阅读说明：本技术 用于监测和控制锡槽的方法 (Method for monitoring and controlling a tin bath ) 是由 R·J·亨德肖特 何亮 M·J·加拉赫尔 R·高希 于 2020-03-20 设计创作，主要内容包括：一种控制锡槽炉中生产的玻璃制品中的缺陷的方法,包含测量与锡槽炉相关联的气氛的至少一个参数,其中参数选自由露点和密度组成的群组；将测量的参数与玻璃制品中的缺陷相关联；以及通过控制工艺气体相对于炉的流速,在对应于玻璃制品中的缺陷减少的方向上控制测量的参数,其中工艺气体包含氢气和氮气中的一种或多种。(A method of controlling defects in glass articles produced in a tin bath furnace, comprising measuring at least one parameter of an atmosphere associated with the tin bath furnace, wherein the parameter is selected from the group consisting of dew point and density; correlating the measured parameter with a defect in the glass article; and controlling the measured parameter in a direction corresponding to a reduction in defects in the glass article by controlling a flow rate of a process gas relative to the furnace, wherein the process gas comprises one or more of hydrogen and nitrogen.)

1. A method of controlling defects in glass articles produced in a tin bath furnace, comprising:

measuring at least one parameter of an atmosphere associated with the tin bath furnace, wherein the parameter is selected from the group consisting of a dew point of the atmosphere and a density of the atmosphere;

correlating the measured parameter with a defect in the glass article; and

controlling the measured parameter in a direction corresponding to a reduction in defects in the glass article by controlling a flow rate of a process gas relative to the furnace, wherein the process gas comprises one or more of hydrogen and nitrogen.

2. The method of claim 1, wherein the at least one parameter is a dew point of the atmosphere, and wherein the dew point corresponds to a water vapor concentration in the atmosphere.

3. The method of claim 1, wherein the at least one parameter is a density of the atmosphere, and wherein the density corresponds to a hydrogen concentration in the atmosphere.

4. The method of claim 1, wherein the at least one parameter is a density of the atmosphere, and wherein the density corresponds to a gas composition in the atmosphere indicative of oxygen leakage into the furnace.

5. The method of claim 2, further comprising:

measuring a density of the atmosphere associated with the furnace, wherein the measured density corresponds to a hydrogen concentration in the atmosphere; and

in addition to controlling the dew point, a ratio of hydrogen to water vapor concentrations in the atmosphere is controlled in a direction corresponding to a reduction in defects in the glass article by controlling the flow rate of the process gas relative to the furnace.

6. The method of claim 2, further comprising:

measuring a density of the atmosphere associated with the furnace, wherein the measured density corresponds to a gas composition in the atmosphere indicative of oxygen leakage into the furnace; and

in addition to controlling the dew point, controlling a gas composition in the atmosphere in a direction corresponding to a reduction in defects in the glass article by controlling the flow rate of the process gas relative to the furnace.

7. The method of any one of claims 1, 2, 5, and 6, wherein controlling the flow rate of the process gas results in a decrease in the dew point of the atmosphere.

8. The method of any one of claims 1,3 and 5, wherein controlling the flow rate of the process gas results in an increase in the hydrogen concentration in the atmosphere.

9. The method of any one of claims 1, 4 and 6, wherein controlling the flow rate of the process gas results in a decrease in the oxygen concentration in the atmosphere.

10. The method of any of the preceding claims, further comprising:

correlating a line speed of glass production with a defect in the glass article; and

controlling the flow rate of the process gas in a direction corresponding to a reduction in defects in the glass article.

11. The method of any of the preceding claims, further comprising:

periodically changing the bandwidth of the glass articles being produced in the tin bath furnace.

12. The method of claim 11, wherein the changing of the bandwidth is accomplished by reducing the bandwidth.

13. The method according to any one of the preceding claims, wherein the controlled flow rate is selected from the group consisting of: the flow rate of process gas entering the furnace and the flow rate of gas exiting the furnace.

14. The method of any preceding claim, wherein the atmosphere is within the furnace.

15. The method of any one of the preceding claims, wherein the atmosphere is an exhaust stream from the furnace.

16. The method according to any one of the preceding claims, wherein the atmosphere is a recycle gas that is vented from the furnace and recycled back into the furnace.

