WO2021152238A1

WO2021152238A1 - Method and device for bending a glass sheet by pressing against a bending mould

Info

Publication number: WO2021152238A1
Application number: PCT/FR2021/050104
Authority: WO
Inventors: Juan Felipe GIRALDO RESTREPO; David Valcke; Christophe Machura; Jérôme PELLETIER
Original assignee: Saint-Gobain Glass France
Priority date: 2020-01-31
Filing date: 2021-01-20
Publication date: 2021-08-05
Also published as: FR3106827A1; CN113490648A; FR3106827B1

Abstract

The pressing device (100) comprises a frame (110) for pressing a softened glass sheet (1) against a bending mould (25) in order to bend said sheet. The pressing frame (110) comprises a track (120) for contacting the glass sheet (1) and a track support (130) that is supported by a chassis (180). A heating system (140) is used to heat the track (120), which is subdivided into successive segments (121-i) separated in each case by a clearance forming an expansion joint between them. Each track segment (121-i) is mounted on the track support (130) with a possibility of movement between the track segments in the circumferential direction by virtue of a sliding connection in order to compensate for a relative dimensional variation due to the expansion during the heating of the track (120). The risks of damaging the glass sheet during pressing are thus reduced.

Description

DESCRIPTION

TITLE: method and device for bending a glass sheet by pressing against a bending form

The present invention relates to a pressing device for pressing a glass sheet brought to a softening temperature against a bending shape to bulge the glass sheet. It also relates to a device for bending a sheet of glass previously heated to a softening temperature which comprises such a pressing device, as well as a method for bending a sheet of glass which uses such a bending device.

In order to produce glass sheets having a convex shape, for example automotive glazing, it is known to convey the glass sheets in the planar state one by one on a bed of rollers through a heating furnace. to bring them to a softening temperature. The glass sheets are then conveyed, right out of the oven, to a bending station in which a lower frame lifts a glass sheet to come and press it against an upper form and thus give it the desired form. The glass sheet thus curved is then redeposited on the conveyor to be taken to a cooling station such as a quenching station.

This technique is considered a cold technology, this qualifier defining the location of the bending station outside an enclosure maintained at temperature to heat the sheet of glass. This means that controlling the positioning of the bending tools is simpler than in the case of hot technologies, and that in return the bending process is a race against time since as soon as it leaves the furnace, the glass sheet will cooling: the modifications to the bending operation or its conditions are therefore delicate and limited.

US 4,872,898 illustrates this technique. In the bending station, the glass sheet is lifted from the conveyor by a pressing frame having the desired shape to the glass sheet. The pressing frame is discontinuous so as to be able to pass through the bed of rollers on which the sheet of glass initially rests. The pressing frame then lifts the glass sheet to press it against an upper solid form whose shape is complementary to that of the pressing frame and therefore corresponds to the desired shape for the glass sheet. After pressing, the pressing frame descends to a level below the bed of rollers and thus redeposits the glass sheet on said bed of rollers. The rollers then start to move again to drive the sheet of glass to the quenching station. WO 02/06170 A1 and WO 2016/156735 A1 describe improvements made to this technique, the first concerning the transport of the curved glass sheet to the cooling station by a mobile shuttle with shaped rollers and the second concerning the addition of 'an intermediate support in the bending station which firstly allows the glass sheet to be lifted very quickly from the conveyor before a pressing frame then comes to press the glass sheet against the bending form. US 2010/0050964 A1 further discloses providing means for heating or cooling the bending form.

A difficulty with this technique lies in the fact that the pressing frame of the bending station is, in a stabilized state, at a temperature less than or equal to 100 ° C, which is notably lower than the temperature of the glass sheet carried. prior to a softening temperature. When the pressing frame contacts the glass sheet, there is an abrupt cooling of the glass sheet in the contact zone of the pressing frame, in other words towards the periphery of the glass sheet. This has damaging consequences. For example, in the case of semi-tempered glass sheets, small cracks (also called “cracks”) appear at the edge of the glass sheet, especially if the thickness of the glass sheet is between 1 and 2 , 85 mm. This effect also exists to a lesser extent for glass sheets greater than 2.85 mm thick which are then tempered or semi-tempered. These cracks can lead to breakage during cooling of the glass during the heat treatment of toughening or semi-toughening or else to fragile products which can lead to deferred “spontaneous” breakages which occur without apparent cause, sometimes when the sheet glass is already installed on the motor vehicle, it being specified that these edge cracks are difficult to detect, which makes it difficult to rule out products at risk.

In the case of very thin glass sheets having a thickness less than 1 mm, the contact of the pressing frame with the glass sheet induces a temperature gradient perpendicular to the edge of the glass sheet, and this generally over the entire periphery of the glass. glazing. As the glass sheet cools, compressive stresses appear at the cold periphery of the glass sheet and cause unwanted corrugations of a length generally between 20 and 80 mm. In general, the contact of the pressing frame with the sheet of glass can have the consequence, even for toughened glasses of thickness greater than 3 mm, that the extended zone which balances the part in compression is the cause of fragilities leading to low resistance to the impact of chippings or even increased sensitivity to surface defects of the glass such as scratches sometimes invisible to the naked eye which can induce spontaneous breakage, without apparent cause. To remedy this difficulty, it has been proposed to heat the pressing frame so as to limit the temperature difference between the pressing frame and the glass sheet.

Such a solution is taught by US 5,178,660. This document describes a pressing frame shaped at the periphery of the glass sheet to be pressed. Each of its four sides is defined by a respective rail forming a track intended to come into contact with the sheet of glass, the track possibly being covered with an insulating material to soften the contact with the sheet of glass. A longitudinally shaped heating element is placed against the underside of the rail to heat it, and thermocouples are provided at various locations along the rails to measure their temperature in order to adjust the temperature of the heating elements. Each rail and its heating element are supported by vertical spacers each time by means of a yoke and an articulated clevis, the spacers being mounted at their other end on a base plate mounted on a carriage movable vertically by means of a cylinder to press the pressing frame against the crowning form installed above.

This solution, however, requires the use of relatively long spacers so as to be able to flex elastically to compensate for the elongation of the rails due to their expansion under the effect of the heating of their heating element. Indeed, the mounting points of two successive spacers of a rail will move apart under the effect of expansion while their distance remains substantially constant at their opposite end at the level of the base plate which remains at a close temperature. ambient temperature.

