EP2321232A2

EP2321232A2 - Unit and process for treating the surface of flat glass with thermal conditioning of the glass

Info

Publication number: EP2321232A2
Application number: EP09784299A
Authority: EP
Inventors: Wolf Stefan Kuhn
Original assignee: Fives Stein SA
Current assignee: Fives Stein SA
Priority date: 2008-07-30
Filing date: 2009-07-24
Publication date: 2011-05-18
Also published as: TW201022171A; CN102112407B; KR101661487B1; WO2010013149A1; CN102112407A; WO2010012890A4; MX2011000900A; FR2934588A1; AU2009275776A1; EP2326600A1; WO2010012890A2; US20110162411A1; FR2934587B1; BRPI0916821A2; JP5564500B2; AU2009275776B2; KR20110049817A; KR20110049816A; MY159092A; CN102112405B

Abstract

Unit for the surface treatment of flat glass, in particular in the form of a ribbon or a sheet, especially by modifying the chemical, optical or mechanical properties, or the deposition of one or more thin films, comprising heating and cooling means for creating a controlled temperature gradient through the thickness of the glass, means for heating that face to be treated, in order for it to always be at the required temperatures and for the times necessary for obtaining effective treatments of the surface thereof and means for cooling the opposite face in order for this opposite face to have a viscosity of between 10¹³ dPa.s and 2.3´10¹⁰ dPa.s.

Description

UNIT AND METHOD FOR FLAT GLASS SURFACE TREATMENTS WITH THERMAL CONDITIONING OF GLASS.

The invention relates to a unit for flat glass surface treatments, in particular in the form of a ribbon or a plate, with a thermal conditioning of the glass making it possible to increase the temperature of one of the faces of the glass. at the required temperatures and for the times necessary to obtain effective treatments of its surface, in particular by changes in the chemical, optical or mechanical properties or the deposition of one or more thin layers.

This conditioning of the glass is implemented on a glass ribbon produced continuously by the float glass process, the rolling process or the drawing process. It is also used in processes for treating glass plates whether in scrolling or in batch mode. The glass may have been previously treated, for example by the deposition of a layer made in the tin bath.

The invention relates more particularly, but not exclusively, to a processing unit for the manufacture of flat glass for architecture, automotive or solar applications.

It is recalled that some of the applications described above require more and more treatment of the glass surface by the deposition of thin layers, often consisting of several successive layers. These layers make it possible, for example, to obtain solar reflection, low emissivity, electrical conductivity, coloring, antifouling and other properties.

For the sake of simplification of the description, it will be considered later that the surface treatment is performed on the upper face. Nevertheless, according to the invention, the face to be treated can indifferently be the upper or lower face or both.

Modifications of the optical or mechanical properties of the glass surface may be obtained by a method of producing a structure using an engraving roller on one side of a glass ribbon. Other applications require the transformation of the mechanical, chemical or optical properties of glass by methods of changing chemical and structural composition in a limited depth of the glass.

The main processes used at atmospheric pressure for the deposition of thin films are CVD (pyrolysis deposition of a vapor - chemical vapor deposition), flame CVD, atmospheric plasma, SP (pyrolysis of a fog - spray pyrolysis ). These processes can heat or cool the glass surface to varying degrees. Pyrolysis processes require a high glass temperature to achieve reagent decomposition and layer formation. They are therefore particularly suitable when the flat glass is still at elevated temperature during its manufacture or during its transformation (tempering glass for example).

The manufacture of float glass involves the forming of the glass ribbon on a bath of liquid tin from a temperature of 1000 ^° C. to a temperature of about 620 ° C. for soda-lime glass. The forming of the ribbon at a constant thickness and width stops at about 800 ^° C. Below this temperature, the geometry of the ribbon remains stable and controlled cooling of the ribbon is continued on the tin. A maximum temperature of 620 ⁰ C, slightly lifts the tape by mechanical rollers out of the bath to pass in a lehr. In this drying room, the ribbon is cooled from 620 ^° C. to about 50 ^° C. before being cut into panels.

The maximum temperature of approximately 620 ^° C., equivalent to a viscosity of approximately 2.3 × 10 ¹⁰ dPas, makes it possible to obtain a quality in accordance with EN or ASTM standards. For lower quality requirements concerning marking by the glass support means or unevenness, the bath outlet temperature may be higher.

For glass compositions different from those of standard soda-lime glass, the maximum temperature at the outlet of the bath may also be different.

Part of the CVD processes are installed in the tin baths so as to benefit from a high temperature of the glass favorable to the deposit, despite the difficult accessibility of the surface of the ribbon. The tin bath is protected by a reducing atmosphere consisting of an N2 + H2 mixture for prevent the oxidation of liquid tin. This atmosphere promotes the deposition of layers requiring a reducing atmosphere such as metal layers. Other methods, for example SP, can not be used in the tin bath because they pollute the atmosphere above the bath.

In an annealing tunnel such as a lehr, the atmosphere is air and the transport of the ribbon usually takes place on rollers. The surface of the glass is thus more easily accessible for a deposition process. All the SP systems and part of the CVD processes are thus installed in the initial section of the cabinets in which the temperature of the glass is limited to a maximum value of 620 ^° C.

The temperature of the ribbon surface plays a key role in the efficiency and quality of the pyrolytic deposition and surface transformation processes, for example by diffusion.

