, a glass ribbon with a thickness of 6.1 mm and a width of 89 mm is produced. For a forming roll assembly with a 2-inch outer diameter and the same molten glass flow rate, (i) a glass ribbon with a smaller thickness of 4.6 mm and a slightly larger width of 106 mm is produced; and (ii) a glass ribbon with a larger width of 140 mm and a thickness of approximately the same 6.1 to 6.7 mm is produced. This embodiment demonstrates that, generally speaking, for a given flow rate, as the outer diameter of the forming roll decreases, the width of the glass ribbon increases and the thickness of the glass ribbon decreases.

[0150] Comparative Example 2: For Comparative Example 2, a single-tube outlet feed device was used to supply the molten glass stream into the gap between the forming rollers to form a molten glass pit. The molten glass stream had a viscosity of 10 poise and a temperature of 1140°C. No dam was used to regulate the width or height of the molten glass pit. The forming rollers formed a glass ribbon from the molten glass pit. Horizontal temperature distribution was measured at several longitudinal locations below the horizontal plane extending through the axis of rotation of the forming roller pair. Figure 16 The graph reproduces the horizontal temperature distribution measurement. The two data lines on the graph correspond to the horizontal temperature distribution measurement taken before the glass ribbon cools to the glass transition temperature.

[0151] The upper line in the graph corresponds to a horizontal temperature distribution measurement taken closer to the horizontal plane extending through the forming roller (i.e., approximately 2 inches away). Reading the upper line from left to right indicates the maximum temperature above 700°C near the left lateral edge. The temperature drops rapidly horizontally to the right, reaching a minimum of approximately 640°C between the left lateral edge and the center portion of the glass ribbon. The temperature then increases towards the center portion of the glass ribbon, reaching approximately 670°C. The temperature then drops again to a local minimum of approximately 640°C, moving to the right, and then increases again to a local maximum of over 690°C near the right lateral edge. This represents a horizontal temperature variation of approximately 60°C to the left of the center portion and approximately 50°C to the right of the center portion.

[0152] The lower line, representing horizontal temperature measurements further down from the glass band (i.e., approximately 6 inches from the horizontal plane), reveals the same pattern of temperature variation. The left lateral edge has a maximum temperature exceeding 600°C. Moving to the right, the temperature drops below 570°C near the left lateral edge, rises to approximately 590°C in the center, then drops again below 570°C near the right lateral edge, and then rises again above 590°C at the right lateral edge. This represents a horizontal temperature variation of approximately 30°C to the left of the center and approximately 20°C to the right of the center.

[0153] Computer modeling was used to provide an explanation of why the use of a single-tube outlet to supply molten glass to the gap between the rolls results in a wide range of horizontal temperature variations on the glass belt. Figure 17 The reproduced modeling output shows that the molten glass in the pit is higher in the center than at the lateral edges, and consequently, the contact between the molten glass from the center and the roller is greater than that at the lateral edges. This greater contact with the roller results in greater cooling in the center of the molten glass in the pit compared to the lateral edges. Therefore, the lateral edges of the glass ribbon have a higher temperature than the center of the ribbon.

[0154] After cooling to below the glass transition temperature, the glass ribbon breaks when an attempt is made to scribe lines on it to separate the glass sheets. Figure 18 The image of the shattered glass ribbon was reproduced. As mentioned above, without being bound by theory, it is hypothesized that the horizontal temperature change on the glass ribbon and the excessively rapid cooling of the glass ribbon before cooling to the glass transition temperature locked the glass ribbon with too high an internal stress that it could not tolerate to prevent shattering after cooling to the glass transition temperature.

[0155] Comparative Example 3: In Comparative Example 3, a single-tube outlet feed device was used to supply the molten glass stream into the gap between the forming rolls to form a sump of molten glass. No attempt was made to cool the outer cylindrical surface of the forming rolls as they formed the glass ribbon from the molten glass sump. The result was a glass ribbon with significant thickness variations, such as... Figure 19 The reproduced image illustrates this. Specifically, the thickness of the glass strip at the lateral edge was measured to be approximately 1.75 mm or greater, while the thickness of the glass strip at the center was measured to be as thin as 1.5 mm.

[0156] Comparative Example 4 and Example 5: For Comparative Example 4, a single-tube outlet feeder supplies molten glass stream into the gap between the forming rolls to form a pit of molten glass. No dam is used to regulate the width or height of the pit of molten glass. The forming rolls form a glass ribbon from the pit of molten glass. Before the glass ribbon cools to the glass transition temperature, the horizontal temperature distribution is measured at a position below the horizontal plane extending through the axis of rotation of the forming roll pair. Figure 20 The graph of the horizontal temperature distribution measurement was reproduced. The maximum temperature of the glass ribbon was at the horizontal edge and was measured at approximately 805°C. The minimum temperature of the glass ribbon was in the central part and was measured at approximately 735°C. Therefore, the horizontal temperature variation of the glass ribbon is approximately 70°C.

