DE102004060759A1 - Glass melting device, includes two mixed cells that are arranged one behind other in gas flow, where one mixed cell is melted cell with agitator, where agitating device includes mixing blade - Google Patents

Abstract

The device has mixed cells that include an inlet and a discharge, where one of mixed units is arranged between the inlet and the discharge. Two mixed cells are arranged one behind the other in a gas flow. One of the mixed cells is a melted cell with an agitating device, where the agitating device includes a mixing blade. An axis of rotation of the agitating device is arranged vertically. One of the mixed cells is a static mixed cell (100).

Description

The The present invention relates to a device for homogenizing of molten glass.

A decisive factor for product quality in glass production is the homogeneity of the molten glass mass, which is supplied to a corresponding shape. This is especially true in the production of flat glass for special applications. An example of such a special flat glass is the substrate glass for liquid crystal (LCD) displays. These LCD substrate glasses are produced, inter alia, with the so-called micro-float glass process, as it is known from the prior art, for example the DE 3 142 567 , is known.

A insufficient homogenization of the glass mass before entry the molten metal bath leads to streaking in the finished glass. This is called streaking mostly thread-like or straggly Areas in the glass that are different due to their different from the base glass Optically perceive refractive index. Often the streaks come from the refractory material, e.g. Alumina or zircon, of the melting furnace. The streaks usually go from a punctiform contamination, a so-called node. The knot dissolves by diffusion and he pulls threads floating in the glass behind him, which later became streaks appear. Because of the low diffusion speed in viscous glass The streaks have a very long life.

To step the streaks appear as very fine veils, so they are called winds designated. Glass showing winds also becomes windy glass called. Such windy glass arises when inside the glass mass Temperature gradients, in particular between a colder surface layer and the warmer Inside the glass mass occurs. Along the temperature gradient ions diffuse and accumulate in the colder areas of the glass at. In this way, the glass mass is also inhomogeneous, so that it for Training different optical densities comes.

By way of illustration is in 1a an optical photograph of a glass surface with streaks and in 1b a glass surface without streaks shown.

Out the prior art are glass stirring for homogenization of molten glass prior to introduction into a form or a flat glass trough known.

In the DE 10 69 345 discloses a glass stirrer, which consists of a body of revolution with a completely closed surface, with the help of this stirring body, the formation of turbulence in the molten glass to be avoided.

The DE 14 96 443 shows a stirred cell for glass, the mixer blades of the agitator decrease in the direction of the glass flow in their length.

The DE 199 35 686 A1 shows a stirred cell with an agitator, wherein the flowed through by the molten glass annulus cross-section of the stirred cell tapers in the flow direction.

When disadvantageous proves in the known from the prior art stirred cells, that the stirring cells and with it the agitators ever larger radii Must have or annular space cross-sections, if the glass flow rate elevated shall be. The increase the glass flow rate by increasing the radius of the stirring cells pushes very fast to their limits, because even at constant angular velocity of the agitator the speed of the stirring blades with increasing distance from the axis of rotation increases. From a certain Radius of the stirring cell reach the mixing blades in their from the axis of rotation of the agitator remote areas such high speeds over the sluggish Glass mass that it comes to a so-called mechanical "reboil". In this case, a secondary bubble formation occurs in the molten glass. These bubbles are at a supersaturation to be solved Gases formed in the molten glass, the gas being at the concerned Temperature in the stirred cell the highest Has partial pressure, is excreted in the form of bubbles. The mixing blades of the agitator with their high speeds act as it were as Precipitation nuclei. The bubbles themselves form inhomogeneities in the bubble Glass melt and reduce the quality of the finished glass. Would you the angular velocity of the agitator reduce to avoid the "reboil", so it would come again to increased streaking, because now the speeds near the axis of rotation of the agitator are no longer sufficient to make the molten glass in these areas sufficient to homogenize.

Of the increased demand for substrate glasses for liquid crystal displays and displays, however, it requires ever larger quantities on glass with high quality and kindness to manufacture.

Of the The present invention is therefore based on the object, a device to provide homogenizing molten glass, which allows, big ones Produce quantities of flat glass, especially for liquid crystal displays, with high quality, where both a "reboil" and a streak and winding is prevented.

