Patent Application
20200346965
The invention relates to the bending of glass by gravity on a skeleton. A counter-skeleton is arranged above the glass in order to avoid the formation of ripples at its edges.
Bending glass by gravity is well known and in particular documented in EP448447, EP0705798 and EP885851. In US999558, the glass is forced to bend by pressure on the edge.
Bending sheets of glass of a thickness greater than 2.1 mm by gravity can be performed by methods described in the prior art. The trend is to increasingly reduce the thickness of the sheets of glass intended to be assembled in laminated glazing. The trend is to associate a thin sheet, with a sheet of greater thickness. It has been found that the bending of a sheet of glass of a thickness less than or equal to 2.1 mm by gravity produced, on a conventional skeleton, ripple defects on the edges of the glass, more particularly in the zone of the middle of the various sides of the glass. The phenomenon responsible for creating folds at the periphery of the glazing while it is supported at the periphery is an instability phenomenon similar to the buckling (or warping) of elastic plates. As in the case of thin elastic plates, the peripheral instability phenomenon observed in the forming of sheets of glass is all the more marked when the thickness of the glass is small and the temperature at the periphery of the glass is high.
If the formation of these ripples is sought to be counteracted by pressing on the top face of the glass during the bending, that tends to produce marks on this face and on the bottom face, and even to hamper the bending since the glass is wedged between a bottom tool and a top tool, like in a jaw, which slows down its subsidence. The “marks” correspond to slight mechanical indentations created by the tools on the glass while it is being bent. They are particularly damaging when they are situated on the bottom surface of the glass during the bending because they are then visible from the outside of the vehicle. The glazing is then scrapped. The “marks” which are situated on the top face of the glass during the bending are generally more readily accepted because they are located inside the vehicle once mounted thereon and these imperfections are therefore hidden from the view of an observer outside the vehicle. Also, these marks inside the vehicle are hidden only if they are on the periphery of the glazing and therefore in the zone of bonding of the interior glass on the body.
According to the invention, the bending of glass, in particular of thin glass, is correctly performed using a device for bending, by gravity, a sheet of glass or a stack of sheets of glass comprising a plurality of sides, called the glass, comprising a skeleton for supporting the glass in its peripheral zone by a contact track, said contact track comprising concave curvatures on each of the sides of said skeleton, and a counter-skeleton capable of entering into contact with the glass in the zone of the middle of at least one side of the peripheral zone of the top main face of the glass. Preferably, the counter-skeleton enters into contact with the zone of the middle of all the sides, generally four sides, of the peripheral zone of the top main face of the glass. The peripheral zone is the zone between the edge of the glass and a distance from the edge of the glass of 50 mm, whether it be the top face or the bottom face of the glass. Preferably, the counter-skeleton is removable (synonym: retractable).
The invention relates also to a method for bending, by gravity, a sheet of glass or a stack of sheets of glass, called the 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 bottom main face, a counter-skeleton comprising a metal bar being in contact with the glass during the bending in the peripheral zone of its top face, at the points where ripples appear in the absence of the counter-skeleton. The method comprises the bending of the glass by gravity on a skeleton supporting the glass in its peripheral zone by a contact track, said contact track comprising concave curvatures on each of the sides of said skeleton, a counter-skeleton coming into contact with the glass in the zone of the middle of at least one of the sides of the glass in the peripheral zone of its top main face.
The glass placed on the skeleton can be an individual sheet of a thickness less than or equal to 2.1 mm, even of a thickness less than or equal to 1.2 mm. 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 sheets of glass, in particular of sheets whose thicknesses have just been given. The stack can also comprise sheets of different thicknesses. This stack can comprise 2, 3 or 4 sheets. It is in particular possible to use the device according to the invention to bend the following two sheets in the superposed state: one sheet whose thickness lies in the 1.4 to 2.7 mm range, generally in the 1.4 to 2.5 mm range, with a sheet whose thickness lies within the 0.4 to 1.6 mm range, in particular in the 0.4 to 1.2 mm range, the thicker sheet being preferably located under the thinner sheet during the bending on the skeleton. The sheets bent together by the device according to the invention are not necessarily intended to be joined together in one and the same laminated glazing. For the purposes of simplification, the terms “the glass” is employed to denote an individual sheet or a stack of sheets.
