EP3749619A1

EP3749619A1 - Curved glass or glass-ceramic pane and method for the production thereof

Info

Publication number: EP3749619A1
Application number: EP19704592.5A
Authority: EP
Inventors: Markus Vollmer; Hubertus Bader; Gregor Arnold; Manuel WALOSCHEK; Thomas Kraus; Friedrich Georg Schröder; Oliver Mühlke
Original assignee: Schott AG
Current assignee: Schott AG
Priority date: 2018-02-09
Filing date: 2019-02-07
Publication date: 2020-12-16
Also published as: WO2019154922A1; DE102018102932A1; JP7379349B2; JP2021512842A

Abstract

A glass or glass ceramic pane (1), in particular as an inspection window for a stove, wherein the glass-ceramic pane (1) has at least one simply curved section (3), to which two flat areas (5, 7) connect, which enclose an angle with each other of at most 150°, preferably at most 120°, particularly preferably at most 100° because of the connection via the curved section (3), wherein the glass or glass-ceramic pane (1) has a thickness of at least 2 millimetres, and wherein fluctuations in the curvature in the curved section (3) along the surface in the azimuthal direction of the curved section (3) in a length range of a length corresponding to the thickness of the glass or glass-ceramic pane up to a quarter of the arc length of the curve section (3) have an amplitude of no more than 0.005 mm^-1.

Description

i

Curved glass or glass-ceramic disc and method for its production

description

The invention generally relates to glass or glass ceramic discs which are provided with at least one bend or curvature. Such discs are used, for example, as windows for stoves or for household appliances.

The use of glass ceramic panes as a viewing window for stoves is well known. In order to increase the spatial view into the stove, circular curved or angled fireplace viewing windows have been used for a long time. The curved fireplace fireplace panes can be made by so-called gravity lowering. There are special gas powered bending machines for angled blades.

The starting material for both processes are so-called green glass panes in plate form. Green glasses are precursor glasses of glass-ceramics, which in one

Ceramization process then be converted into glass ceramic discs. The conversion of precursor glasses into glass ceramics can take place in parallel to the forming process or after forming in a separate process step. A conversion parallel to the forming is used in gravity lowering. Here is exploited that the glasses at the

Conversion are brought to a temperature at which the glasses are also sufficiently soft for a transformation. If a bending machine is used, the bending step precedes the ceramization as a separate process step.

The forming process of gravity lowering is generally and for large

Bending angle in particular, clearly illustrated in DE10102576 B4. Characteristic of this method is the warming of the glass together with the bending tool in chamber or tunnel ovens, which are heated either electrically or with gas. In this process, the entire glass surface is uniformly heated and bent. This method is used when, for example, the bent part is to represent a section of a cylinder.

Since the starting glass transforms very quickly into glass ceramic at the forming temperatures and then changes from a very soft state very quickly into a very solid state, it is no longer deformable from a certain high viscosity. For this reason, only a very limited temperature / time range is available for gravity lowering glass ceramic green glass. With the limitation of the achievable viscosity is generally accompanied by a limitation of the achievable bending radii. In general, it can be said that with this method, with glass thicknesses of 4mm-5mm without additional external forces, radii smaller than 200 mm are difficult to achieve. If smaller radii are to be produced with this method, the deformations must be supported by external forces.

Such a transformation is described in DE 10 2009 012 018 A1. With this method, bending radii between 30 mm and 200 mm can be achieved using the gravity-lowering method. However, this method has the disadvantage that the bending tools are relatively complex and less variable with respect to a change of the desired radii.

An alternative method to the gravity sinking described above is forming in a bending machine with gas powered burners. Here is achieved by the rapid introduction of high amounts of energy softening of the green glass before the conversion. Such a bending method is known from JP41 1 1408 B2 and DE 100 39 027 C1.

JP 411 1408 B2 describes in particular a gas burner operated

Bending machine as it is already known in principle from US 2,176,999 A. The forming comprises the three steps of preheating in a chamber or tunnel kiln, local heating by means of two gas burners from both sides of the glass surface and finally one

Relaxation process, which in turn happens in a tunnel or chamber furnace. Without further aids, bending radii of about 7 to 10 mm for a 4 mm thick disk and a bending angle of 90 ° typically occur at such a bending installation during the process. With thicker or thinner discs, the typical bending radii change accordingly. The radii can only be changed to a very limited extent with this simple method without further aids. They depend on the temperatures, the

Viscosities of the green glasses, the heating geometries, the heating times and the material thicknesses of the green glasses from. Since temperatures can not be increased unrestricted and concomitantly the viscosities of the precursor glass can not be arbitrarily lowered and in green glasses for glass ceramics a time limitation by the conversion in these temperature-time processes in glass ceramics in appearance, the achievable bending radii in the usual methods are set narrow limits.

According to DE10039027 C1, the green glass is preheated in an oven and then heated by a local heating by gas burner from one side in an oven to the extent that it can be transformed. This method has some disadvantages; it will be expensive forms It is slow, because only one bent part in the oven is reheated, reshaped and relaxed. Likewise, the one-sided heating with gas burners is disadvantageous. It has been found that both the energy density required to achieve reshaping prior to the ceramization and the short heating time necessary with one-sided heating by means of gas burners are difficult to achieve.

For this purpose, two burner strips can be used on both sides of the glass sheet for angularly deformed products by a method as described in JP41 11408 B2. In FR 2726350 A1, this process of bending glass ceramics by means of gas burners, including the required pre- and post-Temperöfen is descriptive.

WO 2013/184893 A1 describes a method for bending thin glass panes for the production of housings for electronic devices. The glass sheet is heated together with a bending device and then heated in a strip on until softening. An arm is applied to the glass, to which a force is exerted. The glass sheet is thus bent by the applied force on the softened strip.

Another general problem with producing bent glass surfaces is that the force exerted during forming generally leads to undesirable surface unevenness. These can be clearly visible because they have a refractive power on the glass surface, which leads to optical distortion when viewed. The invention is therefore based on the object to achieve a low-distortion view through a reshaped glass or glass-ceramic disc. Also, a high dimensional accuracy is synonymous with large

Be given bending radii.

This object is solved by the subject matter of the independent claims.

Advantageous embodiments of the invention are specified in the dependent claims.

