WO2020174185A1

WO2020174185A1 - Production of glazing with reduced extension stress

Info

Publication number: WO2020174185A1
Application number: PCT/FR2020/050376
Authority: WO
Inventors: Hervé Thellier
Original assignee: Saint-Gobain Glass France
Priority date: 2019-02-28
Filing date: 2020-02-26
Publication date: 2020-09-03
Also published as: EP3931157A1; CN111867991B; FR3093333B1; FR3093333A1; CN111867991A

Abstract

The invention relates to a device and a method for bending and cooling a glass sheet or a stack of glass sheets, referred to as glass, comprising gravity bending of the glass heated to a maximum bending temperature on a gravity support, during which the glass rests on the gravity support in the peripheral zone of the lower surface thereof, said peripheral zone comprising 50 mm from the edge of the lower surface, then said method comprising the cooling of the glass leading to its solidification, the subsequent sequence being performed at least once during said cooling leading to its solidification, picking up of the glass by a separation tool separating it from the gravity support and leaving the lower surface thereof free from any contact in the peripheral zone thereof, then supporting of the glass again on the gravity support in the peripheral zone of the lower surface thereof.

Description

CONSTRUCTION GLASS MANUFACTURING

REDUCED EXTENSION

The invention relates to a method for manufacturing curved glazing, in particular laminated, and proposes an improvement in the step of cooling the glass after it has been bent with a view to obtaining reduced extension stresses. The invention relates to bending processes involving a bending step on a gravity bending support called gravity support. The invention relates in particular to the production of laminated glazing of the windshield or roof type for a road vehicle (automobile, truck, bus), but also any glazing for aeronautics or buildings.

In gravity bending processes, the tooling supporting the so-called “gravity support” glass, with a shape adapted to the final geometry of the glass, is in contact with the periphery of the underside of the glass during all the shaping phases c that is, the preforming of the bending, the bending and the cooling. Thus, for each glazing model, it is necessary to have available a train of particular gravity supports, the number of which is at least equal to the number of different steps carried out in the process. Gravity support is usually in the form of a frame. It is preferably coated with a refractory fibrous material well known to those skilled in the art to come into contact with glass. The width of its contact track with the glass is generally in the range from 2 to 20 mm, including refractory fibrous material.

When the glass leaves the bending step to start the cooling phase, it is, according to the prior art, usually in contact through its periphery with the last gravity support, in particular between 5 and 10 mm from the edge of the glass. When the glass freezes and cools, a physical phenomenon of the genesis of permanent stresses is created which corresponds to the conversion of the temperature distribution within the glass into a stress field. This phenomenon is initiated when the glass freezes and ends at the end of cooling when a homogeneous temperature distribution is reached. It can be considered that the glass freezes substantially at the strain point temperature. Qualitatively, the parts where the glass is fixed in the first place correspond to the parts where the compressive stresses are concentrated, while the parts where the glass is fixed with delay concentrate the stress zones in extension. The edge stresses described in the present invention are membrane stresses which can be defined at any point of the material and for a given direction, as the average of the stress field at this point and in this direction, the average being taken over the whole of the material. 'glass thickness. At the glass edge, only the membrane stress component parallel to the edge is appropriate; the perpendicular component has a zero value. Also any measurement method allowing a measurement of the average stresses along an edge and through the thickness of the glass is relevant. The methods for measuring edge stresses use photoelasticimetry techniques. The two methods described in the ASTM standards cited below make it possible to measure the edge stress values:

- the method using the Babinet compensator and described in standard ASTM C1279 - 2009 - 01, procedure B;

- the measurements carried out with commercial devices such as the Sharples model S-67 marketed by the company Sharples Stress Engineers, Preston, UK and using a so-called Sénarmont or Jessop-Friedel compensator; the principle of measurement is described in standard ASTM F218-2005-01;

Both of these methods use polarized light that passes through the measured sample. It is therefore impossible to implement them directly when the product to be analyzed has an opaque peripheral decoration, usually in black enamel as is customary for automotive glazing. In this case, it is possible to remove the opaque layer either by mechanical abrasion or by chemical attack and then carry out the measurement.

Another method of measuring membrane stresses and adapted from the principles described in standard ASTM F218-2005-01, has been developed by various suppliers of measuring devices and makes it possible to measure glazing that has a peripheral decoration without the need for remove it first. These devices operate according to the following principle: a polarized light source illuminates the sample from its face which has no decorations. The light passes through the sample and is partially reflected by the decoration. located on the opposite side of the sample. The light passes through the sample a second time and then finally passes through a Sénarmont compensator. The following two devices are thus able to measure the edge stresses on glazing having a peripheral opaque decoration:

- the Sharples model S-69 marketed by the company Sharples Stress

Engineers, Preston, UK;

- the VRP-100, manufactured by the company Strainoptics, 108 W. Montgomery Ave., North Wales, PA 19454 USA.

In the context of the present application, the values of compressive stresses are determined by the method described in standard ASTM F218-2005-01, optionally adapted in order to measure only the stress of the glass outside the laminated glazing as mounted on the vehicle. . The stresses can therefore be either measured on the outer glass sheet alone before laminated assembly or on the outer glass sheet after laminated assembly using the Sharples S-69 or VRP-100 devices mentioned above. For the measurement carried out after assembly to be relevant, it is necessary to color the inner surface of the outer glass sheet of the glazing using a black or metallic paint or enamel. This sheet in the external position on the vehicle corresponds to the sheet in the lower position during the bending by gravity by the method according to the invention. The extension measurements are carried out by the same method in an area parallel to the edge of the glazing but located slightly more towards the interior of its main face.

Generally edge compressive stress values are determined between 0.1 and 2 mm from an edge and preferably between 0.1 and 1 mm from an edge. When taking the measurement near the edge and inside the glazing, an extended edge stress zone is generally identified which is included in a peripheral zone between 3 and 100 mm from the edge of the glass.

Current specifications for glazing properties require permanent edge compression values, greater than 8 MPa, and the smallest possible edge extensions to maintain the mechanical strength of the glazing during assembly and use.

