Abstract: Due to the existence of a flexible isolation layer the flow pattern of granular ore rock in the synchronous filling shrinkage method breaks through the description range of the traditional ore drawing theory,so studies on the flow pattern of granular ore rock in a single funnel under a flexible isolation layer have important significance for enriching the ore drawing theory. Based on the similarity principle,a physical test model was designed,by which the morphology of the draw ore body and the loosen ore body was delineated and drawn by marking particles. The basic data of testing were recorded with a high-definition camera. The evolution laws of the spatial morphology of the draw ore body,loosen ore body,and cavity during single funnel drawing under a flexible isolation layer were analyzed on the basis of these basic data. The draw ore body showed completely closed and quasi-ellipsoidal morphology before the highest horizon ore settled; but after this settlement the draw ore body was gyrostatic. Before settlement of the highest horizon ore occurred,the loosen ore body showed completely closed and quasi-ellipsoid morphology; but after this settlement appeared,the loose body shape was trumpet-shaped on the whole,with an exponential curve in the upper part and a quasi-ellipsoid in the lower part. The cavity began to form at the moment when the settlement of the highest horizon ore occurred. The isolation layer was tangent to the ore layer at the cavity boundary. The cutting angle increased with the increasing fall depth of the isolation layer and kept invariant after it reached to the natural repose angle. With the sinkage of the isolation layer,the position of the tangent point gradually changed from the center to both sides until the end of ore drawing.
Abstract: Backfilling material specimens were prepared with Pb-bearing ore tailings and a blast furnace slag-steel slag based cementing agent(BSCA) used as a replacement for cement in traditional backfilling materials. Other types of specimens with ordinary Portland cement(P·I 42.5) as cementing agents were also made for comparison. Flowability and compressive strength tests were performed to study the working performance of the specimens,and leaching tests were done to investigate the immobilization of Pb2+ in the specimens. The phase composition of the hydrated specimens was analyzed by means of X-ray diffraction,Fourier transform infrared spectroscopy and differential scanning calorimetry. It is found that the backfilling material with BSCA has a flowability of 50 mm higher than that with ordinary cement. The 28-d compressive strength of the BSCA-based specimens reaches 3.0 MPa,which meets the strength requirement for underground backfilling. The quantities of Pb2+ leached from the BSCA-based specimens aged for 28 d are below 0.05 mg·L-1,which is the threshold value of Pb2+ concentration for Type Ⅲ ground water in Chinese quality standard for ground water GB/T 14848-93. In comparison,the quantities of Pb2+ leached from the cement-containing specimens aged for 28 d are 0.1 mg·L-1. The reason for this higher immobilization degree of Pb2+ in the hydrated BSCA-based specimens is that a higher amount of ettringite forms in them. Moreover,the formation of zeolite-like facies in the hydrated BSCA-based specimens is favorable for immobilizing Pb2+.
Abstract: Since the column and the top beam of the present four-bar hydraulic support fail to bear the lateral force,the lateral force is transferred to the rod via the shield beam,which often leads to the falling down of the support or damage of the support mechanism. With regard of such a theoretical shortcoming,this article introduces a new type of double parallel hydraulic support based on the 3-RPC parallel mechanism. The working space of the hydraulic support is analyzed and the trajectory formula of the top beam is presented. Through the force analysis of the hydraulic support under the condition of partial load and large dip angle,the hydraulic support can bear the forces from three directions and an accurate mechanical relational expression is given. ADAMS is applied to do the stability simulation of the hydraulic support. The results show that the design of such a hydraulic support meets the supporting requirements of coal mines and it is feasible in technology.
Abstract: In order to provide a theoretical basis for the production of high iron and low silica sinter,the basicity(R) was set to 1.8,1.9 and 2.0,the SiO2 content was variable for each alkalinity,and then 12 groups of ore blending schemes were generated to proceed with sinter pot tests. After that,the influences of SiO2 on the metallurgical properties and microstructure of sinter were researched. The results show that when the SiO2 content increases from 4.8% to 5.7%,the cold intensity gradually increases,and the greatest growing rate is 8%; the sinter reducibility tends to lower,and the decreasing range is from 86.80% to 81.01%; the reduction degradation index(RDI+3.15) gradually increases,and the growing range is from 75.95% to 87.21%. For softening-melting properties,the apparent initial softening temperature(T10) previously increases in the range from 4.8% to 5.4% and then decreases in the range from 5.4% to 5.7%,and the softening range has a widening trend. Selected a alkalinity level R=2.0,when the SiO2 content changes in the range of 4.8% to 5.7%,the microstructure of sinter develops from an ablation shape to a needle-like and columnar shape,the structural uniformity gradually improves,and the main mineral composition changes from hematite to calcium ferrite. Skeletal crystalline hematite,which leads to a low temperature reduction degradation phenomenon,gradually disappears.
