Kinematics of variable-amplitude screen and analysis of particle behavior during the process of coal screening

Screening is an indispensable unit process for separation of particulate materials in various industrial processes. The variable-amplitude screen (VAS) has been widely used for particle classification because of its large production capacity and good screening performance. In this paper, a novel VAS driven externally by an unbalanced two-axle excitation was proposed. Kinematics characteristics of the VAS and particle behavior under different operational conditions were investigated using vibration test and dynamic image analysis system. The results show that the displacement amplitude of the VAS decreased gradually along the direction of material flow. Consequently, the migration velocity of particles was larger and the screening time of particles was long, due to the larger and smaller displacement amplitudes at the feed and discharge ends, respectively. Both of these effects are conducive to improved screening performance. The operational factors unbalanced excitation force coefficient (k(f)), relative beam span (l(reb)) and feed rate (Q) all showed significant influences on the kinematics of the VAS, particle behavior and screening efficiency. The difference between the amplitudes of the feed end and the discharge end increased with increasing kf and l(reb), thus resulting in the increase of particle velocity; however, these variables showed an inverse relationship with Q. The screening efficiency showed a maximum with the increase of all three of the test parameters. It was found that the screening efficiency was higher than 94% when k(f)=1.22, l(reb)=45%, and Q <= 4.80 t/h. This indicated that the VAS has excellent performance for coal screening. (C) 2016 Published by Elsevier B.V.