METHOD FOR CONTINUOUSLY PRODUCING GLASS INGOTS COMPOSITE OPTICAL GLASS COMPOSITIONS - Patent application

Abstract

To provide a method and apparatus for continuously manufacturing a glass ingot according to a continuous casting method.SOLUTION: A method and apparatus for continuously manufacturing a glass ingot comprises: supplying liquid dissolution optical glass from a supply device (3) to a die (5); forming a glass strand (6) supplied to a cooler (9) through a conveyer belt (7) and supplied to a cutting device; and dividing the cooled glass strand (6) in the cutting device to form an individual glass ingot (2). In this case, the projection of the outer shell of the glass strand (6) is continuously required by a non-contacted measuring device (10) before supplying the glass strand (6) to the cooler (9) at the latest, and parameters, i.e., the temperature of the supply device and / or the speed of the conveyer belt are controlled on the basis of the obtained value.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method and apparatus for continuously producing glass ingots, in particular glass ingots made of optical glass compositions. According to a further aspect, the present invention relates to the glass ingots and further to the use of the glass ingots for producing optical elements. [Background technology]

[0002] The production of glass ingots, in particular optical glass, is basically known from the prior art and is typically carried out by a horizontal continuous casting method, in which liquid molten glass is taken from a feeder and fed into a mold, a so-called ingot withdrawal shaft, into which the liquid molten glass, usually fed centrally, spreads out in the width direction and forms glass strands, which are then fed via a transport device, for example a conveyor belt, to a cooling device.

[0003] In the case of ingot production, the quality requirements are particularly important in terms of geometric accuracy of the ingot cross section, prevention of cracks and indentations, and the highest possible optical homogeneity without schlieren.

[0004] In particular, achieving the highest possible optical homogeneity is currently not possible solely through process technology, since there are no measuring devices that allow direct control of the process.

[0005] Until now, the measurement methods known from the prior art have only been able to perform measurements intermittently at the end of the manufacturing process, i.e., after the glass strand has passed through a heat treatment furnace and been divided into individual glass ingots. However, measurements at the cold end of the glass strand result in measurement wastage due to the passage time through the heat treatment furnace, which can range from several minutes to several hours. Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention is therefore based on the object of providing a method and an apparatus that overcomes the drawbacks of the prior art, and in particular, to provide a method and an apparatus that allows the production of glass ingots with the highest possible homogeneity. [Means for solving the problem]

[0007] According to the invention, this problem is solved by a method having the features set forth in the claims.

[0008] The dependent claims describe further advantageous embodiments of the invention. The features described individually in the dependent claims can be combined with one another in a technically meaningful manner, and these features define further embodiments of the invention. In addition, the features described in the respective claims are specifically and precisely defined and explained in the description, thereby indicating further preferred embodiments of the invention.

[0009] The method according to the present invention is suitable for the continuous production of glass ingots of a glass composition and is carried out according to the continuous casting method. In this process, liquid molten glass is first fed from a feeder into a mold to form a glass strand. This glass strand is then fed via a conveying device, in particular a conveyor belt, to a cooling device and then to a cutting device, where the cooled glass strand is split into individual glass ingots. The present invention proposes that, at the latest before the glass strand is fed into the cooling device, a projection of the outer dimensions of the glass strand is continuously determined by a contactless measuring device, and parameters, i.e., the feeder temperature and / or the conveying speed, in particular the conveyor belt speed, are adjusted based on the values ​​obtained.

[0010] The invention also relates to an apparatus for continuously producing glass ingots of a glass composition. The apparatus comprises a feeder for feeding liquid molten glass into a mold, preferably a bath or a channel, so that a glass strand is formed; a conveying device, in particular a conveyor belt, for conveying the glass strand; a cooling device for cooling the glass strand; and a cutting device by which the cooled glass strand can be divided into individual glass ingots. The invention proposes that the apparatus comprises a measuring device arranged upstream of the cooling device, by means of which the projection of the outer dimensions of the glass strand, in particular of the glass strand present on the conveying device, can be determined continuously and without contact, and parameters, namely the feeder temperature and / or the conveying speed, can be adjusted based on the values ​​thus obtained.

