WO2014134108A1

WO2014134108A1 - Method of cooling glass ribbon in a fusion draw

Info

Publication number: WO2014134108A1
Application number: PCT/US2014/018527
Authority: WO
Inventors: Anmol AGRAWAL; Steven Roy Burdette; William Anthony Whedon
Original assignee: Corning Incorporated
Priority date: 2013-02-28
Filing date: 2014-02-26
Publication date: 2014-09-04
Also published as: TW201434765A; JP6321686B2; TWI622558B; CN105431386B; KR20150138207A; CN105431386A; KR102166758B1; JP2016515087A

Abstract

Controlled cooling of a glass ribbon in a draw of a fusion draw machine including obtaining a target temperature profile of the glass ribbon and providing at least two ports in the draw. Temperature change profiles of the glass ribbon resulting from fluid injection at each of the ports and temperature change profiles of the glass ribbon resulting from fluid extraction at each of the ports are measured. Temperature gain factors are calculated using the above measurements. The injection fluid flow rate or an extraction fluid flow rate for each port is calculated by solving a least squares problem using the temperature gain factors in an iterative manner to implement the target temperature profile of the glass ribbon.

Description

METHOD OF COOLING GLASS RIBBON IN A FUSION DRAW

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application Serial No. 61/770362 filed on February 28, 2013.

BACKGROUND Field

[0002] The present specification generally relates to controlled cooling of glass ribbons in an ultra- high- flow fusion draw method. More specifically, the present specification is directed to injecting fluid into a fusion draw machine and extracting fluid from a fusion draw machine at multiple points in the fusion draw machine to control the temperature profile of the glass ribbon being formed.

Technical Background

[0003] The demand for glass substrates for use is various commercial applications is increasing. To keep pace with this demand, the glass flow rates in glass manufacturing processes are correspondingly increased. Glass Flow rates in fusion draw processes are increasing to lower manufacturing costs. One hurdle for obtaining high glass flow rates in the fusion draw process is the lack of capability to cool the glass in a controlled manner. Traditionally, increasing the height of the draw, improving the insulation of the draw, and providing additional water cooled surfaces have been used in an attempt to control cooling in a high glass flow rate fusion draw process. However, such measures have proven inadequate.

[0004] Active air cooling is used in other glass manufacturing methods, but it has not been used in a fusion draw process. Extracting fluids, such as air, from the top, middle, or bottom of a draw has been attempted with limited success. Increasing airflow inside a draw using extraction only (i.e., without air injection) increases the convective heat loss of the glass ribbon. However, air extraction leads to maximum cooling in the lower part of the draw, and it is not always possible to achieve a desired temperature profile of the glass ribbon, such as when the glass flow rate is high. [0005] Accordingly, alternative methods for cooling a glass ribbon are needed.

SUMMARY

[0006] According to one embodiment, a method for controlled cooling of a glass ribbon in a draw of a fusion draw machine is provided. The method may comprise obtaining a target temperature change profile of the glass ribbon and providing at least two ports in the draw. Temperature change profiles of the glass ribbon resulting from fluid injection at each of the ports and temperature change profiles of the glass ribbon resulting from fluid extraction at each of the ports may be measured. Temperature gain factors using the temperature change profiles of the glass ribbon resulting from fluid injection at each of the ports and the temperature change profiles of the glass ribbon resulting from fluid extraction at each of the ports may be evaluated. An injection fluid flow rate or an extraction fluid flow rate for each port may be calculated by solving a least squares problem using the temperature gain factors. An actual temperature change profile of the glass ribbon that is similar to the target temperature change profile may be obtained by applying the determined airflow for each port.

[0007] In another embodiment, an active fluid flow scheme for cooling of a glass ribbon in a draw of a fusion draw machine is provided. The active fluid flow scheme may comprise obtaining a target temperature change profile of the glass ribbon, and providing at least two ports in the draw. Temperature change profiles of the glass ribbon resulting from fluid injection at each of the ports and temperature change profiles of the glass ribbon resulting from fluid extraction at each of the ports may be measured. Temperature gain factors using the temperature change profiles of the glass ribbon resulting from fluid injection at each of the ports and the temperature change profiles of the glass ribbon resulting from fluid extraction at each of the ports may be calculated. An injection fluid flow rate or an extraction fluid flow rate may be calculated for each port by solving a least squares problem using the temperature gain factors to obtain an actual temperature change profile of the glass ribbon that is similar to the target temperature change profile. The respective calculated injection fluid flow rate or extraction fluid flow rate for each port may be applied. A tolerance for the difference between the actual temperature change profile of the glass ribbon and the target temperature change profile of the glass ribbon may be determined, and it may be evaluated whether the difference between the actual temperature change profile of the glass ribbon and the target temperature change profile of the glass ribbon is within the tolerance. When the difference between the actual temperature change profile of the glass ribbon and the target temperature change profile of the glass ribbon is outside of the tolerance, the scheme returns to the step where gain factors are calculated again and moves on to the calculating step again. When the difference between the actual temperature change profile of the glass ribbon and the target temperature change profile of the glass ribbon is within the tolerance, the scheme rests for a predetermined amount of time and then returns to the evaluating step.

[0008] Additional features and advantages of embodiments will be set forth in the detailed description that follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the embodiments described herein, including the detailed description that follows, the claims, as well as the appended drawings.

