DE2234720A1 - METHOD AND DEVICE FOR THE PRODUCTION OF FLAT GLASS - Google Patents

Description

DR. MÖLLER-BORe Dl PL-PHYS. DR.MANI1 Z DIPL-CHEAA. DR. DEUFEL DIPL-ING. FINSTERWALD DIPL-ING. GRÄMKOW

Wed 1972

• G 2234 Glaverbel, Watörmael-Boitsfort / Belgium

Method and device for the production of flat glass

The invention relates to a method for producing Flat glass, in which molten glass is fed to a drawing zone, and glass is drawn off from this zone in the form of an endless belt which is guided through zones, in which the glass solidifies and cools. The invention also relates to a device for manufacturing of flat glass using this process.

There are several methods of manufacturing flat glass by pulling a ribbon of molten glass from a Draw zone to which molten glass is fed is known. When performing some of these procedures, the tape becomes from the surface of a certain amount of a melted Glass that flows into the drawing zone is removed. An example for such a procedure the classic Pittsburgh

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A method in which the molten glass flowing into the belt is carried out from the upper level of a Bath of molten glass. Another example of such a process is the classic Libbey-Owens or Oolburn process, when carried out melted Glass flows into the ribbon from the full depths of a relatively shallow bath.

Surface drawing methods are not limited to the classical methods mentioned above. For example it is known to pull the ribbon from a molten glass which is fed to the drawing zone during it on a bath or on a layer of a molten material, for example molten metal, with a higher one specific gravity floats, with this molten material acting as a lubricant between the molten glass and serves on the bottom of a refractory furnace in which the molten materials are stored. According to another As an example of a special surface drawing process, the ribbon of glass is not drawn off over a meniscus, which forms on a free fluid surface of the molten glass, but can reach the vent from a meniscus, which is cooled to prevent molten glass from pouring over the meniscus (see GB-PS 988 128).

Attention should also be drawn to the procedures involved in carrying them out extruding the ribbon of molten glass at a location below the surface of the molten glass. The most notable process of this type is the classic Fourcault process, when carried out the molten Glass in an upward direction through a slot in a pubic nozzle, which is partially immersed in the molten glass,

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this flows into the drawing zone, is extruded. Such extrusions procedures differ in many ways fundamentally from the surface drawing processes and require a considerable amount to be carried out satisfactorily practical knowledge not based on experience with surface drawing processes can build. Even if the present invention, which will be explained in more detail below, with Advantageously can be applied to the extrusion process, it should nevertheless be pointed out that the invention with even greater advantage in connection with surface drawing processes is carried out due to the other thermal and rheological conditions encountered in such Procedures are available. .

When all known methods for drawing flat glass are carried out, the ribbon of molten glass is drawn from the drawing zone through a drawing chamber in which the ribbon is dimensionally solidified, whereupon the ribbon is drawn through a shaft in which the ribbon is increasingly in front of the Cutting into individual sections cools. This shaft, which is known as a cooling shaft can be vertical and be placed on the pull chamber ", so as this is the case, for example, in the classic Pittsburgh process. Optionally, the shaft can be a horizontal shaft into which the strip is inserted after bending by a bending roller. A horizontal shaft is used in the classic Libbey-Owens process. Of course, the classic procedures can be subjected to many changes. A given method can combine features of different classical methods. For example, a horizontal well is used in certain processes which, when carried out, draw the ribbon from a bath of molten glass to a substantial depth, as is the case with the classic Pittsburgh process, but by one

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Bending roll is bent, as happens when performing the classic Libbey-Owens method.

When performing all known glass drawing processes the glass ribbon is exposed to the influence of ambient gas currents, which exert a cooling effect on the ribbon, both with respect to Time and space is immense. These currents have different causes. As a result of the connection between the drawing chamber and the cooling shaft, the shaft exerts a chimney effect as a result of which gases flow through the pull chamber and the cooling shaft. Hot gas streams flow in an upward direction along the central section of the strip from the intensely hot drawing zone through the drawing chamber into the Cooling shaft, while cooler gas flows back into the pull chamber from the cooling shaft along the walls of the device stream. The chimney effect is very pronounced when the cooling shaft is vertical. However, the chimney effect is also a very important factor in carrying out the classical Libbey-Owens or Colburn processes, as well as other processes that use a horizontal cooling shaft is used.

The rising currents of hot gas generated by the chimney effect mentioned above, decrease in temperature and speed as they move through the pull chamber and cause turbulence in the upper part of the chamber. There is an interaction between these turbulent ones Streams and the natural gas streams flowing from. the drawing chamber into the cooling shaft and vice versa. These Interaction creates a complex system of currents that play a role in creating an adverse heat distribution plays across the tape.

Some of the cooler gas that is in the pull chamber from the

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Cooling shaft flows back, tends to be inside the pulling chamber to flow down along their side walls and, after it .has been heated, inwardly longitudinally generally upward sloping paths to flow to see the upward one Main convection flow or gas along the central longitudinal section of the tape path to be connected «With such a" Part of the - colder gas - flows over the edge zones the tape path out, creating adverse conditions will.

Another cause of thermal irregularities in the ambient conditions is the ingress of ambient air currents into the drawing chamber through hoists in the refractory walls or by incompletely sealed connections between walls and components that look through such walls into the Extend the drawing chamber.

Another source of ambient gas streams that pose problems is coolers that may be installed in the pulling chamber. Usually, a cooler is installed on one side or on each side of the ribbon of glass at a level close to its source to accelerate the cooling of the ribbon when it is withdrawn from the molten glass. The gases cooled by such cubes are noticeable; the molten glass at the drawing zone and influence; tröm, etli: |, ok © by the mentioned chimney effect: are caused:., It is difficult, temperature differences in such® abat @ ig © n (3.e; cooled gases between certain. sections; ⁰ : epier to: to eliminate the bandwidth, Circa occurring Unregelmas ^ igkei regarding the Kühlwirfcung these gases have drawn naturlioh e-rnathafte adverse effects on the · e. glass ribbon ,. da se Uniregelmässigkeiten on \ the OberfläQhe e. 4njsiirkeB ,, what that: glass has a very low viscosity ,,

When performing some methods, one or more additional coolers are provided at higher points in the pull chamber. Any other such coolers that are present increase the cooling rate of the glass ribbon, the influence of such coolers on the course of the convection currents in the drawing can but very different from the influence of a cooler located near the tape source. Thermally heterogeneous gas flows exert their own effect on the tape at such higher points as a result of the characteristic flow properties as well as the velocities of such currents, in particular the condition of the belt surfaces at the higher ones Place the drawing chamber.

It is known that ambient gas flows have an irregular cooling effect is the cause of errors in the dimensions of the drawn flat glass. In particular, prevents the irregular cooling effect the drawing of flat glass with surfaces that are actually flat and parallel in all places are. Are the surfaces not actually flat and paral-Ie, Then the flat glass produced diffracts light waves that pass through the glass, so that objects that pass through the Glass viewed under certain conditions may appear distorted.

These defects in the drawn flat glass can be of various types be. Some defects are expressed in the form of waves, which are more or less parallel to the drawing line of the glass get lost. These defects are mainly due to the effect the cool air caused by the cooler (s) drop attached near the source of the tape is or are. These wave defects are then visible when objects are at a shallow angle through the flat glass be viewed in a plane perpendicular to the

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Draw line runs, especially when changing the viewing angle.

Another type of defect is called "martelage" or "hammering" known. This type of defect manifests itself in 'a Form of an arbitrary distribution of flat surface impressions, usually 1 to 4 cm in cross-section. These defects, which are mainly caused by the action of one or more other coolers, are in use higher up in the pull chamber are less obvious than waves, but they can nonetheless are recognized during normal viewing as a result of their distorting effect on objects which are affected by the Glass can be viewed at shallow angles relative to the glass. .

Another type of defect is a series of intersecting ones to recognize diagonal and vertical lines, especially at the outer points of the bandwidth, with the diagonal lines run upwards from the side edges to the central part of the tape. This kind of Defect is due, among other things, to the movement of longitudinally upwardly directed inclined paths within the pulling chamber transversely the edge parts of the band of some of the gases, which along the walls of such a chamber from the cooling shaft flow back, and also to those mentioned above Due to leakage currents of cooler air which penetrate into the drawing chamber through its walls.

In many cases, drawn flat glass shows defects that appear as dark stripes in a shadow recording device of limited length appear. These defects, hereinafter referred to as "dark streaks", are elongated flat ones Surface impressions. In contrast to waves, these occur

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Defects do not occur continuously along the length of the tape, but are much larger than hammers and show sometimes a length of up to 50 cm or more. These dark ones Stripes are usually seen with a normal viewing then not recognized if it is covered by more serious defects but they become visible when rays of light through the flat glass at shallow angles (less than 15 °), based on the glass, be sent to a light-diffusing screen.

The presence of surface defects in the form of waves is conditional necessarily small local variations in the thickness of the flat glass from one place to another, the However, flat glass also changes in its thickness to a greater extent. These changes are not surface defects but to ascribe differences between the amounts of molten glass drawn from the molten glass in different Parts of the range due to changes in viscosity to be pulled. If the belt surfaces are corrugated, then the general changes in thickness include differences in the mean thickness of the glass, measured at various points across the glass.

The desire to produce drawn flat glass that is free from optical defects has attracted considerable research causes in the glass manufacturing industry, with a view to a more favorable heat distribution in the environment to produce, through which the tape is pulled and in which it is cooled. Many suggestions have been made a predictable and more favorable temperature profile across the board to produce the path of the glass ribbon at a point where the glass des'Bandes has a very low viscosity and against deformation under the influence of

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local temperature changes is most sensitive. These Proposals kept gas flows with predetermined ones Temperature and speed in the lower part of the drawing To generate chamber in order to prevent the arbitrarily distributed cooling effect of the various convection currents. Other Proposals aimed to act on such convection currents in the lower part of the pulling chamber in such a way that that their distribution across the tape path is modified.

