| The rice-rape and rice-wheat are the main planting patterns in the middle and lower reaches of the Yangtze River.It is characterized by soil viscous and compaction,high straw retention and density,and the difficulty of returning straw to the field in order to grab the crop after harvesting.Under this condition,the traditional rotary tiller has the problem of unsatisfactory work quality and easy winding of the cutter shaft.Although the straw returning tillage machine with spiral cross cutter solves the problems of the traditional rotary tiller,it consumes a lot of power by working in dry land and is more suitable for paddy field operations.In view of the above problems,the cutting characteristics of rice stems were studied in this paper.Based on this research,a slip-shear combined straw returning blade was designed,and a six-head spiral straw returning tillage machine was developed.Calibration of discrete element parameters of viscous-wet paddy soil based on penetration resistance and uniaxial unconfined compression method.The soil-whole machine-straw discrete element model was established,and soil particle displacement,straw displacement and blade force were analyzed.The cutter roller of the six-head spiral straw returning cultivator was improved and optimized,and the improved and optimized machine was verified by field test.The main research results were as follows:?1?When the single rice stalk was cut without blade support,the peak cutting force per unit cross-sectional area at the sliding angle of 60°,but the cutting power consumption was higher.The cutting power consumption per unit cross-sectional area was the lowest at the sliding angle of 60°,and there was no significant difference in the cutting force per unit cross-sectional area with the sliding angle of 60°.Therefore,the suitable sliding angle was about 45°.When the single rice stalk was cut with blade support,the minimum peak cutting force per unit cross-sectional area at sliding angle of 30°was30.9%higher than that at sliding angle of 45°and 60°,and as the cutting speed increases,the difference gradually decreases.The minimum power consumption per unit cross-sectional area at sliding angle of 30°was 31.7%lower than that at sliding angle of 45°and 60°,Therefore,the suitable sliding angle was about 30°.The rationality of the above-mentioned sliding angle selection without blade support was verified by using rapid cutting test device,the results were as follows,the peak cutting force per unit cross-sectional area at sliding angle of 45°was 2.5%higher than that at sliding angle of 60°,but the power consumption per unit cross-sectional area was 1.6%lower than the latter.On the premise of ensuring that the peak cutting force did not affect the operation of the machine,the sliding angle with lower power consumption,i.e.45°,was selected,which verified the rationality of the sliding angle selection in cutting without blade support.?2?Akind of slid-shear combined straw returning blade was designed.According to the research on the relationship between the blade cutting process,the initial values of key parameters of the slid-shear combined straw returning blade were determined to meet the requirements of reducing the power consumption of rice,wheat and rape sowing in the middle and lower reaches of the Yangtze River.The soil discrete element model was established.The main parameters of the model,such us,coefficient of recovery,static friction and rolling friction of soil-soil,were calibrated with the power consumption of power consumption as the evaluation index.Based on the soil discrete element model after calibration,the key parameter of the slid-shear combined straw returning blade were optimized and analyzed,and the best key parameters were obtained.Field test results showed that the average soil pulverization,straw crushing rate,straw burial rate,smoothness and power consumption of the cultivator with slip-shear combined straw returning blade were 86.5%,85.0%,87.5%,2.8cm and 31.3kW,respectively,which meet the national standards and agronomic requirements of rice,wheat and rape sowing in the middle and lower reaches of the Yangtze River.Compared with the traditional rotary tillage blade,the straw crushing rate increased by 2.1%and the power consumption decreased by 3.7%of the slid-shear combined straw returning blade.?3?An equal sliding angle secondary cutter and a six-head spiral straw returning cultivator cutter roll were designed.The range of operating parameters such as the speed of the cutter roll,the tillage depth and the ratio of rotation speed were determined by analyzing the soil cut pitch,working depth and height of the bottom of the ditch.Test results showed that,the effects of various factors on straw burial rate and straw crushing rate were significant from large to small,such as tillage depth,operating speed,cutter roll speed and cutter roll speed,operating speed,tillage depth,respectively.The effects of various factors on soil pulverization and power consumption were significant from large to small,such as cutter roll speed,operating speed,tillage depth and cutter roll speed,tillage depth,operating speed,respectively.The straw burial rate increased first and then decreased with the increase of tillage depth and operating speed,and reaching the maximum when the tillage depth was 14.7cm and the operating speed was 0.71m/s.The straw crushing rate also increased first and then decreased with the increase of tillage