This solution has a first drawback linked to the fact that the circumferential dimensional stability of the annular shape of the pressing frame is not ensured. Indeed, each corner of the pressing frame is each time defined by a longitudinal end of a first rail placed contiguous with a lateral part of the end region of a second rail. As a result, the two opposite rails which are arranged between the two other rails which are perpendicular to them, will push the latter back owing to their elongation linked to their thermal expansion. The correspondence between the pressing frame and the bending shape is therefore adversely affected. For the same reason, the corners of the pressing frame deform slightly under the effect of expansion, which has the disadvantage that the geometry of the pressing frame no longer corresponds to that of the glass sheet: this can result in a over-pressing of the glass sheet by the pressing frame against the bending shape and in particular a risk of breakage of the glass sheet.

Furthermore, given the distribution of the spacers over the entire circumference of the pressing frame, the installation of the conveyor rollers is made difficult since they must be installed between successive spacers. It could be envisaged to mount each of the rails forming the two opposite sides of the pressing frame which are perpendicular to the conveying rollers on a horizontal bar supported by two side uprights fixed on the base plate so as to clear a passage under the horizontal bar. between the two side uprights to define a free window for mounting the rollers. However, in doing so, the fixing of these two rails on the corresponding horizontal bar would be done by means of spacer elements of short length, for example screws, which would not be able to flex to compensate for the expansion of the rails. Therefore, this would cause irreversible and detrimental deformation of parts, for example the contact surface of the rail could warp. US 5,441,551 also discloses a system for heating the pressing frame which also deforms under the effect of thermal expansion, which leads to drawbacks similar to those discussed for the previous document.

The aim of the present invention is to provide a technical solution at least partially overcoming the aforementioned drawbacks.

To this end, according to a first aspect of the invention, there is provided a pressing device intended to press a glass sheet brought to a softening temperature against a bending shape to bend the glass sheet, the pressing device comprising a pressing frame for pressing the periphery of the glass sheet against the bending form, and a support structure supporting the pressing frame.

The pressing frame includes a track provided to contact the periphery of the glass sheet and a track support supported by the support structure. The track support supports at least a section of the track. It will be understood that the expression "section of the track" is understood to mean a circumferential section of the track, in other words a portion of the track bounded in the circumferential direction of the track. The pressing frame also includes a heating system for heating the track at least in the region of said section of track.

The track section is subdivided into several distinct track segments arranged successively in the circumferential direction of the track, being separated each time by a clearance forming an expansion joint between them. It will be understood that this clearance extends in the circumferential direction of the track. Each of the track segments is mounted on the track support with the possibility of relative displacement between at least part of the track segment relative to the track support in the circumferential direction of the track to compensate for a relative dimensional variation between the track segment. track and the track support in the circumferential direction of the track due to thermal expansion when the track is heated by the heating system. The mounting of each of the track segments on the track support involves a sliding connection to provide said possibility of relative displacement.

Thanks to the heating system, the temperature difference between the glass sheet and the contact part of the track of the pressing frame with the glass sheet can be reduced or canceled, thereby reducing or even eliminating the detrimental effect. on the glass sheet described above. Furthermore, the segmentation of the track with the interposition of games forming an expansion joint makes it possible to better manage the thermal expansion of the track and has the effect of ensuring or at least significantly improving the circumferential dimensional stability of the annular shape of the track despite its heating, and therefore, it provides a better correspondence between the track and the shape of the bending.

According to preferred embodiments, the invention comprises one or more of the following features: the sliding connection is a sliding connection in the circumferential direction of the track;

- a track segment is rigidly fixed to the track support at a first location so as to define a fixed point between them during said relative dimensional variation, the track segment being connected to the track support by the sliding link in one second location separated from the first location in the circumferential direction of the track; the track segment is rigidly fixed to the track support at the first place by means of a screw passing through a circular passage hole and is connected to the track support by the sliding link at the second place by means of a screw passing through a hole oblong or slit; the pressing device comprises spacers of adjustable length for adjusting the curvature of the track, the support structure supporting the track support through at least some of the spacers which act on the track section through the track support; at least a first section of the track support is supported by the support structure with the possibility of relative displacement by means of a sliding connection to compensate for a relative dimensional variation between the track support and the support structure due to expansion when heating the track by the heating system; the first section of the track support corresponds to at least a preponderant part of the length of a first side of the track corresponding to a first side of the pressing frame; the first section of the track support is mounted on the support structure by a sliding connection formed in a middle zone on the first side of the track, the sliding link allowing only a translational movement in a direction substantially perpendicular both to the first side of the track and to the intended direction of pressing of the pressing device against the bending form; and the support structure further supports the first section of the track support on either side of the slide link by plane links allowing relative omnidirectional sliding in a plane perpendicular to the intended direction of pressing of the pressing device against the bending shape, which makes it possible to compensate for a dimensional variation between the track support and the support structure due to expansion during the heating of the track by the heating system; the support structure supports the first section of the track support by means of lugs movably mounted on the support structure, one so as to implement the slide connection and the others so as to implement the plane connections; preferably, the first section of the track support is fixed to one, more or all of the lugs by means of a respective screw with a captive head free in rotation making it possible to adjust the spacing between the first section of the track support and the structure support, e which therefore makes it possible to indirectly adjust the curvature of the part of the track corresponding to the first section of the track; the first section of the track support is supported by a support bar of the support structure, the support bar extending substantially parallel to the direction of longitudinal extension of the first side of the track; two uprights of the support structure support the support bar respectively in a first region and in a second region of the support bar which are separated from each other in the direction of longitudinal extension of the bar; and the two uprights are separated from each other by a distance corresponding to at least a preponderant part of the length of the first side of the track and define under the support bar a free passage between them; the heating system is arranged to heat a track segment from below in an area facing the contact part of the track segment which is intended to contact the periphery of the glass sheet, the track segment being mounted on the track support exclusively in mounting regions of the track segment which are offset outwardly of the pressing frame with respect to the contact portion of the track segment; the track segment and the track support are separated by wedges made of thermally insulating material; the track segment comprises a series of holes arranged between the contact portion of the track segment and the mounting regions of the track segment so as to limit the thermal conduction of the contact part towards the mounting regions, it being specified that this limitation of the conduction is understood in this case in relation to the case where the holes do not exist; the heating system comprises at least one electrically insulated heating conductor wire which is held under the track segments by jumpers spaced apart and secured to the track segments by screws, the at least one conductive wire being surrounded by a material of thermal insulation, the assembly formed by the at least one heating conductor wire, the jumpers and the thermal insulation material being preferably protected by a casing; the clearance forming an expansion joint between two successive track segments is provided between two longitudinal ends facing the two track segments which may be nested one inside the other. In this way, the clearance forming an expansion joint between the two track segments is defined between transverse ridges facing the two track segments; the track support has radiator fins on a side opposite the track section and / or a coolant circuit is arranged against the track support; it will be understood that these radiator fins serve for heat dissipation purposes; the track has a generally annular shape and the track support has a corresponding generally annular shape, the support structure supporting the entire track through the track support;