17. The method of any preceding claim, wherein the atmosphere is a gas stream entering the furnace.

18. The method of any of the preceding claims, further comprising:

the furnace gas usage is optimized by taking into account differences between one or more conditions of the intake, furnace and exhaust gases.

19. The method of claim 18, further comprising:

determining a component concentration difference between the furnace gas and the exhaust gas; and

when the difference is large, the intake air flow rate is increased.

20. The method of claim 18, further comprising:

extracting raw recycle gas from the furnace;

cleaning the raw recycle gas to produce a purified recycle gas;

mixing the purified recycle gas with the intake air;

flowing the mixture of the feed gas and the purified recycle gas into the furnace;

determining a component concentration difference between the unpurified cycle gas and the purified cycle gas; and

when the difference is large, the intake air flow rate is increased.

21. The method of claim 14, further comprising:

measuring a pressure differential within the furnace; and

and determining the furnace flow direction according to the measured pressure difference.

22. The method of claim 15, further comprising:

measuring pressure and temperature differences in the exhaust stream; and

determining an exhaust flow direction and an exhaust flow rate from the measured differential pressure and the measured differential temperature.

Background

Measurements have been used in the past in a tin bath atmosphere. For example, a commercial system of Siemens measures O₂、H₂And dew point, CN106977080A discusses the use of H₂And O₂The sensors control the atmosphere. Furthermore, the use of H in the tin bath atmosphere₂/N₂The related patents can be traced back at least to 1967 (see, e.g., US 3,337,322). See also Glass technology, Eur.J. Glass Sci.technology.A., 12.2012, 53(6), 261-.

However, although H is used₂And N₂Has a long history, the marketing of measurement systems and methods has also been successful, but challenges remain in controlling the atmosphere to minimize the occurrence of glass defects. These challenges stem from the cost of purchasing on-line analytical equipment and the challenges associated with associating measurements with the defects that occur. The present invention seeks to overcome these challenges.

Disclosure of Invention

Aspect 1. a method of controlling a tin bath furnace atmosphere, comprising: measuring a density of an atmosphere associated with the furnace; measuring a second parameter of the atmosphere associated with the furnace, wherein the second parameter is selected from the group consisting of: oxygen concentration and dew point; correlating the measured density and the measured second parameter to a defect in the finished glass article; and controlling a flow rate of a process gas relative to the furnace, wherein the process gas comprises one or more of hydrogen and nitrogen.

Aspect 2. the method of aspect 1, wherein the controlled flow rate is selected from: the flow rate of process gas entering the furnace and the flow rate of gas exiting the furnace.

Aspect 3. the method of aspect 1, wherein the atmosphere is within the furnace.

Aspect 4. the method of aspect 1, wherein the atmosphere is an exhaust stream from the furnace.

Aspect 5. the method of aspect 1, wherein the atmosphere is a recycle gas that is vented from the furnace and recycled back into the furnace.

Aspect 6. the method of aspect 1, wherein the atmosphere is a gas stream entering the furnace.

Aspect 7 the method of aspect 1, further comprising: the furnace gas usage is optimized by taking into account differences between one or more conditions of the intake, furnace and exhaust gases.

Aspect 8 the method of aspect 7, further comprising: determining a component concentration difference between the furnace gas and the exhaust gas; and increasing the intake air flow rate when the difference is large.

Aspect 9. the method of aspect 7, further comprising: extracting raw recycle gas from the furnace; cleaning the raw recycle gas to produce a purified recycle gas; mixing the purified recycle gas with the intake air; flowing the mixture of the feed gas and the purified recycle gas into the furnace; determining a component concentration difference between the unpurified cycle gas and the purified cycle gas; and increasing the intake air flow rate when the difference is large.

Aspect 10 the method of aspect 4, further comprising: measuring pressure and temperature differences in the exhaust stream; and determining an exhaust flow direction and an exhaust flow rate from the measured differential pressure and the measured differential temperature.

Aspect 11 the method of aspect 3, further comprising: measuring a pressure differential in the furnace; and determining the furnace flow direction based on the measured differential pressure.

