Based on the condition of a fully-mechanized working face, two research means, i. e. microseismic monitoring and FLAC3D numerical simulation, were introduced to study the formation and evolution of floor failure and water conducted pathways caused by coal mining. The space-time evolution law of microseismic rupture events was studied for the floor rock mass during the changing process of the mining stress field. The process of inoculation, development and penetration of potential water channels was also revealed under the condition of coal mining. Field microseismic monitoring shows that microseismic event accumulation is directly proportional to drilling footage. The number of microseismic events to some extent reflects the disturbance degree of mining activities on the floor rock. The distribution of microseismic events is intensive near the coal mining face, which shows that the floor rock mass is seriously damaged during coal mining. The greatest failure depth of the floor estimated from mine microseismic monitoring is 15 m. Numerical analysis indicates that due to mining disturbance effect, the rock stress around the mine stope is redistributed during coal mining. The abutment pressure increases in front of the coal mining face and the stress reduces in the mined areas. Stress concentration and release make contribution to the destroying of the floor rock. The maximum failure depth is up to 14 m calculated from numerical simulation.
Abstract: In view of the problems of ‘blind spots’ in complicated goaf detecting by using laser scanning and point cloud density distribution inhomogeneity, this article introduced multi-point laser scan and point cloud merging and compression. Multi-point scan in complicated goaf avoided ‘blind spots’ and densified sparse point cloud regions. The merging algorithm of point cloud data was put forward based on a common coordinate system and the least-squares principle to solve the target transformation matrix. After the distribution rule of point cloud concentration areas was analyzed, the scattered point cloud compression algorithm was proposed, in which the point cloud was divided into portions along the y direction firstly, then intralayer data were divided by the extreme values of x and z, and each point was sorted on the x value and screened on step k. Error analysis of an instance of large versed goaf shows that the merging algorithm based on the least-squares principle will achieve high precision with an error range of about 0.1 mm. The compression algorithm can achieve a compression proportion of 15% to 25% and ensure the integrity of 3D boundary information at the same time.
Abstract: To obtain the cavity volume accurately, a calculus algorithm of cavity volume was researched according to data surveyed with a three-dimensional laser scanning system. In the algorithm, the main sectioning axis is fixed first, the model is cut by a group of equally interval parallel planes, and the intersection points are got, so the initial edge contour line is generated by using a convex hull impressed method. Then other intersections within the initial edge contour line are added to the cross-section to form a complete cross-section shape. Finally the volume of the model is got by superposition of the triangular directed area. Experimental results show that the algorithm program is stable and has a higher accuracy, and can be used as an effective algorithm of cavity volume.
Full tailings cemented backfills were produced by taking Daye iron ore tailings as a raw material and cement as a cementing material. The relations of the backfills' strength with slurry concentration, sand-to-lime mass ratio and curing period, together with the sensitivity of the backfills' strength to these influencing factors, were studied by using single-factor five-level experiment design. The strength of the backfills follows an exponential function with slurry concentration and curing period, but a linear function with sand-to-lime mass ratio. Moreover, the sensitivity of the backfills' strength to curing period is the highest, but is the weakest to sand-to-lime mass ratio. Compressive failure test results show that destruction of the backfills goes through four stages, including micro-crack closure stage, linear elastic stage, micro-crack propagation stage, and crack coalescence stage.
Abstract: To prevent the accidents of mine tailing ponds, a complex network of relevance between accidents and associated hazards was established and a system dynamics (SD) model of hazard states and risk evolution was illustrated for mine tailing ponds. The complex network and SD model were combined and applied in a case study. The results demonstrate that the hazard and risk evolution rule of mine tailing ponds can be precisely characterized by an ingenious combination of the complex network, tristate method, and SD model. The key findings include hazard action relations, evolution pathways, risks levels, etc. By means of a case study on the Linsteel 980 Ditch tailing pond, the simulation results coincide with the actual development of accidents and also effectively demonstrate the accident evolution diversifications of mine tailing ponds in time and space as well as the risk level, so the model can be used to predict the occurrence of risks.
