JP5698753B2 - Sheet thickness control method and apparatus - Google Patents

Description

Explanation of related applications

  This application claims the benefit of priority of US Patent Application No. 61 / 251,148, filed October 14, 2009.

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

  Patent Document 1 describes a system for controlling the thickness of a sheet formed from molten glass. In the system of Patent Document 1, molten glass flows down the facing surface of the molding member, and this melts at the wedge-shaped bottom of the molding member to form a glass sheet. The glass sheet passes between a pair of opposing housings, each housing having a front wall facing the glass sheet. The front wall is made of a material having high thermal conductivity, low expansion, and low emissivity, such as silicon carbide. A fluid conduit is arranged in the housing, wherein the nozzles of the fluid conduit are positioned on the back of the front wall in spaced relation. Each fluid conduit has an associated flow meter that includes a control valve and is connected to the manifold. Each fluid conduit supplies cooling or heating fluid to the back area of the adjacent front wall. Typically, the fluid supplied is air. In order to control the thickness of the glass sheet, heat exchange by thermal radiation occurs between the glass sheet and the front wall. If the glass sheet thickness waveform indicates that a specific area across the glass sheet width is thicker than desired, the glass sheet zone adjacent to the thicker area is cooled, i.e., the thinner area is cooled. Then, the thickness waveform is corrected. The fluid conduit corresponding to this adjacent zone is driven to cool the adjacent zone (ie, the thinner area). This patent also proposes supplying heated fluid to the back of the front wall instead of supplying cooling fluid. In this case, the heated fluid will be supplied from the fluid conduit corresponding to the thicker area. This reduces the viscosity of the thicker area and then becomes thinner. Heated fluid may be supplied in association with the electrical windings in the fluid conduit.

US Pat. No. 3,682,609

  The system described above has been used for many years to control the thickness of sheets formed from molten glass. While this system is effective, there are several challenges associated with the use of this system. For example, although typically air, the cooling fluid supplied from the fluid conduit can sometimes leak into the stretch where the glass sheet is located. This leakage can cause uncontrolled heat loss in the glass sheet, resulting in a discontinuous thickness of the glass sheet. This system cannot be easily adapted to numerical control devices and feedback systems required for automatic control. The resolution of the system viewing range is limited by the use of convective cooling of this wall, since the intervening wall later diffuses the effect due to its heat conduction. That is, because of this diffusion, attempts to generate a shaped thermal signature have no effect.

  That is, according to the first aspect of the present invention, a method for controlling the thickness profile of a glass ribbon is provided. The method comprises (A) finding one or more areas in a strip having a thickness that deviates from a target thickness for the selected strip of glass ribbon exhibiting viscous behavior. And (B) applying radiant heat to the one or more areas to reduce the viscosity of the glass in the one or more areas of the strip.

  In certain embodiments of the first aspect of the invention, the method further comprises (C) repeating steps (A) and (B) for different strips of glass ribbon exhibiting viscous behavior.

  In certain embodiments of the first aspect of the invention, in step (A), the thickness of each of the one or more areas is greater than the target thickness, and in step (B), the thickness of each of the one or more areas is Reduce thickness.

  In certain embodiments of the first aspect of the invention, step (B) operates to position the radiant heater adjacent the strip and to apply the radiant heat to the one or more areas. Including a step.

  In certain embodiments of the first aspect of the invention, in step (B), the radiant heater includes an array of radiant heating elements, and step (B) includes (D) adjacent radiant heating elements in the array. The method further includes overlapping the fields of view.

  In a particular embodiment of the first aspect of the invention, in step (D), the radiant heating element is straight and inclined with respect to the direction of travel of the glass ribbon.

  In certain embodiments of the first aspect of the invention, in step (B), the radiant heater has a non-linear shape and maximizes the radiant form factor between the radiant heater and the one or more areas. .

  In certain embodiments of the first aspect of the present invention, the method further comprises (E) forming a glass ribbon by fusing a separate stream of molten glass at the wedge-shaped bottom of the forming member.

  In certain embodiments of the first aspect of the present invention, in step (B), the radiant heater is positioned proximate to the wedge-shaped bottom.

  In certain 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. This system is a forming member for forming a glass ribbon, wherein the glass ribbon is formed by fusing a separated flow of molten glass at the wedge-shaped bottom of the forming member, and the viscous behavior and the target thickness. A radiant heater disposed to selectively apply radiant heat to a selected area of the glass ribbon exhibiting a thickness deviating from.

