Glass products and methods for manufacturing the same

Abstract

To provide a glass product which contains a very few defects such as an air bubble and / or a particle, and a method of manufacturing the glass product, especially, an extremely thin glass or extremely thin glass plate.SOLUTION: There is provided a method of manufacturing a glass product, preferably, a method of manufacturing a sheet type glass product, and the method comprises: transferring a molten silicate glass 2 from one region to another region of a glass product manufacturing unit through a noble metal-containing conduit system; and guiding, by the noble metal-containing conduit system, a current such that Joule heat is generated in the noble metal-containing conduit system, especially, in noble metal with a current guided to pass through the noble metal, the current being an AC current, and a time integral value over one positive half wave and one negative half wave being substantially zero.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] FIELD OF THE INVENTION The present invention relates generally to glass products and methods for making same.

[0002] Background of the Invention In glass production, particularly in the production of products made of or including glass, the glass melt is transported from the melting bath area to the forming area via a conduit system. To ensure that temperatures appropriate for the individual glass melts and forming processes are achieved at the corresponding locations, the conduit system must be maintained at a predetermined temperature by a corresponding design of the heat-dissipating section. Therefore, the conduit system must typically be heated, particularly to provide the required viscosity for the molten glass transport process with the required production reliability.

[0003] It is known to heat indirectly, for example by band heaters or by heat radiators configured differently, whereby the conduit system guiding the glass is maintained at a predetermined temperature indirectly via a heat conduction process.

[0004] It is also known to heat directly, typically by heating the walls of the conduit system that guides the glass, via resistive heating, in which Joule heat is released into the glass.

[0005] Australian Patent No. 473784 discloses a method for producing flat glass, whereby the glass to be thermoformed is subjected to electrical heating to adjust the viscosity before forming it into a glass ribbon. In this case, an electric current is passed through the glass to control the temperature and flow of the glass. A drawback of this method is that it can cause bubble formation and electrochemical reactions.

[0006] DE 10 2016 107 577 A1 describes an apparatus and a method for producing glass products from a glass melt, according to which the apparatus has a crucible, such as a stirred crucible, for processing the glass melt and a component, such as a rotatably mounted stirring mechanism, arranged in the crucible, and furthermore, in this case, the apparatus has an alternating current unit that supplies power to the crucible or the stirred crucible via a current connection element in order to heat the glass melt.

[0007] German Patent Application Publication No. 102005015651 generally discloses a method and circuit arrangement for determining impedance in an electrically heated glassmelting tank, as well as the use of this method and a method for producing glass. This publication also describes the use of a heating flow that passes through the glass itself. Impedance measurements are used to identify wear on the melting tank's heating electrodes or palisades and to determine whether platinum-coated stirrers are exhibiting eccentric stirring motion. It is also desirable to detect undesired ground shorts in or on the glassmelting tank, calculate the current flowing between all electrodes in the glassmelting tank, and calculate or determine DC paths that may cause undesired bubble formation and corrosion.

[0008] WO 2020 / 023218 describes a method for directly heating a metal container in a glass manufacturing process, whereby several electric heating circuits, for example with different phase angles, can be selected for heating.

[0009] Typically, when heating a current-carrying conductor element, the applied voltage and the current flowing through the duct system are controlled to regulate the heat generated, and if necessary, the alternating current is modulated. This modulation can be achieved by conversion or by pulse modulation using pulse groups, and in particular by conduction angle control. In circuit technology, this can usually be achieved by transformers, transducers, or even thyristors.

[0010] A drawback of direct heating is that the presence of electrical power generally leads to electrochemical reactions between the precious metal and the glass, especially at the interface, which can cause glass defects in the product, such as bubbles and / or metal particles and / or reduced transparency.

[0011] A drawback of indirect heating is that the heat conduction process causes a time delay in temperature regulation relative to the temperature of the glass present in the conduit system.

[0012] Direct heating of the molten glass during transport along the path from the melting bath to the forming area can result in defects, for example, as a result of interactions between the glass melt and the heat-resistant material. Typically, the glass melt is guided from the melting bath area to the forming area through a conduit system made of or containing a noble metal, such as platinum or a platinum-containing alloy. For example, platinum can be alloyed with rhodium, iridium, and / or gold, and / or the platinum can additionally contain zirconium dioxide and / or yttrium oxide for grain stabilization. The advantage of using noble-metal-containing components as the conduit material is that they are electrically conductive, allowing them to be electrically heated, preferably by passing an alternating current through the components to generate Joule heat that heats the components.

[0013] However, it has been found that during the transport of molten glass, interactions between the glass melt and the precious metal-containing components of the conduit system may occur precisely at the point of contact between the components and the glass melt. These interactions may manifest themselves as defects, such as air bubbles or particles, such as precious metal particles. This is disadvantageous because the air bubbles and / or particles can typically be disruptive to the individual products being handled, potentially increasing the number of defective products.

[0014] This is especially critical in the case of specialty glass, where particularly high requirements are often placed on product quality. For the production of extremely thin glass products, i.e., so-called ultra-thin glass or ultra-thin glass sheets, only a very small number of defects are permitted. In this case, attention must be paid not only to the absolute number of defects, but also to their type and size, depending on the specific requirements for the product. For example, very small particles can be tolerated with little difficulty, whereas larger particles, regardless of their number, always risk causing a defective product.

[0015] Therefore, there is a need for glass products, particularly ultra-thin glass or glass sheets, that contain very few defects such as bubbles and / or particles. Additionally, there is a need for methods for producing such products.

[0016] Problem to be solved by the invention SUMMARY OF THE INVENTION It is an object of the present invention to provide a glass product and a method for producing the same which at least alleviates the weaknesses of known products and methods.

[0017] Summary of the Invention This problem is solved by the subject matter of the independent claims. The dependent claims as well as the description and drawings indicate preferred and / or special embodiments.

[0018] According to a first aspect, the present invention relates to glass products in general, and in particular to sheet glass products, the glass products preferably having a thickness of at most 1100 μm and at least 15 μm, and comprising silicate glass, the glass products having less than 4 particles of precious metal-containing material per kilogram of glass, preferably less than 3 particles of precious metal-containing material per kilogram of glass, preferably at a particle size of less than 200 μm, p is the longest distance in one spatial direction of the constituents (atoms or molecules) of a particle. The average diameter of a particle can therefore be smaller than the particle size defined above.

[0019] By silicate glass, in the sense of the present disclosure, is meant a non-metallic glass containing a high concentration of SiO2 content, for example, a SiO2 content of at least 50% by weight, preferably at least 55% by weight, and advantageously at most 87% by weight.

[0020] A silicate glass melt is a glass melt containing a silicate glass as defined in the previous paragraph.

[0021] Glasses for producing the glass products disclosed herein include, for example, the group of borosilicate (BS) glasses, aluminosilicate (AS) glasses, or boroaluminosilicate glasses, or lithium aluminum silicate glass-ceramics (LAS), which are mentioned here by way of example without prejudice to generality. A glass product according to one embodiment comprises a glass containing at least 50% by weight of SiO2, preferably at most 87% by weight of SiO2.

[0022] According to one variant embodiment of the glass product, the glass further comprises, in addition to the SiO component, an AlO component, preferably in an amount of up to 25% by weight, particularly preferably at least 3% by weight, wherein BO can also be present in the glass.

