DE102007011900B4 - Float bath apparatus and method for producing flat glass - Google Patents

Abstract

Float bath device (10), which is divided in the longitudinal direction into float bath sections (1-8), with a float bath housing (11) which has a float bath tub (12), a float bath roof and side walls (24, 20), wherein the float bath tub (12 ) a float bath (16) made of liquid metal is located for the production of a glass ribbon (18) floating on the float bath (16), and with a suction device (30) for sucking off a forming gas atmosphere in the float bath housing (11), the suction device (30) at least a suction line (32) with at least one suction opening in at least one side wall (14, 20) and at least one suction means outside the float bath housing (11), characterized in that the suction opening is a slot opening (34) extending in the horizontal direction and that the The suction line (32) in the side wall (20) has a gradient from the inside to the outside.

Description

The invention relates to a float bath apparatus according to the preamble of patent claim 1. The invention also relates to a method for producing flat glass, in particular TFT glass, according to the preamble of patent claim 20.

The production of flat glass by the float process, known as float glass, has been known since the last century and is essentially based on the fundamental intellectual property rights of Pilkington ( US 3,083,551 A . DE 147 19 50 A ).

In the float process, liquid glass, which is produced by means of a trough from the working trough, is allowed to flow onto a bath of molten metal, generally tin. The flow rate of the glass is controlled by a movable slide, with its setting, among other things, the glass thickness is set. As seen in the direction of flow of the glass behind the slide is the pouring lip, from which the molten glass flows continuously to the metal bath, where the glass melt is formed into a dimensionally stable glass ribbon and solidifies. Subsequently, the solidified glass ribbon is removed from the metal bath.

The float bath is located in a float bath enclosure, which is usually divided into 7 or 8 float bath sections, known as bays.

The float glasses produced in this way, which generally have a thickness of less than 1.5 mm, are used as thin glass substrates, inter alia, for the production of flat screens, z. Plasma Display Panels (PDP), Field Emission Display (FED), Thin Film Transistor (TFT) Liquid Crystal Displays (STN), Super Twisted Nematic (STN) Liquid Crystal Display (STN) Plasma Assisted Liquid Crystal Displays (PALC), Electro-Luminescent Displays (EL) and the like, or for the production of thin-film solar cells.

In the flat panel displays, depending on the type of display, either a thin layer of liquid crystal compound is sandwiched between two sheets of glass or dielectric layers are formed on the front and back surfaces of the back and front sheets, respectively, from which cells are formed containing phosphors ,

It is important in this case that the layer thickness of the liquid-crystal layer or the thickness of the dielectric layer is exactly adhered to, so that no disturbing color distortions or similarity deviations occur, in particular for large dimensions of a screen. Since the layer thicknesses, currently about 30 microns, smaller and smaller and the screens are getting bigger, this condition is becoming increasingly important.

The surface quality of the float glass is affected by surface defects called top bacons, which are caused by deposits of Sn and SnO ₂ particles on the glass ribbon when using a tin bath. Despite the flooding of the interior with forming gas (typical composition 12% H ₂ , 88% N ₂ ), the atmosphere above the float bath contains residual amounts of oxygen which penetrate into the tin bath and form SnO ₂ particles there. As the bath temperature increases, both tin and tin oxide evaporates and enriches the atmosphere, with the result that the tin and tin oxide particles can precipitate on the glass ribbon.

From the WO 2005-097692 A1 It is known to suck the atmosphere and thus the Zinnoxidpartikel means of suction tubes, which are arranged in the side wall.

Out JP 11-302024 A . JP 50-3414A and JP 11-021137 A Floatbadvorrichtungen are known which have ventilation systems. About the float bath roof forming gas from N ₂ and H _{2 is introduced} into the interior of the Floatbadgehäuses, being set by suspended partitions a certain flow within the Floatbadgehäuses. The introduced forming gas sets an overpressure in the interior. Through vent pipes in the side walls, the gas atmosphere is discharged to the outside. Active suction devices are not described.

From the GB 1 217 047 A For example, a float bath is known in which tubes extending in the horizontal direction are arranged on the edge of the glass band and have slot-shaped openings. By means of this pipe system, the forming gas is sucked off and introduced via the ceiling of the Floatbadvorrichtung in the interior of the float bath. By means of this device, the glass ribbon is stretched and the edge of the glass band stabilized.