For example, standard pyrolytic CVD treatment consists of a deposition of a thin layer of amorphous Si used as a reflective layer in the architecture. The deposition is carried out by decomposition of the silane gas. The kinetics of the pyrolytic decomposition of the silane is slow for temperatures <650 ^° C. and is only very partial at temperatures below 610 ^° C. The limited temperature of the glass in a drying rack considerably reduces the efficiency of the deposition process. The cooled reactor being very close to the glass, it also leads to a thermal loss thereof.

The SP treatment cools the glass ribbon more than the CVD process, which causes glass deformation problems when its temperature drops locally below about 570 ^° C. for soda-lime glass. This low temperature also leads to a decrease in the reagent decomposition yield and a poor adhesion of the layer.

Processes for transforming the surface of the glass, for example to obtain diffusion coloration of the coloring ions in the glass or chemical or mechanical curing by alumina diffusion, require a high glass temperature. An electric field can also be implemented so as to promote the diffusion of ions in a deposited layer and / or in the glass.

The deposition of the chemical species on the glass surface can be achieved by various processes such as the creation of nanoparticles in a flame or by the decomposition of a reagent present in a CVD reactor. The diffusion rate of the elements in the glass is directly related to the temperature. This is limited in the drying rack so that the glass remains below about 620 ^° C. for soda-lime glass.

U.S. Patent 4,536,204 discloses heating the tape on the upper side before coating so as to reduce temperature heterogeneity across the width of the tape. Radiative heating means are implemented. However, the thermal flux injected into glass must remain limited so as to avoid exceeding the maximum permissible temperature. The temperature level reached on the upper face and the temperature holding time are therefore limited.

U.S. Patent 4,022,601 discloses a coating device SP placed between the tin bath and the lehr. The maximum permissible temperature for the glass produced and the required quality level is 649 ° C at the outlet of the bath. The coating device inducing a strong cooling of the glass, a heating device is located on the upper face just upstream of the coating device so as to compensate for this cooling and return the glass to its initial temperature. A second heating means placed on the lower face at the level of the coating device makes it possible to compensate for the cooling induced by the coating process in order to avoid the deformation that would result from the beginning of the setting of the glass. This invention does not allow the glass to be brought to a temperature higher than that which it has at the exit of the bath.

The object of the invention is, above all, to make it possible to raise the temperature of the face to be treated with glass for greater efficiency of the processes described above, without causing deformation and / or marking of the glass by the means of support placed on the opposite side to that treated, including support rollers.

The invention consists mainly of a flat glass surface treatment unit, in particular in the form of a ribbon or a plate, in particular by modifications of the chemical, optical or mechanical or by deposition of one or more thin layers, characterized in that it comprises means for heating and cooling to create a controlled temperature gradient in the thickness of the glass, heating means of the face to be treated for that it is always at the required temperatures and for the times necessary to obtain effective treatments of its surface and cooling means of the opposite face so that this opposite face is at a viscosity of between 10 ¹³ dPas and 2.3 x 10 ¹⁰ dPas, preferably about 1.9x10 ¹² dPas.

Advantageously, the unit comprises successively: an initialization zone with means for heating the face to be treated and means for cooling the opposite face to reach the temperatures targeted opposite to be treated and opposite side,

a treatment zone with heating means and means for treating the face to be treated, and cooling means for the face opposite to that treated,

a homogenization zone, with cooling means,

and devices are placed at the input and at the output of the treatment unit to limit thermal losses and the exchange of atmospheres.

The length of the initialization zone to reach the target temperatures in front to treat and opposite face can be determined so that the number of Peclet Pe

_ _ Tdiff (épaisseur- 0.5) ² t _conv diffuse speed iv Hey _thermique length

between 0.5 and 15, favorably between 3 and 5, with

- t _d i _ff = characteristic time for the diffusion of heat at depth, Um being given by Um = (thickness / 2) ² / thermal diffusivity,

- t _∞ nv = characteristic time for the horizontal transport of the ribbon in the initialization zone, t _∞nv being given by t _∞nv = length zone / speed ribbon.

The unit can integrate one or more successive treatment devices placed on the same face or on the opposite faces of the glass.

The flat glass surface treatment unit comprises cooling means for maintaining the opposite face at a temperature which makes it possible to avoid the marking of the glass by the support means and / or the deformation glass for lack of mechanical strength, while avoiding the freezing of the glass that would result from excessive cooling.

The invention also consists of a flat glass surface treatment process, in particular in the form of a ribbon or a plate, in particular by modifications of the chemical, optical or mechanical properties or by deposition of one or more thin layers characterized in that a controlled temperature gradient is created in the thickness of the glass by means of heating the face to be treated so that it is always at the required temperatures and for the times necessary to obtain treatments. effective from its surface and by cooling means of the opposite face so that this opposite face is at a viscosity between

10 ¹³ dPas and 2.3 x 10 ¹⁰ dPas, preferably about 1.9x10 ¹² dPas.

Advantageously, according to the method: in an initialization zone, the face to be treated is heated and the opposite face is cooled to reach the temperatures targeted opposite to be treated and opposite face,

in a treatment zone the face to be treated is heated and undergoes a treatment, while the face opposite to that treated is cooled, in a homogenization zone, the face opposite to that which has been treated is cooled.

Preferably, in the initialization zone, the heat fluxes, positive and negative, on both sides are not balanced, which makes it possible to slightly increase the average temperature of the ribbon. In the treatment zone the heating and cooling can be balanced on both sides, which allows to maintain a stable temperature gradient across the glass ribbon.

In the homogenization zone it is possible to stop the heating while maintaining the cooling. According to the method, the opposite face is maintained at a temperature which makes it possible to prevent the glass from being marked by the support means and / or the deformation of the glass by lack of mechanical strength, while avoiding the freezing of the glass which would result from a excessive cooling.

