WO2012093184A1

WO2012093184A1 - Method and unit for the production of thin glass sheets

Info

Publication number: WO2012093184A1
Application number: PCT/ES2011/070006
Authority: WO
Inventors: Luis Grijalba Goicoechea
Original assignee: Luis Grijalba Goicoechea
Priority date: 2011-01-07
Filing date: 2011-01-07
Publication date: 2012-07-12
Also published as: TW201233644A

Abstract

The invention relates to a method and the corresponding unit for the production of thin glass sheets. The method comprises the following steps: a) melting (21) and refining (23) of glass obtained from vitrifiable materials; b) distributing and dosing molten glass in a planar stream (38) using a dosing unit comprising glass-driving means (27) with rotary devices (29) and an overflow; c) shaping the molten glass into a solid glass sheet, including modifying one of the surfaces thereof using a cleaning element (41), cooling in a forming body (42) and final drawing (51); and d) dividing into an end product. The end thin glass sheet (50) can be formed by a single piece of glass or by two different pieces of glass, each occupying half of the thickness of the sheet.

Description

PROCEDURE AND INSTALLATION FOR THE MANUFACTURE OF THIN GLASS SHEETS

SECTOR OF THE TECHNIQUE

The present invention fits within the glass industry and has application on the thin flat glass usable in the TFT-LCD screens, and in the field of electronics.

STATE OF THE PREVIOUS TECHNIQUE

Currently, the manufacture of thin sheets of thin glass used in TFT-LCD screens and in the field of electronics, is mainly done through the "float" procedure, or through the downward stretching procedure "downdraw overflow" "

The process for manufacturing glass sheets known as the "float method" (US 3266880, US 3771985, EP 1739062, and US 2008/0223079) uses a molten tin bath on which the glass floats at the same time as it is cooled and Stretched to form a solid sheet of glass.

In the "float" method, each of the two surfaces of the molten glass is in different media: a) the lower one in molten tin; and b) the upper one in the atmosphere of the tin bath. This fact causes different heat exchanges to be generated through each of the two surfaces of the glass during cooling. On the other hand, there is a contamination of the surfaces of the glass sheet due to the diffusion of the chemical components coming from the bath of molten tin. These drawbacks require a subsequent polishing process that leads to a quality of the surface of the thin sheet of glass inferior to the quality of the one obtained by the "overflow downdraw" method.

The "overflow downdraw" method (US 3338696; US 3682609; WO 2005/121 182) is based on a main conformation apparatus, called "isopipe", which performs at the same time the functions of: a) static distribution of a flow of glass in two flat streams of molten glass; b) cooling of the glass; and c) joining or melting the two said currents of molten glass to form a single stream of glass capable of being stretched. In FIGURE 1, a shaped body or "isopipe" (11) is shown; the molten glass, coming from an oven, enters the area (12) communicating with the throat (13) carved in the upper area of the forming body (11); this forming body has two side walls (14) through whose upper edges (15) the molten glass overflows. The glass advances through the throat (13) and overflows by its edges (15) while decreasing its cross section with a flow rate per unit length that must be constant. Then, the molten glass flows in two streams (16) on the outside of the two side walls of the forming body (11) at the same time it is cooled, until it reaches its lower vertex (17) where the two currents meet to form a single sheet of molten glass (18), which is stretched to a solid state. The two surfaces that form the sheet come from inside the mass of molten glass that has flowed down the throat and overflowed over its side walls without having contacted solid surfaces. The patent (US 3338696) still represents the state of the art practiced today; however, the "overflow downdraw" process has some limitations, as indicated in the patent (US 7155935).

A first drawback of the method "overflow downdraw" is the variation of the thickness of the glass sheet because of the complex distribution of the flow of liquid glass that overflows by the two laterals of the throat of the body of formed or "isopipe"; This distribution is sensitive to phenomena inherent to the process, such as: a) the variation of the temperature distribution of the molten glass at the entrance of the "isopipe", since each point of the entrance section follows its own trajectory down the throat and always goes to the same place of the formed sheet; b) the variation of the glass flow rate from the melting furnace, since the glass flow overflowing the two sides of the "isopipe" is not a linear function of the height of the glass over the overflows, and the transient variations of the flow and temperature cause variations in the thickness of the final glass sheet; c) the hot plastic deformation of the "isopipe" itself, since the warpage arrow in the main body modifies the overflow heights of the molten glass during a manufacturing campaign so that the thickness can vary undesirably; d) the temperature of the external environment of the upper area of the gorge and of the overflows influences the distribution of the thickness of glass in the final sheet; and e) the zone of the sheet closest to the entrance is formed by a glass that has flowed in the vicinity of the periphery of the entrance section to the "isopipe" and is prone to have a lower quality. For To solve these cited disadvantages, various solutions have been proposed (WO 2005/0268657, US 2005/0268659, US 2005/0183455, US 2008/0202165, WO 2007/070825).

A second disadvantage of the method "overflow downdraw" is the difficulty of extrapolation to greater extractions and dimensions of sheets due to the warping of the "isopipe", of the hot deformation, and of the dimensions of the throat, whose side walls are subjected to stresses caused by the hydraulic pressure of the molten glass. In some cases, supplementary couplings are used to increase the width of the fabricated glass sheet (WO 2006/1 15792).

A third drawback of the method "overflow downdraw" comes from the devitrification of the glass, which can occur as a function of the time of the glass stay at temperatures below the "Liquidus temperature" in the different areas of the "isopipe". To avoid devitrification of the glass during its shaping, solutions have been proposed such as that of the patent (US 2004/0093900 Al).

Therefore, in the field of the manufacture of thin glass sheets, there is a need to solve the drawbacks of the current manufacturing methods already mentioned.

DESCRIPTION OF THE INVENTION

Technical problem raised

The method of the present invention and the design of the corresponding manufacturing facility solve the drawbacks of the present methods of manufacturing thin flat glass. In the "float" method, during the formation of the molten glass sheet, its two surfaces are in two different media, with different heat exchange coefficients, which causes a variation in the thickness of the glass sheet and it makes a subsequent polishing process necessary. In the "overflow downdraw" method, a single forming body performs a static distribution of the molten glass in its upper part and in its lower part the cooling of the molten glass, hindering the uniformity in the thickness of the final sheet, extrapolation to larger dimensions, and the duration of the manufacturing period due to devitrification of the glass.

Brief description of the Figures To complement the description of the present invention and in order to help a better understanding of its characteristics, a series of figures are attached where, with illustrative and non-limiting character, the following has been represented:

FIGURE 1.- Views and cross section of a forming apparatus,

"isopipe", according to the state of the art of overflow and stretched down, "overflow downdraw", for the manufacture of thin flat glass.

FIGURE 2.- Perspective view of an installation for the manufacture of thin sheets of glass according to the method of the invention.

FIGURE 3.- Overall views of a manufacturing system with a dosing group, with the driving modules, and with a forming device provided with a rotating cylinder cleaning element.

FIGURE 4.- Overall views of a manufacturing system with a dosing group, with the driving modules, and with a forming device provided with a submerged plate cleaning element.

FIGURE 5.- Section of profile and view in plan of a module of impulsion of glass with two rotating devices.

FIGURE 6.- Profile section and plan view of a glass impulse module with a single rotating device.

FIG. 7.- View of a rotating cylinder cleaning element, which floats on the molten glass contained in the upper concave part of a forming body.

FIGURE 8.- View of a rotating cylinder cleaning element and operating detail on a forming body with a concavity in its upper part and with a great relation between its height and its width.

