Abstract: Based on No.1318 shooting case in Huaxing Coal Mine,the changing process of air leakage flow,components (oxygen,CO and methane),and temperature in the flow field of goaf during air reversing were solved and described,and the changing rule of gas emission volume of different components along the boundaries of the working face while air reversing was given.It is simulated that after air reversing the content distribution centers of different components are reversed,the upper high temperature area is cooled down while the lower area with low temperature becomes a new high temperature area,making the temperature rising process in goaf at a low start point,which is favorable for slowing down the rising velocity of temperature and thus preventing spontaneous combustion of coal from taking place.During air reversing,the emission volume of CO has a jumping process of sudden decrease→increase→slow attenuation→gradual increase.After this process,the increase range of gas emission volume becomes slowed.By burying pipes to extract gas,harmful gases within the working face could be prevented from exceeding limit during air reversing.At the same time,the condition to realize air reversing is given,namely there is no naked flame in goaf.
Abstract: When the rock is difficult to cut and support in fracture zones,forepoling is usually used as auxiliary reinforcement support.In order to study the arch structure mechanism of bolt forepoling in surrounding fractured rock and its displacement evolution,bolt forepoling at the Ramp 230 in Wupin Zijin Mining Company was taken as an example,and the displacement evolution of the arch structure,which is taken as a flawed one,was analyzed on the basis of the buckling theory and the membrane theory.This study improves the simplification problem of reinforced arches.
Abstract: Static flocculation and sedimentation experiments with polyacrylamide and unclassified tailings from a mine were completed to study the effects of feeding concentration and flocculants’ unit consumption on the maximum sedimentation velocity and limit concentration of tailings under static sedimentation.A simple model of sedimentation velocity was established through regression analysis on experimental data.The model was divided into six phases including turbulent flow affected segment,accelerating sedimentation segment,terminal velocity segment,interference sedimentation segment,dewatering sedimentation segment,and limit sedimentation segment.The rationality of the model was explained by the two-phase flow theory and the flocculation theory.The results show that at a certain unit consumption of flocculants (20g·t-1),the sedimentation velocity is negatively correlated and the limit concentration is positively correlated to the feeding concentration.At the feeding concentration of 20%,the critical value of unit consumption is 30g·t-1,and the limit concentration is negatively correlated to the unit consumption.A project was proposed that the feeding concentration is 20% and the unit consumption of flocculants is 20g·t-1.
Abstract: By adding a flux and using a direct reduction roasting and magnetic separation method,iron and nickel enrichment from refractory low-grade nickel laterite ore,in which nickel is mainly contained in silicates,was studied.Better technical indicators were obtained by adding the flux.The optimal conditions are coal as the reducer with a dosage of 15%,KD-2 as the flux with a dosage of 20%,and roasting at 1200℃ for 40min.A concentrate of the Ni content of 10.83% and the Fe content of 52.87%,with the Ni recovery of 82.15% and the Fe recovery of 54.59%,was produced under the optimal conditions.The action mechanisms of KD-2 and coal were also investigated by XRD and TEM.The results show that KD-2 can react with quartz and silicates containing Ni,leading to releasing Ni from the quartz and silicates.An overdosage of coal in the reduction roasting process can result in the formation of pure iron,in company with a decrease in nickel recovery.
Abstract: The magnetizing roasting-magnetic separation process of limonite ores from Anhui Province in east China was experimentally studied,which covers determining the mineralogy of raw ores and optimizing the magnetizing roasting-magnetic separation process parameters.It is shown that the limonite ores contain low phosphorus and sulphur and high loss on ignition (LOI);the iron minerals and gangue have complicated occurrence,indicating that the limonite ores are extraordinarily refractory iron ores.Through magnetizing roasting of raw ores assaying 48.01% Fe and blending 5% coal fines at 850℃ for 15min,the best magnetization ratio of roasted iron ores is achieved,where almost limonite is transferred to magnetite.This result was proven by X-ray diffraction.By the magnetizing roasting-magnetic separation process,an iron ore concentrate with 62.94% TFe and 87.99% recovery is produced.
