EP3697734A1

EP3697734A1 - Gravity-bending glass in the presence of a radiative counter-frame

Info

Publication number: EP3697734A1
Application number: EP18814988.4A
Authority: EP
Inventors: Thierry Olivier; Jérôme PELLETIER
Original assignee: Saint Gobain Glass France SAS; Compagnie de Saint Gobain SA
Current assignee: Saint Gobain Glass France SAS; Compagnie de Saint Gobain SA
Priority date: 2017-10-19
Filing date: 2018-10-18
Publication date: 2020-08-26
Also published as: US20210188686A1; US20200346965A1; EP3697733A1; CN109937192B; CN109952276A; CN109952276B; WO2019077277A1; CN109937192A; WO2019077278A1

Abstract

The invention relates to a device and a method for gravity-bending a glass sheet or stack of glass sheets, referred to as the glass, involving gravity-bending the glass on a frame that comprises a contact track for bearing the glass in the peripheral zone of its lower main face, said contact track having concave curvatures at each of the sides of said frame, and a counter-frame that comprises a metal bar which, as bending takes place, is at a distance d from the edge or from the peripheral zone of the upper main face of the glass, wherein said peripheral zone of a main face is the zone between the glass rim and a distance of 50 mm from the glass rim of the main face in question, and d is in the range from 0.1 to 50 mm. The invention is particularly useful for bending thin glass and for reducing the ripples that tend to form towards the middle of the sides.

Description

GLASS BOMBAGE BY GRAVITY

IN THE PRESENCE OF A RADIATIVE BACK-SKELET

The invention relates to gravity bending of glass on a skeleton. A counter-skeleton is arranged opposite the peripheral zone or the edge of the glass which prevents the formation of corrugations at its edges. This works even in the absence of contact between the skeleton and the glass.

The gravity bending of glass is well known and in particular documented in EP448447, EP0705798, EP885851. In US1999558, the glass is forced to bulge by pressing on the wafer.

The trend of car manufacturers is to reduce more and more the thickness of the glass sheets to be assembled in a laminated glazing. It tends to associate a thin sheet with a sheet of greater thickness. It has been found that the gravity bending of a glass sheet with a thickness of less than or equal to 2.1 mm produced, on a conventional skeleton, ripple defects on the edges of the glass, more particularly in the middle of different sides of the glass. The phenomenon responsible for the creation of folds at the periphery of the glazing during its support at the periphery is a phenomenon of instability similar to buckling (or buckling) of elastic plates. In the same way as in the case of thin elastic plates, the phenomenon of peripheral instability observed in the forming of glass sheets is all the more important that the thickness of the glass is low and the temperature at the periphery of the glass is high.

If one seeks to thwart the formation of these undulations by pressing the upper face of the glass during bending this tends to produce marks on this face and on the underside, and even to hinder the bending since the glass is found stuck between a lower tool and a superior tool as in a jaw, which slows down its collapse. The "marks" correspond to slight mechanical indentations created by the tools on the glass during its bending. They are particularly troublesome when they are on the lower surface of the glass (convex side) after bending because they are then visible from outside the vehicle. The "marks" that are on the upper side of the glass (concave side) after bending are generally more easily accepted because they are inside the vehicle once mounted on it and these imperfections are hidden from the view of the vehicle. an observer outside the vehicle.

According to the invention, the bending of glass is achieved by means of a device for bending by gravity of a glass sheet or a stack of glass sheets, said glass, comprising a skeleton comprising a contact track to support the zoned peripheral of the lower main face of the glass, said contact track comprising concave curvatures in each of the sides of said skeleton, and a counter-skeleton comprising a metal bar, said counter-skeleton being configured so that its metal bar is present at a distance d positive from the peripheral area of the upper main face of the glass or its edge. The fact that the distance d is positive and therefore non-zero implies the absence of contact of the back-skeleton with the glass at the point where the distance d is measured. The distance d is measurable in a vertical (virtual) plane perpendicular to the edge of the glass. The vertical plane in which the back-skeleton does not touch the glass is also perpendicular to the outer edge of the skeleton since the latter is substantially parallel to the edge of the glass. The counter-skeleton bar is the element of the latter active for bending and the closest to the glass during bending. There is no solid element between the glass and the counter-squell bar. The distances d and D of the present application relate to the metal bar of the back-skeleton.

In order not to touch the glass, the device according to the invention comprises a means

(distinct from the glass itself) to impose a distance d between the glass and the bar of the back-skeleton. The counter-skeleton does not touch the glass at least in the middle zone of at least one of its sides. It is not excluded that it touches at least one corner of the glass but it is neither necessary nor preferred. If the glass is of thickness e, the means of imposing a distance d between the bar of the back-skeleton and the glass is also a means (distinct from the glass itself) of imposing a positive distance D between the bar of the counter-skeleton and skeleton, D being equal to d + e, if d is between the back-skeleton and the upper face of the glass, or at d + f if d is between the back-skeleton and the edge of the glass, f being the overflow of the glass towards the outside of the skeleton. At a place where the distance d is respected, then the back-skeleton does not touch the glass, and it does not touch the skeleton even if one does not place the glass on the skeleton. In the device according to the invention, the skeleton and the back-skeleton therefore have the same positions relative to each other, whether glass has been loaded on the skeleton or not. Thus, the device for bending glass (of thickness e) by gravity is also such that it comprises a skeleton comprising a contact track for supporting the peripheral zone of the lower main face of the glass and a counter-skeleton comprising a bar metal, said backbone being configured to have at least one face directed towards the upper face of the skeleton or towards the outer face of the skeleton, said at least one face of the backbone being without contact with the skeleton, in the absence even of glass.

The skeleton supports the lower main face of the glass in its peripheral zone, that is to say the area between the edge of the glass and a distance from the edge of the glass of 50 mm. The area of the glass touching the skeleton contact track is entirely included in this peripheral zone. The counter-skeleton comes opposite the peripheral zone of the upper main face of the glass and / or towards the edge of the glass. Preferably, the metal bar of the back-skeleton is above and substantially opposite the skeleton.

The metal bar of the back-skeleton is made of a compact metal, that is to say without porosity, it being understood that it may be for example a tube or a T-shaped profile. rigid. It is substantially parallel to the glass and the skeleton so as to act on a whole portion or even the entire peripheral area parallel to the edge of the glass. The preferred portions of action of the backbone are the zones of the middle of the sides of the glass.

Viewed from above, the back-skeleton may possibly not cover the glass and thus not impede the loading of the glass on the skeleton, nor its unloading. In this case, the back-skeleton is generally arranged vis-à-vis the edge of the glass next to the edge of the glass. The back-skeleton can then possibly be connected to the skeleton by a fixed connection passing through the outside of the glass. This fixed link is in this case the means for imposing a distance d between the glass and the back-skeleton (and therefore also the bar of the back-skeleton). Of course, this connection is sized according to the dimensions of the glass and so that any face of the counter-skeleton facing the glass does not touch the glass.

