DE102007028977B9 - Arrangement of heaters, Floatbadvorrichtung and method for producing flat glass - Google Patents

Abstract

Arrangement of heaters (20, 20a-e) over a metal bath (3) having Floatbadwanne (2) with Floatbadanfang (9a) and Floatbadende (9b), characterized in that at least two heaters in the transverse direction of the Floatbadwanne (2) are arranged whose center distance L _M is, and that at least two in the longitudinal direction of the Floatbadwan ne (2) one behind the other heaters (20a, b) by at least 10% in the transverse direction of the Floatbadwanne (2) extending center distance L _M in the direction Floatbadende (9b) heater located further forward (20, 20a-e) are offset from one another.

Description

The The invention relates to an arrangement of heaters over a float bath tub having a metal bath according to the generic term of claim 1. The invention also relates to a float bath apparatus according to the generic term of claim 12 and a method of making Flat glass according to the preamble of claim 13.

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 ).

At the Float method leaves you liquid glass on a bath of molten metal, generally tin flow. Of the Volume flow of the glass is over a movable slider regulated, with its setting under other things, the glass thickness is set. In the flow direction of Glases seen behind the slider 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. This process takes place in a device downstream of the metal bath for lifting the glass ribbon instead.

The Float glasses made in this way, usually a thickness of less than 1.5 mm are used as thin glass substrates used among other things for the production of flat screens, z. From plasma display panels (PDP), field emission screens (FED = Field Emission Display), TFT Liquid Crystal Displays (TFT = Thin Film Transistor), STN liquid crystal displays (STN = Super Twisted Nematic), Plasma Assisted Liquid Crystal Displays (PALC = Plasma assisted liquid crystal), electro-luminescence displays (EL) and the like or for the production of thin-film solar cells.

In the 1 is a conventional float bath device 1 shown in vertical section. The float bath device 1 has a float bath tub 2 made of refractory material, which contains a metal bath 3 , in particular of liquid tin. At the beginning 9a There is a pouring lip in the float bath 8th , about which a molten glass on the metal bath 3 is poured, the further course to a glass ribbon 4 is formed. At the end 9b of the float bath, the thus formed glass ribbon is lifted from the metal bath and fed to another (not shown) processing device.

Above the float bath tub is the float bath roof, which is a false ceiling 11 has, in the a variety of heaters 20 are arranged. The heaters 20 serve the space 6 above the glass ribbon or the metal bath 3 heat.

For the heating elements 20 Different forms are common. What they all have in common is that, depending on the type of electrical heating, there are two or three connections for mounting the electrical supply in a relatively cold room 7 above the false ceiling 11 lie. The commonly used heaters thereby have the shape of a U, a W or similar shapes, with lying in a common direction connecting legs.

Since the material of the heater, usually made of silicon carbide, difficult to produce in a round curved shape, the heaters exist 20 usually made of straight pipe sections 21 or heating rods, as stated in the 2 is shown. The straight pipe sections form the actually active zones of the heaters 20 , At the lower end of the pipe sections via a connector 22 connected together, in which usually significantly less heat energy is released. The hot and less hot areas of the heater 20 are in the 2 characterized by a different hatching.

Usual heater arrangements, as used in the 3 Shown schematically for one half of a float bath, provide that the individual heaters 20 transverse to the drawing direction, which is indicated by the arrow, be installed to the less radiating lower part of the heater 20 to act over as wide a range as possible of the glass ribbon running underneath. However, to simplify the arrangement of as many heaters as possible on a structurally simple ceiling structure, the heaters lying one behind the other in the drawing direction are in a row. In the 3 are a total of 5 heater rows 23 shown.

The JP 08-325024 A describes a float bath apparatus having a plurality of heaters disposed above the float bath. The heaters are grouped in heating zones, whereby the heaters of each heating zone are controlled together, so that each heating zone gives off a certain heat output. In each heating zone two or more heaters are arranged.

The float bath is divided longitudinally into seven fields (bays), each field having several heating zones adjacent to each other, perpendicular to the drawing direction. The length of the heating zones corresponds to the width of the relevant field, while the width of the heating zones can be different. The heating zones are offset in the pulling direction too arranged one another.

Statements about the Arrangement and orientation of the heaters in the individual heating zones are not made.

