DE102006050141A1 - Optical glass refining comprises use of high temperature zone, conditioning zone, homogenization zone, finishing zone, and helium recovery zone - Google Patents

Abstract

In a process to refine glass and remove air bubbles, helium is introduced directly to molten glass by diffusion through the walls of the surrounding crucible, followed by forming the optical glass product. The molten glass is subject to further refining, or conditioning, or cutting and shaping of the glass product, or all of these processes. The crucible is made of pure or dosed SiO2, SiO2 ceramic or SiO2 glass. The crucible wall in contact with the molten glass is a refraction metal or refraction metal alloy, a noble metal or a noble metal alloy. An independent claim is included for a helium diffusion assembly with a high temperature zone, a conditioning zone, a homogenization zone, a finishing zone, and a helium recovery zone.

Description

The The invention relates to a method and an apparatus for manufacturing a glass product.

It is known during the production of high quality glass products, in particular should have a small number of bubbles, helium, in particular to the laughter or to improve the purification, into a glass melt. From a glass product with a low number of bubbles say one in particular when the glass product less than 10 bubbles per Kg of glass, preferably less than 5 bubbles per kg of glass and even less than in the case of particularly high-quality glass products 1 bubble per Kg of glass or even less than 0.2 bubbles per Kg of glass contains. counted In doing so, all the bubbles which are visible to the naked eye and / or cause a light scattering. For special applications (e.g. optical glasses) It may also be necessary for bubbles with diameters up to counted in the nm range become.

From the Scriptures US 3,622,296 is the refining of glass melts using NaCl and helium known. The best result - low number of bubbles in the resulting glass, short refining time - was achieved by a mixed clarification of NaCl and helium. Purification with helium alone gave better results than purification with NaCl only.

Helium by means of a bubble dispenser, which includes a porous body with open pores to initiate in a molten glass is from the Scriptures EP 1 184 343 A1 known. By adjusting the pressure volume and / or the working pressure of helium, a helium bubble diameter of <20 mm is set.

In writing EP 1 577 270 A1 An apparatus for producing a molten glass from batch raw materials is described. To reduce the number of bubbles in the resulting glass helium and / or neon is introduced into the glass melt and distributed in this. The average bubble diameter of the helium bubbles introduced into the glass melt by means of gas inlet tubes is equal to or less than 150 mm.

task It is the object of the present invention to provide a method and an apparatus to find a glass product. It should, in particular to the laughter or to improve the purification and to reduce the number of bubbles in the resulting glass product, Helium be introduced into a molten glass. Also should the each required amount of helium cost-effectively introduced into the molten glass become. Furthermore, enough should Helium in the molten glass be provided to the refining to effectively support the molten glass.

Solution of the task:

• – herstellen einer Glasschmelze aus Gemengerohstoffen,
• – einleiten von Helium in die Glasschmelze, wobei Heliums mittels Diffusion durch eine mit der Glasschmelze in Kontakt stehenden Wandung direkt in die Glasschmelze eingeleitet wird,
• – formen der Glasschmelze zu dem Glasprodukt.

The object is achieved by a method for producing a glass product, which has at least the following method steps:

• - producing a glass melt from vegetable raw materials,
• Introducing helium into the molten glass, wherein helium is introduced by diffusion through a wall in contact with the molten glass directly into the molten glass,
• - Forming the glass melt to the glass product.

Under Diffusion becomes the helium penetration, the wall impermeable to the molten glass, from the outside the wall (not in contact with the molten glass) on the inside of the wall (in contact with the molten glass standing side). Helium migrates from the outside with high helium concentration on the inside with low helium concentration and is thus introduced into the molten glass. Especially because of the flow the molten glass, the helium diffusion within the molten glass and by stirring the molten glass, the helium is distributed in the molten glass.

• – läutern der Glasschmelze
• – konditionieren der Glasschmelze
• – homogenisieren der Glasschmelze
• – nachverarbeiten des Glasproduktes.

The method may additionally comprise at least one of the following method steps:

• - purify the glass melt
• - conditioning the glass melt
• - Homogenize the glass melt
• - post-processing of the glass product.

