Research On Working Performance Of Serrated And Rotary Blades Based On Straw Returning To Field Machine

Straw mechanization and returning to field is an important measure to realize agricultural sustainable development.Crop's straw is crushed,plowed and then decomposed into field to fertilize soil in a wide range.For soil after straw returning,there is rarely theoretical basis for designing tillage units due to lacking of deep understanding for mechanical properties of soil-straw mixture and their interaction mechanism,which makes such design unreasonable.Therefore,it is significant to research mechanical properties of soil with different straw contents,based on which to study the movement,deformation and failure of soil and straw which has been plowed by machine.As a traditional tillage machine,rotary blade is a crucial component which contacts soil directly.Generally speaking,rotary blade can meet the requirements of ordinary field work.However,the working efficiency and performance of rotary blade cannot satisfy the new requirements of surface with high straw content,which is that the displacement of surface straw should be large and evenly distribute on surface and the displacement of soil should be small to reduce soil losses.Interaction mechanism between blade,straw and soil that blade interacts with straw before contacting soil is complex because of the existence of straw.Based on this mechanism that blade interacts with straw before contacting soil,it is necessary to study rotary blade.The main research contents and conclusions are as follows:1.Design of serrated blade.The type of serrated.width and depth of serrated blade were taken as structure parameters through analysis of the motion parameters of blade during soil-rototilling and stubble-breaking,the interaction between straw and positive.side cutting edge of blades,and nine kinds of serrated blades were designed based on the national rotary blade.The quality of straw length is less than 15cm was taken as the evaluation index.The optimal structure parameters of serrated blade were determined through the experiments of soil-rototilling and stubble-breaking in an indoor soil bin.It was demonstrated that the optimal combination of structure parameters were as trapezoid serrated.the width of serrated blade is 3.5?4mm?the depth of serrated blade is 5mm.With 65Mn as the material,according to the national standard processing technology,the serrated blade were produced.The designed blade and national rotary blade were both simulated and tested in soil bin and in field under different straw content.The results show that the torque of serrated blade was less the one of standard blade on the surface of 50%straw content,while was larger than standard blade on the surface of 100%straw content.Two torques were approximately the same.The surface quality after being plowed by serrated blade was better obviously than by standard blade under three different situations.2.The displacement of straw and soil under different rotating speed and the interaction mechanism between blade and straw when actual working were studied through bending and shearing tests indoor and positive and negative rotation tests at field.The bending and shearing tests' results show that bending strengths of wheat and rice straw at N1,N2 and N3 decreased first then increased with the increase of loading rate;The shearing strengths of wheat straw at N1,N2 and N3 increased with the increase of loading rate,while the shearing strengths of wheat straw increased with the increase of loading rate.The bending and shear strength of N1,N2 and N3 segments were compared to obtain:N3>N2>N1.The largest bending and shearing strength located in N3.The 2D-surface research of wheat and rice show that the displacement of straw when negative rotating was more than that when positive rotating.The former one increased with the increase of velocity,while the later one decreased.Each marker arranged in a spiral shape on 2D-surface after being plowed and didn't change with velocity.When negative rotating,the movement of straw and soil concentrated on the reserve direction of blade and distributed evenly.The movement of longitudinal straw and soil when positive rotating distributed on both sides of the markers,and the transverse straw concentrated.The straw cover when positive rotating was higher than that when negative rotating,while the soil fragmentation was on the contrary.The analysis of 3D-surface shows that The displacements of wheat straw which was less than that of rice straw decreased with the increase of loading rate under three velocities.Two arrangements corresponded to two distributions.The longitudinally marked straw distributed symmetrically on both sides of the X axis,and the transversely marked straw distributed symmetrically on both sides of the X and Z axis.The displacement variation coefficient of longitudinally marked straw increased with the increase of loading rate,and then decreased,while the one of transversely marked straw decreased gradually with the increase of loading rate,which means the uniformity of straw's displacement after plowing was not positive correlated to velocity.3.Simulation model of the interaction of straw-soil-saw tooth and blade was established in EDEM,by which micro and macro motion of straw and soil and forces and torques of blade on three directions were analyzed.The research results show that resultant force,vertical force and forward resistance of two kinds of blades when covered by straw were larger than those when uncovered by straw by comparing the simulation results of single blade and multi-blades.In a working cycle,each force grew from 0 to the largest value,and then dropped to nearly 0.The vertical force was larger than vertical force and lateral force.The force of standard blade was less than serrate blade.The interaction mechanical of blades and straw in two arrangements in multi-blades simulation was different.The blade's main cutting edge sheared and slipped on the longitudinally marked straw,and squeezed against and tore the transversely marked straw.The side cutting edge squeezes against the longitudinally marked straw.The serrate blade had advantages on shearing,slipping and squeezing because of its saw tooth.The horizontal,lateral and vertical displacements