Resorting to the modified rock mass rating system, the rock mass classification was performed for Hemushan Iron Mine in east China. Ore pillars in the mine were researched based on the thickness-span ratio method, the structural mechanics beam theory and Pu's arch theory. The failure mode and the evolutionary process of destabilization were gained for the backfill stope. The influences of stope size and the consistent coefficient, tensile strength and the internal friction angle of ore rock on the stability of the backfill stope were analyzed due to transforming from block caving to stage backfill. A safety factor equation of the ore pillars was established on the basis of the limit equilibrium method. Results show that the effects of the consistent coefficient and tensile strength of ore rock on the roof critical thickness of the backfill stope are obvious, and the cohesion exerts a tremendous influence on the safety factor of the ore pillars. Finally, the results above were applied to analyze the stability of the backfill stope in Hemushan Iron Mine, the roof critical thickness of the backfill stope and the safety factor of ore pillars at the lump ore belt were obtained, and causes for the failure of the 19th room were understood from these theories.
Abstract: A two-stage compulsory stirred tank with a pitched-blade opening-type turbine was designed based on the process intensification of pulp pretreatment before fine coal flotation. The mixing characteristics of the stirred system were evaluated by investigating its flow dimensionless number, power dimensionless number, shear characteristics, cycle characteristics and mixing efficiency. Coal flotation experiment of anthracite coal from Yongcheng Mine in central China was performed by two-stage compulsory pulp-mixing. When the rotational speed goes up, the energy input and the mixing efficiency of the stirred system increase, the pulp cycle performance and shear performance by unit energy consumption decrease, but the decreasing trend of the latter is less than that of the former. At the same rotational speed, high shear characteristics and mixing efficiency as well as low circulation/shear ratio can be obtained with a large diameter impeller by unit energy consumption. A cyclone-static micro-bubble flotation column can achieve a better flotation index and a greater capacity at the mode of two-stage compulsory stirred pulp-mixing. A large diameter impeller and high rotational speed favor to recover hard-to-float coal particles. The recovery of coarse particles is improved by two-stage compulsory stirred pulp-mixing when the processing capacity in appropriate conditions, but in large capacity conditions, the fine-particle ash increases in flotation railings.
Abstract: The mechanism of adding sodium carboxymethyl cellulose (CMC) to improve the strength of hematite ore and coal briquettes was investigated by infrared spectroscopy (IRS), X-ray photoelectron spectroscopy (XPS) and contact angle measurements. It is found that -OH and -COOH in CMC chemically absorb at the surface of hematite ore and reduce the hydrophilic character of ore particles, while hydrocarbon chains in CMC bond on the surface of coal and reduce the hydrophobic character of coal particles. Hematite ore and coal grains are bonded by the organic skeleton of CMC, and form a supporting network bridged by CMC chains between the particles to ensure the good strength of the briquettes. Therefore, the strength of hematite ore and coal briquettes is highly improved with the addition of CMC.
Abstract: In order to research the differences of degradation effect on coke between potassium and sodium gaseous adsorption experiments on coke in potassium and sodium atmospheres were carried out, and the coke samples were analyzed by scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD) and thermal properties test. It is found that sodium more easily covers the surface of coke in surface-absorbed form, so the absorption amount of sodium is greater than that of potassium in the alkali atmospheres with the same mass ratio. Alkali metals absorbed on the surface of micropores have resistant effect on the solution loss reaction of coke. Compared with sodium in sodium-adsorbed coke, in the same absorption amount condition, more potassium in potassium-absorbed coke chemically combines with carbon and thus potassium-absorbed coke has a higher reactivity. In addition, potassium has strong destroying effect on coke. Potassium atoms can intercalate into carbon layers and cause the multidimensional expansion of microcrystals, which leads to breakages in the microstructure of coke. These new cracks result in the different ways of solution loss between potassium-adsorbed coke and sodium-adsorbed coke.