It has been shown that helium can diffuse through the wall in contact with the glass melt made of certain materials and can be introduced in sufficient quantities in the molten glass. Helium diffuses particularly well through walls made of the following materials: pure or doped SiO ₂ , SiO ₂ -containing ceramic, SiO ₂ -containing glass. In particular, the materials may be melt-cast and / or sintered. The composition and the type of microstructure of the material can be used to influence helium diffusion. Less dense, fine-grained structure usually allows increased helium diffusion. The diffusion of helium (but also hydrogen or neon) by quartz glass or fused quartz increases with increasing temperature and is at 700 ° C for helium 2.1 × 10 ^-8 cc / sec / cm 2 / mm / cm Hg. By doping, eg with iron oxide, the permeability to helium can be further increased ( US 6,231,642 B1 ).

The rate of diffusion of helium gas through solids is about three times that of air and about 65% of hydrogen.

Farther It has been shown that the wall of essentially the material how the molten glass itself can exist. That the wall faces the same or a very similar one Composition like the molten glass on. Especially in glass melting processes, in which the solidified glass melt is in contact with the liquid glass melt (e.g., glass melting processes carried out in so-called skull crucibles), Through the solidified glass melt, helium can enter the liquid glass melt be initiated. The solidified glass melt is used in such Method as a wall and glass contact material.

The Wall can also be made of precious metal or a precious metal alloy consist. Precious metals or noble metal alloys, e.g. Platinum and Platinum alloys, find a wide application as contact material to the glass melt (e.g., crucibles, gutters, refining chambers, stirrer). By Diffusion of helium through walls made of these materials Helium can simply be introduced into the molten glass. Suitable noble metals are in particular ruthenium, rhodium, palladium, Rhenium, osmium, iridium, platinum, gold.

Next Precious metals or precious metal alloys are basically all suitable Metals as wall material that provide adequate helium diffusion enable and due to the contact with the molten glass, this is not negative influence. Suitable metals are, for example, refractory metals, such as Titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum and tungsten, or refractory metal alloys.

Preferably the wall is part of the wall of a glass melting unit. Provided helium-permeable materials in existing glass melting units anyway used as a wall and glass contact material (e.g., platinum alloys, Fused silica), helium can easily from the outside through such walls diffuse and be introduced directly into the molten glass. But it can also helium-impermeable Walls or walls that pass helium poorly are replaced by helium-permeable ones become.

A another possibility Introducing helium into the molten glass is by passing pipes through to lead the glass melt. The wall of the tubes is permeable to helium, so that helium through the Wall can diffuse into the molten glass. By the size of the the glass melt in contact wall, the introductory Helium amount can be influenced. The larger the contact area, the more more helium can be introduced into the molten glass. Farther is true that through thin walls more helium can be introduced than by thick. The higher the Temperature of the wall, the more helium can be introduced.

helium is preferably during or before the purification introduced into the molten glass. Additional can helium directly introduced into the molten glass and / or the glass melt a helium-containing atmosphere get abandoned.

Next Helium can other gases by diffusion through the with the molten glass in Contact standing wall, like neon or hydrogen, or direct into the molten glass, such as oxygen, are introduced.

From the known isotopes of helium are 3He and 4He stable. The ratio of the two stable isotopes varies depending on the place of origin, production method or helium supplier.

to support the purification and thus to reduce the number of bubbles in the glass product can additionally chemical Refining methods (eg. B. addition of chemical refining agents, such as polyvalent oxides, halides and / or sulfates to the batch raw materials) and / or physical refining methods (eg high-temperature explanation, Vacuum refining) be used. Helium can be used in addition to diffusion The wall also by injecting (He-bubbling) and / or introduction through the surface of the Glass melt (eg over a He-containing furnace atmosphere) be introduced.

• – Einschmelzbereich, in dem aus Gemengerohstoffen eine Glasschmelze hergestellt wird,
• – Heliumquelle,
• – Gaseinleitungsbereich, in dem Helium mittels Diffusion durch eine mit der Glasschmelze in Kontakt stehenden Wandung direkt in die Glasschmelze eingeleitet wird,
• – Heißformgebungsbereich, in dem aus der Glasschmelze das Glasprodukt geformt wird.

Furthermore, the object is achieved by a device for producing a glass product, wherein the device has at least the following ranges:

• - melting range, in which a glass melt is made from batch raw materials,
• - helium source,
• Gas introduction region, in which helium is introduced by diffusion through a wall in contact with the molten glass directly into the molten glass,
• - Hot forming area, in which the glass product is formed from the glass melt.

