DE2408867C3 - Method and device for producing an endless ribbon of glass - Google Patents

Description

The invention relates to a method for the production of an endless glass ribbon, in which one melted Glass from a conditioning vat through a discharge device onto a bath of molten Metal flows between guide bodies, the stream of molten glass over the surface of the Metal bath leads away, this cools to a dimensionally accurate glass ribbon and the endless glass ribbon from the Metal bath decreases.

The invention also relates to a device for producing an endless ribbon of glass with a glass melting furnace which is connected to a conditioning device, with an outlet device, which are thermally insulated to a shaping chamber with a bath of molten metal and lateral Leit- or delimitation bodies is aligned and with means with which one the endless dimensionally stable Pulling glass ribbon down from the metal bath.

It has already been proposed to manufacture an endless ribbon of glass in such a way that one melts Glass on a bath of molten metal, the density of which is greater than that of the glass, for example molten tin or tin alloys, pour the glass over the molten metal while cooling pulls away, it becomes a dimensionally stable glass ribbon or a dimensionally stable endless one Pulls out the glass plate and then removes the tape or plate from the bath for further processing.

In its beginnings, this procedure is an example in U.S. Patents 7,10,357 and 7,89,911. After this, molten glass becomes continuous

lerart on a bath of molten metal luigegossen that it forms a ribbon of glass on it, whereupon nan pulls it over the bath of molten metal while cooling and then removes it as a finished product Glass ribbon decreases

A glass made by the processes of US Pat. Nos. 7,10,357 and 7,89,911 has, as in the US patent 32 20 816, severe deficiency in terms of its optical quality. This is followed by optical distortions in glasses then, if it does not succeed, the bottom surface of a bath that is poured onto a metal bath To loosen the glass flow. Such a non-loosening of the floor surface has the effect that deficiency, which previously formed during conventional refining and conditioning of the glass, are retained.

Within the publication of US Patent No. 7 10357 _an d 7 89 911 following period of half a century, there was some further developments that made it possible to carry out the manufacture of flat glass a large scale by a float process. These fundamental developments relating to the float process are described in US Pat. No. 3,083,551 and 3,220,816. After this, molten glass poured onto a bath of molten metal spreads sideways unhindered until it comes to a state of equilibrium in its width and thickness, and the molten glass that is poured onto the molten metal and floating on it can be drawn out into an endless ribbon of glass . According to the cited patents, molten glass is poured freely falling onto molten metal. After hitting the molten metal, the molten glass divides into a backward-flowing and a forward-flowing layer, both of which flow laterally. As described in US Pat. No. 3,220,816, the backward flowing layer is glass which has come into contact with an outlet device made of refractory material and has been contaminated as a result. This part of the glass spreads outwards, that is, into the edge zones of the finished strip, and can be separated therefrom without difficulty. According to the inventions described in the patents mentioned, glass ribbons can be produced with an equilibrium thickness which satisfactorily meets the requirements of their use in terms of their surface properties and their chemical homogeneity.

In US-PS 35 40 872, which a method and a chamber device for flat glass production; regards, is the amount of heat transfer in a glass stream of greater width than depth means Controlled materials with different levels of thermal conductivity. In the course of further developments on the The field of glass production, especially of developments that relate to the production of glasses with an over or strength below the equilibrium thickness, it has been found that the for the Manufacture of flat glass previously used method, the main characteristics of which are unimpeded Lateral glass flow at the beginning of the glass production, the application of the glass melt in free falling and that Backward flow of at least part of the glass melt is one of the optical defects in the finished glass and make it unsuitable for uses for which it is significantly higher optical quality than it should have a few years ago. For example, it has been used for the production of Windshields made of glass produced by the float process have been found to be useful to use relatively thin glass, that is, a glass thinner than equilibrium glass and a A thickness of 1.52 to 3.81 mm, preferably 2.25 mm, according to the float process, has a thickness of Glass manufactured less than about 3.81 mm has been found to exhibit greater optical distortion than a jar of equilibrium thickness. There are great difficulties in making a glass that is like this small thickness which is of the quality required for automobile windshields.

The invention relates to a method and an apparatus for producing flat glass from excellent optical quality. Further, the flat glass according to the invention has the following details properties described and favorable for its processing.

The method according to the invention of the type described in the introduction is characterized in that (a) sets the glass flow in the conditioning vat in a laminar flow, (b) at least the glass flow partly as a relatively thin and wide glass ribbon over a support body, the outlet device can flow through while maintaining its laminar flow structure on the metal bath, the Glass stream flows horizontally or on a downward sloping path onto the metal bath without freely reaching the To attract metal bath, and (c) behind the outlet device higher temperatures of the two edge zones of the Adjusts the glass flow and lower temperatures of its middle zone so that the viscosity of the glass in the Proximity of the guide body in relation to the viscosity in the middle zone decreases and thereby the laminar Maintains the flow structure of the glass stream until the glass is removed.

The device according to the invention is characterized by one by means of a threshold and one The metering device is much wider than the high opening of the glass outlet device, its support device in terms of the height of the metal bath is arranged so that the glass flow is horizontal or on flows onto the metal bath in a downwardly inclined path without falling freely onto the metal bath, Cooling devices centrally above the glass ribbon on the metal band and heating devices above the edge zones of the glass ribbon in the vicinity of the guide body, with a laminar flow structure of the glass in the conditioning device as well as in the shaping chamber.

According to the invention, molten glass is transferred from a glass melting furnace into a refining or conditioning tank initiated, in which the glass melt is brought to a laminar flow. The laminar flowing glass is discharged from the refining or conditioning tub through an outlet device diverted and thereby traverses a relatively short path to a bath of molten metal. in the In cross section, the outlet device presents itself as an opening of elongated, rectangular shape, which below from the top of a support block or a threshold, above from a measuring lock, for example a lifting door and is bordered on the sides by counter brackets or walls. Here is the distance between the upper and lower boundary body smaller than between the side walls, so that the molten glass passes through the opening in one through the distance between the side walls certain width flows through, which is a multiple

their thickness determined by the distance between the upper and lower boundary lines power.

