Abstract: Primary selection of mining methods was handled as a classification problem with Chengchao Iron Mine as the engineering background.Fuzzy clustering was used to make primary classification in accordance with the similarity degree of technical factors.This can decrease the subjective arbitrariness of using the engineering analog method and improve the scientific accuracy of the primary selection.In consideration of economic benefit,resource utilization,labor productivity,safety and environment factors,a comprehensive hierarchy structure of evaluation indexes for mining method optimization was built to get a reasonable weight matrix.This provides a better solution for weight distribution in multi-factor decision-making when the judging indexes of mining programs show cross superiority.Finally,the optimal mining method was selected by fuzzy comprehensive judgment.
Abstract: Mine accident data for nearly 6 years from the work safety administration of Qinghai Province in northwestern China were studied from the two aspects of mine accident probability and mine accident death probability. The risk analysis of mine accidents in high-altitude, cold and drought areas was performed by means of the information diffusion theory. A mine accident model was built which is suitable for these areas with special requirements. The analysis model, parameters and prediction results coincide with the actual situation. It is revealed that the information diffusion theory can be applied to the risk analysis of mine accidents in high-altitude, cold and drought areas and predict the average annual probabilities of mine accidents and personnel death in the mine enterprises for technical support and policy recommendations.
Taking the slope at the East Open Pit Mine of Pingshuo Coal Industry Co. where two soil landslides occurred successively as the research background, in consideration of the current situation that valid data lacks and relatively large error exists in experience evaluation, data of geological survey points in interfaces between rock and soil layers were fully used and the drilling data range was effectively expanded to provide valid data for high-precision interface fitting. A Closest Point algorithm-based structural analysis model was applied to conduct Kriging interpolation calculations, which made the two algorithms coupled. Thus a three-dimensional fitting model of all rock and soil layers can be completed. By comparing the data of measuring points selected from the field, the accuracy of the interface fitting method is much higher than the traditional method of human experience.
Abstract: A direct reduction method was proposed which uses soda ash as the flux and coal as the reductant. By using this method hematite is reduced to iron, which can be recovered by magnetic separation, while Al2O3 is translated into sodium aluminate, which can be recovered from the solution. The effects of reduction temperature, reduction time, Na2CO3 dosage and reductant dosage on the grade of iron powder, the recovery of iron powder and the recovery of alumina were investigated on the basis of the single factor alteration principle. The process and reaction mechanism were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). Orthogonal experiments were designed for optimizing the experimental parameters. Under the optimum condition of the reduction temperature of 1 150℃, the reduction time of 45 min, the Na2CO3 dosage of 40.47% and the reduetant dosage of 11.9%, the grade of iron powder is 95.88%, the recovery of iron powder is 89.92%, and the recovery of alumina is 75.92%.
Abstract: The influences of reduction temperature,reduction time and the C/O molar ratio on the reduction of vanadium titano-magnetite carbon composite pellets were investigated by single factor experiments.The mechanism of reduction was explained in combination with scanning electron microscopy(SEM).Raising the reduction temperature,prolonging the reduction time and increasing the C/O molar ratio properly can promote the reduction of vanadium titano-magnetite.With the rise of reduction temperature,the metallization rate ascends quickly before 1 350℃ and gently then.With the increase of reduction time and C/O molar ratio,the metallization rate moves up firstly and then down,but the carbon residue content decreases with the reduction proceeding.When the reduction temperature is 1 350℃,the reduction time is 30 min and the C/O molar ratio is 1.2,the metallization rate of the pellets reaches the maximum.SEM observation shows that iron coupling crystals form in the reduction process,and their size and shape vary from each other under different reducing conditions.
A numerical simulation method was applied to investigate the fluid flow as well as the inclusion collision and growth behavior in a swirling flow nozzle induced by a rotating magnetic field during continuous casting.Numerical results indicate that the divergent angle at the submerged entry nozzle(SEN) outlet agrees well with the experimental values of low melting point alloys.The rotating magnetic field has positive and negative effects on the deposition rate of inclusions on the SEN sidewall.On one hand,the turbulence flow near the SEN sidewall enhanced by the rotating magnetic field increases the deposition rate of inclusions on the sidewall;on the other hand,inclusions near the SEN sidewall have a tendency to move towards the SEN center under the rotating magnetic field,which decreases the deposition rate of inclusions on the SEN sidewall.Due to these two paradoxical factors,there is an optimum magnetic induction intensity to minimize the deposition rate of inclusions on the SEN sidewall and the clogging phenomenon can be weakened.
Abstract: Based on experimental phase diagram data in literatures, thermodynamic assessment on the Be-Cr system was carried out using the Calphad method. Liquid and terminal solution phases in the Be-Cr system were described with the substitutional solution model, and the thermodynamic functions of stoichiometric intermediate compounds CrBe2 and CrBe12 were explained by the Neumann-Kopp rule. Thermodynamic parameters obtained by optimization were used to calculate the phase diagram of the Be-Cr system and the result shows a reasonable fit to the accepted experimental data. The enthalpies of formation for CrBe2 and CrBe12 intermediate compounds were also calculated by the Miedema model, and the obtained data are well consistent with those calculated using the thermodynamic parameters.
