Abstract: Geo-stress distribution in a mining area was analyzed by means of a partial least squares regression method (PLSRM). Based on data measured in Wushaoling tunnel ridge section, a numerical simulation of the initial geo-stress field around the area was performed using the commercial software ANSYS. Partial least squares regression analysis was carried out through actual measurement data and calculation results of geo-stress, and then fitting data was ready. Compared with the traditional least squares method, due to the advantage of principal component analysis in applying PLSRM, the present method decreases the regression error caused by the correlation between response variables. It can more effectively reflect the features of discontinuous geo-stress distribution and thus provides effective data support for establishing the geo-stress field.
Abstract: The equipment and model test rig were designed for the chemical ignition of underground coal gasifi-cation (UCG) in a deep coal seam after analyzing the coal seam condition and coal quality which were suitable for UCG ignition. When the volmne ratio of silane to oxygen in the igniting composition keeps 1:3.33 and the pressure of the igniting composition maintains 0.3 MPa, the temperature rise rate in the ignition zone reaches 600℃·h-1 the maximum temperature rises to 800℃, which can achieve UGC ignition in a deep coal seam. The temperature field of the coal seam was simulated on computer by the numerical simulation software FEMLAB. When the temperature in the ignition zone of the coal seam sets to 1366℃, the growth rate of the temperature field is 28.75℃·min-1, which is consistent with the temperature change trend in model experiment.
Abstract: Based on coal seam deep-hole cumulative blasting experiments in Jiulishan Coal Mine of Jiaozuo Coal Group, the law of stress change in a blasting coal body was analyzed by numerical simulation. It is found that cumulative blasting effect leads to the increase of peak stress and enlarges the crack zone range of the coal body. Drilling parameters for cumulative blasting, such as blast hole diameter, blast hole spacing, distance between the blast hole and the adjacent gas drainage hole, and distance from the blast hole to the coal seam roof and floor, were determined by optimization. Field experimental results show that after using these optimized drilling parameters the cumulative blasting not only gets remarkable permeability increasing effect but also ensures blasting safety.
Abstract: Two rock burst risk index functions were built based on stress and stress change rate respectively by using a parabolic membership function model. The burst risk index with multiple factors was calculated under the maximum membership degree principle. The spatial distributions of bearing pressure and burst risk of the working face were demonstrated comprehensively and directly by cloud pictures. Finally a cloud-based risk early warning system was obtained. This system had been applied in more than 20 coal mines with risk bursts and achieved good results.
Abstract: Since it is difficult to extract nickel from laterite ores with low nickel grade by traditional beneficiating methods, the microstructure and phase transformation of a nickel laterite ore with the nickel grade of 1.49% were investigated by using a selective reduction roasting method at different roasting temperatures and time. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) results show that after selective reduction roasting at different roasting temperatures and time, nickel-ferrous minerals in the nickel laterite ore are reduced to ferronickel gradually, while ferrous minerals are mainly transformed to wustite. Silicate nfinerals exist in the formation of olivine in the roasted ore. Reduction roasting and magnetic separation experiments illustrate that when the nickel laterite ore with the addition of 7% NCS as the additive and 2% soft coal as the reductant roasts for 50 min at 1200℃, the ferronickel product obtained from magnetic separation has the nickel grade of 9.78% with the nickel recovery of 92.06%, and the recovery difference of nickel and iron is 62.51%. The experimental result indicates that nickel-ferrous and ferrous minerals were reduced selectively.
Abstract: The reduction kinetics tests of Shougang sintering iron ores were performed from 1173 to 1373 K with 100% CO by thermogravimetric analysis, from which the values of reduction reaction apparent activation energy were determined. It could be predicted that the reduction of iron ore sinter is controlled by interracial chemical reaction at the initial stage, and solid-state diffusion at the final stage. According to the unreacted core model and the kinetic model of solid-state diffusion separately, the mutational timing of each rate controlling step was given at various temperatures by using phasewise analysis. The reaction rate constants and solid diffusion coefficients were derived from the kinetic formulas at various temperatures. Changes in morphology were analyzed with an optical microscope, and the mechanism of reduction kinetics was also verified. At the same time, the use of the volume-dwindled unreacted core model in the diffusion stage was proved to be feasible.
