Flat glass and methods for manufacturing flat glass

Abstract

Method for selecting a sealing compound for sealing recesses and / or depressions (11) in a device (1) for producing flat glass with a processing temperature -VA - of more than 1,100 °C, in particular more than 1,200 °C, in particular more than 1,250 °C, in particular more than 1,300 °C, comprising the steps - Provide (S1) at least one sealing mass (SM1, SM2, SM3, SM4), - Provision (S2) of at least one test specimen per closure mass (SM1, SM2, SM3, SM4), - Measuring (S3) a first length of the respective test specimens along at least one spatial direction, - Heating (S4) the respective test specimens to a predetermined temperature for a predetermined time, - Measuring (S5) a second length of the respective test specimens along at least one spatial direction, - Determining (S6) a length difference between the first and second lengths of the respective test specimen, - Check (S7) the respective length difference of the test specimens to see if the relative length difference is related to the first length of the test specimen. ◯ at a predetermined temperature of 1,400 °C less than 1%, preferably less than 0.5%, and / or ◯ at a predetermined temperature of 1,500 °C less than 2%, in particular less than 1% and If not, the respective closure mass (SM1, SM2, SM3, SM4) will not be taken into account further, and - Select (S8) the sealing compound (SM1, SM2, SM3, SM4) whose test specimen has the smallest relative length difference.

Description

[0001] The invention relates to a method for selecting a sealing compound for closing recesses, depressions or the like in a device for producing flat glass with a processing temperature - VA - of more than 1,100 °C, in particular more than 1,200 °C, in particular more than 1,250 °C, in particular more than 1,300 °C.

[0002] The invention further relates to a trough for hot forming of a flat glass with a processing temperature of more than 1,100 °C, in particular more than 1,200 °C, in particular more than 1,250 °C, in particular more than 1,300 °C.

[0003] The invention further relates to a method for manufacturing a hot forming trough for flat glass with a processing temperature of more than 1,100 °C, in particular more than 1,200 °C, in particular more than 1,250 °C, in particular more than 1,300 °C.

[0004] The invention further relates to a flat glass with a processing temperature of more than 1,100 °C, in particular more than 1,200 °C, in particular more than 1,250 °C, in particular more than 1,300 °C.

[0005] The invention further relates to a method for manufacturing flat glass.

[0006] Production plants for the manufacture of flat glass typically include a steel trough, to which base blocks are attached. These base blocks form the bottom of a tin bath during the flat glass production process. The base blocks are secured to the steel trough by screws. To protect the screw recesses in the base blocks from the tin bath after the blocks are screwed to the steel trough, it is known to fill the recesses with a ceramic sealing compound. This ceramic compound sinters when the tin bath is heated, permanently sealing the recesses and protecting the screws, as is the case, for example, in the production of soda-lime silicate flat glass with a temperature of approximately 1,050 °C.

[0007] In other types of glass, particularly those with a higher softening temperature than the aforementioned soda-lime silicate glass, shrinkage and softening of the sealing compound occurs.

[0008] The disadvantage of this process is that particles are initially released from the sealing compound, rise to the surface, and contaminate the flat glass strip. Subsequently, the sealing compound itself dissolves, rises due to the tin bath above it, and ultimately damages the flat glass strip, leading to costly and time-consuming repairs to the production equipment.

[0009] An object of the present invention is therefore to provide a method for selecting a sealing compound which is simple and quick to carry out, and a sealing compound which is also suitable for the production of glasses with higher VA, in particular with VA of more than 1,100 °C, in particular more than 1,200 °C, in particular more than 1,250 °C, in particular more than 1,300 °C, without the flat glass strip becoming contaminated and without significant shrinkage of the sealing compound.

[0010] Another object of the present invention is to provide a trough for hot forming flat glass and a method for manufacturing a trough that enables simple, fast and cost-effective manufacturing of a trough in order to produce flat glass with few impurities.

