Abstract: In situ stress measurements were carried out at 11 points of 6 levels in the 10th Mine owned by Pingdingshan Coal Group, using a three-dimensional (3D) overcoring stress measurement technique and hollow inclusion strain gages. The maximum measuring depth reaches 1123 m, and it is the first time to apply the overcoring technique to make systematical stress measurements with the measuring depth exceeding 1100 m at coal mines. 3D in-situ stress states at these 11 points were determined by the measurements. Based on measuring results, the regularities of in situ stress states in the mine were obtained and a mathematical model of regional stress field was also established. According to the high risk of coal (rock) bursts and gas explosion in deep mining of the coal mine, a method for predicting coal (rock) bursts was provided as follows. Based on numerical simulation and in situ measurement results, quantitative calculations are made of energy accumulation and its variation with mining process in the rock (coal) mass and surrounding rock, and then according to accumulated energy distribution, the seismology technology is used to predict the place, time and magnitude of coal (rock) bursting induced by future mining.
Abstract: According to gas-geological research, an early-warning model of coal and gas outburst was built based on the stick-slip and catastrophe theory. In the model, gas factors and geological factors were considered as control variables of coal and gas outburst early-warning and were classified to the corresponding early warning indexes, then the coal and gas outburst grades of danger were determined and their warning index limits were divided.Fuzzy mathematics was used to deduce the mutation fuzzy membership function, and the catastrophe series, which can reflect the outburst, was worked out by means of choosing the corresponding mutation model. An example of Yuwu Coal Mine of Lu'an Environmental Energy Development Co., Ltd. verified the feasibility of this early-warning model.
Abstract: The influence of polyacrylamide (PAM) conditioning combined with Al2(SO4)3 coagulant on Tongkeng mine slurry dewatering behavior was investigated by capillary water absorption time (CST) measurements. The depen-dence of the slurry dewatering behavior on interval time of adding chemicals, stirring time, stir intensity, total dosage of chemicals, and chemicals ratio were analyzed in detail. When adding PAM alone in the slurry, the CST reaches its minimum value of 17.4 s at the PAM dosage of 3 mg·g-1. But when simultaneously adding Al2(SO4)3 coagulant and 3 mg·g-1 PAM in the slurry, the CST decreases to 16.9 s at the Al2(SO4)3 dosage of 1.5 mg·g-1. The appropriate opreating conditions were experimentally determined as the interval time of adding chemicals of 45 s, the stirring time of 120 s, and the stirring intensity of 40 r·min-1. By means of orthogonal experiment design, the significance of parameters influencing the slurry dewatering behavior is in the order of total dosage of chemicals 〉 chemicals ratios, and the optimal total dosage of chemicals is 4 mg·g-1, with the mass ratio of PAM and Al2(SO4)3 of 1:3.
Abstract: Taking copper tailings as an experimental object, dynamic thickening experiments were conducted by adding 0, 10, 25, 40 and 55 g of anionic polyacrylamide (APAM) pei tonne of the tailings, respectively. It was found that the thickening concentration of the tailings at the prophase (1 h) increased gradually from 63.98% to 68.20% with increasing flocculant dosage, but at the anaphase (12 h) the value fell slightly when the flocculant dosage increased. In combination with experimental results, the flocculant dosage was divided into four intervals from less to more, low concentration (0 to 10 g per tonne of the railings), appropriate concentration (10 to 25 g per tonne of the tailings), high concentration (25 to 40 g per tonne of the tailings), and ultrahigh concentration (40 to 55 g per tonne of the tailings). The influence mechanisms of fiocculant dosage on railings thickening in the different intervals were put forward, which present partial adsorption, adsorption bridging, protection, and encapsulation roles, respectively.
Abstract: This article studies the existing form of iron particles in direct reduction clinker and their selective recovery technology. It is found that the existing form of iron in tailings is micro-fine iron particles. In direct reduction clinker, the particles greater than 10μm can be recovered by magnetic separation, however those less than 5μm cannot. Considering both the grade and recovery of iron powders, it is necessary to conduct a selective recovery of different types of iron powders. Increasing the monomeric liberation of coarse intergrowths and recovering iron particles specifically from the intergrowths are the key to improve the recovery index of iron powders. Though the recovery of iron can be improved by increasing the magnetic field intensity, the quality of iron powders reduces. Technological parameters have been optimized for the separation by orthogonal test. Under the optimization condition the TFe content of iron powders and the recovery rate of iron is 92.91% and 92.03%, respectively.