The implementation of the invention makes it possible to increase the temperatures at which the surface treatments will be carried out so as to improve their performance. This temperature increase can be carried out briefly when it is necessary to carry out a short-term treatment or it can be maintained over a longer period when the surface treatment requires it.

This increase in temperature is made possible by the simultaneous cooling obtained opposite face to the face to be treated according to the invention. This simultaneous cooling makes it possible to limit the temperature of the opposite face so as to limit the marking and the collapse of the glass. It must be controlled so as to avoid a lack of flatness caused by partial freezing of the glass.

The method according to the invention is also characterized in that the thermal conditioning of the glass is carried out before and / or after the treatment device. It can also be applied during treatment.

In the case where the thermal conditioning is performed during the treatment, the treatment device may include heating and / or cooling means.

The method according to the invention is also characterized in that the temperature of the upper face of the glass is adapted along the treatment unit so as to optimize the treatments performed. Depending on the nature of the treatment, the upper face is brought to the target temperature and maintained at this temperature for the time necessary for carrying out the treatment.

Heating on the upper face and cooling on the opposite side leads to a large temperature gradient in the glass. After the end of the treatment, temperature homogenization is favored in the thickness of the glass, for example by means of a cooling of the upper face, so as to find the usual thermal conditions at the outlet of the treatment unit and in the entrance of lehr.

According to an alternative embodiment of the invention, the glass has not reached its usual temperature at the lehr end at the outlet of the treatment unit.

In this case, adaptation of the initial cooling of the drying rack is necessary, for example by means of a reinforced upper cooling and / or by an extension of the first zone.

According to another example of treatment, the temperature at which the ribbon surface is carried is adapted along the thermal conditioning unit so as to optimize the efficiency of the treatment, the temperature of the face to be treated being greater than 620.degree. ⁰ C while ensuring that the temperature of the face Opposite remains in the recommended temperature range, between 55O ⁰ C and 620 ⁰ C for soda-lime glass.

For other qualities of glass, an equivalence of these temperature levels is obtained by expressing these by a viscosity. The viscosity of the face to be treated will be greater than about 2.3 x 10 ¹⁰ dPas while ensuring that the temperature of the opposite face remains within the recommended viscosity range, between about 10 ¹³ dPas and 2.3 x 10 ¹⁰ dPas.

According to an exemplary embodiment of the invention, the temperature of the face to be treated is alternated at a point on the glass between a high value and a low value around an average temperature while maintaining the opposite side at a temperature of about 570 ⁰ C for soda-lime glass, corresponding to a viscosity of about 1.9 x 10 ¹² dPas. This embodiment makes it possible to reinforce the diffusion treatments in the thickness of the glass when this diffusion follows an Arrhenius-type law because the temperature peaks lead to a greater diffusion than a simple maintenance at the average temperature.

The method according to the invention is also characterized in that the processing unit integrates one or more successive devices for processing the glass, for example to perform a stack of different layers, to combine a layer with a diffusion process, or to realize a single layer of great thickness. These successive devices of treatments can be of different natures, like a SP followed by a CVD then a CVD by flame. This unit of surface treatments according to the invention makes it possible to produce in the unit the treatments usually carried out in the tin bath or in the lehr. It also makes it possible to overcome current constraints by allowing to reverse the order in which the processes are implemented. It is indeed possible to perform SP treatment first and then a high temperature CVD treatment, as performed in the tin bath, whereas this was not possible before because the implementation of an SP in the bath is excluded.

The method according to the invention makes it possible to place treatment devices on one side or on both sides of the glass. The implementation of treatments on both sides allows for example to combine a functional layer on one side, for example anti-reflection, and a transparent electrically conductive layer on the opposite face. The nature and order of the treatment processes used will be adapted to the result targeted by the glass treatment.

The thermal requirements of the different treatments may be different, which leads to modulating the heat flux imposed on both sides of the glass. The modulation of the flow on the face to be treated makes it possible to obtain the required temperature for each of the treatments. For example, it will be necessary to heat more intensively upstream and downstream of an SP.

The method according to the invention is also characterized in that the temperature of the upper face of the glass is adapted along the thermal conditioning unit so as to optimize each successive treatment.

The process according to the invention is also characterized in that the temperature of the face to be treated is greater than 620 ^° C., preferably greater than 640 ^° C., and that of the opposite face of the glass is between 550 ^° C. and 620 ^° C. ° C in the thermal conditioning unit in the case of a soda-lime glass supported by mechanical means such as rollers.

According to an exemplary embodiment of the invention, when a large flow and surface temperature are necessary for carrying out the treatment, a cooling of the treated face is also performed after the treatment so as to evacuate more calories.

The heating means according to the invention makes it possible to obtain a transverse temperature profile with an alternation between different temperature levels. The cooling intensity of the lower face is also transversely adapted. These different temperature levels on the upper face make it possible to obtain a variation on the width of the glass of the thickness of a deposit, the importance of diffusion or any other modification. For example for the manufacture of photovoltaic cells, it is possible to perform a metal deposition of the successive strips for contacting several photovoltaic cells.

According to the invention, the chemical composition, the pressure and the temperature of the atmosphere inside the treatment unit are adapted to each processing implemented. A reducing atmosphere is necessary for the deposition of certain layers, such as metal layers.

For safety reasons, the pressure in the unit may be higher or lower than the atmospheric pressure depending on the species present in the treatment unit.

The processing unit may comprise sections in which the atmosphere is different so as to be adapted for the processing performed in each section.