[0011] The basic realization on which the present invention is based is that, insofar as it is possible to achieve glass ingots with particularly high homogeneity, particularly with regard to the height and refractive index of the ingots, by continuously monitoring the maximum elongation of the hot glass strand, it is possible to stabilize the process by directly following and adjusting the parameters.

[0012] Preferably, the individual glass ingots have a refractive index nD dispersion of at most 0.001 per ingot at 589 nm, and more preferably at most 6*10 per ingot. -4 , very particularly preferably up to 3*10 per ingot -4, or even have a dispersion of a refractive index nD of up to 0.0001 per ingot. The refractive index dispersion is the difference between the maximum refractive index measured within an ingot and the minimum refractive index measured. The refractive index can be measured, for example, by measuring the refractive index at at least 4, at least 8, at least 12, or at least 20 points, particularly evenly distributed throughout the ingot. A refractive index that is as homogeneous as possible is advantageous, especially for optical applications of glass, because particularly precise optical elements can be produced from such ingots.

[0013] According to one embodiment, the projection of the outer dimensions of the glass strand is determined by the measuring device used in accordance with the present invention. If the formed glass strand has a sufficient specific illumination coefficient and emits light, this light can be detected by the measuring device. In the case of glass that does not have a sufficient specific illumination coefficient, it is advantageous to use an illumination means. In this case, a distinction must be made between transparent and opaque optical glasses in the visual field.

[0014] In one embodiment, for example, in the case of transparent glass, a focusing light source, such as a white LED light source, is oriented so that it is focused onto the point of the supply device. The transparency of the glass allows for the use of photoconductivity. Light captured by the light source in the glass strand emerges and can thus be detected.

[0015] According to another embodiment, for example in the case of opaque glass, i.e. glass that absorbs light in the visual range, the light source is oriented in such a way that illumination that produces stripes is possible, in particular so that the contrast between the background and the illuminated glass strands is maximized.

[0016] "Opaque" glass is glass that has a transmittance of less than 10% over the spectral range of 380-780 nm under the conditions of the method according to the invention at the observation position. Transmittance is the ratio of the intensity of light incident at the measuring device to the intensity of light emitted from the light source in the direction of the measuring device. The transmittance of glass at the observation position can be easily determined if the net transmittance of the glass is known. Glass with a relatively high transmittance is considered "transparent" herein.

[0017] Alternatively, lighting means in the near-infrared or ultraviolet range can also be used to illuminate the glass strands, especially if the glass has a transmittance of at least 10% under the aforementioned conditions in the respective wavelength ranges.

[0018] Preferably, the measuring device or measuring direction is arranged substantially perpendicular to the longitudinal axis of the glass strand so that the elongation of the glass strand in the height direction can be determined. One or more measuring devices can be used. Alternatively or additionally to a measuring device having a measuring direction substantially intersecting the longitudinal axis of the glass strand, a second measuring device can be used. The second measuring device can also have a measuring direction substantially perpendicular to the longitudinal axis of the glass strand. However, other arrangements of one or more measuring devices are also in accordance with the invention. In particular, when two or more measuring devices are used, triangulation can be performed. For example, the thickness of the glass strand can be determined across the entire width, i.e., at various measuring points along the width of the glass strand.

[0019] According to one embodiment, at least one measuring device is oriented such that the measuring device can capture the width of the glass strand, for example, one measuring device can be positioned substantially above the glass strand.

[0020] In one embodiment, it is proposed that the contactless measuring device is an optical measuring device, particularly preferably formed in the form of a CMOS camera.