Abstract: The physical structure and chemical composition of deashing biomass char coated with potash, as well as its gasification reaction with CO2 were investigated by scmming electron microscopy (SEM) equipped with energy dispersive X-ray spectrometry (EDS) and thermal gravimetry. Experimental data were processed with both the homogeneous model and the shrinking unreacted-core model, and kinetic parameters were obtained for the gasification reaction. It is found that there is an obvious catalytic effect of potash o:a the gasification reaction. This catalysis improves the overall reaction rate and shortens the reaction time. As the potash content increases from 0% to 4%, more adhering catalytic points, rich in kalium, can be detected on the biomass char surface, and the activation energy of the gasification reaction decreased gradually with increasing potash content. Compa:red with the shrinking unreacted-core model, the homegeneous model is more suitable for describing the gasification reaction of deashing biomass char with C02 due to its extremely low ash content.
Abstract: The force condition of spherical inclusion particles in 1873 K liquid steel was investigated by theoretical analysis and numeric simulation. It is found that the pressure gradient Force, virtual mass force, Saffman force and Magnus force are little and can be ignored in static steel and turbulent flow fields. With increasing inclusion particle size, the Brown force imposed on the particles with a bigger size gradually decreases in static liquid steel and homogeneous turbulence fields. When the particle size is bigger than 20 μm, the Brown force will have no influence on particle movement and can be ignored. The Brown motion of the particles with the size smaller than 10 μm is very violent, the Basset force and Brown force imposed on the particles per unit mass become the main force determining particle movement. As for the big-size particles (D>50 μm), the Basset force, mass force and Stokes force work together to influence the movement, collision and removal of the particles.
Abstract: High strength steel with slightly higher S content, deoxidized by aluminum, was smelted in a vacuum induction furnace of 10 kg capacity. Total oxygen in the steel was 0.0010%, and the S content reached 0.0190%. An ASPEX explorer auto-scanning electron microscope (SEM) was used to detect nonmetallic inclusions in the steel. It is found that 98% of the inclusions are dispersed MnS and MnS+Al2O3 complex inclusions. The shape of MnS inclusions is angular, belonging to type III. Al2O3 inclusions, with an average diameter of 1.5 μm, acting as nucleation for MnS precipitation, generate wrapped inclusions of MnS+Al2O3, and they rank 9% to 32% of the total inclusions. The formation process of MnS+Al2O3 can be described as follows:small size Al2O3 inclusions are pushed to liquid phase at melt steel solidification, and then Al2O3 inclusions work as the sites of MnS inclusion precipitation due to Mn and S microsegregation. However, related calculations about the pushing and engulfment behavior of Al2O3 inclusions were carried out. The calculated results indicate that Al2O3 inclusions with the size smaller than 4 μm are pushed in liquid steel, acting as heterogeneous nucleation for the formation of MnS inclusions.
Abstract: The hot deformation behavior of 22MnB5 steel was investigated through tension testing on a Gleeble 3500 thermal-mechanical simulator, over a range of temperature from 700℃ to 900℃ and a range of strain rate from 0.01 s-1 to 10 s-1. It is found that failure strain of the steel increases with the increase of strain rate, and this trend is intensified as the temperature rises. A unified viscoplastic constitutive model coupled with damage, based on dislocation density and incorporated effects of strain, temperature and strain rate, was established to mathematically describe the steep-fall stages of the stress-strain curves. Material constants in the model were determined and optimized by a genetic algorithm. The model can accurately predict the flow stress of the steel in hot stretch and can describe damage evolution in the material.
Abstract: Aiming at the problem of materials corrosion prediction in the natural soil environment, hierarchical linear modeling was used to study the corrosion rules of materials. The hierarchical linear model is a new statistical technique for hierarchical data analysis. Different models for every region can be established to fit regional soil corrosion characteristics and solve the problem of small samples in a specific region, which makes modeling assumptions more consistent with actual situations. A hierarchical linear corrosion model was built with carbon steel corrosion data in soils being the object of study. The test demonstrates that the model can precisely describe and predict the corrosion rate of carbon steel in soils, and it is superior to exponential smoothing algorithm and differential autoregressive integrated moving average (ARIMA) algorithm.