FIGURE 9.- View of a rotary cylinder cleaning element held at its ends, and detail of its operation on a forming body whose upper part is smooth.

FIGURE 10.- View of a submerged plate cleaning element and detail of its operation on the forming body.

FIGURE 1 1.- Assembly diagram and partial views of a manufacturing system with two dosage groups for the same glass from a single oven, and with a forming device provided with a forming body. FIGURE 12.- Assembly diagram and partial views of a manufacturing system with two dosing groups for two glasses from two different ovens, with a forming device, and view of an enlarged detail of the thickness of the final composite glass sheet of two different glasses.

FIGURE 13.- View of the cross section of two dosing groups with their drive modules, rotating devices and overflows; and of a body of formed. NUMBERING USED IN THE FIGURES: 21 melting vessel, 22 vitrifiable materials, 23 refining vessel, 24 inlet channel, 25 level regulator, 26 dosing group A, 27 glass discharge module, 28 partition walls of the modules of impulsion, 29 rotating devices, 30 blades or blades of the rotating devices, 31 volume of direct glass, 32 volume of reflowed glass, 33 bottom infrastructure of the impulsion module, 34 aspiration zone, 35 impulsion zone, 36 overflow, 37 weir, 38 flat stream of molten glass, 39 irregular inner surface, 40 clean outer surface, 41 rotating cylinder cleaning element, 42 forming body, 43 first edge of the forming body, 44 second edge of the forming body, 45 concavity of the forming body, 46 minimum spacing between the rotating cylinder and the forming body, 47 lower vertex of the forming body, 48 running through the first side of the forming body, forming ear, 49 running through the second side of the forming body, 50 glass end sheet, 51 pull rolls, 52 submerged plate cleaning element, 53 direct current on the rotating cylinder, 54 current between the rotating cylinder and the body of formed, 55 singular point in the glass on the rotating cylinder, 56 return current on the rotating cylinder, 57 direct flow in the submerged plate. 58 vortices behind the submerged plate, 59 second flow in the submerged plate, 60 dosing group B, 61 second flat stream of molten glass, 62 and 63 glass streams on the sides of the forming body, 64 forming body, 65 support structure, 66 fusion furnace B, 67 refining vessel B, 68 glass channel B, 69 level regulator B, 70 glass stream A, 71 glass stream B, 72 final sheet formed by the two glasses A and B. Explanation of the invention

The process of the present invention for the manufacture of thin sheets of glass comprises the following parts: a) a melting furnace to obtain a molten glass; b) a dosing group to produce a flat stream of molten glass with uniform flow per unit width; c) a forming device for forming a continuous sheet of solid glass; and, d) cutting means for obtaining glass articles of certain dimensions.

Instead of the static glass distribution using the "overflow downdraw" method, the method of the present invention uses a dynamic distribution in order to control and regulate the flow of glass in each glass drive module belonging to the dosing group ; in this way, the thickness of as many areas of the final glass sheet can be regulated as the number of glass drive modules comprise the dosing group. The regulation of the flow of glass that passes through each impulsion module is done by varying the speed of rotation and / or the position of the axes of rotation of the rotating devices belonging to said module in order to modify the hydraulic height of the glass and the flow of molten glass that passes through the overflow corresponding to the drive module.

The main function of the rotating devices is to dose and regulate the mass flow of glass in each impulse module. In addition, the rotating devices perform the function of physically and thermally mixing and homogenizing the molten glass, directly influencing the final quality of the manufactured articles.

FIGURE 2 shows a perspective view of an installation for the manufacture of thin sheets of glass according to the method of the invention.

In FIGURES 3 and 4 the overall views of two particular embodiments of the method of the invention are set forth; each embodiment consists of an oven (21) for melting the vitrifiable materials (22) and a refining container (23); then, the molten glass passes through a channel (24) to reach the dosing group (26), whose object is to distribute and regulate the flow of glass to convert it into a flat stream (38) of molten glass whose width is of the final glass sheet and whose glass flow is controlled and regulated by several glass drive modules (27) located in parallel, whose number is five in the representation of both figures; the glass discharge modules are separated from each other by side walls (28) and comprise rotating devices (29) that perform the function of driving the molten glass, see FIGURES 5 and 6; these devices produce the increase of the hydraulic height of molten glass with respect to the inlet channel and at the same time regulating the flow that passes through the overflow (36) belonging to each impulsion module. The separation walls (28) continue to the crest of the overflow (36), and when these walls disappear, the molten glass corresponding to each of the drive modules joins in the form of a single flat stream (38) of molten glass which flows and falls from the landfill (37) to move to the next forming step in the forming device.

When a single dosing group is used, one of the two surfaces of the flat glass stream (38), the inner surface that has been in contact with the weir (37), is modified by a cleaning element, belonging to the device of formed. Then, the flow of the flat stream (38) is divided into two streams (48 and 49) of molten glass that flow downwards, on the two lateral faces of the forming body (42), at the same time that the glass is cooled . The two glass currents reach the lower vertex of the forming body and join to form a continuous sheet (50) of glass that is drawn downwards by means of traction machines, and then fractionated into certain articles of flat glass of low thickness. In one embodiment of the method of the invention, the cleaning element comprises a rotating cylinder, FIGURES 7, 8, and 9; In another embodiment of the method of the invention, the cleaning element comprises a flat plate partially submerged in the glass, FIGURE 10.

In FIGS. 1 and 12, overall views of two embodiments of the method of the invention are shown, in which two different dosing groups (26 and 60) are used with their respective drive modules (27), rotating devices (29), partition walls (28) and overflows to form two flat streams of molten glass (38 and 61). The two dosing groups (26 and 60) are partially supported by a structure (65) that is independent and is separated from the area (64) that integrates and supports the forming body, see FIGURE 13. The glass sheet is stretched by means of the traction rollers (51). FIGURE 12 shows a particular embodiment of the invention using two melting furnaces, furnace A (21) and furnace B (66), for the production of two different glasses in order to obtain a thin sheet of glass formed by two different glasses, glass A and glass B, each occupying half the thickness of said glass sheet from the apex (47) of the forming body (64).

The method of the invention allows to have some embodiments, such as:

I ^a ) A melting furnace, plus a dosing group, plus a forming body with a rotating cylinder as a cleaning element, plus cutting means to obtain a sheet formed by a single glass;

2 ^a ) A melting furnace, plus a dosing group, plus a forming body with a submerged plate as a cleaning element, plus cutting means to obtain a sheet formed by a single glass;

3 ^a ) A melting furnace, plus two dosage groups, plus a forming body without cleaning element, plus cutting means to obtain a sheet formed by a single glass;

4 ^a ) Two melting furnaces, plus two dosing groups, plus a forming body without cleaning element, plus cutting means to obtain a sheet composed of two different glasses.

DETAILED DESCRIPTION OF THE INVENTION

The following detailed description is made by way of explanation and not limitation; with it a complete knowledge of the invention will be provided, and it will be sufficient for a person skilled in the art of shaping the glass to understand that the present invention can be applied in other industrial embodiments even though they do not contemplate the specific details set forth herein. On the other hand, some descriptions of the well-known devices, methods and materials used may be omitted so as not to extend the description of the present invention.