- a track segment is removably mounted on the track support, which makes it easier to replace, for example if it was damaged or worn.

According to a second aspect, the invention relates to a device for bending a glass sheet previously brought to a softening temperature, comprising: a bending form; a pressing device according to the first aspect of the invention which has just been described; and a system for actuating at least one of the pressing device and the bending form so that they can be brought together to press the glass sheet against the bending form and so to be able to move them away from each other to release the glass sheet after bending.

According to a third aspect, the invention relates to a method of bending a sheet of glass, comprising: heating the sheet of glass to a softening temperature in a heating zone, transferring the sheet of glass to the softening temperature in a bending device according to the second aspect of the invention which is placed outside the heating zone in an environment at room temperature and of which the track section in its part coming into contact with the glass sheet is previously heated by the heating system to a temperature between room temperature and the softening temperature of the glass sheet, more preferably to a temperature between 200 and 600 ° C, and bending the glass sheet by the bending device while it is still at a softening temperature.

In the context of the invention, thermal toughening of a glass sheet is understood to give the glass sheet a surface stress greater than 90 MPa, generally between 90 and 200 MPa. Thermal semi-hardening - also called thermal hardening - is understood to give the glass sheet a surface stress in the range of 15 to 90 MPa, more generally in the range of 20 to 60 MPa. The above stress values are absolute values. A surface stress can be measured by an apparatus operating on the principle of polariscopy, such as the Scalp-04 polariscope marketed by the company GlasStress Ltd. Its value is determined as an arithmetic mean of five measurements on a major surface of the sheet of glass, one measurement being made in the middle of the sheet of glass - which may be chosen as its center of inertia - and four other measurements. which are distributed at equal distances on a fictitious line going around the main surface of the glass sheet at a distance from the peripheral edge of the glass sheet equal to ten times the thickness of the sheet. But as regards the particular case of the glass sheets with four corners, it is preferable that each of these four measurements be made on this fictitious line in a respective corner of the glass sheet.

The invention is applicable to individual glass sheets preferably having a thickness in the range of 0.1 to 6.1 mm, including the terminals. They may or may not be covered with one or more thin layers such as one or more anti-IR layers, for example with silver, or one or more so-called Low-E layers: these layers are not taken into account in the ranges. of the aforementioned thicknesses.

Other aspects, characteristics and advantages of the invention will become apparent on reading the following description of a preferred embodiment of the invention, given by way of example and with reference to the accompanying drawing.

[Fig 1] schematically shows the situation of a bending installation during a first step of a bending process according to one embodiment of the invention.

[Fig 2] schematically shows the situation of the bending installation during a second step of this bending process. [Fig 3] schematically shows the situation of the bending installation during a third step of this bending process.

[Fig 4] shows schematically the situation of the bending installation during a fourth step of this bending process.

[Fig 5] shows schematically the situation of the bending installation during a fifth step of this bending process.

[Fig 6] shows schematically the situation of the bending installation during a sixth step of this bending process.

[Fig 7] schematically shows the situation of the bending installation after the sixth step of the bending process which in fact corresponds to that of Figure 1, but with respect to a new sheet of glass.

[Fig 8] schematically shows a perspective view of a pressing device according to one embodiment of the invention.

[Fig 9] shows for the pressing device of Figure 8 a schematic top view of part of the track intended to contact the glass sheets.

[Fig 10] is a schematic sectional view through the track support and the track along the section line X-X shown in Figure 8.

[Fig 11] is a local perspective view of a lateral side of the pressing device of Fig. 8.

With reference to FIGS. 1 to 7, we will describe an example of a method for bending a sheet of glass implemented in a bending installation including a device for bending a sheet of glass according to one embodiment of the invention. According to this process, the sheets of planar glass are subjected one after the other to a bending operation to give it a desired convex shape.

As shown in Figure 1, the bending installation comprises a heating zone 10, a bending device 20, a conveyor 30, a cooling device 40 and a shuttle 50.

The heating zone 10 can be implemented conventionally by an oven, preferably of the tunnel type, through which the glass sheets 1 are transported one after the other on the conveyor 30. The conveyor 30 is preferably horizontal and moved. by a series of rectilinear motor rollers aligned in a plane. The glass sheets 1 are thus transported along a horizontal rectilinear path. Inside the heating zone 10, each glass sheet 1 is brought to a softening temperature which is preferably between 600 and 700 ° C.

According to a first step illustrated in FIG. 1, after having left the heating zone 10 where it has been brought to the softening temperature, the conveyor 30 brings a sheet of glass 1 into the bending device 20 where it will be bent, The direction conveying device being indicated by the arrow Y. The bending device 20 is arranged in the immediate vicinity of the outlet of the furnace or heating zone 10, but is located outside the furnace or heating zone 10 in an environment at room temperature. The bending device 20 comprises, on the upper side, a bending form 25 and, on the lower side, a pressing device 100 which will be described in more detail below. In this initial position, the pressing device is at a lower level than that of the conveyor 30.

While a sheet of glass 1 is brought into the bending device 20 by the conveyor 30, another sheet of glass 1a which was previously bent in the bending device 20 has already been carried by the shuttle 50 out of the box. bending device 20 to be brought by the shuttle 50 into the cooling device 40.

