Abstract: To explore the percolation regulation and inducement of waste fine particles in ore drawing by the block caving method, a simulation is undertaken by using discrete element method software EDEM. This simulation contains coarse-to-fine particle amount ratio, diameter ratio and moisture content, and sets marker particles in different regions to trace the migration of adjacent coarse and fine particles. The results indicate that the ore-drawing advance dilution rate decreases with increasing coarse-to-fine particle amount ratio. The percolation rate of waste fine particles increases with increasing diameter ratio and is significantly affected by moisture content. Moreover, the percolation rate of fine particles is greater than the decline rate of adjacent coarse particles. The results provide a theoretical support for further studying and discussing the ore loss and dilution, determining the stope structure parameters and optimizing the ore drawing management system.
Abstract: To solve the problems of the precontrol roof sublevel filling method in deep mining, such as the complexity of the excavation process of precontrol roadway roofs and the suseeptibility of precontrol roofs to blasting vibration, this article introduces a collaborative stoping based sublevel filling method which utilizes horizontal and vertical holes at the same time. The sublevel filling method can effectively solve the roof stability problem of surrounding rock through changing the precontrol roof into a rear control[roof by altering the support order. Furthermore, optimization research is performed on the sublevel filling method based on collaborative stoping:firstly, the structural parameters are optimized by stability analysis using SURPAC and ANSYS; then, the partition drawing and supporting method is applied to solve the problems of the poor support quality of the two sides and the inefficient ore-drawing. A case study of Xincheng Gold Mine shows that the displacement of the roof significantly decreases and the economic indicators:improve, indicating safe and high-efficient mining of the thick and large orebody under high geostress.
Abstract: CH4 is a typical and special detonation mixture. Based on the experimental method, digital image processing was performed to study the detonation stability theory of methane. A premixed CH4 + 2O2 mixture was ignited in a tube with an inner diameter of 50.8 mm under different initial pressures. Smoked foils were used to record the cellular structure of spinning detonation. The average detonation velocity measured is similar with the CJ detonation velocity and it demonstrates that steady detonation happens when the initial pressure is higher than 5 kPa. The triple point trajectory leaves a very irregular pattern in smoked foils. In order to decrease human error, the digital processing technology was utilized and improved. The CH4 + 2O2 mixture shows high degree of irregularity in the computation of histograms and the autocorrelation function. The cellular size and gap of the unstable premixed CH4 + 2O2 were given. It is found that the results measured by digital image processing are accurate and by eyes are too big. The research can calculate the cellular size and the degree of instability of the unstable premixed CH4 + 2O2 and improves the quantitative irregular calculation method.
Abstract: To explore the combustion performance of blended fuels after adding semicoke, the combustion processes of coal, semieoke, and their mixture were studied by thermogravimetric analysis (TGA) and the combustion characteristic parameters were obtained. Due to the different mechanisms in different temperature ranges of combustion reaction, the kinetics of the combustion process was analyzed by the sectioning method, and the shrinking core models of interracial chemical reaction and internal diffusion were used to model the process at the earlier stage and the later stage to obtain the kinetic parameters, respectively. The results show that with increasing semicoke content in blended fuels, the ignition index and the combustion characteristic index decrease, and the combustion activation energy of blended fuels increases from 76.79 kJ·mol-1 to 92.75 kJ·mol-1 at the earlier stage and from 102.62 kJ·mol-1 to 107.94 kJ·mol-1 at the later stage. It is demonstrated that the combustion performance of blended fuel deteriorates with the increasing semicoke content. By comparing the combustion characteristic parameters and kinetic parameters of blended fuels with different semicoke contents, the mass fraction of semicoke should be controlled below 15%.
