In industrial production, vibrating screen as a key screening equipment, widely used in mining, metallurgy, chemical industry, building materials and many other fields, its role is to separate the granular materials in accordance with different particle sizes to meet the needs of the production process. Ordinary vibrating screen is a more common type of screening equipment, while the banana screen with its unique arc design in many aspects to show significant advantages. The curved screen surface design of banana screen is not a simple shape change, but a combination of complex dynamics and engineering experience, aimed at optimising the screening process and improving the overall performance. In this paper, we will analyse the advantages of the curved design of the banana screen over the ordinary vibrating screen in several key dimensions.
一.Overview of the structure of banana sieve and ordinary vibrating screen
1.Structural characteristics of banana screen
Banana screen has unique appearance and structure. The shape of its screen box is similar to banana, so it gets its name. The key lies in its curved screen surface with different inclination angles, usually with a larger sloping screen surface at the feed end, the angle can be up to 30° – 40°, such as the common one may be 34°. A large inclination angle at the infeed end allows the material to be quickly dispersed and start screening at a higher speed, which is conducive to improving the initial screening efficiency. As the material moves towards the discharge end, the angle of the screen surface decreases incrementally, culminating in an angle of approximately 10° at the discharge end. This gradual change in angle matches the movement and characteristics of the material during the screening process. In addition, banana screens are generally equipped with box-type vibrators, which provide stable and efficient vibration energy for the screen surface to ensure that the material can be continuously and fully screened on the screen surface. Its support structure design is also unique, through the vibration damping spring and other devices connected to the lower frame, in order to ensure the stable operation of the screen body at the same time, effectively reduce the vibration of the surrounding equipment and infrastructure.
2.Ordinary vibrating screen structure characteristics
The structure of ordinary vibrating screen is relatively simple and direct. The screen surface is usually flat or nearly flat linear structure, and the material mainly carries out linear reciprocating motion on the screen surface. The common vibration device has a vibration motor or eccentric block exciter, etc., through the vibration generated to make the material jump and move on the screen surface, so as to achieve screening. Ordinary vibrating screen is supported in various ways, common spring support, rubber support, etc., the main role is to support the screen body and buffer vibration. Compared with the banana sieve, ordinary vibrating screen in the structure design is more focused on simple and practical, but the limitations of its screen surface structure and vibration mode, resulting in some complex materials screening and high efficiency screening needs scenarios, the performance is not as good as the banana sieve.
二.Advantages of Screening Efficiency
1.Difference in material trajectory
Banana sieve material trajectory: in the banana sieve, the material from the feed end into the sieve, due to the screen surface arc design and vibration, the material will show a complex and continuous arc trajectory. In the feeding end of the large inclined angle of the role of the screen surface, the material to a higher speed and greater impact quickly dispersed, part of the fine particles of material can quickly through the sieve holes. With the material to the discharge end of the move, the screen surface angle is gradually reduced, the material movement speed is gradually reduced, but the trajectory is more zigzag, increasing the residence time of the material on the screen surface and the contact with the screen surface. Materials in the entire screening process constantly tumbling, jumping, so that the material layer can be fully loose, the internal fine particles have more opportunities to expose and through the sieve holes, greatly improving the screening efficiency.
Ordinary vibrating screen material movement track: ordinary vibrating screen linear screen surface makes the material mainly along a single direction to do linear reciprocating motion. The movement of materials on the screen surface is more regular, lacking the complex tumbling and multi-angle movement of banana screen. In the screening process, the material layer is difficult to fully loose, especially in the case of uneven particle size distribution of materials, viscosity, etc., it is easy to appear the phenomenon of material piling up, the phenomenon of extrusion between particles, resulting in part of the fine particles are wrapped in coarse particles of material, can not contact the screen surface in time and through the screen holes, thus affecting the screening efficiency.