[0023] According to a further variant embodiment of the glass product, the glass further comprises, in addition to the SiO component, preferably at least 5% by weight, particularly preferably at most 25% by weight, of B2O3, wherein Al2O3 can also be present in the glass.

[0024] For Li-Al-Si glasses, in particular, Li2O contents of 4.6 to 5.4 wt. %, Na2O contents of 8.1 to 9.7 wt. % and Al2O3 contents of 16 to 20 wt. % can be applied.

[0025] As a glass that can be ceramized into glass ceramics or as a green glass, for example, Li-Al-Si glasses with the composition Li2O 3.0-4.2; Al2O3 19-23, SiO2 60-69% by weight and TiO2 and ZrO2 can be applied.

[0026] As borosilicate glass, glasses containing the following components (in % by weight) can be used: SiO270~87 B2O37~25 Na2O+K2O 0.5~9 Al2O30~7 CaO 0-3

[0027] As borosilicate glass, it is also possible to use glasses having the following composition in particular: SiO2 70-86% by weight Al2O30~5wt% B2O39.0~25% by weight Na2O 0.5~5.0wt% K2O 0~1.0wt% Li2O 0~1.0wt% Alternatively, glasses containing the following may be used, in particular alkali borosilicate glasses: SiO278.3~81.0wt% B2O39.0~13.0wt% Al2O33.5~5.3wt% Na2O 3.5~6.5wt% K2O 0.3~2.0wt% CaO 0.0~2.0wt% Alternatively, glass containing the following components in weight percent, particularly alkali borosilicate glass, can also be used: SiO255~85 B2O33~20 Al2O30~15 Na2O 3~15 K2O 3~15 ZnO 0-12 TiO20.5~10 CaO 0~0.1

[0028] As the alkali-free alkaline earth silicate glass, for example, glass containing the following composition in weight percent can be used. SiO258~65 B2O36~10.5 Al2O314~25 MgO 0-3 CaO 0-9 BaO 3-8 ZnO 0-2 However, it applies that the sum of the contents of MgO, CaO and BaO is characterized in that it is in the range of 8 to 18% by weight.

[0029] The silicate glass for making the glass products disclosed herein may further include the following components in weight percent on an oxide basis: SiO2 50-65, preferably 55-65 Al2O315~20 B2O30~6 Li2O 0~6 Na2O 8~16 K2O 0~5 MgO 0-5 CaO 0-7, preferably 0-1 ZnO 0-4, preferably 0-1 ZrO20~4 TiO2 0-1, preferably substantially free of TiO2

[0030] The glass may further contain 0 to 1% by weight of P2O5, SrO, BaO, and 0 to 1% by weight of a fining agent, i.e., SnO2, CeO2, or As2O3 or other fining agent, as well as further components, such as fluorine, if necessary.

[0031] According to a second aspect, the present invention relates to glass products in general, and in particular to sheet glass products, which preferably have a thickness of at most 1100 μm and at least 15 μm, and which comprise silicate glass, and in which the glass product has less than 3 bubbles per kilogram of glass, preferably with a bubble size of less than 200 μm, where bubble size refers to the longest distance in each spatial direction within a bubble, and the average diameter of the bubbles may therefore be smaller than the bubble size defined above.

[0032] This is advantageous because particles and / or bubbles are glass defects that can cause defective products, especially precious metal-containing particles. In this case, whether a glass product containing glass defects such as particles or bubbles is defective or still acceptable for a particular application is a matter of glass defect frequency, i.e., the incidence of such defects, generally expressed per unit of weight of glass, and glass defect size. Thus, while glass defects above a certain size will always result in defective products, relatively small glass defects may still be acceptable for a particular glass product application, as long as they are small enough and do not occur excessively frequently.

[0033] This is precisely where the demands on special glass become even higher, and there is therefore a constant need to provide glass products with only a very low percentage of defects in order to enable more economical production in increasingly demanding product areas.

[0034] Glass products of this kind with improved product quality, i.e., glass products with reduced particle and / or bubble rates and / or only minimal glass defects such as particles and / or bubbles, can be produced in a surprisingly simple manner in a glass product production method according to yet another aspect of the present disclosure.

[0035] It has thus been found that the type, amount and / or size of defects that occur can be influenced by the manner in which the current is conducted in the noble metal-containing component that is in contact with the glass melt.

[0036] Further advantageously, it has been found that the method according to the present disclosure also allows for the elimination of ingredients in the glass composition that are critical to the stability and durability of the precious metal-containing component.

[0037] Therefore, advantageously, the method according to the embodiment also allows the glass to be melted without using SnO2 as a fining agent. In particular, it is possible to use table salt, for example, for fining. Therefore, in general, and without being limited to the glass product embodiments described herein, it is possible to say that the glass product comprises a glass containing, by weight, at most 2500 ppm, preferably 2000 ppm, particularly preferably at most 1000 ppm, even more preferably at most 500 ppm, and even preferably at most 100 ppm, of SnO2. In other words, the glass product in general can comprise a glass containing SnO2 at most in the form of an unavoidable impurity. The glass product can further generally comprise a glass containing, by weight, chloride Cl - and preferably a glass containing at least 100 ppm to 2500 ppm by weight of each of these.

[0038] Such an embodiment of the glass product is advantageous because, in other words, the glass product thus comprises a glass that can be melted using a milder fining agent, which acts much milder, especially on precious metal-containing components, and thus may or may also advantageously help to reduce particle and / or bubble formation.

[0039] Electrochemical reactions generally depend on the current density at the reaction site.

[0040] The present invention therefore discloses a method for producing glass products, preferably sheet glass products, in which a silicate glass melt is transported from one area of ​​a glass product production unit to another area of ​​the glass product production unit via a noble metal-containing conduit system, the noble metal-containing conduit system conducting an electric current in such a way that Joule heat is generated in the noble metal-containing conduit system, in particular in the noble metal, by the electric current conducted through the noble metal, the electric current being an alternating current whose time integral over one positive half-wave and one negative half-wave is essentially zero, which also means that the direct current component of the electric current used to generate Joule heat has the value zero already over one full wave on time average.

[0041] The conduit system according to the invention is preferably used only for transporting the silicate glass melt and, if necessary, for tempering the silicate glass melt during this transport, but not for further functions, such as, for example, fining or homogenization.

[0042] Within the scope of this disclosure, a precious metal-containing conduit system is understood to mean that the conduit system can be composed, for example, predominantly, i.e., at least 50% by weight, or substantially, i.e., at least 90% by weight, or even entirely, of a precious metal or an alloy containing at least one precious metal, such as a precious metal alloy. However, other embodiments are contemplated. Within the scope of this disclosure, a precious metal-containing conduit system can also be configured, for example, as a conduit member, such as a pipe-like conduit system, having a coating disposed on the inside thereof, the coating including at least one precious metal.

[0043] That is, unlike the prior art, not only is the time-averaged current density considered, but essentially all current densities flowing at any one time are considered, which is surprising in that the effect of pulse modulation on defect formation has not been noted in any publications.

[0044] This is particularly surprising when the conduit system comprises a substantially pipe-shaped conduit element with a noble metal-containing coating on the inside and the alternating current is conducted substantially in the longitudinal direction of the pipe-shaped conduit element, since in this case it can be assumed that the alternating current is conducted entirely through the noble metal, that no voltage is present in the space outside the noble metal, and that the waveforms of the voltage and current profiles therefore have little effect on defects in the glass.

