Abstract: In order to master the regularity of dust mass concentration distribution in a belt conveyer roadway and obtain rational parameters for the design of dust removal by ventilation, taking the 40# belt conveyer drift of the hoisting system in Xishimen Iron Mine as the research background, dust mass concentration in the belt conveyer roadway was simulated using the discrete phase model for computational fluid mechanics, which is based on the theory of gas-solid two-phase flow. By contrast with field measurement of dust mass concentration distribution, the simulating results were essentially coincident with the measured data, indicating that using the Euler-Lagrange method to simulate dust mass concentration distribution in the belt conveyer roadway is feasible. In the design of dust removal by ventilation, the dust mass concentration can be kept within 3 mg·m-3 as the wind velocity is 3 m·s-1. The dust mass concentration is lower at the belt conveyer velocity of 2.5 m·s-1. In addition, regular wall sprinkling can decrease the dust mass concentration.
Abstract: Aerosol flotation technology was used to improve the molybdenum recovery of some copper-molybdenum ores. In the flotation process, kerosene, a primary collector for molybdenum, was added into the pulp in an aerosol form. Kerosene dosage test, flotation speed test, and the influence tests of pH values and grinding fineness on the aerosol flotation process were carried out. It is found that the molybdenum recovery of copper-molybdenum bulk flotation phase increases by 3% and the flotation time shortens by 20%. At the same molybdenum recovery the dosage of kerosene decreases by 40%. The best grinding fineness for aerosol flotation is that particles of 0.074 mm in size account for 65%, and the optimum pH value of the pulp is 9. Compared with traditional flotation, aerosol flotation technology can decrease the dosage of reagents and accelerate the flotation speed, showing more advantages for low-grade refractory ores.
Abstract: Contrast experiments between fluidizing reduction roasting and muffle furnace static roasting were performed with a fluidized bed and a muffle furnace. It is found that the former is obviously better in terms of roasting time and reduction efficiency. CO and N2 were used as reducing gas and fluid medium in fluidizing reduction roasting, respectively, and the effects of operation parameters such as roasting temperature, roasting time, and reducing atmosphere on the reduction efficiency were analyzed. When the roasting temperature is 800℃, the roasting time is 3 min, and the volume fraction of CO is 10%, a reduction efficiency of greater than 97% for MnO2 in pyrolusite can be achieved. The reduction kinetics was also investigated, and it is confirmed that the reduction process is controlled by interface chemical reaction. The apparent activation energy of the reduction is about 38.817 kJ·mol-1.
Abstract: As pretreatment or post-treatment for coking wastewater, two kinds of diatomites from Linjiang and Zhangjiakou in China were selected for the adsorption and purification of coking wastewater. The influences of diatomite calcination temperature on their properties and purification performance were studied during coking wastewater treatment. The feasibility of using the diatomite as a sorbent in coking wastewater treatment was also discussed. Energy dispersive spectroscopy results indicate that raw Zhangjiakou diatomite shows a higher organic content. The morphologies and crystal structures of both the diatomites do not significantly change before and after calcination. A decrease in carbon content was observed for both the diatomites after calcination. As to the color removal at 254 and 269 nm, Linjiang diatomite is particularly superior to Zhangjiakou diatomite whether the diatomites are calcined or not. For example, after calcination at 500℃, the removal of chemical oxygen demand achieves to 61.8% for Linjiang diatomite while it only reaches 30.3% for Zhangjiakou diatomite. In addition, the removal of ammonia nitrogen can achieve to 50.4% for Linjiang diatomite after the calcination. It is concluded that the diatomite involved can be used for the pretreatment and post-treatment of coking wastewater.
