| Maize is widely planted in China and its yield is very high,which can be used not only as food and feed,but also as the industrial raw materials.The air and screen cleaning device is simple and practical,and it is widely used in maize cleaning.With the development of agriculture,the cleaning performance and quality of the cleaning device need to be further improved.At present,most of the researches related to the cleaning device are related to the optimization of the distribution of airflow,particles motion and the structure design of the new type screen,but few reports are reported on the design of new type screen hole.Whether the researches studied by scholars or the cleaning device sold on market,the motion of particles in the cleaning device is chaos motion.It is random Whether the maize particle will penetrate the screen hole after collision with the screen surface.In order to solve the problem above,a new cleaning device is designed based on the plane reciprocating vibration mechanism.The screen hole is with three-dimensional structure,which can make the particle move toward the screen hole and the motion of particles be in relatively orderly on the screen surface.Through the theoretical analysis of the impact position between particle and screen surface,the structural parameters and operating parameters which affect the tendency of particle moving toward the screen hole are determined.Based on CFD-DEM coupling simulation technology,the gas-solid two-phase flow of threshed maize mixture in the double-layer reciprocating vibrating screen cleaning device was simulated.It is determined that H-type arrangement of screen hole is the best arrangement of screen holes.Comparing the behaviors of particle penetrating the round hole screen with those of particle penetrating the countersink screen,the reason why the behaviors of particle penetrating the countersink screen hole can improve the efficiency of particle penetrating the screen hole is analyzed.The influence of different parameters on the cleaning performance was studied through single-factor tests.The mathematical model and response surface of the parameters of the cleaning device on the cleaning rate and loss rate of the particles were obtained through multi-factor testes.The relationship between different factors on the cleaning rate and the loss rate of the particles was determined.The parameters were optimized to determine the best working conditions.The behaviors of particle to penetrate the round hole screen and the countersink screen were compared,and the reasons for the cleaning efficiency of the countersink screen improvement was analyzed.The bench testes of the cleaning device with countersink screen was built and was carried out to verify the cleaning performance of countersink screen the behaviors of particle to penetrate the countersink screen hole.The main conclusions and contents of this paper are as follows:In order to make the particle motion orderly and improve the screening efficiency of cleaning device,a new type of screen hole with three-dimensional structure was designed based on the plane reciprocating vibrating screen movement mechanism.Through the sidewall around the screen hole,the particle moves toward the screen hole,and the tendency of particles penetrating the screen hole appear.The design of the countersink screen is based on the round hole screen,and the diameter of the screen hole and the center distance between the screen holes are consistent with the round hole screen.In order to make the area biggest where the tendency of particle penetrates the screen hole,the shape and size of the opening on the screen hole is determined to be 19 mm square.According to the different collision positions between the particle and screen,the motions of particles are classified and explored.When the particle slides along the sidewall toward the screen hole,the tendency of particle penetrating the screen hole is related to the acceleration of particle along the sidewall;when the particle rebounds toward the screen hole after the collision with the sidewall,the tendency of particle penetrating the screen hole is related to the direction of particle rebounding.The main structural parameters which affect the tendency of particle penetrating the screen hole are determined as well as the operating parameters of the cleaning device.The simulation of gas-solid two-phase flow between the threshed maize mixture and the cleaning device with countersink screen is carried out by CFD-DEM coupling technology.Three kinds arrangements of screen holes are posed.After the experiments carried out under different angle of sidewall around screen hole,the best arrangement of screen holes is determined in H-type agreement of screen hole,and the test range of the angle of sidewall around screen hole is determined in 40°～60°.When the airflow velocity at the inlet of cleaning device is 12.8 m/s,the airflow direction angle is 25° and the feed mass of the threshed maize mixture is 5 kg/s,the screening efficiency of the countersink screen is 35.20% higher than that of the round hole screen.Particle sliding along the sidewall toward the screen hole and rebounding toward the screen hole after the collision with the sidewall are verified.Comparing the behaviors of particle penetrating through the round hole screen and the countersink screen,the reasons for the improvement of the cleaning efficiency of the countersink screen were analyzed.The movement of particle in order on the screen was improved and the invalid collision was reduced.According to the range of the airflow velocity and airflow direction angle in the cleaning device with the round hole screen,the levels of the airflow velocity is determined in 9.6 m/s～14.4 m/s and the airflow direction angle are determined in 15°～35°.Through single factor test,the influence of different factors on cleaning performance of cleaning device is analyzed,and the range of multi factor test is determined.With the increase of the angle of side wall around the screen hole,the tendency of particle moving toward the screen hole increases;with the increase of the airflow velocity,the number of particles sliding into the screen hole decreases,and the number of particles rebounding into the screen hole after colliding with the side wall increases;with the decrease of the air direction angle,the impact angle between the particle and the screen surface increases,which affects the tendency of particle moving toward the screen hole.In order to optimize the structure parameter of the countersink screen and the operating parameters of the cleaning device,the quadratic orthogonal rotational-combinational simulation test was designed.The response surface method is used by using Design Expert software,and the regression mathematical model of evaluation index is optimized with multi-objective.The factors influencing the cleaning rate of particle are determined from strong to weak: the airflow velocity,the angle of sidewall around screen hole,the airflow direction angle.The order of the influence of various factors on the loss rate of particle is: the airflow velocity,the angle of sidewall around screen hole,the airflow direction angle.The optimization parameters of the cleaning device are as follows:the angle of sidewall around screen hole is 60°,the airflow velocity is 13.6 m/s,the airflow direction angle is 30°.The verification testes on the double-layer reciprocating vibrating screen device bench were carry out.According to the bench test results of the cleaning device with countersink screen,it can be seen that the cleaning rate of particles in the countersink screen is 98.57%,the loss rate is 0.89%,and the cleaning rate is 1.49% higher than that of the round hole screen cleaning device and the loss rate is reduced by 1.37%.The motions of maize particles were captured by High-speed video.By comparing the behaviors of maize particles penetrating the screen hole with the behaviors of maize particles penetrating the screen hole in simulation test,it can be seen that the behaviors of maize particles penetrating the screen hole is basically consistent with the behaviors of maize particles penetrating the screen hole in simulation test.In this paper,the countersink screen with sidewall is designed.Through simulation test and bench test,the behavior of particle penetrating through the screen are studied verifies that the countersink screen can make the particle penetrate the screen hole and reduce the invalid collision between the particle and the screen surface,which puts forward a refence for studying on particle screening in orderly ways. |
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