TWI600621B - Method for controlling stress in a heated refractory ceramic body - Google Patents

Description

Method of controlling stress in a heated refractory ceramic body

The present application claims the priority benefit of U.S. Provisional Patent Application No. 61/378,154, filed on Aug. 30, 2010.

The present invention relates to a method of managing stress levels in a heated refractory ceramic body undergoing a stress-riser event. More particularly, the present invention relates to a method of managing stress levels in refractory ceramic fusion isopipes during a fusion pull down process. The present invention is useful in the manufacture of glass sheets such as those used in liquid crystal displays (LCDs).

The glass sheet can be made from molten glass using a fusion pull-down process as described in U.S. Patent No. 3,338,696 (published on August 29, 1967; Dockerty-I) and No. 3,682,609 (published on August 8, 1972; Dockerty-II). Figure 1 illustrates a typical fused pull down device used to make a glass sheet. In Fig. 1, the molten glass 1 is conveyed into a forming tank called an isostatic pressing tube 5 made of a refractory ceramic material. The molten glass 1 flows through the top of the crucible 3 to form two separate streams 7, 9 which flow down the opposing converging sidewalls 11, 13 of the fusion isostatic tube 5. At the root 15 or bottom of the fused isostatic tube 5, the separated streams 7, 9 of molten glass are combined into a single molten glass stream 17, which is then drawn into a glass sheet. The key advantage of this process is a single stream 17 The outer surfaces 12, 14 do not contact the side walls 11, 13 of the fused isostatic tube 5. Thus, the outer surface of the glass sheet drawn from a single stream 17 is pure and flame polished.

Figure 2 illustrates a system for manufacturing glass sheets using a fusion pull-down process. System 19 includes a melting vessel 21 that receives the raw materials and melts the raw materials to produce molten glass 25. The system 19 can include a clarification vessel 27 that receives the molten glass 25 from the melting vessel 21 and processes the molten glass 25 to remove the gas inclusions that may be incorporated into the molten glass 25 when the material is melted. System 19 can include a stirred vessel 29 that receives molten glass 25 from clarification vessel 27 and agitates molten glass 25 within vessel 29 to improve the homogeneity of molten glass 25. System 19 includes a transport container 31 that receives molten glass 25 from a stirred vessel 29. The downflow tube 33 is installed below the conveying container 31 to receive the molten glass 25 from the conveying container 31. The molten glass 25 then flows from the downcomer 33 into the inlet pipe 35, which is connected to the opening 37 of the fused isostatic pipe 5, thereby conveying the molten glass 25 to the isostatic pipe 5. Although not shown in Fig. 2, the fusion isostatic tube 5 is generally disposed within the electric range, and the electric range may include an insulating heating element and a gas tube to control the temperature of different portions of the fusion isostatic tube 5.

At the beginning of the fusion pull-down process, the inlet tube 35 is not coupled to the downflow tube 33. At this time, the fusion isostatic pressure tube 5 is controlled to be heated to the glass manufacturing temperature to receive the molten glass 25, and the melting container 21 receives and melts the raw material to form the molten glass 25. After controlling the heating, the fusion isostatic tube 5 undergoes some events, and at least some of the events are stress concentration events, such as Power redistribution, glass composition conversion, insulation changes, and installation or removal of temporary equipment needed to make glass sheets. The stress concentration event will significantly increase the stress level in the fusion isostatic tube. The increase in the stress level in the fused isopipe is due to the large variation in the temperature gradient across the isostatic tube in a short period of time. If the stress level in the fused isostatic tube exceeds the maximum stress that can be tolerated by the fused isostatic tube at a certain temperature, structural damage will occur in the fused isostatic tube. The rupture system fuses the common damage form of isostatic tubes.

Several aspects of the invention are disclosed herein. It should be understood that the aspects may or may not overlap each other. Therefore, part of one aspect may fall within the scope of another, and vice versa.

Each aspect is illustrated by some embodiments, which in turn may include one or more specific embodiments. It should be understood that the embodiments may or may not overlap each other. Thus, a certain embodiment or a portion of a particular embodiment thereof may or may not fall within the scope of another embodiment or a particular embodiment thereof, and vice versa.