The back-skeleton can be removable (synonymous: retractable) with respect to the skeleton and the glass. This is particularly necessary if, seen from above, the counter-skeleton covers part of the glass.

The glass placed on the skeleton may be an individual sheet of thickness less than or equal to 2.1 mm, or even less than or equal to 1.2 mm thick. Generally, the thickness of an individual sheet is greater than or equal to 0.4 mm. The glass placed on the skeleton can also be a stack of glass sheets, especially sheets whose thickness has just been given. The stack may also include sheets of different thickness. This stack may comprise 2, 3 or 4 sheets. In particular, the device according to the invention can be covered by a stack comprising a sheet whose thickness is in the range from 1.4 to 2.7 mm, generally in the range from 1.4 to 2.5 mm. , and a sheet whose thickness is in the range of 0.4 to 1.6 mm, in particular in the range of 0.4 to 1.2 mm, the thickest sheet being preferably under the thinnest leaf during bending on the skeleton. The sheets curved together by the device according to the invention may be intended to be associated together in the same laminated glazing, but not necessarily. By simplification, the term "glass" is used to designate an individual sheet or a stack of sheets.

The skeleton comprises a metal strip (which may also be called "vertical plate", even if its large faces may optionally be inclined as shown in Figure 2) having one of its slices upwards to support the periphery of the glass. The skeleton also comprises coated on the upper edge of its metal strip, a refractory fibrous material well known to those skilled in the art, forming the contact track for the glass. The metal band is rigid while the fibrous material has some elasticity and compressibility. This refractory metal and / or ceramic fiber material is generally of the felt or knit or fabric type, as is well known to those skilled in the art. These materials reduce the labeling of the glass by the skeleton. The metal strip in the backbone generally has a width in the range of 1 to 10 mm. The fibrous material generally has a thickness in the range of 0.3 to 1 mm. The skeleton provides the glass, via its refractory fibrous material, with a contact track of width generally in the range from 1.6 to 12 mm (which includes the thickness due to the refractory fibrous material), more generally in the range from 3 mm to 10 mm. The skeleton has concave curvatures in its contact face for the glass, and this for each of its sides and generally at least in the middle of each of its sides, the glass having generally four sides. The contact track of the skeleton has concave curvatures for at least 80% and generally at least 90% of its length, said concavity being considered parallel to its contours (inside or outside). The contact track of the skeleton has concave curvatures for at least 80% and generally at least 90% of the length of its longitudinal sides, said concavity being considered parallel to its contours (inside or outside). In particular, the contact track of the skeleton has concave curvatures for the middle zone of its longitudinal sides, in particular for at least up to 20 cm on each side of this medium. The contact track of the skeleton has concave curvatures for at least 80% and generally at least 90% of the length of its transverse sides, said concavity being considered parallel to its contours (inside or outside). In particular, the contact track of the skeleton has concave curvatures for the middle zone of its transverse sides, in particular for at least up to 20 cm on each side of this medium. The glass collapses under the effect of gravity on the skeleton during the bending and takes concave shapes seen from above (the concave face is the upper face) in its central zone and in each of its sides, especially in the middle of its sides, the metal bar being at a distance d at least at the end of the bending. The skeleton has a shape conferring this concavity, since at the end of bending, the glass touches the entire circumference of the skeleton contact track. At the end of bending, the glass being placed on the skeleton, the central zone of the upper face of the glass is concave in all directions. Seen from above, the skeleton has substantially the same shape as the glass it must receive while being smaller since the glass overflows on all sides of the skeleton. The contact track of the skeleton therefore generally has a concave shape in each of its sides, especially in the middle of its sides. The main faces of the glass comprise a plurality of sides, generally four sides, the skeleton has as many sides as the glass and therefore generally four sides (also called "strips"). Before bending, the glass usually overflows all around the skeleton by a distance in the range of 2 to 45 mm. This overflow decreases during the bending. This decrease depends on the importance of the curvatures given to the principal faces of the glass during the bending. At the end of bending, this overflow is generally in the range of 1 to 25 mm. From the beginning to the end of the bending, the skeleton generally supports the glass entirely in its peripheral zone and without overflowing out of this zone, neither outwards nor inwards.

Viewed from above, the skeleton has a continuous annular shape and without interruption. Indeed, if the skeleton was segmented, this segmentation could produce a mark on the underside of the glass, given that in the process according to the invention the glass collapses essentially under the sole effect of its weight and therefore follows quite easily the shape of its support and remains quite sensitive to the unevenness of the skeleton.

The invention relates more particularly to the bending of glass for vehicle glazing (automobile, bus, truck, agricultural vehicle, etc.). It can be windshield, rear window, roof. The glazings considered here comprise a plurality of sides, generally four sides (also called "strips"), one side joining another in a corner of the glazing, this corner comprising a segment of curve comprising radii of curvature much smaller than those of curvatures of the sides. Consideration here is given to the radii of curvature of the perimeter of the main faces in vision perpendicular to the main faces and the edge of the glass. The middle of one side is at approximately equal distance from its two corners. In the case of windshield, rear window and roof, these windows have a PS vertical symmetry plane when mounted on the vehicle, the direction of movement of the vehicle (non-turned wheel) being included in this plane of symmetry . The intersecting sides of this plane of symmetry are said transverse sides, the other two sides being said longitudinal sides. We find the middle of the sides as follows: we place the curved glazing on a horizontal plane, concave side down. The glazing touches the horizontal plane by 4 points of contact corners of the glazing. The points of contact between them are connected by segments of the line. The intersection with the edge of the glass plane perpendicular to the segment and passing through the middle of this segment, is the middle side of the glass. The middle of the transverse sides is also at their intersection with the vertical plane of symmetry PS.

A beneficial effect of the presence of the back-skeleton above the glass has been found, even in the absence of any contact with the glass. This phenomenon is attributed to a favorable thermal effect between the glass and the counter-skeleton. It is not necessary (although this is not excluded) to provide the backbone with a refractory fibrous material coated on its face facing the glass. This thermal effect can on the one hand come from the fact that the back-skeleton shields the glass for thermal radiations coming directly from heating elements in the bending furnace, and on the other hand, that the back-skeleton remains cooler than the periphery of the glass during the rise in temperature and the bending. Indeed, because of the metal it contains, the heat capacity of the back-skeleton is stronger than that of glass. The counter-skeleton is therefore thermally more inert than glass. Consequently, the presence of the backbone could slow the rise in temperature of the periphery of the glass during the temperature rise phase to the bending temperature, producing a decrease in the temperature of the periphery of the glass, which would have a favorable effect on the phenomenon of peripheral instabilities. In the vicinity of the softening temperature, the viscosity of the glass varies very strongly with the temperature and at 620 ° C, a drop of 10 ° C corresponds to an increase in viscosity by a factor of approximately 2. A colder edge is more viscous and is therefore less sensitive to peripheral marking effects.

