Abstract: The change of pore water pressure in saturated rocks was closely associated with its damage deformation. In order to study the precursory characteristics of pore water pressure before the damage of saturated rock, the triaxial compression test and seepage test were used in the paper. The research show that:1) During the process of damage in open saturated rock unit, namely phases of the initial compression, elastic compression, plastic deformation and destruction,the pore water pressure would increase, stay stable, gradually decrease, and sharply decrease respectively; 2) Internal damage intensified, cracks connected with the pore water pressure lost steady state could be used as a precursor to rock failure information; 3) The pore water pressure to the development of damage was more sensitive and the response was more obvious in the condition of large pressure change, high pore pressure and high confining pressure; Pore pressure and damage development were interrelated, that the development of damage caused the decrease of pore pressure. At the same time the decrease of pore water pressure promoted the development of damage; 4) It was proposed that internal pore water pressure could be monitored as a method to predict sudden disasters of the rock instability in deep mining engineering.
Abstract: Rainfall is one of the key factors of unsaturated soil slope instability and the strength of unsaturated soils is closely related to volume water content. Considering two-dimensional rainfall infiltration, on the basis of the Darcy seepage theorem and mass conservation law of unsaturated soils, this paper constructed a two-dimensional infiltration model of unsaturated soils and coded a MATLAB program based on an alternating-direction-implicit (ADI) finite difference method which is used to numerical calculations to study the transient volume water content distribution at different slope locations under different rainfall conditions. The results show that the volume water content changes with the horizontal distance and depth. Moreover, the volume water content at the slope surface changes far greater than that at the deep part. The smaller the initial volume water content is, the greater the change in volume water content of the slope is, which is disadvantageous to slope stability.
Abstract: A new cementing agent, RSGC, designed for filling was prepared with red mud, blast furnace slag, flue gas desulphurization gypsum and a little cement clinker. The adaptability of RSGC used in different mines was studied and the early hydration including microstructure and structural changes of silicates and aluminates were investigated by scanning electron microscopy and nuclear magnetic resonance techniques. It is found that RSGC applies not only to iron ore mines but also to copper mines, gold mines and lead——zinc mines which generally adopt the filling mining method. Filling materials used RSGC exhibit significant strength and water retention advantages over traditional cement filling materials. The RSGC paste hardens at 2.5 h. Ettringite generated before 2.5 h makes important contributions to the setting and hardening. After 4 h, parts of the tetrahedrally-coordinated aluminium turn into an octahedrally-coordinated state, and polymerization of silicates increases. This phenomenon means that ettringite, C——S——H gels and zeolites generate continuously. The combination of these hydration products in various sizes and shapes forms a compact arrangement and a dense structure, which is probably the reason why the RSGC paste obtains strength from 4 h and the strength increases dramatically from that time.
Abstract: The reduction kinetics of sintering ore used as an oxygen carrier in the chemical looping combustion was experimentally investigated by thermogravimetry. The redox reactivity of sintering ore was compared with that of self-made Fe2O3/Al2O3 oxygen carriers prepared by the dissolution method. Experiments were conducted on the reduction of sintering ore by diluted hydrogen during the temperature range of 500 to 1250℃, and 30 cycles of redox reaction experiments were performed at 950℃. Experimental data was analyzed by four kinetic models. It is found that sintering ore can be used as an oxygen carrier with a reduction conversion larger than 80%, complete oxidization, and a good performance of recyclability. The reduction reaction rate and final fractional conversion of sintering ore both increase with rising temperature from 500℃ to 950℃, while both have a trend of decline when the temperature is above 1100℃. The second order reaction model (M2) can properly fit the experimental data of the reduction of sintering ore in the first reaction stage (Fe2O3-Fe3O4/FeO, reduction conversion X < 25%) during the temperature range of 500 to 950℃, achieving the apparent activation energy E=36.018 kJ·mol-1 and the pre-exponential factor A0=1.053×10-2 s-1, whereas the shrinking core model (M4) fits well in the second reaction stage (Fe3O4/FeO-Fe, reduction conversion X > 25%), achieving the apparent activation energy E=51.176 kJ·mol-1 and the pre-exponential factor A0=1.066×10-2 s-1.