Abstract: The reduction process of V-Ti magnetite concentrate pellets was studied under the simulated condition of blast furnaces. Phase compositions in the pellets at different reduction temperatures were determined by X-ray diffraction analysis. The microstructure change of the pellets during reduction was observed by optical microscopy and scanning electron microscopy. The distribution of different elements in oxides was identified by energy dispersive spectrometry. It is found that iron-titanium segregation in the pellets during reduction affects the reducibility of the pellets, and the formed ilmenite spar of high titanium content increases the difficulty in reduction of iron oxides. The dense iron shell formed at high temperature hinders the reduction of inner oxides, leads to stagnation of reduction, and makes the reducibility of the pellets poor at high temperature. When the inner liquid melt dripping down, the oxygen potential increases in the lower part of the blast furnace, which decreases the generation of Ti(C, N).
Abstract: The influence of three effective nucleation particles of Ce2O3, ZrO2 and MgO based on calculations from different heterogeneous nucleation theories oil the refining solidification structure of 16Mn steel was studied by induction furnace contrast experiment. The equiaxed crystal ratio of ingots increases from 32%) to 37% by heterogeneous nucleation MgO particles which are only consistent with the criterion of the lattice disregistry theory; it increases to 40% by ZrO2 particles which only consist with the criterion of the electrostatic effect theory; and it increases to 44%, by Ce2O3 particles which follow the criteria of both the lattice disregistry theory and electrostatic effect theory. Among the above three heterogeneous nucleation particles, Ce2O3 has the maximum ability to refine the solidification structure of 16Mn steel. The prior austenite grain size and microstructure of 16Mn steel are refined in different degrees alter the at)ove three kinds of nucleation particles form in molten steel.
Abstract: The cold deformation characteristics of 316L stainless steel were investigated by compression testing with different deformations. The true stress-strain model and work-hardening model were obtained by fitting the test data with a modified Ludwik model. It is found that the modified Ludwik model can formulate the relationship between stress and strain of the stainless steel. The flow stress of the stainless steel during cold deformation is divided into three stages:the high work-hardening stage, the stable work-hardening stage, and the low work-hardening stage corresponding to the deformation less than 0.02, between 0.02 and 0.29, and greater than 0.29, respectively. Electron microscopy results indicate that the work-hardening mechanism and microstructure characteristics of the stainless steel are different in the three stages.
Abstract: The effect of the content of molybdenum as an alloying element on the corrosion resistance performance of weathering steel was investigated by microstructure observation, cycle immersion corrosion test, rust layer micro-analysis and electrochemical impedance spectra techniques. It is found that molybdenum can promote the formation of bainite in the steel and the rust layer denser. The rust layer has a better protection on the steel substrate and increases the corrosion resistance of the steel. With the increasing of molybdenum content in the steel, the corrosion potential of the rust layer on the steel shifts positively, the self-corrosion current density decreases, the anodic dissolution of the rust layer is impeded, which makes the rust layer better protective.
Abstract: The effects of Ca2+ concentration on the corrosion behavior of X80 steel in Hami soil simulated solutions were investigated by using weight loss measurements, electrochemical testing, scanning electron microscopy (SEM), and X-ray diffraction (XRD). When the steel is immersed in the simulated solutions with different Ca2+ concentrations for 60 d, uniform corrosion occurs on the steel surface and the corrosion products mainly consist of β-FeOOH. The corrosion rate of the steel in the simulated solution gradually increases with the decrement of Ca2+ concentration. When the steel is immersed in the simulated solution with the Ca2+ concentration of 63.5 mmol·L-1 for 180 d, calcium salts continuously deposit on the steel surface to form a crystalline salt layer with the increasing of time. The calcium salt layer effectively hinders the migration process of dissolution oxygen, then promotes the formation of an oxygen concentration cell under its coverage region, and finally leads to the generation of pitting corrosion on the steel surface. At the same time, the compactness of the calcium salt layer that deposited on the inner corrosion product is gradually improved during this process, which can inhibit the corrosion effects of Cl- and dissolved oxygen on the steel to a certain extent, and also makes the uniform corrosion of the steel gradually slow down.