[0009] It is to be understood that both the foregoing general description and the following detailed description describe various embodiments and are intended to provide an overview or framework for understanding the nature and character of the claimed subject matter. The accompanying drawings are included to provide a further understanding of the various embodiments, and are incorporated into and constitute a part of this specification. The drawings illustrate various embodiments described herein, and together with the description serve to explain the principles and operations of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 schematically depicts an embodiment of a glass manufacturing process that includes a fusion draw machine;

[0011] FIG. 2 schematically depicts the draw of a fusion draw machine;

[0012] FIG. 3 is a graph showing a temperature change profile of a glass ribbon in a draw that is designed to optimize the change in temperature profile of a glass ribbon at a glass flow rate of lx, according to embodiments; [0013] FIG. 4 is a graph showing the temperature profile of a glass ribbon without any cooling at a glass flow rate of 2x, according to embodiments;

[0014] FIG. 5A is a graph showing a change in temperature profile that, generally, shows the shape of a change in temperature profile upon extraction, according to embodiments;

[0015] FIG. 5B is a graph showing change in temperature profile that, generally, shows the shape of a change in temperature profile upon injection, according to embodiments;

[0016] FIG. 6 is flow chart for an active fluid flow scheme according to embodiments;

[0017] FIG. 7 is a graph showing change in temperature profiles of a glass ribbon for a target temperature, a fluid extraction only scheme, and a fluid injection/extraction scheme, according to Example 1;

[0018] FIG. 8 schematically depicts the location of ports in a draw according to embodiments;

[0019] FIG. 9 is a graph showing change in temperature profiles at each port resulting from fluid extraction in a seven-port system according to Example 1;

[0020] FIG. 10 is a graph showing change in temperature profiles at each port resulting from fluid injection in a seven-port system according to Example 1 ;

[0021] FIG. 11 is a bar graph showing an calculated fluid extraction only scheme and a calculated fluid injection/extraction scheme in a seven-port system according to Example 1;

[0022] FIG. 12A is a graph showing a comparison between a baseline temperature profile of a glass ribbon at a lx glass flow rate, a temperature profile of a glass ribbon at a 2x glass flow rate without cooling, a temperature profile of a glass ribbon at a 2x flow rate with fluid injection/extraction cooling, and a temperature profile of a glass ribbon at a 2x flow rate with fluid extraction only cooling according to Example 2;

[0023] FIG. 12B is a bar graph showing a calculated fluid extraction only scheme and a calculated fluid injection/extraction scheme in a seven-port system at a 2x glass flow rate according to Example 2; [0024] FIG. 13A is a graph showing a comparison between a baseline temperature profile of a glass ribbon at a lx glass flow rate, a temperature profile of a glass ribbon at a 3x glass flow rate without cooling, and a temperature profile of a glass ribbon at a 3x flow rate with fluid injection/extraction cooling according to Example 2;

[0025] FIG. 13B is a bar graph showing a calculated fluid injection/extraction scheme in a seven-port system at a 3x glass flow rate according to Example 2;

[0026] FIG. 14A is a graph showing a comparison between a baseline temperature profile of a glass ribbon at a lx glass flow rate, a temperature profile of a glass ribbon at a 4x glass flow rate without cooling, and a temperature profile of a glass ribbon at a 4x flow rate with fluid injection/extraction cooling according to Example 2; and

[0027] FIG. 14B is a bar graph showing a calculated fluid injection/extraction scheme in a seven-port system at a 4x glass flow rate according to Example 2.

DETAILED DESCRIPTION

[0028] Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts. One embodiment of a fusion draw machine is shown in FIG. 1, and is designated generally throughout by the reference numeral 100.

[0029] As used herein, the term "fluid" should be understood to encompass any gas, mixture of gasses, gas/liquid mixture, vapor, or combinations thereof that is capable of moving through the draw in a gas-like manner. Fluids may include, but are not limited to, air, nitrogen, boron vapor, and other gasses or vapors originating from the glass manufacturing process.

[0030] Referring to FIG. 1, there is shown a schematic view of an exemplary glass manufacturing system 100 that uses the fusion process to make a glass sheet 105. The glass manufacturing system 100 may include a melting vessel 110, a fining vessel 115, a mixing vessel 120 (e.g., stir chamber 120), a delivery vessel 125 (e.g., bowl 125), a fusion draw machine (FDM) 140a, and a traveling anvil machine (TAM) 150. The melting vessel 110 may be where the glass batch materials are introduced as shown by arrow 112 and melted to form molten glass 126. The fining vessel 115 (e.g., finer tube 115) may have a high temperature processing area that receives the molten glass 126 (not shown at this point) from the melting vessel 110 and in which bubbles may be removed from the molten glass 126. The fining vessel 115 may be connected to the mixing vessel 120 (e.g., stir chamber 120) by a finer to stir chamber connecting tube 122. And, the mixing vessel 120 may be connected to the delivery vessel 125 by a stir chamber to bowl connecting tube 127. The delivery vessel 125 may deliver the molten glass 126 through a downcomer 130 into the FDM 140a that may include an inlet 132, a forming vessel

135 (e.g., isopipe 135), and a pull roll assembly 140.

[0031] As shown in FIG. 1, the molten glass 126 from the downcomer 130 may flow into an inlet 132 that leads to the forming vessel 135. The forming vessel 135 may include an opening

136 that receives the molten glass 126 that may flow into a trough 137 and then may overflow and run down two sides 138a and 138δ (138& is behind 138a and is not visible). The root 139 is where the two sides 138a and 138b come together and where the two overflow walls of molten glass 126 rejoin (e.g., refuse) before being drawn downward by the pull roll assembly 140 to form the glass sheet 105. The area between the root 139 and the pull roll assembly 140 is referred to herein as the draw. It is within the draw that the temperature of the glass is to be controlled according to embodiments. The TAM 150 then cuts the drawn glass sheet 105 into distinct pieces of glass sheets 155.