Abstract: The high temperature properties of 10 iron ores from Brazil,Australia and China were measured.By comparison with the optimal zone acquired from practical production statistics,several results were obtained as the following.The assimilability of Brazilian and Australian ores is lower and higher than the optical zone,respectively,but that of Chinese concentrate powders is close to the optical zone.The liquid-phase fluidity of two Brazilian ores,one Australian ore and one Chinese concentrate powder is optimal,one Brazilian ore,one Australian ore and two Chinese concentrate powders have low liquid-phase fluidity,but one Australian ore and one Chinese concentrate powder possess high liquid-phase fluidity.The self-strength of bonding phases in Australian ores is low,but optimal for Brazilian ores and Chinese concentrate powders,while the self-strength of bonding phases in Chinese concentrate powders is higher than in Brazilian ores.On the basis of experimental research,a new concept,which makes the high temperature properties of mixed ores optimal based on complementation of high temperature properties,was proposed,and the optimization schemes of ore blending were designed.The result of sinter pot test indicates that good sintering indexes are obtained,which proves the superiority of ore blending based on high temperature properties of iron ores.
Abstract: The oxidation-reduction reaction can easily happen between Al contained in liquid steel and SiO2 component in mold fluxes during continuous casting of TRIP steel containing Al.As a result,the Al2O3 component sharply increases from 3% to 30%,and the w(Al2O3)/w(SiO2) ratio simultaneously ascends from 0.10 to 1.44,so the viscosity could have a bigger fluctuation accordingly.The effects of Al2O3 content and w(Al2O3)/w(SiO2) ratio on the viscosity of mold slags were investigated for producing TRIP steel containing Al.A model was built to predict the viscosity of the high Al2O3 slag system.The results indicate that when the comprehensive basicity is less than 1,the viscosity of mold fluxes initially rises and then reduces again with increasing the Al2O3 content from 3% to 17%,but it changes slightly when the basicity is greater than 1.The viscosity of mold fluxes dramatically rises when the Al2O3 content changes from 17% to 30%.With increasing w(Al2O3)/w(SiO2) ratio,the viscosity of mold fluxes for TRIP steel containing Al initially reduces and then abruptly rises.
Abstract: Local dynamic equilibrium reaction process for the reactions involving complex inclusions,molten steel,slag and refractory materials in steelmaking of high carbon hard wire 82B steel melt was studied and the compositional variation of the inclusions using Mn,Si and Al deoxidation was discussed.The formation condition of plastic inclusions for the Al2O3-SiO2-MgO-CaO-MnO system was calculated and analyzed by the thermodynamic software FactSage.The results reveal that the mass fractions of [Al] and [O] in molten steel are controlled at 25×10-6 to 100×10-6 and 5×10-6 to 20×10-6,respectively.In the low-melting point zone,the mass fraction of Si is controlled at 0.1% to 1.5% and that of Mn at 0.2% to 1%.
Abstract: The morphology,composition and hot deformation of oxide-sulfide duplex inclusions in resulfurized gear steel DIN 18CrNiMo7-6 were studied by metallographic examination,scanning electron microscopy (SEM) and electron spectroscopy analysis.The results show that the hot deformability of the oxide-sulfide duplex inclusions decreases with the increase of calcium content in the peripheral sulfides until the atom fraction of about 5.0%.Increasing the area ratio of the core oxides with high melting point makes the duplex inclusions less susceptible to deformation,while the oxides with low melting point have not obvious effect on it.
Abstract: A cellular automata method with determined step length was used to simulate normal grain growth,and the influence of step length on the simulation results was investigated.Within the same equivalent time,the use of a larger step length leads to a smaller grain size,the grain size distribution accords well with the Weibull function,and the correlation between grain area ratio (An/Aa) and grain sides is closer to a linear relation.Whichever step length is used,the average grain sides in the simulation process are close to 6,the distribution of grain sides after simulation accords with the normal distribution,and the agreement is improved with the decrease in step length.In a comprehensive consideration,a step length of 100 s is in favor of simulating the grain growth of actual materials.
Abstract: For NbCxN1-x in low-carbon microalloyed steels,x values in the formula are calculated by existing methods.As shown in the calculation results,the x values are mainly influenced by temperature and composition.The x values increase with increasing C content and decreasing N content,as well as decreasing temperature.It is indicated that in a certain range of composition and temperature,the calculation results is in good agreement with experimental data from related references.On the other hand,for the steel with composition over the range,the calculation results should be treated as a reference only.The ranges of temperature and composition are 1050 to 1250℃ and 0.10%C-0.005%N-0.20%Nb to 0.20%C-0.005%N-0.20%Nb,respectively.
