The dynamic response of particles is closely related to screening efficiency. To study the dynamic response of particles, the dynamic equations of a particle on a screening surface are established based on the elastoplastic contact model of spherical particles and are solved for the coal particle. Then, the trajectories of the particles are given with different falling heights and particle radii. The completely different trajectories with slight changes in the falling height and particle radius indicate strong nonlinearity. Second, the nonlinear dynamic behavior under different amplitudes and frequencies is discussed, and the route of transition from quasiperiodic motion to chaotic motion is revealed. Finally, we discuss the average speed along the screening surface considering the frequency, amplitude, friction coefficient, inclination angle, and vibration direction angle. In addition, the convergence conditions of particle motion are proposed, and they are only affected by the inclination angle and friction angle. The results show that in the normal direction of the vibrating screen, the particle motion is quasiperiodic at low frequencies. With increasing frequency, the motion of the particle becomes chaotic, and its Poincaré map becomes petal-shaped. In addition, the number of petals increases at the mutation of the bifurcation diagram. The increase in frequency, amplitude and inclination angle and the decrease in friction coefficient lead to an increase in particle speed along the screen surface. In addition, the particle speed reaches a maximum when the vibration direction angle is 65°. This work provides a theoretical basis for controlling the thickness of granular material flow on a vibrating screen and selecting screening process parameters.

In coal dry screening, online detection for screening efficiency is a significant challenge. Notwithstanding, the method of image processing is strenuous to implement in this field due to the complex surface texture of shattered coal. This method identifies the fractal phenomenon before and after coal screening is discovered for the indirect detection of screening efficiency. For better fractal dimension distribution, an image denoising and filter method for wiping off the coal image surface texture is applied. Additionally, an enhanced Kirsch edge-detection algorithm is employed to obtain coal particle edges. Furthermore, the relation between fractal dimension and screening efficiency is presented by using the box-counting method. In this research, we skilfully transform the tough problem of image detection for particle size distribution into the calculation of the fractal dimension of the coal-edge image, and closely associate the fractal dimension with screening efficiency. With this method, it will be easier to predict the screening efficiency in real-time.

Recycling waste concrete has become a large problem in developing countries. The aim of this work is to provide guidance for screening concrete particles and improving screening efficiency. First, the elastoplastic collision model is established for calculating the coefficient of restitution for concrete particles with different compressive strengths. Then, a bar circular vibrating screen is applied to simulate the screening process of concrete particles by using the discrete element method (DEM). The optimal vibrating parameters, which contain amplitude, frequency and inclination angles, is analyzed for the representative concrete particles containing C15, C45 and C80 by comparing the screening efficiency. The results show that the optimal screening parameters of amplitude and frequency is smaller with the increase in the compressive strength of the concrete particles. Appropriately, the large inclination angle is suitable for screening fine concrete particles with a gap vibrating screen. This work should be helpful for the screening process of concrete waste particles and provides a theoretical basis and simulation case for screening and recycling other particles, such as sand, stone, iron ore and copper ore. In the screening processes of construction wastes, the optimal screening parameters can be selected quickly by calculating the coefficient of restitution and adopting the DEM simulation.