A method for manufacturing high-quality glass products from a high-viscosity melt.

Abstract

The present disclosure relates to high quality glass products, methods for their manufacture, and uses thereof.

Description

[Technical Field]

[0001] This invention relates to a method for manufacturing high-quality glass products and to high-quality glass products.

[0002] background There are various types of glass compositions. Some glass compositions can be manufactured relatively easily and to high quality, while others require complex equipment and / or a very well-balanced manufacturing process. Generally, the glass compositions used in the manufacture of beverage glasses and ordinary window glass are of the former type. One reason for this is that the melting point of the glass used in these products is quite low, and the viscosity-temperature curve is steep; in addition, the quality standards for the manufactured products are not very strict. For example, ordinary window glass and beverage glasses may occasionally contain air bubbles, and slight variations in shape and dimensions are acceptable.

[0003] Glass compositions used in many mass-produced products, such as soda-lime glass compositions, have low melting points due to the large amounts of alkali metal oxides and alkaline earth metal oxides they contain. Each glass melting facility achieves very high throughput, often exceeding 200 tons, and even 400 tons, of glass per day. Naturally, the amount of energy required to produce 200 tons of low-melting-point glass is significantly less than that required for high-melting-point glass.

[0004] The quality required for a given product depends on its application. Some high-quality glass is used to manufacture products where even occasional air bubbles are unacceptable, and these must meet stringent standards regarding variations in shape and dimensions. Many of these glasses are quite difficult to manufacture, not only because of the stringent standards but also because of their high melting temperatures. High melting temperatures may be necessary to achieve sufficient melt viscosity for homogenization and removal of air bubbles from the melt.

[0005] The objective of this invention is to provide glass products that meet high quality standards.

[0006] Summary of the Invention In a first aspect, the present invention relates to a method for producing high-quality glass products from a high-viscosity melt, • Heating glass raw materials to obtain glass melt, • Heating molten glass in a molten tank, wherein the molten tank has a bottom and the molten glass has a body and a molten surface. • Removing air bubbles from the molten liquid. • Melt glass, melt volume 1 m³ per 24 hours. 3 To remove the material from the molten tank at a speed of 2.0 tons or less per unit. To obtain glass products having fewer than 20 air bubbles per kilogram of glass. Includes, At least a portion of the molten glass is 10 2.5 The glass melt is heated using one or more heat sources to have a viscosity of dPas or less. Heating the glass melt includes heating the surface of the melt and / or directly heating the body of the glass melt, and furthermore, the amount of thermal energy directly introduced into the body of the glass melt is more than 60% of the total amount of thermal energy introduced into the melt in the melt tank. The maximum temperature difference between the temperature at a location on the surface of the molten glass and the temperature at the bottom of the molten tank located vertically below that location is such that the difference in molten glass density corresponding to the above temperature is 0.05 g / cm³ per meter of distance between the two locations. 3 The difference is less than The glass melt is at a temperature exceeding 1580°C for 10 2 Having a viscosity of dPas, Regarding the method.

[0007] The present invention relates to glass compositions having very high melting temperatures, such as glass compositions containing only limited amounts of alkali metal oxides and alkaline earth metal oxides. The glass composition is such that the melt has a viscosity of 100 dPas at temperatures above 1580°C. The present invention relates to a viscosity of 10 2.5This involves heating the melt to a temperature high enough to reduce its viscosity to below dPas. This means that a lot of energy is required. Low viscosity and correspondingly high temperatures are desirable for bubbles to form in the melt.

[0008] The method involves introducing most of the thermal energy directly into the glass molten body. For example, the glass molten can be directly heated using one or more electrodes. One or more electrodes may be partially or completely positioned within or on the wall of the molten tank. One or more electrodes may be partially or completely positioned within or on the bottom plate of the molten tank. In one embodiment, one or more electrodes constitute the wall portion and / or bottom plate portion of the molten tank.

[0009] It has been found that the occurrence of short-circuit glass flow can be prevented if the maximum difference in glass melt density between (a) the position on the surface of the glass melt in the melting tank and (b) the position at the bottom of the melting tank vertically below the above position is limited. Short-circuit glass flow is undesirable because it means that a portion of the melt shortcuts to the outlet of the melting tank. These portions have a short residence time in the melting tank. The resulting glass product typically contains a large amount of bubbles and / or striations.

[0010] The glass compositions of the methods disclosed herein have a high viscosity. These compositions often contain large amounts of SiO2 and Al2O3. Each of these components has a rather high melting temperature. In most glass melts, SiO2 is the last component to liquefy in the batch. This means that there may be a portion within the melt body where the proportion of the high melting point components has decreased before all the components of the batch have liquefied. Naturally, the mentioned portion within the melt body contains a larger amount of the low melting point components, especially alkalis. The method described herein prevents short - circuit glass flow by restricting the difference in the density of the glass melt within the melting tank. Restricting the density difference as described herein reduces the undesirable volume flow within the melting tank caused by the density difference. Thereby, very high - quality glass products can be obtained. In particular, the glass products manufactured by the method described herein can have particularly few bubbles and / or can have very few or no striae.

[0011] In a second aspect, the invention relates to a glass product having less than 20 bubbles per kg of glass, the glass having a viscosity of 10 2 dPas at a temperature above 1580 °C, and the glass having a temperature dependence of the glass melt density of at least 9.0 mg / cm 3 per °C in the temperature range from T4 to T2, where T4 is the temperature at which the glass has a viscosity of 10 4 dPas and T2 is the temperature at which the glass has a viscosity of 10 2 dPas.

[0012] The invention also includes glass products obtained using this method. The glass products have a very low number of bubbles. In particular, by preventing short - circuit glass flow, the residence time of the glass melt within the melting tank becomes sufficiently long, and the bubbles rise to the surface of the glass melt and leave the melt body. This is relevant to melts with a high viscosity because bubbles rise to the surface more slowly in melts with a high viscosity compared to melts with a low viscosity. This also applies to glass compositions with a rather high temperature dependence of the glass melt density.