The atmosphere present in the treatment unit can come from the tin bath, after a possible filtering. In general, the atmosphere inside the treatment unit must be free of dust which may require filtering of the injected gases.

In the case of a float glass process, the treatment unit according to the invention is placed between the bath outlet and the lehr or integrated at the beginning of lehr. It can be separated or contiguous to the bath of tin and / or the lehr.

In order to define the thermal parameters for the thermal conditioning of the glass, it is necessary to take into account:

. The thickness to be heated to the desired temperature for the treatment,

. The speed of the glass,

. The thermal diffusivity of the glass,

. The enthalpy of glass,. The emissivity of glass

The treatment unit according to the invention makes it possible to treat a wide range of glass thicknesses, for example from 2 to 25 mm. The variety of possible treatments therefore requires a thermal dimensioning adapted to achieve the desired result while avoiding overheating of the glass, an installation too large or excessive energy consumption.

A method according to the invention allows a quick and easy way to determine the optimum conditions for heating and cooling the ribbon to be printed at different depths for a wide range of float glass production. It will be described for an exemplary embodiment. The invention consists, apart from the arrangements described above, in a certain number of other arrangements which will be more explicitly discussed hereinafter with regard to exemplary embodiments for soda-lime glass described with reference to the appended drawings. but which are in no way limiting. On these drawings:

- Fig. 1 is a schematic longitudinal section of a float glass production line, implementing the method of the invention

- Fig. 2 is a schematic view on a larger scale of a portion of FIG. 1 showing in greater detail the thermal conditioning unit - FIG. 3 is a diagram representing ordinate ribbon temperatures as a function of the longitudinal position on the abscissa in the case of a constant treatment temperature.

- Fig. 4 is a diagram showing ordinate ribbon temperatures as a function of the position in the abscissa thickness in the case of a constant treatment temperature.

- Fig.5 is a longitudinal section of a processing unit according to the invention comprising 4 successive treatment devices in the upper face.

FIG. 6 is a diagram showing the absorption spectrum of a clear soda-lime float glass and the spectrum of a black body.

- Fig. 7 is a diagram showing ordinate ribbon temperatures as a function of the longitudinal position on the abscissa in the case of a modulated treatment temperature with the implementation of 4 CVD reactors, 3 on the upper face and 1 on the lower face.

The transport of a ribbon at a high temperature encounters major problems such as marking by the rollers or the slump and deformation of the glass between two rolls.

For soda-lime glass, experience shows that for a typical running speed of 10 to 20 m / min, a temperature of about 620 ⁰ C is the upper limit to avoid the marking of the tape by the support rollers or the slump between the rollers. For lower speeds, such as in furnaces for processing glass plates, the maximum permissible temperature is lower, of the order of 580 ^° C.

For soda-lime glass experience also shows that a temperature of about 570 ⁰ C is the low limit from which the glass begins to congeal. When cooling a glass plate or ribbon, make sure to cool both sides symmetrically. For a glass that is above the transition temperature Tg _1, a symmetrical cooling first leads to the symmetrical freezing of the two faces and then to the freezing of the volume. When the freezing does not occur symmetrically on both sides, this causes a curvature of the glass. If only one side begins to freeze then the glass plate or ribbon will deform.

To take into account these risks, the invention provides to maintain the opposite side in contact with the rolls at a temperature of between 550 ^c C and 620 ⁰ C for soda-lime glass.

The sagging and deformation between the rolls is a function of the temperature of the glass. A homogeneous temperature of about 620 ^° C. for soda-lime glass has the upper limit from which a significant slump of the glass is observed for a distance between rolls of 500 mm, a standard distance in a drying rack.

Excessive sagging between the rollers could cause permanent ripples in the glass. For certain glass treatments, such as the deposition of a thin layer by CVD _1, it is essential to maintain excellent flatness of the glass because of the reduced clearance between the glass surface and the CVD reactor.

Levitation tables are also used for the transport of glass. The absence of mechanical contact may allow a temperature slightly above 620 ^° C. However, the drop in viscosity leads rapidly to a lower mechanical strength of the glass.

A temperature of about 620 ^° C. therefore has the upper limit of a soda-lime glass in a flat glass heat treatment system with mechanical transport.

So as to increase the performance of a surface treatment process, for example by CVD, the invention provides for increasing the temperature of the face to be treated, for example at 650 ^° C. A heater placed just upstream of the CVD reactor makes it possible to increase the temperature of the upper face, more generally the face to be treated, of the glass without this leading to an increase in temperature of the opposite face. This heat flow must be rapidly evacuated after the CVD reactor so as not to exceed the maximum admissible temperature on the lower face. In the case where the reactor causes little thermal losses, which is desirable for the deposition of the target layer, a cooling of the treated face may be performed after the reactor. Nevertheless, this option is not satisfactory for a glass of a usual thickness, from 3 to 5 mm, because the heat diffusion which occurs during the heating and during the deposition leads to a rapid and excessive increase of the temperature of the opposite side that can cause the glass to be marked by the rollers. In the case where several consecutive CVD reactors are used to make a stack of layers, the problem of diffusion of heat in the thickness of the tape would be even more pronounced. This configuration would also lead to further collapse of the ribbon between the rolls detrimental to the CVD treatment.

The invention provides for a cooling of the opposite face to maintain it at a temperature which makes it possible to prevent the glass from being marked by the support means and / or the deformation of the glass due to a lack of mechanical strength, while avoiding the freezing of the glass. result from excessive cooling.

Referring to Fig.1 of the drawings, there is shown a first embodiment of the invention, schematically shown, a glass ribbon production facility according to the float glass method.