These Task is inventively characterized solved, that one Device for homogenizing molten glass provided is arranged at which two mixing cells in the glass stream one behind the other are.

Of the Expression "in the glass stream in a row " understood that the Mixed cells from the molten glass serially, i. successively, flows through become.

By the inventive arrangement at least two mixing cells in the stream of glass one behind the other must flow through Annular space cross section of the mixing cells are not increased, so that at the same Angular velocity of an agitator in one or both mixing cells no "reboil" at the radially outer portions of the mixing vanes of agitator occurs. By the sequential arrangement of two mixing cells the residence time of the glass mass is increased in the mixing area of the plant, while at the same time the flow rate surprisingly disproportionately elevated can be.

On this way can be Homogeneous mixing of the molten glass even at higher glass flow rates of up to 200 tons per day. In contrast, let itself with the systems known from the prior art only Produce glass quantities of up to 30 tons per day.

With "mixed cells" are the following all facilities or plant sections referred to, the one Mixing and therefore homogenization of the molten glass serve. Such mixed cells can both stirring cells with a stirrer as well as static mixing cells, which do not actively rotate or having moving elements, be.

is one of the mixing cells is a stirring cell, so it is advantageous if the agitator has mixing blades, which the flowing through Mix the jar.

Preferably is the axis of rotation of the agitator arranged vertically.

In a preferred embodiment In accordance with the invention, one of the mixing cells is a static mixing cell without rotatable or movable elements, e.g. a stirrer.

there it is useful if the agitator for low Angular speeds is provided. It is important to take into account that this also for embodiments without additional static mixing plates applies.

Prefers is an embodiment the invention, wherein one of the mixing cells at least one static Device for insertion a change the flow direction of the glass stream. It is under a static device understood such a device that no rotation or otherwise having movable elements, which are flowed around by the molten glass and due to their geometric shape, orientation and arrangement one effect better mixing of the molten glass. Such facilities are advantageous because the direction change high velocity gradients occur in the glass stream and transfer shear forces to the glass mass become. In this way, the streaks are torn apart, and the molten glass is homogenized.

Especially it is appropriate, such static facilities for introducing at least one change the flow direction of the glass stream in a static mixing cell. however can these devices can also be advantageously arranged in a stirred cell.

It is appropriate if the static means for introducing a change in the direction of flow a mixing sheet is. Such mixing sheets can be horizontal or vertical be arranged in the mixing cell. Also are curved devices or mixing plates advantageous.

In a particularly preferred embodiment The invention is the static device for introducing a change the flow direction the glass stream substantially perpendicular to the flow direction arranged the mixing cell. It is under the flow direction a direction substantially parallel to the connecting line between Inlet and Outlet of Mixing cell and / or the inlet side and outlet side Understood end of the mixing cell.

In a preferred embodiment According to the invention, the static device has at least one passage opening. Such passage openings can For example, holes in an otherwise annular plate be.

Conveniently, are the means of introduction a change the flow direction the glass flow with the walls or a fixed core of the mixing cell.

In a particularly preferred embodiment of the invention, the mixing cells have a circular or annular cross-section. In particular, a concentric arrangement of the mixing cells is advantageous. In mixing cells arranged in this way, the glass flow can first flow through the inner or outer cell and subsequently through the other cell. This embodiment allows in particular a compact and temperature-stable design of the mixing cells.

In a preferred embodiment the invention is the inlet of the first mixing cell in the flow direction arranged below the outlet of the first mixing cell, the inlet the second mixing cell in height the outlet of the first mixing cell and the outlet of the second mixing cell below the inlet of the second mixing cell. In this way, for example Concentric arrangement of the mixing cells a compact design be achieved at the inlet to the first mixing cell and the spout from the second mixing cell in the same vertical Level are arranged.

In a particularly preferred embodiment According to the invention, the device has a static mixing cell as well a stirred cell on.

there it is useful if the static mixing cell in the direction of the glass flow in front of the stirred cell is arranged and serves as a premixing chamber.

there it is particularly advantageous if the static mixing cell in a concentric arrangement of the mixing cells arranged radially outside is.