The molten glass flows through the outlet device onto a bath of molten metal, for example tin or a tin alloy. The glass melt is according to the invention on a flow onto the metal on a horizontal track or on a downward sloping track. No way However, the molten glass may fall freely on the metal bath because the molten glass falls freely the even laminar flow that it has assumed in the lautering or conditioning tub, rips off. This tear-off is most clearly evident after the glass melt has fallen freely Edges of a ribbon of glass. The width of the glass flow can be determined by parallel guide bodies, the are attached along the glass path and practically prevent the glass melt from flowing sideways, especially when the molten glass maintains a high temperature and consequently has such a low viscosity, that sideways flow would be inevitable. The guide bodies can be short. You can in practice designed as the side parts of the outlet device or over a longer distance downstream be arranged. The guide bodies are preferably produced from a material which is different from the glass melt Strongly over a certain length of the guide body, at the ends of the guide body where the glass melt has cooled more, but can practically no longer be wetted. One can use the guide body with funds too their heating or cooling and thereby the degree of their wetting by the glass melt regulate. Furthermore, a layer of lubricant can be applied between the glass melt and the guide bodies will. The guide bodies are insulated from their surroundings in order to prevent the glass melt from settling in undesirably cools their edge zones.

An important feature of the invention is based on the fact that the glass stream in its edge zones along the Guide bodies has such a high temperature and such a low viscosity that it is important, as is the case with the Method according to U.S. Patents 7,10,357 and 7,89,911 is the case, no excessive pull is exerted. Therefore, the glass produced according to the invention shows in its Edge zones no herringbone-like distortions. Of the experts in the field of glass production Common expression "herringbone-like distortion" denotes one in the edge zones of a ribbon of glass in a series of angular lines presenting a distortion. It is believed that this phenomenon is caused by a excessive speed gradient is caused in the glass. You submit the show from the room the guide bodies moving downstream glass ribbon for further cooling. At the same time one lets on it in its direction of movement pulling forces act to it while maintaining the width that it is at Leaving the space delimited by the guide bodies has to take off to its final thickness. the The width of the ribbon of glass usually varies less than plus or minus five percent of its average Broad. In addition, the ribbon of glass generally pulls less than five on its way over the metal bath Percent in its width together.

The threshold forming part of the outlet device consists of a refractory one of which Molten glass wettable material, for example quartz glass. It extends, the measuring device opposite, over the entire width of the glass outlet zone. You can simply melt the glass over the Let the fire-proof threshold flow away. You can between the refractory threshold and the glass melt however, a lubricant or a lubricating film, for example made of molten metal or molten Salt. Alternatively, one can also use one made of an inert material, especially platinum that is, the bottom part that is not reactive with the glass. This bottom part is in part formed into a threshold over which the molten glass flows. It can be downstream in one arranged at a certain distance from the intended lower glass flow level and with a layer of be covered molten metal, which is in communication with the metal bath. The one after this Embodiment lying under the mirror of the metal bath bottom part can on its the refining or The end facing the conditioning tub should be slightly raised. This is to prevent that molten metal overflows into the refining or conditioning tub. One can do this for this purpose also build in a footbridge or a weir or a threshold that removes the metal bath from the refining or Separate conditioning zone.

The lifting door against which the molten glass flows can consist of quartz glass and preferably at least be clad with platinum on the side facing the lautering or conditioning tub. Man can also make them from molybdenum. Alternatively, you can place one at a short distance from the surface of the Use a mechanical lock fitted with glass outlet nozzles and with this between establish a gas barrier in the refining or conditioning zone and the glass forming zone. As a result the great width which the glass flow flowing off through the glass outlet device in relation to its Height, small changes in the height of the outlet opening result in significant changes in the

Cross-sectional area of the glass flow. Therefore, the problem of a controlled measurement of the glass flow, which has so far been solved in such a way that the width of the glass flow leaving the outlet opening to a significantly lesser extent than the width of an unobstructed glass flow produced glass ribbon corresponds to a precise setting of the dosing device (lifting door) in relation required to the bottom surface of the draining glass melt. Therefore one uses for the preferred

ten embodiments of the invention working with great accuracy and reliability metering and measuring systems.

A particularly suitable method for regulating the cross-sectional opening in a glass feeder

is described in US Pat. No. 3,764,285.

In a simplified representation, according to the invention a glass flow is transferred from a melting furnace into a conditioning vat, in this into a laminar flow and then fed to an outlet device (10 direction, the opening of which is significantly wider than is high and which is shorter in its longitudinal direction than the outlet opening is wide. In general, the Outlet device a length of less than about 20% of the width of its opening. From the Konditionic rungszonc a stream of glass passes through the glass outlet device through it while maintaining its laminar flow structure onto a bath of molten metal The flowing glass melt remains with the outlet

direction in connection. During the flow through the outlet device and when flowing up the metal bath, the glass stream remains aligned in one direction across its entire width. The glass stream is prevented from draining sideways, cooled and turned into one in the direction of the glass web dimensionally stable, endless ribbon of glass pulled out.

In the method according to the invention, the glass stream becomes transverse to its direction of flow at one width held, which is essentially no greater than the ι ο width in which the glass melt from the conditioning zone is fed to the outlet device. This, along with making and maintaining a laminar flow structure, constitutes the excellent optical quality of the according to the invention made of glass that is much better than that of glasses made by the conventional float process getting produced.

According to the invention, this remains on the surface of the prior to flow through the glass outlet device Glass bath flowing glass at or near the surface during the glass forming process of the glass ribbon, while the glass flowing through the glass outlet device in contact with its bottom part, the bottom surface of the finished glass ribbon forms with which it will be used during the duration of the glass forming process rests on the metal bath. Glass that flows through the glass outlet opening on its sides remains also in the finished glass ribbon essentially at this point. These flow conditions, which up to the end of the Glass molding process remains unchanged, is the improved optical quality of the glass after the Attributing invention.