[0045] According to one preferred embodiment, the alternating current is substantially sinusoidal and has only one fundamental frequency ω 0 and substantially no other frequency components.

[0046] According to a preferred embodiment, the deviation of the time integral of an alternating current signal over one full wave from the time integral of an ideal sinusoidal pulse signal curve is less than 10%, preferably less than 5%, particularly preferably less than 2%.

[0047] According to yet another particularly preferred method for producing glass products, preferably sheet glass products, a silicate glass melt is transported from one area of ​​a glass product production unit to another area of ​​the glass product production unit via a precious metal-containing conduit system that conducts an electric current in such a manner that Joule heating is generated in the precious metal-containing conduit system, in particular in the precious metal, by the electric current being conducted through the precious metal, and a phase angle θ between the current and the voltage at a fundamental frequency ω is measured.

[0048] In this determination of the fundamental frequency ω, the phase angle θ between the current and the voltage is measured, and this measurement is preferably carried out at least once for each glass of the silicate glass melt used for the method disclosed herein, and is carried out before or at the start of the method, respectively. Although it is in principle sufficient to measure the fundamental frequency ω only at a value at which the phase angle θ between the current and the voltage is at a minimum as a function of the frequency ω, or when it is infinitesimally close to this value, or when the phase angle θ between the current and the voltage is less than ±10°, preferably less than ±5°, particularly preferably less than ±2°, it has nevertheless proven advantageous to measure the fundamental frequency preferably at a value less than about 4*10°. -2 Hz ~ approx. 10 6 Hz range, so that the corresponding above-mentioned phase angle ranges can be identified with higher process safety.

[0049] In this case, the result is that for each individual glass, the angle θ is obtained at which the phase angle θ between the current and the voltage is at a local minimum as a function of the frequency, so that at this minimum the local derivative of the phase angle θ takes the value zero as a function of the frequency ω, and also the following range is obtained: within this range, the phase angle θ between the current and the voltage is less than ±10°, preferably less than ±5°, particularly preferably less than ±2°.

[0050] In this case, the expression that the phase angle θ between the current and the voltage is measured at least once for a silicate glass melt at a fundamental frequency ω also means that, if done in this way, there will be a measured value of the phase angle θ between the current and the voltage as a function of the frequency ω for each silicate glass melt used in the method disclosed herein. As long as the composition of the glass melt remains unchanged, this measurement can be retained for subsequent adjustments of the fundamental frequency ω as described below, and in particular for subsequent implementations of the method without the need to measure this phase angle θ again.

[0051] However, if the composition of the silicate melt changes, i.e., if the components of the silicate glass melt change, then the phase angle θ between the current and the voltage is measured again at least once at the fundamental frequency ω as described above, preferably for the silicate glass melt with the changed glass composition. In this case, if the changed composition of the silicate melt is maintained, the measured values ​​obtained can continue to be used as long as the changed composition of the silicate melt is maintained as is. A change in the glass composition of the silicate melt is considered to be a composition change in which at least one glass component of the silicate melt changes by more than ±5% by weight.

[0052] In this case, based on the measurements already described, preferably the fundamental frequency ω 0 is adjusted based on the measured phase angle θ 0 between the current and the voltage for the subsequent execution of the method.

[0053] Particularly preferably, the fundamental frequency ω is adjusted so that the phase angle θ between the current and the voltage is at a local minimum as a function of frequency, at which the local derivative of the phase angle θ assumes the value zero as a function of the frequency ω.

[0054] In addition to this optimally preferred adjustment, the phase angle θ between the current and the voltage can also be less than ±10° during the method, preferably less than ±5°, and particularly preferably less than ±2°. In the sense of the present description, the term phase angle θ means that the subscript "0" indicates that these phase angles θ can occur not only at frequencies at which a differential minimum of the phase angle θ occurs with the frequency ω, but also within the preferred range in which the phase angle θ between the current and the voltage is less than ±10°, preferably less than ±5°, and particularly preferably less than ±2°; therefore, within the framework of the present disclosure, these phase angles θ are also referred to as minimized phase angles.

[0055] Similarly, the subscript "0" in the description of the frequency ω means that the frequency ω 0 is the frequency at which the minimum phase angle θ 0 occurs within the meaning of the definition given above.

[0056] According to the embodiments described herein, a time-dependent, in particular a periodic voltage with respect to time, having a voltage curve U(ω) that generates the alternating current used in the methods disclosed herein can also be used, the signal components of which have two or more discrete frequencies ω, thus for example at discrete frequencies ω, ω, ω, ... ω. n where n is a non-zero natural number, in which case the overall voltage curve (ω) obtained by superposition of the individual voltage signals is given by: U(ω)=U1(ω1)+U2(ω2)+U3(ω3)+...U n (ω n )

[0057] In this case, U1(ω1),U2(ω2),U3(ω3)...U n (ω n ) are the individual frequencies ω1,ω2,ω3,...ωn The voltage signals are in the form of sine waves or cosine waves having a waveform of . These signals can be generated by sine wave generators, superimposed accordingly, and then amplified as required depending on the application.

[0058] For voltage curves containing multiple discrete frequency components, ω1,ω2,ω3,...ω n For any of the discrete frequency components having frequencies ω1, ω2, ω3, ... ω, the following conditions are satisfied as given above for the fundamental frequency ω: n For each of these frequency components, the individual frequencies θ1(ω1), θ2(ω2), θ3(ω3),...θ n (ω n ) are each less than ±10°, preferably less than ±5°, and particularly preferably less than ±2°.

[0059] According to yet another embodiment, a time-dependent, in particular periodic with respect to time, voltage having a voltage curve U(ω) that generates the alternating current used in the methods disclosed herein can also be used, the signal component of this voltage being ω x From ω y The various frequency components ω belonging to the spectral range or frequency interval up to i A sinusoidal or cosine-like signal component U i (ω i ) and the frequency ω i Regarding ω x <ω i <ω y holds true, However, ω x represents the frequency at which the phase angle θ between the current and voltage is -10°, and ω y represents the frequency at which the phase angle θ between the current and voltage is +10°.

[0060] A signal containing such frequency components can be generated, for example, by a noise generator that provides substantially white noise as an output voltage signal, which is then filtered by a bandpass filter, the passband of which is ω x From nearby y The signal thus obtained can then be further amplified in an application-specific manner.

[0061] For the glasses disclosed herein, but without limiting generality for the temperature range of silicate melts disclosed herein, the fundamental frequency ω is at least 5*10 2 Hz, preferably at least 1*10 3 Hz, up to 1.5*10 4 Hz, preferably up to 2*10 4 Hz. Similarly, the frequencies ω1, ω2,...ω n up to and ω i is at least 5*10 2 Hz, preferably at least 1*10 3 Hz up to 1.5*10 4 Hz, preferably up to 2*10 4 Located within the interval up to Hz.

[0062] ω x Further components of the voltage curve U(ω) having frequency components higher than 15% of the time average of the absolute value of these frequency components, preferably less than 5%, particularly preferably less than 3% of the time average of the absolute value of the voltage curve U(ω), are preferred.