The skeleton supports the bottom main face of the glass in its peripheral zone. The skeleton comprises a metal band (that can also be called “vertical flat”, even though its large faces can possibly be inclined) having one of its edges uppermost to support the periphery of the glass. The skeleton also comprises, as covering on the top edge of its metal band, a refractory fibrous material that is well known to the person skilled in the art, forming the contact track for the glass. The metal band is rigid whereas the fibrous material has a certain elasticity and compressibility. This material is generally of the felt type or a knit or fabric of metallic and/or ceramic refractory fibers, as is well known to the person skilled in the art. These materials reduce the risk of marking of the glass by the skeleton. The metal band in the skeleton generally has a width lying within the 1 to 10 mm range. The fibrous material generally has a thickness lying within the 0.3 to 1 mm range. The skeleton offers the glass, via its refractory fibrous material, a contact track of a width generally lying within the 1.6 to 12 mm range (which includes the thickness due to the refractory fibrous material), more generally within the 3 mm to 10 mm range. The skeleton has, on its contact face for the glass, concave curvatures, and has these for each of its sides and generally at least in the middle of each of its sides, 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 outlines (internal or external). 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 outlines (internal or external). In particular, the contact track of the skeleton has concave curvatures for the zone of the middle of its longitudinal sides, in particular for at least up to 20 cm of each side from this middle. 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 outlines (internal or external). In particular, the contact track of the skeleton has concave curvatures for the zone of the middle of its transverse sides, in particular for at least up to 20 cm of each side from this middle. The glass subsides under the effect of gravity on the skeleton during the bending and assumes a concave form when seen from above (the concave face is the top face) in its central zone and on each of its sides, in particular in the middle of its sides. The skeleton has a form conferring this concavity, since, at the end of bending, the glass touches all the perimeter of the contact track of the skeleton. At the end of bending, the glass being placed on the skeleton, the central zone of the top face of the glass is concave in all the directions. Seen from above, the skeleton has substantially the same outline as the glass that it has to receive while being smaller since the glass extends beyond all the outer perimeter of the skeleton. The contact track of the skeleton therefore generally has a concave form on each of its sides, in particular in the middle of its sides. The skeleton has as many sides as the glass and therefore generally has four sides (also called “bands”). Before bending, the glass generally extends beyond all the perimeter of the skeleton by a distance lying within the 2 to 45 mm range. This extension diminishes during the bending. This diminution depends on the scale of the curvatures given to the main faces of the glass during the bending. At the end of bending, this extension generally lies within the 1 to 25 mm range. From the start to the end of the bending, the skeleton generally supports the glass entirely within its peripheral zone and without extending out of this zone, either outward or inward. Seen from above, the skeleton has a continuous and uninterrupted annular form. Indeed, if the skeleton were segmented, this segmentation could produce a mark on the bottom face of the glass given the fact that, in the method according to the invention, the glass subsides essentially solely under the effect of its weight and therefore fairly readily follows the form of its support and remains fairly sensitive to the unevennesses of the skeleton.
The invention relates more particularly to the bending of glass for the production of glazings intended to equip vehicles (motor vehicles, buses, trucks, agricultural vehicles, etc.). It can be a windshield, a rear window, roof, sliding or fixed side window. The glass considered here comprises a plurality of sides, generally four sides (also called “bands”), one side meeting another at a corner of the glass, this corner comprising a curved sector comprising radii of curvature very much smaller than those of the curvature of the sides. The radii of curvature of the perimeter of the main faces seen at right angles to the main faces and to the edge of the glass are taken into consideration here. The middle of a side is located substantially equidistantly from two corners of this side. Such glasses have a vertical plane of symmetry PS when they are mounted on the vehicle, the direction of displacement of the vehicle (steering wheel not turned) lying within this plane of symmetry. The sides intersecting with this plane of symmetry are called transverse sides, the two other sides being called longitudinal sides. The middle of the sides is found as follows: the bent glass (preferably in the non-deformable assembled glazing state) is placed on a horizontal plane, concave side downward. The glass touches the horizontal plane by 4 points of contacts at its corners. The points of contact are linked to one another by straight-line sectors. The intersection with the edge of the glass of the plane at right angles to the sector and passing through the middle of this sector is the middle of the side of the glass. The middle of the transverse sides is also located at their intersection with the vertical plane of symmetry PS.