Abstract: Non-isothermal experiments were carried out at different heating rates to further study the gasification reaction kinetics of semieoke with CO2, and the gasification mechanisms of Fuding semicoke with CO2 were confirmed in different stages. Then, it is reasonable to adopt a attempting method of subsection to study the gasification reaction kinetics and confirm the mechanism functions of the earlier and later periods in the reaction process, which are f(α)=(1-α)[1-φ1n(1-α)]1/2 and f(α)=(3/2)[(1-α)-1/3-1]-1, so the related kinetic parameters and corresponding dynamic models in different stages of the process are established. After data-fitting of the kinetic models in different stages, experimental data fit well with these models and the correlation coefficients are above 0.98. At last, according to the calculated kinetic parameters, it is clearly realized that there is compensatory effect for the activation energy at different heating rates, which is a relational expression between the activation energy and the pre-exponential factor.
Abstract: To explore the effect of high temperature interaction between sinter and lump ores on the formation behaviors and characteristics of primary slags, experimental and theoretical methods were used to study the primary-slag formation behaviors and characteristics of sinter, lump ores and their integrated burdens in a blast furnace. The results show that the primary-slag formation temperature intervals of single iron ores are wide. Due to the high temperature interaction the primary-slag formation behavior markedly improves and the viscosity of primary slags decreases. However, the high temperature interaction is influenced by the chemical composition, reducing properties and porosity of iron ores.
Abstract: Dynamic oxidation is not only in favor of that Ti components in molten Ti-bearing blast furnace slag enrich into the design phase (perovskite), but also promotes the coarsening and growth of perovskite phase. The enrichment and settlement of coarsened perovskite are carried out under the action of gravity. The nucleation rate and the crystal growth rate of perovskite phase in molten Ti-bearing blast furnace slag under dynamic oxidation condition were studied by using the kinetic equation of glass formation. The results show that low valence titanium (Ti2+) and (Ti3+) are oxidized to (Ti4+) under dynamic oxidation condition by blowing oxygen, which can promote the precipitation of perovskite and increase the crystal growth rate. When continuing to blow oxygen, the oxidizing time would be too long, TiC and TiN particles decrease and finally almost vanish, the slag viscosity decreases, and the crystallization of perovskite phase transforms from heterogeneous nucleation into homogeneous nucleation. As a result, the precipitation temperature decreases and the precipitation temperature range shortens, which restrain the coarsening and growth of perovskite.
Abstract: The continuous cooling transformation (CCT) diagrams of SDAH13 hot extrusion die steels with different mass fractions of Al (0.77% and 1.43%) and without Al were measured by dilatometry. The effects of Al on the CCT diagrams, microstructure and hardness of SDAH13 steels were studied by optical microscopy, scanning electron microscopy (SEM) and Vickers hardness test. The results show that the phase transformation temperature points (Ac1, Ac3 and Ms) of SDAH13 steels significantly increase, tile contents of retained austenite in the quenched steels decrease, and the a-y multi-phase region expands with the increase in mass fraction of Al. However, when austenited at 1060 ℃, Al has no obvious influence on the critical cooling rate (0.30 ℃·s-1) of bainite transformation, but bainite phase region broadens. Meanwhile, the critical cooling rates of pearlite transformation of SDAH13 steels with the Al content of 0.77% and 1.43% are 0.05 ℃·s-1 and 0.3 ℃·s-1, respectively, which are higher than the critical cooling rate (0, 02 ℃·s-1) of pearlite transformation of SDAH13 steel without Al. Pro-eutectoid ferrite appears at the cooling rate from 0.02 ℃·s-1 to 0.08 ℃·s-1 when the mass fraction of AI reaches 1.43%. Nevertheless, the quenched hardness decreases with Al addition.