EP2532625 teaches a device for supporting glass after having cooled its surface below its strain point. The central area of the glass is cooled under the strain point before the border. This technique is applied to annealing glass. Cooling of the interior of the glass is necessary in order to be able to lift the glass from its support. This causes the compression of this central zone, which must necessarily be counterbalanced by an extension zone at the periphery thereof. The cooling of the central zone therefore runs the risk of resulting in the creation of greater peripheral extension constraints which may possibly weaken the glass. In addition, if the annealing step is insufficiently controlled and the periphery of the glazing remains too long at too high temperature during this phase, the level of edge compressions could be insufficient.

US5071461 teaches the bending of a stack of glass sheet then its cooling during which the glass is lifted from the bending mold by means of lifting rods supporting an area adjacent to the peripheral area in order to rapidly cool the more strongly convex part. glass.

WO2018154247 teaches a device and a method for the bending and cooling of glass sheets comprising the gravity bending of the glass on a gravity support during which the glass rests on the gravity support in the peripheral zone consisting of the 50 mm from the edge of its lower face, then the separation of the glass from the gravity support while the glass is at more than 560 ° C, then cooling of the glass during which its lower face is free of any contact in its peripheral zone between at least 560 ° C and 500 ° C. According to this document, the glass is never rested on its gravity support during cooling and after separation, so that the shape of the glass may possibly deviate a little from that desired during cooling.

The invention makes it possible to reduce the disturbance of the temperature distribution induced by the presence of the gravity support in the vicinity of the periphery of the glass. The desired edge compression levels cited above are more readily achievable with larger safety margins, and extension stress levels are reduced. The desired shape for the glass and corresponding to that of the gravity support is well preserved during cooling.

The invention relates to a method for bending and cooling a glass sheet or a stack of glass sheets, called glass, comprising the bending by gravity of the glass heated to a maximum temperature in its plastic deformation temperature range on a gravity support during which the glass rests on the gravity support in the peripheral zone of its lower face, said peripheral zone consisting of 50 mm from the edge of the underside, the glass bulging by sagging under the effect of its own weight, then said process comprising cooling the glass leading to its freezing, the following sequencing being carried out at least once during said cooling leading to its freezing:

the handling of the glass by a separation tool separating it from the gravity support and leaving its underside free of any contact in its peripheral zone, then

the support again of the glass on the gravity support in the peripheral zone of its lower face.

The expression "cooling leading to freezing of the glass" means cooling before the complete freezing of the glass and therefore at a temperature higher than its freezing temperature. Thus, the contact areas of the glass with the separation tool and with the gravity support are areas not yet fixed at the time of sequencing. During the cooling leading to the freezing of the glass, the glass hardens, loses its malleable state and internal stresses in the glass are created. These stresses are formed as a result of the fact that the entire mass of the glass does not cool simultaneously. It is considered that the freezing is completed when the glass has reached the temperature of 450 ° C and even 480 ° C during cooling, that is to say substantially its glass transition temperature. The cooling leading to the freezing of the glass is generally controlled cooling, that is, the speed of which is controlled.

Preferably, the sequencing is carried out while the glass is cooling leading to its freezing, at least once when its temperature is between the maximum bending temperature and 480 ° C and preferably between 560 and 500 ° C.

Preferably, the sequencing is carried out during the cooling of the glass leading to its freezing at least twice and preferably at least 3 times and preferably at least 4 times and preferably at least 5 times, or even at least 6 times, or even at least 6 times. minus 7 times when its temperature is between the maximum bending temperature and 480 ° C. The separation / (resupport) sequencing is preferably carried out at least 2 times between 560 and 500 ° C. Even more preferably, the sequencing is carried out at least once between the maximum bending temperature and 560 ° C, at least twice between 560 and 500 ° C, and at least once between 500 and 480 ° C.

The bending is thermal, the glass being brought to a temperature allowing its plastic deformation. The maximum glass gravity bending temperature is greater than 560 ° C and generally greater than 570 ° C, and is generally less than 680 ° C.

In the context of the present invention, the central region of the lower face of the lens, in particular the region at a distance greater than 200 mm from the edge, is generally at a temperature at least equal to that of the peripheral zone of the lower face of the lens. glass when the glass is taken over by a separation tool before freezing of the glass, whether it is a first sequencing or a subsequent sequencing. Thus, the entire glass is not yet frozen at the time of sequencing and its temperature in any zone is therefore higher than that of its strain point. The "strain point" is determined by the method of measuring the viscous elongation rate of a fiberglass, by extrapolation from the annealing point, and in accordance with standard ASTM C336-71 (re-approved in 2005). The expression "strain point" can also optionally be said "point of constraint" in French, but the expression "Strain Point" has passed into the everyday language of those skilled in the French art who no longer uses the expression French. One thus speaks of temperature of strain point or more simply of “strain point”.

The gravity support influences the temperature of the glass in its contact zone. When the glass is separated from the gravity support into ¹ time sequencing, glass is homogenized in temperature in this zone. In doing so, without contact with the gravity support, its shape risks deviating slightly from the desired final convex shape. By finding the gravity carrier in the 2 ^nd time sequencing, the glass found the desired bulging final shape. Thanks to the sequencing, which is preferably repeated during the cooling of the glass leading to its freezing, one obtains both a homogenization of the temperature of the glass in its contact zone with the gravity support, and a shape faithful to the desired final shape. . Permanent contact with one support as produced according to the prior art, detrimental for the extension constraints is, within the framework of the present invention, “shared” on two tools (gravity support and separation tool) touching the glass in two different places and at different times. At each separation of the gravity support and redeposit on the gravity support, there is a succession of thermal gradient removal and regeneration (this is also true for the gravity support and the separation tool). The extension levels in the glass are thereby reduced and the mechanical strength improved. The homogenization of the temperature of the glass in its zone of contact with the gravity support makes it possible to obtain reduced extension stresses while maintaining good edge compressive stresses.

The average cooling rate during the cooling leading to the freezing of the glass, in particular between 560 and 500 ° C, is preferably in the range from 0.3 to 3 ° C / second and preferably in the range from 0, 4 to 2.7 ° C / second.