It is observed that the glass ripple problems mainly occur in the middle of the sides and, to remedy this problem, the counter-skeleton comes into contact with the glass in the zone of the middle of at least one of its sides and generally in the zone of the middle of all of its sides. The counter-skeleton can also enter into contact with the glass in the peripheral zone out of the zone of the middle of a side and even above the corners of the glass, but that is not generally necessary. The counter-skeleton can therefore possibly be absent above corners of the glass, the glass being better formed at these points. This is in particular possible when the complexity of the glazing is not too excessive, typically when its main bow is less than 100 mm. The zone of the middle of a side is the zone surrounding this middle in the peripheral zone of the glass. In particular, the zone of the middle of a side is the peripheral zone in the vicinity and on either side of the middle, 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 on each side of the middle, parallel to the edge of the glass and in the peripheral zone. This zone of the middle of a side is entirely concave at least up to 20 cm on each side of the middle. The counter-skeleton bears on the glass in this zone, but not necessarily throughout this zone. The counter-skeleton bears sufficiently to prevent the formation of the ripples, but not enough to mark the glass. The counter-skeleton bears, if necessary continuously, throughout the length of this zone parallel to the edge of the glass, but generally not throughout the width of this zone. If appropriate, the contact with the glass can therefore be only partial, that is to say along the periphery of the glass, the counter-skeleton may touch the glass only in certain zones and not in others. The counter-skeleton is preferably facing the skeleton on the other side of the glass during the bending. However, it may be located a little offset inward or outward relative to the skeleton, but its contact with the glass is made preferably only in the peripheral zone of the top face.
The glazings targeted here generally have four corners and are symmetrical relative to their plane of symmetry passing through the middle of their transverse sides. The two transverse sides are generally of a length lying within the range from 80 cm to 250 cm (length of sectors between points of contact, when the glazing is placed on a horizontal plane with the concave face turned downward). The two longitudinal sides generally have a length lying within the range from 60 cm to 180 cm (length of sectors between points of contact, when the glazing is placed on a horizontal plane). The two longitudinal sides generally have the same length.
The counter-skeleton comprises a metal bar at least partially covering, when seen from above, the peripheral zone of the top face of the glass. The counter-skeleton has a form complementing that which has to be given to the glass (final form after bending at the periphery), at the point where it touches the glass. Its form can deviate from that of the glass (and therefore of the skeleton) at the point where it does not touch the glass. The counter-skeleton has convex curvatures to face the concave curvatures of the top face of the glass. Since the skeleton has the form of the glass, the counter-skeleton has curvatures parallel to those of the skeleton, at least at the point where the counter-skeleton touches the glass.
The counter-skeleton enters into contact with the glass by a refractory fibrous material. At the points where the counter-skeleton touches the glass, it preferably has a structure similar or identical to that of the skeleton, that is to say that its metal bar comprises a metal band (or vertical flat) having one of its edges downward, said bottom edge being possibly covered with a refractory fibrous material already described for the skeleton. All the materials and thicknesses given for the skeleton (metal band and refractory fibrous material) are then valid for the counter-skeleton.
The refractory fibrous material can be compressed and is compressed during the bending under the effect of the force of gravity acting on the counter-skeleton. This property of the fibrous material can be exploited to distribute the pressure exerted by the counter-skeleton on the glass. The beneficial effect on the reduction of the unwanted peripheral ripples is also associated with the mechanical effect of the two tools (skeleton and counter-skeleton) which physically prevent any possibility of the glass being deformed in a vertical direction in line with the tools. The beneficial effect is linked to the use of the refractory fibrous material coupled with the control of the gap between the skeleton and the counter-skeleton; a slight local modulation of the distance between these two tools is reflected by a light compression of the fibrous material, which is insufficient to induce a mark on the glass. If necessary, a system of counterweights linked to the counter-skeleton reduces the force of pressure of the counter-skeleton on the glass.
Two variants can be distinguished:
The variant V1 involves the use of a means of imposing a given minimal distance Dm between the metal band of the skeleton and the metal bar of the counter-skeleton. The skeleton and the counter-skeleton cannot come close enough to one another for the distance between the metal band of the skeleton and the metal bar of the counter-skeleton to drop below Dm. This means serves to prevent the counter-skeleton from exerting an excessive pressure on the glass. In addition to the reduction of the risk of marking of the glass, that also allows the glass to slide over the skeleton during the bending, without being retained because of an excessive clamping between skeleton and counter-skeleton. This favors obtaining bending cycle time.
The curvatures of the glazings are characterized by the concepts of bow and of double-bending. For the definitions of these characteristics, reference can be made to
The invention is perfectly suitable for bending glass in which the complexity of form is moderate (bow less than 100 mm and/or double-bending less than 20 mm) or greater (bow greater than 100 mm and/or double-bending greater than 20 mm).
