Bacterial desulfurization and column leaching were used to decrease the content of sulfur in sulfide ores' surface to a extreme low level even below the critical value so that the spontaneous combustion tendency of the desulfurized ores weakened.The experiment results show that the maximal desulfurization rate can reach 61.82% after 44 d treatment,and gradually increases with prolonging time.Based on the analysis of the spontaneous combustion tendency of sulfide ores,it is indicated that the oxidation weight gain rate of sulfide ores in 5 d decreases from 2.044% to 0.902% while the ores' spontaneous combustion point increases from 209.6℃ to 319.8℃.As a result,the spontaneous combustion tendency downgrades from level Ⅰ to level Ⅲ and the risk of spontaneous combustion is lowered.
After a proper engineering geological evaluation with rock mechanics rating(RMR) method,Q system and geological strength index(GSI),the mechanical parameters of rock masses were obtained by the extended Hoek-Brown failure criterion.According to the pillar layout of Baiyang ore section,a formula of pillar load was derived,and some parameters for calculating the pillar strength were also determined.The pillar instability mechanisms were respectively analyzed in view of main failure modes.Orthogonal design was introduced to optimization of the stope structure parameter.On this basis,the three-dimensional numerical simulation of each mining program was carried out.The sensitivity of influencing factors for pillar stability was assessed using the method of orthogonal range analysis.The practice shows that the stability of retention pillars can be safeguarded when the stope height is controlled in the range of 3.5 to 4.5 m,the stope width less than 5 m,and the pillar diameter not less than 3.5 m.
Abstract: The process of sticking of Fe2O3 and iron particles during fluidization was investigated with a visual fluidized bed reactor.The results showed that Fe2O3 would defluidize in reduction gases but not in inert gases,and the sticking point happened around the initial stage of iron nucleation.The sticking of iron particles was observed in both reduction and inert gases.It is indicated that the premise of sticking was the formation of iron.When the fluidization temperature increased from 700℃ to 750℃,the critical point of sticking occurred 11 min in advance.It is the temperature-determined surface property of metallic iron that leads to the sticking.Scanning electron microscope(SEM) analysis proved that the sticking of Fe2O3 in fluidized bed reduction resulted mainly from iron surfaces with nano/micro structures.
Abstract: High[Al] content in 38CrMoAl([Al]=0.7%-1.1%) is liable to cause nozzle blockage in continuous casting.Shape control of Al2O3 inclusions is needed to ensure the castability of molten steel.The results of thermodynamic calculations and experiments demonstrate that high content in the steel has strong reducibility to SiO2 in slag even with a small quantity,and Al2O3 with a higher melting point can be changed to spherical calcium aluminate inclusions with a lower melting point through slag infiltration during converter tapping instead of the conventional calcium wire feeding process.Meanwhile,the slag-steel reaction,which may cause an increase in the amount of inclusions,can be avoided by using tundish covering fluxes based on CaO-Al2O3 with low SiO2 content.The results of industrial tests show that the steel's cleanness is higher and the castability of molten steel is better.The nozzle has no blockage after five heats of continuous casting steel.
Abstract: A mathematical model for thermal transmission and solidification of beam blanks was established,and it was discretized and solved by finite element method(FEM).A dynamic secondary cooling control model of beam blanks was developed on the basis of the mathematical model.The dynamic secondary cooling control model can dynamically calculate the entire real-time temperature field of beam blanks with a cycle of five seconds,set up and optimize the amount of water for second cooling by using virtual casting speed and target surface temperature.A dynamic secondary cooling control system of beam blanks was programmed by using Visual C++ 6.0.Under the same conditions of casting processes,the simulation result of the dynamic secondary cooling control system is in a good accordance with that produced by Marc software,indicating that the dynamic secondary cooling control system can be applied to online control or offline design and optimization for secondary cooling in beam blank continuous casting.