[0021] The further optical measuring device for determining the projection of the outer dimensions of the glass strand preferably comprises a confocal interferometer or a laser device, which according to one embodiment determines the projection of the outer dimensions of the glass strand according to a triangulation method. The laser device can use one or more wavelengths, the projection images of which can optionally be formed as a point or a line.

[0022] According to a further advantageous embodiment, the measuring device is a radiometric measuring device for measuring the absorption of beta rays and / or an ultrasound-based measuring device, such as for example an ultrasound ToF.

[0023] According to a particularly preferred embodiment, the external dimensions of the glass strand are determined using image processing with the aid of a threshold derivative of the contrast. The determined data can be displayed, for example, to an operator.

[0024] In this way, by measuring the outer dimensions or the elongation of the glass strand at the latest before the hot glass strand is fed into the cooling device, i.e., immediately before or immediately after forming, it is possible to derive direct measured quantities, such as the maximum outer dimension of the glass strand in the direction across the drawing or conveying device or the change in the maximum elongation of the glass strand over time in a continuous process, and / or indirect measured quantities assuming further boundary conditions. The indirect measured quantity is the volume flow if the glass strand width and conveying speed are predetermined, or the mass flow if the thickness is predetermined. Continuous monitoring thus makes it possible to keep the volume flow, mass flow, and / or extrusion rate constant.

[0025] According to one embodiment, the glass is 10 4 ~10 13The external dimensions of the glass strand are determined in a section of the manufacturing process that has a temperature corresponding to the viscosity in dPas. The viscosity of the glass is temperature dependent. The relationship between viscosity and temperature is described using the VFT curve (Vogel-Fulcher-Tammann equation). If this relationship is not known for a particular glass, the viscosity measurement can be determined according to the section of DIN ISO 7884 that is applicable to the particular viscosity range.

[0026] Thus, by continuously monitoring the stretching of the glass strands, oversizing is reduced and understretching of the glass strands is prevented, as well as reducing height variations along the ingot.

[0027] This measurement device therefore reduces dead time and allows the dimension quantity to be controlled by the transport or withdrawal speed and / or the supply device temperature. This allows for direct control of the glass ingot, resulting in particularly high refractive index constancy and low schlieren formation. It has also been found that the glass ingot has a particularly low susceptibility to breakage.

[0028] The term "fracture vulnerability" refers to the brittleness that is sought in a glass strand that is still hot and present on a conveying device. To determine the fracture vulnerability, a metal measuring probe is used to form cracks in the still hot glass strand by touching the glass strand with the measuring probe. In this case, the cracks occur due to the spontaneous temperature difference between the metal measuring probe, which is heated to room temperature, and the hot glass strand, which is about 300°C. Surprisingly, it has been found that the cracks formed by the metal measuring probe can be reduced by up to 15%, preferably up to 25%, compared to glass strands produced according to conventional methods.

[0029] Since the use of measuring contacts can damage the ingot, the method of the present invention preferably does not use such contacts. Rather, the advantage of this method is that the dimensions of the ingot can be determined without using measuring contacts. This further reduces the risk of damage to the ingot, which is certainly reduced but still exists.

[0030] According to a further preferred embodiment, the glass strand is guided through a roller device with at least one bottom roller and at least one top roller before being measured with the contactless measuring device, thus forming a rolled glass strand. In this embodiment, the projection of the outer dimensions of the rolled glass strand is continuously determined using the contactless measuring device. Based on the obtained values, the parameters of the feeder temperature and / or the conveyor belt speed, as well as the parameter of the distance between the bottom roller and the top roller, are adjusted.

[0031] According to one advantageous embodiment, the determined extension of the glass strand is displayed, for example, to an operator, who then adjusts (e.g., manually) one of the following parameters based on a control map: the feeder temperature, the conveyor belt speed, and / or the spacing between the bottom and top rollers. Alternatively, one or more of these parameters can be adjusted automatically via a control loop.