The shuttle 50 is designed in the form of a support frame or ring or in any other suitable form which is able to transport the glass sheet 1a from the bending device 20 to the cooling device 40 while supporting it from the outside. adequate manner to keep it the convex shape which was conferred on it in the bending device 20 until it is again stiffened under the effect of a cooling applied in the cooling device 40. The shuttle 50 can in particular be designed as taught in WO 02/06170. More generally, the transport of the curved glass sheet 1a from the bending device 20 into the cooling device 40 can be carried out by any other suitable means as long as it makes it possible to preserve the curved shape of the curved glass sheet. 1a while waiting to be stiffened by cooling in the cooling device 40.

In the cooling device 40, the curved glass sheet 1a is subjected to forced cooling reducing the temperature of the glass sheet enough so that the curved glass sheet retains its curved shape as it leaves the cooling device 40.

The cooling device 40 is preferably provided for subjecting the curved glass sheet 1a either to thermal toughening or to thermal hardening, also called semi-toughening. The cooling device 40 can be produced by air blowing nozzles in a manner known per se. As a consequence of the forced cooling, the temperature of the curved glass sheet 1a is lowered to a temperature preferably between 400 and 500 ° C.

According to a second step illustrated by FIG. 2, the glass sheet 1 is stopped in the conveying direction Y on the conveyor 30 in the bending device 20. The glass sheet 1 is thus stopped by stops 26. At this time , the rolls of the conveyor 30 preferentially cease to be driven in rotation at least in the bending device 20 in order to avoid marking the glass sheet 1. In this position, the glass sheet 1 is ready to undergo the bending operation in the bending device 20.

For its part, the curved glass sheet 1a is moved by the shuttle 50 out of the cooling device 40 after application therein of the toughening or semi-toughening or more generally of the planned cooling.

According to a third step illustrated by FIG. 3, the pressing device 100 moves vertically upwards. In doing so, he lifts the glass sheet 1 from the conveyor 30, then presses it against the bending form 25. A suction creating a vacuum is preferably applied through suction openings opening onto the bending surface of the bending form. 25 to even better press the glass sheet 1 against the bending form 25. As a result of this operation, the desired curved shape will be imparted to the glass sheet 1. After lifting the glass sheet 1 from the conveyor 1, the stops 26 are retracted if necessary to allow the pressing device 100 to continue its movement towards the bending form 25.

For its part, the curved glass sheet 1a is removed from the shuttle 50, for example by being ejected upwards by means of a blowing device - not shown - located under the shuttle 50. The curved glass sheet 1a is gripped at the top. at this time by a gripping device 60, for example with suction cups, to remove the bent glass sheet 1a from the bending installation.

According to a fourth step illustrated in FIG. 4, the pressing device 100 descends to its position under the conveyor 30 while the vacuum is maintained through the suction openings of the bending form 25. This has the effect of maintaining the vacuum. glass sheet 1 bent and still hot against the bending form 25, and therefore above the conveyor 30. The shuttle 50, released from the bent glass sheet 1a (which is no longer shown) in the previous step, moves towards the bending device 20 in the opposite direction to the Y direction.

According to a fifth step illustrated in FIG. 5, after the pressing device 100 has returned to its initial position under the conveyor 30 while the curved glass sheet 1 remains held against the bending form 25 by the vacuum, the shuttle 50 enters in the bending device 20 and is placed between the conveyor 30 and the bending form 25.

According to a sixth step illustrated in FIG. 6, the suction applied at the level of the bending surface of the bending form 25 is cut, which has the effect of releasing the bent glass sheet 1 which consequently falls on the shuttle. 50. The shuttle 50 then transports the curved glass sheet 1 from the bending device 20 into the cooling device 40 similarly to the case of the bent glass sheet 1a mentioned above. After the bent glass sheet 1 leaves the bending device 20, the stops 26 are again put in place to stop a next glass sheet lb.

As illustrated in FIG. 7, the method is then again in the situation of the first step, but with respect to the curved glass sheet 1 and a new glass sheet lb. In other words, the curved glass sheet 1 is then subjected to forced cooling in the cooling device 40 while a new glass sheet lb is fed by the conveyor 30 from the heating zone 10 into the bending device 20 by displacement. in the Y direction. The method then repeats the above steps with respect to the glass sheets 1b and 1 instead of the glass sheets 1 and 1a respectively, and so on.

We will now describe in more detail an embodiment of a bending device 20 according to the invention capable of being used to implement the method described above with reference to Figures 1 to 7.

As can already be seen from the above description, the bending device 20 comprises a bending form 25, a pressing device 100, as well as a system for actuating the pressing device 100.

The actuation system of the pressing device 100 serves to move the pressing device 100, and therefore a glass sheet 1 disposed thereon, in the direction of the bending form 25 and to press the glass sheet 1 against the latter. , then to move it away again from the bending form 25. It can conventionally be implemented with one or more jacks. The bending form 25 is preferably arranged in a fixed manner. The bending shape 25 can be produced in a manner known per se. It can in particular comprise heating or cooling means as taught in US 2010/0050694 A1. As mentioned during the description of the bending process, the bending form 25 is provided with channels opening onto the bending surface for the creation of 'a vacuum serving to intimately press a sheet of glass 1 against the bending surface. Such a form of bending is described in particular by US Pat. No. 6,318,125 B1. Reference may also be made on this subject to WO2017 / 178733.

FIGS. 8 to 11 specifically illustrate an embodiment of the pressing device 100 of the bending device 20.

The pressing device 100 includes a pressing frame 110 and a support structure 170. The pressing frame 110 serves to press against the crown form 25 la. periphery of a sheet of glass 1 in the plan state which has previously been brought to a softening temperature in the heating zone 10.

The support structure 170 fixedly supports the pressing frame 110 as a whole. The actuation system of the pressing device 100 - not shown - acts through the support structure 170. In other words, the actuation system moves vertically - cf. the Z axis in Figure 8 - the support structure 170 and consequently the pressing frame 110.

The pressing frame 110 is provided with a track 120 intended to contact the periphery of the glass sheet and a track support 130 which supports the track 120.

Track support 130 is supported by support structure 170 through spacer elements detailed below. Track 120 is supported by support structure 170 exclusively through track support 130.

