Method for cutting the edges of a continuous glass ribbon, a device for implementing said method, and a glass plate cut using said method

Description of the invention

The present invention relates to a method and an apparatus for cutting a continuous glass strip.

The invention relates to the field of flat glass production.

By continuous glass strip is meant a glass strip that has emerged from a continuous forming process, in particular from a fleet process or glass lamination process.

The continuous glass ribbon is generally the product coming out of the glass furnace into which glass raw materials are fed, which are melted to form a viscous glass. This thick-flowing glass feeds a forming tool, such as for example a fleet device, in which the thick-flowing glass is directed into a bath of molten tin maintained in a reducing atmosphere, or into a rolling device. In this way, a continuous glass strip is obtained at the exit of the forming tool, which should be cut for end-use applications, in particular for construction and possibly automotive applications.

The traditional way to cut glass consists of initially stressing the glass strip by annealing, then cutting it in the transverse direction into the panes, and finally trimming in the longitudinal direction of the edges of the panes.

Stress relieving is commonly referred to as an operation in which the glass strip is subjected to a controlled cooling cycle so as to gradually relax the stress caused by the forming step.

The transverse direction is an axis which is essentially perpendicular to the axis of movement of the glass strip exiting from the forming tool.

The longitudinal direction is the axis which is essentially parallel to the axis of travel of the glass strip exiting the forming tool.

Panels are elements of a glass strip after it is cut in the transverse direction.

There is a known method of cutting continuous glass strip comprising four main steps after the glass strip has been annealed:

First step: longitudinal tracing, especially with a circular cutter, of a substantially continuous cut on each edge of the strip face in the longitudinal direction. This scribing takes place from a few centimeters to tens of centimeters from the outer edge of the tape and is designed to create surface defects on the glass in preparation for later cutting the edges of the tape in an operation called stripe separation.

Second step: tracing a continuous cut on the end face of the strip in the transverse direction. This tracing is carried out by means of a circular cutter that moves obliquely with respect to the axis of glass ribbon advance so as to obtain a tracing perpendicular to the axis of travel on the ribbon.

Stage three: separating the strip at the level of the transverse markings in order to obtain the panes from a continuous strip. This step is called a cross break. The pane thus formed is generally transported on rollers at a speed much greater than that of the continuous glass ribbon.

Fourth step: strip separation: separating the zone between the outer edge of the pane and the alignment, the zone known as the strip, from the rest of the board to obtain a board that is either an end product or a blank that is finally stored, generally substantially vertically, and then shipped to customer on stands.

This fourth step, strip separation, initially comprises a phase in which an impact is produced, for example by a metal wheel, on the face of the pane at the point where the longitudinal scribing has been made. The stroke applies energy so that a scratch forms and follows the defect line of the scribe mark. The scratch formed under such conditions propagates very quickly, namely at the speed of sound, i.e. about 1000 m per second. The strip then separates from the pane and is removed. In the case of thick glass, crack propagation can be assisted by using a hammer, especially a pneumatic one, which produces regular blows on the frontal bottom surface of the pane.

The technique of transverse breaking is known in particular from USPN 4,072,259.

The belt separation technique is the subject of numerous improvements as disclosed in, for example, USPN 4196830, USPN 4285451, US 4,466,562, USPN 4,489,870.

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From these descriptions, there are known improvements to the above-mentioned classical technique, and in particular the possibility of facilitating strip separation by locally heating / cooling the glass, cutting the strips starting from two parallel longitudinal alignments on the same face or starting from two longitudinal alignments side by side on each other. from the front surfaces of the glass, developing means for applying a certain moment to the belt by applying a certain load near the outer edge of the belt so as to initiate a crack starting from the alignment.

It should be mentioned that all these improvements relate to the means that operate after the continuous tape is cut to form the sheet, i.e. after breaking transversely.

These traditional strip separation techniques are relatively well suited to industrial processes for the production of standard thickness glass, namely 3 to 8 mm thick.