[0032] The draw, where the glass is drawn from the root 139, may be divided into three distinct regions. Referring now to FIG. 2, the glass ribbon is represented by dashed lines and the walls of the draw is represented by solid lines. The first region 210 is a transition region where the glass transitions from the upper portion of the FDM (not shown in FIG. 2) into the draw. The second region of the draw 220 is a region where the glass has viscous properties and elastic properties and, thus, the glass may be referred to as viscoelastic in this region of the draw. In the third region 230, which is toward the bottom of the draw, the glass may be elastic. [0033] Sources of thermal artifacts may vary from one fusion draw machine to another. One potential source of glass ribbon thermal artifacts is the design of the FDM, e.g., if the draw enclosure wall is not made of a single continuous material across the width of the draw. Another potential source of glass ribbon thermal artifacts may be equipment inserted into the FDM, e.g., a temperature measurement device inserted into the draw to measure thermal radiation in the draw. Another potential source of thermal artifacts may be non-uniform separation distances between the glass ribbon and the drawing machine enclosure walls, which may be related to the design of the FDM or to variations in the thickness of the glass ribbon due to, for example, poor temperature control within the draw. If a glass ribbon thermal artifact is present in the glass ribbon while the glass ribbon is either in the viscous or viscous-elastic state, the glass ribbon thermal artifact may induce stress in the glass ribbon. At the glass-setting zone, the induced stress may become frozen into the glass. This frozen induced stress may appear as an undesirable vertical stress band in the final glass sheet.

[0034] The design of the FDM including, for example, the height of the draw and the insulation of the draw, is engineered to optimize the temperature profile of the glass ribbon at a specified glass flow rate (referred to hereinafter as lx glass flow rate). Referring to a non-limiting embodiment depicted in FIG. 3, the optimized temperature change profile within the draw at a lx glass flow rate may have a large change in temperature from the root of the glass ribbon to about the midpoint of the draw. In this embodiment, the change in temperature within the draw is not as rapid after the maximum change in temperature is reached around the middle of the draw. Such a temperature profile may provide a glass ribbon with desired stress profile. However, it should be understood that temperature profiles other than that depicted in FIG. 3 may be better suited for other types of process and other glass compositions.

[0035] When the glass flow rate is increased, heat capacity of the glass flowing through the FDM is increased. Due to increased heat entrapped in the glass, the glass ribbon does not cool at its desired rate, which can lead to high stresses and cracking. As shown in FIG. 4, the temperature profile of the draw at a 2x glass flow rate without any form of cooling (shown by curve 410) is shifted upward from a baseline temperature profile of the glass ribbon at a lx glass flow rate (shown by curve 420). This shift in temperature profile may result in increased stresses and cracking of the glass ribbon caused by inadequate cooling. Embodiments of the method disclosed herein may provide precision control of the temperature profile of a glass ribbon within the draw at increased glass flow rates. In embodiments, the glass ribbon temperature profile within the draw at increased glass flow rates (shown by curve 430) may be modified to be the same as, or similar to, the baseline temperature profile in the draw at a lx flow rate 420. In embodiments, the method may include glass flow rates of about 2x, or even glass flow rates of about 3x. In other embodiments, the method may include glass flow rates of about 4x, or even glass flow rates of about 5x.

[0036] In addition to controlling the temperature profile within the draw, embodiments of the method disclosed herein may be used to control the fluid flow up and down the draw. The direction and amount of fluid flow through the draw may be controlled to reduce introduction of impurities that may negatively affect the quality of the glass ribbon as it is pulled through the draw. For example, if fluid enters at the top of the draw and flows down through the transition portion 210, boron vapor that may be present in the transition region 210 may cool as the fluid pulls the boron vapor down the draw. This cooling of the boron vapor may cause the boron vapor to condense on the glass ribbon as it cools, which is not desirable. Likewise, if a high volume of fluid flows from the bottom of the draw to the top of the draw, solid particles that are present near the bottom of the draw may be carried up the draw with the fluid and deposited on the viscous glass. These deposited solid particles are referred to as onclusions, and are not desirable. In addition to controlling the temperature profile of the glass ribbon, various embodiments may use fluid extraction and/or fluid injection to control the flow of fluid up and down the draw. It is understood that the choice of fluid injection or fluid extraction to control fluid flow within the draw may be determined not only based on desired temperature profile, but also based on the fluid flow within the draw and the desired change to the fluid flow within the draw.

[0037] According to embodiments, extracting fluid from the draw may provide a change in the temperature profile of the glass ribbon as shown, for example, in FIG. 5A. The change in the temperature profile of the glass ribbon for fluid extraction may provide the largest change in temperature of the glass ribbon near the bottom of the draw, which does not closely coincide with the desired temperature change profile of the glass ribbon shown in FIG. 3. [0038] In embodiments, injecting fluid into the draw may provide a change in temperature profile of the glass ribbon as shown in FIG. 5B. The change in temperature profile of the glass ribbon for fluid injection has a maximum at or near the location where the fluid is injected. For example, in FIG. 5B, the fluid is injected at a location that is approximately 125 inches down the draw from the root of the glass ribbon 139 and, thus, the maximum change in temperature profile of the glass ribbon is also located approximately 125 inches down the draw from the root of the glass ribbon 139. Embodiments disclosed herein combine fluid extraction and fluid injection to control the temperature profile of the glass ribbon within the draw when the temperature profile of the glass ribbon deviates from the target temperature profile of the glass ribbon shown in FIG. 3, such as when the glass flow rate is increased above lx, as described below. Although the description below is directed to a change in the temperature profile of the glass ribbon caused by an increase in glass flow rate, the methods disclosed herein may be used to adjust the deviation of an actual temperature profile of the glass ribbon from a target temperature profile caused by any temperature artifact.

