KR101497748B1 - Isopipe heating method - Google Patents

Abstract

Embodiments in accordance with the present invention provide a method, a control system and a computer program product based on determined material properties and computerized stress analysis, wherein the computerized stress analysis is performed such that the proposed heating schedule before the start of any heating transition, Allowing, during heating, a substantially non-uniform thermal strain gradient after reaching a critical temperature; Slowly ramming a substantially non-uniform thermal strain gradient such that the maximum thermal stress is not too close to the fracture strength of the material; And minimizing the heating time so that the glass production is not unnecessarily delayed.

Description

[0001] ISOPIPE HEATING METHOD [0002]

This application claims priority from U.S. Provisional Patent Application No. 61/004894, filed November 30, 2007.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to a glass manufacturing method, and more particularly to a fusion process for manufacturing a glass sheet.

Glass manufacturing can be described as a process that converts raw materials to high-temperature homogenous melt and then through an appropriate forming process to provide the raw product. One exemplary process for glass manufacturing is the "Sheet Forming Apparatus", owned by Stuart M. Dockerty, inventor of two patents, and US Pat. No. 3,338,696, filed on August 29, 1967, August 8, 1972 Quot; Controlling Thickness of Newly Drawn Glass Sheet "of U.S. Patent No. 3,682,609, which is incorporated herein by reference in its entirety and is incorporated herein by reference.

One component of the fusing process is called a trough, typically isopipe, in which molten glass flows sideways to form a glass sheet. Isopipe is further described in, for example, U.S. Patent No. 6,794,786, entitled " Sag Control of Isopipes Used In Making Sheet by Glass Fusion Process ", filed December 13, 2005 by Helfinstine et al. All of which are incorporated by reference and are incorporated herein by reference.

An overflow process for making glass or sheet glass to form the troughs used in the refractory isopipe or fusion operates at a vertical temperature gradient to facilitate the formation of the glass sheet (The viscosity of the glass increases with decreasing temperature). The top of the isopipe is a thin walled trough filled to flow over the molten glass, which operates at the temperature of the glass introduced at one end. The lower part is the solid triangular part of the refractory with the glass flowing down and cooling down the outer wall. Thus, the isopipe has various vertical temperature profiles. To prevent glass flow problems, if a new isopipe is first implemented in service, the isopipe is heated to its thermal profile before the molten glass enters. This type of temperature profile produces a very large thermal stress on the refractory material. Such stresses can cause cracks or fractures in the material. Cracks in the isopipe have a negative impact on the amount of sheet glass produced, and the ruptured isopipe has to be replaced, and this process is generally long and expensive.

Therefore, there is a need for a method of controlling an isopipe heating process, some of which is described above and overcomes many of the attempts found in the art.

One way to overcome some of the described attempts is to design a thermal schedule that introduces a predetermined temperature profile before the thermal stresses are sufficient to damage the isopipe, so that the hot creep behavior of the material alleviates thermal stress. Embodiments of the heating method described in the present invention are developed to produce a thermal profile in a timely and safe manner against thermal stress cracking of the isopipe.

One embodiment according to the present invention is a method of heating an isopipe. This method includes determining the maximum thermal stress for the isopipe and determines the critical temperature (T _t ) for the isopipe. T _t is the temperature at which the high temperature creep mechanism in the isopipe begins to relieve thermal stress from the isopipe. The isopipe is heated at a first rate so that the isopipe undergoes a substantially uniform uniform thermal strain gradient to about T _t and this substantially uniform thermal strain gradient is greater than the maximum thermal stress in the isopipe Produces low thermal stress. Above the T _t temperature, the isopipe is heated in a manner that develops the vertical thermal gradients needed for satisfactory performance of the process. A heating rate of at least _t T is substantially non-through the high temperature creep of the material - so that a thermal stress generated in the piping isometric relaxation by a uniform thermal strain gradient. The thermal stress in the isopipe during heating will be substantially below the maximum allowable thermal stress to avoid cracking of the isopipe. Upon achieving the desired vertical gradient, the overall temperature of the isopipe can be adjusted to the process target (depending on the glass composition), which can uniformly reduce the temperature at all locations of the isopipe to produce additional stress Because.

Yet another embodiment according to the present invention is a method of heating an isopipe by providing an isopipe comprising at least one substance and having a given shape. Determine the maximum thermal stress for the isopipe. This maximum thermal stress is determined, at least in part, by the given shape of the isopipe and one or more materials that form the isopipe. The critical temperature (T _t ) is determined for the isopipe. T _t is the temperature at which the hot creep mechanism in one or more of the materials that form the isopipe begins to relieve thermal stress from the isopipe. The isopipe is heated to about T _t so that the isopipe experiences a substantially uniform thermal strain gradient. This substantially uniform thermal strain gradient produces a lower thermal stress in the isopipe than the maximum allowable thermal stress. The isopipe is heated to about _Tt or higher so that the isopipe experiences a substantially non-uniform thermal strain gradient. Heating above T _t occurs at such a rate that the isopipe undergoes simultaneous stress-relief during heating, reducing the thermal stress generated in the isopipe by a substantially non-uniform thermal strain gradient by heat-relaxation, The thermal stress generated in the pipe is lower than the maximum allowable thermal stress.

