How Is The Inclination Angle Of The Banana Screen Plate Designed
In coal preparation plants, metal mines and sand and gravel aggregate production lines, Banana screen is highly favored for its unique multi-segment zigzag screen plate design. Compared with traditional linear screens or circular vibrating screens, the Banana screen achieves uniform thickness screening through the gradient change of the screen plate’s inclination Angle. Its processing capacity can reach 1.5 to 2 times that of ordinary screens of the same specification, and the screening efficiency is increased by more than 50%. This paper will start from the principle of equal thickness sieving and deeply analyze the design logic, parameter selection and engineering optimization strategy of the inclination Angle of the Banana screen plate.
Banana screen and the principle of equal thickness sieving
What is Banana screen
Banana screen, also known as equal-thickness vibrating screen or linear equal-thickness screen, is composed of a screen box, screen mesh, box-type vibrator, vibration damping spring and driving device, and its running trajectory is linear vibration. The Banana screen plate is not a single plane. Instead, it adopts a zigzag design with multiple segments and different inclination angles, with the inclination angles decreasing section by section from the feeding end to the discharging end. In 1965, the French scholar E. Bourstrain first proposed the equal thickness screening method (HCC screening method). Its basic principle is: by adjusting the ejection acceleration of each section of the screen plate or the inclination Angle of the screen plate, the material can obtain a greater movement speed and ejection intensity at the feeding end, promoting rapid stratification of the material. At the discharge end, reduce the ejection acceleration and discharge speed to increase the probability of fine particles passing through the screen.
The key role of inclination Angle in screening
The inclination Angle of the screen plate directly determines the movement speed of the material on the screen plate. The greater the inclination Angle, the faster the material slides down under the action of its own weight and vibration force, and the thinner the material layer, which is conducive to rapid stratification and the screening of easily sieved particles. The smaller the inclination Angle, the slower the material flow rate, and the more stable the material layer, providing more sufficient sieving time for difficult-to-screen particles close to the size of the sieve holes.
In the Banana screen, the inclination Angle at the feeding end is usually set between 25° and 34°. The material passes through at a relatively high speed, and the material layer rapidly thinens and completes the initial stratification. As the screen plate extends towards the discharge end, the inclination Angle decreases section by section to 0° to 10°, and the material flow rate decreases simultaneously. Since a considerable amount of fine-grained materials have passed through the screen in the front section, the material layer in the back section will not thicken, thus maintaining an approximately equal-thickness material distribution throughout the screen plate.
The core advantage of equal-thickness screening
Due to the uniform thickness of the material layer, the contact opportunities between fine-grained materials and the screen plate increase significantly, and the screening efficiency improves accordingly. For working conditions with a high content of fine particles, especially when the proportion of materials with particle size less than half of the classification particle size is large, the screening advantage of Banana screen is particularly prominent.
The core design parameters of the screen plate inclination Angle
Recommendations for inclination angles of different types of jobs
Medium removal, dehydration and sludge removal operations
The inclination Angle of the feeding end of the Banana screen is usually set at 25°, and the inclination Angle of the discharging end is controlled within the range of 0° to 5°. It is suitable for scenarios such as medium removal in coal washing plants, fine particle material dewatering, and material processing with high mud content. A smaller inclination Angle at the discharge end helps to prolong the residence time of the material on the screen plate, improving the efficiency of medium removal and dehydration.
Graded assignment
The inclination Angle range of the feeding end has been expanded to 25° to 35°, while that of the discharging end is 5° to 10°. A larger feed end inclination Angle is conducive to particle size classification and screening, enabling rapid separation of materials of different particle sizes. The inclination angles of each screen plate of the Banana screen used for classification are generally larger than those of the screens used for medium removal and dewatering to ensure that the materials have sufficient movement speed to complete the particle size classification.
The design of the number of segments and the inclination gradient
Banana screen plates are usually divided into 4 to 7 sections, and each section adopts a different inclination Angle to form a zigzag screen plate. The design of the number of segments and the inclination gradient directly affects the screening effect and the lifespan of the screen plate.