Abstract: The reduction behavior of zinc ferrite, an important constituent of zinc-bearing metallurgical dust, with CO-CO2 gas was calculated and analyzed according to the thermodynamic principles. The reduction of ZnFe2O4 obeys a stepwise mechanism. ZnFe2O4 is easy to be reduced to ZnO and Fe3O4. ZnO is easier to be reduced than FeO, and a lower volume fraction of CO gas is needed to reduce ZnO at a higher temperature. If the reaction temperature increases from 1100 K to 1400 K, the reducing potential expressed by the volume fraction of CO decreases from 0.4 to 0.01. Aiming to the reduction and separation of metallic zinc from zincbearing dust, it is not necessary to reduce iron oxides to metallic iron, but Fe3O4 or FeO, while zinc oxide should be reduced to metallic zinc. In the upper of the blast furnace, zinc reduction and internal circulation occur and bring harms to blast furnace production, and therefore the zinc load of the blast furnace should be reduced and controlled strictly.
Abstract: The effect of CaO content on the liquidus of a CaO-Al2O3-22% MgO-1% SiO2-2% FeO system and the influence of CaF2 and B2O3 contents on the liquid content of the slag at 1700℃ were calculated using Phase Diagram and Equilib module in thermodynamic software FactSage. The starting and ending melting temperatures of the slag obtained from production were measured by differential thermal analysis. When the CaO content in the slag is controlled at 25% approximately for FeV alloy production by the electrical thermite method, the melting property of the slag is good. The effect of CaF2 on the melting point depression of the slag is better than that of B2O3. Meanwhile, these two fluxes are not suitable to be used together when the mass ratio of Al2O3/MgO is high in the slag. Considering industrial application and environmental protection, the best addition of CaF2 in the slag is 2% to 5%.
Abstract: To understand the knowledge of liner thermal expansion and thermal expansion coefficient of Q450NQR1 casting steel, dilatometry experiments were performed at two different cooling rates of 5℃·min-1 and 20℃·min-1. A mathematical model was developed to quantitatively extract the kinetic information of austenite transformation based on the concept of average atomic volume. The model was verified by microstructure examinations, indicating that the model was appropriate to describe the behavior of austenite transformation and could be applied to multi-phase transformations during steel continuous casting. The influence of cooling rate on the austenite transformation was discussed with the model. it is found that, with increasing cooling rate, two peaks associated to the precipitation of ferrite and pearlite on the thermal expansion coefficient curve shifted towards a lower temperature region with higher values. As the cooling rate increases from 5℃·min-1 to 20℃·min-1, the initial temperatures of ferrite and pearlite precipitation decrease by 32℃ and 37℃, and the final volume fractions of ferrite and pearlite gradually change from 0.894 and 0.106 to 0.945 and 0.055, respectively.
Abstract: Ultra-heavy plate steel for marine engineering usually requires good hardenability, and rational design of chemical composition of this steel is one of the main methods for improving its hardenability. Traditional composition design of steel is mostly experiment-based and costly. In this paper, thermodynamic calculation software Thermo-Calc and material property calculation software JMatPro were introduced to design the chemical composition of B-containing micro-alloyed ultra-heavy plate steel, with calculation, prediction and testing combined to obtain high hardenability. Thermodynamic equilibrium precipitates in the steel were calculated with Thermo-Calc. Composition design principles were interpreted for the steel from the perspective of thermodynamics by analyzing the precipitation temperature; precipitation amount and phase relationships, and then the chemical composition of the steel with high hardenability was designed. In addition, the hardenability of the steel designed was predicted using JMatPro and the results illustrates that the composition design of the steel is feasible. The rationality of the optimization design was further affirmed by hardenability testing and chemical analysis. Theoretical calculation and experimental results show that high aluminum content can help to improve the hardenability of the steel.
Abstract: The hot deformation behavior of 5Cr9Si3 valve steel was investigated by hot working simulation test at different hot working parameters. When the deformation temperature increases from 850 to 900℃ or from 1000 to 1100℃, the peak stress decreases; but when the deformation temperature increases in the range of 900 to 1000℃, the peak stress rises. Further microstructural and phase transformation analyses show that a transformation from α-ferrite to austenite occurring within the deformation temperature range from 900℃ to 1000℃ causes austenite phase transformation strengthening, inducing the increasing of hot deformation resistance. Also, with the increasing of deformation temperature, the dissolution of carbides leads to solution strengthening for the matrix. Thus, phase transformation strengthening and solution strengthening at elevated temperatures are the main reason for the abnormal variation of flow stress for 5Cr9Si3 valve steel.
