| Maize is one of the main grain crops in Heilongjiang,and the bowl-tray seeding cultivation technique is the main way to increase maize yield.The soil mixture for cultivating maize seedlings with industrial and agricultural residue is an effective means to protect farmland and reduce farmland land consumption.Mixing soil mixture by manual work can not meet the need for mass production,so it is significant to develop a mixing machine for soil mixture.The Gravity mixer has the advantages of high working efficiency,wide application,covering a small area,easy to move and low price.Therefore,based on the gravity mixer,the size of the mixing drum,the speed of the mixer,the form of the mixing blades,and the installation angle were optimized,and the mixing process of soil mixture for cultivating maize seedlings mixer was simulated and analyzed by using EDEM software.And then the optimal simulation results were used to improve the mixer,and the test was performed to verify the simulation results.The main research work in this paper is as follows:(1)The density,three-dimensional dimension,stacking angle,plasticity index and other physical properties of particles of soil mixture for cultivating maize seedlings were tested,and the specific parameters of soil mixture were obtained.All data were provided for particle modeling in the discrete element method simulation of soil mixture for cultivating maize seedlings.(2)The dynamtic characteristics of solid particles in the soil mixture for cultivating maize seedlings were summarized and analyzed,and the mixer was designed according to the physical characteristics of the soil mixture.The self-falling type was determined for the mixer.The key parts of the mixer,such as the mixing drum,the shape of the mixing blade,the installation angle of the mixing blade and the rotation speed of the mixer were optimized.Solidworks2018 was used to build three-dimensional model for mixer and virtual assembly,and no component interference phenomenon occured.(3)The mixing process of soil mixture for cultivating maize seedlings in mixer was simulated and analyzed by the discrete element EDEM2018.The particle model was established according to the physical characteristics of the soil mixture after the three-dimensional model of mixer was imported.The influence factors of the simulation test are the rotation speed of mixer,the number of the stirring blades and the installation angle of the stirring blades.the quadratic regression orthogonal combination experiment with these three factors and three levels was carried out to evaluate the uniformity of soil mixture.The same best combination of simulation parameters was obtained by evaluating the largest dosage of phosphogypsum and the least dosage of cornstalk powder by mass respectively.Design-Expert11 software was used to analyze the response surface,and the result of the simulation was optimized.The same central point is obtained: the soil mixture arrived the best uniformity when the speed of the mixer is 30r/min,the corresponding number of blades is 4 and the blade mounting angle is 20°.All these provided the concrete parameter basis for the subsequent mixer optimization and improvement.The factors order is: the blade installation angle > the number of blades >the rotation speed of mixing drum.(4)Based on the results of simulation and analysis,the key parts of the mixer were improved,and the mixing effects of the mixer before and after improvement were tested respectively.The results show that the mixing uniformity reaches 92.41% and the mixing effect is improved by more than 10%.The mixing uniformity of the improved mixer was compared with the simulation results.And the error between the optimized mixing uniformity and the simulation results is 1.52% to2.48%.All the work in this paper can provide technical support for the whole mechanized development of maize seedling cultivation. |
