Application of Roller Screen in Coal Preparation Plants
Roller screen is mainly applied in coal classification in industries such as coal mines and power plants. Compared with the traditional vibrating screen, the roller screen is less prone to clogging when grading wet and sticky coal, can ensure the processing capacity and screening effect, and has no vibration, low noise and good dust-proofing performance during operation. In recent years, it has been widely used in the raw coal preparation screening and fine-grained powder removal operation links of coal preparation plants, and has achieved remarkable results.
Working principle and structural features
Working principle
The screen surface of the Roller screen is composed of multiple screen shafts arranged in parallel and equipped with screen plates. The screen shafts are driven to rotate through a transmission device, and their rotation direction is the same as the flow direction of the materials. The gap between the screen shaft and the screen plate forms the screen holes. Materials smaller than the screen holes pass through the holes under the action of their own weight and the rotational force of the screen shaft, while materials larger than the screen holes continue to move forward along the screen surface and become the materials on the screen. Eventually, the classification of materials is achieved. To prevent materials from getting stuck on the screen shaft, electrical and mechanical overload protection functions are provided. The screening particle size needs to be adjusted according to the user’s requirements, by adjusting the gap of the screen shaft and the size of the screen plates.
Structural features
Roller screen has the characteristics of simple structure, no vibrating parts, low noise, small daily maintenance, the screen holes are not easy to clog, and it is easy to seal and remove dust. The roller screen is generally cast from manganese steel. An electrical overload protection device is installed on the drive motor control circuit. When the screen shaft is stuck, it can automatically alarm and stop the machine. The connection between the screen shaft and the reducer generally adopts nylon rods and pins. When the screen shaft gets stuck, the nylon rods and pins can be cut off instantly. Protect the motor. A cleaning device is installed at the lower part of the screen shaft to keep the screen plates clean.
The main structural differences of Roller screen
Shape of the sieve plate
The common shapes of sieve plates include plum blossom-shaped, parabolic, elliptical, toothed, etc. The selection of screen plates mainly considers disturbing the materials, better loosening and screening the materials, and conveying the materials forward along the screen surface to ensure that the process is less likely to get stuck. Among them, the parabolic screen plate generally has a greater rotational deflection than other types of screen plates, causing the material to be thrown forward at approximately 45° during its movement along the screen surface. The elliptical screen plates, when performing circular motion, generate sinusoidal wave trajectories that disturb the materials, breaking up and stratifying the materials on the screen surface. As the materials move forward along the screen with a certain inclination Angle, efficient screening is achieved.
Screen plate arrangement method
The screen plates are divided into parallel arrangement and interlaced arrangement. The interlaced arrangement can reduce the jamming of materials between the screen plates by the movement of adjacent screen shaft screen plates.
Driving mode
The driving methods of Roller screen are mainly divided into three forms: single-axis single-motor independent transmission, multi-axis chain transmission, and multi-axis linkage gearbox transmission.
(1) The advantage of single-axis single-motor drive is that when a single screen shaft fails, the material can utilize the inertia of the inclined surface, be pushed by the previous screen shaft to pass over the faulty screen shaft and continue to move forward. The roller screen can still operate as usual, and single-axis overload detection can be achieved. The drawback is that each shaft needs to be equipped with a separate drive device, resulting in many failure points and maintenance points.
(2) The advantages of multi-axis chain drive and multi-axis linkage gearbox drive are that multiple axes share one set of drive device, which requires less maintenance. The disadvantage is that when a single screen shaft fails, the entire screen shaft section will be unable to work.
Screen surface layout method
According to the different angles of the roller screen surface and the horizontal, the layout of the screen surface is divided into two types: horizontal and inclined.
Horizontal arrangement
When the incoming coal is too wet, the screen holes on the screen surface are blocked. The horizontal layout is prone to poor fluidity of the raw coal on the screen surface, with a longer retention time, which is likely to cause coal blockage. Moreover, the screen shaft at the feeding end is subjected to a large impact force.
Inclined layout
To better enable the materials to move forward on the screen surface, the screen surface is generally arranged at a certain Angle. The inclination Angle arrangement is further divided into two types: equal inclination Angle and variable inclination Angle. Among them, the variable inclination Angle arrangement method utilizes the principle of equal thickness screening of materials, and the screen surface is arranged in sections at different angles. Due to the large volume of materials at the feeding end, a large Angle is adopted to accelerate the forward movement speed of the materials and reduce the thickness of the material layer, which is conducive to the screening of the materials. The middle screen surface adopts a medium inclination Angle. As the material volume in this section is still relatively large, it can keep the material moving at a certain speed, reduce the thickness of the material layer, and effectively screen during the movement process. The screen surface Angle at the discharge end is generally set to the minimum, which can ensure that the material is fully screened and ultimately achieve thorough screening of the material.
Operation and maintenance
(1) Before starting, it is necessary to check whether all the foundation bolts of the roller screen bearing housing, motor reducer and gearbox are complete and tightened.
(2) Before starting, make sure all observation doors are closed. It is strictly forbidden to enter or insert tools to clear debris without power off.
(3) After the Roller screen is just put into operation, it is necessary to focus on checking the current of the motor, the temperature of each bearing, whether the vibration and sound are normal, and the tightness of the foundation bolts and connecting bolts, etc.
(4) When the equipment is in operation, the cleaning blades under the screen shaft are prone to accumulate soft debris and need to be cleaned regularly to prevent excessive accumulation of debris from damaging the screen plates Wear and tear.
(5) After each stop of the roller screen, check if there are any stuck materials on the screen surface and clean them up.
(6) Regularly check whether the oil level of the reducer meets the requirements, and the type of lubricating oil added should be in compliance with the requirements. The screen shaft, bearings, gearboxes, etc. should be inspected and lubricated regularly.
Common Fault Handling
(1) The screen plates and elastic nylon pins are vulnerable parts. If they are cut or damaged, it is necessary to check whether the screen shaft is jammed by iron objects, gangue, etc. After identifying the cause of the fault, they should be replaced in a timely manner.
(2) If any abnormality in current, temperature, sound or vibration is detected during normal operation, the machine should be stopped for handling.
(3) If the motor or reducer experiences abnormal vibration, noise or overheating, check whether the foundation bolts are loose and whether the motor or reducer is damaged.
(4) If there is material accumulation during the operation of the roller screen, consider reasons such as wet and sticky coal quality, excessive impurities, blockage of the chute under the screen, and excessive coal supply. At this time, the machine should be stopped to clean the screen surface or the coal supply should be appropriately reduced.
Conclusion
Compared with traditional vibrating screens, roller screen is less prone to clogging when classifying wet and sticky coal, which can ensure the processing capacity and screening effect. Meanwhile, roller screen also has the advantages of simple structure, no vibrating parts, good sealing performance, no dust overflow and low noise. When choosing screening equipment for coal preparation plants, roller screen can be given priority consideration.