In a first aspect of the invention, a method of fabricating a glass sheet using a fusion pull-down process comprises (a) forming a molten glass, (b) heating a fused isostatic tube made of refractory ceramic to a glass manufacturing temperature in a furnace (c) subjecting the fused isostatic tube to a first stress concentration event during which the stress level in the fused isostatic tube will increase, and (d) after step (c), maintaining the fused isostatic tube at a temperature For a period of time, the temperature distribution in the furnace remains stable The temperature level in the fused isostatic tube will decrease during temperature maintenance.

In an embodiment of the first aspect of the present invention, the method further comprises, after step (d), subjecting the fusion isostatic tube to a second stress concentration event, wherein the stress level in the fusion isostatic tube is increased.

In an embodiment of the first aspect of the present invention, the method further comprises: introducing the molten glass formed in the step (a) into a groove of the fusion isostatic tube, flowing the molten glass through the surface of the isostatic tube; The molten glass flows down the opposite side of the fused isostatic tube in two separate streams, and the two separate streams of molten glass are combined at the root of the fused isostatic tube into a single molten glass stream, and a single The molten glass is drawn in a stream to form a glass piece.

In an embodiment of the first aspect of the present invention, the method further comprises monitoring the fusion isostatic tube for an unplanned stress concentration event, and if the non-planned stress concentration event is detected, the non-planned stress concentration After the event, the furnace is kept at a temperature.

In an embodiment of the first aspect of the present invention, for an unplanned stress concentration event, monitoring the isostatic isopipe and/or the furnace includes measuring the absolute temperature difference between the top surface of the crucible and the root of the fusion isostatic tube, and Estimate the rate of change of the absolute temperature difference over time.

In an embodiment of the first aspect of the present invention, the first stress concentration event is accompanied by a rate of change of the absolute temperature difference between the surface of the crucible and the root, and the rate of change of the absolute temperature difference is greater than 1 ° C / hour.

In an embodiment of the first aspect of the present invention, the first stress concentration event is accompanied by a rate of change of absolute temperature difference between the surface of the crucible and the root, and the absolute temperature The rate of change of difference is greater than 5 ° C / hour.

In an embodiment of the first aspect of the present invention, the first stress concentration event occurs with an absolute temperature difference change rate between the surface of the crucible and the root, and the absolute temperature difference change rate is greater than 10 ° C / hour.

In an embodiment of the first aspect of the invention, the method further comprises selecting the length of the temperature retention period of step (d) such that the length of the temperature retention period is proportional to the amount of stress released from the fused isostatic tube.

In an embodiment of the first aspect of the invention, wherein the length of the selection comprises determining a damage condition, the damage condition determines how much stress the fusion isopipe can tolerate and how long it does not occur at a particular temperature.

In a second aspect of the invention, a method of controlling the stress in a heated refractory ceramic body comprises subjecting the heated refractory ceramic body to a series of stress concentration events, wherein during each stress concentration event, the stress level in the heated refractory ceramic body is Raise. Between every two consecutive stress concentration events in the sequence, the fused isostatic tube is maintained at a temperature for a period of time wherein the temperature distribution within the furnace remains stable. During the temperature hold, the stress level in the fused isostatic tube will decrease.

In an embodiment of the second aspect of the present invention, the at least one stress concentration event occurs with an absolute temperature difference change rate between two reference points on the refractory ceramic body, and the absolute temperature difference change rate is greater than 1 ° C / hour.

In an embodiment of the second aspect of the present invention, the at least one stress concentration event occurs with an absolute temperature difference change rate between two reference points on the refractory ceramic body, and the absolute temperature difference change rate is greater than 5 ° C / hour.

In an embodiment of the second aspect of the present invention, at least one stress concentration The rate of change of the absolute temperature difference between the two reference points on the refractory ceramic body occurs, and the absolute temperature difference change rate is greater than 10 ° C / hour.

In an embodiment of the second aspect of the invention, the method further comprises determining the damage condition, the damage condition determining how much stress can be tolerated in the refractory ceramic body and how long the refractory ceramic body does not undergo structural damage at a particular temperature.

In an embodiment of the second aspect of the present invention, the method further includes specifying an event schedule for the refractory ceramic body, the event schedule does not violate the damage condition, and the event schedule includes the sequence stress concentration event, and The temperature is maintained between every two consecutive stress concentration events in the sequence.

