Abstract: Based on the high-stress condition and the development characteristic of tectonic stress in excavating deep buried tunnels, the rockburst process of dolomite was simulated with a deep rockburst experimental system in two kinds of tectonic stress conditions:instantaneously unloading the minimum principal stress on a rectangle specimen, keeping others unchanged or maintaining the intermediate principal stress and increasing the maximum principal stress. The stress-time curve, the stress-strain curve, the acoustic emission characteristic and the rockburst law were tested. The results show that the possibility of dolomite rockburst caused by tectonic stress in the project area is striking. The critical depth of rockburst is 290 m. Rockburst caused by vertical tectonic stress shows partial sheet avalanche, belongs to lag rockburst. The intensity of rockburst caused by horizontal tectonic stress is stronger, shows massive ejection and overall fragmentation, and belongs to instantaneous rockburst. The acoustic emission (AE) peak presents in the crevice growth section, and the highest value of AE density occurs in the rock rupture segment. The maximum principal stress corresponding to the AE peak is 77.4% of that corresponding to the rock breakdown stage.
Abstract: Simulation experiments of coal and gas delay outburst in rock cross-cut coal uncovering were done under the condition of fixed vertical stress or horizontal stress with a large-scale test device for simulating the coal and gas outburst and the outburst port closed by a mixing-material of coal powder and gypsum-simulated hard coal. The results show that the relationship of critical gas pressure and horizontal stress at delay outburst is exponential and reversely changes under fixed vertical stress, but relationship of critical gas pressure and vertical stress at delay outburst is a quadratic polynomial and reversely changes under fixed horizontal stress. The intensity of outburst reflects the degree of damage at delay outburst. It is a positive correlation with critical gas pressure and a negative correlation with ground stress.
Abstract: Aimed at the characteristics of much crushed coal and soft coal seams in an outburst coal seam, pressure injection with solidified liquid was used to reinforce coal bodies and plug methane channels for reducing or eliminating gas outburst. A composite slurry was prepared by remixing cement with polymer latex, which breaks through the limit of present injection materials for coal bodies. The material match of the composite slurry and the strength, dry shrinkage, compactness, water retention and viscosity of the induration were tested by laboratory experiment. The best material match was selected to reinforce coal particles, and the experimental result indicates that the conglomerated coal particles have better mechanical strength and reinforcement effect. Used to reinforce coal bodies, the composite slurry has the characteristics of good viscosity, large reinforcement capability, low material cost and no pollution.
Abstract: In order to solve the problems of high cost in mine backfilling and environmental pollution brought by the stockpiling of tailings and red mud, cemented whole-tailings backfilling materials were prepared with red mud as the main component in cementitious materials. The backfilling materials have a higher compressive strength than those prepared with cement. The compressive strength of samples made of the backfilling materials cured for 28 d was up to 7 MPa, which meets the requirements of materials for mine backfilling. In addition, the new backfilling materials have good workability such as applicable flow plasticity, good water-retaining property, non-bleeding and a much lower cost than traditional cemented backfilling materials. The hydrated products and their microstructures of the hardened samples were analyzed by XRD and SEM. The results showed that most of the raw materials were transformed into ettringite and low crystallized complexity gel during the hydration reaction. As hydration went on, the structure became much denser with the interlacing of ettringite and gel, and thus good mechanical properties were obtained.
Abstract: Based on the similarity theory, the interaction of fluid flow and gas flow in gas-liquid two-phase flow and the expansion of argon in actual continuous casting were taken into account, and the relation between argon flow rate in a plant and gas flow rate in experiment was established by modified Froude numbers. The transformation formulas of flow rate between four kinds of simulation gases and argon in a plant were obtained. A 0.6:1 scale water model was undertaken to simulate the technological process in a prototype with the cross section of 210 mm×900 mm. The results show that the experimental phenomena agree well with the practical ones. When the water flow rate is 3.80 m3·h-1 and the gas flow rate is 0.93 L·min-1 in modeling, bubbles do not lead to excessive level fluctuation due to their relatively homogeneous dispersion in the mold. When the water flow rate is 3.80 m3·h-1 and the gas flow rate is 2.79 L·min-1, most bubbles float up in the vicinity of the submerged entry nozzle and there is strong fluctuation around the submerged entry nozzle, so opening of slag layers occurs in the mold. The correctness of similarity transformation of gas flow rate was validated with consistencies between simulation results and practical phenomena.