In addition to those described, the method according to the invention in its preferred embodiments offers further advantages over the known float methods, which are believed to be attributable to an improved interaction between the refining zone of the glass melting furnace and the float forming zone. In the known processes for producing float glass, the glass forming chamber is clearly closed off from the glass source in the mechanical and hydrodynamic sense. According to this method, glass is drawn into a narrow channel from any point in the refining zone of a glass melting furnace, whereby the flow structures present in the refining zone in the glass bath are destroyed. The glass melt leaving the channel in a narrow stream is allowed to fall freely onto a metal bath, where it spreads out in all directions. With the known floal processes, the effects that are brought about at the entrance and exit of narrow channels in glass flows, and the free fall of the glass shape causing two bends of 90 ° in the direction of flow, allow the glass to fall onto the metal bath for processing the glass bottom with significantly different flow conditions and in other ways, too, in a substantially different quality than were present in the melting furnace and in the refining zone in the glass. ⁽ '°

According to the invention you put in the Lauter or Conditioning zone laminar flows expediently by creating such thermal conditions so that a large and therefore stable convection cell is formed. One sets the same '-s thermal conditions in a zone that extends from that in the end wall of the Kondilionierungswanne in the Outlet / .onc leading opening from at least 15 m extends upstream into the conditioning tub. The zone expediently extends with same thermal conditions over 23 to 37 dr. upstream. You can, however, without doing a other than an economic disadvantage would go even further. This is required Compliance with temperature gradients in the glass melt, what with a surface radiation pyrometer can be measured. In the mentioned zone, the temperature should be on average at least Decrease 1.1 ° C to 30 cm, but no more than about 8.3 ° C to 30 cm. Preferably men represents one Temperature drop averaging 2.2 to 3.9 ° C 30 cm ago. Too little temperature drop prevents the development of a full laminar flow, while too high a temperature drop results in sporadic segregation, which leads to irregularities in the composition and consequently leads to differences in the refractive index.

In the preferred embodiments of the invention, each is applied to the glass in the refining zone Applied heat control is advantageously used to keep the bottom of the glass flow through the outlet device to relocate the forming level to a level above that in the purification or conditioning zone produced neutral flow plane. The neutral flow level in the lautering or conditioning zone is the level under the surface of the glass bath in which the glass practically does not flow. Above the neutral At the same level, the glass flows with increasing speed in the direction of the process flow. Right away forms below the neutral plane, caused by that present in the purification or conditioning zone natural thermal convection, a glass flow opposite to the general flow of glass. According to a preferred embodiment is used to cool the refining or Conditioning zone mainly immersed in the ribbon of glass and under its refractory floor built-in cooler.

Thereby the flowing glass layer on the surface of the glass bath in the refining zone lifts off and lets it flow through the outlet device onto the metal bath, they remain in the The refining zone produced laminar flows until the end of the glass preparation process. So far The glass has chemical irregularities, these occur as a result of sporadic mixing not to light, because no optical lenses can be seen as long as glass elements with different Refractive indices are retained in flat, parallel planes.

An unexpected and particularly useful result of the method according to the invention may dcrr Cooperation between the Lauter or conditioning zone and the glass outlet device trains be written. With the glass outlet device nacl of the invention cannot alone stabilize the flow conditions established in a glass stream it also has a beneficial effect on the flow and heat conditions in the Lauter or Konciilio nation zone. The fact is likely that the method according to the invention is relatively düiim Glass layer from the glass bath in the Lauteröler Konditio nicrungszonc is removed, ascribed to the fact that dii Flow rate is within the Gcsamischich of the glass bath changes, with the forward flowing part of the glass mass close to the surface de

Glass bath becomes more uniform in its depth and width. Therefore, the hot glass mass in the refining or The conditioning zone gives off heat to its surroundings to a greater extent without being in the glass bath undesirable thermal stresses arise.

Since molten glass absorbs and radiates heat excellently, the heat loss is at one relatively thin glass layer is significantly larger than a relatively thick layer of the same glass. Hence is in contrast to the conventional float process, which works with a strong glass flow, in which The method according to the invention removes the glass from the refining or conditioning tank in a relatively wide manner and thin stream derived. Furthermore, in the method according to the invention, the heat can be significant remove more effectively. This has been found in experiments and shows that the method according to the Invention provides a higher production output than the known method, without adding the equipment must be expanded. The process has also proven to be energy-saving.

The emergence and persistence of laminar flows when performing the method according to the The invention can easily be determined from the cross-sectional area of a finished glass ribbon. When Even with the known float process, laminar flows can be produced, as is the case with the finished ones Glass ribbons, seen in cross-section, can be recognized by their parallel layers, so shows one after the US Patents 30 83 551 and 32 20 816 produced glass ribbon at its edge zones but a definite and distinctive "J-hook" pattern. This indicates that in this procedure the laminar flows have not been consistently maintained. The glass made according to the invention does not show such a "J-hook" pattern. Rather, it shows in cross section a pattern of telescopically nested uniform layers that are not characteristic in the edge zones of the glass ribbon Form distortion lines. The characteristic features of the after a known method and the after The glasses made according to the invention are drawn from those drawn from photographs on an enlarged scale Figures 8 and 9 can be seen. It is also assumed that the characteristic internal structure of float glass is after glass produced according to the invention is reduced.

The glass currents created in the refining or conditioning zone achieved with them Advantages and the flow of the glass melt through the glass outlet device are in the above description discussed in detail. Also that the glass between guide bodies over the metal bath slides is important for a high quality of the glass.

Ribbons of glass, which in the past were made by cooling thin, laterally delimited streams of glass produced, were in their two-sided peripheral zones to a depth of about 10 to 15% of the Bandwidth interspersed with strong optical distortions. For example, the distortion increases in one Tape 3 m wide into an edge zone 15 to 60 cm deep. So long glass ribbons by cooling If the streams of glass were limited by lateral barriers, glass losses were considered to be due to strong ones Edge trimmings as unavoidable and were accepted.

It has now been found that the

Use of a suitable thermal system ii the roughness delimited by the side lobes optical distortions in the peripheral zones; Glass ribbon can restrict to a zone width which is less than about 1% of the bandwidth. The glass ribbons usually have beaded edges, di < have to be removed later, because edge trimmings are required anyway by the Distortions at the edge of the glass ribbons no glass ver

losses.

The thermal systems preferably used in the method according to the invention differ of the known systems essentially in that they are directly in the glass forming zone

behind the glass outlet device, higher temperatures on the two edge zones and lower temperatures be applied to the middle zone of the glass flow. While an increase in temperatures in the vicinity of the guide or delimitation body

Increased wetting, which alone can cause a stronger pull on the glass, as was determined the viscosity of the glass is increased by producing suitable temperature gradients across the width of the glass in the vicinity of the guide or delimitation body in the

in relation to the viscosity in the middle zone so can be greatly reduced so that less tension is exerted on the glass stream. For better understanding it is useful to see the flow of the glass as the flow of two immiscible liquids

imagine, the main glass flow almost in its entire width having a relatively flat velocity profile, while the glass flow in the vicinity of the guide or delimiting body has a very steep velocity profile. One can observe the main glass flow w ^nte u, ^{application of} the sand grain test. In accordance with the laws of flow and assuming a flow position directly on the outer wall of each leu or delimiting body, the flow of currents can be determined

η · η ^ ⁿⁿ ^ ^{ip The glass sniffing at the edge of the} glass ribbon acts as a lubricant for the main flow. Given the general nature of glass, this may seem surprising.

