Abstract: According to the gradual deformation principle of surrounding rock mass under the in-situ three-dimensional stress condition after tunnel excavation, the deformation characteristics of the rock mass was analyzed and the rock mass was zoned rationally. It is assumed that the rock mass is governed by the twin shear stress three-parameter criterion in the unified strength theory. The analyti-cal solutions of some factors were deduced under axisymmetric loads, including the stress field, strain field, support force and plastic radius in the plastic zone. The case analysis result shows that this selected strength theory matches to the actual strength characteristics of the rock mass due to taking the effect of intermediate principal stress into account.
Abstract: The grain growth and cleavage characteristics of metallic phase were studied in direct reduction of a low-grade iron ore. The effects of reducing agent dosage and roasting time on the grain growth were discussed. The results of X-ray diffraction and scanning electron microscopy show that decreasing the reducing agent dosage can limit the reducing atmosphere and restrict the generation of crystallization centers, thereby it is conducive to the grain growth of metallic phase, but the further grain growth is confined due to the partly losing of iron in gangue. Prolonging the roasting time can promote the grain agglomeration and growth, which can decrease the activity of metallic products and thus prohibit the reoxidation reaction. The generation of amorphous substances and the hardness differ-ence between metallic phase and gangue are beneficial to the cleavage of metallic iron when the grinding fineness is coarse.
Abstract: Experiments were done to study the physical dissociation of phosphorus and iron elements in typical high-phosphorus hematite ore samples from the Enshi area of Hubei Province, China. The basic characteristics analyses of the ore samples show the ore is a typical oolitic hematite in which iron and phosphorus elements are not in a chemical combination state, indicating that by the high-speed jet mill technology, the high-phosphorus hematite is finely ground to an average particle size of 2 p,m. It is found that the contents of iron and phosphorus are not evenly distributed in the ultra-fine powders, meaning that the effective dissociation of iron and phosphor-us elements is achieved in the ore. Then a fluidization device for pneumatic separation was designed and manufactured to investigate the fluidization characteristics of the uhra-fine powders. The result shows that the ultra-fine powders have different fluidization characteris-tics from the conventional particles, and this provides basic parameters for the pneumatic separation of iron and phosphorus. Based on the different densities of Fe-rich or P-rich materials, an experimental facility of pneumatic separation can be designed and manufactured, and preliminary make iron and phosphorus separated from the ultra-fine high-phosphorus hematite.
Abstract: Based on the characteristics of some Bayer red mud, deep reduction-magnetic separation experiments were done to study the effects of influencing factors such as reductant dosage, additive quantity, reduction temperature, reduction time, grinding fineness and magnetic field intensity on the grade of iron ore concentrate and the iron recovery rate. The phase compositions and char-acteristics of red mud and iron ore concentrate were determined by chemical analysis, X-ray diffraction (XRD), scanning electron mi-croscopy (SEM) and energy dispersive spectroscopy (EDS). It is shown that the grade of iron ore concentrate is 85.66% and the iron recovery rate is 91.86% without any additive. When the additive is used, the grade of iron ore concentrate is 91.23% and the iron recovery rate is 93.13%.
Abstract: In order to leach and recover nickel from high-silicon low-grade nickel-pyrrhotite, some factors were determined, including roasting pretreatment control, sulfuric acid use ratio, inoculated ThiobaciUus. ferrooxidans or uninoculated. Then sulfate-reducing bacteria (SRB) were immobilized by intact rice chaff in an up-flow anaerobic bed reactor. The leach liquor was treated by the reactor. It is shown that roasting results in the sintering of minerals and makes nickel wrapped, which is not conducive to the leaching of nickel. Thiobacillus ferrooxidans form a biofilm on the mineral surface, which plays a key role in the dissolution of minerals, and oxidizes Fe2+ to be Fe3+, which does a further dissolution of minerals. The leaching rate of nickel reaches to 92.16% and the concentration of Ni2+ is 973.22 mg·L-1. When the influent passes through the reactor at a speed of 2 200 to 3 600 mL·L-1·d-1, the recovery of Ni2+, which adsorbs on the rice chaff in the form of NiS, is above 98%, and 98% of magnesium exists in the solution in the form of ions. The NiO content increases from 1.69% of the crude ore to 11.84% of the rice chaff.