In practice, some of these suggestions have proven to be so proven to be beneficial to improve the optical qualities of the flat glass, in particular by avoiding or reducing them the appearance of waves. Despite this refining and corrective measures, however, the flat glass is still afflicted with certain minor surface defects, which not the optical quality of the flat glass in that A.Us measures like waves deteriorate, but none the less contribute to optical distortion and the glass for make those points unsuitable where it is on a glass arrives with very good optical qualities. The smaller defects are called "dark streaks". These defects occur despite the known corrective measures of avoidance of irregularities in ^ cooling. There is currently still a need for a method by which Flat glass with flat surfaces and ■ even thickness as well as optimal optical properties with constant reproducibility can be drawn.

The object of the invention is to create another shape a corrective action that affects the conditions, which the surfaces of drawn glass ribbon -, 'now so that further improvement of the feasible Quality of flat glass is possible. ~ In particular

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the invention seeks to provide a corrective measure, if observed, the appearance of dark Streak is avoided or reduced.

This object is achieved by the method according to the invention Manufacture of flat glass, in which molten glass is fed to a drawing zone, and glass from this zone in In the form of an endless band, the band is guided through zones in which the glass solidifies and cools down, dissolved. This method is characterized in that in at least one zone along the tape path, in which the viscosity of the glass is not less than 10 ''

13th
Poise and not more than 10 poise, a gas-displacing force is periodically exerted in at least one direction transverse to the belt path, whereby the gases are displaced in a fluctuating manner transverse to the belt.

It has been found that if there is a displacement of gases takes place at a point at which the glass is within the specified viscosity range, such Displacement has a very beneficial effect on surface quality of the flat glass. Such a displacement can avoid or reduce the occurrence of dark stripes namely, the streaks which, despite the application of known corrective measures, cannot be eliminated was. This result that can be achieved according to the invention is surprising. So far, attempts to improve the gaseous environment through which the glass is drawn have the interest is concentrated on those zones of the "belt path" in which the viscosity of the glass is very low. at Most of the glass drawing processes are carried out by viscosity of the glass in the zone of critical formation of the ribbon in the lower part of the drawing chamber is considerably lower

7 6
than 10 'poise. In contrast to the aforementioned,

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"Corrective measures proposed so far, which on Appearances that occur in the zones where the ribbon glass is hottest, 'takes into account Invention of the vicinity of the belt at a different stage of travel. According to numerous embodiments of the invention, the effect according to the invention takes effect within the cooling shaft

The results obtained according to the invention lead to the assumption to that annoying dark streaks that haven't been eliminated so far could be attributed in part or even mainly to an action of the complex system of gas flows are, which are located in the upper part of the drawing chamber as a result of the Interaction of turbulent and natural flows adjusts in the manner described above. The exact reasons for the favorable results that can be achieved according to the invention however, not yet known with certainty.

There is another advantage that can be achieved by the invention is that when it is applied using a given drawing machine, a flat glass of a given quality can be manufactured at a greater speed since these dark streaks have hitherto generally appeared when using higher drawing speeds was intensified. .

The exercise of the gas displacement forces according to the invention is carried out, helps prevent abrupt changes in temperature across the belt path or across the part of the same, on which the specified gas displacement is carried out, to eliminate. It is essential that it be within that portion of the tape path that extends between the viscosity limits (10 'and 10 poise) there is at least one direction transverse to the tape in which a gas-displacing

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Force is exerted periodically. In other words, this means that a gas displacement force is exerted and at least is partially withdrawn, whereupon it is again exercised and at least partially taken away, whereby this Process repeated. Due to the periodic exertion of the gas displacement force, the gases are displaced across the belt, the displacement being fluctuating. The volume velocity of the gas displacement caused by a such force is produced is not steady, but increases and decreases. The important factor is that there is a gas displacement force which is repeatedly exerted and then at least partially withdrawn will. The importance of this repeated exertion of force is that of a periodic disturbance of the conditions takes place in the vicinity of the belt at the point where such a force is exerted. Consequently can

there are no constant temperature maxima at a certain one Set the edge position or at certain edge positions transversely to the tape path, such as then, for example, the Pail is when a constant and continuous gas displacement force is exercised in one direction.

Preferably, the gas displacement force is periodically in exercised at least one zone along the tape path in which

10 rather the viscosity of the glass not less than 10 poise amounts to.

The invention is particularly useful for preventing the appearance of dark streaks when gas displacement forces be exercised in at least one zone in which the vis-

10
the viscosity of the glass is 10 poise or more.

According to certain embodiments of the invention, the Glass ribbon cooled while it was moving upward through a

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vertical cooling shaft migrates, the cross-section of which is local is reduced at the bottom to form an entry slot for the tape, the gas displacement force periodically in is exercised on the closing date. It was found that the appearance of dark stripes can be achieved very easily if a gas displacement force is in this position is exercised. This is likely due to that the natural draft currents, which partly generate the complex system of gas flows in the immediately adjacent Part of the drawing chamber by interacting with the turbulent currents in it, have a high speed in the inlet slot, due to the reduced cross-section of the gas flow. at this point.

The scope of the invention also includes methods in which the glass ribbon is cooled while it travels upwards through a vertical cooling shaft, the cross-section of which is locally reduced at the bottom, whereby an entry slot for the ribbon is formed, and wherein the gas displacement force is periodically in at least one zone in the vertical shaft is exercised. Applying such a force to such a zone or zones is very effective in preventing the formation of dark streaks. This is probably due to the fact that the velocities of the natural tensile currents which are in contact with the glass, although these velocities are not as great as in the entrance slit, are also noticeable and are certainly greater than in the tensile chamber. If the gas displacement force or ■ the gas displacement forces are exerted in a zone or in zones within the cooling shaft, then ± 3 t it is of course essential for such a zone or for at least one of these zones that it is a zone,

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in which the glass is within the aforementioned viscosity range of 10 ^ · to 10 ¹⁵ poise. It is of course permissible and advantageous to exert a gas displacement force both in the mentioned entry slot and in one or more zones within the cooling shaft.

If the invention is applied to a method in which The glass ribbon is bent over by means of a bending roller before it is passed through a horizontal cooling shaft, then it is preferable that the gas displacement force be periodic is exercised in at least one zone downstream of the bending roll along the belt path. The best results in terms of the absence of dark streaks in the drawn flat glass are achieved when the gas displacement forces in such a zone or in such zones, i.e. within the cooling shaft, or, if spatial conditions permit, between the Bending roll and the entrance to such a shaft are exercised. This may be due to the fact that the zone immediately before the entry to the cooling shaft is the zone of formation of the complex gas flow system, which at the interaction of natural drafts and turbulent currents arises, whereby the natural drafts contribute to the complex system having a very high speed in the shaft.

It goes without saying that the required according to the invention Fluctuating gas displacements must be generated without a new unfavorable heat distribution which would negate the benefits achieved by the gas displacements. It is possible that the Gas displacements are carried out in such a way that the supply of heat or cold to the environment of the

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Tape has no adverse effect on heat distribution. According to preferred embodiments of the invention takes place the fluctuating displacement of gases essentially without increasing the rate of cooling of the glass ribbon. A A very significant advantage is that the invention improves the surface quality of the flat glass in the implementation of a given method as well as using a given system, without being involved the cooling rate of the glass ribbon can be modified got to. This cooling rate can be controlled entirely by other factors, as in normal practice the case is.

A periodically exerted gas displacement force, as it is according to the invention is required, a permanently exerted force can be superimposed that a gas displacement in the direction of the periodically exerted force, whereby the permanently exerted force constantly prevents natural Draft currents arise. According to preferred embodiments According to the invention, however, there is at least one zone along the belt path in which there is a displacement of gases occurs transversely to the tape path, such displacement occurring exclusively through the periodic exercise of the gas-displacing force takes place in at least one direction. Are only periodically exerted forces for the displacement of Gases across the tape path responsible, then it is possible to substantially reduce the influence of such displacements entirely to one side of the tape. This is important in performing some procedures, and that is due to the difference between the natural ambient conditions on opposite sides of the tape. Such a difference often occurs particularly in procedures in appearance, when carried out the tape by one

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Bending roll is bent before entering a horizontal cooling shaft.

The periodically exerted gas displacement force required according to the invention can only be exercised in one direction in at least one zone along the tape path. The necessary Gas displacements can then be carried out in a very simple manner, since in this case it is only necessary is to take structural measures to this force through the peripheral walls of the pulling device at one point around the To allow tape path to enter.

According to the most preferred embodiments of the invention the gas displacement force becomes periodic in one direction and in a reverse direction across the tape path in at least exerted a longitudinal zone, the forces in the different directions transverse to the tape path outside a Phase to be exercised and taken away. In this way there is a displacement of gases on one or each Side of the tape first in a direction across the tape and then in a reverse direction across the tape. It was empirically found that in exerting such a reciprocating motion of gases across the belt, the pulling of the highest quality glass possible. By creating such a reciprocating motion, it is easy possible to completely establish any constant state in the ambient gas flow in any given zone along the tape path. In addition, the The size of the gas displacing forces that are required to ensure that a given width of the tape path is passed through the gas displacements is less affected when such forces act in different effects across the tape path than is the pail when the forces are only exerted in one direction. Are gas displacement forces above

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If exercised half a certain size, then there is a tendency to create adverse turbulent conditions in one or more local zones across the belt path. Therefore, the exertion of forces outside of a phase in different directions is advantageous in order to avoid this Problem. -

Becomes a gas displacement force periodically in one direction as well as in a reverse direction across the tape path in the manner described above, then the Forces acting in different directions are advantageously exerted at locations which are essentially direct face on such a path. The exercise of forces in such directly opposite positions it is recommended that there is a coincidence or a high degree of overlap between the zones of effective gas displacements takes place, which are caused by the forces outside of a phase.