[0013] As explained earlier, this method prevents a portion of the molten metal from short-circuiting to the outlet of the melting tank. This is especially true for the low-viscosity portion of the molten metal, which tends to have a lower relative amount of SiO2. In the method of this invention, the low-viscosity portion of the molten metal cannot escape from the melting tank before the final glass composition is achieved within the tank. As a result, high-quality glass products are obtained.

[0014] definition "Glass melt" refers to 10 7.6 This is a batch body for glass raw materials having a viscosity of less than dPas.

[0015] A “melting tank” is a vessel used to melt glass. The vessel defines a volume capable of containing molten glass. A melting tank may have a substantially rectangular bottom or bottom plate, which may have walls for holding the molten glass within the tank. Typically, a melting tank is not filled to the rim. A melting tank may have a cover above the surface of the molten glass (a “covered melting tank”). The cover may be an arched ceiling. A “melting tank” may be part of a larger melting facility, which may include additional parts such as a clarification tank or clarification area. Some melting facilities have a composite tank with separate sections for melting and clarification, in which case “melting tank” as used in this disclosure refers to the entire composite tank including the clarification section.

[0016] The "bottom plate" is the part of the molten tank that forms the bottom of the molten tank. The bottom plate may be a single piece of material, or it may be composed of multiple parts or sections. The bottom plate may be closed, that is, essentially impermeable to the molten glass, or it may have a closable opening that allows the molten glass to be drained from the molten tank through the bottom opening.

[0017] The "highest temperature location on the glass melt surface" is the point on the glass melt surface within the melting tank that has the highest temperature compared to other locations on the glass melt surface within the melting tank. The temperature of the glass melt surface can be easily measured using a thermocouple and / or pyrometer. The temperature at the bottom of the melting tank can be measured, for example, using a thermocouple extending into the bottom plate or into the melt. The thermocouple may be water-cooled. The "glass melt surface" is the portion of the melt that is in direct contact with the surrounding atmosphere (e.g., air). The melting tank may include a portion where unmelted raw material swims on the molten material, for example, a portion near the raw material inlet port. Such a portion (which may correspond to 10-30% of the melting tank area) is not considered part of the glass melt surface.

[0018] The shortest distance between the "glass melt surface" and the bottom of the molten tank in contact with the melt is the "glass melt depth" at the target location.

[0019] A "bubble" is a gaseous inclusion in glass or glass melt, optionally having a diameter of at least 10 μm. "Diameter" refers to the maximum diameter of the gaseous inclusion.

[0020] "Residence time" is the time a given portion of the glass melt spends in the melting tank before it is removed from the tank. Residence time can be measured using so-called tracers, i.e., components added to the glass melt so that they can be detected in the product, thereby determining the time spent in the melting tank. Examples of tracer compounds are Ca, Sr, and Y. "Minimum residence time" is the time required for a portion of the glass melt to pass through the melting tank via the fastest path, i.e., the time from when a certain amount of tracer compound is added to the melting tank until the tracer first appears in the product. "Average residence time" is, (Volume of the melting tank [m³] 3 ]) / (Throughput of the melting tank [m 3 / h]) It is defined as follows. [Brief explanation of the drawing]

[0021] [Figure 1] This is a diagram of a melting tank that can be used in the method according to the embodiment of the present invention. [Figure 2] This is a diagram of a melting tank that can be used in the method according to the embodiment of the present invention. [Figure 3] This is a diagram of a melting tank that can be used in the method according to the embodiment of the present invention. [Figure 4] This is a diagram showing the relationship between glass melt density and temperature in the temperature range of approximately 800 to 1700°C. [Figure 5] This is a diagram showing the relationship between glass melt density and temperature in the temperature range of approximately 800 to 1700°C. [Figure 6] This diagram shows the velocity of the glass molten flow in a molten tank with a large density difference. [Figure 7] This diagram shows the velocity of a glass melt flow after additional electrode heating was applied to reduce the density difference and thus lower the velocity of the melt flow. [Figure 8] These are viscosity curves for four exemplary industrial glass compositions that can be manufactured using the method of the present invention.

[0022] Detailed explanation The method involves heating glass raw materials to obtain glass melt. Heating is typically carried out in a molten tank having a molten tank bottom. The molten tank may have a molten tank wall and / or an optional arched ceiling cover. The molten tank is filled to a certain level with glass melt. The glass melt has a molten surface at the interface between the molten body and the atmosphere above the molten. Heating may include high-frequency heating in a molten tank having cooled walls. The walls of the molten tank can be cooled using a coolant such as water. Cooling may include flowing the coolant through a channel in the molten tank wall. Cooling the molten tank wall has the advantage of reducing corrosion of the molten tank wall material.

[0023] The method includes removing bubbles from the melt. Removal of bubbles from the melt can be performed within the melting tank, or optionally outside the melting tank, for example, in a separate tank. The separate tank may be a clarification tank. Bubbles can be removed from the melt using chemical and / or physical methods. In one embodiment, removing bubbles from the melt includes allowing the bubbles to rise to the surface of the glass melt in the melting tank. In several embodiments, bubbles are removed from the melt in the melting tank by rising to the surface of the glass melt, after which further bubble removal is performed in a separate tank. Due to the improved method of the present invention, bubble removal within the melting tank contributes to achieving excellent bubble quality in the glass product. In several embodiments, the method includes the step of removing bubbles from the melt in the melting tank and / or in a separate clarification tank after the manufactured glass has been removed from the melting tank. The temperature of the glass melt in the clarification tank may be higher than the highest temperature of the glass melt in the melting tank. Preferably, the method of the present invention does not involve vacuum clarification and / or bubbling of the melt.