The cooling leading to the freezing of the glass is advantageously controlled cooling, which is advantageously carried out in a series of controlled cooling chambers traversed by the glass and its gravity support, the temperature of these chambers decreasing from one chamber to the other during of the glass path. The glass passes from one chamber to another while being supported by its gravity support, then in a chamber, a separation tool separates it from the gravity support for a separation period then rests it on top, then the gravity support supporting the glass go to the next room. Each controlled cooling chamber is at a lower temperature than the one before it. The separation time is generally in the range from 1 to 45 seconds and more generally in the range from 2 to 30 seconds. The rooms can be separated by sliding doors that open to let a gravity support pass carrying its glass and close to keep the room at the desired temperature. Generally, the train of gravity supports crosses the suite of chambers making stops so that each glass stops successively in all the chambers. Below 400 ° C, the glass can be considered as completely frozen and it can then be cooled quickly or slowly without any particular precaution as to its areas of contact with a tool.

Generally, from the end of the bending at over 560 ° C and up to 400 ° C during cooling, the glass is in contact only with the gravity support or a separation tool. Generally, below 450 ° C and at least up to 350 ° C, the glass can rest on the gravity support without further contact with another tool.

While in contact with the separation tool, the peripheral zone of the underside of the lens is in contact only with ambient air and with no tools. While the gravity support of any part only touches the lens in the peripheral area of the underside of the lens, the separation tool does not touch it in this area.

Advantageously, air cooler than the glass can be blown over the peripheral area of the underside of the glass while the glass is being taken over by the separation tool. This blowing can be done using an air blowing ramp to cool the periphery of the glass more strongly. The blown air is at a lower temperature than that of glass. It was found that by blowing in this way on the peripheral zone of the underside of the lens, the extension stresses were even more reduced. Blowing is carried out on the contact area with the gravity support, in the absence of contact with the gravity support. Thus, the device according to the invention can comprise an air blowing ramp capable of blowing on the peripheral zone of the underside of the glass during the taking up of the glass by the separation tool.

The separation tool may include an upper form capable of acting on the upper face of the lens for its handling, such as that referenced 33 in FIG. 1 of WO2018 / 154247. A homogenization of the temperature of the glass is obtained by maintaining the glass by suction on its upper face and without any contact with its lower face, thanks to this upper form provided with a skirt and a suction means sucking the air between the edge of the glass and the skirt, the suction of the skirt providing the force to hold the glass against the form (even a stack of sheets of glass). The air sucked in by the skirt and circulating in the vicinity of the edge of the lens promotes the homogenization of the temperature of the peripheral zone of the lower face of the lens. If necessary, we can equip the skirt with an air blowing ramp to cool the peripheral zone of the underside of the glass more strongly.

The upper form is preferably in the form of a frame, this frame preferably being covered with a refractory fibrous material in order to reduce the risk of marking the surface of the upper face of the glass. This frame may have a width within the range of 2 to 20 mm, including the fibrous material. Preferably, this upper form comes into contact with the glass without protruding from the edge of the glass. This upper form can come into contact with the glass so that its outer edge comes at a distance from the edge of the glass (towards the inside of the glass) in the range of 3 to 20 mm.

A top form as a separation tool and the gravity support can be animated with a relative vertical movement allowing them to move towards each other so that one of these tools takes up the glass or leaves it take over by the other, as part of performing separation / sequencing (support again). The expression "relative vertical movement" means that only one of the two tools (the separation tool and gravity support) can move vertically, or that both can move vertically for the passage of the glass from one to the other. 'other. For the separation step, the upper form and the gravity support approach (the glass being between these two tools, on the gravity support), then the suction of the upper form is triggered and the upper form then takes charge of the glass , then the upper form (holding the glass against it) and the gravity support move away, then, with a view to “support again” these two tools come together, the suction is stopped and the glass is dropped on the gravity support , then the two tools move away from each other again.

For reasons of cost, the separation tool is advantageously a tool coming into contact with the glass via its lower face and only coming into contact with the glass at a distance greater than 50 mm from the edge of the glass. The separation tool does not come into contact with the lens in the peripheral zone of the underside of the lens. The separation tool can come into contact with the glass in an area between 50 mm from the edge of the glass and 200 mm from the edge of the glass and preferably between 50 mm and 150 mm from the edge of the glass. Advantageously, the separation tool comes into contact with the glass exclusively in this zone. The separation tool can be a support coming into contact with the underside of the glass; it could be :

a) a continuous or crenellated frame such as that referenced 10 in Figure 18 of WO2018 / 154247, or

b) of a set of pads supported on a frame such as the tool referenced 400 in Figure 20b of WO2018 / 154247, or as one of the supports shown in Figures 6 to 9 of WO2018 / 154248.

The pads of the supports b) above can be mounted to move by means of a spring placed under their contact surface for the glass, like the pads of Figures 1, 2, 3, 4, 10 of WO2018 / 154248. Note that the term “support” in the context of the present application designates a tool on which the glass rests and is therefore in contact with the underside of the glass.

The separation tool, if it supports the glass, preferably has a discontinuous support surface, and therefore provides the glass with a plurality of support zones. This discontinuity favors the circulation of air and the more homogeneous cooling of the underside of the glass.

The separation tool, if it supports the glass, can form an on-board assembly with the gravity support. The separation tool then circulates with the gravity support in an on-board manner on a “gravity support / separation tool” assembly. In this case the separation tool and the gravity support can be animated with a relative vertical movement allowing one to pass above the other or to pass below the other in order to take charge the glass or let it take over by the other, as part of the separation / sequencing performance (support again). The expression "relative vertical movement" means that only one of the two members (the separation tool and the gravity support) can move vertically, or that both can move vertically for the passage of the glass from one to the other. 'other. Preferably, the difference in height dimension of the contact track of one of the two members with respect to the other, when they are not in motion, is at least 10 mm and preferably at least. less 30 mm. Such a distance makes it possible, on the one hand, to eliminate heat transfers by conduction but also to sufficiently minimize heat transfers by radiation between the glass and the component (either the separation tool or the gravity support) that we have just separated from the glass. The gravity support supporting the glass is placed in an oven for the thermal bending of the glass. The bending being carried out, the gravity support carrying the glass is moved into a cooling zone to cool the glass. The controlled cooling first leads to the freezing of the glass, then the geometry of the glass being fixed, the glass is cooled to room temperature. The bending and the controlled cooling leading to the freezing of the glass are advantageously carried out in a succession of chambers arranged one behind the other on the path of the glass. These chambers are at different temperatures in order to apply the desired thermal profile to the glass. A plurality of glasses circulate one behind the other, each glass being on a different gravity support.

