Abstract: According to the actual parameter of across vein roadway tunneling in alpine mine, the numerical simulation was set up, and the computation grids were piecemeal-divided. Referring to the tunneling footage and the distance between venting duct and heading face, the diffusion law of blasting fume under different operating modes was simulated by the Fluent fluid analysis software. The simulation results show that the slower the preclusion speed of CO is, the longer the distance between venting duct and heading face, and the ventilation time has a certain functional relationship between the length of across vein roadway and the distance from venting duct to heading face.
A mathematical model of ore blending was constructed for underground mines on the basis of an immune clone selection optimization algorithm. In combination with the actual production of an underground zinc mine in China, the model was calculated by programming computer software with Java. The calculated results were compared with the production plan and the data calculated by a fuzzy optimization method. It is shown that the immune clone selection algorithm is feasible and reliable for ore blending of an underground mine.
Abstract: The effects of chemical mutation by hydroxylamine hydrochloride on the activity and growth of strains and the tailing leaching system were investigated with the superior bacteria of Acidthiobacillus ferrooxidans (T.f6) as an original strain. The results showed that chemical mutation by hydroxylamine hydrochloride produced an evident mutation in the strain T.f6, which can improve its bioactivity and bioleaching properties. The strain T.f6 had the best oxidation after chemical mutation by hydroxylamine hydrochloride with a mass fraction of 1.0%. The oxidation rate of Fe2+ reached 100% after culturing for 32h, which was 32h in advance in comparison with the original strain. After a 30d leaching, the copper leaching rate of the mutant strain T.f6 was improved by 20.7% as compared with that of the original strain and it was 85% higher than the acid leaching rate. In addition, utilizing the mutant strain could shorten the leaching time of 5 to 8d. It is indicated that the effect of bioleaching with the mutant strain is better than that with the original strain, and much better than that of the acid leaching. Scanning electron microscope analyses of the original strain and the mutant strain showed that the shape of the mutant strain did not change but the cell size did, the surface changed smooth and extracellular secretion occurred, while the clustering of cells was obvious.
Abstract: The movement tracks of inclusions in liquid steel in the tundish with a filter and the inclusion removal rate during continuous casting were studied by numerical simulations through constructing a multiphase flow model. This model was testified by sampling at the inlet and outlet of the tundish during continuous casting in a steel mill. Afterward the samples were investigated by bulk-sample-electrolysis to get the proportion of inclusions in liquid steel, and the effect of casting process on the inclusion removal rate was analyzed. It is shown that the velocity of inclusions decreases due to filtering, and the residence time of inclusions in the tundish prolongs, leading to an increase in the probability of inclusion removal, so filters can increase the inclusion removal rate. Fluctuations in inclusion removal rate are found when the diameter of inclusions is less than 80 μm, however the fluctuations are not so severely for inclusions whose diameter is more than 100 μm. There occurs even the increasing of inclusions at the outlet when the diameter of inclusions is less than 20 μm during the later period of casting. The inclusion removal is a transient process.
Abstract: Non-reactive mould fluxes were designed, and the effects of Li2O on the crystallization and heat transfer of the fluxes were investigated by using the single hot thermocouple technique (SHTT) and a heat-flux simulator. The results show that increasing the Li2O content which is less than 2% can weaken the crystallization property of the fluxes. Whereas, when the Li2O content increases from 2% to 5%, the crystallization temperature, critical cooling rate and crystallization rate constant enhance, but the incubation time of the slag system decreases, indicating that Li2O improves the crystallization of the fluxes in this range. It is also found that the maximum heat flux density, average heat flux density and characteristic time of the fluxes reduce with the increase of Li2O content within the range of 2% to 5%.
Abstract: Heat treatment processes were simulated with a thermo-analyse simulator for niobium-bearing low carbon steel (0.028%C-0.25%Si-1.82%Mn-0.085%Nb). In the processes, the samples were cooled down to a final cooling temperature of 350 to 550℃ after being normalized at 950℃, then reheated at different ratios, and tempered at different temperatures for different holding time periods. The morphology, the size and distribution of martensite-austenite (MA) constituents obtained under different tempering conditions were investigated by optical microscopy, scanning electron microscopy (SEM) and image analysis. The results show that the enhancement of reheating ratio and the final cooling temperature in the range of bainite transition lead to an increase of MA volume fraction, and the maximum volume fraction of MA constituents is up to 7.9%. Tempering at high holding temperature for long holding time can result in an occurrence of the volume fraction peak of MA constituents. The average grain size of MA constituents is 0.77 to 1.48 μm after tempering. MA grains grow up and tend to be in polygonal shape when the final cooling temperature, reheating ratio and holding temperature increase and the holding time prolongs. The volume fraction and average grain size of MA constituents are mainly affected by the quantity of untransformed austenite after intermediate cooling, the evolution of carbon diffusion from ferrite to retained austenite during tempering and the stability of retained austenite after tempering.
