In the material processing procedures of industries such as coal, mining and building materials, the banana screen, with its unique "banana-shaped" screen surface design (with an inclination gradually decreasing from large to small) and efficient screening performance, has become a key equipment for classifying and purifying medium and fine-grained materials.
This article will introduce you comprehensively to this efficient screening solution from the equipment principle, structural features to practical applications.
What Is A Banana Screen?
The Banana Screen is an efficient vibrating screening equipment specially designed for medium and fine-grained materials. It integrates four functions: classification, dehydration, desliming, and desilting. It can precisely separate materials of different particle sizes and effectively remove moisture, soil, and impurities such as magnetite powder in heavy medium coal separation, significantly improving the purity of coal and providing high-quality raw materials for subsequent processes while reducing operating costs.
The equipment offers two structural options: the single-layer type is suitable for coarse coal classification or simple dehydration and has the characteristics of high processing efficiency and simple structure; the double-layer type is equipped with upper and lower screen surfaces, which can simultaneously achieve two precision screenings and meet the complex process requirements such as coal slurry classification and dehydration that require "one step for multiple screenings".
Working Principle Of Banana Screen
The high efficiency of the banana screen stems from its "segmented variable inclination" screen surface design. This design enables the materials to be processed in a "gradual and orderly manner", ensuring both processing speed and improving screening accuracy. It can be divided into three key stages:
- ● Feed End (High Inclination Section)
The inclination angle of the feed end screen surface is the greatest. After the materials enter the screen surface from the silo, they will move forward at a high acceleration under the action of a large inclination angle and vibration. At this time, the materials will quickly complete the "layering" - heavy particles (such as qualified fine coal particles) will sink to the screen surface due to gravity, while light particles (such as coal gangue and large impurities) will float to the surface layer.
During the rapid forward movement, a large amount of fine particles smaller than the screen holes will directly pass through the screen and complete the "initial screening". This step can quickly reduce the subsequent processing pressure on the screen surface and improve the overall efficiency.
- ● Intermediate Transition Section
As the materials move towards the middle of the screening machine, the inclination angle of the screening surface gradually decreases, and the forward speed of the materials also slows down. At this time, the materials remaining on the screening surface are mainly medium-sized particles. The slowed speed enables these materials to fully contact the screening surface. The fine particles that were originally stuck at the edge of the sieve holes or failed to pass through completely will be completely screened out under the vibration effect, further improving the screening accuracy.
- ● Discharge End (Small Inclination Section)
At the discharge end, the inclination angle of the sieve surface has been reduced to the minimum, and the materials move at a low speed and slowly. The core function of this stage is "finishing" - ensuring that the remaining small particles are completely screened out, avoiding the qualified fine materials being discharged along with the large-sized impurities (in the industry, this is called "running coarse"). At the same time, the low-speed movement can also reduce the impact of large particles on the discharge port of the screening machine, extending the service life of the equipment.
Banana Screen Structure
The stable operation and efficient screening of the Banana Screen rely on the precise design and coordinated work of its core components. The overall structure of the sieve mainly includes the sieve box, sieve plate, exciter, transmission device, vibration damping system, etc. Each component has its own unique design features and process requirements.
Exciter
The exciter is the core power component of the Banana Screen . Its design directly determines the screening performance and lifespan of the equipment. It has the following highlights:
- Structural Design:It adopts the ZYQX series box-type exciter. The internal part is equipped with imported SKF large-clearance vibration mechanical special bearings, which can withstand high-frequency vibration and heavy loads, and has a long service life;
- Lubrication And Protection:It uses high-precision heavy-duty helical gears, and ensures full lubrication of gears and bearings through "splash lubrication"; it is equipped with a magnetic oil drain plug, which can adsorb iron filings in the lubricating oil to avoid component wear caused by impurities; the special sealing design at the shaft end enables internal gas and heat exchange, while preventing coal dust and moisture from entering and eliminating lubricant leakage;
- Adjustableness:The eccentric torque of the eccentric wheel inside the exciter can be adjusted as needed, and can change the amplitude of the screening machine according to the material characteristics (such as particle size, moisture content), to meet different screening requirements.