• – Läuterbereich, in dem die Temperatur erhöht und die Glasschmelze geläutert wird,
• – Konditionierbereich, in dem die Temperatur der Glasschmelze erniedrigt wird und eventuell verbleibende Restblasen vom der Glasschmelze resorbiert werden,
• – Homogenisierbereich, in dem z.B. Schlieren aufgelöst werden,
• – Nachverarbeitungsbereich, in dem das Glasprodukt nachverarbeitet wird, z. B. getempert, geschnitten, poliert, beschichtet, keramisiert,
• – Heliumzurückgewinnungsbereich, in dem das aus der Glasschmelze aufsteigende Helium zurückgewonnen oder der Zurückgewinnung zugeleitet wird.

Advantageously, the device for producing the glass product additionally comprises at least one of the following ranges:

• - refining area, where the temperature is raised and the glass melt is purified,
• Conditioning area, in which the temperature of the molten glass is lowered and any remaining bubbles are absorbed by the molten glass,
• Homogenizing area in which, for example, streaks are dissolved,
• - Post-processing area where the glass pro product is processed, for. B. annealed, cut, polished, coated, ceramized,
• - Helium recovery zone, where the helium rising from the molten glass is recovered or sent for recovery.

Of the Gas inlet area can the refining area upstream (and downstream of the smelting area), part of the refining area or the refining area be yourself.

helium becomes common from the helium source by means of possible Helium gas-tight lines fed to the gas inlet region. advantageously, Helium will be as possible across from the outside atmosphere helium gas-tight Space led, which comes close to the wall in contact with the molten glass. This will ensure the little helium during transport from the helium source to the molten glass get lost. The gap can also be designed pressure-resistant, so one reaches that of the one in contact with the molten glass Wall adjacent helium gas pressure relative to the atmospheric pressure can be increased and so more helium can be introduced into the molten glass.

While or helium escaping from the glass melt after helium initiation can be collected above the molten glass, if necessary prepared and z. B. again by means of the device according to the invention or the inventive method in the glass melt are introduced.

Advantage of the invention:

• - helium will be at atomic scale introduced into the molten glass, thus very good of the molten glass recorded and distributed and is available in particular Quantities for purification to disposal. With smaller or just as big Helium amounts are thus more effective than in the past known methods.
• - big helium bubbles, as introduced by known methods in the molten glass are poorly absorbed by the molten glass and insufficient distributed, much of the Helium bubbles rise through the molten glass to the surface and thus stands for purification no longer available. To have to much larger quantities at helium melt into the glass in the form of bubbles are introduced to dissolve the same amount of helium in the molten glass as in the introduction according to the invention by diffusion. The inventive method is therefore more economical and more effective and environmentally friendly.

EXAMPLES

Common raw materials for glassmaking were in the Einschmelzkammer (meltdown area) of a continuous operated melted glass melted down. Typical melting temperatures are in the range of 1000 to 1650 ° C. The glass melt was in a refining chamber (Refining) of the glass melting unit transferred. Usually is during the purification Temperature of the molten glass increased and so the viscosity the glass melt is lowered, with temperatures of up to 2000 ° C or even about that be achieved. From a liquid helium tank (Helium source) helium gas of purity> 99.96% was removed and on the outside the refining chamber wall applied. By diffusion through the with the molten glass in Contact standing refining chamber wall helium was introduced directly into the molten glass (gas inlet area). After the purification was the glass melt on the for the subsequent one hot forming necessary processing temperature brought. By means of a hot forming device (Hot-forming area) was formed from the molten glass flat glass.

In several series of tests within the production plant and in Technikumanlegen were flat glasses different composition according to the inventive method produced.

By hot forming the molten glass on a liquid Tin baths (floats) were alkali-free aluminoborosilicate glasses, the especially as display glasses for LCD TFT screens Find use, manufactured.

By hot forming By rolling the glass melt were lithium alumino-silicate green glass produced. Leave such green glasses by ceramization (in the post-processing area) in glass-ceramics convert and in particular are undyed as Kaminsichtscheiben and colored as cooking surfaces used. Both glass products are high quality glasses, which must have a low number of visible bubbles. by virtue of the production of the invention mentioned flat glasses could reduce the number of visible bubbles by a factor of 2 to 100 across from the previously known and applied manufacturing process clearly be lowered.

