DE112006003321B4 - Process for the production of flat glass by the float process and pour lip (Spout Lip) for the float process - Google Patents

Abstract

Process for the production of flat glass by the float process, in which molten glass is flowed over a pouring lip onto a bath of molten metal, the glass forms a continuous dimensionally stable glass ribbon on the bath, and the solidified glass ribbon is continuously removed from the metal bath, characterized the glass is allowed to flow over a pouring lip of pressed and sintered refractory material from the group ZrO ₂ , Al ₂ O ₃ , ZrSiO ₄ , the content of Fe ₂ O ₃ in the ZrO ₂ and ZrSiO ₄ refractory material being less than 0 , 08 wt .-% and in the Al ₂ O ₃ fireproofing material is not more than 0.2 wt .-%.

Description

object The invention relates to a method for producing flat glass the float process and a pour lip (Spout Lip) for the float process.

The Production of flat glass after the float process is since the previous Century well known. Leave it you liquid Glass, which is brought from the work tub by means of a gutter a bath of molten metal, generally tin, flowing. Of the Volume flow of the glass is over a movable slider (Tweel) regulated, with its setting u. a. also the glass thickness is adjusted. In the flow direction of Glases seen behind the slider is the pouring lip (Spout Lip), from which the molten glass continuously on the molten metal flows, there is formed into a dimensionally stable glass ribbon and solidifies, subsequently the solidified glass ribbon is removed from the metal bath.

Of the Wear the pouring lip and related areal Washouts in their surface to lead to errors in the peeled glass band. This can u. a. solid glass defects (crystalline inclusions), be different thicknesses or ripples in the glass ribbon. Also can also at the interface FF material / glass melt Blistering occur. This is especially at very high quality Thin glasses are not permissible and greatly reduces the yield. Be through a worn lipstone too many glass defects generated, which is an economical production strongly negative influence, the lip stone must be changed, which is usually associated with a considerable effort.

As lip material for soda-lime glass, quartz glass or melt-cast Al ₂ O _{3 is described} as suitable ( DE 27 47 549 C3 ). Also melt-molded lips with a high proportion of Al ₂ O ₃ and ZrO ₂ (trade name Zac) are out DE 21 22 702 A known. Although these lips are very useful for soda-lime glass and can last up to 3 years, they are still inadequate to meet the demands of aggressive and higher-melting glasses and are subject to high wear. The consequences of this wear are ripples in the glass and an increased number of holes and stripes on the underside of the glass.

In JP 33 85 539 B2 describes a Spout Lip made of HZFC material (HZFC: High Zirconia Fused Cast) with a ZrO ₂ content of 85-97% and a remainder of a glassy material. These materials reduce the number of streaks and holes on the bottom of the glass ribbon and increase the life of the spout lip in making higher melting glasses to about one year. A disadvantage of the HZFC material is its low thermal shock resistance, so that it can easily cause flaking in the surface during temperature changes, in extreme cases even to cracks that lead to quality defects in the glass. Another disadvantage is the high price for HZFC.

Out US 2005/0130830 A1 For example, a ZrSiO ₄ refractory is known for the overflow-fusion process to which Fe ₂ O ₃ (in addition to the already existing impurities) has been added to improve the sag. However, at high glass transition temperatures above about 1250 ° C., this material shows a markedly increased interaction with the molten glass.

In DE 42 43 538 A1 describes a zirconium material which has good corrosion resistance to boric acid-containing glass melts at high temperatures. This material is prepared by adding phosphorus compounds and TiO ₂ as a sintering aid. Disadvantage of this material is its low thermal shock resistance.

Out DE 102 09738 A1 is described a Spout Lip, which consists of a SiO ₂ ceramic, which is provided on its coming into contact with the glass flow side with a metal layer of molybdenum or tungsten. Between the SiO ₂ ceramic and the metal layer is still a ceramic layer is provided to prevent the back attack by diffusing oxygen on the metal. The handling of this Spout Lip with its air oxidation sensitive metal layer is difficult, especially when the Spout Lip is hot, e.g. B. in a repair, must be replaced.