[0024] The method involves removing the molten glass from the melting tank. The method of the present invention is a relatively low-throughput method that focuses on the quality rather than the quantity of glass products. In one embodiment, the molten glass has a molten volume of 1 m³ per 24 hours. 3 2.0t per unit (t / (m 3 *The molten glass is removed from the molten tank at a rate of less than 24 hours. This means that per day, 1 m³ of molten glass is removed from the molten tank. 3 This means that less than 2.0 tons of molten glass are withdrawn from the melting tank per unit area ("withdrawal rate"). Optionally, the withdrawal rate can be 1.5 t / (m). 3 *Less than 24h), 1.3t / (m 3 *Less than 24 hours, 1.1t / (m 3 *Less than 24h, or 0.9t / (m 3 *Less than 24h. In one embodiment, the extraction rate is at least 0.1t / (m 3 *24h), at least 0.3t / (m 3 *24h), or at least 0.5t / (m 3(*24 hours)

[0025] The present invention involves a method for obtaining a glass product. Optionally, the glass product may have fewer than 20 bubbles per kilogram of glass. In preferred embodiments, the glass product may have fewer than 10, 5, 3, or 2 bubbles per kilogram of glass.

[0026] The method involves heating a glass molten material using one or more heat sources. In one embodiment, the heat source includes an electrode in contact with the glass molten material. The electrode may include or consist of a metal, alloy, or metal oxide such as platinum, iridium, tungsten, molybdenum, or tin oxide. Alternatively or additionally, the heat source may include a burner such as a gas burner and / or microwave heater. The gas may be natural gas. In some embodiments, the gas used in the burner may include or consist of a non-fossil gas such as a biofuel (e.g., biogas) and / or hydrogen, particularly hydrogen obtained from renewable resources. In a preferred embodiment, the amount of thermal energy obtained from the combustion of a fossil fuel is less than 10.0%, less than 5.0%, or less than 1.0% of the total amount of thermal energy introduced into the molten material.

[0027] In one embodiment, the carbon dioxide footprint of a glass product is less than 500 g of CO2 per kilogram of glass. In another embodiment, the carbon dioxide footprint of a glass product is less than 400 g, less than 300 g, less than 200 g, less than 100 g, or even 0 g of CO2 per kilogram of glass. For example, glass products with a zero carbon dioxide footprint can be manufactured using energy from renewable resources only, such as biofuels derived from renewable resources, hydrogen, or electricity. The carbon dioxide footprint refers to the CO2 emissions resulting from Scope 1 emissions under the GHG protocol. In relation to this specification, this refers to the CO2 emissions per kilogram of glass material caused by the combustion of fossil fuels and released by carbon-containing raw materials during the manufacture of glass products. Optionally, the raw materials used in the method of the present invention are carbonate-free; that is, carbonates may be present as impurities in the raw materials (<0.1% by weight), but they are not intentionally added to the composition.

[0028] The amount of thermal energy introduced into the melt by heating the surface may be less than 40.0% of the total amount of thermal energy introduced into the melt. Optionally, this value may be less than 30.0%, less than 25.0%, less than 15.0%, less than 5.0%, less than 1.0%, or even 0%.

[0029] In several embodiments, heating the molten surface includes heating the surface using one or more microwave heaters and / or burning biofuels and / or hydrogen. Direct heating of the molten body may include electrode heating.

[0030] The glass melt is such that at least a portion of it is 10 2.5 It is heated to a viscosity of dPas or less. Optionally, at least a portion of the glass melt is 10 2.3The viscosity can be less than dPas. Preferably, the viscosity of the glass melt is 5 dPas or higher, or 10 dPas or higher. Heating the glass to a very low viscosity is undesirable because it increases the risk of short-circuit glass flow and increases erosion of the walls of the molten tank. Furthermore, low viscosity corresponds to very high temperatures, which is undesirable in terms of power consumption. Optionally, the minimum viscosity of the glass melt in the glass melt body is 10 dPas or higher.

[0031] Heating the glass includes heating the molten surface and / or directly heating the body of the molten glass. In one embodiment, heating includes directly heating the body of the molten glass, or alternatively, heating the molten surface and directly heating the body of the molten glass. It has been found that an appropriate balance between heating the molten surface and heating the body of the molten glass is beneficial for obtaining high-quality glass products from high-viscosity glass compositions. As described in this disclosure, balancing the heating of the molten glass surface and heating the body of the molten glass can reduce the maximum molten glass density difference between a position on the molten glass surface and a position at the bottom of the molten tank vertically below that position.

[0032] The amount of thermal energy directly introduced into the glass melt body is more than 60% of the total amount of thermal energy introduced into the melt. This refers to the thermal energy introduced into the melt in the melting tank. The introduction of thermal energy may differ in optional clarification tanks or other optional parts of the glass melting equipment. In preferred embodiments, the introduction of thermal energy described herein can also be applied to optional clarification tanks and / or clarification sections in a composite melting tank. In one embodiment, the amount of thermal energy directly introduced into the glass melt is more than 70%, more than 76%, more than 80%, or more than 90% of the total amount of thermal energy introduced into the melt. Optionally, more than 99%, or essentially all, of the total amount of thermal energy introduced into the melt is directly introduced into the glass melt body. In one embodiment, all thermal energy is directly introduced into the melt; that is, the glass melt surface is not heated. The precise balance of thermal energy introduction depends on the properties of the glass melt, such as the temperature dependence of the glass melt density and viscosity properties such as the VFT parameter. In one embodiment, the maximum density difference can be reduced by distributing electrodes across the entire volume of the molten tank so that the introduction of heating energy is sufficiently uniform to achieve the desired density difference. For example, if the region near the bottom of the molten tank is too cold, electrodes can be positioned so that more thermal energy reaches that cold point. Alternatively, if the cold point is closer to the surface, longer electrodes extending from the bottom to the surface of the molten liquid can be used to prevent the formation of the cold point. In one embodiment, the molten tank includes multiple electrodes. For example, the number of electrodes can be determined according to the surface area of ​​the glass molten liquid surface. In one embodiment, the molten tank includes electrodes over a 1 m² area of ​​the glass molten liquid surface. 2 Each contains at least 1.0 electrode. In some embodiments, the glass melt surface is 1 m 2 The number of electrodes per square meter may be at least 2.0, at least 3.0, or at least 6.0. Optionally, the number of electrodes per square meter of the glass melt surface may be up to 8.0 electrodes / m². 2 Or up to 7.0 pieces / m 2It may be within this range. Optionally, the heat sources can be arranged so that a uniform heat distribution is achieved.