Aspect 12. a method of controlling a tin bath furnace atmosphere, comprising: measuring the redox state of molten tin in the tin bath; measuring a density of an atmosphere associated with the furnace; correlating the redox state and the measured density with defects in the finished glass product; and controlling a flow rate of a process gas relative to the furnace, wherein the process gas comprises one or more of hydrogen and nitrogen.

Aspect 13. a method of controlling a tin bath furnace atmosphere, comprising: measuring the inlet molten glass temperature of the tin bath; measuring a second parameter of an atmosphere associated with the furnace, wherein the second parameter is selected from the group consisting of: oxygen concentration and dew point; correlating the inlet molten glass temperature of the tin bath and the measured second parameter with a defect in the finished glass product; and controlling the local temperature in the tin bath and/or the upstream glass temperature in the glass furnace.

Aspect 14. a method of controlling a tin bath furnace atmosphere, comprising: measuring a density of an atmosphere associated with the furnace; measuring the hydrogen sulfide concentration in the atmosphere; correlating the measured density and hydrogen sulfide concentration to defects in the finished glass product; and controlling the exhaust stream from the furnace to minimize sulfur species from vaporization in the atmosphere.

Aspect 15. a method of controlling defects in glass articles produced in a tin bath furnace, comprising: measuring a dew point of an atmosphere associated with the tin bath furnace; correlating the measured dew point to a defect in the glass article; and controlling the dew point in a direction corresponding to a reduction in defects in the glass article by controlling a flow rate of a process gas relative to the furnace, wherein the dew point corresponds to a water vapor concentration in the atmosphere, and wherein the process gas comprises one or more of hydrogen and nitrogen.

Aspect 16 the method of aspect 15, further comprising: measuring a density of the atmosphere associated with the furnace, wherein the measured density corresponds to a hydrogen concentration in the atmosphere; and controlling a ratio of hydrogen to water vapor concentrations in the atmosphere in a direction corresponding to a reduction in defects in the glass article by controlling a flow rate of the process gas relative to the furnace in addition to controlling the dew point.

Aspect 17. the method of aspect 15 or aspect 16, wherein controlling the flow rate of the process gas results in a decrease in the dew point of the atmosphere.

Aspect 18. the method of aspect 17, wherein controlling the flow rate of the process gas results in a decrease in the hydrogen concentration in the atmosphere.

Aspect 19. the method of any of aspects 15 to 18, further comprising: correlating a line speed of glass production with a defect in the glass article; and controlling the flow rate of the process gas in a direction corresponding to a reduction in defects in the glass article.

Aspect 20 the method of any of aspects 15-19, further comprising: periodically changing the bandwidth of the glass articles being produced in the tin bath furnace.

Aspect 21 the method of aspect 20, wherein the changing of the bandwidth is accomplished by reducing the bandwidth.

Aspect 22. a method of controlling defects in glass articles produced in a tin bath furnace, comprising: measuring at least one parameter of an atmosphere associated with the tin bath furnace, wherein the parameter is selected from the group consisting of dew point and density; correlating the measured parameter with a defect in the glass article; and controlling the measured parameter in a direction corresponding to a reduction in defects in the glass article by controlling a flow rate of a process gas relative to the furnace, wherein the process gas comprises one or more of hydrogen and nitrogen.

Aspect 23 the method of aspect 22, wherein the one parameter is a dew point, and wherein the dew point corresponds to a water vapor concentration in the atmosphere.

Aspect 24. the method of aspect 22, wherein the one parameter is density, and wherein the density corresponds to a hydrogen concentration in the atmosphere.

Aspect 25. the method of aspect 22, wherein the one parameter is density, and wherein the density corresponds to a composition of gas in the atmosphere indicative of oxygen leaking into the furnace.

Aspect 26 the method of aspect 23, further comprising: measuring a density of the atmosphere associated with the furnace, wherein the measured density corresponds to a hydrogen concentration in the atmosphere; in addition to controlling the dew point, a ratio of hydrogen to water vapor concentrations in the atmosphere is controlled in a direction corresponding to a reduction in defects in the glass article by controlling the flow rate of the process gas relative to the furnace.

