Research Of Modern Design Method For Air-and-Screen Cleaning Device

During the crop planting, the cleaning of agricultural materials plays an important role. The air-and-screen flat cleaning vibrating screen has been commonly used in modern combine, however, the air-and-screen flat shaker screening process is a very complex random process. With the development of physical testing technology and computer technology, many specialists focus on using modern design theory and methods for system analysis and research of air-and-screen cleaning device, therefore, concerning to the selecting of rice, the air-and-screen cleaning device was systematically studied. The main contents included.1. The composition of4LZ1.0type combine effluent was measured. Analysis showed that the loss was smaller for using this type of machine, however, Grain and immature grain was not effectively isolated in the effluent. The three-dimensional size, density, stiffness and shear strength and other physical parameters of grain and immature grain were measured, at the same time, the interaction between the three physical parameters, such as the restitution coefficient, friction coefficient was measured, too.2. Air-and-screen cleaning device was designed, and the shaker assembly was carried by three-dimensional reconstruction and we used kinematics analysis tools for curve fitting for movement of points which were on the screen surface. Analysis showed that the points on the surface of screen did periodic motion; the motion curve can be expressed by the sine function. Meanwhile, the influence for changing cleaning device size to the surface acceleration was analyzed by ADMAS, and the sizes are optimized. Optimization results showed that crank speed and the radius had sensitive influence to the acceleration on the surface of the screen. The acceleration of the points on the surface of screen is the best when crank rotation speed n=360r/min and crank radius r=2.5cm.3. Based on the gas-solid phase fluid mechanics theory, the force of the grain in the screen surface was analyzed.3D models were established by the Gambit software and divided into structured tetrahedron grid. In the constant pressure boundary, the cleaning device was numerical simulation through the standard k-s turbulent model of the CFD software and wall function method. Analysis showed that the biggest wind speed was out of the fan, in the boundary of the duct and fan cylinder, the air did centrifugal motion, and air blow out along the tangent of the fan blades and formed a smooth flow whose size and direction was changed in the scale sieve net. In the scale sieve net openings, the speed gathered and air blow out from the screen which was good for blowing out debris flow. Due to the influence of the scales openings, in the screen surface above, the face of the recent screen surface was with bigger air velocity. The analysis showed that in the guarantee of cleaning and choosing efficiency, the vertical distance of the cleaning device could be shortened. Numerical simulation also indicated that the airflow velocity in the wall had certain impact phenomenon, there exists significant pressure gradient. Through the orthogonal experiments, the screen surface wind field was optimized, and the optimization results showed that, centrifugal fan speed for700RPM, centrifugal fan angle of25degrees and the scales screen angle20degrees were helpful to reduce the impurity rate and loss.4. Based on reverse engineering theory, the three-dimensional models of rice grain and flat valley were reconstructed. With the idea of three-dimensional discrete element shape model theory, the3D models of rice grain, immature rice and short stem were established using bonding method. The error between this model and actual one was less than5%in shape, size and density values. In other words, this model could be the dynamics, kinematics and mechanics basis of grain screening analyses.5. The3D discrete element numerical simulation research was conducted, focusing on screening behavior of rice emergence mixture on the vibrating screen. Through numerical simulation, the layering and screening progresses of particle flow were represented with the excitation of the screen plane. The movement principles of particle flow were analyzed as well as the influence from each parameter on the grain and immature rice movement on the screen. At the same time, the regression equation was formed by curving fitting so as to explore the layering and screening mechanism of particle flow on the screen plane.6. The study on screening efficiency of plane vibrating screen was conducted systematically based on the3D discrete element analysis simulation theory. The concept of dynamic screening efficiency was introduced in order to analyze the disciplines of vibration frequency, amplitude and screen inclination which influenced screening efficiency during the screening progress. On the basis, we conducted an orthogonal simulation experiment to obtain the parameters of the best screening efficiency, namely vibration frequency for5Hz, amplitude for25mm and dip angle for4degree. Meanwhile, multiple elemental nonlinear model of screening efficiency was established to enrich particle vibrating and screening theory. In addition, the model provided theoretical basis for optimization design of traditional screen machine and new cleaning device research.7. The simulation of numerical value was verified by series of experiments. Using high-speed image processing system, the movement tracer of the screening process was conducted on the test-bed, the analysis of the results obtained from Discrete Element simulation and experiment showed that the move tendency of the particle obtained from the two different measures were basically the same; Through the statistics of the tested things under the screen, the regularity of distribution of the screening efficiency along the screen surface was obtained, screening efficiency on the screen belongs to normal distribution, the screening efficiency of the front screen is the highest, which is in accordance with the law obtained from the discrete element simulation. The air speed of the sieve halfway point and the outlet were measured with anemometer under the condition of different fan speed and fan angle, then, the compared analysis of the result and the simulation result of CFD was formed, which showed the change of simulation results and experimental results were basically identical, so using CFD on the wind field analysis is feasible.