Abstract: The principle and process of underground segmentation point hydraulic fracturing for low-permeability coal seams were studied by means of numerical analysis and field test.Underground segmentation hydraulic fracturing is intended to change the traditional force way to make coal more force and interaction,and finally to produce the effect of fracturing.The hydraulic fracturing test at the west second mining area of Chenshan Coal Mine in northeastern China shows that when the fractured radius is 5 to 7m,the critical injection pressure is 14 MPa,and it is suitable for the hydraulic fracturing that the injection pressure is 14 to 20 MPa.The test procedure is so simple that the hydraulic fracturing can be completed within 5 min,and the average gas flow and volume fraction of gas drainage are significantly increasing after the hydraulic fracturing.
Abstract: Aimed at dust raising on transport roadways in open mines,the complex suppressant was researched and applied in practice.Two excellent complex suppressants were developed through theoretical analysis and experiments,and a comparison was made between their performances.The moving rules of dust on transport roadways in open mines were simulated by using FLUENT software,and the most appropriate area was determined for dust monitoring.Practical applications show that by using the complex suppressant the mass concentration of dust is below 4 mg·m-3,and the effective time of dust suppression is 6h.
Abstract: Based on the distinguishing feature of mine water from Tongkeng Mine in south China, a complex coagulation method was selected to treat the mine water. Through single-factor and orthogonal tests, the effects of some factors, such as coagulants, coagulant aid content, pH values, stirring speed, and stirring time, on removing Zn2+ in the mine water were studied and the best level of each factor was determined. The best synergistic effect can be achieved when the volume ratio of polyaluminium chloride (PAC) to polyacrylamide (PAM) is 2:1, and the best treatment effect is obtained when the pH value is 9, the stirring speed is 80 r·min-1 and the stirring time is 10 min. The results of actual water treatment tests show that the removal rate of Zn2+ reaches 93.9%, and the mass concentration of Zn2+ in the discharged water can meet the national emission standards of China.
Abstract: The electrical conductivity of the CaO-Al2O3-SiO2 system was modeled based on the concept of optical basicity. The model can reflect the effect of the amphoteric behavior of Al2O3on the electrical conductivity and the phenomenon that the electrical conductivity decreases when substituting Al2O3for SiO2. According to the comparison between the diffusion coefficients of different ions, it is indicated that the charge transport process is mainly completed by Ca2+. The self-diffusion coefficient of Ca2+ was calculated by the estimated electrical conductivity and the Nernst-Einstein equation. The deviation between the calculated diffusion coefficient and that measured by a tracer atom method was discussed, and a theoretical interpretation for the decrease of deviation with increasing temperature was also given.
Abstract: In order to control the nitrogen content of liquid steel, two different deoxidation methods were applied:(Ⅰ) Al blocks were added for deoxidation when tapping; (Ⅱ) Si-Mn alloys without Al were added for deoxidation at first when tapping, and then Al wires were fed at the LF station. The oxygen content, nitrogen content and inclusions in steel deoxidized by the two methods were analyzed by gas analyzer and scanning electron microscopy (SEM). It is found that the total oxygen content of the final product is almost the same with the two deoxidation methods, while the method (Ⅱ) is more advantageous to control the nitrogen content and by using the deoxidation method the nitrogen content can decrease by about 5 × 10-6. Both the deoxidation methods affect little the type and size of inclusions in the final product, and most of the inclusions are globular CaS and CaO-MgO-Al2O3 inclusions. The formation process of inclusions during Si-Mn deoxidation was inferred according to SEM observations and thermodynamics.
Abstract: The influences of slag-metal reaction and calcium treatment on inclusion modification in high-strength low-alloy steel were studied by means of Thermo-Calc thermodynamic software and ASPEX automated scanning electron microscope. The results of industrial trials show that by increasing the basicity, reducibility and w(CaO)/w(Al2O3) of slag, Al2O3 inclusions are partially modified to CaO-MgO-Al2O3 complex inclusions nearby the liquid phase zone at 1 600℃, as well as a few MgO·Al2O3 spinel. On the basis of this change, the purpose of inclusion modification is still achieved with the addition of CaSi-wire decreasing from 800 m to 300 m for a heat.
Abstract: A process was developed to dispose blast furnace (BF) dust. The separation of Fe and Zn from BF dust at non-molten state was studied by this process including non-molten reduction, magnetic separation and the recovery and enrichment of zinc. It is found that at temperatures between 910 and 1 010℃ the reduction reactions from Fe2O3(s) to Fe(s) and ZnO(s) to Zn(g) are achieved by using pure H2 or CO as a reductant. The average metallization rate and the de-zinc rate are 90% and 99% respectively, and there is no sintering during the reduction process. The iron-rich material with 90% TFe is obtained directly by magnetic separation. After the recovery and enrichment of zinc-bearing volatile, the content of ZnO in the zinc-rich material is over 92%. It is concluded that BF dust can be transformed to valuable resources such as MFe and ZnO. This process has low reduction temperature, low energy consumption and no pollution.