However, in edge trimming, when the thickness of the strip is either less than or greater than that of the standard glasses, numerous problems arise.

In the case of thin glasses, namely glasses whose thickness is equal to or less than 1 mm, the presence of lateral cracks is very often observed (see, for example, lateral cracks, Fractography of Glass - Bradt, RC; Tressler, RE, Plenum Press, New York , 1994) on the episode after the stripes are separated by traditional techniques. This type of defect adversely affects the mechanical properties of the glass. Such defects are unacceptable to the customer and lead to a high percentage of defects.

In the case of thick glasses, namely glasses whose thickness is greater than or equal to 10 mm, in particular greater than or equal to 15 mm, sections are observed which, after separation of the strips by traditional techniques, have numerous defects. On the one hand, the sections are generally not perpendicular to the larger faces (faces corresponding to the horizontal faces of the continuous glass strip), but oblique.

There are also numerous defects that can be the source of mechanical weakness, namely defects that specialists refer to as chipping, beaks, broken corners, branched cracks.

This type of defect should be eliminated for the use of panes, such as finished articles, and especially for applications where glass is required to be toughened, since the toughening operation entails very severe glass defects and often leads to breakage if defects are present.

It should be mentioned that the essence of thick glass production is related to applications where glass toughening is required.

In order to eliminate such defects caused by the separation of the belts by traditional techniques, a machining step is proceeded which consists in removing the material, especially by abrasion, in such a way as to straighten the edges and obtain a face free from defects that can lead to cracks during quenching. and such an operation is long and costly.

A device for cutting a continuous glass ribbon is also known, comprising a longitudinal scribing means, a means for creating and causing a longitudinal scratch to propagate over at least a significant part of the thickness of the continuous glass ribbon, and in particular over the entire thickness of said continuous glass ribbon, from the alignment, scribing means. transverse and transverse fracture means. Cutting glass with this device has the same disadvantages as mentioned for the cutting methods of the prior art.

The object of the present invention is to remedy the above drawbacks, in particular to obtain sections, after strip separation, free from major defects, thus allowing the produced panes to be used with little or no machining in the final steps leading to a finished or semi-finished product.

A method of cutting a continuous glass strip having an upper face and a lower face and sliding, including a longitudinal scribing step in which an alignment is formed, especially with a circular cutter, a final transverse routing step, and then a transverse breaking step, followed by a longitudinal scribing the step of creating at least one longitudinal scratch on at least a substantial part of the thickness of the continuous glass strip, in particular over the entire thickness of said continuous glass strip, from the alignment, according to the invention is characterized in that the continuous glass strip is advanced at a speed

The transverse fracture step is performed after the step in which at least one longitudinal crack is formed.

The step of forming the at least one longitudinal scratch is performed as an intermediate step between the longitudinal scribing step and the transverse scribing step.

The longitudinal scratch is formed and made to propagate by the progressive bending of the continuous glass strip in the area located below the longitudinal scribe between the longitudinal scribe and the transverse scribe.

The bending of the continuous glass strip is achieved by applying a certain force to the lower face of the continuous glass strip, the glass strip being slightly lifted in the area below or adjacent to the longitudinal line on the side of the line farthest from the outer edge. glass tape, taking into account the closest outer edge.

A certain force is applied to the top face of the continuous glass ribbon in the zone between the longitudinal alignment and the outer edge closest to the longitudinal alignment, whereby the longitudinal scratch formation and propagation is promoted.

The continuous glass strip is heated and / or cooled to form and propagate a longitudinal crack.

Longitudinal scribing is performed on only one of the faces of the glass ribbon, and transverse scribing is performed on only one of the faces of the glass ribbon.

Apparatus for cutting a continuous glass ribbon, comprising a longitudinal scribing means, a means for creating and causing a longitudinal scribe to propagate over at least a significant portion of the thickness of the continuous glass ribbon, and in particular over the entire thickness of said continuous glass ribbon, from the alignment lines, cross-scribing means and the transverse breaking means according to the invention is characterized by that the transverse breaking means are positioned downstream of the longitudinal scribing means, the longitudinal scribe forming and propagating means and the transverse scribing means with respect to the direction of belt travel.