Abstract: The corrosion behavior of X65 carbon steel under different deposits in CO2 saturated formation water was studied by weight loss measurements, electrochemical measurements, wire beam electrode and microscopic analysis. The results show that the corrosion rate of the steel slightly decreases by being covered with sand, clay or ferrous carbonate. However, covered with ferrous sulfide, elemental sulfur or mixture, the corrosion rate obviously accelerates, especially in the specimen covered with elemental sulfur. The corrosion rate of the specimen covered with mixture deposits also significantly increases, in which elemental sulfur plays a dominant role. The significant increase in corrosion rate of the specimen covered with elemental sulfur is attributed to the self-catalytic action of elemental sulfur on the cathodic reaction of steel corrosion. The current and potential distributions of wire beam electrodes indicate that the potentials of the electrodes covered with mixture deposits are more positive than those without deposits. During the corrosion, severe localized corrosion occurs on the electrodes under mixture deposits. The current and potential maps of wire beam electrodes can effectively reflect the localized corrosion behavior of the steel under deposits due to the change of local environment.
Abstract: The effect of pH values on the corrosion behavior of Q235 steel in simulated acidic soils was investigated by weight-loss measurement, scanning electron microscopy (SEM), X-ray diffraction (XRD) analysis and polarization curve analysis. When the pH values are 4.0, 4.5 and 5.1, the corrosion rate of Q235 steel are 0.68, 0.48 and 0.42 mm·a-1, respectively. With the increase of soil pH values, the rust becomes more compact and the etch pits change from narrow and deep to wide and shallow. All the corrosion products are mainly composed of SiO2, α-FeOOH, γ-FeOOH, Fe2O3 and Fe3O4, and the mass ratio of α-FeOOH/γ-FeOOH in the corrosion products is higher with increasing pH values. Additionally, polarization curve analysis shows that when the soil pH value rises, the corrosion potential of Q235 steel increases, the corrosion current density decreases, and the corrosion rate becomes lower.
Abstract: Hot compression deformation experiment of pure nickel N6 was conducted on a Gleeble-3800 thermomechanical simulator at a deformation temperature range of 800 to 1100℃, a deformation rate range of 5 to 40 s-1 and at a deformation of 70%. The hot deformation behavior of this material was analyzed at high temperature and high deformation rate. The microstructural evolution and the flow stress curves were obtained at different deformation parameters. The processing maps were drawn by using the dynamic material model. Through analyzing the microstructures and the processing maps, two reasonable regions are introduced for processing pure nickel N6:the deformation temperature range of 1000 to 1100℃ and the deformation rate range of 5 to 7 s-1 or 20 to 40 s-1; the deformation temperature range of 800 to 900℃ and the deformation rate range of 5 to 10 s-1. In these two regions, the microstructure of pure nickel N6 is uniform, while in the region of rheological instability the microstructure is disordered and the grain size is varied. The grain size of pure nickel N6 after hot deformation goes up as the deformation temperature rises or the deformation rate declines.
Abstract: Mo2NiB2 based cermets were prepared using element powders of boride, nickel and molybdenum. The phase transformation and dimensional change in the sintering stage as well as the effects of sintering temperature and holding time on the mechanical properties and microstructure of Mo2NiB2 based cermets were studied. The results show that with the increasing of sintering temperature, the phase gradually transfers from elemental phase to diboride and then to ternary boride phase, the dimension of the cermets also firstly slightly decreases, then obviously increases in the boronizing sintering process, and finally significantly reduces in the subsequent liquid sintering process. The bending strength and hardness of the cermets firstly increase and then decrease when the sintering temperature rises. The cermets sintered 1290℃ for 60 min show the best mechanical properties with the bending strength of 1346.5 MPa and the hardness of 83.7 HRA. Holding time has a similar effect on the mechanical properties of the cermets. When the holding time is 30 min at 1290℃, the bending strength reaches the maximum of 1453.3 MPa.
Abstract: In order to realize reliable sealing and combination of constructional glass and Kovar alloy, the effects of temperature, holding time, roughness and oxide layers on their wetting property were studied. When the temperature increased from 800℃ to 900℃, the viscosity of liquid glass reduced, so the wetting angle decreased from 69.5° to 31.1°. When the holding time prolonged from 5 min to 40 min at 850℃, the liquid glass had enough time to diffuse under the condition of low viscosity, and the wetting angle increased by 30%. With an increase in roughness of steel sheet surfaces, the barrier increased which was needed to overcome by the liquid glass to spread around. When the roughness value Ra increased from 0.186 μm to 0.563 μm, the wetting angle increased from 46.9° to 69.5°. The oxide layer on the surface of Kovar alloy and the liquid glass had diffusion reaction that could form strong ionic bonds, which increased the wetting property considerably, and the wetting angle could decrease by 23.6%. Therefore, during the actual sealing process, increasing the temperature and holding time, decreasing the roughness of steel sheet surfaces, and steel sheet pretreatment could effectively improve the wetting property of the glass and Kovar alloy.
