Research On The Mechanism Of Linear Vibrating Screening Of Ellipsoidal Particles

Screening is the main technical means for particle size grading in various fields;Ellipsoidal or ellipsoidal-like particles accounted for a large proportion in all kinds of screening materials,the long diameter of the ellipsoidal particles is much larger than the short diameter makes the screening properties more complex than that of the spherical particles.At present,the research of mechanism and the device of ellipsoidal particles screen is lacking,using the traditional screening method and screening the ellipsoidal particle by the way of controlling the parameters of spherical particles make the screening performance poor.So,this thesis combines linear vibration screening with high screening efficiency,high productivity and good adaptability characteristics for ellipsoidal particle screening,a method for linear vibrating screening of ellipsoidal particles is proposed,mechanism of ellipsoidal particle linear vibration screening is studied by using wolfberry as ellipsoidal particles.The main research work and conclusions are as follows:(1).Theoretical study on linear vibrating sieving of ellipsoidal particlesBased on the theory of linear vibration sieving,particle separation size and comprehensive sieving efficiency are as basic screening performance index,the kinematic characteristics,the passage characteristics and its influencing factors of the particles in the process of linear vibratory screening of ellipsoidal particles are studied;The results show: particle separation size is an interval range(?d),the larger the relative velocity of the particles along the screen surface,the smaller the separation size;Ellipsoidal particles are relative to the screen surface do cyclical slideing up and down movement,and do cyclical Scrolling up and down at the same time,so,if the relative bounce in the direction of being perpendicular to the screen surface is very large,the big size ellipsoidal particles that should not pass through the sieve will do with the state of being perpendicular or incline to the screening pore,make upper limit of separation size increase and interval range of separation size increase,so that comprehensive sieving efficiency is reduced.The stratification principle and its influencing factors of linear vibration of thick layer ellipsoidal particles are studied,and a stratification performance index detection method is designed;The results show: The kinetic energy difference of different size particles is the main reason for stratification,the changing rate of volume concentration of fine or coarse particles is an effective and feasible method for detecting particle stratification.(2)Simulation analysis of linear vibrating screening of ellipsoidal particlesThe motion characteristics of single-layer ellipsoidal particles on the sieve surface are simulated and analyzed by the discrete element software EDEM,the results show: The relative velocity and absolute velocity of the particles in the x-direction have the same periodicity as the vibration screen,relative velocity of particle group is cosine curve to the time,the average relative velocity and average absolute velocity increase with the increase of sieving parameters(incline angle of screen,amplitude,frequency,vibration direction angle);The particle group bounce in the direction of being perpendicular to the screen surface When the sieving parameters are greater than a certain value,the larger the sieving parameter value,the greater the relative bounce amount.The factors affecting separation size and comprehensive screening Efficiency of single-layer ellipsoidal particles screening are simulated and analyzed,the results show: particle separation size is an interval range(mind ~maxd),particle separation size(upper limit maxd,lower limitmind,centercd)decreases as the sieving parameters increase;It is Verified that by the effect of particle bounce,the ?d increases as amplitude,frequency and vibrating direction angle increase when the particle group bounce in the direction of being perpendicular to the screen surface,the comprehensive screening efficiency decreases,incline angle of screen is in the range of values,because the particle group will not bounce in the direction of being perpendicular to the screen,?d isn’t changed,which doesn’t affect the screening efficiency.Linear vibrating stratification characteristics of thick layer ellipsoidal particles and its Influencing factors are simulated and analyzed,the results show:In the process of ellipsoidal particles vibrating stratification,the kinetic energy difference between the big particles and the small particles in the direction of being perpendicular to the screen surface increases with the increase of the amplitude,frequency and vibration direction angle,which the incline angle of screen has little effect on;The particle stratification rate increases with increasing amplitude,frequency and vibration direction angle,and the incline angle of screen have little effect on stratification rate,stratification rate is getting smaller and smaller with the passage of the time.(3)Experimental study on linear vibration sieving performance of ellipsoidal particlesThe linear vibration screening test device is designed,the performance test and result Analysis of elliptical particle wolfberry by linear vibrating screening is done,The rule of the influence that the vibration amplitude,the vibration frequency and incline angle of screen on separation size and the comprehensive sieving efficiency are verified by the test results;The rule of the influence that the vibration amplitude,the vibration frequency and incline angle of screen on particles stratification rate in the process of thick layer screening are verified.the better screening parameters that amplitude is 4mm,frequency is 20 HZ,incline angle of screen is 8°are obtained,under which condition,the sieving efficiency was 93.6% and the sieving productivity was 1.54t/h.