Study On Mechanism Of Hulling Breaking And Separation Loss And The Process Optimization For Rubber Roll Huller

Rice is one of the most important food crops in the world.Reducing losses in rice processing is of great significance for ensuring food production and national food security.Rice hulling is one of the main stages that lead to a decline in the yield and quality of rice processing.During this stage,about 95%of rice manufacturing enterprises use rubber roller hullers for rice hulling.The prominent problems of this process are low one-time hulling rate,high brown rice breakage rate,and incomplete separation of shell and brown rice mixture.Specifically,in the process of rice hulling,about 10-20%of the paddy grain needs to be repeatedly hulled,and the broken rate of brown rice generally exceeds 5%.It can be seen that the losses caused by the large total yield of staple grains are staggering;The phenomenon of brown rice loss or rice husk retention in rice processing is also one of the main factors leading to grain losses and declining economic benefits,and is an urgent problem to be solved in the rice processing industry.The key to solving the problems is to reveal the shelling mechanism,the broken characteristics of brown rice,and the reasons for incomplete mixture separation.Conducting in-depth research on rice hulling issues not only provides optimal design guidance for achieving the goals of improving hulling rate,reducing crushing rate,and completing primary air separation of rubber roller rice hullers,but also provides theoretical basis and research methods for hulling research on other shelled crops.In this paper,the hulling process of rubber rolled rice hulling is studied.Firstly,the hulling principle is analyzed,and the breaking mechanism and influencing factors of brown rice during hulling are explored.On this basis,the distribution and adjustment mechanism of orientation angle of the paddy grains are explored,so as to explore the direction for the optimization design of the feeding system structure.Study the mixture separation mechanism,and explore the optimization design method of step flow plate based on the mixture separation mechanism.Theoretical analysis,simulation,and experimental verification were used to study the hulling,crushing,and air separation of rubber roller hullers,and structural optimization and pilot test verification were conducted.The specific research conclusions are as follows:（1）Reveal the breakage mechanism of brown rice.The breakage mechanism of brown rice in the hulling process is that pressure and shear force make the paddy particles rotate,resulting in bending tension and shear stress,and brown rice is broken when it exceeds the stress limit.The effective way to reduce the breakage rate and increase the hulling rate is that to make the angle between the long axis of paddy grains and the roll shaft is 90°during the paddy entering the hulling area,to limit the rotation of paddy grains,reduce the bending tension and shear stress of brown rice,and make the shear force most efficiently used to rub and tear the rice husk,so as to improve the hulling rate and reduce the breakage rate.（2）Adjustment mechanism of paddy grains orientation angle.The adjustment mechanism of paddy grains orientation angle is that the shear occurs between the grain stratospheres due to the velocity difference,and the driving particles rotate.When the rice grain stratosphere thickness N≥1,the rice long axis is gradually parallel to the flow direction,which is beneficial for the particles to enter the rice hulling area with 90°orientation.When the inclination angle of the feed plate is large,it is difficult to form a stable rice accumulation,which is not conducive to the adjustment of orientation angle.When the inclination angle is small,it is not conducive to the acceleration of the particle group,and it is difficult for the particle group to enter the hulling area quickly.（3）Feed plate design and parameter optimization.Based on the adjustment mechanism of paddy grains orientation angle,a parabolic flow feed plate is designed,which can provide the accumulation area for the paddy particle group and make the paddy particle group have a certain acceleration region.Through parameter optimization,the better feeding effect can be obtained when the inclination angle of the accumulation area is 35°,the length is 200 mm,the v₀is 0.6 ms^-1,the end tangent angle is 68°and the total length of the flow plate is 900 mm.The S can reach about 0.183,and the velocity of paddy particles reaches 3.245ms^-1,which realizes the optimal adjustment of paddy particles orientation angle.（4）Reveal the causes of rice husk retention and brown rice loss.Under the optimal airflow velocity,the loss of brown rice and the retention of rice husk are caused by the interdoping mixture and not sufficiently segregation on the conveying plate.When entering the separation area,the rice husk and brown rice collide with each other under the action of the airflow.It is difficult to solve the problem of incomplete separation between rice husk and brown rice only by adjusting air velocity.（5）To clarify the segregation mechanism of rice husk and brown rice mixture.The rice husk and brown rice mixture segregates naturally in the chute flow,and the segregation degree（DOS）decreases with the increase of the chute Angle.The segregation mechanism is that the surface roughness and density of rice husk and brown rice are different,which makes it easier for the brown rice to flow to the bottom cavity,and the rice husk is trapped in the upper layer.Therefore,further segregation of the rice husk and brown rice at the bottom requires more space for vertical particle flow direction of the mixture,allowing the brown rice to move downward more fully.（6）Design and parameter optimization of ladder feed plate.Based on the segregation law and mechanism of rice husk and brown rice in chute feed plate,the design of ladder feed plate can effectively improve the segregation degree of brown rice and rice husk and reduce the number of bottom rice husk.When the angle of ladder feed plate is 30°,the step height is 1.86 times the length of brown rice（about 13 mm）,and the length of the running board is 400mm,the DOS at the exit of the feed plate can be increased to 0.9.（7）Rice hulling performance verification of rubber roller huller.Based on the improved structure and optimized parameters,parabolic and ladder rubber rolls paddy hulling platforms are constructed and paddy hulling tests are carried out.Husking performance has been improved remarkably.In the husking test,the one-time husking rates of long,medium and short rice have been improved by 54.8-61.2%,63.1-71.1%and 78.8-91.2%,respectively,and the breakage rates have been reduced by 13-23%,28.6-39.4%and 45-51%.The retention rate of rice husk and the loss of brown rice can meet the requirements of the regulation.The details results are as follows:retention rate of rice husk are 0.51%,0.5%,0.46%,respectively;the loss of brown rice are 0.67（total 2 grains in 10 groups）,0.33（total 1 grains in 10 groups）,1（total 3 grains in 10 groups）,respectively.The research results of this study can provide reference for further study on the mechanism of hulling and the improvement of hulling rate,the reduction of breaking rate and the optimization design of one-time air separation for industrial hulling machine.