[0157] Example 5 presents the same glass ribbon formation process as Comparative Example 4, except that a second pipe outlet is used to blow cooling gas (specifically, air) at the second transverse edge of the glass ribbon. Before the glass ribbon cools to the glass transition temperature, the horizontal temperature distribution is measured at a horizontal position below the level of the axis of rotation extending through the forming roller pair. Figure 21 The horizontal temperature distribution measurement graph was reproduced. The maximum temperature of the glass ribbon was measured at the first transverse edge, approximately 805°C, which is attributed to the absence of cooling gas blowing at the first transverse edge (for further comparison). The minimum temperature of the glass ribbon was measured at the center, approximately 740°C. A local maximum temperature was indeed observed at the second transverse edge, but it was measured below 760°C because the blowing cooling gas cooled the second transverse edge. Blowing cooling gas onto the second transverse edge of the glass ribbon resulted in a temperature decrease of approximately 45°C compared to the first transverse edge. Furthermore, the horizontal temperature variation between the center and the second transverse edge was approximately 20°C, while the horizontal temperature variation between the center and the first transverse edge was approximately 55°C. This confirms that blowing cooling gas at the transverse edges of the glass ribbon reduced the horizontal temperature variation of the glass ribbon. Additionally, blowing cooling gas at the second transverse edge of the glass ribbon reduced the thickness variation of the second transverse edge compared to the center.

[0158] Example 6: In Example 6, a single-tube outlet feed device is used to supply the molten glass stream into the gap between the forming rollers to form a molten glass pit. No dam is used to adjust the width or height of the molten glass pit. The forming rollers form a glass ribbon from the molten glass pit. A pair of clamping rollers is used to reduce the thickness of the second transverse edge of the glass ribbon (but not for the first transverse edge). The clamping rollers reduce the thickness of the glass ribbon at the second transverse edge from 3 mm to 2.26 mm. The thickness of the glass ribbon near the second transverse edge is approximately 2.2 mm. The thickness of some portions of the glass ribbon decreases to 1.9 mm.

[0159] The horizontal temperature distribution at the horizontal position was measured before the clamping rollers reduced the thickness of the second transverse edge of the glass ribbon. The horizontal temperature distribution at the lower position was measured again after the clamping rollers reduced the thickness of the second transverse edge of the glass ribbon. Figure 22 The horizontal temperature distribution measurement graph was reproduced. Before the clamping rollers reduced the thickness of the second transverse edge, the temperature of the second transverse edge was approximately 790°C, while the temperature of the center portion was below 730°C, providing a horizontal temperature variation of over 60°C. After the clamping rollers reduced the thickness of the second transverse edge, the temperature of the second transverse edge was approximately 745°C, while the temperature of the center portion was approximately 705°C, providing a horizontal temperature variation of approximately 40°C. Therefore, the reduction in the thickness of the second transverse edge caused a decrease in the horizontal temperature variation of approximately 20°C. The temperature of the first transverse edge was approximately 775°C, which was approximately 30°C higher than the second transverse edge after contact with the clamping rollers. The maximum temperature of the glass ribbon was at the transverse edge and was measured at approximately 805°C. The minimum temperature of the glass ribbon was within the center portion and was measured at approximately 735°C. Therefore, the horizontal temperature variation of the glass ribbon was approximately 70°C.

[0160] Comparative Examples 7 and 8: In both Comparative Examples 7 and 8, a single-tube outlet feed device is used to supply the molten glass stream to the gap between the forming rollers to form a sump of molten glass. No dam is used to adjust the width or height of the sump. The forming rollers form a glass ribbon from the molten glass sump. In Comparative Example 7, no heat loss reduction element is placed facing the main surface of the glass ribbon, allowing the glass ribbon to cool without restriction. In Example 8, a heat loss reduction element in the form of an insulating substrate is placed facing both main surfaces of the glass ribbon, with the insulating substrate centered so that the lateral edges of the glass ribbon are exposed but the central portion is insulated, such as... Figure 25 As shown.