[0039] The change in temperature profile of the glass ribbon within the draw during lx glass flow rate may be measured by any conventional techniques. According to embodiments, the change in temperature profile of the glass ribbon may be similar to the profile shown in FIG. 3. After the change in temperature profile of the glass ribbon is measured for the draw at a lx glass flow rate, a number of ports for injecting or extracting fluid from the draw may be determined. The number and location of the ports is not particularly limited, and may be determined based on cost and desired control of the temperature profile within the draw. In embodiments, a higher number of ports may be used to provide better control of the temperature profile of the glass ribbon within the draw. In other embodiments, a lower number of ports may be included to reduce cost.

[0040] In embodiments, at least two ports for injecting or extracting fluid from the draw may be included at one or more regions of the draw. In embodiments, the draw may include three or more ports for injecting or extracting fluid from the draw, such as four or more ports. In other embodiments, the draw may include five or more ports for injecting or extracting fluid from the draw, or even six or more ports. In some other embodiments, the draw may include seven or more ports for injecting or extracting fluid from the draw, or even eight or more ports. Fluid may be injected into the draw using any known mechanism. In embodiments, a pump or pressurized fluid may be used to inject fluid into the draw. Fluid may be extracted from the draw by any known mechanism. In embodiments, pumps or a vacuum source may be used to extract fluid from the draw.

[0041] The flow rate of fluid injected into the draw or extracted from the draw is not particularly limited and will vary from draw to draw depending on the required cooling and other thermal characteristics of the draw. In embodiments, the flow rate of fluid injected into the draw or extracted from the draw is measured relative to a baseline flow rate of fluid through the draw without injection or extraction. For example, as fluid moves through a draw (e.g., from top to bottom or from bottom to top) without injecting fluid into the draw or extracting fluid from the draw; this fluid flow rate may be considered the baseline flow rate. In embodiments, the baseline

3 3 3 fluid flow rate may be from about 0.010 m /s to about 0.040 m /s, or even from about 0.015 m /s to about 0.035 m³/s. In other embodiments, the baseline fluid flow rate may be from about 0.020 m³/s to about 0.030 m³/s, or even from about 0.022 m³/s to about 0.025 m³/s. However, it should be understood that the baseline fluid flow rate may vary greatly from draw to draw and, thus, other baseline flow rates are not outside the scope of this disclosure.

[0042] Fluid need not be injected into the draw or extracted from the draw at each port and, thus, the flow rate of a fluid injected into the draw or extracted from the draw may be zero, according to some embodiments. According to other embodiments, the flow rate of fluid injected into the draw or extracted from the draw may be the same as the baseline fluid flow rate. In embodiments, the flow rate of fluid injected into the draw, or extracted from the draw may be about two times the baseline fluid flow rate, about three times the baseline fluid flow rate, or even about four times the baseline fluid flow rate. In some embodiments, the flow rate of fluid injected into the draw, or extracted from the draw may be about five times the baseline fluid flow rate, about six times the baseline fluid flow rate, or even about seven times the baseline fluid flow rate. In other embodiments, the flow rate of fluid injected into the draw, or extracted from the draw may be about eight times the baseline fluid flow rate, about nine times the baseline fluid flow rate, or even about ten times the baseline fluid flow rate. In yet other embodiments, the flow rate of fluid injected into the draw, or extracted from the draw may be about eleven times the baseline fluid flow rate, about twelve times the baseline fluid flow rate, or even about thirteen times the baseline fluid flow rate. In still other embodiments, the flow rate of fluid injected into the draw, or extracted from the draw may be about fourteen times the baseline fluid flow rate, about fifteen times the baseline flow rate, or even about sixteen times the baseline fluid flow rate. In some embodiments, the flow rate of fluid injected into the draw, or extracted from the draw may be about seventeen times the baseline fluid flow rate, or even about eighteen times the baseline fluid flow rate.

[0043] Once the number and location of ports for extracting or injecting fluid into the draw is determined, the actual change in temperature profile of the glass as a result of fluid injection and fluid extraction at each port may be measured. For example, in embodiments where the draw has three ports, fluid may be injected into the first port at a flow rate just high enough to measure the effect that this injection flow rate has on the change in temperature profile. Similarly, fluid will separately be injected into the second port and into the third port (i.e., fluid will only be injected into one port at a time) at an injection flow rate just high enough to measure the effect that this injection flow rate has on the change in temperature profile. An example of an obtained change in temperature profile of the glass ribbon from injection of a seven-port embodiment is shown in FIG. 10, which is discussed in more detail in the examples below. In embodiments, fluid may be extracted from the first port at an extraction flow rate just high enough to measure the effect that this extraction flow rate has on the change in temperature profile of the glass ribbon. Likewise, in embodiments, fluid will separately be extracted from the second port and the third port (i.e., fluid will only be extracted from one port at a time) at an extraction flow rate just high enough to measure the effect that this extraction flow rate has on the change in temperature profile of the glass ribbon. An example of an obtained change in temperature profile resulting from extraction of a seven-port embodiment is shown in FIG. 9, which is discussed in more detail in the examples below. In embodiments, these changes in temperature profiles of the glass ribbon effectuated by injecting a fluid and effectuated by extraction a fluid may be obtained experimentally by injecting or extracting a fluid in a test draw. In other embodiments, these change in temperature profiles of the glass ribbon effectuation by fluid injection and effectuated by fluid extraction may be obtained theoretically or numerically using computer modeling programs known in the art, including, without limitation, Fluent produced by AN SYS. [0044] After obtaining the change in temperature profiles of the glass ribbon that result from extraction of a fluid and injection of a fluid at the various ports, optimal fluid convection schemes may be determined by linearizing the effects of fluid extraction and fluid injection using the following equations. First, the change in temperature profiles may be used to calculate the temperature gains, AGain, at each port using equation (1):