[0011] Another object of the present invention is to provide a flat glass and a method for producing a flat glass which enables the production of a flat glass with few impurities despite high VA.

[0012] Another object of the present invention is to provide alternative methods, an alternative tub and an alternative flat glass.

[0013] In one embodiment, the present invention solves the aforementioned problems with a method according to claim 1.

[0014] In a further embodiment, the present invention solves the aforementioned problems with a tub according to claim 5.

[0015] In a further embodiment, the present invention solves the aforementioned problems with a method for manufacturing a tub according to claim 6.

[0016] In a further embodiment, the present invention solves the aforementioned problems with a flat glass according to claim 7.

[0017] In a further embodiment, the present invention solves the aforementioned problems with a method for producing a flat glass according to claim 13.

[0018] One of the advantages achieved is that a sealing compound can be selected simply and reliably, enabling the production of flat glass with minimal, if any, contamination. Surprisingly, it was found that the particle release from the sealing compound into the molten metal, such as molten tin, and ultimately into the flat glass, could be reduced. This resulted not only in less softening but also in a reduced tendency for the sealing plugs to rise from the depressions in the base blocks and damage the flat glass strip. Another advantage is the production of flat glass with minimal contamination. Furthermore, it ensures the reliable operation of a hot-forming furnace for producing flat glass with a high VA (viscosity equivalent).

[0019] The term "adherence" is to be understood in the broadest sense here and includes - Particles that adhere to or are located on the surface of the glass, - Dents or bulges in the surface of the glass caused by temporarily present particles or bubbles, and also - Particles that are partially, but not completely, enclosed by the glass.

[0020] Adhesions can include metallic and / or non-metallic particles. In other words, particles in the form of adhesions have a maximum immersion depth in the glass that essentially corresponds to the particle size.

[0021] The determination of the number and size of the adhesions according to embodiments of the invention can be carried out using the method described below: Visible light is coupled into a glass plate to be examined, made of manufactured flat glass, in a darkened room. The light is directed perpendicular to the thickness of the glass plate, preferably at a straight cut edge and parallel to the area formed by its two largest dimensions (length and width). The particles are identified by reflecting the light off any deposits on, within, or partially embedded in the glass plate. A handheld microscope, such as the PEAK "Wide Stand Microscope," can be used to differentiate between dust particles and deposits embedded in the glass plate, for example, in the size range < 20 µm. The particles and deposits thus optically identified are then visibly marked.The marked glass plate is viewed along the normal to its surface under a light microscope, for example, the Zeiss Axio Imager M2m, with an LD EC Epiplan 50x / 0.55 HD DIC objective and a PI 10x / 2 eyepiece. This allows the adhesions to be classified and their size to be measured. The size of the adhesions refers to their longest visible dimension in the viewing plane. This method of measurement deliberately accepts that three-dimensional adhesions may extend along the optical axis of the microscope at their maximum length during measurement, i.e., along the normal to the viewing plane. In this case, the measured value for the adhesion will be smaller than the actual length of the adhesion, for example, of the crystal or crystallite.

[0022] Are the adhesions per m 2specified and a glass plate has a surface area on one side whose size is more or less than 1 m² 2 If the area is more than 1 m, the adhesions are calculated proportionally. 2 If a substance adheres to the glass plate, the number of adhesions is multiplied accordingly. The surface area of ​​the glass plate is not particularly limited.

[0023] The phrase "no adhesion" referring to an upper limit of the adhesion dimension, for example, "no adhesion with dimensions of 40 µm or less," is to be understood, particularly in the claims, preferably in the description, as meaning that, with the aforementioned detection method for adhesions, an adhesion of the specified dimensions cannot be determined unambiguously, and in particular, no adhesion at all. The phrase "no adhesion" referring to a lower limit of the adhesion dimension, for example, "no adhesion with dimensions of more than 10 µm," is to be understood, particularly in the claims, preferably in the description, as meaning that, with the aforementioned detection method for adhesions, no adhesion of the specified minimum size or larger can be determined, or at least not unambiguously, and in particular, no adhesion at all.

