TWI540106B - Method and apparatus for controlling sheet thickness - Google Patents

Description

Method and apparatus for controlling panel thickness [related case]

The present application claims priority to U.S. Patent Application Serial No. 61/251,481, filed on Jan. 14, 2009.

The present invention generally relates to methods and apparatus for forming glass sheets. In particular, the invention relates to a method and apparatus for controlling the thickness of a glass sheet made from molten glass.

In U.S. Patent No. 3,682,609, a system for controlling the thickness of a sheet formed from molten glass is described. In the system of U.S. Patent No. 3,682,609, the molten glass flows down to opposite sides of a forming member and fuses at the wedge-shaped root of the forming member to form a glass sheet. The glass sheet passes between a pair of mutually facing outer casings having front walls that face the glass sheets. The front wall is made of a material having high thermal conductivity, low expansion, and low emissivity, such as silicon carbide. A plurality of fluid conduits are arranged in the housings and have nozzles, the nozzles of the conduits being disposed on the back side of the front walls in a spaced relationship. Each conduit has an associated flow meter having a control valve and connected to a manifold. Each fluid conduit delivers a cooling fluid or heating fluid to a backside region of an adjacent front wall. Typically, the fluid delivered is air. Heat exchange is performed between the glass sheet and the front wall by heat radiation to control the thickness of the glass sheet. If the thickness trace of the glass sheet shows that the thickness of a particular area over the entire width of the glass sheet is greater than a desired value, the area adjacent to the thicker area of the glass sheet can be cooled, that is, the cooling is thin. Area to correct the thickness trajectory. Fluid conduits corresponding to the adjacent regions are activated to cool the adjacent regions (ie, the thinner regions). The patent also suggests delivering a heated fluid to the back side of the front wall instead of the step of delivering a cooling fluid. In this example, a fluid conduit corresponding to a thicker region can be utilized to deliver the heated fluid. This reduces the viscosity in thicker areas and thins the area. Heating fluid can be provided using electrical windings connected to the fluid conduit.

It has been a long time since the above system was used to control the thickness of the glass sheet formed by the molten glass. Although the system is quite effective, there are still some challenges in the use of the system. For example, a fluid conduit is used to deliver a cooling fluid (typically air), and sometimes the cooling fluid may leak to the draw where the glass sheet is located. Such leakage may result in uncontrolled heat loss of the glass sheet and discontinuity in the thickness of the glass sheet. The system cannot be easily adapted for use in numerical control and feedback systems, but numerical control systems and feedback systems are required for automated control. The solution in the field of view of the system is limited only to the convective cooling effect of the intermediate wall, followed by diffusion of the cooling effect by heat conduction. Due to this diffusion, the intent to create a shape of a thermal signature is ineffective.

Thus, in accordance with one aspect of the present invention, a method of controlling the thickness profile of a glass ribbon is provided. The method comprises the steps of: (A) a selected strip of viscous behavior for the ribbon, and finding one or more regions of the strip at a thickness that deviates from the target thickness of the strip. And (B) illuminating the one or more regions of the strip portion with radiant heat to reduce glass viscosity in the one or more regions.

In certain embodiments of the first aspect of the invention, the method comprises the step of: (C) repeating steps (A) and (B) of the different strip portions of the glass ribbon exhibiting viscous behavior.

In some embodiments of the first aspect of the present invention, in step (A), each of the one or more regions has a thickness greater than a target thickness, and in step (B), the one or The thickness of each of the plurality of regions.

In some embodiments of the first aspect of the invention, step (B) includes positioning a radiant heater adjacent to the strip portion and operating the radiant heater to illuminate the radiant heat on the one or more regions .

In some embodiments of the first aspect of the invention, in step (B), the radiant heater comprises an array of a plurality of radiant heating elements, and step (B) further comprises step (D) for The field-of-view of adjacent radiant heating elements overlaps.

In certain embodiments of the first aspect of the invention, in step (D), the radiant heating elements are linear and inclined relative to the direction of travel of the glass ribbon.

In some embodiments of the first aspect of the invention, in step (B), the radiant heater has a non-linear shape such that a radiation viewing angle between the radiant heater and the one or more regions (radiation view) Factor) reaches the maximum.

In certain embodiments of the first aspect of the invention, the method further comprises the step (E) of fusing the separated molten glass stream at a wedge-shaped root of the forming member to form a glass ribbon.