Abstract: The roasting properties and solidification behaviors of high-titanium pellets were studied systematically in this paper.The results show that increasing the content of TiO2 in pellets can lead to a greater difficulty in their roasting process. When the content of TiO2 increases from 10% to 21%,the proper preheating time prolongs from 12 min to more than 26 min,while the strength of roasted pellets still decrease from 2486 N to 1728 N per pellet. The reason is that high-titanium pellets contain high content of FeTiO3,which leads to a lower oxidization velocity of magnetite and a lower pre-oxidization degree. This phenonmenon is further adverse to the growth and connection of haplotypite crystals,which finally worsen the consolidation strength of pellets. By simultaneously adding Na OH and applying the wet-grinding process,the surface energy and surface activity of ore particles increase,which contribute to improving the diffusion of solid phases and generating a small amount of low-melting-point compounds. These improvements are conducive to the diffusion of recrystallization and then facilitate the growth of titanium hematite grains and the enrichment of Ti in Fe2TiO5. As a consequence,the proper preheating time shortens to 16 min and the pellet strength increases to 2141 N per pellet for pellets containling 21% of TiO2.
Abstract: Through measuring the pore structure features of coke reacted with H2O or CO2 using a mercury porosimeter,the influence of average pore size,specific surface area and pore size distribution on the high temperature tensile strength of coke were studied in this paper. It is found that the porosity and average pore diameter of coke increase with the increase of reaction degree. When the average pore size is less than 30 μm,the gasification reaction is mainly pore-creating,and the surface area of coke increases firstly and then decreases with increasing reaction degree; but when the average pore size is more than 30 μm,the gasification reaction is mainly pore-expanding. Compared with CO2,coke reacted with H2O has a smaller average pore diameter,larger specific surface area and tensile strength. The tensile strength of coke decreases with the increase of porosity and average pore diameter. At an average pore diameter smaller than 30 μm,the tensile strength decreases with the increase of specific surface area; but at an average pore diameter larger than 30 μm,the tensile strength decreases with the decrease of specific surface area. The small pore increases the tensile strength of coke,while the large pore decreases the tensile strength. At the same reaction rate,coke reacted with H2O has a large amount of small pores and large specific surface area,which are conducive to protect the structure of the air pore wall and to prevent from the reduction of tensile strength at high temperature.
Abstract: Microsegregation in low carbon Fe-25Mn-3Si-3Al TWIP steel produced in the laboratory and steel plant were systematically investigated by electron microprobe analysis. The results show that the dendritic segregation is serious in both the laboratorial ingot and mold casting after AOD steelmaking at the industrial plant. Additionally,microsegregation in the AOD ingot is higher,and the greatest amounts of segregation of Mn and Al are measured to be 6.8% and 2.4%,respectively. After electroslag remelting in the steel plant,the grain boundary segregation is serious,and it completely improves after a forging process. A higher alloy composition and a wider crystallization temperature interval are the main reasons for the serious microsegregation. All specimens of the TWIP steel have the same law. Mn shows obvious negative segregation,Al and Si exhibit positive segregation,and Al has the highest degree of segregation. The elements' solute distribution coefficient K of the TWIP steel was calculated using the Thermo-Calc software. It is found that the microsegregation laws of Mn and Al in theory are opposite to those in the experiment,and the main reason is silicon content.
Abstract: The solubility of silicon in a Zn-50%Al-xFe-ySi(in atomic fraction) molten bath and the content of silicon in a Zn-30%Al-2%Fe-xSi(in mass fraction) molten bath corresponding to the appearing of τ5 slag phase and the disappearing of FeAl3 phase were calculated at different temperatures using the Thermo-Calc software. At the same time,the solubility of silicon in liquid phase in the Zn-50%Al-xFe-ySi alloy and the phase equilibrium relationship of the Zn-30%Al-2%Fe-xSi alloy were experimentally determined by using the equilibrium alloy method. The results show that the calculated solubility of silicon in liquid phase in the Zn-50%Al-xFe-ySi system at 540,560,580,600 and 620℃ are 0.82%,0.95%,1.11%,1.28% and 1.47%,respectively,which agree well with the experimental data. When the temperature of the molten bath is 580,600,and 620℃,the calculated content of silicon in the Zn-30%Al-2%Fe-xSi alloy corresponding to the appearing of τ5 phase in the molten bath is 0.6%,0.72% and 0.84%,and the values corresponding to the disappearing of FeAl3 phase are 1.12%,1.22% and 1.34%,respectively,which agree basically with the experimental results.