depth and operating speed,and reaching the maximum when the tillage depth was 14.2cm and the operating speed was 0.74m/s.Field test was carried out to verify the optimal combination of parameters obtained by the response surface methodology.The results showed that the power consumption was 31.9kW,the straw burial rate was 93.1%,the straw crushing rate was 87.5%and the soil pulverization was 78.3%.The error with the software prediction results were 4.7%,1.4%,1.9%and 2.6%,respectively.Compared with the cultivator for straw returning in paddy field and dry land,the field test results showed that the burial rate and power consumption were increased by 8.8%and 2.3%,however,the straw crushing rate and soil pulverization were decreased by 3.0%and 6.1%,respectively.?4?A calibration method for discrete element parameters of viscous-wet paddy soil based on penetration resistance and uniaxial unconfined compression was proposed.The results showed that a total of 11 sets of calibration parameters were obtained according to cone penetration simulation and test.After the uniaxial unconfined compression simulation and experiment,the parameters with the smallest error were combined into a particle radius of 4.4mm,static friction coefficient of 0.48,and surface energy of 27J·m-2.The soil-whole machine-straw discrete element model was established based on the parameters above.The simulation analysis found that the upper soil particles were both thrown forward and backward,while the middle and bottom soil particles were mainly thrown backward.Due to the spiral arrangement of the blades,the cutter roll had an axial pushing effect on the soil,so the soil particles had a tendency to move toward the spiral direction.For the vertical displacement,the upper soil particles had a downward trend,while the middle and bottom soil particles had an upward trend.Therefore,the six-head spiral straw returning cultivator was beneficial to the soil mixing.Straw can be thrown both forward and backward,and it had a tendency to move to both sides of the machine.The analysis of blade showed that the force of rotary tillage blade and secondary cut blade increased first and then decreased during a rotation period,and the maximum reached at the maximum tillage depth.Among the three directions,the force on the Y axis was the largest and the force on the X axis is the smallest.The finite element model of cutter roll of six-head spiral straw returning cultivator was established.The finite element software ANSYS Workbench was used to simulate the stress,strain and total deformation cloud picture.The results showed that the maximum stress during the operation of the cutter roll was 83.9MPa,which occurs at the joint between the holder and cutter shaft.The maximum deformation was 0.93mm,which occurs at the cutting edge of the rotary tillage blade.The field test results showed that the errors of lateral displacement,longitudinal displacement,vertical displacement of the upper,middle and bottom soil particles by simulation were 4.9%,2.8%,6.4%,5.4%,2.8%,6.5%and 8.5%,10.0%,29.9%,respectively.The lateral displacement and longitudinal displacement of the laterally placed straw were both positive and negative,but the vertical displacement was positive.The lateral displacement of the longitudinally placed straw was positive and negative,but the straw were mostly thrown behind the machine.The longitudinal displacement and the vertical displacement were both positive,that was,the straw had a movement trend towards the inside of the machine and under soil.The lateral displacement,longitudinal displacement and vertical displacement of the inclined placed straw were positive,that was,the straw in the right cutter roll operation area had a tendency to move to the inside,rear,and bottom of the machine.?5?Through field test observation and analysis,it was concluded that the main factor affecting the soil inclusion of the six-head spiral straw returning cultivator was the spatial area size of two adjacent straw returning blades installed opposite to the cutting edge and the secondary cutter blade which entered soil next moment.The smaller the spatial area size was,the easier it was to clamp soil.The main improvement measure was to adjust the angle between the secondary cutter blade and the adjacent straw returning blade which entered soil next moment,and adjust it to 55°.Field test results showed that there was no soil clamping phenomenon when the improved cutter roll operated at low speed,which verified the rationality of the improvement.The results of field test showed that the six-head spiral straw returning cultivator solved the problems that the quality of traditional rotary tiller was not ideal and easy to be twisted under the condition of viscous and compacted soil in the paddy-dry rotation mode.Its power consumption was lower than that of traditional rotary tiller and the cultivator for straw returning in paddy field and dry land.Test results of the six-head spiral straw returning cultivator indicated that soil pulverization and straw crushing when operating in rice straw field was lower than that in wheat straw field,while the straw burial rate was higher than the latter.In addition,it also brought out that the soil pulverization rate,straw crushing rate and straw burial rate were not only related to the operation parameters,but also closely related to the characteristics of straw and soil. |
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