Abstract: The dieless drawing forming of BFel0-1-1 alloy tubes with continuous columnar grains was performed in a temperature range of 750-900℃ at a drawing speed of 0.6-0.9 mm·s-1. The mierostructural evolution and mechanism of the tubes after the deformation was studied by optical microscopy, transmission electron microscopy, and X-ray diffraction analysis. It is found that the straight grain boundaries of colmnnar grains in the tubes become zigzag after dieless drawing within the process parameters of this paper. The sawtooth depth increases both with increasing drawing speed and temperature. Dislocations tend to pile up adjacent to grain boundaries and then travel over the grain boundaries, leading to gliding steps at the grain boundaries and consequently zigzag grain boundaries. Accompanied with the gliding deformation, thick continuous columnar grains start to rotate, increasing the zigzag degree. The high thermal activation energy and deformation-stored energy failed to release in time are the cause of maintaining continuous columnar grains in BFe10-1-1 alloy.
Abstract: A carbonate co-precipitation method was used to synthesize Li[Li0.17Mn0.58Ni0.25]O2 amples with different morphologies via controlling the crystal process. The Li[Li0.17Mn0.58Ni0.25]O2 samples were characterized by X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), field emission scanning electron microscopy (FESEM), galvanostatic charge-discharge testing, and electrochemical impedance spectroscopy (EIS). It is found that the Li[Li0.17Mn0.58Ni0.25]O2 samples, with high crystallinity, can all be indexed as a α-NaFeO2 phase (space group R3m). Moreover, the sample with the hexagonal primary particles aggregated along with the long axis shows a much better rate capability than the other. Li[Li0.17Mn0.58Ni0.25]O2 delivers the initial discharge capacities of 205.4, 195.5 and 158.5 mA.h·g-1, in the voltage range of 2.5-4.8 V at the rates of 0.5C, 1.0C and 3.0C, respectively. After 100 cycles, the discharge capacities are 203.5, 187.2and 151.2 mA.h·g-1, which correspond to 99%, 96% and 95% retention of their initial capacities. The special aggregated morphology of Li[Li0.17Mn0.58Ni0.25]O2 particles contributes to the reduced charge transferring impedance and the improved rate capability. Additionally, the electrochemical properties of the materials in different potential windows were also comparatively studied.
Abstract: Magnesium sulfate heptahydrate was made from salt lake magnesium chloride and sulfuric acid, then anhydrous magnesium sulfate was obtained from magnesium sulfate heptahydrate by dehydration, and finally high-purity magnesia was prepared from anhydrous magnesium sulfate by natural gas reduction pyrolysis. The effects of pyrolysis temperature, pyrolysis time, particle size, and gas flow rate on the conversion rate of magnesium sulfate were investigated by single factor experiment. These experimental parameters were optimized by orthogonal experiment. The reduction pyrolysis product was analyzed and characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The optimal experimental parameters are as follows:the pyrolysis temperature is 1000℃, the pyrolysis time is 30 min, the particle size of anhydrous magnesium sulfate is 75 μm, and the flow rate of natural gas is 25 mL·min-1. The pyrolysis temperature is the main factor which influences the conversion rate. Under the optimal condition, the conversion rate of magnesium sulfate reaches 99.27%, and the purity of magnesia is 99.5%. The unimolecular MgO features well-distributed particle size, porous and fluffy surfaces, and high specific surface area.
Abstract: Medium temperature coal tar pitch with quinoline insoluble compounds removed was used as the raw material. Coal-based needle coke was prepared in a home-made reactor with a magnetic field. The temperature and the maximum pressure for the formation of the mesophase under the magnetic field were discussed during the preparation of the needle coke. The structure and electrochemical properties of the needle coke prepared under different conditions were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). Under the action of the magnetic field, when the maximum pressure is 0.4 MPa and the maximum temperature is 520℃, the needle coke has the best structure and electrochemical properties.
