RU2153480C2 - Method of making refractory compounds for monolithic linings - Google Patents

Abstract

FIELD: refractories industry. SUBSTANCE: refractory compound comprises ceramic binder which is essentially highly concentrated suspension of ceramic binder and refractory aggregate, ratios of components being as follows, wt % by dry matter; binder 25-50 and aggregate 50-75. Use is made of ceramic binders of bauxite suspension with moisture content of 12-18 with content of particles of not greater than 5 mcm of 20-40%. Aggregate includes bauxite or electrocorundum which further contain up to 18 wt % of silicon carbide. In order to improve rheological and technological properties of refractory compounds and materials based thereon, plasticizing and sintering additives are introduced into original highly concentrated suspensions of ceramic binders. EFFECT: thermomechanical properties of binding system are superior over those of refractory aggregate. 2 cl, 1 ex

Description

 The invention relates to the refractory and metallurgical industries, in particular to the manufacture of monolithic linings from unformed refractories based on various masses. The latter can be used for monolithic lining of steel casting and intermediate ladles, induction furnaces, blast furnace chutes, etc.

 In industry, for these purposes, unformed refractories such as quartz bulk (vibronic) or quartz-clay packing masses are widely used [1]. In these refractory masses, the binder is liquid glass or clay. Monolithic linings based on these masses are characterized by both reduced thermomechanical properties and high porosity, as well as low strength. All this leads to a relatively low durability of the linings of these masses.

A certain improvement in the refractory masses of this class is achieved in the application [2]. For siliceous masses based on quartzite or quartz sand, a plasticized bond based on binders of the same materials was used. However, due to SiO polymorphism, monolithic linings of these masses are characterized by insufficient heat resistance (for example, when serving in the trenches of blast furnaces), as well as relatively low mechanical strength. Interval tensile strength indicator values at compression σ _{compression channel} after heat treatment at 800 ^o C and 1300 for these refractories is within 6 - 12 and 15 - 30 MPa.

In this regard, new low-cement high-alumina refractory concretes obtained using high-alumina cements with high (up to 80 - 85%) Al ₂ O ₃ content have certain advantages. Such low-cement refractory concretes, also called thixotropic refractory masses, are widely used for the manufacture of monolithic linings of steel casting ladles, blast furnace chutes, etc. [3]. The manufacture of linings in this case is carried out both by the method of vibrocasting and casting from self-flowing masses [4]. Lining of these masses and the method of manufacture are characterized by a number of disadvantages, namely, fast hardening, which is not technologically advanced, and their predisposition to “explosive” destruction [4]. The latter effect is associated with dehydration of the HCV during the heating of the lining, which requires a slow and carefully controlled regime.

For monolithic lining of the trenches of blast furnaces, ram refractory masses are widely used in the Al ₂ O ₃ -SiO ₂ -SiC - C system [4]. If the aggregate of these masses is represented by bauxite or electrocorundum and carborundum, then the binder is represented by kaolin and a carbon-containing component (such as pitch) with graphite. The carbon content of C in these masses is 8-17%, and SiC is 8-19%. The pitch bonds used in these masses are low-temperature, concertogenous, and their volatilization during service leads to an increase in the porosity of the lining and reduced durability.

 Thus, all the considered analogues are characterized by specific shortcomings, determined mainly by the behavior when heated from a binder (binder system). In all the cases noted, the thermomechanical properties of the binder system of refractory masses are significantly lower compared to the material of the refractory aggregate.

 It was shown [5] that it is possible in principle to obtain the characteristics of binders based on highly concentrated binders and refractories using them.

It is an object of the present invention to provide a method for manufacturing such refractory masses whose thermomechanical properties of the cementitious system would not be inferior or superior to those of a refractory aggregate. Indicators σ _{compression channel} such masses even after low temperature heat treatment (1000 ^o C) should be higher than 60 - 80 MPa.

This goal is achieved by the fact that as a binder system of refractory masses use highly concentrated ceramic binder suspensions - HCBS [5] based on the respective refractory materials with a moisture content of 12 - 18% in an amount of 25 - 50 wt.%. The most promising in this case are HCBS of aluminosilicate materials (shemot with different contents of Al ₂ O ₃ , mullite, bauxite, kyanite, sillimanite), etc. For certain purposes, HCBS of zircon, alumina, silicon carbide, periclase, spinel, fused silica, etc. can also be used.

 In order to regulate the rheological and technological properties of HCBS, as well as the properties of monolithic linings based on them, the latter can have a complex composition. For example, in order to impart plasticity to mixtures formed by the packing method, refractory clay additives are introduced into the HCBS of silica and aluminosilicate composition. In order to increase the mechanical strength of concrete after low-temperature treatment, additives of highly dispersed fused silica are introduced into the HCBS of a high-alumina composition. Thanks to the latter, during the heating process in the cementitious system, low-temperature mullite formation is observed, which contributes to a sharp hardening of concrete.