Key Components Of The Screen Box
The screen box is the core component that supports the materials and enables vibration. The design and manufacturing process of its key structure are particularly rigorous:
- Side Plate And Outer Guard Plate: Made of Q355D low-alloy high-strength steel, this type of steel has high strength, good resistance to fatigue, excellent cold resistance, and is easy to process, fully meeting the working conditions requirements of the vibrating screen; Through CAD design + laser cutting, they are formed in one piece without any joint gaps. The manufacturing accuracy is ≤ ±03mm (higher than AS3678-250 standard), and the flatness error per square meter does not exceed 1mm; Reinforcement plates, guard plates and angle steel reinforcing bars are added in the concentrated force areas. All connections are fixed by high-strength rivets without welding process, completely avoiding deformation and cracking of the side plate caused by welding stress.
- Crossbeam:It adopts a rectangular hollow structure, featuring both "high rigidity" and "light weight", and completely eliminates vertical connection methods. After the end connection flanges are fully welded through, a heat treatment process is required to eliminate welding stresses. The connection surfaces of the flanges need to be finely machined to ensure verticality. The lower crossbeam uses a unique polyurethane protective process, which is resistant to erosion and wear, and can effectively resist material impact. The longitudinal rail beams for fixing the screen plates are sealed and welded with the crossbeam through angle supports to prevent liquid from seeping in and corroding the crossbeam.
- Exciter Base Beam:It adopts a box-shaped cross-section design, with additional reinforcing plates inside to ensure rigidity while reducing weight. The installation flange for large exciter is specially strengthened. All weld seams need stress relief treatment, and the installation surface is processed according to high-precision standards to ensure the stability of the exciter installation and prevent displacement during vibration.
Vibration Damping System
The vibration damping system of the Banana Screen is centered around a steel cylindrical spiral compression spring. The spring material is 60Si2Mn steel, which has good elasticity and strong load-bearing capacity. After special parameter design, the damping effect is excellent, capable of effectively absorbing the vibration energy of the sieve machine and reducing the impact on the ground foundation.
According to test data, the service life of this vibration damping spring is not less than 10,000 hours, and it does not need frequent replacement, thereby reducing the maintenance cost in the later stage; at the same time, the stable damping effect can also reduce the vibration wear of each component of the equipment, and extend the service life of the entire machine.
The Core Manufacturing Process Of The Banana Screen
Apart from the component design, the manufacturing process of the Banana Screen is also highly rigorous, with each step serving the goals of "durability" and "precision":
- Welding Process: Core components such as the crossbeam and the exciter base beam are assembled using special tooling fixtures to ensure assembly accuracy; weld seams are fully welded in accordance with the JB/ZQ40008-86 standard, and the welding materials comply with the GB1300-77 standard. The welding rods need to be dried at 300-350℃ for 30-60 minutes and then kept at that temperature for a period of time; the flatness error of the flange after welding is controlled within 1mm.
- Stress Relief Treatment: The welded components such as the lower crossbeam, upper crossbeam, and exciter base beam need to be sent to an intelligent temperature-controlled bench-type annealing furnace for stress relief annealing. - The furnace temperature is raised at a rate of 100 to 150℃/h to 500 to 650℃, and then held for 2 to 4 hours. After that, it is cooled at a rate of 50 to 100℃/h to below 200 to 300℃ before being removed from the furnace for air cooling, completely eliminating the welding stress.
- Surface Treatment: After the components are stress-relieved, they need to undergo shot blasting treatment through a roller conveyor-type shot blasting machine to achieve the effect of rust removal and removal of surface oxide scale. The surface finish reaches Sa2.5 grade; for flow components and vulnerable parts, polyurea material is additionally sprayed, and in some scenarios, adhesive wear-resistant rubber plates will be added to form "dual wear protection".
- Factory Inspection: Before leaving the factory, each Banana Screen must undergo meticulous assembly and rigorous no-load test runs to ensure uniform vibration, stable operation, no abnormal noise or leakage. Only after meeting the standards can it be shipped.
Why Is The Banana Screen Superior To Traditional Screening Equipment?
Compared with traditional linear screens, circular vibrating screens, etc., the advantages of the Banana Screen mainly lie in the three dimensions of "efficiency, adaptability, and energy consumption". These advantages directly bring value of cost reduction and efficiency improvement to enterprises:
- High screening efficiency
The "segmented variable inclination" design of the banana screen has fundamentally enhanced the screening efficiency. The large inclination angle at the feed end enables the materials to quickly separate, with heavy particles sinking to the screen surface, creating conditions for subsequent screening; the speed gradually slows down in the middle and at the discharge end, allowing the materials to fully pass through the screen.
