Basic Research On The Layered Tillage Technology By Biaxial Rotary Tillage Component For Vegetable Bed Former

Bed forming is one of the most important and key links in vegetable production,and its operation quality of ridge surface has an important impact on the further planting and harvesting mechanization.Compared with the quality of soil preparation of grain crops,vegetable ridge operation requirements are more refined,soil in the plough layer should be loose and broken up,the ridge surface is flat and the furrow is straight.Importantly,the soil structure in ridged vegetable fields is comprised of two layers:small soil particles in the loose less-compacted top layer and large soil particles in the dense bottom layer.Therefore,the new design requirements of vegetable bed former are put forward.The single shaft rotary tillage is often used in the soil breaking operation of the existing vegetable bed former,which cannot achieve the purpose of soil layered tillage.Although there are a few bed formers with biaxial shafts,but after the operation of the key working part-biaxial rotary tillage component still have some problems,such as poor breaking quality of ridge surface,wear and adhesion of tillage blade and cutter teeth,high energy consumption due to soil blockage between two shafts,which seriously restrict the process of full mechanization of vegetables in China.In this paper,the theories and methods of metal surface modification,bionic optimization,mechanical soil dynamics and soil adhesion mechanics,and sensor measurement were used.The theory of layered tillage by biaxial rotary tillage component was established.The wear resistance and anti-adhesive properties of the tillage blade and cutter teeth were optimized firstly,and then through the combination of discrete element simulation and layered tillage performance test,the dynamic law of layered tillage and the influence mechanism of operation quality of biaxial rotary tillage component were systematically studied,and the structure of soil crushing roller,the relative spatial distances and rotating speed ratio of the two shafts were optimized.In the end,the verification test of biaxial rotary tillage component was carried out in the field.The above research is expected to provide a theoretical basis for the research and development of high-performance ridging machine.The detailed research contents and results are as follows:(1)The surface coating modification of rotary blade was studied based on the principle of material tribology,and a new way to improve the comprehensive performance of anti-wear and drag reduction of rotary blade was proposed.Four different materials TiAlN,CrN,PTFE and Ni-P-PTFE were selected to modified original blades.The mechanical properties,crystalline structure,wear performance,surface morphology,element analysis,soil cutting resistance were tested and analyzed to investigate wear mechanism and evaluate the improvement of tribological and anti-adhesive properties of different coating methods.The results showed that four different coating materials(TiAlN,CrN,PTFE and Ni-P-PTFE)modified rotary blades all have improved the mechanical properties,wear resistance and anti-adhesive properties of original blades.TiAlN and CrN coated blades showed higher flexural strength and hardness than PTFE based coating.In the experimental wear sliding and outside field test,PTFE based coating all reveal better wear resistance.Especially Ni-P-PTFE coated blade had the lowest average friction rate(0.32)and specific wear rate(3.556×10^-7m³·(N·m)^-1.And in the practical field operation(2 times,total 14days),it also had lowest weigh loss rate(0.4 g/ha)and highest wear resistance index(WRI,2.24),also the soil cutting resistance was the lowest.However,if combined with the operation life and production cost,PTFE coating is more suitable and economically method to improve quality and durability of rotary blades.(2)The structure and surface material of the cutter tooth were modified by the bionics principle,and a new method of anti-adhesion and drag reduction was proposed based on the synergistic effect on the configuration bionics of badger claw toe and anti adhesion coating material.The simulation models of conventional and bionic cutter teeth were established respectively in ANSYS/LS-DYNA software and the simulated soil cutting process was analyzed.The results showed that compared with conventional cutter teeth,the bionic cutter teeth could effectively reduce the average cutting resistance,cutting stress,soil energy and the maximum cutting resistance,obtaining better soil cutting effect.Through FTIR,water contact angle and abrasion resistance tests,the mixed PTFE and FAA resin coatings after sintering were found to have good combination with the cutter teeth as a new anti-adhesion layer of great wear-resistance.When the coating thickness was 10?m,the tillage force was lowest,and the abrasion resistance was highest,exhibiting the best comprehensive performance.The SEM images indicated that coating material can protect the surface and prevent abrasion.The field test results also proved that the average power consumption of uncoated and coated(10?m)bionic cutter teeth was reduced by2.95%and 30.26%respectively,and the soil adhesion was reduced by 64.46%and84.29%respectively.On the whole,the bionic structure of the cutter teeth is conducive to reducing the soil adhesion and power consumption,the combination of bionic structure of badger claws and fluorosilicone acrylic surface coating materials have better anti-adhesion and consumption reduction effects on the cutter teeth.