It will be in the JP 08-325024 A also described the problem associated with the usually somewhat cooler limits of the heating zones, which lead to undesirably high thickness variations in the glass. There is proposed as a solution to arrange the extending in the drawing direction transitions between transverse to the drawing heating zones offset.

It However, it has been shown that in the production of very thin flat glass with thicknesses between 0.3 and 1 mm short-wave thickness variations with amplitudes of more than 0.5 μm with wavelengths transverse to the longitudinal direction, d. H. Draw direction of the tape between 0.8 and 8 mm occur.

Furthermore, in the JP 08-325024 A described that the points of the glass ribbon, which run under the abutting edges of two contiguous to the drawing direction heating zones, experience a different temperature radiation, as adjacent glass ribbon areas. It turns out, however, that this different temperature radiation due to the design of the heater not only at the abutting edges of adjacent heating zones, but also occurs between transverse to the drawing juxtaposed heater rows within a heating zone and in accordance with high quality requirements unacceptably high thickness variations in the short-wave range. Schematically, the temperature distribution on the glass ribbon in the partial section of 4 shown.

It Object of the invention, a heater assembly and a method for the production of flat glass, which gives a uniform temperature distribution over the Guaranteed glass ribbon.

The The object is achieved by an arrangement of heaters according to claim 1.

The staggered arrangement of heaters has the advantage that the irradiated Heating power over the Glass band width is evened out, so that variations in thickness, in particular in the short-wave range, be reduced. It turned out that in particular in the production of flat glass with a thickness of up to 1 mm, the thickness variations Values below 0.4 μm can be lowered.

Preferably are used as heaters electric radiant heaters. electrical Radiant heaters have the advantage of keeping the atmosphere within the Floatbadvorrichtung where the Floatbadwanne is not impaired and that the heating power is constant.

Preferably, the heaters are offset by at least 20%, in particular up to 50% of the center distance L _M against each other

Preferably the heaters are in longitudinal rows in longitudinal direction the float bath tub, with at least one heater in the area between two longitudinal rows is arranged. Such an arrangement has the advantage that the radiated heat energy over the width of the glass ribbon is distributed very evenly. Another Another advantage is that a relatively simple ceiling construction chosen can be.

According to a further embodiment, the heaters are arranged in transverse rows in the transverse direction of the float bath tub, wherein at least two transverse rows are arranged offset from one another. Preferably, the two transverse rows are arranged offset in space. This means that the heaters of one transverse row are each arranged in the gap between the heaters of the other transverse row. In this arrangement, the offset is exactly 50% of the length L _M.

The Heaters preferably extend vertically and / or in parallel to the longitudinal direction the float bath tub. To the residence time of individual places of the glass ribbon under the colder Divide the heater as possible will be the predominant Number of heaters with their longitudinal direction vertical to the longitudinal direction the float bath tub arranged. However, it has turned out that it is for a uniform temperature distribution is advantageous if at least a part of the heaters also parallel to the longitudinal direction the Floatbadwanne is aligned, in particular, if parts of the Heaters are staggered, otherwise "gaps" would arise.

The mutually offset heaters are preferably arranged over a glass ribbon section where the glass ribbon has a viscosity below 10 ⁹ Pas. In particular, the mutually offset heaters are provided where the glass ribbon has a viscosity between 10 ^3.5 and 10 ⁶ Pas. If the glass has a viscosity in said viscosity range, it is best to influence the short-wave thickness variations. The glass ribbon is in the viscosity range of 10 ^3.5 to 10 ⁶ Pas in the area to about the middle of the float bath. After the usual division into bays, which ranges for example from 1 to 7, the staggered heaters are to be arranged in the Bays 1 to 4. For longer float baths with more bays, the information applies accordingly.

Preferably is at least one extending parallel to the longitudinal direction of the Floatbadwanne Heater in the area next to the glass ribbon above the free metal surface. These Arrangement has the advantage that gaps in the heating arrangement avoided can be.

The Floatbadvorrichtung invention provides that the false ceiling is constructed of ceiling modules, each ceiling module preferably has at least one heater and wherein at least two in the longitudinal direction of the Floatbadwanne one behind the other ceiling modules at least 10% of extending in the transverse direction of the Floatbadwanne center distance L _M 'in the direction Floatbadende further forward ceiling modules are offset from each other. The construction of individual preferably identical ceiling modules has the advantage that an exchange of heaters is possible in a simple manner.

