What are the Factors That Affect the Screening Effect of the Flip Flow Screen

Preface

Screening is an important step in coal washing and selection. Due to the fact that fine and wet coal is difficult to loosen and separate, it is prone to clog the sieve holes, deteriorating the screening process and reducing the screening efficiency. Therefore, the deep screening of wet fine coal has become a hot and challenging issue in the screening industry. Currently, it is already quite difficult to grade raw coal with a particle size of 6-13mm using ordinary screening machinery, and the screening of 3mm wet coal cannot be effectively carried out. In recent years, new and highly efficient screening machines specifically designed for the deep screening of wet fine coal have been continuously introduced. The Flip flow screen has advantages such as a large screen surface acceleration, high screening efficiency, large processing capacity, low clogging tendency, strong adaptability, small overall dynamic load of the screening machine, and moderate price. It has relatively significant advantages and wide application prospects and market potential. Now, let’s discuss what factors affect the screening effect of the Flip flow screen?

Flip flow screen

The Flip flow screen achieves this by means of the elastic movement of the sieve net, where the net alternately stretches and contracts. Under the influence of the sieve net’s amplitude and elasticity, the materials continuously come into contact with the sieve surface, bounce off, become loose, and then pass through the sieve, completing the dry and efficient screening of difficult-to-sieve materials with high viscosity and high production capacity.

Structural composition

The Flip flow screen is composed of the main sieve frame, the floating sieve frame, the sieve plate, the shear spring, the vibration damping spring, etc. The beams of the Flip flow screen can be divided into two groups, namely the fixed beam and the floating beam. The two groups of beams are arranged alternately. The fixed beam is directly fixed on the side plate and together with the side plate, the exciter, the support beam, etc., forms the main sieve frame system; the floating beam passes through the side plate at both ends and is softly connected to the side plate through the shear spring. The floating beam and its fixing device form the floating sieve frame system. The polyurethane sieve plate is installed between the fixed beam and the floating beam and performs a slackening movement as the distance between the fixed beam and the floating beam changes.

Working principle

The Flip flow screen is a dual-mass vibration system. It uses polyurethane rubber as the screen surface. The fixed beam I and the floating beam II supporting the screen surface belong to two vibration masses. One of the masses is the screen box, and the other is the counterweight. When the Flip flow screen is in operation, the two masses vibrate with a phase difference of π. Any two adjacent beams or those close to or far from each other cause the elastic screen surface to either relax or tighten, and the screen mesh either tightens or loosens, thereby causing the material to undergo forward and bouncing movements. At the same time, the Flip flow screen is designed based on the equal thickness screening method. The angle of the screen surface gradually decreases from the input end to the output end. The large inclination angle at the input end enables the material to move quickly and be quickly stratified on the screen surface, thus avoiding the material adhering to the screen mesh or even blocking the sieve holes, and also improving the processing capacity of the screening machine.

Factors Affecting Screening Effect of Flip Flow Screen

Amplitude

The movement law of difficult-to-sieve materials indicates that to achieve good screening results, a sufficiently large amplitude and vibration intensity are necessary. However, the amplitude is not necessarily the larger the better. To obtain better screening results, larger amplitudes should be selected for coarse and difficult-to-sieve materials, while smaller amplitudes should be used for powdery materials. Although the Flip flow screen has a larger amplitude, its transmission mechanism and screen box still operate under a relatively low vibration intensity. Therefore, the transmission system of this equipment has a longer service life than that of conventional components.

Screen Surface Width

The dynamic analysis of the screen surface reveals that the change in screen surface width has a certain impact on the screening process of the Flip flow screen. Increasing the screen surface width has almost no effect on the movement speed of the screen surface, but it can increase the screen surface amplitude, which is beneficial for the thorough screening of materials; when the screen surface width reaches a certain level, the amplitude of the screen surface acceleration decreases, which may lead to the occurrence of “trapping of ore”, and is not conducive to the screening of materials. At the same time, the increase in screen surface width can also reduce the stress on the screen surface during the screening process and reduce the loss caused by the concentrated distribution of stress on the screen surface; however, for ordinary vibration machinery, if the screen width is doubled, the strain of the pipe frame will increase by 16 times, so the diameter of the pipe frame will also increase accordingly, which will increase the difficulty of mechanical manufacturing.

Screen Surface Tension

The screen surface tension refers to the difference between the maximum distance between the crossbeams at both ends of the screen surface and the length of the screen plate. By simplifying the screen plate of the Flip flow screen into a simply supported beam with both ends freely movable, and using the elastic body vibration model for research, it is found that within a certain range, changes in screen surface tension will cause the peak of screen surface acceleration to continuously change. This change can effectively promote the bouncing, loosening and stratification of materials on the screen surface, which is beneficial for the screening of damp fine-grained materials. The smaller the tension, the smaller the average speed of the screen surface, the slower the movement of the screen surface, and thereby hinder the transmission of motion between the screen surface and the materials, which is not conducive to the loosening and stratification of the material layer, and reduces the screening efficiency; but an excessive screen surface tension will increase the burden on the screen surface, reducing the lifespan of the screen mesh.

Speed

The magnitude of the angular velocity of the Flip flow screen directly affects the ejection condition of the screened materials. When the angular velocity increases, the vibration of the screen surface accelerates, and wet and sticky materials are more likely to be ejected, which can promote the dispersion and screening of the materials. When the rotational speed of the Flip flow screen is constant, the time it takes for the material to be ejected once is equal to the time it takes for the screen surface to rotate once. Thus, after one ejection, the material can still return to the previous ejection state. At this time, the screening effect is better, and this rotational speed is the first critical speed. According to experience, when other conditions are constant, the better the screening effect, the closer the rotational speed of the Flip flow screen is to the first critical speed. The on-site experience rotational speed is usually 520 r/min.

Conclusion

The flip flow screen, as an efficient screening equipment for sticky and wet fine-grained materials, its screening effect is influenced by multiple factors such as amplitude, screen surface width, tension, and rotational speed. In practical applications, parameters should be reasonably matched according to the specific material characteristics and process requirements to achieve the best screening efficiency and equipment lifespan.