Abstract: Based on energy conservation and transformation caused by the interaction of caving rock and air in the course of roof caving in large-size mined-out area,a wind speed model of impact waves was constructed and an experimental device was designed.Experimental results show that with the increasing of rock falling height,the amplitude of wind speed of impact waves slowly increases.The small-size inflator model in a large cross-section space could better describe air flow during roof caving,but air shock waves should be expressed by the inflator and external flow compound model.The established experimental and theoretical models have a great similarity.
Abstract: Equivalent oxygen concentration,thermal comfort effective temperature,air quality index and dust concentration were selected as indexes from three aspects including respiratory physiology,thermal comfort and toxicology for grey clustering estimation of plateau underground working environment.Clustering weights were determined by using the fuzzy consistent matrix to reduce the influent of subjective factors.Due to considering the special case of plateau regions,this method can draw a more comprehensive and objective conclusion.
Abstract: Based on the characteristics of some unwieldy oolitic hematite,experimental studies were done by deep reduction and magnetic separation method.The effects of experimental conditions,such as reduction temperature,reduction time,binary basicity,grinding fineness,and magnetic field intensity on the separation efficiency and product indexes were analyzed.The phase composition and characteristics of run-of-the-mine and products were determined by comprehensive methods such as optical microscopy,X-ray diffraction,SEM and chemical analysis.The reduction temperature,reduction time and binary basicity are 1 200 ℃,2 h and 0.2,respectively.The results show that the grade and the recovery of the iron ore concentrate are 91.94% and 95.85%,respectively,indicating that the obtained product is of high quality and of less harmful impurities.
Abstract: In order to improve the quality and quantity indices of sinter with high proportion of limonite,the influence of factors such as binary basicity and calcareous flux on the quantity,strength and type of bonding phase as well as the quality and quantity indices of sinter were studied through micro-sintering test and sintering pot test based on the characteristics of blending ores for sintering.The experiment results show that the quality and quantity indices of sinter with high proportion of limonite can be improved through the following measures:the binary basicity of sinter increases to 2.0,the proportion of quicklime increases in a certain range,and the sintering negative pressure and the depth of the sintering bed increase properly.
Abstract: Assimilation of 19 kinds of ores from Brazil,Australia,South Africa and China was evaluated and analyzed,based on which the ore matching method was researched and 9 groups of optimizing ore matching schemes were designed.The ores of different types have apparently differences in assimilation,for example,Brazilian hematite ore and Chinese magnetite ore have very low assimilation,while Australian limonite ore has high assimilation.The assimilation of the ores has positive correlation with burning loss,porosity and Al2O3 content.The iron ores in which SiO2 and Al2O3 exist in the form of clay and the iron ores with small crystal size have relatively higher assimilation.By using the ore matching method introduced in this study,sinter ores with good sintering indexes and metallurgical properties can be obtained when low quality ores are used by the proportion of 50%,indicating the validity and superiority of the ore matching method according to complementary assimilation.
Abstract: The nonisothermal crystallization behavior of mold fluxes bearing various TiO2 was studied by using the single hot thermocouple technique.The mineral components of the mold fluxes were analyzed by X-ray diffraction (XRD) and microscopically observed by mine-phase microscope.The results indicate that cuspidine is the main phase of the casting mold fluxes.With a certain amount of TiO2 (2% to 8%) added into the mold fluxes at high basicity (ΣR=1.3),the phase precipitation increases.Small amount of Ca2SiO4,Ca2Al(AlSi7O7),Ca2SiO2F2 and CaTiO3 are crystallized.While the time of crystallization process of the mold fluxes is lengthened,the crystallization ratio and crystallization rate of the mold fluxes is decreased.Thus,crystallization of the mold fluxes is inhibited,leading to improvement in the glass property and the lubrication between casting strands and molds in view of the heat flow control of slag films.