The finding that forces. In one direction and in one reverse direction across the tape path, does not mean that the lines of action of the opposing forces are necessarily parallel. Much more it is meant that in one part of a cycle there is a force in a direction away from one edge and towards the opposite Edge of the tape path is exerted, and that in the subsequent part of the cycle a force in one direction away from the opposite edge and towards one Edge of the tape path to exercise. The lines of action of the forces acting across the tape path in opposite directions may, for example, be opposing Edges of the tape path converge towards a central longitudinal zone of such path. However, it is

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preferable for forces outside a phase, that they act in directly opposite directions, as in this case the interaction between the zones that are influenced by the successive gas displacements is greatest.

According to another preferred feature that is then applicable is when the gas displacement forces lying outside a phase applied in opposite directions across the tape path, each application of the force follows in one Direction immediately a withdrawal of the force that is being exerted in the opposite direction, or the aforementioned exertion and the withdrawal coincide. The advantage of this feature is that there is a continuous back and forth Movement of the gases is generated.

According to an important embodiment of the invention, at least one zone is provided along the tape path in which a displacement of gases across the path as a result of successive ones Exertion of force in this zone occurs with such a frequency that no stable state of the gas flows is adjusted along the tape path, or does not occur during a period of time that is sufficient for the glass is adversely affected.

The existence of such a stable state harbors the danger in itself that a disadvantageous temperature distribution between different zones across the strip from the already mentioned reasons occurs. Any given zone along the ribbon of glass will be exposed to such conditions during exposed to a period of time that exceeds a certain period of time, which depends on the viscosity of the glass in the zone, then the surface of the glass can be adversely affected. A stable state of natural draft gas flows can be zoned lengthways for a longer period of time

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of the tape path are tolerated in which the glass ribbon has a relatively high viscosity ", for example a

'13 Viscosity in the order of 10 ■ poise, namely in contrast to zones in which the glass viscosity is significant is lower.

According to certain embodiments of the present invention, at least one zone is provided along the tape path in which an exercise outside of a phase is provided and withdrawal of gas-displacing forces takes place, whereby the frequency of the exertion of the force in each direction, is such that the time span of each cycle from the beginning of one exercise to the beginning of the next force exercise in this direction is not more than 10 minutes. Empirical values show that by working at frequencies within this range the ambient conditions can be so disturbed that no normal Can set patterns of natural draft currents, whereby it is not necessary to exert very strong forces. In advantageous The force exertion period and the force reduction period of each cycle are related from 1: 2 to 2: 1. This area provides a very satisfactory energy distribution over time represent.

To carry out optimal methods in their practice the back and forth gas displacements * are generated, each force application period of each cycle varies from 1 to Seconds. It was found that by adhering to this Condition the ambient conditions can be periodically disturbed in a corresponding manner without thereby new adverse stable conditions may arise, as may then be the pail if a given one Persistent force exertion for a long period of time

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would. When performing certain methods, there will be an optimal energy distribution over time in the manner realizes that work is carried out according to a cycle in which the force exertion period and the force reduction period are one each cycle are of substantially equal duration.

It is not essential that the gas displacement force which a displacement of the gases is exerted over the entire width of the belt, since, if the gas displacement occurs only a part of the bandwidth is limited, an improvement in the glass quality is achieved. In the one that usually occurs Cutting the tape into pieces, these come from the higher quality areas of the tape. However, it is preferable to carry out the gas displacement over essentially the entire width of the strip, so that the quality improvement is achieved to an even greater extent over the entire drawn flat glass.

For best gas flow conditions across the ribbon, it is recommended that the gas displacement force be periodic is applied substantially parallel to the faces of the belt.

The gas displacement force has also been found to be advantageous periodically in at least one direction substantially perpendicular to the direction of movement of the belt stands.

In practicing certain embodiments, there is at least one zone along the tape path in which the gas displacement force periodically applied to only one side of the belt. ■ j

The main advantage.il the exercise of forces on only one side of the Volume consists in the fact that the forces affect the environmental conditions

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only on one side of the tape, or mainly, on one Side can influence. This is sometimes important for example when carrying out methods in which Running one side of the tape tends to be in opposition; to assume dark stripes on the other side. Will the invention When applied to a classic Pittsburgh drawing process, it is often more beneficial to apply the gas displacement forces to the to let the back side of the tape act, while when performing a classic Libbey-OwensW method the The face of the belt, i.e. the side that contacts the bending roll, is the side that is usually of lesser magnitude Quality is cross and the most of the gas crowding to the tape path benefits. Furthermore, in the construction of a system, the advantage is achieved that it is easier to use Exercising the forces on one side of the belt and not on it to carry out on both sides »'

The one with regard to the system construction by allowing it to act The advantage that can be achieved with the force on only one side of the belt can even be realized if necessary is to perform the displacement of gases transversely on both sides of the belt. There can be at least one zone along the tape path exist in which a gas displacement force is periodic is exerted on only one side of the belt, but in such a way that a displacement of gases across the belt takes place on both sides of the same. When performing certain Embodiments of the invention, in the implementation of which there is at least one zone in which the ambient conditions on both sides of the belt are influenced by gas displacements across the belt, however, the gas displacement force allowed to act periodically on each side of the tape. That way, it's easier to find a predetermined one To perform displacement of gases on both sides of the belt,

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The methods according to the present one are of particular importance Invention to be assigned, in the execution of which the gas displacement force is carried out periodically in at least one of the zones along the tape path by blowing of gas in the vicinity of the belt. A significant advantage of this embodiment is that the required Forces can be exerted without the need for moving parts near the belt where they are exposed to the high temperatures prevailing there. Another important benefit lies in the fact that by. Injection of gas into the vicinity of the belt increases the gas displacement forces can be exercised in a precisely defined direction «

Preferably, a gas displacement force is periodically in at least one zone is exerted in such a way that gas is released into the vicinity of the belt at a speed of 1 to 50 m / second is blown in.

It has been found that the most remarkable improvements in the quality of drawn flat glass are usually obtained when working within this area.

A periodically exerted gas displacement force is advantageously exerted in such a way that gas enters the vicinity of the The tape is blown in under a pressure of 100 to TOOO g / cm. Under such prints! can the displaced gases be accelerated and provided with kinetic energy, so that the displacement has a very beneficial effect on the environmental conditions with regard to achieving the desired improvement in glass quality.

The invention includes methods, when carried out, the Gas displacement force periodically in at least one zone

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is exerted along the tape path by the action of mechanical means in the vicinity of the tape. if it is also necessary when performing this working method is to install a moving part or parts near the belt, the The advantage achieved is that the gas-displacing forces do not change the composition of the environment through introduction are exercised by further amounts of grass, consequently there is no noticeable change in the belt cooling pattern, and furthermore there is no risk of unwanted substances being introduced into the atmosphere that are in "contact with the" atmosphere Tape stands.

Further measures can be taken when carrying out the invention be taken to the appearance of ripples on the surface of the ribbon of glass to avoid or reduce such occurrence - Various corrective measures for this purpose are known as such and have already been explained. A particularly effective method of wave formation counteracting is the replacement of gases across the tape path in a zone or zones in which the tape has a very low viscosity. With certain according to the invention Methods are in addition to the exertion of gas displacing forces in at least one longitudinal zone the tape path where the viscosity of the glass is not less than 10 'poise and not more than 10 poise, gas displacement forces, which displacements of the gases in at least one direction transverse to the belt on one side or on each side of the tape, applied in at least one zone along the tape path where the viscosity of the Glass is less than 10 "poise. If such a measure is taken, its effect appears to be relative a counteraction to wave formation through the exertion of gas-displacing forces in a zone or in zones with

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higher viscosities according to the present invention to become. In other words, this means that in this relationship there is an interaction between the effects exists, which can be traced back to the two measures. In most cases it is useful and advisable to such additional gas-displacing forces in a lower one Exercise part of the zone through which the glass ribbon is drawn and in which it is dimensionally stabilized to counter a wave formation.

The invention can be successfully applied to a variety of glass drawing processes, for example to a process in which molten glass is carried out into the ribbon from the full depth of the amount of molten Glass flows in a channel to which molten glass is continuously fed. Furthermore, the invention is based on a method applicable in which molten glass is carried into the ribbon from the upper level of a mass of molten glass in a channel through which molten glass is continuously carried flows. In the end comes an application to a. Consider a method in which, when carried out, the ribbon of molten glass is peeled off that floats on a mass made of a material with a greater specific gravity.

In the. The scope of the invention also includes a device which is used for the production of flat glass and consists of a drawing chamber and an adjoining cooling shaft and means are further provided for feeding an endless ribbon of glass into such a drawing chamber withdrawing from a drawing zone supplied with molten glass and guiding the tape along a path which extends through the pull chamber and the cooling shaft. The-

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The device is characterized in that it has devices by means of which a gas displacement force is periodically exerted in at least one zone along the belt path, the viscosity of the glass in this zone being not less than 10 '* poise and not more than 10 poise, and wherein the force is exerted in at least one direction transverse to the belt path, with the result that a fluctuating displacement of gases is effected transversely to the belt.

Such a device has the remarkable advantage that it enables the drawing of flat glass, which essentially is free of dark streaks. Various beneficial Device features are explained in more detail below. Many of these features are suitable for process variants to fall back on, which has already been discussed above. The advantages of these device features are also evident, as are the advantages of the corresponding Procedural features.