The variant V1 is preferably used when the geometrical instability (ripples) occurs in a highly localized manner on the glazing such as, for example, at the middle of the top band of a windshield (horizontal top edge when mounted on the vehicle). The distance between the skeleton and the counter-skeleton in this particular region then has to be finely adjusted. It is naturally possible to use this variant V1 over all the periphery of the glass, particularly when the propensity to geometrical instabilities is distributed over all the periphery of the glass.
The variant V2 is preferably used when the adjustment of the distance between the skeleton and the counter-skeleton is particularly difficult. This variant V2 operates not by adjusting the geometrical dimensions, but by pressure by virtue of the force of gravity exerted on the counter-skeleton pressing on the glass. This type of tool results in a bending method that is particularly reproducible, but less sensitive to the small geometrical variations of the tools, in particular for different successive heating and cooling cycles.
The function of the counter-skeleton is not to bend the glass (that is the role of gravity), but simply to prevent the formation of edge ripples. A bending without the counter-skeleton would culminate in an identical bending in the central zone of the glass compared to a bending with counter-skeleton, all other production conditions being the same. In particular, the counter-skeleton must not press too strongly on the glass because that would be reflected by a clamping of the glass, hindering its sliding on the skeleton during the bending and slowing down, even preventing, its bending. This is why the pressure exerted by the counter-skeleton has to be finely apportioned. In the device according to the invention, preferably, during the bending the counter-skeleton exerts a weight on the glass per linear meter of counter-skeleton (parallel to the skeleton) less than 2 kg/m and preferably less than 1 kg/m. Preferably, the counter-skeleton exerts a weight on the glass per linear meter of counter-skeleton (parallel to the skeleton) greater than 0.1 kg/m.
The counter-skeleton acts positively (by reducing the ripples) on the glass by thermal effect, at the points that it touches as at the points that it does not touch but that it approaches, notably to less than 50 mm. This thermal effect depends essentially on three criteria: 1) the relatively moderate temperature of the counter-skeleton on entering the kiln, preferably less than 250° C., 2) the propensity of the counter-skeleton to remain colder than the periphery of the glass while the glass is between 300 and 650° C., and in particular during the bending, 3) the area of glass exposed to the counter-skeleton.
The criterion 1 is ensured by a sufficient cooling of the counter-skeleton after a bending has been performed. A part of this cooling takes place in the bending kiln itself but also on the line of return of the tools when they go back from the kiln exit to the kiln entry. Complementary cooling systems specifically dedicated to the cooling of the counter-skeleton can be installed, such as additional fans or air jets directed toward this tool. It is also possible to provide a dedicated cooling circuit, directly fixed to the counter-skeleton, and activated over its return path out of the kiln. It can in particular be a tube capable of receiving a current of a coolant of fresh air (that is to say air generally at ambient temperature, generally between 0 and 50° C.). Such a metal tube can be attached to the metal bar of the counter-skeleton. It can also be a counter-skeleton whose metal bar comprises a metal tube with square or rectangular section in which fresh air is made to circulate. The criterion 2 is ensured, either by increasing the mass of metal embedded in the counter-skeleton, with the result of increasing its thermal inertia and therefore the quantity of heat needed to reheat it, or by limiting heat supplied to the counter-skeleton by covering the latter with a thermal insulation. Thus, the heating elements arranged in the crown of the kiln can heat the glass without in any way pointlessly losing energy to directly reheat the counter-skeleton. The periphery of the glass is then all the colder since it is on the one hand concealed from the direct heating by the heating elements of the kiln (generally in the crown) and on the other hand since it faces the counter-skeleton which is kept at lower temperature. It should be noted that the cooling of a counter-skeleton coated with an insulating material is slower because the surface directly exposed to the open air on the line of return of the tools is reduced. The criterion 3 is a function of the geometry of the counter-skeleton and of the distance between the counter-skeleton and the glass.
The counter-skeleton can be segmented. It then comprises as many bands (or “segments”) as the glass a has sides, generally four. One side of the glass has a band of the counter-skeleton associated with it. Each band of the counter-skeleton can cover the zone of the middle of one side, and if necessary, not go as far as the corners of the glass.