The device according to the invention can comprise both at least one separation tool coming into contact with the glass via its lower face as already described and also at least one separation tool of the upper form type provided with a suction means and coming into contact with the glass via its upper face as described above. Each of these separation tools is used as part of a different "separation / (support again)" sequencing applied one after another. These different sequencing are preferably applied in different chambers, which have different temperatures.

In particular, it is possible to apply at least one sequencing by contact with the upper face, then at least one sequencing by contact with the lower face, these two types of sequencing being applied in two different chambers, the second chamber being at a lower temperature than the second chamber. first.

It is also possible to apply at least one sequencing to the glass in a first chamber by a separation tool comprising an upper form provided with a suction means acting on the upper face of the glass for its handling, and at least one sequencing in a second chamber by a separation tool coming into contact with the underside of the glass in an area between on the one hand 50 mm from the edge of the glass and on the other hand 200 mm and preferably 150 mm from the edge of the glass, the second chamber being disposed after the first chamber on the path of the glass, the second chamber being at a temperature lower than that of the first chamber. The device according to the invention then comprises a first chamber comprising at least one separation tool of the upper form type provided with a suction means coming to the contact of the glass via its upper face and a second chamber comprising at least one separation tool coming into contact with the glass via its lower face. Usually the first chamber precedes the second chamber on the glass path.

It is also possible to apply at least one sequencing by contact with the upper face in a first chamber, then at least a second sequencing by contact with the upper face in a second chamber, then at least one sequencing by contact with the lower face in a third. chamber, the second chamber being at a lower temperature than the first and the third chamber being at a lower temperature than the second.

For the glass, the separation tool generally has the shape corresponding to its desired final shape, it being understood that its shape may deviate from the desired final shape as soon as it has members capable of orienting itself in order to take the shape of the glass when it is picked up and under the effect of the weight of the glass. In fact, just before coming into contact with the separation tool, the glass had just been curved on the gravity support and therefore took the desired final convex shape, so that a separation tool having organs allowing it to orient itself with respect to the shape of the glass therefore takes in contact with the latter substantially the final shape desired for the glass. Supports offering the glass a discontinuous surface by pads and capable of modifying the orientation of the pad contact zone and / or damping the reception of the lens under the effect of the weight of the lens when it is received by the support have been described in WO2018 / 154248 and can be used as a separation tool in the context of the present invention. The greater the number of pad contact zones, the smaller the contact area of each zone. The sum of the areas of all the contact areas of the pads may represent 0.2 to 5% of the area of the underside of the lens. The contact area of each pad contact zone can be in the range from 50 mm ² to 5500 mm ² and preferably from 500 mm ² to 4000 mm ² . Preferably, the separation tool comprises 4 to 20 or even 6 to 20 contact zones of relatively high area each, that is to say of area each within the range from 500 mm ² to 4000 mm ^2. . The separation tool, as a support capable of supporting the lens by coming into contact with its lower face, can therefore include a discontinuous contact surface for the lens. The separation tool can also be a continuous or crenellated frame.

The separation tool, if it supports the glass by its 1 ^st main face (that is to say the outer face of the outer glass of the glazing as it is mounted on the vehicle), may have a contact surface for glass having a shape, called a compensation shape, deviating from the final shape desired for the glass in order to compensate for a possible defect in shape that the glass could take if the separation tool had exactly the desired shape for the glass . In fact, such a separation tool supports the glass in a relatively internal zone of the underside of the glass and at a temperature at which the glass is not completely fixed. As a result, the portion of the glass outside the separation tool may have a tendency to collapse. This collapse can be avoided by giving the separation tool a so-called compensation form which comprises concave curvatures more accentuated than those of the gravity support in its final form. Thus, the support-type separation tool may have a contact surface for the lens, which is concave when viewed from above and more curved than that of the gravity support which is to support the lens in the same region at the end of bending.

Conversely, and to correct the same phenomenon of preferential deformation of the periphery of the lens when it is supported by the separation tool, it is possible to give the form of compensation not to the separation tool but to the gravity support. -even. The latter therefore then has a concave shape, seen from above, which is slightly more curved than the final shape of the glass.

All tools coming into contact with glass above 400 ° C (gravity support, separation tool such as a top form or discontinuous support) have at their contact surface for the glass a refractory fibrous material well known to man of the trade to reduce the risk of marking hot glass with a tool. This fibrous material may be a fabric or felt or knit and in particular a “tempering knit” usually used to coat the tempering frames of the glass and having the advantage of being very perforated. The refractory fibrous material contains refractory fibers and has a large open porosity which gives it a thermal insulating property.

The gravity support generally has, at least at the end of bending, a shape corresponding to the final geometry desired for the glass. During the bending of the glass, it is in contact with the periphery of the underside of the glass. The gravity support generally has the shape of a frame and can be called a skeleton by those skilled in the art. A skeleton is a metal strip, one edge of which serves as a contact track for the glass. The gravity support is generally continuous at least at the end of bending. It is preferably coated with a refractory fibrous material well known to those skilled in the art to come into contact with the glass. The width of its contact track with the glass is generally in the range from 2 to 20 mm, including refractory fibrous material.

The gravity support can include articulated parts that rise during bending and / or several frames supporting the glass one after the other during bending. Such gravity supports have been described in WO2015 / 128573, WO2013132174, W02007077371, EP448447, EP0705798. The separation of the glass from the gravity support takes place after the glass has taken its final shape at the periphery and therefore once the gravity support has taken the final shape desired for the glass. This shape offered to the glass by the gravity support does not change until its last separation from the glass. The separation / sequencing (support again) takes place with the gravity support in its final form.

If the separation tool supports the lens from its underside, then it touches it in its zone inside its peripheral zone, that is to say at more than 50 mm from the edge of the lens (without contact at less than 50 mm from the edge) and preferably more than 60 mm from the edge of the glass (contactless less than 60 mm from the edge). Generally, the contact area of the separation tool is entirely within 200 mm of the edge of the glass (contactless then more than 200 mm from the edge of the glass) and preferably less than 150 mm from the edge of the glass (contactless then more than 150 mm from the edge of the glass). Such a tool can be integrated into a device comprising the gravity support, in which case all the contact areas of the separation tool are circumscribed in top view by the gravity support when the latter has its final shape.