First there are the longitudinal scribing means, then the means for forming and causing the longitudinal crack to propagate, then the transverse marking means, and then the transverse breaking means with respect to the running direction of the tape.

The means for creating and propagating the longitudinal crack comprises mechanical means.

The at least one mechanical means for creating and causing the longitudinal crack to propagate is a circle that contacts the bottom face of the continuous glass strip.

The at least one wheel is coupled to automatic control means, including in particular a jack connected in particular to the base.

The at least one mechanical means for creating and causing the longitudinal crack to propagate is a circle located on the upper face of the continuous glass strip, more particularly a wheel connected to the jack.

The device comprises at least one means for applying heat and / or cooling to at least one surface zone of the continuous glass ribbon, located between the longitudinal and the transverse marks.

The at least one means for supplying heat and / or cooling is a heated or cooled roller in contact with the top or bottom surface of the continuous glass strip.

At least one heat supply means is a laser.

The problem of obtaining sections free from major defects after separating the strips from the panes from the continuous glass ribbon was solved by using the process of cutting the edges of the continuous glass ribbon moving at the speed V_Rcomprising a longitudinal scribing step that produces an alignment, in particular with a circular cutter, a final transverse scribing step, and then a transverse cracking step, and which includes an intermediate step between the longitudinal routing step and the transverse routing step of creating at least one longitudinal scribe at least over at least a significant part of the thickness of the continuous glass strip, and more particularly over the entire thickness of said continuous glass strip, starting from the alignment, and causing said longitudinal crack to propagate at a speed V_F. essentially equal and in the opposite direction to velocity V._R continuous glass tape is moving.

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The inventors were therefore able to show that in this way it is possible to obtain panes which have edges clearly perpendicular to the faces of said panes and that these edges have an almost smooth surface, known as a mirror surface.

This significant effect is particularly unexpected as the skilled person knows that the edges obtained after separating the strips by classical techniques are of poor quality and have numerous defects, especially in the case of thin glass panes and thick glass panes.

By using the method according to the invention, smooth and free from major defects edges are observed for all thicknesses of glass panes, and especially for thin glasses and thick glasses.

The use of this method leads to a device that is much simpler, but highly effective.

The means used to form the longitudinal scratch are preferably disposed at each outer edge of the continuous glass ribbon so as to cause the tear to propagate simultaneously on each side of the ribbon and eventually proceed to the edge separation on each side at the same time.

Thus, in the line of appearance of a scratch over a significant portion of the glass thickness, and in particular at least half the thickness, even a through crack is observed downstream of the scratch-forming means and before the longitudinal markers. This scratch is referred to as a longitudinal scratch in the following text. This longitudinal scratch, visible to the naked eye almost all over the lenses, seems clearly motionless to the observer on the side of the line. Therefore, the resultant of the speed between the speed of the glass strip V_R and the speed of crack propagation V._F. it is basically nil. By basically it is meant a possible change in the order of the factor 2. This change may give the observer to the side of the line the impression that the scratch is moving while remaining between the center which enables its formation and the slitting means.

Changes in the crack propagation speed may be related in particular to inhomogeneities in the residual stresses in the glass following annealing operations by annealing.

After a longitudinal crack has been formed, the continuous glass strip thus consists of three zones: two edge zones and one central zone. When the crack is transverse, these zones appear to border each other, and it can usually be said that they remain glued to each other, although there is no bond between them. Finally, the transverse routing operation takes place through these three zones. Thereafter, the breaking step itself takes place, using known means to initiate and cause the transverse crack to propagate, leading to the separation of the pane from the glass strip.

Breaking is carried out by lifting the strip to the level of the transverse mark by a roller in contact with the strip along its entire width, bending the entire cross-section.

In the case of the method according to the invention, this step plays a double role, since the pane is separated from the strip at the same time as well as the edge zones, the strips, which then lose their rigid connection with the central zone and are discharged into the traps.

