Abstract: Based on the gently inclined medium thick phosphate rock at the deep part of the east mining section of Jinning-Six Mine, Yunnan Phosphate Co. Ltd. from open pit mining to underground mining, floor friction model tests under the condition of different slope heights and boundary thicknesses were carried out with a floor friction model instrument. The results show that the deformation and failure response features of the slope can be divided into three stages:fracture and loose in a small range, unstable failure in a local range, and instability failure in the whole range of slope rock sliding to the goaf. The main deformation and failure modes of the slope are tension cracking, breakage, and sliding failure. When the slope height is fixed, with the boundary thickness gradually decreasing from 30 m to 20 m and 10 m, the stability of the slope is directly proportional to the boundary thickness, and the reasonable boundary thickness is 20 m to 30 m. When the boundary thickness is fixed, with the slope height increasing from 60 m to 108 m, the stability of the slope is inversely proportional to the slope height, and the slope of 108 m from open pit mining to underground mining is unstable.
Abstract: The slope of Dading open-pit iron mine in south China has the characteristic of low rock strength and bad stability. Its basic information on engineering-geological conditions, hydro-geological conditions and rock mass structures together with physical and mechanical properties of rock mass was derived from systematical field and laboratory investigations, experiments and tests. Stability analysis and optimum design were done for the slope by using a combined method of numerical modeling and limit equilibrium analysis. The slope angle increases more than 3° compared with the original design.
Abstract: To solve the problems of environmental pollution brought by the stockpiling of unclassified tailings and red mud, a mine backfilling material was prepared with red mud from sintering process, unclassified tailings and other solid wastes. The experimental results show that the optimal mass proportions of the cementing agent are red mud 49.2%, slag 32.8%, clinker aggregate 10%, and plaster 8%; the strength of the backfilling material block reduces sharply with the increase of the unclassified tailings addition; the hydration products of cttringite and C-S-H gel generated in the test block at the early stage of hydration help for the early strength. Differential scanning calorimetry-thermo gravimetrie (DSC-TG) analysis shows that the test block concretes lots of water at the early stage. The prepared paste backfilling material has the characteristic of high early strength, large water concretion, high quantity wastes utilization, etc., and it can meet the requirement of mine backfilling.
Abstract: The failure of infilled rock joints can be divided into interface damage and filling damage, which one dominates depends on the stress conditions of the two parts. When the filling was damaged, its plane stress state was analyzed. A theoretical shear strength formula was obtained and the effects of normal stress and filling thickness were studied. With the increase of normal stress the shear strength of infilled rock joints increases first and then decreases, but the influence of filling thickness is not obvious. Some direct shear tests of infilled rock joints were also carried out. The results show that the shear strength is related to the failure modes of the joints, and under the same mode it is independent of filling thickness.
Abstract: To improve the prediction accuracy of gas emission, a BP neural network was applied to establish a dynamic prediction model of gas emission under the MATLAB environment by using BP neural networks' characteristics of self-learning, self-organizing and self-adapting. The model was trained and tested by analyzing the real-time monitoring data of gas signals from Tangshan Mine. Test results show that the model has higher prediction speed and accuracy. By using the model the dynamic prediction of gas emission in the working face can be realized, the safety state and the potential hazard can be synthetically estimated to provide security for safety production.
Abstract: Case-based reasoning was used to predict the starting temperature of molten steel in second refining so as to avoid the long training time of a BP (back propagation) neural network. Analytic hierarchy process (AHP) was applied to determine the weights of factors influencing the starting temperature. Grey relational degree was adopted to compute the similarity between cases. Thus the shortcoming of difficulty in obtaining accurate cases with incomplete information is conquered. A four-step search method, including class search, rough search, delicate search, and optimized search, was provided, by which the search time decreases greatly. Experimental results using both artificial neural networks and case-based reasoning were compared. It is shown that case-based reasoning has got a higher hit rate and a shorter response time than artificial neural networks.