The method of aspect 27. according to aspect 23, further comprising: measuring a density of the atmosphere associated with the furnace, wherein the measured density corresponds to a gas composition in the atmosphere indicative of oxygen leakage into the furnace; and controlling a gas composition in the atmosphere in a direction corresponding to a reduction in defects in the glass article by controlling the flow rate of the process gas relative to the furnace in addition to controlling the dew point.

Aspect 28. the method of any one of aspects 22, 23, 26, and 27, wherein controlling the flow rate of the process gas results in a decrease in the dew point of the atmosphere.

Aspect 29. the method of any one of aspects 22, 24, and 26, wherein controlling the flow rate of the process gas results in an increase in the hydrogen concentration in the atmosphere.

Aspect 30. the method of any one of aspects 22, 25 and 27, wherein controlling the flow rate of the process gas results in a decrease in the oxygen concentration in the atmosphere.

Aspect 31. the method of any of aspects 22 to 30, further comprising: correlating a line speed of glass production with a defect in the glass article; and controlling the flow rate of the process gas linear velocity to be lower than a value corresponding to an acceptable value in a direction corresponding to a decrease in a level of a defect in the glass article.

Aspect 32. the method of any one of aspects 22 to 31, wherein the controlled flow rate is selected from: the flow rate of process gas entering the furnace and the flow rate of gas exiting the furnace.

The method of any of claims 22-32, wherein the atmosphere is within the furnace.

Aspect 34. the method of any of aspects 22-33, wherein the atmosphere is an exhaust stream from the furnace.

Aspect 35. the method of any one of aspects 2 to 34, wherein the atmosphere is a recycle gas that is vented from the furnace and recycled back into the furnace.

Aspect 36. the method of any one of aspects 22 to 35, wherein the atmosphere is a gas stream entering the furnace.

Aspect 37. the method of any of aspects 22 to 36, further comprising: the furnace gas usage is optimized by taking into account differences between one or more conditions of the intake, furnace and exhaust gases.

Aspect 38 the method of aspect 37, further comprising: determining a component concentration difference between the furnace gas and the exhaust gas; and increasing the intake air flow rate when the difference is large.

Aspect 39 the method of aspect 37, further comprising: extracting raw recycle gas from the furnace; cleaning the raw recycle gas to produce a purified recycle gas; mixing the purified recycle gas with the intake air; flowing the mixture of the feed gas and the purified recycle gas into the furnace; determining a component concentration difference between the unpurified cycle gas and the purified cycle gas; and increasing the intake air flow rate when the difference is large.

Aspect 40 the method of aspect 33, further comprising: measuring a pressure differential in the furnace; and determining the furnace flow direction based on the measured differential pressure.

Aspect 41 the method of aspect 34, further comprising: measuring pressure and temperature differences in the exhaust stream; and determining an exhaust flow direction and an exhaust flow rate from the measured differential pressure and the measured differential temperature.

Drawings

The present invention will hereinafter be described in conjunction with the following drawing figures, wherein like numerals denote like elements:

FIG. 1 is a schematic view of a tin bath illustrating an embodiment of a system and method for monitoring and controlling a tin bath as described herein.

FIG. 2 is a schematic view of a tin bath illustrating an embodiment of a system and method for monitoring and controlling a tin bath as described herein.

FIG. 3 is a schematic view of a tin bath illustrating an embodiment of a system and method for monitoring and controlling a tin bath as described herein.

FIG. 4 is a schematic view of a tin bath illustrating an embodiment of a system and method for monitoring and controlling a tin bath as described herein.

FIG. 5 shows O in a molten tin bath₂Potential (in ppm O)₂Measurement) of the dependence on the dew point of the atmosphere above the glass, and of the atmosphere O above the glass bath₂A graph lacking correlation is measured. The top line in the figures with small triangle symbols is the O indicated in the tin bath₂Concentration, the middle line in the graph with open circle symbols is the dew point at the position above the glass bath, and the bottom line in the graph with small square symbols is the O in the atmosphere above the tin bath₂And (4) concentration.