One can describe the gas flow between the guide or ^Öe S ^renzun gskörperern on the basis of the following mathematical analysis. In this analysis,

«, * M ^GE " ^Ucrnun 8 ^from any point on the center line of the glass flow to one of the

Leu or delimiting body out, where .van the

Center line O is
* the distance from an arbitrarily assumed

menen reference point to any

u- ii ^Un S-'ir ^e . ^rDirection 8 of ^the glass flow.

half of the space between the guide or

Ölimiting bodies corresponding Glasbreilc, A Ta ^{an d} 5 ^Leit body wall λ- - wist.

Depending on the width of the edge flow, i.e. the glass mass flowing close to the wall, which has a lower viscosity than the glass of the main flow, μ is the viscosity of the glass

hMi 5 ^eschw _D ^{in the} direction of the glass flow at a ^point 'η of the main flow direction of the

Distance in the direction of the ΔP pressure drop over .lic distance L.

Note to I and Il 1 refers to the

Main glass flow II refers to the glass flow at the edge

<5 * = 6Iw

ρ = μ, II μ Ι

Based on a differential equation of motion, the following terms apply:

1 ΛΡ Γ_νν ^ _ (W - fif (w - f. M *> - _2L ^ _n /, II " ⁺ /, I

«I.

2L L α «Π

[2Λ * -Λ * ² + ρ (1 -2 (5 * + ό * ² - ** ² )]

2d *

A * 2

11th

1-x * ²

2Λ * -.

-A * f

If a soda-lime-silicate glass is produced according to the invention, high velocity gradients can be effectively set in boundary zones so that the main stream remains essentially flat over 90% of its flow width. A glass of the composition: 73% SiO ₂ ; 13.5% Na ₂ O; 0.4% K ₂ O; 8.7% CaO; 3.8% MgO; 0.15% Al ₂ O ₃ ; 0.3% SO ₃ and 0.15% Fe ₂ O ₃ , for example, has the viscosity-temperature relationships given in Table 1 below:

Table 1

viscosity temperature (Poise) ( ⁰ C) 2 1439 3 Π 87 4th 1023 5 908 6th 877 7.6 723 13th 547

In the manufacture of glass from the composition described in US Pat. No. 7,10,357, the falls The temperature in the edge zones of the glass is well below the temperature of the glass in its central zone. As a result of the natural loss of heat through the sidewalls, the temperature is in the Edge zones of the glass 55 to 11TC below that which the Glass in its middle zone hai. The result is that the viscosity of the glass in the vicinity of the walls is five to ten times as high as that of the glass in its central zone. This will affect the glass in the Edge zones exerted a pull, causing them to appear in large parts of the edge zones as "herringbone-like Distortions «form known sequences of optically distorting vortex lines.

When considering glass of this composition according to those described in US Pat. No. 3,083,551 and 3,220,816 Process, the glass has about the same temperature along its edges as in his middle zone. In general, only one caused by the free fall of the glass mass is produced one connected with the constriction of the glass flow to its unimpeded flow to the side Edge distortion fixed This distortion in the form

ίο a dashed line differs significantly from the distortion caused by tension. However, there are "herringbone-like distortions" sometimes to a very strong cooling in the edge zones, this is because even without deep Temperature drops create an elongated, parabolic shaped velocity profile in the transverse direction of the glass ribbon is created. Here is the process that prevents "herringbone-like distortion" arrives, metastable at best.

In the method according to the invention, the glass flowing in the middle is cooled more quickly than the glass flowing along the edges. For this purpose, cooling devices or heating devices are arranged centrally over the glass path or over the edge zones of the flowing glass. In order to heat the glass flow in its edge zones, the guide or delimiting bodies can also be heated or they can be thermally insulated from the side walls of the glass forming chamber. Keeping the glass stream in its edge zones at a temperature that is at least the pressure prevailing in the central portion of the glass stream temperature equal to, this, however, preferably 11 to Ul ⁰ C exceeds. Normally, the glass is supplied isothermally with a temperature of about 1090 ^° C. at the point

between the control and limitation of bodies on which the medium, consisting of about 90% of the fed glass glass stream has a temperature of about 980 ⁰ C, the glass stream has in its edge zones has a temperature of about 1040 ⁰ C. When the

Glass stream downstream reaches the ends of the control or limitation body, it has in its central part a temperature of about 870 ⁰ C and in its edge zones, a temperature of about 890 ⁰ C. The velocity profiles resulting from this temperature

door patterns are practically flat over 90% of the glass width, with the speed in the middle about 1.1 times the speed at a point on either side of the ribbon of glass in a distance of 5% of the bandwidth in the band. One can use the above math Equations derive a whole series of possible velocity profiles. The actual Speed profiles can be used for a specific; thermal pattern can be confirmed by experiments ss the one with grains of sand in the inner zone de; Glass flow.

You can use the speed profiles that occur with the known traversers according to the method of the invention using the above equations and through experiments on a large scale Easily compare small scales with each other. In the equations, the speed is critical in the interior Zone of the glass flow based on that of a zone which corresponds to 5% of the width of the glass ribbon

ds distance from the edge of the tape inwards Typical examples of this speed ratio are: 10 to 20 in a process in which the glass flow comes into contact with the outer walls; 4 to 6 bt

a float process of the known type with an isothermal width profile; 1 to 5 or better 1 to 3 for the method according to the invention, d. This means that the velocity of the glass flow is in its mean Zone is preferably up to five times greater, particularly preferably up to three times greater than the speed, which the glass stream has at a distance of about 5% of a width from the outer edge inward.

From this it follows that the glass stream in the method according to the invention over its entire width ι ο is more uniform than with the known method with the result that there is less glass loss There is distortion in the edge zones of the finished glass ribbon.