Accordingly, the invention provides a glass or glass ceramic pane for a variety of uses, in particular as a viewing window for a stove, wherein the glass or glass ceramic pane has at least one simply curved, or uniaxially bent portion, to which join two flat surfaces, which due to the connection over the bent portion to each other at an angle of at most 150 °, preferably at most 120 °, more preferably at most 100 ° include, wherein in the bent portion variations in the curvature along the surface in the azimuthal direction of the bent portion, or in the direction perpendicular to Curvature axis, ie in the direction along a path from a flat surface over the curved portion to the other flat surface in a length range of a length corresponding to the thickness of the glass or glass-ceramic disc to a quarter of the arc length of the bent portion has an amplitude of maximum 0.005 mm- ¹ . Fluctuations in the curvature in this length range and above said

Limit value of 0.005 mm- ¹ prove to be visually particularly conspicuous with respect to a distortion of the transparency, as well as the reflection under flat viewing angles. The arc length is greater, preferably at least twice, more preferably at least four times as large as the thickness of the glass or glass ceramic disc. As a glass ceramic is understood within the meaning of this disclosure, a glassy material containing crystalline components. The term "glassy" refers to the constituents of inorganic glasses. The glassy material accordingly corresponds in its composition to an inorganic glass.

According to another embodiment, the fluctuations of a maximum of 0.005 mm- ¹ in a length range of 2 to 30 mm are suppressed. Above a quarter of the

Arc length of the bent portion and / or above 30 millimeters can

Deviations of the curvature from the desired course are regarded as long-wave distortions whose refractive power and thus their influence on the transparency is only slight.

The method is particularly suitable for glass or glass ceramic discs having a thickness of at least 2 millimeters. This among other things with regard to the above-described method of gravity lowering and the associated disadvantages,

In order to scan the surfaces for the determination of the curvature, a coordinate measuring machine with a probe known to those skilled in the art can be used.

The local curvature k at a measuring distance on the surface of the glass or

Glass-ceramic disc is given by:

In this case, f denotes the course of the measuring path, or the function which describes the course of the measuring path. The first derivative f and the second derivative f ^" are local derivatives of the course of this measurement segment .The curvature k represents the inverse radius of curvature R of the surface: k = R- ¹

As flat surfaces, the sections of the integral disc are considered, which have only very small curvature values. In particular, according to one embodiment of the Invention provided that the curvature of the bent portion at its transitions to the flat surfaces to a value less than 0.0025 mm- ¹ drops. This is advantageous since even slight curvature values, for example due to larger-area deformations, are clearly noticeable on the flat parts of the pane. Although there is no appreciable distortion due to a refraction of such a deformation more, however, the deformations can distort light reflections on the disc and become visible in this way.

Such a glass or glass-ceramic pane can be produced by a method according to the invention, in which generally the heating and subsequently the shaping are not carried out simultaneously over the entire forming area. Rather, the heating and deformation is continuously passed through in time sequence along the radian measure.

The method for forming a glass sheet and producing a glass or glass-ceramic pane according to the invention provides to provide a glass pane with a thickness of at least 2 millimeters to heat a strip extending from one edge to the opposite edge of the glass pane until it softens to bend the glass sheet then on the heated and softened strip, so that on the heated strip a simple, or uniaxial bent curve is formed and adjacent the strip adjacent flat surfaces are inclined to each other, the strip under broadening of the heated area of the glass pane transverse to the longitudinal direction of which is moved across the glass sheet while increasing the inclination of the flat surfaces to each other and widening the bent portion until the two flat surfaces incline to each other at an angle of at most 150 °, preferably at most 120 °, more preferably at most 100 ° eat.

For the bent portion, a mean radius of curvature in the range of 15 to 100 millimeters is preferred. These values correspond to mean curvatures in the range of 0.0667 mm ^-1 to 0.01 mm ^-1 . These values refer to the side of the glass or glass-ceramic pane on which the curved section is convexly curved.

Particularly preferably, the simply curved, or simply bent portion is bent cylindrically. Such a cylindrical bend is easy to produce with the method according to the invention and also facilitates the mounting of a frame for holding the disc. In the case of a cylindrically curved section, the curvature along the curved section is ideally constant, corresponding to the ideally constant one

Radius of curvature. In order to avoid variations in the curvature along the bent portion, it has proved to be very effective when the bending operation is path-controlled. This means that the bending movement along a given path is independent of the force required for the bending. This is a technique that stands in contrast to a force-controlled bend. If, as described for example in WO 2013/184893 A1, a predetermined force is applied, then the local or total bending angle and also the bending radius at least partly also depends on the viscosity of the glass and thus on its temperature. In contrast, the locally inserted curvature is forcibly given in the course of a predetermined movement. Again, fluctuations in the

Curvature are caused, namely, when the position of the softened strip and its movement fluctuates or is not precisely defined. Obviously, however, such effects are much smaller. It has also been shown that the forced movement of

Glass pane causes no high risk of breakage, although the acting forces are not limited in principle or only by the maximum exerted by the bending device moments.

The bending movement is mediated via a bending device and takes place after a predetermined coupling of the bending movement of the bending device and the movement of the heating zone generated by a heating device relative to the glass pane. The heating zone is the area of the surface of the glass pane in which the heating device introduces heat energy. When the heating device is stationary, the width of the heated strip is thus about as wide as the heating zone. The coupling can also take place according to a predetermined sequence as a function of time. Accordingly, in one embodiment, the bending of the glass sheet on the heated and softened strip and the movement of a heating zone over the glass sheet to produce the heated and softened strip are coupled to each other transversely to its longitudinal direction, in particular positively coupled. As mentioned, this coupling can take place after a predetermined movement-time sequence. In addition to the movement of the glass pane, this movement-time sequence can also include the movement of the heating zone via the pane over the glass pane.

The invention including the particular method for producing the bent glass or glass-ceramic discs is explained in more detail below with reference to the accompanying figures. Show it:

1 is a sketch of a bent glass sheet showing the bending radius of the neutral fiber, Fig. 2 is a schematic view of an apparatus for carrying out the

inventive method,

3 and FIG. 4 in side view the device at the beginning and after completion of the forming process,

5 is a formed glass sheet,

6 shows diagrams of the temperature distribution at the surfaces and the glass center during bending of the disk,

7 shows a glass pane inserted into a mold for the ceramization.