The present invention provides a process for the manufacture of thin flat glass of high quality comprising the following steps: 1) melting and refining vitrifiable materials to obtain a mass of molten and refined glass, using a melting furnace with an outlet channel what it comprises a level regulator to keep the hydraulic height of the molten glass constant; 2) distribution and dosing of the glass in a flat stream of molten glass with uniform flow rate per unit width, using a dosing group comprising several glass drive modules, each of these modules consisting of at least one rotating device and with an overflow, at the end the glass of all the impulse modules is joined to obtain the aforementioned flat stream of molten glass, which passes to the next stage by means of a weir; 3) transforming a flat stream of molten glass into a continuous sheet of solid glass, using a forming device comprising a forming body and a pulling means, and, optionally, a "cleaning" element for modifying the lower face of the flat stream of molten glass; and 4) fractionation of the continuous sheet, by means of cutting means, to obtain glass articles of certain dimensions.

The method of the invention begins, see overall views in the

FIGURES 3, 4, 11, and 12, from the melting of the vitrifiable materials (22) in a melting vessel (21) and the refining of the molten glass in a refining vessel (23); the molten glass is led through a channel (24) to the dosing group (26); in the channel (24) a constant glass level is maintained, Ho, using a level regulator (25), constituted by a lateral channel / weir, FIGURES 5 and 6.

The molten glass conveyed by the channel (24), with a constant level Ho of glass, reaches the area where the dosing group (26) acts, whose object is to generate a flat stream (38) of molten glass whose size in width is similar to the width of the future manufactured glass sheet, and whose flow per unit width is uniform. The dosing group collects the molten glass from the channel (24) and distributes it between several impulse modules (27), five in the representation of the figures, located in parallel; each of the glass discharge modules (27) is separated from the border modules by means of partition walls (28) constructed of an alloy of platinum and / or rhodium. The glass is driven by means of at least one rotating device (29) which controls and controls the hydraulic height Hi of molten glass before passing through an overflow (36) belonging to the same drive module (27); for each overflow flows only the volume of glass already controlled and regulated by the devices Swivel (29) of the drive module. The walls (28) that separate each of the drive modules from each other continue to the crest of the overflow (36), and, when these walls (28) disappear, all the molten glass corresponding to each of the drive modules it joins in the form of a single flat stream of molten glass (38) that flows and falls from the landfill (37) to move on to the next forming phase. The dosing group (26) and the glass discharge modules (27) may be partially supported on their infrastructure (33) and / or partially suspended from the top of the side walls (28).

As shown in FIGS. 5 and 6, the dosing of the molten glass flow rate is carried out by the rotating devices (29), which cause the molten glass to move from the inlet channel (24), which performs the function of suction zone with a constant glass height Ho, up to the discharge zone (35), with a glass height Hi, where the overflow (36) is located. The space between the rotating devices and the side walls (28) of each module in the direction (31) of the glass flow is greater than the space for the opposite direction (32); therefore, the flow of glass is pushed and propelled in the direction of manufacture. The rotating devices (29) are not limited to the designs represented in the figures, and a wide variety of models can be used: lobe, gear, fin, or eccentric elements, all within the field or spirit of the present invention. The rotating devices are directed by at least one driving mechanism that controls and regulates its speed of rotation and / or by a position mechanism that controls and regulates the position of the rotating devices with each other and with respect to the drive module to which they belong.

In a particular embodiment of a drive module in which two rotating devices have been used, FIGURE 5, it can be seen that each drive module (27) is composed of a bottom infrastructure (33) that continues with an overflow (36) and ends with a landfill (37) that pours the glass in the form of a flat stream of molten glass (38) with a uniform flow per unit of width towards the forming device that is located next to said landfill: Each drive module also it consists of side walls (28) that separate it from the adjacent drive modules and that belong to the same dosing group; these walls laterals (28) conduct the molten glass to the crest of the overflow (36). The molten glass is collected from the suction zone (34) with a hydraulic height Ho, and raised to the drive zone (35) near the overflow (36) at a hydraulic height Hi. The axes of rotation belonging to the two rotating devices (29) are separated from each other by a magnitude DE, and in their part immersed in the molten glass have blades or blades (30) whose shapes, trajectories, speed and direction of rotation determine the movement of the glass in the entire volume of the impulse module, which can be decomposed into two different volumes: a) direct volume, (3 1) VD, in which the glass moves in the direction of manufacture; and b) reflowed volume, (32) VR, in which the glass moves in the opposite direction to that of manufacturing. The direct volume (3 1) is greater than the reflux volume (32), so that the glass increases its hydraulic height ΔΗ = Hi-Ho in a regulated manner by changing the rotation speed w and / or the DE position , di, and Ú2 of the axes of rotation of the rotating devices (29) with respect to the drive module (27) to which they belong.

FIG. 6 shows a diagram comprising a single mobile element in each drive module; the hydraulic lift is achieved by changing the speed of rotation w and / or the eccentric position di and di of the axis of rotation of the rotary device with respect to the side walls (28) of the drive module; with the variation of the position of the axes of rotation, di and Ú2, the two aforementioned volumes, the direct VD and the reflux VR, are simultaneously modified.

The rotating devices (29) of FIGURE 5 using the method of the invention for the regulation of the flow rate, constitute essentially a rotary pump with two parallel axes that collects the molten glass from an inlet channel (24) with a height of glass Ho, and elevates it to a height of Hi glass near the thick-walled overflow (36). The height Hi of the glass already raised maintains the balance between the net flow of glass driven and the flow of glass that passes through the aforementioned overflow.

As the glass height Ho in the entrance area (34) remains constant, the glass height Hi in the exit area (35) depends on the height I of the crest of the overflow (36); the flow rate of the molten glass QM produces an increase in the hydraulic height ΔΗ of:

ΔΗ = Ηι - Η ₀ (1) where: ΔΗ is the height increase produced by the rotating devices; Hi, it is the glass height at the outlet or drive zone; and Ho, it is the glass height at the entrance or aspiration zone.

At each turn or turn, FIGURE 5, the rotating devices move a volume of direct glass (3 1), VD, through the two sides of the module to the drive zone (35), and move a volume of glass through the central area. reflux (32), VR, towards the suction or inlet zone (34); at the speed of rotation w; the displacement of these volumes generates a flow QM in each module of:

where: fi (w), is a function that depends on the speed of rotation of the rotating devices; VD, is the volume of direct glass; VR, is the volume of reflowed glass; and QM, is the net flow rate of glass in the drive module.

The length and height Yo of the crest of the overflow (36) constitute an obstacle to the movement of the glass driven by the rotating devices (29), so that the molten glass acquires an increase in hydraulic height ΔΗ that can be expressed from the shape:

ΔΗ = K _H · w · μ · (V _D - V _R ) (3)

where: KH, is a constant; w, is the rotation speed of the rotating devices; and μ, is the dynamic viscosity of the glass.

For a certain width LM of the drive module, the direct theoretical volume VD of driven glass and the volume of reflowed glass VR depend on the distance DE between the axes of rotation of the rotating devices, according to a relationship that can be expressed as:

where: DE, is the distance between the axes of rotation of the rotating devices; It is a constant; and f ₂ (DE) ¹⁴² , is a function dependent on the geometry of the rotating devices, the dynamic viscosity of the glass, and the glass height in the drive module.

In this way the hydraulic height increase ΔΗ can be expressed as:

ΔΗ = K _H · w · μ · f ₂ (D _E ) ^k2 (5)

where: KH, is a constant. With constant viscosity operation, the hydraulic height increase can be controlled and regulated by the variation of the speed of rotation w, and / or of the distance DE between the axes of rotation of the rotating devices.