According to certain embodiments of the device according to the invention a vertical KühTschaeht is provided, its Cross-section is reduced locally on the ground in such a way that an entry slot for the tape is formed. The device is characterized by the fact that a device is provided is, with the help of which periodically a gas displacement force can be exercised in the inlet syringe.

According to another embodiment of the invention is a vertical cooling shaft is provided, the cross-section of which is locally reduced at the bottom part, whereby an entry slot for the tape is formed. The device is characterized by that a device is provided with whose

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₂₆ _ 223472Ü

Periodically help a gas displacement force.in at least a zone in such a vertical shaft can be exercised.

Another embodiment of the device according to the invention provides a bending or deflecting roller, around which when Operation of the device, the glass ribbon is bent before it is passed through the cooling shaft. This view is im essential horizontally. The device is characterized in that a device is provided with which Help periodically a gas displacement force is exerted in at least one zone, which is longitudinal behind the bending roller the tape path is provided.

The device according to the invention can have a device with the aid of which a gas displacement force t is continuously exerted in a given direction across the tape path is, in at least one zone along the tape path, and for periodically exerting a gas displacement force in this direction, this force being superimposed on the continuously exerted force.

Another preferred embodiment of the invention Device has a device with the help of which periodically a gas displacement force in one direction as well exercising in a reverse direction transverse to the tape path in at least one zone along the path, further comprising a control device is present, which causes the forces in the different directions transverse to the Tape path exercised repeatedly and out of phase be withdrawn, causing a displacement of gases first in a direction transverse to the belt and then in a reverse direction takes place across the tape. The positions at which such forces are in different

20988570927

are exercised in different directions across the tape path, directly opposite across the path. It is advantageous if the establishment and the reverse direction directly across from the tape path.

In certain devices according to the invention, in which means is provided which periodically applies a gas displacement force in one direction and in a reverse In a direction transverse to the tape path in at least one zone, a control device is provided which has the effect that Immediately withdraws from any exertion of force in one direction the force exerted in the opposite direction, or which collapses which produces two effects.

In some devices according to the invention, a device is provided with the help of which a gas-displacing device is periodically Force in at least one direction and only on one side of the tape in at least one zone along the tape path is exercised.

The invention also provides a device in which a device is provided by means of which a grass displacement force is periodically applied in at least one direction each side of the tape is applied in at least one zone along the tape path. In devices of this type there is an advantageous arrangement therein, a device for periodic Applying the gas displacement force in at least one To provide a zone on each side of the belt as well as in the vicinity of its edge and a control device which has the effect of that the forces are alternately exerted on opposite sides of the belt. Such a device can Used in such a way that any exertion of force on one side of the belt causes a displacement of gases

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in a direction across the side of the belt and in the reverse Direction on the other side of the ligament causes, or the exertion of force on one side of the ligament, regardless of which side it is, noticeably only affects the environment on that side.

Furthermore, according to the invention, a device is provided in which a device is installed, with the help of which a Gas displacement force periodically in at least one zone in near an edge of the tape as well as in a direction transverse to the tape, this force also being periodic near the opposite edge of the tape and in a reverse direction across the tape on the same Side of the same can be exercised. Furthermore, a control device is provided with the aid of which these forces alternate can be brought to exercise in the opposite direction.

The invention also provides an apparatus in which a device is installed, with the help of which periodically gas-displacing Forces in at least one zone near each opposing edge of the belt and on each Side of the belt to cause gas displacements across the belt, "further comprising a control device is available, with the help of which it is possible to determine the gas displacement forces at the points mentioned according to a predetermined Exercise cycle, causing gas displacements first in one direction and then transversely in a reverse direction to the tape on either side of the same. Such works according to some embodiments of the invention Control device in such a way that the gas displacement forces which are opposed to one another in a direction transverse to the belt Sides of the same act in a given zone

209885/0927

along the tape path simultaneously and alternately to the Forces exerted in the opposite direction. act across the tape in this zone. This repression scheme is advantageous because it ensures that the Surroundings of the tape in a given zone along the tape path is affected in the same way on both sides of the belt at the same time. In another according to the invention Device or in at least one other zone In the same device, a control device is provided which works in such a way that the forces that are generated in acting in a direction transverse to the tape on one side thereof, simultaneously with the forces being exerted in the opposite direction across the other side of the band to be exerted, these forces alternating with. Forces act which reverse the gas displacement on either side of the belt. This repression scheme is advantageous because any risk of turbulent conditions at the edge points of the strip as a result of the meeting is avoided of transverse gas flows, which move across the strip in the same direction and at the edge zone meet, be generated.

In a further preferred embodiment of the invention Device, a device is provided with the help of which periodically the gas displacement force in at least a zone along the tape path is created in such a way that gas is blown into the vicinity of the tape. In particular this device consists of at least one gas nozzle and a device with the help of which periodically the gas displacement force is exercised in such a way that gas enters the Surrounding the tape is blown through the nozzle. An arrangement which offers the advantage of a very effective and precise control, provides that gas nozzles for exercising the Displacement forces at various points in the area

2098 85/092 7

of the tape is provided in at least one zone along the tape path are, wherein a common feed line is provided for the nozzles and a gas distribution device is available which has electrically controlled pneumatic valves that sequentially activate the various nozzles connect the common line.

According to the invention, a device is also provided in which openings are provided in the wall of the cooling shaft, with controllable closing devices also being present which control the pilling of the gases through such openings under the action of natural pull, so that gas displacement forces periodically in at least one Direction transverse to the tape are exerted by the pilling of such gases. This feature enables savings in energy since use is made of the natural tensile forces to cause the displacement of the gases across the belt path. Heating devices, for example gas burners, can be provided in order to heat the gases which are in enter the cooling shaft through these openings.

Devices according to the invention are possible in which at least one propeller is located in at least one zone along the belt path is provided, which periodically exerts the gas displacement force. Using propellers can make the required Gas displacement can be carried out without changing the composition of the gaseous environment of the belt will.

It is advisable to use the device according to the invention to provide a device by means of which gas displacement forces can be exerted transversely to the tape path, namely on each side of the tape in a lower part of the pull chamber.

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The device according to the invention can be based on one of the build known devices. For example, the invention provides a device that has a channel for supply of molten glass to maintain a bath of molten glass with such a depth that the molten Glass flows into the band from the full depth of the bath. It also falls within the scope of the invention a device having a channel for the supply of molten glass for maintaining a bath with such Depth that the molten glass flowing into the belt originates from the upper level of the bath. Furthermore is a Device provided which is provided with a channel for the supply of molten glass, wherein the molten glass, which is fed to the drawing zone, on a mass of a. Material with a larger specific weight floats.

Flat glass also falls within the scope of the invention one of the methods according to the invention or using one of the embodiments of the device according to the invention has been made. '

The invention is explained in more detail with reference to the accompanying drawings explained. Show it:

FIG. 1 shows an elevation of the pulling chamber and the cooling shaft of a Pittsburgh glass pulling device.

FIG. 2 shows a cross section through part of this device along the line H-II from FIG. 1,

FIG. 3 shows in detail one of the components which is used in the device according to FIGS. 1 and 2.

FIG. 4 shows a cross section through the cooling shaft of another embodiment of the pulling device according to the invention.

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FIG. 5 shows a cross-section in elevation of part of an an- ^;

their embodiment of the glass pulling device according to the invention. .

FIG. 6 shows a front section through part of another embodiment of the device according to the invention.

FIG. 7 shows a front section through part of an embodiment a device according to the invention with a horizontal cooling shaft. _

FIG. 8 shows a front section through the horizontal cooling shaft of another embodiment of the glass pulling device according to the invention .

FIG. 9 shows a horizontal cross section through part of a Libfcey-Owens glass pulling device which is used to carry out the according to the invention is equipped.

FIG. 10 shows a front section through another embodiment the inventive device with a vertical Cooling shaft that is used to carry out the method according to the invention is designed.

FIG. 11 is an elevation cross-section through part of a Fourcault glass pulling device, which is used to carry out the inventive Procedure is equipped.

FIG. 12 shows a plan cross section through the cooling shaft of another embodiment of the invention.

Figure 13 is a top view cross-section through the cooling shaft)

another embodiment of the device according to the invention. j *

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The various embodiments of the invention, which explained by the drawings, are described in more detail below *

In the drawings, horizontal lines are used to indicate the heights at which the viscosity values between 10? * And 10 ¹ * poise occur Characteristics of the pulling device as well as depend on the pulling conditions that occur when performing this process. The positions of these horizontal lines in the drawings apply to the respective device and the respective process conditions.

Figures 1 and 2 explain a method in its implementation a band of .Glas from a bath 1 of molten Glass contained in an oven that is peeled off a bottom wall 3, an end wall 4 and upper wall sections 5 and 6.

Molten glass. Flows in that shown in the drawing Oven from right to left. At one point just before the zone at which the glass ribbon 2 is pulled from the surface of the molten glass, a shut-off element 8 plunges into it the upper layers of molten glass in the furnace to create the atmosphere 7 associated with the glass melting furnace, not shown is associated with separating from the atmosphere in contact with the glass in the drawing zone. In the drawing zone is the position of the foot 27 of the glass ribbon by a Stabilized pull rod 9, which is immersed in the bath 1 of molten glass. The glass ribbon 2 is through in the upward direction a drawing chamber 10 and drawn through a cooling shaft 11, who sits on the drawing chamber. The belt is in the upward direction

20 98 85/092 7

Device drawn by rollers 12, which are arranged in the KÜhlschaeht 11 are.

The drawing chamber 10 is defined by I-shaped blocks 13 and 14 as well by upper wall sections 15 and 16 which connect the tops of the L-shaped blocks to the bottom of the refrigerator connect, and through side walls 1? and 18 (Figure 2).