In all known solutions it has been found that the extraction of the Formiergasatmosphäre is not effective enough to significantly reduce the number of surface defects.

It is therefore an object of the invention to provide a Floatbadvorrichtung, with which the number of surface defects on the glass ribbon, which is produced by the float process, can be reduced. It is also an object of the invention specify appropriate method for the production of flat glass.

The object is achieved with a float bath device, which is characterized in that the suction opening is a slot opening extending in the horizontal direction and that the suction line has a gradient from inside to outside in the side wall.

The advantage of the invention is that the Formiergasatmosphäre is sucked off over a large-scale, contiguous area above the float bath. Harmful particles in the Formiergasatmosphäre be detected more effectively and completely than with round suction tubes, which are distributed over greater distances along the side walls of the Floatbadgehäuses.

The slope in the suction line has the advantage that in the suction condensed particles drain to the outside and thus not contaminate the metal bath.

Preferably, in each case at least one slot opening is arranged in at least two float bath sections in the two opposite side walls. The atmosphere above the glass ribbon is much more effectively extracted because two streams are created in opposite directions that prematurely capture the harmful particles prior to impacting the glass ribbon.

Preferably, the slot openings are arranged at least in the first two Floatbadabschnitten. In the float bath sections in which the hot forming takes place, these are in particular the float bath sections 1 and 2 , optionally Floatbadabschnitt 3 , the temperature of the float bath is highest, so there is the greatest enrichment of the atmosphere with harmful particles. By means of suction through slit openings in the float bath sections, the effectiveness of the decontamination of the atmosphere can be significantly increased.

Preferably, at least two slot openings are arranged in the horizontal direction next to one another.

The distance between two slit openings should be minimized as far as possible and should be less than 10 cm so as not to allow any dead spaces in which harmful particles can not be detected by the extraction system.

Preferably, the slot openings extend a total of at least 50% of the length of a Floatbadabschnittes. Preferably, the slot openings extend over at least 70%, more preferably over at least 80% of the length of the float bath section.

Preferably, the slot openings extend for a total of at least 50% of the length of the entire float bath. Preferably, the slot openings extend over 70%, in particular over 80% of the length of the entire float bath.

With this arrangement of the suction openings, the Formiergasatmosphäre is sucked over the entire surface of the metal bath, so that no dead spaces can arise in which accumulate the harmful particles and may possibly rise up inside the Floatbadgehäuses. From there, the particles generally return down the center of the housing and settle on the glass ribbon. A large-scale extraction over almost the entire length of the side wall, in particular over both side walls, prevents this adverse effect and leads to a significant decrease in the so-called top bacon.

Flat glass made in a float bath apparatus of the invention shows a significantly lower number of surface defects. The number of surface defects per m ² could be reduced on average from 30-50 top bacon / m ² to 0-20 top bacon / m ² . In addition, it has been shown that the size of the surface defects decreases to a diameter below 25 μm.

Preferably, the horizontal length of the slot opening is 30 cm to 150 cm.

The cross-sectional area of the slot opening is advantageously 20 to 40 cm ² . This means that in the claimed lengths of the slot openings, the vertical width of the slot opening may be in the range of 2 to 10 mm. By maintaining these values, a laminar flow is maintained within the slot opening.

The slot opening should be arranged as close as possible to the metal bath surface in order to be able to extract as much of the particles as possible. Preferably, the lower edge of the slot opening is located between 5 cm and 10 cm above the mirror of the float bath.

Preferably, the suction line has a slot nozzle. Slot nozzles essentially have a triangular shape in plan view. Towards the outside, the cross section tapers and merges into the cross section of the connected suction line. The slot nozzle may be a separate component or may be integrally formed on the suction tube forming the suction line.

A slot-shaped nozzle can be arranged at a small distance above the Floatbadspiegel, so that opens the possibility to suck the gas atmosphere immediately above the float.

Preferably, in the slot nozzle an opening angle α of 14 ° to 20 ° to maintain a laminar flow within the slot to ensure.

The angle α is in this case the angle between the tapered side walls of the slot nozzle.

Preferably, the slot nozzle is arranged in a side wall box.

The side wall box preferably has two shaped blocks, in particular of refractory material, which delimit at least the slot nozzle. The slit nozzle is formed in this case in the mold bricks, wherein preferably the dividing line between the two shaped bricks passes through the slit nozzle.

