Calculation of pillar unloading parameters during mining of ore deposits

Numerical and analytical methods are considered for determining stresses normal to the bedding in carrying elements for a chamber-and-pillar mining system for the complex mining-geological and mining-technical conditions of the North Ural bauxite mines. Features were revealed and pressure distribution was analyzed in pillars taking account of the influence of the size of the technogenic gap, natural compliance, depth, angle of dip, and ore deposit thickness. State Scientific-Research Institute of Mining Mechanics and Mine Surveying, Saint-Petersburg, Russia. Translated from Fiziko-Tekhnicheskie Problemy Razrabotki Poleznykh Iskopaemykh, No. 1, pp. 27–35, January–February     

Dynamic viscosities of pure tin and Sn-Ag,Sn-Cu,and Sn-Ag-Cu eutectic melts

The dynamic viscosities of the melts of pure tin and eutectic Sn-Ag, Sn-Cu, and Sn-Ag-Cu alloys are studied in heating followed by cooling, and the maximum heating temperature was 1200°C. An irreversible decrease in the viscosity is found in the temperature range 800–1000°C in the polytherms of all melts. This finding is related to the loss of a local order in a melt and can be used to develop temperature regimes for the production of lead-free solders.     

Carbonization of coal pitch with additives

The ability of organic and inorganic additives (polyethylene terephthalate, titanium dioxide, finely disperse carbon, petroleum bitumen) to reduce the carcinogenic impact of coal-pitch carbonization is studied. Additives may reduce the quantity of pitch sublimates and their content of carcinogenic polycyclic aromatic hydrocarbons. Some additives are able to reduce the benz[a]pyrene content in the exhaust gases, but its complete elimination is impossible, since benz[a]pyrene is a natural product of the high-temperature pyrolysis of organic materials. For this reason, additions of petroleum products to coal pitch cannot reduce the benz[a]pyrene emissions in the exhaust gases.     

Countercurrent flow of gas and water in perforated plates

An experimental investigation is performed of countercurrent flow of steam and water through perforated plates in the pressure rangeP = 0.6-4.0 MPa. An equation is suggested that describes the correlation between the countercurrent flow rates under conditions of “flooding.” The experimental results are compared with the data of previous studies. The effect of the geometric and process parameters on the processes involved is treated.     

Laser radiation confinement at 1.06 μm in compensated gallium arsenide

Experimental data on the YAG:Nd laser radiation (λ=1.06 μm) confinement by self-defocusing in compensated GaAs are reported. It is demonstrated that low-threshold confinement at an energy threshold below 10 pJ is possible for a 10 ns laser pulse width.     

Critical Heat Flux in Vertical Steam-Generating Channels in the Absence of Circulation of Heat-Transfer Agent: Critical Power of Channels of Different Shapes

An experimental investigation is performed of the critical heat flux in vertical channels in the absence of circulation of heat-transfer agent through the lower cross section. Experiments are performed in tubes 30, 40, and 80 mm in diameter, as well as in 19- and 40-rod assemblies. Equations are suggested for the calculation of critical power, which are valid in a wide range of the geometric and process parameters, including at a low pressure.     

Oxidation resistance before and after heat treatment for compacted Al<Subscript>2</Subscript>O<Subscript>3</Subscript>–SiC–C mixtures with aluminum-chromium-phosphate binder

Oxidation resistance has been examined for compacted Al₂O₃–SiC–C mixtures, which contain an aluminum-chromium-phosphate binder without firing (DTA method) and ones that have been previously fired and given isothermal heat treatment at 800°C (as indicated by the mass loss). To obtain oxidation-resistant materials, the content of silicon carbide should not exceed 10 wt.% and the recommended graphite content is not more than 20 wt.%. Translated from Novye Ogneupory, No. 2, pp. 38 – 43, February, 2009.     

Service experience of refractory products and mixtures in metallurgical plant lining at the Magnitogorsk Metallurgical Works

The authors describe the experience of production of refractories and mixtures and their service in blast furnaces and steel melting, as well as the service of corundum-graphite products for protecting metal strands on machines for continuous slab casting. __________ Translated from Novye Ogneupory, No. 8, pp. 9–11, August, 2007.