 The aggregate of the refractory masses obtained by this method can be represented by the same refractory materials as the binder system. It can also have a complex composition, for example, chamotte or bauxite with the addition of carborundum, corundum-mullite, etc.

 The composition of the refractory masses can be uniform (for example, HCBS bauxite and bauxite aggregate), or heterogeneous (HCBS bauxite and chamotte aggregate, etc.).

 Below, by the example of the preparation and use of chute masses for blast furnaces, the features of the proposed method for producing refractory masses for monolithic linings are illustrated.

Bauxite containing 85 - 92% Al ₂ O ₃ and 3 - 8% SiO _{2 is} used as material for HCBS. Wet grinding is carried out in a ball mill with a constant load of material, observing the basic principles of obtaining HCBS [4]. In order to accelerate the grinding process and improve the rheological properties of the obtained suspensions during wet grinding, additives of finely dispersed fused silica are introduced in the form of a discharge - a waste product of the production of quartz refractories molded by the centrifugal method [4]. The addition of SiO ₂ in this case is 2 - 6% (on a dry matter basis). After wet grinding, HCBS is characterized by a moisture content of 12-18%, a particle content of less than 5 microns in the range of 20-40% and larger than 63 microns, 5-15%. The resulting suspension is subjected to gravitational mixing with a previously obtained suspension of refractory clay, the content of which in HCBS varies from 1 to 4%. For certain molding compositions, clay additives may not be added. In order to lower the viscosity of the mixed suspension during the mixing process, additives that regulate the pH of the system can be added. A filler from bauxite to obtain refractory masses is prepared by crushing, grinding and sieving with the release of various groups of fractions: 37 mm; 1 - 3 mm; 0 - 1 mm. The composition of the masses may be introduced polydispersed carborundum aggregate. The refractory mass is prepared in special runners in the following ratio of components (dry):
VKVS (knitting system) - 33 - 40%
Polyfraction bauxite aggregate - 48 - 67%
Carborundum aggregate polydisperse - 0 - 18%
When mixing the possible introduction of reinforcing additives such as lignosulfonate, introduced in an amount of 0.5 - 1% (in excess of 100% wet). The humidity of the mixture varies between 4.6 - 5.6%. The mass is packaged in airtight containers and sent to the consumer.

The masses of the described composition are used for monolithic lining of the gutters of blast furnaces, performed both by the stuffing method (pneumatic ramming) and by the vibronic filling method. If the packing from the described masses is carried out at a moisture content of 4.7 - 5.3%, then for the manufacture of vibronic filling linings, their preliminary additional moistening by 0.3 - 0.5% is required, followed by mixing and vibro-laying. Monolithic linings are initially subjected to natural drying, followed by heating to 600 - 900 ^o C. The required performance characteristics of refractory masses are formed directly in the service.

The advantage of the considered masses in comparison with the analogue is obvious from the following data. If the known masses in the Al ₂ O ₃ - SiO ₂ - SiC - C - system are characterized by porosity of 28 - 35%, then the proposed mass is 16 - 18%. Indicators of compressive strength σ _{compression channel} after heat treatment at 1000 - 1300 ^o C in the first case fluctuate within 8 - 20, in the second - 80 - 160 MPa. After firing (or service) at 1500 ^o C indicators increase to 200 - 250 MPa. In addition, the proposed masses are characterized by high volume constancy and the temperature of the onset of deformation under load - more than 1650 ^o C.

 Refractory masses obtained by the proposed method, retain their properties over time and allow freezing. After the last, thawing is required before use.

 Monolithic lining of intermediate and steel-pouring ladles can be made from masses of a similar composition. The latter can be reinforcing (for intermediate) and working (steel-pouring ladle). In the latter case, spinel-containing monolithic linings are very effective. For this purpose, medium-grained (0.1 - 0.5 mm) fractions of alumino-magnesian spinel or MgO, which is a spinel-forming additive in refractory masses of this composition, are introduced into the composition of the granular aggregate. The MgO content in the masses varies between 4 - 8%.

 For reinforcing lining a refractory mass can be used in the bauxite VKVS system - chamotte aggregate, for steel buckets - bauxite VKVS - dense bauxite aggregate or electrocorundum.

 Taking into account the fact that the density of bauxite and chamotte are significantly different, with approximately equal volume content of the binder (35 - 40%), its content when using a component of different density in the mass varies significantly. So, for the mass in the HCBS system of bauxite - chamotte aggregate, the optimum binder content is 45 - 50%, and for a system with bauxite binder and aggregate - 30 - 40%. In the case of applying the method of molding from self-flowing (foundry) masses, the content of the binder in them, ceteris paribus, should be 3 - 5% higher than that of printed or vibronic bulk.