Another embodiment according to the present invention is a control system for heating an isopipe. The control system includes a first control module for operating one or more processors, which can be controlled using a finite element analysis program (e.g., a program developed by ANSYS, Inc. (Canonsburg, Pa. 15317) Determines the critical temperature for an isopipe containing a material and having a given shape. The critical temperature is the temperature at which the hot creep mechanism in one or more of the materials that form the isopipe begins to relieve thermal stress from the isopipe. Such a system further includes a second control module for operating one or more processors to control the heating device for heating the isopipe. The isopipe is heated to about T _t to experience a substantially uniform thermal stress, the heating being such that the substantially uniform thermal strain gradient is less than the maximum allowable thermal stress in the isopipe . The control system further includes a third control module for operating one or more processors, which controls the heating device after the isopipe has reached _Tt or higher, and such isopipe has a substantially non- . The heating is controlled so that the isopipe experiences heat stress relief at the same time during heating so that the stress generated in the isopipe by the substantially non-uniform heat distortion gradient is reduced by the stress-relief and the maximum allowable thermal stress Lt; RTI ID = 0.0 > thermal stress. ≪ / RTI >

Yet another embodiment according to the present invention is a computer program product comprising code executable by a processor of a computer device for processing tasks for controlling heating of an isopipe. The computer program product includes a first executable code portion that sets an environment for determining a critical temperature (T _t ) for the isopipe and a maximum allowable thermal stress. This T _t is the temperature at which the high temperature creep mechanism in one or more of the isopipe forming materials begins to relieve the thermal stress from the isopipe and the maximum permissible thermal stress is the heat-induced stress (Thermal-induced stress level). Such a computer program product further comprises a second executable code portion for controlling heating of the isopipe to experience a substantially uniform thermal strain gradient up to about T _t . This substantially uniform thermal strain gradient produces a lower thermal stress than the maximum allowable thermal stress in the isopipe. The computer program product further comprises a third executable code portion for controlling heating of the isopipe to experience a substantially non-uniform thermal strain gradient after the isopipe reaches a temperature above T & _lt ; RTI ID = 0.0 > t. ≪ / RTI > Heating at temperatures above T _t occurs at a rate for the isopipe to simultaneously experience stress-relief during heating, reducing the thermal stress generated in the isopipe by a substantially non-uniform thermal strain gradient by heat- The thermal stress created in the pipe is even lower than the maximum allowable thermal stress.

Additional advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate certain embodiments of the instant invention and, together with the description, serve to explain the principles of the invention and, It appears as part of everywhere:
Figure 1A shows an exemplary computing device that may be used to implement embodiments of the preferred embodiments;
FIG. 1B is an alternative embodiment of the processing system shown in FIG. 1A that may be used in embodiments according to the present invention; FIG.
Figure 2a is a side view of an exemplary isopipe that may be heated in accordance with embodiments of the present invention.
FIG. 2B is a cross-sectional view of the isopipe shown in FIG. 2A when cutting along a line AA.
Figure 3 is a partial illustration of an exemplary fusion process involving isopipe.
Figure 4 is a flow diagram illustrating an exemplary process for preheating an isopipe, an embodiment in accordance with the present invention;
5 is a flow diagram illustrating an alternative representative process for pre-heating an isopipe of an embodiment in accordance with the present invention;
Figure 6 shows an exemplary proposed thermal profile of an embodiment according to the present invention.
Figure 7 is a chart showing stresses generated by typical isopipes during heating according to embodiments in accordance with the present invention.
Figure 8 shows an embodiment of a control system for heating an exemplary isopipe in accordance with the present invention.

The invention will be more readily understood by reference to the following detailed description of the invention and the embodiments and drawings contained herein and the foregoing description and the following description.

Before the system, article, apparatus and / or method of the present invention is disclosed and described, it is to be understood that the invention is not limited to the particular system, specific apparatus, or methodology, do. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting.

The following description of the invention is provided by way of illustration of the best mode known to those skilled in the art. Because of this, one of ordinary skill in the pertinent art will be able to make many changes to the various embodiments of the invention described herein or still recognize and appreciate the beneficial results of the invention. It will also be apparent that certain preferred advantages of the invention may be obtained by selecting some features of the invention without the use of other features. Accordingly, those skilled in the art will appreciate that many modifications and adaptations of the invention are possible, and may even be preferred in certain circumstances and are intended to be part of the present invention. Therefore, the following description is provided as an illustration of the principles of the present invention and is not intended to be limiting thereof.