Abstract: Synthetic natural gas(SNG) is an important developing direction of the clean utilization of coal. The present pipeline steel may cause hydrogen-induced delayed cracking when used to transit SNG due to the hydrogen partial pressure in SNG perhaps up to 0.72 MPa. Therefore,the safety assessment of pipeline steel for long-term service is very important and necessary. In this work,hydrogen damage and hydrogen-induced delayed cracking in X-70 pipeline steel and 20#steel at different hydrogen contents were studied by using autoclave constant load test and electrochemical hydrogen charging methods. The service safety of the steels in SNG was evaluated. There is no hydrogen damage in the two kinds of steel after being placed in the autoclave in which the total pressure 12 MPa(10 MPa N2+ 2 MPa H2) is kept for one month. Hydrogen-induced delayed cracking does not occur in the U-bending specimen. And the constant load samples do not fail after they are kept at the yield stress for one month. The hydrogen content entering into X-70 and 20# samples is much lower than the threshold hydrogen content for hydrogen-induced delayed cracking and that for hydrogen damage.Therefore,both X-70 steel and 20# steel have high safety factors during the long-term service of transiting SNG.
Abstract: Through indoor simulated experimental equipment,mitigation methods which contained the bond resistor method,galvanic anode method and metallic shield method were studied to mitigate DC stray current interference caused by the impressed current cathodic protection system on pipelines without cathodic protection at the external. The influences of bond resistance,galvanic anode location and materials,metallic shield location and connecting methods on the mitigation and regularity for different types of interference were investigated,and the applicability for different mitigation methods was also analyzed. In addition,it can also provide reference for practical engineering with putting forward recommendations and application conditions for different types of interference.
Abstract: The high temperature deformation behavior of SAE8620 H gear steel in a temperature range of 950 to 1100℃ and a strain rate range of 0.01 to 10 s-1 was studied by high temperature compression tests. The flow stress of the steel has steady state characteristics. The flow stress decreases with the increase of deformation temperature and the decrease of strain rate. The constitutive equation of the steel can be described by a hyperbolic sine equation. Based on the related data of peak stress,strain rate and temperature,the hot deformation activation energy of the steel was deduced to be about 280359.9 J·mol-1. The processing maps were drawn according to 40% and 60% deformation. The forming parameters can be determined by the processing maps. Low strain rate should be used for small deformation,while high strain rate and high forming temperature or low strain rate and low forming temperature should be used for large deformation.
Abstract: The formability of corners was improved by heating the corner area of high strength square tubes with induction coils.Under the premise of not impacting the undeformed zone,we obtained the ideal sectional dimension,microstructure and properties of products. In the hot roll forming process,the billet accumulated at the outside area of square corners without mold restrictions. With rising temperature,the accumulation became more serious. At the same time,microcracks deteriorated on the surface of the inner tube,while the cracks grew up in a form of arborization. A self-tempering process would be produced by residual temperature after hot roll forming,which could significantly reduce the residual stress. The residual stress sharply decreased as the temperature increased.When the heating temperature was above 650℃,the influence of self-tempering on the residual stress was greater than the extended capability of macrocracks and played a leading role; there was no crack when the distance was larger than 2/3 of diagonal length at flattening test.
Abstract: A tungsten inert gas(TIG) welding-brazing technology using an Mg-based filler was developed for joining Mg alloys to steel. The effects of heat input on the microstructure and mechanical properties of Mg/steel joints were investigated. The results indicate that the joining strength of the joints is poor with low heat input,owing to insufficient metallurgical reaction between the Mg alloy and steel. But with excessive heat input,the growth of the brittle second phase in the seam occurs,resulting in the decrease of mechanical properties. The joining strength of the joints increases first and then decreases with the increase of welding current and welding speed. An acceptable joint is obtained with a welding current of 70 A,representing 88.7% joint efficiency relative to AZ31B base material. With this parameter,fracture occurs at the fusion zone and the fracture surface is characterized by equiaxed dimple patterns accompanied with lamellar tearing. The fracture surface embodies the characteristics of plastic fracture.
Abstract: The flexure hinge is the key part to implement the movement of lamina emergent mechanisms(LEMs). Designing a flexure hinge with good flexibility and high accuracy is always the key problem to research compliant mechanisms. Considering the bending and tension equivalent stiffness comprehensively which influence the stiffness and accuracy characteristics of LEMs hinges and taking the LET hinge as an example,the effects of different parameters on bending and tension equivalent coupling stiffness are analyzed under different loads and the concept of bending torsion and tension compression coupling is introduced. Through the calculations and analyses of a large number of examples,an empirical formula of bending torsion and tension compression equivalent coupling stiffness is derived for the LET flexure hinge. The LEMs slider mechanism is studied based on equivalent coupling stiffness. By the comparison of theoretical calculation and simulation results,the calculating accuracy of the slider's displacement is proved to be improved by the application of the equivalent coupling stiffness formula,and thus the applicability of the equivalent coupling stiffness formula is verified.