Abstract: Solidification processes of AISI304 austenitic stainless steel at cooling rates of 0.05℃·s-1 and 3.0℃·s-1 were observed in situ by confocal laser scanning microscopy. When the cooling rate is 0. 05℃·s-1 the solidification front is cellular morphology and the solidification mode belongs to FA mode. B ferrite appears firstly in liquid steel, and then γ phase precipitates prior at B-grain boundaries at 1 448.9℃ by means of the periteetic reaction (L+δ→γ). At 1 431.3℃ the liquid steel disappears. Finally the B ferrite transforms to γ phase by solid diffusion, and the retained ferrite which enriches in Cr and depletes in Ni locates between the cellular dendrites. When the cooling rate is 3.0℃·s-1, the solidification interface morphology is dendritic. The peritectic reaction takes place at interfaces between B-grains and the remained liquid at 1 346.4℃, and the retained ferrite locates in the dendrite arm. Compared to 0.05℃·s-1, the degree of enrichment in Cr and depletion in Ni in the residual ferrite decreases but the amount of them increases.
Abstract: The effects of inclusion characteristics, such as type, size distribution and volume fraction on the formation of intra-granular acicular ferrite (IAF) in steels containing rare earth (RE) elements were investigated by optical microscopy, scanning electron microscopy and the point counting method, It is shown that the type and volume fraction of inclusions both play a critical role in IAF formation. A low mismatch value of 1.9% between ferrite and RE-oxides (including RE-oxysulfide) decreases the energy barrier on the inclusion surface for IAF nucleation and accelerates the nucleation on RE oxides. But RE-sulfides which have a high mismatch value of 42.5% with ferrite cannot induce IAF. The volume fraction of IAF increases with the volume fraction of inclusions increasing. When the volume fraction of inclusions reaches 9.5×10-4, the volume fraction of IAF is 53%.
Inclusions and MA islands in X80 pipeline steel were observed and their statistical size characters were obtained by scanning electron microscopy and transmission electron microscopy. The mechanism of microvoid nucleation in X80 pipeline steel was studied through a series of tensile tests with different necking degrees. Microvoid nucleation firstly occurs around calcium treatment inclusions at the early necking stage, while at the deep necking stage, microvoids nucleate by decohesion of MA island/matrix interfaces. Finally the tensile process was analyzed, the curves of true stress to true strain of X80 samples were determined, and the strengths of calcium treatment inclusion/matrix interfaces and MA island/matrix interfaces were calculated by the finite element method.
Abstract: In order to improve the utilization of blast furnace slag and steel slag into high strength building materials to great extent, the effect of slag particle size on the compressive strength of cementitious systems prepared with a great deal of blast furnace and steel slag was investigated by grey correlation analysis. The blast furnace slag and steel slag account for 50% and 30% in mass respectively with the water-binder ratio of 0.34. Slag particles of less than 8.39 μm in size can contribute to the 3 d and 28 d compressive strengths, but the particles of more than 8.39 μm in size have negative effect on them. It is indicated that slag particles with the size between 5.03 μm and 8.39 μm should be increased in the cementitious system so as to improve the 28 d compressive strength.
Abstract: Aluminum matrix composites reinforced by ZrB2 particles were fabricated with Al-KBF4-K2ZrF6 components via a melt direct reaction method. The suitable synthesizing temperature and reaction time are 850 to 870℃ and 25 to 30 rain, respectively. Scanning electron microscopy observations indicate that the size of the particles is 300 to 400 nm and the interval between them is about 200 nm. Some of the particles stick together, leading to clusters with a size of 30 to 40 μm. When the theoretical volume fraction of the particles is 3%, the nucleation amount is 6.68 × 1017 m-3, and the average linear growth velocity is 47.3 nm·s-1. The reason for clustering is that abundant fine and infusible ZrB2 particles increase the viscosity of the composite melt. High diffusion resistance prohibits the particles from migrating. Thus the particles have higher density and sedimentation velocity, which make them cluster easily. In situ reaction analysis shows that the particles can be obtained by molecular combination between Al3Zr and AlB2 or atomic combination between Zr and B atoms, and they are stable at high temperature.
Abstract: Opaque and translucent physical models of double-ceramic-layer thermal barrier coatings(DCL-TBCs) were established with the theory of heat conduction,convection and radiation.The steady temperature field was simulated with ANSYS software.When the ceramic is opaque,with the top ceramic layer thickness increasing,the upper side temperature of the top ceramic layer linearly increases,but that of the second ceramic and bonding layers linearly decrease.When the double ceramic is weakly translucent,the trend of temperature is similar to the opaque's.When the ceramic is highly translucent,with the top ceramic layer thickness increasing,the upper side temperature of the top ceramic layer is a little lower and that of the second ceramic layer is higher than the opaque's;the upper side temperature of the bonding layer firstly fast,secondly slowly decreases and then keeps constant,but much higher than the opaque's.