[0033] For example, the heat absorption of a glass melt can affect the balance of thermal energy input desired to achieve the best results. For glass melts with greater heat absorption, it may be appropriate to increase the proportion of direct heating of the glass melt. In one embodiment, the heat absorption coefficient (κ at 1600°C) of the glass melt is at least 8.0 m -1 Optionally, up to 60.0m -1 Thus, the amount of thermal energy directly introduced into the glass melt is greater than 60% or greater than 70%. In one embodiment, the thermal absorption coefficient (κ at 1600°C) of the glass melt is at least 10.0 m -1 at least 12.0m -1 , or at least 14.0m -1 In addition, or alternatively, the thermal absorption coefficient (κ at 1600°C) of molten glass is up to 55.0 m -1 , up to 45.0m -1 , or up to 40.0m -1 That is the case.

[0034] In a melting tank, the maximum temperature difference between the temperature at a location on the surface of the molten glass and the temperature at the bottom of the melting tank, vertically below that location, is such that the difference in molten glass density corresponding to the above temperature is 0.05 g / cm³ per meter of distance between the two locations. 3 The difference is less than 0.04 g / cm³ ("maximum density difference"). This "maximum density difference" means that the difference between any two described locations, vertically below the surface and bottom of the molten tank, is not greater than indicated. As mentioned above, minimizing the vertical density difference helps reduce or completely prevent short-circuit glass flow in the molten tank, which ultimately improves the quality of the product obtained using this method. Preferably, the density difference is 0.04 g / cm³. 3 Less than 0.03 g / cm³ 3 Less than 0.02 g / cm³ 3 It is less than 0.001 g / cm³. In certain embodiments, it is at least 0.001 g / cm³.3 , or at least 0.005 g / cm³ 3 Limited density differences are sometimes unavoidable. The "maximum density difference" relates to the magnitude of the difference between locations; that is, the density at the surface may be higher or lower than the density at the bottom. Alternatively, or in addition, the "maximum density difference" applies to the first half of the molten tank, i.e., the half of the molten tank that includes the raw material inlet after the molten tank has been (conceptually) divided in a cross section perpendicular to its longitudinal axis.

[0035] Alternatively, or in addition, the difference between the temperature at the hottest point on the surface of the molten glass and the temperature at the bottom of the molten tank, vertically below the hottest point, is such that the difference in molten glass density corresponding to the above temperature is 0.04 g / cm³ per meter of distance between the two points. 3 This is a difference such that it is less than 0.03 g / cm³ ("density difference"). As mentioned above, minimizing the vertical density difference in the molten tank helps to reduce or completely prevent short-circuit glass flow in the molten tank, which ultimately improves the quality of the product obtained using this method. Preferably, the density difference is 0.03 g / cm³. 3 Less than 0.025 g / cm³ 3 Less than 0.02 g / cm³ 3 It is less than 0.001 g / cm³. In certain embodiments, it is at least 0.001 g / cm³. 3 , or at least 0.005 g / cm³ 3Limited density differences are sometimes unavoidable. The "density difference" is related to the magnitude of the difference between locations. That is, the density at the surface may be higher or lower than the density at the bottom. The temperature distribution, and thus the density distribution, can be achieved using electrodes of the desired size and shape. For example, if more thermal energy is needed near the surface of the molten glass, longer electrodes can be used. In one embodiment, heating the molten glass may involve heating using one or more electrodes that extend upward from the bottom of the molten tank to at least 50% of the depth of the molten glass, preferably at least 60%, at least 70%, or at least 80%. Optionally, one or more electrodes may extend up to 100%, 95%, or 90% of the depth of the molten glass from the bottom of the molten tank. Optionally, one or more electrodes may extend 50% to 100%, 60% to 95%, or 70% to 90% of the depth of the molten glass from the bottom of the molten tank.

[0036] In one embodiment, the melting tank has electrode surfaces that come into contact with the molten glass during heating, and this is called the "electrode surface area". The "total electrode surface area" is the sum of the surface areas of all electrodes in the melting tank. This value is equal to the volume of molten glass per cubic meter. 3 At least 0.15m per unit area 2 Glass melt liquid volume 1 m 3 At least 0.2m per unit area 2 , or glass melt liquid volume 1 m 3 At least 0.25m per unit area 2 It may be so. Optionally, the total electrode surface area is the glass melt volume of 1 m². 3 Up to 1.5m per unit 2 , or 1m 3 Maximum 1.25m per unit 2 It may be within that range.

[0037] 10 2 In this specification, the temperature at which a glass melt has a viscosity of dPas is referred to as temperature T2. Similarly, if the glass melt is 10 4In this specification, the temperature at which a viscosity of dPas is obtained is referred to as temperature T4. For glass compositions containing a large amount of alkali metal oxides or alkaline earth metal oxides, such as soda-lime glass and other glass compositions, temperature T2 is less than 1500°C. The glass compositions used in the present invention have much higher T2 and / or T4 temperatures. The T2 temperature of the glass melt in the melting tank in the method of this disclosure is greater than 1580°C, preferably even greater than 1600°C or 1620°C. In some embodiments, the T2 temperature of the glass composition may be less than 1800°C, less than 1750°C, or less than 1700°C. Glass compositions with very high T2 temperatures are very difficult to process and require a lot of energy to melt.

[0038] The T4 temperature of the glass composition in the molten tank in the method of this disclosure is greater than 1000°C, preferably more preferably greater than 1050°C or greater than 1120°C. In some embodiments, the T4 temperature of the glass composition may be less than 1400°C, less than 1350°C, or less than 1300°C. Glass compositions with very high T4 temperatures are very difficult to process and require a lot of energy to melt.

[0039] Because high-melting-point glass compositions require high melting temperatures, significant cooling of the molten tank walls may be necessary to prevent excessive corrosion of the wall material. Significantly cooling the molten tank can negatively impact the glass molten flow, as it greatly accelerates the viscosity of the molten flow and increases the risk of short-circuit glass flow.