[0161] For both Comparative Example 7 and Example 8, the horizontal temperature distribution was measured at two longitudinal positions: a first horizontal position slightly below the bottom of the insulating substrate, and a second horizontal position even lower and closer to the glass ribbon where the temperature is close to the glass transition temperature. The horizontal temperature distribution is illustrated. Figure 23 For comparison, and Figure 24 (See Example 8). In Comparative Example 7, the lack of elements to reduce heat loss resulted in a significant increase in horizontal temperature variation as the glass ribbon approached the glass transition temperature. More specifically, the first transverse edge of the glass ribbon measured in the first horizontal temperature distribution had a temperature of approximately 606°C, while the temperature of the central portion was approximately 574°C, exhibiting a horizontal temperature variation of approximately 32°C. In a lower horizontal temperature distribution measurement, the temperature of the first transverse edge was approximately 516°C, while the temperature of the central portion was approximately 470°C, exhibiting a horizontal temperature variation of approximately 46°C.

[0162] Conversely, in Comparative Example 8, two heat-loss-reducing elements in the form of insulating substrates (one insulating substrate facing the center portion of one main surface of the insulating substrate, and a second insulating substrate facing the center portion of the other main surface of the insulating substrate) are used, resulting in the temperature at the transverse edges being approximately equal to that at the center. For upper horizontal temperature distribution measurements, the center portion has a highest temperature of approximately 612°C, while a lowest temperature of approximately 604°C is near, but not at, the second transverse edge of the glass ribbon. As the glass ribbon approaches its glass transition temperature, the horizontal temperatures remain equal. For lower horizontal temperature distribution measurements, the first transverse edge has a highest temperature of approximately 526°C, while a lowest temperature of approximately 518°C is at the center portion of the glass ribbon. The horizontal temperature change from the center portion to the second transverse edge is less than 4°C. In Example 8, it is possible to separate the glass sheet from the glass ribbon without it breaking, as... Figure 26 The recreated photo is shown.

[0163] Example 9: In Example 9, a single-tube outlet feed device is used to supply molten glass stream to the gap between forming rollers to form a molten glass pit. The mass flow rate of the molten glass stream is adjusted to change the height of the molten glass pit, which is approximation of using a dam to control the height of the molten glass pit. The forming rollers form a glass ribbon from the molten glass pit. Initially, the mass flow rate of the molten glass stream is high, and therefore the molten glass pit is high. Then, the horizontal temperature distribution of the resulting glass ribbon formed when the pit is high is determined. Figure 26 In the reproduced graph, this horizontal temperature distribution is labeled "high pit". The horizontal temperature variation does not exceed approximately 40°C. The mass flow rate of the molten glass stream is then adjusted to a lower level, resulting in a lower molten glass pit. The horizontal temperature distribution of the resulting glass ribbon when the pit is low is then determined. This horizontal temperature distribution is labeled "low pit" in the graph. The horizontal temperature variation is high, approximately 80°C. The mass flow rate of the molten glass stream is then changed to a level between lower and higher mass flow rates, resulting in a medium-height molten glass pit. The horizontal temperature distribution of the resulting glass ribbon is then determined. The horizontal temperature distribution of the "medium pit" scenario reveals the smallest overall horizontal temperature variation across different scenarios. The horizontal temperature variation obtained from the "medium pit" scenario does not exceed approximately 10°C.

[0164] Example 10: For Example 10, a computer model is generated to show the temperature of the glass strip as a function of its distance from the horizontal plane, thereby achieving a constant rate of thermal strain change (i.e., a linear strain distribution) throughout the entire “solidification zone” centered on a glass transition temperature of 600°C. Figure 27 The modeling results were reproduced. To achieve a constant rate of thermal strain change down the glass ribbon during the glass transition through the glass transition temperature (i.e., from 650°C to 550°C), the glass ribbon needs to cool relatively slowly from approximately 250 mm to approximately 350 mm above the horizontal plane when the temperature is above 600°C, and then cools relatively quickly from 350 mm above the horizontal plane and forward when the temperature is below 600°C. Note that, according to the model, the glass ribbon should require 100 mm to cool from 650°C to 600°C (from approximately 250 mm to approximately 350 mm), but only 75 mm is needed to cool from 600°C to 550°C (from approximately 350 mm to approximately 425 mm).

