Design and Key Parameter Optimization of Conic Roller Shelling Device Based on Walnut Moisture-Regulating Treatments

The quality of walnuts deteriorates owing to the poor quality of the shelling equipment. The improvement of shelling quality is urgently required for walnut processing. In this study, systematic research was carried out on the changes in walnut mechanical properties, mechanical model of walnut shelling, and the key parameters of the equipment. The key parameters were determined as the angles of the shelling conic roller (X-1), speeds of the shelling conic roller (X-2), clearance between the shelling conic roller and the static roller (X-3), and the moisture content of walnuts (X-4). The Box-Behnken design method was used for the experimental design, an analysis of variance was applied to determine the graded significance of each variable on the rate of high-quality kernel (RHQK) and rate of shell rushing (RSC), and the multi-objective optimization method was used to obtain the optimal parameters for RHQK and RSC. The ranking of factors affecting RHQK and RSC were: (X-3) > (X-4) > (X-2) > (X-1) for RHQK, and (X-2) > (X-3) > (X-4) > (X-1) for RSC. The ranks of significant interactive effects among the factors were as follows: (X-1 X-2) > (X-2 X-3) for RHQK and (X-2 X-3) > (X-3 X-4) > (X-2 X-4) for RSC. The multi-objective optimization results showed that the optimal combination was X-1 = 15.83 degrees, X-2 = 17.93 rpm, X-3 = 45 mm, and X-4 = 9.5%, yielding RHQK = 84.54%, and RSC = 99.15%. The verification test of the optimal results further illustrates the accuracy of the optimization. The obtained results showed that the quality of walnut shelling can be improved by adjusting the moisture content of walnuts and optimizing key parameters of the equipment. This method also represents a potential solution for improving the shelling quality of other nuts.