BACKGROUND

1. Cross-Reference to Related Application

[0001] This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application Serial No. 63/332773 filed on April 20, 2022, the content of which is relied upon and incorporated herein by reference in its entirety.

2. Field of the Disclosure

[0002] The present disclosure relates to devices and methods providing preferential cooling or heating of precise regions within a continuous glass ribbon. The devices and methods disclosed can provide control of the glass ribbon temperature to ensure the temperature difference between thick and thin regions remains at or near zero. The temperature must be controlled in this way to avoid thermally induced shape (warp) and residual stress. These disclosed devices and methods can be applied before and after the visco-elastic region.

3. Description of the Related Art

[0003] Back covers for certain smartphones and mobile devices or any glass body for an electronic component or enclosure design that have a non-uniform thickness, the non- uniform thickness being thicker in the camera region than the other portions, allow for improved camera lens designs (see, for example U.S. PG Pub. 2019/0364179 Al). As an example, the glass thickness can be 1.5-3.0 mm in thicker portions and <0.8 mm elsewhere. To fabricate the thicker section for the device back-cover or enclosure, a relatively thick glass sheet can be ground, lapped, and polished to define a thicker area and a thinner area. In such a case, to make a glass article with a 1.6 mm thickness in the thicker region and a 0.6 mm nominal thickness elsewhere, a glass sheet with a 1.9 mm thickness can be used. That is, 0.3 mm of material would be removed from the thicker portion and 1.3 mm of material from the thinner portion everywhere else. This approach has poor glass utilization, is time consuming, costly, inefficient, and not environmentally friendly.

[0004] In an alternative method of forming glass articles with non-uniform thickness, two glass substrates could be fused together (see, for example U.S. PG Pub. 2017/0210111A1). For example, a 25 mm x 25 mm x 1.0 mm glass piece can be fused to a larger glass piece of 70 mm x 150 mm x 0.6 mm piece by bonding or pressing together under high temperatures. This method improves glass utilization but is energy intensive, can result in bubble formation at the fused interface, and can be costly and a more time consuming. [0005] When the grinding process is not cost effective and produces too much waste, and when fusing two glass pieces together is not a viable option, another solution is to define a continuous glass ribbon having the desired thickness differences. Producing a glass ribbon with a variation in thickness can require generating a significant difference in temperatures between the thicker portion and the thinner portion. To manufacture such a glass ribbon with low stress and warp, therefore, requires the ability to preferentially cool the thicker portion at a prescribed rate that is different from the cooling rate of the base ribbon (or the thinner portion of the glass ribbon). It may also be required to preferentially heat the base ribbon (or thin region) to slow down its normal rate of cooling with respect to that of the thick portion

[0006] The present disclosure provides solutions to this technical challenge.

SUMMARY

[0007] To overcome the problems described above, embodiments of the present disclosure provide apparatus and methods that minimize stress and warp in variable thickness glass sheets by cooling a thicker portion of a glass ribbon at a higher rate than cooling a thinner portion by managing thick-to-thin and top-to-bottom temperature gradients. The cooling can be performed through convection and/or radiation, and from top and/or bottom of the glass ribbon. Optionally, localized heating can be used along with preferential cooling to control the desired temperature parameters within the glass.

[0008] The embodiments described can be applied to a hot glass ribbon that is traveling in a lehr and/or controlled cooling apparatus (CCA). The CCA is a modified lehr, or a roller hearth lehr, or a roller kiln that produces glass ribbons. The present disclosure provides solutions to the thermal management challenges that must be overcome to produce a glass ribbon with variable thicknesses.

[0009] Without the thermal management methods presently described, stresses generated in glass ribbons with variable thicknesses will be too high. Such would require scoring sheets, cutting high-stress portions out of sheets, or providing extra finishing processes to produce glass to the desired size, shape, and thicknesses. Alternative methods to reduce stresses in glass ribbons would be to significantly increase the lehr length or adding an annealing step. Both of these methods involve significant cost and space requirements.

