An innovative walnut cracker: Self‐grading and multi‐station extrusion mechanism with high efficiency

Abstract The walnut cracking process is the most critical and delicate step for achieving high‐quality kernels. The traditional method for cracking (manually) is labor‐intensive, time‐consuming, and tedious. The existing cracking approaches are low production efficiency and serious walnut kernel breakage. Increasing cracking efficiency with minimum kernel breakage has been a challenging issue in the preliminary processing of walnuts. Therefore, this study develops an innovative walnut cracker with self‐grading and multi‐station extrusion, combined with theoretical investigation and experiment verification. First, a statistical analysis of walnut physical properties was conducted, including dimensions, shell thickness as well as shape characteristics. The mechanical properties of walnut cracking were examined by a series of experiments. Based on mechanical theory, a grading mechanism was designed for preliminary processing before walnut cracking. Then a shaftless screw conveying mechanism and an extrusion cracking mechanism were developed. To evaluate the cracker's performance, a comprehensive examination was carried out. The experiments yielded impressive results, with a grading rate of 87.3%, a shell‐breaking rate of 91.50%, and a kernel‐exposed rate of 84.72%. These outcomes signify a substantial improvement in production efficiency while minimizing kernel breakage. The developed walnut cracker plays a crucial role in walnut processing and kernel extraction, thereby elevating economic value. Practical Application A self‐grading multi‐station extrusion walnut cracker is developed, which includes a grading mechanism with a shaftless screw conveyor and a grid‐type trommel screen for conveying and classifying walnuts. This cracker can adapt to different walnut varieties by changing the gap‐adjusting guide to control the breaking gap. Compared to similar extrusion‐type walnut crackers, the developed cracker not only incorporates preliminary classification but also exhibits superior performance. Highlights A novel multi‐station extrusion mechanism for walnuts cracking is developed. The cracker can accommodate various walnut sizes for self‐grading and screening. The design with semi‐arc plates converts extrusion force into alternating stress. The shell‐breaking rate and kernel‐exposed rate achieves 91.50% and 84.72%.