The separation of walnut kernels from shells is a crucial step in walnut processing. Pneumatic sorting is the mainstream method. However, due to the overlapping suspension speeds of half-shells and eighth-shells, complete separation was not achieved. This paper proposes using a toothed vibrating screen to separate the two. Using EDEM to simulate and analyze the motion forms, collision processes, and stress conditions of walnut shells and kernels on the vibrating screen, the effectiveness of this method was demonstrated, and the mechanisms of shell–kernel retention and loss during the separation process were revealed. Results indicate that 1/8 kernels, being smaller, easily fall into tooth grooves and move upward step by step under the excitation force during reciprocating vibration. The 1/2 shells, being larger, are difficult to fall into the teeth grooves, and their smooth surfaces cause them to slide easily, moving downward continuously under the action of reciprocating vibration and gravity. Using the cleaning rate and loss rate as evaluation indicators, it was found that as the inclination angle of the vibrating screen increased step by step, the cleaning rate consistently increased monotonously. The loss rate initially rose slowly, then surged sharply after reaching 22°, at which point the loss rate was at its lowest, around 10%, and the cleaning rate was at its maximum, at 95%. The shortest retention time of walnut shells on the screen is 2.85 s, and the longest is 10.6 s, with the number of collisions being 458 and 2619, respectively; the collisions between the shells and the kernels account for 51.8%. The failure to thoroughly separate is due to the shell and kernel entangling within the separation area, making it impossible to segregate them. They enter the opposite region, collide, and cause loss and retention phenomena.

The low level of mechanization in the production process of cumin seeds is one of the primary factors limiting their yield and economic efficiency. To enhance the mechanization of cumin seed production, this study focused on cumin seeds as the research subject. Physical parameters of cumin seeds were determined through physical experiments; based on these parameters, a discrete element model of cumin seeds was established, and the shear modulus was calibrated using angle of repose tests. The established model was used to simulate the seeding process of a seed drill, the model’s accuracy was verified by analyzing the seed trajectory, movement velocity, seeding quality, and the dynamic angle of repose of seeds inside the drill. Results indicated that the collision recovery coefficient, static friction coefficient, and rolling friction coefficient between cumin seeds and ABS plastic, stainless steel plates, and other cumin seeds were 0.3, 0.35, and 0.21; 0.49, 0.39, 0.24; and 0.24, 0.38, 0.18, respectively. Calibration via simulated cylinder accumulation tests yielded a deviation of 0.28% between the simulated accumulation angle and the physical accumulation angle at a shear modulus of 100 MPa; the simulated seed trajectory during dispensing closely matched physical dispensing tests. The average deviation in particle drop velocity within the bridge channel region was 4.23%, with a maximum deviation of 6.07%; the average deviation in dynamic packing angle from start to finish for the particle group was 2.84%, with a maximum deviation of 4.18%; and the average mass discharged from the 14 simulated seed nozzles was 0.0446 g, compared to 0.043 g in physical tests, with a deviation of 3.72%. These results demonstrate the high accuracy and reliability of the established cumin discrete element model and its parameters, providing technical support for the design and optimization of full-process mechanical cumin production systems.

Shell–kernel separation is a critical stage in walnut processing; however, the presence of kernel loss and shell retention during separation markedly limits overall performance. In this study, discrete element method (DEM) simulations were conducted using EDEM 2022 software, in conjunction with experimental validation, to investigate the vibratory screening behavior of walnut shell–kernel mixtures under varying vibration frequencies and sieve surface inclinations. The underlying mechanisms of kernel loss and shell retention were elucidated by analyzing particle kinematics and contact characteristics, including velocity, collision frequency, and contact force on the sieve surface. The results indicate that both cleaning rate and loss rate exhibited an increasing trend with increasing sieve inclination. In contrast, as vibration frequency increases, the cleaning rate decreases while the loss rate increases. These findings reveal an inherent and irreconcilable trade-off between cleaning efficiency and material loss when solely adjusting operating parameters. Even under the selected operating conditions (vibration frequency of 14 Hz and screen inclination of 16°), the cleaning rate reached only 93.14% and 93.44%, while the loss rate remained as high as 14.74% and 19.92%, respectively. Mechanistically, kernel loss is primarily attributed to frequent particle–particle collisions during transport, which reduce kernel velocity and may even induce reverse motion, preventing effective recovery. Shell retention, however, arises from early-stage entrainment within dense particle beds and subsequent collision-driven migration toward the kernel outlet, ultimately hindering complete separation. Based on these mechanisms, an airflow-assisted reduction strategy was proposed and experimentally validated. Compared with the optimal single-factor operating conditions, the proposed strategy improved the cleaning rate by 2.04 and 1.74 percentage points and reduced the loss rate by 6.59 and 11.77 percentage points. These findings provide valuable references for the design and optimization of mechanized sorting equipment.