| The impurity rate of rapeseed after the operation of combine harvester directly affects the quality of subsequent the safe storage of rapeseed and processing of oil.Based on the systematically study on rapeseed combine harvester and the screening technology and equipment at home and abroad.After the operation of combine harvester,high impurity rate and large labor consumption due to the small size of rapeseed that makes the seed hard to be separated,are still the problems that remained to be solved,highlighting the necessity of the mechanized re-cleaning equipment before the drying process.As a solution,a re-cleaning machine after operation of the combine harvester for rapeseed(hereinafter referred to as re-cleaning machine for rapeseed)was put forward.The functions of conveying,screening and air-flow sorting meet the requirements of the re-cleaning machine for rapeseed.The main research contents are as follows:(1)Carried out the overall design and key parameter analysis of the re-cleaning machine for rapeseed.According to the test of material characteristics,the proportion of rapeseeds in impurity rapeseed and related mechanical physical properties have obtained,which provides a basis for the the process route and determination of the screen structure of the re-cleaning machine for rapeseeds.The re-cleaning machine for rapeseed is composed of a screw conveyor,a centrifugal-vibrating screening device and a lateral winnowing device.Respectively realize the functions of compulsory transportation,screening and air selection of impurity rapeseed.Expounds the process route of re-cleaning machine for rapeseed,namely,firstly screen the large impurities thorugh vibration of grading screen caused by rotation of the eccentric block,and then through air separation to remove small impurities.In combination with the working efficiency of the existing domestic rapeseed combine harvester,the volume of the grain tank and the output per unit area of rapeseed,the analysis determined that the re-cleaning machine for rapeseed in order to meet the requirements of rapeseed recleaning after combine haveresting,the production efficiency is 2.7～5.4t/h.(2)Based on the principle of kinematics and dynamics,the design and analysis of the key components of the re-cleaning machine for rapeseed were carried out.Through the analysis of the force on the spiral blades of the screw conveyor,it is determined that the spiral blade pitch is 160 mm,and then calculated helix angle is 18°,the speed of the spiral blade should not be less than 138r/min.The centrifugal-vibration equation of was established,the different motion of the screening device is solved and it can be obtained that under the action of the vector of the rotation excitation,the screen body moves in a circle with the center of mass,and under the action of the torque of the rotation excitation,the screen body swings around the plane of the center of mass.The circular movement promotes the diffusion and discharge of the impurities,and the swing of the cone surface promotes the vibration and classification of the materials.According to the centrifugal-vibrating screening device should have the function of preliminary screening of large impurities(short stems,pods),the relevant structural parameters were determined,it is concluded that the upper screen is a circular punching screen with a diameter of 5mm,and the lower screen is a square woven screen with a size of 8 mesh,and the diameter of each layer of the screen was 600 mm.The minimum speed required by the DC motor,is the eccentric block also,is 796.55r/min calculated from the force analysis of materials on the screen surface,to ensure the smooth discharge of the impurities.The structure of the cleaning enclosure and compare and select the centrifugal fan has been designed.According to the function of blowing light impurities that lateral air separation device should be equipped,through analysis determined that the minimum air volume inside the cleaning enclosure is 0.23 m~3/s,which meets the requirements of air separating.(3)Based on CFD,the numerical analysis of the cleaning enclosure of the lateral winnowing device of re-cleaning machine for rapeseed was carried out.Using software caled Fluent to establish an airflow field simulation project.The simulation results show that the overall flow of the airflow field is normal,and the wind speed attenuation is weak.The wind speed of the air inlet section and the outlet section of the cleaning enclosure are basically the same.The distribution cloud map and the velocity vector diagram of the speed of internal airflow field are analyzed and compared when there is back baffle or not.The research shows that the vortex area inside the cleaning enclosure is significantly reduced when the back baffle was removed,which can reduce the accumulation of materials and avoid affecting screening efficiency.At the same time,combined the internal flow field state of the cleaning enclosure and material aerodynamics,the wind speed of the air inlet section of the cleaning enclosure is within the range of 3～7m/s,the effect of air separating is better.(4)The research and analysis of experiment on the re-cleaning machine for rapeseed was carried out.The single factor experiment considering the impurity rate and screening efficiency as evaluation indexes,and taking the air velocity of the fan outlet,the vibration frequency,and the vertical amplitude as influencing factors.The result shows that the air velocity of the centrifugal fan outlet in better cleaning performance should be in the range of 5～7 m/s,and the vibration frequency should be in the range of 12.08～14.61Hz,the vertical amplitude should be in the range of 3.59～3.64mm.On the results of single factor experiment,an orthogonal experiment was done.According to the orthogonal experiment,the optimal parameter combination was obtained when the air velocity of the fan outlet,the vibration frequency,and the vertical amplitude were 7 m/s,13.48Hz,and 3.61mm,respectively.A confirmatory test was carried out under this parameter combination,the results shows that the average impurity rate is 0.50%,and the average screening efficiency is 98.11%,which can meet the subsequent storage standard of rapeseed(impurity rate<3%).This research has provided a reference for the optimization of the structure and working parameters of the re-cleaning equipment for rapeseed. |
