Vol 56, No 6 (2016)

The equipment installed in the chambers of a continuous-caster tundish is examined. An improvement made to this equipment is ensuring the efficient formation of flows of metal in the tundish and creating the conditions necessary for improving the quality of the cast metal.

An improved design of lining has been developed for the cars of short PG-30 tunnel furnaces, which are used to fire ceramic tooling: crucibles, cores, and molds for casting products made of heat-resistant alloys. The top part of the refractory layer that is installed on the heat-insulating layer consists of two superimposed panels. All of the panels except for the top panel contain interrupted holes (a total of 44 such holes) that are arranged in staggered fashion and open onto the panels’ main surfaces. The top panel contains blind holes (totalling 22). In assembling the refractory layer, the ends of the panels are connected to one another in such a way that the holes their surfaces are coaxial. The top panel is positioned so that the surface without holes faces upward and the holes on the other surface face downward. The box-inserts that hold the ceramic products which are to be fired are placed on the top panel. Such a design of car significantly reduces its weight while also increasing its service life. Durability is improved in particular for high-speed operation of the cars, such as in the firing of foundry molds for casting nickel alloys.

This article presents results obtained from numerical modeling of external heat exchange in an innovative gas-fired glass-founding furnace with an output of 2.92 tons/m²·day). Unit heat consumption in the furnace is 4.187 MJ/kg. Boundary conditions are determined for designing and building a lining for the working space of the furnace. It is established that the average and maximum temperatures are 1512.6 and 1608.4°C for the roof, 1548.3 and 1596.3°C for the longitudinal wall (on the burner side of the furnace), and 1553.2 and 1622.2°C for the end wall (next to the flow). The average temperatures of the surface of the bath in the founding and fining zones are 1404.8 and 1426.6°C, respectively.

Changes in structure, phase composition and crystal structure parameters are studied for materials of the ZrO₂–MgO system after cyclic thermal shock effects. Features are revealed for formation of ceramic structure and phase condition with implementation of internal stresses connected with a sharp change in temperature. Optimum compositions are established for refractory materials based on ZrO₂ answering high specifications for thermal shock resistance and refractoriness.

The effect of temperature on foaming a mixture of diatomite and sodium hydroxide solution during glass ceramic foam preparation is studied. Composite foaming temperature is established conforming to optimum structural porosity and average specimen density required for heat insulation materials. The effect of temperature on the content within specimens of free sodium hydroxide is analyzed, and its reduction with an increase in temperature is revealed. The practical significance of this research is demonstrated on the example of preparing granular glass ceramic foam.

Arelationship has been experimentally established between the parameters of hydroabrasive machining on the one hand and the morphology of the working surfaces and geometry of VOK71 plates on the other hand. It is determined that hydroabrasive machining significantly improves the reliability of the plates by favorably changing the morphology of their working surfaces and cutting edge and improving the radius of curvature of the cutting edge.

Possibilities are considered for using carbon fibers as a reinforcing elements within the structure of periclasecarbon refractories. Laboratory research results are provided.

The effect of firing temperature on sintering and mullitization of six batches of specimens prepared from HCBS based on high-alumina bauxite and very fine quartz glass (VFQG) is studied. In the range 900 – 1200°C (soaking 1 h) normal sintering is noted accompanied by insignificant (0.4 – 0.5%) shrinkage and a sharp increase in ultimate strength in bending (110 – 130 MPa). In the range 1200 – 1400 of 1500°C (depending on composition) specimen growth by 1.0 – 2.5% is noted, due to mullitization. Depending on composition and solid phase fineness the start of sintering for mullitized specimens is noted at temperatures exceeding 1400 – 1500°C. Specimen material modeling a matrix system of high-alumina refractories has high strength and volume constancy after prolonged thermal ageing.

The effect of modifying coal tar pitch with different additives is studied; surfactant substances (SAS), carbon-containing modifiers, and high-temperature binder additives. Using SAS a reduction is observed in viscosity for a system of original pitch–modifier, and with a concentration of 7 wt.% it is most effective to use oleic acid, but with a concentration of 10 wt.% to use myristic acid. In both cases viscosity is reduced by almost a factor of ten with respect to original pitch viscosity. In the case of carbon-containing additives viscosity increases, the same as with use of a high-temperature binder. The effect of modifiers on coke residue yield is studied. On modifying pitch with SAS the reduction in coke residue obeys an additivity rule, which is explained by total removal of SAS from a pitch–modifier system. With use of carbon-containing modifiers and high-temperature binder the coke residue also increases by an additive rule.

The stress-strained state of a surface layer of oxide-carbide ceramic under action of a concentrated force, heat flow, and combined loading is studied. The possibility is demonstrated of using the correlation revealed for predicting the nature of ceramic surface breakdown with jet-abrasive treatment.

Results are provided for a study of the microstructure, phase composition, and physicochemical properties of domestic and imported graphites for the refractory industry. It is established that graphites of different origin have a different morphological surface, crystal lattice structure, and oxidation resistance.

A description is presented of the system used by the Serov Ferroalloys plant for the pneumatic transport of lime dust that contains nanoparticles. The morphology of the particles of well-burnt lime is discussed. Recommendations are given on ensuring stable operation of the system and subjecting the dust to additional comminution.

Boundary conditions and a method of calculation are examined for determining parameters that characterize heat transfer through the lining of a tunnel furnace. An energy-efficient structure is conceived for the linings of the roof and walls of the furnace and the floor of the cars used in the furnace. It is established that the improvements made in the structure of the furnace’s protective elements make the production process more energy-efficient and create the conditions necessary for also improving the quality of heat treatment of the raw materials/semifinished products. The author determines the amount heat loss and the temperature of the outside surface of the lining for which the temperature gradients from the tunnel axis to the furnace walls and roof and the car floor are no greater than 17, 25, and 43°C, respectively.

Wet milling in a ball mill is used to prepare a suspension based on amorphous and crystallized magnesium aluminum silicate glass. The stabilizing additives used are hydrochloric and oxalic acids, and also an aqueous ammonia solution. Raw material is molded by slip casting in porous molds. Optimum ranges are provided for magnesium aluminum silicate glass suspension casting parameters in order to prepare green workpieces with not more than 30% porosity.

A mathematical model and computer program for use in calculating the separation region at the inlet to a funnel situated above an impermeable plane are developed by means of stationary discrete vortex rings. The basic computational relationships and algorithms for calculating the characteristic regions of detached flow, the limiting trajectories of dust particles, and the ventilation region are presented.