Abstract: Raw biomass was carbonized by two different heating patterns to produce biomass char at 400, 500, 600 and 700℃ for 30, 60 and 90 min. The composition, microstructure, and combustibility of the derived biomass char were investigated by scanning electron microscopy (SEM) and thermogravimetric analysis (TG-DTG). The effects of preparing conditions on the biomass char's yield and reactivity for reacting with CO2 were studied. It is shown that the biomass char has typical duct structure or sheet structure, which is different from coal. The contents of N, S, ash and alkali metals in the biomass char are much lower, but its combustibility is better than coal samples, suitable for using as a reducing agent and a heating agent in ironmaking to partially replace coal and coke. The optimum preparing condition of biomass char for ironmaking is to carbonize raw biomass by a constant temperature heating pattern at 500℃ for 30 min.
Abstract: The effect of forced intermediate water cooling on austenite grains in plates was studied to find a method of controlling grain growth in intermediate slabs due to staying for cooling. Changes in grain size of the intermediate slabs of low alloy steel Q345B and Nb-Ti bearing steel during cooling processes were analyzed by thermal simulating, which includes deforming at 1 050℃ and then rapidly cooling to scheduled temperature from 1 050 to 950℃ for a certain time. Control methods of grain growth were suggested for plates during cooling processes and grain growth models were established for Q345B steel and Nb-Ti bearing steel during the intermediate cooling process. The stability of austenite grains is poor for Q345B steel during the intermediate cooling process, whereas austenite grains in Nb-Ti bearing steel have good stability due to the pinning effect of precipitates, which mainly consist of niobium. Austenite grain growth in the intermediate slabs can be controlled by forced water cooling. The average grain size of 63 mm-thick intermediate slabs after forced water cooling reduces by about 20 μm. In actual production the impact toughness of 16 mm-thick Q345B steel plates after forced intermediate water cooling increases by 25% to 70%.
Abstract: A two-dimensional mathematical model of solidification and heat transfer for a bloom with the cross section of 425 mm × 320 mm was established, which simulated the growth process of the solidified shell. The model was verified by nail-shooting experiments in the narrow side of the bloom. The solidified shell thickness distribution at any fixed location in the casting direction and the position of the solidification end point were got by the model. It is found that the traditional solidification square root law is not fit for describing the solidification process. A mathematical relationship was regressed between the solidified shell thickness and the square root of solidification time in the center of the wide side. The regression results show that it is approximately linear from the mold meniscus to the secondary cooling zone export, which satisfies the square root law. However, from the secondary cooling zone export to the solidification end point, it is a non-linear relationship, which no longer follows the square root law.
Abstract: The effects of coiling temperature on the microstructure and nano-scaled precipitates of ultra-low carbon steel with deep drawability, together with the corresponding textures of the annealed cold-rolled sheet, were investigated by Gleeble-1500 hot simulator, X-ray diffraction, optical microscopy and transmission electron microscope. It is found that nano-scaled precipitates in the hotrolled steel sheet are mainly CuS and CuS-MnS. The precipitates are less, coarse, and sparse when the coiling temperature is lower. To obtain a strong favorable texture and a better drawing property, the best coiling temperature should be under 600℃.
Abstract: The microstructure, phase composition and mechanical properties of hot rolled C-Mn-Si transformation-induced plasticity (TRIP) steel which was low-alloyed with Nb and V were investigated by means of electron back scatter diffraction (EBSD). It is found that the deformation of austenite by hot rolling and the cooling process followed has direct impact on the microstructure concerning the shape, size, and distribution of ferrite, bainite and retained austenite, which determines the ultimate mechanical properties of the TRIP steel. The simulated results for coiling temperature of the TRIP steel show that the hot strips coiled at 400℃ obtain the best comprehensive mechanical properties compared to those coiled at 450 and 350℃.
Abstract: A type of Q125 grade high-strength low-alloy oil well casing steel was designed and the effects of heat treatment processes on its microstructure and properties were investigated. Compared with the process of quenching at 870℃ and tempering at 500℃, the steel quenched at 850℃ and tempered at 500℃ has preferable combination of strength and toughness. In comparison with quenching at 870℃, the steel quenched at 850℃ has better mechanical properties because of smaller original austenite grains, which lead to a smaller size of packets and blocks. Quenching temperature has little influence on the precipitation behavior. TiN with a larger size or TiC and TiN associated precipitations can restrain original austenite grain coarsening through pitting austenite grain boundaries; TiC with a smaller size, which is rich Mo, can be an effective barrier to dislocation motion, and therefore has great contributions to improve the strength of the steel.