As used in this specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. Thus, for example, referring to " reflector ", it includes two or more such reflectors and the like.

Ranges may be expressed herein as from "about" one particular value and / or to "about" another specific value. When expressing such a range, it includes from a specific value of one embodiment to another and / or other specific values. Likewise, when values are expressed roughly by using the " about " antecedent, it will be understood that the particular value forms another embodiment. The range of each endpoint will be more importantly understood in terms of the other endpoints and independently at all other endpoints. It is also to be understood that there are a number of values described herein, and that such values are also disclosed herein as " about " to certain values in addition to their value itself. For example, if the value is " 10 ", then " about 10 " is also disclosed. Values are also understood as well understood by those skilled in the art if their values are also " below " and " above " For example, the value " 10 " is also disclosed as " 10 or more " as well as " 10 or less ". Throughout the use example, it is also understood that the data provides a number of different formats, which represent endpoints and starting points, and that any combination of data points is included in the scope. For example, if a particular data point " 10 " and a particular data point " 15 " are disclosed, it is understood that 10 and 15, more than, more than, less than, It is also understood that each unit between two specific units is also disclosed. For example, if 10 and 15 are disclosed, then 11, 12, 13, and 14 are also disclosed.

&Quot; Optional " or " optionally " means that the event or circumstance described thereafter may or may not occur, and such description includes instances where the event or circumstance has occurred and instances where it has not.

As can be appreciated by those skilled in the art, embodiments in accordance with the present invention may be implemented as a method, data processing system, or computer program product. Thus, all embodiments may be in the form of embodiments that are all hardware embodiments, all software embodiments, or combinations of embodiments of software and hardware. Moreover, the practice of the preferred embodiment may take the form of a computer program product in a computer-readable storage medium having computer-readable program instructions (e.g., computer software) embodied in the storage medium. More specifically, the implementation of embodiments may take the form of web-implemented computer software. Any suitable computer-readable storage medium may be used including hard disks, CD-ROMs, optical storage devices, or magnetic storage devices.

Embodiments in accordance with the present invention are described below with reference to block diagrams and flowchart illustrations of methods, apparatus (i.e., systems) and computer program products in accordance with embodiments of the present invention. It will be understood that each block in the block diagrams and flowchart illustrations, and combinations of blocks in the block diagrams and flowchart illustrations, may be executed by computer program instructions, respectively. Such computer program instructions may be stored on a computer or other program that makes a means for implementing the functions specified in the flowchart block or blocks, a general purpose computer for producing a machine to execute instructions on a data processing apparatus operable, A computer, or other program-enabled data processing device.

Such computer program instructions may also be stored in a computer-readable memory, which may direct a computer, or other program-enabled data processing apparatus to function in a particular manner so that instructions stored in the computer- Readable instructions for executing a function assigned to a block or blocks. In addition, such computer program instructions may be loaded into a computer or other program-enabled data processing apparatus causing a series of operating steps that may be performed on a computer or other program-enabled data processing apparatus, The instructions for creating a computer-executable process to execute on a data processing device capable of operating a computer or other program provide steps for executing the functions specified in the flowchart block or blocks.

Thus, examples of blocks and flow diagrams in block diagrams support a combination of means for performing a specified function, a combination of steps for performing a specified function, and program instruction means for performing a specified function. It should also be understood that each block and block diagram in the block diagrams and flowchart illustrations and combinations of blocks in the flowchart illustrations may be combined with specific purpose hardware-based computer systems for performing specified functions or steps or combinations of special purpose hardware and computer instructions Lt; / RTI >

In the referenced embodiment of the present specification, reference may be made to "computer", "computing device", "controller", or "server". Such a computer may be, for example, a hand held device such as a mainframe, a desktop, a notebook or a portable computer, a data recognition and storage device, or it may be a hand held device such as, for example, And may be a processing apparatus embodied in an apparatus. In some instances, the computer may be a simple terminal ("dumb" terminal) for connecting to data, or a device with limited processing capability, such as a processor on the network, or a controller. Referring to FIG. 1A, One embodiment of the present invention may be used to implement embodiments of embodiments according to the present invention. In Figure 1A, a processor 1, such as a microprocessor, And is used to execute software instructions to perform the defined steps. The processor receives power from a power supply 17 that provides power to other components as needed. The processor 1 communicates using a data bus 5 that is typically 16 or 32 bits wide (e.g., in parallel). The data bus 5 is typically used to transfer data and program instructions between the processor and the memory. In an embodiment of the present invention, the memory may be considered a main memory 2, The main memory 2 (RAM) or any other form of holding content only during operation, or the memory may be a non-active memory 3, such as ROM, EPROM, EEPROM, , Flash (FLASH), or any other type of memory that always holds memory contents. Further, the memory may be an auxiliary memory 4, for example, a disk storage for storing a large amount of data. In some embodiments, the disk storage may communicate with the processor instead of the I / O bus 6 or using a dedicated bus (not shown). The secondary memory may be a floppy disk, a hard disk, a compact disk, a DVD, or any other type of mass storage device known to those of ordinary skill in the computer arts.