According to the invention, the skeleton can comprise a metal band whose edge is directed upward, said edge being covered with a refractory fibrous material forming the contact track for the glass, the counter-skeleton can comprise a metal bar, the device comprising a means of imposing a given minimal distance Dm between the metal band of the skeleton the metal bar of the counter-skeleton. The means of imposing Dm can in particular comprise a limit stop-forming element, called limit stop, secured to the skeleton and on which a prop-forming element, called prop, secured to the counter-skeleton, can rest. The limit stop is fixed directly or indirectly to the rigid metal band of the skeleton. It can be the top surface of a plurality of pillars or jack screws. The prop is fixed directly or indirectly to the rigid metal bar of the counter-skeleton. The device generally comprises a frame on which the skeleton is fixed. Any limit stop element can be fixed onto the frame or onto the skeleton, which still amounts to the fact that the limit stop is secured directly or indirectly to the skeleton. Advantageously, the means of imposing Dm can be adjusted so as to adjust the value of Dm. That makes it possible in particular to adjust the degree of compression of the refractory fibrous material with which the counter-skeleton and the skeleton are equipped and that presses on the glass, and therefore the pressure on the top face of the glass and the pressure on the bottom face of the glass. The adjustment means can be situated at the limit stop and/or the prop.
In practice, the distance between the two tools (skeleton and counter-skeleton) can be adjusted and controlled by the tool makers using shims. For the adjustment of the heightwise dimension of the counter-skeleton, the tool maker can proceed by introducing a shim between the top face of a previously bent glass and the refractory fibrous material of the counter-skeleton by exerting a certain lateral effort. In this adjustment, the fibrous material contracts slightly and diminishes a little in thickness. The rib measurement performed by the tool maker is therefore the resultant of the distance between the glass and the counter-skeleton, of the thickness of the fibrous material which covers it, of the compressibility of the fibrous material, of the thickness of the shim itself, and of the lateral force exerted by the tool maker when checking or when adjusting the distance between the two tools. By proceeding in this way, the operator appreciates whether a given shim passes easily or not between the glass and the counter-skeleton and, by routine tests, he or she learns to finely adjust the device.
For the case of pronounced curvatures or of complex forms, in particular including pronounced curvatures in mutually orthogonal directions, it may be advantageous for the device according to the invention to comprise a system capable of modifying the distance between the skeleton and the counter-skeleton during the bending. In fact, the counter-skeleton has a form closer to that of the top face of the glass at the end of the bending, rather than at the start of the bending. Now, when the glass is placed on the skeleton, the glass is flat or only slightly bent by virtue of its natural flexibility. The counter-skeleton therefore has a more curved form than the glass at the start of the bending and could touch it and, by elastic deformation, force it to adopt the peripheral form of the skeleton. Such a situation risks resulting in the glass breaking on entering the kiln. This is why, without precluding the counter-skeleton from being able to touch the glass from the start of the bending (on entering the kiln), it may be preferable for the counter-skeleton to first of all be fairly far away from the skeleton then approach it during the bending. The gap between the counter-skeleton and the glass (and therefore between the counter-skeleton and the skeleton) is then reduced as the glass softens and molds to the contours of the skeleton. The duration of the phase of convergence between the glass and the counter-skeleton can be adjusted between five tenths of a second and 30 seconds, even up to a minute, depending on the previous thermal history and the complexity of the glazing itself.
If the efforts applied to the glass on entering the kiln and during the bending are moderate enough to avoid a breaking of the glass, it is on the one hand perfectly possible for the counter-skeleton to be in partial contact with the glass, particularly at the middle or in proximity to the middle of the top and bottom sides of the glass (in position mounted on a motor vehicle) from kiln loading and, on the other hand, it is possible to force the glass to be bent by the action of the counter-skeleton pressing on the glass. The counter-skeleton presses on the glass as it is lowered, which forces the peripheral bending. Such a kinematic scenario is advantageous because it makes it possible to simplify the main bending of the glass and thus reduce the forming cycle time. Note that, at the start of the method towards entering the kiln, the glass is at low temperature and less sensitive to the marking and that is why apart from the case of breakage, the fairly insistent contact of the counter-skeleton at this stage is not necessarily a problem, and can even be advantageous. The triggering of the convergence between glass and counter-skeleton can be relatively abrupt (simple triggering, that is to say switching in one go from a separated configuration to a close configuration) or else gradual. A triggering system can be actuated through the lateral walls of the kiln or else through the bed of the kiln. A triggering system can in particular be similar to that described in U.S. Pat. No. 8,156,764. As an example, the distance between the glass and the counter-skeleton in the zone of the middle of a side can lie within the range from 0 to 10 mm at the start of the bending, to finish at 0 mm at the end of bending while, concomitantly, the distance between the glass and the skeleton in the zone of the middle of a side can lie within the range from 0 to 300 mm at the start of the bending to finish at 0 mm at the end of bending. Thus, the skeleton and the counter-skeleton can possibly converge gradually during the bending.