[0010] According to an embodiment of the present disclosure, a glass ribbon processing apparatus produces a glass ribbon having a first portion with a first thickness immediately adjacent to a second portion with a second thickness, the apparatus comprising a water wick contacting the first portion of the glass ribbon to cool the first portion as the glass ribbon travels passed the water wick, wherein the first thickness is greater than the second thickness, wherein the first portion cools at a first rate and the second portion cools at a second rate wherein the first rate is greater than the second rate.

[0011] In an embodiment, the first and second portions are oriented longitudinally along a length of the glass ribbon.

[0012] The glass ribbon processing apparatus can further include a heater upstream of the water wick.

[0013] In an embodiment, the water wick is a strip of fabric and is fixed at one end above the glass ribbon.

[0014] In an embodiment, the water wick is round and rotates on an axis and the water wick is under the glass ribbon as the glass ribbon travels in a horizontal direction.

[0015] In an embodiment, the water wick is attached to a substantially planar plate.

[0016] According to another embodiment, a glass ribbon processing apparatus produces a glass ribbon with variable thickness, the apparatus comprising an atomizer to spray a cooling liquid and/or cooling air on a thicker portion of the glass ribbon to cool the thicker portion as the glass ribbon travels passed the atomizer.

[0017] According to another embodiment, a glass ribbon processing apparatus produces a glass ribbon with variable thickness, the apparatus comprising a heater to heat a thinner portion of the glass ribbon as the glass ribbon travels passed the heater. In an embodiment, the heater is two heaters located symmetrically across a width of the glass ribbon. In an embodiment, the heater is two heaters, one located above the glass ribbon and one located below the glass ribbon.

[0018] According to another embodiment, a glass ribbon processing apparatus produces a glass ribbon with variable thickness, the apparatus comprising an airbar to force air on a portion of the glass ribbon as the glass ribbon travels passed the airbar. In an embodiment, the airbar is below the bar is below the glass ribbon. In an embodiment, the airbar supports the glass ribbon. In an embodiment, the airbar forces cooling air onto a thicker portion of the glass ribbon. In an embodiment, the air includes steam and is forced onto a thinner portion of the glass ribbon.

[0019] According to an embodiment, a glass ribbon processing apparatus produces a glass ribbon including a first thickness and a second thickness, the apparatus comprising: a roller to support the glass ribbon as the glass ribbon travels passed the roller; and a nozzle to force cooling air onto a portion of the roller that contacts the glass ribbon, wherein the first thickness is greater than the second thickness. In an embodiment, the portion of the roller that contacts the glass ribbon corresponds to the first thickness.

[0020] The above and other features, elements, characteristics, steps, and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Fig. 1A shows a water wick cooling a thicker region of a glass ribbon.

[0022] Fig. IB shows a manifold including a water wick cooling intermittent thicker regions of a glass ribbon.

[0023] Fig. 2 shows a wicking wheel cooling a thicker portion of a glass ribbon.

[0024] Figs. 3-5 show an atomizing device cooling a thicker region of a glass ribbon.

[0025] Fig. 6 shows stress birefringence measurements for thicker portion cooled with a water spray experiment.

[0026] Fig. 7 shows heaters used to preferentially heat portions of a glass ribbon.

[0027] Fig. 8 shows an arrangement and relative spacing of four heaters located relative to a glass ribbon.

[0028] Fig. 9 is a graph showing a relationship of a heater face temperature versus glass ribbon temperature for a ribbon passing through a heater.

[0029] Fig. 10 plots modelled data of glass temperature to distance of the glass from a viscous turn. [0030] Fig. 11 is a plot of modeled data comparing the thick-to-thin thermal gradient reduction by the pre-CCA heaters against a standard equipment setup.

[0031] Fig. 12 represents a portion of a lehr including heat reflectors.

[0032] Figs. 13 and 14 shows the use of an airbar using force air to cool a thicker portion of a glass ribbon.

[0033] Figs. 15 and 16 show optical retardation test data of at the thicker portion and B- side part size warp.

[0034] Fig. 17 represents a side view of a glass ribbon traveling over airbars.