8, 9 and 10 show curves of the curvature of glass ceramic disks along the bent portion with a bending radius of 54 mm,

11 shows the course of the curvature of a glass-ceramic disc with a bending radius of 70 mm,

12 shows the course of the curvature of a glass-ceramic disc with a bending radius of 95 mm,

13 shows a stove with a glass or glass ceramic pane,

Fig. 14 is a door of a working aggregate.

15 shows a further embodiment of a door of a working unit,

16 is a glass or glass-ceramic disc with two curved sections,

FIGS. 17 and 18 show speed-time curves of the bending movement and the movement of the fleece zones.

The bending of glass by means of line gas burners arranged on both sides of the glass surface is known. Also for the bending of glass ceramic green glass, this method is known and tested. Depending on the flame width, which is typically around 10-20 mm for line burners, the radian measure of the area to be reshaped results. The resulting bending radius can be calculated with reference to the sketch of a formed glass sheet shown in FIG. 1 as follows:

R (NF) = (BM-180) / (p -W).

Where R (NF) is the bending radius of the neutral fiber, BM is the radian measure of the neutral fiber in the formed area, and W is the opening angle of the deformed area.

Assuming that the energy density is constant over the heating widths, such as a flame or irradiation width, this may approximate the flame width equated with the radian measure. Depending on the heating time, temperature profile of a burner or a heating jet and the heating power, it may, however, due to the

Heat conduction to slight deviations come.

Accordingly, with a typical effective heating width of 12 mm, an opening angle of 90 ° and a glass thickness of 4 mm, the bending radius of the neutral fiber would be about 7.6 mm. In this case, the effective heating width is assumed to be the area on the pane in which the power density is greater than 80%. In this

Power density range, the glass is heated quickly enough so that it is deformable without incipient ceramization. The average area over the heating width, or in the heated strip 8 effective area performance is according to a development of the invention at least 10 W / cm ² . The effective area performance refers to the heat energy actually deposited in the glass per unit of time. Preferably, the averaged effective

Area performance in a range of 20 W / cm ² to 1000 W / cm ² . For gas burners, the effective area performance is rather higher than when using a laser, such as a CO2 laser. Preferably, however, with said heating sources, powers in the stated range of 20 W / cm ² to 1000 W / cm ² are provided. For gas burners, the area output is higher due to power losses and blurred area of flames, the effective

Area performance should be in the above range. The effective heating power may be further selected depending on the glass thickness, the bend line length, or the width of the bent portion, the width of the heating strip and the power of the heating source, such as the laser power.

If larger radii are required, an attempt could be made to use a correspondingly wide heating source in order to bring the region to be formed uniformly to a temperature sufficient for bending. However, there are limits to this, since in the case of very wide burners, the exhaust gases must escape from the inner heating area through the outer area, which leads to inhomogeneities of the temperature distribution in the heating area and thus to waviness in the bending area.

Fig. 2 shows an arrangement for carrying out the method according to the invention in a schematic view. The glass sheet 1 is fixed at one end by means of a holding device 17. A preferred embodiment of a holding device 17 comprises a vacuum table, to which the glass pane is firmly sucked with one of its sides 9, 10. In the illustrated Example, the glass sheet 1 is placed with its side 10 on the holding device 17 and held.

By means of one or more heating devices, a strip-shaped section extending from an edge 12 of the glass pane 1 to the opposite edge 13, or a strip 8 in the region of the heating zones 190, 200, to which the

Heating 19, 20 bring heating energy, heated until it softens. In the illustrated example, two opposing heaters 19, 20 are provided, so that the strip 8 on both sides 9, 10 of the glass sheet 1 can be heated quickly.

If the glass pane 1 is heated to such an extent that the glass softens, the glass pane 1 is then bent on the heated and softened strip 8 by moving the glass pane 1 with a bending device 21 with respect to the section held by the holding device 17. In the illustrated example, the bending device 21 comprises two grippers 22. In this way, the heated strip 8 is formed into a single or uniaxial curved one

Curvature. The adjacent to the strip 8 flat surfaces 5, 7 are thereby inclined to each other. The bending device 21 may comprise at least one robot arm according to a preferred embodiment. The robot arm then also includes the gripper 22 shown in FIG. 2 without limitation to the example shown represents the

Bending device 21 preferably a non-positive connection to the glass ago, in order to perform a bending movement of the write in a predetermined way. For the non-positive connection, as in the example shown, grippers 22 or corresponding devices can be used.

Without limiting to the example shown, the heating power of

Heating devices, or registered in the heating zones 190, 200 heat output can also be chosen differently. This can be advantageous to control the bending behavior. So it may be convenient to choose the heating power on the side, which is bent convex, higher than the heating power of the opposite side, which is bent concavely.

A more detailed procedure is shown in FIGS. 3 and 4.

For this purpose, as shown in FIG. 3, the heating devices 19, 20 start at the beginning of the intended forming region 16. After a short residence time of 0-5 seconds, a strip 8 is heated sufficiently to be deformable. At the latest then start the

Heating devices 19, 20 with a transverse travel in the direction of the end of the forming area 16th io

Thereby, since the heated strip 8 is moved by moving the heaters 19, 20 along the disc, the total heated area is widened until it occupies at least the forming area 16. During the movement of the heaters 19, 20, the inclination of the flat surfaces 5, 7 to each other is increased by bending one flat surface over the heated and softened strip 8 opposite the other flat surface. At the same time, the curved section widens accordingly. This is continued until the two flat surfaces 5, 7 form an angle α of preferably at most 150 °, in particular at most 120 °, particularly preferably at most 100 °.

The finished bent glass pane 1 with the angle α enclosed between the two flat surfaces or sections 5, 7 is shown in FIG. 5. It will be apparent to the person skilled in the art that the relative movement between the glass pane 1 and the heater (s) 19, 20 arrives. Therefore, it is also possible to hold the heaters 19, 20 and move the glass sheet 1. The process as shown, however, is easier to implement, since in this case the bending movement does not have to be additionally coupled with a translation. It is therefore generally provided in a preferred embodiment of the method according to the invention that the glass sheet is held, while the at least one

Heating device 19, 20 is guided over the glass sheet 1 during bending.