The invention relates to a method of gravity bending a glass sheet or a stack of glass sheets, said glass (which has a thickness e), comprising the bending of the glass by gravity on a skeleton comprising a track contact strip supporting the glass in the peripheral zone of its lower main face, said contact track comprising concave curvatures at each of the sides of said skeleton, a counter-skeleton comprising a metal bar being present during the bending at a distance d from the slice or the peripheral zone of the upper main face of the lens, the peripheral zone of a main face being the zone between the edge of the lens and a distance from the edge of the lens of 50 mm from said main face, d being included in the range ranging from 0.1 to 50 mm. The back-skeleton can be present without interruption vis-à-vis the entire peripheral zone of the glass or its edge. In particular, it can be in one piece. In particular, it can not touch the glass anywhere. However, the counter-skeleton may not be present with respect to certain areas of the glass such as the corners of the glass. The counter-skeleton is preferably present vis-à-vis of the middle zone of at least one side of the glass and even on all sides of the glass, the expression "vis-à-vis" concerning the peripheral zone of the upper face of the glass or its edge. In fact, the problems of rippling of the glass mainly occur in the zone of the middle of the sides and the counter-skeleton is therefore preferentially present with respect to the zone of at least one middle of one of the sides of the glass. , and even on all sides of the glass. The distance d is thus verified for the middle zone of at least one side of the glass, and preferably the middle zone on all sides, the glass having generally four sides. The counter-skeleton may also be opposite the corners of the glass, but this is not usually necessary.

The invention also relates to a method of gravity bending a glass sheet or a stack of glass sheets, said glass (which has a thickness e), comprising the bending of the glass by gravity on a skeleton comprising a contact track supporting the glass in the peripheral zone of its lower main face, a counter-skeleton comprising a metal bar being present during the bending with respect to the peripheral zone of the glass or its edge, and at a distance of in places where undulations appear in the absence of the counter-skeleton.

The distance between the back-skeleton and the glass is not necessarily the same for the entire peripheral zone of the glass. As regards the middle zone of at least one side it is preferably at least 0.1 mm throughout this area, and preferably for all sides of the glass. The middle zone of one side is the area on either side of the middle in the peripheral zone of the glass. In particular, the middle zone of one side is the peripheral zone portion at least up to 5 cm on each side of the middle, and even at least up to 10 cm on each side of the middle, and even at least up to 20 cm each side of the middle.

Thus, a vertical (virtual) plane, perpendicular to the edge of the glass, in which the condition over the distance d is verified preferably passes in the middle zone of at least one side of the glass, which is included in the peripheral zone until 20 cm (or even up to 10 cm or even up to 5 cm) on either side of the middle of the side, parallel to the edge of the glass, and this, preferably for all sides. Preferably, the condition over the distance d is verified for at least 50%, and preferably at least 80%, of the length of the middle zone of at least one side of the glass parallel to the edge of the glass, preferably without otherwise contacting any tool with the wafer or the peripheral zone of the glass in the rest of this middle area of at least one side of the glass. Preferably, the condition over the distance d is verified for any vertical plane perpendicular to the edge of the glass and passing in the middle zone of at least one side of the glass (which implies in particular that the back-skeleton (or any other tool ), does not touch not the glass in this middle area), and this, preferably for all sides of the glass, generally four in number.

Generally, the counter-skeleton does not touch the glass anywhere, and in particular neither the upper main surface of the glass nor its edge. So there is always an air gap between the back-skeleton and the glass during bending. The distance d in a vertical plane perpendicular to the edge of the glass (and therefore also perpendicular to the skeleton since it is parallel to the edge of the glass) is that between the point of the back-skeleton on the one hand and the point of the glass in the peripheral area on the other hand, the closest. The counter-skeleton can possibly touch the glass at the beginning of bending, given that the glass is not yet curved but it does not touch the glass when the glass is in contact on its entire periphery with the skeleton, particularly at the end of bending. Thus, the counter-skeleton (and therefore necessarily also its metal bar) does not preferably touch the glass at the moment when the glass comes into contact with the entire periphery of the skeleton.

Preferably, d is at least 1 mm, preferably greater than 2 mm, in particular at least 5 mm. In particular, d may be at most 30 mm. Preferably, d is in the range of 1 mm to 50 mm and preferably in the range of 5 mm to 30 mm. These are distances d at the end of the bending while the glass touches all around the skeleton. The back-skeleton may be at least partly on the side of the glass, or even not be above the glass, but vis-à-vis the edge of the glass. The values of distance d given above are preferably verified at least at the end of the bending, it being understood that the distance d may vary during bending. The counter-skeleton, particularly its metal bar, is preferably at least partially above the center point of the contact track for the skeleton glass. This center is the point midway away from the width of the skeleton contact track in a vertical plane perpendicular to the skeleton (and thus also to the glass). The centers form a central line all along the skeleton contact track. When the back-skeleton is at least partly above the glass, the back-skeleton is preferably at a distance from the edge of the glass less than or equal to 20 mm at the end of bending.

The device according to the invention involves a means of imposing a non-zero distance between the glass and the back-skeleton, and therefore also a gap between the contact track of the skeleton and the back-skeleton. This means serves to prevent the backbone from touching the glass. It has been observed that the greater the mass of metal of the backbone vis-à-vis the glass, the more the back-skeleton could be removed from the glass while maintaining the desired beneficial effect (no ripple edge). This thermal effect can be enhanced by covering part of the counter-skeleton on at least one of its faces opposite to the glass and therefore also to the skeleton, of a thermally insulating material. This has the effect of slowing the rise in temperature of the back-skeleton when heating the glass for bending. It has indeed been found that the counter-skeleton thus coated has a reinforced beneficial effect. At a distance from the glass to which an uncoated backbone has no effect on the glass, the same backing covered with a thermal insulating material has a beneficial effect on the glass. The insulating material covering, if appropriate, the back-skeleton is a material that conducts heat less well than the metal bar. It may be a fibrous material of refractory fibers, metal and / or ceramic.

The glass slides on the skeleton during the bending. The formation of curvatures desired during bending is not slowed down because of a nip between skeleton and counter-skeleton if it does not touch the glass. This is favorable for obtaining a shorter bending cycle time and this also allows a more reproducible operation because it is not necessary to very finely adjust the gap between the backbone and the glass.

