Abstract: By analyzing the relation and difference between collapse columns and leakage wells, a physical model of predicting water inrush caused by collapse columns was established in combination with the correlative theories of leakage wells, the hazardous area of water inrush in the model was identified. The hazardous area of water inrush between collapse columns and working face divided into three parts:plastic failure zone around the collapse column, plastic failure zone ahead of the mine stope, and permeability zone around the collapse column. A theoretical criterion of predicting water inrush caused by collapse columns was proposed on the basis of plastoelasticity and hydromeehanies. This criterion can be used to predict water inrush caused by collapse columns in a coal mine.
Abstract: For detecting the interior conformation and mechanics capability of cement-tailing backfill, the sampling method of bore drilling was adopted from filling blocking walls or other corresponding parts which could cover all the stope to get backfill cores. The acoustic wave velocity of the samples was tested by use of SY-1 type acoustic testing apparatus, and then the spectra and waveforms were analyzed by way of correlative software. Testing results indicate the difference between acoustic wave velocity and elasticity mechanics index derives from the difference of backfill's strengtb and inner density structure. Although different backfill samples have different acoustic speeds, their acoustic waves have similar waveforms and spectrum components basically. The acoustic wave with a longer delay, main spectrum convergence, sententiousness spectra and a higher swing shows that the backfill has little lacuna such as impurities, holes and cavities and its configuration is integrated.
Abstract: The granule morphology and particle size distribution of milled iron tailings from Qidashan Iron Mine of China were investigated by scanning electron microscopy (SEM), field emission scanning electron microscope (FE-SEM) and laser particle sizer (LPS). The grindabilities of iron railings and blast furnace slag were compared by taking specific surface area as an evaluating index of milling. The results show that the iron ore railings have a much better grindability than blast furnace slag. The milled tailing product obtained by milling for 140 min contains 62.60% grain particles smaller than 5 μm which can fill spaces between cement particles; among them, much smaller particles with submicron or nanometer size were also observed.
Abstract: The effect of roasting temperature on the coal-based direct reduction of vanadium tailings was investigated by X-ray diffraction (XRD) analysis and scanning electron microscopy (SEM). A metallic iron separation test of the roasting products was done by using a grinding-magnetic separation method. It is shown that the roasting temperature of 1 200℃ is needed for the generation, merger and growing up of metallic iron and for monomer dissociation between metallic iron particles and slag phase in the roasting products. Fe2O3 in vanadium tailings is completely reduced into metal iron, and Fe2TiO5 is basically transformed into metallic iron and TiO2 at 1 200℃. The metal iron powder with a total iron mass fraction of 90.90% and a TiO2 mass fraction of 0.56% is obtained from roasting products of vanadium tailings with a total iron mass fraction of 36.54% and a TiO2 mass fraction of 9.28% at 1200℃ using the grinding-magnetic separation method.
A physical model was developed to study bubble movement and distribution behavior in consideration of the coupled effects of electromagnetic brake (EMBr) and argon gas injection in a slab continuous casting mold with high casting speed. Mercury and argon gas were employed to simulate the molten metal and argon gas two-phase flow. The resistance probe was applied to study the gas bubble statistical behavior in the mold with and without EMBr under different argon gas flow rates. The effects of EMBr and argon gas flow rate on the local void fraction, number and pulse width of gas bubbles were investigated. The results show that when the magnetic field is imposed under a given casting speed, the distribution of gas bubbles in the mold changes, the floating up rate of gas bubbles increases, the penetration depth of gas bubbles becomes lower, and the number of gas bubbles reaching the narrow face of the mold decreases. The number of gas bubbles with wide pulse increases between the 1/4 width of the mold and the nozzle with EMBr or with the argon gas flow rate increasing.
Abstract: The effect of oxygen content on the morphology of sulfides was investigated by experiment. Experimental results show that the morphology of MnS inclusions changes from Type 11 to Type I with increasing oxygen content, the diameter and area fraction of MnS inclusions increase, but the number and mean aspect ratio of MnS inclusions decrease. The influence mechanism of oxygen content on the morphology of sulfides was studied on the basis of the mathematic model, the Fe-Mn-S ternary system diagram and the Fe-Mn-S-O quaternary system diagram. In the case of the oxygen mass fraction up to 0.022%, the liquid low-melting oxides rich with MnO were found at the early stage of solidification, these oxides made the formation behavior of MnS from eutectic reaction to monoteetic reaction, and Type I MnS formed. In the case of the low oxygen content less than about 0.01%, little liquid low-melting oxides rich with MnO were found at the early stage of solidification, most of MnS precipitated in an euteetie mode at final solidification, and Type Ⅱ MnS formed.