Preferably, a plurality of suction tubes are arranged distributed along the two side walls. The suction power through the suction tubes is preferably individually adjustable via the corresponding suction means. This embodiment offers the advantage that the different temperature conditions inside the float bath housing can be easily taken into account. Thus, in the hotter areas, a larger volume of gas per unit time can be extracted than is necessary in the colder sections.

Advantageously, in at least two sections (bay) of the float bath tub, at least one suction tube is arranged in the two opposite side walls.

Preferably, the suction line has a suction pipe extending in the direction of the float bath mirror. This embodiment is used in particular where the suction line is arranged in a side wall box, the type must be arranged conditionally at a greater distance to the metal bath surface.

The arrangement of the suction line (s) in the sidewall box allows quick replacement of the suction lines, for example when smaller or larger cross-sections or larger or smaller numbers of suction lines are needed in the respective sidewall area. Such an adaptation may become necessary if, under certain circumstances, the temperature conditions within the float bath housing and thus the concentration of the particles should change.

Preferably, the suction means is an injector pump. The injector pump generates a vacuum at the outlet of the suction tube.

Injector pumps have two inputs and one output and consist in principle of two nested tubes, which are referred to as inner tube and outer tube. The inner tube ends in the outer tube and has an outlet nozzle. The suction fluid exits under the full line pressure from the outlet nozzle in the outer tube and thereby tears the fluid to be sucked, d. H. the Formiergasatmosphäre from the second input with. This happens due to the generated negative pressure. For example, a water jet pump works according to this principle.

Since the suction power of the injector pump can be easily adjusted with high accuracy via the pressure of the suction fluid, the desired adaptation to the different concentrations of the particles in the interior of the floating bath housing is possible. The accuracy is ± 5 m ³ (i.N) / h. The term m ³ (i.N) is understood to mean a standard cubic meter, which is specified in DIN 1343. A standard cubic meter is the quantity corresponding to one cubic meter of gas at a pressure of 1.01325 bar, a relative humidity of 0% (dry gas) and a temperature of 0 ° C.

Preferably, the injector pump is operated with compressed air as a suction fluid.

Accordingly, the injector pump is preferably connected to at least one compressed air generator.

Furthermore, the compressed air generator may be connected to a control device for controlling the pressure of the compressed air or the compressed air generator has such a control device.

It is also possible that a control device for controlling the pressure of the compressed air is arranged between the injector pump and the compressed air generator. Such a control device may be for example a compressed air valve. Preferably, such a compressed air valve is arranged in front of each injector pump so that each injector pump can be adjusted individually

One or more suction lines can be connected to an injector pump. The group-wise arrangement of suction lines lends itself to when the suction power of each Floatbadabschnittes should be set individually. If within a Floatbadabschnittes several Suction lines are provided, are to be sucked through the individually set gas quantities per unit time, preferably each suction is connected to a separate injector pump.

The control device is preferably connected to at least one temperature sensor, which is arranged in the interior of the float bath. The corresponding temperature changes can thus be implemented directly via the control device in the relevant suction, which is necessary to ensure optimal extraction of the particles.

The method for producing flat glass, in particular TFT glass, provides that the Formiergasatmosphäre is sucked in the horizontal direction slit-shaped and with a slope from the inside to the outside.

Preferably, the Formiergasatmosphäre is sucked through at least one slot opening.

It is preferable to perform the extraction at several points along the Floatbadvorrichtung, wherein in at least two Floatbadabschnitten (Bay) of the Floatbadwanne the Formiergasatmosphäre is sucked.

Preferably, the Formiergasatmosphäre, preferably at both sidewalls of the Floatbadgehäuses, over at least 50%, in particular at least 70%, particularly preferably sucked off over at least 80% of the Floatbadlänge.

It is also advantageous that the amount of gas extracted in each Floatbadabschnitt per unit time is set in dependence of the temperature of the Floatbadabschnittes.

Exemplary embodiments of the invention are explained below with reference to the drawings.

