Numerical Simulation and Experimental Study of a Pelletizing Coating Machine for Astragalus membranaceus Seeds

To address the poor coating quality and low efficiency of Astragalus membranaceus seed pelletizing, this study combined theoretical analysis, DEM simulations, and experiments. The motion and force conditions of seed-powder particles were analyzed to identify key parameters. Using the coefficient of variation (Cv) as the evaluation index, the disc diameter, pan edge inclination, and rotational speed were optimized via response surface methodology. The optimal structural parameters were 605.5 mm, 15.7°, and 20.3 r·s−1. Liquid adhesion was represented by a custom time-varying cohesion model in DEM. Physical experiments showed that the optimized structure increased the pelletization qualification rate from 74.8% to 94.3%. Orthogonal experiments further optimized the process parameters: a single powder feed of 20 g, a single binder solution feed of 25 mL, and a coating duration of 8 min, achieving a qualification rate of 98.3%. Seedling emergence tests revealed that pelleted seeds had a significantly higher emergence rate (97.6%) than non-pelleted seeds (67.3%). These findings provide theoretical and technical references for pelletizing the coating of irregularly shaped seeds.