FIG. 6 illustrates the relationship between dew point above the glass and defects in the glass, and shows a graph of the benefit of maintaining a consistently low dew point.

Fig. 7 shows the relationship between the linear velocity (production rate of glass article) and the glass defect, and shows a graph in which the linear velocity variation is one factor that affects the defect (temporal), and there is a positive correlation between the linear velocity and the defect.

FIG. 8 shows bandwidth, dew point, O in tin₂And defects in the glass, and shows O in tin after the bandwidth is reduced₂And a map in which the dew point is immediately reduced and the defect is also reduced.

FIG. 9 shows H near the glass surface₂/H₂A pair of graphs showing the correlation between the O ratio (upper graph) and the defect in glass (lower graph), andwhen H is present₂/H₂When the O ratio is low, the occurrence rate of defects is large.

FIG. 10 shows a prior art diagram of an important aspect of the tin bath process for making glass.

Detailed Description

Referring to fig. 10, it is well known in the float glass industry that oxygen in the tin bath furnace can negatively affect the quality of the glass. The source of oxygen in the tin bath furnace is typically due to furnace leaks or oxygen from the glass itself.

Hydrogen (H) in the atmosphere above the tin bath₂) Can help prevent oxygen from oxidizing the tin bath due to furnace leakage, and generate water vapor (H) in the atmosphere above the tin bath due to reaction of the hydrogen with the oxygen₂O)。

The oxygen in the glass can react with (a) the hydrogen in the atmosphere at the top surface of the ribbon (above the tin bath) to form H in the atmosphere₂O (i.e., 2H)₂+O₂->2H₂O); or (b) tin on the bottom surface of the glass ribbon to form SnO₂(solid) or SnO (gas).

SnO₂(solid tin dioxide) typically floats on the tin surface and moves to the near-exit of the tin can, causing the glass floor to scratch or adhere to the glass floor.

SnO (gaseous tin oxide) comes from the tin bath and enters the atmosphere. Once it rises to the top of the furnace space (relatively low temperature away from the tin bath) near the top region of the furnace, 2SnO->Sn+SnO₂Reaction, products Sn and SnO₂And dropping to the tin bath. SnO₂The Sn is also reduced by the hydrogen in the atmosphere, and the Sn is also generated and falls to the tin bath.

In view of the foregoing, the tin bath in a flat/float glass facility uses nitrogen (N) multiple times₂) And hydrogen (H)₂) To reduce oxidation of the tin and thereby reduce defects on the finished glass. An atmosphere monitoring system is implemented herein for use with a tin bath. By continuously collecting data from various installed sensors, the system can monitor and control H entering the furnace₂/N₂Mixture, current atmosphere composition in a furnace, direction of flow of atmosphere in a tin bath furnace, and rowAnd (4) discharging the purge gas.

H can be measured and controlled by using various methods₂/N₂Mixture composition, containing thermal conductivity or molecular weight (calculated by standard methods such as gas chromatography or by measuring density, pressure and temperature, then using the accepted equation of state for gases).

A similar method can be used to measure the tin bath atmosphere gas composition, and additional parameters can be used to measure parameters such as dew point or water concentration, O₂Concentration, H₂S or other sulfur compounds, tin bath metal and/or glass melting temperature, tin redox state, and/or other parameters. The temperature and pressure sensors are installed at different locations to obtain a better tin bath furnace atmosphere flow pattern, which helps to further reduce the oxygen level in the tin bath furnace, mainly by removing oxygen from the hot end. All of these parameters can be used to verify that the tin bath atmosphere is operating at optimum conditions and to determine the optimum operation of the tin bath atmosphere control system by correlating the atmosphere conditions with the defectivity of the finished glass.

In the vent position, measurements similar to the tin bath atmosphere can be taken, except that methods are used to verify the outward flow of gases to reduce the likelihood of air entering through any vents. The flow of gas can be verified by using standard accepted flow methods or pressure or temperature differentials, where higher upstream pressures or temperatures indicate gas flow outward from the tin bath atmosphere.