The cross section of the bottom of the cooling shaft is through collecting pans 19 and 20, which form an entry slot through which the glass ribbon enters the cooling duct 11. The cooling shaft has a right-angled cross-section and is closed on the sides by the walls 21 and 22 (FIG. 2).

There are consecutive ones within the cooling shaft Compartments which are formed by the elements 23, 24, which consist of panels optionally provided with openings.

Inside the drawing chamber are the main coolers 25, 26, which are arranged close to the surface of the molten glass are and serve to solidify the glass ribbon to accelerate, which migrates in the upward direction between these coolers. At a higher level within the pulling chamber there are second coolers 28 and 29, which further accelerate the cooling of the glass ribbon. The first and the second coolers consist of ducts through which a Cooling medium, usually water, circulates.

The ribbon of glass gradually cools down as it moves upwards is pulled through the pull chamber and the cooling shaft, which has the consequence that the viscosity of the glass in the tape increases steadily. The drawing shows the positions

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- 55 -

along the path of the glass ribbon, where the viscosity of the glass is 1Cr * poise or 10 ^y poise.

During the drawing of the flat glass, the intense heating of the gaseous atmosphere in the drawing zone has taken place with. the chimney effect of the shaft results in the generation of hot gas convection currents along the central part ascend the band. These ascending gas streams not only come from the pull chamber, but also contain gas, that into the Zietikammer from places below the L-shaped Blocks 13 and 14 is withdrawn. The central upward Convection currents flow in countercurrent to currents from colder gas, which descends along the walls of the Zühlschachtes and into the. Drawing chamber 10 get through the slot, which is formed by the collecting pans 19 and 20. When these descending gas streams get into the pull chamber, they expand and create turbulence. These Turbulence is also favored by the inclination of the main upward currents of hot gases, which are slowing down increase and expand in the upper part of the pull chamber. The interaction between the in this way ' turbulent flows formed in the upper part of the drawing chamber and the vertically directed main flows causes There is a very complex flow system in this part of the pulling chamber adjusts. As mentioned above, the results obtained by the specific corrective action can be taken, leading to the presumption that this complex system of flows for the most part if is not even fully responsible for the appearance of dark streaks in the drawn flat glass.

About the occurrence of these defects in the drawn flat glass To reduce, gas displacement forces are exerted according to the invention, which transversely result in a fluctuating displacement of gases

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cause to the tape path in at least one zone in which the viscosity of the glass between the mentioned viscosity limits of 10 '* and 10 poise.

These gas displacement forces are exerted in such a way that Gas is blown into the area around the tape through pairs of nozzles located on opposite sides of the tape path in the lower part of the cooling duct. On one side of the tape path, a pair of nozzles 30, 32 is provided, as can be seen from FIG. 2, while on the opposite side of the A similar pair of nozzles is attached to the tape path, of which only one nozzle, namely nozzle 31, appears in the drawings. The nozzles are located at a level between the collecting pans 19 and 20 and the first pair of rollers 12 in the Cooling shaft. The nozzles of each pair of nozzles are located near the opposite edges of the tape path one side and are arranged to blow gas into the vicinity of the belt in a direction that is substantially perpendicular to the line of movement of the belt and substantially parallel to its faces. The nozzles of each pair of nozzles are directed directly in opposite directions across the tape path.

As can be seen from Figure 2, the nozzles 30 and 32 are connected by lines 33, 34 to a gas distributor 35, the has an electrically controlled flap valve, the position of which determines whether the pressurized gas which the Flows to the distributor from a source not shown, the Nozzle 30 or the nozzle 32 is fed. The flap valve is controlled in such a way that the gas first passes through one of these nozzles and then alternately fed to the other, so that the gas flows first in one direction across tape path ^ and then in the opposite direction across tape path j is blown while pulling the glass. The gas that j

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is pressed through the nozzles is preheated in such a way that that it is conducted in heat exchangers (not shown) in heat exchange with a hotter fluid.

Satisfactory tests could be carried out "at carrying gas "the nozzles under a pressure of 40 g / cm was supplied, the gas streams emerging from the nozzles at a speed of 10 m per second. The flapper valve in the manifold 35 was controlled so that the period of force application as well as the following "Dead Time", each representing a duty cycle of each Represent nozzle, were in a ratio of 1: 1. The period of each cycle was 20 seconds. It was found that as a result of the gas displacements transverse to the Tape path a remarkable reduction in the occurrence of dark streaks could be achieved.

A similar improvement in the quality of the flat glass was obtained when another test was carried out, at its execution the direction in which daa gas transversely to blown along the tape path, flipped over once per minute was adjusted accordingly, the pressure and the speed at which the gas was supplied to the nozzles became.

The method described can be modified in such a way that the nozzles 50, 32 ^{are attached below the catch pans 19, 20 (ie just above the 10 7} » ⁶ 'poise viscosity level) and not at the lower end of the vertical cooling shaft. The nozzles are operated exactly in the way that was explained in connection with the method described by FIGS. 1 and 2. It can be seen that the gas displacements caused by the operation of the nozzles at such a low

20 98 8 6/09 27

at a higher level, a noticeable improvement the quality of the glass insofar as the occurrence of dark stripes is practically completely avoided will, these streaks appear when the glass is drawn without the use of such bosoms. The results are less satisfactory than is the case when the nozzles at the one shown in FIG Bodies are used.

Figure 5 shows a typical nozzle which can be used to practice the invention. The nozzle is a so-called Giffard or Venturi nozzle. The nozzle is made from a supply pipe 36 from which the gas is discharged via an end opening 37 within a surrounding jacket exits ,, with an end portion 38 of this sheath converges towards the zone where the gas exits the tube 36, while the other end portion 39 diverges from this zone. The use of such a nozzle offers significant advantages, especially with regard to the consumption of pressurized gas, the heat consumption, since the dragged along Gases take on a higher temperature, as well as with regard to the large amount of ambient gases that are carried along, as well as the rate of gas displacement, which is well above the rate at which the gas is conveyed through the nozzle tube.

It was observed that it is sufficient to blow air preheated to a temperature of about 60 ° G has been. After mixing this blown air with the ambient gas inside the outer casing 39 of the nozzle shows the mixture of gases, which leaves the nozzle tube and enters the free environment of the glass ribbon, a temperature that is very close to normal

209885/0927

. - 39 is the ambient temperature in this zone.

As an alternative to the exertion of gas displace the forces by supplying gas in the vicinity of the belt, such forces can be exerted in a mechanical manner, such as this can be seen from FIG. This figure shows in cross section the cooling shaft 40 of another glass pulling device, which is used to practice the invention. The ribbon of glass that is pulled through this cooling shaft is with denoted by the reference number 41. A pair of small propellers 42, 43 is on opposite sides of the belt plane attached to the shafts 45, 46, which is through one of the Sidewalls of the chute 40 extend to a level where the viscosity of the glass in the ribbon is not less than

10
10 poise. These shafts are connected to electric motors 47, 48, which in turn are connected to a control unit 49. The propellers can be fastened in the drawing shaft at a height which is comparable to the height at which the nozzles are fastened in the embodiment described in FIGS. 1 and 2, ie at a height between the collecting pans and the first pair of drawing rollers. The control unit 49 serves to first set the propeller 42 and then the propeller 43 in motion and to maintain this rhythm while the flat glass is being pulled. In other words, this means that each propeller serves to periodically apply a gas displacement force in a direction across one side of the belt. The rotation of the propeller 42 generates a gas displacement, as can be seen from the solid arrows, while the subsequent operation of the propeller 43 causes such a gas displacement, which is represented by the broken arrows _β The operation of the control unit 49 takes place in such a way that each propeller then is started while the

■ 209885/0927

other propeller leaks out, leaving a short period of overlap with regard to their operation is available.

A test was carried out with the system, which was carried out by Figure 4 is reproduced. Each operating cycle of each propeller, consisting of a period of rotation and a subsequent period Composed of idle period, lasts 4 to 10 seconds. Carrying out such tests shows a remarkable improvement in the quality of the flat glass fixed as a result of the action of the propellers. The glass produced is essentially free of dark Stripes.

It has proven beneficial to have a longer period of rotation of the propeller on the cul-de-sac side of the glass ribbon acts than adjust the propeller acting on the other side. The cul-de-sac side of the ribbon is the side that faces the end of the furnace from which the glass is drawn. During execution a test in which very satisfactory results were obtained using a 10 second cycle the rotation time of the propeller 43, which was directed to the cul-de-sac side, was set to 6 seconds, while the period of rotation of the other propeller was 4 seconds. By setting different periods of rotation of the various propellers in each cycle, one can Set different environmental conditions on the two sides of the tape, making one side more sensitive than the other to the appearance of dark streaks.

Another variant was tested, which is also good Delivers results. The propellers were mounted in such a way that their axes were inclined to the horizontal in planes,

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223472Q

which ran parallel to the tape. The! "Propellers practiced • Forces that are mainly, in the upward direction, transverse to were directed to the tape path,

According to a further modification, the propellers were fastened at a height in the upper part of the pulling chamber, in

7 6 which the viscosity of the glass is slightly above -10 '* Toise fraud. It has been found to be very satisfactory results can be achieved in that the tendency for dark streaks to appear in the glass is suppressed could,

'The ligur 5 shows part of a pulling device which the by! Figure 1 reproduced pulling device is similar. In the Apparatus of Figure 5 is a ribbon of glass 50 in an upward direction between two I-shaped blocks 51 and 52, which form parts of the walls of the drawing chamber Upward direction between second coolers 53 and 54, which are shown in are attached to the upper part of the pulling chamber, and then enters the cooling shaft between the collecting pans 55 and The tape is drawn up through the cooling duct by the roller pairs 57 mounted in the duct The drawing shows the height at which the upper viscosity limit of 10 poise is present, -,

According to one embodiment of the invention, gas displacement forces te>. exercised in the Xühlschacht in a zone, , which is slightly below the upper viscosity level, in such a way that gas is in the vicinity of the belt first through one and then through the other nozzle of a nozzle pair with the nozzles on the same side de, s "band as well as in the amount of its-opposite Margins. One of these nozzles is shown in the drawing and identified by the reference number 58. The page

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of the tape to which the nozzles are attached is the.:- .; ; Cul-de-sac side. The gas that pulls the nozzles under pressure /; leads is preheated by means of a device not shown.