Abstract: In consideration of the devolatilization of lump coal in the upper zone ot the melter gasmer anti the burning of tar and hydrocarbon in volatile matter with oxygen, an operating line diagram of the melter gasifier was established by utilization of the improved Rist operating line principle. The Rist operating line diagram can directly reflect the effect of various factors on the energy consumption of the ironmaking process. Changes of the Rist operating line were discussed after the burning of volatile matter and hydrocarbon with blowing oxygen in the upper zone of the melter gasifier. The oxygen consumption and energy consumption were compared when charging different lump coals and semi coke. The changes in gas oxidation degree, temperature and volume change as well as their influence on the energy consumption were analyzed when charging semi coke after volatile matter removal.
Abstract: According to the working conditions of the hot coil box in a domestic steel 2250 hot rolling production line, the birth-death element and re-start technology of the finite element analysis software ANSYS was adopted to simulate the production rhythm of coiling, insulation and uncoiling of intermediate slabs. The interface heat transfer coefficients of intermediate slabs were determined in different heat transfer conditions. The effects of process parameters and environmental factors on the temperature of intermediate slabs in the hot coil box were analyzed on the basis of simulation data. A mathematical model of three-dimensional temperature fields was established for intermediate slabs in the hot coil box. Finally, the outlet temperature of intermediate slabs in the hot coil box was calculated, which can provide us with some feasible suggestions for hot rolling temperature control.
Abstract: Non-oriented silicon steel strips were rolled on a four-high cold rolling mill lubricated by a traditional cold rolling liquid and a nano-TiO2 cold rolling liquid, with emphasis on studying the roiling lubrication performance of both the liquids and their effect on the surface quality and corrosion resisting property of the silicon steel strips. The surface micrograph and composition of the silicon steel strips after being rolled with both the liquids were characterized by field emission scanning electron microscopy and energy-dispersive spectroscopy. The anti-wear and friction-reducing mechanism of TiO2 nanoparticles in cold rolling was given on the basis of experimental results. The nano-TiO2 cold roiling liquid has excellent lubricant performance and can improve the surface quality of the silicon steel strips remarkably when rolled with heavy load. Meanwhile, TiO2 nanoparticles are compressed into the silicon steel matrix by high load and a sliding system is formed to bear the load, leading to a higher wear resistance of the lubricant film.
Abstract: The mechanical properties and microstructure of plastically deformed Fe-Mn-C and Fe-Mn-Si-AI series high manganese twinning induced plasticity (TWIP) steels were investigated at different strains. The roles of TWIP effect in the two series TWIP steels were analyzed so as to clarify the strengthening mechanisms. It is found that the two series TWIP steels have high work hardening ability, while the work hardening ability of Fe-Mn-C TWIP steel with a lower stacking fault energy (SFE) is stronger. The two series TWIP steels deformed under the same conditions exhibit different work hardening rates, since different deformation mechanisms play a leading role during different deformation stages. There is a strong correlation between the microstructure morphology and the work hardening behavior. Multiplication of dislocations and generation of deformation twins have obvious effect on the work hardening index curves of the two series TWIP steels. In high-strain stages, the plenty of primary deformation twins T1 and secondary deformation twins T2 in Fe-Mn-C TWIP steel and high-density dislocation areas adhering to twin boundaries lead to its high work hardening ability. But the close-set primary deformation twins T1 and dislocations between twins are the reasons for the high work hardening behavior of Fe-Mn-Si-Al TWIP steel, whose microstructure is more uniform and finer.
Abstract: The effects of cooling temperature and cooling rate on the size and volume fraction of M-A islands in thermal simulation samples of high grade X100 pipeline steel were investigated by the microstructure analysis method. The results show that reducing the cooling temperature and increasing the cooling rate can refine the microstructure, decrease the volume fraction of M-A islands, and make the M-A islands from larger blocks and strips into smaller and dispersed ones. The morphology of M-A islands in X100 pipeline steel with different cooling rates after hot rolling was observed by transmission electron microscopy (TEM). It is found that the M-A islands consist of retained austenite and different sizes and orientations of martensite plates at low cooling rate. Microtwins in the martensite plates prove carbon diffusion and show that martensite in the M-A islands is twinned martensite. At high cooling speed, the M-A islands, which change into the acicular and flaky, weaken the ferrite lath interface and reduce the toughness of the pipeline steel. So in order to obtain small size and dispersive M-A islands, the cooling speed must be controlled in a certain range.