Abstract: To explore the mechanism of reduction and melting-separation in carbon-bearing pellets, cold-bound pellets were made of analytically pure Fe2O3, oxides, and different reductants, and their isothermal reduction experiment was carried out. The influences of reduction parameters, such as temperature, reduction time, carbon/oxygen mole ratio, and type of reductants, on the metallization degree and melting behavior were discussed on the basis of experimental data. The microstructure and phase transformation of the pellets were characterized by X-ray diffraction and scanning electron microscopy. It is found that the pellets cannot be molten well at too low or too high temperature. An increase in carbon/oxygen mole ratio can improve the reduction and melting rate of the pellets. The appropriate temperature, carbon/oxygen mole ratio, and reducing agent are 1400℃, 1.2, and pulverized coal, respectively. The reduction and melting-separation reactions of the pellets contain direct reduction reaction, indirect reduction reaction, carbon gasification re-action, carburization reaction and iron melting reaction, and finally realize the separation of iron and slag.
Abstract: The composition, distribution and microtopography of titaniferous inclusions in Ti-IF steel during steelmaking and in the casting billets were investigated systematically, and the evolution of the titaniferous inclusions was described subsequently. Both thermodynamic analysis and experimental results indicate that TiN could not precipitate in the steelmaking process, while the titaniferous inclusions exist in the form of a combination of titanium oxides which mainly consists of TiO2 and other oxides. In the solidification process of continuous casting, TiN inclusions precipitate in the heterogeneous nucleation way due to the decrease of liquid steel temperature and the segregation effect. The main non-metallic inclusions in the casting billets are large size Al2O3 particles and TiN-Al2TiO5-Al2O3 triple-layer complex inclusions with the middle layer of Al2TiO5. The nucleation and growth process of TiN-Al2TiO5-Al2O3 complex inclusions is that[Al],[Ti] and[N] form the middle layer of Al2TiO5 firstly on the Al2O3 core surface, then TiN nucleates and grows up on the Al2TiO5 surface. Since TiN inclusions in the casting billets are difficultly removed during the steelmaking process, it is feasible to control titaniferous inclusions in the steel by inclusion modification.
Abstract: The morphology, size and distribution of interphase precipitation particles formed in Ti- Mo-bearing low-carbon steel after isothermal transformation were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area diffraction analysis. The mechanical properties of the hot-rolled plate were also tested. The results show that as the isothermal temperature decreases, the strength and the ratio of yield strength to tensile strength increase, but the ductility decreases. Two different types of interphase precipitation carbides, planar interphase precipitation and curved interphase precipitation, were observed in the TEM specimens. The average diameter of these carbides is 4.30 nm with an average aspect ratio of 1.375. Interphase precipitation isothermally treated at 650℃ for 1 h can strengthen the ferrite phase by above 400 MPa.
Abstract: This article focuses on texture evolution in 50W270 high-brand non-oriented silicon steel produced by CSP in hot rolling, normalizing, cold rolling, and annealing processes. The texture in the whole process was measured and analyzed by electron back-scatter diffraction. It is found that the texture along the thickness direction in hot-rolled strips changes obviously:there are mainly copper, brass, and Goss textures in the surface layer; the 1/4 layer has weak Goss texture and rotating cube texture; γ-fiber texture, rotating cube texture, and weak α-fiber texture appear in the center layer. Compared with hot rolled strips, the texture changes little for the normalized strip surface and 1/4 layer, but rotating cube texture and α-fiber texture are enhanced in the center layer. Quite strong α-fiber texture and γ texture appear in every layer for cold-rolled strips. Compared with cold-rolled strips, α-fiber texture almost disappears, but cube texture and Goss texture appear in annealed strips.
Abstract: The high temperature oxidation behavior of oxide dispersion strengthened 310 (ODS-310) alloy was investigated by oxidation test. The morphology, composition and phase of the oxidation layer were analyzed by scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. It is found that the oxidation kinetic curves at all the temperatures approximately obey the parabolic law. After oxidizing at 700 and 900℃ for 100 h, the alloy shows a good resistance to oxidation. But after oxidizing at 1100℃, the oxide layer becomes thicker with the phenomenon of porosity and discontinuousness, which is harmful to the oxidation resistance. The oxidation degree of the alloy increases with the rising of temperature and the prolonging of time. Energy dispersive spectroscopy and X-ray diffraction analysis results indicate that the phase of the oxide layer is Cr2O3.