The device according to the invention can comprise an oven and a plurality of gravity supports each capable of supporting a glass, said gravity supports forming a train of gravity supports able to circulate in the oven. A plurality of gravity supports are produced for producing a batch of glasses having a specific shape. These supports, each carrying a glass (a sheet or several stacked sheets) are conveyed one behind the other, forming a train of gravity supports, in a bending furnace in order to bend the glass and then cool it in a controlled manner at least until it freezes. The controlled cooling zone leading to the freezing of the glass is considered to be part of the furnace. In fact, this zone generally comprises thermal insulation and heating means in order to regulate and maintain the desired temperature. The furnace generally comprises a plurality of chambers crossed one after the other by the gravity supports following one after the other, and this, for the bending and controlled cooling. After removal from the oven and when the glass is frozen, the gravity supports can be unloaded from their glass and returned empty to the loading station. They then take over a non-curved glass and return to the oven for the bending of this new glass. These gravity supports can be part of a device integrating them as well as a separation tool. In this case, it is a plurality of such gravity support / separation tool devices which are manufactured and circulate in the furnace.

The invention relates in particular to the production of laminated glazings combining two sheets of glass, the thickness of one of which is in the range from 1.4 to 3.15 mm and the thickness of the other of which is included in the range ranging from 0.5 to 3.15 mm. For the case where the sheets have different thicknesses, the face 1 of the laminated glazing (outer convex face of the sheet in the outer position when the glazing is mounted on the vehicle) is one side of the thicker sheet. In the method according to the invention, the glass can be a stack of two sheets of glass of different thickness, the thinner preferably being the thicker. In particular, these two sheets can be intended to be assembled together in a laminated glazing, in which case, the fact that they are the one on the other of the bending until the freezing guarantees an excellent compatibility of form.

Each sheet of glass may be covered before bending with one or more layers of enamel or one or more thin layers of the anti-solar (low-e), conductive or other type usually applied to automotive glazing.

The curved glass produced according to the invention relates more particularly to the production of glazing, in particular laminated, of the windshield or roof of a road vehicle type. The area of one of their main surface is generally greater than 0.5 m ² , especially between 0.5 and 4 m ² . Usually, in the central region of the glass, one can place a virtual circle with a diameter of at least 100 mm and even at least 200 mm and even at least 300 mm, all of the points of which are farther than 200 mm away. of all the edges of the glass, which characterizes a certain size of the glass. Glass generally has four edges (also called bands), the distance between two opposite edges being generally greater than 500 mm and more generally greater than 600 mm and more generally greater than 900 mm.

Thanks to the invention, the edge compressive stresses of the final glass in its sheet comprising the underside are greater than 8 MPa, or even greater than 10 MPa. The extension levels are low, less than 5 MPa and even less than 4 MPa, or even less than 3 MPa. The maximum stress in extension is generally located at a distance from the edge of between 5 and 40 mm and more generally between 10 and 40 mm. The sheet in the lower position during bending and cooling therefore exhibits remarkable mechanical properties making this sheet well suited to be mounted in an external position facing the outside, of an automobile glazing. Indeed, the face of the glazing facing outward (face 1 convex) is the one most likely to receive projectiles such as, for example, gravel.

In particular, the invention makes it possible to obtain a curved glazing, in particular laminated, comprising at least one sheet of glass comprising an edge compressive stress greater than 8 MPa, a maximum extension stress of less than 5 MPa or even less than 4 MPa. For the case where at least one separation tool of the type coming into contact with the glass from below has been used, and this tool has been loaded with the gravity support, a visible trace in polariscopy is observed at the places of contact with the 'separation tool, i.e. more than 50 mm from the edge. The trace visible in polariscopy has the shape of the separation tool, that is to say that of a frame or a discontinuous set of tasks located between on the one hand 50 mm from the edge of the glass and on the other hand 200 mm and if necessary 150 mm from the edge of the glass. The glazing can be laminated and include two sheets of glass, the thickness of one being in the range from 1.4 to 3.15 mm and the thickness of the other being in the range from 0 , 5 to 3.15 mm. For the case where the separation tool is an upper form of the frame type as already mentioned above and coming into contact with the area peripheral of the upper face of the lens without touching the lens beyond this peripheral zone, this upper shape does not cause any trace in polariscopy beyond the peripheral zone from the edge of the lens in the final lens, and therefore also beyond 150 mm from the edge of the glass, and therefore also beyond 200 mm from the edge of the glass. Thus, the invention also relates to a curved glazing, in particular laminated, comprising at least one sheet of glass comprising an edge compressive stress greater than 8 MPa, a maximum extension stress of less than 5 MPa or even less than 4 MPa and without visible trace in polariscopy more than 200 mm from the edge and even more than 150 mm from the edge and even more than 50 mm from the edge of the glass. In particular, the glazing can be laminated and comprise two sheets of glass, the thickness of one being in the range from 1.4 to 3.15 mm and the thickness of the other being in the range from from 0.5 to 3.15 mm.

FIG. 1 shows a gravity bending device 1 comprising a gravity support with double skeleton (2, 3) and a separation tool 4 in the form of a continuous ring. FIG. 1a shows the device in top view and FIGS. 1 b and 1 c show, along the section plane AA 'of FIG. 1 a, the device seen from the side at two different times. In figures 1 b and 1 c, the dashed lines correspond to the contact surface for the glass of the various supports 2, 3, 4. The gravity support comprises a blank skeleton 3 supporting the glass at the start of bending and a finishing skeleton 2 supporting the glass at the end of bending. The curvatures of the blank skeleton 3 are concave seen from above and less pronounced than those of the finishing skeleton 2. In top view, the separation tool 4 is circumscribed by the blank skeleton 3 and the blank skeleton 3 is circumscribed by the finishing skeleton 2. Glass is not shown for clarity. Figure 1 b) shows the relative position of the various elements (2,3,4) of the device at the end of bending, the glass then following the entire periphery of the contact track of the finishing skeleton, which is in a higher position than the two other elements 3 and 4. This figure therefore does not show the relative position of the elements 1, 2,4 in the prebombing phase on the blank skeleton 3, this phase being prior to the representations of this figure 1. Figure 1 c) shows the relative position of the different elements (2, 3, 4) of the device just after separation of the glass from the finisher skeleton 2 following the lifting of the separation tool 4, the glass then hugging the entire periphery of the tool separation 4. Here we are at the first step of the “separation / (support again)” sequencing, which is followed by the second step of the same sequencing according to which the separation tool descends and the glass is again supported by the skeleton finisher 2.