The function of the counter-skeleton is not to bend the glass (this is the role of gravity), but just to prevent the formation of edge ripples. A bending without the counter-skeleton would result in an identical bending in the central zone of the glass compared to a bending with counter-skeleton, all other conditions of realization being identical. If it is possible that the back-skeleton touches the glass at the beginning of bending, it is preferably no longer the case at the end of bending. In this way, at the end of the bending and when the underside of the glass touches the entire periphery of the skeleton, the upper face of the glass is not in contact with any tool and is therefore in contact only with the air ambient. The final shape of the glass is thus obtained in the last moments of the bending by the effect of gravity alone.

The curvatures of glazing are characterized by the notions of arrow and double-bending. For the definitions of these characteristics, reference may be made to FIGS. 1a and 1b and to the description corresponding to them of WO2010 / 136702.

The invention is well suited to the bending of glass whose complexity of shape is moderate, including the arrow is less than 100 mm and the double bending is less than 20 mm (typically a glass windshield). These latter criteria are given as an indication because the propensity for edge instabilities also depends on other criteria, either geometric values of the glass itself (such as the size of the glass or its peripheral cutouts) or of parameters related to the process (such as thermal history of the glass during the bending, the temperature of its edges, or the initial temperature of the back-skeleton during the charging), or the constitution of the back-skeleton itself, in particular the mass of embedded metal, and whether it is coated or not in its face opposite to the glass (and thus also to the skeleton) of thermally insulating material. The device according to the invention is not very demanding in terms of geometric tolerances. Indeed, the beneficial effect on the peripheral instabilities of the glass during forming comes from heat transfers by radiation which depend moderately on an inaccuracy of realization of the distance d. Also, this distance can be generally adjusted with tolerances greater than 0.1 mm, especially between 0.1 and 0.5 mm.

The shape of the back-skeleton seen from above does not necessarily correspond exactly to that of the skeleton (and therefore of the glass). The counter-skeleton acts by thermal effect and the important thing is that it contains a metal mass likely to provide this effect and that it is close to the periphery of the glass, especially near the middle zone of the sides of its sides. main faces. This thermal effect depends essentially on three criteria: 1) the temperature of the furnace counter-skeleton which must be relatively moderate, preferably less than 250 ° C, 2) the propensity of the back-skeleton to remain colder than the periphery of the glass while the glass is between 300 and 650 ° C, and especially during bending, 3) the effectiveness of the cooling of the edge of the glass by the back-skeleton, which depends on the area of glass exposed to the back-skeleton . Criterion 1 is provided by sufficient cooling of the backbone after bending. Part of this cooling takes place in the bending furnace itself but also on the tool return chain when they go up empty from the furnace outlet to the furnace inlet. Additional cooling systems specifically dedicated to cooling the backbone can be installed, such as additional fans or air jets directed to this tool. It is also possible to provide a dedicated cooling circuit, directly attached to the backbone, and which is activated on the return path of the tools, and more particularly the back-skeleton. It may in particular be a tube capable of receiving a current of a cooling fluid, especially fresh air (that is to say generally at room temperature, generally between 0 and 50 ° C). Such a metal tube can be attached to the metal bar of the back-skeleton. It may also be a counter-skeleton whose metal bar comprises a metal tube with square or rectangular section in which fresh air is circulated. Criterion 2 is ensured, either by increasing the mass of metal embedded in the back-skeleton, which has the consequence of increasing its thermal inertia and therefore the amount of heat necessary to heat it, or by limiting the heat input to back-skeleton by covering the latter with thermal insulation. Thus, the heating elements arranged in the vault of the furnace can heat the glass without unnecessarily losing energy to directly heat the back-skeleton. The periphery of the glass is then all the colder that it is on the one hand masked from the direct heating by the heating elements of the oven (usually vaulted) and on the other hand that it faces the counter-skeleton that is kept at reduced temperature. It should be noted that the cooling of a backbone coated with an insulating material is slower because the surface directly exposed to the open air on the tool return chain is reduced. Criterion 3 is provided mainly by the geometry of the back-skeleton coupled to the distance between the back-skeleton and the glass.

The general form of the backbone is preferably complementary to that of the backbone. The counter-skeleton then has convex curvatures to face the concave curvatures of the upper face of the glass. The back-skeleton thus generally has curvatures substantially parallel to those of the skeleton.

The means for imposing the distance d between the back-skeleton and the glass (and thus also a minimum distance between the back-skeleton and the skeleton) can include a stop member, said abutment, integral with the skeleton and on which an abutment element, said abutment, integral with the counter-skeleton rests. The stop is fixed directly or indirectly to the rigid metal band of the skeleton. It may be the upper surface of a plurality of candles or screw-jack. The abutment is attached directly or indirectly to the rigid metal bar of the backbone. If the back-skeleton does not interfere with the loading and unloading of the glass, the skeleton and back-skeleton can be bound together in a fixed manner.

The device generally comprises a frame on which the skeleton is fixed.

Any stop element can be fixed on the frame or on the skeleton, it always amounts to the fact that the abutment is integral directly or indirectly with the skeleton. Advantageously, the means of imposing the distance d between the back-skeleton and the glass (and therefore also between the back-skeleton and the skeleton) is adjustable. The device according to the invention may therefore comprise means for adjusting the distance d. The adjustment means can be located at the abutment and / or abutment.

For the case of pronounced curvatures or complex shapes, in particular comprising pronounced curvatures in directions orthogonal to each other, it may be advantageous for the device according to the invention to comprise a system able to modify during bending the distance between the skeleton and the counter-skeleton. Indeed, the counter-skeleton preferably has a shape closer to that of the upper face of the glass at the end of the bending, rather than at the beginning of the bending. When the glass is placed on the skeleton, the glass is flat or only slightly curved because of its natural flexibility. The counter-skeleton therefore has a shape more curved than the glass at the beginning of the bending and could touch it and, by elastic deformation, force it to adopt the peripheral shape of the skeleton. Such a situation may cause a breakage of the glass at the entrance of the oven. That is why, without excluding that the counter-skeleton can touch the glass from the beginning of the bending (from the oven entrance), it may be preferable that the back-skeleton is at first quite far from the skeleton and then gets closer to it during the bending. This reduces the gap between the skeleton and the glass (and therefore between the skeleton and the skeleton) as the glass softens and follows the contours of the skeleton. The duration of the approach phase between the glass and the back-skeleton can be adjusted between five tenths of a second to 30 seconds, or even up to one minute depending on the previous heat history and the complexity of the glazing itself.