A further advantageous embodiment of the method according to the invention is characterized in that the faster cooling of the middle zone of the glass flow means that the edge zone of the glass flow near the downstream end of a delimiting body receives a temperature that is at least H ₁ I ⁰ C above the temperature of the glass flow lies on a line along its central zone, which connects the downstream ends of the two delimiting bodies.

In summary, it can be said that the method according to the invention compared to the known float method offers a number of advantages that are of significant benefit to glass manufacture. Some these advantages are mentioned again below.

In that the glass mass is removed from the feeding device can no longer spread unhindered to the side, this is greatly simplified Problem of feeding a glass stream centrally through a glass forming chamber to the peel rolls and transferring them to a cooling device. It also greatly reduces the difficulty of evenly removing Counteract the heat from the glass mass.

Furthermore, one cannot use the device Invention use lower glass temperatures in the refining zone because, since the glass melt is not in the free falling is applied to the metal and a backward flow of the glass stream is excluded, the risk of devitrification when the glass passes from the refining tank into the glass forming chamber is reduced to a minimum. This is because, according to the method of the invention, a glass jam practically does not occur. As a result of the lower temperatures in the refining zone, in a glass melting furnace and a refining tank of a given size can be operated at higher throughputs.

Furthermore occurs in the glass according to the invention by the according to the invention across the width of the glass flow flat velocity gradients produced in conventional glass at the edge "Herringbone" optical distortion to a much lesser extent.

In addition to the production of glass, the invention also offers advantages in the case of subsequent processing. For example, according to the invention, gas can be used in all common strengths in the form of endless Make webs of substantially uniform width so that you can check and use Cutting the webs apparatus for glasses of various thicknesses use k ^ .p.n and these in their Brick setting do not need to be regulated. According to the invention, glasses of any composition suitable for floatvciionniing can be used manufacture, for example soda-lime-silicate glass or borosilicate glass.

The invention is based on the drawings in the following description with reference to more preferred Embodiments shown and explained in greater detail.

In the drawing shows

Fig. 1 in longitudinal section a device for the production of glass according to the invention and as part of this device means by which the glass melt flowing through it and onto a bath of molten metal,

F i g. 2 the device according to FIG. 1 in section on line 2-2 from above,

3 shows a further embodiment of the glass outlet device in a longitudinal section in an enlarged representation,

4 also in longitudinal section and also in enlarged form, a further embodiment of the Glass outlet device and

F i g. 5, 6 and 7 those in the lautering or conditioning zone immediately before the molten glass flows off in the glass.: d existing flow pattern. Here shows Fig. 5 shows the typical speed profiles for glass production using known processes, while the F i g. 6 and 7 show the speed profiles as they are for the glass bath during glass production after Invention are typical.

Also shows

8 in a true-to-scale representation in cross section a glass ribbon made according to US Patents 3,083,551 and 3,220,816 and

F i g. 9 shows a glass ribbon according to the invention in the same representation.

An apparatus for producing glass according to the method according to the invention is shown in FIGS. 1 and 2 shown in the drawing. According to FIG. 1 of the drawing contains a lauter or conditioning tub as End member of a glass melting furnace molten glass 12. The refining vat It is provided with a discharge device 13 connected through the molten glass 12 in a measured amount into the glass forming chamber 15 flows. The forming chamber 15 contains a metal bath 16 which has a greater density than the glass 12. the The level of the metal bath 16 is so high that the molten glass 12 can flow without affecting the Metal bath 16 to fall and, flowing in one direction, following on the metal bath 16 in the forming chamber a device 17 is drawn towards where a finished endless glass ribbon from the forming chamber 15 takes out. Parts of the refining tub 11 are a fireproof floor 19, side walls 21 and a roof 23. In a preferred embodiment, the zone connected to the outlet device 13 is fused glass zone a cooled lauter tun with a stepped floor. The refining or conditioning tank containing the molten glass is arranged so that the glass flowing through it towards the outlet device slowly cools down. The step shapes of the bottom of the lauter tun and the bottom cooling have the effect of stabilize laminar flows. The glass melt 12 is cooled so that they still is flowable and, after further moderate cooling, can be worked out into a dimensionally stable glass plate can. For glasses with the typical soda-lime-silicate composition, choose directly from the The outlet point of the refining bath has a temperature of about 930 to 1200 ° C.

Part of the outlet device 13 is a threshold 25 or a similar block-like body, which is under the Surface of the molten glass lies and the molten glass in the refining bath from the metal bath in the Forming chamber separates. This threshold 25 is provided with a device 26 for regulating the temperature fitted. With its upper side, the threshold 25 is preferably about 5 to 46 cm below the glass level in the lauter tun. In relation to the process according to the invention, this means that the glass stream is used upstream from the point at which the glass stream flows out of the refining zone, via a below the Surface of the glass bath arranged threshold can flow, the threshold with its top 5 to 46 cm lies deep below the surface of the glass bath and runs parallel to the surface of the glass bath Preferred embodiment is made of refractory material threshold 25 with means 26 to her Heating or cooling equipped This allows the temperature of the flowing over them Regulate the glass melt and the degree of its wetting by the glass melt. To the outlet device also include counterholders 27 and 27 'as a lateral delimitation of a channel for the flow of the Molten glass. It also includes an adjustable measuring device 29 which extends down into the molten glass reaches in. A lifting door that can be moved up and down is used as a measuring device and the size of the horizontal formed by it, the threshold 25 and the counter brackets 27 and 27 ' Longitudinal slot determined.

According to the vertical position that the lifting door 29 assumes, a stream of glass from the refining bath is called through the outlet slot onto the tin bath 16. The width of the glass stream is held by the counterholders 35, 27 and 27 'limited The width of the glass flow is determined by the distance between the counterholders 27 and 27 '. In order to keep the glass flow in this width, guide or delimitation bodies 31 and 3Γ are arranged on. The guide or delimiting bodies 31 'and 31 are arranged parallel to one another and are made of one material produced, which is wetted to a limited extent by molten glass, for example graphite or alumina. You can equip them with means for temperature control, for example with heating or cooling means. In A preferred embodiment can be in the guide or delimiting body over its entire length away set a temperature gradient so that they are relatively close to the gas passage device are wetted more by the glass melt than at their downstream end, i.e. shortly before the glass flow is no longer limited by the guide bodies. The lei'i- or delimiting bodies have such a length that the molten glass between them cools so that the glass practically does not run off to the side when it is no longer contained. One can refer to that for the same purpose Let a molten salt flow out of the metal downstream of the guide or restriction bodies, that hits the glass and practically prevents it from flowing to the side. Please refer to the US-PS 33 56 470 referenced.