[0032] According to a further aspect, the present invention relates to a glass ingot that can be produced in particular according to the method according to the invention, which has a dispersion of the refractive index nD at 589 nm of at most 0.001 per ingot, and more preferably at most 6*10 per ingot. -4 , very particularly preferably up to 3*10 per ingot -4, or even have a dispersion of a refractive index nD of up to 0.0001 per ingot. The refractive index dispersion is the difference between the maximum refractive index measured within an ingot and the minimum refractive index measured. The refractive index can be measured, for example, by measuring the refractive index at at least 4, at least 8, at least 12, or at least 20 points, particularly evenly distributed throughout the ingot. A refractive index that is as homogeneous as possible is advantageous, particularly for optical applications of glass, because particularly precise optical elements can be produced from such ingots. Preferably, the glass ingot can be produced according to the method described herein.

[0033] The glass ingot according to the invention is advantageously distinguished by excellent geometrical properties, in particular the format dispersion of the glass ingot over both the width and the length. V is the maximum width of the ingot B max and minimum width B min The difference between the length dispersion L V is the maximum length of the ingot L max and minimum length L min The relative width dispersion is the difference between B V / (0.5*(B max +B min )). The relative length dispersion is L V / (0.5*(L max +L min )) is.

[0034] Preferably, the glass ingot has a width dispersion of at most 4.0 mm, more preferably at most 3.0 mm, very particularly preferably at most 2.0 mm or at most 1.0 mm. The relative width dispersion is preferably less than 2.0%, in particular less than 1.0%. Advantageously, the length dispersion is at most 4.0 mm, more preferably at most 3.0 mm, and most preferably at most 2.0 mm. The relative length dispersion is preferably less than 1.0%, in particular less than 0.7% or less than 0.5%.

[0035] According to one embodiment, the average width of the ingot (0.5*(B max +B min )) is at least 50 mm, in particular at least 70 mm or at least 100 mm. The average width may be at most 500 mm, at most 300 mm or at most 200 mm. According to one embodiment, the average length of the ingot (0.5*(L max +L min )) is at least 100 mm, in particular at least 150 mm or at least 200 mm. The average length may be at most 2000 mm, at most 1000 mm or at most 500 mm.

[0036] In the case of the manufacturing method described herein, the length of the ingot can be easily achieved by appropriately separating the produced strands to the desired length. The width can also be adjusted relatively easily based on the width of the ingot shaft, as required. In contrast, controlling the height, or adjusting it to a height as constant as possible, is much more demanding and is only possible using the control of the method based on contactless measurement described herein. This method therefore makes it possible to obtain ingots with extremely small height dispersion. The height dispersion H V is the standard deviation of the ingot height of one ingot. This can be measured, for example, by measuring the thickness of the ingot at at least 4, at least 8, at least 12, or at least 20 points, particularly evenly distributed over the ingot. The relative height dispersion is the standard deviation of the ingot height. HighThe relative height variance is the quotient of the height variance and the average height (expressed as a percentage). The average height is the arithmetic mean of the height values ​​measured to determine the standard deviation. According to one embodiment, the relative height variance of the ingots is not higher than 3.0%, not higher than 2.0%, not higher than 1.5%, or not higher than 1.25%. Optionally, the relative height variance can be in the range of 0.1-3.0%, or at least 0.5%. Ingots with such a small relative height variance are eminently suitable for optical applications. The height of the ingots can be, for example, at least 10 mm or at least 15 mm. Optionally, the height can be up to 400 mm, in particular up to 300 mm, or up to 200 mm.

[0037] The glass is preferably an optical glass, i.e., the glass is intended for optical applications, where even small dispersions in the properties of the glass can lead to serious defects in demanding optical applications.