Abstract: Calcium treatment experiments were carried out on six heats of X70 pipeline steel.The results show that the Ca content of the steel dropped a lot and the composition and morphology of inclusions varied obviously in producing the steel after calcium treatment.Reoxidation deteriorates the effect of calcium treatment,but dissolved calcium and CaO-Al2O3 compound inclusions with high CaO content can play a role of modification on Al2O3 caused by reoxidation.The calcium treatment effect of high grade pipeline steel is related with the concentrations of calcium,oxygen and sulphur,reoxidation degree,and time after treatment,but evaluating calcium treatment with calcium content,[%Ca]Tot/[%Al]s,[%Ca]Tot/T[O],ACR and [%Ca]Tot/[%S] is improper.A evaluation standard is put forward as the following:(1) pure MnS inclusions do not exist in the central area of slabs or rolled plates,(2) nCaO/Al2O3 of inclusions in the tundish and mould is controlled around that of 12CaO·7Al2O3,and (3) nCaO/Al2O3 of inclusions after calcium treatment is higher than that of 12CaO·7Al2O3.It is also be careful that calcium treatment is carried out at the end of the final refining procedure so as to prevent reoxidation of liquid steel.
Abstract: A numerical method was used to analyze and calculate important microstructural parameters in dendrite growth under different continuous casting conditions.The dendrite tip radius,dendrite growth velocity,and dendrite arm spacing were investigated and the effects of casting speed on these parameters were studied in combination with continuous casting properties of medium carbon steel.C,Si,Mn,P and S microsegregation in the steel was discussed.The validation of this model shows good and reasonable agreements with previous models.
Abstract: In order to simulate 3D microstructures during solidification with porosity,the physical essence and numerical calculation principles of the finite element-cellular automaton (CAFE) method were analyzed.Then,the CAFE method was used to simulate the solidification processes,porosity,and 3D microstructure of 9SMn28 free-cutting steel castings.It is shown that under the condition of air cooling,the solidification of casting surface layers occurs in the process of continuous cooling,but in the casting interiors there exist firstly isothermal solidification and then cooling solidification.The simulation result of porosity is basically identical with experimental castings.The 3D microstructure of 9SMn28 free-cutting steel can be simulated by the CAFE due to its agreement with experimental results.
Abstract: The Cr3 compound cast steel backup roller was researched as a subject.A backup roller satisfying the required properties was produced by the differential heat treatment process.The temperature distribution of the backup roller in the differential heat treatment process was studied.The hardness and microstructure of the roller's working layer were analyzed.The temperature field of the backup roller in the oil quenching process was simulated by using a developed simulation system of quenching temperature fields.The simulated results were compared with the experimental ones.It is shown that different temperatures in the core and body of the backup roller can be gained by using the differential heat treatment process,and therefore,different microstructures can be obtained in the following oil quenching process.When the backup roller is heated by the differential heat treatment process,the hardness and microstructure of the roller's working layer can meet the usage requirements.The oil quenching process of the backup roller was simulated by using the developed simulation system.The simulated and experimental results are basically consistent,indicating that the simulation system has a higher reliability.The simulation system can be used to optimize the heat treatment process and provides a quantificational reference basis for practical production.
Abstract: Water-atomized iron powders were used by warm flow compaction to fabricate cross-shaped parts.The degrease process and microstructure of sintered parts were investigated.The optimal degrease process is to raise the temperature from ambient temperature to 160 ℃,then raise to 300 ℃ at a rate of 1 ℃·min-1 and hold at 300 ℃ for 0.5 h,followed by raising the temperature to 450 ℃ at a rate of 1.5 ℃·min-1 and hold at 450 ℃ for 0.5 h.Sintering was carried out at 1 300 ℃.It is shown that at the proper degreasing parameters the warm flow compaction method can produce complex-shaped components with low cost.
Abstract: A composite cutting tool material,consisting of Q235 and CrWMn steel,was prepared by composite casting and hot rolling process.Through vacuum melting and casting,followed by hot rolling deformation with a relative reduction larger than 90%,excellent metallurgical bonding between the component materials was obtained,with an interface layer of only 10 to 40 μm wide.Heat treatment experiments with different cooling modes were carried out.The results showed that after air cooling or oil quenching,a mixture microstructure of ferrite and pearlite in Q235 was formed.While in the side of CrWMn,a martensite structure with a micro hardness of 600 to 750 HV was found.The composite material exhibits the excellent comprehensive mechanical properties of both high toughness and strength.