For installation the staggered heater, it is advantageous that the ceiling modules, from which the ceramic false ceiling is constructed, in which the heaters are installed, in turn, in two in the drawing direction each other following rows are installed offset. Since the installation locations of Heater through the bushings are given in the ceiling modules, this results in a constructive simple execution the staggered arrangement of the heaters.

The by a staggered arrangement of the ceiling modules resulting half Ceiling modules are preferred directly on the side walls of the float bath built-in. Heaters can also be installed in these smaller modules become. Here it is advantageous because of the limited size of the modules that Heater at 90 ° opposite the normal installation direction to rotate, so these heaters parallel to the longitudinal direction the float bath tub are arranged.

The method for producing flat glass, in particular of TFT glass by the float method, provides that the glass ribbon is heated more uniformly over the glass ribbon width at least in a first glass ribbon section than in at least one second glass ribbon segment, at least two in the longitudinal direction of the first glass ribbon segment Float bath tub one behind the other heaters offset by at least 10% of extending in the transverse direction of the Floatbadwanne center distance L _M in the direction Floatbadende further forward heaters are offset from each other.

Preferably, the first glass ribbon section is placed in the region of the glass ribbon, where the glass ribbon has a viscosity of less than 10 ⁹ Pas. In particular, this glass ribbon section is placed in the area where the glass ribbon has a viscosity of 10 ^3.5 to 10 ⁶ Pas.

The Process is particularly suitable for the production of borosilicate glasses, alkali-free glasses, aluminosilicate, Aluminolithiumsilikatgläsern and precursor glasses for glass-ceramic.

Particularly suitable is the method for producing borosilicate glass, z. For fire protection applications, having a composition of (all of the following in terms of weight percent based on oxide):
SiO ₂ 70-85, B ₂ O ₃ 7-13, Na ₂ O + K ₂ O + Li ₂ O 3-8, MgO + CaO + SrO 0-3, Al ₂ O ₃ 2-7,
for the preparation of alkali-free alumino (boro) silicate glass with a composition of
SiO ₂ 50-70, B ₂ O ₃ ≤15, Al ₂ O ₃ 10-25, MgO 0-10, CaO 0-12, SrO 0-12, BaO 0-15, with MgO + CaO + SiO + BaO 8 -26, ZnO 0-10, ZrO ₂ 0-5, TiO ₂ 0-5, SnO ₂ 0-2,
z. B. for the production of display glass, in particular with a composition of
SiO ₂ > 55-65, B ₂ O ₃ 5-11, Al ₂ O ₃ > 14-25, MgO 0-8, CaO 0-8, SrO 0-8, BaO ≤ 10 with MgO + CaO + SrO + BaO 8-21, ZnO 0-5, ZrO ₂ 0-2, TiO ₂ 0-3, SnO ₂ 0-2,
in particular SiO ₂ > 58-65, B ₂ O ₃ > 6-10.5, Al ₂ O ₃ > 14-25, MgO 0- <3, CaO 0-9, BaO> 3-8 with MgO + CaO + BaO 8-18, ZnO 0- <2, As ₂ O ₃ -free, Sb ₂ O ₃ -free,
preferably Zn oxide, Ce oxide, Zr oxide, Ti oxide free.

It is also particularly suitable for the production of various green glasses for glass-ceramic, such. B. with
SiO ₂ 55-69, Al ₂ O ₃ 19-25, Li ₂ O 3-5, Na ₂ O 0-1.5, K ₂ O 0-1.5, Σ Na ₂ O + K ₂ O 0.2 -2, MgO 0.1-2.2, CaO 0-15, SrO 0-1.5, BaO 0-2.5, Σ MgO + CaO + SrO + BaO below 6, ZnO 0-1.5, TiO ₂ 1-5, ZrO ₂ 1-2.5, SnO ₂ 0 to less than 1, Σ TiO ₂ + SrO + SnO _{2 2} 2.5-5, P ₂ O ₅ 0-3
or a glass-ceramic precursor glass having a composition of
SiO ₂ 55-75, Al ₂ O ₃ 15-30, Li ₂ O 2.5-6, Σ Na ₂ O + K ₂ O less than 6, Σ MgO + CaO + SrO + BaO less than 6, B ₂ O ₃ 0 to less than 4, ΣTiO ₂ + ZrO ₂ less than 2
or a glass-ceramic precursor glass having a composition of
SiO ₂ 60-72, Al ₂ O ₃ 18-28, Li ₂ O 3-6, Σ Na ₂ O + K ₂ O 0.2-2, Σ MgO + CaO + SrO + BaO less than 6, ZnO 0-1 , 5, B ₂ O ₃ 0 to less than 4, SnO 0.1-1.5, ΣTiO ₂ + ZrO ₂ less than 2, P ₂ O ₅ 0-3, F 0-2.

