A circular vibrating screen, a kind of reciprocating vibrating screens, has two advantages over other types of sifters: smaller production area compared to a large screen mesh, and higher separation efficiency due to the longer relative motion of material particles. The unique feature of a circular vibrating screen is its three-dimensional motion in the space, which leads to high screen efficiency, high throughput and low power consumption. In addition, due to its simple structure and easy assembly and disassembly, different raw materials can be sorted by grain size in a single plant.
The materials in the circular vibrating screen perform sliding and projection motions while drawing a spiral motion path on the screen surface during sieving. This motion is due to the use of a vertically installed vibrating motor vibrating device that provides the spatial motion of the screen box. Here, the sliding and projection motions of the material affect the path of the material on the screen surface and provide the material delivery rate that allows the material to move outward to the screen surface. Especially, when the materials are in a projection motion, the materials in the material layer are mixed with each other, and the opportunity for fine particles to pass through the screen increases the sieving efficiency. Therefore, the sliding and projection motions of raw materials should be controlled properly to ensure constant throughput and improve screening efficiency.
Many researchers have worked on determination of the parameters of a circular vibrating screen that are being applied to its design. It is very important to clarify the theory of the motion of material on the vibrating surface in determining the kinetic parameters of a vibrating machine, but unfortunately, the kinetic theory of material on the surface of a circular vibrating screen has not been studied in detail.
Hwang Je Hyon, a section head at the Faculty of Mechanical Science and Technology, conducted a dynamic analysis of a circular vibrating screen and the motion characteristics of screen surface, based on which he carried out a theoretical analysis of sliding and projection motions of material, and then, he verified it using EDEM.
The analysis results are as follows.
First, the screen surface of a circular vibrating screen undergoes a plane rotational motion around the vertical symmetry axis and a swinging motion around the center of mass.
Second, the theoretical transport rate of the material sliding motion in a straight vibrating screen is proportional to the angular frequency and vibration amplitude, whereas in a circular vibrating screen, it is proportional to the angular frequency and oscillation angle.
Third, the projection index of material motion at the end of the screen surface of a circular vibrating screen can be determined from 3 to 7 taking into account the motion characteristics of material and the strength of vibrating parts. In this case, the sieving properties tend to improve gradually and then deteriorate again.