Time evolution of kinematic characteristics of variable-amplitude equal-thickness screen and material distribution during screening process

Abstract

The equal-thickness screen has been widely used in coal cleaning and utilization due to its good performance. In this paper, the time evolution of the kinematic characteristics and spatial trajectories of a novel equal-thickness screen with variable-amplitude (VAETS) were investigated using vibration testing method. The motion-related parameters of tracer particles, and distribution of various size fractions in different sections with stable feeding were analyzed using high-speed imaging technique. The results show that the operational process was divided into four different stages, namely the start-up stage, the transition stage, the steady-state stage and the shutdown stage. Furthermore, the kinematic characteristics at different stages were found to differ significantly from each other. During the steady-state stage, the spatial trajectories of all measuring points were elliptical and the dominant frequency was 16.67 Hz, which was consistent with the rotational speed of the excitation motor. The minor axis of the ellipse exhibited a smaller difference, while the major axis of the ellipse decreased gradually along the direction of material flow. The kinematic statistical results of tracer particles show that, smaller the particle size, lower was the average migration velocity. However, the difference in average migration velocities of the same size fraction in feed and discharge ends was small. The amplitude at the feed end was found to be large, and therefore, the material rapidly moved towards the discharge end, which overcame material accumulation. In addition, the amplitude at the discharge end was found to be relatively small, which prolonged the screening time of particles. Therefore, the equal-thickness screening of the material was formed, whereas the screening efficiency was greater than 91.80% for the designated size of 6 mm under different excitation conditions.