[0063] Similarly, it is preferable to have ω y Further components of the voltage curve U(ω) having frequency components higher than 15% of the time average of the absolute value of these frequency components, preferably less than 5%, particularly preferably less than 3% of the time average of the absolute value of the voltage curve U(ω), are preferred.

[0064] Surprisingly, it has been found that such process control, also referred to as minimized phase angle process control, results in glass products with significantly fewer particles and / or bubbles than conventional resistance heating of precious metal-containing components.

[0065] The inventors do not know the reason for this effect, but speculate that it may be that, when the phase angle is minimized, the charge carriers in the precious metal-containing component are able to follow the AC signal better, or that the movement of positive charge carriers is counterbalanced by the movement of negative charge carriers, thereby reducing the load on the precious metal-containing component and thus improving its mechanical stability. This results in fewer particles being observed in the glass product.

[0066] According to the method disclosed herein, the temperature of the glass melt is between 1200° C. and 1500° C. In manufacturing conditions, glass melt temperatures between 1000° C. and 1650° C. are also contemplated.

[0067] According to the methods disclosed herein, glass products, particularly sheet glass products, are produced or can be produced to thicknesses of up to 1100 μm and minimum 15 μm, and comprise silicate glass, wherein the glass products have fewer than 4 particles of precious metal-containing material per kilogram of glass, preferably fewer than 3 particles of precious metal-containing material per kilogram of glass, preferably at a particle size of less than 200 μm.

[0068] According to the methods disclosed herein, glass products, particularly sheet glass products, are produced or can be produced to thicknesses of up to 1100 μm and minimum 15 μm, and comprise silicate glass, wherein the glass products have less than 3 bubbles per kilogram of glass, preferably with a bubble size of less than 200 μm.

[0069] Within the framework of this disclosure, the following definitions apply:

[0070] Within the framework of this disclosure, noble metals refers to metals belonging to the following list: platinum, rhodium, iridium, osmium, rhenium, ruthenium, palladium, gold, silver and alloys of these metals.

[0071] Within the scope of this disclosure, a component is designated as containing a precious metal if it contains a significant amount of at least one metal from the above list, i.e., more than unavoidable traces, in particular at least 0.1% by weight, preferably at least 1% by weight, and particularly preferably at least 5% by weight. This also includes components that consist primarily, i.e., more than 50% by weight, or essentially, i.e., more than 90% by weight, or even entirely, of at least one precious metal, or a mixture of several precious metals, or an alloy of one or more precious metals. Typical alloys used are, for example, PtIr1 and / or PtIr5, i.e., platinum alloys containing 1% by weight of iridium or 5% by weight of iridium.

[0072] The glass melt of the present invention comprises an oxide melt, in particular a silicon-containing oxide melt, and thus a silicate melt.

[0073] Within the scope of this disclosure, glass refers to an amorphous material obtained in a melting process. Glass products refer to products (or outcomes or articles) that contain glass as a material, in particular products that are primarily, i.e., more than 50% by weight, or substantially, i.e., more than 90% by weight, or even completely, made of glass.

[0074] Within the scope of this disclosure, a sheet-like product is a product whose lateral dimension in a first spatial direction of a Cartesian coordinate system is at least an order of magnitude smaller than its dimensions in the other two spatial directions perpendicular to this first spatial direction. This first spatial direction can also be considered the thickness of the product, and the other two spatial directions can also be considered the length and width of the product. In other words, in the case of a sheet-like product, the thickness is at least an order of magnitude smaller than the length and width of the product.

[0075] Within the scope of this disclosure, bubbles are defined as fluid-filled, usually gas-filled, cavities in a material and / or product. Bubbles can be sealed, i.e., surrounded in all directions by the material, for example by the material of a product made of that material, or they can be open, for example when they are located at the periphery of the product and therefore not completely surrounded by the material forming or contained in the product.

[0076] In the context of the present disclosure, particles refer in particular to particles made of or at least containing a noble metal. In particular, the particles may contain platinum or a platinum alloy, or may be formed from platinum or a platinum alloy. The platinum can be formed in various forms. For example, spherical particles are possible, i.e., particles formed at least approximately as spheres, but needle-like or needle-shaped particles or rods are also possible. The particle dimensions can be up to 100 μm, and typically the particle dimensions are up to about 30 μm. The dimensions stated in the context of the present disclosure are, as already defined above, related to the maximum transverse dimension of the particle or the cell in question. Thus, in the case of needle-shaped particles, the stated size is the length in the direction of the particle's longest extension.

[0077] A glassware production unit is an apparatus that performs or is capable of performing typical process steps for the production of glass and glass products. Typical process steps include feeding and melting the mixture, fining, conditioning, and thermoforming. The area of ​​the unit refers to an area of ​​the apparatus where a specific process step is performed. These areas can be spatially separated from other areas of the apparatus, and thus, for example, a transport device can be present from one area of ​​the apparatus to another. Such a transport device, through which the glass melt is transported from one area of ​​the apparatus to another, is also referred to as a conduit or conduit system within the scope of this disclosure. Such a conduit or conduit system may also be referred to as a duct. Typical areas of a glassware production unit are, for example, a fining chamber or working vessel. In particular, a glassware production apparatus can include, for example, a so-called melting vessel in which the mixture is melted, a fining vessel in which the glass melt is fining, and a holding or working vessel in which conditioning takes place. Homogenization usually takes place in a stirring section, where the glass melt is homogenized by a stirrer.

[0078] This type of optimized process control using minimized phase angles can be achieved, for example, via amplitude modulation. Typically, thyristor regulators are used to generate the alternating current that directly heats the conduit system that guides the glass melt. If this is still the case, a separate circuit can be used to neutralize the conduction angle control so that an at least partially sinusoidal signal curve is generated, resulting in a pulse signal curve that is as sinusoidal as possible, or at least similar to a sine wave.

[0079] In this case, the circuit can include, for example, in addition to the anti-parallel connected thyristors, a further variable transformer on the primary side, so that the voltage on the primary side can be reduced as far as necessary to the operating point, so that the subsequent conduction angle control is less and the signal curve no longer has discontinuities or at least has only very few discontinuities, i.e. it becomes significantly more sinusoidal.

[0080] Furthermore, according to one embodiment of the method, it is advantageous if the harmonic content of the time-averaged absolute value of the pulse signal curve is less than 15%, preferably less than 5%, particularly preferably less than 3%.