Abstract: An AlCrN coating was prepared on the surface of a Ni-Fe-Cr-based superalloy by cathodic arc ion plating. The morphology, energy spectra, phase composition, and binding energy of the coating surface and interface were analyzed by means of scanning electron microscopy, energy disperse spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The high temperature oxidation resistance and mechanism of the coating were studied by high temperature oxidation tests at 800 and 900℃. It is found that the coating is mainly composed of Al, Cr and N elements, showing strong preferred orientation of AlN after adding Al element. The peak spectrum of Al2p is Al-N and Al-O binds, the peak spectrum of Cr2p is Cr-O and Cr-N binds, and the peak spectrum of N1s is in the form of Cr-N and Al-N, also contains a small amount of N-Cr-O and N-Al-O bonds. The oxide in the coating surface is Cr2O3 after high temperature oxidation, which has good protective effect on the Ni-Fe-Cr-based superalloy.
Abstract: The characteristics of precipitates and plastic damage in GH4710 alloy, both under original and different hot-forming conditions, were studied based on thermomechanical calculation by the Thermal Calc software and microstructural analysis by optical microscopy and scanning electron microscopy. The relationship between the precipitation characteristic and plastic damage evolution during the hot-forming process was also discussed. It is found that the equilibrium phases of the alloy mainly consist of γ', MC and M23C6 carbides, and γ/γ' eutectic structure. The MC carbides and eutectic structure act as damage sources during the deforming process, leading to the nucleation and connection of micropores, and then the propagation of macrocracks through the grain boundaries. The γ' phase precipitates preferentially at the MC and eutectic structure region of as-solidified structure, which impedes the nucleation and expanding of micropores by the γ/γ' coherent stress distribution, resulting in a lower plastic damage at sub-solvus deformation temperatures and a higher plastic damage at super-solvus deformation temperatures.
Abstract: The microstructure and magnetic properties of 38UH, 42SH and N50 magnets with and without Dy diffusion treatment were contrastively investigated. The intrinsic coercivity of the magnets by Dy diffusion increases over 400 kA·m-1 correspondingly but the remanence shows little decrease. The maximum energy product enhances with the increases in intrinsic coercivity and square degree. The evident enhancement of the intrinsic coercivity of the magnets results from the increases in magnetic anisotropy and nucleation field of the extensive layer of Nd2Fe14B grains. Based on the Fick's first law, the depth, mass concentration and mass fraction of Dy element with process time at a certain temperature can be approximately calculated.
Abstract: Carriers of TiO2, ZrO2 and TiO2-ZrO2 with different ratios were prepared by sol-gel method. Some manganese-cerium (Mn-Ce) active components were loaded on these carriers by ultrasonic immersion. The catalysts were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, and Brunauer-Emmett-Teller (BET) method. The activity of the catalysts was studied under the condition of low-temperature catalytic reduction of NOx with ammonia as a reductant. The results show that the TiO2-ZrO2 (3:1, molar ratio) carrier was a mesoporous material, the particle size is smaller, the particles are highly dispersed, and the specific surface area reaches up to 151 m2· g-1. By doping ZrO2, Zr4+ ions replace Ti4+ ions and enter the lattice, leading to TiO2 lattice distortion. The addition of ZrO2 inhibits crystal transfer from anatase to rutile phase, and so the thermal stability of this carrier improves. Furthermore, the active components mainly exist in amorphous state and the Ce3+/Ce4+ redox couple appears on the carrier surface, thus the catalytic reduction activity at low temperature improves. The highest activity of the 10% Ce(0.4)-Mn/TiO2-ZrO2 (3:1) catalyst is obtained under calcination at 550℃. At 140℃ and a space velocity of 67000 h-1, the conversion rate of NOx reaches 99.28%. The 10% Ce(0.4)-Mn/TiO2-ZrO2 (3:1) catalyst provides strong anti-poisoning capacity to H2O and SO2 in the presence of 10% H2O alone, or 10% H2O with 2×10-4 SO2 at 140℃.
Abstract: The porous structures and their evolution of graphitic cathode materials at various baking temperatures were investigated using the image analysis method. The porous structure parameters, such as porosity, pore size distribution, aspect ratio, specific surface area, and pore connectivity, were statistically calculated and the fractal features showing the degree of porous complexity were also analyzed. It is found that the porosity increases with increasing baking temperature, while the specific surface area, aspect ratio, and connectivity first decrease and then increase. The porous structure evolution of graphitic cathodes abides by the law of fractal behaviors and hence an evolution model has been proposed. This result indicates that the image analysis parameters and the fractal dimension can apply for characterizing the degree of porous structure evolution when subjected to a given baking temperature.