[0038] Preferably, the glass composition is selected from the group consisting of fluorine-containing glasses, phosphate-containing glasses, fluorophosphate glasses, phosphate glasses, boron-containing glasses, silicon-containing glasses, and / or lead-containing glasses. According to a particularly preferred embodiment, the glass ingot, or the glass produced from the glass ingot, has the following composition (in wt. % on an oxide basis): [Table 1]

[0039] These glasses may contain small amounts of Sb2O3 and / or As2O3, for example less than 0.1 wt. %, less than 0.03 wt. %, or less than 0.01 wt. %, respectively.

[0040] The following table shows preferred percentage ranges for glasses that can be used in accordance with the present invention. [Table 2]

[0041] The glass preferably contains P2O5 in a content of at least 1% by weight, preferably at least 5% by weight or at least 10% by weight, although the glass is preferably limited with respect to the maximum P2O5 content: the glass therefore preferably contains at most 60% by weight of P2O5, preferably at most 30% by weight, more preferably at most 25% by weight or at most 15% by weight of P2O5.

[0042] Furthermore, the glass preferably contains BaO in a content of at least 1% by weight, or at least 5% by weight, preferably at least 10% by weight. However, the glass is preferably limited with respect to the maximum BaO content. The glass therefore preferably contains at most 60% by weight of BaO, preferably at most 50% by weight, and even more preferably at most 45% by weight of BaO. Optionally, the BaO content is at most 30% by weight or at most 20% by weight.

[0043] Furthermore, the glass preferably contains at least 5% by weight of fluorine, preferably at least 10%, at least 15% or at least 25% by weight, although the glass is still preferably limited in terms of its maximum fluorine content. The glass therefore preferably contains at most 50% by weight of fluorine, preferably at most 45% by weight, more preferably at most 40% or at most 35% by weight.

[0044] The glass can contain SiO2, but the proportion must not be too high, since otherwise crystallization and devitrification may occur. The SiO2 content is therefore preferably at most 10% by weight, more preferably at most 5% by weight, and even more preferably at most 1% by weight. Very particularly preferably, the glass is SiO2-free.

[0045] Additionally, the glass may contain Al2O3. Preferably, the content is at least 1 wt%, more preferably at least 2 wt%, at least 5 wt%, or at least 10 wt%. However, too much Al2O3 is undesirable, since otherwise the mixture will not dissolve well and the glass will have an increased tendency to crystallize. Therefore, the glass preferably has an Al2O3 content of at most 30 wt%, preferably at most 25 wt%, more preferably at most 20 wt% or at most 15 wt%.

[0046] Preferably, the glass contains 0 to a maximum of 10% by weight of B2O3, preferably 0 to a maximum of 5% by weight. Even more preferably, the glass contains a maximum of 1% by weight of B2O3. Very particularly preferably, the glass is free of B2O3.

[0047] Preferably, the glass contains from 0 to a maximum of 15% by weight of alkali metal oxides, preferably from 0 to a maximum of 10% by weight or up to 5% by weight. More preferably, the glass contains a maximum of 1% by weight of alkali metal oxides. Very particularly preferably, the glass is free of alkali metal oxides.

[0048] Preferably, the glass contains 0 to a maximum of 10% by weight of MgO, more preferably 1 to a maximum of 5% by weight, or 2 to 4% by weight, which can lower the melting temperature of the glass.

[0049] Preferably, the glass contains 0 to a maximum of 25% by weight of CaO, preferably 1 to a maximum of 20% by weight, or 5 to 10% by weight, since otherwise crystallization may occur.

[0050] The glass may contain SrO, preferably in an amount of up to 30% by weight, more preferably from 1 to up to 25% by weight, and even more preferably from 5 to up to 25% by weight, since otherwise crystallization may occur. Optionally, the SrO content may be at least 10% by weight, or at least 15% by weight, and / or up to 25% by weight.

