Abstract: The thixotropy of pastes is a complex rheology phenomenon,which concerns paste mixing preparation,pipeline transportation,flowing in stopes and many other aspects. But currently it is difficult to interpret many kinds of thixotropy-related phenomena in unclassified tailing paste technology due to the lack of a common understanding of its mechanism. To explain the thixotropic behavior of a unclassified tailing paste in the process of stirring,the impacts of unclassified tailing particle size,slurry concentration,addition of cement and standing time on the paste thixotropy were studied by conducting rheological experiments of the paste in different conditions of a certain mine,and the thixotropic behavior of the paste and its influence on the stability were analyzed. The results show that unclassified tailing particles disperse in the slurry in the form of three-dimensional network structure,and their thixotropy and yield stress are relevant to the stability of the slurry. Influenced by ultrafine composition,cement-tailing ratio and slurry concentration,the thixotrophic characteristics of the paste can be divided into two process,shear failure and standing recovery. Besides,the paste's rheology characteristics will change over time.
Using the Fluent dynamic mesh model to realize the 4D dynamic movement of a gob and inputting the kinetic mechanism of coal low-temperature oxidation and the dynamic change of heterogeneous porosity into Fluent through the user defined function,4D dynamic simulation is performed on the spontaneous heating law in a gob for U + L ventilation of a certain mine. The results show that unsteady heterogeneous porous media can be more realistic in response to the change of porosity,which exponentially decreases with time. The greater the advancing speed of the working face, the smaller the heating rate, and the average heating rate at an advancing speed of 3.6 m·d-1 is 1/5 of that at an advancing speed of 1.2 m·d-1. However, the higher the advancing speed, the deeper the depth of the high temperature region, which is unfavorable for the prevention from spontaneous combustion of coal. Because of the existence of a tail roadway in the gob, the temperature field expands, the temperature rises, the main way to release CO is the tail roadway, and the amount of CO from the tail roadway is 10 times that from the outlet. Finally, the results are verified by the field test data, indicating that the simulation results are correct and reliable.
Abstract: The adsorption kinetics and conformation change of sodium dodecyl sulfonate(SDS) onto Fe2O3-coated crystal sensors were studied by quartz crystal microbalances with dissipation(QCM-D). The results show that the adsorption of SDS onto Fe2O3 surfaces is a rapid adsorption process. The p H value has a great influence on the adsorption of SDS. When the p H value increases,the viscoelasticity of the adsorption layer improves,the stability of the adsorption layer deteriorates,and thus the recovery of hematite flotation gradually decreases. There is only one adsorption stage which is best fitted by the pseudo-first order model without any change in conformation in the p H range of 3 to 9. At the p H values of 10 and 11,the adsorption of SDS markedly increases and the recovery of hematite flotation also recovers. There are two distinguishable adsorption stages with the first adsorption stage best-fitted by the pseudosecond order model and the second adsorption stage by the Elovich equation. The adsorption layer also experiences an obvious conformation change as the adsorption continues.
Abstract: The roasting consolidation characteristics of chromite pellets were systematically studied in this paper. The results show that preheating time has little effect on the compressive strength of preheating chromite pellets. Under the appropriate preheating time of 10 min,increasing the preheating temperature can improve the compressive strength and oxidation rate of preheating chromite pellets linearly. The appropriate preheating temperature is 1050℃,at which the compressive strength of preheating chromite pellets can reach more than 400 N. In addition,compared with conventional iron ore pellets,a higher roasting temperature is required for chromite pellets. The compressive strength of chromite pellets increases from 1078 N to 1973 N when the roasting temperature increases from 1250℃ to 1350℃. During the preheating and roasting of chromite pellets,(Fe,Mg)(Cr,Fe,Al)2O4 is oxidized into(Fe,Mg)(Cr,Fe,Al)2O4 and(Cr,Fe,Al)2O3. The new phase(Cr,Fe,Al)2O3 is obviously generated when the temperature surpasses 1000℃.(Cr,Fe,Al)2O3 mainly distributes in the outer layer of the particles in a ring shape,while the acicular(Cr,Fe,Al)2O3 interlaces together with(Fe,Mg)(Cr,Fe,Al)2O4 in the internal part. Decreasing the Cr/Fe ratio in the raw ore concentrate or increasing the roasting temperature can facilitate the aggregation of(Cr,Fe,Al)2O3 around the outer layer of the particles,which in terms assists in the pellet consolidation and then enhances the compressive strength of chromite pellets.