In an embodiment of the second aspect of the invention, determining the damage condition comprises stressing the modeled baseline refractory ceramic body and the baseline refractory ceramic body experiences the sequence of stress concentration events.

In an embodiment of the second aspect of the invention, the baseline refractory ceramic body is damaged by the sequence of stress concentration events.

In an embodiment of the second aspect of the invention, the method further comprises monitoring the refractory ceramic body for an unplanned stress concentration event and causing the refractory ceramic body to maintain temperature if an unplanned stress concentration event occurs.

In one or more embodiments, the method of the present invention prevents or reduces the risk of damage to the fused isostatic tube in the event of a deliberate stress concentration event.

In one or more embodiments, the method of the present invention ensures that the fusion isostatic tube is at a manageable stress level at all times.

Additional features and advantages of the present invention will be described in detail later, and the The drawings will become more apparent and understandable to some extent.

The above summary and the following detailed description are intended to be illustrative of the invention The accompanying drawings are included to provide a further understanding of the invention

Unless otherwise indicated, all numerical values, such as percentages by weight and percentages of moles, size, and certain physical properties, in the specification and claims are hereby understood to be modified by the word "about" in all instances. It is also understood that the precise numerical values in the specification and claims are intended to constitute an additional embodiment of the invention. However, any measured value essentially has some error due to the standard deviation of the measurement technique.

The indefinite article "a" or "an" or "an" For example, "a hold value" includes an embodiment having one, two or more hold values, unless the context clearly dictates otherwise.

The detailed descriptions set forth below are set forth to provide a It will be apparent to those skilled in the art that the embodiments of the present invention may be practiced without the specific details. In other instances, well-known features or processes are not described in detail to avoid obscuring the invention. In addition, similar or identical component symbols can be used to Show common or similar components.

Fusion pull-down processes are currently leading the way in manufacturing thin glass substrates with high surface quality to make some display devices, including but not limited to liquid crystal displays (LCDs). This forming technique was first developed by Corning, Inc., New York, USA, and the technology involves the transport of molten glass stream into a forming tank commonly referred to as an "isostatic tube" or a "fusion isostatic tube". The forming tank contains two entities. The vertical wall (called 堰) causes the molten glass to overflow the top surface of the two crucibles, and flows down along the side surface of the isostatic tube as two separate streams, and the separated bottoms merged into the bottom surfaces of the two sides. Single glass ribbon. A single glass ribbon is then drawn down to a predetermined width and thickness at a predetermined temperature, viscosity, and speed, and then cooled to an elastic state, cut, and finally processed to produce a plurality of sheets of glass. Since the two major surfaces of the glass ribbon do not contact the solid surface of the isostatic tube and only contact the surrounding environment, the glass ribbon will exhibit the pure surface quality expected of the LCD glass substrate. The thermal management of molten glass and isopipes is key to a successful and reliable glass forming process and consistent and acceptable product quality. For this reason, during the entire production run, the isopipe is usually placed in a furnace (sometimes referred to as a "electric cooker"), and the temperature field in the furnace is continuously measured and controlled.

Isostatic tubes are typically made from a large refractory material, such as refractory ceramics including zircon, zirconia, alumina, magnesia, xenotime or the like. The size and geometry stability of isostatic tubes are important for successful and reliable manufacturing processes. The isostatic tube itself is a very expensive part of the glass sheet manufacturing system. Therefore, it is always necessary to maintain structural and geometric integrity and extend isopipe life.

A large number of literatures discuss the thermal stress in isostatic tubes. Isostatic tubes generally contain large pieces of ceramic material. The thermal stress is generated by the temperature difference between different areas of the isostatic tube body. In particular, the present invention provides a means of managing thermal stress in an isostatic tube during initial life, normal operation, temporary stop process, process shutdown, emergency treatment, problem solving, etc. during the life of the isostatic tube.