In this embodiment, each operation cycle becomes one each nozzle, "consisting of a force application period and a" dead period ", is driven in such a way that the force application and the dead periods are of substantially equal duration, the pressure under which the gas is one is fed to each nozzle is adjusted so that the rate of gas displacement at the nozzle envelope opening is in the order of 10 m per second.

In a manner similar to FIG. 5, FIG. 6 shows a pulling device in which the glass ribbon 59 is in an upward direction is drawn from a bath of molten glass 60 through a draw bar made of two L-shaped blocks 61, 62, two main coolers 63, 64 and two secondary coolers 65 and 66 exists. The glass ribbon rises in an upward direction between the collecting pans 67 and 68 into a vertical cooling shaft 69 on and is pulled up by the roller pairs 70 between plates 71 and 72, which the cooling shaft in a Separate rows of related departments.

In the lower part of the draw chanels there are nozzles 73, 74, which are mounted near the I-shaped blocks and behind the main coolers 63, 64. The gas is alternating. blown in through the nozzles 73, 74 in order to prevent the setting of an unfavorable temperature profile across the strip path, as is the case when the normal pattern of vertical convection currents due to the chimney effect of the shaft is set in the drawing chamber. Consequently has

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the action of these nozzles in the lower part of the drawing chamber result in a reduction in the occurrence of wave defects in the drawn flat glass.

According to the invention, gas displacement forces are also periodic applied across the tape path at various points on the moving tape where the viscosity of the glass is noticeable is higher. In this embodiment, the gas displacement forces exerted in the slot between the catch pans 67 and 68. The forces are exerted by a gas that is in the vicinity of the belt on each side of the same is injected through two nozzles 75 »76. Only one nozzle of each pair is shown, but actually showing the nozzles of each pair in opposite directions and are located near the opposing sanders of the Band. The gas is delivered to the nozzles of each pair like this supplied that the nozzles work outside of a phase. As a result, gas displacement occurs first in one direction and then in the opposite direction across the tape path on each side of the tape. The gas coming through the nozzle is pressed, is preheated to a temperature of about 60 ° C. For a test performed using the Figure 6 was carried out with very good results, gas was the nozzles below a pressure of 250 g / cm supplied. Each operating cycle of each nozzle, consisting of a force application period and a relaxation period is 4 seconds. The force application period and the relaxation period are essentially the same. A drawn flat glass was obtained which is essentially free from dark stripes.

In the apparatus represented by FIG. 7, the molten glass is withdrawn from a furnace, from which part of the end wall 77 and part of a cover 78

209885/09 2 7

are shown in the drawing. The atmosphere above the molten glass 79 in zone 80 is in communication with the glass melting furnace from which the molten glass is fed. This atmosphere is isolated from the atmosphere above the molten glass in the drawing zone by a valve 81 which is immersed in the upper layers of the molten glass. The molten glass is drawn upward in the form of a ribbon into a drawing chamber consisting of L-shaped blocks 82 and 83, an upper wall section 84 and a top wall 85. The drawing chamber is connected to the. Denoted by reference number 86. The position of the root of the drawn glass band is stabilized by the rollers 88, 89. The tape is drawn vertically upward into the draw chamber between main coolers 90, 91 and travels past a secondary cooler 92 located at a higher level in the draw chamber. The tape is then bent around a bending roller 93 located in the drawing chamber and is transported by the rollers 94 through a horizontal cooling duct 95. The interior of the cooling shaft is separated from the pulling chamber by partitions 96, 97 which are arranged at such a distance that they form a slot for the passage of the strip " for example an asbestos grille.

The drawing shows the by means of a broken line

ν ß Height at which the glass bound a viscosity of 10 '* poise owns.

In order to avoid the excessive cooling effect of the thermally heterogeneous To encounter gas flows which prevail in the lower part of the pull chamber 86, gas will be in the upper part of the pull chamber introduced through the nozzles 98, 99 that are close

20988S / 0927

of L-shaped blocks 82 and 83 are located. These nozzles work in a manner analogous to the nozzles 73, 74, which have been described in connection with FIG. 6, so that the The formation of waves in the drawn flat glass is counteracted. Such waves occur when the thermal heterogeneous flows are not disturbed.

There may be another pair of nozzles in the top of the draw chamber provided near the entrance to the cooling shaft be. Only one nozzle of this nozzle pair is shown in the drawing. The two nozzles are close to each other opposite edges of the tape path and point in opposite directions. Gas will go through first 4ie one nozzle and then blown through the other nozzle, whereby this rhythm repeats itself.

A test was carried out using this device. Hot gas was supplied to the nozzles under a pressure of 300 g / cm supplied. The gas supply to the different nozzles was controlled so that the moment the gas enters a nozzle coincides with the moment which stops the supply of gas to the other nozzle. The rim of this is that a glass ribbon is obtained which is essentially free from dark streaks.

According to a modified embodiment, the nozzles 100 fixed so that they can be moved parallel to their own axes, so that their positions are transverse to the tape path can be varied. That way it is possible the displacement of gases over only part of the Perform bandwidth. In this case you can go for this Part of the range the occurrence of. prevent dark streaks.

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223472Q

Figure 8 shows part of a device that essentially is identical to the device shown in Figure 7, in which, however, the gas displacement forces periodically in Directions are exerted which are transverse to the tape path - by forcing gas through nozzles 101, 102, which are on opposite sides of the tape path in positions within the cooling shaft and very are attached close to the position in which the glass ribbon has a viscosity of 10 poise (see the broken vertical line). It's actually two nozzles 101, two nozzles 1Ok and two nozzles 102 are provided, the Nozzles of each pair close to each other Edges of the tape are attached and in opposite directions Directions, but with only one nozzle of each Pair appears in the drawing. It should be noted that the nozzles 101 are mounted in a position that are provided along the tape path at a slightly further distance than the adjusting ring of the nozzles 102. When performing von Eests was gas under pressure through the nozzles of 200 g / cm blown, causing gas distortions along the tape path at a rate equal to that of started about 10 meters per second. Me nozzles of each pair were alternately operated lying outside of a pliase. It can be seen that the glass ribbon had a noticeably better quality due to the lack of dark stripes, namely in the Compared to a glass obtained when the device was not supplied with gas to the nozzles, but otherwise was operated under identical conditions ^ ".

The Figtir 9 is a classic Libbey-Owens type puller again. In this apparatus, a ribbon of glass is drawn from the free surface of the bath 104 of molten glass, held in an oven 105 is sucked off. The atmosphere

- - 47 - ■

the pull chamber 106 above the molten glass bath of the atmosphere in zone 107, which communicates with the glass furnace (not shown), through a Wall 108 separated.

The drawing chamber is partially formed by elements 109, 110, which are near the surface of the molten glass bath. In positions close to the inner surfaces of these elements as well as on opposite sides of the glass ribbon are main coolers 111, 112 and at a higher level the Drawing chamber a secondary cooler 113 is provided. The position of the end of the tape is stabilized by rollers 114, 115. To moving up between main coolers 110, 112 and Passing the cooler 1.13, the glass ribbon 103 is one The bending roller 116 is bent and then passes through a horizontal cooling duct 117, being carried by the conveyor rollers 118 will.

The drawing shows by means of a horizontal broken line the level along the tape path at which the tape glass has a viscosity of 10 ^ »poise. The invention is carried out in such a way that gas is released into the environment of the tape is blown through a pair of nozzles 119, of which only one appears in the drawing. These nozzles are in a position which is provided after the bending roller 116. The nozzles are located near opposite edges of the tape path and point in opposite directions, the gas being blown first through one nozzle and then through the other nozzle. This rhythm continues. This causes a fluctuating displacement of gases across the strip in each direction. The repressions in the opposite directions are outside a phase. The zone in which the nozzles are placed

209885/092 7.

is such a zone in which the surroundings of the Volume is influenced by cold gas streams "which from come to the cooling shaft and flow along the lower wall of this shaft into the drawing chamber as well as through air currents, which are cooled by contact with the bending roller 11 β. These relatively cool gas streams interact with the hot gas streams, which run longitudinally in an upward direction of the ribbon rise up from the bath of molten glass 104 and contribute to a complex gas flow system, the one not uniform. Has a cooling effect on the belt and is probably responsible for the defects, known as dark streaks. The gases in the vicinity of the belt in this zone are subject to the gas displacement forces which act across the tape path by blowing gas through the nozzles 119 in the above as described, then it is possible to reduce the occurrence of these defects in the glass ribbon or even to be completely eliminated.

Figure 10 shows another embodiment of the invention. According to this embodiment, the glass ribbon 120 is drawn from a supply of molten glass 121, which floats on an Ead of molten material 122 having a specific gravity higher than the weight of the molten glass, "for example, of molten tin. The molten material is in a Furnace which has the end wall 123 and a barrier 124 which extends across the furnace to a level above the surface of molten tin, so that this material is confined to the zone between the barrier and the end wall 123. An At the point where the ribbon of glass is peeled off, there is a wall 125 which extends from the bottom of the furnace to a level just below the surface of the molten glass

209885/0927

Wall 125 is stranded with openings 126, soft the free Passage of molten material from one side of the wall to allow the other. The glass ribbon is drawn in an upward direction through a drawing chamber 127, the two! -Blocks 128, 129, two main coolers 130, 131 and two secondary coolers 132, 133 has. The tape migrates out of the upward direction Pull chamber between the collecting pans 134, 135 and arrives into the vertical cooling duct 136 containing a pair of drawing rollers having.