In both glass products helium was clearly detected by mass spectrometry. Typical helium concentrations are in the range of 0.0001 μl to 2 μl, in particular 0.01 μl to 2 μl per g of glass (0 ° C, 1 bar). Even the 3He / 4He isotope ratio could be determined in the glass product. It is usually smaller that way natural isotope ratio, presumably due to isotopic enrichment effects during helium production or within the glass melt.

• – Quarzal-Wandung (reines > 99 %, gesintertes und teilgeschmolzenes SiO₂)
• – Quarz-Wandung (reines > 99 %, geschmolzenes SiO₂)
• – Platin- bzw. Platinlegierung-Wandung
• – Skull-Kruste mit im wesentliche Zusammensetzung der Glasschmelze als Wandung

Within the gas introduction region, ie the region of the glass melt aggregate in which helium is introduced directly into the glass melt by diffusion through a wall in contact with the glass melt, it was found that the following wall materials are particularly suitable with regard to helium permeability and resistance (fire resistance). prove against the hot and corrosive glass melt:

• - Quarzal wall (pure> 99%, sintered and semi-molten SiO ₂ )
• - Quartz wall (pure> 99%, molten SiO ₂ )
• - Platinum or platinum alloy wall
• - Skull crust with in the essential composition of the molten glass as a wall

ever thinner the wall, the higher the helium diffusion, the more helium can be in the molten glass be initiated. The bigger the In comparison with the molten glass in contact surface of the wall to the volume of molten glass in the gas inlet area (eg volume of the Molten glass in the refining chamber), the more helium can be introduced into the molten glass. Porous, in particular finely porous Wall material supported the helium diffusion. The higher the temperature of the wall, the more helium can be introduced. The diffusion rate depends strongly on the composition and the structure of the wall material. It is advantageous if the wall material a large helium diffusion allows and at the same time resistant across from the glass melt is.

Has been Helium through the wall in contact with the molten glass, which is the wall of a pipe, introduced, quartz, platinum or palladium tubes proven. The helium gas pressure in the tubes can be advantageously adjusted and be regulated. You feed from helium to the diffusion tubes also takes place here by possible helium-gas-tight lines.

Especially the purification of arsenic and / or antimony-free, tin-containing or -reduced Glass melts led to a reduction in the number of bubbles in the resulting glass product.

Claims (10)

A process for the production of a glass product, characterized in that the process comprises the following process steps: producing a glass melt from mixed raw materials, introducing helium into the molten glass, whereby helium is introduced by diffusion through a wall in contact with the molten glass directly into the molten glass, forming the Glass melt to the glass product. Method according to claim 1, characterized in that that the procedure in addition has at least one of the following method steps: purify the Molten glass, conditioning the molten glass, homogenize the Glass melt, post-processing of the glass product. A method according to claim 1 or 2, characterized in that helium through the standing in contact with the molten glass wall of refractory material, in particular of pure or doped SiO ₂ , from a SiO ₂ -containing ceramic, from a SiO ₂ -containing glass or from in essentially the material such as the molten glass is introduced. Method according to claim 1 or 2, characterized that helium through the ones in contact with the molten glass Wall of metal, in particular of refractory metal or a refractory metal alloy, made of precious metal or a precious metal alloy is introduced. Method according to at least one of the preceding Claims, characterized in that helium through with the glass melt wall in contact, the part of the wall of a glass melting unit is, is initiated. Method according to at least one of the preceding Claims, characterized in that helium through with the glass melt in contact wall, which is the wall of a pipe introduced becomes. Method according to at least one of the preceding Claims, characterized in that the helium during or before the refining is introduced into the molten glass. Method according to at least one of the preceding Claims, characterized in that additional Helium introduced directly into the molten glass and / or the molten glass a helium-containing atmosphere is suspended. Method according to at least one of the preceding Claims, characterized in that in addition to helium other gases by diffusion through the wall in contact with the molten glass, such as Neon, or directly into the molten glass, such as oxygen, introduced become. Device for producing a glass product, characterized by a meltdown region in which a glass melt is made from batch raw materials, at least one helium source, at least one gas introduction region in which helium is introduced by diffusion through a wall in contact with the glass melt directly into the glass melt, at least one hot forming region in which the glass melt the glass product is molded.