Abstract: The effect of phosphorus on the pitting propagation of low carbon steels was studied by specific occluded corrosion cell tests and by analyzing the corrosion products with an energy dispersive spectrometer.The results showed that there were phosphate ions in sediments on the surface of the steels in the occluded hole,and the phosphate ions were the production of phosphorus in the steels.During the activation of pits in corrosion,phosphorus converted into phosphate ions on the surface of the metal,then phosphates formed and deposited,and these phosphates inhibited the propagation of pits.Different contents of phosphorus in the steels could lead to a great difference of phosphate content on the surface of the steels,and the effects of pit propagation inhibition had a large difference too.In the same steel sample,because of phosphorus segregation,the corrosion rate was lower in the region of high phosphorus content than that of low phosphorus content.The formation of convexo-concave corrosion grooves was due to phosphorus segregation.
Abstract: The pitting corrosion and intergranular corrosion resistance performances of 409 L and 430 hot-rolling plates were contrastively investigated by using electrochemical measurements and chemical immersion tests.The results show that the difference between breakdown potential and protection potential of 409 L stainless steel is little,and the restorability of the passive film is strong with small-scale shallow pits.The pitting corrosion resistance of 430 stainless steel is better than that of 409 L stainless steel because of a higher breakdown potential,but its banding microstructure has the apparent effect of a corrosion microcell,represented with a more serious general corrosion.The intergranular corrosion resistance of 409 L stainless steel performs worse than that of the 430 stainless steel because of the low content of Cr and the lack of stabilizing processes under the hot-rolled condition.Through microstructure analysis,409 L stainless steel presents a classic intergranular corrosion appearance along equiaxial grain boundaries,while 430 stainless steel exhibits a delamination corrosion trace at the phase interface between carbides(M23C6) and the matrix.
Abstract: The continuous cooling transformation(CCT) curves of experimental steel were determined by thermal dilation method with a DIL805 thermal dilatometer.Optical microscopy and scan electron microscopy(SEM) were used to analyze the effect of heating temperature on the CCT curves and the microstructure of cooled samples.Experimental results show that when the heating temperature decreases from the complete austenitizing temperature to a higher temperature of the two-phase region,the ferrite transformation of the CCT curve shifts to the left.And when the heating temperature changes in the two-phase region,the ferrite transformation is postponed with the heating temperature decreasing,leading to that the CCT curve shifts to the right.The epitaxial growth mode of new ferrite and the carbon enrichment difference of austenite are principal factors that cause the shifts mentioned above.
Abstract: The distribution of second phase particles in conventional grain-oriented electrical steels during manufacturing processes with MnS as inhibitors was observed by field emission scanning electron microscopy,while the areal particle density,the average particle size and the corresponding size distribution were statistically determined.It is indicated that hot rolling leads to dispersive precipitation of a large amount of fine second phase particles and the matrix keeps a supersaturated state further.Certain dissolution behaviors of second phase particles can be induced by cold rolling,in which the supersaturated state may reduce the dissolution.The precipitation nucleation of new particles and the coarsening of the particles coexist during the intermediate annealing and decarburizing annealing processes,after which the second-phase particles experience predominately the coarsening process during the final temperature rising stage of secondary recrystallization annealing.
Abstract: The electrochemical behavior of Alloy 690 in primary circuit simulated solutions was investigated by potentiodynamic polarization,electrochemical impedance spectroscopy(EIS),dynamic electrochemical impedance spectroscopy(DEIS) and capacitance measurements.It is shown that Alloy 690 has a narrow passive anodic region in the test solutions.But the second passive phenomenon is found at the 0.5 V potential.EIS results indicate that the impedance value of the passive film in the solution without Cl- anions is higher than that in the solution containing Cl- anions.DEIS results demonstrate that the transfer trend of the passive films with increasing potential in both the test solutions is similar.The results of DEIS measurements are in agreement with the potentiodynamic polarization curve well.Mott-Schottky analysis of the passive film formed on Alloy 690 at the 0.2 V potential presents that the donor density and the acceptor density become larger with the addition of Cl-.