As heaters laser can be used as shown. Since the heating and bending according to the invention is carried out sequentially along the deformation region 16 to be deformed, the entire deformation region 16 does not have to be heated simultaneously until the glass softens. Therefore, the required heating power in the inventive method is also relatively lower. This makes the use of a laser as

Heating device particularly suitable. In order to heat the entire strip 8, the laser beam can be guided over the glass, for example, by means of a galvano scanner. The laser beam preferably deposits an effective area performance of at least 10 W / cm ² , more preferably in a range of 20 W / cm ² to 1000 W / cm ² .

But it is also possible alternatively or additionally to use a burner as a heater 19, 20. A suitable burner can have for stripe-shaped heating of the glass a row of adjacent burner nozzles or else a slot nozzle.

In order that the forming can begin at the beginning of the forming area, the

Glass sheet 1 at this point over the entire thickness sufficient for the deformation low viscosity. The deformability is determined by the lowest temperature on the glass thickness in the glass center.

To illustrate this, FIG. 6 shows diagrams (a) to (f) from a simulation. The simulation was created on the assumption that gas burners are used for heating. The diagrams show a time sequence of the glass transition temperatures at the top (curve 30), the bottom (curve 32) and the glass center (curve 31). The elapsed time is indicated in the diagrams. The simulation starts with a starting time of 10 seconds (diagram (a)). The abscissa axis of the diagrams describes the travel of the heating device (0 mm = start of forming area, 90 mm = end of forming area). On the ordinate axis the temperature is plotted. At the beginning of the heating process is the

Evenly preheat the glass plate to approx. 600 ° C. After 2.5 s heating time (diagram (b)), the top and bottom have reached their maximum temperature. The heater now begins the cross travel along the forming area. As you can see, the center temperature at this time is just over 700 ° C, which is not enough for a transformation. In the further course, the temperature peak moves with the advancing heater across the area to be reshaped. After about 5 seconds, the glass center at the beginning of the forming area has exceeded 900 ° C (diagram (c)). Now you can start with the forming at this point. Depending on the center temperature can now follow the transformation of the burner movement with a distance. Accordingly, the heated and softened strip 8 is not necessarily directly opposite the heater (s), but may be displaced counter to the direction of movement.

In order to produce a corresponding glass-ceramic pane from the glass pane 1 shaped in accordance with the invention, as shown, for example, in FIG. 5, the glass pane 1 is in

Development of the invention in a mold 25 with two mutually angled bearing surfaces 50, 70 inserted so that the glass sheet 1 rests with their flat surfaces 5, 7 on the support surfaces 50, 75 and guided together with the mold 25 through a Keramisierungsofen, wherein the Glass of the glass sheet 1 converted into a glass ceramic. Such a mold with an inserted glass pane 1, Fig. 7. As shown, the mold 25 of several

Moldings 250, 251, 252 be composed. In particular, separate moldings may be provided as a support for each of the flat surfaces 5, 7 and the bent portion 3 of the glass sheet. Although the glass softens during ceramification, variations in the curvature of the surface are retained even after ceramization or may even be exacerbated by the shrinkage of the material during ceramization. This is especially true for the bent portion 3. Therefore, the feature of the present invention is that variations of the curvature along the surface in the azimuthal direction of the bent portion 3 in a length range of a length corresponding to the thickness of the glass or glass-ceramic disc up to a quarter of Arc length of the bent portion 3 have an amplitude of at most 0.005 mm ^-1 , both for glass panes, and for glass ceramic discs, which were then ceramized.

This will be clarified with reference to FIGS. 8, 9 and 10. These figures show curves of the curvature of glass ceramic discs 1 over the bent portion 3 of time. To determine the curvature, the surface of the glass or glass-ceramic disc 1 is scanned with a probe. This measuring distances are traveled, which extend from a flat surface 5 on the curved portion 3 away to the other flat surface 7. In Fig. 5, three such measuring sections 35, 36, 37 are located. Two of the measuring sections 35 and 37 run parallel and in the vicinity of the edges of the glass or glass-ceramic pane 1, a further measuring section 36 between them in the middle of the glass or glass-ceramic pane 1. FIG. 8 shows the course of the curvature along a measuring section 35, FIG. 9 the course along the central measuring section 36 and FIG. 10 the course along the measuring section 37 at the

opposite edge of the glass or glass-ceramic disc. 1 Each of the diagrams contains two graphs labeled "A" and "B". The graphs labeled "A" in each case represent values of curvature of bent and subsequently ceramized according to the invention

Glass panes. The graphs marked "B" are glass ceramic panes according to WO 2010/102858 A1, which were placed in a mold whose moldings were folded at the beginning of the ceramization on softening of the glass, so that as well as in a glass or glass-ceramic pane according to the invention a corresponding shape with two flat surfaces and a bent portion is obtained. The transformation and

Ceramization corresponds to the process described in WO 2010/102858 A1. On the abscissa the arc length of the measuring section is plotted.

The measured glass-ceramic discs were made with a bending radius of the bent portion of 52 mm. In this case, the bending radius refers to the center of the disc, or the neutral fiber, as already explained with reference to FIG. 1. All graphs show a more or less stepped profile. It is in the

Areas in which the probe scans the flat surfaces 5, 7, the curvature small. At the transition to the bent portion 3, the curvature jumps to a higher value. All graphs "A" have in common that the curvature remains at a slightly fluctuating value. The substantially constant curvature shows that the bent portion 3 is bent cylindrically, ie the bending radius remains the same in the bent portion 3.

The flat surfaces 5, 7 have no significant curvature values. As can be seen with reference to FIGS. 8 to 10, the curvature in the flat surfaces adjacent to the transitions to the bent section 3 is consistently less than 0.0025 mm ^-1 .

Furthermore, the curvature values are in accordance with the invention

Glass ceramic discs 1 for all three graphs between 0.015 and 0.020 mm- ¹ . Thus, the variation of the curvature along the surface in the azimuthal direction of the bent portion (3), ie also along the measuring sections 35, 36, 37 not only in a length range of a length corresponding to the thickness of the glass or glass-ceramic disc to a Quarter of the arc length of the bent portion (3), but apart from the transitions over the entire length of the bent portion at less than 0.005 mm- ¹ . In contrast, the graphs "B" have short-wave variations in curvature. Thus, all the graphs "B" of FIGS. 8, 9, 10 show a significant variation in an arc length of about 325 mm.

In particular, such fluctuations in one in a length range of 2 to 30 mm, which are not present in a glass-ceramic disc according to the invention or less than 0.005 mm- ¹ , may interfere due to lens effects.