According to the embodiment V2, the counter-skeleton touches the glass and no limit stop/prop system stops the progress of the counter-skeleton toward the glass (and therefore also toward the skeleton) under the effect of gravity. The glass itself acts as limit stop. In this case, the counter-skeleton rests on the glass, which results in a greater or lesser compression of the fibrous material with which it is equipped. If the counter-skeleton is relatively light, it can be allowed to rest by all of its weight on the glass. If the counter-skeleton is too heavy and exerts an excessive pressure on the glass despite the presence of the fibrous material with which it is equipped, a part of the weight of the counter-skeleton can be compensated by a system of counterweights. In this case, the weight of the counter-skeleton is lightened by a counter-weight acting at the end of a lever. This lever is linked to the frame supporting the skeleton by a pivot link with substantially horizontal axis, one end of the lever bearing the counter-skeleton, the other end of the lever being linked to the counter-skeleton and pulling the latter upward under the effect of the counterweight at the other end of the lever.
The invention also relates to a method for bending glass by gravity, using the device according to the invention. The bending of the glass is performed by gravity on a skeleton supporting the glass in its peripheral zone, a counter-skeleton coming into contact with the glass in the zone of the middle of at least one of the sides of the glass in the peripheral zone of its top main face. In particular, the glass is bent by gravity at a temperature lying within the range from 570 to 650° C., more generally within the range from 610 to 650° C. To produce this bending, the skeleton/counter-skeleton charged with glass can be conveyed through a tunnel kiln raised to the plastic deformation temperature of the glass. This kiln can be passed through by such assemblies each charged with glass and circulating one behind the other in the kiln, the skeleton and the counter-skeleton forming a carted assembly capable of being conveyed together horizontally but without horizontal displacement relative to one another. The kiln can comprise different temperature zones for gradually heating then gradually cooling the glass.
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 kiln while being conveyed in the kiln. In the kiln, the glass undergoes a rise in temperature, the bending and after bending, a controlled lowering of the temperature. Likewise, in the kiln, the counter-skeleton generally also touches the glass for longer than 10 minutes and generally at the same time as the glass touches the skeleton. The bending is performed by gravity. In the absence of counter-skeleton, during the bending, the glass would touch all of the skeleton, then, certain zones (in particular in the zone of the middle of at least one side of the peripheral zone) would be raised to no longer have contact with the skeleton. The counter-skeleton serves to prevent this raising of the glass and guarantee a total contact of the glass with all the contour of the skeleton at the end of bending. The skeleton and the counter-skeleton form a carted assembly capable of being conveyed in the kiln by a conveying means. The device according to the invention does not allow a relative horizontal displacement of the skeleton and of the counter-skeleton relative to one another, even as the skeleton/counter-skeleton assembly is conveyed in the kiln. The device can comprise means allowing the skeleton and the counter-skeleton to move closer or further apart by a relative vertical movement without relative horizontal displacement relative to one another, and do so even as the skeleton/counter-skeleton assembly is conveyed in the kiln. The term “relative” qualifying a movement means that the latter can be attributable to the counter-skeleton alone or the skeleton alone or both these elements. The absence of relative horizontal displacement of the skeleton and of the counter-skeleton relative to one another means that these two elements remain facing one another when seen from above during the horizontal displacement of the skeleton/counter-skeleton assembly during the bending in the kiln. Thus, the device according to the invention generally comprises a kiln and a conveying means capable of horizontally displacing the skeleton and the counter-skeleton together in the kiln while they are facing one another, and vertical translation means allowing the skeleton and the counter-skeleton to approach one another or move away from one another by a relative vertical movement during their horizontal displacement and without relative horizontal displacement relative to one another. If necessary, the device can be such that a counter-skeleton can be placed on a glass before entering the kiln and be removed after exiting from the kiln.
After bending, the glass is cooled. For this cooling and in order not to generate excessive edge extension stresses in the glass, the counter-skeleton is advantageously moved away from the glass. The separation of the counter-skeleton is advantageously performed during the cooling of the glass and when the latter is at a temperature lying between 620 and 500° C. This separation can be performed by different systems. It can be a re-engaging system which performs the reverse function of the “triggering” described above. Alternatively, the counter-skeleton can be composed of laterally retractable bands, generally four of them. The bands of the counter-skeleton are separated vertically and laterally at the moment of retraction so as to be no longer above the top face of the glass. The system controlling the retraction of the bands can be similar to one of those described in U.S. Pat. No. 8,156,764, that is to say, for example, through the lateral walls of the kiln.
The skeleton and the counter-skeleton are advantageously independent of one another, that is to say that the counter-skeleton can then be separated entirely without any longer having a link with the skeleton. The glass can then be loaded on the skeleton then the counter-skeleton is put in place.