[0165] Comparative Example 11 and Example 12: In Comparative Example 11 and Example 12, a single-tube outlet feed device was used to supply the molten glass stream to the gap between the forming rollers to form a pit of molten glass. No dam was used to adjust the width or height of the pit of molten glass. The forming rollers formed a glass ribbon from the pit of molten glass. In Example 12 (similar to Example 8), a heat loss reduction element in the form of an insulating substrate was placed facing the two main surfaces of the glass ribbon, with the insulating substrate centered so that the lateral edges were exposed but the central portion of the glass ribbon was insulated. In Comparative Example 11, no heat loss reduction element was used, and the glass ribbon was cooled by exposure to ambient air. The temperature of the glass ribbon was measured at three locations via an infrared camera (location 1 is when the ribbon leaves the forming roller; location 2 is where the glass ribbon passes the insulating substrate in Example 11; and location 3 is further down the glass ribbon, before the glass sheet is separated from the glass ribbon). Figure 28 The diagram illustrates the recorded temperature as a function of position. The insulating substrate caused the glass strip 12 of Example 12 to cool more slowly than the glass strip of Comparative Example 11. The temperature of the glass strip of Example 12 at position 2 was approximately 40°C higher than that of the glass strip of Comparative Example 11 at position 2. From position 2 to position 3, where the glass strip of Example 12 no longer faces the insulating substrate, the cooling rate (i.e., temperature decrease) increased compared to the cooling rate from position 1 to position 2. The cooling rate of Example 12 from position 1 to position 2 resulted in a thermal strain distribution that was closer to linear than that of Comparative Example 11.

[0166] Example 13: In Example 13, a dispensing feeder is used to supply molten glass stream to the gap between forming rollers to form a molten glass pit. The composition of the molten glass is configured to form a glass sheet with a refractive index of 1.8. A dam is used to increase the height of the molten glass pit (compared to the case without a dam). The forming rollers form a glass ribbon from the molten glass pit. The forming rollers have an outer cylindrical surface with an outer diameter of 104 mm. The forming rollers rotate at a speed of 0.8 m / min. No elements for reducing heat loss are used. The horizontal temperature change is then reduced. The glass sheet is separated from the glass ribbon. Figure 29 The photograph of the glass slide was reproduced. As the photograph revealed, the glass slide did not have internal fractures. The profile of the glass slide was measured using a profilometer. Figure 30 The diagram representing the measurements was reproduced. The glass slide has a thickness of 1.4 mm at the center, 1.6 mm at the lateral edges, a width of 130 mm, and a length of 450 mm. The glass slide has an estimated warpage of approximately 200 micrometers and a total thickness variation of approximately 300 micrometers.

[0167] Example 14: In Example 14, a distribution feed device is used to supply the molten glass stream into the gap between the forming rollers to form a sump of molten glass. The composition of the molten glass is configured to form a glass sheet with a refractive index of 1.8. The delivered molten glass has a viscosity of 10 poise. No dams are used. The forming rollers form a glass ribbon from the sump of molten glass. No elements for reducing heat loss are used. The glass sheet is separated from the glass ribbon.

[0168] The rotational speed of the forming rollers was varied between 0.5 m / min and 1.0 m / min, and the outer diameter of the outer cylindrical surface was varied between 70 mm and 110 mm, thus determining the effect on the thickness of the resulting glass ribbon (and the glass sheets separated from it). For each batch, the volumetric flow rate of the molten glass transferred to the gap between the forming rollers was kept relatively constant. Figure 31 The reproduced graphs show that, at a rotational speed of 0.5 m / min, the forming roller with an outer diameter of 110 mm forms a glass ribbon with a median thickness of 1879 μm (1.9–mm), while the forming roller with an outer diameter of 70 mm forms a glass ribbon with a median thickness of 1601 μm (–1.6 mm), representing a thickness reduction of approximately 15%. At a rotational speed of 1.0 m / min, the forming roller with an outer diameter of 110 mm forms a glass ribbon with a median thickness of 1257 μm (1.3–mm), while the forming roller with an outer diameter of 70 mm forms a glass ribbon with a median thickness of 1102 μm (–1.1 mm), representing a thickness reduction of approximately 12%.

[0169] Furthermore, glass ribbons formed by forming rolls with smaller outer diameters are wider than those formed by forming rolls with larger outer diameters. This is a result of volume conversion. For any given forming roll rotation speed and the volumetric flow rate of the molten glass reaching the forming roll, a decrease in thickness necessarily leads to an increase in width. In other words, under these conditions, thickness and width are inversely proportional.

Claims

1. A method for forming a glass slide, comprising: Forming rollers are used to form glass ribbons from molten glass; Before the glass ribbon is cooled to the glass transition temperature, the horizontal temperature variation of the glass ribbon is controlled to be 10°C or less over 80% of the entire width of the glass ribbon. As the glass ribbon moves longitudinally downwards in the solidification zone, the cooling rate of the glass ribbon is controlled such that the glass ribbon has a first average cooling rate before cooling to the glass transition temperature and a second average cooling rate after cooling to the glass transition temperature, wherein the first average cooling rate is less than the second average cooling rate, and the temperature contained in the solidification zone is the glass transition temperature + / - 50°C; and Separate the glass sheet from the glass ribbon.