The track 120 and the track support 130 have a corresponding annular shape, but the track 120 is somewhat offset towards the center of the pressing frame 110 with respect to the track support 130 as is particularly visible in Figure 10.

The track 120 is made of stainless steel or any other suitable material. Its thickness is preferably 3 to 5 mm. Its annular shape corresponds to the contour of the glass sheet 1. The span of the track 120 - in other words the width of the track 120 which is covered by the glass sheet 1 - can vary according to the construction adopted, but is preferably 6. at 20 mm.

The contact portion 122 of the track 120 with the glass sheet 1 preferably has a docking angle of the glass sheet 1 which is 0 to 10 °, or even more, with the plane tangent to the surface of the sheet. glass 1 in its curved state and at any point of its periphery. A non-zero docking angle makes it possible to limit the area of heat exchange between the track 120 and the periphery of the glass sheet 1. On the other hand, it is preferable not to exceed a docking angle of 10 ° because at- Beyond that, there is a geometric instability factor on the curved glass sheet 1 in the event of faulty positioning of the glass sheet on the pressing frame 110, which results in peripheral parts of the curved glass sheet 1 in under-curve and others in over-curve with respect to the desired shape. A docking angle of 5 ° represents a good compromise for limiting heat exchanges and ensuring good geometric stability at the periphery of the curved glass sheet 1.

The pressing frame 110 is provided with a heating system 140 for heating the track 120 and which is illustrated in FIG. 10. The heating system 140 comprises one or more heating elements 141 placed directly under the track 120. The elements heaters 141 preferably extend over the entire circumference of the track 120 so as to provide uniform heating of the latter in its direction circumferential. In this case, the heating elements 141 are electrically insulated resistive conductor wires. They may be electrical resistors formed by monofilaments passing through electrically insulating ceramic beads or even resistive conductive wires coated with stainless steel with intermediate alumina powder.

The heating elements 141 are preferably held against the underside of the track 120 using jumpers 142 distributed over the circumference of the track 120. The jumpers can be secured to the track 120 by means of countersunk screws 143 whose head is embedded in track 120, or by any other suitable means. The assembly formed by the heating elements 141 and the jumpers 142 is preferably insulated on its side parts and on its lower part by a thermal insulator 144, for example of the fibrous type. It is also preferable that this assembly, as well as the thermal insulation, are protected from external mechanical attacks by casing elements 145 over the entire circumference of the pressing frame 110. These casing elements 145 can also be attached to the track 120. using screws 143.

The heating elements 141 are preferably placed in thermal conduction contact against the underside of the contact part 122 of the track 120 with the glass sheet 1, which makes it possible to locate the hot part of the pressing frame 110 directly at the level of the contact. with the glass sheet 1. The contact portion 122 of the track 120 is preferably heated to a temperature between 200 and 600 ° C. Also, when the heating system 140 is activated, the temperature of the track support 130 is intermediate between the temperature of the contact portion 122 of the track 120 and the temperature of the support structure 170 which remains close to room temperature. Furthermore, there is a significant thermal gradient which can reach several hundred degrees between the inner part of the track 120 and the outer part of the track 120, or in other words over the width of the track 120 from the contact part 122 up to at the peripheral edge of the track 120 on the side outside the pressing frame 110. One or more thermocouples - not shown - are preferably arranged at different places on the track 120 to measure its temperature in order to adjust the temperature of the heating elements 141, and therefore of the track 120. This or these thermocouples are preferably also placed in thermal conduction contact against the underside of the contact portion 122 of the track 120 with the glass sheet 1. As a variant, it / they may / may be. housed in dedicated housings - not shown - made in the thickness of the track 120, preferably in the contact part 122.

In order to manage the thermal expansion of the track 120, the latter is subdivided into segments 121-1 to 121 -n visible in figure 8, but illustrated in more detail for a part of the track 120 shown in figure 9. We designate such a segment of track unspecified by the reference 121-i in the following. More precisely, the track 120 is subdivided into distinct segments 121-i arranged successively in the circumferential direction L of the track 120, being separated each time by a clearance 'e' forming an expansion joint between them. The clearance 'e' forming an expansion joint is preferably formed between the end edges facing two consecutive track segments 121-i, and not between an end edge of one and a lateral part of the end region of the other as is the case in US 5,178,660. These end edges can be in the form of a respective straight edge as illustrated in Figure 9, but alternatively each end edge can have a more complex shape so that the two edges overlap with each other, for example one may have a T-shaped end and the other a corresponding cutout.

As can be seen, the track 120 is thus subdivided into several segments 121-i for each of the sides of the pressing frame 110. The length of a segment of track 121-i is preferably between 100 and 400 mm, this length being measured along the center line of longitudinal extension of a segment of track 121-i.

The contact portion 122 of the track segments 121-i is preferably covered with a fibrous insulating material suitable for contact with the hot glass sheet 1.

Each of the track segments 121-i is mounted on the track support 130 with the possibility of relative displacement in the circumferential direction L of the track 120 to compensate for a relative dimensional variation between the track segment 121-i and the track support 130 in the circumferential direction L of the track 120 due to expansion during heating of the track 120 by the heating system 140.

This possibility of relative movement between any segment of track 121-i and the track support 130 is provided by a sliding connection, more preferably a sliding connection, between at least part of the track segment 121-i and the support of the track. track 130.

In a preferred implementation illustrated by Figures 9 and 10, the track segment 121-i is, on the one hand, rigidly fixed to the track support 130 at a first location by means of a screw 125 passing through a hole circular passage 123 of the segment of track 121-i - or in any other suitable manner - so as to define a fixed point between them during their relative dimensional variation linked to thermal expansion. On the other hand, the track segment 121-i is connected to the track support 130 by a sliding connection at a second location separated from the first location in the circumferential direction L of the track 120, for example by means of a through screw. an oblong hole 124 of the segment of track 121-i. For this, the direction of extension of the oblong hole 124 is parallel to the circumferential direction L of the track 120 and of the track support 130. The length of the oblong hole 124 is chosen to be greater than or equal to the variation. relative dimension linked to the thermal expansion that it has to compensate. For convenience, the projecting areas of the track segments 121-i comprising the holes 123 and 124, as well as the corresponding screws have not been shown in Figures 8 and 11. On the other hand, a circular through hole 123 and a corresponding screw 125 are visible in FIG. 10. The degree of tightening of the fixing screw passing through the oblong hole is chosen so as to ensure correct retention of the track segment 121-i on the track support 130 while allowing sliding relative forced of the screw into the oblong hole of track segment 121-i during differential thermal expansion between track segment 121-i and track support 130.