Figure 2 shows a gravity bending device 20 comprising a gravity support with double skeleton (21, 22) and a discontinuous separation tool 23 comprising a plurality of pads 24 mounted on a common frame 25. The gravity support comprises a blank skeleton 21 supporting the glass at the start of bending and a finishing skeleton 22 supporting the glass at the end of bending. In top view, the set of pads 24 forming a discontinuous contact surface for the lens is circumscribed by the blank skeleton 21 and the blank skeleton 21 is itself circumscribed by the finishing skeleton 22. The lens is not shown. for the sake of clarity. The frame 25 moves up or down to move up or down all of the pads, depending on the "separation / (support again)" sequencing step to be performed. After the glass has hugged the entire circumference of the finisher skeleton 22, the frame 25 rises so that the runners 24 support the glass and frees the finisher skeleton. The pads 24 touch the lens in an area inside the peripheral area of the underside of the lens. The frame 25 then descends to replace the glass on the finishing skeleton.

FIG. 3 represents in a) a lens 30 resting on a finishing skeleton 31, then in b) its separation from this skeleton following the raising of a separation tool 33, then in c) the redeposition of the lens 30 on the skeleton finisher following the descent of the separation tool 33. The same references are used from a) to c). This figure 3 represents in section in a transverse plane of the furnace (that is to say seen in the longitudinal axis of the furnace) and very schematically, a lifting system 40 itself composed of two sub-assemblies: the part upper 41 and lower part 42. These two sub-assemblies 41 and 42 form an integral part of the oven and are surrounded by a layer of fibrous insulation 39 which provides thermal insulation of the oven. The upper part 41 can be translated vertically using bars 36 which pass through the roof of the oven. A coupling system 37 makes it possible, in the low position, to separate the upper 41 and lower 42 parts of the lifting system 40 in order to accommodate any differential expansion of the two sub-assemblies or in order to separate them during a maintenance operation. This coupling system makes it possible to translate the sub-assembly 42 upwards during the ascent of the sub-assembly 41.

The separation tool 33 rests on the lower part of the lower sub-assembly 42 of the lifting system which can therefore give it a series of vertical movements up or down. The separation tool 33 is here resident in a chamber 43 of the furnace whose atmosphere is at a specific temperature. More precisely, the separation tool 33 is introduced into this chamber 43 during the change of manufacture and it remains there immobile in the low position when the glass 30 and its skeleton are translated into the following chamber. The separation tool 33 will leave its chamber 43 during the next production change when all the tooling specific to the glazing that has just been produced is removed from the installation.

The separation tool 33 comprises a structure having vertical and horizontal bars 34 and an upper part provided with pads 35. A glass 30 has been bent on a gravity support of the double skeleton type and rests in a) on the finishing skeleton 31 gravity support. The blank skeleton 32 has already supported the lens at the start of bending and therefore appears here retracted and below the level of the finishing skeleton 31. The double skeleton rests on the member 38 which makes it possible to support it vertically and to perform a longitudinal horizontal translation. thus allowing the skeleton and the glass 30 to pass from one chamber of the furnace to the next. The member 38 may be a movable carriage which rolls on a fixed rail, a chain which translates in the oven, or a bed of rollers which pass through the side walls of the oven.

After bending the lens in a), the separation tool 40 is raised and the lens is supported (see FIG. 3b) in a zone inside its peripheral zone by the contact surfaces 35 of the separation tool 33. This lifting is actuated here by the vertical translation of the lower sub-assembly 42 of the lifting system, itself driven upwards by the upper sub-assembly 41, itself pulled upwards thanks to the bars 36 which are connected to a motorization system not shown.

After holding for a period of separation on the separation tool, the glass is rested in c) on the finishing skeleton of the gravity support. The separation tool and its lifting system are here permanently in the chamber 43 whose atmosphere is at a specific temperature. Several bedrooms, each with a specific temperature, can be juxtaposed and be equipped with their own separation tool and their own lifting system. A plurality of gravity supports can thus circulate one behind the other, each carrying a glass and pass from one chamber to another, in particular the chamber 43, as part of the glass cooling cycle.

In this variant as represented by this FIG. 3, the separation tool is resident in a cooling chamber, that is to say that it does not circulate with the gravity support but that it processes the glasses in circulation. one after the other. It would be possible to use a lifting system similar to that in Figure 3 except that the separation tools would be on board with the gravity supports. In this case, the separation tool 34 of Figures 3a), 3b) and 3c) would be reduced to a simple frame with taller vertical bars and which would lift the on-board separation tool with the gravity skeleton. In such a situation (separation tool on board the gravity skeleton), it is possible to envisage a simpler lifting system, consisting of four vertical bars passing through the bottom of the furnace. As the kiln cells do not contain a resident separation tool, the hearth can then be closer to the gravity skeleton, just below organ 38.

Figure 4 shows schematically the kinematics of separation and support again glass on a skeleton of a gravity support. This graph represents the dimension (z) of the lifting bars 36 of FIG. 3, in millimeters as a function of time. At Z> 625 mm, the glass is on the separation tool. The difference in height dimension of the contact tracks of the two tools (gravity support and separation tool) is 35 mm (660-625 = 35). The glass is successively and according to a defined and regular cycle:

separated from the gravity support 6 times at times t _mi ,, t _m 3, etc., and replaced on the gravity support 6 times at times t _di , t _d 2, t _d 3, etc.