The average curvature of about 0.0175 mm ^-1 in the preferred field of application of the invention with curvatures in the range of 0.0667 mm- ¹ to 0.01 mm- ¹ , measured as in the example of FIG. 8 to FIG the side of the glass or glass-ceramic disc 1, on which the curved portion 3 is concavely curved.

The radius of curvature at a curvature of 0.0175 mm ^-1 is 1 / 0.0175 mm ^-1 = 57.1 mm. This is slightly more than the nominal radius of curvature on the outside of 54 mm,

FIGS. 11 and 12 show two further examples of the course of curvature

Glass-ceramic discs according to the invention. The examples show in particular that the invention is also suitable for large bending radii of the bent portion 3. The glass-ceramic disk 1 of FIG. 1 1 has a bending radius of 70 mm, the disk of the example of FIG. 12 has a bending radius of 95 mm. As can be seen, the fluctuations are even lower than at In the graph of Fig. 1 1, although there is about 330 mm arc length a single significant fluctuation with a short period, but this is not in the

Glass surface present, but caused by surface contamination. The fluctuation at 270 mm in FIG. 12 is again a metrological artifact.

One field of application for the invention is the use of the glass or glass-ceramic pane for a door, in particular a door of a stove, or more generally one

Diligence aggregate. The door can form a corner of the working unit with an angled disk according to the invention. As a material for the disc both glass ceramic, and glass, such as a borosilicate glass in question.

As shown, the glass or glass-ceramic pane 1 forms a glazing of the door 40, the glazing around an edge 42 of the body 41 of the stove 1 1 passes. The edge 42 is continued by the bent portion 3.

The invention has not only aesthetic effects by avoiding distortions due to refraction or reflection of light sources at shortwave

Curvature fluctuations of the surface. The uniform curvature also results in increased strength under certain dynamic loads. These come into effect when closing such a door. When the door 40 is hit, in particular, the bent section is heavily loaded dynamically. The load arises because, as the door is rotated about one of the edges running parallel to the bent portion, the planar surface adjacent to the edge is guided in a pivoting motion while the other planar surface performs a tangential motion or at least a tangential component motion. When the door arrives, this results in moments of different directions meeting in the bent section. If the door slammed violently, it may cause the glass or glass-ceramic disc 1 in the bent portion to break. It has surprisingly been found that an inventively bent glass or glass-ceramic disc has a higher resistance to such loads. In general, without being limited to the illustrated examples, the invention therefore also provides a door 40 of a working aggregate, as illustrated by way of example in FIG. 14. The door 40 with a glass or glass-ceramic pane 1 according to the invention comprises a holder 44 for pivotally attaching the door 40 to the appliance (such as that shown in FIG

Stove 1 1) such that the glass or glass-ceramic disc 1 when opening and closing the door is pivoted at one of its along the curved portion 3, in particular parallel to this curved portion 3 extending transverse edges 14, 15. For pivoting, hinges 46 can be used, in particular as shown in FIG.

The holder 44 comprises in a preferred embodiment, two strips 48, 49 which hold the glass or glass-ceramic disc 1 at its longitudinal edges 12, 13. For reasons of ease of assembly and an attractive, slim design, it is further desirable if the transverse edge 15 of the glass or glass-ceramic pane 1 is exposed on the outside as shown in FIG. 14, or is not supported. Unlike shown in the figure, a strip of the holder 44 may extend along the transverse edge 15, wherein the glass or glass-ceramic disc 1 but then is not attached to this bar, or the door comprises a peripheral frame, wherein the disc but not kept circulating. Especially in the case illustrated in FIG. 14 with non-supported transverse edge 15, however, the problem explained above occurs in a sharpened form such that when the door 40 is closed and struck, the bent portion is subjected to particularly mechanical stress. The surface adjacent to the transverse edge 15 exerts a moment along the longitudinal edges 12, 13 due to the inertial forces during abrupt deceleration at the stop, which must be intercepted at the bent section 3. The moment is enhanced by not being partially received by the bracket 44 at the transverse edge 15 remote from the pivot axis 50 defined by the hinges 46. Especially in such a configuration, therefore, the method according to the invention for bending the glass pane 1 and the glass or glass-ceramic pane produced therewith with the increased strengths mentioned offers particular advantages.

In general, without limitation to the particular example shown in FIG. 14, a door 40 with a glass or glass-ceramic pane 1 according to the invention and a holder 44 for pivotally fixing the door 40 is provided in an embodiment of the invention, with which the glass - Or glass-ceramic disc 1 is pivotally supported, wherein the remote from the pivot axis 50 of the holder 44 transverse edge 15 of the glass or

Glass ceramic disc 1 is not supported by the holder 44.

Fig. 15 shows in cross-section at the edge with the pivotable holder 44 such an embodiment of a door 40. In this embodiment, a peripheral frame 52 is provided as part of the holder 44. The glass or glass-ceramic disc 1 is pressed by means of the here L-shaped strips 48, 49 against a displaced between disc and frame 52 seal 54 and so supported. Since the strips 48, 49 only at the top and bottom Run edges of the glass or glass-ceramic disc 1, here also the remote from the pivot axis 50 of the holder 44 transverse edge 15 of the glass or glass-ceramic disc 1 is not supported by the holder 44. The arrangement according to FIG. 15 is purely exemplary. To attach the glass or glass-ceramic pane 1 to the frame 52, a variety of other arrangements are possible. Another arrangement, which is also preferred, is to support the disc on the other side of the frame 52 so that the concave-arched side of the bent portion faces the frame 52.

In the embodiments explained so far, a single curved section 3 was provided. However, it is also possible without complicated bending forms to provide a plurality of curved sections. Such an embodiment is shown in FIG. 16. In general, without

Restriction to the specific illustrated example, the invention provides this so in

Further development that the glass or glass-ceramic disc 1 has two curved sections 3, 4 with an intermediate flat surface 6. Unlike shown in Fig. 16, the bent portions 3, 4 may also be bent in opposite directions.

In order to achieve the above-explained low variations in the curvature along the bent portion, a forced movement in bending the glass sheet 1 is performed. Thus, the movement sequence is specified without the forces required for deformation being regulated. If, for example, one or both of the heating devices 19, 20 fails in the example shown in FIG. 2 and no softened strip 8 is produced, the course of the bending program could lead to breakage of the pane if the forces exerted are not limited. This risk does not exist with a force-controlled deformation, in which only a predetermined, permissible bending force is exerted. However, the forced movement causes even with slight temperature fluctuations in the heated strip 8 of the predetermined bending angle and bending radius is reached.