[0035] Fig. 18 represents a top view of three airbars.

[0036] Fig. 19 represents an embodiment where the temperature difference between the thicker and thinner portions of the glass ribbon is reduced at the roll forming stage prior to the viscous turn.

DETAILED DESCRIPTION

[0037] Glass ribbon geometries including thinner portions and thicker portions are made possible by devices and methods described in the present disclosure. Drawn glass ribbon geometries can include a certain width where a portion of the width is thicker than other portions. For example, the thicker portion can be in the center of the glass ribbon. Optionally, there can be more than one thicker portion spaced across the width of a glass ribbon. The geometry is usually designed for specific products.

[0038] Conventional thermal management inside the lehr and/or CCA led to the thicker portion being constantly hotter than the thinner base glass throughout the controlled cooling section. This persistent thermal gradient between the thicker and thinner portions present during ribbon cooling, though reasonably well managed by controlling the lehr, caused high stress and warp in the as-formed products. This causes a pressing need for preferential thermal management tools used with the lehr to lower the thermal gradient and reduce resulting stress.

[0039] An important factor is that extra cooling is provided via the preferential thermal tools so that the glass ribbon achieves near identical temperatures in the thicker and thinner portions to maintain the thick-to-thin temperature difference (delta T or DT) close to zero. The preferential cooling of the thicker portion of the glass ribbon can be combined with preferential heating of the thinner portion. Heating of the thinner portions can be accomplished either by local heating tools or by keeping the overall lehr temperature higher than the temperature of thinner portions (while the cooling tools preferentially cool the thinner portions).

[0040] Cooling flow, stress, and warp data illustrates that as the thicker portion is cooled such that the temperature difference between the thicker and thinner portions is reduced, the stress in the glass ribbon also goes down. From the data, it is noted that cooling device features can be optimized based on the particular application and desired results.

[0041] Providing cooling can be done using any combination of techniques including forced air (convection), radiation, and conduction. Cooling system design includes consideration of factors including emissivity, the ideal gas law and expansion of the heated air, removal of the heated air from the manufacturing building, and occupant safety.

[0042] Any type of cooling (convention, radiation, conduction, and combinations), heating, or heating/cooling can be provided such that each device providing the treatment can be independently moveable and positioned to align with any portion of the glass ribbon. Any device can be placed in the center of the glass ribbon to cover a wider thicker portion or devices can be spread apart toward the edges of the glass ribbon to cover a narrower edgestrip configuration. Any of the devices can be independently located above, below, to the side, or parked out of the way when not in use with respect to the glass ribbon and be placed in position manually or by an automated electro-mechanical positioning system. Optionally, any number of positions of any number of devices that heat and/or cool can be located by automation and preprogrammed so that different configurations of processes of glass ribbons can be repeatable.

[0043] As shown in Fig. 1A, a water wick 10 can be used to preferentially cool a thicker region of a traveling glass ribbon 20. As shown in Fig. 1A, where the glass ribbon 20 is moving from left to right, the water wick 10 can be hung from a gantry 30 that is suspended above the glass ribbon conveying system and be placed in contact with the glass ribbon 20 and dragged as the glass ribbon 20 travels. Thus, the thicker region can be cooled as a continuous strip in the portions of the glass ribbon 20 in which the water wick 10 contacts. [0044] Alternatively, as shown in Fig. IB, the glass ribbon can include thicker regions that are intermittently repeated rather than a continuous strip or portion of a width of the glass ribbon. For example, Fig. IB shows a glass ribbon 25 that includes intermittently repeated thicker regions 28. As shown, the thicker regions 28 can be shaped as substantially rectangular, although other shapes are possible. Fig. IB also shows a cooling manifold 40 above the glass ribbon 20 that is used to cool only the thicker portions 28.