advantageous embodiments The invention will be explained in more detail with reference to the drawings. It demonstrate:

1 a vertical section through a float bath tub according to the prior art,

2 a schematic representation of a heater according to the prior art,

3 an arrangement of heaters over a float bath according to the prior art,

4 schematically two juxtaposed heaters and the associated temperature distribution of the glass ribbon according to the prior art,

5 and 6 heater assemblies according to the invention according to two embodiments and

7 a partial vertical section through a glass ribbon, which has been produced by the process according to the invention.

In the 5 a heater assembly according to the invention is shown. Under the heaters 20 is the glass ribbon 4 drawn in, the glass band edge 5 spaced to the edge of the float bath tub 2 lies. The metal bath 3 is not completely from the glass band 4 covered, so that a strip-shaped edge region with a free Floatbadoberfläche 3a remains.

The heaters 20 . 20a are in longitudinal rows 23 arranged, with the heaters 20 . 20a perpendicular to the longitudinal direction of the Floatbadwanne 2 extend. The center of the heater 20 is marked by L _M (see also 4 ). In each longitudinal row 23 are the heaters 20 arranged one behind the other. Between the longitudinal rows 23 there are intermediate areas 25 , Further, the heaters 20 . 20a . 20b also in transverse rows 24 arranged.

In the glass band section 4a in which the glass band 4 have a viscosity of <10 ⁹ Pas are in these intermediate areas 25 more heaters 20b arranged. The heaters are in transverse rows 24 arranged, wherein within the glass ribbon section 4a in the left section two transverse rows 24a . 24b offset from one another. These heaters are arranged in a gap, the offset being 50%. The overlap of the heater 20a . 20b is about 10% at each end. This ensures almost complete heating over the entire glass band width. In the right part of the glass band section 4a are a total of 3 staggered transverse rows 24b arranged, with the heaters 20 the staggered three transverse rows 24b in the longitudinal direction of the float bath tub 2 Seen in a row.

Over the free metal bath surface 3a are also heaters 20 provided so that the heat losses through the walls can be compensated.

The left glass band section 4b has a viscosity of> 10 ⁹ Pas, so that it is not necessary to arrange there also staggered heater. In the right glass band section 4b also staggered heaters can be introduced, which is in 5 not shown.

In the 6 a further arrangement is shown, which differs from the arrangement shown above substantially in that in the area 4a over the free float bath surface 3a longitudinally aligned heaters 20e are provided. There are also four ceiling modules 12a . 12b the false ceiling 11 located. In the embodiment shown here are each two heaters 20 on each a ceiling module 12a . 12b , In order to achieve a staggered arrangement, the ceiling modules, which have a center distance L _M ', also arranged offset.

In the 7 is a section through a produced by the process according to the invention glass ribbon 4 shown. The average glass band thickness is 0.7 mm. The wavelength λ of the thickness variations is 1 mm and the thickness variation ΔD = D ₁ -D _{2 of} these short-wave thickness variations is 0.2 μm. The presentation of the 7 is not to scale to better represent the details.

1

float device

2

Floatbadwanne

3

metal

3a

metal bath

4

glass tape

4a, b

Glass tape section

5

edge of the glass band

6

room

7

room

8th

pouring lip

9a

Floatbadanfang

9b

Floatbadende

10

Floatbaddach

11

false ceiling

12a, 12b

ceiling module

15

Floatbadgehäuse

20

stoker

20a-e

stoker

21

heater

22

joint

23

longitudinal row

24

transverse row

24a, b

transverse row

25

intermediate area

L _M

center distance stoker

L _M '

center distance ceiling modules

Claims (15)

