Title of Invention

"METHOD FOR THE MANUFACTURE OF GLASS BATCHES OF DIFFERENT DENSITIES IN A CONTINUOUS SEQUENTIAL RUN"

Abstract

The present invention provides a method for the manufacture of glasses of different densities sequentially and continuously without requiring stoppage of the manufacturing plant. The method comprises creating convection current in the glass tank by maintaining a predetermined designated temperature profile in the tank and monitoring the changeover progress on the basis of a predetermined changeover assumption. The first charge is replaced by sequentially fed one or more further charges.

Full Text

METHOD FOR THE MANUFACTURE OF GLASS BATCHES OF DIFFERENT DENSITIES IN A CONTINUOUS SEQUENTIAL RUN Field of the invention The present invention relates to a method for the manufacture of glass batches of different densities in a continuous and sequential run. The present invention particularly relates to a method for the manufacture of glass batches continuously from low density glasses to high density glasses without requiring shutdown of the manufacturing plant. Background of the invention Different applications require glass batches of different densities. For example for the manufacture of black and white cathode ray or cathode display tubes, low density glasses based predominantly on barium glasses are used whereas for the manufacture of colour cathode ray or display tubes and funnels high density lead based glasses are used. High barium glasses are useful in the manufacturing of front panel glass for black and white cathode ray tubes and high lead glasses with high X-ray absorption with high operation potentials up to 30kV, in particular for color funnel in television and monitor tubes. Hitherto known processes for the manufacture of different density glasses required different sets of apparatuses including different furnaces and feed inputs and product outlets. While in developed countries, such manufacture is easily segregated, the manufacture of different density glasses in the same plant has posed a problem in developing countries due to the high cost factor and disadvantages involved. As explained above, one method of achieving production of glasses of different density is to segregate the respective manufacturing operations. While this solves the problem vis a vis manufacture of glasses for black and white and colour applications, the problem of manufacturing glasses with slightly varying densities in the same category viz. black and white or colour remains. It has been known to manufacture glasses of different densities in the same unit. However, the procedure adopted in the art is cumbersome and results in both tremendous loss of material as well as in wear and tear of the apparatus used. Generally, the method adopted in order to replace one glass run with another is to shut down the machinery, clean out the furnace and the tanks and input and output ports, and then load the fresh glass batch therein. This involves several disadvantages: 1. The manufacture of glass is done at high temperatures of ~1600°C. Shutting down and restarting the system results in tremendous thermal shock to the system with consequent wear and tear to the system. Evidently, the maintenance and repair costs involved also are high. 2. The shutting down and restarting of the plant also requires the use of a large amount of fuel during the restart in order to bring the tank temperature to operational levels where the ingredients of the charge are melted and admixed. Again, the costs involved in the consumption of fuel render this method not very feasible commercially, since the final costs are added to the product. 3. The removal of the prior glass batch results in a loss of large amounts of material and also involves the expenditure in terms of labour and machinery. Normally, when a changeover is required between two glass of different composition having a density difference more than O.lgm/cc, it is done by drain and fill method explained above. The existing glass in the tank is drained out and new glass is filled in. During this process there is immense shock to the tank refractories. This complete process takes approximately 12 to 15 days and is also very unsafe and hazardous since it involves the draining of hot glass at more than 1000°C. The drain and fill method can be done only once or twice in a life since doing it regularly would mean giving immense shock to furnace structure, thereby weakening it and increasing the potential for its collapse at any time. It is therefore important to devise a system for the manufacture of glasses of different densities wherein glasses of different densities can be produced while overcoming or minimizing the problems identified above. Objects of the invention It is therefore an object of the invention to provide a method for the manufacture of glasses of varying densities which overcomes the problems associated with the prior art. It is another object of the invention to provide a method for the manufacture of glasses of different densities in a continuous sequential manner without requiring the shutdown of the glass manufacturing system. It is a further object of the invention to provide a method for the manufacture of