The processor 1 uses the I / O bus 6 It also communicates with various peripherals or peripherals. In this embodiment, the peripheral I / O controller 7 It is used to provide standard interfaces such as RS-232, RS422, DIN, USB, or any other interface suitable for interfacing various input / output devices. A typical input / output device includes a local printer 18, a monitor 8, a keyboard 9, and a mouse 10 or other typical pointing device (e.g., a roller ball, trackpad, joystick, etc.).

The processor 1 is typically also communicatively coupled with an external communication network using a communication I / O controller 11 and may be coupled to various interfaces, such as data communication oriented protocol 12, for example, X.25, ISDN, DSL, Cable modem or the like can be used. In addition, the communication controller 11 may include a modem (not shown) for interfacing with and communicating with the standard telephone line 13. Finally, the communication I / O controller may include an Ethernet interface 14 for communicating over a LAN (LAN). Any such interface may be used to connect a wide area network such as the Internet www, intranet, LAN, or other data communication facility.

Finally, the processor 1 may communicate with the air interface 16, For example, using one of the IEEE 802.11 protocol, the 802.15.4 protocol, or a standard 3G wireless communication protocol, such as CDMA2000 1x EV-DO, GPRS, W-CDMA, And an antenna 15 for wireless communication.

Available An alternative embodiment of the treatment system is shown in FIG. In this embodiment, a distributed communication and processing architecture is shown including a server 20 that communicates with a local client computer 26a or a remote client computer 26b. The server 20 may include a processor 21 that typically communicates with a database 22, The database 22 includes a main memory 24, But also as a form of auxiliary memory. The processor also typically interfaces with the LAN 25 And communicates with an external device using the I / O controller 23. The LAN may be provided as a local connection to the network printer 28 and the local client computer 26a. This need not be the same, but can be located in the same facility as the server. Communication using a remote device is typically carried out over a wide area network 27, such as the Internet, It is accompanied by setting the data path from the LAN 25. The remote client computer 26b can execute a web browser and as a result the remote client computer 26b can request the data sent to the server 20 via the wide area network 27, And interact with the server as shown.

It will be appreciated by those skilled in the art of data networking that many other alternatives and architectures are possible and that embodiments according to the present invention may be practiced. The embodiments illustrated in Figs. 1A and 1B may be modified in other ways and may be within the scope of the invention as claimed.

Glass manufacturing can be described as a process that converts raw materials to high-temperature homogenous melt and then through an appropriate forming process to provide the raw product. In one embodiment, the glass manufacturing process comprises a fusion technique known in the art as one of ordinary skill in the art. One component of the fusion process is a generally trough-shaped device called isopipe. An exemplary isopipe 200 has a vertical axis 208 and a horizontal axis 210 and is shown in Figures 2a and 2b. In the fusion technique of making glass, the molten glass flows over the wall 202 of the isopipe 200, flows down to the root 204, and then fused again at the bottom to form a glass sheet. Some of the exemplary fusion techniques including isopipe 200 are shown in FIG. The upper portion 200 of the isopipe is a thin sheet of trough 206 (called weir) that runs over the temperature of the glass entering the trough 206 and overflows with molten glass. The bottom, or root, is the solid triangular portion 204 of the refractory material with the glass flowing and cooling on the outside. The transition section 212 from the wear 206 to the root 204 is called a brake. Therefore, in operation, the isopipe has a varying (non-uniform) vertical temperature profile (from ware to root) as the molten glass overflows and cools towards the root. In order to alleviate the problem of glass flow when the new isopipe is run as the first service, the isopipe is heated to an imposed thermal profile before the molten glass is introduced. This type of non-uniform temperature profile creates thermal stresses in the refractory material. If the safety allowable stress is not sufficiently reduced, such stress may cause the material to break or crack. Cracks in the isopipe have a negative effect on the quality of the sheet glass produced, and the shredded isopipe has to be replaced, which is generally a long process and expensive.

When a substantially non-uniform thermal strain gradient is applied to the material, thermal stress is created in the material. A non-uniform thermal strain gradient is induced in the isopipe 200 by applying non-uniform heating to the isopipe 200 from the weir 206 to the root 204. In other words, the profiled non-uniform vertical heating is applied to the isopipe.