Within the pull chamber 127 are a pair of nozzles 138, only one of which appears in the drawing. These nozzles siiKi between the Cui-de-sae-side of the L-block 129 waa the main cooler 131 attached. The nozzles 138 are on the other side of the opposite edges of the tape and point in opposite directions across the tape path. Gas under pressure is alternately supplied to the opposed nozzles 138, thereby displacing gas across the tape path in the lower part of the pull chamber, first in one direction and then in the reverse direction. This back and forth shifting of gases causes disturbance of the normal convective flow pattern due to the chimney action of the device, thereby eliminating or reducing the formation of waves on the drawn sheet glass. '

According to the invention, gas can also enter the vicinity of the belt are passed through pairs of nozzles 139 * HO, which are on opposite sides of the tape path at different heights of the cooling shaft. Gas is fed under pressure first to one nozzle and then to the other nozzle, each of which Couple a gas shift first in one direction and then in the opposite direction across the tape path on the

209885/0927

The side on which the pair of nozzles is located. The nozzles 139 »HO are attached along the tape path at positions where the viscosity of the glass is well above

7 6
10 "Poise lies, the positioSj, & b which this viscosity predominates, is indicated in the drawing by, a horizontal broken line, the gas displacement in the vicinity of the belt ₅ caused by the supply of (Jas to this environment through the nozzles 139 $ 140 , disturbs the surroundings of the tape in such a way that the drawn glass tape is essentially free of dark streaks.

FIG. 11 explains the application of the invention to the drawing of flat glass according to the so-called Fourcault method.

In carrying out this process, molten glass is extruded in an upward direction through a die 142 to form the ribbon 141, the die dipping into the molten glass 143. The glass ribbon 141 travels upwards through the drawing chamber 144, the atmosphere in this chamber being separated from the atmosphere 145 which is connected to the glass melting furnace 1 a, not shown. The separation is carried out by a bridge wall 146 _5, the lower rope of which is immersed in the molten glass 145. Inside the drawing chamber, coolers 147 »148 are provided, which are mounted on opposite sides of the belt path. The tape travels from the pull chamber into a vertical cooling well 149 through a slot 150 formed in the top wall of the viewing chamber. Pairs of rollers 151 are provided inside the cooling shaft, which take care of the transport and guiding of the strip. At the lower end of the cooling shaft 149 there is a pair of nozzles 152, 153. One nozzle of each pair appears in the drawing. The nozzles of each pair are mounted near opposing ribbons of the collar and point in opposite directions across the ribbon path. Preheated

209885/092?

Gas is first, through one nozzle and then through the other Each pair of nozzles is blown so that gas is displaced in the vicinity of the belt, first in one Direction and then in the opposite direction across that Tape path on each side of the tape. The duty cycle of the various nozzles is controlled so that the nozzles which pointing in the same direction across the tape path and being near the same edge of the tape, at the same time operated and alternate with nozzles that are attached near the opposite edge of the belt and exert their effect in the reverse direction across the tape path. ~

The effect of the nozzles 152, 153 has the consequence that essentially the occurrence of dark streaks in the drawn flat glass is avoided.

FIG. 12 shows a further embodiment of the invention. The device shown has a cooling shaft which is formed by refractory walls 154, 155 and by metal end walls 156, 157. The glass ribbon is guided by rollers (not shown) along a path which runs centrally in the cooling shaft. In the end walls 156, 157 there are openings 159, 160, 161, 162 which create a connection between the interior of the cooling duct and the interior of the ducts 163, 164. The openings are equipped with valves for regulating the amount of gas that flows through the openings, whereby turbulence is to be avoided. The openings in the opposite end walls are provided with closures 165, 166, ύοώ each of which can be moved from the position in which he closes one of the two openings in the wall to a position in which he closes the other of the openings. The closures are with racks 167, 168

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223472Q

connected, which engage pinions 16% 170, which are driven by electric motors 171 and 172, respectively. The motors 171 »172 are connected to a control unit 173, which the electric motors 171 ? 172 controls in such a manner that the Yerschlüsse 165, 166 included in a phase are reciprocated _t which means that if one of the fasteners is in a position in which it closes the opening on one side of the tape path, the other Closure is in such a position that the opening in the opposite wall, which is on the same side of the tape path, leaves open two openings are open on the same side of the tape path.

The ducts 163, 164 are provided with gas burner tubes 174, 175 through which combustible gas is introduced and burned to preheat the air which passes through the duct into the cooling duct under the action of the natural tensile forces existing along the interior of the duct. If the closures are in the position shown, then the natural tensile forces have the consequence that gas is drawn into the Eühlschaeht through the open openings, the gas thus drawn into the Eühlschacht moves transversely to the tape path, as is done through the solid arrows is displayed. After a predetermined period of time, the shutters 165, 166 are moved to their other positions. In the following initiated in this way, phase of the cycle, the natural tensile forces to .folge ₉ have the gas is · drawn into the cooling shaft and moves in the opposite directions transverse to the path of the tape ,, as indicated by the broken arrows. As a result, there is a

20988S / 092?

displacement of gases across each side of the belt, and first in one direction and then in the opposite direction Direction while pulling the flat glass.

The I ¹ XgUr 13 shows another embodiment of the invention. The drawing shows only the general shape of the cooling shaft of the pulling device, the rollers which are responsible for the further transport and guiding of the strip are omitted, and the pulling chamber is also not shown. The cooling shaft is formed by refractory walls 176, 177 and by metal end walls 178, 179, which are provided with openings 180, 181, in which closed gas supply pipes 182, 183 are inserted, which are branched within the cooling shaft and the release of gases on opposite sides Allow sides of the glass ribbon. When operating the device, preheated gas, d..h. In heat exchangers, not shown, which are located in the cooling shaft, preheated gas is fed to the tubes 182, 183. Outside these tubes there are flap valves 184, 185, which are actuated at predetermined time intervals in order to feed preheated gas from a manifold to the to enable others. The flap valves are operated at the same time. Their relative positions are always such that while the gas is being released from one tube 182 on one side of the belt, gas is being released from the other tube on the opposite side of the belt directions indicated by the solid arrows 187 »188. After a predetermined period of time, the flap valves are rotated by 90 °, with the result that the preheated gases are released in the directions which are passed through the under-

209885/0927

_ 54-2234120

broken arrows 189 _S 190 are indicated.

Very satisfactory results are obtained when carrying out ice tests _β The positions of the flap valves were changed 10 times per minute.

When carrying out the method according to the invention one finds that the periodic gas displacement is opposite to one another Sides of the ribbon significantly reduce the occurrence of iron dark streaks on the drawn flat glass causes.

209885/0927

Claims (50)