Abstract: A continuous casting mould with a cross section of 1 400 mm × 230 mm was simulated by software Fluent 6.3, and the effects of casting speed, immersion depth and submerged nozzle (SEN) opening-angle on its flow field were investigated. It is shown that with the increase of casting speed, the maximum horizontal and vertical velocities of the liquid surface increase, and the position of the impact point on the narrow side does not change. With the increase of distance to the liquid surface, the velocity of the narrow side first increases and then decreases, till near to zero. When the casting speed is greater than 1.2 m·min-1, the horizontal velocity of the liquid surface obviously increase. With the increase of SEN immersion depth, the maximum horizontal velocity of the liquid surface decreases, and the maximum vertical velocity increases. SEN immersion depth has little effect on the impact point on the narrow side. When the SEN immersion depth is greater than 140 mm, the change of the maximum horizontal velocity is small. With the increase of SEN downward opening-angle, the maximum horizontal velocity of the liquid surface first decreases and then increases. When the SEN downward opening-angle is 12.5°, the maximum horizontal velocity of the liquid surface is the smallest, but the minimum velocity at the impact point on the narrow side can be obtained when the SEN downward opening-angle is 10° to 12.5°. KEY WORDS
Abstract: The effects of mist cooling and water cooling in the secondary cooling zone on the surface temperature, solidification strLlcture and macro-segregation of wheel steel casting billets were studied to explore the high-quality low-cost production technology of wheel steel. The results show that the surface temperature of the casting billets in the straightening segment is above 950℃ by both the cooling methods, which belongs to a high temperature plasticity zone and can avoid straightening cracks. A symmetrical solidification structure is obtained by both the cooling methods. Although mist cooling can slightly increase the proportion of equiaxed grains and decrease the central segregation of the casting billets, the dendrite arm spacing and the segregation degree around the half-radius region increase, which are even more unfavorable to the subsequent process and the quality of the finished product. Considering experimental results and production costs, water cooling should be more suitable for the production of high quality wheel steel.
Abstract: The continuous cooling transformation (CCT) curves of 36Mn2V steel were obtained on the basis of the expansion curves of continuous cooling at 4 finish rolling temperatures measured on a Gleeble-1500 thermal simulator in combination with metallo-graphic and hardness methods. The experimental results show that with increasing cooling rate the starting temperature of γ/α transformation gradually lowers, but the starting temperature of bainite transformation increases to a plateau and then decreases, and the grains are refined. With the finishing rolling temperature decreasing, the experimental dynamic CCT curves shift to the left and upper wholly, the ferrite along grain boundaries and intra-granular ferrite decrease, and the grains are slightly refined. No bainite appears in the specimen finally rolled at 950 22.
Abstract: High Mn-high Nb micro-alloyed steels were investigated by electron back-scattering diffraction (EBSD) to determine the effect of cooling rate and ausforming on the characteristic of misorientation and the distribution of high angle boundaries (HABs) in low carbon bainitic microstructure. The results indicate that there is a dispersion of HABs interspacing from prior austenite grain boundaries to the grain interior. Both fast cooling and ausforming raise the drive force of coherent transformation, weaken variants selection, and are helpful for the increasing of HABs density near the boundaries and in the grains. Moreover, a larger deformation below the non-recrystallization temperature not only can flatten the austenite grains fully, but also can generate incoherent nucleation of fine ferrite grains at the prior austenite boundaries. Also the fine ferrite grains have significant misorientations with adjacent microstructure.
Abstract: Hot compressive tests were carried out on a Gleeble-1500 thermal simulation test machine to investigate the hot deformation behavior of T91 steel at elevated temperatures of 1 100 to 1250℃ and strain rates of 0. 01 to 1 s-1. The relations of flow stress to strain rate and deformation temperature were analyzed for calculating the stress exponent and the deformation activation energy at the elevated temperatures. The constitutive equation was constructed by introducing the Zener-Hollomon parameter. The dynamic recrystallization map and the processing map of plastic deformation of T91 steel at the elevated temperatures were drawn. The true stress-strain curves of the steel show a bimodal characteristic. Distinct dynamic recrystaflization takes place in the steel, and its mechanism is continuous dynamic recrystallization. The deformation activation energy of the steel is 484 kJ·mol-1. The instability zones and optimum processing parameters of hot deformation under the condition can be attained by using the two maps. The steel has excellent mechanical properties when rolled at deformation temperatures of 1 200 to 1 250℃ and strain rates which are not greater than 0. 1 s-1.