Abstract: A thermodynamic model is proposed for calculating the mass action concentration of structural units in the Al-Ti binary melt system based on the atom-molecule coexistence theory. The standard equilibrium constants of reactions for forming three associated molecules as Al3Ti,Al Ti,and Al11Ti5 in the Al-Ti binary melt system at the temperature of 2073 to 2273 K are calculated based on the activity reported in the literature,and the expressions of the standard molar Gibbs free energy change of reactions are obtained.Meanwhile,the calculated mass action concentrations NAl and NTi of Al and Ti are compared with the reported activities of both Al and Ti in the full composition range of the Al-Ti binary melt system at different temperatures from the literature. The results show that the calculated mass action concentrations NAl and NTi are in agreement with the activities aAl and aTi in the reported literature. The relationship between the calculated mass action concentration Ni and the calculated equilibrium amount of substance ni of Al3Ti and Al11Ti5 in the Al-Ti binary melt system is rod-type. However,the relationship between the calculated mass action concertation NAlTi and the calculated equilibrium amount of substance nAlTi in this binary melt system is spindle-type.
Abstract: Preparing high added-value materials from molten slag directly by modifying molten slag has drawn a great interest in the utilization of molten slag because of its high efficiency during the integrated utilization of the heat and slag. In this paper,molten steel slag and sands were selected as typical molten slag and modifiers,respectively. The effects of the amount of added modifiers on the waste liquid sensible heat of modified molten slag were studied during the modification process,which was subsequently confirmed by industrial test. It is indicated that the sensible heat of modified molten slag increases at first and then decreases with the addition of modifiers. The sensible heat improves with the increase in mass fraction of modifiers from 5% to 11% and reaches the maximum at the mass fraction of 11%. The optimal amount of modifiers ranges from 11% to 19% in consideration of both the utilization of sensible heat and the performance of modified molten slag. Furthermore,the industrial test verifies that both the fluidity of modified molten slag and the stability of cooled modified slag are significantly improved at the addition of about 12% modifiers.
Abstract: A 1/4 scale water model of slab molds was built to investigate the fluid flow and its symmetry during casting. The model was established according to a 200 mm×2040 mm actual mold. The velocity in the mold was measured by using particle image velocimetry(PIV). By analyzing the velocity field,the fluid flow behaviors such as flow patterns,level fluctuation,time history of speed on symmetrical points,horizontal speed below the meniscus,vertical speed nearby the narrow face and impingement depth could be studied. The effect of casting speed on the fluid flow behaviors mentioned above was investigated. The results show that the PIV technology can not only measure the velocity field,but also show the flow symmetry in a distinctive perspective so that proposing measures for the continuous casting process,such as casting speed,the geometric of the submerged entry nozzle(SEN) and submergence depth of SEN. After analysis,a conclusion can be drawn that the casting speed at 0.5 m·min-1 is better than 0.6 m·min-1 under the casting condition. The results show that the PIV technology is a useful method to optimize the continuous casting conditions.
Abstract: In view of the difficulty in environmental and economic treatments of lead-bearing wastes generated in lead and zinc smelter,a new reducing-matting smelting process was proposed to recycle secondary lead from multiple lead-bearing wastes in this paper. In the process,the designed mixture of lead sludge,lead slag,lead ashes and pyrite cinder was used as a smelting object,and ferric oxide,soda and mirabilite and coal powders were a sulfur-fixing agent,additive and reductant,respectively. The effects of factors on the direct recovery rates of lead and silver during the smelting process were studied in detail based on thermodynamic calculations. The optimum conditions are obtained as the following:the mass ratio of FeO to SiO2 is 1.10,the mass ratio of CaO to SiO2 is 0.30,the mass ratio of Na2CO3 to Na2SO4 is 0.7:0.3,the dosage of coal powders is 15% of lead-bearing wastes,the smelting temperature is 1200℃,and the smelting time is 2 h. Comprehensive experiments show that under the optimum conditions,the direct recovery rates of lead and silver are 85.95% and 83.15%,respectively. The process has significant advantages of sulfur fixation,comprehensive utilization and one-step lead smelting.
Abstract: Twenty-nine species samples of higher plants which belong to twenty families and seven soil samples were collected from a vanadium smelter. The contents of heavy metals in the native plants and soil were analyzed by ICP-MS and ICP-OES. The results show that the soil of the smelting plant area has general Cr,Cd and V pollution phenomena; moreover,V and Cr pollution is conspicuous. V,Cr,Cd and Pb are detected from all these collected polluted higher plants,and the content of V is the highest. Pteris vittata L,the native plant,has the highest V content; the accumulation amounts of the aboveground part and the underground part are 86.51 mg·kg-1 and 814.25 mg·kg-1,respectively. The enrichment and transport capacity of Daucus carota L is obviously higher than that of other plants; the accumulation amounts of the aboveground part and the underground part are 18.56 mg·kg-1 and 5.66 mg·kg-1,respectively. These two kinds of plants show high tolerance to heavy metal pollution in the vanadium smelting plant area,and they can be used as pioneer species of pollution remediation.