It has also been shown that it is particularly advantageous both for the avoidance of variations in the curvature curve, as well as for the processing of ceramizable glasses, when the bending speed is not uniform, but increases in the course of the bending operation. This does not only refer to the beginning of the movement, which indeed starts from a rest position and is thus inevitably accelerated at first, but also to the greater part of the movement. Therefore, it is provided in development of this embodiment that for the bending movement of the glass sheet 1 at least one of the following conditions applies: the bending movement accelerates over more than half the duration of the bending of the glass sheet 1,

- The bending movement accelerates over more than half of the way that travels a moving part of the glass sheet 1 during bending.

Furthermore, it has also proved to be favorable for the above-mentioned advantages, when the bending movement and the movement of the heating zone are carried out with a time offset.

In particular, it is advantageous if the movement of the heating zone, or both heating zones 190, 200 begins before the bending movement and ends in time before the stop of the bending movement.

Fig. 17 illustrates in a schematic example these embodiments. Specifically, Fig. 17 shows a speed-time diagram of the bending speed and the speed of the heating zones 190, 200. The curve 60 is the path-time curve of the bending movement, the curve 62 the path-time curve of the movement of the heating zones 190, 200. The processing starts first with a heating at fixed heating zones 190, 200 at a time to until the glass is heated in a strip 8 at least on the surface of the top and bottom sufficiently for forming. Since the center of the glass takes longer to reach the forming temperature and the bending movement does not yet start, there does not yet have to be a forming temperature over the entire glass thickness at this time.

The movement is then relative to the glass pane 1 and can therefore be achieved both by a movement of the heating devices 19, 20 relative to the glass pane 1, and vice versa by a movement of the glass pane 1 relative to the heating devices 19, 20 done. Time delayed after the beginning of the

Movement of the heating zones 190, 200 at time ti starts at a time fe

Bending movement. As can be seen from the path-time curve 60, the speed of the bending movement increases over the majority of the bending process. Already before the end of the bending movement, the movement of the heating zones 190, 200 stops at a time fe. Thereafter, the bending movement also stops with a time delay at a time t4. As can also be seen from the curve 60, a braking phase can be provided, within which the bending speed is lowered. In the example shown, this braking phase is between the times t ₃ and t 4, which is not mandatory, however. Such a braking phase may, inter alia, be advantageous in order to reduce vibrations when stopping the bending movement. Otherwise these vibrations can possibly cause curvature fluctuations in the bent section cause. The bending speed may be the speed of the edge of the glass sheet 1 moved by the bending device or also the angular velocity of the angle between the flat surfaces adjoining the bent portion. In any case, regardless of what speed is measured, the speeds depend on the accelerated motion curve described here. According to a preferred embodiment, the acceleration of the bending movement is such that the

Maximum speed is at least a factor of 1, 5 greater than that

Average speed in the time interval of the bending movement, or the

Average speed during the period in which the glass sheet 1 is bent. In particular, the bending motion may vary within an interval of 0.2 to 3 times the average speed.

In a practical example, the heaters are started at the time t0 and the glass pane is heated in the fleece zones 190, 200. About 3.5 seconds after the start of the heating process then the heaters 19, 20 are moved, this corresponds to the

Time ti in Fig. 17. 8 seconds after the start of the heating, the bending operation begins, corresponding to the time fe in Fig. 17. The time lag between the movement of

Heating devices 19, 29 and the start of the bending movement is thus 4.5 seconds. The heaters 19, 20 are stopped after a running time of about 14 seconds and off (time t ₃ ). The glass sheet 1 is then further bent for a period of 1 to 2 seconds to the intended end angle until the time t4 of

Bending process is complete.

Surprisingly, it has also proved to be favorable, the bending speed in

Determine the dependence of the bending radius, or the average radius of curvature for a given bending angle. In particular, for a given bend angle, e.g. 90 ° with a larger bending radius selected an overall smaller bending speed. Then the speed of movement of the heating zones can be independent of the mean

Radius of curvature can be selected. Fig. 18 shows, for clarity, speed-time diagrams corresponding to Fig. 17 but with a smaller bending radius at the same angle (for example 90 °) between the flat surfaces. The speed-time profile for the bending movement is denoted by the reference numeral 61 in this example. For comparison, the speed-time profile 60 of the example of FIG. 17 is also shown. The

The speed of movement of the heating zones 19, 20 remains opposite to the example of FIG. 17 unchanged (curve 62). The distances between the times ti and fe, and between t ₃ and t ₄ remain the same. But because of the intended smaller middle

Radius of curvature of the travel of the heating zones 19, 20 is smaller, the distance between the times ti and fe is smaller. The time interval between fe and t4 within which the bend takes place until the end angle is shortened accordingly. This is accompanied by the fact that the speed is increased so that within the time interval, the same predetermined bending angle is established. Accordingly, the average speed v2 of the

Speed-time profile 61 for a smaller mean bending radius greater than the average speed v2 of the speed-time profile 60. According to a

Further development of the invention is thus provided for the bending process, that for a given angle between the flat surfaces of the glass pane 1 the

Bending speed as a function of the mean radius of curvature of the bent

Section is set, with a reduction in the average radius of curvature, a higher average bending speed is selected.

To the low variations in curvature when bending with the here

To achieve the described method of positively guided bending movement, special properties of the glasses with respect to the temperature-viscosity curve are particularly advantageous. This is especially true for thick glass sheets with a thickness of 2 millimeters or more.

In general, it is particularly preferred if the glass of the glass pane, or its composition is selected so that at least one of the following features is satisfied. According to a first feature, the quotient T2.3 / T9 of the temperatures T2.3 and T9 is less than two. T2.3 denotes the temperature in degrees Celsius, at which the viscosity has a value of 10 ² · ³ dPa-s. Similarly, T9 denotes the temperature at which the viscosity of the glass is 10 ⁹ dPa · s.