Show it

1 a plan view of a float bath with glass ribbon;

2 a side view of a section of a side wall of a Floatbadgehäuses according to another embodiment;

3 a section along the line IV-IV in the 2 ;

4 a perspective view of a sidewall box;

5 a top view of the in 4 shown slot nozzle;

6 a side view of a section of a side wall according to another embodiment;

7 a side view of a section of a side wall according to another embodiment;

8th a cross section through the in 7 shown side wall along the line IX-IX;

9 a partial vertical section through the edge of a float bath with an injector pump;

10 another sectional view similar to the 9 according to a further embodiment;

11 a plan view of a section of a side wall with a slot nozzle according to another embodiment;

12 a vertical section through a side wall according to a further embodiment; and

13 a vertical section through a side wall according to another embodiment.

In the 1 is the top view of one in a Floatbadgehäuse 11 Float bath tub 12 a float bath device 10 shown, which is divided into Floatbadabschnitte, with the so-called Bay numbers 1 to 8th are provided. The float bath tub 12 is with a bath 16 of liquid metal, in particular tin, filled. On the bath 16 a glass ribbon floats 18 which is pulled off in the direction of the arrow. The area between the edge 19 of the glass band 18 and the side walls 14 the float bath tub 12 forms the free float bath surface from which tin and tin oxide particles can evaporate. These particles then deposit on the surface of the glass ribbon 18 and cause the above-described top bacon.

In the side walls of the Floatbadvorrichtung 10 are suction lines 32 a suction device 30 arranged in the form of suction tubes, only part of the suction lines 32 are drawn in for clarity. In Bay Number 2 is in the right side wall representative of further suction a suction line 32 drawn to an injector pump 40 connected by a compressed air generator 60 via a compressed air line 49 is supplied. To control the compressed air is in front of the injector pump 40 as a control device, a control valve 64 intended. The control of the valve 64 can be done manually or electrically.

In Bay Number 3 is also a suction line 32 and in bay number 4 are two suction lines 32 shown. The two suction lines 32 from Bay 4 are connected to a common injector pump 40 connected. Both injector pumps 40 for Bay 3 and Bay 4 are via a common compressed air line 49 to the compressed air generator 60 connected, which is electrically connected to a control device 62 connected is. This control device 62 is via an electrical connection line 52 with temperature sensors 50 connected to the inside of the side walls 14 the Floatbadgehäuses 11 are arranged. The in the 1 Embodiments shown are only examples of applications of suction lines 32 and injector pumps 40 as well as control valves 64 and control devices 62 represents.

In the 2 is a section of a sidewall 20 the Floatbadgehäuses 11 shown. It is the plan view of the inner surface of the side wall, in the area shown sidewall boxes 22 that exists on the sidewall 14 the float bath tub are arranged. Every sidewall box 22 has a slot-shaped suction opening 34 on. The slit-shaped suction openings 34 are close together at a distance of less than 10 cm and close above the mirror 17 of the metal bath 16 arranged at a distance of about 5 cm. The suction openings 34 are located at the bottom of the sidewall boxes. The dense arrangement of the slot-shaped suction openings 34 has the advantage that the Formiergasatmosphäre can be sucked off almost over the entire area of the side wall without dead spaces arise in which the harmful particles can accumulate.

In the 3 is a section along the line III-III through the in 2 shown side wall 20 shown. The slot-shaped intake opening 34 belongs to the suction line 32 , which in terms of the cross section on the cross section of the outer suction tube 33 rejuvenated. The suction line 32 points inside the sidewall box 22 a slope outwards. Sucked particles can be inside the sidewall box 22 and thus within the suction line 32 condense to droplets. Due to the gradient, these condensed particles can not be returned to the Floatbadgehäuse and thus into the metal bath 16 but these condensed droplets flow outward into the outer suction tube 33 from.

In the 4 is a perspective view of a sidewall box 22 shown in the embodiment shown here of two refractory bricks 23 and 24 is formed. In these stones 23 . 24 is a slot nozzle 31 formed. The dividing line 25 between the two form stones 23 . 24 passes through the slot nozzle 31 , which brings appropriate manufacturing advantages. A horizontal section through the slot nozzle 31 is in the 5 shown. It can be seen that the opening angle α of the slot nozzle 31 through the two boundary walls of the slot nozzle 31 is defined. This angle is in the representation shown here at α = 20 °.