Abstract: The principles of Ti2O3 and TiN formation in 430 ferritic stainless steel were theoretically analyzed. The steel's compositions including Ti, Al, O and N for forming Ti2O3 + TiN complex nuclei on solidification fronts were put forward. According to composition requirements, the experiment was conducted in a vacuum induction furnace to get an ingot. Some metallographie samples were prepared for observing the feature of precipitates under scanning electron microscopy (SEM) and transmission electron microscope (TEM). It was observed by SEM that these precipitates were fine and dispersively distributed. Their sizes were about 2 μm and titanium nitride precipitates around titanium oxide. It was further confirmed by TEM diffraction patterns of precipitates that the center layer of precipitates was Ti2O3 and the outer layer of precipitates was TiN. If the steel's composition was reasonably controlled, Ti2O3 + TiN complex nuclei can form even under a low titanium content.
Abstract: By analyzing the thermal/mechanical simulation test data under dynamic recrystallization (DRX) of cold heading steel SCM435 in a temperature range of 950 to 1 150% and a strain rate range of 0.1 to 1 s-1 such characteristic Values as critical strain εc,peak strain εp,critical stress σc and peak stress σp.were derived from the curves of strain hardening rate to flow stress (θ-σ).The Avrami kinetic curves of dynamic recrystallization and the time exponent n of SCM435 steel were calculated by the stress-strain (σ-ε) method.It is shown that the average value of εc/εp,is 0.73 and the average value of n was 1.91 under DRX.The DRX Avrami kinetic of SCM435 steel is sensitive to strain rate and not temperature-sensitive in the temperature range of 950 to 1 150% and the strain rate of 0.1 to 1 s-1.The time when the crystallization ratio is 50% is inversely proportional to strain rate.
Abstract: The continuous annealing process of ultra-high strength cold-rolled dual phase steels was simulated using a Gleeble-3500 thermal simulator. The effects of continuous annealing parameters on the microstructure and mechanical properties of the 1 000 MPa grade dual phase steel were investigated by optical microscope, scanning electron microscope, transmission electron microscope and tensile tests. It is shown that a dual phase (DP) steel with a tensile strength of 1 030 MPa and a total elongation of 14% was obtained after being soaked at 800 qC for 60 s. With the increase of annealing temperature, the yield strength and tensile strength decrease. When the annealing temperature reaches 830℃, the volume fraction of granular non-martensite in the microstructure increases obviously. When the over-aging temperature is lower than 300℃, the yield strength and the tensile strength change slightly. When the over-aging tempe'rature is higher than 300℃, the tensile strength decreases strongly, whereas the yield strength reduces first and then increases. There is yield point elongation when the over-aging temperature is 360℃.
Abstract: Based on the geometric model established for rotary roiling of high helical finned tubes, the motional behavior of a rolling piece in the deformation zone was investigated, and the results show that the phenomena of axial elongation has a connection with the distribution of circumferential velocity. It is the essential reason to make a rolling tube elongate along the axial direction that the axial velocity in the deformation zone increases along with the circumferential velocity in the condition that the pitch value of the groove keeps changeless along the axis. A formula of axial elongation rate was given on the basis of theoretical analysis. In order to verify the formula of elongation rate, rolling experiments for two types of rolling pieces in different reductions were conducted and the results approximately agreed with the theoretical values.
Abstract: Single crystal pure copper bars with large-diameter were prepared by a self-developed vacuum melting and argon protecting continuous unidirectional solidification equipment, the effects of process parameters on their solidified structure and surface quality were investigated, and their mechanical properties and electrical properties were tested and analyzed. The results show that single crystal pure copper bars of φ16 mm with bright surface can be continuously and stably produced under the conditions of the melting temperature of 1 150℃ to 1 180℃, the mould outlet temperature of 750℃, the cooling water volume of 900 L·h-1, the cooling distance of 50 ram, and the drawing speed of 9 mm·min-1. The tensile strength, elongation and conductivity of the single crystal pure copper bars are 128.52 MPa, 76.7% and 105.2% IACS, respectively, which show excellent mechanical properties and electrical properties.