Abstract: There exist high extrusion force and its inaccurate forecast in the extrusion process of an IN690 superalloy tube.After the flow function method was used to analyze the extrusion process and to construct a mathematical model of solving the extrusion force,the flow lines of the superalloy were presented in the stable extrusion state.The relationship between technological parameters and extrusion force of the IN690 superalloy tube was determined on the basis of studying the effects of extrusion temperature,friction coefficient and mold angle on the extrusion force.The extrusion temperature and mold angle were optimized by minimizing the extruding force.
Abstract: A 93W-4.9Ni-2.1Fe heavy alloy was prepared by spark plasma sintering with 93W-4.9Ni-2.1Fe composite powders synthesized by high energy ball milling as raw materials,and the influences of sintering temperature on its microstructure and properties were studied.The fracture morphology and composition of the alloy were measured by scanning electron microscopy and energy dispersive spectrometry,respectively.It is shown that the properties of samples change significantly with sintering temperature,and the tensile strength appears a peak of 981 MPa at 1 350℃,where the relative density and the W crystalline grain size arrive at 98.9% and 5 μm,respectively.Ni element in samples tends to volatilize when the sintering temperature reaches 1 375℃,and it is completely volatilized when the sintering temperature hits 1 425℃.The fracture mode of the alloy sintered from 1 250℃ to 1 350℃ changes from W-W cleavage to tungsten-matrix fracture,while it transforms into W-W cleavage again beyond 1 350℃.Grain growth can be effectively inhibited by spark plasma sintering,which prompts fine grain strengthening of the alloy.
Abstract: Graded cemented carbides with a cubic carbide-free layer(CCFL) in the surface were synthesized by one-step sintering.The microstructure,phase composition and element distribution of the graded cemented carbides were investigated by scanning electron microscopy,X-ray diffraction analysis and electron probe microanalyzer,respectively.The typical microstructure of the graded cemented carbides and the effect of sintering procedures on gradient structures in the graded cemented carbides were discussed in detail.It is shown that the depth of CCFL significantly increases with increasing sintering temperature and prolonging holding time,and there exists a linear dependence approximately between the depth of CCFL and the square root of holding time.The depth of CCFL becomes larger at a higher cobalt content,but narrows with increasing Ti(C,N) content for the same sintering procedure.
Abstract: Based on the assumption that the damage mechanisms of materials under tension and compression are different,the nonlinear damaging behavior of refractory materials was studied by micro-mechanics and a multi-scale generalized self consistent scheme(GSCS) model at constant temperature.A method of simulating the nonlinear damage behavior of refractory materials under loading was put forward.By utilizing this technique,the damage of magnesium carbon refractory was simulated under tension and compression.The results of simulation are in agreement with experimental data.
Abstract: CaCl2 was used to chlorinate ZnFe2O4,an important component in metallurgical dust.The changes of the reaction surface between ZnFe2O4 and CaCl2 and the microstructure of reaction products were investigated by scanning electron microscopy(SEM) and energy dispersive spectrometry(EDS),and the reaction mechanism was discussed.It is considered that the whole process includes a solid-liquid reaction and a gas volatilization.ZnFe2O4 particles are coated by melted CaCl2 and the chlorination reaction occurs at the liquid-solid interface,the product ZnCl2 dissolves in the liquid membrane of CaCl2 and escapes from the gas-liquid interface.During the chlorination reaction,the product layer of ZnFe2O4 increases companying with the adhering and growing up of the particles.
Abstract: The calculation method of material energy dissipation coefficients was introduced to solve the problem of snakelike deviation in the burden distribution of a parallel-hopper bell-less top,which leads to an asymmetrical burden surface and the out-of-control of adjusting gas permeability in the burden layer.The effects of particle velocity direction on the effective length of falling movement in the chute and the particle velocity at the chute outlet were analyzed.Some reasons for snakelike deviation and the drop-point differences of charging trajectories were also discussed.It is concluded that the particle collide trajectory in the chute is not an ellipse shape but two semi-ellipses,and the long axis of the smaller semiellipse equals the short axis of the larger semiellipse.
