Abstract: Based on experience and actual situation, a far-pressing-near-absorption (FPNA) ventilation system which matches with heading machines was determined with a fully mechanized excavation face in Mine 11 of Pingmei Group as the research back-ground. Dust distributions in a fully mechanized excavation face were studied by numerical simulations and in situ measurements. A geometric model of the face was built with GAMBIT technology, and dust distributions before and after applying the ventilation system were respectively simulated using computational fluid dynamics software FLUENT. The simulation results of dust mass concentration are in agreement with the in situ measurement data. It is shown that the dust collection efficiency is more than 95% with the use of the ventilation system and the dust mass concentrations in the excavation face meet with or come close to 1.0×10-5 kg·m-3.
Abstract: In order to study life support techniques in a confined space, seven cases were examined with four test personnel living a confined space. The test data of oxygen consumption and carbon dioxide production were obtained under different active states, and the respiratory quotient of the human body in the confined space was numerically calculated.
Abstract: Direct reduction-roasted products and final products after magnetic separation, which are reduced from high-phosphorus oolitic hematite in west Hubei Province of China by adding a dephosphorization agent, were investigated by XRD and SEM. The results show that the dephosphorization agent added in the reduction-roasting process can remove phosphorus and promote iron reduction. The dephosphorization agent not only transforms partial phosphorus ores into easy removed solvable phosphate but also breaks the oolitic structure, leading to an easy separation of iron from gangue after fine grinding and magnetic separation in order to remove phosphorus. The grade and recovery of iron also improve due to adding the dephosphorization agent.
Abstract: Based on the characteristics of Jinchuan nickel residue, a comprehensive utilization experimental study on iron recovery was done by the deep reduction-magnetic separation method to get iron concentrate whose grade of iron is 89.84% and recovery rate of iron is 93.21%. The effects of some experimental conditions such as reduction temperature, reduction time, binary basicity, grinding fineness and magnetic field intensity on the separation efficiency and product indexes were researched. The phase compositions and characteristics of nickel residue and iron concentrate were determined by X-ray diffraction, optical microscopy, SEM and chemical analysis.
Abstract: Based on the material balance principle, a functional relation of the total vanadium content of tailings with the total vanadium content of calcination-clinker, calcination conversion rate and leaching rate was established, and the validity of the equation was proved with industrial production data. The effects of interactions between independent variables in the equation on the total vanadium content of railings were systematically studied; as a result, the original equation was further simplified. The results show that the internal relation of the total vanadium content of tailings to the above-mentioned factors can be accurately reflected through the original equation and the reduced equation, which can provide a basis of judgment for technical control of the total vanadium content of tailings in actual production. On the other hand, the reduced equation is so simple that it is more favorable to practical applications.
Abstract: A quantitative method was proposed for evaluating the consistency of burden distribution in the width direction of a sinter machine. Based on the theory of sintering processes and the basic principle of aerodynamics, a mathematical model that describes the evaluation index of evenness was established by testing the exhaust gas temperature of the sintering machine to solve the shortage of artificial and qualitative judgments, and an online monitoring software system was developed by use of the mathematical model. The resuits show that the mathematical model can objectively and quantitatively reflect the difference in density along the width of charge beds.
Abstract: Determining the content of silicon in Si-Mn ferroalloys was investigated by a novel resistivity measurement technique, which is based on the single-valued change of electrical resistivity with the content of one alloy element in a quasi-binary alloy. The relationship between silicon content and electrical resistivity in Si-Mn alloys was obtained by a series of experiments. It can be expressed as [Si%]=-12.51+2×107ρ-4×1012ρ2, When the content of silicon in Si-Mn alloys is less 6%, the ratio of Mn to Fe has little influence on the electrical resistivity. Furthermore, the error in determining the silicon content can be controlled within 0.005% to 0.178%. To avoid the effect of some factors including slag inclusions, voids and other defects on the measuring accuracy, samples applied to measure the electrical resistivity are 6.00 to 6.50 mm in diameter and about 1 cm in length.
