DE102013110755A1 - Carbonaceous or carbon-bonded refractory products with a hybrid glaze system and process for their preparation - Google Patents

Abstract

Pressed or cast carbonaceous oxide-based refractory products containing at least 5% by weight of a refractory oxide consisting of a mixture of carbonaceous binders, additional carbonaceous supports having a high carbon content and other oxides and / or non-oxides, and having an oxidation protective surface glaze, characterized in that in the molding compositions additionally 1 to 20 wt .-% finely powdered metals or alloys based on silicon, 1 to 10 wt .-% finely ground flux and 1 to 20 wt .-% of fine silica are included and in addition after coking an outer glaze is applied.

Description

The invention relates to pressed, carbonaceous or carbon-bonded refractory products and to a method for their production. The refractory products according to the invention find z. As application as Monoblocstopfen, immersion spouts and ladle manifolds that are used in the casting of metals, especially when casting the metals or slags. In addition, such inventive carbonaceous or carbon-bonded products as a housing in pore burners, in porous structures z. B. can be used as flame arresters or heat exchangers.

Refractory products of the material group Al ₂ O ₃ -C are widely used as functional products in steelmaking. Components such as monobloc plugs, immersion nozzles and ladle manifolds are used primarily in the steel industry for continuous casting. The combination of alumina and graphite achieves some excellent properties, such as corrosion resistance, thermal shock resistance, erosion resistance, mechanical and thermomechanical strength, as well as low wetting and infiltration of slags and molten steel. The main disadvantage of these refractory products is the low oxidation resistance due to the carbon content. While the carbon binder oxidizes at temperatures as high as 300-400 ° C, the burnout of the graphite does not begin until around 600 ° C. The oxidation of the carbon can lead to a deterioration of the properties of the refractory materials to failure, which can cause not only health but also economic dangers.

In order to reduce this impairment, two measures are taken according to the prior art mainly. In order to protect the carbon from oxidation, different antioxidants are used, in particular fine-grained powders of readily oxidizable metals such as silicon, aluminum, magnesium, manganese and others and combinations thereof. The addition of easily oxidisable metals protects the carbon from oxidation. In the oxygen attack, the metals react with the oxygen and form a protective layer of the respective metal oxides. This prevents oxidation of the carbon. In addition, these metals react with the carbon and form metallic carbides and / or nitrides, which lead to a reinforcement of the refractory products and improve their thermomechanical properties. The addition of easily oxidizable metals thus has a dual function. On the one hand, the oxidation of the carbon is prevented by the metals reacting with the oxygen instead of the carbon, and on the other hand, the metals themselves react with the carbon, form carbides and / or nitrides and solidify and improve the properties of the refractory functional components. Nevertheless, this measure is not a direct oxidation protection in the sense that the oxidation of the carbon is not completely prevented, but the rate of oxidation of the carbon is reduced. The oxidation rate of the carbon is lowered. Such a self-glaze system is in the DE 10 2009 037 540 B4 described.

The second measure is to coat the surface of the products with coatings that are as dense as possible. As a glaze to provide. The requirements for these coatings and the cost of coating the refractory products are high. First, the coatings should have as broad a softening range as possible so that the carbon can be successfully protected from oxidation at this broad temperature range. Ideally, this range covers temperatures from 300 ° C up to 1600 ° C. Furthermore, the coatings must be as dense as possible, so that the access of oxygen on the carbon can be excluded. Thus, as accurate as possible coatings are required, which do not include cracks, flaking, pinholes and other errors. As for the methods of application, several methods are known that have been developed in recent decades. Methods such as dipping, spraying and painting can be mentioned here as examples. In the most widely used method, which may also have the least expense, the refractory functional products are immersed in an aqueous suspension of the coating.

The invention has for its object to develop carbonaceous or carbon-bonded refractory products with a hybrid glaze system of a self-glaze and an outer glaze, which provides a durable oxidation protection layer on the surface and in the event of damage to the glaze on the surface leads to a self-healing of the outer glaze. Moreover, the hybrid glaze system results in sealing of the open porosity at the surface and in the interior of the carbonaceous product. In the case of a diving spout so that no air is sucked in during the casting process. Clogging phenomena in the sense of adhesion of oxides inside the immersion nozzle are suppressed.