Abstract: Activity interaction coefficients between elements Ti and Mo in iron-based systems were estimated on the basis of the thermodynamical theory. The solubility of Ti, C and N in austenite of Ti-Mo micro-alloy steel from 800 to 1300℃ was theoretically calculated at different Ti and Mo contents. Mo can decrease the activity of Ti in iron-based systems and restrain the precipitation of Ti, but its influence is little. The influence degree decreases with the rise of temperature. When the Ti content is constant, the influence degree heightens with the increase of Mo content in the steel. But when the Mo content is constant, the influence strengthens firstly and then weakens with the increase of Ti content in the steel. Finally, the calculated results were compared with experimental data. It is indicated that when the atomic ratio of Ti/C is about 0.5, the mechanical properties of the steel are the best and the Mo content has the greatest impact on the precipitation of Ti(C,N).
Abstract: Experiments were performed to investigate the effects of the key factors such as the mass concentrations of adding sulfur agent TS and additive SB as well as current density on the sulphur content and physical appearance of nickel buttons. Differences in electrochemical activity were analyzed between the 1# electrolysis nickel and the products of activated nickel buttons. The process and the optimum parameters of adopting the soluble anode electrolysis with nickel sulfide were decided for developing the activated nickel buttons by experiment. The optimum technological conditions were obtained as follows:the mass concentrations of adding sulphur agent TS and additive SB are 7.53 mg·L-1 and 36.97 mg·L-1 respectively, the average apparent current density is 1300 A·m-2, and other technological parameters are the same as those of the 1# electrolytic nickel. Nickel buttons with smooth surface and regular shape were developed at the parameters above, which contain sulphur from 0.01% to 0.03%. The products possess high electrochemical activity, and their chemical composition accords with the requirements of the 1# electrolysis nickel. The technology has been used in industry, and the products meet the requirements of special plating anodes for the precision electroplating industry.
Abstract: The paper reports on the effects of Zr ion implantation parameters,incident dose and incident current, on the surface composition,morphology,hardness and wear resistance of NiTi shape memory alloys.When Zr ions are implanted in the NiTi alloy surface,their content presents Gaussian distribution but the Ni content is reduced in the surface.After Zr ion implantation,groove structures appear on the surface,and the nano-hardness,Young’s modulus and the microhardness of the surface increase obviously.Friction and wear experiments show that Zr-ion implantation reduces the initial friction coefficient and significantly prolongs the time maintaining a lower initial friction coefficient. The width and depth of wear tracks for Zr-NiTi alloy decrease by 30%to 50%and 28%to 50%,respectively.The choice of appropriate ion implantation parameters can get the best wear resistance of NiTi alloys.
Abstract: This paper reports the high temperature tensile deformation behaviors and mechanisms of twin-roll cast AZ31 magnesium alloy. At constant temperatures ranging from 300℃ to 450℃, the elongation-to-failure test was conducted under constant tensile strain rates of 10-3 s-1 and 10-2 s-1, and the strain-rate-change tensile test was performed under strain rates from 2×10-4 s-1 to 2×10-2 s-1. The elongations of specimens at 400℃ and 450℃ are both higher than 100% when the tensile rate is 10-2 s-1. But when the tensile rate is 10-3 s-1,the elongation values at 400℃ and 450℃ are both higher than 200%, the stress exponent n is about 3, the creep activation energy Q is 148.77 kJ·mol-1, and the deformation mechanism is a collaborative mechanism of grain boundary sliding and solute-drag dislocation creep. Optical microscopy and scanning electron microscopy observations show that coarse grains develop at the failure ends due to dynamic recrystallization and grain growth, and the fracture is of a ductile pattern caused by cavity growth and interlinkage.
Abstract: Based on measured temperature by thermocouples, a finite element model of heat transfer and a nonlinear estimation model of heat flux were built for a continuous casting wide-thick slab mold for peritectic steel. The heat flux of the mold was inversely computed by using the model. In comparison with the average heat flux calculated by heat balance, the model was proved to be valid. The temperature distribution of cooper plates in the mold was analyzed under actual production conditions by the model. The averaged heat flux is 1.141 and 1.119 MW·m-2 for the wide and the narrow face, respectively. The temperature near the mold back appears to be waved with a maximum difference about 29.6℃, whereas presents to be fiat far away from the mold back. Although the temperature decreases with the increase of the distance below the meniscus, it picks up near the mold exit. The heat flux and temperature distributions of the mold differ from those of conventional slab molds.