Abstract: The deformation resistance of medium manganese steel at different temperatures was measured on a Gleeble-3500 thermo-simulator system. Reverted austenite transformation in medium manganese steel during warm rolling was investigated by means of tensile testing by stages, scanning electron microscopy (SEM), electron back scattered diffraction (EBSD), and X-ray diffraction (XRD). It is shown that wa:rm rolling at 600℃ and annealing after hot rolling result in more reverted austenite, and excellent mechanical proper;ies are gained with 859 MPa strength and 36% elongation. In the earlier stage of tensile deformation, serrate flow stress behavior is obviously observed because of sustained TRIP effect produced by reverted austenite. During the deformation, reverted austenite with a larger grain size is prior to transform because its stability is poor. In the later stage of tensile deformation, serrate flow stress behavior disappears. Ultrafine grain ferrite and martensite undergo plastic deformation, and martensite strengthening and dislocation strengthening of ferrite become the main strengthening mechanism.
Abstract: Keeping chemical composition and other parameters unchanged, the effects of coiling temperature (625 and 579℃) on the microstructure and properties of Ti-microalloyed high strength steel were investigated during compact strip production (CSP). Experimental results of mechanical properties show that compared with steel strips coiled at 625℃, the yield strength of steel strips coiled at 579℃ decreases by 205 MPa, but the impacting energy at -20℃ increases from 11.7 J to 47 J. Optical microscopy and electron microscopy were used to study the microstructure and precipitates in the steel. It is found that the primary microstructural constituent of steel strips coiled at 625℃ is ferrite grains, but the microstructure of steel strips coiled at 579℃ is finer and characterized with bainite grains. The volmne fraction of uanometer carbides in steel strips significantly reduces with decreasing coiling temperature, which weakens the precipitation hardening effect and causes a marked reduction of strength. However, the toughness is improved due to grain refinement and volume fraction decreasing of precipitates. Coiling temperature needs to be strictly controlled, because it is a more important parameter of producing Ti-microalloyed high strength steel.
Abstract: The hardenability curves of low alloy ultra-heavy plate steel containing boron under different quench processes were obtained by Jominy end quenching test. Under low cooling rate conditions, the microstructures of the ultra-heavy plate steel were observed by optical microscopy (OM) and the grain boundary segregation of boron was tested by auger electronic spectroscopy (AES). It is demonstrated that at the quenching temperature not higher than 920℃, the ultra-heavy plate steel has a better hardenability when the quenching temperature is higher or the holding time is properly longer, and a more perfect hardenability is got by appropriate double quenching. However, when the quenching temperature is higher than 920℃, the hardenability of the ultra-heavy plate steel deteriorates sharply by using single or double quenching.
Abstract: Orthogonal test was designed and emulsion volume fraction on the wettability to investigate the efect of emulsifier mass fraction, oiliness additives of emulsions for strip cold rolling. The influence mechanism of complex emulsifiers with different anionic-to-nonionic ratios on the wettability of emulsions was also discussed in detail. It is found that the ranking of effect on the contact angle and spreading coefficient of emulsions is emulsion volume 〉 emulsifier mass fraction 〉 oiliness additives. Compared with the single nonioaic or anionic emulsifier, the complex emulsifiers present a more excellent ability of enhancing the wettability of emulsions. The surface tension of Q235 steel substrates and the emulsion-substrate interfacial tension were calculated by the Y-G-G empirical equation. The results show that surface tension of Q235 steel substrates is 43 mN·m-1. In comparison with the single anionic emulsifier, when the mass fraction of the anionic emulsifier is 50%, the emulsion-substrate interracial tension is the lowest, which is decreased by 10.78%.
Abstract: The hot deformation behavior of nickel-based superalloy GH4700 was investigated by isothermal compression tests at temperatures of 1120 to 1210℃ and strain rates of 0.1 to 20 s-1 with deformations of 15% to 60%. The flow curves at high strain rate and low temperature were corrected in consideration of the deformation-heating effect. Accurate constitutive equations were established between peak stress and deformation parameters, i.e., temperature and strain rate. The activation energy of the alloy was determined to be 322 kJ. Microstructure analysis results show that dynamic recrystallization (DRX) is the principal softening mechanism during hot working. Strain-induced-grain-boundary-migration is the nucleation mechanism, which is promoted by the increase of both temperature and strain rate. The ratio of DRX grains is increased by temperature and strain, while the iso-ratio contour of DRX exhibits an "anti-C" type in the strain rate-temperature coordinate system. The relationship between DRX grain size and deformation parameters was calculated to be a piecewise function which depends on strain rate.