In some embodiments of the first aspect of the invention, in step (B), the radiant heater is disposed in an adjacent region of the wedge-shaped root.

In some embodiments of the first aspect of the invention, in step (B), the radiant heater is an infrared heater.

According to a second aspect of the invention, a system for controlling the thickness profile of a glass ribbon is provided. The system includes: a forming member for forming a glass ribbon, the forming member having a wedge-shaped root, and a separate flow of molten glass fused at a wedge-shaped root to form a glass ribbon; and a radiant heater configured to selectively Radiant heat is applied to selected areas of the glass ribbon that exhibit viscous behavior and whose thickness deviates from the target thickness.

In certain embodiments of the second aspect of the invention, the radiant heater is positioned adjacent the wedge root.

According to a third aspect of the present invention, there is provided a method of making a glass sheet, the method comprising the steps of:

(i) providing a glass ribbon having a width defined by two opposing edges and at a temperature that causes the glass to exhibit a viscoelastic behavior;

(ii) moving the glass ribbon when the glass exhibits a viscoelastic behavior;

(iii) heating the glass ribbon using an array of a plurality of heating elements, the power of which can be individually adjusted.

In certain embodiments of the third aspect of the invention, step (i) comprises forming the glass ribbon from a glass melt using a spacer tube.

In some embodiments of the third aspect of the invention, in step (iii), the heating elements are arranged to have overlapping fields of view.

In certain embodiments of the third aspect of the invention, in step (iii), the heating elements differentially heat the glass ribbon from one edge to the other across the width of the glass ribbon.

According to some embodiments of the third aspect of the invention, step (iii) comprises:

(iii-1) determining the thickness variation of the glass ribbon in the width;

(iii-2) The glass ribbon is heated differently within the width depending on the thickness variation such that the drawn glass ribbon has a substantially uniform thickness.

In some embodiments of the third aspect of the invention, in step (iii-2), the heating elements are applied to the region of the glass ribbon having the largest thickness region of heat greater than the heat applied to the region having the smallest thickness. .

In certain embodiments of the third aspect of the invention, in step (iii), the heater array is essentially a linear array.

In certain embodiments of the third aspect of the invention, in step (iii), the array of heating elements is capable of applying heat to the full width of the ribbon.

In some embodiments of the third aspect of the invention, in step (iii), the heating elements apply heat by the action of the infrared beam.

In certain embodiments of the third aspect of the invention, step (i) includes forming a glass ribbon from the glass melt using a separator tube, and in step (iii), the heating elements are disposed adjacent the root of the separator tube At the office.

In certain embodiments of the third aspect of the invention, in step (iii), the heating elements are arranged to apply heat to the glass ribbon before the glass ribbon reaches the root of the isolation tube.

In some embodiments of the third aspect of the invention, in step (iii), the array of heating elements is disposed on each side of the isolation tube such that the two glass ribbons on either side of the isolation tube merge at the root Individual glass ribbons can be heated separately before.

In some embodiments of the third aspect of the invention, in step (iii), the array of heating elements is arranged to apply heat to the glass ribbon located below the root of the isolation tube.

In certain embodiments of the third aspect of the invention, in step (iii), an array of heating elements is disposed on each side of the isolation tube to apply heat to each side of the glass ribbon located below the root of the isolation tube.

Advantages and other aspects of the present invention will be apparent from the description and appended claims.

The invention will be described in detail below with reference to the accompanying drawings. In the detailed description, numerous specific details are set forth, However, it will be apparent to those skilled in the art that the present invention may be practiced without a part or all of these details. In other instances, well-known features and/or method steps may not be described in detail to avoid unnecessarily obscuring the invention. In addition, similar or identical component reference symbols may be used to indicate common or similar components.

Figure 1 shows a method and system for forming a glass ribbon 113 having a controlled thickness. A pull-down forming member 101 of known construction is shown in U.S. Patent Nos. 1,829,641 and 3,338,696, having converging sidewalls 103 and 105, and converging sidewalls 103 and 105 terminating in a wedge-shaped root 107. The glass ribbon 113 begins with two molten glass streams 109 and 111 flowing down the converging sidewalls 103, 105 of the forming member 101 and merges at the wedge root 107 to form a glass sheet. The molten glass stream 109, 111 is formed by transporting the molten glass 115 into the passage 117 in the forming member 101 and allowing the molten glass 115 to overflow the passage 117 as in the known method described in U.S. Patent Nos. 1,829,641 and 3,338,696. . The glass ribbon 113 is pulled out from the wedge-shaped root 107 in a plate form. When the glass ribbon 113 is pulled out, the glass ribbon 113 is cooled to convert the glass from a viscous regime to an elastic regime. The cooling pattern of the viscous glass ribbon 113 affects the thickness profile of the elastic glass ribbon. Uneven cooling during viscous properties may result in uncontrolled thickness during elastic texture, such as uneven thickness uniformity. The method of Fig. 1 corrects the cooling mode of the glass ribbon 113 and the thickness of the glass ribbon 113 by reducing the heat loss in selected regions of the glass ribbon 113, as will be explained below.

