Method and apparatus for progressif bending of glass sheets

IS 2 170 930 T3

DESCRIPTION

Procedure and device for the progressive bending of glass sheets.

The present invention refers to a process for the progressive bending of glass sheets in which the glass laminates, heated to the bending temperature, are bent in a horizontal position and gradually, until their final shape, in at least two positions. successive bending lines, are lifted by aspiration at the last bending station by an upper convex bending shape provided with suction holes and are deposited on a movable support frame. The invention also refers to a device for the execution of the procedure.

Progressive compression multistage bending procedures are advantageous for a number of reasons. In particular, such multistage bending processes make it possible to manufacture complicated shapes of glass sheets, for example spherical bends, the realization of which by means of a single bending step presents difficulties.

For example, from DE-4203751 C2, a two-stage bending process and a suitable device for carrying out the process are known. In the case of this known bending procedure, the lower bending form and the upper bending form are conceived, in the two bending stations, as rigid pressing tools, the upper bending forms being convex shapes each time. curved by aspiration, covering the entire surface. The previously bent glass sheet is transferred, using the first suction bending form, to the next compression bending station, while simultaneously, the finished bent glass sheet is transported by the aspiration bending form of the second station. of bending by compression, to a transfer station, in which the glass sheet is deposited on the carrier frame. The repeated apprehension of glass laminates during the bending process by aspiration bending devices raises the risk that the glass surface will be altered due to relative displacements between the glass lamina and the bending devices. by aspiration.

The object of the invention is to develop a progressive bending process that comprises two or more than two bending stations in such a way as to reduce the relative displacements between the carrier devices that transport the glass sheets through the bending facility. stage by stage. Furthermore, the process was particularly convenient for bending relatively thin glass sheets and also to allow spherical bending.

This object is achieved, according to the invention, by a process of progressive bending of glass sheets, in which the glass sheets heated to the bending temperature are gradually bent in a horizontal position to their final shape, at least in two successive bending stations, they are lifted by aspiration at the first bending station by means of an upper convex bending shape and placed on a first movable supporting frame, said glass laminates being transported, deposited on a support cloth flexibly mounted on a second rigid support frame, with the support cloth and the aforementioned second support frame (stage by stage) through the bending installation and bending together with the cloth. support, which adapts to the shape of glass laminates.

Thanks to the process according to the invention, a number of essential advantages are obtained. On the one hand, the glass sheet that exhibits the bending temperature remains sustained throughout the bending operation over its entire surface, which reduces to the same degree the risk of undesirable deformation of the glass sheet, for example, under the effect of of gravity. On the other hand, the relative displacements between the glass sheet and the supports that transport the glass sheet through the installation and therefore the risks of alteration of the glass surface are completely avoided. In addition, the precision of the positioning of the glass sheet in the different positions of the bending installation is increased, which improves the maintenance of the shape of the finished glass sheet. Finally, the process according to the invention is particularly convenient, based on the aforementioned advantages, for spherical bending of very thin glass laminates, for example, glass sheets with a thickness of less than 3 mm. In accordance with the invention, the manufacture of small thickness spherically curved glasses is indeed a particularly chromatic operation since very thin glass laminates particularly have a tendency to slightly ripple at the edge during the bending operation.

In an advantageous embodiment of the invention, the glass sheet is bent during the course of a first bending stage, by means of a concave lower molding tool whose outer surface, which holds the edge of the glass sheet, is practically on a plane. During prebending, the glass sheet is first pre-curved in this way and stretched through its central part, while the edge of the glass sheet remains in the initial plane. If the definitive bending then occurs, during the course of a second bending stage, the risk of undulations at the edge level is considerably reduced.

Another embodiment of this procedure is that, during the course of the first bending stage at the edge of the glass sheet - a tool is used that acted from the top on said edge and compresses the immediate marginal zone against the edge. flat marginal zone of inferior concave shape. Suitably, the conditions for the case have been chosen such that only the outer extreme marginal zone of the glass laminae is clamped or maintained.

The method according to the invention can be carried out, for example, in such a way that

ES 2 170 930 T3 the bending operation is carried out in two stages, the glass sheet can also be previously bent in the course of the first bending stage by means of a convex bending shape that covers the entire surface and that can be lower on the glass plate. Suitably, the upper convex bending shape cooperates in this case with a lower concave bending shape, which is mounted so that it can be raised and lowered below the transport plane of the support fabric.

