Abstract: Studies on the shape of an isolated extraction zone are the basis for investigating the flow laws of caved ore and rock and optimizing a stope's structural parameters. Based on the method of labeled markers, the shape of an isolated extraction zone and its changing law under both infinite and semi-infinite boundary conditions were analyzed, and the reliability and suitability of the ex-pectation body theory were validated through bottom and side drawing tests. On this basis, research on the rate of advance during ore breaking in side drawing was performed at the structural parameter of 18 m×20 m. The results show that the actual shape of the isola-ted extraction zone is not a standard ellipsoid, but more similar to the expectation body. Under both infinite and semi-infinite boundary conditions, the mass drawn has a power function relation with the height of the isolated extraction zone and has an exponential function relation with the radius of the isolated extraction zone. It is suggested that the non-dilution drawing mode and the 4.6-m rate of ad-vance during ore breaking should be preferentially used at the structural parameter of 18 m×20 m.
Abstract: In order to examine the effect of long-term hard rain on the layered gravel soil slope stability of a waste dump, the for-mula derivation relating natural water content, natural unit weight and natural volumetric water content was conducted to help to con-firm the initial suction of the slope rapidly. A numerical analysis model of a waste dump with a layered gravel soil slope based on the finite element method was established to analyze the saturated-unsaturated seepage, coupled stress-pore pressure and slope stability. The results show that a seepage channel will be formed in the slope surface due to its high permeability during the rain. If there exists a water-resisting soil layer in the bottom of the slope, water will come out from the slope toe. The displacement of the slope increases with a decreasing rate during the rain and decreases immediately after the rain. The stability coefficient of the slope decreases rapidly at the beginning of the rain. Then the stability coefficient barely changes till the rain stops as the seepage in the slope surface becomes stable. After the rain, the stability coefficient increases slowly. It is most possible for the layered gravel soil slope of a waste dump to fail in the middle and late stages of long-term hard rain.
Abstract: To study the impact of acid environment on the water-rich filling materials, experimental methods including intensity detection, scanning electron microscopy and X-ray diffraction were used to analyze the macro and micro changes of water-rich filling materials in acid environment and to discuss the corrosion and deterioration mechanism. After soaking for 180 d in hydrochloric solu-tions of pH 1 and pH 3, the compressive strength of the materials decreases by 88.8% and 58%, respectively, compared with that of standard curing for 28 d. After soaking in a sulfuric acid solution of pH 3, the compressive strength decreases by 68%. When the ma-terials were soaked in a sulfuric acid solution of pH 1, the compressive strength is zero. Microscopic tests show that dihydrate gypsum is generated in the materials with the prolongation of immersion time in the sulfuric acid solution. In the hydrochloric acid solution, di-hydrate gypsum is produced only in the solution of pH 1 after soaking for 180 d. The corrosion of the hydrochloric acid solution on the materials is mainly the dissolution corrosion of hardened structure with the neutralization effect of H+. The corrosion of the sulfuric acid solution on the materials is the dissolution corrosion of hardened structure with the neutralization effect of H+ and the expansion corrosion of dihydrate gypsum. The corrosive action of the sulfuric acid solution on the materials is stronger than that of the hydrochlo-ric acid solution.
Abstract: The flotation behavior of typical silicates was studied at wet grinding conditions with different grinding media (iron ball and zircon ball) when dodecylamine or sodium oleate was chosen as a collector. The mechanism of these systems was systematically il-lustrated through measuring the zeta potential of pure minerals and micro scanning by X-ray photoelectron spectroscopy (XPS). When dodecylamine is chosen for a collector, below the optimum pH value, the recoveries of zircon, beryl, spodumene and quartz are higher by zircon balls as grinding media than those by iron balls. Above the optimum pH value, the recoveries of these four silicates are very similar whether by iron balls or zircon balls. However, different grinding methods have little effects on the recovery of feldspar. The recoveries of these five silicates with iron balls as grinding media are higher than those with zircon as grinding media when sodium ole-ate is chosen as a collector. The results show that the zeta potential of zircon, beryl, spodumene and quartz is higher by zircon balls, compared with iron balls. So the recoveries of these four minerals are higher by zircon balls versus iron balls when dodecylamine is chosen as a collector. The Fe content on the surface of these five minerals is higher significantly by wet grinding with iron balls, com-pared with zircon balls. So the recovery of the former grinding methods is higher than the latter because of activation by iron ions.