[0051] According to one embodiment, the glass contains a relatively high proportion of alkaline earth metal oxides (MgO, CaO, BaO, SrO), in particular at least 25%, at least 30%, or at least 35% by weight of alkaline earth metal oxides. The proportion of these components can be limited to a maximum of 60% or a maximum of 50% by weight. Glasses containing such constituents are extremely well suited as optical glasses for demanding applications.

[0052] The glass may further contain CuO, preferably in an amount of up to 10% by weight, more preferably from 0 to up to 5% by weight, even more preferably from 0 to up to 1% by weight, optionally 1 to 7% by weight or 2 to 5% by weight.

[0053] Preferably, the glass contains La2O3 in a content of 0 to a maximum of 10% by weight, preferably in a content of 0 to a maximum of 5% by weight, very particularly preferably in a content of 0 to a maximum of 1% by weight.

[0054] Preferably, the glass contains Gd2O3 in a content of 0 to a maximum of 15% by weight, preferably 0 to a maximum of 10% by weight.

[0055] Preferably, the glass contains Y2O3 in a content of 0 to a maximum of 15% by weight, preferably 0 to a maximum of 10% by weight.

[0056] Preferably, the glass contains Nb2O3 in a content of 0 to a maximum of 10% by weight, preferably 0 to a maximum of 5% by weight.

[0057] The glass is preferably free of Pb, Cd, Ni and / or As due to the toxicity and ecological concerns of these elements.

[0058] When a glass is described herein as being free of a certain component or as not containing a particular component, what is meant by this is that the component may possibly be present in the glass as an impurity. This means that the component is not present in a major amount and / or is not added to the glass as a glass component. A minor amount, according to the present invention, is an amount less than 1000 ppm, preferably less than 500 ppm, and most preferably less than 100 ppm.

[0059] Preferably, the glass is also free of components not listed herein as glass constituents.

[0060] Preferably the glass has a refractive index n of at least 1.40. d and more preferably has a refractive index n of at least 1.45 d and more preferably a refractive index n of at least 1.50. d However, the refractive index preferably does not exceed a value of 2.0, more preferably a value of 1.80, and even more preferably a value of 1.70.

[0061] Preferably, the glass has a mean coefficient of linear thermal expansion of 4.5 to 13.7 ppm / K, more preferably 4.5 to 6.5 ppm / K, and even more preferably 5.0 to 6.0 ppm / K or 6.0 to 13.0 ppm / K. "Coefficient of thermal expansion" or "CTE" refers to the mean coefficient of linear thermal expansion within the temperature range of 20°C to 300°C. It is defined in accordance with DIN ISO 7991:1987.

[0062] The internal transmittance of a glass is preferably greater than 60%, more preferably greater than 85%, more preferably greater than 90%, more preferably greater than 93%, and even more preferably greater than 95% for a 10 mm sample thickness in the wavelength range of 400 nm to 600 nm. The term "internal transmittance" (English: "Internal Transmission") refers to the light transmittance without reflection losses. The internal transmittance or internal transmission can be measured by methods well known to those skilled in the art, for example, according to DIN 5036-1:1978. In this specification, the internal transmittance is related to a 10 mm sample thickness. The "sample thickness" does not imply that the glass or glass ingot has this thickness, but merely indicates the thickness to which the internal transmittance is related.

[0063] Unless otherwise stated or apparent to one skilled in the art, measurements described herein are made at 20° C. and a pressure of 101.3 kPa.

[0064] According to these yet further aspects, the present invention also relates to the use of a glass ingot according to the invention for producing optical elements selected from the group consisting of lenses, prisms, light guide rods, arrays, optical fibers, gradient elements and optical windows in the fields of imaging, sensor mechanisms, microscopy, medical technology, digital projection, telecommunications, optical communication / information transmission, optics / lighting in the automotive sector, as well as solar technology, photolithography, steppers, excimer lasers, wafers, computer chips and / or integrated circuits and electronic devices containing such circuits and chips.