Especially preferred is an embodiment of the present invention, wherein the elements of the mixing cells made of platinum metal. In an alternative embodiment the elements of the mixing cells are made of a heat-resistant material, preferably molybdenum, and are coated with platinum sheet metal.

Conveniently, is the material for the mixing cells or walls of the mixed cells platinum or a Platinum alloy, e.g. a rhodium / platinum alloy with typically 20-30% Rhodium share and correspondingly 70-80% platinum content, which of course also other relative proportions, especially smaller rhodium proportions are used can. Platinum and corresponding platinum alloys have the one required temperature resistance on and show no or at least no significant chemical Reaction with the usual used glass materials, so that neither the glass through the Material of mixed cells is contaminated, still chemically cells be attacked by the molten glass.

In principle, however, could also electrically conductive Ceramic materials used instead of platinum or platinum alloys become.

there be among the elements of the mixing cell all their with the melt coming in contact Components, such as the walls, the mixing plates, the agitator with his mixing wings and understood more elements.

The Manufacture from platinum or the coating with platinum sheet makes it possible the mixed cells directly, i. through a current through the platinum metal of the respective element to heat electrically. In an alternative embodiment the mixing cells are inductively heated electrically, wherein the electric Transfer power to the plate using induction coils becomes. In both cases it is an electrical resistance heater.

The direct or inductive heatability of the elements of the mixing cells allows advantageously the sequential arrangement of several mixing cells, because of this advantageous heating the temperature of the glass mass also over longer stretches of river can be held. In contrast, leads the known from the prior art unheated mixing cells the sequential arrangement of several mixing cells to a cooling of the Glass flow, which in turn adversely affects the glass quality or even makes such an arrangement impossible.

In a preferred embodiment The invention relates to the static mixing cell at the level of the glass level in the mixing cell a process for removing the surface glass on. That way you can Impurities, which are mainly found in surface glass, i.e. floating glass, settle, separated.

Furthermore it is useful if the stirring cell has at its bottom a drain for removing test glass. The test glass thus obtained provides an indication of the homogeneity of the Mixed cells leaving glass mass.

Particularly preferred is an embodiment of the invention in which in a radial arrangement of mixing cells, the inner mixing cell is formed as a conductive and double-walled tube, ie as a tube in which both the inner wall and the outer wall are electrically conductive, inner and outer walls at one end of the mixing chamber, preferably at the upstream end of the mixing chamber, are directly connected to each other, but otherwise the two tube walls are separated and electrically insulated from each other, wherein at the other, preferably at the upstream end of the outlet tube inner tube and outer tube one Have power connection. Connecting these two power connections with a power source, the inner wall and outer wall of the mixing chamber are electrically connected in series one behind the other. Between the inner and outer wall either a corresponding air gap or vacuum or an insulating material, such as a ceramic tube, be provided. The double-walled mixing chamber may for example also be made such that a corresponding insulating ceramic tube is coated internally and externally with the conductive material, wherein the coating extends beyond the downstream end face of the ceramic tube, so that the inner and outer walls of the double-walled tube in this Area are interconnected. At the opposite end then still inner and outer walls must be provided with separate power connections.

The double-walled version in particular a radially inner mixing cell has the special Advantage that a direct heating of the wall of the mixing cell over the entire length of the mixing cell away possible is without the upstream End of the cell a complex power supply through the glass stream is required.

Further Features, advantages and applications of the present invention based on the description of preferred embodiments and the accompanying figures clear.

1a shows a photograph of a glass with streaks.

1b shows a photograph of a glass without streaks.

2 shows a first embodiment of the invention in a side sectional view.

3 shows a side sectional view of an alternative preferred embodiment.

4 shows two horizontal cuts through the mixing cells 3 ,

5a C show top views of three different embodiments of the mixing sheets according to the invention.

6 shows a side sectional view of an alternative embodiment of the stirring cell 2 ,

In 2 a first preferred embodiment of the invention is shown in a cross-sectional view. The individual elements of the plant for the production of LCD substrate glass are described in the order of the manufacturing process below.