[0081] Next, the present invention will be further described with reference to the drawings. [Brief explanation of the drawings]

[0082] [Figure 1] FIG. 1 is a schematic diagram of an experimental setup. [Figure 2] FIG. 2 shows a photographic image of a silicate glass melt obtained with the experimental structure according to FIG. 1. [Figure 3] FIG. 2 shows a photographic image of a silicate glass melt obtained with the experimental structure according to FIG. 1. [Figure 4] FIG. 10 shows a schematic of yet another experimental setup for electrochemical impedance spectroscopy. [Figure 5] 5 shows an impedance spectrum showing the absolute value of the complex impedance Z as a function of frequency ω, obtained with an experimental configuration according to FIG. 4. [Figure 6] FIG. 5 shows the impedance spectrum showing the phase angle θ as a function of frequency ω obtained with the experimental structure according to FIG. 4. [Figure 7] FIG. 1 shows a substantially pipe-shaped conduit member of a conduit system, the member having a coating on the inside containing at least one precious metal, and an alternating current being guided through the precious metal by means of a generator G. [Figure 8] FIG. 1 shows an oscilloscope image in which a periodic voltage curve is displayed on the image as a function of time, where the voltage curve deviates significantly from a sinusoidal waveform, and the deviation is substantially caused by conduction angle control. [Figure 9]FIG. 1 shows an oscilloscope image in which a periodic voltage curve is displayed on the image as a function of time, where the voltage curve deviates only slightly from a sinusoidal waveform. [Figure 10] 1A-1C illustrate particle incorporation into a glass melt for various waveforms of alternating current used to heat a glass melt disposed in a conduit member containing a precious metal. [Figure 11] 11 is a diagram showing an oscilloscope image on which a voltage curve is displayed to explain the current flow during a period T1 in FIG. 10. FIG. [Figure 12] 11 is a diagram showing an oscilloscope image on which a voltage curve is displayed to explain the current flow during period T3 in FIG. 10. FIG. [Figure 13] FIG. 1 shows a basic circuit diagram of an exemplary circuit arrangement. [Figure 14] 1A-1C show exemplary scanning electron micrographs of precious metal-containing particles. [Figure 15] 1A-1C show exemplary scanning electron micrographs of precious metal-containing particles. [Figure 16] FIG. 10 shows yet another substantially pipe-shaped conduit member of the conduit system, the member having a coating on the inside thereof containing at least one precious metal, and wherein a respective alternating current is guided by means of a respective generator G through the precious metal in one of three sections depicted as overflow 0 (UEL0), overflow 1 (UEL1) and overflow 2 (UEL2).

[0083] DETAILED DESCRIPTION OF THE EMBODIMENTS DISCLOSED HEREIN 1 shows a schematic, not-to-scale, experimental setup for determining the effect of pulse modulation on the generation of an alternating current I(ω) in a silicate glass melt. A silicate glass melt 2 is melted in a crucible made of a heat-resistant material containing SiO, for example in a so-called QUARZAL® crucible.

[0084] Two identically sized, noble-metal-containing electrodes 31, 32 with an area of ​​0.5 cm × 1 cm were inserted into each half of the crucible 1. The crucible halves were connected via a glass melt bridge, which means that the current I(ω) flowing between the electrodes 31, 32 was guided so that it passed completely through the glass melt 2. The individual electrodes 31, 32 were formed here, for example, from a noble metal alloy, i.e., from an alloy of platinum and rhodium, which can also be referred to as “PtRh10”, i.e., 10% by weight of rhodium and 90% by weight of platinum. The glass melt 2 was a melt of silicate glass.

[0085] In order to prevent gas phase transport reactions with respect to the noble metal-containing electrodes 31, 32, the space surrounding the crucible 1 is flushed with an inert gas (here argon).

[0086] The crucible 1 is heated to a temperature of, for example, 1450° C. in a furnace.

[0087] Next, between both electrodes 31 and 32, various modulators in generator G, which constitutes an AC power supply, were used to obtain a current of 25 mA / cm between the electrodes 31 and 32 in each experiment. 2 Under the boundary condition that a geometrically time-averaged current density of ω flows, the signal waveform of the current I(ω) flowing between the electrodes 31 and 32 was changed.

[0088] Three experiments, described in more detail below, were carried out in which the electrodes 31, 32 were each subjected to modulation and in contact with the glass melt for 24 hours.

[0089] After a waiting period of 24 hours, one of the electrodes 31, 32 was removed from the crucible half and quickly frozen together with the adhered glass, photographic images of which are shown in Figures 2a-2c.

[0090] As shown in Figure 2, the noble metal contained in the electrodes and the structure of the individual electrodes do not have any changes in grain structure upon currentless heating (image a in Figure 2) and an at least approximately sinusoidal signal curve (image b in Figure 2).

[0091] 9 shows an exemplary oscilloscope image in which a periodic voltage curve U(ω) at a fundamental frequency ω is displayed as a function of time, where the voltage curve only slightly deviates from a sinusoidal waveform and represents the waveform of an alternating current I(ω). In this case, the full wave of one exemplary sinusoidal wave is shown in the interval V. W1 The fundamental frequency ω was, for example, 50 Hz.

[0092] However, when conduction angle control is applied when generating an AC current I(ω), for example using a thyristor (image c in Figure 2), a significant change in the reflective properties of the coarse-grained precious metal crystals can be identified, and it can therefore be inferred that a chemical reaction has occurred.

[0093] 8 shows an exemplary oscilloscope image of a periodic voltage curve U(ω) at a fundamental frequency ω0 as a function of time, where the voltage curve deviates significantly from a sinusoidal waveform, which deviation is essentially caused by conduction angle control, and represents the waveform of the alternating current I(ω) used in the case. The fundamental frequency ω0 was, for example, 50 Hz. In this case, an exemplary first non-sinusoidal half-wave generated by conduction angle control is shown in the interval H W1 The second non-sinusoidal half-wave generated by the conduction angle control is marked by the interval H W2 It is marked by.

[0094] Next, the temperature of the entire crucible 1 was lowered, and the glass body of the half of the crucible from which the corresponding electrode had been removed was scooped out and the bottom surface was polished. Figures 3a-3c show transmitted light images of the samples.

[0095] What is clear here is that no bubbles are discernible in the case of the current-free signal curve (image a in Figure 3), and that only a very small number of bubbles are present in the case of the signal curve that is at least approximately sinusoidal (image b in Figure 3).

[0096] However, when the conduction angle control by thyristor is applied (image c in Figure 3), not only can significant bubble formation be observed, but also darkening of the glass around the formed bubbles, which can be attributed to the formation of precious metal particles.

[0097] In yet another method of his own, the inventors applied electrochemical impedance spectroscopy with the aim of being able to more precisely distinguish the properties of the individual glasses used.

[0098] A schematic experimental setup for electrochemical impedance spectroscopy is shown in Figure 4. In this case, glass was melted in a platinum crucible 50 with a diameter of approximately 10 cm, with the fill level F of the silicate glass melt 51 being approximately 10 cm. The crucible 50 was maintained at a predetermined temperature in a furnace, and the electrode to be tested, here a rectangular platinum electrode 53 with dimensions of approximately 2 x 4 cm, was inserted into the glass melt 51.

[0099] Both the crucible 50 and the electrodes 52, 53 are electrically responsive via a platinum wire 54. Furthermore, an O2|Pt|ZrO2 reference electrode 52 (which is washed with 1 bar O2 as a reference) was inserted into the glass melt 51 to obtain an independent reference potential for the electrochemical measurements.

[0100] The electrochemical impedance spectrometer was connected in the following configuration:

[0101] The working electrode 53 constitutes the platinum electrode under test, the reference electrode 52 is an inserted O2|Pt|ZrO2 reference electrode, and the crucible 50 constitutes the counter electrode.

[0102] Impedance spectra were recorded using potentiostatic electrochemical impedance spectroscopy, and an excitation voltage of 25 mV was selected.

[0103] In this way, the following impedance spectrum of a glass melt 51 of composition corresponding to glass AS87 was obtained: 6 Hz~5*10 -3 Hz frequencies were recorded at melting temperatures of 1200°C, 1300°C, 1400°C, and 1500°C.