Abstract: In order to master the flatness characteristics of strips with different widths for ultra-wide tandem cold rolling mills, taking the sufficient flatness detection data of 1900 mm strips from 2180 mm cold rolling mills as a research object and considering the idea of big data and the cluster analysis method of data mining, this article proposed a cluster algorithm based on density and grid, applied this cluster algorithm to the analysis of flatness detection data under several typical strip widths, and then obtained the flatness characteristics of strips with different widths. A piecewise polynomial function was introduced to describe the strip flatness characteristics, and the analysis results of polynomial coefficients for strips with different widths were gotten. The proposed cluster algorithm based on density and grid and the piecewise function analysis method can be applied to analyze plenty of flatness detection data quickly and accurately, and the flatness defect characteristics and parameterized expression can be obtained, which will be a data basis of roll contour improvement and strip flatness control strategy optimization for cold rolling mills, especially ultra-wide cold rolling mills.
Abstract: The hot ductility behaviors of Fe-36Ni alloy in the temperature range of 900-1200 ℃ were investigated by using a Gleeble-3800 thermal simulator. The influence factors and mechanism of action on the hot ductility were systematically analyzed by FaetSage software, scanning electron microscopy and transmission electron microscopy. The results show that inclusions in the investigated alloy are mainly Al2O3 + Ti3O5 + MnS, and most inclusion sizes are below 0.5 μm. The hot ductility of the alloy in the temperature range of 900-1050 ℃ is influenced by grain boundary sliding and dynamic recrystallization. Nano-scale size (<200 nm) inclusions at grain boundaries effectively inhibit the occurrence of dynamic recrystallization as a result of the pinning effect and decrease the grain boundary cohesion. Moreover, micro-scale size (>200 nm) inclusions at grain boundaries promote the nucleation and propagation of cracks during grain boundary sliding and decrease the hot ductility of the alloy. Increasing the temperature makes the driving force for dynamic reerystallization larger than the pinning effect, and thus increases the hot ductility significantly by the occurrence of dynamic recrystallization when the temperature exceeds 1050 ℃. In the temperature range of 1100-1200 ℃, the formation of interdendritic cracks, the coarsening of recrystallized grains and the enhanced grain boundary sliding deteriorate the hot ductility of the alloy.
Abstract: A quasi-static method for measuring the magnetostrictive coefficient of Fe-Ga alloys by using laser Doppler effect was put forward, and its working principle was also analyzed. The quasi-static magnetostrictive coefficient of Galfenol was measured. The results show that strains obtained from the measuring setup are consistent with factory data, and the dynamie characteristics curve of Galfenol driven by 10 Hz current is obtained. This method has the following advantages:(1) noncontact measurement can be implemented, (2) the strain of magnetostrietion in any point of the rod surface can be measured, (3) the accuracy is better, and (4) little operator skill is required.
Abstract: To extend the service life of MgO-C bricks which used as the linings of vanadium-extraction converters, MgO-Fe-C bricks were fabricated in this study. The service properties of this novel refractory were comparatively investigated between traditional MgO-C bricks and MgO-Fe-C bricks. The results show that the poor sinterability and anti-erosion property of the decarburized layer at the service temperature of 1400 ℃ are responsible for the short service life of MgO-C bricks. However, for MgO-Fe-C bricks, Fe particles are oxidized in the oxidized layer and in-situ MgO-FeOss forms under the working condition. This can effectively improve the sintering performance, form a decarburized layer with enhanced compactness and bonding strength, and significantly improve the oxidation resistance and slag corrosion resistance of this layer, contributing to extend the service life. MgO-Fe-C bricks have a promising prospect of applications in the substitute for MgO-C bricks as the linings of vanadium-extraction converters.
Abstract: An in-situ transformed carbon fiber toughened alumina ceramic matrix composite was prepared by vacuum hot pressure sintering technology, and the slurry erosion wear behaviour of the composite was tested at different impact angles and velocities on a modified MSH tester. The wear mechanism of the composite and the toughening effect of carbon fiber in the wear process were also analyzed by observing its erosion surface morphology. The results show that Cf/Al2O exhibits a better wear resistance under the conditions of a larger impact angle and a higher impact velocity. The slurry erosion wear mechanism of Cf/Al2O3 is brittle spalling when the surface is repeatedly impacted. The effect of carbon fiber on the erosive wear is bridging the matrix and absorbing the impact energy after cracking. It can inhibit cracks from extending and reduce the loss of the composite.