Abstract: Based on the discrete phase model of the Euler-Lagrange equation,the concentration fields of three different types of zinc dross under a circulating purification system were calculated by using the numerical simulation method. The result shows that the deposition rate increases with the decrease of zinc dross size. When the zinc dross size is smaller than 80 μm,the order of deposition rate from high to low is suspending dross,top dross,and bottom dross. The average residence time of the top dross in the back area of the strip exit is the longest,and it will be beneficial to the removal of the top dross to install a pumping tube in this area. On the inner part of the V-shaped zone,the mass concentration of the suspending dross is the highest,and it has the biggest influence on the surface quality of steel strips. The main travel area of the bottom dross is close to the bottom of the zinc pot,and the bottom dross cannot adhere to the strip surface and it has minimal impact on the surface quality of steel strips.
Abstract: The effect of initial rolling temperature on the hydrogen-induced delayed fracture resistance of Nb alloyed hot stamping steel was studied by the constant load test and the electrochemical hydrogen permeation method. When the initial rolling temperature drops from 1000℃ to 950℃,the hydrogen diffusion coefficient and the corrosion resistance of the steel decrease,but the hydrogen-induced delayed fracture resistance increases. TEM test shows that when the initial rolling temperature is 1000℃,the MX precipitated phase has an average size of 30 nm,and the Cr2C3 precipitated phase can be observed with an average size of 100 nm; when the initial rolling temperature is 950℃,the MX precipitated phase has an average size of 5 nm. The main reason leading to the improvement of delayed fracture resistance is the hydrogen trapping effect of the MX precipitated phase. The reason for the difference of precipitated phases is that a higher rolling start temperature will prompt the coarsening of the MX precipitated phase,which will suppress the precipitation of the Cr2C3 phase.
Abstract: Hot tearing tends to occur when K424 superalloy is used for a turbocharger turbine wheel. To solve this problem,the alloy characteristics of K424 and K418 superalloys and the factors impacting the susceptibility to hot tearing were studied by microstructure observations and casting simulations. The research proposed the main factors which affected the susceptibility to hot tearing and also the method to reduce hot tearing in the turbine wheel. It is found that the susceptibility to hot tearing of the turbine wheel is influenced by both the alloy characteristics and casting characteristics. K424 superalloy shows a higher susceptibility to hot tearing when compared with K418. Because of high amount of aluminum and titanium in K424 superalloy,the size and the amount of γ + γ' eutectics increase,resulting in more prior forming and propagating areas of hot tearing. On the other hand,due to a smaller thickness and a larger curvature change in the blade margin of the turbine wheel,the uneven distribution of the thermal stress is induced in the end of the solidification process,which leads to hot tearing in this paper. In order to decrease the susceptibility to hot tearing of the turbine wheel,the contents of aluminum and titanium should be controlled,and the reasonable technological parameters of casting should be set to ensure the final effect.
Abstract: Based on the analysis of aging behavior of ethylene propylene diene rubber(EPDM) and the mechanism of action of climate on EPDM,the aging data of EPDM exposed for 3 years in 11 typical material weathering test stations and the meteorological data there were studied to find out the relation between atmospheric environment and EPDM aging properties. By using the factor analysis and the technique for order preference by similarity to ideal solution(TOPSIS),the comprehensive values of aging properties were gained. With the grey correlation analysis,sever environmental parameters including irradiance,humidity,temperature were found to be the key climate factors which had a significant relation with the degradation of EPDM. Then a BP artificial neural network that connected the climate factors and EPDM aging properties was built. By inputting the meteorological data of cities,the comprehensive values of EPDM aging properties where weathering test had not been performed were predicted and a distribution map of these comprehensive values was draw out. The results show that the aging of EPDM in the south of Guangdong Province,Hainan Island,Taiwan Island,Tibet,and south of Xinjiang are the most serious.