As a variant, the long ob holes 124 can be replaced by slots arranged on a projection of the track segment 121-i forming a tab towards the outside of the pressing frame 110, these slots opening onto an outer edge of the tab at one end. their longitudinal end.

Thanks to the screw fixing, the mounting of the track segments 121-i on the track support is removable, which allows their replacement when necessary.

It is preferable that the clearance 'e' at room temperature is chosen sufficient so as to prevent two segments of track 121-i from coming into contact and pushing against each other under the effect of their thermal expansion during the heating of the track 120 by the heating system 140 when the bending device 20 is in operation. From these points of view, the play ‘e’ at room temperature is preferably between 1 and 4 mm.

As emerges from the above, the track 120 has discontinuities corresponding to the clearances ‘e’ forming an expansion joint. On the contrary, the track support 130 is made in one piece and continuously in order to give it an appropriate rigidity to support the track 120. The track support 130 is preferably made of steel or any other suitable material, in particular in terms of strength. mechanical and thermal. It can be obtained by mechanically welded assembly or otherwise of several consecutive sections in the circumferential direction.

The heating system 140 described above is also preferably carried out continuously over the entire circumference of the track 120, the casing elements 145 preferably having an oblong passage hole for the screws 143 to compensate for its thermal expansion in the circumferential direction. of the pressing frame 110.

On the other hand, taking into account the fixing of the heating system 140 under the contact part 122 of the track 120, there is a thermal gradient transversely through a segment of track 121-i, that is to say in the direction radial of the pressing frame 110. As a result, the parts of the end edges of the track segments 121-i will bring the inward side of the pressing frame 110 closer than the outward side of the pressing frame 110.

As can be seen in Figures 9 and 10, the fixing of the segments 121-i on the track support 130 is preferably made in mounting areas on the outward side of the pressing frame 110 outside the part of the track. contact 122 of the track segment 121-i, and more preferably still on lugs of the track segment 121-

1 protruding outwardly from the pressing frame 110. Thus, the mounting takes place in a cooler part of the track segment 121-i, which provides a more stable positioning of the track segment 121-i on the support of the track. track 130 in view of its thermal expansion and limits the heat transfer from the track segment 121-i to the track support 130. It is in fact desirable, when the pressing device 100 is in operation, to limit heating of the track support 130. Thus, its thermal expansion is limited, and therefore also the dimensional variation of the annular shape of the track support 130 in its circumferential direction. As a consequence, it provides better dimensional stability to the annular shape of the track 120 in the circumferential direction and therefore a better correspondence of the track 120 with the crowning shape 25. From this point of view, it is preferable that the temperature of the track support 130 remains below 150 ° C. in operation.

Several measures can contribute to limiting the temperature of the track support 130. As can be seen in FIG. 10, the track segments 121-i and the track support 130 can be kept apart by spacers made of thermally insulating material, for example. example in mica, such as wedges or washers 138 at the level of the fixing screw passages 125, which makes it possible to limit the thermal conduction between them, and therefore heating of the track support 130 by the track 120 and consequently the expansion of the track support 130. The separation distance is preferably greater than 0.5mm, but more preferably is between

2 and 10 mm. It will be taken into account in the implementation that the track 120 is supported by the track support 130 with an appropriate rigidity, having regard to the mechanical forces applied during the pressing against the bending form 25.

As visible in Figure 9, there may also be provided a series of holes 126 interposed between the contact portion 122 of the track segment 121-i and the mounting areas of the track segment 121-i on the track support 130 where the holes 123 and 124 are formed in order to limit thermal conduction between them. This measure further limits the thermal diffusion of the contact portion 122 towards the screws 125 or other fasteners of the track segment 121-i on the track support 130, and, consequently, it limits heating of the track support. 130. Furthermore, the track support 130 may have radiator fins - not shown - on the outward side of the pressing frame 110 for the purpose of heat dissipation, which also contributes to limiting its heating.

There can also be provided a cooling fluid circuit - not shown - arranged in contact with the track support 130 in order to cool it. It may be a cooling fluid circulation pipe, placed against the underside of the track support 130 around the entire circumference of the pressing frame 110. The cooling fluid may be water or air.

In the illustrated embodiment, the support structure 170 comprises a base plate 172 to which is rigidly fixed a frame 180 preferably formed from tubular bars of metal or other suitable material. The pressing frame 110 is mounted on the frame 180 by means of spacer elements 250, 260 distributed over the circumference of the pressing frame 110. More particularly, the spacer elements 250, 260 are mounted on the track support 130, the elements spacers 250, 260 supporting the track 120 by means of the track support 130. The spacer elements 250, 260 are designed so as to have sufficient rigidity to rigidly support the pressing frame 110, having regard to the pressing forces to be transmitted to the pressing frame 110. Furthermore, they are preferably of adjustable length to allow adjustment, in this case by means of the track support 130, the curvature of the track 120 in order to adapt it to the shape of the track. crowning 25.

The frame 180 defines for the pressing device 100 a free central volume space 190 with respect to the pressing frame 110 and which is designed to accommodate the rollers of the conveyor 30.

As shown in Figure 8, the bars of the frame 180 on the front 173 and rear 174 sides of the pressing device 100 - defined with respect to the Y direction of conveying the glass sheets 1 by the conveyor 30 - extend at a distance. lower level with respect to an upper horizontal bar 181a, 181b of the frame on each lateral side 171, 172 of the pressing device 100. The bars 181a, 181b are each supported in their front and rear end regions respectively by a front upright 182a , 182b and a rear pillar 183a, 183b. A free passage is thus defined under each of the bars 181a, 181b between the two corresponding front and rear uprights 182a, 183a, 182b, 183b respectively. This free passage allows easy mounting of the conveyor rollers 30 in the central volume space 190.

