Abstract: Based on the particle flow theory and PFC3D code,a draw model was constructed to research the flow characteristics of caved ore and rock in the multiple draw-point condition and visualize the form-changing process of the isolated extraction zone(IEZ) and the ridge hangover body. Simultaneously,the suitability and reliability of this draw model were validated in the flow characteristics study of caved ore and rock by comparative analysis between simulated results and existing research conclusions. Due to interactions among multiple draw-points,the IEZ's form produces different degrees of variation in the multiple draw-point condition,including interlacement and deficiency,which result in that the IEZ's form is not a regular ellipsoid. The height changing trend of the IEZ in both the isolated draw-point condition and the multiple draw-point condition can be divided into two stages:in the first stage,the IEZ's height rapidly increases in an exponential form at the initiation of draw and its growth rate decreases with the increase of ore-drawn mass; in the second stage,the IEZ's height linearly increases with the increase of ore-drawn mass. The ore loss ratio decreases when the draw-point dimension and the height of the caved ore layer increase,but it increases with the increasing of draw-point spacing.When adjacent draw-points interact with each other,compared with a facade draw mode,the ridge hangover mass is less in a plane draw mode,and the contact surface of caved ore and rock horizontally drops.
Abstract: This paper reports the magnetizing roast of oolitic hematite ore,including the dependency of the magnetization effect upon magnetization temperature,magnetization time,biomass content and ore particle size. It is indicated that the oolitic hematite ore with a particle size of 0.074 mm(>72.5%) is completely magnetized in 30 min by biomass-generated gases and tar at 600℃ when the ore-to-biomass mass ratio is 10:2,which verifies the feasibility of this substitution of biomass for coal as a reductant for magnetizing roast. In addition,the particle size of the oolitic hematite ore has great effect on the reduction index of magnetizing roast. The larger the particle size,the longer the complete magnetization time is. According to the character of biomass,the magnetic properties of the oolitic hematite ore can be effectively improved by appropriately decreasing the particle size.
Abstract: The recovery of iron-bearing silicate minerals is a key on the re-separation middlings of Anshan type lean magnetite,but this recovery process should be conducted selectively. The iron grade of stage 1 tailing is only 3.92%,so there is no need to recover it. However,the iron grade of stage 2 tailing is 34.51%,thus this tailing can be returned to the mixing process before direct reduction and its iron is indirectly recovered. Under the condition of the direct reduction temperature of 1150℃,the direct reduction time of 45 min,the limestone dosage of 16% and the coal dosage of 12%,the optimum TFe and εFe obtained from closed-circuit experiment is 92.69% and 91.17%. Iron and silicon in the iron-bearing silicate are reduced to elemental iron and reengineered to aedelforsite,respectively.
Abstract: By using a thermal-state visualizable fluidized bed,the sticking of iron ore fines with different particle sizes was investigated under the condition of certain superficial gas velocity at 1073 K. It is found that according to different influences of particle size on the sticking,iron ore fines can be divided into three particle size ranges:small particle size at which sticking occurs in the neutral atmosphere under 1073 K,medium particle size at which defluidization happens when iron ore fines are reduced to low metallization ratio on the fluidized bed,and large particle size at which sticking does not appear on the fluidized bed,even to the end of reduction.The influence mechanism of particle size was analyzed in this paper. Moreover,under the normal fluidization condition,the swelling degree of the fixed bed after defluidization decreases with increasing particle size.
Abstract: Based on in-situ observation,mineral evolution in high-phosphorous iron ore during the reduction process was investigated in the H2 atmosphere at different temperatures,and the influence of temperature on the morphology of iron was discussed. During the reduction process,ooliths in the iron ore remain. The mineral phases evolve faster with rising temperature,and so does the precipitation of iron from hematite phase. Significant segregation of iron happens at a higher temperature. Temperature has significant impact on the precipitation morphology of metallic iron. At 700℃,the precipitation of metallic iron forms a dense layer on the surface of particles. At 800℃,the precipitation morphology of metallic iron is complex,the density of the iron layer decreases,little holes appear while a small number of short iron whiskers are found. But at 900℃,the number of iron whiskers significantly increases with abundant porous sponge iron. Therefore,by adjusting the temperature and time,the sticking problem during the gas-based reduction process can be avoided,and meanwhile,efficient reduction of high phosphate iron ore is achieved.