Abstract: The mechanism of slag entrapment at the overflow weir in a tundish was studied by the combined methods of numerical simulation, water modeling experiment and industrial test. The results show that liquid steel between the dam and weir is at the risk of being exposed to air and being oxidized when its level (surface) is close to the weir top. At the same time, steel-slag emulsification and slag entrapment at the weir outlet area may happen. The possibility of slag entrapment is higher at the triangle area from the weir to the tundish wall. The liquid steel flow over the weir will erode the weir, and also shorten the life of the tundish. In addition, the entrapped slag is easier to enter the mould. This result is confirmed and verified by water modeling experiment and industrial test.
Abstract: Ultrasonic treatment was used by way of an ultrasonic wave probe directly inserted into molten steel to improve the cleanliness of steel and decrease the amount of inclusions in steel. A comparative study of ultrasonic and argon-blowing treatment was carried out on inclusion removal efficiency in molten steel. Experimental results showed that the amount of inclusions decreased when the ultrasonic wave was inputted into molten steel. But the inclusions removal rate was low, about 4% to 12%. When ultrasonic treatment was carried out solely, with decreasing power and increasing treatment time, the inclusions removal rate was increased. When argon-blowing was carried out solely, the inclusions removal rate was high, from 29% to 41%. With increasing argon-blowing flux, the inclusions removal efficiency was found a trend of rising.
Abstract: The formation and transformation of inclusions in high speed wheel steel during refining were studied in ultra-low oxygen steelmaking by LD-LF-VD-CC process. Sufficient aluminium was added to the experimental steel for final deoxidation during tapping, and refining slag with strong deoxidation, high basicity and strong reducibility was used during LF refining. The results show that the casting blanks are of high cleanliness and the total oxygen is only 7×10-6. Oxide inclusions in the experimental steel have finished the transformation of Al2O3 → MgO·Al2O3 spinel → CaO-MgO-Al2O3 complex inclusions during LF refining, and the complex oxide inclusions obtained are liquid and easy to remove by collision, coalescence and flotation at steelmaking temperature. Residual oxide inclusions in the steel are CaO-MgO-Al2O3 system complex inclusions with a relatively lower melting point, which have a little deformability during hot-working and can improve the fatigue properties of high speed wheel steel effectively.
Abstract: In order to improve Ti inclusions removal technology for controlling their formation and size, Ti contents in melting steel specimens of 80-grade tire cord steel, obtained from the melting process, were measured by laser ablation inductively coupled plasma mass spectrometry. It was found that the average Ti content firstly increased and then decreased during the process of EAF tapping → refining → continuous casting. Under current control conditions of 80-grade tire cord steel in Nanjing Iron and Steel United Co. Ltd. (NISUCL), the calculation results of formation thermodynamics, solidification segregation and growth kinetics of TiN particles show that TiN formation takes place only in the two-phase region where the solidification ratio is greater than 98% or the solid region. The greater the cooling rate during solidification, the smaller the size of precipitated TiN particles. The size of precipitated TiN particles is 3 to 7 μm, in agreement with that measured in the metallographic image of TiN inclusions found in wire rod specimens.
Abstract: Four manganese steels with different deoxidization degrees were selected. Their susceptibility to pit initiation was compared by means of potentiodynamic polarization tests in a 3% NaCl solution with pH 10. The pitting propagation rate was evaluated by indoor interval hanging plate tests in a 3% sea salt solution. The composition of inclusions and the corrosive feature were studied by scanning electro microscopy (SEM) and electron probe micro-analyzer (EPMA). The results indicate that the shape of sulphide inclusions change from a short spindle shape to a long strip shape with increasing deoxidization degree. Under the same condition, the lower the deoxidization degree, the stronger the thermodynamic stability becomes, and the weaker the susceptibility to pit initiation. Additionally, the results of interval hanging plate tests indicate that the manganese steel with a stronger deoxidization degree exhibit a stronger pit propagation rate.
Abstract: The long-term structure stability of heat-resistant steel Super304H, which is used as superheater/reheater tubes for ultra-supercritical power plant boilers, was studied by means of SEM, TEM and 3DAP (three-dimensional atom probe). The results show that Cu-rich phase, MX and M23C6 are the main precipitates in Super304H steel. With increasing aging time, M23C6 carbide coarsens quickly and its morphology changes from separate particles to continuous precipitating at grain boundaries. The number of MX increases with increasing aging time and its average size is about 150 nm. Cu-rich phase dispersive particles precipitate in grains and their size keeps in the range of 3 to 35 nm. It is indicated that most of the strengthening effect in Super304H attributes to Cu-rich phase, with the complement of MX and partially M23C6 carbide.