Arrangement of heaters ( 20 . 20a -E) over a metal bath ( 3 ) Floatbadwanne ( 2 ) with Floatbadanfang ( 9a ) and float bath end ( 9b ), characterized in that at least two heaters in the transverse direction of the Floatbadwanne ( 2 ), whose center distance is L _M , and that at least two in the longitudinal direction of the float bath ( 2 ) heaters (one behind the other) 20a , b) at least 10% of the width of the float bath tub in the transverse direction ( 2 ) extending center distance L _M towards Floatbadende ( 9b ) further forward heater ( 20 . 20a -E) are offset from each other. Arrangement according to claim 1, characterized in that the heaters ( 20a -E) are electric radiant heaters. Arrangement according to claim 1 or 2, characterized in that the heaters ( 20 . 20a -E) are offset from one another by at least 20% of the length L _M. Arrangement according to one of claims 1 to 3, characterized in that the heaters ( 20 . 20a -E) are offset by up to 50% of the length L _M. Arrangement according to one of claims 1 to 4, characterized in that the heaters ( 20 . 20a -E) in the longitudinal direction of the float bath tub ( 2 ) in longitudinal rows ( 23 ) and that at least one heater ( 20 . 20a -E) in the intermediate area ( 25 ) between two longitudinal rows ( 23 ) is arranged. Arrangement according to one of claims 1 to 5, characterized in that the heaters ( 20 . 20a -E) in the transverse direction of the float bath tub ( 2 ) in transverse rows ( 24 . 24a , b) are arranged, and that at least two transverse rows ( 24a , b) are offset from one another. Arrangement according to claim 6, characterized in that at least two transverse rows ( 24a , b) are arranged offset in space. Arrangement according to one of claims 1 to 7, characterized in that the heaters ( 20 . 20a D) perpendicular and / or parallel to the longitudinal direction of the float bath trough ( 2 ). Arrangement of heaters ( 20 . 20a E) according to any one of claims 1 to 8, wherein a glass ribbon ( 4 ) on the metal bath ( 3 ), characterized in that the staggered heaters ( 20a , b) over a glass ribbon section ( 4a ) are arranged where the glass ribbon ( 4 ) has a viscosity below 10 ⁹ Pas. Arrangement according to claim 9, characterized in that the mutually offset heater ( 20a , b) over a glass ribbon section ( 4a ) are arranged where the glass ribbon ( 4 ) has a viscosity of between 10 ^3.5 and 10 ⁶ Pas. Arrangement according to one of claims 1 to 10, characterized in that at least one parallel to the longitudinal direction of the Floatbadwanne ( 2 ) extending heater ( 20e ) in the area next to the glass ribbon ( 4 ) above the metal bath surface ( 3a ) is arranged. Float bath device ( 1 ) with a Floatbadgehäuse ( 15 ), which has a float bath tub ( 2 ) and one above the float bath tub ( 2 ) arranged float bath roof ( 10 ), wherein the Floatbaddach ( 10 ) a false ceiling ( 11 ), characterized in that the false ceiling ( 11 ) from ceiling modules ( 12a , b), each ceiling module ( 12a , b) at least one heater ( 20 . 20a E) and that at least two longitudinally of the float bath tub ( 2 ) ceiling modules ( 12a , b) at least 10% of the width of the float bath tub in the transverse direction ( 2 ) extending center distance L _M 'in the direction Floatbadende further forward ceiling modules are offset from each other. Process for the production of flat glass, in particular of TFT glass, according to the float process, in which a glass melt is applied to a bath ( 3 ) is poured from liquid metal, the poured molten glass to a glass ribbon ( 4 ) and the molded glass ribbon ( 4 ) from the metal bath ( 3 ), wherein at least the glass ribbon ( 4 ) from above by means of heaters ( 20 . 20a , e) is heated, characterized in that the glass ribbon ( 4 ) at least in a first section of glass ribbon ( 4a ) is heated more uniformly over the glass ribbon width than in at least one second glass ribbon segment ( 4b ), wherein at least two in the longitudinal direction of the Floatbadwanne ( 2 ) heaters (one behind the other) 20a , b) at least 10% of the width of the float bath tub in the transverse direction ( 2 ) extending center distance L _M towards Floatbadende ( 9b ) further forward heater ( 20 . 20a -E) are offset from each other. A method according to claim 13, characterized in that the first glass ribbon section ( 4a ) in the region of the glass ribbon ( 4 ), where the glass ribbon ( 4 ) has a viscosity of less than 10 ⁹ Pas. A method according to claim 14, characterized in that the first glass ribbon section ( 4a ) in the region of the glass ribbon ( 4 ) is placed where the glass ribbon has a viscosity of 10 ^3.5 to 10 ⁶ Pas.