摘要：
Seed pelleting coating is an important step in the pretreatment of forage seeds, and understanding the dynamic process of pelleting can better set up coating parameters and improve the qualified rate of pelleting. In order to understand the characteristics of pelleting movement of pelleted seed coating machine, the dynamic movement law of pellets needs to be studied accurately. The theoretical analysis, simulation and experimental verification of the BYW-400 type vibrating pelleting machine for wheatgrass seeds were studied. Based on Hertz contact theory, the vibration model and rotation model of single particle impact workpiece surface were established for vibration coating of pill coating machine. Meanwhile, the flow characteristics of material flow were analyzed. The results of theoretical analysis showed that the pelleting of wheatgrass seeds was related to the collision depth, maximum load, roughness of material flow and the thickness of cohesive bottom. The introduction of vibration can change the speed and increase the inertia force. Thus, the collision depth and maximum load of seed and powder were affected, the roughness height was increased. Besides, the turbulent flow property was enhanced, and the movement complexity between particles was increased. At the same time, the mixing degree between seed powder was improved, and the qualified rate of seed pelleting was finally improved. The same solution can be achieved when the pot body angle should not be smaller than the natural feet of the material, otherwise the material would stick on the pan surface, and lost the role of rolling together with its rotation. So it was necessary for us to choose the right size of the dip angle. The analysis of material flow characteristics showed that the introduction of vibration can increase the inertia force and increase the Reynolds number, which can improve the turbulent flow property, increase the irregular movement degree between particles, and improve the qualified rate of seed pelleting. In addition, EDEM software was used to simulate the simulation which the vibration intensity was 21% and no vibration and different tilt angles were simulated by 10 s, respectively. At the same time, the trajectory curve was plotted. The simulation results were analyzed by mixing degree, and the broken line diagram was obtained. Besides, the specific data was used to reflect the quality of mixed pelleting. The simulation results were consistent with the theoretical analysis, and the effect of vibration and inclination angle on the results of coating pelleting was verified. In addition, the effect of vibration and rotation angle was determined by coating single factor contrast experiment. Single factor experiments with six different factors were carried out, and the average value of each group was calculated many times. The qualified rate(the percentage of the coated area more than 80% particles accounting for the total number of samples and the weight is 7~10 times that of the original), seed rate (the percentage of the pelleted seed to account for the percentage of the total) and single seed rate(the percentage of the pelleted seed only 1 grains account for the total number of the samples) of pelleted seeds were calculated as the evaluation index of coating quality. When the speed of coating machine was 48.6 r/min., the dip angle of coating pot was 40.3° and the vibration intensity was 21%, the qualified rate of pelleting was 89.5%. Therefore, the change of vibration intensity can obviously affect the rate of pelleting. When the tilt angle of the coating pot was about 45°, the qualified rate of pelleting reached 89.7%. Thus, the dip angle of the coating pot was 45°, which was an ideal coating state. The results provide reference for the coating of irregular seeds.%为探究冰草种子丸化包衣运动特性,揭示冰草种子丸化包衣机理.该文采用理论分析、数值模拟、试验验证相结合的方法,研究冰草种子丸化规律及运动特性.建立了基于Hertz接触理论的振动模型与转动模型,对物料流流动特性进行了分析.利用离散元仿真软件EDEM对振动强度为21%和无振动以及不同的包衣锅倾斜角度进行10 s模拟仿真及其混合度分析,并通过单因素对照试验验证了丸化包衣中振动和转角对丸化合格率的影响.研究结果表明:冰草种子的丸化与种子和粉料的碰撞深度、种粉间的最大载荷、黏性底层厚度有关;振动的引入,可以改变速度的大小,提高湍流流动性和颗粒间运动复杂程度,最终可以提高种子丸化合格率;包衣机在包衣锅转速为48.6 r/min、包衣锅倾角40.3°的情况下,改变振动强度可以明显影响丸化率,且当振动强度为21%、倾斜角度约为45°时,丸化合格率能达到89.5%.该研究为揭示冰草种子丸化包衣机理提供参考依据.