In one embodiment of the invention that is used for the manufacture of glass that is thicker than conventional Equilibrium glass is, offers particular advantages, are in the forming chamber side walls 33 and 33 'on one Place where the glass is already like this. that scratches and others Damage to the glass is unlikely. Further, a layer of molten salt 34 is in embedded in a space formed by the side walls 21 of the molding chamber 15, the dams 33 and 33 ', the Leit- odei delimiting bodies 31 and 31 'and the emerging glass ribbon 14 is formed.

The molding chamber 15 is covered with a roof 35. Along the roof 35 are on the flowing endless glass ribbon 14 directional heating element 37 and cooling element 39 attached. With these it can Glass ribbon 14 can be heated and cooled controllably, so that the glass is drawn out and becomes a dimensionally stable one Glass ribbon of the desired width and thickness can be cooled as the forming chamber Also connected to the chamber 15 is an inert gas source and expediently a reducing gas source, this for the purpose of preventing the oxidation of the molten metal in the chamber. These gas sources are not shown in the drawing, but are known in the art and in US Pat 33 37 322 described. In general, nitrogen and hydrogen are fed into the gas sources from the gas sources Chamber a.

At the downstream end of the forming chamber 15, transverse to the glass web, there is a doffing roller 41 arranged. This roller lifts the glass ribbon 14 from the metal ribbon 16. On the surface of the glass ribbon 14 rests on a series of barriers 43, which are in the forming chamber 15 above the glass surface prevailing atmosphere against influences from downstream glass processing equipment lock forth. Flexible asbesite foils, which are attached to the roof part 45, are preferably used as barriers 43 attached in such a way that they hang down on the glass ribbon.

In addition to the Abnnahmirwalze 41 and the locks 43 belong to the removal device 17 rollers 47, the take up the glass ribbon, pulling it out of the forming chamber 15 and moving it further Feed processing to a cooling furnace, for example. In connection with the rollers 47 are brushes 49 which also close off the molding chamber 15 from downstream equipment. From the reels 47 as well as from further rollers arranged downstream, pulling force is applied to the glass to a certain extent exercised that the glass ribbon is drawn in only one direction to the desired final thickness, especially if the desired thickness is to be less than the equilibrium thickness. It has been shown that through appropriate temperature control, the application of a temperature gradient along the Guide or delimitation bodies 31 and 3Γ and applied by the rollers 47 on the glass Draw force can produce glass of less than equilibrium thickness without, as in U.S. Patents 32 22 154, 34 93 359 and 36 95 859 described, further lateral holding devices must be attached and lateral stretching is required. The result of the operation according to the invention is a thin glass with a significantly lower optical distortion, especially in its edge zones, than it screened on a glass shows that it is on a large scale according to conventional methods chen float process is produced.

However, if the flow path is laterally limited, the glass ribbon can also be opened to di < Pull out the desired thickness and keep it constant in its width. This purpose is served in connection edge rollers 61 with the device according to the invention

24

According to a preferred embodiment of the invention, the cooling effect of a step floor Reinforcing means for cooling the molten glass are also built into the bottom of the refining tank will. For example, a cooling tube 63 can be placed through it, immersed in the molten glass which a coolant, for example water, is continuously pumped through. An arrangement of this type is in the US-PS 38 36 349 described. By using a cooling pipe, you can also use the thermal Stabilize conditions and cause the glass to flow in a laminar manner.

The heating and cooling bodies 37 and 39 provided downstream of the outlet device 13 are arranged above the glass flowing through between the guide or delimiting bodies 31 and 3 'so that the glass is preferably cooled in its central zone. However, it is also possible to heat the glass preferably in its edge zones. The guide or delimitation bodies are equipped with heating bodies 65 for this purpose.

Another preferred embodiment of the invention is shown in FIG. Fig.3 shows a Glass outlet device 13 in which molten metal 16 extends below the molten glass which passes through one formed by the counterholders 27 and 27 ', the measuring device 29 and the metal bath slit-like horizontal channel flows. The space in which the Metal bath is located, transversely from the side walls 21 of the refining tub and one in the refining tub built-in threshold 51 limited An inert one is preferably used for the manufacture of the threshold Material, for example quartz glass or molybdenum, graphite, boron nitride or the like. One can also use a platinum-coated block of refractory material. In a preferred embodiment, the threshold is through a sealing layer 53 made of a powdery material, for example powdery graphite, from the bottom 18 of the molding chamber separated. Furthermore, a water tank 52 for cooling the threshold 51 and for temperature control is in the gas outlet zone arranged.

The amount of glass melt flowing through the outlet device is determined by the space between the bottom of the measuring device 29 and the opposite interface between the Molten glass and the metal bath. By a downward thrust of the measuring device 29 and as a result of different hydrostatic pressures in the refining or conditioning zone and in the forming chamber prevail, changes are caused in the depth at which the interface is located between the metal bath and the molten glass to the horizontal upper side of the threshold. in the in general, without the use of additional apparatus, the interface lies below it less deeply of the measuring device 29 as it is in the refining or conditioning zone or in the forming chamber located.

A particular advantage of the embodiment according to FIG. 3 is that the contact of the glass with the Top of the threshold made of refractory material is not only extremely low, but takes place upstream at a point so far away that the glass viscosity is significant here is lower than during the preparation of the glass, so that any scratches or damage

Impurities are effectively removed during the glass forming process.

Another preferred embodiment of the invention is shown in FIG. 4 shown. In the embodiment according to Figure 4 is a thin sliding film 59 of molten metal between one of the bottom of the The refractory block 56 forming the glass passage channel and the glass melt 12. The glass melt 12 flows on the thin film 59 covering the block 56 forming the bottom of the outlet device 13 from the refining tub Ii over a threshold 55 and a metal bath 58 of relatively shallow depth, which with the metal bath 16 is in communication, into the glass forming chamber 15. The passage channel of the Glass feed device 13 is of the counterholders 27 and 27 ', the movable lifting door 29 and the Upper side of the support block 56 limited. A feed device 57 is built into the support block 56, through which molten metal is continuously supplied to the metal bath 58. The one through the outlet device 13 flowing glass stream exerts a pulling force on the metal bath 58. This forms a sliding film 59 of molten metal, which the glass flow through the metal bath located in the forming chamber 15 16 takes with you. This embodiment has the particular advantage that by forming a thin Molten metal film has a glass feed path of such cross-sectional dimensions and size Length is created that even without a particularly careful pulling out of the glass mass and without special heat regulation measures in the forming chamber a glass ribbon of finely measured thickness is obtained.

