| Seed coating treatment technology is an important part of seed science and technology.It is an important means to ensure and improve seed quality,and it plays an important role in agricultural mechanization,modernization and agricultural sustainable development in the era of large agriculture.Soybean seeds treated with coating can ensure the uniformity of grain size,facilitate mechanized sowing,reduce the chance of disease in seedling stage,resist the erosion of pests in the field,promote the growth of seedlings and seedlings,ensure the uniformity of seedlings,which also play a protective role in the ecological environment.In recent years,the seed processing industry and the domestic market demand have become more and more demanding for the quality of seed coating,the coating process and the automation of coating equipment,which has promoted the comprehensive reform of the mechanical structure of domestic seed coating equipment.In order to solve the problems of uneven seed coating,high break rate and serious sticky wear of key parts mixing blade in existing domestic batch soybean seed coating mixing device,this project will combine the optimization structure of agricultural machinery equipment by using bionic method and analysis the mixing mechanism of granular body by discrete element method,design the soybean seed coating mixing device based on the theoretical analysis,apply three-factor five-level quadratic regression orthogonal rotation center combined test method,optimize and experimental research the structure and operation parameters which influence the performance of the mixing device,and implement field comparison experiment of soybean seeds treated with the new coating mixing device equipped with the bionic mixing blades and the soybean seeds treated with the existing coating mixing device equipped with the planar mixing blades,obtain soybean seed germination index and the characteristics of plant traits at seedling stage,compare the coating effect of two kinds of coating mixing devices,verify the superiority of the new coating mixing device over the existing ones in coating quality,and provide data support and practical reference for the improvement and optimization of coating equipment key technology,the main conclusions are as follows:(1)According to the characteristics of the mixing device of soybean coating machine,the motion model of soybean seed particles in the mixing device before and after coating was established on the basis of assumptions,and the kinematics and dynamics analysis of soybean seed particles in the mixing process were carried out.Meanwhile,Hertz and Mindlin-Deresiewicz theory were used to analyze the normal force and tangential force in the contact process between the soybean seed particles before and after coating with the mixing blades.It was concluded that the normal force and tangential force in the mixing process were related to the average curvature radius ρy of the mixing blades.By reducing the average curvature radius py of the mixing blades,the curved mixing blade was used instead of the planar mixing blade.The method can reduce the normal and tangential forces in the contact process of soybean particles with mixing blades before and after coating,and then reduce the damage and breakage of soybean seeds during coating.(2)The three-dimensional inverse scanning of the body surface features of the Cassis cornuta shell was carried out by using a three-dimensional optical measuring instrument to obtain the surface slice data and the surface point cloud data of the shell.After scanning,38054 points,1270 edges,612 faces,400001 mesh triangles and one entity were obtained.NX Imageware software is used to fit the collected data to the surface,adjust the deviation to the allowable range,and re-collect the data from the bad points or the points with unsatisfactory fitting.A more uniform curvature change is selected,which is suitable for making the surface nodules of the bionic mixing blade to construct the mixing blade model.The solidworks software was used to build the solid model of the bionic mixing blade.After adjusting the deviation,try to make a bionic mixing blade.(3)When the rotating speed is 25 r/min,the phase difference is 90°,the rotating angle is 65°and the total mixing time is 9.2 s,the comparative analysis of two kinds of mixing devices with bionic mixing blade and planar mixing blade is made by discrete element simulation.It is concluded that after collision between coated soybean seed particles and bionic mixing blade,soybean seed particles continue to move in many directions and angles,and continue to emit with other soybean seed particles.After collision,the speed of collision is higher,the collision between particles,rubbing and adhering seed coating agent are completed,which enhances the coating effect of soybean seeds.After collision between coated soybean particles and planar mixing blades,the particles only move in the direction opposite to the initial velocity,and the probability of collision with other soybean seed particles is smaller,and the particle movement speed after collision is smaller.When the uniformity of particle mixing is reached,the uniformity of particle mixing is evaluated by variation coefficient,which is 1.89%under the action of bionic mixing blade and 2.53%under the action of planar mixing blade.When the bionic mixing blade is mixed,the coefficient of variation is smaller.When the coated soybean particles are mixed by the bionic mixing blade,the number of particles in contact with each other is smaller and the mixing uniformity is better.