Abstract: A one-dimensional mathematical model based on heat transfer and reaction kinetics was developed for an oxygen blast furnace and was validated with the operating conditions and dissected data of a conventional blast furnace. The influence of oxygen concentration and upper gas volume on the smooth operation and process variables of the oxygen blast furnace was investigated by the model combined with coal combustion at tuyeres and top gas balance for separation and preheating. When the oxygen blast furnace with top gas recycling is of low oxygen concentration and upper gas volume, the reduction of iron ore is worsen and massive unreduced iron oxide comes into slag. In the oxygen blast furnace with top gas recycling, oxygen concentration and upper gas volume have significant effect on the temperature, reducing ability of gas and reduction rate. A comparative analysis of the conventional blast furnace and the oxygen blast furnace with top gas recycling show that the oxygen blast furnace has a higher reducing ability of gas (1.0 to 1.5 times higher for CO content), faster reduction rate (1.49 m higher for the position of ore reduction), and less direct reduction (55.2% to 79.2% less for direct reduction degree).
Abstract: The ball mill coal-pulverizing (BMCP) system is a multivariable coupled system with long time-delay, large inertia and parameter uncertainties. This paper analyzes the dynamic characteristics of the BMCP system and proposes a control strategy based on a decentralized linear active disturbance rejection controller (LADRC). The proposed control strategy has simple structure, strong disturbance rejection ability, and is independent of accurate mathematical models. When it is applied to the BMCP system, parameter uncertainties, disturbances and coupling in the BMCP system can be estimated and actively compensated. Based on industrial control requirements, set point tracking simulation, perturbation simulation and random Monte-Carlo experiment are carried out. In comparison with a PID controller, the LADRC achieves better control results and has a stronger robustness.
Abstract: In order to improve the set accuracy of rolling force for a finishing mill in the hot rolling process, high precision prediction of rolling force is very important. In this paper, an approximate value of rolling force is calculated through theoretical formulae. And then, a correction coefficient of rolling force is computed using big field data. Firstly, different product states are classfied by the clustering method. Secondly, the correction coefficient is computed based on a weighted least square support vector machine. Through a combination of these two results, the rolling force value with high precision is predicted. The average relative prediction error of rolling force is 3.2%, which can meet the requirements of field production.
Abstract: In combination with the rigid-body replacement synthesis design approach, a double parallelogram lifting platform based on a lamina emergent mechanism is designed, which overcomes the disadvantage of a single parallelogram mechanism and improves the parallelism. Then a bi-stable grasper is designed, which is limited the slider movement to control the clamping force, using the second balanced state as a working condition to maintain a constant clamping force. At last these two parts are combined by subsidiary in order to drive the lift and clamp movement by only one motion. At the same time, based on a pseudo-rigid-body model, the force-displacement relationship is derived. One practical example is calculated according to this theory and is analyzed by finite element simulation to verify the correctness of the theory and the usability of the mechanism.
Abstract: Based on actual production and management situation, this paper investigates an enterprise-level coal mine equipment management system, aiming at solving problems in electrical equipment management in mining companies. The proposed management system fuses the cloud computing framework, the workflow technology and the enterprise asset management (EAM) model. Nine function modules are designed according to the EAM concepts, such as lifecycle management, preventive maintenance, and spot inspection management. A four-layer cloud platform is constructed adopting a three-level cloud service architecture model and two types of cloud deployment. Using a workflow engine to assist in the EAM system, the coal mine equipment management system could flexibly transfer its business processes and effectively manage multi mine equipment at enterprise-level. Take a typical domestic coal mining enterprise as a case, the feasibility and effectiveness of the EAM system of coal mine equipment based on cloud computing and workflow technology is verified.
Abstract: As a local image feature description approach, LBP (local binary pattern) is regarded as one of the most effective textural features to describe images. In this paper, a general classification algorithm via sparse representation of LBP features is proposed for ear recognition. This algorithm expresses LBP features of the input ear image as a sparse combination of LBP features extracted from all the training ear images. The recognition performance for salt and pepper noise, Gaussian noise and various levels of random occlusion in which the location of occlusion is randomly chosen to simulate real scenario is investigated. Experimental results on USTB ear database reveal that when the test ear image is contaminated by noise or is occluded, the proposed approach exhibits a greater robustness and achieves a better recognition performance.
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