The loading of the glass on the device according to the invention can be performed manually. With the counter-skeleton separated, operators place the glass on the skeleton. Then, they place the counter-skeleton in its planned position. The position of the counter-skeleton is advantageously given by positioning means fixed to the skeleton or to the frame. These positioning means guide the counter-skeleton in its placement. This guidance is made possible for example by orifices in guiding tabs linked to the counter-skeleton and through which positioning columns pass.
The loading and unloading of the glass can also be automated, in particular using robots, one for the loading, the other for the unloading. The use of robots makes it possible to have accurate and reproducible movements as well as a reliant and tolerant coupling system between the skeleton and its associated counter-skeleton. This system according to which the counter-skeleton is entirely separable from the skeleton makes it possible 1) to have a minimum of functions embedded in the tool and thus minimize the weight thereof, which is an important energy consumption factor, 2) to minimize the risk of mechanical seizing and 3) to minimize the servicing operations, which are usually costly, on the forming tools.
Alternatively, the counter-skeleton can form part of a system directly embedded on the skeleton itself and capable of retracting counter-skeleton. To do this, by way of example, the counter-skeleton can be composed of four separate bands secured to the skeleton and which can be moved away from or rejoin one another by displacements that have both a horizontal component and a vertical component making it possible to move away from the glass, without slipping on the latter, while moving away laterally from the skeleton. Such a movement can be performed by a simple rotation whose axis is shrewdly chosen, in particular outside of the skeleton. When these bands move away, the skeleton becomes accessible for glass to be unloaded or loaded.
If the counter-skeleton is of too light a construction, its rigidity may be too weak and its form may alter slightly during its use, following the thermal constraints undergone in the heating and cooling cycles. In this case, it may possibly be observed that the gap between skeleton and counter-skeleton (and therefore between the metal band of the skeleton and the metal band of the counter-skeleton) is no longer uniform and as it was set initially. The glass may possibly be, at certain points excessively clamped between skeleton and counter-skeleton, reducing the bending at these points by preventing the glass from slipping on the skeleton. Thus, depending on the bending cases, a simple adjustment of gap only at the corners of the device, in particular by four jack screws, may prove insufficient. This is why, advantageously, the counter-skeleton comprises a structural element arranged above its metal bar, the structural element and the metal bar being linked to one another by a plurality of adjustable spacers making it possible to locally adjust the distance between the structural element and the metal bar. The structural element is rigid and non-deformable despite the multiple thermal heating and cooling cycles undergone to bend glass sheets industrially. It can be used as reference for adjusting the form of the metal bar. The structural element advantageously comprises a metal tube, in particular of framework type. This tube can in particular have a square or rectangular section. It can comprise lateral extensions to come above the adjustment zones, the top end of the spacers being linked to the extensions. The top end of the spacers can also be linked directly to the structural element. Thus, the counter-skeleton can comprise a structural element provided with a dimension greater than that of its metal bar, the structural element and the metal bar being linked by a plurality of adjustable spacers making it possible to locally adjust the distance between the structural element and the metal bar, and, locally, the counter-skeleton/skeleton distance. The plurality of spacers is distributed regularly over all the perimeter of the counter-skeleton.
In order to reduce to the minimum the risks of deformation of the counter-skeleton due to thermal constraints, its metal strip can be given the structure of a chain, by breaking down the counter-skeleton into a plurality of sectors linked to one another by articulations. A sector is a piece of metal band having one of its edges downward, said edge being covered or not, depending on the case, with a refractory fibrous material. A sector comprises a length and a height, its thickness being that of the metal band. Its length is substantially parallel to the edge of the glass and to the skeleton. The edge of the sector turned downward is substantially parallel to the edge of the skeleton at the same point. The sectors are linked to one another like a chain so that their edges directed downward are aligned and substantially parallel to the edge of the glass and to the skeleton. A sector is linked to two other sectors by articulations comprising a pivot link with substantially horizontal axis situated at its two ends of its length, except a chain-end sector, in which case it is linked only to one other sector by an articulation at one of its ends. A counter-skeleton with sectors can be composed of four bands (corresponding to the four sides of the glass and of the skeleton) each coming, in use, to face a side of the skeleton and therefore also a side of the glass. Each of these bands has a plurality of sectors, for example from 2 to 10 sectors. Thus, according to the invention, the counter-skeleton can comprise a metal bar of the vertical metal band type of which one edge is turned downward, comprising a plurality of sectors linked to one another by articulations, each articulation comprising a pivot link with substantially horizontal axis linking two sectors to one another.