the glasses of different densities whereby the losses of material are minimized during the changeover. It is another object of the invention to provide a safe method for the changeover during glass manufacture, which is also not expensive. Summary of the invention The above objects are achieved by the method of the present invention wherein a changeover in short time is achieved without requiring shutdown of the apparatus and with minimal loss of material. Accordingly the present invention provides a method for the manufacture of glasses of different densities continuously and sequentially, comprising feeding a first glass charge of a particular density into a glass tank and operating the tank at predetermined temperature levels according to conventional methods to obtain glass of the required density, providing one or more further glass charges of different densities sequentially as required and creating a convection current in the glass tank by maintaining a predetermined designated temperature profile in the tank and monitoring the changeover progress on the basis of a predetermined changeover assumption, in order to ensure that the first charge is replaced by sequentially fed one or more further charges. In one embodiment of the invention, the first glass charge if of a lower density than the one or more further glass charge. In another embodiment of the invention, the glass tank is equipped with a plurality of firing ports. In another embodiment of the invention, wherein said glass tank is fired by said plurality of ports comprising either Eiger end ports or Cross ports. In another embodiment of the iavention, the convection current is created in the glass tank by selecting burners of the said firing ports according to predetermined temperature profile requirements. In another embodiment of the invention, the said plurality of ports comprise of at least four ports. In a further embodiment of the invention, the said at least four ports are maintained at temperatures in the range of First port (up to 1/4th of tank) = 1400 - 1600°C Second port (up to 1 /2th of tank) = 1500 - 1600°C Third port (up to 3/4 of tank) = 1400 - 1550°C Fourth port (remaining of tank) = 1400 - 1500°C Other port = 1400 - 1500°C In another embodiment of the invention, the changeover assumptions used to ensure speedy changeover from one glass charge to the other glass charge comprise 0.5 turnover = 15 to 40% 1 turnover = 25 to 70% 2 turnover = 70 to 90% 3 turnover = 90 to 100% In another embodiment of the invention, the same glass tank is utilized for making low density glass and high density glass. In another embodiment of the invention, the total time of changeover is less than 10 days from one composition to another composition. In another embodiment of the invention, the total range of transmittance change is 1 to 94%. Brief description of the accompanying drawings The figure accompanring this specification is a schematic representation of a glass tank used in the method of the invention. Detailed description of the invention The method of the invention comprises feeding a first glass charge of a particular density into a glass tank and operating the tank at predetermined temperature levels according to conventional methods to obtain glass of the required density. One or more further glass charges of different densities can be fed sequentially as required. In order to ensure that the run is continuous and sequential, a convection current is created in the glass tank by maintaining a predetermined designated temperature profile in the tank and monitoring the changeover progress on the basis of a predetermined changeover assumption. The first charge is replaced by sequentially fed one or more further charges. Preferably, the first glass charge if of a lower density than the one or more further glass charge. The glass tank used is equipped with a plurality of firing ports, whether Eiger end ports or Cross ports. The convection current is created in the glass tank by selecting burners of the said firing ports according to predetermined temperature profile requirements. While the number of ports depend on the size of the tank, below is a description of a preferred feature where at least four ports are used. The changeover assumptions and preferred operational temperatures of each port are also given below. First port (up to 1 /4th of tank) = 1400 - 1600°C Second port (up to 1 /2th of tank) = 1500 - 1600°C Third port (up to 3/4 of tank) = 1400 - 1550°C Fourth port (remaining of tank) = 1400 - 1500°C Other port = 1400 - 1500°C Changeover assumption 0.5 turnover = 15 to 40% 1 turnover = 25 to 70% 2 turnover = 70 to 90% 3 turnover = 90 to 100% As a result of the method of the invention, the same glass tank can utilized for making low density glass and high density glass. The total time of changeover is less than 10 days from one composition to another composition. The total range of transmittance change is 1 to 94%. The changeover method of the invention comprises an 'on the fly" which does not require a drain of the existing glass and refilling by the new glass. The invention will now be described with reference to the schematic drawing accompanying this disclosure. In the figure, the glass feeds are