[0040] It has been found that the minimum residence time in the molten tank can be set to at least 10 hours, at least 12 hours, or at least 14 hours. Sufficient residence time is useful for producing high-quality glass products. Optionally, the minimum residence time may be up to 70 hours, up to 65 hours, or up to 60 hours. In addition, or instead, the average residence time may be 48 hours ± 12 hours. Given that longer residence times increase the carbon dioxide footprint of glass products, residence times that are too long are undesirable. In one embodiment, the minimum residence time is at least 20% of the average residence time. Optionally, the minimum residence time may be at least 25%, at least 35%, or at least 45% of the average residence time. Naturally, the higher the ratio of minimum residence time to average residence time, the higher the energy efficiency of the process will be. The method of the present invention helps to achieve a desirable ratio of minimum residence time to average residence time, for example, 20% to 100%, or up to 90%, up to 80%, or up to 70%.

[0041] Melting tanks can be manufactured from a variety of heat-resistant materials. In one embodiment, the bottom plate and / or walls of the melting tank contain or consist of a refractory material. The refractory material may be a ceramic material, a metallic material, or a combination thereof. A suitable metal is platinum. Platinum is very expensive and can contaminate the melt if dissolved by aggressive melt components. In a preferred embodiment, the refractory material does not contain or consist of platinum and / or other metals. In one embodiment, the refractory material is an oxide ceramic, i.e., a material containing or consisting of one or more oxides such as metal oxides. Preferably, the refractory material has heat resistance up to at least 1400°C, at least 1600°C, and even up to at least 1700°C. In this context, "heat resistance" means that the refractory material has a melting point or melting range above the indicated temperature. In one embodiment, the refractory material is selected from ZrO2, Al2O3, SiO2, and combinations thereof.

[0042] The method disclosed herein can be used with a glass melt having a resistivity of at least 1.5 Ωcm at 1700°C. A minimum resistivity is useful for effective heating and current reduction. Optionally, the resistivity of the glass melt may be in the range of up to 30 Ωcm, up to 25 Ωcm, or up to 20 Ωcm. In one embodiment, the resistivity of the glass melt may be at least 2.0 Ωcm, at least 3.0 Ωcm, or at least 4.0 Ωcm. Optionally, the resistivity of the glass melt may be in the range of 1.5 Ωcm to 30 Ωcm, 2.0 Ωcm to 25 Ωcm, or 3.0 Ωcm to 20 Ωcm.

[0043] Depending on the amount of thermal energy introduced into the molten glass, the density of the molten glass at a location on the surface of the molten glass may be lower than that at the bottom of the molten tank, vertically below that location. This can occur when a considerable amount of thermal energy is introduced into the molten glass by heating its surface. Alternatively, the density of the molten glass may be higher at the location on the surface of the molten glass than at the bottom of the molten tank, vertically below that location. In other words, the "concentration difference" and the "maximum concentration difference" are related to the magnitude of the difference between the locations.

[0044] Generally, density increases with decreasing temperature. The more thermal energy directly introduced into the body of the molten glass compared to the heating energy introduced into the surface of the molten glass, the hotter the bottom of the melting tank becomes. In one embodiment, heating the body of the molten glass includes introducing heat using electrodes at the bottom of the melting tank and / or electrodes inside or on the bottom plate of the melting tank. The risk of short-circuit glass flow is particularly high when the density of the molten glass at the surface of the molten glass significantly exceeds the density at the bottom. In one embodiment, the density of the molten glass at the hottest point on the surface of the molten glass is 0.045 g / cm³ compared to the density of the molten glass at the bottom of the melting tank below the hottest point. 3 Below, 0.035g / cm 3 The following, or 0.025 g / cm³ 3 The following are above average.

[0045] It has been found that there are glass compositions in the temperature range from T4 to T2 in which the temperature dependence of the glass melt density is relatively high. This temperature range is particularly relevant to the glass melting and methods described herein. In several embodiments, the temperature dependence of the glass melt density in the temperature range from T4 to T2 is at least 9.0 mg / cm³ per 100°C. 3 Therefore, optionally, a maximum of 19.0 mg / cm³ per 100°C is possible. 3 This value may be related to the average change in density within the given temperature range. Optionally, this temperature dependence of the glass melt density is at least 10.0 mg / cm³ per 100°C temperature difference. 3 at least 11.0 mg / cm³ 3 at least 12.0 mg / cm³ 3 , or at least 13.0 mg / cm³ 3 Therefore, optionally, this temperature dependence of the glass melt density is up to 18.0 mg / cm³ per 100°C temperature difference. 3 , maximum 17.0mg / cm 3 , maximum 16.0mg / cm 3 , or up to 15.0 mg / cm³ 3 That is the case.

[0046] As described above, the method of the present invention is for producing high-quality products of high-viscosity glass compositions. The focus is on quality rather than quantity, and throughput is low, which may limit the size of the melting tank. Optionally, the vertical distance between the position on the glass melt surface and the position at the bottom of the melting tank vertically below that position is less than 1250 mm or less than 1100 mm. In addition, or instead, the distance may be at least 750 mm or at least 850 mm. In some embodiments, the same applies to the vertical distance between the glass melt surface and the bottom of the melting tank.

[0047] Viscosity can be measured using, for example, a rotational viscometer, such as the one described in DIN ISO7884-2:1998-2. The temperature dependence of viscosity is described according to the VFT equation (Vogel-Fulcher-Tammann). The VFT equation is shown below. lg(η / dPas)=A+B / (t-t0) In the VFT formula, t is the temperature of the subject. A, B, and t0 are so-called VFT constants specific to each glass composition. As mentioned above, the viscosity behavior of the glass compositions used in this method is of particular importance. The temperature dependence of the glass melt viscosity can be described using the VFT formula. Optionally, the glass melt has a VFT constant B in the range of 5,000 to 9,000 K and / or t0 in the range of 75°C to 240°C. Preferably, the VFT constant A is -5.0 to 0.0. In one embodiment, A is -1.0 or less, for example -4.0 to -1.0. In several embodiments, the VFT constant B is 5,000 K to 9,000 K, for example 4,500 to 8,500 K. Optionally, t0 may be at least 75°C and at most 240°C; t0 may be at least 200°C.