[0104] For illustrative purposes only, the resulting current is designated I(ω) and the resulting voltage is designated U(ω). The complex impedance then also depends on the frequency, Z(ω) = U(ω) / I(ω), and its absolute value |Z| is shown in the impedance spectrogram of Figure 5 for various temperatures.

[0105] The phase angle θ(ω) between the current I(ω) and the voltage U(ω) shown in frequency dependence, represented as "Theta" in FIG. 6, shows a clear frequency dependence with a significant minimum, the use of which according to the method will be explained in more detail below.

[0106] According to this experiment, an apparatus such as that shown in Figure 7 will be simulated and the interaction of precious metals, particularly precious metal-containing conduit systems, with silicate melt will be specifically investigated.

[0107] Surprisingly, it has now been found that the experimental results obtained with the apparatus shown in FIGS. 1 and 4 are substantially transferable to other embodiments, such as the embodiment shown in FIG. 7, in which the current is not substantially conducted directly through the silicate melt or glass melt 2, but is instead conducted substantially through the noble-metal-containing region, and thus through the coating or lining 62, which will be described in more detail below. While this positive effect appears to be incompletely understood, one reason for the transferability of the obtained results may be the skin effect of AC-frequency currents in conductors, which results in higher current densities at the conductor surface than within the conductor, since the conductor tends to keep its interior free of electromagnetic fields and voltages. Nevertheless, this relatively high current density, which occurs on the surface of each conductor, is in direct contact with the glass melt 2 adjacent to the conductor 62.

[0108] 7 shows a substantially pipe-like conduit member 60 in a conduit system for conveying a glass melt, which may extend, for example, between a melting unit and a thermoforming device.

[0109] The conduit member 60 includes a pipe section 61 made of a non-combustible, heat-resistant material, having on its interior a coating 62 containing at least one precious metal or a lining 62 containing a precious metal.

[0110] As previously mentioned, the precious metal may include, for example, platinum or an alloy with platinum, such as platinum alloyed with rhodium, iridium, and gold, and / or platinum may additionally include zirconium dioxide and / or yttrium oxide for grain stabilization.

[0111] An alternating current I(ω) is passed through the precious metal by means of a generator G, whereby an alternating voltage U(ω) is generated in the generator, as shown in FIGS.

[0112] In this case, the fundamental frequency ω0 was adjusted based on the phase angle θ0 between the current and the voltage.

[0113] In particular, the fundamental frequency ω is adjusted so that the phase angle θ between the current and the voltage is at a local minimum as a function of the frequency ω, at which the local derivative of the phase angle θ takes on the value zero as a function of the frequency ω.

[0114] Such a minimum value can be read, for example, from the graph of FIG. 6 for the value of the frequency ω0.

[0115] However, depending on the implementation of the method, this minimum is not located in a sharply localized position with a pronounced peak, but rather in a region with a slight gradient. For the embodiments disclosed herein, this angular region with a slight gradient has also proven advantageous, in which the phase angle θ between current and voltage is less than ±10°, preferably less than ±5°, and particularly preferably less than ±2°.

[0116] Generally, the fundamental frequency ω is preferably at least about 2*10°F when the phase angle θ between the current and the voltage is −10°F within the temperature range of 1000°C to 1650°C for the glasses disclosed herein, as can be seen, for example, from the graph of FIG. 6, when the phase angle θ between the current and the voltage is less than ±10°F. 2 Hz~5*10 2 Hz, which is around ω x If the phase angle θ0 between the current and voltage is +10°, the maximum is about 1.5*10 4 Hz~2*10 4 Hz, which is ω y corresponds to.

[0117] Although the apparatus shown in FIG. 7 essentially only has current I(ω) flowing through the glass melt 2 in the direction of arrow P, as already explained above, experiments have shown that the results obtained with the apparatus shown in FIG. 1 are surprisingly transferable to the conduit element 60 shown in FIG. 7, and that this method of minimizing phase angles significantly reduces both bubble formation and particle entrapment.

[0118] The results of the impedance spectroscopy are shown in two graphs in Figures 5 and 6. In Figure 5, the absolute value of the complex impedance Z is plotted as a function of frequency. Curve 101 was measured at a melting temperature of 1500°C, curve 102 at a melting temperature of 1400°C, curve 103 at a melting temperature of 1300°C, and curve 104 at a melting temperature of 1200°C.

[0119] What can be clearly seen here is that the absolute value of the impedance depends on the temperature and is approximately at least about 2*10 2 Hz~5*10 2 Hz up to approx. 1.5*10 4 Hz~2*10 4 This means that it passes through a minimum at frequencies up to 100 Hz.

[0120] In Figure 6, the phase angle θ is plotted as a function of frequency. For the same glass, curve 105 was measured at a melting temperature of 1500°C, curve 106 at a melting temperature of 1400°C, curve 107 at a melting temperature of 1300°C, and curve 108 at a melting temperature of 1200°C. Again, at these temperatures, a minimum of 5*10 2 Hz up to 2*10 4 It has been found that at frequencies up to 100 Hz, the phase angle has a minimum value, i.e. a very small value of between a maximum of ±10°, for example between a maximum of ±5°, or even at most between a maximum of ±2°.

[0121] The results achievable by the method according to the invention are shown, by way of example only, in FIG.

[0122] FIG. 10 shows the results of the production of an alkali-free alkaline earth silicate glass in an exemplary glassware manufacturing apparatus, also referred to as a vessel for short, the exemplary composition of which has already been given above.

[0123] In this vessel, between the finer tube and the crucible of the device connected before or part of the thermoforming apparatus, there is a connection by a transfer tube, i.e., a conduit member 60 shown in yet another embodiment in Figures 7 and 16. This conduit member 60 is initially heated via three heating circuits designated overflow 0 (UEL0), overflow 1 (UEL1), and overflow 2 (UEL2). Although Figure 16 shows the overflow 0 (UEL0), overflow 1 (UEL1), and overflow 2 (UEL2) heating circuits arranged in tandem as an example, these heating circuits could also be arranged in parallel with each other in the embodiment shown in Figure 7.

[0124] In this case, all three heating circuits are initially driven via a transformer with a 10 V tap, which essentially corresponds to what is shown in Figure 7, where, by way of example and for the sake of clarity, only one heating circuit is shown, which supplies a voltage U(ω) and a current I(ω) by means of a generator G. This situation is again shown in more detail in Figure 16.

[0125] The action of the heating circuit is shown via corresponding current measurement curves 701, 703, 705, where measurement curve 701 is assigned to overflow 2, measurement curve 703 is assigned to overflow 1 and measurement curve 705 is assigned to overflow 0, and measurement curves 702, 704, 706 relate to the electrode potential E (written as voltage U), where measurement curve 702 is assigned to overflow 2, measurement curve 704 is assigned to overflow 1 and measurement curve 706 is assigned to overflow 0.

[0126] Further illustratively, the number of precious metal-containing particles that were mixed into the glass melt during this period is indicated as 8, and these particles are indicated in the form of square symbols, although not all are shown for clarity.

[0127] The three different states are described below.

[0128] Period T1 is approximately 6.5 days

[0129] All three heating circuits were powered through a transformer with a 10V tap.