of serrate blade were larger than those of standard blade.From analyzing the surface marked soil,the horizontal displacement of soil is larger than its lateral and vertical displacements under both kinds of blades,and all three displacements of serrated blade were larger than standard blade.The horizontal displacement of soil was contrary to the one of both blades.The lateral displacement happened along both axial directions.Positive and negative of vertical displacements represented the surface's convex and concave shape after being plowed.More straws were covered under the surface after being plowed by serrated blade,which made the surface convex more obviously.The horizontal displacements of shallow,middle and deep soil were always larger than lateral and vertical displacement by analyzing all three layers,which was similar with the former surface results.The moving displacement of shallow soil particles was the largest,the middle soil was the second,and the deep soil was the smallest,which means soil's moving direction depended on the force on three directions.The torque changing trend of single blade in simulation was the same with that of multi-blades,and the change of serrated blade was a little bit larger than that of standard blade.When working after a while,the changes of both blades were identical approximately.It is because the interference between the blades will affect the simulation results.But the simulation results of single blade could be used as reference to multi-blades.4.The forces on three directions and torques of blade roller of two kinds of blades under different straw-content were analyzed in indoor soil bin test.The research results show that with the increase of straw content,both forward resistances increased,while the lateral force was little impressed by the content.When working under 100%straw-content,the maximum resistances of both serrated and standard blade were nearly the same.The main and side cutting edge sheared and squeezed with longitudinally and transversely straw because of saw tooth,leading to the obvious increase of vertical force.In a working circle,the torques of both blades increased and then decreased.With the increase of straw content,the torque of serrated blade decreased gradually and was larger than that of standard blade,while the maximum torque of standard blade was basically constant.There were no shearing and slipping forces on standard blade since most straw slipped from the surface of main and side cutting edge.When working under 50%straw-content,the torque of standard blade was larger than that of serrated blade.When the straw-content increased from 0%to 50%,while the torque of standard blade increased 41.7%,the torque of serrated blade increased 14.3%.When the straw content increased from 50%to 100%,the torque of standard blade increased 25%,while the torque of serrated blade increased 10.6%,which means with the increase of straw-content,touching and processing times of serrated blade and straw increased,leading to an obvious increase of its torque.The covering rate of serrated blade was larger than standard and reached its peak when working under 50%straw content.The length of surface straw was less than 15cm and its weight was larger than being plowed by standard blade after being plowed by serrated blade.when the straw content was doubled,the length was less than 15cm and its weight increased 97%after serrated blade tilling,while the weight after tilling by national blade increased 81%.5.The trends of field test result and indoor test result were nearly identical.With the increase of straw content,the output of both blades increased.When working under 50%straw content,the output after being plowed by serrated blade was a little bit less than that after being plowed by standard blade.When the straw content increased from 0%to 100%,the power consumption of serrate and standard blade increased 25.19%and 28.56%,respectively.Three displacements of soil and straw after being plowed by serrated blade were larger than those of standard blade,which was caused by the different interaction mechanism between main,side cutting edge and straw.The shearing of side cutting edge and longitudinal straw preformed mainly as the displacement along X axis,while the tearing and squeezing of main cutting edge and longitudinal straw preformed as the displacement along Y axis,which was contrary to transverse straw.The displacements along X and Y axis of longitudinal straw were larger than those of transverse straw,which means the shearing of side cutting edge and straw was larger than the squeezing of main cutting edge and straw.By simulation,indoor test and field test comparison:torque under field test is larger than the indoor test and simulation test;with the increase of straw content,the trend of indoor and field test was the same;straw displacement of field test one is greater than that under simulation experimental and field test two;soil displacement of simulation experimental is greater than that of field test one and two.Mainly due to the differences of test conditions and test environment.In addition,the simulation model can be used as a reference for field experiments,and can predict the displacement of soil and straw within a certain range.Moreover,side cutting edge can shear straw easier since its working width was larger than the main cutting edge and the saw tooth's working width.With the increase of straw content,the rate of straw-burying.straw-crushing and straw crashing decreased.Both two rates of serrated blade were higher than those of standard blade.The straw-burying rate of serrated blade reached its peak when under 50%straw content.When the straw content increased from 50%to 100%,the torque and power consumption after being plowed by serrated blade were larger than those of standard blade,while the length of straw was less than 15cm and it weight increased 93%and the weight after being plowed by standard blade increased 76%.Besides,performance of crushing straw,covering and crushing soil was better than those of standard blade.Therefore,considering its economic benefits and performances,the serrated blade can be used as reference to straw burying?soil and straw crashing under rototilling,and the design can meet the requirements of Chinese national standard.