| In recent years,with the increase of maize planting scale,a large amount of maize stalk is remained in the field after maize harvest.stalk returning is a major stalk treatment method.The most of the organic matter of stalk can be retained in the soil by stalk rotary burying,and the stalk can fully contact with the microorganisms in the soil to accelerate the stalk decomposition rate.It is a common stalk returning method.However,the stalk rotary burial quality of the traditional stalk returning machine is poor,the distribution uniformity of stalk in the soil is bad,and the number of stalk in the shallow soil is large,resulting in the poor quality of the seed bed(depth of0～5 cm soil)when corn is sown,which is not conducive to direct sowing in spring.In this paper,to solve the above problems,a rotary blades and burying fingers combined tillage machine was designed to improve the distribution uniformity of stalk in the soil,improve the quality of seedbed,and provide a good seedbed environment for direct sowing in spring.The main research contents of this paper mainly include the determination of the physical and mechanical parameters of black soil in Northeast China,the design of rotary blades and burying fingers combined tillage machine for maize stalks returned to field,the establishment of soil-stalk-root and stubble-machine discrete element simulation model and single factor test.The influence of various factors of the combined machine on the distribution uniformity of stalks,the percentage of stalk mass in the seed bed and the power consumption of the machine were analyzed.The parameters of the machine were optimized by quadratic orthogonal rotation combination test,and the optimum structure and working parameters of the machine were determined.The performance of the combined machine was verified by field experiments and compared with the traditional stalk returning machine.The main research contents and conclusions are as follows:(1)The physical and mechanical properties of the soil were measured,including:the moisture content of the soil was determined to be 20.1%～23.7%by the drying test,the soil density was determined to be 1.308 g/cm~3～1.473 g/cm~3by the ring knife soil weighing test,and the soil cohesion was determined to be 60.6 k Pa～66.6 k Pa by the soil shear test.The range of internal friction angle is 16.0°～18.2°,and the Poisson’s ratio range is 0.413～0.420.The sliding friction coefficient between soil and 65Mn was determined to be 0.63～0.82 by slope test.A important reference was provided for subsequent machine designing and virtual simulation parameter setting.(2)A rotary blades and burying fingers combined tillage machine was designed.The stalk was rotary buried preliminary by rotary blades of the machine,then the gathered stalk group was further buried and dispersed by the burying fingers,so as to improve the rotary burying depth and the distribution uniformity of stalk.Based on the slide-cutting principle between the stalk and the burying fingers,and the establishment of the mechanical equation,the equal slide-cutting angle logarithmic curve burying fingers mechanism was designed,and the slide-cutting angle range was determined to be 40°～80°.According to the national standard,the forward speed range of the machine was determined to be 0.30 m/s～1.30 m/s.To improve the buried depth of the stalk and the distribution uniformity of the stalk,the burying depth of the burying fingers was determined to be8 cm～16 cm.To make the burying fingers act on all the stalk,the number of burying fingers around the axis was determined to be 6.(3)A discrete element model of soil-stalk-root-stubble-combined machine was established.The working process of the combined machine was analyzed,and the working mechanism of burying fingers was explored.The forward speed of the machine,the depth of the burying fingers into the soil and the slide-cutting angle of the burying fingers were selected as the test factors to carry out the single factor simulation test,and the influence of each factor on the distribution uniformity of stalk,the percentage of stalk mass in 0～5 cm soil and the power consumption of the machine were explored.The results showed that with the increase of the forward speed of the machine,the distribution uniformity of stalk decreased gradually,the percentage of stalk mass in0～5 cm soil decreased first and then increased,and the power consumption of the machine increased gradually.With the increase of buried depth of the burying fingers,the distribution uniformity of stalk increased gradually,the percentage of stalk mass in 0～5 cm soil decreased first and then increased,and the power consumption of the machine gradually increased.With the increase of the slide-cutting angle of the burying fingers,the stalk distribution uniformity,the percentage of stalk mass in 0～5 cm soil and the power consumption of the machine first decreased and then increased.(4)Based on the results of single factor test,a three-factor and five-level quadratic orthogonal rotation center combination test was designed.The significant effects of various factors and interaction items on the index were analyzed by response surface method.The test results show that the order of the influence of various factors on the distribution uniformity of stalk is as follows:the forward speed of the machine,the buried depth of the burying fingers,and the slide-cutting angle of the burying fingers.The order of influence on the percentage of stalk mass in0～5 cm soil from large to small is as follows:the slide-cutting angle of burying fingers,the buried depth of the burying fingers,and the forward speed of the machine.The order of the influence on the power consumption of the machine from large to small is as follows:the buried depth of the burying fingers,the forward speed of the machine,and the slide-cutting angle of the burying fingers.The regression mathematical model was multi-objective and optimized by Design-Expert10.0.7 software,and the optimal combination of the parameters of the combined machine was determined.When the forward speed of the machine is 0.50 m/s,the buried depth of the burying fingers is 12.75 cm,and the slide-cutting angle of the burying fingers is 69.62°,the standard deviation of the stalk distribution is 0.0419,the percentage of stalk mass in the 0～5 cm soil is16.71%,and the power consumption of the machine is 41.18 k W.(5)According to the optimization results,the rotary blades and burying fingers combined tillage machine was processed,and a measuring device was designed to monitor and record the torque of the tractor power output shaft in real time.When the machine is working in the without stubble field,the forward speed of the machine is 0.5 m/s,the buried depth of the burying fingers is 13 cm,and the slide-cutting angle of the burying fingers is 70°,the standard deviation of the stalk distribution is 0.0448,the percentage of stalk mass in 0～5 cm soil is 18.58%,and the power consumption of the machine is 43.12 k W.The stalk returning performance of combined stalk returning machine and traditional rotary tiller in high stubble field,low stubble field and without root stubble field.The test results show that compared with the traditional rotary tiller,the standard deviation of the distribution of stalk in the soil after the combined tillage machine works in three kinds of land conditions decreased by 15.89%,19.78%and 23.5%,respectively.The percentage of stalk mass in 0～5 cm soil decreased by 12.47%,12.41%and 13.20%,respectively,and the power consumption of the machine increased by 19.01%,20.59%and 20.85%,respectively.In this paper,a reference can be provided for improving the distribution uniformity of stalk in soil after stalk returning,improving the quality of seed bed,and providing a good seed bed environment for direct sowing in spring. |