[0045] The cooling manifold 40 can be substantially planar and include a water connection fitting 42 to connect the manifold 40 to a water source, a water passage 44 to route water from the water connection fitting 42, and a wick 50 that absorbs water routed to it via the water passage 44. The water manifold 40 is located at a position above the glass ribbon 20 such that the thicker regions 28 of the glass ribbon 20 contact the wick 50 as the glass ribbon 20 travels past the manifold 40. The manifold 40 is at a distance away from the glass ribbon 20 such that the thicker regions 28 can contact the wick 50 but the thinner regions do not. Therefore, the manifold 40 can cool the thicker regions 28 without cooling the thinner regions of the glass ribbon 20.

[0046] The wick material allows for precise deposition of water onto the surface of the glass ribbon being cooled. The water flow rate is controlled through a valve and adjusted such that the rate of evaporation matches the rate of water flow. This ensures maximum heat removal without excessive water uncontrollably delivered to the glass ribbon. For example, by dragging a water wick 10 in the manner shown in Fig. 1A, the thicker-to-thinner temperature difference (delta T or DT) by was reduced by ~8° C. It is desirable to reduce this temperature difference as much as possible without cooling the thinner portion of the glass ribbon or adding stress to the glass ribbon.

[0047] The water wick can be made of any water absorbing material that is suited for the temperature and material being cooled. For example, the water wick can be made from a woven silica yarn. The length, width, thickness, and material of the wick can be adjusted to meet the cooling needs of the glass ribbon product.

[0048] Fig. 2 illustrates using a wicking wheel to cool a thicker region in a glass ribbon according to another embodiment as an alternative device to the water wick 10 shown in Fig. 1A. A wicking wheel is a perforated liquid distribution wheel wrapped with a water wick material. Although any number is possible, the top portion of Fig. 2 shows an arrangement of two wicking wheels that are used to cool a thicker center strip of a continuous glass ribbon. The wicking wheel operates on the same principle of using the saturated cloth of the water wick 10 to precisely deposit water onto the surface of the glass ribbon being cooled. The wicking wheel has some benefits over the water wick 10. In particular, the wicking wheel can be deployed to cool the bottom side of the glass ribbon as it does not rely on gravity to keep the wick material wetted and in contact with the glass ribbon. As with the water wick 10, the water flow rate supplied through the wicking wheel is throttled such that the flow rate matches the rate of evaporation for optimal cooling impact with maximum control. The thicker portions of the glass ribbon are hotter than the thinner portions. As mentioned, it is desirable to reduce the DT as much as possible to 0° C without overcooling the thicker portions.

[0049] The upper portion of Fig. 2 shows that the wicking wheels can be supported by a frame and held into place respective to the glass ribbon. Each wicking wheel can be free to rotate about an axis of rotation defined by an axel that doubles as a conduit for the water supply. The water supply can be attached to a rotary union on an end of the axel. The lower portion of Fig. 2 is a side view of the frame and wicking wheels that shows the rotary union to attach to the water supply, a pipe to transfer water to the wicking wheels, and two bearings.

[0050] Figs. 3-5 show an atomizing device cooling a thicker region in a glass ribbon according to another embodiment of the present disclosure. The atomizing device directs an atomized liquid onto the glass ribbon. The liquid can be water, a mixture with water, or any other suitable fluid.

[0051] Fig. 3 is a side view of the atomizing device spraying air and/or a liquid on a glass ribbon that is traveling in a left to right direction. Fig. 4 is another view looking upstream towards the atomizing device. Fig. 5 is an image of the atomizing device spraying from a perspective angle. As shown, the atomizing device can include a frame or gantry that is supporting atomizing sprayers. Although three atomizing sprayers are shown, any number is possible. The frame can include a mechanism to adjust the height or distance of the atomizing sprayers from the glass ribbon. Each atomizing sprayer can be surrounded by an air purged enclosure with a heat shield.