Abstract: A three-dimensional unsteady mathematical model,which is coupled with the turbulent flow,temperature field and magnetic field,was established to analyze the special stirrer.Then,the fluid flow in the secondary cooling zone of a thin slab by compact strip production(CSP) was calculated under electromagnetic stirring,and the effects of induced current and the ends of the stirrer coil on the magnetic field were considered in this calculation.The results show that the flow field of molten steel in the secondary cooling zone is changed by electromagnetic force,leading to horizontal recirculation flow within the stirring zone.The magnetic field generated by the stirrer is uneven because its magnitude and phase vary with penetration depth,and its magnitude decreases with increasing penetration depth.The induced magnetic field caused by fluid motion linearly moves in the direction of the external field and should not be ignored.Molten steel could be uniformly stirred by a one-sided stirrer.
Abstract: The corrosion behavior of two low-alloy weathering steels, A588 and SPA-H, in an environment containing chloride ions was investigated by alternate wet-dry accelerated corrosion tests. The effects of Ni and Mn elements on the corrosion behavior were studied by using optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) and electron microprobe analysis (EMPA). It is shown that the rust layer is mainly composed of Fe3O4, γ-FeOOH and α-FeOOH; however, their contents are somewhat different for the two experimental steels. The content of Ni in the inner rust layer is higher than that in the outer rust layer, and Mn is enriched at pores in the rust layer. The inner rust layer is more compact than the outer rust layer. The compactness of the inner rust layer is improved by increasing the Ni and Mn contents, thereby increasing the corrosion resistance of the low-alloy steel.
Abstract: Microstructural evolution in 0.2C-1.51Si-1.84Mn steel during partitioning process was studied by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and electron microprobe analysis (EMPA). When partitioning at 400℃, carbon atoms have redistributed within 10 s, and the volume fraction of retained austenite is 13.4%. When the partitioning time increases, martensite is tempered and austenite decomposes, leading to the decrease of strength and elongation. However, when the partitioning time is 1 000 s, the tensile strength and elongation suddenly increase. The reason is that the elongation loss caused by decomposition of retained austenite is offset by tempered martensite, the precipitation of carbides and cementite impedes dislocation movement, and thus its tensile strength increases. EPMA results show that carbon atoms diffuse during partitioning process, and carbides and cementite precipitate when the partitioning time increases, which decreases the content of carbon in retained austenite.
Abstract: A optimization method based on LabVIEW parallel operation was proposed to improve the computing speed of the traditional genetic algorithm. When applied in a multi-core computer, the optimization method can achieve multithreading concurrent operations, thereby improving the efficiency of computation obviously. The initial speed-path of Ni-Ti alloy wire dieless drawing was optimized in an eight-core computer by using the optimization method. Compared with a method based on MATLAB program, the operation time of the optimization method is only about 1/8 as long as that of the former. Experimental results show that after adopting the optimized speed-path, the length of diameter fluctuation is about 24 mm, which is far less than that of other speed-paths such as the S-line style or linear path.
Abstract: Copper cladding aluminum (CCA) rods with the section dimensions of 50 mm × 30 mm × 3 mm × R4 mm were fabricated by horizontal core-filling continuous casting (HCFC) technology, and then CCA flat bars with the section dimensions of 60 mm × 8 mm were formed from the CCA rods by multi-pass rolling and finishing drawing process. The reasonable rolling process, mechanical properties and electrical properties of the flat bars were investigated subsequently. The results confirm the correlation between the width of the flat bars after rolling and the side-edge cracking behavior. The width of the flat bars can be controlled by allocating the pass reduction and setting the temperature of the rolling process, thereby suppressing the side-edge cracking in the flat bars. The reasonable rolling temperature range is from room temperature to 200℃. When rolling at room temperature, the much reasonable rolling schedule is 5 passes flat rolling, the 1st pass reduction of about 20% and the highest pass reduction of about 30%. Through 1 pass finishing drawing after the rolling process, the flat bars can be obtained with precise section size and excellent surface quality. After annealing treatment, the electrical resistivity of the flat bar is 2.084 × 10-8 Ω·m, the tensile strength is 122.7 MPa, the elongation is 22.0% and the shear bonding strength of the interface is 25.9 MPa.
Abstract: The strength of a cementitious material made from steel slag, iron slag, cement clinker and flue gas desulfurization (FGD) gypsum was optimize by orthogonal tests to prepare a concrete for building high-strength artificial reefs. When the ratio of steel slag to iron slag is 5:3 and when 10% cement clinker and 10% FGD gypsum are mixed with 80% iron and steel slag powder, the mixed cementitious material has an optimized strength. A concrete with a compressive strength over 50 MPa can be prepared by using such a mixture as a cementitious material and steel slag grains as its aggregates which have been stabilized by a hot-simmering method. Hydration processes of the net slurry were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results show that early hydration products in the system are mainly AFt and C-S-H gel, and in the later stage the pozzolanic reaction of iron and steel slags contributes mainly to the increase in strength.