AGain = ^ (1)

⁽ 111. where i is the port, T(y) is a temperature function along the vertical direction of the draw, and m_;- is the mass of injected or extracted fluid at port i. In embodiments, T(y) and m_;- may be determined experimentally by injecting or extracting air in a test draw. In other embodiments, or ii and T(y) may be determined theoretically using computer modeling software. Once AGairii has been determined for each port, a least squares may be performed using Equation (2) to calculate each Am,:

F{Am) =

where wl and w2 are weight factors and AT(y) is the required temperature change. Weights wl and w2 could be any positive real numbers, and may be chosen according to the glass composition and process being used. They were set at 0.5 in all the examples. After minimizing the least square equation (2) for Am the new values of m_;- are calculated by adding m_;- to Am The newly obtained m_;- values may be used to calculate a subsequent AGaini values using Equation (1). Using Equation (1) And Equation (2) in combination, m_; may be refined iteratively for each port until the actual change in temperature profile of the glass ribbon using fluid injection and fluid extraction matches, or closely approximates, the target change in temperature profile of the glass ribbon measured using lx flow. Thus, using this methodology, the actual temperature profile of the glass ribbon may be modified to match the target temperature profile of the glass ribbon when the glass flow rate increases from lx using the same draw that was used for lx flow.

[0045] According to embodiments, an active fluid flow scheme for cooling a FDM may be provided. An embodiment of the active fluid flow scheme is shown in FIG. 6. In step 1, a model or draw is selected that is designed to optimize the temperature profile of the glass ribbon in a draw at a glass flow rate of lx. In step 2, the temperature profile in the chosen model or draw is determined to yield a target change in temperature profile of the glass ribbon within the draw. In embodiments, the target change in temperature profile of the glass ribbon may be determined experimentally, and in other embodiments, the target change in temperature of the glass ribbon may be obtained though modeling. In step 3, numerical experiments (such as experiments using computer modeling programs) or physical experiments are conducted to evaluate AGairii factors for each injection/extraction port, as discussed above. In step 4, the least square problem of Equation (2) is solved for each m_; using AGairii values from Equation ( 1) to find the optimum fluid mass flow rates m_;- for each port. In step 5, the fluid mass flow rates for each port calculated in step 4 are imposed into the model or draw. In step 6, it is determined whether the difference between the achieved temperature change profile of the glass ribbon in the test draw or model and the target temperature change profile of the glass ribbon is at or below a predetermined tolerance value, which was determined in step 2. If the answer to the evaluation in step 6 is "yes", then the active fluid flow scheme rests for a predetermined about of time and then returns to step 6. The predetermined amount of time is not particularly limited and may be, for example 5 or more seconds. If the answer to the evaluation in step 6 is "no", then the active fluid flow control scheme returns to step 3, where the new gain factors are evaluated again and are used to solve the least squares problem to refine the flow.

[0046] The active fluid control scheme may be implemented by a device include a processor, input/output hardware, network interface hardware, a data storage component (which stores temperature change profiles), and a memory. The memory may be configured as volatile and/or nonvolatile memory and, as such, may include random access memory (e.g., SRAM, DRAM, and/or other types of random access memory), flash memory, registers, compact discs (CDs), digital versatile discs (DVDs), and/or other types of non- transitory storage components.

Additionally, the memory may be configured to store a program that calculates fluid injection flow rates or fluid extraction flow rates (each of which may be embodied as a computer program, firmware, or hardware, as an example).

[0047] The processor may include any processing component configured to receive and execute instructions (such as from the data storage component and/or memory). The input/output hardware may include a monitor, keyboard, mouse, printer, camera, microphone, speaker, and/or other device for receiving, sending, and/or presenting data. The network interface hardware may include any wired or wireless networking hardware, such as a modem, LAN port, wireless fidelity (Wi-Fi) card, WiMax card, mobile communications hardware, and/or other hardware for communicating with other networks and/or devices.

[0048] Using the active fluid control schemes of embodiments may allow the fluid mass flow rate at each port to be monitored to and to be modified if difference between the achieved temperature change profile of the glass ribbon and the target temperature change profile of the glass ribbon becomes too large. Thus, the temperature profile using the fluid injection/extraction process according to embodiments may consistently correspond to the target temperature profile of the glass ribbon at any given time in the fusion draw process by using air injection/extraction scheme to compensate for process drifts.

EXAMPLES

[0049] Embodiments will be further clarified by the following examples.

