Analysis of the hulling mechanism for the buckwheat and improvement of texture of hulling unit

Buckwheat shucking has been one of the important technologies during processing. At the same time, a large number of efforts have been focused mainly on the design of buckwheat shucking machines, in order to explore the best shucking parameters. Among them, the upper and lower sand tray-type buckwheat sheller has been widely used in recent years, because of the high processing efficiency and excellent sheller performance. The optimal sheller parameters have also been explored on the upper and lower tray-type buckwheat sheller. However, it is unclear on the mechanism of the buckwheat rolling sheller. The low accuracy of the sheller gap and the strong random posture of buckwheat sheller have led to the low efficiency of a single sheller and the high rate of broken kernel after the sheller. This study aims to carry out the analysis and experimental investigation of the buckwheat hulling mechanism. The 6QB-150 buckwheat sheller was taken as the research object. The specific mechanism of the buckwheat hulling and mathematical modeling was proposed to determine the possible hulling posture of buckwheat during hulling. The mathematical model was established to compare the husking mechanism of the grinding and the end pressing and tearing. The grinding was suitable for the case, where the gap between the upper and lower sand pans was slightly smaller than the equivalent particle size of the material; The end pressing, tearing, and rolling were suitable for the case, where the gap between the upper and lower sand tray was slightly larger than the equivalent particle size of the material and smaller than the length of the material. Engineering discrete element method (EDEM) software was used to analyze the motion state of the buckwheat husking. After that, the husking unit was improved to explore the influence of different texture structures on the husking. EDEM simulation analysis showed that the regular structure of surface texture was added into the working interval of the upper sand tray under the same shucking gap condition. There was an increased friction coefficient between the buckwheat shell and the upper sand tray. The movement speed of buckwheat was effectively regulated in the process of shucking. The stability of buckwheat movement was improved for the high efficiency and quality of the machine during shucking. The damage of buckwheat kernel was also reduced during shucking. Finally, the husking performance test was carried out on the buckwheat with the equivalent particle size (similar to the width and height of buckwheat) from 4.6 to 4.8 mm. The results showed that there were similar kernel breaking rates and significant differences in the kernel whole rates, indicating that the texture structure had a great influence on the husking efficiency. The angle of the shucking mechanism showed that the efficiency of the grinding and rolling was lower than that of end pressing and tearing. Therefore, the appropriate shucking gap should be selected for the most buckwheat at the end pressing and rolling state in actual production. When the shucking gap was greater than or equal to the equivalent diameter of buckwheat and less than the length of buckwheat, the end pressing and tearing were the dominant mechanisms with the highest shucking efficiency. In addition, the triangular texture was used to improve the surface texture in the working area of the upper sand tray, when the rotating speed of the upper sand tray was 950 r/min and the shucking gap was 4.9 mm, the kernel integrity rate of a single shucking was 44.03% and the kernel breaking rate was 5.59%. Compared with the unimproved shucking unit, the regular structure of the triangular convex significantly reduced the randomness of the buckwheat shucking attitude. The single peeling rate of the kernel also increased 16.98%.