Abstract: An approach which integrates support vector machines (SVM) and genetic algorithms (GA) was proposed to do ore grade interpolation. With the global searching characteristics, GA was used to select the optimal parameters of SVM, including the penalty parameter C, the insensitive coefficient ε and the kernel function parameter σ, so this approach can overcome the limitation of a pure SVM method in determining parameters by experience. The optimal parameters were substituted into SVM iterative training, and then an ore grade interpolation model based on SVM optimized by GA was established. Taking an underground mine in China as an example, the feasibility and validity of the ore grade interpolation model were verified by comparing the model calculation results with the actual data of mine production and the calculation results of traditional interpolation methods.
Starting with interface effects, the motion state of the leaching solution was analyzed to find out the seepage rule in unsaturated leaching. The total suction in ore heaps is composed of the matric suction from interface effects and the osmotic suction from absorption and diffusion of the ore and solution. The inhomogeneity of medium distribution in pores and the randomness of ore shape are causes for the diversity of interface effects, which make the motion state of the leaching solution complicated. Capillary rise experiment was conducted to prove the existence of suction in ore heaps. The result reveals that the capillary rise height increases faster at the beginning of infiltration under driving force than that at the later period of infiltration. Moreover, the fitting curve reveals that the capillary rise height increases by a power function with infiltration time. Theoretical studies show that the interface effects of unsaturated seepage in leaching can be regulated by changing the physical properties of solid phase, liquid phase and gas phase.
In order to investigate the feasibility of biodesulfurization by an extreme thermophile in high iron concentration, high acidity and elevated temperature environment, four groups of pyrite column bioleaching experiments at variable initial pH values were carried out by using a novel strain of extreme thermophilic Thiobacillus which was isolated from Rehai acidic hot spring in Tengchong in southwestern China. It is found that the new strain is resistant to high acid and high iron environment in which the pH value is 0.58 and the soluble iron concentration is 38.9 g·L-1, while the redox potential maintains at a low level from 580 to 640 mV. The highest value of iron recovery can reach up to 17.8% after leaching for 28 d when the initial pH value is 2. The bacterial growth evidently represents a lag phase, a logarithmic phase and a stationary phase sequentiMly in the traditional bioleaching route, while reducing the initial pH value can prolong the time of reaching the steady periodical. In addition, precipitation formation of jarosite and a little sulfur is promoted in the high iron system of which the total iron concentration is 38.9 g·L-1 and the temperature is 70℃. The novel strain can oxidize the majority of SO to SO42- even when the pH value is lower than 0.9.
Abstract: In order to ease the shortage of fossil energy and to come up to the stricter effluent standard, this article introduces an innovative green ironmaking technology integrated of the direct reduction process and the development and utilization of biomass energy. Biomass was mixed together with iron ore powder and additives for producing green pellets. Hydrogen-rich syngas produced by biomass catalytic gasification was used as a reducing agent, and the heat produced by biomass combustion was used as the heat source of pellet preheating and reduction. Investigations on the effects of preheating, reduction temperature and green pellet size on the quality of direct reduction iron (DRI) show that increasing the preheating and reduction temperature and decreasing the pellet size can improve the quality of DRI. When iron concentrate with the iron grade of 65.21% was taken as raw materials, high-quality DRI with the total iron TFe of 86.1% and the metallization rate of 94.9% can be obtained at optimum operation conditions (pellet size of 8 to 10 mm, preheating at 900℃for 30 min and reduction at 1000℃ for 30 min).
