In mineral processing plant, vibrating screen is one of the common classifiers, which has large influence on the following works. Therefore, how to improve the screening effect is one of important problem to be concerned. In this paragraph, we will analyze what the factors are and how they influence the vibrating screen.
There are many problems influences the screening effect of vibrating screen. The most important ones are the characteristics of the screening material, the screen surface parameters of the vibrating screen, and the motion parameters of the vibrating screen. Next we will analyze them one by one.
Different materials have unique characteristics in density, hardness, moisture content and other aspects of the difference. Generally speaking, the screening effect of materials with higher hardness and brittleness is better than those with lower hardness and brittleness. For sieving materials, there are two aspects that can directly affect the screening effect: material size and material moisture content.
When the material size is close to the size of the screen, the screening efficiency will decrease obviously. These particles may block the screen, resulting in a reduction in the effective screen area. This is a common phenomenon in the process of closed-circuit crushing, which can be improved by increasing the vibration screen amplitude, which can promote the fine material through the screen surface, reducing the phenomenon of blockage. In addition, the passing rate of the middle part of the sieve can be increased to improve the screening effect. Can also be changed by changing the feeding way to improve the shaker screen surface utilization rate, can use multiple feeding, reduce the screen material movement time and distance on the screen surface, improve the screening effect.
When the material moisture content is large, the material is prone to adhesion, so that the screening efficiency is reduced. Generally speaking, wet materials with large water content can improve the screening effect by increasing the screen hole, but if the mud content of the material is more than 8%, it should be treated by wet screening or pre-washing.
The screen surface parameters of the vibrating screen includes the shape of screen hole, opening rate of screen surface of vibrating screen, the material of vibrating screen and so on. Generally speaking, the long screen surface, material residence time is long, screening opportunities, high efficiency, and wide screen surface processing capacity is better. Practice improved that the suitable aspect ratio is 2:1~3:1.
Here, the opening rate of screen surface of vibrating screen can be understood as the effective screening area. That is, the ratio of the screen area to the total area of the screen surface. The larger the effective screen area is, the higher the productivity per unit screen surface is, and the higher the screening efficiency is. As for the mesh shape, it is chosen by the shape of material particles. Generally speaking, the circular particles is suitable for square mesh shape.
In terms of material, different screen surface materials will also have an impact on the screening effect, which can directly affect the adhesion coefficient between minerals and the screen. For viscous minerals, rubber, polyurethane and other elastic screen surface materials should be used to ensure the material on the screen is loose. However, this kind of material usually has the disadvantage of small porosity.
In combination with the above several aspects, we know that in the selection of shaker screen surface, should be a comprehensive consideration of different materials and the opening rate.
The motion parameters of the vibrating screen includes two aspects:the vibration frequency and direction angle of vibrating screen. The materials on the screen can be thrown from the screen surface. The coarse materials reach the upper side, while the fine materials reach lower side, close to the surface. The screen layers is uniform and increases the passing rate of fine materials. For the materials with large particle size, the higher frequency is, the more times the pulse number on the screen is, the more chances to reach the screen surface. It can reduce the mesh blocking. Therefore, improving the vibrating frequency can effectively increase the screening effect.
The direction angle of vibrating screen is the angle between vibrating direction line and the screen surface. The larger angle is, the smaller the horizontal distance of material is, relatively the lower moving speed on the screen. In practice, the angle should be small when screening material easy to screen, while the angle should be large when screening materials hard to screen. The direction angle of liner vibrating screen is 30~60 degree, and the direction angle of circular screen is 90 degree.
Through the analysis above, we knows some factors influences the screening efficiency of vibrating screen and how to improve it. All in one, we need to choose vibrating screen according to the demands with suitable material of the screen surface and improving the motor adjusting the excitation force, and make sure a low material water-content. Improve screening effect while ensuring processing capacity.