Abstract: TiO2 nanopowders were synthesized via a simple, quick and sol-gel low-temperature combustion method. Their formation mechanism was explained from the chelating action of citrates. The effects of the molar ratio of metal ions to citric acid and the presence of impurity ions on the phase forming of TiO2 nanoparticles and the crystallite size of the synthesized powders were investigated by thermal analyses (DTA/TG), X-ray diffraction (XRD) and transmission electron microscopy (TEM). Spheric TiO2 nanoparticles whose sizes are in the range of 40 to 90 nm are successfully prepared in the experiment. XRD results show that the mass fraction of rutile in the synthesized powers reaches 91% when the molar ratio of metal ions to citric acid is 0.5.
Abstract: In compliance with the computational principle of coal blending, a coal blending model for the best combustion was put forward based on summing up and comparing some common coal blending methods. A curve to describe the relation between the ignition point of mixed coal and the proportion of high-volatile coal was obtained by curve-fitting. It is found that the proportion of high-volatile coal at which the descent rate of the ignition point of mixed coal reaches to a certain tiny value is considered as the optimum proportion. This method was used to optimize the proportion of high-volatile coal in four different groups of mixed coal and it is proved by static burning experiment that the computed results are accurate, reliable and practical.
Abstract: A numerical simulation of a dense flow absorber with Fluent software was performed to study the effects of the flue gas rectifier system and the chain agitator on the flow field and turbulent flow of flue gas, the trajectory of circulating ash and the pressure loss of the dense flow absorber. The optimal layout form of the baffle plate was determined under the simulated condition. It is found that the chain agitator obviously amplifies the turbulent kinetic energy inside the dense flow absorber, while the increase of revolving speed cannot obviously improve the whole turbulent intensity of flue gas. The double-deck chain agitator can enlarge the area with high turbulent intensity and retard turbulent dissipation. Under this condition, the desired speed of the double-deck chain agitator is 100 r·min-1. Meanwhile, the uniform distribution of flue gas inside the dense flow absorber and the gas-solid sufficient contact can be realized, most of particles are involved in internal recycling, and a small quantity of particles enter the dust catcher. The pressure loss of the system is approximately 200 Pa.
Abstract: Based on the ring rolling theory and the principle of invariable volume during the rolling process, the design principle of flange blanks and the limit scope of process parameters were determined for producing high neck flanges. The closed ring rolling process of the flange blanks was simulated by a finite element model (FEM). According to the simulated results the optimal process parameters were obtained by analyzing the influences of process parameters on the product quality and the mechanical parameters. Closed ring rolling experiments of high neck flanges were carried out in a D51-450 ring rolling mill with a self-designed mould. The reliability of the finite element simulation was proved by comparing the simulated results with the experimental ones.
Abstract: In hot rolling, actual production data were not used to improve the thickness quality of products. For this phenomenon, an online data-driven modeling algorithm was proposed for strip thickness control based on subtractive clustering. Firstly, the input space is divided into several clusters by subtractive clustering, in each cluster a sub-model is built by a least square support vector machine (LS-SVM), and an offline model is obtained by weighting the outputs of these sub-models. Then, when the online data constantly increase, the clustering subsets are adjusted on-line by a subtractive clustering algorithm, and the parameters of the sub-models are determined using the recursive algorithm of the least squares support vector machine. The predictive outputs of the sub-models are the final outputs. Experimental results demonstrate that the method has good prediction accuracy and online learning ability.
Abstract: To deal with the structure jumping problem resulting from elastic load force and external load force jumping in different working conditions, an adaptive backstepping control method of multi-model switching was presented based on the common Lyapunov function method and the adaptive backstepping method. This approach combines the features of adaptive backstepping control and the design requirements of a common Lyapunov function, and the adaptive controller for every sub-system and the parameter adaptive estimators for the uncertainty upper bound are designed by backstepping control, then taking the Lyapunov function designed by backstepping as a common Lyapunov function to ensure that the system is asymptotically stable under arbitrary switching. It is easy to select the common Lyapunov function by the combination of backstepping and the common Lyapunov function method, and the problem of parameter jumping and parameter slow time-varying existing at the same time is solved. Simulation results demonstrate that the designed controllers can ensure not only good dynamic and static performance for the hydraulic servo position system of a rolling mill, but also good robustness for the system parameter jumping and parameter slow time-varying.
Abstract: With the consideration of 13 different stiffness ratios, different stiffener arrangements and boundary conditions, the linear buckling and non-linear buckling behaviors of a stiffened plate with large-scale thin-walled steel structure were investigated using a finite element method. It is found that the effect of flexural stiffness ratio on the buckling performance of the stiffened plate is significant. At the critical stiffness ratio, which is ranging from 10 to 20, the buckling modes of the stiffened plate are divided into two main types, overall buckling and local buckling. The non-linear buckling load increases with the flexural stiffness ratio of the stiffened plate increasing. The increment of stiffeners in the loading direction can increase the local buckling load of the stiffened plate; however the increase of stiffeners in the non-loading direction has little effect on the local buckling behavior of the stiffened plate.
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