Abstract: Laterite nickel ore as raw materials, pulverized coal as a reductant, CaO as a flux, binder and water were pressed into carbon-containing pellets by using a twin-roller ball press. The pelletizing characteristic of laterite nickel ore was studied and the effects of some factors such as the reductant, water amount and binder on the pellet strength were investigated. It is shown that laterite nickel ore has a better pelletizing property and the pellets still have a certain strength without adding any binder. Fine-grained coal reduces the pellet strength but an appropriate content of coarse-grained coal can improve it. The compressive strength of the pellets gradually increases with the water addition amount increasing and reaches the maximum when the water addition amount comes up to 18%; however, if the water addition amount continues to increase, the compressive strength shows a decreasing tendency. The falling strength of the pellets gradually increases with the increase of water addition amount. When the bentonite addition amount increases the pellet strength gradually increases and reaches the maximum at the bentonite addition amount of 2%; however, if the bentonite addition amount continues to increase, the pellet strength declines slightly. What is more, bentonite contains higher contents of SiO2 and Al203, which can reduce the grade of useful elements in the pellets, so the addition amount of bentonite should not be too high.
Abstract: This article studied the smelting process and machinability of BN-type free cutting steel. Samples with different B and N contents were prepared by cold crucible induction melting. The precipitation of main inclusions in sample was investigated by theoretical calculation. After that, the morphology, size and composition of BN type inclusions were analyzed. The mechanical test and machining test of the samples were carried out. It is found that adding B and N elements into steel can improve the machinability of the steel, but do not affect the mechanical properties.
Abstract: In-situ tracing metallographic observation, Vickers hardness test, transmission electron microscopy and electron back-scattered diffraction were carried out to investigate the evolution and thermal stability of bainite in a low-carbon steel during reheating in a temperature range of 550 to 675℃. Experimental results show that the bainite evolves into polygonal ferrite through the way of recovery and recrystallization. In this process the granular bainite changes into polygonal ferrite firstly and then the polygonal ferrite consumes bainitic ferrite, so the bainitic ferrite exhibits a higher thermal stability than the granular bainite. During recovery, low degree boundaries between adjoining ferrite laths are partially removed, and the ferrite laths are tilted and merged. There is an evolutionary stable stage between recovery and recrystallization during reheating of bainite, and the duration of the stable stage is significantly prolonged with the drop of temperature.
Abstract: The precipitation and ripening behavior of secondary phases in automobile beam steel with different nitrogen contents were investigated by the thermo-kinetic theory and the Ostwald ripening theory. It is found that increasing the content of nitrogen in the steel can promote the precipitation of V(C,N) in austenite, thus the ferrite grains are greatly refined, and the ferrite grain size is decreased to 4.7μm when the content of nitrogen increases to 4.2×10-4. The curve of nucleation rate to temperature calculated by the thermodynamic theory shows that nitrogen can effectively expand the temperature zone of the biggest nucleation rate, and the precipitation-temperature-time curve demonstrates that the shortest incubation temperature can rise from 840℃ to 968℃ when the content of nitrogen increases from 5.5×10-5 to 4.2×10-4. Transmission electron microscopy observations reveal that the size of precipitated V(C,N) is effectively decreased with the increasing content of nitrogen. The calculated Ostwald ripening rate of VN in austenite indicates that the ripening rate weakens with the temperature dropping, and moreover increasing the content of nitrogen also can decrease the ripening rate to inhibit the ripening growth of the precipitated secondary phases.
Abstract: Oxidation films were prepared on ZA1Sil2 alloy surfaces by micro-arc oxidation (MAO). The effect of Li2SO4 addition into the electrolyte on the performance of the oxidation films was investigated by thickness measurement, scanning electron microscopy (SEM), X-ray diffraction (XRD), and electrochemical test. It is found that the oxidation film thickens and coarsens with increasing Li2SO4 content. The results of XRD analysis indicate that the oxidation film is mainly composed of Al2O3 phase and mullite phase. Compared with untreated ZA1Sil2 alloy samples, the samples treated by micro-arc oxidation with Li2SO4 addition have a better corrosion resistance.
