Semi-Theoretical Analyses on Mechanical Performance of Flexible-Belt Shearing Extrusion Walnut Shell Crushing

Abstract

<abstract> <b><i><ext-link ext-link-type=uri xlink:href=http://dict.youdao.com/w/abstract/>Abstract</ext-link></i></b> To complement the process of breaking walnut shells with mechanical approaches, a walnut shell-kernel separation device was designed. Stiffness at different positions of the walnut shell was analyzed by the theory of elastic mechanics, which contributed the critical force of instability of different positions. The internal force and deformation of the walnut shell upon extrusion were analyzed by the theory of thin shells. The results showed that the position at which the forces are concentrated is the point of fracture. The critical force of cracking and breakage at different positions of the walnut shell were reported. Based on the flexible-belt shearing extrusion breakage system, conditions for the walnut entering the extrusion space as well as the squeezing-in angle (?₀) and the extrusion angle (?) of the walnut during breakage were assessed theoretically and empirically. Results show that when 0°<?₀?44°, the walnut can enter the extrusion space. When the upper working belt (i.e., the squeezing roller) is 23 mm away from the lower working belt, walnut shells crack when ? is 20° and break when ? is 15°. A mathematical model of extrusion force and shear force on walnut shells by upper and lower working belts was built theoretically. Conditions for crack extension after walnut shell breakage were analyzed and calculated by the fracture mechanics theory. The results demonstrated when the mean crack length is 20 mm, the critical external force for crack extension is 19.1 N.