Claims 1. Process for the production of flat glass by feeding molten glass to a drawing zone and by pulling glass from this zone in the form of an endless belt that passes through Zones in which see the glass solidified and cools, characterized in that in at least one zone along the belt path in which the viscosity of the Glass not less than 10 '* poise and not more than 10 Poise is, at least in one sighting, across the tape path periodically exerting a gas displacement force to effect a fluctuating gas displacement across the belt .. 2. The method according to claim 1, characterized in that the gas displacement force periodically in at least one Zone is exercised along the path of the ligament in which the vis- The viscosity of the glass is not less than 10 poise. 3. The method according to any one of the preceding claims, wherein the glass ribbon is cooled while it is in the upward direction migrates through a vertical cooling shaft, the cross-section of which is locally reduced at the bottom, around an entry slot for forming the tape, characterized in that the gas displacement force is exerted periodically in the entry slot. 4. The method according to any one of the preceding claims, wherein the glass ribbon is cooled while it travels in an upward direction through a vertical cooling shaft, the Cross-section is locally reduced at the bottom to form an entry slot for the tape, characterized in that that the gas displacement force is exerted periodically in at least one zone in the vertical shaft. 209885/0927 5. The method according to claims 1 or 2, that is to say Glass ribbon is bent over a bending roller before it is guided through a horizontal cooling shaft, characterized in that that the gas displacement force is exerted periodically in at least one zone which is located behind the bending roller along the tape path. 6. The method according to any one of the preceding claims, characterized characterized in that the fluctuating gas displacement is carried out in such a way that essentially no increase the cooling speed of the glass ribbon occurs. 7. The method aacli one of the preceding claims, characterized ,, that at least one zone along the tape path exists _f to which a gas displacement transversely occurs to the tape path, whereby such displacement ausschlless · lent by the periodic application of a gas displacement force in at least one sighting is effected. S. method aaeli one of the preceding claims, characterized ge characterizing ze leans ₉ that ia at least one zone along the tape path a öasverärängungskraft periodically bucket in a sighting and la reverse direction wirdj transversely applied to the tape path whereby the forces ₉ which different in these sightings transversely su dam band path, - optionally exercised outside a phase ιπιά smriickgeaommen, whereby a displacement iron S-ssea on one side or on each side of the band -stierst in a direction across the band and then in a uisgekearten Siohtuiig cpier so. the tape takes place. 9 * Method according to claim S _9, characterized in that in at least one zone along the belt path a gas displacement force is exerted periodically in one direction and in a reverse direction transversely to the belt path, the forces 209885/0927 acting in these different directions., at positions are exerted which are substantially directly opposite across the tape path, the forces be exercised and withdrawn alternately outside of a phase. 10. The method according to claims 8 or 9, characterized in that that in at least one zone along the tape path the gas displacement force periodically in one direction and exerted in a reverse direction across the tape path, each unidirectional exertion of force being immediate replaced by a relaxation of force in the opposite direction or where the two effects coincide. 11. The method according to any one of the preceding claims, characterized in that at least one zone along the tape path is provided in which a displacement of gases transversely to the tape path as a result of successive exertions of force in this zone occurs with such a frequency; that is no steady state of the gas streams along the belt path sets or sets during such a period of time that sufficient to adversely affect the glass,. 12. The method according to any one of claims 1 to 10, characterized in that that at least one zone is provided along the tape path in which one occurs outside of a phase Exercise and withdrawal of gas displacement forces takes place, with the frequency of force exertion in each Direction is such that the length of time of each cycle from the beginning of one exercise to the beginning of the next exercise in this direction is no longer than 10 minutes. 209885/0927 13. The method according to claim 12, characterized in that the force application period and the withdrawal or relaxation period, that make up each cycle are in a ratio of 1: 2 Ms 2: 1. 14. The method according to claims 12 or 13, characterized in that that each force application period of each cycle lasts 1 to 10 seconds. 15. The method according to claim 14 »characterized in that the force application period and the withdrawal period of each cycle are of substantially equal duration. 16. The method according to any one of the preceding claims, characterized characterized in that in at least one zone along the tape path a gas displacement force periodically on only one side of the tape is exercised. 17. The method according to any one of the preceding claims, characterized characterized in that in at least one zone along the tape path a grass displacement force periodically on each side of the tape is exercised. 18. The method according to any one of the preceding claims, characterized characterized in that in at least one zone along the tape path a gas displacement force is periodically exerted in the manner that gas is blown into the vicinity of the belt. 19. The method according to claim 18, characterized in that a gas displacement force in at least one zone along the tape path periodically in such a way that gas is released into the vicinity of the belt at a speed of 1 to 50 m / second is blown. 209885/0927 223472Q 20. Procedure according to. Claim. 18 or 19, characterized in that that in at least one zone along the tape path a gas displacement force is periodically exerted in such a way that that gas in the vicinity of the belt under a pressure between 100 and 1000 g / cm is blown. 21. The method according to any one of the preceding claims, characterized characterized in that in at least one zone along the tape path a gas displacement force periodically in the Wise is exercised that mechanical devices in the vicinity of the belt develop an effect. 22. The method according to any one of the preceding claims, characterized in that gas displacement forces which cause a displacement of gases in at least one direction transverse to the belt on one side or on both sides of the belt are also exerted in at least one zone along the belt path, in which the viscosity of the glass is less than 10 * ⁷ ' ⁶ poise. 23. The method according to claim 22, characterized in that Gas displacement forces, which cause a shift of gases in effect at least one direction transverse to the tape on one side or on both sides of the tape, in a deeper one Part of the zone through which the glass ribbon is drawn and in which it is dimensionally stabilized. 24. The method according to any one of the preceding claims, characterized characterized in that molten glass is poured into the ribbon from the full depth of a supply of molten glass in one Channel .flows, to which molten glass is continuously fed will. 25. The method according to any one of claims 1 to 23, characterized 20 98 8S / Ö927 223472Q draws that molten glass into the ribbon from the top Layers of a mass of molten glass flows in a channel to which the molten glass is continuously fed will. 26. The method according to any one of claims 1 Ms 23, characterized in that the glass ribbon is peeled off from molten glass that floats on a mass of material that has a greater specific weight. 27. Device which is used in the production of flat glass, consisting of a drawing chamber and an adjoining cooling shaft as well as devices for drawing a continuous glass ribbon into such a drawing chamber from a drawing zone which is supplied with molten glass, the ribbon along a Path is guided, which extends through such a pulling chamber and the cooling shaft, characterized in that the device has means to periodically exert a gas displacement force in at least one zone along the belt path in which the viscosity of the glass during operation of the device is not less than * 10 poise and is not 'more than 10 poises, wherein the gas-displacing force is exerted transversely in at least one direction to the tape path, to a fluctuating displacement of gases across zn to cause the tape. 28. The device according to claim 27, wherein the cooling shaft is a vertical shaft, the cross-section of which is local to the ground to form an entry slot for the tape is reduced, characterized in that devices are provided are to periodically exert a gas displacement force in the entry slot. 29. Device according to claims 27 and 28, in which 209885/0927 the cooling shaft is a vertical shaft, the cross-section of which is located locally on the ground to form an entry slot for the band is reduced, characterized in that facilities are provided, with the help of which periodically a displacement force is exercised in at least one zone in the vertical shaft. 30. The apparatus of claim 27, wherein a bending roll is provided, . around which the tape is bent when the device is in operation, before it is passed through the cooling shaft, the shaft being substantially horizontal, characterized in that that devices are provided with the help of which periodically a gas displacement force in at least one 3one is exercised, which is located behind the bending roller along the Tape path is located. 31. Device according to one of claims 27 to 30, characterized in that a device is provided with whose help periodically has a grass displacement force in a Direction and in a reverse direction is exercised across the tape path in at least one zone along the tape path, wherein a control device is present, which causes the forces acting in different directions transversely to the tape path, exercised outside a phase and withdrawn causing a displacement of gases first in a direction transverse to the belt and then in a reverse Direction across the tape is effected. 32. Apparatus according to claim 31, characterized in that a facility is provided with the help of which outside a phase a force is exerted in positions that are face substantially directly across the tape path. 209885/0927 33. Device according to claims 31 or 32, characterized in that that a device is provided »with the help of which periodically a gas displacement force in a Direction and in a reverse direction across the tape path in at least one zone, further including one Control device is present, with the help of which it is effected that each exercise of force in one direction is immediate a relaxation of the force follows, which is exerted in the opposite direction, or which causes, that the two effects overlap ", 34. Device according to one of claims 27 to 33, characterized characterized in that a device is provided with the help of which periodically a gas displacement force in at least in one direction and only on one side of the tape in at least one zone along the tape path. 35. Device according to one of claims 27 to 34, characterized in that a device is provided with the help of which periodically apply a gas displacement force in at least one direction on each side of the belt in at least one direction a zone along the tape path. 36. Device according to claim 33? characterized in that a device is provided, periodically a gas displacement force in at least e _(iner by means of which zone is applied the same on each side of the strip and in the vicinity of an edge, further comprising a control device is present, which causes the forces on opposite sides of the tape are exercised alternately. 37. Device according to one of claims 27 to 36, characterized in that a device is provided with whose help a gas displacement force periodically in little 209885/0927 ■ - ■■■ 'ι ' at least one zone in the vicinity of a band of the band and is exerted in a direction transverse to the ligament, and also periodically, an exertion of force in the vicinity of the opposite edge of the tape and in a reverse direction across the tape on the same side the same takes place, wherein a control device is also installed, which causes the forces that act in opposite directions across the tape path, be exercised alternately. 38. Device according to one of claims 27 to 37 »thereby characterized in that a device is available, with the help of which periodically gas displacement forces in at least one zone near each of them opposite edges of the tape and on one side of the same are exerted to displace gas across the To effect tape, wherein there is also a control device which causes gas displacement forces be exercised at the named locations according to a predetermined cycle in order to displace gas first in a Direction and then in a reverse direction across the tape on either side of the same. 39. Apparatus according to claim 38, characterized in that a control device is provided which works in such a way that the gas displacement forces acting in a direction transverse to the belt are opposed to one another Sides of the same act simultaneously and alternately in a given zone along the tape path the forces exerted in the reverse direction across the belt in this zone. 40. Apparatus according to claim 38, characterized in that that a control device is provided, which in 209885/0927 the way that the forces acting in a direction transverse to the belt on one side of the same work simultaneously with the forces exerted in the opposite direction across the other side of the belt act, alternating with forces that reverse the gas displacement on either side of the belt. 41. Device according to one of claims 27 to 40, characterized characterized in that a device is present, with the help of which periodically a gas displacement force in at least a zone along the tape path such that gas is blown into the vicinity of the tape. 42. Device according to claim 41> characterized in that that at least one gas nozzle is provided in at least one zone along the tape path, a device being present is, with the help of which periodically a gas displacement force is applied in such a way that gas is blown into the vicinity of the belt through such a nozzle. 43. Apparatus according to claim 42, characterized in that gas nozzles in at least one zone along the strip path are provided which exert gas displacement forces in different positions in the vicinity of the belt, wherein a common supply line for these nozzles and a gas distribution device are provided, which are electrically has controlled pneumatic valves, which successively different nozzles to the common supply line connects. 44. Device according to one of claims 27 to 43, characterized in that openings in the outer wall of the cooling 209885/0927 Manhole as well as controllable closing devices for controlling of the gas flow through such openings are provided under the action of natural tensile forces, which act in such a way that gas displacement forces are periodic in at least one direction across the belt by such flow of gases be exercised. 45. Device according to one of claims 27 to 44, characterized characterized in that at least one propeller is present in at least one zone along the tape path, which is periodically exerts a gas displacement force. 46. Device according to one of claims 27 to 45, characterized characterized in that a device is provided, with the help of which gas displacement forces transverse to the tape path on a Side or on both sides of the tape in a lower part of the drawing chamber. 47. Device according to one of claims 27 to 46, characterized in that it has a feed channel for molten, zenes glass in which a charge of molten glass is held with a depth such that molten Glass into the band from the full depth of such a bath flows. 48. Device according to one of claims 27 to 46, characterized characterized in that it has a feed channel for molten glass in which a charge of molten Glass is held to such a depth that the molten glass flowing into the belt from the upper layers this bath comes from. 49. Device according to one of claims 27 to 46, characterized in that it has a feed channel for molten material Glass has in the molten glass in the way 209885/0927 the drawing zone is fed that it is made on a mass a material floats that has a greater specific weight ". 50. Flat glass, characterized in that it is produced by a method according to one of Claims 1 to 26 has been. 209885/09 2 7