FeTiO3 and FeTiO3-Fe2O3 solid solution systems were synthesized based on the ceramic method. The synthetic FeTiO3-Fe2O3 solid solutions were subjected to isothermal carbothermal reduction experiments at 1150℃ combining with thermodynamic anal-ysis. The synthetic products were systematically studied by X-ray diffraction and scanning electron microscopy-energy dispersive spec-troscopy. The results show that the synthetic products are all ideal with homogeneous components. From the view of reduction, the smaller the value of x, the molar fraction of FeTiO3, the earlier the carbothermal reduction of xFeTiO3-(1-x)Fe2O3 solid solutions start, and the higher the maximum reduction rate is. As an intermediate phase, pseudobrookite (FeTi2O5-Fe2TiO5 (Fe3Ti3O10)) does not disappear during the whole initial reduction stage until the formation of metal iron (Fe) and ulv-spinel (Fe2TiO4).
Abstract: To solve the problem that the parameter of silicon content ([Si]) in hot mental is difficult to be directly detected and obtained by manual analysis with large time delay, a method of sparse and robust least squares support vector regression (R-S-LS-SVR) was proposed to establish a dynamic model of[Si] with the help of the multi-objective genetic optimization of model parame-ters. First, owing to the issue that the Lagrange multiplier of the standard least squares support vector machine (LS-SVR) is directly proportional to the error term and solves the lack of sparsity, the maximal independent set of sample data in the feature space mapping set was extracted to realize the sparse of the training sample set and reduce the computational complexity of modeling. Next, in view of the problem that the standard least squares support vector machine has no regularization term, a method to improve the modeling ro-bustness was proposed by introducing the IGGⅢ weighting function into the obtained sparse least squares support vector regression (S-LS-SVR) model. Last, the multi-objective evaluation index that synthesizes the modeling residue and the estimated trend was presented to compensate for the deficiency of the single root mean square error (RMSE) index. Based on those, an on-line soft sensor model of hot metal[Si] with the optimal parameters was obtained by using the multi-objective genetic algorithm (NSGA-Ⅱ) with the non-dominated sort and elitist strategy. Industrial verification and analysis show the effectiveness and superiority of the proposed method.
Abstract: The experiment of air flowing high-temperature steel slag particles was done and the experimental correlation of non-di-mensional average Nusselt number was fitted. A three-dimensional numerical simulation of air-cooled high-temperature steel slag parti-cles was performed to study the criterion equations in different conditions and to analyze the influencing factors of air sweeping solid steel slag particles. The experimental correlation and numerical calculation of air-cooled solid steel slag particles were gained, and the error between the experimental and numerical calculation is very small, which verifies the reliability of the SST k-ω model. The results show that the average Nusselt number of slag particles increases with the increase of streaming Reynolds number, particle diameter, and air velocity. The particle diameter effect on the average Nusselt number is larger than the air velocity under the same conditions. The influence of the steel slag particle diameter on the solidification time is the largest, the thermal conductivity is the second, and the air stream temperature is the smallest.
Abstract: To research the oxidation status of billets in a reheating furnace when oxygen-enriched combustion was used, the influence rule of oxygen-enriched combustion atmospheres on the oxidation process of billets was studied by the self-designed experimental platform in the controlled atmosphere. The morphology of the oxide layer at different temperatures was analyzed. The results show that the oxidation process is divided into a fast oxidation stage and a slow oxidation stage. In the high temperature environment, CO2 and H2O have more effect on the oxidation of billets and the billets will be badly oxidized by high concentration of CO2 and H2O. The oxide layer is mainly composed of Fe3O4 and FeO.
Abstract: In-situ observation of the behavior of MnS inclusions in non-quenched and tempered steel with a sulfur mass fraction of 0.065% was performed during tensile tests by using a laser confocal scanning microscope (LCSM) to investigate the effects of the morphology and distribution of MnS inclusions on the tensile property anisotropy of the steel. The result shows that there exist a large number of rod-like MnS inclusions in the forged steel, which have different orientations with the load during transverse and longitudinal tensile tests. The rod-like MnS inclusions separate much easier from the steel base during transverse tensile tests to form initial cracks, and then the cracks spread along the MnS inclusions. In this way, the cracks grow up and lead to the fracture of the steel. In contrast, the MnS inclusions have little effects on the longitudinal tensile properties because the length direction of MnS is parallel to the tensile force. MnS inclusion aggregation promotes the assembling and growth of single cracks, thus accelerating the fracture of the steel during tensile tests.
