I. General Design and Working Process

The banana screen got its name due to the screening surface shaped like a curve resembling a banana. It is a highly efficient heavy vibrating screening equipment. Material enters from the loading side onto the screening surface, where under the action of vibrational excitation force it moves along the surface, passing through a multi-section surface with different inclination angles for stratification, screening, and transportation. Material of the required size passes through the sieve holes, forming the undersize product, while material of unsuitable size is discharged from the end of the surface as the oversize product.

II. Main Working Principles

1. Principle of the Banana-Shaped Screening Surface

Multi-section design with variable angles:

• The screening surface consists of 3-5 sieve sections with different inclination angles.
• From the loading end to the unloading end, the angles gradually decrease.
• Typical configuration: first section 35°-45°, second 25°-30°, third 15°-20°, fourth 10°-15°.
• The junctions of the sections form smooth transitions, overall creating a banana-shaped curve.

Purpose of the variable angle design:

• Loading section (large angle) Material quickly accelerates, rapidly expands and disperses, forming a thin layer.
• Middle sections (medium angle) Material moves at a moderate speed, fully stratifies and screens, fine particles quickly pass through the holes.
• Unloading section (small angle) Material movement slows down, residence time increases, ensuring complete screening of hard-to-screen particles.
• This overcomes the contradiction of traditional flat screens between clogging at the loading end and insufficient screening at the unloading end.

2. Vibration Excitation System

Vibrator configuration:

• Usually a two-shaft self-synchronizing vibrator or inertial vibrator is used.
• The vibrator creates a circular or elliptical vibration trajectory.
• Design with large excitation force, force can reach 150-300 kN.
• Amplitude usually 6-10 mm, frequency 800-1000 rpm.

Vibration transmission mechanism:

• The vibrator drives two eccentric shafts to rotate synchronously in opposite directions via a drive shaft or gearbox.
• The centrifugal force of the eccentric blocks sums up into the excitation force.
• The excitation force is transmitted through the screen box to the entire screening surface.
• The screen box is isolated from the frame by springs or rubber shock absorbers.

Effect of vibration parameters:

• Throwing intensity Large excitation force provides high acceleration of throwing (usually 3-5g), material is effectively thrown and stratified.
• Vibration direction The vibration direction is perpendicular or close to perpendicular to the screening surface, facilitating material passage through the holes.
• Amplitude adjustment Amplitude can be changed by replacing eccentric blocks or adjusting eccentricity to adapt to different materials.

3. Material Movement and Screening Mechanism

Material movement process:

(1) Acceleration phase at loading:

• Material from the loading opening enters the first section with a large inclination angle.
• Under gravity and vibration, it quickly accelerates.
• The material layer quickly expands, thick layer becomes thin, increasing screening probability.
• Preliminary stratification: fine particles move to the lower layer, coarse remain on top.

(2) Stratification and screening phase:

• Material enters the middle sections with medium inclination angles.
• Movement speed is moderate, material on the surface makes full jumps and rolls.
• Continuous vibration constantly stratifies material, fine particles gradually descend and contact the surface.
• A large amount of fine particles pass through the holes; this is the zone of maximum screening efficiency.
• Material thickness gradually decreases, proportion of coarse particles increases.

(3) Precise screening phase:

• Material enters the end section with a small inclination angle.
• Movement speed decreases, residence time increases.
• Hard-to-screen particles (critical size) get more opportunities for screening.
• Screening accuracy and efficiency are ensured.
• Finally, un-screened coarse particles are discharged from the unloading end.

Stratification mechanism:

• Gravitational stratification : During vibration, small particles with small gaps settle faster; large ones with bigger gaps remain in the upper layer
• Accelerated stratification : Acceleration from vibration causes particles to stratify by density and size
• Effect of holes : Small particles quickly pass through holes when approaching the surface, large ones are retained on the surface
• Continuous stratification : Material on each section continuously stratifies, screening efficiency constantly increases

Screening process:

• Small particles under the combined action of vibration, gravity, and surface inclination reach the holes
• At the moment of detachment during tossing, the material separates from the surface, particles with a certain probability pass through the holes
• Hole size is designed on the principle of "retaining large, passing small"
• Passed material falls into the under-screen bunker, unpassed material continues moving forward

4. Mechanism of unique advantages of the banana screen

High performance:

• Large angle in the loading section ensures rapid dispersion of material, higher load per unit area
• High utilization coefficient of effective screening area, the entire surface works efficiently
• Compared to a flat screen, performance can be 1.5-2 times higher

High screening efficiency:

• Multi-section design with variable angles ensures screening of materials of different sizes in the most suitable zones
• Material residence time on the surface is long and distributed rationally
• Screening efficiency can reach 85%-95%

Design preventing clogging:

• High movement speed in the loading section reduces material accumulation
• Large amplitude and high vibration frequency prevent hole clogging
• Polyurethane or perforated steel screens with good self-cleaning properties can be used

High adaptability:

• Can process sticky materials with high moisture content
• Section angles and hole sizes can be adjusted according to material characteristics
• Suitable for coarse, medium, fine screening and dewatering

III. Key technical parameters

1. Configuration of screening surface angles

• First section: 35°-45° (fast dispersion section)
• Second section: 25°-30° (main screening section)
• Third section: 15°-20° (precise screening section)
• Fourth section: 10°-15° (final section)
• Specific angles are adjusted according to material properties and screening requirements

2. Vibration parameters

• Amplitude: 6-10 mm (adjustable)
• Frequency: 800-1000 rpm
• Tossing intensity: 3-5g
• Vibration direction angle: 45°-60° (angle with horizontal)

3. Characteristics of screening surface

• Surface width: 1500-3600 mm
• Surface length: 3000-8000 mm
• Hole size: 2-200 mm (selected as required)
• Number of layers: single or double layer

IV. Detailed breakdown of the working process

Stage 1: Feeding and initial dispersion

Material is evenly fed onto the loading end of the banana screen through a loading chute or belt feeder. Upon contact with the first section with a large inclination angle, the material quickly accelerates under the combined action of gravity and vibration force, the thick layer rapidly spreads into a thin one, significantly increasing material dispersion.

Stage 2: Rapid stratification and coarse screening

On the first and second sections, the material performs intense jumping and rolling at high speed. Small particles quickly settle under gravity and vibration, approaching the surface and beginning to be screened. Large particles remain in the upper part of the layer due to inertia and size, continuing to move forward. At this stage, most of the easily screened particles are separated.

Stage 3: Main screening and precise stratification

Material enters the third section with medium and small inclination angles, movement speed decreases, residence time on the surface increases. Layer thickness is noticeably reduced, screening conditions optimized. Medium-sized particles and some difficult-to-screen particles are fully screened at this stage. Screening efficiency reaches its maximum.

Stage 4: Processing of difficult-to-screen particles and unloading

The remaining material, mainly large particles and a small amount of particles of critical size, enters the fourth section with a small angle. The movement speed is further reduced, the material on the surface fully vibrates and rolls over, making it easier for hard-to-sieve particles to come into contact with the openings. As a result, all fine particles of the required size pass through the openings, while the unsuitable large particles are discharged from the unloading end.

Stage 5: Collection of undersize material

Material that has passed through the openings falls into the undersize hopper or collection container and is transported to the next operation or finished product warehouse. For a two-layer screen, the second surface performs secondary screening of the undersize material, producing products of several fractions.