In a smelting unit 1 From isostatically pressed zirconia glass basins, the glass raw materials are melted and refined, so that a glass melt 2 arises. In this case, the glass melt in the unit 1 a water level, which as glass level 3 referred to as. During the melting process at temperatures up to 1700 ° C, the zirconia of the aggregate corrodes 1 as a function of time, causing the molten glass 2 Having contaminants through the zirconium, which subsequently leads to the formation of Zirkonschlieren in the substrate glass to be produced. In order to prevent the formation of these zirconia streaks with the resulting inhomogeneity of the substrate glass, the glass melt is passed through a connecting tube 4 made of platinum two stirred cells arranged one behind the other 7 . 7a fed. The stirring cells 7 . 7a have an identical structure. They are from the molten glass 2 in each case in the vertical direction flows from top to bottom, wherein the melt from the outlet 8th the stirring cell 7 over a connecting pipe 9 to the inlet 10a the second stirred cell 7a is directed. Each of the stirring cells 7 . 7a has a stirrer 11 . 11a on, the vertically extending axis of rotation rotates at an angular velocity ω. On each of the axles are mixing blades 12 . 12a provided, which extend from the axes radially outward. The mixing blades 12 . 12a stir those through the stirring cells 7 . 7a flowing glass melt 2 through and tear the streaks and winds present in the molten glass.

From the outlet 8a the second stirred cell 7a the molten glass is connected via a connecting line 13 to the micro-float system 15 guided. Before the spout 17 the micro-float system 15 there is a dispensing needle 16 for dosing the glass mass flowing into the micro-float system. The glass mass 2 flows through the spout 17 on the tin bath 18 , In the illustrated embodiment, all elements are 4 . 7 . 9 . 7a . 13 . 17 made of platinum sheet metal. This also applies to the agitators 11 . 11a or the mixing blades 12 . 12a , The platinum sheet has the advantage that it is heat resistant and does not react with the molten glass. In addition, the individual elements are directly electrically heated, which makes it possible to melt the glass along the way of the unit 1 to the micro float system 15 to maintain a constant temperature without temporal and spatial temperature gradients between the individual elements of the plant. In this way it is possible to extend the residence time of the molten glass in the mixing cells, without having to accept disadvantages due to cooling of the melt. Due to the possibility of arranging two stirring cells 7 . 7a One after the other, it is possible to increase the throughput of molten glass in the system to up to 30 tonnes per day. Exemplary is in 2 an electrical connection 19 drawn for heating the platinum elements of the system.

In 3 is a further preferred embodiment of the invention in lateral cross-section shown. Elements that have the same function as the elements 2 meet or are identical to these are marked with the same reference numerals. This concerns in particular the aggregate 1 to the molten glass and the micro float system 15 for the production of the substrate flat glass.

From the aggregate 1 The molten glass is passed through a connecting pipe 4 to the inlet of a hollow cylindrical static mixing cell 100 guided. This static mixing cell 100 serves as premixer for the downstream stirred cell 103 , The static mixing cell 100 has no rotating or movable elements. Their mixing effect is based on the fact that the cell 100 mixing plates 101 . 107 has, which force the glass stream locally to change its direction of flow. At the in 3 In the embodiment shown, the molten glass meanders in the radial direction on the way from the lower end of the cell 100 to its upper end. Due to the changes in direction, the glass melt has large velocity gradients, with shear forces acting on the melt, which tear the streaks and winds apart.

The mixing plates of the mixing cell 100 are alternately fixedly connected in the vertical direction with the inner and outer side wall of the hollow cylindrical cell.

In the 4a and 4b are two horizontal cuts through the mixing cells 100 . 103 shown. The cuts are in different vertical planes, so that in the first sectional view 4a an annular, with the inner wall of the hollow cylindrical cell 100 connected mixing sheet 107 is shown while in the 4b a mixing plate connected to the outer wall 101 can be seen.