Abstract: Experiments were performed to investigate the effect of extrusion ratio and temperature on the microstructure, texture and mechanical properties of Ti-6A1-4V titanium alloy. When the extrusion temperature is in the range of 150 to 350℃ above the phase transition temperature (T~) and the extrusion ratio (A) is in the range of 25 to 85, dynamic recrystallization has completed and there is a uniform Widmanst~tten structure in the extruded section. Increasing the extrusion ratio and decreasing the extrusion temperature can refine grains in the extruded section. When the extrusion ratio is low at 25, the texture strength is weak and random distributed. With the extrusion ratio increasing, the texture strengthens and is inclined to evolve into the (1219) fiber texture. The perfect (1219) fiber texture is achieved when the extrusion ratio is 85. The comprehensive performance of the extruded section obtained under different extrusion conditions is stable because of the combined effect of texture and grain refinement, the difference in strength is less than 35 MPa, and the differences in elongation and necking rate are all less than 3%.
Abstract: Sewage sludge incineration ash is comprised of large amounts of SiO2, a certain amount of P and many kinds of heavy metals. By utilizing sewage sludge incineration ash as the composition adjustment agent, nucleation agent and flux, glass ceramics with good mechanical performance and chemical stability were successfully synthesized by synergistic preparation with blast furnace slag without adding any chemicals. The influence of heat treatments on the glass-ceramic properties and the crystallization process of the glass ceramics were studied by differential scanning calorimetry (DSC), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS), mechanical properties test, and chemical stability test. It is found that the optimum heat treatment condition for preparing the glass ceramics is heating at 850~C for 1 h as a nucleation and sintering process and then heating at 980~C for 2 h as a crystallization process. Under this heat regime, the glass ceramics have the best performance with the rupture strength of 45 MPa, the compressive strength of 200 MPa and the mass lost rate of acid or alkali resistant of less than 0.2%. The initial crystallization temperature of the glass ceramics is 880~C, and crystalline phases in the glass ceramics mainly contain anorthite and a small amount of gehlenite. However the proportion of gehlenite in the glass ceramics increases with the crystallization temperature raising and the crystallization time prolonging. The gehlenite shows a radial needle-like structure, which can contribute to the improvement in bending strength of glass ceramics; but too long crystallization time is harmful to their properties due to grain growth and coarsening.
Abstract: Pre-oxidized polyacrylonitrile (PAN) fibers were used as a precursor and they were in situ transformed into carbon fibers to toughen alumina ceramics in vacuum sintering. The chemical structure and phase of the pre-oxidized PAN fibers were studied by thermogravimetric/differential thermal analysis (TG/DTA) and X-ray diffraction to determine a suitable sintering process of the composites. The effects of pressing ways and pre-oxidized PAN fiber content on the microstructure and properties of the composites were explored. It is found that the exothermic peak around 444~C in the DTA curve and the diffraction peak around 17~in the XRD pattern of the pre-oxidized PAN fibers are due to incompletely oxidized PAN molecules during pre-oxidation, while the endothermic peak at 1073~C and the diffraction peak around 25.5~show the pre-oxidized PAN fibers having begun to transform into carbon fibers during the sintering. The mechanical properties of the composites prepared by hot pressing are superior to those by pressureless sintering. With the pre-oxidized PAN fiber content increasing, the density and microhardness of the composites decline, however the fracture toughness increases first and then decreases. When the volume fraction of the pre-oxidized PAN fibers is 20%, the fracture toughness of the composites is up to 9.39 MPa·m1/2. It illustrates that the in situ transformation carbon fibers improve the fracture toughness of the composites. The toughening mechanism is mainly fiber pulling-out and deboning.