Abstract: ZrO2 powders and ceramics doped with Y2O3 and Al2O3 respectively were prepared by a copreeipitation-gel method using low temperature calcining and medium temperature sintering. The structure stability and sintering properties of ZrO2 phase doped with the different oxides were studied by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. The results show that calcined at 870℃ for 15 min, ZrO2 powders doped with Y2O3 of 5% in molar fraction have a cubic phase, but those doped with Al2O3 of 5% in molar fraction have a tetragonal phase. After sintering the formed powders at 1 400℃ for 4 h, the former remains the cubic phase at room temperature, but the latter has a monoclinic phase. In the calcining powders, Al3+ dissolves into the lattice of ZrO2 and stabilizes the ZrO2 tetragonal lattice; whereas in their ceramic, Al3+ diffuses from the ZrO2 lattice to the grain boundaries, so it can not afford a stabilizing effect on the ZrO2, only plays a role in promoting the sintering and thinning grain.
Abstract: The synthesis kinetics and phase structure of La2(Zr0.7Ce0.3)207 (LZ7C3) ceramic was investigated. The preparation composition was designed according to the mass loss in the synthesis process. LZTC3 powder was prepared successfully by a solid state reaction method and its atom ratio of La:Zr:Ce is close to the theory value of 10:7:3. The phase composition, microstructure, and thermophysical properties of the powder were studied by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), the laser-flash method and the pushing-rod method. XRD results reveal that LZ7C3 is a mixture of La2Zr207 (LZ) with pyrochlore structure and La2Ce207(LC) with fluorite structure, and its main phase is the LZ solid solution. The thermal conductivity of LZ7C3 decreases gradually with increasing temperature; at 1473 K its value is 0. 79 W·m-1·K-1, which is almost 50% lower than that of LZ. The thermal expansion coefficient is 20% larger than that of LZ, and its value is 11.6 x 10-6 K-1 at 1 473 K. These results show that LZ7C3 ceramic can be explored as a novel prospective candidate material for use in new thermal barrier coating systems in the future.
Abstract: High performance anisotropic NdFeB flexible bonded magnets were prepared by a two-step method which includes calendering and magnetic alignment steps utilizing hydrogenation-disproportionation-desorption-recombination (HDDR) NdFeB powder, and their magnetic and mechanical properties were investigated. It is found that the degree of alignment (DOA) of the flexible bonded magnets goes up sharply. The maximum energy product (BH)max is 97 kJ·m-3 for the composition of 96.5% magnetic powder, 1% coupling agent, and 2. 5% bonded rubber after heated at 120℃ for 30 min during magnetic alignment, while the coercivity of the flexible bonded magnets only decreases by 1.3%, which further proves the feasibility of the two-step method in industrial production. Because the mechanical properties of the flexible bonded magnets will deteriorate with the amount of epoxy resin lubricant increasing, the mass fraction of epoxy resin lubricant should be less than 1%.
Abstract: Solution spray-oxidation as a novel method was developed to prepare cobalt oxide powders. Engineering tests were conducted to investigate the effects of some main factors such as temperature, atomization pressure and CoCl2 solution flow rate on the conversion efficiency of cobalt oxide, the particle size and the apparent density of the powders. The optimum conditions to obtain cobalt oxide were determined as follows:temperature 750℃, solution concentration 120 g·L-l, air pressure 0.23 MPa, solution pressure 0.15 MPa, solution flow rate 40 L·h-1, heat treatment temperature 750℃, and heat treatment time 2 h. Under these conditions, the conversion efficiency of cobalt oxide is 100%, the content of cobalt in the product is 73.04%, the apparent density of the powder is 0.48 g·cm-3, and the average particle size of the powder is 7.61 μm. It is shown by the engineering test results that the solution spray-oxidation method is available for Co3O4 preparation and the process is simple, fast and environmental friendly.