In the 6 is another embodiment of a side wall 20 with sidewall boxes 22 shown. The sidewall boxes 22 For example, as in the 4 be formed and each a slot nozzle 31 exhibit. The arrangement of such sidewall boxes 22 with slot nozzles 31 is not consistently over the entire Floatbadlänge possible because at certain points within the float bath from outside to inside so-called top rollers must be introduced, which must have a corresponding mobility. In the middle sidewall box 22 is such a top roller 70 indicated by way of example and schematically. In order to be able to extract the area under the Toprollern so that there can occur no dead space, in the embodiment shown here is a cover 80 provided that a horizontal middle section 82 and downwardly sloping sections 83 having. The inclined sections 83 extend to just above the mirror 17 the float bath. The cover elements may extend to the edge of the glass ribbon. Due to the inclined arrangement can thus the area under the Toproller 70 be sucked off as well.

In the 7 another embodiment is shown. The suction pipes 32 have a curved downward suction 38 on which in the horizontal direction a pipe 36 is arranged, which has a slot-shaped opening 34 having.

In the 8th is a section along the line IX-IX shown. In modification to 7 is the slot-shaped suction opening 34 at the bottom of the tube 36 intended.

In the 9 is a partial vertical section through a float bath tub 12 with bottom wall 13 and sidewall 14 shown. On the sidewall 14 the float bath tub 12 is a sidewall box 22 with suction line 32 shown.

The suction line 32 flows above the float bath 16 in the interior of the Floatbadgehäuses 11 , The suction pipe opens outwards 32 in the injector pump 40 made of an outer tube 42 and an inner tube 44 consists, at the upper end of a nozzle 46 is arranged. The inner tube 44 is to a pressure generator 60 connected, in turn, to a control device 62 electrically connected. Over the electrical connection line 52 is the controller 62 with the one on the inside of the wall 20 arranged temperature sensor 50 connected. The in the pressure generator 60 generated compressed air flows into the inner tube 44 and then out of the nozzle 46 in the interior of the outer tube 42 one. It is therefore in the outer tube 42 in the mouth area of the suction line 32 generates a negative pressure, due to which the Formiergasatmosphäre from the interior of the Floatbadgehäuses 11 is sucked off. Compressed air and gas atmosphere from inside the Floatbadgehäuses 11 Be up together through the drainpipe 48 discharged.

In the 10 another embodiment is shown. At the suction pipe 32 is a proboscis 38 arranged, which allows the Formiergasatmosphäre from the interior of the Floatbadgehäuses 11 suck off immediately above the surface of the float bath. in modification to the presentation of the 9 is between the pressure generator 60 and the injector pump 40 a compressed air valve 64 arranged as a control device to control the compressed air and thus the suction power of the injector 40 adjust.

In the 11 is shown a further embodiment, wherein the suction tube 32 an extending into the interior slot nozzle 31 with slit-shaped opening 34 having. This makes it possible, the suction opening closer to the mirror 17 the float bath 16 in bringing.

In the 12 and 13 Further embodiments are shown in which a trunk 38 is provided in the 12 vertically downwards on the inner wall of the sidewall box 22 extends, leaving the suction opening immediately above the mirror 17 the float bath 16 is arranged. In the 13 is the trunk 34 executed kinked, so that the end portion is oriented horizontally and the suction opening 34 a horizontal suction allows.

LIST OF REFERENCE NUMBERS

1

Bay number

2

Bay number

3

Bay number

4

Bay number

5

Bay number

6

Bay number

7

Bay number

8th

Bay number

10

Floatbadvorrichtung

11

Floatbadgehäuse

12

Floatbadwanne

13

bottom wall

14

Side wall

16

bath

17

Floatbadspiegel

18

glass tape

19

Edge of the glass ribbon

20

Side wall

22

Sidewall box

23

cast stone

24

cast stone

25

parting line

30

suction

31

slot

32

suction

33

outer suction tube

34

suction

36

pipe

38

proboscis

40

injector pump

42

outer tube

44

inner tube

46

jet

48

drain pipe

49

Compressed air line

50

Temperature sensor

52

electrical connection line

60

Air compressor

62

control device

64

control valve

70

Toproller

80

cover

82

midsection

83

side panel

Claims (24)