If the forces applied to the glass in the oven inlet and during the bending are sufficiently moderate to avoid breakage of the glass, it is firstly possible that the back-skeleton is in partial contact with the glass, particularly at medium or near the middle of the top and bottom sides of the glass (in position mounted on a motor vehicle) from the time of charging and secondly, it is possible to force the glass to bulge due to the descent of the counter- skeleton. The counter-skeleton presses on the glass during its descent, which forces the peripheral bending. Such kinematics is advantageous because it facilitates the main bending of the glass and thus reduces the forming cycle time. Let us note that at the beginning of the process towards the entrance of the furnace, the glass is at low temperature and less sensitive to the marking and that is why, except the case of breakage, the sufficiently supported contact of the back-skeleton at this stage is not necessarily embarrassing. The initiation of the approximation between glass and back-skeleton can be relatively brutal (simple trigger that is to say, passing from a single stroke of a remote configuration to a close configuration) or progressive. A trip system can be operated through the side walls of the oven or through the oven floor. A triggering system may in particular be similar to that described in US8156764. By way of example, the distance between the glass and the backbone in the middle zone of one side can be in the range from 0 to 30 mm at the beginning of the bending, to finish in the range from 0 to , 1 to 30 mm at the end of bending.

The glass is bulged by gravity at a temperature in the range of 570 to 650 ° C, more generally in the range of 610 to 650 ° C. To achieve this bending, we can convey the skeleton / counter-skeleton charged with glass through a tunnel kiln heated to the plastic deformation temperature of the glass. The device generally comprises a plurality of skeleton / backskeletal assemblies each loaded with glass and circulating behind each other in the oven. This furnace may be traversed by a plurality of such sets each loaded with glass and circulating behind each other in the oven. The oven can include different temperature zones to gradually heat up and gradually cool the glass. The Skeleton and counter-skeleton form an embedded assembly capable of being conveyed together horizontally but without relative horizontal displacement of one relative to the other.

The glass is in contact with the skeleton for more than 10 minutes and generally more than 15 minutes and more generally between 15 and 30 minutes in the oven while being conveyed into the oven. The backbone bar is generally at a distance from the glass and preferably at least partially above the glass, for more than 10 minutes in the oven. The bending is done by gravity. In the absence of counter-skeleton, during the bending, the glass will touch the entire skeleton, then some areas (especially in the middle area of at least one side of the peripheral area) would rise to leave the contact with the skeleton. The counter-skeleton, by its radiative effect, serves to prevent this raising of the glass and to guarantee a total contact of the glass with the skeleton at the end of the bending. The skeleton and the counter-skeleton form an embedded assembly capable of being conveyed into the furnace by a conveying means. The device may include means for the skeleton and backbone to move toward or away from each other by relative vertical movement without relative horizontal displacement relative to each other, even though skeleton / counter-skeleton is conveyed into the oven. The term "relative" qualifying a movement means that it may be the effect of the single backbone or the skeleton alone or both. The absence of relative horizontal movement of the skeleton and the back-skeleton relative to each other means that these two elements remain vis-à-vis one another in view-over while moving horizontal skeleton / counter-skeleton assembly during bending in the oven. Thus, the device according to the invention generally comprises an oven and a conveying means capable of moving horizontally together the skeleton and the back-skeleton, said skeleton / back-skeleton assembly in the furnace and without relative horizontal displacement of the one by report to the other. It may include means of vertical translation allowing the skeleton and the back-skeleton to move toward or away from each other by relative vertical movement during their horizontal movement and without relative horizontal displacement from one to the other. .

After bending, the glass is cooled. For this cooling and so as not to cause in the glass too large edge extension stresses, advantageously moves the back-skeleton of the glass. The removal of the back-skeleton is advantageously carried out during cooling of the glass and when the latter is at a temperature of between 620 and 500 ° C. This distance can be achieved by different systems. It can be a re-engagement system that performs the inverse function of the "trigger" described above. Alternatively, the counter skeleton may comprise or be composed of retractable strips laterally, generally four in number, such as glass since one side of the glass is associated with a retractable band (see Figure 10). The strips of the back-skeleton deviate at least laterally and if necessary also vertically if necessary at the time of the retraction so as to move away from the glass. The system which controls the retraction of the belts may be similar to one of those described in US Pat. No. 8,156,664, that is to say for example through the side walls of the oven or the hearth of the furnace.

The backbone and the backbone are advantageously independent of each other, that is to say that the backbone can then be separated entirely without having any link with the backbone. The glass can then be loaded on the skeleton and then the back-skeleton is put in place.

The loading of the glass on the device according to the invention can be carried out manually. The back-skeleton being removed if necessary, operators put the glass on the skeleton. Then they place the counter-skeleton according to its intended position. The position of the backbone is advantageously given by positioning columns (or any other means) attached to the skeleton or the frame. These positioning columns guide the counter-skeleton during its installation. This guidance is made possible for example by orifices in guide tabs connected to the back-skeleton and through which the positioning columns pass.

The loading and unloading of the glass can also be automated, in particular using robots, one for loading, the other for unloading. The use of robots makes it possible to have precise and reproducible movements as well as a reliable and tolerant coupling system between the skeleton and its associated counter-skeleton. This system in which the back-skeleton is completely separable from the skeleton, allows 1) to have a minimum of embedded functions in the tool and thus to minimize the weight of the latter, which is an important factor of energy consumption , 2) to minimize the risk of mechanical seizure and 3) to minimize costly maintenance operations on forming tools. These advantages make this system more advantageous than that described hereinafter (boarding of the backbone on the skeleton).

Alternatively, the back-skeleton can be part of a system directly embedded on the skeleton itself and able to retract the back-skeleton. To do this, by way of example, the back-skeleton may be composed of four separate strips integral with the skeleton and which are retractable. They can move away or meet each other by displacements having both a horizontal component and if necessary a vertical component to move away from the glass, without sliding on it, while moving away laterally skeleton. Such a movement can be performed by a simple rotation whose axis is carefully chosen, especially outside the skeleton. As these bands move away, the skeleton becomes accessible for unloading or loading glass.

If the back-skeleton is of too light constitution, it may be of low rigidity and its shape may change slightly during its use, due to thermal stresses during the heating and cooling cycles. In this case, one can possibly find that the gap between skeleton and back-skeleton is no longer uniform and as it had been initially adjusted. Thus, depending on the case of bending, a simple adjustment of deviation by a system located only at the corners of the device, in particular by four jack screws, may be insufficient. Therefore, especially if the back-skeleton is very close to the glass, advantageously, a rigid structural element is disposed above the metal bar, the structural element and the metal bar being interconnected by a plurality of spacers preferably adjustable in length for locally adjusting the distance between the structural member and the metal bar. The structural element is rigid so that it is considered indeformable despite the multiple thermal cycles of heating and cooling undergone to bombard glass sheets industrially. It can be used as a reference to adjust the shape of the metal bar. The structural element advantageously comprises a metal section, in particular a metal tube, in particular of the frame type. This tube may in particular have a square or rectangular section. It may include lateral extensions to come over the adjustment areas, the upper end of the struts being connected to the extensions. The upper end of the spacers can also be connected directly to the structural element.