Abstract: Electroless nickel plating was used to improve the weldability of diamond/Cu composites. Experiments were performed to study the influence of nickel plating process on the phosphorous content of Ni-P alloy coatings as well as the effects of phosphorous content on the bond strength between the coatings and diamond/Cu substrates, the corrosion resistance of the coatings and the spreading area of AgCu28 filler on the coatings. Besides, the coating thickness and process were optimized. It is found that AgCu28 filler on the coatings with 5.8% to 8.7% phosphorus shows good spreadability, and the coating of 8.7% P has a better corrosion resistance than that with a lower P content. In comprehensive consideration with bond strength and filler spreadability on the coatings, the coating with 10 to 20 rain plating time, namely the thickness of 5 to 8 μm, is ideal.
Abstract: Using BOF slag as raw materials, glass ceramics with the basicity (w(CaO)/w(SiO2) of 0.5, 0.6, and 0.7 were produced by sintering. Their structure and properties were studied under different heat treatment conditions by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometry (EDS), sample shrinkage and mechanical strength testing. Experimental results show that the mechanical strength of the glass ceramics is mainly dependent on the sintering property of parent glass and internal crystal structure. At a higher sintering shrinkage rate, internal crystals in the glass ceramics exhibit a cylindrical intertwined form and the mechanical strength of the glass ceramics performs better. Main crystal phases in the glass ceramics are melilite and pyroxene, and high-temperature conditions are in favor of melilite growth and pyroxene.to-melilite ratio decrease. The maximum shrinkage rate belongs to the glass-ceramic with the basicity of 0.6, in which melilite performs columnar interwoven constituting a crystal skeleton that forms the microstructure of high mechanical strength with residual glass phase. Thereby this glass ceramic has excellent mechanical properties.
Abstract: In order to solve the transverse wall thickness variation problem of thick-walled seamless steel tubes produced by hot rolling, a coupled thermo-mechanical finite element model was established to simulate the stretch reducing hot rolling process, and industrial trials were performed to verify the model. Based on simulation results, the authors analyzed temperature, strain and friction force distributions in the rolling process, studied the radial and circumferential flow laws of metal in single pass rolling, the transverse flow law in the whole rolling process and the formation of thickness variation, discussed the influence of temperature on metal flow behavior, and finally summarized the reasons of transverse wall thickness variation. The metal circumferential flow direction is from the roller top to roller gap after rolled by a single pass. Circumferential flow of metal near the ±30℃ position of roller groove angle is the most active, and circumferential flow of metal near the roller top and gap positions is much weaker. However, after the whole rolling process, metal flows from the roller top and gap position to the ±30℃ position of roller groove angle along circumference. This causes that the thickness of the ±30℃ position is bigger than the roller top and gap position. Temperature has huge influence on metal transverse flow behavior. Because of plastic work, metal temperature at the ±30℃ position of roller groove angle increases higher than other positions, which softens and lowers the resistance of this place. So the metal fluidity of the roller top and gap positions toward the ±30℃ position is strengthened, leading to tube cross section appearing a hexagonal bore.
Abstract: The purpose of this article is how to eliminate slab cambering at a slab sizing press in the hot rolling steel production line in some Chinese steel plants. A finite element:model of slab sizing pressing was established with the finite element software LS-DYNA. Slab cambering was analyzed aL different slab center-line offsets and asymmetrical hammerhead inclination angles. It is found that slab center-line offset is the main influence factor of slab cambering during slab sizing pressing, and then a quantitative expression of influence was gained.
Abstract: In order to solve pose and illumination variation problems in ear recognition, an information fusion method was proposed to fuse 2D and 3D ear information at the decision level. For a 2D ear, the ear images will become nonlinear manifold structure due to pose variation, so the manifold learning method, isometric mapping (Isomap), was used to extract features. For a 3D ear, the 3D local binary pattern (3DLBP) method was adopted for feature extraction. Then 2D ear recognition and 3D ear recognition were implemented separately. Finally, results from the 2D and 3D were fused at the decision level. Experiments were done on a database of 79 persons, one of which has eight 2D ears with pose variation and six 3D ears with illumination variation. It is found that both the recognition rate and verification rate are significantly improved compared with 2D ear recognition and 3D ear recognition alone.
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