In DE 103 08 031 A1 is described a pouring lip of Magnesiumaluminatspinell, which is coated on its upper side with a noble refractory metal, generally platinum or a platinum alloy. Between the metal and the spinel is also arranged a gas-tight diffusion barrier. The metal coating must be made very precisely, so that when heating the pouring lip no wrinkles or warping in the precious metal arise, which leads to stripes on the underside of the glass ribbon and thus to the loss of production. Below the lipstone, a nozzle is provided for purging this area with nitrogen to prevent the forming gas from the float bath from reducing constituents or contaminants of the refractory that react with the noble metal to low melting alloys or embrittle the precious metal. In both cases, this means damage to the spout lip, which too Glass defects leads. If the nitrogen purge fails, protection against the reducing float bath atmosphere is no longer present.

by virtue of The problems mentioned and because of the high costs are always still lipstones without metal coating prefers. However, it has been shown that melt-cast Lipstones often then cause problems when leaving a melted block be worked out or if they are for a high precision of the to be produced glass ribbon to be cut to exact size.

It is well-known that melt-cast ceramic materials have inhomogeneities in the structure of the structure as a result of the zonal solidification during the production process. For example, melt-cast AZS materials (Al ₂ O ₃ -ZrO ₂ -SiO ₂ ) with a proportion of 41% by weight of ZrO ₂ in the area of the mold base have a significantly higher proportion of zirconium oxide than in the top of the stone. The difference may be more than 10% by weight. As a result of the rapid cooling, a mostly very fine-grained microstructure forms on the mold walls. Inside the solidifying block, the solidification is delayed, so that there is usually formed a coarse structure, which is partially interspersed with pores and in which the glass phase enriched with the impurities from raw materials is present in larger quantities, see Figure 1 and Figure 2 (Fig. light micrographs of polished sections). Figure 1 shows the fine structure of an HZFC material forming near the mold wall in a melt-cast block, while Figure 2 shows the much coarser structure inside the same block. One clearly recognizes the inhomogeneities in the microstructure and the accumulation of the (black appearing) glass phase ("worm tracing").

Particularly polyvalent impurities such as TiO ₂ and Fe ₂ O ₃ can lead to blistering in glass contact. If the lipstone is worked out of a melt-cast block, it is unavoidable that surfaces are revealed that differ in the structure and composition of the glass phase. In places with locally increased glass phase content, there is increased corrosive erosion. Also, areas in the refractory material that have pores or pores accumulate places of enhanced corrosion, which can also contribute to glass defect formation. These disadvantages are more pronounced in higher melting glasses.

A Reduction of the proportion of the glassy phase is only up to one certain limit possible because the glassy phase for the casting is necessary and a refinement of the coarse texture through faster cooling new problems, eg. B. stresses in the casting, entails. you Therefore, it is important to the desired shape of the spout lip as possible precise to pour, around a properties deteriorating rework so small as possible too hold.

The The object of the invention is a process for the preparation of flat glass after the float process, with which also found in the use of higher melting glasses very high quality achieve as well as a pouring lip (Spout Lip), with a highly precise surface shape can be produced.

These The object is achieved by the method according to claim 1 and the pouring lip according to claim 8 solved.

It was found that a pour lip (lip stone, Spout Lip) of pressed and sintered refractory material from the group ZrO ₂ , Al ₂ O ₃ , ZrSiO ₄ , with a Fe ₂ O ₃ content of less than 0.08 wt. %, if the refractory material of ZrO ₂ or ZrSiO ₄ and less than 0.2 wt .-%, if the refractory material consists of Al ₂ O ₃ , is particularly suitable, since these materials have a very uniform structure in terms of particle size, glass phase and have pore distribution. In the case of ZrO ₂ and ZrSiO ₄ material, an Fe ₂ O ₃ content of at most 0.05% by weight and, for Al ₂ O ₃ firing solid materials of not more than 0.1, in particular not more than 0.08% by weight, is preferred. %.

