DE102004010739A1 - Ceramic batch for fireproofing applications comprising refractory base in a grain fraction of less than 8mm, SiO2 carrier and other constituents useful for fireproofing applications - Google Patents

Abstract

Ceramic batch for fireproofing applications comprising (wt.%):(A) at least one refractory base (83-99.5) in a grain fraction of less than 8mm, (B) at least one separate SiO2 carrier (0.5-12) and (C) other constituents. An independent claim is included for a product based on the batch.

Description

The The invention relates to a refractory ceramic offset.

refractory ceramic offsets with refractory Basic materials are used to produce refractory ceramic products and find application in many areas of technology, in particular for lining and repair of metallurgical melting vessels or Industrial furnace linings. Furthermore, such raw materials used for the production of so-called functional products, for example for sinks, dip tubes, Shadow tubes, slide plates, etc., as in the mentioned melting units and stoves needed.

to Adjustment of certain material properties, in particular for Improvement of chemical resistance to slags, improvement the ductility as well as the temperature change resistance and the hot strength are different refractory ceramic offsets in combination with different ones additives known from which then the corresponding unshaped or shaped Products are manufactured.

unformed Products, for example castables, become offsets formed by water or other liquids and optionally Additives (such as plasticizers, Dispersant) in a desired Processing consistency brought to a certain viscosity become. These masses are subsequently called monolithic masses directly processed, for example for monolithic lining a metallurgical melting vessel, or they are used for the production of so-called prefabricated components. In this case can the offenses also as such or in combination with certain additives be processed, for example, poured into molds.

at the mentioned casting compounds, including refractory ones Concrete masses counted can, it may be in a subsequent drying and / or shrinkage while later Sintering leads to the formation of cracks, which increase the durability reduce the delivery or prefabricated part.

Such Cracks are common in the delivery of ladles the steel industry with non-basic castables observed. To the To counteract are in the prior art spinel-forming masses been proposed. In spinel formation, an increase in volume occurs, counteracts the shrinkage. Cracking often occurs already at temperatures below the temperatures for spinel formation lie. The desired higher Durability can not be achieved then.

Also with fired, molded products, the above-mentioned influences, such as Slag attack, temperature changes, etc. to an often inadequate Life of refractory products. This is especially true for applications where, for example, with mechanical or thermomechanical Tension is to be expected. These include refractory linings of aggregates in which periodically changing deformations occur for example, rotary kilns for the production of cement. But also in kiln aggregates in the area The steel and non-ferrous metals industry become refractory products with reduced brittleness (or in other words: with increased "flexibility") needed.

To reduce the brittleness, it is known to mix a proportion of granular, stabilized zirconium oxide (zirconium dioxide) to the offset. The disadvantage here is that only a relatively small reduction in brittleness is achieved and ZrO _{2 is} expensive.

Of the Invention is based on the object, a refractory ceramic Offset for producing unshaped and shaped products, and while offering both fired and non-fired products, a symbiosis of the mentioned having required property characteristics. In particular, the Off-set products in use a reduced brittleness (ie improved ductility), good Thermal shock properties, advantageous hot strengths and the best possible corrosion resistance have and at the same time be inexpensive to produce.

The invention is based on the recognition that the brittleness of refractory products or products intended for refractory applications can be significantly reduced if the formation of macroscopically recognizable (large) cracks is avoided and the system is adjusted so that it only to the formation of microcracks in the structure comes. Although the crack density is increased (for example expressed as the number of cracks per square meter of the surface). However, the cracks have a much smaller crack width (in particular <20 μm), ie they are significantly smaller than the macroscopically visible cracks in products in the prior art. These micro-cracks do not affect the durability of the products in the same way. Also, thermo-mechanical loads in the application, for example by thermal shocks, better withstand these products.