[0024] The term "surface" in the context of a glass plate made from flat glass refers to the respective surface area of ​​the two largest surfaces, which are arranged parallel to each other. Essentially, the glass plate is cuboid in shape, with one dimension (thickness) being significantly smaller than the other two (length and width). Thus, such a glass plate has two large, parallel surfaces—a top and a bottom—and a circumferential edge connecting the top and bottom surfaces. In the claims, and preferably in the description, the "bottom" of the flat glass refers specifically to the surface that was temporarily in contact with molten metal during the production of the flat glass.The underside of the flat glass can be determined in a known manner, for example, in the case of molten tin, by means of a tin-side detector that can identify the tin side of flat or float glass using short-wave UV light. The "top side" of the flat glass is therefore understood, particularly in the claims and preferably in the description, to be the surface that was not in contact with a molten metal during the production of the flat glass, but preferably with a protective gas, for example, a forming gas comprising a mixture of N2 and H2.

[0025] The term "number per square meter" with regard to adhesions refers to the number of adhesions within a predefinable surface area, where the adhesions are counted when viewed perpendicular to one of the two surfaces defined by length and width according to the method described above. Furthermore, particularly in embodiments of the present invention, the adhesions are counted starting from a surface, namely the underside of the glass plate, which is in contact with the molten metal, especially a tin bath, during manufacturing, according to the definition of the term "adhesion" above.

[0026] The following also applies to the number of particles: If, for example, the number of particles per square meter of surface is limited to 30 or fewer within a size range, such as between 125 µm and 500 µm, a glass plate may, for example, have 25 particles per square meter of surface area with a size of 200 µm, any number and size of particles smaller than 125 µm, and any number of particles larger than 500 µm. Conversely, the glass plate mentioned as an example may not have, for example, 40 particles with a size of 200 µm.

[0027] Large deposits can easily be detected using conventional measuring techniques, for example, directly after the glass plate has been manufactured and / or before further processing, and the glass plate can then be completely or partially rejected. The embodiments of the invention described herein can also significantly reduce large deposits.

[0028] Further features, advantages and further embodiments of the invention are described below or become apparent therein.

[0029] According to an advantageous embodiment of the invention, to perform a pressure softening test, the test specimen is heated at a constant rate while a pressure force is applied to it. The advantage of this is a simple and defined pressure softening test and good comparability between different sealing compounds.

[0030] According to a further advantageous embodiment of the invention, the pressure softening test is carried out in accordance with DIN EN ISO 1893, and the determined T2 value is calculated for the respective test specimen. Only one sealing compound is considered for further selection if the difference between the T2 value and the VA (viscosity) is positive, particularly more than 50 °C, and especially more than 100 °C. The advantage of this is that only sealing compounds with a low softening tendency are considered, thus enabling increased reliability of the sealing of the cavities even at higher VA values.

[0031] According to a further advantageous embodiment of the invention, the respective test specimen is provided by heating a sealing compound formed into a test specimen, wherein the heating is carried out to a predetermined temperature for a predetermined time, in particular wherein the predetermined temperature is below the VA, and in particular wherein the predetermined temperature is 1,000 °C and the predetermined time is 4 hours. This allows a test specimen of the respective sealing compound to be provided in a simple and reliable manner in a defined and thus comparable way.

[0032] According to a further advantageous embodiment of the flat glass, the underside of the flat glass has less than 0.5, in particular less than 0.25, preferably no deposits per square meter with a size greater than 0.5 mm. The advantage of this is that a particularly pure glass with few or no larger deposits is provided.

[0033] According to a further advantageous embodiment of the flat glass, the underside of the flat glass has fewer than 35 adhesions, particularly fewer than 30, preferably fewer than 20, and particularly fewer than 10 adhesions per square meter, with a size between 0.125 mm and 0.5 mm, in particular between 0.1 mm and 0.5 mm, preferably between 0.075 mm and 0.5 mm. The advantage of this is that only a few adhesions are present, thus enabling the production of specialty glasses with high purity and high VA (viscosity), which reduces the cleaning effort required for subsequent use of the flat glass.