Abstract: The kinetics behaviors and leaching mechanisms of rare earths by acidolysis were studied for Zhijin Xinhua phosphorite ores. It is shown that the ∑REO conversion ratio increases with increasing temperature and sulfuric acid concentration in the reacting solution, which is similar to the kinetics process of P2O5. The acidolysis kinetics of ∑REO reveals that the Drozdov equation can describe the dissolution progress of the ores quite well. The correlation coefficient fitting experimental data is more than 0. 99. The reaction apparent activation energy of P2O5 calculated by the Arrhenius equation indicates that the main reaction of Zhijin Xinhua phosphorire ores dissolved by sulfuric acid is a solid-film diffusion control process, as well as for ∑ REO because of its special presentation in the form of ions in the lattices of collophanite. In addition, studies on the leaching mechanisms of ∑REO dissolved by sulfuric acid show that RE2(SO4)3 is the main existence state in the solution, while RE2(SO4)3 and rare earths enwrapped by calcium sulphate crystals are the main existence state in phosphogypsum.
Abstract: A prediction model of sulphide capacity in CaO-SiO2-MgO-Al2O3 slag systems was developed based on the ion and molecule coexistence theory (IMCT) of slags, i. e., IMCT-CS2-model. The predicted sulphide capacity by the IMCT-CS2-model was compared with the measured one from experiments and the predicted one by other five prediction models of sulphide capacity. The predicted sulphide capacity of CaO-SiO2-MgO-Al2O3 slags at 1 773 K by the developed IMCT-CS2-model has a higher accuracy than the measured one as well as the predicted one by other sulphide capacity models. The developed IMCT-CS2-model can calculate not only the total sulphide capacity of the slags but also the respective sulphide capacity of free CaO and MgO in the slags. Increasing the Al203 content from 10% to 17%, increasing the CaO content from 38% to 44% and decreasing the MgO content from 12% to 4% can improve the contribution ratio of free CaO from 97% to 99% and decrease the contribution ratio of free MgO from 3% to about 1% to the total sulphide capacity of CaO-SiO2-MgO-Al2O3 slags.
Abstract: Based on the generalized similarity principle, stirring characteristics of argon blowing from the ladle bottom were studied by water model experiments. In the research, the harmonic number was considered as an evaluating indicator, and four influencing factors were modified Froude number, liquid-gas density ratio, melting bath depth-to-diameter ratio, and purging plug position. Experimental results show that all the four influencing factors have remarkable effect on the evaluating indicator, and the liquid-gas density ratio is the most obvious. According to the significance, the four influencing factors is in the order of liquid-gas density ratio, modified Froude number, melting bath depth-to-diameter ratio, and purging plug position. Furthermore, the best stirring effect will be achieved while using a single purging plug, the position of which is 0. 55R away from the bottom center.
Abstract: The temperature filed of 22CrMoH billets in continuous casting was simulated by using a moving boundary method. Based on a CAFE (cellular automaton-finite element analysis) approach, the microstructure of 22CrMoH billets was obtained and it agrees reasonably well with experimental data. The effects of alloying elements such as Cr, Mo, Si and Mn on the microstructure of 22CrMoH billets were studied. The results suggested that within the specified scope of the 22CrMoH grade, with the contents of Si and Mn increasing, the proportion of equiaxed grains increased, and the number of grains raised, hence the average radius reduced. The increased content of Mo tends to enhance the formation of nuclei, and a proper decrease of Cr element is conducive to raise the ratio of equiaxed grains while has little influence on the number and average radius of grains. Finally, the contents of Cr, Mo, Si and Mn in 22CrMoH steel was optimized, and the simulated results show that the microstructure of 22CrMoH billets is greatly improved:the proportion of equiaxed grains becomes near double, the number of grains increases by 19.96%, and the average grain radius decreases by 9.20%.
Abstract: Microstructure and texture evolution due to recrystallization in cold rolled interstitial free (IF) steel during batch annealing (BA) and continuous annealing (CA) was investigated by mechanical properties testing, optical microscopy, X-ray diffraction and electron back-scattered diffraction. The mechanism responsible for the evolution was discussed experimentally from different aspects. It is shown that batch annealing and continuous annealing have different thermal histories, so the transition temperature of recrystallization and the reerystallized grain size are different. But the nucleation sites and evolution modes of new recrystallization nuclei are consistent, which belong to the same nucleation mechanism. The formation of recrystallization textures is well explained by the oriented nucleation mechanism rather than the selective growth mechanism.
Abstract: The relationship between grain size and cleavage fracture toughness KIC, i.e., conditional fracture toughness KQ, was investigated for a high speed wheel steel with 0.5% C by compact tension testing. It is indicated that the grain size has an evident effect on the fracture toughness. The fracture toughness is more dependent on the largest grain size than the average grain size of the C50 wheel steel. When the average size of the 5% largest grains is in the range of 30 to 73 μm, the cleavage fracture toughness KQ decreases linearly with the logarithm of average size of these largest grains increasing.