  In certain embodiments of the second aspect of the present invention, the radiant heater is positioned near the wedge-shaped bottom.

According to a third aspect of the present invention, a method for producing a glass sheet, comprising:
(I) providing a glass ribbon having a width defined by two opposing edges at a temperature at which the glass exhibits viscoelastic behavior;
(Ii) moving the glass ribbon while the glass exhibits viscoelastic behavior; and
(Iii) heating the glass ribbon with an array of heater elements, wherein the output of the heater elements is separately adjustable;
Is provided.

  In certain embodiments of the third aspect of the present invention, step (i) comprises fusion molding a glass ribbon from the glass melt using an isopipe.

  In a particular embodiment of the third aspect of the invention, in step (iii) the heater elements are arranged to have overlapping fields of view.

  In a particular embodiment of the third aspect of the present invention, in step (iii), the heater element heats the ribbon differentially from one edge to the other across the width of the ribbon.

In certain embodiments of the third aspect of the invention, step (iii) comprises:
(Iii-1) determining ribbon thickness variation within a width;
(Iii-2) heating the ribbon in a distinguished manner within the width according to this thickness variation so that the ribbon is drawn to a substantially uniform thickness;
including.

  In a particular embodiment of the third aspect of the invention, in step (iii-2) the heater element is placed in an area having the thickest thickness within the width of the ribbon, with the thinnest thickness within this range. Apply more heat than an area with

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

  In certain embodiments of the third aspect of the present invention, in step (iii), the array of heater elements can apply heat to the full width of the glass ribbon.

  In a particular embodiment of the third aspect of the invention, in step (iii) the heater element applies heat by irradiation with an infrared beam.

  In certain embodiments of the third aspect of the invention, step (i) comprises forming a glass ribbon from the glass melt using an isopipe, and in step (iii) the heater element is iso Located near the bottom of the pipe.

  In a particular embodiment of the third aspect of the invention, in step (iii), the heater element is positioned such that the heater element applies heat to the glass ribbon before reaching the bottom of the isopipe.

  In a particular embodiment of the third aspect of the invention, in step (iii), before the two glass ribbons on the two faces of the isopipe are joined at the bottom to form a single glass ribbon An array of heater elements is positioned on each side of the isopipe so that it is heated separately.

  In a particular embodiment of the third aspect of the invention, in step (iii), an array of heater elements is positioned to apply heat to the glass ribbon below the bottom of the isopipe.

  In certain embodiments of the third aspect of the present invention, in step (iii), an array of heater elements is placed on each side of the isopipe to apply heat to each side of the glass ribbon below the bottom of the isopipe. Position on the side.

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

  The following is a description of the figures contained in the accompanying drawings. The figures are not necessarily drawn to scale, and certain features and figures may be shown enlarged or reduced in scale or schematic for clarity and brevity.

Schematic diagram of a system for forming a thickness-controlled glass ribbon Side view of the system of FIG. Sectional view along line 3-3 of the system of FIG. Diagram showing a radiant heater with an array of radiant heating elements A diagram showing a radiant heater comprising a radiant heating element array arranged to eliminate dead zones and a controller for selectively operating the radiant heating elements Sectional view of the system of FIG. 5 showing overlapping radiation beams Diagram showing a radiant heating element having a non-linear shape

  The present invention will now be described in detail with reference to the accompanying drawings. In this detailed description, numerous specific details will be set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without some or all of these specific details. In other instances, well-known features and / or processing steps may not be described in detail in order not to unnecessarily obscure the present invention. Moreover, similar or identical reference numerals may be used to identify common or similar elements.