[0034] According to a further advantageous embodiment of the flat glass, the flat glass has a maximum thickness of 8 mm, in particular 5 mm, and a minimum thickness of 0.3 mm, in particular 0.5 mm, preferably 0.7 mm, in particular 1 mm, preferably 3 mm. The advantage of this is the provision of thin special flat glass with high VA and high quality.

[0035] According to a further advantageous embodiment of the flat glass, the flat glass comprises at least 14 wt.% Al₂O₃, in particular at least 18 wt.%, and at least 1 wt.% Li₂O, in particular at least 3 wt.%. The advantage of this is the provision of a special flat glass of the LAS glass type.

[0036] According to a further advantageous embodiment of the flat glass, it comprises less than 10 wt.% Al2O3, in particular at least 1 wt.% and at most 7 wt.%, and at least 1 wt.%, in particular at least 5 wt.% and at most 15 wt.% boron trioxide B2O3. The advantage of this is the provision of a special flat glass of the borosilicate glass type.

[0037] The adhering material of the flat glass is at least completely free of zirconium and calcium. This means that, for example, flat glass can be supplied with no or minimal particle contamination or adhering material from the tamping or sealing compound, even when using a calcium aluminate sealing compound or a zirconium oxide or zirconium silicate-based sealing compound.

[0038] According to an advantageous embodiment of the process for producing a flat glass, the sealing mass of the tub comprises zirconium, in particular zirconium oxide and / or zirconium silicate, and / or calcium, in particular calcium oxide, wherein if the produced flat glass has adhesions, the adhesions are at least partially, in particular completely, zirconium-free, in particular zirconium oxide-free and / or zirconium silicate-free, and / or calcium-free, in particular calcium oxide-free.

[0039] Further important features and advantages of the invention will become apparent from the dependent claims, the drawings and the accompanying description of the figures based on the drawings.

[0040] It is understood that the features mentioned above and those to be explained below can be used not only in the combination specified, but also in other combinations or on their own, without leaving the scope of the present invention.

[0041] Preferred embodiments and configurations of the present invention are shown in the drawings and are explained in more detail in the following description, wherein identical reference numerals refer to identical or similar or functionally identical components or elements.

[0042] This shows Fig. 1 Steps of a method for selecting a sealing compound according to an embodiment of the present invention; Fig. 2 steps of a process for manufacturing a hot forming trough for flat glass; Fig. 3 steps of a process for manufacturing flat glass; Fig. 4. An overview of the softening tendency of various sealing compounds depending on the temperature; Fig. 5. An overview of the shrinkage of various sealing materials as a function of temperature; Fig. 6 a tub according to an embodiment of the present invention in cross-section; and Fig. 7 a cross-section through a closure element for forming the bottom area of ​​a tub according to an embodiment of the present invention.

[0043] Fig. Figure 1 shows in schematic form the steps of a method for selecting a sealing compound according to an embodiment of the present invention.

[0044] In detail, it shows Fig. 1. Steps of a method for selecting a sealing compound for closing recesses, depressions or the like in a device for the production of flat glass with a processing temperature - VA - of more than 1,100 °C, in particular more than 1,200 °C, in particular more than 1,250 °C, in particular more than 1,300 °C.

[0045] The process includes the following steps: - Provide S1 at least one sealing mass, - Provide S2 of at least one test specimen per closure mass, - Measure S3 of a first length of the respective test specimens along at least one spatial direction, - Heating S4 of the respective test specimens to a predetermined temperature for a predetermined time, - Measure S5 of a second length of the respective test specimens along at least one spatial direction, - Determine S6 a length difference between the first and second lengths of the respective test specimen, - Check S7 of the respective length difference of the test specimens to see if the relative length difference is related to the first length of the test specimen. ◯ at a predetermined temperature of 1,400 °C less than 1%, preferably less than 0.5%, and / or ◯ at a predetermined temperature of 1,500 °C less than 2%, in particular less than 1% and If not, the respective closure mass will not be taken into account further, and - Select S8 of the sealing compound whose test specimen has the smallest relative length difference.