(3)Based on the discrete element method,mechanical soil dynamics and particle contact theory,the dynamic simulation model of biaxial rotary tillage component and clay soil was established,the layered soil disturbance process and dynamic characteristics caused by the biaxial rotary tillage component were discussed.It was found that the rotary blade roller began to contact with the bottom soil at 8.3 s,the soil crushing roller collided with the throwing soil by forward rotary blade at 8.7 s,the number of soil particles between two shafts reached the maximum at 9 s,and the energy consumption was the highest.The layered tillage operation was the most stable at 9 s to 10.8 s,the layered structure of clay soil was completed after 10.8 s,at this time,total number of broken bonds reached the highest.Aiming at the lowest energy consumption and the best soil breaking effect of 5 cm topsoil layer,the structural parameters of the crushing roller were optimized by simulation test.Through the single factor test,it was found that with the increase of cutter tooth spacing,the installation inclination angle and the number of rows,the total number of broken bonds and the total power consumption showed a downward,first slow and then upward trend respectively.The orthogonal test results showed that the influence order of total power consumption was inclination angle>cutter tooth spacing>number of rows,and the influence order of total number of broken bonds was cutter tooth spacing>number of rows>inclination angle.When the cutter tooth spacing was 9cm,the inclination angle was 8°and the number of rows was 5,the comprehensive score was highest,which formed a better combination of structural parameters of soil crushing roller.(4)A field mobile test bench with the functions of throwing soil with forward rotary blade roller and crushing soil with backward crushing roller was developed,which can effectively solve the problems that the existing rotary tillage test benches are difficult to meet the needs of biaxial tillage component test,and it is difficult for indoor test remolded soil to reflect the real environment of the operation site.The working range of the relative space distance between the two shafts,the structural parameters of the position adjustment device of crushing roller shaft,and the motion parameters of the rotary speed adjustment device of rotary blade shaft were analyzed theoretically.The hydraulic pump,hydraulic motor,hydraulic valve,torque sensor,PLC communication module and data acquisition software were calculated and selected respectively.The working principle,test method and data acquisition process of the whole machine were described in detail.A field experiment with the homemade test bench was carried out to optimize the matching parameters between the relative spatial distances and rotating speed ratio of the two shafts.The horizontal distance and vertical distance between two shafts and the rotation speed of soil crushing roller shaft were taken as three factors which influenced the average power consumption and ratio of soil breakage of top 5 cm soil layer,and the regression model and significant between each factor and average power consumption and ratio of soil breakage was studied respectively by the central composite experimental design method,and the influencing factors were comprehensively optimized in the end.The results showed that in terms of impact on average power consumption,the three determinants were ranked in the order of horizontal distance between two shafts>vertical distance between two shafts>rotating speed of crushing roller shaft,while in terms of impact on ratio of soil breakage,the determinants were ranked in the order of horizontal distance between two shafts>rotating speed of crushing roller shaft>vertical distance between two shafts.The best work parameters were as bellow:when the horizontal distance between two shafts was 570 mm,the vertical distance between two shafts was 96 mm and the rotating speed of crushing roller shaft was 340 r·min^-1,the average power consumption was 17.92 k W,and the ratio of soil breakage was91.65%.Through comparing the theoretical optimization model and the valid test result,it was found that the relative error between each evaluation index and its theoretical optimization value was less than 5%.(5)A new prototype of biaxial vegetable bed former was developed.Through the field test and the operation quality comparison with other ridging machines,the comprehensive performance evaluation of the new biaxial rotary tillage component was realized.The test results showed that with the increase of soil moisture content(7.3%,13.5%and 20.4%),the qualified rate of ridge top width decreased,but the values were more than 80%,the qualified rate of ridge height was more than 90%.The soil breaking quality of the ridge surface decreased slightly,soil cracks and uneven phenomenon appeared,but the change was not obvious,the ratio of soil breakage was more than 89.57%.The flatness of the ridge surface was 1.53 cm,soil in the top layer and bottom layer were loose and dense respectively.The whole operation quality could meet the industry standard and the agronomic requirements of vegetable production.Compared with other two types of similar machines,no matter what moisture content,the ratio of soil breakage,flatness and hardness of top 5 cm soil layer after the operation of new bed former prototype were better,which indicates that the biaxial bed former with the key part-biaxial rotary tillage component has stronger adaptability to clay soil environment and high moisture content,with better comprehensive performance.