According to an embodiment of the invention, the longitudinal crack is formed and propagated by the progressive bending of the continuous glass strip in the zone located below the longitudinal mark, between the longitudinal mark and the cross mark.

In this way, the bending allows the longitudinal crack to develop from the longitudinal alignment and propagate in the opposite direction to that of the glass strip.

The progressive bending therefore makes it possible to very accurately control the opening of the longitudinal crack and to control the propagation rate of the crack thus formed.

According to a particularly preferred variant, the bending of the continuous glass strip is achieved by applying a certain force F 1 to the lower face so as to raise the glass ribbon slightly in the area below the longitudinal alignment or rather adjacent to the longitudinal alignment on the side of the line farthest from the outer edge of the tape taking into account the closest outer edge.

In order to establish an ideal order of magnitude, the load applied to such a wheel is of the order of 1000 N, i.e. preferably 500 to 2000 N.

In the case of a 15 mm thick glass strip for which rims approximately 200 mm wide are required to be removed, a force of approximately 900 N in particular can be applied when the force is applied at a distance of approximately 70 cm from the fulcrum.

In the case of a 19 mm thick glass strip for which edges approximately 250 mm wide are required to be removed, a force of approximately 1200 N in particular can be applied.

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These indications are by no means limiting as the load applied depends on the relaxation state of the glass and can easily be determined by one skilled in the art by slightly varying said load and observing the effect of this load variation on the progression of the longitudinal scratch.

According to another preferred embodiment of the invention, a force Fs is applied to the top face of the continuous glass ribbon in the area comprised between the longitudinal marking line and the outer edge of the continuous glass ribbon in order to contribute to t ^ or ^^n and to cause the longitudinal tear to propagate.

This solution corresponds in particular to the production of glass of low or medium thickness and makes it possible to assist in the longitudinal guidance of the crack in order to facilitate its reliable propagation along the longitudinal mark.

Although the application of a force acting on the upper surface is not necessary in the case of thick glasses, especially those with a thickness greater than 15 mm, such a solution is not excluded for these glasses and may even be particularly advantageous if the width of the strips is to be reduced, and so way to save materials, which allows you to increase the efficiency of the production line.

According to another embodiment of the method according to the invention, the supply or application of heat and, if appropriate, cooling contribute to the formation and propagation of the longitudinal crack.

The heat input can be achieved by using a laser beam that interacts with the glass, the laser beam being collimated to focus it on the upper face of the glass strip.

Cooling can in particular be carried out by means of a roller, preferably a roller located on either side of the scratch, in contact with the lower face of the glass. This type of cooling roller is suitable for cooling by the liquid with which it is in contact, for example from a chilled liquid tank in which the roller is immersed.

The device for severing the edges of a continuous glass ribbon comprises longitudinal scribing means, transverse scribing means, transverse fracture means and further comprises means, in particular mechanical means, for creating and causing a longitudinal scratch to propagate.

In a preferred embodiment of the device according to the invention, the at least one mechanical means that allows the formation and propagation of the longitudinal scratch is a circle which is capable of contacting the lower face of the continuous glass strip.

In a particularly preferred version, at least one wheel is adjustable by automatic control means, namely comprising a jack connected in particular to the base such that either there is a fixed position of the wheel or there is a constant force F | placed under a continuous glass tape.

According to one embodiment of the device, the at least one mechanical means for creating and causing the longitudinal scratch to propagate is a circle situated on the upper face of the continuous glass strip, connected in particular to the jack.

In a manner equivalent to the wheels described above, one or more rollers can be used on which the glass can slide without damage, for example copper rollers coated with a MoS2 layer can be used.

According to another variant of this device, the mechanical means are replaced or supplemented by at least one means for supplying heat or for cooling at least one zone of one end face of the continuous glass strip located between the longitudinal and the transverse marks.

According to an advantageous embodiment of the invention, at least one means for supplying heat and / or cooling is a heated or cooled roller in contact with the upper or lower surface of the continuous glass strip.