Thus, the device according to the invention may comprise a structural element arranged at a dimension higher than that of the metal bar of the back-skeleton, the structural element and the metal bar being connected by a plurality of adjustable spacers to adjust locally. the distance between the structural element and the metal bar, and locally the distance between the metal bar and the glass and therefore also the distance between the metal bar and the skeleton. The plurality of spacers is evenly distributed all around the counter-skeleton.

The device is configured to perform the method according to the invention.

The figures below are not to scale.

FIG. 1 represents in section and in a vertical plane perpendicular to the edge of the glass and the skeleton, a device according to the invention comprising a backbone 300 and a backbone 301. A stack of two sheets of glass 310 rests at its periphery on the skeleton. The two tools each have an annular shape whose central zone is located to the left of their representation in the figure. The skeleton 300 comprises a metal strip 302 of width 303 whose upper edge 304 is covered with a refractory fibrous material 305 forming a contact track of width 306 for the glass 310. The counter-skeleton comprises a metal bar 301 disposed above the glass and without contact with him. The distance d between the metal bar of the backskeleton and the glass is in the range of 0.1 to 50 mm. This distance is the distance between the nearest points of the counter-skeleton and the glass. The metal bar of the back-skeleton, is above the dimension (horizontal line H in the figure) of the center 307 (mid-width) of the contact track for the skeleton glass.

FIG. 2 represents in section and in a vertical plane perpendicular to the edge of the glass and the skeleton, a device according to the invention comprising a skeleton 333 of which a wafer 335 is directed upwards and a counter-skeleton 331. The counter-skeleton is located relatively inwardly of the glass, but it is at a distance of less than 50 mm from the peripheral zone 332 of the upper face of the glass 334.

3 shows in section and in a vertical plane perpendicular to the edge of the glass and the skeleton a device according to the invention comprising a skeleton 320 and a backbone 321. A stop 327 is fixed to the metal strip 322 of the skeleton. The edge of this upwardly-turned metal strip is covered with a refractory fibrous material 323. The back-skeleton comprises a metal bar 324 not coated with fibrous material, and not in contact with the glass. A abutment 326 is connected to the metal bar 324 and can rest on the abutment 327, blocking the progression of the backbone to the skeleton and preventing contact of the backbone with the glass.

FIG. 4 shows various possible configurations of a device according to the invention comprising a skeleton 401 and a radiative counter-skeleton 402, that is to say without contact with the glass 400 (here a stack of two sheets of glass) but stabilizing the periphery of the glass during bending. This view is made in a vertical plane perpendicular to the edge of the glass and the skeleton. We distinguish the following variants:

a) The counter-skeleton is a T-shaped metal bar, the vertical plate of the T is in alignment with the skeleton band. The horizontal bar helps to form a screen between the furnace resistors and the periphery of the glass.

b) The backbone 402 T of a) is covered in its upper part with an insulating material 403 which delays the heating of the metal bar of the backbone.

c) The back-skeleton 402 comprises a bar 404 of the horizontal band-type forming a screen between the heating resistors and the glass, said bar being covered with an insulating material 403. d) The backbone is L-shaped and is opposite to the edge 41 1 of the glass and vis-à-vis the outer face 410 of the skeleton. Backbone 402 is not above the skeleton or above the glass. By cons, most of the metal bar 412 of the back-skeleton is above the dimension H of the center line of the contact track of the skeleton. Thanks to this shape and arrangement, the counter-skeleton forms an effective shield for the glass for the radiation of the furnace resistances coming from lateral directions. An insulating material 413 covers the opposite sides of the skeleton opposite the glass. This arrangement of the back-skeleton frees the space above the glass, which is advantageous for the loading and unloading of the glass.

e) The back-skeleton comprises a T-shaped metal bar 405, the upper part of which is covered with an insulating material 403. Metal tubes 406 traversed by a cooling fluid make it possible to cool the back-skeleton.

f) The back-skeleton comprises a metal rod 407 of the tube type rectangular section. This bar is hollow, and a cooling fluid can flow through its interior 409 to cool it. Its upper part is covered with an insulating material 408.

FIG. 5 represents a device according to the invention at the moment when a backbone 8 (grayed in the figure) is being placed in position above the glass, the latter not being represented in the figure by concern for clarity. There is a frame 1 on which is fixed the skeleton 2 via lugs 3 and 4. The glass (not shown) is placed on the skeleton 2. Operators hold the back-skeleton 8 by handles 6. These handles are fixed to a frame 7 on which the backbone 8 is fixed by means of tabs 9 and 10. The exact positioning of the backbone is ensured by guidance by means of four positioning columns (11 and 12 in the foreground ), one at each corner. These columns are integral with the frame 1. Tabs 13 and 14 fixed to the frame 7 of the backbone each comprising an orifice, are threaded onto the columns 1 1 and 12 through their orifices. Candles 15 and 16 are part of the means of imposing a non-zero distance d between the glass and the back-skeleton. They are each provided with bearing surfaces 17 and 18 adjustable in height by means of screws 19 and 20. The frame 7 connected to the counter-skeleton comprises tabs 21 and 22 which rest on the support surfaces 17 and 20. 18 when the operators have finished depositing the counter-skeleton. The weight of the back-skeleton therefore rests on the bearing surfaces 17 and 18, the height thereof being adjusted so that the spacing between the back-skeleton and the glass is the one chosen. The bearing surfaces 17 and 18 form abutments integral with the skeleton and the pasta 21 and 22 are integral abutments against the backbone. In this example, the back-skeleton is present without interruption vis-à-vis the entire peripheral zone of the glass. It is in one piece and, once installed, it does not touch anywhere the glass at least at the end of bending. The skeleton and the counter-skeleton form here an embedded assembly able to be moved horizontally in an oven. The four positioning columns (1 1 and 12 in the foreground) are part of vertical translation means allowing the skeleton and the back-skeleton to move towards or away by a relative vertical movement without relative horizontal displacement of the one compared to each other. In this way, the skeleton and the back-skeleton remain opposite one another (on both sides of the glass) during the horizontal displacement of the skeleton / back-skeleton assembly in the oven.

Figure 6 shows a top view of a rigid structural member 50 above a portion 51 of the back-skeleton comprising a vertical plate (non-visible) just above the glass and serving as a metal bar. The visible part 51 is a horizontal plate 57 coming just above the vertical plate and to which it is connected. The structural element 50 is in a metal square and has the shape of a rectangular frame in plan view. It comprises a plurality of extensions 52 connected to its inner or outer vertical faces, said extensions coming, in top view, above areas 53 of distance adjustment d with the glass. These adjustments are made by jack screws 54 passing through the rigid structural element 50 here.

