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Rice grains breakage during hulling in a rubber roll huller influences the desired final rice quality and thus its economic value. Clarifying the grains breakage mechanism in the hulling process is the key to reducing the breakage ratio and improving quality. The breakage mechanism was clarified by quasi-static compression, three-point bending, compression-shear and hulling tests. The results show that rigid compression and three-point bending breakage cannot be used to characterise grains breakage mechanism in the hulling process, and flexible compression cannot break grains. The breakage mechanism involved is flexible compression; the application of shear load rotates grains resulting in the action of bending and shear and this finally produces bending tension and shear failure. Shear force and pressure increase with the increase of shear direction, resulting in increasing breakage ratio. • Rice grain breakage is not caused by excessive pressure in the hulling process. • Shearing force is closely related to the grain breakage in the hulling process. • Grain breakage is caused by bending tension and shear breakage. • Limiting the rotation of grains can reduce breakage ratio in the hulling process. [ABSTRACT FROM AUTHOR]

Aerodynamic separation of rice husks from brown rice grains after paddy husking is one of the important processes in rice processing. So far, the realisation of complete separation of rice husks from brown rice is still a challenging task. In this study, computational fluid dynamics (CFD) and discrete element method (DEM) were used to simulate the process, and the simulation results were verified by experiment. Based on this, the process of the separation of rice husks from the mixture was clarified. The mechanisms of brown rice loss and the rice husk retention were explored by analysing the collision process of the husks and rice in the separation duct. The interaction between mixture particles and airflow was explored. The results show that feeding of the mixture particles led to the decrease in the airflow velocity; however, it did not disturb the airflow stability or produce obvious turbulence. Adjustment of airflow velocity significantly influences the separation; nonetheless, incomplete separation of rice husks and brown rice still remains. The mechanism of brown rice loss and rice husk retention in the separation process occurred simultaneously to some extent in the separation region. As a result, brown rice and rice husk entered the opposite regions and collided with each other in their opposite region, respectively. • The separation process of mixture particles was studied by DEM-CFD simulation method. • Feeding mixture doesn't disturb the airflow stability and produce turbulence. • Adjusting the airflow can not solve the problem of incomplete separation. • Brown rice losing is caused by rice husk collision. • The rice husk remaining is caused by brown rice coercion and collision. [ABSTRACT FROM AUTHOR]

The orientation of paddy grains during hulling is one of the main factors that determines the one-time hulling ratio and breakage ratio during processing with rubber rollers. Understanding the adjustment mechanism of paddy grain orientation angle in feeding process is the key to controlling the orientation angle, but the mechanisms involved remain poorly understood. The feeding process using an inclined plate feeder was simulated using the discrete element method (DEM). The effect of the inclination angle of the long feeding plate was analysed and the requirements for an adjustment mechanism were clarified. The results showed that the uniformity of inclination angle of paddy grains decreased with the increasing inclination angle for the long feeding plate. The results showed that the regular movements of paddy grains were controlled by shear action of paddy grain flow. The depth of the grain layer determines the distribution of paddy grain orientation angle. This study could provide guidance for the design and optimisation of feeding systems and help understand the adjustment mechanism requirements for orientating non-spherical grains in grain flow • Adjustment mechanisms of orientation angle of paddy grain examined numerically. • Paddy grains rotate around one of their vertices. • Regular rotational motion is caused by the shear action of the grain flow. • Number of flow layer determines the change of orientation angle. • Regular rotational movements can align orientation angle to flow direction. [ABSTRACT FROM AUTHOR]

The low ratio of one-time hulling is one of the main factors restricting the development of rice processing. Understanding the hulling mechanism and the effect of feeding direction of paddy grain on the hulling performance is the key to increasing the one-time hulling ratio of rubber roll hullers, but the mechanism remains poorly understood. In this work, the effects of the feeding direction on rotation movements were explored using the discrete element method (DEM), observing the microstructure of paddy grain, and conducting the static shearing experiments. The effect of feeding direction on the hulling ratio and hulling pattern were investigated. The results showed that rotation angle increases as feeding direction increases and the axis of rotation of the grain changes from the short to long axis. This difference in rotation leads to differences in the shearing effect of the rubber rolls on the apexes of the grain. From the microstructure of the grain it can be seen that the grain core is wrapped by the lemma and palea under a process of bonding and interlocking. The experimental results show that the process of hulling destroys bonding and interlocking by a shearing action. Therefore, hulling ratio changes with changes in feeding direction. The results were confirmed by hulling experiments using a rubber roll huller and it was verified that feeding direction has a significant effect on the breakage ratio. • The mechanism of hulling is to release the bond and the interlocking between lemma. • Different feeding direction affects stresses and rotation of paddy in hulling process. • Hulling performance is related to the feeding direction of paddy grain. • The vertical feeding of paddy can effectively increase hulling performance. [ABSTRACT FROM AUTHOR]