Research On Hulling And Crushing Mechanism Based On Structure Property Of Rice Paddy

Rice is one of the three major food crops in China,its production is related to the initiative of Chinese food security.With the rapid development of manufacturing industry,rice paddy has been realized completely mechanized in harvesting,circulation and processing,which has also caused the increase of broken rice rate of grains,not only causing non-essential economic loss,but also reducing rice paddy quality.Hulling process is the first process to produce broken rice,and rubber roller huller is the most widely used hulling equipment in this process,and in view of the problems of low one-time hulling rate and high broken rice rate of paddy in rubber roller huller,it is significant to understand the crushing mechanism and hulling process of rice paddy at this stage for subsequent processing.In this study,based on the physical properties of rice paddy,the mechanical properties of rice paddy under different loading mechanisms were analyzed in-depth,the main factor causing rice grain breakage under the hulling condition was clarified,and the microscopic hulling mechanism of rice grain in the hulling process was obtained through a self-designed hulling test device,which provided a theoretical basis for reducing the rice grain breakage rate in the hulling process and improving the one-time hulling rate.Main conclusions of this paper are as follows:(1)Physical properties of rice paddy were tested and analyzed.Three typical rice grain samples were selected(X1 was indica rice,J1was japonica rice,N1 was sticky rice).Hull tensile test and rice paddy compression test were conducted by a texture analyzer to obtain force-time graphs,fracture strength,fracture energy and other key mechanical data.Long-axis tensile fracture force of husk was 5.5N,and fracture process was longer due to the connection of husk fibers,while the short-axis tensile fracture force on both sides of husk was 1.5N,indicating that both sides of husk were weak points.Stress-damage failure process of rice paddy can be divided into three stages:hull stress stage;brown rice brittle fracture stage;rice grain damage stage,brown rice brittle fracture force was 159.7N and rice grain rupture force was214.2N.Fracture energy of three kinds rice paddy was negatively correlated with rate and moisture content,and regression models of rice paddy fracture energy under different rate and moisture content conditions were obtained,R~2values were all bigger than 0.97,regression effect was good.(2)Analysis of rice paddy mechanical properties under hulling conditions.Based on the working principle of rubber roller huller,the force mechanism of rice grain during hulling was obtained,rubber roller exerted compression and shearing effect on rice grain during the rotation process,so polyurethane film was placed at the bottom of rice grain,and mechanical tests under hulling conditions were conducted by a texture analyzer.Test results showed that polyurethane film absorbed most of energy generated by compression,and rice paddy fracture process under hulling force mechanism can be divided into two stages:husk subjected to extrusion and rice grain fractured,fracture force was 120.6N.The trend of fracture energy of three kinds rice paddy under hulling stress test and compression test was same under different rate,moisture content and temperature conditions.The glass transition of rice grain reduces its resistance to damage,rice paddy has the smallest fracture energy at 60℃,indicating that glass transition temperature is 60℃.(3)Fracture characteristics and crack expansion pattern of rice paddy.In compression test,deformation of rice paddy was dominated,in which plastic deformation occurred at the stress concentration in the center of brown rice,and X1 crack form was long-axis crack,crack forms of J1 and N1 were both short-axis cracks.Fracture forms of all three kinds rice paddy were shear fracture,rice paddy shape is similar to ellipsoid,the fracture all appeared at the center of the paddy,indicating that shear force is the main factor resulting in the breakage of the rice paddy during the hulling process.Fracture degree of three kinds paddy increased with the increase of rate;the process of absorbing external moisture produced hygroscopic cracks in the paddy,and reduced the bonding force of the inner and outer lemma,so X1 inner and outer lemma fracture during the test,and internal fracture degree increased,when the water absorption was close to saturation,rice paddy elasticity increased,shear resistance increased,and rice paddy fracture form was compression fracture;shear fracture degree of rice husk and brown rice increased when drying temperature was 150℃.(4)Simulated hulling test analysis.The rice grain profile showed that rice paddy was wrapped by the hooking of inner and outer lemma,and rice paddy was driven to rotate by the movement of rubber roller under hulling conditions,and the fracture process of the hull was the first fracture on both sides of the inner and outer lemma,and then the union of inner and outer lemma fractured,finally husk was peeled off from the surface of rice paddy,hulling process completed.The breaking force of rice paddy and the degree of hull breaking increased with the increased of polyurethane hardness,rate.