A heated and optionally cooled roll can be used in an equivalent manner. Moreover, the wheel and, if appropriate, the roller can simultaneously be a mechanical means capable of applying a form of force F 1 or Fs, respectively below or above the glass strip and may be a cooling or heat supplying means, respectively.

For example, wheels or rollers in which a heat transfer fluid, such as liquid nitrogen, or a heated fluid, is circulated may be used.

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By creating a thermal gradient across the thickness of the glass, it is possible to introduce a tension system equivalent to that introduced by bending, and thus create and cause a longitudinal crack to propagate.

According to another embodiment of the invention, at least one heat supply means is a laser.

As mentioned above, the method and apparatus according to the invention make it possible to produce sheets of particular advantage and allow the final processing operations to be significantly reduced.

Thick glass panes according to the invention are suitable in particular for the production of thick glass products, in particular with a thickness of at least 10 mm, and even with a thickness of greater than or equal to 15 mm, or even a thickness of greater than or equal to 17 mm, for example for use with in the building or in the interior decoration.

Thin glass panes according to the invention are suitable in particular for the production of thin glass products, in particular with a thickness of less than or equal to 1 mm, for example for use as shields.

Glass sheets made according to the invention are generally suitable for the production of toughened glass articles.

The subject of the invention is illustrated in the drawing in which Fig. 1 shows a partial plan view of a continuous flat glass strip production and cutting line, Fig. 2 a partial view of the production line along section AA 'in Fig. 1, Fig. 3 - glass strip in a partial view, cross-section to the axis of glass strip travel, Fig. 4 - variant of the glass strip in a partial view, cross-section perpendicular to the axis of glass strip travel, Fig. 5 - a strip-cut edge of a thick glass sheet obtained from a continuous glass strip by traditional strip-separation techniques, Fig. 6 - a stripped edge of a thick glass sheet obtained from a continuous glass strip according to the invention.

First of all, it should be made clear that, for the sake of clarity, the proportions between the various elements depicted are not strictly respected in all figures.

Figure 1 shows a partial plan view of a continuous flat glass strip production and cutting line.

The flat glass ribbon 10 typically comes from the relaxation zone and enters the cut zone at the speed of the ribbon V_R carried by the drive rollers 12. This belt generally has defects on each of its extreme edges, the defects being caused by marks from tools, e.g., called an upper roller, which allow the width of the belt to be controlled by pulling or pinching the edges. In the case of a thick glass strip, the edges are generally thinner than the average thickness of the strip, and conversely, in the case of a thin glass strip, the edges have a thickness greater than the average thickness of the strip.

In order to remove these edges, a stripe separation operation is performed. The operation usually begins with a longitudinal scribing step with scribing means 51 near each of the extreme edges of the tape, in particular with a circular cutter 11. In this way, a quasi-continuous glass score line 30 is marked in the longitudinal direction of the tape.

The line for the production and cutting of glass strip comprises, after the longitudinal markers 51, a transverse means 52 that produces a transverse mark 41, followed by a transverse breaker 53, shown here in the form of a roller that rises under each of the transverse marks 41. to separate the sheets 62 from the continuous glass strip 10. Drive shafts 13 located downstream of the breaking means 53 drive the cut sheets at a speed V_P. greater than the speed of the continuous belt V_R to enable the panes to be finally drained off, usually by lifting and then stacking them.

According to the invention, a center is provided between the longitudinal markings 51 and the transverse marks 52, allowing the formation of a transverse scratch starting from the transverse markings. This measure is shown here in the form of a wheel 21 underneath the glass strip and mounted on a base provided with a jack 22.

The circle is located approximately halfway between the longitudinal markers 51 and the transverse markers 52. This circle can be located in particular from 0.60 to 1 meter behind the longitudinal marking means 51. A longitudinal, and especially a through, crack extends on either side of the outer edges of the glass strip 10. After a transverse fracture performed by a roller acting as a means 53 for the

The transverse breaking sheet 61 separates from the glass strip 10 and at the same time the strips 61 on either side of the sheet 62 are separated and withdrawn.

