Optimization and experiment on key parameters of dehuller for dried mung beans

Mung bean is one of the widely cultivated crops in China, and its yield and exports account were the first in the world. However dehulling technology and operation quality of mung bean have not been significantly improved over the long term due to insufficient attention. The poor qualified dehulling rate and dehulled mung beans rate restricted the development of mung bean industry. The unreasonable working parameters (speed of dehulling roller, speed of sand drum, operation time) of the dehuller were the main reason of this problem, which had a negative impact on operation quality. In this experiment, quadratic orthogonal rotation and response surface method were used to obtain the best operation quality, and key working parameters were optimized using Design-Expert. The properties of tested mung beans were analyzed, and the results showed that the color of the mung beans was dark green. With the moisture content of the mung bean at 9.2%, the thousand seeds weight was 63.5 g, and the length, width, thickness were about 5.70, 4.18, 4.33 mm respectively, the repose angle of mung beans was 23.71°, the crushing force of 60% mung beans was about 36 N. The data analysis of the dehulling experiment showed that primary and secondary factors for qualified dehulling rate was speed of dehulling roller > operation time > speeds of sand drum. Regarding to the dehulled mung beans rate, the order was: operation time> speed of dehulling roller > speeds of sand drum. The result of interaction analysis showed that the interaction between speed of dehulling roller and operation time had a significant impact on the qualified dehulling rate, while the interactions between other parameters were not significant. The interaction between speed of dehulling roller and operation time had a significant effect on dehulled mung beans rate, and the interaction between the speed of the sand drum and operation time also had a significant effect on dehulled mung beans rate. The optimal working parameters of dehuller for dried mung beans were speed of dehulling roller of 25.20 r/min, speed of sand drum of 1642.61 r/min, and operation time of 108.8 min. With the optimal working parameters, qualified dehulling rate and dehulled mung beans rate of the dehuller were 99.72% and 86.57%, respectively. The results of verification test and optimization result were highly consistent. Production tests were carried out 20 times in the factory according to the optimization results. With the optimal parameters applied by dehuller for dried mung beans, qualified dehulling rate and dehulled mung beans rate were 99.3% and 85.6%, respectively. The results of the production verifications were very close to the results got from the previous model results, and the quality of the dehuller improved greatly. This study is helpful for the improvement of the dehuller for dried mung beans.