Figure 3 shows the relationship between the maximum fusion isostatic tube stress and the absolute temperature difference in different fusion isostatic tubes 301, 303, 305, 307, 309, 310, 311, 313. The size of the fusion isostatic tube is 301<303<305<307<309<310<311<313. The temperature difference between the dome surface and the root of the fused isostatic tube was measured. The dot on the temperature difference axis in Fig. 3 refers to the temperature difference required to form a damage stress condition when applied for 1 hour. It can be seen from Fig. 3 that the maximum fusion isostatic tube stress increases with the temperature difference and the size of the fusion isostatic tube. It has also been found that a slight increase in temperature difference (between the dome surface and the root) results in a substantial increase in the maximum applied stress state. Therefore, stress concentration events are especially difficult for large fusion isostatic tubes. Eliminating stress concentration events is not a viable solution because many stress concentration events are necessary to start or operate the fusion pull-down process, and others are outside the plan.

In one aspect of the invention, the heated refractory ceramic body is subjected to a sequence of stress concentration events. The heated refractory ceramic body is maintained at a temperature for a period of time between every two consecutive stress concentration events in the sequence. The stress concentration event is represented by SE, and the temperature retention period is expressed by TE. It is in the form of an event schedule applied to the heated refractory ceramic body: SE ₍₁₎ , TE _{(1) (2)} , SE ₍₂₎ , TE _{(2) (3)} , SE ₍₃₎ ,... , TE( _n-1)(n) , SE( _n) , where n is the number of stress concentration events and n is greater than 1. In another aspect of the invention, the heated refractory ceramic body is subjected to a stress concentration event schedule. The heated refractory ceramic body is maintained at a temperature for a period of time after each stress concentration event. The form of this alternative event schedule is: SE ₍₁₎ , TE ₍₁₎ , SE ₍₂₎ , TE ₍₂₎ , ..., SE _(n) , TE _(n) , where n is the number of stress concentration events And n is at least 1. The inventive aspect can monitor the heated refractory ceramic body for non-planned stress concentration events. When an unplanned stress concentration event occurs, the temperature is maintained for a period of time after the event of an unplanned stress concentration event.

The stress concentration event is characterized by a significant change in the absolute temperature gradient throughout the refractory ceramic body in a short period of time, or a significant change in the absolute temperature difference between the two reference points on the refractory ceramic body in a short period of time. In one embodiment, when an event occurs, if the rate of change of the absolute temperature difference between the two reference points on the refractory ceramic body is greater than 1 ° C / hour, then the event is considered a stress concentration event. In another embodiment, when the event occurs, if the absolute temperature difference change rate between the two reference points on the refractory ceramic body is greater than 5 ° C / hour, then the event is regarded as a stress concentration event. In still another embodiment, when the event occurs, if the absolute temperature difference change rate between the two reference points on the refractory ceramic body is greater than 10 ° C / hour, then the event is regarded as a stress concentration event. The reference point is the spacing point on the refractory ceramic body. In the case where the refractory ceramic body is a fused isostatic tube, one reference point may be located on the dome surface of the fused isostatic tube, and another reference point may be located at the root of the fused isostatic tube. The reference point temperature of the dome surface can be seen as the top surface of the two turns Single point temperature. Alternatively, several temperatures of the two top surfaces of the two turns can be measured, and a single temperature representing a plurality of temperatures (eg, the average or median of several temperatures) can be used as the reference point temperature of the dome surface. Similarly, the reference point temperature of the root can be seen as the single point temperature of the root. Alternatively, several temperatures of the root may be measured, such as along a horizontal line along the root, and a single temperature representing a plurality of temperatures (eg, an average or median of several temperatures) may be used as the reference point temperature of the root. Any solution used to determine the reference point temperature should be consistent to measure the absolute temperature difference between the reference points over time.

In one embodiment, an important stress concentration event occurs after the fusion isostatic tube is heated in a controlled manner to a glass manufacturing temperature in a fusion pull-down process. Such stress concentration events include, but are not limited to, power redistribution, glass composition conversion, insulation changes, and the installation or removal of temporary equipment required to manufacture the glass sheets. Special cases of stress concentration events that may occur after heating the isostatic pressure tube to the glass manufacturing temperature include cutting off the auxiliary heater power supply for heating the isostatic isopipe, self-fusion isostatic tube or internal fusion isopipe The electric cooker removes the auxiliary heater and couples the downcomer to the fusion isostatic tube. Non-scheduled stress concentration events can occur at any time during the fusion pulldown process. Examples of non-scheduled stress concentration events include sudden failure of the auxiliary heater, total failure of the power supplied to the fusion pull-down machine, and material defects or stress concentrations in the fusion isostatic tube. After a scheduled or non-scheduled stress concentration event, maintaining the heated fused isostatic tube for a period of time helps to reduce the stress level in the heated fusion isopipe to a safe level.