[0048] The present invention also relates to glass products. Glass products can be obtained by the methods described herein. Therefore, properties related to the composition of the glass melt can be appropriately applied to the composition of the glass product.

[0049] Glassware may have fewer than 20 bubbles per kilogram of glass. In preferred embodiments, glassware may have fewer than 10, fewer than 5, fewer than 3, or fewer than 2 bubbles per kilogram of glass.

[0050] Glass may have a coefficient of thermal expansion of 3.0 ppm / K to 8.5 ppm / K, preferably less than 7.0 ppm / K, or less than 5.5 ppm / K, in the temperature range of 20°C to 300°C. The coefficient of thermal expansion is the mean linear thermal expansion coefficient according to DIN ISO 7991:1987.

[0051] Glass products may be sheets, wafers, plates, tubes, rods, ingots, or blocks.

[0052] The glass composition may be borosilicate glass, aluminoborosilicate glass, or aluminosilicate glass. The glass composition may contain alkali metal oxides in amounts of less than 20% by weight, less than 15% by weight, less than 12% by weight, less than 10% by weight, or less than 5% by weight. Optionally, the glass composition may not contain alkali metal oxides. In alternative embodiments, the amount of alkali metal oxide in the glass composition may be at least 1% by weight.

[0053] The glass composition may contain alkaline earth metal oxides in amounts of less than 20% by weight, less than 15% by weight, less than 12% by weight, less than 10% by weight, or less than 5% by weight. Optionally, the glass composition may not contain alkaline earth metal oxides. In alternative embodiments, the amount of alkaline earth metal oxide in the glass composition may be at least 1% by weight.

[0054] The glass composition may contain SiO2 in an amount of at least 48% by weight, at least 55% by weight, at least 65% by weight, at least 70% by weight, or at least 75% by weight. Optionally, the amount of SiO2 may be in the range of up to 85% by weight, up to 82.5% by weight, or up to 80% by weight.

[0055] Optionally, the glass composition may be a glass-ceramic composition, i.e., a glass composition that can be further processed into a glass-ceramic by appropriate heat treatment. If the glass composition is a glass-ceramic composition, the composition may contain a nucleating agent such as TiO2 and / or ZrO2. Optionally, the total amount of TiO2 and / or ZrO2 may be at least 2.0% by weight, for example, at least 2.5% by weight. The glass composition may be, for example, a lithium aluminosilicate glass composition containing at least 2.0% by weight of Li2O.

[0056] The glass composition may contain one or more clarifying agents. The clarifying agents can be selected from polyvalent metal oxides, halides, sulfates, and combinations thereof. In one embodiment, the clarifying agent is selected from tin oxide, cerium oxide, chloride, sulfate, and combinations thereof.

[0057] An optional glass composition contains at least 1.5% by weight, or at least 5.0% by weight, and even more preferably at least 10.0% by weight of Al2O3. The amount of Al2O3 may be up to 23.0% by weight, up to 20.0% by weight, or up to 18.0% by weight. In certain embodiments, the amount of Al2O3 may be in the range of 1.5% to 23.0% by weight, 5.0% to 20.0% by weight, or 10.0% to 18.0% by weight.

[0058] In addition, or instead, the glass composition may contain B2O3 in an amount of at least 0.0 wt%, or at least 8.0 wt%, and even more precisely, at least 10.0 wt%. The amount of B2O3 may be up to 20.0 wt%, up to 16.0 wt%, or up to 14.0 wt%. In certain embodiments, the amount of B2O3 may be in the range of 0.0 wt% to 20.0 wt%, 8.0 wt% to 16.0 wt%, or 10.0 wt% to 14.0 wt%.

[0059] Many high-viscosity glass compositions contain large amounts of SiO2, Al2O3, and B2O3. Optionally, the glass compositions used in the present invention have a total content of at least 75.0% by weight, at least 78.0% by weight, and even more specifically, at least 85.0% by weight of SiO2, Al2O3, and B2O3. The total amount of SiO2, Al2O3, and B2O3 may be limited to 97.0% by weight or less, up to 93.5% by weight, or up to 90.0% by weight. Optionally, the amounts of SiO2, Al2O3, and B2O3 may be in the range of 75.0% to 95.0% by weight, 78.0% to 92.5% by weight, or 85.0% to 90.0% by weight.

[0060] The following embodiments describe optional aspects and embodiments of the present invention.

[0061] This invention includes a method for producing high-quality glass products from a high-viscosity melt, and this method is • Heating glass raw materials to obtain glass melt, • Heating molten glass in a molten tank, wherein the molten tank has a bottom and the molten glass has a body and a molten surface. • Removing air bubbles from the molten liquid. • Melt glass, melt volume 1 m³ per 24 hours. 3 To remove the material from the molten tank at a speed of 2.0 tons or less per unit. To obtain glass products having fewer than 20 air bubbles per kilogram of glass. Includes, At least a portion of the molten glass is 10 2.5 The glass melt is heated using one or more heat sources to have a viscosity of dPas or less. Heating the glass melt includes heating the surface of the melt and / or directly heating the body of the glass melt, and furthermore, the amount of thermal energy directly introduced into the body of the glass melt is more than 60% of the total amount of thermal energy introduced into the melt in the melt tank. The maximum temperature difference between the temperature at a location on the surface of the molten glass and the temperature at the bottom of the molten tank located vertically below that location is the difference in molten glass density corresponding to the above temperature, which is 0.05 g / cm³ per meter of distance between the two locations. 3 The difference is less than The glass melt is heated to a temperature exceeding 1580°C for 10 2 It has a viscosity of dPas.