Due to the number of gas sampling ports available and/or the limitations of the various points at which oxygen leakage may occur, oxygen leakage may not be detected or prevented by the tin bath atmosphere measurement alone, and thus tin metal oxidation may not be detected or prevented. One remedy to this is to use a Tunable Diode Laser (TDL) that spans the length and/or width of the tin bath atmosphere and provides a line average of the concentration along the beam path. The use of multiple lasers allows spatial resolution of the atmospheric conditions and thus spatial control of the gas flow. In addition, it would be advantageous to include a tin redox sensor to monitor the dissolved oxygen content in the tin metal bath and adjust the tin bath atmosphere flow, composition, and/or required exhaust gases during operation to minimize tin metal oxidation.

The temperature of the glass entering the tin bath may also be a parameter that can be used to optimize the tin bath exhaust or tin bath gas inlet flow. For example, the glass temperature is related to the solubility of the tin bath atmosphere constituents and/or dissolved gas constituents (such as oxygen, water vapor, and/or sulfur species) in the glass melt itself, and thus the temperature also affects tin bath operation and glass defect rates. The temperature of the glass entering the tin bath cannot be controlled within the tin bath itself and must be controlled in the upstream glass melting furnace and/or refining zone. Thus, the optimum conditions for operation of the tin bath may be in conjunction with upstream processes throughout the glass melting process.

Various configurations are shown in fig. 1-4. For the sake of clarity not all possible configurations or measuring positions are shown, but by combining the options shown different configurations as part of the invention may be put together. For example, differential pressure (dP) and differential temperature (dT) measurements are shown at only one exhaust stream, but one or both may be placed at all exhaust streams to gather the required information. Further, if "measure" is shown in the figure, it may be a measure of some of all of the aforementioned options. Other measurement points may also be used as required by the operation.

Fig. 1 shows an embodiment that combines several features, which can be applied separately or together. The tin bath furnace has a direction of glass flow. One or more measurement locations on the furnace may be used to determine density, one or more gas concentrations, dew point, or other relevant parameters. At least one gas stream inlet provides a flow of a mixture of hydrogen and nitrogen into the furnace. Each intake gas flow may contain a measurement location to determine density, one or more gas concentrations, dew point, or other relevant parameters. At least one exhaust stream allows exhaust gas to exit the furnace. Each exhaust stream may contain a measurement location to determine density, one or more gas concentrations, dew point, or other relevant parameters.

Differential pressure and/or differential temperature measurements may be taken at various points. Such measurements of exhaust flow may indicate flow direction and flow rate. Such measurements between the furnace and the exhaust stream or between two furnace locations may similarly indicate flow direction and/or flow rate.

Fig. 2 shows an embodiment that also incorporates several features, which can be applied separately or together. FIG. 2 differs from FIG. 1 in that a common header supplies the intake air flow, thereby reducing the number of necessary measurement points.

Fig. 3 shows an embodiment that also incorporates several features, which can be applied separately or together. Figure 3 differs from figure 2 in that a recycle stream is added. An unpurified recycle stream is withdrawn from the furnace, cleaned to convert to a purified recycle stream, and then recycled back to the intake manifold. The measured positions in the raw cycle gas and the purified cycle gas can be used to assess whether the intake air flow should be increased or decreased.

Fig. 4 shows an embodiment that also incorporates several features, which can be applied separately or together. FIG. 4 differs from FIG. 3 in that flow control of at least one of the intake air flows is added. The intake air flow rate may be controlled based on any of the aforementioned measurements.

Combining the collected information with defect data requires consideration of the time lag between atmospheric conditions (including input, exhaust, and cycling conditions) and the defect steps and observation of the defects. This can be done using standard accepted analytical methods.

Once the correlation between the measured conditions and the defects is better understood, which can be used for control purposes, it is recognized that the optimal conditions can be a function of the following items: glass composition, tin bath condition and purity, furnace heat loss due to aging and other conditions, ambient atmospheric conditions including temperature, pressure and humidity, N₂And H₂The purity of the tin bath, the gas injection temperature, and the conditions of the heating element and the temperature difference in the tin bath atmosphere.

Experiments were conducted to measure various parameters on a running tin bath furnace to better understand the correlation between these parameters and defects in the glass, and to determine which parameters can be controlled in order to potentially reduce the occurrence of such defects.