[0046] Fig. Figure 2 shows in schematic form the steps of a process for manufacturing a tub for hot forming of flat glass.

[0047] In detail, it shows Fig. 2 steps of a method for manufacturing a hot forming trough for flat glass with a processing temperature of more than 1,100 °C, in particular more than 1,200 °C, in particular more than 1,250 °C, in particular more than 1,300 °C.

[0048] The procedure includes the following steps - Provide T1 with at least two walls and a floor to form a basin, - Arranging T2 of tub floor and / or wall blocks on the floor and / or walls of the tub, wherein the tub floor and / or wall blocks have recesses for fixing them to the floor and / or wall of the tub, - Fixing T3 of the tub floor and / or wall blocks to the floor and / or wall by means of form-fitting and / or force-fit connecting elements in the recesses, and - Filling T4 of the recesses with a sealing compound selected by a method according to one of claims 1-4.

[0049] Fig. Figure 3 shows in schematic form the steps of a process for manufacturing flat glass.

[0050] In detail, it shows Fig. Three steps of a method for manufacturing a flat glass according to one of claims 7-12.

[0051] The process includes the following steps: - Providing W1 of starting components for the flat glass to be produced, - Providing W2 of a tub, claim 5, - Heating W3 of the provided starting components to provide a glass melt, - Hot forming W4 of the glass melt on a metal melt in the provided tank with a processing temperature of more than 1,100 °C, in particular more than 1,200 °C, in particular more than 1,250 °C, in particular more than 1,300 °C, and - Cooling W5 of the hot-formed glass melt to provide the flat glass.

[0052] Fig. Figure 4 shows an overview of the softening tendency of various sealing compounds depending on temperature and Fig. 5. An overview of the shrinkage of various sealing materials as a function of temperature.

[0053] In Fig. Figure 4 shows the results of pressure softening tests with various known sealing compounds or tamping compounds. Three known tamping compounds, SM1-SM3, with different water contents were subjected to different firing programs. Fig. Figure 5 shows an overview of the shrinkage of various sealing materials as a function of temperature. In addition to the figures already mentioned in Figure 5, the following figures are also shown: Fig. Of the four designated stamping compounds SM1-SM3, another well-known stamping compound is SM4. Fig. 5 additional ones shown.

[0054] The stamping compounds SM1-SM4 have the following basic composition in wt.%: - 15 - 25 % Al2O3 - 0 - 2 % Fe2O3 - 35 - 50 % SiO2 - 0 - 2 % TiO2 - 0 - 3 % CaO - 0 - 1.5% Na2O - 0 - 1.5% K2O - 30 - 40 % ZrO2

[0055] The in the Fig. 4 and Fig. The five designated stamping compounds SM1, SM2, SM3 and SM4 differ in terms of the firing program used: - Firing program 1,000 °C for 4 hours: SM1a, SM2b, SM4a, SM3d, - Firing program 1,200 °C for 4 hours: SM1b, SM2a, SM2c, SM3a, SM3c, SM4b and - Firing program 1,200 °C for 12 hours: SM3b.

[0056] The softening tendency of the sealing compounds SM1-SM3 was determined by means of the pressure softening test. The pressure softening test was performed according to DIN EN ISO 1893 and represents a measure of the deformation behavior of shaped refractory ceramic products under constant pressure and increasing temperature. During the test, a ceramic specimen is heated at a constant rate (5 K / min) while a pressure load (0.2 MPa) is applied to it. The change in length of the specimen is recorded during heating.

[0057] To test the softening tendency of the ramming compounds SM1-SM3, test specimens were first formed from the ramming compounds SM1-SM3 and fired (for example, for 4 hours at 1,000 °C, see Fig. 4, column firing program) from which test specimens for measuring printer softening were produced.