[0062] This invention includes a method for producing high-quality glass products from a high-viscosity melt, and this method is • Heating glass raw materials to obtain glass melt, • Heating molten glass in a molten tank, wherein the molten tank has a bottom and the molten glass has a body and a molten surface. • Removing air bubbles from the molten liquid. • Melt glass, melt volume 1 m³ per 24 hours. 3 To remove the material from the molten tank at a speed of 2.0 tons or less per unit. To obtain glass products having fewer than 20 air bubbles per kilogram of glass. Includes, At least a portion of the molten glass is 10 2.5 The glass melt is heated using one or more heat sources to have a viscosity of dPas or less. Heating the glass melt includes heating the surface of the melt and / or directly heating the body of the glass melt, and furthermore, the amount of thermal energy directly introduced into the body of the glass melt is more than 60% of the total amount of thermal energy introduced into the melt in the melt tank. The difference between the temperature at the hottest point on the surface of the molten glass and the temperature at the bottom of the molten tank, located vertically below the hottest point, corresponds to a difference in the density of the molten glass of 0.04 g / cm³ per meter of distance between the two points. 3 The difference is less than The glass melt is heated to a temperature exceeding 1580°C for 10 2 It has a viscosity of dPas.

[0063] This invention includes a method for producing high-quality glass products from a high-viscosity melt, and this method is • Heating glass raw materials to obtain glass melt, • Heating molten glass in a molten tank, wherein the molten tank has a bottom and the molten glass has a body and a molten surface. • Removing air bubbles from the molten liquid. • Melt glass, melt volume 1 m³ per 24 hours. 3 To remove from the molten tank at a speed of 1.5 tons or less per unit. To obtain glass products having fewer than 5 air bubbles per 1 kg of glass. Includes, At least a portion of the molten glass is 10 2.5 The glass melt is heated using one or more heat sources to have a viscosity of dPas or less. Heating the glass melt includes heating the surface of the melt and / or directly heating the body of the glass melt, and furthermore, the amount of thermal energy directly introduced into the body of the glass melt is more than 60% of the total amount of thermal energy introduced into the melt in the melt tank. The maximum temperature difference between the temperature at a location on the surface of the molten glass and the temperature at the bottom of the molten tank located vertically below that location is the difference in molten glass density corresponding to the above temperature, which is 0.05 g / cm³ per meter of distance between the two locations. 3 The difference is less than The glass melt is heated to a temperature exceeding 1580°C for 10 2 It has a viscosity of dPas.

[0064] Detailed description of the drawing Figure 1 shows a schematic, simplified cross-sectional view of a melting tank 1 having a bottom 2, side walls 3, and a cover 4 (arch-shaped). The melting tank 1 may further have a raw material inlet (not shown) and an outlet (not shown). The melting tank 1 has a burner 6 and a number of electrodes 7 as heat sources. Inside the melting tank is a glass melt 10 having a glass melt surface 11. The glass melt surface 11 has a position 20, i.e., a point on the glass melt surface 11 corresponding to the greatest density difference compared to other points on the glass melt surface 11. The melting tank 1 has a position 21 vertically below position 20. The distance between positions 20 and 21 may be, for example, about 1 meter.

[0065] Electrode 7 directly heats the glass melt 10, while burner 6 heats the glass melt surface 11. The proportion of thermal energy directly introduced into the glass melt 10 may exceed the amount of thermal energy introduced into the melt via the glass melt surface 11. In some embodiments, 60% of the total thermal energy introduced into the glass melt 10 is directly introduced into its body using electrode 7. Optionally, burner 6 can burn hydrogen, biofuels, or other combustible materials derived from renewable resources.

[0066] Generally, the electrode 7 may have any shape. In the drawings, a rod-shaped electrode 7 that extends long into the melt 10 from the bottom 2 of the melting tank 1 is shown.

[0067] FIG. 2 shows a schematic and simplified cross-sectional view of a melting tank 1 similar to that of FIG. 1. Instead of a burner, the melting tank 1 has a microwave heat source 8. Microwave heating is particularly interesting when the amount of thermal energy that should be directly introduced into the glass melt 10, for example using the electrode 7, is considerably larger compared to the amount of thermal energy introduced by heating the melt surface 11. In one embodiment, the amount of thermal energy directly introduced into the glass melt 10 using the electrode 7 is at least 70%, or more, for example 75% or more.

[0068] FIG. 3 shows a schematic and simplified cross-sectional view of a melting tank 1 similar to that of FIG. 1. The melting tank 1 has no burner or other heat source for heating the glass melt surface 11. As a result, essentially all of the thermal energy is directly introduced into the glass melt 10 using the electrode 7.

[0069] FIG. 4 shows the temperature dependence of the glass melt density of a non-alkali high-viscosity glass composition. This composition has a density of about 2.3 g / cm at about 870 °C, while at about 1,540 °C the density is about 2.2 g / cm. Therefore, the temperature dependence of this particular glass is about 15 mg / cm per 100 °C. 3 On the other hand, at about 1,540 °C the density is about 2.2 g / cm. 3 Therefore, the temperature dependence of this particular glass is about 15 mg / cm per 100 °C. 3

[0070] FIG. 5 shows the temperature dependence of the glass melt density of an alkali-containing high-viscosity glass composition. This composition has a density of about 2.4 g / cm at about 840 °C, while at about 1,540 °C the density is about 2.3 g / cm. Therefore, the temperature dependence of this particular glass is about 15 mg / cm per 100 °C. 3 On the other hand, at about 1,540 °C the density is about 2.3 g / cm. 3 Therefore, the temperature dependence of this particular glass is about 15 mg / cm per 100 °C. 3

[0071] ​​Figure 6 shows the melt body. The different arrow sizes indicate the velocity of the glass melt flow within the melting tank, with smaller arrows being associated with slower velocities and larger arrows being associated with faster melt flow velocities. The designations "left" and "right" are to be understood only with reference to Figures 6 and 7.

