How to determine the dynamic parameters of Banana Screen
The working principle of Banana Screen
Banana Screen, also known as equal thickness screen, utilizes the asymmetrically rotating dual unbalanced vibrators to excite, with two sets of eccentric masses in the vibrators rotating in opposite directions. At each instantaneous position, the centrifugal forces generated by the two sets of eccentric masses always add up along the vibration direction, while the forces in the normal direction always cancel each other out, thereby forming a single-direction excitation force, causing the screen box to perform reciprocating linear vibration. The overall motion trajectory of the screen machine is at a 45° angle to the horizontal. The vibrating part of Banana Screen is supported by four sets of supporting devices through rubber springs.
Under the action of the excitation force, the material on the screen surface performs continuous upward throwing motion at different angles. Materials smaller than the sieve hole size pass through the screen surface, while materials larger than the sieve hole size continue to perform upward throwing motion until they finally leave the screen surface, thereby achieving operations such as material classification, dehydration, mud removal, and medium removal.
Determination of process parameters of Banana Screen
The width of the screen surface
Generally speaking, when other conditions for screening are the same, the production rate mainly depends on the width of the screen surface, and the screening efficiency mainly depends on the length of the screen surface. The width of the screen surface is the main factor determining the production rate of the vibrating screen. Because to ensure the screening effect of the material, the material on the screen surface needs to have an appropriate thickness. When the material thickness is constant, the throughput of the material on the screen surface mainly depends on the width of the vibrating screen, so the wider the screen surface, the greater the production capacity.
The length of the screen surface
The length of the screen surface affects the screening efficiency of the material. Because the screening time is directly related to the length of the screen surface. The longer the screen surface, the longer the screening time, and the higher the screening efficiency. Different operations have different requirements for the accuracy of screening, so the length of the screen surface required for different operations is also different. In the production practice of coal preparation plants, it is believed that for pre-sieving screens, the length of the screen surface is generally about 4 meters; while for final screening, dehydration, and medium removal screens, the length of the screen surface is generally about 6 meters. Such length screens have a screening efficiency of approximately 90%. For Banana Screen, the recommended length of the screen surface with a 50mm sieve hole is 6.5m. Therefore, based on the effective area of the screen surface, it can be calculated that the width of the screen surface of this screen machine is 3.6m, that is, the screen surface size is set at 3600mm X 6500mm.
The inclination angle of the screen surface
The inclination angle of the screen surface refers to the angle between the screen surface and the horizontal line. The size of the inclination angle affects the movement speed of the material on the screen surface. When the inclination angle of the screen surface is large, the material moves faster and the production volume is greater, but the screening efficiency will decrease accordingly. In different situations, various screens need to have their own suitable inclination angles.
Sieve machines that perform linear motion are generally installed horizontally, with an inclination angle of zero. However, for Banana Screen, its screen surface is divided into several segments, and each segment has a different inclination angle. According to the research, for Banana Screen with a 50mm sieve hole, it is recommended that the number of screen surface segments be 5, with inclination angles from discharge to input of each segment being 5°/10°/15°/20°/25°.
Determination of vibration parameters
Amplitude
Amplitude is half of the working stroke of the screen box. The amplitude is an important parameter characterizing the movement characteristics of the screen surface. Its size determines the speed and acceleration of the movement of the screen box. The larger the amplitude, the greater the speed and acceleration of the screen box. During the operation of the vibrating screen, the screen box must have a sufficiently large acceleration to make the material on the screen surface move forward. Therefore, the screen box must have a sufficiently large amplitude. However, the acceleration of the sieve box cannot be too high, because if the acceleration is too large, it will not only damage the normal operation of the sieve box, but also impose higher requirements on the structure of the sieve box. Or it may exceed the allowable range of the sieve structure.
The vibration frequency of the sieve box
Frequency refers to the number of vibrations per minute, and it is also an important parameter that characterizes the movement characteristics of the sieve surface. The higher the frequency, the greater the movement speed and acceleration of the sieve box. Since the acceleration is proportional to the square of the frequency, increasing the frequency has a much greater impact than increasing the amplitude.
Conclusion
Through the analysis and optimization design of the dynamic parameters of the Banana Screen and combined with industrial tests, reasonable parameters were determined. The reasonable selection of these parameters not only provides a theoretical basis for the future development of the Banana Screen, but also provides technical guarantees for improving the reliability of the Banana Screen, and is of great significance for promoting technological progress.