Fig. 5 shows measurements during operation of the oxygen potential in the tin bath (oxygen concentration in ppm), the dew point of the atmosphere at a uniform location above the tin bath and the oxygen concentration in the atmosphere above the tin bath at the same location. It is noted that the oxygen potential in the tin bath is difficult to measure and that the sensor does not last for a long time during the measurement, so that it is necessary to find another parameter that is easier to measure to represent the oxygen potential. In this case, it can be seen that the dew point of the atmosphere above the tin bath has a fairly good correlation with the oxygen potential in the tin bath and is easier to measure consistently over a long period of time. Thus, the dew point may be used alone or in combination with one or more other parameters (discussed below) to control defects in the glass. In contrast, the oxygen concentration in the atmosphere above the tin bath does not appear to correlate particularly well with the oxygen potential in the tin bath.

Fig. 6 shows a direct positive correlation between dew point measured in an atmosphere above tin and defects in the glass. In particular, defects decrease when the dew point decreases, and increase when the dew point increases. Furthermore, when the dew point is stable, the defect also remains stable. One way to control the dew point to produce low levels of defects is to increase the flow rate of the purge gas to reduce the dew point.

Figure 7 shows that there is also a direct positive correlation between line speed (i.e. the linear rate of float glass production through the system) and defects. In particular, faster line speeds appear to cause more defects, while an increase in line speed results in an increase in defects. Thus, maintaining a constant and possibly relatively low line speed may cause a lower defect level. Note that linear velocity may also be inversely proportional to bandwidth (discussed below).

Figure 8 shows that there is a direct positive correlation between the bandwidth (and the dew point in the atmosphere above the tin bath and the oxygen concentration in the tin bath) and the glass defect. More specifically, a significant reduction in glass defects was observed as a function of bandwidth. In the center of the graph, as the dew point and oxygen concentration in the tin bath decrease, the bandwidth decreases and the defects also decrease dramatically. But even with increasing bandwidth (with increasing dew point and oxygen concentration in the tin bath), the defects are still low. It is believed that the periodic variation in bandwidth may be beneficial in reducing glass defects. This may be due to the periodic reduction in glass coverage of the tin bath, allowing the tin bath oxygen level to be regenerated.

FIG. 9 shows the ratio of hydrogen to dew point (water vapor content) in the atmosphere above the tin bath (i.e., H₂/H₂O ratio) leads to higher defects and vice versa. Thus, maintaining a relatively high H₂/H₂The O ratio helps to keep defects at a low level. Further, control H₂/H₂The O ratio, in combination with controlling the dew point, can be an effective method of controlling glass defects.

In the vicinity of the tin bath and the hot-end glass surface, H₂/H₂O ratio control oxygen conversion to steam (i.e., 2H)₂+O₂->2H₂O) which helps to carry oxygen out of the tin bath and hot end glass. In the vicinity of the furnace roof, H₂/H₂The O ratio controls the reaction rate of tin reduction (i.e., SnO₂+H₂->Tin + H₂O), which will solidify SnO₂Reduction to liquid Sn increases the likelihood of top surface defects in the glass article. In float glass production, which aims to reduce glass defects, it is necessary to convert oxygen to water vapour in the lower region near the tin bath and near the hot end glass surface, but there is no need to reduce tin in the upper region near the roof. Thus, in both zones, it may be desirable to maintain different H by separately and precisely adjusting the process gas flow into and/or out of the furnace (where the process gas flow comprises one or both of nitrogen and hydrogen) of each zone₂/H₂The O ratio.

Furthermore, it should be understood that when measuring the density of the atmosphere in the tin bath furnace, the density corresponds to the gas composition, which may not only take into account the concentrations of hydrogen and nitrogen. In particular, an increase in the measured gas density may indicate a leakage of oxygen into the furnace. In such a case, defects in the glass can be reduced by increasing the density in response to changes in the process gases flowing into or out of the furnace. In particular, the concentration of hydrogen in the furnace is increased, for example, by removing some excess oxygen due to an indicated leak, to increase the flow of hydrogen into the furnace, thereby reducing glass defects.

While the principles of the invention have been described above in connection with preferred embodiments, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the invention.