Abstract: Magnetic polystyrene microspheres were prepared by a modified suspension polymerization method and were characterized by scanning electron microscopy (SEM) and vibrating sample magnetometry (VSM). The number of the magnetic microspheres was detected with a giant magnetoresistance biosensor. The results show that the magnetic microspheres are spherical, their sizes range from 0. 5 to 50 μm, and their specific saturation magnetization is 4.56 A·m2 ·kg-l. The magnetic microspheres have a very good response to the sensor. With the amount of the magnetic microspheres increasing, the output signal of the biosensor intensifies. Under a given amount of the magnetic microspheres, the change in electrical resistivity of the sensor increases first and then decreases with the increase of the magnetic microsphere size.
Abstract: The effects of potassium and sodium on coke degradation are commonly thought to be similar by studying the influence of alkali carbonates on coke gasification, and the amounts of potassium and sodium into the blast furnace (BF) are controlled without considering the differences. But BF investigations indicate that alkali carbonates have decomposed and in coke the potassium content is always larger than the sodium content, where the enrichment of alkali metals is obviously aggravated. In this article it is found by thermodynamic calculations that alkali metals exist as simple substance vapors instead of carbonates or oxides in the alkali enriched regions. Based on that, experiments for testing the autonomic absorption and damage of potassium and sodium vapors on coke with or without carbon dioxide were designed to simulate the alkali enriched regions. Atomic absorption spectrometry (AAS), X-ray diffraction (XRD) and scanning electron microscope-energy dispersive spectrometry (SEM-EDS) analysis reveal that the absorbance and damage of potassium vapor on coke are much larger than those of sodium vapor because of easy combination with ash in coke to form kaliophilite, which induces volume expansion and crack propagation. So it is proposed that the ash content in coke should be low and potassium into BF should be strictly controlled. Coke gasification tests with different contents of potassium vapor show a steep ascent in coke reaction index (CRI) when the mass ratio of potassium vapor to coke in the gas-solid system is above 3%. According to the different absorption and damage effects of potassium and sodium on coke, quantificational control models are constructed for determining the upper limits of potassium and sodium as well as the total amount into BF.
Abstract: A study on stripe shape rolled with a temper mill in a continuous annealing line was done. Through analyzing production data, based on the ideas of both reducing the unfavorable contact area and improving the roll bending force control ability, the optimization objectives of backup roller contour in the temper mill were proposed by using the influence function method to calculate the elastic deformation of the roller system. A lexicographic method was adopted to cope with the multi-objective function, the optimal calculation was implemented by a hybrid genetic algorithm, and a new plan for roll contour configuration was offered. A finite element model of the roller system was established by the 2-dimensional varying-thickness theory to calculate and collate the roll gap horizontal rigidity and the roll bending force control ability. After the result is applied to real production, the stripe shape control effect of the temper mill is improved and the roll bending burden is decreased.
Abstract: Experimental research on non-isothermal combustion characteristics and dynamic parameters of biomass char and coal blends was conducted with a thermo gravimetric balance. The combustion characteristic parameters such as ignition temperature, peak temperature at maximum weight loss rate, burnout temperature, and maximum combustion rate were studied by thermo-gravimetric analysis. The kinetic parameters of reaction such as activation energy and frequency factor for samples in different ratios were calculated. It is shown that both the activation energy and the frequency factor decrease with increasing biomass char content in the blend and the kinetic compensation effect exists in the two parameters. The combustion of biomass char and coal blends is divided into two stages, corresponding to the regularities of the U-shaped curve and the ladder-shaped curve for activation energy, respectively. Biomass char has more remarkable effect on pyrolysis than charcoal combustion. It is indicated for the calculating results of activation energy that biomass char can improve the ignition property of coal.
Abstract: Stability control for a class of single-input single-output (SISO) uncertain nonlinear system with lower triangular structure was studied. Cascade control with active compensation based on the backstepping approach was proposed. The designed controller, with the characteristics of simple structure, controlled convergence rate and good robustness, achieves the asymptotic stability of a closed-loop system. To solve the uncertainty of the closed-loop system, a new observer was designed to track the uncertainty in time. The stability of the closed-loop system is proved by introducing the singular perturbation theory. Simulation results show the effectiveness of the control method.
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