Abstract: Rapid(vacuum) pressure swing adsorption(RPSA or RVPSA) is featured by short cycle time and quick pressure change,which may lead to great variations of flow and mass and heat transfer in the adsorber. The effects of adsorption and desorption pressure on the velocity and cycling performance in an oxygen-production RPSA bed were investigated in this paper. The results show that during the feed pressurization(PR) step in the RPSA process,the up-flow velocity is far larger than the limit value,and slightly larger than it for the rapid vacuum pressure swing adsorption(RVPSA) process. During the blow-down step in both RPSA and RVPSA,the down-flow velocity is greater than the limit value. In comparison to RPSA,RVPSA exhibits a similar gas temperature change around 10℃ but a larger gas temperature gradient. The bed size factor can be effectively reduced with increased oxygen recovery by increasing the adsorption pressure for RPSA,while by lowering the desorption pressure for RVPSA.
Abstract: The impulse Poiseuille flow of generalized second grade fluid was discussed in this paper. Combining the Riemann-Liouville fractional constitutive equation of second grade fluid with the fractional momentum equation of incompressible fluid,a new governing equation was established. The velocity analytical solution was obtained based on the Fourier sine transform and the fractional Laplace transform. The numerical simulation was performed by Stehfest algorithm method. The influences of various relevant parameters such as fractional derivative parameters and retardation time were elucidated through graphs. The results show that the velocity overshoot phenomenon mainly depends on the time fractional parameter of the momentum equation.
Abstract: A design method of H∞ optimal guaranteed performance preview controllers was investigated for a class of polytopic uncertain discrete system with time-delay and constant parameters. First,different from the previous approaches,in order to keep the dimension of the state vector in the augmented error system from increasing with the addition of time-delay,the time-delay terms were maintained in that system. Then,a memory state feedback controller was designed for the augmented error system. The existence condition and the design method of the controller were obtained by the linear matrix inequality(LMI) method. At last,by solving an optimization problem with LMI constraint conditions,the H∞ optimal guaranteed performance controller,which was the H∞ guaranteed performance preview controller to the original system,was gained.
Abstract: The clustering algorithm based on sparse feature vector for categorical attributes(CABOSFVC) is an efficient high-dimensional clustering method for categorical data. Sparse feature dissimilarity(SFD) is used to calculate the distance and sparse feature vector is used to achieve data compression. However,CABOSFVC algorithm is dependent upon SFD upper limit parameter for which there is no guidance for configuration. Aimed at solving the problem that CABOSFVC algorithm is sensitive to this parameter,a new heuristic hierarchical clustering algorithm of categorical data based on SFD(HABOS) was proposed in this paper. With the constraint of the upper limit number of clusters,this algorithm applied agglomerative hierarchical clustering and the new internal clustering validation index based on SFD(CVISFD) which was used to measure the results heuristically to achieve the best choice of the clustering level. Three UCI benchmark data sets were used to compare the improved algorithm with the traditional ones. The empirical tests show that HABOS increases the clustering accuracy and stability effectively.
Abstract: In consideration of the impact of road gradient on the vehicle driving demand,a predictive energy management strategy was proposed for plug-in hybrid electric vehicles(PHEVs) on the basis of road gradient provided by the vehicle navigation system.The knowledge of route data(trip distance,road gradient and altitude) was used to predict the electricity consumption. Then the state-of-charge(SOC) trajectory was planned for the charge depleting(CD) mode and the charge sustaining(CS) mode. With exact calculations of the charge timing,the SOC was charged to the target value before uphill and reached to the threshold after uphill in case of battery electricity shortage and over-discharge during uphill. The proposed adaptive SOC control strategy can improve the vehicle performance and is in favor of the full absorption of regenerative braking energy. Based on the MATLAB/Simulink platform,a simulation model was built for the plug-in hybrid electric system. The proposed energy management strategy based on road gradient prediction was verified to avoid battery over-discharge and to ensure sufficient electric energy during uphill.
Abstract: Based on seismic performance tests on frame-supported grid-mode lightweight slab structure(FSGL slab structure) specimens,the mechanical behavior of the structure was quantitatively analyzed and seismic design suggestions were put forward. The results showed that constructional columns for the both sides of an open hole compensated for strength degradation caused by the hole,improved the safety-reserved capacity of the wall,but increased the damage degree of the wall at the late stage and deteriorated the repairable capacity. The oblique frame-grid design was able to change the way of transmission-loading to make strength degradation more uniform and let the structure have a better deformation recovery ability,and this design could obviously decrease the damage degree of the wall,but the overall safety-reserved capacity was not much improved. In engineering design,the proposed initial stiffness-ratio range of the transfer layer was approximately 1.3 to 1.6. Due to an obvious decrease in stiffness-ratio of the transfer layer under loading,the initial stiffness-ratio should properly increase in the design process. The displacement and angle values between inter-layers are within the safety limits,indicating that the structure has good collapse-resistant capacity and energy dissipation performance.
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
