RU2129535C1 - Magnesia-carbon refractory material - Google Patents

Abstract

FIELD: refractory materials. SUBSTANCE: invention, which can find use for linings of steel-smelting and other metallurgical assemblies, provides refractory material containing, wt %: finely dispersed aluminum-magnesium alloy with eutectic composition passivated by organosilicon coating, 2-4; crystalline graphite, 7-20; organic binder, 5-7 (above 100%); and refractory base - fired magnesite, and/or molten magnesite, the balance. EFFECT: increased wear resistance due to reduced rate of oxidation of carbon component and reduced its manufacture safety. 2 tbl, 15 ex

Description

 The invention relates to the refractory industry, in particular, to the production of magnesia-carbon refractories for lining steelmaking, steel-casting and other metallurgical units.

Known magnesite-carbon refractory containing: 8-30% high purity carbon (> 98% C); 0.1-1% of the antioxidant - metallic aluminum, metallic magnesium or mixtures thereof, the rest is magnesite with a Mg0 content of at least 98%. In addition, the refractory contains a carbon binder of 1.5-6 wt.%. (International application N 91/14661, MKI 5 C 04 V 35/04, 03/22/90.)
The specified refractory due to its high chemical purity is characterized by high durability in service when working in an oxygen-free environment. However, in the actual operating conditions of the linings of metallurgical units, when the reducing lining is exposed to alternating reducing and oxidizing media, the working layer of the refractory decarburizes relatively quickly, due to difficult sintering it loses strength and quickly collapses, which is associated with the insufficient content of antioxidants - metal additives.

Known magnesia-carbon refractory with a high content of antioxidant, including (wt.%):
- 60-95 refractory base (tightly calcined dolomite, spinel clinker);
- 5-40 flake graphite;
- 1-10 aluminum-magnesium alloy with a particle size of not more than 100 mesh. (0.15 mm.);
- 2-6 ligaments in the form of pitch, phenolic or furan resins.

These components are mixed, products are molded from the prepared mass, which, depending on the type of binder, are cured or fired in a reducing medium at 1000-1500 ^o C (Application 2311352 Japan, MKI 5 C 04 V 35/00, 35/02, 26.05.89) .

 A sufficiently high content of an effective antioxidant, an aluminum-magnesium alloy, increases the oxidation resistance of this refractory.

 However, to ensure a high level of explosion safety of the production of refractory, expensive measures are taken to hardware design the process and an enlarged (0.15 mm.) Powder of aluminum-magnesium alloy is used. The latter significantly reduces the effectiveness of this metal additive as an antioxidant.

The closest in composition to the proposed magnesia-carbon refractory is a refractory of the following composition (wt.%):
Graphite, preferably crystalline - 5-25
Fine-milled mixture of not less than 60% tightly calcined, preferably containing not less than 95% MgO, magnesite with aluminum-magnesium alloy - 7.5-12.5
Phenolic Binder - 4-6
Deadly calcined and / or fused magnesite of a fraction of 5-0 mm with a Mg0 content of at least 90%, preferably at least 95% - The rest
After mixing the components in the indicated ratio, products are formed from the prepared mass, which are then cured during the heat treatment at 125-250 ^o C. (US 5438026, C 04 V 35/52, 08/01/95).

 Introduction to the composition of the known magnesite-carbon refractory aluminum-magnesium alloy in the form of a finely ground mixture with magnesite increases its resistance to oxidation and cracking during thermal shock, reduces the temperature coefficient of linear expansion and, as a result, increases the durability of finished products in service. However, the performance of refractories achieved in this case does not fully meet the modern requirements of the service of linings of metallurgical units.

 The use in the production of a finely ground mixture of aluminum-magnesium alloy, with at least 60 wt.% Tightly calcined magnesite, provides sufficient explosion-proof technology, starting from the grinding stage. At the same time, the issues of ensuring proper explosion safety of the process during reception, storage and transportation of aluminum-magnesium alloy until it is ground with magnesite are difficult and require the use of expensive equipment in explosion-proof performance.

 The task that needed to be solved is to increase the wear resistance of the refractory by reducing the rate of oxidation of its carbon component, as well as increasing the safety of the process of manufacturing a refractory.

To achieve these technical results, the proposed magnesia-carbon refractory, including a refractory base — calcined magnesite, fused magnesite or mixtures thereof, graphite, a finely divided antioxidant and phenolic binder — contains an eutectic aluminum-magnesium alloy as an antioxidant (51 wt.% Al + 49 wt.% Mg), passivated with an organosilicon coating, in the following ratio of components (wt.%):
Fine-dispersed aluminum-magnesium alloy of eutectic composition, passivated by silicone coating - 2-4
Crystalline Graphite - 7-20
Organic Binder - 5-7
Refractory base - calcined magnesite and / or fused magnesite - Else
Due to the fact that no studies have been previously conducted to study the effect of the composition of aluminum-magnesium alloy introduced into the composition of magnesia-carbon refractories on their properties, the mentioned alloys containing 10.30.49% magnesium (the last composition is eutectic) were tested. Alloys containing more than 49% Mg are characterized by too high explosiveness and therefore were not considered as an antioxidant additive.