Abstract: Nickel-free stainless steel powders contained nitrogen were prepared by gas atomization, formed by hot isostatic pressing (HIP), and treated by solution. The HIPed materials have excellent strength, plasticity, and toughness; their tensile strength, yield strength, elongation, area reduction and impact energy are 850 MPa, 505 MPa, 44.5%, 47.5%, and 44 J, respectively. After solution treatment at 1 100℃ for 1 h the plasticity and toughness improve obviously; the elongation, area reduction, and impact energy is 50.0%, 55.5%, and 68 J, respectively. Experimental data show that the prepared nickel-free stainless steel 17Cr10Mn2MoN has better strength and corrosion resistance than 316L stainless steel.
Abstract: The flow behaviors of 6005A and 6082 aluminum alloys were investigated by high-temperature isothermal compression on a Glebble-1500 thermal-mechanical simulator at deformation temperatures of 450 to 550℃ and strain rates of 0.005 to 10 s-1. The flow stress curve of 6005A aluminum alloy exhibits a waveform character at different deformation temperatures under the condition of low strain rate. With increasing strain rate the competition between softening and hardening closely reaches to a balance so that the flow stress appears as a steady state. At high strain rate, the hardening is dominant during the hot deformation and there is a waveform increase in the flow stress curve because of the competition between reverting and hardening. The flow stress curve of 6082 aluminum alloy, however, does not show the waveform character at low strain rate. A steady-state stress is also displayed at medium strain rate. But the waveform flow curve is shown at high strain rate. Both of the alloys are positive strain rate sensitive materials and their hot deformation is controlled by the thermal activation. Finally the relationships among flow stress, strain rate and deformation temperature were proposed for 6005A and 6082 aluminum alloys, respectively.
Abstract: 1060 aluminium cladding AZ31 magnesium alloy composite ingots were prepared under gas protection to investigate and improve the interfacial combination. The microstructure, phase constituents and microhardness of the matrix and the interface were studied by use of optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction (XRD). It is found that the microstructure of the as-cast AZ31 magnesium alloy consists mainly of the α-Mg matrix and the typical divorced eutectic of α-Mg and β-17Al12 phases distributed along grain boundaries. A diffusion fusion layer forms in the interface, leading to a complex metallurgical interface with a multilayer of the α-Mg solid solution zone, the eutectic (α-Mg + β-17Al12) zone and the Mg-Al intermetallic compound zone. The Mg-Al intermetallic compounds are made up of β-17Al12 and AlMg. It is proposed that the formation mechanism of the complex interface layer is due to the emergence of a molten bath on the 1060 Al plate surface at AZ31 melt pouring moment and the rapid solidification subsequently.
Abstract: The corrosion behavior and electrochemical characteristics of pure Zn and Zn-Al pseudo-alloy coatings in chlorine ioncontaining environment were investigated by salt spray test and electrochemical impedance spectroscopy (EIS). The surface morphologies and phase compositions of the coatings and the corrosion products were analyzed by scanning electron microscopy (SEM) and Xray diffraction (XRD). A preliminary discussion was carried out on the corrosion mechanisms of the two kinds of the coatings. It is found that the corrosion product layer on the pure zinc coating sample is loose and porous with prolonging test time, the main corrosion products are Zn5(OH)8Cl2H2O, ZnO and Zn5(CO3)2(OH)6, and some areas in the corrosion product layer have cracked after salt spray testing for 768 h. A compact corrosion product layer forms on the zinc-aluminum pseudo-alloy coating with the time prolonging, and the main corrosion products consist of Zn5(OH)8Cl2H2O、Zn0.71Al0.29(OH)2(CO3)0.145·xH2O and ZnAl2O4. EIS results indicate that the charge transfer resistance of the two coatings increases during the corrosion process. The impedance of the zinc-aluminum pseudo-alloy coating is significantly greater than that of the pure zinc coating, showing a better corrosion resistance.