The mixing sheets can also have other shapes and configurations, as they are alternatively incorporated in the 5a C are shown. The sheets 201 . 207 the in 5a illustrated embodiment are substantially part-circular and alternately on the outer wall and on the inner wall of the cell 200 attached. The part-circular plates may be offset in height from each other, as already described with reference to 3 was presented. In 5b is an annular mixing plate 307 represented, which through-flow openings in the form of circular holes 308 having. Vertically on top of each other are again, as in 3 shown several of these mixing sheets 307 arranged, wherein the mixing plates are rotated against each other so that the flow openings 308 of two superimposed mixing sheets never overlap congruently. That way, that's the cell 300 forced through glass mass to change direction, thereby also in this embodiment of the mixing plate 307 a dissolution of the streaks is achieved. In 5c an alternative embodiment of the mixing plates is shown, wherein the basic shape of the mixing plates of 5a equivalent. This show the mixing plates 401 . 407 Flow openings 408 in various forms, shown here as triangles and hexagons.

From the 4a and 4b is clearly the concentric arrangement of the mixed cells 100 . 103 to recognize. While the radially inner stirring cell 103 has a circular cross section, is the cross section of the radially outer static premix cell 100 annular.

In 3 It can be seen that the supply of the glass mass to the static mixing chamber 100 over the connecting pipe 4 at the bottom of the cell 100 he follows. From there, in operation, the flow of molten glass, apart from the meandering movement, moves vertically upward in the radial direction until it passes through the openings 104 in the inner wall of the static mixing cell 100 or outer wall of the stirred cell 103 from the static mixing cell 100 into the stirred cell 103 transgresses. In the stirred cell 103 the flow of molten glass moves substantially vertically from top to bottom, ie from the inlet ports 101 to the bottom of the cell 103 , At the bottom of the cell 103 there is an outlet 109 that with the spout 13 connected is. About the connection line 13 the glass mass arrives as in the 2 illustrated embodiment in the micro-float system 15 , At the top of the static mixing cell 100 is a drain 110 provided with outlet tube, with the help of which the surface glass can be removed. In addition, at the end of the connecting line 13 a process for removing test glass is provided.

In the stirred cell 103 is a stirrer 105 with mixing blades 106 arranged for mixing the glass mass. In this case, the axis of rotation of the agitator extends 105 parallel to the hollow cylindrical outer walls of the cell 103 ie in the vertical direction.

In the in the 2 and 3 In the illustrated embodiments, all the elements which contact the molten glass except the aggregate 1 , made of platinum sheet metal.

These platinum sheets are directly heated by connection to corresponding power sources by an electric current through the walls of the individual elements, such as the connecting pipe 4 or the outer or inner walls of the static mixing cell 100 , is directed.

In 6 is an alternative embodiment the stirred cell 3 shown schematically. Shown is a double-walled embodiment of the outer walls of the stirred cell. The cylindrical wall consists of a U-shaped body 510 made of insulating and heat-resistant material. This one is with a platinum sheet 511 coated, with the outer side of the coating 512 and the inside of the coating 513 at the upper end 514 the cell are interconnected. Likewise, the bottom of the cell is coated by means of the platinum sheet. Now apply a voltage between the lower end of the outer platinum coating 512 and the floor 515 to the platinum metal, so flows a current which heats the platinum sheet and keeps the molten glass at a defined temperature. The illustrated embodiment allows direct electrical heating of the stirring cell 500 although this forms an upwardly completely open tank. If this stirred cell in a concentric arrangement, as shown in 3 is used, it is the glass mass possible to overflow at the upper end of the premixing chamber in the stirred cell without openings must be provided in the walls of the stirred cell. In this way, the flow rate can be further increased. At the same time, it is heatable to the top of the cell 103 possible.

By the arrangement of the mixing cell 100 and the stirring cell 103 it is possible to increase the throughput of molten glass in the plant up to 200 tons per day.

For purposes the original one Revelation is noted that all features as they are from the present description, the drawings and the claims for a To open up a specialist, even if they are specific only in connection with certain others Characteristics have been described, both individually and in any Compilations with other features disclosed herein or Feature groups are combinable, unless this is expressly excluded or technical conditions such combinations were impossible or make pointless. On the comprehensive, explicit representation of all conceivable combinations of features is here only for brevity and omitted for the readability of the description.