Abstract: Modified polyester fiber reinforced concrete with different additions was prepared. The dispersivity of modified polyester fibers in concrete by five different mixing methods was studied by an image processing method. With a series of durability tests, the carbonation resistance, chloride penetration resistance and frost resistance of the fiber reinforced concrete were also investigated. The results indicate that the image processing method can evaluate the dispersivity of the fiber reinforced concrete well. The mixing method of "aggregate and binding materials for 60 s + water for 60 s + fiber for 60 s" makes the best dispersivity of modified polyester fibers. It is in accord with direct observations by naked eyes. The compressive strength is increased by the addition of modified polyester fibers. After adding 1.1 kg·m-3 modified polyester fibers, the compressive strength of concrete increases by 14%; but with more modified polyester fibers, the compressive strength no longer increases. The existence of modified polyester fibers in concrete can slow down the diffusion of CO2, the carbonation rate of concrete decreases by 12.6% to 18.9%, and with more modified polyester fibers, the carbonation resistance became better. After the addition of modified polyester fibers, the chloride diffusion coefficient of concrete also decreases. The modified polyester fibers can reduce the surface spalling of concrete during freeze-thaw cycles, which improves the frost resistance of concrete significantly.
Abstract: The theoretical open circuit voltage (OCV) of solid oxide fuel cells (SOFCs) fed with carbon-based fuels and the amount of deposited carbon on the anode were calculated by the minimum Gibbs free energy method. The OCV values of Ni-YSZ Ⅱ YSZ LI LSM anode-supported cells using methane-based fuels were experimentally measured. The resuks indicate that the amount of deposited carbon decreases from the C-comer of the C-H-0 diagram to the carbon deposition boundary at a constant rate. In the case that most of deposited carbon is electrochemically oxidized, feeding fuels with high C:H ratio can enhance the value of OCV; Conversely, fuels with low C:H ratio are suggested. Theoretical analysis shows the rapidly decreasing value of OCV near the OCV boundary (OCV=0 V). Experimental results also reveal that the value of OCV dramatically decreases when the volume fraction of CO2 in fuel gas increases to be higher than 80%. These results imply that the compositions of carbon-based fuels should be near the carbon deposition boundary in the C-H-0 diagram, which is beneficial to suppress carbon deposition without significant OCV reduction. A relatively high value of OCV can be obtained at the H-corner in the non-carbon-deposition zone near the carbon deposition boundary, and the sequence of the value of OCV is CH4 > H2 > CO in the CO2-diluted ambiance at 600 ℃. Furthermore, the value of OCV cannot be significantly elevated via raising the proportion of external reforming or decreasing the temperature.
Abstract: Experimental and numerical studies on double P-type radiant tubes were performed in this article firstly. According to the results, it is found that the deviations of parameters are within 1% except the NOx concentration with big error, indicating that the model has certain reliability. Based on this, the concept of air classification was applied to double P-type radiant tubes, a gas-fired radiant tube with branch pipe nozzles was introduced, and the corresponding mathematical and physical models were verified in this paper. Simulation results show that average flow velocities of the zoned and staged gas-fired radiant tube and the double P-type gas radiant tube are 25.8 m·s-1 and 21.0 m·s-1, and the thermal efficiencies are 65.9% and 64.2%, respectively. The highest wall surface temperature of the zoned and staged gas fired radiant tube is 1047 ℃, and the maximum wall temperature difference is 73 ℃, 15 ℃ less than that of the double P-type radiant tube. The gas average flow velocity increases after being zoned and staged, and the flue gas temperature and wall temperature of the straight pipe and backflow connection rises with a better uniformity of temperature.
