鲜莲子低损伤单颗连续送料系统设计与试验

Design and experiments of the sequential and continuous feeding system for fresh lotus seeds with low damage

针对鲜莲子在机械去心自动送料过程中存在的堵料和机械损伤问题,该研究提出一种采用气流辅助的鲜莲子振动送料方法,实现向去心工位单颗连续送料。该系统通过间歇喷气与振动,使鲜莲子有序进入出料溜槽实现连续送料;通过控制下料管底端至输送链条滚轮顶端的间距以及下料管的开槽长度,实现不同大小鲜莲子的单颗输送。采用离散元法对鲜莲子振动送料过程进行仿真,分析了振动送料盘结构、振动频率对送料连续性的影响,及不同气嘴布置位置对振动送料盘内部流场分布的影响。试验结果表明:在相同振动频率下,振动送料盘气嘴外侧布置的空工位率较内侧布置低,送料连续性更好;随着振动频率增大,空工位率降低,莲子损伤率增大。试验获得的最优工艺条件为:采用圆弧Ⅱ型振动送料盘,气嘴布置在振动送料盘外侧,振动频率12Hz。在该工艺条件下,空工位率为0.37%,单颗输送率为99.67%,莲子损伤率为0.2%,满足鲜莲子加工要求。研究结果可为鲜莲子送料系统设计及优化提供理论依据。

Lotus seeds have been commonly consumed as functional food and traditional Chinese herbal medicine. However,the congestion and damage often occur in the automatic feeding process of the mechanical plumule removal for fresh lotus seeds. In this study, an airflow stirring-assisted vibrating feeding system was proposed to realize the sequential and continuous feeding to the plumule-removing post. Firstly, the feeding system consisted of the linear vibrator, the vibrating feed tray, the stirring nozzles, the feeding pipes, and the roller chain. An intermittent jet and vibration were also utilized to make the lotus seeds enter the discharge chute in an orderly manner for continuous feeding. Specifically, the movement of the roller chain was combined to realize the sequential delivery of fresh lotus seeds of different sizes, particularly at the appropriate distance h between the feeding pipe and roller, and the length L of the slot set on the feeding pipe. The feeding failure was avoided by two fresh lotus seeds when entering the same station, where the distance h was in the range of 3 mm to 4.33 mm. Besides, the large-size lotus seeds were also smoothly sliding out from the feeding pipe, where the length L was 8 mm. In addition, the feeding pipe was made of elastic silica gel(Shore hardness was 50), in order to prevent the lotus seeds from mechanical damage. Secondly, the discrete element method(DEM) was used to simulate the vibrating feeding process of fresh lotus seeds.Some factors were also determined, such as the structural parameters of the vibrating feed tray, and the vibration frequency of the continuity of fresh lotus seeds feeding. The simulation results show that the congestion rate of vibrating feed trays with different structures decreased significantly, with the increase of the vibration frequency. The average congestion rate of the circular arc II vibrating feed tray was 2.06%. Once the vibration frequency was higher than 12 Hz, the congestion rate basically tended to be flat, and then the ever increasing frequency also posed no outstanding effect on the congestion rate. Therefore, the vibration frequency was reduced for better continuous feeding. Hence, the circular arc Ⅱ type vibrating feed tray was selected as the preferred structure, where the optimal vibration frequency was 12 Hz. In addition, the FLUENT software was used to analyze the effect of the nozzle position on the internal flow field distribution of the vibrating feed tray. When the air nozzle was arranged on the outside, the air flow from the air nozzle quickly flowed down the splitter plate, indicating a uniform and stable speed. The direction of the airflow was exactly aligned with the lotus seeds on the inner side, which greatly contributed to pushing the lotus seeds away for better stirring. The air flow inside the discharge chute was more uniform for the better continuous feeding of the lotus seeds. Finally, the actual feeding test was carried out to clarify the effect of the nozzle position and the vibration frequency of the optimal vibrating feeder(circular arc Ⅱ type vibrating feed tray) on the continuity of fresh lotus seeds feeding. The results show that the better feeding continuity was achieved when the stirring air nozzle was arranged on the outer side of the vibrating feed tray, and the vacancy rate was lower than that on the inner side. The vacancy rate decreased gradually, whereas, the breakage rate of fresh lotus seeds increased at the same time, as the vibration frequency increased. The optimal process conditions were achieved for the sequential and continuous feeding without damage to fresh lotus seeds, where the air nozzle was arranged on the outside of the vibrating feed tray, the vibration frequency was 12 Hz, the slot length of the feeding pipe was 8 mm, and the distance between the roller and the feeding pipe was 3.5 mm. Under these process conditions, the vacancy rate was 0.37%, the sequential delivery rate was 99.67%, and the breakage rate of fresh lotus seeds was 0.2%, fully meeting the requirements of lotus seed plumule-removing equipment. The findings can provide a strong reference to optimize the feeding system of fresh lotus seeds, or granular agricultural products.