Kinematic Characteristics Of Multi Stage Equal Thickness Screen With Variable Inclination And Co-optimization Of Screening Process

Coal is an important industrial raw material in China and it is the most abundant mineral resource.Coal preparation is the core technology of coal resource processing and clean utilization.Deep screening is a significant segment of coal washing and processing.As the main carrier equipment of screening operation,vibrating screen is widely used in the coal resource dewatering,desliming,medium removing and classification in coal preparation plant.Due to the huge proven reserves of coal resources in China,the scale of coal washing has gradually increased,the demand for equal thickness vibrating screens with optimum production capacity and screening effect is increasing rapidly.However,the equal thickness screen with a fixed inclination angle is used in coal preparation plant to screen raw coal with different material characteristics at a depth of 6 mm,and there 60 still some technical problems,such as the deterioration of screening effect,the lag of production capacity and the accumulation of coal seams,which seriously hinder the scale of coal resource upgrading and processing.Given the problems existing in the traditional equal thickness screen screen.In this paper,a new type of multi-stage variable inclination vibrating screen was developed as the carrier,which was equipped with a dual-axis counter-rotating excitation system.Based on the theoretical modeling and screening experiment,research on the surface kinematic characteristics,the spatial distribution of coal seams,the law and particle size composition of screening,the adaptability of different material characteristics,and the process strengthening mechanism was carried out by using the testing method of vibration test and high-speed dynamic analysis.Put forward a multi-stage equal thickness screening method with variable inclination angle to adapt to different material characteristics.The stable differential equation of the motion of the mass center of the screen body on was established.The mechanical model of a single particle was put forward,and the vector mathematical equation of a single particle of different screen surfaces was obtained.By using the high-speed dynamic test and analysis system,the variation rule of the moving speed and distance in different areas of the multi-stage screen surfaces was studied.It was revealed that the vibration energy transferring mechanism of different screen surfaces:in strong out weak.The vibration test and analysis system were used to clarify the time-frequency response characteristics,and to reproduce the spatial motion displacement of multi-stage screen surfaces.The mathematical equations of the relationship between different screen surface areas and displacement,acceleration and velocity were established,which mathematical equation accords with y=bx+a model and is linear.The model had high fitting accuracy and strong reliability.By using the method of multiple single factors,the influence of the exciting resultant force and the frequency of excitation on the effect was analyzed.The optimum operating conditions were determined as the exciting resultant force Ft=8.66 kN and the frequency of excitation f=11.84 Hz.The influence law of coal group distribution and screening performance of 3,4 and 5 stages were clarified.It was found that the coal samples were all concentrated in the middle of the screen face for the leaking screen,and the maximum amount of leaking screen was found in the second stage of the screen surface.The screening efficiency,particle size distribution and separation accuracy all reached the best value in the second stage of the screen surface,and the screening effect of 5 stages was higher than that of 3 and 4 stages.When the number of screen stages increased,it caused the vibration energy echelon transmission,and the material group migration speed and displacement altered in many echelons,which was conducive to increase the probability of passing through the screen.The influence of handling capacity and inclination gradient of coal samples with different material characteristics was clarified.The operating range of the optimal handling capacity and inclination gradient of coal samples with different material characteristics was determined.The spatial distribution characteristics on the screen and the granularity composition under the screen of the coal group were clarified.Compared with single angle screen surface structure,the screening efficiency was increased by 2.24 percentage points,and the total misplaced material was reduced by 1.74 percentage points.The matching characteristics of handling capacity and inclination gradient of coal samples with different ratios of thickness were studied.The adaptation mechanism of coal samples with different material characteristics was revealed.The orthogonal experiment was designed to obtain the influence degree and significant level of the operation parameter handling capacity and inclination gradient.The optimization scheme of handling capacity and inclination gradient for different material characteristics was proposed.In the range of 40%-60%of the thickness of+6 mm coal sample,the optimized parameter combination was handling capacity per unit area q=25t/h·m~2 and inclination gradient△θ=4°;in the range of 60%-80%,the optimized parameter combination was handling capacity per unit area q=30 t/h·m~2 and inclination gradient△θ=6°;in the range of 20%-40%,the optimized parameter combination was handling capacity per unit area q=25 t/h·m~2 and inclination gradient△θ=3°.The BBRSM was used to design and analyze the experiment,and to explore the cooperative strengthening effect of exciting resultant force,excitation frequency,and screen surface inclination gradient.The results have shown that operational parameters have a significant effect on the screening efficiency,and there is a significant cooperative effect between the parameters.The mathematical correlation model between the exciting resultant force,the excitation frequency,the inclination gradient and the screening efficiency was established.The cooperative strengthening of equal thickness screening process was studied,and parameters combination of strengthening conditions were determined.The screening test of coal samples with different material characteristics was carried out on the condition.The results showed that the screening efficiency was more than 86%,the particle size of coal samples was close to the target classification particle size of 6 mm,and the separation accuracy was less than 1.1 mm,which was smaller than the result of the prediction model,which verified the accuracy and reliability of the prediction model.Combining the orthogonal optimization analysis and response surface model optimization,the final significant level order wasβ>f>△θ>Q.