Abstract: Tuyere sampling was conducted in a COREX melter gasifier during down time. Through the detection analysis of tuyere samples, the effect of gas phase on the liquid permeability of the stock column was expressed by the reciprocal of pressure difference degree, while the effect of liquid phase on the liquid permeability was expressed by the product of voidage and temperature intensity. Based on those, a formula was established to characterize the liquid permeability of the stock column. Investigations on 2 batches of tuyere samples show that there is a compatible corresponding relation between the liquid permeability index and residue iron of tuyere samples at different positions in the melter gasifier. Moreover, some influencing factors of the liquid permeability index were analyzed. it is found that residual acid gangue can directly fall into the hearth in unsteady furnace conditions, which leads to the slag melting temperature in a certain position over 1500℃ and thus affects the fluidity of iron slag. Several technical measures are proposed, such as increasing material layer thickness, adopting a proper slagging regime, and controlling uniform gas flow distribution, to provide helps to improve the liquid permeability of the stock column in the melter gasifier.
Abstract: A full scale water model of continuous casting was built to investigate the effect of solidified shell on fluid flow and level characteristics under high speed casting. It is found that a slight asymmetry of fluid flow occurs in the model with solidified shell. Furthermore, the average level fluctuation and the meniscus velocity of the mold with solidified shell is 31% and 35% larger than those without solidified shell at a high casting speed of 2.4 m·min-1, respectively. The deformation of the top level profile of the mold with solidified shell is also larger than that without solidified shell, which can be vulnerable to slag entrapment. In addition, the fast Fourier transformation analysis of level oscillation shows that the amplitude of high frequency fluctuation in the mold with solidified shell is larger than that without solidified shell due to a narrower space in the lower part of the mold, indicating that a more turbulence energy exists in the upper recirculation zone than that without solidified shell and thus results in a higher level fluctuation and a larger surface velocity. So taking solidified shell into consideration is necessary to minimize the difference between the model and actual steel casters.
Abstract: Equivalent heat transfer coefficients are key input factors for work roll temperature field analysis models in hot strip rolling, and the coefficients are usually calculated with genetic algorithms, but the rolling process of alternating material and width in a work roll service period for a 1800 mm hot strip rolling mill makes the coefficients difficult to be calculated accurately. The surface temperature distributions of a serviced work roll under multiple rolling schedules were taken as the optimization goals, and the equivalent heat transfer coefficients with a higher adaptability were obtained by using a multi-objective genetic algorithm. The optimizing process was improved by changing the genetic operators, which avoided the disadvantages of premature convergence and local convergence. The optimization model was proved effectively by comparing the simulation results with measured data. The effects of rolling parameters on the thermal crown were analyzed with the optimization model. It is predicted that under alternating width rolling, the thermal crown exponentially increases; but under alternating material and width rolling schedules, the thermal crown has a fluctuation of 6 to 21.8 μm between the continuous two strips, and towards stability gradually.
Abstract: A framework of multi-agent joint firefighting and rescue operation was proposed by applying the multi-agent theory and technology to studies on joint firefighting and rescue operation. It can realize information exchange between the commanders and display the interacted course of operation. Based on the description of command agent, operation agent and environment agent in the system, interaction rules between the agents and between the agent and environment were defined to describe the system's interrelation, a multi-agent coordination algorithm was given, and a joint firefighting and rescue simulation model was built. At last, a simulation is made on SWARM software to validate the proposed model.
Abstract: The 1-hour average mass concentration of particulate matter from March to May 2013 obtained from monitoring stations was used to characterize the concentration variation of particulate matter with time scale and its regional distribution in the Beijing area. The mass concentrations of PM2.5 and PM10 were studied to find out their seasonal variation characteristics, and their spatial resolution was improved. Based on that, the possible factors and pollution sources of particulate matter were then preliminary discussed. The results show that there are a periodical variation and a significant correlation on the average mass concentration of particulate matter from March to May in the Beijing area. Interpolation results on the particulate concentration distribution by using MATLAB spatial interpolation tools have certain precision to extrapolate and reveal the regional pollution characteristics. According to analysis, the main factors affected particulate concentration in the Beijing area are cold front and snowfall in late winter, dust and wind in spring, rainfall and hot-humid weather in early summer, and so on. The particulate concentration distribution shows an overall trend of high in the south and low in the north, and the pollution sources are very likely caused by local anthropogenic sources as well as the transmission of surrounding area. The conjoint analysis on time series and spatial interpolation of particulate concentration has significance for further research of the time-space relationship of particulate matter, and it also provides a method for understanding regional pollution characteristics.
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