The physical changes of the structure can be achieved according to the invention by adding a separate, granular SiO ₂ support in certain proportions by mass. The term "SiO _{2 support} " encompasses all crystalline SiO ₂ modifications which have sufficient stability at room temperature. These include primarily quartz (β-form), cristobalite (β-form) and tridymite (γ-tridymite). Another suitable SiO ₂ modification is coesite. Fused silica can also be used as SiO ₂ carrier. This also applies to substances which have been processed from the abovementioned SiO ₂ precursors by physical and / or chemical processes (pretreatment). For example, quartz can be ground, compacted, sintered and then processed in a suitable grain size. In this case, the pretreatment or preparation of the SiO ₂ support can be used to reduce its bulk density to values of <2.65 g / cm ³ , for example to values of between 2.2 and 2.5 g / cm ³ . By admixtures such as CaO further, the chemical composition of the SiO ₂ support can be varied.

• – 83–99,5 Gew.-% eines refraktären Grundstoffs in einer Kornfraktion < 8 mm, und
• – 0,5–12 Gew.-% eines separaten, gekörnten SiO₂-Trägers, sowie
• – etwaiger Rest: sonstige Bestandteile.

In its most general embodiment, the invention then relates to a refractory ceramic offset with

• - 83-99.5 wt .-% of a refractory base in a grain fraction <8 mm, and
• - 0.5-12 wt .-% of a separate, granular SiO ₂ support, and
• - any remainder: other ingredients.

The refractory base material can be a basic substance such as doloma (ie calcined dolomite) or magnesia (ie MgO), or a non-basic substance, for example based on Al ₂ O ₃ or ZrO ₂ .

In one embodiment, the fraction of the refractory base is 90-99% by weight. The proportion of the granular SiO ₂ support is for example between 1 and 7 wt .-%, each based on the total offset.

The principle of microcrack initiation by a separate, granular SiO ₂ carrier is basically independent of the raw material (the refractory base component) and therefore, for example, on ceramic bonded, chemically bonded, carbon bonded, hydraulically bonded, shaped and unshaped, fired and unfired refractory sets and products applicable.

For the selection of the SiO ₂ support, the temperature can be a criterion.

Thus, it may be useful, for example, in the mentioned prefabricated parts, casting compounds or carbon-bonded refractory products to use as SiO ₂ carrier cristobalite. At 270 ° C, β-cristobalite is converted to α-cristobalite and results in micro-crack initiation due to increased volume. In this way, even at a very low temperature level, for example, already during the heating of the casting compounds, the desired microcracks are formed. The unwanted shrinkage cracks can be avoided.

This also applies for example for the drying of monolithic materials or the hardening (tempering) of resin-bonded or pitch-bonded refractory products.

A significant group for the application of the invention are unshaped products such as concrete compounds or castables for the production of refractory linings or prefabricated components. These masses can harden hydraulically or semi-hydraulically, so for example masses based on cement, in particular alumina cement. Likewise, the Invention applicable to low-cement or cementless casting compounds, for example those based on bauxite as a non-basic refractory raw material.

Of the dry offset (for example from bauxite and cristobalite) is to achieve a desired Processing consistency mixed with the required amount of water. If necessary, additives such as condenser added. Already while The drying takes place from 270 ° Celsius the described conversion of β-cristobalite in α-cristobalite instead of.

The described mode of action is largely independent of the grain fraction of the refractory base component. However, it has proved to be advantageous if the SiO _{2 support has} a particle size d _{5 0} or d ₀₅ which is greater than a maximum grain (or greater than at least 95 wt .-%) of the fines content of the non-basic base material.

typically, becomes the refractory Base material used in a relatively wide grain spectrum. In addition to one Coarse grain fraction (<8 mm), for example 1-6 mm, the component may have a proportion of a mean grain, for example 0.25- <1 mm and one Fine grain content (flour content) <0.25 mm have.

The Border grain size between Coarse grain and medium grain can also be set at 1.5 or 2 mm. As well For example, the multigrain fraction can be set to a particle size fraction <0.125 mm (125 μm) become. This information refers in each case to 100% of the refractory basic component.