In contrast, uniform thermal strain gradients generally do not cause thermal stresses. When the isopipe 200 is uniformly heated (from wear 206 to root 204) a uniform thermal strain gradient occurs. In the case of isopipe, In operation, the thermally-induced strain gradient may become too large to exceed the static fatigue strength of the material. Therefore, the embodiment according to the present invention provides a method for evaluating the case where the proposed heating schedule for preheating the isopipe causes the risk of damage caused by the heat distortion in the isopipe. The heating schedule may include, for example, heating the isopipe (uniformly or non-uniformly) at a certain temperature level for a certain amount of time. For example, the heating schedule after reaching the critical temperature during heating of the isopipe may include a first step that allows only a substantially non-uniform thermal strain gradient. This limiting temperature is the temperature at which the thermal stress can be relieved in the high temperature creep mechanism in the refractory material, and relaxation of the thermal stress is generally described as stress-relief in the process. The second step is to slowly ramming a substantially non-uniform thermal strain gradient such that the maximum thermal stress is not too close to the fracture strength of the material. Slowly reducing the rate at which a substantially non-uniform thermal strain gradient is ramped reduces the maximum thermal stresses as the thermal stress increases due to the increase of the non-linear thermal gradients, And the combined effect of slower ramping is given a longer time for stress relief due to creep and a reduction in maximum thermal stress is reached. The third step is to minimize the heating time so that the glass production is not unnecessarily delayed.

The representative method described herein provides a method based on the determined material properties and computerized stress analysis wherein the proposed heating schedule can be used during the heating of the isopipe to reach a critical temperature Allowing only a substantially non-uniform thermal strain gradient; Ramping a substantially non-uniform thermal strain gradient so that the maximum thermal stress is not too close to the breaking strength of the material; And minimizing the heating time so that the glass production is not unnecessarily delayed. This prediction occurs before any heating of the isopipe. Because the creep mechanism of the isopipe forming material is too slow at lower temperatures, in order to avoid damaging the isopipe and inducing thermal stresses that can not be mitigated through the creep mechanism, . For example, substantially uniform heating may have a temperature difference (DELTA T) of 30 DEG C or less between the weir and the root. The critical temperature T _t is determined for the isopipe, which is related to the material containing the isopipe. T _t is the approximate temperature at which the creep mechanism of the material including the isopipe reaches a rate at which it can relax the thermal stress generated in the heating process at a rate that allows substantially non-uniform (vertical) heating of the isopipe . For example, substantially non-uniform heating may have a DELTA T above 100 DEG C between the weir and the root. Although processes that can be applied to other pre-preheating scenarios are contemplated within the scope of the present invention, one embodiment according to the present invention is to control the process for pre-heating the isopipe in the glass manufacturing process A control method, and a computer program product.

The composition and size of the isopipe affects its thermal profile. Such an isopipe may comprise, for example, one or more refractory materials such as zircon. For example, U.S. Patent Publication No. 20050130830, "Creep Resistant Zircon Refractory Material Used In A Glass Manufacturing System," U.S. Patent Application No. 10 / 738,425, published June 16, 2005, Quot ;, which is incorporated herein by reference in its entirety, describes an isopipe comprising a zircon refractory material. Moreover, the shape of the isopipe may affect its thermal profile.

4 is a flow diagram illustrating an exemplary process for pre-heating an isopipe of an embodiment in accordance with the present invention. In this figure, reference numerals and symbols mean:

402: Receiving information on unique material properties including isopipe;

404: generate a model of the isopipe stress experienced during the proposed heating schedule;

406: comparing the predicted maximum stress during the proposed heating schedule with the determined failure strength of the isopipe material;

408: Is the proposed heating schedule acceptable?

410: end;

Y: Yes;

N: No.