According to the invention the object is achieved in that z. For example, in the known aluminum oxide-based molding compositions containing at least 5% by weight of aluminum oxide, 1 to 20% by weight of finely powdered metals or alloys based on silicon, 1 to 10% by weight of finely ground flux and 1 to 20% by weight of fine silica are present the surface of the refractory products made from this molding compound is additionally offered an outer glaze. Particularly advantageous are molding compositions consisting of 50 to 60 wt .-% alumina and / or MgO and / or ZrO ₂ and / or MgAl ₂ O ₄ , 10-30 wt .-% carbon carriers with a high carbon content, 4-12 wt. % carbonaceous binders, 2-7% by weight of finely powdered metals or alloys based on silicon, 1-4% by weight of finely ground fluxes and 2 to 7% by weight of fine silica. As finely powdered metals or alloys based on silicon, Si and / or FeSi and / or SiMn are particularly suitable. The finely ground fluxes contained are sodium and / or potassium waterglass and / or various frits and / or boron trioxide and / or sodium tetraborate and / or boric acid and / or feldspar. The fine silica is contained in the form of silica glass and / or quartz glass and / or silica. In Tab. 1, the hybrid glaze system is demonstrated using example 1 of a submersible nozzle according to the invention consists of additives in the molding compound for the design of a self-glaze and additionally an externally applied glaze with frit. base formula Additives for self-glaze Outside glaze composition raw materials Dimensions [%] raw materials Dimensions [%] raw materials Dimensions [%] Fused corundum Treibacher 30.00 Sl (met.) Elkem 4.00 Frit A 3390 p 56.50 Tabular Alumina Almatis 40,00 RW filler 4.00 Sl met. 20.00 Graphite Kropfmühl AF 96-97 (fine) 10.00 Borax Na ₂ B ₄ O ₇ (anhydrous) 2.00 MnO 3.50 Graphite Kropfmühl NFL (coarse) 10.00 ZrSlO ₄ 9.00 Zusoplast G63 1.00 Bl ₂ O ₃ 1.00 Novolack liquid PF 7280 FL 01 11.00 Ton Löthain 5.00 Hexa 1.00 White tone RS 100 5.00 magnesium stearate 1.00 total 100.00 Peptaphone 44 0.20 water 100.00

The refractory products according to the invention are prepared by homogeneously mixing the starting materials, compacting the molding compositions at pressures of between 50 and 200 MPa to give moldings, moldings are coked at temperatures of 600 to 1500 ° C in reducing or inert gas atmosphere and so by known methods obtained cooled moldings are subsequently heated at a heating rate of 5 to 40 K / min in air atmosphere to temperatures between 1000 and 1500 ° C. According to the invention can serve as a molding process, the casting. To heal the outer glaze in the event of damage by means of the inventively introduced additives in the molding compound to form a self-glaze, a pore network according to the invention is required, which has an average pore diameter in the carbonaceous product in the order of 200 to 900 nm.

Further examples follow.

Example 2

Carbon-based alumina-based refractory products are used, which are used in the casting of steel. Commercially available fractions of aluminum oxide and graphite are used for the preparation of the Al ₂ O ₃ -C functional products. The composition of the offset is as follows: component Wt .-% Aluminum oxide graphite resin with hardener 50-60 20-30 8-12

The following components are added to the offset in fine powder form during the mixing process: component Wt .-% Silicon Silica Anhydrous sodium tetraborate 2-6 3-7 1-4

After mixing all the components, the refractory products are cold isostatically pressed according to commercial practice and then coked in a reducing atmosphere. Subsequently, an outer glaze according to Tab. 1 is applied.

For the production of the hybrid glaze system, the Al ₂ O ₃ -C functional products are subjected to a special thermal treatment. The products are heated to 1300 ° C in air at a heating rate of about 20 K / min and held at this temperature for 5 hours.