Of the above-mentioned fine grain content of the refractory base is according to various embodiments at 10-30 Wt%, 15-25 Wt .-% or 25-30 wt .-%, each based on the total offset.

Of the For example, the average grain fraction as stated above may be Orders of magnitude 5-30% by weight, 10-25 Wt.% Or 10-20 Wt .-%, again based on the total offset.

Out above fractions of the fine grain or middle grain calculated according to the coarse grain fraction.

According to a further embodiment, the refractory, in particular oxidic base material is proposed in the following particle size distribution:
50-60% by weight 1-6 mm,
10-25% by weight 0.25- <1 mm,
25-30% by weight <0.25mm,
wherein the sum is 100 wt .-%.

The granular SiO _{2 support} according to one embodiment has a particle size of up to 6 mm, wherein the grain upper limit can also be selected at 3.0 or 1.5 mm. Typically, the SiO ₂ carrier is present in a grain fraction between 0.5 and 3 mm.

At least one of the following components may be selected as the non-basic refractory raw material: chamotte, sillimanite, andalusite, kyanite, mullite, bauxite, corundum raw materials such as corundum or brown corundum, tabular earth, calcined clay, zirconium oxide-containing base materials such as zirconium mullite, zirconium corundum, zirconium silicate or zirconium oxide, titanium oxide (TiO ₂ ), Mg-Al spinel, silicon carbide.

Also Quartzite may be considered refractory Base material can be used, in which case cristobalite is used as an additive becomes.

Furthermore the offset may contain other components in relatively small proportions contain, for example, at least one of the following components: (elemental) carbon, graphite, resin, pitch, soot, coke, Tar.

This of course especially for Applications of misalignments in carbonated products or products that are soaked in tar.

These include, in particular, so-called ASC products whose designation derives from the main components A (for Al ₂ O ₃ supports), S (for SiC and / or Si metal) and C (for the carbon support). Magnesia carriers (for spinel formation) as well as Mg-Al spinels can also be constituents of the formulation. Such offsets are bonded with a synthetic resin, such as a phenolic resin, as a binder. They are used, for example, for pig iron pans, but also for shadow tubes, dip tubes, etc.

For such resin-bonded products, the curing process can be performed so that, for example, the transformation temperature of β-cristobalite in α-cristobalite is reached or exceeded, so that there are already microcracks in the product at the delivery of prefabricated moldings. Alternatively, however, it is also possible to cure (temper) at a lower temperature (for example 160-220 °) and to postpone the process of microcracking to subsequent use. The microcracking then takes place heating of the product after its delivery.

As already executed, serves the described offset especially for the production baked refractory products, in particular fired refractory Moldings. The offset is - as usual - a binder, in particular a temporary one Binder, for example, a Ligninsulfonatlösung mixed in and the mixture then, for example, pressed into stones, dried and fired. A typical firing temperature is 1300-1700 ° Celsius. When choosing the firing temperature, the usual in the refractory technology apply Experience: Too high a firing temperature can be due to too intense Resintering the brittleness again increase and even the desired one Effect of brittleness reduction at all prevent. The exact firing temperature is so far from the concrete selected Components of the offset depending and to determine empirically.

The Invention will be described below with reference to various embodiments explained in more detail. All in all will be 5 offsets below lists where respectively the raw material composition and the chemical composition in the form of an oxide analysis.

The offsets of Examples 1-3 are used to produce fired, shaped products based on non-basic materials. It is understood that the offset components a
temporary binder must be added. This may be, for example, sulfite liquor, phosphoric acid or monoaluminum phosphate. A binding clay can also be included in the recipe. From the offsets, stones or other shaped parts can be produced at conventional pressing pressures (for example 65-130 MPa), which are then fired. The firing temperature is
so choose that the sintering is sufficient, but not so high that too intensive sintering counteracts the effect of reducing the brittleness. For a given composition of the components in particular the granulometry of the fine grain content of the non-basic base material and the binder is crucial.