Abstract: The CO2 corrosion behavior of 3Cr low-alloy pipeline steel and its weld joints were researched with a high-pressure high-temperature autoclave and electrochemical techniques.The results showed that the corrosion product scales enriched Cr element were compact,which is the main reason that the CO2 corrosion resistance of 3Cr low-alloy pipeline steel is superior to that of X65 steel.The product scales of the base metal,heat affected zone (HAZ) and weld metal in 3Cr low alloy pipeline steel weld joints were similar with each other,with Cr enrichment and compact structure.Compared with X65 steel,the corrosion potential of 3Cr low alloy pipeline steel was more positive and the corrosion current density was lower.The base metal of 3Cr low alloy pipeline steel weld joints as an anode would be suffered corrosion firstly,and the weld metal and HAZ of the weld joints as cathodes would be protected.
Abstract: Al2O3-Mo3Si/Mo5Si3 nanocomposite powders were synthesized by mechanochemical reduction method with MoO3,Si and Al powders as raw materials.The solid-state reaction process and synthesized composite powders were investigated by XRD,laser particles size analytic instrument,TEM,SEM and DTA-TG method.Experimental results indicated that Al2O3-Mo3Si/Mo5Si3 composite powders were obtained by milling of MoO3-Si-Al powders for 5 h by the mechanical induced self-propagating reactions.The grain sizes of Mo3Si,Mo5Si3 and Al2O3 were 27.5 nm,23.3 nm and 31.8 nm respectively after milling of 20 h.The composite powders possessed nano-crystalline structure and the average particle size was 3.988 μm,with spherical shapes and uniform distribution after 20 h.DTA analysis results showed that the first reaction was a thermite reaction of MoO3 and Al in the milling process,followed by a series of reactions to form Mo3Si and Mo5Si3 in the Mo-Si system.
Abstract: A series of Eu3+ and Y3+ doped TiO2 nanopowders were prepared by sol-gel method.The microstructures and properties of the samples were characterized by means of XRD,BET,SEM,UV-Vis and fluorescence spectra.It is indicated that the doping of Eu3+ and Y3+ together in TiO2 can inhibit the phase transformation of nano TiO2,increase the specific surface area and induce the blue shifting in the UV-Vis spectra.All the systems co-doped with Eu3+ and Y3+ show the characteristic fluorescence spectra of Eu3+,and the emission intensity of Eu3+ increases with Y3+ replacing Eu3+.The photocatalytic activities of TiO2 nanopowders co-doped with Eu3+ and Y3+ were tested for degradation of methyl blue solutions.The results show that the doping of Eu3+ and Y3+ together,compared with the doping of Eu3+ or Y3+ respectively,can increase the photocatalytic activities of TiO2 nanopowders and the best molar ratio of Eu3+∶Y3+ is 1∶4.
Abstract: The high-temperature rupture strength and the bending creep behavior at 1 400 ℃ of two types of corundum-mullite pushers were investigated by three-point bending test.The results show that the pusher produced oversea which introduces andalusite as an aggregate has excellent microstructure.Corundum bonded by uniform mullite forms in the matrix and no glass phase is detected.This structure leads to high rupture strength and good bending creep resistance.For the pusher produced domestically,few glass phase leads to lower rupture strength and poor bending creep resistance at 1 400 ℃ though mullite forms a network in the matrix.The morphology of mullite and the glass phase are important factors which affect the high-temperature mechanical properties of a pusher.
Abstract: Based on the concrete design logic of the densified mixture design algorithm (DMDA),this paper investigated aggregates with different densities,i.e.,aggregates sintered by using a reservoir's waste sludge,natural aggregates (stones),and aggregates of solid steel balls,whose aggregate densities are 1.7,2.6,and 7.8 kg·m-3,respectively.Through the DMDA accumulation,lightweight,normal weight,and heavyweight high-performance concrete materials as well as their mixing ratios were obtained.The characteristics of these aggregate concretes,including the mixture properties and the effect of hardening behavior,were compared and analyzed.