Abstract: The manufacturing system under the smart manufacturing model is required to timely respond to the changing customization and individuation production demand of diversified small-lot products through quick dynamic reconfiguration. For the general Petri net with different input/output functions and non-conservative Tokens,a modified net rewriting system(MNRS) is proposed according to the production process on the basis of NRS. Reconfiguration cells in the rule class library of MNRS are encapsulated systematically and modularly based on the manufacturing process of the products,and the corresponding boundary coupling and internal enabling rules of the reconfiguration area are formulated. The class library with reconfiguration cells in MNRS has the characteristic of behavioral property inheritance,which can guarantee the liveness,boundedness and reversibility of the manufacturing system after the local area reconfiguration,so that the autonomous,quick and dynamic reconfiguration of the manufacturing system can be achieved according to the rewriting rules and reconfiguration mechanism of MNRS. Simulation results and application cases verify the usability of MNRS.
Abstract: Based on the time-varying mesh stiffness and the Blok flash temperature theory,the influence of tooth profile modification parameters on the load sharing ratio,transmission error and tooth surface flash temperature were systematically analyzed in this paper. The optimum tooth profile modification parameters were identified under the single-objective condition. On the other side,based on the fuzzy comprehensive decision theory,the optimum tooth profile modification parameters were identified under the multi-objective condition. The correction factor Xc was proposed,and its value was also given. Then a formula was introduced for calculating the modification amount. By the comprehensive optimum parameters of tooth profile modification,the maximum amount of tooth profile modification is the Xc times of the deformation of the alternating points B or D of the single and double tooth meshing regions under the condition that the modification index is 1.43 and the modification form is long modification.
Abstract: A kind of three-stage burner for double-P type radiant tubes was designed by using diffusion-type low-NOx-burning technology. Numerical simulation was performed to verify the model. The structure and operation parameters of the burner were analyzed by orthogonal test and single factor analysis. The research results show that air preheating temperature,air staged proportion and excess air coefficient have significant effect on the outlet NOx emission concentration without mutual interaction. When the primary air increases from 10% to 20%,the amount of NOx increases from 65.2×10-6 to 108.2×10-6; but when the primary air increases to more than 30%,the outlet NOx concentration increase rate decreases. The maximum combustion temperature increases about 50℃ with each increase in air preheating temperature of 100℃,and the NOx emission concentration increases from 50.9×10-6 at the rates of 22%,23.2%,25.3%,27.2%,27.3% and 29.5%. With the increase of excess air coefficient,the outlet NOx concentration increases from 82×10-6 at the rates of 22.1%,1.9%,2.1%,24% and 2.5%.
Abstract: As a special slender structure,a wind turbine tower with a turbine on the top of the structure is sensitive to dynamic loading. Therefore,it is critical to accurately assess the vibrational behaviors of the wind turbine tower. To facilitate field testing of wind turbine towers,a laser Doppler vibrometer was proposed in the ambient vibration testing. Comparisons between the conventional contact accelerometer method and the laser based remote sensing method were made in the aspects of testing efficiency and result validity. Based on a series of vibration signals collected from a 1.5 MW wind turbine tower,the natural frequencies of this tower were obtained by using different vibration analysis methods.
Abstract: Due to the present situation of frequent fire accidents caused by the mobile power pack,fire risk based on the energy transfer theory and the fuzzy synthetic evaluation model was analyzed in the paper. Furthermore,fault tree analysis and the relative difference function are combined with the model to determine the weight values and memberships of evaluation factors. The evaluation results show that the risk level of fire accidents caused by the mobile power pack is between the safe and the more dangerous,which is agreed with the practical situation.
Abstract: In intermittent connected wireless networks,the energy resources of nodes are limited and the link duration is short,so the network resources cannot be fully used. This article introduces a data forwarding strategy with an adaptive asynchronous wakeup schedule,which synthesizes the energy consumption and dormancy mechanism of nodes,combines with the gray model to forecast the inter-node meeting duration,thus optimize the energy consumption of nodes in the detection and data forwarding phase,and finally achieves the purpose of efficient data forwarding. The results show that the proposed data forwarding strategy can effectively utilize the residual energy and communication opportunity of nodes. Compared with the existing forwarding strategies,this strategy can effectively improve the detection rate and communication time delay of the networks under low energy consumption.
Abstract: Aiming at the false negative problem and the overlap problem in pattern instance detection,in order to improve the accuracy of the design pattern recovery,this article introduces an approach for design pattern detection based on the formal context-free grammar relation driver. Focusing on the attribute and relationship of classes in pattern instances,the formal grammar of pattern instance identification is established using the visual language,and an improved formalism grammar is presented for identifying the additional relationships and the sharing problem of design pattern instances. Experimental results show that,compared with other wellknown algorithms by precision,recall and F-score,the proposed method can reduce the false negative results and the overlap problem in pattern instance detection,indicating the effectiveness of the proposed 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
