Volume 59, Nº 4 (2018)

The efficiency of briquetting kaolin raw material in a roller press is investigated as a measure for combatting dust formation during clay firing. It is established that use of a roller press for briquetting with a claw-grooved configuration of molding elements compared with extrusion by a vacuum press makes it possible to prepare briquettes of better quality, distinguished by improved breakage resistance during heat treatment. A rational clay moisture content is determined for briquetting in a roller press (21%). It is established that briquette preparation with this moisture content makes it possible to minimize briquette breakage during heat treatment and energy expended in material drying before compaction, and also to increase the yield of finished briquettes from a press with provision of good crude briquette strength.

Efficient production processes are studied for extraction of associated valuable components from ore raw material by combined physicochemical methods for enrichment with chemical technology methods. It is established by experiment that with heating by an external heat source dispersed droplets of melted precious metal move towards the ore surface through pores under action of thermocapillary pressure. After melting associated rocks droplets float with gas bubbles. A pyrometallurgical unit is developed for extracting dispersed precious metal from mineral raw material that is difficult to process during preparation of cast refractory materials.

Results are provided for a detailed mineral and petrographic study of the phase and structural transformations for corundum, silicon carbide, and graphite in specimens of different areas of a concrete crucible during testing under extreme conditions (1600°C, 10 h, variable oxidizing-reducing gas atmosphere). The relative slag resistance of the main concrete minerals is established, decreasing in the series: graphite, silicon carbide, corundum, mullite, and glass phase.

The physical, chemical and structural developments taking place in aluminum-phosphate composites when heated under a load were investigated in the present work. X-ray diffraction analysis, electronic-optical and scanning microscopy with an embedded energy-dispersive spectral measurement system were used to investigate the composition of the products of hardening of an α-Al₂O₃ – phosphate binder mixture and the transformations of these products in high-temperature interaction regions. Investigation results make it possible topredict the deformation behavior of ceramics as they are used and to optimize the technology of production of refractory ceramic materials with tailored characteristics.

Results of studying drying of crude corundum granules confirm the assumption that alumina-foam polystyrene mixture exhibits low sensitivity towards drying, which makes it possible to combine drying and firing in a single heating unit. Since intense liberation of foam polystyrene pyrolysis products and combustion products may lead to crude granule destruction the heating rate should be selected in order that gaseous products manage to diffuse from the material without disrupting structure continuity. A rational firing regime is proposed.

A developed procedure is used to evaluate the reliability of cutters fitted with replaceable multifaceted plates of oxide VO13, oxide-carbide VOK71, and nitride RKS22ceramics during turning hardened steel 35KhGSA (44 – 48 HRC). The high efficiency of the set of operational characteristics formed and established wear criteria is demonstrated.

Drying of refractory concrete using a statistical percolation model of its structure is considered. Various mechanisms are considered for removing moisture, including diffusion in a solid phase and movement through open pores. Temperature ranges are determined within which moisture movement mechanisms predominate in concrete. Use of a model is demonstrated for calculating moisture removal from an actual concrete lining or concrete objects. A concrete percolation model is used for analyzing weight loss curves for dense concretes and calculating water diffusion in concrete under different conditions.

Ablation of composites based on phenol-formaldehyde resin, silica fabric, and hollow corundum microspheres was investigated. Addition of corundum microspheres reduced the thermal conductivity of the composite. As a result, the temperature at the exposure site increased, which increased (by 2.7 times) the linear rate of erosion and decreased (by 2.3 times) the length of the composite coking front. Ablation caused high-temperature mechanical and chemical erosion that led to several sequential and parallel chemical reactions that increased the composite porosity and formed high-temperature reaction products, mainly silicon carbide.

The influences of mechanical and thermal actions specific to abrasive-jet machining on the distribution of stresses in various surface-layer phases of Si₃N₄ ceramic were investigated. An approach to selecting the operating modes during preliminary and finishing processes was proposed based on the established trends.

The effect of eutectic composition additive content in the Al₂O₃–MgO–MnO system on sintering of structural ceramic based on electrocorundum is studied. The starting material used is electrocorundum grade F-1000 with an average particle size of 10 μm. Additive powder is prepared by thermolysis of manganese carbonate, magnesium carbonate and aluminum hydroxyl salts. Spinel MgO·Al₂O₃ and MnO·Al₂O₃ are synthesized separately. It is established that with a content of 15 wt.% additive after firing at 1550°C ceramic density reaches 3.86 g/cm³ with 0.3% open porosity, and the ultimate strength in bending comprises 211 MPa.

We consider a method aimed at screening contaminants with the help of local exhaust ventilation whose important element is a local suction gun. We investigate the influence of the ratio of the geometric sizes of the suction gun and the circular hole and the ratio of the flow rates of intake and suction air on both the distance of suction entrapment and reduction of the dust flows in local closed-type suction guns. We also consider local suction guns in unbounded, semibounded, and bounded spaces.