Study On Dynamics And Screening Characteristics Of Flip-flow Screen With Crankshaft-link Structure

Coal is the main primary energy in China.Coal preparation is an effective means to realize clean and efficient utilization of coal.Screening operation is the key link of coal preparation.Due to the lack of vibration intensity,dry screening of wet fine coal is one of the difficult problems in coal production in China.The traditional screening equipment is difficult to realize effective screening because of the serious hole plugging phenomenon when dealing with wet fine coal.The remarkable characteristics of the flip-flow screen were high vibration intensity of screen surface,low vibration intensity of screen body,and high screening efficiency when screening the wet fine coal.At present,the flip-flow screen used in China’s coal preparation plant mainly relies on imports,which were expensive and have problems such as frequent replacement of key parts.Therefore,this article is based on the flip-flow screen with crankshaft-link structure(FFSCLS),and combines theoretical analysis and experimental research methods to study the dynamics and screening characteristics of the FFSCLS.The experimental prototype of the FFSCLS has been developed and enlargementized in order to provide reference for the design and efficient operation of the FFSCLS,and to provide reliable classification equipment for dry screening of wet fine coal.The main work and conclusions were summarized as follows:Through theoretical analysis,the kinematics model of the FFSCLS was established,the vibration differential equations of main and floating screen boxes were established,and the time-domain characteristic equations of displacement,velocity and acceleration of main and floating screen boxes were obtained.The effects of crankshaft eccentricity,crankshaft rotational speed and mass ratio of screen boxes on the motion characteristics of screen body including displacement amplitude,velocity amplitude and acceleration amplitude were revealed.Based on ADAMS softwwere,the multi-body dynamics simulation of the FFSCLS was carried out,and the motion curves and space trajectories of the main and floating screen boxes were obtained.The kinematics parameters of the FFSCLS were tested by vibration testing system.The kinematics characteristics of the FFSCLS at different running stages and the spatial motion trajectory of the main and floating screen boxes during steady running were analyzed.The resonant phenomenon would appear in the starting and stopping stages,and the running track is relatively chaotic.In the steady-state operation stage,the main and floating screen boxes displacement waveform were sine wave.The theoretical results,simulation results and experimental test results were compared to verify the accuracy of the theoretical model.The dynamic model of elastic screen surface was established.The kinematic characteristics of elastic screen surface were analyzed.The influences of crankshaft eccentricity,crankshaft rotational speed and screen surface tension length on the motion characteristics of screen surface,including the displacement,velocity and acceleration of screen surface midpoint were revealed.Parameterized analysis was carried out on the structural response of elastic screen surface,and the effects of coal mass,acceleration,free length of screen surface and tension length on the structural response of elastic screen surface were expounded.The variation law of distributed load,shear force,torque and bending stress on screen surface with coal mass,screen surface acceleration and tension length is analyzed.The influence mechanism about free length of screen surface on motion characteristics and service life of screen surface was discussed,and the value range of ideal length of screen surface was determined.The kinematic characteristics of the elastic screen surface were simulated,and the deviation between the simulation results and the theoretical results was less than 6.70%.The dynamic test results were compared with the theoretical results,which proves that the theoretical results were in good agreement with the experimental results.The mechanical model of the FFSCLS was established.Based on multi-body dynamics,the time domain variation curve of the alternating load at the hinge point between the crankshaft and the bearing was given.The influence mechanism of crankshaft rotational speed and spring stiffness on the alternating load was revealed,and the selection of spring was optimized.Based on the finite element softwwere,the modal analysis and transient dynamics analysis of the screen body were carried out,and the natural frequency of the screen body was revealed to avoid resonance during normal operation.The stress distribution of the screen was improved by the plate spring structure of GFRP material.An enlargement scale FFSCLS was developed,and the dynamic test of the enlargement FFSCLS was conducted.The results show that the displacement time domain response curves of the main and floating screen boxes of the enlargement FFSCLS were approximately straight lines during steady operation,and the test results were consistent with the theoretical calculation results.The bearing selection and service life were discussed theoretically.The reliability test shows that the enlargement scale FFSCLS works well.The screening experimental platform of the FFSCLS for wet fine coal was set up.The effects of feeding speed,crankshaft rotational speed,screen surface inclination and screen surface tension length on the screening effect were studied by single factor test.The test factors influencing the screening performance were selected,such as rotational speed,screen surface inclination angle and screen surface tension length.The multifactor test design was carried out by using the Response Surface Method,and the model fitting was carried out to the test results.According to the analysis of the fitting model,the optimal factor level condition was determined.The order of significance of each test on screening efficiency was obtained,the screen surface inclination angle has the most significant effect,the next was the screen surface tension,and the final was the crankshaft speed.According to the fitting model,the quadratic polynomial regression equation of each test factor on screening efficiency was established.According to the regression equation,a parameter optimization scheme with the highest screening efficiency was obtained.The results of screening experiment show that the FFSCLS has good screening effect and can realize the deep and efficient screening of wet coal.There were 83 pictures,31 tables and 151 references in this thesis.