2. The method of claim 1, further comprising: Heat is drawn from one or both of the forming rollers.

3. The method of claim 2, wherein: Heat absorption from one or both of the forming rollers includes one or more of the following: (i) transferring a heat exchange fluid into the forming roller, the heat exchange fluid being in thermal communication with the outer surface of the forming roller; (ii) spraying a liquid at a temperature lower than the outer surface of the forming roller onto the outer surface; (iii) bringing the forming roller into contact with a liquid-cooled metal brush; and (iv) positioning the forming roller opposite a liquid-cooled slider.

4. The method of any one of claims 1-3, further comprising controlling the horizontal temperature variation of the glass ribbon over 80% of its entire width to be 5°C or less before the glass ribbon is cooled to the glass transition temperature.

5. The method of claim 4, further comprising controlling the horizontal temperature variation of the glass ribbon over 90% of its entire width to be 10°C or less before the glass ribbon is cooled to the glass transition temperature.

6. The method of claim 4, further comprising controlling the horizontal temperature variation of the glass strip across its entire width to be 10°C or less before the glass strip is cooled to the glass transition temperature.

7. The method according to any one of claims 1-3, further comprising: Before forming the glass ribbon from the molten glass by the forming rollers, the molten glass is fed into the inner chamber of the feeding device, which includes a bottom plate below the inner chamber; as well as Molten glass is fed from the inner chamber of the feeding device through the bottom plate and into the gap that separates the forming rollers.

8. The method of claim 7, further comprising: The heat output of each of the multiple heating elements in the feeding device is independently controlled, and the multiple heating elements are in thermal communication with the molten glass in the inner chamber of the feeding device.

9. The method according to any one of claims 1-3, wherein, Controlling the horizontal temperature variation of the glass ribbon before it cools to the glass transition temperature involves increasing the heat loss of the transverse edges of the glass ribbon relative to the central portion of the glass ribbon arranged between the transverse edges.

10. The method of claim 9, wherein: Increasing heat loss at the transverse edges of the glass strip relative to the central portion of the glass strip arranged between the transverse edges includes blowing cooling gas onto the transverse edges.

11. An apparatus for rolling glass ribbons by the method of claim 1, the apparatus comprising: A pair of forming rolls separated by a gap, each roll in the pair having a pivot such that: the pivots are parallel to each other, the gap has a minimum spacing along a horizontal plane extending through the two pivots, and a longitudinal plane parallel to the pivots extending through the gap; The molten glass stream is fed into a feed device in the gap. The feed device is arranged longitudinally above the horizontal plane of the rotating shaft extending through the forming roller pair. The feed device includes an inner chamber, a bottom plate, and a groove through the bottom plate to provide a passage from the inner chamber. as well as A heat loss reduction element is arranged on each side of the longitudinal surface extending through the gap between the forming roller pair, and each heat loss reduction element is arranged below the horizontal plane extending through the two rotating shafts of the forming roller pair. Specifically, when the glass ribbon moves longitudinally downward in the solidification zone, the cooling rate of the glass ribbon is controlled so that the glass ribbon has a first average cooling rate before cooling to the glass transition temperature and a second average cooling rate after cooling to the glass transition temperature, wherein the first average cooling rate is less than the second average cooling rate.

12. The device of claim 11, wherein: The feeding device also includes multiple heating elements that are in thermal communication with the inner chamber, each of which has an independently controllable heat output.

13. The apparatus of claim 11, further comprising: The molten glass in the inner chamber and the molten glass exiting the inner chamber from the tank, the molten glass having a viscosity of 0.01 poise to 3000 poise.

14. The device as claimed in any one of claims 11-13, wherein: Each element that reduces heat loss has a width parallel to the axis of rotation of the forming roller pair. The forming roller pair has a width parallel to the axis of rotation of the forming roller pair, and Each heat loss reduction element is narrower than the width of the forming roller pair.

15. The device as claimed in any one of claims 11-13, further comprising: A glass ribbon extending downwards from a horizontal plane, the glass ribbon having two main surfaces facing roughly opposite directions, each of which faces a flat surface of one of the elements designed to reduce heat loss. The glass ribbon has a width parallel to the axis of rotation of the forming roller pair, and Each heat loss reduction element has a width parallel to the axis of rotation of the forming roller pair, and the width of each heat loss reduction element is smaller than the width of the glass ribbon.

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