The shear stress produced by the movement of the glass in the drive module due to the rotating devices, deforms the heterogeneities existing in the molten glass decreasing its thickness. The deformation of an initial thickness heterogeneity δι in a period of time t and in a velocity field defined by its gradient of velocity grad.v is given by the expression:

5F = δι / (t · grad v) (6)

where: 5F, is the final thickness of the deformation; δι, is the initial thickness of the deformation; t, is the dwell time of the deformation in the velocity field, and (grad.v = dv / dn) the average velocity gradient [Jan Hlavác: "The Technology of Glass and Ceramics", Elsevier SP C, page 132 ]

In the present invention, the rotating devices have the fundamental purpose of controlling and regulating the flow rate of glass passing through the overflow, and therefore the thickness of the final sheet. On the other hand, the rotating devices also homogenize the molten glass analogously to the mechanical stirrers, "stirrers", used according to the current state of the art of glassmaking; the demand for high quality glass has allowed mechanical agitation to be used with the aim of reducing heterogeneities and / or to improve the thermal homogeneity of molten glass [Wolfgang Trier, "Glass Furnaces, Design Construction and Operation", Society translation of Glass Technology Sheffield, page 1 75 \.

The molten glass driven by the rotating devices (29) in the drive modules (27) passes over the crest of its corresponding overflow (36) and, when the side walls (28) that separate the modules from each other end up. drive, FIGURES 5 and 6, the glass flows corresponding to all the drive modules (27) belonging to the dosing group come together and flow downstream to fall by gravity from the landfill (37) in the form of a flat stream of glass melted (38), towards the forming stage.

The two surfaces of the flat stream of molten glass (38) of uniform thickness that falls from the weir (37), present different states: a) the outer surface (40), FIGURES 7 to 9, is "clean", since the Molten glass has not been in contact with static solid materials; and b) the surface interior (39), coming from the contact with the landfill, is "irregular" and must be modified and / or replaced in the forming stage, in an operation that is carried out by means of a "cleaning" element, which is also the object of this invention.

The flow of molten glass that has been regulated and dosed in the discharge modules passes through an overflow, FIGURE 5, the flow of molten glass that passes through the crest of the overflow of each drive module follows the expression:

Q _M = Ki · μ-ι · L _M · (Hi - Y ₀ ) ^3/2 (7)

where: QM, is the flow of glass that passes through the drive module; μ, is the dynamic viscosity of the glass; LM, is the width of the drive module; Hi, it is the height of the glass level in the drive zone; Me, it is the height of the crest of the overflow; and Ki, it's a constant.

The glass flow per unit width of the overflow is directly related to the thickness of the final glass sheet, and corresponds to the expression:

q = Q _M / L _M (8)

where: q, is the flow rate of molten glass per unit width in each drive module.

From the above equations it is obtained that the flow rate per unit width q is a function of the geometries of the drive module and of the rotating devices, of the viscosity of the glass, of the speed of rotation w of the rotating devices, and of the distance OF between the axes of rotation of the rotating devices; it is expressed in the following way:

q = [w, μ, D _E ] (9)

In the embodiments of the invention in which a single dosing group is used, the sum of the flow rates of all the driving modules equals the total manufacturing flow rate of the glass sheet; For the set of N drive modules that make up the dosing group, the total flow is:

Q = (ΣQ _M ) the N (10) where: N, is the number of drive modules that the dosing group has; and Q, is the total flow of glass manufacture, equal to the sum of the N overflows. The sum of the widths of all the modules corresponds to the total width of the manufactured glass sheet:

L = (ΣL _M ) the N (1 1) where: L, is the total width of the final sheet of glass, which essentially coincides with the sum of the dimensions of the N overflows that make up the dosing group.

The drive modules can have the same width LM and dose the same flow rate QM, although the edge modules can dose a different flow per unit area to facilitate the stretching operation.

In a certain operating regime, the set of rotating devices and overflow is defined by the values Ho, Ηι, Υο, w, μ, VD, and VR, which generate a flow QM in each impulse module; these values are determined in such a way that the nominal speed of rotation w is sufficient to: a) provide an adequate precision of the dosing of the glass flow rate; and b) generate a sufficient homogenization of the molten glass. In this way, the rotating devices act simultaneously as elements for regulating the flow rate of glass and as elements for homogenising the mass of molten glass.

With the modification of the rotation speed w and the distance between axes DE, the method of the present invention allows a more dynamic flow control and regulation of the glass flow and with greater precision than the traditional "overflow downdraw" method.

From the equations 1, 3 and 7, it appears that in the process of the present invention, the decrease in temperature or the increase in the viscosity of the glass, influence the variation of the flow in two ways that are compensated: ) increasing ΔΗ indirectly increases QM, since ΔΗ increases with increasing viscosity μ (equation 3); and b) increasing μ (equation 7) directly decreases QM. In this way, in the process of the present invention, the variation of the temperature implies a smaller variation in the flow of glass than in the "overflow downdraw" method, in which the variation of the viscosity directly influences the variation of the flow .

The variation of the rotation speed w of the rotating devices influences the glass flow q in the impulse module, by means of the coefficient (C _q w) i, defined by: (C _q w) i = (% Aq /% Aw) (12) where: (C _q w) i, is the coefficient of variation of the flow rate when changing the speed at the operating point Fl; % Aq, is the percentage of the variation of the flow; and% Aw, is the percentage of the variation of the speed of rotation. Both variations,% Aq and% Aw, have the same meaning.

[0046] The variation of the distance DE between the axes of rotation of the rotating devices influences the glass flow q in the drive module, by means of the coefficient (C _Q DE) i, defined by:

(C _qDE ) i = (% Aq /% AD _E ) (13) where: (C _Q DE) i, is the coefficient of variation of the flow rate when the distance between axes varies at the operating point Fl; and% Δ DE, is the percentage of the variation of the wheelbase. Both variations,% Aq, and% DE, have the opposite direction.

The modification of the glass flow from an initial operating regime Fl, defined by qi, wi, and DEI up to the final operating regime F2, defined by q2, W, and DE2, is carried out by varying the speed of rotation wy / or the variation of the distance D _E between the axes of rotation, so that the relationship is fulfilled

(qa-q / qi =% Aw · (C _qW ) i +% AD _E · (C _qDE ) i (14)

where: (q2-qi) / qi, is the relative variation of the flow q from the operating point Fl.

The method of the invention makes it possible to carry out various options for modifying the glass flow rate q per unit width in a given drive module of the dosing group, which is equivalent to modifying the thickness of the final glass sheet in the area corresponding to that mentioned. module, from the operating point Fl, defined by the flow qi, the speed wi, and the distance between axes DEI, up to the operating point F2, defined by (¾ W2, and DE2- For this it is necessary that the variation of the speed of rotation,% Aw, and the variation of the wheelbase,% ADE, meets the (equation 14) cited above.

The variation or modification of the flow of glass driven in a drive module depends mainly on: a) the geometry of the module; b) the geometry of the rotating devices; c) the viscosity of the glass; d) the glass height Ho in the inlet channel; e) the height I of the crest of the overflow; Y f) simultaneously, of the rotational speed w and the wheelbase DE. Once the geometries of the module and of the impulsion devices, as well as the glass heights and the crest of the overflow, are fixed, the glass flow rate per unit width q follows the expression of equation (9) above.

The expression of equation (9), q = / [w, μ, DE], is determined: a) by numerical calculation; and b) by physical modeling of the drive module with the rotating devices and with the overflow, in which the viscosity, inertia, gravity, and surface tension forces are represented.