Abstract: Lubrication experiments of medium plates in hot rolling were carried out under different lubrication conditions to analyze the relationship between rolling force and compressibility and study the effect of lubrication on the slab surface quality. The influence of lubrication conditions on the structural transformation in the steel plates was also discussed in combination with the continuous cooling transformation curve of the experimental steel. It is shown that lubrication oil with high concentration can reduce more rolling force than that with low concentration, and this effect is more obvious in rough rolling than finish rolling. Lubrication in hot rolling improves the slab surface quality, decreases the slab surface roughness, promotes ferrite transformation, reduces zonal structure near the slab sur-face, and makes the deformation uniform and the probability of surface defects lower.
Abstract: The morphologies, microstructure and composition distribution of magnesium alloy anodic materials for seawater batteries were studied by metallographic microscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The corrosion behavior and electrochemical properties of the Mg alloys were also investigated by the constant current method, potential polarization and collecting gas through drainage. The results showed that tin restrained β-Mg17Al12 phase precipi-tation along grain boundaries. With the content of tin increasing, granular Mg2Sn phase improved. After uniform heat treatment, most of β-Mg17Al12 phase dissolved, but most of Mg2Sn phase did not. Tin could improve the self-corrosion potential and the release hydrogen rate. The magnesium alloy anode with 1% tin had high discharge potential and current efficiency. With the current density increasing, the release hydrogen rate augmented. The current efficiency reached 82.28% at 20mA·cm-2. The main compositions of the corrosion products were MgO and Al2O3 which were easily peeled off. As a result, more negative and stable work potential was produced and the reaction was accelerated continuously.
Abstract: A porous titanium based alloy containing 7.5% molybdenum was prepared by gelcasting. The microstructure, total porosity and mechanical properties of the sintered porous Ti-7.5Mo alloy were investigated by using electron microscopy, X-ray diffraction, compression and bending tests. The effect of gelcasting parameters on the porosity and mechanical properties of the porous Ti-7.5Mo alloy were studied. It is shown that the rheological behavior of the mixture metal slurry by adding 7.5% Mo powders improves in comparison with pure Ti powders. The open and closed three-dimensional pore morpbologies and the total porosity around 39. 15% to 45.97% can be achieved. The average pore size around 5 to 98 μm and equiaxed cL crystal grains + β phases were observed in the sintered alloy. In contrast to porous Ti by gelcasting available before, the porous Ti-7.5Mo alloy presents excellent properties, therefore being suited for medical applications.
Abstract: A microwave carbothermal reduction process of weakly magnetic Fe2O3 powders to ferromagnetic Fe3O4 powders was experimentally studied with argon gas as a protective gas and activated carbon as a reduetant. The influences of roasting temperature, holding time and SiO2 addition on the ingredients of reduced resultants and the magnetization effect of Fe2O3 powders were discussed. Under quantificational carbon, roasting temperature is a key factor of the microwave carbothermal reduction. The content of Fe3O4 in reduced resultants regularly changed with the roasting temperature increasing. Pure Fe3O4 powders were made at a roasting temperature of 650℃ for a holding time of 5 min, and their magnetisability and percent reduction reach the theoretical values of 2.33 and 11.11%, respectively. Above the roasting temperature of 750℃, a plenty of FeSiO4 and FeO formed in reduced resultants after the microwave carbothermal reduction of Fe2O3 powders containing SiO2, making Fe3O4 in reaction resultants decrease and the magnetization effect worsen. It is concluded that the best boasting temperature of Fe2O3 powders is from 570℃ to 650℃.
Abstract: The effects of Ca2+, Mg2+, and Zn2+ ions on the morphology of iron oxide red seeds produced by ammonium process were studied according to the situation in Zhongyuan Gold Smelter. It is shown that the presence of Ca2+, Mg2+ and Zn2+ ions has influence on the color, composition and morphology but their influencing degrees are different. The maximum concentrations influencing the seed quality are 0. 04g·L-1 for Zn2+, 0. 25g·L-1 for Mg2+, and 0. 1 g·L-1 for Ca2+, respectively. The results also reveal that the treatment of tap water by adding ammonia water can eliminate the influences of Mg2+ and Ca2+ ions.