[0065] The present invention and the technical environment will be described in detail below with reference to the drawings. It should be noted that the present invention is not limited to the illustrated embodiments. In particular, unless explicitly stated otherwise, partial aspects of the matters described in the drawings can be extracted and combined with other components and concepts belonging to this specification and / or the drawings. It should be particularly noted that the drawings and particularly the illustrated size ratios are merely approximate. The same reference numerals represent the same objects, and therefore, descriptions belonging to other drawings can be used complementary as necessary. [Brief explanation of the drawings]

[0066] [Figure 1] 1 shows a highly simplified schematic diagram of one embodiment of the device according to the invention; [Figure 2] 2 is a partial perspective view of the embodiment shown in FIG. 1; FIG. [Figure 3] FIG. 2 shows the refractive index value profile over time in minutes for the manufacturing process for a fluorophosphate glass described herein. DETAILED DESCRIPTION OF THE INVENTION

[0067] It should be noted that the drawings are merely schematic in nature and are used solely for the understanding of the invention. Identical elements are provided with identical reference numerals. The various features of the various embodiments can in principle also be combined with one another in any way.

[0068] In FIG. 1, an embodiment of a device 1 according to the invention is shown in a highly simplified schematic manner.

[0069] The apparatus 1 is suitable for the continuous production of glass ingots 2, for example consisting of an optical glass composition, and includes a feed device 3 for feeding liquid molten glass 4 into a mold 5, for example into a bath or a groove. In the illustrated embodiment, the liquid molten glass 4 is fed centrally into the mold 5 and spreads across its width within the mold, thus forming glass strands 6. As can be seen from FIG. 1 , the glass strands 6 are subsequently fed via a conveyor belt 7 in the direction of arrow 8 to a cooling device 9, for example a heat treatment furnace, where the still-hot glass strands 6 are cooled. The embodiment illustrated in FIG. 1 further includes a cutting device (not shown), where the cooled glass strands 6 are subsequently separated into individual glass ingots 2.

[0070] According to the invention, it is proposed that the device 1 has an optical measuring device 10 arranged before the cooling device 9, by means of which the projection of the outer shell of the glass strand can be determined continuously and without contact, and that the parameters, i.e. the feeder temperature and / or the conveying speed, can be adjusted based on the values ​​thus obtained. It is preferably proposed that the measuring device 10 or the measuring direction be arranged transversely to the longitudinal axis of the glass strand 6 (FIG. 2).

[0071] Figure 2 shows a partially excerpted view of the embodiment shown in Figure 1 in a very simplified, schematic perspective view. This view shows, in particular, the arrangement of a measuring device 10, which preferably includes a CMOS camera, relative to the glass strand 6. As can be seen in detail in Figure 2, the measuring device 10 is arranged laterally of the glass strand 6 as follows: the line of sight 11 of the measuring device 10 is oriented perpendicular to the longitudinal axis of the glass strand 6, and therefore the measuring direction is also essentially perpendicular to the glass strand 6.

[0072] A measuring device 10, preferably in the form of a CMOS camera, can be used to determine the projection of the outer shell of the glass strand 6, since the formed glass strand 6 has a sufficient intrinsic illumination coefficient and emits light 12, which is detected by the measuring device 10.

[0073] An exemplary refractive index profile over time (in minutes) for the manufacturing process for the fluorophosphate glass described herein is shown in Figure 3. It can be seen that the determined refractive index profile is stable over several hours and never deviates from specifications.