Abstract: The finish rolling temperature was determined at 830, 800 and 775℃ to investigate its effect on the microstructure and mechanical properties of high deformability pipeline steel. The grain size and volume fraction of ferrite and M/A islands in the steels were measured by metallographic microscopy and image processing software. Electron backscatter diffraction (EBSD) analysis was conducted to ascertain the effective grain size and the volume fraction of high angle grain boundaries. The M/A island forms were observed by transmission electron microscopy (TEM). A quasi-static tensile testing machine was used to test the yield strength, tensile strength and uniform elongation of the three steels. It is indicated that when the finish rolling temperature is 800℃, the steel has the best mechanical properties and can meet the requirements of X80 high deformability pipeline steel.
Abstract: The surface morphology and segregation of spangles on a batch hot-dipped Zn-0.05Al-0.2Sb alloy coating were investigated by scanning electron microscopy (SEM), atomic force microscopy (AFM), energy dispersive spectroscopy (EDS), X-ray diffraction analysis (XRD) and X-ray photoelectron spectroscopy (XPS). It is found that the coating surface usually exhibits three kinds of spangles:shiny, feathery and dull spangle, with the surface roughness and segregation of Al and Sb increasing in turn. Electrochemical impedance spectroscopy (EIS) tests show that their corrosion-resistances decrease in turn. On the coating surface, acicular β-Sb3Zn4 precipitates from the segregated Sb, and Al mainly exists as Al2O3 in the oxide film of the Zn coating. The above phenomena were discussed by a crystal growth model of spangles and the Zn-Sb phase diagram.
Abstract: The electrochemical corrosion behavior of epoxy heavy-duty coatings immersed in seawater at different temperatures was investigated by electrochemical impedance spectroscopy (EIS). The results show that the increase in capacitance and the decrease in resistance of the coatings both change faster with rising temperature, indicating that higher seawater temperatures accelerate degradation of the coatings. At the initial immersed period, the diffusion process of seawater through the coatings follows the second Fick diffusion law at any seawater temperature and the diffusion activation energy is 49.7 kJ·mol-1. The diffusion coefficient of seawater across the coatings increases as the seawater temperature rises, and the time for the coatings to reach the maximum water absorption capacity shortens, but the saturated capacity for water absorption of the coatings changes little.
Abstract: A Ag-SiO2 film was prepared on a stainless steel surface using sol-gel method and soak-lifting method. The structure of the film was studied by X-ray diffraction analysis, the hydrophilicity was characterized by measuring the contact angle, the corrosion resistance was determined in a 10% FeCl3 solution, and the adhesion properties and antibacterial performance were tested. It is shown that the antibacterial Ag-SiO2 film can be obtained on the stainless steel by sol-gel method. After oxidization for 10 min and five times dip-coating, as well as heat treatment, the film is firmly bonded with the stainless steel. The hydrophilicity and corrosion resistance of the film are improved, and the inhibitory rate to Staphylococcus aureus reaches up to 100%.
Abstract: A process of preparing Fe-Cr-C composite powder for precursor carbonization-composition process was developed using the compacts of mixed ferrotitanium, chromium, iron and carbon precursor (saccharose) powers as raw materials, and Fe-Cr-C and Fe-Cr-C-Ti composite coatings were synthesized and deposited on Q235 steel substrates by plasma cladding technology. The phase composition and microstructure of the composite coatings were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). It is shown that the Fe-Cr-C composite coating consists of (Cr,Fe)7C3 primary phase, (Cr,Fe)7C3 eutectics with a petal-like distribution and austenite, but the Fe-Cr-C-Ti composite coating is composed of in situ TiC and (Cr,Fe)7C3 eutectics and austenite. The two types of composite coatings are also metallurgically bonded to the substrates. The volume content of TiC in the coating shows a gradient distribution. Generally, TiC phases in the fusion zone and central regions are equiaxed, and TiC phase in the surface is dendritic. Compared with the Fe-Cr-C composite coating, the Fe-Cr-C-Ti composite coating has better anti-cracking. The average microhardnesses of the Fe-Cr-C and Fe-Cr-C-Ti composite coatings are about 750 HV0.2, 3.2 times as large as the microhardness of the based metal, and this value changes little from the surface to the fusion zone.