EXAMPLE 1

[0050] Example 1 shows how to modify an actual change in temperature profile of a glass ribbon to approximate a target change in temperature profile of a glass ribbon. A change in temperature profile of a glass ribbon is determined experimentally or theoretically using modeling software for a draw that is designed to optimize the temperature profile of a glass ribbon without cooling at a glass flow rate of lx. This target change in temperature profile of the glass ribbon is shown in FIG. 7 as 710. Seven ports are included at various positions in the draw as depicted in FIG. 8. In FIG. 8, the walls of the draw are depicted by solid lines and the glass ribbon is depicted by dashed lines. Referring to FIG. 8, the first port 810 is positioned approximately 40 inches from the root, the second port 820 is positioned approximately 60 inches from the root, the third port 830 is positioned approximately 65 inches from the root, the fourth port 840 is positioned approximately 80 inches from the root, the fifth port 850 is positioned approximately 105 inches from the root, the sixth port 860 is positioned approximately 125 inches from the root, and the seventh port 870 is positioned approximately 140 inches from the root.

[0051] The influence of fluid extraction on the glass ribbon temperature profile is measured. Fluid is extracted from the first port 810 at a rate of about 280 lb/hr, and the change in temperature profile of the glass ribbon is measured along the vertical direction of the draw. The resulting change in temperature profile of the glass ribbon is shown in FIG. 9 as 910. Likewise, fluid is extracted from the second port 820 at a rate of 280 lb/hr, and the change in temperature profile of the glass ribbon is measured along the vertical direction of the draw. The resulting change in temperature profile of the glass ribbon is shown in FIG. 9 as 920. Similarly, fluid is extracted individually from the third port 830, the fourth port 840, the fifth port 850, the sixth port 860, and the seventh port 870 at a flow rate of 280 lb/hr, and the change in temperature of the glass ribbon is measured along the vertical direction of the draw. The resulting change in temperature profiles are shown in FIG 9 as 930, 940, 950, 960, and 970, respectively. As can be seen from FIG. 9, air extraction results in bulk cooling of the glass with more cooling in the lower regions of the draw than in the upper regions of the draw. No backflow is observed the exit.

[0052] Subsequent to the extraction measurements, the influence of injecting room temperature air on glass temperature is measured. Room temperature air is injected into the first port 810 at a rate of about 280 lb/hr, and the change in temperature profile of the glass ribbon is measured along the vertical direction of the draw. The resulting change in temperature profile of the glass ribbon is shown in FIG. 10 as 1010. Likewise, room temperature air is injected into the second port 820 at a rate of 280 lb/hr, and the change in temperature profile of the glass ribbon is measured along the vertical direction of the draw. The resulting change in temperature profile of the glass ribbon is shown in FIG. 10 as 1020. Similarly, room temperature air is injected into the draw individually to the third port 830, the fourth port 840, the fifth port 850, the sixth port 860, and the seventh port 870 at a flow rate of 280 lb/hr, and the change in temperature of the glass ribbon is measured along the vertical direction of the draw. The resulting change in temperature profiles are shown in FIG. 10 as 1030, 1040,1050, 1060, and 1070, respectively. As can be seen from FIG. 10, room temperature air injection cools the glass near and above the injection site, but it heats the glass in the lower regions of the draw (i.e., portions furthest from the root). No backflow is expected at the outlet.

[0053] Using the change in temperature profiles from the extraction and injection measurements made above, AGaim is calculated for each port using Equation (1):

AGaim

dm, _{( 1 )}

Once AGaim is calculated for each port, a least squares is performed using Equation 2 to calculate the m_; value for each port:

F(m) =

(2)

Each mi obtained from the least squares calculation is then introduced into the physical experimental draw or software model. Using the calculated m values, temperature change profiles are again measured for each port. These new temperature change profiles, may then be used as new baselines to calculate additional AGaim values, and the additional AGaim values may be used in Equation (2) to further refine the temperature change profiles. This process may be repeated until the obtained temperature change profiles closely match the temperature change profile from the draw that was optimized for lx flow. Using this method, the combined fluid injection/extraction scheme shown in FIG. 1 1 is developed. In FIG. 1 1, positive airflow signifies extraction of fluid from the draw and negative airflow signifies injection of room temperature air into the draw. FIG. 11 also compares the air injection/extraction method to an extraction only method, where fluid is extracted from the draw at more than 40 lb/hr from the first port 810. As shown in FIG. 7, the change in temperature profile of the glass ribbon using the injection/extraction method (shown by curve 720) is able to more closely approximate the shape of the change in temperature profile of the glass ribbon obtained from the lx glass flow rate without cooling (shown by curve 710) than the change in temperature profile of the glass ribbon achieved by extraction only (shown by curve 730).

[0054] Accordingly, this example shows that combined injection/extraction cooling is capable of more closely approximating a target change in temperature profile than extraction only cooling. Specifically, the change in temperature profile of the glass ribbon achieved by injection, as shown, for example, in FIG. 10 have more degrees of freedom that allow customization of the achieved change in temperature profile of a glass ribbon.

EXAMPLE 2

[0055] Using a method disclosed herein, and shown in Example 1, fluid injection/extraction cooling may be used to control the temperature profile of a glass ribbon when the glass flow rate is increased within the draw.

2x Glass Flow Rate

[0056] A baseline temperature profile of a glass ribbon is obtained by measuring the temperature profile within a draw that is designed to optimize the temperature profile of a glass ribbon at glass flow rate of lx. The fluid flow in this baseline draw is natural fluid flow up the draw and is not induced by injection or extraction. The baseline airflow is about 0.0022 m /s. The baseline temperature profile of the glass ribbon is shown as 1210 in FIG. 12A.