According to another feature, the quotient T2.3 / T8 of the temperature T2.3, at which the viscosity of the glass 10 is ² × ³ dPa · s, to the temperature T8, at which the viscosity of the glass is 10 × ⁸ dPa · s, less than 1, 9. Both sizes indicate glasses that have a steeper drop in viscosity with increasing temperature. This steeper viscosity drop has several advantages in connection with the method described herein. The forming area remains limited with the steeper viscosity curve closer to the heated area. This applies even more to the preferably processed thick glass sheets with at least 2 millimeters thickness. The relatively short uniform area also does not lead to fluctuations in the curvature, since the local deformation and curvature is mainly dictated by the movement of the bending device.

Although the quotients T2.3 / T9 and T2.3 / T8 are parameters of a glass, they can also be assigned to a glass ceramic article produced correspondingly from a glass, since the glass and the glass ceramic produced therefrom have the same composition.

However, if the quotients are too small, ie the glass is very short, a wide range of viscosity may result in the transformation range, or the glass may become very soft locally. Therefore, lower limits are favorable. The quotient T2.3 / T9 is preferably greater than 1.85. Thus, this quotient in training ranges from 1.85 to 2. The quotient

T2.3 / T8 is preferably greater than 1.75. According to yet another embodiment, the quotient thus lies in a range from 1, 75 to 1, 9.

Also relevant and a measure of the viscosity curve is the quotient T2.3 / T13 the temperatures T2.3 and T9 at the viscosities 10 ^{2 3} dPa-s, or 10 ¹³ dPa-s. This is according to one embodiment at a value of at most 2.5, in particular in a range of 2.2 to 2.5.

The table below gives the minimum and maximum values of the above quotients for a group of five ceramizable glasses, as well as maximum and minimum values of T2.3 T8, T9 and T13:

The viscosity profile of a glass can also be described by the Vogel-Fulcher-Tammann model, or described by a curve according to this model. According to this model, the viscosity curve can be determined by the equation

be described with the constants A, B and To. According to one embodiment, the constants of the equation are at least one, preferably all of the following Conditions:

A is in the range of -2.95 to -3.45,

B is in the range of 7700 to 8700 ° C,

To is in a range of 100 ° C to 250 ° C, preferably in a range of 200 ° C to 250 ° C,

Glasses for the production of glass ceramic disks and thus also the glass ceramics themselves produced according to one embodiment contain the components U2O with 3 to 5 weight percent, preferably 3.6 to 3.9 weight percent, and as nucleating agent of one of the oxides or preferably both oxides T1O2 and ZrO 2. These may be in the composition having a T1O2 content of from 2 to 4 percent by weight, preferably from 2.3 to 3.3 percent by weight, and a ZrO2 content of from 0.8 to 2.2 percent by weight, more preferably 1.2 to 1.8

Weight percent be provided. According to a further embodiment, a glass or a glass ceramic produced therefrom is provided with the following components in percent by weight:

U ₂ 0 3 - 5,

AI2O3 18-25,

Si0 ₂ 55 - 75.

In addition, for glass ceramics, preferably as T1O2 and / or Zr02 in the abovementioned amounts, preferably as mentioned above.

Green glasses with these components can in particular also have the above-stated favorable viscosity properties. In general, it is favorable for ceramizable glasses or green glasses if the viscosity curve is steeper, ie if the quotients T2.3 / T8 and T2.3 / T9 are not too large. This allows for a faster

Bending process and thus reduces premature nucleation during bending.

The method according to this disclosure is not limited to the processing of glasses, which are limited to the production of glass ceramic, or more generally of vitreous materials, but rather glasses can generally be formed into curved glass sheets. Preferred types of glass are in addition to the above-mentioned LAS glasses

Borosilicate glasses and aluminosilicate glasses. Suitable borosilicate glasses may according to one embodiment have a composition with the following components in percent by weight:

Component: (wt.%)

Si0 ₂ 60-85 Component: (wt.%)

AI2O3 0-10

B2O3 5-20

U ₂ 0 + Na ₂ 0 + K ₂ 0 2-16

MgO + CaO + SrO + BaO + ZnO 0-15

T1O2 + ZrÜ2 0-5

P2O5 0-2

According to a further embodiment, the glass of the glass pane is an alkali aluminosilicate glass. This may in particular a composition with the following

Components in weight percent have:

Component: (wt.%)

Si0 ₂ 40-75

AI2O3 10-30

B2O3 0-20

U ₂ 0 + Na ₂ 0 + K ₂ 0 4-30

MgO + CaO + SrO + BaO + ZnO 0-15

T1O2 + ZrÜ2 0-15

P2O5 0-10

It will be apparent to those skilled in the art that the invention is not limited to the embodiments illustrated in the figures. Rather, within the scope of the claims varied variations. Thus, the holder shown in Fig. 14 is merely exemplary. It would also be conceivable inter alia to provide a holder which has no strips along the longitudinal edges 12, 13, but is designed frameless and only comprises hinges attached to the pane 1. The glass or glass-ceramic pane can also be used in doors or windows that are not intended for hot aggregates. In general, a glass or glass-ceramic pane according to the invention can be used not only as a pane of a wood-burning stove or a baking oven, preferably as a pane of a door of a stove or oven, but also as an inner lining, in particular an inner lining

Hot aggregate, as a cover, as a cooking table or cooking surface, in particular with an integrated splash guard wall, as an outer lining of chimney or heaters and as Exterior cladding in general, as well as used as a facade element. Yet another application is the inner lining of coating equipment. Here, advantageously, a shock-to-impact shoring at the corners of the coating chamber can be avoided.

LIST OF REFERENCE NUMBERS

Claims

claims

1. glass or glass-ceramic disc (1), in particular as a viewing window for a

Wood-burning stove, wherein the glass-ceramic pane (1) has a single-curved section (3) adjoined by two flat surfaces (5, 7) which due to the connection over the bent section (3) are at an angle of at most 150 ° , preferably at most 120 °, particularly preferably at most 100 °, wherein in the bent portion (3) variations of curvature along the surface in the azimuthal direction of the bent portion (3) in a length range of a length corresponding to the thickness of the glass or glass ceramic Disc up to a quarter of the arc length of the bent portion (3) have an amplitude of at most 0.005 mm- ¹ .

2. glass or glass-ceramic disc (1) according to the preceding claim, characterized in that fluctuations in the curvature in a length range of 2 to 30 mm in the bent portion (3) are less than 0.005 mm- ¹ .