In the first figure, the radiant heater 119 is disposed adjacent to the surface 121 of the glass ribbon 113. Radiant heater 119 illuminates radiant heat (as indicated by line 123) onto a selected area of glass ribbon 113. The criteria used to select the radiant heat irradiation area will be discussed below. As indicated by the checkered shadow area 125, the radiant heat 123 moves with the glass ribbon 113 as the glass ribbon 113 pulls downward away from the wedge-shaped root 107. The footprint of the radiant heat on the glass ribbon 113 determines the width 127 of the heated region 125. The spacing between the radiant heater 119 and the surface 121 and the geometry and output of the radiant heater 119 can be suitably selected to deliver a desired amount of radiant heat to the surface 121. In Fig. 1, the position of the radiant heater 119 can be set such that it can illuminate the radiant heat to the glass ribbon 113 above the wedge-shaped root 107. In an alternate configuration, the location of the radiant heater 119 can be set to illuminate the radiant heat to the glass ribbon 113 located below the wedge root 107 or at the wedge root 107. Generally, the position of the radiant heater 119 is set to illuminate the radiant heat to a region where the glass ribbon 113 exhibits viscous behavior. In general, the area of the glass ribbon 113 that exhibits viscous behavior may be near the wedge-shaped root 107. A second radiant heater (not shown separately) may be disposed on the opposite side of the glass ribbon 113 and be used in the same manner as the first radiant heater to illuminate the radiant heat onto the glass ribbon 113.

In order to control the thickness of the glass ribbon 113, a strip of glass ribbon can be selected along the width of the glass ribbon 113. Typically, the strip portion of the glass ribbon 113 may be the portion of the glass ribbon 113 adjacent the radiant heater 119 at any given time during the processing of the glass ribbon 113. For the sake of explanation, Fig. 2 shows a side view of the system of Fig. 1. In Fig. 2, the strip portion 201 is defined by a broken line, and the radiant heater 119 and the strip portion 201 face each other. Figure 3 shows a cross-sectional view of the system of Figure 2 taken along strip portion 201. For the strip portion 201, it has an anomalous region 301 whose thickness deviates from the target thickness or normal thickness of the strip portion 201. Since the thickness of the abnormal region 301 is larger than the target or conventional thickness of the strip portion, the region 301 is generally regarded as "abnormal". The strip portion 201 may typically have one or more such anomalous regions, or no anomalous regions. The process of controlling the thickness of the glass ribbon 113 includes finding any anomalous regions on the strip portion 201. The step of finding such anomalous regions may involve performing an active measurement on the strip portion 201, or possibly finding an anomalous region based on historical data obtained using a particular set of process settings and parameters.

Once the abnormal area on the strip portion 201 is found, the radiant heater 119 is controlled to illuminate the radiant heat onto the abnormal regions. In the example shown in Fig. 3, as indicated by the checkered hatched area 303, the radiant heater 119 illuminates the radiant heat onto the abnormal region 301. The radiant heat delivered to the anomalous region 301 will heat the region 301. This will reduce the viscosity in the abnormal region 301 and reduce the thickness of the abnormal region 301. The thickness is reduced such that the thickness of the corrected abnormal region 301 conforms to the target thickness or the conventional thickness of the strip portion 201. Typically, this heating step will produce a corrected temperature profile across the strip portion 201, for example, the corrected temperature profile may be more uniform than the temperature profile prior to heating the anomalous region 301 using the radiant heater 119. This corrected or more uniform temperature profile will move as the strip portion 201 travels along the direction of travel of the glass ribbon 113. Later, the other strip of glass ribbon 113 will be adjacent to radiant heater 119. The method of finding an abnormal region and illuminating the radiant heat on the abnormal region may be repeatedly performed for the other strip portion and other strip portions adjacent to the radiant heater in the future. However, this does not mean that the radiant heater 119 must be stationary. When the other portions of the glass ribbon 113 have abnormal regions, and these abnormal regions exhibit viscous behavior, and the portions need to be heat-treated, the radiant heater 119 can be repositioned.