Abstract: Compared to the explosion cladding method and explosion-rolling cladding method, TA1/Q345 clad plates produced by the vacuum rolling method can better meet the demands of large-scale production. A TA1 titanium alloy sheet was packed between two Q345 steel plates to obtain a composite slab. The composite slab was vacuumized to 0.1 Pa and then sealed. At temperatures of 840 to 930℃ the composite slab was rolled to a cladding plate. The mechanical properties of the cladding plate were tested, and the interracial microstructure and bonding were analyzed by scanning electron microscopy, X-ray diffraction, and micro hardness tester. In the laboratory condition, the shear strength of the cladding plate is above 159 MPa, more than the standard requirement of Class 1 clad plates. The bonding mechanical properties are excellent when the rolling temperature is 870℃. During rolling at 900℃ and 930℃ there occur phase transitions in the titanium and a great deal of intermetallics form near the interface. Too much deformation resistance difference between the titanium and the steel brings about more uncoordinated deformation and internal stress near the interface, which decrease the shear strength of the interface. The lower shear strength at 840℃ is due to the low rolling temperature, which leads to slow element diffusion near the interface.
Abstract: Carbon nanotubes/aluminum (CNT/Al) composites were prepared by magnetic stirring in combination with spark plasma sintering. Their microstructures were characterized by scanning electron microscopy and transmission electron microscopy. Experiments were performed to investigate the inechanical properties, friction and wear character-istics, electric conductivity and thermal conductivity of CNT-free and CNT-added specimens. It is found that when the mass fraction of CNTs is 1%, CNTs can uniformly disperse within the Al matrix and interracial bonding at the CNT/Al interface is strong. In comparison with the unreintbrced Al specimen, the tensile strength and hardness of the CNT/Al composites increase by 29.4% and 15.8%, respectively. When the CNT/Al composites achieve the optimal mechanical enhancement and antifriction effect, their electrical conductivity only decreases by 8.0% compared with pure Al. The thermal conductivity of pure A1 could be enhanced with the incorporation of CNTs, but this enhancement effect is not obvious.
Abstract: According to a reasonable hypothesis, the rolling deformation zone of H-beams was divided into two regions and the velocity field in each deformation region was set,lp by the flow function method. A rolling energetic parameter model of H-beams based on the flow function method was established. Parameters of deformation regions were optimized with the Powell method to minimize the value of total power. Finally, the rolling energetic parameters of H-beams were obtained. The Gauss integral method was used to get more accurate results. Calculation results show that errors between the results of the model and the finite element model verified by test do not exceed 1.53% when the elongations of the web and flange are the same. If the hypothesis is not satisfied, the model in this paper also has well calculation accuracy with proper modification. When the ratio of elongation between flange and webA is around 1, the trend of the model's rolling force is the same as the results of the finite element model. When the arm coefficients are reasonable, the rolling force of the model matches with the results of the finite element model well.
Abstract: The spur gear with an asymmetric involute is a new kind of gear. Its bending stress could not be calculated by existing analytical methods. Through analyzing the tooth profile characteristics, a solving method of bending stress for the gear was proposed on the basis of the plane cross-section method, and an analytical formula was derived to calculate the root bending stress of tile gear. Spur gears with symmetric and asymmetric involutes, with the same module and teeth numbers, were as the research objects. In the same working conditions, the bending strengths of the two gears were studied by the analytical method and finite element method during forward and reverse rotation. Five special positions were selected during the meshing period and their bending stresses on both sides were analyzed comparatively. Finally, by the ladder loading fatigue test method, the two gears were tested in tooth root bending fatigue strength experiment. The experimental data verified the theoretical analysis result.
Abstract: Nowadays, the complex organization mode of multi-steel grade production exists in many steelmaking plants in China. The matching between metallurgical furnaces and casters has effect on the smooth running of production in the workshops. With a typical steel plant in China as an example, the issue about furnace-caster matching was analyzed based on previous studies. The concept of equivalent period was proposed to solve the furnace-caster matching mode in combination with product structure. The index of furnace-caster matching degree was suggested to evaluate the furnace-caster matching mode.
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