2.Sieving area utilisation efficiency
Banana sieve screening area utilisation: the curved screen surface design of banana sieve makes the distribution of materials on the whole screen surface more uniform and reasonable. From the feeding end to the discharging end, the material can always cover the screen surface more closely, making full use of the effective screening area of the entire screen surface. Moreover, due to the arc-shaped trajectory of the material, in different positions of the material and the screen surface of the contact mode and frequency are different, to further ensure that the entire screen surface of the various areas can be efficiently involved in screening work. For example, in the feeding end of the material speed, impact force, can quickly on a large number of materials for preliminary screening; in the discharge end of the material movement is relatively slow but more fully, the remaining more difficult to screen materials for fine screening, so that the screening capacity of the entire screen surface has been given full play.
Ordinary vibrating screen screening area use: ordinary vibrating screen in the screening process, the material is easy to be concentrated in some areas of the screen surface accumulation or uneven distribution. Especially in the vicinity of the inlet, the material tends to focus on the influx, resulting in excessive load on the screen surface in the area, while the screen surface in other areas may not be fully utilised. In addition, due to the characteristics of the linear movement of the material, in the edge part of the screen surface, the movement and contact of the material is relatively less, resulting in lower screening efficiency in these areas, and the overall effective utilisation of the screen surface is not as good as banana screen. After actual testing and production experience, in the same screen size and material handling conditions, the effective utilisation of the screening area of the banana sieve can be 20% – 30% higher than the ordinary vibrating screen, which is one of the important reasons for the higher screening efficiency of the banana sieve.
三.Capacity Advantages
1.Differences in feed end design
Advantage of banana sieve infeed end: The large incline of the banana sieve infeed end is one of the key design features that increase the processing capacity of the sieve. The large angle of inclination enables the material to be dispersed on the screen surface at a high speed under the combined effect of gravity and vibration, forming a thin layer of material. This is not only conducive to rapid screening of materials, but also allows more materials to enter the screening area within a unit of time, greatly improving the feed rate and processing capacity. For example, in the coal screening operation, the feeding end of the banana sieve can quickly accept a large amount of raw coal and quickly screen it initially, separating the fine coal particles that meet the requirements of particle size in a timely manner, reducing the burden for the subsequent screening and processing processes, and improving the efficiency of the overall production process.
Disadvantage of the feeding end of the ordinary vibrating screen: the feeding end of the ordinary vibrating screen is usually more gentle, and after the material enters the screen surface, it takes a certain amount of time and distance to be gradually dispersed and spread all over the screen surface. When the material flow is large, it is easy to appear inlet blockage and material accumulation, which limits the feeding speed and overall processing capacity. Moreover, because the material can not be quickly dispersed to form a thin material layer, in the screening process, it is easy to have the problem of material squeezing each other and screening insufficiency, which further affects the improvement of processing capacity.
2.Material layering effect
Banana sieve material layering effect: the curved screen surface of banana sieve and the curved trajectory of the material are conducive to achieving good layering in the screening process. Under the action of vibration, the coarse particles in the material gradually move to the upper layer of the material layer due to the larger mass and large inertia, while the fine particles are more likely to move downward and contact the screen surface under the combined action of vibration and gravity. This natural layering effect makes the fine particles can be more quickly and smoothly through the sieve holes, improve the screening efficiency at the same time, but also indirectly improve the processing capacity of the equipment. Because only the material to achieve a good stratification, in order to ensure the effective screening of the screen surface, to avoid the interference of coarse particles on the screening of fine particles, so that more materials can complete the screening process in a unit of time.
Ordinary vibrating screen material layering effect: ordinary vibrating screen due to the linear movement of the material and the movement is relatively single, the layering effect of the material on the screen surface is not as obvious as the banana screen. In the screening process, coarse particles and fine particles are easily mixed together, resulting in part of the fine particles being blocked by coarse particles, which can not contact the screen surface in time, affecting the screening speed and processing capacity. Especially for materials with a wide range of particle size distribution, ordinary vibrating screen is difficult to achieve effective stratification and screening of materials in a short time, which is easy to cause clogging of the screen surface and reduce the processing capacity.