Take the five-section zigzag design as an example. A classic configuration is that from the feeding end to the discharging end, the sequence is 25°, 20°, 15°, 10°, and 5°, with each section decreasing by 5°. Another common configuration is to reduce from 34° to 10°, which is suitable for working conditions that require a larger processing capacity.
The recommended range of the inclination gradient is from 3° to 6°, decreasing step by step. Gradient design should take into account the characteristics of the materials and the screening targets: when the gradient is large, the material velocity changes sharply, which is suitable for processing large volumes of materials that are easy to screen. When the gradient is small, the transition of the inclination Angle is gentle, which is conducive to prolonging the service life of the screen plate and improving the screening rate of difficult-to-screen materials.
The influence of material properties on the design of inclination angles
When the content of fine particles in the material is relatively high, it is recommended to adopt a gentle inclination transition design to allow the material to have more sufficient sieving time on the screen plate and reduce the wear of the screen plate at the same time. If the proportion of coarse particles reaches about 55%, a smaller inclination gradient (3° to 4°) should be selected to avoid insufficient screening due to overly rapid material movement.
The vibration parameters and the inclination Angle of the screen plate need to be adjusted in coordination. The vibration direction Angle of Banana screen is usually set at 45°, the vibration frequency is 900 revolutions per minute, and the amplitude is controlled at about 5 millimeters (9 to 11 millimeters for double amplitudes). In practical engineering, the vibration amplitude can be adjusted by regulating the eccentric block of the exciter, complementing the inclination Angle design to meet the screening requirements of different materials.
Screen plate Tilt adjustment and maintenance tips
On-site adjustable parameters
The inclination adjustment range of the Banana screen plate is generally from 5° to 30°. In addition to adjusting the installation Angle of the screen plate itself, the operator can also adjust the vibration amplitude through the eccentric block of the exciter to change the throwing intensity and movement speed of the material on the screen plate. It is recommended that the vibration frequency be maintained within the range of 10 to 18 Hertz, working in conjunction with the inclination Angle design to achieve the best screening process effect.
The relationship between the wear of the sieve plate and the inclination Angle
The smooth transition of the inclination Angle of the screen plate is not only beneficial to the screening efficiency, but also can significantly extend the service life of the screen plate. In areas with drastic changes in inclination Angle, the impact and friction of materials are concentrated, accelerating the wear of the screen plate. The gentle transition of the inclination Angle enables the material flow rate to change uniformly, and the wear distribution is more balanced.
Selection of sieve plate material
The combined application of polyurethane and stainless steel screen bars is becoming increasingly widespread. The polyurethane part has the advantages of wear resistance and noise reduction, while the stainless steel part has high strength and a large opening rate. The two are installed through a tight plastic fit, which is firm and not easy to loosen. For the areas at the feeding end that are subject to greater impact, stainless steel roller screen plates can be specially arranged to take advantage of their strong impact resistance to extend the overall service life of the screen plate.
Key points for maintenance and care
Due to long-term vibration, the fixing bolts of the screen plate may loosen, causing the actual inclination Angle to deviate from the design value and affecting the screening effect. Meanwhile, the condition of the vibration damping spring directly affects the stability of the vibration transmission of the screen body, and its stiffness and fatigue degree should be monitored regularly. The maintenance of the lubrication system should not be overlooked either. The bearings of the exciter usually adopt thin oil gear splash lubrication, and it is necessary to ensure that the oil level and quality meet the requirements.
Conclusion
The design of the inclination Angle of the Banana screen plate needs to comprehensively consider multiple factors such as the principle of equal thickness screening, operation type, material characteristics and vibration parameters. Overall, a large inclination Angle at the feeding end can achieve rapid stratification of materials, while a small inclination Angle at the discharging end provides sufficient screening time for fine-grained materials. The design of an inclination Angle with a gradient decrease in segments is the core to ensuring screening efficiency and processing capacity.