FIG. 5 represents the temperature T of the glass in ° C as a function of time in the controlled cooling phase. The temperatures indicated are those recorded at each of 6 separations of the glass from the gravity support taking place approximately at the instants t _mi ,, t _m 3, etc., as defined in FIG. 4. FIG. 6 represents the influence of the contact surface of a support-type separation tool coming into contact with the underside of the glass on the collapse or not of the zone of the glass outside the separation tool. In all the figures, the glass 60 has already been curved on a skeleton 61 of a gravity support. The separation tool 64 includes a contact surface 62 for the lens, which substantially matches the shape desired for the lens at the point of contact. In b1, the separation tool 64 is mounted and supports the glass during the separation time. During this period, the outer zone z of the lens tends to collapse, giving the lens an unwanted curvature at 63. The desired curvature is shown superimposed on FIG. 6b1 by a dashed curve 65. FIGS. 6a1 and 6b1 represent the case where the separation tool offers the lens a surface having exactly the final shape desired for the lens at the point of contact. An unwanted collapse can therefore result. FIGS. 6a2 and 6b2 show how this collapse can be combated by varying the shape of the contact surface 62 of the separation tool 64. In fact, the contact surface 62 of the separation tool here has a concavity. accentuated in the direction orthogonal to the edge of the glass with respect to the concavity it would have if it had the desired final shape for the glass (the concavity corresponding to the desired shape of the glazing is shown in dashed lines 66 in Figures 6a2) and 6b2). Rather, this accentuated concavity causes the z zone of the lens to rise or even reduce or prevent this collapse. In order to better visualize the difference in geometry of the glazing obtained, a dotted curve 67 in FIG. 6b2) is represented by the curvature taken by the glass in the situation of FIG. 6b1). The separation tool here has a form of compensation to compensate for the effect of the collapse and therefore to avoid too great a collapse of the zone z.

FIG. 7 schematically represents a method according to which a plurality of devices 70 each comprising a gravity support supporting a glass passes one after the other in a tunnel furnace 71, which ensures the heating of the glass, its bending by gravity then its controlled cooling then its forced cooling. The furnace is shown in top view at 72 and in side view at 73. The vacuum gravity supports 75 are each loaded with a flat glass 74 at the loading station 76 before entering the furnace 77. A loaded gravity support. of a glass 70 then enters the oven and is then conveyed into the furnace to pass successively through chambers 1 to 13. It first passes through a heating zone "h" comprising chambers 1 to 4 causing the glass to reach its bending temperature, then into a bending zone "b" comprising the rooms 5 to 8, then in a controlled cooling zone called "cc" (controled cooling) in rooms 9 to 11, then in a forced cooling zone called "fc" (forced cooling) in rooms 12 and 13. The gravity support loaded with its curved and frozen glass leaves the furnace through the furnace outlet 78. The glass is then unloaded from the gravity support at the unloading station 79 and the vacuum support is returned to the loading station 76 to be loaded with a new one. flat glass and undergo the bending and cooling cycle again. This entire cycle is carried out by a plurality of bending supports, each loaded with a glass and running one behind the other, forming a train in the process. They move through the oven so that each of the chambers 1 to 13 can be occupied by a support loaded with glass and they move step by step in the oven after having spent a defined time in a chamber. During the controlled cooling in the chambers 9 to 11, the glass undergoes twice in each of the chambers 9 to 11 (that is to say 6 times) the sequencing separation / (support again) according to the invention. The separation tool can be loaded and conveyed together with the gravity support on the same device. Each room can also include its own separation system and remain permanently assigned to its room. From room 9 to room 11, each room is less hot than the one before it. The glass is frozen on leaving the chamber 11, its temperature being about 480 ° C or lower. It can then be cooled more rapidly in chambers 12 and 13 in which it undergoes forced cooling, that is to say by convection of relatively cold air. The glass comes out of the oven at 78 at about 220 ° C.

FIG. 8 represents the different stages of a separation / sequencing (support again), the separation of the glass 80 being carried out by virtue of an upper form 82 in the form of a frame provided with a skirt 81 as suction means. The skirt is provided with a blowing ramp 83. In a), the glass is on a gravity support 84 of the skeleton type and supports the glass in the peripheral zone of its lower face. In b), the upper form 82 and the gravity support supporting the glass are approached by a relative vertical movement. The suction through the skirt was then triggered and the glass was fixed to frame 82 as shown in c). The upper form 82 carrying the glass and the gravity support moved away and the ramp 83 began to blow air on the peripheral zone of the lower face of the glass in order to exert a stronger cooling in this. zoned. The blowing is carried out on the contact zone with the gravity support 84, in the absence of contact with the gravity support. The upper form 82 and the gravity support 84 then approached by a relative vertical movement, the suction by the skirt 81 was stopped and as a consequence, the upper form dropped the glass 80 on the gravity support 84 as shown in d ).

EXAMPLES

A series of tests were carried out on stack type glasses each comprising a sheet of glass 1.8 mm thick on which was superimposed a sheet of glass 1.4 mm thick. The glasses were curved by gravity at 630 ° C then they underwent a controlled cooling with a variable number of sequencing / separation (support again), the separation being effected by contact with the underside of the glass starting at 80 mm from the edge of the glass. The controlled cooling was carried out according to the protocol shown in FIGS. 4 (with a different number of separations depending on the glass) and 5. Four glasses V1 to V4 were carried out under the conditions and with the results given in Table 1.

Table 1

The last 2 columns are the results of a test consisting in indenting a glazing using a 3.4 gram Vickers point and the radius of curvature at point level 0.2 mm and dropping from a height of 700 or 900 mm. The indentation was performed on the main surface of the glazing at the level of the maximum edge extension. This is a% of breakages. The performance in extension (the lower the value, the better the result) and in indentation (the lower the value, the better the result) are better from V1 to V4. We see a clear correlation between edge extension stress values and impact performance. Thus, the earlier the glazing is separated (and at high T °) from the gravity support, the lower the number of breaks and the lower the extension value.

Claims

1. Process for bending and cooling a sheet of glass or a stack of sheets of glass, called glass, comprising the bending by gravity of the glass heated to a maximum bending temperature on a gravity support (2 ) during which the glass rests on the gravity support in the peripheral zone of its lower face, said peripheral zone consisting of 50 mm from the edge of the lower face, then, said method comprising cooling the glass leading to its freezing , the following sequencing being carried out at least once during said cooling leading to its freezing:

- the support of the glass by a separation tool (4) separating it from the gravity support and leaving its lower face free of any contact in its peripheral zone, then

- the support again of the glass on the gravity support in the peripheral zone of its lower face.

2. Method according to the preceding claim, characterized in that the sequencing is carried out during said cooling of the glass at least once while its temperature is between the maximum bending temperature and 480 ° C and preferably between 560 and 500 ° C.