Abstract: The solidification process of 8Cr13MoV martensitic stainless steel was calculated by using Thermo-Calc software. The solidification microstructure, morphology and type of carbides were analyzed by optical microscopy, scanning electron microscopy and X-ray diffraction. The static continuous cooling transformation curve was measured by Gleeble thermal simulator. The results indicate that the microstructure of 8Cr13MoV includes ferrite and M23C6 under the equalized solidification condition, while ferrite, martensite, retained austenite, M7C3 and M23C6 in the practical solidification condition. The main carbides are M7C3, and a small number of M23C6 with lamellar or dendritic morphology distribute on the grain boundaries, which can be attributed to element segregation. Because of high C and Cr contents, austenite can transform to martensite at a cooling rate of 0.1℃·s-1.
Abstract: A multi-field coupling mathematical model was established to analyze the hot-top semi-continuous casting of a large-scale aluminum alloy of 630 mm in diameter with ultrasonic treatment (UST). The finite volume method combined with the self-com-piled function was used to get the distribution of the acoustic field, flow field and temperature field, and the industrial experimental re-search was also performed. The mechanism of ultrasonic treatment on the grain refinement of the large-scale aluminum alloy produced by hot-top semi-continuous casting was analyzed based on the simulation and experiment results. The simulation results show that ultra-sonic markedly influences the macroscopic physic field. With ultrasonic treatment, an upward recirculation zone forms beneath the end face of the radiation rod, the heat and mass transfer is promoted by the strong turbulence, the sump gets shallower and gentler, the ini-tial solidifying point on the ingot surface in the mold moves down, the transition zone becomes narrower, the width of it in the center drops from 342 mm to nearly 120 mm. The experimental results show that with ultrasonic treatment, the grain size becomes smaller and more homogeneous, the average grain size reduces by 103μm, the gap between the maximum and minimum grain size decreases from 135 to 64μm, and the grain boundary of the solidification structure becomes thinner.
Abstract: To study the microstructural stability of GH4169C alloy with high content of phosphorus and niobium, the microstruc-ture and hardness of GH4169C alloy and GH4169 alloy after long time aging were comparatively analyzed in this paper. These two su-peralloys were subjected to aging treatment at 600, 650, 704 and 720℃ for different times from 30 h to 10000 h. The microstructural evolution of the alloys was characterized by using a field emission scanning electron microscope and a Brinell hardness tester. The re-sults indicate that, at the service temperature of 650℃, GH4169 alloy and GH4169C alloy show excellent structure stability. Howev-er, above the service temperature, GH4169 alloy and GH4169C alloy have poor structure stability. In a short period of time, the two alloys lose stability. In contrast, the microstructure stability of GH4169C alloy is higher than that of GH4169 alloy with aging at 704℃, while GH4169C alloy shows a lower stability compared with GH4169 alloy at 720℃. It is thought that the stability of γ'phase in GH4169C alloy increases with increasing Nb and P contents. GH4169C alloy shows a better microstructure stability than GH4169 alloy at 704℃. However, the content of δphase will also increase with increasing Nb content, leading to the decrease in microstructure sta-bility of GH4169C alloy. At ultrahigh temperature (720℃), the microstructure stability of GH4169C alloy is inferior to GH4169 al-loy. This means that, compared with GH4169 alloy, the modified GH4169C alloy can be used in a higher temperature, whereas the temperature increase is limited, the microstructure stability of GH4169C alloy will decrease at ultrahigh temperature.
Abstract: Ignition-combustion test was carried out and the combustion samples of GH4169 and GH4202 superalloys were ana-lyzed by using optical microscopy, scanning electron microscopy and energy dispersive spectrometry. A model of mass transfer, heat transfer and oxygen transfer was built to analyze the combustion mechanism of the alloys. Some methods to improve the ability of com-bustion resistance for new superalloys were proposed. The results show that both the alloys burn in the test condition, but GH4202 per-forms better than GH4169. Both the alloys burn in liquid phase, there is a combustion section composed of oxides and metal particles in front of the reaction zone, and the burning behavior of elements in the combustion section decides the combustion ability of the whole alloys. A selective combustion rule of elements is present in the combustion section, the elements such as Nb, Ti, Al and Cr will burn with oxygen easily, while Ni is of delayed combust with low heat and can protect the alloy from combustion.
Abstract: Crystalline and amorphous SiO2/Al2O3 nanocomposite powders were prepared by a sol-gel method. The structure and morphology of the nanocomposite powders were characterized by X-ray diffraction and transmission electron microscopy, while the in-frared stealth property was detected by Fourier transform infrared spectroscopy spectrometry. The results show that both the nanocom-posite powders have irregular shapes, in which the average grain size of the crystalline one is about 18 nm. The crystalline nanocom-posite powder is a kind of composite nanomaterial with low infrared emissivity, and its average emissivity is 45.65% in 3-5μm and 46.19% in 8-14μm, which are lower than those of the amorphous one in 2.5-25μm.