Once the molten glass has been distributed and dosed in each of the drive modules (27) belonging to the dosing group (26) and has passed through the overflow (36) corresponding to each module, the side walls (28) that separate each module from the modules bordering it, disappear and all the molten glass that has passed through the dosing group (26) rejoins to give rise to a flat stream of molten glass (38) that falls vertically by gravity , from a landfill (37) to the forming device, where the next stage of the manufacture of the glass sheet according to the present invention is carried out.

It is a known fact that molten glass can evolve towards the formation of stable crystalline species in a process called devitrification, which begins with the formation of crystalline nuclei and continues with the growth of these crystals; Devitrification depends on the residence time of the molten glass at temperatures lower than the "Liquidus temperature", TL, and therefore, the useful life of some manufacturing equipment could be conditioned by this devitrification process. During the entire dosing stage of the glass and even after the formation of the flat glass stream (38), the method of the invention uses a temperature above the devitrification temperature, so that the useful life of the dosing group it does not depend on the devitrification of glass and is only determined by the mechanical resistance, depending on time, of the materials used such as platinum, rhodium, or some of its alloys.

The glass that falls vertically by gravity from the landfill (37), forming a flat stream of molten glass (38) with a uniform flow per unit width, has the following quality: a) the outer surface (40) that has not been in contact with the solid materials of the overflow is "clean" and can be used directly to form one of the two surfaces of the future sheet of glass; and b) the inner surface (39) that has passed in contact with the overflow and with the spillway, is irregular and should not be part of a final surface of the glass sheet.

In some particular embodiments of the process of the present invention, in which a single dosing group is used, the outer surface of the flat stream of molten glass (38) directly becomes part of the outer surface of the glass sheet, and the inner surface of the flat stream (38) must be modified by a cleaning element, which is part of the forming device and is located above the forming body and separated from it. In other particular embodiments of the invention, two different dosage groups are used, FIGURE 12, there being two flat streams of molten glass (38 and 61) whose two outer surfaces pass directly to form each of the two surfaces of the final glass sheet .

In a particular embodiment of the method of the invention shown in the overview of FIGURE 3 and in the detail views of FIGS. 7 to 9, the forming device uses as a cleaning element a rotating cylinder (41) to modify or " cleaning "the inner surface (39) of the flat stream (38) that has been in contact with the landfill (37); the cylinder (41) rotates at a speed wc in the direction indicated in the figures and is located below the flat stream of molten glass (38) and above the forming body (42). The effect produced by the rotation of the cylinder on the two surfaces of the flat stream (38) is as follows: a) the outer surface (40), which was already "clean", passes directly towards a first edge (43) of the body formed (42) which is located at a height Z3; and b) the interior surface (39), which is "irregular", is dragged towards the interior of the glass mass that rotates attached to the cylinder.

The flat glass stream of molten glass (38) that falls from the landfill (37), is superimposed on the return current (56) existing on the periphery of the cylinder, forming a current (53) that is conducted by the cylinder towards an area in which the forces of gravity and drag are added, see FIGURE 7. Part of the current (53) is directed towards the first edge (43) of the forming body, which is located at a height Z3, and generates the stream (48) that descends by an outer side wall of the forming body (42), while the rest of the stream (53) ), forms a stream (54) which is conducted between the space between the rotating cylinder (41) and the forming body (42), which space has a certain minimum spacing (46). The current (54) reaches the height of the second edge (44) of the forming body, which is located at a height Z ₄ ; part of the stream (54) overflows the edge (44) and generates the stream (49) that descends through the other outer side wall of the forming body (42). The remaining glass of the flow (54) is driven by the rotating cylinder (41), forming a current (66) attached to the rotating cylinder which is directed towards an area in which the driving force of the cylinder goes in the opposite direction to the force of the gravity of the glass; when the molten glass reaches the singular zone (55) in which the force of gravity on the glass is similar to the pulling force exerted by the rotating cylinder (41), a break or take-off occurs on the surface of the molten glass with two different streams: a) a part of the glass stream (56) continues attached to the rotating cylinder (41), and is conducted by it until it joins the irregular part (39) of the flat stream of molten glass ( 38) and again form part of the current (53), closing the cycle; and b) another part of the glass is directed towards the edge (44), forming the outer surface of the stream (49) that descends on the outside of the forming body (42). In this way, the two surfaces of the currents (48 and 49), which will form the surfaces of the final sheet (50), are clean, since the molten glass particles (39) that were in contact with the landfill (37). ) were already incorporated into the interior of the molten glass mass in the stream (53).

The upper part of the forming body (42) can have a concavity (45) as in FIGURES 7 and 8, or it can be smooth as in FIGURE 9. At the same time, the rotating cylinder (41) can be: a) solid with a resistant core formed by molybdenum and / or refractory materials such as ZrÜ2, AI2O3, and S1O2, with or without a metallic outer coating containing platinum, rhodium or some of its alloys; or b) hollow and formed by platinum, by rhodium or by some alloy containing platinum and / or rhodium; or with a core formed by molybdenum and / or tungsten, with an outer coating containing platinum or some of its alloys. The rotating cylinder (41) is in rotation by means of external mechanical means for controlling and adjusting the speed wc of rotation necessary to control the layer of molten glass adhered to the cylinder during its rotation, and to adjust the inertial forces, of viscosity and gravity that are exerted on the particles of the molten glass during the rotation of said rotating cylinder.

In a particular embodiment of the invention, when the rotating cylinder (41) is hollow, FIGURES 7 and 8, and is located on the concavity (45) carved in the forming body (42), the gravitational force FG corresponding to the weight of the cylinder and the weight of the glass located above, is counteracted by the pushing force FE exerted by the glass of the concavity (45) displaced by the cylinder (41); in this way, the cylinder "floats" on the molten glass and is not subject to deformations caused by its own weight.

In another embodiment of the invention, when the upper part of the forming body is smooth, FIGURE 9, and the rotating cylinder (41) is located above this surface, the force of gravity F _G is not counteracted by the force of FE push, and the rotating cylinder behaves like a beam in flexure that is supported by its two ends.

The two streams (48 and 49) coming from the edges (43 and 44) of the forming body (42), flow through the two sides of the said forming body towards its lower area, which has the shape of a wedge, forming an angle in its vertex (47); upon reaching this vertex the two streams (48 and 49) join to form a single flow of glass that is stretched by a pulling means (51) to originate the final sheet of glass; this final sheet is subsequently divided with means not shown here for obtaining thin sheets of glass of certain dimensions. In their displacement by the two sides of the forming body (42), the two streams (48 and 49) are cooled to reach the apex (27) with a viscosity / temperature suitable for shaping downwards.

The distribution of the flat stream of molten glass (38), having a uniform flow rate per unit width, between the two substantially similar currents (48 and 49), is carried out, see FIGURE 7: a) through the fixed heights Z3 and Z ₄ , heights of the upper edges of the forming body; b) by modifying the vertical separation (58) between the cylinder and the concavity (52) of the forming body (53); c) by modifying the horizontal separation Evc between the axis of fall of the glass and the axis of the rotating cylinder, and of the horizontal separation Ecc between the axis of the rotating cylinder and the axis of the forming body; and d) by varying the rotational speed wc of the rotating cylinder.