3. Method according to one of the preceding claims, characterized in that the sequencing is carried out during said cooling of the glass at least twice and preferably at least 3 times and preferably at least 4 times and preferably at least 5 times, or even at least 6 times, or even at least 7 times when its temperature is between the maximum bending temperature and 480 ° C.

4. Method according to one of the preceding claims, characterized in that the sequencing is carried out at least twice between 560 and 500 ° C.

5. Method according to the preceding claim, characterized in that the sequencing is carried out at least once between the maximum bending temperature and 560 ° C, and at least twice between 560 and 500 ° C, and at least once between 500 and 480 ° C.

6. Method according to one of the preceding claims, characterized in that the maximum bending temperature is greater than 570 ° C.

7. Method according to one of the preceding claims, characterized in that the maximum bending temperature is less than 680 ° C.

8. Method according to one of the preceding claims, characterized in that the central region of the lower face of the lens, in particular the region at a distance greater than 200 mm from the edge, is at a temperature at least equal to that of the zone. peripheral of the underside of the lens when the lens is taken over by the separation tool.

9. Method according to one of the preceding claims, characterized in that the glass is a stack of two sheets of glass, the thickness of one of which is in the range from 1.4 to 3.15 mm and of which the thickness of the other is in the range from 0.5 to 3.15 mm.

10. Method according to one of the preceding claims, characterized in that the glass is a stack of two sheets of glass of different thickness, the thinner being on the thicker.

11. Method according to one of the preceding claims, characterized in that the average glass cooling speed between 560 and 500 ° C is in the range from 0.3 to 3 ° C / second and preferably in the range. ranging from 0.4 to 2.7 ° C / second.

12. Method according to one of the preceding claims, characterized in that the separation tool comes into contact with the underside of the glass in an area between 50 mm from the edge of the glass and 200 mm and preferably between 50 mm from the glass. edge of the glass and 150mm from the edge of the glass to support the glass.

13. Method according to one of claims 1 to 11, characterized in that the separation tool is an upper form provided with a suction means acting on the upper face of the glass for its support.

14. Method according to one of the preceding claims, characterized in that during the cooling of the glass leading to its freezing, the gravity support charged with the glass passes through a series of chambers, the temperature of the chambers decreasing from one chamber to another. during the course of the glass.

15. Method according to the preceding claim, characterized in that several sequencing are carried out successively, at least one sequencing being carried out in a first chamber and at least one sequencing being carried out in a second chamber.

16. Method according to the preceding claim, characterized in that at least one sequencing is applied to the glass in a first chamber by a separation tool comprising an upper form provided with a suction means acting on the upper face of the glass for its handling, and at least one sequencing is applied to the glass in a second chamber by a separation tool coming into contact with the underside of the glass in an area between on the one hand 50 mm from the edge of the glass and from on the other hand 200 mm and preferably 150 mm from the edge of the glass, the second chamber being arranged after the first chamber on the path of the glass, the second chamber being at a temperature lower than that of the first chamber.

17. Method according to one of the preceding claims, characterized in that for the bending and cooling leading to the freezing of the glass, a train of a plurality of said gravity support each carrying a glass passes through a series of chambers (5-11) by making stops so that each glass stops successively in all the rooms.

18. Method according to one of the preceding method claims, characterized in that air cooler than the glass is blown onto the peripheral zone of the underside of the glass during the taking up of the glass by the separation tool .

19. Device for bending and cooling a glass sheet or a stack of glass sheets, called glass, comprising a gravity support (2) capable of supporting the glass in the peripheral zone of its lower face, said peripheral zone consisting of 50 mm from the edge of its lower face, and comprising at least one separation tool (4) capable of separating the glass from the gravity support without coming into contact with the peripheral zone of its lower face, said device being configured to perform at least once after a first support of the glass by the gravity support, the following sequencing:

- handling of the glass by the separation tool separating it from the gravity support and leaving its underside free of any contact in its peripheral zone, then

- positioning of the glass again on the gravity support in the peripheral zone of its lower face.

20. Device according to the preceding claim, characterized in that the separation tool is a support capable of supporting the glass by coming into contact with its lower face more than 50 mm from the edge of the glass, and preferably less than 200 mm and preferably less than 150 mm from the edge of the glass.

21. Device according to the preceding claim, characterized in that the separation tool has a discontinuous contact surface for the glass.

22. Device according to one of the two preceding claims, characterized in that the separation tool circulates with the gravity support so embedded on a gravity support / separation tool assembly.

23. Device according to one of the three preceding claims, characterized in that it comprises a separation tool (64) of the support type having a contact surface for the glass more curved than that of the gravity support (61) to support the. glass in the same region at the end of bending.

24. Device according to claim 19, characterized in that the separation tool comprises an upper form provided with a suction means capable of acting on the upper face of the lens for its support.

25. Device according to one of the preceding device claims, characterized in that it comprises an oven and a plurality of gravity supports (70) each capable of supporting a glass (74), said gravity supports forming a train of gravity supports. suitable for circulation in the oven.

26. Device according to the preceding claim, characterized in that the furnace comprises a plurality of chambers crossed one after the other by the gravity supports following one after the other.

27. Device according to one of the preceding device claims, characterized in that it comprises a first chamber comprising at least one separation tool of the upper form type provided with a suction means coming into contact with the glass via its face. upper and a second chamber comprising at least one separation tool coming into contact with the glass via its lower face.

28. Device according to the preceding claim, characterized in that the first chamber precedes the second chamber on the path of the glass.

29. Device according to one of the preceding claims of the device, characterized in that an air blowing ramp (83) is adapted to blow on the peripheral zone of the underside of the lens during the taking up of the lens by the separation tool.

30. Curved glazing, in particular laminated, comprising at least one sheet of glass produced by the method or the device of one of the preceding claims.

31. Curved glazing, in particular laminated, comprising at least one sheet of glass comprising an edge compressive stress greater than 8 MPa, a maximum extension stress of less than 5 MPa or even less than 4 MPa and without visible trace in polariscopy at more than 200 mm from the edge and even more than 150 mm from the edge and even more than 50 mm from the edge of the glass.

32. Glazing according to one of the preceding glazing claims, characterized in that it is laminated and comprises two sheets of glass, the thickness of one being in the range from 1.4 to 3.15 mm. and the thickness of the other being in the range from 0.5 to 3.15 mm.