| Straw returning to the field can effectively utilize straw resources and prevent straw resources from being wasted and burned.However,because straw is not easy to rot,leaving on the ground will affect the sowing quality and emergence rate,and will also lead to the increase of soil bacteria and crop diseases.Due to unreasonable cultivation mode and long-term high-intensity development of cultivated land in northeast brown soil area,the problem of"shallowness,compactness and scarcity"appears in the soil layer.In view of the above problems,relevant experts proposed to combine straw returning to the field and to construct a reasonable tillage layer structure for straw returning to the field.Returning straw deep into the field can not only improve soil fertility but also provide a good sowing environment,forming a rational,deep and fertile plough layer to improve the farming environment.This topic comes from the public welfare industry(agriculture)scientific research special fund project"Research on Technical Index of Reasonable Plough Layer Construction in Dryland(201503116)" aiming at the obstacle problem of plough layer construction in northeast brown soil area,based on in-depth analysis and research on straw returning machines,their key components and key technologies at home and abroad,Through theoretical research methods such as mechanical analysis,kinematic analysis,gas-solid coupling simulation,discrete element simulation and field experiments,the key components of the pneumatic straw deep-buried returning machine,such as picking and crushing device,conveying device,ditching and soil separating device,are studied.The developed pneumatic straw deep-buried returning machine has been tested and studied.The main research results are as follows:(1)According to the technical requirements of reasonable tillage layer of brown soil in Northeast China Plain and the agricultural technical requirements of deep straw returning,a pneumatic deep straw returning machine was designed.Through the analysis of the mechanism and kinematics of key components,the structural parameters and motion parameters of key components are designed.(2)The straw is picked up and crushed by means of a flail knife roller and a movable fixed knife support.When the operation speed is 3?4km/h and the pickup rate and crushing rate are both required to be greater than 90%,the reasonable rotation speed range is 1900?2100 r/min.(3)Through the theoretical analysis of the conveying process of pneumatic conveying device,the motion law of broken straw and airflow in pneumatic conveying device is analyzed by using the numerical simulation method of coupling gas-solid two-phase fluid mechanics and CFD-DEM.By changing the rotating speed,blade bending angle and conveying pipe structure,the Fluent and EDEM software are used for simulation analysis.When the fan speed is 1 800 r/min,the blades are bent at a 30 degree angle,and the side-to-diameter ratios of the conveying pipe 1 and the conveying pipe 2 are 0.2 and 0.125respectively,the conveying performance of the conveying device is the best.Orthogonal test of pneumatic conveying device shows that the optimal combination of fan speed parameters is blade bending angle 30,straw coverage rate 1.2 kg/m~2,and fan speed 1 800 r/min.(4)Based on the sliding cutting characteristics,an eccentric circle design method is adopted to design a counter-rotating ditching cutter.Its main structural parameters include:The eccentric coefficient e of the cutting edge curve is 1.2,r_a is 284 mm,?_a is 65°,r_b is 335mm,?_b is 56°,and the length of the side cutting edge is 70mm;The dynamic slip angle ?_k increases from 36° to 41°;The tillage range is 102;The bending angle is 70°;The bending radius is 55 mm;The gap angle is 5°.Based on the discrete element theory and EDEM software,the simulation test results of ditching device show that the order of influencing factors is clearance angle,bending angle and bending radius.After trenching,the residual amount of soil particles in the trench is 6%,and the trench wall and trench bottom are flat to ensure the trenching quality.The increase of the operating speed of the ditching and soil separating device and the decrease of the rotating speed of the cutter will both reduce the ditching depth,but have little effect on the ditching width.When the working speed is 3?4km/h,the reasonable rotating speed range of the cutter head is 215?245 r/min.(5)Through the orthogonal combination experiment of 3 factors and 5 levels quadratic regression,the variance analysis of the experimental results is carried out,and the regression equation is optimally solved.When the operation speed is 3km/h,the qualified rate of deep burying is 93.2%,and the qualified rate of straw crushing is 93.2% when the trench depth is 268.7 mm When the operation speed is 4km/h,the qualified rate of deep burying is 90.4%,and the qualified rate of straw crushing with ditching depth of 264.7mm is 92.5%. |
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