[0130] The heating circuit UEL0 has a voltage with an effective value of about 8.2 V, a current with an effective value of about 1700 A, and a relatively small conduction control, but ω y The oscillating current was driven by conduction angle control, which generated harmonics with frequencies above 100 kHz.

[0131] The heating circuit UEL1 was driven with a voltage having an effective value of about 2.9 V, a current having an effective value of about 700 A, and a strong conduction angle control. The heating circuit UEL2 was driven with a voltage having an effective value of about 3.1 V, a current having an effective value of about 500 A, and a conduction angle control. y The harmonics generated by the FET are of high frequency and are driven by a strong conduction angle control.

[0132] 12 shows an oscilloscope image with the voltage curve for overflow 1 in period T3 displayed on the image. The conduction angle control is less pronounced in this case.

[0133] In Figure 11, an oscilloscope image is shown in which the voltage curve for overflow 1 in period T1 is displayed on the image. The conduction angle control is strongly evident here, and therefore ω y These frequencies occur within one full wave of U(ω) at the strongly-marked voltage jumps Sp1, Sp2, Sp3, and Sp4, which can be clearly identified in Figure 11. In this case, the preferred frequency, i.e., ω y It was also found that exceeding these frequencies had a worse effect than falling below them.

[0134] When the above-described method was carried out, the number of noble metal particles, particularly platinum particles, mixed into the glass melt 2 was about 7.0 particles per kg on average.

[0135] Period T2, which is approximately 15 days and follows period T1

[0136] The heating circuits UEL1 and UEL2 were combined, resulting in one new heating circuit (UEL1).

[0137] Both heating circuits were powered via a transformer with a tap having a voltage rms of 10 V.

[0138] The heating circuit UEL0 was driven with a voltage having an effective value of about 8.2 V, a current having an effective value of about 1650 A, and a relatively slight conduction angle control.

[0139] The heating circuit UEL1 was driven with a voltage having an effective value of about 4.7 V, a current having an effective value of about 640 A, and with a reduced conduction angle control than that shown in FIG.

[0140] When carrying out the method just described, the number of noble metal particles, in particular platinum particles, entrained in the glass melt 2 was, on average, about 3.8 particles per kg.

[0141] Period T2 was followed by period T3, which lasted approximately 9.5 days. The heating circuit UEL0 was powered via a variable transformer with a tap having an effective voltage of 8 V.

[0142] The heating circuit UEL1 was powered via a transformer with a tap having a voltage of 10 V rms.

[0143] The heating circuit UEL0 was driven with a voltage having an effective value of about 7.6 V, a current having an effective value of about 1550 A and with a conduction angle control that was as optimized as possible, ie smoothed.

[0144] The overflow UEL1 was driven with a voltage having an effective value of about 4.7 V, a current having an effective value of about 640 A, and a conduction angle control reduced from that shown in FIG.

[0145] The fact that the rms voltage was lower than the rms voltage of the tap in the above operation during periods T1 to T3 represents the typical case for current-loaded transformers, which may exhibit a drop in rms voltage as the level of rms current increases.

[0146] 12 shows an oscilloscope image on which the voltage curve for overflow 1 in period T3 is displayed. As can be seen, the conduction angle control is significantly reduced in this case compared to the voltage curve shown in FIG. 11, as already mentioned above for the voltage curve with reduced conduction angle control.

[0147] When carrying out the method just described, the number of noble metal particles, in particular platinum particles, entrained in the glass melt 2 was, on average, about 2.5 particles per kg.

[0148] These examples show that the effect of conduction angle control is reduced and the sinusoidal AC current I(ω) is increased, resulting in minimal particle contamination in the melt 2.

[0149] FIG. 13 shows a simplified basic circuit diagram of an exemplary circuit arrangement. Conductors L1, L2, L3, and N are conductors that carry the phases of a power supply network 70, which can be part of an internal or external power supply network. This power supply network 70 can supply an AC voltage of 230 V rms between each pair of conductors of phases L1, L2, and L3 at a network frequency of 50 Hz, or even higher in the case of an internal power supply network. With this arrangement, in which the fundamental frequency ω has not yet been optimally selected, it has already been shown that blocking harmonics of frequencies ω outside the desired frequency range, especially those above the desired frequency range, has a positive effect on the objective of the proposed task.

[0150] Via a fused protection device or switch 71, the conductors with phases L1 and L3 are led into a further circuit which will be explained in more detail below.

[0151] When the protective device 71 is closed, the phase L3 is supplied to the parallel circuit including the thyristors T1 and T2, which are controlled in a regular manner by the control circuit 72 and in particular fired respectively.

[0152] In this case, thyristors T1 and T2 are typically arranged between potentials designated U1 and U2, respectively, to provide conduction angle control and to feed variable transformer 73 together with phases L3 and L1 having conduction angle control.

[0153] The variable transformer 73 is configured to convert the voltage with conduction angle control formed by the thyristors T1 and T2 into a defined low voltage.

[0154] Moreover, using such a variable transformer 73 is also a good option for re-equalizing, ie smoothing, the conduction angle control provided by thyristors T1 and T2.

[0155] The variable transformer 73 supplies at its terminals U and V the voltage and current as described above for the electrodes 31 and 32 as described above. The terminal designated PE can contain a ground potential E for grounding a corresponding assembly, for example a conduit element or conduit system, also called a duct.

[0156] An internal or external power supply network 70, a fused protection device or switch 71, a control circuit 72, and thyristors T1 and T2, as well as a variable transformer 73, essentially provide the generator G already described.

[0157] If the power supply network 70 is configured as an internal power supply network, instead of an effective voltage specified, for example, as 220 V and an AC voltage specified, for example, as a fundamental frequency ω of 50 Hz, this power supply network can also be operated with other effective voltages and other fundamental frequencies ω.

[0158] In this case, this fundamental frequency ω0 can correspond to the frequencies shown in FIGS. 5 and 6, for example, especially if it is an internal power supply network.

[0159] 14 shows a scanning electron micrograph of an exemplary needle-shaped particle containing at least one precious metal, which may also be referred to as a precious metal-containing needle. The needle herein has a maximum lateral dimension of about 100 μm, and therefore has a size G within the meaning of this disclosure of about 100 μm. p The aspect ratio of such needles is typically 100, meaning that the needles are about 100 μm long and only about 1 μm wide and deep. The scale 9 in the lower region of Figure 14 represents a length of 60 μm.