As described above with reference to Figs. 1 to 3, the thickness of the glass ribbon 113 is controlled without using a fluid, and the thickness of the glass ribbon 113 is controlled by "direct" radiant heat, thereby avoiding leakage of fluid to the pull-out portion. The surface of the glass ribbon 113 causes a chimney effect. The term "direct" means that the heat exchange between the radiant heater 119 and the glass ribbon 113 is not hindered by the structure, such as by the front wall of the system mentioned in the prior art. The radiant heater 119 can be placed at a surface very close to the glass ribbon 113 to maximize heating efficiency. The geometry of the radiant heater 119 and the spacing of the radiant heater from the surface of the glass ribbon 113 can also be manipulated to achieve high resolution field of view radiation. Referring to the systems described in Figures 1 through 3, automatic control may also be provided by itself and will be described below.

In Figs. 1 to 3, the radiant heater 119 generates electromagnetic radiation having a wavelength equivalent to that of the glass ribbon 113 such that the radiant heat energy is absorbed by the glass to produce a viscosity lowering effect. Typically, radiant heater 119 can be an infrared radiant heater. The radiant heater 119 may comprise a single radiant heating element or comprise an array of radiant heating elements. Such radiant heating element may be manufactured of refractory metal such as platinum (Pt), platinum alloys, tungsten, molybdenum silicide and metal bis (MoSi ₂₎ is similar to, or made of a ceramic material such as silicon carbide (SiC). The heating elements may be formed by filament wires, such as tungsten wires, or by emissive plate shapes, such as ceramic plates. Typically, a radiant heating element made of a filament wire can include a wire loop to increase the surface area used to generate radiant heat. The radiant heating elements may be disposed in transparent enclosures, such as a quartz enclosure. The outer casing may be coated with a reflective material to increase the amount of radiant heat delivered to the glass ribbon 113. The radiant heater 119 can be an electric radiant heater or an induction radiant heater. The radiant heater 119 may or may not extend across the entire width of the glass ribbon 113 (203 of Figure 2). A plurality of radiant heaters 119 may be disposed across the entire width (203 of FIG. 2) across the glass ribbon 113, and the radiant heaters 119 are operated to illuminate the radiant heat over a plurality of abnormal regions.

Figure 4 shows a radiant heater 119 comprising an array of a plurality of radiant heating elements 401. The radiant heating elements 401 are linear radiant heating elements. The radiant heating elements 401 are spaced apart from each other and aligned with the direction of travel of the glass ribbon 113 (as indicated by arrow 403). For simplicity, only the relevant portions of the glass ribbon 113 are shown in FIG. Since the radiant heating elements 401 are spaced apart from one another and the radiant heating elements 401 are aligned in alignment with the direction of travel 403 of the glass ribbon 113, the glass carries portions (with a gap between the radiant heating elements 401) The corresponding part of 404) cannot receive direct radiant heat. These parts are called "dead zones". In order to eliminate the dead zone, the radiant heating elements 401 can be arranged such that their field of view or imprints that illuminate the glass ribbon 113 overlap. Figure 5 shows how to do this. In Fig. 5, four radiant heating elements 501, 503, 505, 507 are spaced apart from each other and are inclined with respect to the direction of travel of the glass ribbon 113 indicated by arrow 508 such that one of the radiation beams produced by the radiant heating element The radiation beam generated by the adjacent radiant heating element overlaps, for example the radiation beam produced by the radiant heating element 501 will overlap with the radiation beam produced by the radiant heating element 503, and so on. Figure 6 shows overlapping radiation beams 601, 603, 605, 607 corresponding to the radiant heating elements 501, 503, 505, 507. It should be noted that the lattice shadow density of the radiation beams is only used as a visual effect tool to distinguish one radiation beam from another.

