| The mechanical film spreading hole sowing technology can increase the temperature and moisture,improve the field water and heat conditions,stimulate crop yield potential,and is widely used in spring rapeseed areas.For the actual production of rapeseed mechanical film laying hole sowing machine has to be improved,laying film hole sowing grain number is difficult to accurately control and other problems,compared and analyzed different film hole sowing planting agronomic requirements,developed a combination of positive and negative air pressure rapeseed hole sower.The seeds were sucked under negative pressure,unloaded under positive pressure,and perforated on the film with a duckbill hole former to achieve 1～3 grains hole sowing of rapeseed,providing a reference for structural improvement and optimization of rapeseed mechanized film hole sowing equipment.The specific research contents include:(1)The overall structure of positive and negative pressure combined hill planter for rapeseed was designed and its key parameters were determined by analysis.Which adopted the principles of negative pressure seed suction,positive pressure seed unloading,duck mouth hole forming and secondary seed feeding.This paper expounds the main structure and working process of the dibbler,mainly including the structure design and parameter analysis of the seed metering wheel,the type hole of the seed metering wheel,the air chamber cavity,the seed feeding tube and other parts;through the analysis,it is determined that the type hole of the seed metering wheel is a parallel double row type,the axial spacing of the double row type hole is 6 mm,and the diameter range of the type hole is 1.02～1.26 mm;the number of the radial type holes of the seed metering wheel is the same as that of the duck beak hole former,and the type hole is the same,the number of holes is 10 or 12.(2)Based on the dynamics,the process of two stages seed absorption,seed carrying and unloading was analyzed.In the process of seed suction,three states of the seed moving to the hole were analyzed,and the main factors affecting the seed arrangement performance of the seeder are analyzed,the main factors influencing the seed adsorption rate were determined by the seed absorption process analysis,such as the rotation speed of seed row wheel spindle,seed layer height,negative pressure and shape of hole,the critical negative pressure value of the absorbable seeds in the type hole is-428.69 Pa.The analysis of seed carrying process shows that the seed carrying adsorption force is related to the radius of the seed discharge wheel,the speed of the seed discharge wheel spindle and the coefficient of dynamic friction between the seed discharge wheel and the seed contact,determines that the seeds can be carried stably under the negative pressure of the type hole absorbable seeds;the analysis of seed unloading process shows that the acceleration of seeds along the direction of positive airflow at the moment of seed release from the seed discharge wheel is related to the positive pressure,the spindle speed of the seed discharge wheel and the angle of seed discharge,the seeds can be carried stably under the negative pressure condition of the type after the hole,the projectile is thrown at a certain initial speed.(3)The numerical analysis of the profile cross section and the suction end cross section for different hole diameter,hole shape and radial holes number airflow fields were investigated by simulations using ANSYS FLUENT software.The simulation results show that: the average air pressure of seed suction end section with 1.2 mm diameter is the largest in different hole diameters,and the pressure distribution is more uniform;the average air pressure of seed suction end section with straight hole is the largest,and the average air pressure of seed suction end section with tapered hole is the second in different hole shapes;when the number of radial holes is 10 holes and 12 holes,the distribution of gas velocity is uniform,but compared with 10 holes,the change of gas velocity of 12 holes is more violent;the comprehensive pressure is higher according to the distribution of force field and air flow field,the best combination of die hole and its arrangement is 1.2 mm diameter tapered hole and 12 radial holes.(4)The simulation experiment of seed filling performance is carried out by using EDEM.Based on the EDEM,the movement track of seed flow in the seed tube was extracted,and the influence of shape structure of the hole,height of seed layer and rotation speed of the spindle of seeding wheel on the drag angle and average speed of population were clarified.The simulation results show that the shape of seed tube can ensure the seed can enter the cavity of seed filling chamber smoothly;shape structure of the hole,the height of seed layer and the rotation speed of the seed row wheel spindle have an influence on the drag angle and the population dynamics characteristics.Tapered holes have a more pronounced effect on drag angle and population dynamics characteristics than straight holes;when the seed layer height is 50～70 mm,the rotation speed of the seed row wheel spindle is 5～30 r/min,the drag angle and population dynamics characteristics are greatly affected.(5)The performance evaluation test of dibbler was carried out.Taking negative pressure,the rotation speed of seed metering wheel spindle,the height of seed layer and positive pressure as the test factors,taking the right rate of seeds per hill and rate of no seed hill as the test index,the single factor test of seed metering performance of dibbler was carried out,and the influence rules of various parameters on seed metering performance were obtained;on the basis of single factor test,the quadratic orthogonal rotation center was carried out with the rotation speed of seed metering wheel spindle,negative pressure and positive pressure of seed metering wheel spindle as independent variables combination test.The results of single factor test showed that the performance of the dibbler was better when the height of seed layer at 50 mm,the rotation speed of seed metering wheel spindle was 5～20 r/min,the negative pressure was-800～-2000 Pa,and the positive pressure was 600～1500 Pa;The results of quadratic orthogonal rotation center combination test show that the main and secondary factors affecting the right rate of seeds per hill were negative pressure>rotation speed of seed metering wheel spindle>positive pressure.The optimal working parameters of seed metering performance was rotation speed of seed metering wheel spindle at 7.5 r/min,negative pressure at-2000 Pa and positive pressure at 850 Pa,The results of bench verification test showed that the right rate of seeds per hill was 88.15%,and the rate of no seed hill was 4.43%,which met the requirements of rapeseed production requirements of mechanical film laying and hole sowing. |
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