| In agricultural production,screening is an essential step in the delicate process of tea.As an important part of agricultural material screening device,the performance of vibrating screen directly affects the operating performance of screening equipment.Tea shaking screen machine is one of the equipment for tea refining and processing.It can carry out continuous up and down displacement stratification on the screen surface according to the different dimensions of the linear reciprocating motion and the inclined screen surface with a certain size of sieve,so as to realize the sifting separation of tea fragments,tea dust,tea stems and other fine impurities,and improve the quality of finished tea.In order to solve the problems of low screening rate and high error rate in the process of tea shaking and sifting,this thesis takes tea shaking and sifting machine as the research object,establishes the vibration mechanism model of tea shaking and sifting machine based on ADAMS software,and obtains the changing trend of the acceleration and displacement of the screen surface through simulation analysis.Then,the motion of granular materials in the screen under different working parameters(vibration frequency,vibration amplitude,screen surface inclination,etc.)was simulated.EDEM software was used to analyze the force and motion law of tea screening process,and the key parameters of the shaking screen machine were simulated to obtain the influence law of different working parameters on the screen clean rate and the wrong rate of screening.Single factor verification test and quadratic rotation orthogonal parameter optimization test were designed to obtain the best working parameter combination conducive to the tea shaking sieve machine to carry out the division of tea screening order,and to provide a theoretical basis for improving the screening quality of tea shaking sieve machine.The main work of this thesis is as follows:(1)The moisture content,angle of repose,density,static friction angle,dynamic friction coefficient and other physical properties of the studied tea were measured.The moisture content of tea was 5.5%,the angle of repose was 30.7°,the density was 532.4kg/m~3,and the static friction angle was 30.3°.The sifting probability theory of a single tea particle is analyzed,which provides theoretical basis and data support for the subsequent research of tea shaking sifting machine.(2)Through the software of Solid Works,the transmission mechanism of the shaking screen machine is designed and analyzed,and the spring support plate is checked for stability,normal stress strength check and allowable stress check,to ensure that the design parameters of the spring support plate meet the design and production requirements.Using ANSYS Workbench software,the modal analysis of the tea shaking screen machine was carried out to study the natural frequency characteristics of the pedestal of the shaking screen machine.Taking tea particles as the research object,the force and movement rules of tea on the screen surface were analyzed,and the optimal range of rotational speed of the tea shaking screen machine was obtained according to the technological conditions that the tea needs to continue to produce relative motion with the screen surface without throwing body motion.(3)The 3D model of tea shaking screen machine was established and imported into ADAMS.Virtual prototype modeling and multi-body dynamics simulation were carried out on the tea shaking screen machine by using ADAMS software,and the change law of displacement and acceleration of the vibrating screen in the complete cycle under stable state was obtained.The change law of influence of different plate spring length on motion acceleration of tea particles was analyzed.The length of the plate spring under the optimal screening performance of the tea shaking screen machine was investigated,and then Hamming window was selected in ADAMS to analyze the acceleration under the optimal state,which verified the rationality of the structure design of the shaking screen machine.(4)The research methods of loose granular materials were analyzed,and the ball fitting tool of EDEM software was used to establish the tea particle model on the screen and the tea particles under the screen of tea fragments,tea dust,tea stalk,etc.The numerical simulation of the screening process of tea shaking sieve machine was carried out to obtain the separation mechanism of tea particles at each stage.Setting different parameters of screening simulation tests,combined with the average velocity-time,the kinematics and dynamics curves of the extrusion pressure between particles-time to quantify the movement of tea particles and the size of the force,analyze the different parameters on the screening performance indicators such as the net rate and error rate of the shaking screen machine.(5)With vibration frequency,vibration amplitude and inclination Angle of screen surface as the influencing factors,and sieve net rate and error rate as the evaluation index,a single factor test was designed to verify the simulation results,and a quadratic orthogonal rotation combination test with three factors and three levels was designed using Design-Expert software.The interaction between various factors and the significant order of impact on the screening performance were analyzed combined with the response surface.The test results show that the interaction among independent variables is significant,and the order of influence on screen clean rate is vibration frequency,vibration amplitude,screen surface inclination.The order of influence on the error screen rate is the inclination of screen surface,vibration amplitude and vibration frequency.With the maximum clean screening rate and the lowest missed screening rate as the parameter optimization objectives,the constraint equation was set to carry out optimization tests.The optimal parameter combination was obtained as vibration frequency 4.1Hz,vibration amplitude26mm and screen surface inclination 2.8°.At this time,the net screening rate and missed screening rate were 94.8%and 4.7%,respectively.The screening verification test was designed for the optimized structural parameters,and it was obtained that the net rate and error rate of the actual tea shaking screen machine were 93.9%and 4.82%,respectively.The verification test results were basically consistent with the optimization results. |
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