[0160] FIG. 15 shows yet another scanning electron micrograph of an exemplary particle comprising at least one precious metal, which has a size G within the meaning of this disclosure of about 32 μm. p , which has a significantly smaller aspect ratio than the needles in Figure 14. Although the particle shape deviates from an ideal circular or spherical shape, such particles are still referred to as spherical. The scale depicted in the lower region of Figure 15 represents a length of 10 μm. [Explanation of symbols]

[0161] 1 crucible 2. Glass melt 8. Number of precious metal-containing particles 9 Scale 31, 32 electrode 41, 42 conductor 50 Crucible containing precious metals 51 Glass Melt 52 Reference electrode 53 Working electrode 54 Conductor 60 Pipe members that are part of a pipe system 61 60 pipe sections made of non-combustible heat-resistant material 62 a coating or lining of the conduit member 60 containing at least one precious metal 70 an internal or external power supply network having an effective voltage of, for example, 220 V and an exemplary AC voltage fundamental frequency ω0 of 50 Hz; 71 Fused protective devices or switches 72 Control circuit for thyristors T1 and T2 73 Variable Transformer 81 Noble metal-containing particles formed as needles 82 Spherically formed precious metal-containing particles 101, 105 Measurement curve at melting temperature of 1500℃ 102, 106 Measurement curve at melting temperature of 1400℃ 103, 107 Measurement curve at melting temperature of 1300℃ 104, 108 Measurement curve at melting temperature of 1200℃ 701, 703, 705 Current measurement curves 702, 704, 706 Electrode potential measurement curves F Glass fill level during impedance measurement G generator G p Size of precious metal-containing particles P direction of current I(ω) inside glass melt 2 Voltage jumps within one full wave of Sp1 U(ω) Voltage jumps within one full wave of Sp2 U(ω) Voltage jumps within one full wave of Sp3 U(ω) Voltage jumps within one full wave of Sp4 U(ω) T1 thyristor T2 thyristor U1: the first potential at which thyristors T1 and T2 are placed U2: the second potential at which thyristors T1 and T2 are placed U Terminal of variable transformer to electrode 31 UEL0 Heating circuit overflow 0 UEL1 Overflow 1 heating circuit UEL2 Overflow 2 heating circuit V terminal of variable transformer to electrode 32 PE Terminal with earth potential E Ground potential for grounding corresponding assemblies, e.g., conduit elements or conduit systems also called ducts V W1 Full wave of substantially sinusoidal current I(ω) H W1 The first half-wave of the substantially non-sinusoidal current I(ω) H W2 Second half-wave of the substantially non-sinusoidal current I(ω)

Claims

1. 1. A method for producing a glass product, preferably a sheet glass product, comprising the steps of: a silicate glass melt is transported from one area of ​​a glassware production unit to another area of ​​said glassware production unit via a precious metal-containing conduit system; the noble metal-containing conduit system conducts an electric current in such a manner that the electric current conducted through the noble metal generates Joule heat in the noble metal-containing conduit system, in particular in the noble metal; In a method for manufacturing glass products, the current is an alternating current I(ω) whose integral with time over one positive half-wave and one negative half-wave is substantially equal to zero; a phase angle θ 0 between the current and the voltage at a fundamental frequency ω 0 is measured at least once; the fundamental frequency ω 0 is adjusted based on the phase angle θ 0 between current and voltage; The phase angle θ 0 between the current and the voltage is less than ±10°. Manufacturing methods for glass products.

2. the conduit system includes a substantially pipe-shaped conduit member having a precious metal-containing coating on the inside of the conduit member, and the alternating current is guided substantially in the longitudinal direction of the pipe-shaped conduit member; A method for producing a glass product according to claim 1.

3. The alternating current I(ω) is substantially sinusoidal and has a fundamental frequency ω ０ having The method for producing a glass product according to claim 1 or 2.

4. the deviation of the time integral of the alternating current signal over one full wave from the time integral of an ideal sinusoidal pulse signal curve is less than 10%, preferably less than 5%, particularly preferably less than 2%; The method for producing a glass product according to claim 1, 2 or 3.

5. The fundamental frequency ω ０ is the phase angle θ between the current and the voltage ０ is adjusted to lie at a local minimum as a function of frequency, at which the local derivative of the phase angle θ assumes the value zero as a function of the frequency ω; A method for producing a glass product according to any one of claims 1 to 4.

6. The phase angle θ between the current and the voltage ０ is less than ±5°, particularly preferably less than ±2°; A method for producing a glass product according to any one of claims 1 to 5.

7. The time-dependent progression of the voltage curve U(ω) generating said alternating current I(ω) has signal components with two or more discrete frequencies ω, i.e. preferably with two or more discrete frequencies ω １ , ω ２ , ω ３ ,. . . ω ｎ where n is a natural number other than zero, and the overall voltage curve U(ω) obtained by the superposition of the individual said signal components is such that: U (ω) = U １ (oh) １ )+N ２ (oh) ２ )+N ３ (oh) ３ )+...U ｎ (oh) ｎ ) It arises like this, However, U １ (ω １ ), U ２ (ω ２ ), U ３ (ω ３ )...U ｎ (ω ｎ ) are the individual frequencies ω １ , ω ２ , ω ３ ,. . . ω ｎ a voltage signal in the form of a sine wave or cosine wave having a Preferably, ω １ , ω ２ , ω ３ ,. . . ω ｎ For any of the discrete frequency components up to ω, the following condition is satisfied: １ , ω ２ , ω ３ ,. . . ω ｎ and the phase angles θ 1 (ω 1 ), θ 2 (ω 2 ), θ 3 (ω 3 ) between the current and voltage at each frequency are , .... θ n (ω n ) is less than ±10°, preferably less than ±5°, particularly preferably less than ±2°; A method for producing a glass product according to any one of claims 1 to 6.

8. The time-dependent progression of the voltage curve U(ω) that generates the alternating current I(ω) is ｘ From ω ｙ Various frequencies ω belonging to a spectral range or frequency interval up to ｉ a sinusoidal or cosine-shaped signal component U ｉ (ω ｉ ) signal components including a continuous spectrum, and the frequency ω ｉ Regarding oh ｘ <ω ｉ <ω ｙ holds true, However, ω ｘ represents the frequency at which the phase angle θ between the current and the voltage is −10°, and ω ｙ represents the frequency at which the phase angle θ between the current and the voltage is +10°, The method for producing a glass product according to claim 7.

9. The fundamental frequency ω ０ is at least 2*10 ２ Hz, preferably 5*10 ２ Hz, up to 2*10 ４ Hz, preferably 1.5*10 ４ Hz, up to 9. The method according to any one of claims 1 to 8.

10. the temperature of the glass melt is 1000°C to 1650°C; 10. The method according to any one of claims 1 to 9.

11. The glass product preferably has a thickness of up to 1000 μm and a minimum of 15 μm and comprises silicate glass; the glass product has less than 4 particles of precious metal-containing material per kilogram of glass, preferably less than 3 particles of precious metal-containing material per kilogram of glass, preferably with a particle size of less than 200 μm; 11. The method according to any one of claims 1 to 10.

12. The glass product preferably has a thickness of up to 1000 μm and a minimum of 15 μm and comprises silicate glass; The glass product preferably has less than 3 bubbles per kilogram of glass with a bubble size of less than 200 μm.

11. The method according to any one of claims 1 to 10.

13. The glass product contains at least 50% by weight of SiO ２ , preferably up to 87% by weight of SiO ２、 Glass containing The glass is preferably SiO ２ In addition to the components, preferably up to a content of 25% by weight, particularly preferably at least 3% by weight, of Al ２ O ３ Contains ingredients, and further contains B ２ O ３ may also be included in the glass. or The glass is preferably SiO ２ In addition to the component, preferably at least 5% by weight, particularly preferably up to 25% by weight, of B ２ O ３ component, and further Al ２ O ３ may also be included in the glass.

13. The method according to any one of claims 1 to 12.

14. The glass product contains up to 2500 ppm by weight of SnO ２ , preferably up to 500 ppm by weight of SnO ２ , more preferably up to 100 ppm by weight of SnO ２ and / or a glass containing at least 100 ppm chloride by weight, preferably at most 2500 ppm chloride by weight, 14. The method according to any one of claims 1 to 13.

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