四.Advantage of material adaptability
1.Handling of viscous materials
Advantage of banana sieve in dealing with viscous materials: for the more viscous materials, such as wet coal, clay, etc., the curved design of banana sieve has significant advantages. First of all, the complex trajectory of the material on the curved screen surface, so that the friction and shear force between the material and the screen surface is more evenly distributed, and it is not easy to appear in the large area of the material on the screen surface adhering to the accumulation of the situation. Secondly, the vibration mode of banana sieve can produce strong vibration force, which helps to destroy the bonding force between the sticky materials, so that the materials are more easily dispersed and sieved. In addition, the large inclination design of the banana screen feeding end can let the sticky material pass quickly, reduce the residence time of the material in the feeding end, and reduce the possibility of the material sticking on the screen surface. In the practical application of some coal processing plants, banana screen for viscous coal slurry screening, can effectively improve the screening efficiency and processing capacity, reduce the material viscosity caused by equipment failure and production interruption.
Ordinary vibrating screen processing viscous material disadvantage: ordinary vibrating screen faces many difficulties in processing viscous materials. Due to the linear movement of materials and the relatively simple form of movement, sticky materials are easy to adhere to the screen surface and gradually accumulate, blocking the screen holes, resulting in a sharp decline in screening efficiency. Ordinary vibrating screen vibration force is relatively single, it is difficult to effectively destroy the bonding structure of viscous materials, so that the fluidity of the material on the screen surface deteriorates, further aggravating the problem of screen clogging. Moreover, once the screen surface is clogged, the cleaning work is more cumbersome, and it needs to stop the machine for manual cleaning, which seriously affects the continuity and efficiency of production.
2.Treatment of different particle size materials
Advantage of banana sieve on different particle size material processing: banana sieve’s multi-section different inclination angle arc screen surface design makes it has good adaptability to different particle size materials. At the feeding end, the large inclination screen surface and high material movement speed are suitable for preliminary screening and rapid separation of large particles, and can quickly screen out a large number of coarse particles from the material flow. With the material to the discharge end of the movement, the screen surface angle gradually reduced, the material movement speed is reduced, this time is more suitable for small and medium-sized particles of material for fine screening. This sectional screening method, according to the characteristics of different particle size materials, in different screen area to achieve high efficiency screening, to ensure that a variety of particle size materials can be fully processed.
Disadvantages of ordinary vibrating screen for different particle size materials: the single screen structure and relatively fixed vibration parameters of ordinary vibrating screen make it less flexible in dealing with different particle size materials. For large-grained materials, it may be due to insufficient vibration intensity of the screen surface or the short residence time of the material on the screen surface, resulting in inadequate screening; for small-grained materials, it may be due to the screen surface movement is not conducive to the material stratification and through the sieve holes, the sieve holes clogging, screening efficiency is low. When dealing with materials with a wide range of particle size distribution, ordinary vibrating screen is often difficult to take into account the screening requirements of various particle size materials, resulting in poor overall screening effect.
Through the detailed comparative analysis of the banana sieve arc design and ordinary vibrating screen in many aspects such as screening efficiency, processing capacity, material adaptability and equipment wear and maintenance, it can be clearly seen that the arc design of the banana sieve has significant advantages. The unique curved screen surface and multi-section different inclination design of banana screen makes it outstanding in material movement trajectory, screening area utilisation, feeding end processing, material stratification, etc., so as to achieve higher screening efficiency and processing capacity. In terms of material adaptability, banana screen has better processing effect on sticky materials and materials with different particle size. In terms of equipment wear and maintenance, banana screen surface wear is uniform, low maintenance difficulty and low cost. In today’s industrial production is constantly pursuing high efficiency, energy saving, stability, banana screen with its arc design brings many advantages, in many screening fields has a broad application prospects and promotion value, is expected to become a replacement for the ordinary vibrating screen preferred equipment, for the optimisation of the production process and development of various industries to provide strong support.