The process of determining the allowable heating schedule for the isopipe includes receiving information about the intrinsic properties of the isopipe, such as the breaking strength of the material, which material is not only the isopipe in step 402, Includes the creep rate. At step 404, a model of the isopipe stress encountered during a predetermined heating schedule is generated using finite element analysis (FEA) techniques for computerized stress analysis. This model involves predicting both the elastic behavior of the material and the high temperature creep behavior of the material. For any given heating schedule, this FEA model predicts temperature, material expansion data due to the hot creep mechanism, and maximum stress in the isopipe based on stress relaxation. In step 406, the predicted maximum stress then determines the stability of its heating schedule in comparison to the measured breaking strength of the material. Stability, as defined herein, means that the maximum stress predicted through the heating schedule is less than the fracture strength of the material. In step 408, it is determined whether the proposed heating schedule being evaluated is acceptable or not. If the proposed heating schedule is not acceptable then various heating rates can be assessed and a rational solution can be reached between rapidly applying new equipment and applying the required heat gradient in a stable manner back to step 404 The heating rate to be provided is selected. In step 408, if the proposed heating schedule is allowed, then in step 410 the process ends. In general, the heating schedule from a given rate, such as, for example, 10 DEG C per hour, 5 DEG C per hour, 4 DEG C per hour, 3 DEG C per hour, 2 DEG C per hour, etc. up to the maximum permissible stress in the isopipe, ≪ / RTI > In general, the maximum allowable stress is the amount of experimentally determined stress that causes failure in the isopipe. For example, it can be determined, and can be determined, for example, when the heat-induced stress experiences 1500 to 1600 psi for about 200 hours, or when the heat-induced stress experiences about 1600 to 1700 psi for about 150 hours, Can be destroyed. In this way, the thermal schedule can be developed so as not to exceed the maximum allowable stress.

Figure 5 is a flow diagram illustrating an alternative representative process for pre-heating an isopipe for an embodiment in accordance with the present invention. Reference numerals in this figure mean:

502: Determination of the maximum thermal stress of a typical isopipe;

504: Determination of the critical temperature range (T _t ) for a representative isopipe;

506: uniformly heating the isopipe to about T _t so that the isopipe does not experience a thermal strain gradient due to exceeding the maximum thermal stress;

508: non-uniformly heating the isopipe after the temperature of the isopipe exceeds about T _t so that the thermal stress generated in the isopipe is less than the maximum thermal stress by heating; And

510: Finish.

In step 502, the maximum thermal stress is determined for a representative isopipe. In step 504, the limit temperature T _t is determined for the isopipe. T _t is the temperature range at which the high temperature creep mechanism in the isopipe begins to relax thermal stress from the isopipe at such a rate that it can offset the stress induced by the speed at which the isopipe is heated. In step 506, the isopipe is uniformly heated at a given rate, such as, for example, 10 DEG C per hour, 5 DEG C per hour, 4 DEG C per hour, 3 DEG C per hour, 2 DEG C per hour, During this heating step, the isopipe is substantially uniform so that the weir and root are at approximately the same temperature (i.e., DELTA T is less than about 30 DEG C) and the isopipe does not experience a thermal strain gradient exceeding the maximum determined stress level Lt; / RTI >

Figure 6 shows three representative proposed heating schedules for isopipe. In this figure, 6.1 is an upper curve, 6.2 is an intermediate curve, and 6.3 is a bottom curve. As shown in Figure 6, in one embodiment, even though other speeds are contemplated within the scope of the present invention, the temperature of a representative isopipe during heating at a first rate is about T _{t < /} RTI & _gt; until _t .

Figure 7 shows the curve of the maximum stress (curve 7.1) in the isopipe as a function of time. The straight line (curve 7.2) dashed at the top in the figure shows a static fracture stress for 10 hours. 7, in one embodiment, even though other speeds are contemplated within the scope of the present invention, as the isopipe is heated according to FIG. 6 during heating at the first speed, Lt; RTI ID = 0.0 & _gt ; T & _lt ; / RTI & _gt; at a rate of about 3.2 psi per hour. A substantially uniform thermal strain gradient produces less thermal stress in the isopipe than the maximum thermal stress. Then, in step 508, the isopipe is heated non-uniformly (i.e., the ΔT between the weir and the root changes to about 100 ° C. or more). Since the high temperature creep mechanism of the material comprising isopipe occurs at a speed fast enough to mitigate some of the stress induced by non-uniform heating, it is therefore possible to maintain the stress induced in the isopipe lower than the maximum thermal stress It is possible to do. T _t refers to the temperature range at which the creep mechanism of the material including the isopipe reaches a rate at which some stress induced by the heating of the isopipe can be removed. This process ends at step 510.

Figure 6 shows an exemplary proposed heating profile of an embodiment according to the present invention. In Fig. 6, the proposed isopipe heating schedule shows the temperature at the top, middle (approximately halfway down) and bottom (root) of a typical isopipe. In the exemplary isopipe of Figure 6, this limit temperature T _t is determined to be about 800 ° C. Therefore, as shown in Fig. 6, after the isopipe reaches about 800 DEG C, a non-uniform heating rate is used. The value of T _t depends on the composition of the isopipe material.

Figure 7 is a chart showing stresses generated by typical isopipes during heating, in accordance with embodiments of the present invention. In Fig. 7, the maximum predicted stress in the isopipe for the proposed heating schedule shown in Fig. 6 is illustrated. The stress levels shown in FIG. 7 were predicted using the method described in FIG. Also shown in Figure 7 is 3000 psi static stress, which, when applied for more than about 10 hours, It is expected to cause material destruction of isopipe. Since the stress is below the 3000 psi stress level, it is confirmed that the heating schedule proposed in FIG. 6 is stabilized by the graph of FIG.