[0052] Each atomizing sprayer can also include a coupling for actuation air used to turn the atomizing sprayer on and off, a coupling for atomization air, a coupling for liquid i.e., water or other coolant, a mechanism to adjust the liquid flowrate, and a nozzle. The atomization air can always but on, where the liquid spray is only introduced when needed. Using actuation air allows the valve to control the cooling liquid to be located at the nozzle which makes the timing of liquid spray more precise and reduce drip. As shown in Fig. 5, the nozzle can be changeable to spray cooling air or a liquid. The nozzle can output air and/or liquid in a fan shape or another suitable geometry. Optionally, each of the atomizing sprayers can be adjusted differently than another of the atomizing sprayers such that the output pattern is different, or one is spraying air and another one is spraying liquid. Optionally, the atomizing device can be located above the glass ribbon before the glass ribbon enters a CCA.

[0053] Table 1.

[0054] Table 1 includes empirical data taken on a glass ribbon before entrance into a CCA that shows the impact of glass thermals on stress and warp*. The baseline condition is with no cooling and Cond 1-3 are each with different levels of cooling, all at the same rate of travel. The warp* is of bowing or global warp and not curtain warp, which arises from mechanical sources. Table 1 includes data for the condition in which the data was taken, a temperature of a thinner portion of the glass ribbon, a temperature of a thicker portion of the glass ribbon, the difference in temperature between the thinner portion and the thicker portion (all temperatures are in degrees Celsius), stress measured across the strip of thicker glass (in megapascals), and the warp*across the width of the glass ribbon (in millimeters). [0055] The empirical conditions included an atomizing device with three consecutive atomizing sprayers located above the top surface (A side) of the glass ribbon before the glass ribbon entered a CCA. The cooling set-up is shown in Fig. 5 with three atomizing sprayers lined up consecutively above the thicker strip of the glass ribbon just before the CCA entrance, which is to the right of the picture. The thicker strip was 80 mm wide, the thinner portion of the glass ribbon was about 2.0 mm thick, and the thickness delta between the thicker strip to the thinner portion was about 0.35 mm. The pre-CCA thermal data was captured using a thermal camera. Table 1 shows the impact of spray cooling on DT, stress, and warp. As Table 1 shows, water spray cooling was very effective in cooling the thicker strip and reducing DT from +40° C to -20° C, i.e. an impact of 60° C.

[0056] As shown in Table 1, spray cooling provided in condition 1 (Cond 1) and condition 2 (Cond 2) reduced the stress of the thicker strip. However, condition 3 (Cond 3) provided a similar stress as the baseline condition (Baseline). The optimum cooling level will depend on the ribbon geometry and thermal parameters. For example, extrapolating to a higher thickness delta of 0.8 mm, the thick-to-thin DT at the CCA entrance might be about 80° C without any preferential cooling of the strip. In such a case, cooling conditions with DT of 60-100° C will likely provide the least stresses.

[0057] Note that both conditions 1 and 2 with the lowest stresses resulted in increased warp. The warp increase can be avoided by applying cooling while keeping the glass ribbon constrained to a flat surface, e.g. using a vacuum conveyor.

[0058] Fig. 6 shows stress birefringence measurements for a thicker region cooled with a water spray experiment, as with the conditions of Table 1. Twin fluid atomizing sprayers were utilized to selectively cool the thicker portion of a glass ribbon. Benefits of the twin fluid atomizing sprayer include precise control of water and air flowrates, ability to cycle on/off for non-continuous cooling, and ability to tune water droplet size to reduce Leidenfrost effect and improve heat removal. Fan shaped spray pattern nozzles were used to encourage uniform cooling rates across the patch.

[0059] The left hand image shown in Fig. 6 is of the glass ribbon with no cooling, the baseline condition with a stress of 6.7 MPa. The right hand image shown in Fig. 6 is of a glass ribbon has water spray cooling on the thicker portion. The right hand image is from condition 2 in Table 1 having a stress of 3.75 MPa.