Abstract: Taking a Nb-bearing high-strength IF steel with super-fine grains as an object of study, cold rolling and simulative continuous annealing experiments were carried out in the laboratory. The results show that its microstructure can be refined and homogenized by choosing a feasible annealing time, with a number of cake-shaped grains. The steel is solid-solution strengthened by adding solid-solution elements such as Si and Mn; fine Nb(C,N) forms in its microstructure by adding micro-alloy element Nb. The tensile strength of the steel is improved by fine-grain strengthening and precipitation strengthening due to a dispersive distribution of fine niobium earbonitride and the strengthen mechanisms are solid solution strengthening, fine-grain strengthening and precipitation strengthening. It is noted that the yield strength is low but the tensile strength is high since precipitated free zones exist on one side of grain boundaries. In contrast to a conventional IF steel, the steel has super fine grains and exhibits excellent formability such as low yield strength and high r-values.
Abstract: Continuous cooling transformation (CCT) curves of NVE36 steel were measured by thermal dilatometer. The microstructures at room temperature were observed by optical microscope and the hardness was tested with a Vickers hardness tester. Data processing was carried out at the platform of Matlab software, and the relationship model of phase transformation temperature and cooling rate and the kinetic regression model were established. After regressive calculations the optimal coefficients of the models for this steel were obtained. Finally, the measured and calculated kinetic behaviors during continuous cooling of NVE36 steel were compared. It is shown that the calculated result is in reasonable agreement with the experimental data, proving the rationality of the models established and the feasibility of data processing methods.
Abstract: Ni-P alloy particles were synthesized by pulse discharge, and then their microstructure and effect on the thermal decomposition of ammonium perchlorate (AP) were studied. The results show that amorphous Ni-P alloy particles are composed of aggregates. The chord counts increase with increasing discharge voltage, leading to the reduction in diameter of Ni-P particles. The sizes of particles prepared at discharge voltages of 700, 900 and 1 100 V are 350 to 500, 250 to 400 and 150 to 300 nm, respectively. Ni-P alloy particles are beneficial to the thermal decomposition of AP at both low and high temperatures. In comparison with pure AP, Ni-P particles result in a decrease of the first (low temperature decomposition) and second exothermic (high temperature decomposition) peak temperature, and the decrease ranges are within 12℃ and about 53℃, respectively. The first exothermic peak is intensified with a reduction in size of Ni-P particles, but the second exothermic peak becomes weakened. In addition, the mass loss of low-temperature decomposition increases from 15.97% for pure AP to 42.78% for the mixture of AP and Ni-P particles, while the mass loss of high-temperature decomposition decreases from 81.62% to 47.58% and the end of high temperature decomposition is reduced by a range of 26 to 43℃.
Abstract: The effects of differential speed ratio on the microstrueture and the texture of AZ31 magnesium alloy sheets processed by differential speed rolling (DSR) were investigated by optical microscopy and X-ray diffraction analysis. The results show that differential speed ratio has a significant effect on the grain morphology but a little influence on the grain size. As the differential speed ratio increases to 2.800, lots of long-strip grains are found. The intensity of {0002} basal textures is much higher on the side of fast rolling than on the side of slow rolling and the distributions of {0002} orientations are different between the two surfaces of the sheet. Differential speed ratio has also a great influence on the strength of basal textures and when the differential speed ratio increases, the intensity of (0002) basal textures increases firstly and then reduces. This special texture change could be attributed to shear deformation introduced throughout the thickness during the differential speed rolling process.
Abstract: The galvanic corrosion of AZ91D magnesium alloy coupled with H62 brass alloy using accelerated testing in salt fog spraying was investigated by using the scanning Kelvin probe technique (SKP). The results show that the galvanic corrosion effect of AZ91D magnesium alloy is influenced by the potential difference between anode and cathode materials. The potential difference between AZ91D magnesium alloy and H62 brass alloy is about -1.22 V during accelerated testing in the initial stage of salt fog spraying. The galvanic corrosion effect of AZ91D magnesium alloy is very significant. Galvanic corrosion occurs mainly at the interface near to AZ91D magnesium alloy, and H62 brass alloy is of no significant corrosion. As the corrosion products of AZ91D magnesium alloy have a protective effect, the potential difference between the corrosion products and matrix is significant, and then new corrosion products occurs in the matrix of AZ91D magnesium alloy. With prolonging the salt spray test time, the galvanic corrosion effect of AZ91 D magnesium alloy reduces and the corrosion of H62 brass alloy accelerates.