 In certain cases, structuring additives of high-alumina cement in an amount of 0.5 - 3% can be introduced into the refractory masses of the considered compositions immediately before application (laying).

 The refractory masses obtained by the proposed method can effectively replace the general-purpose aluminosilicate packing masses produced by the refractory industry. The latter, as a rule, are produced using phosphoric acid as a binder.

 If necessary, large-sized shaped shaped refractory products such as nesting blocks, burners, etc. can be made of the considered masses. Forming methods - pressing, stuffing (tamping), vibration casting, etc.

 Lining or products from the proposed masses are characterized not only by increased durability in service, but also by reduced factory cost, and are environmentally friendly.

An example of the implementation of the proposed method (for example, the mass for vibronic bulk monolithic lining of the gutters of a blast furnace)
In an industrial ball mill with a capacity of 3.2 m ³ by wet grinding using the principle of step-by-step loading of crushed material [5] get a binder highly concentrated suspension of bauxite. The initial pre-heat treated (1400 - 160 ^o C) Chinese bauxite is characterized by the content of Al ₂ O ₃ = 85 - 88%, SiO ₂ = 5 - 8% and porosity 10 - 20%. In this case, the initial bulk material is crushed and sieved into fractions, followed by magnetization. For wet grinding, fractions of 0 - 1 and 1 - 3 mm are used.

Obtaining a suspension of bauxite is carried out using a 5 - 10% additive of finely dispersed fused silica, introduced in the form of a waste-discharge from the production of centrifugally formed quartz refractories. In this case, the drain is introduced together with water, calculated on the final humidity of the suspension of 11.5 - 13%. Along with the loading of the material, thinning additives, for example, liquid glass solution, are introduced to maintain the pH in the range of 8.5 - 10.0. The process temperature reaches 60 - 80 ^o C. Grinding is carried out with 2 - 5-fold loading of the material, which is accompanied by a gradual increase in the density of the suspension to 2.65 - 2.75 g / cm ³ . Grinding is carried out until this density and dispersion is achieved, corresponding to a content of 3-10% of particles larger than 63 microns (20-40% of particles less than 5 microns). After grinding, the suspension is poured into a storage drum - stabilizer and subjected to mechanical stirring at a peripheral speed of 1.2 - 1.8 m / s for at least 6 - 10 hours. At the same time, the pH value of the suspension is adjusted to achieve maximum dilution.

Using the obtained suspension of bauxite in a slider mixer, a molding mixture is prepared containing (dry):
32% finely ground (from suspension) bauxite;
55% refractory aggregate based on electrocorundum fraction 0.1 - 8 mm;
13% silicon carbide aggregate with a grain of 0.02 - 0.2 mm.

 Above 100%, refractory clay additives (0.5 - 1.5%) and 1.5 - 3% of crushed (below 0.2 mm) coal tar pitch are introduced.

If the clay addition in combination with the SiO ₂ additive determines an elevated deformation temperature under load, the pitch additive helps to increase the slag resistance of the lining during service.

 The masses of the given composition after mixing are characterized by a moisture content of 4 - 4.5%. The mass is loaded into sealed containers - bags. At the consumer plant, the masses are mixed and additionally moistened to a moisture content of 5.3 - 5.8%. From this mass, using vibration devices, the process of manufacturing a monolithic lining of the blast furnace troughs is carried out.

Sources of information
1. Velikin B.A., Karklit A.K., Kuznetsov Yu.D. and other. Lining of steel-pouring ladles. - M.: Metallurgy, 1990 .-- 246 p.

 2. Pivinsky Yu.E., Rozhkov EV, Cherevatova A.V. Siliceous refractory mass. Application for the grant of patent N 97117135/03 (018385) from 10.23.1997.

 3. Pivinsky Yu.E. New refractory concrete. - Belgorod: Bel GTASM, 1996.

 4. Pivinsky Yu.E. New refractory concretes and cementitious systems are a fundamental direction in the development, production and use of refractories in the 21st century. Part IV Low cement concretes and cementless unformed refractories.// Refractories and technical ceramics, 1998, N 5, p. 2-10.

 5. Pivinsky Yu.E. Ceramic binders and ceramic concrete. - M.: Metallurgy, 1990 .-- 272 p.

Claims (1)

1. A method of manufacturing refractory masses for monolithic linings, including the preparation of a coarse-grained component and a binder in the form of a previously obtained highly concentrated suspension of the refractory component, mixing them, molding by packing, vibrocasting or casting, characterized in that a highly concentrated suspension based on bauxite with a moisture content of 12 is used 18% with a particle content of up to 5 microns 20 - 40 wt.%, And bauxite or electrocorundum, additionally containing silicon carbide up to 18 wt. .% when the following content of components on a dry matter, wt.%:
Astringent - 25 - 50
Placeholder - 50 - 75
2. The method according to p. 1, characterized in that plasticizing and sintering additives are introduced into the binder suspension.