Abstract: Iron oxides were nonstoichiometric chemical compounds. Their reduction processes were remarkably influenced by nonstoichiometries. Dieckmann's defect model of magnetite and Weiss's ideal solid solution model of wustite were adopted to analyze the thermodynamic influences on the reduction processes. The dependences of deficiency degree δ on weight loss and Fe2+ mole ratio were analyzed by using the charge conservation and mass conservation principles. These relationships were recommended to judge the final product of the reduction processes. According to theoretical analyses and calculations,the predominance area diagrams including different nonstoichiometries of magnetite and wustite were determined in equilibrium with the reduction potentials PCO(H2) at different temperatures. It comes to a conclusion that when the reduction weight loss ratio is less than 6%(without metallic Fe),magnetite is predominant in the pure hematite reduction at a certain temperature and reduction potential; but when the reduction weight loss ratio is higher than 6%,the process then enters the zone of wustite.
Abstract: The effect of various states of Fe(Fe,FeO,and Fe2O3) on the reduction of Cr2O3 was investigated by conducting isothermal experiments on the reduction of Fe-Cr2O3,Fe2O3-Cr2O3 and FeCr2O4 by graphite at 1350-1550℃ combined with X-ray diffraction and scanning electron microscopy with energy-dispersive spectrometry. It is shown that the tendency of final reduction degree is Fe2O3-Cr2O3-C 〉 FeCr2O4-C 〉 Fe-Cr2O3-C at each temperature,and the transformation path of the three samples is oxides → carbides → Fe-Cr-C alloy. Liquid alloy which earlier emerges and low carbon-content carbides promote the reduction of Fe2O3-Cr2O3. Low carbon dissolution in liquid alloy limits the reduction degree of FeCr2O4. The large amount of carbides and little liquid alloy retard the reduction of Fe-Cr2O3. The apparent activation energies of Fe-Cr2O3-C,FeCr2O4-C and Fe2O3-Cr2O3-C are 142.90,111.84 and 128.9 kJ·mol-1,respectively.
Abstract: To make full use of symplesite resources in China,CaO + CaF2,CaC2+ CaF2 and Si-Ca-Ba alloy + CaF2 were used as an agent in molten steel dearsenization experiment. The Si-Ca-Ba alloy + CaF2 agent shows the most obvious dearsenization effect.Their dearsenization rate is as high as 67.7%. Under the same operation conditions,the effects of temperature,mass transfer coefficient and S content on the dearsenization of the three dearsenization agents were analyzed and compared by laboratory research.
Abstract: The effect of anisotropic surface tension on the growth behavior of column crystals at quasi-steady state is considered in this article. By using the method of asymptotic expansion,a mathematic expression is obtained to describe the interface patterns of column crystals,and the interface morphology change with different anisotropic parameters is discussed. The results show that anisotropic surface tension has a great effect on the interface morphology. During the initial stage,some part of the interface shrinks inward first,and then it starts to move outward after the shrink reaches a critical value. In the direction of preferred growth,the interface of column crystals grows faster. The effect of anisotropic surface tension leads to bulge formation of the interface. As the anisotropic parameters increase,the bulge formation gets obvious.
Abstract: According to the hot-rolled microstructure of medium manganese steel,a geometry model and initial conditions of intercritical austenitization were established,and the DICTRA dynamic analysis software was used to calculate the austenitization on the martensitic matrix. It is found that supersaturated carbon and manganese in martensite quickly transfer from ferrite to austenite and aggregate at the austenitic side of the phase interface in the initial austenite nucleation stage. In the subsequent transformation,carbon rapidly homogenizes in austenite,but the aggregation degree of manganese in the austenitic side of the phase interface increases. The migration velocity of the austenite phase interface in the initial stage is several orders of magnitude higher than that in the middle and late stages,but rapidly decreases. The phase interface movement in the early transformation stage is dominated by carbon diffusion,but is restricted by manganese diffusion rate in austenite in the middle and late stages. Increasing the temperature can significantly improve the phase interface velocity. Under the condition of achieving the same amount of austenite,the low-temperature and longtime annealing is benefit for manganese transferring from ferrite to austenite and enriching in austenite,which will improve the stability of austenite.