In a particularly advantageous way, the bending operation was carried out at the first bending station, under the effect of a pneumatic pressure difference and this, with the help of a concave bending shape covering the entire surface and on which it can act a depression through the holes made in the molding surface. The suction bending form is also mounted so that it can be raised and lowered below the transport plane of the support fabric. After the suction bending operation, under the effect of a short exposure to air, the support cloth with the previously bent glass sheet is released from the molding surface, the suction bending form is lowered and the frame is transported. carrier, together with the previously bent glass lamina, to the final bending station. A device has also been proposed for the execution of the procedure according to the invention, said device comprising a pre-bending station, a final bending station that comprises an upper convex bending shape provided with suction means, a transfer device that is you can move between the final pump station and a cooling station, as well as a carrier device that is movable between the pre-bending station and the final bending station, characterized in that the carrier device consisted of a rigid carrier frame and a support fabric flexibly mounted on the carrier frame.

Other particularities and advantages of the invention will become apparent in the dependent claims and in the following description of some preferred embodiments, with the aid of the following drawings:

Figure 1 is a schematic perspective view of a first embodiment of a bending installation, according to the invention, Figure 2, is also a schematic perspective view of a second embodiment of a bending installation. bending, according to the invention, figure 3, is a sectional view of a device for bending by aspiration, according to the invention, figure 4, is also a sectional view, of a device for bending by aspiration, with an additional retaining plate for the edge of the glass sheet, Figure 5 is a view also in section, of a device for bending by aspiration, with an additional pressure supply.

Before the glass sheets 1 are bent in a bending installation according to the invention, they are heated in a suitable oven to the bending temperature. With regard to the furnace, which is not represented as such in the figures, it could be, for example, a roller hearth furnace through which the glass sheets are conveyed on driven transport rollers 2. At the exit of the roller hearth furnace, they are lifted from the transport rollers by means of a suction plate 3, flat on its underside. The suction plate 3 can be moved linearly in a suitable way and extracts the glass sheet 1 from the furnace, to take it to the bending installation.

The bending installation comprises a pre-bending station 10 and a final bending station 20. Furthermore, the bending installation that is represented in figure 1, comprises a transport system for the glass sheets, which includes several carrier frames 30 that can be moved in the direction of the arrow F, on which in turn each time it extends a section 31 of cloth, flexibly mounted. This section 31 of cloth serves as a support for the hot glass sheets. Suitable materials for this fabric are composed in particular of refractory metal fibers which are known as such and which are available on the market. According to the elasticity and flexibility that this support material is desired to present, instead of fabrics, suitable mesh fabrics, composed of refractory metal fibers, could also be used. The fabric sections 31 rest on two opposing studs 32 of the frame 30 and run freely under the studs 32. Metallic bars 33 have been fixed at their ends, which are intended to be made of material of a certain weight in such a way that, on the one hand, they ensure the necessary tension of the supporting fabric and, on the other hand, limit the tension of the support fabric to a value such as to allow this fabric to retain, after the previous bending operation, the shape predefined by the glass sheet, under the effects of the weight of this glass sheet. The carrier frames 30, provided with carrier fabrics 31, are channeled, stage by stage and cyclically, through the bending installation. The transport system as such has not been represented, in order to obtain a better overview.

The first bending station, which is called the pre-bending station 10 of the bending installation, comprises a lower suction bending form 12 which is mounted so that it can be raised and lowered, for example with the aid of a lift 13. The Aspiration bending shape 12, it has a concave molding surface 14, into which numerous holes 15 open which can be fed by a depression. The curvature of the concave molding surface 14 corresponds roughly to half the curvature of the final shape of the glass sheet. Surface 16 of the shape of

ES 2 170 930 T3 bent by aspiration, adjacent to the concave molding surface 14, lies in a plane such that the edge of the glass sheet - after this pre-bending step - is also in a plane, regardless of the shape presented by the glass lamina and its contour, after the last bending stage.

Similarly, at the final bending station 20, the lower bending shape 22 was mounted so that it can be raised and lowered with the aid of a lift 23. In the case of this lower bending shape 22, it could be a bending shape. covering the entire surface or in a box-like bending shape. This lower bending shape 22 cooperates with the upper bending shape 24 which covers the entire surface which is also mounted so that it can be raised and lowered by means of a suitable drive device, such as an elevator for example. The convex bending shape 24 that covers the entire surface is usually provided, in a known way, with holes that can be fed, on the one hand by a depression and on the other hand by an overpressure and is covered, on the side of the molding surface, by a fabric made from refractory fibers.