It demonstrate:

image 1: microstructure / microstructure HZFC material, fine crystalline region;

image 2: microstructure / microstructure of HZFC material in the area of so-called "worm tracing": inhomogeneities in the microstructure enrichment of Glass phase;

image 3: microstructure / microstructure of pressed and sintered aluminum oxide, very fine grained and homogeneous structure;

image 4: microstructure / microstructure of pressed and sintered zirconium oxide, very homogeneous structure;

image 5: microstructure / microstructure of melt cast α / β alumina, relative coarsely crystalline structure;

image 6: Blistering behavior of pressed and sintered material compared to melt-cast α / β-alumina (T = 1380 ° C / alkali-free Glass);

Picture 7: Blistering rate at Zirkonsili Kat material with different Fe ₂ O ₃ content in contact with a molten glass at 1400 ° C.

image Figure 3 shows a polished section of a pressed and sintered α-alumina and FIG. 4 shows a polished section of a pressed and sintered zirconium oxide. One recognizes clearly that opposite the melted bodies much finer and more homogeneous texture.

The Production of refractory ceramic products by pressing and sintering of correspondingly assembled masses is known per se and is also partly carried out on an industrial scale. The Production of the pouring lip according to the invention can also be done according to these well-known methods.

The Pressing may be uniaxial, but the isostatic is preferred Presses that give better results in complicated shapes. The hot isostatic Pressing (HIP procedure) is also possible with good success, because of the size of the too pressing lips however, generally not announced for economic reasons.

The material to be pressed should have such a particle size distribution that during pressing a very uniform structure is formed. The smaller the grain size of the material to be pressed, the more homogeneous the structure of the body produced therefrom and the better its mechanical properties. In practice, however, in many cases, in particular in the case of very large bodies, larger grains mixed with finer material are used in order to reduce sintering shrinkage. The material to be pressed can ggfls. still known sintering aids such. As SiO ₂ , TiO ₂ and stabilizing agents such. B. oxides from the group of lanthanides, in particular Y ₂ O ₃ or CaO or MgO are added. In particular with a ZrO ₂ ceramic, stabilization is customary and up to 10% by weight Y ₂ O _{3 is} added for full stabilization. But there are also partially stabilized masses with a correspondingly lower proportion of stabilizing oxides usual.

After sintering, the material has an open porosity of up to 12%. Preference is given to an open porosity of up to 7%, in particular of up to 2%. Obtainable are open porosities of about 0.5%. Materials with higher porosity have better stability against thermal cycling, materials with lower porosity have less blistering potential and higher corrosion resistance. Blistering can, for. B. caused by air released from the pores. Since the Spout Lip is always cut new pores in the chemical corrosion (dissolution in the glass mass), a Spout Lip with small pores / lower pore fraction clearly has the advantage. The skilled person must therefore choose depending on the operating conditions of his float glass process or his Spout Lip the most favorable for his process compromise between the properties such as pore fraction / pore size and thermal shock resistance. Generally it is preferred that zirconium silicate materials for use as spout-lip have a maximum density of 4.15 g · cm ^-3 with corresponding porosity to ensure good thermal shock resistance.

To avoid possible repercussions on the glass, the materials making up the Spout Lip should be as pure as possible. Impurities are not always completely ruled out. In general, TiO ₂ or P ₂ O ₅ can each be tolerated up to about 1% by weight. The P ₂ O ₅ content should preferably not exceed 0.4% by weight and the TiO ₂ content should not exceed 0.8% by weight, in particular 0.5% by weight. However, the total amount of the above impurities should not exceed 1 wt .-%. Isostatically pressed, sintered zirconium oxide or zirconium silicate-containing materials with a proportion of ZrO ₂ of more than 60% and aluminum oxide with a proportion of Al ₂ O ₃ of at least 90% in glass contact also prove to be suitable.

The natural Occurrence of zirconium as zirconium oxide or as zirconium silicate always contain a small proportion (usually 1.5-2.5 wt .-%) to hafnium oxide or silicate. When specifying the zirconium oxide or the Zirkoniumsilikatanteils is therefore always the zirconium oxide content including of hafnium oxide content.