 Figure 8 shows an embodiment of a control system for heating an exemplary isopipe in accordance with the present invention. In the drawings, reference numerals have the following meanings:

801: isopipe material;

802: heating device;

803: Isopipe formation;

804: isopipe;

806: temperature element;

808: controller;

810: Control module 1;

812: Control module 2; And

814: Control module 3.

In FIG. 8, one or more heating devices 802 are attached or incorporated into exemplary isopipes 804. This heating device 802 may be any one or more devices arranged to heat the isopipe 804 uniformly or non-uniformly according to the heating schedule. Such one or more heating devices may include, for example, one or more electrical elements, one or more gas burners, one or more heaters, etc., arranged to heat the isopipe 804 uniformly or non- Or any other device. A thermal profile is obtained from the isopipe 804 by one or more temperature elements 806, which may be incorporated, attached or connected to the isopipe 804. Representative temperature elements may include, for example, a thermocouple device and an infrared thermometer.

One or more heating devices 802 and one or more temperature elements 806 are operatively connected to a controller 808. The controller 808 may receive information from one or more temperature elements 806 to cause the isopipe 804 to heat according to the heating schedule and to control the operation of the one or more heating devices 802 according to the heating schedule. One or more heating devices 802, one or more temperature elements 806, and both controllers operate in accordance with one or more controller modules that operate one or more computing devices. 8 represent separate components for the controller 808, the control module 1 810, the control module 2 812, the control module 3 814 and the computing device 816 On the other hand, it will be appreciated that all or one or more of these components may be combined with a single computing device or processor and operated with a single computing device or processor, or may be more independent than that illustrated in FIG. 8 Module or device.

An embodiment of the control system 800 of FIG. 8 includes a control module 1 810 that operates one or more processors of the computing device 816. Control module 1 810 determines the maximum thermal stress and threshold temperature (T _t ) for isopipe 804 based on input information or materials including isopipe and its formation. Lt; RTI ID = 0.0 > T & _lt ; / RTI > Is the temperature range over which the high temperature creep mechanism begins to relax thermal stress from the isopipe 804 at a rate fast enough to offset at least a portion of the thermal stress induced in the isopipe by the non-uniform heating. The control system 800 further includes a control module 2 812 that operates one or more processors of the computing device 816. The control module 2 812 controls the isopipe 804 to experience a substantially uniform thermal strain gradient (caused by a substantially uniform vertical thermal profile) while the isopipe is heating to about T _t (Not shown). The heating is further controlled by the control module 2 812 so that the substantially uniform thermal strain gradient produces a lower thermal stress in the isopipe than the maximum thermal stress. The control system 800 further includes a control module 3 814 that operates one or more processors of the computing device 816. The control module 3 is iso-pipe 804 is substantially non-uniform thermal strain gradient (substantially non-being caused by the thermal profile of a uniform vertical) the iso-pipe (804 in the above T _t temperature at a rate so as to experience ) Reaches one or more heating devices (802). Moreover, the heating of the isopipe 804 is controlled by the material of the hot creep mechanism including the isopipe during heating such that the isopipe experiences simultaneous stress-relief, so that the isopipe 804 is cooled by the substantially non- Stresses generated in the pipe are reduced by stress-relief and produce lower thermal stresses than the maximum allowable thermal stresses in the isopipe.

The direction for controlling the exemplary control system 800 shown in FIG. 8 may be embodied as computer executable code in a processor in the form of a computer program product. Such a computer program product may include a first executable code portion that sets an environment for determining a threshold temperature range ( _Tt ) for the isopipe and a maximum allowable thermal stress. Such a computer program product comprises a second executable code portion for controlling the heating of the isopipe such that the isopipe experiences a substantially uniform thermal strain gradient to about T & _lt; RTI ID = 0.0 > _t , <Lt; RTI ID = 0.0 > permissible < / RTI > thermal stress. Such a computer program product may further comprise a third executable code portion for controlling the heating of the isopipe to experience a substantially non-uniform thermal strain gradient after the isopipe reaches a temperature above T & _lt ; This heating causes the isopipe to experience stress-relief at the same time, stress-relieving the stress produced in the isopipe by the substantially non-uniform heat distortion gradient, Lt; RTI ID = 0.0 > thermal stress. ≪ / RTI >

Although various embodiments of the invention have been disclosed in the foregoing specification, it will be understood by those skilled in the art that many modifications and other embodiments of the invention may be devised by those skilled in the art to which the invention pertains, I understand that I can have the benefits presented. It is therefore to be understood that the invention is not to be limited to the specific embodiments disclosed herein, but that many modifications and other embodiments may be included within the scope of the appended claims. Moreover, notwithstanding the specific terminology used herein, as well as the claims set out below, they are used in a generic and descriptive sense only and not for the purpose of limiting the invention described above.