According to industry test data, the unit area processing capacity of the banana screen can reach 1.5-2 times that of traditional linear screens. For example, after a large coal preparation plant replaced its traditional linear screen with a banana screen, under the same screen area, the coal classification processing capacity increased from 80 tons per hour to 140 tons, with an efficiency increase of 75%.
- Strong Adaptability To Materials
The particle size, humidity and fluidity of different materials vary greatly. The banana screen achieves the adaptation to different materials through the "adjustable design":
- ● Adjustable Inclination Angle:For high-humidity and easily agglomerated materials (such as wet coal sludge, slag), the inclination angle of the input end can be increased to enhance the forward speed of the materials and avoid agglomeration and blockage. For materials with finer particle size and good fluidity (such as fine coal particles), the inclination angle can be reduced to extend the screening time and improve the accuracy. When a cement plant processed high-humidity slag, it adjusted the inlet inclination angle from 30° to 35°, directly increasing the production capacity by 12%.
● Wear-Resistant Adaptation: For high-erosion materials (such as iron ore, gravel), a screen plate and crossbeam with dual protection of polyurethane and wear-resistant rubber can be selected to extend the service life of the components; for corrosive materials (such as certain non-ferrous metal ores), stainless steel components can be selected to avoid corrosion damage.
- Energy Consumption And Stability Advantages
- ● Low Energy Consumption: If traditional screening equipment uses a large inclination angle throughout the process, it will cause excessive load on the motor; if it uses a small inclination angle throughout, it will reduce efficiency. The segmented design of the banana screen avoids this problem - the input end has a large inclination angle for rapid processing, and the discharge end has a small inclination angle for low-speed finishing. The overall energy consumption is approximately 15%-20% lower than that of traditional equipment, and it can save a lot of electricity over the long term.
● Strong Stability:The design of the banana screen strictly follows the BS7608 (Fatigue Design and Evaluation for Steel Products) standard. Before leaving the factory, finite element force analysis will be conducted to simulate the stress and displacement of important components such as side plates, cross beams, and exciter base, ensuring no deformation or cracking under high-frequency vibration; key weld seams will also undergo first-level UT (Ultrasonic Testing) and magnetic particle testing to eliminate welding defects, and the average downtime without faults of the equipment is long.
Application Of Banana Screen
Thanks to its high efficiency and strong adaptability, the banana screen has been widely applied in various industries such as coal, mining, and building materials, mainly focusing on the processing of medium and fine-grained materials.
Main Application Industries And Scenarios
- ► Coal Industry (Core Application Field)
Raw coal classification: Divide raw coal by particle size into large coal, medium coal, and fine coal, providing different specifications of products for subsequent coal washing and sales;
Coal dehydration / desliming: Remove moisture and coal sludge from washed coal to increase coal calorific value and reduce transportation costs;
Desilting: In the heavy medium coal separation process, remove the magnetite powder (heavy medium) adsorbed on the surface of coal to achieve medium recycling and reuse.
- ► Mining Industry
Mineral classification: Classify iron ore, limestone, and other minerals, screen out qualified particle sizes of minerals to enter the grinding process, avoiding large pieces of minerals from wearing out the mill;
Mineral dehydration: Remove moisture from mineral washing, facilitating subsequent drying, storage and transportation.
- ► Building Materials Industry
Gravel and sand grading: Classify gravel and sand aggregates, screen out different particle sizes of aggregates for use in concrete and cement product production;
Slag treatment: Screen and dehydrate the blast furnace slag from cement plants to separate usable particles and reduce solid waste emissions.
Typical Applicable Materials
Coal-based: raw coal, coal gangue, coal sludge, washed coal;
Mineral-based: iron ore, limestone, copper ore, bauxite, etc. (medium to fine-grained minerals);
Other types: gravel aggregates, blast furnace slag, chemical particles (non-corrosive).
The Banana Screen, with its innovative design of "segmented variable inclination", has overcome the problems of "low efficiency and poor adaptability" of traditional screening equipment, and has become the preferred equipment for handling medium and fine-grained materials. Whether it is the efficient classification in the coal industry or the precise screening in the mining and building materials industries, it can achieve "high efficiency, energy saving, and durability", helping enterprises reduce costs and increase profits. As the demand for "refinement and low-carbonization" in industrial production increases, the application scenarios of banana screens will further expand, providing stronger support for industry development.