The interaction between the refining zone or conditioning zone and the outlet or feed zone is described in greater detail in the following examples for better understanding. The dem Process according to the invention, specific heat and foot conditions are shown in FIGS. 5,6 and 7 can be seen, which are therefore representative of the information in the examples.

example 1

You work with three different lautering or conditioning and shaping units and investigate For comparison purposes, the prevailing flow and temperature conditions in them. Any of the three Has refining or conditioning tubs, as shown in FIGS. 5, 6 and 7, a step floor construction Each of the three refining or conditioning tubs hai a clear width of 9.15 m. 5 the refining or conditioning tub protrudes over a channel a width of 1 m and a depth of 30.5 cm the surface line of the in the lautering or conditioning tub The glass bath contained in it in conjunction with a conventional float bath. Ir F i g. 6 is the lautering or conditioning tub nacl of the invention connected to a float bath by a threshold that is 30.5 cm deep below the surface de: Glass bath and has an overflow width of 4.57 m in the transverse direction of the tub. According to FIG. 7 becomes the the same refining or conditioning tub as in FIG. 6 is used, only in this case the threshold « 15.2 cm below the surface of the glass bath. Either of the three refining or conditioning tubs are at the bottom on the surface of the glass bath, with gaps on the center line of the tub immediately in front of the outlet device on which

if 2-

upstream ropes, on the center line and iahe on the outer walls or counter brackets of the ^ pushing device according to the invention and on the vlittellinie of the channel in the known system F i g. 5 thermocouples arranged.

The three units are used to produce 5001 glasses per day under the same conditions. The temperatures and the flow velocities at different depths

Table Il
Flow rate (cm / min) of the glass mass in each unit are shown in Tables 1 and 11 and in Figs. 5,6 and 7 called. The stated values are calculated from values which have been operated with simulation models that are accurate to scale in small format in such a way that the Reynolds numbers that occur in units of normal operating size are reproduced. The values are given for units of normal size.

Type of glass outlet device

Flow depth Position of the measuring probes for the speed measurement to the right of the center line in the direction of the float bath

50.8 cm

152.4 cm 254.0 cm 355.6 cm

With a channel 1.02 m wide + 30.48 cm deep
working conventional exhaust device

Outlet device according to the invention with 4.57 m
wider + 30.48 cm deeper outlet opening

Outlet device according to the invention with 4.57 m
wide + 15.24 cm deep outlet opening

Table ul
Glass temperature ( ⁰ C)

surface 119.93 92.96 40.13 30.99 12.7 cm deep 139.7 76.2 40.13 40.13 25.4 cm deep 81.28 72.23 30.48 40.13 38.1 cm deep 68.59 48.26 23.37 <0 50.8 cm deep 35.5 26.67 14.22 <0 63.5 cm deep <0 <0 <0 <0 surface 21.34 20.83 14.73 6.1 12.7 cm deep 5.59 38.10 17.78 6.1 25.4 cm deep 44.2 33.53 17.78 4.57 38.1 cm deep 27.94 26.67 17.78 4.06 50.8 cm deep 15.75 14.22 12.19 2.79 63.5 cm deep <0 <0 <0 <0 surface 55.88 55.88 40.64 14.22 12.7 cm deep 45.72 45.72 38.1 10.41 25.4 cm deep 33.53 35.56 22.86 7.62 38.1 cm deep 16.51 15.24 12.7 7.62 50.8 cm deep 12.7 12.7 7.62 <0 63.5 cm deep <0 <0 <0 <0

Type of glass outlet device

Arrangement of the thermocouples

on the center line of the lauter or
Conditioning tub;

Bottom '/ 3 2/3 upper

surface

on the bottom of the glass feeder

left center right

Conventional system (as Tab. 1) 1135 1118 Π 85

Plant according to the invention; Glass feeder 1127 1113 1185

12 inches deep

Plant according to the invention; Glass feeder 1127 1118 1185

15.24 cm deep

1168 1177 1085

UlO 1110 1085

1177

1085

1110

1085

The improved thermal conditions in the lautering or conditioning zone are from the table HI to be seen.

A comparison of the flow rates and the temperatures in the three systems shows that the method of operation according to the invention in the width of the refining or conditioning zone form velocity profiles which are flatter, less curved Create a level so that the laminar flow is intensified in the discharge area of the lauter zone. Furthermore, it can be seen from the comparison of the speeds and temperatures that the lauteroder Conditioning zone supplied glass in the method of operation according to the invention without loss of stability is cooled more than during glass production conventional method. This makes it possible, according to the invention, without further cooling devices or without the use of a larger refining or conditioning tub with larger throughputs work than with the known methods. It is preferable to use the one with a flat threshold procedures carried out. In each of the three methods, the neutral flow level is above the Center line of the flow path at approximately the same height between the bottom of the lautering or conditioning tub and the surface of the glass bath. However, the positive flow integral is above the neutral one Level more evenly in the entire width of the lautering or conditioning tub according to the invention than with a lauter or conditioning tub

of the conventional kind. This greater evenness of the speed professional in the width of the refining or conditioning tub shows an improved laminar flow of the gas as it approaches the outlet device.

Example 2

IO

In a device according to FIG. 1 and 2, a glass melt of the composition mentioned elsewhere is allowed to dissolve in an amount of 450 liters per day in a bath of molten tin. The glass has arranged from the roof of the forming chamber and directed onto the glass radiation pyrometers of the conventional type shown in the flow onto the tin bath in a whole width, a temperature of 1066 ⁰ C. The lateral boundary or Leitkorper are three meters apart and about 1 , 80 m long They are not heated and are thermally insulated from the walls of the chamber. They have at their Glasauslaßvorrichtung the end facing a temperature of about 1038 ⁰ C and close to its opposite end a temperature of about 899 ° C. The temperatures of the guide or delimitation bodies are determined using platinum / platinum-rhodium thermocouples, which are built into the refractory alumina material of the guide and delimitation bodies so that they are about 2.5 cm above the molten glass and about 5 cm laterally be away from it. On the roof of the chamber, above the glass in the middle between the guide or delimitation bodies, two coolers are also mounted, each of which has a cooling surface that measures about 1.5 m in the transverse direction of the chamber and about 60 cm along the glass path. The cooler is charged with water at 23.9 ° C in such an amount that it leaves the cooler at a temperature of only 25.6 ° C. Each cooler draws 2520 Kcal of heat from the chamber

Minute. ,.