As a result of the experiments, it was found that a finely dispersed aluminum alloy of eutectic composition, characterized by submicron sizes of Al and Mg crystals and therefore having an extremely developed specific surface, introduced into the composition of the proposed refractory in the required and sufficient amount, reduces the decarburization rate of the latter (see table 2 , compare compositions 1; 2 with composition 5). This effect is achieved due to the rapid hardening of the internal structure of the refractory in the service at high temperatures by the formation of carbides and then spinel, which is accompanied by the formation of a layer densified by MgO and MgO • Al ₂ O ₃ near the working surface of the refractory, and therefore making it difficult to access the inside of the refractory oxidizing agents (oxygen and slag) from the working space of the unit.

 Explosiveness of the eutectic composition of an aluminum-magnesium alloy is suppressed by the presence of a passivating silicone coating on its particles, which ensures the explosion safety of the entire technological process for the manufacture of refractory materials, including redistributions prior to grinding redistribution.

 In addition, the use of finely dispersed passivated aluminum-magnesium alloy makes it possible to create a glassy silicate film on the surface of the refractory, a product of the interaction formed upon thermal destruction of the coating of active silica with impurities of the refractory base. Such a coating further complicates the diffusion of oxidizing agents into the refractory.

 It was also found that the use of finely dispersed passivated aluminum-magnesium alloy allows to achieve maximum uniformity of its distribution in the structure of the refractory and thereby improve the heat resistance of the latter.

 Thus, the combination of the above factors provides an increase in the main technical characteristics of the refractory - oxidation resistance, slag and thermal shock, which determine its resistance in the lining of metallurgical units.

Examples
The present invention is realized when fired magnesite with a MgO content of at least 95% and / or fused magnesite with a MgO content of at least 95% is used as a refractory base; crystalline graphite (GOST 4596-75); as an antioxidant - finely dispersed aluminum-magnesium alloy of eutectic composition (GOST 5393-76), including passivated coating of organosilicon liquid (polyethylsiloxane (GOST 13004-71) or polyphenylhydrosilane (TU 6-02-807-78); as organic binder - phenolic powder binder (TU 6-0575-1768-35-94) in combination with liquid ethylene glycol (GOST 19710-83) or phenol-formaldehyde resin (GOST 4959-78).

 The preparation of prototypes of the proposed refractory and prototype is as follows. The masses are prepared in a laboratory scraper mixer. Granular fractions of fillers are loaded into the mixer and mixed with a liquid binder. Antioxidant powder and crystalline graphite are then introduced into the mixer. Mix them with granular fillers. After this, a finely divided component of the charge is added, a phenolic powder binder is added, and the mixture is mixed until a homogeneous state.

Samples of the required test form are formed from the prepared masses. The pressed samples are heat treated in air at 200 ^° C. to cure the binder. Then, part of the samples is fired in coke backfill at 1000 ^o C in order to transfer them to the coked state.

The bending strength of coked samples is determined at 1400 ^o C in air.

Oxidation is evaluated by the depth of the decarburized zone when the samples are heated in an oxidizing (air) environment at 1300 ^o C with a holding time of 4 hours.

Resistance to thermal shock is evaluated by the value of the loss of mechanical strength during compression of the samples after 5-fold thermal cycling in the range 1600-1000 ^o C (in a neutral environment).

Slag erosion is estimated by the weight loss of the samples after rotating them in a molten metallurgical slag with a basicity of 3 at 1600 ^o C (see table 1).

 As can be seen from the data in table 2, samples with compositions according to the invention superior to the prototype in terms of basic technical properties of oxidizability, ability to thermal shock and slag erosion. Going beyond the declared antioxidant content leads to deterioration of the properties of the samples. Samples according to the invention are characterized by increased resistance to corrosion by the main slag, due to the increased oxidation resistance they better withstand thermal shocks.

 The above determines the increased wear resistance of the proposed refractory in comparison with the prototype in the lining of metallurgical units.

Claims (1)

A magnesia-carbon refractory comprising a refractory base — calcined and / or fused magnesite, graphite, a finely divided antioxidant — an aluminum-magnesium alloy and an organic binder, characterized in that the refractory contains an aluminum-magnesium alloy of eutectic composition, passivated with an eutectic composition, with a passive cream the following ratio of components, wt.%:
Fine-dispersed aluminum-magnesium alloy of eutectic composition, passivated by silicone coating - 2 - 4
Crystalline graphite - 7 - 20
Refractory base - calcined and / or fused magnesite - Rest
Organic binder, in excess of 100% - 5 - 7

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