On the front and rear side 173, 174 of the pressing device 100, the track support 130 is supported on a respective tubular bar of the frame 180 by means of several spacer elements 250. The spacer elements 250 are preferably of adjustable length, for example example of screw spacers. These spacers 250 are relatively long, which allows them to flex elastically to compensate for the elongation of the track support 130 between the mounting points of two spacer elements 250 successive to the track support 130 which is due to its thermal expansion under the effect of the system of heating 140. The length of the spacer elements 250 is preferably between 100 and 200 mm.

On the lateral sides 171, 172 of the pressing device 100, the track support 130 is supported on the horizontal bars 181a, 181b by means of several spacer elements 260, which is best seen in Figure 11. In view of the of the high-level arrangement of the bars 181a, 181b compared to the rest of the frame 180, the spacer elements 260 are very short compared to the spacer elements 250 and are not able to compensate by elastic deflection for the elongation of the track support 130 due to its thermal expansion between the mounting points of the successive spacer elements 260 with respect to the bars 181a, 181b remaining cooler. The spacing provided by the spacer elements 260 is preferably in the range from 2 to 80 mm, limits included. In this case, the spacer elements 260 are vertical screws. On the track support side 130, their head is received in a tab 132 of the track support 130 projecting towards the outside of the pressing frame 110. Their head is trapped, but free to rotate so as to allow adjustment by screwing or unscrewing. the curve of the track 120 by means of the track support 130. On the bars side 181a, 181b, they are screwed into support lugs 300 and 301. Preferably, the vertical screws are in odd number and the central screw is located in the reference transverse axis R of the pressing frame 110. Alternatively, the central screw on each lateral side 171, 172 can be replaced by a spacer element of fixed length, since the other spacer elements 250, 260 are sufficient to adjust the curvature of the track 120 with reference to the central spacer element and adapt it to the shape of the crown 25.

The support legs 300 and 301 are taken between the corresponding horizontal bar 181a or 181b and horizontal counterplates 310.

The spacing between the bars 181a, 181b and the counterplates 310 is kept constant by spacers not shown. Sufficient play is provided to allow each support leg 300 to move horizontally with respect to the respective bar 181a, 181b. In other words, the support pads 300 are connected to the frame 180 by plane links allowing relative omnidirectional sliding in a plane perpendicular to the vertical pressing direction Z of the pressing device 100 against the bending form 25.

The central support leg 301 which is connected to the central screw is constrained on either side by a respective stop 320 so that the support leg 301 can only move by sliding in a horizontal direction X perpendicular to the direction Y. In other words, the support tab 301 is mounted in a pure slide connection in the horizontal direction X.

Thus designed, the system of support legs 300 and 301 makes it possible both to accommodate the expansion of the track support 130 in the Y direction thanks to the possibility of displacement of the support legs 300 in this direction and the expansion of the track support. 130 in the X direction thanks to the possibility of displacement of the support legs 300 and 301 in this direction. Because the central support leg 301 can only move along the X axis, the transverse reference axis R of the pressing frame 110 remains fixed relative to the support structure 170.

Compared to the embodiment which has just been described, many variations are possible. For example, the plane connection and sliding connection system of the track support 130 relative to the frame 180 implemented by the support legs 300, 301, as well as the short spacer elements 260 can also be applied on the front sides and rear of the pressing frame 110 replacing the long spacer elements 250, by adapting the frame 180.

According to another variant, the annular track support 130 is replaced by two separate track supports of more limited extension, one being assigned to the support of the track 120 subdivided into segments 121-i only on the lateral side 171 of the device. pressing 100 and the other being assigned to the support of the track 120 subdivided into segments 121-i only on the opposite lateral side 172, while the track 120 is carried out continuously - that is to say without being subdivided in distinct segments separated by sets' e 'forming an expansion joint' - on the front and rear sides 173 and 174 of the pressing device 100 while being directly supported there by the spacer elements 250. It will be understood, however, that it is more advantageous to have a one-piece track support 130 of complete and continuous annular shape and for the track 120 to be subdivided into segments 121-i on the different sides of the pressing in order to obtain the resulting advantages for the whole frame pressing 110.

When, as in the embodiment described, the pressing frame 110 has a continuous annular shape, i.e. the annular track support 130 is continuously formed and so is the track 120, except for the clearances 'e' forming expansion joints between the consecutive track segments 121-i, the rollers of the conveyor 30 in the bending device are installed inside the central free volume space 190 of the device. pressing 100. This allows the movement of the pressing frame 110 during the operations of pressing the glass sheets 1 against the bending form 25 without interfering with the conveying rollers 30 similar to the situation illustrated in Figure 1 of WO 2016/156735 or in FIG. 1 of US 2010/050694 A1. Alternatively, the pressing frame 110 can be discontinuous and present interruptions at the places corresponding to the rollers of the conveyor 30 if they have a length such that they protrude outside the pressing frame 110, these interruptions then being provided to allow the pressing frame 110 to pass beyond beyond these rollers during the pressing operations of the conveyor 30. In this case, the pressing frame 110 can be provided with a track support 130 supporting several track segments 121-i at least for both sides of the pressing frame 110 which are substantially parallel to the rollers of the conveyor 30.

Of course, the present invention is not limited to the embodiments described and shown, as well as to the examples and variants mentioned, but it is susceptible of numerous other variants accessible to those skilled in the art.

Claims

RE VENDIC ATION S

1. A pressing device (100) for pressing a glass sheet (1) brought to a softening temperature against a bending form (25) for bending the glass sheet, the pressing device comprising:

- a pressing frame (110) for pressing the periphery of the glass sheet (1) against the bending form (25), and

- a support structure (170) supporting the pressing frame (110); wherein the pressing frame (110) comprises:

- a track (120) provided to contact the periphery of the glass sheet (1),

- a track support (130) supported by the support structure (170), the track support supporting at least one section of the track (120), and

- a heating system (140) for heating the track (120) at least in the region of said section of track; in which: the track section is subdivided into several distinct track segments (121-1, 121-2, 121-3, ..., 121-i, ..., 121-n) arranged successively in the circumferential direction of the track (120) being separated each time by a clearance (e) forming an expansion joint between them, and each of the track segments (121-i) is mounted on the track support (130) with a possibility of relative displacement between at least part of the track segment (121-i) relative to the track support (130) in the circumferential direction (L) of the track to compensate for a relative dimensional variation between the track segment (121-i ) and the track support (130) in the circumferential direction (L) of the track (120) due to thermal expansion upon heating of the track (120) by the heating system (140), wherein the mounting of each of the track segments (121-i) on the track support involves a sliding link (124) to provide said capability. bility of relative displacement.