Abstract: Two low alloy weathering steels were exposed in three different environments which are indoor, freezing in door and outdoor to investigate the influence of freezing-thawing cycles on their initial corrosion behavior. The corrosion resistance of the tested steels was evaluated by weight loss measurements and an electrochemical method. The rust morphology and alloy elements distribution in rust layers were analyzed by scanning electron microscopy and energy dispersed spectroscopy, respectively. It was found that the environment with low temperature and humidity is favorable to form a compact rust layer, while a rust layer formed in the environment with high temperature and humidity is loose. Freezing-thawing cycles produce cracks in a loose rust layer. The reason is that there is much liquid water in pores in a loose rust layer; when the liquid water transits solid phase, the water will produce a greater stress resulting in cracks in the rust layer. However, there is not liquid water in a compact rust layer; the influence of freezing-thawing cycles on a compact rust layer is negligible.
Abstract: The three-dimensional deformation behavior of continuous casting blooms with soft reduction was theoretically characterized and quantitatively analyzed by the finite element method (FEM) under different soft reduction conditions. The results show that the longitudinal elongation ratio is proportional to the soft reduction amount after the balance between lateral spreading deformation and longitudinal spreading deformation. Under the same soft reduction condition, the lateral elongation efficiency and longitudinal elongation efficiency decrease with the increases in aspect ratio and non-solidification ratio of casting billets, whereas the reduction efficiency increases.
Abstract: Spatial analytic geometry is introduced to analyze the essentially geometric characters of integral helical finned tubes and the spatial relationship between rollers and rolled pieces in the rotary rolling process. A mathematical model is constructed for helical finned tubes based on the concept of helicoidal surfaces and cylindrical helixes. The binormal vector and tangential vector of any point on the helix, corresponding to the roller's axial vector on the point of the tube surface, are achieved by an expression with the main structural parameters of helical finned tubes. In order to research the spatial relationship between rollers and rolled pieces, two coordinate systems are established to set rollers and rolled pieces respectively, and a coordinate transformation expression between the two coordinate systems is deduced. Based on coordinate transformation, the process is introduced to deduce the value of roller radius and the coordinate values of contact points between rollers and rolled pieces.
Abstract: Based on nickel and iron valuable metallic elements in Jinchuan slag, the rule of the reduction of iron-nickel oxide in slag and the conductive characteristics of oxygen ion-permeable membranes were discussed by the no-contacting smelting reduction method and the continual and divided charging method. The results show that carbon-free ferronickel can be obtained with liquid silver as a cathode. The reduction rate of iron-nickel oxide can be improved by the continual and divided charging method. The reduction rate in the earlier stage of reduction increases and the reduction time in the terminal stage decreases with the proportion of NiO in iron-nickel oxide increased. In addition, the reduction rate of iron-nickel oxide will be improved by increasing the reduction temperature, but the electric quantity through the external circuit will be decreased.
Abstract: Isothermal and uniform temperature-rise experiments were done to study the oxidation kinetics of iron ore concentrate with a TG instrument. The results indicated that the major control unit of the oxidation process changed from out-diffusion to inner-diffusion, and out-diffusion finally during uniform temperature rise. After oxidation, partial hematite decomposed into magnetite and oxygen; as a result, the mass change ratio on the TG curve gradually decreases. The isothermal experiment also proves that the main step is inner-diffusion and the apparent activation energy of oxidation is 26.193 kJ·mol-1. Oxidation of iron ore concentrate accelerates titanium enrichment and changes the microstructure of oxidized products.
Abstract: Long chain branching polypropylene (LCB-PP)/organomontmorillonite (OMMT) nanocomposites were prepared in a twin-screw extruder via a melt-blending method, and their microstructures, rheology and mechanical properties were investigated. The results of transmission electron microscopy (TEM) showed that the clay layers were mostly exfoliated in the LCB-PP matrix. Rheology test results showed that when the clay loading reached a threshold value, the nanocomposite exhibited an increased storage modulus at low frequency and more obvious shear-shinning behavior, indicating that a compact and stable network structure formed and hindered macromolecular chain relaxation and mobility. The results of mechanical property test showed that the addition of OMMT improved the tensile strength, notched impact strength, and flexural modulus of LCB-PP, but reduced its flexural strength.