  FIG. 1 illustrates a system and process for forming a glass ribbon 113 with a controlled thickness. A downdraw molded member 101 of known construction as shown in U.S. Pat. Nos. 1,829,641 and 3,338,696 has a confluence surface 103 that terminates in a wedge-shaped bottom 107. , 105. First, the glass ribbon 113 starts as two molten glass streams 109 and 111 that flow down the joining surfaces 103 and 105 of the forming member 101, and then fuses at the position of the wedge-shaped bottom 107 to form a glass sheet. Molten glass streams 109 and 111 are formed by supplying molten glass 115 to grooves 117 of forming member 101 and causing molten glass 115 to overflow from grooves 117 in a known manner. This technique is described in US Pat. Nos. 1,829,641 and 3,338,696. The glass ribbon 113 is stretched from the wedge-shaped bottom portion 107 in a sheet state. When the glass ribbon 113 is drawn, the glass ribbon 113 is cooled so that the glass transitions from a viscous state to an elastic state. The cooling pattern of the viscous glass ribbon 113 affects the thickness profile of the elastic glass ribbon 113. If the cooling in the viscous state is not uniform, the thickness in the elastic state can be uncontrolled (eg, not uniform). In the process of FIG. 1, the cooling pattern of the glass ribbon 113 is modified and the thickness of the glass ribbon 113 is controlled by reducing the heat loss from selected areas of the glass ribbon 113. This will be described below.

  In FIG. 1, a radiant heater 119 is provided adjacent to the surface 121 of the glass ribbon 113. The radiant heater 119 applies radiant heat indicated by a line 123 to a selected area of the glass ribbon 113. The criteria for selecting the area to apply radiant heat will be discussed later. As the glass ribbon 113 is drawn from the wedge-shaped bottom 107, the radiant heat 123 moves with the glass ribbon 113 as indicated by the cross hatch area 125. The radiant heat trace on the glass ribbon 113 determines the width 127 of the heated area 125. The spacing between the radiant heater 119 and the surface 121 and the shape and power of the radiant heater 119 are appropriately selected to provide the surface 121 with the desired amount of radiant heat. In FIG. 1, the radiant heater 119 is positioned at a position where the radiant heat can be applied to the glass ribbon 113 above the wedge-shaped bottom portion 107. As an alternative arrangement, the radiant heater 119 may be positioned at a position where the radiant heat can be applied to the glass ribbon 113 below the wedge-shaped bottom portion 107 or at the position of the wedge-shaped bottom portion 107. Generally, the radiant heater 119 is positioned so that the radiant heat can be applied to an area where the glass ribbon 113 exhibits a viscous behavior. In general, an area where the glass ribbon 113 exhibits a viscous behavior is in the vicinity of the wedge-shaped bottom portion 107. A second radiant heater (not shown separately) is provided on the opposite side of the glass ribbon 113 and is used in the same manner as the first radiant heater 119 to apply radiant heat to the glass ribbon 113. It may be.

  In order to control the thickness of the glass ribbon 113, a strip of glass ribbon (along the width of the glass ribbon 113) is selected. Typically, the strip of glass ribbon 113 will be the portion of the glass ribbon 113 that is adjacent to the radiant heater 119 at any given point in the process of forming the glass ribbon 113. For illustration purposes, FIG. 2 shows a side view of the system of FIG. In FIG. 2, the strip 201 is separated by a broken line, and the radiant heater 119 is in a positional relationship facing the strip 201. FIG. 3 shows a cross-section along the strip 201 of the system of FIG. The strip 201 has an abnormal area 301 having a thickness that deviates from the target thickness or the normal thickness of the strip 201. Typically, area 301 is considered “deviation” because the thickness of area 301 is greater than the target thickness or normal thickness of the strip. The strip 201 may generally have one or more such abnormal areas or may not include abnormal areas. The process of controlling the thickness of the glass ribbon 113 includes finding any abnormal areas in the strip 201. The step of finding anomalous areas may include active measurements on the strip 201, or may be based on past data obtained using a particular set of process settings and parameters.

  Once an abnormal area is found on the strip 201, the radiant heater 119 is controlled to apply radiant heat to the abnormal area. In the example shown in FIG. 3, the radiant heater 119 applies radiant heat to the abnormal area 301 as shown by the cross hatch area 303, and the radiant heat supplied to the abnormal area 301 heats the area 301. . This reduces the viscosity of the abnormal area 301 and decreases the thickness of the abnormal area 301. Due to this thickness reduction, the corrected abnormal area 301 thickness can now be matched to the target thickness or normal thickness of the strip 201. Typically, this heating will modify the temperature distribution across the strip 201, for example, to make the modified temperature distribution more uniform than before heating the abnormal area 301 with the radiant heater 119. Can do. This corrected or more uniform temperature distribution will move with the strip 201 along the direction of travel of the glass ribbon 113. After some time, another strip of glass ribbon 113 will be adjacent to the radiant heater 119. The process described above for finding the anomalous area and applying radiant heat to the anomalous area may be repeated for this other strip and further other strips adjacent to the radiant heater 119. However, this does not mean that the radiant heater 119 must be fixed. Even if the radiant heater 119 is rearranged as necessary in order to heat-treat other portions where the glass ribbon 113 has such an abnormal area, provided that the abnormal area exhibits viscous behavior. Good.