Abstract: In order to solve the issue of uneven cooling of square tube aluminum profiles,three-dimensional transient numerical simulation for the temperature field of a square tube aluminum profile in spray cooling was carried out by the finite element analysis software Fluent.The change in temperature field at characteristic points in the square tube aluminum profile was analyzed.The influence of extrusion velocity,nozzle vertical separation distance and nozzle horizontal separation distance on the temperature field was researched.The results show that extrusion velocity and nozzle vertical separation distance have a great influence on the temperature field in the vertical direction;and nozzle horizontal separation distance has a great influence on the temperature field in the horizontal direction.With the maximum extrusion speed,minimum nozzle vertical separation distance and a nozzle horizontal separation distance of 80 mm,the temperature field of spray cooling can be more uniform.
Abstract: A model of amplification mechanisms was designed on the basis of long-length flexure beams.According to the force-deflection relationship and the amplification ratio derived from analytical method,a parametric study on mechanism performances was carried out.The effects of the key structural parameters of the mechanisms on the mechanism performances were identified by theoretical calculation and finite element simulation of a set of examples.
Abstract: A technique for dealing with confidence limit-reliability-stress (C-R-S) curves of up-and-down test was presented to obtain a more accurate endurance limit.Firstly,a distribution hypothesis was tested and its parameters were estimated with regard to the random variables of stress level and reliability.According to 3-parameter Weibull distribution,C-R-S curves were fitted by the least square method.Lastly,the endurance limit was obtained concerning reliability.The endurance limit with a confidence limit of 95% and a reliability of 99% was deduced as 283.76 MPa from up-and-down test of gear tooth bending tests on the quenched and tempered alloy steel 38SiMnMo.This result falling into the square chart of Chinese standard GB3480 can verify the technique presented.
Abstract: The computational domain was meshed by Delaunay triangulation method.A Monte Carlo direct simulation program was developed for unstructured grids and its validity was checked.On that case,the two-dimensional flow and heat transfer of rarefied gas in parallel plate micro-channels with triangular roughness elements were simulated.The pressure of the micro-channels' inlet and outlet and the temperature of the plates above and below were constant.The influences of the height,width and distribution density of roughness elements were computed and analyzed.The results show that roughness elements in the micro-channels can create obvious disturbance for the flow and heat transfer.The greater the roughness elements,the more visible the oscillation of velocity,even vortexes occur,which increases the pressure loss;but roughness elements can enhance the heat transfer.
Abstract: A method of fault pattern recognition for rolling bearings was proposed on the basis of sparse matching of a characteristic waveform (CW).With a well-designed search algorithm,multi-section CWs were extracted from a vibration signal.A representative CW was obtained by learning from the extracted CWs.Then,the representative CW was acted as an atom model to construct a dictionary and a pattern matching dictionary.Pattern recognition was conducted through one-order matching analysis in the pattern matching dictionary.Employing the signals of a normal bearing,ball fault,inner race fault and outer race fault for pattern recognition,the result indicates that the method is valid and robust.
Abstract: A global path planning method for mobile robots based on the guaranteed convergence particle swarm optimization algorithm is presented.A solution is provided for mobile robots to find the shortest path avoiding obstacles in a limited period of time.Firstly,an environmental map is set up and a path connecting the start point and the end point is coded as a particle.Then,a particular active region for particles is mapped out according to the location of obstacles.The initial particle population is generated within this region and particles fly in the active region to search for the optimum path.In the search process,both the acceleration coefficient and inertia weight of the particle swarm optimization algorithm are self-adaptively adjusted along with iteration processes.It is proved that the algorithm can plan out a simple and safe optimum path connecting the start point and the end point by simulation experiments.Comparative studies with a recently reported method show that the proposed algorithm has advantages such as faster search speed and higher search quality.
Abstract: Taking the Third Nanjing Yangtze River Bridge as an engineering background,a pile-cap pier model was designed and built by using the similar principles with a scale factor of 1∶50.A shaking table test of this pier model was carried out by loading a sine wave and Tianjin wave in the two cases around water and around air.The result showed that the largest rate of acceleration increased from 20% to 40% under different waves,and the displacement and strain increased accordingly.The curves of earthquake hydrodynamic pressure along pile height indicated that the distribution of pressure was relevant to the intensity of earthquake waves.
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