The installation comprises a furnace 1 in which is introduced the raw material, sand, flux, cullet, etc., used for the manufacture of glass. A pasty glass ribbon B comes out of the oven 1 while being supported by a molten tin bath 2 occupying the lower part of a flotation chamber 3 under a reducing atmosphere, in particular a nitrogen and hydrogen atmosphere. . The forming of the glass on the tin bath takes place at a temperature of between approximately 1000 ^° C. and 600 ^° C.

At the outlet end of the chamber 3, the glass ribbon B is lifted from the tin bath and passes into the "drossbox" DB (or bath outlet) on rollers 4 called "LOR rollers" (Lift Out Rollers). ). The ribbon B then passes through a space 5 in the open air, over a length of a few tens of centimeters. This space is sometimes closed and provided with means for evacuating gas from the tin bath. The ribbon B then enters a unit A of surface treatments according to the invention. This comprises rollers 6 as a means for transporting the glass, a heating device 7 and a treatment unit 8 on the upper face of the glass, and a cooling device 9 on the lower face, with the opposite of the heating device 7. E devices placed at the inlet and outlet of the processing unit 8 can limit thermal losses and the exchange of atmospheres.

Following the processing unit, the glass enters the lehr L. Throughout the lehr the glass ribbon is supported horizontally by rollers 10 driven in rotation at the feed speed of the ribbon. An adjustable tensile force F is exerted on the ribbon B. The intensity of the traction F makes it possible to act on the forming of the ribbon B in the tin bath 3. Chillers K are provided above and below ribbon. The data taken into account for this example of realization is the following ones:

. A ribbon of clear soda-lime glass without a thin layer with a width of 3.7 m, a thickness of 4 mm, and a running speed of 15 m / min. The surface treatment is carried out after the LOR rollers 4 but before the beginning of the annealing of the ribbon, the glass being at a temperature of 610 ^° C.,

. the surface treatment requires heating the upper face at a temperature of 650 ^° C. The surface treatment requires a maintenance of this temperature for 12 seconds, corresponding to a length of 3m to 15m / min.

. The surface treatment system has no impact on the thermal ribbon, that is to say, it does not change the temperature of the ribbon. Other exemplary embodiments given below will make it possible to treat the case where the surface treatment system has an impact on the thermal of the ribbon.

Now we will specify in more detail this embodiment. To obtain the desired temperature and duration, a heating and cooling system is designed according to the invention as follows, shown in FIG. 2:

One imposes a positive heat flow of 60 kW / m ² on the upper side over a length of 0.7m (initialization zone 11), in particular by heating by combustion 11a.

On the opposite side, it is cooled to the same length with a heat flow of -15 kW / m ² , in particular by convection cooling devices 11b, with air blowing. Then, the upper surface is heated with a flow of 25kW / m ² over a length of 3.1m (holding zone 12), in particular with radiative heaters 12a.

On the opposite side, from the position 0.7 m, we cool with a flow of -25kW / m ² over a length of 4m.

A homogenization zone 13 follows the holding zone 12.

Figure 3 shows the temperature profiles in the glass ribbon, with the Tsup curves for the upper surface temperature, Tinf for the lower surface temperature, Tcentre for the center temperature. The temperature in ⁰ C is plotted on the ordinate, and the position in meters is plotted on the abscissa.

The heat flow of the reinforced heating at the beginning of the conditioning serves to establish more quickly a temperature gradient in the ribbon. The thermal fluxes, positive and negative, on both sides are not balanced in this section which allows to slightly increase the average temperature of the ribbon.

The desired temperature of 650 ^° C. is rapidly obtained on the surface of the ribbon. The cooling prevents the increase in the temperature of the underside above 620 ⁰ C, critical temperature for the marking of the tape by the rollers.

The temperature on the underside falls to about 580 ⁰ C. This temperature is still sufficient to avoid early solidification of the strip with the risk of deformation. The heating and cooling are then balanced on both sides over a distance of 3.1 m, between the positions 0.7 m and 3.8 m, which allows to maintain a stable temperature gradient through the glass ribbon. Throughout the surface treatment process, a temperature of 650 ° C is maintained at the top face and 580 ^° C at the bottom face.

At the position of 3.8m in the diagram of FIG. 3, the heating of the upper face is stopped while maintaining the cooling so as to homogenize the temperature of the ribbon in its thickness (homogenization zone). The temperature of the upper face therefore decreases rapidly even without cooling of the upper face due to the heat diffusion depth of the ribbon. Cooling of this upper face would accelerate this temperature homogenization. Cooling continues on the underside to the 4.8 m position. Of In this way, the average temperature of the ribbon is lowered, which makes it possible to recover the initial temperatures of the ribbon at approximately 7m before the thermal conditioning according to the invention is implemented.

The thermal conditioning unit can end at a position of 3.8m if the first zone of the lehr is thermally adapted.

It is appropriate in this case to compensate for the difference in temperature of the ribbon at the entrance of the outrigger by a reinforced cooling of the upper face for a limited distance.

The diagram in FIG. 4 shows the evolution of the vertical temperature profile of the ribbon along the thermal conditioning zone. The temperature is plotted on the ordinate, and the position in the thickness is plotted on the abscissa. The solid curve corresponds to the profile at the 0.7m position in the unit, the dotted line corresponds to the profile at the 1m position and the dashed line at the 3.8m position. The temperature of 650 ⁰ C is reached with a still curved profile which linearizes quickly. At the 1m position, the temperature profile is still slightly curved. At the position of 3.8 m, the profile is linear. However, the surface treatment of glass can already start at the 0.7m position because the target temperature is reached.