Abstract: Hot compression tests were conducted on a Gleeble-1500 simulator at a true strain of 0.7 at different temperatures and different strain rates to investigate the dynamic recrystallization behavior of GH625 superalloy. Optical microscopy (OP) and transmission electron microscopy (TEM) were employed to analyze the effect of strain rate on the microstructural evolution and nucleation mechanisms of dynamic recrystallization (DRX). The results show that the actual deformation temperature of the sample deformed at a strain rate of 10.0s-1 is higher than the preset temperature, resulting in a deformation thermal effect. It is also found that the DRX of GH625 superalloy is controlled by both strain rate and deformation temperature. When the strain rate ? ≤ 1.0s-1, the size and volume fraction of DRX grains decrease with increasing strain rate. The nucleation mechanism of DRX is composed of discontinuous dynamic recrystallization (DDRX) characterized by the bulging of original grain boundaries and continuous dynamic recrystallization (CDRX) characterized by progressive subgrain rotation. However the size and volume fraction of DRX grains increase at a strain rate of 10.0s-1 due to the deformation thermal effect. The nucleation mechanism of DRX for GH625 superalloy deformed at a strain rate of 10.0s-1 is operating by DDRX with the bulging of original grain boundaries.
Abstract: Cu-12%Al alloy wires with a diameter of 6 mm were prepared by vacuum melting and argon shield vertical continuous unidirectional solidification process. The effects of melt temperature, crystallizer length and drawing velocity on the surface quality, microstructure and mechanical properties of the alloy wires were investigated. The results show that single-crystalline or columnar-crystalline wires can be fabricated at a crystallizer length of 20 to 40 mm, a melt temperature of 1100 to 1250℃ and a drawing velocity of 10 to 70 mm·min-1. Shortening the crystallizer length, raising the melt temperature and/or increasing the drawing velocity are in favor of improvements in the surface quality, but the continuous columnar-crystalline wires can be obtained at a lower melt temperature, a longer crystallizer length and/or a higher drawing velocity. With the increase of drawing velocity, the cross-sectional grain size of the wires decreases firstly and then increases in the parameter regions of the crystallizer length of 30 mm, the melt temperature of 1 100 to 1 150℃ and the drawing velocity of 10 to 70 mm·min-1. The continuous columnar-crystalline wires manufactured at the crystallizer length of 30 mm, the melt temperature of 1 150℃ and the drawing velocity of 30 mm·min-1 have a good elongation percentage of 25.7%.
Abstract: Based on the compression experimental data of BFe10-1-1 alloy with continuous unidirectionally solidified columnar grains, a prediction model for the relation of true stress to temperature, strain rate and true strain was developed using an adaptive network based fuzzy inference system (ANFIS). The temperature at which the alloy was compressed was from 25 to 500℃ with the strain rate ranging from 0.01 to 10s-1. Simulation results show that the mean percentage error, root mean square error and correlation coefficient between the ANFIS model and measured data of flow stress are 0.75%, 2.13 and 0.999 6, respectively, indicating that the ANFIS model can well reflect the real feature of the alloy during practical deforming process. In comparison with the regression model, whose mean percentage error is 6.28% under the same condition, ANFIS parades more accurate prediction performance for flow stress.
Abstract: Cementitious materials special for high performance concrete with high volume of fly ash and slag and less cement clinker were prepared by optimizing the proportion of ingredients and the size fraction and using an additive. The effects of grinding modes, gypsum amount and the mix proportion of slag to fly ash on the strength of the cementitious materials were studied. X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM) were used to observe the microstructure and hydration products and investigate the collaborative optimization effect between the activity and grading of the cementitious materials. The results show that cementitious materials have good mortar fluidity when the water-binder ratio (W/C) is 0.36, the compressive strength of colloidal mortar specimens cured for 28d is 58.9 MPa and the 28d flexural strength is 14.2 MPa, which have favorable properties of erosion resistance to sulfates. The concrete made from the cementitious materials has a better ability of carbonation resistance.