In another particular embodiment of the method of the invention shown in the overview of FIGURE 4 and in the detail views of FIGURE 10, the forming device uses a plate (52) partially submerged in the glass to clean the uneven surface (39) of the flat stream of molten glass (38) coming from the contact with the base of the landfill (37) belonging to the dosing group; said flat stream passes to a plate (52) partially submerged in a concavity (45) carved in the forming body (42), and is divided into two flows: a) a first direct flow (57) passing through a side of the forming body located at a height Zi and generating a shape the stream (48) traveling down an outer side wall of the forming body (42); and b) a second flow (59) occupying the concavity (45) cut into the forming body (42) and passing underneath the submerged plate (52), located at a distance (46) from the concavity (45). ); this second flow (59) is directed towards the other edge of the forming body, located at a height Z2, and generates the current (49) that moves downwards through the other outer side wall of the forming body (42). The geometry of the concavity (45) of the forming body and the position of the submerged plate (52), together with the viscosity of the molten glass, produce swirl currents (58) at the rear of the submerged plate (52). that perform the function of "cleaning" the surface that was in contact with the landfill; therefore the current (49) is, like the current (48), a clean surface. The two glass streams (48 and 49) flow through the walls of the forming body (42) at the same time as they are cooled and reach the lower vertex (47), where both currents join to form a single flow of glass, which is stretched by pulling means (51) to form the glass sheet (50).

The distribution of the flat stream of molten glass (38), which has a uniform flow per unit width, in the two streams (48 and 49) is made, see FIGURE 10: a) by the heights Zi and Z of the edges upper parts of the forming body (42); b) by modifying the horizontal distance EPC between the axis of the forming body (42) and the vertical plane of falling of the molten glass on the plate (52); and c) by modifying the vertical distance (46) of separation between the plate (52) and the concavity (45) of the forming body (42).

In another embodiment of the process of the present invention, a single furnace is used for the melting of a glass and then two different glass dosing groups are used, overall views in FIGURE 1 and detail in FIGURE 13; each of the two dosage groups (26 and 60) comprises several drive modules (27); in turn, each drive module comprises separation walls (28), at least one rotating device (29), and an overflow.

From each glass dosing group a flat stream of molten glass of uniform flow per unit width is obtained, and in this way the two flat glass streams (38 and 61) are produced that fall vertically by gravity on each of the two side walls of the forming body (64). The outer surfaces of the two flat streams of molten glass (38 and 61) come directly from the surface glass that has passed through the overflows and are "clean" surfaces and will continue to be clean in the currents (62 and 63) that will later form the two surfaces of the final glass sheet (50); the inner surfaces of the flat streams of molten glass (38 and 61) coming from the glass that has passed in contact with the base of the overflows continue to contact the walls of the forming body (64) within the two streams (62). and 63) and subsequently they will be integrated into the interior of the final glass sheet.

The two streams (62 and 63) descend each of them for each side wall of the forming body (64), at the same time as they are cooled as they approach the lower and final part of the forming body. The forming body (64) ends at a vertex (47), and when the two lateral currents (62 and 63) reach the aforementioned vertex, they join to form a single glass stream with the proper viscosity to be stretched by means of rollers of pulling (51) and forming the glass sheet (50); this sheet is subsequently fractioned, with means not shown here, in specific articles or products.

The two dosage groups (26 and 60) are supported wholly or partially by a structure (65) that is independent of the structure of the forming body (64); both structures (64 and 65) can move relative to each other to adjust the distance of the forming body (64) to the corresponding weir (37), so that the vertical fall of the flat currents (38 and 61) is adequate.

In another particular embodiment of the process of the present invention, a glass sheet formed by two different glasses A and B separated in the middle plane of the thickness of the glass sheet is manufactured. The process begins, FIGURE 12, from the fusion of the vitrifiable raw materials A and B in the fusion vessels (21 and 66), and the refining of the molten glasses in the containers (23 and 67). Then, glasses A and B are led through the channels (24 and 68) to the dosage groups (26 and 60); in the channels (24 and 93) the levels of the glasses are kept constant by means of the level regulators (25 and 69). Each of the dosing groups (26 and 60) comprises several drive modules (27); and, in turn, each drive module comprises separation walls (28), at least one rotating device (29) and its own overflow, so that a flat glass stream is obtained from each dosing group. melt of uniform flow per unit of width, and in this way two flat glass streams (38 and 61) are produced which fall vertically by gravity on each of the two side walls of the forming device (64) and flow downwards according to two streams of molten glass (70 and 71) formed by two different glasses, the stream (70) formed by the glass A, and the stream (71) formed by the glass B.

The outer surfaces of the two flat streams of molten glass (38 and 61) come directly from the surface glass that has passed through the overflows, and are "clean" surfaces and continue to be clean in the currents (70 and 71) that will later form the two surfaces of the final glass sheet. The interior surfaces of the flat streams of molten glass (38 and 61) that come from the glass that has passed in contact with the base of the overflows, continue to contact the walls of the forming body (64) within the two streams ( 70 and 71) and subsequently will be integrated into the interior glass mass of said final glass sheet.

each of the two streams (70 and 71) descends through one of the side walls of the forming body (64), at the same time that they are cooled as they approach their final part; this final part has an angle in its vertex (47), and when the two lateral currents (70 and 71) reach the aforementioned vertex, they join to form a single glass stream with the suitable viscosity to be stretched by traction rollers (51) and form the sheet of glass (72); this sheet is subsequently fractioned, with means not shown here, in specific articles or products. The final thin sheet (72) of glass is formed by the two glasses A and B, separated in the middle plane of the thickness of the glass sheet, as shown in FIGURE 12.

The two dosage groups (26 and 60) are supported totally or partially by a structure (65) that is independent of the structure of the forming body (64); both structures (64 and 65) can move relative to each other to adjust the distance of the forming body (64) to the corresponding overflow (36), so that the vertical fall of the flat currents (38 and 61) is the adjusted one.

The place or stage of the process of the invention in which the glass passes through the devitrification temperature, or "Liquidus temperature", TL, is as follows: a) in embodiments of the invention in which a single group is used of dosing, and therefore in the forming step a rotating cylinder cleaning element is used, FIGURES 7 to 9, or a partially submerged plate, FIGURE 10, the devitrification temperature is reached once the lateral currents have been formed (FIG. 48 and 49) that descend along the sides of the forming body (42) at the same time they are being cooled; and b) in the embodiments of the invention in which two dosage groups are used, FIGURES 1 to 13, the devitrification temperature is reached once the two melted glass streams (38 and 61) corresponding to each of the two dosage groups (26 and 60). Both currents pass to the forming body (64) forming two lateral currents (62 and 63) that descend on the outside of said body (64) at the same time they are being cooled.

The decrease of the residence time of the molten glass below the devitrification temperature, together with the fact that the dosage stage of the molten glass is carried out separately and in different apparatuses that the cooling stage, has as a consequence that the useful life of the equipment used with the method of the invention is greater than the useful life of the equipment used with the manufacturing method "overflow downdraw". The angle of the lower zone of the formed body, which ends at the apex (47) influences the stability of the flow [H.-J.Lin, W.-K. Chang: "Design of a sheet forming apparatus for overflow fusion process by numeñcal simulation"; of Non-Crystalline Solids 353 (2007) 2817-2825]; a small angle gives more stability to the flow of the molten glass above the vertex, and the method of the present invention allows a smaller angle to be provided at the apex (47) than the angle used with the "overflow downdraw" method.

A higher viscosity at the apex (47) where the stretching begins makes the flow more uniform; however, the viscosity is influenced by the devitrification temperature of the glass and by the residence time of the glass below this temperature. In the process of the invention, the distribution of the glass in the width of the glass sheet is carried out in the dosing group, and the forming body is used essentially for cooling the glass to the stretching temperature. The advantages of the method of the invention come from the following facts: a) a forming body without glass flow commitments in its interior needs a smaller width, which leads to a smaller angle at the apex (47); and b) the forming body is not limited in height by its mechanical strength and by the arrow in its lower edge, since these aspects do not affect the distribution of the glass in width, or, what is the same, the uniformity of the thickness of the final glass sheet.