Abstract: A finite element model of a heat exchange tube with a semi-elliptical crack in the cross section of the inner surface, which simulates the crack tip's stress singularity, was established by ANSYS software. After discretizing the crack front, crack fronts in different crack propagation orientations were presented. Under different thermal-mechanical coupling loads, the stress intensity factors KI of the finite element model were calculated and compared at different crack parameters. The distribution rule of KI and its influence factors were discussed in detail.
Abstract: The boiling liquid expanding vapor explosion (BLEVE) is an explosion caused by bulk boiling and rapid expanding of superheated liquid. It often happens in liquefied petroleum gas (LPG) tanks during stationary and transportation storage. Based on experimental results from the Health and Safety Executive of England on LPG tanks under pool and jet fires, the authors investigated the thermo-physical processes including internal pressure change, wall temperature change and LPG mass release in LPG tanks as well as the relations among the dependent variables. Physical and mathematical models were presented in PLGS99 (pressure liquefied gas simulation) software to simulate the temperature and pressure responses of LPG tanks. The predictions were validated by experimental data and the explosion mechanism of LPG tanks caused by BLEVE was analyzed.
Abstract: A six-freedom degree coupled dynamic model was proposed for gear transmission systems on the basis of tribology and gear system dynamics. In the model the wear, time-varying mesh stiffness, eccentricity mass and tooth errors of gears were taken into account to simulate the practical working condition. The nonlinear vibrations of gears were studied by applying the self-adapt and variable step method of numerical simulation. Vibration characteristics were compared between the standard and cracked teeth. Finally, the authors analyzed the effects of the gear tooth root crack on the time domain, frequency domain and time-frequency domain for the dynamic load spectra of gear transmission systems.
A open-pit-mining operational planning model was constructed from the view point of minimizing the mining and transportation cost. Based on the theory of swarm intelligence optimization, a method was proposed that uses a particle swarm optimization (PSO) algorithm to optimize the open-pit mining operation plan, and a search strategy with the core particle and double attractor was designed for particles in the calculation process. The optimal operation plan was calculated by using MATLAB software as a computation platform. A case study was performed by taking an open-pit iron mine as an engineering background. By comparing the optimization results of the PSO algorithm with the actual planning results and the calculated results of nonlinear programming, it is proved that the PSO algorithm is feasible and reliable for optimizing the open-pit mining operation plan.
Abstract: The semantic Web technology was introduced into publish/subscribe systems and an intelligent seman-tic matching algorithm (ISMA) was proposed by domain ontology. With double-index hash tables, predicate, variable filter and type tables as the data structure of resource description framework (RDF) graph patterns which stores subscrip-tion conditions, the algorithm adopts meta-statement match counting method to efficiently process atomic subscription factor match only once, and the subscription conditions are an "and" serial sequence matching relationship. The time and space complexities of the algorithm were derived and analyzed by quantitative and qualitative methods. Experi-mental results demonstrate that the algorithm is efficient and scalable, and it is suitable for large-scale publish/subscribe systems.
Abstract: Ten strains of potassium-releasing bacteria were isolated from the tobacco rhizosphere soil. Four strains with an obvious transparent zone and high efficiency proliferation were selected to investigate their potassium-releasing capacity. The K+ mass concentration in the fermentation broth of the strain GJ07 is 54.5% higher than that of the blank control group. The strain GJ07 was identified as Bacillus megaterium by the identification of 16S rDNA analysis. The batch culture conditions of the strain GJ07 were optimized via adjusting carbon sources, nitrogen sources carbon-to-nitrogen mass ratio, temperature, pH values and loading liquid. It is found that sucrose is the best carbon source, peptone is the optimal nitrogen source, the optimal carbon-to-nitrogen mass ratio is 10:1, the best temperature and initial pH value are 35℃ and 7.00 respectively, and the optimal loading liquid is 25 mL.
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
