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

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%.