  As described above with reference to FIGS. 1 to 3, when the thickness of the glass ribbon 113 is controlled by using “direct” radiant heat, a chimney on the surface of the glass ribbon 113 due to fluid leakage to the stretched portion. The effect can be avoided because no fluid is used to control the thickness of the glass ribbon 113. “Directly” means that the heat exchange between the radiant heater 119 and the glass ribbon 113 is not obstructed by structures such as the front wall used in the systems described in the background art. In order to maximize the heating efficiency, the radiant heater 119 can be installed very close to the surface of the glass ribbon 113. Further, by utilizing the shape of the radiant heater 119 and the distance from the surface of the glass ribbon 113 of the radiant heater 119, a radiation field with high resolution can be achieved. The system described above with reference to FIGS. 1 to 3 is also suitable for automatic control, which will be described below.

1-3, the radiant heater 119 generates electromagnetic radiation at a wavelength that matches the absorption characteristics of the glass ribbon 113 so that the glass can absorb radiant heat and reduce viscosity. A typical radiant heater 119 would be an infrared radiant heater. The radiant heater 119 may include a single radiant heating element or may include an radiant heating element array. The radiant heating element may be made of a heat-resistant metal such as Pt, Pt alloy, tungsten, MoSi ₂ or a ceramic material such as SiC. The heating element may take the form of a filament wire, such as a tungsten wire, or a radiation plate, such as a ceramic plate. Typically, a radiant heating element made of filament wire will include a winding loop of wire to increase the surface area that generates radiant heat. The radiant heating element may be placed in a transparent enclosure, such as a quartz enclosure. In order to increase the amount of radiant heat supplied to the glass ribbon 113, the enclosure may be coated with a reflective material. The radiant heater 119 may be an electric radiant heater or an induction radiant heater. The radiant heater 119 may extend over the width of the glass ribbon 113 (203 in FIG. 2) or may not extend. A plurality of radiant heaters 119 may be installed over the width of the glass ribbon 113 (203 in FIG. 2) and operated so that radiant heat is applied to a plurality of abnormal areas.

  FIG. 4 shows a radiant heater 119 that includes an array of radiant heating elements 401. The radiant heating element 401 is a linear radiant heating element. These radiant heating elements 401 are spaced and arranged in a line with respect to the direction of travel of the glass ribbon 113 indicated by the arrow 403 (FIG. 4 shows the relationship of the glass ribbon 113 for simplicity. Only the part to be shown). With respect to the direction 403 in which the glass ribbon 113 travels, a space is provided between the radiant heating elements 401, and the portions are arranged in a line so that they do not receive direct radiant heat. Will be present on the glass ribbon. These parts are called “dead zones”. In order to eliminate the dead zone, the radiant heating elements 401 can be arranged so that their fields of view (i.e. radiant heat traces on the glass ribbon 113) overlap. FIG. 5 shows a technique that can accomplish this. In FIG. 5, four radiant heating elements 501, 503, 505, 507 are spaced and inclined with respect to the direction of travel of the glass ribbon 113 indicated by the arrow 508. A radiation beam generated by one radiant heating element overlaps a radiation beam generated by an adjacent radiant heating element, such as the radiation beam generated by 501 overlaps with the radiation beam generated by radiant heating element 503. . FIG. 6 shows overlapping radiation beams 601, 603, 605, 607 corresponding to radiant heating elements 501, 503, 505, 507. Note that the cross-hatch density of the radiation beam is only used as a visual tool to distinguish one radiation beam from the next.

