Optimization of Coating Process Parameters for Pelleted Coating of Astragalus Seeds and Sowing Performance Tests

Astragalus seeds are characterized by irregular shapes, rough surfaces, and poor flowability, which often lead to missed seeding and repeated seeding under conventional sowing methods, thereby constraining the mechanization and precision level of Astragalus production. To address this issue, this study proposes the use of pelleted coating technology to improve the external characteristics of Astragalus seeds and systematically optimizes the coating process parameters. A simulation model of Astragalus seeds was constructed based on three-dimensional modeling and the EDEM discrete element simulation software. Using rotating disc speed, single powder-feeding amount, single liquid-feeding time, and pelletizing time as experimental factors, and the coefficient of dispersion and pelletizing qualification rate as evaluation indices, single-factor experiments were conducted to clarify the influence patterns of each factor on pelletizing quality. On this basis, a quadratic regression model relating the pelletizing qualification rate to the process parameters was established using the Box–Behnken response surface method, followed by analysis of variance and multi-factor comprehensive optimization. The results showed that rotating disc speed, single powder-feeding amount, and single liquid-feeding time had highly significant effects on the pelletizing qualification rate, while pelletizing time had a significant effect. The optimal combination of process parameters was determined as a rotating disc speed of 558 r/min, a single powder-feeding amount of 8.99 g, a single liquid-feeding time of 7.38 s, and a pelletizing time of 6.19 min, under which the pelletizing qualification rate reached 97.51%. Bench tests of an air-suction precision seed-metering device using the pelleted seeds showed a mean qualification index exceeding 85%, a missed-seeding rate below 5%, and a repeated-seeding rate below 8%, indicating that the pelleted seeds met the requirements of precision sowing under the tested conditions. The findings provide a theoretical basis and technical support for determining the coating process parameters for pelleted Astragalus seeds and for the development of precision sowing equipment.