(4)When the rotating speed is 25 r/min,the phase difference is 90 °,the rotation angle is 65°and the mixing time is 9.2 seconds,the prototype verification test was carried out by using a new coating mixing device equipped with a bionic mixing blade and an existing coating mixing device equipped with a planar mixing blade,respectively.The results showed that the pass rate of coating was 93.26%and the break rate of coating was 0.089%for the soybean seeds treated by the existing coating mixing device,and the pass rate of coating and break rate of coating was 95.07%and 0.072%for the soybean seeds treated by the new coating mixing device,which met the requirements of seed coating quality,and the coating effect of bionic mixing blade was qualified compared with that of planar mixing blade.The coating break rate was reduced by 0.017%and the coating pass rate was increased by 1.81%.The validity and feasibility of the simulation results were verified.(5)Taking speed nj,phase difference β and rotation angle aj as test factors,the coating pass rate and the coating break rate as test indicators,three-factor five-level quadratic regression orthogonal rotation center combined test was used to study the structure and operation parameters affecting the performance of mixing device.The influence of each parameter on coating pass rate was rotating speed,phase difference and rotation angle in turn.The influence of coating break rate is rotation angle,phase difference and rotation speed in turn.When the rotation angle is 65°,the phase difference is 86°to 93°and the rotational speed is 26 to 32 r/min,the coating pass rate of soybean seeds can be more than 95%and the coating break rate is less than 0.1%.The optimum combination of parameters affecting the multi-objective function in the range of experiment is:phase difference 90°,rotation angle 65°and rotating speed 30 r/min.At this time,the pass rate of coating is 95.47%,and the break rate of coating is 0.06%.It belongs to the first-class coating product and meets the requirements of soybean seed coating.The comparison between the experimental value and the optimized value shows that the optimum result is accurate and credible.(6)Comparing the surface tension measurements of planar mixing blade and bionic mixing blade,the results show that the adhesion work and critical surface tension of planar mixing blade are larger than those of bionic mixing blade,which indicates that the surface of planar mixing blade is more easily wetted by seed coating agent,and its wettability is better,and it is easier to be adhered by seed coating agent.The bionic mixing blade is not easy to be adhered to by seed coating agent,so it is more suitable for coating mixing operation.Seed coating agent adhered flaky on the planar mixing blade,especially near the top of the mixing tank,i.e.near the spraying position of the seed coating agent,the degree of adherence was more serious,while the seed coating agent adhered patchy on the bionic mixing blade,the adherence position was close to the edge of the bionic mixing blade,and the degree of adherence was lighter.Bionic mixing blades can effectively reduce the adhesion of seed coating agent to the surface of mixing blades by utilizing the visbreaking effect of marine shellfish such as Cassis cornuta.(7)Taking uncoated soybean seeds as control group ck,the soybean seeds treated by the new coating mixing device as treatment 1,and the soybean seeds treated by the exist coating mixing device as treatment 2,field comparative experiments were carried out.The results showed that there were significant differences in germination index,fresh root weight and main root length between the new coating mixing device and the existing coating mixing device.In the germination index,treatment 1 increased 19.87%compared with control group,treatment 2 increased 10.51%compared with control group,and treatment 1 increased 8.5%compared with treatment 2;In the root fresh weight index,treatment 1 increased by 18.78%compared with the control group,treatment 2 increased by 6.76%compared with the control group,and treatment 1 increased by 11.45%compared with treatment 2;In the main root length index,treatment 1 increased by 46.86%compared with the control group,treatment 2 increased by 5.36%compared with the control group,and treatment 1 increased by 13.75%compared with treatment 2.In the germination index,root fresh weight and main root length,treatment 1,treatment 2 and control ck were significantly different at 0.01 level,and treatment 1 and treatment 2 were significantly different at 0.05 level. |
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