[0057] The glass flow rate in the draw is then increased to 2x and the fluid flow rate is determined for each of the seven ports using the method described above and in Example 1. When the fluid flow rate for each port is calculated, the injection/extraction scheme as shown in FIG. 12B is obtained. In FIG. 12B the air flow rate is measured as a function of the baseline air flow in the draw where the glass flow rate is lx (e.g., 2 on the y axis in FIG. 12B is twice the baseline airflow). Positive flow shown in FIG. 12B indicates fluid extraction from the draw, and negative flow indicates fluid injection into the draw. In FIG. 12B the extraction only scheme is calculated by extracting fluid at a rate of about 3.5 at the first port only. FIG. 12A shows the baseline temperature profile (measured at a glass flow rate of lx) as 1210, the temperature profile at a glass flow rate of 2x without any fluid cooling as 1220, the temperature profile at a glass flow rate of 2x with fluid injection/extraction cooling using the scheme shown in FIG. 12B as 1230, and the temperature profile at a glass flow rate of 2x with fluid extraction only as 1240. As FIG. 12A shows, the temperature profile at a glass flow rate of 2x without fluid cooling has a slope that does not approximate the baseline temperature profile, which indicates that less cooling takes place in the draw when a glass flow rate is set to 2x. However, both the injection/extraction scheme and the extraction only scheme closely approximate the baseline temperature profile. Thus, for a glass flow rate of 2x, an injection/extraction scheme as well as an extraction only scheme may provide adequate cooling in the draw. However, as shown in FIG. 12A, the temperature profile obtained using fluid injection/extraction cooling is nearly identical to the baseline temperature profile. This shows the improved temperature control that is possible by using an injection/extraction scheme.

3x Glass Flow Rate

[0058] A baseline temperature profile of a glass ribbon is obtained by measuring the temperature profile within a draw that is designed to optimize the temperature profile of a glass ribbon at glass flow rate of lx. The fluid flow in this baseline draw is natural fluid flow up the draw and is not induced by injection or extraction. The baseline airflow is about 0.0022 m³/s. The baseline temperature profile of the glass ribbon is shown as 1310 in FIG. 13 A.

[0059] The glass flow rate is then increased to 3x and the fluid flow rate is determined for each of the seven ports using the methodology described in Example 1. When the fluid flow rate for each port is calculated, the injection/extraction scheme as shown in FIG. 13B is obtained. In FIG. 13B the air flow rate is measured as a function of the baseline air flow in the draw where the glass flow rate is lx (e.g., 2 on the y axis in FIG. 13B is twice the baseline airflow). Positive flow shown in FIG. 13B indicates fluid extraction from the draw, and negative flow indicates fluid injection into the draw. FIG. 13 A shows the baseline temperature profile (measured at a glass flow rate of lx) as 1310, the temperature profile at a glass flow rate of 3x without any fluid cooling as 1320, and the temperature profile at a glass flow rate of 3x with fluid injection/extraction cooling using the scheme shown in FIG. 13B as 1330. As FIG. 13B shows, the temperature profile at a glass flow rate of 3x without fluid cooling has a slope that does not approximate the baseline temperature profile, which indicates that less cooling takes place in the draw when a glass flow rate is set to 3x. At a glass flow rate of 3x, extraction alone cannot cool the glass sufficiently without flow reversal at the transition zone. This flow reversal will heat the glass instead of cooling it and may cause condensation problems. As shown in FIG. 13A a fluid injection/extraction scheme may be used to provide a temperature profile that is nearly identical to the baseline temperature profile. Therefore, using an injection/extraction scheme, the flow rate of the glass may be increased to 3x without altering the physical dimension or insulation of the draw.

4x Glass Flow Rate

[0060] A baseline temperature profile of a glass ribbon is obtained by measuring the temperature profile within a draw that is designed to optimize the temperature profile of a glass ribbon at glass flow rate of lx. The fluid flow in this baseline draw is natural fluid flow up the draw and is not induced by injection or extraction. The baseline airflow is about 0.0022 m³/s. The baseline temperature profile of the glass ribbon is shown as 1410 in FIG. 14A.

[0061] The glass flow rate is then increased to 4x and the fluid flow rate is determined for each of the seven ports using the methodology described in Example 1. When the fluid flow rate for each port is calculated, the injection/extraction scheme as shown in FIG. 14B is obtained. In FIG. 14B the air flow rate is measured as a function of the baseline air flow in the draw where the glass flow rate is lx (e.g., 2 on the y axis in FIG. 14B is twice the baseline airflow). Positive flow shown in FIG. 14B indicates fluid extraction from the draw, and negative flow indicates fluid injection into the draw. FIG. 14A shows the baseline temperature profile (measured at a glass flow rate of lx) as 1410, the temperature profile at a glass flow rate of 4x without any fluid cooling as 1420, and the temperature profile at a glass flow rate of 4x with fluid injection/extraction cooling using the scheme shown in FIG. 14B as 1430. As FIG. 14A shows, the temperature profile at a glass flow rate of 4x without fluid cooling has a slope that does not approximate the baseline temperature profile, which indicates that less cooling takes place in the draw when a glass flow rate is set to 4x. At a glass flow rate of 4x, extraction alone cannot cool the glass sufficiently without flow reversal at the transition zone. This flow reversal will heat the glass instead of cooling it and may cause condensation problems. As shown in FIG. 14A a fluid injection/extraction scheme may be used to provide a temperature profile that is nearly identical to the baseline temperature profile. Therefore, using an injection/extraction scheme, the flow rate of the glass may be increased to 4x without altering the physical dimension or insulation of the draw. [0062] It will be apparent to those skilled in the art that various modifications and variations can be made to the embodiments described herein without departing from the spirit and scope of the claimed subject matter. Thus it is intended that the specification cover the modifications and variations of the various embodiments described herein provided such modification and variations come within the scope of the appended claims and their equivalents.