Float bath device ( 10 ), longitudinally in Floatbadabschnitte ( 1 - 8th ), with a Floatbadgehäuse ( 11 ), which has a float bath tub ( 12 ), a float bath roof and side walls ( 24 . 20 ), wherein in the Floatbadwanne ( 12 ) a float bath ( 16 ) is made of liquid metal for producing a floatation bath ( 16 ) floating glass ribbon ( 18 ), and with a suction device ( 30 ) for aspirating a Floatbadgehäuse ( 11 ) Formiergasatmosphäre, wherein the suction device ( 30 ) at least one suction line ( 32 ) with at least one suction opening in at least one side wall ( 14 . 20 ) and at least one suction agent outside the float bath housing ( 11 ), characterized in that the suction opening has a slot opening extending in a horizontal direction (FIG. 34 ) and that the suction line ( 32 ) in the side wall ( 20 ) has a slope from inside to outside. Apparatus according to claim 1, characterized in that in at least two Floatbadabschnitten ( 1 to 8th ) in both opposite side walls ( 14 . 20 ) at least one slot opening ( 34 ) is arranged. Apparatus according to claim 2, characterized in that the slot openings ( 34 ) at least in the first two Floatbadabschnitten ( 1 . 2 ) are arranged. Device according to one of claims 1 to 3, characterized in that at least two slot openings ( 34 ) are arranged side by side in the horizontal direction. Device according to one of claims 1 to 4, characterized in that the slot openings ( 34 ) extend over at least 50% of the length of a Floatbadabschnittes. Device according to one of claims 1 to 5, characterized in that the slot openings ( 34 ) over at least 50% of the length of the float bath ( 16 ). Device according to one of claims 1 to 6, characterized in that the horizontal length of the slot opening ( 34 ) Is 30 cm to 150 cm. Device according to one of claims 1 to 7, characterized in that the cross-sectional area of the slot opening ( 34 ) Is 20 to 40 cm ² . Device according to one of claims 1 to 8, characterized in that the lower edge of the slot opening ( 34 ) between 5 cm and 10 cm above the mirror ( 17 ) of the float bath ( 16 ) is arranged. Device according to one of claims 1 to 9, characterized in that the suction line ( 32 ) one the slot opening ( 34 ) having slot nozzle ( 31 ) having. Apparatus according to claim 10, characterized in that the slot nozzle ( 31 ) in a sidewall box ( 22 ) is arranged. Apparatus according to claim 11, characterized in that the side wall box ( 22 ) two shaped stones ( 23 . 24 ), which at least the slot nozzle ( 31 ) limit. Device according to one of claims 1 to 12, characterized in that the suction line ( 32 ) in the direction of the Floatbadspiegels ( 17 ) extending proboscis ( 38 ) having the slot opening ( 34 ) having. Device according to one of claims 1 to 13, characterized in that the suction means an injector pump ( 40 ) located at the exit of the suction tube ( 32 ) generates a negative pressure. Apparatus according to claim 14, characterized in that the injector pump ( 40 ) to at least one compressed air generator ( 60 ) connected. Apparatus according to claim 14 or 15, characterized in that the compressed air generator ( 60 ) at least one control device ( 62 ) for controlling the pressure of the compressed air or to at least one such control device ( 62 ) connected. Device according to one of claims 14 to 16, characterized in that between injector pump ( 40 ) and compressed air generators ( 60 ) at least one control device ( 62 ) is arranged to control the pressure of the compressed air. Apparatus according to claim 17, characterized in that the control device ( 62 ) a control valve ( 64 ). Device according to one of claims 16 to 18, characterized in that the control device ( 62 ) to at least one temperature sensor ( 50 ), which is located inside the Floatbadgehäuses ( 11 ) is arranged. A process for the production of flat glass, in particular of TFT glass, in which in a side walls Floatbadgehäuse under a Formiergasatmosphäre poured a molten glass on a liquid metal bath, formed a glass ribbon and the glass ribbon is lifted from the metal bath, the Formiergasatmosphäre over the metal bath over at least one Side wall of Floatbadgehäuses is sucked off, characterized in that the Formiergasatmosphäre is sucked in the horizontal direction slit-shaped and with a slope from the inside to the outside. A method according to claim 20, characterized in that the Formiergasatmosphäre is sucked at several points along the side wall. Method according to one of claims 20 or 21, characterized in that the Formiergasatmosphäre is sucked slot-shaped in at least two Floatbadabschnitten the Floatbadgehäuses. Method according to one of claims 20 to 22, characterized in that the Formiergasatmosphäre is sucked off over at least 50% of the Floatbadlänge. Method according to one of claims 20 to 23, characterized in that the extracted Gas quantity per unit time is set in each Floatbadabschnitt depending on the temperature of the Floatbadabschnittes.

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