Useful is also a pressed and sintered alumina with a Proportion of up to 20 wt .-%, in particular up to 10 wt .-% zirconium oxide.

If due to the local Conditions due to stray electrical currents with increased electrochemical Blistering on the Spout Lip must be reckoned materials with low electrical conductivity, z. As zirconium silicate or α-alumina as material for the Spout Lip is preferred.

With regard to the blistering behavior, pressed and sintered ceramics may e.g. Example of zirconia or alumina have a lower blistering potential in comparison with melt-cast α / β-alumina, which is very often used as Spout Lip material. Figure 5 shows a cut through a melt-cast α / β-alumina. It can be clearly seen the comparatively coarsely crystalline Struk in addition to α-Al ₂ O ₃ crystals also β-Al ₂ O ₃ crystals and small areas of glass phase can be seen. This material has a higher blistering potential compared to pressed and sintered material. The difference in blistering performance between fused α / β alumina material and pressed and sintered α-alumina material in contact with alkali-free glass at a temperature of 1380 ° C is shown in Figure 6. Blistering was performed by the method of Dunkl et al .: A Novel Method for the Determination of the Blistering Rate at the Refractory / Glass Interface; UNITECR '89: Proc. Unified Int Techn. Conf. to Refractories, Annaheim CA, 1-4 Nov. 1989, Westerville, 1989, 795-806.

Figure 7 shows the positive influence of a low Fe ₂ O ₃ content on the bubble formation rate of zirconium silicate materials in contact with a molten glass at a temperature of 1400 ° C.

One particular advantage of the found Spout Lip is that It can be processed by grinding and / or polishing without their good qualities impaired become. It is therefore possible a spout lip from the whole, d. H. a pressed and sintered It is also possible to work out a material block and a pressed and sintered one Spout lip by milling, grinding and / or polishing to a desired level or to produce a particularly smooth and even surface. A spout Lip with a cut to size (Milled) and / or polished surface is due to the very good quality of the produced glass ribbon particularly preferred. A treatment of the surface by grinding and / or Polishing is generally only for those with liquid glass in contact surface required.

The found Spout Lip is particularly suitable for the production of glass, placed on the particularly high demands in terms of surface finish and / or a higher melting point has as soda lime glass.

Such glasses are in particular borosilicate glasses, alkali-free glasses, aluminosilicate glasses, Alumolithiumsilikatgläser and precursor glasses for glass-ceramic.

Particularly suitable is the Spout Lip for the production of borosilicate glass with a composition of (in wt .-% based on oxide): 55-65 SiO ₂ , 12-20 Al ₂ O ₃ , at most 5 B ₂ O ₃ , 0-5 BaO, 3-9 CaO, 1-5MgO and 1-5 SrO; for the preparation of display glass with a composition of 55-70 SiO ₂ , 12-20 Al ₂ O ₃ , 5-15 B ₂ O ₃ , 0-6 BaO, 0-12 CaO, 0-7 MgO, 0-10 SrO. It is also particularly suitable for the production of various green glasses for glass-ceramic, such. With 55-69 SiO ₂ , 19-25 Al ₂ O ₃ , 3-5 Li ₂ O, 0-1.5 Na ₂ O, 0-1.5 K ₂ O, ΣNa ₂ O + K ₂ O 0 , 2-2, MgO 0.1-2.2, CaO 0-15, SrO 0-1.5, BaO 0-2.5, ΣMgO + CaO + SrO + BaO below 6, ZnO 0-1.5, TiO ₂ 1-5, ZrO ₂ 1-2.5, SnO ₂ 0- less than 1, ΣTiO ₂ + SrO ₂ + SnO ₂ 2,5-5, P ₂ O ₅ 0-3 or a glass-ceramic precursor glass having a composition of SiO _{2 2} 55-75, Al ₂ O ₃ 15-30, Li ₂ O 2.5-6, ΣNa ₂ O + K ₂ O less than 6, ΣMgO + CaO + SrO + BaO less than 6, B ₂ O ₃ 0 to less than 4 , ΣTiO ₂ + ZrO ₂ smaller 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, ΣNa ₂ O + K ₂ O 0.2-2 , ΣMgO + CaO + SrO + BaO less than 6, ZnO 0-1.5, B ₂ O ₃ 0-less than 4, SnO 0.1-1.5, ΣTiO ₂ + ZrO ₂ less than 2, P ₂ O ₅ 0- 3, F 0-2.

