Parameter Optimization and Performance Validation of a Cone-Type Macadamia Nut Sheller Based on the Discrete Element...

This study investigates the shelling characteristics of macadamia nuts using the discrete element method (DEM), aiming to improve the shelling rate and whole kernel rate. First, the three principal dimensions (hilum, width, and horizontal directions) of macadamia nuts from Lincang, Yunnan, were measured using a caliper. A universal testing machine was used to measure the shelling force and contact characteristics of the nuts. An EDEM model with BondingV2 adhesive bonds was developed and validated through cylinder-lifting experiments, with a simulation error of less than 5%. Single-factor simulations were conducted to evaluate the effects of equipment parameters. Using rotational speed, pitch, taper ratio, and thread turns as factors and whole kernel rate and shelling rate as response variables, a four-factor, three-level Box-Behnken experiment was performed. The results showed that the factors affecting the whole kernel rate, in descending order, were thread turns, pitch, rotational speed, and taper ratio; for the shelling rate, the order was thread turns, rotational speed, pitch, and taper ratio. Optimization using Design-Expert indicated that, at a rotational speed of 129 r/min, a pitch of 32.8 mm, a taper ratio of 0.097, and 1.3 thread turns, the whole kernel rate reached 79% and the shelling rate reached 94.3%. Bench tests of the prototype yielded a whole kernel rate of 78% and a shelling rate of 91%, with relative errors of 1.28% and 3.63%, respectively, verifying the reliability of the simulation results. PRACTICAL APPLICATIONS: A macadamia nut sheller with a taper-ratioed rotating cylinder based on the discrete element method (DEM) was developed. The device includes a compression-based shelling mechanism composed of a rotating cylinder and a stationary cylinder, as well as a spacing control unit consisting of adjustable bolts for shelling operations and parameter tuning. By adjusting key parameters such as rotational speed, pitch, taper ratio (of the rotating cylinder), and the number of thread turns, the sheller enables precise control of the shelling process, accommodating the hardness and size variability of macadamia nut shells. Compared with similar shelling devices, this sheller not only achieves parameter optimization through a BondingV2-based DEM model but also demonstrates superior shelling performance.