Abstract: The precipitation,microstructure and mechanical properties of low carbon steel at different coiling temperatures were investigated by tensile testing,metallography,quantitative analysis of precipitates,TEM and EDS.The results show that with the coiling temperature increasing,the strength and grain size grade of the steel and the content of nitrogen in solution decrease gradually;at a coiling temperature of 740℃,the content of nitrogen in solution is almost zero.Thermodynamic and kinetic analyses indicate that AlN precipitates in coiling chiefly.The sizes of AlN,with complex chemical composition,are between 10nm and 50nm.
Abstract: The effects of annealing processing on the mechanical properties and microstructure evolution of high strength hot dip galvanizing TRIP steel were investigated.The results show that the tensile strength over 780.00MPa and elongation over 24.00% can be obtained,and the mechanical properties are significantly influenced by intercritical annealing temperature and isothermal bainitic transformation time.When the intercritical annealing temperature is 850℃ and the isothermal bainitic transformation time is 30s,the steel has the best mechanical properties.Partial metastable austenite (with a lower carbon content) remained after bainitic transformation will be transformed into martensite in the later cooling stage.Therefore,the annealing microstructure is composed of ferrite,bainite,retained austenite and martensite.
Abstract: The effective distribution coefficient of solidification structures under shearing and stirring was investigated to understand the effects of solidification velocity and rotation speed on solidification structures.A mathematical model of solidification structure evolution to solidification velocity and rotation speed was set up.Simulation results show that the morphology of solidification structures is strongly dependent on solidification velocity and rotation speed.With decreasing solidification velocity or increasing rotation speed,the shape factor of solidification structures increases.The mathematical model shows a very good agreement with experimental results.
Abstract: Billets of Al-12Zn-2.4Mg-1.1Cu-0.20Zr-0.30Sc-0.30Ni alloys were fabricated by spray deposition (the Osprey process),and the effects of heat treatment at different temperatures on the microstructural evolution were investigated by DSC,XRD,SEM,and TEM.The results show that many η-phase particles disperse in the as-deposited alloy base at room temperature.The re-dissolution and precipitation effect of solute elements occurred at different heating temperatures can affect the microstructure and mechanical properties of the alloys.The metastable T phase ((Al,Zn)49Mg32) forms around η-phase particles with a high Cu content after a heat treatment at 460℃ for 8h,and disappears at 490℃ for 8h.Al3(Sc,Zr) dispersoids are precipitated at 490℃/8h,the highest hardness (192 HV) of the as-deposited alloys after treatment at 490℃/8h is attributed to the precipitation hardening of Al3(Sc,Zr) dispersoids and the solution hardening effect caused by Cu.
Abstract: Take an AZ91D alloy architectural scraper for example,the rheo-diecasting process was implemented by combining a self-developed taper barrel rheomoulding (TBR) machine with a TOYO BD-900V4-T cold chamber die-casting machine.The microstructural characteristics of the components were investigated in different rheo-diecasting processes,and the microstructure formation and solidification behavior of the semi-solid slurry were analyzed.The results show that the process is able to obtain components in which the primary α-Mg particles are fine,spherical or nearly spherical and uniformly distributed.The microstructure of rheo-diecasting components is relatively round and homogeneous when the rotation speed is 700r·min-1.The primary α-Mg particles have an average size of about 45 μm and a shape factor of about 0.81.Solidification of the alloy melt taking place in the rheo-diecasting process is composed of two distinct stages:primary solidification and secondary solidification.
Abstract: Fe-Ni based high temperature wear-resistant powder was cladded on 45# round steel to obtain an Fe-Ni based alloy roller by plasma cladding.Scanning electric microscope,energy spectrometer and X-ray diffractometer were adopted to study the microstructure of the Fe-Ni based alloy coating and the failure surface of the Fe-Ni based alloy roller.It is shown that the morphology of the Fe-Ni based high-temperature wear-resistant coating is well and the morphology is planar crystal at the coating-substrate bonding,while the morphology becomes dendrite at the middle and the top of the coating.The γ-(Fe,Ni) content reduces following the bottom-middle-top order in the coating,but the (Cr,Fe)7C3 is just the opposite.The failure mechanism of the Fe-Ni based alloy roller is thermal fatigue cracking and grain wear.
