The invention relates to the bath of molten metal, generally of tin, that is found in a production line for the continuous production of flat glass (float glass). This equipment placed between the furnace and the annealing lehr makes it possible to form the glass ribbon having the desired thickness and the desired width on a bath of molten metal, in particular of tin.
The invention provides a solution for supporting the crown of a bath of molten metal, generally of tin, on a flat glass production line, which reduces or eliminates the risk of leakages appearing between the inside of the bath and the outside, leakages caused by different displacements between the roof and the bottom casing.
Indeed, any appearance of oxygen in the chamber of the tin bath, normally filled with a controlled gas atmosphere, mainly nitrogen with a certain proportion of hydrogen, is capable of creating oxides, especially tin oxides, which themselves participate in processes for generating defects on the glass sheet. To avoid this phenomenon, airtightness between the various parts constituting the chamber of the tin bath is achieved by what a person skilled in the art refers to as sealing, which is a joint created between two neighboring components. The contiguous surfaces produce a V-shaped notch filled by a special mortar that sets by drying, with or without the addition of ceramic fibers.
This sealing is deliberately fragile in order to allow the rapid dismantling of the airtight components, thanks to the breaking of the layer of mortar, for maintenance intervention purposes. This sealing must be reviewed frequently following the appearance of cracks which are due to differentiated movements between the tank containing the tin bath and the roof.
In a more detailed manner,
On each section of the roof 6 of the tin bath, a set of 4 or 6 hangers 14 ensures the suspension of the crown during each phase of its life cycle: cold assembly, during the heating up of the bath, throughout the operating period of the bath and during the total or partial maintenance phases.
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However, the most inconvenient phenomenon is linked to the temperature differences on the one hand of the metal portion 8 containing the refractory tank 9 of the bath itself, and on the other hand of the metal structure 13 from which the roof is suspended. These temperature differences may lead to differential expansions, which are even greater since the expansion of the tank 5 along the axis of the process is guided and directed, whereas the expansion of the roof 6 takes place freely in all the directions of the horizontal plane.
Since the sealing 19 is produced based on a relatively fragile refractory mortar and fibber, the slightest variation in the geometry of the joint is capable of creating cracks and therefore an inlet of outside air that may give rise to the oxidation of the bath and thus create potential defects in the product. It is therefore sometimes necessary to act on the hangers in such a way that the movements due to the expansion of the roof in all directions are compensated. This operation is tricky and comprises the risk of lowering the roof 6 too far and ending up blocking the side casings, which may make difficult or prevent their removal during urgent operations, for the recovery of the ribbon in the event of rupture of the ribbon in the bath for example. The operation for adjusting the height of the roof is therefore complicated and requires sufficient personnel since the adjustment must take place simultaneously on the various tie rods.
During the heating up of the bath, it is understood that the difference in expansion of the metal support structures 8 and of the metal portion of the roof of the bath 4 will lead to a misalignment of the hangers, the position of which will move away from the vertical position, which will create a shearing effect on the joint in the horizontal plane and move the roof 4 away from its initial vertical position as preset at the start-up of the plant. This vertical movement of the crown 4 or its horizontal movement or any combination of these two movements may create a shearing or a local deterioration of the joint 19, which creates leakages between the atmosphere of the bath and the outside of the float bath. These leakages may lead to an oxidation of the tin bath and the appearance of quality defects on the glass.
It is therefore necessary to install a device for supporting the roof 6 that ensures its precise positioning relative to the tank 1 and that avoids displacements of the roof in the vertical and horizontal directions in order to ensure the airtightness thereof in order to eliminate the risk of the appearance of leakages, including during changes in thermal regimes of the bath that modify the expansion of the various portions of the roof support, in particular the steel frame that overhangs the roof and all of the hangers.
The invention consists firstly of a roof resting on sliding or rolling supports that guide and direct the thermal expansions of the whole of the roof along the direction of the process, and comprising a “fixed point” in the vicinity of the perpendicular to the fixed point of the tank.
The invention also consists of a process for controlling the thermal expansions of the bath casing and of the roof, so as to eliminate or reduce the differences in expansions of the two assemblies, and therefore to eliminate or reduce the stresses on the sealing.
According to the invention, a tin bath of a production line for producing float glass comprising a roof covering a tank in which liquid tin is found, is characterized in which the roof concerns by a “fixed point” in the vicinity of the perpendicular axis to the “fixed point” of the tank.
More specifically, according to the invention, a bath of molten metal, in particular of tin, of a production line for producing float glass comprises a chamber formed of three main constituents, a bath tank, in which liquid metal, in particular tin, is found, a roof overhanging it, and side-sealing casings, creating the join between the two preceding components, the bath tank consisting of a metal casing, packed with refractory material, that may be moved on a frame along the axis of the process, with the exception of fixed supports, referred to as “fixed points”, formed by a zone for rigidly connecting the casing to the steel frame, and is characterized in that the crown rests on sliding or rolling supports that guide and direct the thermal expansions of the whole of the crown along the direction of the process, and comprises a “fixed point” in the vicinity of the perpendicular axis to the “fixed point” of the tank.