Figure 7 shows the back-skeleton of Figure 6 according to section AA 'in a) and the side view in the direction B in b). The metal square of the rigid structural element 50 is found, an extension 52 being welded to an outer vertical face of said square. This extension is also in a metal square. The vertical plate 55 (metal bar) is connected indirectly to the rigid structural element 50 so that it is integral. The lower edge 56 of this vertical plate 55 comes just above the glass and it is its distance from the glass that should be adjusted. This adjustment is ensured by the screw jack 54 by screwing or unscrewing the nuts 58 and 59. The vertical plate 55 is welded by its upper edge to a horizontal plate 57, in order to stabilize the position of the plate 55. The horizontal plate 57 is connected to the lower end of the jack screw 54 via a pivot connection

60 whose pivoting is adjustable and biocable in a given position thanks to the nuts

61 and 62. The adjustment of this pivoting makes it possible to adjust the local inclination of the edge 56 so that it is well parallel to the skeleton and that the distance between the backbone and the glass is constant for the entire periphery of the edge. glass.

FIG. 8 represents a back-skeleton according to the invention seen entirely in a), a portion being enlarged in b). A structural member 75 is made from segments of metal squares welded together. View from above, this structural element has a shape similar to that of the skeleton and therefore the glass to be bomber. Lateral extensions 76 have been welded to inner vertical faces of the structural member. Caliper adjustment cylinder screws traverse these extensions vertically. The adjustment of a jack screw makes it possible to locally adjust the height dimension of the lower edge 77 of a vertical plate 78 serving as a metal bar. This vertical plate is secured to a horizontal plate 79 by a system of brackets 80 and screws and nuts. A pivot connection 81 above the horizontal plate 79 makes it possible to adjust the local inclination of the horizontal plate 79 in the context of the adjustment of the height dimension of the edge 77. There are also some handles 82 enabling operators to manipulate this against skeleton and lay it over the glass. The correct lateral positioning of the back-skeleton is ensured by means of focusing not shown and can be of the candle type 1 1 of Figure 5.

Figure 9 shows in section a schematic view of a backbone 205 comprising laterally retractable strips. For simplicity, only one side of the counter-skeleton has been shown, and seen in the direction of its length. The glass rests with its lower main surface 201 on the skeleton 202, which comprises a metal strip 203, a slice of which is directed upwards. The counter-skeleton comprises as a metallic bar a vertical plate 214 and a horizontal plate 215. Both skeleton and counter-skeleton are provided with a refractory fibrous material (not shown) for contacting the glass. The backbone 205 is secured to a U-shaped structure returned 208. The latter is connected to a foot 206 itself secured to the structure 207 of the skeleton 202 via a substantially horizontal axis pivot connection 209. During bending, the back-skeleton is held above the upper main surface of the glass 210, without touching it at least at the end of bending. The pivot connection allows to retract the whole 'back-skeleton + structure' U 'once the bending of the glass is achieved, which allows to easily clear the curved glass. The assembly 'back-skeleton + structure' U 'is shown in the retracted position in dashed line 212. The position of the axis of rotation 209 of the structure of the back-skeleton, both quite high and away from the edge glass 21 1, which allows the back-skeleton to deviate from the glass by a rotational movement (arrow 213) causing it both upwards but also laterally. The retraction system is made by a trigger system not described here but may for example pass through the side walls of the oven or the oven floor. The retraction performed during cooling makes it possible to obtain good glass edge stresses. Moreover, the retraction also makes it possible to remove the skeleton glass by a conventional harrow system pushing it from below, and to easily load it in the oven inlet, using a robot for example. The counter-skeleton is again set up by a rotary movement reverse once the next glass is loaded onto the skeleton. It can be seen that the contact track of the skeleton is well concave along the entire length of the visible side of the figure, parallel to its inner and outer contours, this concavity being in the plane of the figure.

FIG. 10 shows an automobile glazing 450 in plan view on its concave main face, surmounted by retractable strips (451, 452, 453, 454) of the back-skeleton as explained for FIG. 9. These retractable strips are above the edge of the glass and can be retracted laterally towards the outside of the glass (according to the arrows) as explained in FIG. 9, so as not to be above the upper face of the glass.

Figure 1 1 shows a windshield-type automotive glazing seen from above, and placed on a horizontal plane, concave face facing downwards. It comprises four sides, two transverse sides 350 and 351 and two longitudinal sides 352 and 353. One side joins another side by a corner whose edge has radii of curvature R (in vision perpendicular to the glass surface and in each corner ) very small relative to the radii of curvature of the edges towards the middle of the sides. This glazing is symmetrical with respect to the vertical plane of symmetry PS. This PS plane passes through the mediums 354 and 355 of the transverse sides. This glazing rests on four points 356, 357, 358, 359 located in the corners. Dotted lines 360, 361, 362 and 363 connecting these four points. These are the segments closest to the edges. At an edge is associated a segment. Each of these segments has a medium 364, 365, 366, 367. For each segment, there is a plane perpendicular (368, 369, 370, 371) to the segment and passing through its middle. Each of these planes intersects with its associated edge at a point 372, 355, 373, 354 which is their middle. The glazing is concave (in this figure, the concave face is facing downwards) at least at the midpoints of the edges 372, 355, 373, 354 and in all the shaded areas on either side of these midpoints, said concavity being considered parallel to the outer edge of the glazing. It is the same for the skeleton having supported this glass and for the zones of the skeleton corresponding to the zones of the middle of the sides of the glass, said concavity being considered parallel to the contours (inside or outside) of the skeleton and top view in a bending situation. . The dotted line 376 is 50 mm from the edge of the glass and forms the boundary of the peripheral zone, which is between the edge of the glass and this line. The middle zone of the side 353 of the peripheral zone of the upper main face of the glass is the hatched area on the left. This zone surrounds the middle point 373. The hatched area is included in the peripheral zone between points 374 and 375 on the edge. Between these points 374 and 375, there is a vertical plane 377 perpendicular to the edge of the glass in which the condition over the distance d is verified. The points 374 and 375 are each distant from point 373 by 20 cm, even from 10 cm or even 5 cm. The counter-skeleton is located opposite this zone (above the glass or facing its edge) at least in this zone and, where appropriate, continuously over the entire length of this zone parallel to the edge of the glass, that is to say without discontinuity between the points 374 and 375, but not necessarily throughout the width of this zone.