Abstract: Critical simulations of model hypoeutectic alloys were carried out with the KKSO multi-phase field model to study the lamellarrod eutectic transition. The result shows that the lamellar-rod eutectic transition does not appear abrupt but occurs over a range of compositions. Under the condition of isotropic interface energy, when the volume fraction of the minor phase is far lower than 1/π, the lamellar-rod transition occurs, and a rod microstructure forms. When the volume fraction of the minor phase is near to 1/π, the lamellar-rod transition does not occur completely, and it occurs later with the volume fraction of the minor phase increasing. When the volume fraction of the minor phase is far larger than I/π, it does not occur any longer. The simulations also show that the transition is related with initial lamellar spacing, which is in accordance with the experiment results qualitatively.
Abstract: Abrasion resistances of five kinds of alumina based refractory products at elevated temperatures were determined using a new developed high-temperature abrasion facility. The results show that the wear volume of the refractory products during elastic deformation has a little change with temperature rising, but in the plastic deformation range it drops sharply. The refractory products with a high hardness mineral as the main crystal phase have a better abrasion resistance. Sintering degree has a more obvious effect on the abrasion resistance. For the refractory products with the same main mineral phase, the denser the sintering degree, the better the abrasion resistance is. When a low melting point liquid phase forms in the refractory products at elevated temperatures, the wear volume decreases, and the liquid phase has a more effect on the abrasion resistance than the hardness of the mineral phase. The wear volume has a close relation with hot modulus of rupture ( HMOR). The higher the HMOR, the smaller the wear volume is during elastic deformation. The HMOR and wear volume decrease rapidly with temperature rising during plastic deformation.
Abstract: The doping content dependence of crystalline structures, saturation magnetization and coercivities of BiFe1-xCoxO3 was compared with that of BiFe1-xNixO3. All the samples are fabricated by solid-state sintering. It is found that ferromagnetic cubic structure in doping samples is the main source of magnetic properties. The Curie temperatures of Ni-doped samples are higher than those of Co-doped samples. The difference in Curie temperature might be due to the variation of magnetic super-exchange coupling between magnetic cations which is caused by interatomie distance and the kinds of cations. Ni-doped samples have smaller eoereivities than Codoped samples. The large coercivity results from the lattice distortion and the strong single ion anisotropy of Co cations. The results of hysteresis loops of BiCoO3 at different temperatures show that the magnetocrystalline anisotropy of BiCoO3 samples increases with decreasing temperature.
Abstract: P-type semiconductor uhrafine cuprous oxide was prepared and used for the photocatalytic degradation of p-nitrophenol liquid. The main influence factors and levels were ascertained by single factor experiments, and response surface methodology (RSM) was used in optimizing the main influence factors of photocatalytic degradation. Through analyzing the results of response surface methodology experiments, a quadratic polynomial model of photocatalytic degradation for p-nitrophenol by using uhrafine cuprous oxide was obtained. The optimum conditions are the following: the mass concentration of p-nitrophenol solution is 30 mg·L-1, the volume of H2O2 is 0.28 mL, the pH value is 3.6d, and the amount of Cu2O is 0.11 g. Experiments were carried out under the predicted optimum conditions, the relative error between actual and predicted values is 3.02%, and the actual decolorization efficiency is in good agreement with the predicted decolorization efficiency.
Abstract: Simulation research was carried out on a 1 780 m3 Hoogovens internal hot blast stove in Shougang using the CFD method. The research contents mainly include the flow status of air and gas in the rectangular burners before mixing, combustion status of mixture gas, concentration and temperature distributions in the combustion chamber, flame shape, and velocity and temperature distributions in the doom. The result shows that there is heterogeneity in some degree about flow filed in the air nozzle outlet and gas outlet. Along the width direction of the combustion chamber, the flame height changes greatly. A little carbon monoxide remains in the outlet of the doom. On the surface of the checker chamber, the velocity distribution of smoke is not uniform, and the maximum temperature difference is also very large.