Abstract: In order to obtain a kind of high temperature-resistant and wear-resistant material for continuous casting molds, yttria partially stabilized zirconia (YPSZ) coatings were prepared on pure copper substrates by high-efficiency supersonic atmosphere plasma spraying (SAPS). The microstructure of the coatings was characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), color 3D laser scanning microscopy and image software (Image-pro Plus). The wear resistance of the coatings and the effect of chemical hardening on the wear resistance were investigated through a pin-on-disk tribometer under dry friction at room temperature. It is found that the composition of the coatings is completely t'-ZrO2 phase. The fracture microstructure is composed of columnar crystals and a small amount of partially melted particles. The cross-sectional morphology exhibits good integrity. The porosity and the surface roughness are 1.2% and 6.457 tim, respectively. Pin-on-disk test against corundum show that the friction coefficient, average wear width and wear volume of the coatings before chemical hardening is 0.5 to 0.6, 3638.8 μm and 1.25508×10-2 mm3, respectively. The wear mechanism is abrasive wear resulting from brittle fracture. The wear resistance of the coating after chemistry hardening is greatly improved that the width and volume of wear reduce drastically and the degree of brittle fracture is lighter.
Abstract: Three kinds of carriers TiO2, TiO2-ZrO2 with the molar ratio of 1:1, and TiO2-ZrO2 with the molar ratio of 4:1 were prepared by a sol-gel method, and then the corresponding catalysts were obtained through loading a certain amount of active ingredient MnOx on the carriers. The carriers and catalysts were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Some experiments on the selective catalytic reduction of NO with ammonia (NH3-SCR) were performed in order to investigate the activity of the catalysts. It is found that TiO2-ZrO2 (4:1) has the minimum particle size and its particles are highly dispersive among the three carriers. When adding ZrO2, Zr4+ ions dope into the TiO2 lattice by substituting Ti4+ ions, and thus the lattice distortion is triggered and the crystal transformation is restrained in the TiO2. Furthermore, Zr also promotes the dispersion of the active ingredient on the carrier, thereby improves the activity of the catalysts. The 10%Mn/TiO2-ZrO2(4:l) catalyst that adding 10% Mn to TiO2-ZrO2(4:l) has the highest activity among the three catalysts. The conversion of NO can reach 92.6% when catalyzed by this catalyst at 130℃. The activity of 10%Mn/TiO2-ZrO2(4:l) decreases when adding 10% of water vapor at 150℃, and it can restore when cutting off water vapor. But water vapor has no effect on the activity of 10%Mn/TiO2-ZrO2(4:l) at 200℃.
Abstract: The effect of iron oxide content in fly ash on the adsorption characteristics of polycarboxylate super-plasticizers with different structures was studied by the experiments of fluidity of paste,~potential, total organic carbon (TOC) and infrared spectra. The influence mechanism of iron oxides on the cement dispersion properties of polycar-boxylate superplasticizers was discussed and the improved method was put forward. It is found that iron oxide content in fly ash has a significant impact on the fluidity of cement paste mixed with polycarboxylate superplasticizers. When iron oxides are 18% of the total fly ash by mass, the corresponding slurry fluidity will be nearly lost; adding sodium sulfide can reduce the adsorption characteristics of iron oxides onto polycarboxylate superplasticizers, and the slurry fluidity is improved. Compared with common fly ash, high iron oxide fly ash has stronger adsorption characteristics onto polycarboxylate superplasticizers, with organic carbon content in the additive solution decreasing by one-third. Electrophoresis experiments indicate that the more the iron oxide content, the smaller the absolute value of~potential and the poorer the dispersion stability. Infrared spectra show that the adding of sodium sulfide reduces the adsorption characteristics of high iron oxide fly ash onto polycarboxylate superplasticizers.
Abstract: In order to solve the problem of high exhaust gas temperature in W-shaped gas-fired radiant tubes, three kinds of structures were designed to improve the heat exchanger performance. Numerical simulation was carried out by using ANSYS FLUENT software. The performance parameters of heat exchangers with different structures were obtained, such as exhaust gas outlet temperature, preheated air temperature, pressure loss, heat flux in each surface, and heat resistance change with and without baffles. It is shown that the quantity of heat exchange increases by 57.6% after the central air tube changes from one tube of φ79 mm to six tubes of φ33 mm and by 20.7% through adding a double trip of exhaust gas. After inserting the sealed baffle and porous baffle, the quantity of heat exchange increases by 5.7% and 5.3% respectively, and the thermal resistance between air and exhaust gas decreases both by about 20%. The pressure loss of the porous baffle is lower by 47.4% than the sealed-baffle.