By virtue of the articulations, the counter-skeleton with sectors closely follows the deformations of the glass. Likewise, its own tendency to be deformed is counteracted by the set of articulations. Thus, the counter-skeleton with sectors unstick much less from the glass than if it were of a single piece and without articulation. The marks on the glass depend essentially on the actual pressure exerted by the counter-skeleton on the glass, and therefore on the following parameters: the weight of the various sectors of the counter-skeleton, the contact surface of the fibrous material covering the counter-skeleton and, finally, the texture of the fibrous material itself which preferably has a small resilient surface. A system of counterweights, already described above, can be used to reduce the pressure of the sectors on the glass. In this case, the end of the lever linked to the counter-skeleton with sectors is linked preferably to an articulation joining two sectors.
Two sectors linked to one another by an articulation can be juxtaposed locally at the articulation. The areas of juxtaposition of the two sectors are then juxtaposed in a direction at right angles to the axis of the articulation, said axis passing through the zones of juxtaposition of the two sectors. The zone of juxtaposition of at least one of the two sectors can be, when seen from above, offset relative to its downward-turned edge, so as to form a space that can be occupied by the zone of juxtaposition of the other associated sector in the articulation. This local offset can in particular be produced by local embossing. This local offset can also be produced by cutting the zone of juxtaposition so as to form a tongue that can be offset by deformation of the metal relative to the plane of the sector when seen from above. In this way, even if, locally in the juxtaposed zones of the articulation the set of two articulated sectors is two times thicker than a single sector, the downward-turned edges of two sectors linked to one another by an articulation can be aligned when seen from above. Thus, the downward-turned edges of two sectors linked to one another by an articulation can be aligned when seen from above, the zone of juxtaposition of at least one of the two sectors being, when seen from above, offset relative to its downward-turned edge, so as to form a space occupied by the zone of juxtaposition of the other sector. A counter-skeleton with sectors can operate according to the modes V1 or V2 mentioned above and the advantage resulting from the existence of the articulations applies in both cases. In fact, the counter-skeleton with sectors is not deformed as much as if it were of a single piece. Its bottom edge follows the surface of the glass much better during the bending despite the thermal stresses. In this way, the pressure exerted by the counter-skeleton on the glass is more uniform and better distributed over all its zone of contact.
According to the mode V1, a counter-skeleton with sectors can touch the glass via a fibrous material whose compression is limited by virtue of the presence of a means of imposing a given minimal separation Dm between the metal band in the skeleton and the metal band in the counter-skeleton. For this, the skeleton can comprise a metal band whose edge is directed upward and a plurality of limit stops linked to the metal band. These limit stops are advantageously placed facing articulations of the counter-skeleton. Props are then linked to the counter-skeleton and placed facing the limit stops, notably to the rods forming axes of the articulations, so that they can come to bear on the limit stops, such that a minimal distance Dm between the metal band of the skeleton and the metal bar of the counter-skeleton can be imposed on each sector when the props rest on the limit stops, and therefore when the counter-skeleton is arranged on top of the glass. The articulations ensure that despite the thermal stresses, each sector rests on its associated limit stop. According to this construction, the sectors situated at the ends of each segment are slightly shorter in order to not hamper their movement about their horizontal axis.
A specific cutout at the articulation of the sectors situated at the ends of each band makes it possible to limit their vertical downward movement and thus not interfere with the movement of the counter-skeleton when the glass is loaded and unloaded. In effect, the sectors can be grouped into as many bands as the glass has sides, each band corresponding to a side of the glass and being substantially parallel to it, the ends of the bands not being linked to their neighboring bands.
The figures described hereinbelow are not to scale.
The sectors S2 and S3 can therefore be moved freely in rotation relative to the bridge 119 and according to the articulation 112. A rod 118 is linked to the articulation 112 via a bridge 119 and can have a free vertical movement relative to the rigid structural element 116. This rod 118 is topped by an articulation 120. The counterweight system is composed of a vertical bar 121 provided with an articulation 124 at its top end, of a rod 122 revolving, at a point situated between its ends, freely about the articulation 124 and of a weight 123 attached to the end of the rod 122. The bar 121 is secured to the rigid structure 116 and situated in proximity to the rod 118. The second end of the rod 122 is linked to the articulation 120 linked to the rod 118.
| Number | Date | Country | Kind |
|---|---|---|---|
| 1759859 | Oct 2017 | FR | national |
| 1759862 | Oct 2017 | FR | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/FR2018/052596 | 10/18/2018 | WO | 00 |
