Vol 58, No 1 (2017)

Construction of a modernized submersible nozzle is developed with an efficient working surface. New submersible nozzles, installed in CBCM crystallizers, make it possible to reduce steel turbulence and flow rate, and to reduce eddy formation at the level of the metal meniscus. Due to this particles of the slag-forming mixture cover the metal meniscus, and are not drawn into a slab. This provides efficient formation of steel flow into the crystallizer and creates conditions for improved metal quality.

A method is described for modeling sinter stability of periclase-spinel refractory composition produced by Gruppa Magnezit. Refractory microstructure is studied after testing, and the degree of resistance of new forms of refractory to action of a corrosion agent is determined.

Anew version of a steeply inclined pivoted bucket belt conveyor with slippage of the traction belts relative to the shells of the reels is proposed. The natural vibrations of the buckets in the course of travel, taking into account the total rigidity of the two joined belts and the planks clamped between them, are estimated. The resonant speed of the conveyor belts is determined and the coefficient of dynamism is found.

A new approach to the analysis of the heat work of glassmaking furnaces is proposed. A generalized equation of the thermal balance of a furnace at the boundaries between the smoke stack and the glass melt channel is obtained. Boundary conditions on the temperature for media whose heat content defines the cost items of the thermal balance are formulated. It is shown that the heat rate (specific consumption of heat) in melting of 1 kg glass influences the percentage content of the cost items of the generalized thermal balance. A calculation of the thermal balance of the melting area of a 320 t/day container glass furnace with specific consumption of heat 1000 kcal/kg is carried out.

SiC nanoparticles that could be used as an antioxidant for periclase-carbon (PC) refractories were synthesized from the organic—inorganic complex (–CH₃)–(SiO₂)_n that formed during heating of silicon alkoxide and thermal destruction of its gels. Use of phenolformaldehyde resins modified with silicon alkoxide and its sols was proposed and enabled the formation of an organic—inorganic complex (–CH₃)–(SiO)_n –C with a high C content. This increased the yield of SiC synthesized in the carbon binder. The addition of Ni precursors (additional antioxidant) formed an even more complicated organic—inorganic complex. Use of the complex (–CH₃)–(SiO₂)_n –Ni(NiO)–C together with Al improved the operating characteristics of the PC refractories. It was found that their resistance to oxidation was increased after the complex antioxidant Al + SiC + Ni(NiO) formed.

A short review is given of existing methods for preparing highly porous silicon nitride materials. The possibilities of a method described are based on consolidation of previously prepared elements from a thermoplastic slip with thixotropic rheological properties. Different combinations of thermal and mechanical action during element consolidation in the form of shavings may lead to different distribution of porosity throughout the volume of the objects prepared.

Porous ceramic materials exhibit high permeability, specific surface, and thermal shock resistance, and therefore they may be used successfully in the production of filters, membranes, and as a substrate for catalytic reactions, etc. One method for preparing high material porosity is addition of a pore-forming substance. Porosity (open and closed), pore size distribution, their size and shape, depend on the nature, amount, and morphology of pore-forming substance. In this article the effect is elucidated of three different types of carbon additives on porosity of ceramic prepared from clay and chemical binder precursor. Carbon materials are studied in an x-ray diffractometer. Ceramic material properties are studied using a mercury porosimeter, the Archimedes method, scanning electron and optical microscopes, and microcomputer tomography.

Results are provided for a study of the effect of pitch nanomodification on the density of carbon-carbon structural material frameworks. It is established that addition of carbon nanomaterials to pitch facilitates formation within them of more condensed structures with improved thermal shock resistance. It is shown that the density of workpieces based on modified pitch is higher than for workpieces based on original pitch.

The effect of titanium carbide coating thickness on transformation of the stressed state of a Si₃N₄–TiC–Y₂O₃-ceramic surface layer under action of heat flow is studied. It is established as a result of numerical experiments that an increase in TiC coating thickness from 5 to 15 μm, applied to nitride ceramic, leads to a reduction in ceramic temperature, and increase in σ₁₁, σ₂₂, σ₁₂, and σ_i, and indices of their structural inhomogeneity in a ceramic surface layer.

Carbon material thermal conductivity is an important factor for providing thermal shock resistance. The effect of production factors on the reproducibility of thermal conductivity values during manufacture of three-dimensional reinforced high-density carbon-carbon composite is considered. An average level of thermal conductivity applies to more than 82% of workpieces. From 4.6 to 12.5% of workpieces have thermal conductivity not less than 44 and not more than 70 W/(m·K). It is established that a change in carbon fiber treatment temperature from 1600 to 2400°C may lead to an increase in materials thermal conductivity by 0.21 W/(m·K) for each 100°C. Adifference in framework structure may change average thermal conductivity within the limits of 3 W/(m·K). Variation of material apparent density from 1.89 to 1.98 g/cm³ gives a change in thermal conductivity by 1.1 W/(m·K) for each +0.1 g/cm³. A connection is established for a carbon-carbon composite of electrical conductivity ρ and thermal conductivity λ, corresponding in form to the Weidemann-Franz rule λρ = const.

Research is conducted for synthesis of artificial ceramic binders of mullite-silicon carbide composition and composites based on them. Binder rheological and physicomechanical properties are studied. Dependences are established for composite compaction in relation to molding conditions and starting raw material type. The possibility is demonstrated of using artificial ceramic binders for preparing highly dense ceramic composites with good operating properties.

Amethod for determining the absorption-reflection properties of a single grain of vermiculite and a dense single-layer array of intumescent vermiculite located on a planar surface under thermal radiation is considered. Based on the experimental graph of dehydration, the whole process of calcination and mechanical transformation of vermiculite can be broken down into stages. For each stage the averaged reflection and absorption coefficients are determined based on the idealized notion that the lateral faces of the grains due to the scaly structure completely absorb radiant energy of the heating elements, and the end faces completely reflect it. Based on the weighted average optical coefficients for a single grain and a single-layer array as a whole throughout the entire heat treatment period, a finite static optical model of the array was constructed.

This work is devoted to studying production aspects of preparing electrode materials based on TiC–Co precipitation hardened with tungsten carbide particles that form in the course of synthesis from original tungsten and carbon black components and are distributed uniformly throughout the volume of a specimen during extrusion.