input into the glass tank (1) by means of one or more inlets (2, 2'). The temperature profile in the tank (1) is controlled by means of a plurality of firing ports (3, 3') provided on opposite sides of the tank (1). The temperature of the glass tank (1) is increased or decreased as desired during operation through the firing ports (3,3*) which are supplied with respective temperature generation source (4) which in turn are supplied with burners (not shown herein). The temperature profile created within the glass tank due to the action of the firing ports operating at different temperatures creates a convection current (5) which results in the minimising the mixing of the different glass batches fed in through the inlets (2,2*). The desired glass is output through one or more outiets (6, 6*) after passing through a refiner (7) for removal of manufacturing defects such as bubbles and the like in the glass batch so formed. It is observed that due to the maintenance of a specific temperature profile in the glass tank, the glass of different batches do not mix when used in the form of cullets. The changeover method of the present invention will now be described with reference to the following examples which are illustrative and should not be construed as limiting the scope of the invention in any manner. Example 1 a. A colour funnel cuUet was put in a crucible. The crucible was heated up to 1000°C, and the cullet held for 1 hour. b. After one hour a black and white television cullet was added iato the crucible having the colour funnel glass and the temperature raised to 1100°C. It was then held for 1 hour. c. After another hour, another colour funnel cullet was added to the crucible having black and white TV glass and held for 2 hours. Result: The colour funnel glass settled at the bottom, with the black and white television glass forming a separate layer on the top at the end of step (b). However, when the second colour funnel glass was fed on the black and white television glass, the colour funnel glass passed through to the bottom and mixed with the lower first colour funnel glass. Thus, separate layer of black and white and color funnel glass were formed. Conclusion: In the cullet form, the stirring and mixing of color funnel glass in black and white glass does not take place even at high temperature inside the furnace. Example 2 a. Colour funnel cullet was put in a crucible and was melted in the crucible at 1000°C and held for one hour. b. Black and white television cullet was added into the crucible at 1000°C having colour funnel glass. The temperature of the crucible was raised up to 1100°C and was held for 2 hours. c. After slow cool down the glass was taken out. Result: Colour funnel glass settled at the bottom and the black and white television glass floated on top. There was no mixing in both the glass compositions at all. Conclusion: In the cullet from, mixing of black and white glass and color funnel glass also does not take place at a high temperature inside the furnace. Example 3 a. Black and white television cullet was put in a crucible and was melted in crucible at 1000°C and held for 1 hour. b. Colour funnel cullet was added into the crucible having black and white television glass at 1000°C and the temperature raised up to 1100°C and held for 2 hours. Result: Colour funnel glass settled into the bottom and the black and white television glass floated on the top. The glasses changed their places and formed separate layers without any mixing. Conclusion: Colour funnel glass cullet and black and white glass cullet will not mix even at such a high temperature. Example 4 a. Black and white TV cullet and colour funnel cullet were thoroughly mixed and put in a crucible. Temperature was raised up to 1100°C from room temperature and was held for 3 hours. b. The glass was cooled and taken out and inspected. Result: Colour funnel glass settled into the bottom, black and white TV glass floated on the top. They have change their occupied place without any mixing in both the glass compositions and made separate layers. Conclusion: Colour funnel glass and black and white has a very strong separation tendency if used in cullet form. Example 5 a. Black and white TV batch with 35% cullet was put in a crucible and was melted in crucible at 1000°C and held for 1 hour. b. Colour funnel batch with 35% cullet was added into he crucible having black and white TV glass at 1000°C. The temperature of the crucible was raised up to 1100°C and was held for 2 hours. Result: Partial mixing took place between color funnel and black and white glass with lower one more towards color funnel glass and higher side towards black and white glass. Conclusion: In the batch form, it is possible to mix the color funnel and black and white glass at high temperature. Example 6 a. Black and white TV batch with 35% cuUet was put in a crucible and was melted in crucible at 1000°C and held for 1 hour. b. Colour funnel batch with 35% cullet was added into the crucible having black and white TV glass at 1000°C. The temperature of the crucible was raised up to 1100°C and was held for 2 Hrs. c. It was stirred with a rod at 1100°C for 30 seconds and was held for another 2 hours. Result: There was complete mixing