The axis, or the direction, of the process are synonymous with the axis, or the direction, of feed motion of the glass ribbon.
The invention relates to a solution to the differential expansions of two main metal structures, of the tank and of the roof, in the form of casings. The expansions of refractory materials contained inside these casings are treated by hangers for the crown refractory materials and by a dowel assembly with expansion joints for the bottom, or tank, refractory materials.
Advantageously, the roof consists of a self-supporting structure which rests directly, on each side of the tank, on a support frame, by means of a limited and suitable number of sliding or rolling supports.
The self-supporting structure of the roof does not create shear stresses on the lateral structure, consisting of the support frame, which only takes up vertical stresses.
The displacement of the roof which results from its expansion may be guided by a guiding system integrated into the supports. As a variant, the displacement of the roof which results from its expansion may be guided by a guiding system external to the supports.
The roof “fixed point” may consist of a zone for rigidly connecting the crown to a frame, which is firmly attached to the frame that supports the tank.
Advantageously, the transformers for powering the electrical heaters for heating the crown rest directly on the self-supporting structure of the roof.
The metal bath, in particular tin bath, of a production line for producing float glass may comprise a gantry crane that enables the rapid assembly and dismantling of sections of the roof, and also the handling operations for the assembly and repair of equipment of the metal bath.
The invention also relates to a process that makes it possible to limit the differential expansions between a tank and a roof of a bath of molten metal, in particular of tin, of a production line for producing float glass, so as to prevent the degradation of the sealing joints between the tank and the roof that may give rise to gas leakages between the atmosphere of the bath and the outside of the tank, which process is characterized in that it consists in monitoring the longitudinal differential expansion between the roof and the tank by a continuous measurement thereof and in adjusting the cooling of the tank so as to keep the longitudinal differential expansion within defined limits.
More specifically, according to the invention, the process that makes it possible to limit the differential expansions between a tank and a roof of a bath of molten metal, in particular of tin, of a production line for producing float glass, when side-sealing casings create the join between the two preceding components, the bath tank consisting of a metal casing, packed with refractory material, that may be moved on a frame along the axis of the process, with the exception of fixed supports, referred to as “fixed points”, formed by a zone for rigidly connecting the casing to the frame, the crown resting on sliding or rolling supports that guide and direct the thermal expansions of the whole of the crown along the direction of the process, and comprising a “fixed point” in the vicinity of the perpendicular axis to the “fixed point” of the tank, which process is characterized in that it consists in monitoring the longitudinal differential expansion between the roof and the tank by a continuous measurement thereof and in adjusting the cooling of the tank so as to keep the longitudinal differential expansion within defined limits, so as to prevent the degradation of the sealing joints between the tank and the roof that may give rise to gas leakages between the atmosphere of the bath and the outside of the tank.
The measurement of the longitudinal differential expansion between the roof and the tank may be carried out by means of expansion sensors.
Advantageously, the longitudinal differential expansion is maintained at less than ±0.05 mm/m.
The invention consists, apart from the arrangements set out above, of a certain number of other arrangements, which will be mentioned more explicitly below with reference to
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During different production regimes, different temperature regimes exist in the roof and the bath, the respective temperatures of their metal structures may be different and may give rise to a different expansion of each assembly, which is a source of stresses and, ultimately, cracks in the sealing. In order to prevent any differential horizontal displacement between tank and roof, it is possible to act on the tank temperature by continuously adapting the forced cooling thereof, so as to maintain the longitudinal differential expansion of the metal structure of the tank of the bath relative to that of the roof, within a strict tolerance. In order to drive the forced cooling and regulate the differential expansions, an automatism may monitor not only temperatures, but also, by means of expansion sensors, the displacements both of the tank and of the roof. As may be observed, this control method cannot be carried out with a hangers suspension system according to the prior art.
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The elimination of the upper frame 15 and of the hangers 14 also enables the use of equipment handling means such as an integrated mobile crane 30 or the use, without risk of interference, of an overhead travelling crane integrated into the building. The integrated mobile crane 30 may be used for positioning the roof sections and also for the installation of the transformers 27. Since this crane is permanent, it may also be used during cold repair operations or in case of a serious incident regarding the bath (hot repair operations).
The invention allows, during the initial assembly, a complete assembly of the frame of the bath without however disturbing the installation of the roof subsequently. The elimination, according to the invention, of the portion of the metal structure used for suspending the roof by the hangers, makes it possible to reduce the necessary height of the building. The installation of walkways allows access to the equipment for controlling and operating the bath.
Number | Date | Country | Kind |
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2013/0669 | Oct 2013 | BE | national |
Filing Document | Filing Date | Country | Kind |
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PCT/EP2014/071352 | 10/6/2014 | WO | 00 |