  The radiant heating element array may be connected to a controller. This is illustrated in FIG. 5, where the radiant heating elements 501, 503, 505, 507 are connected (or in communication) with the controller 509. The controller 509 can be operated to individually activate and deactivate the radiant heating elements 501, 503, 505, 507. The controller 509 may receive an external input as indicated by 511. An example of an external input 511 would be a thickness profile or a temperature profile across a strip of glass ribbon 113. The controller 509 uses this information to activate any of the radiant heating elements 501, 503, 505, 507 to achieve the targeted thickness or temperature distribution across the strip of glass ribbon 113. Further, it may be determined which one is to be stopped. This could also be an ongoing process, in which case the thickness profile or temperature profile was measured at a specific location across the glass ribbon 113 and the radiant heating elements 501, 503, 505, 507 were measured. Note that it is controlled to provide heat to the desired strip of glass ribbon 113 based on the thickness profile or temperature profile. An optical sensor or a temperature sensor may be used to measure the thickness profile or temperature profile, respectively. It is also possible to visually inspect the glass ribbon 113 to determine which of the radiant heating elements 501, 503, 505, 507 is to be activated or deactivated. The controller 509 may be operated using information obtained by visual inspection.

  It should be noted that the radiant heater 119 described in FIG. 1 may include a single radiant heating element or may include a radiant heating element array. Multiple radiant heaters 119 may be used in the system, or a single radiant heater 119 with an array of radiant heating elements may be used in the system. The width of the radiant heater 119 may extend over the width of the glass ribbon 113 or may be smaller than the width of the glass ribbon 113. If a radiant heating element array is used, the controller can be used to individually control which radiant heating element is operated at any given 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 a linear radiant heating element as shown, for example, in FIGS. A radiant heating element having a non-linear shape may be used to maximize or increase the radiant form factor. The radiation form factor is the fraction of thermal energy that leaves the surface of the first object and reaches the surface of the second object, and is determined entirely from geometric considerations. In FIG. 7, an elliptical radiant heating element 701 and an arbitrarily shaped radiant heating element 703 are shown. Element 703 is arbitrary shaped, and element 703 shows how the present invention helps to address the shape of the part that has the characteristic that needs correction by generating the shape specifically. The purpose is that. For example, an “L” shaped element may be positioned to obtain a wider and more diffused effect in the L horizontal segment, while producing a concentrated heating effect in the L vertical segment. Eventually, the glass will have an asymmetric effect. In general, this non-linear shape may be selected based on the typical shape of the area of the glass ribbon that is heated with a radiant heater.

  While the invention has been described with reference to a limited number of embodiments, those skilled in the art who have the benefit of this disclosure can devise other embodiments that do not depart from the scope of the invention disclosed herein. It will be obvious. Accordingly, the scope of the invention should be limited only by the attached claims.

DESCRIPTION OF SYMBOLS 101 Molding member 107 Wedge-shaped bottom part 109,111 Molten glass flow 113 Glass ribbon 119 Radiation heater 201 Strip 301 Abnormal area 401 Radiation heating element 501,503,505,507 Radiation heating element 509 Controller

Claims (7)

A method for producing a glass sheet,
(I) providing a glass ribbon having a width defined by two opposing edges at a temperature at which the glass exhibits viscoelastic behavior;
(Ii) moving the glass ribbon while the glass exhibits viscoelastic behavior; and
(Iii) heating the glass ribbon with an array of heater elements, the output of the heater elements being separately adjustable;
Only including,
Said step (iii)
(Iii-1) measuring a thickness variation of the glass ribbon within the range of the width; and
(Iii-2) heating the glass ribbon with distinction within the width according to the thickness variation so that the glass ribbon is stretched to a substantially uniform thickness;
A method comprising the steps of:   The method of claim 1, wherein in step (iii), the heater elements are arranged to have overlapping fields of view. In step (iii-2), the heater element has more heat in the area having the thickest thickness in the range of the glass ribbon than in the area having the thinnest thickness in the range. The method according to claim 1 or 2 , characterized in that: 3. A method according to claim 1 or 2, characterized in that in step (iii) the heater element is arranged such that the heater element applies heat to the glass ribbon before reaching the bottom of the isopipe. . In step (iii), the heater element such that the two glass ribbons on the two faces of the isopipe are separately heated before being joined at the bottom to form a single glass ribbon 5. The method of claim 4 , wherein the array is arranged on each side of the isopipe. The method of claim 1 or 2, wherein in step (iii), the array of heater elements is arranged to apply heat to the glass ribbon below the bottom of the isopipe. In step (iii), the array of heater elements is positioned on each side of the isopipe such that heat is applied to each side of the glass ribbon below the bottom of the isopipe. Item 3. The method according to Item 1 or 2.

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