Numerical simulation and experimental study on the pelletized coating of small grain forage seeds

Abstract: Pelleting coating can be widely used to improve the accuracy and emergence rate of mechanized precision sowing of seeds in modern agriculture. There are low quality and qualification rates of pelleting during pelleting, due to small particle size and irregular shape. In this study, a theoretical analysis was implemented to determine the motion process and force of seed powder particles during pelleting. A mechanical interaction model between the seed powder particles and coating pot was also established to obtain the main influencing factors on the seed coating quality. Taking the red clover seeds as the research object, the subject was then modified for the numerical simulation of Hertz-Mindlin with the JKR model in EDEM software. Specifically, the macroscopic and microscopic characteristics of particle flow were also obtained in the coating pot, in order to reveal the seed movement and the mixing effect of seed powder. The mixing of materials in the coating equipment was selected to simulate the seed movement using EDEM software, in order to explore the influence of structural parameters on the mixing effect of seed powder. Furthermore, a single-factor test was performed on the coating machine under different diameters, the edge inclination angle, and the speed. The coefficient of variation of the powder decreased monotonously with the increase of the coating time. Nevertheless, there was no variation in the coefficient of variation after the mixing process lasted for a period of time. The particles reached a better mixing degree during this time. Box-Behnken optimization test was carried out with the coefficient of variation as the evaluation index, while the casting disc diameter, the edge angle, and the speed of the coating machine as the influencing factors. The optimal combination of the parameter was obtained: The casting disc diameter of the coating machine was 309.9 mm, the edge Angle of the coating machine was 61.9°, and the speed of the coating machine was 10.1 r/s. The seed pelleting coating test was carried out on the physical test platform, where the average pellet coating pass rate of the optimized coating pot physical test increased from 78.6% to 93.1%. The results showed that the developed pelletizing coating machine fully met the relevant industry standards in practical production. The seed pelleting coating quality was further optimized after the experiment. The qualified pelleting rate differed greatly between different batches, in order to explore the influence of powder and liquid on the seed pelleting coating in the process of bonding. The orthogonal test was conducted on the process parameters for the pill granulation coating machine. The best combination of process parameters was obtained with a single powder supply of 10 g, a single liquid supply of 15 mL, and a coating time of 7 min. The single power supply was the most significant influencing factor on the test after the extreme difference analysis, while there was less influence of coating length on the test. Consequently, the seed pelletizing coating test can be expected to obtain high quality with the optimal combination of working structure and process parameters. The finding can also provide a strong reference basis for the irregular seed coatings.