Abstract: Single-side and double-sided welding tests of T2 copper with thicknesses of 30 mm and 50 mm were done by friction stir welding, while the microstructure and mechanical properties of welds were analyzed. The results show that butt joints with good superficial shaping quality, almost no deformation, and no internal defects can be achieved within certain ranges of process parameters. The average tensile strength of the T2 copper single-side weld with a thickness of 30 mm is 177.2 MPa, reaching 81.7% of the strength of the base metal, while the average elongation after fracture is 25.4%. The microhardness distribution of the weld transverse section fluctuates obviously, with the minimum locating at the bottom of the heat affecting zone along the advancing side, where it is welding weakness.
Abstract: The effect of hydrogen on nanoindentation creep at room temperature and plastic deformation of nanoindentation in preferentially orientated polycrystalline Ni50Mn30Ga20 was investigated by nanoindentation. The results show that nanoindentation creep in the preferentially orientated polycrystalline Ni50Mn30Ga20 could occur at room temperature. After the specimens was hydrogen charged in vacuum at room temperature, the introduced hydrogen could not only promote the nanoindentation creep, but also release the elastic energy stored in martensitic pseudoelastieity and induce reversible martensitic transformation, which resulted in the partial recovery of plastic deformation.
Abstract: The growth kinetics behaviors of CuO particles in reactive synthesis AgCuO composites were investigated by analyzing the reaction of copper and oxygen on the surface of a silver-copper alloy and calculating the precipitation amount of copper in the silvercopper alloy, the diffusion rate of copper in silver matrix and the size of CuO particles. It is indicated that the growth kinetics of CuO particles in the reactive synthesis process follows a parabolic law, the reaction of copper and oxygen on the surface of the silver-copper alloy is controlled by copper diffusion, and the growth of CuO particles is influenced by the content, diffusion rate and location (grains or grain boundaries) of copper in the silver-copper alloy. The calculated size of copper oxide particles agrees with the measured one.
Abstract: Novel mixed rare earth Sc2O3 and Y2O3 doped ZnO-Bi2O3 based varistor ceramics were prepared by a solid reaction route, their electrical properties and microstructure were studied. The results show that mixed rare earth doping can improve the comprehensive performance of ZnO-Bi2O3 based varistor ceramics more remarkably than single rare earth doping, but the effect of mixed rare earth doping on their electrical properties is consistent with that of single rare earth doping. When the content of Sc2O3 is the same, the voltage gradient of mixed rare earth Sc2O3 and Y2O3 doped ZnO-Bi2O3 based varistor ceramics increases with the increase of the amount of Y2O3; when the content of Y2O3 is the same, the nonlinear coefficient of the varistor ceramics increases with the increase of the amount of Se2O3. After adding 0.12% Sc2O3 and 0.20% Y2O3 (molar fraction), mixed rare earth Sc2O3 and Y2O3 doped ZnO-Bi2O3 based varistor ceramics exhibit comparatively ideal comprehensive electrical properties:the threshold voltage is 410 V·mm-1 the nonlinear coefficient is 38.0, and the leakage current is 0.58 μA.
Abstract: The anti-scale performance of polytetrafluoroethylene (PTFE)/polyphenylene sulfide (PPS) composite coatings was studied by scanning electron microscopy (SEM) and energy dispersion spectrometry (EDS). The effect of the surface microstructure of PTFE/PPS coatings on the nucleation behavior of CaCO3 scale was analyzed. The results indicate that the surface microstructure of PTFE (latex)-blended PPS composite coatings is poriferous, and PTFE asymmetrically distributes inside and outside holes on the coating surface, inducing CaCO3 scale to nucleate firstly on the hole inside and wall. The contact angle of PTFE/PPS coatings decreases with prolonging immersion time. The increasing rate of scaling on PTFE/PPS coatings is obviously less than that of 304 stainless steel and PPS coatings.
Abstract: The solid flow in a 5 000 m3 blast furnace was studied by a three-dimensional discrete element method from the aspects of velocity, stress distribution, stress acting on the wall and bottom under circumferential non-uniform coke consumption in the raceway. The results show that an asymmetric solid flow forms in the blast furnace, including the asymmetric distributions of burden layer, particle velocity and stress between particles and the asymmetric stress acting on the wall and bottom. It is also found that the height of deadman increases and there is a slipping region near the surface of deadman.