To determine the thermal fluxes necessary for the thermal conditioning of the ribbon, it is first necessary to know the conductivity of the glass. The peculiarity of glass is its simultaneous conductivity by phonons and photons: But only the photons that are emitted in the 'opaque' part of the absorption spectrum contribute to the conductivity called 'active'.

The active conductivity of a clear soda-lime float glass was determined in the range of 600-700 ^° C. by a linear approximation:

λ (T) = (aO + al - T) [W / m - K]

With coefficients a0 = 0.9 and a1 = 8.9 * 10 ^{"4 *} K ^{" 1} There are articles in the literature which deal in more detail with conductivity, thermal diffusivity and its determination for other qualities of glass, for example M Lazard, S. André, D. Maillet, Int. J. of heat and mass transfer 47 (2004), 477-487.

With the thickness of the glass sheet (4mm) and the surface temperature necessary for the treatment (650 ^° C.), and the temperature set for the face lower (580 ⁰ C) then determines the heat flow imposed across the sheet.

q _ Λ (T _sup ) + λ (T _{m {} ) (T _sup -T _{m {} ) 2 thickness With the parameters of the example described above, a flow of 25 kW / m ² is obtained in the zone keeping. This flow was used in the simulation presented in FIG. 3. Temperatures close to the target temperatures are effectively obtained.

To determine the length of the initialization zone, that is to say the time to reach the target temperatures on the upper and lower face and a more or less linear gradient establishment, another approach is used. which makes it possible to determine the length of the initialization for different speed of the glass, different thicknesses or thermal diffusivities.

A nondimensional number called "number of Peclet" makes it possible to determine the optimal conditions for a thermal diffusion process combined with a mass transport such as that implemented according to the invention for heating the glass in displacement. In our case, the direction of diffusion of the temperature is perpendicular to the mass transport direction corresponding to the scrolling of the ribbon. This feature requires a redefinition of the number of classic Péclet using a one-dimensional approach with the same direction of diffusion and transport.

This redefinition is based on 2 characteristic times, the characteristic time for the diffusion of the heat in depth and the characteristic time for the horizontal transport of the glass.

The characteristic time for diffusion of heat towards t _d i _ff is given by Um = (thickness / 2) ² / thermal diffusivity.

The characteristic time for the horizontal transport of the ribbon in the initialization zone t _co n _v is given by t _co nv = zone length / ribbon speed. The ratio between Wt _conv defines the number of Peclet Pe.

p _ W _ (thickness • 0.5) ² speed t _conv diffus ivite _thermic length The length of the initialization zone is such that the number of Peclet is between 0.5 and 15 and favorably between 3 and 5. The thermal profile is thus sufficiently established in depth to ensure good temperature stability on the lower and upper faces. .

In the example above, the length of the initialization zone was determined at 0.7 m based on a Peclet number of 3. Figure 4 shows that this length leads to a temperature profile in the glass thickness with good heat diffusion in depth at the 0.7m position. It is therefore possible to start the targeted treatment.

After defining the length, the heat flow to be injected into the initialization zone is easy to estimate. The average temperature between the initial temperature of the glass and the target surface temperature is calculated. Then, with the speed, the density and the specific heat of the glass, one calculates the flow of energy necessary to reach this average temperature. The division of this stream by the length of the initialization zone gives the thermal flux density to be injected into the glass.

The same reasoning is used to determine the thermal flux density of the cooling of the lower face in the initialization zone. The same method is then used to dimension the length and the flows of the successive thermal conditioning zones of the treatment unit.

The following example embodiment of the invention shown in FIG.

5 shows a processing unit comprising a thermal initialisation zone 11, a treatment zone 12 and a thermal homogenization zone 13.

The initialization zone 11 includes a combustion heater 11a.

In treatment zone 12, several successive units make it possible to perform a chemical transformation of the glass and / or a stack of layers. According to the example of FIG. 5, the treatment zone 12 comprises: - above the glass ribbon supported by rollers, successively, a plasma treatment unit 12b1, a unit (or reactor) CVD 12b2 and a unit SP 12b3, a flame CVD unit 12b4, - Then, for the treatment of the underside of the ribbon, below the latter, a CVD unit 12b5 with levitation means by blowing a gas under the ribbon to support it in the absence of rollers.

heating means 12a, for example radiative by infrared or microwave.

Cooling devices 11b, in particular by blowing air, are provided on the face opposite to that treated.

The homogenization zone 13 comprises a water chiller 13b with insulation, followed by a device 13c with upper and lower transverse beams provided with thermocouple means for measuring the temperature of the ribbon.

The surface temperature of the treated face is adjusted along the length of the zone according to the invention to optimize each treatment, the temperature of the lower face being maintained in the target range, between 550 ^° C. and 620 ^° C. for soda-lime glass. This adjustment of the temperature is carried out by means of heating, equalizing, or cooling depending on whether it is necessary to heat, equalize or cool the upper face of the glass as a function of the temperature at the outlet of the treatment preceding and the one referred to at the entry of the next treatment. This FIG. 5 shows the temperature measuring means 14, for example by optical pyrometry or using thermocouples integrated in the depositing equipment. We also see the devices 15 for recovery of gases from the heating (combustion fumes), deposition systems and coolers. The cooling air preheated by the tape could be resumed for combustion of the melting furnace. Depending on the nature of the ribbon processing gases, these may be filtered and / or resumed by the combustion of the melting furnace.