Abstract: Burden distribution in a blast furnace was estimated based on least squares approximations and multi-radar data. Firstly, a three-segment curve, which includes two straight lines and a quadratic curve, was used to describe the burden distribution. Secondly, based on the burden distribution principles, some constraint equations were obtained to estimate parameters in the three-segment curve, which makes the burden surface profile more reasonable. Then, the burden distribution was estimated by using least squares approximations and multi-radar data, and a real-timely display of the burden surface profile could be achieved. A numerical example with real multi-radar data obtained from a steel plant shows the effectiveness of the estimate method.
Abstract: Local fluid flow and mass transfer in a converter bath were studied by a cold model. According to the conductivity measured in different regions, the local mass transfer and mixing effect were determined in the bath by using different lance nozzles, lance heights and bath shapes. The effects of the three factors on the mass transfer, dead volume distribution, mixing time and velocity uniformity were analyzed. It is found that the dead volume mainly lies in the bottom near the sidewall and the vortex heart for a standard bath (diameter-to-depth ratio=3.1), but does in the sidewall region for a shallow bath (diameter-to-depth ratio=5.2). Increasing the inclination angle of the lance nozzle and the ratio of bath diameter to depth is beneficial to increasing the circulation radius of the bath, improving the bath flow and reducing the dead volume.
Abstract: A system for fast measuring hydrogen content in aluminum alloy melt was developed based on dynamic measurement of hydrogen partial pressure and Sieviet's law. The system consists of a changing volume vacuum chamber unit, a changing volume driven unit and a data acquisition and processing unit. The hydrogen content in aluminum alloy melt was gotten by monitoring the real pressure and computing the theoretical pressure in the vacuum chamber, calculating the difference between the two pressures, finding the hydrogen partial pressure, and using the empirical formula. The system is fast and accurate in testing, simple in operating, and low in testing cost.
Abstract: Asymmetric work rolls in hot strip mills can give consideration to both shape control and schedule free rolling; however, their key parameters are usually designed with experience and lack for corresponding basis. This paper proposed a theoretical design method for key parameters of asymmetry work rolls in hot strip mills. As known conditions could not be accurately given during the design process, multi-criterion satisfactory optimization was introduced to the parameters design of asymmetry work rolls. Then a comprehensive satisfaction objective function was established and the optimal value was solved with a simulated annealing genetic algorithm. Using the satisfactory solution instead of the optimal solution makes the optimization results of the roll shape parameters more scientific. An application on a certain hot rolling production line indicates that the optimized roll contour achieves desired results in both shape control and schedule free rolling.
Abstract: Both transport time and temperature drop in transport processes were analyzed for the 304 stainless steel smelting flow in an electric arc furnace (EAF). The relationship between the temperature schedule in each process and continuous casting heats was established. In the existing temperature schedule the number of continuous casting heats was two. The temperature schedule with different continuous casting heats was presented by taking the process of six continuous casting heats for example. The transport energy during transport processes was calculated so as to analyze the relationship between continuous casting heats and different types of transport energy. A method for determining the optimum number of continuous casting heats was proposed which takes the transport energy into account. When the transport energy of increasing the continuous casting heats is less than the consumables' energy consumption of a new casting, the most number of continuous casting heats is the optimum.
Abstract: The hybrid direct hot charge rolling (DHCR) production of continuous casting to hot rolling and the production mode of reheating furnaces were analyzed. A schedule model of reheating furnaces based on hybrid DHCR production was established. On the basis of meeting the requirements of the reheating furnace process, the model considers the waiting time before slabs entering the reheating furnaces and the idle time of the hot rolling mill. The Tabu search algorithm was used in the model. Finally, two slab groups, which are few varieties with large quantities and many varieties with small quantities, were simulated in a 1 580 mm hot rolling line for specific and non-specific reheating furnace modes. Simulation results show that the specific reheating furnace mode can significantly improve the thermal efficiency of reheating furnaces.
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