Abstract: To solve the wear failure problem existing in the hinges of the rotary mechanism in a KDIA tap-hole drill machine, a comprehensive analysis platform was established through kinematic and dynamic simulations of the mechanism and the corresponding wear depth was calculated based on a combined wear calculation model. The optimization design was conducted for slowing down the velocity and lightening the unevenness of hinge wear, using the mechanism dimensions as design variables, and no loss of other design specifications as constraints. The results show that optimizing the kinematic and dynamic performance of the mechanism through resizing the design dimensions is an effective way of solving mechanism problems such as transmission accuracy losing and wear failure.
Abstract: This research focused on the influence of existing nozzles arrangement at the straightening zones of a caster on the cooling effect of slabs. Through a series of tests for combined nozzles on the nozzle automatic testing platform, the relationship between the spray overlap degree of adjacent nozzles and the uniformity of water distribution in the slab width direction was analyzed from three aspects including nozzle flowrate, injection height and hydraulic pressure. Based on the above research results, an optimization scheme was put forward for the secondary cooling system. Experiment results show that the internal quality of slabs improves significantly after optimization. Transverse corner cracks in slabs are almost eliminated, the center segregation level reduces from B 1.0 to C 1.5, and the ratio of equiaxed grains increases by 4.1%.
Abstract: This article took a tensiometer looper during hot rolling as the object of study. A three-dimensional finite element model was built for a tensiometer looper with roller-height-difference and a hot rolling strip. Considering roller-height-difference as a basic variable, the measurement error of flatness caused by roller-height-difference and its distribution rule under different situations were obtained by changing the arrangement of high and low rollers, the strip thickness, and the average tensile stress of the strip.
Abstract: There are many kinds of spare parts and optional suppliers in metallurgical enterprises, so it is more complicated to select suppliers of spare parts than to select those of raw materials. The multi-attribute decision method was used for selecting the suppliers on the basis of the rough set theory. First, when a decision attribution system was selected, the rough set theory was used to analyze the relationship between historical attribute data and historical suppliers selecting results in order to find out objective weights for each attribute. Both objective and subjective weights were considered in synthetical weights. Then, with the synthetical weights and normalized results of attribute data of candidates, all the suppliers were evaluated. Finally, a case was used to prove the feasibility and validity of this method.
Abstract: A clustering algorithm is proposed based on set dissimilarity. Through defining set dissimilarity and set reduction, it does not calculate the distance between each pair of objects but computes the general dissimilarity of all the objects in a set directly, reduces high-dimensional categorical data enormously without loss of computation accuracy and gets the clustering result by only once data scanning. The time complexity of the algorithm is almost linear. An example of real data shows that the clustering algorithm is effective.
Abstract: An integral-equality approach for studying time-delay systems was extended to investigate switched systems with time-varying delays. A new approach which can analyze switched systems with time delays was proposed, and this approach gives sufficient conditions and switching design of linear switched systems with time delays. According to the rules in the choice of free terms, the free weighting matrices were investigated to construct a integral equality. Less conservative stability criteria can be obtained because no extra conservative is introduced. An example was given to show the validity of the presented method.
Abstract: The finite element method was used to analyze weak positions of load and deformation in the steel structure system of a large-scale selective catalytic reactor and study the buckling behavior of thin steel sheets with ribbed stiffeners. Based on these simulations, the stability of the sheets was discussed by experiment. The results indicate that the sheets are strengthened when rectangular holes are attached to ribbed stiffeners, which should choose L-ribbed stiffeners for the whole structure. The stronger the boundary constraint condition of thin steel sheets with ribbed stiffeners is, the bigger the critical buckling loading is, and the more difficult to buckle the sheets are. The experimental data are in better agreement with the simulation results.
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