In the process of the present invention, once the two lateral streams of molten glass reach the lower vertex (47) of the forming body, the glass is stretched by traction rollers (51) at the same time that it is cooled to become in a solid and continuous sheet of glass of a certain thickness; in this stretching process, the forces caused by the surface tension manifest themselves adversely, tending to produce a transverse contraction of the glass sheet in formation.

Finally, the glass is fractioned by cutting machines to produce the desired dimensions for the article or final product. DETAILED DESCRIPTION OF AN EXAMPLE OF THE INVENTION.

In the following example, the process of the invention is used for the manufacture of a glass sheet 2500 millimeters wide and 0.70 millimeters thick. The flow or extraction of manufactured glass is 20 tons per day.

The fusion from the vitrifiable raw materials and the refining of the molten glass are carried out according to conventional methods according to the current techniques for a glass whose viscosity / temperature ratio is determined by the following values: (μ = 8000 poises, Tv = 1321 ° C); (μ = 16000 poises, Tv = 1279 ° C); (μ = 25000 poises, Tv = 1253 ° C); and (μ = 100000 poises, Tv = 1 182 ° C). Where: μ, is the dynamic viscosity of the glass; and TV, the temperature of the glass.

After the melting and refining, the molten glass passes to a channel, FIGURES 2, 3 and 5, provided with a level regulator that maintains the level of glass at a height Ho, up to the entrance area of a dosage group of glass. This input zone of the dosing group is common for all the drive modules that make up the aforementioned group; the pumping of all the groups is carried out at the same temperature and from the same initial hydraulic height Ho. Once thermally conditioned, the glass reaches the zone of the impulsion modules at a temperature of 132 1 ° C, that is, with a viscosity of 8000 poises.

The dosing group consists of: a) five delivery modules separated from one another by lateral separators of platinum / rhodium, each module comprising two rotating devices and one overflow; and b) a final spillway, which collects the glass that has passed through each of the overflows of each impulse module and pours it in the form of a single flat stream of molten glass towards the forming stage.

The width LM of each drive module is 500 millimeters; The height of the glass Ho in the suction channel is determined by the level regulator so that the operating conditions of the impulse module produce the passage of the glass flow over the overflow, whose ridge has a height I of 180 millimeters.

The five drive modules are separated from one another by intermediate spacers having a thickness of 1.5 millimeters, and are constructed of a platinum / rhodium alloy, and continue to the ridge of the overflow, where the flows of the five modules join to form a flat stream of molten glass of 2500 millimeters in width.

In the cross section of each of the drive modules, two rotating devices with an external diameter D equal to 220 millimeters are located; the separation between the rotation axes of the two rotating devices is 180 millimeters, and the line joining the axes of rotation is perpendicular to the direction of the glass in the drive module. With a diameter of influence of the axis of each rotating device of 90 millimeters, the width AD of direct flow passage is 230 millimeters and the width of passage AR of the reflowed glass is 90 millimeters.

The nominal speed of rotation w of the two rotating devices is 6 revolutions per minute; both rotate in the opposite direction, in favor of the direction of the glass on the sides of the module, see FIGURE 5, and against the direction of the glass at the center. The thrust blades and shafts of the two rotating devices are made of a material with 80% platinum and 20% rhodium; The weight of each rotating device is 2.2 kilograms. Under the operating conditions of temperature, mechanical working voltage, and resistance of the platinum-rhodium alloy, the duration in time of each rotating device is 18 months.

The movement of the rotating devices generates in each of the drive modules a refluxed glass flow rate of 0.00046 cubic meters per second, which is 26 times higher than the flow rate of glass manufacture. When encountering an obstacle like the overflow, the glass driven by the rotating devices increases its hydraulic height Hi, which limits the direct flow of impulsion until the difference V _D -V _R equals the flow rate of glass manufacture.

The average dwell time of the glass in each drive module is 37 minutes; during this time, each of the two rotating devices performs 222 complete turns, and each particle of molten glass has made an average path of 63 meters.

With a viscosity of glass μ = 8000 poises, a height Zo of passage of the glass at the beginning of the ridge of the overflow of 8 millimeters, a distance DE between the axes of the rotating devices of 180 millimeters, and a speed of rotation of the devices revolving of 6 rpm, the values that reach CQW and CQW are: CQW = (% Aq /% Aw) = 0.91; by increasing the speed of rotation from 6 to 7 revolutions per minute, the flow increases by 16.7%.

CQDE = (% Aq /% ADE) = -6.6; by increasing the distance DE between the axes of rotation from 180 to 181 millimeters, the flow decreases by 3.6%.

With these values, by increasing the speed of rotation w from 6 to 6.5 revolutions per minute, the flow rate in the drive module passes from 4 to 4.3 1 tons per day, and the final thickness of the glass sheet passes from 0.70 to 0.75 millimeters. This same effect is achieved by keeping the speed of rotation constant at 6 revolutions per minute and decreasing the distance between axes, from 180 to 177.8 millimeters.

By increasing the distance DE between the axes of the rotating devices from 180 to 183 millimeters, and at the same increasing speed from 6 to 7 revolutions per minute, the flow rate in the drive module passes from 4 to 4, 1 tons per day, and the final thickness of the glass sheet passes from 0.70 to 0.72 millimeters.

The reduction of the temperature of the glass at 1 ° C in the impulse module, from 132 1 ° C to 1320 ° C, produces an increase in the viscosity of the molten glass from 7982 poises to 81 14 poises. The effect on the glass flow q is as follows: a) in the passage through the rotating devices increases the hydraulic height increase ΔΗ, which has an effect on a first variation of the flow rate of qA = 1.50%; and b) in the passage through the overflow, the increase in viscosity produces a second variation of the flow rate of qB = - 1, 64%. In this way, the decrease in temperature by 1 ° C supposes a decrease in the flow rate of q = qA + qB = -0, 14%; the rotating devices have a damping effect on the temperature of the glass in the area of the drive modules.

The control and regulation of the flow passing through a certain drive module has a direct effect on the thickness in its corresponding area of the final sheet, since the final glass from all the drive modules is formed by the same device. formed, and is stretched by the same means of traction.

The method of the invention makes it possible to precisely regulate the flow rate of glass by suitably combining the operating parameters, w and D _E ; the application of (equation 14) to this example gives the relation: (Aq / q) = 0.9 1 · Aw% - 6.6 ·% AD _E.

Once the molten glass approaches the crest of the overflow and is out of the influence of the two rotating devices, the side separators disappear, and all the glass that has passed through the overflows of the impulse modules joins together to form a flat stream of molten glass that flows until it passes through a landfill, at the same time that it is cooled from the outside by radiation.

From the landfill, the flat stream of molten glass falls on a rotating cylinder, which acts as a cleaning element on the surface of the flat stream that has been in contact with the landfill. The glass passes through the area of this rotating cylinder with a viscosity of 16,000 poises, at a temperature of 1279 ° C; that is, the glass has a temperature below 43 ° C at the temperature of the molten glass in the area of the rotating devices belonging to the drive modules.