Abstract: In order to apply the technology of slag splashing into a nickel smelting converter,the thermal simulation of slag splashing in a nickel converter was carried out with a Mg-Cr crucible in the laboratory.The results show that the FeO-Fe2O3-SiO2-MgO system is a reasonable slag type for slag splashing,increasing the contents of MgO and Fe2O3 in the slag can remarkably raise the molten temperature,and accordingly,such high melting phases as ferrohortonolite and magnetite increase dramatically.The slag splashing layer with high melting temperature can be formed by means of such a kind of slag.The inner surface of the crucible includes a reaction layer and a slag sticking layer.Phases in the reaction zone are Mg-Fe solid solution and Mg-Cr-Fe-Al spinal,while phases in the slag sticking layer are ferrohortonolite and magnetite.The Fe2O3 content can be increased by air injection,which is an ideal gas for slag splashing.
Abstract: Seven samples of a blast furnace at representative positions were analyzed by scanning electron microscopy(SEM),energy dispersive spectrometry(EDS),X-ray diffraction(XRD) and atomic absorption spectrometry to study the erosion of carbon bricks at the BF hearth sidewall by harmful elements and the mechanism of pulverizing fracture.The results show that the erosion mechanism of carbon bricks at different parts of the hearth is different.In the first layer the erosion is mainly caused by the catalytic effects of harmful elements in the carbon loss reaction and the generation of leucite;in the upper area,penetration of K into brick work joints leading to a quality change of carbon bricks plays the leading role;in the tuyere,Zn is the main cause of erosion;but in the taphole the content of K is larger,with enrichment of Pb.It is also found that a harmful element has different effects at different parts of the hearth.In the upper area,the erosion mechanism is mainly the catalytic effect of K in the erosion reaction,but in lower part is the penetration of K into carbon bricks leading to a quality change of carbon bricks;Zn significantly crystallizes on carbon bricks in the tuyere,however in the hearth bottom Zn attaches to carbon bricks without obvious crystallization.
Abstract: An acceleration telemetry system was used to make the integrated test and signal analysis of torsional vibration and axial vibration in a rolling mill.A computer simulation of the vibrations was carried out with the harmonic response module in ANSYS software.It is shown that the axial vibration of the drive spindle causes the frequent damage of the oil collecting box,and the reason for the axial vibration of the oil collecting box is the torsional vibration of the motor shaft,meaning that the axial vibration of the drive spindle is due to the torsional vibration of the mill's drive system.Through improving the structure of the oil collecting box,the carrying capacity of axial vibration is increased a lot and the service life of the oil collecting box is prolonged dramatically.
Abstract: For the new configuration of a palletizing robot whose revolute pair is drived with a rocker-crank mechanism,its instantaneous inertial force system was transformed into a static system by using kineto-static methods.A kineto-static model of a TH50 palletizing robot was derived from the force equilibrium equations of the robot and its subsystems.Computer programs for calculating the forces of the robot's key components were written in Matlab and a sample was given and analyzed.The results show that the kineto-static model is correct and it has been successfully used in the design of a TH50 palletizing robot.
Abstract: A simplified calculation method of hydrodynamic force which acts on elevated pile caps was proposed on the basis of the Morison hydrodynamic force theory,and it can be applied to the seismic design of long span deepwater bridges.Shaking table tests of elevated pile caps were performed with the south tower base of the Nanjing Yangtze 3rd River Bridge as a prototype.A comparison between the results of shaking table tests and those of the calculation method under dynamic loads verified the accuracy and reliability of the proposed method.At last,the influencing factors on the hydrodynamic force were discussed.
Abstract: In view of that factors influencing construction safety have some gray characteristics,a safety evaluation model based on the gray Euclid relational theory was established and a safety evaluation index system for construction sites was constructed.The weight of each index was decided by the interval analytic hierarchy process(IAHP),which was also introduced to the application of safety checklists.After the gray relative Euclid weighted relational grade was calculated,a safety management level was obtained for the evaluated construction sites.It is shown that under the condition of mastering the inspection data of actual construction sites,better safety evaluation results can be achieved through the model.
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