On the roof of the glass forming chamber, three pyrometers are aimed at the glass web on a line connecting the two downstream ends of the guide or delimiting bodies. One of these pyrometers is set to the center line of the glass track, while the other two pyrometers are each set to a point about 15 cm inward of the guide or delimitation body. The glass ribbon has in its central zone, a temperature of about 87O ⁰ C and in its two marginal zones a temperature of about 900 ° C.

A dimensionally stable glass ribbon with a thickness of 5.334 mm and a width of 3 m ± 2.5 cm is obtained.

No edge rollers are used to stretch the glass sheet sideways.

The ribbon of glass is free of distortions in its central, 285 cm wide zone, but only in the outermost, about 5 cm wide zone, strong herringbone-like distortions occur.

According to the method of the invention, an endless ribbon of glass with a better optical quality is obtained Quality than that which could be achieved using conventional methods in the manufacture of float glass. This quality improvement, which characterizes the glass according to the invention, is evident when looking through the glass in the usual way, that is, on a line of sight, which is generally stands perpendicular to the main plane of the glass, but definitely cuts it The cut surface of a glass ribbon of the type according to the invention cut transversely to its length is considered, then a pattern of a completely different kind appears than on the cut surface of a conventional float glass ribbon.

From the F i g. 8 and 9 of the drawing, the uniqueness and novelty of the glass produced according to the invention clearly visible. These illustrations give an enlarged scale Scale in cross section the edge zones one by a known method and one by the Invention made glass ribbon again. The drawings are after enlarged photographic Recordings of real glass sections have been made. Each of the recordings was made on the way made by immersing a glass sample with a cut surface in a container with a liquid, which has the same refractive index as the glass in order to avoid refractive and reflective phenomena on the cut surface to remove it, back-lit it and photograph it through a wide-angle lens. the Main patterns are reflected in the drawings with minor imperfections shown in both cases have been eliminated.

Glass that has been made by conventional methods shows near its bulb-like shape It ends with a distinctive J-hook pattern. This pattern in which the layer lines are not telescopic telescoping is typical of a glass made according to U.S. Patents 3,083,551 and 3,220,816. in the In contrast to this, a glass produced according to the invention shows a pattern telescopically up to the edge of the glass layers pushed into one another. While the glass produced by known processes has a characteristic Has a distortion line that appears in the pattern of the discontinuous layer line in the form of a J-hook corresponds, the glass made according to the invention has a continuous line of distortion.

For this purpose 4 sheets of drawings

Claims (8)

Patent claims: 1. Process for the production of an endless glass ribbon, in which mau molten glass is made a conditioning tub through a discharge device onto a bath of molten metal between guide bodies allows the stream of molten glass to flow over the surface of the Metal bath, this cools to a dimensionally stable glass ribbon and the endless glass ribbon from decreases from the metal bath, characterized in that that he a) the glass flow in the conditioning tank set in a laminar flow, b) the gas stream at least partially as a relatively thin and wide ribbon of glass over a Support body through the outlet device while maintaining its laminar Let the measuring structure flow onto the metal bath, the glass stream being horizontal or on a downward sloping path flows onto the metal bath without falling freely onto the metal bath, and c) behind the outlet device, higher temperatures of the two edge zones of the glass flow and lower the temperature of its central zone, so that the viscosity of the glass in the proximity of the guide body in relation to the viscosity in the middle zone and thereby maintaining the laminar measuring structure of the glass flow until the glass is removed. 2. A method for the production of glass according to claim 1, characterized in that the Glass flow upstream from the point at which the glass flow flows out of the refining zone via a Under the surface of the glass bath arranged threshold can flow, the threshold with its The top is 5 to 46 cm below the surface of the glass bath and parallel to the surface of the Glass bath runs. 3. A method for producing glass according to claim 1, characterized in that the glass flow is produced in such a way that the temperature is raised upstream over a distance of at least 15 m from the point at which the glass melt flows out of the refining zone lets the surface of the glass bath drop by at least I ₁ I ⁰ C to 30 cm. 4. The method for the production of glass according to claim 3, characterized in that one is im Glass bath from the point at which the glass stream flows out of the refining zone, upstream over a distance of 23 to 37 m increases the temperature at the surface of the bath by about 2.2 to 3.9 ° C Drops 30 cm. 5. The method according to claim 1, characterized in that that the velocity of the glass stream in its central zone is up to five times greater than the speed that the glass stream moves at a distance of about 5% of its width from the Has outer edge from inwards. 6. The method according to claim 1, characterized in that that the speed of the glass flow in its central zone is up to three times greater than the speed that the glass stream moves at a distance of about 5% of its width from the Has outer edge from inwards. 7. The method according to claim 1, characterized in that the faster cooling middle zone of the glass flow that is near the downstream end of a delimiting body The edge zone of the glass flow located at a temperature of at least 11. Γ C above the temperature of the glass stream lies on a line along its central zone, which is the downstream ends of the two limiting body connects 8. Device for the production of an endless glass ribbon with a glass melting furnace with a conditioning device with outlet means leading to a forming chamber with a bath of molten metal and laterally thermally insulated guide or delimitation bodies is aligned, and with means with which one takes the endless, dimensionally accurate glass ribbon down from the metal ribbon, marked by means of a threshold (25) and a metering device (29) much wider than high designed opening of the glass outlet device (13), its support device (56) with regard to the Height of the metal bath is arranged so that the glass stream (12) horizontal or on a downward inclined path flows onto the metal bath (16) without falling freely on the metal bath, cooling devices (37) centrally above the glass ribbon on the metal bath and heating devices (39) above the Edge zones of the glass ribbon in the vicinity of the guide body (31), with a laminar flow structure of the glass in the conditioning device (11) and is present in the shaping chamber (15).