The final bending station 20 was followed by a refrigeration station, in this case it is a common device that has not been shown here. With the aid of a movable carrier frame 26, which corresponds to the shape of the edge of the bent glass sheet, the bent sheet of glass is removed from the upper bending shape 24 and brought to the refrigeration station.

The working mode of the device represented in figure 1 is as follows: the movable suction plate 3 takes the glass sheet 1 heated to the bending temperature and, with the help of the suction plate, it is taken to the bending station 10 and deposited there on the support cloth 31. During the return of the suction plate 3, the bending form 12 is lifted and carried by aspiration against the support fabric 31, a depression then being established at the level of the aspiration bending form 12. Under the effect of the suction of the suction bending shape, the glass lamina, together with the support cloth 31, is pressed towards the concave molding surface 14. During this operation, the flexible elastic fabric is stretched, while at the same time, faced with the effect of gravity exerted on the bars 33 fixed to its ends, the active length of the fabric is increased. Upon completion of the suction operation, the depression is removed and the shape is released from the support fabric 31 by a short overpressure pulse. The suction bending form 12 is lowered and the frame 30 is moved, with the pre-formed glass sheet, to the final bending station 20. After positioning the frame 30 carrying the pre-bent sheet of glass, the bending shape 22, the lower concave and the upper convex bending shape 24 are brought into a juxtaposition at the same time and the glass laminate is pressed from that moment on. to its final form. The upper bending shape, for example provided with suction holes, then lifts from the support fabric by suction effect of the curved and finished glass laminate, which then recovers its flat shape under the pulling effect of the bars 33. The The carrier frame 26 is then placed in the bending shape 24, receives the bent glass sheet from the bending shape and carries it to the next refrigeration station.

The bending installation represented in FIG. 2 also functions in a manner that is similar in principle and is in this case in the form of a carousel with four stations, namely a loading station 37, a pre-bending station 38, a final bending station 39 and a supplementary station 40 in which the support fabric 41 can, if necessary, be oriented. The support fabric sections 41 rest in this case, on the arms 42 of a turnstile-type frame that is rotated 90 ° at each stage, in the direction of rotation of the arrow F '. The operations at the loading station 37, at the pre-bending station 38 and at the final bending station 39, are carried out in this case at the same time, which makes this embodiment particularly economical. Furthermore, the conception of the bending tools and the development of the procedure are the same as in the case of the embodiment described above, so that, as regards this concept, reference should be made to the description of figure 1.

Figure 3 is, once again, a sectional view of the essential features of the pre-bending station. The suction bending shape 12 is already in the upper final position, in contact, on the part of its flat surface 16, with the support fabric 31, on which the glass sheet 1 rests in a centered position. Holes 15, made in the suction bending shape 12, connect the molding surface 14 with the enclosure 18 to which a vacuum pump 17 has been connected. As a variant, the enclosure 18 can be connected by means of a flexible duct by depression to a depression reservoir, in such a way that when opening a valve in this duct, a vacuum is established very quickly in the form of bending by suction, pressing He roasted the glass lamine 1 with the backing cloth 31, against the molding surface 14. The suction bending form 12 is then immediately exposed to the air and lowered again, transporting the glass plate 1 with the support cloth, to the final bending station.

In the case of the embodiment represented in FIG. 4, the glass sheet 1 is held, during the preliminary bending operation, on its upper face at the edge level, by means of a flat plate 45 that cooperates with the flat surface 16 of the suction bending form 12. The use of such a plate 45 is advisable if the risk of waviness at the edge of the glass lamina is particularly high, as for example in the case of particularly large spherical bends. Furthermore, the suction bending shape has been manufactured with the same precision as that of the device described in figure 3.

In the case of particularly large spherical bends, it could be advantageous

ES 2 170 930 T3 complement the suction forces of the bending form 12 by suction, by means of pneumatic pressure forces acting from above on the glass lamina. Figure 5 shows a suitable device for this purpose, in which the edge of the glass sheet 1 is held at the same time to avoid undulations. In this case a flat compression plate 48 is used, which cooperates with the surface 16 of the suction bending form 12 and which is lowered onto the glass sheet 1.

The plate 48 is attached by means of holes 49 to an enclosure 50 that is subjected to overpressure by means of a pressure conduit 51, at the moment in which the depression is established at the level of the bending shape 12 by aspiration, through enclosure 18.

In all the cases described, the pre-bending stage is followed by the final bending stage with a bending press in the manner described above.