Abstract: The effect of hydrogen on the conductivity of PZT-5H ferroelectric ceramics was investigated by experiment and first-principles calculations.The resistivity of PZT-5H ferroelectric ceramics decreases with the increase of the content of hydrogen doped into the ceramics.When the total hydrogen content is 11.2×10-6,the resistivity approaches to 1.51×109Ω·cm,which is between the semiconductor and insulator.Further increasing the hydrogen content,the PZT-5H ceramics become an n-type semiconductor from the Hall effect.The results of first-principles calculations show that the [Pb(Zr0.5Ti0.5)O3]32H system,with the hydrogen content of 96×10-6,becomes a semiconductor.The density of states (DOS) moves toward the lower energy with the increase of hydrogen content.The [Pb(Zr0.5Ti0.5)O3]nH system becomes a conductor while the hydrogen content is larger than 96×10-6.
Abstract: The hydrogen sensitivity of a hydrogen sensor with the Nafion112 membrane as electrolyte was studied under different working environments.The results show that the hydrogen sensor has good hydrogen sensitivity and can quickly detect a tiny hydrogen leak.The generated electromotive force increases linearly with the logarithm of hydrogen volume fraction in the range of (500 to 3000)×10-6,which provides a basis for calibrating the relationship between hydrogen content and the sensor's electromotive force.The electromotive force decreases with the increase in temperature under a fixed humidity condition.The effect of humidity on the sensor's electromotive force also relates to temperature.When the temperature is low,the electromotive force decreases with the increase in humidity;while the temperature is high,the electromotive force increases with the increase in humidity.
Abstract: The mode condition of elastic waves in solid-fluid rectangle phononic crystals was derived from the restriction condition of elastic waves,and the mode characteristics of elastic waves were studied on the base of the mode condition.The response of defect modes to mode quantum number and rectangular length was calculated by the characteristic matrix method.Some new defect mode structures different from those of 1D non-confined phononic crystals were obtained.Defect modes of the rectangle doping phononic crystals are determined by mode quantum number;the frequency and full-width at halt-maximum of the defect modes are dependent on mode quantum number and rectangular length.
Abstract: The rule of metal flow during cross wedge rolling was studied through FEM analysis in which some specific points were taken in the work piece and their positions were tracked.The squeezing amount of the small round part on the cam is smaller in the course of rolling,so the amounts of axial and radial metal flows in this area are smaller than those in other deformation zones.Uneven metal flow can influence the forming quality of the work piece.The small round part on the cam meshes with the cam groove on the tool,this kind of meshing function decreases the circumferential torsion applying on the small round part on the cam by the tool,and so the amount of circumferential metal flow in this area is smaller than that in other deformation zones.The centre metal offset of the cam part is bigger than that of other parts of the work piece because the cross-section of the cam is not circular and metal flow in this area is uneven.
Abstract: The influences of the number of rolled strips,the quality of measured data and the tolerance of rolling force prediction were taken into account for building a self-learning speed optimization model of rolling force.The grades and values of thickness and width were considered in the determinant condition of long-term self-learning to reduce the frequency of size change.The information of equipment states which was separated from the data of the last strip was used into the calculation of long-term self-learning factor to improve the continuity of the self-learning model.Offline simulation results show that the accuracy of the rolling force model is improved after the self-learning algorithm is optimized.
Abstract: The projective synchronization of a class of master-slave chaotic system with unknown sector input nonlinearity,unknown uncertainty and external disturbance was discussed.By choosing an appropriate sliding mode surface,a sliding mode controller and adaptive update laws were designed to achieve synchronization based on the Lyapunov stability theory.The proposed controller has strong robust property since it is beyond the impact of unknown uncertainty and external disturbance.Simulation results of the uncertain master-slave Duffing-Holmes systems show the efficiency of the proposed controller.
Abstract: When the standard genetic algorithm is applied into job-shop scheduling problems,it has the common defects of early convergence and easily falling into local minimization.A dynamic double-population genetic algorithm based on domain knowledge is applied into job-shop scheduling problems.Since the optimal schedule is active,the active scheduling technique is used to reduce the search space.Moreover,the forward and backward scheduling strategies are adopted to improve the population diversity by the two subpopulations,respectively.A new chromosome encoding is used to represent the active schedule.With this coding scheme,the initialization strategy,the genetic operations of every subpopulation and the crossover operator between the two subpopulations are proposed.Experimental results of the Benchmark instances taken from literatures indicate that it outperforms current approaches in computational time and quality of the solutions.
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