During the temperature maintenance period, the thermal environment of the refractory ceramic body is controlled to make the fire resistant The temperature distribution within the ceramic body remains stable (or constant) for a period of time. The thermal environment constitutes all configurations that affect the temperature distribution in the fused isopipe, such as heating equipment, cooling equipment, insulation, and air chambers. The control of the thermal environment is such that the monitored temperature remains substantially constant by monitoring the temperature of one or more points on the refractory ceramic body and correspondingly adjusting the heat input to the refractory ceramic body. The stress level in the refractory ceramic body will decrease during temperature maintenance. A decrease in the stress level may indicate a decrease in the average stress or maximum stress of the refractory ceramic body. During the temperature maintenance period, since the refractory ceramic body has a certain viscoelasticity, the stress is released from the refractory ceramic body, which will be described in further detail later. During temperature maintenance, the maximum stress in the refractory body may be lower than the stress threshold, resulting in structural damage to the refractory ceramic body. The length of the temperature retention period depends on how much stress is to be released from the refractory ceramic body, and the temperature retention period is typically up to several hours. A priori modelling of one or more stress concentration events results in an expected stress rise in the refractory ceramic body, and an estimate of how long the temperature maintenance period should be to release sufficient stress from the refractory body.

In order to make the strategy of maintaining the isostatic tube at a temperature for a period of time, the refractory ceramic material preferably exhibits creep and stress release at high temperatures. Creep becomes a viscoelastic behavior that allows the material to deform over time without changing the load applied to the material. The stress release σ can be expressed as: = f ( ε , T , P , t )<0 (1), where ε represents strain, T represents temperature, P represents material properties, and t represents time. For a viscoelastic material whose stress is released over time, the function f of equation (1) is always less than zero. Exemplary refractory materials that exhibit creep and stress relief at elevated temperatures are zirconia, alumina, and other ceramic materials.

The following examples are provided to further illustrate the principles of the invention.

In one example, the stress in the isostatic tube is modeled in the initial phase of the fusion pull-down process. The fusion isostatic tube system is made of zircon. The electric isolator with the isostatic pressure tube or the integrated isostatic pressure tube is equipped with an auxiliary heater (ie, the auxiliary heater is disposed adjacent to the fusion isostatic pressure tube to transfer heat to the fusion isostatic tube). The model results are shown in Figure 4 and are described below. The dashed line 401 represents the temperature difference between the dome surface and the root of the isostatic tube, and the solid line 403 represents the stress level in the fusion isostatic tube.

A typical heating schedule 405 is applied to the fusion isostatic tube. At the end of the heating schedule 405, the fused isostatic tube stress was about 245 pounds per square inch and the absolute temperature difference between the dome surface and the root was about 49 °C. Next, at the time of the stress concentration event 407, the auxiliary heater is removed from the fused isostatic tube or the electric cooker. At the end of the stress concentration event 407, the stress level of the fusion isostatic tube is increased to approximately 2678 pounds per square foot (the stress level increases by approximately 993% compared to the previous stress level) and the absolute between the dome surface and the root The temperature difference is about 88 ° C (the temperature difference growth rate during the stress concentration event 407 is about +10.7 ° C / hour). Next, the temperature hold period 409 is applied to the fusion isostatic tube. After the temperature hold period 409, the fusion isostatic tube stress drops to about 1888 pounds per square inch (the stress is reduced by about 29% compared to the previous stress level), and the absolute temperature difference is still 88 °C due to the temperature. Next, at the stress concentration event 411, the downcomer is coupled to the fusion isostatic tube. At the end of the stress concentration event 411, the fusion isostatic tube stress is increased to approximately 2,408 pounds per square foot and between the dome surface and the root The absolute temperature difference is about 89 °C. During the stress concentration event 411, a stress spike of about 3566 pounds per square foot and an absolute temperature difference peak between the dome surface and the root of about 112 °C occurred. It can be seen that if there is no temperature retention period 409, the stress level in the fusion isostatic tube will be much higher than 3566 pounds per square inch after the stress concentration event 411, resulting in a high risk of damage to the fusion isostatic tube.