Abstract: Fluent software was used to numerically simulate the functions of three key components (gas distributed ring, cooling pre-processor, and vortex collision component) during vortex collision desulfurization. The influence rules of the three components on the flow field of sintering flue gas were fit with MATLAB software, It is shown that under the optimal distribution of flue gas the installation location of the gas distributed ring is linear with the ring width. The greater the water-jet velocity from the cooling pre-processor, the lower the temperature of flue gas is. When the water-jet velocity exceeds 30 m·s-1, the temperature of flue gas does not change significantly with increasing water-jet velocity; as a result, the best range of water-jet velocity is 25 to 30 m·s-1. The pressure loss of flue gas increases with the tangential velocity of the vortex collision component increasing. When the tangential velocity is over 20 m·s-1, the pressure loss rises sharply. The tangential velocity of the vortex collision component should be controlled at about 20 m·s-1, indicating that the rotational speed of the tray is about 85 r·min-1.
Abstract: Taking the d-stand PL-TCM cold rolling mill of Masteel as a research object, an explicit dynamic finite element method was adopted to build a combination simulation model for the roll stacks of the 6-high mill and silicon steel strips. Based on analyzing its edge drop control ability, the method of optimizing the intermediate roll shift position was proposed to reduce the edge drop of silicon steel strips. By using the U-EDC work roll contour which was self-designed and used to edge drop control for the UCM cold rolling mill, a remarkable production result was achieved that the qualification rate of silicon steel strips with the anaverage edge drop less than 5 μm increases from 46.0% to above 99.3%, and high precision shape control has been successfully accomplished in the 6-high mill without work roll shifting.
Abstract: An ideal mathematical model of flexible articulated arm coordinate measuring machines (FAACMM) was established based on the local product-of-exponentials (Local POE) formula, and then an actual kinematic model was obtained by amending the ideal mathematical model according to various errors. Various kinematic parameter errors which affect the system's measuring precision were analyzed detailedly. Simulation results show that the errors of length kinematic parameters do not cause the measurement results to zoom in or out, but the errors of angle kinematic parameters should result in serious amplification.
Abstract: In order to improve the control accuracy and quality of automatic gauges in hot trip rolling, a nonlinear muhiple-input multiple-output (MIMO) model of hydraulic loopers was built close to the working point in consideration of strip weight and the nonlinearity of hydraulic cylinders and loopers, and its validity was verified. A decoupling method based on back-stepping and extended state observers (ESO) was proposed for this new model taking all unmodelled dynamics and various disturbances into account. The robust stability of the closed-loop system was proved with the Lyapunov stability theory. Simulation results show that the proposed model and decoupling control method are available.
Abstract: To tackle the problem of slippage during the cold rolling process of a tandem mill, a schedule optimization model for preventing slippage was established based on slip factor. Aiming to the shortages of the standard genetic algorithm, such as premature convergence, oscillation and over-randomization, an improved adaptive genetic algorithm was applied to optimize the system. In the algorithm a population-sorted multi-roulette-wheel selection operator was put forward for reducing the selected error generated by roulette-wheel randomization and promoting the probability of selecting better individuals. Simultaneously the algorithm decides the crossover rate and mutation rate of chromosome based on the individual adaptive value in the calculation process, makes the start phase variable obviously and the later phase stable slowly, and ensures population development, seeking balance and entire convergence. Experimental results and actual application show that the schedule optimization model can reduce the slip probability prominently, improve the product quality, and achieve a better economic benefit.
Abstract: An algorithm of PID controller parameters identification based on the fastest model was presented to tune PID controller parameters for an inertial feature system. With input and output data of the inertial feature system, this method identifies the first-order characteristic system by the least square method (LSM) firstly, then identifies the second-order fastest model of the inertial feature system according to the demands of the first-order characteristic system, control signal, the stable and dynamic properties of the inertial feature system, and then the PID controller parameters were calculated synchronously. Simulation results show that the algorithm makes the PID controller have the characteristic of the fastest response and provides an effective method for calculating the PID controller parameters.
Abstract: A network synchronization model was proposed for two different complex networks with time-varying delay coupling. The two networks in the model were different in the number of nodes, topological structure, inner coupling, coupling delay, and node dynamics. Based on Lasalle's invariance principle, an adaptive controller was designed to achieve synchronization between these two networks. When the topological structures of two networks were fully unknown, the adaptive synchronization problem was also discussed. Numerical results were presented to verify the effectiveness of the proposed method.
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