Abstract: Accordion-like MnO2-coated graphene composites were successfully prepared by a facile hydrothermal method at 160℃. The as-products were characterized by field emission scanning electron microscopy, transmission electron microscopy, X-ray dif-fraction, energy dispersive spectrometry, BET and Raman spectroscopy. The high capacitance of 138 F·g-1 at 0.2 A·g-1 is achieved with MnO2/graphene composites as a supercapacitor electrode, much higher than that of a single MnO2 or graphene electrode. The ex-cellent electrochemical performance is attributed to the uniform MnO2 nanosheet morphology, large surface area of graphene and stable chemical bonding of MnO2 on the graphene substrate.
Abstract: A three-dimensional (3D), macroporous and highly conductive grapheme foam (GF) was synthesized by chemical vapor deposition using a nickel foam as a template. ZnO nanowire arrays were vertically grown on the surface of the prepared GF using hydrothermal synthesis. The morphologies and structure of the ZnO NWAs/GF were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction and Raman spectroscopy. The results show that the prepared GF is high-quality and defect free, and the ZnO NWAs with uniform size vertically grows on the surface of 3D GF. The ZnO NWAs/GF was used as an elec-trochemical electrode for determining levodopa (LD). The results of electrochemical tests show that the oxidation current of LD is well linear with its concentration in the range of 0-80μmol·L-1 with a sensitivity of 0.41μA·(μmol·L-1)-1, and the ZnO NWAs/GF electrode also shows good reproducibility and stability. The ZnO NWAs/GF can detect LD with high selectivity in the presence of uric acid.
Abstract: The viscosity of epoxy resin was tested by viscometer, and an engineering viscosity model was constructed by the fitting method. In this simulation, the viscosity model was applied to predict the flow process of epoxy resin with different initial temperatures by using PAM-RTM. The influence of the viscosity change of epoxy resin on resin transfer molding (RTM) was discussed in detail. The results show that the filling time of RTM decreases first and then increases as the initial temperature increases, and the shortest filling time is acquired at 40℃. The viscosity change of epoxy resin has remarkable influence on the RTM of large scale structure.
Abstract: An analytical model of section elastoplastic state evolution paths was built for bimetal composite plates under different assemble patterns during bending and leveling based on engineering elastoplastic mechanics. Based on this model, the bending and re-bounding process of stainless steel clad plates was analyzed, the section reverse yield phenomenon during rebounding was explained, and the bending process of stainless steel clad plates was contrasted to that of single material sheets. The results show that five elasto-plastic states of the bimetal composite plate section occurs along with different neutral layer offset laws, and the residual stress distribution is more uneven and may enter the reverse yield state after bending. The relative difference of bending moment between the bimetal composite plate and the single sheet increases with increasing yield strength ratio, and the absolute value first increases then decreases with increasing curvature.
Abstract: Aiming at the characteristics of rolling bearing fault vibration signals and considering the merits of variational mode decomposition in mono-component separation and calculus enhanced energy operator in transient impulse detection, this article introduces a new method termed fault diagnosis of rolling bearings based on variational mode decomposition and calculus enhanced energy opera-tor. Firstly, the vibration signal is decomposed into several intrinsic mode functions by variational mode decomposition to reduce the noise interferences and to satisfy the mono-component requirement by energy operator. Then, the sensitive intrinsic mode function containing the main fault information about the bearing is selected by the proposed criterion. Finally, the impulses are strengthened using calculus enhanced energy operator, and the bearing fault is diagnosed by the time domain waveform and Fourier spectrum of the sensitive mono-component instantaneous energy. The analysis results show that the proposed method can effectively diagnose the rolling bearing faults.
Abstract: For a wallboard in an electrostatic precipitator casing playing stressed skin effect under vertical uniform pressure on the top, the failure mode and bearing capacity were investigated by nonlinear finite element method. The influences of structural factors such as wall thickness, wall width, stiffener spacing, column brace spacing and column section size on the wallboard bearing capacity were analyzed. The results show that, shear yielding failure of the wallboard occurs when the stressed level of the column is comparatively lower. Shear yielding failure and compression yielding failure occur simultaneously when the stressed level of the column is medium. Compression yielding failure occurs when the stressed level of the column is comparatively higher. Under the equal column stressed level, the bearing capacity of the wallboard increases with the increase of wall thickness and with the decrease of wall width, stiffener spacing or column brace spacing. The bearing capacity of the wall increases as the column stiffness is increased resulting from the enlargement of column section and its stability increases.
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