Claims

What is claimed is:

1. A method for controlled cooling of a glass ribbon in a draw of a fusion draw machine, the method comprising:

obtaining a target temperature change profile of the glass ribbon;

measuring temperature change profiles of the glass ribbon resulting from fluid injection at at least two ports in the draw;

measuring temperature change profiles of the glass ribbon resulting from fluid extraction at each of the ports;

evaluating temperature gain factors using the temperature change profiles of the glass ribbon resulting from fluid injection at each of the ports and the temperature change profiles of the glass ribbon resulting from fluid extraction at each of the ports;

calculating an injection fluid flow rate or an extraction fluid flow rate for each port based on the temperature gain factors to obtain an actual temperature change profile of the glass ribbon that is similar to the target temperature change profile; and

adjusting the current flow rates to the calculated injection fluid flow rate or the extraction fluid flow rate for each port.

2. The method of claim 1, wherein fluid is extracted from the draw at a first port, and fluid is injected into the draw at a second port.

3. The method of claim 2, wherein a flow rate of fluid extracted from the draw through the first port differs from a flow rate of fluid injected into the draw through the second port.

4. The method of claim 1 , wherein fluid is extracted from the draw at a port nearest to a root of the glass ribbon.

5. The method of claim 1, wherein five or more ports are provided in the draw.

6. The method of claim 1, wherein a flow rate of fluid injected into the draw and a flow rate of fluid extracted from the draw is from about zero to about eighteen times a baseline fluid flow rate.

7. The method of claim 6, wherein the flow rate of fluid injected into the draw and the flow rate of fluid extracted from the draw is from about two times the baseline fluid flow rate to about fifteen times the baseline fluid flow rate.

8. The method of claim 6, wherein the baseline fluid flow rate is from about 0.010 m³/s to about 0.040 m³/s.

9. The method of claim 1, wherein the temperature gain factors are calculated by:

_{AGain =}? dm, _{( 1 )} where i is the port,

T(y) is a temperature function along the vertical direction of the draw, and

nti is the mass of injected or extracted fluid at port i.

10. The method of claim 9, wherein the injection fluid flow rate or an extraction fluid flow rate are calculated by solving a least squares problem using Equation (2):

where wl and w2 are weight factors, and

AT(y) is the required temperature change.

11. The method of claim 1, wherein the measuring of the temperature change profiles of the glass ribbon resulting from fluid injection at each of the ports, and the measuring of the temperature change profiles of the glass ribbon resulting from fluid extraction at each of the ports is performed physical experimentation.

12. The method of claim 1, wherein the measuring of the temperature change profiles of the glass ribbon resulting from fluid injection at each of the ports, and the measuring of the temperature change profiles of the glass ribbon resulting from fluid extraction at each of the ports is performed using data modelling.

13. The method of claim 1, wherein the target temperature change profile of the glass ribbon is measured at a glass flow rate of lx.

14. The method of claim 13, wherein the actual temperature change profile of the glass ribbon is measured at a glass flow rate of 3x.

15. The method of claim 13, wherein the actual temperature change profile of the glass ribbon is measured at a glass flow rate of 4x.

16. An active fluid flow scheme for cooling of a glass ribbon in a draw of a fusion draw machine, the active fluid flow scheme comprising:

obtaining a target temperature change profile of the glass ribbon;

measuring temperature change profiles of the glass ribbon resulting from fluid injection at each of the ports;

calculating an injection fluid flow rate or an extraction fluid flow rate for each port by solving a least squares problem using the temperature gain factors to obtain an actual temperature change profile of the glass ribbon that is similar to the target temperature change profile;

adjusting the fluid flow rates to the calculated injection fluid flow rate or extraction fluid flow rate for each port;

determining a tolerance for the difference between the actual temperature change profile of the glass ribbon and the target temperature change profile of the glass ribbon; and

evaluating whether the difference between the actual temperature change profile of the glass ribbon and the target temperature change profile of the glass ribbon is within the tolerance.

17. The method of claim 16, wherein the scheme returns to the step where gain factors are evaluated when the difference between the actual temperature change profile of the glass ribbon and the target temperature change profile of the glass ribbon is outside of the tolerance.

18. The method of claim 16, wherein the scheme rests for a predetermined amount of time and then returns to the step where the difference between the actual temperature change profile of the glass ribbon and the target temperature change profile of the glass ribbon is evaluated when the difference between the actual temperature change profile of the glass ribbon and the target temperature change profile of the glass ribbon is within the tolerance.

19. The method of claim 16, wherein the temperature gain factors are calculated using Equation (1):

dT(y)

AGain,

dm.

(1)

where i is the port,

T(y) is a temperature function along the vertical direction of the draw, and

nti is the mass of injected or extracted fluid at port i.

20. The method of claim 19, wherein the calculating step comprises solving a least squares problem using Equation (2): where wl and w2 are weight factors, and

AT(y) is the required temperature change.

21. The method of claim 16, wherein the target temperature change profile of the glass ribbon is measured at a glass flow rate of lx.

22. The method of claim 16, wherein the actual temperature change profile of the glass ribbon is measured at a glass flow rate of 3x.