Abstract: The precipitation behavior of V-N microalloyed steel at the normalizing process was studied by physicochemical phase analysis and high resolution transmission electron microscopy. The effect of this precipitation behavior on the mechanical properties of the steel was discussed by theoretical calculations. At soaking of the normalizing process,32.9% of V(C,N) precipitations keep undissolved into austenite,and they prevent austenite from growing up. At the subsequent cooling process,the undissolved V(C,N)precipitations induce intra-granular ferrite nucleating,which can refine ferrite grains; besides,the dissolved V(C,N) precipitations re-precipitate and play the role of precipitation strengthening. Compared with the hot-rolled steel,the normalized steel gains a 31 MPa increment in grain-refined strengthening but a 45 MPa decrease in precipitation strengthening.
Abstract: A new testing method based on direct current potential drop(DCPD) and pin loading tension(PLT) method was introduced for evaluating the fatigue crack growth rate of steam generator tubes. In analogy to compact tension(CT) specimens,a testing model was established by using thin-walled tube specimens,and the corresponding mechanical and electrical finite element analyses were made respectively,which determined the data acquisition plan based on DCPD method. Fatigue test was taken on nickel-based alloy 690 used for nuclear power steam generators,and the effects of applied load and temperature were discussed. The result was modeled with the Paris-Erdogan equation and accorded well with this model. Scanning electron microscopy(SEM) examination of the fatigue fracture surfaces revealed transgranular attack,and the transgranular regions of the fatigue fracture surfaces were covered with striation-like features.
Abstract: To solve the problem of forging cracks,the hot deformation behavior of Cr20Ni80 electrothermal alloy was investigated by compression tests on a Gleeble-1500 D thermal simulation machine in a temperature range of 900 to 1220℃ and a strain rate of 0.001 to 10 s-1. The hot processing map of the alloy was established according to the dynamic materials model(DMM). It is found that the true stress-true strain curves have steady-state flow characteristics. The peak stress increases with decreasing deformation temperature or increasing strain rate. The flow behavior is described by a hyperbolic sine constitutive equation,and the activation energy of the alloy is about 371.29 kJ·mol-1. Based on the processing map,the process of hot deformation in the temperature range at different strain rates can be attained,of which the optimum hot deformation temperature ranges in 1050-1200℃ and the strain rate is 0.03-0.08 s-1,and the instability zones of flow behavior can also be recognized. The optimal hot-working technology is validated to be successful in production.
Abstract: By adding an electrochemical test system on a PLINT fretting wear test machine,the fretting corrosion behavior of an NC30 Fe heat transfer tube in a sodium chloride solution was investigated using cross-contacting configuration under different loading conditions,i. e.,three different normal loads of 20,50 and 80 N with a 100 μm reciprocating amplitude. An electrochemical workstation was used to record the open circuit potential during the fretting corrosion process,and the polarization curves were measured by the potential scanning method. The morphology of wear scars was observed by scanning electron microscopy. The 3D morphology and wear volume loss were determined by optical profilometry. It is found that metal atoms in the worn area are more active and more prone to corrosion because of fretting motion,leading to accelerated corrosion of NC30 Fe alloy. As a result of lubrication action by the corrosion product film,the friction coefficient in the sodium chloride solution is smaller than that in pure water. However,the wear volume loss in the sodium chloride solution is greater than that in pure water due to the interaction of corrosion and wear. Abrasive wear and delamination are considered to be the main wear mechanism in the sodium chloride solution.
A duplex process was designed to modify the surface of LY12 CZ aluminum alloy by using surface mechanical attrition treatment(SMAT) prior to microarc oxidation(MAO). A surface nanocrystalline(SNC) layer was formed on the alloy surface by SMAT,a ceramic outer layer grew on the SNC layer by MAO,and finally an SNC-MAO composite coating was fabricated. The tribological behaviors of the MAO coating and SNC-MAO composite coating were comparatively evaluated. Experimental results showed that the SNC-MAO composite coating had a better wear resistance than the MAO coating in the same test condition due to a higher hardness of the ceramic coating. The wear mechanism of the MAO coating and SNC-MAO composite coating involved materials transfer from the steel ball to the coating and oxidation wear.