By with the invention realizable use of materials with small pore sizes and open porosities from in the cheap Case less than 1% also adds the material by grinding / polishing or by corrosion exposed pores in the glass contact no risk with regard to blistering in the glass. The isostatically pressed high zirconia-containing materials exhibit, despite their low porosity a better temperature change behavior with respect to the change the bulk density and volume than conventional melt-cast HZFC material. A special advantage over the previous ones for Spout Lips used materials is also that one from very fine-grained Raw materials can use sintered material while retaining the outstanding performance characteristics of the spout thus produced Lip respect Blistering and rippling cut to size and / or polished can be.

Claims (14)

Process for the production of flat glass by the float process, in which molten glass is flowed over a pouring lip onto a bath of molten metal, the glass forms a continuous dimensionally stable glass ribbon on the bath, and the solidified glass ribbon is continuously removed from the metal bath, characterized the glass is allowed to flow over a pouring lip of pressed and sintered refractory material from the group ZrO ₂ , Al ₂ O ₃ , ZrSiO ₄ , the content of Fe ₂ O ₃ in the ZrO ₂ and ZrSiO ₄ refractory material being less than 0 , 08 wt .-% and in the Al ₂ O ₃ fireproofing material is not more than 0.2 wt .-%. A method according to claim 1, characterized in that the glass is flowed over a ZrO ₂ - or ZrSiO ₄ -Firefestmaterial having a Fe ₂ O ₃ content of at most 0.05 wt .-%. Process according to claims 1, characterized in that the glass is a Flow Al ₂ O ₃ solid material having a Fe ₂ O ₃ content of not more than 0.1 wt .-%, in particular not more than 0.08 wt .-% has. Method according to one of claims 1 to 3, characterized that you have the glass over one isostatically pressed and sintered pouring lip flows. Method according to at least one of claims 1 to 4, characterized in that the glass via a pouring lip with an open porosity of less than 12% flow leaves. Method according to claim 5, characterized in that that you put the glass over a pouring lip with an open porosity less than 7%, in particular less than 2%. Method according to at least one of claims 1 to 7, characterized in that the glass over a ground and / or polished pouring lip flow leaves. Casting lip for the float glass process, characterized in that the pouring lip of pressed and sintered refractory material from the group ZrO ₂ , Al ₂ O ₃ , ZrSiO ₄ , wherein the content of Fe ₂ O ₃ in the ZrO ₂ - and the ZrSiO ₄ -Firefestmaterial less than 0.08 wt .-% and in the Al ₂ O ₃ fireproofing material is not more than 0.2 wt .-%. Casting lip according to claim 8, characterized in that the Fe ₂ O ₃ content in the ZrO ₂ - and the ZrSiO ₄ -Feuerfestmaterial is at most 0.05 wt .-%. Casting lip according to claim 8, characterized in that the Fe ₂ O ₃ content in the Al ₂ O ₃ fireproof material is at most 0.1% by weight, in particular not more than 0.08% by weight. pouring lip according to one of the claims 8 to 10, characterized in that the pouring lip of isostatically pressed and sintered refractory material. pouring lip according to at least one of the claims 8 to 11, characterized in that they have an open porosity of less than 12%. pouring lip according to claim 12, characterized in that it has an open porosity of less than 7%, in particular less than 2%. pouring lip according to at least one of the claims 8 to 13, characterized in that their in contact with the glass next page has a ground and / or polished surface after sintering to measure.