2. A pressing device according to claim 1, wherein the sliding connection is a sliding connection (124) in the circumferential direction (L) of the track (120).

3. Pressing device according to claim 1 or 2, wherein a track segment (121-i) is rigidly fixed on the track support (130) at a first location (123) so as to define a fixed point between them. during said dimensional variation relative, the track segment (121-i) being connected to the track support (130) by the sliding connection at a second location (124) separated from the first location in the circumferential direction (L) of the track (120).

4. A pressing device according to claim 3 in that it depends on claim 2, wherein the track segment (121-i) is rigidly fixed on the track support (130) at the first location by means of a screw (125) passing through a circular passage hole (123) and is connected to the track support (130) by the sliding link at the second location by means of a screw passing through an oblong hole (124) or a slot.

5. Pressing device according to any one of claims 1 to 4, comprising spacers (250, 260) of adjustable length to adjust the curvature of the track (120), the support structure (170) supporting the support. track (130) through at least some of the spacer elements which act on the track section (120) through the track support (130).

6. A pressing device according to any one of claims 1 to 5, wherein at least a first section of the track support (130) is supported by the support structure (170) with a possibility of relative displacement by means of. a slip connection (300, 301) to compensate for a relative dimensional change between the track support (130) and the support structure (170) due to expansion during heating of the track (120) by the heating system ( 140).

7. Pressing device according to claim 6, wherein: the first section of the track support (130) corresponds to at least a major part of the length of a first side of the track corresponding to a first side (171) of the track. pressing frame (110): the first section of the track support (130) is mounted on the support structure (181a) by a slide connection (301) provided in a middle zone on the first side of the track, the slide connection does not allowing translational movement in a direction (X) substantially perpendicular to both the first side of the track (120) and to the intended pressing direction (Z) of the pressing device (100) against the crowning form ( 25), and the support structure (181a) further supports the first section of the track support (130) on either side of the slide link (301) by plane links (300) allowing relative omnidirectional sliding in a map perpendicular to the intended pressing direction (Z) of the pressing device (100) against the crowning form (25).

8. Pressing device according to claim 7, wherein the support structure (181a) supports the first section of the track support (130) by means of tabs (300, 301) movably mounted on the support structure, the one (301) so as to implement the slide link and the others (300) so as to implement the plane links.

9. A pressing device according to claim 8, wherein the first section of the track support (130) is fixed to one, more or all of the legs (300, 301) by means of a respective screw with captive head free to rotate. allowing adjustment of the spacing between the first section of the track support (130) and the support structure (181a).

10. Pressing device according to any one of claims 6 to 9, wherein: the first section of the track support is supported by a support bar (181a) of the support structure (170), the support bar extending substantially parallel to the direction of longitudinal extension of the first side of the track, two uprights (182a, 183a) of the support structure (170) support the support bar (181a) respectively in a first region and in a second region of the support bar (181a) which are separated from each other in the direction of longitudinal extension of the bar, the two uprights (182a, 183a) are separated from each other by a distance corresponding to at least a preponderant part of the length of the first side of the track (120) and define under the support bar (181a) a free passage between them.

11. Pressing device according to any one of claims 1 to 10, wherein the heating system (140) is arranged to heat a track segment (121 -i) from below in an area facing the part of the track. contact (122) of the track segment which is intended to contact the periphery of the glass sheet (1), the track segment (121 -i) being mounted on the track support (130) exclusively in mounting regions ( 123, 124) of the track segment (121-i) which are offset outwardly of the pressing frame (110) with respect to the contact portion (122) of the track segment (121-i).

12. Pressing device according to claim 11, wherein the track segment (121 -i) and the track support (130) are separated by wedges (138) of thermally insulating material.

13. A pressing device according to claim 11 or 12, wherein the track segment (121 -i) comprises a series of holes (126) arranged between the contact portion (122) of the track segment (121 -i) and the mounting regions (123, 124) of the track segment so as to limit thermal conduction from the contact portion (122) to the mounting regions.

14. A pressing device according to any one of claims 11 to 13, wherein the heating system comprises at least one electrically insulated heating conductor wire (141) which is held under the track segments (121 -i) by jumpers. (142) spaced apart and secured to the track segments by screws (143), the at least one conductor wire being surrounded by a thermal insulation material, the assembly formed by the at least one heating conductor wire, the jumpers and the thermal insulation material preferably being protected by a casing (145).

15. Pressing device according to any one of claims 1 to 14, wherein the clearance (e) forming an expansion joint between two successive track segments (121 -i) is formed between two longitudinal ends facing the two segments of track which are possibly nested one inside the other.

16. Pressing device according to any one of claims 1 to 15, wherein the track support (130) has radiator fins on a side opposite the track section and / or a cooling fluid circuit. is arranged against the track support (130).

17. A pressing device according to any one of claims 1 to 16, wherein the track has a generally annular shape and the track support has a corresponding generally annular shape, the support structure (170) supporting the whole of the track. track (120) through the track support (130).

18. Device for bending (20) a sheet of glass (1) previously brought to a softening temperature, comprising:

- a form of bending (25),

- a pressing device (100) according to any one of claims 1 to 17, and - an actuation system of at least one of the pressing device (100) and the bending form (25) so as to be able to bring them together to press the glass sheet (1 ) against the bending form (25) and so as to be able to move them away from one another to release the glass sheet (1) after bending.

19. A method of bending a glass sheet, comprising: heating the glass sheet (1) to a softening temperature in a heating zone (10), transferring the glass sheet (1) to the softening temperature in a bending device (20) according to claim 18 placed outside the heating zone (10) in an environment at room temperature and of which the track section (120) in its part coming into contact with the glass sheet (1) is preheated by the heating system (140) to a temperature between room temperature and the softening temperature of the glass sheet, more preferably to a temperature between 200 and 600 ° C, and the bending of the glass sheet (1) by the bending device (25) at a time when it is still at a softening temperature.