Abstract: The effect of argon-to-hydrogen mole ratio on the discharging behavior of argon-hydrogen plasma was simulated and studied on the assumption that argon-hydrogen plasma is in a local thermodynamic equilibrium. The kinetic theory of ideal gases and the classical Chapman-Enskog method were employed in the study. The plasma thermodynamic and transport parameters consistent with the actual condition of the DC arc plasma jet method were firstly found, and secondary development was made on FLUENT software platform. Equations, like current continuum and Ampere's law, and source items, like Lorentz force and Joule heat, which are associated with electromagnetic fields were also taken into account. The results show that when the gas pressure and operating current are 8 kPa and 150 A, respectively, and the argon-to-hydrogen mole ratio changes from 3:1 to 1:3, the maximum flow rate of plasma increases from 829 to 1127 m·s-1, the maximum temperature falls from 20600 K to 16800 K, and the heating capacity of the DC arc improves while the substrate surface temperature uniformity deteriorates. Under the other conditions being unchanged, when the argon-to-hydrogen ratio is 1:2, a relatively uniform and proper substrate surface temperature can be obtained for the growth of diamond films.
Abstract: Hydrodynamic simulations were performed on a bionic water propulsion unit, and the mechanical properties of the propulsion unit were analyzed according to several simulation data under different conditions. This study was focused on the change laws of the lift, thrust and power curves of the propulsion unit at different speeds and altitude conditions, and several conclusions were summarized which would be helpful to design and optimize the bionic propulsion unit. Finally, relevant tests were done by means of an impeller mechanism test system, and the rationality of these conclusions was confirmed through test data. The results show that with increasing speed, the lift and thrust generated by the propulsion unit increase, the machinery efficiency and propulsion efficiency improve, but the lift efficiency decreases. The longer the distance between the axis of the propulsion unit and the water surface, within a certain range the greater the propulsion efficiency and lift efficiency are. Reasonable structure design can significantly improve the propulsion efficiency and lifts efficiency.
Abstract: In response to the problems of artificial low-operation efficiency, high labor intensity, high altitude and high risk in drainage board bolt tightening for high voltage transmission line, a bolt tightening live maintenance robot with double arms and double manipulators was designed in this paper. The key to the successful completion of maintenance work is that double working arms and their ends move from the initial position to the bolt and nut alignment state through the trajectory planning of each joint of the robot. The existed polynomial interpolation of joint trajectory planning depends on trajectory endpoint time, leading to some issues such as the low practicability of the method and the neglect of the constraints of the drive mechanism on the joint state in joint trajectory motion, so an improved polynomial interpolation joint trajectory planning method based on Min-Max time standardization was presented. Based on the method, a solving method of joint motion time ranges which meet the requirements of joint trajectory motion constraints was proposed with articulation motion time as the optimization target. Simulation results show that the joint trajectory of the improved algorithm is only with regard to trajectory endpoint state and motion time, but not to trajectory endpoint time, which further dilutes the influence of trajectory endpoint time on the joint trajectory, and the practicality of the algorithm is also improved. By selecting the optimal trajectory articulation motion time which meets the requirements of whole joint state constraints, the improved algorithm not only avoids the occurrence of overshooting and optimizes the trajectory of each joint, but also improves the efficiency of joint motion. Finally, the engineering practicality of the improved algorithm was verified by field operation test.
Abstract: In order to improve the efficiency of infrared small target detection against complex background, the image was decomposed into three regions flat region, edge region and small target region. A method of nonlinear local filter detection using the Laplaclan pyramid was presented based on each character of the three components. Firstly, Gaussian pyramids were built for the image, each level was subtracted from the original image with matching size, and the flat region was restrained by simple threshold operation. Secondly, the minimum difference between the marked pixel gray value and the mean value of the hollow annular region was used as quota to filter out the edge region. At last, each layer coefficient of the Laplacian pyramid was generated from the results of nonlinear local filtering and then a high-contrast detection image was reconstructed. The isolated noise points were removed based on the character of the neighborhood and the infrared small target was marked by simple threshold operation. Compared with other existing methods, the experimental results show that this method can effectively restrain complex background and the detection speed is fast.
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