Figure 5 is a flow chart of an additional aspect of the present invention. An example of a refractory ceramic body that incorporates an isostatic tube as the workflow of Figure 5. In step 41, the data collected during the application of the first event schedule to the baseline fusion isostatic tube is obtained. After controlling the heated baseline fusion isostatic tube to the glass manufacturing temperature, the first event schedule is applied to the baseline fusion isostatic tube. The first event schedule includes one or more stress concentration events. Preferably, during the application of the first event schedule, the baseline fusion isostatic tube is damaged (eg, ruptured), so that the useful information from the data collection baseline fusion isostatic tube is limited by the first event schedule. . Preferably, the data contains a thermal history of the baseline fusion isostatic tube during the first event schedule. In step 43, additional information related to the thermal history of the data and the baseline fusion isopipe (such as the geometry and material properties of the baseline fusion isopipe) is used to model the baseline during the first event schedule. Fusion of thermal stress in isostatic tubes.

In one embodiment, a creep model (referred to as the Norton model) is used to fuse the isostatic tube stress modeling. Strain rate in creep model Expressed as: = Aσ ⁿ _e ^{-C / T} (2), where σ represents stress and T represents temperature. The parameters A , n and C are the measured material properties. σ can be expressed by equation (2) as: Assuming that the strain rate is constant over time (ie, secondary creep), then: Therefore, the stress σ is a function of time at a specific temperature and strain. Equation (4) is numerically solved to model the stress in the isostatic tube.

In step 45, from the static fatigue data of the modeled stress and the baseline fusion isostatic tube material in the baseline fusion isostatic tube, the fusion orthostatic tube having the same or similar structure as the baseline fusion isostatic tube is derived. Damage conditions. Static fatigue data can be collected a priori by studying the conditions under which the fused isopipe material will be broken. This may involve subjecting the material to various tensile stresses at different temperatures to determine which tensile stress and temperature combination will cause the material to rupture. The modeled stress provides a stress that varies with time at a certain temperature by the isothermal isopipe. The condition of the damage is determined by the same or similar fused isopipes as the baseline fusion isopipe. How much stress can be tolerated and how long it will not be damaged at a specific temperature or temperature range. In step 47, a target fusion isostatic tube of the same or similar as the baseline fusion isostatic tube is constructed, and a new event schedule that does not violate the damage condition is designed and specified.

In step 49, after heating the target fusion isostatic tube to the glass manufacturing temperature, the new event schedule is applied to the target fusion isostatic tube. The new event schedule includes one or more of the stress concentration events described above and one or more temperature retention periods. Figure 4 shows an example of a new event schedule. Damage condition To determine how long each temperature retention period should be. It is important to release sufficient stress between each stress concentration event or a continuous stress concentration event, so that the new event schedule is applied to the fusion isostatic tube caused by the second fusion isostatic tube. The cumulative stress level is still less than the damage threshold specified by the damage condition.

As described above, the method of manufacturing a glass sheet by a fusion pull-down process involves transporting molten glass to a heated fused isostatic tube, flowing the molten glass through a dome surface of a heated fusion isostatic tube, and causing the molten glass to have two The manner of separating the streams flows down the sides of the fused isopipe, the two separate streams of molten glass are combined into a single stream of molten glass, and a single stream of molten glass is drawn into a glass sheet. The raw material is melted in the initial stage to form molten glass while heating the fused isostatic tube to the glass manufacturing temperature. The glass manufacturing temperature is several hundred degrees and depends on the composition of the glass. After heating the fused isostatic tube to the glass manufacturing temperature, some events are performed in the fusion pull-down system, and some events can be considered as stress concentration events of the fused isostatic tube. As described above, the temperature application period is strategically applied between the stress concentration event or every two consecutive stress concentration events to control the stress level in the heated fusion isostatic tube. Next, the molten glass is transferred to a heated fused isopipe and a glass piece is formed. When forming a glass sheet, the heated fusion isostatic tube can be monitored for unplanned or unexpected stress concentration events; and when an unplanned stress concentration event is found, the stress in the isothermal compression tube can be reduced. The level of the program. In one embodiment, the absolute temperature difference between the dome surface and the root of the heated fusion isostatic tube is measured over a period of time. (Apply the above method for determining the absolute temperature difference) law). The rate of change of the absolute temperature difference over time can be determined from the absolute temperature difference and time data. If the absolute temperature difference change rate indicates that the fusion isostatic tube has been or is undergoing a stress concentration event, the temperature holding event can be applied to the fusion isostatic tube after the stress concentration event to make the stress level in the fusion isostatic tube Achieve safety standards. This procedure is repeated over the entire operational phase of the fusion pulldown process.

