| As a key step in the efficient and clean utilization of mineral resources,the screening technology bears the functions of preparing screening,inspecting screening,desliming,dehydration,and media removal during the beneficiation process.In the process of traditional dry screening,mineral particles are easy to jam the screen plate and adhere to form clusters,leading to serious pore plugging on the screen plate and deterioration of the screening environment.This makes it difficult for the particle group to penetrate the screen and deteriorates the screening effect,which seriously affects the subsequent sorting operation.Therefore,it is important to study high-efficiency dry depth screening technology to provide technical support for the efficient separation and recovery of useful minerals in the beneficiation process,which is of great significance for the efficient and clean utilization of mineral resources in China.In recent years,the flip-flow screening technology has unique advantages in solving the problem of deep dry screening and has broken through the problem of 3mm high-efficiency dry screening.In order to further reduce the lower limit of particle size to 1 mm for large-scale dry deep screening,a high-speed operating condition for the excitation system of the flip-flow screen is proposed to increase the frequency of particle contact during the screening process,and achieve efficient screening.This thesis focuses on the interactive impact between particles and the screen plate,collisional separation,and particle group migration and screening behavior during the flip-flow screening process under high-speed excitation.In the laboratory stage,a laboratory principle machine for flip-flow screen based on displacement excitation was built.From the perspective of the effect of particles on the flip-flow screen plate,a displacement excitation time-varying impact load calculation model for flip-flow screen plate deflection was established,and it was converted into two parts:an analytical geometric model based on lateral displacement excitation and a forced vibration numerical model based on longitudinal impact load,finally obtaining the midpoint deflection curve of flip-flow screen plate.Based on momentum quantification,a mathematical expression for the maximum impact force of particles on the screen plate during the collision between particles and the flip-flow screen plate was derived.The kinematic characteristics of particles impacted by the screen plate are revealed,and the variation laws of translational kinetic energy and rotational kinetic energy of particles during collision were clarified.Further,the kinematic characteristics of particles subjected to continuous impact from multiple screen plates during flip-flow screening were investigated.Using the finite element simulation method,the simulation model of particle impact on the flip-flow screen plate was established,the stress distribution characteristics of the flip-flow screen plate under no-load condition were clarified,and the maximum impact stress variation rule of the flip-flow screen plate impacted by particles was investigated.The mathematical expressions for calculating the probability of screen-penetration and the distribution rate of products during the flip-flow screen process were established.In response to the complex particle-size distribution characteristics of materials during the flip-flow screen process,the influence of six typical particle-size distribution characteristics on the probability and screening performance of screen-penetration was explored.When the particle-size distribution obeyed a normal distribution,the influence of the uniformity and dispersion of the particle-size distribution on the probability and screening performance of screen-penetration in the flip-flow screening process was clarified.The response mechanism of the screening probability of complex particle-size composition materials to the high-speed excitation of the excitation system was revealed.Based on the principle of nonlinear least square regression,the dynamic model of particle-group screening in the whole stage of the flip-flow screening process was established,and the time-varying characteristics of the sieving rate during the flip-flow screening process were clarified.The influence of displacement excitation amplitude,displacement excitation frequency,and the tension of screen plate on the dynamic evaluation index of the flip-flow screening process was investigated,and the interaction rules of various key parameters at different screening stages of the flip-flow screening process were revealed.A mathematical correlation model between the screening rate coefficient and the key parameters in the rapid and stable screening stages was established.The particle-size distribution characteristics through the screen during the flip-flow screening process was further investigated.Furthermore,the 0618 flip-flow screening experimental system was designed and constructed.The kinematics characteristics of flip screen were explored,the time-domain characteristics of floating frame and fixed frame were clarified,obtaining their frequency-domain characteristic curves and spatial motion tracks.For ilmenite raw ore,the 1 mm dry flip-flow screening experiment was carried out.Combined with the actual working conditions in industrial production,the effects of screening material characteristics(grading of difficult to screen particles,grading of obstructed particles)and operating parameters(feeding speed,speed of excitation system)on the effect of dry deep flip-flow screening were emphatically investigated.It is found in the experiment that when the speed of excitation system was 986 rpm,the screening efficiency reached 80.41%,and the total misplaced materials were8.45%,which further elucidated the spatial distribution characteristics of particle-groups in the flip-flow screening process,as well as the influence of the spatial structural parameters of the screen plate on the effectiveness of 1 mm dry deep flip-flow screening.Finally,the 0.8 mm dry flip-flow screening experiment was conducted on spodumene minerals.When the processing capacity of the flip-flow screen per unit area was 13.5 t/(h?m~2),the screening efficiency reached 70.56%,and the total misplaced materials was 8.55%.This study initially achieved dry deep flip-flow screening,reducing the particle size limit of traditional dry deep screening to 1 mm and providing theoretical and technical support for large-scale dry deep flip-flow screening in the industrial stage.The dissertation includes 120 figures,12 tables,and 235 references. |
PDF Full Text Request