3. glass or glass-ceramic disc (1) according to one of the preceding claims, characterized in that the glass or glass-ceramic disc (1) has a thickness of at least 2 millimeters.

4. glass or glass-ceramic disc (1) according to one of the preceding claims, characterized in that the bent portion (3) has a central

Radius of curvature in the range of 15 to 100 millimeters, corresponding to a curvature in the range of 0.0667 mm- ¹ to 0.01 mm- ¹ , measured on the side (9) of the glass or glass-ceramic disc (1) on which the bent portion (3) is convexly curved.

5. glass or glass-ceramic disc (1) according to one of the preceding claims, characterized in that the curvature of the bent portion (3) whose transitions to the flat surfaces decrease to a value less than 0.0025 mnr ¹ .

6. glass or glass-ceramic disc according to one of the preceding claims, characterized in that the bent portion (3) is bent cylindrically.

7. Glass or glass-ceramic pane according to one of the preceding claims,

characterized by two curved sections (3, 4) with an intermediate flat surface (6).

8. Glass or glass-ceramic pane according to one of the preceding claims,

characterized by at least one of the following features:

the glass of the disk has a quotient T2,3 / T8 of temperature T2,3 at which the viscosity of the glass is 10 ^{2 3} dPa-s, to the temperature T8 at which the viscosity of the glass is 10 ⁸ dPa-s, which is less than 1, 9,

- the glass of the disk has a quotient T2,3 / T8 which is greater than 1, 75,

the glass of the pane has a quotient T2,3 / T9 of the temperature T2,3 at which the viscosity of the glass is 10 ^{2 3} dPa-s, to the temperature T9 at which the viscosity of the glass is 10 ⁹ dPa-s, which is less than 1, 9

- The glass of the disk has a quotient T2.3 / T9, which is greater than 1.85.

- The quotient T2.3 / T9 of the temperatures T2.3 and T13 at the viscosities 10 ^{2 3} dPa-s and 10 ¹³ dPa-s is at a value of at most 2.5.

9. Glass or glass-ceramic pane according to one of the preceding claims, characterized in that for the composition of the glass or the glass-ceramic at least one of the following features applies:

- The glass or glass ceramic contains 3 to 5 weight percent LhO, preferably 3.6 to 3.9 weight percent, and 2 to 4 weight percent Ti0 ₂ , preferably 2.3 to 3.3 weight percent, and 0.8 to 2.2 weight percent Zr0 ₂ , in particular 1, 2 to 1, 8 weight percent.

- The composition contains the following components in weight percent:

LhO 3 - 5, AI2O3 18-25,

Si0 ₂ 55 - 75.

A method of forming a glass sheet (1) in which a glass sheet having a thickness of at least 2 millimeters is provided, and a strip (8) extending from one edge (12) of the glass sheet (1) to the opposite edge (13) heats is softened until it softens, wherein the glass sheet is then bent on the heated and softened strip (8), so that the curved strip produces a simple or uniaxial curvature and the flat surfaces (5, 7) adjacent to the strip are inclined relative to one another wherein the strip (8) is moved across the glass sheet (1) broadening the heated area of the glass sheet (1) transversely to its longitudinal direction, while increasing the inclination of the flat surfaces (5, 7) and widening the bent portion, until the two flat surfaces (5, 7) to each other an angle of at most 150 °, preferably at most 120 °, particularly preferably at most 100 ° incl eat.

1 1. Method according to the preceding claim, characterized in that the glass pane (1) is held stationary while the at least one heating device (19, 20) is guided over the glass pane (1) during bending.

12. The method according to any one of the two preceding claims, characterized in that the bending movement of the glass sheet (1) via a bending device (21) is mediated and after a predetermined coupling of the bending movement of the bending device (21) and the movement of the heating zone generated by a heater (190, 200) relative to the glass pane (1).

13. Method according to the preceding claim, characterized in that at least one of the following conditions applies to the bending movement of the glass sheet:

the bending movement accelerates for more than half the duration of the bending of the glass sheet (1),

- The bending movement accelerates over more than half the way, the one when moving moving part of the glass sheet (1) travels,

- The movement of the heating zone (190, 200) begins in time before the bending movement and ends in time before the stop of the bending movement.

14. Method according to the preceding claim, characterized in that the acceleration of the bending movement is such that the maximum speed is at least a factor of 1.5 greater than the average speed in the time interval of the bending movement, preferably, wherein the bending speed is within an interval of zero , 2 to 3 times the average speed varies.

A method according to any one of claims 12 to 14, characterized in that for a given angle between the flat surfaces (5, 7) of the glass sheet (1), the bending speed is set in dependence on the mean radius of curvature of the bent portion (3) with a reduction of the mean radius of curvature, a higher average bending speed is selected.

16. The method according to any one of the preceding claims, wherein from the glass pane, a glass ceramic pane is produced by the glass pane (1) inserted into a mold (25) with two mutually angled bearing surfaces, so that the

Glass pane 1 with its flat surfaces (5, 7) rests on the bearing surfaces (27, 29) and guided together with the mold through a Keramisierungsofen, wherein the glass of the glass pane (1) converts into a glass ceramic.

17. door (40) for a hot aggregate, comprising a glass or glass ceramic pane (1) according to one of claims 1 to 5, with a holder (44) for pivotally mounting the door (40) on the hot aggregate such that the glass - or glass-ceramic disc 1 when opening and closing the door at one of its along the curved portion (3), in particular parallel to this curved portion (3) extending transverse edges (14, 15) is pivoted.

18. The door (40) according to the preceding claim, wherein the transverse edge (15) of the glass or glass-ceramic pane (1) remote from the pivot axis (50) of the holder (44) is not supported by the holder (44).

19. Stove (11) with a door (40), wherein the door is a glazing with a glass or

Glass-ceramic pane (1) according to claim 1, wherein the glazing extends around an edge (42) of the body (41) of the stove (11) and wherein the edge (42) through the bent portion (3) of the glass or glass ceramic Slice (1) is continued.

20. Use of a glass or glass-ceramic pane (1) according to one of claims 1 to 9 as a pane of a stove or a baking oven, preferably as a pane of a door of a stove or oven, as an inner lining, in particular inner lining of a hot aggregate, as a cover, as Cooking table or cooking surface, in particular with an integrated splash guard wall, as

Exterior cladding of chimney or heating appliances and as external cladding in general, as facade element, as inner lining of coating plants.