Experimental Research of Walnut Hulling and Kernel Extraction Based on Shearing and Extrusion Mechanism

A flexible belt shearing and extrusion system for walnut shell crushing, kernel extraction, and shell–kernel separation was used to study the effects of hulling and kernel extraction from incompletely cracked walnuts. A one-factor test was conducted to explore the influences of upper–lower belt spacing (A), speed difference (B), and upper belt tension (C) on hulling. An orthogonal experiment was also designed to analyze the influences and determine the optimal configuration of the three factors. According to the experimental results, the influences of the three factors follow the trend of A>C>B for kernel exposing ratio I and II and C>A>B for kernel-breaking ratio and unreleased kernel ratio. The optimal hulling effect can be obtained with a kernel exposing ratio I of 77%, kernel exposing ratio II of 16.7%, a kernel breaking ratio of 4.3%, and an unreleased kernel ratio of 2% (hulling ratio=98% and unbroken kernel ratio=93.7%) when A=14 mm, B=0.19 m/s, and C=231 N. This study provides a foundation for the development of more efficient walnut processing technologies.