The various possibilities of heating the glass are now considered. Heating methods can be classified into surface methods, particularly suitable for injecting heat through the surface, and into known volume methods for their ability to heat materials in volume.

1 / Surface methods:

Radiation (radiation absorption heating in the opaque spectrum of glass), eg electrical resistance, radiant flame or laser, Hot air (convection and conduction on the glass surface) Hot gas (radiation, convection and conduction of a combustion)

Plasma (ionized gas in contact with the glass sheet).

2 / Volume methods: Microwaves (dielectric heating), Induction (heating by dissipation of electric currents), Radiation, with wavelengths corresponding to an optical thickness of about 1 depending on the nature and thickness of the glass.

In general, the heating of thin glass plates by microwaves or induction reveals two major difficulties:

. poor absorption and poor performance, especially for low temperature glass

. deep penetration into the volume (instead of limited depth)

The volume heating means have the advantage of being able to achieve a heat "reserve" under the treated surface with a non-linear temperature profile in the thickness of the glass. This will limit the drop in surface temperature of the treated face during a cooling treatment thereof. Simultaneously, the cooling of the lower face keeps it at the target temperature.

An electrically conductive coating, a reflective or low emissive coating leads to the reflection of infrared radiation. It would therefore be possible to effectively heat the glass with infrared radiation through the coated side. The heating of the glass or the layer may be achieved by radiation if it is of a different length, for example microwave or induction. The heating means used may also be convective.

The heating means may also be selected so as to exploit the properties of previously deposited layers. Thus, induction heating will mainly heat a conductive layer, for example metal. The heating means may make it possible to obtain a particular temperature transverse profile, for example an alternation between two temperature levels so as to create a treatment of variable intensity over the width of the glass.

The face heating means may comprise a burner ramp extending transversely across the width of the ribbon and whose flames are directed at the engraving side of the ribbon.

The heating and cooling means of the upper face of the glass can be integrated in the treatment units.

The cooling means may be a radiative means, for example formed by a tube extending transversely across the width of the glass and internally traversed by a cooling fluid, in particular air or water, this tube being located at near the treated side. The cooling means can also be a convective means by blowing a gas on the glass. This gas may be different or identical to that present in the treatment unit.

The method according to the invention is also characterized in that the cooling means of the lower face of the glass does not lead to excessive cooling of the mechanical glass support equipment.

When a cooling of a face is necessary, it can be obtained by a cooling device or a natural cooling related to the design of the enclosure of the surface treatment unit. For example, a low thermal insulation of the enclosure or the opening of traps can promote a natural cooling of the glass.

We will now study in more detail the case of an electric heater, that is to say by radiation of electrical resistors that is commonly used in the closets. If it is desired to heat only the surface of the glass, it is necessary to consider the spectral aspects of such heating.

FIG. 6 shows, in solid line, the absorption spectrum of a clear soda-lime float glass, 4 mm thick, and in dash the spectrum of a black body at 825 ° C. The wavelengths expressed in micrometers are reported in abscissa. The optical thickness is plotted on the ordinate on the left scale, while the black body radiation expressed in W / m ² μm is plotted on the ordinate on the right scale.

It can be seen in this figure that the radiation of a black emitter will be essentially absorbed by the glass surface for wavelengths above 2.7 μm. The calculation of a radiative exchange between two infinite plates makes it possible to find the conditions necessary to transmit the net thermal radiation of 25 kW / m ² required under stabilized conditions according to the first exemplary embodiment. The black transmitter must have a surface temperature of 825 ° C. At this temperature, it also emits 22 kW / m ² in the optical window of the glass. This radiation passes through the ribbon and heats the rollers and other equipment underneath. A black or gray emitter is therefore only partially suitable for heating the surface of the glass. It is better to use a spectral emitter with a reduction of emissions below 2.7mum. Another solution lies in the use of convective heating with air or low emission fumes.

FIG. 7 represents a thermal simulation of another exemplary embodiment according to the invention with three CVD reactors placed on the upper face and a CVD reactor placed on the lower face. The float glass ribbon has a thickness of 3 mm and a speed of 15m / min. The glass is of the clear soda-lime type. The reactors are 800 mm in length and cause heat loss at the surface of the tape which varies between 25 kW / m ² at the reactor start to finish at 10 kW / m ^2. In FIG. 7, the position expressed in meters following the treatment unit is plotted on the abscissa, while the temperature in ⁰ C is plotted on the ordinate. The curve in solid line corresponds to the temperature of the upper face of the glass ribbon, that in thick dashes corresponds to the temperature of the lower face, and the dotted intermediate corresponds to the temperature of the center of the ribbon.

An initialization zone makes it possible to establish the thermal gradient in the thickness of the glass, as described in the first exemplary embodiment. Then, to anticipate the thermal loss of the CVD reactors, short-term heating is applied upstream of each reactor. This heating makes it possible to wear the face to be treated at a temperature of approximately 750 ^° C. so that the temperature of the glass surface at the central position of the reactor remains greater than 650 ^° C. The position of the first reactor (length 0.8 m ) is between 1m (start of reactor) and 1.8m (end of reactor) as indicated in Figure 7. The other reactors are at equivalent positions after short-time heating.

After the third reactor placed on the upper face, a new initialization zone makes it possible to reverse the thermal gradient in the glass. The upper face is now at a temperature of about 580 ⁰ C and thus ensures the mechanical stability of the tape. The bottom surface must be heated to about 750 ⁰ C for the treatment to be performed and then cooled. The usual distance available between two support rollers is insufficient to effect this heating, treatment and cooling of the glass. The CVD reactor is thus designed to also ensure the levitation of the ribbon. The upstream heating and cooling devices downstream of the reactor also contribute to the support of the glass. At the 7m position, the ribbon support will be picked up by rollers. At this position, the temperature is almost homogenized in the thickness and is close to 610 ° C, the inlet temperature of the tape in the processing unit.