1

smelting unit

2

molten glass

3

glass level

4

connecting pipe

7, 7a

stirred cells

8th, 8a

outlet

9

connecting pipe

10 10a

Inlet

11 11a

agitators

12 12a

mixing blades

13

connecting line

15

Micro-float system

16

Dispense

17

outlet

18

tin bath

19

electrical connections

100

mixing cell

101

mixed plate

103

stirred cell

104

openings

105

agitator

106

mixing blades

107

mixed plate

109

outlet

201

mixed plate

207

mixed plate

300

mixing cell

307

mixed plate

308

circular punctures

401

mixed plate

407

mixed plate

500

stirred cell

510

body

511

platinum foil

512

outside the coating

513

inside the coating

514

upper End of the cell

515

ground

Claims (25)

Apparatus for homogenizing molten glass with a mixing cell having an inlet, a drain and at least one mixing element arranged therebetween, characterized in that two mixing cells are arranged one behind the other in the glass flow. Device according to claim 1, characterized in that that at least one of the mixing cells is a stirred cell with a stirrer is. Device according to claim 2, characterized in that that this agitator mixing blades having. Device according to Claim 2 or 3, characterized that the Rotary axis of the agitator vertical is arranged. Device according to one of claims 1 to 4, characterized that one the mixing cells is a static mixing cell. Device according to one of claims 1 to 5, characterized in that one of the mixing cells has a static device for changing the direction of flow of at least part of the glass flow has. Device according to claim 6, characterized in that that the Device is a mixing plate. Device according to claim 6 or 7, characterized that yourself the device extends substantially horizontally. Device according to claim 6 or 7, characterized that yourself the device extends substantially vertically. Device according to one of claims 7 to 9, characterized that the Vaulted furnishings is. Device according to one of claims 7 to 10, characterized that the Device substantially perpendicular to the flow direction of the Mixed cell is arranged. Device according to one of claims 7 to 11, characterized that the Device has at least one passage opening. Device according to one of claims 1 to 12, characterized that the Mixed cells have a circular or annular cross-section. Device according to one of claims 1 to 13, characterized that the arranged in series mixing cells arranged concentrically to each other are. Device according to one of claims 1 to 14, characterized that the Enema of the river direction arranged first mixing cell below the outlet of the first mixing cell is that the enema the second mixing cell about in height the outlet of the first mixing cell is arranged and that the outlet the second mixing cell below the inlet of the second mixing cell is arranged. Device according to one of claims 1 to 14, characterized that the Enema of the river direction arranged first mixing cell above the outlet of the first mixing cell is that the enema the second mixing cell about in height the outlet of the first mixing cell is arranged and that the outlet the second mixing cell above the inlet of the second mixing cell is arranged. Device according to one of claims 5 to 16, characterized that the static mixing cell in the direction of the glass flow in front of the stirred cell is arranged. Device according to one of claims 5 to 17, characterized that the static mixing cell radially outside the stirring cell and is arranged concentrically to this. Device according to one of claims 1 to 18, characterized that the Elements of the mixing cells at least partially made of platinum metal, a Platinum alloy and / or a conductive ceramic. Device according to one of claims 1 to 19, characterized that the Elements of the mixing cells made of a heat-resistant material, in particular molybdenum exist and with conductive sheet metal and / or a conductive one Ceramic are coated. Device according to one of claims 1 to 20, characterized that at least one of the mixing cells by directly passing electrical Current through walls or other elements of the mixing cell heated is. Device according to one of claims 1 to 21, characterized that the Mixed cells are inductively heated electrically. Device according to one of claims 1 to 22, characterized that one the mixing cells in height the glass level a process for removing surface glass having. Device according to one of claims 1 to 23, characterized that she has a process for removing test glass. Device according to one of claims 1 to 24, characterized that at least the lower portion of one of the mixing cell is double-walled is, with inner wall and outer wall of the Mixing cell at one, in particular the upstream end of the cell with each other are connected and the rest separated by an insulating layer, with inner and outer wall have separate electrical connections at the other end of the tube, so that at Connection of separate power connections with a power source outer wall and inner wall of the tube electrically connected in series are.