For the example 1, a firing temperature of 1450 ° Celsitus was chosen. The from the offenses 2 and 3 produced (pressed) stones were at 1550 ° Celsius burned.

offset No. 4 is used to produce a so-called ASC product, ie a C-linked product as presented above with an addition to cristobalite. about the cristobalite conversion is carried out during annealing (400 ° Celsius) the products made from the offset initiate microcracks in the microstructure.

example 5 shows an offset for a casting material with a proportion of alumina cement. The offset was with water turned on and molded parts were made from it, at temperatures up to 380 ° Celsius were dried or tempered. Next to it was a Comparative mass, but without Cristobalitzusatz, manufactured and it were prepared analogous samples and also at 380 ° Celsius dried or tempered. In the comparative sample were the missing 4% cristobalite is replaced by additional bauxite in the grain area <1 mm.

The table below shows the comparative values for the specific energy of fracture G _F , the nominal notched tensile strength σ _KZ and the quotient of both. The determination of these values was carried out according to the reference K. Rieder et al. "Fracture mechanical cold and hot testing of refractory coarse ceramic materials", Progress Reports of the German Ceramic Society, Materials - Process - Application - Volume 10 (1995), No. 3, ISSN 0177-6983, 62-70.

The product according to the invention shows a more than doubled quotient of specific energy of fracture and nominal notched tensile strength, resulting in a significantly reduced brittleness can be read.

example 1

Example 2

Example 3

Example 4

Example 5

Claims (18)

Refractory ceramic offset with a) 83-99.5 wt .-% of a refractory base in a grain fraction <8 mm and b) 0.5-12 wt .-% of a separate, granular SiO ₂ support, and c) any remainder : other ingredients An offset according to claim 1, whose refractory base material at least partially a non-basic base material. An offset according to claim 1, whose refractory base material at least partially Doloma and / or Magnesia. An offset according to claim 1 comprising a) 90-99% by weight of the refractory base, and b) 1-7% by weight of the granular SiO ₂ support An offset according to claim 1, whose granular SiO _{2 support} consists of at least one of the following SiO ₂ modifications: quartz, cristobalite, tridymite, fused silica. An offset according to claim 1, whose SiO ₂ carrier has a particle size d _{5 0} , which is greater than 95 wt .-% of the fine grain content of the refractory base material. An offset according to claim 1, whose SiO ₂ carrier has a particle size d ₀₅ , which is greater than 95 wt .-% of the fine grain fraction of the refractory base material. An offset according to claim 1, whose refractory base material has a fine grain content of 95 wt .-% <250 microns. An offset according to claim 1, whose refractory base material has a fine grain content of 95 wt .-% <125 microns. An offset according to claim 8 or 9, the fine grain content thereof of the refractory Basic substance 10-30 Wt .-% of the total offset is. An offset according to claim 1, whose SiO ₂ carrier has a particle size of up to 6 mm. An offset according to claim 1, whose SiO ₂ carrier has a grain size of up to 3 mm. An offset according to claim 1, whose SiO ₂ carrier has a particle size between 0.5 and 3 mm. An offset according to claim 1, whose refractory base material has a particle size <6 mm. An offset according to claim 1, whose refractory base material having the following particle size distribution: a) 50-60% by weight 1-6 mm, b) 10-25 Weight% 0.25- <1 mm, c) 25-30 Wt .-% <0.25 mm in which the sum is 100% by weight. Offset according to claim 2, whose non-basic refractory Base material has at least one of the following components: chamotte, Silimanite, andalusite, kyanite, mullite, bauxite, corundum raw materials like Corundum or brown osmosis, tabular earth, calcined clay, Quartzite, zirconium-containing basic materials such as zirconium mullite, zirconium corundum, Zirconium silicate or zirconium oxide, titanium oxide, Mg-Al spinel, silicon carbide. Offset according to claim 1, as other components having at least one of the following components: carbon, Graphite, resin, pitch, soot, Coke, tar. An offset according to claim 1, whose SiO _{2 support is} a pretreated product having a bulk density <2.65 g / cm ³ .