of the color funnel and black and white glass. A uniform new glass was obtained of intermediate composition. Conclusion: It is totally possible to mix the color funnel and black and white glass inside a tank at high temperature if some amount of convection current is generated inside the furnace. Summary of the Conclusion of the Experiments Colour funnel glass in cullet form will not mix with black and white TV glass composition during glass changeovers for black and white TV to colour funnel and vice versa. During glass conversion from black and white TV to colour funnel glass, colour funnel glass in cullet form will settle into the bottom and black and white glass will remain at the top. In the batch form, there it is possible to mix the color funnel and black and white glass at high temperature in the furnace. It is possible to mix the color funnel and black and white glass inside a tank at high temperature if some amount of convection current is generated inside the furnace. Example 7 Changeover method of the invention was conducted in a glass tank from black and white glass to colour glass using the parameters given in Table I below. The results of the changeover method are also given in Table I. It is seen that the time frame required for complete changeover was less than 10 days. (Table Removed) Table II below provides specimen compositions of low density glasses and Table III gives a specimen range of high density glasses that can be used in the method of the invention. However, it must be clearly understood that the method of the invention is independent of the composition of the glass and is generally applicable across a range of glass compositions. Table II Low density glass specimen Table Removed) Table III High Density glass Table Removed) The object of the present invention to provide a changeover method in a continuous glass tank furnace. This changeover is predominantly applicable for a changeover from a low density glass to high density glass whereby the above mentioned method the problems of drain and refill and risk of refractory cracking in the tank refractories is drastically reduced. WE CLAIMS We claim: 1. A method for the manufacture of glass batches of different densities in a continuous sequential run, comprising feeding a first glass charge of a predetermined density into a glass tank provided with a plurality of firing ports, running the tank at predetermined temperature levels to obtain a glass of the required density, feeding one or more further charges of glasses of different densities sequentially and continuously, creating a convection current in the glass tank by maintaining a predetermined temperature profile therein and monitoring the changeover progress on the basis of a predetermined changeover assumption to ensure that the first glass charge is replaced by the immediately following further glass charge and the further glass charge is replaced by the immediately following further charge, to obtain glass batches of different densities in a sequential and continuous manner. 2. A method as claimed in claim 1 wherein the first glass charge is of a lower density than the immediately following further glass charge. 3. A method as claimed in claim 1 wherein the plurality of ports comprise either Eiger end ports or Cross ports. 4. A method as claimed in any preceding claim wherein the convection current is created in the glass tank by creating differential temperature profiles at the ports using burners dependent on predetermined temperature profile requirements. 5. A method as claimed in any preceding claim wherein the plurality of ports comprise at least four ports, said ports being maintained at temperatures in the range of First port (up to 1/4 of tank) = 1400 - 1600°C Second port (up to 112 of the tank) = 1500-1600°C Third port (up to 3/4 of the tank) = 1400 - 1550°C Fourth port (remainder of tank) = 1400 - 1500°C 6. A method as claimed in claim 5 wherein additional ports are provided maintained at a temperature in the range of 1400 - 1500°C. 7. A method as claimed in claim 5 or 6 wherein the changeover assumption used to ensure speedy changeover from one glass charge to the other glass charge comprise 0.5 turnover = 15 to 40% 1 turnover = 25 - 70% 2 turnover = 70 - 90% 3 turnover = 90-100% 8. A method as claimed in any preceding claim wherein the same glass tank is utilized to make both low density glass and high density glass. 9. A method as claimed in any preceding claim wherein the total time of changeover is less than ten days from one glass composition to another glass composition. 10. A method for the manufacture of glass batches of different densities in a continuous sequential run substantially as described hereinbefore and with reference to the accompanying examples and as illustrated in the accompanying drawings.

Documents:

117-del-2002-abstract.pdf

117-del-2002-claims.pdf

117-del-2002-complete specification (granted).pdf

117-del-2002-correspondence-others.pdf

117-del-2002-correspondence-po.pdf

117-del-2002-description (complete).pdf

117-del-2002-drawings.pdf

117-DEL-2002-Form-1 (27-12-2007).pdf

117-del-2002-form-1.pdf

117-del-2002-form-19.pdf

117-del-2002-form-2.pdf

117-del-2002-form-3.pdf

117-del-2002-gpa.pdf