Example 3:

Carbon-based alumina-based refractory products are used, which are used in the casting of steel. Commercially available fractions of aluminum oxide and graphite are used for the preparation of the Al ₂ O ₃ -C functional products. The composition of the offset is as follows: component Wt .-% Alumina graphite carbon black synthetic resin 50-60 15-20 5-10 8-12

The following components are added to the offset in fine powder form during the mixing process: component Wt .-% Ferrosilicon silicon dioxide boron trioxide 2-7 2-6 1-4

After the mixture of all components, according to commercial practice, the refractory products are cold-isostatically pressed and coked in a reducing atmosphere. Subsequently, an outer glaze according to Tab. 1 is applied.

For the production of the hybrid glaze system, the Al ₂ O ₃ -C functional products are subjected to a special thermal treatment. The products are heated to 1300 ° C at a heating rate of 30 K / min. After cooling the Al ₂ O ₃ -C materials, these can be used.

Example 4

Carbon-based alumina-based refractory products are used, which are used in the casting of steel. Commercially available fractions of corundum and graphite are used for the preparation of the Al ₂ O ₃ -C functional products. The composition of the offset is as follows: component Wt .-% Corundum graphite resin based on formaldehyde hexamethylenetetramine (hardener) 59 25 6 0.5

The following components are added to the offset in fine powder form during the mixing process: component Wt .-% Silicon Silica Anhydrous sodium tetraborate 4 4 2

After the mixture of all components, according to commercial practice, the refractory products are cold isostatically pressed with a pressure of 100 MPa and then coked in a reducing atmosphere at 1400 ° C. Subsequently, an outer glaze according to Tab. 1 is applied. For the production of the hybrid glaze system, the Al ₂ O ₃ -C functional products are subjected to a special thermal treatment. The products are heated to 1300 ° C at a heating rate of 20 K / min in an air atmosphere and heat treated at this temperature for 5 hours.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• DE 102009037540 B4 [0003]

Claims (7)

Pressed or cast carbonaceous oxide-based refractory products containing at least 5% by weight of a refractory oxide consisting of a mixture of carbonaceous binders, additional carbonaceous supports having a high carbon content and other oxides and / or non-oxides, and having an oxidation protective surface glaze, characterized in that in the molding compositions additionally 1 to 20 wt .-% finely powdered metals or alloys based on silicon, 1 to 10 wt .-% finely ground flux and 1 to 20 wt .-% of fine silica are included and in addition after coking an outer glaze is applied. Pressed or cast carbon-containing or carbon-bonded refractory products according to claim 1, characterized in that for healing of the outer glaze with the aid of the incorporated additives based on fluxes, metals and silicon or alloys of silicon in the molding compound, a pore network with an average pore diameter in the carbon-bonded or Carbonaceous product of the order of 200 to 900 nm is required. Pressed or cast carbon-containing or carbon-bonded refractory products provided with an outer glaze according to claim 1 and 2, characterized in that the molding compound of 50 to 60 wt .-% alumina and / or MgO and / or ZrO ₂ and / or MgAl ₂ O ₄ , 10-30 wt% high carbon carbon carriers, 4-12 wt% carbonaceous binders, 2-7 wt% finely powdered metals or silicon based alloys, 1-4 wt% finely ground fluxes, and 2-7 Wt .-% fine silica exists. Pressed, carbonaceous or carbon-bonded refractory products according to claim 1, 2 and 3, characterized in that as finely powdered metals or alloys based on silicon Si and / or FeSi and / or SiMn are included. Pressed, carbonaceous or carbon-bonded refractory products according to Claims 1, 2 and 3, characterized in that the finely ground fluxes contained are sodium and / or potassium waterglass and / or various frits and / or boron trioxide and / or sodium tetraborate and / or boric acid and / or feldspar , Pressed, carbonaceous or carbon-bonded refractory products according to claim 1, 2 and 3, characterized in that silica gel and / or quartz glass and / or silica are contained as fine silica. A process for the production of pressed, carbonaceous or carbon-bonded refractory products according to claim 1, in which the starting materials are homogeneously mixed, the molding compositions pressed at pressures of between 50 and 200 MPa into shaped bodies, the shaped bodies are heated at temperatures of 600 to 1500 ° C. in reducing or inert gas Be coked atmosphere, characterized in that the cooled moldings thus obtained are subsequently heated at a heating rate of 10 to 40 K / min in air atmosphere to temperatures between 900 and 1500 ° C and heat treated at these temperatures up to 6 hours.