The detail views of FIGS. 7 and 8 represent the forming device with a cleaning element constituted by a rotating cylinder and a forming body; the shaped body has a width of 20 centimeters and presents in its upper part a concavity with a depth of 14 centimeters; The rotating cylinder is made of a platinum-rhodium alloy and has an outer diameter of 12 centimeters and a thickness of 2 millimeters. Taking into account the density corresponding to an alloy of platinum-rhodium, a density of molten glass of 2.60 grams per cubic centimeter, and an average thickness of 15 millimeters of glass over the non-submerged area of the rotating cylinder, the hollow cylinder floats on the molten glass contained in the concavity of the formed body, with a 55 mm immersion. The rotational speed of the rotating cylinder is 0.5 revolutions per minute.

The shearing of the glass located between the static wall of the concavity of the forming body and the dynamic wall of the part of the rotating cylinder immersed in the glass, forces the rotating cylinder to withstand a total torsional force of 149 Newtons.

Once the rotating cylinder has modified or "cleaned" the lower surface of the flat stream of molten glass and two glass streams have formed that pass through the upper edges of the forming body, the molten glass flows through each of them. the two sides of the mentioned body of formed. The viscosity of the glass in this area is 24000 poises, corresponding to a temperature of 1255 ° C. Then, the two currents that descend on each side of the forming body are cooled to reach the lower vertex with a viscosity of 100000 poises, corresponding to a temperature of 1 182 ° C; in this place the two streams of glass join to form a sheet of molten glass. The vertical height of the forming body is 81 centimeters, and the drop in glass temperature occurs at a rate of 0.9 ° C per centimeter of height of the forming body.

At the lower vertex of the forming body, the molten glass sheet is stretched by traction rollers to form a solid and continuous thin sheet of glass, which is then fractionated to obtain sheets of thin flat glass of given dimensions.

Claims

1. - A process for the manufacture of a thin sheet of glass, characterized in that it comprises the following phases:

(a) melting and refining of molten glass from vitrifiable raw materials by means of a melting furnace;

(b) transforming a molten glass mass from a melting furnace into a flat stream of molten glass with a uniform flow rate per unit width, by means of a glass dosing group;

(c) forming a solid and continuous glass sheet from a flat stream of molten glass from a dosing group, by a forming device comprising a cleaning element, a forming body, and a pulling means;

(d) fractioning a solid and continuous sheet of glass into articles of certain dimensions;

and in which, in the formation of a solid and continuous sheet of glass from a flat stream of molten glass by a forming device, a cleaning element constituted by a rotating cylinder is used.

2. A method for manufacturing a thin sheet of glass according to claim 1, characterized in that in the formation of a solid and continuous sheet of glass from a flat stream of molten glass from a dosage group, by a forming device, a cleaning element consisting of a plate partially submerged in the glass is used.

3. - A process for the manufacture of a thin sheet of glass, characterized in that it comprises the following phases:

(a) melting and refining of a single molten glass from vitrifiable raw materials by means of a melting furnace;

(b) transformation of a molten glass mass from a melting furnace into two flat streams of molten glass with uniform flow per unit width, by means of two glass dosing groups;

(c) forming a solid and continuous sheet of glass from two flat streams of molten glass from two dosage groups, by means of a forming device comprising a forming body and pulling means;

and in which the sheet of glass is constituted by a single glass.

4. - A process for the manufacture of a thin sheet of glass, characterized in that it comprises the following phases:

(a) melting and refining of two different molten glasses from vitrifiable raw materials by means of two melting furnaces;

(b) transformation of two masses of molten glass from two melting furnaces into two flat streams of molten glass with uniform flow per unit width, by two glass dosing groups;

(c) forming a solid and continuous sheet of glass from two flat streams of molten glass from two dosing groups, by means of a forming device comprising a forming body and a pulling means;

and in which the glass sheet is constituted by two different glasses, each occupying half the thickness of the glass sheet.

5. - A glass dosing group for transforming a mass of molten glass into a flat stream of molten glass with uniform flow per unit width, usable in a process for the manufacture of a thin sheet of glass, according to claims 1 to 4, characterized in that it comprises:

(a) an entrance zone of the molten glass from a melting furnace;

(b) a set of several molten glass drive modules independent of each other, each module comprising at least one rotating glass drive device with means for controlling the speed of rotation and the position of the axes rotation of the devices rotating with respect to the side walls of the drive module in which they are installed;

(c) an overflow in each of the drive modules, independent of the rest of the overflows corresponding to the rest of the glass drive modules; Y

(d) a common spillway through which the molten glass flows from each of the overflows of the discharge modules and which is poured in the form of a flat stream of molten glass with uniform flow per unit width.

6. A glass dosing group according to claim 5, characterized in that the number of rotating devices in one of the glass delivery modules is two.

7. A glass dosing group according to claims 5 and 6, characterized in that the variation of the speed of rotation and / or the position of the axes of rotation of the rotating devices, produces the variation of the hydraulic height of the glass molten in its corresponding impulsion module, and modifies the flow of molten glass that passes through the overflow of said impulsion module.

8. - A glass dosing group according to claims 5 to 7, characterized in that both the separation walls between the drive modules and the rotating devices, are made totally or partially of platinum, rhodium, or some alloy of platinum or of rhodium.

9. - A forming device for converting a flat stream of molten glass into a solid and continuous sheet of glass, usable in a process for the manufacture of a thin sheet of glass according to claims 1 and 2, characterized in that it comprises:

(a) a cleaning element for modifying one of the two surfaces of the flat stream of molten glass;

(b) a forming body located below the cleaning element and through whose two side walls flow two streams of glass that are being cooled as they move towards its lower part, said body of formed ends in a wedge shape with the vertex downwards, where the two lateral currents converge to form a single sheet of molten glass;

(c) pulling means for drawing a sheet of molten glass from the lower apex of a forming body, to become a solid and continuous sheet of glass;

and in which, the cleaning element is constituted by a rotating cylinder located above the upper area of a forming body, with means for controlling the speed of rotation of the cylinder and the position of the cylinder relative to the forming body.

10. - A forming device for converting a flat stream of molten glass into a solid and continuous sheet of glass according to claim 9, characterized in that the cleaning element is constituted by a plate partially submerged in the upper part of the forming body.

1 - A forming device for converting two flat streams of molten glass from two glass dosing groups into a solid and continuous sheet of glass, usable in a process for the manufacture of a thin glass sheet according to claims 3 and 4, characterized in that it comprises:

(a) a forming body with two side walls each receiving one of the two flat streams of molten glass, which are cooled as they move towards their lower region, said forming body ending in a wedge shape with the vertex downwards, where the two lateral currents converge to form a single sheet of molten glass; Y

(b) pulling means for drawing a sheet of molten glass from the lower apex of a forming body, to become a solid and continuous sheet of glass.

12. - A forming device for converting two flat streams of molten glass, coming from two glass dosing groups, into a solid and continuous sheet of glass according to claim 1, characterized because the two flat streams of molten glass come from two different glasses that have been melted and / or refined in different compartments.

13. - A manufacturing facility for a thin sheet of glass for carrying out any of the processes of claims 1 to 4, characterized in that it comprises:

(a) at least one compartment for the melting and refining of vitrifiable materials;

(b) at least one molten glass dosing group;

(c) a forming device; Y

(d) cutting means for fractionating a solid and continuous sheet of glass into articles of certain dimensions.

14. - A thin sheet of glass characterized in that it has been manufactured according to a method described in claims 1 to 4 above, and using an installation according to claim 13.

15. - A thin sheet of glass according to claim 14, characterized in that it is formed by two different glasses, each of the glasses occupying half the thickness of the glass sheet.