Abstract: The energy-saving effect of high emissivity coatings for BF hot-blast stoves was studied and analyzed by comparing numerical simulations with industrial applications. It is showed that the simulation data agree with the industrial application results, proving a positive effect of the coating on energy transfer in a hot blast stove. The simulation results indicate that with the coating applied, the hot blast temperature can increase by 25 ℃ and the flue gas temperature decreases by 13 ℃. The energy-saving mechanism of the high emissivity coating in a hot blast stove was discussed based on the simulation results and thermal balance analysis. It is thought that the coating intensifies radiative heat transfer between gas and checker-brick surfaces during the combustion period, and further increases the energy storage capability and the surface temperature of checker bricks. In addition, the simulations show that CO2 in the gas plays an important role in intensifying radiative heat transfer, and generally increasing 5% CO2 in flue gas will make the temperature of hot air increase by 6 to 8 ℃.
Abstract: A temperature field model of work rolls is established with an HVC work roll as the object of study by a method of two-dimensional alternating direction finite difference. The model can be used to simulate the temperature field and thermal contour of work rolls at any time, and its computing time meets the online requirement, with absolute stability. The calculated values are in good agreement with online measured data, indicating the accuracy of the model.
Abstract: A novel fluid pulsation attenuation elbow was studied by the bidirectional coupling method, and the effects of structural parameters on its fluid-solid interaction characteristics were discussed. The results show that the internal total pressure difference is 29.506 27 kPa in the original elbow, the internal flow field is very uneven, the maximum deformation is 20.689 μm, the maximum stress is 180.08 kPa, and the deformation mode is that the structure is elongated in both sides, concaved in the middle and shows a double oval, and the deformation leads to the flare-out effect on the elbow. When guide plates are designed according to the golden ratio, the number, the radius and the length are 2 200 mm and 40 mm respectively, the total pressure difference is 10.707 87 kPa, it decreases by 63.71% in comparison with the result of the original elbow, but the maximum deformation is 330.39mm, and the maximum stress is 1 569.10 kPa. When the number of guide plates is 3, and the thickness is 3 mm in the final optimized structure, the internal total pressure difference is 12.469 56 kPa, it decreases by 57.74% in comparison with the result of the original elbow, the maximum deformation is 20.898 mm, the maximum stress is 259.80 kPa, and the internal flow field is very even.
Abstract: In order to improve the matter flow control level of the iron/steel interface, based on the theory of metallurgical process engineering, an operational control technique of torpedo ladles was summarized with torpedo ladles of A steel plant in China as the object of study. This study included five contents:operation process analysis, operation time analysis, calculating method of employed torpedo ladles, two evaluating indicators for the operational control level, and operation optimization. Satisfactory effects are obtained after applying the technique in production. The turnover number of torpedo ladles decreases from 22 to 18, the cycling rate increases by 0.5, the continuation degree coefficients increase by 0.09 for BF 1 and 0.08 for BF 2, respectively.
Abstract: The manufacturing flow between steel-making and continuous-casting, which is a complex multistage and multi-product production process, was modeled using colored Petri nets. The model had characteristics of graphic representation and easily analyzing the model properties and model performance. Two important modeling problems were discussed:different guard functions were placed in different transport transitions to implement route selection, and the input and output function of a single procedure transition was programmed to realize different processing time for different products. The bounded constraints were verified and the solution method to get the best makespan was proposed based on occurrence graphs. The effective method was shown by an applied instance.
Abstract: A localization algorithm based on semi-supervised manifold learning is proposed. Manifold structures hidden in the information of received signal strength can be obtained by the algorithm. It is used to compute a subspace mapping function between the signal space and the physical space by using a small amount of labeled samples and a large amount of unlabeled samples. Existing theories and experiential signal propagation models need not to be known in the algorithm, and localization errors generated by inaccurate models can be avoided. A number of unlabeled samples were used to decrease the difficulty of collecting data and increase the practicality of the algorithm. Real nodes were used to setup the network in metallurgical industry environments. Experimental results in metallurgical enterprises show that a higher accuracy with much less calibration effort is achieved in comparison with RADAR localization systems.
Abstract: The stability of uncertain discrete-time systems with time-varying delay is studied. The uncertain parameters are in linear fractional form. Based on a piecewise analysis approach, the time-delay interval is divided into several subsections. By defining a novel Lyapunov functional, the less conservative stability criteria are proposed in terms of linear matrix inequalities. Numerical examples are given to show that the results are effective.
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