Abstract: A surface film generates on AZ21 magnesium alloy in magnesium sulfate solutions,resulting in serious voltage delay.Pulse current is conducive to the application of AZ21 magnesium alloy in a battery,for it can shorten the lag time,reduce the initial discharge voltage drop and increase the discharge stability. The voltage delay of AZ21 magnesium alloy in a 2 mol·L-1 MgSO4 solution was investigated by chronopotentiometry,multi-current steps,electrochemical impedance measurement,and scanning electron microscopy. After a 50 mA pulse current was applied for 1 s,the voltage lag time of AZ21 magnesium alloy decreased from 6.35 s(3.23 V) to 0.59 s(0.034 V).
Abstract: The input shaft is an important part in a vehicle gearbox. A novel compound forming technique was designed due to the special structure of an input shaft. This forming technique is named once heating and combining rolling with forging,meaning that the cylindrical billet is first heated,rolled by cross wedge rolling and forged sequentially. The input shaft was deformed by the novel technique combining cross wedge rolling with die forging. The dies of cross wedge rolling and forging were designed in this paper,and the accuracy of finite element simulation was determined compared to experimental data. A great agreement between simulated and experimental results validates the predictability of finite element simulation. Extrusion was used to form the axis fillet in the forging process to avoid folding defects. The multidiameter semi-manufacture is both the product of cross wedge rolling and the billet of die forging,so it plays an important role in the whole process. The effect of cone angle and diameter was researched by experiments to determine the optimum values of parameters. Finally,the input shaft with full teeth and no defect was formed by the novel forming technique.
Abstract: This article reports the flow characteristics and oxygen-enriched effect of round outlet oxygen diffusion at a large space.Experimental results show that the axial maximum velocity and oxygen concentration of oxygen diffusion both decrease with axial distance,and there are large velocity and oxygen concentration gradients within an axial direction range of 0 to 0.6 m. The oxygenenriched regions are similar at different outflow velocities and their concentration profiles are closer to a semi-elliptical form by a smaller outlet diameter at the downstream,which contributes to forming a much larger oxygen-enriched region. A relation between the extended half-width of outer boundary enriched area and the axial distance and a relationship between the oxygen-enriched area and the outflow rate are obtained through function fitting. The oxygen-enriched area formed by dual outlet oxygen diffusion approximately decreases 10% than that by single outlet oxygen diffusion with the same outflow rate; the oxygen-enriched area formed by 6 mmdiameter outlet oxygen diffusion increases about 10% compared to 8 mm-diameter outlet oxygen diffusion.
Abstract: A robust H∞ preview control problem is proposed for a class of uncertain discrete-time systems. A new method is derived to construct an augmented error system,avoiding applying the difference operator to the time-varying matrix,and simplify the augmented error system. Then for the augmented error system of the uncertain system,the problem of guaranteed cost robust H∞ control is considered via a state feedback with integral and preview actions. The sufficient condition for the existence of the robust H∞ controller and H∞ state feedback controller design methods are presented. The condition can be realized by solving a linear matrix inequality optimization problem. By putting the controller obtained into the original system,we can get the preview controller. Moreover,introducing an integrator makes the closed-loop system robustly track the reference signal without steady-state error. The effectiveness of the proposed method is shown by numerical simulation.
Abstract: The changes of sludge dewaterability and bound water content at various pH values were investigated in this study. The protein and polysaccharide contents in each layer of extracellular polymeric substances(S-EPS、LB-EPS and TB-EPS) and the organic acid and organic functional group contents in S-EPS were determined in an attempt to explain the influence of EPS on the sludge dewaterability and bound water content. The results indicate that the sludge dewaterability under acidic conditions is obviously better than that under neutral conditions,and the water content of dewatered sludge(WC) and the capillary suction time(CST) can be decreased to 60.8% and 25.4 s at pH 3.03,respectively. Under alkaline conditions,the bound water content in dewatered sludge,the WC and CST significantly increase,and the sludge dewaterability deteriorates. The addition of acid or alkali reduces TB-EPS,on the contrary,increases LB-EPS and S-EPS. Each layer of extracellular polymeric substances has significant correlation with the WC,CST and the bound water content,and S-EPS has most significant correlation with the sludge dewaterability and bound water content. In the process of acid-alkali conditioning,the amount and type of organic-functional groups improve obviously and hydrolysis of partly EPS generates organic acids and other small molecules.
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