An array of radiant heating elements can be coupled to the controller, which is depicted in FIG. 5, which are coupled to or in communication with controller 509. The controller 509 can be operated to individually turn the radiant heating elements 501, 503, 505, 507 on or off. Controller 509 can receive external input 511. An example of external input 511 may be a thickness or temperature profile across a strip of glass ribbon 113. The controller 509 can use the information to determine which of the radiant heating elements 501, 503, 505, 507 is turned on and off to achieve a target thickness or temperature distribution across the strip of the glass ribbon 113. . It should be noted that this may be a continuous process in which the thickness or temperature profile across the glass ribbon 113 is measured at a particular location and the radiant heating elements 501, 503, 505, 507 are controlled based on the measured thickness or temperature profile. Heat is delivered to the desired strip of the glass ribbon 113. The thickness or temperature profile can be measured separately using an optical or thermal sensor. It is also possible to visually inspect the glass ribbon 113 and determine which of the radiant heating elements 501, 503, 505, 507 is turned on or off. The information obtained by visual inspection can be used to operate the controller 509.

It should be noted that the radiant heater 119 depicted in Figure 1 may comprise a single radiant heating element or comprise an array of radiant heating elements. The system can use a plurality of radiant heaters 119, or the system can use a single radiant heater 119 having an array of radiant heating elements. The radiant heater 119 may have a width that may span the width of the glass ribbon 113, or the width may be less than the width of the glass ribbon 113. When an array of multiple radiant heating elements is used, the controller can be used to individually control the heating elements in the radiant heating elements to operate at any time. The controller can also be used to adjust the output of the radiant heating element. It should be noted that the radiant heating element is not limited to the linear radiant heating elements as illustrated in Figures 4, 5 and 6. A non-linearly shaped radiant heating element can be used to increase or maximize the radiation view factor. The radiation viewing angle factor is the fraction of thermal energy that leaves the surface of the first object and reaches the surface of the second object, which is entirely determined by geometric factors. Figure 7 shows an elliptical radiant heating element 701, as well as a radiant heating element 703 of any shape. Element 703 is of any shape and is intended to show how the invention itself can be used to create a particular shape for the feature shape that needs to be corrected. For example, an "L" shaped element can be placed such that the vertical section of the L-shaped element creates a concentrated heating effect while the horizontal section creates a relatively wider, more dispersed heating effect, and The net result produced on the glass is an asymmetrical effect. Typically, this non-linear shape can be selected based on the typical shape of the area of the glass ribbon that is to be heated by the radiant heater.

Although the present invention has been described with reference to a limited number of embodiments, those skilled in the art will be able to make other embodiments without departing from the scope of the invention. Therefore, the scope of the invention is limited only by the scope of the appended claims.

101. . . Forming member

103, 105. . . Converging sidewall

107. . . Wedge root

109, 111. . . Molten glass flow

113. . . Glass belt

115. . . Molten glass

117. . . aisle

119. . . Radiant heater

121. . . surface

123. . . Radiant heat

125. . . Heated area

127. . . width

201. . . Strip

203. . . width

301. . . Abnormal area

303. . . Checked shadow area

401. . . Radiant heating element

403. . . Arrow / direction of travel

404. . . gap

501, 503, 505, 507. . . Radiant heating element

508. . . arrow

509. . . Controller

511. . . External input information

601, 603, 605, 607. . . Radiation beam

701, 703. . . Radiant heating element

The following is a description of the drawings in conjunction with the drawings. The figures are not necessarily to scale, and some of the features and partial views of the drawings may be exaggerated or simplified in proportion to clarity and conciseness.

Figure 1 is a schematic diagram of a system for forming a glass ribbon of controlled thickness.

Figure 2 is a side view of the system of Figure 1.

Figure 3 is a cross-sectional view of the system of Figure 2 taken along line 3-3.

Figure 4 shows a radiant heater having an array of radiant heating elements.

Figure 5 shows a radiant heater having a controller and an array of a plurality of radiant heating elements arranged to eliminate dead zones and the controller for selectively operating the radiant heating element.

Figure 6 is a cross-sectional view of the system of Figure 5 showing the overlapping radiation beams.

Figure 7 shows a radiant heating element with a non-linear shape.