Abstract: The thermal state and insulation capacity of ladles with different insulating layer thicknesses were simulated and calculated by building a two-dimensional model of ladles based on the finite element method. A ladle with an insulating layer can effectively improve its thermal insulation. With the increasing of insulating layer thickness, the insulating effect becomes more prominent, but it grows slower. When the insulating layer thickness reaches 20 mm, the preheating time of the ladle is shortened by 1 h, the coal gas is saved by 1 000 m3, and the steel temperature drop is decreased by 6℃ compared with a ladle without any insulating layer. During the heat saturating stage, the outside shell temperature of the ladle decreases by 100℃, and the heat loss at the ladle shell falls down. Due to the insulating layer, the energy of 1 255 680 kJ could be saved per hour, which is equivalent to 43 kg standard coal. A comparison of the calculation results with measured data proves that the simulation results are reliable.
Abstract: The ovality of shafts with light area reduction by cross wedge rolling was simulated by finite element software. The influence of technological parameters on the ovality of rolled pieces was studied by the orthogonal regression of the numerical results. Results show that the influences of stretching angle and area reduction on the ovality of rolled pieces are significant, and the ovality of rolled pieces increases with the stretching angle increasing or the area reduction decreasing. However, the forming angle has little influence on the ovality of rolled pieces. The reasons for these influences were explained. Finally the reliability of the numerical results was verified by roiling experiments.
Abstract: Aimed at CVC and HC mill types which are widely used, finite element models of 4-high and 6-high mills were established through ANSYS9.0 software. The vertical rigidities of rolling force and bending force were analyzed under different working conditions of roll shifting and bending force by the model. It is revealed that the vertical rigidity of rolling force of the 4-high mill is larger than that of the 6-high in the same working condition. The axial shifting of the intermediate roll or work roll has a greater effect on the vertical rigidities of rolling force and bending force of the HC mill than the CVC mill.
Abstract: Causes for plate thickness variation in the rolling process were analyzed.Uncertain disturbances in the rolling process were attributed to mill stiffness modulus perturbation and stock plastic coefficient perturbation,and then a dual perturbation automatic gauge control(AGC) theory was established.Considering the external disturbances of the rolling mill system,especially uncertainties between passes,the thickness information was converted to boundary specifications in the frequency domain.For disturbance attenuation,a controller based on the external excited adaptive quantitative feedback theory(QFT) was designed with loop shaping.The controller can effectively suppress external disturbances in the rolling process,and has a good robust performance,which can ensure robust stability in system adjustment.The proposed method is suitable for industrial production.
Abstract: A novel construction method of classifier models based on the fuzzy cognitive map was proposed,which consists of model structure,activation functions,inference rules and learning algorithms.The model employs dynamically self-adaptive crossover and mutation operators to automatically adjust the evolution process within populations.Simulation experiments prove that the model enhances the capabilities of local random search and global convergence.Compared with other classical classification algorithms,the model not only shows a better classification performance,but also has powerful noise-immune ability which renders it robust.
Abstract: In order to overcome the shortage that attribute weights are not taken into consideration in the existing extensions of rough sets under incomplete information systems,a new rough set model is proposed based on the weighted threshold tolerance relation.The new model calculates the weights according to the information quantity of the incomplete information system without outside knowledge,so the weights are objective.Moreover,the model introduces a threshold to adjust the strictness degree of the weighted threshold tolerance class,which not only combines subjective requirements into consideration,but also excludes objects in advance that do not reach the threshold and can not be in the same weighted threshold tolerance class with other objects.This exclusion will not influence the completeness of the classes.Contrastive analysis of an example shows that the proposed extension of a rough set based on the weighted threshold tolerance relation accords with the fact of an incomplete information system and is more applicable compared with other models.
Abstract: Based on the successful isolation of a bacterial strain of Lactobacillus sp. USTB-08 for producing lactic acid, the optimal control conditions including carbon source, nitrogen source, mass ratio between carbon and nitrogen source, temperature and pH values were investigated for the growth of Lactobacillus sp. USTB-08 and the production of lactic acid in batch cultivation and fed-batch fermentation. Sucrose as the sole carbon source, yeast extract as the sole nitrogen source, the mass ratio of carbon to nitrogen source of 5:1, 35℃, the inoculum amount of 1.0% and initial pH 6.50 are the optimal parameters for the growth of Lactobacillus sp. USTB-08 in batch cultivation. In fed-batch cultivation by feeding a mixture of 10% sodium hydroxide and 25% sucrose to control the pH value and supply the carbon source in a 50 L automatic fermenter, the maximum biomass of Lactobacillus sp. USTB-08 (OD680nm 13.2) and the maximum content of lactic acid (28.0g·L-1) are obtained at pH 6.50 and pH 7.00 in a pH range from 6.00 to 7. Off, respectively. The strategy of feeding sucrose and controlling the pH value simultaneously was firstly used in the fed-batch cultivation of Lactobacillus sp., and both high cell density and high lactic acid content were obtained.
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