The heating means of the face to be treated makes it possible to heat the previously deposited layers.

The heating means of the face to be treated is such that the majority of the radiation emitted is in the wavelengths where the glass is opaque.

An electric field is implemented in the treatment unit so as to promote the diffusion of ions in a deposited layer and / or in the glass.

Claims

Flat glass surface treatment unit, in particular in the form of a ribbon or a plate, in particular by modification of the chemical, optical or mechanical properties or by deposition of one or more thin layers, characterized in that it comprises means for heating and cooling to create a controlled temperature gradient in the thickness of the glass, means for heating the face to be treated so that it is always at the required temperatures and for the periods necessary to obtain effective treatments of its surface and cooling means of the opposite face so that the opposite face is at a viscosity of between 10 ¹³ dPas and 2.3 x 10 ¹⁰ dPas.

2. Unit according to claim 1, characterized in that it comprises successively:

an initialization zone (11) with means for heating the face to be treated and means for cooling the opposite face to reach the temperatures targeted opposite to be treated and opposite side, - a treatment zone (12) with heating means and means for treating the face to be treated, and means for cooling the face opposite to that treated,

a homogenisation zone (13), with cooling means,

and in that devices (E) are placed at the inlet and at the outlet of the treatment unit (8) to limit thermal losses and the exchange of atmospheres.

3. Unit according to claim 2, characterized in that the length of the initialization zone to reach the opposite target temperatures to be treated and opposite side is determined so that the number of Peclet Pe p _ tώff (thickness - 0.5) speed t _com diffusivity _thermic length

between 0.5 and 15, favorably between 3 and 5, with

- tdiff = characteristic time for the diffusion of the heat in depth, tam being given by f _tfff = (thickness / 2) ² / thermal diffusivity,

- tconv = characteristic time for the horizontal transport of the ribbon in the initialization zone, t _∞nv being given by t _conv = length zone / ribbon speed.

4. Unit according to one of claims 1 to 3, characterized in that it incorporates one or more successive processing devices placed on the same face or on the opposite faces of the glass.

5. Process for flat glass surface treatments, in particular in the form of a ribbon or a plate, in particular by modifications of the chemical, optical or mechanical properties or by deposition of one or more thin layers, characterized in that a controlled temperature gradient is created in the thickness of the glass, by means of heating the face to be treated so that it is always at the required temperatures and for the times necessary to obtain efficient treatments of its surface and by cooling means of the opposite face so that this opposite face is at a viscosity of between 10 ¹³ dPas and 2.3 x 10 ¹⁰ dPas.

6. Method according to claim 5, characterized in that:

in an initialization zone (11), the face to be treated is heated and the opposite face is cooled to reach the temperatures targeted opposite to be treated and opposite face, - in a treatment zone (12) the face to be treated is heated and undergoes treatment, while the opposite side to that treated is cooled,

- In a homogenization zone (13), the opposite face to that which has been treated is cooled.

7. Method according to claim 5 or 6, characterized in that, in the initialization zone, the heat fluxes, positive and negative, on both sides are not balanced, which makes it possible to slightly increase the average temperature of the ribbon. .

8. Method according to one of claims 5 to 7, characterized in that in the treatment zone the heating and cooling are balanced on both sides, which allows to maintain a stable temperature gradient through the glass ribbon .

9. Method according to one of claims 5 to 8, characterized in that in the homogenization zone the heating is stopped while maintaining the cooling.

10. Method according to one of claims 5 to 9, characterized in that the cooling of a face of the glass results from a cooling device or natural cooling related to the design of the enclosure of the unit surface treatments.

11. Method according to one of claims 5 to 10, characterized in that the temperature of the upper face of the glass is adapted along the surface treatment unit so as to optimize the treatments performed.

12. Method according to one of claims 5 to 11, characterized in that the temperature of the face to be treated of the glass is greater than 620 ⁰ C, while the temperature of the opposite face of the glass is between 550 ⁰ C and 620 ° C in the thermal conditioning unit in the case of a soda-lime glass supported by mechanical means such as rollers.

13. Method according to one of claims 5 to 12, characterized in that the temperature of the upper face is alternated at a point on the glass between a high value and a low value around a mean temperature.

14. Method according to one of claims 5 to 13, characterized in that the heating means provides a transverse temperature profile with an alternation between different temperature levels.

15. Method according to one of claims 5 to 14, characterized in that the heating of the face to be treated is achieved by means of a volume heating to achieve a heat reserve under the surface to be treated leading to a temperature profile non-linear in the thickness of the glass.

16. Method according to one of claims 5 to 15, characterized in that the heating means of the face to be treated allows to heat the previously deposited layers.

17. Method according to one of claims 5 to 16, characterized in that the heating means of the face to be treated allows to heat the previously deposited layers.

18. Method according to one of claims 5 to 17, characterized in that the heating means of the face to be treated are such that the majority of the radiation emitted is in the wavelengths where the glass is opaque.

19. Method according to one of claims 5 to 18, characterized in that an electric field is implemented in the processing unit so as to promote the diffusion of ions in a deposited layer and / or in the glass .

20. Method according to one of claims 5 to 19, characterized in that the chemical composition, the pressure and the temperature of the atmosphere inside the unit are adapted to each treatment implemented.