101. . . Forming member

103, 105. . . Converging sidewall

107. . . Wedge root

109, 111. . . Molten glass flow

113. . . Glass belt

115. . . Molten glass

117. . . aisle

119. . . Radiant heater

121. . . surface

123. . . Radiant heat

125. . . Heated area

127. . . width

Claims (23)

A method of controlling a thickness profile of a glass ribbon, comprising: (A) a selected strip portion exhibiting viscous behavior for the glass ribbon, and finding a thickness at which the thickness of the strip portion deviates from a target thickness of the strip portion Or a plurality of regions; and (B) illuminating the one or more regions of the strip portion with radiant heat to reduce glass viscosity in the one or more regions (i) wherein step (B) comprises: positioning one Irradiating the heater such that the radiant heater is adjacent to the strip portion, and operating the radiant heater to illuminate radiant heat on the one or more regions; and (ii) the radiant heater comprises a plurality of radiant heating elements An array, and wherein step (B) further comprises: (D) overlapping field-of-views of adjacent radiant heating elements in the array. The method of claim 1, further comprising: (C) repeating steps (A) and (B) of the different strip portions of the glass ribbon exhibiting viscous behavior. The method of claim 1, wherein in the step (A), each of the one or more regions has a thickness greater than the target thickness, and in the step (B), reducing the one or The thickness of each of the plurality of regions. The method of claim 1, wherein in step (D), the radiant heating elements are linear and inclined relative to a direction of travel of the glass ribbon. The method of claim 1, wherein in the step (B), the radiant heater has a non-linear shape such that a radiation viewing angle factor between the radiant heater and the one or more regions (radiation) View factor) reaches the maximum. The method of claim 1, further comprising the step (E) of: (E) fusing the separated molten glass stream at a wedge-shaped root of the forming member to form the glass ribbon. The method of claim 6, wherein in the step (B), the radiant heater is disposed adjacent to the wedge-shaped root. The method of claim 1, wherein in the step (B), the radiant heater is an infrared heater. A system for controlling a thickness profile of a glass ribbon, comprising: a forming member for forming a glass ribbon, the forming member having a wedge-shaped root portion, and a separate flow of molten glass is fused at the wedge-shaped root to form the glass Belt; a radiant heater configured to selectively illuminate radiant heat over a plurality of selected regions of the glass ribbon, the regions exhibiting viscous behavior and the thickness of the regions deviates from a target thickness; wherein the radiant heater comprises An array of adjacent radiant heating elements of a plurality of overlapping fields of view. The system of claim 9 wherein the radiant heater is positioned adjacent the wedge root. A method of making a glass sheet comprising the steps of: (i) providing a glass ribbon having a width defined by two opposing edges and at a temperature that causes the glass to exhibit a viscoelastic behavior; (ii) Moving the glass ribbon when the glass exhibits a viscoelastic behavior; and (iii) heating the glass ribbon using an array of a plurality of heating elements, the power of the heating elements being individually adjustable; wherein in step (iii) The heating elements are arranged to have overlapping fields of view. The method of claim 11, wherein the step (i) comprises: forming the glass ribbon from a glass melt using a spacer tube. The method of claim 11 or 12, wherein in step (iii), the heating elements span the width of the glass ribbon from one side The edge of the glass tape is differentially heated to the other edge. The method of claim 11 or 12, wherein the step (iii) comprises: (iii-1) determining a thickness variation of the glass ribbon in the width; (iii-2) according to the thickness variation, The glass ribbon is heated differentially within the width such that the drawn glass has a substantially uniform thickness. The method of claim 14, wherein in the step (iii-2), the heating elements are applied to one of the regions of the glass ribbon having a maximum thickness more than one of the minimum thicknesses The heat of the area. The method of claim 11 or 12, wherein in step (iii), the heater array is essentially a linear array. The method of claim 11 or 12, wherein in step (iii), the array of heating elements is capable of applying heat to the full width of the glass ribbon. The method of claim 11 or 12, wherein in the step (iii), the heating elements apply heat by the action of the infrared beam. For example, the method described in claim 11 or 12, wherein the step Step (i) includes forming the glass ribbon from a glass melt using a spacer tube, and in step (iii), the heating elements are disposed adjacent to the root of the isolation tube. The method of claim 19, wherein in the step (iii), the heating elements are disposed to cause the heating elements to apply to the glass ribbon before the glass ribbon reaches the root of the isolation tube heating. The method of claim 20, wherein in step (iii), an array of one of the plurality of heating elements is disposed on each side of the isolation tube such that the two glass ribbons merge at the root to form a single The two glass ribbons on either side of the separator tube are each heated prior to the glass ribbon. The method of claim 19, wherein in step (iii), an array of one of the plurality of heating elements is disposed to apply heat to the glass ribbon located below the root of the isolation tube. The method of claim 19, wherein in the step (iii), an array of one of the plurality of heating elements is disposed on each side of the isolation tube to apply heat to the underlying portion of the isolation tube. The glass strips are on each side.