Milling Mechanism And The Numerical Simulation Approach To Predict The Abrasion Rate Of Rice During Milling

Rice as one of the three major crops in China is normally consumed in whole milled form.The essence of the milling process is the interaction between rice grains and rice grains-mill geometry,resulting in the surface of rice grains being whitened,which is manifested in the removal of rice bran layer.However,the mechanism of milling in the rice mill is not clear,which leads to the control of milling degree can only rely on experience.In order to scarify the different requirements of consumers for nutritional quality and taste of rice,as well as control the milling degree,the milling characteristics of rice were explored.The milling mechanism was revealed.The numerical relationship between the essential influence rice mill on rice and milling degree was established.Then accurately predicting the abrasion rate of rice grains during the process is of great significance to control the rice processing grade,meet the needs of consumers at all levels,design and improve rice milling equipment,improve rice milling quality and efficiency and reduce energy consumption.The results provide a theoretical basis for the prediction and control of rice milling degree,as well as the guidance for the optimization design and improvement of rice mill.Taking the milling characteristics of rice grains as the starting point,this study built a single grain milling test platform to study the influence of key factors on the milling characteristics of rice grains.Olan this basis,using the combination of theory,experiment and numerical simulation,the dominant mechanism in the process of rice grain milling is explored.The movement characteristics and milling rate of rice grains in the sand disc rice mill were explored to provide the basis for parameter selection for achieving uniform and efficient milling objectives.The best parameter combination was obtained through the combination test.On this basis,the dominant mechanism in the process of rice milling is found out.By obtaining the contact information of rice grains in the milling chamber,a numerical prediction method of rice milling rate is proposed,combining with Archard equation.Its applicability was discussed.The main conclusions of the study are as follows:(1)The milling characteristics of single grain was clarified.A single rice grain milling test was performed to analyze the milling characteristics and morphology characteristics of milled rice grains.The milling mass of rice increased with the increase of sliding distance,and there was a non-linear growth relationship between them.In the initial stage of milling,the increase of milling mass is very large,but with the further increase of sliding distance,the increase of milling mass became smaller.Under the action of normal force and sandpaper grit,the milling coefficient of rice grain decreased gradually with the increase of sliding distance,while the specific milling area of rice increased rapidly at first,and then slowed down.The milling coefficient of rice grain ranged from 0.03 to 0.05.At the same time,with the increase of normal force,the milling coefficient increased,while with the increase of sandpaper grit,the milling coefficient decreases.(2)The motion characteristics of rice whitening in the sand disc rice mill were explored.The rotational speed of the sand disc and filling mass significantly affected the tangential movement ability of rice grains in the milling chamber.Lower speed of sand disc was conducive to uniform milling,but the milling efficiency was low.Properly increasing the rotational speed of the sand disc was conducive to improve the ability of internal and external translocation of rice grains and improve the problem of poor milling uniformity.The increase of filling mass was conducive to improve the milling efficiency,but the milling uniformity was poor.When the filling mass was 14g,the internal and external translocation ability of rice grain was the strongest,which was conducive to uniform milling.With the increase of milling time,the relationship between milling rate and milling time accorded with the first-order dynamic model.The milling rate increased with the increase of sand disc rotational speed and filling mass.The relationship between micro numerical simulation results(collision energy)and macro milling performance(milling rate)was established.The milling rate can be evaluated quantitatively by numerical simulation results.(3)The influence order of the grit of sand paper,filling mass and milling time on the rice milling performance was found.The influence law of various factors on the performance index was revealed.The influence order of various factors on head rice yield was as follows:grit of sand disc,milling time,filling mass;the order of influence on whiteness is:filling mass,grit of sand disc,milling time;the order of influence on specific energy consumption is:milling time,grit of sand disc,filling mass.The optimum operation parameters of the sand disc mill were obtained when the head rice yield and whiteness were the highest and the specific energy consumption was the lowest,that is,when the grit of sand disc was 100~#,the filling mass was 18g,and the milling time was 20s,the head rice rate was 90.27%,the whiteness was 62.42,and the specific energy consumption was 19.48k J/kg.(4)A numerical prediction method of rice abrasion rate was developed and its applicability was verified.By analyzing the size distribution characteristics of milled rice in the sand disc rice mill,it was determined that the abrasion mechanism played a dominate role in the process of rice milling.The contact information of rice in the process of rice milling was obtained by numerical simulation.The numerical simulation results were applied to the Archard equation.The calculated abrasion rate was in good agreement with the experimental results.It is proved that the method was an effective method for predicting the abrasion rate of rice grains in the rice mill.The applicability of the proposed numerical prediction method of rice abrasion rate was tested by using a friction mill.The contact information of rice grains in the rice mill at different roller shaft rotational speed was obtained.The milling rate was predicted to verify the applicability of the proposed method.The results of this research can provide reference for improving the milling quality of brown rice,controling the degree of milling and the numerical design of rice mill.