Claims (12)

(A) determining a maximum allowable thermal stress for the isopipe;
(B) determining a threshold temperature range (T _t ) for the isopipe, wherein T _t is the rate at which the hot creep mechanism in the isopipe counteracts at least a portion of the thermally-induced stress in the isopipe A temperature range at which to begin to relax thermal stress from the isopipe;
(C) uniformly heating the isopipe so that the isopipe experiences a uniform thermal strain gradient up to T & _lt ; 1 >, wherein the uniform heat distortion gradient produces less thermal stress than the maximum allowable thermal stress in the isopipe; And
(D) non-uniformly heating the isopipe so that the isopipe experiences a non-uniform thermal strain gradient after the temperature has risen above T _t , said heating being accomplished by said non- The step occurring at a rate such that thermal stresses generated in the pipe are at least partially reduced by the hot creep mechanism and produce lower thermal stresses than the maximum allowable thermal stresses in the isopipe
And heating the isopipe.
The method according to claim 1,
Wherein the isopipe is made of zircon.
The method of claim 2,
Wherein said isopipe comprises a weir, a break and a root, and step (C) comprises heating said isopipe to a temperature difference between said weir and said root below 30 ° C And heating the isopipe.
The method of claim 2,
Wherein the isopipe comprises a weir, a brake and a root, and step (D) comprises heating the isopipe to a temperature difference between the weir and the root of at least 100 ° C .
A first control module for operating one or more processors to determine an isopipe having a maximum permissible thermal stress and a critical temperature range T _t for such isopipe for an isopipe containing one or more materials and having a given configuration, Wherein T _t is a temperature range in which the high temperature creep mechanism in the at least one material forming the isopipe begins to relax thermal stress from the isopipe at a rate that cancels at least a portion of the thermally- A first control module;
Controlling at least one heating device for heating the isopipe A second control module for operating at least one processor, wherein the heating device is controlled in that the iso-pipe is the iso-pipe is heated uniformly so as to experience a thermal deformation gradient which the iso-pipe uniform as heated to T _t, the heating A second control module in which the uniform thermal strain gradient is controlled to produce a lower thermal stress in the isopipe than a maximum allowable thermal stress;
A third control modules operating at least one processor for controlling the at least one heating apparatus after experiencing a uniform thermal strain gradient - said iso-pipe reaching the above T _t temperature, and the iso-pipe is a non-uniform heating and a non- , The heating being controlled such that during heating the isopipe experiences a stress-relief such that the stress produced in the isopipe by the non-uniform heat distortion gradient is reduced by stress-relief, A third control module for causing a thermal stress less than a maximum allowable thermal stress in the isopipe to be generated,
And a control device for heating the isopipe.
The method of claim 5,
Wherein the isopipe is made of zircon.
The method of claim 6,
And said second module is configured to control heating of said isopipe so that a temperature difference between said weir and said root is less than or equal to 30 DEG C, characterized in that said isopipe comprises weirs, brakes and roots.
The method of claim 6,
Wherein the isopipe comprises a weir, a brake and a root, and the third module is configured to control heating of the isopipe so that the temperature difference between the weir and the root is above < RTI ID = 0.0 & .
A first executable code portion configured to determine a critical temperature range for the isopipe (T _t ) and a maximum allowable thermal stress, wherein T _t is the temperature at which the high temperature creep mechanism in the at least one material forming the isopipe occurs at the isopipe Wherein the isopipe is a temperature range that begins to mitigate thermal stress from the isopipe at a rate that cancels at least a portion of the thermal-induced stress, and wherein the maximum permissible thermal stress exceeds a thermal- A first executable code portion that is an induced stress level;
Wherein said isopipe experiences a uniform thermal strain gradient up to T & _lt; RTI ID = 0.0 > _{t < /} RTI > and said uniform heat strain gradient is greater than or equal to < RTI ID = 0.0 > A second executable code portion; And
After the iso-pipe reaching the above T _t temperature of the iso-pipe non-ratio of the iso-pipe so as to experience a uniform thermal strain gradient - a third executable code portion for controlling the uniform heating, the heating is the ratio The isopipe simultaneously experiences stress-relief by the high temperature creep mechanism during heating such that the stress generated in the isopipe by the uniform heat distortion gradient is at least partially relieved by the stress relaxation, A third executable code portion that occurs at a rate such that a thermal stress less than the maximum allowable thermal stress in the pipe is generated
And code executable by a processor of a computing device for processing tasks to control heating of the isopipe. delete delete delete

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