Study On Working Mechanism And Experimental Research Of Cleaning Device For Millet

China is one of the main producing areas of millet in the world,and has a good market prospect and economic advantage in the international market.Grain harvesting is one of the main aspects of the whole mechanization of grain production,the use of combined harvesting can be completed once the grain harvesting,threshing and separation,cleaning and other processes,and gradually become the development trend of grain harvesting technology.The cleaning device is the "digestive system" of the combine harvester,mainly in the form of vibrating screen,airflow,drum and so on.Grain wind sieve type cleaning device,as the mainstream cleaning device of the current grain combine harvester,mainly suffers from the problems of local accumulation of detritus at the shaking plate,small difference in suspension speed between the seeds and other components in the detritus,and uneven flow rate of cleaning air.In this study,by reviewing the domestic and foreign research on screening mechanism and wind sieve type cleaning equipment,to explore the mechanism of sieve body movement and airflow on the action of the particle group in the cleaning process,combined with theoretical analysis,simulation analysis bench test and other methods and means to carry out the wind sieve type cleaning device screening mechanism and performance test research.The main content is as follows:(1)Determination of material characteristics of the separates: The separates mainly consisted of seeds,spike flaps,short stalks and small miscellaneous residues such as prickly hairs,glumes,etc.The components were easily adhered to each other,aggregated,poorly mobile and had a certain degree of cohesiveness.The basic physical parameters such as shape,geometry,thousand grain weight and moisture content of seeds,spike flaps and short stalks were measured.the mechanical parameters were measured on the test bench and the air-blown agricultural material collision recovery coefficient test bench,and the rest angle,friction coefficient and collision recovery coefficient were measured by the high-speed camera technology.The mechanical parameters,such as rest angle,friction coefficient,collision recovery coefficient,etc.,are measured by the mechanical parameters determination test bench and the air-blown agricultural material collision recovery coefficient determination test bench,and the material group distribution characteristics are measured by the threshing and separation test bench,which provide data basis for the subsequent research on grain cleaning mechanism,theoretical model establishment and virtual simulation analysis.(2)Analysis of particle motion mechanism in wind sieve type cleaning device: Take grain wind sieve type cleaning device as carrier,establish kinematic model of vibrating sieve,get kinematic equation of any point on the sieve.combine mathematical and physical analysis methods,establish kinematic model of particles in shaking plate,deduce the equation of throwing coefficient of particles on vibrating sieve,get the relationship between particle motion and throwing state.carry out kinetic analysis of particles thrown from shaking plate to cleaning sieve,get the motion law of particles under the joint action of vibrating sieve and wind field.establish probability model of particle penetration sieve,get the influence law of separation material layer structure on particle penetration sieve.(3)Dissociation behavior analysis of separation: Discrete element method(DEM)was used to establish the particles of each component of the separation,and the interparticle interaction parameters were determined by Plackett-Burman screening test and Box-Behnken test.A model for the dissociation behavior of single spike and single stalk particles and a model for the dissociation behavior of isolate particle clusters were established,and the relationships between particle characteristics,vibration conditions and particle dissociation patterns were obtained.to "Brazil fruit(BN)".The segregation mode of the grain group mainly existed in two segregation modes,"Sandwich" and "BN".The transformation of the disintegration mode was related to the number,volume and density of spike and stalk particles relative to the total particles.(4)Analysis of sieve permeation behavior of separation: The discrete element method is used to simulate the sieve permeation process of each component of separation,and the model of particle permeation behavior of separation through static sieve body and particle permeation behavior through dynamic sieve body is established,and the simulation test results show that the sieve permeation performance of plain square hole sieve is the best.The simulation test results show that the sieve penetration performance of the plain square hole sieve is the best.The influence law of different layer structures on the sieve penetration is investigated,and it is found that when the seeds are in the bottom layer,the seed penetration rate is the highest,which is about 3-8 times of other layer structure models.The hindering effect increased with the increase of the volume of the lower layer particles.(5)Research on the flow field distribution law on the clearing screen based on the lattice Boltzmann method: Taking three different kinds of vibrating screen as the carrier,using the lattice Boltzmann method(LBM)to analyze the flow field distribution characteristics inside the clearing device,establish the simulation model of airflow through the static screen surface,explore the flow field distribution law of airflow through the static screen surface,and obtain the uniformity of the flow field distribution of airflow through the static screen body: plain square hole screen > fisheye screen > perforated screen.Establish the simulation model of airflow through the dynamic screen surface,investigate the flow field distribution law of airflow through the dynamic screen surface,and obtain the uniformity of flow field distribution in the dynamic process of the screen body: plain square-hole screen > perforated screen > fisheye screen.Design the wind speed and air volume monitoring and collection system,the wind speed change curve of plain square hole screen is similar to the sine curve,and the wind speed change curve of perforated screen and fisheye screen is a double wave peak curve.Three kinds of sieves are compared with loss rate and impurity rate as the performance index,and the results show that the plain square hole sieve has the best performance.(6)Bench test research: Select vibration sieve amplitude,vibration frequency,wind speed and wind angle as test factors,loss rate and impurity rate as evaluation index,and conduct single-factor test to investigate the influence law of each factor on the cleaning performance.Using four factors and five levels of quadratic orthogonal rotational combination design experimental research,establish the mathematical model between the test factors and performance indexes,and obtain the optimal combination of working parameters of grain wind sieve type cleaning device: vibrating screen amplitude 20.85 mm,vibration frequency 6.97 Hz,wind speed4.89m/s,wind angle 27.62°,the best cleaning performance indexes are loss rate 2.67%,impurity rate 3.97%.The validation test obtained a loss rate of 2.82% and a trash rate of 4.33% for the grain wind sieve type cleaning device,meeting the agronomic requirements of grain cleaning.