[0074] Example Example 1 Ingots were produced from two fluorophosphate glasses according to the present invention in an ingot drawing process, where the glass compositions are listed below in weight percent. [Table 3]

[0075] In both cases, the method was first carried out without the contactless measurement of the outer dimensions of the glass strand according to the invention and the associated control of the temperature of the feeder and / or the conveying speed (interval 1). Then, the method was carried out with the contactless measurement of the outer dimensions of the glass strand and the associated control of the temperature of the feeder and / or the conveying speed (interval 2). The table below shows the effect of carrying out the method on the refractive index homogeneity of the glass. It can be seen that the measures described here led to a significant improvement in the homogeneity of the refractive index values. The homogeneity of the refractive index values ​​is expressed in this case as the standard deviation of the refractive index over 250 measurements along the glass strand. [Table 4]

[0076] Example 2 Ingots were produced from glasses of the fluorophosphate composition according to the conditions described for interval 2 in Example 1. The thickness of the ingots was measured and the relative height variation was determined, which was 1.1%. [Explanation of symbols]

[0077] 1 device 2 Glass Ingots 3 Feeding device 4. Liquid molten glass Type 5 6 glass strands 7. Conveyor equipment 8 Arrows 9 Cooling device 10. Measuring equipment 11 line of sight 12 light

Claims

1. A method for continuously producing glass ingots (2) according to a continuous casting process, comprising: Liquid molten glass is fed from a feeder (3) into a mold (5) to form glass strands (6); The glass strand (6) is fed via a conveying device (7), in particular a conveyor belt, to a cooling device (9) and then to a cutting device, in which the cooled glass strand (6) is split to form individual glass ingots (2). In the method, at the latest before the glass strand (6) is fed into the cooling device (9), the projection of the outer dimensions of the glass strand (6) is continuously determined by a contactless measuring device (10), and on the basis of the values ​​obtained, the parameters, i.e. the feeder temperature and / or the conveying speed, are adjusted, the glass strand (6) is guided through a roller arrangement having at least one bottom roller and at least one top roller before being measured by the contactless measuring device (10), and the distance between the bottom roller and the top roller is adjusted based on the measured value. method.

2. The measuring direction is arranged perpendicular to the longitudinal axis of the glass strand (6), The method of claim 1.

3. the non-contact measuring device (10) is an optical, radiometric and / or ultrasonic-based measuring device (10); 3. The method according to claim 1 or 2.

4. The glass ingot (2) has a relative height dispersion of not more than 3.0%.

4. The method according to any one of claims 1 to 3.

5. The glass ingot (2) contains the following components (in weight percent on an oxide basis): Table 1 Including, 5. The method according to any one of claims 1 to 4.

6. The glass ingot (2) is used to manufacture optical elements selected from a range of optical elements including lenses, prisms, light guide rods, arrays, optical fibers, gradient elements and optical windows in the fields of imaging, sensor mechanisms, microscopy, medical technology, digital projection, telecommunications, optical communication engineering / information transmission, optics / lighting in the automotive sector, as well as in solar technology, photolithography, steppers, excimer lasers, wafers, computer chips and / or integrated circuits and electronic devices containing such circuits and chips.

6. The method according to any one of claims 1 to 5.

7. An apparatus (1) for continuously producing glass ingots (2), said apparatus (1) comprising: a feeding device (3) for feeding liquid molten glass (4) into a mold (5) so as to form glass strands (6); a conveying device (7), in particular a conveyor belt, for conveying said glass strands (6); a cooling device (9) for cooling the glass strand (6); a cutting device capable of dividing the cooled glass strand (6) so that individual glass ingots (2) are formed; a roller device disposed before the measuring device (10) and including at least one bottom roller and at least one top roller; In a device (1) comprising: a measuring device (10) arranged upstream of the cooling device (9) that allows the projection of the outer dimensions of the glass strand (6) to be determined continuously and without contact, and that allows the adjustment of the parameters, i.e., the feeder temperature and / or the conveying speed, based on the values ​​obtained. Device (1).

8. The measuring device (10) is arranged perpendicular to the longitudinal axis of the glass strand (6). The device (1) according to claim 7.

9. the measuring device (10) is an optical, radiometric and / or ultrasound-based measuring device (10); Device (1) according to claim 7 or 8.

10. The mold (5) comprises a trough or a groove; Device (1) according to any one of claims 7 to 9.

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