While the invention has been described in the foregoing embodiments, the embodiments of the invention may be Therefore, the scope of the invention is defined by the scope of the appended claims.

1‧‧‧ molten glass

3‧‧‧堰

5‧‧‧Isostatic tube

7, 9, 17‧ ‧ stream

11, 13‧‧‧ side wall

12, 14‧‧‧ surface

15‧‧‧ Root

19‧‧‧System

21‧‧‧melting container

25‧‧‧Solder glass

27‧‧‧Clarification container

29‧‧‧Stirring container

31‧‧‧Transport container

33‧‧‧ downflow tube

35‧‧‧Inlet pipe

37‧‧‧ openings

41, 43, 45, 47, 49 ‧ ‧ steps

301, 303, 305, 307, 309, 310, 311, 313‧‧‧ etc.

401‧‧‧ dotted line

403‧‧‧solid line

405‧‧‧ Schedule

407, 411‧‧ events

409‧‧‧ Temperature retention period

The above is a description of the drawings. The figures are not necessarily to scale, and are in the

Figure 1 illustrates the molten glass flowing through the dome surface of the fused isopipe during the fused pull down process.

Figure 2 illustrates a glass sheet manufacturing system.

Figure 3 is a graph showing the relationship between the maximum stress and the temperature difference between the dome surface and the root for a range of fused isopipes.

Figure 4 is a graph showing stress versus time and major difference versus time for a fusion isostatic tube as it undergoes a sequence of events in accordance with an embodiment of the present invention.

Figure 5 is a process flow diagram for controlling stress in a refractory ceramic body in accordance with one aspect of the present invention.

401‧‧‧ dotted line

403‧‧‧solid line

405‧‧‧ Schedule

407, 411‧‧ events

409‧‧‧ Temperature retention period

Claims (5)

A method for manufacturing a glass sheet by a fusion pull-down process, the method comprising the steps of: (a) forming a molten glass; (b) forming a fusion isopipe made of a refractory ceramic in a furnace Heating to a glass manufacturing temperature; (c) subjecting the fusion isostatic tube to a first stress concentration event, wherein a stress level in the fusion isostatic tube rises during the first stress concentration event; After the step (c), applying a temperature maintaining period to the fused isopipe, wherein a temperature distribution in the furnace remains stable, wherein the stress in the fused isostatic tube during the temperature retention period a level decrease; and (e) after the step (d), subjecting the fusion isostatic tube to a second stress concentration event, the stress level in the fusion isostatic tube during the second stress concentration event A quasi-elevation is then applied and a temperature holding period is applied to the fused isopipe, wherein a temperature profile within the furnace remains stable, wherein the stress level in the fused isopipe decreases during the temperature hold. The method of claim 1, further comprising the steps of: monitoring the fusion isostatic tube for a plurality of non-planned stress concentration events, and if an unplanned stress concentration event is detected, the non-planned stress concentration is event Thereafter, a temperature is applied to the fused isostatic tube. The method of claim 1, wherein the first stress concentration event occurs with an absolute temperature difference change rate between a top surface of the plurality of crucibles and a portion, the absolute temperature difference change rate being greater than 1 ° C / hour. The method of claim 1, further comprising the step of: selecting one of the temperature holding periods of the step (d) such that the length of the temperature maintaining period is one of a stress amount released from the fusion isostatic tube ratio. The method of claim 4, wherein the step of selecting the length comprises determining a damage condition that determines how much stress the fusion isopipe can tolerate and how long the fusion isopipe does not occur at a particular temperature. damage.