Screening Theory And Experiment Of Typical Agricultural Materials On The Three-dimensional Parallel Vibration Screen

As an important equipment of particle material layered equipment, vibration screen has been widely used in agricultural machinery, coal preparation, mineral processing, metallurgy, petroleum, chemical industry, architecture, grain and feed industry, etc. Now the single degree of freedom linear reciprocating vibration screen has been widely used, but it has so less degree of vibration freedom that the particle material couldunt be dispersed uniformly, which effect the layered consequent and efficiency. The application of parallel mechanism to the design vibration screen equipment is the new thinking to solve the defects such as less degree of vibration freedom, large general size, low efficiency and easy to plugging hole of the traditional reciprocating vibration screen and easy to cause resonance, short serve life, unstable screening performance of circular vibrating screen. The application has an important practical significance and applied value to for setting up new theory of vibration screen and developing practical vibration screen equipment.By the financial aid of National Natural Science Foundation "the research of motion theory of agricultural materials particles in air-and-screen cleaning device (50875113)" and Jiangsu province university important natural science research project" the applied basic research of the multi-degree-of-freedom vibration theory of agricultural materials particles(11KJA460002)", this dissertation puts forward the using of complete decoupling parallel or hybrid mechanism as the main exciting vibration mechanism of the vibration screen and three-dimensional parallel vibration screen has been developed to solve the three-dimensional vibration problem of vibration screen in practical production. The main research achievements of the dissertation as follows:1. Taken wheat and rice as research objects, the mechanical characteristics. The parameters such as moisture content, three-axis size, elastic modulus, sliding friction coefficient, angle of repose and density of the wheat and rice were tested and analyzed. The device for measuring restitution coefficient of agricultural materials has been put up and the restitution coefficient of the wheat sample has been measured actually. The effect degree of material type, thickness and moisture content factors on restitution coefficient of the wheat has been analyzed by orthogonal test. The experimental data acquired provided the basis for subsequent numerical simulation and bench test. 2. EDEM software has been taken to simulate the dispersion process of ellipsoidal particle material on three-dimensional vibration screen surface base on the discrete element analysis method. This dissertation set up the two types dispersion evaluation index and investigated the influence law of the parameters such as vibration degree of freedom, amplitude, frequency and particle aspect ratio etc. on dispersion.3. Test research has been taken ellipsoidal particle material system on the three-dimensional vibration screen surface to simulate the layered process under the vibration applied from X, Y, Z dimension. This dissertation analyzed the force and layered limiting condition of the particle material on the three-dimensional vibration screen surface, established the layered velocity measurement index, discussed the influence law of the parameters on particle layered velocity such as vibration degree of freedom, amplitude, frequency and particle fineness ratio etc. Analyzed the layered mechanism of ellipsoidal particles from the view of the change of normal force, tangential force, average kinetic energy and average rotational kinetic energy of the particles.4. Research has been carried out on numerically simulating the screening process of the mixture of wheat and straw on the three-dimensional vibration screen surface. This dissertation analyzed the motion state of the particle group in the three-dimensional vibration screen, established the two types screening efficiency measurement indexs including percent through screen and percentage of trash content of undersized compost, and investigated the influence law of the physical characteristics of mixture on the screen surface feed end(aspect ratio, doping extent) and the change of vibration parameters(vibration degree of freedom, amplitude, frequency) on the screening performance of the three-dimensional vibration screen.5. Based on the theory of parallel mechanism topological structure and the motion theory analysis of the agricultural material particles on the three-dimensional vibration screen surfaceabove the type synthesis of the3-dof translational parallel mechanism suitable for three-dimensional parallel vibration screen has been taken to determine the optimal machine type. The dissertation put forward a new design program for multi-dimensional vibration screening and three-dimensional parallel vibration screen base on complete decoupling parallel mechanism3PRRR which use the hybrid structure2PRRR-P(2R) as main exciting mechanism can realize the vibration of the screen box along X,Y,Z dimensions. 6. The multi-dimensional vibration screen test bench four degrees of freedom which has four degrees of freedom at most and the prototype of three-dimensional parallel vibration screen were researched and manufactured base on the theory of parallel mechanism topological structure, and the orthogonal test was carried out on the test bench. The ideal structure design and kinematics and dynamic analysis of the three-dimension parallel vibration screen were completed based on the results of numerical simulation, and the prototype manufacture of the optimal practical three-dimensional parallel vibration screen and performance test has been completed base by the dissertation. The results of the orthogonal test were matched to the numerical simulation.At last, this dissertation comes up the following conclusions:the three-dimensional parallel vibration screen has the capacity of separating agricultural materials with highly efficiently. The research results put a good theoretical foundation for further understanding the dispersion of particles material on multi-dimensional degree of freedom vibration screen surface, layered mechanism, and for perfecting the theory of multi-dimensional degree of freedom vibration screening. And put forward a new thinking to improve the efficiency of screening and cleaning the agricultural materials and to decrease the size of screening and cleaning equipment. The three-dimensional parallel vibration screen theory researched and the prototype of manufactured by the dissertation is a new type of vibration screening equipment which has developing prospect. Some items of invention patents and utility model patent have been applied based on innovative equipment involved by the dissertation.