Figure 2 shows a partial view of the production line along section AA 'in the previous figure. The observation is made towards the length of continuous glass ribbon 10 and allows the exact stage of formation and propagation of the longitudinal crack 32 to be determined. In the case shown, this longitudinal crack is a through crack. After marking the line 30 with the circular cutter 11 on the upper face 15 of the glass strip, the crack begins to develop from the point 31 called the start of the crack, progressively passing through the thickness of the glass strip 10. This crack propagates at velocity V_F. in the opposite direction to the belt speed V_Rand of essentially equal value.

To create and cause this crack 32 to propagate, a force is applied to the lower face 17 of the glass strip by means of a wheel 21 mounted on a jack 22 which is attached to the substrate by a support, for example a tripod 23.

Figure 3 shows a partial view of the glass ribbon in a partial view perpendicular to the axis of travel of the glass ribbon situated between the scribing center 51 and the circle 21. This figure shows an enlarged view of the zone near the outer edge of the ribbon 10 as seen transversely to the axis of travel of the glass ribbon. . In this way, the position of the wheel 21 in contact with the lower face 17 of the glass strip is clarified. In this representation, the circle 21 is located in a zone close to the scribe 32 situated on the side opposite to the scribing line 30 with respect to the outer edge 16 of the glass strip 10. This circle can also be placed below the scribing line 30. In this way, a force F | is applied which will form a widened zone 35 in the strip section.

As also shown in Fig. 3, it is possible to provide a wheel 25 that rests against the upper face 15 of the glass strip, which allows the application of a force Fs, which also contributes to the generation of tensile stress perpendicular to the alignment 30 in zone 35. This wheel 25 is located in the zone between the alignment 30 and the outer edge 16 of the glass ribbon 10.

Figure 4 shows a variant of the solution according to the invention, shown in a manner identical to that shown in Figure 3.

In this variant, rollers 81, 82 are placed in contact with the lower face 17 of the continuous glass strip 10 on both sides of the longitudinal alignment. These rollers are cooled by immersion in the liquid 85 contained in the reservoir 86 at a temperature lower than the ambient temperature.

Hence the forces appear which lead to the formation and then propagation of the scratch 32 from the alignment 30.

Another embodiment of this variant can be achieved with rollers 81, 82 cooled by the circulation of liquid nitrogen inside the rollers.

This device is especially suited for the production of thin glasses.

It is also possible to connect to the shaft 21 described in Fig. 3 one of the above cooling systems.

Figure 5 shows a section 101 of a thick glass pane whose edge has been stripped by traditional techniques. This example of observation corresponds to the section where the edge has been separated by an impact, in particular a jackhammer impact that will strike under the sheet to cause a crack propagation which allows the edge strips to be separated from the main body of the sheet. Numerous defects are observed, in particular the lines 102 which lead to the formation of scales 103, the roughened zone 104 attributable to the rapid crack propagation, the generally oblique zone 105.

Figure 6 shows a section 201 of a thick sheet of glass, the edge of which has been separated from the strip by a method according to the invention. The surface of this section 201 is smooth. There is a trace of the longitudinal alignment 30. The zone situated on that side of this alignment is a mirror zone 202.

The invention is not limited to such details of execution and should be interpreted in a non-limiting manner and includes any method of severing the edges of a continuous glass moving at velocity V_Rcomprising a longitudinal scribing step in which an alignment is produced, in particular with a circular cutter, a final transverse routing step followed by a transverse breaking step, and which includes an intermediate step between the routing step

And a transverse scribing step consisting of forming at least one longitudinal scratch over at least a significant portion of the thickness of the continuous glass ribbon, especially the entire thickness of said continuous glass ribbon, from the alignment, and causing said longitudinal scratch to propagate at a velocity V_F., essentially equal and in the opposite direction to velocity V._R continuous glass tape is moving.