Study On The Screening Mechanism And Key Technology Of The Horizontal Varied-trajectory Equal-thickness Screen

Coal is the main energy in China.Coal preparation is the valid method for effective application and clean production of coal.As the key process of coal preparation,screening is widely used for coal classification,dewatering,desliming and medium-draining.The equal-thickness vibrating screen is one of the most significant screening equipments with advantages of high efficiency and large capacity.While the structure of the traditional equal-thickness vibrating screen is complex with high workspace demand.Meanwhile the unsmooth dynamic parameters distribution transition of which limits the further screening efficiency improvement.In response,the horizontal varied-trajectory equal-thickness screen was investaged by combining the varied-trajectory thchnique and the equal-thickness screening method,aiming to achieve the similar screening performance of the equal-thickness screening method with the varied-trajectory motion of the horizontal screen surface.The effect factors of the screening performance of the traditional equal-thickness vibrating screen were anayized.With the certain screening capacity and the geometric parameters of the screen surface,the factors that influence the screening performance include the vibration amplitude,the vibration frequency,the angle between vibration direction and the horizontal direction and each deck incline angle of the screen surface.The steady screening efficiency was introduced as the performance index.The orthogonal experiment was designed and the screening process of the banana vibrating screen was simulated with the EDEM software.The screening process was considered as the implicit function of the effect factors.Which was fitted based on the LRGA-GRNN and the parameters were optimized with the local reinforced genetic algorithm.Through which the optimal dynamic parameters distribution of the traditional equal-thickness screening method was obtained.The kinematics principle of the horizontal varied-trajectory equal-thickness screen was analyzed.The force model of single particle on the screen surface was established.Based on which the effect factors of the screening performance were determined as the relative position of the screen surface to the centroid,the centroid vibration amplitude,the vibration frequency,the centroid vibration direction angle and the swing angle amplitude with the certain screening capacity and the geometric parameters of the screen surface.By using the EDEM software the orthogonal experiment of the screening process was conducted.The screening process implicit function was fitted and optimized by means of the LRGA-GRNN and the local reinforced genetic algorithm,through which the optimal dynamic parameters distribution of the horizontal varied-trajectory equal-thickness screen was obtained.By comparing with the linear screen with horizontal screen surface and the banana vibrating screen,it was verified that the screening efficiency of the horizontal varied-trajectory equal-thickness screen can perform better genenally.The basic principle of the horizontal screen surface varied-trajectory motion realization with the method of harmonic force offset-exciting was analized.The four-axis forced-synchronous offset-exciting system was investigated with numerical simulation and experiment.The results indicate that the system response with varying tendency similar to the optimal dynamic parameters distribution of the horizontal varied-trajectory equal-thickness screen can be obtained with this method.The offset-exciting design method of the optimal dynamic parameters distribution realization was discussed.And the design result was analized with numerical simulation.The effectiveness of the method was certified by comparing the simulation results and the optimum values.The dynamic model of the horizontal varied-trajectory equal-thickness screen self-synchronous coupling-driving offset-exciting vibration system was established.The basic principle of changing the motor output characteristics was analized.The average-small-parameters method was extensed and applied to the coupling-driving system.The self-synchronization cirterion and vibratory synchronization transmission mechanism of the horizontal varied-trajectory equal-thickness screen coupling-driving offset-exciting vibration system were analized.The effect of the phase difference between two exciting axis on the resultant exciting force was investigated.Which illustrated that the esultant exciting force would not coincidence with the midperpendicular of the rotation axises and additional couple would be generated when the phase difference is not equal to 0°.The self-synchronization electromechanical coupling equation of the horizontal varied-trajectory equal-thickness screen with coupling-driving mode was established.Based on which the numerical simulation was conducted by using the AMESim software,and the effect of the output chatacteristics difference of the motors on self-synchronization was analized.The frequency control method and the vibratory synchronization transmission method for the varied-trajectory motion of the horizontal screen surface was investigated with simulation and experiment,respectively.The system response changing law of the frequency control method was achieved.The self-synchronization offset-exciting method for optimal dynamic parameters distribution of the horizontal varied-trajectory equal-thickness screen was discussed based on the electromechanical coupling simulation.The simulation resules are quite close to the optium values,which certified the feasibility of this method.To enchance the avoiding mesh blocking ability of the horizontal varied-trajectory equal-thickness screen surface,the avoiding-mesh-blocking screen surface with multi-degree of freedom was proposed for classification.The dynamic model of the avoiding-mesh-blocking screen surface with multi-degree of freedom was established,and the equivalent stiffness of the connectors were calculated.The numerical simulation and experimental validation indicate that the vibration intensity can be strengthened significantly relative to the screen body via using the avoiding-mesh-blocking screen surface with multi-degree of freedom,and the mesh size keeps changing during the vibration.Throuth which the mesh blocking prevention performance similar to the flip-flow screen can be obtained.