A method of gravity bending a glass sheet or a stack of glass sheets, said glass, comprising bending the glass by gravity on a skeleton comprising a contact track supporting the glass in the peripheral zone of its face lower main, said contact track comprising concave curvatures at each of the sides of said skeleton, a counter-skeleton comprising a metal bar being present during the bending at a distance d from the edge or the peripheral zone of the upper main face of the glass , the peripheral zone of a main face being the zone between the edge of the glass and a distance from the edge of the glass of 50 mm from said main face, d being in the range from 0.1 to 50 mm. Method according to the preceding claim, characterized in that it gives the glass concave shapes seen from above in its central zone and in each of its sides, in particular in the middle of its sides, the metal bar being at least at a distance d end of bending.

Method according to one of the preceding claims, characterized in that the condition on the distance d is verified in at least one vertical plane perpendicular to the edge of the glass passing in the middle zone of at least one side of the glass, said zone of the medium being included in the peripheral zone up to 20 cm on both sides of the middle of the side, and this, preferably for all sides.

Method according to the preceding claim, characterized in that the condition on the distance d is verified in at least one vertical plane perpendicular to the edge of the glass passing in the middle zone of at least one side of the glass, said middle zone being comprised in the peripheral area up to 10 cm on either side of the middle of the side, preferably for all sides. Method according to one of the two preceding claims, characterized in that the condition on the distance d is satisfied for any vertical plane passing through the middle zone of at least one side of the glass, preferably for all sides .

Method according to the preceding claim, characterized in that the glass comprises four sides.

Method according to one of the preceding claims, characterized in that d is in the range of 1 mm to 50 mm and preferably in the range of 5 mm to 30 mm.

Claims

8. Method according to one of the preceding claims, characterized in that the back-skeleton does not touch the upper main face of the glass or its slice at least at the end of bending.

9. Method according to one of the preceding claims, characterized in that the back-skeleton is covered with a thermal insulator on at least one of its faces opposite the glass.

10. Method according to one of the preceding claims, characterized in that the back-skeleton shields the glass to thermal radiation coming directly from heating elements.

1 1. Method according to one of the preceding claims, characterized in that the back-skeleton slows the rise in temperature of the periphery of the glass during the temperature rise phase for bending.

12. Method according to one of the preceding claims, characterized in that the glass is a stack of glass sheets, in particular a stack comprising a sheet of thickness in the range of 1, 4 to

2.7 mm, generally in the range of 1.4 to 2.5 mm and a thickness sheet in the range of 0.4 to 1.6 mm.

13. Method according to one of the preceding claims, characterized in that the glass is bulging by gravity at a temperature in the range of 570 to 650 ° C.

14. Method according to one of the preceding claims, characterized in that the back-skeleton is colder than the periphery of the glass during bending.

15. Method according to one of the preceding claims, characterized in that the bending is carried out in an oven, the back-skeleton being at a temperature below 250 ° C entering the bending furnace.

16. Method according to one of the preceding process claims, characterized in that the skeleton and the back-skeleton are conveyed together in an oven, the glass being in contact with the skeleton for more than 10 minutes in the oven.

17. Method according to one of the preceding claims, characterized in that the back-skeleton does not touch the glass at the moment when the glass comes into contact with the entire periphery of the skeleton.

18. Method according to one of the preceding claims, characterized in that at the moment when the glass comes into contact with the entire periphery of the skeleton, the upper face of the glass is in contact only with the ambient air.

19. Device for bending by gravity of a glass sheet or a stack of glass sheets, said glass, comprising a skeleton comprising a track contact member for supporting the peripheral zone of the lower main face of the lens, said contact track comprising concave curvatures at each of the sides of said skeleton, and a counter-skeleton comprising a metal bar, said counter-skeleton being configured so that its bar metal is present at a positive distance from the peripheral zone of the upper main face of the glass or its edge.

20. Device according to the preceding claim characterized in that it gives the glass concave shapes seen from above in its central zone and in each of its sides, particularly in the middle of its sides, the distance d being respected at least at the end of bending.

21. Device according to one of the preceding device claims, characterized in that the condition on the distance d is verified in at least one vertical plane perpendicular to the edge of the glass passing in the middle zone of at least one side of the glass, said middle zone being in the peripheral zone up to 20 cm on either side of the middle of the side, and this, preferably for all sides.

22. Device according to the preceding claim, characterized in that the condition on the distance d is verified in at least one vertical plane perpendicular to the edge of the glass passing in the middle zone of at least one side of the glass, said middle zone. being included in the peripheral zone up to 10 cm on either side of the middle of the side, and this, preferably for all sides.

23. Device according to one of the preceding device claims, characterized in that the condition on the distance d is verified for any vertical plane passing in the middle zone of at least one side of the glass, and this, preferably for all sides.

24. Device according to one of the preceding device claims, characterized in that the glass comprises four sides.

25. Device according to one of the preceding device claims, characterized in that the distance d is in the range from 0.1 to 50 mm and preferably in the range from 1 mm to 50 mm and preferably in the range from 1 mm to 50 mm. the range from 5 mm to 30 mm.

26. Device according to one of the preceding device claims, characterized in that the metal bar of the back-skeleton is at least partially above the skeleton and / or vis-à-vis the outer face of the skeleton.

27. Device according to one of the preceding device claims, characterized in that the metal bar of the back-skeleton is at least partially above the coast of the center of the contact strip for the skeleton glass.

28. Device according to one of the preceding device claims, characterized in that the skeleton comprises a metal strip whose one edge is directed upwards, said wafer being covered with a refractory fibrous material forming the contact track for the glass .

29. Device according to one of the preceding device claims, characterized in that the back-skeleton is removable.

30. Device according to the preceding claim, characterized in that the backbone comprises laterally retractable strips.

31. Device according to one of the preceding device claims, characterized in that it comprises means for imposing the distance d comprising an abutment integral with the skeleton and a fixed abutment against the back-skeleton, the abutment being able to rest on the abutment .

32. Device according to one of the preceding device claims, characterized in that it comprises a means for adjusting the distance d.

33. Device according to one of the preceding device claims, characterized in that the back-skeleton is covered with a thermal insulator on one of its faces opposite the skeleton.

34. Device according to one of the preceding device claims, characterized in that the back-skeleton comprises a tube adapted to receive a current of a cooling fluid.

35. Device according to one of the preceding device claims, characterized in that it comprises a rigid structural element disposed above the metal bar of the back-skeleton, the structural element and the metal bar being interconnected by a plurality of spacers preferably adjustable in their length.

36. Device according to one of the preceding device claims, characterized in that it comprises an oven and a conveying means capable of horizontally moving together the skeleton and the back-skeleton, said skeleton / counter-skeleton assembly in the oven and without relative horizontal displacement of the one relative to the other.

37. Device according to the preceding claim, characterized in that it comprises a plurality of skeleton / back-skeleton assemblies each loaded with glass and circulating behind each other in the oven.