[0072] The viscosity of the melt flow was modeled based on a glass melt density of 2.5 g / cm at 1550 °C. 3 The temperature is 100 °C higher on the right side of the melt body. That is, Too is 1550 °C on the left side and 1650 °C on the right side. This is similar to the situation of a melting tank having a clarification section on the right side. The melt was assumed to have a viscosity of 80 Pas at 1650 °C. The other values of the glass melt were set as follows: volume expansion coefficient β: 50 ppm / K, specific heat capacity c p : 1400 Jkg -1 K -1 , thermal conductivity λ eff : 150 W·m -1 K -1 , glass viscosity η at 1550 °C: 80 Pas, heat transfer coefficient of the bottom plate at an outside air temperature of 27 °C: h = 15 W / (m 2 *K), heat transfer coefficient of the side wall at an outside air temperature of 27 °C: h = 15 W / (m 2 *K), heat loss by the cover of the melting tank: h = 100 W / (m 2 *K) towards Too(x), radiative emission with ε = 1 towards Too(x).

[0073] When the melt flows from the inlet to the clarification section, a very fast glass flow occurs in the first two-thirds of the melt body.

[0074] Figure 7 shows the same melt body as described with respect to Figure 6. The only difference is that additional electrode heating was performed near the inlet on the left side of the melt. The electrode heating reduced the density difference in the vertical direction, thereby significantly reducing the velocity of the melt flow. From Figure 7, it can be seen that when the additional electrode heating reduces the vertical temperature and as a result the density difference on the left side of the melting tank, the flow of the glass melt becomes much gentler throughout the right side of the melt body.

[0075] Figure 8 shows the viscosity curves of four glass compositions that can be processed into glass products using the method of the present invention. All of these glass compositions show a T2 temperature above 1580°C and a T4 temperature above 1000°C. The circles surround the highest temperature of the glass melt in the method of the exemplary embodiment of the present invention. [Explanation of symbols]

[0076] 1. Melting tank 2. Bottom of the molten tank 3 side wall 4 Covers 6 burners 7 electrodes 8. Microwave heat source 10. Melt of glass 11. Surface of molten glass 20 Glass melt surface position Position at the bottom of 21 20 in the vertical direction

Claims

1. A method for manufacturing high-quality glass products from a high-viscosity melt, - Heating glass raw materials to obtain glass melt, - Heating the glass molten liquid in a melting tank, wherein the melting tank has a melting tank bottom, and the glass molten liquid has a body and a melting surface. - Remove air bubbles from the melt, - The aforementioned glass melt has a melt volume of 1 m³ per 24 hours. ３ To remove from the molten tank at a speed of 2.0 tons or less per unit, - To obtain glass products having fewer than 20 air bubbles per kilogram of glass. Includes, At least a portion of the glass melt is 10 ２．５ The glass melt is heated using one or more heat sources so that it has a viscosity of dPa or less. Heating the glass melt includes directly heating the glass melt body, and further, the amount of thermal energy directly introduced into the glass melt body is more than 60% of the total amount of thermal energy introduced into the melt in the melt tank. The maximum difference between the temperature at the location on the surface of the molten glass and the temperature at the bottom of the melting tank located vertically below that location is such that the difference in the density of the molten glass corresponding to the temperature is 0.05 g / cm³ per meter of distance between the two locations. ３ The difference is less than The glass melt is heated to a temperature exceeding 1580°C for 10 ２ Having a viscosity of dPas, method.

2. The method according to claim 1, wherein the density of the glass melt at the highest temperature location on the surface of the glass melt is less than or greater than the density of the glass melt at the bottom of the melting tank.

3. The method according to claim 1 or 2, wherein the minimum viscosity in the glass melt body is 10 dPas or more.

4. The temperature dependence of the glass melt density in the temperature range from T4 to T2 is at least 9.0 mg / cm³ per 100°C. ３ Optionally, up to 19.0 mg / cm³ per 100°C. ３ Therefore, T4 is the glass of 10 ４ The temperature at which the glass has a viscosity of dPas is such that T2 is 10 ２ The method according to any one of claims 1 to 3, wherein the temperature is such that the viscosity is dPas.

5. The method according to any one of claims 1 to 4, wherein the distance between the hottest point on the surface of the molten glass and the point on the bottom of the molten tank vertically below the hottest point is less than 1250 mm, and optionally at least 750 mm.

6. The method according to any one of claims 1 to 5, wherein the amount of thermal energy obtained from the combustion of fossil fuels is less than 1.0% of the total amount of thermal energy introduced into the melt.

7. The method according to any one of claims 1 to 6, wherein heating the glass melt further includes heating the surface of the melt, and the amount of thermal energy introduced into the melt by heating the surface is less than 40.0% of the total amount of heat introduced into the melt.

8. The method according to claim 7, wherein heating the molten surface includes heating the surface using one or more microwave heaters and / or burning biofuel and / or hydrogen.

9. The method according to any one of claims 1 to 8, wherein the direct heating of the molten body includes electrode heating.

10. The glass melt has a VFT constant B in the range of 5,000 to 9,000 K and a t in the range of 75°C to 240°C ０ The method according to any one of claims 1 to 9, having the above characteristics.

11. A glass product having fewer than 20 bubbles per kilogram of glass, wherein the glass is heated to a temperature exceeding 1580°C for 10 ２ The glass has a viscosity of dPas, and the glass has a viscosity of at least 9.0 mg / cm³ per 100°C in the temperature range from T4 to T2. ３ The glass melt density has a temperature dependence, and T4 is when the glass is 10 ４ The temperature at which the glass has a viscosity of dPas is such that T2 is 10 ２ A glass product having a viscosity of dPas at a given temperature, wherein the glass contains 8.0 to 20.0% by mass of B2O3.

12. The glass melt has a VFT constant B in the range of 5,000 to 9,000 K and a T in the range of 75°C to 240°C. ０ A glass product according to claim 11, having the following characteristics.

13. The temperature dependence of the glass density in the temperature range from T4 to T2 is up to 19.0 mg / cm³ per 100°C. ３ The glass product according to claim 11 or 12.

14. The glass product according to any one of claims 11 to 13, wherein the glass has a coefficient of thermal expansion of 3.0 ppm / K to 8.5 ppm / K in a temperature range of 20°C to 300°C.

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