[0058] For a concrete ramming compound used in embodiments of the present invention, particularly in high-temperature float baths, the tendency to deform as a function of temperature can be investigated in this way. The term "high temperature" in relation to a float bath means glass inlet temperatures of more than 1,100 °C, particularly more than 1,200 °C, particularly more than 1,250 °C, and particularly more than 1,300 °C.

[0059] During the measurement, after an initial expansion of the test specimen, a maximum expansion is reached, beyond which the test specimen is compressed by the applied load. The temperature at the beginning of the compression is recorded (see Fig. 4, column “Onset”). Further characteristic temperatures are determined when the sample length, relative to the maximum expansion, has been reduced by 0.5%, 1%, 2% and, if necessary, further percentages (see Fig. 4, columns T 0,5, T1, T2, ...). The higher the characteristic temperatures T n The higher the temperature, the more stable the ceramic under investigation is against deformation at lower temperatures. Suitable tamping compounds SM1-SM3 are, in particular, those used, for example, for sealing the fixing holes of ceramic materials, but which do not soften noticeably at the locally occurring temperatures.

[0060] The selection criterion used is the T2 value determined according to DIN EN ISO 1893. The T2 value should be above the processing temperature of the glass in question (V). A ) are, preferably the difference between T2 and V should be A The temperature should be at least 50 °C, or better yet at least 100 °C.

[0061] The shrinkage caused by post-sintering of the relevant sealing or tamping compounds SM1-SM4 was assessed by determining the sintering shrinkage at elevated temperatures. For this purpose, test specimens were first formed from the tamping compounds SM1-SM4 and, after firing (e.g., 4 hours at 1,000 °C), Fig. 4, column “Firing Program”) test specimens are produced from this for measuring post-sintering. The post-sintering of the ramming compounds SM1-SM4 is evaluated from the length of these test specimens before and after a heat treatment (for example, 24 hours at 1300 °C, 1400 °C, and 1500 °C). The post-shrinkage should be less than 1% at 1400 °C, preferably <0.5%. At 1500 °C, the post-shrinkage should be less than 2%, preferably <1%.

[0062] A suitable mashing mixture can be made from the following: Fig. 4 and Fig. 5. For example, determine the tamping mass SM2.

[0063] Fig. Figure 6 shows a tub according to an embodiment of the present invention in cross-section and Fig. 7 a cross-section through a closure element for forming the bottom area of ​​a tub according to an embodiment of the present invention.

[0064] In detail, a tub 1 for the hot forming of flat glass is shown schematically in cross-section. The tub 1 has at least two walls 2a, 2b and a base 3. Several base blocks 10 are arranged on the base 3 of the tub 1; only two are shown here as examples. These blocks form the base of the tub 1. The wall blocks adjacent to the walls 2a, 2b (not shown) are higher than the base blocks 10 to prevent molten metal in the tub 1 from coming into contact with walls 2a, 2b made of, for example, steel. The base blocks 10 have one or more openings 11. A fixing element 13, such as a screw, bolt, or the like, can be inserted through the openings 11 to fix the base block 10 to the base 3 of the tub 1.To fill the respective opening 11, a tamping mass 12 is then poured into the opening 11, which is then sintered during the ongoing operation of the furnace 1 for flat glass with a processing temperature of more than 1,100 °C, in particular more than 1,200 °C, in particular more than 1,250 °C, in particular more than 1,300 °C and protects the fixing element 13 from the molten metal during the production of the flat glass.