Abstract: Calcined diatomite/α-Fe2O3 composite particle materials (CD/α-F) were prepared with calcined diatomite and α-Fe2O3 as raw materials by a mechanochemical method in the system of wet grinding. Scanning electron microscopy, energy dispersive spectrometry, hiding power and oil absorption measurements were used to characterize the morphologies and pigment properties of CD/α-F. The reaction mechanism of the composite particles was analyzed by X-ray diffraction and Fourier transform infrared spectroscopy. It is shown that mechanochemical effect enhances the particle surfaces of calcined diatomite and α-Fe2O3 to form hydroxide radicals further, thus promotes dehydration-condensation reactions between hydroxide radicals from the two raw materials and then Si…O…Fe bonds form with weak linking forces. Moreover, the core-shell CD/α-F composite powder has similar pigment properties to pure α-Fe2O3 in experimental conditions desired.
Abstract: Black silicon was prepared with polycrystalline silicon by plasma immersion ion implantation. The microstructure, optical absorbance and lifetime of minority carriers of the black silicon were characterized by scanning electron microscopy (SEM), UV-VIS-NIR spectrophotometer and microwave photoconductive decay (μ-PCD), respectively. The results show that the black silicon has a porous structure. The average absorbance of the black silicon is above 94% in the visible region. The average lifetime of minority carriers in the black silicon is 5.68 μs. The effect of immersion parameters on the black silicon was investigated. It is found that the gas flux ratio of SF6 to O2 plays an important role in the microstructure and properties, and its optimum value is 2.80.
Abstract: Based on numerical calculations and an artificial neural network (ANN) model as well as intelligent control technology, a set of intelligent control simulation system was founded for the injection process of standard tensile samples. The results show that this system can automatically optimize injection parameters according to the requirement of injection bodies to the properties (such as density distribution). It is found, after the introduction of the intelligent control simulation system to injection processing, that the uniformity of density distribution in injection bodies is obviously improved and can meet the expected density distribution, proving that this intelligent control simulation system is feasible.
Abstract: With the hot blast stove in Shougang Qianan No.2 blast furnace as an object of study, the vault temperature and combustion efficiency under different operating conditions were solved by a numerical simulation method. Two mathematical models were constructed for the relations of vault temperature and combustion efficiency to air preheat temperature, gas flow, air-fuel ratio and gas composition. Considered the combustion efficiency of the hot blast stove as an optimization objective, the best operation mode for the hot blast stove could be obtained under the constraint condition of vault temperature by the mathematical models.
Abstract: The steady flow field and chemical reactions in a duel-chamber regenerative thermal oxidizer (RTO) were studied with the CFX software. Flow circumstances in the duel-chamber RTO were described by numerical simulation. Some influencing factors such as combustion temperature, the mass concentration of volatile organic compounds (VOC) and the mass fraction of oxygen, which affect the VOC destruction and removal efficiency of the duel-chamber RTO, were revealed quantitatively. The simulation results show that combustion temperature is the most important factor which directly affects the destruction and removal efficiency of the duel-chamber RTO, the inlet temperature of waste gas and the mass concentration of VOC influence indirectly by changing the combustion temperature, but the mass fraction of oxygen which is more than 0.03 has little effect on it. Based on the numerical results, a duel-chamber RTO was design, and an anticipated effect was achieved in applications.
Abstract: In order to solve the problem that excessive axial force causes a displacement accident of the main motor bearing box and horizontal axis bearing box in the drive system of a 2250 hot continuous rolling R2 rolling mill, an on-line monitoring system of axial force was developed to monitor the axial force for a long time on-line. The main reason for axial force generation was theoretically analyzed and a computer simulation was carried out. It is shown that the axial force is closely related to the roll cross angle, and can be effectively controlled by reducing the gap between roll bearing box and the arch. This result was verified by field experiment.
Abstract: A constraint satisfaction model whose objective is to minimize the slab number was built for slab production in consideration of the slab designing problem with a fixed demand of order weight and a minimum limitation of order weight assigned in one slab. The problem was proved to be NP-hard by reducing a known NP-hard three-partition problem to the discussed problem in polynomial time. Concerning with special characteristics of the problem, variable selection strategies and value selection strategies were presented. A constraint-satisfaction-based algorithm was proposed and it was proved to be convergent. The effectiveness of the proposed algorithm was verified with simulation experiments.
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