[0060] The birefringence data of Fig. 6 shows a difference in optical properties in different portions of the glass ribbon and represents differences in stress. Birefingence: S1-S2 = retardation/(thickness*SOC)

S1-S2 = difference between in-plane principal stresses Retardation unit: mm

SOC (stress optic coefficient) ~ 3nm/MPa-mm

[0061] In another embodiment of the present disclosure, Fig. 7 shows heaters that can be used to preferentially heat portions of the glass ribbon to lower the thermal gradient between the thicker and the thinner portions. The heaters shown are located above the glass ribbon before the glass ribbon enters a CCA but any suitable location is possible, including below the glass ribbon. In this example, there are two sets of heaters, each with two heating elements placed symmetrically on each side of the glass ribbon and away from a thicker center strip area to provide preferential heating primarily to the outer thinner portions of the glass ribbon.

[0062] Fig. 8 shows an arrangement and relative spacing of four heaters located relative to a 330 mm wide glass ribbon with an 80 mm wide thicker center strip in an actual trial. In Fig. 8, the glass ribbon is traveling from right to left between the viscous turn VT, where the glass ribbon turns from moving vertical to horizontal, and the CCA.

[0063] Analytical estimation and numerical modeling demonstrate the heater effectiveness and show the advantage of this preferential heating approach over an equipment setup without such heaters. To evaluate the heater effectiveness, Fig. 9 is a graph showing a relationship of the heater face temperature versus the glass ribbon temperature for a 1.3 mm thick ribbon passing through a 12" long heater. There are two conditions shown in this graph: a glass ribbon entering the heater either at 850° C or 750° C, both with about 1400 Ibs/hr of glass flow at a speed of about 0.14 m/s. The glass ribbon has a total width of 330 mm and the thicker center strip has a width of 80 mm. The thinner portion is 1.3 mm thick and the thicker center strip is 2.9 mm thick such that there is a 1.6 mm delta thickness. Assuming that an upper working limit of the heater is 900° C for the face temperature, it is expected from this analytical relation that the base ribbon temperature could increase by about 8° C for the 850° C case exiting the heater and by about 22° C for the 750° C case, where Fig. 9 shows the base temperature increase where the curves for the two cases cross 900° C. A takeaway from this analytical estimation is that higher temperature delta between the heater face and the base ribbon leads to larger temperature increase. Heaters can thus be placed more downstream or considering a higher working temperature to maximize the heating effectiveness.

[0064] To demonstrate the thermal management advantage over a conventional lehr with no additional localized heating, Fig. 10 is a graph of numerical modeling comparing the glass ribbon thermal history in the pre-CCA section with and without the additional localized heaters. Fig. 10 plots modelled data of glass temperature to distance of the glass from the VT. The heater configuration considered in the model is as shown in Fig. 8. Again, two initial conditions are considered: the glass ribbon starting at a temperature of either 850° C or 750° C. The plotted solid lines are temperatures of glass irradiated with heaters with their face temperatures maintained at 900° C. The dashed lines are with an equipment setup where there are Zircar boards, a low expansion high strength reinforced silica matrix composite used to retain heat, over two module portions (M2 and M3) of the lehr as the main thermal management tool. The bumps in the graph show the glass ribbon temperature increase by the two sets of heaters and their magnitudes are in a range as predicted by the scaling relation, i.e., around 5° C and 10° C for the two consecutive sets of heaters for the 850° C case and around 15° C for both sets of heaters for the 750° C case. As the sub-table in Fig. 10 shows, adding the two sets of heaters increases the glass ribbon temperature by 8° C (from 684° C to 676° C) as the glass ribbon reaches the CCA entrance for the 850° C case and by 20° C (from 637° C to 617° C) for the 750° C case.

[0065] Fig. 11 is modeled data that further compares the thick-to-thin thermal gradient reduction by the pre-CCA heaters against the standard equipment setup. The same conditions apply in Fig. 11 as described with respect to Fig. 10. Here, as the sub-table in Fig. 11 shows, adding the two sets of heaters reduces the thick-to-thin DT by around 30° C (141° C - 113° C) for the 850° C case at the CCA entrance and by around 40° C (196° C - 157° C), compared to the standard equipment setup. From the analytical estimation and the numerical modeling, it is demonstrated that base ribbon heaters in the pre-CCA area can be implemented as an effective preferential thermal management tool contributing to lowering the thick-to-thin DT.