Abstract: With the increasing of wind power generation facilities, structure safety is particularly important in the service of wind power towers. Wind power towers are a typical top-heavy structure which is similar to a kind of thin-wall cylindrical structure. The supporting structure of a wind power tower is forced under the pressure of the upper engine room, rotor and blades, the side of the tower is thrust by ocean wind, and when earthquakes happen the tower undergoes the horizontal and vertical seismic action. Since the whole structure of the tower is asymmetric, in order to clarify the mechanical characteristics and ensure the structure safety, the tower structure was studied by foreign and domestic numerical calculation methods. The differences in force of the tower structure were analyzed under wind load only, earthquake load only and the wind-earthquake load combination case. Then the dynamic responses of the tower structure were performed under the combined action of wind and earthquake load with different earthquake input directions. The results pointed out the earthquake input direction which is most disadvantageous to the tower structure and the weak position of the tower structure is door opening location under this condition.
Abstract: LF refining process plays an important role in the temperature adjustment of molten steel, and precisely predicting the LF end-point temperature of molten steel is of great importance to actual production. Generally speaking, the prediction models of LF end-point temperature include the mechanism model and the black box model. The mechanism model can reflect the influence of each factor on the end-point temperature of molten steel, but it is dimcult to obtain the expected prediction accuracy due to the limited comprehension of heat transfer in LF refining process. The black box model can usually achieve high prediction accuracy, whereas it does not reveal the effect of each factor. Moreover, the black box model has limited applications when process conditions are changed. Taking LF refining process in Fangda special steel plants as an object of study, this paper establishes a grey box model for predicting the LF end-point temperature of molten steel based on the mechanism model and the black box model. The grey box prediction model can not only indicate the impact of each factor, but also provide the precise prediction of LF end-point temperature. Verification results show that the hit rate of the grey box model is greater than 95% while the predictive error is within ±5℃.
Abstract: This article introduces a novel algorithm to solve the large time-consuming problem of the existing improved ant colony optimization (ACO) based on particle swarm optimization (PSO). A new pheromone update method which combines the global asynchronous feature and elitist strategy was used in the algorithm. Moreover, the iteration steps of ACO invoked by PSO were reasonably reduced. The algorithm was applied to solve the path planning problem of landfill inspection robots in Asahikawa, Japan. It is shown that the algorithm has a better performance in search speed compared with other algorithms recently reported.
Abstract: The effect of hydrodynamic pressure on bridge piers was considered by a simplified model of additional water and the interaction between ice and bridge piers was taken into account by a dynamic ice force model, then a seismic response analysis model was established for a single-column pier surrounded by sea ice and the nonlinear seismic responses of the pier subject to different types of earthquakes were analyzed by using the time-history analysis method. It is shown that the least favorite seismic responses of the pier occur when the mass of sea ice is 5×106 to 5×107 kg, which can be used as the design mass of sea ice to design a bridge pier. The mass of sea ice under the maximum curvature condition of the pier increases with the water depth increasing. The curvature ductility demand coefficient, the maximum displacement and the residual displacement of the pier surrounded by sea ice are several times larger than the seismic responses of the pier which is not. Since sea ice also makes the moment-curvature hysteretic curves of the pier's bottom cross-section present a downfallen ‘S’ form significantly, the deformability and energy dissipation capability of the pier drop remarkably. Compared with the pier subjected to a near-field seismic wave, the effects of sea ice on the maximum displacement and residual displacement of the pier subjected to a far-field seismic wave are more remarkable.
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