[0065] In summary, at least one embodiment of the present invention provides at least one of the following features or enables at least one of the following advantages: - Use of a ceramic mass for sealing the fixing holes in the bottom bricks of a float bath for the production of flat glass, wherein the post-shrinkage of a mass sample previously fired for 4 hours at 1,000 °C after 24 hours at 1,400 °C is less than 1%, preferably less than 0.5%. - Use of a ceramic mass for sealing the fixing holes in the bottom bricks of a float bath for the production of flat glass, wherein the post-shrinkage of a mass sample previously fired for 4 hours at 1,000 °C after 24 hours at 1,500 °C is less than 2%, preferably less than 1%. - The ceramic mass exhibits a T2 value in a pressure softening test on a mass sample previously fired for 4 hours at 1,000 °C, which is greater than the processing temperature V. A , especially larger than V A +50 °C, preferably larger than V A +100 °C. - Flat glass or floated glass with a VA of at least 1,250 °C with less than 0.5, in particular less than 0.25, preferably no adhesions per square meter with a size of more than 0.5 mm. - Flat glass or floated glass with a VA of at least 1,250 °C with fewer than 40 adhesions per square meter with a size of less than 0.2 mm, in particular less than 0.15 mm, preferably less than 0.125 mm. - Flat glass with a maximum thickness of 8 mm, in particular 5 mm, and a minimum thickness of 0.3 mm, in particular 0.5 mm, preferably 0.7 mm, in particular 1 mm, preferably 3 mm. - Reliable and therefore cost-effective production of flat glass with high VA, especially with a VA of more than 1,250 °C. - Fewer impurities or defects in the flat glass, especially on the underside. - Reduction of particle release from the sealing compound or the tamping compound onto the flat glass during manufacturing.

[0066] Although the present invention has been described using preferred embodiments, it is not limited to these, but can be modified in many ways.