Abstract: Magnesia-zirconia bricks with the microstructure of periclase covered by zirconia were prepared by improved technology after the technological parameters were determined by orthogonal test. In the microstructure of the magnesia-zirconia bricks, periclase crystals directly bond zirconia and zirconia is between two adjacent periclasc crystals; meanwhile, many micro closed porosities and fine zirconia crystals exist in the periclase crystals. Microcracks due to phase transformation of zirconia in the magnesia-zirconia bricks can absorb the fracture energy and result in the thermal shock performance of materials increasing; at the same time, micro closed porosities in the magnesia-zirconia bricks can reduce the heat stress and improve the mechanical properties of materials at high temperature. Fine zirconia crystals in the periclase crystals possess pinning effects which diminish and prevent creeping slippage in MgO-ZrO2, and ulti-mately improve the hot modulus of rupture of the magnesia-zirconia bricks.
Abstract: A physical-mechanical model of casing connetion joints was bulit for the premium thread and then the axial deformation of a single thread tooth was analyzed. According to the deformation compatibility equation of meshing thread teeth, a set of equations for calculating the contact stress of the casing thread were deduced. Then the inhomogeneous stress distribution of the casing thread was obtained. The reference of the analytic method for connection capability analysis was verified by finite element calculation results. Combining the elasticity theory and the calculation criterion of the API buttress thread, the limit state equations of non-API casing connection's failure modes were derived from the reliability theory. The random sampling of thread processing parameters was carried out with the Monte Carlo method, and then the failure probability and its corresponding reliability were obtained by statistics. The calculation results show that the failure modes' reliability values of non-API casing connection should be ordered below:thread thread slipping > pipe yield > shear failure > joint rupture.
Abstract: A mathematical model was established to describe complicated heat and mass transport processes in a 90 m-long alumina clinker rotary kiln. The effects of heat absorption and release induced by sintering on the temperature distribution in the rotary kiln were studied by using the chemical dynamics method. It is suggested that the reaction between alumina and sodium carbonate is an end mark of the clinker sintering reaction. Research results show that the clinker sintering reaction should complete at the place about 85 m away from the kiln head. The reaction rate increases with rising temperature, and increasing the pulverized coal has a greater impact on the pre-heating zone and the calcining zone than on other zones.
Abstract: The effects of five natural-mineral additives on the combustion characteristics of anthracite were investigated with a synthetical thermal analyzer. The five natural-mineral additives are DG-dolomite, RF-humite, DR-humite, LL-limestone and calcite. Combustion characteristic parameters such as ignition temperature, maximum combustion rate, release property index and burn-out characteristic index were studied by thermo-gravimetric analysis, and the kinetics parameters of samples such as activation energy and frequency factor were also calculated. Experimental results show that DG-dolomite, RF-humite and DR-humite can promote the combustion of anthracite, decrease the ignition temperature, increase the release property index and burn-out characteristic index, and make the maximum rate of combustion move ahead the volatile matter combustion contemporaneously; nevertheless, LL-limestone and calcite have the opposite effect. Kinetics calculation results reveal that the addition of DG-dolomite, RF-humite and DR-humite decreases the activation energy by 10.4%, 14.5% and 10.7% respectively, and the decrease has a combustion-supporting effect in the combustion of blends. Adding LL-limestone and calcite increases the activation energy by 2.0% and 4.3% respectively, and the increase exhibits a fire-retardant effect in the combustion of blends.
Abstract: The three-dimensional steady laminar flow of an incompressible non-Newtonian power-law fluid over a rotating infinite disk with heat transfer was studied. The governing partial differential equations, including the continuity equation, the momentum equation and the energy equation, were transformed to ordinary differential equations by utilizing the generalized Karman similarity transformation. The corresponding nonlinear two-point boundary value problem was solved by the multi-shooting method. Numerical re-sults were obtained for the shear-thinning fluid, the Newtonian fluid and the shear-thickening fluid. It is shown that the power-law character index and the Prandtl number affect the velocities in all directions and the temperature of the fluid in the boundary layer. The results are compared with those of Andersson et al. without considering heat transfer.
Abstract: Based on the motion equations of rolling mills, the relation between the parameters of an automatic gauge control system and Smale chaos and the effect of chaos existing in the automatic gauge control system on the control precision were analyzed through discussing the homoclinic orbit and the Melnikov function. The condition that Smale horseshoe chaos occurs in the automatic gauge con-trol system was given. A new idea was proposed and verified that roll eccentricity disturbances on gauge control is chaotic during roll-ing. Simulation results show that the thickness deviation of the rolled will be large when chaos occurs and the product quality can be improved by chaos control.
Monthly, started in 1955 Supervising institution：Ministry of Education Sponsoring Institution：University of Science and Technology Beijing Editorial office：Editorial Department of Chinese Journal of Engineering Publisher：Science Press Chairperson：Ren-shu Yang Editor-in-Chief：Ai-xiang Wu ISSN 2095-9389CN 2095-9389