[0066] Fig. 12 represents a portion of a lehr including heat reflector (Zircar Tunnel & Radiation Principles). In Fig. 12, the glass ribbon is traveling from right to left after the viscous turn. Experiments showed that two Zircar boards on lehr modules M2 and M3 can increase the glass ribbon temperature at the CCA entrance by ~25° C. By placing the Zircar boards above the thinner portion alone and ensuring that the thicker portion either keeps radiating to a much colder surface (<200° C to 300° C) or is cooled convectively, using more than two Zircar boards or similar heat reflectors can help reduce the thick-to-thin DT by 25° C or more.

[0067] Figs. 13 and 14 shows the use of an "airbar" that uses forced air to cool a thicker portion of a glass ribbon. Fig. 13 shows a configuration with an airbar above the glass ribbon and Fig. 14 shows a configuration with three airbars below the glass ribbon. Using convection, the forced air allows focused heat removal from the thicker portion of the glass ribbon while not removing heat from the thinner portion, thus reducing the thick-to-thin DT. The forced air can include steam injection as a means of humidification that increases the heat capacity of the air and thus the effectiveness of the airbar to reduce the temperature of the thicker portion.

[0068]

Table 2.

[0069] Table 2 lists thermal set-up conditions used for thermal testing, the results of which are shown in the graphs of Figs. 15 and 16. Figs. 15 and 16 show the maximum optical retardation at the thicker portion and B-side part size warp (PSW). Both A and B side cooling reduced the thick-to-thin DT and stresses in the thicker portion by up to 25%. With A-side cooling, warp level remained unchanged compared to the baseline case with Zircar boards. On the other hand, warp increased for B-side cooling cases C15 and C16 due to a colder glass ribbon because of no Zircar board being used above the glass ribbon. Warp was relatively lower for condition C17, which had both B-side cooling and Zircar boards above the glass ribbon, though still somewhat higher than the baseline conditions and A-side cooling cases.

[0070] The results were consistent with expectations that the slower cooling rate applied to the thicker portion before flattening rollers FR1 and FR2 could reduce stress without increasing warp.

[0071] Fig. 17 represents a side view of a glass ribbon traveling over airbars. The airbars provide support for the glass ribbon and the air flow is such that the air can escape between the airbars and the glass ribbon. The width of the airbars can be changed to provide more or less area for air flow to exit the airbars.

[0072] Fig. 18 represents a top view of three airbars. The grey areas correspond to the thicker portion of a glass ribbon and the pink areas correspond to the thinner portion. The grey area could be cooled to reduce the temperature and increase the conductive heat transfer rate in the areas corresponding to the thicker portion. The pink areas can be coated with a thermal barrier coating (e.g., zirconia) to increase the temperature of the thinner portion and decrease the heat transfer rate between the glass ribbon and the airbar in the areas corresponding to the thinner portion of the glass ribbon. Optionally, super-heated steam (at ~900°C) can be used in the pink areas instead of room temperature compressed air used with the airbars to float the glass to increase the temperature and decrease the heat transfer rate in the areas corresponding to the thinner portions of the glass ribbon. [0073] Fig. 19 represents an embodiment where the temperature difference between the thicker and thinner portions of the glass ribbon is reduced at the roll forming stage prior to the viscous turn. In this embodiment, forced air is directed from nozzles to the forming rollers at portions in which the thicker portion of the glass ribbon traverses. The forced air directed at the thicker portion of the rollers reduces the surface temperature of the rollers and maximizes the amount of heat energy removed from the thicker portion of the glass ribbon. The compressed air directed at the thicker portion removes heat directly out of the glass ribbon corresponding to where the air is focused. The forced air can be complimented with steam injection to increase the heat capacity the effectiveness of the forced air to remove heat.

[0074] It should be understood that the foregoing description is only illustrative of the present invention. Various alternatives and modifications can be devised by those skilled in the art without departing from the present invention. Accordingly, the present invention is intended to embrace all such alternatives, modifications, and variances that fall within the scope of the appended claims.