Claims

[1] Method for selecting a sealing compound for sealing recesses and / or depressions (11) in a device (1) for producing flat glass with a processing temperature -VA - of more than 1,100 °C, in particular more than 1,200 °C, in particular more than 1,250 °C, in particular more than 1,300 °C, comprising the steps - Provide (S1) at least one sealing mass (SM1, SM2, SM3, SM4), - Provision (S2) of at least one test specimen per closure mass (SM1, SM2, SM3, SM4), - Measuring (S3) a first length of the respective test specimens along at least one spatial direction, - Heating (S4) the respective test specimens to a predetermined temperature for a predetermined time, - Measuring (S5) a second length of the respective test specimens along at least one spatial direction, - Determining (S6) a length difference between the first and second lengths of the respective test specimen, - Check (S7) the respective length difference of the test specimens to see if the relative length difference is related to the first length of the test specimen. ◯ at a predetermined temperature of 1,400 °C less than 1%, preferably less than 0.5%, and / or ◯ at a predetermined temperature of 1,500 °C less than 2%, in particular less than 1% and If not, the respective closure mass (SM1, SM2, SM3, SM4) will not be taken into account further, and - Select (S8) the sealing compound (SM1, SM2, SM3, SM4) whose test specimen has the smallest relative length difference. [2] Method according to claim 1, wherein, to carry out a pressure softening test, the specimen is heated at a constant rate and a pressure force is applied to the specimen during this process. [3] Method according to claim 2, wherein the pressure softening test is carried out in accordance with DIN EN ISO 1893 and the determined T2 value is determined for the respective test specimen and wherein only one sealing mass (SM1, SM2, SM3, SM4) is further considered for selection if the difference between the T2 value and the VA is positive, in particular more than 50 °C, in particular more than 100 °C. [4] Method according to one of claims 1-3, wherein the provision of the respective test specimen is carried out by heating a sealing mass formed into a test specimen, wherein the heating is carried out to a predetermined temperature for a predetermined time, in particular wherein the predetermined temperature is below the VA, in particular wherein the predetermined temperature is 1,000 °C and the predetermined time is 4 hours. [5] Tub (1) for hot forming a flat glass with a processing temperature of more than 1,100 °C, in particular more than 1,200 °C, in particular more than 1,250 °C, in particular more than 1,300 °C, comprising a wall (2a, 2b) and a bottom region (3), wherein recesses and / or depressions (11) are arranged in the wall (2a, 2b) and / or bottom region (3), which are closed by means of a sealing compound (SM1, SM2, SM3, SM4) selected by a method according to one of claims 1-4, wherein the sealing compound (SM1, SM2, SM3, SM4) is in contact with a molten metal in the tub (1). [6] Method for producing a hot forming tub (1) for flat glass with a processing temperature of more than 1,100 °C, in particular more than 1,200 °C, in particular more than 1,250 °C, in particular more than 1,300 °C, comprising the steps - Providing (T1) at least two walls (2a, 2b) and a floor (3) to form a trough (1), - Arranging (T2) tub floor (10) and / or wall blocks on the floor (3) and / or walls (2a, 2b) of the tub (1), wherein the tub floor (10) and / or wall blocks have recesses (11) for fixing them to the floor (3) and / or wall (2a, 2b) of the tub (1), - Fixing (T3) the tub floor (10) and / or wall blocks to the floor (3) and / or wall (2a, 2b) by means of form-fit and / or force-fit connecting elements (13) in the recesses (11), and - Filling (T4) the recesses (11) with a sealing compound (SM1, SM2, SM3, SM4) selected by a method according to one of claims 1-4. [7] Flat glass with a processing temperature of more than 1,100 °C, in particular more than 1,200 °C, in particular more than 1,250 °C, in particular more than 1,300 °C, preferably produced using a tank (1) according to claim 5, wherein the flat glass has a top and a bottom surface and the flat glass has on the bottom surface adhesions in a number of 40 or less in a size between 0.125 mm and 0.5 mm, preferably between 0.1 mm and 0.5 mm, in particular between 0.075 mm and 0.5 mm, per square meter before the application of a cleaning process and wherein the adhesions are completely free of zirconium and calcium. [8] Flat glass according to claim 7, wherein the flat glass has less than 0.5, in particular less than 0.25, preferably no adhesions per square meter with a size of more than 0.5 mm on the underside. [9] Flat glass according to one of claims 7-8, wherein the flat glass has on the underside less than 35 adhesions, in particular less than 30 adhesions, preferably less than 20 adhesions, in particular less than 10 adhesions per square meter, in a size between 0.125 mm and 0.5 mm, preferably between 0.100 mm and 0.5 mm, in particular between 0.075 mm and 0.5 mm per square meter. [10] Flat glass according to one of claims 7-9, wherein the flat glass has a maximum thickness of 8 mm, in particular 5 mm, and a minimum thickness of 0.3 mm, in particular 0.5 mm, preferably 0.7 mm, in particular 1 mm, preferably 3 mm. [11] Flat glass according to one of claims 7-10, comprising at least 14 wt.% Al2O3, in particular at least 18 wt.%, and at least 1 wt.% Li2O, in particular at least 3 wt.%. [12] Flat glass according to one of claims 7-10, comprising less than 10 wt.% Al2O3, in particular at least 1 wt.% and at most 7 wt.%, and at least 1 wt.%, in particular at least 5 wt.% and at most 15 wt.%, boron trioxide B2O3. [13] Method for producing a flat glass according to any one of claims 7-12, comprising the steps - Providing (W1) of starting components for the flat glass to be produced, - Providing (W2) a tub (1) according to claim 5, - Heating (W3) the provided starting components to provide a glass melt, - Hot forming (W4) of the glass melt with a processing temperature of more than 1,100 °C, in particular more than 1,200 °C, in particular more than 1,250 °C, in particular more than 1,300 °C, on a metal melt in the provided tank (1) and - Cooling (W5) of the hot-formed molten glass to provide the flat glass. [14] Method according to claim 13, wherein the sealing mass of the tub (1) comprises zirconium, in particular zirconium oxide and / or zirconium silicate, and / or calcium, in particular calcium oxide, and wherein if the produced flat glass has adhesions, the adhesions are at least partially, in particular completely, zirconium-free, in particular zirconium oxide-free and / or zirconium silicate-free, and / or calcium-free, in particular calcium oxide-free.

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